Hard coat film and method for manufacturing the same, and image display device

Abstract

A polyimide film (1) has a first main surface (1A) and a second main surface (1B). The polyimide film comprises a polyimide resin and an ultraviolet absorber, wherein the concentration CA of the ultraviolet absorber on the first-main-surface side is up to 0.5 times the concentration CB of the ultraviolet absorber on the second-main-surface side. When the polyimide film is disposed on the viewing side of an image display panel, the polyimide film is disposed so that the first main surface thereof faces the image display panel. Due to this, the polyimide film can be inhibited from suffering photodeterioration caused by external light.

Description

Technical Field

[0001] The present invention relates to , a hard coat film having a hard coat layer on the surface of a polyimide film and the manufacturing method thereof and further relates to an image display device having a polyimide film or hard coat film on the visual side surface of an image display panel.

Background Art

[0002] The miniaturization and weight reduction of portable terminal devices have progressed, and terminal devices typified by smartphones have become widely popular. In recent years, as a method for achieving both a large screen size and portability, foldable portable terminal devices equipped with flexible displays, particularly organic EL panels using flexible substrates, have been proposed.

[0003] In flexible devices, not only the display substrate but also surface protection materials such as cover windows need to have flexibility. In Patent Document 1, it has been proposed to use a polyimide film excellent in transparency, surface hardness, and bending durability as a cover window material for an image display device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the cover window of an image display device is located in the outermost layer, it is easily exposed to external light, and it is required that changes in optical properties and mechanical strength be small even when exposed to ultraviolet rays or the like. In order to impart light resistance to a transparent resin film, it is generally common to add an ultraviolet absorber.

[0006] Patent Document 1 describes that polyimide has excellent light resistance even without the use of ultraviolet absorbers because it has a biphenyl structure. However, the cover window of an image display device requires even higher light resistance, for example, against an irradiance of 500 W / m². 2 With the increasing requirement for light resistance in carbon arc testing, it is difficult to achieve sufficient light resistance in polyimide films without including UV absorbers.

[0007] The more UV absorbers a polyimide film contains, the more UV light is absorbed by the UV absorbers and the less UV light is absorbed by the polyimide itself, thus suppressing the degradation of the polyimide film due to UV light from ambient light. On the other hand, if the amount of UV absorbers added to improve light resistance is increased, the film becomes discolored due to the light absorption of the UV absorbers, reducing its transparency. In other words, UV absorbers contribute to improving the light resistance of the film, but they also cause a decrease in transparency.

[0008] In view of the above, the present invention aims to provide a polyimide film that has better light resistance while maintaining transparency. [Means for solving the problem]

[0009] One aspect of the present invention is a polyimide film containing an ultraviolet absorber, wherein the ultraviolet absorber is unevenly distributed in the thickness direction. The polyimide film consists of one layer and has a first main surface and a second main surface. The concentration of the ultraviolet absorber on the first main surface side is C A This is the concentration C of the UV absorber on the second main surface side. B It is preferable that it be 0.5 times or less.

[0010] The thickness of the polyimide film may be 5 to 100 μm. Benzotriazole compounds or triazine compounds are preferred as the ultraviolet absorbers contained in the polyimide film. The content of the ultraviolet absorber in the polyimide film is preferably 0.1 to 4.5% by weight.

[0011] A polyimide film is obtained by applying a solution containing polyimide resin and an ultraviolet absorber to a substrate, heating the solution on the substrate to dry and remove the organic solvent, and then peeling it off the substrate, thereby obtaining a polyimide film in which the ultraviolet absorber is unevenly distributed in the thickness direction. In this polyimide film, the peeled surface (Side B) from the substrate is the second main surface, and the concentration of the ultraviolet absorber is relatively high.

[0012] A hard coat film can be obtained by providing a hard coat layer on the surface of a polyimide film. Preferably, the hard coat film has the hard coat layer on the second main surface of the polyimide film.

[0013] Polyimide films and hard coat films can be used, for example, as surface protective materials (cover windows) placed on the viewing surface of an image display panel in an image display device. The image display device may be foldable. Preferably, the first main surface of the polyimide film is positioned facing the image display panel, and the second main surface of the polyimide film is positioned on the viewing side of the image display device. [Effects of the Invention]

[0014] In films where the UV absorber is unevenly distributed in the thickness direction, by positioning the side with a higher UV absorber concentration on the viewing side of the display device, even with a low concentration of UV absorber, the amount of UV light absorbed by the polyimide from ambient light is reduced, thus suppressing photodegradation caused by ambient light. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view of a polyimide film. [Figure 2] This is a cross-sectional view showing an example of the composition of a hard coat film. [Figure 3] This is a cross-sectional view showing an example of the configuration of an image display device. [Figure 4] This is a cross-sectional view showing an example of the configuration of an image display device. [Modes for carrying out the invention]

[0016] Figure 1 is a cross-sectional view of a polyimide film according to an embodiment of the present invention. The polyimide film 1 is a single-layer film and has a first major surface 1A and a second major surface 1B. The polyimide film 1 contains an ultraviolet absorber. By including an ultraviolet absorber in the polyimide film, the light resistance is improved, and the yellowing of the polyimide film tends to be suppressed even after long-term ultraviolet exposure.

[0017] In the polyimide film 1, the concentration C of the ultraviolet absorber on the second major surface 1B side B is greater than the concentration C of the ultraviolet absorber on the first major surface 1A side. A That is, the polyimide film 1 has a concentration distribution of the ultraviolet absorber in the thickness direction, and the ultraviolet absorber is unevenly distributed on the second major surface side.

[0018] Incidentally, the concentration C of the ultraviolet absorber on the first major surface side A is the concentration of the ultraviolet absorber in the region Ta of 30% of the thickness of the polyimide film 1 from the first major surface 1A, and the concentration C of the ultraviolet absorber on the second major surface side B is defined as the concentration of the ultraviolet absorber in the region Tb of 30% of the thickness of the polyimide film 1 from the second major surface 1B. The concentration C of the ultraviolet absorber on the first major surface side A is measured with a sample obtained by polishing the polyimide film 1 from the second major surface side so that the region Ta remains. The concentration C of the ultraviolet absorber on the second major surface side B is measured with a sample obtained by polishing the polyimide film 1 from the first major surface side so that the region Tb remains. When the chemical structure of the ultraviolet absorber is known, the concentration of the ultraviolet absorber is measured by NMR. When the chemical structure of the ultraviolet absorber is unknown, the concentration of the ultraviolet absorber is measured based on the absorption spectrum.

[0019] Figure 2 is a cross-sectional view of a hard coat film having a hard coat layer 3 on the surface of a polyimide film 1. The hard coat film 10 has the hard coat layer 3 on the second main surface 1B of the polyimide film 1, that is, on the side with a relatively higher concentration of ultraviolet absorber. The hard coat film may have hard coat layers on both sides of the polyimide film 1.

[0020] Figure 3 is a cross-sectional view of an image display device in which a polyimide film 1 is placed on the viewing surface of an image display panel 5. In the image display device 101 of Figure 3, the polyimide film 1 is arranged such that the first main surface 1A, which has a relatively low ultraviolet absorption density, faces the image display panel 5, and the second main surface 1B, which has a relatively high ultraviolet absorption density, is on the viewing side.

