KR20210039978A - Optical film and its manufacturing method, polarizing plate, and image display device - Google Patents

Abstract

The optical film 1 includes a release layer 15 on the surface of the transparent film substrate 11. The release layer 15 contains a binder resin and fine particles. The content of the alkali component of the release layer 15 is 5 to 75 ppm. A release layer can be formed by applying a binder resin or a composition for forming a release layer containing a precursor thereof, fine particles, an alkali component, and a solvent on a transparent film substrate and heating it. The optical film can be used as a polarizer protective film.

Description

Optical film and its manufacturing method, polarizing plate, and image display device

The present invention relates to an optical film including an easy-to-use layer on the surface of a transparent film base material, and a method for producing the same. In addition, the present invention relates to a polarizing plate to which an optical film having a release layer is bonded on a surface of a polarizer, and an image display device including the polarizing plate.

As various image display devices such as mobile devices, car navigation devices, personal computer monitors, and televisions, liquid crystal displays and organic EL displays are widely used. In a liquid crystal display device, a polarizing plate is disposed on the surface on the viewing side of a liquid crystal cell based on its display principle. In a transmissive liquid crystal display device, polarizing plates are disposed on both sides of a liquid crystal cell. In an organic EL display device, a circular polarizing plate (typically a laminate of a polarizing plate and a 1/4 wavelength plate) is disposed on the surface on the viewing side to prevent external light from being reflected by the metal electrode (cathode) and being visually recognized like a mirror surface. There are cases.

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

As a polarizer protective film bonded to the surface of a polarizer, a polarizing plate to which a low moisture permeable film made of a resin material such as acrylic, polyester, polycarbonate, or cyclic polyolefin is bonded has a small change in optical properties even when exposed to a high humidity environment for a long time, It tends to be excellent in durability. Patent Document 1 describes that by providing a release layer containing fine particles and a binder resin on the surface of an acrylic film, blocking when the film is wound up in a roll shape can be suppressed. In the example of Patent Document 1, a polarizer protective film is disclosed in which a urethane resin layer having an average thickness of 400 nm (thickness range 300 to 500 nm) containing 1 to 7% by weight of silica fine particles is provided on the surface of an acrylic film.

Japanese Patent No. 5354733

While the image display device is in the process of increasing the size and brightness of the image display device, the polarizing plate constituting the image display device is required to have a small change in optical properties even in a harsher environment (eg, conditions of higher temperature and higher humidity). When the polarizing plate provided with the polarizer protective film disclosed in Patent Document 1 is exposed to a high-humidity environment for a long time, optical defects such as streak-like irregularities occur, and a problem in that the display characteristics may be deteriorated has been newly revealed.

In view of the above problems, an object of the present invention is to provide an optical film in which blocking is unlikely to occur and optical defects are unlikely to occur even when exposed to a high temperature and high humidity environment for a long time.

In view of the above problems, the inventors have studied that, for the purpose of improving the dispersibility of fine particles, it is found that alkali components such as ammonia and amine added to the composition for forming a release layer remain in the release layer in a humidified environment. It is one cause of the decrease in durability, and it has been found that the above problem can be solved by setting the amount of alkali remaining in the leased layer into a predetermined range.

The present invention relates to an optical film including a release layer on the surface of a transparent film substrate, and a method for producing the same. The lubricating layer contains a binder resin and fine particles. The average primary particle diameter of the fine particles is, for example, 10 to 250 nm, and preferably 10 to 100 nm. The content of the alkali component in the lubricating layer is preferably 5 to 75 ppm. The thickness of the lubricating layer is preferably 40 to 280 nm.

As the transparent film base material, an acrylic film or the like is used. Urethane-based resins and the like are used as the binder resin for the lubricating layer. The content of the fine particles in the active layer is preferably about 3 to 50% by weight, more preferably 10 to 50% by weight. The fine particles of the lubricating layer may be embedded in the transparent film substrate.

A release layer is formed by applying and heating the composition for forming a release layer on the surface of the transparent film substrate. The composition for forming an easily active layer contains a binder resin or a precursor thereof, fine particles, an alkali component, and a solvent. When the composition for forming an easily lubricating layer contains an alkali component, the dispersibility of fine particles is improved, and an optical film excellent in sliding properties is obtained. In addition, the alkali component can also act as a catalyst for accelerating the reaction of the binder resin (precursor). From the viewpoint of accelerating the volatilization of the alkali component by heating, the boiling point of the alkali component is preferably 150°C or less. An amine, ammonia, etc. are mentioned as an alkali component.

By increasing the heating temperature after application of the composition for forming an lubricating layer, the volatilization of the alkali component can be promoted, and an lubricating layer with few remaining alkali components can be formed. For example, you may heat the composition for releasing layer formation at a temperature 10°C or more higher than the glass transition temperature of the transparent film base material. By increasing the heating temperature, a region in which fine particles of the release layer are embedded in the transparent film base material is liable to be formed, and thus the adhesion between the transparent film base material and the release layer tends to be improved.

After applying the composition for forming an easily lubricating layer on the transparent film substrate, stretching may be performed while heating the transparent film substrate. In particular, by stretching the transparent film base material while heating the composition for forming an easily release layer at a temperature higher than the glass transition temperature of the transparent film base material by 10° C., the adhesion between the transparent film base material and the release layer tends to be improved.

The release layer can also contribute to the improvement of adhesion to other films or glass substrates. The optical film can be used as a polarizer protective film, for example. For example, a polarizing plate is obtained by bonding an optical film to the surface of a polyvinyl alcohol-based polarizer through an adhesive layer. In the optical film, either of the easily-adhesive layer forming surface and the easily-adhesive layer non-forming surface may be bonded to a polarizer. An image display device can be formed by disposing a polarizing plate on the surface of an image display cell such as a liquid crystal display cell or an organic EL cell.

(Effects of the Invention)

The optical film of the present invention has excellent adhesiveness, is less likely to cause blocking, and is less likely to cause optical defects even when exposed to a high temperature and high humidity environment for a long time, so it is suitably used as a film for a display device such as a polarizer protective film. do.

1 is a cross-sectional view showing an example of a configuration of an optical film including an lubricating layer.
2A is a cross-sectional view showing a configuration example of a polarizing plate.
2B is a cross-sectional view showing a configuration example of a polarizing plate.
3 is a cross-sectional TEM observation image of an optical film in which an interface layer is formed at an interface between a film base material and a release layer.
Fig. 4 is a cross-sectional TEM observation image of an optical film in which an interface layer is not formed at an interface between a film base material and a release layer.

1 is a schematic cross-sectional view showing a configuration example of an optical film according to an embodiment of the present invention. The optical film 1 includes a release layer 15 on at least one surface of the film substrate 11. A release layer may be provided on both sides of the film base material. The optical film is used by bonding with another film or a glass substrate.

