KR102544911B1 - Polarizer and image display device - Google Patents

Abstract

Provided is a polarizing plate in which stripe-like stains are unlikely to occur even when exposed to a high-temperature, high-humidity environment for a long time and exhibits excellent display uniformity. In the polarizing plate 100, a transparent protective film 1 is bonded to one surface of a polyvinyl alcohol-based polarizer 5 via an adhesive layer 6. The transparent protective film (1) is provided with an easily adhesive layer (15) on the surface of an acrylic film (11). The easily bonding layer 15 contains a urethane resin and fine particles, and has a thickness of 280 nm or less.

Description

Polarizer and image display device

The present invention relates to an easily-adhesive film having an easily-adhesive layer on the surface of a transparent film, and a polarizing plate in which the easily-adhesive film is bonded together as a transparent protective film on the surface of a polarizer. Further, the present invention relates to 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 display devices and organic EL display devices are widely used. In the liquid crystal display device, a polarizing plate is arranged on the viewing side surface of the liquid crystal cell from the display principle. In a transmissive liquid crystal display device, polarizers are arranged on both sides of a liquid crystal cell. In an organic EL display device, a circularly polarizing plate (typically, a laminate of a polarizing plate and a quarter wave plate) is disposed on the viewing side surface in order to prevent external light from being reflected by a metal electrode (cathode) and being viewed as a mirror surface. There may be cases

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

As a transparent protective film bonded to the surface of the polarizer, cellulose-based films such as cellulose acetate are widely used because of their excellent adhesiveness with PVA-based polarizers. As the transparent protective film, an acrylic film is also intended to be used. Since an acrylic film has lower moisture permeability than a cellulose film, a polarizing plate using an acrylic transparent protective film tends to have a small change in optical properties and excellent durability even when exposed to a high humidity environment for a long time. Further, since the acrylic film has low birefringence, improvement in optical properties (for example, reduction of light leakage in an image display device) can also be expected.

Acrylic films tend to have lower adhesion to PVA-based polarizers than cellulose-based films. In order to improve the adhesion between the PVA-based polarizer and the acrylic film, it has been proposed to form an easily bonding layer on the surface of the acrylic film. For example, Patent Literature 1 discloses that an easily adhesive film having an easily adhesive layer containing a urethane-based resin formed on the surface of an acrylic film has excellent adhesiveness with a PVA-based polarizer. Further, in Patent Document 1, it is described that by containing fine particles in the easily adhesive layer, blocking when the easily adhesive film is wound in a roll shape can be suppressed, and an average thickness of 400 nm (thickness) containing 1 to 7% by weight of fine particles An example in which a polarizing plate was produced using an easily adhesive film provided with a urethane easily adhesive layer having a range of 300 to 500 nm) as a polarizer protective film is shown.

Japanese Patent No. 5354733

While the size of the image display device and the increase in brightness are progressing, a polarizing plate constituting the image display device is required to have a small change in optical characteristics even in a harsher environment (eg, higher temperature and higher humidity conditions). A polarizing plate using an acrylic transparent protective film having an easily bonding layer described in Patent Document 1 has excellent adhesion between a polarizer and a transparent protective film, and has high adhesion reliability. However, upon examination by the present inventors, when the polarizing plate provided with the easily adhesive film disclosed in Patent Literature 1 is exposed to a high humidity environment for a long time, stripe-like unevenness is formed on the polarizing plate, resulting in a deterioration in display characteristics. It became.

In view of the above problems, an object of the present invention is to provide an easily adhesive film usable as a polarizer protective film. Another object of the present invention is to provide a polarizing plate having excellent adhesion between a polarizer and a transparent protective film, and excellent uniformity of display that does not cause stripe-like unevenness even when exposed to a high-temperature, high-humidity environment for a long time.

The easily-adhesive film of the present invention is provided with an easily-adhesive layer on the surface of an acrylic film. The polarizing plate of the present invention includes a transparent protective film bonded to one surface of a polyvinyl alcohol-based polarizer through an adhesive layer. A transparent protective film may be provided also on the other side of the polarizer.

It is preferable that the transparent protective film bonded to one surface of the polarizer is an easily bonding film equipped with an easily bonding layer on the surface of an acrylic film, and that the bonding easily bonding layer formation surface is bonded to the polarizer. The easily bonding layer formed on the surface of the acrylic film contains a urethane resin and fine particles, and has a thickness of 280 nm or less.

The thickness of the easily bonding layer is preferably 50 nm or more. As for content of the microparticles|fine-particles in an easily bonding layer, 8 to 50 weight% is preferable. It is preferable that content of an alkali component of an easily bonding layer is 5 ppm or less.

The polarizing plate provided with the easily-adhesive film of the present invention is hard to generate stripe-shaped stains even when exposed to a high-temperature, high-humidity environment for a long time, and has excellent durability. Therefore, an image display device excellent in display uniformity can be obtained by using the polarizing plate of the present invention.

1 is a cross-sectional view showing a structural example of an easily adhesive film.
2 is a schematic cross-sectional view showing a laminated structure of a polarizing plate according to an embodiment.
3 is an orthogonal nicol observation photograph of the polarizing plates of Examples 1 and 2 and Comparative Example 1 before and after the heating and humidification endurance test.
4 is an orthogonal nicol observation photograph of the polarizing plates of Example 4 and Comparative Example 2 before and after the heating/humidification durability test.

