JP2010204616A - Optical film, polarizing plate using the same, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film of which the breakage resistance in a film transfer process etc., the dimensional stability when used as a polarizing plate, and the so-called "picture frame unevenness prevention" are improved significantly, and to provide a polarizing plate which uses using the same, and to provide a liquid crystal display device. <P>SOLUTION: The optical film includes a modified cellulose ester, having a repeating unit with a predetermined structure; another cellulose ester which is different from the modified cellulose ester and which has an average acyl group substitution of 2-2.5; and, as an additive, another kind of compound with a carboxyl group of 0.5-10 mass%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film, a polarizing plate using the same, and a liquid crystal display device. More specifically, an optical film that has improved resistance to breakage in a film transporting process and the like, and dimensional stability and so-called frame unevenness prevention when the film is used for a polarizing plate, and a polarizing plate using the optical film and The present invention relates to a liquid crystal display device.

  Cellulose ester is often used as a material for optical films. Among them, cellulose acetate propionate (hereinafter abbreviated as “CAP”) has a low melt viscosity and excellent extrusion characteristics. Suitable for membranes (see, for example, Patent Document 1).

  However, when a polarizer was bonded to a film formed using CAP to produce a polarizing plate, there was a problem that the polarizing plate exposed to high-humidity heat conditions contracted.

  As a result of diligent investigation of this cause, the polarizer has the property of shrinking in the casting direction under wet heat conditions. Therefore, when an optical film is laminated to form a polarizing plate, it is in a poor environment (for example, a high temperature and high humidity environment). It has been found that the optical film using CAP may not be able to sufficiently suppress the shrinkage of the polarizer when exposed to (lower) for a long time.

  Among the cellulose esters used in the melt casting method, an optical film using cellulose diacetate (hereinafter abbreviated as “DAC”) has good surface adhesion with a polarizer (see, for example, Patent Document 2), and CAP. Although it is known that it has a high elastic modulus, there is a problem that it is difficult to stretch at a high magnification and the retardation development property is insufficient when used as a retardation film.

  Moreover, since the melt viscosity is high, it is difficult to increase the casting speed, and when the winding speed is increased to increase the film thickness adjustment and the production speed, or when the film is stretched in the width direction, breakage is likely to occur.

  Therefore, in order to reduce the viscosity to a sufficient level for melt casting, when a large amount of plasticizer is placed in the DAC to form a film, the elastic modulus of the formed film decreases, and the polarizer and the paste are bonded. As a result, a polarizing plate was produced. As a result, the polarizing plate exposed to high humidity and heat conditions contracted.

  Also, the more a low molecular plasticizer is added to the DAC, the easier it is to cause frame unevenness under high-humidity heat conditions when it is processed into a polarizing plate and attached to a liquid crystal panel.

  It has been found that a modified cellulose ester obtained by graft polymerization of ε-caprolactone to a cellulose ester can be stretched without adding a plasticizer when blended with a thermoplastic resin and has good dimensional stability under high-humidity heat conditions ( For example, see Patent Document 3.)

  Therefore, when a modified cellulose ester was added instead of adding a plasticizer to the DAC, it became possible to stretch at a high magnification without the addition of a plasticizer, but when increasing the film-forming speed or handling the film formed There was a problem that the breakage occurring in the process still does not improve.

Japanese Patent Laying-Open No. 2005-88578 (paragraph [0040]) JP 2006-290929 A JP 2007-231050 A

  The present invention has been considered in view of the above problems / situations, and the problem to be solved is the resistance to breakage in the film transport process and the like, and the dimensional stability and the so-called non-uniformity of the frame when the film is used for a polarizing plate. It is to provide an optical film that has been dramatically improved. Moreover, it is providing the polarizing plate and liquid crystal display device which used the said optical film.

  The present inventor added a small amount of an additive having a carboxyl group to the cellulose ester and the modified cellulose ester having an average acyl group substitution degree of 2.0 to 2.5 in the course of intensive studies to solve the above-mentioned problems. As a result, it was found that the film was hardly broken, and the present invention was achieved.

  That is, the said subject which concerns on this invention is solved by the following means.

  1. A modified cellulose ester having a repeating unit represented by the following general formula (1) or (2), a cellulose ester having an average acyl group substitution degree of 2 to 2.5 different from the modified cellulose ester, and an additive As an optical film, 0.5 to 10 parts by mass of a compound having a carboxyl group, which is different from the two types of cellulose esters, is contained.

[In formula, A and B represent a C1-C12 bivalent hydrocarbon group or a C1-C12 bivalent hydrocarbon group substituted by the hydroxyl group. However, A and B may be the same or different. ]
2. 2. The optical film as described in 1 above, wherein the modified cellulose ester and the cellulose ester are contained in a mass ratio of 5:95 to 30:70.

  3. A polarizing plate using the optical film described in 1 or 2 above.

  4). 4. A liquid crystal display device using the polarizing plate described in 3 above.

  By the above means of the present invention, it is possible to provide an optical film having dramatically improved resistance to breakage in a film transporting process and the like, and dimensional stability when the film is used as a polarizing plate, and so-called frame unevenness prevention. . In addition, a polarizing plate and a liquid crystal display device using the optical film can be provided.

  Although the mechanism of action of the present invention is not known in detail, it is presumed as follows. That is, it has been found that both the cellulose ester and the modified cellulose ester have both an ester bond and a hydroxyl group. These two are similar in molecular structure, but are difficult to mix because of their high molecular weight. When an additive having a carboxyl group is added here, the hydroxyl groups of the cellulose ester and the modified cellulose ester and the carboxyl group of the additive form a hydrogen bond, assisting the bonding of the cellulose ester and the modified cellulose ester. Guessed.

Optical film manufacturing equipment using elastic touch rolls.

  The optical film of the present invention is different from the modified cellulose ester having a repeating unit represented by the general formula (1) or (2) and the modified cellulose ester, and has an average acyl group substitution degree of 2 to 2.5. It contains 0.5 to 10 parts by mass of a cellulose ester and, as an additive, a compound having a carboxyl group, which is a different type from the two types of cellulose esters.

  This feature is a technical feature common to the inventions according to claims 1 to 4.

  As an embodiment of the present invention, it is preferable that the modified cellulose ester and the cellulose ester are contained in a mass ratio of 5:95 to 30:70 from the viewpoint of the effect of the present invention.

