JP2009173818A - Cellulose ester film, polarizing plate, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellulose ester film having excellent optical performance by solving a problem in a prior art of the cellulose ester film manufactured by a fusion film forming method, a polarizing plate using the same, and a liquid crystal display. <P>SOLUTION: This cellulose ester film manufactured by the fusion film forming method contains 0.05-2.0 mass% of at least one kind selected from the group comprising glycerine fatty acid esters, diglycerine fatty acid esters and sorbitan fatty acid ester. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cellulose ester film produced by a melt film-forming method and excellent in optical performance, a polarizing plate using the same, and a liquid crystal display device.

  Since the cellulose ester film is excellent in transparency and optical isotropy, it is applied to various optical films. Moreover, since the film surface can be hydrophilized by alkali saponification treatment, it has good adhesion to a polarizer and is particularly suitable for a polarizing plate protective film.

  On the other hand, the cellulose ester film has generally been formed by a solution film forming method, but in recent years, the film forming examination by the melt film forming method has been advanced. The cellulose ester film formed by the melt film forming method has a problem that coloring (yellowing) is likely to occur due to thermal deterioration as compared with the cellulose ester film formed by the solution film forming method.

  Moreover, when the melt-formed cellulose ester film was used as a polarizing plate protective film, it turned out that adhesiveness with a polarizer deteriorates. This is because the contact angle (hereinafter referred to simply as “contact angle”) of the melt-formed cellulose ester film with water is higher than that in the case of solution film formation. Is considered to be slow.

  Although the reason why the contact angle of the melt-formed cellulose ester film increases is not known, when the cellulose ester film whose contact angle is lowered by saponification treatment or the like is heated, a phenomenon that the contact angle increases may be observed. This is presumably because the state in which the polar group is present on the surface is unstable in terms of energy, so that when the fluidity is increased by heating, the polar group is embedded in the film in order to obtain a more stable state. Also in the case of melt film formation, the polar group is likely to enter the interior when the temperature from extrusion to cooling is high, and as a result, it is estimated that the contact angle is higher than that in the case of solution film formation.

  In recent years, the alkali saponification time tends to be shortened in order to improve the productivity of polarizing plate manufacturers, and this effect has become more prominent. As measures against this, methods such as raising the alkali concentration of the alkali saponification solution and raising the temperature of the alkali saponification solution can be considered, but in these methods, the cellulose ester film additive elutes in the saponification solution and the saponification solution It was found that this could cause the failure of the polarizing plate.

  In addition, as liquid crystal displays become more common, they are used under a variety of environmental conditions, increasing the need for durability against high temperatures, high temperatures and high humidity, and ultraviolet rays. It is coming. In particular, there are concerns about dimensional change of the polarizing plate at high temperature or high temperature and high humidity, deterioration of the polarizer or liquid crystal due to high temperature and high humidity and ultraviolet rays.

  As a result of the examination, it was found that the cellulose ester film made by the melt casting method has a lower elastic modulus than the cellulose ester film made by the solution casting method even with the same composition. For this reason, when the cellulose ester produced by the melt film forming method is used as a polarizing plate protective film, when the finished polarizing plate is evaluated for durability at high temperature (for example, 90 ° C.) and high temperature and high humidity (for example, 60 ° C. and 90% RH). It was found that the polarizing plate protective film could not suppress the contraction of the polarizer, and the dimensional change of the polarizing plate was increased.

Patent Documents 1 to 3 describe examples in which glycerin fatty acid ester or diglycerin fatty acid ester is added. In this method, the contact angle can be reduced, but since both are added as a plasticizer, the addition amount is 2% or more, the elastic modulus is too low, and the dimensional change of the polarizing plate becomes large. It was also found that the polarizing plate failed because the amount of elution into the saponification process increased.
JP 2004-131670 A JP 2007-51304 A JP 2007-144883 A

  The present invention has been made in view of the above-described problems and circumstances, and its solution is a cellulose ester film that solves the conventional problems of cellulose ester films produced by a melt film-forming method and has excellent optical performance. Is to provide. Furthermore, it is providing the polarizing plate and liquid crystal display device using the same.

  The above-mentioned problem according to the present invention is solved by the following means.

  1. A cellulose ester film produced by a melt film-forming method, comprising 0.05 to 2.0% by mass of at least one of glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester Ester film.

  2. 2. The cellulose ester film as described in 1 above, wherein the cellulose ester film is stretched within a range in which the total of the draw ratio in the fluent direction and the draw ratio in the direction perpendicular to the fluent direction is 20 to 300%.

  3. The cellulose ester film as described in 1 or 2 above, which contains 2 to 20% by mass of at least one of pentaerythritol aromatic carboxylic acid esters.

  4). A polarizing plate using the cellulose ester film according to any one of 1 to 3 above.

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

  By the above means of the present invention, the conventional problems of the cellulose ester film produced by the melt film-forming method can be solved, and a cellulose ester film excellent in optical performance can be provided. Furthermore, a polarizing plate and a liquid crystal display device using the same can be provided.

  The cellulose ester film of the present invention is a cellulose ester film produced by a melt film forming method, and 0.05 to 2.0% by mass of at least one of glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester. It is characterized by containing. This feature is a technical feature common to the inventions according to claims 1 to 5.

  As an embodiment of the present invention, the sum of the draw ratio in the fluent direction (hereinafter referred to as “MD direction” as appropriate) and the draw ratio in the direction perpendicular to the fluent direction (hereinafter referred to as “TD direction” as appropriate). It is preferable that the film is stretched within a range of 20 to 300%. Moreover, it is preferable that the said cellulose-ester film contains 2-20 mass% of at least 1 type in the aromatic carboxylic acid ester of pentaerythritol.

  Especially the cellulose-ester film of this invention can be used suitably for the polarizing plate used for a liquid crystal display device.

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

<Fatty acid esters such as glycerin fatty acid ester>
Examples of fatty acids constituting the glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester used in the present invention include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, 12-hydroxystearic acid, oleic acid, and linoleic acid. The main component is one or a mixture of two or more selected from aliphatic fatty acids having 12 to 22 carbon atoms, such as acid, erucic acid, and 12-hydroxyoleic acid.

  In the present invention, the glycerin fatty acid ester and diglycerin fatty acid ester are preferably composed mainly of monoesters and diesters.

  As a sorbitan fatty acid ester, it is preferable to have a monoester, a diester, and a triester as a main component. Moreover, the hydroxyl group which is not esterified with the aliphatic fatty acid having 12 to 22 carbon atoms may be a hydroxyl group or may be esterified with acetic acid.

  In addition, it is preferable that the carbon number is 12 to 22 from the viewpoints of contamination of the manufacturing / processing apparatus due to volatility during heating, environmental pollution prevention, compatibility with cellulose ester, and the like. In addition, from the viewpoints of deodorization during storage, prevention of discoloration, and the like, esters of saturated fatty acids are preferred over unsaturated fatty acids.

  The addition amount of glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester is 0.05% by mass to 2.0% by mass, and more preferably 0.1% by mass to 1.5% by mass. If the addition amount is too small, the necessary effect cannot be obtained, and if the addition amount is too large, bleeding out occurs, and the change in the dimensions of the polarizing plate and the failure of the polarizing plate deteriorate.

  Esterification reaction of glycerin, diglycerin, sorbitol and the above fatty acids is beef tallow, lard, chicken tallow, fish oil, soybean oil, corn oil, rapeseed oil, palm oil, sunflower oil, safflower oil, castor oil or their Methods such as molecular distillation, solvent fractionation, recrystallization, column chromatography, and supercritical gas extraction of reactants obtained by transesterification of one or a mixture of hydrogenated oils with glycerin, diglycerin, and sorbitol In general, molecular distillation is suitable from the viewpoint of ease of production, quality, and price.

  By using any one of glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester, coloring (yellowing) and minute surface defects of the melt film-forming film of the present invention can be improved. This is because glycerin fatty acid ester, diglycerin fatty acid ester, sorbitan fatty acid ester act like a lubricant, improve the retention in the extruder, fluted die, etc., and reduce the friction between metal and molten resin, This is thought to be due to the prevention of heat generation and stress due to frictional heat.

  Moreover, it was found that the contact angle to water can be improved by our examination. The reason for this is not known, but it is thought that the surface state of the melt-formed film is changed by acting like a surfactant.

<Cellulose ester>
Although there is no limitation in particular in the cellulose ester used for this invention, It is preferable that it is a C2-C22 carboxylic acid ester of a cellulose, The ester of aromatic carboxylic acid may be sufficient, and especially C2-C6 of a cellulose. More preferably, it is a lower fatty acid ester.

  The acyl group bonded to the hydroxyl group may be linear or branched, and may form a ring. Further, another substituent may be substituted.

  Examples of preferred cellulose esters include cellulose acetate, cellulose propionate, cellulose butyrate, and the like, JP-A-10-45804, 08-231761, U.S. Pat. No. 2,319,052, and the like. Examples thereof include mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate.

  Preferred cellulose esters for the present invention are those that simultaneously satisfy the following formulas (1) and (2).

Formula (1): 2.0 ≦ X + Y ≦ 3.0
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. The portion that is not substituted with an acyl group usually exists as a hydroxyl group. The measuring method of the substitution degree of an acyl group can be measured according to ASTM-D817-96.

  The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 60,000 to 300,000, more preferably 70,000 to 200,000, from the viewpoints of melt viscosity and mechanical strength.