1 is a schematic cross-sectional view showing a configuration example of an easily adhesive film according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a laminated configuration of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes a first transparent protective film 1 bonded to one surface (first main surface) of the polarizer 5 via an adhesive layer 6 . The first transparent protective film 1 is an easily adhesive film, and has an easily adhesive layer 15 on the surface of an acrylic film 11 . It is preferable that the 2nd transparent protective film 2 is bonded to the other surface (2nd main surface) of the polarizer 5 via the adhesive bond layer 7.

[Transparent protective film (easily adhesive film)]

The transparent protective film 1 bonded to one side of the polarizer 5 is an easily adhesive film provided with an easily adhesive layer 15 on one side of an acrylic film 11 . In the case of producing the polarizing plate, it is preferable that the easily bonding layer 15 formed surface of the transparent protective film 1 is bonded to the PVA-based polarizer 5 via the adhesive layer 6.

<Acrylic film>

The acrylic film 11 includes an acrylic 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, methyl (meth)acrylate-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate -(meth)acrylic acid norbornyl copolymer, etc.).

In this specification, "(meth)acryl" means an acryl and/or methacryl. 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.

Acrylic resins having a glutaric anhydride structure described in Japanese Unexamined Patent Publication No. 2006-283013, Japanese Unexamined Patent Publication No. 2006-335902, Japanese Unexamined Patent Publication No. 2006-274118, etc. as the acrylic resin; and/or Japanese Unexamined Patent Publication No. 2000-230016, Japanese Unexamined Patent Publication No. 2001-151814, Japanese Unexamined Patent Publication No. 2002-120326, Japanese Unexamined Patent Publication No. 2002-254544, Japanese Unexamined Patent Publication No. 2005-146084, etc. You may use acrylic resin which has a tone ring structure. Since the acrylic resin having a glutaric anhydride structure and the acrylic resin having a lactone ring structure have high heat resistance, high transparency and high mechanical strength, they are suitable for producing a polarizing plate having a high degree of polarization and excellent durability.

The content of the acrylic resin in the acrylic film 11 is preferably 50% by weight or more, more preferably 60 to 98% by weight, still more preferably 70 to 97% by weight. The acrylic film 11 may contain a thermoplastic resin other than the acrylic resin. For example, by blending another thermoplastic resin, 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 or the like, a thermoplastic resin other than the acrylic resin may be blended.

Examples of 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, polyethersulfone, polyoxybenzylene, polyamideimide, rubber polymers and the like.

The acrylic film 11 may contain additives such as antioxidants, stabilizers, reinforcing agents, ultraviolet absorbers, flame retardants, antistatic agents, colorants, fillers, plasticizers, lubricants and fillers. You may form a film after mixing an acrylic resin, another thermoplastic resin, an additive, etc. and setting it as a thermoplastic resin composition, such as a pellet, beforehand.

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

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

The glass transition temperature Tg of the acrylic film 11 is preferably 100°C or higher, more preferably 110°C or higher, and still more preferably 120°C or higher. As described above, by using an acrylic resin having a glutaric anhydride structure or an acrylic resin having a lactone ring structure as the acrylic resin, the Tg of the acrylic film 11 can be increased and heat resistance can be improved. The upper limit of the Tg of the acrylic film 11 is not particularly limited, but is preferably 170°C or less from the viewpoint of moldability and the like.

<Easily bonding layer>

The adhesive layer 15 provided on the surface of the acrylic film 11 includes a urethane resin and fine particles. By providing the easily bonding layer 15 containing a urethane resin, the adhesiveness of the easily bonding film 1 and the polarizer 5 can be improved. When the easily bonding layer 15 contains fine particles, fine unevenness is formed on the surface of the easily bonding film 1, and the sliding property of the film is improved. Therefore, it contributes to reduction of the damage at the time of roll conveyance of the easily adhesive film 1, and blocking suppression at the time of winding up in roll shape.

One feature of the easily-adhesive film of the present invention is that the thickness of the easily-adhesive layer 15 provided on the surface of the acrylic film 11 is 280 nm or less. By reducing the thickness of the easily bonding layer 15, even when exposed to a high-temperature, high-humidity environment for a long time, a highly durable polarizing plate with little change in polarization degree is obtained that is unlikely to generate stripe-like unevenness.

(urethane resin)

The urethane resin, which is the main component of the easily bonding layer 15, is typically a reaction product of polyol and polyisocyanate. As the polyol component, polymer polyols such as polyacrylic polyols, polyester polyols, and polyether polyols are preferably used.

Polyacrylic polyols are typically obtained by polymerization of (meth)acrylic acid esters and hydroxyl group-containing monomers. As (meth)acrylic acid ester, methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, etc. are mentioned, for example. 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 4-hydroxypropyl (meth)acrylate. Hydroxyalkylester of (meth)acrylic acid, such as hydroxybutyl and 2-hydroxypentyl (meth)acrylic acid; (meth)acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N-methylol (meth)acrylamide etc. are mentioned.

The polyacryl polyol may contain monomer components other than those described above. 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.

A polyester polyol is typically obtained by reaction of a polybasic acid and a polyol. 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, and 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 acid anhydrides, alkyl esters, and acid halides thereof.

Polyols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, and 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 heard

Polyether polyols are typically obtained by adding an alkylene oxide to a polyhydric alcohol through 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 the 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 easily bonding layer 15 preferably has a carboxyl group. When the urethane resin of the easily bonding layer 15 has a carboxyl group, introduction of a cross-linked structure becomes possible, and there is a tendency that adhesion durability between the easily bonding film 1 and the polarizer 5 or the like is improved. The urethane resin having a carboxyl group is obtained, for example, by reacting a chain lengthening agent having a free carboxyl group in addition to a polyol and 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 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-stage method in which the monomer components are reacted in stages. When introducing a carboxyl group into a urethane resin using a chain lengthening agent having a free carboxyl group, a multi-step method is preferred. In manufacture of a urethane resin, you may use a urethane reaction catalyst as needed. After applying an easily adhesive composition containing a precursor of urethane (polyol, polyisocyanate, etc.) onto an acrylic film, a urethanization reaction may be performed by heating or the like.