[0021] Figure 4 is a cross-sectional view of an image display device in which a hard coat film 10 is placed on the viewing surface of an image display panel 5. In the image display device 102 of Figure 4, similar to the image display device 101 of Figure 3, the polyimide film 1 is positioned so that the first main surface 1A faces the image display panel 5 and the second main surface 1B is the viewing side, and a hard coat layer 3 is provided on the second main surface 1B, which is the viewing surface of the polyimide film 1.

[0022] In the image display devices 101 and 102, ambient light is incident from the viewing side, i.e., from the second main surface 1B side of the polyimide film 1. When ambient light is incident on the polyimide film 1, the ultraviolet rays contained in the ambient light are absorbed by the ultraviolet absorber contained in the polyimide film. A portion of the ultraviolet rays that are not absorbed by the ultraviolet absorber is absorbed by the polyimide.

[0023] Polyimide film 1 has a concentration C of UV absorber on the second main surface 1B side. BBecause the UV absorber is large, more ultraviolet light is absorbed in the region Tb on the second main surface side compared to when the UV absorber is uniformly distributed in the thickness direction, resulting in less ultraviolet light reaching the region Ta on the first main surface side. Since a lot of ultraviolet light is absorbed in region Tb at the beginning of light incidence, and less ultraviolet light reaches the deeper region Ta, when considering the polyimide film 1 as a whole, the amount of ultraviolet light absorbed by the polyimide is small, and photodegradation of the polyimide caused by ultraviolet light is suppressed.

[0024] In this way, by arranging the polyimide film 1 so that the second main surface 1B, which has a relatively higher concentration of UV absorber, becomes the visible side (light incident side), the photodegradation of polyimide can be suppressed more efficiently with the same UV absorber concentration. In other words, it is possible to suppress the photodegradation of polyimide and improve its light resistance with a smaller amount of UV absorber added (lower concentration of UV absorber). Because the UV absorber concentration is low, discoloration of the polyimide film (reduction in transparency) caused by the visible light absorption of the UV absorber is suppressed, thus achieving both light resistance and transparency in the polyimide film.

[0025] The concentration distribution of the UV absorber in the thickness direction of polyimide film 1 is large, and the concentration of the UV absorber on the first main surface 1A side is C. A and the concentration C of the ultraviolet absorber on the second main surface 1B side B The greater the difference, the more photodegradation is suppressed when the second main surface is the light incident surface, and the smaller the change in the yellowness ΔYI of the polyimide film 1 tends to be. Concentration C of the ultraviolet absorber on the first main surface 1A side A This is the concentration C of the ultraviolet absorber on the second main surface 1B side. B A ratio of 0.5 times or less is preferred, 0.4 times or less is more preferred, and 0.3 times or less is even more preferred.

[0026] [Polyimide film] The preferred forms of polyimide film 1 will be described below in order. Unless otherwise specified, the compounds exemplified herein may be used alone or in combination (coexistence) of two or more types.

[0027] Polyimide film 1 contains polyimide resin. The polyimide resin content in polyimide film 1 is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more.

[0028] <Composition of polyimide> Polyimides are generally obtained by dehydrating and cyclizing polyamic acids, which are produced by the reaction of tetracarboxylic dianhydrides (hereinafter sometimes simply referred to as "acid dianhydrides") with diamines. That is, polyimides have structures derived from acid dianhydrides and structures derived from diamines. As described above, the composition of the polyimide resin contained in polyimide film 1 is not particularly limited, as long as the ultraviolet absorber is unevenly distributed in the thickness direction.

[0029] In the production of transparent polyimide films, a method is preferably employed in which a solution of polyimide resin dissolved in an organic solvent is applied to a substrate, and the solvent is dried and removed by heating (solution casting method). Therefore, it is preferable that the polyimide is not only transparent but also soluble in organic solvents.

[0030] Examples of polyimides that exhibit transparency and solubility in organic solvents include those containing one or more of the following acid dianhydrides and one or more of the following diamines.

[0031] Acid dianhydride group: 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)propane dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropanoic acid dianhydride, 9,9-bis(3, 4-Dicarboxyphenyl)fluorenidioanhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, p-phenylenebis(trimellitate) dianhydride, and bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl

[0032] Diamine group: 2,2'-bis(trifluoromethyl)benzidine, 2,2'-dimethylbenzidine, isophoronediamine, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 9,9-bis(4-aminophenyl)fluorene, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2-bis(4-(4-aminophenoxy)phenyl)propane

[0033] In the solution casting method, it is preferable to use a low-boiling point organic solvent such as dichloromethane. By using a low-boiling point solvent, the solvent can be dried and removed by heating at low temperatures and for a short time, thereby improving the productivity of polyimide films. Furthermore, by using a low-boiling point solvent, heating at high temperatures (e.g., 200°C or higher) is not required to reduce the amount of residual solvent, and thermal degradation of the polyimide can be suppressed.

[0034] An example of a polyimide soluble in dichloromethane is a polyimide containing a tetracarboxylic dianhydride represented by general formula (1) and a tetracarboxylic dianhydride having an alicyclic structure as acid dianhydride components, and containing a fluoroalkyl-substituted benzidine as a diamine component.

[0035] [ka]

[0036] In general formula (1), n ​​is either 1 or 2. 1 ~R 4 Each of these is independently a hydrogen atom, a fluorine atom, and an alkyl group or fluoroalkyl group having 1 to 20 carbon atoms.

[0037] (Dianhydrides with ester structure) The compound represented by the above general formula (1) is an acid dianhydride having an ester structure. 1 ~R 4 Examples of alkyl groups when the group is an alkyl group or fluoroalkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, cyclobutyl group, n-pentyl group, isopentyl group, neopentyl group, cyclopentyl group, n-hexyl group, and cyclohexyl group. Examples of fluoroalkyl groups include monofluoromethyl group, difluoromethyl group, trifluoromethyl group, and pentafluoroethyl group.

[0038] Since a polyimide exhibiting high solubility in dichloromethane is obtained, among the compounds represented by general formula (1), n=2 and R 1 ~R 4 Compounds in which at least one of the elements is an alkyl group or fluoroalkyl group having 1 to 20 carbon atoms are preferred. Among these, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl (TAHMBP), represented by the following formula (2), is preferred.

[0039] [ka]

[0040] (Dianhydrides with an alicyclic structure) Examples of tetracarboxylic dianhydrides having an alicyclic structure include those having a cyclobutane structure, such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,4-dipropyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, and cyclobutane-1,2:3,4-bis(tetramethylene)-1,2,3,4-tetracarboxylic dianhydride.

[0041] Other alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2”-norbornane-5,5”,6,6”-tetracarboxylic dianhydride, 2,2'-binorbornane-5,5',6,6'tetracarboxylic dianhydride, 3-(carboxymethyl)-1, 2,4-Cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, bicyclo[2.2.2]octa-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylate Rubonic anhydride, 5,5'-[cyclohexyllidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofrandione, 5-isobenzofurancarboxylic acid, 1,3-dihydro-1,3-dioxo-,5,5'-[1,4-cyclohexanediylbis(methylene)] ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid 2,3:5,6-dianhydride, Examples include decahydro-1,4,5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride, tricyclo[6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic dianhydride, octahydro-1H,3H,8H,10H-biphenyleno[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetron, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetron, etc.

