CN110998381A - Polarizing plate and image display device - Google Patents

Polarizing plate and image display device Download PDF

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Publication number
CN110998381A
CN110998381A CN201880049655.4A CN201880049655A CN110998381A CN 110998381 A CN110998381 A CN 110998381A CN 201880049655 A CN201880049655 A CN 201880049655A CN 110998381 A CN110998381 A CN 110998381A
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CN
China
Prior art keywords
easy
polarizing plate
film
adhesion
adhesion layer
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Pending
Application number
CN201880049655.4A
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Chinese (zh)
Inventor
徐菁璠
冈田康彰
品川雅
道下空
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Nitto Denko Corp
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Nitto Denko Corp
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Priority claimed from PCT/JP2018/048392 external-priority patent/WO2019155791A1/en
Publication of CN110998381A publication Critical patent/CN110998381A/en
Pending legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/02—Physical, chemical or physicochemical properties
    • B32B7/023—Optical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J175/00—Adhesives based on polyureas or polyurethanes; Adhesives based on derivatives of such polymers
    • C09J175/04—Polyurethanes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
    • G02B1/14—Protective coatings, e.g. hard coatings
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/50—OLEDs integrated with light modulating elements, e.g. with electrochromic elements, photochromic elements or liquid crystal elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B32B2457/20—Displays, e.g. liquid crystal displays, plasma displays
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2203/00—Applications of adhesives in processes or use of adhesives in the form of films or foils
    • C09J2203/318—Applications of adhesives in processes or use of adhesives in the form of films or foils for the production of liquid crystal displays
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2301/00—Additional features of adhesives in the form of films or foils
    • C09J2301/30—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier
    • C09J2301/312—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier parameters being the characterizing feature

Abstract

Provided is a polarizing plate which is less likely to cause stripe-like unevenness even when exposed to a high-temperature and high-humidity environment for a long period of time, and which has excellent display uniformity. In the polarizing plate (100), a transparent protective film (1) is bonded to one surface of a polyvinyl alcohol-based polarizing plate (5) via an adhesive layer (6). The transparent protective film (1) is provided with an easy-adhesion layer (15) on the surface of an acrylic film (11). The easy-adhesion layer (15) contains a polyurethane resin and fine particles and has a thickness of 280nm or less.

Description

Polarizing plate and image display device
Technical Field
The present invention relates to an easy-adhesion film having an easy-adhesion layer on a surface of a transparent film, and a polarizing plate having an easy-adhesion film as a transparent protective film bonded to a surface of a polarizing plate. The present invention also relates to an image display device including the polarizing plate.
Background
Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile devices, car navigation devices, displays for personal computers, and televisions. In the liquid crystal display device, a polarizing plate is disposed on the viewing side surface of the liquid crystal cell in view of the display principle. In a transmissive liquid crystal display device, polarizing plates are disposed on both sides of a liquid crystal cell. In an organic EL display device, in order to suppress the appearance of a mirror surface due to reflection of external light by a metal electrode (cathode), a circularly polarizing plate (typically a laminate of a polarizing plate and an 1/4 wavelength plate) is sometimes disposed on the appearance side surface.
In general, a polarizing plate includes a transparent film for the purpose of protecting a polarizing plate or the like on one or both surfaces of the polarizing plate. As the polarizing plate, a polarizing plate in which a polyvinyl alcohol (PVA) film is adsorbed with iodine and molecules are oriented by stretching or the like is widely used.
As a transparent protective film to be bonded to the surface of a polarizing plate, a cellulose-based film such as cellulose acetate is widely used because of its excellent adhesion to a PVA-based polarizing plate. As the transparent protective film, an acrylic film is also used. Since the acrylic film has a lower moisture permeability than the cellulose film, a polarizing plate using the acrylic transparent protective film tends to have less change in optical characteristics and excellent durability even when exposed to a high-humidity environment for a long time. Further, since the acrylic film has a low birefringence, improvement of optical characteristics (for example, reduction of light leakage in an image display device) can be expected.
The acrylic film tends to have lower adhesiveness to a PVA-based polarizing plate than a cellulose-based film. In order to improve the adhesion between the PVA-based polarizing plate and the acrylic film, a method of providing an easy-adhesion layer on the surface of the acrylic film has been proposed. For example, patent document 1 describes an easy-adhesion film in which an easy-adhesion layer containing a polyurethane resin is provided on the surface of an acrylic film, but does not disclose that the easy-adhesion film has excellent adhesion to a PVA-based polarizing plate. Patent document 1 describes that blocking when the easy adhesion film is wound into a roll can be suppressed by including fine particles in the easy adhesion layer, and shows an example of manufacturing a polarizing plate using an easy adhesion film provided with a urethane easy adhesion layer containing 1 to 7% by weight of fine particles and having an average thickness of 400nm (thickness range of 300 to 500nm) as a polarizer protective film.
Documents of the prior art
Patent document
Patent document 1: japanese patent No. 5354733
Disclosure of Invention
Problems to be solved by the invention
In the process of increasing the size and brightness of an image display device, a polarizing plate constituting the image display device is required to have less change in optical characteristics even in a severer environment (for example, under conditions of higher temperature and higher humidity). In the polarizing plate using the acrylic transparent protective film having an easy-adhesion layer described in patent document 1, the adhesion between the polarizer and the transparent protective film is excellent, and the adhesion reliability is high. However, according to the study of the present inventors and the like, the following problems have newly been found: when the polarizing plate including the easy-adhesion film disclosed in patent document 1 is exposed to a high humidity environment for a long time, the polarizing plate is subject to stripe-like unevenness, which causes a decrease in display characteristics.
In view of the above problems, an object of the present invention is to provide an easy-adhesion film which can be used as a polarizer protective film. Further, another object of the present invention is to provide a polarizing plate having excellent adhesion between a polarizer and a transparent protective film, being less likely to cause stripe-like unevenness even when exposed to a high-temperature and high-humidity environment for a long period of time, and having excellent display uniformity.
Means for solving the problems
The easy-adhesion film of the present invention has an easy-adhesion layer on the surface of an acrylic film. The polarizing plate of the present invention includes a transparent protective film attached to one surface of a polyvinyl alcohol polarizer via an adhesive layer. The other side of the polarizer may be provided with a transparent protective film.
The transparent protective film to be bonded to one surface of the polarizing plate is an easy-adhesion film having an easy-adhesion layer on the surface of an acrylic film, and the easy-adhesion layer-formed surface is preferably bonded to the polarizing plate. The easy-adhesion layer provided on the surface of the acrylic film contains a polyurethane resin and fine particles and has a thickness of 280nm or less.
The thickness of the easy adhesion layer is preferably 50nm or more. The content of the fine particles in the easy-adhesion layer is preferably 8 to 50 wt%. The easy adhesion layer preferably contains an alkali component in an amount of 5ppm or less.
ADVANTAGEOUS EFFECTS OF INVENTION
The polarizing plate comprising the easy-adhesion film of the present invention is less likely to cause stripe-like unevenness even when exposed to a high-temperature and high-humidity environment for a long period of time, and has excellent durability. Therefore, by using the polarizing plate of the present invention, an image display device having excellent display uniformity can be obtained.
Drawings
Fig. 1 is a sectional view showing a configuration example of an easy-adhesion film.
Fig. 2 is a schematic cross-sectional view showing a laminated structure of polarizing plates according to one embodiment.
Fig. 3 is a cross-prism observation photograph of the polarizing plates of examples 1 and 2 and comparative example 1 before and after the heating/humidifying durability test.
Fig. 4 is a cross-prism observation photograph of the polarizing plates of example 4 and comparative example 2 before and after the heating/humidifying durability test.