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. 10-50 are preferable and, as for the acid value of a urethane resin, 20-45 are more preferable.

The urethane resin of the easily bonding layer 15 may have a crosslinked structure. There exists a tendency for the adhesive durability of the easily adhesive film 1 and the polarizer 5 to improve by introduce|transducing a crosslinked structure into a urethane resin. As the crosslinking agent, those capable of reacting with the crosslinkable functional group of the urethane resin may 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 an oxazoline group has a low reactivity with a carboxyl group at normal temperature, the pot life when mixed with a urethane resin is long, and it can respond flexibly to the lead time of a process.

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

The amount of the crosslinking agent 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)

The material and particle size of the fine particles of the easily bonding layer 15 are not particularly limited as long as they can form fine concavo-convex shapes on the surface of the easily bonding layer. From the viewpoint of improving the sliding properties of the easily adhesive film 1 by the concavo-convex shape on the surface of the easily adhesive layer, the particle diameter (average primary particle diameter) of the fine particles is preferably 10 nm or more, more preferably 15 nm or more, and 20 nm The above is more preferable. When 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 urethane resin and the fine particles is suppressed, and the influence on optical properties such as depolarization of the polarizing plate can be reduced. Therefore, the particle diameter of the fine particles is preferably 150 nm or less, more preferably 100 nm or less, still more preferably 60 nm or less, and particularly preferably 50 nm or less.

The fine particles may be any of inorganic fine particles and organic fine particles. Examples of inorganic fine particles include inorganic oxides such as silica, titania, alumina, and zirconia; Calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. are mentioned. Examples of the organic fine particles include silicone-based resins, fluorine-based resins, and acrylic resins. In order to suppress light scattering caused by the fine particles, it is preferable that the difference in refractive index between the urethane resin and the fine particles is small. Since the refractive index difference with the urethane resin is small and the dispersibility is excellent, as the fine particles of the easily bonding layer 15, inorganic fine particles are preferred, and silica particles are particularly preferred.

When forming the easily bonding layer 15 with an aqueous composition, it is preferable to use fine particles having high water dispersibility. An aqueous dispersion of microparticles may be blended into the composition. In order to improve the dispersibility of the fine particles, it is preferable to make the easily adhesive composition weakly alkaline by adding an alkali component such as amine or ammonia.

As the water-dispersible silica particles, colloidal silica is preferably used. As colloidal silica, you may use commercially available products, such as the Quartron PL series by Fuso Chemical Co., Ltd., the SNOWTEX series by Nissan Chemical Industries, Ltd., the AERODISP series by Nippon Aerosil Co., Ltd., and the AEROSIL series.

From the viewpoint of improving the sliding properties of the easily bonding film 1 by forming irregularities on the surface of the easily bonding layer 15, the content of fine particles in the easily bonding layer 15 is preferably 8% by weight or more, and is 10% by weight. The above is more preferable, and 12% by weight or more is even more preferable. In the easily bonding film of the present invention, since the thickness of the easily bonding layer 15 is as small as 280 nm or less, the content of the microparticles is increased to increase the amount (number density) of the microparticles per unit area to uniformly form irregularities on the surface of the easily bonding layer 15. It is desirable to form When the content of the fine particles in the easily bonding layer 15 is excessively large, a decrease in optical properties due to an increase in light scattering at the interface between the urethane resin and the fine particles may be caused. Moreover, since the relative content of a urethane resin becomes small with the increase of fine particle content, the adhesiveness of the easily adhesive film 1 and the polarizer 5 may fall. Therefore, the content of the fine particles in the easily bonding layer 15 is preferably 50% by weight or less, more preferably 40% by weight or less, and still more preferably 30% by weight or less.

In the easily bonding layer 15, the amount of the fine particles relative to 100 parts by weight of the urethane resin (total of the urethane resin and the crosslinking agent when the crosslinking agent is included) is preferably 11 to 100 parts by weight, more preferably 12 to 65 parts by weight, and 13 -40 parts by weight is more preferred.

(Amount of remaining alkali)

When an alkali component such as amine or ammonia is used to enhance the dispersibility of the fine particles, the alkali component inevitably remains in the easily bonding layer. In the polarizing plate in which the easily-adhesive film 1 is bonded to the surface of the polarizer 5, when the remaining alkali component of the easily-adhesive layer 15 is eluted by moisture or the like, the polarizer is deteriorated and the polarization degree of the polarizing plate is lowered or the stripe-shaped Optical defects such as stains may occur.

From the viewpoint of enhancing the humidification durability of the polarizing plate, the amount of residual alkali in the easily bonding 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 amount of residual alkali in the easily bonding layer 15 is preferably as small as possible.

On the other hand, when the amount of residual alkali in the easily bonding layer 15 is excessively small, the dispersibility of the fine particles is impaired, and appearance defects such as cloudiness due to aggregation of the fine particles may occur. In addition, due to aggregation of fine particles due to a decrease in dispersibility or dropout of fine particles from the easily bonding layer, appropriate unevenness is not formed on the surface of the easily bonding layer, and the sliding property of the easily bonding film tends to decrease. Therefore, the amount of residual alkali in the easily bonding layer 15 is preferably 5 ppm or more, more preferably 10 ppm or more, and still more preferably 20 ppm or more.