  The optical film of the present invention can be suitably used for a polarizing plate. The polarizing plate can be suitably used for a liquid crystal display device.

  Hereinafter, the present invention, its components, and modes for carrying out the present invention will be described in detail.

(Modified cellulose ester)
The modified cellulose ester according to the present invention is a cellulose ester having a repeating unit represented by the following general formula (1) or (2). Hereinafter, the modified cellulose ester will be described.

[In formula, A and B represent a C1-C12 bivalent hydrocarbon group or a C1-C12 bivalent hydrocarbon group substituted by the hydroxyl group. However, A and B may be the same or different. ]
Specific examples of A will be given below.

A-1-CH ₂ CH _{2-
A-2 -CH 2 CH 2 CH} 2 -
A-3 -CH = CH-

A-6 —CH ₂ C (CH ₃ ) ₂ —
Specific examples of B are given below.

B-1 _{-CH 2} CH 2 -
B-2-CH ₂ CH ₂ CH ₂ CH _2-

  The cellulose ester having at least one repeating unit represented by the general formula (1) or (2) is a cellulose having an unsubstituted hydroxyl group (hydroxyl group), or an acetyl group, a propionyl group, a butyryl group, a phthalyl group, etc. In the presence of a cellulose ester in which a part of hydroxyl groups (hydroxyl groups) has already been substituted by an acyl group, an esterification reaction between a polybasic acid or an anhydride thereof and a polyhydric alcohol, or L-lactide or D-lactide It can be obtained by ring-opening polymerization, self-condensation of L-lactic acid and D-lactic acid.

  Examples of the polybasic acid anhydride used in the esterification reaction include, but are not limited to, maleic anhydride, phthalic anhydride, and fumaric anhydride.

  Examples of the polyhydric alcohol that can be used in the esterification reaction include glycerin, ethylene glycol, and propylene glycol, but are not particularly limited.

  As the catalyst used for the esterification reaction, the reaction can be carried out without a catalyst, but a known Lewis acid catalyst or the like can be used. Examples of catalysts that can be used include metals such as tin, zinc, titanium, bismuth, zirconium, germanium, antimony, sodium, potassium, and aluminum, and derivatives thereof. Particularly, the derivatives include metal organic compounds, carbonates, oxides, halides. Is preferred. Specific examples include octyl tin, tin chloride, zinc chloride, titanium chloride, alkoxy titanium, germanium oxide, zirconium oxide, antimony trioxide, and alkyl aluminum. Moreover, an acid catalyst typified by p-toluenesulfonic acid can also be used as the catalyst. Moreover, in order to accelerate | stimulate the dehydration reaction of carboxylic acid and alcohol, you may add well-known compounds, such as carbodiimide and dimethylaminopyridine.

  Such a reaction may be a reaction in an organic solvent capable of dissolving cellulose ester and other compounds to be reacted, or a reaction using a batch kneader capable of heating and stirring while adding a shearing force. It may be by reaction using a uniaxial or biaxial extruder.

  The repeating unit represented by the general formula (1) or (2) can be appropriately contained in the range of 0.5 to 190% by mass with respect to cellulose.

  Although the substitution degree of this cellulose ester can be selected suitably, it is preferable that it is 2.2-3 from the point of thermoplasticity and heat workability.

  In the cellulose ester having at least one repeating unit represented by the general formula (1) or (2), when the hydrogen atom of the hydroxyl group (hydroxyl group) portion of the cellulose is a fatty acid ester with an aliphatic acyl group, an aliphatic group The acyl group has 2 to 20 carbon atoms and specifically includes acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl, hexanoyl, octanoyl, lauroyl, stearoyl and the like.

  The polymerization degree of the cellulose ester having at least one repeating unit represented by the general formula (1) or (2) is not particularly limited, and is, for example, a viscosity average polymerization degree of 70 or more (for example, 80 to 800). It can be selected from a range, and may be 100 to 500, preferably 110 to 400, and more preferably about 120 to 350.

  The repeating unit represented by the general formula (1) or (2) is, for example, 80 to 10,000, preferably 100 to 5000, more preferably about 200 to 2000, particularly 300 to 1500, as the number average molecular weight of the portion. Usually, it may be less than 1000. In addition, the number average molecular weight of only the repeating unit which the said cellulose ester has is compared by the GPC (gel permeation chromatograph) data which converted the cellulose ester before esterification reaction, and the cellulose ester after reaction into polystyrene, or 1H-NMR. And asked.

  An oligomer or polyester having the repeating unit represented by the general formula (1) or (2) as a side reaction when the repeating unit represented by the general formula (1) or (2) is introduced into cellulose or cellulose ester. However, since these compounds act as plasticizers, they need not be completely removed by purification. If content is 30 mass% or less with respect to a cellulose ester, there will be little change in the property of a cellulose ester. From the viewpoint of plasticity, it is preferably 0.5 to 20% by mass. These oligomers and polyesters have a number average molecular weight of 300 to 10,000, and preferably 500 to 8,000 from the viewpoint of plasticity.

  In addition, a graft copolymerized modified glucan derivative (modified cellulose derivative) described in JP-A-2008-197561 is also a cellulose or cellulose ester film having a repeating unit represented by the general formula (1) or (2) of the present invention. Can be used as

  Moreover, it is preferable that the cellulose-ester film which has a repeating unit represented by General formula (1) or (2) has the following characteristic.

Transmittance: 80% or more Film thickness: 20-90 μm
0nm ≦ Ro ≦ 330nm
−100 nm ≦ Rt ≦ 340 nm
Ro = (nx−ny) × d
Rt = ((nx + ny) / 2−nz) × d
(Where nx is the refractive index in the slow axis direction in the plane of the cellulose ester film, ny is the refractive index in the direction perpendicular to the slow axis in the plane, nz is the refractive index in the thickness direction, and d is the refractive index in the thickness direction) (Represents the thickness (nm) of the cellulose ester film. The refractive index is measured at 590 nm.)
The refractive index can be obtained at a wavelength of 590 nm under an environment of 23 ° C. and 55% RH using, for example, KOBRA-21ADH (Oji Scientific Instruments). The content of the solvent is preferably 0.01% by mass or less. In addition, the cellulose ester film preferably has a length of 100 m to 6000 m and a width of 1.2 m or more, more preferably 1.4 to 4 m. By making the length and width of the base film within the above ranges, the handleability and productivity are excellent.

