TWI877269B - Composite polarizing plate and liquid crystal display device - Google Patents

Abstract

An object of the present invention is to provide a composite polarizing plate capable of suppressing poor appearance even in a high temperature durability test and a liquid crystal display device using the same. The composite polarizing plate of the present invention includes a polarizing plate having a protective layer on at least one side of a linearly polarizing layer, and a brightness improving film; a first pressure-sensitive adhesive layer, a buffer layer, and a brightness improving film are laminated in this order on the protective layer side of the polarizing plate. The tensile elastic modulus at a temperature of the buffer layer of 23℃ and a relative humidity of 55% is 1.5 GPa or more.

Description

Composite polarizing plate and liquid crystal display device

The present invention relates to a composite polarizing plate and a liquid crystal display device using the same.

In the past, it is known that a composite polarizing plate having a polarizing plate and a brightness enhancement film is used to enhance the brightness of a liquid crystal display device (Patent Documents 1 to 5). In addition, in recent years, with the increase in the size of portable terminals such as smartphones, in order to achieve long-term driving with limited battery capacity, a brightness enhancement film is used to improve the efficiency of light utilization.

[Prior Art Literature]

[Patent Literature]

[Patent document 1] Japanese Patent Publication No. 11-248941

[Patent Document 2] Japanese Patent Publication No. 11-248942

[Patent Document 3] Japanese Patent Publication No. 11-64840

[Patent Document 4] Japanese Patent Publication No. 11-64841

[Patent Document 5] Japanese Patent No. 4880719

When the composite polarizing plate was subjected to a high-temperature durability test, wrinkles were found in the brightness enhancement film and the composite polarizing plate had a poor appearance. This poor appearance may cause a decrease in viewing quality when the composite polarizing plate is used in a liquid crystal display device.

The purpose of the present invention is to provide a composite polarizing plate that can suppress poor appearance even in a high-temperature durability test and a liquid crystal display device using the same.

The present invention provides the following composite polarizing plate and liquid crystal display device.

[1] A composite polarizing plate comprising: a polarizing plate having a protective layer on at least one side of a linear polarizing layer, and a brightness enhancement film, wherein:

The first adhesive layer, the buffer layer and the brightness enhancement film are sequentially laminated on the protective layer side of the polarizing plate.

The tensile elasticity of the aforementioned buffer layer at a temperature of 23°C and a relative humidity of 55% is above 1.5 GPa.

[2] The composite polarizing plate as described in [1], wherein the buffer layer and the brightness enhancement film are bonded together via a second adhesive layer.

[3] The composite polarizing plate as described in [1] or [2], wherein the buffer layer is a resin film.

[4] The composite polarizing plate as described in [3], wherein the resin film comprises a film composed of at least one resin selected from the group consisting of cellulose ester resins, (meth) acrylic resins and cyclic olefin resins.

[5] The composite polarizing plate as described in [1], wherein the buffer layer is in direct contact with the brightness enhancement film.

[6] The composite polarizing plate as described in [1] or [5], wherein the buffer layer is a cured layer of a resin composition containing a curable component.

[7] The composite polarizing plate as described in [6], wherein the curable component contains an active energy ray-curable compound.

[8] A composite polarizing plate as described in any one of [1] to [7], wherein the in-plane retardation Re(590) of the buffer layer at a wavelength of 590 nm is less than 20 nm.

[9] The composite polarizing plate as described in any one of [1] to [8], wherein the first adhesive layer is bonded to the protective layer and the buffer layer of the polarizing plate.

[10] A composite polarizing plate as described in any one of [1] to [9], wherein the polarizing plate has the protective layer on both sides of the linear polarizing layer.

[11] A composite polarizing plate as described in any one of [1] to [10], wherein a third adhesive layer is provided on the side of the polarizing plate opposite to the side of the brightness enhancement film.

[12] The composite polarizing plate as described in [11], wherein a release film is provided on the side of the third adhesive layer opposite to the side of the polarizing plate.

[13] A liquid crystal display device comprising: a composite polarizing plate as described in any one of [1] to [12], and a liquid crystal unit.

[14] A liquid crystal display device as described in [13], further comprising a backlight, wherein:

The aforementioned composite polarizing plate is arranged between the aforementioned liquid crystal unit and the aforementioned backlight in such a manner that the aforementioned brightness enhancement film side becomes the aforementioned backlight side.

According to the present invention, a composite polarizing plate capable of suppressing poor appearance even in a high-temperature durability test and a liquid crystal display device using the same can be provided.

1,2: Composite polarizing plate

5,6: LCD display device

10: Polarizing plate

11: Linear polarizing layer

12: 1st protective layer

13: Second protective layer

15a,15b: Buffer layer

18: Brightness enhancement film

31: 1st adhesive layer

32: Second adhesive layer

33: Third adhesive layer

35: Peeling membrane

41: Liquid crystal unit

42: Backlight

FIG1 is a schematic cross-sectional view showing an example of a composite polarizing plate of the present invention.

FIG2 is a schematic cross-sectional view showing another example of the composite polarizing plate of the present invention.

FIG3 is a schematic cross-sectional view schematically showing another example of the composite polarizing plate of the present invention.

FIG4 is a schematic cross-sectional view schematically showing another example of the composite polarizing plate of the present invention.

FIG5 is a schematic cross-sectional view schematically showing an example of a liquid crystal display device of the present invention.

FIG6 is a schematic cross-sectional view schematically showing another example of the liquid crystal display device of the present invention.

The following is a reference to the drawings to illustrate the preferred implementation of the composite polarizing plate of the present invention and the liquid crystal display device using the same.

〈Compound polarizing plate〉

The composite polarizing plate of the present invention comprises: a polarizing plate having a protective layer on at least one side of the linear polarizing layer, and a brightness enhancement film.

The first adhesive layer, buffer layer and brightness enhancement film are sequentially layered on the protective layer side of the polarizing plate.

The tensile elasticity of the buffer layer at a temperature of 23°C and a relative humidity of 55% is above 1.5 GPa.

The brightness enhancement film can reflect linear polarized light with a predetermined polarization axis or circular polarized light with a predetermined direction among incident natural light and allow other light to pass through. Therefore, in a composite polarizing plate having a brightness enhancement film and a polarizing plate including a linear polarizing layer, light from a light source such as a backlight of a liquid crystal display device is incident to obtain penetrating light of a predetermined polarization state, and light other than the predetermined polarization state is not penetrated but can be reflected. When the composite polarizing plate having a brightness enhancement film and a linear polarizing layer is used in a liquid crystal display device, the light reflected on the surface of the brightness enhancement film is reversed in advance by a reflective layer disposed on the rear side thereof and is incident on the brightness enhancement film again, and a part or all of it is penetrated as light of a predetermined polarization state, thereby increasing the amount of light penetrating the brightness enhancement film. In addition, by supplying polarized light that is not easily absorbed by the linear polarizing layer to the polarizing plate, the amount of light that can be used for image display can be increased, and the brightness of the liquid crystal display device can be improved.

In this way, the brightness enhancement film repeats the following steps: instead of allowing light with a polarization direction absorbed by the linear polarization layer to enter the linear polarization layer, it is first reflected on the brightness enhancement film, and then reversed by a reflective layer disposed on the rear side thereof and enters the brightness enhancement film again. Thus, among the light reflected and reversed between the linear polarization layer and the brightness enhancement film, only the polarization direction that can pass through the linear polarization layer passes through the brightness enhancement film, and this penetrating light can be supplied to the linear polarization layer. Therefore, by using a composite polarizing plate including a brightness enhancement film and a polarizing plate as described above, light such as backlight can be efficiently used in the image display of the liquid crystal display device in the liquid crystal display device, so that the screen becomes brighter.

As described later, the buffer layer included in the composite polarizing plate may be a resin film or a cured layer of a resin composition containing a curable component. The above-mentioned tensile elasticity of the buffer layer may be 3 GPa or more, or 5 GPa or more, and is usually 10 GPa or less, or 8 GPa or less. The tensile elasticity can be measured by the method described in the embodiments described later. The tensile elasticity in the case where the buffer layer is a cured layer can be measured by the following steps. The resin composition is applied to the demolding surface of the demolding polyethylene terephthalate film (hereinafter sometimes referred to as "PET film") using a wet film coater in such a manner that the thickness after drying becomes 100 μm. Then, it is placed at room temperature for 30 minutes for pre-drying, and then placed at 100°C for 5 minutes for main drying, so that the solvent contained in the resin composition applied on the PET film can be fully volatilized. Finally, a predetermined curing treatment (heating treatment or ultraviolet irradiation treatment, etc.) is performed to produce a cured layer on the PET film, and the cured layer obtained by peeling off the PET film is used as a measurement sample, and then the tensile elasticity is measured by the method described in the embodiment described below.

The wrinkles on the brightness enhancement film after the high-temperature durability test are known to be caused by the shrinkage of the polarizing plate in a high-temperature environment. The composite polarizing plate of this embodiment has a buffer layer between the polarizing plate and the brightness enhancement film. Since the buffer layer has a tensile elasticity within the above range, it is not easily deformed. Therefore, even if the polarizing plate shrinks during the high-temperature durability test of the composite polarizing plate, the presence of the buffer layer that is not easily deformed between the polarizing plate and the brightness enhancement film can prevent the brightness enhancement film from shrinking along with the shrinkage of the polarizing plate. Since wrinkles can be prevented from occurring at the ends of the brightness enhancement film, poor appearance on the composite polarizing plate after the high-temperature durability test can be prevented. In addition, when this composite polarizing plate is applied to a liquid crystal display device, it is possible to suppress the degradation of the visibility of the image displayed on the screen of the liquid crystal display device.

The in-plane retardation Re(590) of the buffer layer at a wavelength of 590 nm is preferably 20 nm or less, and may be 10 nm or less, or 5 nm or less, or 0 nm. By making the Re(590) of the buffer layer within the above range, the reduction in viewing angle characteristics when the composite polarizing plate is applied to a liquid crystal display device can be suppressed. The in-plane retardation Re(590) can be measured by the method described in the embodiment described below. The in-plane retardation Re (590) when the buffer layer is a cured layer is determined by following the steps for preparing a sample for measuring the tensile modulus when the buffer layer is a cured layer, except that the thickness after drying is set to the actual thickness of the buffer layer included in the composite polarizing plate, and then measuring it by the method described in the following embodiment.

The first adhesive layer is preferably an adhesive layer for bonding the protective layer and the buffer layer of the polarizing plate. In this case, the first adhesive layer is provided in a manner that directly contacts both the protective layer and the buffer layer of the polarizing plate.

The following is a detailed description of the implementation of the above-mentioned composite polarizing plate.

[Implementation Type 1]

FIG. 1 and FIG. 2 are schematic cross-sectional views schematically showing an example of a composite polarizing plate of the present embodiment. The composite polarizing plate 1 of the present embodiment is sequentially laminated with: a polarizing plate 10, a first adhesive layer 31, a buffer layer 15a, a second adhesive layer 32, and a brightness enhancement film 18. The second adhesive layer 32 is an adhesive layer for bonding the buffer layer 15a and the brightness enhancement film 18, and the second adhesive layer 32 is arranged in a manner of contacting both the buffer layer 15a and the brightness enhancement film 18.

The polarizing plate 10 shown in FIG. 1 and FIG. 2 has: a first protective layer 12 disposed on the brightness enhancement film 18 side of the linear polarizing layer 11, and a second protective layer 13 disposed on the side of the linear polarizing layer 11 opposite to the brightness enhancement film 18 side. The polarizing plate 10 may also have the first protective layer 12 and not have the second protective layer 13.

