JP7014755B2 - Polarizing plate and image display device - Google Patents

Description

The present invention relates to a polarizing plate in which an easy-adhesion film having an easy-adhesion layer on the surface of a transparent film substrate is bonded to the surface of a polarizing element, and an image display device including the polarizing plate.

Liquid crystal displays 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. Due to the display principle of the liquid crystal display device, a polarizing plate is arranged on the visible side surface of the liquid crystal cell. In the transmissive liquid crystal display device, polarizing plates are arranged on both sides 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 visually recognized as a mirror surface, a circular polarizing plate (typically, a polarizing plate and 1 /) on the viewing side surface is used. A laminate of four wave plates) may be arranged.

Generally, the polarizing plate is provided with a transparent film (polarizer protective film) for the purpose of protecting the polarizing element on one side or both sides of the polarizing element. As the polarizing element, one in which iodine is adsorbed on a polyvinyl alcohol (PVA) -based film and the molecules are oriented by stretching or the like is widely used.

As the polarizing element protective film bonded to the surface of the polarizing element, a cellulose-based film such as cellulose acetate is widely used because of its excellent adhesiveness to the PVA-based polarizing element. As the transparent protective film, a film made of a resin material such as acrylic, polyester, polycarbonate, and cyclic polyolefin has also been used. The film made of these resin materials has lower moisture permeability than the cellulose-based film, and the polarizing plate having the low moisture permeability resin film bonded to the surface of the polarizing element is exposed to a high humidity environment for a long time. However, the change in optical characteristics is small and the durability tends to be excellent.

On the other hand, a film made of a resin material such as acrylic, polyester, polycarbonate, or cyclic polyolefin tends to have lower adhesiveness to a PVA-based polarizing element than a cellulose-based film. Therefore, a method has been proposed in which an easy-adhesive layer is provided on the surface of a transparent film used as a polarizing element protective film to improve the adhesiveness with a polarizing element.

For example, in Patent Document 1, an easy-adhesive film provided with an easy-adhesive layer containing fine particles and a binder resin on the surface of an acrylic film has excellent adhesiveness to a polarizing element and is used when the film is wound into a roll. It is described that blocking can be suppressed. In the embodiment of Patent Document 1, an easily adhesive film having a urethane easy-adhesive layer having an average thickness of 400 nm (thickness range of 300 to 500 nm) containing 1 to 7% by weight of silica fine particles is provided on the surface of the acrylic film as a polarizing element protective film. An example used as is shown.

Patent No. 5354733

As image display devices become larger and brighter, the polarizing plates that make up image display devices have small changes in optical characteristics even in harsher environments (for example, higher temperature and higher humidity conditions). It is now required. The polarizing plate using the easy-adhesion film described in Patent Document 1 as the splitter protective film has excellent adhesion between the polarizing element and the polarizing element protective film, and has high adhesive reliability. However, when the polarizing plate using the easily adhesive film disclosed in Patent Document 1 as a polarizing element protective film is exposed to a high humidity environment for a long time, streak-like unevenness may occur and the display characteristics may be deteriorated. A new issue has been identified.

In view of the above problems, the present invention has excellent adhesiveness to a polarizing element and the like, is less likely to cause blocking, and has optical defects such as streak-like unevenness even when exposed to a high temperature and high humidity environment for a long time. The purpose is to provide a difficult-to-adhere easy-adhesive film.

As a result of studies by the present inventors in view of the above problems, it is found that alkaline components such as ammonia and amines added to the easy-adhesion composition for the purpose of improving the dispersibility of fine particles remain in the easy-adhesion layer. It has been found that this is one of the causes of the decrease in durability in a humid environment, and the above problem can be solved by setting the amount of residual alkali in the easy-adhesion layer within a predetermined range.

The present invention relates to an easy-adhesive film provided with an easy-adhesive layer on the surface of a transparent film base material and a method for producing the same. The easy-adhesion layer contains a binder resin and fine particles. The content of the alkaline component of the easy-adhesion layer is preferably 5 to 75 ppm, and the total content of amine and ammonia is preferably 5 to 75 ppm. The thickness of the easy-adhesion layer is preferably 40 to 280 nm.

An acrylic film or the like is used as the transparent film base material. Urethane-based resin or the like is used as the binder resin for the easy-adhesive layer. The content of the fine particles in the easy-adhesion layer is preferably about 8 to 50% by weight. The fine particles of the easy-adhesion layer may be embedded in the transparent film base material.

The easy-adhesive layer is formed by applying the easy-adhesive composition to the surface of the transparent film base material and heating it. The easy-adhesive composition contains a binder resin or a precursor thereof, fine particles, an alkaline component and a solvent. Since the easy-adhesion composition contains an alkaline component, the dispersibility of the fine particles is improved, and an easy-adhesive film having excellent slipperiness can be obtained. The alkaline component can also act as a catalyst for accelerating the reaction of the binder resin (precursor). From the viewpoint of promoting the volatilization of the alkaline component by heating, the boiling point of the alkaline component is preferably 150 ° C. or lower. Examples of the alkaline component include amines and ammonia.

By raising the heating temperature after applying the easy-adhesive composition, it is possible to promote the volatilization of the alkaline component and form an easy-adhesive layer having a small amount of residual alkaline component. For example, the easy-adhesion composition may be heated at a temperature higher than the glass transition temperature of the transparent film substrate by 10 ° C. or higher. By increasing the heating temperature, a region in which fine particles of the easy-adhesion layer are embedded in the transparent film base material is likely to be formed, and the adhesion between the transparent film base material and the easy-adhesion layer tends to be improved.

After applying the easy-adhesive composition on the transparent film base material, stretching may be performed while heating the transparent film base material. In particular, by stretching the transparent film base material while heating the easy-adhesion composition at a temperature 10 ° C. or higher higher than the glass transition temperature of the transparent film base material, the adhesion between the transparent film base material and the easy-adhesion layer is improved. Tend to do.

The above-mentioned easy-adhesive film has excellent adhesiveness to other films, glass substrates, and the like. The easy-adhesive film can be used, for example, as a polarizing element protective film. For example, a polarizing plate can be obtained by adhering an easily adhesive film to the surface of a polyvinyl alcohol-based polarizing element via an adhesive layer. An image display device can be formed by arranging a polarizing plate on the surface of an image display cell such as a liquid crystal display cell or an organic EL cell.

The easy-adhesive film of the present invention has excellent adhesiveness, is less likely to cause blocking, and is less likely to have optical defects even when exposed to a high temperature and high humidity environment for a long time. It is suitably used as a film.

It is sectional drawing which shows the structural example of the easy-adhesion film. It is sectional drawing which shows the structural example of a polarizing plate. It is a cross-sectional TEM observation image of an easy-adhesion film in which an interface layer is formed at the interface between a film base material and an easy-adhesion layer. It is a cross-sectional TEM observation image of an easy-adhesion film in which an interface layer is not formed at the interface between a film base material and an easy-adhesion layer. It is a cross Nicol observation photograph before and after the durability test of the polarizing plate.

FIG. 1 is a schematic cross-sectional view showing a configuration example of an easily adhesive film according to an embodiment of the present invention. The easy-adhesive film 1 is provided with an easy-adhesive layer 15 on at least one surface of the film base material 11. Easy-adhesive layers may be provided on both sides of the film substrate. The easy-adhesive film is used by being bonded to another film, a glass substrate, or the like.

