阅读说明：本技术 保护盖、其用途和制造保护盖的方法 (Protective cap, use thereof and method for producing a protective cap ) 是由 和峰 达宁 J·齐默 M·瑶茨 于 2018-05-02 设计创作，主要内容包括：本发明涉及一种保护盖,该保护盖包括至少一个透明无机层和至少一个透明粘合剂层。透明无机层可以包括玻璃或玻璃陶瓷。在优选实施例中,无机层由玻璃或玻璃陶瓷组成。在实施例中,保护盖还包括设置在无机层和粘合剂层之间的聚合物层。(The invention relates to a protective cover comprising at least one transparent inorganic layer and at least one transparent adhesive layer. The transparent inorganic layer may comprise glass or glass-ceramic. In a preferred embodiment, the inorganic layer consists of glass or glass-ceramic. In an embodiment, the protective cover further comprises a polymer layer disposed between the inorganic layer and the adhesive layer.)

1. A protective cover comprising at least one layer of transparent inorganic material and at least one layer of transparent adhesive.

2. The protective cover of claim 1, comprising at least one polymer layer disposed between the transparent inorganic material layer and the adhesive layer.

3. The protective cover of claim 1 or 2, wherein the difference between the refractive indices nd of the inorganic material layer and the adhesive layer is less than 0.3.

4. Protective cover according to at least one of the preceding claims, wherein the inorganic material layer has a coefficient of thermal expansion of 1 to 10 ppm/K.

5. Protective cover according to at least one of the preceding claims 2 to 4, wherein the coefficient of thermal expansion of the polymer layer is 1 to 15 ppm/K.

6. Protective cover according to at least one of the preceding claims 2 to 5, wherein the difference in coefficient of thermal expansion CTE between the inorganic material layer and the polymer layer and/or between the inorganic material layer and the adhesive layer is less than 15 ppm/K.

7. Protective cover according to at least one of the preceding claims, wherein the thickness of the layer of inorganic material is less than 250 μ ι η.

8. Protective cover according to at least one of the preceding claims 2 to 7, wherein the thickness of the polymer layer is less than 250 μm.

9. The protective cover of at least one of the preceding claims, wherein the thickness of the adhesive layer is less than 100 μ ι η.

10. Protective cover according to at least one of the preceding claims, wherein the layer of inorganic material comprises or consists of glass or glass ceramic.

11. The protective cover of at least one of the preceding claims, wherein the adhesive layer comprises an adhesive selected from the group consisting of OCA, acrylates, methacrylates, polystyrene, silicones, epoxies, and mixtures thereof.

12. The protective cover according to at least one of the preceding claims 2 to 11, wherein the polymer layer comprises at least one polymer selected from the group consisting of: polystyrene (PS), polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PETG), poly (ethylene-vinyl acetate) (EVA), Polycarbonate (PC), Polyimide (PI), polyvinyl chloride (PVC), polyvinyl butyral (PVB), Thermoplastic Polyurethane (TPU) or poly (methyl methacrylate) (PMMA), more preferably selected from polyvinyl butyral (PVB), Thermoplastic Polyurethane (TPU), glycol-modified polyethylene terephthalate (PETG), poly (ethylene-vinyl acetate) (EVA), Polycarbonate (PC), Polyethylene (PE) and combinations thereof.

13. The protective cover according to at least one of the preceding claims 2 to 11, wherein the polymer layer comprises at least one polymer selected from the group consisting of: silicone polymers, sol-gel polymers, Polycarbonates (PC), polyethersulfones, polyacrylates, Polyimides (PI), inorganic silica/polymer blends, cyclic olefin copolymers, polyolefins, silicone resins, Polyethylene (PE), polypropylene polyvinylchloride, polystyrene, styrene-acrylonitrile copolymers, thermoplastic polyurethane resins (TPU), Polymethylmethacrylate (PMMA), ethylene-vinyl acetate copolymers, polyethylene terephthalate (PET), polybutylene terephthalate, Polyamides (PA), polyacetals, polyphenylene ethers, polyphenylene sulfides, fluorinated polymers, chlorinated polymers, ethylene-tetrafluoroethylene (ETFE), Polytetrafluoroethylene (PTFE), Polyvinylchloride (PVC), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), Polyethylene naphthalate (PEN), terpolymers made of tetrafluoroethylene, terpolymers made of hexafluoropropylene and terpolymers made of vinylidene fluoride (THV) or polyurethane and mixtures thereof.

14. The protective cover according to at least one of the preceding claims 2 to 13, wherein the contact angle of a water droplet of the polymer layer differs from the contact angle of a water droplet of the inorganic material by less than 30 °.

15. Protective cover according to at least one of the preceding claims, having an internal transmission of electromagnetic radiation in the wavelength range of 50nm in the spectral range of 380 to 800nm of more than 25% at a thickness of 2 mm.

16. The protective cover of at least one of the preceding claims, exhibiting a weight loss of less than 10% after crushing.

17. The protective cover of at least one of the preceding claims, exhibiting a particle size after crushing in the range of 0.1 to 10 mm.

18. Protective cover according to at least one of the preceding claims, which is bendable and/or foldable and has a bending axis arranged perpendicular to the longitudinal axis of the inorganic material layer.

19. The protective cover of at least one of the preceding claims, being bendable and/or foldable and having a bending axis arranged perpendicular to a longitudinal axis of the inorganic material layer, wherein the protective cover withstands at least 100,000 bending and/or folding events without breaking.

20. The protective cover of at least one of the preceding claims, being bendable and/or foldable and having a bending axis arranged perpendicular to a longitudinal axis of the inorganic material layer, wherein the protective cover withstands at least 200,000 bending and/or folding events without breaking.

21. The protective cover of at least one of the preceding claims, wherein the inorganic material layer has a vickers hardness of 400 to 800 MPa.

22. The protective cover of at least one of the preceding claims, wherein the inorganic material layer has a scratch resistance of greater than 6H.

23. Protective cover according to at least one of the preceding claims, wherein the inorganic material layer has a pen-fall height in an unbent state of more than 30 mm.

24. The protective cover of at least one of the preceding claims, wherein a ratio of a pen-down height of the inorganic material layer in a flexed state to a pen-down height in an unflexed state is not less than 30% when a bend radius of the inorganic material is greater than 4 mm.

25. The protective cover of at least one of the preceding claims, wherein the average flexural strength of the inorganic material layer and/or the protective cover is greater than 850 MPa.

26. Protective cover according to at least one of the preceding claims, wherein the inorganic material of the inorganic material layer has at most 20 μmol/dm²The alkaline leaching factor of (1).

27. Protective cover according to at least one of the preceding claims, wherein the inorganic material of the inorganic material layer has at most 20 μmol/dm²Acid leaching factor of (1).

28. Protective cover according to at least one of the preceding claims, wherein the crushing height of the layer of inorganic material in mm is at least a number of the thickness of the layer in mm multiplied by 50.

29. Protective cover according to at least one of the preceding claims, wherein the inorganic material layer in mm and/or the radius of fracture bending of the protective cover is smaller than the thickness of the layer in mm multiplied by 100,000, wherein the result is divided by the number of surface compressive stresses in MPa measured at the surface.

30. The protective cover of at least one of the preceding claims, wherein the inorganic material layer has a fracture toughness K_ICCompressive stress CS, characteristic depth of penetration x_cAnd a thickness d, wherein the layer conforms to the equation:

wherein, for

Wherein, forB＝0，

Wherein, forB＝0，

Wherein, m is 1m,

wherein x is_cIs > 0 μm, and

wherein the survival parameterIs more than 250 MPa.

31. The protective cover of at least one of the preceding claims, wherein the inorganic material layer has a crack initiation load of at least 1.5N.

32. The protective cover of at least one of the preceding claims, wherein the crushing force in N of the layer of inorganic material and/or the protective cover is at least a number of the thickness in mm of the layer multiplied by 30.

33. Protective cover according to at least one of the preceding claims, wherein the inorganic material of the inorganic material layer is selected from alkali containing glasses, such as alkali aluminosilicate glasses, alkali silicate glasses, alkali borosilicate glasses, alkali aluminoborosilicate glasses, alkali boron glasses, alkali germanate glasses, alkali borogermanate glasses, alkali soda lime glasses and combinations thereof.

34. Protective cover according to at least one of the preceding claims, wherein the inorganic material of the layer of inorganic material is glass comprising the following constituents in cat. -% based on the total molar amount of cations in glass: silicon 40 to 75cat '-, boron 0 to 23 cat' -, aluminum 0 to 20cat '-, lithium 0 to 18 cat' -, sodium 0 to 25cat '-, potassium 0 to 15 cat' -, magnesium 0 to 10cat '-, calcium 0 to 9 cat' -, barium 0 to 4cat '-, zinc 0 to 7 cat' -, titanium 0 to 5cat '-, zirconium 0 to 3 cat' -.

35. Protective cover according to at least one of the preceding claims, wherein the inorganic material of the layer of inorganic material is glass comprising the following constituents in cat. -% based on the total molar amount of cations in glass: silicon 48 to 60cat. -%, boron 10.5 to 15.5cat. -%, aluminum 2 to 8.5cat. -%, sodium 8 to 14cat. -%, potassium 5.5 to 13.5cat. -%, zinc 2 to 6cat. -%, titanium 1 to 5cat. -%.

36. The protective cover of at least one of the preceding claims, wherein the layer of inorganic material has two parallel major surfaces on opposite sides and an edge portion connecting the two major surfaces, wherein at least a portion of the edge portion comprises a convex curvature such that at least one major surface merges into the portion of the edge portion; wherein the portion of the edge portion may have a curvature with an arc length of at least 1/30 a thickness of the inorganic material layer.

37. The protective cover of claim 36, wherein said portion of said rim portion includes a notch in the form of a groove in the region of said convex curvature.

38. The protective cover of claim 37, wherein the depth of the groove is at least 10nm and at most 5 μ ι η.

39. The protective cover of at least one of the preceding claims, wherein the protective cover is arranged on a display screen of an electronic device; or wherein the protective cover is an integral part of the display screen; or wherein the protective cover constitutes a display screen of the electronic device.

40. The protective cover of claim 39, wherein the adhesion strength of the protective cover on the display of the electronic device is such that the protective cover can be removed again from the display, for example, the adhesion strength is in the range of 0.01N/25mm to 0.3N/25 mm.

41. The protective cover of claim 40, wherein the display is a polyimide display.

42. The protective cover of claim 40 or 41, wherein the electronic device is a smartphone, tablet, laptop, smart band, or any other handheld and/or portable electronic device.

43. The protective cover of any of the preceding claims, comprising an adhesive layer disposed between the inorganic material layer and the second inorganic material layer.

44. Protective cover according to any one of the preceding claims, wherein the inorganic material layer has a TTV of not more than 10 μ ι η.

45. Protective cover according to any one of the preceding claims, wherein the layer of inorganic material has at least one region of reduced thickness.

46. The protective cover of claim 45, wherein the region of reduced thickness is in the form of a groove, gap, or groove.

47. The protective cover of claim 45 or 46, wherein the region of reduced thickness extends substantially parallel to a bending axis of the protective cover.

48. The protective cover of one of claims 43 to 47, wherein the thickness of the inorganic material layer is 10 to 150 μm.

49. The protective cover of one of claims 43 to 48, wherein the thickness of the second layer of inorganic material is 100 to 300 μm.

50. The protective cover of any one of claims 43 to 49, wherein the adhesive layer has a thickness of less than 100 μm.

51. Method of using the protective cover according to at least one of the preceding claims as a display screen, as an integral part of a display screen and/or for protecting a display screen, in particular a smartphone display screen, in particular a polymer smartphone display screen, in particular a polyimide display screen, in particular a foldable display screen, in particular an OLED display screen, the method comprising the step of applying the protective cover onto the display screen.

52. Method for manufacturing a protective cover according to at least one of the preceding claims, the method comprising the steps of:

-providing a layer of inorganic material;

-attaching an adhesive layer directly or indirectly on the inorganic material layer.

53. The method of claim 52, wherein providing the inorganic material layer comprises determining one or more of the following parameters of the inorganic material layer: pen drop height, bending strength, alkali leaching factor, acid leaching factor, crushing height, crushing bending radius, survival parameter, strength parameter, crack initiation load and bending strength.

54. The method of claim 52 or 53, wherein providing the inorganic material comprises fabricating a layer of inorganic material of glass or glass-ceramic according to a method selected from the group consisting of down-draw, overflow fusion, and redraw.

55. The method of at least one of claims 52 to 54, wherein the method further comprises attaching a polymer layer to the inorganic material layer.

56. The method of claim 55, wherein attaching the polymer layer to the inorganic material layer comprises coating or laminating the polymer to the inorganic material layer.

57. The method of at least one of claims 52 to 56, wherein attaching an adhesive layer on the inorganic material layer comprises coating or laminating the adhesive layer directly onto the inorganic material layer or indirectly attaching the adhesive layer onto the inorganic material by coating or laminating the adhesive layer onto the polymer layer.

Technical Field

The present application relates to protective caps, methods of making the protective caps, and methods of using the protective caps. The protective cover of the present invention may be arranged on the display screen of the electronic device, or the protective cover may be an integral part of the display screen, or the protective cover itself may constitute the display screen of the electronic device. The electronic device may be a device having an LCD or OLED display screen. The electronic device may be a smartphone, tablet, laptop, smart band, or any other handheld and/or portable electronic device.

Background

New generation electronic displays for mobile devices, for example, will be foldable or rollable. The surface of these displays will be made of thin polymers such as PI (polyimide) or ultra thin glass. These devices also need to be able to be folded or rolled, for example, over 100,000 times over the typical product lifetime without causing any damage. Scratch and shatter resistance are critical to the equipment. Impact resistance (e.g., pen down or other sharp impact) is also critical and should not cause damage to the surface or electronic functionality of the display screen or touch sensor.

There is an increasing demand in the market for curved, bendable and foldable electronic devices (e.g., smart phones and tablets) or other electronic devices with display screens. Such devices are described, for example, in US2017/0294495a1, which is incorporated herein by reference in its entirety. Many manufacturers use polymeric display screen cover materials such as polyimide, PET or other polyesters, polycarbonate, acrylic polymers or other polymers. When used in a sufficiently small thickness, polymeric display screen cover materials have the advantage of being inherently elastic, bendable or even foldable. On the other hand, these materials are less resistant to scratches, light radiation, cleaning agents, temperature and overall wear.

There are many inorganic materials that are resistant to scratching and radiation and are easily amenable to the use of cleaning agents. However, most of these materials can be used as covers for curved surfaces, but cannot be used for bendable or even foldable devices. In addition, many of these materials are very brittle. In particular, glass has been used as a cover material for display screens for many years.

It is expected that mobile phone manufacturers will in the near future offer truly foldable mobile phones, e.g. where the display of the phone almost completely covers one side of the phone and is foldable, and where its bending axis may be oriented perpendicular to the longitudinal axis of the display, dividing the display into substantially equal parts. In other words, such electronic devices open and close like books.

Prior art disclosures such as WO2017/123899 a1 rely on a foldable cover assembly comprising a foldable glass layer and a polymer layer as outer layers, i.e. the surface facing away from the electronic device is covered by a polymer layer, such that the cover assembly is able to withstand pen drops. Other disclosures such as WO2017/136507 a1 rely on an outer layer of glass having indentations on the outer surface of the cover glass.

It would be useful to have a protective cover that imparts the beneficial properties of inorganic material resistance to the display screen while maintaining the flexible or even foldable properties of the display device and without significantly compromising any touch screen functionality of the device, which may be, for example, a capacitive touch sensor assembly, a resistive touch sensor assembly, an acoustic touch sensor assembly, a force-based touch sensor assembly, or a light-based touch sensor assembly.

Disclosure of Invention

The present invention relates to a protective cover which overcomes the disadvantages of the prior art by providing an article having a layer of inorganic material as its outer surface. The protective cover of the present invention comprises at least one layer of transparent inorganic material and at least one layer of transparent adhesive. The protective cover can have a thickness of less than 500 μm, less than 250 μm, or less than 150 μm.

The layer of inorganic material may be used to cover, may be an integral part of, or may be used to constitute a display screen of a bendable and/or foldable electronic device. The present inventors have identified measures that make the inorganic material strong enough to withstand the strains and stresses imposed on the protective cover during use of the electronic device it protects. In order to solve the above-mentioned problems of the prior art, a removable bendable glass-like protective film (protective cover) may be applied to the surface of the device, either as an integral part of the surface of the device, or constituting the surface of the device. The glass film is able to meet the folding requirements of the equipment and protect the original surface from impact and scratches.

In one embodiment, the protective cover of the present invention can be considered a glass film that is bonded to the original polymer or glass surface of the device in a non-permanent (removable) manner with an adhesive layer. The adhesive layer may be composed of a single layer or multiple layers of adhesive (e.g., silicone, PSA, etc.). Thus, in an embodiment, the adhesive layer may form one of the outer layers of the protective cover.

Possible bending radii of the protective cover may be less than 50mm, less than 20mm, less than 15mm, less than 10mm or less than 7 mm.

The adhesive layer and/or the optional further polymer layer may also be used for chip protection. Upon breakage, the glass fragments should not substantially be released from the surface of the protective cover but should stick to the surface in order to avoid any injury to the user of the device or to any other person or material surrounding the device, such as any other part of the device. In an embodiment, in case of surface chipping or appearance defects, the protective cover may be removed and replaced by a new cover.

