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

Abstract

The polyimide film (1) has a first main surface (1A) and a second main surface (1B). The polyimide film contains a polyimide resin and an ultraviolet absorber, the concentration C A of the ultraviolet absorber on the first main surface side is 0.5 times or less of the concentration C B of the ultraviolet absorber on the second main surface side. In the case where the polyimide film is arranged on the recognition side of an image display panel, by arranging in a manner that the first main surface of the polyimide film faces the image display panel, it is possible to suppress light degradation of the polyimide film caused by external light.

Description

Technical Field

[0001] This invention relates to polyimide films and methods for manufacturing the same, as well as hard coatings having a hard coating layer on the surface of the polyimide film. Furthermore, this invention relates to an image display device having a polyimide film on the recognition side surface of an image display panel. Background Technology

[0002] Portable terminal devices are becoming thinner and lighter, with smartphones being a prime example of widespread adoption. In recent years, flexible displays, especially foldable portable terminal devices equipped with organic EL panels made using flexible substrates, have been proposed as a method to balance large screen sizes and portability.

[0003] In flexible devices, not only the display substrate needs to be flexible, but surface protection materials such as cover windows also need to be flexible. Patent document 1 proposes using polyimide film, which has excellent transparency, surface hardness, and bending durability, as a cover window material for image display devices.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2020 / 004236 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The cover window of an image display device, being the outermost layer, is easily exposed to external light, requiring minimal changes in its optical properties and mechanical strength when exposed to ultraviolet light. To impart lightfastness to transparent resin films, ultraviolet absorbers are typically added.

[0009] Patent document 1 describes that polyimide has a biphenyl structure, thus exhibiting excellent lightfastness even without the use of ultraviolet absorbers. However, higher lightfastness is required for the cover windows of image display devices, for example, at an irradiance of 500 W / m². 2 The lightfastness in the carbon arc test is difficult to achieve with polyimide films without ultraviolet absorbers.

[0010] The more UV absorber a polyimide film contains, the more UV light is absorbed by the absorber, and the less UV light is absorbed by the polyimide itself. Therefore, the degradation of the polyimide film caused by UV light from external sources is suppressed. On the other hand, if the amount of UV absorber added is increased to improve lightfastness, the film will become colored due to the light absorption by the absorber, thus reducing transparency. In other words, while UV absorbers help improve the lightfastness of the film, they can also reduce transparency.

[0011] In view of the above, the object of the present invention is to provide a polyimide film that maintains transparency and has superior light resistance.

[0012] Solution for solving the problem

[0013] One aspect of the invention is a polyimide film comprising a UV absorber, the UV absorber being biased towards the thickness direction. The polyimide film is formed in a single layer and has a first main surface and a second main surface. The concentration C of the UV absorber on the first main surface side is... A The preferred concentration C of the ultraviolet absorber on the second main surface side B Less than 0.5 times.

[0014] The thickness of the polyimide film can be 5–100 μm. Benzotriazole compounds or triazine compounds are preferably used as ultraviolet absorbers in the polyimide film. The content of the ultraviolet absorber in the polyimide film is preferably 0.1–4.5% by weight.

[0015] A solution containing polyimide resin, ultraviolet absorber, and organic solvent is coated onto a substrate. After heating and drying the solution on the substrate to remove the organic solvent, the solution is peeled off from the substrate, thereby obtaining a polyimide film in which the ultraviolet absorber is predominantly distributed in the thickness direction. The peel surface (B-side) of this polyimide film, after peeling from the substrate, is the second principal surface, where the concentration of ultraviolet absorber is relatively high.

[0016] A hard coating film is obtained by applying a hard coating layer to the surface of a polyimide film. Preferably, the hard coating layer is present on the second main surface of the polyimide film.

[0017] Polyimide films and hard coatings can be used, for example, as surface protective materials (covering windows) disposed on the recognition side surface of an image display panel in an image display device. The image display device can be flexible. The polyimide film is preferably disposed with its first main surface facing the image display panel, and the second main surface of the polyimide film is disposed on the recognition side of the image display device.

[0018] The effects of the invention

[0019] The film in which the ultraviolet absorber is concentrated in the thickness direction is configured such that the side with the higher concentration of ultraviolet absorber is located on the recognition side of the display device. As a result, even with a low concentration of ultraviolet absorber, the amount of ultraviolet light absorbed by the polyimide from external light is small, thus suppressing light degradation caused by external light. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of a polyimide film.

[0021] Figure 2 This is a cross-sectional view showing an example of the composition of a hard coating film.

[0022] Figure 3 This is a cross-sectional view showing an example of the configuration of an image display device.

[0023] Figure 4 This is a cross-sectional view showing an example of the configuration of an image display device. Detailed Implementation

[0024] Figure 1 This is a cross-sectional view of a polyimide film according to one embodiment of the present invention. The polyimide film 1 is a single-layer film having a first main surface 1A and a second main surface 1B. The polyimide film 1 contains an ultraviolet absorber. By including an ultraviolet absorber in the polyimide film, lightfastness is improved, and the tendency for yellowing of the polyimide film can be suppressed even after prolonged ultraviolet exposure.

[0025] In the polyimide film 1, the concentration C of the ultraviolet absorber on the second main surface 1B side is... B The concentration C of the ultraviolet absorber on the first principal surface 1A side is greater than that of the ultraviolet absorber. A That is, in the polyimide film 1, the ultraviolet absorber has a concentration distribution in the thickness direction, and the ultraviolet absorber is more concentrated on the second main surface side.

[0026] It should be noted that the concentration C of the ultraviolet absorber on the first main surface side... A The concentration of ultraviolet absorber is defined as the concentration of ultraviolet absorber in the region Ta, which is 30% of the thickness of the polyimide film 1 at a distance from the first main surface 1A, and the concentration C of ultraviolet absorber on the second main surface side. B The concentration of the ultraviolet absorber is defined as the concentration of the ultraviolet absorber within a region Tb that is 30% of the thickness of the polyimide film 1 at a distance from the second main surface 1B. The concentration C of the ultraviolet absorber on the first main surface side is also defined. A The concentration C of the ultraviolet absorber on the second main surface side was measured using a sample obtained by grinding the polyimide film 1 from the second main surface side in a manner that leaves region Ta. B The sample obtained by grinding the polyimide film 1 from the first main surface side in a manner that leaves region Tb is used for measurement. When the chemical structure of the ultraviolet absorber is known, the concentration of the ultraviolet absorber is determined using NMR. When the chemical structure of the ultraviolet absorber is unknown, the concentration of the ultraviolet absorber is determined based on the absorption spectrum.

[0027] Figure 2This is a cross-sectional view of a hard coating film 10 having a hard coating layer 3 on the surface of the polyimide film 1. The hard coating film 10 has the hard coating layer 3 on the second main surface 1B of the polyimide film 1, that is, on the side with a relatively high concentration of ultraviolet absorber. The hard coating film can have hard coatings on both sides of the polyimide film 1.