As shown in FIG. 2 , the composite polarizing plate 1 may have a third adhesive layer 33 on the side of the polarizing plate 10 opposite to the brightness enhancement film 18 side. The third adhesive layer 33 may be used in the liquid crystal display device described later to bond the composite polarizing plate 1 to the liquid crystal unit. The composite polarizing plate 1 may have a peeling film 35 ( FIG. 2 ) on the side of the third adhesive layer 33 opposite to the polarizing plate 10 side to cover and protect the surface of the third adhesive layer 33 .

The buffer layer 15a provided in the composite polarizing plate 1 is preferably a resin film. The resin film is preferably formed by a resin material having excellent transparency, mechanical strength, thermal stability, moisture shielding property, and stability of phase difference value, and the resin material is preferably a thermoplastic resin. The resin film can be a single-layer structure or a multi-layer structure. The resin film can be a stretched film. For example, the stretching elasticity can be adjusted by selecting the type of resin constituting the resin film, stretching the resin film, and the like. The details of the resin (resin material) used to form the resin film constituting the buffer layer 15a will be described later, but it is preferred to use a film composed of at least one resin selected from the group consisting of cellulose ester resins, (meth) acrylic resins and cyclic olefin resins.

The composite polarizing plate 1 can be obtained by laminating the first protective layer 12 side of the polarizing plate 10 and the buffer layer 15a through the first adhesive layer 31, and laminating the buffer layer 15a and the brightness enhancement film 18 through the second adhesive layer 32. When the composite polarizing plate 1 has a third adhesive layer 33, for example, an adhesive sheet having the third adhesive layer 33 formed on a release film 35 can be laminated on the polarizing plate 10.

[Implementation Type 2]

FIG. 3 and FIG. 4 are schematic cross-sectional views schematically showing another example of the composite polarizing plate of the present embodiment. The composite polarizing plate 2 of the present embodiment is sequentially laminated with a polarizing plate 10, a first adhesive layer 31, a buffer layer 15b, and a brightness enhancement film 18. The polarizing plate 10 shown in FIG. 3 and FIG. 4 has: a first protective layer 12 disposed on the brightness enhancement film 18 side of the linear polarizing layer 11, and a second protective layer 13 disposed on the side of the linear polarizing layer 11 opposite to the brightness enhancement film 18 side. The polarizing plate 10 may also have the first protective layer 12 and not have the second protective layer 13.

As described in the composite polarizing plate 1 shown in FIG. 2 , the composite polarizing plate 2 may have a third adhesive layer 33 and a release film 35 in sequence on the side of the polarizing plate 10 opposite to the side of the brightness enhancement film 18 ( FIG. 4 ).

The buffer layer 15b provided on the composite polarizing plate 2 is provided in direct contact with the brightness enhancement film 18 without other layers such as an adhesive layer. The buffer layer 15b is preferably a hardened layer of a resin composition containing a hardening component. The buffer layer 15b as a hardened layer can be formed by, for example, coating the above-mentioned resin composition on one side of the brightness enhancement film 18 and hardening the hardening component. The buffer layer 15b as a hardened layer can adjust the tensile elasticity within the above-mentioned range, for example, by selecting the type of hardening component. The details of the curable component constituting the buffer layer 15b will be described later, and it is preferably a curable layer of a resin composition containing an active energy ray-curable compound as a curable component.

The composite polarizing plate 2 can be obtained by bonding the buffer layer 15b side of the laminate formed with the buffer layer 15b on the brightness enhancement film 18 and the first protective layer 12 side of the polarizing plate 10 by the first adhesive layer 31. When the composite polarizing plate 2 has the third adhesive layer 33, the third adhesive layer 33 can be provided by the method described in the case where the composite polarizing plate 1 is provided with the third adhesive layer 33.

〈Liquid crystal display device〉

FIG. 5 and FIG. 6 are schematic cross-sectional views schematically showing an example of a liquid crystal display device of this embodiment. The liquid crystal display device 5, 6 of this embodiment has: the above-mentioned composite polarizing plate 1 or composite polarizing plate 2, and a liquid crystal unit 41, and usually also has a backlight 42. The composite polarizing plates 1, 2 are preferably arranged on the backlight 42 side of the liquid crystal unit 41 (the side opposite to the viewing side). In this case, as shown in FIG. 5 and FIG. 6, the composite polarizing plates 1, 2 are preferably arranged on the backlight 42 side in a manner such that the brightness enhancement film 18 side is arranged on the backlight 42 side, and are laminated on the liquid crystal unit 41 via the third adhesive layer 33 arranged on the polarizing plate 10 side.

In the liquid crystal display device 5, 6 having the composite polarizing plate 1 or the composite polarizing plate 2, as described above, since the composite polarizing plate 1, 2 includes the brightness enhancement film 18, the light of the backlight 42 can be efficiently used for the image display of the liquid crystal display device 5, 6, making the screen brighter.

Since the composite polarizing plates 1 and 2 respectively have the buffer layers 15a and 15b with the above-mentioned tensile elasticity, it is not easy to produce poor appearance when performing high-temperature durability tests. Thus, the liquid crystal display device 5 and 6 having the composite polarizing plate 1 or the composite polarizing plate 2 can suppress the reduction of viewing quality even when exposed to high temperature conditions.

The following is a detailed description of the components that make up the above-mentioned composite polarizing plate and liquid crystal display device.

[Buffer layer]

The buffer layer has a tensile elasticity within the above range. The buffer layer preferably has an in-plane retardation Re (590) within the above range. The buffer layer may be a resin film or a hardened layer of a resin composition containing a hardening component.

The thickness of the buffer layer is preferably greater than 20 μm, more preferably greater than 25 μm, and even more preferably greater than 30 μm, and is usually less than 80 μm, and can be less than 70 μm or less than 60 μm.

[Resin film constituting the buffer layer]

When the buffer layer is a resin film, the resin material (resin) constituting the resin film is preferably excellent in transparency, mechanical strength, thermal stability, moisture shielding and stability of phase difference value. The resin material is preferably a thermoplastic resin. This resin material is not particularly limited, and examples thereof include: cellulose ester resins; (meth) acrylic resins; olefin resins such as chain aliphatic olefin resins and cyclic olefin resins; polyvinyl chloride resins; styrene resins; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; polyvinyl acetate resins; polyvinylidene chloride resins. Resins; polyamide resins; polyacetal resins; polycarbonate resins; modified polyphenylene ether resins; polyester resins such as polybutylene terephthalate resins and polyethylene terephthalate resins; polysulfone resins; polyethersulfone resins; polyarylate resins; polyamide imide resins; polyimide resins, etc., can be used alone or in combination of two or more. Among them, it is preferred to use a resin selected from cellulose ester resins, (meth) acrylic resins and cyclic olefin resins. The so-called "(meth) acrylic acid" in this specification means any one of acrylic acid and methacrylic acid. The "(meth)" in (meth)acryloyl etc. has the same meaning.

The resin material constituting the resin film may also be used after any appropriate polymer modification, such as copolymerization, crosslinking, molecular end modification, stereoregularity control, and mixing including modifications accompanied by reactions between different types of polymers.

Cellulose ester resins are cellulose organic acid esters or cellulose mixed organic acid esters in which part or all of the hydrogen atoms in the hydroxyl groups of cellulose obtained from raw cellulose such as cotton wool or wood pulp (broad-leaved tree pulp, softwood tree pulp) are replaced by acetyl, propionyl and/or butyryl groups. For example, cellulose acetate, propionate, butyrate and mixed esters thereof can be listed. Among them, cellulose triacetate, cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate are preferred.

(Meth)acrylic resins are resins that have a compound having a (meth)acryloyl group as a main constituent monomer. Specific examples of (meth)acrylic resins include: poly(meth)acrylic acid esters such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymers; methyl methacrylate-(meth)acrylic acid ester copolymers; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers; methyl (meth)acrylate-styrene copolymers (MS resins, etc.); copolymers of methyl methacrylate and compounds having alicyclic hydrocarbon groups such as methyl methacrylate-cyclohexyl methacrylate copolymers and methyl methacrylate-norbornyl (meth)acrylate copolymers. It is preferred to use a polymer containing poly(meth)acrylic acid C _1-6 alkyl esters such as poly(methyl)acrylate as a main component, and it is particularly preferred to use a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight).

The (meth)acrylic resin may have a structural unit showing positive birefringence. As long as the structural unit showing positive birefringence and the structural unit showing negative birefringence are present, the phase difference of the film formed by the (meth)acrylic resin can be controlled by adjusting the existence ratio, and a (meth)acrylic resin film with a low phase difference can be obtained. Examples of the structural unit showing positive birefringence include: structural units constituting lactone rings, polycarbonates, polyvinyl alcohols, cellulose acetates, polyesters, polyarylates, polyimides, polyolefins, etc., and structural units represented by the general formula (1) described below. Structural units showing negative complex refraction include, for example: structural units derived from styrene monomers, styrene imide monomers, etc., structural units of polymethyl methacrylate, structural units represented by the general formula (3) described below, etc.

The (meth)acrylic resin preferably has a lactone ring structure or a glutarimide structure. The (meth)acrylic resin having a lactone ring structure or a glutarimide structure has excellent heat resistance. The (meth)acrylic resin having a glutarimide structure is particularly preferred. If a (meth)acrylic resin having a glutarimide structure is used, a (meth)acrylic resin film having low moisture permeability and small phase difference and ultraviolet transmittance can be obtained. The (meth) acrylic resin having a glutaryl imide structure (hereinafter also referred to as "glutaryl imide resin") is described in, for example, Japanese Patent Publication No. 2006-309033, Japanese Patent Publication No. 2006-317560, Japanese Patent Publication No. 2006-328329, Japanese Patent Publication No. 2006-328334, Japanese Patent Publication No. 2006-337491, Japanese Patent Publication No. 2006-337492, Japanese Patent Publication No. 2006-337493, Japanese Patent Publication No. 2006-337569, Japanese Patent Publication No. 2007-9182, and Japanese Patent Publication No. 2009-161744. The contents of these descriptions are cited in this specification as references.

The pentylene imide resin preferably contains: a structural unit represented by the following general formula (1) (hereinafter also referred to as a "pentylene imide unit"), and a structural unit represented by the following general formula (2) (hereinafter also referred to as a "(meth)acrylate unit").

In the general formula (1), ^R1 and ^R2 are independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R3 is hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or a substituent containing an aromatic ring having 5 to 15 carbon atoms;

In the general formula (2), ^R4 and ^R5 are independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R6 is hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or a substituent containing an aromatic ring having 5 to 15 carbon atoms.

The glutaramide resin may also contain a structural unit represented by the following general formula (3) (hereinafter also referred to as "aromatic vinyl unit") as needed.

In the general formula (3), ^R7 is hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R8 is an aryl group having 6 to 10 carbon atoms.

In the above general formula (1), preferably ^R1 and ^R2 are independently hydrogen or methyl, and ^R3 is hydrogen, methyl, butyl or cyclohexyl. More preferably, ^R1 is methyl, ^R2 is hydrogen, and ^R3 is methyl.

The glutarimide resin may contain only a single type as the glutarimide unit, and R ¹ , R ² and R ³ in the general formula (1) may contain plural types.

