JP2020204777A - Polarizing film - Google Patents

Abstract

To provide a polarizing film indicating a high level of a piercing strength which is 5.0 gf/μm or more, even if an absorbance A (700) of a wavelength 700nm is 3.0 or more.SOLUTION: A polarizing film is formed by adsorbing and orienting a dichroic dye to a uniaxially-stretched polyvinyl alcohol resin layer. The polarizing film shows: an absorbance (A700) of a wavelength 700 nm that is 3.0 or more; a b value of a transmitted hue that is 2-3.5; a piercing strength per unit film thickness that is 5.0-7.0 gf/μm; and a shrinkage force per 2 mm width in an absorption axis direction when it is held for 240 minutes at the temperature of 80°C that is 1.6 N or less.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a polarizing laminated film and a polarizing plate.

Polarizing plates are widely used as polarization supply elements and polarization detection elements in display devices such as liquid crystal display devices. Generally, the polarizing plate has a structure in which a protective film is attached to one or both sides of a polarizing film using an adhesive. In recent years, with the thinning of liquid crystal display devices, there is also a demand for thinning of polarizing plates.

In Patent Document 1, a polyvinyl alcohol-based resin layer is formed on a base film, and the laminate is stretched, dyed, or the like to obtain a polarizing laminated film, and a protective film is laminated thereto to prepare a polarizing plate. How to do it is described. According to this method, a polarizing film having a thin wall thickness and a small shrinkage force can be produced, but the strength of the polarizing laminated film and the polarizing film decreases as the wall thickness decreases, so that there is a problem that the handleability deteriorates. there were.

The polarizing film is required to have high absorbance at a wavelength of 700 nm in order to suppress red discoloration during the heat resistance test. However, the inventors have so far found that when the absorbance of the polarizing plate at a wavelength of 700 nm is increased, the puncture strength per unit film thickness when the polarizing film is torn in the absorption axis direction tends to decrease. Specifically, when the hues of the polarizing films are the same, when the draw ratio is increased, the piercing strength per unit film thickness when the polarizing film is torn in the absorption axis direction decreases, and the absorbance at a wavelength of 700 nm increases. I found a trend. Further, it is possible to increase the absorbance at a wavelength of 700 nm by reducing the elemental hue b value and making the transmitted hue blue, but it is preferable that the hue is not changed as much as possible. That is, on the premise that the hue is not changed as much as possible, it is necessary to increase the piercing strength and the absorbance at a wavelength of 700 nm at the same time, and a polarizing plate having both of these is required.

Japanese Unexamined Patent Publication No. 2013-72951

An object of the present invention is to provide a method for producing a polarizing laminated film having a thin wall thickness and excellent strength.

That is, the present invention includes the following.
[1] A method for producing a polarizing laminated film having a polarizing film layer on a base film.
The manufacturing method is
A process of forming a polyvinyl alcohol-based resin layer on a base film,
A step of stretching the laminate obtained in the step of forming the resin layer, and a step of dyeing the polyvinyl alcohol-based resin layer with a dichroic dye to form a polarizing film layer are provided after the stretching step. In the step of forming the polarizing film layer, after dyeing the polyvinyl alcohol-based resin layer with a dichroic dye, the temperature parameter represented by the product of the drying temperature (° C.) and the drying time (minutes) is 220 to 350. A method for producing a polarizing laminated film, which comprises a drying process.
[2] The method for producing a polarizing laminated film according to [1], wherein the drying treatment includes a drying treatment performed at a temperature of at least 50 to 90 ° C.
[3] A method for manufacturing a polarizing plate, comprising a step of laminating a first protective film on a polarizing film layer of the polarizing laminated film according to [1] or [2].
A step of obtaining a laminated film in which a first protective film is laminated on a polarizing film layer of the polarizing laminated film according to [1] or [2].
A method for manufacturing a polarizing plate, which comprises a step of peeling and removing a base film to obtain a polarizing plate with a single-sided protective film.
[4] The method for producing a polarizing plate according to [3], further comprising a bonding step of bonding a second protective film to the polarizing film layer surface to obtain a polarizing plate with a double-sided protective film.

According to the present invention, it is possible to manufacture a polarizing plate having a thin wall thickness and a small shrinkage rate when heat is applied. This polarizing plate has excellent durability because cracks generated in the polarizing film are suppressed in an environment where high temperature and low temperature are repeated.

The present invention is a method for producing a polarizing laminated film having a polarizing film layer on a base film, wherein a polyvinyl alcohol-based resin layer is formed on the base film (resin layer forming step), and a resin layer is formed. It includes a step of stretching the laminate obtained in the step (stretching step) and a step of dyeing the polyvinyl alcohol-based resin layer with a bicolor dye to form a polarizing film layer (dyeing step) after the stretching step. The dyeing step includes a drying process in which the temperature parameter represented by the product of the drying temperature (° C.) and the drying time (minutes) is 220 to 350 after dyeing the polyvinyl alcohol-based resin layer with a bicolor dye. It is characterized by. The produced polarizing laminated film can produce a polarizing plate by including a step of laminating a protective film on the polarizing film layer.

[Manufacturing method of polarizing laminated film]
(Resin layer forming process)
This step is a step of forming a polyvinyl alcohol-based resin layer by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of the base film and then drying the film to obtain a laminated film. This polyvinyl alcohol-based resin layer is a layer that becomes a polarizing film through a stretching step and a dyeing step. The polyvinyl alcohol-based resin layer can be formed by applying a coating liquid containing a polyvinyl alcohol-based resin to one side or both sides of the base film and drying the coating layer. The method of forming the polyvinyl alcohol-based resin layer by such coating is advantageous in that a thin polarizing film can be easily obtained.

The base film can be made of a thermoplastic resin, and more preferably it is made of a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, stretchability, and the like. Specific examples of such thermoplastic resins include, for example, polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins; polyester resins; (meth) acrylic resins; celluloses such as cellulose triacetate and cellulose diacetate. Ester-based resin; Polycarbonate-based resin; Polyvinyl alcohol-based resin; Polyvinyl acetate-based resin; Polyallylate-based resin; Polystyrene-based resin; Polyether sulfone-based resin; Polysulfone-based resin; Polyamide-based resin; Polygon-based resin; and mixtures thereof , Copolymers and the like.
As used herein, the term "(meth) acrylic" means at least one selected from acrylic and methacrylic. The same applies to "(meth) acryloyl".

The base film may have a single-layer structure composed of one resin layer made of one or more kinds of thermoplastic resins, or a plurality of resin layers made of one kind or two or more kinds of thermoplastic resins are laminated. It may have a multi-layer structure.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resin and polypropylene resin, and copolymers composed of two or more kinds of chain olefins. A base film made of a chain polyolefin resin is preferable because it can be stably stretched at a high magnification. Among them, the base film is mainly composed of polypropylene-based resin (polypropylene resin which is a homopolymer of propylene or a copolymer mainly composed of propylene) and polyethylene-based resin (polyethylene resin which is a homopolymer of ethylene and ethylene as a main component). It is more preferable that it is made of a copolymer of ethylene.

The propylene-based copolymer, which is one of the examples preferably used as the thermoplastic resin constituting the base film, is a copolymer of propylene and another monomer copolymerizable therewith. Examples of other monomers copolymerizable with propylene include ethylene and α-olefin. As the α-olefin, an α-olefin having 4 or more carbon atoms is preferably used, and more preferably, an α-olefin having 4 to 10 carbon atoms. The α-olefin having 4 to 10 carbon atoms is a linear monoolefin such as 1-butene, 1-pentene, 1-hexene, 1-hexene, 1-octene and 1-decene; 3-methyl-1- Branched monoolefins such as butene, 3-methyl-1-pentene and 4-methyl-1-pentene; vinylcyclohexane and the like can be mentioned. The copolymer of propylene and another monomer copolymerizable therewith may be a random copolymer or a block copolymer.

The content of the other monomer is, for example, 0.1 to 20% by weight, preferably 0.5 to 10% by weight in the copolymer. The content of other monomers in the copolymer is determined by infrared (IR) spectrum measurement according to the method described on page 616 of the "Polymer Analysis Handbook" (published by Kinokuniya Bookstore, 1995). Can be sought.

Among the above, as the polypropylene-based resin, a propylene homopolymer, a propylene-ethylene random copolymer, a propylene-1-butene random copolymer or a propylene-ethylene-1-butene random copolymer is preferably used.

It is preferable that the three-dimensional regularity of the polypropylene-based resin is substantially isotactic or syndiotactic. A base film made of a polypropylene-based resin having substantially isotactic or syndiotactic stereoregularity has relatively good handleability and excellent mechanical strength in a high temperature environment.

The polyester resin is a resin having an ester bond, and is generally composed of a polyvalent carboxylic acid or a derivative thereof and a polycondensate of a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylic acid. As the polyhydric alcohol, a divalent diol can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol and the like.

A typical example of the polyester resin is polyethylene terephthalate, which is a polycondensate of terephthalic acid and ethylene glycol. Polyethylene terephthalate is a crystalline resin, but the one in the state before the crystallization treatment is easier to perform a treatment such as stretching. If necessary, it can be crystallized by heat treatment during stretching or after stretching. Further, a copolymerized polyester having reduced crystallinity (or amorphous) by copolymerizing another kind of monomer with the skeleton of polyethylene terephthalate is also preferably used. Examples of such resins include those obtained by copolymerizing cyclohexanedimethanol and isophthalic acid. Since these resins are also excellent in stretchability, they can be preferably used.

Specific examples of polyester resins other than polyethylene terephthalate and its copolymers include polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, and polycyclohexanedimethyl terephthalate. , Polycyclohexanedimethylnaphthalate, and mixtures and copolymers thereof.

The (meth) acrylic resin is a resin containing a compound having a (meth) acryloyl group as a main constituent monomer. Examples of the (meth) 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. Combined; methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymer; (meth) methyl acrylate-styrene copolymer (MS resin, etc.); with a compound having methyl methacrylate and an alicyclic hydrocarbon group (For example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.) and the like. As the (meth) acrylic resin, a polymer containing a poly (meth) acrylic acid alkyl ester having an alkyl group having 1 to 6 carbon atoms as a main component is preferable, and methyl methacrylate as a main component (50 to 100% by weight). , Preferably 70 to 100% by weight), more preferably a methyl methacrylate-based resin.

The polycarbonate-based resin is an engineering plastic made of a polymer in which monomer units are bonded via a carbonate group, and is a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate in which the polymer skeleton is modified in order to lower the photoelastic coefficient, or a copolymerized polycarbonate having improved wavelength dependence. As the polycarbonate resin, an appropriate commercially available product can be used. Examples of commercially available products are "Panlite (registered trademark)" manufactured by Teijin Chemicals Ltd., "Iupilon (registered trademark)" manufactured by Mitsubishi Engineering Plastics Co., Ltd., and Sumika Stylon Polycarbonate Co., Ltd. "SD Polycarbonate (registered trademark)", "Calibre (registered trademark)" manufactured by Dow Chemicals, etc.

Among the above, polypropylene-based resins are preferably used from the viewpoint of stretchability, heat resistance, and the like.

For the cyclic polyolefin resin and the cellulose ester resin used as the base film, the matters described about the protective film are cited. In addition, the chain polyolefin resin, polyester resin, (meth) acrylic resin, and polycarbonate resin described above in relation to the base film can also be used as constituent materials of the protective film.

In addition to the above-mentioned thermoplastic resin, any suitable additive may be added to the base film. Examples of the additive include an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a mold release agent, a color retardant, a flame retardant, a nucleating agent, an antistatic agent, a pigment, and a colorant. The content of the thermoplastic resin in the base film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, still more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. If the content of the thermoplastic resin in the base film is less than 50% by weight, the high transparency inherent in the thermoplastic resin may not be sufficiently exhibited.

The thickness of the base film can be appropriately determined, but in general, it is preferably 1 to 500 μm, more preferably 300 μm or less, further preferably 200 μm or less, and 5 to 150 μm from the viewpoint of workability such as strength and handleability. Most preferred.

The tensile elastic modulus of the base film is preferably 100 MPa to 1500 MPa, more preferably 140 MPa to 1000 MPa, and even more preferably 150 MPa to 500 MPa at 80 ° C. If the tensile elastic modulus is too small, the hardness of the base film is insufficient during the stretching process, and defects such as wrinkles are likely to occur. If the tensile elastic modulus is too high, the processability in stretching is deteriorated.