Detailed Description
Fig. 1 is a schematic cross-sectional view showing an example of the structure of an easy-adhesion film according to an embodiment of the present invention, and fig. 2 is a schematic cross-sectional view showing a laminated structure of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes a first transparent protective film 1 bonded to one surface (first main surface) of a polarizer 5 with an adhesive layer 6 interposed therebetween. The first transparent protective film 1 is an easy-adhesion film, and has an easy-adhesion layer 15 on the surface of the acrylic film 11. The second transparent protective film 2 is preferably bonded to the other surface (second main surface) of the polarizing plate 5 via an adhesive layer 7.
[ transparent protective film (easy-to-adhere film) ]
The transparent protective film 1 bonded to one surface of the polarizing plate 5 is an easy-adhesion film having an easy-adhesion layer 15 on one surface of an acrylic film 11. In the production of the polarizing plate, the easy-adhesion layer 15-formed surface of the transparent protective film 1 is preferably bonded to the PVA-based polarizing plate 5 via the adhesive layer 6.
< acrylic film >
The acrylic film 11 contains an acrylic resin. Examples of the acrylic resin include poly (meth) acrylates such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymers, methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymers, methyl (meth) acrylate-styrene copolymers (MS resins, etc.), and polymers having an alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymers, methyl methacrylate- (meth) acrylic acid norbornyl ester copolymers, etc.).
In the present specification, "(meth) acrylic" means acrylic acid and/or methacrylic acid. The acrylic resin contains acrylic acid or a derivative thereof as a constituent monomer component and methacrylic acid or a derivative thereof as a constituent monomer component.
As the acrylic resin, acrylic resins having a glutaric anhydride structure described in japanese patent application laid-open nos. 2006-283013, 2006-335902, and 2006-274118; and/or acrylic resins having a lactone ring structure described in Japanese patent laid-open Nos. 2000-230016, 2001-151814, 2002-120326, 2002-254544, 2005-146084, and the like. Acrylic resins having a glutaric anhydride structure and acrylic resins having a lactone ring structure have high heat resistance, high transparency, and high mechanical strength, and therefore, are suitable for producing a polarizing plate having high polarization degree and excellent durability.
The content of the acrylic resin in the acrylic film 11 is preferably 50% by weight or more, more preferably 60 to 98% by weight, and still more preferably 70 to 97% by weight. The acrylic film 11 may contain a thermoplastic resin other than an acrylic resin. For example, an acrylic film having excellent optical isotropy can be obtained by adding another thermoplastic resin to eliminate birefringence of the acrylic resin. In addition, a thermoplastic resin other than an acrylic resin may be blended for the purpose of improving the mechanical strength of the film or the like.
Examples of the thermoplastic resin other than the acrylic resin include olefin polymers, halogenated vinyl polymers, polystyrene, copolymers of styrene and acrylic monomers, polyesters, polyamides, polyacetals, polycarbonates, polyphenylene ethers, polyphenylene sulfides, polyether ether ketones, polysulfones, polyether sulfones, polyoxy benzyl esters, polyamide imides, rubber polymers, and the like.
The acrylic film 11 may contain additives such as antioxidants, stabilizers, reinforcing materials, ultraviolet absorbers, flame retardants, antistatic agents, colorants, fillers, plasticizers, lubricants, fillers, and the like. The acrylic resin may be mixed with other thermoplastic resins, additives, etc. and formed into a thermoplastic resin composition such as pellets in advance, and then the mixture may be made into a film.
Examples of the method for producing the acrylic film 11 include a solution casting method, a melt extrusion method, a calendering method, a compression molding method, and the like. The acrylic film 11 may be an unstretched film or a stretched film. From the viewpoint of improving mechanical strength, a biaxially stretched film is preferably used as the acrylic film 11. In order to eliminate the birefringence of the acrylic resin, an acrylic film having a small retardation and excellent optical isotropy even when stretched can be obtained by blending another thermoplastic resin.
The thickness of the acrylic film 11 is about 5 to 200 μm. The thickness of the acrylic film is preferably 10 to 100 μm, more preferably 15 to 60 μm, from the viewpoints of mechanical strength, transparency, handling property, and the like.
The glass transition temperature Tg of the acrylic film 11 is preferably 100 ℃ or higher, more preferably 110 ℃ or higher, and particularly preferably 120 ℃ or higher. As described above, by using an acrylic resin having a glutaric anhydride structure or an acrylic resin having a lactone ring structure as the acrylic resin, the Tg of the acrylic film 11 can be increased, and the heat resistance thereof can be improved. The upper limit of Tg of the acrylic film 11 is not particularly limited, but is preferably 170 ℃ or lower from the viewpoint of moldability and the like.
< easy adhesion layer >
The easy-adhesion layer 15 provided on the surface of the acrylic film 11 contains a urethane resin and fine particles. By providing the easy adhesion layer 15 containing a urethane resin, the adhesion of the easy adhesion film 1 to the polarizing plate 5 can be improved. The easy-adhesion layer 15 contains fine particles, thereby forming fine irregularities on the surface of the easy-adhesion film 1 and improving the sliding property of the film. This contributes to reducing scratches on the easy-to-adhere film 1 during roll transportation and suppressing blocking when wound into a roll.
One feature of the easy-adhesion film of the present invention is: the easy adhesion layer 15 provided on the surface of the acrylic film 11 has a thickness of 280nm or less. By reducing the thickness of the easy-adhesion layer 15, a highly durable polarizing plate can be obtained in which streaky unevenness is less likely to occur even when exposed to a high-temperature and high-humidity environment for a long time, and a change in polarization degree is small.
< polyurethane resin >
The urethane resin as the main constituent of the easy adhesion layer 15 is typically a reaction product of a polyol and a polyisocyanate. As the polyol component, a polymer polyol such as a polyacrylic polyol, a polyester polyol, and a polyether polyol is preferably used.
Polyacrylic polyols are typically obtained by polymerization of (meth) acrylates with hydroxyl group-containing monomers. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate. Examples of the hydroxyl group-containing monomer include hydroxyalkyl esters of (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxypentyl (meth) acrylate; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; n-methylol (meth) acrylamide and the like.
The other monomer components include unsaturated monocarboxylic acids such as (meth) acrylic acid, unsaturated dicarboxylic acids such as maleic acid and anhydrides and diesters thereof, (unsaturated nitriles such as (meth) acrylonitrile, (unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide), vinyl esters such as vinyl acetate and vinyl propionate, vinyl ethers such as methyl vinyl ether, α -olefins such as ethylene and propylene, halogenated α -unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride, and α -unsaturated aromatic monomers such as styrene and α -methylstyrene.
Polyester polyols are typically obtained by the reaction of a polybasic acid with a polyhydric alcohol. Examples of the polybasic acid include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1, 4-naphthalenedicarboxylic acid, 2, 5-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, tetrahydrophthalic acid, and the like; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, Sebacic acid (sebasic acid), Decanedioic acid (decadic acid), dodecanedioic acid, octadecanedioic acid, tartaric acid, alkylsuccinic acid, linolenic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1, 3-cyclohexanedicarboxylic acid, and 1, 4-cyclohexanedicarboxylic acid; or reactive derivatives thereof such as acid anhydrides, alkyl esters, and acid halides.