Polymeric caps have the disadvantages of high scratch and chemical sensitivity. The tactile experience of polymers is also worse than that of glass surfaces for consumers.

The adhesive layer should support easy and bubble-free application to the protective cover and easy removal in case a film change is required.

The transparent inorganic material layer may comprise glass or glass-ceramic. In a preferred embodiment, the layer of inorganic material consists of glass or glass-ceramic. In an embodiment, the protective cover further comprises a polymer layer disposed between the inorganic material layer and the adhesive layer.

In a preferred embodiment, the layer of inorganic material is an outer layer, i.e. the layer of inorganic material is in contact with the surrounding atmosphere (e.g. air). On the other hand, it may be determined that the adhesive layer provides suitable adhesion of the protective cover to a display of the electronic device (e.g., a polyimide display), or it may provide adhesion of the layer of inorganic material to any other layer of the protective cover (e.g., a layer of another inorganic material). The size and type of adhesive layer may be selected to provide good adhesion strength, but also to provide the ability to be removed again from the protected display, for example by peeling off the protective cover.

The polymer layer may be disposed between the inorganic material layer and the adhesive layer. The polymer layer may improve the mechanical stability of the protective cap. The polymeric layer may also provide safety to the user of the protective cover by holding the particles of the fragmented inorganic material layer together to secure the particles. The polymer layer may also protect the display screen by keeping particles of the inorganic material fixed to the polymer layer in case the inorganic material is broken.

The protective cover may be inwardly foldable and/or outwardly foldable, i.e., the protective cover may be folded such that the inorganic layer is inside the folded protective cover or outside the folded protective cover.

The inorganic material of the inorganic material layer may be toughened or not, chemically toughened or not, or partially toughened.

The following are some illustrative and preferred embodiments of the invention in which a left-to-right character sequence shows the sequence of layers from top to bottom in the protective cover in the direction of the device being protected. "l 1" represents at least one inorganic material layer, "a" represents an adhesive layer, "P" represents a polymer layer, and "l 2" represents a second inorganic material layer. Illustrative embodiments a through G may include the layers shown, or they may be composed of these layers.

Type (B)	First layer	Second layer	Third layer	The fourth layer
					A	l1	A
B	l1	P	A
					C	l1	P	A	l2
D	l1	P	l2
					E	l1	A	l2
F	l1	P	l2	A
					G	l1	A	l2	A
H	l1	A	P	A

In an embodiment, all layers of the first inorganic material layer, the adhesive layer, the polymer layer and/or any other inorganic material or protective cover are transparent. Refractive index n between any layers_dThe difference may be limited to 0.3 or 0.1. The different layers in the above-described sequence of layers of the protective cover may be adjacent to each other and/or in direct contact with each other, i.e. without any further layers in between. In an embodiment, at least one, some or all of the layers are coextensive, i.e., have the same width and length, such that each layer substantially completely covers its adjacent layer. When used, the first layer of inorganic material l1 is the outer layer, i.e., facing away from the electronic device and/or towards its user. In embodiments, more than one adhesive layer may be used, for example, an adhesive layer may be used on each side of a polymer layer to attach the polymer layer to a display screen and/or to an adjacent layer, such as an inorganic material layer. The polymer layer may be a polyethylene layer.

Thickness (t or d): the thickness (e.g., thickness of a layer) is the arithmetic average of the thicknesses of the layers to be measured.

Compressive Stress (CS): after ion exchange on the surface layer of the glass, an induced compression of the glass network is produced. This compression is not released by the deformation of the glass and remains as stress. CS decreases from a maximum at the surface of the glass article (surface CS) towards the interior of the glass article. CS can be measured by a waveguide mechanism or by SLP1000 ("orihra) using a commercially available testing machine such as FSM6000 (" Luceo limited ", japan/tokyo), which measures CS by a scattered light mechanism.

Depth of layer (DoL): the thickness of the ion exchange layer, i.e. the region where CS is present. DoL can be measured by a waveguide mechanism using a commercially available testing machine such as FSM6000 ("Luceo ltd", japan/tokyo).

Center Tension (CT): when CS is induced on one or both sides of a glass sheet, a tensile stress, called central tension, must be induced in the central region of the glass in order to balance the stress according to the third principle of newton's law. CT can be calculated from the measured CS and DoL.

Average roughness (R)_a): a measure of surface texture. It is quantified by the vertical deviation of the actual surface from its ideal form. Typically, the amplitude parameter characterizes the surface based on the perpendicular deviation of the roughness profile from the mean line. R_aIs the arithmetic mean of the absolute values of these vertical deviations.

Breaking force: the crushing force is the force (in N) that an object can exert before the object is crushed (i.e. cracks are generated). The breaking force is determined by a steel rod sandpaper pressing test (steel rod and paper pressing test), which is described in more detail below.

Crushing height: the height of fracture refers to the height (in mm) from which an object having a certain weight can fall onto an article or layer before the article or layer fractures (i.e., cracks). The height of the fractures was determined by the sandpaper ball drop test, which will be described in more detail below.

Breaking Bend Radius (BBR): break bend radius (in mm) refers to the minimum radius (r) of the arc at the bend location where the article (e.g., layer) reaches maximum deflection before kinking or damage or failure. It is measured at the inner curvature of the article at the location of the bend. A smaller radius means greater flexibility and deflection of the article. The bending radius is a parameter that depends on the thickness, young's modulus and material strength of the article. For example, ultra-thin glass or glass-ceramic may be small in thickness, low in Young's modulus, and high in strength. All three of these factors contribute to a reduction in bend radius and increased flexibility. The test for determining the BBR will be described in detail below. And (3) transparency: a substance, component, item or layer is considered transparent if the internal transmission of electromagnetic radiation at a thickness of 2mm in the wavelength range of 50nm, at a wavelength of 400nm and/or 700nm or in the spectral range of 380 to 800nm, is greater than 25%, greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%.

In an embodiment, the invention comprises a protective cap, wherein the refractive index n of the inorganic material layer and the adhesive layer and/or the polymer layer and/or the further inorganic material layer_dThe difference is less than 0.3, preferably less than 0.2 or less than 0.1. The difference of the refractive indexes is limited, so that the use of the protective cover on the display screen can be reducedReflection loss in time, thereby reducing power consumption and extending the battery life of the mobile device.

In an embodiment, the inorganic material layer has a Coefficient of Thermal Expansion (CTE) (20 to 300 ℃) of 1 to 20ppm/K, in particular less than 18ppm/K, less than 16ppm/K or less than 14 ppm/K. In an embodiment, the polymer layer has a coefficient of thermal expansion (20 to 300 ℃) of at least 1ppm/K, preferably 4 to 30 ppm/K. Preferably, the difference in CTE between adjacent layers (e.g. between the inorganic material layer and the polymer layer, and/or between the inorganic material layer and the adhesive layer, and/or between the adhesive layer and a further inorganic material layer, and/or between the polymer layer and a further inorganic material layer) is low, in particular less than 40ppm/K, less than 30ppm/K, less than 25ppm/K or even less than 20 ppm/K. Similar CTEs prevent delamination of the layers and extend product life.

The protective caps of the present invention can exhibit a weight loss of less than 10% or less than 5% or less than 2% or less than 1% of the inorganic material after crushing. The weight loss, defined by comparing the difference in weight of the broken protective cover and the unbroken protective cover, can be measured by a precision balance with an accuracy of 0.01 g. The particle size after crushing is in the range of 0.01-10mm, preferably less than 5mm, less than 3mm, less than 2mm, less than 1mm or less than 0.5 mm. Particle size can be measured using a microscope. The diameter may be a martensitic diameter.

The protective cover of the present invention is preferably bendable and/or foldable. It may have a bending axis, which may be arranged perpendicular to the longitudinal axis of the inorganic material layer and/or the protective cover. The bending axis may be substantially perpendicular to the longitudinal axis, or substantially parallel to the longitudinal axis, depending on how the protective cover is supposed to be bent or folded. The bending axis extends at the surface of the inorganic material layer and the tensile stress peaks during bending. The protective cover of the present invention is preferably bendable and/or foldable and has a bending axis that can be arranged perpendicular to the longitudinal axis of the inorganic material layer, wherein the protective cover withstands at least 100,000 bending and/or folding events without breaking. The protective cover of the present invention is preferably bendable and/or foldable and has a bending axis that can be arranged perpendicular to the longitudinal axis of the inorganic material layer, wherein the protective cover withstands at least 200,000 bending and/or folding events without breaking. The bending and/or folding event may be achieved by bending and/or folding the protective cover from an unbent state to a bent state and then back to the unbent state, the bend radius being 50mm or less, or 20mm or less, or 10mm or less, or 5mm or less, or 2mm or less. The bend radius may be at least 1 mm.

In a preferred embodiment, the cover is arranged on, or forms an integral part of, or constitutes a display screen of the electronic device. The placement of the cover on the display screen may be accomplished by simply placing the cover on the display screen and flattening the cover with a finger.

The invention also relates to a method for protecting a display screen, such as an industrial display screen or a consumer product display screen, in particular a smartphone display screen, in particular a polymer smartphone display screen, in particular a polyimide display screen, in particular a foldable display screen, in particular an OLED display screen, using a protective cover, comprising the step of applying the protective cover to the display screen.

In a preferred embodiment, the adhesive layer, the polymer layer and/or any other layer of the protective cover may compensate for the restoring force of the inorganic material layer when bent or folded. In a preferred embodiment, the adhesive layer is not under tensile stress.

Layer of inorganic material

The following features described with respect to the inorganic material layer may characterize the at least one inorganic material layer and/or any further inorganic material layer of the protective cover.

The inorganic material layer may be a glass layer, a glass ceramic layer, a ceramic layer, or a crystal layer. In a preferred embodiment, the inorganic material layer is a glass layer or a glass-ceramic layer. The inorganic material layer may be additionally coated to achieve, for example, anti-reflection, anti-scratch, anti-fingerprint, anti-microbial, anti-glare, and combinations of these functions; such a coating may be arranged on the side facing away from the display screen to be protected, i.e. the side facing away from the adhesive layer. The protective cover may comprise more than one layer of inorganic material. The inorganic material layer may have a surface nitrided to increase its surface resistance.

The thickness of the layer of inorganic material may be less than 700 μm, less than 500 μm, less than 300 μm, less than 250 μm, less than 200 μm, less than 150 μm, less than 100 μm, less than 75 μm, less than 70 μm, less than 50 μm, less than 30 μm or less than 15 μm. The thicker the glass, the higher its mechanical stability. The thinner the glass, the higher its ability to bend and fold.

The inorganic material layer may have a Vickers hardness HV of from 400 to 800MPa_0.2/25. The toughened inorganic layer may have a Vickers hardness HV from 450 to 1000MPa_0.2/25. Knoop hardness HK of non-toughened inorganic layers_0.1/20May be from 350 to 750 MPa. Knoop hardness HK of toughened inorganic layers_0.1/20May be from 400 to 800 MPa.

In certain embodiments, the inorganic material layer, which may be a glass or glass ceramic layer, may have a thickness of less than 0.2mm, less than 0.175mm, less than 0.145mm, less than 0.1mm, less than 0.07mm, or even less than 0.05 mm.

Height of pen falling

In certain embodiments, particularly for a thickness of at least 0.07mm, the inorganic material layer has a scratch resistance of greater than 6H and/or a pen-drop height of greater than 30 mm. The weight of the pen was about 5g, and the tip of the pen was made of tungsten carbide with a radius of 150 μm. In certain embodiments, the inorganic material layer exhibits a pen-fall height of at least 50mm, at least 60mm, at least 70mm, at least 80mm, at least 90mm, at least 100mm, or at least 120mm, or at least 150mm in an unbent state. When the inorganic material is not bent, the pen-fall height of the inorganic material, particularly the inorganic material in the protective cover, is preferably set to be more than 40 mm.

The pen-fall height of the inorganic material, in particular the inorganic material in the protective cap, may be at least 20mm when the inorganic material has a bending radius of more than 6mm, in particular when the inorganic material has a bending radius of at most 10mm or at most 8 mm. The pen height is preferably at least 15mm when the inorganic material has a bending radius of more than 4mm, in particular when the inorganic material has a bending radius of at most 8mm or at most 6 mm. When the inorganic material has a bending radius of more than 2mm, in particular when the inorganic material has a bending radius of at most 6mm or at most 4mm, the pen-fall height is preferably more than 10 mm.

It is desirable that the ratio of the pen-falling height of the protective cover in the bent state to the pen-falling height in the unbent state is not less than 30%, not less than 25% or not less than 20% when the bending radius of the inorganic material is larger than 4mm, particularly when the bending radius of the inorganic material is at most 8mm or at most 6 mm. The measurement results of the pen-down test are shown in fig. 5 and 6.

In a preferred embodiment, the protective cap can be folded at least 100,000 times, in particular at least 200,000 times without breaking. This may be applied to a bending radius of 20mm or less. Furthermore, it may be applicable to inwardly foldable and/or outwardly foldable display screens and/or protective covers.

The inorganic material may be a glass containing an alkali metal oxide so that it may be chemically toughened. For the inorganic material of the toughened glass, the CS (compressive stress) may be in the range of 200 to 2000MPa, and/or the DoL (depth of layer) may be in the range of 2 μm < DoL < half the thickness of the layer of inorganic material.

Bending strength

The flexural strength may be measured using the 2PB method and the average flexural strength of the inorganic material layer and/or the protective cover may be greater than 850MPa, preferably greater than 900MPa, still more preferably greater than 950MPa, still more preferably greater than 1000 MPa. Foldability is measured by a bend radius, which may be less than 20mm, less than 10mm, less than 7mm, less than 5mm, or even less than 4 mm. In embodiments, the bend radius may be at least 1mm, or at least 2mm, or at least 3 mm.

The hardness of the inorganic material may be as follows: HV (high voltage) device_0.2/25> 400MPa and/or HK_0.1/20Is more than 350 MPa. The value after toughening may be HV_0.2/25> 450MPa and/or HK_0.1/20Is more than 400 MPa. The value after surface nitriding for toughening can be HV_0.2/25> 500MPa and/or HK_0.1/20＞450MPa。

The Young's modulus may be greater than 50GPa, greater than 55GPa, or greater than 60 GPa. The Young's modulus may be less than 110GPa, less than 105GPa, or less than 100 GPa.

In preferred embodiments, the inorganic material has a light transmittance of greater than 85% at 400nm and/or greater than 88% at 700 nm.

Alkaline leaching factor

The inorganic material of the present invention may have a molar content of at most 20. mu. mol/dm²Up to 10. mu. mol/dm²Up to 5. mu. mol/dm²Or even up to 3. mu. mol/dm²The alkaline leaching factor of (1). To determine the alkaline leaching factor, a sample of the material was first washed in deionized water at 80 ℃ for 8 minutes and then rinsed with deionized water at room temperature. The samples were then soaked (incubate) in50 ml of deionized water at 80 ℃ for 24 hours. Thereafter, the amount of alkali metal ions in the water was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The alkaline leaching factor is defined as the amount of alkali metal ions in water (in μmol) and per surface area of the material sample (in dm)²Meter) of the measured values.

Acid leaching factor

It is also advantageous if the inorganic material has a high acid resistance. Thus, the acid leaching factor of the material may be at most 20 μmol/dm before, after and/or without chemical toughening²Up to 10. mu. mol/dm²Up to 5. mu. mol/dm²Or up to 3. mu. mol/dm²。

To determine the acid leaching factor, a sample of the material was first washed in deionized water at 80 ℃ for 8 minutes and then rinsed with deionized water at room temperature. Then, the sample was immersed in 100 ml of nitric acid having a concentration of 0.01mol/l at 100 ℃ for 1 hour. Thereafter, the amount of alkali metal ions in the acid solution was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The acid leaching factor is defined as the amount of alkali metal ions in the acid solution (in μmol) and per surface area of the material sample (in dm)²Meter) of the measured values.

The inorganic material layer may be a chemically toughened glass layer having a thickness (t) of less than 0.4mm, having a first surface and a second surface and a compressive stress region extending from the first surface to a first depth (DoL) in the glass layer, the region defined by a Compressive Stress (CS), wherein the surface CS at the first surface is at least 100 MPa. The first surface and the second surface are located on opposite sides of the glass layer.

Height of crushing

The height of fracture (in mm) of the layer of inorganic material may be at least the thickness of the layer (t in mm) multiplied by a number of 50 or 60 or 70 or 80. The height of the fractures was determined by a sandpaper ball drop test. In this test, the second surface of the layer was placed on a steel plate and a load was applied to the first surface of the layer until it was broken by a 4.5g acrylic ball falling from above, with a P180 sand paper placed on the first surface of the layer with the abrasive side of the sand paper in contact with the first surface. The height of the drop increases until the layer breaks. The final height at which the layer is unbroken is considered the height of breakage.

In the sandpaper ball drop test described above, the height of fracture (in N) of the layer may be greater than or equal to 50 t (t is a number of individual thicknesses of the layer in "mm").