The tensile elastic modulus can be determined by cutting a base film into a test piece having a predetermined size and performing a tensile test. In order to obtain the tensile elastic modulus at 80 ° C., a tensile tester equipped with a constant temperature bath is used.

The coating liquid containing the polyvinyl alcohol-based resin to be coated on the base film is preferably a polyvinyl alcohol-based resin solution obtained by dissolving the powder of the polyvinyl alcohol-based resin in a good solvent (for example, water). The coating liquid may contain additives such as a plasticizer and a surfactant, if necessary. As the plasticizer, a polyol or a condensate thereof or the like can be used, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol and polyethylene glycol. The blending amount of the additive is preferably 20% by weight or less of the polyvinyl alcohol-based resin.

The method of applying the coating liquid onto the base film is a wire bar coating method; a roll coating method such as reverse coating and gravure coating; a die coating method; a comma coating method; a lip coating method; a spin coating method; a screen coating method; It can be appropriately selected from known methods such as fountain coating method; dipping method; spray method. When the coating liquid is applied to both sides of the base film, it can be applied one side at a time using the above method, or the base film can be applied by using a dipping method, a spray coating method or other special equipment. It is also possible to apply on both sides of the.

The drying temperature and drying time of the coating layer (polyvinyl alcohol-based resin layer before drying) are set according to the type of solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200 ° C, preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C. or higher. The drying time is, for example, 2 to 20 minutes.

The polyvinyl alcohol-based resin layer may be formed on only one side of the base film, or may be formed on both sides. When formed on both sides, curling of the film that may occur during the production of the polarizing laminated film can be suppressed, and two polarizing plates can be obtained from one polarizing laminated film, so that the production efficiency of the polarizing plate is also improved. It is advantageous.

The thickness of the polyvinyl alcohol-based resin layer in the laminated film is preferably 3 to 60 μm, more preferably 3 to 30 μm, and even more preferably 5 to 20 μm. When the thickness is within this range, a polarizing film having good dyeability of the dichroic dye, excellent polarization performance, and a sufficiently small thickness can be obtained. If the thickness of the polyvinyl alcohol-based resin layer exceeds 60 μm, the thickness of the polarizing film may exceed 20 μm, and if the thickness of the polyvinyl alcohol-based resin layer is less than 3 μm, the thickness becomes too thin after stretching and dyeing. Sex tends to worsen.

Prior to coating the coating liquid, in order to improve the adhesion between the base film and the polyvinyl alcohol-based resin layer, at least the surface of the base film on the side where the polyvinyl alcohol-based resin layer is formed is subjected to corona treatment. Plasma treatment, frame (flame) treatment, etc. may be performed.

Further, prior to coating the coating liquid, in order to improve the adhesion between the base film and the polyvinyl alcohol-based resin layer, a polyvinyl alcohol-based resin layer is placed on the base film via a primer layer or an adhesive layer. It may be formed.

The primer layer can be formed by applying a coating liquid for forming a primer layer to the surface of a base film and then drying it. The coating liquid for forming a primer layer contains a component that exerts a certain degree of strong adhesion to both the base film and the polyvinyl alcohol-based resin layer. The coating liquid for forming a primer layer usually contains such a resin component and a solvent. As the resin component, a thermoplastic resin having excellent transparency, thermal stability, stretchability and the like is preferably used, and examples thereof include (meth) acrylic resin and polyvinyl alcohol resin. Of these, a polyvinyl alcohol-based resin that gives good adhesion is preferably used.

Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol resins and derivatives thereof. Derivatives of polyvinyl alcohol resin include polyvinyl formal, polyvinyl acetal and the like, as well as polyvinyl alcohol resin modified with olefins such as ethylene and propylene; modified with unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid. Those modified with an alkyl ester of unsaturated carboxylic acid; those modified with acrylamide and the like. Among the above-mentioned polyvinyl alcohol-based resins, it is preferable to use a polyvinyl alcohol resin.

As the solvent, a general organic solvent or an aqueous solvent capable of dissolving the resin component is usually used.
Examples of solvents include aromatic hydrocarbons such as benzene, toluene and xylene; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate and isobutyl acetate; chlorine such as methylene chloride, trichloroethylene and chloroform. Hydrocarbons; alcohols such as ethanol, 1-propanol, 2-propanol and 1-butanol. However, if the primer layer is formed using a primer layer forming coating solution containing an organic solvent, the base film may be dissolved. Therefore, the solvent should be selected in consideration of the solubility of the base film. Is preferable. Considering the influence on the environment, it is preferable to form the primer layer from the coating liquid using water as a solvent.

A cross-linking agent may be added to the coating liquid for forming the primer layer in order to increase the strength of the primer layer. As the cross-linking agent, an appropriate one is appropriately selected from known organic and inorganic cross-linking agents according to the type of thermoplastic resin used. Examples of the cross-linking agent include epoxy-based, isocyanate-based, dialdehyde-based, and metal-based cross-linking agents.

As the epoxy-based cross-linking agent, either a one-component curing type or a two-component curing type can be used, and ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6- Examples thereof include hexanediol diglycidyl ether, trimethyl propan triglycidyl ether, diglycidyl aniline, and diglycidyl amine.

Examples of the isocyanate-based cross-linking agent include tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylolpropane-tolylene diisocyanate adduct, triphenylmethane triisocyanate, methylenebis (4-phenylmethane) triisocyanate, isophorone diisocyanate, and ketooximes thereof. Examples include block products and phenol block products.

Examples of the dialdehyde-based cross-linking agent include glioxal, malondialdehyde, succindialdehyde, glutardaldehyde, malondialdehyde, phthaldialdehyde and the like.

Examples of the metal-based cross-linking agent include metal salts, metal oxides, metal hydroxides, and organometallic compounds. Examples of metal salts, metal oxides, and metal hydroxides include divalent or higher valent atoms such as magnesium, calcium, aluminum, iron, nickel, zirconium, titanium, silicon, boron, zinc, copper, vanadium, chromium, and tin. Valuable metal salts, oxides and hydroxides can be mentioned.

The organic metal compound is a compound having at least one structure in the molecule in which an organic group is directly bonded to a metal atom or an organic group is bonded via an oxygen atom, a nitrogen atom, or the like. The organic group means a monovalent or polyvalent group containing at least a carbon element, and can be, for example, an alkyl group, an alkoxy group, an acyl group or the like. Further, the bond does not mean only a covalent bond, but may be a coordinate bond by coordination such as a chelate compound.

Preferable examples of organometallic compounds include organotitan compounds, organozirconium compounds, organoaluminum compounds, and organosilicon compounds. As the organometallic compound, only one kind may be used alone, or two or more kinds may be used in combination.

Examples of the organic titanium compound include titanium orthoesters such as tetranormal butyl titanate, tetraisopropyl titanate, butyl titanate dimer, tetra (2-ethylhexyl) titanate and tetramethyl titanate; titanium acetylacetonate, titanium tetraacetylacetonate and poly. Titanium chelate such as titanium acetylacetonate, titanium octylene glycolate, titanium lactate, titanium triethanolaminate and titanium ethylacetacetate; titanium acylate such as polyhydroxytitanium stearate can be mentioned.

Examples of the organic zirconium compound include zirconium normal propionate, zirconium normal butyrate, zirconium tetraacetylacetate, zirconium monoacetylacetonate, zirconium bisacetylacetonate, zirconium acetylacetonate bisethylacetate acetate and the like.

Examples of the organoaluminum compound include aluminum acetylacetonate and aluminum organic acid chelate. Examples of the organic silicon compound include compounds in which the ligands exemplified above in the organic titanium compound and the organic zirconium compound are bonded to silicon.

In addition to the above cross-linking agents (low molecular weight cross-linking agents), polymer-based cross-linking agents such as methylolated melamine resin and polyamide epoxy resin can also be used. To give examples of commercially available polyamide epoxy resins, "Sumirace Resin (registered trademark) 650 (30)" and "Sumiraizu Resin (registered trademark) 675" sold by Taoka Chemical Co., Ltd. under their respective trade names. "and so on.

When the primer layer is formed from a polyvinyl alcohol-based resin, a polyamide epoxy resin, a methylolated melamine resin, a dialdehyde-based cross-linking agent, a metal chelate compound-based cross-linking agent, or the like is preferably used as the cross-linking agent.

The ratio of the resin component and the cross-linking agent in the coating liquid for forming the primer layer is in the range of about 0.1 to 100 parts by weight of the cross-linking agent with respect to 100 parts by weight of the resin component, and the type of the resin component and the type of the cross-linking agent. It may be appropriately determined according to the above, and it is particularly preferable to select from the range of about 0.1 to 50 parts by weight. Further, it is preferable that the coating liquid for forming a primer layer has a solid content concentration of about 1 to 25% by weight.

The thickness of the primer layer is preferably about 0.05 to 1 μm, more preferably 0.1 to 0.4 μm. If it is thinner than 0.05 μm, the effect of improving the adhesion between the base film and the polyvinyl alcohol-based resin layer is small, and if it is thicker than 1 μm, it is disadvantageous for thinning the polarizing plate.

The method of applying the coating liquid for forming the primer layer to the base film can be the same as the coating liquid for forming the polyvinyl alcohol-based resin layer. The primer layer is applied to the surface (one side or both sides of the base film) to which the coating liquid for forming the polyvinyl alcohol-based resin layer is applied. The drying temperature and drying time of the coating layer composed of the coating liquid for forming the primer layer are set according to the type of the solvent contained in the coating liquid. The drying temperature is, for example, 50 to 200 ° C, preferably 60 to 150 ° C. When the solvent contains water, the drying temperature is preferably 80 ° C. or higher. The drying time is, for example, 30 seconds to 20 minutes.

When the primer layer is provided, the order of coating on the base film is not particularly limited. For example, when the polyvinyl alcohol-based resin layer is formed on both sides of the base film, the primer is applied to both sides of the base film. After forming the layer, a polyvinyl alcohol-based resin layer may be formed on both sides, or a primer layer and a polyvinyl alcohol-based resin layer may be formed on one side of the base film in order, and then a primer may be formed on the other side of the base film. The layer and the polyvinyl alcohol-based resin layer may be formed in this order.

(Stretching process)
This step is a step of subjecting a laminated film composed of a base film and a polyvinyl alcohol-based resin layer to a stretching treatment to obtain a stretched film composed of the stretched base film and a polyvinyl alcohol-based resin layer. The draw ratio of the laminated film can be appropriately selected according to the desired polarization characteristics, but is preferably more than 5 times and 17 times or less, more preferably more than 5 times and 8 times the original length of the laminated film. It is as follows. If the draw ratio is 5 times or less, the polyvinyl alcohol-based resin layer is not sufficiently oriented, so that the degree of polarization of the polarizing film may not be sufficiently high. On the other hand, if the draw ratio exceeds 17 times, it becomes difficult to obtain a high piercing strength P.
Further, the film is likely to break during stretching, and the thickness of the stretched film becomes thinner than necessary, which may reduce processability and handleability in a subsequent process. The stretching treatment is usually uniaxial stretching.

The stretching treatment is not limited to one-stage stretching, and can be performed in multiple stages. In this case, all of the multi-step stretching treatment may be continuously performed before the dyeing step, or the second and subsequent stretching treatments may be performed at the same time as the dyeing treatment and / or the crosslinking treatment in the dyeing step. .. When the stretching treatment is performed in multiple stages in this way, it is preferable to perform the stretching treatment so that the total stretching ratio of all the stages of the stretching treatment is more than 5 times.

The stretching treatment may be a longitudinal stretching that stretches in the film longitudinal direction (film transport direction), or may be a transverse stretching or an oblique stretching that stretches in the film width direction. Examples of the longitudinal stretching method include inter-roll stretching using rolls, compression stretching, stretching using a chuck (clip), and the like, and examples of the transverse stretching method include a tenter method. As the stretching treatment, either a wet stretching method or a dry stretching method can be adopted, but it is preferable to use the dry stretching method because the stretching temperature can be selected from a wide range.

