JP5631274B2 - Cellulose acetate film and method for producing the same, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a cellulose acetate film and a method for producing a cellulose acetate film. The present invention also relates to a polarizing plate and a liquid crystal display device comprising the cellulose acetate film.

  Conventionally, various optical films have been used for liquid crystal display devices, and optical films to which various additives are added are known. Such optical films are manufactured by various film forming methods. As a typical method, the optical film is manufactured by a solution casting method in which a dope in which cellulose acylate is dissolved in a solvent is poured onto a support to form a film. It is widely done.

  In recent years, the use of cellulose diacylate having a low degree of total acyl substitution has been studied from the viewpoint of inexpensively producing a film expressing retardation Rth in the film thickness direction. On the other hand, in the case where a film using cellulose diacetate having a low degree of total acyl substitution is produced by solution casting, a method for improving the peelability from the support has not yet been fully studied. Met.

  In Patent Document 1, the cellulose acetate dope before solution casting is controlled to a specific range for cellulose acetate having a low substitution degree of all acyl groups of 2.1 to 2.7, and cellulose acetate and It is disclosed that the whitening of the resulting film can be suppressed by setting the ΔSP value (solubility value) of the solvent (solvent) to an appropriate range. In the same literature, no consideration was given to peelability. In the examples of the same document, citric acid half ester was used as a release agent (release accelerator).

JP 2009-263619 A

When the present inventors manufactured a film using cellulose diacetate (hereinafter also referred to as DAC) having a low degree of total acyl substitution by solution casting, it was compared with the case where cellulose triacetate having a high degree of total acyl substitution was used. Thus, it was found that although the Rth expression was good, peeling from the support became even more difficult.
On the other hand, the present inventors have a relatively expensive cellulose acetate propionate (hereinafter referred to as “acyl group”) having a substitution degree of about 2.0 to 2.7 and a propionyl group to some extent as an acyl group. Surprisingly, it has the same degree of total acyl substitution and is more releasable than an inexpensive cellulose diacetate film having only an acetyl group as an acyl group. It was found to be good.
Although not bound by any theory, the difference in peelability from the support of CAP and DAP having the same amount of hydroxyl groups is due to the fact that the side chain propionyl chain of cellulose acetate is longer than the acetyl chain. It is expected that the separation load is reduced by increasing the distance between the unsubstituted hydroxyl group and the unsubstituted hydroxyl group and decreasing the interaction between the support and the hydroxyl group.
For this reason, it has been found that the problem of improving the peelability from the support when the total acyl substitution degree is lowered is a problem peculiar to DAC.
Accordingly, the present inventors have found that the support from the support, which is unique when solution casting film formation is performed using cellulose diacetate having a lower total acyl substitution degree, which is cheaper and lower in production cost than such CAP. We decided to conduct intensive research with the aim of improving the peelability of the film.
On the other hand, with reference to the method described in Patent Document 1, the present inventors referred to cellulose acetate having a low substitution degree of all acyl groups of 2.1 to 2.7, and citric acid half ester as a peeling accelerator. When a solution casting film was formed on a metal support using a mixture of 40% monoester of acid ethyl ester, 40% diester and 10% triester, the peelability of the film from the metal support was improved to some extent. However, it was found that there was a problem of corrosion of the metal support. Therefore, in solution casting film formation using cellulose diacetate with a low degree of total acyl substitution, the corrosiveness of the metal support, dope preparation tank, piping and die can be improved, thereby reducing the maintenance cost of manufacturing equipment. We decided to do earnest research as the purpose.

  That is, the problem to be solved by the present invention is that a cellulose acetate film that is easy to peel off from a metal support when cast by a solution, has good corrosiveness in manufacturing equipment, and has good Rth expression. It is to provide a manufacturing method.

Under the above-mentioned problems, the present inventors have conducted intensive studies and have conducted research on the peeling properties of the cellulose acetate film from the metal support and the improvement of the corrosivity of the metal support, dope preparation tank, piping and die. By using an organic acid that forms an ester bond between polyhydric alcohol and polyhydric carboxylic acid and meets specific requirements, the metal support, dope preparation tank, and piping are peeled off from the support satisfactorily. The inventors have found that the corrosiveness of the die can be improved, and have completed the present invention.
Specifically, the above problem has been solved by the following means.