The glutarimide unit can be formed by imidizing the (meth)acrylate unit represented by the above general formula (2). In addition, the glutarimide unit can also be formed by imidizing an acid anhydride such as maleic anhydride, or a half ester of this acid anhydride and a linear or branched alcohol having 1 to 20 carbon atoms; acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid, fumaric acid, citric acid, etc. α,β-ethylenically unsaturated carboxylic acids.

In the above general formula (2), preferably ^R4 and ^R5 are independently hydrogen or methyl, and ^R6 is hydrogen or methyl. More preferably, ^R4 is hydrogen, ^R5 is methyl, and ^R6 is methyl.

The glutarimide resin may contain only a single type as the (meth)acrylate unit, and R ⁴ , R ⁵ and R ⁶ in the above general formula (2) may contain different plural types.

The pentylene imide resin preferably contains styrene, α-methylstyrene, etc. as the aromatic vinyl unit represented by the general formula (3), and more preferably contains styrene. By using the pentylene imide resin having the aromatic vinyl unit, the positive birefringence of the pentylene imide structure can be reduced to obtain a (meth) acrylic resin film with a lower phase difference.

The glutarimide resin may contain only a single species as the aromatic vinyl unit, and ^R7 and ^R8 in the above general formula (3) may contain plural different species.

The content of the pentylimide unit in the pentylimide resin is preferably changed, for example, according to the structure of R ^3. The content of the pentylimide unit is preferably 1 wt % to 80 wt %, more preferably 1 wt % to 70 wt %, more preferably 1 wt % to 60 wt %, and particularly preferably 1 wt % to 50 wt %, based on the total structural units of the pentylimide resin. If the content of the pentylimide unit is within this range, a (meth) acrylic resin film with excellent heat resistance and low phase difference can be obtained.

The content of aromatic vinyl units in the pentylimide resin can be appropriately set according to the purpose or required characteristics. Depending on the application, the content of aromatic vinyl units can be 0. When containing aromatic vinyl units, the content is preferably 10 wt% to 80 wt%, more preferably 20 wt% to 80 wt%, more preferably 20 wt% to 60 wt%, and particularly preferably 20 wt% to 50 wt%, based on the pentylimide units of the pentylimide resin. If the content of aromatic vinyl units is within this range, a (meth) acrylic resin film with low phase difference and excellent heat resistance and mechanical strength can be obtained.

In the pentylene imide resin, other structural units other than the pentylene imide unit, (meth)acrylate unit and aromatic vinyl unit can be copolymerized as needed. Examples of the other structural units include: structural units composed of nitrile monomers such as acrylonitrile or methacrylonitrile; cis-butenediamide monomers such as cis-butenediamide, N-methyl cis-butenediamide, N-phenyl cis-butenediamide, and N-cyclohexyl cis-butenediamide. These other structural units can be directly copolymerized or grafted in the pentylene imide resin.

Olefinic resins are resins composed of structural units derived from chain aliphatic alkenes such as ethylene and propylene, or alicyclic alkenes such as norbornene or its substitution products (hereinafter collectively referred to as norbornene monomers). Olefinic resins may be copolymers using two or more monomers.

The olefin resin is preferably used as a cyclic olefin resin which is a resin mainly containing a structural unit derived from an alicyclic olefin. Typical examples of the alicyclic olefin constituting the cyclic olefin resin include norbornene monomers. Norbornene is a compound in which one carbon-carbon bond of norbornene becomes a double bond, and is named bicyclo[2,2,1]hept-2-ene according to the IUPAC nomenclature. Examples of substitution forms of norbornene include 3-substituted forms, 4-substituted forms, and 4,5-disubstituted forms when the double bond position of norbornene is 1,2-position. In addition, dicyclopentadiene or dimethanol octahydronaphthalene can also be listed.

The cyclic olefin resin may or may not have a norbornene ring in its structural unit. The norbornene monomer forming the cyclic olefin resin without a norbornene ring in its structural unit is, for example, a 5-membered ring formed by ring opening, and representative examples include norbornene, dicyclopentadiene, 1- or 4-methylnorbornene, and 4-phenylnorbornene. When the cyclic olefin resin is a copolymer, the arrangement state of the molecule is not particularly limited, and it may be a random copolymer, a block copolymer, or a graft copolymer.

More specific examples of cyclic olefin resins include: ring-opening polymers of norbornene monomers, ring-opening copolymers of norbornene monomers and other monomers, polymer modified products to which maleic acid or cyclopentadiene has been added, and polymers or copolymers obtained by hydrogenating these monomers; addition polymers of norbornene monomers, and addition copolymers of norbornene monomers and other monomers. Other monomers used in the case of forming a copolymer include α-olefins, cycloolefins, and non-conjugated dienes. In addition, cyclic olefin resins may also be copolymers using one or more norbornene monomers and other alicyclic olefins.

Cyclic olefin resins are preferably used: resins obtained by hydrogenating ring-opening polymers or ring-opening copolymers using norbornene monomers.

The resin material constituting the above-mentioned resin film can be formulated with appropriate additives within the range of not damaging transparency. Examples of additives include: antioxidants, ultraviolet absorbers, antistatic agents, smoothing agents, nucleating agents, antifogging agents, anti-caking agents, phase difference reducing agents, stabilizers, processing aids, plasticizers, impact-resistant aids, matting agents, antibacterial agents, mildew-proof agents, etc. Multiple types of these additives can be used in combination.

The method of using the above resin materials to make a resin film can be selected by appropriately selecting any most appropriate method. For example, the following can be listed: a solvent casting method in which a resin dissolved in a solvent is poured onto a metal belt or drum and the solvent is dried and removed to obtain a film; a melt extrusion method in which a resin is heated to a temperature above its melting point, kneaded, extruded from a die, and then cooled to obtain a film. In the melt extrusion method, a single-layer film can be extruded, and a multi-layer film can be extruded simultaneously.

As described above, the resin film may be a stretched film after being subjected to a stretching process. The tensile elasticity rate may also be adjusted to a desired range by applying a stretching process. The stretching process may include uniaxial stretching or biaxial stretching, etc.

[The hardened layer of the resin composition containing the hardening component constituting the buffer layer]

When the buffer layer is a hardened material layer of a resin composition containing a hardening component, the hardening component contained in the resin composition is preferably an active energy ray hardening compound hardened by irradiation with active energy rays or a thermosetting hardener hardened by heating. The hardening component is particularly preferably an active energy ray hardening compound.

[A] Resin composition containing active energy ray-hardening compound

The active energy ray curing compound may be an electron beam curing compound, an ultraviolet curing compound or a visible light curing compound. Among them, the ultraviolet curing compound or the visible light curing compound is preferred, and the ultraviolet curing compound is particularly preferred. The resin composition containing the ultraviolet curing compound or the visible light curing compound may be a free radical polymerization type resin composition or a cationic polymerization type resin composition. The ultraviolet ray in this specification refers to the active energy ray with a wavelength of more than 10nm and less than 380nm, and the visible light refers to the active energy ray with a wavelength of more than 380nm and less than 800nm.

[A1] Free radical polymerization resin composition

The radical polymerizable resin composition contains a radical polymerizable compound as a curing component. Examples of the radical polymerizable compound include compounds having radical polymerizable functional groups of carbon-carbon double bonds such as (meth)acryl and vinyl. The radical polymerizable compound may be any of a monofunctional radical polymerizable compound and a difunctional or higher polyfunctional radical polymerizable compound. The radical polymerizable compound may be used alone or in combination of two or more. The radical polymerizable compound is preferably a compound having a (meth)acryl group, for example.

(Monofunctional free radical polymerizable compound)

Examples of monofunctional free radical polymerizable compounds include (meth)acrylamide derivatives having (meth)acrylamide groups. (Meth)acrylamide derivatives are preferred in terms of fast polymerization speed and excellent productivity in addition to ensuring the adhesion between the brightness enhancement film and the cured layer. Specific examples of (meth)acrylamide derivatives include: N-methyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N-hexyl (meth)acrylamide and other N-alkyl (meth)acrylamide derivatives; N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-hydroxymethyl -N-propane (meth)acrylamide and other N-hydroxyalkyl (meth)acrylamide derivatives; aminomethyl (meth)acrylamide, aminoethyl (meth)acrylamide and other N-aminealkyl (meth)acrylamide derivatives; N-methoxymethylacrylamide, N-ethoxymethylacrylamide and other N-alkoxy (meth)acrylamide derivatives; methyl (meth)acrylamide, ethyl (meth)acrylamide and other N-alkyl (meth)acrylamide derivatives, etc. Heterocyclic (meth)acrylamide derivatives in which the nitrogen atom of the (meth)acrylamide group forms a heterocyclic ring include: N-acryloyl pyroline, N-acryloyl piperidine, N-methylacryloyl piperidine, N-acryloyl pyrrolidine, etc.

Among (meth)acrylamide derivatives, when the cured layer is provided in direct contact with the brightness enhancement film, N-hydroxyalkyl (meth)acrylamide derivatives are preferred from the viewpoint of adhesion, and N-hydroxyethyl (meth)acrylamide is particularly preferred.

Monofunctional free radical polymerizable compounds include, for example, various (meth)acrylic acid derivatives having a (meth)acryloyloxy group. For example, (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-propyl ester, (meth)acrylic acid isopropyl ester, (meth)acrylic acid 2-methyl-2-nitropropyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid dibutyl ester, (meth)acrylic acid tertiary butyl ester, (meth)acrylic acid n-pentyl ester, (meth)acrylic acid tertiary pentyl ester, (meth)acrylic acid 3-pentyl ester, (meth)acrylic acid 2,2-dimethylbutyl ester, (meth)acrylic acid n-hexyl ester, (meth)acrylic acid cetyl ester, (meth)acrylic acid n-octyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid 4-methyl-2-propylpentyl ester, (meth)acrylic acid n-octadecyl ester and other (meth)acrylic acid (carbon number 1 to 20) alkyl esters.

Examples of (meth)acrylic acid derivatives include: (meth)acrylic acid cycloalkyl esters such as cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate; (meth)acrylic acid arylalkyl esters such as benzyl (meth)acrylate; (meth)acrylic acid 2-isoborneol, (meth)acrylate 2-norbornenyl methyl ester, (meth)acrylate 5-norbornen-2-yl methyl ester, (meth)acrylate 3-methyl-2-norbornenyl methyl ester, (meth)acrylate dicyclopentenyl ester, (meth)acrylate; Polycyclic (meth)acrylates such as dicyclopentenyloxyethyl and dicyclopentyl (meth)acrylate; alkoxy or phenoxy (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, and alkylphenoxy polyethylene glycol (meth)acrylate.

The (meth)acrylic acid derivatives include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, etc. (meth)acrylate derivatives include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, etc. hydroxyalkyl (meth)acrylates; hydroxy (meth)acrylates such as [4-(hydroxymethyl)cyclohexyl] methacrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate; (meth)acrylates containing epoxy groups such as glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether; (meth)acrylates containing 2,2,2-trifluoroethyl (meth)acrylate, and (meth)propylene glycol; Halogen-containing (meth)acrylates such as 2,2,2-trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; alkylamine (meth)acrylates such as dimethylaminoethyl (meth)acrylate; 3-oxomethyl (meth)acrylate, 3-methyl -oxycarbonyl methyl ester, (meth)acrylate 3-ethyl-oxycarbonyl methyl ester, (meth)acrylate 3-butyl-oxycarbonyl methyl ester, (meth)acrylate 3-hexyl-oxycarbonyl methyl ester and other oxygen-containing carbonyl (meth)acrylate esters; (meth)acrylate tetrahydrofurfuryl, (meth)acrylate butyrolactone and other heterocyclic (meth)acrylate esters; hydroxytrimethylacetic acid neopentyl glycol (meth)acrylate adduct; (meth)acrylate p-phenol, etc.