The stretching temperature is set to be equal to or higher than a temperature at which the polyvinyl alcohol-based resin layer and the entire base film exhibit fluidity to the extent that the entire base film can be stretched, and preferably −30 ° C., which is the phase transition temperature (melting point or glass transition temperature) of the base film. It is in the range of -30 ° C to + 30 ° C, more preferably in the range of -30 ° C to + 5 ° C, and further preferably in the range of -25 ° C to + 0 ° C. When the base film is composed of a plurality of resin layers, the phase transition temperature means the highest phase transition temperature among the phase transition temperatures exhibited by the plurality of resin layers.

When the stretching temperature is lower than the phase transition temperature of −30 ° C., it tends to be difficult to achieve high-magnification stretching of more than 5 times, or the fluidity of the base film is too low to make the stretching treatment difficult. When the stretching temperature exceeds the phase transition temperature of + 30 ° C., the fluidity of the base film tends to be too large and stretching tends to be difficult. Since it is easy to perform high-magnification stretching of more than 5 times, the stretching temperature is within the above range, more preferably 120 ° C. or higher. This is because when the stretching temperature is 120 ° C. or higher, there is no difficulty in the stretching treatment even if the stretching is performed at a high magnification of more than 5 times.

The stretching treatment may be performed while heating the laminated film. As a heating method, a zone heating method (for example, a method of blowing hot air to heat in a stretching zone such as a heating furnace adjusted to a predetermined temperature); a method of heating the roll itself when stretching with a roll; a heater heating method ( Infrared heaters, halogen heaters, panel heaters, etc. are installed above and below the laminated film and heated by radiant heat). In the inter-roll stretching method, the zone heating method is preferable from the viewpoint of uniformity of stretching temperature. In this case, the two nip roll pairs may be installed in the temperature-controlled stretching zone or outside the stretching zone, but are installed outside the stretching zone in order to prevent the laminated film and the nip roll from adhering to each other. Is preferable.

The stretching temperature means the atmospheric temperature in the zone (for example, in the heating furnace) in the case of the zone heating method, and also means the atmospheric temperature in the furnace when heating is performed in the furnace in the heater heating method. In the case of a method of heating the roll itself, it means the surface temperature of the roll.

Prior to the stretching step, a preheat treatment step for preheating the laminated film may be provided. As the preheating method, the same method as the heating method in the stretching treatment can be used. When the stretching treatment method is inter-roll stretching, the preheating may be performed at any timing before, during, or after passing through the nip roll on the upstream side. When the stretching treatment method is thermal roll stretching, preheating is preferably performed at a timing before passing through the thermal roll. When the stretching treatment method is stretching using a chuck, preheating is preferably performed at a timing before increasing the distance between the chucks. The preheating temperature is preferably in the range of −50 ° C. to ± 0 ° C. of the stretching temperature, and more preferably in the range of −40 ° C. to −10 ° C. of the stretching temperature.

Further, a heat fixing treatment step may be provided after the stretching treatment in the stretching step. The heat fixing treatment is a treatment in which heat treatment is performed at a crystallization temperature or higher while maintaining a tense state while holding the end portion of the stretched film with a clip. This heat fixing treatment promotes the crystallization of the polyvinyl alcohol-based resin layer. The temperature of the heat fixing treatment is preferably in the range of −0 ° C. to −80 ° C. of the stretching temperature, and more preferably in the range of −0 ° C. to −50 ° C. of the stretching temperature.

(Dyeing process)
This step is a step of dyeing a polyvinyl alcohol-based resin layer of a stretched film with a dichroic dye and adsorbing and orienting the stretched film to form a polarizing film to obtain a polarizing laminated film. Through this step, a polarizing laminated film in which a polarizing film is laminated on one side or both sides of a base film can be obtained. The dyeing step can be performed by immersing the entire stretched film in a solution containing a dichroic dye (dyeing solution). As the dyeing solution, a solution in which the above dichroic dye is dissolved in a solvent can be used. Water is generally used as the solvent for the dyeing solution, but an organic solvent compatible with water may be further added. The concentration of the dichroic dye in the dyeing solution is preferably 0.01 to 10% by weight, more preferably 0.02 to 7% by weight, and further preferably 0.025 to 5% by weight. preferable.

When iodine is used as the dichroic dye, it is preferable to further add iodide to the dyeing solution containing iodine because the dyeing efficiency can be further improved. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like. Can be mentioned. The concentration of iodide in the dyeing solution is preferably 0.01 to 20% by weight. Among the iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably in the range of 1: 5 to 1: 100, more preferably in the range of 1: 6 to 1:80 by weight. It is preferably in the range of 1: 7 to 1:70, more preferably.

The immersion time of the stretched film in the dyeing solution is usually in the range of 15 seconds to 15 minutes, preferably 30 seconds to 3 minutes. The temperature of the dyeing solution is preferably in the range of 10 to 60 ° C, more preferably in the range of 20 to 40 ° C.

The stretched film may be further stretched during the dyeing step. In this case, 1) the stretching treatment is performed at a magnification lower than the target in the stretching step, and then the stretching treatment is performed so that the total stretching ratio becomes the target magnification during the dyeing treatment in the dyeing step. In the case of performing the cross-linking treatment after the dyeing treatment, 2) the stretching treatment is performed at a magnification lower than the target in the stretching step, and then the total stretching ratio is performed during the dyeing treatment in the dyeing step. Examples thereof include a mode in which the stretching treatment is performed until the target magnification is not reached, and then the stretching treatment is performed during the cross-linking treatment so that the final total stretching ratio becomes the target magnification.

The dyeing step can include a cross-linking process that is carried out following the dyeing process. The cross-linking treatment can be performed by immersing the dyed film in a solution containing a cross-linking agent (cross-linking solution). As the cross-linking agent, conventionally known substances can be used, and examples thereof include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde.
Only one type of cross-linking agent may be used alone, or two or more types may be used in combination.

Specifically, the cross-linking solution can be a solution in which a cross-linking agent is dissolved in a solvent. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further contained. The concentration of the cross-linking agent in the cross-linking solution is preferably in the range of 1 to 20% by weight, more preferably in the range of 6 to 15% by weight.

The crosslinked solution can include iodide. By adding iodide, the in-plane polarization performance of the polarizing film can be made more uniform. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like. Can be mentioned. The concentration of iodide in the crosslinked solution is preferably 0.05 to 15% by weight, more preferably 0.5 to 8% by weight, and even more preferably 0.5 to 7% by weight.

In addition, the cross-linked solution may contain other components such as a pH adjuster. As the pH adjuster, for example, sulfuric acid, hydrochloric acid, acetic acid, ascorbic acid and the like may be added.

The immersion time of the dyed film in the cross-linking solution is usually 15 seconds to 20 minutes, preferably 30 seconds to 15 minutes. The temperature of the crosslinked solution is preferably in the range of 10 to 90 ° C.

The cross-linking treatment can be performed at the same time as the dyeing treatment by blending a cross-linking agent in the dyeing solution. Further, the stretching treatment may be performed during the crosslinking treatment. The specific embodiment in which the stretching treatment is carried out during the crosslinking treatment is as described above.

In the dyeing step, it is preferable to perform a washing treatment and a drying treatment after the dyeing treatment. The cleaning process usually includes a water cleaning process. The water washing treatment can be performed by immersing the film after the dyeing treatment or the cross-linking treatment in pure water such as ion-exchanged water and distilled water. The water washing temperature is usually in the range of 3 to 50 ° C, preferably 4 to 20 ° C. The immersion time is usually 2 to 300 seconds, preferably 3 to 240 seconds.

The cleaning treatment may be a combination of a water cleaning treatment and a cleaning treatment with an iodide solution. In addition to water, the cleaning liquid used in the water cleaning treatment and / or the cleaning treatment with the iodide solution can appropriately contain liquid alcohols such as methanol, ethanol, isopropyl alcohol, butanol and propanol.

As the drying step performed after the washing step, any appropriate method such as natural drying, blast drying, and heat drying may be adopted. For example, in the case of heat drying, the drying temperature is usually 20 to 95 ° C., and the drying time is usually about 1 to 15 minutes. The drying process is divided into multiple stages, and the drying temperature and drying time of each stage may be different. The drying step is preferably two-stage or three-stage or more multi-stage drying.

In the drying step, the drying temperature in at least one drying step is preferably in the range of about 50 to 90 ° C. If the temperature is too low, the drying time becomes long, and the production efficiency tends to decrease. On the other hand, if the drying temperature is too high, the single hue b value becomes large, and the obtained polarizing film tends to be yellowish. The drying time may be appropriately adjusted together with the drying temperature so as to satisfy the temperature parameters, but from a preferable range of the drying temperature, it is preferably about 100 seconds to 10 minutes, more preferably 2 minutes or more, and preferably 9 minutes. Below, it is more preferably 8 minutes or less.

The temperature parameter is expressed by the product of the drying temperature (° C.) and the drying time (minutes), and in the present invention, the drying treatment is performed so that this value becomes 220 to 350. If the temperature parameter is less than 220, the strength of the polarizing film tends to be difficult to increase, and if it exceeds 350, the hue of the polarizing film tends to change to yellow. The temperature parameter is preferably 300 or less. The drying treatment may be performed only once or divided into a plurality of times, and when the drying treatment is performed a plurality of times, the total temperature parameters in each drying treatment are in the range of 220 to 350. ..

When the drying step is two-stage drying, it is preferable that the temperature parameter of the second stage is larger than the temperature parameter of the first stage. When the drying step is three or more stages of drying, it is preferable that there is at least one stage in which the temperature parameter of a certain stage is larger than the temperature parameter of the immediately preceding stage.

The strength of the polarizing film can be indexed by the piercing strength per unit film thickness.
The piercing strength per unit film thickness varies depending on the protective film, adhesive layer, adhesive layer, etc. used, but for example, if it is 3.6 gf / μm or more, it can be practically used. The puncture strength per unit film thickness is preferably 3.6 to 15.0 gf / μm, more preferably 5.0 to 10.0 gf / μm, and even more preferably 5.0 to 7.0 gf / μm. It is μm.

The piercing strength per unit film thickness is the strength at which a piercing jig is pierced perpendicularly to the polarizing film and the polarizing film is torn along the stretching axis (absorption axis). For example, a load cell. It can be measured with a compression tester equipped with. Examples of the compression tester include a handy compression tester "KES-G5 type" manufactured by Kato Tech Co., Ltd. and a small desktop tester "EZ Test" manufactured by Shimadzu Corporation.

The polarizing film used for the measurement may be one before laminating the protective film to form a polarizing plate, or one obtained by removing the protective film from the polarizing plate on which the protective film is laminated with an adhesive or the like. A polarizing film in which the protective film is removed from the polarizing plate is preferable in consideration of the influence of the load and the like.
As a method of removing the protective film from the polarizing plate, if the polarizing film is not damaged, the protective film is dissolved with a solvent, or the protective film is peeled off by immersing it in a solution having a good affinity with an adhesive. , Conventionally known methods can be used.

Examples of the method for removing the protective film from the polarizing plate include a method for dissolving the protective film with a solvent. The solvent that dissolves the protective film may be any solvent that dissolves the protective film and does not dissolve the polarizing film. When the protective film is a cellulosic resin film, an alkyl halide-based solvent is preferable, and dichloromethane is particularly preferable. When the protective film is an olefin resin film, a cycloalkane-based solvent is preferable, and cyclohexane is particularly preferable. When the protective film is an acrylic resin film, a benzene-based solvent or an alkyl halide-based solvent is preferable. Among the benzene-based solvents, toluene is preferable. Among the alkyl halide-based solvents, dichloromethane is preferable.

The measurement is performed by sandwiching a polarizing film between two sample stands having a circular hole with a diameter of 15 mm or less through which a piercing jig can pass. The piercing jig is preferably a columnar rod, and preferably includes a piercing needle having a spherical or hemispherical tip in contact with the polarizing film. The spherical portion or hemispherical portion at the tip has a diameter of 0.5 mmφ or more and preferably 5 mmφ or less, and its radius of curvature is preferably larger than 0R and smaller than 0.7R. The piercing speed of the compression tester is 0.05 cm / sec or more, and preferably 0.5 cm / sec or less.