  The cellulose ester used in the present invention preferably has a weight average molecular weight (Mw) / number average molecular weight (Mn) value of 1.4 to 3.0, more preferably 1.4 to 2.2. It is. By setting Mw / Mn within this range, white turbidity is less likely to occur when the cellulose ester film is stretched, and the elastic modulus is likely to increase. It is considered that the smaller the Mw / Mn value, the smaller the molecular weight distribution, so that the polymer molecules are easily oriented and a uniform film with few voids is likely to be formed.

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

  The measurement conditions of the number average molecular weight and the weight average molecular weight using high performance liquid chromatography are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. It is preferable to obtain 13 samples at approximately equal intervals.

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

  In the cellulose ester 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, 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.

  Unlike the 2nd and 3rd positions, the glucose unit constituting the cellulose ester has a highly reactive primary hydroxyl group, and this primary hydroxyl group is sulfated during the production of cellulose ester using sulfuric acid as a catalyst. Esters are preferentially formed.

  Therefore, by increasing the amount of catalytic sulfuric acid in the esterification reaction of cellulose, it is possible to increase the average substitution degree at the 2nd and 3rd positions rather than the 6th position of the glucose unit as compared with a normal cellulose ester.

  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 6-position hydroxyl group by tritylation, 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, a cellulose ester produced by the method described in JP-A No. 2005-281645 can also be preferably used.

  In addition, it is preferable to purify the synthesized cellulose ester to remove low molecular weight components, or to remove unacetylated or low acetylated components by filtration.

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

  Cellulose esters are also affected by trace metal components in cellulose esters. 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 alkaline earth metal content of the cellulose ester used in the present invention is preferably in the range of 1 to 50 ppm. If the alkaline earth metal content is in the above range, lip deposits are reduced, and no breakage occurs at the slitting part during or after hot stretching. Furthermore, the range of 1-30 ppm is preferable. The alkaline earth metal as used herein refers to the total content of Ca and Mg, and can be measured using an X-ray photoelectron spectrometer (XPS).

  The residual sulfuric acid content in the cellulose ester used in the present invention is preferably in the range of 0.1 to 45 ppm in terms of elemental sulfur. These are considered to be contained in the form of salts. When the residual sulfuric acid content is in the above range, the deposit on the die lip portion during heat melting is reduced, and breakage does not occur during slitting during heat stretching or after heat stretching. Furthermore, the range of 1-30 ppm is preferable. The residual sulfuric acid content can be measured by a method prescribed in ASTM-D817-96.

  The free acid content in the cellulose ester used in the present invention is preferably 1 to 500 ppm. When the free acid content is within the above range, the deposits on the die lip are reduced, and no breakage occurs during hot stretching or slitting after hot stretching. Furthermore, it is preferable that it is the range of 1-100 ppm, and also it becomes difficult to fracture | rupture. A range of 1 to 70 ppm is particularly preferable. The free acid content can be measured by a method prescribed in ASTM-D817-96.

<Aromatic carboxylic acid ester of pentaerythritol>
The aromatic carboxylic acid ester of pentaerythritol used in the present invention is obtained by esterifying some or all of the hydrogen atoms of the four hydroxyl groups of pentaerythritol with an aromatic carboxylic acid.

  Examples of preferred aromatic carboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, those in which a polar group such as a methoxy group or a hydroxyl group is introduced into the benzene ring of benzoic acid, Examples thereof include aromatic carboxylic acids having two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, tetralin carboxylic acid, and derivatives thereof. In particular, benzoic acid is preferred.

  Moreover, it is preferable that at least two of the four hydroxyl groups of pentaerythritol are esterified with an aromatic carboxylic acid. Hydroxyl groups that are not esterified with an aromatic carboxylic acid may be esterified with other types of carboxylic acids, or may remain hydroxyl groups without esterification.

  There is no restriction | limiting in particular as carboxylic acid other than aromatic carboxylic acid used for esterification of pentaerythritol, A well-known aliphatic carboxylic acid, alicyclic carboxylic acid, etc. can be used. Use of an alicyclic carboxylic acid is preferable in terms of improving moisture permeability and retention. Examples of preferred carboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic carboxylic 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 carboxylic acid.

  Preferred aliphatic carboxylic 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, and laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid. Examples of preferred alicyclic carboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Moreover, the aromatic ring of aromatic carboxylic acid and the cycloalkyl group of alicyclic carboxylic acid may be substituted. Preferred substituents include halogen atoms such as chlorine atom, bromine atom and fluorine atom, hydroxyl group, alkyl group, alkoxy group, cycloalkoxy group, aralkyl group, alkenyl group such as vinyl group and allyl group, phenyl group, Examples thereof include an acyl group having 2 to 8 carbon atoms such as a phenoxy group, an acetyl group and a propionyl group, and an unsubstituted carbonyloxy group having 2 to 8 carbon atoms such as an acetyloxy group and a propionyloxy group.

  Examples of the alkoxy group include an alkoxy group having 1 to 8 carbon atoms, specifically, methoxy, ethoxy, n-propoxy, n-butoxy, n-octyloxy, isopropoxy, isobutoxy, 2-ethylhexyloxy, or and each alkoxy group such as t-butoxy.

  Examples of the cycloalkoxy group include cycloalkoxy groups having 1 to 8 carbon atoms, and specific examples include groups such as cyclopropyloxy, cyclopentyloxy, and cyclohexyloxy.

  Examples of the aralkyl group include groups such as a benzyl group, a phenethyl group, and a γ-phenylpropyl group.

  Examples of the aryloxy group include a phenoxy group.

  Examples of the aralkyloxy group include a benzyloxy group and a phenethyloxy group.

As an acyl group, C2-C8 acyl groups, such as an acetyl group and a propionyl group, are mentioned. (Acyl hydrocarbon groups include alkyl, alkenyl and alkynyl groups)
Examples of the carbonyloxy group include acyloxy groups having 2 to 8 carbon atoms such as acetyloxy group and propionyloxy group (the hydrocarbon group of the acyl group includes alkyl, alkenyl and alkynyl groups), and benzoyloxy groups. An arylcarbonyloxy group is mentioned.

  The oxycarbonyl group represents an alkoxycarbonyl group such as a methoxycarbonyl group, an ethoxycarbonyl group or a propyloxycarbonyl group, or an aryloxycarbonyl group such as a phenoxycarbonyl group.

  The oxycarbonyloxy group represents an alkoxycarbonyloxy group having 1 to 8 carbon atoms such as a methoxycarbonyloxy group.

  The aromatic carboxylic acid ester of pentaerythritol used in the present invention can be easily obtained by an esterification reaction of pentaerythritol and carboxylic acid or acid chloride. In some cases, it can also be produced by transesterifying a previously prepared pentaerythritol ester with a carboxylic acid compound. The pentaerythritol ester compound of the present invention preferably has a 1% weight loss temperature (Td1) of 250 ° C. or higher, more preferably 280 ° C. or higher, and particularly preferably 300 ° C. or higher.

  The addition amount of the aromatic carboxylic acid ester of pentaerythritol used in the present invention is preferably 2% by mass to 20% by mass from the viewpoint of the effect of the present invention, bleed out, etc., and 4% by mass to 15% by mass. % Is more preferable.

  Pentaerythritol aromatic carboxylic acid ester has good compatibility with cellulose ester, so it has excellent properties as a plasticizer in the solution casting method. However, the melt casting method further reduces melt viscosity and causes volatilization. It is also preferable in terms of suppressing process contamination.

  Moreover, when it is set as a polarizing plate protective film, the effect which suppresses polarizer deterioration on high temperature, high humidity conditions is also excellent.

<Additives>
The present invention is characterized in that a melt containing a cellulose ester is formed into a film, and the melt contains an additive other than the cellulose ester. About the addition amount of an additive, it is preferable that all the additives are totaled and it is 2-50 mass% of the whole cellulose-ester film.

  Preferred additives are described below.

《Plasticizer》
In the production of the cellulose ester film according to the present invention, 2 to 30% by mass of at least one plasticizer is contained in the film forming material.

  Generally, a plasticizer is an additive having an effect of improving brittleness or imparting flexibility by being added to a polymer, but in the present invention, a cellulose ester alone is used. In order to lower the melting temperature than the melting temperature, and to lower the melt viscosity of the film constituting material containing the plasticizer than the cellulose ester alone at the same heating temperature, a plasticizer is added. Moreover, since it adds also in order to improve the hydrophilic property of a cellulose ester and to improve the equilibrium moisture content of a cellulose ester film, it has a function as a hydrophobizing agent.

  Here, the melting temperature of the film constituting material means a temperature at which the material is heated and fluidity is developed. In order to melt and flow the cellulose ester, it is necessary to heat at least a temperature higher than the glass transition temperature.

  Above the glass transition temperature, the elastic modulus or viscosity decreases due to heat absorption, and fluidity is exhibited. However, cellulose ester may melt at the same time as it melts at the same time, resulting in a decrease in the molecular weight of the cellulose ester, which may adversely affect the mechanical properties of the resulting film. Therefore, it is necessary to melt the cellulose ester at the lowest possible temperature. is there.

  In order to lower the melting temperature of the film constituent material, it can be achieved by adding a plasticizer having a melting point or glass transition temperature lower than the glass transition temperature of the cellulose ester.

  The above aromatic carboxylic acid ester of pentaerythritol also has a function as a plasticizer.

