JP2012118177A - Cellulose acylate film, production method of cellulose acylate film, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose acylate film showing no irregularity at an end portion even when the film is used as a protective film for a backlight side polarizing plate, and to provide a production method of the cellulose acylate film, and a liquid crystal display device using the cellulose acylate film.SOLUTION: The cellulose acylate film contains cellulose acylate. When indices of birefringence within the film plane are measured, the film satisfies nx>ny, where nx and ny are refractive indices in directions perpendicular to each other. When dimensional variations in the nx and ny directions are denoted by Sx and Sy, respectively, the film satisfies Sx>Sy.

Description

  The present invention relates to a cellulose acylate film, a method for producing a cellulose acylate film, and a liquid crystal display device using the cellulose acylate film.

  In recent years, display unevenness failure at the edge of the panel has become a problem in IPS and VA liquid crystal panels. This edge unevenness (hereinafter simply referred to as edge unevenness) is a structure in which a polarizing plate with a cellulose acylate film bonded to both sides of a polarizer is attached to both sides of a liquid crystal cell as a protective film. When the liquid crystal display screen is displayed black over time under the conditions, display unevenness due to elliptical light leakage is observed at the four corners.

  FIG. 1 is a schematic diagram showing the edge unevenness.

  The upper part of the figure shows a polarizing plate composed of a polarizer 2, a liquid crystal cell side protective film 3, and a backlight side protective film 4 on the backlight 1. A liquid crystal cell (not shown) is bonded to the liquid crystal cell side protective film 3.

  According to the analysis of the present inventors, the cause of the edge unevenness is mainly caused by the warp of the polarizing plate. That is, a polarizing plate is usually bonded to both sides of the liquid crystal cell via an adhesive, but the polarizing plate on the backlight side has a higher temperature and humidity than the polarizing plate on the viewing side surface. Therefore, when the polarizing plate on the backlight side is exposed to high temperature and high humidity over time, the edge of the protective film on the polarizing plate on the backlight side starts to absorb water, but the central portion is difficult to absorb water, so gradually. Stress begins to bend in the panel surface starting from the edge.

  At this time, due to this stress, the backlight 1 and the backlight side protective film 4 come into contact with each other at the center portion, but the panel is distorted such that the end portions do not come into contact with the backlight. When such distortion occurs, the phase difference of the protective film changes between the central portion and the end portion, which is considered to cause display unevenness due to elliptical light leakage.

  The edge unevenness is described in Patent Documents 1 and 2 (referred to as circle unevenness), and a technique for adjusting the distance between the backlight side polarizing plate and the backlight side optical member is disclosed.

  However, with the thinning of liquid crystal display devices, the distance between the backlight-side polarizing plate and the backlight tends to be closer, especially in direct-type backlights, because the amount of heat generated increases as the brightness increases. The polarizing plate tends to be easily damaged by heat, and the above technique is insufficient for solving the edge unevenness.

JP 2007-187841 A JP 2007-225922 A

  Therefore, an object of the present invention is to use a cellulose acylate film that does not cause edge unevenness even when used as a backlight-side polarizing plate protective film, a method for producing the cellulose acylate film, and the cellulose acylate film. The object is to provide a liquid crystal display device.

  The above object of the present invention is achieved by the following configurations.

  1. It contains cellulose acylate, and when the birefringence in the film plane is measured, nx> ny when the birefringence in the direction orthogonal to each other is nx, ny, and the dimensional variation in the nx, ny directions A cellulose acylate film, wherein Sx> Sy when Sx and Sy, respectively.

  2. 2. The cellulose acylate film as described in 1 above, wherein the cellulose acylate is a cellulose triacetate having an acyl substitution degree in the range of 2.80 to 2.95.

  3. 3. The cellulose acylate film as described in 1 or 2 above, which comprises a polyester plasticizer represented by the following general formula (1) and having a weight average molecular weight of 300 to 5,000.

General formula (1) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
4). A liquid crystal display device, wherein a polarizing plate using the cellulose acylate film described in any one of 1 to 3 on at least one surface of a polarizer is used for an IPS type liquid crystal panel.

  5). 5. The liquid crystal display device as described in 4 above, wherein the cellulose acylate film is disposed on the backlight side of the polarizing plate on the liquid crystal cell side.

  6). The method for producing a cellulose acylate film according to any one of the above 1 to 3, wherein the temperature during stretching in the width direction is in the range of 180 to 210 ° C, and the magnification during stretching is 30 to 30. A method for producing a cellulose acylate film, wherein the film is stretched in a range of 55%.

  According to the present invention, even when used as a backlight-side polarizing plate protective film, a cellulose acylate film having no edge unevenness, a method for producing the cellulose acylate film, and a liquid crystal display using the cellulose acylate film An apparatus can be provided.

It is a schematic diagram of edge part nonuniformity.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The cellulose acylate film of the present invention contains cellulose acylate, and when the birefringence in the film plane is measured, nx> ny when the birefringence in the directions orthogonal to each other is nx, ny, and Sx> Sy when the dimensional variations in the nx and ny directions are Sx and Sy, respectively.

  The present invention is a protective film for a polarizing plate used in an IPS mode liquid crystal display device and a VA mode liquid crystal display device, wherein the nx (also referred to as slow axis) direction and the direction Sx with large dimensional variation are in the same direction. Because the cellulose acylate film is stretched at high temperature and high magnification, it has stable stress distribution and optical distribution both in the width direction and in the longitudinal direction, and even in a large area film, it depends on the temperature and humidity of each part. When the dimensional fluctuation and phase difference fluctuation are small and this is used as a protective film, even if the liquid crystal panel is warped over time under the above high temperature and high humidity conditions, the central portion As a result, it was found that the phase difference of the protective film did not change at the part, and the present invention was achieved.

