JP6580769B2 - Polarizing plate and image display device - Google Patents

Description

  The present invention relates to an easy-adhesion film having an easy-adhesion layer on the surface of a transparent film, and a polarizing plate in which an easy-adhesion film is bonded to the surface of a polarizer as a transparent protective film. Furthermore, this invention relates to an image display apparatus provided with the said polarizing plate.

  Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile devices, car navigation devices, personal computer monitors, and televisions. In the liquid crystal display device, a polarizing plate is disposed on the viewing side surface of the liquid crystal cell because of its display principle. In the transmissive liquid crystal display device, polarizing plates are arranged on both surfaces of the liquid crystal cell. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and viewed like a mirror surface, a circularly polarizing plate (typically, a polarizing plate and 1 / There are cases where a laminate of four-wave plates is disposed.

  The polarizing plate generally includes a transparent film for the purpose of protecting the polarizer on one or both sides of the polarizer. As a polarizer, one in which iodine is adsorbed on a polyvinyl alcohol (PVA) film and molecules are oriented by stretching or the like is widely used.

  Cellulose films such as cellulose acetate are widely used as the transparent protective film to be bonded to the surface of the polarizer because of its excellent adhesiveness with the PVA polarizer. An acrylic film is also used as a transparent protective film. Acrylic films are less permeable to moisture than cellulose films, so polarizing plates using acrylic transparent protective films have little change in optical properties even when exposed to high humidity environments for long periods of time, making them durable. There is a tendency to excel. Further, since the acrylic film has low birefringence, an improvement in optical characteristics (for example, reduction in light leakage of an image display device) can be expected.

  Acrylic films tend to have lower adhesion to PVA polarizers than cellulose films. In order to improve the adhesion between the PVA polarizer and the acrylic film, it has been proposed to provide an easy adhesion layer on the surface of the acrylic film. For example, Patent Document 1 discloses that an easy-adhesion film in which an easy-adhesion layer containing a urethane resin is provided on the surface of an acrylic film is excellent in adhesiveness with a PVA polarizer. Moreover, in patent document 1, it is described that the blocking at the time of winding an easily-adhesive film in roll shape can be suppressed by containing microparticles | fine-particles in an easily bonding layer, and the average containing 1-7 weight% microparticles | fine-particles is described. The example which produced the polarizing plate by making an easily-adhesive film provided with the urethane easily-adhesive layer of thickness 400nm (thickness range 300-500nm) into a polarizer protective film is shown.

Japanese Patent No. 5354733

  As the size and brightness of image display devices increase, the polarizing plate constituting the image display device has a small change in optical characteristics even in a harsher environment (for example, higher temperature and higher humidity conditions). It has come to be required. The polarizing plate using the acrylic transparent protective film provided with the easily bonding layer of patent document 1 is excellent in the adhesiveness of a polarizer and a transparent protective film, and its adhesive reliability is also high. However, as a result of the study by the present inventors, the polarizing plate provided with the easy-adhesion film disclosed in Patent Document 1 causes streaky unevenness in the polarizing plate when exposed to a high-humidity environment for a long time, resulting in deterioration of display characteristics. A new issue has been identified that may invite.

  In view of the above problems, an object of the present invention is to provide an easily adhesive film that can be used as a polarizer protective film. Furthermore, the present invention provides a polarizing plate that has excellent adhesion between the polarizer and the transparent protective film, and is less likely to cause streak-like unevenness even when exposed to a high temperature and high humidity environment for a long time. For the purpose of provision.

  The easy-adhesion film of the present invention includes an easy-adhesion layer on the surface of an acrylic film. The polarizing plate of the present invention includes a transparent protective film bonded to one surface of a polyvinyl alcohol polarizer via an adhesive layer. A transparent protective film may also be provided on the other surface of the polarizer.

  The transparent protective film bonded to one surface of the polarizer is an easy-adhesive film having an easy-adhesive layer on the surface of the acrylic film, and the easy-adhesive layer forming surface is preferably bonded to the polarizer. . The easy adhesion layer provided on the surface of the acrylic film contains a urethane resin and fine particles and has a thickness of 280 nm or less.

The thickness of the easy adhesion layer is preferably 50 nm or more. The content of fine particles in the easy-adhesion layer is preferably 8 to 50% by weight. The easy adhesion layer preferably has an alkali component content of 75 ppm or less.

  The polarizing plate provided with the easy-adhesive film of the present invention is less likely to cause streak unevenness even when exposed to a high temperature and high humidity environment for a long time, and is excellent in durability. Therefore, by using the polarizing plate of the present invention, an image display device excellent in display uniformity can be obtained.

It is sectional drawing which shows the structural example of an easily bonding film. It is a schematic sectional drawing which shows the laminated structure of the polarizing plate of one Embodiment. It is a cross Nicol observation photograph before and after the heating and humidification endurance test of the polarizing plates of Examples 1 and 2 and Comparative Example 1. It is a cross Nicol observation photograph before and after the heating and humidification endurance test of the polarizing plate of Example 4 and Comparative Example 2.

  FIG. 1 is a schematic cross-sectional view illustrating a configuration example of an easy-adhesion film according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view illustrating a stacked configuration 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 the polarizer 5 via an adhesive layer 6. The first transparent protective film 1 is an easy adhesion film, and includes 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 polarizer 5 with an adhesive layer 7 interposed therebetween.

[Transparent protective film (adhesive film)]
The transparent protective film 1 bonded to one surface of the polarizer 5 is an easy-adhesion film including an easy-adhesion layer 15 on one surface of the acrylic film 11. At the time of producing the polarizing plate, it is preferable that the surface of the transparent protective film 1 on which the easy adhesion layer 15 is formed is bonded to the PVA polarizer 5 through the adhesive layer 6.

<Acrylic film>
The acrylic film 11 includes an acrylic resin. Examples of acrylic resins include poly (meth) acrylates such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymers, methyl methacrylate- (meth) acrylic acid ester copolymers, and methyl methacrylate. -Acrylic acid ester- (meth) acrylic acid copolymer, methyl (meth) acrylate-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (for example, methyl methacrylate-methacrylic acid) Cyclohexyl copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.).

  In this specification, “(meth) acryl” means acrylic and / or methacrylic. Acrylic resins include those containing acrylic acid or a derivative thereof as a constituent monomer component, and those containing methacrylic acid or a derivative thereof as a constituent monomer component.

  As the acrylic resin, an acrylic resin having a glutaric anhydride structure described in JP-A-2006-283013, JP-A-2006-335902, JP-A-2006-274118, and the like; Acrylic resins having a lactone ring structure described in JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544 A, JP 2005-146084 A, etc. It may be used. Acrylic resin having a glutaric anhydride structure and an acrylic resin having a lactone ring structure have high heat resistance, high transparency, and high mechanical strength, and therefore have a high degree of polarization and excellent durability. Suitable for manufacturing.

