Laminate and display

Abstract

A laminate (11) is provided with a functional layer (3) on the main surface of a transparent film (1). The transparent film contains a polyimide resin and a resin other than the polyimide resin (for example, an acrylic resin). The functional layer contains a bluing agent. The functional layer may be a hard coating layer. The laminate has a total light transmittance of 90.3% or more and a yellowness of-1.0 to 1.0 inclusive. The laminate according to the present invention has high total light transmittance, low yellowness, and little coloration, and thus can be suitably used as a material for a display.

Description

Technical Field

[0001] The present invention relates to a laminate having a functional layer on a transparent film, and a display including the laminate. Background Art

[0002] A film containing a transparent polyimide has excellent mechanical strength and is expected to be used as a cover window for a flexible display. However, since the absorption bands of the transparent polyimide overlap in the short wavelength region of visible light, there are problems as follows: it is colored yellow, has a high yellowness degree, a low transmittance, and lower transparency than highly transparent resins such as acrylic resins.

[0003] Patent Document 1 proposes adding a blueing agent to a polyimide film or a hue adjustment layer provided thereon in order to reduce the coloring of the transparent polyimide film.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-123319 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Since the blueing agent has relatively large absorption in the long wavelength region of visible light, if the blueing agent is compounded in a film containing a polyimide-based resin or a functional layer such as a hue adjustment layer provided thereon, the hue tends to be neutralized and the yellowness degree decreases. However, if the yellowness degree of the film is reduced only by adding the blueing agent, the light transmittance decreases due to the light absorption of the blueing agent. That is, there is a trade-off relationship between the decrease in yellowness degree (reduction in coloring) and the increase in transmittance.

[0009] An object of the present invention is to provide a laminate having a functional layer on a film containing a polyimide-based resin, having a high total light transmittance and less coloring.

[0010] Solutions to the Problems

[0011] The present invention relates to a laminate having a functional layer containing a blueing agent on a main surface of a transparent film. The total light transmittance of the laminate is 90.3% or more, and the yellowness degree is -1.0 or more and 1.0 or less. As an example of the blueing agent contained in the functional layer, an anthraquinone-based dye can be mentioned.

[0012] The transparent film contains a polyimide-based resin and a resin other than the polyimide-based resin. The transparent film may contain an ultraviolet absorber.

[0013] The polyimide-based resin is polyimide or polyamideimide and contains a structure derived from a tetracarboxylic dianhydride and a structure derived from a diamine. As the resin other than the polyimide-based resin, an acrylic resin is preferred, and among them, a resin mainly composed of methyl methacrylate is preferred.

[0014] For the polyimide-based resin, preferably, as the tetracarboxylic dianhydride, it contains an alicyclic tetracarboxylic dianhydride and a fluorine-containing aromatic tetracarboxylic dianhydride, and as the diamine, it contains a fluorine-containing diamine.

[0015] The total light transmittance of the transparent film is 90.3% or more, and the yellowness can be greater than 0 and 3.0 or less. The refractive index of the transparent film can be 1.60 or less. The transparent film can be a stretched film and can have refractive index anisotropy. The thickness of the transparent film can be 20 μm or more.

[0016] As an example of the functional layer provided on the transparent film, a hard coat containing a curable resin can be cited. As examples of the curable resin material for the hard coat, an acrylic-based hard coat material and a siloxane-based hard coat material can be cited. The content of the bluing agent in the hard coat can be 20 ppm or more.

[0017] Effects of the Invention

[0018] The above laminate has a high total light transmittance, a small yellowness, and little coloring, and thus can be suitably used as a material for a display. Description of the Drawings

[0019] Figure 1 It is a cross-sectional view of a laminate of an embodiment. Detailed Embodiments

[0020] Figure 1 It is a cross-sectional view of a laminate of an embodiment of the present invention. The laminate 11 has a functional layer 3 on the transparent film 1. The total light transmittance of the laminate 11 having the functional layer 3 on the transparent film 1 is 90.3% or more, and the yellowness is -1.0 or more and 1.0 or less.

[0021] The functional layer 3 contains a bluing agent and has a function as a hue adjustment layer. The functional layer 3 can be a layer that also imparts various functions to the transparent film 1 on the basis of the function as a hue adjustment layer, and can be a hard coat, an ultraviolet absorption layer, an adhesive layer, a refractive index adjustment layer, an easy adhesion layer, etc. The laminate can have a plurality of functional layers on the transparent film. The laminate can have a functional layer only on one surface of the transparent film, or can have functional layers on both surfaces of the transparent film.

[0022] [Transparent Film]

[0023] The transparent film 1 is a resin film containing at least one polyimide resin selected from the group consisting of polyimide and polyamideimide and a resin other than the polyimide resin (hereinafter sometimes referred to as "other resin").

[0024] <Polyimide resin>

[0025] Polyimide is obtained by dehydrating and cyclizing polyamic acid, and the polyamic acid is obtained by the reaction of tetracarboxylic dianhydride (hereinafter sometimes referred to as "acid dianhydride") and diamine. Polyamideimide is obtained by replacing a part of the tetracarboxylic dianhydride of polyimide with a dicarboxylic acid derivative such as dicarboxylic acid dichloride. As the polyimide resin, polyimide and polyamideimide can be used in combination. From the viewpoint of compatibility with other resins, etc., polyimide is sometimes preferred as the polyimide resin.

[0026] (Tetracarboxylic dianhydride)

[0027] For the polyimide resin used in the present embodiment, preferably, as the acid dianhydride component, it contains an alicyclic tetracarboxylic dianhydride. By making the acid dianhydride component have an alicyclic structure, there is a tendency for the compatibility of the polyimide resin with other resins to be improved. The alicyclic tetracarboxylic dianhydride only needs to have at least one alicyclic structure, and it may have both an alicyclic ring and an aromatic ring in one molecule. The alicyclic ring can be a polycyclic ring or have a spiro ring structure.

[0028] Examples of the alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride, meso-butanetetracarboxylic 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'-bicyclonorbornane-5,5',6,6'-tetracarboxylic dianhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic 1,4:2,3-dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, cyclohexane-1,4-diylbis(methylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 5,5'-[cyclohexylidenebis(4,1-phenyleneoxy)]bis-1,3-isobenzofurandione, 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, 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-biphenylene[4a,4bc:8a,8b-c']difuran-1,3,8,10-tetrone, ethylene glycol bis(trimellitic anhydride) ester, decahydro[2]benzopyrano[6,5,4,-def][2]benzopyran-1,3,6,8-tetrone, etc. Among the alicyclic tetracarboxylic dianhydrides, from the viewpoints of the transparency and mechanical strength of the polyamide-based resin, 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, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride is particularly preferred.

[0029] From the viewpoint of improving the compatibility of the polyimide resin with other resins, based on 100 mol% of the total amount of the acid dianhydride component, the content of the alicyclic tetracarboxylic dianhydride is preferably 1 mol% or more, more preferably 3 mol% or more, still more preferably 5 mol% or more, and may also be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 12 mol% or more, or 15 mol% or more. The amount of the alicyclic tetracarboxylic dianhydride required for compatibility with other resins may vary depending on the type of other resins, the type of the alicyclic tetracarboxylic dianhydride, etc. For example, when the alicyclic tetracarboxylic dianhydride is 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), based on 100 mol% of the total amount of the acid dianhydride component, the content of CBDA is preferably 6 mol% or more, more preferably 8 mol% or more, still more preferably 10 mol% or more.

[0030] From the viewpoint of ensuring the solubility of the polyimide resin in an organic solvent, based on 100 mol% of the total amount of the acid dianhydride component, the content of the alicyclic tetracarboxylic dianhydride is preferably 80 mol% or less, more preferably 78 mol% or less, still more preferably 76 mol% or less, and may also be 74 mol% or less, 72 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, or 50 mol% or less. In order to make the polyimide resin soluble in a low-boiling halogen-based solvent such as dichloromethane, the content of the alicyclic tetracarboxylic dianhydride is preferably 45 mol% or less, more preferably 40 mol% or less, and may also be 35 mol% or less.

[0031] From the viewpoint of making the polyimide resin soluble in an organic solvent, as the acid dianhydride component, it is preferable to contain a fluorine-containing aromatic tetracarboxylic dianhydride and / or a bis(trimellitic anhydride) ester in addition to the alicyclic tetracarboxylic dianhydride.

[0032] Examples of the fluorine-containing aromatic tetracarboxylic dianhydride include 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride, etc.

[0033] Examples of the bis(trimellitic anhydride) ester include bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2’,3,3’,5,5’-hexamethylbiphenyl-4,4’-diyl ester (abbreviation: TAHMBP), etc.

[0034] From the viewpoint of making the polyimide-based resin soluble in an organic solvent, the total content of the fluorine-containing aromatic tetracarboxylic dianhydride and the bis(trimellitic anhydride) ester is preferably 15 mol% or more, more preferably 20 mol% or more, still more preferably 25 mol% or more, and may also be 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more, based on 100 mol% of the total amount of the acid dianhydride component. The total content of the fluorine-containing aromatic tetracarboxylic dianhydride and the bis(trimellitic anhydride) ester is preferably 99 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less, and may also be 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less, based on 100 mol% of the total amount of the acid dianhydride component.