  Conventional cellulose acylate films usually exhibit nx (slow axis) in the width direction by stretching in the width direction, but the direction in which the dimensional variation is large is the direction opposite to the stretching direction. Direction, and Sx <Sy. Therefore, in a film in which nx> ny and Sx <Sy are normal, the phase difference is different between the center and the end due to the warp of the panel, and end unevenness is observed.

  As a result of intensive studies, the present inventor used a specific cellulose acylate having a degree of acyl substitution of cellulose acylate in the range of 2.80 to 2.95, and more preferably represented by the above general formula (1). At least one selected from acetic acid, benzoic acid, p-troyl acid, and troyl acid is used as the sealant, and at least one selected from phthalic acid, terephthalic acid, adipic acid, and 1,2-propanediol as the main chain. A polyester plasticizer having a weight average molecular weight of 300 to 5,000, a temperature during stretching in the width direction in the range of 180 to 210 ° C., and a magnification during stretching in the range of 30 to By stretching the film in a range of 55%, the cellulose acylate film satisfying nx> ny and Sx> Sy does not cause edge unevenness. It has been found to be able to realize a cellulose acylate film.

  Hereinafter, the present invention will be described in detail.

<Cellulose acylate>
The cellulose acylate used in the cellulose acylate film of the present invention is a carboxylic acid ester having about 2 to 22 carbon atoms, and is particularly preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. The acyl group bonded to the hydroxyl group may be linear or branched or may form a ring. Furthermore, another substituent may be substituted. When the degree of substitution is the same, birefringence decreases when the number of carbon atoms is large, and therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms.

  Among them, the cellulose acylate particularly preferably used in the present invention is preferably cellulose acetate, and is preferably cellulose triacetate having an acyl substitution degree (acetyl group substitution degree) in the range of 2.80 to 2.95.

  The cellulose acylate may be an acyl group derived from a mixed acid, preferably an acyl group having 2 and 3 carbon atoms, or 2 and 4 carbon atoms. In the present invention, a mixed fatty acid ester of cellulose to which a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate can also be used.

  As the cellulose acylate according to the present invention, those which simultaneously satisfy the following formulas (1) and (2) are preferable.

Formula (1) 2.80 ≦ X + Y ≦ 2.95
Formula (2) 0 ≦ Y ≦ 1.5
In the formula, X is the degree of substitution of the acetyl group, and Y is the degree of substitution of the propionyl group or butyryl group. Those satisfying the above two formulas can obtain a film exhibiting excellent physical properties and optical properties that meet the object of the present invention.

  The measuring method of the substitution degree of an acyl group can be measured according to ASTM-D817-96.

  When the acyl group has a degree of substitution of less than 2.80, the unreacted portion increases with respect to the hydroxyl group of the pyranose ring constituting the skeleton of the cellulose resin. By the treatment, cellulose acylate satisfying nx> ny and Sx> Sy cannot be obtained. Moreover, the humidity change of a phase difference and the ability to protect a polarizer as a polarizing plate protective film may decrease, which is not preferable.

  If the substitution degree of the acyl group exceeds 2.95, the stretching treatment at a high stretching ratio as in the present invention becomes difficult and easily causes breakage and the like, and the productivity is greatly lowered and haze tends to increase. There is no transparency, and the visibility of the panel cannot be secured.

  The ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the cellulose acylate according to the present invention is preferably 1.4 to 3.0. In the present invention, the cellulose acylate film may contain, as a material, cellulose acylate having a Mw / Mn value of 1.4 to 3.0, but the cellulose acylate contained in the film (preferably Is a cellulose triacetate or cellulose acetate propionate) The Mw / Mn value of the whole is more preferably in the range of 1.4 to 3.0. More preferably, it is 1.7-2.2.

  The molecular weight of the cellulose acylate used in the cellulose acylate film of the present invention is preferably 80000-200000 in terms of number average molecular weight (Mn). More preferred are 100,000 to 200,000, particularly preferably 150,000 to 200,000.

  The average molecular weight and molecular weight distribution of cellulose acylate can be measured by a known method using high performance liquid chromatography. Using this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

  Measured by high performance liquid chromatography under the following conditions.

Solvent: Acetone Column: MPW × 1 (manufactured by Tosoh Corporation)
Sample concentration: 0.2 (mass / volume)%
Flow rate: 1.0 ml / min Sample injection volume: 300 μl
Standard sample: Standard polystyrene Temperature: 23 ° C
Although there is no limitation in particular as a cellulose of the raw material of the cellulose acylate used for this invention, Wood pulp (a softwood pulp, a hardwood pulp), a cotton linter, etc. can be used. The Mw of cellulose acylate can be controlled by the type of cellulose and the use of a plurality of raw material celluloses. For example, when esterification is performed using hardwood hydrolyzed kraft pulp, Mw of cellulose acylate increases, and when softwood sulfite pulp is used, Mw tends to decrease. Therefore, cellulose may be used singly or in combination of two or more. For example, softwood pulp and cotton linter or hardwood pulp may be used in combination. As cellulose, usually pulp (particularly softwood pulp) is often used. In addition, the α-cellulose content (% by mass) of cellulose is usually from 94 to 99 (for example, 95 to 99), preferably from about 96 to 98.5 (for example, 97.3 to 98). .

In the cellulose acylate according to the present invention, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as acetic acid or an organic solvent such as methylene chloride is used. The reaction is carried out using a protic catalyst such as sulfuric acid. 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 with reference to the method described in JP-A-10-45804.

  The cellulose acylate used in the present invention preferably has an average substitution degree of the acyl group at the 6-position of the glucose unit of 0.5 to 0.9.