Examples of the usage form of the easy-adhesive film include a polarizing element protective film. FIG. 2 is a cross-sectional view showing a configuration example of a polarizing plate including the easy-adhesion film 1 as a polarizing element protective film. The polarizing plate 100 includes an easily adhesive film 1 bonded to one surface (first main surface) of the polarizing element 5 via an adhesive layer 6. In the polarizing plate 100 shown in FIG. 2, the easy-adhesion film 1 has an easy-adhesion layer 15 on the bonding surface of the film base material 11 with the polarizing element 5. An easy-adhesive layer may be provided on the surface to which the polarizing element 5 is not bonded. In the polarizing plate 100 shown in FIG. 2, the transparent protective film 2 is bonded to the other surface (second main surface) of the polarizing element 5 via the adhesive layer 7.

[Easy adhesive film]
The easy-adhesive film 1 includes an easy-adhesive layer 15 on at least one surface of the film base material 11.

<Film base material>
A transparent film is preferable as the film base material 11. The total light transmittance of the transparent film substrate is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more. Examples of the resin material constituting the film base material 11 include acrylic resin, polyester resin, polycarbonate resin, polyolefin resin, cyclic polyolefin resin, polystyrene resin, polyamide resin, and polyimide resin. When the easy-adhesion film is used as an optically isotropic polarizing element protective film, an acrylic resin or a cyclic polyolefin resin is preferable as the resin material of the film base material 11 because the birefringence is small, and the acrylic resin is preferable. Especially preferable.

Examples of the cyclic polyolefin resin include polynorbornene. Examples of commercially available cyclic polyolefin resins include Zeonoa and Zeonex manufactured by Zeon Corporation, Arton manufactured by JSR, Appel manufactured by Mitsui Chemicals, and Topas manufactured by TOPAS ADVANCED POLYMERS. The cyclic polyolefin-based film preferably contains 50% by weight or more of the cyclic olefin-based resin.

Examples of the acrylic resin include poly (meth) acrylic acid esters 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, (meth) methyl acrylate-styrene copolymer (MS resin, etc.), polymer having alicyclic hydrocarbon group (for example, methyl methacrylate-methacrylic acid) Cyclohexyl copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.) can be mentioned.

As used herein, "(meth) acrylic" 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, the acrylic resin having a glutaric acid anhydride structure described in JP-A-2006-283013, JP-A-2006-335902, JP-A-2006-274118, etc .; and / or JP-A. Acrylic resins having a lactone ring structure described in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, JP-A-2005-146804, etc. You may use it. Acrylic resins having a glutaric acid anhydride structure and acrylic resins having a lactone ring structure have high heat resistance, high transparency, and high mechanical strength, and thus have a high degree of polarization and excellent durability. Suitable for manufacturing.

When the film base material 11 is an acrylic film, the content of the acrylic resin in the film base material is preferably 50% by weight or more, more preferably 60 to 98% by weight, still more preferably 70 to 97% by weight. The acrylic film may contain a thermoplastic resin other than the acrylic resin. For example, by blending another thermoplastic resin, the birefringence of the acrylic resin can be canceled out, and an acrylic film having excellent optical anisotropy can be obtained. Further, a thermoplastic resin other than the acrylic resin may be blended for the purpose of improving the mechanical strength of the film.

Thermoplastic resins other than acrylic resins include olefin polymers, vinyl halide polymers, polystyrenes, styrene and acrylic monomer and copolymers, polyesters, polyamides, polyacetals, polycarbonates, polyphenylene oxides, polyphenylene sulfides, and polys. Examples thereof include ether ether ketone, polysulfone, polyethersulfone, polyoxybenzylene, polyamideimide, and rubber-based polymers.

The film substrate 11 may contain additives such as antioxidants, stabilizers, reinforcing materials, ultraviolet absorbers, flame retardants, antistatic agents, colorants, fillers, plasticizers, lubricants and fillers. A resin material and an additive or the like may be mixed to prepare a thermoplastic resin composition such as pellets in advance, and then filmed.

The thickness of the film base material 11 is about 5 to 200 μm. From the viewpoint of mechanical strength, transparency, handleability, etc., the thickness of the film substrate 11 is preferably 10 to 100 μm, more preferably 15 to 60 μm.

The glass transition temperature Tg of the film substrate 11 is preferably 100 ° C. or higher, more preferably 110 ° C. or higher. When the film base material 11 is an acrylic film, as described above, by using an acrylic resin having a glutaric acid anhydride structure or an acrylic resin having a lactone ring structure as the acrylic resin, the acrylic film can be obtained. Tg can be increased and heat resistance can be improved. The upper limit of Tg of the film base material 11 is not particularly limited, but is preferably 170 ° C. or lower from the viewpoint of moldability and the like.

Examples of the method for producing the film base material 11 include a solution casting method, a melt extrusion method, a calendar method, and a compression molding method. The film base material 11 may be either an unstretched film or a stretched film. When the film base material 11 is an acrylic film, the acrylic film is preferably a stretched film stretched in at least one direction from the viewpoint of improving mechanical strength, and a biaxially stretched film is particularly preferable. By blending another thermoplastic resin so as to cancel the birefringence of the acrylic resin, an acrylic film having a small retardation and excellent optical anisotropy can be obtained even when stretched.

<Easy adhesive layer>
The easy-adhesion layer 15 provided on the surface of the film base material 11 contains a binder resin and fine particles. By providing the easy-adhesion layer 15, the adhesiveness to a film such as a polarizing element, a glass substrate, or the like can be improved. When the easy-adhesion layer 15 contains fine particles, fine irregularities are formed on the surface of the easy-adhesion layer 15, and the slipperiness of the film is improved. Therefore, it contributes to the reduction of scratches when the easy-adhesive film 1 is conveyed in a roll and the suppression of blocking when the film is wound into a roll.

(Binder resin)
As the binder resin, since it has excellent adhesion to a film substrate such as an acrylic film, it has a crosslinkability such as a polyurethane resin, an epoxy resin, an isocyanate resin, a polyester resin, polymers containing an amino group in the molecule, and an oxazoline group. A resin (polymer) having a reactive group such as an acrylic resin having a functional group is used. As the binder resin of the easy-adhesion layer 15, a polyurethane resin is particularly preferable. The easy-adhesive layer 15 containing the polyurethane resin binder has high adhesion to the film base material 11. Further, the easy-adhesive film 1 in which the easy-adhesive layer 15 contains a polyurethane resin binder tends to show high adhesiveness when a film such as a polarizing element is laminated via an adhesive layer.

Urethane resins are typically reaction products of polyols and polyisocyanates. As the polyol component, a polymer polyol such as a polyacrylic polyol, a polyester polyol, or a polyether polyol is preferably used.

The polyacrylic polyol is typically obtained by polymerizing a (meth) acrylic acid ester with 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, and (meth). Hydroxyalkyl esters of (meth) acrylic acids such as 4-hydroxybutyl acrylate and 2-hydroxypentyl (meth) acrylic acid; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethyl propane; N-methylol (Meta) acrylamide and the like can be mentioned.

The polyacrylic polyol may contain a monomer component other than the above. Other monomer components include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid and their anhydrides and diesters; unsaturated nitriles such as (meth) acrylonitrile; (meth). 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 Halogenized α, β-unsaturated aliphatic monomers such as; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

Polyester polyols are typically obtained by the reaction of polybasic acids with polyols. Examples of the polybasic acid include aromatics such as orthophthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid. Dicarboxylic acid; oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decandicarboxylic acid, dodecandicarboxylic acid, octadecanedicarboxylic acid, tartaric acid, alkylsuccinic acid, linoleic acid , Maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid and other aliphatic dicarboxylic acids; hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like. Formula dicarboxylic acids; or reactive derivatives such as these acid anhydrides, alkyl esters, acid halides and the like can be mentioned.