[1] Cellulose acetate having a total substitution degree of 2.0 to 2.7, a solvent, and an organic that satisfies the following requirements (1) to (3) of 0.01% by mass to 20% by mass with respect to the cellulose acetate A method for producing a cellulose acetate film, comprising: a step of casting a dope containing an acid on a metal support; and a step of peeling the dope film from the metal support.
(1) Includes a structure in which a polyhydric alcohol and a polycarboxylic acid are bonded by forming an ester bond.
(2) The total number of molecules of the polyhydric alcohol and polycarboxylic acid forming the compound is 3 or more.
(3) It has at least one unsubstituted carboxyl group derived from a polyvalent carboxylic acid.
[2] In the method for producing a cellulose acetate film according to [1], it is preferable that 15% by mass or more of the solvent is an alcohol, and the average carbon number of the alcohol is 1.5 to 4.
[3] The method for producing a cellulose acetate film according to [2] preferably includes ethanol as the alcohol.
[4] In the method for producing a cellulose acetate film according to any one of [1] to [3], the metal support is a moving belt-like support, and the doped film of the metal support is In the area to be peeled off, it is preferable that a cooling body having a surface temperature of 10 ° C. or less is brought into contact with the surface of the metal support opposite to the dope film peeling side.
[5] The method for producing a cellulose acetate film according to any one of [1] to [4] preferably includes a retardation Rth control agent in the film thickness direction in the dope.
[6] The retardation value Rth in the film thickness direction measured at a wavelength of 590 nm is 80 nm or more, which is produced by the method for producing a cellulose acetate film according to any one of [1] to [5]. Cellulose acetate film.
[7] The cellulose acetate film according to [6] preferably has a haze of less than 0.5%.
[8] The cellulose acetate film according to [6] or [7] preferably has a retardation value Re in the in-plane direction of the film measured at a wavelength of 590 nm of 30 to 100 nm.
[9] A polarizing plate comprising a polarizer and at least one cellulose acetate film according to any one of [6] to [8].
[10] A liquid crystal display device comprising the cellulose acetate film according to any one of [6] to [8].

  According to the present invention, there is provided a method for producing a cellulose acetate film which is easy to peel off from a metal support when cast into a solution, has good corrosiveness in production equipment, and has good Rth expression. Can do.

FIG. 1 shows an outline of a preferable apparatus for controlling casting film formation and stripping conditions in the production method of the present invention in a solution casting apparatus having an endless band stretched between two rolls. FIG.

  Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit and an upper limit.

[Method for producing cellulose acetate film]
The method for producing a cellulose acetate film of the present invention (hereinafter also referred to as the production method of the present invention) comprises a cellulose acetate having a total substitution degree of 2.0 to 2.7, a solvent, and 0.01 mass relative to the cellulose acetate. % To 20% by mass of a solution containing an organic acid satisfying the following requirements (1) to (3): a step of casting a solution on a metal support; and a step of peeling the dope film from the metal support. Including.
(1) Includes a structure in which a polyhydric alcohol and a polycarboxylic acid are bonded by forming an ester bond.
(2) The total number of molecules of the polyhydric alcohol and polycarboxylic acid forming the compound is 3 or more.
(3) It has at least one unsubstituted carboxyl group derived from a polyvalent carboxylic acid.
Hereinafter, the production method of the present invention will be described.

  The cellulose acetate film of the present invention (hereinafter also referred to as the film of the present invention) is produced by a solution casting method (solvent casting method). Examples of the production of cellulose acetate films using the solvent cast method are described in US Pat. Nos. 2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069 and 2,739,070, British Patent Nos. 640731 and 736892, and Japanese Patent Publication Nos. 45-4554, 49-5614, JP-A-60-176834, JP-A-60-203430 and JP-A-62-115035 can be referred to. In addition, the film of the present invention is preferably subjected to a stretching treatment. Regarding stretching methods and conditions other than those specified in the present specification, for example, JP-A-62-115035, Publications such as 4-152125, 4-284221, 4-298310, and 11-48271 can be referred to.

<Preparation of dope>
In the solvent cast method, a film can be produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent.

(Dope)
The dope used in the production method of the present invention is a cellulose acetate having a substitution degree of all acyl groups of 2.0 to 2.7, a solvent, and 0.01% by mass to 20% by mass of the following with respect to the cellulose acetate. It comprises an organic acid that satisfies the requirements (1) to (3). By using such a dope, a cellulose acetate film having good Rth expression can be obtained. Hereinafter, the dope used for the film of this invention and each component contained in dope are demonstrated.

