KR20200117974A - Polarizer and image display device - Google Patents

Abstract

Even when exposed to a high temperature and high humidity environment for a long period of time, it is difficult to generate streaky spots, and a polarizing plate having excellent display uniformity is provided. The polarizing plate 100 has a transparent protective film 1 bonded to one surface of a polyvinyl alcohol-based polarizer 5 through an adhesive layer 6. The transparent protective film 1 includes an easily adhesive layer 15 on the surface of the acrylic film 11. The easily adhesive layer 15 contains 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 to which an easily-adhesive film is bonded to the surface of a polarizer as a transparent protective film. 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 displays and organic EL displays are widely used. In a liquid crystal display device, a polarizing plate is disposed on the surface on the visual 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 a metal electrode (cathode) and being visually recognized like a mirror surface. There are cases.

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

As a transparent protective film to be bonded to the surface of a polarizer, a cellulose-based film such as cellulose acetate is widely used because of its excellent adhesion to a PVA-based polarizer. As the transparent protective film, an acrylic film is also intended to be used. Since the acrylic film has a lower moisture permeability than the cellulose film, the polarizing plate using the acrylic transparent protective film tends to exhibit 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 a low birefringence, an improvement in optical properties (for example, reduction of light leakage in an image display device) can be expected.

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

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 characteristics even in a harsher environment (for example, conditions of higher temperature and higher humidity). The polarizing plate using the acrylic transparent protective film provided with the easily adhesive layer described in Patent Document 1 has excellent adhesion between a polarizer and a transparent protective film, and has high adhesion reliability. However, as a result of the review of the present inventors, the problem that 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 may cause streak-like unevenness on the polarizing plate, resulting in deterioration of display characteristics. Became.

In view of the above problems, the present invention aims at providing an easily adhesive film usable as a polarizer protective film. Further, an object of the present invention is to provide a polarizing plate having excellent adhesion between a polarizer and a transparent protective film and excellent in uniformity of display in which streak-like unevenness is less likely to occur even when exposed to a high temperature and high humidity environment for a long time.

The easily-adhesive film of the present invention includes an easily-adhesive layer on the surface of the acrylic film. The polarizing plate of the present invention includes a transparent protective film bonded to one side 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.

The transparent protective film bonded to one surface of the polarizer is an easily-adhesive film having an easily-adhesive layer on the surface of an acrylic film, and it is preferable that the easily-adhesive layer formation surface is bonded to the polarizer. The easily adhesive 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 adhesive layer is preferably 50 nm or more. The content of the fine particles in the easily adhesive layer is preferably 8 to 50% by weight. It is preferable that the content of the alkali component in the easily adhesive layer is 5 ppm or less.

(Effects of the Invention)

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

1 is a cross-sectional view showing a configuration example of an easily adhesive film.
2 is a schematic cross-sectional view showing a laminated configuration of a polarizing plate of an embodiment.
3 is a photograph of orthogonal Nicole observation before and after heating/humidifying durability tests of polarizing plates of Examples 1 and 2 and Comparative Example 1. FIG.
4 is a photograph of orthogonal Nicole observation before and after heating/humidifying durability tests of polarizing plates of Example 4 and Comparative Example 2. FIG.

1 is a schematic cross-sectional view showing a configuration example of an easily-adhesive film according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a lamination 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 through an adhesive layer 6. The first transparent protective film 1 is an easily adhesive film, and includes an easily adhesive layer 15 on the surface of the 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 layer 7.

[Transparent Protective Film (Easy Adhesive Film)]

The transparent protective film 1 bonded to one surface of the polarizer 5 is an easily-adhesive film including an easily-adhesive layer 15 on one surface of the acrylic film 11. When producing a polarizing plate, it is preferable that the surface of the transparent protective film 1 on which the easily adhesive layer 15 is formed is bonded to the PVA-based polarizer 5 through the adhesive layer 6.

<Acrylic film>

The acrylic film 11 contains an acrylic 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 alicyclic hydrocarbon groups (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 JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544, JP 2005-146084 A, 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 high polarization degree and excellent durability.