Examples of the polyhydric alcohol include ethylene glycol, 1, 2-propanediol, 1, 3-butanediol, 1, 4-butanediol, neopentyl glycol, pentanediol, 1, 6-hexanediol, 1, 8-octanediol, 1, 10-decanediol, 1-methyl-1, 3-butanediol, 2-methyl-1, 3-butanediol, 1-methyl-1, 4-pentanediol, 2-methyl-1, 4-pentanediol, 1, 2-dimethyl-neopentyl glycol, 2, 3-dimethyl-neopentyl glycol, 1-methyl-1, 5-pentanediol, 2-methyl-1, 5-pentanediol, 3-methyl-1, 5-pentanediol, 1, 4-butanediol, 1, 3-methyl-1, 5-pentanediol, 1, 4-butanediol, 1, 3-octanediol, 1, 3-methyl-1, 5-pentanediol, 1, 2-dimethylbutylene glycol, 1, 3-dimethylbutylene glycol, 2, 3-dimethylbutylene glycol, 1, 4-dimethylbutylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1, 4-cyclohexanedimethanol, 1, 4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and the like.
Polyether polyols are typically obtained by ring-opening polymerization of alkylene oxides and addition to polyols. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, and trimethylolpropane. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran.
Examples of the polyisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate, dodecamethylene diisocyanate, 1, 4-butane diisocyanate, hexamethylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, 2,4, 4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1, 5-diisocyanate and 3-methylpentane-1, 5-diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4' -cyclohexylmethane diisocyanate, 1, 4-cyclohexane diisocyanate, methylcyclohexane diisocyanate and 1, 3-bis (isocyanatomethyl) cyclohexane, alicyclic diisocyanates such as tolylene diisocyanate, 2' -diphenylmethane diisocyanate, 2,4' -diphenylmethane diisocyanate, 4,4' -diphenyldimethylmethane diisocyanate, 4,4' -dibenzyl diisocyanate, 1, 5-naphthylene diisocyanate, xylylene diisocyanate, 1, 3-phenylene diisocyanate and 1, 4-phenylene diisocyanate, aromatic diphenylmethane diisocyanate such as tetramethyldiphenylmethane diisocyanate and α.
The urethane resin constituting the easy adhesion layer 15 preferably has a carboxyl group. The urethane resin of the easy-adhesion layer 15 has a carboxyl group, so that a crosslinked structure can be introduced, and the adhesion durability between the easy-adhesion film 1 and the polarizing plate 5 tends to be improved. The polyurethane resin having a carboxyl group can be obtained, for example, by reacting a chain extender having a free carboxyl group on the basis of a polyol and a polyisocyanate resin. Examples of the chain extender having a free carboxyl group include dihydroxycarboxylic acid, dihydroxysuccinic acid and the like. Examples of the dihydroxy carboxylic acid include dialkyl alkanoic acids such as dimethylol alkanoic acids (e.g., dimethylol acetic acid, dimethylol butyric acid, dimethylol propionic acid, dimethylol butyric acid, and dimethylol valeric acid).
The method for producing the polyurethane resin is not particularly limited, and may be any of a one-step method in which monomer components are reacted at once and a multistage method in which the monomer components are reacted at once. When a chain extender having a free carboxyl group is used to introduce a carboxyl group into a polyurethane resin, a multistage method is preferable. When producing a polyurethane resin, a polyurethane reaction catalyst may be used as needed. An easily adhesive composition containing a precursor of polyurethane (e.g., a polyol or a polyisocyanate) may be applied to an acrylic film and then subjected to a urethane formation reaction by heating or the like.
The number average molecular weight of the polyurethane resin is preferably 5000 to 600000, and more preferably 10000 to 400000. The acid value of the polyurethane resin is preferably 10 to 50, and more preferably 20 to 45.
The urethane resin of the easy adhesion layer 15 may have a cross-linked structure. By introducing a crosslinked structure into the urethane resin, the adhesion durability between the easy-adhesion film 1 and the polarizing plate 5 tends to be improved. As the crosslinking agent, a crosslinking agent capable of reacting with a crosslinkable functional group of the polyurethane resin can be used without particular limitation. When the polyurethane resin has a carboxyl group, a crosslinking agent containing an amino group, an oxazoline group, an epoxy group, a carbodiimide group, or the like can be used. Among these, a crosslinking agent having an oxazoline group is preferable. Since the oxazoline group has low reactivity with a carboxyl group at normal temperature, the pot life when it is mixed with a urethane resin is long, and the lead time (lead time) of the process can be flexibly coped with.
The crosslinking agent may be a low-molecular compound or a polymer. The crosslinking agent is preferably an acrylic polymer because of its high solubility in the aqueous composition and excellent compatibility with the polyurethane resin. In particular, when an oxazoline group-containing acrylic polymer is used as the crosslinking agent, the adhesiveness between the easy-to-adhere film 1 and the polarizing plate 5 tends to be improved.
The amount of the crosslinking agent used is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight, based on 100 parts by weight of the polyurethane resin.
(Fine particles)
The fine particles of the easy-adhesion layer 15 may be formed into a fine uneven shape on the surface of the easy-adhesion layer, and the material and the particle diameter thereof are not particularly limited. From the viewpoint of improving the slidability of the easy-adhesion film 1 by forming irregularities on the surface of the easy-adhesion layer, the particle diameter (average primary particle diameter) of the fine particles is preferably 10nm or more, more preferably 15nm or more, and still more preferably 20nm or more. When the average primary particle size of the fine particles is smaller than the visible light wavelength, scattering of visible light at the interface between the urethane resin and the fine particles is suppressed, and the influence of depolarization of the polarizing plate and the like on the optical characteristics can be reduced. Therefore, the particle diameter of the fine particles is preferably 150nm or less, more preferably 100nm or less, further preferably 60nm or less, and particularly preferably 50nm or less.
The fine particles may be inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include inorganic oxides such as silica, titania, alumina, and zirconia; calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like. Examples of the organic fine particles include silicone resins, fluorine resins, and acrylic resins. In order to suppress light scattering by the fine particles, the difference in refractive index between the polyurethane resin and the fine particles is preferably small. The fine particles of the easy-adhesion layer 15 are preferably inorganic fine particles, and particularly preferably silica particles, because of a small difference in refractive index from the polyurethane resin and excellent dispersibility.
When the easy-adhesion layer 15 is formed of an aqueous composition, fine particles having high water dispersibility are preferably used. An aqueous dispersion of fine particles may be blended in the composition. In order to improve the dispersibility of the inorganic fine particles, it is preferable to make the easy-to-bond composition weakly alkaline by adding a basic component such as amine or ammonia.
As the water-dispersible silica particles, colloidal silica is preferably used. As the colloidal silica, commercially available products such as quartron pl series manufactured by hibiscus chemical industries, SnowTex series manufactured by NIPPON chemical industries, NIPPON AEROSIL co., aerodip series manufactured by ltd, and AEROSIL series can be used.
The content of the fine particles in the easy-adhesive layer 15 is preferably 8 wt% or more, more preferably 10 wt% or more, and even more preferably 12 wt% or more, from the viewpoint of improving the slidability of the easy-adhesive film 1 by forming the irregularities on the surface of the easy-adhesive layer 15. In the easy-adhesion film of the present invention, since the thickness of the easy-adhesion layer 15 is small and 280nm or less, it is preferable to increase the content of fine particles to increase the amount (number density) of fine particles per unit area, thereby uniformly forming irregularities in the surface of the easy-adhesion layer 15. If the content of the fine particles in the easy-adhesion layer 15 is too large, light scattering at the interface between the urethane resin and the fine particles may increase, and optical characteristics may be degraded. Further, as the content of fine particles increases, the relative content of the urethane resin decreases, and thus the adhesiveness between the easy-to-adhere film 1 and the polarizing plate 5 may decrease. Therefore, the content of the fine particles in the easy-adhesion layer 15 is preferably 50 wt% or less, more preferably 40 wt% or less, and further preferably 30 wt% or less.
