阅读说明：本技术 聚酰亚胺基膜及包括该聚酰亚胺基膜的柔性显示面板 (Polyimide base film and flexible display panel comprising same ) 是由 金贤贞 朴相胤 于 2021-04-30 设计创作，主要内容包括：本发明涉及一种聚酰亚胺基膜、窗覆盖膜和包括其的显示面板。更具体地,本发明涉及一种聚酰亚胺基膜,其特征在于,通过拉曼光谱分析测量1610-1630cm～(-1)处的芳香族环的峰时,厚度方向上的强度的最大值和最小值之差△I为0.6以内,在所述拉曼光谱分析中,将激发波长设置为532nm,将激光光斑设置为1-2μm,将厚度方向上的测量间隔设置为1μm。(The present invention relates to a polyimide base film, a window cover film and a display panel including the same. More particularly, the present invention relates to a polyimide-based film characterized by 1610-1630cm measured by Raman spectroscopy ‑1 The difference DeltaI between the maximum value and the minimum value of the intensity in the thickness direction is 0.6 or less, and in the Raman spectrum analysis, the excitation wavelength is set to 532nm, the laser spot is set to 1-2 μm, and the measurement interval in the thickness direction is set to 1 μm.)

1. A polyimide-based film characterized by 1610-1630cm measured by Raman spectroscopy^-1The difference DeltaI between the maximum value and the minimum value of the intensity in the thickness direction is 0.6 or less, and in the Raman spectrum analysis, the excitation wavelength is set to 532nm, the laser spot is set to 1-2 μm, and the measurement interval in the thickness direction is set to 1 μm.

2. The polyimide-based film according to claim 1, wherein a warpage amount of the polyimide-based film is 5mm or less.

3. The polyimide-based film according to claim 1, wherein the polyimide-based film has a light transmittance of 5% or more at 388nm and a total light transmittance of 87% or more at 400-700nm, a haze of 2.0% or less, a yellow index of 5.0 or less, and a b value of 2.0 or less, measured according to ASTM D1746.

4. The polyimide-based film according to claim 1, wherein the polyimide-based film has a modulus of 3GPa or more and an elongation at break of 8% or more according to ASTM D882.

5. The polyimide-based film according to claim 1, wherein the thickness of the polyimide-based film is 10 to 500 μm.

6. The polyimide-based film according to claim 1, wherein Δ I is 0.4 or less.

7. The polyimide-based film according to claim 1, wherein the polyimide-based film is formed of a polyimide-based resin containing a polyamideimide structure.

8. The polyimide-based film according to claim 7, wherein the polyimide-based resin comprises units derived from a fluorine-based aromatic diamine.

9. The polyimide-based film according to claim 7, wherein the polyimide-based resin comprises a unit derived from an alicyclic dianhydride.

10. The polyimide-based film according to claim 7, wherein the polyimide-based resin comprises a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, and a unit derived from an aromatic diacid chloride.

11. The polyimide-based film according to claim 10, further comprising a unit derived from an alicyclic dianhydride.

12. A window covering film, comprising:

the polyimide-based film of any one of claims 1 to 11; and

a coating layer formed on one side of the polyimide base film.

13. The window covering film according to claim 12, wherein the coating layer is any one or more selected from the group consisting of an antistatic layer, an anti-fingerprint layer, an anti-staining layer, an anti-scratch layer, a low refractive layer, an anti-reflection layer and an impact absorption layer.

14. A flexible display panel comprising the polyimide base film of any one of claims 1 to 11.

Technical Field

The present invention relates to a polyimide base film, a window cover film and a display panel including the same.

Background

Thin display devices such as liquid crystal display devices (liquid crystal displays) and organic light emitting diode display devices (organic light emitting diode displays) are implemented in the form of touch screen panels (touch screen panels), and are widely used not only in smart phones (smart phones) and tablet PCs (tablet PCs), but also in various smart devices (smart devices) featuring portability, such as various wearable devices (wearable devices).

In such a portable touch screen panel-based display device, a window cover for protecting a display is provided on a display panel in order to protect the display panel from scratches or external impacts, and in recent years, as foldable (foldable) display devices that can be folded and unfolded and have flexibility are developed, glass of the window cover is replaced with a plastic film.

In order to be used as a base material of the window covering film as described above, excellent mechanical physical properties and transparency like glass are required, and in recent years, there is a need for a window covering film that can minimize the occurrence of warpage or the like due to asymmetry of both sides of the film even under high temperature, high humidity conditions.

In the production of a polyimide film, usually, a polyamic acid is prepared as a precursor and subjected to a process of imidizing the polyamic acid, and heating at a high temperature is required for sufficient imidization of the polyamic acid. However, when heating is performed at a high temperature as described above, a difference in heat history occurs between the surface layer and the inside of the film, and thus a difference occurs in imidization rate and in the orientation state of molecules between the surface layer and the inside.

Therefore, there are problems in that physical properties such as strength of the surface layer and the inside of the prepared polyimide film are different, and deformation such as warpage or bending occurs when the polyimide film is applied to a window covering film due to the difference in physical properties.

[ Prior art documents ]

[ patent document ]

Korean laid-open patent No. 10-2017-0028083 (03 month 13 of 2017)

Disclosure of Invention

Technical problem to be solved

It is an object of the present invention to provide a polyimide base film for a window covering, which has excellent dimensional stability over the entire area of the film and can prevent deformation phenomena such as warping or bending.

It is an object of the invention to provide a flexible display panel with improved durability and mechanical properties.