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, 1 , 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-Pench Lene glycol, 3-methyl-1,5-pentylene glycol, 1,2-dimethylbutylene glycol, 1,3-dimethylbutylene glycol, 2,3-dimethylbutylene glycol, 1,4-dimethylbutylene glycol, diethylene glycol, tri Examples thereof include ethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F.

The polyether polyol is typically obtained by ring-opening polymerization of an alkylene oxide on a polyhydric alcohol and adding it. 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 tetramethylene diisocyanate, dodecamethylene diisocyanate, 1,4-butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate, 2. -Adicyclic diisocyanates such as methylpentane-1,5-diisocyanate and 3-methylpentane-1,5-diisocyanate; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-cyclohexamethylene diisocyanate, 1,4-cyclohexanediisocyanate , Methylcyclohexylene diisocyanate, alicyclic diisocyanate such as 1,3-bis (isocyanatemethyl) cyclohexane; tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate , 4,4'-Diphenyldimethylmethane diisocyanate, 4,4'-dibenzyldiisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylenedi isocyanate, 1,4-phenylenedi isocyanate and other aromatic diisocyanates Examples thereof include aromatic aliphatic diisocyanates such as dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene diisocyanate.

The urethane resin constituting the easy-adhesion layer 15 preferably has a carboxy group. Since the urethane resin has a carboxy group, a crosslinked structure can be introduced, and the adhesive durability between the easy-adhesive film 1 and the polarizing element tends to be improved. The urethane resin having a carboxy group can be obtained, for example, by reacting a chain lengthing agent having a free carboxy group in addition to a polyol and a polyisocyanate. Examples of the chain length agent having a free carboxy group include dihydroxycarboxylic acid and dihydroxysuccinic acid. Examples of the dihydroxycarboxylic acid include dialkylol alkanoic acid 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 may be either a one-shot method in which the monomer components are reacted at once or a multi-step method in which the monomer components are reacted stepwise. When introducing a carboxy group into a urethane resin using a chain lengthing agent having a free carboxy group, a multi-step method is preferable. When producing the urethane resin, a urethane reaction catalyst may be used if necessary.

The number average molecular weight of the urethane resin is preferably 5,000 to 600,000, more preferably 10,000 to 400,000. The acid value of the urethane resin is preferably 10 to 50, more preferably 20 to 45.

The urethane resin may have a crosslinked structure. By introducing a crosslinked structure into the urethane resin, the adhesive durability between the easy-adhesive film 1 and the polarizing element or the like tends to be improved. As the cross-linking agent, one that can react with the cross-linking functional group of the urethane resin can be used without particular limitation. When the urethane resin has a carboxy group, a cross-linking agent containing an amino group, an oxazoline group, an epoxy group, a carbodiimide group and the like is used. Among these, a cross-linking agent having an oxazoline group is preferable. Since the oxazoline group has a small reactivity with the carboxy group at room temperature, the pot life when mixed with the urethane resin is long, and the lead time of the process can be flexibly adjusted.

The cross-linking agent may be a small molecule compound or a polymer. An acrylic polymer is preferable as the cross-linking agent because it has high solubility in an aqueous composition and is also excellent in compatibility with a urethane resin. In particular, when an acrylic polymer having an oxazoline group is used as the cross-linking agent, the adhesiveness between the easy-adhesive film 1 and a film such as a polarizing element tends to be improved.

The amount of the cross-linking 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 urethane resin.

(Fine particles)
When the easy-adhesive layer 15 contains fine particles, a fine uneven shape is formed on the surface of the easy-adhesive layer, the slipperiness of the easy-adhesive film 1 is improved, and blocking can be suppressed. From the viewpoint of forming irregularities that contribute to the improvement of slipperiness, the particle size (average primary particle size) of the fine particles is preferably 10 nm or more, more preferably 15 nm or more, still more preferably 20 nm or more. The average primary particle diameter of the fine particles is preferably smaller than the thickness of the easy-adhesion layer. Since the particle size of the fine particles is smaller than the thickness of the easy-adhesive layer, it is possible to suppress the falling of the fine particles from the easy-adhesive layer. The particle size of the fine particles is preferably 250 nm or less, more preferably 200 nm or less. Further, since the average primary particle diameter of the fine particles is smaller than the visible light wavelength, scattering of visible light at the interface between the binder resin and the fine particles can be suppressed. From the viewpoint of improving transparency, the particle size of the fine particles is preferably 100 nm or less, more preferably 80 nm or less, further preferably 60 nm or less, and particularly preferably 50 nm or less.

The fine particles of the easy-adhesion layer 15 may be either inorganic fine particles or organic fine particles. Inorganic fine particles are preferable as the fine particles because they are excellent in dispersibility and uniformity of particle size. Examples of the inorganic fine particles include inorganic oxides such as 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. Of these, inorganic oxides are preferable. Examples of the organic fine particles include silicone-based resin, fluororesin, acrylic-based resin and the like. In order to suppress light scattering caused by fine particles, it is preferable that the difference in refractive index between the binder resin (generally, a refractive index of about 1.5) and the fine particles is small. Silica particles are preferable as the fine particles of the easy-adhesion layer 15 because the difference in refractive index from the binder resin is small and the dispersibility is excellent.

When the easy-adhesion layer 15 is formed from an aqueous composition, it is preferable to use fine particles having high water dispersibility. An aqueous dispersion of fine particles may be added to the composition. In order to enhance the dispersibility of the fine particles, it is preferable to add an alkaline component such as amine or ammonia to make the easy-adhesion composition weakly alkaline.

Colloidal silica is preferably used as the water-dispersible silica particles. As colloidal silica, Quattron PL series manufactured by Fuso Chemical Industry Co., Ltd., Snowtex series manufactured by Nissan Chemical Industry Co., Ltd., AERODISP series and AEROSIL series manufactured by Nippon Aerosil Co., Ltd., and Seahorse Star manufactured by Nippon Shokubai Co., Ltd. Commercially available products such as the KE 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 3% by weight or more, more preferably 5% by weight or more. In particular, when the thickness of the easy-adhesion layer 15 is small (for example, when it is 280 nm or less), the surface of the easy-adhesion layer 15 is increased by increasing the content of the fine particles to increase the amount (number density) of the fine particles per unit area. It is preferable to form unevenness uniformly inside. The content of the fine particles in the easy-adhesion layer 15 is preferably 8% by weight or more, more preferably 10% by weight or more, still more preferably 12% by weight or more. If the content of the fine particles in the easy-adhesion layer 15 is excessively large, the optical properties may be deteriorated due to the increase in light scattering at the interface between the binder resin and the fine particles. Further, as the content of fine particles increases, the relative content of the binder resin decreases, so that the adhesiveness of the easy-adhesion layer may decrease. Therefore, the content of the fine particles in the easy-adhesion layer 15 is preferably 50% by weight or less, more preferably 40% by weight or less, still more preferably 30% by weight or less.