<Plasticizers other than pentaerythritol aromatic carboxylic acid ester>
A plasticizer other than the aromatic carboxylic acid ester of pentaerythritol may be added to the cellulose ester film of the present invention as necessary. The plasticizer that can be used is not particularly limited. For example, a polyhydric alcohol ester plasticizer, a polyester plasticizer, a trivalent or higher aromatic polycarboxylic acid ester plasticizer, a glycolate plasticizer, Phosphate ester plasticizers, phthalate ester plasticizers, fatty acid ester plasticizers, sugar ester compounds, acrylic polymers, and the like can be used. Particularly preferred are polyhydric alcohol plasticizers. Moreover, it is preferable that the addition amount of a phosphoric ester plasticizer shall be 6 mass% or less from a durable viewpoint of a polarization degree.

  The plasticizer preferably has a 1% weight loss temperature (Td1) of 250 ° C. or higher, more preferably 280 ° C. or higher, and particularly preferably 300 ° C. or higher.

  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 used for the polyhydric alcohol ester is represented by the following general formula (1).

Formula (1): R1- (OH) _n
In the formula, R1 represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic hydroxyl group or a phenolic hydroxyl group.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  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, 1,2,3-hexanetriol, 1,2, 6-hexanetriol, glycerin, diglycerin, galactitol, inositol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, etc. It can gel. Of these, glycerin, trimethylolethane, and trimethylolpropane are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this invention, 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 the present invention is 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, and laccelic acid, undecylenic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  Preferred alicyclic monocarboxylic acids are preferably cycloalkyl groups having 3 to 8 carbon atoms, and specific examples include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, and cyclooctanecarboxylic acid.

  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 biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. An aromatic monocarboxylic acid possessed can be mentioned. In particular, benzoic acid is preferred.

  These alicyclic monocarboxylic acids and aromatic monocarboxylic acids may be substituted, and preferred substituents include halogen atoms such as chlorine atom, bromine atom, fluorine atom, hydroxyl group, alkyl group, alkoxy group. Group, cycloalkoxy group, aralkyl group (this phenyl group may be further substituted with an alkyl group or a halogen atom), alkenyl groups such as vinyl group, allyl group, phenyl group (this phenyl group has an alkyl group) Or a phenoxy group (this phenyl group may be further substituted with an alkyl group or a halogen atom), an acetyl group, a propionyl group, or the like. ˜8 acyl groups, acetyloxy groups, propionyloxy groups, etc. Unsubstituted carbonyloxy group of 8 and the like.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but from the viewpoint of volatility, compatibility and the like, the molecular weight is preferably in the range of 300 to 1500, and more preferably in the range of 400 to 1000.

  One type of monocarboxylic acid used for polyhydric alcohol ester may be sufficient, and 2 or more types of mixtures may be sufficient as it. 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 polyhydric alcohol ester can be synthesized by a known method. For example, a method of condensing and esterifying the monocarboxylic acid and the polyhydric alcohol in the presence of an acid, a method of previously reacting an organic acid with an acid chloride or acid anhydride and reacting with the polyhydric alcohol, There is a method of reacting a phenyl ester and a polyhydric alcohol, and it is preferable to select a method with a good yield appropriately depending on the target ester compound.

  As the polyester plasticizer, it is preferable to use a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule. Although it does not specifically limit as a preferable polyester plasticizer, For example, it represents with the following general formula (i).

General formula (i): 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 2 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.)
In the general formula (i), a benzene 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 group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the polyester plasticizer used in the present invention include benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, and normalpropyl. There are benzoic 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.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester plasticizer include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2- Methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl 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-pentanediol, 2-ethyl 1,3-hexanediol, 2- Chill 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, there are 1,12-octadecane diol, these glycols may be used as alone or in combination of two or more.

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

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester of the present invention include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are each 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, isophthalic acid, terephthalic acid, 1,5 naphthalene dicarboxylic acid, and 1,4 naphthalene dicarboxylic acid.

  The polyester plasticizer used in the present invention has a number average molecular weight of preferably 400 to 2000, more preferably 500 to 1500. The acid value is preferably 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.

  The trivalent or higher aromatic polyvalent carboxylic acid ester plasticizer is preferably trimesic acid ester, trimellitic acid ester or pyromellitic acid ester. The alcohol that forms an ester with the aromatic polycarboxylic acid is preferably an alcohol having 1 to 8 carbon atoms.

  Examples of particularly preferred trivalent or higher aromatic polycarboxylic acid ester plasticizers include tributyl trimesate, trihexyl trimesate, tri-2-ethyl-hexyl trimesate, tricyclohexyl trimesate, tributyl trimellitic acid, trimellitate Trihexyl acid, tri-2-ethyl-hexyl trimellitic acid, tricyclohexyl trimellitic acid, tetrabutyl pyromellitic acid, tetrahexyl pyromellitic acid, tetra-2-ethyl-hexyl pyromellitic acid, tetracyclohexyl pyromellitic acid, etc. However, the present invention is not limited to these.

  As glycolate plasticizers, ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, and phosphate ester plasticizers are triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl. For phthalate ester plasticizers such as phosphate, trioctyl phosphate, tributyl phosphate, 1,3-phenylene bis (dixylenyl phosphate), 1,3-phenylene bis (diphenyl phosphate), diethyl phthalate, dimethoxyethyl phthalate, dimethyl Phthalate, dioctyl phthalate, dibutyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate and the like can be used. In addition, citrate plasticizers such as acetyltributyl citrate, epoxidized oil plasticizers, and the like can also be used.

《Sugar ester compound》
The cellulose ester film of the present invention may be obtained by melt-forming a molten composition containing a sugar ester compound obtained by esterifying a hydroxyl group of a sugar compound in which 1 to 12 at least one structure selected from a furanose structure and a pyranose structure is bonded. preferable.

  Examples of the sugar compound of the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc., particularly those having both a furanose structure and a pyranose structure. preferable. An example is sucrose.

  In the sugar ester compound of the present invention, part or all of the hydroxyl groups of the sugar compound are esterified with a carboxylic acid such as acetic acid, propionic acid, butyric acid, and benzoic acid. Esterification may be carried out with one kind of carboxylic acid or with two or more kinds of mixed acids.

《Acrylic polymer》
In the present invention, in order to adjust the optical properties in addition to the additive, it is preferable to melt and form a molten composition containing an acrylic polymer having a weight average molecular weight of 500 to 350,000.

  Specific examples of the acrylic polymer include acrylic acid esters such as methyl acrylate, ethyl acrylate, and butyl acrylate, and methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-hydroxyethyl methacrylate. A homopolymer or copolymer having an acid ester as a main component can be given. Moreover, it is also preferable to contain vinyls such as N-vinylpyrrolidone, styrenes such as styrene and 4-hydroxystyrene, acrylamides such as acryloylmorpholine, and the like as copolymerization components.

  These polymer plasticizers may be a homopolymer composed of one type of repeating unit or a copolymer having a plurality of repeating structures. Two or more of the above polymers may be used in combination.

<< Antioxidant, Heat degradation inhibitor >>
In the present invention, as an antioxidant and a thermal degradation inhibitor, generally known degradation inhibitors (antioxidants, peroxide decomposition agents, radical inhibitors, metal deactivators, acid scavengers, amines, etc.) ) Can be used. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used. The deterioration preventing agents are described in JP-A-3-199201, JP-A-5-1907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854.

  As said phenol type compound, what has the structure of 2, 6- dialkylphenol is preferable, for example, what is marketed by the brand name Irganox1076 and Irganox1010 from Ciba Japan KK is preferable.

  The phosphorous compounds are, for example, Sumitomo Chemical Co., Ltd., Sumilizer GP, ADEKA Co., Ltd., ADK STAB PEP-24G, ADK STAB PEP-36 and ADK STAB 3010, Ciba Japan Co., Ltd. IRGAFOS P-EPQ, What is marketed with the brand name of GSY-P101 from Sakai Chemical Co., Ltd. is preferable.

  As the hindered amine compound, for example, those commercially available from Ciba Japan Co., Ltd. under the trade names of Tinuvin 144 and Tinuvin 770 and ADEKA Co., Ltd. as ADK STAB LA-52 are preferable.

  The sulfur compound is preferably commercially available from Sumitomo Chemical Co., Ltd. under the trade names Sumilizer TPL-R and Sumilizer TP-D.

  The above-mentioned double bond compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names Sumilizer GM and Sumilizer GS.

  Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

  The amount of these antioxidants and the like to be added is appropriately determined in accordance with the process for recycling and use, but is generally in the range of 0.05 to 5% by mass relative to the resin that is the main raw material of the film. Is added.

  These antioxidants and thermal deterioration inhibitors can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Retardation modifier>
The cellulose ester film of the present invention may contain a compound for adjusting the retardation.

  The compound added to adjust the retardation can be an aromatic compound having two or more aromatic rings as described in EP 911,656A2.

  Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. An aromatic heterocyclic ring is particularly preferred, and the aromatic heterocyclic ring is generally an unsaturated heterocyclic ring. Of these, compounds having a 1,3,5-triazine ring are particularly preferred.

《Colorant》
In the present invention, it is preferable to use a colorant. The colorant means a dye or a pigment. In the present invention, the colorant means an effect of making the color tone of a liquid crystal screen blue, adjusting the yellow index, and reducing haze.

  Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective.