A polarizer protective film is mentioned as a usage mode of an optical film. 2A and 2B are cross-sectional views showing a configuration example of a polarizing plate including the optical film 1 as a polarizer protective film. The polarizing plate 100 shown in FIG. 2A and the polarizing plate 101 shown in FIG. 2B are provided with an optical film 1 bonded to one surface (first main surface) of the polarizer 5 through an adhesive layer 6. . In the polarizing plate 100, the optical film 1 has a release layer 15 on the bonding surface of the film substrate 11 with the polarizer 5. In the polarizing plate 101 shown in FIG. 2B, the polarizer 5 is bonded to the surface of the optical film 1 on which the release layer 15 is not provided. In the polarizing plate 100 shown in FIG. 2A and the polarizing plate 101 shown in FIG. 2B, the transparent protective film 2 is bonded to the other surface (second main surface) of the polarizer 5 through the adhesive layer 7.

[Optical film]

The optical film 1 includes a release layer 15 on at least one surface of the film substrate 11.

<Film Substrate>

As the film base material 11, a transparent film is preferable. The total light transmittance of the transparent film substrate is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Examples of the resin material constituting the film substrate 11 include acrylic resins, polyester resins, polycarbonate resins, polyolefin resins, cyclic polyolefin resins, polystyrene resins, polyamide resins, and polyimide resins. have. When an optical film is used as an optically isotropic polarizer protective film, since birefringence is small, an acrylic resin or a cyclic polyolefin resin is preferable as the resin material of the film base material 11, and an acrylic resin is particularly preferable.

As a cyclic polyolefin resin, polynorbornene is mentioned, for example. Commercially available cyclic polyolefin resins include ZEONOR and ZEONEX manufactured by Zeon Corporation, ARTON manufactured by JSR, APEL manufactured by Mitsui Chemicals Inc., TOPAS manufactured by Topas Advanced Polymers Co., Ltd., and the like. It is preferable that the cyclic polyolefin-based film contains 50% by weight or more of the cyclic olefin-based resin.

Examples of acrylic resins include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, and methyl methacrylate-acrylic acid ester- (Meth)acrylic acid copolymer, (meth)acrylate methyl-styrene copolymer (MS resin, etc.), polymers having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate) -(Meth)acrylate norbornyl copolymer, etc.) are mentioned.

In this specification, "(meth)acryl" means acrylic and/or methacrylic. The acrylic resin includes acrylic acid or a derivative thereof as a constituent monomer component, and methacrylic acid or a derivative thereof as a constituent monomer component.

As acrylic resins, acrylic resins having a glutaric anhydride structure described in JP 2006-283013 A, JP 2006-335902 A, and JP 2006-274118 A; And/or Japanese Patent Laid-Open No. 2000-230016, Japanese Patent Laid-Open No. 2001-151814, Japanese Patent Laid-Open No. 2002-120326, Japanese Patent Laid-Open No. 2002-254544, Japanese Patent Laid-Open No. 2005-146084, etc. You may use an acrylic resin having a tone ring structure. Since the 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, they are suitable for manufacturing a polarizing plate having a high degree of polarization and excellent durability.

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, and still more preferably 70 to 97% by weight. The acrylic film may contain thermoplastic resins other than acrylic resins. For example, by blending other thermoplastic resins, the birefringence of the acrylic resin is canceled, and an acrylic film excellent in optical isotropy is obtained. Further, for the purpose of improving the mechanical strength of the film, etc., a thermoplastic resin other than an acrylic resin may be blended.

Thermoplastic resins other than acrylic resins include olefin polymers, halogenated vinyl polymers, polystyrene, styrene and acrylic monomers and copolymers, polyesters, polyamides, polyacetals, polycarbonates, polyphenylene oxides, polyphenylene sulfides, and polyethers. Ether ketone, polysulfone, polyether sulfone, polyoxybenzylene, polyamideimide, rubber-based polymer, and the like.

The film substrate 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. After mixing a resin material and an additive, and making it into a thermoplastic resin composition, such as a pellet, in advance, you may film-form.

The thickness of the film substrate 11 is about 5 to 200 μm. From the viewpoints of mechanical strength, transparency, and handling properties, 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, and more preferably 110°C or higher. When the film substrate 11 is an acrylic film, 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 is increased and heat resistance is improved. I can make it. Although the upper limit of the Tg of the film base material 11 is not particularly limited, from the viewpoint of moldability and the like, it is preferably 170° C. or less.

As a manufacturing method of the film base material 11, a solution casting method, a melt extrusion method, a calender method, a compression molding method, etc. are mentioned. 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, from the viewpoint of improving mechanical strength, the acrylic film is preferably a stretched film stretched in at least one direction, and a biaxially stretched film is particularly preferred. By blending another thermoplastic resin so as to cancel the birefringence of the acrylic resin, an acrylic film having low retardation and excellent optical isotropy even when stretched is obtained.

<Separate layer>

The release layer 15 provided on the surface of the film substrate 11 contains a binder resin and fine particles. When the release layer 15 contains fine particles, fine irregularities are formed on the surface of the release layer 15, and the sliding property of the film is improved. Therefore, it contributes to reduction of damage at the time of roll conveyance of the optical film 1, and blocking suppression at the time of winding up in a roll shape.

(Binder resin)

As a binder resin, since it has excellent adhesion to film substrates such as acrylic films, polyurethane resins, epoxy resins, isocyanate resins, polyester resins, polymers containing amino groups in the molecule, and crosslinkable functional groups such as oxazoline groups A resin (polymer) having a reactive group such as an acrylic resin is used. Polyurethane resin is particularly preferable as the binder resin for the release layer 15. The release layer 15 containing a polyurethane resin binder has high adhesion to the film substrate 11.

The urethane resin is typically a reaction product of a polyol and a polyisocyanate. As the polyol component, polymer polyols such as polyacrylic polyol, polyester polyol, and polyether polyol are preferably used.

Polyacrylic polyols are 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, and cyclohexyl (meth)acrylate. Examples of the hydroxyl-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and Hydroxyalkyl esters of (meth)acrylic acid such as hydroxybutyl and 2-hydroxypentyl (meth)acrylate; (Meth)acrylic acid monoester of polyhydric alcohol, such as glycerin and trimethylolpropane; N-methylol (meth)acrylamide, etc. are mentioned.

The polyacrylic polyol may contain monomer components other than the above. Examples of other monomer components include unsaturated monocarboxylic acids such as (meth)acrylic acid; Unsaturated dicarboxylic acids such as maleic acid, and anhydrides and diesters thereof; Unsaturated nitriles such as (meth)acrylonitrile; Unsaturated amides such as (meth)acrylamide and N-methylol (meth)acrylamide; Vinyl esters such as vinyl acetate and vinyl propionate; Vinyl ethers such as methyl vinyl ether; Α-olefins such as ethylene and propylene; Halogenated α,β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; And α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

Polyester polyols are typically obtained by reaction of polybasic acids and polyols. Examples of polybasic acids include orthophthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalene dicarboxylic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, tetrahydrophthalic acid. Aromatic dicarboxylic acids such as; 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, alkyl Aliphatic dicarboxylic acids such as succinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, and itaconic acid; Alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexane dicarboxylic acid, and 1,4-cyclohexane dicarboxylic acid; Or reactive derivatives such as these acid anhydrides, alkyl esters, and acid halides.