  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 the acrylic resin. For example, by blending another thermoplastic resin, an acrylic film excellent in optical isotropy can be obtained by canceling the birefringence of the acrylic resin. Moreover, you may mix | blend thermoplastic resins other than an acrylic resin for the purpose of the mechanical strength improvement of a film, etc.

  Examples of thermoplastic resins other than acrylic resins include olefin polymers, vinyl halide polymers, polystyrene, copolymers of styrene and acrylic monomers, polyester, polyamide, polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide, poly Examples include ether ether ketone, polysulfone, polyether sulfone, polyoxybenzylene, polyamideimide, and rubber-based polymer.

  The acrylic film 11 may contain additives such as an antioxidant, a stabilizer, a reinforcing material, an ultraviolet absorber, a flame retardant, an antistatic agent, a colorant, a filler, a plasticizer, a lubricant, and a filler. The acrylic resin may be mixed with other thermoplastic resins, additives, etc., and formed into a film after forming a thermoplastic resin composition such as pellets in advance.

  Examples of the method for producing the acrylic film 11 include a solution casting method, a melt extrusion method, a calendar method, and a compression molding method. The acrylic film 11 may be an unstretched film or a stretched film. From the viewpoint of improving the mechanical strength, it is preferable to use a biaxially stretched film as the acrylic film 11. By blending another thermoplastic resin so as to cancel the birefringence of the acrylic resin, an acrylic film having small retardation and excellent optical isotropy can be obtained even when stretched.

  The acrylic film 11 has a thickness of about 5 to 200 μm. From the viewpoint of mechanical strength, transparency, handling properties, and the like, the thickness of the acrylic film is preferably 10 to 100 μm, and more preferably 15 to 60 μm.

  The glass transition temperature Tg of the acrylic film 11 is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and further preferably 120 ° C. 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 can be improved. The upper limit of Tg of the acrylic film 11 is not particularly limited, but is preferably 170 ° C. or lower from the viewpoint of moldability and the like.

<Easily adhesive layer>
The easy adhesion layer 15 provided on the surface of the acrylic film 11 includes a urethane resin and fine particles. By providing the easy-adhesion layer 15 containing a urethane resin, the adhesiveness between the easy-adhesion film 1 and the polarizer 5 can be improved. When the easy-adhesion layer 15 contains fine particles, fine irregularities are formed on the surface of the easy-adhesion film 1, and the slipperiness of the film is improved. Therefore, it contributes to the reduction of the damage at the time of roll conveyance of the easy-adhesion film 1, and the blocking suppression at the time of winding up in roll shape.

  One feature of the easy-adhesion film of the present invention is that the thickness of the easy-adhesion layer 15 provided on the surface of the acrylic film 11 is 280 nm or less. By reducing the thickness of the easy-adhesion layer 15, even when exposed to a high temperature and high humidity environment for a long time, a highly durable polarizing plate is obtained in which streak-like unevenness hardly occurs and the change in polarization degree is small.

(Urethane resin)
The urethane resin that is the main component of the easy-adhesion layer 15 is typically a reaction product of a polyol and a polyisocyanate. As the polyol component, polymer polyols such as polyacryl polyol, polyester polyol and polyether polyol are preferably used.

  The polyacryl polyol is typically obtained by polymerization of a (meth) acrylic acid ester and a hydroxyl group-containing monomer. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, (meth) Hydroxyalkyl esters of (meth) acrylic acid such as 4-hydroxybutyl acrylate and 2-hydroxypentyl (meth) acrylate; (meth) acrylic monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N-methylol (Meth) acrylamide etc. are mentioned.

  The polyacryl polyol may contain monomer components other than those described above. 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 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; Vinyl chloride and vinylidene chloride Halogenated α, β-unsaturated aliphatic monomers such as α; β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

  The polyester polyol is typically obtained by a reaction between a polybasic acid and a polyol. Polybasic acids include aromatics such as orthophthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, tetrahydrophthalic acid, etc. Dicarboxylic acid; oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, tartaric acid, alkylsuccinic acid, linolenic acid Aliphatic dicarboxylic acids such as maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid; alicyclic rings such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid Formula dicarboxylic acid; These acid anhydrides, alkyl esters, reactive derivatives such as acid halides and the like.

  Examples of the polyol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, , 8-octanediol, 1,10-decanediol, 1-methyl-1,3-butylene glycol, 2-methyl-1,3-butylene glycol, 1-methyl-1,4-pentylene glycol, 2-methyl -1,4-pentylene glycol, 1,2-dimethyl-neopentyl glycol, 2,3-dimethyl-neopentyl glycol, 1-methyl-1,5-pentylene glycol, 2-methyl-1,5-penty Lenglycol, 3-methyl-1,5-pentylene glycol, 1,2-dimethylbutyleneglycol 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, , 4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and the like.

  The polyether polyol is typically obtained by adding an alkylene oxide to a polyhydric alcohol by ring-opening polymerization. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran.

  Examples of polyisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, 1,4-butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2 -Aliphatic diisocyanates such as methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-cyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate Alicyclic diisocyanates such as methylcyclohexylene diisocyanate and 1,3-bis (isocyanatomethyl) cyclohexane Tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1 , 5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate and other aromatic diisocyanates; dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene Examples include aromatic aliphatic diisocyanates such as range isocyanate.

  The urethane resin constituting the easy-adhesion layer 15 preferably has a carboxy group. When the urethane resin of the easy-adhesion layer 15 has a carboxy group, it is possible to introduce a cross-linked structure, and the adhesion durability between the easy-adhesion film 1 and the polarizer 5 tends to be improved. The urethane resin having a carboxy group can be obtained, for example, by reacting a chain extender having a free carboxy group in addition to a polyol and a polyisocyanate. Examples of the chain extender having a free carboxy group include dihydroxycarboxylic acid and dihydroxysuccinic acid. Examples of the dihydroxycarboxylic acid include dialkylol alkanoic acids such as dimethylol alkanoic acid (for example, dimethylol acetic acid, dimethylol butanoic acid, dimethylol propionic acid, dimethylol butyric acid, dimethylol pentanoic acid).

  The method for producing the urethane resin is not particularly limited, and any one of a one-shot method in which monomer components are reacted at a time and a multistage method in which stepwise reaction is performed may be used. When introducing a carboxy group into a urethane resin using a chain extender having a free carboxy group, a multistage method is preferred. In producing the urethane resin, a urethane reaction catalyst may be used as necessary. After applying an easy-adhesion composition containing a urethane precursor (polyol, polyisocyanate, etc.) on an acrylic film, the urethanization reaction may be carried out by heating or the like.