The film containing a cellulose ester having a repeating unit represented by the general formula (1) or (2) is preferably one having few bright spot foreign substances. The bright spot foreign matter preferably has a bright spot diameter of 0.01 mm or more and 200 pieces / cm ² or less, more preferably 100 pieces / cm ² or less, and preferably 50 pieces / cm ² or less. 30 / cm ² or less, preferably 10 / cm ² or less, and most preferably none.

Moreover, it is preferable that it is 200 pieces / cm < ² > or less also about a bright spot of 0.005-0.01 mm or less, Furthermore, it is preferable that it is 100 pieces / cm < ² > or less, and it is 50 pieces / cm < ² > or less. The number is preferably 30 pieces / cm ² or less, more preferably 10 pieces / cm ² or less, and most preferably none.

<Additives>
The optical film of the present invention is further characterized by containing, as an additive, 0.5 to 10 parts by mass of a compound having a carboxyl group, which is different from the cellulose ester.

  The additive is selected from an acrylic polymer and a sugar ester compound in which at least one of the pyranose structure or furanose structure is 1 to 12 and all or part of the OH groups of the structure are esterified It is preferable to contain at least one of the above.

<Sugar ester compound>
Examples of the sugar ester compound include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose and the like, and those having both a furanose structure and a pyranose structure are particularly preferable. An example is sucrose.

The sugar ester compound is a compound obtained by condensing 1 or more and 12 or less of at least one of a pyranose structure or a furanose structure represented by the following general formula (A). _{However, R 11 ~R 15, R 21} ~R 25 is an acyl group or a hydrogen atom having 2 to 22 carbon atoms, m and n each represent an integer of 0 to 12, m + n represents an integer of 1 to 12.

R _{11 to} R ₁₅ and R _{21 to} R ₂₅ are preferably a benzoyl group or a hydrogen atom. The benzoyl group may further have 0 to 5 substituents introduced into the benzene ring, and examples thereof include an alkyl group, an alkenyl group, an alkoxyl group, and a phenyl group. Further, these alkyl groups, alkenyl groups, and phenyl groups include It may have a substituent.

  Specific examples are shown below.

  As a commercial item, monopet SB (Daiichi Kogyo Seiyaku Co., Ltd. product) etc. are mentioned, for example.

(Cellulose ester)
In the present invention, the cellulose ester is different from the modified cellulose ester and has an average acyl group substitution degree of 2 to 2.5.

  The cellulose ester according to the present invention is not particularly limited as long as it is a cellulose ester conventionally used in the field of optical films.

  As the compound constituting the resin, for example, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate can be used. Cellulose diacetate, cellulose acetate propionate, and the like can be used. Nate is preferred. Two or more types of cellulose esters may be used in combination.

  The cellulose used as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp (conifer pulp, hardwood pulp), and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

Cellulose esters are prepared by using an organic acid such as acetic acid or an organic solvent such as methylene chloride when the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, or butyric anhydride). Synthesize using a protic catalyst. When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized by the method described in JP-A-10-45804. The acyl group is reacted with the hydroxyl group of the cellulose molecule. Cellulose molecules are composed of many glucose units linked together, and the glucose unit has three hydroxyl groups. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution. For example, cellulose triacetate has an acetyl group bonded to all three hydroxyl groups of the glucose unit.

  The cellulose ester used in the present invention has an average acyl group substitution degree of 2.0 to 2.5 and an acyl group substitution degree of 3 to 7 carbon atoms of 0 to 0, particularly from the viewpoint of improving brittleness and transparency. Preferably it is 1.2. As the acyl group having 3 to 7 carbon atoms of the cellulose ester of the present invention, a propionyl group is particularly preferably used.

  When the average acyl group substitution degree of the cellulose ester is less than 2.0, that is, when the residual degree of the hydroxyl groups (hydroxyl groups) at the 2, 3, and 6 positions of the cellulose ester molecule is more than 1.0, the modification When used as an optical film because it is not sufficiently compatible with cellulose ester, haze becomes a problem. Moreover, even if the average substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms exceeds 1.2, still sufficient compatibility cannot be obtained, Brittleness will decrease. For example, even when the average substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is low, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it exceeds 2, compatibility falls and haze rises.

  The acyl substitution degree of the cellulose ester of the present invention is 1 to 2, although the average substitution degree is 2.0 to 2.5 and the substitution degree of the acyl group having 3 to 7 carbon atoms is 0 to 1.2. When the film thickness is 2 or more, the elastic modulus of the film decreases, and when a polarizing plate produced using this film is exposed to high-humidity heat conditions, shrinkage increases.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the cellulose ester has an aromatic acyl group as a substituent, the number of substituents X substituted on the aromatic ring is preferably 0 to 5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 0 to 1.2.

  The cellulose ester according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, that is, having 3 carbon atoms. Or what has an acyl group of 4 as a substituent is preferable.

  Among these, particularly preferred cellulose esters are cellulose acetate propionate and cellulose propionate.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester according to the present invention is 75,000 or more from the viewpoint of improving brittleness, preferably in the range of 75,000 to 300,000, more preferably in the range of 100,000 to 24,000, Those of 160000 to 240000 are particularly preferred. In the present invention, two or more kinds of cellulose resins can be mixed and used.

(Antioxidant)
In the present invention, the resin mixture such as cellulose ester preferably contains an antioxidant in order to improve the thermal decomposability and thermal colorability during the molding process.

  In the present invention, a preferable antioxidant is a phosphorus-based or phenol-based antioxidant, and it is more preferable to combine a phosphorus-based and a phenol-based antioxidant at the same time.

  Hereinafter, the antioxidant that can be suitably used in the present invention will be described.

<Phenolic antioxidant>
In the present invention, a phenolic antioxidant represented by the following general formula (AO1) can be used.