Examples of monofunctional free radical polymerizable compounds include: (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, cis-butenedioic acid, fumaric acid, crotonic acid, isocrotonic acid and other carboxyl group-containing monomers.

Examples of monofunctional free radical polymerizable compounds include: N-vinylpyrrolidone, N-vinyl-ε-caprolactam, methylvinylpyrrolidone and other vinyl monomers of lactamide; vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine and other vinyl monomers having nitrogen-containing heterocyclic rings.

As the monofunctional free radical polymerizable compound, for example, a free radical polymerizable compound having an active methylene group can be used. The free radical polymerizable compound having an active methylene group is a compound having an active double bond group such as a (meth)acrylic group at the end or in the molecule and having an active methylene group. Examples of the active methylene group include acetoacetyl group, alkoxypropanoyl group, or cyanoacetyl group, and the active methylene group is preferably acetoacetyl group. Specific examples of free radical polymerizable compounds having an active methylene group include: acetyloxyalkyl (meth)acrylates such as 2-acetyloxyethyl (meth)acrylate, 2-acetyloxypropyl (meth)acrylate, and 2-acetyloxy-1-methylethyl (meth)acrylate; 2-ethoxypropanoyloxyethyl (meth)acrylate, 2-cyanoacetyloxyethyl (meth)acrylate, N-(2-cyanoacetyloxyethyl)acrylamide, N-(2-propionylacetyloxybutyl)acrylamide, N-(4-acetylacetyloxymethylbenzyl)acrylamide, and N-(2-acetylacetylaminoethyl)acrylamide. The free radical polymerizable compound having an active methylene group is preferably acetyl acetoxyalkyl (meth)acrylate.

(Multifunctional free radical polymerizable compound)

Examples of the polyfunctional free radical polymerizable compound having two or more functional groups include: N',N'-methylenebis(meth)acrylamide as a polyfunctional (meth)acrylamide derivative, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 2-ethyl-2-butylpropylene glycol di(meth)acrylate, bisphenol A di(meth)acrylate, bisphenol A ethylene oxide adduct di(meth)acrylate, bisphenol A propylene oxide adduct di(meth)acrylate, bisphenol A dihydrate, Esterification products of (meth)acrylic acid and polyols such as oleyl ether di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, cyclotrihydroxymethylpropane dimethanol formal (meth)acrylate, dioxanediol di(meth)acrylate, trihydroxymethylpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, EO-modified diglycerol tetra(meth)acrylate, etc.; 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene, etc. Specific examples are preferably ARONIX M-220 (manufactured by Toagosei Co., Ltd.), LIGHT ACRYLATE 1,9ND-A (manufactured by Kyoeisha Chemical Co., Ltd.), LIGHT ACRYLATE DGE-4A (manufactured by Kyoeisha Chemical Co., Ltd.), LIGHT ACRYLATE DCP-A (manufactured by Kyoeisha Chemical Co., Ltd.), SR-531 (manufactured by Sartomer Co., Ltd.), CD-536 (manufactured by Sartomer Co., Ltd.), etc. When using such polyfunctional (meth)acrylamide derivatives, the radical polymerizable resin composition may contain various epoxy (meth)acrylates, urethane (meth)acrylates, polyester (meth)acrylates, or various (meth)acrylate monomers, etc., as needed. In addition to having a fast polymerization speed and excellent productivity, multifunctional (meth)acrylamide derivatives have excellent crosslinking properties when the resin composition is formed into a cured product, so they are preferably contained in a free radical polymerization type resin composition.

The free radical polymerizable compound containing a multifunctional free radical polymerizable compound is preferably used for controlling the water absorption rate of the cured product of the resin composition. Among the multifunctional free radical polymerizable compounds, the one with a high logPow value described below is preferred.

The resin composition containing the curable compound used to constitute the buffer layer preferably has a high octanol/water partition coefficient (hereinafter sometimes referred to as "logPow value"). The so-called logPow value is an indicator of the lipophilicity of a substance, which means the logarithmic value of the octanol/water partition coefficient. A high logPow means lipophilicity, which means low water absorption. The logPow value can be calculated by measurement (flask penetration method described in JIS-Z-7260) or by calculation. In this manual, the logPow value calculated by ChemDraw Ultra manufactured by CambridgeSoft is used. The logPow value of the resin composition can be calculated by the following formula.

The logPow of the resin composition = Σ(logPowi×Wi)

logPowi: logPow value of each component contained in the resin composition

Wi: (molar number of component i)/(total molar number of resin composition)

The logPow value of the resin composition is preferably greater than 1, more preferably greater than 2, and most preferably greater than 3.

Examples of free radical polymerizable compounds with high logPow values include: alicyclic (meth)acrylates such as tricyclodecane dimethanol di(meth)acrylate (logPow=3.05) and isoborneol (meth)acrylate (logPow=3.27); long-chain aliphatic (meth)acrylates such as 1,9-nonanediol di(meth)acrylate (logPow=3.68) and 1,10-decanediol diacrylate (logPow=4.10); hydroxytrimethylacetate neopentyl glycol (meth)acrylate adduct (logPow=3.35), 2-ethyl-2-butylpropylene glycol di(meth)acrylate (logPow=3.92 ) and other multi-branched (meth)acrylates; bisphenol A di(meth)acrylate (logPow=5.46), bisphenol A ethylene oxide 4 mole adduct di(meth)acrylate (logPow=5.15), bisphenol A propylene oxide 2 mole adduct di(meth)acrylate (logPow=6.10), bisphenol A propylene oxide 4 mole adduct di(meth)acrylate (logPow=6.43), 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene (logPow=7.48), (meth)acrylate p-phenyl ester (logPow=3.98) and other (meth)acrylates containing aromatic rings.

From the perspective of both the adhesion of the brightness enhancement film and the cured layer and the optical durability in harsh environments, the free radical polymerizable compound is preferably used in combination with a monofunctional free radical polymerizable compound and a polyfunctional free radical polymerizable compound. Generally, relative to 100% by weight of the free radical polymerizable compound, it is preferred to use a ratio of 3 to 80% by weight of the monofunctional free radical polymerizable compound and 20 to 97% by weight of the polyfunctional free radical polymerizable compound.

(Photopolymerization initiator)

In the case of containing an active energy ray-hardening component as a hardening component, the radical polymerizable resin composition can be used as a composition containing an active energy ray-hardening compound. In this case, the radical polymerizable resin composition preferably contains a photopolymerization initiator.

The photopolymerization initiator contained in the free radical polymerizable resin composition may be a photopolymerization initiator that is broken by ultraviolet light or visible light. Examples of the photopolymerization initiator include benzyl, diphenyl ketone, benzoyl benzoate, 3,3'-dimethyl-4-methoxydiphenyl ketone and other diphenyl ketone compounds; aromatic ketone compounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, α-hydroxy-α,α'-dimethylacetophenone, 2-methyl-2-hydroxypropiophenone, α-hydroxycyclohexylphenyl ketone and other aromatic ketone compounds; methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, 2-methyl -1-[4-(methylthio)-phenyl]-2-oxo-1-propane-1 and other acetophenone compounds; benzoin methyl ether, Benzoin ether compounds such as benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, and anisole methyl ether; aromatic acetal compounds such as benzyl dimethyl acetal; aromatic sulfonyl chloride compounds such as 2-naphthalenesulfonyl chloride; photoactive oxime compounds such as 1-benzophenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone; camphorquinone; halogenated ketones; acylphosphine oxides; acylphosphonates, etc. Among the photopolymerization initiators, those with higher logPow values are preferred. The logPow value of the photopolymerization initiator is preferably 2 or more, particularly preferably 3 or more, and most preferably 4 or more.

The content of the photopolymerization initiator in the free radical polymerizable resin composition is less than 20 parts by weight relative to the total amount of 100 parts by weight of the curing component (free radical polymerizable compound). The amount of the photopolymerization initiator is preferably 0.01 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 5 parts by weight.

When the free radical polymerizable resin composition contains a visible light curable compound, it is particularly preferred to use a photopolymerization initiator that is highly sensitive to light above 380nm.

Examples of photopolymerization initiators include compounds represented by the following general formula (4) (hereinafter sometimes referred to as "compound (4)").

[0081]

In the formula, R ¹¹ and R ¹² are independently -H, -CH ₂ CH ₃ , -iPr (isopropyl) or -Cl, and R ¹¹ and R ¹² may be the same or different.

In the free radical polymerizable resin composition, compound (4) can be used alone or in combination with a photopolymerization initiator having high sensitivity to light of 380 nm or more described below. By using compound (4), the adhesion between the brightness enhancement film and the curing layer can be improved compared to the case where a photopolymerization initiator having high sensitivity to light of 380 nm or more is used alone. Among compound (4), diethylthioxanthone in which R ¹¹ and R ¹² are -CH ₂ CH ₃ is particularly preferred. The content of compound (4) in the free radical polymerizable resin composition is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 4 parts by weight, and even more preferably 0.9 to 3 parts by weight, relative to 100 parts by weight of the total amount of the curable component (free radical polymerizable compound).

Examples of photopolymerization initiators that are highly sensitive to light above 380 nm include: 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholino)phenyl]-1-butanone, 2,4,6-trimethylbenzyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzyl)-phenylphosphine oxide, bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl) titanium, etc.

The free radical polymerizable resin composition preferably contains a compound represented by the following general formula (5) (hereinafter sometimes referred to as "compound (5)") in addition to compound (4).

In the formula, R ¹³ , R ¹⁴ and R ¹⁵ are independently -H, -CH ₃ , -CH ₂ CH ₃ , -iPr or -Cl, and R ¹³ , R ¹⁴ and R ¹⁵ may be the same or different from each other.

Compound (5) can also preferably use commercially available 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one (trade name: IRGACURE 907, manufactured by BASF). In addition, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (trade name: IRGACURE 369, manufactured by BASF) and 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholino)phenyl]-1-butanone (trade name: IRGACURE 379, manufactured by BASF) are also highly sensitive and therefore preferred.

The free radical polymerizable resin composition may contain a polymerization initiation auxiliary as required. Examples of the polymerization initiation auxiliary include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isopentyl 4-dimethylaminobenzoate, etc., and ethyl 4-dimethylaminobenzoate is particularly preferred. When a polymerization initiation auxiliary is used, the content of the polymerization initiation auxiliary in the free radical polymerizable resin composition is generally 0 to 5 parts by weight, preferably 0 to 4 parts by weight, and most preferably 0 to 3 parts by weight, relative to 100 parts by weight of the total amount of the curing component (free radical polymerizable compound).

(Free radical polymerizable compound (a1) having active methylene group and free radical polymerization initiator (a2) having hydrogen abstraction function)

When a radical polymerizable compound (a1) having an active methylene group is used as the radical polymerizable compound contained in the radical polymerizable resin composition, it is preferably used in combination with a radical polymerization initiator (a2) having a hydrogen abstracting effect. According to this radical polymerizable resin composition, even if the curing layer is provided in direct contact with the brightness enhancement film, good adhesion can be ensured, especially in a high humidity environment. Although the reason is still unclear, it can be inferred as follows. The radical polymerizable compound (a1) having an active methylene group is polymerized together with other radical polymerizable compounds constituting the curing layer, and is incorporated into the main chain and/or side chain of the base polymer in the curing layer to form the curing layer. When a free radical polymerization initiator (a2) having a hydrogen abstracting effect is present in this polymerization process, a base polymer constituting the cured layer is formed on one side, while hydrogen is abstracted from the free radical polymerizable compound (a1) having an active methylene group, thereby generating free radicals in the methylene group. Then, the methylene group generating the free radical reacts with the hydroxyl group of the brightness enhancement film to form a common bond between the cured layer and the brightness enhancement film. As a result, it can be considered that the adhesion between the brightness enhancement film and the cured layer can also be improved, especially in a high humidity environment.

