JP2007083397A - Manufacturing method of optical film, optical film manufactured by method, polarizing plate using optical film, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress rise in haze of an optical film and occurrence of cutting chips from the optical film. <P>SOLUTION: In this manufacturing method of the optical film by casting a thermoplastic resin on a metal support from the slits of a die, the shearing stress of the slits of the die when the resin flows through the slits is set at 0.01-0.4[MPa] and the passing time of the resin is set at 0.1-2.0[sec]. The polymer molecule in a dope and the particles of a matting agent or the like added to the dope, thereby receive shearing stress. That is, since the polymer molecule and particles while passing through the slit, receive the shearing stress to flow, uniformity is raised. As a result, concretely, the interval of the slits of the die is set at 0.2-3.0 mm. It is preferable to set the length of each of the slits at 40-250 mm which is longer than conventional ones so as to reduce the amount of the cutting chips and haze. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

   The present invention relates to an optical film manufacturing method.

  Various types of liquid crystal display devices such as IPS, VA, and OCB have been proposed, and the need for retardation films in these liquid crystal display devices is increasing. As means for giving a phase difference to a film, a method of stretching a polycarbonate, a cycloolefin film, or a cellulose ester resin film has been proposed. In the case of using a polycarbonate or cycloolefin film, it is necessary to attach a retardation plate to the polarizing plate, but in the case of a cellulose ester film, the protective film of the polarizing plate can also serve as the retardation film. It is suitable as a retardation film in terms of reduction, simplification of manufacturing process, cost reduction and the like. Particularly in recent years, with the widespread use of large-sized liquid crystal televisions, the demand for cellulose ester films as protective films and retardation films is growing rapidly.

  This cellulose ester film has been produced by a casting film forming method in which a film is formed by casting from a slit part of a die on a belt-like or drum-like support, drying and then peeling. . In this casting film forming method, an attempt has been made to increase the production rate by increasing the concentration of the dope in order to meet the growing demand. For example, Patent Document 1 describes a method of high-speed casting at a casting speed of 40 m / min or more by a solution casting film forming method.

JP 2004-66545 A

However, when the concentration of the raw material solution (called dope) is increased by solution casting and the film-forming speed is increased by high-speed casting, the haze of the film increases, or when the film edge is slit. Deterioration in quality, such as easy generation of powder, occurred. In recent years, even in the melt extrusion film forming method that does not use a solvent, which has been promoted for the environment, the same problem has occurred when the film forming speed is increased.

  This invention is made | formed in view of such a condition, and it aims at providing the optical film by which the raise of the haze and generation | occurrence | production of the cuttings by a slit were suppressed.

   In order to achieve the above object, the invention according to claim 1 is a manufacturing method in which an optical film is formed by casting a thermoplastic resin from a slit of a die onto a metal support, and the resin flows through the slit. The film is formed with a shear stress of 0.01 to 0.4 [MPa] and a time for the resin to pass through the slit in a range of 0.1 to 2.0 [sec].

  While the dope passes through the slit of the die, polymer molecules in the dope and particles such as added matting agent flow under shear stress. Therefore, by setting a shear stress in the range described in claim 1 and passing the slit through the dope over the passage time according to claim 1, polymer molecules in the dope and particles such as a matting agent added. Can flow sufficiently and have a uniform distribution. As a result, it is possible to suppress haze reduction and generation of chips during slitting in the optical film.

The best mode for carrying out the present invention will be described below, but the present invention is not limited thereto.
The film forming method according to the present invention is a method for forming a film by casting a dope dissolved in a solvent by heating or melting a thermoplastic resin from a die onto a metal support.

  The film according to the present invention is easy to manufacture, has good adhesion to the actinic radiation curable resin layer, is optically isotropic, is optically transparent, etc. It is mentioned as a preferable requirement.

  The term “transparent” as used in the present invention means that the visible light transmittance is 60% or more, preferably 80% or more, and particularly preferably 90% or more.

Although it will not specifically limit if it has said property, Substitution degree of acyl groups, such as a cellulose acetate, a cellulose acetate propionate, a cellulose acetate butyrate, is 1.8-2 as resin used preferably in this invention. .80 cellulose ester resin; cellulose ether resin having an alkyl group substitution degree of 2.0 to 2.80 such as cellulose methyl ether, cellulose ethyl ether, cellulose propyl ether; polyamide resin of a polymer of alkylene dicarboxylic acid and diamine; alkylene Polymer of dicarboxylic acid and diol, polymer of alkylene diol and dicarboxylic acid, polymer of cyclohexane dicarboxylic acid and diol, polymer of cyclohexane diol and dicarboxylic acid, polymer of aromatic dicarboxylic acid and diol, etc. Of the Ester resin; Vinyl acetate resin such as polyvinyl acetate and vinyl acetate copolymer; Polyvinyl acetal resin such as polyvinyl acetal and polyvinyl butyral; Polyurethane such as epoxy resin, ketone resin, linear polymer of alkylene diisocyanate and alkylene diol Resins and the like can be mentioned, and it is preferable to contain at least one selected from these. Of these, cellulose triacetate film, polycarbonate film, and polysulfone (including polyethersulfone) are preferable. In addition, two or more compatible polymers may be blended and dope dissolution described later may be performed, but the present invention is not limited to these.

  Examples of the other resin include a homopolymer or a copolymer having an ethylenically unsaturated monomer unit, and more preferably polymethyl acrylate, polyethyl acrylate, polypropyl acrylate. Homopolymers or copolymers of acrylic acid or methacrylic acid ester, such as polycyclohexyl acrylate, alkyl acrylate copolymer, polymethyl methacrylate, polyethyl methacrylate, polycyclohexyl methacrylate, alkyl methacrylate ester copolymer, etc. Further, acrylic acid or methacrylic acid esters are excellent in transparency and compatibility, and are homopolymers or copolymers having acrylic acid ester or methacrylic acid ester units, in particular acrylic acid or methyl methacrylate units. Homopolymer or copolymer having It is preferred. Specifically, polymethyl methacrylate is preferable. An alicyclic alkyl ester of acrylic acid or methacrylic acid such as polyacrylic acid or polymethacrylic acid cyclohexane is preferred because it has advantages such as high heat resistance and low hygroscopicity.

  In addition, as an epoxy resin, a compound having two or more epoxy groups in one molecule is a resin formed by a ring-opening reaction, and typical commercial products are Araldide EPN1179 and Araldide AER260 (Asahi Ciba Co., Ltd.). Made). Araldide EPN1179 has a weight average molecular weight of about 405.

  The ketone resin is obtained by polymerizing vinyl ketones, and typical commercially available products include Hilac 110 and Hilac 110H (manufactured by Hitachi Chemical Co., Ltd.).

[Material for forming dope]
In the present invention, a cellulose ester solution containing a cellulose ester and an organic solvent is referred to as a dope, which is used for solution casting to form a cellulose ester film.

(Cellulose ester)
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 used individually or in mixture in arbitrary ratios, respectively.

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

  As a cellulose ester which can be used for a cellulose ester film, the total acyl group substitution degree is preferably 2.4 to 2.8.

  The molecular weight of the cellulose ester used in the present invention is a number average molecular weight (Mn) of 50,000 to 200,000. More preferred are 60,000 to 200,000, and 80,000 to 200,000 are particularly preferred.

  In the cellulose ester used in the present invention, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw / Mn is preferably 1.4 to 3.0 as described above, more preferably It is in the range of 1.7 to 2.2.