The amount of alkali in the easily bonding layer can be quantified by liquid chromatography, ion chromatography or the like depending on the type of alkali component. Alkaline components may be quantified by an analytical method (for example, LC/MS) in which chromatography and mass spectrometry (MS) are combined. When a plurality of alkali components are contained in the easily bonding layer, the total of each component is referred to as the alkali component content (residual amount) of the easily bonding layer. When quantifying the amount of alkali in the easily bonding layer from a polarizing plate in which an easily bonding film and a polarizer are bonded together, the amount of alkali eluted by immersing the polarizing plate in warm water or the like to dissolve the easily bonding layer together with the polarizer may be quantified.

<Formation of easily bonding layer>

The method of forming the easily bonding layer 15 on the surface of the acrylic film 11 is not particularly limited. Preferably, the easily adhesive layer 15 is formed by applying an easily adhesive composition (solution) containing a urethane resin or its precursor and fine particles onto the acrylic film 11 and drying it.

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

You may perform surface treatment of the acrylic film 11 before formation of the easily bonding layer 15. By surface treatment, the wetting tension of the acrylic film 11 can be adjusted, and adhesiveness with the easily bonding layer 15 can be improved. Examples of the surface treatment include corona treatment, plasma treatment, ozone blowing, ultraviolet irradiation, flame treatment, and chemical treatment. Among these, corona treatment or plasma treatment is preferable.

(Easy-adhesive composition)

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

The water-based easily adhesive composition includes water as a solvent (and dispersion medium), a urethane resin or a precursor thereof, and fine particles, and further includes a crosslinking agent as necessary. It is preferable that the easily bonding composition further contains an alkali component. As described above, the alkaline component has an effect of accelerating the dispersion of fine particles. Therefore, when the easily bonding composition contains an alkali component, the dispersibility of the fine particles is improved, and an easily bonding film having excellent appearance and sliding properties is obtained.

On the other hand, if the alkali contained in the easily bonding composition remains in the easily bonding layer, it may cause a decrease in 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 alkaline component contained in an easily adhesive composition, weak alkali components, such as ammonia and an amine, are preferable. As for the pH of an easily bonding composition (coating liquid), about 7.5-9 are preferable from a viewpoint of achieving both the improvement of the dispersibility of microparticles|fine-particles, and prevention of deterioration of a polarizer.

From the viewpoint of improving the dispersibility of the fine particles, the amount of the alkali component contained in the easily bonding composition is preferably 300 ppm or more, and more preferably 500 ppm or more with respect to the solid content of the easily bonding composition. On the other hand, when the content of the alkali component is excessively large, it may be difficult to reduce the amount of residual alkali. Therefore, the amount of the alkali component contained in the easily bonding composition is preferably 50000 ppm or less, and 10000 ppm or less with respect to the solid content of the easily bonding composition. is more preferable, and 5000 ppm or less is even more preferable.

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

By heating after apply|coating the easily bonding composition on the acrylic film 11, the alkali component can be volatilized off and the remaining alkali component of the easily bonding layer 15 can be reduced. It is preferable that the boiling point of the alkali component contained in an easily bonding composition from a viewpoint of accelerating volatilization of the alkali component by heating is 150 degreeC or less. The boiling point of the alkali component is more preferably 130°C or lower, more preferably 120°C or lower, and particularly preferably 110°C or lower. The boiling point of the alkali component may be 100°C or lower or 90°C or lower. When a some alkali component is contained in an easily bonding composition, it is preferable that the boiling point of at least 1 alkali component is the said range, and it is preferable that the boiling point of two or more alkali components is the said range. It is preferable that the boiling point of 50% by weight or more of the alkali component is in the above range with respect to 100 parts by weight of the total amount of alkali contained in the easily bonding layer. It is ideal that the boiling points of all the alkali components contained in the easily adhesive composition are within the above range.

The easily bonding composition may contain resin components and additives other than the urethane resin. Examples of additives include catalysts such as crosslinking accelerators, antioxidants, ultraviolet absorbers, leveling agents, antiblocking agents, antistatic agents, dispersion stabilizers, antifoaming agents, thickeners, dispersants, surfactants, and lubricants.

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

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

The smaller the thickness of the easily bonding layer 15 is, the more the humidification durability of the polarizing plate is improved, and the occurrence of streak-like stains tends to be suppressed. In addition, the smaller the thickness of the easily bonding layer 15, the lower the polarization degree and the single transmittance when the polarizing plate is exposed to a humid environment tends to be suppressed. On the other hand, when the thickness of the easily bonding layer 15 is too small, the adhesiveness of the easily bonding film 1 and the polarizer 5 may fall. Therefore, the thickness of the easily bonding layer 15 is preferably 50 nm or more, more preferably 80 nm or more, and still more preferably 100 nm or more. The thickness of the easily bonding layer 15 may be 110 nm or more, 120 nm or more, 130 nm or more, or 140 nm or more. When the thickness of the easily adhesive layer is within the above range, in addition to excellent adhesiveness between the easily adhesive film and the polarizer, the processability when cutting the polarizing plate into a predetermined sheet size is excellent, and the occurrence of microcracks tends to be suppressed. there is.

The thickness of the easily bonding layer 15 can be made into the said range by adjusting the solid content concentration of an easily bonding composition and application|coating thickness. The thickness of the easily bonding layer 15 in the polarizing plate is obtained from cross-section observation of the polarizing plate. When there is unevenness in thickness, let the average thickness in an observation range be the thickness of an easily bonding layer.