Surprisingly, the inventors found that the fracture height criterion of the layer can be described by the mentioned factor 50 and the thickness of the layer. This factor will be valid if the height of fracture of the layer is determined in the sandpaper ball drop test. In the dynamic test, the second surface of the layer is placed on a steel plate and the first surface of the layer (which may or may not be chemically toughened in the case of a glass layer) is oriented upwards. Acrylic balls weighing 4.5g were dropped onto the layer from above. The drop height of the ball is increased stepwise until the layer breaks, with one drop per step, and the distance between each step is chosen reasonably, for example 2mm or 5 mm. The test was performed on small samples (11 mm. times.11 mm) using P180 sandpaper (e.g., #180Buehler sandpaper manufactured by "Buehler" company) at room temperature of about 20 ℃ and a relative humidity of about 50% according to ISO 6344. If a larger size layer is to be tested, a smaller sample will be cut using a diamond cutting wheel. The small samples were not edge treated. The height of disruption (also referred to as "sandpaper ball height") is the maximum height that can be applied before the layer is disrupted. By broken is meant that the layer is visibly cracked on the surface (cracked) or broken into two or more pieces. Fragmentation was determined visually.

This test is adapted to be particularly suitable for layers and reproduces in a very simple way the above-mentioned problem, namely the impact contact between a layer and a sharp hard object when the layer is dropped or hit.

Radius of crushing bend

Furthermore, the breaking bend radius (in mm) of the inorganic material layer and/or the protective cover is smaller than the thickness (t in mm) of the layer multiplied by 100,000, wherein the result is divided by the number of the surface compressive stress (in MPa) measured at the surface of the inorganic material layer.

The inorganic material layer of the present invention may have an optimized stress distribution. It strikes a balance between a small bending radius and high resistance to sharp contact (e.g., impact resistance). It has surprisingly been found that this layer will be strong enough to accommodate the application of the protective cover, especially in everyday use, especially if the following conditions are met:

in the case of inorganic material layers made of glass, the breaking bending radius (in mm) thereof may be <100,000 t/CS, where t is the thickness of the glass layer (in mm) and CS is the number of measured surface compressive stresses (in MPa). This means that in the following calculations, the product is divided by a number corresponding to the surface compressive strength (in MPa) measured at the first surface of the glass layer, respectively.

With the aid of these criteria it can be determined whether the layer is suitably strong and flexible enough for the respective application before it becomes part of the protective cover. Surprisingly, it was found that the height of the fracture is closely related to the layer thickness. Thus, thinner layers are particularly sensitive to breakage due to impact of hard and sharp objects.

In an advantageous embodiment of the invention, the fracture bend radius (in mm) of the chemically toughened glass layer (i.e. the inorganic material layer) is smaller than the thickness (t in mm) of the glass layer multiplied by 100,000 or 80,000, wherein the result is divided by the number of surface compressive stresses (in MPa) measured at the first surface (< t 80,000/CS). The fracture bend radius (in mm) may preferably be less than the thickness of the inorganic material layer (t in mm) multiplied by 70,000, where the result is divided by the surface compressive stress measured at the surface (in MPa alone)Bit) may be less than the thickness of the inorganic material layer (t in mm) multiplied by 60,000, wherein the result is divided by the number of surface compressive stresses (in MPa) measured at the first surface (< t 60,000/CS), the inventors surprisingly found that the criterion of the breaking bend radius of the glass layer as an inorganic material layer may be described by the inventive factor 100,000, the thickness of the glass layer and the measured surface CS, if the breaking bend radius of the inorganic material layer is determined by the two-point bending test as described above, the inventive factor will be valid, the breaking bend radius is determined on a small sample (20mm × 70mm) at room temperature of about 20 ℃ and relative humidity of about 50% by using a UTM (universal testing machine), if a larger size glass layer is to be tested, a small sample will be cut using a diamond cutting wheel, the small sample is no longer subjected to edge treatment, and the relative humidity is about 50% determined on a small sample (20mm 3570 mm), and the breaking bend radius of the inorganic material layer is calculated from the grinding bend radius of the two inorganic material layers, wherein the breaking bend radius of the inorganic material layer is measured by a grinding machine, and the grinding bend radius of the inorganic material layer is calculated by a grinding machine, wherein the grinding bend radius of the grinding machine is measured by several mm-measured by the grinding machine₃、H₂SO₄、NH₄HF₂Or a mixture thereof) is etched and then optionally toughened) the bend radius will be even smaller compared to a corresponding inorganic material layer without edge treatment, since the edge treatment increases the strength and thus reduces the bend radius.

The two-point bending test is adapted and particularly suitable for inorganic material layers, such as glass layers, and reproduces the above problem, i.e. the bending of a glass layer when a load is applied thereto, in a very simple manner. In the context of the present invention, the two-point bending method has been found to be more meaningful than other known bending strength tests, such as the three-point bending test and the four-point bending test.

As described above, the inorganic material layer may have completely different sizes. Therefore, in determining the crushing height and the crushing bend radius, the following factors must be considered:

in the case of larger layers (e.g., rolls or large glass sheets), the height of breakage of multiple samples was measured using the sandpaper ball drop test. For this, a random sample of N values is taken. N should be high enough to obtain a statistically guaranteed average. Preferably at least 20, more preferably at least 30 samples are tested. The number of samples depends on the respective size of the layer to be tested. The measured values were statistically evaluated using the Weibull (Weibull) method. The B10 value for the weibull distribution (i.e., the calculated height in mm of 10% of the sample breaks) was determined and used to represent the desired height of break.

However, in the case of small layers, for example less than 25cm²A single measurement of the shatter height is sufficient and is used to indicate the desired shatter height (e.g. a single small piece of cover glass).

In case of a number of measurements between 2 and 19, the average of the measured crushing heights is used to represent the required crushing height.

For the crushing bend radius, an average value can be calculated. For this, a random sample of N values is taken. The number of samples depends on the respective size of the layer to be evaluated. Preferably, N should be high enough to obtain a statistically assured average. Preferably at least 20, more preferably at least 30 samples are tested. Thus, the bending radius R for crushing₁...R_NTaking random samples of N values, calculating the average value of the values of these random samples

Sum variance

Taking average crushing curve halfDiameter is used to indicate the required crushing bend radius. However, in the case of small layers, for example less than 25cm²A single measurement of the break bend radius is sufficient and is used to indicate the required break bend radius.

The mean and variance of the crushing height are calculated accordingly.

Survival parameter

It is an object of the present invention to provide a protective cover with improved resistance to bending and folding. In other words, the inorganic material layer and the entire protective cover are highly likely to undergo bending and folding. The possibility of withstanding bending and folding should remain high even in the event of scratching or impact forces exerted on the lid and in particular on the layer of inorganic material.

In an embodiment, the invention comprises a protective cover having a layer of inorganic material comprising or consisting of a transparent material which may have a certain brittleness. The inorganic material layer has fracture toughness K_ICCompressive stress CS, characteristic depth of penetration x_cAnd a thickness d, wherein the layer conforms to the equation:

wherein, for

Wherein forB＝0，

Wherein for

B＝0，

Wherein m is 1m, and m is a linear,

wherein x_cIs > 0 μm, and

wherein the survival parameterIs more than 250 MPa.

In a preferred embodiment, the present invention provides a set of protective covers, or at least one protective cover comprising a set of layers of inorganic material, wherein the number of layers n in the one or more covers is at least 2, 3, 4, 5, 10, 20, 50 or even at least 100.

According to the present description, if the brittleness S of the material is greater than 0.1 μm^-1/2Preferably greater than 0.2 μm^-1/2Greater than 0.5 μm^-1/2Greater than 0.8 μm^-1/2Greater than 1 μm^-1/2Greater than 1.5 μm^-1/2Greater than 2 μm^-1/2The material is considered brittle. Preferably, the brittleness S is at most 20 μm^-1/2Up to 18 μm^-1/2Up to 15 μm^-1/2At most 12 μm^-1/2At most 10 μm^-1/2Of at most 9 μm^-1/2Or at most 8 μm^-1/2. Preferably, the brittleness S is 0.1 μm^-1/2To 20 μm^-1/2In the range of (1), preferably 0.2 μm^-1/2To 18 μm^-1/2Within the range of (1), preferably from 0.5 μm^-1/2To 15 μm^-1/2In particular from 0.8 μm^-1/2To 12 μm^-1/2Or from 1 μm^-1/2To 10 μm^-1/2Preferably 1.5 μm^-1/2To 9 μm^-1/2More preferably 2 μm^-1/2To 8 μm^-1/2. The brittleness S is calculated as the Vickers hardness H and the fracture toughness K according to the following formula_ICThe ratio of.

S＝H/K_IC。

This ratio is used as described in "law, b.r.; marshall d.b.; haedness, Toughress, andBorritteness: An indexing Analysis; a measure of brittleness in the Journal of the American Ceramic Society (1979) ". The skilled person knows how to determine this brittleness by experimentation. Preferably, according to the general formula in "Sehgal, j.; ito, s.; brittleness of glass; the brittleness is determined by the explanation given in Journal of Non-crystallline Solids (1999) ".

The transparent and optionally also brittle inorganic material is preferably selected from the group consisting of glass, glass-ceramic, ceramic and crystalline. Preferred crystals are selected from sapphire, diamond, chromium, ruby, topaz, quartz and orthoclase. Sapphire is the preferred crystal. Preferably, the transparent and optionally also brittle material is glass or glass-ceramic, in particular glass. In particular, the material may be borosilicate glass or aluminosilicate glass. Preferably, Li in the material₂O+Na₂The proportion of O is more than 1% by weight, more preferably more than 3% by weight, more preferably more than 5% by weight. In a particularly preferred embodiment, the material comprises Na₂O but not containing Li₂O、Rb₂O and Cs₂O。

When bending brittle materials without further measures, tensile stresses are observed on the convex surface of the material, which can lead to fracture when the tensile stress exceeds a threshold value. It has been found that it is possible to manufacture objects which are flexible or even foldable, for example, inorganic material layers of the protective caps of the invention, when the parameter fracture toughness K is chosen_ICCompressive stress CS, characteristic depth of penetration x_cAnd thickness d, such that the survival parameter is in accordance with the equation given aboveIs more than 250 MPa. The survival parameter has the magnitude of tensile stress, in units of MPa. It was surprisingly found that articles such as inorganic material layers of transparent or even brittle materials are particularly flexible if said parameters are selected such that the survival parameter is larger than 250MPa, preferably at least 300MPa, at least 350MPa, at least 400MPa, at least 450MPa, at least 500MPa, at least 600MPa, at least 700MPa or even at least 800 MPa. Preferably, the survival parameter is at most 1,000,000MPa, at most 100,000MPa, at most 20,000MPa, at most 10,000MPa, at most 7500MPa, at most 5000MPa, at most 4000MPa, at most 3000MPa, even at most 2000 MPa. Preferably, the survival parameter is between 250MPa and 1,000,000MPa, 300MPa and 100,000MPa, 350MPa and 20,000MPa, 400MPa and 10,000MPa, 450MPa to 7500MPa, 500MPa to 5000MPa, 600MPa to 4000MPa, 700MPa to 3000MPa, 800MPa to 2000 MPa.

Fracture toughness K_ICFracture toughness under tensile stress (mode I) is preferred. Fracture toughness is given in MPa m and is preferably measured according to the Precracked Beam method (Precracked Beam method) as given in ASTM C1421-15 (page 9 and below). Fracture toughness K_ICPreferably by one or more reference articles. For determining fracture toughness K_ICPreferably without toughening, in particular without chemical toughening. Preferably, the fracture toughness is greater than 0.4MPa · m. Preferably, the fracture toughness is at least 0.45MPa m, more preferably at least 0.5MPa m, preferably at least 0.6MPa m, at least 0.7MPa m, at least 0.8MPa m, at least 0.9MPa m, or at least 1MPa m, or at least 1.1MPa m, or at least 2MPa m. Preferably, the fracture toughness is at most 100MPa · m, at most 75MPa · vm, at most 50MPa · vm, at most 10MPa · vm, in particular at most 8MPa · vm, or at most 5MPa · vm.

The shape of the chemical toughening profile corresponds to the inverse error function. The diffusion coefficient D is different for different ion species, different temperatures and different materials. In m²The diffusion coefficient D is measured in units of/s. From the diffusion coefficient D and the toughening time t, the equation can be used:to calculate the feature penetration depth x_c. The toughening time t is the time during which the article (e.g., inorganic material layer) remains in the salt bath. The diffusion coefficient D can be measured in different ways. Preferably, after a defined toughening temperature and time, the diffusion coefficient D is calculated from the depth distribution of the exchanged ions. For example, the depth distribution can be measured using EDX (energy dispersive X-ray spectroscopy). Alternatively, a TOF-SIMS (time-of-flight secondary ion mass spectrometry) method can be used. In the ToF-SIMS method, a material is released from the surface of an object (e.g., an inorganic material layer) by an ion beam, and the proportion of ions released therefrom is measured. By releasing material from the surface, the ion beam essentially "drills" into the article (e.g., inorganic)Material layer) so that the variation of the ion distribution can be determined. Other suitable methods are known to the skilled person.

The characteristic penetration depth has units of length. Preferably, it is at least 2 μm, at least 3 μm, at least 0.843 x 4 μm, preferably at least 4 μm, at least 6 μm, at least 8 μm or at least 10 μm. Preferably, the characteristic penetration depth is at most 50 μm, at most 30 μm, at most 27 μm, at most 25 μm, at most 24 μm, at most 22 μm or at most 20 μm.

In a preferred embodiment, the characteristic penetration depth should not exceed a certain value with respect to the thickness d of the inorganic material layer. Preferably, the characteristic penetration depth is highest d/2, highest d/3, highest d/3.5, highest d/4, highest d/5, highest d/6 or highest d/7. However, the characteristic penetration depth should be at least d/40, at least d/30, at least d/27, at least d/25, at least d/20, at least d/15 or at least d/10.

The tensile stress on the convex side of the inorganic material layer is approximately proportional to the young's modulus of the material. Therefore, for the lifetime of the bendable and preferably foldable protective cover and the layer of inorganic material, preferably the young's modulus should not be too high. Preferably, the young's modulus of the inorganic material is at most 200GPa, preferably at most 150GPa, at most 120GPa, or at most 100GPa, or at most 90 GPa. Preferably, the young's modulus of the inorganic material is at least 40GPa, at least 50GPa, at least 60GPa, or at least 70GPa, or at least 80GPa, or at least 90GPa, or at least 100 GPa.

The lifetime of the bendable and optionally foldable protective cover and/or the layer of inorganic material may be improved if the tensile stress is relocated to the outside of the article. According to the invention, this can be achieved by providing a further material on the side of the article which is subjected to tensile stress. The further material may cover the entire area of the respective side of the article, or it may cover a partial area of the respective side of the article. In a preferred embodiment, the strip of metal or polymer material is arranged on at least one side of the article, for example on the layer of inorganic material and/or on the protective cover, in particular on the side which is subjected to tensile stress. Metals have the advantage of higher young's modulus, while polymeric materials may have the advantage of transparency. The one or more strips of metal or polymer material may be arranged near an edge of the layer of inorganic material and/or on the protective cover, for example within a distance of no more than 30%, 20% or 10% of the width of the layer from the respective edge, or within a distance of at least 10 x d but no more than 50 x d, preferably no more than 20 x d, from the respective edge, where "d" is the thickness of the layer of inorganic material. Preferably, this applies to the edges extending perpendicular to the bending or folding axis, in particular along the length direction of the inorganic material layer, i.e. along the longitudinal axis. Strips of additional material having a width less than 30%, 20%, 10%, 5%, 3% or 1% of the width of the layer of inorganic material may be used. The width may be at least 0.1%, at least 0.3%, or at least 0.9% of the width of the inorganic material layer and/or the protective cover.

The further material may have a young's modulus of more than 10GPa, preferably at least 20GPa, at least 50GPa, at least 75GPa or at least 100 GPa. In a preferred embodiment the further material has a young's modulus of at most 1000GPa, preferably at most 800GPa, at most 700GPa or at most 650 GPa. In particular, the value of the young's modulus of the further material compared to the young's modulus of the inorganic material layer is in the range 1/10 to 10 times the value of the young's modulus of the inorganic material, preferably in the range 1/5 to 5 times, or in the range 1/2 to 2 times.

The brittleness S of the further material is preferably less than 20 μm^-1/2Less than 10 μm^-1/2Less than 5 μm^-1/2Less than 2 μm^-1/2Less than 1 μm^-1/2Or less than 0.5 μm^-1/2Less than 0.25 μm^-1/2Less than 0.1 μm-^-1/2Less than 0.05 μm^-1/2Or less than 0.005 μm^-1/2. Preferably, the thickness of the further material is in the range of 0.2 to 5, preferably in the range of 0.5 to 2, where d is the thickness of the layer of inorganic material. Preferably, the thickness of the further material is at least 10 μm, preferably at least 50 μm, at least 100 μm, at least 200 μm or at least 500 μm. In particular, the thickness of the further material should not exceed 5mm, 4mm, 3mm, 2mm or 1 mm. Preferably, the further material is selected from polymeric (e.g. plastic) and metallic materials (e.g. plastic)Such as a metal or metal alloy). The preferred plastic is polyethylene.

As mentioned above, the tensile stress is preferably relocated out of the article and into the further material. It is therefore advantageous if the further material has a rather high offset yield point (or test stress). Preferably, the additional material (in particular the metallic material) has a 0.2% offset yield point of at least 50N/mm²More preferably at least 75N/mm²More preferably at least 100N/mm²More preferably at least 150N/mm². The 0.2% offset yield point is the (uniaxial) mechanical tension at which the sustained elongation after load release is 0.2% based on the initial length of the sample. The 0.2% offset yield point can be unambiguously determined from the stress-strain curve.