(Amount of residual alkali)
When an alkaline component such as amine or ammonia is used to enhance the dispersibility of the fine particles, the alkaline component inevitably remains in the easy-adhesion layer. When the easy-adhesion film 1 is used as a polarizing element protective film, when the residual alkaline component of the easy-adhesion layer 15 elutes due to moisture or the like, the polarizing element is deteriorated, the degree of polarization of the polarizing plate is lowered, and streak-like unevenness is caused. Optical defects 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 amount of residual alkali in the easy-adhesion layer 15 is small.

On the other hand, if the amount of residual alkali in the easy-adhesion layer 15 is excessively small, the dispersibility of the fine particles may be impaired, resulting in poor appearance such as cloudiness due to the aggregation of the fine particles. Further, due to the aggregation of fine particles and the detachment from the easy-adhesive layer due to the decrease in dispersibility, appropriate irregularities are not formed on the surface of the easy-adhesive layer, and the slipperiness of the easy-adhesive 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, still more preferably 20 ppm or more.

Specific examples of the residual alkaline component in the easy-adhesion layer include amines and ammonia, and it is preferable that the total content of amines and ammonia in the easy-adhesion layer is within the above range. 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 alkaline component. Alkaline components may be quantified by an analytical method (eg, LC / MS) that combines chromatography and mass spectrometry (MS). When a plurality of alkaline components are contained in the easy-adhesive layer, the total of each component is taken as the alkaline component content (residual amount) of the easy-adhesive layer.

<Formation of easy-adhesive layer>
The method for forming the easy-adhesion layer 15 on the surface of the film substrate 11 is not particularly limited. Preferably, the easy-adhesive composition (coating liquid) containing the binder resin and fine particles is applied onto the film substrate 11 and heated to form the easy-adhesive layer 15.

(Easy-adhesive composition)
The easy-adhesion composition is preferably an aqueous composition using water as a solvent (and a dispersion medium for fine particles). The concentration of the solid content (nonvolatile component) in the easy-adhesion composition is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, still more preferably 3 to 15% by weight.

The water-based easy-adhesion composition contains water as a solvent (and a dispersion medium), a binder resin fat or a precursor thereof, and fine particles. The easy-adhesion composition preferably further contains an alkaline component. As described above, the alkaline component has an action of promoting the dispersion of fine particles. Fine particles with a small particle size tend to aggregate easily, but the easy-adhesion composition contains alkaline components such as ammonia and amines to improve the dispersibility of the fine particles and obtain an easy-adhesion film with excellent appearance and slipperiness. Be done.

On the other hand, if the alkali contained in the easy-adhesion composition remains in the easy-adhesion layer, it may cause a decrease in the moisture-heat resistance of the polarizing plate. In particular, strong alkalis such as caustic can cause deterioration of the stator even in a small amount. Therefore, as the alkaline component contained in the easy-adhesion composition, a weak alkaline component such as ammonia or amine is preferable. 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 and preventing the deterioration of the polarizing element.

From the viewpoint of improving the dispersibility of the fine particles, the amount of the alkaline 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 alkaline component is excessively large, it may be difficult to reduce the residual alkaline amount. Therefore, the amount of the alkaline component contained in the easy-adhesion composition is determined by the solid content of the easy-adhesion composition. On the other hand, 50,000 ppm or less is preferable, 10,000 ppm or less is more preferable, and 5,000 ppm or less is further preferable. As described above, specific examples of the alkaline components contained in the easy-adhesion composition include amines and ammonia, and it is preferable that the total content of these alkaline components is within the above range.

The alkaline 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, when the binder resin is a urethane resin, a tertiary amine such as triethylamine may be contained in the easy-adhesion composition as a urethanization catalyst for a polyurethane precursor (polyol, isocyanate, etc.).

By applying the easy-adhesive composition on the film substrate and then heating it, the alkaline component can be volatilized and removed, and the residual alkaline component of the easy-adhesion layer 15 can be reduced. From the viewpoint of promoting the volatilization of the alkaline component by heating, the alkaline component contained in the easy-adhesion composition preferably has a boiling point of 150 ° C. or lower. The boiling point of the alkaline component is more preferably 130 ° C. or lower, further preferably 120 ° C. or lower, and particularly preferably 110 ° C. or lower. The boiling point of the alkaline component may be 100 ° C. or lower or 90 ° C. or lower. When the easy-adhesion composition contains a plurality of alkaline components, the boiling point of at least one alkaline component is preferably in the above range, and the boiling point of two or more alkaline components is preferably in the above range. It is preferable that the boiling point of the alkaline component of 50% by weight or more is in the above range with respect to the total amount of alkali contained in the easy-adhesion layer. Ideally, the boiling points of all alkaline components contained in the easy-adhesion composition are in the above range. For example, when the alkaline components are amine and ammonia, the boiling point of the amine is preferably within the above range.

The easy-adhesion composition may contain a cross-linking agent in addition to a binder resin (or a precursor thereof), fine particles and an alkaline component. The easy-adhesion composition includes catalysts such as cross-linking accelerators, antioxidants, ultraviolet absorbers, leveling agents, blocking inhibitors, antistatic agents, dispersion stabilizers, defoamers, thickeners, dispersants, and surfactants. , Additives such as lubricants may be included.

(Formation of easy-adhesive layer on film substrate)
Before applying the easy-adhesion composition on the film base material 11, the surface treatment of the film base material may be performed. By performing the surface treatment, the wetting tension of the film substrate can be adjusted and the adhesion to the easy-adhesion layer 15 can be improved. Examples of the surface treatment include corona treatment, plasma treatment, ozone spraying, ultraviolet irradiation, flame treatment, chemical treatment and the like. Among these, corona treatment or plasma treatment is preferable.

Examples of the method for applying the easy-adhesion composition include a bar coat method, a roll coat method, a gravure coat method, a rod coat method, a slot orifice coat method, a curtain coat method, and a fountain coat method. The easy-adhesive layer 15 is formed by heating the easy-adhesive composition after coating to remove the solvent. The precursor of the binder resin may be reacted and cured by heating. For example, when the easy-adhesion composition contains a cross-linking agent, the cross-linking reaction can be promoted by heating.

The heating temperature at the time of forming the easy-adhesive layer is, for example, about 50 to 200 ° C. The heating temperature is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, from the viewpoint of accelerating the curing reaction of the resin component in the easy-adhesive composition and efficiently volatilizing and removing the alkaline component contained in the easy-adhesive composition. 130 ° C. or higher is more preferable, and 135 ° C. or higher is particularly preferable. Further, the heating temperature is preferably higher than the boiling point of the alkaline component contained in the easy-adhesion composition.

The heating temperature at the time of forming the easy-adhesion layer is preferably higher than the glass transition temperature (Tg) of the film substrate. By heating at a high temperature, the curing reaction of the resin component in the easy-adhesion composition can be promoted, and the alkaline component contained in the easy-adhesion composition can be efficiently volatilized and removed. The heating temperature is preferably 10 ° C. or higher higher than the Tg of the film substrate.

By heating at a temperature higher than Tg of the film base material, the efficiency of volatilization and removal of alkali in the easy-adhesion composition is enhanced, and the easy-adhesion composition easily permeates the surface of the film base material, so that the film base material 11 It is considered that the adhesion between the film and the easy-adhesion layer 15 is improved. From the viewpoint of improving the adhesion of the easy-adhesion layer, the heating temperature is preferably Tg + 10 ° C. or higher, more preferably Tg + 15 ° C. or higher, and even more preferably Tg + 20 ° C. or higher for the film substrate.