In general formula (AO1), R ₁ , R ₂ and R ₃ represent an alkyl substituent which is further substituted or unsubstituted. Specific examples of phenolic antioxidants include n-octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, n-octadecyl 3- (3,5-di-t-butyl). -4-hydroxyphenyl) -acetate, n-octadecyl 3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate, n-dodecyl 3 , 5-di-t-butyl-4-hydroxyphenylbenzoate, neo-dodecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, dodecyl β (3,5-di-t-butyl -4-hydroxyphenyl) propionate, ethyl α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n- Octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (n-octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-phenylacetate, 2- (n-octadecyl) Thio) ethyl 3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (2-hydroxy Ethylthio) ethyl 3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol bis- (3,5-di-t-butyl-4- Droxy-phenyl) propionate, 2- (n-octadecylthio) ethyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearamide N, N-bis- [ethylene 3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino N, N-bis- [ethylene 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2- ( 2-stearoyloxyethylthio) ethyl 3,5-di-tert-butyl-4-hydroxybenzoate, 2- (2-stearoyloxyethylthio) ethyl 7- (3-methyl-5-tert-butyl-4-hydroxy) Phenyl) heptanoate, 1,2-propylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxypheny ) Propionate], ethylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], neopentyl glycol bis- [3- (3,5-di-t-butyl-4) -Hydroxyphenyl) propionate], ethylene glycol bis- (3,5-di-t-butyl-4-hydroxyphenylacetate), glycerin-ln-octadecanoate-2,3-bis- (3,5 -Di-t-butyl-4-hydroxyphenyl acetate), pentaerythritol-tetrakis- [3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate], 1,1,1- Trimethylolethane-tris- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], sorbitol Oxa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl 7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, 2- Stearoyloxyethyl 7- (3-methyl-5-t-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol-bis [(3 ', 5'-di-t-butyl-4-hydroxy Phenyl) propionate], pentaerythritol-tetrakis (3,5-di-t-butyl-4-hydroxyhydrocinnamate). Phenol compounds of the above type are commercially available from Ciba Specialty Chemicals under the trade names “Irganox 1076” and “Irganox 1010”, for example.

<Phosphorus antioxidant>
As the phosphorus-based antioxidant that can be used in the present invention, a phosphorus-based compound such as phosphite, phosphonite, or phosphinite can be used.

  Conventionally known compounds can be used as the phosphorus-based antioxidant. For example, Japanese Patent Application Laid-Open Nos. 2002-138188, 2005-344444, paragraph numbers 0022 to 0027, Japanese Patent Application Laid-Open No. 2004-18279, paragraph numbers 0023 to 0039, Japanese Patent Application Laid-Open No. 10-306175, Japanese Patent Application Laid-Open No. 1-254744, and Japanese Patent Application Laid-Open No. -270892, JP-A-5-202078, JP-A-5-178870, JP-T-2004-504435, JP-T-2004-530759, and JP-A-2005-353229 Is preferred.

  Preferable phosphorus compounds include those described in paragraph 21 of JP-A-2008-257220, but are not limited thereto.

  In addition to the above, specific examples of phosphorus compounds that can be used in the present invention include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) phosphite, tris (dinonylphenyl). ) Phosphite, Tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10 -Phosphaphenanthrene-10-oxide, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butyldibenz [d, f ] [1.3.2] Monophosphite compounds such as dioxaphosphine and tridecyl phosphite; Diphosphites such as -butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl phosphite), 4,4'-isopropylidene-bis (phenyl-di-alkyl (C12-C15) phosphite) Compounds; triphenylphosphonite, tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4'-diylbisphosphonite, tetrakis (2,4-di-tert-butyl) Phosphonite compounds such as -5-methylphenyl) [1,1-biphenyl] -4,4'-diylbisphosphonite; Phosphinite compounds such as triphenylphosphinite and 2,6-dimethylphenyldiphenylphosphinite Phosphine such as triphenylphosphine and tris (2,6-dimethoxyphenyl) phosphine Emissions-based compounds; and the like.

  Phosphorus compounds of the above type are, for example, from Sumitomo Chemical Co., Ltd. “Sumilizer GP”, from ADEKA Co., Ltd. “ADK STAB PEP-24G”, “ADK STAB PEP-36”, “ADK STAB 3010”, “ADK STAB 2112”. ”,“ IRGAFOS P-EPQ ”and“ IRGAFOS 168 ”from Ciba Japan Co., Ltd., and“ GSY-P101 ”from Sakai Chemical Industry Co., Ltd.

《Other antioxidants》
Dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, pentaerythrityltetrakis (3-laurylthiopropioate) Nate) and the like, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy) 3,5-di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenyl acrylate, 3,4-dihydro-2H-1 described in JP-B-08-27508 -Benzopyran compounds, 3,3'-spirodichroman compounds, 1,1-spiroindane compounds, morpholine, thiomorpho Emissions, thiomorpholine oxide, thiomorpholine dioxide, a compound having a piperazine skeleton partial structure, oxygen scavenger dialkoxy benzene type compound in JP-03-174150 Patent describes the like. These antioxidant partial structures may be part of the polymer or regularly pendant into the polymer and introduced into part of the molecular structure of additives such as plasticizers, acid scavengers, and UV absorbers. It may be.

(Other additives)
《Plasticizer》
In the optical film of the present invention, a plasticizer can be used in combination in order to further improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the optical film of the present invention. When the addition amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky and is not preferable for practical use. Therefore, it is preferable to make the amount as small as possible. However, the modified cellulose ester of the present invention is different from the modified cellulose ester and has an average acyl. By using an optical film characterized by containing 0.5 to 10% by mass of a cellulose ester having a group substitution degree of 2 to 2.5 and another type of compound having a carboxyl group, the amount of plasticizer added can be reduced to a small amount. Can be suppressed.

<Ultraviolet absorber>
The optical film of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole-based, 2-hydroxybenzophenone-based or salicylic acid phenyl ester-based ones. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine A hybrid system having both structures can be mentioned, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

  Furthermore, an antistatic agent can be added to the optical film of the present invention to impart antistatic performance to the optical film.

  For the optical film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphates, halogen-containing condensed phosphonates, halogen-containing phosphites, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

  According to the optical film of the present invention, improvement in low hygroscopicity, transparency, high heat resistance, and brittleness that could not be achieved with conventional resin films can be achieved at the same time.

  In the optical film of the present invention, the tension softening point is preferably controlled to 105 ° C to 145 ° C, particularly 110 to 130 ° C.

  The tension softening point of the optical film is determined by, for example, using a Tensilon tester (ORIENTEC Co., RTC-1225A), cutting the optical film at 120 mm (length) × 10 mm (width) and pulling it at a tension of 10 N at 30 ° C. / The temperature can be continuously increased at a rate of temperature increase of min, and the temperature at 9 N can be measured three times, and the average value can be obtained.