  The number average molecular weight of the urethane resin is preferably 5,000 to 600,000, and more preferably 10,000 to 400,000. 10-50 are preferable and, as for the acid value of a urethane resin, 20-45 are more preferable.

  The urethane resin of the easy adhesion layer 15 may have a crosslinked structure. By introducing a crosslinked structure into the urethane resin, the adhesion durability between the easy-adhesive film 1 and the polarizer 5 tends to be improved. As the crosslinking agent, those capable of reacting with the crosslinkable functional group of the urethane resin can be used without particular limitation. When the urethane resin has a carboxy group, a crosslinking agent containing an amino group, an oxazoline group, an epoxy group, a carbodiimide group, or the like is used. Among these, a crosslinking agent having an oxazoline group is preferable. Since the oxazoline group has low reactivity with the carboxy group at room temperature, the pot life when mixed with a urethane resin is long, and the lead time of the process can be flexibly handled.

  The crosslinking agent may be a low molecular compound or a polymer. An acrylic polymer is preferred as the cross-linking agent because of its high solubility in aqueous compositions and excellent compatibility with urethane resins. In particular, when an acrylic polymer having an oxazoline group is used as a crosslinking agent, the adhesion between the easy-adhesive film 1 and the polarizer 5 tends to be improved.

  The amount of the crosslinking agent used is preferably 1 to 30 parts by weight and more preferably 3 to 20 parts by weight with respect to 100 parts by weight of the urethane resin.

(Fine particles)
The fine particles of the easy-adhesion layer 15 are not particularly limited in material and particle diameter as long as fine irregularities can be formed on the surface of the easy-adhesion layer. From the viewpoint of improving the slipperiness of the easy-adhesive film 1 by forming irregularities on the surface of the easy-adhesive layer, the particle diameter (average primary particle diameter) of the fine particles is preferably 10 nm or more, more preferably 15 nm or more, and further preferably 20 nm or more. preferable. When the average primary particle diameter of the fine particles is smaller than the visible light wavelength, the scattering of visible light at the interface between the urethane resin and the fine particles is suppressed, and the influence on the optical characteristics such as depolarization of the polarizing plate can be reduced. Therefore, the particle diameter of the fine particles is preferably 150 nm or less, more preferably 100 nm or less, further preferably 60 nm or less, and particularly preferably 50 nm or less.

The fine particles may be either inorganic fine particles or organic fine particles. Examples of inorganic fine particles include inorganic oxides such as silica, titania, alumina, 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 caused by the fine particles, it is preferable that the refractive index difference between the urethane resin and the fine particles is small. The difference in refractive index between the urethane resin is small, and because of excellent dispersibility, the fine particles of the adhesive layer 15 inorganic fine particles good preferred, silica particles are particularly preferred.

  When the easy-adhesion layer 15 is formed from an aqueous composition, it is preferable to use fine particles with high water dispersibility. You may mix | blend the fine particle aqueous dispersion in a composition. In order to improve the dispersibility of the fine particles, it is preferable to add an alkali component such as amine or ammonia to make the easily adhesive composition weakly alkaline.

  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 Fuso Chemical Industry Co., Ltd., Snowtex series manufactured by Nissan Chemical Industry Co., Ltd., Aeroerosp series produced by Nippon Aerosil Co., Ltd., and AEROSIL series may be used.

  From the viewpoint of enhancing the slipperiness of the easy-adhesive film 1 by forming irregularities on the surface of the easy-adhesive layer 15, the content of fine particles in the easy-adhesive layer 15 is preferably 8% by weight or more, more preferably 10% by weight or more. 12% by weight or more is more preferable. In the easy-adhesion film of the present invention, since the thickness of the easy-adhesion layer 15 is as small as 280 nm or less, the amount of fine particles per unit area (number density) is increased by increasing the content of the fine particles. It is preferable to form unevenness uniformly in the plane. If the content of the fine particles in the easy-adhesion layer 15 is excessively large, optical characteristics may be deteriorated due to an increase in light scattering at the interface between the urethane resin and the fine particles. Moreover, since the relative content of the urethane resin decreases as the content of fine particles increases, the adhesion between the easy-adhesive film 1 and the polarizer 5 may decrease. Therefore, the content of fine particles in the easy-adhesion layer 15 is preferably 50% by weight or less, more preferably 40% by weight or less, and further preferably 30% by weight or less.

  In the easy-adhesion layer 15, the amount of fine particles is preferably 11 to 100 parts by weight, more preferably 12 to 65 parts by weight, relative to 100 parts by weight of the urethane resin (when the crosslinking agent is included, the total of the urethane resin and the crosslinking agent). More preferred is ˜40 parts by weight.

(Residual alkali amount)
When an alkali component such as amine or ammonia is used in order to improve the dispersibility of the fine particles, the alkali component inevitably remains in the easy adhesion layer. In the polarizing plate in which the easy-adhesive film 1 is bonded to the surface of the polarizer 5, when the residual alkali component of the easy-adhesive layer 15 is eluted by moisture or the like, the polarizer is deteriorated, and the polarization degree of the polarizing plate is reduced or streaks. Optical defects such as unevenness may occur.

  From the viewpoint of enhancing the humidification durability of the polarizing plate, the residual alkali amount of the easy-adhesion layer 15 is preferably 75 ppm or less, more preferably 70 ppm or less, further preferably 60 ppm or less, and particularly preferably 55 ppm or less. From the viewpoint of improving the humidification durability of the polarizing plate, it is preferable that the residual alkali amount of the easy-adhesion layer 15 is smaller.

  On the other hand, if the residual alkali amount of the easy-adhesion layer 15 is too small, the dispersibility of the fine particles is impaired, and appearance defects such as white turbidity due to the aggregation of the fine particles may occur. In addition, due to aggregation of fine particles due to a decrease in dispersibility and dropping of fine particles from the easy adhesion layer, appropriate unevenness is not formed on the surface of the easy adhesion layer, and the slipperiness of the easy adhesion film tends to decrease. . Therefore, the residual alkali amount of the easy adhesion layer 15 is preferably 5 ppm or more, more preferably 10 ppm or more, and further preferably 20 ppm or more.

  The amount of alkali in the easy-adhesion layer can be quantified by liquid chromatography, ion chromatography, or the like depending on the type of alkali component. The alkali component may be quantified by an analysis method (for example, LC / MS) that combines chromatography and mass spectrometry (MS). When a plurality of alkali components are contained in the easy-adhesion layer, the total of each component is defined as the alkali component content (residual amount) of the easy-adhesion layer. When quantifying the amount of alkali in the easy-adhesion layer from the polarizing plate bonded with the easy-adhesive film and the polarizer, the polarizing plate is immersed in warm water and the easy-adhesion layer is dissolved together with the polarizer, and the eluted alkali What is necessary is just to quantify the quantity.

