阅读说明：本技术 柔性塑料膜 (Flexible plastic film ) 是由 金惠珉 郑赫 张影来 朴真荣 郑顺和 于 2016-08-03 设计创作，主要内容包括：本发明涉及柔性塑料膜,并且更具体地涉及在具有优异的柔性的同时表现出高硬度的柔性塑料膜。本发明的柔性塑料膜表现出柔性、弯曲性、高硬度、耐磨性和高透明度,并且即使在反复弯曲的状态下也使得膜损坏的风险低,从而可以有效地应用于柔性移动装置、显示装置、多种仪表板的前面板和显示单元等。(The present invention relates to a flexible plastic film, and more particularly, to a flexible plastic film exhibiting high hardness while having excellent flexibility. The flexible plastic film of the present invention exhibits flexibility, bendability, high hardness, abrasion resistance, and high transparency, and causes a low risk of damage to the film even in a repeatedly bent state, so that it can be effectively applied to flexible mobile devices, display devices, front panels and display units of various instrument panels, and the like.)

1. A flexible plastic film comprising:

supporting a substrate; and an ultraviolet-curable coating layer formed on at least one surface of the support substrate,

wherein when the film was placed at an interval of 4mm in the middle of the film and the process of folding and spreading both sides of the film at 90 degrees with respect to the bottom surface at room temperature was repeated 100,000 times, no crack occurred,

wherein the ultraviolet-curable coating layer includes an acrylate-based binder and inorganic fine particles.

2. The flexible plastic film of claim 1, wherein the acrylate-based adhesive and inorganic fine particles comprise: crosslinked copolymers of adhesives based on 3-to 6-functional acrylates with adhesives based on 7-to 20-functional urethane acrylates; and inorganic fine particles.

3. The flexible plastic film according to claim 2, wherein the weight average molecular weight of the adhesive based on 7-to 20-functional urethane acrylate is from 2000 to 8000 g/mol.

4. The flexible plastic film according to claim 2, wherein the acrylate equivalent weight of the adhesive based on a 7-to 20-functional urethane acrylate is from 200g/mol to 1500 g/mol.

5. The flexible plastic film according to claim 1, wherein the thickness of the uv-curable coating is from 3 to 20 μ ι η.

6. The flexible plastic film according to claim 1, wherein the support substrate has a thickness of 20 to 200 μ ι η.

7. The flexible plastic film of claim 1 wherein the support substrate has an elastic modulus of 4GPa to 9GPa as measured according to ASTM D882.

8. The flexible plastic film of claim 1, wherein the film exhibits a pencil hardness of 6H or greater at a load of 750 g.

9. The flexible plastic film of claim 1 wherein the inorganic fine particles have a bimodal particle size distribution comprising a first population of inorganic fine particles having a d50 of 20nm to 35nm and a second population of inorganic fine particles having a d50 of 40nm to 130 nm.

10. The flexible plastic film according to claim 2, wherein the weight ratio between the 3-to 6-functional acrylate based adhesive and the 7-to 20-functional urethane acrylate based adhesive is from 1:9 to 4: 6.

11. The flexible plastic film according to claim 9, wherein the ultraviolet-curable coating layer comprises the 3-to 6-functional acrylate-based binder in an amount of 10 to 50 parts by weight, the 7-to 20-functional urethane acrylate-based binder in an amount of 40 to 70 parts by weight, the first inorganic fine particle group in an amount of 5 to 50 parts by weight, and the second inorganic fine particle group in an amount of 5 to 50 parts by weight, based on 100 parts by weight of the ultraviolet-curable coating layer.

12. The flexible plastic film according to claim 9, wherein the first inorganic fine particle group and the second inorganic fine particle group are the same or different, each independently being surface-modified with any one or more silane coupling agents selected from: (meth) acryloylsilanes, methacryloyloxysilanes, vinylsilanes, epoxysilanes and mercaptosilanes.

13. The flexible plastic film according to claim 9, wherein d of the first inorganic fine particle group₁₀Is 10nm to 19nm and d₉₀D of the second inorganic fine particle group of 25nm to 40nm₁₀Is 25nm to 110nm and d₉₀60nm to 150 nm.

14. The flexible plastic film according to claim 9, wherein a weight ratio between the first inorganic fine particle group and the second inorganic fine particle group is 9:1 to 3: 7.