[0042] Among alicyclic tetracarboxylic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), or 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic-3,4:3',4'-dianhydride (H-BPDA) are preferred from the viewpoint of polyimide transparency and mechanical strength, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0043] (Fluoroalkyl-substituted benzidine) Specific examples of fluoroalkyl-substituted benzidines include 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenzidine, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2,2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2',3-trifluorobenzidine, 2,3,3'-trifluorobenzidine, and 2,2',5 -Trifluorobenzidine, 2,2',6-Trifluorobenzidine, 2,3',5-Trifluorobenzidine, 2,3',6-Trifluorobenzidine, 2,2',3,3'-Tetrafluorobenzidine, 2,2',5,5'-Tetrafluorobenzidine, 2,2',6,6'-Tetrafluorobenzidine, 2,2',3,3',6,6'-Hexafluorobenzidine, 2,2',3,3',5,5',6,6'-Octafluorobenzidine, 2-(Trifluoromethyl)benzidine, 3-(Trifluoromethyl)benzidine, 2,3 -Bis(trifluoromethyl)benzidine, 2,5-Bis(trifluoromethyl)benzidine, 2,6-Bis(trifluoromethyl)benzidine, 2,3,5-Tris(trifluoromethyl)benzidine, 2,3,6-Tris(trifluoromethyl)benzidine, 2,3,5,6-Tetrakis(trifluoromethyl)benzidine, 2,2'-Bis(trifluoromethyl)benzidine, 3,3'-Bis(trifluoromethyl)benzidine, 2,3'-Bis(trifluoromethyl)benzidine, 2,2',3-Bis(trifluoromethyl)benzidine Examples include zidine, 2,3,3'-tris(trifluoromethyl)benzidine, 2,2',5-tris(trifluoromethyl)benzidine, 2,2',6-tris(trifluoromethyl)benzidine, 2,3',5-tris(trifluoromethyl)benzidine, 2,3',6-tris(trifluoromethyl)benzidine, 2,2',3,3'-tetrakis(trifluoromethyl)benzidine, 2,2',5,5'-tetrakis(trifluoromethyl)benzidine, and 2,2',6,6'-tetrakis(trifluoromethyl)benzidine.

[0044] Among these, fluoroalkyl-substituted benzidines having a fluoroalkyl group at the 2-position of the biphenyl skeleton are preferred, and 2,2'-bis(trifluoromethyl)benzidine is more preferred. By having a fluoroalkyl group at the 2-position of the biphenyl skeleton, the steric hindrance of the fluoroalkyl group causes the aromatic ring of the biphenyl skeleton to twist, and the electron-withdrawing properties of the fluoroalkyl group reduce discoloration.

[0045] (Other acidic dianhydrides and diamines) Polyimide may contain other acid dianhydride components and diamine components, provided that they do not impair solubility in low-boiling point solvents such as dichloromethane, and do not impair transparency or mechanical strength.

[0046] Examples of compatible acid dianhydride components include pyromellitic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropanoic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, ethylenetetracarboxylic acid dianhydride, butanetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, and 2,2',3,3'-benzophenone tetracarboxylic acid dianhydride. 1,1-bis(2,3-dicarboxyphenyl)anhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-Bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-Bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-Bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, Bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, Bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-Bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'- Bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,Examples include 2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride.

[0047] Examples of diamines that can be used in combination include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 9,9-Bis(4-aminophenyl)fluorene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-di(3-aminophenyl)-1-phenylene Tan, 1,1-di(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)ben Zen, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-Bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-( 3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethyl [Benzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenylsulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl Lusulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobindan, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobindan, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-Bis(4-aminobutyl)tetramethyldisiloxane, α,ω-Bis(3-aminopropyl)polydimethylsiloxane, α,ω-Bis(3-aminobutyl)polydimethylsiloxane, Bis(aminomethyl) ether, Bis(2-aminoethyl) ether, Bis(3-aminopropyl) ether, Bis(2-aminomethoxy)ethyl] ether, Bis[2-(2-aminoethoxy)ethyl] ether, Bis[2-(3-aminoprothoxy)ethyl] ether, 1,2-Bis(aminomethoxy)ethane, 1,2-Bis(2-aminoethoxy)ethane, 1,2-Bis[2-(aminomethoxy)ethoxy]ethane, 1,2-Bis[2-(2-aminoethoxy)ethoxy]ethane, Ethylene glycol bis(3-aminopropyl) ether, Diethylene glycol bis(3-aminopropyl) ether, Triethylene glycol bis(3-aminopropyl) ether, Ethylenediamine, 1,3-Diaminopropane, 1,4-Diaminobutane, 1,5-Diaminopentane, 1,6-Diaminohexane, 1,7-Diaminoheptane, 1,8-Diaminooctane, 1,9-Diaminononane, 1,10-Diaminode Cane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans-1,4-diaminocyclohexane, 1,2-di(2-aminoethyl)cyclohexane, 1,3-di(2-aminoethyl)cyclohexane, 1,4-di(2-aminoethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane Butane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene, 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5,6-trifluorobenzene, 1,4-diamino-2,3,5,6-tetrafluorobenzene, 1,4-diamino-2-(trifluoromethyl)benzene, 1,4-diamino-2,3-bis(trifluoromethyl)benzene, 1,4-diamino-2,5-bis(trifluoromethyl)benzene, 1,4-diamino-2,Examples include 6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, and 1,4-diamino,2,3,5,6-tetrakis(trifluoromethyl)benzene.

[0048] (Specific examples of polyimide composition) As described above, the polyimide of one embodiment includes, as an acid dianhydride component, an acid dianhydride having an ester structure represented by general formula (1) and an acid dianhydride having a cyclobutane structure, and as a diamine component, a fluoroalkyl-substituted benzidine.

[0049] The amount of the acid dianhydride represented by general formula (1) is preferably 40 to 85 mol%, more preferably 45 to 80 mol%, and even more preferably 50 to 70 mol%, based on 100 mol% of the total amount of acid dianhydride components. By using this range, a polyimide with high solubility in low-boiling point solvents such as dichloromethane and excellent mechanical strength can be obtained. As mentioned above, among the acid dianhydrides represented by general formula (1), TAHMBP represented by formula (2) is particularly preferred.

[0050] The amount of alicyclic dianhydride is preferably 15 to 60 mol%, more preferably 20 to 55 mol%, and even more preferably 25 to 50 mol%, based on 100 mol% of the total amount of alicyclic dianhydride components. By using this range, a polyimide can be obtained that has solubility in low-boiling point solvents such as dichloromethane, has little discoloration, and has excellent mechanical strength. As mentioned above, among alicyclic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is particularly preferred.

[0051] An example of a polyimide composition is one in which, based on 100 mol% of the total diamine component, 40 mol% to 100 mol% of fluoroalkyl-substituted benzidine is included, and based on 100 mol% of the total acid dianhydride component, 40 mol% to 85 mol% of an acid dianhydride having an ester structure represented by formula (1) is included, and 15 mol% to 60 mol% of an acid dianhydride having an alicyclic structure is included.