  Unlike the 2nd and 3rd positions, the glucose unit constituting the cellulose acylate has a highly reactive primary hydroxyl group, which is a process for producing cellulose acylate using sulfuric acid as a catalyst. To preferentially form sulfate esters. Therefore, by increasing the amount of catalytic sulfuric acid in the esterification reaction of cellulose, it is possible to increase the average degree of substitution at the 2nd and 3rd positions rather than the 6th position of the glucose unit as compared with normal cellulose acylate. Furthermore, if the cellulose is tritylated as necessary, the hydroxyl group at the 6-position of the glucose unit can be selectively protected. Therefore, the trityl group protects the hydroxyl group at the 6-position, and after esterification, the trityl group (protection) The average substitution degree at the 2nd and 3rd positions can be increased from the 6th position of the glucose unit. Specifically, cellulose acylate produced by the method described in JP-A No. 2005-281645 can also be preferably used.

  In the case of acetylcellulose, it is necessary to extend the time for the acetylation reaction in order to increase the acetylation rate. However, if the reaction time is too long, the decomposition proceeds at the same time, and the polymer chain is broken and the acetyl group is decomposed, resulting in undesirable results. Therefore, it is necessary to set the reaction time within a certain range in order to increase the degree of acetylation and suppress decomposition to some extent. It is not appropriate to define the reaction time because the reaction conditions are various and greatly change depending on the reaction apparatus, equipment and other conditions. As the decomposition of the polymer proceeds, the molecular weight distribution becomes wider. Therefore, in the case of cellulose acylate, the degree of decomposition can be defined by the value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is usually used. In other words, in the process of acetylation of cellulose triacetate, the weight average molecular weight used as one index of the reaction degree for allowing the acetylation reaction to be carried out for a sufficient time for acetylation without being excessively decomposed too much. The value of (Mw) / number average molecular weight (Mn) can be used.

  An example of a method for producing cellulose acylate is shown below. 100 parts by weight of a cotton linter was crushed as a cellulose raw material, 40 parts by weight of acetic acid was added, and pretreatment activation was performed at 36 ° C. for 20 minutes. Thereafter, 8 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride and 350 parts by mass of acetic acid were added, and esterification was performed at 36 ° C. for 120 minutes. After neutralization with 11 parts by mass of a 24% magnesium acetate aqueous solution, saponification aging was carried out at 63 ° C. for 35 minutes to obtain acetylcellulose. This was stirred for 160 minutes at room temperature using a 10-fold acetic acid aqueous solution (acetic acid: water = 1: 1 (mass ratio)), then filtered and dried to obtain purified acetylcellulose having an acetyl substitution degree of 2.85. . This acetylcellulose had Mn of 92000, Mw of 156000, and Mw / Mn of 1.7. Similarly, cellulose acylates having different degrees of substitution and Mw / Mn ratios can be synthesized by adjusting the esterification conditions (temperature, time, stirring) and hydrolysis conditions of cellulose acylate.

  In addition, the synthesized cellulose acylate is preferably purified to remove low molecular weight components or to remove unacetylated or low acetylated components by filtration.

  In the case of mixed acid cellulose acylate, it can be obtained by the method described in JP-A-10-45804.

  Cellulose acylate is also affected by trace metal components in cellulose acylate. These are considered to be related to water used in the production process, but it is preferable that there are few components that can become insoluble nuclei, and metal ions such as iron, calcium, and magnesium contain organic acidic groups. Insoluble matter may be formed by salt formation with a polymer degradation product or the like that may be present, and it is preferable that the amount is small. The iron (Fe) component is preferably 1 ppm or less. As for the calcium (Ca) component, it is easy to form a coordination compound, that is, a complex with an acidic component such as carboxylic acid or sulfonic acid, and many ligands. Starch, turbidity).

  The cellulose acylate of the present invention has a calcium content of 10 to 50 ppm, preferably 15 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-treated with absolutely digested cellulose acylate by micro digest wet cracking device (sulfuric acid decomposition) and alkali melting. Can be analyzed using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer).

  Next, the additive used for the cellulose acylate film of the present invention will be described.

(Plasticizer)
In order to obtain the effect of the present invention, the cellulose acylate film of the present invention preferably uses a polyester plasticizer represented by the following general formula (1) and having a weight average molecular weight of 300 to 5,000.

General formula (1) B- (GA) n-GB
In the formula, B is a monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A is An alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms is represented, and n represents an integer of 1 or more.

  In the general formula (1), a monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic acid represented by A And is obtained by the same reaction as a normal polyester plasticizer.

  Examples of the monocarboxylic acid component of the polyester plasticizer used in the present invention include acetic acid, benzoic acid, p-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal There are propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively. In particular, at least one selected from acetic acid, benzoic acid, p-troyl acid, and troyl acid is preferable.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer that can be used in the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1, 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neo Pentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3propanediol (3,3-dimethylolheptane) 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-penta Diol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. It is used as one kind or a mixture of two or more kinds. In particular, alkylene glycols having 2 to 12 carbon atoms are particularly preferable because of excellent compatibility with cellulose acylate.

  In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. It can be used as a seed or a mixture of two or more.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and the like.

  The polyester plasticizer used in the present invention has a number average molecular weight of preferably 300 to 5,000, more preferably 400 to 2,000.

  The molecular weight of the polyester plasticizer of the present invention can be measured using the measurement method by GPC and the terminal group determination method (hydroxyl value).

  The acid value is 0.5 mgKOH / g or less, the hydroxyl value is 25 mgKOH / g or less, more preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl value is 15 mgKOH / g or less.

  Hereinafter, synthesis examples of aromatic terminal ester plasticizers that can be used in the present invention will be shown.

<Sample No. 1 (Aromatic terminal ester sample)>
A reaction vessel was charged with 410 parts of adipic acid, 610 parts of benzoic acid, 737 parts of dipropylene glycol, and 0.40 part of tetraisopropyl titanate as a catalyst. While refluxing the monohydric alcohol, heating was continued at 130 to 250 ° C. until the acid value became 2 or less, and water produced was continuously removed. Next, the distillate is removed under reduced pressure at 200 to 230 ° C. under a reduced pressure of 1.33 × 10 ⁴ Pa to 4 × 10 ² Pa or less, and then filtered to remove an aromatic terminal ester plastic having the following properties: An agent was obtained.