It is also advantageous if the further material has a relatively high tensile strength. Preferably, the further material (in particular a polymer plastic) has a tensile strength of at least 50N/mm²More preferably at least 60N/mm²More preferably at least 70N/mm²More preferably at least 80N/mm². The tensile strength is preferably determined according to one of the following criteria: EN ISO 6892-1, ISO6892, ASTM E8, ASTM E21, DIN50154, ISO 527, ASTM D638.

It has been found that geometric effects in the inorganic material layer result in a reduction of the compressive stress at the edge of the layer. This effect can be produced by rounding the edges. It has proved advantageous if the thickness d of the layer of inorganic material, the characteristic penetration depth x_cAnd fillet radius OVR have the following relationship:

d/3＞OVR＞x_c/5。

preferably, the fillet radius OVR is smaller than d/3 and larger than x_c/5. The fillet radius is measured at the transverse crack of the respective inorganic material sheet. The fillet radius is the radius of the largest possible circle that can be fitted to the edge of a transverse crack. The edge is the cross-section at the edge of the original sheet. Preferably, the OVR of an individual item is measured indirectly by using one or more reference items, which are able to draw conclusions about the OVR of the individual item. For example, can be usedThe OVR of a particular batch or lot of items is determined by determining the OVR of one or more reference items of that batch or lot, provided that there is no or only a slight difference between the individual items of the batch or lot. Preferably, the minor difference is at most 20%, more preferably at most 15%, more preferably at most 10%, more preferably at most 5%, more preferably at most 2%, more preferably at most 1% between the maximum and minimum values in the respective batches or batches.

Intensity parameter OFP

The effectiveness of the compressive stress distribution on the survival of curved articles can be represented by strength measurements of the corresponding inorganic material layer. Two-point bending measurements were performed, with the strength being measured according to Matthewson and Kurkjian (J.am.Ceram.Soc., 69[11], Seiten 815-. Preferably, the intensity of the individual item is indirectly measured by using one or more reference items, which are able to draw conclusions about the intensity of the individual item. For example, the intensity of an item of a particular batch or lot may be determined by determining the intensity of one or more reference items of the respective batch or lot, provided that there is no or only little difference between the individual items of the batch or lot. Preferably, the minor difference is at most 20%, more preferably at most 15%, more preferably at most 10%, more preferably at most 5%, more preferably at most 2%, more preferably at most 1% between the maximum and minimum values in the respective batches or batches.

It has been found that an inorganic material layer is particularly resistant to fracture if there is a specific relationship between the average value MW of the strength measurement, the standard deviation STABW, the number of samples N in the measurement range and the strength parameter OFP, which specific relationship is calculated according to the following formula:

preferably, the OFP is at least 2, greater than 4, at least 5, at least 10, or at least 20. In particular, the OFP is at most 100, at most 80, at most 70 or at most 60.

Crack initiation load

Crack initiation load is the resistance to crack formation upon body intrusion. The crack initiation load is substantially applicable to an event of impact on the article, such as an event of impact on the inorganic material layer. Higher crack initiation loads are preferred. The crack initiation load of the inorganic material layer is preferably at least 1.5N, at least 3N, at least 5N or at least 10N at a relative humidity of air of 50%. In particular, the crack initiation load may be at most 200N, at most 150N, at most 75N, at most 65N, at most 55N, at most 45N or at most 30N.

Crack initiation loads were measured with a Vickers indenter as described by Sehgal and Ito (J.am. Ceram. Soc., 81[9], pp. 2485 to 2488 (1998)).

Another aspect associated with the impact resistance of the inorganic material layer is critical compression. The critical compression is the limit of compressive stress that the material can withstand before cracks form. This value is related to strain, without units. Preferably, the critical compression of the inorganic material layer is at least 8% or at least 10%. The threshold compression may be determined using cylinder compression. A sample of the object to be investigated can be placed between the end faces of the two cylinders so that pressure can be applied to the sample through the cylinders. This method may be performed using a general purpose measurement device (e.g., INSTRON 6025).

In an embodiment, the inorganic material layer comprises glass or glass-ceramic as described below. Preferably, the inorganic material layer is composed of the following materials.

In an embodiment, the inorganic material layer is a chemically toughened glass layer. In other embodiments, the inorganic material layer may be a glass layer that is not chemically toughened. Alternatively, the inorganic material may be a material that has been partially chemically toughened.

The inorganic material layer may be a chemically toughened glass layer having a thickness (t) of less than 0.4mm, a first surface and a second surface and a compressive stress region extending from the first surface to a first depth (DoL) in the glass layer, the region defined by a Compressive Stress (CS), wherein the surface CS at the first surface is at least 100 MPa. The first surface and the second surface are located on opposite sides of the glass layer.

Breaking force

The layer of inorganic material and/or the protective cover may have a crushing force (in N) of at least the thickness of the layer (t in mm) multiplied by 30. The breaking force was determined in a sandpaper press test. In this test, the second surface of the layer was placed on a steel plate and a load and pressure was applied to the first surface of the layer until it was broken down on its flat front face by a steel rod of 3mm diameter, with a sandpaper of type P180 placed between the front face of the steel rod and the first surface of the layer, with the abrasive face of the sandpaper in contact with the first surface. Furthermore, a layer according to the invention may have a fracture bend radius (in mm) that is less than the thickness of the layer (t in mm) multiplied by 100,000, wherein the result is divided by the number of surface compressive stresses (in MPa) measured at the first surface.

The inorganic material layer may have an optimized stress distribution. It is balanced between a small bending radius and a high resistance to sharp contact, especially to pressure. It was surprisingly found that this layer would be strong enough to be suitable for applications in daily use of electronic devices, in particular if the following conditions are fulfilled:

in the above sandpaper test, the breaking force (in N) of the layer of inorganic material and/or the protective cover may be ≥ 30 ≥ t, ≥ 40 ≥ t, ≥ 50 ≥ t or ≥ 60 ≥ t (t is a number in mm for the respective thickness of the layer) and/or its breaking bend radius (in mm) may be <100,000 ≤ t/CS, where t is the thickness of the layer (in mm) and CS is a number in MPa for the measured surface compressive stress. This means that in the following calculations the product is divided by a number corresponding to the respective measured surface compressive strength (in MPa) at the first surface of the layer.

With the aid of these criteria it can be determined whether the layer of inorganic material is suitably strong and soft enough for the respective application before it becomes part of the protective cover. It was surprisingly found that the breaking force is closely related to the layer thickness. Thus, thinner layers are particularly sensitive to breakage due to contact with hard, sharp objects.

Surprisingly, the inventors found that the criterion for the breaking force of the inorganic material layer can be described by the mentioned factor 30 and the thickness of the layer. This factor will be valid if the breaking force of the layer is determined in a sandpaper press test recorded using a Universal Test Machine (UTM). In this test, the second surface of the layer is placed on a steel plate, and a load is applied to and pressed against the first surface of the layer (which may be chemically toughened) until its flat front face is broken by a 3mm diameter steel bar, with a sandpaper of type P180 placed between the front face of the steel bar and the first surface of the layer, with the abrasive face of the sandpaper in contact with the first surface. The longitudinal axis of the steel rod is oriented perpendicular to the first surface of the layer. The steel bar was continuously moved in the direction corresponding to its longitudinal axis at a loading speed of 1mm/min until breaking. The test was performed according to ISO 6344 using P180 sandpaper (e.g., #180 sandpaper manufactured by "Buehler" company) on a small sample (11 mm. times.11 mm) at about 20 ℃ at a relative humidity of about 50%. If larger sized layers of inorganic material are to be tested, a small sample will be cut using a diamond cutting wheel. The sample was not edge processed. The sample was pressed by a rod until it broke (cracked). The breaking force (also referred to as "sandpaper pressure") is the maximum force that can be applied before the layer breaks. By broken is meant that the layer exhibits surface cracks or breaks into two or more pieces. Fragmentation is determined by the signal of the UTM software.

This test is adapted to be particularly suitable for inorganic material layers and reproduces the above problem in a very simple way, namely the pressure contact between a layer (for example, an FPS or a touch display screen) and a sharp hard object. Preferably, the inorganic material layer is subjected to the tests described herein before being processed into the protective cover of the present invention.

As mentioned above, inorganic material layers are used in many areas of everyday use, for example as protective covers for fingerprint sensors, in particular in smart phones and tablets. To increase the strength of the protective cover, toughening (e.g., chemical toughening) may be performed. In this case, in the prior art, it is generally assumed that high compressive stress and high DoL are required to ensure flexibility and strength of an inorganic material (e.g., glass). Thus, such known toughened glass layers typically have a high Compressive Stress (CS) and a DoL of more than 20 μm, which results in a high Central Tension (CT) inside the glass. However, the inventors have surprisingly found that the sharp contact resistance of such known toughened glasses decreases rapidly with increasing DoL and reaches a minimum when the ratio between DoL (in μm) and thickness (in μm) is approximately between 0.1 and 0.2, if there is no additional surface protection to prevent sharp contact. In certain embodiments, the ratio DoL/d is less than 0.2. Thus, if a conventional toughened glass layer is pressed or impacted by a high hardness object (e.g., sand sticking to a finger when pressing the protective cover glass of an FPS), it will cause a crack to propagate through the strengthened layer of the cover glass (i.e., as defined by the Compressive Stress (CS)), even if the contact force is small, the crack reaches the tensile portion of the glass. Known glass articles spontaneously develop cracks and the cover glass is damaged due to the high central tensile stress in this glass region.

The inventors have surprisingly found that the inorganic material layer used according to the invention is more reliable in terms of flexibility and contact resistance during further processing and in everyday use. In some embodiments this may be due to an improved and optimized stress distribution of the layer according to the invention. Conversely, if the layer of inorganic material meets the required crushing force and the required crushing bend radius (referring to its respective thickness and measured surface CS), the risk of crushing the layer when in use (e.g. in a protective cover) is low.

As described above, the inorganic material layer may have completely different sizes. Therefore, in determining the crushing force and the crushing bend radius, the following factors must be considered:

in the case of larger layers (e.g., larger glass plates), the breaking force of multiple samples was measured using a sandpaper press test. For this, a random sample of N values is taken. N should be high enough to obtain a statistically guaranteed average. Preferably at least 20, more preferably at least 30 samples are tested. The number of samples depends on the respective size of the layer to be tested. The measurements were statistically evaluated using the weibull method. The B10 value for the weibull distribution (i.e., the force (in N) calculated in the case where 10% of the sample was destroyed) was determined and used to represent the required crushing force.

However, in the case of small layers (e.g. a single small protective cover glass), a single measurement of the breaking force is sufficient and is used to represent the breaking force.

In case the number of measurements is between 2 and 19, the measured crushing force is averaged to represent the crushing force.

Inorganic material

In an embodiment, the inorganic material of the at least one layer of inorganic material and/or any other layer of inorganic material is an alkali-containing glass, such as alkali aluminosilicate glass, alkali silicate glass, alkali borosilicate glass, alkali aluminoborosilicate glass, alkali borosilicate glass, alkali germanate glass, alkali borogermanate glass, alkali soda lime glass, and combinations thereof. The inorganic material layer is flexible or even foldable. Typically, the outer layer of the protective cover is subjected to tensile stresses due to bending or folding, impact stresses, for example due to objects falling onto the protective cover, and stresses due to hard objects scratching.

The inorganic material may be a borosilicate glass, a soda lime glass, a lithium aluminosilicate glass or a glass ceramic.

In a preferred embodiment, the inorganic material of the inorganic material layer comprises or consists of glass, which may be characterized by one or more of the following compositional features listed below as glass compositions I or II.

Glass composition I

In this specification we refer to the cationic component of the glass. In these compositions-if not otherwise stated-silicon means Si⁴⁺By "boron" is meant B³⁺"aluminum" means Al³⁺By "lithium" is meant Li⁺And "sodium" means Na⁺By "potassium" is meant K⁺And "magnesium" means Mg²⁺"calcium" means Ca²⁺And "barium" means Ba²⁺"Zinc" means Zn²⁺"titanium" means Ti⁴⁺And "zirconium" means Zr⁴⁺"arsenic" means As³⁺And As⁵⁺The sum of (1), "antimony" means Sb³⁺And Sb⁵⁺The sum of (1), "Fe" means Fe³⁺And Fe⁴⁺In the sum, "cerium" means Ce³⁺And Ce⁴⁺"tin" refers to Sn²⁺And Sn⁴⁺"sulfur" refers to the total amount of sulfur in all its valence states and oxidation levels.

The glass has certain preferred compositions, as will be outlined below. The glass typically contains both cationic and anionic components. The composition of the cations in the glass will be given as cation percentage (cat. -%), i.e. the molar ratio representing the respective cation relative to the total molar amount of cations in the composition. Preferably, the glass comprises the following components in cat' -%, based on the total molar amount of cations in the glass: silicon 40 to 75cat '-, boron 0 to 23 cat' -, aluminum 0 to 20cat '-, lithium 0 to 18 cat' -, sodium 0 to 25cat '-, potassium 0 to 15 cat' -, magnesium 0 to 10cat '-, calcium 0 to 9 cat' -, barium 0 to 4cat '-, zinc 0 to 7 cat' -, titanium 0 to 5cat '-, zirconium 0 to 3 cat' -. In a preferred embodiment, the cations in the glass consist of the cations mentioned in the above list and are present in an amount of at least 95%, more preferably at least 97%, most preferably at least 99%. In the most preferred embodiment, the cationic component of the glass consists essentially of the cations.

As the anionic component, the glass preferably contains fluorine (F)^-) Oxygen (O)^2-) Chlorine (C)^l-) At least one anion of the ions. Most preferably, the anions present in the glass consist of oxygen and are present in an amount of at least 95%, more preferably at least 97%, most preferably at least 99%. In the most preferred embodiment, the anionic component of the glass consists essentially of oxygen.

As used herein, the terms "X-free" and "ingredient X-free" preferably refer to glasses that are substantially free of the recited ingredient X, i.e., the ingredient may be present in the glass at most as an impurity or contaminant, but is not added to the glass composition as a separate ingredient. This means that the component X is not added in the necessary amount. An optional amount according to the present invention is an amount of less than 100ppm (n/n), preferably less than 50ppm, more preferably less than 10 ppm. Thus, "X" may refer to any constituent, such as a lead cation or an arsenic cation. Preferably, the glasses described herein do not substantially contain any ingredients not mentioned in the present specification.

A particularly preferred glass composition comprises the following ingredients in cat' -%, based on the total molar amount of cations in the glass: 45 to 60cat. -%, aluminium 14 to 20cat. -%, sodium 15 to 25cat. -%, potassium 1.5 to 8.5cat. -%, magnesium 2 to 9cat. -%, zirconium 0.1 to 1.3cat. -%, cerium 0.01 to 0.3cat. -%. In a preferred embodiment, the cations in the glass consist of the cations mentioned in the above list and are present in an amount of at least 95%, more preferably at least 97%, most preferably at least 99%. In the most preferred embodiment, the cationic component of the glass consists essentially of the cations described above.

Preferably, the glass comprises silicon in a proportion of 40 to 75cat. -%, more preferably in a proportion of 45 to 60 cat-%. Silicon is an important network former in the glass matrix and is very important to the performance of the glass. In particular, silicon cations are important for the chemical resistance, hardness and scratch resistance of glass. In a preferred embodiment the glass comprises at least 41 cat-% silicon, more preferably at least 42 cat-% silicon, more preferably at least 43.5 cat-% silicon, most preferably at least 45 cat-% silicon. However, too high a silicon cation content may result in an increase in glass transition temperature, making the glass uneconomical to produce. It is therefore particularly preferred that the content of silicon cations is at most 75cat. -%, further preferably at most 70cat. -%, still more preferably at most 65cat. -%, most preferably at most 60cat. -%.

The glass may also comprise at least one second network former in addition to the silicon cations. The glass may comprise boron cations as further network formers in a proportion of 0 to 23 cat-%, more preferably 0 to 1 cat-%. The boron cations may support the stability of the glass by its network forming properties. In a preferred embodiment, the glass comprises at least 0 cat' -% boron. However, in the case where the content of boron cations in the glass is too high, the viscosity is greatly reduced, and thus it is necessary to accept a reduction in crystallization stability. It is therefore particularly preferred that the content of boron cations is at most 10cat. -%, further preferably at most 5cat. -%, still more preferably at most 2cat. -%, most preferably at most 1cat. -%. In a preferred embodiment, the glass is free of boron cations.

In the glass, the total amount of silicon and boron cations is preferably 40 to 95 cat-%, more preferably 45 to 60 cat-%. In a preferred embodiment, the total amount of silicon and boron cations in the glass is at least 41 cat-%, more preferably at least 42 cat-%, still more preferably at least 43.5 cat-%, and most preferably at least 45 cat-%. It is particularly preferred that the total amount of silicon and boron cations in the glass is at most 75cat. -%, further preferably at most 70cat. -%, still more preferably at most 65cat. -%, most preferably at most 60cat. -%.

It has been found that the temperature dependence of the refractive index is influenced by the network formers aluminium, silicon and boron in the glass. Therefore, the glass preferably has a ratio of the total amount of aluminum and boron expressed as cation percentage to the amount of silicon of 0 to 1. Preferably, the ratio is > 0 to 0.8, more preferably > 0.20 to 0.6, most preferably 0.25 to 0.4.