[0052] When using acid dianhydrides other than those represented by general formula (1) and acid dianhydrides having an alicyclic structure in combination, the amount is preferably 45 mol% or less, and more preferably 30 mol% or less, based on 100 mol% of the total amount of acid dianhydride components. From the viewpoint of obtaining polyimides with excellent solubility, transparency, and mechanical strength, preferred examples of acid dianhydrides to be used in combination include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA), 4,4'-oxydiphthalic acid dianhydride (s-ODPA), and 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA).

[0053] The amount of fluoroalkyl-substituted benzidine is preferably 40 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more, based on 100 mol% of the total amount of diamine components. By setting the amount within this range, a polyimide with excellent transparency and solubility can be obtained without impairing mechanical strength. As mentioned above, among fluoroalkyl-substituted benzidines, 2,2'-bis(trifluoromethyl)benzidine (TFMB) is particularly preferred.

[0054] When using diamines other than fluoroalkyl-substituted benzidines in combination, the amount is preferably 60 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less, based on 100 mol% of the total diamine component. From the viewpoint of the transparency and solubility of the polyimide, it is preferable to use fluoroalkyl-substituted benzidines such as TFMB in combination with 3,3'-diaminodiphenylsulfone (3,3'-DDS) or 4,4'-diaminodiphenylsulfone (3,3'-DDS). The amount of diaminodiphenylsulfone relative to 100 mol% of the total diamine component is preferably 5 to 40 mol%, and more preferably 10 to 30 mol%.

[0055] As described above, the polyimide preferably contains 40-85 mol% TAHMBP and 15-60 mol% CBDA as acid dianhydride components, and 40-100 mol% TFMB as a diamine component. Furthermore, from the viewpoint of improving solubility in solvents and transparency of the film, it is preferable to include 5-40 mol% diaminodiphenylsulfone (3,3'-DDS and / or 4,4'-DDS) as a diamine component, and may also contain 6FDA, s-BPDA, s-ODPA, etc. as acid dianhydrides.

[0056] <Preparation of polyimide resin> The method for producing polyimide resin is not particularly limited, but a preferred method involves reacting a diamine with an acidic dianhydride in a solvent to prepare polyamic acid, which is a polyimide precursor, and then imidizing the polyamic acid by dehydration and cyclization. For example, a polyimide solution can be obtained by adding an imidization catalyst and a dehydrating agent to a polyamic acid solution and dehydrating and cyclizing the polyamic acid. The polyimide resin can then be obtained by mixing the polyimide solution with a poor solvent for polyimide to precipitate the polyimide resin and then separating the solid and liquid components.

[0057] (Synthesis of polyamic acid) A polyamic acid solution is obtained by reacting an acidic dianhydride with a diamine in a solvent. It is preferable to use substantially equimolar amounts of the acidic dianhydride and the diamine. That is, the molar ratio of the acidic dianhydride component to the diamine is preferably in the range of 95:105 to 105:95.

[0058] In the polymerization of dianhydrides and diamines, the usable organic solvent is not particularly limited, as long as it dissolves the dianhydride, diamine, and the polymerization product, polyamic acid. Specific examples of organic solvents include urea-based solvents such as methylurea and N,N-dimethylethylurea; sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N'-diethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, and hexamethylphosphate triamide; alkyl halide-based solvents such as chloroform and dichloromethane; aromatic hydrocarbon-based solvents such as benzene and toluene; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. Among these, N,N-dimethylacetamide, N,N-dimethylformamide, or N-methylpyrrolidone are preferred due to their excellent polymerization reactivity and solubility of polyamic acid.

[0059] The reaction temperature in the polymerization of acid dianhydride and diamine is not particularly limited, but is preferably between 0°C and 80°C, and more preferably between 20°C and 45°C. A temperature above 0°C tends to suppress a decrease in the reaction rate, and a temperature below 80°C tends to suppress a decrease in the degree of polymerization due to ring opening of the acid dianhydride.

[0060] (Imidization) Polyimides can be obtained by the dehydration and cyclization of polyamic acids. For imidation in solution, a chemical imidation method is suitable, in which a dehydrating agent and an imidation catalyst are added to the polyamic acid solution. The polyamic acid solution may be heated to accelerate the imidation process.

[0061] A tertiary amine is used as the imidation catalyst. Heterocyclic tertiary amines are preferred. Specific examples of heterocyclic tertiary amines include pyridine, picoline, quinoline, and isoquinoline. Carboxylic acid anhydrides are used as dehydrating agents, specifically acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride.

[0062] The amount of imidization catalyst added is preferably 0.5 to 5.0 times the molar equivalent of the amide group of the polyamic acid, more preferably 0.7 to 2.5 times, and even more preferably 0.8 to 2.0 times. The amount of dehydrating agent added is preferably 0.5 to 10.0 times the molar equivalent of the amide group of the polyamic acid, more preferably 0.7 to 5.0 times, and even more preferably 0.8 to 3.0 times.

[0063] (Polyimide resin precipitation) It is preferable to precipitate the polyimide resin as a solid from the polyimide solution obtained by imidization of polyamic acid. The polyimide resin precipitates by mixing the polyimide solution with a poor solvent. The poor solvent is preferably a poor solvent for the polyimide resin that is miscible with the solvent in which the polyimide resin is dissolved, and examples include water and alcohols. Examples of alcohols include methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, triethylene glycol, 2-butyl alcohol, 2-hexyl alcohol, cyclopentyl alcohol, cyclohexyl alcohol, phenol, and t-butyl alcohol. Alcohols such as isopropyl alcohol, 2-butyl alcohol, 2-pentyl alcohol, phenol, cyclopentyl alcohol, cyclohexyl alcohol, and t-butyl alcohol are preferred because they do not easily cause ring opening of the polyimide, and isopropyl alcohol is particularly preferred.

[0064] <Preparation of polyimide film> A polyimide film can be manufactured by applying a polyimide solution (film-forming dope), obtained by dissolving polyimide resin in an organic solvent, onto a substrate and drying and removing the solvent. Any organic solvent capable of dissolving the polyimide resin is acceptable, and can be appropriately selected depending on the application of the polyimide resin. Low-boiling point solvents such as dichloromethane, methyl acetate, tetrahydrofuran, acetone, and 1,3-dioxolane are preferred, with dichloromethane being particularly preferred due to its low boiling point and ease of drying and removal. As described above, by adjusting the composition ratio of the acid dianhydride component and the diamine component, a polyimide exhibiting high solubility even in low-boiling point solvents such as dichloromethane can be obtained.

[0065] The solid content concentration of the polyimide solution can be appropriately set according to the molecular weight of the polyimide, the film thickness, and the film-forming environment. A solid content concentration of 5 to 30% by weight is preferred, and 6 to 20% by weight is more preferred.

[0066] (UV absorber) As described above, the polyimide film 1 according to one embodiment of the present invention contains an ultraviolet absorber. In the preparation of a polyimide containing an ultraviolet absorber, it is preferable to include the ultraviolet absorber in the polyimide solution.

[0067] Examples of UV absorbers included in polyimide films include triazine-based UV absorbers, benzotriazole-based UV absorbers, benzophenone-based UV absorbers, cyanoacrylate-based UV absorbers, and hydroxybenzoate-based UV absorbers. Among these, benzotriazole-based UV absorbers and triazine-based UV absorbers are preferred because they absorb little visible light and provide good light resistance.