  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 this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

  The cellulose ester used in the present invention is a carboxylic acid ester having about 2 to 22 carbon atoms, and is particularly preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate phthalate, etc., JP-A-10-45804, Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate as described in US Pat. No. 8,231,761, US Pat. No. 2,319,052 can be used. Alternatively, an ester of an aromatic carboxylic acid and cellulose and cellulose acylate described in JP-A Nos. 2002-179701, 2002-265639, and 2002-265638 are also preferably used. Among the above descriptions, the lower fatty acid esters of cellulose particularly preferably used are cellulose triacetate and cellulose acetate propionate. These cellulose esters can also be mixed and used.

  A preferred cellulose ester other than cellulose triacetate has an acyl group having 2 to 4 carbon atoms as a substituent, the substitution degree of acetyl group is X, and the substitution degree of propionyl group or butyryl group is Y, It is a cellulose ester that simultaneously satisfies (a) and (b).

Formula (a) 2.4 ≦ X + Y ≦ 2.8
Formula (b) 0 ≦ X ≦ 2.5
The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  These acyl group substitution degrees can be measured according to the method prescribed in ASTM-D817-96.

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

  An example of a method for producing a cellulose ester is shown below: 100 parts by mass of a flocculent linter was crushed as a cellulose raw material, 40 parts by mass of acetic acid was added, and pretreatment activation was performed at 36 ° C. for 20 minutes. Thereafter, 8 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride and 350 parts by mass of acetic acid were added, and esterification was performed at 36 ° C. for 120 minutes. After neutralizing with 11 parts by mass of a 24% by mass magnesium acetate aqueous solution, saponification aging was performed at 63 ° C. for 35 minutes to obtain acetylcellulose. This was stirred for 160 minutes at room temperature using a 10-fold acetic acid aqueous solution (acetic acid: water = 1: 1 (mass ratio)), then filtered and dried to obtain purified acetylcellulose having an acetyl substitution degree of 2.75. . This acetylcellulose had Mn of 92,000, Mw of 156,000, and Mw / Mn of 1.7. Similarly, cellulose esters having different degrees of substitution and Mw / Mn ratios can be synthesized by adjusting the esterification conditions (temperature, time, stirring) and hydrolysis conditions of the cellulose ester.

  The synthesized cellulose ester is preferably purified to remove low molecular weight components or to remove unacetylated components by filtration.

  In the case of mixed acid cellulose ester, it can be obtained by the method described in JP-A-10-45804. The measuring method of the substitution degree of an acyl group can be measured according to the rule of ASTM-D817-96.

  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 iron (Fe) component is preferably 1 ppm or less. About calcium (Ca) component, it is contained in a lot of ground water and river water, etc., and it becomes hard water, and it is unsuitable as drinking water. It easily forms a coordination compound, that is, a complex with a ligand, and forms scum (insoluble starch, turbidity) derived from many insoluble calcium.

  The calcium (Ca) component is 60 ppm or less, preferably 0 to 30 ppm. The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably in the range of 0 to 30 ppm because too much will cause insoluble matter. Metal components such as iron (Fe) content, calcium (Ca) content, magnesium (Mg) content, etc. are pre-processed by completely digesting cellulose ester with micro digest wet cracking equipment (sulfuric acid decomposition) and alkali melting. After performing, it can obtain | require by performing an analysis using ICP-AES (inductively coupled plasma optical emission spectrometry).

(Organic solvent)
Organic solvents that dissolve cellulose esters and are useful for forming cellulose ester solutions or dopes include chlorinated organic solvents and non-chlorinated organic solvents. Methylene chloride (methylene chloride) can be mentioned as a chlorinated organic solvent, and it is suitable for dissolving cellulose esters, particularly cellulose triacetate. Due to recent environmental problems, the use of non-chlorine organic solvents has been studied. Examples of the non-chlorine organic solvent include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1, Examples include 1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like. When these organic solvents are used for cellulose triacetate, a dissolution method at room temperature can be used, but an insoluble material can be obtained by using a dissolution method such as a high-temperature dissolution method, a cooling dissolution method, or a high-pressure dissolution method. Can be reduced, which is preferable. Methylene chloride can be used for cellulose esters other than cellulose triacetate, but methyl acetate, ethyl acetate, and acetone are preferably used. Particularly preferred is methyl acetate. In the present invention, an organic solvent having good solubility with respect to the cellulose ester is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is a main (organic) solvent or a main ( Organic) solvent.

  The dope according to the present invention preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. These are gelling solvents that make dope film (web) gel when the dope is cast on a metal support and the solvent starts to evaporate and the ratio of alcohol increases, making the web strong and easy to peel off from the metal support. When these ratios are small, there is also a role of promoting the dissolution of the cellulose ester of the non-chlorine organic solvent. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, and has good drying properties. These organic solvents are called poor solvents because they are not soluble in cellulose esters alone.

  It is preferable that the concentration of the cellulose ester in the dope is adjusted to 15 to 30% by mass and the dope viscosity is adjusted to a range of 100 to 500 Pa · s in order to obtain good film surface quality.

  Additives added to the dope include fine particles such as a plasticizer, an ultraviolet absorber, an antioxidant, a dye, and a matting agent. In the present invention, these additives may be added when preparing a cellulose ester solution, or may be added when preparing a fine particle dispersion such as a matting agent. It is preferable to add a plasticizer, an antioxidant, an ultraviolet absorber, or the like that imparts heat and moisture resistance to the polarizing plate used in the liquid crystal image display device. Hereinafter, the additive will be described.

(Plasticizer)
To the cellulose ester solution or dope according to the present invention, a compound known as a so-called plasticizer is added for the purpose of improving mechanical properties, imparting flexibility, imparting water absorption resistance, reducing water vapor permeability, adjusting retardation, etc. For example, phosphoric acid esters and carboxylic acid esters are preferably used.

  Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like.

  Examples of carboxylic acid esters include phthalic acid esters and citric acid esters; phthalic acid esters such as dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethyl hexyl phthalate; and citrate esters such as acetyl triethyl citrate and acetyl citrate. Mention may be made of tributyl. Other examples include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and triacetin. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, Octyl phthalyl octyl glycolate is preferably used. These alkyl phthalyl alkyl glycolates may be used in combination of two or more.

  Polyhydric alcohol esters are also preferably used.

  The polyhydric alcohol used in the present invention is represented by the following general formula (1).

Formula (1) R _1- (OH) n
However, R ₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising 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. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  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, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred 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 side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable 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-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. The aromatic monocarboxylic acid which has, or those derivatives can be mentioned. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  It is preferable that these compounds are contained so that it may become 1-30 mass% with respect to a cellulose ester, Preferably it is 1-20 mass%. In order to suppress bleeding out during stretching and drying, a compound having a vapor pressure at 200 ° C. of 1400 Pa or less is preferable.

  These compounds may be added together with the cellulose ester or the solvent during the preparation of the cellulose ester solution, or may be added during or after the solution preparation.

  As other additives, polyesters and polyester ethers described in JP-A No. 2002-22956, urethane resins described in JP-A No. 2003-171499, rosins and rosin derivatives described in JP-A No. 2002-146044, epoxy resins, and ketone resins , Toluenesulfonamide resin, ester of polyhydric alcohol and carboxylic acid described in JP-A-2003-96236, compound described in general formula (1) of JP-A-2003-165868, polyester weight described in JP-A-2004-292696 Examples thereof include a coalescence or a polyurethane polymer. These additives can be contained in the dope or the fine particle dispersion.