Viscosity (25 ° C., mPa · s); 43400
Acid value: 0.2
<Sample No. 2 (Aromatic terminal ester sample)>
Sample No. 1 was used except that 410 parts of phthalic acid, 610 parts of benzoic acid, 341 parts of ethylene glycol, and 0.35 part of tetraisopropyl titanate as a catalyst were used in the reaction vessel. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25 ° C., mPa · s); 31000
Acid value: 0.1
<Sample No. 3 (Aromatic terminal ester sample)>
Sample No. 1 was used except that 410 parts of terephthalic acid, 610 parts of p-troyl acid, 418 parts of 1,2-propanediol and 0.35 part of tetraisopropyl titanate as a catalyst were used in the reaction vessel. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.

Viscosity (25 ° C., mPa · s); 38000
Acid value: 0.05
<Sample No. 4 (Ester sample)>
Sample No. 1 was used except that 410 parts of adipic acid, 610 parts of acetic acid, 418 parts of 1,2-ethanediol, and 0.35 part of tetraisopropyl titanate as the catalyst were used in the reaction vessel. An ester having the following properties was obtained in the same manner as in Example 1.

Viscosity (25 ° C., mPa · s); 37000
Acid value: 0.05
<Sample No. 5-9>
Sample No. 1 was synthesized using the raw materials shown in Table 1.

  It is preferable that the said compound contains 1-35 mass% in an optical film, especially 5-30 mass%. Within this range, it is preferable that the excellent effects of the present invention are exhibited and there is no bleeding out during storage of the raw material.

(Other plasticizers)
As the plasticizer that can be used, phosphate ester plasticizers and non-phosphate ester plasticizers are preferably used. Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like. Non-phosphate ester plasticizers include phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol plasticizers, glycolate plasticizers, and citrate ester plasticizers. Agents, fatty acid ester plasticizers, polycarboxylic acid ester plasticizers, and the like can be preferably used, and polyhydric alcohol plasticizers and polycarboxylic acid ester plasticizers are preferably used. The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol is represented by the following general formula (2).

R1- (OH) n (2)
In the formula, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.

  Examples of preferred polyhydric alcohols include, but are not limited to, the following. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, 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, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, pentaerythritol, dipentaerythritol and the like. Of these, trimethylolpropane and pentaerythritol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferable in terms of improving moisture permeability and retention. Examples of preferred monocarboxylic acids include the following, but are not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10. The use of acetic acid is preferred because the compatibility with the cellulose ester is increased, and it is also preferred to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid. Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof. Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. The aromatic monocarboxylic acid which has, or those derivatives can be mentioned. In particular, benzoic acid is preferred.

  The molecular weight of the polyhydric alcohol ester is preferably in the range of 300 to 1500, and more preferably in the range of 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester. The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are. The specific compound of a polyhydric alcohol ester is shown below.

  The content of the polyhydric alcohol ester is preferably 1 to 15% by mass, and particularly preferably 3 to 10% by mass in the cellulose ester film.

  Hereinafter, although the specific example of a polyhydric alcohol ester is shown, it is not limited to this.

(UV absorber)
The cellulose acylate film of the present invention preferably contains an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

  The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

  As the UV absorber, a polymer UV absorber can also be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  The method for adding the UV absorber is to add the UV absorber to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane, or a mixed solvent thereof. Or you may add directly in dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose acylate to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the cellulose acylate film is 30 to 200 μm, it is 0.5 with respect to the cellulose acylate film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Fine particles)
The cellulose acylate film of the present invention preferably contains fine particles from the viewpoint of slipperiness and storage stability.

  As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include magnesium silicate and calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable. The content of these fine particles in the cellulose acylate film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of a cellulose acylate film having a multilayer structure formed by a co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available, for example, under the trade names Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the haze of the cellulose acylate film low. In the cellulose acylate film of the present invention, the dynamic friction coefficient of at least one surface is preferably 0.2 to 1.0.

(dye)
A dye may be added to the cellulose acylate film of the present invention for color adjustment. For example, a blue dye may be added to suppress the yellowness of the film. Preferred examples of the dye include anthraquinone dyes.

  The anthraquinone dye may have an arbitrary substituent at an arbitrary position from the 1st position to the 8th position of the anthraquinone. Preferred substituents include an anilino group, hydroxyl group, amino group, nitro group, or hydrogen atom. In particular, it is preferable to contain a blue dye described in JP-A-2001-154017, particularly an anthraquinone dye.

  Various additives may be batch-added to the dope that is a cellulose acylate-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferably dissolved in a small amount of cellulose acylate in order to improve mixing with the dope. A preferable amount of cellulose acylate is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

(Method for producing cellulose acylate film)
Next, the manufacturing method of the cellulose acylate film of this invention is demonstrated.

  Whether the cellulose acylate film of the present invention is a film produced by a solution casting method or a film produced by a melt casting method, both can be preferably used.

  The cellulose acylate film according to the present invention is produced by a solution casting method in which cellulose acylate and the additive are dissolved in a solvent to prepare a dope, and the dope is cast on an endless metal support that moves infinitely. A step of drying the cast dope as a web, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. The concentration of cellulose acylate in the dope is preferably higher because the drying load after casting on the metal support can be reduced, but if the concentration of cellulose acylate is too high, the load during filtration increases and the filtration accuracy Becomes worse. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more. However, it is preferable in terms of production efficiency that a good solvent and a poor solvent of cellulose acylate are mixed and used. A larger amount is preferable from the viewpoint of the solubility of cellulose acylate. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose acylate to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent. Therefore, depending on the average degree of acetylation (acetyl group substitution degree) of cellulose acylate, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, cellulose acylate acetate (acetyl group substitution degree 2.4) Cellulose acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  The good solvent is not particularly limited, and examples thereof include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although a poor solvent is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope. Moreover, the solvent used for melt | dissolution of a cellulose acylate collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again. The recovered solvent may contain trace amounts of additives added to cellulose acylate, such as plasticizers, UV absorbers, polymers, and monomer components. Can be purified and reused if necessary.