[0068] Specific examples of benzotriazole-based UV absorbers include 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (ADEKA's "ADEKA Stab LA-24"), 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (ADEKA's "ADEKA Stab LA-29"), 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] (ADEKA's "ADEKA Stab LA-31G" and "ADEKA Stab LA-31RG"), and 2-(2H-benzotriazole-2-yl)-p-cresol (ADEKA's "ADEKA Stab"). LA-32), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (BASF "TINUVIN 571"), 2-(2H-benzotriazol-2-yl)-p-cresol (BASF "TINUVIN P"), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (BASF "TINUVIN PS"), 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (BASF "TINUVIN 234"), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (BASF "TINUVIN 326"), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (BASF "TINUVIN" 328"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF "TINUVIN 329"), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (BASF "TINUVIN 900"), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF "TINUVIN 928"), 2-[2-hydroxy-3-(3,4,5,Examples include 6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole (Sumitomo Chemical's "Sumisorb250").

[0069] Specific examples of triazine-based UV absorbers include 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADEKA "ADEKA Stab LA-46"), 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine (ADEKA "ADEKA Stab LA-F70"), and the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl and [(alkyloxy)methyl]oxirane (BASF "TINUVIN"). Reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and (2-ethylhexyl)-glycidic acid ester (BASF "TINUVIN 405"), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (BASF "TINUVIN 460"), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (BASF "TINUVIN 479"), 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]-phenol (BASF "TINUVIN 405") Examples include 577), bisethylhexyloxyphenol methoxyphenyl triazine (BASF's "Tinosorb S"), etc.

[0070] From the viewpoint of suppressing photodegradation of polyimide film, the amount of ultraviolet absorber in the polyimide solution is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and may be 0.5 parts by weight or more, 0.7 parts by weight or more, or 1 part by weight or more, per 100 parts by weight of total solids. The greater the amount of ultraviolet absorber, the more suppressed photodegradation tends to be. On the other hand, if the amount of ultraviolet absorber is excessively large, the ultraviolet absorber may not be sufficiently miscible with the polyimide, which may cause clouding of the polyimide film or bleed-out of the ultraviolet absorber to the surface. Therefore, the amount of ultraviolet absorber in the polyimide solution is preferably 4.5 parts by weight or less, more preferably 4 parts by weight or less, and may be 3.5 parts by weight or less, or 3 parts by weight or less, per 100 parts by weight of total solids.

[0071] (Additives) The polyimide solution may contain resin components and additives other than polyimide resin and UV absorbers. Examples of additives include crosslinking agents, dyes, surfactants, leveling agents, plasticizers, and fine particles. The polyimide resin content of the polyimide resin composition is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, and even more preferably 80 parts by weight or more, per 100 parts by weight of solids.

[0072] Specific examples of the above dyes include anthraquinone compounds, phthalocyanine compounds, and indigo compounds. Among these, anthraquinone compounds are preferred from the viewpoint of heat resistance. The amount used is, for example, about 0.1 to 100 ppm based on the polyimide resin, but may also be 1 to 90 ppm, 10 to 80 ppm, or 20 to 70 ppm. By including dyes, the color tone of the polyimide film can be adjusted. Polyimide and UV absorbers are slightly yellow in color because they absorb light in the short wavelength range of visible light, but the hue can be neutralized by adding dyes that function as bluing agents. Known bluing agents can be used as appropriate, and commercially available products include "Macrolex Blue RR", "Sumiplast Violet B", "Sumiplast Violet OR", "Plast Blue 8580", "Plast Blue 8590", and "Plast Violet 8840".

[0073] (Application and drying) A known method can be used to apply the polyimide solution to a substrate, for example, by a bar coater or a comma coater. Suitable substrates for applying the polyimide solution include glass substrates, metal substrates such as SUS, metal drums, metal belts, and plastic films. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or metal belt, or a long plastic film, as the support, and to manufacture the film by roll-to-roll. When using a plastic film as the support, a material that does not dissolve in the film-forming doping solvent should be appropriately selected. Suitable plastic materials include polyethylene terephthalate, polycarbonate, polyacrylate, and polyethylene naphthalate.

[0074] Heating is preferable when drying the solvent. The heating temperature is not particularly limited, but from the viewpoint of suppressing coloration of the polyimide film and volatilization of the ultraviolet absorber, it is preferably 200°C or lower, and more preferably 180°C or lower. The heating temperature may be increased in stages when drying the solvent. Drying the solvent may also be performed under reduced pressure.

[0075] By using a low-boiling point solvent such as dichloromethane, residual solvent can be easily reduced even with heating below 200°C, thereby suppressing the volatilization of colorants and UV absorbers. The amount of residual solvent in the polyimide film (mass of solvent contained in the film relative to the mass of the film) is preferably 1.5% or less, and more preferably 1.0% or less. When the amount of residual solvent is within this range, the mechanical strength of the polyimide film tends to improve. The solvent may be heated and dried on the substrate, and after peeling the polyimide film from the substrate, the solvent may be further removed by heating.

[0076] The thickness of the polyimide film is not particularly limited and can be set appropriately depending on the application. For example, the thickness of the polyimide film is about 5 to 100 μm. From the viewpoint of achieving both mechanical strength and transparency, the thickness of the polyimide film is preferably 30 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more. In particular, when used in applications where strength is required, such as cover windows for displays, the thickness of the polyimide film is preferably 40 μm or more. The thickness of the polyimide film is preferably 90 μm or less, and more preferably 85 μm or less.

[0077] A solution containing polyimide resin, an ultraviolet absorber, and an organic solvent is applied to a substrate, the solution is heated on the substrate to dry and remove the organic solvent, and then peeled off from the substrate, thereby determining the concentration C of the ultraviolet absorber on the peeled surface (side B) from the substrate. B The concentration of the UV absorber on the air surface (Side A) is C A A polyimide film is obtained in which the ultraviolet absorber is more unevenly distributed in the thickness direction. That is, in the polyimide film 1 prepared by the solution casting method, the substrate side (side B) is the second main surface 1B, and the air side (side A) is the first main surface 1A.

[0078] Concentration of UV absorber on side B: C B One factor contributing to the relatively larger drying behavior is the difference in drying behavior between side A and side B. When the solution on the substrate is heated to dry and remove the solvent, most of the solvent evaporates from side A, so drying proceeds from side A.

[0079] In solution, the orientation of polyimide molecular chains is random, and the UV absorber is uniformly distributed in the solution. When the solvent is removed by heating, the polyimide molecular chains tend to orient inward. When the solvent on side A evaporates due to heating, and the polyimide molecular chains orient, the UV absorber moves to side B where the solvent remains, thus reducing the UV absorber concentration on side A. A The amount is small, and the UV absorber concentration on side B is C B As the thickness increases, it is thought that the UV absorber will be unevenly distributed in the thickness direction.

[0080] When an organic solvent remains and is heated to a temperature above the boiling point of the organic solvent, C B and C A The difference becomes large, C A / C B The ratio tends to decrease. Therefore, the shorter the time between applying the solution to the substrate and starting heating at a temperature above the boiling point, the more pronounced the uneven distribution of the UV absorber in the thickness direction becomes. A / C B It tends to become smaller. A / C B To obtain a polyimide film with a hardness of 0.5 or less, the time from applying the solution to the substrate until heating at a temperature above the boiling point is preferably 50 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.