Technical scheme

One embodiment of the present invention for achieving the above technical problem provides a polyimide-based film characterized by 1610-1630cm measured by raman spectroscopic analysis^-1In the peak of the aromatic ring, the difference Δ I between the maximum value and the minimum value of the intensity (intensity) in the thickness direction is 0.6 or less, preferably 0.4 or less, and more preferably 0.3 or less, and in the raman spectroscopic analysis, the excitation wavelength is set to 532nm, the laser spot is set to 1 to 2 μm, and the measurement interval in the thickness direction is set to 1 μm.

As an embodiment, the warpage amount of the polyimide-based film may be 5mm or less, preferably 4mm or less, and more preferably 3mm or less.

As an embodiment, the polyimide-based film may have a light transmittance of 5% or more at 388nm and a total light transmittance of 87% or more at 400-700nm, a haze of 2.0% or less, a yellow index of 5.0 or less, and a b value of 2.0 or less, measured according to ASTM D1746.

As an embodiment, the polyimide-based film may have a modulus according to ASTM D882 of 3GPa or more and an elongation at break of 8% or more.

As an embodiment, the thickness of the polyimide-based film may be 10 to 500 μm.

As an embodiment, the polyimide-based film may include a polyamideimide structure. More specifically, the polyimide-based film may include units derived from a fluorine-based aromatic diamine. Further, the polyimide-based film may further include a unit derived from an alicyclic dianhydride.

As one embodiment, the polyimide-based film may be formed of a polyimide-based resin including a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, and a unit derived from an aromatic diacid chloride. In addition, a unit derived from an alicyclic dianhydride may be contained.

Another embodiment of the present invention provides a window covering film comprising: a polyimide-based film according to an embodiment; and a coating layer formed on one side of the polyimide base film.

As an embodiment, the coating layer may be any one or more selected from an antistatic layer, an anti-fingerprint layer, an anti-fouling layer, an anti-scratch layer, a low refractive layer, an anti-reflection layer, and an impact absorption layer.

Another embodiment of the present invention provides a flexible display panel including a polyimide-based film according to an embodiment.

Advantageous effects

The polyimide-based film of the present invention is flexible and has no difference in structure between the surface layer and the inside of the film, and has a uniform structure, little occurrence of warpage, and excellent light transmittance and transparency, thus having an effect suitable for use as an optical film.

Therefore, it can be applied to a window cover film for a display, a foldable (foldable) device, or the like.

Detailed Description

The present invention will be described in more detail below with reference to examples. However, the following specific embodiments or examples are merely one reference for illustrating the present invention in detail, and the present invention is not limited thereto, and the present invention can be realized by various embodiments.

In addition, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Furthermore, as used in the specification and claims, the singular forms "a", "an", and "the" include plural forms unless the context clearly dictates otherwise.

Furthermore, unless specifically stated to the contrary, the description of a portion "comprising" or "including" a constituent means that other constituents may be included, but not excluded.

The polyimide-based resin used in the present invention is a term including a polyimide resin or a polyamideimide resin. The same is true of polyimide-based films.

The "polyimide-based resin solution" used in the present invention has the same meaning as the "composition for forming a polyimide-based film" and the "polyamideimide solution". In addition, in order to form a polyimide-based film, a polyimide-based resin and a solvent may be included.

The "film" in the present invention is obtained by coating the "polyimide-based resin solution" on a support and drying and peeling it, and may be 10 to 500 μm, preferably 20 to 250 μm, and more preferably 30 to 150 μm, but is not limited thereto.

In the present invention, "warpage" may represent bending deformation of the film, and "warpage amount" may represent a vertical height from a lowest position of the film to a position where the film is warped up by bending when the film in which warpage occurs is placed on a plane.

The term "warpage-suppressing property" used in the present specification may mean a property that the "warpage amount" displayed is small.

As a result of many studies to solve the above-described technical problems, the inventors of the present invention have found that a polyimide base film in which the occurrence of warpage of the film is suppressed and the shrinkage rate is low can be provided by observing the structure of the surface and the inside of the film by raman spectroscopy, and in a range satisfying a specific range, and that physical properties suitable for use as an optical film such as a window covering film can be provided because the change rates of light transmittance and haze are small, thereby completing the present invention.

Further, the present invention has been completed by confirming that the polyimide-based film may be a polyimide-based film using a polyimide-based resin containing a fluorine atom and an aliphatic cyclic structure, more preferably, a polyimide-based film using a polyamideimide resin prepared by the preparation method of the present invention, which is a specific monomer composition containing a fluorine atom and an aliphatic cyclic structure and having a polyamide repeating unit, and then reacted with a dianhydride, or may be realized by combination of monomers or adjustment of various processes, so long as the physical properties of the present invention are satisfied, the polyimide-based film is not limited.

In the case of the process in which two or more stretching regions and heat-treated regions are repeatedly formed, the stretching region at the rear end is performed at a lower temperature than the stretching region at the front end located right in front thereof, and is performed at a smaller stretching ratio, a film having no difference in structure between the surface layer and the inside, a uniform structure, less occurrence of warpage, and excellent light transmittance and transparency, and thus being suitable for use as an optical film, can be produced, and thus the physical properties of the present invention can be obtained, but are not necessarily limited to the above conditions.

Hereinafter, a polyimide base film according to an embodiment will be described in more detail.

< polyimide-based film >

In one embodiment of the present invention, the polyimide-based film has excellent optical and mechanical physical properties, and may be formed of a material having elastic and restoring forces.

In one embodiment of the invention, the polyimide-based film is characterized by 1610-1630cm as measured by Raman spectroscopy^-1In the peak of the aromatic ring, the difference Δ I between the maximum value and the minimum value of the intensity in the thickness direction is 0.6AU (arbitrary unit) or less, and in the above range, in which the excitation wavelength is set to 532nm, the laser spot is set to 1 to 2 μm, and the measurement interval in the thickness direction is set to 1 μm, the physical properties of the surface and the inside of the film desired in the present invention can be exhibited uniformly. The Δ I is preferably 0.4AU or less, more preferably 0.3AU or less, because the effect of the present invention can be more favorably exhibited.