The content of the acrylic resin in the acrylic film 11 is preferably 50% by weight or more, more preferably 60 to 98% by weight, and still more preferably 70 to 97% by weight. The acrylic film 11 may contain 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 acrylic film 11 may contain additives such as an antioxidant, a stabilizer, a reinforcing material, an ultraviolet absorber, a flame retardant, an antistatic agent, a colorant, a filler, a plasticizer, a lubricant, and a filler. An acrylic resin may be mixed with other thermoplastic resins or additives to form a thermoplastic resin composition such as pellets beforehand, followed by film formation.

As a manufacturing method of the acrylic film 11, a solution casting method, a melt extrusion method, a calendering method, a compression molding method, etc. are mentioned. The acrylic film 11 may be either an unstretched film or a stretched film. From the viewpoint of improving mechanical strength, it is preferable to use a biaxially stretched film as the acrylic film 11. By blending another thermoplastic resin so as to cancel the birefringence of the acrylic resin, an acrylic film having small retardation and excellent optical isotropy even when stretched is 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 from the viewpoint of moldability and the like, 170°C or less is preferable.

<Easy adhesive layer>

The easily adhesive layer 15 provided on the surface of the acrylic film 11 contains a urethane resin and fine particles. By providing the easily-adhesive layer 15 containing a urethane resin, the adhesiveness between the easily-adhesive film 1 and the polarizer 5 can be improved. When the easily-adhesive layer 15 contains fine particles, fine irregularities are formed on the surface of the easily-adhesive film 1, and the sliding property of the film is improved. Therefore, it contributes to the reduction of damage at the time of roll conveyance of the easily adhesive film 1, and blocking suppression at the time of winding up in a 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 adhesive layer 15, even when exposed to a high temperature and high humidity environment for a long time, it is difficult to generate a stripe-like unevenness, and a highly durable polarizing plate with a small change in polarization degree can be obtained.

(Urethane resin)

The urethane resin, which is the main component of the easily adhesive layer 15, 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 polyol is typically obtained by polymerization of a (meth)acrylic acid ester and a hydroxyl group-containing monomer. Examples of the (meth)acrylic acid ester include methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 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. As polybasic acid, 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.

Polyols include 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.

Polyisocyanates include 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; Aromatic aliphatic diisocyanates such as dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate, and the like.

The urethane resin constituting the easily adhesive layer 15 preferably has a carboxyl group. When the urethane resin of the easily-adhesive layer 15 has a carboxyl group, introduction of a crosslinked structure becomes possible, and the adhesion durability of the easily-adhesive film 1 and the polarizer 5 tends to be improved. 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 dimethylol pentanoic 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. In the case of introducing a carboxyl group into the urethane resin using a chain lengthening agent having a free carboxyl group, a multistage method is preferred. In the production of the urethane resin, a urethane reaction catalyst may be used as necessary. An easily-adhesive composition containing a precursor of urethane (polyol, polyisocyanate, etc.) may be applied onto an acrylic film and then subjected to a urethanization reaction 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. The acid value of the urethane resin is preferably 10 to 50, more preferably 20 to 45.

The urethane resin of the easily adhesive layer 15 may have a crosslinked structure. By introducing a crosslinked structure into the urethane resin, the adhesion durability between the easily-adhesive film 1 and the polarizer 5 tends to be improved. As the crosslinking agent, those capable of reacting with the crosslinkable functional group of the urethane resin can be used without particular limitation. When the urethane resin has a 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 little 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 urethane resin is also excellent, an acrylic polymer is preferable as a crosslinking agent. In particular, when an acrylic polymer having an oxazoline group is used as a crosslinking agent, the adhesion between the easily-adhesive film 1 and the polarizer 5 tends to be improved.