15. The flexible plastic film of claim 1, wherein the support substrate is at least one selected from the group consisting of: polyimide, polyimide amide, polyetherimide, polyethylene terephthalate, polyethylene naphthalate, polyetheretherketone, cyclic olefin polymer, polyacrylate, polymethyl methacrylate, and triacetyl cellulose.

16. The flexible plastic film of claim 1, further comprising an antistatic layer or a low refractive index layer on the upper or lower surface of the coating.

17. The flexible plastic film of claim 1, wherein no cracks appear when wound on a mandrel having a diameter of 4 mm.

Technical Field

Cross Reference to Related Applications

The present application claims priority benefits based on korean patent application No. 10-2015-.

The present invention relates to flexible plastic films. More particularly, the present invention relates to a flexible plastic film having excellent flexibility while exhibiting high hardness.

Background

Recently, with the development of mobile devices such as smart phones and tablet PCs, thinning and thinning of display substrates are required. Glass or tempered glass is generally used as a material having excellent mechanical properties on a window or a front plate of a display of a mobile device. However, the glass causes an increase in weight of the mobile device due to its own weight, and has a problem of breakage due to external impact.

Therefore, plastic resins are being studied as substitutes for glass. The plastic resin composition is lightweight with little risk of cracking, and thus is suitable for the trend of pursuing lighter mobile devices. In particular, in order to realize a film having high hardness and abrasion resistance characteristics, a composition for applying a hard coating layer made of a plastic resin onto a supporting substrate has been proposed.

As a method for increasing the surface hardness of the hard coat layer, a method for increasing the thickness of the hard coat layer may be considered. In order to ensure a surface hardness sufficient to replace glass, it is necessary to achieve a hard coating of a certain thickness. However, as the thickness of the hard coating layer increases, the surface hardness may increase, but the occurrence of wrinkles and curling increases due to curing shrinkage of the hard coating layer, and at the same time, cracking and peeling of the coating layer may occur. Therefore, practical application of the method is not easy.

Korean patent laid-open publication No. 2010-0041992 discloses a plastic film composition using a binder resin containing a uv-curable urethane acrylate-based oligomer and eliminating monomers. However, the plastic film disclosed above has a pencil hardness of about 3H and is not strong enough to replace the glass panel of the display.

Meanwhile, a display in which a portion of a display device is bent or flexibly bent for aesthetic and functional reasons has recently attracted attention, and this tendency is particularly noticeable in mobile devices such as smart phones and tablet PCs. However, since glass is not suitable for a cover plate for protecting such a flexible display, it is necessary to replace it with a plastic resin or the like. However, for this purpose, it is not easy to manufacture a film having sufficient flexibility while exhibiting high hardness at the glass level.

Disclosure of Invention

Technical problem

In order to solve the above problems, an object of the present invention is to provide a flexible plastic film having excellent flexibility and bending durability while exhibiting high hardness.

Technical scheme

In order to achieve the above object, the present invention provides a flexible plastic film comprising:

supporting a substrate; and an ultraviolet-curable coating layer formed on at least one surface of the support substrate,

wherein the film exhibits a pencil hardness of 6H or greater at a load of 750g, and

wherein when the film was placed at an interval of 4mm in the middle of the film and the process of folding and spreading both sides of the film at 90 degrees with respect to the bottom surface at room temperature was repeated 100,000 times, no crack occurred.

Technical effects

The flexible plastic film according to the present invention exhibits flexibility, bendability, high hardness, abrasion resistance, and high transparency, and has little risk of damaging the film even under repeated, continuous bending, or long-time folding conditions. Therefore, the plastic film can be effectively applied to bendable, flexible, rollable, or foldable mobile devices, display devices, front surfaces of various instrument panels, display units, and the like.

Drawings

Fig. 1 is a diagram schematically showing a method for performing a bending durability test of a film according to an embodiment of the present invention.

Detailed Description

The flexible plastic film of the present invention comprises: supporting a substrate; and an ultraviolet curable coating layer formed on at least one surface of the support substrate, wherein the film exhibits a pencil hardness of 6H or more under a load of 750g, and wherein when the film is placed at an interval of 4mm in the middle of the film and a process of folding and spreading both sides of the film at 90 degrees with respect to a bottom surface at room temperature is repeated 100,000 times, cracks do not occur.

In the present invention, terms such as first, second, etc., are used to describe various components, and these terms are used only for the purpose of distinguishing one component from another component.

