Polarizing plate, display component, method for manufacturing a polarizing plate

Abstract

To provide a polarizing plate thinner than before, a display member using the polarizing plate, and a method of manufacturing the polarizing plate.SOLUTION: A polarizing plate provided herein comprises a polarizer, and a cured resin layer formed of a curable composition containing (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator and laminated directly on one surface of the polarizer without other layers in between, where content ratio of the cationic polymerizable compound and the radical polymerizable compound is in a range of 95:5 to 70:30 by mass.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarizing plate, a display member, and a method for manufacturing a polarizing plate.

Background Art

[0002] In liquid crystal displays (LCDs) and organic EL displays (OLEDs), a polarizing plate is used to prevent reflection of external light. A protective film for protecting the polarizer is provided on the polarizing plate. The protective film of the polarizing plate generally has a configuration in which a hard coat layer is provided on a transparent substrate. As the material of the transparent substrate, triacetyl cellulose (TAC), polymethyl methacrylate (PMMA), cycloolefin polymer (COP), etc. are used in consideration of the adhesion to PVA. Since the transparent substrate has a thickness of 20 to 40 μm, it has been difficult to meet the demand for further thinning of the polarizing plate.

[0003] Therefore, as a thinner polarizing plate, a configuration in which a two-layer structure of an intervening layer made of a thermosetting resin and a hard coat layer made of a photocurable resin is laminated on a polarizer has been studied (see Patent Document 1).

Prior Art Documents

Patent Documents

[0007] The polarizing plate according to the present invention comprises a polarizer and a curable resin layer, wherein the curable resin layer is made of a curable composition containing (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator, and is laminated on one surface of the polarizer without any other layers in between, and the content ratio of the cationic polymerizable compound to the radical polymerizable compound is 95:5 to 70:30 by mass ratio. Furthermore, the cationic polymerizable compound is 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate, the radical polymerizable compound is pentaerythritol triacrylate, and the pencil hardness of the cured resin layer is 2H or higher. It is characterized by the following:

[0008] The present invention relates to a method for manufacturing a polarizing plate comprising a polarizer and a cured resin layer, wherein a curable composition containing (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator is coated onto one surface of the polarizer without any other layers, and the coating film is cured to form a cured resin layer, and the content ratio of the cationic polymerizable compound to the radical polymerizable compound is 95:5 to 70:30 by mass ratio. Furthermore, the cationic polymerizable compound is 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate, the radical polymerizable compound is pentaerythritol triacrylate, and the pencil hardness of the cured resin layer is 2H or higher. It is characterized by the following: [Effects of the Invention]

[0009] The present invention can provide a polarizing plate that is thinner than conventional ones, a display component using a polarizing plate, and a method for manufacturing a polarizing plate. [Brief explanation of the drawing]

[0010] [Figure 1] Cross-sectional view showing a polarizing plate according to an embodiment. [Modes for carrying out the invention]

[0011] Figure 1 is a cross-sectional view showing a polarizing plate according to an embodiment.

[0012] The polarizing plate 1 comprises a polarizer 2 and a hard coat layer 3 provided on one side of the polarizer 2.

[0013] The polarizer 2 is made by adsorbing iodine or a dye onto a hydrophilic resin film such as polyvinyl alcohol (PVA), and then uniaxially stretching it to orient the iodine or dye. Since the hydrophilic resin film constituting the polarizer 2 has poor strength and water resistance, a protective hard coat layer 3 is provided on at least one side of the polarizer 2.

[0014] The hard coat layer 3 is a functional layer that imparts hardness to the polarizing plate 1 and protects the polarizer 2. The hard coat layer 3 is formed directly on the surface of the polarizer 2 without any other layers in between. The hard coat layer 3 can be formed by applying a coating liquid containing a polymerizable compound to the surface of the polarizer 2 and curing the coating film.

[0015] In detail, the hard coat layer 3 is a cured resin layer obtained by curing a curable composition containing (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator. In this specification, "polymerizable compound" is a general term for monomers, oligomers, prepolymers, and polymers having polymerizable functional groups.

