JP6123677B2 - Optical film and manufacturing method thereof, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to an optical film, a manufacturing method thereof, a polarizing plate, and a liquid crystal display device.

  Liquid crystal display devices are widely used as liquid crystal displays for televisions and personal computers. The liquid crystal display device includes a liquid crystal cell, a pair of polarizing plates sandwiching the liquid crystal cell, and a backlight. The polarizing plate usually has a polarizer and a pair of protective films that sandwich the polarizer.

  In the manufacturing process of the liquid crystal display device, the polarizing plate and the liquid crystal cell are bonded together with an adhesive. At that time, if a bonding error occurs, the polarizing plate may be peeled off from the liquid crystal cell and reattached. However, when the polarizing plate is peeled off from the liquid crystal cell, there is a problem that the polarizing plate is easily torn. Therefore, the protective film constituting the polarizing plate is required to be able to be easily peeled off without tearing the polarizing plate from the liquid crystal cell when a bonding error occurs (good reworkability). .

  As protective films with improved reworkability, cellulose ester films with adjusted water absorption modulus (for example, Patent Document 1), cellulose ester films with adjusted tan δ (for example, Patent Document 2), and acyl group substitution degree are adjusted. A film containing cellulose ester (for example, Patent Document 3) has been proposed. In addition, a pressure-sensitive adhesive composition containing a (meth) acrylic resin and a crosslinking agent (for example, Patent Document 4) has been proposed as a pressure-sensitive adhesive for bonding a polarizing plate and a liquid crystal cell and improving reworkability. Yes.

  By the way, as a protective film, depending on the required optical properties, not only a film mainly composed of cellulose ester but also a film mainly composed of (meth) acrylic resin is used. As a molding material containing a (meth) acrylic resin as a main component, for example, a resin composition containing a (meth) acrylic resin and an alkyl phosphate metal salt is known (for example, Patent Document 5).

JP 2003-232926 A JP 2004-206038 A JP 2009-249386 A JP 2011-137065 A Japanese Patent Laid-Open No. 7-216179

  However, the film which has a (meth) acrylic resin as a main component is harder and more brittle than the film which has a cellulose ester as a main component as described in Patent Documents 1 to 4. Therefore, the polarizing plate including a film containing a (meth) acrylic resin as a main component has a problem that when it is peeled off from the liquid crystal cell once bonded, it is easily torn and has low reworkability.

  In addition, as the liquid crystal display device is made thinner, the protective film is required to be thinner. A protective film having a thin film thickness has a problem that reworkability is further lowered because of its low mechanical strength.

  Thus, a thin film thickness and high reworkability; that is, a highly flexible (meth) acrylic resin film is required. The (meth) acrylic resin film is usually produced by a melt film forming method. Therefore, in order to increase the flexibility of the (meth) acrylic resin film, it is effective to increase the melting temperature and increase the fluidity of the molten resin. However, when the melting temperature is increased, there is a problem that the molten resin is easily deteriorated, and the resulting film is colored, is brittle and has low flexibility, or does not satisfy desired optical characteristics.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical film containing a (meth) acrylic resin as a main component, having no coloring, a thin film thickness, and excellent reworkability. To do.

[1] An optical film comprising a composition containing a (meth) acrylic resin and an acid trapping agent, having a breaking stress of 70 MPa or more, a tear strength of 10 mN or more, and a film thickness of 10 to 45 μm. .
[2] The optical film according to [1], wherein the acid trapping agent is an alkyl phosphate metal salt.
[3] The optical film according to [1] or [2], wherein the content of the acid trapping agent is 0.1 to 5% by mass with respect to the composition.
[4] The optical film according to any one of [1] to [3], wherein the composition further contains a cellulose ester.
[5] The optical film according to [4], wherein the cellulose ester is cellulose acetate propionate.
[6] The content ratio of the (meth) acrylic resin and the cellulose ester is (meth) acrylic resin / cellulose ester = 90/10 to 50/50 by mass ratio, according to [4] or [5]. Optical film.
[7] The optical film according to any one of [1] to [6], wherein the (meth) acrylic resin has a lactone ring structure.
[8] The optical film according to any one of [1] to [7], wherein the composition further contains an acrylonitrile / styrene copolymer.

[9] A polarizing plate protective film comprising the optical film according to any one of [1] to [8].
[10] The polarizing plate protective film according to [9], which is defined by the following formula and has a retardation Rth in the thickness direction measured at a wavelength of 590 nm of −5 nm to 5 nm.
Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction in the film plane, ny: refractive index in the direction perpendicular to the slow axis in the film plane, nz: refractive index of the film in the thickness direction, d: film thickness (Nm))
[11] A polarizing plate comprising a polarizer and the polarizing plate protective film according to [9] or [10] disposed on at least one surface of the polarizer.
[12] A liquid crystal display device comprising a liquid crystal cell and the polarizing plate according to [11] disposed on at least one surface of the liquid crystal cell.
[13] The method for producing an optical film according to any one of [1] to [8], wherein the resin composition containing the (meth) acrylic resin and the acid trapping agent is melt-kneaded. The manufacturing method of an optical film including the step extruded in a film form.
[14] The method for producing an optical film according to [13], wherein the resin composition further contains a cellulose ester.
[15] The method for producing an optical film according to [13] or [14], wherein the melting temperature of the resin composition is 240 to 270 ° C.

  According to the present invention, it is possible to provide an optical film that contains a (meth) acrylic resin as a main component, is not colored, is thin, and has excellent reworkability.

It is a schematic diagram which shows an example of the manufacturing apparatus of a film. It is a schematic diagram which shows an example of the basic composition of a liquid crystal display device.

1. Optical film The optical film of this invention contains the composition containing a (meth) acrylic resin and an acid trap agent. The composition preferably further contains a cellulose ester.

(Meth) acrylic resin The (meth) acrylic resin is preferably a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and another copolymerizable monomer. The content ratio of the structural unit derived from methyl methacrylate in the copolymer is preferably 50% by mass or more, and more preferably 70% by mass or more.

  Examples of the copolymerization monomer in the copolymer include an alkyl methacrylate having 2 to 18 carbon atoms in the alkyl portion; an alkyl acrylate having 1 to 18 carbon atoms in the alkyl portion; a hydroxyl group that can form a lactone ring structure described later. Alkyl (meth) acrylate having 1 to 18 carbon atoms in the alkyl moiety; α, β-unsaturated acid such as acrylic acid and methacrylic acid; unsaturated group-containing divalent carboxylic acid such as maleic acid, fumaric acid and itaconic acid Aromatic vinyl compounds such as styrene and α-methylstyrene; α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, acryloylmorpholine (ACMO); ) And the like; N-vinylpyrrolidone (VP) and the like. These may be used alone or in combination of two or more.

  Among these copolymerization monomers, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate are used to improve the thermal decomposition resistance and fluidity of the copolymer. Alkyl (meth) acrylates having a hydroxyl group such as methyl 2- (hydroxymethyl) acrylate and ethyl 2- (hydroxymethyl) acrylate are preferred. In order to enhance the compatibility with the cellulose ester, acryloylmorpholine and the like are preferable.

The (meth) acrylic resin preferably contains a lactone ring structure from the viewpoint of enhancing the heat resistance of the resulting optical film or adjusting the photoelastic coefficient. The lactone ring structure contained in the (meth) acrylic resin is preferably represented by the following general formula (1).

In Formula (1), R < ¹ > -R < ³ > shows a hydrogen atom or a C1-C20 organic residue each independently. The organic residue may contain an oxygen atom. Examples of organic residues include linear or branched alkyl groups, linear or branched alkylene groups, aryl groups, -OAc groups (Ac is an acetyl group), -CN groups, and the like. The lactone ring structure represented by the formula (1) is a structure derived from an alkyl (meth) acrylate having a hydroxyl group, as will be described later.

The (meth) acrylic resin containing a lactone ring structure further includes a structural unit derived from an alkyl (meth) acrylate having 1 to 18 carbon atoms in the alkyl portion, and if necessary, a monomer containing a hydroxyl group, an unsaturated carboxylic acid A structural unit derived from an acid, a monomer represented by the general formula (2), or the like may be further included. R ⁴ in the general formula (2) represents a hydrogen atom or a methyl group. X is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, -OAc group (Ac: acetyl group), -CN group, acyl group or -C-OR group (R is a hydrogen atom or 1 to carbon atoms) 20 organic residues).

  The content ratio of the lactone ring structure represented by the formula (1) in the (meth) acrylic resin containing a lactone ring structure is preferably 5 to 90% by mass, more preferably 10 to 80% by mass, More preferably, it is 15-70 mass%. When the content of the lactone ring structure is more than 90% by mass, the molding processability is low, and the flexibility of the obtained film tends to be low. When the content of the lactone ring structure is less than 5% by mass, it is difficult to obtain a film having a necessary retardation, and heat resistance, solvent resistance, and surface hardness may not be sufficient.

  The content ratio of the structural unit derived from alkyl (meth) acrylate in the (meth) acrylic resin containing a lactone ring structure is preferably 10 to 95% by mass, more preferably 20 to 90% by mass, Preferably it is 30-85 mass%.

  In the (meth) acrylic resin containing a lactone ring structure, the content ratio of the structural unit derived from the hydroxyl group-containing monomer, the unsaturated carboxylic acid or the monomer represented by the general formula (2) is preferably preferably 0 to 30. It is mass%, More preferably, it is 0-20 mass%, More preferably, it is 0-10 mass%.

  The (meth) acrylic resin containing a lactone ring structure is obtained by polymerizing a monomer component containing at least an alkyl (meth) acrylate having a hydroxyl group and another alkyl (meth) acrylate to form a hydroxyl group in the molecular chain. It can be produced through a step of obtaining a polymer having an ester group; a step of introducing a lactone ring structure by heat-treating the obtained polymer.