Furthermore, the terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Unless the context clearly dictates otherwise, singular expressions include plural expressions. It will be understood that terms such as "comprising," "including," "having," and the like, as used herein, specify the presence of stated features, integers, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components, and/or groups thereof.

Since the invention is susceptible to various modifications and embodiments, specific embodiments will be shown and described in detail below. However, it is not intended to limit the present invention to the specific embodiments, but it should be understood that all changes, equivalents, and substitutions without departing from the spirit and technical scope of the present invention are encompassed by the present invention.

The flexible plastic film of the present invention will be described in more detail below.

A flexible plastic film according to one embodiment of the present invention includes: supporting a substrate; and an ultraviolet curable coating layer formed on at least one surface of the support substrate, wherein the film exhibits a pencil hardness of 6H or more under a load of 750g, and the film is characterized by no occurrence of cracks when a process of placing the film with a space in the middle of the film of 4mm and folding and spreading both sides of the film at 90 degrees with respect to a bottom surface is repeated 100,000 times.

In the present invention, "flexible" means a state having such a degree of flexibility: cracks having a length of 3mm or more do not occur when wound on a cylindrical mandrel having a diameter of 4 mm. Thus, the flexible plastic film of the present invention may be applied to cover films for bendable, flexible, rollable or foldable displays and the like.

In mobile devices such as smart phones and tablet PCs and displays such as LCDs, a form in which a portion of the display device is bent or flexibly bent for aesthetic and functional reasons has recently attracted attention, and this tendency is particularly noticeable in mobile devices. However, since glass is not suitable as a cover plate for protecting such a flexible display, it is necessary to replace it with a plastic film containing an ultraviolet-curable or heat-curable resin or the like.

In the cover sheet made of plastic resin, heretofore, a curved film forming a constant curvature and having a fixed form, or a film having a degree of flexibility that can be bent by hand has been developed, but it is not sufficient to develop a film having a degree of flexibility that does not develop cracks even in a repeatedly bent or long-time folded state. Thinner films are advantageous for achieving flexibility but are relatively disadvantageous in terms of surface hardness. Therefore, it is not easy to provide a film having both high flexibility and high hardness.

The present invention provides a plastic resin film including an ultraviolet-curable coating layer, which is implemented to simultaneously satisfy a physical property balance between flexibility and high hardness, and a flexible plastic film exhibiting high hardness and hardly risking damage to the film, particularly even by repeated bending or folding operations, and thus can be applied to a bendable, flexible, rollable, or foldable mobile device or display device.

Namely, the flexible plastic film according to the present invention includes: supporting a substrate; and an ultraviolet curable coating layer formed on at least one surface of the support substrate, wherein the film exhibits a pencil hardness of 6H or more under a load of 750g, and the film exhibits bending durability to the extent that cracks do not occur when the film is placed at an interval of 4mm in the middle of the film and the process of folding and spreading both sides of the film at 90 degrees with respect to the bottom surface at room temperature is repeated 100,000 times.

Fig. 1 is a diagram schematically illustrating a method for measuring bending durability characteristics of a flexible plastic film according to an embodiment of the present invention.

Referring to fig. 1, the film was placed horizontally to the bottom, and disposed such that the interval between the folded portions at the middle portion of the film was 4 mm. Then, the process of folding and spreading both sides of the film at 90 degrees with respect to the bottom surface at room temperature at a speed of about 1 to about 3 times/second was repeated 100,000 times, thereby measuring the bending resistance durability.

At this time, in order to keep the distance between the folded portions constant, for example, the film is placed in contact with a rod having a diameter (R) of 4mm, the remaining portion of the film is fixed, and the process of folding and spreading both sides of the film around the rod may be performed. Further, the folded portion is not particularly limited as long as it is inside the film, and for convenience of measurement, the center portion of the film may be folded such that the remaining portion of the film excluding the folded portion is symmetrical.

In measuring such durability, the flexible plastic film of the present invention does not generate cracks of 1cm or more, or 3mm or more, and substantially does not generate cracks even after being bent 100,000 times.

Therefore, even in practical application conditions such as repeated folding, curling, or bending, the possibility of occurrence of cracks is very low, and thus the flexible plastic film can be suitably applied to the cover sheet of the flexible display.

Further, the flexible plastic film of the present invention may have a pencil hardness of 6H or more or 7H or more under a load of 750 g.