When the film substrate is heated at a temperature of Tg + 10 ° C. or higher, the film substrate changes from a glass state to a rubber state and the surface is easily deformed. Therefore, at the interface between the film substrate 11 and the easy-adhesion layer 15, the resin of the film substrate An interface layer in which the components and the constituent components of the easy-adhesion layer are mixed is likely to be formed. By forming the interface layer, the adhesion between the film base material 11 and the easy-adhesion layer 15 tends to be improved.

In particular, as shown in the cross-sectional observation image of FIG. 3, when the surface of the film base material 11 has a region where the fine particles of the easy-adhesive layer 15 are embedded and embedded, the film base material 11 and the easy-adhesive layer 15 are combined. An easy-adhesive film with high adhesion can be obtained. When the fine particles are embedded in the film substrate in a rubber state in which the film substrate is heated to a temperature higher than Tg, and then the film substrate returns to the glass state, the fine particles embedded in the surface of the film substrate and their surroundings are present. Since the binder resin adheres to the surface of the film base material, it is considered that the adhesion between the film base material 11 and the easy-adhesion layer 15 is improved.

An easy-adhesion layer may be formed in the process of manufacturing the film substrate. Further, the easy-adhesion layer may be formed by utilizing the heating at the time of forming the film base material. For example, when the film substrate is a stretched film, the 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 by a tenter is used. Then, the solvent can be dried and the resin can be cured.

When the film substrate is stretched after the easy-adhesion composition is applied, the draw ratio is preferably 5 times or less, more preferably 4 times or less, from the viewpoint of suppressing defects such as cracks in the easy-adhesion layer. It is more preferably times or less, and particularly preferably 2.5 times or less. The lower limit of the draw ratio is not particularly limited, but from the viewpoint of improving the film strength, the draw ratio is preferably 1.3 times or more, more preferably 1.5 times or more. When the film base material is an acrylic film, it is preferable to carry out stretching at the above stretching ratios in each of the transport direction (MD) and the width direction (TD) from the viewpoint of improving the film strength.

When biaxial stretching of the film substrate is performed, the biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. Further, diagonal stretching may be performed. In the case of sequential biaxial stretching, as described above, the film is stretched in one direction (MD) by roll stretching, then the easy-adhesive composition is applied onto the film, and the easy-adhesive composition is heated during stretching with a tenter. May be done.

As described above, the stretching temperature is preferably higher than the Tg of the film substrate, preferably Tg + 10 ° C. or higher, more preferably Tg + 15 ° C. or higher, still more preferably Tg + 20 ° C. or higher, as the heating temperature of the easy-adhesion layer. In particular, it is preferable to apply the easy-adhesion composition and then stretch it in at least one direction at the above temperature. When stretching is performed in a rubber state at a temperature higher than Tg of the film substrate, a region in which fine particles in the easy-adhesion composition are embedded is likely to be formed on the surface of the film substrate, and the film substrate 11 and the easy-adhesion layer 15 are attached to each other. Adhesion tends to improve. The reason why the fine particles are easily embedded in the film base material by stretching at a high temperature is that when the film base material is stretched in a rubber state, the easy-adhesive composition easily wets and spreads when the film base material is deformed, and the surface unevenness formed at the time of deformation is formed. It is easy for fine particles to be fitted in the recesses. Further, when cooling is performed while releasing the stress after stretching, the particles fitted on the surface of the film substrate are fixed when the film substrate shrinks, so that a region in which the fine particles are embedded is formed in the film substrate. It is considered easy.

The thickness of the easy-adhesion layer 15 can be adjusted by adjusting the solid content concentration and the coating thickness of the easy-adhesion composition. When the film substrate is stretched after the easy-adhesion composition is applied, the thickness of the easy-adhesion layer 15 can be adjusted by the draw ratio.

The thickness of the easy-adhesion layer 15 is not particularly limited, but is preferably 280 nm or less, more preferably 250 nm or less, still more preferably 230 nm or less, from the viewpoint of promoting removal of alkaline components by heating. When the easy-adhesive film 1 is used as a polarizing element protective film, the smaller the thickness of the easy-adhesive layer 15, the better the humidification durability of the polarizing plate, and the less the occurrence of optical defects such as streak-like unevenness tends to occur. There is. Further, the smaller the thickness of the easy-adhesion layer 15, the more the decrease in the degree of polarization when the polarizing plate is exposed to the humidified environment tends to be suppressed.

If the alkaline component is excessively removed during heating and drying of the easy-adhesion composition, the dispersibility of the fine particles in the binder resin is lowered, and the fine particles are aggregated and the fine particles from the surface of the easy-adhesive layer are accompanied by the aggregation. Is likely to fall off. When the fine particles are agglomerated or dropped off, the slipperiness of the easy-adhesive film is lowered, and scratches during transportation and blocking during winding are likely to occur. Therefore, the thickness of the easy-adhesion layer 15 is preferably 40 nm or more, more preferably 50 nm or more, further preferably 80 nm or more, and particularly preferably 100 nm or more. The thickness of the easy-adhesion layer may be 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, or 150 nm or more. The thickness of the easy-adhesion layer 15 is preferably in the above range from the viewpoint of appropriately exhibiting the effect of improving the adhesiveness of the easy-adhesion layer 15.

[Polarizer]
The polarizing plate may be provided with a transparent protective film on only one surface of the polarizing element, or may be provided with a transparent protective film on both sides of the polarizing element 5 as shown in FIG. By laminating the above-mentioned easy-adhesive film as a polarizing element protective film on one surface of the polarizing element, a polarizing plate having a transparent protective film on only one surface of the polarizing element is formed. A polarizing plate having a polarizing element protective film on both surfaces of the polarizing element may have the above-mentioned easy-adhesive film bonded to at least one surface of the polarizing element. The polarizing plate may be one in which the above-mentioned easy-adhesive film is bonded to both sides of the polarizing element. The polarizing element 5 and the easy-adhesive film 1 are bonded to each other via the adhesive layer 6.

<Polarizer>
The polarizing element 5 is polyvinyl alcohol (PVA) in which a dichroic substance such as iodine or a dichroic dye is adsorbed on a polyvinyl alcohol-based film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and oriented in one direction. A system splitter is used. For example, a PVA-based polarizing element can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching.

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

As the polarizing element 5, a thin PVA-based polarizing element having a thickness of 10 μm or less can also be used. Examples of the thin polarizing element are described in JP-A No. 51-06644, JP-A-2000-338329, WO2010 / 100917 Pamphlet, Patent No. 46910205, Patent No. 4751481, and the like. Can be mentioned as a thin polarizing element. These thin polarizing elements are obtained by a production method including a step of stretching a PVA-based resin layer and a stretching resin base material in a laminated state, and a step of dyeing with iodine. With this manufacturing method, even if the PVA-based resin layer is thin, it can be stretched without any trouble such as breakage due to stretching because it is supported by the stretching resin base material.

<Adhesive>
The material of the adhesive layer 6 used for bonding the modulator 5 and the easy-adhesive film 1 is not particularly limited as long as it is optically transparent, and the material is not particularly limited, and it is an epoxy resin, a silicone resin, an acrylic resin, or polyurethane. , Polyamide, polyether, polyvinyl alcohol and the like. The thickness of the adhesive layer 6 is, for example, about 0.01 to 20 μm, and is appropriately set according to the type of adherend, the material of the adhesive, and the like. When a curable adhesive that exhibits adhesiveness by a cross-linking reaction after coating is used, the thickness of the adhesive layer 6 is preferably 0.01 to 5 μm, more preferably 0.03 to 3 μm.