(UV absorber)
The cellulose ester film of the present invention can contain an ultraviolet absorber. Examples of ultraviolet absorbers that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, triazine compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621, JP-A-8-337574, JP-A-2001-72782, JP-A-6-148430, JP-A-2002-31715, JP-A-2002-169020, 2002-2002. Polymer ultraviolet absorbers described in 47357, 2002-363420, and 2003-113317 are also preferably used. As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred.

  Specific examples of UV absorbers useful in the present invention include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) Benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy-3'- ert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5 -Chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used. An example of the polymeric ultraviolet absorber is a reactive ultraviolet absorber RUVA-93 manufactured by Otsuka Chemical Co., Ltd.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The ultraviolet absorber described above preferably used in the present invention is preferably a benzotriazole-based ultraviolet absorber or a benzophenone-based ultraviolet absorber, which has high transparency and is excellent in the effect of preventing the deterioration of the polarizing plate and the liquid crystal element, and unnecessary coloring. A benzotriazole-based ultraviolet absorber with a lower content is particularly preferably used.

  The UV absorber can be added to the dope without limitation as long as the UV absorber is dissolved in the dope, but in the present invention, the UV absorber is cellulose such as methylene chloride, methyl acetate, dioxolane. A good solvent for esters, or a mixture of a good solvent and a poor solvent such as lower aliphatic alcohol (methanol, ethanol, propanol, butanol, etc.) dissolved in an organic solvent and added to the cellulose ester solution as an ultraviolet absorber solution or directly You may add during dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and the polymer to be dispersed and then added to the dope. The content of the ultraviolet absorber is 0.01 to 5% by mass, particularly 0.5 to 3% by mass.

  In the present invention, these ultraviolet absorbers may be used alone or in a mixture of two or more different types.

(Antioxidant)
As the antioxidant, hindered phenol compounds are preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t- Butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3 , 5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1,3 , 5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanate Examples include nurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose ester.

(Matting agent)
In the present invention, fine particles can be added to improve slipperiness and facilitate conveyance and winding.

As the fine particles, those containing silicon are preferable, and silicon dioxide is particularly preferable. Preferred fine particles of silicon dioxide for the present invention include, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (Nippon Aerosil Co., Ltd.) manufactured by Nippon Aerosil Co., Ltd. What is marketed by a brand name can be mentioned, Aerosil 200V, R972, R972V, R974, R202, R812 can be used preferably. Examples of polymer fine particles include silicone resin, fluorine resin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. Examples include Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.). Can do. In addition, various carbonates such as calcium carbonate, magnesium carbonate, manganese carbonate, cobalt carbonate, zinc carbonate, barium carbonate, various oxides represented by titanium oxide, MgSO ₄ .5Mg (OH) ₂ .3H ₂ O, _{6CaO · 6SiO 2 · H 2 O} , etc. _{9Al 2 O 3 · 2B 2 O} 3 and the like. Also, polystyrene or acrylic resin is preferably used.

  These fine particles are preferably surface-treated with an organic substance 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 matting agent may have any shape such as a spherical shape, a plate shape, a needle shape, a rod shape, or an indefinite shape.

  The fine particles of silicon dioxide preferably have a primary average particle size of 20 nm or less and an apparent specific gravity of 70 g / L or more. The average diameter of primary particles is more preferably 5 to 16 nm, further preferably 5 to 12 nm. A smaller primary particle average diameter is preferred because haze is low. The apparent specific gravity is preferably 90 to 200 g / L or more, and more preferably 100 to 200 g / L or more. Higher apparent specific gravity makes it possible to produce a high-concentration fine particle dispersion, which is preferable because no haze or aggregates are generated.

The addition amount of the matting agent in the present invention is preferably 0.01 to 1 g per 1 m ^{2 of} the cellulose ester film.

(Surfactant)
The dope or fine particle dispersion used in the present invention preferably contains a surfactant, and is not particularly limited to phosphoric acid, sulfonic acid, carboxylic acid, nonionic, cationic, and the like. These are described in, for example, JP-A-61-243837. The addition amount of the surfactant is preferably 0.002 to 2% by mass and more preferably 0.01 to 1% by mass with respect to the cellulose acylate. If the addition amount is less than 0.001% by mass, the effect of addition cannot be sufficiently exerted, and if the addition amount exceeds 2% by mass, precipitation or insoluble matter may occur.

  Nonionic surfactants include surfactants having nonionic hydrophilic groups such as polyoxyethylene, polyoxypropylene, polyoxybutylene, polyglycidyl and sorbitan, and specifically include polyoxyethylene alkyl ethers, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl ethers. Oxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyhydric alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, fatty acid diethanolamide, triethanolamine Mention may be made of fatty acid partial esters.

  Examples of the anionic surfactant include carboxylate, sulfate, sulfonate, and phosphate ester salt. Representative examples include fatty acid salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfonate, α-olefin sulfonate, dialkylsulfosuccinate, α-sulfonated fatty acid salt, N-methyl-N oleyl taurine, petroleum sulfonate, alkyl sulfate, sulfated oil, polyoxyethylene alkyl ether sulfate, Examples thereof include polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate, and naphthalene sulfonate formaldehyde condensate.

Examples of the cationic surfactant include amine salts, quaternary ammonium salts, pyridinium salts, etc., and primary to tertiary fatty amine salts, quaternary ammonium salts (tetraalkyl ammonium salts, trialkylbenzyl ammonium salts, Alkyl pyridium salt, alkyl imidazolium salt, etc.). Examples of amphoteric surfactants include carboxybetaine and sulfobetaine, such as N-trialkyl-N-carboxymethylammonium betaine and N-trialkyl-N-sulfoalkyleneammonium betaine. The fluorosurfactant is a surfactant having a fluorocarbon chain as a hydrophobic group. Examples of the fluorine-containing _{surfactant, C 8 F 17 CH 2 CH} 2 O- (CH 2 CH 2 O) 10 -OSO 3 Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O _{) 16 -H, C 8 F 17} SO 2 N (C 3 H 7) CH 2 COOK, C 7 F 15 COONH 4, C 8 F 17 SO 2 N (C 3 H 7) (CH 2 CH 2 O) 4 _{- (CH 2) 4 -SO 3} Na, C 8 F 17 SO 2 N (C 3 H 7) (CH 2) 3 -N + (CH 3) 3 · I -, C 8 F 17 SO 2 N (C _{3 H 7) CH 2 CH 2} CH 2 N + (CH 3) 2 -CH 2 COO -, C 8 F 17 CH 2 CH 2 O (CH 2 CH 2 O) 16 -H, C 8 F 17 CH 2 CH ₂ O (CH ₂ ) ₃ —N ⁺ (CH ₃ ) ₃ .I ⁻ , H (CF ₂ ) ₈ —CH ₂ CH ₂ OCOCH ₂ CH (SO ₃ ) COOCH ₂ CH ₂ CH ₂ CH ₂ (CF ₂ ) _{8 -H, H (CF 2) 6} CH 2 _{CH 2 O (CH 2 CH 2} O) 16 -H, H (CF 2) 8 CH 2 CH 2 O (CH 2) 3 -N + (CH 3) 3 · I -, H (CF 2) 8 CH 2 _{CH 2 OCOCH 2 CH (SO 3} ) COOCH 2 H 2 CH 2 CH 2 C 8 F 17, C 9 F 17 -C 6 H 4 -SO 2 N (C 3 H 7) (CH 2 CH 2 O) 16 - H, C ₉ F ₁₇ —C ₆ H ₄ —CSO ₂ N (C ₃ H ₇ ) (CH ₂ ) ₃ —N ⁺ (CH ₃ ) ₃ · I ^−, etc. Absent.