[0035] From the viewpoint of obtaining a polyimide-based resin having both solubility in an organic solvent and compatibility with other resins, the total content of the alicyclic tetracarboxylic dianhydride, the fluorine-containing aromatic tetracarboxylic dianhydride, and the bis(trimellitic anhydride) ester is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 65 mol% or more, and may also be 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more, based on 100 mol% of the total amount of the acid dianhydride component.

[0036] In the polyimide resin, as the acid dianhydride component, an acid dianhydride other than an alicyclic tetracarboxylic dianhydride, a fluorine-containing aromatic tetracarboxylic dianhydride, and a bis(trimellitic anhydride) ester may be included. Examples of the acid dianhydride other than the above include ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, 3,3’,4,4’-benzophenonetetracarboxylic dianhydride, 2,2’,3,3’-benzophenonetetracarboxylic dianhydride, 2,2’,3,3’-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3’,4,4’-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-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, 9,9-bis(3,4-dicarboxyphenyl)fluorene 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-[4-(3,4-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-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid)-1,4-phenylene ester.

[0037] (dicarboxylic acid)

[0038] As mentioned above, the polyimide resin may also be a polyamide-imide in which a portion of the tetracarboxylic dianhydride component is replaced with a dicarboxylic acid derivative. Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bis(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-furandicarboxylic acid.

[0039] From the perspective of solubility of polyamide-imide and compatibility with other resins, aromatic dicarboxylic acids and alicyclic dicarboxylic acids are preferred as dicarboxylic acids, with aromatic dicarboxylic acids being particularly preferred. Among aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred. Among these, terephthalic acid and isophthalic acid are preferred, with terephthalic acid being particularly preferred.

[0040] As the dicarboxylic acid derivative used as the raw material monomer of the polyamideimide, dicarboxylic acid dichloride, dicarboxylic acid ester, dicarboxylic acid anhydride and the like can be used. Among them, dicarboxylic acid dichloride is preferred due to its high reactivity.

[0041] From the perspective of the solubility of the polyamide-imide and its compatibility with other resins, the proportion of the dicarboxylic acid derivative relative to the total of the tetracarboxylic dianhydride and the dicarboxylic acid derivative is preferably 40 mol% or less, more preferably 35 mol% or less, and even more preferably 30 mol% or less. The polyimide-based resin may be a polyimide having a dicarboxylic acid derivative ratio of 0 (i.e., containing no structure derived from a dicarboxylic acid derivative).

[0042] (Diamine)

[0043] The diamine component of the polyimide resin used in this embodiment is not particularly limited. From the perspective of solubility, the diamine of the polyimide resin preferably has one or more selected from the group consisting of a fluoro group, a trifluoromethyl group, a sulfone group, a fluorene structure, and an alicyclic structure. Among them, from the perspective of taking into account both the solubility and transparency of the polyimide resin, the polyimide resin preferably contains a fluorine-containing diamine such as a fluoroalkyl-substituted benzidine as the diamine component.

[0044] Examples of the fluoroalkyl-substituted benzidine as the diamine containing fluorine include 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, 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, 2,2',6,6'-tetrakis(trifluoromethyl)benzidine, etc.

[0045] Among them, fluoroalkyl-substituted benzidine having a fluoroalkyl group at the 2-position of biphenyl is preferred, and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB") is particularly preferred. By having fluoroalkyl groups at the 2-position and 2'-position of biphenyl, in addition to the decrease in π-electron density caused by the electron-withdrawing property of the fluoroalkyl group, the bond between the two benzene rings of biphenyl is twisted due to the steric hindrance of the fluoroalkyl group, resulting in a decrease in the planarity of π-conjugation. Therefore, the absorption end wavelength undergoes a short-wavelength shift, and thus the coloring of the polyimide-based resin can be reduced.

[0046] Relative to 100 mol% of the total amount of the diamine component, the content of the fluoroalkyl-substituted benzidine is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 70 mol% or more, and may also be 80 mol% or more, 85 mol% or more, or 90 mol% or more. By increasing the content of the fluoroalkyl-substituted benzidine, the coloring of the film can be suppressed, and the mechanical strengths such as pencil hardness and elastic modulus tend to increase.

[0047] For polyimide-based resins, as the diamine component, diamines other than fluoroalkyl-substituted benzidine can be included. Examples of diamines other than fluoroalkyl-substituted benzidine 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-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 1,1-bis(3-aminophenyl)-1-phenylethane, 1,1-bis(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(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-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'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 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-(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxy)ethyl]ether, bis[2-(3-aminopropoxy)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, 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-tetrakis(trifluoromethyl)benzene, 2,2'-Dimethylbenzidine, 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. For example, by using diamino diphenyl sulfone as a diamine on the basis of fluoroalkyl-substituted benzidine, the solubility and transparency of the polyimide resin in a solvent are sometimes improved. Among diamino diphenyl sulfone, 3,3'-diamino diphenyl sulfone (3,3'-DDS) and 4,4'-diamino diphenyl sulfone (4,4'-DDS) are preferred. 3,3'-DDS and 4,4'-DDS can be used in combination. The content of diamino diphenyl sulfone can be 1 to 40 mol%, 3 to 30 mol%, or 5 to 25 mol% relative to 100 mol% of the total amount of diamines.,

[0048] (Preparation of Polyimide Resin)

[0049] By reacting an acid dianhydride with a diamine, a polyamic acid as a polyimide precursor is obtained, and a polyimide is obtained by dehydration cyclization (imidization) of the polyamic acid. The method for preparing the polyamic acid is not particularly limited, and all known methods can be applied. For example, a diamine and a tetracarboxylic dianhydride are dissolved in an organic solvent in a substantially equimolar amount (molar ratio of 90:100 to 110:100), and stirred to obtain a polyamic acid solution.

[0050] In the case of preparing a polyamideimide, in addition to a diamine and a tetracarboxylic dianhydride, a dicarboxylic acid or its derivative (dicarboxylic acid dichloride, dicarboxylic acid anhydride, etc.) can also be used as a monomer. In this case, the amounts of the respective monomers are adjusted so that the total of the tetracarboxylic dianhydride and the dicarboxylic acid or its derivative and the diamine become a substantially equimolar amount.

[0051] As described above, by adjusting the composition of the polyimide resin, that is, the types and ratios of the acid dianhydride and the diamine, the polyimide resin has transparency and solubility in an organic solvent, and exhibits compatibility with other resins.

[0052] The concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight. In the case of the concentration in this range, the polyamic acid obtained by polymerization has an appropriate molecular weight, and the polyamic acid solution has an appropriate viscosity.

[0053] When polymerizing the polyamic acid, in order to inhibit the ring-opening of the acid dianhydride, it is preferable to add the acid dianhydride to the diamine. When adding a plurality of diamines and a plurality of acid dianhydrides, they can be added all at once or in multiple times. By adjusting the addition order of the monomers, the physical properties of the polyimide resin can also be inhibited.

[0054] The organic solvent used in the polymerization of the polyamic acid is not particularly limited as long as it does not react with the diamine and the acid dianhydride and can dissolve the polyamic acid. Examples of the organic solvent include urea solvents such as methylurea and N,N-dimethylethylurea, sulfoxide or sulfone solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone, amide solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), γ-butyrolactone, and hexamethylphosphoric triamide, halogenated alkane 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. Usually, these solvents can be used alone or in combination of two or more as appropriate according to needs. From the viewpoints of the solubility and polymerization reactivity of the polyamic acid, it is preferable to use DMAc, DMF, NMP, etc.

[0055] The polyimide resin is obtained by the dehydration cyclization of the polyamic acid. As a method for preparing the polyimide resin from the polyamic acid solution, a method of adding a dehydrating agent, an imidization catalyst, etc. to the polyamic acid solution and performing imidization in the solution can be cited. In order to promote the progress of imidization, the polyamic acid solution can be heated. The solution containing the polyimide resin generated by the imidization of the polyamic acid is mixed with a poor solvent, whereby the polyimide resin precipitates in the form of a solid substance. By separating the polyimide resin in the form of a solid substance, impurities generated during the synthesis of the polyamic acid, residual dehydrating agent, imidization catalyst, etc. can be washed and removed with the poor solvent, and coloring and an increase in yellowness of the polyimide resin can be prevented. In addition, by separating the polyimide resin in the form of a solid substance, solvents suitable for film formation such as low-boiling solvents can be applied when preparing a solution for making a film.

[0056] The molecular weight of the polyimide-based resin (weight-average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC)) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and still more preferably 40,000 to 200,000. When the molecular weight is too small, the strength of the film may be insufficient. When the molecular weight is too large, the compatibility with other resins may be poor.

[0057] The polyimide-based resin is preferably soluble in low-boiling solvents such as ketone solvents and halogenated alkane solvents. The polyimide-based resin showing solubility in a solvent means that it dissolves at a concentration of 5% by weight or more. In one embodiment, the polyimide-based resin shows solubility in dichloromethane. Dichloromethane has a low boiling point and it is easy to remove the residual solvent during film production. Therefore, by using a polyimide-based resin soluble in dichloromethane, an improvement in the productivity of the film can be expected.