The weight average molecular weight Mw of the (meth) acrylic resin is preferably in the range of 8.0 × 10 ^{4 to} 5.0 × 10 ⁵ , more preferably 9.0 × 10 ^{4 to} 4.5 × 10 ⁵ . It is in the range, and more preferably in the range of 1.0 × 10 ^{5 to} 4.0 × 10 ⁵ . If the weight average molecular weight Mw of the (meth) acrylic resin is less than 8.0 × 10 ⁴ , the resulting film may be too brittle, and if it exceeds 5.0 × 10 ⁵ , the viscosity of the melt It is too high or the resulting film has a high haze.

The weight average molecular weight Mw of the (meth) acrylic resin can be measured by gel permeation chromatography. The measurement conditions are as follows.
Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2800000-500 calibration curves with 13 samples are used. The 13 samples are preferably used at approximately equal intervals.

  The (meth) acrylic resin can be produced by a known method such as suspension polymerization, emulsion polymerization, solution polymerization or bulk polymerization. As the polymerization initiator, a normal peroxide compound, azo compound, or redox compound can be used. The polymerization temperature can be about 30 to 100 ° C. for suspension polymerization or emulsion polymerization; it can be about 80 to 160 ° C. for solution polymerization or bulk polymerization. In order to adjust the reduced viscosity of the resulting polymer, alkyl mercaptan or the like may be used as a chain transfer agent.

  Examples of commercially available (meth) acrylic resins include Delpet 60N, 80N (Asahi Kasei Chemicals Corporation), Dialnal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electricity). Chemical Industry Co., Ltd.).

  The (meth) acrylic resin may be one type or a mixture of two or more types.

Cellulose ester Cellulose ester is a compound obtained by esterifying cellulose with aliphatic carboxylic acid or aromatic carboxylic acid. The acyl group contained in the cellulose ester is an aliphatic acyl group or an aromatic acyl group, preferably an aliphatic acyl group. The aliphatic acyl group may be linear or branched and may further have a substituent. The portion that is not substituted with an acyl group usually exists as a hydroxyl group.

  The cellulose ester has a total acyl group substitution degree (Dall) of 2.0 to 3.0 from the viewpoint of enhancing compatibility with the (meth) acrylic resin or imparting brittleness of the resulting film. Is preferable, and it is more preferable that it is 2.5-3.0. When the total substitution degree of the acyl group of the cellulose ester is less than 2.0, the (meth) acrylic resin and the cellulose ester may not be sufficiently compatible, and the resulting film may have high haze.

  Among these, it is preferable that the substitution degree of a C3-C7 acyl group is 1.2-3.0, and it is more preferable that it is 2.0-3.0. When the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, the (meth) acrylic resin and the cellulose ester are not sufficiently compatible with each other, and the resulting film has high haze or high brittleness. Because it does.

  The substitution degree of the acyl group can be measured by a method prescribed in ASTM-D817-96.

  Examples of cellulose esters include cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, cellulose butyrate, preferably cellulose acetate propionate, cellulose propionate. It is.

The weight average molecular weight Mw of the cellulose ester resin is preferably 7.5 × 10 ⁴ or more, and is preferably 7.5 × 10 ^{4 to} 2.4 × 10 ⁵ from the viewpoint of enhancing the compatibility with the (meth) acrylic resin. more preferably in the range of, more preferably in the range of ^{1.0 × 10 5 ~2.4 × 10 5} , in the range of 1.6 × ^{10 5} ~2.4 × ¹⁰ 5 Particularly preferred. When the weight average molecular weight Mw is less than 7.5 × 10 ⁴ , the resulting film has low flexibility and heat resistance may be insufficient. On the other hand, when the weight average molecular weight Mw is more than 2.4 × 10 ⁵ , the melt has a high viscosity and is difficult to melt and extrude, and has a low compatibility with the (meth) acrylic resin. Haze tends to rise.

  The Tg of the cellulose ester is preferably 100 ° C. or higher, and more preferably 120 ° C. or higher. The upper limit of the Tg of the cellulose ester can be about 190 ° C. Tg of cellulose ester can be measured by a method based on JIS K7121.

  Cellulose esters can be synthesized by known methods. Specifically, cellulose is esterified with an organic acid having at least 3 carbon atoms containing acetic acid or an anhydride thereof or an anhydride thereof in the presence of a catalyst to synthesize a triester of cellulose. The cellulose triester is then hydrolyzed to synthesize a cellulose ester resin having the desired degree of acyl substitution. After the obtained cellulose ester resin is filtered, precipitated, washed with water, dehydrated and dried, a cellulose ester resin can be obtained (see the method described in JP-A-10-45804).

  As the raw material cellulose, for example, cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like can be used. The cellulose used as a raw material may be only one type or a mixture of two or more types.

  The total content of the (meth) acrylic resin and the cellulose ester in the optical film of the present invention is preferably 55% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass with respect to the optical film. That's it.

  The content ratio (mass ratio) of the (meth) acrylic resin and the cellulose ester is preferably (meth) acrylic resin: cellulose ester = 95: 5 to 30:70, and preferably 90:10 to 50:50. More preferably, it is more preferably 90:10 to 60:40.

  When the content ratio of the (meth) acrylic resin is more than 95% by mass with respect to the total of the (meth) acrylic resin and the cellulose ester, the effect of the cellulose ester is not sufficiently obtained, and when it is less than 30% by mass, The resulting film may have sufficient heat and humidity resistance.

  The optical film of the present invention may further contain other resins other than the (meth) acrylic resin and the cellulose ester as long as the effects of the present invention are not impaired.

  Preferable examples of other resins include styrene resins. The styrenic resin is a homopolymer of styrene monomer (polystyrene), a copolymer of a styrene monomer and another copolymerizable monomer, or a modified product of these polymers, preferably styrene monomer and other It is a copolymer with a copolymerizable monomer. The content ratio of the structural unit derived from the styrene monomer in the copolymer is preferably in the range of 0 to 20% by mass.

  Examples of styrene monomers and other copolymerizable monomers include maleic anhydride, acrylonitrile, maleimide and the like, preferably acrylonitrile. The styrene / acrylonitrile copolymer can impart flexibility to a film containing the copolymer.

Acid Trap Agent The composition constituting the optical film of the present invention further contains an acid trap agent. Preferable examples of the acid trapping agent include alkyl phosphate metal salts and compounds containing an epoxy group.

  The alkyl phosphate metal salt is a metal salt of an alkyl phosphate having 2 to 20 carbon atoms. The metal atom constituting the alkyl phosphate metal salt is a Group 2 or Group 12 metal atom, and preferably includes zinc, calcium, magnesium and the like.

  Examples of the alkyl phosphoric acid having 2 to 20 carbon atoms constituting the metal alkyl phosphate include ethyl phosphoric acid, butyl phosphoric acid, lauryl phosphoric acid, stearyl phosphoric acid and the like, preferably stearyl phosphoric acid.

  Examples of commercially available alkyl phosphate metal salts include LBT-1830 manufactured by Sakai Chemical Co., Ltd.

  Examples of compounds containing epoxy groups include epoxidized vegetable oils such as epoxidized soybean oil, epoxidized linseed oil, epoxidized fatty acid alkyl esters, epoxidized 1,2 polybutadiene and the like. Examples of the epoxidized fatty acid alkyl ester include epoxidized fatty acid octyl ester (Adeka Sizer D-32 manufactured by Asahi Denka Co., Ltd.), epoxidized fatty acid isobutyl ester (Adeka Sizer D-55 manufactured by Asahi Denka Co., Ltd.), and the like. Examples of the epoxidized 1,2 polybutadiene include Adekasizer BF-1000 (average molecular weight 10,000). Examples of the compound containing an epoxy group include compounds containing an epoxy group described in US Pat. No. 4,137,201.

  As will be described later, the optical film of the present invention can be obtained through a step of extruding after melt-kneading a resin composition containing a (meth) acrylic resin and an acid trapping agent. In order to obtain an optical film having high reworkability; that is, to obtain an optical film having high flexibility, it is effective to increase the resin fluidity by increasing the melting temperature when melt-kneading the resin composition. However, when the melting temperature is increased, the monomer remaining in the raw material (meth) acrylic resin is thermally decomposed to generate an acid, or the ester portion of the cellulose ester is hydrolyzed to generate an acid. Acid tends to cause thermal degradation of the resin. On the other hand, since the acid trapping agent can trap these acids, thermal degradation of the resin can be suppressed even if the melting temperature is increased.

  The content of the acid trapping agent is preferably 0.1% by mass or more, preferably 0.5% by mass or more with respect to the composition in order to suppress thermal decomposition of the resin during melt kneading described later. More preferably, it is more preferably 1.0% by mass or more. On the other hand, when the content of the acid trapping agent is too large, the resulting optical film is prevented from bleeding out or from fading the polarizer when the obtained optical film and the polarizer are bonded together. Therefore, the content of the acid trapping agent is preferably 5.0% by mass or less.

  The optical film of the present invention further contains additives such as a lubricant, an antioxidant, a thermal degradation inhibitor, an ultraviolet absorber, a colorant, and fine particles (matting agent) as long as the effects of the present invention are not impaired. Also good.

Lubricant The composition constituting the optical film of the present invention may further contain a lubricant in order to improve transparency and surface quality. The lubricant can not only lower the melt viscosity of the resin composition described later and improve the kneadability, but also can suppress the retention of the molten resin in the extruder or the die during the melt extrusion.

  The lubricant can be an ester wax or a polyhydric alcohol fatty acid ester. Ester waxes are compounds obtained by esterifying all hydroxyl groups of a polyhydric alcohol with a fatty acid. Polyhydric alcohol fatty acid esters are compounds obtained by esterifying a part of hydroxyl groups of a polyhydric alcohol with a fatty acid.

  As will be described later, the fatty acid constituting the ester wax or the polyhydric alcohol fatty acid ester has 12 carbon atoms from the viewpoint of suppressing contamination of the process due to volatilization under heating and increasing the compatibility with the cellulose ester. A fatty acid of ˜22 is preferred. The fatty acid may be a saturated fatty acid or an unsaturated fatty acid, but a saturated fatty acid is preferable from the viewpoint of deodorization and prevention of discoloration during storage.