As described above, making the thickness of the film thin is advantageous for achieving flexibility, but the surface hardness becomes relatively low. Therefore, it is not easy to provide a film having high hardness while having high flexibility. However, the flexible plastic film of the present invention achieves a bending durability of 100,000 times or more and a high hardness of 6H or more or 7H or more under a load of 750g by matching these two contradictory physical properties.

That is, the present invention has been completed on this basis, and when a plastic film has a structure including a support substrate and a coating layer formed on at least one surface of the support substrate and simultaneously satisfies physical properties of 6H or more pencil hardness under a load of 750g and a degree that cracks do not occur under predetermined conditions for repeated bending or folding operations, it can be practically applied to a bendable, flexible, crimpable or foldable mobile device, a display device, and the like.

The flexible plastic film of the present invention satisfying both of these bending durability and surface hardness can be obtained by optimizing a support substrate and an ultraviolet-curable coating layer (hereinafter, referred to as a coating layer) formed on the support substrate.

For example, in the flexible plastic film of the present invention, the support substrate on which the ultraviolet-curable coating layer is formed is an optically transparent plastic resin having an elastic modulus of about 4GPa or more and a thickness of 20 μm to 200 μm as measured according to ASTM D882, in order to ensure flexibility and hardness, and the support substrate may be used without particularly limiting the method and material for producing the support substrate such as a stretched film or a non-stretched film.

In the condition of supporting the substrate, the elastic modulus may be about 4GPa or more, or about 5GPa or more, or about 5.5GPa or more, or about 6GPa or more, and the upper value may be about 9GPa or less, or about 8GPa or less, or about 7GPa or less. If the elastic modulus is less than 4GPa, sufficient hardness cannot be achieved, and if the elastic modulus exceeds 9GPa (which is too high), it may be difficult to form a film having flexibility.

The support substrate may have a thickness of about 20 μm or more, or about 25 μm or more, or about 30 μm or more, and an upper limit value thereof may be about 200 μm or less, or about 150 μm or less, or about 100 μm or less, or about 60 μm or less. If the thickness of the support base material is less than 20 μm, there is a possibility that cracks or curls occur in the process of forming the coating layer, and it may be difficult to achieve high hardness. On the other hand, if the thickness exceeds 200 μm, flexibility decreases and it may be difficult to form a flexible film.

From the viewpoint of ensuring the workability of the flexible film and achieving the balance of physical properties between high hardness and flexibility as described above, a support substrate having an elastic modulus of 4GPa or more and 9GPa or less and a thickness of 20 μm to 200 μm may be used.

More specifically, according to an embodiment of the present invention, the support substrate satisfies the above elastic modulus and thickness ranges, and for example, it may be a film comprising: polyimide (PI), polyimide amide, Polyetherimide (PEI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), Polyetheretherketone (PEEK), cycloolefin polymer (COP), Polyacrylate (PAC), Polymethylmethacrylate (PMMA), triacetyl cellulose (TAC), and the like. The above support substrate may have a single-layer structure or a multi-layer structure including two or more substrates composed of the same or different substances, if necessary, and is not particularly limited.

Alternatively, according to one embodiment of the present invention, the support substrate may be a substrate comprising Polyimide (PI).

Further, according to an embodiment of the present invention, the thickness ratio between the support substrate and the coating layer may be from about 1:0.05 to about 1:1, or from about 1:0.1 to about 1: 0.8. When the thickness ratio between the support substrate and the coating layer is within the above range, a flexible plastic film exhibiting high hardness and flexibility can be more easily formed.

The flexible plastic film of the present invention includes an ultraviolet-curable coating layer formed on at least one surface of a support substrate.

According to one embodiment of the present invention, a coating layer may be formed on both surfaces of the support substrate.

In the flexible plastic film of the present invention, the coating layer comprises: adhesion of adhesives based on 3-to 6-functional acrylates to adhesives based on 7-to 20-functional urethane acrylatesA crosslinked copolymer of the agent; and has a structure including d₅₀A first group of inorganic fine particles of 20nm to 35nm and d₅₀Inorganic fine particles of a bimodal particle size distribution of a second inorganic fine particle group of 40nm to 130 nm.

As used herein, acrylate-based means not only acrylate but also methacrylate, or a derivative introducing a substituent to acrylate or methacrylate.