  As a method for dissolving cellulose acylate when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamaco. In addition, a method in which cellulose acylate is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  A higher heating temperature with the addition of a solvent is preferable from the viewpoint of the solubility of cellulose acylate, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used, whereby cellulose acylate can be dissolved in a solvent such as methyl acetate.

  Next, this cellulose acylate solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is easily clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose acylate by filtration.

The bright spot foreign matter was placed with two polarizing plates placed in a crossed Nicol state, a cellulose acylate film was placed between them, and light was applied from one polarizing plate side, and observed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side sometimes leaks, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

  Here, the dope casting will be described.

  The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The cast width can be 1 to 4 m. Since the width of the cellulose acylate film of the present invention is preferably 1.6 to 4 m, the cast width is inevitably wide. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate. A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent. The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

  In order for the cellulose acylate film to exhibit good flatness, the amount of residual solvent when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. %, Particularly preferably 20 to 30% by mass or 70 to 120% by mass.

  In the present invention, the amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  In the drying step of the cellulose acylate film, the web is peeled off from the metal support, and further dried, so that the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less. Particularly preferably, it is 0 to 0.01% by mass or less.

  In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged on the upper and lower sides are alternately passed through and dried) or a method of drying while transporting the web by a tenter method is adopted.

[Stretching process]
In the cellulose acylate film of the present invention, when the birefringence in the film plane is measured, nx> ny when the birefringence in the directions orthogonal to each other is nx, ny, and the dimensions in the nx, ny directions In order to impart the characteristics of Sx> Sy when the variation is Sx and Sy, respectively, cellulose acylate having a specific degree of acyl substitution is used, and the temperature during the stretching process in the width direction (TD direction) is 180. It is preferable to stretch the film in a range of ˜210 ° C. and a ratio in the stretching treatment of 30 to 55%.

  The stretching in the width direction is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  Assuming that the glass transition temperature of the cellulose acylate film during the stretching treatment is Tg, Tg varies depending on the material type constituting the film and the ratio of the constituting materials, but is usually 190 ° C. or lower or 170 ° C. or lower. However, in the cellulose acylate film of the present invention, in order to satisfy the relationship of nx> ny and Sx> Sy, it is necessary to perform a stretching process at a high temperature, and it is in the range of 180 to 210 ° C., more preferably 185. Stretching is performed in the range of ˜200 ° C. The Tg of the film can be determined by the method described in JIS K7121.

  Further, in general, a triacetyl cellulose film (so-called TAC film) is generally stretched within 20%, and at most within 10%. In the present invention, the stretching ratio is in the range of 30 to 55%. It has been found that a cellulose acylate film satisfying the relations of nx> ny and Sx> Sy can be obtained by carrying out in the range of 40 to 50%. The stretching treatment may be performed once or a plurality of times.

  The film transport tension in the film forming process such as in the tenter depends on the temperature, but is preferably 120 N / m to 200 N / m, and more preferably 140 N / m to 200 N / m. 140 N / m to 160 N / m is most preferable.

  In the stretching step, the film can be sequentially or simultaneously stretched in the longitudinal direction (MD direction) of the film in addition to stretching in the width direction of the film. Stretching treatment in the MD direction is performed in a range of 0.5 to 20%. For example, a method in which a difference in peripheral speed is given to a plurality of rolls and stretching in the MD direction using the difference in peripheral speed between the rolls is given. It is done.

  The cellulose acylate film is preferably heat-set after stretching, but the heat-setting is higher than the final TD direction stretching temperature and is usually heat-set within a temperature range of Tg-20 ° C. or lower for usually 0.5 to 300 seconds. It is preferable. Under the present circumstances, it is preferable to heat-fix, heating up sequentially in the range from which a temperature difference is set to 1-100 degreeC in the area | region divided into 2 or more.

  The heat-set film is usually cooled to Tg or less, and clip holding portions at both ends of the film are cut and wound. At this time, it is preferable to perform a relaxation treatment of 0.1 to 10% in the TD direction and / or the MD direction within a temperature range not higher than the final heat setting temperature and not lower than Tg. In addition, it is preferable that the cooling is gradually performed from the final heat setting temperature to Tg at a cooling rate of 100 ° C. or less per second. Means for cooling and relaxation treatment are not particularly limited, and can be performed by a conventionally known means. In particular, it is preferable to carry out these treatments while sequentially cooling in a plurality of temperature ranges from the viewpoint of improving the dimensional stability of the film. The cooling rate is a value obtained by (T1-Tg) / t, where T1 is the final heat setting temperature and t is the time until the film reaches Tg from the final heat setting temperature.

  The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but it is preferably performed with hot air in terms of simplicity.

  The drying temperature in the web drying step is preferably 90 ° C to 200 ° C, more preferably 110 ° C to 160 ° C. The drying temperature is preferably increased stepwise.

  Although preferable drying time is based also on drying temperature, 5 minutes-60 minutes are preferable and 10 minutes-30 minutes are more preferable.

  Although the film thickness of a cellulose acylate film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is preferably 30 to 65 μm, more preferably 57 to 63 μm.

  The cellulose acylate film of the present invention has a width of 1 to 4 m. From the viewpoint of productivity, those having a width of 1.6 to 4 m are preferably used, and particularly preferably 1.8 to 3.6 m. If it exceeds 4 m, conveyance becomes difficult.