[0058] From the viewpoints of the thermal stability and light stability of the transparent film, the polyimide-based resin preferably has low reactivity. The acid value of the polyimide-based resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and still more preferably 0.2 mmol / g or less. The acid value of the polyimide can be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. From the viewpoint of reducing the acid value, the polyimide-based resin preferably has a high imidization rate. By making the acid value small, the stability of the polyimide-based resin can be improved, and the compatibility with other resins tends to be improved.

[0059] <Other resins>

[0060] As described above, the transparent film 1 contains a resin other than the polyimide-based resin in addition to the polyimide-based resin. As the resin other than the polyimide-based resin ("other resin"), there is no particular limitation as long as it can be mixed with the polyimide-based resin to form a transparent film, and examples thereof include resins compatible with the polyimide-based resin, resins forming microphase separation structures such as sea-island structures, columnar structures, and layered structures. Among them, the other resin is preferably compatible with the polyimide-based resin. When the polyimide-based resin is compatible with the other resin, regardless of the film processing conditions, the film tends to have high transparency and excellent mechanical properties such as elastic modulus and pencil hardness.

[0061] Examples of the resin showing compatibility with the polyimide-based resin include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, polyether resins, cellulose resins, silicone resins, cyclic olefin resins, etc. A plurality of these resins can be used.

[0062] From the aspect of high compatibility with polyimide-based resins, as other resins, acrylic resins, polycarbonate resins, and polyester resins having a fluorene structure are preferred. Among them, acrylic resins are particularly preferred from the aspects of high compatibility with polyimide-based resins, low refractive index, and easy formation of high-hardness films.

[0063] Examples of acrylic resins include poly(meth)acrylates such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylate copolymers, methyl methacrylate-acrylate-(meth)acrylic acid copolymers, and (meth)acrylate-styrene copolymers. The acrylic resin may be modified to introduce a succinimide structural unit or a lactone ring structural unit.

[0064] From the viewpoints of transparency, compatibility with polyimide-based resins, and mechanical strength, the acrylic resin preferably has methyl methacrylate as the main structural unit. The amount of methyl methacrylate in the acrylic resin relative to the total amount of monomer components is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The acrylic resin may be a homopolymer of methyl methacrylate. In addition, the acrylic resin may also be one obtained by introducing a succinimide structure or a lactone ring structure into an acrylic polymer in which the content of methyl methacrylate is in the above range.

[0065] From the viewpoint of the heat resistance of the transparent film, the glass transition temperature of the acrylic resin is preferably 100°C or higher, more preferably 110°C or higher, and may also be 115°C or higher or 120°C or higher.

[0066] From the viewpoints of solubility in organic solvents, compatibility with polyimide-based resins, and film strength, the weight average molecular weight (polystyrene conversion) of the acrylic resin is preferably 5,000 to 500,000, more preferably 10,000 to 300,000, and further preferably 15,000 to 200,000.

[0067] From the viewpoints of the thermal stability and light stability of the film, it is preferable that the acrylic resin has a low content of reactive functional groups such as ethylenically unsaturated groups and carboxyl groups. The iodine value of the acrylic resin is preferably 10.16 g / 100 g (0.4 mmol / g) or less, more preferably 7.62 g / 100 g (0.3 mmol / g) or less, and still more preferably 5.08 g / 100 g (0.2 mmol / g) or less. The iodine value of the acrylic resin can be 2.54 g / 100 g (0.1 mmol / g) or less or 1.27 g / 100 g (0.05 mmol / g) or less. The acid value of the acrylic resin is preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, and still more preferably 0.2 mmol / g or less. The acid value of the acrylic resin can be 0.1 mmol / g or less, 0.05 mmol / g or less, or 0.03 mmol / g or less. By making the acid value small, the stability of the acrylic resin tends to increase, and the compatibility with the polyimide resin also tends to increase.

[0068] <Composition of the transparent film>

[0069] The ratio of the polyimide resin to other resins in the transparent film is not particularly limited. The mixing ratio (weight ratio) of the polyimide resin to other resins can be 98:2 to 2:98, 95:5 to 10:90, 90:10 to 15:85, or 65:35 to 50:50. The higher the ratio of the polyimide resin, the higher the elastic modulus and pencil hardness of the film tend to be, and the mechanical strength is excellent. The higher the ratio of other resins, the less coloring of the film, the higher the total light transmittance, the smaller the yellowness index (YI), and the higher the transparency tend to be.

[0070] In order to fully exhibit the effect of improving transparency brought about by the mixing of the polyimide resin and other resins, the ratio of other resins is preferably 10 to 90% by weight, more preferably 15 to 85% by weight, still more preferably 20 to 80% by weight, and can be 30 to 70% by weight, 35 to 65% by weight, or 40 to 60% by weight.

[0071] In addition to the polyimide resin and other resins, the transparent film may further contain organic or inorganic low-molecular compounds, etc. As additives, it may contain ultraviolet absorbers for the purpose of imparting light resistance, dyes, pigments, etc. (such as bluing agents) for the purpose of adjusting the hue. The transparent film may contain flame retardants, stabilizers, crosslinking agents, surfactants, leveling agents, plasticizers, fine particles, etc. as additives.

[0072] By including an ultraviolet absorber in the transparent film, there is a tendency to improve light resistance and suppress resin deterioration caused by ultraviolet rays. Examples of the ultraviolet absorber include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, hydroxybenzoate-based ultraviolet absorbers, etc. Among them, from the aspect of obtaining good light resistance, triazine-based ultraviolet absorbers or benzotriazole-based ultraviolet absorbers are preferred. The ultraviolet absorber can be used alone or in combination of two or more kinds.

[0073] The content of the ultraviolet absorber in the transparent film is preferably 0.1 part by weight or more, more preferably 1 part by weight or more, further preferably 3 part by weight or more, and can also be 4 part by weight or more or 5 part by weight or more, based on 100 parts by weight in total of the resin components. The more the content of the ultraviolet absorber, the more the light resistance tends to be improved. On the other hand, there is a tendency for YI to increase as the content of the ultraviolet absorber increases. From the viewpoint of suppressing coloring, the content of the ultraviolet absorber is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, further preferably 7 parts by weight or less, and can also be 6 parts by weight or less.

[0074] For the purpose of improving anti-blocking property, refractive index adjustment, etc., the transparent film can include organic fine particles such as polystyrene and crosslinked acrylic resins, and inorganic fine particles such as silica and layered silicates. However, if the fine particles are compounded, it will cause a decrease in the transmittance of the film and an increase in haze. In particular, although silicon oxides such as silica are useful for reducing the refractive index of the film, they are likely to have poor dispersion in the resin matrix and are likely to cause a decrease in transparency, mechanical strength, and flexural resistance. Therefore, the content of the silicon oxide is preferably 5 parts by weight or less, preferably 1 part by weight or less, further preferably 0.5 part by weight or less, can be 0.1 part by weight or less, and can also be 0, based on 100 parts by weight in total of the resin components.

[0075] <Manufacture of the transparent film>

[0076] The forming method of the transparent film is not particularly limited, and either a melting method or a solution method can be used. From the viewpoint of producing a film with excellent transparency and uniformity, the solution method is preferred. In the solution method, a film is obtained by coating a solution containing the above-mentioned polyimide-based resin and other resins on a support and drying and removing the solvent.

[0077] The solvent is not particularly limited as long as it can dissolve both the polyimide resin and other resins. Examples of the solvent include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methyl cyclohexanone; and halogenated alkane solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and dichloromethane. Among them, from the aspects of excellent solubility of polyimide resins, etc., low boiling point, and easy removal of residual solvents during film production, ketone solvents and halogenated alkane solvents are preferred.

[0078] As a method of coating the resin solution on the support, known methods using a bar coater, comma coater, etc. can be applied. As the support, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, etc. can be used.

[0079] Heating is preferably carried out during drying of the solvent. The heating temperature is not particularly limited as long as it can remove the solvent and can suppress coloring of the obtained film, and is suitably set at room temperature to about 250 °C, preferably 50 °C to 220 °C. The heating temperature can also be increased stepwise. In order to improve the solvent removal efficiency, after drying to a certain extent, the resin film can be peeled off from the support and dried. Drying can be carried out in an air atmosphere or a nitrogen atmosphere. In order to promote the removal of the solvent, heating can be carried out under reduced pressure.

[0080] The film obtained by coating a solution containing a resin, a solvent, and an ultraviolet absorber on a support and drying and removing the solvent has the following tendency: the ultraviolet absorber is preferentially present on the surface in contact with the support (support surface) during coating / drying. When the transparent film has a distribution in the content (concentration) of the ultraviolet absorber in the thickness direction, if ultraviolet rays are irradiated from the surface with a relatively high concentration of the ultraviolet absorber, more ultraviolet rays are absorbed near the irradiated surface. Therefore, the amount of ultraviolet rays reaching the inside in the thickness direction of the film and the surface on the opposite side of the irradiated surface is small, and the deterioration of the resin caused by ultraviolet rays can be suppressed. Therefore, when the transparent film has a concentration distribution of the ultraviolet absorber in the thickness direction, it has the following tendency: the light resistance when irradiated with ultraviolet rays from the surface with a relatively high concentration of the ultraviolet absorber (the support side surface during coating / drying) is better than the light resistance when irradiated with ultraviolet rays from the surface with a relatively low concentration of the ultraviolet absorber (the air side surface during coating / drying) (ΔYI described later becomes smaller).