As polyol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octane Diol, 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-pentylene glycol , 3-methyl-1,5-pentylene glycol, 1,2-dimethylbutylene glycol, 1,3-dimethylbutylene glycol, 2,3-dimethylbutylene glycol, 1,4-dimethylbutylene glycol, di Ethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, etc. Can be lifted.

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, and trimethylolpropane. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran.

As polyisocyanate, tetramethylene diisocyanate, dodecamethylene diisocyanate, 1,4-butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate , Aliphatic diisocyanates such as lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; Isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-cyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane Alicyclic diisocyanates such as; Tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, Aromatic diisocyanates such as 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate; And aromatic aliphatic diisocyanates such as dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate.

The urethane resin constituting the release layer 15 preferably has a carboxyl group. When the urethane resin has a carboxyl group, introduction of a crosslinked structure becomes possible. The urethane resin having a carboxyl group is obtained, for example, by reacting a chain lengthener having a free carboxyl group in addition to a polyol and a polyisocyanate. Examples of the chain lengthening agent having a free carboxyl 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, and dimethylolpentanoic acid).

The method for producing the urethane resin is not particularly limited, and may be a one-shot method in which a monomer component is reacted at once, or a multistage method in which a monomer component is reacted in stages. When a carboxyl group is introduced into the urethane resin by using a chain lengthening agent having a free carboxyl group, a multistage method is preferred. In the production of a urethane resin, a urethane reaction catalyst may be used as necessary.

5,000-600,000 are preferable and, as for the number average molecular weight of a urethane resin, 10,000-400,000 are more preferable. 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 adhesion between the release layer 15 and the film substrate 11 and the hardness of the release layer 15 tend 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 carboxyl 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 carboxyl group at room temperature, the pot life when mixed with the urethane resin is long, and it can flexibly respond to the lead time of the process.

The crosslinking agent may be a low molecular weight compound or a polymer. Since solubility in an aqueous composition is high and compatibility with a urethane resin is also excellent, an acrylic polymer is preferable as a crosslinking agent, and an acrylic polymer having an oxazoline group is particularly preferable.

The amount of the crosslinking agent used is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight, based on 100 parts by weight of the urethane resin.

(Fine particles)

By containing fine particles in the release layer 15, a fine uneven shape is formed on the surface of the release layer, the sliding property of the optical film 1 is improved, and blocking can be suppressed. From the viewpoint of forming irregularities contributing to the improvement of the sliding property, the particle diameter (average primary particle diameter) of the fine particles is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. It is preferable that the average primary particle diameter of the fine particles is smaller than the thickness of the release layer. When the particle diameter of the microparticles is smaller than the thickness of the release layer, it is possible to suppress the microparticles from falling off from the release layer. The particle diameter of the fine particles is preferably 250 nm or less, and more preferably 200 nm or less. Further, since the average primary particle diameter of the fine particles is smaller than the wavelength of visible light, 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 diameter of the fine particles is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, and particularly preferably 50 nm or less.

The fine particles of the easily adhesive layer 15 may be either inorganic fine particles or organic fine particles. From the viewpoint of excellent dispersibility and uniform particle diameter, inorganic fine particles are preferable as the fine particles. 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. Among these, inorganic oxides are preferred. Examples of the organic fine particles include silicone resins, fluorine resins, and acrylic resins. In order to suppress light scattering due to the fine particles, it is preferable that the difference in the refractive index between the binder resin (generally about 1.5 refractive index) and the fine particles is small. Silica particles are preferable as the fine particles of the release layer 15 because the difference in refractive index with the binder resin is small and dispersibility is excellent.

When forming the release layer 15 with an aqueous composition, it is preferable to use fine particles having high water dispersibility. An aqueous dispersion of fine particles may be blended into the composition. In order to increase the dispersibility of the fine particles, it is preferable to add an alkali component such as amine or ammonia to make the composition for forming an lubricating layer weakly alkaline.

Colloidal silica is preferably used as the water-dispersible silica particles. As colloidal silica, Quartron PL series from Fuso Chemical Co., Ltd., SNOWTEX series from Nissan Chemical Industries, Ltd., AERODISP series and AEROSIL series from Nippon Aerosil Co., Ltd., Nippon Shokubai Co. A commercial product such as SEAHOSTAR KE series manufactured by Ltd. may be used.

From the viewpoint of enhancing the slidability of the optical film 1 by formation of irregularities on the surface of the release layer 15, the content of the fine particles in the release layer 15 is preferably 3% by weight or more, and 5% by weight or more. This is more preferable. In particular, when the thickness of the release layer 15 is small (for example, 280 nm or less), the content of the particles is increased to increase the amount (number density) of the particles per unit area. It is preferable to form irregularities. The content of the fine particles in the release layer 15 is preferably 8% by weight or more, more preferably 10% by weight or more, and even more preferably 12% by weight or more. When the content of the fine particles in the lubricating layer 15 is excessively large, the optical properties may be deteriorated due to an 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, and thus the adhesiveness of the lubricating layer may decrease. Therefore, the content of the fine particles in the release layer 15 is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less.

(Amount of Alkali Remaining)

When an alkali component such as amine or ammonia is used in order to increase the dispersibility of the fine particles, the alkali component inevitably remains in the release layer. When the optical film 1 is used as a polarizer protective film, the elution of the residual alkali component of the release layer 15 into moisture or the alkali component that has passed through the film substrate 11 deteriorates the polarizer, reducing the degree of polarization of the polarizing plate. However, there are cases where optical defects such as stripe-shaped spots occur.

From the viewpoint of enhancing the humidification durability of the polarizing plate, the amount of alkali remaining in the lubricating layer 15 is preferably 75 ppm or less, more preferably 70 ppm or less, still more preferably 60 ppm or less, and particularly preferably 55 ppm or less. From the viewpoint of improving the humidification durability of the polarizing plate, the smaller the amount of alkali remaining in the lubricating layer 15 is, the more preferable.

On the other hand, when the amount of alkali remaining in the release layer 15 is excessively 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. Further, due to aggregation of fine particles due to a decrease in dispersibility or dropping from the release layer, appropriate irregularities are not formed on the surface of the release layer, so that the sliding property of the optical film tends to decrease. Therefore, 5 ppm or more is preferable, 10 ppm or more is more preferable, and 20 ppm or more is still more preferable as for the residual alkali amount of the easily active layer 15.

Specific examples of the residual alkali component in the active layer include amine and ammonia, and it is preferable that the sum of the content of the amine and ammonia in the active layer is within the above range. The amount of alkali in the lubricating layer can be quantified by liquid chromatography or ion chromatography, depending on the type of alkali component. The alkali component may be quantified by an analysis method (eg, LC/MS) in which chromatography and mass spectrometry (MS) are combined. When a plurality of alkali components are contained in the release layer, the sum of the components is referred to as the alkali component content (remaining amount) of the release layer.

<Formation of a movable layer>

The method of forming the release layer 15 on the surface of the film substrate 11 is not particularly limited. Preferably, the release layer 15 is formed by applying a composition for forming a release layer (coating liquid) containing a binder resin and fine particles on the film substrate 11 and heating it.

(Composition for forming a release layer)

The composition for forming an easily lubricating layer is preferably an aqueous composition in which water is used as a solvent (and a dispersion medium for fine particles). The concentration of the solid content (non-volatile component) in the composition for forming an active layer is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and still more preferably 3 to 15% by weight.