  Examples of such saturated fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, erucic acid, 12-hydroxyoleic acid, etc. Stearic acid is preferred. One type of fatty acid may be used, or a mixture of two or more types may be used.

  Examples of the polyhydric alcohol constituting the ester wax or polyhydric alcohol fatty acid ester include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propane Diol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol 1,6-hexanediol, 1,2,3-hexanetriol, 1,2,6-hexanetriol, glycerin, diglycerin, galactitol, inositol, mannitol, 3-methylpentane-1,3,5-triol The Call, sorbitol, trimethylol propane, trimethylol ethane, pentaerythritol, dipentaerythritol, and the like xylitol. These alcohols may be one kind or a mixture of two or more kinds.

  Preferable examples of the ester wax include pentaerythritol tetrafatty acid ester, dipentaerythritol hexafatty acid ester, glycerin trifatty acid ester and the like.

  Preferred examples of the polyhydric alcohol fatty acid esters include glycerin or diglycerin fatty acid monoester or diester; sorbitol fatty acid monoester, diester or triester; sorbitan fatty acid monoester, diester or triester, more preferably Is fatty acid monoester or diester of glycerin or diglycerin, fatty acid monoester, diester or triester of sorbitan, more preferably glycerin fatty acid monoester.

  Ester waxes can reduce friction between an inner wall surface (metal surface) of an extruder and a molten resin, which will be described later, and can reduce shear heat generation. However, since ester waxes have low compatibility with (meth) acrylic resins and cellulose esters, the effect of lowering the melt viscosity is small, and the resulting film tends to bleed out.

  Polyhydric alcohol fatty acid esters have a smaller effect on reducing the friction between the inner wall (metal surface) of the extruder and the molten resin than ester waxes, but the effect of lowering the melt viscosity is great, so shear heat generation can be reduced. . In addition, since polyhydric alcohol fatty acid esters are highly compatible with (meth) acrylic resins and cellulose esters, the resulting film is less likely to bleed out. Therefore, it is preferable to use polyhydric alcohol fatty acid esters.

  The esterification reaction of ester waxes or polyhydric alcohol fatty acid esters is beef tallow, pork tallow, chicken tallow, fish oil, soybean oil, corn oil, rapeseed oil, palm oil, sunflower oil, safflower oil, castor oil or their hydrogen. One or a mixture of two or more of the additive oils and glycerin, diglycerin or sorbitol are subjected to a transesterification reaction, and then the resulting reaction product can be purified. The purification method may be a method such as molecular distillation, solvent fractionation, recrystallization, column chromatography, or supercritical gas extraction, and molecular distillation is generally used from the viewpoint of ease of production, quality, and price.

  The content of the ester wax or the polyhydric alcohol fatty acid ester is preferably 0.05 to 2.0% by mass, more preferably 0.1 to 1.0% by mass with respect to the optical film. . If these contents are less than 0.05% by mass, the effect of the lubricant is difficult to obtain, and if the content is more than 2.0% by mass, the heat-and-moisture resistance of the resulting film decreases and the haze increases. Cheap.

Ultraviolet absorber The ultraviolet absorber is a compound that absorbs ultraviolet light having a wavelength of 400 nm or less, preferably a compound having a transmittance at a wavelength of 370 nm of 10% or less, more preferably 5% or less, and even more preferably 2% or less. is there.

  The light transmittance of the ultraviolet absorber can be measured with a spectrophotometer by a conventional method using a solution obtained by dissolving the ultraviolet absorber in a solvent (for example, dichloromethane, toluene, etc.). The spectrophotometer is, for example, a spectrophotometer UVIDFC-610 manufactured by Shimadzu Corporation, a 330-type self-recording spectrophotometer manufactured by Hitachi, Ltd., a U-3210-type self-recording spectrophotometer, a U-3410-type self-recording spectrophotometer, U A −4000 self-recording spectrophotometer or the like can be used.

  UV absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders, and polymer UV absorbers. In order not to impair the transparency of the obtained film, benzotriazole-based UV absorbers and benzophenone-based UV absorbers are preferable, and benzotriazole-based UV absorbers are more preferable.

  Specific examples of UV absorbers include 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl)- 6- (linear and side chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone and the like are included. Examples of commercially available ultraviolet absorbers include TINUVIN109, TINUVIN171, TINUVIN326, TINUVIN327, TINUVIN328, TINUVIN900, TINUVIN928, and LA-31 manufactured by ADEKA Co., Ltd., manufactured by Ciba Japan.

  Examples of the polymeric ultraviolet absorber include polymer type ultraviolet absorbers described in JP-A-6-148430. The ultraviolet absorber may be one kind or a mixture of two or more kinds.

  Although content of a ultraviolet absorber is based also on the kind of ultraviolet absorber, it is preferable that it is 0.5-4 mass% with respect to an optical film, and it is more preferable that it is 0.6-3.5 mass%. preferable.

Antioxidant In the process of producing a film by the melt extrusion method, a film material such as a resin is melted and kneaded at a high temperature, so that the film material such as a resin is easily decomposed by heat or oxygen. In order to suppress such decomposition of the film material such as resin due to heat or oxygen, the composition constituting the optical film of the present invention preferably further contains an antioxidant as a stabilizer.

  Examples of the antioxidant include a sulfur compound, a phenol compound, a hindered amine compound, a phosphorus compound, a compound containing an unsaturated double bond, and the like.

  Examples of the sulfur compound include Sumitizer TPL-R, Sumilizer TP-D, and the like manufactured by Sumitomo Chemical Co., Ltd.

  Examples of the phenol compound include a compound having a 2,6-dialkylphenol structure (for example, 2,6-di-t-butyl-p-cresol). Examples of commercially available phenolic compounds include Irganox 1076 and Irganox 1010 manufactured by BASF Japan Ltd.

  Examples of the phosphorus compound include tris (2,4-di-t-butylphenyl) phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol-diphosphite, and the like. Examples of commercially available phosphorous compounds include Sumitizer GP manufactured by Sumitomo Chemical Co., Ltd., ADK STAB PEP-24G manufactured by ADEKA Co., Ltd., ADK STAB PEP-36 and ADK STAB 3010, IRGAFOS P-EPQ manufactured by BASF Japan Co., Ltd. This includes GSY-P101 manufactured by Kogyo Co., Ltd.

  Examples of hindered amine compounds include Tinuvin 144 and Tinuvin 770 manufactured by BASF Japan, and ADK STAB LA-52 manufactured by ADEKA.

  Examples of the compound containing an unsaturated double bond include Sumitizer GM and Sumilizer GS manufactured by Sumitomo Chemical Co., Ltd.

  The antioxidant may be only one type or a mixture of two or more types, but is preferably a mixture of two or more types. For example, it is preferable to use a phosphorus compound, a phenol compound, and a compound containing an unsaturated double bond in combination.

  The content of the antioxidant is preferably 0.05 to 5% by mass and more preferably 0.1 to 4% by mass with respect to the resin component (total of (meth) acrylic resin and cellulose ester). preferable.

Colorant The composition constituting the optical film of the present invention contains a colorant for imparting bluishness to the color tone of the liquid crystal display screen, adjusting the yellow index (yellowness), and reducing haze. Furthermore, you may contain. Examples of the colorant include dyes such as anthraquinone dyes and azo dyes, and pigments such as phthalocyanine pigments.

Fine particles (matting agent)
The composition constituting the optical film of the present invention may further contain fine particles (matting agent) in order to enhance the slipperiness of the surface of the obtained optical film. When the optical film is a multilayer, the layer on the outermost surface preferably contains fine particles.

  The fine particles may be inorganic fine particles or organic fine particles. Examples of inorganic fine particles include silicon dioxide (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples include magnesium silicate and calcium phosphate. Of these, silicon dioxide and zirconium oxide are preferable, and silicon dioxide is more preferable in order to reduce an increase in haze of the obtained film.

  Examples of the fine particles of silicon dioxide include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Seahoster KE-P10, KE-P30, KE-P50, KE-P100 (manufactured by Nippon Shokubai Co., Ltd.) and the like are included.

  Examples of the fine particles of zirconium oxide include Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.).

  Examples of the polymer constituting the polymer fine particle include a silicone resin, a fluororesin, and an acrylic resin, preferably a silicone resin, and more preferably a silicone resin having a three-dimensional network structure. Examples of the polymer fine particles include Tospearl 103, 105, 108, 120, 145, 3120 and 240 (manufactured by Toshiba Silicone Co., Ltd.).

  Among these, Aerosil R972V, NAX50, Seahoster KE-P30 and the like are particularly preferable because the friction coefficient can be reduced while keeping the turbidity of the obtained film low.

  The fine particles are preferably subjected to a surface treatment in order to increase dispersibility and reduce the increase in haze of the resulting film. Examples of the surface treatment agent include halosilanes, alkoxysilanes, silazane, siloxane and the like.

  The primary particle diameter of the fine particles is preferably 5 to 50 nm, and more preferably 7 to 20 nm. A larger primary particle size has a greater effect of increasing the slipperiness of the resulting film, but transparency tends to decrease. Therefore, the fine particles may be contained as secondary aggregates having a particle diameter of 0.05 to 0.3 μm. The size of the primary particles or the secondary aggregates of the fine particles is determined by observing the primary particles or secondary aggregates with a transmission electron microscope at a magnification of 500,000 to 2,000,000 times, and measuring 100 primary particles or secondary aggregates. It can be determined as an average value of the particle diameter.

  The content of the fine particles is preferably 0.05 to 1.0% by mass and more preferably 0.1 to 0.8% by mass with respect to the resin component described above.

  The optical film may be a single-layer film made of a composition containing the above-mentioned (meth) acrylic resin and an acid trapping agent; or made of a composition containing the above-mentioned (meth) acrylic resin and an acid trapping agent. It may be a laminated film including layers.

Physical Properties of Optical Film The thickness of the optical film is not particularly limited, but is preferably 20 to 200 μm, more preferably 25 to 100 μm, further preferably 30 to 80 μm, and more preferably 10 to 45 μm. It is particularly preferred. If the thickness of the film is too small, it is difficult to obtain a desired retardation. On the other hand, if the thickness of the film is too large, the retardation tends to fluctuate due to the influence of humidity and the like.