More specifically, the difference Δ I between the maximum value and the minimum value may be 0.1 to 0.6, and in this range, a polyimide base film having a uniform structure in the thickness direction of the film, less occurrence of warpage, excellent light transmittance and transparency, and thus useful as an optical film may be provided.

The raman spectroscopy may be conventional raman spectroscopy, but preferably the laser spot is made fine by micro-raman spectroscopy, wherein the laser spot is preferably 1-2 μm. When the laser spot is too large, it is difficult to perform accurate measurement, and on the other hand, when the laser spot is too small, an error may be generated, and thus it is preferable to be 1 to 2 μm. Further, it is preferable that the excitation wavelength used in the raman spectroscopy is 1064nm and the wavelength resolution (sampling interval) is 1cm^-1The above.

In one embodiment of the present invention, the thickness of the polyimide-based film may be 10 to 500 μm, 20 to 250 μm, or 30 to 110 μm.

In one embodiment of the present invention, the polyimide-based film may have a light transmittance of 5% or more or 5 to 80% measured at 388nm according to ASTM D1746, and a total light transmittance of 87% or more, 88% or more or 89% or more measured at 400-700nm, a haze of 2.0% or less, 1.5% or less or 1.0% or less according to ASTM D1003, a yellow index of 5.0 or less, 3.0 or less or 0.4 to 3.0 according to ASTM E313, and a b value of 2.0 or less, 1.3 or less or 0.4 to 1.3. Within the above range, it is possible to provide optical physical properties suitable for use as a window covering film.

In one embodiment of the present invention, the polyimide-based film may have a modulus of 3GPa or more, 4GPa or more, or 5GPa or more according to ASTM D882, and an elongation at break of 8% or more, 12% or more, or 15% or more. Within the above range, mechanical and physical properties suitable for use as a window covering film can be provided.

In one embodiment of the present invention, the polyimide-based film is formed of a polyimide-based resin, particularly a polyimide-based resin having a polyamideimide (polyamideimide) structure.

In addition, thePreferably, the polyimide-based film may be a polyamideimide-based resin containing a fluorine atom and an aliphatic cyclic structure, and various conditions such as monomer change, stretching or heat setting may be combined to satisfy 1610-1630cm measured by raman spectroscopy, which is desirable in the present invention^-1The difference Δ I between the maximum value and the minimum value of the strength in the thickness direction at the peak of the aromatic ring at (a) is in the range of 0.6 or less, and the aromatic ring can have characteristics of excellent appearance quality, mechanical physical properties, and dynamic bending characteristics.

In one embodiment of the present invention, as an example of the polyamideimide-based resin containing a fluorine atom and an aliphatic cyclic structure, when an amine-terminated polyamide oligomer derived from a first fluorine-based aromatic diamine and an aromatic diacid chloride is prepared and the amine-terminated polyamide oligomer, a second fluorine-based aromatic diamine, and a monomer derived from an aromatic dianhydride and an alicyclic dianhydride are polymerized to prepare a polyamideimide polymer, the object of the present invention can be more preferably achieved, and thus it is preferable. The first fluorine-based aromatic diamine and the second fluorine-based aromatic diamine may be used in the same or different kinds from each other.

In one embodiment of the present invention, when an amine-terminated oligomer forming an amide structure in a polymer chain by an aromatic diacid chloride is included as a monomer of a diamine, optical physical properties, particularly mechanical strength including a micro bending modulus, can be improved, and dynamic bending (dynamic bending) characteristics can be further improved, and thus it can be suitably used as a window cover film for a flexible display that repeats folding and unfolding operations.

In one embodiment of the present invention, when having a polyamide oligomer block as described above, the diamine monomer comprising the amine-terminated polyamide oligomer and the second fluoro aromatic diamine and the dianhydride monomer comprising the aromatic dianhydride and the alicyclic dianhydride may be preferably used in a molar ratio of 1:0.9 to 1.1, more preferably in a molar ratio of 1: 1. Further, when the content of the amine-terminated polyamide oligomer is 30 mol% or more, preferably 50 mol% or more, and more preferably 70 mol% or more with respect to the total diamine monomers, it is more advantageous to satisfy the mechanical physical properties, yellowness index, and optical properties of the present invention, but the content of the amine-terminated polyamide oligomer is not particularly limited. Further, the composition ratio of the aromatic dianhydride and the alicyclic dianhydride is not particularly limited, but is preferably used in a ratio of 30 to 80 mol% to 70 to 20 mol% in view of achieving transparency, yellowness index, mechanical physical properties, and the like of the present invention, but is not necessarily limited thereto.

In one embodiment of the present invention, the polyamideimide-based resin may include a unit derived from a fluorine-based aromatic diamine, and may have physical properties excellent in mechanical and optical physical properties by including a unit derived from a fluorine-based aromatic diamine.

In one embodiment of the present invention, the polyamideimide-based resin may include a unit derived from an alicyclic dianhydride, and may have excellent optical physical properties by including a unit derived from an alicyclic dianhydride.

In one embodiment of the present invention, the polyamideimide-based resin may include a unit derived from a fluoro-based aromatic diamine, a unit derived from an aromatic dianhydride, and a unit derived from an aromatic diacid chloride, and may have excellent mechanical and physical properties by including the above-mentioned units.

In one embodiment of the present invention, the polyamideimide-based resin uses a tetrapolymer comprising a unit derived from a fluoro-aromatic diamine, a unit derived from an aromatic dianhydride, a unit derived from an alicyclic dianhydride, and a unit derived from an aromatic diacid chloride, so that it is possible to provide a film which can satisfy optical characteristics such as transparency and mechanical physical properties, prevent the occurrence of bending under high temperature and high humidity conditions, and reduce the change in haze and heat shrinkage, and particularly, when the film is prepared by the preparation method of the present invention, it is possible to provide a film having more uniform physical properties in the thickness direction of the film after stretching, and thus is more preferable.