  From the viewpoint of heat resistance, the optical film preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. Point glass transition temperature (Tmg).

  In the measurement according to JIS-K7127-1999, the optical film of the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  The thickness of the optical film of the present invention is preferably 20 μm or more. More preferably, it is 30 μm or more.

  The upper limit of the thickness is not particularly limited, but in the case of forming a film by a solution casting method, the upper limit is about 250 μm from the viewpoint of applicability, foaming, solvent drying, and the like. In addition, the thickness of a film can be suitably selected according to a use.

  The optical film of the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact part (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roll, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the resin.

  The optical film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

<Optical film formation>
An example of a method for producing an optical film will be described, but the present invention is not limited to this.

  As a method for forming the optical film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the standpoints of suppressing optical defects such as die lines and suppressing optical defects, melt casting by casting is preferred. In the present invention, the melt casting film forming method using a touch roll is particularly preferable.

  In the present application, “melt film formation” means that a composition containing additives such as a modified cellulose ester, a cellulose ester, and a plasticizer is heated and melted to a temperature showing fluidity, and then the fluid cellulose ester and modified Casting a melt containing cellulose ester or the like is defined as melt film formation.

  More specifically, the heat melting molding method can be classified into a melt extrusion molding method, a press molding method, an inflation method, an injection molding method, a blow molding method, a stretch molding method, and the like. Among these, in order to obtain an optical film excellent in mechanical strength and surface accuracy, the melt extrusion method is excellent.

≪Film forming process≫
Hereinafter, the film forming process of the film will be described.

<Melted pellet manufacturing process of cellulose ester and additives>
It is preferable that a plurality of raw materials used for melt extrusion are usually kneaded and pelletized in advance.

  Pelletization may be performed by a known method. For example, cellulose ester, modified cellulose ester, plasticizer, and other additives are fed to an extruder with a feeder and kneaded using a single-screw or twin-screw extruder. It can be formed by extruding into a strand, cooling with water or air, and cutting.

  It is important to dry the raw material before extruding to prevent decomposition of the raw material. In particular, since the cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer, and to keep the moisture content at 200 ppm or less, and further 100 ppm or less.

  A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly. Mixing of the antioxidants may be performed by mixing solids, or if necessary, the antioxidant may be dissolved in a solvent and impregnated with a resin such as cellulose ester, or may be sprayed. You may mix.

A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Further, if the contact with air, such as the exit from the feeder unit or die, it is preferable that the atmosphere such as dehumidified air and dehumidified N ₂ gas.

  In addition, it is preferable to keep the supply hopper and the like to the extruder warm because moisture absorption can be prevented. Matting agents, UV absorbers, and the like may be applied to the obtained pellets or added in an extruder during film formation.

  In an extruder, it is preferable to process at as low a temperature as possible so that the shearing force is suppressed and the resin can be pelletized so that the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  Kneader discs can improve kneadability, but care must be taken against shearing heat generation. Mixability is sufficient without using a kneader disk. The suction from the vent hole may be performed as necessary. Since there is almost no volatile component at low temperatures, there may be no vent hole.

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 at a viewing angle of 10 ° using a spectrocolorimeter CM-3700d (manufactured by Konica Minolta Sensing Co., Ltd.) and a light source of D65 (color temperature 6504K).

  A film is formed using the pellets obtained as described above. Of course, the raw material powder can be directly fed to the extruder by a feeder without being pelletized to form a film as it is.

<Process of extruding the resin mixture melt from the die>
Dehydrated hot air or polymer dried under vacuum or reduced pressure using a uniaxial or biaxial extruder, the die outlet partial melting temperature Tm of the extruder is about 200-300 ° C, and a leaf disk type filter After removing the foreign matter by filtration, etc., it is cast from a T die into a film.

  When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances.

  If flaws or foreign matter adhere to the die, streaky defects may occur. Such defects are also referred to as die lines, but in order to reduce surface defects such as die lines, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

  The inner surface that contacts the molten resin such as an extruder or a die is preferably subjected to surface treatment that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material having a low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

  Additives such as plasticizers may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

<Process of casting a melt extruded from a die between a cooling roll and an elastic touch roll to form a film>
In this step, the film-like melt extruded from the die is nipped between a cooling roll and an elastic touch roll to form a predetermined film shape and film thickness.

  In this invention, it is preferable to convey the film obtained by extruding the melt containing a cellulose ester from a die | dye into a film form, and having a draw ratio of 10 or more and 45 or less to an chill roll with an elastic touch roll. The draw ratio is a value obtained by dividing the lip clearance of the die by the average film thickness of the film solidified on the cooling roll. The draw ratio can be adjusted by the die lip clearance and the take-up speed of the cooling roll. The die lip clearance is preferably 900 μm or more, and more preferably 1 mm or more and 2 mm or less.

(Cooling roll)
The cooling roll used in the present invention is not particularly limited, but is a roll having a structure in which a heat medium or a coolant that can be controlled in temperature flows through a highly rigid metal roll, and the size is not limited. The size may be sufficient to cool the extruded film, and the diameter of the cooling roll is usually about 100 mm to 1 m.

  Examples of the surface material of the cooling roll include carbon steel, stainless steel, aluminum, and titanium. Further, in order to increase the surface hardness or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The surface roughness of the surface of the cooling roll is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less.

  It is preferable to have two or more cooling rolls. When there is only one, the surface temperature Tr of the cooling roll is set to Tg-50 ≦ Tr ≦ Tg. In the case of two or more, the surface temperatures of the first cooling roll and the second cooling roll are set to Tg−50 ≦ Tr1 ≦ Tg and Tg−50 ≦ Tr2 ≦ Tg. Tg here refers to the glass transition temperature (° C.) of the mixture of cellulose esters.

  The glass transition temperature Tg was measured according to JIS K7121 using a differential scanning calorimeter DSC220 manufactured by Seiko Electronics Industry.

  Set about 10 mg of sample, raise the temperature from room temperature to 250 ° C. at 20 ° C./min under a nitrogen flow rate of 50 ml / min and hold for 10 minutes (1st scan), then 30 at a rate of 20 ° C./min. The temperature was lowered to 0 ° C. and held for 10 minutes (2nd scan), and further raised to 250 ° C. at 20 ° C./min (3rd scan) to obtain a DSC curve. The glass transition temperature was obtained from the obtained 3rd scan DSC curve.