Examples of the free radical polymerization initiator (a2) having a hydrogen abstracting effect include thioxanthone-based free radical polymerization initiators and diphenyl ketone-based free radical polymerization initiators. The free radical polymerization initiator (a2) is preferably a thioxanthone-based free radical polymerization initiator. Examples of the thioxanthone-based free radical polymerization initiator include the above-mentioned compound (4). Specific examples of the compound (4) include thioxanthone, dimethylthioxanthone, diethylthioxanthone, isopropylthioxanthone, chlorothioxanthone, and the like. Among the compounds (4), diethylthioxanthone wherein R ¹¹ and R ¹² are -CH ₂ CH ₃ is particularly preferred.

In the case of a free radical polymerizable resin composition containing a free radical polymerizable compound (a1) having an active methylene group and a free radical polymerization initiator (a2) having a hydrogen abstraction effect, when the total amount of the curable component (free radical polymerizable compound) is 100 weight %, it is preferred to contain 1 to 50 weight % of the free radical polymerizable compound (a1) having an active methylene group, and relative to 100 weight parts of the total amount of the curable component, it is preferred to contain 0.1 to 10 weight parts of the free radical polymerization initiator (a2).

As described above, it is considered that in the presence of the radical polymerization initiator (a2) having hydrogen abstraction, a free radical is generated in the methylene group of the radical polymerizable compound (a1) having an active methylene group, and the methylene group reacts with the hydroxyl group of the brightness enhancement film to form a co-bond. Therefore, in order to generate a free radical in the methylene group of the radical polymerizable compound (a1) having an active methylene group to sufficiently form a co-bond, when the total amount of the curable component (radical polymerizable compound) is 100 wt%, it is preferred that the radical polymerizable compound (a1) having an active methylene group is contained in an amount of 1 to 50 wt%, and more preferably 3 to 30 wt%. In order to sufficiently improve water resistance and improve adhesion between the brightness enhancement film and the cured layer in a high humidity environment, the radical polymerizable compound (a1) having an active methylene group is preferably set to 1 wt% or more. On the other hand, when it exceeds 50 weight percent, the hardening of the hardened layer may be poor. In addition, the free radical polymerization initiator (a2) having hydrogen abstraction effect preferably contains 0.1 to 10 weight parts relative to the total amount of 100 weight parts of the hardening component, and more preferably contains 0.3 to 9 weight parts. In order to fully carry out the hydrogen abstraction reaction, it is preferred to use more than 0.1 weight parts of the free radical polymerization initiator (a2). On the other hand, when it exceeds 10 weight parts, it may not be completely dissolved in the free radical polymerization resin composition.

[A2] Cationic polymerizable resin composition

Cationic polymerizable resin compositions contain cationic polymerizable compounds as curing components. Cationic polymerizable compounds are classified into monofunctional cationic polymerizable compounds having one cationic polymerizable functional group in the molecule and polyfunctional cationic polymerizable compounds having two or more cationic polymerizable functional groups in the molecule. Since the liquid viscosity of monofunctional cationic polymerizable compounds is relatively low, the liquid viscosity of the resin composition can be reduced by containing them in the cationic polymerizable resin composition. In addition, most monofunctional cationic polymerizable compounds have functional groups that exhibit various functions, so by containing them in a cationic polymerizable resin composition, various functions can be exhibited in the resin composition and/or the cured layer of the resin composition.

Since the multifunctional cationic polymerizable compound can three-dimensionally crosslink the cured material layer, it is preferably contained in the resin composition. The mixing ratio of the monofunctional cationic polymerizable compound to the multifunctional cationic polymerizable compound in the cationic polymerizable resin composition is preferably in the range of 10 parts by weight to 1000 parts by weight of the monofunctional cationic polymerizable compound.

Examples of cationic polymerizable functional groups include epoxy groups, oxadiazole groups, and vinyl ether groups. Examples of compounds having epoxy groups include aliphatic epoxy compounds, alicyclic epoxy compounds, and aromatic epoxy compounds. From the perspective of excellent curability or adhesion, it is preferred to contain alicyclic epoxy compounds as cationic polymerizable resin compositions.

Examples of alicyclic epoxy compounds include: 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, caprolactone-modified products, trimethylcaprolactone-modified products, or valerolactone-modified products of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and specific examples include: CELLOXIDE 2021, CELLOXIDE 2021A, CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2083, CELLOXIDE 2085 (all manufactured by Daicel Chemical Industries, Ltd.), CYRACURE UVR-6105, CYRACURE UVR-6107, CYRACURE 30, R-6110 (all manufactured by Dow Chemical Japan Co., Ltd.), etc.

The compound having an oxycarbonyl group has the effect of improving the curability of the cationic polymerization type resin composition or reducing the liquid viscosity of the composition, and therefore it is preferably contained. Compounds with oxadiazole groups include: 3-ethyl-3-hydroxymethyloxadiazole, 1,4-bis[(3-ethyl-3-oxadiazole)methoxymethyl]benzene, 3-ethyl-3-(phenoxymethyl)oxadiazole, di[(3-ethyl-3-oxadiazole)methyl]ether, 3-ethyl-3-(2-ethylhexyloxymethyl)oxadiazole, phenol-phenolaldehydeoxadiazole, etc. The compounds sold on the market include: ARONE OXETANE OXT-101, ARONE OXETANE OXT-121, ARONE OXETANE OXT-211, ARONE OXETANE OXT-221, ARONE OXETANE OXT-212 (all manufactured by Toa Gosei Co., Ltd.), etc.

Compounds with vinyl ether groups have the effect of improving the curing property of cationic polymerization resin compositions or reducing the liquid viscosity of the compositions, so it is preferable to contain them. Compounds with vinyl ether groups include: 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, triethylene glycol divinyl ether, cyclohexanedimethanol divinyl ether, cyclohexanedimethanol monovinyl ether, tricyclodecane vinyl ether, cyclohexyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, pentaerythritol tetravinyl ether, etc.

(Photocatalytic polymerization initiator)

The cationic polymerization type resin composition contains at least one compound selected from the above-mentioned compounds having epoxy groups, compounds having oxadiazole groups, and compounds having vinyl ether groups as curable components. These compounds are all cured by cationic polymerization, so the cationic polymerization type resin composition preferably contains a photo-cationic polymerization initiator. This photo-cationic polymerization initiator generates cationic species or Lewis acids by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams to start the polymerization reaction of epoxy groups or oxadiazole groups. The photo-cationic polymerization initiator is preferably a photoacid generator described later.

When the resin composition containing the curable compound includes a visible light curable compound, it is particularly preferred to use a photo-cationic polymerization initiator that is highly sensitive to light of 380 nm or longer. However, the photo-cationic polymerization initiator is generally a compound that exhibits maximum absorption in the vicinity of 300 nm or in a wavelength region shorter than that. Therefore, by preparing a photosensitizer that exhibits maximum absorption in a longer wavelength region, specifically, in a wavelength longer than 380 nm, the photo-cationic polymerization initiator can be sensitive to light of the vicinity and promote the generation of cationic species or acid. Examples of photosensitizers include anthracene compounds, pyrene compounds, carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, photoreduction pigments, etc. Two or more of these can be mixed and used. Anthracene compounds are particularly preferred because of their excellent photosensitization effect. Specific examples include ANTHRACURE UVS-1331 and ANTHRACURE UVS-1221 (manufactured by Kawasaki Chemical Co., Ltd.). The content of the photosensitizer is preferably 0.1% to 5% by weight, and more preferably 0.5% to 3% by weight.

[A3] Other ingredients

The resin composition containing active energy ray-curable compounds may contain: (meth) acrylic oligomers, photoacid generators, compounds containing epoxy or alkoxy groups, silane coupling agents, compounds having vinyl ether groups, and additives other than these. These components are described below.

((Meth)acrylic acid oligomer)

The radical polymerizable resin composition or cationic polymerizable resin composition may contain, in addition to the radical polymerizable compound or cationic polymerizable compound (curing component), a (meth)acrylic acid oligomer obtained by polymerizing a (meth)acrylic acid monomer. By including the (meth)acrylic acid oligomer in the resin composition, the curing shrinkage when the resin composition is irradiated with active energy rays for curing is reduced, and the interfacial stress between the cured layer and the brightness enhancement film can be reduced. As a result, the reduction in the adhesion between the cured layer of the resin composition and the brightness enhancement film can be suppressed. In order to fully suppress the curing shrinkage of the cured layer, it is preferred to contain 3 parts by weight or more of the (meth)acrylic acid oligomer relative to 100 parts by weight of the total amount of the curing component, and it is particularly preferred to contain 5 parts by weight or more. When the content of (meth)acrylic oligomer in the above resin composition is too high, the reaction rate decreases rapidly when the resin composition is irradiated with active energy rays, which may lead to poor curing. In order to fully suppress the decrease in reaction rate, it is preferred to contain 20 parts by weight or less of (meth)acrylic oligomer, and more preferably 15 parts by weight or less, relative to 100 parts by weight of the total amount of curable components.

Considering the workability or uniformity during coating, since the free radical polymerization type resin composition or the cationic polymerization type resin composition is preferably low in viscosity, the (meth)acrylic oligomer is preferably low in viscosity. The (meth)acrylic oligomer having low viscosity and preventing the curing shrinkage of the cured layer is preferably one having a weight average molecular weight (Mw) of 15,000 or less, preferably 10,000 or less, and particularly preferably 5,000 or less. On the other hand, in order to fully suppress the curing shrinkage of the cured layer, the weight average molecular weight (Mw) of the (meth)acrylic oligomer is preferably 500 or more, preferably 1000 or more, and particularly preferably 1500 or more.

Examples of (meth)acrylic monomers constituting the (meth)acrylic oligomers include: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, dibutyl (meth)acrylate, tertiary butyl (meth)acrylate, n-pentyl (meth)acrylate, tertiary pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, propyl (meth)acrylate, 2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, dibutyl (meth)acrylate, tertiary butyl (meth)acrylate, n-pentyl (meth)acrylate, tertiary pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, 2-nitropropyl (meth)acrylate, 2-nitropropyl (meth)acrylate, 2-nitropropyl (meth)acrylate, 2-nitropropyl (meth)acrylate, 2-nitrobutyl ... (meth)acrylate (carbon number 1 to 20) alkyl esters such as n-hexyl (meth)acrylate, cetyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and N-octadecyl (meth)acrylate; cycloalkyl (meth)acrylates (e.g., cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, etc.); arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate, etc.); polycyclic (meth)acrylates (e.g., 2-isoborneol (meth)acrylate, 2-norborneol (meth)acrylate, etc.); methyl (meth)acrylate, 5-norbornyl-2-yl-methyl (meth)acrylate, 3-methyl-2-norbornyl methyl (meth)acrylate, etc.); hydroxyl (meth)acrylates (e.g. hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2,3-dihydroxypropylmethyl-butyl (meth)acrylate, etc.); alkoxy or phenoxy (meth)acrylates (2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, (meth)acrylate ethyl carbitol ester, (meth)acrylate phenoxyethyl ester, etc.); epoxy group-containing (meth)acrylates (such as (meth)acrylate glycidyl ester, etc.); halogen-containing (meth)acrylates (such as (meth)acrylate 2,2,2-trifluoroacetate, (meth)acrylate 2,2,2-trifluoroethyl ethyl ester, (meth)acrylate tetrafluoropropyl ester, (meth)acrylate hexafluoropropyl ester, (meth)acrylate octafluoropentyl ester, (meth)acrylate heptadecafluorodecyl ester, etc.); (meth)acrylate alkylamine alkyl esters (such as (meth)acrylate dimethylaminoethyl ester, etc.). These (meth)acrylates can be used alone or in combination of two or more.