《Other additives》
In addition to the above compounds, the cellulose ester film of the present invention can contain an additive that can be added to a normal cellulose ester film.

  Examples of these additives include ultraviolet absorbers and fine particles.

  The ultraviolet absorber used in the present invention is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal, and has a small absorption of visible light having a wavelength of 400 nm or more from the viewpoint of good liquid crystal display properties. Is preferably used. In the present invention, the transmittance at a wavelength of 370 nm is particularly preferably 10% or less, more preferably 5% or less, and further preferably 2% or less.

  As the ultraviolet absorber added to the cellulose ester film of the present invention, an ultraviolet absorber having two or more aromatic rings in the molecule is particularly preferably used.

  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. It is good also as a polymer type ultraviolet absorber. The UV absorber preferably used in the present invention is preferably a benzotriazole-based UV absorber or a benzophenone-based UV absorber that has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and has less unnecessary coloring. Benzotriazole ultraviolet absorbers are particularly preferred. As specific examples of the ultraviolet absorber used in the present invention, for example, TINUVIN109, TINUVIN171, TINUVIN326, TINUVIN327, TINUVIN328, TINUVIN900, TINUVIN928, LA-31 manufactured by ADEKA, etc. manufactured by Ciba Japan Co., Ltd. are preferably used. However, the present invention is not limited to these. 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. An ultraviolet absorber may be used independently and 2 or more types of mixtures may be sufficient as it.

  The amount of the UV absorber used is not uniform depending on the type of compound, use conditions, etc., but when the dry film thickness of the cellulose ester film is 30 to 200 μm, 0.5 to 4.0 mass relative to the cellulose ester film. % Is preferable, and 0.6 g to 3.5% by mass is more preferable.

  As fine particles used in the present invention, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, and hydrated silicic acid. Mention may be made of calcium, aluminum silicate, magnesium silicate and calcium phosphate.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable. The matting agent fine particles are preferably surface-treated with an organic material because the haze of the film can be reduced. Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like.

  The larger the average diameter of the fine particles, the greater the mat effect, and the smaller the average diameter, the better the transparency. Therefore, in the present invention, the average particle diameter of the primary particles of the fine particles is preferably 5 to 50 nm, and more preferably 7 ~ 20 nm. These are preferably contained mainly as secondary aggregates having a particle size of 0.05 to 0.3 μm.

  The content of these fine particles in the cellulose ester film is preferably 0.05 to 1% by mass, particularly preferably 0.1 to 0.5% by mass. In the case of a cellulose ester film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  As the fine particles of silicon dioxide, for example, trade names such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  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 turbidity of the cellulose ester film low.

<Melt film forming method>
The optical film of the present invention is formed by melt casting. In the present application, “melt film formation” means that a composition containing additives such as a cellulose ester and a plasticizer is heated and melted to a temperature showing fluidity, and then a melt containing the flowable cellulose ester is cast. It is defined as to do.

  Molding methods that are heated and melted without using a solvent (such as methylene chloride) used in the solution casting method include melt extrusion molding method, press molding method, inflation method, injection molding method, blow molding method, stretch molding method, etc. Can be classified. Among these, in order to obtain a cellulose ester film excellent in mechanical strength and surface accuracy, the melt extrusion molding method is excellent.

  Hereinafter, the manufacturing method of the optical film of the present invention will be described by taking the melt extrusion molding method as an example. In the method for producing an optical film, the conditions for melt extrusion can be performed in the same manner as the conditions used for other thermoplastic resins such as polyester.

<< 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, dry cellulose ester, plasticizer, and other additives are fed to an extruder using a feeder, kneaded using a single or twin screw extruder, and extruded from a die into a strand. Can be done by water cooling or air cooling and cutting.

  Matting agents, UV absorbers, and the like may be prepared as high-concentration master pellets and mixed with main pellets in an extruder during film formation.

  It is important to dry the raw material before extruding to prevent decomposition of the raw material. In particular, since the cellulose ester is easy to absorb 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 to keep the moisture content at 200 ppm or less, and further 100 ppm or less.

  The additives may be mixed before being supplied to the extruder, or may be supplied by individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

  A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Moreover, when contacting with air, such as an exit from a feeder part or die, it is preferable that the atmosphere be dehumidified air or dehumidified nitrogen gas.

  In addition, it is preferable to keep the supply hopper and the like to the extruder warm because moisture absorption can be prevented.

  The extruder is preferably processed at as low a temperature as possible so that the shearing force is suppressed and the resin can be pelletized so as not to 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).

  It is preferable to form a film using the pellets obtained as described above. Without forming into pellets, the raw material powder can be supplied as it is to the extruder with a feeder to form a film.

<Process for extruding melt of cellulose ester and additive from die>
It is preferable to dry materials such as pellets in advance. It is desirable to dry the moisture to 200 ppm or less, preferably 100 ppm or less using a vacuum or reduced pressure drier or a dehumidifying hot air drier.

  The polymer dried under dehumidified hot air, vacuum or reduced pressure is melted using a uniaxial or biaxial extruder, filtered through a leaf disk type filter, etc. to remove foreign matter, and then cast into a film from a fluted die. And solidify on a cooling roll.

  Various extruders available on the market can be used as the extruder, but a melt-kneading extruder is preferable, and a single-screw extruder or a twin-screw extruder may be used.

  It is preferable from the viewpoint of suppressing oxidative decomposition that the portion introduced from the supply hopper to the extruder and the inside of the extruder are replaced with an inert gas such as nitrogen gas or reduced in pressure to reduce the oxygen concentration.

  The melting temperature of the optical film constituent material in the extruder varies depending on the viscosity and discharge amount of the optical film constituent material, the thickness of the sheet to be produced, etc., but is preferably 150 to 300 ° C, more preferably 180 to 270 ° C, 200-260 degreeC is further more preferable. If the temperature is too low, poor dissolution and an increase in melt viscosity occur, and if the temperature is too high, thermal decomposition of the material occurs.

  The melt viscosity at the time of extrusion is 10 to 100,000 poise, preferably 100 to 10,000 poise. If the melt viscosity is too high, the residence time in the extruder becomes longer due to an increase in pressure. The residence time of the optical film constituting material in the extruder is preferably shorter, and is within 5 minutes, preferably within 3 minutes, more preferably within 2 minutes.

  The residence time depends on the type of extruder and the extrusion conditions, but it can be shortened by adjusting the material supply amount, L / D, screw rotation speed, screw groove depth, etc. is there.

  The shape of the screw and the number of rotations of the extruder are appropriately selected depending on the viscosity and the discharge amount of the optical film constituting material. In the present invention, the shear rate in the extruder is from 1 / second to 10000 / second, preferably from 5 / second to 1000 / second, and more preferably from 10 / second to 100 / second.

  The molten resin extruded from the extruder is sent to a casting die and extruded from the slit of the casting die into an optical film. The casting die is not particularly limited as long as it is used for producing a sheet or an optical film.

  As the material of the casting die, hard chromium, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide), etc. are sprayed or plated and surface processed Buffing, lapping using a # 1000 or higher whetstone, surface cutting using a diamond whetstone of # 1000 or higher (the cutting direction is perpendicular to the resin flow direction), electrolytic polishing, electrolytic composite polishing, etc. And the like. The preferred material of the lip portion of the casting die is the same as that of the casting die 4. The surface accuracy of the lip is preferably 0.5S or less, and more preferably 0.2S or less.

  The slit of the casting die is configured so that the gap can be adjusted.

  Of the pair of lips forming the slit of the casting die, one is a flexible lip having low rigidity and easily deformed, and the other is a fixed lip.

  A large number of heat bolts are arranged at a constant pitch in the width direction of the casting die. Each heat bolt is provided with a block having an embedded electric heater and a cooling medium passage, and each heat bolt vertically penetrates each block.

  The base of the heat bolt is fixed to the die body, and the tip is in contact with the outer surface of the flexible lip. Then, while constantly cooling the block, the input of the embedded electric heater is increased or decreased to raise or lower the temperature of the block, thereby thermally expanding and contracting the heat bolt, and displacing the flexible lip to adjust the thickness of the optical film.

  Thickness gauges are installed at the required locations in the wake of the die, and the web thickness information detected thereby is fed back to the control device. The thickness information is compared with the set thickness information by the control device, and correction control comes from the same device. It is also possible to control the power or the ON rate of the heat bolt heating element by the amount signal.

  The heat bolt preferably has a length of 20 to 40 cm and a diameter of 7 to 14 mm, and a plurality of, for example, several tens of heat bolts are preferably arranged at a pitch of 20 to 40 mm.

  Instead of the heat bolt, a gap adjusting member mainly composed of a bolt for adjusting the slit gap by manually moving back and forth in the axial direction may be provided.

  The slit gap adjusted by the gap adjusting member is usually 200 to 2000 μm, preferably 300 to 1000 μm, more preferably 400 to 800 μm.

  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.

  A stainless steel fiber sintered filter is a united stainless steel fiber body that is intricately entangled and then compressed and sintered at the contact location. The density is changed according to the thickness of the fiber and the amount of compression, and the filtration accuracy is improved. Can be adjusted.

  The filter is preferably a multilayer body formed by combining filter media having different filtration accuracy. Further, it is preferable to adopt a configuration in which the filtration accuracy is sequentially increased or a method in which coarse and dense filtration accuracy is repeated, so that the filtration life of the filter can be extended and the accuracy of supplementing foreign matters and gels can be improved.