(Peeling accelerator)
Furthermore, a peeling accelerator for reducing the load during peeling may be added to the dope. Of these, surfactants are effective, and phosphoric acid-based, sulfonic acid-based, carboxylic acid-based, nonionic-based, cationic-based and the like are not particularly limited thereto. These peeling accelerators are described in, for example, JP-A-61-243837. Japanese Patent Application Laid-Open No. 57-500833 discloses a polyethoxylated phosphate ester as a peeling accelerator. JP-A-61-69845 discloses that a mono- or di-phosphoric acid alkyl ester in which a non-esterified hydroxy group is in the form of a free acid can be rapidly removed by adding to the cellulose ester. JP-A-1-299847 discloses that the peeling load can be reduced by adding a phosphate ester compound containing a non-esterified hydroxyl group and a propylene oxide chain and inorganic particles.

  Moreover, it is preferable that the compound represented by following formula (2) or (3) is contained.

_{(2) (R 1 -B 1} -O) n1 -P (= O) - (OM 1) n2
(3) R ₂ -B ₂ -X
In the formula, R ₁ and R ₂ are each a substituted or unsubstituted alkyl group, alkenyl group, aralkyl group or aryl group having 4 to 40 carbon atoms; M ₁ is an alkali metal, ammonia, or a lower alkyl amine. Yes; B ₁ and B ₂ are each a divalent linking group; X is a carboxylic acid or a salt thereof, a sulfonic acid or a salt thereof, or a sulfate ester or a salt thereof; n1 is 1 or 2; Yes; and n2 is 3-n1.

The cellulose acylate film contains at least one release agent represented by the formula (2) or (3). Hereinafter, these release agents will be described. Preferred examples of R ₁ and R ₂ include substituted and unsubstituted alkyl groups having 4 to 40 carbon atoms (for example, butyl, hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, eicosanyl, docosanyl, myricyl). , Etc.), substituted with 4 to 40 carbon atoms, unsubstituted alkenyl groups (for example, 2-hexenyl, 9-decenyl, oleyl, etc.), substituted with 4 to 40 carbon atoms, unsubstituted aryl groups (for example, phenyl, Naphthyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, propylphenyl, diisopropylphenyl, triisopropylphenyl, t-butylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isopentylphenyl, octylphenyl, Isooctylphenyl, isononyl phen Nyl, diisononylphenyl, dodecylphenyl, isopentadecylphenyl).

  Among these, more preferred are alkyl as hexyl, octyl, 2-ethylhexyl, nonyl, dodecyl, hexadecyl, octadecyl, docosanyl, alkenyl as alkenyl, phenyl, naphthyl, trimethylphenyl, diisopropylphenyl, tripropyl as aryl groups. Isopropylphenyl, di-t-butylphenyl, tri-t-butylphenyl, isooctylphenyl, isononylphenyl, diisononylphenyl, dodecylisopentadecylphenyl.

Next, the divalent linking group of B ₁ and B ₂ will be described. C1-10 alkylene, poly (degree of polymerization 1-50) oxyethylene, poly (degree of polymerization 1-50) oxypropylene, poly (degree of polymerization 1-50) oxyglycerin, and a mixture thereof. . Preferred linking groups among these are methylene, ethylene, propylene, butylene, poly (degree of polymerization 1-25) oxyethylene, poly (degree of polymerization 1-25) oxypropylene, and poly (degree of polymerization 1-15) oxyglycerin.

  X is carboxylic acid (or salt), sulfonic acid (or salt), sulfate ester (or salt), and particularly preferably sulfonic acid (or salt) or sulfate ester (or salt). Preferred salts are Na, K, ammonium, trimethylamine and triethanolamine. Specific examples of preferred compounds of the present invention are described below.

RZ-1 C ₈ H ₁₇ O—P (═O) — (OH) ₂
RZ-2 C ₁₂ H ₂₅ O—P (═O) — (OK) ₂
RZ-3 C ₁₂ H ₂₅ OCH ₂ CH ₂ O—P (═O) — (OK) ₂
RZ-4 C ₁₅ H ₃₁ (OCH ₂ CH ₂ ) ₅ O—P (═O) — (OK) _{2
RZ-5 {C 12 H 25} O (CH 2 CH 2 O) 5} 2 -P (= O) -OH
_{RZ-6 {C 18 H 35} (OCH 2 CH 2) 8 O} 2 -P (= O) -ONH 4
_{RZ-7 (t-C 4} H 9) 3 -C 6 H 2 -OCH 2 CH 2 O-P (= O) - (OK) 2
_{RZ-8 (iso-C 9} H 19 -C 6 H 4 -O- (CH 2 CH 2 O) 5 -P (= O) - (OK) (OH)
RZ-9 C ₁₂ H ₂₅ SO ₃ Na
RZ-10 C ₁₂ H ₂₅ OS ₃ Na
RZ-11 C ₁₇ H ₃₃ COOH
RZ-12 C ₁₇ H ₃₃ COOH · N (CH ₂ CH ₂ OH) _{3
RZ-13 iso-C 8 H} 17 -C 6 H 4 -O- (CH 2 CH 2 O) 3 - (CH 2) 2 SO 3 Na
_{RZ-14 (iso-C 9} H 19) 2 -C 6 H 3 -O- (CH 2 CH 2 O) 3 - (CH 2) 4 SO 3 Na
RZ-15 sodium triisopropyl naphthalene sulfonate RZ-16 sodium tri-t-butyl naphthalene sulfonate RZ-17 C ₁₇ H ₃₃ CON (CH ₃ ) CH ₂ CH ₂ SO ₃ Na
RZ-18 C ₁₂ H ₂₅ -C ₆ H ₄ SO ₃ .NH ₄
The amount of these compounds used is preferably 0.002 to 2% by mass in the dope. More preferably, it is 0.005-1 mass%, More preferably, it is 0.01-0.5 mass%. The addition method is not particularly limited, but it may be liquid or solid as it is and added together with other materials before dissolving, or may be added later to a cellulose acylate solution prepared in advance.

(Other additives)
In addition, thermal stabilizers such as inorganic fine particles such as kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, and alumina, and alkaline earth metal salts such as calcium and magnesium may be added. Furthermore, an antistatic agent, a flame retardant, a lubricant, an oil agent, etc. may be added.

[Solution casting film forming method]
The cellulose ester film of the present invention is formed by a solution casting film forming method. Here, the solution casting film forming method will be described with reference to FIG.

  FIG. 1 is a diagram showing an example of a process schematically showing a dope preparation process, a casting process, and a drying process of the solution casting film forming method according to the present invention.

(1) Fine Particle Dispersion Preparation Step The method for preparing the fine particle dispersion of the present invention is not particularly limited, but is preferably performed by the following method a) or b).

  a) An organic solvent and a fine particle-dispersing resin are introduced into a dissolution vessel, and dissolved by stirring to obtain a resin solution. Separately, a mixed liquid of an organic solvent and fine particles is transferred to a disperser such as a Menton gorey or a sand mill by a liquid feed pump and pre-dispersed. This is added to the resin solution, stirred and agglomerated with a filter to remove the agglomerates and stock as a fine particle dispersion (slightly different from FIG. 1). The prepared fine particle dispersion may be further repeatedly dispersed and filtered several times.

  b) Add an organic solvent and a resin in a dissolution vessel, dissolve by stirring to obtain a resin solution, add fine particles to this resin solution, disperse it with a disperser such as Manton Gorin or Sandmill, and filter it with a liquid feed pump To remove the agglomerate to obtain a fine particle dispersion (the same operation may be repeated several times). Then, the fine particle dispersion is transferred from the switching valve to the stock tank, and after standing and defoaming, transferred by a liquid feed pump (for example, a pressurized metering gear pump), filtered by a filter and transferred by a conduit.