  The slow axis or fast axis (direction perpendicular to the slow axis) of the cellulose acylate film of the present invention exists in the film plane, and θ1 is −1 ° or more and +1 when the angle formed with the film forming direction is θ1. It is preferably at most 0 °, more preferably from −0.5 ° to + 0.5 °. This θ1 can be defined as an orientation angle, and the measurement of θ1 can be performed using an automatic birefringence meter KOBRA-21ADH or KOBRA-WR (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

<Physical properties, optical properties>
The moisture permeability of the cellulose acylate film of the present invention, 40 ° C., preferably 10~1200g ^/ m 2 · 24h at 90% RH, preferably more ^{20~1000g / m 2 · 24h, 20~850g} / m 2 · 24h Is particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

  The breaking elongation of the cellulose acylate film of the present invention is preferably 10 to 80%, more preferably 20 to 50%.

  The visible light transmittance of the cellulose acylate film of the present invention is preferably 90% or more, and more preferably 93% or more.

  The haze of the cellulose acylate film of the present invention is preferably less than 1.0, particularly preferably 0.1 to 0.5.

  The cellulose acylate film of the present invention preferably has a retardation value Ro represented by the following formula of 0 to 20 nm and Rth of 0 to 70 nm.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = ((nx + ny) / 2−nz) × d
(In the formula, Ro is the retardation value in the film plane, Rth is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is (The refractive index in the thickness direction of the film, d represents the thickness (nm) of the film.)
The refractive index can be obtained at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH using, for example, KOBRA-21ADH or KOBRA-WR (Oji Scientific Instruments).

  Furthermore, the retardation value Ro is preferably in the range of 0 to 10 nm, and Rth is preferably in the range of 0 to 50 nm in order to enhance the effect of the present invention.

  In order to obtain the retardation values Ro and Rth, it is preferable that the cellulose acylate film has the structure of the present invention, and the refractive index is controlled by a stretching operation.

(Functional layer)
In producing the cellulose acylate film of the present invention, before and / or after stretching, an antistatic layer, a hard coat layer, a back coat layer, a slippery layer, an adhesive layer, a barrier layer, an antiglare layer, an antireflection layer, and an optical layer. A functional layer such as a compensation layer may be provided.

<Polarizing plate, liquid crystal display>
The polarizing plate of the present invention and a liquid crystal display device using the same will be described.

(Polarizer)
The polarizing plate used in the present invention is a polarizing plate formed by sandwiching at least one surface of a polarizer with the cellulose acylate film of the present invention.

  The polarizing plate can be produced by a general method. The cellulose acylate film of the present invention is preferably bonded to at least one surface of a polarizer produced by subjecting the polarizer side to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. . The cellulose acylate film may be used on the other surface, or another thermoplastic resin film (polyethylene film, polycarbonate film, norbornene resin film, cellulose acylate film, etc.) may be used. It is preferable to use a rate film because it has suitability for saponification treatment. As the cellulose acylate film, a commercially available cellulose acylate film (for example, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, HC8UY, KC8UY-1) KC8UX-RHA, KC8UE, KC4UE, KC4HR-1, KC4KR-1, KC4UA, KC6UA or more manufactured by Konica Minolta Opto Co., Ltd.) are also preferably used.

  In the case of the IPS type liquid crystal display device, when the cellulose acylate film of the present invention is the cellulose acylate film A, the cellulose acylate film B used on the opposite side through the polarizer is an in-plane retardation Ro measured at a wavelength of 590 nm. Is preferably a cellulose acylate film having no retardation of 0 to 10 nm and Rth = −10 to 10 nm.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is 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. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

  Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used. Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used.

  A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability, and has few color spots, and is particularly preferably used for a large-sized liquid crystal display device.

  The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side, but as an adhesive used for bonding, a PVA-based adhesive is used. Among them, a PVA type adhesive is preferably used.

(Liquid crystal display device)
By incorporating the polarizing plate of the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. The cellulose acylate film of the present invention can be used in liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. An IPS liquid crystal display device and a VA liquid crystal display device are preferable, and an IPS liquid crystal display device is particularly preferable.

  The IPS type liquid crystal layer is homogeneously aligned in parallel with the substrate surface in the initial state, and the director of the liquid crystal layer in a plane parallel to the substrate has a parallel or somewhat angle with the electrode wiring direction when no voltage is applied. When the direction of the director of the liquid crystal layer is shifted to the direction perpendicular to the electrode wiring direction at the time of application, and the director direction of the liquid crystal layer is inclined 45 ° to the electrode wiring direction as compared to the director direction when no voltage is applied, When the voltage is applied, the liquid crystal layer rotates the azimuth angle of polarized light by 90 ° like a half-wave plate, and the transmission axis of the output side polarizing plate coincides with the azimuth angle of the polarized light to display white. is there.

  In general, the thickness of the liquid crystal layer is constant, but since it is driven by a transverse electric field, the effect can be maximized even when the thickness of the liquid crystal layer is not constant. Therefore, even when the liquid crystal panel is warped as in the present invention, the function of the liquid crystal is more effective than the liquid crystal of other driving methods.

  In this invention, since there is little influence with respect to the change of the thickness of a liquid crystal layer, the thickness of the liquid crystal layer which can exhibit the effect in this invention largely is 2-6 micrometers, Preferably it is 3-5.5 micrometers.

  The IPS type of the present invention includes a fringe-field switching (FFS) type.

  The cellulose acylate film of the present invention is preferably used as a polarizing plate protective film on the backlight side with respect to the liquid crystal cell. Between the cellulose acylate film of the present invention and the backlight, there may be optical members such as a brightness enhancement film, a brightness enhancement film, a light diffusion sheet, a light diffusion plate, and a prism sheet as an optical member.

  The backlight is divided into a direct method and an edge method. The direct method is a method in which the backlight is placed on the lower surface of the liquid crystal display device and directly illuminates the front surface of the substrate. It is a system that is placed on the side surface or both side surfaces, and reflects and diffuses light to the light guide plate and the reflection plate.

  The edge type backlight has a light diffusing film, a prism sheet and a brightness enhancement film arranged on the front surface of a plurality of cold-cathode tubes arranged in parallel, and the side and back of the cold-cathode tube are covered with a reflective film. It is. In such a backlight, a cold cathode tube is used as a light source, so that the backlight can be thinned to some extent, but there are disadvantages that it is complicated and expensive because of its many components, and further, a linear light source. Must be used instead of a surface light source, a light guide plate is absolutely necessary, and the luminance unevenness is somewhat large.