Specific examples of (meth)acrylic acid oligomers include: "ARUFON" manufactured by Toagosei Co., Ltd., "ACTFLOW" manufactured by Soken Chemical Co., Ltd., and "JONCRYL" manufactured by BASF Japan Co., Ltd. Among (meth)acrylic acid oligomers, those with higher logPow values are preferred. The logPow value of (meth)acrylic acid oligomers is preferably 2 or more, particularly preferably 3 or more, and most preferably 4 or more.

(Photoacid generator)

The resin composition containing an active energy ray-curable compound may contain a photoacid generator. When the resin composition contains a photoacid generator, the water resistance and durability of the cured layer can be dramatically improved compared to the case where the photoacid generator is not contained. The photoacid generator can be represented by the following general formula (6).

L ⁺ X ^- ． ． ． (6)

_In the formula, L ⁺ represents an arbitrary onium cation; and ^X- represents ^a relative anion selected from the group consisting of _PF6- , ^SbF6- , _AsF6- , _SbCl6- , ^{BiCl5- ,} _SnCl6- ^, _ClO4- ^, dithiocarbamate anions ^, and SCN- _.

^X- is preferably _PF6- , ^SbF6- _or ^AsF6- _, ^particularly _preferably ^PF6- or ^SbF6- _.

Preferable onium salts constituting the photoacid generator include, for example, CYRACURE UVI-6992, CYRACURE UVI-6974 (both manufactured by Dow Chemical Japan Co., Ltd.), ADEKAOPTOMER SP150, ADEKAOPTOMER SP152, ADEKAOPTOMER SP170, ADEKAOPTOMER SP172 (both manufactured by ADEKA Co., Ltd.), IRGACURE 250 (manufactured by Ciba Specialty Chemicals Co., Ltd.), CI-5102, CI-2855 (manufactured by Nippon Soda Co., Ltd.), SAN-AID SI-60L, SAN-AID SI-80L, SAN-AID SI-100L, SAN-AID SI-110L, SAN-AID SI-250L, SAN-AID SI-250L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L, SAN-AID SI-300L SI-180L" (all manufactured by Sanshin Chemical Co., Ltd.), "CPI-100P", "CPI-100A" (all manufactured by SunApro Co., Ltd.), "WPI-069", "WPI-113", "WPI-116", "WPI-041", "WPI-044", "WPI-054", "WPI-055", "WPAG-281", "WPAG-567", "WPAG-596" (all manufactured by Wako Junyaku Co., Ltd.).

The photoacid generator is less than 10 parts by weight relative to 100 parts by weight of the total amount of curable components contained in the resin composition containing the active energy ray curable compound, preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight, and particularly preferably 0.1 to 3 parts by weight.

(Compounds containing epoxy or alkoxy groups)

The resin composition containing the active energy ray-curable compound may include a compound containing an epoxy group or an alkoxy group together with a photoacid generator.

Compounds containing epoxy groups include compounds having one or more epoxy groups in the molecule or compounds having two or more epoxy groups in the molecule, which may be high molecular weight compounds (epoxy resins). When using these compounds, compounds having two or more functional groups reactive with epoxy groups in the molecule may also be used in combination. The so-called functional groups reactive with epoxy groups include, for example, carboxyl groups, phenolic hydroxyl groups, hydroxyl groups, primary or secondary aromatic amine groups, etc. Considering the three-dimensional curability, it is particularly preferred that these functional groups have two or more in one molecule.

Examples of compounds having one or more epoxy groups in the molecule include epoxy resins, such as bisphenol A type epoxy resin derived from bisphenol A and epichlorohydrin, bisphenol F type epoxy resin derived from bisphenol F and epichlorohydrin, bisphenol S type epoxy resin, phenol-novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, aliphatic epoxy resin, diphenyl ether type epoxy resin, Resins, hydroquinone epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, fluorene epoxy resins, trifunctional epoxy resins or quadrifunctional epoxy resins and other multifunctional epoxy resins; glycerol ester epoxy resins; glycerol amine epoxy resins; hydantoin epoxy resins; isocyanurate epoxy resins; aliphatic chain epoxy resins, etc. These epoxy resins can be halogenated or hydrogenated.

Commercially available epoxy resin products are not particularly limited, and examples thereof include: JER COAT 828, 1001, 801N, 806, 807, 152, 604, 630, 871, YX8000, YX8034, YX4000 manufactured by Japan Epoxy Resin Co., Ltd.; EPICLON 830, EXA835LV, HP4032D, HP820 manufactured by DIC Co., Ltd.; EP4100 series, EP4000 series, EPU series manufactured by ADEKA Co., Ltd.; CELLOXIDE series (2021, 2021P, 2083, 2085, 3000, etc.), EPOLEAD series, EHPE series manufactured by Industries Co., Ltd.; YD series, YDF series, YDCN series, YDB series, phenoxy resins (polyhydroxy polyethers synthesized from bisphenols and epichlorohydrin and having epoxy groups at both ends; YP series, etc.) manufactured by Nippon Steel Chemical Co., Ltd.; DENACOL series manufactured by Nagase Chemtex Co., Ltd.; EPOLIGHT series manufactured by Kyoeisha Chemical Co., Ltd., etc. These epoxy resins can be used in combination of two or more.

The compound having an alkoxy group in the molecule is not particularly limited as long as it has one or more alkoxy groups in the molecule, and generally known compounds can be used. Examples of such compounds include melamine compounds, amino resins, silane coupling agents, etc.

The compound containing epoxy or alkoxy groups is usually contained in an amount of 30 parts by weight or less, preferably 20 parts by weight or less, relative to 100 parts by weight of the total amount of curable components contained in the resin composition containing the active energy ray curable compound. When the content of the compound containing epoxy or alkoxy groups is too high, the adhesion of the cured layer relative to the brightness enhancement film is reduced, and the impact resistance relative to the drop test may sometimes deteriorate. From the point of view of water resistance, the compound containing epoxy or alkoxy groups is preferably contained in an amount of 2 parts by weight or more, and more preferably 5 parts by weight or more, relative to 100 parts by weight of the total amount of curable components contained in the above-mentioned resin composition.

(Silane coupling agent)

The resin composition containing an active energy ray-curable compound may contain a silane coupling agent. In this case, the silane coupling agent is preferably an active energy ray-curable compound, but even if it is not an active energy ray-curable compound, it can also impart water resistance to the cured layer.

Examples of active energy ray-curable silane coupling agents include vinyl trichlorosilane, vinyl trimethoxysilane, vinyl triethoxysilane, 2-(3,4-epoxyhexyl)ethyl trimethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 3-glycidoxypropyl triethoxysilane, p-phenylenediyl trimethoxysilane, 3-methacryloxypropyl methyldimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropyl methyldiethoxysilane, 3-methacryloxypropyl triethoxysilane, and 3-acryloxypropyl trimethoxysilane. Among them, 3-methacryloxypropyltrimethoxysilane and 3-acryloxypropyltrimethoxysilane are preferred.

The non-active energy ray-curable silane coupling agent is preferably a silane coupling agent having an amine group. Examples of silane coupling agents having an amino group include γ-aminopropyl trimethoxysilane, γ-aminopropyl triethoxysilane, γ-aminopropyl triisopropoxysilane, γ-aminopropyl methyldimethoxysilane, γ-aminopropyl methyldiethoxysilane, γ-(2-aminoethyl)aminopropyl trimethoxysilane, γ-(2-aminoethyl)aminopropyl methyldimethoxysilane, γ-(2-aminoethyl)aminopropyl triethoxysilane, γ-(2-aminoethyl)aminopropyl methyldiethoxysilane, γ-(2-aminoethyl)aminopropyl triisopropoxysilane, γ-(2-(2-aminoethyl)aminoethyl)aminopropyl trimethoxysilane, γ-(6-aminohexyl)aminopropyl trimethoxysilane, 3-(N- Amine-containing silanes such as (2-aminoethyl)-2-methylpropyl trimethoxysilane, γ-ureapropyl trimethoxysilane, γ-ureapropyl triethoxysilane, N-phenyl-γ-aminopropyl trimethoxysilane, N-benzyl-γ-aminopropyl trimethoxysilane, N-vinylbenzyl-γ-aminopropyl triethoxysilane, N-cyclohexylaminomethyl triethoxysilane, N-cyclohexylaminomethyl diethoxysilane, N-phenylaminomethyl trimethoxysilane, (2-aminoethyl)aminomethyl trimethoxysilane, N,N’-bis[3-(trimethoxysilyl)propyl]ethylenediamine; ketimine-type silanes such as N-(1,3-dimethylbutylene)-3-(triethoxysilyl)-1-propaneamine.

Other silane coupling agents that are not active energy ray curable include: 3-ureapropyl triethoxysilane, 3-chloropropyl trimethoxysilane, 3-butyl methyl dimethoxysilane, 3-butyl trimethoxysilane, bis(triethoxysilylpropyl) tetrasulfide, 3-isocyanatopropyl triethoxysilane, imidazole silane, etc.

Among these, in order to ensure good adhesion, the preferred ones are γ-aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, and N-(1,3-dimethylbutylene)-3-(triethoxysilyl)-1-propaneamine. Silane coupling agents having an amino group can be used alone or in combination of two or more.

The silane coupling agent preferably contains 0.01 to 20 parts by weight, more preferably 0.05 to 15 parts by weight, and even more preferably 0.1 to 10 parts by weight relative to 100 parts by weight of the total amount of the curable components contained in the resin composition containing the active energy ray curable compound. When the content of the silane coupling agent is too high, the storage stability of the above-mentioned resin composition deteriorates. In addition, when the content of the silane coupling agent is too low, the water resistance effect is not easy to exert.

(Compounds with vinyl ether groups)

The resin composition containing the active energy line curable compound may contain a compound having a vinyl ether group. By containing a compound having a vinyl ether group, the water resistance of the bonding between the brightness enhancement film and the cured layer can be improved. This can be inferred that the vinyl ether group interacts with the brightness enhancement film to improve the bonding strength. In order to further improve the water resistance of the bonding between the brightness enhancement film and the cured layer, the compound having a vinyl ether group is preferably a free radical polymerizable compound. The compound having a vinyl ether group preferably contains 0.1 to 19 parts by weight relative to 100 parts by weight of the total amount of the curable component contained in the resin composition containing the active energy line curable compound.