  Since the optical film is manufactured by a melt extrusion molding method, the residual solvent amount of the optical film is preferably 0.01% by mass or less.

The amount of residual solvent in the optical film can be measured by the following method.
1) Prepare a calibration curve of the solvent used in the optical film production process by the following gas chromatography.
2) 20 ml of a sample obtained by pulverizing the optical film is placed in a sealed glass container and heat-treated under headspace heating conditions.
3) The volatile component obtained by the heat treatment of 2) is quantified by gas chromatography with reference to a calibration curve, and the amount of residual solvent in the optical film is measured. The residual solvent amount is expressed as a part by mass with respect to the total mass of the optical film.
Equipment: HP 5890SERIES II
Column: J & W Company DB-WAX (inner diameter 0.32 mm, length 30 m)
Detection: FID
GC temperature rise condition: held at 40 ° C. for 5 minutes, then raised to 100 ° C. at 80 ° C./min. Headspace heating condition: 20 minutes at 120 ° C.

  The breaking stress of the optical film of the present invention under an atmosphere of 23 ° C. and 55% RH is preferably 70 MPa or more, and more preferably 80 MPa or more, in order to enhance the reworkability of the polarizing plate containing the optical film. . On the other hand, from the viewpoint of facilitating cutting (slit), the breaking stress of the optical film is preferably 200 MPa or less.

  The measurement of the breaking stress can be performed by the following procedure. That is, the optical film is cut into a size of 10 mm × 150 mm to obtain a sample piece. This sample piece was subjected to a tensile test with a tensile tester (Strograph-R2 (manufactured by Toyo Seiki)) at a chuck distance of 100 mm, a temperature of 25 ° C., and a stretching speed of 10 mm / min. Let it be stress.

  The elongation at break in at least one direction, measured according to JIS-K7127-1999, of the optical film of the present invention is 30% or more, more preferably 50% or more. The upper limit of the elongation at break is practically about 250%. In order to increase the elongation at break, the melting temperature is increased, the flexibility of the film is increased, or defects in the film due to foreign matter or foaming are reduced.

  The tear strength of the optical film of the present invention in an atmosphere of 23 ° C. and 55% RH is preferably 10 mN or more, more preferably 20 mN or more in order to improve the reworkability of the polarizing plate containing the optical film. . On the other hand, from the viewpoint of facilitating cutting (slit), the tear strength of the optical film is preferably 100 mN or less.

  The tear strength can be measured as follows. That is, the optical film is cut into a size of 65 mm × 50 mm to obtain a sample piece. The tear load of this sample piece by the Elmendorf method is measured with a light load tear device manufactured by Toyo Seiki Co., Ltd. according to JIS K 7128-1991.

  The retardation Ro in the in-plane direction measured at a wavelength of 590 nm under an environment of 23 ° C. and 55% RH of the optical film is preferably in the range of −5 nm to 5 nm, and in the range of −3 nm to 3 nm. It is more preferable. The retardation Rth in the thickness direction is preferably in the range of −5 nm to 5 nm, and more preferably in the range of −3 nm to 3 nm.

Retardation _R0 and Rth are each represented by the following formula.
Formula (I) R ₀ = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction in the film plane, ny: refractive index in the direction perpendicular to the slow axis in the film plane, nz: refractive index of the film in the thickness direction, d: film thickness (Nm))

The retardations _R0 and Rth can be determined by the following method, for example.
1) The average refractive index of the film is measured with a refractometer.
2) The retardation _R0 in the in-plane direction when light having a wavelength of 590 nm from the normal direction of the film is incident is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments.
3) The retardation value R (θ) when light having a wavelength of 590 nm is incident from the angle θ (incident angle (θ)) with respect to the film normal direction is measured by KOBRA-21ADH manufactured by Oji Scientific Instruments. . θ is larger than 0 °, preferably 30 ° to 50 °.
4) From the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, nx, ny and nz are calculated by KOBRA-21ADH manufactured by Oji Scientific Instruments, and Rth is calculated. The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

  The angle θ1 (orientation angle) formed by the in-plane slow axis of the optical film and the width direction of the film is preferably −5 ° or more and + 5 ° or less, and more preferably −1 ° or more and + 1 ° or less. . The orientation angle θ1 of the optical film can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments).

  The haze of the optical film measured in accordance with JIS K-7136 is more preferably 0.5% or less in order to obtain sufficient brightness and high contrast in a liquid crystal display device, and 0.35% More preferably, it is more preferably 0.05% or less. In order to reduce the haze of the optical film, the melting temperature may be increased or the substitution degree of the acyl group having 3 to 7 carbon atoms of the cellulose ester may be increased.

The haze of the optical film can be measured by a method based on JIS K-7136; specifically, the following method.
1) The obtained optical film is conditioned at 23 ° C. and 55% RH for 5 hours or more. Thereafter, dust attached to the surface of the film is removed with a blower or the like.
2) Next, the haze of the optical film is measured with a haze meter (turbidimeter) (model: NDH 2000, manufactured by Nippon Denshoku Co., Ltd.) under the condition of 23 ° C. and 55% RH. The light source of the haze meter may be a 5V9W halogen sphere, and the light receiving part may be a silicon photocell (with a relative visibility filter).

  The visible light transmittance of the optical film is preferably 90% or more, and more preferably 92% or more.

  The optical film of the present invention preferably has no streak-like defects. A streak-like defect is a streak extending in the longitudinal direction of the film on the optical film surface, and the height of the streak (the height from the top of the streak peak to the bottom of the valley) in the film width direction cross section is 300 nm or more. And the streak slope is 300 nm / mm or more.

The shape of the streak defect can be measured by the following procedure.
1) Using Mitutoyo SV-3100S4, film is applied at a measuring speed of 1.0 mm / sec while applying a measuring force of 0.75 mN to a stylus (diamond needle) having a tip shape of cone 60 ° and a tip curvature radius of 2 μm. Scan in the width direction and measure the cross-sectional curve in the film width direction with a Z-axis (thickness direction) resolution of 0.001 μm.
2) From the obtained cross-sectional curve, the vertical distance (H) between the top of the streak peak and the bottom point of the trough is read and set as the streak height. Also, the horizontal distance (L) between the peak of the mountain and the bottom of the valley is read, and the value obtained by dividing the vertical distance (H) by the horizontal distance (L) is defined as the slope of the stripe.

  The (meth) acrylic resin and cellulose ester contained in the optical film of the present invention are preferably compatible with each other. Whether or not the (meth) acrylic resin and the cellulose ester are compatible can be confirmed by, for example, the glass transition temperature Tg of the optical film. For example, as for the glass transition temperature of the optical film in which the (meth) acrylic resin and the cellulose ester are compatible, the glass transition temperature derived from each resin is not confirmed, and only one glass transition temperature is confirmed.

  The glass transition temperature is measured as a midpoint glass transition temperature (Tmg) by a method according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer). The heating rate can be 20 ° C./min.

  The optical film of the present invention may further have other functional layers (an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorption layer, a polarizing layer, etc.) as necessary.

  The optical film of the present invention is a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for widening the viewing angle, etc. for liquid crystal display devices. It can be preferably used. Examples of the polarizing plate protective film include a protective film further having a retardation adjustment function, an optical compensation function, and the like.

2. Manufacturing method of optical film The optical film of the present invention is a method in which the resin composition containing the (meth) acrylic resin and the acid trapping agent is heated and melted, and then cast and formed (melting film forming method). Can be obtained by: Examples of melt film forming methods include melt extrusion molding methods, press molding methods, inflation methods, injection molding methods, blow molding methods, stretch molding methods, etc., because it is easy to obtain a film with high surface accuracy, etc. A melt extrusion method is preferred. That is, the optical film of the present invention can be obtained through a step of extruding after melt-kneading a resin composition containing a (meth) acrylic resin and an acid trapping agent.

  First, a film manufacturing apparatus used for the melt extrusion method will be described. FIG. 1 is a schematic diagram illustrating an example of a film manufacturing apparatus. As shown in FIG. 1, a film manufacturing apparatus 10 includes an extruder 12 that melts and kneads a resin, a die 14 that discharges the molten resin into a film, and multi-stage cooling of the high-temperature resin discharged from the die 14. The first, second and third cooling rolls 16, 18 and 20, the peeling roll 22 for peeling the film obtained by cooling and solidification, the stretching device 24 for stretching the film, and the winding for winding the stretched film A take-off device 26.

  The extruder 12 is a melt-kneading extruder, and has a cylinder and a screw rotatably provided therein. A hopper (not shown) for supplying film material is provided at the supply port of the cylinder. The shape of the screw may be full flight, mudock, dull mage, etc., and is selected according to the viscosity of the molten resin and the required shearing force. The extruder 12 may be a single screw extruder or a twin screw extruder.

  A filter 28 for filtering the molten resin may be further provided between the extruder 12 and the die 14. The filter 28 is, for example, a leaf disk type filter, and is preferably a stainless fiber sintered filter. The filtration accuracy of the filter is preferably 3 to 15 μm. The filter 28 is preferably a multilayer body of filtration media having different filtration accuracy from the viewpoint of increasing the accuracy of capturing foreign substances or gels.

  Between the extruder 12 and the die 14, a mixing device such as a static mixer 30 for uniformly mixing the resin, a gear pump (not shown) for stabilizing the extrusion flow rate, and the like may be further provided. Good.

  The die 14 may be a known one, such as a T die. The material of the die 14 body is sprayed or plated with hard chromium, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide), etc .; buff, It may further be subjected to surface processing such as plane cutting or electrolytic polishing. The material of the lip portion of the die 14 can be the same as that of the die body. The surface accuracy of the lip portion of the die 14 is preferably 0.5S or less, and more preferably 0.2S or less.

  The slit of the die 14 is configured such that the gap can be adjusted. Of the pair of lips forming the slit of the die 14, one is a flexible lip having low rigidity and is easily deformed, and the other is preferably a fixed lip because the slit gap can be easily adjusted. The slit gap (die lip clearance) is preferably 900 μm or more, and more preferably 1 mm or more and 2 mm or less. When the die lip clearance is out of the above range, spotted unevenness tends to occur in the obtained film.