In the easy-adhesion layer 15, the amount of the fine particles is preferably 11 to 100 parts by weight, more preferably 12 to 65 parts by weight, and still more preferably 13 to 40 parts by weight, based on 100 parts by weight of the urethane resin (when the crosslinking agent is included, the total amount of the urethane resin and the crosslinking agent).
(residual alkali amount)
When an alkaline component such as amine or ammonia is used to improve the dispersibility of the fine particles, the alkaline component inevitably remains in the adhesive layer. In the polarizing plate in which the easy-adhesion film 1 is bonded to the surface of the polarizing plate 5, when the residual alkaline component in the easy-adhesion layer 15 is eluted by moisture or the like, the polarizing plate may be deteriorated, and optical defects such as a reduction in the polarization degree of the polarizing plate and stripe-like unevenness may occur.
The amount of residual alkali in the easy-adhesive layer 15 is preferably 75ppm or less, more preferably 70ppm or less, still more preferably 60ppm or less, and particularly preferably 55ppm or less, from the viewpoint of improving the humidification durability of the polarizing plate. From the viewpoint of improving the humidification durability of the polarizing plate, the amount of the residual alkali in the easy-adhesive layer 15 is preferably smaller.
On the other hand, when the amount of the residual alkali in the easy-adhesion layer 15 is too small, dispersibility of the fine particles is impaired, and appearance defects such as cloudiness due to aggregation of the fine particles may occur. Further, the particles aggregate and fall off from the easy-adhesion layer due to the decrease in dispersibility, and appropriate irregularities are not formed on the surface of the easy-adhesion layer, so that the slidability of the easy-adhesion film tends to decrease. Therefore, the amount of the residual alkali in the easy-adhesion layer 15 is preferably 5ppm or more, more preferably 10ppm or more, and still more preferably 20ppm or more.
The amount of the base in the easy-adhesion layer can be determined by liquid chromatography, ion chromatography, or the like, depending on the type of the base component. The quantification of the basic component can be performed by an analytical method combining chromatography with Mass Spectrometry (MS), such as LC/MS. When a plurality of alkali components are contained in the easy adhesion layer, the total of the respective components is defined as the alkali component content (residual amount) of the easy adhesion layer. When the amount of alkali in the easy-adhesion layer is determined from the polarizing plate to which the easy-adhesion film and the polarizing plate are bonded, the polarizing plate is immersed in warm water or the like to dissolve the polarizing plate and the easy-adhesion layer together, and the amount of alkali eluted is determined.
< formation of easy adhesion layer >
The method for forming the easy adhesion layer 15 on the surface of the acrylic film 11 is not particularly limited. The easy-adhesion layer 15 is preferably formed by applying an easy-adhesion composition (solution) containing a urethane resin or a precursor thereof and fine particles to the acrylic film 11 and drying the composition.
The easy adhesion layer can be formed in the process of manufacturing the acrylic film. The easy adhesion layer may be formed by heating in the film base forming step. For example, when the acrylic film 11 is a stretched film, the surface of the film before stretching or the surface of the film after longitudinal stretching may be coated with an easy-adhesion composition, and the solvent may be dried and the resin may be cured by heating in the transverse stretching or simultaneous biaxial stretching by a tenter.
Before the easy adhesion layer 15 is formed, the surface of the acrylic film 11 may be treated. By performing the surface treatment, the adhesion between the easy-adhesive layer 15 and the acrylic film 11 can be improved by adjusting the wetting tension of the acrylic film. Examples of the surface treatment include corona treatment, plasma treatment, ozone blowing, ultraviolet irradiation, flame treatment, and chemical treatment. Among these, corona treatment or plasma treatment is preferable.
(easy adhesion composition)
The easy-adhesion composition is preferably an aqueous composition containing water as a solvent (and a dispersion medium for fine particles). The concentration of the solid content (nonvolatile content) in the easy-adhesion composition is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and still more preferably 3 to 15% by weight.
The aqueous easy-adhesion composition contains water as a solvent (and a dispersion medium), a urethane resin or a precursor thereof, and fine particles, and further contains a crosslinking agent as needed. The easy adhesion composition preferably further comprises an alkaline component. As described above, the alkali component has an action of promoting dispersion of fine particles. Therefore, the easy-adhesion composition containing the alkali component can improve the dispersibility of the fine particles and can provide an easy-adhesion film having excellent appearance and sliding property.
On the other hand, if the base contained in the easy-adhesion composition remains in the easy-adhesion layer, the base may cause a decrease in the moist heat resistance of the polarizing plate. In particular, a strong alkali such as caustic alkali causes deterioration of the polarizing plate even in a small amount. Therefore, as the basic component contained in the easy-adhesion composition, a weakly basic component such as ammonia or amine is preferable. From the viewpoint of improving the dispersibility of the fine particles and preventing the deterioration of the polarizing plate, the pH of the easy-adhesion composition (coating liquid) is preferably about 7.5 to 9.
From the viewpoint of improving the dispersibility of the fine particles, the amount of the alkali component contained in the easy-to-bond composition is preferably 300ppm or more, and more preferably 500ppm or more, with respect to the solid content of the easy-to-bond composition. On the other hand, when the content of the alkali component is too large, it may be difficult to reduce the amount of the residual alkali, and therefore the amount of the alkali component contained in the easy-to-bond composition is preferably 50000ppm or less, more preferably 10000ppm or less, and further preferably 5000ppm or less, relative to the solid content of the easy-to-bond composition.
The easy-adhesion composition may contain an alkaline component having a catalytic action in addition to improving dispersibility of the fine particles. For example, the easy-adhesion composition may contain a tertiary amine such as triethylamine as a urethane-forming catalyst for a polyurethane precursor (e.g., a polyol, a polyisocyanate, or the like).
By applying the easy-adhesion composition to the acrylic film 11 and then heating, the alkali component can be volatilized and removed, and the residual alkali component in the easy-adhesion layer 15 can be reduced. The alkali component contained in the easy-adhesion composition preferably has a boiling point of 150 ℃ or lower from the viewpoint of promoting volatilization of the alkali component by heating. The boiling point of the basic component is more preferably 130 ℃ or lower, still more preferably 120 ℃ or lower, and particularly preferably 110 ℃ or lower. The boiling point of the basic component may be 100 ℃ or lower or 90 ℃ or lower. When the easy-adhesion composition contains a plurality of basic components, the boiling point of at least 1 basic component is preferably in the above range, and the boiling point of 2 or more basic components is preferably in the above range. The boiling point of the alkali component is preferably 50 wt% or more with respect to 100 parts by weight of the total amount of the alkali contained in the easy-adhesion layer. It is desirable that all of the alkaline components contained in the easy-adhesion composition have boiling points within the above-mentioned range.
The easy-adhesion composition may contain resin components other than the urethane resin, additives, and the like. Examples of the additives include catalysts such as crosslinking accelerators, antioxidants, ultraviolet absorbers, leveling agents, antiblocking agents, antistatic agents, dispersion stabilizers, defoaming agents, thickeners, dispersants, surfactants, lubricants and the like.