[0028] Figure 3 This is a cross-sectional view of an image display device on the recognition side surface of the image display panel 5, where a polyimide film 1 is disposed. Figure 3 In the image display device 101, the polyimide film 1 is configured such that a first main surface 1A with a relatively low ultraviolet absorption concentration faces the image display panel 5, and a second main surface 1B with a relatively high ultraviolet absorption concentration becomes the recognition side.

[0029] Figure 4 This is a cross-sectional view of an image display device on which a hard coating 10 is disposed on the recognition side surface of the image display panel 5. Figure 4 In the image display device 102, with Figure 3 Similarly, in the image display device 101, the polyimide film 1 is arranged with the first main surface 1A facing the image display panel 5 and the second main surface 1B serving as the recognition side, and a hard coating 3 is provided on the recognition side surface of the polyimide film 1, i.e., the second main surface 1B.

[0030] In the image display devices 101 and 102, external light is incident from the recognition side, i.e., the second main surface 1B side of the polyimide film 1. When external light is incident on the polyimide film 1, the ultraviolet rays contained in the external 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 are absorbed by the polyimide.

[0031] In polyimide film 1, due to the concentration C of the ultraviolet absorber on the second main surface 1B side... B Because the UV absorber is uniformly distributed in the thickness direction, region Tb on the second main surface absorbs more UV radiation, resulting in less UV radiation reaching region Ta on the first main surface. In the initial stage of light incidence, region Tb absorbs a large amount of UV radiation, while region Ta receives less. Therefore, considering the polyimide film 1 as a whole, the amount of UV radiation absorbed by the polyimide is small, and the photodegradation of the polyimide caused by UV radiation is suppressed.

[0032] By configuring the polyimide film 1 such that the second main surface 1B side, with a relatively high concentration of ultraviolet absorber, becomes the identification side (light incident side), the photodegradation of the polyimide can be suppressed more effectively with the same concentration of ultraviolet absorber. In other words, the photodegradation of the polyimide can be suppressed with a smaller amount of ultraviolet absorber added (lower concentration of ultraviolet absorber), thus improving lightfastness. By keeping the ultraviolet absorber concentration low, the coloration (reduction in transparency) of the polyimide film caused by visible light absorption by the ultraviolet absorber is suppressed; therefore, both the lightfastness and transparency of the polyimide film can be balanced.

[0033] There is a tendency that the greater the concentration distribution of ultraviolet absorber in the thickness direction of the polyimide film 1, the higher the concentration C of ultraviolet absorber on the first main surface 1A side. A The concentration C of the ultraviolet absorber on the second main surface 1B side B The greater the difference, the better the light degradation can be suppressed when the second principal surface is set as the light incident surface, and the smaller the change in yellowness ΔYI of the polyimide film 1 becomes. The concentration C of the ultraviolet absorber on the first principal surface 1A side. A The concentration C of the ultraviolet absorber on the second main surface 1B side is preferably [missing information]. B It is less than 0.5 times, more preferably less than 0.4 times, and even more preferably less than 0.3 times.

[0034] [Polyimide film]

[0035] The preferred form of the polyimide film 1 will be described below. It should be noted that, unless otherwise specified, the compounds illustrated in this specification may be used alone or in combination (two or more may coexist).

[0036] The polyimide film 1 comprises a polyimide resin. The content of the polyimide resin in the 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.

[0037] Composition of polyimide

[0038] Polyimide is generally obtained by dehydrating and cyclizing polyamic acid, which is obtained by reacting tetracarboxylic dianhydride (hereinafter sometimes abbreviated as "acid dianhydride") with a diamine. That is, polyimide has a structure derived from acid dianhydride and a structure derived from diamine. As mentioned above, if the ultraviolet absorber is predominantly present in the thickness direction, the composition of the polyimide resin contained in the polyimide film 1 is not particularly limited.

[0039] In the fabrication of transparent polyimide films, a preferred method is to coat a solution containing polyimide resin dissolved in an organic solvent onto a substrate and then remove the solvent by heating and drying (solution casting). Therefore, polyimide is preferably transparent and soluble in organic solvents.

[0040] Examples of polyimides that exhibit transparency and solubility in organic solvents include substances containing one or more of the following acid dianhydrides and one or more of the following diamines.

[0041] 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'-oxobisphthalic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropionic acid dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic acid dianhydride, p-phenylene bis(trimethoxymethyl ester) dianhydride, and bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4' diester.

[0042] Diamine group: 2,2'-bis(trifluoromethyl)benzidine, 2,2'-dimethylbenzidine, isophorone diamine, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 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.

[0043] Solution casting preferably uses low-boiling-point organic solvents such as dichloromethane. By using low-boiling-point solvents, the solvent can be dried and removed by heating at low temperature and for a short time, thus improving the production rate of polyimide films. In addition, if low-boiling-point solvents are used, it is not necessary to heat at high temperatures (e.g., above 200°C) to reduce the amount of residual solvent, which can suppress the thermal degradation of polyimide.

[0044] As an example of a polyimide soluble in dichloromethane, one can be listed as a polyimide comprising a tetracarboxylic dianhydride as shown in general formula (1) and a tetracarboxylic dianhydride having an alicyclic structure as an acid dianhydride component, and a polyimide comprising a fluoroalkyl-substituted benzidine as a diamine component.

[0045]

[0046] In general formula (1), n ​​is 1 or 2. 1 ~R 4Each is independently composed of hydrogen atoms, fluorine atoms, and alkyl or fluoroalkyl groups having 1 to 20 carbon atoms.

[0047] (Acidic dianhydrides with ester structures)

[0048] The compound represented by the general formula (1) above is an acid dianhydride with an ester structure. As R 1 ~R 4 Examples of alkyl groups when they are alkyl or fluoroalkyl include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, n-hexyl, cyclohexyl, etc. Examples of fluoroalkyl groups include monofluoromethyl, difluoromethyl, trifluoromethyl, pentafluoroethyl, etc.

[0049] From the perspective of obtaining polyimides that exhibit high solubility in dichloromethane, among the compounds represented by general formula (1), those with n=2 and R are preferred. 1 ~R 4 At least one of them is an alkyl or fluoroalkyl compound having 1 to 20 carbon atoms. Preferably, it is bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4' diester (TAHMBP) as shown in formula (2) below.

[0050]

[0051] (Acidic dianhydrides with alicyclic structures)

[0052] Examples of tetracarboxylic dianhydrides with alicyclic structures include 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, which have cyclobutane structures.