The composition for forming an aqueous release layer contains water as a solvent (and a dispersion medium), a binder resin or a precursor thereof, and fine particles. It is preferable that the composition for forming an easily lubricating layer further contains an alkali component. As described above, the alkali component has an action of promoting dispersion of fine particles. Fine particles having a small particle diameter tend to agglomerate easily, but when the composition for forming an easily lubricating layer contains an alkali component such as ammonia or amine, the dispersibility of the fine particles is improved, and an optical film excellent in appearance and sliding properties is obtained.

On the other hand, if the alkali contained in the composition for forming the movable layer remains in the movable layer, it may be a cause of lowering the heat-and-moisture resistance of the polarizing plate. In particular, even a small amount of strong alkali such as caustic may cause deterioration of the polarizer. Therefore, as an alkali component contained in the composition for forming an easily lubricating layer, weak alkali components such as ammonia and amine are preferred. From the viewpoint of improving the dispersibility of the fine particles and preventing deterioration of the polarizer, the pH of the composition for forming an easily lubricating layer (coating liquid) is preferably about 7.5 to 9.

From the viewpoint of improving the dispersibility of the microparticles, the amount of the alkali component contained in the composition for forming an easily lubricating layer is preferably 300 ppm or more, and more preferably 500 ppm or more with respect to the solid content of the composition for forming an easily lubricating layer. On the other hand, if the content of the alkali component is excessively large, it may become difficult to reduce the amount of remaining alkali, so the amount of the alkali component contained in the composition for forming an easily release layer is preferably 50000 ppm or less based on the solid content of the composition for forming the release layer. And 10000 ppm or less is more preferable, and 5000 ppm or less is still more preferable. As described above, specific examples of the alkali component contained in the composition for forming an easily lubricating layer include amine and ammonia, and it is preferable that the total content of these alkali components is within the above range.

In addition to improving the dispersibility of fine particles, the alkali component contained in the composition for forming an easily active layer may have a catalytic action or the like. For example, when the binder resin is a urethane resin, a tertiary amine such as triethylamine may be contained in the composition for forming a release layer as a catalyst for urethanization of a polyurethane precursor (polyol, isocyanate, etc.).

By heating after coating the composition for forming a release layer on the film substrate, the alkali component can be removed by volatilization and the remaining alkali component of the release layer 15 can be reduced. From the viewpoint of accelerating the volatilization of the alkali component by heating, it is preferable that the alkali component contained in the composition for forming an easily lubricating layer has a boiling point of 150° C. or less. The boiling point of the alkali component is more preferably 130°C or less, more preferably 120°C or less, and particularly preferably 110°C or less. The boiling point of the alkali component may be 100°C or less or 90°C or less. When a plurality of alkali components are contained in the composition for forming an easily active layer, the boiling point of at least one alkali component is preferably within the above range, and the boiling point of two or more alkali components is preferably within the above range. It is preferable that the boiling point of the alkali component of 50% by weight or more with respect to 100 parts by weight of the total amount of alkali contained in the release layer is within the above range. Ideally, the boiling points of all the alkali components contained in the composition for forming an easily lubricating layer are within the above range.

The composition for forming an easily active layer may contain a crosslinking agent in addition to the binder resin (or a precursor thereof), fine particles, and an alkali component. The composition for forming an easily active layer may contain additives such as a catalyst such as a crosslinking accelerator, an antioxidant, an ultraviolet absorber, a leveling agent, an antiblocking agent, an antistatic agent, a dispersion stabilizer, an antifoaming agent, a thickener, a dispersant, a surfactant, and a lubricant.

(Formation of a release layer on the film substrate)

Before applying the composition for forming an easily lubricating layer on the film substrate 11, the film substrate may be subjected to surface treatment. By performing the surface treatment, it is possible to adjust the wetting tension of the film base material to improve the adhesion to the release layer 15. Examples of the surface treatment include corona treatment, plasma treatment, ozone blowing, ultraviolet irradiation, flame treatment, and chemical treatment. Among these, corona treatment or plasma treatment is preferred.

Examples of the coating method of the composition for forming an lubricating layer 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, a fountain coating method, and the like. The release layer 15 is formed by heating the composition for forming a release layer after application to remove the solvent. The precursor of the binder resin may be reacted and cured by heating. For example, when the composition for forming an easily lubricating layer contains a crosslinking agent, the crosslinking reaction can be accelerated by heating.

The heating temperature at the time of forming the lubricating layer is, for example, about 50 to 200°C. From the viewpoint of promoting the curing reaction of the resin component in the release layer-forming composition and efficiently volatilizing and removing the alkali component contained in the release layer-forming composition, the heating temperature is preferably 100° C. or higher, and 120° C. The above is more preferable, 130 degreeC or more is still more preferable, and 135 degreeC or more is especially preferable. In addition, it is preferable that the heating temperature is higher than the boiling point of the alkali component contained in the composition for forming an easily lubricating layer.

It is preferable that the heating temperature at the time of forming the release layer is higher than the glass transition temperature (Tg) of the film substrate. By heating at a high temperature, while accelerating the curing reaction of the resin component in the composition for forming an easily release layer, it is possible to efficiently volatilize and remove the alkali component contained in the composition for forming an easily release layer. It is preferable that the heating temperature is 10°C or more higher than the Tg of the film substrate.

By heating at a higher temperature than the Tg of the film substrate, the efficiency of volatilization removal of alkali in the composition for forming the release layer is increased, and the composition for forming the release layer is easily penetrated into the surface of the film substrate, so that the film substrate 11 and the release layer It is thought that the adhesion of (15) is improved. From the viewpoint of improving the adhesiveness of the release layer, the heating temperature is preferably Tg+10°C or higher, more preferably Tg+15°C or higher, and still more preferably Tg+20°C or higher.

When the film substrate is heated at a temperature of Tg+10°C or higher, the film substrate becomes a rubbery state from a glass state and the surface is easily deformed. Therefore, at the interface between the film substrate 11 and the release layer 15, the It is easy to form an interface layer in which the resin component and the constituent components of the release layer are mixed. By forming the interface layer, there is a tendency that the adhesion between the film substrate 11 and the release layer 15 is improved.

In particular, as shown in the cross-sectional observation of Fig. 3, when there is an area buried by inserting fine particles of the release layer 15 on the surface of the film base material 11, the film base material 11 and the release layer (15) An optical film with high adhesion is obtained. When the film substrate is heated to a higher temperature than Tg in the state of rubber, fine particles are embedded in the film substrate, and then the film substrate returns to the glass state, the fine particles embedded in the surface of the film substrate and the binder resin present around the film substrate It is considered that the adhesion between the film base material 11 and the release layer 15 is improved because it adheres to the surface of the film.

You may form a release layer in the manufacturing process of a film base material. Moreover, you may form a release layer using heating at the time of formation of a film base material. For example, when the film substrate is a stretched film, a composition for forming a release layer is applied to the surface of the film before stretching or after longitudinal stretching, and using heating during transverse stretching or simultaneous biaxial stretching by a tenter, the solvent Drying or curing of the resin can be performed.