  On the other hand, the direct method is aimed at improving the luminance unevenness and reducing the thickness of the backlight member, and the backlight using a flat fluorescent lamp, the red (R) LED, the green (G) LED, and the blue (B) LED. Various studies have been made on LED backlights for color liquid crystal display devices having white light, white backlights using organic electroluminescence element substrates, and the like.

  A preferred direct type backlight is an LED backlight for a color liquid crystal display device having a red (R) LED, a green (G) LED, and a blue (B) LED, for example, the peak wavelength of the red (R) LED. Is preferably 610 nm or more, the peak wavelength of the green (G) LED is in the range of 530 ± 10 nm, and the blue (B) LED has a peak wavelength of 480 nm or less. Examples of types of green (G) LEDs having a peak wavelength within the above range include DG1112H (manufactured by Stanley Electric Co., Ltd.), UG1112H (manufactured by Stanley Electric Co., Ltd.), and E1L51-3G (manufactured by Toyoda Gosei Co., Ltd.). E1L49-3G (manufactured by Toyoda Gosei Co., Ltd.), NSPG500S (manufactured by Nichia Chemical Co., Ltd.), and the like. The types of LEDs used as red (R) LEDs include, for example, FR1112H (manufactured by Stanley Electric Co., Ltd.), FR5366X (manufactured by Stanley Electric Co., Ltd.), NSTM515AS (manufactured by Nichia Corporation), GL3ZR2D1COS (Sharp) GM1JJ35200AE (manufactured by Sharp Corporation) and the like. As types of LEDs used as blue (B) LEDs, DB1112H (manufactured by Stanley Electric Co., Ltd.), DB5306X (manufactured by Stanley Electric Co., Ltd.), E1L51-3B (manufactured by Toyoda Gosei Co., Ltd.), E1L4E-SB1A (manufactured by Stanley Electric Co., Ltd.) Toyoda Gosei Co., Ltd.), NSPB630S (Nichia Chemical Co., Ltd.), NSPB310A (Nichia Chemical Co., Ltd.), and the like.

  A backlight can be formed by combining the above-described three-color LEDs. Alternatively, a white LED can be used.

  In addition, as a direct type backlight (or direct type), a direct type backlight described in JP-A No. 2001-281656, a direct type backlight using a point light source such as an LED described in JP-A No. 2001-305535, Examples include a direct backlight described in JP-A-2002-311412, but are not limited thereto.

  In particular, a polarizing plate using the cellulose acylate film of the present invention can impart excellent visibility and front contrast when used in a large-screen liquid crystal display device.

  In a large-screen liquid crystal display device with a 17-inch or larger screen, especially a 30-inch or larger screen, there is no distortion such as color unevenness and wavy unevenness in addition to the effects of the present invention, so eyes are not tired even during long-time viewing. There was an effect.

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

Example 1
The plasticizer used in the examples is shown below.

Plasticizer A: A polyester mixture represented by the following formula formed by polymerizing phthalic acid / adipic acid / 1,2-propanediol / benzoic acid. (Weight average molecular weight Mw; 600-700)
Plasticizer B: A polyester structure represented by the following formula formed by polymerizing terephthalic acid / 1,2-propanediol / p-toluic acid. (Weight average molecular weight Mw; 400-500)
Plasticizer C: A polyester structure represented by the following formula formed by polymerizing ethylene glycol / adipic acid / terephthalic acid / acetic acid. (Weight average molecular weight Mw; 1000 to 2000)
The structures of the plasticizers A to C are shown below.

TPP: Triphenyl phosphate EPEG: Ethyl phthalyl ethyl glycolate <Preparation of cellulose acylate film 1>
(Silicon dioxide dispersion)
Aerosil R812 (Nippon Aerosil Co., Ltd.) 10 parts by mass Ethanol 90 parts by mass The above was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. 88 parts by mass of methylene chloride was added to the silicon dioxide dispersion while stirring, and the mixture was stirred and mixed for 30 minutes with a dissolver to prepare a silicon dioxide dispersion dilution. It filtered with the fine particle dispersion | distribution dilution liquid filter (Advantech Toyo Co., Ltd .: Polypropylene wind cartridge filter TCW-PPS-1N).

(Preparation of dope of cellulose acylate)
TAC: Triacetyl cellulose (acetyl group substitution degree 2.88, Mw = 200000) 100 parts by mass Tinuvin 928 (manufactured by BASF Japan Ltd.) 3 parts by mass Plasticizer A 5 parts by mass Methylene chloride 432 parts by mass Ethanol 38 parts by mass or more Was put into a sealed container, heated, stirred and completely dissolved and filtered. To this, 4 parts by mass of the silicon dioxide dispersion dilution was added with stirring, and the mixture was further stirred for 30 minutes.

(Film formation / stretching / drying)
Next, using a belt casting apparatus, a cellulose acylate dope was uniformly cast on a stainless steel band support at a temperature of 35 ° C. and a width of 2 m. With the stainless steel band support, the solvent was evaporated until the residual solvent amount reached 100% by mass, and the stainless steel band support was peeled off. The peeled cellulose acylate film web is conveyed at 35 ° C., slitted, and then stretched by 40% in the width direction (TD direction: direction orthogonal to the film conveying direction) with a tenter at a temperature of 190 ° C. And dried at a drying temperature of 160 ° C. At this time, the residual solvent amount when starting stretching with a tenter was 20%. Then, after being dried for 15 minutes while being transported in a drying apparatus at 120 ° C. by a number of rolls, slitting is performed, and both ends of the film are knurled with a width of 15 mm and a height of 10 μm, wound on a core, and cellulose acylate. Film 1 was obtained. The residual solvent amount of the film was less than 0.1%, the film thickness was 60 μm, the width was 2 m, and the winding length was 6000 m.