Examples of the method for applying the easy-adhesion composition include bar coating, roll coating, gravure coating, bar coating, slot coating, curtain coating, and jet coating. The easy-adhesion layer 15 is formed by heating the easy-adhesion composition after coating to remove the solvent. The heating temperature is, for example, about 50 to 180 ℃. In the case where the easy-adhesion composition contains a crosslinking agent, crosslinking of the polyurethane resin can be promoted by heating. As described above, when the easy-adhesion composition contains an alkali component, the alkali component can be volatilized and removed by heating, and the alkali component remaining in the easy-adhesion layer 15 can be reduced. The heating temperature is preferably 100 ℃ or higher, more preferably 120 ℃ or higher, further preferably 130 ℃ or higher, and particularly preferably 135 ℃ or higher, from the viewpoint of efficiently volatilizing and removing the alkaline component contained in the adhesive composition. The heating temperature is preferably higher than the boiling point of the alkali component contained in the easy-adhesion composition.
The easy adhesion layer 15 has a thickness of 280nm or less. By reducing the thickness of the easy-adhesion layer 15, the polarizing plate is improved in humidification durability, and the occurrence of streaky unevenness is suppressed even when exposed to a humidified environment for a long time, whereby the in-plane uniformity of display can be maintained. From the viewpoint of suppressing the occurrence of stripe-like unevenness in the polarizing plate after the humidification test, the thickness of the easy-adhesion layer 15 is preferably 250nm or less, more preferably 200nm or less, and still more preferably 170nm or less.
As the thickness of the easy-adhesive layer 15 is smaller, the humidification durability of the polarizing plate tends to be improved, and the occurrence of stripe-like unevenness tends to be suppressed. Further, as the thickness of the easy-adhesion layer 15 is smaller, the decrease in the degree of polarization and the decrease in the single-sheet transmittance when the polarizing plate is exposed to a humidified environment tend to be suppressed. On the other hand, when the thickness of the easy-adhesion layer 15 is too small, the adhesion between the easy-adhesion film 1 and the polarizing plate 5 may be reduced. Therefore, the thickness of the easy adhesion layer 15 is preferably 50nm or more, more preferably 80nm or more, and further preferably 100nm or more. The easy adhesion layer 15 may have a thickness of 110nm or more, 120nm or more, 130nm or more, or 140nm or more. When the thickness of the easy-adhesion layer is within the above range, the easy-adhesion film and the polarizing plate have excellent adhesion, and the polarizing plate has excellent workability when cut into a predetermined single size, and the occurrence of microcracks tends to be suppressed.
The thickness of the easy-adhesion layer 15 can be set within the above range by adjusting the solid content concentration and the coating thickness of the easy-adhesion composition. The thickness of the easy-adhesion layer 15 in the polarizing plate can be determined by observing the cross section of the polarizing plate. When the thickness varies, the average thickness in the observation range is defined as the thickness of the easy-adhesion layer.
When the easy-adhesion composition contains an alkaline component, the volatilization removal efficiency of the alkaline component by heating tends to be higher as the thickness of the easy-adhesion layer is smaller. The thickness of the easy-adhesion layer 15 is preferably within the above range from the viewpoint of keeping the residual amount of the alkaline component within a suitable range, ensuring the dispersibility of the fine particles, and improving the moist heat resistance of the polarizing plate.
[ polarizing plate ]
As the polarizing plate 5, a polyvinyl alcohol (PVA) -based polarizing plate in which a dichroic substance such as iodine or a dichroic dye is adsorbed to a polyvinyl alcohol-based film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and oriented in 1 direction can be used. For example, a PVA-based polarizing plate can be obtained by iodine dyeing and stretching a polyvinyl alcohol-based film.
In the process of producing the polarizing plate 5, treatments such as washing with water, swelling, and crosslinking may be performed as necessary. The stretching may be performed before or after the iodine dyeing, or may be performed while dyeing. The stretching may be performed by stretching in air (dry stretching) or stretching in water or an aqueous solution containing boric acid, potassium iodide, or the like (wet stretching), or a combination thereof may be used. The thickness of the polarizing plate 5 is not particularly limited, but is generally about 1 to 50 μm.
As the polarizing plate 5, a thin PVA-based polarizing plate having a thickness of 10 μm or less can be used. Examples of the thin polarizing plate include those described in jp 51-069644 a, jp 2000-338329 a, WO2010/100917 pamphlet, japanese patent No. 4691205, japanese patent No. 4751481, and the like. These thin polarizing plates can be obtained by a production method including a step of stretching a PVA-based resin layer and a stretching resin substrate in a laminated state and an iodine dyeing step. In this production method, the PVA-based resin layer is thin, but is supported by the resin base material for stretching, and therefore can be stretched without causing troubles such as breakage due to stretching.
< adhesive agent >
The material of the adhesive layer 6 for bonding the polarizing plate 5 and the easy-adhesion film 1 is not particularly limited as long as it is optically transparent, and various types of adhesives such as water-based adhesives, solvent-based adhesives, hot-melt adhesives, radical polymerization curing adhesives, and the like can be used. Among these, an aqueous adhesive or an active energy ray-curable adhesive is preferable in terms of high adhesiveness to the PVA-based polarizing plate 5 and the urethane easy-adhesive layer 15.
Examples of the polymer component of the aqueous adhesive include vinyl polymers, gelatin, vinyl latexes, polyurethane, polyester, epoxy, and the like. Among these, vinyl polymers are preferable, and polyvinyl alcohol resins are particularly preferable, from the viewpoint of excellent adhesion between the polarizing plate 5 and the easy-adhesion film 1. Among the polyvinyl alcohol resins, polyvinyl alcohol containing an acetoacetyl group is preferable.
From the viewpoint of adhesiveness, the polyvinyl alcohol resin preferably has an average polymerization degree of about 100 to 5000, more preferably 1000 to 4000. The average saponification degree of the polyvinyl alcohol resin is preferably 85 mol% or more, and more preferably 90 mol% or more.
The aqueous adhesive composition (solution) may contain a crosslinking agent in addition to a polymer such as a polyvinyl alcohol resin. As the crosslinking agent, a compound having at least two functional groups in 1 molecule, which are reactive with the polymer constituting the adhesive, can be used. Examples of the crosslinking agent for the polyvinyl alcohol resin include alkylenediamines; isocyanates; epoxy resin; aldehydes; amino-formaldehydes such as methylol urea and melamine. Among these, amino-formaldehydes are preferred. As the amino-formaldehyde resin, a compound having a methylol group is preferable, and methylolmelamine is particularly preferable. The amount of the crosslinking agent to be blended in the adhesive composition is preferably about 10 to 60 parts by weight, more preferably 20 to 50 parts by weight, per 100 parts by weight of the polyvinyl alcohol resin.
The aqueous adhesive composition is preferably an aqueous solution. The resin concentration of the aqueous adhesive solution is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight, from the viewpoints of coating properties, solution stability, and the like. The viscosity of the aqueous adhesive composition is preferably about 1 to 50 mPas.
The active energy ray-curable adhesive is an adhesive that can undergo radical polymerization, cationic polymerization, or anionic polymerization by irradiation with an active energy ray such as an electron beam or ultraviolet ray. Among these, photo radical polymerizable adhesives that initiate radical polymerization by irradiation with ultraviolet rays are preferred in terms of being curable at low energy.
Examples of the monomer of the radical polymerizable adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Among them, compounds having a (meth) acryloyl group are preferable. Examples of the compound having a (meth) acryloyl group include (meth) acrylic acid C1-20Chain alkyl ester, (meth) acrylic acidAlkyl (meth) acrylates such as alicyclic alkyl esters and polycyclic alkyl (meth) acrylates; a hydroxyl group-containing (meth) acrylate; epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate, and the like. The radical polymerizable adhesive may contain a nitrogen-containing monomer such as hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, or (meth) acryloylmorpholine. The radical polymerizable adhesive may contain a polyfunctional monomer such as tripropylene glycol diacrylate, 1, 9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate or EO-modified diglycerol tetraacrylate as a crosslinking component.