[0053] Examples of alicyclic tetracarboxylic dianhydrides other than those mentioned above include 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-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, and 3-(carboxymethyl)-1 2,4-Cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-en-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-carboxylic acid ester), 5-(2,5-dioxotetrahydrofuranyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid Anhydride, 5,5'-[cyclohexylbis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 5-isobenzofuran carboxylic acid, 1,3-dihydro-1,3-dioxo-,5,5'-[1,4-cyclohexanediylbis(methylene)] ester, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic anhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic anhydride, 3,5,6-tricarboxylated norbornane-2-acetic acid 2,3:5,6-dianhydride, decahydro -1,4,5,8-dimethylbridged naphthalene-2,3,6,7-tetracarboxylic acid dianhydride, tricyclic [6.4.0.0(2,7)]dodecane-1,8:2,7-tetracarboxylic acid dianhydride, octahydro-1H,3H,8H,10H-biphenylenzo[4a,4b-c:8a,8b-c']difuran-1,3,8,10-tetraone, ethylene glycol bis(hydrogenated trimellitic anhydride) ester, decahydro[2]benzopyran[6,5,4,-def][2]benzopyran-1,3,6,8-tetraone, etc.

[0054] From the viewpoint of the transparency and mechanical strength of polyimide, 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'-biscyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride (H-BPDA) are preferred, with 1,2,3,4-cyclobutanetetracarboxylic dianhydride being particularly preferred.

[0055] (Fluoroalkyl-substituted benzidine)

[0056] 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, 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-(Trifluorobenzidine) 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-Tetra(trifluoromethyl)benzidine, 2,2'-Bis(trifluoromethyl)benzidine, 3,3'-Bis(trifluoromethyl)benzidine, 2,3'-Bis(trifluoromethyl)benzidine, 2,2',3-Bis(trifluoromethyl)benzidine 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'-tetra(trifluoromethyl)benzidine, 2,2',5,5'-tetra(trifluoromethyl)benzidine, 2,2',6,6'-tetra(trifluoromethyl)benzidine, etc.

[0057] Preferably, the biphenyl substituted benzidine is a fluoroalkyl-substituted benzidine having a fluoroalkyl group at the 2-position of the biphenyl skeleton, more preferably 2,2'-bis(trifluoromethyl)benzidine. By having a fluoroalkyl group at the 2-position of the biphenyl skeleton, the aromatic ring of the biphenyl skeleton is twisted due to the stereohindrance of the fluoroalkyl group, and the coloring is reduced due to the electrophilicity of the fluoroalkyl group.

[0058] (Other acids: dianhydrides and diamines)

[0059] Polyimide can contain acid dianhydride and diamine components other than those mentioned above, without impairing its solubility in low-boiling-point solvents such as dichloromethane, or without compromising its transparency and mechanical strength.

[0060] Examples of dianhydride components that can be used in combination include pyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropionic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, 4,4'-oxobisphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, and 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride. 1,1-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]phenyl dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]phenyl 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}one dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}one 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}one dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}one dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone Dihydrides, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}thioether dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}thioether 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-anthracitetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride, etc.

[0061] 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'-diaminodiphenyl ketone, 4,4'-diaminodiphenyl ketone, 3,4'-diaminodiphenyl ketone, 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-phenylethane, 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)benzene, 1,4-bis(3-aminobenzoyl)benzene, 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 Ethers, bis[4-(3-aminophenoxy)phenyl] sulfones, bis[4-(4-aminophenoxy)phenyl] sulfones, bis[4-(3-aminophenoxy)phenyl] ethers, bis[4-(4-aminophenoxy)phenyl] ethers, 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-dimethylbenzyl]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]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'- Diphenyloxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenyloxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spiroindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spiroindane, 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-aminomethyl) ether [2-(2-aminoethoxy)ethyl] ether, bis[2-(3-aminopropoxy)ethyl] ether, bis[2-(3-aminoethoxy)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-diaminopropane ...ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine, ethylenediamine Aminodecane, 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, 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-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-2,6-bis(trifluoromethyl)benzene, 1,4-diamino-2,3,5-tris(trifluoromethyl)benzene, 1,4-diamino-2,3,5,6-tetra(trifluoromethyl)benzene.

[0062] (Specific examples of the composition of polyimide)

[0063] As described above, in one embodiment of the polyimide, the acid dianhydride component includes an acid dianhydride having an ester structure as shown in general formula (1) and an acid dianhydride having a cyclobutane structure, and the diamine component includes fluoroalkyl-substituted benzidine.

[0064] The amount of the acid dianhydride shown in general formula (1) relative to 100 mol% of the total acid dianhydride component is preferably 40 to 85 mol%, more preferably 45 to 80 mol%, and even more preferably 50 to 70 mol%. By setting it within this range, it is possible to produce a polyimide with high solubility in low-boiling-point solvents such as dichloromethane and excellent mechanical strength. As described above, among the acid dianhydrides shown in general formula (1), THAHMBP shown in formula (2) is particularly preferred.

[0065] The amount of alicyclic dianhydride relative to 100 mol% of the total alicyclic dianhydride content is preferably 15 to 60 mol%, more preferably 20 to 55 mol%, and even more preferably 25 to 50 mol%. By setting it within this range, a polyimide with good solubility in low-boiling-point solvents such as dichloromethane, minimal coloration, and excellent mechanical strength is obtained. As described above, among alicyclic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) is particularly preferred.

[0066] As an example of the composition of a polyimide, the following polyimide can be listed: wherein, relative to the total amount of diamine, it contains 40 mol% or more and 100 mol% or less of fluoroalkyl-substituted benzidine, relative to the total amount of dianhydride, it contains 40 mol% or more and 85 mol% or less of dianhydride having an ester structure as shown in formula (1), and contains 15 mol% or more and 60 mol% or less of dianhydride having an alicyclic structure.

[0067] When using acid dianhydrides other than those shown in general formula (1) and acid dianhydrides having an alicyclic structure in combination, the amount of acid dianhydrides is preferably 45 mol% or less, more preferably 30 mol% or less, relative to 100 mol% of the total acid dianhydride content. From the viewpoint of obtaining polyimides with excellent solubility, transparency and mechanical strength, preferred examples of acid dianhydrides used in combination include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA), 4,4'-oxybis(phthalic acid) dianhydride (s-ODPA), and 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA).

[0068] The amount of fluoroalkyl-substituted benzidine relative to 100 mol% of the total diamine content is preferably 40 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more. By setting it within this range, polyimides with excellent transparency and solubility can be obtained without compromising mechanical strength. As described above, among the fluoroalkyl-substituted benzidines, 2,2'-bis(trifluoromethyl)benzidine (TFMB) is particularly preferred.

[0069] When using diamines other than fluoroalkyl-substituted benzidines in combination, the amount of such diamines relative to 100 mol% of the total diamine content is preferably 60 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less. From the viewpoint of the transparency and solubility of polyimide, it is preferable to use fluoroalkyl-substituted benzidines such as TFMB in combination with 3,3'-diaminodiphenyl sulfone (3,3'-DDS) or 4,4'-diaminodiphenyl sulfone (3,3'-DDS). The amount of diaminodiphenyl sulfone relative to 100 mol% of the total diamine content is preferably 5 to 40 mol%, more preferably 10 to 30 mol%.