The piercing strength can be measured by fixing this test piece to a jig, piercing it from the normal direction, and measuring the strength when it is torn in one place horizontally with the stretching direction (absorption axis direction). .. The measurement is performed on five or more polarizing film test pieces, and the average value thereof can be obtained as the piercing strength. The piercing strength per unit film thickness can be calculated by dividing the measured piercing strength by the film thickness of the polarizing film used for the measurement. In this method, since the polarizing film can be pulled in the transmission axis direction and the breaking strength when the polarizing film is torn in the absorption axis direction can be quantitatively measured, the transmission axis cannot be measured because the polarizing film is easily torn. The strength in the direction can be measured.

[Manufacturing method of polarizing plate]
The polarizing laminated film produced by the above method includes a step of laminating a first protective film on the polarizing film layer (first bonding step) and a step of peeling and removing the base film (peeling step). This makes it possible to manufacture a polarizing plate. This method for manufacturing a polarizing plate can include a step of laminating a second protective film on the other surface of the polarizing film (second laminating step) after the peeling step.

When the first bonding step and the second bonding step are performed to produce a polarizing plate in which the protective film is laminated on both sides of the polarizing film, the second protective film is laminated in the first bonding step and the second bonding is performed. The first protective film may be laminated in the joint process.

(1st bonding process)
This step is a step of laminating the first protective film on the polarizing film of the polarizing laminated film, that is, on the surface of the polarizing film opposite to the base film side to obtain the laminating film. When the polarizing laminated film has polarizing films on both sides of the base film, the protective films are usually laminated on the polarizing films on both sides. In this case, these protective films may be the same type of protective film or different types of protective films.

(Peeling process)
This step is a step of peeling and removing the base film from the bonded film obtained by bonding the first protective film to obtain a polarizing plate with a single-sided protective film. Through this step, a polarizing plate with a single-sided protective film in which the first protective film is laminated on one side of the polarizing film can be obtained. When the polarizing laminated film has polarizing films on both sides of the base film and a protective film is attached to both of these polarizing films, this peeling step is performed from one polarizing laminated film to two single sides. A polarizing plate with a protective film can be obtained.

The base film can be peeled off by the same method as the separator (peeling film) peeling step performed by a normal polarizing plate with an adhesive. The base film may be peeled off immediately after the first bonding step, or may be wound into a roll once after the first bonding step and then peeled off while being unwound in the subsequent steps.

(Second bonding process)
In this step, the other protective film is bonded via an adhesive on the polarizing film of the polarizing plate with a single-sided protective film, that is, on the surface opposite to the protective film bonded in the first bonding step. This is the process of obtaining a polarizing plate. When the second bonding step is performed, the second protective film may be bonded in the first bonding step. In this case, the first protective film is bonded in this step.

[Polarizer]
The polarizing plate obtained by the above-mentioned production method is thin and has a small shrinkage rate when heat is applied. This polarizing plate has excellent durability because cracks generated in the polarizing film are suppressed in an environment where high temperature and low temperature are repeated.

(Optical characteristics of polarizing film)
The polarization performance of the polarizing film can be mainly expressed by numerical values called simple transmittance and degree of polarization, each of which is defined by the following equations.
Elemental transmittance (λ) = 0.5 × (Tp (λ) + Tc (λ))
Polarization degree (λ) = 100 × (Tp (λ) -Tc (λ)) / (Tp (λ) + Tc (λ))

Here, Tp (λ) is the transmittance (%) of the polarizing plate or the polarizing film measured in relation to the incident linearly polarized light having a wavelength of λnm and parallel Nicol, and Tc (λ) is the linearly polarized light having an incident wavelength of λnm. It is the transmittance (%) of the polarizing plate or the polarizing film measured in relation to the polarization and the cross Nicol, and both are the measured values obtained by the polarization ultraviolet visible absorption spectrum measurement by the spectrophotometer. Further, the single transmittance (λ) and the degree of polarization (λ) obtained for each wavelength are subjected to a sensitivity correction called luminosity factor, and the luminosity factor correction single transmittance (Ty) and the luminosity factor correction polarization are obtained, respectively. It is called degree (Py). These Ty and Py values can be easily measured with, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

In order to ensure good clarity of the image when the polarizing plate is applied to a display device such as a liquid crystal display device, the polarizing film according to the present invention has a luminosity factor correction single transmittance (Ty) of 40% or more. It is preferable that the polarization degree (Py) is 99% or more. It is more preferable that the transmittance of the luminosity factor correction unit is 41% or more and the luminosity factor correction polarization degree is 99.95% or more. Further, it is more preferable that the luminosity factor correction single transmittance is 41.5% or more and the luminosity factor correction polarization degree is 99.99% or more.

The polarizing film preferably has an absorbance (A700) at a wavelength of 700 nm of 2.8 or more, and more preferably 3.0 or more. The larger the value of the absorbance, the more the deterioration of the optical characteristics in the high temperature environment is suppressed. The absorbance at a wavelength of 700 nm can be obtained from the orthogonal transmittance (Tc) of the polarizing film, and the MD transmittance and TD transmittance of the polarizing film can be measured and calculated by the following formula.
Tc (700) (%) = [MD (700 nm) / 100] x [TD (700 nm) / 100] x 100
A700 = -log [Tc (700) / 100]

In the formula, "MD" is the MD transmittance, which is the transmittance when the direction of polarized light emitted from the Gran Thomson prism and the transmission axis of the polarizing film sample (exfoliated from the base film) are parallel. Yes, and "TD" is the TD transmittance, which is the transmittance when the direction of polarized light emitted from the Gran Thomson prism and the transmission axis of the polarizing plate sample are orthogonal to each other. The optical properties of the polarizing film can be measured, for example, with a spectrophotometer with an integrating sphere. For this measurement, the MD transmittance and the TD transmittance may be measured by setting the measurement sample (polarizing plate sample) in the spectrophotometer with the polarizing film side as the detector side.

The polarizing film preferably has a transmitted hue b value in the range of 1 to 6, more preferably in the range of 2 to 4, and most preferably in the range of 2 to 3.5. The single hue b value is appropriately designed in combination with the hue of the color filter of the liquid crystal display device, but if it is within the above range, it can be within the hue design range of the color filter of the general liquid crystal display device.

The above-mentioned transmitted hue means the hue of light transmitted from one surface of the polarizing plate when light is applied to the other surface. The hue here can be represented by a value and b value in the Lab color system, and is measured using standard light. In the present invention, the transmission hue of the polarizing film is actually measured in a state where an adhesive layer is provided on one side of the polarizing film and the pressure-sensitive adhesive layer is attached to a glass plate. The Lab color system is represented by the hunter's lightness index L and hues a and b, as described in "5.5 Accelerated Weathering Test" of JIS K 5981: 2006 "Synthetic Resin Powder Coating Film". It is a thing. As a concept similar to the Lab color system, there is an L ^* a ^* b ^* color system defined in JIS Z 8781-4: 2013 "Color measurement-Part 4: CIE 1976 L ^* a ^* b ^* Space". However, in the present invention, the Lab color system is adopted. The values of the brightness index L and the hues a and b are calculated by the following formulas from the tristimulus values X, Y and Z specified in JIS Z 8722: 2009 "Color measurement method-reflection and transmission object color". ..

L = 10Y ^1/2
a = 17.5 (10.2XY) / Y ^1/2
b = 7.0 (Y-0.847Z) / Y ^1/2 .

In the Lab color system, the hue a value and the b value can indicate the positions corresponding to the saturation, and when the hue a value increases, the hue becomes red, and when the hue b value increases, the hue becomes yellow. Change. Also, the closer it is to 0, the closer it is to achromatic color.

(Polarizing film)
The polarizing film can be a uniaxially stretched polyvinyl alcohol-based resin layer in which a dichroic dye is adsorbed and oriented. Generally, when the thickness of the polarizing film is 20 μm or less, the polarizing plate can be thinned. In the present invention, a polarizing film having a thickness of 10 μm or less is used, but the thickness of the polarizing film is preferably 8 μm or less.

As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, acrylamides with ammonium groups and the like.

The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80 mol% or more, preferably in the range of 90 to 99.5 mol%, and more preferably in the range of 94 to 99 mol%. The polyvinyl alcohol-based resin may be a partially modified modified polyvinyl alcohol. For example, the polyvinyl alcohol-based resin may be an olefin such as ethylene and propylene; an unsaturated carboxylic acid such as acrylic acid, methacrylic acid and crotonic acid. ; Examples include those modified with alkyl esters of unsaturated carboxylic acids and acrylamide. The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000.

The dichroic dye contained (adsorption orientation) in the polarizing film can be iodine or a dichroic organic dye, and conventionally known dyes can be used. As the dichroic dye, only one kind may be used alone, or two or more kinds may be used in combination.

When the polarizing film is held at a temperature of 80 ° C. for 240 minutes, the shrinkage force per width 2 mm in the absorption axis direction is preferably 2N or less, more preferably 1.8N or less. It is more preferably 6N or less. When this shrinkage force is larger than 2N, the amount of dimensional change in a high temperature environment becomes large, and the shrinkage force of the polarizing film becomes large, so that the polarizing film tends to be easily cracked. The shrinkage force of the polarizing film tends to be 2N or less when the draw ratio is lowered and the thickness of the polarizing film is reduced.

(1st protective film and 2nd protective film)
The first protective film is laminated on at least one side of the above polarizing film. When the first protective film is laminated on one side of the polarizing film and the second protective film is laminated on the other side, the same second protective film as the first protective film may be used, or another protective film may be used. A resin film may be used. Each of the first protective film and the second protective film can be a transparent resin film composed of a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins such as polypropylene resins; cellulose ester resins such as cellulose triacetate and cellulose diacetate; polyethylene terephthalate and polyethylene naphthalate. And polyester resins such as polybutylene terephthalate; polycarbonate resins; (meth) acrylic resins; or mixtures and copolymers thereof.

Cyclic polyolefin resin is a general term for resins that are usually polymerized using a cyclic olefin as a polymerization unit, and is described in, for example, JP-A 1-2240517, JP-A-3-14882, JP-A-3-122137, and the like. Examples of the resin used. Specific examples of the cyclic polyolefin resin include an open (co) polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a chain olefin such as ethylene and propylene and a cyclic olefin (typically). Random copolymers), graft polymers obtained by modifying them with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Of these, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer is preferably used as the cyclic olefin.

Various products of the cyclic polyolefin resin are commercially available. Examples of commercially available cyclic polyolefin resins are "TOPAS" (registered trademark) and JSR Co., Ltd., which are produced by TOPAS ADVANCED POLYMERS GmbH and sold by Polyplastics Co., Ltd. in Japan. "Arton" (registered trademark) sold by, "Zeonoa" (registered trademark) and "Zeonex" (registered trademark) sold by Nippon Zeon Co., Ltd., and "Apel" sold by Mitsui Chemicals Co., Ltd. (Registered trademark) and so on.

Further, a commercially available product of the formed cyclic polyolefin resin film may be used as the protective film. Examples of commercially available products are "Arton Film" ("Arton" is a registered trademark of JSR Corporation) sold by JSR Corporation and "Ssina" sold by Sekisui Chemical Industry Co., Ltd. Examples include "SCA40" (registered trademark) and "Zeonoa film" (registered trademark) sold by Nippon Zeon Co., Ltd.

The formed cyclic polyolefin resin film is stretched as in uniaxial stretching or biaxial stretching, or a liquid crystal layer or the like is formed on the film to give an arbitrary retardation value. It can also be an retardation film.

Cellulose ester-based resins are usually esters of cellulose and fatty acids. Specific examples of the cellulose ester resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Further, those obtained by copolymerizing these or those in which a part of the hydroxyl group is modified with another substituent can also be used. Among these, cellulose triacetate (triacetyl cellulose: TAC) is particularly preferable. Many products of cellulose triacetate are commercially available, which is advantageous in terms of availability and cost. Examples of commercially available cellulose triacetate products are all trade names, such as "Fujitac (registered trademark) TD80", "Fujitac (registered trademark) TD80UF", and "Fujitac (registered trademark) TD80UZ" sold by FUJIFILM Corporation. And "Fujitac (registered trademark) TD40UZ", TAC film "KC8UX2M" and "KC4UY" manufactured by Konica Minolta Co., Ltd., etc.