The photocurable adhesive such as a radical photopolymerizable adhesive preferably contains a photopolymerization initiator. The photopolymerization initiator may be appropriately selected according to the reaction species. For example, in the radical polymerizable adhesive, it is preferable to blend a photoradical generator that generates radicals by light irradiation as a photopolymerization initiator. The content of the photo radical generator is usually about 0.1 to 10 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the monomer. When an electron beam curing adhesive is used as the radical polymerizable adhesive, a photopolymerization initiator is not necessarily required. A photosensitizer typified by a carbonyl compound may be added to the radical polymerizable adhesive as needed. The photosensitizer is used to improve the curing speed and sensitivity by electron beams. The amount of the photosensitizer used is usually about 0.001 to 10 parts by weight, preferably 0.01 to 3 parts by weight, based on 100 parts by weight of the monomer.
The adhesive composition may contain an appropriate additive as needed. Examples of the additives include coupling agents such as silane coupling agents and titanate coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion traps, antioxidants, tackifiers, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat stabilizers, and hydrolysis stabilizers.
[ production of polarizing plate ]
The easy-adhesion film 1 is bonded to one surface (first main surface) of the polarizer 5 via an adhesive layer 6, whereby a polarizing plate can be produced. Specifically, it is preferable to apply an adhesive composition to either or both of the polarizing plate 5 and the easy-adhesion film 1, bond the polarizing plate 5 and the easy-adhesion film 1 by a roll laminator or the like, and cure the adhesive to bond the polarizing plate 5 and the easy-adhesion film 1.
In the easy-adhesion film 1, the easy-adhesion layer-formed surface may be bonded to the polarizing plate 5 via an adhesive layer, or the non-easy-adhesion layer-formed surface may be bonded to the polarizing plate 5 via an adhesive layer. As shown in fig. 2, by bonding the polarizing plate 5 to the surface of the easy-adhesion film 1 on which the easy-adhesion layer 15 is formed via the adhesive layer 6, a polarizing plate having high adhesion between the polarizing plate 5 and the transparent protective film (the easy-adhesion film 1), and excellent mechanical strength and durability can be obtained. When the non-adhesive layer-formed surface is bonded to the polarizing plate 5 via the adhesive layer, the adhesiveness to other films, adhesive layers, glass substrates, and the like provided on the easy-adhesive film can be improved.
Examples of the method of applying the adhesive composition to the polarizing plate 5 and/or the easy-adhesion film 1 include roll coating, spraying, dipping, and the like. Before the surface of the polarizing plate 5 and/or the easy adhesion film 1 is coated with the adhesive composition, surface treatment such as corona treatment, plasma treatment, saponification treatment, or the like may be performed.
After the polarizing plate 5 and the easy-adhesion film 1 are bonded, the adhesive is cured according to the type of the adhesive to form an adhesive layer 6. When an aqueous adhesive is used, the adhesive is cured by heat drying. The drying time is typically 120 seconds or more, preferably 300 seconds or more.
< second transparent protective film >
The second transparent protective film 2 may be bonded to the second main surface of the polarizing plate 5 via an adhesive layer 7. As the second transparent protective film 2, any suitable transparent film can be used. The thickness of the second transparent protective film 2 is about 5 to 200 μm. The thickness of the second transparent protective film 2 is preferably 10 to 100 μm, and more preferably 15 to 60 μm from the viewpoint of mechanical strength, transparency, handleability, and the like. The thickness of the first transparent protective film 1 and the thickness of the second transparent protective film 2 may be the same or different.
Examples of the material forming the second transparent protective film 2 include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); cellulose polymers such as diacetylcellulose and triacetylcellulose; styrene polymers such as polystyrene and acrylonitrile-styrene copolymer; cyclic polyolefins such as norbornene; polycarbonates, and the like.
As the second transparent protective film 2, an acrylic film can be used. When the second transparent protective film 2 is an acrylic film, the same film as the acrylic film 11 of the first transparent protective film 1 can be used. When the second transparent protective film 2 is an acrylic film, the durability of the polarizing plate tends to be improved as compared with the case of using a cellulose film.
The second transparent protective film 2 may also include an easy-adhesion layer (not shown). When the second transparent protective film 2 is an acrylic film, an easy-adhesion layer is preferably provided, similarly to the first transparent protective film 1. When the second transparent protective film 2 is an acrylic film, an easy-adhesion layer containing a urethane resin and fine particles is preferably used as the easy-adhesion layer provided on the surface thereof, similarly to the easy-adhesion layer 15 of the first transparent protective film 1.
When both the transparent protective films 1 and 2 bonded to the surface of the polarizer 5 are acrylic films having an easy-adhesive layer, the occurrence of stripe-like unevenness when the polarizing plate is exposed to a high-temperature/high-humidity environment tends to be remarkable. By setting the thickness of the easy-adhesion layer provided on the surface of the second transparent protective film to 280nm or less in addition to the easy-adhesion layer 15 provided on the surface of the transparent protective film 1, even when an acrylic film is used as the double-sided transparent protective film, streaky unevenness is less likely to occur, and a polarizing plate having excellent humidification durability can be obtained.
As the adhesive layer 7 for bonding the polarizing plate 5 and the second transparent protective film 2, various types of adhesives such as an aqueous adhesive, a solvent adhesive, a hot-melt adhesive, a radical polymerization curing adhesive, and the like can be used. Among these, an aqueous adhesive containing a polyvinyl alcohol resin and a crosslinking agent is preferable, as in the adhesive layer 6 for bonding the polarizing plate 5 and the first transparent protective film 1. The same adhesive composition can be used for the adhesive layer 6 and the adhesive layer 7. After the first transparent protective film 1 is laminated on the first main surface of the polarizing plate 5 and the second transparent protective film 2 is laminated on the second main surface of the polarizing plate 5, the adhesive layers 6 and 7 on the front and back surfaces of the polarizing plate 5 may be simultaneously cured by heating or the like.
< estimation principle of suppression of stripe unevenness >
As described above, in the polarizing plate in which the polarizing plate is bonded to the surface of the easy-adhesion layer 15 of the easy-adhesion film 1, the durability of the polarizing plate tends to be improved and the occurrence of stripe-like unevenness tends to be suppressed as the thickness of the easy-adhesion layer 15 is reduced. The primary cause of the non-uniformity of the streaks is iodide ion (I)3 -And I5 -) It is considered that the smaller the thickness of the easy-adhesion layer is, the more the release of iodide ions from the polarizing plate is suppressed, and thus the occurrence of stripe unevenness is suppressed.
In the PVA-based polarizing film having iodine adsorbed thereon, a polymer chain of PVA forms a complex with iodide ions, and when the PVA-based polarizing film is exposed to a high-temperature and high-humidity environment, the iodide ions are detached from the PVA chain. The dissociation of iodide ions from the PVA chain can be represented by the following formula.
PVA-I5 -→PVA-I3 -+I2
PVA-I5 -→PVA+I3 -+I2
PVA-I3 -→PVA+I3 -
I of iodine in PVA-based polarizing plate3 -Ions and I5 -Free I with ions present in a certain proportion but detached from PVA chains5 -The ions are unstable and thus give rise toTo form I3 -Ions and iodine (I)2). If the free iodine and iodide ions remain in the polarizer, the reaction of removing the iodide ions from the PVA chain becomes difficult to proceed. On the other hand, when the concentration of free iodine in the polarizing plate decreases due to sublimation of iodine, movement of iodine and iodine ion substances, the reaction proceeds to the right side, and thus the dissociation of iodine ions from the PVA chains proceeds further.