[0016] (A) Cationic polymerizable compounds Cationic polymerizable compounds are preferably compounds having one or both of an epoxy group and an oxetanyl group as polymerizable functional groups. Examples of cationic polymerizable compounds include 3-ethyl-3-hydroxyethyl oxetane, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, 3,3-dimethyl oxetane, 3,3-bis(chloromethyl)oxetane, 2-hydroxymethyl oxetane, 3-methyl-3-oxetane methanol, 3-methyl-3-methoxymethyl oxetane, 3-ethyl-3-phenoxymethyl oxetane, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, and resorcinol bis(3-methyl-3-oxetanyl ethanol). Examples include oxetanes such as (3-ethyl-3-oxetanyl ethyl ether), xylylene bis-oxetane, and m-xylylene bis(3-ethyl-3-oxetanyl ethyl ether); and alicyclic epoxys such as cyclohexene oxide, 1,13-tetradecadienone dioxide, limonene dioxide, (3,4,3',4'-diepoxy)bicyclohexyl, 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate, bis(3,4-epoxycyclohexyl) adipate, and bis(3,4-epoxycyclohexyl) sebacate.

[0017] Of these, one or more selected from 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, (3,3′,4,4′-diepoxy)bicyclohexyl, and 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate are preferred.

[0018] (B) Radical polymerizable compounds Radical polymerizable compounds can use (meth)acrylates having one or both of an acryloyl group and a methacryloyl group as polymerizable functional groups. It is preferable to use polyfunctional (meth)acrylates having multiple polymerizable functional groups. In this specification, "(meth)acrylate" is a general term for both acrylate and methacrylate, and "(meth)acryloyl" is a general term for both acryloyl and methacryloyl.

[0019] Examples of the bifunctional (meth)acrylate include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxydiacrylate, 1,6-hexanediol diacrylate, and the like.

[0020] Examples of the trifunctional or higher functional (meth)acrylate include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, isocyanuric acid-modified tri(meth)acrylate, and the like.

[0021] In addition, the above (meth)acrylate monomer may be one in which a part of the molecular skeleton is modified, and those modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc. can also be used.

[0022] In addition, the polyfunctional (meth)acrylate oligomer is not particularly limited as long as it is a bifunctional or higher functional (meth)acrylate-based oligomer. For example, various (meth)acrylate-based oligomers such as urethane (meth)acrylate oligomer, epoxy (meth)acrylate oligomer, polyester (meth)acrylate oligomer, polyether (meth)acrylate oligomer, etc. can be used.

[0023] The urethane (meth)acrylate oligomer can be obtained, for example, by the reaction of a polyhydric alcohol, an organic diisocyanate, and a hydroxy (meth)acrylate.

[0024] Furthermore, preferred epoxy (meth)acrylate oligomers include (meth)acrylates obtained by reacting trifunctional or higher aromatic epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins, etc. with (meth)acrylic acid; (meth)acrylates obtained by reacting bifunctional or higher aromatic epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins, etc. with polybasic acids and (meth)acrylic acid; and (meth)acrylates obtained by reacting bifunctional or higher aromatic epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins, etc. with phenols and (meth)acrylic acid.

[0025] In the curing composition for forming a hard coat layer, (A) the cationic polymerizable compound plays a role in improving the adhesion between the hard coat layer 3 and the polarizer 2. The cationic polymerizable compound has cationic polymerizable functional groups such as epoxy groups and oxetanyl groups, and cationic polymerization generates ether bonds derived from the cationic polymerizable groups. The ether bonds derived from the cationic polymerizable compound form hydrogen bonds with the hydroxyl groups of the hydrophilic resin such as PVA that serves as the base material for the polarizer 2. This is thought to improve the adhesion between the hard coat layer 3 and the polarizer 2. On the other hand, (B) the radical polymerizable compound plays a role in improving the hardness of the hard coat layer 3.