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

(Fine particles)

The material and particle diameter of the fine particles of the easily-adhesive layer 15 are not particularly limited as long as it is capable of forming a fine uneven shape on the surface of the easily-adhesive layer. From the viewpoint of enhancing the sliding property of the easily-adhesive film 1 by the uneven 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 visible wavelength, 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 polarization disappearance 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 either inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include inorganic oxides such as silica, titania, alumina, and zirconia; Calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like. Examples of the organic fine particles include silicone resins, fluorine resins, and acrylic resins. In order to suppress light scattering caused by fine particles, it is preferable that the difference in refractive index between the urethane resin and the fine particles is small. Since the difference in refractive index with the urethane resin is small and the dispersibility is excellent, inorganic fine particles are preferable as the fine particles of the easily bonding layer 15, and silica particles are particularly preferable.

When forming the easily adhesive 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 make the easily-adhesive composition weakly alkaline by adding an alkali component such as amine or ammonia.

Colloidal silica is preferably used as the water-dispersible silica particles. As colloidal silica, commercially available products such as 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. may be used.

From the viewpoint of enhancing the sliding properties of the easily-adhesive film 1 by formation of irregularities on the surface of the easily-adhesive layer 15, the content of the fine particles in the easily-adhesive layer 15 is preferably 8% by weight or more, and 10% by weight. The above is more preferable, and 12 weight% or more is still more preferable. In the easily-adhesive film of the present invention, since the thickness of the easily-adhesive layer 15 is as small as 280 nm or less, the content of the fine particles is increased to increase the amount (number density) of fine particles per unit area, thereby uniformly forming irregularities in the plane of the easily-adhesive layer 15. It is desirable to form. If the content of the fine particles in the easily adhesive layer 15 is excessively large, the optical properties may be deteriorated due to an increase in light scattering at the interface between the urethane resin and the fine particles. In addition, as the content of fine particles increases, the relative content of the urethane resin decreases, and thus the adhesiveness between the easily-adhesive film 1 and the polarizer 5 sometimes decreases. Therefore, the content of the fine particles in the easily adhesive 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 adhesive layer 15, the amount of fine particles per 100 parts by weight of the urethane resin (in the case of including a crosslinking agent, the sum of the urethane resin and the crosslinking agent) is preferably 11 to 100 parts by weight, more preferably 12 to 65 parts by weight, and 13 More preferably-40 parts by weight.

(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 easily adhesive layer. In the polarizing plate in which the easily-adhesive film 1 is bonded to the surface of the polarizer 5, when the residual alkali component of the easily-adhesive layer 15 is eluted by moisture or the like, the polarizer is deteriorated to reduce the polarization degree of the polarizing plate, or a stripe shape. Optical defects such as spots may occur.

From the viewpoint of enhancing the humidification durability of the polarizing plate, the amount of alkali remaining in the easily adhesive 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 easily-adhesive layer 15 is, the more preferable.

On the other hand, when the amount of alkali remaining in the easily adhesive layer 15 is excessively small, the dispersibility of the fine particles may be impaired, resulting in appearance defects such as white turbidity due to aggregation of the fine particles. In addition, due to aggregation of fine particles due to a decrease in dispersibility or dropping of fine particles from the easily-adhesive layer, there is a tendency that appropriate unevenness is not formed on the surface of the easily-adhesive layer, so that the sliding property of the easily-adhesive film is lowered. Therefore, the amount of alkali remaining in the easily adhesive layer 15 is preferably 5 ppm or more, more preferably 10 ppm or more, and even more preferably 20 ppm or more.

The amount of alkali in the easily bonding 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 easily adhesive layer, the total of each component is referred to as the alkali component content (remaining amount) in the easily adhesive layer. When quantifying the amount of alkali in the easily-adhesive layer from the polarizing plate in which the easily-adhesive film and the polarizer are bonded, the amount of alkali eluted by dissolving the easily-adhesive layer together with the polarizer may be quantified by immersing the polarizing plate in warm water or the like.

<Formation of Easy Adhesive Layer>

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

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

Before the formation of the easily adhesive layer 15, the acrylic film 11 may be subjected to surface treatment. By performing the surface treatment, the wetting tension of the acrylic film 11 can be adjusted, and the adhesiveness with the easily adhesive 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 preferred.