The urethane-based easy-adhesion layer is considered to have a function of absorbing iodine and/or iodide ions released from the PVA chain of the polarizing plate. Since the amount of iodine and/or iodine ions absorbed increases as the thickness of the easy-adhesion layer increases, iodine and/or iodine ions released in the polarizing plate easily migrate from the polarizing plate to the easy-adhesion layer. When the free iodine and/or iodine ions migrate from the polarizing plate to the easy-adhesion layer, the reaction proceeds to the right, so that the iodine ions are likely to be released from the polarizing plate, which may cause stripe unevenness.
On the other hand, when the thickness of the easy adhesion layer is small, the amount of iodine and/or iodine ions occluded by the easy adhesion layer is small, and even if iodine ions are released from the PVA chain of the polarizing plate, the iodine ions are likely to remain in the polarizing plate. When free iodine or iodide ions remain in the system, the reaction rate of the reaction from the left side to the right side (i.e., the rate of release of iodide ions from the PVA chain) is small, and therefore, it is considered that the release of iodide ions from the PVA chain is suppressed, and the streaking is suppressed.
[ use of polarizing plate ]
The polarizing plate of the present invention may be provided with an adhesive layer for bonding a liquid crystal cell, an organic EL cell, or the like. As the adhesive for forming the adhesive layer, an adhesive containing a polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine, or a rubber as a base polymer can be suitably selected and used. In particular, acrylic adhesives are preferred because they have excellent optical transparency, exhibit appropriate wettability and cohesiveness, and are excellent in weather resistance, heat resistance, and the like.
The adhesive layer may be attached to the polarizing plate in an appropriate manner. Examples thereof include: a method of preparing a pressure-sensitive adhesive solution having a solid content concentration of about 10 to 40 wt% in which a base polymer or the like is dissolved or dispersed in a solvent such as toluene or ethyl acetate, and attaching the pressure-sensitive adhesive solution to a polarizing plate, or a method of transferring a pressure-sensitive adhesive layer formed on an appropriate substrate to a polarizing plate.
An adhesive layer may be provided on both sides of the polarizing plate. When the adhesive layers are provided on both surfaces of the polarizing plate, the composition and thickness of the adhesive layers on the front and back surfaces may be the same or different. The thickness of the adhesive layer is generally about 5 to 500 μm.
On the surface of the adhesive layer, a separator may be temporarily attached for the purpose of preventing contamination of the adhesive layer and the like. As the separator, a separator obtained by coating the surface of a plastic film with a release agent such as a silicone release agent, a long-chain alkyl release agent, or a fluorine release agent is preferably used.
The polarizing plate of the present invention may be a laminated polarizing plate in which other optical layers are laminated. Examples of the optical layer include a retardation plate, a viewing angle compensation film, and a brightness enhancement film.
The polarizing plate of the present invention is bonded to the surface of an image display unit such as a liquid crystal unit or an organic EL unit, thereby forming an image display device. The liquid crystal display device is formed by: the liquid crystal cell and the polarizing plate, and if necessary, the components such as the illumination system are appropriately assembled, and the drive circuit and the like are incorporated. In an organic EL display device, a circular polarizing plate in which the polarizing plate of the present invention and a retardation film (typically, an 1/4 wavelength plate) are combined is bonded to the surface of an organic EL cell, whereby re-emission of reflected light of external light due to a metal electrode or the like can be reduced, and visibility can be improved.
[ examples ]
The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. The "%" described below refers to% by weight unless otherwise specified.
[ example 1]
(preparation of polarizing plate A)
While a long roll of a polyvinyl alcohol (PVA) resin film (PE 4500, ltd) having a thickness of 45 μm was uniaxially stretched in the longitudinal direction so that the length direction thereof was 5.9 times, the film was conveyed in the order of the swelling bath, dyeing bath, crosslinking bath 1, crosslinking bath 2, and washing bath shown in table 1, and dried at 70 ℃ for 5 minutes to prepare a polarizing plate having a thickness of 18 μm by a roll stretcher. The iodine concentration and the potassium iodide concentration in the dyeing bath were adjusted so that the single-sheet transmittance of the polarizing plate became 43.4%.
[ Table 1]
Composition of aqueous solution Temperature (. degree.C.) Draw ratio
Swelling bath Pure water 20 2.2
Dyeing bath Iodine: potassium iodide 1: 7 (weight ratio) 30 1.4
Cross-linking bath 1 5.0% boric acid, 3.0% potassium iodide 40 1.2
Cross-linking bath 2 4.3% boric acid, 5.0% potassium iodide 65 1.6
Cleaning bath 2.6% Potassium iodide 20 -
(preparation of adhesive composition)
20 parts by weight of methylolmelamine was dissolved in pure water at a temperature of 30 ℃ to obtain an aqueous solution having a solid content of 0.5% per 100 parts by weight of an acetoacetyl group-containing polyvinyl alcohol resin (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, degree of acetoacetyl group modification: 5 mol%).
(preparation of easy-adhesion composition)
An easily adhesive composition was prepared by mixing 21.3 parts by weight of a 35% solid polyester polyurethane aqueous solution ("Super Flex 210" manufactured by first Industrial pharmaceutical Co., Ltd.), 5.3 parts by weight of a 25% solid oxazoline-containing polymer aqueous solution ("EpocrossWS-700" manufactured by Nippon catalyst Co., Ltd.), 3.2 parts by weight of 1% aqueous ammonia, 7.8 parts by weight of a 20% aqueous dispersion of colloidal silica having an average primary particle diameter of 35nm ("Quartron PL-3" manufactured by Hibiscus chemical Co., Ltd.), and 62.4 parts by weight of pure water. The easy-adhesion composition contained 15.0 parts by weight of silica particles per 100 parts by weight of the solid content, and the solid content concentration was 10% by weight.
(preparation of easily adhesive film)
One side of a biaxially stretched acrylic film (thickness 40 μm) formed of a mixture of an acrylic resin having a lactone ring structure and an acrylonitrile-styrene (AS) resin was subjected to corona treatment. An easy-adhesion composition was applied to the corona-treated surface of the acrylic film by a wire bar coater provided with a wire bar (#2), and the resultant was dried at 140 ℃ for 5 minutes to obtain an easy-adhesion film having an easy-adhesion layer with a thickness of 110nm formed on one surface of the acrylic film.
(production of polarizing plate)
The easy-adhesion film having the easy-adhesion layer of 110nm was used as a polarizer protective film on both sides. After 30 minutes from the preparation of the adhesive composition, the adhesive composition was applied to the easy-adhesion layer-forming surface of the easy-adhesion film so that the thickness after drying became 50nm, and the easy-adhesion films were laminated on both surfaces of the polarizing plate a, and dried at 70 ℃ for 5 minutes, thereby obtaining a polarizing plate.
Example 2, example 3 and comparative example 1
In the production of the easy-adhesion film of example 1, the winding bar used in applying the easy-adhesion composition was changed. The thicknesses of the easy adhesion layers formed on the surfaces of the acrylic films were 60nm in example 2, 140nm in example 3, and 340nm in comparative example 1. These easy-adhesion films were bonded to both surfaces of the polarizing plate a with an adhesive in the same manner as in example 1, to obtain a polarizing plate.
[ example 4]
(preparation of polarizing plate B)
The ratio of iodine to potassium iodide in the dye bath was maintained at 1: the iodine concentration and the potassium iodide concentration were increased so that the sheet transmittance of the polarizing plate became 42.1% without changing 7. Except for this, a polarizing plate having a thickness of 18 μm was produced in the same manner as the production of the polarizing plate a.