  The draw ratio in the longitudinal direction (MD direction: film transport direction) calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 5%.

<Production of Cellulose Acylate Films 2-28>
Cellulose acylate films 2 to 28 listed in Table 2 in the same manner as in cellulose acylate film 1 except that the acetyl group substitution degree, plasticizer type, addition amount, and stretching conditions (magnification, temperature) of cellulose acylate were changed. Was made.

<Preparation of polarizing plates 101-128>
Next, the cellulose acylate films 1 to 28 produced above, and Konica Minolta Tack KC4UY (manufactured by Konica Minolta Opto Co., Ltd.) or Fujitac NRT (manufactured by Fuji Film Co., Ltd.), which is a cellulose acylate film, and the following polarizer Was used to prepare a polarizing plate.

(Preparation of polarizing plate 101)
A 120 μm thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times) to obtain a long roll film.

  This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a long roll-shaped polarizer.

  Subsequently, according to the following processes 1-5, the polarizing plate 101 was produced by bonding the long roll-shaped polarizer, the cellulose acylate film 1, and Konica Minolta Tack KC4UY which is a cellulose acylate film.

  Step 1: Cellulose acylate film 1 that was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water, dried, and saponified on the side to be bonded to the polarizer, and Konica Minoltac KC4UY Obtained.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped, and this was placed between the cellulose acylate film 1 treated in Step 1 and Konica Minoltack KC4UY.

Step 4: The cellulose acylate film 1 / polarizer / Konica Minolta Tack KC4UY laminated in Step 3 was bonded at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 2 m / min.

  Process 5: The sample which bonded the cellulose acylate film 1 / polarizer / Konica Minolta Tack KC4UY produced by the process 4 in the 80 degreeC dryer with the roll to roll was dried for 2 minutes, and the polarizing plate 101 was produced.

(Production of polarizing plates 102 to 128)
Polarizers 102 to 128 were produced in the same manner as the production of the polarizing plate 101 with the combinations shown in Table 2.

<Production of liquid crystal display devices 201-228>
The liquid crystal panel is taken out from the liquid crystal television TH-32LX500 (manufactured by Matsushita Electric Industrial Co., Ltd.), the polarizing plate attached to the backlight side is peeled off, and the produced polarizing plate is used as the cellulose acylate film 1 The liquid crystal display devices 201 to 228 were manufactured by pasting so that ˜28 is on the backlight side and the same orientation as before the absorption axis of the polarizer was peeled off.

<Evaluation>
(Measurement of refractive index)
Using an automatic birefringence meter KOBURA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the film surface is measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH, The direction of nx having a large refractive index was determined.

(Measurement of dimensional variation)
Using the cellulose acylate films 1 to 28, the dimensional variation was measured by the following procedure.

A 10 × 10 cm ² film was cut out, marked at two points 7 cm apart in the two directions of the nx direction and the direction orthogonal thereto, and measured in the two directions at 23 ° C. and 55%, then 140 ° C. After putting it in an oven for 45 minutes and adjusting the humidity at 23 ° C. and 55% for 24 hours, the dimension between the two points marked again was measured and the rate of change was observed.

  The obtained dimensional variation in two directions was compared with the refractive index in two directions of the film, and the relationship between the direction nx, ny of the refractive index and the direction Sx, Sy of the dimensional variation was observed.

  In the cellulose acylate film of the invention, the direction (nx) in which the refractive index is large and the direction Sx in which the dimensional variation is large are parallel.

(Haze measurement)
Using cellulose acylate films 1 to 28, NDH2000 was used, and three films were stacked for measurement.

(Evaluation of edge unevenness)
The above-mentioned liquid crystal television was set at 50 ° C. and 80% for 72 hours. After conditioning, the temperature is 2 hours at 23 ° C. and 55%. Left to observe the surface.

◎: No edge unevenness is observed ○: Edge unevenness is not observed ○ △: Edge unevenness is slightly observed △: Edge unevenness is observed ×: Edge unevenness is clearly observable

  From Table 2, the polarizing plate and the IPS liquid crystal display device using the cellulose acylate film satisfying nx> ny and Sx> Sy of the present invention have improved edge unevenness and low haze. It can be seen that an IPS liquid crystal display device with good visibility can be obtained.

  Further, when a polarizing plate using the cellulose acylate film of the present invention was similarly incorporated into a VA liquid crystal display device, a liquid crystal display device having good visibility and reproducing the effects of the present invention was obtained.

DESCRIPTION OF SYMBOLS 1 Backlight 2 Polarizer 3 Liquid crystal cell side protective film 4 Backlight side protective film

Claims (6)

  It contains cellulose acylate, and when the birefringence in the film plane is measured, nx> ny when the birefringence in the direction orthogonal to each other is nx, ny, and the dimensional variation in the nx, ny directions A cellulose acylate film, wherein Sx> Sy when Sx and Sy, respectively.   The cellulose acylate film according to claim 1, wherein the cellulose acylate is a cellulose triacetate having an acyl substitution degree in the range of 2.80 to 2.95. The cellulose acylate film according to claim 1 or 2, comprising a polyester plasticizer represented by the following general formula (1) and having a weight average molecular weight of 300 to 5,000.
General formula (1) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)   A liquid crystal display device, wherein a polarizing plate using the cellulose acylate film according to claim 1 on at least one surface of a polarizer is used for an IPS liquid crystal panel.   The liquid crystal display device according to claim 4, wherein the cellulose acylate film is disposed on a backlight side of a polarizing plate on a liquid crystal cell side.   It is a manufacturing method of the cellulose acylate film of any one of Claims 1-3, Comprising: The temperature at the time of the extending | stretching process of the width direction is the range of 180-210 degreeC, and the magnification at the time of this extending | stretching process is 30. A method for producing a cellulose acylate film, wherein the film is stretched in a range of -55%.

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