  If foreign matter such as scratches or agglomerated plasticizer adheres to the inner wall surface of the die 14, streaky defects (die lines) may occur on the surface of the extruded molten resin. In order to reduce surface defects such as die lines, the inner wall surface from the extruder 12 to the tip of the die 14 should have a structure in which a resin staying portion is difficult to adhere; for example, from the extruder 12 to the tip of the die 14 It is preferable that the inner wall surface is not scratched.

  The inner wall surfaces of the extruder 12 and the die 14 are preferably subjected to surface processing for reducing the surface roughness or reducing the surface energy in order to make the molten resin difficult to adhere. Examples of such surface processing include processing for polishing to have a surface roughness of 0.2 S or less after hard chrome plating or ceramic spraying.

  The 1st cooling roll 16, the 2nd cooling roll 18, and the 3rd cooling roll 20 are highly rigid metal rolls, and have the structure which can distribute | circulate the medium which can be temperature-controlled inside. The material of the surface of the cooling rolls 16, 18 and 20 can be stainless steel, aluminum, titanium or the like. The surface of the cooling rolls 16, 18 and 20 may be subjected to a surface treatment such as hard chrome plating in order to make the resin easy to peel off. The surface roughness Ra of the cooling rolls 16, 18, and 20 is preferably 0.1 μm or less, and more preferably 0.05 μm or less, in order to keep the haze of the resulting film low.

  The elastic touch roll 32 is disposed to face the cooling roll 16. The molten resin extruded from the die 14 is nipped between the cooling roll 16 and the elastic touch roll 32. As the elastic touch roll 32, a silicon rubber roll covered with a thin film metal sleeve described in JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096 and the like is used.

  The stretching device 24 is not particularly limited, but a roll stretching machine, a tenter stretching machine or the like is preferably used. A roll stretching machine and a tenter stretching machine may be combined. The tenter stretching machine preferably has a preheating zone, a stretching zone, a holding zone, and a cooling zone, and preferably has a neutral zone for insulating between the zones.

  Various rolls in the manufacturing apparatus 10 may be further provided with a mechanism for cleaning the roll surface. Examples of the roll cleaning method may include a method of niping a brush roll, a water absorption roll, an adhesive roll, a wiping roll, an air blow method of spraying clean air, a laser incineration method, or a combination thereof.

  Next, the step of obtaining an optical film using the film manufacturing apparatus 10 will be described. The optical film of the present invention is, for example, a step of preparing pellets made of the above-described resin composition (pelletizing step); a step of melt-kneading a film material containing pellets with an extruder 12 and then extruding from a die 14 (melting) It can be obtained through a step of cooling and solidifying the extruded molten resin to obtain a film (cooling and solidifying step); a step of stretching the film (stretching step).

1) Pelletization process It is preferable that the resin composition containing the (meth) acrylic resin and the acid trapping agent is previously kneaded and pelletized. Pelletization can be performed by a known method. For example, the above resin composition is melt-kneaded with an extruder and then extruded from a die in a strand shape. The molten resin extruded in a strand shape can be cooled with water or air, and then cut to obtain pellets.

  The ultraviolet absorber or the fine particles (mat agent) may be contained in the main pellet made of the above-mentioned resin composition, or may be contained in a high-concentration master pellet different from the above-mentioned resin composition.

  The pellet raw material is preferably dried before being supplied to the extruder in order to prevent decomposition. For example, since the cellulose ester easily absorbs moisture, it is preferable that the moisture content be 200 ppm or less, preferably 100 ppm or less by drying at 70 to 140 ° C. for 3 hours or more.

The plural types of additives supplied to the extruder may be mixed in advance or may not be mixed. A small amount of an additive such as an antioxidant is preferably mixed in advance before being supplied to the extruder in order to mix uniformly. Since the raw materials can be dried and mixed at the same time, the raw materials are preferably mixed with a vacuum nauter mixer. In addition, the atmosphere near the hopper of the extruder or the exit of the die is preferably an atmosphere of dehumidified air or N ₂ gas in order to prevent deterioration of the raw material of the pellet. The hopper of the extruder is preferably kept warm to prevent moisture absorption of the raw materials.

  The extruder 12 is preferably kneaded at a low shearing force or at a low temperature so as not to cause deterioration of the resin (decrease in molecular weight, coloring, formation of gelled foreign matters, etc.). For example, when kneading with a twin screw extruder, it is preferable to use a deep groove type screw and to rotate the two screws in the same direction. In order to knead uniformly, it is preferable that two screw shapes mesh with each other.

  The color of the pellet is preferably such that the b * value, which is an index of yellowness, is in the range of -5 to 10, more preferably in the range of -1 to 8, and in the range of -1 to 5. More preferred. The b * value can be measured with a spectrocolorimeter CM-3700d (manufactured by Konica Minolta Sensing Co., Ltd.) with the light source as D65 (color temperature 6504K) and the viewing angle as 10 °.

  Instead of pelletizing the resin composition, an optical film may be produced by melting and kneading the resin composition not melt-kneaded as a raw material with the extruder 12 as it is.

2) Melt extrusion process It is preferable to dry film materials such as pellets in advance. It is preferable that the moisture content contained in the material such as pellets is dried to 200 ppm or less, preferably 100 ppm or less with a vacuum or reduced pressure dryer or a dehumidifying hot air dryer.

  The film material containing the pellets is supplied to the extruder 12 from a hopper (not shown). The supply of pellets is preferably performed under vacuum, reduced pressure, or an inert gas atmosphere in order to prevent oxidative decomposition of the pellets. And the film material containing a pellet is melt-kneaded in the extruder 12.

  The melting temperature of the film material in the extruder 12 depends on the type of the film material, the viscosity and discharge amount of the melt, the thickness of the obtained film, etc., but preferably when the glass transition temperature of the film is Tg ° C. It is in the range of Tg ° C. to (Tg + 150) ° C., more preferably in the range of (Tg + 50) ° C. to (Tg + 130) ° C. Specifically, in the case of a (meth) acrylic resin / cellulose ester mixture, the melting temperature is about 150 to 300 ° C, preferably 200 to 270 ° C, more preferably 240 to 270 ° C, Preferably it is 260-270 degreeC. If the melting temperature is too low, the film material may not be sufficiently kneaded, and if the melting temperature is too high, the film material may be thermally deteriorated.

  Optical film having high reworkability; Specifically, in order to obtain an optical film having high flexibility, it is considered effective to increase the melting temperature and increase the fluidity of the molten resin. However, if the melting temperature is increased, the resin is likely to be thermally deteriorated, so that the resulting film is colored, becomes brittle, or does not satisfy desired optical properties.

  The mechanism of thermal degradation of the resin when the melting temperature is increased is not necessarily clear, but the monomer remaining in the raw material (meth) acrylic resin is thermally decomposed to generate an acid, and this acid is the resin. This is presumed to cause thermal degradation of the material. Thermal degradation of the resin when the melting temperature is increased is particularly likely to occur particularly when the resin composition contains a (meth) acrylic resin and a cellulose ester. It is presumed that the ester portion of the cellulose ester is hydrolyzed to generate an acid, which also causes the resin to thermally deteriorate.

  In the present invention, the resin composition containing a (meth) acrylic resin further contains an acid trap agent. The acid trapping agent can trap an acid that decomposes the resin component, particularly when the melting temperature is increased. Thereby, even if the melting temperature is increased, the resin can be melt-kneaded without causing thermal degradation.

  The melt viscosity of the film material in the extruder 12 is preferably 1 to 10000 Pa · s, and more preferably 10 to 1000 Pa · s. When the melt viscosity of the melt is too high, the pressure rises, so that the residence time in the extruder 12 tends to be long. The residence time of the film material in the extruder 12 is preferably short, preferably within about 5 minutes, preferably within 3 minutes, and more preferably within 2 minutes. The residence time can be adjusted by the supply amount of the film material, L / D which is the ratio of the cylinder length (L) to the cylinder inner diameter (D), the number of rotations of the screw or the depth of the groove of the screw. .

  The rotational speed and shape of the screw of the extruder 12 are appropriately selected depending on the melt viscosity and the discharge amount of the film material. The shear rate in the extruder 12 is 1 / second to 10000 / second, preferably 5 / second to 1000 / second, and more preferably 10 / second to 100 / second.

  The molten resin extruded from the extruder 12 is filtered by a filter 28 or the like as necessary, and further mixed by a static mixer 30 or the like, and extruded from the die 14 into a film. The melting temperature Tm of the resin at the exit portion of the die 14 can be about 200 to 300 ° C.

3) Cooling and solidifying step The resin extruded from the die is nipped between the cooling roll 16 and the elastic touch roll 32 so that the film-like molten resin has a predetermined thickness. Then, the film-like molten resin is cooled stepwise with a plurality of cooling rolls 18 and 20 and solidified.

  The surface temperature Tr1 of the first cooling roll 16 and the surface temperature Tr2 of the second cooling roll 18 can be independently set to (Tg−50) ° C. or more and Tg or less. Further, Tr2> Tr1 is preferable, and 0 <Tr2-Tr1 <50 is more preferable. This is because by setting Tr2> Tr1, the condensation of the additive on the second cooling roll 18 is suppressed and the film is easily remelted.

  The re-dissolution of the additive into the film can be adjusted by the contact time between the film and the second cooling roll 18, and specifically, it is preferably 1.0 to 3.0 seconds. The contact time is a second obtained by dividing the distance between the point where the film and the second cooling roll 18 start to contact and the point where the second cooling roll 18 starts to peel by the film conveyance speed. Is a number.

  The peripheral speed R2 of the second cooling roll 18 is preferably larger than the peripheral speed R1 of the first cooling roll 16. Tension is applied to the film between these two cooling rolls, thereby improving the adhesion between the film and the first cooling roll 16. The ratio of the peripheral speeds is preferably in the range of 1.00 to 1.05. If the ratio of the peripheral speeds exceeds 1.05, the film may be broken. Similarly, the peripheral speed of the third cooling roll 20 is preferably larger than the peripheral speed of the second cooling roll 18.