In the case of stretching the film substrate after applying the composition for forming an easily lubricating layer, the draw ratio is preferably 5 times or less, more preferably 4 times or less, from the viewpoint of suppressing defects such as occurrence of cracks in the release layer. , 3 times or less is more preferable, and 2.5 times or less is particularly preferable. The lower limit of the draw ratio is not particularly limited, but from the viewpoint of improving the strength of the film, the draw ratio is preferably 1.3 times or more, and more preferably 1.5 times or more. When the film base material is an acrylic film, it is preferable to perform stretching at the aforementioned draw ratio in each of the conveying direction (MD) and the width direction (TD) from the viewpoint of improving the film strength.

When performing biaxial stretching of the film base material, the biaxial stretching may be successively biaxially stretching, or simultaneous biaxial stretching may be employed. Further, oblique stretching may be performed. In the case of sequential biaxial stretching, the film is stretched in one direction (MD) by roll stretching as described above, and then a composition for forming a release layer is applied on the film, and a release layer is formed during stretching by a tenter. You may heat the composition.

The stretching temperature is the heating temperature of the release layer, as described above, preferably higher than the Tg of the film substrate, preferably Tg+10°C or higher, more preferably Tg+15°C or higher, and Tg+20°C or higher. More preferable. In particular, it is preferable to perform stretching in at least one direction at the above temperature after applying the composition for forming an easily lubricating layer. When stretching is performed in a rubber state higher than the Tg of the film base material, the area in which fine particles in the composition for forming a release layer are embedded is easily formed on the surface of the film base material, and the adhesion between the film base material 11 and the release layer 15 is improved. Tend to be. This is the reason that fine particles are easily buried in the film substrate due to stretching at high temperature. If stretching is performed in a rubber state, the composition for forming the release layer is easily wetted and diffused when the film substrate is deformed, and concave surface irregularities formed at the time of deformation. Examples include those that tend to be in a state in which fine particles are sandwiched in the part. In addition, when cooling is performed while releasing the stress after stretching, it is considered that when the film substrate shrinks, the particles embedded in the surface of the film substrate are fixed, so that a region in which fine particles are embedded in the film substrate is likely to be formed.

The thickness of the release layer 15 can be adjusted by adjusting the solid content concentration and the coating thickness of the composition for forming the release layer. In the case where the film base material is stretched after the composition for forming an easily lubricated layer is applied, the thickness of the movable layer 15 can be adjusted also by the draw ratio.

Although the thickness of the release layer 15 is not particularly limited, 280 nm or less is preferable, 250 nm or less is more preferable, and 230 nm or less is still more preferable from the viewpoint of promoting the removal of the alkali component by heating. When the optical film 1 is used as a polarizer protective film, the smaller the thickness of the release layer 15 is, the more likely the humidification durability of the polarizing plate is improved.

When the alkali component is excessively removed during heating and drying of the release layer-forming composition, the dispersibility of the microparticles in the binder resin decreases, resulting in agglomeration of the microparticles and the resulting dropout of the microparticles from the release layer surface. . When agglomeration or dropping of the fine particles occurs, the sliding property of the optical film decreases, and scratches at the time of conveyance and blocking at the time of winding are liable to occur. Therefore, the thickness of the release layer 15 is preferably 40 nm or more, more preferably 50 nm or more, even more preferably 80 nm or more, and particularly preferably 100 nm or more. The thickness of the release layer may be 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, or 150 nm or more.

[Polarizer]

The polarizing plate may be provided with a transparent protective film only on one surface of the polarizer, or may be provided with a transparent protective film on both surfaces of the polarizer 5 as shown in Figs. 2A and 2B. By bonding the optical film as a polarizer protective film to one surface of the polarizer, a polarizing plate having a transparent protective film is formed only on one surface of the polarizer. As for the polarizing plate which has a polarizer protective film on both surfaces of a polarizer, it is sufficient that the said optical film is bonded to at least one surface of a polarizer. The polarizing plate may be one in which the optical film is bonded to both surfaces of a polarizer. The polarizer 5 and the optical film 1 are bonded through the adhesive layer 6.

<polarizer>

As the polarizer 5, a polyvinyl alcohol (PVA) system in which a dichroic substance such as iodine or a dichroic dye is adsorbed to a polyvinyl alcohol-based film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and oriented in one direction. A polarizer is used. For example, a PVA-based polarizer is obtained by performing iodine dyeing and stretching on a polyvinyl alcohol-based film.

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

As the polarizer 5, a thin PVA-based polarizer having a thickness of 10 μm or less can also be used. As a thin polarizer, it is described in Japanese Patent Laid-Open No. 51-069644, Japanese Patent Laid-Open No. 2000-338329, WO2010/100917 pamphlet, Japanese Patent No. 4691205, Japanese Patent No. 44751481, for example. A thin polarizer is mentioned. These thin polarizers are obtained by a manufacturing method including a step of stretching a PVA-based resin layer and a resin substrate for stretching in a laminated state, and a step of iodine dyeing. With this manufacturing method, even if the PVA-based resin layer is thin, since it is supported by the resin substrate for stretching, it becomes possible to stretch without defects such as fracture due to stretching.

<Adhesive>

As long as the adhesive layer 6 used for bonding the polarizer 5 and the optical film 1 is optically transparent, the material is not particularly limited, and an epoxy resin, a silicone resin, an acrylic resin, polyurethane, polyamide, Polyether, polyvinyl alcohol, etc. are mentioned. 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 the adherend, the adhesive material, and the like. When using a curable adhesive that exhibits adhesiveness by crosslinking reaction after application, 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 types of adhesives such as water-based adhesives, solvent-based adhesives, hot melt adhesives, and active energy ray-curable adhesives are used. Among these, a water-based adhesive or an active energy ray-curable adhesive is preferable from the viewpoint that the thickness of the adhesive layer can be reduced.

Examples of the polymer component of the water-based adhesive include vinyl polymer, gelatin, vinyl latex, polyurethane, polyester, and epoxy. Among these, a vinyl polymer is preferable, and a polyvinyl alcohol-based resin is particularly preferable from the viewpoint of excellent adhesion to a polarizer. Among the polyvinyl alcohol-based resins, polyvinyl alcohol containing an acetacetyl group is preferable.

From the point of adhesiveness, the average degree of polymerization of the polyvinyl alcohol-based resin is preferably about 100 to 5000, and more preferably 1000 to 4000. The average degree of saponification of the polyvinyl alcohol-based resin is preferably 85 mol% or more, and more preferably 90 mol% or more.

The water-based adhesive composition (solution) may contain a crosslinking agent in addition to a polymer such as a polyvinyl alcohol-based resin. As the crosslinking agent, a compound having at least two functional groups reactive with the polymer constituting the adhesive is used per molecule. Examples of the crosslinking agent of the polyvinyl alcohol-based resin include alkylene diamines; Isocyanates; Epoxys; Aldehydes; And amino-formaldehyde such as methylol urea and methylol melamine. 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 crosslinking 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 beams or ultraviolet rays. Among them, a photoradical polymerizable adhesive in which polymerization is initiated by irradiation with ultraviolet rays, a photocationic polymerizable adhesive, or a hybrid adhesive in which photocationic polymerization and photoradical polymerization are used in combination are preferred from the viewpoint of being curable with low energy.