(Cellulose acetate)
The cellulose acetate used in the present invention is not particularly defined as long as the substitution degree of all acyl groups is 2.0 to 2.7. If it is 2.0 or more, the compatibility with water is sufficiently high. The resulting film is difficult to whiten. Examples of cellulose acetate as a raw material for cellulose acetate include cotton linter and wood pulp (hardwood pulp, softwood pulp). Cellulose acetate obtained from any raw material cellulose can be used, and in some cases, a mixture may be used. Detailed descriptions of these raw material celluloses can be found in, for example, Marusawa and Uda, “Plastic Materials Course (17) Fibrous Resin”, published by Nikkan Kogyo Shimbun (published in 1970), and the Japan Institute of Invention and Innovation Technical Bulletin No. 2001. The cellulose described in No.-1745 (pages 7 to 8) can be used.

First, the cellulose acetate preferably used in the present invention will be described in detail. Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acetate is a polymer obtained by esterifying some or all of these hydroxyl groups with an acyl group having 2 or more carbon atoms. The degree of acyl substitution means the ratio of the cellulose hydroxyl groups located at the 2nd, 3rd and 6th positions being esterified (100% esterification has a degree of substitution of 1).
The total acyl substitution degree, that is, DS2 + DS3 + DS6 is preferably 2.1 to 2.55, more preferably 2.2 to 2.55, particularly preferably 2.35 to 2.50, and more particularly preferably 2. .40 to 2.50. DS6 / (DS2 + DS3 + DS6) is preferably 0.08 to 0.66, more preferably 0.15 to 0.60, and still more preferably 0.20 to 0.45. Here, DS2 is the degree of substitution of the hydroxyl group at the 2-position of the glucose unit with an acyl group (hereinafter also referred to as “degree of acyl substitution at the 2-position”), and DS3 is the degree of substitution of the hydroxyl group at the 3-position with an acyl group (hereinafter, DS6 is the substitution degree of the hydroxyl group at the 6-position with an acyl group (hereinafter also referred to as “acyl substitution degree at the 6-position”). DS6 / (DS2 + DS3 + DS6) is the ratio of the acyl substitution degree at the 6-position to the total acyl substitution degree, and is hereinafter also referred to as “acyl substitution ratio at the 6-position”.

  The acyl group of cellulose acetate used for the dope is an acetyl group.

  In the acylation of cellulose, when an acid anhydride or acid chloride is used as an acylating agent, an organic acid such as acetic acid or methylene chloride is used as an organic solvent as a reaction solvent.

As the catalyst, when the acylating agent is an acid anhydride, a protic catalyst such as sulfuric acid is preferably used, and when the acylating agent is an acid chloride (for example, CH ₃ CH ₂ COCl), Basic compounds are used.

  The most common industrial synthesis method of cellulose mixed fatty acid ester is cellulose acylated with mixed organic acid component containing fatty acid corresponding to acetyl group (acetic acid, propionic acid, valeric acid, etc.) or their acid anhydrides. It is a method to convert.

  The cellulose acetate used for this invention is compoundable by the method described in Unexamined-Japanese-Patent No. 10-45804, for example.

  In the dope used in the present invention, the amount of cellulose acetate is preferably adjusted so that it is contained in an amount of 10 to 40% by mass in the obtained dope. The amount of cellulose acetate is more preferably 10 to 30% by mass.

(solvent)
As the solvent used in the present invention, known solvents can be adopted as long as they are used for solution casting. From the viewpoint of further reducing haze, ethers having 3 to 12 carbon atoms and the number of carbon atoms. Preferably contain a solvent selected from a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms and a halogenated hydrocarbon having 1 to 6 carbon atoms. The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as a solvent. The solvent may have another functional group such as an alcoholic hydroxyl group. In the case of a solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.
The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen in the halogenated hydrocarbon is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is most preferable that it is 40-60 mol%. Examples of halogenated hydrocarbons include dichloromethane (hereinafter also referred to as “methiclo”), chloroform, methyl chloride, carbon tetrachloride, trichloroacetic acid, methyl bromide, methyl hydride, tri (tetra) chloroethylene, etc., at least dichloromethane It is preferable to contain.