[0026] In a curing composition for forming a hard coat layer, the mixing ratio of solids between (A) a cationic polymerizable compound and (B) a radical polymerizable resin is preferably 95:5 to 70:30 by mass. If the mixing ratio of the cationic polymerizable compound exceeds 95% by mass, the proportion of radical polymerizable groups decreases, which is undesirable because it reduces the hardness of the hard coat layer 3. Also, if the mixing ratio of the cationic polymerizable compound falls below 70%, the adhesion between the hard coat layer 3 and the polarizer 2 decreases, which is undesirable.

[0027] (C) Photopolymerization initiator As photopolymerization initiators, a photocationic polymerization initiator and a radical polymerization initiator are used. Because a photocationic polymerization initiator and a radical polymerization initiator are used in combination, the cationic polymerization reaction and the radical polymerization reaction can be carried out simultaneously by ultraviolet irradiation.

[0028] Examples of photocationic polymerization initiators include aryldiazonium salts such as p-methoxybenzenediazonium hexafluorophosphate, diaryliodonium salts such as diphenyliodonium hexafluorophosphate and diphenyliodonium hexafluoroantimonate; triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate, diphenyl[4-(phenylthio)phenyl]sulfonium hexafluoroantimonate, diphenyl[4-(phenylthio)phenyl]sulfonium pentafluorohydroxyantimonate, diphenyl[4-(phenylthio)phenyl]sulfonium tris(pentafluoroethyl)trifluorophosphate, and 4,4-bis(thianthrenium-9-yl)-diphenyl Examples include triarylsulfonium salts such as nyl ether dihexafluorophosphate; triarylselenonium salts such as triphenylselenonium hexafluorophosphate, triphenylselenonium tetrafluoroborate, and triphenylselenonium hexafluoroantimonate; dialkylphenacylsulfonium salts such as dimethylphenacylsulfonium hexafluoroantimonate and diethylphenacylsulfonium hexafluoroantimonate; dialkyl-4-hydroxy salts such as 4-hydroxyphenyldimethylsulfonium hexafluoroantimonate and 4-hydroxyphenylbenzylmethylsulfonium hexafluoroantimonate; and sulfonic acid esters such as α-hydroxymethylbenzoin sulfonate, N-hydroxyimido sulfonate, α-sulfonyloxyketone, and β-sulfonyloxyketone.

[0029] Commercially available triarylsulfonium salts that can be used include "AT-6992" and "AT-6976" (product names, both manufactured by ACETO); "ADEKA optomer SP-150," "ADEKA optomer SP-170," and "ADEKA optomer SP-171" (product names, all manufactured by ADEKA Corporation); "CPI-100P," "CPI-110P," "CPI-110A," and "CPI-210S" (product names, all manufactured by Sunapro Co., Ltd.); "TS-91" and "TS-01" (product names, both manufactured by Sanwa Chemical Co., Ltd.); "Esacure 1187" and "Esacure 1188" (product names, both manufactured by Lamberti); and "Omnicat 550" and "Omnicat 650" (product names, both manufactured by IGM Resin).

[0030] Among those mentioned above, from the viewpoint of curability and transparency, the cationic polymerization initiator is preferably a triarylsulfonium salt, more preferably at least one selected from diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate, diphenyl[4-(phenylthio)phenyl]sulfonium tris(pentafluoroethyl)trifluorophosphate, and 4,4-bis(thianthrenium-9-yl)-diphenyl ether dihexafluorophosphate, and even more preferably diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate.

[0031] Examples of radical polymerization initiators include acetophenone, benzophenone, α-hydroxyalkylphenone, Michler ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, α-acyloxime esters, and thioxanthones. Among these, α-hydroxyalkylphenone is preferred from the viewpoint of curability and transparency. Radical polymerization initiators can be used alone or in combination of two or more.

[0032] Organic solvents may be added to the hard coat layer forming curing composition as appropriate. As organic solvents, one or more of the following can be used in combination: alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butanol, isopropyl alcohol, isobutanol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone; ketone alcohols such as diacetone alcohol; aromatic hydrocarbons such as benzene, toluene, and xylene; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; glycol ethers such as ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, diethyl carbitol, and propylene glycol monomethyl ether; esters such as methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, and amyl acetate; ethers such as dimethyl ether and diethyl ether; N-methylpyrrolidone, dimethylformamide, etc.