As the adhesive, various forms such as a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive-based adhesive, and an active energy ray-curable adhesive are used. Among these, a water-based adhesive or an active energy ray-curable adhesive is preferable because the thickness of the adhesive layer can be reduced.

Examples of the polymer component of the water-based adhesive include vinyl polymer, gelatin, vinyl-based latex, polyurethane, polyeste-based, and epoxy. Among these, a vinyl polymer is preferable, and a polyvinyl alcohol-based resin is particularly preferable, because the adhesiveness between the easy-adhesive film and the polarizing element is excellent. Among the polyvinyl alcohol-based resins, polyvinyl alcohol containing an acetoacetyl group is preferable.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably about 100 to 5000, 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, more preferably 90 mol% or more.

The water-based adhesive composition (solution) may contain a cross-linking agent in addition to a polymer such as a polyvinyl alcohol-based resin. As the cross-linking agent, a compound having at least two functional groups reactive with the polymer constituting the adhesive in one molecule is used. Examples of the cross-linking agent for the polyvinyl alcohol-based resin include amino-formaldehydes such as alkylenediamines; isocyanates; epoxys; aldehydes; trimethylolurea and trimethylolmelamine. Among these, amino-formaldehyde is preferable. As the amino-formaldehyde resin, a compound having a methylol group is preferable, and methylol melamine is particularly preferable. The blending amount of the cross-linking agent in the adhesive composition is preferably about 10 to 60 parts by weight, more preferably 20 to 50 parts by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin.

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

Examples of the monomer of the radically polymerizable adhesive include a compound having a (meth) acryloyl group and a compound having a vinyl group. Of these, compounds having a (meth) acryloyl group are preferable. Examples of the compound having a (meth) acryloyl group include alkyl (meth) acrylates such as C _1-20 chain alkyl (meth) acrylate, alicyclic alkyl (meth) acrylate, and polycyclic alkyl (meth) acrylate; hydroxyl group. Containing (meth) acrylate; Examples thereof include epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate. Radical polymerizable adhesives include hydroxyethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, (meth) acrylamide, and (meth) acryloylmorpholin. It may contain a nitrogen-containing monomer such as. The radically polymerizable adhesive has tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, and EO-modified diacrylate as cross-linking components. It may contain a polyfunctional monomer such as glycerin tetraacrylate.

The photocurable adhesive such as a photoradical polymerizable adhesive preferably contains a photopolymerization initiator. The photopolymerization initiator may be appropriately selected depending on the reaction species. For example, it is preferable to add a photoradical generator that generates radicals by light irradiation to the radically polymerizable adhesive as a photopolymerization initiator. The content of the photoradical 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 the radically polymerizable adhesive is used as an electron beam curing type, a photopolymerization initiator is not particularly required. A photosensitizer typified by a carbonyl compound or the like can be added to the radically polymerizable adhesive, if necessary. Photosensitizers are used to increase the curing rate and sensitivity of 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 may contain an appropriate additive, if necessary. Examples of additives include silane coupling agents, coupling agents such as titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trap agents, and antioxidants. , Adhesive-imparting agents, fillers, plasticizers, leveling agents, foaming inhibitors, antistatic agents, heat-resistant stabilizers, hydrolysis-resistant stabilizers and the like.

[Preparation of polarizing plate]
A polarizing plate is manufactured by bonding the easy-adhesion film 1 to one surface (first main surface) of the polarizing element 5 via the adhesive layer 6. In the easy-adhesive film 1, the easy-adhesive layer forming surface may be bonded to the polarizing element 5 via the adhesive layer, and the non-adhesive layer non-forming surface may be bonded to the polarizing element 5 via the adhesive layer. May be. As shown in FIG. 2, by adhering the splitter 5 to the surface of the easy-adhesive film 1 on which the easy-adhesive layer 15 is formed via the adhesive layer 6, the splitter and the polarizing element protective film (easy-adhesive film 1) are attached to each other. A polarizing plate having high adhesiveness and excellent mechanical strength and durability can be obtained. When the non-formed surface of the easy-adhesive layer is bonded to the polarizing element 5 via the adhesive layer, the adhesiveness with other films, the adhesive layer, the glass substrate, etc. provided on the easy-adhesive film can be improved. ..

In the bonding of the polarizing element 5 and the easy-adhesive film 1, the adhesive composition is applied to either or both of the polarizing element 5 and the easy-adhesive film 1, and then the polarizing element 5 and the easy-adhesive film 1 are attached. It is preferable to cure the adhesive by laminating with a roll laminator or the like. Examples of the method for applying the adhesive composition to the polarizing element 5 and / or the easy-adhesive film 1 include a roll method, a spray method, and a dipping method. Before applying the adhesive composition to the surface of the polarizing element 5 and / or the easy-adhesive film 1, surface treatment such as corona treatment, plasma treatment, or saponification treatment may be performed.

The adhesive layer 6 is formed by curing the adhesive depending on the type of the adhesive after the polarizing element 5 and the easy-adhesive film 1 are bonded to each other. When a water-based adhesive is used, the adhesive is cured by heating and drying. When an active energy ray-curable adhesive is used, the adhesive is cured by irradiation with an active energy ray such as an electron beam or ultraviolet rays.

<Transparent protective film>
The transparent protective film 2 may be attached to the second main surface of the polarizing element 5 via the adhesive layer 7. As the transparent protective film 2, any suitable transparent film may be adopted. The thickness of the transparent protective film 2 is about 5 to 200 μm. From the viewpoint of mechanical strength, transparency, handleability, etc., the thickness of the transparent protective film 2 is preferably 10 to 100 μm, more preferably 15 to 60 μm. The thicknesses of the easy-adhesive film 1 and the transparent protective film 2 may be the same or different.

Materials for forming the transparent protective film 2 include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose; polystyrene and acrylonitrile. -A styrene polymer such as a styrene copolymer; a cyclic polyolefin such as polynorbornene; a polycarbonate and the like can be mentioned.

The transparent protective film 2 may be provided with an easy-adhesion layer (not shown) on the surface to be bonded to the polarizing element 5. The transparent protective film 2 may be provided with an easy-adhesive layer similar to the easy-adhesive layer 15 of the easy-adhesive film 1.

The adhesive layer 7 used for bonding the polarizing element 5 and the transparent protective film 2 has various forms such as a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive-based adhesive, and an active energy ray-curable adhesive. Is used. The same adhesive composition may be used for the adhesive layer 6 and the adhesive layer 7.

[Use of polarizing plate]
The polarizing plate 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 that forms the pressure-sensitive adhesive layer, those using polymers such as acrylic polymers, silicone-based polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, and rubber-based polymers as base polymers are appropriately selected and used. Can be done. 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 pressure-sensitive adhesive layer may be attached to the polarizing plate by an appropriate method. For example, a method in which 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 is prepared and attached onto a polarizing plate, or on an appropriate substrate. Examples thereof include a method of transferring the pressure-sensitive adhesive layer formed in the above to a polarizing plate.

Adhesive layers may be provided on both sides of the polarizing plate. When the pressure-sensitive adhesive layers are provided on both sides of the polarizing plate, the composition and thickness of the pressure-sensitive adhesive layers on the front and back surfaces 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 material obtained by coating the surface of a plastic film with a release agent such as a silicone-based mold release agent, a long-chain alkyl-based mold release agent, or a fluorine-based mold release agent is preferably used.

The polarizing plate 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 luminance improving film.