When the easily bonding composition contains an alkali component, the volatilization and removal efficiency of the alkali component by heating tends to increase as the thickness of the easily bonding layer decreases. It is preferable that the thickness of the easily bonding layer 15 is the said range also from a viewpoint of maintaining the residual amount of an alkali component in an appropriate range, and ensuring the dispersibility of microparticles|fine-particles, and improving heat-and-moisture resistance of a polarizing plate.

[Polarizer]

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

In the manufacturing process of the polarizer 5, processes, such as water washing, swelling, and bridge|crosslinking, may be performed as needed. Stretching may be performed before or after iodine dyeing, or stretching may be performed while dyeing. Stretching may be either stretching in air (dry stretching) or stretching in water or in an aqueous solution containing boric acid, potassium iodide or the like (wet stretching), or a combination thereof. 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 type polarizer having a thickness of 10 µm or less may be used. As a thin polarizer, for example, Japanese Patent Laid-Open No. 51-069644, Japanese Patent Laid-Open No. 2000-338329, WO2010/100917, pamphlet, Japanese Patent No. 4691205, Japanese Patent No. 4751481, etc. A thin polarizer is mentioned. These thin polarizers are obtained by a manufacturing method including a process of stretching a PVA-based resin layer and a resin substrate for stretching in a laminated state, and a process of dyeing with iodine. According to this manufacturing method, since the PVA-based resin layer is supported by the resin base material for stretching even if it is thin, stretching can be performed without defects such as breakage due to stretching.

<Adhesive>

The material of the adhesive layer 6 used for bonding the polarizer 5 and the easily adhesive film 1 is not particularly limited as long as it is optically transparent, such as water-based adhesives, solvent-based adhesives, hot melt adhesives, radical polymerization curing type adhesives, etc. Various types of are used. Among these, a water-based adhesive or an active energy ray curable adhesive is preferable from the viewpoint of high adhesiveness with the PVA-based polarizer 5 and the urethane easily bonding layer 15.

As the polymer component of the water-based adhesive, vinyl polymer, gelatin, vinyl latex, polyurethane, polyester, epoxy and the like can be exemplified. Among these, from the point which is excellent in the adhesiveness of the polarizer 5 and the easily adhesive film 1, a vinyl polymer is preferable and a polyvinyl alcohol-type resin is especially preferable. Among the polyvinyl alcohol-based resins, polyvinyl alcohol containing an acetoacetyl group is preferred.

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 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 polymers such as polyvinyl alcohol-based resin. As the crosslinking agent, a compound having at least two functional groups having reactivity with the polymer constituting the adhesive is used in one molecule. Examples of crosslinking agents for polyvinyl alcohol-based resins include alkylene diamines; isocyanates; epoxies; aldehydes; and amino-formaldehyde such as methylol urea and methylolmelamine. Among these, amino-formaldehyde is preferable. As the amino-formaldehyde resin, a compound having a methylol group is preferred, and methylolmelamine is particularly preferred. 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 water-based adhesive composition is preferably an aqueous solution. From the viewpoint of applicability, solution stability, etc., the resin concentration of the water-based adhesive solution is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight. The viscosity of the water-based adhesive composition is preferably about 1 to 50 mPa·s.

An active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization, or anion polymerization by irradiation with active energy rays such as electron beams or ultraviolet rays. Among them, a photo-radically polymerizable adhesive in which radical polymerization is initiated by irradiation of 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. Especially, the compound which has 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 are hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide Nitrogen-containing monomers such as amide and (meth)acryloylmorpholine may be included. As a cross-linking component, the radically polymerizable adhesive includes tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, and dioxane glycol diacrylate. , polyfunctional monomers such as EO-modified diglycerol tetraacrylate may be included.

Photocurable adhesives such as radically photopolymerizable adhesives preferably contain a photopolymerization initiator. What is necessary is just to select a photoinitiator suitably according to a reactive species. For example, it is preferable to incorporate a photoradical generating agent that generates radicals upon irradiation with light as a photopolymerization initiator in the radically polymerizable adhesive. 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. In the case of using a radically polymerizable adhesive as an electron beam curing type, a photopolymerization initiator is not particularly required. A photosensitizer represented by a carbonyl compound or the like may be added to the radically polymerizable adhesive if necessary. Photosensitizers are used to increase the curing speed and sensitivity by electron beams. The 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 composition may contain suitable additives as needed. Examples of additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, deterioration inhibitors, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, fillers, plasticizers, and leveling agents. agents, foam inhibitors, antistatic agents, heat-resistant stabilizers, hydrolysis-resistant stabilizers and the like.

[Production of Polarizing Plate]

A polarizing plate is manufactured by bonding easily adhesive film 1 to one surface (1st main surface) of polarizer 5 via adhesive bond layer 6. Specifically, by applying an adhesive composition to any one or both of the polarizer 5 and the easily adhesive film 1, bonding the polarizer 5 and the easily adhesive film 1 with a roll laminator or the like, and curing the adhesive. It is preferable to bond the polarizer 5 and the easily adhesive film 1 together.

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

As a coating method of the adhesive composition to the polarizer 5 and/or the easily adhesive film 1, a roll method, a spray method, a dipping method, etc. are mentioned. Before applying the adhesive composition to the surfaces of the polarizer 5 and/or the easily adhesive film 1, surface treatment such as corona treatment, plasma treatment, and saponification treatment may be performed.

After bonding the polarizer 5 and the easily adhesive film 1 together, the adhesive layer 6 is formed by hardening the adhesive depending on the type of adhesive. When a water-based adhesive is used, the adhesive is cured by heating and drying. The drying time is typically 120 seconds or longer, preferably 300 seconds or longer.