Examples of the radical polymerizable adhesive monomer include a compound having a (meth)acryloyl group and a compound having a vinyl group. Among them, a compound having a (meth)acryloyl group is suitable. 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; Epoxy group-containing (meth)acrylates, such as glycidyl (meth)acrylate, etc. are mentioned. Radical polymerizable adhesives include hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide. It may contain nitrogen-containing monomers such as amide and (meth)acryloylmorpholine. The radically polymerizable adhesive is a crosslinking component, such as tripropylene glycol diacrylate, 1,9-nonandiol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, and dioxane glycol diacrylate. And polyfunctional monomers such as EO-modified diglycerin tetraacrylate may be contained.

Examples of the curable component of the cationic polymerizable adhesive include compounds having an epoxy group and an oxetanyl group. The compound having an epoxy group is not particularly limited as long as it has at least two epoxy groups in the molecule, and various commonly known curable epoxy compounds are used. As a preferred epoxy compound, a compound having at least two epoxy groups in the molecule and at least one aromatic ring (aromatic epoxy compound), having at least two epoxy groups in the molecule, at least one of which is adjacent 2 constituting an alicyclic ring And compounds formed between two carbon atoms (alicyclic epoxy compounds). A hybrid adhesive can also be obtained by containing a radical polymerizable compound such as a compound having a (meth)acryloyl group in the cationic polymerizable adhesive.

It is preferable that the photocurable adhesive contains a photoinitiator. The photoinitiator may be appropriately selected depending on the reactive species. For example, it is preferable to blend a photo-radical generator that generates radicals by irradiation with light as a photoinitiator in the radically polymerizable adhesive. It is preferable to mix|blend a photocationic polymerization initiator (mineral acid generator) which generates cationics or Lewis acid by light irradiation as a photoinitiator in a cationic polymerizable adhesive. It is preferable to blend a photocationic polymerization initiator and a photoradical generator in the hybrid adhesive.

The content of the polymerization initiator 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. In addition, when using a radically polymerizable adhesive as an electron beam curing type, a photoinitiator is not particularly required. A photosensitizer may be added to the active energy ray-curable adhesive as necessary in order to increase the curing speed and sensitivity. The used amount of the photosensitizer 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 suitable additives as 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, antioxidants, tackifiers, fillers, plasticizers, leveling agents. Agents, foaming inhibitors, antistatic agents, heat-resistant stabilizers, hydrolysis-resistant stabilizers, and the like.

[Manufacture of polarizing plate]

A polarizing plate is manufactured by bonding the optical film 1 to one surface (first main surface) of the polarizer 5 through the adhesive layer 6. The optical film 1 may be bonded to the polarizer 5 through the adhesive layer as shown in FIG. 2A, and the non-release layer formed surface as shown in FIG. 2B is the polarizer 5 through the adhesive layer. ) And may be joined.

The easily active layer 15 can also function as an easily adhesive layer. As shown in FIG. 2A, in the case of bonding the polarizer 5 through the adhesive layer 6 to the surface of the optical film 1 on which the release layer 15 is formed, the release layer 15 is formed of a polarizer and a polarizer protective film (optical It can contribute to the improvement of the adhesiveness of the film (1). As shown in FIG. 2B, when the non-release layer is bonded to the polarizer 5 through the adhesive layer, the release layer 15 is provided on the optical film 1, other films, pressure-sensitive adhesive layers, glass substrates, etc. It can contribute to the improvement of the adhesion of the.

In the bonding of the polarizer 5 and the optical film 1, after applying the adhesive composition to either or both of the polarizer 5 and the optical film 1, the polarizer 5 and the optical film 1 are rolled into a laminator. It is preferable to bond by or the like, and to cure the adhesive. As a method of applying the adhesive composition to the polarizer 5 and/or the optical film 1, a roll method, a spray method, an immersion method, and the like may be mentioned. Before applying the adhesive composition to the surface of the polarizer 5 and/or the optical film 1, surface treatments such as corona treatment, plasma treatment, and saponification treatment may be performed.

After bonding the polarizer 5 and the optical film 1, the adhesive layer 6 is formed by curing the adhesive according to the type of the adhesive. When a water-based adhesive is used, the adhesive is cured by heat 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. When a photocationic polymerizable adhesive is provided on the release layer 15, photoactive species (cations or Lewis acids) are easily deactivated by the action of the remaining alkali components of the release layer, and polymerization disorders may occur. have. Therefore, when a photocationic polymerizable adhesive or a photocationic/photoradical hybrid adhesive is used as the adhesive layer 6, the non-release layer formed surface of the optical film 1 is a polarizer 5 as shown in FIG. 2B. It is preferable to bond with.

<Transparent protective film>

The transparent protective film 2 may be bonded to the second main surface of the polarizer 5 via the adhesive layer 7. As the transparent protective film 2, any suitable transparent film can be adopted. The thickness of the transparent protective film 2 is about 5 to 200 µm. From the viewpoints of mechanical strength, transparency, handling properties, and the like, the thickness of the transparent protective film 2 is preferably 10 to 100 µm, more preferably 15 to 60 µm. The thickness of the optical film 1 and the transparent protective film 2 may be the same or different.

Examples of the material for forming the 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; Styrenic polymers such as polystyrene and acrylonitrile/styrene copolymers; Cyclic polyolefins, such as polynorbornene; Polycarbonate, etc. are mentioned.

The transparent protective film 2 may be provided with a release layer (not shown). The transparent protective film 2 may be provided with a release layer similar to the release layer 15 of the optical film 1.

As the adhesive layer 7 used for bonding the polarizer 5 and the transparent protective film 2, various types of adhesives such as water-based adhesives, solvent-based adhesives, hot melt adhesives, and active energy ray-curable adhesives are 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 a pressure-sensitive adhesive layer for bonding to a liquid crystal cell or an organic EL cell. As the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer, an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyamide, polyether, a fluorine-based or rubber-based polymer can be suitably selected and used as the base polymer. Particularly, an acrylic pressure-sensitive adhesive is preferable because it is excellent in optical transparency, shows moderate wettability and cohesiveness, and is excellent in weather resistance, heat resistance, and the like.

Laying of the pressure-sensitive adhesive layer on the polarizing plate can be performed in an appropriate manner. For example, by dissolving or dispersing a base polymer in a solvent such as toluene or ethyl acetate, a pressure-sensitive adhesive solution having a solid content concentration of about 10 to 40% by weight is prepared and laid on a polarizing plate, or a pressure-sensitive adhesive layer formed on a suitable substrate is prepared. A method of transferring onto a polarizing plate, etc. are mentioned.

You may provide an adhesive layer on both sides of a polarizing plate. When providing the pressure-sensitive adhesive layers on both sides of the polarizing plate, the composition and thickness of the pressure-sensitive adhesive layers on the front and back 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 or the like. As the separator, those obtained by coating the surface of a plastic film with a release agent such as a silicone release agent, a long-chain alkyl release agent, or a fluorine release agent are preferably used.