[0070] As described above, in the polyimide, as the acid dianhydride component, it is preferable to contain 40-85 mol% THAHMBP and 15-60 mol% CBDA, and as the diamine component, it is preferable to contain 40-100 mol% TFMB. Furthermore, from the viewpoint of improving solubility in solvents and the transparency of the film, as the diamine component, it is preferable to contain 5-40 mol% diaminodiphenyl sulfone (3,3'-DDS or / and 4,4'-DDS), and as the acid dianhydride, it may contain 6FDA, s-BPDA, s-ODPA, etc.

[0071] <Production of Polyimide Resin>

[0072] The method for manufacturing polyimide resin is not particularly limited, but the preferred method is as follows: polyamic acid, a precursor of polyimide, is prepared by reacting a diamine with an acid dianhydride in a solvent, and imidization is performed by dehydration and cyclization of the polyamic acid. For example, an imidization catalyst and a dehydrating agent are added to a polyamic acid solution to dehydrate and close the polyamic acid ring, thereby obtaining a polyimide solution. The polyimide resin is precipitated by mixing the polyimide solution with a poor solvent for polyimide, and solid-liquid separation is performed to obtain the polyimide resin.

[0073] (Synthesis of polyamic acid)

[0074] A polyamic acid solution is obtained by reacting an acid dianhydride with a diamine in a solvent. It is preferable to use substantially equimolar amounts of the acid dianhydride and diamine. That is, the molar ratio of the acid dianhydride to the diamine is preferably in the range of 95:105 to 105:95.

[0075] In the polymerization of dianhydrides and diamines, there are no particular limitations on the organic solvents that can be used, as long as they can dissolve the dianhydrides, diamines, and polyamic acid, which is the polymerization product. Specific examples of organic solvents include urea solvents such as methylurea and N,N-dimethylethylurea; sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N'-diethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, and hexamethylphosphotriamide; haloalkyl solvents such as chloroform and dichloromethane; aromatic hydrocarbon solvents such as benzene and toluene; and ether 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 from the perspective of excellent polymerization reactivity and solubility of polyamic acid.

[0076] The reaction temperature in the polymerization of acid dianhydride and diamine is not particularly limited, but is preferably 0°C or higher and 80°C or lower, more preferably 20°C or higher and 45°C or lower. By setting the temperature above 0°C, the decrease in reaction rate is suppressed, and by setting the temperature below 80°C, there is a tendency to suppress the decrease in degree of polymerization due to ring opening of the acid dianhydride.

[0077] (imideation)

[0078] Polyimides are obtained by the dehydration and cyclization of polyamic acid. For in-solution imidization, chemical imidization, which involves adding a dehydrating agent and an imidization catalyst to the polyamic acid solution, is suitable. The polyamic acid solution can be heated to promote imidization.

[0079] Tertiary amines can be used as imidization catalysts. Heterocyclic tertiary amines are preferred. Specific examples of heterocyclic tertiary amines include pyridine, methylpyridine, quinoline, and isoquinoline. Carboxylic anhydrides can be used as dehydrating agents; specifically, acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride are examples.

[0080] The amount of imidization catalyst added is preferably 0.5 to 5.0 molar equivalents relative to the amide group of polyamic acid, more preferably 0.7 to 2.5 molar equivalents, and even more preferably 0.8 to 2.0 molar equivalents. The amount of dehydrating agent added is preferably 0.5 to 10.0 molar equivalents relative to the amide group of polyamic acid, more preferably 0.7 to 5.0 molar equivalents, and even more preferably 0.8 to 3.0 molar equivalents.

[0081] (Extrusion of polyimide resin)

[0082] Preferably, the polyimide resin is precipitated in solid form from the polyimide solution obtained by imidization of polyamic acid. This precipitation occurs by mixing the polyimide solution with a poor solvent. The poor solvent is preferably a solvent that is unsuitable for the polyimide resin and is miscible with the solvent in which the polyimide resin is dissolved; examples include water and alcohols. Examples of alcohols include methanol, ethanol, isopropanol, ethylene glycol, triethylene glycol, 2-butyl alcohol, 2-hexanol, cyclopentanol, cyclohexanol, phenol, and tert-butanol. Alcohols that are less likely to cause ring-opening of the polyimide are preferred, with isopropanol, 2-butanol, 2-pentanol, phenol, cyclopentanol, cyclohexanol, and tert-butanol being particularly preferred.

[0083] <Fabrication of Polyimide Film>

[0084] Polyimide films can be manufactured by coating a polyimide solution (film-forming coating) containing polyimide resin dissolved in an organic solvent onto a substrate and then drying to remove the solvent. The organic solvent used to dissolve the polyimide resin can be any solvent capable of dissolving the polyimide resin; it can be appropriately selected based on the intended use of the polyimide resin. Low-boiling-point solvents such as dichloromethane, methyl acetate, tetrahydrofuran, acetone, and 1,3-dioxolane are preferred. Dichloromethane is particularly preferred due to its low boiling point and ease of solvent removal during drying. By adjusting the composition ratio of the dianhydride and diamine components as described above, polyimides exhibiting high solubility even in low-boiling-point solvents such as dichloromethane can be obtained.

[0085] The concentration of solids in the polyimide solution can be appropriately set based on the molecular weight of the polyimide, the thickness of the film, and the film-forming environment. The preferred concentration of solids is 5–30% by weight, more preferably 6–20% by weight.

[0086] (UV absorber)

[0087] As described above, the polyimide film 1 according to one embodiment of the present invention contains an ultraviolet absorber. In the production of the polyimide containing the ultraviolet absorber, it is preferable to make the polyimide solution contain the ultraviolet absorber.

[0088] 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 hydroxybenzoic acid ester-based UV absorbers. Among these, benzotriazole-based and triazine-based UV absorbers are preferred due to their low absorption of visible light and good lightfastness.

[0089] Specific examples of benzotriazole-based ultraviolet absorbers include 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (ADEKASTAB LA-24 manufactured by ADEKA), 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (ADEKASTAB LA-29 manufactured by ADEKA), and 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] (ADEKASTAB LA-31G and ADEKASTAB LA-29 manufactured by ADEKA). LA-31RG”), 2-(2H-benzotriazol-2-yl)-p-cresol (ADEKASTABLA-32) manufactured by ADEKA, 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (TINUVIN571) manufactured by BASF, 2-(2H-benzotriazol-2-yl)-p-cresol (TINUVIN P) manufactured by BASF, 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (TINUVIN PS) manufactured by BASF, 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (TINUVIN) manufactured by BASF 234”), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (BASF's "TINUVIN 326"), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (BASF's "TINUVIN 328"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF's "TINUVIN 329"), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (BASF's "TINUVIN") 900”), 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF's "TINUVIN 928"), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimide-methyl)-5-methylphenyl]benzotriazole (Sumitomo Chemical's "Sumisorb250"), etc.