<Second transparent protective film>

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

Examples of the material forming the second transparent protective film 2 include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); cellulosic polymers such as diacetyl cellulose and triacetyl cellulose; Styrene-type polymers, such as polystyrene and an acrylonitrile-styrene copolymer; cyclic polyolefins such as polynorbornene; Polycarbonate etc. are mentioned.

As the second transparent protective film 2, an acrylic film may be used. When the second transparent protective film 2 is an acrylic film, the same film as the acrylic film 11 of the first transparent protective film 1 can be used. When the second transparent protective film 2 is an acrylic film, the durability of the polarizing plate tends to be improved compared to the case where a cellulose film is used.

The second transparent protective film 2 may include an easily bonding layer (not shown). When the 2nd transparent protective film 2 is an acrylic film, it is preferable to provide an easily bonding layer similarly to the 1st transparent protective film 1. When the second transparent protective film 2 is an acrylic film, as the easily adhesive layer provided on the surface thereof, as in the easily adhesive layer 15 of the first transparent protective film 1, an easily adhesive layer containing a urethane resin and fine particles desirable.

When both of the transparent protective films 1 and 2 bonded to the surface of the polarizer 5 are alkali-based films having an easily adhesive layer, generation of streak-like stains when the polarizer is exposed to a high-temperature and high-humidity environment is more likely. tends to become prominent. In addition to the easily bonding layer 15 provided on the surface of the transparent protective film 1, the thickness of the easily bonding layer provided on the surface of the second transparent protective film is 280 nm or less, when an acrylic film is used as the double-sided transparent protective film. A polarizing plate with excellent humidification durability is obtained, in which even streak-like unevenness is less likely to occur.

As the adhesive layer 7 used for bonding the polarizer 5 and the second transparent protective film 2, various types of adhesives such as water-based adhesives, solvent-based adhesives, hot-melt adhesives, and radical polymerization curable adhesives are used. Among them, a water-based adhesive containing a polyvinyl alcohol-based resin and a crosslinking agent is preferred, similarly to the easily bonding layer 6 used for bonding the polarizer 5 and the first transparent protective film 1. You may use the same adhesive composition for the adhesive layer 6 and the adhesive layer 7. After laminating the first transparent protective film 1 on the first main surface of the polarizer 5 and laminating the second transparent protective film 2 on the second main surface of the polarizer 5, the polarizer 5 ) may simultaneously cure the adhesive layers 6 and 7 on the front and back.

<Estimation principle of stripe speckle suppression>

As described above, in the polarizing plate in which the easily bonding layer 15 formed surface of the easily bonding film 1 is bonded to the polarizer, the smaller the thickness of the easily bonding layer 15 is, the more the durability of the polarizing plate is improved and the occurrence of streak-like unevenness is suppressed. tend to become The main cause of stripe unevenness is the detachment of iodine ions (l ₃ ^- and l ₅ ^- ) from the polarizer, and since the detachment of iodine ions from the polarizer is suppressed as the thickness of the easily adhesive layer is reduced, it is said that the occurrence of stripe unevenness is suppressed. I think.

In a PVA-based polarizer adsorbed with iodine, a polymer chain of PVA and iodine ions form a complex, and when the PVA-based polarizer is exposed to a high-temperature, high-humidity environment, iodine ions are desorbed from the PVA chain. Desorption of iodine ions from the PVA chain can be expressed by the following formula.

In the PVA-based polarizer, iodine exists in a constant ratio between l ₃ ^- ions and l ₅ ^- ions, but since free l ₃ ^- ions detached from the PVA chain are unstable, l ₃ ^- ions and iodine (l ₂ ) are formed. do. If free iodine and iodine ions remain in the polarizer, the elimination reaction of iodine ions from the PVA chain will hardly proceed. On the other hand, when the concentration of free iodine in the polarizer decreases due to sublimation of iodine or mass transfer of iodine and iodide ions, an action of advancing the reaction in the right-hand direction occurs, so that iodine ions are further desorbed from the PVA chain. .

It is considered that the urethane-based easily bonding layer has an action of occluding iodine and/or iodine ions desorbed from the PVA chain of the polarizer. Since the occlusion amount of iodine and/or iodine ion is large when the thickness of the easily bonding layer is large, free iodine and/or iodine ions in the polarizer easily move from the polarizer to the easily bonding layer. When free iodine and/or iodine ions move from the polarizer to the easily bonding layer, since the reaction proceeds in the right-side direction, desorption of iodine ions from the polarizer tends to proceed, which may cause stripe unevenness.

Conversely, when the thickness of the easily bonding layer is small, since the occlusion amount of iodine and/or iodine ions by the easily bonding layer is small, even if iodine ions are desorbed from the PVA chain of the polarizer, it is easy to stay in the polarizer. If free iodine or iodine ions remain in the system, since the reaction rate from the left side to the right side of the above reaction (i.e., the rate of iodine ion desorption from the PVA chain) is small, the desorption of iodine ion from the PVA chain is suppressed, resulting in stripes. It is thought that staining is suppressed.

[Use of polarizer]

You may provide the adhesive layer for bonding to a liquid crystal cell, an organic electroluminescent cell, etc. to the polarizing plate of this invention. As the pressure-sensitive adhesive forming the pressure-sensitive adhesive layer, those having acrylic polymers, silicone-based polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based or rubber-based polymers as base polymers can be appropriately selected and used. In particular, acrylic pressure-sensitive adhesives are preferred because of their excellent optical transparency, moderate wettability and cohesiveness, and excellent weather resistance and heat resistance.

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

An adhesive layer may be provided on both sides of the polarizing plate. In the case of providing the pressure-sensitive adhesive layer on both sides of the polarizing plate, the composition and thickness of the pressure-sensitive adhesive layer 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. As the separator, one obtained by coating the surface of a plastic film with a release agent such as a silicone-based release agent, a long-chain alkyl-based release agent, or a fluorine-based release agent is preferably used.