In the glass, aluminium cations are preferably contained in a proportion of 0 to 20 cat-%, more preferably 14 to 20 cat-%. The addition of aluminum cations improves glass forming properties and generally supports an increase in chemical resistance. In a preferred embodiment the glass comprises at least 1 cat-% aluminium, more preferably at least 5 cat-% aluminium, still more preferably at least 10 cat-% aluminium, most preferably at least 14 cat-% aluminium. However, too high a content of aluminium cations results in an increased tendency to crystallise. It is therefore particularly preferred that the content of aluminium cations is at most 20cat. -%, further preferably at most 19cat. -%, still more preferably at most 18cat. -%, most preferably at most 17cat. -%.

The glass preferably contains a fluxing agent to improve melting properties, in particular alkali metal cations and/or alkaline earth metal cations, preferably the total amount of fluxing agent ∑ { ∑ R }²⁺(R＝Mg、Ca、Sr、Ba)+∑R⁺(R ═ Li, Na, K) } is 5 to 40cat. In a preferred embodiment, the total amount of fluxing agent in the glass is at least 5cat. -%, more preferably at least 7cat. -%, still more preferably at least 12cat. -%, most preferably at least 15cat. -%. If the content of the flux in the glass is too high, the chemical resistance is reduced. It is particularly preferred that the total amount of fluxing agent in the glass is at most 38 cat-%, further preferably at most 35 cat-%, more preferably at most 33 cat-%, most preferably at most 30 cat-%.

Alkali metal cations improve the meltability of the glass, thus allowing for more economical production. Also, they may be necessary to chemically strengthen the glass by ion exchange treatment. Alkali metal cations are used as fluxing agents during the production of glass. The total amount of alkali metal cations lithium, sodium and potassium in the glass may be 0 to 35 cat-%. In a preferred embodiment, the total amount of alkali metal cations is at least 5cat. -%, more preferably at least 7cat. -%, still more preferably at least 10cat. -%, most preferably at least 15cat. -%. However, if the content of the alkali metal cation is too high, the weatherability of the glass may be impaired, and thus the range of application thereof may be severely limited. Too high a content of alkali metal cations leads to a decrease in chemical stability, since these monovalent ions may damage the bridged Si — O bonds and, in addition, they move more easily in the glass structure than other cations. It is therefore particularly preferred that the total amount of alkali metal cations is at most 35cat. -%, further preferably at most 30cat. -%, more preferably at most 27cat. -%, most preferably at most 25cat. -%.

The inventors have surprisingly found that chemical stability can be further improved when the molar ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations is kept in a favorable range. Preferably, the ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations in the glass is maintained in the range of 0.1 to 2.5. More preferably, the content of the total amount of alkali metal cations (Li, Na, K) in the glass relative to the total amount of boron and aluminum cations is at least 0.2, more preferably at least 0.3, more preferably at least 0.5, more preferably at least 0.8. Preferably, the content of the total amount of alkali metal cations (Li, Na, K) in the glass relative to the total amount of boron and aluminum cations is at most 2.5, more preferably at most 2.2, more preferably at most 2.0, more preferably at most 1.9, more preferably at most 1.7, more preferably at most 1.5. In this way, glasses with very high chemical stability can be obtained.

In the glass, lithium cations are preferably contained in a proportion of 0 to 18 cat-%. Lithium acts as a flux and has excellent ion exchange strengthening properties. However, lithium greatly affects the chemical stability of the glass, and thus the content thereof should be limited. The content of lithium cations is particularly preferably at most 18cat. -%, further preferably at most 10cat. -%, still more preferably at most 3cat. -%, most preferably at most 1cat. -%. In a preferred embodiment, the glass is free of lithium cations.

In the glass, sodium cations are preferably contained in a proportion of 0 to 25 cat-%, preferably 15 to 25 cat-%. Sodium is a good ingredient for ion exchange treatment. But-as with all alkali metal ions-the content of this component should not be too high, since it reduces the chemical stability. In a preferred embodiment, the glass comprises at least 5 cat-% sodium, more preferably at least 10 cat-% sodium, more preferably at least 12 cat-% sodium, and most preferably at least 15 cat-% sodium. Particularly preferably, the content of sodium cations is at most 24cat. -%, further preferably at most 23cat. -%, still more preferably at most 22cat. -%, most preferably at most 21cat. -%.

In the glass, potassium cations are preferably contained in a proportion of 0 to 15 cat-%, more preferably 1.5 to 8.5 cat-%. Potassium has less negative impact on chemical stability than other alkali metal ions. However, potassium is not suitable for ion exchange treatment. In addition, it is preferable to limit the content of potassium because it contains an isotope that emits β rays. In a preferred embodiment the glass comprises at least 1 cat-% potassium, more preferably at least 2 cat-% potassium, more preferably at least 3 cat-% potassium, most preferably at least 3.5 cat-% potassium. It is particularly preferred that the content of potassium cations is at most 15cat. -%, further preferably at most 10cat. -%, still more preferably at most 5cat. -%.

It has been found that the leaching tendency of the substrate glass can be reduced by using sodium and potassium simultaneously in the glass and keeping the ratio of sodium to potassium, calculated as cat < - > in the range of at most 15, more preferably at most 10, more preferably at most 9, preferably at most 8, most preferably less than 6. Keeping this ratio low (i.e., the amount of sodium relative to potassium does not exceed a certain amount) provides the glass with good meltability and excellent chemical and hydrolytic resistance. In particular, such glass will have a glass according to ISO 719: 1989 HGB 1. However, in order to adjust the viscosity in the melt to the desired value, the ratio of sodium to potassium should be greater than 0.5, preferably greater than 1 and most preferably at least 2.

Alkaline earth metal cations can improve the meltability of the glass, thus allowing economical production. They can be used as fluxes in the production of glass. The total amount of the alkaline earth metal cations magnesium, barium and calcium in the glass is preferably 0 to 15 cat-%, more preferably 2 to 9 cat-%. The alkaline earth metal ions affect the chemical resistance of the glass and have little positive effect on the ion exchange treatment. Therefore, in the present invention, the glass preferably does not contain any alkaline earth metal ions. It is particularly preferred that the total amount of alkaline earth metal cations in the glass is at most 13cat. -%, further preferably at most 12cat. -%, still more preferably at most 10cat. -%, most preferably at most 9cat. -%. Furthermore, alkaline earth metal cations and zinc cations can be used to adjust the viscosity of the glass, particularly for fine tuning of the viscosity-temperature curve. Furthermore, alkaline earth metal cations and zinc cations-as with alkali metal cations-may be used as fluxing agents. The glass may be free of at least one cation selected from the group consisting of magnesium cations, calcium cations, strontium cations, barium cations, and zinc cations. Preferably, the glass is free of zinc cations, calcium cations, strontium cations, and barium cations.

In the glass, zinc cations are preferably contained in a proportion of 0 to 7 cat-. It is particularly preferred that the content of zinc cations is at most 6 cat-%, more preferably at most 5 cat-%. In a preferred embodiment, the glass is free of zinc. In the glass, calcium cations are preferably contained in a proportion of 0 to 9 cat-. It is particularly preferred that the content of calcium cations is at most 8cat. -%, further preferred at most 3 cat-%. In a preferred embodiment, the glass is free of calcium. In the glass, barium cations are preferably contained in a proportion of 0 to 4 cat-%. It is particularly preferred that the content of barium cations is at most 4cat. -%, further preferably at most 3cat. -%, still more preferably at most 2cat. -%, most preferably at most 1cat. -%. In a preferred embodiment, the glass is free of barium. In a preferred embodiment, the glass is free of strontium.

In the glass, the magnesium cations are preferably contained in a proportion of 0 to 10cat. -%, more preferably 2 to 9 cat-%. Magnesium cations can be contained in the glass as a further fluxing agent, and the melting point can also be set specifically. The melting point of the glass can be lowered by adding the network modifier magnesium. In a preferred embodiment, the glass comprises at least 1 cat-% magnesium, more preferably at least 2 cat-% magnesium, more preferably at least 3 cat-% magnesium. However, too high a content of magnesium cations may cause a decrease in the melting point of the glass. It is particularly preferred that the content of zinc cations is at most 8 cat-%, further preferably at most 6 cat-%.

In the glass, the titanium cations are preferably contained in a proportion of 0 to 5 cat-%. Titanium cations may be added to the glass to improve its optical properties. In particular, the refractive index of the glass can be set in a targeted manner by means of the addition of titanium. Thus, the refractive index increases with increasing titanium cation content in the glass. The addition of titanium cations has yet another advantage: by this method, the UV edge of the transmission spectrum of the glass can be shifted to higher wavelengths, where the shift is higher when more titanium is added. However, too high a content of titanium cations may lead to undesired crystallization of the glass. Titanium cations can increase the refractive index of the glass. Particularly with zirconium cations, titanium cations may reduce the transmission in the blue spectral range and thus may shift the UV edge into longer wavelengths. Therefore, it is particularly preferred that the content of titanium is at most 5 cat-%, more preferably at most 1 cat-%. In a preferred embodiment, the glass is free of titanium.

In the glass, the zirconium cations are preferably contained in a proportion of 0 to 3 cat-%, more preferably 0.1 to 1.3 cat-%. Zirconium cations can be used to adjust the refractive index of the glass. In a preferred embodiment the glass comprises at least 0.1 cat-% zirconium, more preferably at least 0.2 cat-% zirconium, more preferably at least 0.5 cat-% zirconium. However, too high a content of zirconium cations may decrease the meltability, in particular resulting in stronger crystallization of the glass. It is particularly preferred that the zirconium content is at most 1.3 cat-%, further preferably at most 1.0 cat-%, more preferably at most 0.8 cat-%.

In the glass, cerium cations are preferably included in a proportion of 0.01 to 0.3 cat-. In a preferred embodiment, the glass comprises at least 0.01 cat-% cerium, more preferably at least 0.02 cat-% cerium, more preferably at least 0.05 cat-%. The content of cerium is preferably at most 0.3cat. -%, further preferably at most 0.2cat. -%, still more preferably at most 0.1cat. -%.

Glass composition II

Another preferred glass composition that may constitute an inorganic material comprises the following ingredients in cat' -%, based on the total molar amount of cations in the glass: silicon 48 to 60cat. -%, boron 10.5 to 15.5cat. -%, aluminum 2 to 8.5cat. -%, sodium 8 to 14cat. -%, potassium 5.5 to 13.5cat. -%, zinc 2 to 6cat. -%, titanium 1 to 5cat. -%. In a preferred embodiment, the cations in the glass consist of the cations mentioned in the preceding list and are present in an amount of at least 95%, more preferably at least 97%, most preferably at least 99%. In the most preferred embodiment, the cationic component of the glass consists essentially of the cations described above.

Preferably, the glass comprises silicon in a proportion of 40 to 75 cat-. Silicon is an important network former in the glass matrix, which is critical to the glass properties. Silicon is particularly important for the chemical resistance, hardness and scratch resistance of glass. In a preferred embodiment the glass comprises at least 43 cat-% silicon, more preferably at least 45 cat-% silicon, still more preferably at least 47.5 cat-% silicon, most preferably at least 48 cat-% silicon. However, too high a content of silicon cations results in an increase in glass transition temperature, making the glass uneconomical to produce. It is therefore particularly preferred that the content of silicon cations is at most 75cat. -%, further preferably at most 70cat. -%, still more preferably at most 65cat. -%, most preferably at most 60cat. -%.

In addition to the silicon cations, the glass may also comprise at least one second network former. The glass may contain boron cations as further network formers in a proportion of 0 to 23 cat-%. The boron cations may support the stability of the glass by its network forming properties. In a preferred embodiment the glass comprises at least 0 cat-% boron, more preferably at least 5 cat-% boron, still more preferably at least 7.5 cat-% boron, most preferably at least 10.5 cat-% boron. However, if the content of boron cations in the glass is too high, the viscosity may be greatly reduced, and thus the reduction of the crystallization stability must be accepted. It is therefore particularly preferred that the content of boron cations is at most 23cat. -%, further preferably at most 20cat. -%, still more preferably at most 18cat. -%, most preferably at most 15.5cat. -%.

The total amount of silicon and boron cations in the glass may be 40 to 95 cat-%. In a preferred embodiment, the total amount of cat ' -% of silicon and boron cations in the glass is at least 45cat ' -, more preferably at least 48cat ' -, still more preferably at least 50cat ' -, most preferably at least 60cat ' -. It is particularly preferred that the total amount of cat-% of silicon and boron cations in the glass is at most 95 cat-%, further preferably at most 85 cat-%, still more preferably at most 75.0 cat-%, most preferably at most 72 cat-%.

It has been found that the temperature dependence of the refractive index is influenced by the network formers aluminium, silicon and boron in the glass. Therefore, the ratio of the total amount of aluminum and boron in the glass in terms of cation percentage to the amount of silicon is 0 to 1. Preferably, the ratio is > 0 to 0.8, more preferably > 0.20 to 0.6, most preferably 0.25 to 0.4.

In the glass, aluminium cations may be contained in a proportion of 0 to 20 cat-%. The addition of aluminum cations results in improved glass forming properties and generally supports an increase in chemical resistance. In an embodiment the glass comprises at least 0 cat-% aluminium, more preferably at least 1 cat-% aluminium, still more preferably at least 2 cat-% aluminium, most preferably at least 3 cat-% aluminium. However, too high a content of aluminium cations results in an increased tendency to crystallise. It is therefore particularly preferred that the content of aluminum cations is at most 20cat. -%, further preferably at most 15cat. -%, still more preferably at most 10cat. -%, most preferably at most 8cat. -%.

The glass may contain a fluxing agent to improve melting properties, in particular alkali metal cations and/or alkaline earth metal cations, preferably the total amount of fluxing agent ∑ { ∑ R }²⁺(R＝Mg、Ca、Sr、Ba)+∑R⁺(R ═ Li, Na, K) } is 5 to 40cat. In a preferred embodiment, the total amount of fluxing agent in the glass is at least 5cat. -%, more preferably at least 7cat. -%, still more preferably at least 12cat. -%, most preferably at least 15cat. -%. If the content of the flux in the glass is too high, the chemical resistance is reduced. It is particularly preferred that the total amount of fluxing agent in the glass is at most 35 cat-%, more preferably at most 30 cat-%, even more preferably at most 25 cat-%Most preferably at most 23cat.

Alkali metal cations improve the meltability of the glass, thus allowing for more economical production. In addition, they are necessary for chemical strengthening of glass by ion exchange treatment. During the production of the glass, alkali metal cations are used as fluxing agents. The total amount of alkali metal cations lithium, sodium and potassium in the glass may be 0 to 35 cat-%. In a preferred embodiment, the total amount of alkali metal cations is at least 5cat. -%, more preferably at least 7cat. -%, still more preferably at least 10cat. -%, most preferably at least 15cat. -%. However, if the content of the alkali metal cation is too high, the weatherability of the glass may be impaired, and thus the range of application thereof may be limited. Too high a content of alkali metal cations leads to a decrease in chemical stability, since these monovalent ions may damage the bridged Si-O bonds and their movement in the glass structure is easier than for other cations. It is therefore particularly preferred that the total amount of alkali metal cations is at most 35cat. -%, further preferably at most 30cat. -%, more preferably at most 25cat. -%, most preferably at most 23cat. -%.

The inventors have surprisingly found that chemical stability can be further improved when the molar ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations is kept in a favorable range. Preferably, the ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations in the glass is maintained in the range of 0.1 to 2. More preferably, the ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations in the glass is at least 0.2, more preferably at least 0.3, more preferably at least 0.5, more preferably at least 0.8. Preferably, the ratio of the total amount of alkali metal cations (Li, Na, K) to the total amount of boron and aluminum cations in the glass is at most 1.9, more preferably at most 1.8, more preferably at most 1.7, further preferably at most 1.5, more preferably at most 1.3, more preferably at most 1.2. In this way, glasses with very high chemical stability can be obtained.

In the glass, lithium cations may be included in a proportion of 0 to 18 cat-. Lithium acts as a flux and has excellent properties for ion exchange strengthening. However, lithium largely affects the chemical stability of the glass, and therefore the content thereof should be limited. The content of lithium cations is particularly preferably at most 18cat. -%, further preferably at most 10cat. -%, still more preferably at most 3cat. -%, most preferably at most 1cat. -%. In the examples, the glass does not contain lithium cations.

In the glass, sodium cations may be included in a proportion of 0 to 25 cat-. Sodium is a good ingredient for ion exchange treatment. But-as with all alkali metal ions-the content of this component should not be too high, since it would reduce the chemical stability. In a preferred embodiment, the glass comprises at least 3 cat-% sodium, more preferably at least 5 cat-% sodium, more preferably at least 8 cat-% sodium, and most preferably at least 9 cat-% sodium. It is particularly preferred that the content of sodium cations is at most 23cat. -%, further preferably at most 22cat. -%, more preferably at most 20cat. -%, most preferably at most 15cat. -%.

In the glass, potassium cations may be included in a proportion of 0 to 15 cat-%. Potassium has less negative impact on chemical stability than other alkali metal ions. However, potassium is not suitable for ion exchange treatment. In addition, it is preferable to limit the content of potassium because it contains an isotope that emits β rays. In a preferred embodiment the glass comprises at least 1 cat-% potassium, more preferably at least 2 cat-% potassium, more preferably at least 3 cat-% potassium, most preferably at least 5.5 cat-% potassium. It is particularly preferred that the content of potassium cations is at most 15cat. -%, further preferably at most 13cat. -%, still more preferably at most 12cat. -%.