<Formation of easy adhesion layer>
The formation method of the easily bonding layer 15 to the surface of the acrylic film 11 is not specifically limited. Preferably, the easy-adhesion layer 15 is formed by applying an easy-adhesion composition (solution) containing a urethane resin or its precursor and fine particles on the acrylic film 11 and drying it.

  You may form an easily bonding layer in the manufacturing process of an acrylic film. Moreover, you may form an easily bonding layer using the heating in the formation process of a film base material. For example, when the acrylic film 11 is a stretched film, an easy-adhesive composition is applied to the surface of the film before stretching or the film after longitudinal stretching, and heating during transverse stretching or simultaneous biaxial stretching with a tenter is performed. Utilizing it, the solvent can be dried and the resin can be cured.

  Before the easy adhesion layer 15 is formed, the acrylic film 11 may be subjected to a surface treatment. By performing the surface treatment, the wetting tension of the acrylic film 11 can be adjusted, and the adhesion with the easy adhesion layer 15 can be improved. Examples of the surface treatment include corona treatment, plasma treatment, ozone spraying, ultraviolet irradiation, flame treatment, and chemical treatment. Among these, corona treatment or plasma treatment is preferable.

(Easily adhesive composition)
The easy-adhesion composition is preferably an aqueous composition using water as a solvent (and a dispersion medium for fine particles). 1-30 weight% is preferable, as for the density | concentration of solid content (nonvolatile component) in an easily bonding composition, 2-20 weight% is more preferable, and 3-15 weight% is further more preferable.

  The water-based easy-adhesion composition includes water as a solvent (and a dispersion medium), a urethane resin or a precursor thereof, and fine particles, and further includes a crosslinking agent as necessary. The easy-adhesion composition preferably further contains an alkali component. As described above, the alkali component has an action of promoting the dispersion of the fine particles. Therefore, when the easy-adhesive composition contains an alkali component, an easy-adhesive film that improves the dispersibility of the fine particles and is excellent in appearance and slipperiness can be obtained.

  On the other hand, when the alkali contained in the easy-adhesive composition remains in the easy-adhesive layer, it may cause a decrease in the wet heat resistance of the polarizing plate. In particular, strong alkali such as caustic can cause the polarizer to deteriorate even in a small amount. Therefore, as the alkali component contained in the easy-adhesion composition, weak alkali components such as ammonia and amines are preferable. The pH of the easy-adhesive composition (coating liquid) is preferably about 7.5 to 9 from the viewpoint of achieving both improvement in fine particle dispersibility and prevention of deterioration of the polarizer.

  From the viewpoint of improving the dispersibility of the fine particles, the amount of the alkali component contained in the easy-adhesion composition is preferably 300 ppm or more, more preferably 500 ppm or more, based on the solid content of the easy-adhesion composition. On the other hand, if the content of the alkali component is excessively large, it may be difficult to reduce the residual alkali amount. Therefore, the amount of the alkali component contained in the easy-adhesion composition is based on the solid content of the easy-adhesion composition. On the other hand, 50000 ppm or less is preferable, 10000 ppm or less is more preferable, and 5000 ppm or less is more preferable.

  The alkali component contained in the easy-adhesion composition may have a catalytic action or the like in addition to improving the dispersibility of the fine particles. For example, a tertiary amine such as triethylamine may be included in the easy-adhesion composition as a urethanization catalyst for a polyurethane precursor (polyol, polyisocyanate, etc.).

  By heating after applying the easy-adhesion composition on the acrylic film 11, the alkali component can be volatilized and removed, and the remaining alkali component of the easy-adhesion layer 15 can be reduced. From the viewpoint of promoting the volatilization of the alkali component by heating, the alkali component contained in the easy-adhesion composition preferably has a boiling point of 150 ° C. or lower. The boiling point of the alkali component is more preferably 130 ° C. or less, further preferably 120 ° C. or less, and particularly preferably 110 ° C. or less. The boiling point of the alkali component may be 100 ° C. or lower or 90 ° C. or lower. When a plurality of alkali components are contained in the easy-adhesion composition, the boiling point of at least one alkali component is preferably in the above range, and the boiling points of two or more alkali components are preferably in the above range. The boiling point of the alkali component of 50% by weight or more is preferably in the above range with respect to 100 parts by weight of the total amount of alkali contained in the easy-adhesion layer. Ideally, the boiling points of all alkali components contained in the easy-adhesion composition are in the above range.

  The easy-adhesion composition may contain resin components and additives other than the urethane resin. Additives include catalysts such as crosslinking accelerators, antioxidants, UV absorbers, leveling agents, antiblocking agents, antistatic agents, dispersion stabilizers, antifoaming agents, thickeners, dispersants, surfactants, Examples include lubricants.

  Examples of the method for applying the easy-adhesive composition include a bar coating method, a roll coating method, a gravure coating method, a rod coating method, a slot orifice coating method, a curtain coating method, and a fountain coating method. By heating the easy-adhesion composition after application, the easy-adhesion layer 15 is formed by removing the solvent. The heating temperature is, for example, about 50 to 180 ° C. When the easy-adhesion composition contains a crosslinking agent, the crosslinking of the urethane resin can be promoted by heating. As described above, when the easy-adhesion composition contains an alkali component, the alkali component is volatilized and removed by heating, and the remaining alkali component of the easy-adhesion layer 15 can be reduced. From the viewpoint of efficiently volatilizing and removing the alkali component contained in the easy-adhesion composition, the heating temperature is preferably 100 ° C or higher, more preferably 120 ° C or higher, further preferably 130 ° C or higher, and particularly preferably 135 ° C or higher. Moreover, it is preferable that heating temperature is higher than the boiling point of the alkali component contained in an easily bonding composition.

  The thickness of the easy adhesion layer 15 is 280 nm or less. By reducing the thickness of the easy-adhesive layer 15, the humidification durability of the polarizing plate is improved, and even when exposed to a humidified environment for a long time, the occurrence of streak-like unevenness is suppressed and the in-plane uniformity of the display is maintained. it can. From the viewpoint of suppressing the occurrence of streaky unevenness on the polarizing plate after the humidification test, the thickness of the easy-adhesion layer 15 is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 170 nm or less.