[0033] In addition, various additives such as defoamers, leveling agents, antioxidants, UV absorbers, light stabilizers, polymerization inhibitors, and photosensitizers may be added to the hard coat layer forming curing composition as needed.

[0034] The polarizing plate 1 according to this embodiment can be manufactured by coating at least one side of the polarizer 2 with the hard coat layer forming curing composition described above without interposing any other layers, drying it, and curing the coating film by ultraviolet irradiation. In the manufacturing method of the polarizing plate 1 according to this embodiment, the hard coat layer 3 can be directly laminated onto the polarizer 2 with a single application of the curing composition and a single ultraviolet irradiation, resulting in excellent manufacturing efficiency. Furthermore, as the polymerizable compound in the hard coat layer forming curing composition, a cationic polymerizable compound and a radical polymerizable compound are used in combination, and their blending ratio is within the range described above. As a result, although the hard coat layer 3 is formed on the polarizer 2 without interposing any other layers, both the adhesion between the hard coat layer 3 and the polarizer 2 and the surface hardness of the hard coat layer 3 are excellent.

[0035] The polarizing plate 1 according to this embodiment can be used to construct an image display device by laminating it to an image display panel such as a liquid crystal panel or an organic EL panel. The image display device also includes a configuration that includes a touch panel. In the polarizing plate 1 according to this embodiment, a hard coat layer 3 is formed on at least one side of the polarizer 2 without any other layers in between, and a transparent resin film is not provided on that at least one side. By omitting at least one transparent resin film, it contributes to making the image display device thinner. Because it has excellent stain resistance and scratch resistance on one side, it is suitable as an optical film to be provided on the outermost surface of an image display device.

[0036] In this embodiment, an example was described in which a hard coat layer 3 was formed on one side of the polarizer 2. In this case, a protective film made of a resin film such as triacetylcellulose, polymethyl methacrylate, or cycloolefin polymer may be laminated to the other side of the polarizer 2. Alternatively, a hard coat layer 3 may be formed on the other side of the polarizer 2 without any other layers in between.

[0037] Furthermore, the polarizing plate 1 according to this embodiment may constitute a display component used in an image display device. Examples of display components include a configuration in which an adhesive layer is laminated onto the polarizing plate 1, a configuration in which another resin film is bonded to the polarizing plate 1, and a configuration in which a circular polarizing plate is bonded to the polarizing plate 1. [Examples]

[0038] The following describes specific examples of how the present invention is implemented.

[0039] The materials used in the examples and comparative examples are as follows: <Radical polymerizable compounds> Pentaerythritol triacrylate <Cationic polymerizable compounds> 3',4'-Epoxycyclohexylmethyl-3,4-Epoxycyclohexanecarboxylate (Trade name: Celoxide 2021P, Daicel Corporation) <Radical polymerization initiator> 1-Hydroxycyclohexyl-phenyl ketone (Trade name: Irgacure® 184) <Cational polymerization initiator> Triarylsulfonium salt (Product name: CPI-100P, Sunapro Co., Ltd.) <Solvent> Methyl ethyl ketone (MEK) Methyl isobutyl ketone (MIBK)

[0040] A 25 μm thick triacetylcellulose film was laminated to one side of a PVA film to create a laminated film with a total thickness of 40 μm. The hard coat layer forming curing composition described in Table 1 was applied to the other side of the PVA film using a wire bar coater, dried, and then exposed to ultraviolet light at 100 mJ / cm². 2 A hard coat film was created by irradiating with the specified exposure level and curing the film. The amount of hard coat layer forming curing composition applied was adjusted so that the hard coat layer would have a thickness of 5 μm after curing.

[0041] The mixing ratio (mass of cationic polymerizable compound:mass of radical polymerizable compound) of the cationic polymerizable compound in each example and comparative example is as follows: Example 1: 80:20 • Example 2 95: 5 • Example 3 70:30 • Comparative Example 1: 100: 0 Comparison Example 2: 65:35 Comparison Example 3: 50:50

[0042] The pencil hardness and adhesion of the hard coat layer of the hard coat films in the examples and comparative examples were evaluated by the following method.