[0081] The tendency for UV absorbers to be unevenly distributed in the thickness direction also depends on the composition of the polyimide. Polyimides containing trimellitic anhydride esters represented by general formula (1) (e.g., TAHMBP) and tetracarboxylic dianhydrides with an alicyclic structure (e.g., CHDA) as acid dianhydride components tend to have uneven distribution of UV absorbers in the thickness direction when polyimide films are made by the solution casting method. A / C B A polyimide film with a coefficient of 0.5 or less can be easily obtained.

[0082] <Properties of polyimide film> The total light transmittance of the polyimide film is preferably 80% or higher, more preferably 85% or higher, and even more preferably 88% or higher. The light transmittance of the polyimide film at a wavelength of 400 nm is preferably 35% or higher, and even more preferably 40% or higher. The haze of the polyimide film is preferably 1.5% or less, more preferably 0.9% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0083] The yellowness (YI) of the polyimide film is preferably 3.0 or less, and more preferably 2.5 or less. If the yellowness (YI) of the polyimide film is 3.0 or less, the film has less coloration and can be suitably used as a display film.

[0084] The acidic dianhydride of general formula (1) mentioned above is an ester of phenol and trimellitic anhydride, and is susceptible to photodegradation by ultraviolet light. This is presumed to be because, structurally, it is prone to transition reactions such as the photofleece transition. When a polyimide film contains an ultraviolet absorber, the ultraviolet light incident on the polyimide film is absorbed by the ultraviolet absorber, reducing the amount of ultraviolet light absorbed by the polyimide, and thus tending to suppress discoloration (yellowing) of the polyimide film due to photodegradation.

[0085] The amount of ultraviolet absorber in the polyimide film (ultraviolet absorber concentration) is preferably 0.1 to 4.5% by weight, more preferably 0.3 to 4% by weight, even more preferably 0.5 to 3.5% by weight, and may also be 1 to 3% by weight. By keeping the ultraviolet absorber concentration within this range, it is possible to suppress the increase in YI and maintain the transparency of the polyimide film while suppressing photodegradation of the polyimide film.

[0086] Note that the UV absorber concentration of the polyimide film is the concentration when considering the entire thickness direction as a whole. If the UV absorber is unevenly distributed in the thickness direction, the UV absorber concentration C on the first main surface side of the polyimide film is... A The UV absorber concentration C on the second main surface side of the polyimide film may be below the above range. B It may exceed the above range.

[0087] From the second main surface side of the polyimide film, irradiance of 500 W / m 2 The increase in yellowness of the polyimide film ΔYI when exposed to ultraviolet light for 48 hours under the condition of a black panel temperature of 63°C. B It is preferably 6 or less, more preferably 5 or less, and may be 4.5 or less or 4.0 or less.

[0088] As mentioned above, the concentration C of the ultraviolet absorber on the second main surface 1B side B The UV absorber concentration C on the first main surface 1A side. A When a polyimide film 1 larger than ΔYI is irradiated with ultraviolet light from the second main surface side, the amount of ultraviolet light absorbed by the polyimide is small, and the photodegradation of the polyimide caused by ultraviolet light is suppressed, so ΔYI B The amount decreases. On the other hand, when ultraviolet light is irradiated onto this polyimide film from the first main surface 1A side, the concentration of ultraviolet absorber C on the light incident surface decreases. A Because the amount is small, polyimide absorbs a large amount of ultraviolet light, resulting in an increase in yellowness ΔYI B This is the increase in yellowness ΔYI when ultraviolet light is irradiated from the second main surface side. A It is larger than that.

[0089] In other words, polyimide films in which the concentration of UV absorbers is unevenly distributed in the thickness direction exhibit different light resistance depending on the light-irradiated surface. When the surface with a relatively high concentration of UV absorbers is the light-irradiated surface (light-incident surface), ΔYI is small, and the film exhibits excellent light resistance. Therefore, by suppressing discoloration (decreased transparency) due to an excessive increase in UV absorber concentration, unevenly distributing the UV absorber in the thickness direction, and arranging the film so that the surface with a relatively high concentration of UV absorbers is the light-incident surface (visual side), it is possible to achieve both transparency and light resistance.

[0090] From the viewpoint of preventing damage to the film due to contact with the roll during roll-to-roll transport and contact between films during winding, the pencil hardness of the polyimide film is preferably HB or higher, and more preferably F or higher. When the polyimide film is used in the cover window of a display, scratch resistance to external contact is required, so the pencil hardness of the polyimide film is preferably H or higher. The tensile modulus of the polyimide film is preferably 3.5 GPa or higher, more preferably 4.0 GPa or higher, and even more preferably 5.0 GPa or higher.

[0091] [Hard coat film] The hard coat film comprises a hard coat layer 3 on at least one surface of the polyimide film 1. As shown in Figure 2, it is preferable that the hard coat film 10 comprises a hard coat layer 3 on the second main surface 1B of the polyimide film 1.

[0092] As described above, when the polyimide film 1 is used as a cover window for an image display device, the first main surface 1A faces the image display panel 5 and the second main surface 1B is positioned on the viewing side. By providing a hard coat layer 3 on the second main surface 1B of the polyimide film, the hard coat layer 3 is positioned as the outermost layer in the image display device, thus preventing damage and scratches from external impacts.

[0093] A hard coat layer 3 is formed on the polyimide film 1 by applying a hard coat composition onto the polyimide film, drying and removing the solvent as necessary, and then curing the hard coat composition by irradiating it with active energy rays such as ultraviolet light.

[0094] The thickness of the hard coat layer 3 is preferably 0.5 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and most preferably 5 μm or more. The thickness of the hard coat layer is preferably 100 μm or less, and more preferably 80 μm or less. If the thickness of the hard coat layer is less than 0.5 μm, mechanical properties such as surface hardness may not be sufficiently improved. On the other hand, if the thickness of the hard coat layer is greater than 100 μm, transparency and flexibility may decrease.

[0095] The materials constituting the hard coat layer are not particularly limited, and for example, a photocurable resin composition of a polyfunctional (meth)acrylate monomer can be used. As the hard coat composition, a composition containing a polysiloxane compound having an epoxy group, as disclosed in WO2018 / 096729, WO2014 / 204010, Japanese Patent Application Publication No. 2017-8142, etc., may be used.

[0096] The surface of the polyimide film 1 may be provided with functional layers other than the hard coat layer. Examples of functional layers include anti-reflective layers, anti-glare layers, anti-static layers, and transparent electrodes. These functional layers may be provided on either the first main surface or the second main surface of the polyimide film. Alternatively, these functional layers may be provided on the hard coat layer 3. A transparent adhesive layer may be attached to the polyimide film.