(Easy adhesive composition)

The easily adhesive composition 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 easily-adhesive composition is preferably 1 to 30% by weight, more preferably 2 to 20% by weight, and still more preferably 3 to 15% by weight.

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

On the other hand, if the alkali contained in the easily-adhesive composition remains in the easily-adhesive layer, it may be a cause of lowering the moist heat 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 the alkali component contained in the easily adhesive composition, 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 easily-adhesive composition (coating liquid) is preferably about 7.5 to 9.

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

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

By heating after applying the easily-adhesive composition on the acrylic film 11, the alkali component can be volatilized and removed, and the residual alkali component of the easily-adhesive layer 15 can be reduced. From the viewpoint of accelerating the volatilization of the alkali component by heating, the alkali component contained in the easily-adhesive composition preferably 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 easily-adhesive composition, the boiling point of at least one alkali component is preferably in the above range, and the boiling point of two or more alkali components is preferably in 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 easily adhesive layer is within the above range. Ideally, the boiling point of all the alkali components contained in the easily-adhesive composition is within the above range.

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

As a coating method of the easily adhesive composition, 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 may be mentioned. The easily-adhesive layer 15 is formed by heating the easily-adhesive composition after application to remove the solvent. The heating temperature is, for example, about 50 to 180°C. When the easily adhesive composition contains a crosslinking agent, crosslinking of the urethane resin can be promoted by heating. As described above, when the easily-adhesive composition contains an alkali component, the alkali component is volatilized and removed by heating to reduce the residual alkali component of the easily-adhesive layer 15. From the viewpoint of efficiently volatilizing and removing the alkali component contained in the easily adhesive composition, 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. . In addition, the heating temperature is preferably higher than the boiling point of the alkali component contained in the easily adhesive composition.

The thickness of the easily adhesive 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 humidified environment for a long time, occurrence of streak-like unevenness can be suppressed, thereby maintaining the in-plane uniformity of the display. From the viewpoint of suppressing the occurrence of streaky unevenness on the polarizing plate after the humidification test, the thickness of the easily adhesive layer 15 is preferably 250 nm or less, more preferably 200 nm or less, and still more preferably 170 nm or less.

As the thickness of the easily-adhesive layer 15 is smaller, the humidification durability of the polarizing plate is improved, and the occurrence of streak-like unevenness tends to be suppressed. In addition, as the thickness of the easily adhesive layer 15 is smaller, there is a tendency to suppress a decrease in polarization degree and a decrease in single transmittance when the polarizing plate is exposed to a humidified environment. On the other hand, when the thickness of the easily-adhesive layer 15 is excessively small, the adhesiveness of the easily-adhesive film 1 and the polarizer 5 may decrease. Therefore, the thickness of the easily adhesive layer 15 is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more. The thickness of the easily adhesive 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 the excellent adhesion between the easily-adhesive film and the polarizer, the workability when cutting the polarizing plate into a predetermined sheet size is excellent, and the occurrence of microcracks tends to be suppressed. have.

By adjusting the solid content concentration and coating thickness of the easily-adhesive composition, the thickness of the easily-adhesive layer 15 can be set within the above range. The thickness of the easily adhesive layer 15 in the polarizing plate is obtained from observation of the cross section of the polarizing plate. If there is a non-uniformity in the thickness, the average thickness in the observation range is taken as the thickness of the easily adhesive layer.

When the easily-adhesive composition contains an alkali component, the smaller the thickness of the easily-adhesive layer, the higher the efficiency of volatilization and removal of the alkali component by heating tends to increase. From the viewpoint of maintaining the residual amount of the alkali component in an appropriate range, securing the dispersibility of the fine particles, and improving the moist heat resistance of the polarizing plate, the thickness of the easily adhesive layer 15 is preferably within the above range.