(preparation of easily adhesive film)
In the production of the easy adhesion film of example 1, the winding bar used in applying the easy adhesion composition was changed to the winding bar of # 4. The thickness of the easy adhesion layer formed on the surface of the acrylic film was 240 nm.
(production of polarizing plate)
A polarizing plate having an easy-adhesion film bonded to both surfaces of the polarizer B was obtained in the same manner as in example 1, using the easy-adhesion film having the easy-adhesion layer of 240nm as the polarizer protective film.
Comparative example 2
A polarizing plate was obtained in the same manner as in comparative example 1, except that the polarizing plate B was used instead of the polarizing plate a.
[ evaluation ]
< amount of alkali remaining in easily bondable layer >
The amounts of triethylamine and ammonia remaining in the easy-adhesion layer of the easy-adhesion film before the easy-adhesion film was bonded to the polarizing plate were quantified. The residual amount of triethylamine was quantified by the following method: the powder obtained by scraping the easy-adhesion layer from the surface of the easy-adhesion film was weighed, dissolved in methanol, and quantified by a gas chromatography-mass spectrometry (GC/MS) method of the solution. The residual amount of ammonia was quantified by the following method: the easily adhesive film was immersed in pure water at 25 ℃ and then heated and extracted in a drier at 120 ℃ for 60 minutes, and the amount of ammonia eluted in water was determined by ion chromatography. The total of the amount of triethylamine and the amount of ammonia was used as the amount of residual base.
< adhesion Strength >
The polarizing plate was cut into a size of 200mm in parallel with the stretching direction of the polarizing plate (absorption axis direction) and 20mm in the orthogonal direction (transmission axis direction), and a notch was cut between the easy-adhesion film and the polarizing plate with a cutter knife, and the polarizing plate was attached to a glass plate. The adhesion was measured by a peel test at a peel angle of 90 ° and a peel speed of 1000 mm/min using a tensile compression tester ("TG-1 kN" manufactured by Minebea Mitsumi Inc.).
< humidification durability >
The polarizing plate was cut into a size of 320mm × 240mm, and was attached to a glass plate with an acrylic adhesive having a thickness of 20 μm. The sample was placed in a constant temperature and humidity cell at a temperature of 60 ℃ and a relative humidity of 90%, and kept for 500 hours to conduct a heating/humidifying durability test. The single-sheet transmittance and the degree of polarization of the polarizing plate before and after the durability test were measured, and the amount of change in the single-sheet transmittance and the degree of polarization was calculated. Further, other polarizing plates were disposed on the polarizing plate with crossed prisms, and the presence or absence of streaky unevenness was visually observed. The polarizing plates of example 4 and comparative example 2 were subjected to a heating/humidifying durability test by being held in a constant temperature and high humidity chamber at a temperature of 85 ℃ and a relative humidity of 85% for 120 hours, and the same evaluation was performed. The presence or absence of streaky unevenness of the polarizing plate after the heating/humidifying durability test was evaluated by the following criteria.
Good: no stripe unevenness was recognized
△ slight recognition of streaking
X: clearly identify the stripe unevenness
The polarizing plate configurations (type of polarizing plate, thickness of easy-adhesion layer and amount of residual alkali) and evaluation results of the examples and comparative examples are shown in table 2. Photographs of the polarizing plates of example 1, example 2 and comparative example 1 observed under crossed prisms before and after the durability test (90% Rh500 hours at 60 ℃) are shown in fig. 3 (taken under the unevenness measuring system I-system co., ltd. "EYESCALE-4W"). Photographs (taken under a compact digital camera CASIO COMPUTER Co., Ltd., led. "EXILIMEX-ZR 1100", manufactured by led.) of the polarizing plates of example 4 and comparative example 2, which were observed under crossed prisms before and after the durability test (85 ℃ C., 85% Rh 120 hours) are shown in FIG. 4.
[ Table 2]
Figure BDA0002378396000000241
The polarizing plate of comparative example 1, in which an easy-adhesion film having an easy-adhesion layer with a thickness of 340nm was laminated on both sides of the polarizer a, exhibited good adhesion between the polarizer and the easy-adhesion film, but streaky unevenness occurred after the heating/humidifying durability test. In example 1 using the easy adhesion film having the easy adhesion layer of 110nm and example 3 using the easy adhesion film having the easy adhesion layer of 140nm, slight streaky unevenness was observed after the heating/humidifying durability test, but the unevenness was greatly improved as compared with comparative example 1. In example 2 using the easy-adhesion film having an easy-adhesion layer with a thickness of 60nm, no streaky unevenness was observed even after the heat/humidity durability test, and good durability was exhibited (see fig. 3).
In example 4 using the polarizing plate B having a higher iodine concentration and a higher polarization degree than the polarizing plate a, in comparison with comparative example 2, similarly, in comparative example 2 using the easy-adhesion film having the easy-adhesion layer with a thickness of 340nm, after the heating/humidifying durability test at a temperature of 60 ℃ and a relative humidity of 90%, the polarizing plate had streaky unevenness, whereas in example 4 having the easy-adhesion layer with a thickness of 240nm, the streaky unevenness was not observed, and good durability was exhibited. In the durability test of heating/humidification at 85 ℃ and 85% relative humidity, the polarizing plate of example 4 was observed to have unevenness in stripe form, but the degree of unevenness was reduced as compared with comparative example 2 (see fig. 4).
From these results, it can be seen that: by reducing the thickness of the easy-adhesion layer provided on the surface of the acrylic film, the occurrence of stripe-like unevenness when the polarizing plate is exposed to a heating/humidifying environment for a long time can be suppressed.
From the comparison between examples 1 to 3 and comparative example 1 (the result of the endurance test at a temperature of 60 ℃ C. and a relative humidity of 90%), and the comparison between example 4 and comparative example 2, it can be seen that: by reducing the thickness of the easy-adhesion layer, the occurrence of stripe-like unevenness is suppressed, the variation in the single-sheet transmittance and the polarization degree is reduced, and the durability of the polarizing plate is improved.
In examples 1 to 4 and comparative examples 1 and 2, it is seen that the smaller the thickness of the easy-adhesion layer, the smaller the amount of residual alkali, and the more the occurrence of streaky unevenness after the heating/humidifying durability test tends to be suppressed. It is considered that reducing the thickness of the easy-adhesion layer reduces the amount of residual alkali in the easy-adhesion layer, and also contributes to improvement of durability of the polarizing plate.
Description of the reference numerals
1 transparent protective film (easy adhesion film)
11 acrylic film
15 easy adhesive layer
2 transparent protective film
5 polarizing plate
6. 7 adhesive layer
100 polarizing plate

Claims (6)

1. A polarizing plate comprising: a polyvinyl alcohol-based polarizing plate having a first main surface and a second main surface, and a transparent protective film bonded to the first main surface of the polarizing plate via an adhesive layer,
the transparent protective film has an easy-adhesion layer on the surface of an acrylic film, and the easy-adhesion layer forming surface is bonded to the polarizing plate,
the easy-bonding layer contains polyurethane resin and fine particles, and has a thickness of 280nm or less.
2. The polarizing plate according to claim 1, wherein the easy adhesion layer has a thickness of 50nm or more.
3. The polarizing plate according to claim 1 or 2, wherein the content of the fine particles in the easy-adhesion layer is 8 to 50 wt%.
4. The polarizing plate according to any one of claims 1 to 3, wherein the content of an alkaline component in the easy-adhesion layer is 75ppm or less.
5. The polarizing plate according to any one of claims 1 to 4, further comprising a second transparent protective film attached to the second main surface of the polarizer via an adhesive layer.
6. An image display device comprising an image display unit and the polarizing plate according to any one of claims 1 to 5.
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