The polarizing plate may be a laminated polarizing plate laminated with another optical layer. As an optical layer, a retardation plate, a visual compensation film, a brightness improvement film, etc. are mentioned.

An image display device can be formed by bonding a polarizing plate to the surface of an image display cell such as a liquid crystal cell or an organic EL cell. The formation of a liquid crystal display device is formed by assembling a driving circuit by assembling a liquid crystal cell, a polarizing plate, and constituent parts such as a lighting system as necessary. In the organic EL display device, by bonding the polarizing plate of the present invention and the retardation film (typically 1/4 wavelength plate) to the surface of the organic EL cell with a circular polarizing plate bonded, re-emission of reflected light of external light by a metal electrode or the like is prevented. By reducing, visibility can be improved.

(Example)

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

[Preparation of a composition for forming an lubricating layer]

Aqueous polyurethane having a solid content of 34% containing polyester urethane and isophorone diisocyanate as resin components, and triethylamine as a curing catalyst and methyl ethyl ketone as a dispersion medium ("Superflex 210R" manufactured by DKS Co. Ltd.) 20.6 parts by weight, 25% solid content of oxazoline-containing polymer aqueous solution (Nippon Shokubai Co., Ltd. ``Epocros WS-700'') 5.2 parts by weight, 1% by weight of ammonia water 2.8 parts by weight, a colloid having an average primary particle diameter of 35 nm 7.5 parts by weight of a 20% aqueous dispersion of silica ("Quartron PL-3" manufactured by Fuso Chemical Industry Co., Ltd.) and 63.9 parts by weight of pure water were mixed to prepare a composition for forming a release layer. This 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, a release layer was formed using this composition.

[Example 1]

An optical film was produced using a film production apparatus provided 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) used in the production of the "transparent protective film 1A" described in Examples of JP 2017-26939 A were used. The acrylic resin is melt-extruded from a T-die to form a film to a thickness of 160 μm, and the composition is applied to one side of the film to a wet thickness of about 9 μm with a gravure coater, and simultaneously twin-screwed in a heating furnace at a temperature of 140°C. It was stretched twice in the length direction (MD) and the width direction (TD) by a stretch tenter, respectively, to obtain an optical film including a release layer having a thickness of 50 nm on one surface of an acrylic film having a thickness of 40 µm.

[Examples 2 to 4 and Comparative Examples 1 and 2]

An optical film was obtained in the same manner as in Example 1 except that the coating thickness of the composition for forming an easily active layer was changed. The thickness (after stretching) of the release layer was as shown in Table 2.

[Examples 5 and 6 and Comparative Examples 3 to 5]

The furnace temperature (stretching temperature) at the time of tenter stretching was changed as shown in Table 2. Except having changed the extending|stretching temperature, it carried out similarly to Example 1, and obtained the optical film.

[Manufacture of polarizing plate]

(Manufacture of polarizer)

Table 1 shows a long roll of a 45 μm-thick polyvinyl alcohol (PVA)-based resin film (“PE4500” manufactured by Kuraray Co., Ltd.) being uniaxially stretched in the longitudinal direction so that it becomes 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 sequentially conveyed and dried at 70° C. for 5 minutes to prepare a polarizer having a thickness of 18 μm. The iodine concentration and the potassium iodide concentration in the dyeing bath were adjusted so that the single transmittance of the polarizer was 43.4%.

(Preparation of UV-curable adhesive)

It contains 40 parts by weight of N-hydroxyethyl acrylamide and 60 parts by weight of acryloylmorpholine as a curable component, and as a polymerization initiator 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane- An ultraviolet curable adhesive containing 3 parts by weight of 1-on ("IRGACURE 819" manufactured by BASF) was prepared.

(Joining the polarizer and the polarizer protective film)

As a polarizer protective film on one side, the optical films of each of Examples and Comparative Examples were used, and as a polarizer protective film on the other side, a biaxially stretched cyclic polyolefin film ("ZeonorFilm ZF-14" manufactured by Zeon Corporation) was used. The UV-curable adhesive was applied to a thickness of about 1 µm on the release layer formation surface of the optical film and the surface of ZeonorFilm, bonded to a polarizer with a roll laminator, and irradiated with ultraviolet rays of an accumulated light amount of 1000/mJ/cm 2 to apply the adhesive. By curing, a polarizing plate provided with an acrylic film (optical film) on one surface of the polarizer and ZeonorFilm on the other surface was obtained.

[evaluation]

<Amount of Alkali Remaining in Evidence Layer>

The amount of triethylamine and ammonia remaining in the lubricating layer was quantified. For the residual amount of triethylamine, the powder obtained by removing the release layer from the surface of the optical film was weighed, dissolved in methanol, and quantified by gas chromatography mass spectrometry (GC/MS) of the solution. For the remaining amount of ammonia, after immersing the optical film in pure water at 25°C, heat extraction was performed for 60 minutes in a dryer at 120°C, and ammonia eluted in water was quantified by ion chromatography. The sum of the amount of triethylamine and the amount of ammonia was referred to as the amount of residual alkali.

<Adhesion of the smooth layer>

An adhesive tape ("No. 31B" manufactured by Nitto Denko Corporation) was pressed onto the surface of the optical film at a pressure of 8 kg/m and a compression rate of 0.3 m/min, stored at 50° C. for 48 hours, and then the tip of the adhesive tape. Was gripped, a 180° peeling test was performed at a tensile speed of 30 m/min, and the adhesion of the release layer was determined according to the following criteria.

○: The release layer was not peeled off from the acrylic film, but peeled off at the interface between the adhesive tape and the release layer.

X: Peeling occurred at the interface between the acrylic film and the release layer

<Visual evaluation>

The surface of the optical film was visually observed, and the presence or absence of local turbidity (haze rise) due to aggregation of silica particles, and the presence or absence of a wound on the non-release layer-formed surface were evaluated.

○: No aggregation of silica particles, good in-plane uniformity, and no scratches

△: No cloudiness due to agglomeration of silica particles was observed, but a wound with a depth of 1 μm or less was observed on the non-development layer

×: Cloudiness due to agglomeration of silica particles and scratches on the non-release layer formed surface were confirmed

<Presence of hierarchical layer>

The cross section of the optical film was observed with a transmission electron microscope (TEM), and at the interface between the acrylic film and the releasing layer, the presence or absence of a region (interface layer) in which particles in the releasing layer were embedded in the acrylic film was confirmed. Fig. 3 shows a TEM observation image of Example 3 (with an interface layer), and Fig. 4 shows a TEM observation image of Comparative Example 4 (without an interface layer).

<Humidification durability of polarizing plate>

The polarizing plate was cut out to a size of 320 mm x 240 mm, and the surface on the side of the cyclic polyolefin film was bonded to the glass through an acrylic pressure-sensitive adhesive having a thickness of 20 µm. Put this sample in a constant temperature and humidity tank with a temperature of 60°C and 90% relative humidity (Condition 1), or a constant temperature and humidity tank with a temperature of 85°C and 85% relative humidity (Condition 2), and hold it for 500 hours to conduct a heating/humidification endurance test. did.