In the present invention, the poor solvent is preferably contained in a proportion of 3 to 40% by weight, more preferably 5 to 20% by weight. By including the poor solvent within the above range, the compatibility with cellulose acetate is improved, and the haze tends to be further lowered.
Furthermore, it is preferable that the boiling point of a poor solvent is 120 degrees C or less, and it is more preferable that it is 40-100 degreeC. By setting the boiling point to 120 ° C. or less, the drying rate of the solvent can be further increased, which is preferable.

Preferred examples of such a poor solvent include alcohol (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, n-hexanol) and water. Among them, in the production method of the present invention, it is more preferable to use a primary alcohol (methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol), and ethanol has a peeling property and a drying rate. Most preferable from the viewpoint of compatibility.
In the production method of the present invention, in the dope, 15% by mass or more of the solvent is an alcohol (preferably a primary alcohol), and the alcohol has an average carbon number of 1.5 to 4. And
Here, examples of the primary alcohol having 2 or more carbon atoms include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, and n-hexanol, and among them, ethanol, n- Preferred examples include propanol, isopropanol, n-butanol, and isobutanol. In addition, although the primary alcohol here may include glycols, which are polyhydric alcohols having 3 or more carbon atoms, naturally ethylene glycol, which is a glycol having 2 carbon atoms, is not a primary alcohol.
Moreover, as long as the alcohol average carbon number contained in dope is 1.5-4, you may use the said alcohol in mixture of 2 or more types. Furthermore, as long as the average carbon number is 1.5 to 4, naturally, methanol having 1 carbon atom or alcohol having 5 or more carbon atoms may be used. Specifically, a solvent in which ethanol, which is an alcohol having 2 carbon atoms, methanol having 1 carbon atom, and ethanol / methanol = 1/1 (mass ratio) or more can be used.
The average carbon number of the alcohol contained in the dope as a solvent by 15% by mass or more is preferably 1.5 to 4, more preferably 1.5 to 2.5, and more preferably 1.5 to 2. It is particularly preferred.
Further, the content of the alcohol contained as a solvent in the dope is preferably 18 to 40% by mass of the solvent from the viewpoint of improving releasability, and particularly preferably 20 to 30% by mass.
Furthermore, it is preferable that the total content of the alcohol having 2 or more carbon atoms is 10 to 40% by mass with respect to the total mass of the solvent.
Further, the total content of the alcohol having 2 or more carbon atoms with respect to the total mass of the solvent is preferably 10% by mass or more from the viewpoint of further improving the peelability, and more preferably 10 to 40% by mass. It is particularly preferable to include 15 to 40% by weight, and it is particularly preferable to include 20 to 30% by weight. By containing the alcohol having 2 or more carbon atoms within the above range, the compatibility with cellulose acetate is improved, and the haze tends to be further reduced.
Furthermore, the boiling point of the alcohol having 2 or more carbon atoms is preferably 120 ° C. or less, and more preferably 40 to 100 ° C. By setting the boiling point to 120 ° C. or less, the drying rate of the solvent can be further increased, which is preferable.

<Peeling accelerator>
(Organic acid that satisfies the requirements of (1) to (3))
The film of this invention contains 0.01 mass%-20 mass% of organic acids which satisfy | fill the requirements of following (1)-(3) with respect to this resin.
(1) Includes a structure in which a polyhydric alcohol and a polycarboxylic acid are bonded by forming an ester bond.
(2) The total number of molecules of the polyhydric alcohol and polycarboxylic acid forming the compound is 3 or more.
(3) It has at least one unsubstituted carboxyl group derived from a polyvalent carboxylic acid.

In the organic acid satisfying the above requirements (1) to (3), the detachability from the solution film-forming equipment (metal support when the dope is fluent) can be improved by an unsubstituted carboxyl group, and the present invention. Then, an organic acid satisfying the requirements (1) to (3) can be used as a peeling accelerator.
Further, the unsubstituted carboxyl group adheres to the metal surface of the support, and the polyhydric alcohol part or the hydrophobic group part substituted therewith blocks the metal surface of the support from an oxidizing agent such as oxygen. Compared to organic acids that do not contain a monohydric alcohol moiety or a hydrophobic group moiety substituted therefor, corrosion of the metal can be prevented.
Hereinafter, the organic acid that satisfies the requirements (1) to (3) that can be used as a peeling accelerator in the film of the present invention and other peeling accelerators that may be used in combination will be described.