It has been found that the leaching tendency of the glass can be reduced by using sodium and potassium simultaneously in the glass and keeping the ratio of sodium to potassium, calculated as cat < - > at most 5, more preferably at most 4.5, more preferably at most 3.5, preferably at most 2.0, most preferably less than 1.6. Keeping this ratio low (i.e., the amount of sodium relative to potassium does not exceed a certain amount) provides a glass with good melting and excellent chemical and hydrolysis resistance. In particular, such glass may have a glass thickness according to ISO 719: 1989 HGB 1. However, in order to adjust the viscosity in the melt to the desired value, the sodium to potassium ratio should be greater than 0.5, preferably greater than 0.7, and preferably greater than 0.7, most preferably at least 0.8.

The alkaline earth metal cations improve the meltability of the glass, thus allowing for more economical production. During the production of the glass, they act as fluxes. The total amount of the alkaline earth metal cations magnesium, barium and calcium in the glass may be 0 to 15 cat-%. The alkaline earth metal ions affect the chemical resistance of the glass and have little positive effect on the ion exchange treatment. Therefore, in the present invention, the glass may not contain alkaline earth metal ions. It is particularly preferred that the total amount of alkaline earth metal cations in the glass is at most 13 cat-%, further preferably at most 10 cat-%, still more preferably at most 5 cat-%, most preferably at most 1 cat-%. Furthermore, alkaline earth metal cations and zinc cations can be used to adjust the viscosity of the glass, in particular for fine-tuning of the viscosity-temperature curve. Furthermore, alkaline earth metal cations and zinc cations-as with alkali metal cations-may be used as fluxing agents. The glass may be free of at least one cation selected from the group consisting of magnesium cations, calcium cations, strontium cations, barium cations, and zinc cations. Preferably, the glass is free of magnesium cations, calcium cations, strontium cations and barium cations.

In the glass, magnesium cations may be included in a proportion of 0 to 10 cat-. It is particularly preferred that the content of magnesium cations is at most 8 cat-%, more preferably at most 6 cat-%. In a preferred embodiment, the glass is free of magnesium. In the glass, the content of calcium cations may be 0 to 9cat. It is particularly preferred that the content of calcium cations is at most 8cat. -%, further preferred at most 3 cat-%. In a preferred embodiment, the glass is free of calcium. In the glass barium cations may be included in a proportion of 0 to 4 cat-. It is particularly preferred that the content of barium cations is at most 4cat. -%, further preferably at most 3cat. -%, still more preferably at most 2cat. -%, most preferably at most 1cat. -%. In a preferred embodiment, the glass is free of barium. In a preferred embodiment, the glass is free of strontium.

In the glass, zinc cations may be included in a proportion of 0 to 7 cat-. The zinc cations can be contained in the glass as a further fluxing agent, and the melting point can also be set specifically. The melting point of the glass can be lowered by adding the network modifier zinc. In a preferred embodiment the glass comprises at least 1 cat-% zinc, more preferably at least 2 cat-% zinc, more preferably at least 3 cat-% zinc. However, too high a zinc cation content may result in a decrease in the melting point of the glass.

It is particularly preferred that the content of zinc cations is at most 6 cat-%, further preferably at most 5 cat-%.

In the glass, titanium cations may be included in a proportion of 0 to 5 cat-%. Titanium cations may be added to the glass to improve its optical properties. In particular, the refractive index of the glass can be set in a targeted manner by means of the addition of titanium. Thus, the refractive index increases with increasing titanium cation content in the glass. The addition of titanium cations has another advantage: by this measure, the UV edge of the transmission spectrum of the glass is shifted to higher wavelengths, wherein the shift is higher when more titanium is added. In a preferred embodiment the glass comprises at least 0.1 cat-% titanium, more preferably at least 0.5 cat-% titanium, more preferably at least 1 cat-% titanium, most preferably at least 2 cat-%. However, too high a content of titanium cations may lead to undesired crystallization of the glass. Titanium cations can increase the refractive index of the glass. Particularly with zirconium cations, titanium cations reduce the transmission in the blue spectral range and thus may shift the UV edge into longer wavelengths. Therefore, it is particularly preferred that the content of titanium is at most 5 cat-%, further preferably at most 4 cat-%.

The inventors have surprisingly found that hydrolysis resistance, acid resistance and alkali resistance can be further improved when the molar ratio of zinc cations to titanium cations is kept in a favorable range. The molar ratio of zinc cations to titanium cations in the glass is preferably at most 5, more preferably at most 4, more preferably at most 3. More preferably, the molar ratio of zinc cations to titanium cations in the glass is in the range of between 0.1 and 3.0. More preferably, the molar ratio of zinc cations to titanium cations in the glass is at least 0.5, more preferably at least 0.8, more preferably at least 1.0, more preferably at least 1.2. The molar ratio of zinc cations to titanium cations in the glass is preferably at most 2.5, more preferably at most 2.2, more preferably at most 2.0, further preferably at most 1.7, further preferably at most 1.6.

In the glass, zirconium cations may be included in a proportion of 0 to 3 cat-. Zirconium cations can be used to adjust the refractive index of the glass. However, too high a content of zirconium cation may deteriorate the meltability, and in particular, may increase the crystallinity of the glass. It is particularly preferred that the zirconium content is at most 2 cat-%, further preferably at most 1 cat-%, still more preferably at most 0.5 cat-%. In a preferred embodiment, the glass is free of zirconium.

Shape and size

The thickness of the inorganic material layer is preferably 400 μm or less, preferably 330 μm or less, still preferably 250 μm or less, further preferably 210 μm or less, preferably 180 μm or less, still preferably 150 μm or less, more preferably 130 μm or less, more preferably 100 μm or less, more preferably 80 μm or less, more preferably 70 μm or less, further preferably 50 μm or less, further preferably 30 μm or less, and even preferably 10 μm or less. The thickness may be at least 5 μm. Such a particularly thin layer is desirable for various applications as described above. In particular, the thin thickness imparts flexibility on the layer.

According to an advantageous embodiment, the layer of inorganic material (e.g. glass layer) may be a flat layer and/or a flexible layer and/or a deformable layer. A "flat" layer may, for example, be a substantially planar or planar layer. However, "flat" in the sense of the present invention also includes items that are deformable or deformed in two or three dimensions. Preferably, the layer of inorganic material has a substantially uniform thickness. The inorganic material layer may have a Total Thickness Variation (TTV) of not more than 10 μm, or less than 5 μm, or less than 1 μm. In a preferred embodiment, at least the first layer of inorganic material meets the TTV requirement. In an embodiment, the at least one further layer of inorganic material does not satisfy this embodiment, but comprises a region of reduced thickness therein. This provides increased flexibility in the further inorganic material layer while having excellent surface properties in the first inorganic material layer.

As previously mentioned, the inorganic material layer is preferably very thin. Inorganic materials, particularly materials with a certain brittleness, have a tendency to fracture under stress. In order to reduce the tendency of the inorganic material layer to break, the present invention provides measures that can be applied to the inorganic material layer. Typically, the inorganic material layer has two parallel major surfaces on opposite sides and an edge portion connecting the two major surfaces. To reduce the likelihood of breakage, at least a portion of the edge portion includes a convex curvature such that at least one major surface merges into a portion of the edge portion. A portion of the edge portion may have a curvature with an arc length that is at least 1/30, at least 1/20, or at least 1/10 of the thickness of the inorganic material layer. A part of the edge portion may comprise an indentation in the form of a groove in the area of the convex curvature. The length of the grooves may be greater than their width and/or depth. By means of the plurality of grooves on the edge portion, any cracks present or formed on the surface of the edge portion are mutually influenced, so that the tensile strength at the crack tip is reduced, thereby improving the overall stability of the layer. Therefore, forming the curvature as described above on the edge portion of the inorganic material layer will improve the stability of the protective cover during bending or folding.

The depth of the grooves may be at least 10nm and at most 5 μm, preferably at most 2 μm or at most 1 μm. The grooves may be manufactured by using an abrasive tool having a corresponding abrasive grain size. The portion of the edge portion having a convex curvature may be given a radius of curvature which is a radius of a circle fitted to a start point, a middle point and an end point of an arc of curvature. According to a preferred embodiment, the radius is at least 1/40, at least 1/30, or at least 1/20 of the thickness of the layer of inorganic material. For stability of the inorganic material layer, even larger radii are useful. Thus, the radius of the fitted circle may be at least 1/10 or 1/5, or even half, of the thickness of the inorganic material layer. In other embodiments, the radius of the fitted circle may be greater than the thickness of the layer of inorganic material.

In certain embodiments, a portion of the edge portion may be adjacent to a region of the major surface of the inorganic material layer. In the case where a part of the edge portion and a region of the main surface are adjacent to each other, the radius of curvature may be small. In embodiments, the angle between a tangent of a portion of the edge portion and a tangent of a region adjacent the main surface may be at most 45 °, at most 20 °, or at most 10 °. With such a small radius and the formation of edge lines, the slope of adjacent surfaces changes very quickly.

In order to reduce the propagation of cracks in the inorganic material layer, the grooves are preferably oriented in different directions, for example inclined and/or perpendicular to each other. The grooves may cross each other.

Adhesive layer

The protective cover of the present invention comprises an inorganic material layer and an adhesive layer. The adhesive layer may be used to secure the protective cover to the display screen of the electronic device, or to facilitate adhesion of the protective cover to other portions of the display screen and/or to other layers of the protective cover, such as additional layers of inorganic material or one or more polymer layers. In the case of a removable protective cover, the adhesive layer may be covered by a cover sheet prior to use. The cover sheet may be torn off before the protective cover is mounted on the display screen of the electronic device. The cover sheet may be made of a polymeric material such as plastic.

The adhesive layer may be directly on the inorganic material layer. In certain embodiments, an additional layer or layers may be disposed between the adhesive layer and the inorganic material layer, such as a polymer layer described below and/or an additional adhesive layer between the polymer layer and the inorganic layer, such as an OCA (optically clear adhesive) layer and/or a silicone layer. In other words, in an embodiment, the protective cover comprises the following sequence of layers: a layer of inorganic material, a further layer of adhesive, a layer of polymer, a layer of adhesive. The adhesive layer may comprise or consist of a single or multiple layer of adhesive.

The adhesive strength of the protective cover on a display screen of an electronic device such as a polyimide display screen is preferably in the range of 0.01N/25mm to 0.3N/25mm, preferably 0.03N/25mm to 0.29N/25mm, more preferably 0.05N/25mm to 0.26N/25 mm.

The protective cover may be secured to the display screen of the electronic device by an adhesive layer, wherein the adhesive layer secures the inorganic material layer to the display screen of the electronic device directly or with at least one intermediate polymer layer. If desired, an adhesion promoter or binder may be used on the inorganic material and/or the display to ensure that the inorganic material bonds to the display, or to other layers of the protective cover (e.g., a polymer layer and/or additional inorganic material layers). Adhesion promoters suitable for this purpose are, for example, silicones or OCAs, substituted silanes or hexamethyldisilazane, but epoxy coatings may also be used.

When selecting the adhesion promoter and the binder and polymer for the optional polymer layer, it must be ensured that they do not reduce the transmission of light too much. Furthermore, they should preferably have a refractive index similar to glass. Since glass bends over its entire service life, it is important that the polymer to which it is fixed has a very low tendency to crack and stress whitening.

The adhesive layer may comprise or consist of an adhesive, such as an adhesive polymer or the like. The binder is preferably selected from OCA, acrylates, methacrylates, polystyrene, silicones and epoxides. They may be pressure-sensitive, reactive or hot-melt. The pressure sensitive type has the advantage that the protective cover can be easily replaced in case of damage, while other types provide a more reliable adhesion. In embodiments, the adhesive layer provides adhesion between the layers of the protective cover and/or structural stability of the protective cover. Many of the polymers disclosed herein are capable of providing these and other functions, such as those disclosed herein as polymer layers.

The thickness of the adhesive layer is preferably less than the thickness of the inorganic material layer. In case a polymer layer is present in the protective cover, the adhesive layer is preferably also thinner than the polymer layer. The thickness of the adhesive layer is preferably in the range of less than 100 μm, less than 80 μm, less than 60 μm, less than 40 μm or less than 20 μm or even less than 10 μm. The adhesive layer may be coated, printed or laminated onto the inorganic material layer or the polymer layer. The adhesive layer may substantially completely cover the inorganic material layer or the polymer layer, i.e., the adhesive layer may cover the surface of the inorganic material layer or the polymer layer to an extent of at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99%.

Polymer layer

The protective cover of the present invention may include a polymer layer between the inorganic material layer and the adhesive layer. In an embodiment, the protective cover comprises the inorganic material layer, the polymer layer and the adhesive layer in this order all without any other layers in between. In an embodiment, there may be an additional layer between the inorganic material layer and the polymer layer, the additional layer comprising a binder that promotes bonding between the polymer of the polymer layer and the inorganic material of the inorganic material layer.

Generally, the polymer of the polymer layer should have good compatibility with the inorganic material and the adhesive layer. In a preferred embodiment, the contact angle of a water droplet of the polymer layer differs from the contact angle of a water droplet of the inorganic material by less than 30 °, less than 20 °, less than 10 °. The contact angle can be measured by using a commercial contact angle tester.

The polymer interlayer serves two primary purposes. On the one hand, it provides mechanical reinforcement to the relatively brittle inorganic layer. On the other hand, in case the inorganic layer is broken, it will act as a safety device by fixing the fragments and particles. Thus, there is a need for very good adhesion to inorganic materials, i.e. high peel forces, as well as good resistance to tear propagation and puncture. However, the adhesive layer should allow the protective cover to be peeled off again from the display screen of the electronic device, for example, in case the inorganic material is broken. The polymer of the polymer layer is preferably selected from Polystyrene (PS), polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PETG), poly (ethylene vinyl acetate) (EVA), Polycarbonate (PC), Polyimide (PI), polyvinyl chloride (PVC), polyvinyl butyral (PVB), Thermoplastic Polyurethane (TPU), or polymethyl methacrylate (PMMA), more preferably polyvinyl butyral (PVB), Thermoplastic Polyurethane (TPU), glycol-modified polyethylene terephthalate (PETG), poly (ethylene-vinyl acetate) (EVA), Polycarbonate (PC), Polyethylene (PE), epoxy resins, or combinations thereof.

A polymer layer may be laminated to the inorganic material layer. In another embodiment, a polymer layer may be coated onto the inorganic material layer. The polymeric layer may substantially completely cover the inorganic material layer, i.e., the polymeric layer covers the surface of the inorganic material layer to an extent of at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99%, optionally with one or more additional layers therebetween.

According to an advantageous embodiment, the thickness of the polymer layer is at least 1 μm, preferably at least 5 μm, further preferably at least 10 μm, more preferably at least 20 μm, most preferably at least 40 μm, to achieve the desired resistance. The upper limit of the thickness of the polymer layer may be 250 μm, 200 μm, 150 μm or 100 μm.

The polymer layer may be laminated to the inorganic material layer, or it may be printed or coated. The lamination can be carried out by different known methods.

In addition to or instead of the above polymers, the polymer material for the polymer layer may be selected from, for example, silicone polymers, sol-gel polymers, Polycarbonates (PC), polyethersulfones, polyacrylates, Polyimides (PI), inorganic silica/polymer mixtures, cyclic olefin copolymers, polyolefins, silicone resins, Polyethylenes (PE), polypropylenes, polypropylene polyvinylchloride, polystyrenes, styrene-acrylonitrile copolymers, thermoplastic polyurethane resins (TPU), Polymethylmethacrylate (PMMA), ethylene-vinyl acetate copolymers, polyethylene terephthalate (PET), polybutylene terephthalate, Polyamides (PA), polyacetals, polyphenylene oxides, polyphenylene sulfides, fluorinated polymers, chlorinated polymers, ethylene-tetrafluoroethylene (ETFE), Polytetrafluoroethylene (PTFE), and mixtures thereof, Polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), polyethylene naphthalate (PEN), terpolymers made of polytetrafluoroethylene, terpolymers made of hexafluoropropylene and vinylidene fluoride (THV) or terpolymers made of polyurethane or mixtures thereof. The polymer layer may be applied to the inorganic material layer by any known method.

According to one embodiment, a polymer layer is coated on the inorganic material layer. The coating of the protective layer may be applied by any known coating method, such as Chemical Vapor Deposition (CVD), dip coating, spin coating, ink jetting, casting, screen printing, spray coating, and spraying. However, the present invention is not limited to those procedures. Suitable coating materials are also known in the art. For example, they may comprise a rigid plastic reaction resin, i.e. a polymer selected from the group consisting of phenolics, phenolic resins, aminoplasts, urea-formaldehyde resins, melamine-formaldehyde resins, epoxide resins, unsaturated polyester resins, vinyl ester resins, phenolic acrylate resins, diallyl phthalate resins, silicone resins, cross-linked polyurethane resins, polymethacrylate reaction resins and polyacrylate reaction resins.

Additional layers of inorganic material

The protective cover may comprise at least one further layer of inorganic material, for example a second layer of inorganic material. This additional layer may give the protective cover greater mechanical strength. In an embodiment, the layer consists of a glass according to glass composition I or II described above.