  If flaws or foreign matter adhere to the die, streaky defects may occur. Such a defect is called a die line, but in order to reduce surface defects such as the die line, 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.

《Cooling roll》
The cooling roll of the present invention is not particularly limited, but is a roll having a structure with a high-rigidity metal roll that allows a temperature-controllable heat medium or refrigerant to flow inside, and is not limited in size. It is sufficient that the film is large enough to cool the formed 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 carry out a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The cooling roll is made of a seamless steel pipe having a wall thickness of about 20 to 30 mm, and the surface is finished to a mirror surface.

  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. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable to further polish the surface that has been subjected to surface processing so as to have the surface roughness described above.

  The cooling roll of the present invention is at least one, and preferably has two or more. 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.

  Preferably, Tr2> Tr1, and 0 <Tr2-Tr1 <50.

  As a result, the amount of the additive on the cooling roll is controlled, and the cellulose film is remelted.

  Although re-dissolution can be promoted by the contact time between the cellulose ester film and the first and second cooling rolls, in the present invention, 1.0 second or more and 3.0 seconds or less are preferable.

  The contact time was represented by the number of seconds calculated from the circumferential distance between the contact point at which the film and the roller began to contact and the contact point at which the film began to peel, and the film conveyance speed.

  The circumferential speed R2 of the second cooling roll is preferably larger than the circumferential speed R1 of the first cooling roll. That is, tension acts on the film between the two rolls, and the adhesion between the film and the first roll is increased. The ratio of the peripheral speeds is preferably in the range of 1.00 to 1.05, and if it exceeds 1.05, there is a risk that the film breaks. Similarly, it is preferable that the third and subsequent roll peripheral speeds are greater than the peripheral speed of the cooling roll immediately before.

《Elastic touch roll》
The touch roll that abuts on the cooling roll has an elastic surface, and can be deformed along the surface of the cooling roll by a pressing force to the cooling roll to form a nip with the cooling roll. It is preferable that

  As the elastic touch roll of the present invention, Japanese Patent No. 3194904, Japanese Patent No. 3422798, Japanese Patent Application Laid-Open No. 03-124425, Japanese Patent Application Laid-Open No. 08-224772, Japanese Patent Application Laid-Open No. 07-1000096, Japanese Patent Application Laid-Open No. 10-272676, WO 97- Elastic touch rolls as described in Japanese Patent No. 028950, Japanese Patent Application Laid-Open No. 11-235747, Japanese Patent Application Laid-Open No. 2002-36332, Japanese Patent Application Laid-Open No. 2002-36333, Japanese Patent Application Laid-Open No. 2005-172940, and Japanese Patent Application Laid-Open No. 2005-280217. Can be used.

  The elastic touch roll used in the present invention has a double structure of a metal outer cylinder and an inner cylinder, and has a space so that a cooling fluid can flow between them.

  Furthermore, because the metal outer cylinder has elasticity, the temperature of the surface of the touch roll can be controlled with high accuracy, and the distance to press the film in the longitudinal direction can be increased by utilizing the property of elastically deforming appropriately. With this effect, the effect of the present invention can be obtained that there are no bright and dark stripes and uneven spots when an image is displayed on a liquid crystal display device.

  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. If the radius of the touch roll is large, the metal outer cylinder can be appropriately bent even if the thickness of the metal outer cylinder is large. If the thickness of the metal outer cylinder is too thin, the strength is insufficient and there is a concern of breakage. On the other hand, if it is too thick, the roll mass becomes too heavy and there is a concern about uneven rotation. Therefore, the thickness of the metal outer cylinder is preferably 0.1 to 5 mm.

  The elastic touch roll has a diameter of 100 mm to 600 mm, an effective roll width L = 500 to 1600 mm, and preferably has a horizontally long shape with r / L <1.

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

  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. can be preferably used. Further, in order to increase the hardness of the surface or improve the releasability from the resin, it is preferable to carry out a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying. 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. By giving rigidity to the inner cylinder, it is possible to suppress the rotational shake of the roll. 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 controlled uniformly. 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 touch roll generally presses both ends of the touch roll against the film with a pressurizing unit, but in this case, the touch roll is bent, so that there is a phenomenon that the touch roll is pressed more strongly toward the end. By making the roll into a crown shape, highly uniform pressing becomes possible.

  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.

  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 when pressing the elastic touch roll is 9.8 N / cm or more and 147 N / cm or less. If the linear pressure is smaller than this range, the die line cannot be sufficiently eliminated.

  The linear pressure is a value obtained by dividing the force with which the elastic touch roll presses the film by the film width at the time of pressing. The method for setting the linear pressure within the above range is not particularly limited, and for example, both ends of the roll can be pressed with an air cylinder or a hydraulic cylinder.

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

  In order to satisfactorily eliminate the die line by the touch roll, it is important that the viscosity of the optical film when the touch roll sandwiches the optical film is in an appropriate range.

  Cellulose esters are known to have a relatively large change in viscosity with temperature.

  When the glass transition temperature of the optical film is defined as Tg, the touch roll side film surface temperature Tt immediately before the extruded film is sandwiched between the touch rolls is preferably Tg <Tt <Tg + 110 ° C.

  That is, when the film temperature Tt immediately before being sandwiched between the touch rolls is within the above range, the viscosity of the film when sandwiching the film can be set to an appropriate range, and the die line can be corrected. The film surface and the roll are bonded uniformly, and the die line can be corrected.

  Preferably Tg + 10 ° C. <Tt <Tg + 90 ° C., more preferably Tg + 20 ° C. <Tt <Tg + 70 ° C.

  The method of setting the film temperature at the time of pressing in the above range is not particularly limited. For example, the distance between the die and the cooling roll is made closer, and the cooling between the die and the cooling roll is suppressed, or between the die and the cooling roll. Examples of the method include heat insulation by surrounding with a heat insulating material, or heating by hot air, an infrared heater, microwave heating, or the like.

  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 image clarity C value of the cellulose ester film of the present invention is characterized in that it is 90 or more and 100 or less in transmission measurement of comb teeth of 0.125 mm. This image clarity C value is the image clarity when it passes through the last cooling roll.

  The image clarity after passing through the cooling roll has a correlation as an index representing the state of the cellulose ester film in which the aggregate is remelted on the film surface. It has been experimentally confirmed that the larger the C value is, the more the remelting proceeds.

  The image clarity C value represents the image clarity (gloss value C value%) measured by a transmission (0 degree) measurement with an image measurement instrument ICM-IDP of Suga Test Instruments Co., Ltd. and an optical comb tooth of 0.125 mm.

<< The process of casting while pressing the melt extruded from the die between the cooling roll and the elastic touch roll >>
In the present invention, the die line correction effect is more greatly manifested by reducing the pressure from the opening (lip) of the casting die to the cooling roll to 70 kPa or less.

  The reduced pressure is preferably 50 to 70 kPa. There is no particular limitation on the method of keeping the pressure in the portion from the opening (lip) of the casting die to the cooling roll at 70 kPa or less. is there.

  At this time, the suction device is preferably subjected to a treatment such as heating with a heater so that the device itself does not become a place where the sublimate is attached. In the present invention, if the suction pressure is too small, the sublimate cannot be sucked effectively, so it is necessary to set the suction pressure to an appropriate value.

  A melt containing cellulose ester has a higher melt viscosity and is less likely to be stretched than other thermoplastic resins.

  Therefore, when the draw ratio is large, there is a problem that the film thickness is likely to vary in the conveying direction, and also when the film is stretched in the tenter process, the film tends to be broken, and the drawing ratio is about 7 to 8 at most. However, in the present invention, a melt containing cellulose ester is extruded from a die into a film shape, and a film obtained with a draw ratio of 10 or more and 30 or less is conveyed while being pressed against a cooling 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. By setting the draw ratio within this range, a polarizing plate protective film having good productivity and no bright and dark stripes and uneven spots when an image is displayed on a liquid crystal display device can be obtained.

  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. Even if it is too large or too small, spotted unevenness may not be improved.

  It is preferable to adjust the film temperature on the touch roll side when the film is nipped between the cooling roll and the elastic touch roll to Tg + 110 ° C. or less of the film in order to adjust the image clarity of the film surface. A well-known roll can be used for the roll which has the elastic body surface used for such a purpose.

  When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

《Roll cleaning equipment》
It is preferable to add a device for automatically cleaning the drum and roll to the manufacturing apparatus of the present invention. There is no particular limitation on the cleaning device, but for example, a method of niping a brush roll, a water absorbing roll, an adhesive roll, a wiping roll, an air blow method of spraying clean air, a laser incinerator, or a combination thereof. is there.

  In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

<< Extension process >>
In the present invention, it is preferred that the film obtained as described above is further stretched by 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll. Stretching can improve surface quality, such as streaking, and adjust retardation.

  Preferably, the film is stretched 1.1 to 2.0 times in both the longitudinal (film transport direction) and lateral (width direction) directions.

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

  When the cellulose ester film of the present invention is used as a film having an optical compensation function, the temperature and magnification can be selected so that desired retardation characteristics can be obtained.

  Usually, the draw ratio is 1.01 to 3.0 times, preferably 1.1 to 2.0 times, and the draw temperature is usually Tg to Tg + 50 ° C., preferably Tg to Tg + 40 ° C. of the resin constituting the film. In the temperature range.