[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, treatment 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), and 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 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, pamphlet WO2010/100917, Japanese Patent No. 491205, 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 dyeing iodine. In this manufacturing method, even if the PVA-based resin layer is thin, since it is supported by the resin substrate for stretching, it is 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 easily adhesive film 1 is optically transparent, the material is not particularly limited, and water-based adhesives, solvent-based adhesives, hot melt adhesives, radical polymerization curable 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 adhesive 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, a vinyl polymer is preferable and a polyvinyl alcohol-based resin is particularly preferable from the viewpoint of excellent adhesion between the polarizer 5 and the easily adhesive film 1. 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 aqueous adhesive composition (solution) may contain a crosslinking agent in addition to a polymer such as a polyvinyl alcohol resin. As the crosslinking agent, a compound having at least two functional groups reactive with the polymer constituting the adhesive is used per molecule. Examples of the crosslinking agent of the polyvinyl alcohol resin include alkylene diamines; Isocyanates; Epoxys; Aldehydes; And amino-formaldehydes such as methylol urea and methylol melamine. Among these, amino-formaldehyde is preferred. 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 water-based adhesive composition is preferably an aqueous solution. From the viewpoints of coatability and solution stability, the resin concentration of the aqueous adhesive solution is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight. The viscosity of the water-based adhesive composition is preferably about 1 to 50 mPa·s.

The active energy ray-curable adhesive is an adhesive capable of radical polymerization, cationic polymerization, or anionic polymerization by irradiation of an active energy ray such as an electron beam or ultraviolet rays. Among them, a photoradical polymerizable adhesive in which radical polymerization is initiated by irradiation with ultraviolet rays is preferable because it can be cured at 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; (Meth)acrylate containing a hydroxyl group; 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 radical 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.

It is preferable that a photocurable adhesive such as a photoradical polymerizable adhesive contains a photoinitiator. The photoinitiator may be appropriately selected according to 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 radical polymerizable adhesive. The content of the photo radical generator is usually about 0.1 to 10 parts by weight, and preferably 0.5 to 3 parts by weight based on 100 parts by weight of the monomer. In addition, when using the radically polymerizable adhesive as an electron beam curing type, a photoinitiator is not particularly required. If necessary, a photosensitizer typified by a carbonyl compound or the like may be added to the radically polymerizable adhesive. The photosensitizer is used to increase the curing speed and sensitivity by electron beams. The amount of the photosensitizer used is usually about 0.001 to 10 parts by weight, preferably 0.01 to 3 parts by weight, based on 100 parts by weight of the monomer.

The adhesive composition may contain 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 trapping 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 produced by bonding the easily-adhesive film 1 to one surface (first main surface) of the polarizer 5 through the adhesive layer 6. Specifically, after applying the adhesive composition to one or both of the polarizer 5 and the easily-adhesive film 1, the polarizer 5 and the easily-adhesive film 1 are bonded with a roll laminator or the like, and the adhesive is cured. It is preferable to bond the polarizer 5 and the easily adhesive film 1.

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

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

After bonding the polarizer 5 and the easily adhesive film 1, the adhesive layer 6 is formed by curing the adhesive according to the type of adhesive. When a water-based adhesive is used, the adhesive is cured by heat drying. The drying time is typically 120 seconds or more, preferably 300 seconds or more.

<2nd transparent protective film>

The second transparent protective film 2 may be bonded to the second main surface of the polarizer 5 via an adhesive layer 7. As the second transparent protective film 2, any suitable transparent film can be adopted. The thickness of the second transparent protective film 2 is about 5 to 200 μm. From the viewpoints of mechanical strength, transparency, and handling properties, 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 for forming the second transparent protective film 2 include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); Cellulose polymers such as diacetyl cellulose and triacetyl cellulose; Styrene polymers such as polystyrene and acrylonitrile/styrene copolymers; 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, a film similar to the acrylic film 11 of the first transparent protective film 1 can be used. When the second transparent protective film 2 is an acrylic film, the durability of the polarizing plate tends to be improved compared to the case where a cellulose-based film is used.