An image display device can be formed by attaching a polarizing plate 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 a liquid crystal cell, a polarizing plate, and, if necessary, components such as a lighting system, and incorporating a drive circuit. In an organic EL display device, a metal electrode or the like is formed by bonding the surface of an organic EL cell with a circular polarizing plate in which the polarizing plate of the present invention and a retardation film (typically a 1/4 wave plate) are combined. It is possible to improve the visibility by reducing the re-emission of the reflected light of the external light due to the above.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The description of "%" below is% by weight unless otherwise specified.

[Preparation of Easy Adhesive Composition]
Water-based polyurethane with a solid content of 34% (“Superflex 210R” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) containing polyester urethane and isophorone diisocyanate as resin components, and further containing triethylamine as a curing catalyst and methyl ethyl ketone as a dispersion medium, 20.6 parts by weight, Oxazoline-containing polymer aqueous solution with a solid content of 25% (“Epocross WS-700” manufactured by Nippon Catalyst) 5.2 parts by weight, 1% by weight of ammonia water 2.8 parts by weight, 20% water of colloidal silica with an average primary particle diameter of 35 nm An easy-adhesion composition was prepared by mixing 7.5 parts by weight of a dispersion liquid (“Quatron PL-3” manufactured by Fuso Chemical Industry Co., Ltd.) and 63.9 parts by weight of pure water. This easy-adhesion composition was an aqueous solution having a concentration of 9.8% containing 15.3 parts by weight of silica particles with respect to 100 parts by weight of solid content. In the following examples and comparative examples, this easy-adhesion composition was used to form an easy-adhesion layer.

[Example 1]
An easy-adhesive film was produced using a film manufacturing apparatus equipped with a melt extrusion film forming apparatus, a gravure coater, a tenter type simultaneous biaxial stretching apparatus, and a winding apparatus. As the acrylic resin, pellets of the same imidized MS resin (glass transition temperature: 120 ° C.) as those used for producing the “transparent protective film 1A” described in Examples of Japanese Patent Application Laid-Open No. 2017-26939 were used. Acrylic resin is melt-extruded from a T-die to form a film with a thickness of 160 μm, and the above easy-adhesive composition is applied to one surface of the film with a wet thickness of about 9 μm using a gravure coater, and a heating furnace at a temperature of 140 ° C. An easy-adhesive film that is stretched twice in the longitudinal direction (MD) and the width direction (TD) by a simultaneous biaxial stretching tenter, and has an easy-adhesive layer having a thickness of 50 nm on one surface of an acrylic film having a thickness of 40 μm. Got

[Examples 2 to 4 and Comparative Examples 1 and 2]
An easy-adhesive film was obtained in the same manner as in Example 1 except that the coating thickness of the easy-adhesive composition was changed. The thickness of the easy-adhesive layer (after stretching) was as shown in Table 2.

[Examples 5 and 6 and Comparative Examples 3 to 5]
The temperature inside the furnace (stretching temperature) during tenter stretching was changed as shown in Table 2. An easy-adhesion film was obtained in the same manner as in Example 1 except that the stretching temperature was changed.

[Comparative Example 6]
An acrylic film having a thickness of 40 μm without an easy-adhesion layer was obtained without applying the easy-adhesion composition with a gravure coater.

[Preparation of polarizing plate]
(Manufacturing of a modulator)
Table 1 shows a long roll of a polyvinyl alcohol (PVA) resin film (“PE4500” manufactured by Kuraray) having a thickness of 45 μm, which is uniaxially stretched 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, cross-linking bath 1, cross-linking bath 2, and washing bath were conveyed in this order and dried at 70 ° C. for 5 minutes to prepare a polarizing element having a thickness of 18 μm. The iodine concentration and potassium iodide concentration in the dyeing bath were adjusted so that the single transmittance of the substituent was 43.4%.

(Preparation of UV curable adhesive)
It contains 40 parts by weight of N-hydroxyethylacrylamide and 60 parts by weight of acryloylmorpholin as curable components, and 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropane-1-one (BASF) as a polymerization initiator. Manufactured by "Irgacure 819") An ultraviolet curable adhesive containing 3 parts by weight was prepared.

(Attachment of a polarizing element and a polarizing element protective film)
The easy-adhesive film of each example and comparative example is used as the polarizing element protective film on one side, and the biaxially stretched annular polyolefin film (“Zeonoa film ZF-14” manufactured by Zeon Corporation) is used as the polarizing element protective film on the other side. board. The above-mentioned ultraviolet curable adhesive is applied to the surface of the easy-adhesion film on the easy-adhesion layer forming surface and the surface of the Zeonoa film to a thickness of about 1 μm, and the adhesive is bonded to a polarizing element with a roll laminator, and then the integrated light amount is 1000 / mJ / cm. The adhesive was cured by irradiating with the ultraviolet rays of No. ² to obtain a polarizing plate having an acrylic film (easy-adhesive film) on one surface of the polarizing element and a Zeonoa film on the other surface.

[evaluation]
<Amount of residual alkali in the easy-adhesive layer>
The amount of triethylamine and ammonia remaining in the easy-adhesion layer was quantified. The residual amount of triethylamine was quantified by gas chromatography-mass spectrometry (GC / MS) method of the solution by weighing 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-adhesion film in pure water at 25 ° C., heat-extracting it with a dryer at 120 ° C. for 60 minutes, and quantifying the ammonia eluted in water by ion chromatography. The sum of the amount of triethylamine and the amount of ammonia was taken as the residual alkali amount.

<Adhesion of easy adhesive layer>
Adhesive tape (“No. 31B” manufactured by Nitto Denko) was crimped onto the easy-adhesive layer forming surface of the easy-adhesive film at a linear pressure of 8 kg / m and a crimping speed of 0.3 m / min, and stored at 50 ° C. for 48 hours. The tip of the adhesive tape was grasped and a 180 ° peel test was performed at a tensile speed of 30 m / min, and the adhesion of the easy-adhesive layer was determined according to the following criteria.
〇: The easy-adhesive layer did not peel off from the acrylic film but peeled off at the interface between the adhesive tape and the easy-adhesive layer ×: The easy-adhesive layer peeled off at the interface between the acrylic film and the easy-adhesive layer

<Visual evaluation>
The surface of the easy-adhesive film was visually observed to evaluate the presence or absence of local turbidity (increased haze) due to the aggregation of silica particles and the presence or absence of scratches on the non-formed surface of the easy-adhesive layer.
〇: No agglomeration of silica particles and good in-plane uniformity, no scratches were observed. Δ: No turbidity due to agglomeration of silica particles, but a depth of 1 μm on the non-adhesive layer non-formed surface. The following scratches were observed. ×: Turbidity due to aggregation of silica particles and scratches on the non-formed surface of the easy-adhesive layer were observed.

<Presence / absence of interface layer>
The cross section of the easy-adhesive film is observed with a transmission electron microscope (TEM), and at the interface between the acrylic film and the easy-adhesive layer, the region (interface layer) in which the particles in the easy-adhesive layer are embedded in the acrylic film. Confirmed the presence or absence. The TEM observation image of Example 3 (with an interface layer) is shown in FIG. 3, and the TEM observation image of Comparative Example 4 (without an interface layer) is shown in FIG.