The formed cellulose ester resin film is stretched like uniaxial stretching or biaxial stretching, or a liquid crystal layer or the like is formed on the film to give an arbitrary retardation value. It can also be an phase difference film.

The (meth) acrylic resin is usually a polymer mainly composed of a methacrylic acid ester. The methacrylic acid resin may be a homopolymer of one kind of methacrylic acid ester, or may be a copolymer of a methacrylic acid ester and another methacrylic acid ester, an acrylic acid ester, or the like. Examples of the methacrylic acid ester include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, and the number of carbon atoms in the alkyl group is usually about 1 to 4. In addition, cyclopentyl methacrylate such as cyclopentyl methacrylate, cyclohexyl methacrylate and cycloheptyl methacrylate, aryl methacrylate such as phenyl methacrylate, cycloalkylalkyl methacrylate such as cyclohexylmethyl methacrylate, and aralkyl methacrylate such as benzyl methacrylate. Can also be used.

Examples of the above-mentioned other polymerizable monomers that can constitute the (meth) acrylic resin include acrylic acid esters and polymerizable monomers other than methacrylic acid esters and acrylic acid esters. As the acrylic acid ester, an acrylic acid alkyl ester can be used, and specific examples thereof include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and acrylic. Includes acrylic acid alkyl esters having 1 to 8 carbon atoms in alkyl groups such as t-butyl acid, 2-ethylhexyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. The alkyl group preferably has 1 to 4 carbon atoms. In the (meth) acrylic resin, only one type of acrylic acid ester may be used alone, or two or more types may be used in combination.

Examples of the polymerizable monomer other than the methacrylic acid ester and the acrylic acid ester include a monofunctional monomer having one polymerizable carbon-carbon double bond in the molecule and a polymerizable carbon-carbon double bond in the molecule. A polyfunctional monomer having at least two of these can be mentioned, but a monofunctional monomer is preferably used. Specific examples of monofunctional monomers include styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, styrene halide, and hydroxystyrene; vinyl cyanide such as acrylonitrile and methacrylonitrile; acrylic acid and methacrylic acid. , Unsaturated acids such as maleic anhydride, itaconic anhydride; maleimides such as N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide; allyl alcohols such as metallic alcohol, allyl alcohol; vinyl acetate, vinyl chloride , Ethylene, propylene, 4-methyl-1-pentene, 2-hydroxymethyl-1-butene, methylvinylketone, N-vinylpyrrolidone, N-vinylcarbazole and other monomers.

Specific examples of polyfunctional monomers include polyunsaturated carboxylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, butanediol dimethacrylate, and trimethyl propantriacrylate; allyl acrylate, allyl methacrylate, and silicic acid. Alkenyl esters of unsaturated carboxylic acids such as allyl; polyalkenyl esters of polybasic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate, triallyl isocyanurate, aromatic polyalkenyl compounds such as divinylbenzene including.
As the polymerizable monomer other than the methacrylic acid ester and the acrylic acid ester, only one kind may be used alone, or two or more kinds may be used in combination.

The preferable monomer composition of the (meth) acrylic resin is 50 to 100% by weight of methacrylic acid alkyl ester, 0 to 50% by weight of acrylic acid alkyl ester, and 0 to 0 to other polymerizable monomers based on the total amount of monomers. It is 50% by weight, more preferably 50 to 99.9% by weight of methacrylic acid alkyl ester, 0.1 to 50% by weight of acrylic acid alkyl ester, and 0 to 49.9% by weight of other polymerizable monomers. is there.

Further, the (meth) acrylic resin may have a ring structure in the polymer main chain because the durability of the film can be enhanced. The ring structure is preferably a heterocyclic structure such as a cyclic acid anhydride structure, a cyclic imide structure, or a lactone ring structure. Specific examples thereof include a cyclic acid anhydride structure such as a glutaric anhydride structure and a succinic anhydride structure, a cyclic imide structure such as a glutarimide structure and a succinic anhydride structure, and a lactone ring structure such as butyrolactone and valerolactone. The glass transition temperature of the (meth) acrylic resin can be increased as the content of the ring structure in the main chain is increased. A cyclic acid anhydride structure or a cyclic imide structure is introduced by copolymerizing a monomer having a cyclic structure such as maleic anhydride or maleimide, or a cyclic acid anhydride structure is introduced by a dehydration / demethanol condensation reaction after polymerization. It can be introduced by a method, a method of reacting an amino compound to introduce a cyclic imide structure, or the like. For a resin (polymer) having a lactone ring structure, after preparing a polymer having a hydroxyl group and an ester group in a polymer chain, the hydroxyl group and the ester group in the obtained polymer are required by heating. Accordingly, it can be obtained by cyclization condensation in the presence of a catalyst such as an organic phosphorus compound to form a lactone ring structure.

Polymers having a hydroxyl group and an ester group in the polymer chain include, for example, methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, 2- It can be obtained by using a (meth) acrylic acid ester having a hydroxyl group and an ester group such as n-butyl (hydroxymethyl) acrylate and t-butyl 2- (hydroxymethyl) acrylate as a part of the monomer. it can. A more specific method for preparing a polymer having a lactone ring structure is described in, for example, Japanese Patent Application Laid-Open No. 2007-254726.

A (meth) acrylic resin can be prepared by radically polymerizing a monomer composition containing the above-mentioned monomers. The monomer composition can contain a solvent and a polymerization initiator, if necessary.

The (meth) acrylic resin may contain a resin other than the above-mentioned (meth) acrylic resin. The content of the other resin is preferably 0 to 70% by weight, more preferably 0 to 50% by weight, and further preferably 0 to 30% by weight. The resin is, for example, an olefin polymer such as polyethylene, polypropylene, an ethylene-propylene copolymer, poly (4-methyl-1-pentene); a halogen-containing polymer such as vinyl chloride or a chlorinated vinyl resin; polystyrene. , Sterium-based polymers such as styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; polyallylate composed of aromatic diols and aromatic dicarboxylic acids. Biodegradable polyesters such as polylactic acid, polybutylene succinate; polycarbonate; polyamides such as nylon 6, nylon 66, nylon 610; polyacetal; polyphenylene oxide; polyphenylene sulfide; polyether ether ketone; polyether nitrile; polysalphon; It can be polyether sulfone; polyoxypendylene; polyamideimide or the like.

The (meth) acrylic resin may contain rubber particles from the viewpoint of improving the impact resistance and film forming property of the film. The rubber particles may be particles composed of only a layer exhibiting rubber elasticity, or may be particles having a multi-layer structure having another layer together with the layer exhibiting rubber elasticity. Examples of the rubber elastic body include an olefin-based elastic polymer, a diene-based elastic polymer, a styrene-diene-based elastic copolymer, and an acrylic-based elastic polymer. Among them, an acrylic elastic polymer is preferably used from the viewpoint of light resistance and transparency.

The acrylic elastic polymer can be a polymer mainly composed of alkyl acrylate, that is, containing 50% by weight or more of structural units derived from alkyl acrylate based on the total amount of monomers. The acrylic elastic polymer may be a homopolymer of alkyl acrylate, and contains 50% by weight or more of structural units derived from alkyl acrylate and 50% by weight or less of structural units derived from other polymerizable monomers. It may be a copolymer.

As the alkyl acrylate constituting the acrylic elastic polymer, one having an alkyl group having 4 to 8 carbon atoms is usually used. Examples of the other polymerizable monomers described above include, for example, alkyl methacrylates such as methyl methacrylate and ethyl methacrylate; styrene-based monomers such as styrene and alkylstyrene; and non-residual monomers such as acrylonitrile and methylonitrile. Monofunctional monomers such as saturated nitriles, as well as alkenyl esters of unsaturated carboxylic acids such as allyl (meth) acrylate and metharyl (meth) acrylate; dialkenyl esters of dibasic acids such as diallyl maleate; alkylene It is a polyfunctional monomer such as an unsaturated carboxylic acid diester of glycol such as glycol di (meth) acrylate.

The rubber particles containing the acrylic elastic polymer are preferably particles having a multilayer structure having a layer of the acrylic elastic polymer. Specifically, it has a two-layer structure having a hard polymer layer mainly composed of alkyl methacrylate on the outside of the layer of the acrylic elastic polymer, and an alkyl methacrylate on the inside of the layer of the acrylic elastic polymer. Examples thereof include a three-layer structure having a hard polymer layer mainly composed of.

An example of the monomer composition in the polymer mainly composed of alkyl methacrylate constituting the hard polymer layer formed on the outside or the inside of the layer of the acrylic elastic polymer is given as an example of the (meth) acrylic resin. This is the same as the example of the monomer composition of the polymer mainly composed of alkyl methacrylate, and the monomer composition mainly composed of methyl methacrylate is particularly preferably used. Acrylic rubber elastic particles having such a multi-layer structure can be produced, for example, by the method described in Japanese Patent Publication No. 55-27576.

The rubber particles include the rubber elastic layer (layer of acrylic elastic polymer) contained therein from the viewpoint of film forming property of (meth) acrylic resin, impact resistance of film, and slipperiness of film surface. The average particle size is preferably in the range of 10 to 350 nm. The average particle size is more preferably 30 nm or more, further 50 nm or more, and more preferably 300 nm or less, further 280 nm or less.

The average particle size of the rubber particles up to the rubber elastic layer (layer of acrylic elastic polymer) is measured as follows. That is, when such rubber particles are mixed with a (meth) acrylic resin to form a film and the cross section is dyed with an aqueous solution of ruthenium oxide, only the rubber elastic layer is colored and observed in an almost circular shape, and the mother layer is observed. (Meta) acrylic resin is not dyed. Therefore, a slice is prepared from the cross section of the film dyed in this manner using a microtome or the like, and this is observed with an electron microscope. Then, 100 dyed rubber particles are randomly extracted, the diameter of each particle (diameter to the rubber elastic layer) is calculated, and then the number average value is taken as the above average particle diameter. Since the measurement is performed by such a method, the obtained average particle size is a number average particle size.

When the outermost layer is a hard polymer mainly composed of methyl methacrylate and the rubber elastic body layer (layer of acrylic elastic polymer) is wrapped in the rubber particles, it is used as the base material (meth). ) When mixed with an acrylic resin, the outermost layer of the rubber particles is mixed with the parent (meth) acrylic resin. Therefore, when the cross section is stained with ruthenium oxide and observed with an electron microscope, the rubber particles are observed as particles in a state where the outermost layer is removed. Specifically, when the inner layer is an acrylic elastic polymer and the outer layer is a rubber particle having a two-layer structure which is a hard polymer mainly composed of methyl methacrylate, the acrylic elastic polymer portion of the inner layer Is stained and observed as monolayered particles. Further, the innermost layer is a hard polymer mainly composed of methyl methacrylate, the intermediate layer is an acrylic elastic polymer, and the outermost layer is a hard polymer mainly composed of methyl methacrylate, which has a three-layer structure. In the case of rubber particles, the innermost particle center portion is not dyed, and only the acrylic elastic polymer portion of the intermediate layer is observed as stained two-layer structure particles.

From the viewpoint of film forming property of (meth) acrylic resin, impact resistance of film, and slipperiness of film surface, the total amount of rubber particles is the total amount of the rubber particles with the (meth) acrylic resin constituting the (meth) acrylic resin film. It is preferable that the mixture is blended in a proportion of 3% by weight or more and 60% by weight or less, more preferably 45% by weight or less, still more preferably 35% by weight or less. When the amount of rubber elastic particles is more than 60% by weight, the dimensional change of the film becomes large and the heat resistance decreases. On the other hand, when the amount of rubber elastic particles is less than 3% by weight, the heat resistance of the film is good, but the take-up property at the time of film formation is poor, and the productivity may be lowered. In the present invention, when a multi-layered particle having a layer exhibiting rubber elasticity and another layer is used as the rubber elastic body particle, the weight of the portion composed of the layer exhibiting rubber elasticity and the inner layer thereof is determined. , The weight of the rubber elastic particles. For example, when the acrylic rubber elastic particles having the above-mentioned three-layer structure are used, the total weight of the acrylic rubber elastic polymer portion of the intermediate layer and the hard polymer portion mainly composed of methyl methacrylate in the innermost layer. Let be the weight of the rubber elastic body particles. When the acrylic rubber elastic particles having the above-mentioned three-layer structure are dissolved in acetone, the acrylic rubber elastic polymer portion of the intermediate layer and the hard polymer portion mainly composed of methyl methacrylate in the innermost layer are insoluble. The total weight ratio of the intermediate layer and the innermost layer to the acrylic rubber elastic particles having a three-layer structure can be easily determined.