The second transparent protective film 2 may be provided with an easily adhesive layer (not shown). When the 2nd transparent protective film 2 is an acrylic film, it is preferable to provide an easily adhesive 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 urethane resin and fine particles is 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, the occurrence of streak-like unevenness when the polarizing plate is exposed to a high temperature/high humidity environment is more likely. It tends to be noticeable. In addition to the easily-adhesive layer 15 provided on the surface of the transparent protective film 1, the thickness of the easily-adhesive layer provided on the surface of the second transparent protective film is 280 nm or less, whereby an acrylic film is used as a double-sided transparent protective film Edo-stripe-like unevenness hardly occurs, so that a polarizing plate excellent in humidification durability is obtained.

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, like the easily adhesive layer 6 used for bonding the polarizer 5 and the first transparent protective film 1, a water-based adhesive containing a polyvinyl alcohol-based resin and a crosslinking agent is preferable. The same adhesive composition may be used for the adhesive layer 6 and the adhesive layer 7. After laminating the first transparent protective film 1 on the first main surface of the polarizer 5 and the second transparent protective film 2 on the second main surface of the polarizer 5, the polarizer 5 is heated or the like. You may cure the adhesive layers 6 and 7 on the front and back sides of) at the same time.

<Principle of estimation of streak stain suppression>

As described above, in the polarizing plate in which the easily-adhesive layer 15 formed surface of the easily-adhesive film 1 is bonded to the polarizer, the smaller the thickness of the easily-adhesive layer 15 is, the more durable the polarizing plate is, and the occurrence of streak-like unevenness is suppressed. Tend to be. The main cause of the stripe unevenness, from the polarizer iodide (l ₃ ^- and l ₅ ^-), and desorption of, since the smaller the thickness of the adhesive layer of the iodine ions from the polarizer desorption suppressed, that suppress the generation of stripes stain I think.

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

In PVA polarizer, iodine contains l ₃ ^- ions and l ₅ ^- ions in a certain ratio, but free l ₃ ^- ions desorbed from the PVA chain are unstable, so l ₃ ^- ions and iodine (l ₂ ) are generated. do. When free iodine and iodine ions remain in the polarizer, the reaction of desorption of iodine ions from the PVA chain is difficult to 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 iodine ions, since the reaction proceeds in the right-hand direction, the desorption of iodine ions from the PVA chain further proceeds. .

It is considered that the urethane-based easily adhesive layer has an action of occluding iodine and/or iodine ions desorbed from the PVA chain of the polarizer. As the thickness of the easily-adhesive layer increases, the storage amount of iodine and/or iodine ions is larger, and thus free iodine and/or iodine ions in the polarizer are more likely to move from the polarizer to the easily-adhesive layer. When free iodine and/or iodine ions move from the polarizer to the easily adhesive layer, the reaction proceeds in the right-hand direction, so that the iodine ions are easily desorbed from the polarizer, which may cause streaking.

Conversely, when the thickness of the easily-adhesive layer is small, the amount of iodine and/or iodine ions occluded by the easily-adhesive layer is small, so that even if iodine ions are desorbed from the PVA chain of the polarizer, they tend to stay in the polarizer. If free iodine or iodine ions remain in the system, the reaction rate from the left side to the right side of the reaction (i.e., the rate of desorption of iodine ions from the PVA chain) is small, and thus the desorption of iodine ions from the PVA chain is suppressed. It is thought that staining is suppressed.

[Use of polarizing plate]

The polarizing plate of the present invention 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 polymer, polyester, polyurethane, polyamide, polyether, a fluorine-based or rubber-based polymer such as a base polymer can be suitably selected and used. Particularly, an acrylic pressure-sensitive adhesive is preferred because it is excellent in optical transparency, shows moderate wettability and cohesiveness, and is excellent in weather resistance and heat resistance.

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 the pressure-sensitive adhesive layers are provided on both sides of the polarizing plate, the composition and thickness of the pressure-sensitive adhesive layers on the front and back 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, the surface of the plastic film is preferably coated with a release agent such as a silicone release agent, a long-chain alkyl release agent, or a fluorine release agent.