  A plasticizer, a purple ray absorbent, a dispersant and the like may be further added to the fine particle dispersion.

  Dispersers used in preparing the fine particle dispersion as described above of the present invention are roughly divided into a medialess disperser and a media disperser, and both can be used.

Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type. In the present invention, a high pressure disperser is preferably used. A high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. It is preferable that the maximum pressure condition inside the apparatus is 9.8 × 10 ⁶ Pa or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, it is 19.6 × 10 ⁶ Pa or more. At that time, it is preferable that the maximum reaching speed reaches 100 m / sec or more and the heat transfer speed reaches 100 kcal / hr or more.

  Examples of the media disperser include a ball mill, a sand mill, and a dyno mill that disperse using a collision force of media such as glass beads and ceramic beads. In the present invention, a media disperser is particularly preferably used.

  Aggregates and foreign substances are removed from the fine particle dispersion prepared in this manner by filtration. A dope is prepared using the obtained fine particle dispersion.

(2) Cellulose ester solution preparation step In the present invention, a dope is prepared by mixing the fine particle dispersion prepared in advance by the above method, a solvent, and a cellulose ester. Specifically, it is preferable that a part of the solvent and the fine particle dispersion are added and mixed in the dissolution vessel, and then the remaining solvent and cellulose ester are added and dissolved therein with stirring. Additives such as plasticizers can be added later to the melting pot or later.

  Alternatively, an additive such as cellulose ester or plasticizer may be added to the solvent in the dissolution vessel while stirring, and the fine particle dispersion may be further added during dissolution of the cellulose ester. Alternatively, a solvent can be mixed with an additive such as cellulose ester and a plasticizer to obtain a cellulose ester solution, and the fine particle dispersion can be added thereto with stirring.

  The method for preparing the cellulose ester solution will be described in more detail.

  An additive such as cellulose ester and plasticizer is dissolved in an organic solvent mainly composed of a good solvent for the cellulose ester with stirring. For dissolution, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a high-temperature dissolution method performed by pressurization above the boiling point of the main solvent, a cooling dissolution method performed by cooling and a high-pressure dissolution method performed at a considerably high pressure However, in the present invention, the high temperature dissolution method is preferably used.

  The cellulose ester solution obtained by mixing the fine particle dispersion, the cellulose ester and the solvent in the dissolution vessel is dissolved in the cellulose ester and then sent to a filter by a pump and filtered.

  Filtration is preferably carried out using the cellulose ester solution with an appropriate filter medium such as filter paper for filter press. As the filter medium in the present invention, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matter, etc., but if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged, and absolute filtration A filter medium with an accuracy of 8 μm or less is preferable, a filter medium in the range of 1 to 8 μm is more preferable, and a filter medium in the range of 3 to 6 μm is more preferable.

  There are no particular restrictions on the material of the filter medium for filtration, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark) and metal filter media such as stainless steel do not drop off fibers. preferable. Filtration can be performed by a normal method, but the method of filtering while heating or holding at a temperature in a range not lower than the boiling point of the organic solvent used at normal pressure and in a range where the organic solvent does not boil is a filter medium. The increase in differential pressure before and after (hereinafter sometimes referred to as filtration pressure) is small and preferable. Although a preferable temperature range depends on the organic solvent used, it is 45 to 120 ° C, more preferably 45 to 70 ° C, and further preferably 45 to 55 ° C. The filtration pressure is preferably as small as possible, preferably 0.3 to 1.6 MPa, more preferably 0.3 to 1.2 MPa, and still more preferably 0.3 to 1.0 MPa.

  The dope thus obtained is stored in a stock tank, defoamed and then used for casting.

  As described above, it is preferable to prepare the dope by mixing the fine particle dispersion and the cellulose ester solution in the dope kettle. However, a part or all of the cellulose ester solution and the fine particle dispersion may be mixed in-line. You can also. For example, FIG. 1 shows an example of a process for adding the fine particle dispersion in-line. The fine particle dispersion is merged with the cellulose ester solution (or may be referred to as a dope stock solution) in the merging pipe 20. A filter is disposed immediately before the merging pipe 20, and for example, large foreign matters generated from the path due to filter medium exchange or the like can be removed from the fine particle dispersion or the dope stock solution being fed. Here, a metal filter having solvent resistance is preferably used. The filter medium is preferably a metal, particularly stainless steel, from the viewpoint of durability. From the viewpoint of clogging, it is preferable to have a porosity of 60 to 80%. Most preferably, the filtration is performed with a metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80%, so that coarse foreign substances can be reliably removed over a long period of time. preferable.

  The porosity of the filter medium is preferably 60 to 80%, more preferably 65 to 75%. A higher porosity is preferable from the viewpoint of reducing pressure loss, and a lower porosity is preferable because pressure resistance is excellent. To determine the porosity, first immerse the filter medium in a low surface tension solvent, remove the air in the filter medium, calculate the amount of pores in the filter medium from the increased amount of solvent, and divide by the volume of the filter medium. can do.

(3) In-line addition process When preparing a dope by mixing a fine particle dispersion, a cellulose ester and a solvent in advance in a dissolution vessel, it is usually unnecessary to add the fine particle dispersion in-line. However, if necessary, all or part of the fine particles can be mixed in-line. The in-line addition process will be described with reference to FIG. 1. A cellulose ester solution (sometimes referred to as a dope stock solution) and a fine particle dispersion are respectively transferred by liquid feed pumps 5 and 14 and filtered by filters 6 and 15. And 16 are transported and the two liquids are joined together by the joining pipe 20. Since the combined liquids are transported in layers in the conduit, they are difficult to mix as they are. Therefore, the two liquids are merged and then transferred to the next step while being sufficiently mixed by the mixer 21 such as an in-line mixer.

  (2) The dope prepared by the cellulose ester solution adjustment step and (3) the in-line addition step is preferably adjusted to a solid content concentration of 15% by mass or more, particularly preferably 18 to 30% by mass. If the solid content concentration in the dope is too high, the viscosity of the dope becomes too high, and sharkskin or the like may occur during casting to deteriorate the film flatness. Therefore, it is preferably 30% by mass or less.

(4) Casting process On the metal support 31 such as an endless metal support 31, for example, a stainless steel belt or a rotating metal drum, the dope prepared up to the previous process is fed to the die 30 and transferred infinitely. This is a step of casting the dope from the die 30 at the casting position. The surface of the metal support 31 is a mirror surface. A die 30 (for example, a pressure die) is preferable because the slit shape of the die portion can be adjusted and the film thickness can be easily made uniform. The die 30 includes a coat hanger die and a T die, and any of them is preferably used. In order to increase the film-forming speed, two or more dies may be provided on the metal support 31, and the dope amount may be divided and stacked.
If the gap between the slit portions of the die is too narrow, the liquid feeding pressure becomes too high, and when a minute foreign substance is mixed into the dope, it is caught in the slit, and the portion becomes a streak with the film. Also, the film thickness control becomes very severe. Further, since it is difficult to precisely control the film thickness even if the gap is too wide, the range of 0.2 to 3.0 mm is preferable.
The reason for the ease of haze rise and chipping is not clearly understood, but the shear time and shear stress when the dope flows through the slit portion of the die are effective. The length of the slit portion for achieving both haze and cutting chip reduction is preferably 40 to 250 mm so that a long shear time can be obtained by high-speed film formation. If it is lower than this, the effect of reducing haze and swarf is not seen, and if it is higher than this, the liquid feeding pressure becomes too high and precise film thickness control becomes difficult. The shear stress is preferably in the range of 0.01 to 0.4 [MPa] as determined by the following formula. If it is lower than this, the effect of reducing haze and swarf will not be seen.