  The draw ratio is preferably 5-30. The draw ratio is a value obtained by dividing the lip clearance of the die 14 by the average film thickness of the film obtained by cooling and solidifying on the first, second and third cooling rolls 16, 18 and 20. By setting the draw ratio within the above range, it is easy to obtain a film with few failures that cause bright and dark stripes and spotted unevenness when an image is displayed on a liquid crystal display device. The draw ratio can be adjusted by the die lip clearance and the take-up speed of the cooling roll.

  The discharge of the molten resin from the lip (opening) of the die 14 to the surface of the first cooling roll 16 is preferably performed under reduced pressure at 70 kPa or less, more preferably 50 to 70 kPa. This is because die lines are less likely to occur in the obtained film. The method of reducing the pressure between the lip (opening) of the die 14 and the surface of the first cooling roll 16 is, for example, covering the space including the die 14 and the first cooling roll 16 with a pressure-resistant member and reducing the pressure inside the space. There are methods.

  The surface temperature Tr0 of the elastic touch roll 32 is preferably equal to or lower than the glass transition temperature (Tg) of the film, and more preferably Tg-50 ≦ Tr0 ≦ Tg. If the surface temperature Tr0 of the elastic touch roll 32 exceeds Tg, the film and the first cooling roll 16 may be difficult to peel off.

  It is preferable that the linear pressure of the elastic touch roll 32 when pressed by the elastic touch roll 32 is 9.8 to 147 N / cm. When the linear pressure is less than 9.8 N / cm, it is difficult to sufficiently suppress the die line.

  When the glass transition temperature of the optical film is Tg, the surface temperature Tt of the film-like molten resin extruded from the die 14 immediately before being nipped by the elastic touch roll 32 is preferably Tg < Tt <Tg + 110 ° C., more preferably Tg + 10 ° C. <Tt <Tg + 90 ° C., and further preferably Tg + 20 ° C. <Tt <Tg + 70 ° C. When the surface temperature Tt of the film-like molten resin is in the above range, the viscosity of the film-like molten resin when nipping can be set to an appropriate range, and die lines can be easily suppressed.

  The adjustment of the surface temperature Tt on the elastic touch roll 32 immediately before being nipped by the elastic touch roll 32 of the film-like molten resin, for example, shortens the air gap (distance) between the die 14 and the first cooling roll 16. Then, the method of suppressing the cooling between the die 14 and the first cooling roll 16, the method of keeping the temperature between the die 14 and the first cooling roll 16 with a heat insulating material or the method of heating or the like. it can. The heating can be heating with hot air, an infrared heater or microwave.

  The surface temperature of the film and the surface temperature of the roll can be measured with a non-contact infrared thermometer. Specifically, the surface temperature of the film or roll is determined by using a non-contact handy thermometer (IT2-80, manufactured by Keyence Co., Ltd.), the surface temperature at any 10 locations in the width direction of the film or roll, Or it measures at the position 0.5m away from the surface of the roll.

  The film solidified by the cooling rolls 16, 18 and 20 is peeled off by the peeling roll 22. When peeling the film, it is preferable to adjust the tension applied to the film in order to prevent deformation.

4) Stretching step The obtained film is stretched by a stretching device 24 to obtain an optical film. The stretching may be performed in at least one of the width direction of the film (TD direction), the transport direction (MD direction), or the oblique direction, and both in the film width direction (TD direction) and the transport direction (MD direction). It is preferable to stretch.

  When stretching in both the width direction (TD direction) and the transport direction (MD direction) of the film, stretching in the width direction (TD direction) of the film and stretching in the transport direction (MD direction) may be performed sequentially. You may do it simultaneously.

  The draw ratio can be 1.01 to 3.0 times, preferably 1.1 to 2.0 times in each direction. When stretching in both the width direction (TD direction) and the transport direction (MD direction) of the film, it is finally 1.01 to 3.0 times, preferably 1.1 to 2.0 times in each direction. Is preferred.

  The stretching temperature is preferably Tg to (Tg + 50) ° C., more preferably Tg to (Tg + 40) ° C. Specifically, in the case of a (meth) acrylic resin / cellulose ester mixture, the stretching temperature can be about 100 to 190 ° C. When the stretching temperature is too high, the tear strength of the obtained optical film is high, but the breaking stress may be low. On the other hand, when the stretching temperature is too low, the obtained optical film has a high breaking stress but may have a low tear strength.

  The stretching temperature is preferably uniform in the width direction (TD direction) or the transport direction (MD direction) of the film, and the variation in the width direction or transport direction of the film stretching temperature is preferably ± 2 ° C. or less, The temperature is more preferably ± 1 ° C. or less, and further preferably ± 0.5 ° C. or less.

  In order to adjust the retardation of the film obtained after stretching or to reduce the dimensional change, the film obtained after stretching is shrunk in the transport direction (MD direction) or the width direction (TD direction) as necessary. May be. To shrink the film obtained after stretching in the transport direction (MD direction), for example, release the clip gripped in the width direction and loosen it in the transport direction; gradually reduce the interval between adjacent clips in the transport direction. To relax in the transport direction.

  To gradually reduce the distance between adjacent clips in the transport direction, for example, using a simultaneous biaxial stretching machine, the distance between adjacent clips in the film transport direction (TD direction) is driven by the pantograph method or linear drive method. Then it should be smooth and narrow. In order to reduce the dimensional change rate of the obtained film, it is preferable that the width direction (TD direction) and the conveyance direction (MD direction) of the film are contracted by 0.5 to 10%.

  The width of the obtained optical film may be 0.5 to 4.0 m, preferably 1.0 to 3.0 m, though it depends on the width of the polarizer and the like. The film thickness variation of the optical film is preferably ± 3% or less, and more preferably ± 1% or less.

  After stretching, it is preferable to apply knurl processing (embossing processing) after slitting and cutting off both ends of the obtained optical film. This is for preventing the occurrence of sticking or scratching between the obtained optical films. The knurling can be performed with a knurling apparatus having an embossing ring and a back roll. The optical film thus obtained is wound up by a winder.

  Thus, the optical film of the present invention can be obtained through a step of extruding after melt-kneading a resin composition containing a (meth) acrylic resin and an acid trapping agent. The acid trapping agent contained in this resin composition is produced when the monomer remaining in the (meth) acrylic resin is thermally decomposed and the ester part of cellulose ester is hydrolyzed when the melting temperature is increased. Since the acid can be trapped, the thermal deterioration of the resin can be suppressed. Therefore, it is possible to obtain an optical film that is not colored, satisfies desired optical characteristics, has high flexibility, and has high reworkability.

3. Polarizing plate The polarizing plate of the present invention comprises a polarizer and the optical film of the present invention disposed on at least one surface thereof.

  A polarizer is an element that allows only light having a polarization plane in a certain direction to pass therethrough. A typical example of the polarizer is a polyvinyl alcohol-based polarizing film, and there are one in which a polyvinyl alcohol-based film is dyed with iodine and one in which a dichroic dye is dyed.

  The polarizer may be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing with iodine or a dichroic dye, or after dyeing a polyvinyl alcohol film with iodine or a dichroic dye, A uniaxially stretched film (preferably a film further subjected to durability treatment with a boron compound) may be used. The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 10 to 20 μm.

  The polyvinyl alcohol film may be a film formed from a polyvinyl alcohol aqueous solution. The polyvinyl alcohol film is preferably an ethylene-modified polyvinyl alcohol film because it is excellent in polarizing performance and durability performance and has few color spots. Examples of the ethylene-modified polyvinyl alcohol film include an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 described in JP2003-248123A and JP2003-342322A. ˜99.99 mol% film is included.

  Examples of dichroic dyes include azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes.

  The optical film of the present invention may be disposed directly on at least one surface of the polarizer, or may be disposed via another film or layer.

  The optical film of the present invention may be disposed on the other surface of the polarizer, or a protective film other than that may be disposed. The protective film is not particularly limited, and may be a normal cellulose ester film or the like. Examples of commercially available cellulose ester films include commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4UE, KC4FR-3, KC4FR-4, KC4HR-1, KC8UY-HA, KC8UX-RHA, and the like, manufactured by Konica Minolta Opto Co., Ltd.) are preferably used.

  The polarizing plate can be usually obtained through a step of bonding a polarizer and the optical film of the present invention. Examples of adhesives used for bonding include saponified polyvinyl alcohol aqueous solutions, curable adhesives such as urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, and thermosetting acrylic adhesives. A fully saponified polyvinyl alcohol aqueous solution is preferable.

4). Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell. And at least one is a polarizing plate which has an optical film of this invention among a pair of polarizing plates, Preferably both of a pair of polarizing plates are polarizing plates which have an optical film of this invention.

  FIG. 2 is a schematic diagram showing a basic configuration of an embodiment of the liquid crystal display device 110 according to the present invention. As shown in FIG. 2, the liquid crystal display device 110 includes a liquid crystal cell 120, a first polarizing plate 140 and a second polarizing plate 160 that sandwich the liquid crystal cell 120, and a backlight 180.

  The display method of the liquid crystal cell 120 is not particularly limited, and is a TN (Twisted Nematic) method, an STN (Super Twisted Nematic) method, an IPS (In-Plane Switching) method (including an FFS method), an OCB (Optically Compensated Bceened method). VA (Vertical Alignment) method (MVA; including Multi-domain Vertical Alignment and PVA; Patterned Vertical Alignment), HAN (Hybrid Aligned Nematic) method, and the like. From the viewpoint of a relatively wide viewing angle, the IPS system is preferable, and from the viewpoint of high contrast, the VA system is preferable.

  The first polarizing plate 140 is disposed on the viewing side of the liquid crystal cell 120, and the first polarizer 142 and the protective film 144 (F1) disposed on the viewing side of the first polarizer 142. And a protective film 146 (F2) disposed on the surface of the first polarizer 142 on the liquid crystal cell side. The second polarizing plate 160 is disposed on the backlight 180 side, the second polarizer 162, a protective film 164 (F3) disposed on the liquid crystal cell side surface of the second polarizer 162, And a protective film 166 (F4) disposed on the backlight side surface of the second polarizer 162. One of the protective films 146 (F2) and 164 (F3) may be omitted as necessary.