Further, another example of the polyamideimide-based resin containing a fluorine atom and an aliphatic cyclic structure in the present invention may be a polyamideimide-based resin obtained by mixing a fluorine-based aromatic diamine, an aromatic dianhydride, an alicyclic dianhydride, and an aromatic diacid chloride and polymerizing and imidizing them. Such a resin has a random copolymer structure and can be produced by polymerizing 40 moles or more of aromatic diacid chloride, preferably 50 to 80 moles, of aromatic diacid chloride, 10 to 50 moles of aromatic dianhydride, 10 to 60 moles of alicyclic dianhydride, and 1:0.8 to 1.1 molar ratio of the sum of diacid chloride and dianhydride to the diamine monomer, preferably 1:1 molar ratio, with respect to 100 moles of diamine.

The random polyamideimide of the present invention is different in optical characteristics such as transparency and mechanical and physical properties from the block type polyamideimide resin, but may be within the scope of the present invention.

In one embodiment of the present invention, the fluorine-based aromatic diamine component may be used by mixing 2,2 '-bis (trifluoromethyl) -benzidine with other known aromatic diamine components, but 2,2' -bis (trifluoromethyl) -benzidine may be used alone. By using the fluorine-based aromatic diamine as described above as the polyamideimide base film, excellent optical characteristics can be improved based on the mechanical physical properties required in the present invention, and the yellow index can be improved. Further, by increasing the micro bending modulus of the polyamideimide-based film, the mechanical strength of the hard coating film can be improved, and the dynamic bending characteristics can be further improved.

The aromatic dianhydride may be 4,4 '-hexafluoroisopropylidene diphthalic anhydride (6FDA), biphenyl tetracarboxylic dianhydride (BPDA), 4' -Oxydiphthalic Dianhydride (ODPA), sulfonyl diphthalic anhydride (SO2DPA), isopropylidene diphenoxy bis (phthalic anhydride) (6HDBA), at least one or a mixture of two or more of 4- (2, 5-dioxotetrahydrofuran-3-yl) -1, 2,3, 4-tetrahydronaphthalene-1, 2-dicarboxylic acid dianhydride (TDA), 1,2,4, 5-benzenetetracarboxylic acid dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA), bis (carboxyphenyl) dimethylsilane dianhydride (SiDA), and bis (dicarboxyphenoxy) diphenyl sulfide dianhydride (BDSDA), but the present invention is not limited thereto.

As the alicyclic dianhydride, there can be used, for example, a dianhydride selected from 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 5- (2, 5-dioxotetrahydrofuryl) -3-methylcyclohexene-1, 2-dicarboxylic dianhydride (DOCDA), bicyclo [2.2.2] oct-7-ene-2, 3, 5, 6-tetracarboxylic dianhydride (BTA), bicyclooctene-2, 3, 5, 6-tetracarboxylic dianhydride (BODA), 1,2,3, 4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (CHDA), 1,2, 4-tricarboxyl-3-carboxymethylcyclopentane dianhydride (TMDA), 1,2,3, 4-tetracarboxylcyclopentane dianhydride (TCDA), and derivatives thereof.

In one embodiment of the present invention, when an amide structure is formed in a polymer chain by an aromatic diacid chloride, the optical physical properties can be improved, the mechanical strength can be greatly improved, and the dynamic bending characteristics can be further improved.

As the aromatic diacid chloride, two or more selected from the group consisting of isophthaloyl dichloride (IPC), terephthaloyl dichloride (TPC), 1 '-Biphenyl-4, 4' -dicarboxylic acid chloride ([1,1 '-biphenol ] -4,4' -dicarbonyl dichloride, BPC), 1, 4-naphthaloyl chloride (1, 4-naphthaloyl dichloride, NPC), 2, 6-naphthaloyl chloride (2, 6-naphthaloyl dichloride, NTC), 1, 5-naphthaloyl chloride (1, 5-naphthaloyl dichloride, NEC) and their derivatives may be used, but not limited thereto.

Hereinafter, a method for producing a polyimide-based film will be exemplified.

In one embodiment of the present invention, the polyimide-based film may be prepared by coating a "polyimide-based resin solution" containing a polyimide-based resin and a solvent on a substrate, and then drying or drying and stretching. That is, the polyimide-based film may be prepared by a solution casting method.

In the present invention, the desired physical properties of the present invention can be obtained by preparing a film by various combinations of the monomers or by utilizing the adjustment of the casting method, stretching, heat treatment, and the like of the prepared polymer, and by adding an additive such as silica to the polymer, the desired physical properties of the present invention can be obtained, and thus the method for obtaining the physical properties is not limited.

Therefore, the present invention is only required to obtain 1610-1630cm measured by Raman spectroscopy described below^-1When the difference Δ I (degree of orientation) between the maximum value and the minimum value of the intensity in the thickness direction at the peak of the aromatic ring is 0.6 or less and the amount of warpage is 5mm or less, the method is not limited.

More preferably, Δ I (degree of orientation) is more preferably 0.4 or less, and the amount of warpage described below is 4mm or less, more preferably 3mm or less.

By the above adjustment of the present invention, it is possible to provide a polyimide base film for a window covering, which has excellent dimensional stability over the entire area of the film and can prevent a deformation phenomenon such as warpage or bending.

Accordingly, a flexible display panel having improved durability and mechanical characteristics is also provided.

Hereinafter, the method for producing a polyimide of the present invention is described by using the following polymers of monomers without limitation.