[0081] For the purpose of improving the mechanical strength of the film, etc., stretching can be performed in one direction or multiple directions. When the film is stretched, the polymer chains are oriented in the stretching direction, so there is a tendency for the strength in the in-plane direction of the film to increase and the occurrence of film breakage or cracks to be suppressed.

[0082] For a film of an acrylic resin, which is an example of another resin (a resin other than a polyimide-based resin), the toughness is sometimes low, but by using a compatible system of a polyimide-based resin and an acrylic resin, the strength of the film sometimes increases. In addition, when a film of a compatible system of a polyimide-based resin and an acrylic resin is stretched, there is a tendency for the tensile modulus in the stretching direction to increase and the flexural resistance to increase accordingly.

[0083] For example, a film used as a cover window or a substrate material of a foldable display device (foldable display) is repeatedly bent along the bending axis at the same position, so high mechanical strength in the direction orthogonal to the bending axis is required. Therefore, by arranging the stretching direction of the film to be orthogonal to the bending axis, a device can be provided that is less likely to cause film breakage or cracks at the bending part even when repeatedly bent and has high bending resistance.

[0084] The stretching conditions of the film are not particularly limited. For example, the stretching temperature is about ±40°C from the glass transition temperature of the film, and can be about 120 - 300°C, 150 - 250°C, or 180 - 230°C. The stretching ratio is about 1 - 200%, and can be 5 - 150%, 10 - 120%, 20 - 100%. The larger the stretching ratio, the greater the tendency for the tensile modulus in the stretching direction to increase. On the other hand, when the stretching ratio is too large, there is a tendency for the mechanical strength in the direction orthogonal to the stretching direction to decrease, and sometimes the processability of the film decreases.

[0085] From the viewpoint of improving the strength in any in-plane direction, the film can be biaxially stretched. The biaxial stretching can be simultaneous biaxial stretching or sequential biaxial stretching. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the direction orthogonal to it can be the same or different. If a difference is set in the stretching ratios, there is a tendency for the mechanical strength in the direction with a larger stretching ratio to become relatively larger. When a biaxially stretched film with anisotropic stretching ratios is used for a foldable device, it is preferably arranged such that the direction with a larger stretching ratio is orthogonal to the bending axis.

[0086] The thickness of the transparent film is not particularly limited and can be appropriately set according to the use. The thickness of the transparent film is, for example, 5 to 300 μm. From the viewpoint of achieving both self-supporting property and flexibility and producing a highly transparent film, the thickness of the transparent film is preferably 20 to 100 μm, and can also be 25 to 80 μm, 30 to 70 μm, or 35 to 65 μm. The thickness of the film for use as a cover window of a display is preferably 20 μm or more. When the film is stretched, the thickness after stretching is preferably in the above range.

[0087] The transparent film preferably has a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic viscoelasticity measurement (DMA). When the polyimide resin contained in the transparent film shows compatibility with other resins, a single glass transition temperature is shown.

[0088] The haze of the transparent film is preferably 1% or less, more preferably 0.7% or less, and further preferably 0.5% or less. As described above, the acrylic resin shows high compatibility with the polyimide resin. Therefore, the film containing the polyimide resin and the acrylic resin as other resins has low haze and high transparency.

[0089] The total light transmittance of the transparent film is preferably 90.3% or more, more preferably 90.5% or more, and can be 91.0% or more or 91.5% or more. The higher the total light transmittance, the higher the white brightness of the display and the more excellent the visual recognition tend to be.

[0090] The yellowness index (YI) of the transparent film is preferably 3.0 or less, more preferably 2.0 or less, and can be 1.0 or less. The YI of the film containing the polyimide resin is usually greater than 0. The smaller the YI, the less yellow coloring and the more excellent the visual recognition tend to be.

[0091] As described above, by using a mixed resin system of a polyimide resin and other resins, compared with the case of using only the polyimide resin, light absorption (especially light absorption in the short wavelength region of visible light) is reduced, so a transparent film with high total light transmittance and small YI can be obtained. In addition, the mixed resin system of the polyimide resin and other resins has higher light resistance than the case of the polyimide resin alone, so the blending amount of the ultraviolet absorber can be reduced. The smaller the content of the ultraviolet absorber, the smaller the light absorption in the short wavelength region of visible light and the smaller the YI of the transparent film tend to be.

[0092] Preferably, for the transparent film, the increase amount ΔYI of YI when irradiated with ultraviolet rays for 48 hours under the conditions of a carbon arc light source, an irradiation intensity of 500 W / m 2 , and a black panel temperature of 63 °C is 5.0 or less. The ΔYI of the transparent film is more preferably 4.0 or less, further preferably 2.0 or less, and particularly preferably 1.0 or less.

[0093] The increase in YI caused by ultraviolet irradiation is mainly due to the photo-deterioration of the polyimide-based resin. Therefore, in a mixed resin system of a polyimide-based resin and other resins, the smaller the ratio of the polyimide-based resin, the smaller the YI, the more excellent the transparency, and the smaller the ΔYI and the more excellent the light resistance. When the transparent film contains an ultraviolet absorber, since the ultraviolet absorber absorbs ultraviolet rays, the amount of ultraviolet rays absorbed by the polyimide-based resin decreases and ΔYI tends to become smaller.

[0094] As described above, the more the content of the ultraviolet absorber contained in the transparent film, the more the light resistance is improved and ΔYI becomes smaller. As the content of the ultraviolet absorber increases, the YI (YI0, the yellowness index before ultraviolet irradiation) of the transparent film tends to increase. When the transparent film has a concentration distribution of the ultraviolet absorber in the thickness direction, ΔYI when irradiating ultraviolet rays from the side with a relatively high concentration of the ultraviolet absorber is smaller than ΔYI when irradiating ultraviolet rays from the side with a relatively low concentration of the ultraviolet absorber.

[0095] The refractive index of the transparent film is preferably 1.60 or less. More preferably, the refractive index of the transparent film is 1.58 or less, further preferably 1.56 or less, particularly preferably 1.54 or less, and may be 1.52 or less. The refractive index of a film containing only a polyimide-based resin as a resin component is usually higher than 1.60, and there is a lot of light reflection (high reflectance) due to the refractive index difference at the interface with air or other members, so the light transmittance is small. Compared with the case of a polyimide-based resin alone, the mixed resin system of a polyimide-based resin and other resins has a lower refractive index, so the light reflection at the interface is reduced and the total light transmittance becomes higher. In particular, the refractive index of an acrylic resin is low, so when an acrylic resin is used as the other resin, the transparent film tends to have a lower refractive index and a higher total light transmittance. By adopting a mixed resin system of a polyimide-based resin and a low-refractive-index resin such as an acrylic resin, the refractive index of the transparent film can be adjusted to 1.60 or less (or at a low content) without using low-refractive-index particles such as silica, and the total light transmittance can be improved.

[0096] The refractive index of the stretched film tends to increase in the stretching direction (the orientation direction of the polymer chains). Therefore, when the transparent film is a stretched film, it may have refractive index anisotropy in the plane. The refractive index difference in the plane of the transparent film (the difference between the maximum refractive index and the minimum refractive index in the plane) can be 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. When the transparent film has refractive index anisotropy, the maximum refractive index in the plane (usually the refractive index in the stretching direction) is preferably in the above range.

[0097] The tensile modulus of the transparent film is preferably 3.0 GPa or more, more preferably 3.5 GPa or more, further preferably 4.5 GPa or more, and may also be 5.0 GPa or more, 5.5 GPa or more, or 6.0 GPa or more. The larger the tensile modulus, the more excellent the mechanical strength tends to be. The tensile modulus of the transparent film may have anisotropy in the plane. When the transparent film is a stretched film, the tensile modulus in the stretching direction tends to be larger than that in the direction orthogonal to the stretching direction. When the transparent film is a biaxially stretched film or a film uniaxially stretched through a fixed end, the tensile modulus in all in-plane directions may be larger than before stretching. When the transparent film has in-plane anisotropy of the tensile modulus, the maximum in-plane tensile modulus (usually the tensile modulus in the stretching direction) is preferably in the above range.

[0098] [Functional layer]

[0099] <Blueing agent>

[0100] The functional layer 3 provided on the transparent film 1 contains a blueing agent. The blueing agent is a pigment (dye or pigment) that absorbs light in the long wavelength region of visible light (such as red, orange, yellow light) to adjust the hue.

[0101] From the viewpoints of processability of the functional layer, etc., the blueing agent preferably has high heat resistance. The 1% weight loss temperature of the blueing agent is preferably 200 °C or more, more preferably 220 °C or more, and further preferably 240 °C or more.

[0102] Examples of the blueing agent include inorganic pigments such as cobalt blue and Prussian blue; anthraquinone-based compounds having an anthraquinone ring structure; phthalocyanine-based compounds, indigo-based compounds, methylene-based compounds, etc. From the viewpoints of solubility and dispersibility in resins and solvents, as the blueing agent, anthraquinone-based, phthalocyanine-based compounds, and indigo-based compounds are preferred, and among them, anthraquinone-based compounds are particularly preferred from the viewpoints of heat resistance and light resistance. Examples of commercially available products of anthraquinone-based blueing agents include "Plast Blue" manufactured by Uehara Chemical Industry Co., Ltd. The blueing agent may be used alone or in combination of two or more.