The 3-to 6-functional acrylate-based binder is crosslinked with the 7-to 20-functional urethane acrylate-based binder to form a copolymer, and can impart high hardness to a coating layer formed after curing.

More specifically, the 3-to 6-functional acrylate-based adhesive may include trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxy triacrylate (TMPEOTA), Glycerol Propoxylated Triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), and the like. The above-mentioned adhesives based on 3-to 6-functional acrylates can be used alone or in combinations of different types.

According to one embodiment of the invention, the weight average molecular weight (Mw) of the 3-to 6-functional acrylate-based adhesive is from about 200g/mol to about 2,000g/mol, or from about 200g/mol to about 1,000g/mol, or from about 200g/mol to about 500 g/mol.

According to one embodiment of the invention, the acrylate equivalent weight of the adhesive based on 3-to 6-functional acrylates is from about 50g/mol to about 300g/mol, or from about 50g/mol to about 200g/mol, or from about 50g/mol to about 150 g/mol.

When the weight average molecular weight and the acrylate equivalent weight of the binder based on the 3-to 6-functional acrylate are within the above ranges, respectively, a coating layer having more optimized physical properties may be formed.

The binder based on a 7-to 20-functional urethane acrylate is crosslinked with the binder based on a 3-to 6-functional acrylate to form a copolymer, and can impart high hardness, flexibility and impact resistance to a coating formed after curing. The adhesives based on 7-to 20-functional urethane acrylates can be used alone or in combinations of different types.

According to one embodiment of the present invention, the crosslinked copolymer may be one in which a 3-to 6-functional acrylate-based binder is crosslinked with a 7-to 20-functional urethane acrylate-based binder in a ratio of about 1:9 to about 5:5, preferably 1:9 to about 4:6, more preferably about 1:9 to about 3.5: 6.5. By containing a crosslinked copolymer in which a binder based on a 3-to 6-functional acrylate and a binder based on a 7-to 20-functional urethane acrylate are crosslinked at the above weight ratio, it is possible to exhibit sufficient flexibility and simultaneously achieve high hardness and good physical properties.

According to one embodiment of the invention, the weight average molecular weight of the 7-to 20-functional urethane acrylate-based binder is from about 2,000g/mol to about 8,000g/mol, or from about 3,000g/mol to about 6,000g/mol, or from about 3,000g/mol to about 5,000g/mol, which may be preferred for optimizing the physical properties of the coating.

According to one embodiment of the invention, the acrylate equivalent weight of the adhesive based on the 7-to 20-functional urethane acrylate may be from about 200g/mol to about 1,500g/mol, or from about 200g/mol to about 1,000g/mol, or from about 300g/mol to about 600g/mol, or from about 300g/mol to about 500 g/mol. If the acrylate equivalent weight of the binder based on 7-to 20-functional urethane acrylate is too high, the hardness of the coating may be insufficient, whereas if the equivalent weight is lower, the hardness may increase, but the flexibility may decrease. From the viewpoint of the balance between high hardness and flexibility as described above, the above equivalent weight range is preferable, and about 300g/mol to about 500g/mol may be most preferable.

When the weight average molecular weight and the acrylate equivalent weight of the binder based on the 7-to 20-functional urethane acrylate are within the above ranges, respectively, a coating layer having more optimized characteristics may be formed.

Since the binders based on 7-to 20-functional urethane acrylates contain at least 7 acrylate groups in the molecule which can be cross-linked by ultraviolet light, this is advantageous for achieving a high hardness of the coating. However, the higher the crosslinking density, the more easily curl is allowed to be generated and the adhesion to the substrate is reduced, and thus it is not suitable for forming a flexible film.

Meanwhile, the binder based on a 7-to 20-functional urethane acrylate included in the coating layer of the present invention includes at least 7 multifunctional acrylate groups in the molecule and simultaneously has a urethane bond, and thus has excellent elasticity and flexibility. Therefore, when it is crosslinked with a binder based on a 3-to 6-functional acrylate in an appropriate weight ratio to form a copolymer, it serves to impart sufficient flexibility and high hardness to the coating layer. Adhesives based on 7-to 20-functional urethane acrylates may contain 2 to 20 urethane bonds in one molecule.

As such, the coating layer according to one embodiment of the present invention includes a crosslinked copolymer in which a binder based on 3-to 6-functional acrylate and a binder based on 7-to 20-functional urethane acrylate are crosslinked with each other, thereby imparting high hardness and flexibility to a flexible plastic film. In particular, it has high durability against bending, curling or folding, and thus can ensure excellent flexibility with little risk of damaging the film even when repeatedly bent or folded for a long time.