The polymer for preparing the polyimide-based film may be prepared by a method comprising the steps of: reacting a fluorine-based aromatic diamine and an aromatic diacid chloride to prepare an oligomer; reacting the prepared oligomer with a fluorine-based aromatic diamine, an aromatic dianhydride and an alicyclic dianhydride to prepare a polyamic acid solution; imidizing the polyamic acid solution to prepare a polyamideimide resin; and coating a polyamideimide solution obtained by dissolving a polyamideimide resin in an organic solvent to prepare a film.

The step of preparing the oligomer may comprise the steps of: reacting a fluorine-based aromatic diamine with an aromatic diacid chloride in a reactor; and purifying and drying the obtained oligomer. In this case, the fluorine-based aromatic diamine is added in a molar ratio of 1.01 to 2 relative to the aromatic diacid chloride, whereby the amine-terminated polyamide oligomer monomer can be prepared. The molecular weight of the oligomer monomer is not particularly limited, and for example, when the weight average molecular weight is in the range of 1000-3000g/mol, more excellent physical properties can be obtained.

In addition, in order to introduce an amide structure, it is preferable to use an aromatic carbonyl halide monomer such as terephthaloyl chloride or isophthaloyl chloride, instead of using terephthalate or terephthalic acid itself, and although it is not clear, it is considered that chlorine element affects the physical properties of the film.

Then, the step of preparing the polyamic acid solution may be achieved by a solution polymerization reaction of reacting the prepared oligomer with a fluorine-based aromatic diamine, an aromatic dianhydride, and an alicyclic dianhydride in an organic solvent. In this case, the organic solvent used for the polymerization reaction may be, for example, one or two or more polar solvents selected from dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), Dimethylformamide (DMF), Dimethylsulfoxide (DMSO), ethyl cellosolve, methyl cellosolve, acetone, ethyl acetate, m-cresol, and the like.

More specifically, a polyamic acid solution is prepared by reacting a fluorine-based aromatic diamine and an aromatic diacid chloride to prepare an intermediate in the form of an oligomer including an amide unit, and then reacting the oligomer with the fluorine-based aromatic diamine, an aromatic dianhydride, and an alicyclic dianhydride, whereby a polyamideimide-based film in which the amide intermediate is uniformly distributed can be prepared. As described above, the amide intermediate is uniformly distributed throughout the film, and therefore it is possible to provide a film having excellent mechanical physical properties and excellent optical properties over the entire area of the film, and further improving the coating properties and coating uniformity of the coating composition used in the post-coating process of a hard coat layer or the like, and finally further improving the optical physical properties of the window covering film, and thus having excellent optical properties such as no occurrence of optical streaks such as rainbow lines and patches.

Then, the step of preparing the polyamide imide resin by imidization may be performed by chemical imidization, and more preferably, the polyamide acid solution is chemically imidized using pyridine and acetic anhydride. Next, imidization may be carried out at a low temperature of 150 ℃ or lower, preferably 100 ℃ or lower, preferably 50 to 150 ℃ by using an imidization catalyst and a dehydrating agent.

By the method as described above, it is possible to impart uniform mechanical physical properties to the entire film as compared with the case where the imidization reaction is carried out by heat at a high temperature.

Any one or two or more kinds of catalysts selected from pyridine, isoquinoline and β -quinoline may be used as the imidization catalyst. Further, the dehydrating agent may use any one or two or more selected from acetic anhydride (acetic anhydride), phthalic anhydride (phthalic anhydride), maleic anhydride (maleic anhydride), and the like, and is not necessarily limited thereto.

In addition, additives such as flame retardants, tackifiers, inorganic particles, antioxidants, ultraviolet ray inhibitors, and plasticizers may be mixed in the polyamic acid solution to prepare the polyamideimide resin.

Further, after the imidization is performed, the resin may be purified with a solvent to obtain a solid, and the solid may be dissolved in the solvent to obtain a polyamideimide solution. The solvent may include, for example, N-dimethylacetamide (DMAc) and the like, but is not limited thereto.

The step of preparing the film using the polyamideimide solution may be performed by coating the polyamideimide solution on the substrate and then drying in a drying step divided into drying zones. Further, stretching may also be performed after or before drying, and a heat treatment step may also be provided after the drying step or the stretching step, as necessary. For example, glass, stainless steel, a film, or the like can be used as the substrate, but not limited thereto. Coating may be performed by die coater, air knife coating, reverse roll coating, spray coating, blade coating, casting, gravure coating, spin coating, or the like.

In the present invention, by using specific drying conditions and stretching conditions, it is possible to more easily provide a film satisfying the following physical properties desired in the present invention, namely 1610-1630cm measured by Raman spectroscopy^-1Intensity in thickness direction at peak of aromatic ringHas a difference (Δ I) between the maximum value and the minimum value of 0.6 or less, and has a warpage amount of 7mm or less, preferably 5mm or less, more preferably 3mm or less, and therefore a significantly excellent film can be obtained.

In the present invention, the drying may be performed in a plurality of drying zones, and when the drying is initially performed at an excessively high temperature, a film whose surface and inside are not uniform may be prepared, and therefore, it is preferable that the drying is performed while gradually increasing the temperature as it approaches the rear end of the drying zone. Specifically, for example, it is composed of two or more stages of drying zones, and has the following drying zones: in the drying zone, the temperature of the drying zone located at the rear end is set to a higher temperature than the drying zone located immediately in front thereof, the respective temperatures of the drying zones located at the rear end except for the first drying zone are set to high temperatures equal to or exceeding the temperature of the drying zone located immediately in front thereof, and drying is performed, the solvent content of the film dried in the drying step is adjusted to 10 to 30 wt%, and a stretching step is performed.

Further, as for the drying time in each region, when the solvent content of the finally dried film is satisfied, the drying time in each stage is preferably the same or the same degree (what is called the same degree in which the difference in drying time is within 10% from that of the drying time at the front end) of the drying time.