[Elastic touch roll]
Examples of the elastic touch roll include JP 03-124425, JP 08-224772, JP 07-1000096, JP 10-272676, WO 97-028950, JP 11-235747, JP 2002-36332. No., JP-A-2005-172940 and JP-A-2005-280217 can use a silicon rubber roll coated with a thin film metal sleeve, but a double structure of a metal outer cylinder and an inner cylinder It is preferable to have a space so that a cooling fluid can flow between them.

  If the range of the thickness of the metal outer cylinder is 0.003 ≦ (thickness of the metal outer cylinder) / (touch roll radius) ≦ 0.03, it is preferable because the elasticity is appropriate. The diameter of the elastic touch roll is preferably 100 mm to 600 mm. Moreover, it is preferable that the thickness of a metal outer cylinder is 0.1-5 mm.

  The surface roughness of the metal outer cylinder surface is preferably 0.1 μm or less, more preferably 0.05 μm or less, in terms of arithmetic average roughness Ra.

  The material of the metal outer cylinder is required to be smooth, moderately elastic, and durable. Carbon steel, stainless steel, titanium, nickel produced by electroforming, etc. are preferred. Furthermore, in order to increase the hardness of the surface or to improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, ceramic spraying, or the like. It is preferable that the surface processed is further polished to have the surface roughness described above.

  The inner cylinder is preferably a lightweight and rigid metallic inner cylinder such as carbon steel, stainless steel, aluminum, titanium or the like. A sufficient rigidity can be obtained by setting the thickness of the inner cylinder to 2 to 10 times that of the outer cylinder. The inner cylinder may be further coated with a resin elastic material such as silicone or fluororubber.

  The structure of the space through which the cooling fluid flows can be any structure as long as the temperature of the roll surface can be uniformly controlled. For example, the roll can be made to flow in a spiral direction by going alternately in the width direction and returning. Temperature control with a small surface temperature distribution is possible.

  The cooling fluid is not particularly limited, and water or oil can be used according to the temperature range to be used.

  The surface temperature Tr0 of the elastic touch roll is preferably lower than the glass transition temperature (Tg) of the film. If it is higher than Tg, the peelability between the film and the roll may be inferior. More preferably, it is Tg-50 degreeC-Tg.

  The elastic touch roll used in the present invention preferably has a so-called crown roll shape in which the central portion in the width direction has a diameter larger than that of the end portion.

  The width of the elastic touch roll used in the present invention is preferably wider than the film width because the entire film can be in close contact with the cooling roll. Further, when the draw ratio is increased, both end portions of the film may become ear height (thickness of the end portion becomes thick) due to a neck-in phenomenon.

  In this case, the width of the metal outer cylinder may be made narrower than the film width so as to escape from the height of the ear. Alternatively, the outer diameter of the metal outer cylinder may be reduced to escape the ear height.

  Specific examples of the metal elastic touch roll include molding rolls described in Japanese Patent No. 3194904, Japanese Patent No. 3422798, Japanese Patent Application Laid-Open No. 2002-36332, and Japanese Patent Application Laid-Open No. 2002-36333.

  In order to prevent bending of the elastic touch roll, a support roll may be arranged on the opposite side of the touch roll with respect to the cooling roll.

  You may arrange | position the apparatus which cleans the stain | pollution | contamination of an elastic touch roll. As the cleaning device, for example, a method of pressing the roll surface with a member such as a nonwoven fabric infiltrated with a solvent if necessary, a method of bringing the roll into contact with a liquid, a plasma discharge such as corona discharge or glow discharge, A method for volatilizing dirt can be preferably used.

  In order to make the surface temperature Tr0 of the elastic touch roll even more uniform, a temperature control roll may be brought into contact with the touch roll, temperature-controlled air may be blown, or a heat medium such as a liquid may be brought into contact.

  In the present invention, it is preferable that the touch roll linear pressure at the time of pressing the elastic touch roll is 1 kg / cm or more and 15 kg / cm or less, and the touch roll side film surface temperature Tt is Tg <Tt <Tg + 110 ° C.

  You may press a film indirectly by pressing an elastic touch roll with a support roll.

  The film surface temperature and roll surface temperature can be measured with a non-contact infrared thermometer. Specifically, using a non-contact handy thermometer (IT2-80, manufactured by Keyence Co., Ltd.), 10 locations in the width direction of the film are measured at a distance of 0.5 m from the object to be measured.

  The elastic touch roll side film surface temperature Tt refers to the film surface temperature measured with a non-contact infrared thermometer from the touch roll side in the state where the touch roll is removed from the film being conveyed.

<The process and the extending process of heating the cooled film in the range of Tg + 30 degreeC or more and Tg + 60 degreeC or less>
After the cooling step, it is preferable to provide a step of heating the cooled film again in the range of Tg + 30 ° C. or higher and Tg + 60 ° C. or lower. The heating time is preferably 5 to 60 seconds, more preferably 10 to 30 seconds.

  This reheating step is preferably a reheating step while stretching, and is preferably a transverse stretching step (film width direction).

  In the present invention, it is preferable to stretch at least 1.01 to 5.0 times. Preferably, the film is stretched 1.1 to 3.0 times in both the longitudinal and lateral (width direction) directions.

  You may have multiple processes which heat the cooled film in Tg + 30 degreeC or more and Tg + 60 degreeC or less. In this case, it is preferable to cool by the cooling roll maintained at the temperature below Tg between each heating process.

  As a method of stretching, a known roll stretching machine or tenter can be preferably used.

  The temperature and magnification of the optical film of the present invention can be selected so that desired retardation characteristics can be obtained.

  The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

<Post-stretching process (including winding process)>
In the optical film produced by the above method, after the aggregates such as plasticizers are reduced to such an extent that haze failure does not occur, the film is oriented in the longitudinal direction or the width direction for the purpose of adjusting retardation and reducing the dimensional change rate. It may be contracted.

  In order to shrink in the longitudinal direction, for example, there is a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

  The latter method can be performed by using a general simultaneous biaxial stretching machine, and by gradually and gradually narrowing the interval between adjacent clips in the longitudinal direction by driving the clip portion by, for example, a pantograph method or a linear drive method. it can. You may combine with extending | stretching of arbitrary directions (diagonal direction) as needed. The dimensional change rate of the optical film can be reduced by shrinking 0.5% to 10% in both the longitudinal direction and the width direction.