The polarizing plate of the present invention 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 the polarizing plate of the present invention to the surface of an image display cell such as a liquid crystal cell or an organic EL cell. The 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 an illumination system as necessary. In the organic EL display device, by bonding the polarizing plate of the present invention and the retardation film (typically a quarter wave plate) to the surface of the organic EL cell with a circular polarizing plate, re-emission of reflected light of external light by a metal electrode or the like is prevented. 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 the following "%" is weight% unless otherwise specified.

[Example 1]

(Production of polarizer A)

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 adhesive composition)

Polyvinyl alcohol-based resin containing an acetacetyl group (average degree of polymerization: 1200, degree of saponification: 98.5 mol%, degree of acetacetyl group modification: 5 mol%) 20 parts by weight of methylolmelamine per 100 parts by weight of pure water under a temperature condition of 30°C To obtain an aqueous solution having a solid content concentration of 0.5%.

(Preparation of easy adhesive composition)

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

(Production of easy adhesive film)

Corona treatment was performed on one side of a biaxially oriented acrylic film (40 µm in thickness) 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 an acrylic film by a wire bar coater with a wire bar (#2) set, dried at 140° C. for 5 minutes, and 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 polarizing plate)

As a double-sided polarizer protective film, an easily-adhesive film provided with the 110 nm easily-adhesive layer was used. After 30 minutes from the preparation of the adhesive composition, the adhesive composition was applied to the easily-adhesive layer forming surface of the easily-adhesive film so that the thickness after drying became 50 nm, and the easily-adhesive film was adhered to each of both surfaces of the polarizer A, and dried at 70° C. for 5 minutes. A polarizing plate was obtained.

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

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

[Example 4]

(Production of polarizer B)

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

(Production of easy adhesive film)

In the production of the easily-adhesive film of Example 1, the wire bar when applying the easily-adhesive composition was changed to the wire bar of #4. The thickness of the easily adhesive layer formed on the surface of the acrylic film was 240 nm.

(Manufacture of polarizing plate)

As a polarizer protective film, an easily-adhesive film provided with an easily-adhesive layer of 240 nm was used, and an easily-adhesive film was bonded to both surfaces of the polarizer B in the same procedure as in Example 1 to obtain a polarizing plate.

[Comparison 2]

Except having used the polarizer B instead of the polarizer A, it carried out similarly to Comparative Example 1, and obtained the polarizing plate.

[evaluation]

<Amount of alkali remaining in the easily adhesive layer>

The amount of triethylamine and ammonia remaining in the easily-adhesive layer of the easily-adhesive film before bonding with the polarizer was quantified. For the residual amount of triethylamine, the powder obtained by removing the easily-adhesive layer from the surface of the easily-adhesive film was weighed, dissolved in methanol, and quantified by gas chromatography mass spectrometry (GC/MS) of the solution. As for the residual amount of ammonia, after immersing the easily-adhesive 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 strength>

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

<Humidification durability>

The polarizing plate was cut out to a size of 320 mm x 240 mm, and bonded on a glass plate through an acrylic adhesive having a thickness of 20 µm. This sample was placed in a constant temperature and humidity chamber at a temperature of 60°C and a relative humidity of 90%, and maintained for 500 hours to perform 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. Moreover, another polarizing plate was arrange|positioned on the polarizing plate by orthogonal Nicole, and it observed visually, and the presence or absence of a stripe-shaped unevenness was confirmed. About the polarizing plates of Example 4 and Comparative Example 2, it maintained for 120 hours in a constant temperature high-humidity tank with a temperature of 85 degreeC and a relative humidity of 85%, heating/humidification durability test was performed, and evaluation was similarly performed. The presence or absence of uneven streaks of the polarizing plate after the heating/humidification durability test was evaluated according to the following criteria.