When the (meth) acrylic resin film contains rubber particles, the (meth) acrylic resin composition containing the rubber particles used for producing the film melts and kneads the (meth) acrylic resin and the rubber particles. In addition to being obtained by mixing with or the like, it can also be obtained by first producing rubber particles and then polymerizing a monomer composition as a raw material for a (meth) acrylic resin in the presence of the rubber particles.

In addition to the above rubber particles, the (meth) acrylic resin contains ordinary additives such as ultraviolet absorbers, organic dyes, pigments, inorganic dyes, antioxidants, antistatic agents, and surfactants. You may let me. Among them, the ultraviolet absorber is preferably used for enhancing the weather resistance. Examples of UV absorbers are 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2-yl) phenol], 2- (5). -Methyl-2-hydroxyphenyl) -2H-benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3,5-di) -Tert-butyl-2-hydroxyphenyl) -2H-benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3,5) -Di-tert-butyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3,5-di-tert-amyl-2-hydroxyphenyl) -2H-benzotriazole, 2- (2) Benzoliazole-based UV absorbers such as'-hydroxy-5'-tert-octylphenyl) -2H-benzotriazole; 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, 2,4- 2-Hydroxybenzophenone such as dihydroxybenzophenone, 2-hydroxy-4-methoxy-4'-chlorobenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone UV absorbers; Salicylate phenyl ester UV absorbers such as p-tert-butylphenyl salicylate, p-octylphenyl salicylate; 2,4-diphenyl-6- (2-hydroxy-4-methoxyphenyl)- 1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-ethoxyphenyl) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-propoxyphenyl) ) -1,3,5-triazine, 2,4-diphenyl- (2-hydroxy-4-butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-) Butoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-hexyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2) -Hydroxy-4-octyloxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-dodeci) Luoxyphenyl) -1,3,5-triazine, 2,4-diphenyl-6- (2-hydroxy-4-benzyloxyphenyl) -1,3,5-triazine, 2- (2-hydroxy-4- [1-octyloxycarbonylethoxy] phenyl) -4,6-bis (4-phenylphenyl) -1,3,5-triazine, 4-bis [2-hydroxy-4-butoxyphenyl] -6- (2, 4-Dibutoxyphenyl) -1,3,5-triazine, 2- [4-[(2-hydroxy-3- (2'-ethyl) hexyloxy] -2-hydroxyphenyl] -4,6-bis ( 2,4-dimethylphenyl) -1,3,5-triazine, 2- (4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine-2-yl) -5-hydroxyphenyl , 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine-2-yl] -5- (octyloxy) phenol, 2- [2,6-di (2,6-di) 4-Xylyl) -1,3,5-triazine-2-yl] -5-octyloxyphenol, 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5- [2 -(2-Eethylhexanoyl) ethoxy] phenol, 2,4,6-tris (2-hydroxy-4-hexyloxy-3-methoxyphenyl) -1,3,5triazine and other triazine-based ultraviolet absorbers, etc. And, if necessary, two or more of them may be used.

As the ultraviolet absorber, a commercially available product may be used. For example, as a triazine-based ultraviolet absorber, "Kemisorb 102" (registered trademark) manufactured by Chemipro Kasei Co., Ltd. and "Adecastab (registered trademark)" manufactured by ADEKA Co., Ltd. LA46 ”,“ Adecastab® LAF70 ”, BASF“ TINUVIN® 460 ”,“ TINUVIN® 405 ”,“ TINUVIN® 400 ”and“ TINUVIN® 477 , "CYASORB (registered trademark) UV-1164" manufactured by Sun Chemical Co., Ltd. (these are all product names). As benzotriazole-based ultraviolet absorbers, "Adecastab (registered trademark) LA31" and "Adecastab (registered trademark) LA36" manufactured by ADEKA Co., Ltd., "Sumisorb (registered trademark) 200" and "Sumisorb" manufactured by Sumika Chemtex Co., Ltd. (Registered Trademark) 250 ”,“ Sumisorb (Registered Trademark) 300 ”,“ Sumisorb (Registered Trademark) 340 ”and“ Sumisorb (Registered Trademark) 350 ”,“ Kemisorb 74 ”(Registered Trademark) manufactured by Kemipro Kasei Co., Ltd.,“ Kemisorb 79 "(registered trademark) and" Kemisorb 279 "(registered trademark), BASF's" TINUVIN (registered trademark) 99-2 "," TINUVIN (registered trademark) 900 "and" TINUVIN (registered trademark) 928 "( As mentioned above, all of them are product names) and the like. When the (meth) acrylic resin film contains an ultraviolet absorber, the amount thereof is usually 0.1% by weight or more, preferably 0.3% by weight or more, based on 100% by weight of the (meth) acrylic resin. Yes, and preferably 3% by weight or less.

A conventionally known film-forming method can be adopted for producing the (meth) acrylic resin film. The (meth) acrylic resin film may have a multilayer structure, and the (meth) acrylic resin film having a multilayer structure has various generally known methods such as a method using a feed block and a method using a multi-manifold die. Can be used. Among them, for example, a method of laminating via a feed block, multi-layer melt extrusion molding from a T-die, and contacting at least one side of the obtained laminated film-like material with a roll or a belt to form a film has a good surface quality. It is preferable in that it can be obtained. In particular, from the viewpoint of improving the surface smoothness and surface glossiness of the (meth) acrylic resin film, both sides of the laminated film-like material obtained by the above-mentioned multilayer melt extrusion are brought into contact with the roll surface or the belt surface to form a film. The method of converting is preferable. In the roll or belt used at this time, the surface of the roll or belt in contact with the (meth) acrylic resin has a mirror surface in order to impart smoothness to the surface of the (meth) acrylic resin film. Is preferable.

The (meth) acrylic resin film may be a film produced as described above that has been stretched. Stretching may be required to obtain a film with the desired optical and mechanical properties. Examples of the stretching treatment include uniaxial stretching and biaxial stretching. Examples of the stretching direction include a mechanical flow direction (MD) of the unstretched film, a direction orthogonal to the mechanical flow direction (TD), and a direction obliquely intersecting the mechanical flow direction (MD). The biaxial stretching may be simultaneous biaxial stretching in which the two stretching directions are simultaneously stretched, or sequential biaxial stretching in which the stretching is performed in a predetermined direction and then in the other direction.

In the stretching process, for example, using two or more pairs of nip rolls having an increased peripheral speed on the outlet side, the film is stretched in the longitudinal direction (mechanical flow direction: MD), or both ends of the unstretched film are gripped by chucks for mechanical flow. This is done by expanding in the direction (TD) orthogonal to the direction.

The stretching ratio by the stretching treatment is preferably more than 0%, preferably 300% or less, and more preferably 100 to 250%. If the draw ratio exceeds 300%, the film thickness becomes too thin and the film is easily broken or the handleability is lowered. The draw ratio can be obtained from the following formula.
Stretching ratio (%) = 100 × {(length after stretching)-(length before stretching)} / (length before stretching)

From the viewpoint of enhancing the adhesion to the surface treatment layer and the polarizing film, the stretched (meth) acrylic resin film preferably has an absolute value of the surface orientation coefficient ΔP of the film of 2 × 10 ^-4 or less.

The plane orientation coefficient ΔP is a physical property value that serves as an index regarding the orientation state of the molecular chains of the polymer constituting the film, and is the refractive index in the in-plane slow-phase axial direction (the direction in which the in-plane refractive index is maximized). Is n _x , the refractive index in the in-plane advancing axis direction (direction orthogonal to the in-plane slow phase axis direction) is n _y , and the refractive index in the film thickness direction is n _z , it is defined by the following equation.
Planar orientation coefficient ΔP = (n _x + n _y ) / 2-n _z

For example, in the case of films biaxially stretched in MD and TD, the larger the absolute value of the plane orientation coefficient ΔP, the more perpendicular the molecular chains of the polymer to the thickness direction of the film. Generally, the plane orientation coefficient ΔP of the stretched (meth) acrylic resin film takes a negative value.

Further, in order to impart desired optical properties and mechanical properties, instead of or in combination with the stretching treatment, a heat-shrinkable film is attached to a (meth) acrylic resin film to shrink the film. May be good.

In order to increase the adhesive strength between the (meth) acrylic resin film and the polarizing film, an easy-adhesion layer may be provided on the surface of the (meth) acrylic resin film facing the polarizing film.

The easy-adhesion layer provided on the surface of the protective film facing the polarizing film may be any as long as it can improve the adhesion between the protective film and the adhesive. Examples of the material for forming such an easy-adhesion layer include polyester resins, urethane resins, acrylic resins, etc., which have a polar group in the skeleton and have a relatively low molecular weight and a relatively low glass transition temperature. Can be done. The polar group present in the skeleton is preferably selected so that the resin is hydrophilic or water-dispersible, and examples thereof include a hydrophilic substituent, an ether bond, and a plurality of ether bonds.

More specific examples of hydrophilic substituents include sulfonic acid groups, carboxylic acid groups, phosphoric acid groups and the like, as well as lithium salts, sodium salts, potassium salts and ammonium salts thereof. The ether bond or the plurality of ether bonds can be a structural unit derived from diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and the like. By introducing a monomer having these substituents or structural units into a polyester-based resin, a urethane-based resin, or an acrylic-based resin, a material constituting the easy-adhesion layer can be obtained.

In addition, a cross-linking agent, an organic or inorganic filler, a surfactant, a lubricant, or the like can be added to the material constituting the easy-adhesion layer, if necessary.

The formation of the easy-adhesive is performed, for example, by a solution containing the material constituting the easy-adhesive layer described above, or a solution containing a precursor of such a material and a polymerization initiator (hereinafter, "composition for easy-adhesive layer"). (Sometimes referred to as) can be applied to one side of a protective film made of a methacrylic resin and then dried, or dried and cured. The easy-adhesion layer may be formed immediately after the protective film made of a methacrylic resin is formed, or may be formed immediately before being bonded to the polarizing film.

The thickness of the easy-adhesion layer is preferably 0.01 to 5 μm, more preferably 0.03 to 0.6 μm after drying or drying / curing. If the easy-adhesion layer is too thin, the adhesive strength between the polarizing film and the protective film may be insufficient. On the contrary, if the easy-adhesion layer is too thick, its hydrophilicity becomes excessive, and the obtained polarizing plate may be inferior in water resistance.

The method of applying the composition for the easy-adhesion layer to the surface of the protective film facing the polarizing film is as follows: die coater, comma coater, reverse roll coater, gravure coater, rod coater, wire bar coater, doctor blade coater, air doctor coater, etc. It is sufficient to adopt the usual coating technique using. The method and conditions for drying the applied composition for the easy-adhesion layer are not particularly limited, but for example, a method of drying using a hot air dryer or an infrared dryer can be adopted. Further, when a solution containing a precursor of a material constituting the easy-adhesive layer is used as the composition for the easy-adhesive layer, a curing step may be provided after drying and curing. Even when the curing process is adopted, the heat used to dry the composition for the easy-adhesive layer promotes curing to some extent, and the subsequent bonding process between the polarizing film and the protective film using an adhesive also promotes curing. Sufficient physical properties can be obtained even with normal temperature curing.

In order to adjust the affinity of the surface of the protective film provided with the easy-adhesive layer to the adhesive, the surface of the easy-adhesive layer provided on the protective film is later attached to the polarizing film via the adhesive before being bonded to the polarizing film. For example, corona discharge treatment, plasma treatment, ozone spraying, ultraviolet irradiation, flame treatment, chemical treatment, and other conventionally known surface treatments can also be performed.

The first protective film and the second protective film can also be protective films having an optical function such as a brightness improving film.

The brightness improving film is used for the purpose of improving the brightness in a liquid crystal display device or the like. For example, a plurality of thin films having different refractive anisotropy are laminated so that the anisotropy of the reflectance occurs. Examples thereof include a reflective polarizing separation sheet designed in the above, an alignment film of a cholesteric liquid crystal polymer, and a circular polarization separation sheet in which the oriented liquid crystal layer is supported on a film substrate.