[0090] Specific examples of triazine-based ultraviolet absorbers include 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADEKASTAB LA-46 manufactured by ADEKA), 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine (ADEKA LA-F70 manufactured by ADEKA), and the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(alkoxy)methyl]ethylene oxide (BASF's "TINUVIN"). 400”), the reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl) glycidyl ester (BASF's "TINUVIN 405"), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (BASF's "TINUVIN 460"), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (BASF's "TINUVIN 479"), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol (BASF's "TINUVIN") 577”), bis(ethylhexyloxyphenol) methoxyphenyl triazine (BASF's "Tinosorb S"), etc.

[0091] From the viewpoint of suppressing photodegradation of polyimide films, 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 can be 0.5 parts by weight or more, 0.7 parts by weight or more, or 1 part by weight or more, relative to 100 parts by weight of the total solids. The more ultraviolet absorber present, the more effectively photodegradation can be suppressed. On the other hand, if the amount of ultraviolet absorber is excessive, sometimes the ultraviolet absorber and polyimide may not be sufficiently compatible, resulting in whitening of the polyimide film and seepage 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 can be 3.5 parts by weight or less or 3 parts by weight or less, relative to 100 parts by weight of the total solids.

[0092] (additive)

[0093] The polyimide solution may contain resin components and additives other than polyimide resin and ultraviolet absorbers. Examples of additives include crosslinking agents, dyes, surfactants, leveling agents, plasticizers, and microparticles. The content of polyimide resin relative to 100 parts by weight of the solid components 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.

[0094] Specific examples of the aforementioned dyes include anthraquinone compounds, phthalocyanine compounds, and indigo compounds. Among these, anthraquinone compounds are preferred from the viewpoint of heat resistance. The dosage, for example, is approximately 0.1 to 100 ppm based on the polyimide resin, and can be 1 to 90 ppm, 10 to 80 ppm, or 20 to 70 ppm. By including the dye, the hue of the polyimide film can be adjusted. Polyimide and ultraviolet absorbers are slightly tinted yellow due to the absorption of light in the short wavelength region of visible light, but the hue can be neutralized by adding a dye that functions as a bluing agent. Known substances can be appropriately used as bluing agents; commercially available examples include "Macrolex Blue RR," "Sumiplast Violet B," "Sumiplast Violet OR," "Plast Blue 8580," "Plast Blue 8590," and "Plast Violet 8840."

[0095] (Coating and drying)

[0096] As a method for coating a polyimide solution onto a substrate, known methods can be used, such as a rod coater or a comma coater. As the substrate for coating the polyimide solution, glass substrates, metal substrates such as SUS, metal drums, metal strips, and plastic films can be used. From the viewpoint of improving productivity, it is preferable to use annular supports such as metal drums or metal strips, or long strips of plastic film, and to manufacture the film using roll-to-roll methods. When using a plastic film as the support, any material that is insoluble in the solvent of the film-forming coating can be appropriately selected. As the plastic material, polyethylene terephthalate, polycarbonate, polyacrylate, polyethylene naphthalate, etc., can be used.

[0097] Heating is preferred during solvent drying. The heating temperature is not particularly limited, but from the viewpoint of suppressing coloration of the polyimide film and the volatilization of ultraviolet absorbers, it is preferably below 200°C, more preferably below 180°C. The heating temperature can be increased in stages during solvent drying. Solvent drying can be carried out under reduced pressure.

[0098] By using low-boiling-point solvents such as dichloromethane, residual solvent can be easily reduced even with heating below 200°C, thus suppressing the volatilization of colorants and UV absorbers. The residual solvent content (the mass of solvent contained in the film relative to the film mass) of the polyimide film is preferably 1.5% or less, more preferably 1.0% or less. If the residual solvent content is within this range, there is a tendency for the mechanical strength of the polyimide film to increase. The solvent can be dried by heating on the substrate, and after the polyimide film is peeled off from the substrate, the solvent can be further removed by heating.

[0099] The thickness of the polyimide film is not particularly limited and can be appropriately set according to the application. For example, the thickness of the polyimide film is about 5 to 100 μm. From the viewpoint of balancing 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. Especially in applications requiring strength, such as display cover windows, the thickness of the polyimide film is preferably 40 μm or more. The thickness of the polyimide film is preferably 90 μm or less, more preferably 85 μm or less.

[0100] By coating a substrate with a solution containing polyimide resin, a UV absorber, and an organic solvent, heating and drying the solution on the substrate to remove the organic solvent, and then peeling it off from the substrate, the concentration C of the UV absorber on the peeled surface (surface B) is obtained. B The concentration C of the ultraviolet absorber above the air surface (surface A) A A polyimide film in which the ultraviolet absorber is predominantly distributed in the thickness direction. That is, in the polyimide film 1 produced by solution casting, the substrate side (side B) is the second main side 1B, and the air side (side A) is the first main side 1A.

[0101] Concentration C of ultraviolet absorber on side B B The relative increase can be attributed to the different drying behaviors of sides A and B. When the solution on the substrate is heated to dry and remove the solvent, more than half of the solvent evaporates from side A; therefore, drying proceeds from side A.

[0102] In solution, the molecular chain orientation of polyimide is random, and the UV absorber exists uniformly in solution. If the solvent is removed by heating, the polyimide molecular chains tend to orient in-plane. It can be assumed that if heating causes the solvent on side A to evaporate and the polyimide molecular chains to orient, the UV absorber will move towards side B, where the solvent remains. Therefore, the concentration C of the UV absorber on side A will increase. A The concentration of ultraviolet absorber on side B decreases, C B As the thickness increases, the ultraviolet absorber becomes more concentrated in the thickness direction.

[0103] If heating is performed at a temperature above the boiling point of the organic solvent while the solvent remains, then C will be present. B With C A The difference increases, C A / C B The tendency to decrease. Therefore, there is a tendency that the shorter the time between applying the solution to the substrate and the start of heating at a temperature above the boiling point, the more pronounced the bias of the UV absorber in the thickness direction becomes. C A / C B The smaller it becomes. To obtain C A / C B For polyimide films with a thickness of 0.5 or less, the time from coating the solution onto 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.

[0104] The ease with which ultraviolet absorbers are biased in the thickness direction also depends on the composition of the polyimide. When polyimide films are fabricated using solution casting, polyimides containing trimellitic anhydride esters (e.g., THAHMBP) as shown in general formula (1) and tetracarboxylic dianhydrides (e.g., CHDA) with a cycloalicylic structure as acid dianhydrides tend to have an overemphasis on ultraviolet absorbers in the thickness direction, making it easier to obtain C... A / C B It is a polyimide film with a thickness of less than 0.5.

[0105] Properties of Polyimide Films

[0106] The total light transmittance of the polyimide film is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more. The light transmittance of the polyimide film at a wavelength of 400 nm is preferably 35% or more, more preferably 40% or more. 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.