Although it does not specifically limit as polyvalent carboxylic acid used for the organic acid which satisfy | fills the requirements of said (1)-(3), For example, a succinic acid, a citric acid, tartaric acid, diacetyl tartaric acid, malic acid, and adipic acid are preferable.
In the organic acid satisfying the requirements (1) to (3), the number of polyvalent carboxylic acid molecules is preferably 1 to 20, more preferably 1 to 15, and more preferably 1 to 10. Particularly preferred.

Examples of the polyhydric alcohol used in the organic acid that satisfies the requirements (1) to (3) include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, , 3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3- Examples thereof include methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, and glycerin. Among these, glycerin is preferable.
Among the organic acids that satisfy the requirements (1) to (3), the number of polyhydric alcohol molecules is preferably 1 to 20, more preferably 1 to 15, and particularly preferably 1 to 10. preferable.

In addition to the polyhydric alcohol and polyvalent carboxylic acid that constitute the organic acid, the organic acid that satisfies the requirements (1) to (3) is a monovalent acid having a substituent having 4 or more carbon atoms. You may have the structure which formed the ester bond with the one part hydroxyl group of this polyhydric alcohol. Specific examples of the monovalent acid having a substituent having 4 or more carbon atoms are given below. The substituent in the monovalent acid having a substituent having 4 or more carbon atoms means R when the monovalent acid having a substituent having 4 or more carbon atoms is represented as RCOOH.
"fatty acid"
Caproic acid, heptylic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, ricinolenic acid, undecanoic acid.
《Alkyl sulfate》
Myristyl sulfate, cetyl sulfate, oleyl sulfate.
《Alkylbenzene sulfonic acid》
Dodecylbenzenesulfonic acid, pentadecylbenzenesulfonic acid.
《Alkyl naphthalene sulfonic acid》
Sesquibutyl naphthalene sulfonic acid, diisobutyl naphthalene sulfonic acid.
Among these, a monovalent acid having a substituent having 4 or more carbon atoms, which is a fatty acid, is preferable, caprylic acid, lauric acid, stearic acid, and oleic acid are more preferable, and oleic acid is particularly preferable.
In the organic acid satisfying the requirements (1) to (3), the number of molecules of the monovalent acid having a substituent having 4 or more carbon atoms is preferably 0 to 4, and preferably 0 to 3. More preferred is 0-2.

  In the organic acid satisfying the requirements (1) to (3), the total number of molecules of the polyhydric alcohol and the polycarboxylic acid forming the compound is 3 or more, preferably 3 to 30. More preferably, it is ~ 20.

In the organic acid satisfying the above requirements (1) to (3), the ratio of the polyvalent carboxylic acid, the polyhydric alcohol, and the monovalent acid having a substituent having 4 or more carbon atoms is not particularly limited. Two or more unsubstituted hydroxyl groups may remain, or an unsubstituted hydroxyl group may remain.
The organic acid that satisfies the requirements (1) to (3) has at least one unsubstituted carboxyl group derived from a polyvalent carboxylic acid, and has 1 to 40 unsubstituted carboxyl groups derived from the polyvalent carboxylic acid. It is preferable to have 1-30.

  The organic acid satisfying the requirements (1) to (3) may be used alone or as a mixture. In addition, the organic acid satisfying the requirements (1) to (3) may be ionized depending on the case, and may form a salt with any metal ion depending on the case.

Examples of preferred organic acid compounds that satisfy the requirements (1) to (3) used in the present invention are shown below.
Organic acids (partial condensates of organic acids) having the following composition are preferred.

The addition amount of the organic acid satisfying the requirements (1) to (3) contained in the film of the present invention is 0.01% by mass to 20% by mass with respect to the resin, and 0.05% by mass. It is particularly preferably 10% by mass to 10% by mass, and particularly preferably 0.1% by mass to 5% by mass. In addition, when the organic acid which satisfy | fills the requirements of said (1)-(3) is a mixture as for the addition amount of the organic acid which satisfy | fills the requirements of said (1)-(3), all said (1)-( It means the total amount of organic acid that satisfies the requirement 3).
When the addition amount is 0.001% or more, the polarizer durability improving effect and the peelability improving effect are sufficient. An addition amount of 20% by mass or less is preferable because the organic acid hardly bleeds out at a high temperature and high humidity, and the orthogonal transmittance of the polarizing plate hardly increases.