In one embodiment, the additional inorganic material layer is comprised of an alkali-containing glass, such as alkali aluminosilicate glass, alkali silicate glass, alkali borosilicate glass, alkali aluminoborosilicate glass, alkali borosilicate glass, alkali germanate glass, alkali borogermanate glass, soda lime glass, and combinations thereof. The further layer of inorganic material is bendable or even foldable. Typically, the outer layer of the protective cover is subjected to tensile stresses due to bending or folding or impact stresses.

The thickness of the further layer of inorganic material may be less than 700 μm, less than 500 μm, less than 300 μm, less than 250 μm, less than 200 μm, less than 150 μm, less than 100 μm, less than 75 μm, less than 70 μm, less than 50 μm, less than 30 μm or less than 15 μm. The thicker the layer, the higher the mechanical stability. The thinner the layer, the higher the ability to bend and fold.

Vickers hardness HV of additional inorganic material layer_0.2/25May be 400 to 800 MPa. Vickers hardness HV of toughened additional inorganic material layer_0.2/25May be 450 to 1000 MPa. Knoop hardness HK of non-toughened additional inorganic material layer_0.1/20May be 350 to 750 MPa. Knoop hardness HK of toughened additional inorganic material layer_0.1/20Can be 400 to800MPa。

In certain embodiments, the thickness of the additional layer of inorganic material may be less than 0.175mm, less than 0.145mm, less than 0.1mm, less than 0.07mm, or even less than 0.05 mm.

For the material of the further inorganic material layer, the same properties as the first inorganic material layer may be desired, such as flexural strength, alkaline leaching factor and acid leaching factor.

In an embodiment, the protective cover comprises an adhesive layer and/or a polymer layer disposed between the first and second inorganic material layers.

In an embodiment, the protective cover comprises a first layer of inorganic material and a second layer of inorganic material, wherein the polymer layer is disposed between the two layers of inorganic material. An adhesive layer may be further disposed between the polymer layer and each of the inorganic material layers. The adhesive layer disposed between the first inorganic material layer and the polymer layer may be an OCA layer. The adhesive layer disposed between the second inorganic material layer and the polymer layer may be a silicone layer.

The first layer of inorganic material may be very thin, for example 10 to 150 μm, or 25 to 100 μm, or 30 to 70 μm or about 50 μm. The first layer of inorganic material may be chemically toughened. Due to its very small thickness, the layer may have a very high flexibility, including the ability to bend and/or fold.

The second inorganic material layer may be thicker than the first inorganic material layer. The thickness thereof may be in the range of 50 μm to 300 μm, or 75 μm to 200 μm, or 90 μm to 150 μm. The second inorganic layer is sufficiently flexible but also provides mechanical strength to the protective cover. In an embodiment, the second layer of inorganic material is part of the protective cover that is inwardly foldable, i.e. when the cover is folded, the second layer of inorganic material is on the stretched side of the protective cover. Thicker glass is very sensitive to compression and less sensitive to tension. Thus, the mechanical strength of the second inorganic material layer can be exploited and benefit from the very low thickness of the first inorganic material layer.

In embodiments, the first and second inorganic material layers may be laminated using one or more adhesive layers and/or polymer layers. The first inorganic material layer may have a thickness of about 50 μm, and the second inorganic material layer may have a thickness of about 100 μm. In another embodiment, the protective cover has exactly one layer of inorganic material, which may be thicker than the first layer of inorganic material in a protective cover having more than one layer of inorganic material. In this embodiment, the inorganic material layer may have a thickness greater than 100 μm or greater than 120 μm.

The adhesive layer may comprise or consist of a polymer, such as one of the polymers mentioned above for the adhesive layer and/or for the polymer layer. The polymer layer may comprise or consist of a polymer, such as one of the polymers described above for the polymer layer. The adhesive layer and/or the polymer layer may be very thin, for example less than 100 μm, or less than 70 μm, or less than 50 μm, or less than 30 μm, or less than 15 μm or even less than 5 μm. This layer may be used to securely attach the first inorganic material layer to the second inorganic material layer. The polymer in the adhesive layer may provide sufficient flexibility to the layer to enable the protective cover to bend and fold. A second adhesive layer may be disposed on the other side of the second inorganic material layer to facilitate attachment of the protective cover to the display screen and/or the electronic device.

To enhance the ability of the first and/or second inorganic material layer to bend and fold, the layer may comprise one or more regions of reduced thickness. One or more regions of reduced thickness may be disposed at or near the bending axis. The bending axis extends at the surface of the inorganic material layer where the tensile stress peaks during bending. The bending axis may be located inside the protective cover, for example extending in the width direction on the surface of the inorganic material layer. In an embodiment, the region of reduced thickness may have an elongated shape, i.e. a length that is much larger than the width of the region, e.g. one or more grooves, gaps or trenches in the inorganic material. The region of reduced thickness may be cut or milled into material. The region of reduced thickness may be oriented in a direction substantially parallel to the bending axis and/or substantially perpendicular to the longitudinal axis of the protective cover. The area of reduced thickness may be present at the side facing the display screen and/or the electronic device in order to provide an optimal effect on the bendability and/or foldability of the inwardly foldable protective cover. In an embodiment, the region of reduced thickness may be arranged on a side of the inorganic material layer facing away from the interface of the first inorganic material layer with the ambient air.

The first inorganic material layer and/or the second inorganic material layer may have a plurality of regions of reduced thickness in the form of grooves, trenches or gaps oriented substantially parallel to the bending axis of the respective layer. The plurality may comprise at least 2, at least 4, at least 6, at least 10, at least 15 or at least 20 regions of reduced thickness. In an embodiment, the recess, gap or trench has a very small width, for example a maximum width of less than 1mm, or less than 100 μm, or less than 10 μm, or less than 1 μm, or less than 0.4 μm, or less than 0.2 μm. The very thin reduced thickness region is hardly visible to the user of the protective cover. The region of reduced thickness (e.g. a recess, gap or trench) may extend over at least 40% of the width of the respective layer of inorganic material, or over at least 60%, or at least 80% or at least 90% of the layer. In an embodiment, one or more or all of the gaps, trenches or grooves extend over the entire width of the respective layer. In the case of a gap, this will result in a segmentation of the first and/or second inorganic material layer, wherein the different segments form elongated inorganic material strips separated by the gap. This may provide excellent flexibility and bendability. The polymer and/or adhesive layer may hold the strip in place.

The invention includes embodiments of a protective cover having exactly one layer of inorganic material. In these embodiments, there may be one or more regions of reduced thickness in one layer of inorganic material as described herein. In embodiments having only one layer of inorganic material, this layer may be thicker than in a protective cover having more than one layer of inorganic material, for example greater than 100 μm or greater than 120 μm.

In an embodiment, the first and/or second inorganic material layer may comprise a region of reduced thickness, wherein the region of reduced thickness is characterized in that the thickness of the second inorganic material continuously decreases in the direction of the bending axis, wherein a minimum thickness in the direction of the bending axis may be achieved. Therefore, the bending property is highest at the bending axis where bending is required. The highest thickness may be at a portion of the second inorganic material layer furthest from the bending axis.

For example, the thickness reduction may be achieved by polishing, scoring, cutting (e.g., laser cutting), grinding, and/or etching. Optionally, after any grinding and/or cutting, the resulting grooves, trenches, cracks and/or dents may be etched. The etching is adapted to smooth any cracks or sharp edges so that the layer is not damaged.

In another embodiment, the protective cap can include a single inorganic layer having a relatively large thickness, such as 100 μm to 300 μm, or 150 μm to 250 μm, or 175 μm to 225 μm. As described above, by incorporating a region of reduced thickness, the first inorganic layer may have improved flexibility. The region of reduced thickness and improved flexibility may comprise a region having a thickness of less than 100 μm, such as less than 70 μm, such as less than 50 μm or less than 30 μm. These regions may extend over a central portion of the inorganic material layer corresponding to the region of the bending axis. This area may for example cover 1% to 10% of the inorganic material layer and/or the protective cover.

Generally, the region of reduced thickness may cause fracture of the inorganic material layer. This may be a desired effect if the parts of the inorganic material layer or the inorganic material layer obtained after crushing are firmly attached together by the adhesive layer and/or the polymer layer so that they remain in place after crushing. An advantage of an embodiment that results in the inorganic material layer breaking at the first bend is that the protective cover will have almost infinite flexibility. In this case it is useful to have very thin and straight regions of reduced thickness where the layer of inorganic material may break, resulting in only very thin and straight gaps in the material after breaking, so that no caps appear broken. This may be achieved by scoring, for example.

In the case of a groove or trench, a region of reduced thickness may be formed in the inorganic material layer by scoring. An advantageous way of scoring the region of reduced thickness is described in US2017/0217817 a1, which is incorporated herein by reference as if fully set forth herein. Additionally or alternatively, scoring may be performed using the scoring method described in US 2016/0185647A 1, which is incorporated by reference herein as if fully set forth herein. Additionally or alternatively, scoring may be performed using the scoring method described in US 2016/0152506A 1, which is incorporated by reference herein as if fully set forth herein. The scoring method is particularly useful for creating areas of reduced thickness that result in fracture of the inorganic material layer upon first bending. In embodiments, it may be desirable to cause fracture along the score line prior to bending the protective cap for the first time. In this case, the score line may be forced to fracture by adding a liquid, such as alcohol, in the score line and heating to cause the inorganic material to fracture along the score line. This method results in very fine gaps that are substantially invisible to the naked eye.

In an embodiment, the region of reduced thickness is a gap in the inorganic material. These gaps can be formed by scoring the inorganic material and then forming gaps in the inorganic material along the score line (e.g., using a liquid as described above). In addition, as described above, the gap may be formed using laser cutting.

The region of reduced thickness may be partially or completely filled with a similar refractive index n_dFor example, a material having a refractive index that differs from that of the inorganic material by no more than 0.3, or no more than 0.2, or no more than 0.1. Keeping the refractive index within this range improves the optical appearance of the protective cover. Suitable materials may be selected from the materials described above for the polymer and/or adhesive layers.

Production protective cover

The invention also provides a method for manufacturing the protective cover, which comprises the following steps:

-providing a layer of inorganic material, and

-attaching an adhesive layer on the layer of inorganic material.

Attaching the adhesive layer to the inorganic material layer may include coating the inorganic material layer with the adhesive layer. Where the protective cover comprises a polymer layer, the adhesive layer may be attached to, or coated to, the polymer layer. In case the protective cover comprises any further inorganic material layer, the adhesive layer may be attached to or applied to the further inorganic material layer. The polymer layer may be coated onto the first and/or any further inorganic material layer or it may be laminated onto the inorganic material layer. The polymer layer may be attached or coated directly or indirectly onto the inorganic material layer. An intermediate layer (e.g., an additional adhesive layer, such as an OCA layer) may be attached or coated onto the inorganic layer and/or the polymeric layer. The coating may be performed using any known coating method, such as Chemical Vapor Deposition (CVD), dip coating, spin coating, inkjet, casting, screen printing, spray coating, and spraying.

A preferred method comprises the steps of: the one or more inorganic material layers are provided by selecting the inorganic material layers based on desired parameters given herein, such as those measured according to the sandpaper press test and/or sandpaper ball drop test discussed above.

Preferably, the one or more layers of inorganic material in the protective cover of the present invention may be a layer of glass, such as an ultra-thin glass (UTG) layer. Such a layer can be produced by polishing from a thicker glass. However, this method is uneconomical and leads to poor surface quality, for example by R_aThe coarseness is quantified.

For batch production, direct thermoforming production is preferred, such as the drop-down or overflow fusion processes. The redraw process is also advantageous. These mentioned methods are economical and the glass surface quality is high and glass with a thickness of 5 μm (or even less) to 500 μm can be produced. For example, downdraw/overflow fusion processes impart roughness R to a raw or fire-polished surface_aLess than 5nm, less than 2nm or less than 1 nm. The thickness can also be accurately controlled within the range of 5 μm and 500 μm. The thin thickness gives flexibility to the glass. A special float process can produce glass with pristine surfaces, both economical and suitable for mass production, but the tin side of the float produced glass is different from the other side.The difference between the two sides can lead to glass warpage after chemical toughening and can affect any printing or coating process due to the different surface energies of the two sides. Another variation of the glass layer may be produced by sawing glass articles from thick glass ingots, strips, blocks, or the like.

Optional strengthening (also known as toughening) can be accomplished by immersing the glass in a molten salt bath with potassium ions or covering the glass with a paste containing potassium ions or other alkali metal ions and heating it to an elevated temperature for a period of time. In the glass layer, alkali metal ions having a larger ion radius in the salt bath or paste are exchanged with alkali metal ions having a smaller radius, and a surface compressive stress is formed due to the ion exchange.

The chemically toughened glass layer that can be used as the inorganic material layer is obtained by chemically toughening a chemically toughenable glass layer. The toughening process may be performed by immersing the glass layer in a salt bath containing monovalent ions and exchanging with alkali metal ions inside the glass. The monovalent ionic radius in the salt bath is greater than the alkali ionic radius inside the glass. After ion exchange, Compressive Stress (CS) is created on the glass as larger ions are squeezed into the glass network. The strength and flexibility of the glass are unexpectedly and significantly improved after ion exchange. In addition, CS caused by chemical toughening improves the bending performance of the toughened glass layer and can improve the scratch resistance of the glass.

The most commonly used salt bath for chemical toughening is Na-containing⁺Or contain K⁺Or a mixture thereof. The salt is NaNO₃、KNO₃、NaCl、KCl、K₂SO₄、Na₂SO₄、Na₂CO₃And K₂CO₃. Additives such as NaOH, KOH, and other sodium or potassium salts can be used to better control the rate of ion exchange, CS, and DoL during chemical toughening. Containing Ag⁺Or containing Cu²⁺Salt baths may be used to add antimicrobial functionality to the glass.

Chemical toughening is not limited to a single step. It may comprise multiple steps in one or more salt baths with different concentrations of alkali metal ions to achieve better toughening properties. Thus, the chemically toughened glass layer may be toughened in one step or during several steps (e.g. two steps).

The chemically toughened glass layer may have only one surface (the first surface) at which there is a region of compressive stress extending from the first surface to a first depth in the glass layer, wherein the region is defined by the compressive stress. In this case, the glass layer comprises only one toughened side, which in the case of the protective cover of the invention can be the side facing away from the adhesive layer. Preferably, the glass layer may include a second compressive stress region extending from the second surface to a second depth (DoL) in the glass layer, the region defined by the compressive stress, wherein the surface Compressive Stress (CS) at the second surface is at least 100 MPa. The second surface is opposite to the first surface. Thus, the preferred glass layer is toughened on both sides.

The Compressive Stress (CS) depends mainly on the composition of the glass. Higher content of Al₂O₃Which helps to obtain higher compressive stresses. To achieve a balanced glass hot formability and chemical toughening properties, the surface compressive stress is preferably below 1200 MPa. After toughening, the glass should have a sufficiently high compressive stress to achieve high strength. Therefore, it is preferable that the surface compressive stress at the first surface and/or the second surface is equal to or greater than 100MPa, preferably equal to or greater than 200MPa, more preferably equal to or greater than 300MPa, still preferably equal to or greater than 400MPa, further preferably equal to or greater than 500 MPa. In a particularly preferred embodiment, the surface compressive stress is equal to or greater than 600MPa, further preferably equal to or greater than 700MPa, more preferably equal to or greater than 800 MPa. Of course, the CS on the first surface and the CS on the second surface may be substantially the same or may be different.

In general, DoL depends on the glass composition, but can increase almost indefinitely as the toughening time and toughening temperature are increased. The determined DoL is important to ensure stable strength of the toughened glass, but too high DoL increases self-fracture rate and strength properties of the inorganic material layer under compressive stress.

Thus, according to a variant of the invention, the DoL can be controlled to be very low (low DoL variant). To achieve the specified low DoL, the toughening temperature and/or toughening time is reduced. According to the present invention, lower toughening temperatures may be preferred because DoL is more temperature sensitive and longer toughening times are easily set during mass production. However, it is also possible to reduce the toughening time, thereby reducing the DoL of the glass layer.

The inventors have found that it would be advantageous for the stress profile of the glass layer if the DoL (in μm) of the glass layer is in the range of 0.5 μm to 150 × t/CS μm (t in μm, CS being the number of surface compressive stresses (in MPa) measured at the first surface). Preferably, the DoL (in μm) of the glass layer is in the range of 0.5 to 120 t/CS μm, preferably in the range of 1 to 120 t/CS μm (t in μm, CS being a number of surface compressive stress (in MPa) measured at the first surface), further preferably DoL (in μm) is in the range of 0.5 to 90 t/CS μm, preferably 1 to 90 t/CS μm (t in μm, CS being a number of surface compressive stress (in MPa) measured at the first surface). The DoL (in μm) of some advantageous embodiments may be in the range of 0.5 to 60 t/CS μm, preferably in the range of 1 to 60 t/CS μm (t in μm, CS being the number of surface compressive stresses (in MPa) measured at the first surface). The DoL (in μm) of other advantageous embodiments may be in the range of 0.5 μm to 45 × t/CS μm, preferably in the range of 1 μm to 45 × t/CS μm (t in μm, CS being the number of surface compressive stresses (in MPa) measured at the first surface). The DoL of other advantageous embodiments may be in the range of 0.5 μm to 27 × t/CS μm (in μm), preferably in the range of 1 μm to 27 × t/CS μm (t in μm, CS being the number of surface compressive stresses (in MPa) measured at the first surface). In the calculations given above, "x t/CS" denotes the number of x times the thickness of the glass layer divided by the measured surface CS, where x may be 150, 120, 90, 60, 45 or 27.