[0103] As described above, polyimide has light absorption in the short wavelength region of visible light, so the film containing a polyimide-based resin is slightly colored yellow, and usually YI is greater than 0. By providing the functional layer 3 containing a blueing agent on the transparent film 1, the light absorption in the long wavelength region of visible light increases, so the YI of the transmitted light and the reflected light of the laminate 11 decreases, and the hue is neutralized.

[0104] On the other hand, since the bluing agent absorbs light in the long wavelength region of visible light, the total light transmittance tends to decrease as the amount of the bluing agent increases. As described above, the transparent film 1 is a mixed resin film of a polyimide resin and other resins, and has less coloring (smaller YI) compared to a film of a polyimide resin alone. Therefore, the amount of the bluing agent required to neutralize the hue (make YI close to 0) is small, and a decrease in the total light transmittance can be suppressed, improving the visual recognition of the display.

[0105] The bluing agent can also be added to the transparent film. In the manufacturing process of the film containing a polyimide resin, heating at a temperature higher than the heat resistance temperature of the bluing agent is sometimes required during firing (imidization of polyimide), drying of the solvent, etc. In addition, depending on the resin composition and the type of solvent, the solubility of the bluing agent and its compatibility / dispersibility with the resin may be insufficient, so the application of the bluing agent in the transparent film is sometimes difficult. By making the functional layer 3 provided on the transparent film 1 contain the bluing agent, a reduction in coloring can be achieved even when it is difficult to compound the bluing agent into the transparent film.

[0106] Preferably, in the functional layer 3, the bluing agent is dispersed or compatible in the resin matrix. The resin material of the functional layer can be selected according to the function added to the functional layer, etc. The thickness of the functional layer 3 and the amount of the bluing agent contained in the functional layer 3 can be set according to the YI of the transparent film 1, the hue required for the laminate 11, etc. The larger the amount of the bluing agent contained in the functional layer 3 and the greater the thickness of the functional layer, the smaller the YI of the laminate tends to be.

[0107] The thickness of the functional layer is, for example, 0.1 to 500 μm, preferably 1 to 100 μm, and can also be 3 to 50 μm, 5 to 40 μm, or 10 to 30 μm. The amount (concentration) of the bluing agent contained in the functional layer is preferably 0.1 ppm or more, more preferably 1 ppm or more, still more preferably 10 ppm or more, further preferably 20 ppm or more, and particularly preferably 100 ppm or more. When the amount of the bluing agent is too large, the total light transmittance of the laminate sometimes decreases, and the YI decreases excessively, so that the transmitted light and the reflected light can be visually recognized as being colored blue. Therefore, the amount of the bluing agent contained in the functional layer is preferably 1000 ppm or less, more preferably 500 ppm or less, still more preferably 300 ppm or less, and particularly preferably 250 ppm or less.

[0108] When the concentration of the blueing agent for the entire laminate is A (ppm) and the total thickness of all the layers of the laminate is B (μm), the value of the product (A × B) is preferably 5000 or less, more preferably 3000 or less, still more preferably 2500 or less, and may be 1500 or less. By making A × B within the above range, the total light transmittance can be maintained at a high level. The concentration A of the blueing agent is the ratio of the total amount of the blueing agent contained in the laminate to the total mass of the laminate. When the transparent film 1 also contains the blueing agent in addition to the functional layer 3, the concentration A is calculated including the amount of the blueing agent contained in the transparent film 1.

[0109] <Resin component of the functional layer>

[0110] In addition to the function as a hue adjustment layer, the functional layer 3 also imparts functions to the transparent film. When the functional layer contains a blueing agent in a resin matrix, various functions can be imparted to the functional layer by adjusting the composition of the resin component. The functional layer 3 can be, for example, a hard coat layer, an ultraviolet ray absorbing layer, an adhesive layer, a refractive index adjusting layer, an easy-bonding layer, or the like.

[0111] In one embodiment of the present invention, the functional layer 3 is a hard coat layer containing a cured product of a curable resin. By providing a hard coat layer containing a blueing agent on the main surface of the transparent film 1 as the functional layer 3, coloring can be reduced, and scratch resistance and hardness can be imparted.

[0112] The curable resin material constituting the hard coat layer is not particularly limited as long as it has a function of preventing damage, and examples thereof include polyester-based, acrylic-based, urethane-based, amide-based, siloxane-based, and epoxy-based resins. Among them, from the viewpoint of preventing damage, an acrylic-based hard coat layer which is a cured product of an acrylic-based hard coat resin composition or a siloxane-based hard coat layer which is a cured product of a siloxane-based hard coat resin composition is preferred.

[0113] (Acrylic-based hard coat material)

[0114] In the acrylic-based hard coat material, a monomer or oligomer having a (meth)acryloyl group in the molecule is contained as a curable resin component. The molecular weight of the acrylic-based monomer or oligomer is, for example, about 200 to 10000. The acrylic-based hard coat material can control hardness, scratch resistance, bending resistance, optical properties, etc. by variously combining monomers or oligomers having a (meth)acryloyl group. From the viewpoint of curability based on photo-radical polymerization, the hard coat material preferably has an acryloyl group.

[0115] Specific examples of the oligomer having a (meth)acryloyl group include urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, etc. The oligomer may have two or more (meth)acryloyl groups in one molecule. The molecular weight of the oligomer is preferably 10,000 or less.

[0116] Examples of the acrylic monomer include compounds having one (meth)acryloyl group such as methyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; compounds having two (meth)acryloyl groups in one molecule such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate; compounds having three or more (meth)acryloyl groups in one molecule such as glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane) tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate.

[0117] From the viewpoint of improving the scratch resistance of the hard coat, the acrylic hard coat material preferably contains a polyfunctional (meth)acrylate having three or more functional groups. The functional group equivalent of the (meth)acryloyl group of the polyfunctional (meth)acrylate, that is, the molecular weight per one (meth)acryloyl group is preferably 80 to 150 g / eq. Among the above-exemplified polyfunctional (meth)acrylates, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0118] (Siloxane-based hard coat material)

[0119] The siloxane-based hard coat material contains a curable compound having a siloxane bond as a curable resin component. From the viewpoint of the resistance to damage, the curable compound of the siloxane-based preferably has an epoxy group as a polymerizable functional group, and among them, a polyorganosiloxane compound containing an alicyclic epoxy group is preferred. Such siloxane-based hard coat materials are disclosed in WO2014 / 204010, WO2018 / 096729, WO2020 / 040209, etc., and the descriptions thereof can be referred to / cited.

[0120] The siloxane-based hard coat material having an alicyclic epoxy group as a polymerizable functional group has a small curing shrinkage during curing, so even if the thickness of the hard coat is increased, curling and cracking are not likely to occur.

[0121] The polyorganosiloxane compound having an alicyclic epoxy group is obtained by the condensation of a silane compound represented by the general formula (1).

[0122] [Y-Si(OR 1 ) x R 2 3-x (1)

[0123] In the general formula (1), R 1 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Specific examples of the alkyl group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, ethylhexyl, etc.

[0124] The silane compound represented by the general formula (1) has two or three (-OR 1 ) in one molecule. Si-OR 1 has hydrolyzability, and thus a polyorganosiloxane compound is obtained by the condensation of the silane compound. From the viewpoint of hydrolyzability, the carbon number of R 1 is preferably 3 or less, and particularly preferably R 1 is methyl.

[0125] In the general formula (1), R 2 is a hydrogen atom or a monovalent hydrocarbon group selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 25 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms. Specific examples of the hydrocarbon group include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, cyclohexyl, ethylhexyl, benzyl, phenyl, tolyl, xylyl, naphthyl, phenethyl, etc.

[0126] In the general formula (1), x is 2 or 3. When x = 3 (that is, when three alkoxy groups (or hydroxyl groups) -OR 1 are bonded to the Si atom), the silane compound does not have R 2 . From the viewpoints of the formation of a network polyorganosiloxane compound and increasing the number of epoxy groups contained in the polyorganosiloxane compound to improve the hardness of the cured film, in the general formula (1), x is preferably 3. A silane compound with x = 2 and a silane compound with x = 3 can be used in combination. In addition, for the purpose of adjusting the molecular weight of the polyorganosiloxane compound obtained by condensation, etc., in addition to the silane compound with x being 2 or 3, a silane compound with x = 1 can also be used.

[0127] In general formula (1), Y is a monovalent organic group containing an alicyclic epoxy group. Examples of Y include an alicyclic epoxy group, an alkyl group having an alicyclic epoxy group as a substituent, an alkylene glycol group having an alicyclic epoxy group as a substituent, etc. From the viewpoints of heat resistance and flexural resistance, an alkyl group having an alicyclic epoxy group as a substituent is preferred.