  As the thickness of the easy-adhesion layer 15 is smaller, the humidification durability of the polarizing plate is improved, and the occurrence of streaky unevenness tends to be suppressed. Moreover, there exists a tendency for the fall of the polarization degree at the time of a polarizing plate to be exposed to a humid environment, and the fall of a single transmittance | permeability as the thickness of the easily bonding layer 15 is small. On the other hand, if the thickness of the easy adhesion layer 15 is excessively small, the adhesion between the easy adhesion film 1 and the polarizer 5 may be lowered. Therefore, the thickness of the easy adhesion layer 15 is preferably 50 nm or more, more preferably 80 nm or more, and further preferably 100 nm or more. The thickness of the easy adhesion layer 15 may be 110 nm or more, 120 nm or more, 130 nm or more, or 140 nm or more. If the thickness of the easy-adhesion layer is in the above range, in addition to excellent adhesion between the easy-adhesion film and the polarizer, the workability when cutting the polarizing plate into a predetermined sheet size is excellent, and microcracks It tends to be suppressed.

  By adjusting the solid content concentration and the coating thickness of the easy-adhesive composition, the thickness of the easy-adhesive layer 15 can be adjusted to the above range. The thickness of the easy-adhesion layer 15 in the polarizing plate is determined from cross-sectional observation of the polarizing plate. When the thickness varies, the average thickness in the observation range is set as the thickness of the easy-adhesion layer.

When the easy-adhesion composition contains an alkali component, the smaller the thickness of the easy-adhesion layer, the higher the volatilization removal efficiency of the alkali component by heating. The thickness of the easy-adhesion layer 15 is preferably in the above range from the viewpoint of maintaining the residual amount of the alkali component in an appropriate range, ensuring the dispersibility of the fine particles, and improving the heat and moisture resistance of the polarizing plate.

[Polarizer]
As the polarizer 5, polyvinyl alcohol (PVA) in which a dichroic substance such as iodine or a dichroic dye is adsorbed on a polyvinyl alcohol film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and oriented in one direction. A system polarizer is used. For example, a PVA polarizer can be obtained by subjecting a polyvinyl alcohol film to iodine staining and stretching.

  In the manufacturing process of the polarizer 5, treatments such as washing with water, swelling, and crosslinking may be performed as necessary. Stretching may be performed before or after iodine dyeing, or may be performed while dyeing. Stretching may be either stretching in the air (dry stretching) or stretching in water or an aqueous solution containing boric acid, potassium iodide, etc. (wet stretching), and these may be used in combination. The thickness of the polarizer 5 is not particularly limited, but is generally about 1 to 50 μm.

  As the polarizer 5, a thin PVA polarizer having a thickness of 10 μm or less can be used. Thin polarizers are described in, for example, JP-A-51-069644, JP-A-2000-338329, WO2010 / 100917, Patent No. 4691205, Patent No. 4751481, and the like. A thin polarizer may be mentioned. These thin polarizers are obtained by a production method including a step of stretching a PVA-based resin layer and a stretching resin base material in the state of a laminate, and a step of iodine staining. With this manufacturing method, even if the PVA-based resin layer is thin, it is supported by the stretching resin base material, so that it can be stretched without problems such as breakage due to stretching.

<Adhesive>
The material of the adhesive layer 6 used for bonding the polarizer 5 and the easy-adhesive film 1 is not particularly limited as long as it is optically transparent. A water-based adhesive, a solvent-based adhesive, and a hot-melt adhesive. Various types such as a system and a radical polymerization curable adhesive are used. Among these, since adhesiveness with the PVA polarizer 5 and the urethane easy-adhesion layer 15 is high, an aqueous adhesive or an active energy ray-curable adhesive is preferable.

  Examples of the polymer component of the water-based adhesive include vinyl polymer, gelatin, vinyl latex, polyurethane, polyester, and epoxy. Among these, since it is excellent in the adhesiveness of the polarizer 5 and the easily bonding film 1, a vinyl polymer is preferable and a polyvinyl alcohol-type resin is especially preferable. Among the polyvinyl alcohol resins, acetoacetyl group-containing polyvinyl alcohol is preferable.

  The average degree of polymerization of the polyvinyl alcohol-based resin is preferably about 100 to 5000, and more preferably 1000 to 4000, from the viewpoint of adhesiveness. The average saponification degree of the polyvinyl alcohol-based 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 having reactivity with the polymer constituting the adhesive is used. Examples of the crosslinking agent for the polyvinyl alcohol resin include alkylene diamines; isocyanates; epoxies; aldehydes; and amino-formaldehyde such as methylol urea and methylol melamine. Of these, amino-formaldehyde is preferred. As the amino-formaldehyde resin, a compound having a methylol group is preferable, and methylol melamine is particularly preferable. About 10-60 weight part is preferable with respect to 100 weight part of polyvinyl alcohol-type resin, and, as for the compounding quantity of the crosslinking agent in adhesive composition, 20-50 weight part is more preferable.

  The aqueous adhesive composition is preferably an aqueous solution. From the viewpoints of coatability and solution stability, the resin concentration of the aqueous adhesive solution is preferably 0.1 to 15% by weight, and more preferably 0.5 to 10% by weight. The viscosity of the aqueous adhesive composition is preferably about 1 to 50 mPa · s.

  The active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization, or anion polymerization by irradiation with active energy rays such as electron beams and ultraviolet rays. Among these, a photo-radical polymerizable adhesive that initiates radical polymerization upon irradiation with ultraviolet rays is preferable because it can be cured with low energy.

Examples of the monomer for the radical polymerizable adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Among these, a compound having a (meth) acryloyl group is preferable. Examples of the compound having a (meth) acryloyl group include C _1-20 chain alkyl (meth) acrylate, alicyclic alkyl (meth) acrylate, polycyclic alkyl (meth) acrylate and other alkyl (meth) acrylates; hydroxyl group Containing (meth) acrylate; Epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate and the like. Radical polymerizable adhesives are hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, (meth) acryloylmorpholine Nitrogen-containing monomers such as Radical polymerizable adhesives include tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, EO-modified di-acid as a crosslinking component. A polyfunctional monomer such as glycerin tetraacrylate may be included.

Photocurable adhesives such as photoradical polymerizable adhesives preferably contain a photopolymerization initiator. What is necessary is just to select a photoinitiator suitably according to a reaction seed | species. For example, the radical polymerizable adhesive, as a photopolymerization initiator, are preferably blended photoradical generator which generates radicals by light irradiation. 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 with respect to 100 parts by weight of the monomer. In addition, when using a radically polymerizable adhesive as an electron beam curable type, a photopolymerization initiator is not particularly required. The radical-polymerizable adhesive, if desired, may be added photosensitizer typified by carbonyl compounds. The photosensitizer is used for increasing the curing rate and sensitivity of the electron beam. The usage-amount of a photosensitizer is about 0.001-10 weight part normally with respect to 100 weight part of monomers, Preferably, it is 0.01-3 weight part.

  The adhesive composition may contain an appropriate additive as required. Examples of additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trap agents, and antioxidants. , Tackifiers, fillers, plasticizers, leveling agents, foam inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, and the like.