  If the draw ratio is too small, the streak may not be improved sufficiently, or a desired retardation may not be obtained, and if it is too large, it may break. If the stretching temperature is too low, it may break, and if it is too high, the streak may not be improved sufficiently, or the desired retardation may not 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.

  In the stretching step, known heat setting conditions, cooling, and relaxation treatment may be performed, and adjustment may be made as appropriate so as to have characteristics required for the intended film.

  In order to provide the physical properties of the phase film and the function of the phase film for expanding the viewing angle of the liquid crystal display device, the stretching step and the heat setting treatment are appropriately selected and performed. When such a stretching step and heat setting treatment are included, the heating and pressurizing step is performed before the stretching step and heat setting treatment.

  For the purpose of reducing the retardation of the cellulose ester film produced by the above method and reducing the dimensional change rate, the film may be contracted in the longitudinal direction or the width direction.

  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 driving the clip portions in the longitudinal direction by, for example, a pantograph method or a linear drive method to smoothly and gradually narrow the clip portion. I can do it. 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.

  Since the elastic modulus of the film can be increased by stretching, the stretching is effective as a means for compensating for the low elastic modulus of the melt-formed cellulose ester film. Moreover, it turned out that the contact angle of the cellulose-ester film melt-formed by extending | stretching falls. This is presumably because the polar group that had submerged inside the film emerges on the surface as a result of the surface area per volume being increased by stretching the film.

  When a retardation film is produced as an optical film and the functions of a polarizing plate protective film are combined, it is necessary to control the refractive index. However, the refractive index can be controlled by a stretching operation.

  In the retardation film stretching process, it is required by stretching 1.0 to 2.0 times in one direction of the cellulose resin and 1.01 to 2.5 times in the direction perpendicular to the optical film plane. Retardation Ro and Rth can be controlled. Here, Ro indicates in-plane retardation, and Rth indicates thickness direction retardation.

  In the case of having a phase difference function, Ro is 20 to 200 nm, Rth is 90 to 400 nm, and the ratio Rth / Ro of Rth and Ro is preferably 0.5 to 4, particularly preferably 1 to 3.

In addition, when the refractive index Nx in the slow axis direction of the film, the refractive index Ny in the fast axis direction, the refractive index Nz in the thickness direction, and the film thickness of the film are d (nm),
Ro = (Nx−Ny) × d
Rth = {(Nx + Ny) / 2−Nz} × d
Represented as: (Measurement wavelength 590nm)
The variation in retardation is preferably as small as possible, and is usually within ± 10 nm, preferably ± 5 nm or less, and more preferably ± 2 nm or less.

  The uniformity in the slow axis direction is also important, and the angle θ1 is preferably in the range of −1 to + 1 °, and more preferably in the range of −0.5 to + 0.5 ° with respect to the film width direction. Is preferable, and is particularly preferably in the range of −0.1 to + 0.1 °. These variations can be achieved by optimizing the stretching conditions.

  This θ1 can be defined as an orientation angle, and the measurement of θ1 can be performed using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments).

  Each of θ1 satisfying the above relationship contributes to suppressing or preventing light leakage, and contributes to faithful color reproduction in a color liquid crystal display device.

  The retardation Ro distribution in the in-plane direction of the retardation film is preferably adjusted to 5% or less, more preferably 2% or less, and particularly preferably 1.5% or less.

  The retardation Rth distribution in the thickness direction of the optical film is preferably adjusted to 10% or less, more preferably 2% or less, and particularly preferably 1.5% or less.

  In the retardation film, it is preferred that the retardation value distribution fluctuation is small. When a polarizing plate including a retardation film is used in a liquid crystal display device, the retardation distribution fluctuation is preferably small from the viewpoint of preventing color unevenness and the like. .

  Stretching can be performed, for example, sequentially or simultaneously in the longitudinal direction of the optical film and the direction orthogonal to the longitudinal direction of the optical film, that is, the width direction.

  By stretching in the biaxial directions perpendicular to each other, film thickness variation of the obtained optical film can be reduced. When the film thickness variation of the retardation film is too large, the retardation becomes uneven, and unevenness such as coloring may be a problem when used in a liquid crystal display.

  The film thickness variation of the optical film is preferably in the range of ± 3%, and more preferably ± 1%. For the purposes as described above, a method of stretching in the biaxial directions orthogonal to each other is effective, and the stretching ratio in the biaxial directions orthogonal to each other is finally 1.0 to 2.0 times in the casting direction. The width direction is preferably 1.01 to 2.5 times, the casting direction is 1.01 to 1.5 times, and the width direction is 1.05 to 2.0 times. It is more preferred to obtain the required retardation value.

  After stretching, the edge of the optical film is slit to a product width with a slitter and cut off, and then subjected to knurling (embossing) on both ends of the optical film by a knurling device comprising an embossing ring and a back roll. By taking up with a take-up machine, sticking in an optical film (original winding) and generation of scratches are prevented. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing.

  In addition, since the grip part of the clip of the optical film both ends is deform | transforming normally and cannot be used as an optical film product, it is cut out and reused as a raw material.

  Next, the winding process of the optical film is performed by keeping the shortest distance between the outer peripheral surface of the cylindrically wound optical film and the outer peripheral surface of the mobile transport roll immediately before the optical film as a winding roll. It is to be wound up. In addition, a means such as a static elimination blower for removing or reducing the surface potential of the optical film is provided in front of the winding roll.

  The winder related to the production of the optical film of the present invention may be generally used, and it may be a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. Can be wound up. In addition, it is preferable that the initial winding tension at the time of winding of the optical film is 90.2 to 300.8 N / m.

  In the winding process of the optical film in the method of the present invention, the optical film is preferably wound under environmental conditions of a temperature of 20 to 30 ° C. and a humidity of 20 to 60% RH.

  Thus, by prescribing the temperature and humidity in the winding process of the optical film, the resistance to humidity change of the thickness direction retardation (Rth) is improved.

  If the temperature in the winding process is in the range of 20 to 30 ° C., there will be no wrinkles and there will be no deterioration of the optical film winding quality.

  Moreover, if the humidity in the winding process of the optical film is 20 to 60% RH, it is difficult to be charged, the optical film winding quality deterioration is reduced, the winding quality is excellent, there is no sticking failure, and the transportability is not deteriorated. .

  When winding the optical film into a roll, the wound core may be any material as long as it is a cylindrical core, but is preferably a hollow plastic core, and the plastic material is heated. Any heat-resistant plastic that can withstand the processing temperature may be used, and examples thereof include phenol resins, xylene resins, melamine resins, polyester resins, and epoxy resins.

  A thermosetting resin reinforced with a filler such as glass fiber is preferred. For example, a hollow plastic core: a wound core made of FRP having an outer diameter of 6 inches (hereinafter, 1 inch is 2.54 cm) and an inner diameter of 5 inches is used.

  The number of turns to these winding cores is preferably 100 turns or more, more preferably 500 turns or more, the winding thickness is preferably 5 cm or more, and the width of the optical film substrate is 80 cm or more. It is preferable that it is 1 m or more.

  In the production of the optical film of the present invention, the length of the roll is preferably 10 to 5000 m, more preferably 50 to 4500 m in consideration of productivity and transportability.

  The width of the optical film at this time can be selected from the width of the polarizer and the width suitable for the production line, but the optical film has a width of 0.5 to 4.0 m, preferably 0.6 to 3.0 m. Is preferably wound up into a roll.

  In the cellulose ester film of the present invention, it is preferable that the height from the top of the adjacent mountain to the bottom of the valley is 300 nm or more, and there is no streak continuous in the longitudinal direction with an inclination of 300 nm / mm or more.

  The shape of the streak was measured using a surface roughness meter. Specifically, using a Mitutoyo SV-3100S4, a stylus (diamond needle) with a tip shape of 60 ° cone and a tip curvature radius of 2 μm was used. The film is scanned in the width direction of the film at a measurement speed of 1.0 mm / sec while applying a load of 0.75 mN, and a cross-sectional curve is measured with a Z-axis (thickness direction) resolution of 0.001 μm.

  From this curve, the streak height reads the vertical distance (H) from the top of the mountain to the bottom of the valley. The slope of the streak is obtained by reading the horizontal distance (L) from the top of the mountain to the bottom of the valley and dividing the vertical distance (H) by the horizontal distance (L).

<Optical film>
In the present application, the “optical film” is a functional film used for various display devices such as a liquid crystal display, a plasma display, and an organic EL display. Specifically, a polarizing plate protective film, a retardation film for a liquid crystal display device, An antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for expanding the viewing angle, and the like.

  The film thickness of the optical film is preferably 10 to 200 μm, more preferably 25 to 90 μm. If the film is too thin than this range, the strength is insufficient, and if it is too thick, the productivity is lowered in the polarizing plate preparation process.

  The retardation film is adjusted to have a retardation value suitable for improving the display quality of the VA mode or TN mode liquid crystal cell, and is preferably used for the MVA mode by dividing the retardation film into the above multi-domain as the VA mode. To achieve this, it is required to adjust the in-plane retardation Ro to a value greater than 30 nm and 95 nm or less, and the thickness direction retardation Rth to a value greater than 70 nm and 400 nm or less.

  The above-mentioned in-plane retardation Ro is based on the case of observing from the normal direction of the display surface when two polarizing plates are arranged in crossed Nicols and a liquid crystal cell is arranged between the polarizing plates. In the crossed Nicol state, when observed obliquely from the normal of the display surface, the polarizing plate is displaced from the crossed Nicol state, and light leakage caused by this is mainly compensated.