[0128] Specific examples of the alkyl group having an alicyclic epoxy group as a substituent include (3,4-epoxycyclohexyl)methyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 4-(3,4-epoxycyclohexyl)butyl, 5-(3,4-epoxycyclohexyl)pentyl, 6-(3,4-epoxycyclohexyl)hexyl, 7-(3,4-epoxycyclohexyl)heptyl, 8-(3,4-epoxycyclohexyl)octyl, 9-(3,4-epoxycyclohexyl)nonyl, 10-(3,4-epoxycyclohexyl)decyl, 11-(3,4-epoxycyclohexyl)undecyl, 12-(3,4-epoxycyclohexyl)dodecyl, etc.

[0129] Specific examples of the silane compound represented by general formula (1) include (3,4-epoxycyclohexyl)trimethoxysilane, (3,4-epoxycyclohexyl)methyldimethoxysilane, (3,4-epoxycyclohexyl)dimethylmethoxysilane, (3,4-epoxycyclohexyl)triethoxysilane, (3,4-epoxycyclohexyl)methyldiethoxysilane, (3,4-epoxycyclohexyl)dimethylethoxysilane, {(3,4-epoxycyclohexyl)methyl}trimethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldimethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylmethoxysilane, {(3,4-epoxycyclohexyl)methyl}triethoxysilane, {(3,4-epoxycyclohexyl)methyl}methyldiethoxysilane, {(3,4-epoxycyclohexyl)methyl}dimethylethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}trimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldimethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylmethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}triethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}methyldiethoxysilane, {2-(3,4-epoxycyclohexyl)ethyl}dimethylethoxysilane, etc. Among these, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is preferred from the viewpoints of ease of condensation reaction and hardness of the cured product.

[0130] The polyorganosiloxane compound as a condensate of the silane compound can be a condensate of the silane compound of general formula (1) and other silane compounds. Examples of the other silane compounds, i.e., silane compounds not containing an alicyclic epoxy group, include the silane compounds represented by general formula (2).

[0131] R 3 -(Si(OR 1 ) x R 2 3-x )(2)

[0132] In general formula (2), R 1 , R 2 and x are the same as those in general formula (1). In general formula (2), R 3 is a monovalent organic group that does not contain an alicyclic epoxy group. Examples of R 3 include a substituted or unsubstituted group containing a double bond, a substituted or unsubstituted group containing a cycloalkyl group, a substituted or unsubstituted group containing an aromatic ring, a substituted or unsubstituted alkyl group, a group having a glycidyl group, a group having an oxetanyl group, and a hydrogen atom. Among these, from the viewpoints of reactivity with the silane compound represented by general formula (1), adhesion to the transparent film, and hardness of the hard coat, a group having a glycidyl group is sometimes preferred.

[0133] By reacting the above silane compound with water, the Si-OR 1 portion of the silane compound undergoes hydrolysis, and the hydrolyzates undergo condensation, thereby forming a Si-O-Si bond and generating a condensate (polyorganosiloxane compound) of a silane compound having an alicyclic epoxy group.

[0134] From the viewpoint of improving the hardness of the cured film (hard coat), the weight average molecular weight of the polyorganosiloxane compound is preferably 500 or more. In addition, from the viewpoint of suppressing volatilization, the weight average molecular weight of the polyorganosiloxane compound is also preferably 500 or more. On the other hand, if the molecular weight is too large, cloudiness may sometimes occur due to a decrease in compatibility with other components in the composition. Therefore, the weight average molecular weight of the polyorganosiloxane compound is preferably 20000 or less.

[0135] (Polymerization initiator)

[0136] The hard coat composition preferably contains a polymerization initiator in addition to the above curable resin component. As the polymerization initiator, a photoinitiator is preferably used. An acrylic hard coat composition containing a compound having a (meth)acryloyl group as the curable resin component preferably contains a photo radical polymerization initiator that generates radicals by light. A siloxane-based hard coat composition containing a polyorganosiloxane compound having an epoxy group as the curable resin component preferably contains a photoacid generator (photo cationic polymerization initiator) that generates an acid by light.

[0137] (Additives for the hard coat composition)

[0138] The hard coat composition for forming a hard coat may contain a solvent and various additives in addition to a curable resin component and a polymerization initiator. Examples of the additives include leveling agents such as fluorine-based or silicone-based leveling agents, sensitizers, reactive diluents, fine particles, fillers, dispersants, plasticizers, ultraviolet absorbers, surfactants, antioxidants, colorants, viscosity modifiers, and the like.

[0139] (Formation of hard coat)

[0140] A hard coat composition containing a bluing agent is coated on the transparent film 1. After drying and removing the solvent as needed, it is cured to form a hard coat as the functional layer 3. Examples of the method for coating the hard coat composition include roll coating such as hard coating, gravure coating, comma coating, slot die coating, jet die coating, spin coating, spraying, dip coating, and the like. Before coating the curable resin composition, the surface of the transparent film 1 can be subjected to surface treatment such as corona treatment or plasma treatment. In addition, an easy-bonding layer or the like can be provided on the surface of the transparent film 1.

[0141] By irradiating the hard coat composition with active energy rays or heating, active species such as acids and free radicals are generated from the photoinitiator, and the curable resin component of the hard coat composition is cured. From the viewpoint of curing reactivity, it is preferable that the curable resin composition contains a photoinitiator and is cured by irradiation with active energy rays. Examples of the active energy rays during photocuring irradiation include visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, γ-rays, electron beams, and the like.

[0142] When the functional layer 3 is a hard coat, the thickness of the hard coat is 1 to 50 μm, preferably 3 to 40 μm, may be 5 to 30 μm, or 10 to 25 μm. The greater the thickness of the hard coat, the higher the pencil hardness and the tendency to improve scratch resistance. On the other hand, when the thickness of the hard coat is too large, the bending resistance tends to decrease.

[0143] As described above, the functional layer can be provided only on one surface of the transparent film or on both surfaces of the transparent film. When the transparent film 1 contains an ultraviolet absorber and has a concentration distribution of the ultraviolet absorber in the thickness direction, by providing the functional layer 3 on the surface where the concentration of the ultraviolet absorber is relatively high, the photo-degradation of the transparent film 1 when irradiating the laminate 11 with ultraviolet rays from the functional layer 3 side is suppressed, and the light resistance tends to be improved.

[0144] The thickness of the laminate 11 (the sum of the thickness of the transparent film 1 and the thickness of the functional layer 3) is not particularly limited, preferably 10 μm or more, more preferably 30 μm or more, further preferably 40 μm or more, preferably 200 μm or less, more preferably 100 μm or less, further preferably 80 μm or less, and particularly preferably 60 μm or less.

[0145] [Properties of the laminate]

[0146] As described above, the total light transmittance of the laminate having the functional layer 3 on the transparent film 1 is 90.3% or more, and the yellowness index (YI) is -1.0 or more and 1.0 or less. By making the total light transmittance high, the white brightness of the display can be improved, and by making the YI close to 0, the hue is neutralized. The total light transmittance of the laminate is more preferably 90.5% or more, and still more preferably 91.0% or more. The YI of the laminate is more preferably -0.6 to 0.8, and further preferably -0.5 to 0.5.

[0147] The polyimide-based resin film is slightly colored yellow, but by using a mixed resin system such as an acrylic resin, the light absorption caused by the polyimide-based resin is reduced, so that coloring can be reduced and the total light transmittance can be increased. Generally, the refractive index of the polyimide-based resin is high, and the reflectance at the interface with air and the interface with the functional layer is high. By using a mixed resin system, the refractive index is reduced and the reflectance becomes smaller, so that the total light transmittance can be increased.

[0148] The film of the mixed resin system of the polyimide-based resin and other resins has a smaller YI than the film of the polyimide-based resin alone, but is still slightly colored yellow, the YI is usually greater than 0, and sometimes the YI is greater than 1.0. By providing the functional layer 3 containing a bluing agent on the transparent film 1, the YI of the laminate 11 can be adjusted to a value lower than the YI of the transparent film 1. The YI of the mixed resin system transparent film 1 is lower than the YI of the polyimide-based resin alone film, so that the YI can be made close to 0 (adjusted to 1.0 or less) with a small amount of bluing agent, and the reduction of the total light transmittance caused by the light absorption of the bluing agent can be suppressed.

[0149] By making the functional layer 3 contain a bluing agent, even when the transparent film 1 does not contain a bluing agent, the YI of the laminate 11 can be reduced. Therefore, from the viewpoints of compatibility and dispersibility with the resin matrix and heat resistance, even when it is difficult to compound a bluing agent in the transparent film 1, a laminate with a low YI and a high total light transmittance can be provided.

[0150] The haze of the laminate is preferably 1% or less, more preferably 0.7% or less, and still more preferably 0.5% or less. As the resin material of the transparent film, by using a resin compatible with the polyimide resin, the haze can be reduced. It should be noted that the polyimide resin and other resins do not necessarily need to be completely compatible and may have a small microphase separation structure to such an extent that the optical properties are not affected.

[0151] When irradiating the laminate with a carbon arc light source under the conditions of an irradiation intensity of 500 W / m 2 and a black panel temperature of 63°C for 48 hours, the increase amount ΔYI of YI is preferably 5.0 or less, more preferably 4.0 or less, still more preferably 2.0 or less, and particularly preferably 1.0 or less. Most of the increase in YI during ultraviolet irradiation of the laminate of the transparent film 1 and the functional layer 3 is due to the photo-degradation of the resin contained in the transparent film 1, and the ΔYI of the transparent film 1 is substantially equal to the ΔYI of the laminate 11. The smaller the ratio of the polyimide resin in the transparent film and the larger the amount of the ultraviolet absorber, the smaller the ΔYI tends to be.