(Additive)

The resin composition containing the active energy ray-curable compound may contain various additives in addition to the above-mentioned (meth) acrylic oligomer, photoacid generator, compound containing epoxy group or alkoxy group, silane coupling agent and compound having vinyl ether group within the scope not impairing the purpose and effect of the present invention. The additives include: epoxy resin, polyamide, polyamide imide, polyurethane, polybutadiene, polychloroprene, polyether, polyester, styrene-butadiene block copolymer, petroleum resin, xylene resin, ketone resin, cellulose resin, fluorine oligomer, polysilicone oligomer, polysulfide oligomer and other polymers or oligomers; polymerization inhibitors such as phenothiazine and 2,6-di(tertiary butyl)-4-methylphenol; polymerization initiation auxiliary agent; leveling agent; wettability improver; surfactant; plasticizer; ultraviolet absorber; inorganic filler; pigment; dye, etc. Among the above additives, those with higher logPow values are preferred. The logPow value of the above additives is preferably 2 or more, more preferably 3 or more, and most preferably 4 or more. The above additives usually contain 0 to 10 parts by weight, preferably 0 to 5 parts by weight, and most preferably 0 to 3 parts by weight, relative to 100 parts by weight of the total amount of curable components contained in the resin composition containing the active energy ray curable compound.

[B] Thermosetting compounds

From the perspective of adhesion between the brightness enhancement film and the cured layer, thermosetting compounds can use thermosetting adhesives, hot melt adhesives, etc. Specific examples include: natural rubber adhesives, α-olefin adhesives, urethane resin adhesives, ethylene-vinyl acetate resin emulsion adhesives, ethylene-vinyl acetate resin hot melt adhesives, epoxy resin adhesives, vinyl chloride resin solvent adhesives, chloroprene rubber adhesives, cyanoacrylate adhesives, silicone adhesives, styrene-butadiene rubber solvent adhesives, nitrile rubber adhesives, nitrocellulose adhesives, reactive hot melt adhesives, phenolic resin adhesives, modified silicone adhesives. Adhesives, polyester hot melt adhesives, polyamide resin hot melt adhesives, polyimide resin hot melt adhesives, polyurethane resin hot melt adhesives, polyolefin resin hot melt adhesives, polyvinyl acetate resin solvent adhesives, polystyrene resin solvent adhesives, polyvinyl alcohol adhesives, polyvinyl pyrrolidone resin adhesives, polyvinyl butyral adhesives, polybenzimidazole adhesives, polymethacrylate resin solvent adhesives, melamine resin adhesives, urea resin adhesives, resorcinol adhesives, etc. This adhesive can be used alone or as a mixture of two or more, and the base polymer is used according to the type of adhesive.

Thermosetting adhesives are hardened and cured by heating to show adhesion. Examples of thermosetting adhesives include epoxy-based thermosetting adhesives, urethane-based thermosetting adhesives, and acrylic-based thermosetting adhesives. The curing temperature of thermosetting adhesives is, for example, 100 to 200°C.

The hot melt adhesive is melted or softened by heating and hot-melted to the brightness enhancement film, and solidified by subsequent cooling and thereby bonded to the brightness enhancement film. Examples of hot melt adhesives include: rubber hot melt adhesives, polyester hot melt adhesives, polyolefin hot melt adhesives, ethylene-vinyl acetate resin hot melt adhesives, polyamide resin hot melt adhesives, polyurethane resin hot melt adhesives, etc. The softening temperature (global method) of the hot melt adhesive is, for example, 100 to 200°C. In addition, the melt viscosity of the hot melt adhesive is, for example, 100 to 30000 MPa‧s at 180°C.

[Linear polarizing layer]

The linear polarizing layer has the property of allowing linear polarized light having a vibration plane orthogonal to the absorption axis to pass through when non-polarized light is incident. The linear polarizing layer preferably comprises a polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA") resin film.

Examples of linear polarizing layers including PVA resin films include: polyvinyl alcohol (hereinafter sometimes referred to as "PVA") films, partially formaldehydeated PVA films, ethylene-vinyl acetate copolymer partially saponified films and other hydrophilic polymer films, which have been dyed with dichroic substances such as iodine or dichroic dyes, and stretched. From the perspective of superior optical properties, it is preferred to use a linear polarizing layer obtained by dyeing a PVA resin film with iodine and uniaxially stretching it.

Polyvinyl alcohol resins can be produced by saponifying polyvinyl acetate resins. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate resins can also be copolymers of vinyl acetate and other monomers that can be copolymerized with vinyl acetate. Examples of other monomers that can be copolymerized with vinyl acetate include: unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, acrylamides with ammonium groups, etc.

The saponification degree of polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. Polyvinyl alcohol resin can be modified, for example, polyvinyl formaldehyde or polyvinyl acetal modified with aldehydes can also be used. The degree of polymerization of polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

The polyvinyl alcohol resin is used as a raw material film for a linear polarizing layer. The method for making a polyvinyl alcohol resin film is not particularly limited, and the film can be made by a generally known method. The film thickness of the polyvinyl alcohol resin raw material film is, for example, about 10 to 100 μm, preferably about 10 to 60 μm, and particularly preferably about 15 to 30 μm.

Other methods for manufacturing a linear polarizing layer including a PVA resin film include the following steps: first, a substrate film is prepared, a solution of a resin such as a polyvinyl alcohol resin is applied to the substrate film, and a step of removing the solvent by drying is performed to form a resin layer on the substrate film. A primer layer may be formed in advance on the surface of the substrate film on which the resin layer is formed. The substrate film may be a resin film such as PET. The materials of the primer layer include: a resin obtained by crosslinking the hydrophilic resin used in the linear polarizing layer, etc.

Then, the amount of water or other solvents in the resin layer is adjusted as needed, and then the substrate film and the resin layer are uniaxially stretched, and then the resin layer is dyed with dichroic dyes such as iodine so that the dichroic dyes are adsorbed and aligned on the resin layer. Then, the resin layer adsorbed and aligned with the dichroic dyes is treated with a boric acid aqueous solution as needed, and a washing step is performed to wash away the boric acid aqueous solution. In this way, a resin layer adsorbed and aligned with the dichroic dyes, that is, a film of a linear polarizing layer, is manufactured. Each step can adopt a generally known method.

The uniaxial stretching of the substrate film and the resin layer can be performed before dyeing, during dyeing, or during the boric acid treatment after dyeing, and can also be performed separately in these multiple stages. The substrate film and the resin layer can be uniaxially stretched in the MD direction (film transport direction). In this case, the uniaxial stretching can be performed between rollers with different peripheral speeds, or the uniaxial stretching can be performed using hot rollers. In addition, the substrate film and the resin layer can be uniaxially stretched in the TD direction (direction perpendicular to the film transport direction). In this case, the so-called tentering method can be used. In addition, the stretching of the substrate film and the resin layer can be dry stretching in the atmosphere, or wet stretching in a state where the resin layer is swollen with a solvent. In order to demonstrate the performance of the linear polarizing layer, the stretching ratio is 4 times or more, preferably 5 times or more, and particularly preferably 5.5 times or more. There is no particular upper limit to the stretching ratio, but from the perspective of suppressing cracking, it is preferably 8 times or less.

The linear polarizing layer produced by the above method can be obtained by peeling off the base film after laminating the protective layer described later.

The thickness of the linear polarizing layer is preferably 5 μm or more, more preferably 10 μm or more, and can be 15 μm or more, or 20 μm or more. In addition, the thickness of the linear polarizing layer is 50 μm or less, preferably 40 μm or less, and can be 30 μm or less.

[Polarizing plate]

The linear polarizing layer can be laminated on one or both sides of the linear polarizing layer via a generally known adhesive layer or bonding layer, and the first protective layer or the first protective layer and the second protective layer (hereinafter sometimes the first protective layer and the second protective layer are collectively referred to as "protective layer") can form a polarizing plate. This polarizing plate is a so-called linear polarizing plate. The protective layer that can be laminated on one or both sides of the linear polarizing layer can be, for example, a film formed of a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture barrier, isotropy, elongation, etc. Specific examples of the thermoplastic resin include cellulose resins such as cellulose triacetate; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyether resins; polyester resins; polycarbonate resins; polyamide resins such as nylon or aromatic polyamide; polyimide resins; polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; cyclic polyolefin resins having a ring system and a norbornene structure (also referred to as a norbornene resin); (meth)acrylic resins; polyarylate resins; polystyrene resins; polyvinyl alcohol resins, and mixtures thereof. When the double-sided layer of the linear polarizing layer has a protective layer, the resin composition of the two protective layers can be the same or different.

In order to improve the adhesion with the linear polarizing layer, the film formed by the thermoplastic resin can be subjected to surface treatment (such as corona treatment, etc.), and a thin layer such as a primer layer (also called a base coating layer) can also be formed.

The protective layer may be, for example, the above-mentioned thermoplastic resin that has been stretched or not stretched (hereinafter sometimes referred to as "unstretched resin"). Stretching treatment may include uniaxial stretching or biaxial stretching, etc.

The adhesive layer used for laminating the protective layer on the linear polarizing layer may be the adhesive described in the first adhesive layer, etc. described later. The adhesive layer used for laminating the protective layer on the linear polarizing layer may be a generally known adhesive. The adhesive is an adhesive other than a pressure-sensitive adhesive (adhesive), and examples thereof include a water-based adhesive and an active energy ray-hardening adhesive. Examples of the water-based adhesive include an adhesive obtained by dissolving or dispersing a polyvinyl alcohol-based resin in water. Examples of active energy ray-curable adhesives include solvent-free active energy ray-curable adhesives containing curable compounds that are cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays.

[Brightness enhancement film]

The brightness enhancement film uses: a polarization conversion element that has the function of separating the emitted light from a light source such as a backlight into a transmitted polarized light and a reflected polarized light or a scattered polarized light. The brightness enhancement film can utilize the reflected polarized light or the scattered polarized light that is the return light from the light source to enhance the emission efficiency of the linear polarized light.

Anisotropic reflective polarizers can be used as brightness enhancement films. Examples of anisotropic reflective polarizers include: those that allow linear polarization of a given polarization axis to pass through and reflect other light, such as a multilayer film of a dielectric or a multilayer laminate of layers with different refractive index anisotropies; and those that allow circular polarization of either left or right to pass through, such as an alignment film of a cholesterol liquid crystal polymer or an alignment liquid crystal layer supported on a film substrate. The types of layers constituting the anisotropic reflective polarizer can be set to 2 or more.

For example, the brightness enhancement film may use the following laminate, that is, a laminate obtained by uniaxially stretching alternate layers of materials that produce phase difference by stretching, such as polyethylene naphthalate, polyethylene terephthalate, and polycarbonate, and resins with less phase difference, such as acrylic resins represented by polymethyl methacrylate and norbornene resins represented by "ARTON" (registered trademark) manufactured by JSR Co., Ltd. Specific examples of this structure include: "DBEF" (registered trademark), "APF-V4" (product name), "APF-V3" (product name), and "APF-V2" (product name) manufactured by 3M Company, etc.

The brightness enhancement film may be, for example, a laminate of a cholesterol liquid crystal layer and a λ/4 plate. A specific example of this laminate is the product name "PCF" manufactured by Nitto Denko Co., Ltd.

The brightness enhancement film can be a reflective grating polarizer. Examples of reflective grating polarizers include: metal grid reflective polarizers that are micro-processed to allow reflected polarized light to be emitted even in the visible light region.

The thickness of the brightness enhancement film is usually 5 μm or more, preferably 10 μm or more, and usually 100 μm or less, preferably 50 μm or less, and can be 35 μm or less.