  The retardation in the thickness direction mainly compensates for the birefringence of the liquid crystal cell similarly observed when viewed from an oblique direction when the liquid crystal cell is in a black display state in the TN mode or VA mode, particularly in the MVA mode. To contribute.

  In the liquid crystal display device, when two polarizing plates are arranged above and below the liquid crystal cell, the distribution of the thickness direction retardation Rth can be selected, and both the thickness direction retardation Rth satisfying the above range can be selected. The total value is preferably larger than 140 nm and 500 nm or less.

  In a liquid crystal display device, for example, a TAC film having an in-plane retardation Ro = 0 to 4 nm and a thickness direction retardation Rth = 20 to 50 nm and a thickness of 35 to 85 μm is used as one polarizing plate as a commercially available polarizing plate protective film. The retardation film disposed on the other polarizing plate has an in-plane retardation Ro of more than 30 nm and not more than 95 nm, and a thickness direction retardation Rth of more than 140 nm and not more than 400 nm. Thereby, display quality improves and it is preferable also from the production surface of an optical film.

  An optical film having a laminated structure can be prepared by co-extrusion of a composition containing cellulose esters having different additive concentrations such as the plasticizer, the ultraviolet absorber, and the matting agent.

  For example, an optical film having a structure of skin layer / core layer / skin layer can be produced.

  For example, the matting agent can be contained in the skin layer in a large amount or only in the skin layer. The plasticizer and the ultraviolet absorber can be contained in the core layer more than the skin layer, and may be contained only in the core layer.

  In addition, the type of plasticizer and ultraviolet absorber can be changed between the core layer and the skin layer. For example, the skin layer contains a low-volatile plasticizer and / or an ultraviolet absorber, and the core layer has excellent plasticity. It is also possible to add a plasticizer or an ultraviolet absorber excellent in ultraviolet absorption.

  The glass transition temperature of the skin layer and the core layer may be different, and the glass transition temperature of the core layer is preferably lower than the glass transition temperature of the skin layer.

  At this time, the glass transition temperatures of both the skin layer and the core layer are measured, and an average value calculated from these volume fractions can be defined as the glass transition temperature Tg and similarly handled.

  Also, the viscosity of the melt containing the cellulose ester during melt casting may be different between the skin layer and the core layer, and the viscosity of the skin layer> the viscosity of the core layer or the viscosity of the core layer ≧ the viscosity of the skin layer may be used.

(Polarizer)
When using the cellulose-ester film of this invention as a polarizing plate protective film, the preparation methods of a polarizing plate are not specifically limited, It can produce by a general method.

  The optical film of the present invention is preferably subjected to alkali saponification treatment, and the treated optical film is bonded to at least one surface of a polarizing film produced by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. .

  The optical film of the present invention may be used on the other surface, or another polarizing plate protective film may be used. With respect to the optical film of the present invention, a commercially available optical film can be used as the polarizing plate protective film used on the other surface.

  For example, as a commercially available optical film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UY-HA, KC8UX-RHA (manufactured by Konica Minolta Opto Co., Ltd. is preferably used), etc. It is done.

  Alternatively, it is also preferable to use a polarizing plate protective film that also serves as an optical compensation film having an optical anisotropic layer formed by aligning liquid crystal compounds such as discotic liquid crystal, rod-shaped liquid crystal, and cholesteric liquid crystal. For example, the optically anisotropic layer can be formed by the method described in JP-A-2003-98348.

  By using in combination with the optical film of the present invention, a polarizing plate having excellent flatness and a stable viewing angle expansion effect can be obtained.

  Or you may use optical films, such as cyclic olefin resin other than an optical film, an acrylic resin, polyester, a polycarbonate, as a polarizing plate protective film of the other surface.

  Instead of the alkali treatment, polarizing plate processing may be performed by performing easy adhesion processing as described in JP-A-6-94915 and JP-A-6-118232.

  The polarizing film, which is the main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol film. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxially stretching or dyed, or uniaxially stretched after dyeing, and then preferably subjected to a durability treatment with a boron compound.

  The thickness of the polarizing film is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm.

  On the surface of the polarizing film, one side of the cellulose ester film of the present invention is bonded to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like.

  Since the polarizing film is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction perpendicular to the stretching (usually the width direction) ) Will grow. As the thickness of the polarizing plate protective film becomes thinner, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizing film increases.

  Normally, the stretching direction of the polarizing film is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when making the polarizing plate protective film thin, it is particularly important to suppress the stretching rate in the casting direction. It is. Since the optical film of the present invention is extremely excellent in dimensional stability, it is suitably used as such a polarizing plate protective film.

  That is, even in the durability test under the condition of 60 ° C. and 90% RH, the wavy irregularity does not increase, and good visibility can be provided without fluctuation of the viewing angle characteristic after the durability test.

  In the production of the polarizing plate protective film, functional layers such as an antistatic layer, a hard coat layer, a slippery layer, an adhesive layer, an antiglare layer, and a barrier layer may be coated before or after stretching. At this time, various surface treatments such as corona discharge treatment, plasma treatment, and chemical treatment can be performed as necessary.

  In the film forming process, the clip gripping portions at both ends of the cut optical film are pulverized or granulated as necessary, and then used as raw materials for the same type of optical film or different types of optical film. It may be reused as a raw material.

(Liquid crystal display device)
A polarizing plate comprising the cellulose ester film of the present invention as a polarizing plate protective film (including a case where it also serves as a retardation film) can express a higher display quality than a normal polarizing plate, particularly a multi-domain type. The liquid crystal display device is more suitable for use in a multi-domain liquid crystal display device, more preferably by a birefringence mode.

  The polarizing plate of the present invention includes an MVA (Multi-domain Vertical Alignment) mode, a PVA (Patterned Vertical Alignment) mode, a CPA (Continuous Pinwheel Alignment) mode, an OCB (Optical Compensated InP mode) It can be used, and is not limited to a specific liquid crystal mode and the arrangement of polarizing plates.

  The display quality of the liquid crystal display device is improved by the present invention, and since the contrast is improved and the resistance of the polarizing plate is improved, it is possible to display a moving image faithfully with less fatigue.

  In a liquid crystal display device including at least a polarizing plate including a retardation film, one polarizing plate including a polarizing plate protective film as the optical film of the present invention is disposed on the liquid crystal cell, or both sides of the liquid crystal cell. Place two in a row.

  In such a configuration, the polarizing plate protective film as the optical film of the present invention can optically compensate the liquid crystal cell.

  When the polarizing plate of the present invention is used in a liquid crystal display device, at least one polarizing plate in the liquid crystal display device may be the polarizing plate of the present invention.

  In the polarizing plate of the present invention, a polarizing plate protective film of a cellulose derivative is used on the surface opposite to the polarizing plate protective film as the optical film of the present invention as viewed from the polarizer, and a general-purpose TAC film or the like is used. Can do. The polarizing plate protective film located on the side far from the liquid crystal cell can be provided with another functional layer in order to improve the quality of the display device.

  For example, an anti-glare, anti-glare, scratch resistance, dust adhesion prevention, and an optical film containing a known functional layer as a display as a constituent for improving brightness, or may be attached to the polarizing plate surface of the present invention. It is not limited to these.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1
(Preparation of Sample 1-1)
Sample 1-1 was produced by the melt casting method using the following composition 1.

Composition 1
Cellulose ester (cellulose acetate propionate (acetyl group substitution degree 1.4, propionyl group substitution degree 1.3, molecular weight Mn = 86,000, Mw / Mn = 2.5))
100 parts by mass Trimethylolpropane / tribenzoate 10 parts by mass IRGANOX-1010 (manufactured by Ciba Japan Co., Ltd.) 0.5 parts by mass PEP-36 (manufactured by ADEKA Corporation) 0.1 part by mass Sumizer-GS (Sumitomo Chemical Co., Ltd.) 0.3 parts by mass Glycerin monostearate 0.5 parts by mass TINUVIN 928 (manufactured by Ciba Japan Co., Ltd.) 1.5 parts by mass Seahoster KEP-30 (manufactured by Nippon Shokubai Co., Ltd.) 0.1 parts by mass The composition was dried at 80 ° C. for 6 hours to a moisture content of 200 ppm or less, and further dried with mixing in a vacuum nauter mixer at 80 ° C. and 1 Torr for 3 hours to a moisture content of 50 ppm.

  The obtained mixture was melt-mixed at 235 ° C. using a twin-screw extruder and pelletized. At this time, an all screw type screw was used instead of a kneading disk in order to suppress heat generation due to shear during kneading.

  In addition, evacuation was performed from the vent hole, and volatile components generated during kneading were removed by suction. In addition, between the feeder, hopper, and extruder die supplied to the extruder and the cooling tank, a dry nitrogen gas atmosphere was used to prevent moisture from being absorbed into the resin and to remove oxygen.

  The first cooling roll and the second cooling roll were made of stainless steel having a diameter of 40 cm, and the surface was hard chrome plated. Further, oil for temperature adjustment (cooling fluid) was circulated inside to control the roll surface temperature to 130 ° C.

  The elastic touch roll had a diameter of 20 cm, the inner cylinder and the outer cylinder were made of stainless steel, and the surface of the outer cylinder was hard chrome plated. The wall thickness of the outer cylinder was 2 mm, and the surface temperature of the elastic touch roll was controlled at 130 ° C. by circulating temperature adjusting oil (cooling fluid) in the space between the inner cylinder and the outer cylinder.