○: Streaked spots are not visually recognized

△: Slightly visible streaky spots

×: Stripe unevenness is clearly visually recognized

Table 2 shows the configuration of the polarizing plates of each of the Examples and Comparative Examples (the type of the polarizer, the thickness of the easily adhesive layer, and the amount of residual alkali) and the evaluation results. Observation photographs in orthogonal Nicole before and after the durability test (60° C. 90%Rh 500 hours) of the polarizing plates of Example 1, Example 2, and Comparative Example 1 (low luminance spot measurement system, ``EYESCALE-4W'' manufactured by I System Corporation) 3). Observation photographs (compact digital cameras, taken with CASIO COMPUTER CO., LTD. "EXILIM EX-ZR1100") before and after the durability test of the polarizing plates of Example 4 and Comparative Example 2 (80° C. 85%Rh 120 hours) before and after an orthogonal Nicole 4 shows.

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 surfaces of the polarizer A, had good adhesiveness between the polarizer and the easily-adhesive film, but a stripe-like unevenness occurred after the heating and humidification durability test. In Example 1 using an easily-adhesive film having an easily-adhesive layer having a thickness of 110 nm, and Example 3 using an easily-adhesive film having an easily-adhesive layer having a thickness of 140 nm, a slight stripe-like unevenness was observed after the heating and humidification durability test, but Comparative Example Compared to 1, the stain was greatly improved. In Example 2 in which an easily-adhesive film having an easily-adhesive layer having a thickness of 60 nm was used, even after the heat/humidification durability test, no streaky unevenness was observed, and good durability was exhibited (see Fig. 3).

In contrast between Example 4 and Comparative Example 2 using polarizer B having a higher iodine concentration than polarizer A, in Comparative Example 2 using an easily-adhesive film having an easily-adhesive layer having a thickness of 340 nm, a temperature of 60°C and a relative humidity of 90 In the case where a stripe-like unevenness occurred in the polarizing plate after the% heating/humidification durability test, in Example 4 in which the thickness of the easily-adhesive layer was 240 nm, no stripe-like unevenness was observed, and good durability was exhibited. In the heating/humidification endurance test at a temperature of 85°C and a relative humidity of 85%, the polarizing plate of Example 4 was also confirmed to have a streaky unevenness, but compared with Comparative Example 2, the degree of occurrence of unevenness was alleviated (see Fig. 4).

From these results, it is understood that by reducing the thickness of the easily-adhesive layer provided on the surface of the acrylic film, 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 (durability test results at a temperature of 60° C. and 90% relative humidity) and the comparison between Example 4 and Comparative Example 2, the occurrence of streak-like unevenness by reducing the thickness of the easily adhesive layer In addition to the suppression, the amount of change in the single transmittance and the degree of polarization decreases, and it is understood that the durability of the polarizing plate is improved.

In Examples 1 to 4 and Comparative Examples 1 and 2, the smaller the thickness of the easily-adhesive layer, the smaller the amount of residual alkali is, and the occurrence of streak-like unevenness after the heating/humidification durability test tends to be suppressed. It is considered that the reduction in the amount of alkali remaining in the easily-adhesive layer by reducing the thickness of the easily-adhesive layer also contributes to the durability improvement of the polarizing plate.

1: Transparent protective film (easy adhesive film)
11: acrylic film
15: easy adhesive 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 easily adhesive layer on the surface of the acrylic film, the easily adhesive layer formation surface is bonded to the polarizer,
The easily adhesive layer contains a urethane resin and fine particles, and a polarizing plate having a thickness of 280 nm or less. The method of claim 1,
A polarizing plate having a thickness of the easily adhesive layer of 50 nm or more. The method according to claim 1 or 2,
A polarizing plate in which the content of the fine particles in the easily adhesive layer is 8 to 50% by weight. The method according to any one of claims 1 to 3,
A polarizing plate having an alkali component content of 75 ppm or less in the easily adhesive layer. The method according to any one of claims 1 to 4,
A polarizing plate further comprising a second transparent protective film bonded to the second main surface of the polarizer through an adhesive layer. An image display device comprising an image display cell and a polarizing plate according to any one of claims 1 to 5.

Images