<Humidification durability of polarizing plate>
The polarizing plate was cut into a size of 320 mm × 240 mm, and the surface on the cyclic polyolefin film side was bonded onto glass via an acrylic pressure-sensitive adhesive having a thickness of 20 μm. Place this sample in a constant temperature and humidity chamber with a temperature of 60 ° C and a relative humidity of 90% (condition 1) or a constant temperature and humidity chamber with a temperature of 85 ° C and a relative humidity of 85% (condition 2), and hold for 500 hours to heat. A humidification durability test was conducted.

The degree of polarization P ₀ before the durability test and the degree of polarization P after the durability test were measured, and the amount of change in the degree of polarization ΔP = | PP ₀ | was calculated. Further, another polarizing plate was placed on the polarizing plate after the durability test with a cross Nicol, and the presence or absence of streak-like unevenness was confirmed by visual observation, and the evaluation was made according to the following criteria.
⊚: No sujimura is observed in the sample after the endurance test of either condition 1 or 2. 〇: No sujimura is observed in the sample after the endurance test of condition 1, and a slight amount of sujimura is not observed in the sample after the endurance test of condition 2. △: Slight sizzle is visible in both the samples after the endurance test of condition 1 and condition 2. ×: Szimura is clearly visible in both the samples after the endurance test of condition 1 and condition 2.

Observation photographs (taken with "EYESCALE-4W" manufactured by Eye System, a low-luminance unevenness measurement system) before and after the durability test (60 ° C. 90% Rh 500 hours) of the polarizing plates of Example 1 and Comparative Example 2 were taken. It is shown in FIG.

Preparation conditions of the easy-adhesive film of Examples and Comparative Examples (stretching temperature and thickness of the easy-adhesive layer after stretching), evaluation result of the easy-adhesive film (visual appearance, adhesion, presence / absence of interface layer), and durability test of polarizing plate. The results (presence or absence of sujimura and the amount of change in the degree of polarization ΔP) are shown in Table 2.

In the polarizing plate using the acrylic film of Comparative Example 6 in which the easy-adhesion layer was not formed, no streaks were observed even after the humidification durability test, and the decrease in the degree of polarization was small and good optical characteristics were exhibited. However, the adhesiveness between the acrylic film and the polarizing element was low, and after the humidification durability test, peeling of the acrylic film from the polarizing element was observed at the end of the polarizing plate.

The easy-adhesive film of Comparative Example 2 provided with the easy-adhesive layer having a thickness of 350 nm had good adhesion between the acrylic film and the easy-adhesive layer, and the appearance of the easy-adhesive film was also good. However, in the polarizing plate using this easily adhesive film as the polarizing element protective film, the degree of polarization was greatly reduced after the humidification durability test, and remarkable streak-like unevenness was confirmed. Similar to Comparative Example 2, even in Comparative Examples 3 to 5 in which the stretching temperature (heating temperature at the time of forming the easy-adhesive layer) was 120 ° C. or less, the degree of polarization after the humidification durability test was significantly reduced, and remarkable streak-like unevenness was confirmed. Was done.

The easy-adhesive films of Examples 1 to 4 in which the easy-adhesive layer of 50 nm to 250 nm was formed at a stretching temperature of 140 ° C. did not show white turbidity due to the aggregation of fine particles, and showed a good appearance. The easy-adhesive film of Example 1 had fine scratches on the non-formed surface of the easy-adhesive layer, but it was optically filled with an adhesive or an adhesive when it was bonded to other members. It was a scratch that was not a defect. Further, the polarizing plate using the easy-adhesion film of Examples 1 to 4 was superior in humidification durability to the polarizing plate using the easy-adhesion film of Comparative Example 2, and the generation of streaks was suppressed.

The easy-adhesive film of Comparative Example 1 in which the easy-adhesive layer having a thickness of 30 nm was formed had good humidification durability of the polarizing plate, but white turbidity due to aggregation of silica fine particles and damage to the non-adhesive layer non-formed surface were observed. , The appearance was inferior. It is considered that the occurrence of scratches is caused by the silica fine particles falling off from the surface of the easy-adhesive layer due to the decrease in dispersibility, and the slipperiness of the easy-adhesive film is reduced.

From the comparison between Examples 1 to 4 and Comparative Examples 1 and 2, the smaller the thickness of the easy-adhesive layer and the smaller the residual alkaline component, the more the generation of sujimura after the humidification durability test is suppressed, and the polarizing plate having excellent humidification durability is obtained. You can see that it can be obtained. On the other hand, if the thickness of the easy-adhesion layer is excessively small and the residual alkaline component is excessively small, it can be seen that poor appearance and deterioration of slipperiness occur due to the deterioration of the dispersibility of the fine particles.

In Examples 5 and 6 in which the easy-adhesive layer having a thickness of 200 nm was formed at a stretching temperature of 160 ° C. or 180 ° C., the appearance of the easy-adhesive film and the humidification durability of the polarizing plate were excellent as in Example 3. On the other hand, in Comparative Examples 3 to 5 in which the easy-adhesive layer having a thickness of 200 nm was formed at a stretching temperature of 80 to 120 ° C., the amount of residual alkali in the easy-adhesive layer was large, and as in Comparative Example 2, a remarkable sujimura after the humidification durability test of the polarizing plate. Was confirmed.

From these results, by reducing the amount of residual alkali in the easy-adhesive layer within the range that does not reduce the dispersibility of the fine particles, an easy-adhesive film with excellent humidification durability of the polarizing plate when used as a polarizing element protective film can be obtained. It turns out that it can be done.

In Comparative Examples 3 to 5 which were stretched at a low temperature, the adhesion between the acrylic film and the easy-adhesion layer was inferior to that of the other examples. In Example 3 and the like, an interface layer (see FIG. 3) in which particles were embedded in the acrylic film was formed at the interface between the acrylic film and the easy-adhesion layer, whereas Comparative Examples 3 to 5 were formed. The interface layer was not formed in (see FIG. 4). From these results, by raising the heating temperature after applying the easy-adhesive composition, the alkaline component in the easy-adhesive composition can be efficiently volatilized and the amount of residual alkali can be reduced, and in addition, the film substrate can be used. It can be seen that the adhesion at the interface with the easy-adhesion layer can be improved.

1 Easy-adhesive film 11 Film base material 15 Easy-adhesive layer 2 Transparent film 5 Polarizer 6,7 Adhesive layer 100 Polarizing plate

Claims (7)

A polarizing plate including an easy-adhesive film having an easy-adhesive layer on the surface of a transparent film substrate and a polyvinyl alcohol-based polarizing element having a first main surface and a second main surface.
The easy-adhesive layer contains a binder resin and inorganic fine particles, and contains
The total content of amine and ammonia in the easy-adhesion layer is 5 to 75 ppm.
A polarizing plate in which a non-adhesive layer non-forming surface of the easy-adhesive film and a first main surface of the polarizing element are bonded to each other via an adhesive layer. The polarizing plate according to claim 1, wherein the easy-adhesion layer has a thickness of 40 to 280 nm. The polarizing plate according to claim 1 or 2, wherein the content of the inorganic fine particles in the easy-adhesion layer is 8 to 50% by weight. The polarizing plate according to any one of claims 1 to 3, wherein the transparent film base material is an acrylic film. The polarizing plate according to any one of claims 1 to 4, wherein the binder resin of the easy-adhesive layer is a urethane-based resin. The polarizing plate according to any one of claims 1 to 5, wherein a region in which the inorganic fine particles are embedded in the transparent film substrate exists at the interface between the transparent film substrate and the easy-adhesive layer. An image display device having an image display cell and the polarizing plate according to any one of claims 1 to 6 .

Images