[0152] When the functional layer 3 is a hard coat, the pencil hardness of the surface of the laminate 11 on which the functional layer 3 is formed is preferably 3H or more, more preferably 4H or more, and can be 5H or more or 6H or more. The higher the pencil hardness, the less likely it is to cause damage and dents due to external forces. The higher the pencil hardness, the more excellent the scratch resistance, and it can also be suitably used for applications such as a cover window disposed on the outermost surface of a display. When the laminate is used as a material for a flexible display, the laminate preferably has excellent bend resistance and can be repeatedly bent 100,000 times or more with a radius of 1.5 mm.

[0153] The laminate 11 having the functional layer 3 on the transparent film 1 has a high total light transmittance and little coloring, so it can be used as a display material and can be used as a cover window provided on the surface of an image display panel, a transparent substrate for a display, a transparent substrate for a touch panel, etc. In particular, when the functional layer 3 is a hard coat, it has excellent scratch resistance, so it can be suitably used as a cover window material.

[0154] Examples

[0155] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples. Hereinafter, the flow direction during coating is defined as the MD direction, and the direction orthogonal to the MD direction is defined as the TD direction.

[0156] [Preparation of Polyimide Resin]

[0157] Put dimethylformamide (DMF) into a detachable flask and stir it under a nitrogen atmosphere. Add diamine and tetracarboxylic dianhydride at the ratios (mol%) shown in Table 1, and stir for 5 to 10 hours under a nitrogen atmosphere to carry out the reaction, obtaining a polyamic acid solution with a solid component concentration of 18 wt%.

[0158] Add 5.5 g of pyridine as an imidization catalyst to 100 g of the polyamic acid solution, and after it is completely dispersed, add 8 g of acetic anhydride and stir at 90 °C for 3 hours. After cooling to room temperature, add 100 g of 2-propanol (IPA) dropwise at a rate of 2 to 3 drops / second while stirring the solution to precipitate polyimide. Then add 150 g of IPA, stir for about 30 minutes, and perform suction filtration using a Kiriyama funnel. After washing the obtained solid with IPA, dry it in a vacuum oven set at 120 °C for 12 hours to obtain polyimide resins 1 and 2 (PI1, PI2).

[0159] In Table 1, the compounds are described by the following abbreviations.

[0160] <Tetracarboxylic dianhydride>

[0161] CBDA: 1,2,3,4-Cyclobutanetetracarboxylic dianhydride

[0162] 6FDA: 2,2-Bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride

[0163] TAHMBP: Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)-2,2’,3,3’,5,5’-hexamethylbiphenyl-4,4’-diyl ester

[0164] ODPA: 4,4’-Oxydiphthalic dianhydride

[0165] <Diamine>

[0166] TFMB: 2,2’-Bis(trifluoromethyl)benzidine

[0167] DDS: 3,3’-Diaminodiphenyl sulfone

[0168] [Table 1]

[0169]

[0170] [Production of transparent film]

[0171] <Film 1>

[0172] Dissolve polyimide resin 1 (PI1) and a commercially available acrylic resin ("Parapet G" manufactured by Kuraray Co., Ltd.; copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C, acid value 0.0 mmol / g; hereinafter referred to as "acrylic resin") in dichloromethane at a weight ratio of 55:45 to prepare a solution with a solid content concentration of 11% by weight. Add 5.6 parts by weight of a benzotriazole-based ultraviolet absorber ("Adekastab LA-31RG" manufactured by ADEKA) relative to 100 parts by weight of the total solid content of the resin and stir. Coat this solution on an alkali-free glass plate and heat-dry it at 60°C for 15 minutes, 90°C for 15 minutes, 120°C for 15 minutes, 150°C for 15 minutes, 180°C for 15 minutes, in an air atmosphere. Thereafter, peel the film from the alkali-free glass plate. Hereinafter, the surface of the film that comes into contact with the alkali-free glass plate during coating / drying may sometimes be referred to as the "support surface".

[0173] Using a stretching machine equipped with a heating oven, uniaxially stretch the obtained film at a temperature of 215°C in the MD direction with a stretching ratio of 120% (the length of the MD is 2.20 times that of the film before stretching) to obtain Film 1 with a thickness of 50 μm.

[0174] <Film 2>

[0175] In a solution with a solid content concentration of 11% by weight obtained by dissolving polyimide resin Ⅰ and acrylic resin in dichloromethane at a weight ratio of 55:45, add 5.6 parts by weight of a triazine-based ultraviolet absorber and 0.002 parts by weight of an anthraquinone-based bluing agent ("Plast Blue 8590" manufactured by Uben Chemical Industry Co., Ltd.) relative to 100 parts by weight of the total solid content of the resin and stir. Coat, dry, and stretch using this solution in the same manner as the production of Film 1 to obtain Film 2 with a thickness of 50 μm.

[0176] <Film 3>

[0177] Dissolve polyimide resin 2 (PI2) in dichloromethane to prepare a solution with a solid content concentration of 10% by weight. Add 2.0 parts by weight of a triazine-based ultraviolet absorber ("Tinuvin 477" manufactured by BASF) relative to 100 parts by weight of the solid content of the resin and stir. Coat this solution on an alkali-free glass plate and heat-dry it at 40°C for 60 minutes, 80°C for 30 minutes, 150°C for 30 minutes, 170°C for 30 minutes, 200°C for 60 minutes, in an air atmosphere to obtain Film 3 with a thickness of 50 μm.

[0178] [Preparation of Hard Coat Composition]

[0179] <Acrylic Hard Coat Composition>

[0180] To 100 parts by weight of dipentaerythritol hexaacrylate (“Aronix M-403” manufactured by Toagosei Co., Ltd.), 2 parts by weight of a photo radical polymerization initiator (“Omnirad 184” manufactured by IGM Resins), 0.25 part by weight of a polyether-modified silicone leveling agent (“BYK-300” manufactured by BYK), and an anthraquinone-based bluing agent (“PlastBlue 8590” manufactured by Yuki Gosei Kogyo Co., Ltd.) in the amount shown in Table 2 are added, and propylene glycol monomethyl ether is added as a diluting solvent to obtain an acrylic hard coat composition having a solid content concentration of 50% by weight.

[0181] <Silicone-based hard coat composition>

[0182] In a reaction vessel equipped with a thermometer, a stirring device, and a reflux condenser, 66.5 g (270 mmol) of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (“SILQUEST A-186” manufactured by Momentive Performance Materials) and 16.5 g of 1-methoxy-2-propanol (PGME) are charged and stirred uniformly. To this mixture, a solution obtained by dissolving 0.039 g (0.405 mmol) of magnesium chloride as a catalyst in a mixture of 9.7 g (539 mmol) of water and 5.8 g of methanol is added dropwise over 5 minutes, and the mixture is stirred until homogeneous. Thereafter, the temperature is raised to 80°C, and a polycondensation reaction is carried out for 6 hours with stirring. After completion of the reaction, the solvent and water are distilled off using a rotary evaporator to obtain a condensate of the silane compound (polyorganosiloxane compound).

[0183] The polystyrene-converted weight average molecular weight measured using a GPC device “HLC-8220GPC” (columns: TSKgel GMH XL × 2 columns, TSKgel G3000H XL , TSKgel G2000H XL ) manufactured by Tosoh Corporation is 3,000. Using a 400 MHz-NMR manufactured by Bruker, the residual ratio of the epoxy group calculated from the 1H-NMR spectrum measured using deuterated acetone as a solvent is 95% or more. 1

[0184] To 100 parts by weight of the above polyorganosiloxane compound, 2 parts by weight of a sulfonium-based photoacid generator (“CPI-101A” manufactured by San-Apro), 0.25 part by weight of a polyether-modified silicone leveling agent (“BYK-300” manufactured by BYK), and an anthraquinone-based bluing agent (“Plast Blue 8590” manufactured by Yuki Gosei Kogyo Co., Ltd.) in the amount shown in Table 2 are added, and propylene glycol monomethyl ether is added as a diluting solvent to obtain a silicone-based hard coat composition having a solid content concentration of 50% by weight.​

[0185] [Manufacture of Hard Coat Film]

[0186] [Example 1]

[0187] Using a coater, an acrylic hard coat composition containing a bluing agent was coated on the support surface of Film 1 so that the dry film thickness became 5 μm, and the solvent was removed at 120°C. Thereafter, in a nitrogen atmosphere, using a high-pressure mercury lamp, ultraviolet rays were irradiated so that the cumulative light amount became 1950 mJ / cm 2 to cure the hard coat resin composition, obtaining a laminate (hard coat film) having an acrylic hard coat layer with a thickness of 5 μm on one surface of Film 1.

[0188] [Examples 2 to 4, Comparative Examples 2 to 4]

[0189] Using an acrylic hard coat composition containing the amount of bluing agent shown in Table 2, the coating thickness was changed so that the dry film thickness became 10 μm, and otherwise, the same operations as in Example 1 were performed to obtain a hard coat film having an acrylic hard coat layer with a thickness of 10 μm on one surface of Film 1.