τ = γ × η × 10 ⁻⁶
here,
τ: Shear stress [MPa]
γ: Shear rate [/ sec]
γ = 6 · Q × 10 ³ / (W · H ² )
Q: Dope flow rate [ml / sec]
η: shear viscosity [mPa · s] (apparent viscosity of γ in slit S)
W: Width of slit S [mm]
H :: Slit S gap [mm]
It is.

  The surface temperature of the metal support for casting is 10 to 55 ° C., the temperature of the dope is 25 to 60 ° C., and the temperature of the solution is preferably equal to or higher than the temperature of the support. More preferably, the temperature is set to a temperature of

  The higher the solution temperature and the support temperature, the faster the solvent can be dried. However, if the temperature is too high, foaming or flatness may be deteriorated.

  Although the more preferable range of the temperature of a support body is dependent on the organic solvent to be used, it is 20-55 degreeC, and the more preferable range of solution temperature is 35-45 degreeC.

(5) Solvent evaporation step The web 32 can be peeled from the metal support 31 by heating the web (referred to as the dope film after casting the dope on the metal support) 32 on the metal support 31. This is a step of evaporating the solvent until. In order to evaporate the solvent, there are a method of blowing air from the web 32 side and / or a method of transferring heat from the back surface of the metal support 31 by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. This method is preferable because of good drying efficiency. A method of combining them is also preferable. In the case of backside liquid heat transfer, it is preferable to heat at or below the boiling point of the main solvent of the organic solvent used in the dope or the organic solvent having the lowest boiling point.

(6) Peeling step In this step, the web 32 having the solvent evaporated on the metal support 31 is peeled off at the peeling position 33. The peeled web 32 is sent to the next process. If the residual solvent amount of the web 32 (explained later) at the time of peeling is too large, peeling is difficult, or conversely, if it is peeled off after sufficiently drying on the metal support 31, a part of the web 32 is halfway May come off. In the present invention, when peeling the thin web from the metal support, it is preferable to peel the thin web with a force within 170 N / m from the minimum tension that can be peeled as the peeling tension in order to prevent the flatness from being deteriorated and hung. A force within 140 N / m is more preferred.

  There is a gel casting method (gel casting) as a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible). For example, a poor solvent for the cellulose ester is added to the dope, and the dope is cast and then gelled, and the temperature of the metal support is lowered to gel. By gelling on the metal support 31 and increasing the strength of the film at the time of peeling, peeling can be accelerated and the film forming speed can be increased. The web 32 on the metal support 31 can be peeled in the range of 5 to 150% by mass depending on the strength of the condition, the length of the metal support 31, etc., but peels off when the amount of residual solvent is larger. In this case, if the web 32 is too soft, the flatness at the time of peeling tends to be lost, or a slip or vertical stripe due to the peeling tension is likely to occur, and the residual solvent amount at the time of peeling is determined in consideration of the economic speed and quality. Therefore, in the present invention, the temperature at the peeling position on the metal support 31 is 10 to 40 ° C., preferably 15 to 30 ° C., and the residual solvent amount of the web 32 at the peeling position is 10 to 120% by mass. It is preferable to do.

  In order to maintain good flatness of the cellulose ester film during production, the amount of residual solvent when peeling from the metal support is preferably 10 to 150% by mass, more preferably 70 to 150% by mass. More preferably, it is 100-130 mass%. The proportion of the good solvent contained in the residual solvent is preferably 50 to 90%, more preferably 60 to 90%, and particularly preferably 70 to 80%.

  In the present invention, the residual solvent amount can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is a mass at an arbitrary time point of the web, and is a mass measured by the following gas chromatography. N is a mass when the M is dried at 110 ° C. for 3 hours.

(7) Drying step After peeling, generally, the web 32 is dried using a roll drying device 35 that alternately conveys the web 32 through a plurality of rolls and a tenter device 34 that grips and conveys both ends of the web 32. . In FIG. 1, the roll drying device 35 is arranged after the tenter device 34, but is not limited to this arrangement. As a drying means, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Throughout, the drying temperature is usually in the range of 40 to 250 ° C. The drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used. 37 is winding of the completed cellulose ester film. In the step of drying the cellulose ester film, the amount of residual solvent is preferably 0.5% by mass or less, and more preferably 0.1% by mass or less.

  The stretching process will be described in more detail. The draw ratio at the time of producing the cellulose ester film of the present invention is 1.01 to 3 times, preferably 1.5 to 3 times, with respect to the film forming direction or the width direction. When stretching in the biaxial direction, the side to be stretched at a high magnification is 1.01 to 3 times, preferably 1.5 to 3 times, and the stretching ratio in the other direction is 0.8 to 1.5. The film can be stretched by a factor of preferably 0.9 to 1.2.

  Thereby, the cellulose ester film having the retardation value of the present invention can be preferably obtained, and a cellulose ester film having good planarity can be obtained. These width maintenance or lateral stretching in the film forming step is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  An example of a stretching process (also referred to as a tenter process) for producing the optical compensation film according to the present invention will be described with reference to FIG.

  In FIG. 2, step A is a step of gripping a film that has been transported from a film transport step (not shown), and in the next step B, the film is in the width direction (direction perpendicular to the film traveling direction). In step C, stretching is completed, and the film is conveyed while being held.

  It is preferable to provide a slitter for cutting off the end in the film width direction after the film is peeled off and before the start of the process B and / or immediately after the process C. In particular, it is preferable to provide a slitter that cuts off the film edge immediately before the start of the step A. When the same stretching is performed in the width direction, particularly when the film edge is cut off before the start of step B and the condition in which the film edge is not cut is compared, the former is more optically retarded in the width direction of the film. The effect of improving the axial distribution (hereinafter referred to as orientation angle distribution) can be obtained. This is considered to be an effect of suppressing unintended stretching in the longitudinal direction from the peeling with a relatively large amount of residual solvent to the width stretching step B.

  In the tenter process, it is also preferable to intentionally create compartments with different temperatures in order to improve the orientation angle distribution. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is preferable to implement biaxial stretching in a casting direction and a width direction. Also, when biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise. In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  In addition, the stretching direction in the present invention is usually used in the sense of a direction in which stretching stress is directly applied when performing a stretching operation. It is used to mean the one with a higher draw ratio.

  It is well known that the orientation angle distribution deteriorates when the cellulose ester film is stretched in the width direction. Since the thickness direction retardation Rth and the in-plane retardation Ro are set to a constant ratio, and the orientation angle distribution is in a good state, the film is stretched in the width direction. Exists. When the film temperatures at the end points of Steps A, B, and C are Ta ° C., Tb ° C., and Tc ° C., respectively, it is preferable that Ta ≦ Tb−10. Moreover, it is preferable that Tc ≦ Tb. More preferably, Ta ≦ Tb−10 and Tc ≦ Tb.

  The film heating rate in the step B is preferably in the range of 0.5 to 10 ° C./s in order to improve the orientation angle distribution.

  The stretching time in step B is preferably a short time in order to reduce the dimensional change rate under the conditions of 80 ° C. and 90% RH. However, the minimum required stretching time range is defined from the viewpoint of film uniformity. Specifically, the range is preferably 1 to 10 seconds, and more preferably 4 to 10 seconds. Moreover, the temperature of the process B is 40-180 degreeC, Preferably it is 100-160 degreeC.