[0107] The yellowness (YI) of the polyimide film is preferably 3.0 or less, more preferably 2.5 or less. If the yellowness (YI) of the polyimide film is 3.0 or less, the film has less coloring and can be suitable for use as a display film.

[0108] The dianhydride in the aforementioned general formula (1) is an ester formed from phenol and trimellitic anhydride, which is prone to photodegradation due to ultraviolet light. This can be presumed to be because it is structurally prone to rearrangement reactions such as photo-Fries rearrangement. By including ultraviolet absorbers in the polyimide film, the ultraviolet light incident on the polyimide film is absorbed by the ultraviolet absorbers. Therefore, there is a tendency for the amount of ultraviolet light absorbed by the polyimide to decrease, and for the coloring (yellowing) of the polyimide film caused by photodegradation to be suppressed.

[0109] The content (concentration) of the ultraviolet absorber in the polyimide film 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 can be 1 to 3% by weight. By setting the concentration of the ultraviolet absorber within this range, the increase of YI can be suppressed, the transparency of the polyimide film can be maintained, and the light degradation of the polyimide film can be suppressed.

[0110] It should be noted that the UV absorber concentration of the polyimide film is the concentration when the thickness direction is considered as a single unit. When the UV absorber is predominantly present in the thickness direction, the UV absorber concentration C on the first main surface side of the polyimide film... A The concentration C of the ultraviolet absorber on the second main surface side of the polyimide film can be lower than the range mentioned above. B It can exceed the above range.

[0111] At a radiation irradiance of 500 W / m 2 The increase in yellowness ΔYI of the polyimide film after irradiation with ultraviolet light from the second main surface side of the polyimide film for 48 hours at a black panel temperature of 63℃. B Preferably 6 or less, more preferably 5 or less, and can be 4.5 or less or 4.0 or less.

[0112] As described above, the concentration C of the ultraviolet absorber on the second main surface 1B side... B The concentration C of the ultraviolet absorber on the first principal surface 1A side is greater than that on the first principal surface 1A side. A In the polyimide film 1, when ultraviolet light is irradiated 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. Therefore, ΔYI B It decreases. On the other hand, when the polyimide film is irradiated with ultraviolet light from the first main surface 1A side, the concentration C of the ultraviolet absorber at the light incident surface decreases. A Because of its small size, polyimide absorbs a large amount of ultraviolet light, resulting in a significant increase in yellowness ΔYI. B The increase in yellowness ΔYI is greater than that when ultraviolet light is irradiated from the second principal surface side. A .

[0113] In other words, the lightfastness of polyimide films with a predominantly high concentration of UV absorbers in the thickness direction varies depending on the light-exposed surface. When the surface with a relatively high concentration of UV absorbers is the light-exposed surface (light incident surface), ΔYI is small, and the lightfastness is excellent. Therefore, by suppressing coloration (reduced transparency) caused by excessive increase in UV absorber concentration and by configuring the UV absorbers in a way that predominates in the thickness direction, with the surface with a relatively high concentration of UV absorbers as the light incident surface (identification side), both transparency and lightfastness can be achieved.

[0114] From the viewpoint of preventing film damage caused by contact between the film and the roll during roll-to-roll transport and by contact between the film and the roll 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 for cover windows of displays, etc., resistance to scratches from external contact is sought; therefore, the pencil hardness of the polyimide film is preferably H or higher. The tensile modulus of elasticity 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.

[0115] [Hard coating]

[0116] The hard coating film has a hard coating layer 3 on at least one side of the polyimide film 1. For example... Figure 2 As shown, the hard coating 10 preferably has a hard coating layer 3 on the second main surface 1B of the polyimide film 1.

[0117] As described above, when the polyimide film 1 is used as a cover window for the image display device, it is arranged with the first main surface 1A facing the image display panel 5 and the second main surface 1B serving as the recognition side. By providing a hard coating 3 on the second main surface 1B of the polyimide film, the hard coating 3 is arranged as the outermost layer in the image display device, thus preventing breakage or damage caused by external impacts, etc.

[0118] By coating a hard coating composition onto a polyimide film, drying and removing the solvent as needed, and then irradiating the hard coating composition with active energy rays such as ultraviolet light to cure it, a hard coating layer 3 is formed on the polyimide film 1.

[0119] The thickness of the hard coating 3 is preferably 0.5 μm or more, more preferably 2 μm or more, further preferably 3 μm or more, and most preferably 5 μm or more. The thickness of the hard coating is preferably 100 μm or less, more preferably 80 μm or less. If the thickness of the hard coating is less than 0.5 μm, it may sometimes be impossible to sufficiently improve mechanical properties such as surface hardness. On the other hand, if the thickness of the hard coating is greater than 100 μm, transparency and bending resistance may sometimes decrease.

[0120] The material constituting the hard coating is not particularly limited, and a photocurable resin composition containing a polyfunctional (meth)acrylate monomer can be used, for example. As the hard coating composition, compositions containing a polysiloxane compound having an epoxy group can be used, as disclosed in WO2018 / 096729, WO2014 / 204010, Japanese Patent Application Publication No. 2017-8142, etc.

[0121] Functional layers other than the hard coating layer can be formed on the surface of the polyimide film 1. Examples of functional layers include anti-reflective layers, anti-glare layers, antistatic layers, and transparent electrodes. These functional layers can be formed on either the first or second main surface of the polyimide film. Alternatively, these functional layers can be formed on the hard coating layer 3. The polyimide film may be accompanied by a transparent adhesive layer.

[0122] [Image display device]

[0123] The polyimide film of this invention possesses high transparency and mechanical strength, as well as high light resistance, making it suitable for use as a cover window disposed on the recognition side surface of an image display panel. For example... Figure 3 and Figure 4 As shown, by arranging the polyimide film 1 with its first main surface 1A facing the image display panel 5 and its second main surface 1B serving as the recognition side, the polyimide film is less prone to light degradation when exposed to external light including ultraviolet light from the recognition side of the image display device, thus exhibiting excellent light resistance.

[0124] Example

[0125] The present invention will now be described in more detail with reference to embodiments and comparative examples, but the present invention is not limited to the embodiments described below.

[0126] [Preparation of polyimide resin]

[0127] <Polyimide Resin A>

[0128] 44.2 g (138.1 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 3.8 g (15.3 mmol) of 3,3'-diaminodiphenyl sulfone (3,3-DDS) were added as diamines to a reaction vessel; 47.4 g (76.7 mmol) of bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4' diester (TAHMBP) was added as tetracarboxylic dianhydride; 9.0 g (46.0 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 9.5 g (30.7 mmol) of 4,4'-oxobisphthalic dianhydride (ODPA) were added as solvents; and 800 g of N,N-dimethylformamide (DMF) was added as solvents. The mixture was stirred for 12 hours under a nitrogen atmosphere to obtain a polyamic acid solution.