[0097] [Image display device] The polyimide film of the present invention is suitable for use as a cover window placed on the viewing surface of an image display panel due to its high light resistance in addition to its transparency and mechanical strength. As shown in Figures 3 and 4, by arranging the polyimide film 1 so that the first main surface 1A faces the image display panel 5 and the second main surface 1B faces the viewing side, the polyimide is less likely to degrade from light when ambient light, including ultraviolet rays, is incident from the viewing side of the image display device, and the polyimide film exhibits excellent light resistance. [Examples]

[0098] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0099] [Preparation of polyimide resin] <Polyimide resin A> In the reaction vessel, 44.2 g (138.1 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 3.8 g (15.3 mmol) of 3,3'-diaminodiphenylsulfone (3,3-DDS) were added as diamines, and bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl as the tetracarboxylic dianhydride. 47.4 g (76.7 mmol) of 4,4'-diyl ru-(TAHMBP), 9.0 g (46.0 mmol) of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA), and 9.5 g (30.7 mmol) of 4,4'-oxydiphthalic acid dianhydride (ODPA), along with 800 g of N,N-dimethylformamide (DMF) as a solvent, were added and stirred under a nitrogen atmosphere for 12 hours to obtain a polyamic acid solution.

[0100] To the polyamic acid solution described above, 36.4 g (460 mmol) of pyridine and 7.0 g (460 mmol) of acetic anhydride were added as imidation catalysts, and the mixture was stirred at 90°C for 4 hours. While stirring the solution cooled to room temperature, 2000 g of 2-propyl alcohol (IPA) was added, and the mixture was filtered by suction using a Kiriyama funnel. The resulting solid was washed six times with 1000 g of IPA, and then dried in a vacuum oven set to 120°C for 8 hours to obtain a white polyimide resin A. The monomer composition of polyimide resin A was TFMB / 3,3'-DDS / / TAHMBP / CBDA / ODPA = 90 / 10 / / 50 / 30 / 20 (molar ratio).

[0101] <Polyimide resin B~E> In preparing the polyamic acid solution, the types and molar ratios of the diamine and acidic dianhydride were changed as shown in Table 1. Otherwise, polyimide resins B to E were obtained in the same manner as described above.

[0102] [Preparation of polyimide film] <Example 1> 100 parts by weight of polyimide resin A, along with the ultraviolet absorber (UVA) and bluing agent (PlastBlue 8590, manufactured by Arimoto Chemical Industry Co., Ltd.) shown in Table 1, were dissolved in dichloromethane to obtain a polyimide solution with a solid content of 10% by weight.

[0103] The polyimide solution described above was applied to alkali-free glass using a bar coater and left at room temperature (25°C) for 15 minutes. Then, the solvent was removed by heating at 40°C for 60 minutes, 80°C for 30 minutes, 150°C for 30 minutes, 170°C for 30 minutes, and 200°C for 60 minutes. After peeling from the alkali-free glass, a transparent polyimide film with a thickness of approximately 50 μm was obtained. The side with air bubbles during film preparation was designated "Side A," and the side facing the alkali-free glass was designated "Side B."

[0104] <Examples 2-4, Comparative Examples 1,2> A transparent polyimide film was obtained in the same manner as in Example 1, except that the type of polyimide resin, the type and amount of UV absorber added, and the amount of bluing agent added were changed as shown in Table 1.

[0105] <Comparative Example 3> After applying the polyimide solution to alkali-free glass, the time allowed to stand at room temperature (25°C) before heating was changed to 80 minutes. Otherwise, the polyimide film was obtained in the same manner as in Example 1.

[0106] [evaluation] The following evaluations were performed on the polyimide films of the examples and comparative examples.

[0107] <Concentration distribution of UV absorber in the thickness direction> The UV absorber concentrations in the polyimide films of Examples 1-3 and Comparative Examples 1-3 were measured by NMR, and the UV absorber concentration in the polyimide film of Example 4 was measured from the absorption spectrum.

[0108] (Examples 1-3 and Comparative Examples 1-3) Using abrasive paper (PRESI "P800"), the polyimide film was polished from the B-side until the remaining thickness was 30% (approximately 15 μm). After polishing, the remaining polyimide film (the 30% thickness portion on the A-side) was dissolved in CDCl3. 1 The concentration of the UV absorber C is determined by H-NMR. A The measurement was performed similarly on samples of polyimide film polished from side A. 1 The concentration of the UV absorber C is determined by H-NMR. B The concentration of the UV absorber on side A was measured. A And the concentration of the UV absorber on side B is C B ratio C A / C B They sought it.

[0109] (Example 4) The polyimide film was polished from the B-side using abrasive paper (PRESI "P800") until the remaining thickness was 30% (approximately 15 μm). The polished polyimide film was dissolved in DMF to prepare a 100 ppm solution, and the absorption spectrum at wavelengths of 200-800 nm was measured using a UV-Vis spectrophotometer (JASCO "V-560").

[0110] A 100 ppm solution was prepared by dissolving polyimide resin in DMF, and its absorption spectrum was measured. The difference spectrum between the absorption spectrum of the polished polyimide film and the absorption spectrum of the polyimide resin was used as the absorption spectrum of the ultraviolet absorber contained in the polyimide film.

[0111] The absorption spectra of DMF solutions with varying concentrations of UV absorber were measured, and a calibration curve was created from the absorbance at the wavelength of maximum absorption of the UV absorber. From this calibration curve and the difference spectrum (absorption spectrum of the UV absorber contained in the polyimide film), the concentration C of the UV absorber in the polyimide film remaining after polishing (30% thickness on side A) was determined. A The result was calculated.

[0112] For samples of polyimide film polished from side A, the absorption spectrum of the DMF solution was measured in the same manner as above, and the concentration of the UV absorber C in the 30% thickness portion on side B was determined from the difference spectrum with the polyimide resin and the calibration curve. B The following was calculated. From the results obtained, the concentration C of the UV absorber on side A was determined. A And the concentration of the UV absorber on side B is C B ratio C A / C B They sought it.

[0113] <Yellowness and lightfastness> The film was cut into 3cm squares, and the yellowness (YI0) was measured using a spectrophotometer (SC-P, manufactured by Suga Test Instruments). Subsequently, a fade meter (U48-HB, manufactured by Suga Test Instruments) was used to measure the irradiance at 500 W / m². 2 Under conditions of a black panel temperature of 63°C, ultraviolet light was irradiated from one side of the film (side A or side B) for 48 hours. The yellowness (YI1) of the film after UV irradiation was measured, and the change in yellowness ΔYI before and after irradiation was calculated from the yellowness YI0 before irradiation and the yellowness YI1 after irradiation according to the following formula. ΔYI=YI1-YI0

[0114] The change in yellowness when ultraviolet light is irradiated from side A is ΔYI A ΔYI is the amount of change in yellowness when ultraviolet light is irradiated from side B. B That's what I decided.

[0115] <Tensile modulus> The film was cut into strips 10 mm wide, allowed to stand for 1 day at 23°C / 55%RH to adjust humidity, and then the tensile modulus was measured using Shimadzu Corporation's "AUTOGRAPH AGS-X" under the following conditions. Distance between gripping parts: 100mm Tensile speed: 20.0 mm / min Measurement temperature: 23℃

[0116] <Pencil hardness> The pencil hardness of the polyimide film was measured according to the JIS K-5600-5-4 pencil scratch test.

[0117] <Haze and total light transmittance> The film was cut into 3cm squares, and the haze and total light transmittance (TT) were measured using a Suga Test Instruments HZ-V3 haze meter in accordance with JIS K7136 and JIS K7361-1.