In the drying step, the higher the drying temperature is closer to the rear end indicates that the temperature of the second drying zone in the initial drying zone is set to a higher temperature than the first drying zone, and the temperature of the drying zone at the rear end is not lower than the temperature of the second drying zone. That is, when the drying zones subsequent to the second drying zone are referred to as the rear end, the temperatures of the drying zones at the rear end may be set to be the same or similar.

The stretching step may be further performed in the present invention, and may be prepared only by heat treatment without performing the stretching step within a range satisfying the physical properties of the present invention, and thus the stretching step is not limited as long as the physical properties of the present invention can be achieved.

< Window covering film >

Further, another embodiment of the present invention provides a window covering film comprising the above polyimide base film; and a coating layer formed on the polyimide-based film.

When a coating layer is laminated on a polyimide base film having a specific range of surface hardness change rate, a window covering film with significantly improved visibility can be provided.

In one embodiment of the present invention, the window covering film may satisfy all of the physical properties that a light transmittance measured at 388nm or more according to ASTM D1746 and a total light transmittance measured at 400-700nm is 87% or more, 88% or more or 89% or more, a haze according to ASTM D1003 is 1.5% or less, 1.2% or less or 1.0% or less, a yellow index according to ASTM E313 is 4.0 or less, 3.0 or less or 2.0 or less, and a b x value is 2.0 or less, 1.5 or less or 1.2 or less.

According to an embodiment of the present invention, the coating layer is a layer for imparting functionality to the window covering film, and various applications may be performed according to purposes.

In a specific example, the coating layer may include any one or more layers selected from a repair layer, an impact diffusion layer, a self-cleaning layer, an anti-fingerprint layer, an anti-scratch layer, a low refractive layer, an impact absorption layer, and the like, but is not limited thereto.

Even if various coating layers as described above are formed on the polyimide base film, it is possible to provide a window covering film which is excellent in display quality and has high optical characteristics, particularly significantly reduced in the rainbow streak phenomenon.

In one embodiment of the present invention, specifically, the coating layer may be formed on one or both sides of the polyimide-based film. For example, the coating layer may be disposed on the polyimide base film, and may be disposed on and under the polyimide base film, respectively. The coating layer can protect a polyimide-based film having excellent optical and mechanical properties from external physical or chemical damage.

One embodiment of the inventionIn the embodiment, the solid content of the coating layer may be formed to be 0.01 to 200g/m with respect to the total area of the polyimide-based film². Preferably, the solid content of the coating layer formed may be 20 to 200g/m with respect to the total area of the polyimide-based film². By providing with the above basis weight, the functionality can be maintained, and surprisingly, the rainbow streak phenomenon does not occur, and thus excellent visibility can be achieved.

In one embodiment of the present invention, specifically, the coating layer may be formed by coating on a polyimide-based film in the form of a composition for forming a coating layer comprising a coating solvent. The coating solvent is not particularly limited, but may preferably be a polar solvent. For example, the polar solvent may be any one or more solvents selected from an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an amide-based solvent, a sulfoxide-based solvent, an aromatic hydrocarbon-based solvent, and the like. Specifically, the polar solvent may be any one or more solvents selected from the group consisting of dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, ethyl acetate, propylene glycol methyl ether, m-cresol, methanol, ethanol, isopropanol, butanol, 2-methoxyethanol, methyl cellosolve, ethyl cellosolve, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl phenyl ketone, diethyl ketone, dipropyl ketone, cyclohexanone, hexane, heptane, octane, benzene, toluene, xylene, and the like.

In one embodiment of the present invention, as a method for forming a coating layer by coating a composition for forming the coating layer on the polyimide base film, for example, any one or more methods selected from spin coating, dip coating, spray coating, die coating, bar coating, roll coater, meniscus coating, flexography, screen printing, bead coating, air knife coating, reverse roll coating, blade coating, cast coating, gravure coating, and the like may be used, but is not limited thereto.

In one embodiment of the present invention, the window cover film may further comprise a substrate layer. The base material layer may be formed on the other side of the polyimide base film on which the coating layer is not formed.

In one embodiment of the present invention, the polyimide base film may be laminated on a base material layer after film formation, and may be laminated after coating a polyamic acid resin composition that is a precursor of the polyimide base film, but is not particularly limited as long as the above-described laminated structure can be formed.

In one embodiment of the present invention, the base material layer is not particularly limited as long as it is a base material film of a commonly used window covering film, and for example, the base material layer may include any one or more selected from an ester-based polymer, a carbonate-based polymer, a styrene-based polymer, an acrylic-based polymer, and the like. In a specific example, the substrate layer may include any one or more selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polycarbonate, polystyrene, polymethyl methacrylate, and the like, but is not limited thereto.

In one embodiment of the present invention, the substrate layer may be a single layer or a multilayer in which two or more layers are stacked. Specifically, the base material layer may be laminated including an optical adhesive layer at an interface between two or more base material films.

In one embodiment of the present invention, the thickness of the substrate layer may be 50 to 300 μm, preferably may be 100-300 μm, and more preferably may be 150-250 μm. The substrate layer satisfies mechanical and physical properties by having the thickness as described above, and can significantly reduce the distortion phenomenon of light when the polyimide base films are laminated.

In one embodiment of the present invention, in a specific example, the Optical adhesive layer may include any one or more selected from among an Optically Clear Adhesive (OCA), an Optically Clear Resin (OCR), a Pressure Sensitive Adhesive (PSA), and the like, but is not limited thereto.

In one embodiment of the present invention, the interface between the substrate layer of the window cover film and the polyimide base film may further include a second optical adhesive layer.