[0129] 36.4 g (460 mmol) of pyridine and 7.0 g (460 mmol) of acetic anhydride, acting as imidization catalysts, were added to the above polyamic acid solution, and the mixture was stirred at 90 °C for 4 hours. While stirring the solution, which had cooled to room temperature, 2000 g of 2-propanol (IPA) was added, and the mixture was filtered 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 white polyimide resin A. The monomer composition of polyimide resin A is TFMB / 3,3'-DDS / / TAHMBP / CBDA / ODPA = 90 / 10 / / 50 / 30 / 20 (molar ratio).

[0130] <Polyimide Resin B~E>

[0131] In the preparation of the polyamic acid solution, the types and molar ratios of the diamine and dianhydride were varied as shown in Table 1. Otherwise, the same procedure as described above was followed to obtain polyimide resins B to E.

[0132] [Fabrication of polyimide film]

[0133] <Example 1>

[0134] 100 parts by weight of polyimide resin A1, along with the ultraviolet absorber (UVA) and blueing agent ("PlastBlue 8590" manufactured by Yuhon Chemical Industry Co., Ltd.) shown in Table 1, were dissolved in dichloromethane to obtain a polyimide solution with a solid content concentration of 10% by weight.

[0135] Using a rod coater, the above polyimide solution was coated onto alkali-free glass and left at room temperature (25°C) for 15 minutes. Subsequently, 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. The resulting film was then peeled off from the alkali-free glass to obtain a transparent polyimide film with a thickness of approximately 50 μm. The air side during film fabrication is designated as "side A," and the side facing the alkali-free glass is designated as "side B."

[0136] <Examples 2-4, Comparative Examples 1 and 2>

[0137] As shown in Table 1, the type of polyimide resin, the type and amount of ultraviolet absorber, and the amount of bluing agent were changed. Otherwise, the procedure was the same as in Example 1 to obtain a transparent polyimide film.

[0138] <Comparative Example 3>

[0139] After coating the polyimide solution onto alkali-free glass, the time it was left at room temperature (25°C) until the start of heating was changed to 80 minutes. Otherwise, the procedure was the same as in Example 1 to obtain a polyimide film.

[0140] [evaluate]

[0141] The following evaluation was performed on the polyimide films of the examples and comparative examples.

[0142] <Concentration distribution of ultraviolet absorber in the thickness direction>

[0143] The concentration of ultraviolet absorber in the polyimide films of Examples 1-3 and Comparative Examples 1-3 was determined by NMR, and the concentration of ultraviolet absorber in the polyimide film of Example 4 was determined by absorption spectrum.

[0144] (Examples 1-3 and Comparative Examples 1-3)

[0145] Using abrasive paper (PRESI P800), abrade the polyimide film from the B-side until the remaining thickness reaches 30% (approximately 15 μm). Dissolve the remaining polyimide film (the portion with 30% thickness on the A-side) in CDCl3, and then... 1 The concentration of ultraviolet absorber was determined by ¹H-NMR. A The same procedure is followed for samples obtained by grinding polyimide films from side A. 1 The concentration of ultraviolet absorber was determined by ¹H-NMR. B Calculate the concentration C of the ultraviolet absorber on side A. A The concentration of ultraviolet absorber on side B, C B The ratio of CA / C B .

[0146] (Example 4)

[0147] Using abrasive paper (PRESI P800), the polyimide film was abraded from the B-side until the residual thickness reached 30% (approximately 15 μm). The abraded polyimide film was then dissolved in DMF to prepare a 100 ppm solution. The absorption spectrum at wavelengths of 200–800 nm was measured using a UV-Vis spectrophotometer (Nippon Spectrophotometer V-560).

[0148] Polyimide resin was dissolved in DMF to prepare a 100 ppm solution, and the absorption spectrum was measured. The difference between the absorption spectrum of the ground polyimide film and the absorption spectrum of the polyimide resin was taken as the absorption spectrum of the ultraviolet absorber contained in the polyimide film.

[0149] Absorption spectra of DMF solutions obtained by varying the concentration of the UV absorber were measured, and a standard curve was constructed based on the absorbance at the wavelength of maximum absorption of the UV absorber. Based on this standard curve and the aforementioned difference spectrum (absorption spectrum of the UV absorber contained in the polyimide film), the concentration C of the UV absorber in the residual polyimide film after polishing (the portion with 30% thickness on the A-side) was calculated. A .

[0150] For the sample obtained by grinding the polyimide film from side A, the absorption spectrum of the DMF solution was measured in the same manner as above. Based on the difference spectrum between the DMF solution and the polyimide resin, and the standard curve, the concentration C of the ultraviolet absorber in the 30% thickness portion on side B was calculated. B Based on the results, calculate the concentration C of the ultraviolet absorber on side A. A The concentration of ultraviolet absorber on side B, C B The ratio of C A / C B .

[0151] <Yellowness and Lightfastness>

[0152] The film was cut into 3cm square pieces, and its yellowness (YI0) was measured using a spectrophotometer (Suga Test Instruments "SC-P"). Subsequently, a fading test was performed using a Suga Test Instruments "U48-HB" at an irradiance of 500W / m². 2Under the condition that the black panel temperature is 63℃, the film is irradiated with ultraviolet light from one side (side A or side B) for 48 hours. The yellowness (YI1) of the film after ultraviolet irradiation is measured. Based on the yellowness YI0 before irradiation and the yellowness YI1 after irradiation, the change in yellowness ΔYI before and after irradiation is calculated according to the following formula.

[0153] ΔYI=YI1-YI0

[0154] The change in yellowness when ultraviolet light is irradiated from side A is denoted as ΔYI. A Let ΔYI be the change in yellowness when ultraviolet light is irradiated from side B. B .

[0155] <Tension Modulus>

[0156] The film was cut into 10mm wide strips and conditioned by standing at 23°C / 55%RH for 1 day. The tensile modulus of elasticity was then measured using the "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation under the following conditions.

[0157] Spacing between fixtures: 100mm

[0158] Tensile speed: 20.0 mm / min

[0159] Measurement temperature: 23℃

[0160] <Pencil Hardness>

[0161] The pencil hardness of polyimide films was determined using the JIS K-5600-5-4 pencil scratch test.

[0162] <Haze and Total Transmittance>

[0163] The film was cut into 3cm squares, and the haze and total transmittance (TT) were measured using a haze meter "HZ-V3" manufactured by Suga Test Instruments, in accordance with JIS K7136 and JIS K7361-1.

[0164] <Transmittance at 400nm>

[0165] The transmittance of the thin film in the range of 300–800 nm was measured using a UV-Vis spectrophotometer “V-560” manufactured by Japan Spectrophotometer Co., Ltd., and the transmittance at a wavelength of 400 nm was read.

[0166] The composition of the polyimide films of the examples and comparative examples, the standing time at room temperature from the coating of the polyimide solution onto alkali-free glass to the start of heating, and the evaluation results of the films are shown in Table 1.