The coating according to one embodiment of the present invention comprises a polymer having a structure comprising d₅₀A first group of inorganic fine particles of 20nm to 35nm and d₅₀Inorganic fine particles of a bimodal particle size distribution of a second inorganic fine particle group of 40nm to 130 nm. As described above, the coating uses of the present invention appear to include d each having a particular range₅₀The first and second inorganic fine particle groups of (a) to (b), thereby simultaneously improving hardness and flexibility of the coating while maintaining the flexible property.

In the description of the present invention, when a cumulative particle size distribution corresponding to a particle diameter is measured using a laser diffraction method (measurement method: determination of a size distribution by number by using dynamic laser light scattering, a solvent in which inorganic fine particles are dispersed, a refractive index, a viscosity and a dielectric constant of the inorganic fine particles, a device name: Malvern Zetasizer Nano-ZS 90), the particle diameter at 10% accumulation is set as d₁₀The particle diameter at 50% accumulation is set as d₅₀At 90% accumulationThe particle diameter is set as d₉₀. The particle size distribution by the laser diffraction method may show a distribution substantially the same as a particle size distribution measured with an SEM or TEM by diluting a dispersion in which inorganic fine particles are dispersed in a solvent, or a particle size distribution measured by analyzing a cross section of a coating layer containing inorganic fine particles through an SEM or TEM.

The first inorganic fine particle group having a small particle size range contributes to improvement of hardness, and the second inorganic fine particle group having a larger particle size range contributes to improvement of flexibility and pliability. In this way, since other inorganic fine particle groups having different particle size ranges are mixed and used in addition to the above-described crosslinked copolymer, a coating layer in which physical properties of hardness and flexibility are improved at the same time can be provided.

As the first and second inorganic fine particle groups, for example, silica fine particles, aluminum oxide particles, titanium oxide particles, zinc oxide particles, and the like can be used independently of each other.

According to one embodiment of the present invention, d of the first inorganic fine particle group₅₀May be 20nm or more, or about 21nm or more, 35nm or less, 30nm or less, or 25nm or less, d of the second inorganic fine particle group₅₀May be about 40nm or greater, or about 42nm or greater, or about 45nm or greater, and 130nm or less, or 125nm or less, or 120nm or less.

According to one embodiment of the present invention, d of the first inorganic fine particle group₁₀May be from 10nm to 19nm, d₅₀May be from 20nm to 35nm, and d₉₀And may be 25nm to 40 nm. Further, d of the second inorganic fine particle group₁₀May be from 25nm to 110nm, d₅₀May be from 40nm to 130nm, and d₉₀And may be 60nm to 150 nm.

According to an embodiment of the present invention, in order to contribute to the increase in hardness, the content of the first inorganic fine particle group may be about 5 parts by weight or more, or about 10 parts by weight or more, or about 15 parts by weight or more, based on 100 parts by weight of the coating layer. In order to satisfy flexibility, the content of the first inorganic fine particle group may be about 50 parts by weight or less, or about 45 parts by weight or less, or about 40 parts by weight or less, or about 35 parts by weight or less. By containing the first inorganic fine particle group within the above weight range, a flexible plastic film having excellent physical properties while satisfying both high hardness and flexibility can be formed.

Further, according to an embodiment of the present invention, in order to contribute to the increase in hardness, the content of the second inorganic fine particle group may be about 5 parts by weight or more, or about 10 parts by weight or more, or 15 parts by weight or more, based on 100 parts by weight of the entire coating layer, and may be about 50 parts by weight or less, or about 45 parts by weight or less, or about 40 parts by weight or less, or about 35 parts by weight or less, in order to satisfy flexibility. By including the second inorganic fine particle group within the above weight range, a flexible plastic film having excellent physical properties while satisfying both high hardness and flexibility can be formed.

According to an embodiment of the present invention, in order to contribute to the increase in hardness, the total content of the inorganic fine particles including the first and second inorganic fine particle groups may be about 25 parts by weight or more, or about 30 parts by weight or more, or about 35 parts by weight or more, based on 100 parts by weight of the entire coating layer, and may be about 50 parts by weight or less, or about 45 parts by weight or less, or about 40 parts by weight or less, in order to satisfy flexibility.