In the tenter process, the heat transfer coefficient may be constant or changed. The heat transfer coefficient preferably has a heat transfer coefficient in the range of 41.9 to 419 × 10 ³ J / m ² hr. More preferably, in the range of ^{41.9~209.5 × 10 3 J / m 2} hr, and most preferably a range of ^{41.9~126 × 10 3 J / m 2} hr.

  In order to improve the dimensional stability under the conditions of 80 ° C. and 90% RH, the stretching speed in the width direction in the step B may be constant or may be changed. The stretching speed is preferably 50 to 500% / min, more preferably 100 to 400% / min, and most preferably 200 to 300% / min.

  In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable. By reducing the temperature distribution, it can be expected that the temperature distribution in the width of the film is also reduced.

  In step C, it is preferable to relax in the width direction in order to suppress dimensional changes. Specifically, it is preferable to adjust the film width so that it is in the range of 95 to 99.5% with respect to the film width of the previous step.

  It is preferable to provide a post-drying step after the treatment in the tenter step. It is preferable to carry out at 50-160 degreeC. More preferably, it is the range of 80-150 degreeC, Most preferably, it is the range of 110-150 degreeC.

  In the post-drying step, it is preferable from the viewpoint of improving the uniformity of the film that the atmospheric temperature distribution in the width direction of the film is small. Within ± 5 ° C is preferable, within ± 2 ° C is more preferable, and within ± 1 ° C is most preferable.

  The film transport tension in the post-drying process is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the temperature in the post-drying process, etc., but is preferably 120 to 200 N / m, 140 to 200 N. / M is more preferable. 140 to 160 N / m is most preferable.

  In order to prevent the film from stretching in the transport direction in the post-drying step, it is preferable to provide a tension cut roll. After completion of drying, a slitter 38 is provided before winding, and the end is cut off to obtain a good winding shape.

(9) Winding step This is a step of winding the web after drying as a film. By setting the amount of residual solvent to finish drying to 0.5% by mass or less, preferably 0.1% by mass or less, a film having good dimensional stability can be obtained. The winding method may be a commonly used winder, and there are methods for controlling the tension such as the constant torque method, constant tension method, taper tension method, and program tension control method with constant internal stress. That's fine.

  The film thickness of the cellulose ester film varies depending on the purpose of use, but from the viewpoint of thinning the liquid crystal display device, the finished film is preferably in the range of 10 to 150 μm, more preferably in the range of 30 to 100 μm, and particularly preferably in the range of 40 to 80 μm. A range is preferred. If it is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If it is too thick, the advantage of thinning the conventional cellulose ester film is lost. In adjusting the film thickness, it is preferable to control the dope concentration, the pumping amount, the slit gap of the die base, the extrusion pressure of the die, the speed of the metal support and the like so as to obtain a desired thickness. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

  Hereinafter, the physical properties of the cellulose ester film and the optical film-B according to the present invention are summarized below.

(Transmissivity of cellulose ester film)
High transmittance is required as a member of a liquid crystal display device, and the 500 nm transmittance of the produced cellulose ester film is preferably 85 to 100%, and 90 to 100% when added in combination with the above-mentioned additives. More preferably, 92 to 100% is most preferable. The 400 nm transmittance is preferably 40 to 100%, more preferably 50 to 100%, and most preferably 60 to 100%. Moreover, ultraviolet absorption performance may be calculated | required, In that case, 0 to 10% is preferable, as for 380 nm transmittance | permeability, 0 to 5% is more preferable, and 0 to 3% is the most preferable.

(Thickness distribution in the width direction of cellulose ester film)
The cellulose ester film of the present invention preferably has a film thickness distribution R (%) in the width direction of 0 ≦ R (%) ≦ 5%, more preferably 0 ≦ R (%) ≦ 3. %, Particularly preferably 0 ≦ R (%) ≦ 1%.

(Haze value of cellulose ester film)
The cellulose ester film of the present invention preferably has a haze value of 2% or less, more preferably 1.5%, and most preferably 1% or less.

(Elastic modulus of cellulose ester film)
The elastic modulus is preferably in the range of 1.5-5 GPa, more preferably 1.8-4 GPa, and particularly preferably 1.9-3 GPa.

  Further, the stress at break is preferably in the range of 50 to 200 MPa, more preferably in the range of 70 to 150 MPa, and most preferably in the range of 80 to 100 MPa.

  The elongation at break at 23 ° C. and 55% RH is preferably in the range of 20 to 80%, more preferably in the range of 30 to 60%, and most preferably in the range of 40 to 50%. .

  Further, the hygroscopic expansion coefficient is preferably in the range of −1 to 1%, more preferably in the range of −0.5 to 0.5%, and most preferably 0 to 0.2% or less.

Further, the bright spot foreign matter is preferably 0 to 80 pieces / cm ² , more preferably 0 to 60 pieces / cm ² , and most preferably 0 to 30 pieces / cm ^2. .

  In general, when a cellulose ester film is used as a polarizing plate protective film, an alkali saponification treatment is performed in order to improve the adhesion to the polarizer. Since the film after the alkali saponification treatment and the polarizer are bonded using a polyvinyl alcohol aqueous solution as an adhesive, if the contact angle of the cellulose ester film with the water after the alkali saponification treatment is high, the film cannot be bonded with polyvinyl alcohol. It becomes a problem as a plate protective film.

  For this reason, the contact angle of the cellulose ester film after the alkali saponification treatment is preferably 0 to 60 °, more preferably 5 to 55 °, and most preferably 10 to 30 °.

(Center line average roughness of cellulose ester film (Ra))
When a cellulose ester film is used as an LCD member, high flatness is required to reduce the light leakage of the film. The center line average roughness (Ra) is a numerical value defined in JIS B 0601, and examples of the measuring method include a stylus method or an optical method.

  The centerline average roughness (Ra) of the cellulose ester film of the present invention is preferably 20 nm or less, more preferably 10 nm or less, and particularly preferably 4 nm or less.

(Polarizer)
The polarizing plate of the present invention and the liquid crystal display device of the present invention using the polarizing plate will be described.

  The polarizing plate can be produced by a general method. The cellulose ester film of the present invention subjected to alkali saponification treatment is bonded to at least one surface of a polarizer prepared by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Is preferred. The cellulose ester 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 cellulose ester film of the present invention, a commercially available cellulose ester film can be used as the polarizing plate protective film used on the other surface. For example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used. Or you may use films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate, as a polarizing plate protective film of the other surface. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

  The polarizing plate of the present invention uses the cellulose ester film of the present invention as a polarizing plate protective film on at least one side of a polarizer. At that time, the cellulose ester film is preferably disposed so that the slow axis of the cellulose ester film is substantially parallel or perpendicular to the absorption axis of the polarizer.

  As one polarizing plate disposed across a liquid crystal cell that is a transverse electric field switching mode type, the cellulose ester film of the present invention (particularly preferably, the cellulose ester film A described above) is disposed on the liquid crystal display cell side. It is preferred that

  Examples of the polarizer preferably used for the polarizing plate of the present invention include a polyvinyl alcohol polarizing film, which includes a polyvinyl alcohol film dyed with iodine and a dichroic dye dyed. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. One side of the cellulose ester film of the present invention is bonded to the surface of the polarizer to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Moreover, in the case of resin films other than a cellulose ester film, it can be bonded to the polarizing plate via an appropriate adhesive layer.

  Since the polarizer 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 orthogonal to the stretching (usually normal) Extends in the width direction). As the thickness of the polarizing plate protective film decreases, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizer increases. Usually, the stretching direction of the polarizer is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when the polarizing plate protective film is thinned, it is particularly important to suppress the stretching rate in the casting direction. . Since the cellulose ester film of the present invention is excellent in dimensional stability, it is suitably used as such a polarizing plate protective film.