[Preparation of polarizing plate]
A polarizing plate is manufactured by attaching the easy-adhesion film 1 to one surface (first main surface) of the polarizer 5 via the adhesive layer 6. Specifically, after applying an adhesive composition to one or both of the polarizer 5 and the easy-adhesive film 1, the polarizer 5 and the easy-adhesive film 1 are bonded together with a roll laminator or the like, and the adhesive is applied. It is preferable to bond the polarizer 5 and the easy-adhesive film 1 together by curing.

  The easy-adhesive film 1 may have an easy-adhesive layer forming surface bonded to the polarizer 5 via an adhesive layer, and an easy-adhesive layer non-formed surface bonded to the polarizer 5 via an adhesive layer. It may be. As shown in FIG. 2, the polarizer 5 and the transparent protective film (adhesive film) 1 are bonded to the surface of the easy adhesive film 1 on which the easy adhesive layer 15 is formed through the adhesive layer 6. A polarizing plate having high adhesiveness and excellent mechanical strength and durability can be obtained. When the non-adhesive layer non-forming surface is bonded to the polarizer 5 through the adhesive layer, the adhesion to other films, pressure-sensitive adhesive layers, glass substrates and the like provided on the easy-adhesive film can be improved. .

  Examples of the method for applying the adhesive composition to the polarizer 5 and / or the easy-adhesion film 1 include a roll method, a spray method, and an immersion method. Before applying the adhesive composition to the surface of the polarizer 5 and / or the easy-adhesion film 1, surface treatment such as corona treatment, plasma treatment, and saponification treatment may be performed.

  After bonding the polarizer 5 and the easy-adhesive film 1, the adhesive layer 6 is formed by curing the adhesive according to the type of the adhesive. When an aqueous adhesive is used, the adhesive is cured by heat drying. The drying time is typically 120 seconds or longer, preferably 300 seconds or longer.

<Second transparent protective film>
The second transparent protective film 2 may be bonded to the second main surface of the polarizer 5 via the adhesive layer 7. Any appropriate transparent film can be adopted as the second transparent protective film 2. The thickness of the second transparent protective film 2 is about 5 to 200 μm. From the viewpoint of mechanical strength, transparency, handling properties, and the like, the thickness of the second transparent protective film 2 is preferably 10 to 100 μm, and more preferably 15 to 60 μm. 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.

  Materials for 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 diacetyl cellulose and triacetyl cellulose; polystyrene And styrene polymers such as acrylonitrile / styrene copolymers; cyclic polyolefins such as polynorbornene; polycarbonates and the like.

  An acrylic film may be used as the second transparent protective film 2. When the second transparent protective film 2 is an acrylic film, a film similar to 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 where a cellulose film is used.

  The 2nd transparent protective film 2 may be provided with the easily bonding layer (not shown). When the 2nd transparent protective film 2 is an acrylic film, it is preferable to provide an easily bonding layer similarly to the 1st transparent protective film 1. FIG. When the second transparent protective film 2 is an acrylic film, the easy-adhesion layer provided on the surface thereof is preferably an easy-adhesion layer containing urethane resin and fine particles, like the easy-adhesion layer 15 of the first transparent protective film 1. .

  When both of the transparent protective films 1 and 2 bonded to the surface of the polarizer 5 are acrylic films having an easy-adhesion layer, streaky unevenness when the polarizing plate is exposed to a high temperature and high humidity environment Occurrence tends to be more pronounced. In addition to the easy-adhesion layer 15 provided on the surface of the transparent protective film 1, the acrylic film is used as a transparent protective film on both sides by setting the thickness of the easy-adhesive layer provided on the surface of the second transparent protective film to 280 nm or less. Even when it is used, a polarizing plate that hardly causes streaky unevenness and has excellent humidification durability can be obtained.

  As the adhesive layer 7 used for bonding the polarizer 5 and the second transparent protective film 2, various forms such as a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive, and a radical polymerization curable adhesive are used. Things are used. Among these, like the adhesive layer 6 used for bonding the polarizer 5 and the first transparent protective film 1, an aqueous adhesive containing a polyvinyl alcohol resin and a crosslinking agent is preferable. The same adhesive composition may be used for the adhesive layer 6 and the adhesive layer 7. After laminating the first transparent protective film 1 on the first main surface of the polarizer 5 and laminating the second transparent protective film 2 on the second main surface of the polarizer 5, the polarizer 5 is heated by heating or the like. The adhesive layers 6 and 7 on the front and back sides may be cured simultaneously.

<Estimated principle of streak suppression>
As described above, in the polarizing plate in which the easy-adhesive layer 15 forming surface of the easy-adhesive film 1 is bonded to the polarizer, the durability of the polarizing plate is improved as the thickness of the easy-adhesive layer 15 is reduced, There is a tendency that the occurrence of unevenness is suppressed. The main cause of uneven stripe is the desorption of iodine ions (I ₃ ⁻ and I ₅ ⁻ ) from the polarizer, and the smaller the easy-adhesion layer, the more the desorption of iodine ions from the polarizer is suppressed. It is thought that the occurrence of uneven stripes is suppressed.

In a PVA polarizer with iodine adsorbed, a polymer chain of PVA and iodine ions form a complex, and when the PVA polarizer is exposed to a high temperature and high humidity environment, iodine ions are desorbed from the PVA chain. The elimination of iodine ions from the PVA chain can be represented by the following formula.
PVA-I ₅ ⁻ → PVA-I ₃ ⁻ + I ₂
PVA-I ₅ ⁻ → PVA + I ₃ ⁻ + I ₂
PVA-I ₃ ⁻ → PVA + I ₃ ⁻

In PVA-based polarizer, iodine _{I 3} ^- for ion is unstable, _{I 3} ^{- -} Although ions are present at a constant ratio, _{I 5} free desorbed from PVA chains ^- ion and _{I 5} ion And iodine (I ₂ ) are produced. If free iodine and iodine ions remain in the polarizer, the elimination reaction of iodine ions from the PVA chain hardly proceeds. On the other hand, when the free iodine concentration in the polarizer decreases due to the sublimation of iodine or the mass transfer of iodine and iodine ions, the above reaction proceeds in the right side direction, so that the desorption of iodine ions from the PVA chain occurs. Goes further.

  The urethane-based easy adhesion layer is considered to have an action of occluding iodine and / or iodine ions desorbed from the PVA chain of the polarizer. Since the occlusion amount of iodine and / or iodine ions is larger as the thickness of the easy adhesion layer is larger, free iodine and / or iodine ions in the polarizer are likely to move from the polarizer to the easy adhesion layer. When free iodine and / or iodine ions move from the polarizer to the easy-adhesion layer, the above reaction proceeds in the right-hand side direction, so that the desorption of iodine ions from the polarizer is likely to proceed, which may cause unevenness. .