According to an embodiment of the present invention, the first and second inorganic fine particle groups may be the same or different, and each independently surface-modified with any one or more silane coupling agents selected from the group consisting of: (meth) acryloxysilane, methacryloxysilane, vinylsilane, epoxysilane, and mercaptosilane.

Since the first and second inorganic fine particle groups surface-modified with the silane coupling agent as described above can react with the acrylate group of the binder, adhesion to the substrate is high, they can be uniformly dispersed in the coating layer, and hardness can be increased without decreasing flexibility of the coating layer, which is more advantageous.

According to an embodiment of the present invention, the first and second inorganic fine particle groups may be present in a weight ratio of about 9:1 to about 3:7, or about 8:2 to about 4:6, or about 7:3 to about 5: 5. By including the first and second inorganic fine particle groups in the above weight ratio range, a flexible plastic film having excellent physical properties and improved high hardness and flexibility can be formed.

Meanwhile, the coating layer of the present invention may further include additives commonly used in the art, such as a surfactant, a UV absorber, a UV stabilizer, an anti-yellowing agent, a leveling agent, an antifouling agent, a dye for improving color value, and the like, in addition to the above-mentioned binder, inorganic fine particles, a photoinitiator, and an organic solvent. Further, the content thereof is not particularly limited, because the content can be variously adjusted within a range not to degrade the physical properties of the coating layer of the present invention. However, the additive may be included in an amount of about 0.01 to 10 parts by weight, based on 100 parts by weight of the coating layer.

According to an embodiment of the present invention, for example, the coating may include a surfactant as an additive, and the surfactant may be a monofunctional or bifunctional fluorine-based acrylate, a fluorine-based surfactant, or a silicon-based surfactant. In this case, the surfactant may be contained in a form dispersed or crosslinked in the crosslinked copolymer.

Further, the additive may include a UV absorber, a UV stabilizer, and examples of the UV absorber include benzophenone-based compounds, benzotriazole-based compounds, triazine-based compounds, and the like. Examples of UV stabilizers include tetramethyl piperidine and the like.

The coating layer according to one embodiment of the present invention as described above may be formed by photocuring a coating composition comprising a binder based on a 3-to 6-functional acrylate; adhesives based on 7-to 20-functional urethane acrylates; a photoinitiator; has a structure including d₅₀A first group of inorganic fine particles of 20nm to 35nm and d₅₀Inorganic fine particles of a bimodal particle size distribution of a second inorganic fine particle group of 40nm to 130 nm; an additive; and an organic solvent.

Examples of photoinitiators may include: 1-hydroxy-cyclohexyl-phenylketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1- [4- (2-hydroxyethoxy) phenyl ] -2-methyl-1-propanone, methylbenzoyl formate,. alpha. -dimethoxy-. alpha. -phenylacetophenone, 2-benzoyl-2- (dimethylamino) -1- [4- (4-morpholinyl) phenyl ] -1-butanone, 2-methyl-1- [4- (methylthio) phenyl ] -2- (4-morpholinyl) -1-propanone diphenyl (2,4, 6-trimethylbenzoyl) -phosphine oxide, and mixtures thereof, Or bis (2,4, 6-trimethylbenzoyl) -phenylphosphine oxide, and the like, but is not limited thereto. Further, examples of commercially available products include Irgacure 184, Irgacure 500, Irgacure 651, Irgacure 369, Irgacure 907, Darocur1173, Darocur MBF, Irgacure 819, Darocur TPO, Irgacure 907, Esacure KIP 100F, and the like. These photoinitiators may be used alone or in a combination of two or more.

Examples of the organic solvent include: alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; alkoxy alcohol-based solvents such as 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-propanol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and cyclohexanone; ether-based solvents such as propylene glycol monopropyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethyl ethylene glycol monoethyl ether, diethyl ethylene glycol monopropyl ether, diethyl ethylene glycol monobutyl ether, and diethylene glycol-2-ethylhexyl ether; aromatic solvents such as benzene, toluene, xylene, and the like. These may be used alone or in combination.

The content of the organic solvent is not particularly limited because it may be variously adjusted within a range not to degrade physical properties of the coating composition, but the organic solvent may be contained such that the weight ratio of the solid content to the organic solvent is about 30:70 to about 99:1 based on the solid content of the components contained in the coating composition. When the organic solvent is within the above range, it may have appropriate fluidity and coating characteristics.