Specifically, the second optical adhesive layer formed on the interface of the base material layer and the polyimide base film may be the same as or different from the optical adhesive layer in the above-described base material layer, and for example, the second optical adhesive layer may be formed to a thickness of 20 to 120 μm, and preferably, may be formed to a thickness of 20 to 80 μm. When the second optical adhesive layer is formed to a thickness in the above range, the window cover film as a whole may achieve excellent optical characteristics and an effect of improving optical distortion.

In one embodiment of the present invention, the window covering film has high surface hardness and excellent flexibility, and is light and excellent in durability against deformation compared to tempered glass, and thus is excellent as an outermost window substrate of a flexible display panel.

Another embodiment of the present invention provides a display device including a display panel and the above-described window cover film formed on the display panel.

In one embodiment of the present invention, as for the display device, there is no particular limitation as long as it is a field requiring excellent optical characteristics, and a display panel suitable for the display device can be selected and provided. Preferably, the window cover film may be applied to a flexible display device, and in a specific example, may be applied to any one or more of various image display devices selected from a liquid crystal display device, an electroluminescent display device, a plasma display device, a field emission display device, and the like, but is not limited thereto.

The display device including the window covering film of the present invention described above is excellent in display quality, and remarkably reduces a distortion phenomenon caused by light, particularly a rainbow pattern phenomenon in which rainbow patterns are generated, and has excellent visibility, so that fatigue of eyes of a user can be minimized.

The present invention will be described in more detail below based on examples and comparative examples. However, the following examples and comparative examples are merely one example for illustrating the present invention in more detail, and the present invention is not limited to the following examples and comparative examples.

Hereinafter, the physical properties were measured as follows.

1) Hardness of pencil

For the film, according to jis k5400, a 20mm line was drawn at a speed of 50 mm/sec with a load of 750g, repeated 5 times or more, and pencil hardness was measured with reference to the case where 1 time or more scratches were generated.

2) Modulus/elongation at break

The measurement was carried out according to ASTM D882 on a polyamideimide film having a length of 50mm and a width of 10mm at 25 ℃ under a condition of stretching at 50 mm/min by UTM 3365 of Instron Co.

The thickness of the film was measured and the value was entered into the instrument. Modulus is in GPa and elongation at break is in%.

3) Light transmittance

The total light transmittance was measured at the entire wavelength region of 400 and 700nm using a Spectrophotometer (Spectrophotometer) (Nippon Denshoku, COH-400) for a film having a thickness of 50 μm according to ASTM D1746 standard, and the single wavelength transmittance was measured at 388nm using ultraviolet/visible (UV/Vis) (Shimadzu Corp., UV 3600). The unit is%.

4) Haze (haze)

The measurement was carried out by a spectrophotometer (COH-400, Nippon Denshoku industries Co., Ltd.) based on a film having a thickness of 50 μm according to ASTM D1003. The unit is%.

5) Yellow Index (YI) and b value

The measurement was carried out by a Colorimeter (Colorimeter) (hunterli (HunterLab) corporation, ColorQuest XE) based on a film having a thickness of 50 μm according to the ASTM E313 standard.

6) Weight average molecular weight (Mw) and polydispersity index (PDI)

The weight average molecular weight and polydispersity index of the prepared film were measured as follows: membrane samples were dissolved in DMAc eluent containing 0.05M LiBr and measured using GPC (Waters GPC system (system), Waters 1515 isocratic HPLC Pump, Waters 2414 Refractive Index detector). For measurement, the GPC Column (Column) was connected to an Olexis, Polypore and mixed D Column, and the solvent used was DMAc solution, and the standard used was polymethyl methacrylate (PMMA STD), and analyzed at 35 ℃ at a flow rate of 1 mL/min (flow rate).

7) Degree of orientation

1610-1630cm for polyimide-based films by Raman spectroscopic analysis^-1The difference (Δ I) between the maximum value and the minimum value of the intensity in the thickness direction was measured at the peak of the aromatic ring in (d), and in the raman spectroscopic analysis, the excitation wavelength was set to 532nm, the laser spot was set to 1 μm, and the measurement interval in the thickness direction was set to 1 μm.

The analysis was performed as follows.

The device name: raman Microscope (Raman Microscope)

The manufacturer: leishaw company (Renisshaw) (British)

The model name is as follows: inVia

Laser focusing (focus) was made on the surface of the film (Air) plane, referred to as a plane a), the film was started to enter at a measurement interval (depth interval) of 1 μm in the thickness direction, and 1610 and 1630cm of each data point (data point) was measured^-1Intensity of the peak of the aromatic ring at (a).

At this time, the speed when the laser light passes through the inside of the film is different from the speed when the laser light passes through the air due to the difference in refractive index of the interface of the air and the film, thereby exhibiting different intensities, and therefore, when the laser light is incident from the film surface (a-plane) to the bottom plane (referred to as B-plane), the 7 th point in the direction from the start to the 6 th point (point) and from the bottom plane (B-plane) to the a-plane is removed, and data is calculated.

After removing from the surface (surface A) to the 6 th point, the intensity at the 1 st point was set to I₀In 1 with₀For reference, relative intensity (relative intensity) I of each point measured at intervals of 1 μm in the thickness direction was calculated.

I-intensity/I of each data point₀

The maximum value obtained from the relative intensity values calculated as described above is set as I_maxThe minimum value is set as I_minAnd is combined withTheir difference is calculated as follows.

ΔI＝I_max-I_min

8) Measurement of warpage amount

For the film, a square having a size of 15cm × 15cm was cut in a direction inclined at 45 ° to the MD direction. That is, two vertices are aligned with the MD direction of the film, and the remaining two vertices are aligned with the TD direction of the film. The cut film was left under constant temperature and humidity conditions of 25 ± 3 ℃ and 55 ± 5% for 12 hours, and then a vertical height (in mm) from a lowest position (e.g., center) of the film to a plane connecting the vertices was measured with respect to the plane connecting the vertices, and the maximum value was taken as a warpage amount (mm).