The polarizing plate of the present invention may be a laminated polarizing plate laminated with another optical layer. Examples of the optical layer include a retardation plate, a visual compensation film, and a brightness enhancing film.

An image display device can be formed by bonding the polarizing plate of the present invention to the surface of an image display cell such as a liquid crystal cell or an organic EL cell. A liquid crystal display device is formed by appropriately assembling a liquid crystal cell, a polarizing plate, and, if necessary, constituent parts such as a lighting system and assembling a drive circuit. In an organic EL display device, re-emission of reflected light of external light by a metal electrode or the like is prevented by bonding to a circular polarizing plate in which the polarizing plate of the present invention and a retardation film (typically a quarter wave plate) are bonded to the surface of an organic EL cell. By reducing it, 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 "%" below is % by weight unless otherwise specified.

[Example 1]

(Production of polarizer A)

A long roll of polyvinyl alcohol (PVA)-based resin film ("PE4500" manufactured by Kuraray Co., Ltd.) having a thickness of 45 µm was uniaxially stretched in the longitudinal direction by a roll stretching machine so as to be 5.9 times in the longitudinal direction, as shown in Table 1. The indicated swelling bath, dyeing bath, crosslinking bath 1, crosslinking bath 2, and washing bath were conveyed in this order, 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 adhesive composition)

20 parts by weight of methylolmelamine with respect to 100 parts by weight of polyvinyl alcohol-based resin containing an acetoacetyl group (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, degree of modification of acetic acetyl group: 5 mol%) under a temperature condition of 30 ° C. was dissolved in to obtain an aqueous solution having a solid content concentration of 0.5%.

(Preparation of easily adhesive composition)

21.3 parts by weight of a polyester urethane aqueous solution with a solid content of 35% (manufactured by DKS Co., Ltd. "Superflex 210"), an oxazoline-containing polymer aqueous solution with a solid content of 25% (manufactured by Nippon Shokubai Co., Ltd. "Epocros WS-700") 5.3 parts by weight, 3.2 parts by weight of 1% by weight aqueous ammonia, 7.8 parts by weight of a 20% aqueous dispersion of colloidal silica having an average primary particle size of 35 nm (“Quartron PL-3” manufactured by Fuso Chemical Industry Co., Ltd.), and 62.4 parts by weight of pure water An easily adhesive composition was prepared by mixing parts by weight. The easily bonding composition contains 15.0 parts by weight of silica particles with respect to 100 parts by weight of the solid content, and the solid content concentration is 10% by weight.

(Manufacture of easily adhesive film)

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

(Manufacture of polarizer)

As the double-sided polarizer protective film, an easily adhesive film provided with the aforementioned 110 nm easily adhesive layer was used. 30 minutes after preparing the adhesive composition, the adhesive composition was applied to the easily adhesive layer formation surface of the easily adhesive film so that the thickness after drying was 50 nm, the easily adhesive film was adhered to each of both sides of the polarizer A, and dried at 70 ° C. for 5 minutes, A polarizer was obtained.

[Example 2, Example 3, and Comparative Example 1]

In preparation of the easily bonding film of Example 1, the wire bar at the time of apply|coating the easily bonding composition was changed. The thickness of the easily bonding layer formed on the surface of the acrylic film was 60 nm in Example 2, 140 nm in Example 3, and 340 nm in Comparative Example 1. It carried out similarly to Example 1, and these easily adhesive films were bonded together on both surfaces of polarizing plate A through the adhesive agent, and the polarizing plate was obtained.

[Example 4]

(Production of polarizer B)

The iodine concentration and the potassium iodide concentration were increased so that the single transmittance of the polarizer was 42.1% while maintaining the ratio of iodine and potassium iodide in the dyeing bath to 1:7. Other than that, it carried out similarly to preparation of polarizer A, and produced the polarizer of thickness 18 micrometers.

(Production of easily adhesive film)

In preparation of the easily adhesive film of Example 1, the wire bar at the time of apply|coating the easily adhesive composition was changed to the wire bar of #4. The thickness of the easily bonding layer formed on the surface of the acrylic film was 240 nm.

(Manufacture of polarizer)

Using the easily-adhesive film provided with the said 240 nm easy-adhesive layer as a polarizer protective film, the easily-adhesive film was bonded to both surfaces of polarizer B in the same procedure as Example 1, and the polarizing plate was obtained.

[2 to compare]

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

[evaluation]

<Amount of Residual Alkali in Easily Adhesion Layer>

The quantities of triethylamine and ammonia remaining in the easily bonding layer of the easily bonding film before bonding to the polarizer were quantified. The residual amount of triethylamine was measured by weighing the powder obtained by scraping the easily adhesive layer from the surface of the easily adhesive film, dissolving it in methanol, and quantifying the solution by gas chromatography mass spectrometry (GC/MS). The remaining amount of ammonia was determined by immersing the easily adhesive film in pure water at 25°C, followed by extraction with heat in a dryer at 120°C for 60 minutes, and ammonia eluted in water was quantified by ion chromatography. The sum of the amount of triethylamine and the amount of ammonia was taken as the amount of residual alkali.

<Adhesive Strength>

The polarizing plate was cut into a size of 200 mm in parallel with the stretching direction of the polarizer (in the direction of the absorption axis) and 20 mm in the orthogonal direction (in the direction of the transmission axis), and a cut was made between the easily adhesive film and the polarizer with a cutter knife to bond the polarizing plate to the glass plate. . A peeling test was conducted at a peeling angle of 90° and a peeling speed of 1000 mm/min using a tensile compression tester (MINEBEA CO., LTD. "TG-1 kN") to measure the adhesive strength.