  On the other hand, when the thickness of the easy-adhesion layer is small, the occlusion amount of iodine and / or iodine ions by the easy-adhesion layer is small, so even if iodine ions are desorbed from the PVA chain of the polarizer, they tend to stay in the polarizer. . If free iodine or iodine ions remain in the system, the reaction rate from the left side to the right side of the above reaction (that is, the desorption rate of iodine ions from the PVA chain) is small. It is considered that the detachment of iodine ions is suppressed and uneven stripes are suppressed.

[Use of polarizing plate]
The polarizing plate of the present invention may be provided with an adhesive layer for bonding to a liquid crystal cell, an organic EL cell or the like. As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected and used. Can do. In particular, an acrylic pressure-sensitive adhesive is preferable because it is excellent in optical transparency, exhibits appropriate wettability and cohesiveness, and is excellent in weather resistance, heat resistance, and the like.

  The attachment of the pressure-sensitive adhesive layer to the polarizing plate can be performed by an appropriate method. For example, a method of preparing a pressure-sensitive adhesive solution having a solid content concentration of about 10 to 40% by weight in which a base polymer or the like is dissolved or dispersed in a solvent such as toluene or ethyl acetate, and being attached on a polarizing plate, or on an appropriate substrate And a method of transferring the pressure-sensitive adhesive layer formed on the polarizing plate.

  You may provide an adhesive layer on both surfaces of a polarizing plate. When providing an adhesive layer on both surfaces of a polarizing plate, the composition and thickness of the adhesive layers on the front and back sides may be the same or different. The thickness of the pressure-sensitive adhesive layer is generally about 5 to 500 μm.

  A separator may be temporarily attached to the surface of the pressure-sensitive adhesive layer for the purpose of preventing contamination of the pressure-sensitive adhesive layer. As the separator, a plastic film whose surface is coated 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 laminated with another optical layer. Examples of the optical layer include a retardation plate, a viewing angle compensation film, and a brightness enhancement film.

  An image display device can be formed by bonding the polarizing plate of the present invention to the surface of an image display cell such as a liquid crystal cell or an organic EL cell. The liquid crystal display device is formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate, and an illumination system as necessary, and incorporating a drive circuit. In an organic EL display device, a metal electrode or the like is bonded to the surface of an organic EL cell with a circularly polarizing plate that is a combination of the polarizing plate of the present invention and a retardation film (typically a quarter wave plate). Visibility can be improved by reducing re-emission of reflected light of external light due to.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to these Examples. The following description of “%” is by weight unless otherwise specified.

[Example 1]
(Preparation of polarizer A)
A long roll of polyvinyl alcohol (PVA) -based resin film (“Kuraray“ PE4500 ”) having a thickness of 45 μm is stretched uniaxially in the longitudinal direction so as to be 5.9 times in the longitudinal direction by a roll stretching machine. The shown swelling bath, dyeing bath, crosslinking bath 1, crosslinking bath 2, and washing bath were conveyed in order and dried at 70 ° C. for 5 minutes to produce a polarizer having a thickness of 18 μm. The iodine concentration and potassium iodide concentration in the staining bath were adjusted so that the single transmittance of the polarizer was 43.4%.

(Preparation of adhesive composition)
An acetoacetyl group-containing polyvinyl alcohol resin (average polymerization degree: 1200, saponification degree: 98.5 mol%, acetoacetyl group modification degree: 5 mol%) is 100 parts by weight, and 20 parts by weight of methylolmelamine is 30 ° C. It was dissolved in pure water under temperature conditions to obtain an aqueous solution with a solid content concentration of 0.5%.

(Preparation of easy adhesion composition)
21.3 parts by weight of a 35% solids polyester urethane aqueous solution (Daiichi Kogyo Seiyaku "Superflex 210"), 25% solids oxazoline-containing polymer aqueous solution (Nippon Shokubai "Epocross WS-700") 5.3 weights Part, 1% by weight ammonia water 3.2 parts by weight, 20% aqueous dispersion of colloidal silica having an average primary particle size of 35 nm (“Quatron PL-3” manufactured by Fuso Chemical Industries), and pure water 62 .4 parts by weight were mixed to prepare an easy adhesion composition. The easy-adhesion composition contains 15.0 parts by weight of silica particles with respect to 100 parts by weight of the solid content, and the solid content concentration is 10% by weight.

(Preparation of easy adhesive film)
Corona treatment was performed on one side of a biaxially stretched acrylic film (thickness 40 μm) made of a mixture of an acrylic resin having a lactone ring structure and an acrylonitrile-styrene (AS) resin. An easy-adhesive composition is applied to the corona-treated surface of the acrylic film with a wire bar coater with a wire bar (# 2) set, dried at 140 ° C. for 5 minutes, and a thickness of 110 nm on one surface of the acrylic film. The easy-adhesion film in which the easy-adhesion layer was formed was obtained.

(Preparation of polarizing plate)
The easy-adhesion film provided with said 110-nm easy-adhesion layer was used as a polarizer protective film of both surfaces. 30 minutes after the preparation of the adhesive composition, the adhesive composition was applied to the surface of the easy-adhesive film where the adhesive layer was formed so that the thickness after drying was 50 nm. A film was laminated and dried at 70 ° C. for 5 minutes to obtain a polarizing plate.

[Example 2, Example 3 and Comparative Example 1]
In preparation of the easily bonding film of Example 1, the wire bar at the time of applying an easily bonding composition was changed. The thickness of the easy-adhesion layer formed on the surface of the acrylic film was 60 nm in Example 2, 140 nm in Example 3, and 340 nm in Comparative Example 1. In the same manner as in Example 1, these easy-adhesion films were bonded to both surfaces of the polarizing plate A via an adhesive to obtain a polarizing plate.

[Example 4]
(Preparation of polarizer B)
While maintaining the ratio of iodine and potassium iodide in the dye bath at 1: 7, the iodine concentration and potassium iodide concentration were increased so that the single transmittance of the polarizer was 42.1%. Other than that was carried out similarly to preparation of the polarizer A, and produced the polarizer of thickness 18micrometer.

(Preparation of easy adhesive film)
In preparation of the easily adhesive film of Example 1, the wire bar at the time of apply | coating an easily bonding composition was changed into the wire bar of # 4. The thickness of the easy-adhesion layer formed on the surface of the acrylic film was 240 nm.

(Preparation of polarizing plate)
An easy-adhesion film provided with the 240 nm easy-adhesion layer was used as a polarizer protective film, and an easy-adhesion film was bonded to both surfaces of the polarizer B in the same procedure as in Example 1 to obtain a polarizing plate.