  Of the protective films 144 (F1), 146 (F2), 164 (F3), and 166 (F4), at least one of the protective films 146 (F2) and 164 (F3) arranged on the liquid crystal cell side of the present invention is used. An optical film is preferred.

  The size of the liquid crystal display device can be preferably 30 type or more, more preferably 30 type to 54 type. The liquid crystal display device is preferably used also for outdoor applications such as digital signage.

The liquid crystal display device can be manufactured through a step of bonding a liquid crystal cell and a polarizing plate together with an adhesive. The pressure-sensitive adhesive is preferably a curable pressure-sensitive adhesive, and more preferably a curable pressure-sensitive adhesive having a cured elastic modulus at 25 ° C. of 1.0 × 10 ^{4 to} 1.0 × 10 ⁹ Pa. Examples of such an adhesive include those similar to the above-mentioned curable adhesive.

  As described above, the optical film of the present invention is obtained through a step of melt-kneading a resin composition containing an acid trapping agent at a high melting temperature. Therefore, the optical film of the present invention is not colored and has high flexibility (reworkability) while satisfying desired optical characteristics. Therefore, even after the polarizing plate including the optical film of the present invention is once bonded to the liquid crystal cell, it can be easily peeled off from the liquid crystal cell without tearing the polarizing plate. Moreover, the liquid crystal display device containing the optical film of this invention has a favorable display characteristic.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Preparation of Optical Film Material 1) (Meth) acrylic resin A1: Copolymer of methyl methacrylate / acryloylmorpholine = 85/15 (mass ratio), weight average molecular weight Mw = 100,000 A2: Lactone ring-containing (meth) acrylic copolymer Combined (content ratio of lactone ring-containing structure: 20% by mass, degree of ring closure 95%, weight average molecular weight Mw = 200,000)
A3: Lactone ring-containing (meth) acrylic copolymer (Lactone ring-containing structure content ratio: 20% by mass, ring closure degree 80%, weight average molecular weight Mw = 200,000)
2) Cellulose ester CAP: cellulose acetate propionate (acyl group total substitution degree 2.75, acetyl group substitution degree 0.2, propionyl group substitution degree 2.55, weight average molecular weight Mw: 200000, Tg: 145 ° C.)
3) Acid trapping agent LBT-1830: Sakai Chemical Industry Co., Ltd., zinc stearyl phosphate Adekasizer D-32: ADEKA Co., epoxidized oil 4) Other additives SZ-2000: Sakai Chemical Industry Co., Ltd., stearic acid Zinc PEP-36: Made by ADEKA, Phosphorous antioxidant Irganox 1010: Made by Ciba Japan, Phenolic antioxidant Adekastub LA-52: HALS made by ADEKA
5) Other resins Polycarbonate 1: Panlite AD-5503 (manufactured by Teijin Chemicals Ltd.)
Arton (cyclic olefin resin): Arton G7810 (manufactured by JSR Corporation)

2. Production of optical film (Example 1)
(Meth) acrylic resin A1 and cellulose acetate propionate were dried in a vacuum nauter mixer at 70 ° C. under reduced pressure for 3 hours, and then cooled to room temperature. To this, LBT-1830 was added to obtain a mixture. The composition of the mixture was such that the resulting optical film had the following composition.
<Composition of optical film>
(Meth) acrylic resin A1: 70 parts by mass Cellulose acetate propionate (acyl group total substitution degree 2.75, acetyl group substitution degree 0.2, propionyl group substitution degree 2.55, molecular weight Mw = 200000): 30 parts by mass LBT-1830: 2 parts by mass

  The obtained mixture was melt-kneaded at 235 ° C. with a twin-screw extruder and extruded into a strand shape. The resin composition extruded in a strand form was cooled with water and then cut to obtain pellets.

  Using the obtained pellets, an optical film was produced with the film production apparatus 10 shown in FIG. The obtained pellets were put into a single screw extruder (extruder 12), and melt kneaded at 260 ° C. in a nitrogen atmosphere. Then, it extruded from the die | dye 14 on the 1st cooling roll 16 whose surface temperature is 90 degreeC. Then, the resin extruded onto the first cooling roll 16 was pressed by the elastic touch roll 32 and molded.

  The slit gap of the die 14 was 0.5 mm within 30 mm from the end in the film width direction, and 1 mm at other locations. The surface temperature of the elastic touch roll 32 was 80 ° C.

  From a position P1 at which the resin extruded from the die 14 contacts the first cooling roll 16 to a position P2 at the upstream end of the first cooling roll 16 in the nip portion between the first cooling roll 16 and the elastic touch roll 32 The length L along the peripheral surface of the first cooling roller 16 was set to 20 mm. The linear pressure of the elastic touch roll 32 against the first cooling roll 16 was 14.7 N / cm.

  The film obtained by cooling and solidifying the resin extruded from the die 14 on the first, second and third cooling rolls was peeled off by the peeling roll 22. The obtained film was stretched 1.3 times at 145 ° C. in the width direction by a tenter stretching machine, and then cooled to 30 ° C. while relaxing 3% in the width direction. Next, the clip was removed, and the portions held by the clips at both ends of the film were cut off, and then knurling with a width of 10 mm and a height of 5 μm was applied to both ends of the film. The obtained film was wound up at a winding tension of 220 N / m. The obtained film had a thickness of 40 μm and a width of 1430 mm, and the glass transition temperature measured by the DSC method was 125 ° C.

(Examples 2 to 4)
An optical film was obtained in the same manner as in Example 1 except that the type of the acid trapping agent or the melting temperature was changed as shown in Table 1.

(Examples 5 to 8)
An optical film was obtained in the same manner as in Example 4 except that the content of the acid trapping agent was changed as shown in Table 1.

(Examples 9 to 12)
An optical film was obtained in the same manner as in Example 3 except that the content ratio A / B of (A) (meth) acrylic resin and (B) cellulose ester was changed as shown in Table 1.

(Examples 13 and 14)
(A) An optical film was obtained in the same manner as in Example 3 except that the type of (meth) acrylic resin was changed as shown in Table 1.

(Examples 15 and 16)
An optical film was obtained in the same manner as in Example 1 except that the film thickness was changed as shown in Table 3.

(Comparative Example 1)
An optical film was obtained in the same manner as in Example 1 except that no acid trapping agent was contained.

(Comparative Examples 2 to 5)
An optical film was obtained in the same manner as in Example 1 except that no acid trapping agent was contained and the melting temperature or stretching temperature was changed as shown in Table 2.

(Comparative Examples 6-9)
An optical film was obtained in the same manner as in Example 1 except that the acid trapping agent was changed to the additive shown in Table 2 and the content thereof was changed.

(Comparative Examples 10-13)
An optical film was obtained in the same manner as in Example 1 except that the acid trapping agent was changed to the additive shown in Table 2 and the content and melting temperature thereof were changed as shown in Table 2.

(Comparative Example 14)
An optical film was obtained in the same manner as in Example 1 except that the film thickness was changed as shown in Table 3.

(Comparative Examples 15-18)
An optical film was obtained in the same manner as in Example 1 except that the type of resin, the presence or absence of addition of an acid trapping agent, the stretching temperature, and the film thickness of the film were changed as shown in Table 4.

  The optical film obtained was measured for 1) breaking stress, 2) tear strength, 3) coloring, 4) retardation Rth, 5) reworkability, and 6) polarizer deterioration by the following methods. All measurements were performed in an atmosphere of 23 ° C. and 55% RH. The optical film used was stored for 24 hours in an atmosphere of 23 ° C. and 55% RH in advance.

1) Breaking stress The obtained film was cut into a size of 10 mm × 150 mm to obtain a sample piece. This sample piece was pulled with a tensile tester (Strograph-R2 (manufactured by Toyo Seiki)) at a chuck distance of 100 mm, a temperature of 25 ° C., and a stretching speed of 10 mm / min. The stress when the rupture occurred was defined as the rupture stress.

2) Tear strength The obtained film was cut into a size of 65 mm × 50 mm to obtain a sample piece. The tear load of this sample piece by the Elmendorf method was measured with a light load tear device (TYPE D) manufactured by Toyo Seiki Co., Ltd. according to JIS K 7128-1991.

3) Coloring 10 mg of a finely pulverized optical film was put in an aluminum pan, and heated at 250 ° C. for 60 minutes under N ₂ flow using TG / DTA6200 (manufactured by SII Nanotechnology). The colored state of the optical film in the aluminum pan after heating was visually observed. The evaluation of coloring was performed based on the following criteria.
○: Almost no color △: Lightly colored ×: Colored brown

4) Retardation Rth
i) The average refractive index of the film was measured with a refractometer.
ii) The retardation _R0 in the in-plane direction when light having a wavelength of 590 nm from the film normal direction was incident was measured by KOBRA-21ADH manufactured by Oji Scientific Instruments.
iii) With KOBRA-21ADH manufactured by Oji Scientific Instruments, the retardation value R (θ) was measured when light having a wavelength of 590 nm was incident from the angle θ (incident angle (θ)) with respect to the film normal direction. . θ was 30 ° to 50 °.
iv) From the measured R ₀ and R (θ) and the above-described average refractive index and film thickness, nx, ny and nz were calculated by KOBRA-21ADH manufactured by Oji Scientific Instruments, and Rth was calculated. The retardation was measured under the conditions of 23 ° C. and 55% RH.

  The Rth of the obtained film is preferably ± 3 nm or less.

5) Reworkability Production of Polarizer A 120-μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and the draw ratio in the conveyance direction was 6 times at 50 ° C. To obtain a polarizer having a thickness of 35 μm.