The coating compositions may be applied to the front and back surfaces of the support substrate, each sequentially, or to both surfaces of the support substrate simultaneously.

According to one embodiment of the present invention, the flexible plastic film of the present invention can be obtained by applying a coating composition comprising the above-mentioned components onto both surfaces of a support substrate and then photocuring it to form a coating layer. Here, a method of applying the coating composition is not particularly limited as long as it can be used in the technical field to which the present technology belongs, and for example, a bar coating method, a blade coating method, a roll coating method, a doctor blade coating method, a die coating method, a micro-gravure coating method, a comma coating method (comma coating), a slit die coating method, a lip coating method, a solution casting method, and the like can be used.

After full cure, the thickness of the coating can be about 3 μm or greater, for example about 3 μm to about 20 μm, or about 3 μm to about 15 μm, or about 3 μm to about 10 μm. According to the present invention, when the coating layer having such a thickness is included, a flexible plastic film having high hardness can be provided.

According to one embodiment of the present invention, the flexible plastic film may further comprise at least one selected from the group consisting of on the top surface of the at least one coating layer or between the substrate film and the coating layer: a layer, a film (membrane), a film (film), etc., such as a plastic resin film, an adhesive film, a release film, a conductive layer, a liquid crystal layer, a coating layer, a cured resin layer, a non-conductive film, a metal mesh layer, or a patterned metal layer. For example, an antistatic layer having conductivity is first formed on a support substrate, and then a coating layer is formed thereon to provide an antistatic function, or a low refractive index layer is introduced on the coating layer to achieve a low reflection function.

Further, the layer, film, etc. may be in any form of a single layer, double layer, or laminate type. The layer, film, thin film, etc. may be formed by laminating a separate film with an adhesive, an adhesive film, etc., or may be laminated on the coating layer by a method such as coating, vapor deposition, sputtering, etc., but the present invention is not limited thereto.

The flexible plastic film according to the invention can be produced, for example, by the following method.

According to one embodiment of the invention, the flexible plastic film may be formed by the following two-step process: a first coating composition is first applied and first photocured on one surface of the support substrate, and then a second coating composition is second applied and second photocured on the other surface (i.e., the backside) of the support substrate. At this time, the first and second coating compositions are the same as the above-described coating compositions, and each of them distinguishes the compositions coated on only one surface and the back surface.

In the case of forming a coating layer by this method, in the second photocuring step, ultraviolet irradiation is not performed on the surface coated with the first coating composition but is performed on the opposite surface, and thus the curl that can be generated due to curing shrinkage in the first photocuring step can be cancelled out in the opposite direction to obtain a flat flexible plastic film. Therefore, no additional flattening process is required.

However, the present invention is not limited thereto, and the curling balance may also be adjusted by simultaneously forming coating compositions on both surfaces of a support substrate and then curing the coating compositions.

The flexible plastic film of the present invention exhibits excellent flexibility, bendability, high hardness, abrasion resistance, high transparency, high durability, and bending, curling, or folding stability, and thus can be used as a cover film for next-generation displays having bendable, flexible, rollable, or foldable characteristics, and the like.

For example, the flexible plastic film of the present invention may exhibit such a degree of flexibility: no cracks appeared when wound on cylindrical mandrels with a diameter of 4mm or 3 mm.

Further, the flexible plastic film of the present invention may have a pencil hardness of 6H or more or 7H or more under a load of 750 g.

Further, when steel wool #0000 was attached to a tip having a contact area of 2cm × 2cm with respect to the plastic film in a friction tester and then the surface of the plastic film was reciprocated 400 times under a 500g load, the flexible plastic film may generate 2 or less scratches.

Further, the flexible plastic film of the present invention may have a light transmittance of 88.0% or more, or 90.0% or more, and a haze of 1.5% or less, 1.0% or less, or 0.5% or less.

The flexible plastic film of the present invention can be applied to various fields. For example, the flexible plastic film of the present invention can be used as a cover substrate or an element substrate for flat-shaped as well as curved, bendable, flexible, rollable, or foldable-shaped mobile communication terminals, touch panels for smart phones or tablet PCs, and various displays.

Hereinafter, the operation and effect of the present invention will be described in more detail by specific examples. However, these examples are provided for illustrative purposes only, and the scope of the present invention is not determined thereby.

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