  The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection.

  Hereinafter, examples of the optical film according to the present invention will be described together with comparative examples, but the present invention is not limited to these examples.

Examples 1 to 16 and Comparative Examples 1 to 12 differ only in the time during which the dope passes through the slit portion of the die (passing time) and the shear stress applied to the dope at that time. It is common. First, the common part will be described.
(Preparation of dope)
Cellulose acetate propionate 100 parts by mass (acetyl group substitution degree 1.9, propionyl group substitution degree 0.8)
Triphenyl phosphate 8 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Methylene chloride 300 parts by weight Ethanol 60 parts by weight The above is put into a sealed container, heated and stirred, and completely dissolved. Azumi Filter Paper Co., Ltd. Azumi filter paper No. 24, and the dope liquid B was prepared. The dope solution B was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. in the film production line.
(Silicon dioxide dispersion)
Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 10 parts by mass (average primary particle diameter 16 nm, apparent specific gravity 90 g / liter)
Ethanol 75 parts by mass or more was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. The liquid turbidity after dispersion was 200 ppm. 75 parts by mass of methylene chloride was added to the silicon dioxide dispersion with stirring, and the mixture was stirred and mixed with a dissolver for 30 minutes to prepare a silicon dioxide dispersion dilution.
(Production of in-line additive solution)
Methylene chloride 100 parts by weight Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 4 parts by weight Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 4 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 2 parts by weight It was put into a container, heated, dissolved completely with stirring and filtered. To this was added 20 parts by mass of a silicon dioxide dispersion diluted solution with stirring, and the mixture was further stirred for 30 minutes, and then cellulose ester (cellulose acetate propionate acetyl group substitution degree 1.9, propionyl group substitution degree 0.8) 5 A mass part was added with stirring, and the mixture was further stirred for 60 minutes, and then filtered through a polypropylene wind cartridge filter TCW-PPS-1N manufactured by Advantech Toyo Co., Ltd. to prepare an in-line additive solution.

  In the inline additive solution line, the inline additive solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. Add 4 parts by mass of the filtered inline additive B to 100 parts by mass of the filtered dope solution, mix thoroughly with an inline mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and circulate hot water to 30 parts. The sample was uniformly cast on a stainless steel band support through a die kept at ℃.

  Hot air was blown onto both the front and back surfaces of the stainless steel band support to evaporate the solvent until the residual solvent amount reached 100%, and the web was peeled from the stainless steel band support. After the peeled cellulose ester film web was evaporated at 40 ° C. to a residual solvent amount of 20%, it was stretched 1.3 times at 130 ° C. in the TD direction (direction perpendicular to the film transport direction) with a tenter. . Then, drying was completed, conveying a 120 degreeC drying zone with many rolls.

  And before winding up, both ends of the film were slit by 30 mm with a slitter 38 to obtain a cellulose ester film having a film thickness of 80 μm. The slitter 38 is composed of a pair of rotary cutting blades disposed at both ends in the film width direction so as to sandwich the film. One of the rotary cutting blades is a disc-shaped cutting blade, and the other is a grooved bottom roll that receives the cutting blade. Each of the rotary cutting blades rotates in the film transport direction and continuously cuts the film.

  In Examples 1 to 4 and Comparative Examples 1 to 12, the change in the shear stress and passage time of the dope flowing in the slit of the die is changed to a die having a different slit gap and length, and the dope flow rate is changed. I went there. 3 and 4 show examples of dies having different slit S lengths. The traveling speed of the stainless steel belt was adjusted so that the film thickness of the finished film became 80 μm with the change of the die and the dope flow rate.

  The shear stress τ and the passage time θ in the die slit S are obtained by the following equations.

τ = γ × η × 10 ⁻⁶
θ = L / (Q × 10 ³ / (W · H))
here,
γ = 6 · Q × 10 ³ / (W · H ² )
τ: Shear stress [MPa]
γ: Shear rate [/ sec]
Q: Dope flow rate [ml / sec] (dope volume coming out per unit time from die slit of width W)
η: shear viscosity [mPa · s] (apparent viscosity of γ in slit S)
W: Width of slit S [mm]
H :: Slit S gap [mm]
L: Length of slit S [mm] (length in the dope flow direction)
θ: Passing time of slit S [sec]
It is.

  Here, the shear viscosity η was measured by a method based on JIS K2220 and ASTM D1092, using a pressure type apparent viscosity tester (25Z6-AD2 type) manufactured by Meitec Co., Ltd.

About Examples 1-4 and Comparative Examples 1-12 manufactured as mentioned above, the quantity of a facet and haze were evaluated and it has shown according to the said Table 1 together. In the state of a film roll, even fine chips of about 100 μm are very easy to see. Therefore, the wound film roll was slowly rotated once, and the number of the parts was visually counted and converted to the number per 1 m ² . If the chip is 1 piece / m ² or more and the haze is 3% or more, it is not suitable as an optical film. Moreover, the haze was measured according to the method prescribed | regulated to ASTM-D1003-52, having accumulated three films.

  As is clear from this result, by setting the dope passage time and the shear stress in the die slit to appropriate ranges, the facet can be reduced and the haze can be reduced. This is because when the dope passes through the slit, the polymer molecules in the dope and the particles such as the added matting agent are subjected to shear stress. That is, the polymer molecules and the added matting agent particles flow due to shear stress while passing through the slit, which is considered to increase uniformity. Therefore, if the passage time is too short or the shear stress is too small, the fine particles do not flow sufficiently, so that a sufficient effect cannot be obtained. On the other hand, if the passage time is too long or the shear stress is too large, foreign matter may be caught in the slit, and the fluidity will be lowered and the effect will not be obtained.

  Therefore, the slit gap of the die is preferably 0.2 to 3.0 mm. When the slit gap is too narrow, the liquid feeding pressure becomes high, and when a minute foreign matter is mixed in the dope, it is caught in the slit and the portion becomes a streak with the film. Also, the film thickness control becomes very severe. Also, even if the slit gap is too wide, precise film thickness control becomes difficult. In addition, the slit length is generally about 20 mm in the past, but 40 to 250 mm is preferable for reducing chips and haze. That is, the die shown in FIG. 3 is preferable to the die shown in FIG. When the shear stress at this time was in the range of 0.01 to 0.4 [MPa], the effect of reducing chips and haze was highest.

  In the above description, the case of the solution casting method has been described. However, the present invention can also be applied to a film forming method (for example, a melt casting method) other than the solution casting method.

It is the figure which showed typically the manufacturing process of the solution casting film forming method concerning this invention. It is the schematic which shows an example of the tenter process used for this invention. It is sectional drawing of an example of die | dye. FIG. 6 is a cross-sectional view of another example of a die. It is a front view of an example of a die.

Explanation of symbols

30 Dice 31 Metal support 38 Slitter L Slit length H Slit gap S Slit part W Slit part width

Claims (4)

In the manufacturing method in which a thermoplastic resin is cast from a slit of a die onto a metal support to form an optical film, the shear stress when the resin flows through the slit is 0.01 to 0.4 [MPa], A method for producing a film, characterized in that the time required for the resin to pass through the slit is in the range of 0.1 to 2.0 [sec]. An optical film manufactured by the manufacturing method according to claim 1. A polarizing plate comprising the optical film according to claim 2 on at least one surface. A liquid crystal display device comprising the polarizing plate according to claim 3 on at least one surface of a liquid crystal cell.

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