[0167] In Table 1, diamines, dianhydrides, and ultraviolet absorbers (UVA) are described using the following abbreviations.

[0168] <Diamine>

[0169] TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0170] 3,3-DDS: 3,3'-Diaminodiphenylsulfone

[0171] 4,4-DDS: 4,4'-Diaminodiphenyl sulfone

[0172] <Acid dianhydride>

[0173] TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2',3,3',5,5'-hexamethylbiphenyl-4,4' diester

[0174] BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride

[0175] ODPA: 4,4'-O-diphthalic anhydride

[0176] 6FDA: 2,2-Bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride

[0177] CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride

[0178] <uva>

[0179] LA-F70: "ADEKASTAB LA-F70" (triazine-based ultraviolet absorber) manufactured by ADEKA.

[0180] Tin477: "Tinuvin 477" (triazine-based ultraviolet absorber) manufactured by BASF.

[0181] LA-31RG: "ADEKASTAB LA-31RG" (benzotriazole UV absorber) manufactured by ADEKA.

[0182] In Table 1, the amounts of diamine and dianhydride are in mol%, the amount of UVA is the amount added relative to 100 parts by weight of polyimide resin (parts by weight), and the amount of bluing agent is in ppm.

[0183] [Table 1]

[0184]

[0185] In the polyimide films of Examples 1-4 and Comparative Examples 1-3, the concentration C of the ultraviolet absorber on the A-side is... A The concentration of ultraviolet absorber on the B side is less than C. B An imbalance in the concentration of ultraviolet absorber along the thickness direction was observed. In Examples 1-4, C A / C B A value less than 0.5 indicates a significant bias.

[0186] It can be seen that in Examples 1 to 4, the change in yellowness ΔYI when irradiated with ultraviolet light from the A-side where the ultraviolet absorber concentration is low A The value exceeds 10. In contrast, the change in yellowness ΔYI when irradiated with ultraviolet light from the B-side, where the concentration of ultraviolet absorber is high, is also significant. B When the value is 4 or lower, light degradation is suppressed when light is irradiated from the B-side.

[0187] 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 Approaching 1), ΔYI A and ΔYI B All values ​​were 6 or higher. It can be assumed that in Comparative Example 3, the time from coating the polyimide solution containing the UV absorber to the start of drying (heating) was long, therefore, the UV absorber hardly moved in the thickness direction during drying.

[0188] In Comparative Examples 1 and 2, the drying conditions of the film were the same as in Examples 1-4, and the concentration distribution of the ultraviolet absorber in the thickness direction was small, ΔYI A With ΔYI B The difference is also small. A comparison of the composition of the polyimides in Examples 1-4 with Comparative Examples 1 and 2 shows that when triterpenoid anhydride ester (TAHMBP) and tetracarboxylic dianhydride (CHDA) with an alicyclic structure are included as the tetracarboxylic dianhydride, the concentration distribution of the ultraviolet absorber in the thickness direction increases (C...). A / C B The tendency to decrease (is noted). It should be noted that in Comparative Example 1, ΔYI... A and ΔYI B The overall size is small, but the compatibility between the ultraviolet absorber and polyimide is low, resulting in high haze. Consequently, the YI0 is also large, leading to poor transparency.

[0189] These results show that by using a solution containing a specific polyimide resin and a UV absorber, and by employing a solution casting method to fabricate the film, a film with a high concentration distribution of UV absorber in the thickness direction can be obtained. If this film is positioned in an image display device with the B-side (surface side) having a high concentration of UV absorber as the recognition side, then the photodegradation of the polyimide film caused by external light in the operating environment of the image display device can be suppressed.

[0190] Explanation of reference numerals in the attached figures

[0191] 1. Polyimide film

[0192] 3 Hard coating

[0193] 10 Hard coating

[0194] 5. Image display panel

[0195] Image display devices 101 and 102< / uva>

Claims

1. A hard coating film, comprising: A polyimide film formed of one layer, having a first main surface and a second main surface; and A hard coating disposed on the second main surface of the polyimide film. The polyimide film comprises polyimide resin and ultraviolet absorber. The concentration C of the ultraviolet absorber on the first main surface side A The concentration C of the ultraviolet absorber on the second main surface side B Less than 0.5 times, In the polyimide film As a diamine component, 2,2'-bis(trifluoromethyl)benzidine is used in combination with at least one selected from 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone, wherein the amount of 2,2'-bis(trifluoromethyl)benzidine is 40 mol% or more and 100 mol% or less relative to 100 mol% of the total diamine. As a tetracarboxylic dianhydride component, relative to 100 mol% of the total tetracarboxylic dianhydride component, it includes 40 mol% and 85 mol% of the compound represented by general formula (2) and 15 mol% and 60 mol% of tetracarboxylic dianhydrides having an alicyclic structure. The ultraviolet absorber is selected from one or more compounds grouped together with benzotriazole compounds and triazine compounds.

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

3. The hard coating film according to claim 1, wherein, The content of the ultraviolet absorber is 1-3% by weight.

4. The hard coating film according to claim 1, wherein, The concentration C of the ultraviolet absorber on the first main surface side of the polyimide film A The concentration C of the ultraviolet absorber on the second principal surface side B Less than 0.3 times.

5. The hard coating film according to claim 1, wherein, The thickness of the polyimide film is 5~100μm.

6. The hard coating film according to claim 1, wherein, The thickness of the polyimide film is 40~85μm.

7. The hard coating film according to claim 1, wherein, The thickness of the hard coating is 0.5~100μm.

8. The hard coating film according to claim 1, wherein, The thickness of the hard coating is 5~80μm.

9. The hard coating film according to claim 1, wherein, The hard coating composition used to form the hard coating contains a polyfunctional (meth)acrylate or a polysiloxane compound having an epoxy group.

10. A method for manufacturing a hard coating film, comprising the following steps: A solution containing polyimide resin, ultraviolet absorber, and organic solvent is applied to the substrate. The process of heating and drying the solution on the substrate to remove the organic solvent, and then peeling it off from the substrate to obtain a polyimide film, and... The process of forming a hard coating on the second main surface of the polyimide film, using the peeled surface peeled from the substrate as the second main surface.

11. The method for manufacturing a hard coating film according to claim 10, wherein, The organic solvent contains dichloromethane.

12. The method for manufacturing a hard coating film according to claim 10 or 11, wherein, After the solution is applied to the substrate, the heating is performed at a temperature above the boiling point of the organic solvent for no more than 20 minutes.

13. The method for manufacturing a hard coating film according to claim 10 or 11, wherein, The heating temperature is below 200°C.

14. The method for manufacturing a hard coating film according to claim 10 or 11, wherein, The heating temperature is below 180°C.

15. An image display device, wherein, The image display panel has a hard coating film as described in any one of claims 1 to 9 on its recognition side surface. The hard coating is configured such that the first main surface of the polyimide film faces the image display panel.

16. The image display device according to claim 15, which is flexible.

Images