  Prior to winding, the ends may be slit and cut to the width of the product, and knurling (embossing) may be applied to both ends to prevent sticking or scratching during winding. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing.

  In addition, since the film has deform | transformed and cannot use as a product normally, the holding | grip part of the clip of both ends of a film is cut out and reused as a raw material.

  In the present invention, it is preferable to reduce the humidity change rate and dimensional change rate of retardation (Ro, Rt) by reducing the free volume of the film.

  In order to reduce the free volume, it is effective to have a step of performing a heat treatment near the Tg of the film after the stretching step. The heat treatment time shows an effect from 1 second or more, and the effect becomes higher as the time is longer, but it is saturated at about 1000 hours, and therefore, it is preferably from 1 second to 1000 hours at Tg-20 ° C. to Tg.

  Further, Tg-15 ° C to Tg is preferably 1 minute to 1 hour. In addition, it is preferable to perform heat treatment while slowly cooling the temperature range from Tg to Tg-20 ° C., because the effect can be obtained in a shorter time than heat treatment at a constant temperature.

  The cooling rate is preferably −0.1 ° C./second to −20 ° C./second, more preferably −1 ° C./second to −10 ° C./second. The heat treatment method is not particularly limited, and the heat treatment can be performed by a temperature-controlled oven or roll group, hot air, an infrared heater, a microwave heating device, or the like.

  The film may be heat-treated in the form of a sheet or roll while being conveyed. In the case of feeding, it can be conveyed while being heat-treated using a roll group or a tenter. When heat-treating in a roll shape, the film may be wound in a roll shape at a temperature in the vicinity of Tg and gradually cooled by cooling as it is.

  FIG. 1 is a schematic flow sheet showing the overall configuration of the optical film manufacturing apparatus of the present invention. In FIG. 1, the optical film is manufactured by mixing film materials such as cellulose ester and then using the extruder 1 to melt and extrude from a casting die 4 onto a first cooling roll 5. In addition to circumscribing, the film 10 is further circumscribed on the three cooling rolls of the second cooling roll 7 and the third cooling roll 8 in order, and then cooled and solidified to form the film 10. Next, after the film 10 peeled off by the peeling roll 9 is gripped at both ends of the film by the stretching device 12 and stretched in the width direction, it is wound up by the winding device 16. In addition, a touch roll 6 is provided that clamps the molten film on the surface of the first cooling roll 5 in order to correct the flatness. The touch roll 6 has an elastic surface and forms a nip with the first cooling roll 5.

<Characteristics of manufactured optical film>
The optical film of the present invention is useful as a polarizing plate protective film for protecting a polarizer mainly composed of polyvinyl alcohol, and is also used as an optical compensation film for a liquid crystal display device by adjusting the retardation. be able to.

〔Polarizer〕
When using the optical film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  On the other surface, the optical film of the present invention may be used, or another polarizing plate protective film may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light having a polarization plane in a certain direction to pass through. A typical polarizing film currently known is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

  As the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 4 Pa to 1.0 × 10 9 Pa is preferably used in at least a part of the pressure-sensitive adhesive layer. A curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after applying and bonding the pressure-sensitive adhesive is suitably used.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

[Liquid Crystal Display]
By incorporating the polarizing plate bonded with the optical film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate according to the present invention includes a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), an IPS type (including an FFS type), and the like. It is preferably used in LCDs of various driving methods. In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Synthesis of modified cellulose ester)
70 parts of cellulose acetate (L-20, acyl group substitution degree 2.41 manufactured by Daicel Chemical Industries, Ltd.) was added to the reactor and dried under reduced pressure at 110 ° C. for 4 hours at 533 Pa (4 Torr). Thereafter, purging was performed with dry nitrogen, a reflux condenser was attached, 30 parts of ε-caprolactone and 67 parts of cyclohexanone that had been dried and distilled in advance were added, and the mixture was heated to 160 ° C. and stirred to dissolve cellulose acetate uniformly. To this reaction solution, 0.25 part of monobutyltin trioctylate was added and heated at 160 ° C. with stirring for 2 hours. Thereafter, the reaction solution was cooled to room temperature to terminate the reaction and obtain a reaction product. Furthermore, 10 parts of the reaction product was dissolved in 90 parts of chloroform, and then slowly dropped into 900 parts of a large excess of methanol, and the precipitated precipitate was filtered to remove the homopolymer of ε-caprolactone. . Furthermore, it heat-dried at 60 degreeC for 5 hours or more, and obtained the cellulose ester 1 which (epsilon) -caprolactone reacted with the cellulose acetate. And the primary structure of the cellulose ester obtained by 1H-NMR was analyzed. As a result, the average number of moles of ε-caprolactone reacted per mole of glucose unit was 0.86, the average degree of substitution was 0.12, and the average degree of polymerization was 7.4.

[Production of optical film]
<Preparation of optical film 1>
(Molten resin composition 1)
Cellulose ester (L-20 << acyl group substitution degree 2.41 >>) (manufactured by Daicel Chemical Industries, Ltd.) 90 parts by mass Modified cellulose prepared as above 5 parts by mass Monopet SB (Daiichi Kogyo Seiyaku Co., Ltd.) 5 parts by mass Part Irganox 1010 (manufactured by Ciba Japan Co., Ltd.) 0.5 parts by mass GSYP101 (manufactured by Sakai Chemical Industry Co., Ltd.) 0.075 parts by mass ADKSTAB 2112 (manufactured by ADEKA Co., Ltd.) 0.075 parts by mass Sumilyzer GS (Sumitomo Chemical) 0.2 mass part UV absorber Ti928 (manufactured by Ciba Japan Co., Ltd.) 1.5 mass part matting agent Seahoster KEP-30 manufactured by Nippon Shokubai Co., Ltd. (average particle size 0.3 μm silica fine particles) 0.1 parts by mass (melting of optical film)
The cellulose ester and the modified cellulose resin were dried at 70 ° C. under reduced pressure for 3 hours and cooled to room temperature, and then additives other than the matting agent were mixed.

  The above mixture was formed into a film by a manufacturing apparatus using an elastic touch roll shown in FIG. In a nitrogen atmosphere, it was melted at 240 ° C., extruded from the casting die onto the first cooling roll, and molded by pressing the film between the first cooling roll and the touch roll. Further, a matting agent was added as a slip agent from the hopper opening in the middle of the extruder 1 so as to be 0.1 part by mass.