  Using the above pellets, melted at 250 ° C. in a nitrogen atmosphere, extruded from the casting die onto the first cooling roll, and formed by pressing the melt extruded between the first cooling roll and the elastic touch roll. Sample 1-1 having a film thickness of 80 μm was obtained. The film thickness was controlled by adjusting the extrusion amount and the take-up speed.

  At this time, a T die having a lip clearance of 1.5 mm and an average surface roughness Ra of 0.01 μm was used. Further, an elastic touch roll having a 2 mm thick metal surface was pressed on the first cooling roll at a linear pressure of 10 kg / cm.

  The film temperature on the touch roll side at the time of pressing was 180 ° C. ± 1 ° C. (The film temperature on the touch roll side at the time of pressing here is the film at the position where the touch roll on the first roll (cooling roll) contacts) Is the average value of the film surface temperature measured at 10 points in the width direction from a position separated by 50 cm in a state where there is no touch roll using a non-contact thermometer.)

  Samples 1-2 to 1-26 were obtained in the same manner as Sample 1-1 except that the composition of the additive was changed as shown in Table 1.

  Using the obtained samples 1-1 to 1-26, the contact angle after saponification and bleed-out were evaluated.

《Contact angle after saponification》
The temperature of a 2N potassium hydroxide aqueous solution was adjusted to 50 ° C., and samples 1-1 to 1-26 were immersed for 90 seconds, followed by saponification by washing with running water for 90 seconds. The sample taken out from the running water was dried by absorbing water droplets on the surface with sand paper and placing it in an oven at 100 ° C. for 2 minutes.

  The contact angle to water was measured for the saponified sample using a solid-liquid interface analysis system DropMatter300 manufactured by Kyowa Interface Science Co., Ltd. The amount of water dropped was 3 μl, and the contact angle 15 seconds after dropping was measured.

  The smaller the contact angle, the better the adhesive strength with water paste is preferable. If the contact angle is 40 ° or less, there is no practical problem, but it is more preferably 35 ° or less.

《Bleed Out》
Samples 1-1 to 1-26 were put into a thermostat of 80 ° C. and 90% RH for 300 hours. Separately, it was put into a thermostat of 60 ° C. and 90% RH for 1000 hours. The samples taken out of the thermo were visually examined for the presence of bleed out and ranked according to the following criteria.
○: Neither 80 ° C. 90% RH nor 60 ° C. 90% RH occurred.
Δ: Not generated at 60 ° C. and 90% RH, but partially generated at 80 ° C. and 90% RH.
X: Generated at 60 ° C. and 90% RH, or generated on the front surface at 80 ° C. and 90% RH.

  The bleed out is preferably at the ◯ level, but if it is at the △ level, there is no practical problem. The x level is not preferable because problems such as surface contamination may occur depending on the use environment.

  The evaluation results are shown in Table 1.

  As is clear from the results shown in Table 1, the contact angle of the sample according to the present invention is smaller and better than the comparative example. In addition, there is no bleed out or close to it, and it can be seen that this point is also excellent.

Example 2
Using composition 1, a cellulose ester film having a film thickness of 80 μm was melt-formed in the same manner as in Example 1, and then stretched 1.3 times in the conveying direction at 155 ° C. by a stretching machine using a difference in peripheral speed of the roll. did. Next, it is introduced into a tenter having a preheating zone, a stretching zone, a holding zone, and a cooling zone (there is also a neutral zone for ensuring thermal insulation between the zones), and is 1. After stretching 5 times, the sample was cooled to 30 ° C. while relaxing 2% in the width direction, then released from the clip, and the clip gripping part was cut off to obtain a sample 2-1 having a film thickness of 40 μm.

  Samples 2-2 to 2-7 were obtained in the same manner as Sample 2-1, except that the composition of the additive and the draw ratio were changed as shown in Table 2. At this time, the film thickness before stretching was changed so that the film thickness after stretching was 40 μm. The film thickness before stretching was controlled by adjusting the extrusion amount and the take-up speed.

  Using the obtained samples 2-1 to 2-7, the contact angle after saponification and haze were evaluated.

  Furthermore, using Samples 2-1 to 2-7, a polarizing plate was prepared by the following method, and a change in the polarizing plate dimension was measured.

《Haze》
Samples 2-1 to 2-7 were measured for haze according to the method described in JIS K7136. The measurement used Nippon Denshoku Industries Co., Ltd. turbidimeter NDH2000.

  The haze value is preferably smaller. If it is 0.5% or less, there is no practical problem, but it is particularly preferably 0.35% or less.

(Preparation of polarizing plate)
A 120 μm-thick polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and longitudinally stretched 6 times at 50 ° C. to produce a polarizing film.

  Next, samples 2-1 to 2-7 were used as a polarizing plate protective film on the viewing side, and the opposite side was placed in Konica Minolta Tack KC4UY (manufactured by Konica Minolta Opto Co., Ltd.) at 60 ° C. in a 2 mol / l sodium hydroxide aqueous solution. After soaking for 5 minutes, washed with water, dried at 100 ° C. for 10 minutes, and a polarizing film obtained by laminating the polarizing plate protective film of the present invention on both sides of the polarizing film using an adhesive made of a completely saponified polyvinyl alcohol 5% aqueous solution. A plate was made.

<Polarizer dimensional change (60 ° C 90% RH1000h)>
Each of the produced polarizing plates is cut into a size of 120 mm × 120 mm, and the surface of the polarizing plate is sharpened with a razor or the like at intervals of about 100 mm in the casting direction (MD direction) and the direction perpendicular to the fluent direction (TD direction). Put a cross-shaped mark. The polarizing plate is conditioned for 24 hours or more in an environment of 23 ° C. and 55% RH, and the distance between marks L1 in the MD direction and TD direction before processing is measured with a microscope. Next, the sample was treated for 1000 hours in an environment of 60 ° C. and 90% RH using an electric thermostat. Next, the high-temperature and high-humidity-treated sample was again conditioned for 24 hours under an environment of 23 ° C. and 55% RH, and the distance between marks L2 in the MD direction and the TD direction after treatment was measured with a microscope. The rate of change before and after this treatment was obtained by the following equation, and the dimensional change rate in the MD direction and the TD direction was calculated respectively.

Polarizer dimensional change rate = (L2−L1) / L1 × 100 (%)
The absolute value of the dimensional change rate of the polarizing plate is preferably small. If it is within ± 0.5%, there is no practical problem, but it is preferably within ± 0.4%.

  The evaluation results are shown in Table 2.

  As is apparent from the results shown in Table 2, it can be seen that the samples according to the present invention have substantially no problem in the contact angle after saponification, the haze, and the change in the size of the polarizing plate, and most of the samples are within the preferable range. .

Example 3
Samples 3-1 to 3-18 were prepared in the same manner as Sample 2-1, except that the trimethylolpropane tribenzoate of Composition 1 shown in Example 1 was changed to the additives and addition amounts shown in Table 3. did. Samples 3-1 to 3-18 were used to measure heat loss and bleed out.

  Further, using the obtained sample, a polarizing plate was produced in the same manner as described in Example 2, and the polarizer deterioration was measured.

《Heating loss》
About 0.1 g of the sample is finely cut and dried in a nitrogen atmosphere at 100 ° C. for 3 hours, and the mass (G1) is measured. Furthermore, it heats for 30 minutes in 250 degreeC nitrogen atmosphere, and measures mass (G2). Heat loss was measured according to the following formula.

Loss on heating = (G1-G2) / G1 × 100 (%)
A smaller heating loss is preferable because process contamination by volatile components can be reduced. If it is 2.0% or less, there is no practical problem, but it is preferably 1.0% or less, and more preferably 0.5% or less.

《Polarizer degradation》
The total light transmittance of the polarizing plate produced using the sample was measured using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. At this time, in order to cancel the influence of the polarization of light at the time of measurement, the polarizing plate is measured twice with the reference and tilted by 90 °, and the average value is calculated. The polarizing plate was subjected to a durability test for 2000 hours under the condition of 60 ° C. and 90% RH, and the total light transmittance after the durability test was measured by the same method as described above. The change in the total light transmittance before and after the durability test was calculated according to the following formula, and it was defined as the polarizer deterioration.

Polarizer degradation = (Transmittance after durability test)-(Transmittance before durability test)
The smaller the value of the polarizer deterioration, the better. If it is 20% or less, there is no practical problem, but it is preferably 10% or less, particularly preferably 5% or less.

  The evaluation results are shown in Table 3.

  As is apparent from the results shown in Table 3, it can be seen that the samples according to the present invention have substantially no problem in terms of weight loss on heating, bleed out, and polarizer deterioration, and most of the samples are within the preferred range.

Claims (5)

A cellulose ester film produced by a melt film-forming method, comprising 0.05 to 2.0% by mass of at least one of glycerin fatty acid ester, diglycerin fatty acid ester, and sorbitan fatty acid ester Ester film. The cellulose ester film according to claim 1, wherein the cellulose ester film is stretched within a range in which a total of a draw ratio in a fluent direction and a draw ratio in a direction perpendicular to the fluent direction is 20 to 300%. 3. The cellulose ester film according to claim 1, comprising 2 to 20% by mass of at least one of aromatic carboxylic acid esters of pentaerythritol. A polarizing plate using the cellulose ester film according to claim 1. A liquid crystal display device using the polarizing plate according to claim 4.