A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer and an antifouling layer is provided on the surfaces of the first protective film and the second protective film on the opposite side of the polarizing film. It can also be formed. A known method can be used as a method for forming the surface treatment layer on the surface of the protective film.

The first protective film and the second protective film may be the same protective film or different protective films. Examples of cases where the protective films are different are combinations in which the types of thermoplastic resins constituting the protective film are at least different; presence / absence of optical function of the protective film or at least different combinations in the type; presence / absence of a surface treatment layer formed on the surface. Or there are at least different combinations in the type.

The thickness of the first protective film and the second protective film is preferably thin from the viewpoint of thinning the polarizing plate, but if it is too thin, the strength is lowered and the processability is inferior. Therefore, the thickness of the first protective film and the second protective film is preferably 5 to 90 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less, still more preferably 30 μm or less.

As the first protective film and the second protective film, a cyclic polyolefin resin film is preferable. The cyclic polyolefin resin film has a feature that it has low moisture permeability even if it is thin. When the polarizing film becomes thin, the polarizing film generally tends to deteriorate in a high temperature and high humidity environment, but this can be prevented by using a protective film having low moisture permeability.

(Adhesive layer)
The lamination of the polarizing film and the first protective film and the lamination of the polarizing film and the second protective film are performed via the adhesive layer, respectively. Examples of the adhesive forming the adhesive layer include an active energy ray-curable adhesive that can be cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays, an adhesive component dissolved in water, or an adhesive. Examples include water-based adhesives dispersed in water.

When an active energy ray-curable adhesive is adopted, the adhesive layer becomes the cured product layer. As the adhesive, an active energy ray-curable adhesive containing an epoxy-based compound that is cured by cationic polymerization as a curable component is more preferable, and an ultraviolet curable adhesive containing an epoxy-based compound as a curable component is further preferable. The epoxy compound referred to here means a compound having an average of 1 or more, preferably 2 or more epoxy groups in the molecule. Only one type of epoxy compound may be used alone, or two or more types may be used in combination.

An example of an epoxy-based compound that can be preferably used is a hydride-based compound (fat) obtained by reacting an alicyclic polyol obtained by hydrogenating the aromatic ring of an aromatic polyol with epichlorohydrin. Glycidyl ether of a polyol having a cyclic ring); an aliphatic epoxy compound such as an aliphatic polyhydric alcohol or a polyglycidyl ether of an alkylene oxide adduct thereof; one or more epoxy groups bonded to the alicyclic ring in the molecule Includes an alicyclic epoxy compound which is an epoxy compound having.

The active energy ray-curable adhesive may further contain a radically polymerizable (meth) acrylic compound as a curable component. The (meth) acrylic compound is a (meth) acrylate monomer having at least one (meth) acryloyloxy group in the molecule; obtained by reacting two or more kinds of functional group-containing compounds, and at least two in the molecule. Examples thereof include (meth) acryloyloxy group-containing compounds such as (meth) acrylate oligomers having a (meth) acryloyloxy group.

When the active energy ray-curable adhesive contains an epoxy compound that is cured by cationic polymerization as a curable component, it preferably contains a photocationic polymerization initiator. Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-allene complexes. When the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth) acrylic compound, it preferably contains a photoradical polymerization initiator. Examples of the photoradical polymerization initiator include an acetophenone-based initiator, a benzophenone-based initiator, a benzoin ether-based initiator, a thioxanthone-based initiator, xanthone, fluorenone, camphorquinone, benzaldehyde, and anthraquinone.

The active energy ray-curable adhesive may be filled with a cationic polymerization accelerator such as oxetane or polyol, a photosensitizer, an ion trapping agent, an antioxidant, a chain transfer agent, a tackifier, a thermoplastic resin, and the like, if necessary. Additives such as agents, flow conditioners, plasticizers, defoamers, antistatic agents, leveling agents, solvents and the like can be contained.

The thickness of the adhesive layer formed from the active energy ray-curable adhesive is, for example, about 0.01 to 10 μm, preferably about 0.01 to 5 μm, and more preferably 2 μm or less (for example, 1 μm or less). ).

As the water-based adhesive, for example, an adhesive composition using a polyvinyl alcohol-based resin or a urethane resin as a main component is preferable. The thickness of the adhesive layer formed from the water-based adhesive is usually 1 μm or less.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin includes partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetacetyl group-modified polyvinyl alcohol, and methylol group. It may be a modified polyvinyl alcohol-based resin such as modified polyvinyl alcohol and amino group-modified polyvinyl alcohol. The polyvinyl alcohol-based resin is a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as the common weight of vinyl acetate and another monomer copolymerizable therewith. It may be a polyvinyl alcohol-based copolymer obtained by saponifying the coalescence.

The water-based adhesive containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of the polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol-based resin in the adhesive is usually 1 to 10 parts by weight, preferably 5 parts by weight or less, based on 100 parts by weight of water.

In order to improve the adhesiveness, the adhesive composed of an aqueous solution of polyvinyl alcohol resin contains curable components such as polyhydric aldehyde, melamine compound, zirconia compound, zinc compound, glyoxal, and water-soluble epoxy resin, and crosslinks. It is preferable to add an agent. The water-soluble epoxy resin is a polyamide polyamine epoxy resin obtained by reacting epichlorohydrin with a polyamide amine obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid. Can be preferably used. Commercially available products of such polyamide polyamine epoxy resin include "Sumirace Resin (registered trademark) 650" and "Sumiraizu Resin (registered trademark) 675" manufactured by Taoka Chemical Industry Co., Ltd. and "WS-525" manufactured by Seikou PMC Co., Ltd. "And so on. The amount of these curable component and cross-linking agent added (the total amount when both the curable component and the cross-linking agent are added) is usually 1 to 100 parts by weight, preferably 1 part by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin. ~ 50 parts by weight. When the amount of the curable component or the cross-linking agent added is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving the adhesiveness tends to be small, and the curable component or the above-mentioned curable component or When the amount of the cross-linking agent added exceeds 100 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the adhesive layer tends to be brittle.

When a urethane resin is used as the main component of the adhesive, a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group can be mentioned as an example of an appropriate adhesive composition. The polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton, in which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it is directly emulsified in water to form an emulsion without using an emulsifier.

[Display device]
The polarizing plate produced by the present invention can be cut as needed and used in various display devices. The display device is a device having a display element, and includes a light emitting element or a light emitting device as a light emitting source. Examples of the display device include a liquid crystal display device, an organic electroluminescence (EL) display device, an inorganic electroluminescence (EL) display device, an electron emission display device (for example, an electric field emission display device (FED), and a surface electric field emission display device (SED). )), Electronic paper (display devices using electronic ink and electrophoretic elements, plasma display devices, projection type display devices (for example, display devices having a grating light valve (GLV) display device, digital micromirror device (DMD)) and A piezoelectric ceramic display and the like can be mentioned. The liquid crystal display device includes any of a transmissive liquid crystal display device, a transflective liquid crystal display device, a reflective liquid crystal display device, a direct-view type liquid crystal display device, a projection type liquid crystal display device and the like. These display devices may be display devices that display two-dimensional images, or may be stereoscopic display devices that display three-dimensional images.

In a display device, the polarizing plate is usually laminated on the liquid crystal cell via an adhesive layer or an adhesive layer. In the present invention, it is preferable that the pressure-sensitive adhesive layer is laminated via the pressure-sensitive adhesive layer, and the storage elastic modulus of the pressure-sensitive adhesive layer at 23 ° C. is preferably 100 to 1000 KPa. If the storage elastic modulus of the pressure-sensitive adhesive layer is less than 100 KPa, the shrinkage of the polarizing plate during the high-temperature test cannot be suppressed, and appearance defects such as peeling tend to occur. Further, if the storage elastic modulus of the pressure-sensitive adhesive layer is larger than 1000 KPa, the pressure-sensitive adhesive cannot alleviate the strain generated between the glass and the polarizing plate during the thermal shock test, and PVA cracking tends to occur easily.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples. Among the examples, the corona treatment, the measurement of the storage elastic modulus of the pressure-sensitive adhesive layer, the measurement of the tensile elastic modulus of the protective film, and the measurement of the contraction force in the absorption axis direction of the polarizing film were carried out by the following methods.

<Corona processing>
The corona treatment was performed by a corona discharge device manufactured by Kasuga Electric Works Ltd. Specifically, a corona surface treatment frame "STR-1764", a high frequency power supply "CT-0212", and a high voltage transformer "CT-T02W" were used. The film or sheet to be subjected to the corona treatment was subjected to the corona discharge treatment at an output strength of 280 W on the target surface (bonded surface) of the corona treatment while moving at a speed of 10 m / min.

<Measurement of storage elastic modulus of adhesive layer>
As the storage elastic modulus of the pressure-sensitive adhesive layer, the storage elastic modulus (G') of the pressure-sensitive adhesive layer at 23 ° C. was measured by the following method. First, an adhesive layer is provided on one side of a polarizing plate [trade name "Sumikaran (registered trademark) SRW062" manufactured by Sumitomo Chemical Co., Ltd.) in which a protective film (TAC) having a thickness of 40 μm is laminated on both sides of a polarizing film. A polarizing plate with an agent was prepared, and then a 4 cm × 4 cm fragment was cut from this. The release film is peeled off from the pressure-sensitive adhesive layer, and the exposed pressure-sensitive adhesive layer is in accordance with JIS K7244-10: 1999 "Plastic-Test method for dynamic mechanical properties-Part 10: Complex shear viscosity by parallel plate vibration rheometer". , Anton-Paar's measuring instrument "Physica MCR301" was used to measure the storage elastic modulus. For the measurement, a parallel plate having a diameter of 25 mm was used, and a storage elastic modulus at 23 ° C. was determined by a torsional shear method having a frequency of 1 Hz.

<Measurement of tensile elastic modulus of protective film>
The tensile elastic modulus of the protective film was measured as follows. First, using the universal testing machine "Autograph AG-I" manufactured by Shimadzu Corporation equipped with a constant temperature bath, the protective film to be measured was cut into pieces of width 10 mm x length 200 mm, and the distance between the marked lines of the measuring machine was 100 mm. And set it in this. Next, the elastic modulus when pulled at a test speed of 50 mm / min was determined according to JIS K 7127: 1999 “Tensile test method for plastic films and sheets”. The following are measurement results in an environment of 23 ° C. unless otherwise specified.

<Measurement of shrinkage force in the absorption axis direction of polarizing film>
Ogino Seiki Co., Ltd. made a fragment of 2 mm wide x 50 mm long so that the absorption axis direction of the laminated film is the long axis for the three-layer laminated film (base film / primer layer / polarizing film layer) that has undergone the dyeing process. It was cut with a super cutter made by Seisakusho. The base film was peeled off from the obtained strip-shaped laminated film to prepare a shrinkage force measurement sample. Set the shrinkage force measurement sample in a thermomechanical analyzer [“TMA / 6100” manufactured by Hitachi High-Tech Science Corporation] with a chuck-to-chuck distance of 10 mm, leave the test piece in a room at 20 ° C for a sufficient time, and then sample the sample. The temperature in the room was raised from 20 ° C. to 80 ° C. in 1 minute, and after the temperature was raised, the temperature in the sample room was set to be maintained at 80 ° C. After the temperature was raised and left for 4 hours, the contraction force in the long side direction of the measurement sample was measured in an environment of 80 ° C. In this measurement, the static load was 0 mN, and a SUS probe was used as the jig.

[Example 1]
(1) Resin layer forming step An unstretched polypropylene (PP) film (melting point 163 ° C.) having a thickness of 90 μm was used as a base film, and the surface thereof was subjected to corona treatment to form a primer layer on the corona treated surface. .. For the primer layer, polyvinyl alcohol powder [manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization 1100, saponification degree 99.5 mol%, trade name "Z-200"] is dissolved in hot water at 95 ° C. and has a concentration of 3. A mixed aqueous solution prepared by preparing a weight% aqueous solution and adding 5 parts by weight of a cross-linking agent [manufactured by Taoka Chemical Industry Co., Ltd., trade name "Smiley's Resin (registered trademark) 650]" to 6 parts by weight of polyvinyl alcohol powder. The primer layer was formed by coating the corona-treated surface of the base film with a small-diameter gravure coater and drying the mixed aqueous solution at 80 ° C. for 10 minutes. The thickness of the primer layer was 0.2 μm. Met.