The degree of polarization (P ₀ ) before the endurance test and the degree of polarization (P) after the endurance test were measured, and the amount of change in the degree of polarization (ΔP) = |PP ₀ | was calculated. Moreover, on the polarizing plate after the durability test, another polarizing plate was arrange|positioned by orthogonal Nicols, it observed visually, the presence or absence of a stripe-like unevenness was confirmed, and it evaluated by the following criteria.

◎: No streak unevenness was observed in any of the samples after the endurance test among Condition 1 and Condition 2

○: No streak unevenness was observed in the sample after the endurance test under Condition 1, and some streak unevenness was visually recognized in the sample after the endurance test under Condition 2

△: In both samples after the endurance test of Condition 1 and Condition 2, slight streaks were visually recognized.

×: In both samples after the endurance test under Condition 1 and Condition 2, streaks were clearly visually recognized.

Preparation conditions of the optical films of Examples and Comparative Examples (stretching temperature and thickness of the release layer after stretching), evaluation results of the optical film (visibility, adhesion, presence or absence of an interface layer), and durability test results of the polarizing plate (the presence or absence of streaks, and Table 2 shows the amount of change in polarization degree (ΔP)).

The optical film of Comparative Example 2 provided with a 350 nm-thick release layer had good adhesion between the acrylic film and the release layer, and the appearance of the optical film was also good. However, in the polarizing plate using this optical film as a polarizer protective film, the decrease in the degree of polarization after the humidification endurance test was large, and a remarkable stripe-like unevenness was observed. In Comparative Examples 3 to 5 in which the stretching temperature (heating temperature at the time of forming the release layer) was 120° C. or less, similarly to Comparative Example 2, the decrease in polarization degree after the humidification endurance test was large, and marked uneven streaks were observed.

In the optical films of Examples 1 to 4 in which the releasing layer of 50 nm to 250 nm was formed at a stretching temperature of 140° C., no white turbidity due to aggregation of fine particles was observed, and a good appearance was exhibited. Further, in the optical film of Example 1, a fine wound was observed on the non-release layer formed surface, but was buried by an adhesive or an adhesive during bonding with other members, and thus was a wound at a level at which no optical defects would occur. Moreover, compared with the polarizing plate using the optical film of Comparative Example 2, the polarizing plate using the optical film of Examples 1-4 was excellent in humidification durability, and generation|occurrence|production of uneven streaks was suppressed.

The optical film of Comparative Example 1 in which the release 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-release layer formed surface were observed, and the appearance was deteriorated. It is considered that the occurrence of the wound is due to the fact that the silica fine particles are removed from the surface of the lubricating layer due to the decrease in dispersibility, and the sliding property of the optical film is decreased.

From the comparison between Examples 1 to 4 and Comparative Examples 1 and 2, it was found that the smaller the thickness of the release layer and the smaller the residual alkali component, the more the occurrence of streaks after the humidification durability test was suppressed, and a polarizing plate excellent in humidification durability was obtained. I can. On the other hand, when the thickness of the lubricating layer is excessively small and the residual alkali component is excessively small, it can be seen that poor appearance and poor sliding properties occur due to a decrease in the dispersibility of the fine particles.

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

From these results, it is understood that an optical film excellent in humidification durability of a polarizing plate can be obtained when used as a polarizer protective film by reducing the amount of alkali remaining in the lubricating layer within a range not reducing the dispersibility of the fine particles.

In Comparative Examples 3 to 5, which was stretched at a low temperature, the adhesion between the acrylic film and the release layer was deteriorated compared to other examples. In Example 3 and the like, at the interface between the acrylic film and the release layer, the interface layer (see Fig. 3) was formed in the state where the particles were embedded in the acrylic film, whereas in Comparative Examples 3 to 5, the interface layer was not formed. Did not (see Fig. 4). From these results, in addition to being able to efficiently volatilize the alkali component in the release layer-forming composition by increasing the heating temperature after applying the release layer-forming composition to reduce the amount of remaining alkali, the film substrate and the release layer It can be seen that the adhesion at the interface can be improved.

1: optical film
11: film substrate
15: dividing layer
2: transparent film
5: polarizer
6, 7: adhesive layer
100, 101: polarizer

Claims (19)

As an optical film comprising a release layer on the surface of a transparent film substrate,
The release layer contains a binder resin and fine particles,
An optical film in which the content of the alkali component in the release layer is 5 to 75 ppm. The method of claim 1,
An optical film having a thickness of the release layer of 40 to 280 nm. The method according to claim 1 or 2,
An optical film in which a region in which the fine particles are embedded in the transparent film substrate is present at the interface between the transparent film substrate and the release layer. The method according to any one of claims 1 to 3,
The optical film in which the fine particles are inorganic fine particles. The method according to any one of claims 1 to 4,
An optical film having an average primary particle diameter of the fine particles of 10 to 250 nm. The method according to any one of claims 1 to 5,
The optical film in which the content of the fine particles in the release layer is 3 to 50% by weight. The method according to any one of claims 1 to 6,
The optical film in which the transparent film substrate is an acrylic film. The method according to any one of claims 1 to 7,
The optical film in which the binder resin of the release layer is a urethane-based resin. As a method for producing the optical film according to any one of claims 1 to 8,
On the surface of the transparent film substrate, a binder resin or a composition for forming a release layer containing a precursor thereof, fine particles, an alkali component, and a solvent is applied,
A method for producing an optical film in which the solvent and the alkali component are volatilized by heating the composition for forming a release layer at a temperature higher than the glass transition temperature of the transparent film substrate by 10° C. The method of claim 9,
The method for producing an optical film in which the alkali component has a function of promoting dispersion of the inorganic fine particles. The method of claim 9 or 10,
The composition for forming the release layer contains a polyurethane precursor as a precursor of the binder resin, and a tertiary amine as the alkali component. The method according to any one of claims 9 to 11,
The method for producing an optical film, wherein the composition for forming an lubricating layer contains an amine having a boiling point of 150°C or less as the alkali component. The method according to any one of claims 9 to 12,
A method for producing an optical film in which the transparent film substrate coated with the release layer-forming composition is stretched in at least one direction while heating the release layer-forming composition at a temperature higher than the glass transition temperature of the transparent film substrate by 10°C or more . A polyvinyl alcohol-based polarizer having a first main surface and a second main surface, and a transparent film bonded to the first main surface of the polarizer through an adhesive layer,
The said transparent film is a polarizing plate which is the optical film in any one of Claims 1-8. The method of claim 14,
A polarizing plate in which the release layer non-forming surface of the optical film is bonded to the first main surface of the polarizer. The method of claim 15,
A polarizing plate in which the non-release layer formed surface of the optical film is bonded to the first main surface of the polarizer through a photocationic polymerizable adhesive or a hybrid adhesive of photocationic polymerization and photoradical polymerization. The method of claim 14,
A polarizing plate in which the release layer formation surface of the optical film is bonded to the first main surface of the polarizer. The method of claim 17,
A polarizing plate in which the non-release layer formed surface of the optical film is bonded to the first main surface of the polarizer through a photoradically polymerizable adhesive. An image display device comprising an image display cell and a polarizing plate according to any one of claims 14 to 18.

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