Production of Polarizing Plate As shown below, the obtained optical film was alkali saponified, then washed with water, neutralized and washed with water. Thereafter, the obtained optical film was dried at 80 ° C.
Saponification process 2M-NaOH 50 ° C. 90 seconds Water washing process Water 30 ° C. 45 seconds Neutralization process 10% by mass HCl 30 ° C. 45 seconds Water washing process Water 30 ° C. 45 seconds

  Similarly, KC4UY manufactured by Konica Minolta Opto Co., Ltd. was also alkali saponified. Then, KC4UY subjected to alkali saponification treatment was bonded to one surface of the above polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. Similarly, an alkali film saponified optical film was bonded to the other surface of the polarizer using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. The bonding was performed so that the transmission axis of the polarizer and the in-plane slow axis of the optical film were parallel. The laminated laminate was dried to obtain a polarizing plate.

Production of pressure-sensitive adhesive composition 75 parts by mass of n-butyl acrylate (n-BA), 20 parts by mass of methyl acrylate (MA), 5 parts by mass of 2-hydroxy acrylate (2-HEA), 100 parts by mass of ethyl acetate and azobisiso 0.2 parts by mass of butyronitrile (AIBN) was placed in a reaction vessel, and the air in the reaction vessel was replaced with nitrogen gas. Thereafter, while stirring these components, the temperature in the reaction vessel was raised to 60 ° C. in a nitrogen atmosphere and reacted for 4 hours. After 4 hours, 100 parts by mass of toluene, 5 parts by mass of α-methylstyrene dimer and 2 parts by mass of AIBN were added, the temperature was raised to 90 ° C., and the mixture was further reacted for 4 hours. After the reaction, it was diluted with ethyl acetate to obtain an acrylic polymer solution having a solid content of 20% by mass. To 100 parts by mass of the solid content of the polymer solution, 1.0 part by mass of an isocyanate-based crosslinking agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added and stirred well to obtain an adhesive composition.

  On the film which carried out the peeling process, the obtained adhesive composition was apply | coated so that dry thickness might be set to 25 micrometers, the adhesive layer was formed, and the adhesive sheet was obtained.

The aforementioned polarizing plate was punched into a size of 100 × 100 mm. The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet was transferred to one surface of the obtained polarizing plate to obtain a pressure-sensitive adhesive-attached polarizing plate. The polarizing plate with an adhesive was bonded to the glass substrate. The polarizing plate was slightly peeled from the glass substrate from one of the four corners, and was peeled diagonally while holding the peeled polarizing plate and holding the glass substrate. The same operation was performed on a total of 10 samples, and evaluation was performed according to the following criteria.
○: All 10 sheets were able to be completely peeled without tearing. Δ: The optical film was torn with 1 to 5 pieces, and a part was left on the glass substrate. Torn and part of it remained on the glass substrate, resulting in peeling residue

6) Degradation of polarizer The total light transmittance of the polarizing plate produced in the evaluation of reworkability in 5) was measured using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. In measuring the total light transmittance, in order to cancel the influence of the polarization of light at the time of measurement, the total light transmittance of the polarizing plate is measured so that the absorption axis of the polarizer is in the horizontal direction. Were further measured (measured twice in total) so that their absorption axes were in a direction perpendicular to the horizontal direction (vertical direction), and an average value thereof was calculated. Next, after the polarizing plate was stored for 2000 hours at 60 ° C. and 90% RH and subjected to a durability test, the total light transmittance of the polarizing plate after the durability test was measured by the same method as described above. The obtained values were respectively applied to the following formulas, and the amount of change in the total light transmittance before and after the durability test was calculated.
Change amount of total light transmittance = (total light transmittance after durability test) − (total light transmittance before durability test)

Based on the amount of change in the total light transmittance obtained, the polarizer deterioration was evaluated as follows.
○: Change in total light transmittance is 5% or less. Δ: Change in total light transmittance is more than 5% and 10% or less. X: Change in total light transmittance is more than 10%. If it is △ level, there is no practical problem.

The evaluation results of the optical films of Examples 1 to 14 are shown in Table 1, the evaluation results of the optical films of Comparative Examples 1 to 13 are shown in Table 2, and the evaluation results of the optical films of Examples 15 to 16 and Comparative Example 14 are shown. Table 4 shows the evaluation results of Comparative Examples 15 to 18.

  The films of Examples 1 to 16 containing LBT1830 or Adekasizer D-32, which are acid trapping agents, have higher breaking stress and tear strength than the films of Comparative Examples 1 to 13 that do not contain acid trapping agents, and are colored. It turns out that it does not occur.

  Moreover, it turns out that the film of Examples 1-2 formed into a film at high melting temperature has higher rework property, and coloring does not arise than the film of Examples 3-4 formed into a film with low melting temperature. The reason why the films of Examples 1 and 2 were not colored is considered to be that the thermal degradation of the resin when the melting temperature was increased could be suppressed by containing an acid trapping agent. The high reworkability of the films of Examples 1 and 2 can increase the fluidity of the resin composition containing the (meth) acrylic resin and the cellulose ester by increasing the melting temperature, and the flexibility of the resulting film This is thought to be due to the improvement in performance.

  From the comparison of Examples 4 to 8, if the content of the acid trapping agent is too low, the resulting film is slightly colored; if the content of the acid trapping agent is too high, the resulting film slightly bleeds out. It turns out that it is easy to deteriorate a polarizer.

  The comparison between Example 3 and 9 to 12 suggests that if the content ratio of (meth) acrylic resin is too large, the resulting film tends to be slightly brittle and the tear strength tends to be slightly decreased. On the other hand, when the content ratio of the cellulose ester is too large, it can be seen that the resulting film is slightly colored.

  From the comparison between Example 3 and 13-14, a film containing a (meth) acrylic resin containing a lactone ring has higher film strength and higher reworkability than a film containing a (meth) acrylic resin containing no lactone ring. I understand that. The strength of the film containing the (meth) acrylic resin containing the lactone ring is high because the structural units derived from the uncyclized hydroxyl group-containing monomer contained in the main chain of the (meth) acrylic resin containing the lactone ring are hydrogen. It is considered that this is because a bond is formed and the compatibility between the (meth) acrylic resin and the cellulose ester is high.

  As shown in Example 16, even when the film thickness is as thin as about 10 μm, it can be seen that the inclusion of the acid trapping agent has a tear strength of a certain level or more and exhibits good reworkability.

  On the other hand, in the film of Comparative Example 1, it can be seen that the resulting film is colored or that Rth is slightly increased. Since the film of Comparative Example 1 does not contain an acid trapping agent, it is considered that the resin was thermally deteriorated due to a high melting temperature. Moreover, it is considered that the Rth of the film containing the thermally deteriorated resin is high because the side chain of the cellulose ester is decomposed. Moreover, since the film containing the resin which carried out heat deterioration is weak, it turns out that rework property is also low.

  The optical film of the present invention contains a (meth) acrylic resin as a main component, is not colored, has a thin film thickness, and is excellent in reworkability.

DESCRIPTION OF SYMBOLS 10 Film manufacturing apparatus 12 Extruder 14 Die 16, 18, 20 Cooling roll 22 Peeling roll 24 Stretching apparatus 26 Winding apparatus 28 Filter 30 Static mixer 32 Elastic touch roll 110 Liquid crystal display apparatus 120 Liquid crystal cell 140 First polarizing plate 142 First Polarizer 144 Protective Film (F1)
146 Protective Film (F2)
160 2nd polarizing plate 162 2nd polarizer 164 Protective film (F3)
166 protective film (F4)
180 backlight

Claims (16)

An optical film comprising a composition containing a (meth) acrylic resin as a main component and an acid trapping agent,
The acid trapping agent is a zinc metal salt of stearyl phosphate;
The breaking stress is 70 MPa or more, and the tear strength is 10 mN or more,
An optical film having a thickness of 10 to 45 μm.   2. The optical film according to claim 1, wherein the content of the acid trapping agent is 0.1 to 5 mass% with respect to the composition.   The optical film according to claim 1, wherein the composition further contains a cellulose ester.   The optical film according to claim 3, wherein the cellulose ester is cellulose acetate propionate.   The optical film of Claim 3 or 4 whose content ratio of the said (meth) acrylic resin and the said cellulose ester is (meth) acrylic resin / cellulose ester = 90 / 10-50 / 50 by mass ratio.   The optical film as described in any one of Claims 1-5 whose weight average molecular weights of the said (meth) acrylic resin are 80,000 or more.   The optical film according to claim 1, wherein the (meth) acrylic resin has a lactone ring structure.   The optical film according to claim 1, wherein the composition further contains an acrylonitrile / styrene copolymer. It consists of a composition containing a (meth) acrylic resin as a main component and an acid trapping agent , wherein the acid trapping agent is an alkyl phosphate metal salt, has a breaking stress of 70 MPa or more and a tear strength of 10 mN or more. A method for producing an optical film having a thickness of 10 to 45 μm,
The resin composition containing the (meth) acrylic resin and the acid trapping agent is melt-kneaded and then extruded into a film shape,
The melting temperature of the resin composition is a method for producing an optical film, which is 250 to 270 ° C.   The method for producing an optical film according to claim 9, further comprising a step of stretching the extruded resinous composition at a stretching temperature of 145 ° C. or lower.   11. The method for producing an optical film according to claim 10, wherein the melting temperature of the resin composition is 250 to 260 ° C., and the stretching temperature is 145 ° C. or less.   The manufacturing method of the optical film as described in any one of Claims 9-11 in which the said resin composition further contains a cellulose ester.   The polarizing plate protective film containing the optical film as described in any one of Claims 1-8. The polarizing plate protective film of Claim 13 whose retardation Rth of the thickness direction defined by a following formula and measured in wavelength 590nm is -5 nm or more and 5 nm or less.
Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction in the film plane, ny: refractive index in the direction perpendicular to the slow axis in the film plane, nz: refractive index of the film in the thickness direction, d: film thickness (Nm))   The polarizing plate containing a polarizer and the polarizing plate protective film of Claim 13 or 14 arrange | positioned on the at least one surface of the said polarizer.   A liquid crystal display device comprising: a liquid crystal cell; and the polarizing plate according to claim 15 disposed on at least one surface of the liquid crystal cell.

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