Next, polyvinyl alcohol powder [trade name "PVA124" manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, saponification degree 98.0-99.0 mol%] was dissolved in hot water at 95 ° C. to a concentration of 8% by weight. An aqueous solution of polyvinyl alcohol was prepared. The obtained aqueous solution was applied onto the primer layer using a lip coater and dried at 80 ° C. for 20 minutes to prepare a three-layer laminated film composed of a base film, a primer layer and a resin layer.

(2) Stretching Step The laminated film was stretched 5.3 times at 160 ° C. using a floating longitudinal uniaxial stretching device to obtain a stretched film.

(3) Dyeing Step After that, the stretched film was immersed in a dyeing solution which is a mixed aqueous solution of iodine and potassium iodide at 30 ° C. for about 180 seconds for dyeing, and then the excess iodine solution was washed away with pure water at 10 ° C. Then, it was immersed in the cross-linked solution 1 which is a boric acid aqueous solution at 78 ° C. for 120 seconds, and then immersed in the cross-linked solution 2 at 70 ° C. containing boric acid and potassium iodide for 60 seconds. Then, it was washed with pure water at 10 ° C. for 10 seconds, finally dried at 40 ° C. for 150 seconds, and then dried at 55 ° C. for 150 seconds.
A polarizing film layer was formed from the resin layer by the above steps to obtain a polarizing laminated film. The compounding ratio of each solution is as follows.

<Staining solution>
Water: 100 parts by weight Iodine: 0.6 parts by weight Potassium iodide: 10 parts by weight <Crosslink solution 1>
Water: 100 parts by weight Boric acid: 9.5 parts by weight <Crosslink solution 2>
Water: 100 parts by weight Boric acid: 5.0 parts by weight Potassium iodide: 6 parts by weight

(4) Preparation of Adhesive The following components were mixed and defoamed to prepare an ultraviolet curable resin adhesive in a liquid state. As the photocationic polymerization initiator, one obtained in the form of a 50% propylene carbonate solution was used. The blending amount (2.25 parts) shown below is the amount of solid content.

3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate 75 parts 1,4-butanediol diglycidyl ether 20 parts 2-ethylhexyl glycidyl ether 5 parts triarylsulfonium hexafluorophosphate-based photocationic polymerization initiator
2.25 copies

(5) First Laminating Step As the first protective film, a protective film having a thickness of 23 μm formed from a cyclic polyolefin resin having a corona treatment on the bonded surface [trade name “Zeonoa Film” manufactured by Nippon Zeon Co., Ltd. ZF14-023 ”, tensile elastic modulus in the transport direction: 2100 MPa, tensile elastic modulus in the direction perpendicular to the transport direction: 2100 MPa] was prepared. The same ultraviolet curable adhesive was applied to the corona-treated surface of the first protective film with a microgravure coater, and on the surface of the polarizing film layer of the polarizing laminated film produced in (3) opposite to the base film side. It was pasted together.
After that, using an ultraviolet irradiation device with a belt conveyor equipped with an ultraviolet lamp "D bulb" manufactured by Fusion UV Systems, ultraviolet rays are irradiated from the protective film side so that the integrated light amount becomes 250 mJ / cm ^2, and the ultraviolet curability. The adhesive was cured. From the above, a five-layer film composed of a base film / primer layer / polarizing film layer / ultraviolet curable adhesive layer / first protective film was obtained. The thickness of the polarizing film layer was 5.6 μm. The thickness of the adhesive layer after curing was 1.0 μm.

(6) Peeling Step and Second Laminating Step The base film was peeled off from the five-layer structure film produced in (5) above to obtain a polarizing plate with a single-sided protective film. The base film could be easily peeled off. Next, the same protective film as that used in (5) was used as the second protective film, and the same ultraviolet curable adhesive was applied to the corona-treated surface using a microgravure coater, and this was applied to the single-sided protection. It was bonded to the primer layer surface of the polarizing plate with a film. Next, the adhesive layer was cured by irradiating ultraviolet rays from the second protective film side under the same conditions as in (5) to obtain a polarizing plate. The thickness of the adhesive layer after curing was 1.0 μm.

[Example 2]
(3) A polarizing plate was produced in the same manner as in Example 1 except that the drying conditions in the dyeing step were changed to dry at 50 ° C. for 150 seconds and then at 65 ° C. for 150 seconds. The thickness of the polarizing film layer was 5.7 μm.

[Example 3]
(3) A polarizing plate was produced in the same manner as in Example 1 except that the drying conditions in the dyeing step were changed to dry at 50 ° C. for 150 seconds and then at 85 ° C. for 150 seconds. The thickness of the polarizing film layer was 5.4 μm.

[Comparative Example 1]
(3) A polarizing plate was produced in the same manner as in Example 1 except that the drying conditions in the dyeing step were changed to dry at 40 ° C. for 150 seconds and then at the same temperature for 150 seconds. The thickness of the polarizing film layer was 5.4 μm.

[Comparative Example 2]
(3) Examples except that the blending amount of potassium iodide in the cross-linking solution 2 in the dyeing step was changed to 8 parts, and the drying conditions were changed to dry at 40 ° C. for 150 seconds and then to dry at the same temperature for 150 seconds. A polarizing plate was produced in the same manner as in 1. The thickness of the polarizing film layer was 5.5 μm.

[Comparative Example 3]
After (2) the stretching ratio in the stretching step was changed to 5.8 times, (3) the amount of potassium iodide in the cross-linked solution 2 in the dyeing step was changed to 6 parts, and the drying conditions were dried at 40 ° C. for 150 seconds. A polarizing plate was prepared in the same manner as in Example 1 except that the results were changed so as to dry at the same temperature for 150 seconds. The thickness of the polarizing film layer was 5.7 μm.

<Measurement of piercing strength per unit film thickness of polarizing film>
The polarizing plates produced in Examples and Comparative Examples were subjected to an ultrasonic cleaner while being immersed in cyclohexane, the protective films bonded on both sides were dissolved and removed, and the polarizing film was taken out and pierced. The piercing test uses a handy compression tester "KES-G5 Needle Penetration Force Measurement Specification" manufactured by Kato Tech Co., Ltd. equipped with a needle with a tip diameter of 1 mmφ and 0.5R, and is used in an environment with a temperature of 23 ± 3 ° C. The piercing speed was 0.33 cm / sec. The piercing strength measured in the piercing test was the average value obtained by performing the piercing test on 12 test pieces.
The thickness of the polarizing film was measured with a contact film thickness meter [trade name "DIGIMICRO (registered trademark) MH-15M" manufactured by Nikon Corporation], and the puncture strength (strength P) per unit film thickness was determined.

<Measurement of optical characteristics of polarizing film>
The polarizing films (peeled from the base film) obtained in Examples and Comparative Examples were bonded to soda glass using an optically transparent acrylic adhesive to prepare an optical property measurement sample. The optical characteristics of the polarizing film were measured with a spectrophotometer with an integrating sphere [trade name "V7100" manufactured by JASCO Corporation], and the respective measurement results are shown in Table 1.

At the time of measurement, the optical characteristic measurement sample was set in the spectrophotometer with the polarizing film side as the detector side. Explaining a specific measurement method, MD transmittance (MD) and TD transmittance (TD) are obtained in the wavelength range of 380 to 780 nm, and a single substance at each wavelength is obtained based on the following equations (3) and (4). The transmittance and degree of polarization are calculated, and the luminosity factor is corrected by the 2 degree field (C light source) of JIS Z 8701: 1999 "Color display method-XYZ color system and X10Y10Z10 color system". The transmittance (Ty) and the luminosity factor correction polarization degree (Py) were determined.
Elemental transmittance (%) = (MD + TD) / 2 (3)
Polarization degree (%) = [(MD-TD) / (MD + TD)] × 100 (4)

Here, the "MD transmittance" is the transmittance when the direction of polarized light emitted from the Gran Thomson prism and the transmission axis of the polarizing plate sample are parallel, and the "TD transmittance" is from the Gran Thomson prism. This is the transmittance when the direction of the emitted polarized light and the transmission axis of the polarizing plate sample are orthogonal to each other.

(Measurement of hue)
The single hue (single a, single b) of the polarizing film was also measured with a spectrophotometer with an integrating sphere [trade name "V7100" manufactured by JASCO Corporation]. Here, the single hue means the hue of transmitted light when light is incident on one polarizing plate. The a value and the b value are color values expressed in the Hunter Lab color system, and the tristimulus values X, Y and the tristimulus values specified in JIS Z 8722: 2009 "Color measurement method-reflection and transmission object color". Obtained from Z. The results are shown in Table 1.

(Measurement of absorbance at a wavelength of 700 nm)
The polarization performance on the long wavelength side of the polarizing film was judged by the absorbance at a wavelength of 700 nm. The absorbance is a positive number obtained by taking the logarithm of the orthogonal transmittance (Tc) obtained from the MD transmittance (MD) and the TD transmittance (TD) at a wavelength of 700 nm, and is obtained by the following formula. The larger the absorbance, the smaller the deterioration of the optical properties in a high temperature environment, and the better the heat resistance.
Tc (700) (%) = [MD (700 nm) / 100] x [TD (700 nm) / 100] x 100
A700 = -log [Tc (700) / 100]

<Cold thermal impact test of polarizing plate>
Corona treatment was performed on the second protective film side of the polarizing plates produced in Examples and Comparative Examples, and an adhesive (storage elastic modulus: 390 KPa, thickness: 20 μm) was bonded to prepare a polarizing plate with an adhesive. .. A polarizing plate with an adhesive was cut out with a super cutter on a long side of 100 mm and a short side of 60 mm so that the absorption axis was parallel to the long side, and used as a thermal shock test evaluation sample. This evaluation sample is attached to a non-alkali glass plate [“Eagle-XG (registered trademark)” manufactured by Corning Inc.] on the pressure-sensitive adhesive layer side, and applied in an autoclave at a temperature of 50 ° C. and a pressure of 5 MPa for 20 minutes. It was pressure-treated and left for one day in an atmosphere at a temperature of 23 ° C. and a relative humidity of 60%. After that, in a cold shock tester (TSA-301L-W) manufactured by ESPEC CORPORATION, holding at -40 ° C on the low temperature side for 30 minutes and then holding at 85 ° C on the high temperature side for 30 minutes was set as one cycle. A durability test was conducted for 100 cycles. During the test, it was not exposed to room temperature. Each of the 50 evaluation samples was subjected to a durability test for 100 cycles, and the number of the 50 evaluation samples for which the occurrence of crack-like appearance defects was visually confirmed is shown in the “Cold thermal impact test” column of Table 1. .. For example, "0/50" in Example 1 means that, out of 50 evaluation samples, the number of sheets for which the occurrence of crack-like appearance defects could be visually confirmed was 0.

According to the present invention, there is provided a polarizing plate which is thin and has a small shrinkage rate when heat is applied. Further, according to the present invention, there is provided a polarizing plate having excellent durability in which cracks generated in the polarizing film are suppressed in an environment where high temperature and low temperature are repeated. Since the polarizing plate of the present invention has a small shrinkage rate, even if it is applied to a liquid crystal panel having a narrow frame, the polarizing plate shrinks in a high temperature environment so that the end of the polarizing plate enters the visible area. It can be suppressed.

Claims (4)

The dichroic dye is adsorbed and oriented on the uniaxially stretched polyvinyl alcohol-based resin layer.
The absorbance (A700) at a wavelength of 700 nm is 3.0 or more.
A polarizing film having a transmission hue b value of 2 to 3.5.
The piercing strength per unit film thickness is 5.0 to 7.0 gf / μm.
A polarizing film having a shrinkage force of 1.6 N or less per width of 2 mm in the absorption axis direction when held at a temperature of 80 ° C. for 240 minutes. The polarizing film according to claim 1, which has a thickness of 10 μm or less. A polarizing plate formed by laminating a first protective film on one side of the polarizing film according to claim 1 or 2. The polarizing plate according to claim 3, wherein a second protective film is laminated on the other surface of the polarizing film.