The advantageous values of DoL depend on the glass composition, thickness and CS applied, respectively, of the individual glass layers. In general, the glass layer according to the above advantageous embodiments has a rather low DoL. By decreasing the DoL, CT is decreased. If a sharp object exerts a high pressure on such an embodiment, the induced defect will be exactly on the glass surface. The internal strength of the glass layer cannot be overcome by the induced defects due to the significant reduction in CT, so that the glass layer is not broken into two or more pieces. Such a glass layer with a low DoL has an improved sharp press resistance.

According to another variant of the invention, the DoL of the glass layer may be very high (high DoL variant). If the glass layer has a DoL (in μm) in the range 27 × t/CS μm to 0.5 × t μm (t in μm, CS ═ a number of surface compressive stress (in MPa) measured at the first surface), more preferably a DoL (in μm) in the range 45 × t/CS μm to 0.45 × t μm (t in μm, CS ═ a number of surface compressive stress (in MPa) measured at the first surface, more preferably a DoL (in μm) in the range 60 × t/CS μm to 0.4 × t μm (t in μm), CS ═ a number of surface compressive stress (in MPa) measured at the first surface, more preferably a DoL (in μm) in the range 90 × t/CS μm, and a number of surface compressive stress (in MPa) measured at the first surface, it may be advantageous. In the calculations given above, "y t/CS" represents the number of y times the thickness of the glass layer divided by the measured surface CS, where y may be 27, 45, 60 or 90. "z x t" refers to z times the thickness of the glass layer, where z can be 0.5, 0.45, 0.4, or 0.35. Such glass layers may include coating layers and/or lamination layers in order to obtain a balanced stress distribution. Even if the DoL of the glass layer is high, the coating layer and/or the laminate layer can resist scratch defects caused on the glass surface by sharp objects. Thus, the inventors have found that in addition to reducing the DoL, alternative methods may be applied to deposit a coating and/or laminate a polymer layer on one or both surfaces of the glass layer to improve the resistance to sharp contact. Of course, glass layers having a low DoL may also include coating layers and/or lamination layers.

According to an advantageous embodiment of the invention, the CT of the toughened glass layer is less than or equal to 200MPa, more preferably less than or equal to 150MPa, more preferably less than or equal to 120MPa, more preferably less than or equal to 100 MPa. Some advantageous embodiments may have a CT of less than or equal to 65 MPa. Other advantageous embodiments may have a CT of less than or equal to 45 MPa. Some variations may even have a CT of less than or equal to 25 MPa. These CT values are particularly advantageous for glass layers belonging to the low DoL variant.

The internal CT of these glass layers is reduced due to the low DoL. The reduction in CT can severely affect the pressure resistance of the toughened glass layer. Even if a sharp and hard object damages the toughened surface of a glass layer with a very low CT value, the layer will not break, because the low CT value cannot overcome the internal strength of the glass structure.

Alternatively, for glass layers belonging to the high DoL variant, it may be advantageous if their central tensile stress (CT) is greater than or equal to 27MPa, further preferably greater than or equal to 45MPa, further preferably greater than or equal to 65MPa, further preferably greater than or equal to 100 MPa.

As mentioned above, CS, DoL and CT depend on the glass composition (glass type), glass thickness and toughening conditions.

Drawings

Fig. 1 shows an ultra-thin glass (UTG) that can be used as the inorganic layer in the protective cover of the present invention.

Fig. 2 shows a protective cover according to a preferred embodiment of the invention.

Fig. 3 shows the bending behavior of an inorganic layer without any other layer.

Fig. 4 shows the bending behavior of an inorganic layer with an adhesive layer.

Fig. 5 shows a test setup for pen-down testing of an unbent protective cover.

Fig. 6 shows a test setup for pen-down testing of a bent protective cap.

Fig. 7 shows an example of an inorganic material layer having a region of reduced thickness.

Fig. 8 shows an example of an inorganic material layer having a region of reduced thickness.

Detailed Description

Fig. 1 shows an ultra-thin glass layer that can be used as the inorganic layer 2, including the neutral plane 5. By definition, the neutral plane is a plane within the protective cover that has the same length after bending as before bending. In a preferred embodiment, the neutral plane is located within the inorganic layer, the polymer layer and/or the adhesive layer. In a preferred embodiment, the neutral plane is located in the direction of the adhesive layer with respect to the middle plane of the inorganic layer. The inorganic layer 2 in this figure is shown in an unbent state.

Fig. 2 shows a protective cap 1 according to a preferred embodiment of the invention. The protective cover 1 has an inorganic layer 2 which may be a glass layer. An optional polymer layer 4 (e.g., a polyethylene layer) may be bonded to the inorganic layer 2 using an Optically Clear Adhesive (OCA) layer 8. The further adhesive layer 3 may be formed using silicone suitable for removably attaching the protective cover 1 to an electronic device, for example a smartphone. In a preferred embodiment, the total thickness of OCA layer 8, polymer layer 4 and adhesive layer 3 amounts to about 0.1mm, preferably 75 μm to 125 μm.

Fig. 3 shows a curved inorganic layer 2. The thickness of this layer is t. The outer surface is a tensile surface 6, which elongates due to tensile stress. The inner surface is a compression surface 7, which shortens due to compression. The neutral plane 5 moves towards the compression surface 7.

Fig. 4 shows a situation similar to fig. 3, in which the neutral plane moves even more when the adhesive layer 3 is present on the inorganic layer 2. The neutral plane should not move beyond the compression surface 7 of the inorganic material layer 2 because if this is done a compressive force is exerted on the inorganic layer 2, which may have negative effects, such as external forces on the cover glass and the display screen. Thus, by calculating the area of the curve as shown in fig. 3 and 4, the strain of the stretching surface 6 may be less than 4%.

Fig. 5 shows a pen-down arrangement for an unbent protective cover. The protective cover comprises an inorganic layer 2 and an adhesive layer 3. The adhesive layer 3 is indirectly attached to the inorganic layer 2 by intermediate layers, i.e. a further adhesive layer in the form of an OCA layer 8 and a polymer layer 4. The adhesive layer 3 is attached to the steel plate 11. And (5) performing ball-point pen falling. To simplify the results, a 0.5mm thick steel plate 11 was replaced with a flexible smart phone. The ball-point pen weighed approximately 5 grams. The ball of the pen 12 made of tungsten carbide has a radius of 0.35 mm. The pen drop starts at a height of 10 mm. The height is increased until the protective cap is broken. The maximum height of the inorganic layer 2 before crushing after pen drop is the pen drop height. 30 caps were tested and the average pen drop height was recorded.

Fig. 6 shows a pen down for a protective cover that has been bent or curved. The protective cover comprises an inorganic layer 2 and an adhesive layer 3. The adhesive layer 3 is fixed on the inorganic layer 2. The adhesive layer 3 is attached to the steel plate 11. And (5) performing ball-point pen falling. To simplify the results, a 0.5mm thick steel plate 11 was replaced with a flexible smart phone. The ball-point pen weighed approximately 5 grams. The ball of the pen 12 made of tungsten carbide has a radius of 0.35 mm. The bending radius was 4 mm. The height of the pen drop is 5 mm. The height is increased until the protective cap is broken. The maximum height of the inorganic layer 2 before crushing after pen drop is the pen drop height. 30 caps were tested and the average pen drop height was recorded.

Fig. 7 shows an inorganic material layer 2, which may be used as a further inorganic material layer in embodiments of the present invention, e.g. a second inorganic material layer or a first inorganic material layer. The following description of the drawings is not limited to the specific embodiments shown, but may be applied to all embodiments of the invention having one or more regions of reduced thickness. The inorganic material layer 2 may also be used as the only inorganic material layer in a protective cover having only one inorganic material layer. The inorganic material layer 2 has a plurality of regions of reduced thickness 13 in the form of grooves or trenches. These regions provide flexibility to the inorganic material layer. The reduced thickness region may be disposed on the side facing the electronic device and/or the adhesive layer in order to maintain a smooth surface of the inorganic material layer at the layer/air interface. The reduced thickness area may optionally be filled with an elastic material, such as a polymer material, e.g. epoxy resin-or any other material described above for the polymer layer, to maintain the impact resistance of the inorganic material layer and/or to maintain a good optical appearance. The filler material may have a refractive index n similar to that of the inorganic material_dFor example a refractive index which differs from the refractive index of the inorganic material by no more than 0.3, or by no more than 0.2, or by no more than 0.1. Keeping the refractive index within this range will improve the optical appearance of the protective cover. The adhesive layer may be coatedA region of reduced thickness of the cover to facilitate attachment of the layer of inorganic material to any other layer or display screen or electronic device. The reduced thickness region may provide excellent flexibility and/or bendability.

In an alternative embodiment, the recess or groove extends all the way through the first and/or second inorganic material layer in the thickness direction, thereby forming a gap in the respective layer.

Fig. 8 shows another example of the first or second inorganic material layer 2 having the region 13 of reduced thickness. The following description of the figure is not limited to the specific embodiments shown, but may be applied to all embodiments of the invention having one or more regions of reduced thickness. The inorganic material layer 2 may also be used as the only inorganic material layer in a protective cover having only one inorganic material layer. The minimum thickness may be substantially where the bending axis is located. In this case, the region of reduced thickness may be prepared by etching. The etched portion may have a rectangular shape or other concave shape. As shown, the region of reduced thickness may be arcuate. The arcuate region of reduced thickness is less prone to fracture than the rectangular region of reduced thickness. In an embodiment, the arcuate region of reduced thickness has a cross-sectional shape along a cutting plane perpendicular to the bending axis of the inorganic material layer having an approximately semi-circular shape, wherein a "semi-circle" comprises a circle segment of 10% or 20% or 30% or 40% to about 60% of the circumference of the corresponding circle. In an embodiment, a "semicircle" refers to a circle segment that is about 50% of the circumference of the corresponding circle. In other embodiments, the reduced thickness arcuate region has a cross-sectional shape along a cutting plane perpendicular to the bending axis of the inorganic material layer that has an approximately semi-elliptical shape, wherein "semi-ellipse" includes segments that are from 10% or 20% or 30% or 40% to about 60% of the circumference of the respective ellipse. In embodiments, a "semi-ellipse" refers to a segment that is about 50% of the circumference of the corresponding ellipse. The ellipse has a major semi-axis and a minor semi-axis. In an embodiment, the minor axis is oriented in the thickness direction of the inorganic material layer, and the major axis is oriented parallel to the surface of the inorganic material layer. In an alternative embodiment, the major axis is oriented in the thickness direction of the inorganic material layer, while the minor axis is parallel to the surface of the inorganic material layer. The length of the major semi-axis may be at least 1.1 x mi, or at least 1.3 x mi, or at least 1.5 x mi, or at least 1.8 x mi, even at least 2 x mi, or at least 3 x mi, where mi is the length of the minor semi-axis of the ellipse.

The region of reduced thickness may be edge treated. The edge of the reduced thickness region is where the reduced thickness region meets the surface of the inorganic material layer. The edge treatment may comprise etching, so that a rounded edge is obtained. These rounded edges improve the stability of the inorganic material and avoid breakage in case the edges contact the opposite side of the inorganic material layer during bending.

The region of reduced thickness may extend over the entire width of the respective inorganic material layer parallel to the bending axis, thereby providing excellent flexibility and/or bendability. The region of reduced thickness may have an extension of at least pi x r in a direction perpendicular to the bending axis and parallel to the surface of the layer of inorganic material, where r is the broken bending radius of the layer of inorganic material without the region of reduced thickness (e.g., prior to etching the region of reduced thickness).

The inorganic material layer has a maximum thickness reduction, in which it has a minimum thickness, and a half-maximum thickness reduction, in which the thickness of the inorganic material layer is reduced to an extent of 50% with respect to the maximum thickness reduction present in the same inorganic material layer. In embodiments, the minimum distance between the region of reduced maximum thickness and the region of reduced half-maximum thickness within a region of reduced thickness is at least pi x r/2, where r is the fracture bend radius of the inorganic material layer in the absence of the region of reduced thickness. Such an article will have excellent bending and/or folding properties, since the region of reduced thickness takes into account the bending behaviour of the inorganic material layer. In an embodiment of the invention, the maximum thickness reduction is where the inorganic material layer bends, i.e. at the bending axis. In embodiments having more than one layer of inorganic material, the maximum thickness reduction may amount to 100% of the original thickness of the layer, i.e., it may form a gap in the layer of inorganic material.

Typically, the maximum thickness reduction may be up to 90%, or up to 80%, or up to 60% of the original thickness of the respective layer. Typically, the maximum thickness reduction may be at least 10%, or at least 30% or at least 40% of the original thickness of the respective layer.

Preferably, the maximum thickness reduction is where the maximum tensile stress occurs during bending. The region of reduced thickness will preferably be arranged on the compressive surface of the inorganic material layer, while the tensile stress occurs on the opposite side (tensile surface). Where bending occurs, the tensile stress on the tensile surface is highest. The tensile stress decreases with increasing distance from the bending axis. Preferably, this is also the case for reduced thickness. In a preferred embodiment, the relative local tensile stress (percentage relative to the maximum tensile stress) at a given location on the tensile surface of the inorganic material layer corresponds to the relative thickness reduction (percentage relative to the maximum thickness reduction) at that location. For example, during bending, the tensile stress during bending may be highest where the tensile surface is closest to the bending axis, i.e. where the inorganic material layer preferably has the lowest thickness (maximum thickness reduction). In a preferred embodiment, the tensile stress on the tensile surface is about 50% (i.e., 45% to 55%) of the maximum tensile stress, wherein the inorganic material layer has a half-maximum thickness reduction.

Preferably, the relative local thickness reduction in percentage is substantially the same as the relative local tensile stress in percentage at a given location on the tensile surface of the inorganic material layer during bending, wherein bending comprises bending the protective layer up to a fracture bend radius. Herein, "substantially the same" means that the ratio of the relative local tensile stress (in%) to the relative local thickness reduction (in%) is 0.8: 1 to 1.2: 1. more preferably 0.9: 1 to 1.1: 1. in particular 0.95: 1 to 1.05: 1. Preferably, the relative local thickness reduction is substantially the same as the relative local tensile stress at each location on the tensile surface of the inorganic material layer during bending, wherein bending comprises bending the protective cap to a fracture bend radius.

List of reference numerals

1 protective cover

2 layer of inorganic material

3 adhesive layer

4 Polymer layer

5 neutral plane

6 stretching surface

7 compression surface

8 optically clear adhesive

11 steel plate

12 pens

13 region of reduced thickness

Examples of the invention

Example 1

According to a preferred embodiment of the invention, a pen-down test is performed on the protective cover. The test was performed as described above with reference to fig. 5.

The protective cover film comprises 0.07mm of ultra-thin aluminosilicate glass as the inorganic material layer, the OCA adhesive layer, the polymer layer of PE and the adhesive layer of silicone. The total thickness of the polymer layer, adhesive layer and silicone layer was 0.125 mm. The organic silicon surface is adhered on the inorganic material layer. The OCA adhesive layer is used for lamination with a flexible smartphone. The average CS and DoL of the protective cover film were 650MPa and 10 μm, respectively. And (5) performing ball-point pen falling. 30 caps were tested and the average pen drop height was about 50 mm. In addition, a bending test was performed. 30 caps were tested with a bend radius of 5 mm. All the protective layers passed 100,000 times at room temperature and a humidity of 30%, with a bending speed of 60 times/min.

Example 2

According to a preferred embodiment of the invention, the pen-down test is performed on a curved protective cover. The test was performed as described above with reference to fig. 6.

The protective cover film comprises 0.07mm of ultra-thin aluminosilicate glass as the inorganic material layer, the OCA adhesive layer, the polymer layer of PE and the adhesive layer of silicone. The total thickness of the polymer layer, adhesive layer and silicone layer was 0.125 mm. The organic silicon surface is adhered on the inorganic material layer. The OCA adhesive layer is used for lamination with a flexible smartphone. The average CS and DoL of the protective cover film were 700MPa and 8 μm, respectively. And (5) performing ball-point pen falling. The bending radius was 4 mm. 30 caps were tested and the average pen drop height was about 60 mm.

Example 3

According to a preferred embodiment of the invention, a pen-down test is performed on the protective cover. The test was performed as described above with reference to fig. 8.

The protective cover film comprises 0.21mm ultra-thin aluminosilicate glass as an inorganic material layer, an OCA adhesive layer, a polymer layer of PE, and an adhesive layer of silicone. The central portion of the ultra-thin glass was etched with HF acid to remove a thickness of 0.13 mm. The total thickness of the polymer layer, adhesive layer and silicone layer was 0.125 mm. The organic silicon surface is adhered on the inorganic material layer. The OCA adhesive layer is suitable for lamination with a flexible smartphone. The average CS and DoL of the protective cover film were 800MPa and 10 μm, respectively. Therefore, the protective cover film can be bent at the etched portion with a bending radius of 5 mm. A ball-point pen-down is performed on the thicker portion. 30 caps were tested and the average pen drop height was about 60 mm.