[ example 1]

In the reactor, terephthaloyl chloride (TPC) and 2,2' -bis (trifluoromethyl) -benzidine (TFMB) were added to a mixed solution of dichloromethane and pyridine, and stirred at 25 ℃ for 2 hours under a nitrogen atmosphere. At this time, the molar ratio of TPC to TFMB was set to 300:400, and the solid content was adjusted to 10 wt%. Thereafter, the reactant in excess methanol precipitation, then filtration to obtain solid, the solid at 50 degrees C vacuum drying for more than 6 hours, thereby obtaining oligomers, the preparation of oligomers with molecular Weight (Formula Weight, FW) of 1670 g/mol.

N, N-dimethylacetamide (DMAc) as a solvent, 100 moles of the oligomer, and 28.6 moles of 2,2' -bis (trifluoromethyl) -benzidine (TFMB) were added to the reactor and stirred well. After confirming complete dissolution of the solid raw material, fumed silica (surface area 95 m) was added to the solid material²/g，<1 μm) was added to DMAc in a content of 1000ppm, and dispersed and added by using ultrasonic waves. 64.1 moles of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) and 64.1 moles of 4,4' -hexafluoroisopropylidene diphthalic anhydride (6FDA) were added in this order and sufficiently stirred, followed by polymerization at 40 ℃ for 10 hours. At this time, the solid content was 20%. Then, pyridine and acetic anhydride, each in an amount of 2.5 times by mole with respect to the content of total dianhydride, were sequentially added to the solution, and stirred at 60 ℃ for 12 hours, thereby preparing a polyimide-based resin solution。

The polyimide-based resin solution was continuously coated on a stainless steel belt and then dried in a drying zone designed into four drying zones. Of the drying zones, the first drying zone was dried at 80 ℃ for 5 minutes, the second drying zone was dried at 110 ℃ for 2 minutes, the third drying zone was dried at 130 ℃ for 2 minutes, and the fourth drying zone was dried at 140 ℃ for 2 minutes. The solvent content of the film passing through the drying zone was 20 wt%.

Next, the dried polyimide base film was peeled off from the support, and the substrate film was stretched by a Pin Tenter (Pin tent). The stretching zone consisted of two stretching zones and a heat treatment zone, the first stretching zone was stretched to 102% at 220 ℃ followed by a heat treatment at 350 ℃ for 10 minutes, the second stretching zone was stretched at 160 ℃ at a stretch ratio of 101% followed by a heat treatment at 350 ℃ for 10 minutes. The solvent content of the final film by the stretching and heat treatment process was adjusted to 2 wt%.

As a result of measuring physical properties of the prepared polyamideimide film, the thickness was 50 μm, the total light transmittance was 89.5%, the haze was 0.32%, the Yellow Index (YI) was 1.8, the b x value was 1.0, the modulus was 7.2GPa, the elongation at break was 22.2%, the weight average molecular weight was 310000g/mol, the polydispersity index (PDI) was 2.1, and the pencil hardness was HB/750 g. Table 1 shows the degree of orientation and the occurrence of warpage.

[ example 2]

The preparation was performed by the same method as example 1, except that in the stretching step in said example 1, the first stretched zone was stretched to 105% at 250 ℃, followed by the primary heat treatment at 350 ℃ for 10 minutes, followed by the second stretched zone being stretched at 180 ℃ at a stretch ratio of 101%, followed by the secondary heat treatment at 350 ℃ for 10 minutes.

Physical properties of the prepared polyamideimide film were measured and are shown in the following table 1.

[ example 3]

In a reactor, 100 moles of 2,2' -bis (trifluoromethyl) -benzidine (TFMB) and 39.6 moles of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) were mixed in N, N-dimethylacetamide (DMAc) solvent and polymerized at 40 ℃ for 10 hours. 30 moles of terephthaloyl chloride and 30 moles of isophthaloyl chloride were mixed in the reactants so that the solid content of the total monomers became 10% by weight, and polymerized at 40 ℃ for 2 hours.

Next, pyridine and acetic anhydride, each in an amount of 2.5 times mole, were sequentially added to the solution with respect to the content of total dianhydride, and stirred at 60 ℃ for 12 hours.

After completion of the polymerization, the polymerization solution was precipitated in an excessive amount of methanol, followed by filtration to obtain a solid, and the solid was vacuum-dried at 50 ℃ for 6 hours or more to obtain a polyamide imide powder. The powder was diluted and dissolved to 20% in DMAc, and 1000ppm of fumed silica was added and dispersed to prepare a polyimide-based resin solution.

After the polyimide-based resin solution was prepared, the treatment was performed by the same method as in example 1.

[ example 4]

Preparation was carried out by the same method as example 3, except that stretching was not carried out and a thickness of 80 μm was made in example 3.

Comparative example 1

The preparation was carried out by the same method as in example 3, except that the mole numbers of terephthaloyl chloride and isophthaloyl chloride were set to 20 moles and 10 moles in example 3.

Comparative example 2

An 80 μm film was prepared by the same method as example 3, except that 30 moles of terephthaloyl chloride was used in example 3 and isophthaloyl chloride was not used.

Physical properties of the prepared polyamideimide film were measured and are shown in the following table 1.

[ Table 1]

As described above, the present invention has been described with reference to specific contents and specific examples, but this is provided only to facilitate a more complete understanding of the present invention, and the present invention is not limited to the above examples, and various modifications and variations can be made by those skilled in the art to which the present invention pertains through this description.

Therefore, the inventive concept should not be limited to the described embodiments, but the claims of the present invention and all equivalents or equivalent variations thereof are intended to be included within the scope of the inventive concept.