[0043] <Pencil hardness> Pencil hardness was evaluated in accordance with JIS K5400-1900. The pencil hardness of the hard coat surface was measured using pencils (uni, Mitsubishi Pencil Co., Ltd.) and a Clemens scratch tester (HA-301, Tester Sangyo Co., Ltd.). The test was repeated while varying the pencil hardness, and the change in appearance due to scratches was visually observed. The highest hardness at which no scratches were observed was used as the evaluation value. A pencil hardness of 2H or higher was considered acceptable.

[0044] <Adhesion> The adhesion between the hard coat layer and the PVA film was evaluated in accordance with JIS K5600-5-6. A 1mm peel test was performed on the hard coat layer of the hard coat films in the examples and comparative examples using a grid peel test jig. 2 100 cross-cuts were created. Adhesive tape (CT405AP-24, Nichiban Co., Ltd.) was applied to the created cross-cuts, and after pressing it evenly with a spatula, the adhesive tape was peeled off in a 90° direction, and the remaining hard coat layer (1mm) was measured. 2 The evaluation value was the number of remaining areas. A hard court layer retention rate of 95% or higher was considered a passing grade.

[0045] Table 1 shows the composition of the hardening composition for forming the hard coat layer, and the evaluation results of pencil hardness and adhesion.

[0046] [Table 1]

[0047] The hard coat layer of the hard coat films in Examples 1 to 3 was formed from a curable composition containing a cationic polymerizable compound and a radical polymerizable compound in a mass ratio within the range of 95:5 to 70:30. Therefore, it exhibited excellent adhesion to the PVA film and excellent pencil hardness on the surface of the hard coat layer.

[0048] In Comparative Example 1, the hard coat film was formed with a hard coat layer made of a curable composition that does not contain a radical polymerizable compound. As a result, the pencil hardness of the hard coat layer surface was lower compared to Examples 1-3.

[0049] The hard coat films in Comparative Examples 2 and 3 exhibited reduced adhesion of the hard coat layer to the PVA film compared to Examples 1 to 3, due to a lower proportion of the cationic polymerizable compound than the above range.

[0050] Based on the above, it has been confirmed that, according to the present invention, it is possible to make the overall thickness thinner by directly laminating a hard coat layer on a PVA film (polarizer), and that a polarizing plate with excellent adhesion of the hard coat layer to the PVA film and excellent surface hardness can be realized. [Industrial applicability]

[0051] This invention can be used in polarizing plates for use in image display devices and the like. [Explanation of Symbols]

[0052] 1. Polarizing plate 2 polarizers 3. Hard court layer

Claims

1. Polarizer and, Comprising a cured resin layer, The cured resin layer is made of a curable composition comprising (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator, and is laminated on one surface of the polarizer without any other layers in between. The content ratio of the cationic polymerizable compound to the radical polymerizable compound is 95:5 to 70:30 by mass ratio. The cationic polymerizable compound is 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate, The radical polymerizable compound is pentaerythritol triacrylate. A polarizing plate characterized in that the hardened resin layer has a pencil hardness of 2H or higher.

2. A display member having a polarizing plate as described in claim 1.

3. A method for manufacturing a polarizing plate comprising a polarizer and a cured resin layer, A curable composition comprising (A) a cationic polymerizable compound, (B) a radical polymerizable compound, and (C) a photopolymerization initiator is coated onto one surface of the polarizer without any other layers in between, and the cured resin layer is formed by curing the coating film. The content ratio of the cationic polymerizable compound to the radical polymerizable compound is 95:5 to 70:30 by mass ratio. The cationic polymerizable compound is 3,4-epoxycyclohexylmethyl(3',4'-epoxy)cyclohexanecarboxylate, The radical polymerizable compound is pentaerythritol triacrylate. A method for manufacturing a polarizing plate, characterized in that the hardened resin layer has a pencil hardness of 2H or higher.

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