[0118] <Transmittance at 400nm> Using a UV-Vis spectrophotometer "V-560" manufactured by JASCO Corporation, the light transmittance of the film at 300-800 nm was measured, and the light transmittance at a wavelength of 400 nm was read.

[0119] Table 1 shows the composition of the polyimide films in the examples and comparative examples, the time the polyimide solution was left at room temperature after being applied to alkali-free glass before heating began, and the evaluation results of the films.

[0120] In Table 1, diamines, acidic dianhydrides, and ultraviolet absorbers (UVA) are listed using the following abbreviations. <Diamine> TFMB: 2,2'-bis(trifluoromethyl)benzidine 3,3-DDS:3,3'-Diaminodiphenylsulfone 4,4-DDS: 4,4'-diaminodiphenylsulfone <Acid dianhydride> TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4'diyl BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride ODPA: 4,4'-Oxydiphthalic acid dianhydride 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride <uva> LA-F70: ADEKA "ADEKA Stab LA-F70" (triazine-based UV absorber) Tin477: BASF's "Tinuvin 477" (triazine-based UV absorber) LA-31RG: ADEKA's "ADEKA Stab LA-31RG" (benzotriazole-based UV absorber)

[0121] In Table 1, the amounts of diamine and acidic dianhydride are in mol%, the amount of UVA is the amount added per 100 parts by weight of polyimide resin (parts by weight), and the amount of bluing agent is in ppm.

[0122] [Table 1]

[0123] The polyimide films of Examples 1-4 and Comparative Examples 1-3 all have a UV absorber concentration of C on side A. A The UV absorber concentration on side B is C B It was smaller than that, and uneven distribution of the UV absorber in the thickness direction was observed. In Examples 1-4, C A / C B The value was less than 0.5, indicating a significant uneven distribution.

[0124] In Examples 1-4, the change in yellowness ΔYI was observed when ultraviolet light was irradiated from side A, where the concentration of the ultraviolet absorber was low. A While the value was over 10, the change in yellowness ΔYI when UV light was irradiated from the B-side, which has a higher concentration of UV absorber, was... B The value is 4 or less, indicating that photodegradation is suppressed when light is irradiated from side B.

[0125] The polyimide film of Comparative Example 3 has the same composition as the polyimide film of Example 1, but the concentration distribution of the ultraviolet absorber in the thickness direction is smaller (C A / C B (is close to 1), ΔYI A and ΔYI B In all cases, the values ​​were 6 or higher. In Comparative Example 3, it is thought that there was almost no movement of the UV absorber in the thickness direction during drying because the time between application of the polyimide solution containing the UV absorber and the start of drying (heating) was long.

[0126] In Comparative Examples 1 and 2, the film drying conditions were the same as in Examples 1-4, but the concentration distribution of the UV absorber in the thickness direction was small, and ΔYI A and ΔYI B The difference was also slight. From a comparison of the polyimide compositions of Examples 1-4 and Comparative Examples 1 and 2, it was found that when trimellitic anhydride (TAHMBP) and tetracarboxylic dianhydride with an alicyclic structure (CHDA) were included as tetracarboxylic dianhydrides, the concentration distribution of the ultraviolet absorber in the thickness direction became larger (C A / C B It can be seen that there is a tendency for ( to become smaller). Note that in Comparative Example 1, ΔYI A and ΔYI B Although all of these values ​​were small, the low compatibility between the UV absorber and the polyimide resulted in high haze, a large YI0, and poor transparency.

[0127] These results indicate that by using a solution containing a specific polyimide resin and an ultraviolet absorber, a film with a large concentration distribution of the ultraviolet absorber in the thickness direction can be obtained by the solution casting method. If this film is placed in an image display device with the B-side, which has a high concentration of ultraviolet absorber, facing the viewing side (surface side), photodegradation of the polyimide film due to ambient light in the operating environment of the image display device can be suppressed. [Explanation of Symbols]

[0128] 1. Polyimide film 3. Hard court layer 10 Hard coat film 5. Image display panel 101,102 Image display device< / uva>

Claims

1. A hard coat film comprising a polyimide film consisting of one layer having a first main surface and a second main surface, and a hard coat layer provided on the second main surface of the polyimide film, The polyimide film comprises a polyimide resin and an ultraviolet absorber. The aforementioned ultraviolet absorber is a benzotriazole compound, Concentration C of the UV absorber on the first main surface side Ａ However, the concentration C of the ultraviolet absorber on the second main surface side Ｂ It is less than 0.5 times that amount. Hard coat film.

2. The hard coat film according to claim 1, wherein the content of the ultraviolet absorber in the polyimide film is 0.1 to 4.5% by weight.

3. The hard coat film according to claim 1 or 2, wherein the polyimide resin comprises, as a tetracarboxylic dianhydride component, a tetracarboxylic dianhydride having an ester structure represented by general formula (1), and a tetracarboxylic dianhydride having an alicyclic structure: 【Chemistry 1】 In general formula (1), n ​​is 1 or 2, and R １ ~R ４ Each of these is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a fluoroalkyl group.

4. The aforementioned polyimide resin The diamine component contains 40 mol% to 100 mol% of fluoroalkyl-substituted benzidine relative to 100 mol% of the total diamine amount. As a tetracarboxylic dianhydride component, the product contains 40 mol% to 85 mol% of tetracarboxylic dianhydride having an ester structure represented by the general formula (1) and 15 mol% to 60 mol% of tetracarboxylic dianhydride having an alicyclic structure, based on 100 mol% of the total amount of tetracarboxylic dianhydride components. The hard coat film described in claim 3:

5. In the above general formula (1), n ​​= 2, R １ ~R ４ The hard coat film according to claim 3 or 4, wherein at least one of them is an alkyl group or fluoroalkyl group having 1 to 20 carbon atoms.

6. The hard coat film according to any one of claims 1 to 5, wherein the thickness of the polyimide film is 5 to 100 μm.

7. A method for producing a hard coat film according to any one of claims 1 to 6, A solution containing polyimide resin, an ultraviolet absorber, and an organic solvent is applied to a substrate. A step of heating the solution on the substrate to dry and remove the organic solvent, then peeling it off the substrate to obtain a polyimide film, and The process includes forming a hard coat layer on the second main surface of the polyimide film, with the peeling surface from the substrate being the second main surface. A method for manufacturing hard coat film.

8. The method for producing a hard coat film according to claim 7, wherein the organic solvent contains dichloromethane.

9. An image display device comprising a polyimide film consisting of one layer and having a first main surface and a second main surface on the viewing-side surface of the image display panel, The polyimide film comprises a polyimide resin and an ultraviolet absorber. The aforementioned ultraviolet absorber is a benzotriazole compound, The concentration C A of the ultraviolet absorber on the first main surface is 0.5 times or less of the concentration C B of the ultraviolet absorber on the second main surface. An image display device in which the first main surface of the polyimide film is positioned to face the image display panel.

10. The viewing surface of the image display panel is provided with the hard coat film according to any one of claims 1 to 6. The hard coat film is an image display device in which the first main surface of the polyimide film is positioned to face the image display panel.

11. The image display device according to claim 9 or 10, which is foldable.

Images