  The heat bolt was adjusted so that the gap width of the casting die was 0.5 mm within 30 mm from the end in the width direction of the film and 1 mm at other locations. As the touch roll, a touch roll was used, and 80 ° C. water was allowed to flow therein as cooling water.

  On the peripheral surface of the first cooling roll from the position where the resin extruded from the casting die contacts the first cooling roll to the upstream end position in the first cooling roll rotation direction of the nip between the first cooling roll and the touch roll. The length L along was set to 20 mm. Thereafter, the touch roll was separated from the first cooling roll, and the temperature T of the melted part immediately before being sandwiched in the nip between the first cooling roll and the touch roll was measured. The temperature T of the melted part immediately before being squeezed by the nip between the first cooling roll and the touch roll is 1 mm upstream from the upstream end of the nip and is measured by a thermometer (HA-200E manufactured by Anritsu Keiki Co., Ltd.). It was measured. As a result of the measurement, the temperature T was 141 ° C. The linear pressure of the touch roll against the first cooling roll was 14.7 N / cm.

  Furthermore, after introducing into a tenter and stretching 1.3 times at 160 ° C in the width direction, cooling to 30 ° C while relaxing 3% in the width direction, then releasing from the clip, cutting off the clip gripping part, Was subjected to a knurling process with a width of 10 mm and a height of 5 μm, and wound on a winding core with a winding tension of 220 N / m and a taper of 40%. The winding core had an inner diameter of 152 mm, an outer diameter of 165 to 180 mm, and a length of 1550 mm. A prepreg resin obtained by impregnating glass fibers and carbon fibers with an epoxy resin was used as the core material for the core. The surface of the core was coated with an epoxy conductive resin, the surface was polished, and the surface roughness Ra was finished to 0.3 μm. The optical film 1 was prepared with a film thickness of 80 μm and a winding length of 3500 m.

<Preparation of optical films 2 to 21>
In the production of the optical film 1, the composition ratio of cellulose ester and modified cellulose resin, and the types and addition ratios of additives were changed as shown in Table 1, and the types of cellulose ester were changed as shown in Table 2. Except for the above, optical films 2 to 12 were produced in the same manner.

(Preparation of polarizing plate)
A polarizing film was prepared by adsorbing iodine to the stretched polyvinyl alcohol film, and the saponified optical film 1 was attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive. A commercially available cellulose acetate film (Konica Minoltac KC8UX) was saponified and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. At this time, the transmission axis of the polarizing film and the slow axis of the sample were arranged in parallel. The transmission axis of the polarizing film and the slow axis of the commercially available cellulose acetate film were arranged so as to be orthogonal. Thus, a polarizing plate was produced for each optical film.

  A sample film of a polarizing plate prepared as described above by peeling off a pair of polarizing plates and a retardation plate provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell Was pasted through an adhesive so that it was on the liquid crystal cell side. The crossed nicols were arranged so that the transmission axis direction of the polarizing plate on the observer side was up and down and the transmission axis of the polarizing plate on the backlight side was in the left and right direction.

  Polarizers were similarly prepared for the optical films 2 to 12.

"Evaluation methods"
The following evaluation was implemented about the optical film obtained above.
(Turn resistance during transportation)
At the time of film formation of the optical film, the breakage resistance at the time of conveyance was ranked according to the following criteria with respect to the frequency of breakage of the film during conveyance.
○: No breaks or breaks during film formation, transport, winding, and film handling ×: Frequent breaks occurred during film formation, transport, winding, and film handling.

(Polarizing plate dimension stability)
After conditioning the polarizing plate in a room at 23 ° C and 55% RH for 24 hours, in the same room, mark the surface of the polarizing plate with two crosses at 100 mm intervals in the longitudinal direction and the width direction of the film to accurately measure the dimensions. The distance is a and the treatment is performed at 60 ° C. and 90% RH for 250 hours. The humidity is adjusted again in a room at 23 ° C. and 55% RH for 24 hours, and the distance between the two marks is set to Mitutoyo Corporation. Measurement was performed with a measurement microscope MF-A1720, the value was defined as b, and the dimensional stability of the polarizing plate was determined as a dimensional change rate by the following formula.
Dimensional change rate (%) = [(ba) / a] × 100
(Frame unevenness tolerance)
Each liquid crystal display device manufactured using each of the optical films is lit for 1000 hours, and then visually checked for the presence of white spots (frame unevenness) around the screen in black display, and the following evaluation was performed. It was.
A: No light leakage in the periphery is observed at all. ○: Light leakage is recognized in the periphery a little. X: Light leakage in the periphery is remarkable. The above various evaluation results are shown in Tables 1 and 2. In Table 1, Kyowapol BA is a polyester polyol, and monopet SB is a sugar ester.

  As is apparent from the results shown in Table 1, it can be seen that the examples according to the present invention are superior in the resistance to breakage during conveyance, the dimensional stability of the polarizing plate, and the unevenness resistance of the frame compared to the comparative example. Further, it can be seen from this result that a cellulose ester having a propionyl group substitution degree of 1.2 or less is also effective.

DESCRIPTION OF SYMBOLS 1 Extruder 2 Filter 3 Static mixer 4 Casting die 5 Rotating support body (1st cooling roll)
6 Nipping pressure rotating body (touch roll)
7 Rotating support (second cooling roll)
8 Rotating support (3rd cooling roll)
9, 11, 13, 14, 15 Transport roll 10 Film 12 Stretching machine 16 Winding device

Claims (4)

A modified cellulose ester having a repeating unit represented by the following general formula (1) or (2), a cellulose ester having an average acyl group substitution degree of 2 to 2.5 different from the modified cellulose ester, and an additive As an optical film, 0.5 to 10 parts by mass of a compound having a carboxyl group, which is different from the two types of cellulose esters, is contained.

[In formula, A and B represent a C1-C12 bivalent hydrocarbon group or a C1-C12 bivalent hydrocarbon group substituted by the hydroxyl group. However, A and B may be the same or different. ] The optical film according to claim 1, wherein the modified cellulose ester and the cellulose ester are contained in a mass ratio of 5:95 to 30:70. A polarizing plate using the optical film according to claim 1. A liquid crystal display device using the polarizing plate according to claim 3.

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