[Comparative Example 2]
A polarizing plate was obtained in the same manner as in Comparative Example 1 except that the polarizer B was used in place of the polarizer A.

[Evaluation]
<Remaining alkali amount of easy-adhesion layer>
The amount of triethylamine and ammonia remaining in the easy-adhesion layer of the easy-adhesion film before being bonded to the polarizer was quantified. The residual amount of triethylamine was quantified by gas chromatography mass spectrometry (GC / MS) of the solution after weighing out the powder obtained by scraping the easy-adhesion layer from the surface of the easy-adhesion film and dissolving it in methanol. The residual amount of ammonia was determined by immersing the easy-adhesive film in pure water at 25 ° C., followed by heat extraction for 60 minutes with a dryer at 120 ° C., and quantifying the ammonia eluted in the water by ion chromatography. The total amount of triethylamine and ammonia was defined as the residual alkali amount.

<Adhesive strength>
The polarizing plate is cut into a size of 200 mm parallel to the stretching direction of the polarizer (absorption axis direction) and 20 mm in the orthogonal direction (transmission axis direction), and cut with a cutter knife between the easily adhesive film and the polarizer. The polarizing plate was bonded to a glass plate. A tensile test was performed using a tensile compression tester (“TG-1kN” manufactured by Minebea) at a peeling angle of 90 ° and a peeling speed of 1000 mm / min, and the adhesive strength was measured.

<Humidification durability>
The polarizing plate was cut out to a size of 320 mm × 240 mm and bonded on a glass plate via an acrylic adhesive having a thickness of 20 μm. This sample was placed in a constant temperature and humidity chamber at a temperature of 60 ° C. and a relative humidity of 90%, and held for 500 hours to conduct a heating / humidification durability test. The single transmittance and polarization degree of the polarizing plate before and after the durability test were measured, and the amount of change in the single transmittance and polarization degree was calculated. Further, another polarizing plate was placed on the polarizing plate in a crossed Nicol state and visually observed to confirm the presence or absence of streaky irregularities. About the polarizing plate of Example 4 and the comparative example 2, it hold | maintained for 120 hours in the constant temperature high-humidity tank of temperature 85 degreeC and relative humidity 85%, the heating and humidification endurance test was implemented, and the same evaluation was implemented. The presence or absence of streaky unevenness of the polarizing plate after the heating / humidification durability test was evaluated according to the following criteria.
◯: No streak is visible △: Streak is slightly visible ×: Streak is clearly visible

  Table 2 shows the configurations of the polarizing plates of the examples and comparative examples (type of polarizer, thickness of the easy-adhesion layer and residual alkali amount), and evaluation results. In the crossed Nicols observation photographs before and after the durability test (60 ° C. and 90% Rh 500 hours) of the polarizing plates of Example 1, Example 2 and Comparative Example 1 (“EYESCALE-4W” manufactured by Eye System, a low luminance unevenness measurement system) 3) is shown in FIG. FIG. 4 shows cross Nichol observation photographs (taken with “EXILIM EX-ZR1100” manufactured by Casio Compact Digital Camera) before and after the durability test (85 ° C. and 85% Rh 120 hours) of the polarizing plates of Example 4 and Comparative Example 2. Show.

  The polarizing plate of Comparative Example 1 in which an easy-adhesion film having an easy-adhesion layer having a thickness of 340 nm was bonded to both surfaces of the polarizer A had good adhesion between the polarizer and the easy-adhesion film, but was heated and humidified. Striped unevenness occurred after the test. In Example 1 using an easy-adhesion film having an easy-adhesion layer thickness of 110 nm and Example 3 using an easy-adhesion film having an easy-adhesion layer thickness of 140 nm, slight streaky unevenness was observed after the heating / humidification durability test. However, the unevenness was significantly improved as compared with Comparative Example 1. In Example 2 using an easy-adhesion film having an easy-adhesion layer thickness of 60 nm, no streak-like unevenness was observed even after the heating / humidification durability test, indicating good durability (see FIG. 3).

  In contrast between Example 4 and Comparative Example 2 using a polarizer B having a higher iodine concentration than polarizer A and a high degree of polarization, Comparative Example 2 using an easy-adhesion film having an easy-adhesion layer having a thickness of 340 nm is used. In Example 4 where the thickness of the easy-adhesion layer was 240 nm, while the stripe-shaped unevenness occurred in the polarizing plate after the heating / humidification durability test at a temperature of 60 ° C. and a relative humidity of 90%, No unevenness was observed, and good durability was exhibited. In the heating / humidification durability test at a temperature of 85 ° C. and a relative humidity of 85%, streaky unevenness was confirmed in the polarizing plate of Example 4, but the degree of occurrence 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 streaky 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 (endurance test result at a temperature of 60 ° C. and a relative humidity of 90%), and from the comparison between Example 4 and Comparative Example 2, the thickness of the easy-adhesion layer was reduced to produce a streak shape. It can be seen that the variation in the single transmittance and the degree of polarization is reduced, and the durability of the polarizing plate is improved.

  In Examples 1 to 4 and Comparative Examples 1 and 2 described above, the smaller the thickness of the easy-adhesion layer, the smaller the residual alkali amount, and the tendency to suppress the occurrence of streaky unevenness after the heating / humidification durability test was observed. It was. By reducing the thickness of the easy-adhesion layer, the amount of residual alkali in the easy-adhesion layer is also considered to contribute to the improvement of the durability of the polarizing plate.

1 Transparent protective film (Easily adhesive film)
DESCRIPTION OF SYMBOLS 11 Acrylic film 15 Easy-adhesion layer 2 Transparent protective film 5 Polarizer 6,7 Adhesive layer 100 Polarizing plate

Claims (5)

A polyvinyl alcohol-based polarizer having a first main surface and a second main surface, and a transparent protective film bonded to the first main surface of the polarizer via an adhesive layer,
The transparent protective film has an easy-adhesion layer on the surface of the acrylic film, and the easy-adhesion layer forming surface is bonded to the polarizer,
The easy-adhesion layer contains a urethane resin and inorganic fine particles, and has a thickness of 110 to 250 nm.
The polarizing plate whose content of the said inorganic fine particle in the said easily bonding layer is 10 to 50 weight%.   The polarizing plate of Claim 1 whose content of the alkali component of the said easily bonding layer is 20-75 ppm. The polarizing plate of Claim 1 or 2 whose average primary particle diameter of the said inorganic fine particle is 10-150 nm. Furthermore, the polarizing plate of any one of Claims 1-3 provided with the 2nd transparent protective film bonded together to the 2nd main surface of the said polarizer through the adhesive bond layer. The image display apparatus which has an image display cell and the polarizing plate of any one of Claims 1-4 .