[1st adhesive layer, 2nd adhesive layer, 3rd adhesive layer]

The first adhesive layer, the second adhesive layer, and the third adhesive layer (hereinafter sometimes collectively referred to as "adhesive layer") are layers composed of adhesive. In this manual, "adhesive" means that it is attached to an adherend such as a polarizing plate or a liquid crystal layer to show adhesion, which is called a so-called pressure-sensitive adhesive. In addition, the active energy ray curing adhesive described later can adjust the crosslinking degree or adhesion by irradiating energy rays.

As long as the adhesive is an adhesive with excellent optical transparency that is generally known in the past, it can be used without special restrictions. For example, adhesives with base polymers such as acrylic, urethane, silicone, and polyvinyl ether can be used. In addition, active energy ray-curing adhesives and thermosetting adhesives can also be used. Among these, adhesives with acrylic resins as base polymers that are excellent in transparency, adhesion, re-peelability (hereinafter also referred to as reworkability), weather resistance, and heat resistance are preferred. The adhesive layer is preferably composed of a reaction product of an adhesive composition containing a (meth) acrylic resin, a crosslinking agent, and a silane compound, and may also contain other components.

The adhesive layer can also be formed using an active energy ray curing adhesive. Active energy ray curing adhesives are formed by mixing ultraviolet curing compounds such as multifunctional acrylates into the adhesive composition, and then irradiating ultraviolet rays to cure the adhesive layer after forming the adhesive layer, thereby forming a harder adhesive layer. Active energy ray curing adhesives have the property of curing by receiving energy rays such as ultraviolet rays or electron beams. Since active energy ray curing adhesives also have adhesive properties before energy ray irradiation, they are adhesives with the following properties, namely, they adhere closely to adherends such as optical films or liquid crystal layers, and can be cured by irradiating energy rays to adjust the adhesion.

Active energy ray-curing adhesives generally contain acrylic adhesives and energy ray-polymerizable compounds as main components. A crosslinking agent is usually added, and a photopolymerization initiator or photosensitizer can also be added as needed.

The storage elasticity of the adhesive layer is preferably 0.10 to 10.0 MPa at 23°C, and more preferably 0.15 to 5.0 MPa. When the storage elasticity at 23°C is 0.10 MPa or more, it is preferred because it can suppress defects such as peeling when temperature changes occur. In addition, when it is below 10.0 MPa, it is less likely to cause a decrease in durability due to a decrease in adhesion, so it is preferred. The storage elasticity of the adhesive layer can be measured by the method described in the embodiment.

The thickness of the adhesive layer is preferably 3 μm or more, and more preferably 5 μm or more. In addition, the thickness of the adhesive layer is preferably 40 μm or less, and more preferably 30 μm or less.

[Peeling membrane]

The peeling film is a film that covers and protects the adhesive layer or supports the adhesive layer, and has the function of being a separator that can be peeled off from the adhesive layer. The peeling film can be a film that has been subjected to a release treatment such as silicone treatment on the surface of the adhesive layer side of the substrate film. The resin material constituting the substrate film can be the same as the resin material constituting the protective layer mentioned above. The resin film can be a multi-layer resin film with a single-layer structure or a multi-layer structure of two or more layers.

[Implementation example]

The following are embodiments and comparative examples to more specifically illustrate the present invention, but the present invention is not limited to these examples.

[Measurement of thickness]

The thickness of each layer was measured using a digital micrometer MH-15M manufactured by Nikon Corporation.

[Measurement of in-plane hysteresis]

AxoScan (manufactured by Axometrics) was used to measure the in-plane retardation Re(590) of the buffer layer at a wavelength of 590nm.

[Determination of tensile elasticity]

A rectangular sample for measurement with a length of 100 mm in MD and 20 mm in TD was cut out from the film used as the buffer layer. The MD length is the length in the direction corresponding to the absorption axis direction of the linear polarizing layer of the composite polarizing plate. The upper and lower clamps of the tensile tester [Shimadzu Corporation Autoclave AG-Xplus tester] were used to clamp the two ends of the MD length direction of the test sample with a distance of 5 cm between the clamps. The test sample was pulled in the MD length direction at a tensile speed of 1 mm/min in an environment of 23°C and 55% relative humidity. The tensile modulus [GPa] in the MD length direction at 23°C and 55% relative humidity was calculated from the slope of the initial straight line in the obtained stress-strain curve.

[High temperature durability test]

From the composite polarizing plate obtained in the embodiment or comparative example, a sample with a length of 160 mm in MD and 100 mm in TD was obtained. The release film was peeled off from the sample, and the exposed adhesive layer (third adhesive layer) was attached to a glass plate to form a test piece. The test piece was autoclaved at a temperature of 50°C and a pressure of 0.5 MPa for 15 minutes, and then placed in an oven at a temperature of 95°C for 500 hours. The appearance of the brightness enhancement film side of the test piece was visually observed.

[Implementation Example 1]

(Production of linear polarizing layer)

A 75μm thick polyvinyl alcohol film made of polyvinyl alcohol with an average polymerization degree of about 2,400 and a saponification degree of more than 99.9 mol% was stretched uniaxially by about 5 times in a dry manner, and then immersed in pure water at 60°C for 1 minute while maintaining tension, and then immersed in an aqueous solution of iodine/potassium iodide/water with a weight ratio of 0.05/5/100 at 28°C for 60 seconds. Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water with a weight ratio of 8.5/8.5/100 at 72°C for 300 seconds. Then, it was washed with pure water at 26°C for 20 seconds and dried at 65°C to obtain a 28μm thick linear polarizing layer with iodine adsorbed and aligned on the polyvinyl alcohol.

(Preparation of follow-up agent)

Dissolve 50g of modified PVA resin containing acetyl group (GOHSENX Z-410 manufactured by Mitsubishi Chemical Co., Ltd.) in 950g of pure water, heat at 90℃ for 2 hours and then cool to room temperature to obtain PVA solution. Then, mix PVA solution, maleic acid, glyoxal and pure water in such a way that each compound has the following concentration to prepare PVA adhesive.

(Production of polarizing plates)

The above-mentioned adhesive is applied to one side of the linear polarizing layer obtained above, and the first protective layer (a cellulose triacetate film with a thickness of 40 μm [a product name "KC4UYW" manufactured by Konica Minolta Opto Co., Ltd.]) is laminated thereon. The above-mentioned adhesive is applied to the other side, and the second protective layer (an acrylic resin film with a thickness of 40 μm [a product name "HX-40NE" manufactured by Toyo Kogyo Co., Ltd.]) is laminated thereon, and dried to produce a polarizing plate. When laminating these materials, the laminating surfaces of each material are subjected to a corona treatment.

(Production of composite polarizing plates)

A commercially available sheet of acrylic adhesive with a thickness of 25 μm was bonded to the first protective layer side of the polarizing plate obtained above to form a first adhesive layer, and a triacetate cellulose film [product name "TJ40UL" manufactured by Fujifilm Co., Ltd.] as a buffer layer was bonded to the first adhesive layer side opposite to the polarizing plate side. Then, a commercially available sheet of acrylic adhesive with a thickness of 25 μm was bonded to the buffer layer side opposite to the first adhesive layer side to form a second adhesive layer, and a brightness enhancement film ("AFP-V3 HCS" manufactured by 3M) was bonded to the second adhesive layer side opposite to the buffer layer side. Furthermore, the adhesive layer side of the adhesive sheet having an adhesive layer (the third adhesive layer) of an acrylic adhesive with a thickness of 25 μm formed on a release film (38 μm thick, polyethylene terephthalate film) was attached to the second protective layer side of the polarizing plate. Through the above steps, a composite polarizing plate having the following laminated layers in sequence: a release film, a third adhesive layer, a polarizing plate (the second protective layer, a linear polarizing layer, and the first protective layer are laminated in sequence from the third adhesive layer side), a first adhesive layer, a buffer layer, a second adhesive layer, and a brightness enhancement film was obtained. When bonding the materials, the bonding surfaces of the materials are subjected to corona treatment.

When measuring the in-plane retardation Re(590) of the cellulose triacetate film used as the buffer layer at a wavelength of 590nm, the result was 0.5nm. The tensile elasticity of the buffer layer at a temperature of 23°C and a relative humidity of 55% was 5200MPa. In addition, the obtained composite polarizing plate was subjected to a high-temperature durability test, and no wrinkles were observed in the brightness enhancement film, and the appearance of the composite polarizing plate was good.

[Comparison Example 1]

Except that the buffer layer and the second adhesive layer are not provided, the other parts are the same as Example 1, and the following are laminated in sequence: a release film, a third adhesive layer, a polarizing plate (a second protective layer, a linear polarizing layer, and a first protective layer are laminated in sequence from the third adhesive layer side), a first adhesive layer, and a composite polarizing plate of a brightness enhancement film. The obtained composite polarizing plate was subjected to a high temperature durability test, and a large number of wrinkles were confirmed at the end of the long side of the brightness enhancement film.

1: Composite polarizing plate

10: Polarizing plate

11: Linear polarizing layer

12: 1st protective layer

13: Second protective layer

15a: Buffer layer

18: Brightness enhancement film

31: 1st adhesive layer

32: Second adhesive layer

Claims (13)

A composite polarizing plate comprises: a polarizing plate having a protective layer on at least one side of a linear polarizing layer, and a brightness enhancement film, wherein a first adhesive layer, a buffer layer and the brightness enhancement film are sequentially laminated on the protective layer side of the polarizing plate, the linear polarizing layer is a polyvinyl alcohol resin film with iodine adsorbed and aligned, the thickness of the linear polarizing layer is 15 to 30 μm, the tensile elasticity of the buffer layer at a temperature of 23°C and a relative humidity of 55% is 1.5 GPa or more, the buffer layer is a resin film, and the thickness of the buffer layer is 30 μm or more and 60 μm or less. The composite polarizing plate as described in claim 1, wherein the buffer layer and the brightness enhancement film are bonded together via a second adhesive layer. The composite polarizing plate as described in claim 1, wherein the resin film comprises a film composed of at least one resin selected from the group consisting of cellulose ester resins, (meth) acrylic resins and cyclic olefin resins. The composite polarizing plate as described in claim 1, wherein the aforementioned buffer layer is in direct contact with the aforementioned brightness enhancement film. The composite polarizing plate as described in claim 1 or 4, wherein the aforementioned buffer layer is a cured layer of a resin composition containing a curable component. The composite polarizing plate as described in claim 5, wherein the aforementioned curable component contains an active energy ray curable compound. A composite polarizing plate as described in any one of claims 1, 2 and 4, wherein the in-plane retardation Re(590) of the aforementioned buffer layer at a wavelength of 590nm is less than 20nm. The composite polarizing plate as described in any one of claims 1, 2 and 4, wherein the first adhesive layer is bonded to the protective layer and the buffer layer of the polarizing plate. A composite polarizing plate as described in any one of claims 1, 2 and 4, wherein the polarizing plate has the protective layer on both sides of the linear polarizing layer. A composite polarizing plate as described in any one of claims 1, 2 and 4, wherein a third adhesive layer is provided on the side of the polarizing plate opposite to the side of the brightness enhancement film. The composite polarizing plate as described in claim 10, wherein a release film is provided on the side of the third adhesive layer opposite to the side of the polarizing plate. A liquid crystal display device, comprising: a composite polarizing plate as described in any one of claims 1 to 11, and a liquid crystal unit. The liquid crystal display device as described in claim 12 further has a backlight, wherein the composite polarizing plate is arranged between the liquid crystal unit and the backlight in such a manner that the brightness enhancement film side becomes the backlight side.

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