[0190] [Example 5]

[0191] Using Film 2 instead of Film 1, and otherwise, the same operations as in Example 2 were performed to obtain a hard coat film having an acrylic hard coat layer with a thickness of 10 μm on one surface of Film 2.

[0192] [Comparative Example 1]

[0193] Using Film 3 instead of Film 1, and otherwise, the same operations as in Example 2 were performed to obtain a hard coat film having an acrylic hard coat layer with a thickness of 10 μm on one surface of Film 3.

[0194] [Example 6]

[0195] Using a coater, a silicone hard coat composition was coated on Film 1 so that the dry film thickness became 10 μm, and the solvent was removed at 120°C. Thereafter, in an air atmosphere, using a high-pressure mercury lamp, ultraviolet rays were irradiated so that the cumulative light amount became 1950 mJ / cm 2 to cure the hard coat resin composition, obtaining a hard coat film having a silicone hard coat layer with a thickness of 10 μm on one surface of Film 1.

[0196] [Example 7]

[0197] Using a silicone hard coat composition containing the amount of bluing agent shown in Table 2, the coating thickness was changed so that the dry film thickness became 20 μm, and otherwise, the same operations as in Example 6 were performed to obtain a hard coat film having a silicone hard coat layer with a thickness of 20 μm on one surface of Film 1.

[0198] [Evaluation of Transparent Films and Hard Coat Films]

[0199] By the following method, the tensile modulus, refractive index, total light transmittance and yellowness index (YI) of transparent films 1 to 3, and the total light transmittance, yellowness, light resistance and pencil hardness of the hard coat films of the examples and comparative examples were evaluated.

[0200] [Tensile Modulus]

[0201] The film was cut into strips with a width of 10 mm, conditioned by standing for 1 day at 23°C / 55% RH, and then a tensile test was carried out under the following conditions using a tensile testing machine "AUTOGRAPH AGS-X" manufactured by Shimadzu Corporation to calculate the tensile modulus.

[0202] Distance between clamps: 100 mm

[0203] Tensile speed: 12.5 mm / min

[0204] Measurement temperature: 23°C

[0205] For the tensile test, it was carried out for the MD direction and TD direction respectively, and the higher value was taken as the tensile modulus of the film. The tensile modulus of films 1 to 3 was 5.7 GPa.

[0206] [Refractive Index]

[0207] The film was cut into a 3 cm square, and an orientation angle was measured using a retardation measuring device ("OPTIPRO 21-255MA" manufactured by SHINTEC) to determine the direction with the maximum refractive index. For the stretched films 1 and 2, the refractive index in the stretching direction (MD) was the largest. Using a prism coupler ("2010 / M" manufactured by METRICON), the refractive indices in the direction with the maximum refractive index (MD) and the direction orthogonal thereto (TD) were measured. Cauchy dispersion fitting was performed on the measured values at wavelengths of 404 nm, 594 nm and 827 nm, and the refractive index at a wavelength of 589 nm obtained was taken as the refractive index of the film.

[0208] [Total Light Transmittance]

[0209] Using a haze meter HZ-V3 manufactured by Suga Test Instruments, the total light transmittance was measured by the method described in JIS K7361-1:1999. A D65 light source was used during the measurement.

[0210] [Yellowness Index (YI)] [[ID=4']]

[0211] The yellowness was measured in accordance with JIS K7373 using a spectrophotometer SC-P manufactured by Suga Test Instruments Co., Ltd.

[0212] <Lightfastness>

[0213] Using a fade meter (Fade Meter) (“U48HB” manufactured by Suga Test Instruments), under the conditions of ultraviolet light: carbon arc lamp, irradiance: 500 W / m 2 , black panel temperature: 63 °C, no rain, ultraviolet light was irradiated from the hard coat formation surface side for 48 hours. After the ultraviolet light irradiation, the yellowness YI1 was measured, and the difference ΔYI = YI1 - YI0 from the yellowness YI0 before the ultraviolet light irradiation was calculated.

[0214] <Pencil hardness>

[0215] According to JIS K5600, the pencil hardness of the hard coat surface was evaluated with a load of 750 g. Tests were conducted for scratching along the MD direction (moving the pencil) and scratching along the TD direction, and the higher hardness value was taken as the pencil hardness of the hard coat film.

[0216] The compositions and evaluation results of the hard coat films of the examples and comparative examples are shown in Table 2. The numerical values of the compositions of the transparent film and the hard coat in Table 2 are weight ratios (parts by weight) with the total resin components set to 100.

[0217] [Table 2]

[0218]

[0219] The total light transmittance of the hard coat films of Examples 1 to 7 was 90.3% or more, with high transparency, YI of 1.0 or less, little coloring, and ΔYI of 1.2 or less, showing excellent lightfastness. The hard coat films of Examples 1 to 7 were placed on white paper with the hard coat on the top, and the presence or absence of coloring was visually confirmed. As a result, there were few changes deviating from white.

[0220] In Comparative Example 1 in which the same acrylic hard coat as in Example 2 was formed on the polyimide-alone film 3, the total light transmittance of the transparent film was low, so the transparency was poor. In addition, in Comparative Example 1 (film 3), coloring was suppressed by reducing the amount of the ultraviolet absorber, so YI equivalent to that of Example 2 etc. was shown. However, since the amount of polyimide was large and the amount of the ultraviolet absorber was small, the lightfastness was poor and a large ΔYI was shown.

[0221] From the comparison between Examples 2 to 4 and Comparative Examples 2 to 4, it can be seen that the larger the amount of the bluing agent contained in the hard coat, the more likely the YI is to decrease. In addition, from the comparison between Example 2 and Example 5, it can be seen that by including a bluing agent in the transparent film, the YI can be further reduced.

[0222] In Comparative Example 2 where the hard coat does not contain a bluing agent and Comparative Example 3 where the amount of the bluing agent in the hard coat is small, the YI of the hard-coated film is large. When the hard-coated film is placed on white paper and the presence or absence of coloring is visually confirmed, yellow coloring can be observed as a result. The total light transmittance of Comparative Example 4 where the amount of the bluing agent in the hard coat is 400 ppm is less than 90%. When the hard-coated film of Comparative Example 4 is placed on white paper and the presence or absence of coloring is visually confirmed, blue coloring can be visually identified as a result.

[0223] From the above results, it can be seen that by using a mixed resin film of a polyimide-based resin and another resin (acrylic-based resin) as the transparent film, the YI of the transparent film is reduced and the total light transmittance becomes high. By providing a functional layer containing a bluing agent on the transparent film, the YI can be further reduced.

[0224] The mixed resin system of a polyimide-based resin and another resin has a smaller YI than the case of the polyimide-based resin alone. Therefore, the amount of the bluing agent used can be reduced, which also contributes to the improvement of the total light transmittance. In addition, the ratio of the polyimide-based resin in the mixed resin system of a polyimide-based resin and another resin is lower than that in the case of the polyimide-based resin alone. Therefore, excellent light resistance can be achieved even when the amount of the ultraviolet absorber is small. By reducing the amount of the ultraviolet absorber, the light absorption in the short wavelength region of visible light caused by the ultraviolet absorber can be reduced, which also contributes to the improvement of the total light transmittance and the reduction of YI (neutralization of hue).

Claims

1. A laminate having a functional layer on the main surface of a transparent film, wherein the transparent film contains a polyimide resin and a resin other than the polyimide resin, the functional layer contains a bluing agent, the total light transmittance of the laminate is 90.3% or more, and the yellowness is -1.0 or more and 1.0 or less.

2. The laminate according to claim 1, wherein, The functional layer is a hard coat layer.

3. The laminate according to claim 2, wherein, The hard coat layer is an acrylic hard coat layer.

4. The laminate according to claim 2, wherein, The hard coat layer is a siloxane hard coat layer.

5. The laminate according to claim 2, wherein, The content of the bluing agent in the hard coat layer is 20 ppm or more.

6. The laminate according to any one of claims 1 to 5, wherein, The bluing agent is an anthraquinone compound.

7. The laminate according to any one of claims 1 to 5, wherein, The transparent film contains an ultraviolet absorber.

8. The laminate according to any one of claims 1 to 5, wherein, The total light transmittance of the transparent film is 90.3% or more, and the yellowness is greater than 0 and 3.0 or less.

9. The laminate according to any one of claims 1 to 5, wherein, The transparent film contains a polyimide resin and an acrylic resin.

10. The laminate according to claim 9, wherein, The acrylic resin is an acrylic resin having methyl methacrylate as a main component.

11. The laminate according to any one of claims 1 to 5, wherein, The polyimide resin contains a structure derived from a tetracarboxylic dianhydride and a structure derived from a diamine, as the tetracarboxylic dianhydride, an alicyclic tetracarboxylic dianhydride and a fluorine-containing aromatic tetracarboxylic dianhydride are included, as the diamine, a fluorine-containing diamine is included.

12. The laminate according to any one of claims 1 to 5, wherein, The refractive index of the transparent film is 1.60 or less.

13. The laminate according to any one of claims 1 to 5, wherein, The thickness of the transparent film is 20 μm or more.

14. A display including the laminate according to any one of claims 1 to 5.

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