<humidification durability>

A polarizing plate was cut out to a size of 320 mm x 240 mm, and bonded on a glass plate through an acrylic pressure-sensitive adhesive having a thickness of 20 µm. This sample was placed in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 90%, and held for 500 hours to conduct a heating/humidification durability test. The single transmittance and polarization degree of the polarizing plate before and after the durability test were measured, and the amount of change in the single transmittance and polarization degree was calculated. Further, another polarizing plate was placed on the polarizing plate by cross Nicols, and the presence or absence of stripe-like unevenness was confirmed by visual observation. About the polarizing plate of Example 4 and Comparative Example 2, it maintained for 120 hours in the constant-temperature, high-humidity tank of 85 degreeC temperature and 85% of relative humidity, did the heating/humidification endurance test, and evaluated similarly. The presence or absence of streak-like unevenness of the polarizing plate after the heating/humidification durability test was evaluated according to the following criteria.

○: Stripes and unevenness are not visually recognized

△: Stripes and unevenness are slightly visible

×: Stripes and unevenness are clearly recognized

Table 2 shows the structure (thickness and residual alkali amount of type of polarizer and easily bonding layer) and evaluation results of the polarizing plate of each Example and Comparative Example. Observation photographs of the polarizing plates of Examples 1, 2, and Comparative Example 1 at Cartesian Nicols before and after the durability test (60° C. 90% Rh 500 hours) (stain measurement system for low brightness, “EYESCALE-4W” manufactured by I System Corporation) photographed) is shown in FIG. 3 . Observation photos of the polarizing plates of Example 4 and Comparative Example 2 at Orthogonal Nicol before and after the endurance test (80°C 85%Rh 120 hours) (taken with a compact digital camera, CASIO COMPUTER CO., LTD. "EXILIM EX-ZR1100") is shown in Figure 4.

In the polarizing plate of Comparative Example 1 in which an easily adhesive film having an easily adhesive layer having a thickness of 340 nm was bonded to both sides of the polarizer A, the adhesiveness between the polarizer and the easily adhesive film was good, but after the heating and humidification durability test, stripe-like unevenness was generated. In Example 1 using an easily-adhesive film having an easily-adhesive layer thickness of 110 nm and in Example 3 using an easily-adhesive film having an easily-adhesive layer thickness of 140 nm, some stripe-like unevenness was confirmed after the heating and humidification endurance test, but comparative example Compared to 1, staining was significantly improved. In Example 2 using an easily adhesive film having a thickness of the easily adhesive layer of 60 nm, streak-like unevenness was not observed even after the heating and humidification durability test, and good durability was exhibited (see Fig. 3).

Even in the comparison between Example 4 and Comparative Example 2 using the high polarization degree polarizer B having a higher iodine concentration than that of the polarizer A, in Comparative Example 2 using an easily adhesive film provided with an easily adhesive layer having a thickness of 340 nm, the temperature was 60 ° C. and the relative humidity was 90 In Example 4, in which the thickness of the easily bonding layer was 240 nm, stripe-like unevenness was not seen, and good durability was exhibited. In the heating and humidification endurance test at a temperature of 85 ° C. and a relative humidity of 85%, stripe-like stains were also confirmed on the polarizing plate of Example 4, but the degree of staining was alleviated compared to Comparative Example 2 (see Fig. 4).

From these results, it can be seen that by reducing the thickness of the easily bonding layer provided on the surface of the acrylic film, the occurrence of streak-like unevenness when the polarizing plate is exposed to a heating/humidifying environment for a long time can be suppressed.

From the comparison between Examples 1 to 3 and Comparative Example 1 (endurance test results at a temperature of 60° C. and a relative humidity of 90%) and the comparison between Example 4 and Comparative Example 2, by reducing the thickness of the easily adhesive layer, stripe-like stains occur. In addition to this suppression, the amount of change in single transmittance or polarization degree is reduced, and it is understood that the durability of the polarizing plate is improved.

In the above Examples 1 to 4 and Comparative Examples 1 and 2, the smaller the thickness of the easily bonding layer, the smaller the amount of remaining alkali, and the tendency to suppress the occurrence of stripe-like stains after the heating and humidification endurance test. It is thought that the reduction of the amount of residual alkali in the easily bonding layer by reducing the thickness of the easily bonding layer also contributes to the durability improvement of the polarizing plate.

1: Transparent protective film (easy adhesion film)
11: acrylic film
15: easy bonding layer
2: transparent protective film
5: polarizer
6, 7: adhesive layer
100: polarizer

Claims (6)

A polyvinyl alcohol-based polarizer having a first main surface and a second main surface, and a transparent protective film bonded to the first main surface of the polarizer through an adhesive layer,
The transparent protective film has an adhesive layer on the surface of the acrylic film, and the adhesive layer forming surface is bonded to the polarizer,
The easily bonding layer contains a urethane resin and inorganic fine particles having an average primary particle size of 10 to 60 nm, and has a thickness of 110 to 250 nm,
The polarizing plate whose content of the said inorganic fine particle in the said easily bonding layer is 12 to 50 weight%. According to claim 1,
The polarizing plate whose content of the alkali component of the said easily bonding layer is 20-75 ppm. delete According to claim 1 or 2,
A polarizing plate further comprising a second transparent protective film bonded to a second main surface of the polarizer through an adhesive layer. An image display device comprising an image display cell and the polarizing plate according to claim 1 or 2. delete

Images