  In addition, even if the addition amount is 0.01% or less, the releasability can be achieved even with an addition amount of about 0.001 to 0.01% by combining with a peelability improving technique such as cooling of the peeling part of the casting support. Improvement can be expected.

(Additive)
In the film of the present invention, as an additive, in addition to an organic acid that is a peeling accelerator, an Rth control agent (including a non-phosphate ester compound); inorganic fine particles (matting agent); phthalate ester, phosphorus Additives such as plasticizers such as acid ester compounds; Re developing agents; ultraviolet absorbers; antioxidants can also be added.

(A) Rth Control Agent The production method of the present invention preferably includes a retardation Rth control agent in the film thickness direction in the dope from the viewpoint of controlling the Rth expression of the film to 80 nm or more.
As the Rth control agent, an Rth control agent that is a non-phosphate ester compound can be used.

  The high molecular weight additive is preferably a phosphate ester compound or a non-phosphate ester polyester compound from the viewpoint of reducing haze.

The film of the present invention preferably contains an Rth control agent which is the non-phosphate ester compound. By including such a non-phosphate ester compound, the film of the present invention has an effect that it is difficult to whiten.
In the present specification, the “non-phosphate ester compound” refers to a “compound having an ester bond and the acid contributing to the ester bond other than phosphoric acid”. That is, the “non-phosphate ester compound” means a compound that does not contain phosphoric acid and is an ester compound.
Further, the non-phosphate ester compound may be a low molecular compound or a polymer (polymer compound). Hereinafter, a non-phosphate ester compound which is a polymer (polymer compound) is also referred to as a non-phosphate ester polymer.

  As the Rth control agent, which is a non-phosphate ester compound, known high molecular weight additives and low molecular weight additives can be widely employed as additives for cellulose acylate films.

The high molecular weight additive used as the Rth control agent, which is a non-phosphate ester compound, has a repeating unit in the compound, and preferably has a number average molecular weight of 700 to 10,000. The high molecular weight additive has a function of increasing the volatilization rate of the solvent and a function of reducing the residual solvent amount in the solution casting method. Furthermore, it exhibits useful effects from the viewpoint of film modification such as improvement in mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability.
In addition, about the Rth control agent which is the said high molecular weight additive, the high molecular weight additive of Unexamined-Japanese-Patent No. 2009-263619 can be used preferably.

Here, the number average molecular weight of the high molecular weight additive which is the non-phosphate ester compound is more preferably a number average molecular weight of 700 to 8000, still more preferably a number average molecular weight of 700 to 5000, and particularly preferably. The number average molecular weight is 1000 to 5000.
Hereinafter, the high molecular weight additive which is the non-phosphate ester compound will be described in detail with specific examples, but the high molecular weight additive which is the non-phosphate ester compound is limited to these. It goes without saying that it is not done.

  Examples of the polymer additive that is a non-phosphate ester compound include polyester polymers (aliphatic polyester polymers, aromatic polyester polymers, etc.), copolymers of polyester components and other components, and the like. , Aliphatic polyester polymer, aromatic polyester polymer, polyester polymer (aliphatic polyester polymer, aromatic polyester polymer, etc.) and acrylic polymer and polyester polymer (aliphatic polyester polymer, aromatic A copolymer of an aromatic polyester polymer or the like) and a styrene polymer is preferable, and a polyester compound containing an aromatic ring as at least one of the copolymer components is more preferable.

  Examples of the aliphatic polyester-based polymer include at least one diol selected from aliphatic dicarboxylic acids having 2 to 20 carbon atoms, aliphatic diols having 2 to 12 carbon atoms, and alkyl ether diols having 4 to 20 carbon atoms. The both ends of the reaction product may be left as the reaction product, or the monocarboxylic acid, monoalcohol or phenol may be further reacted to carry out so-called end-capping. Good. It is effective in terms of storage stability that the end capping is performed in particular so as not to contain free carboxylic acids. The dicarboxylic acid used in the polyester polymer in the present invention is preferably an aliphatic dicarboxylic acid residue having 4 to 20 carbon atoms or an aromatic dicarboxylic acid residue having 8 to 20 carbon atoms.

  Examples of the aliphatic dicarboxylic acid having 2 to 20 carbon atoms preferably used in the present invention include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and azelaic acid. , Sebacic acid, dodecanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid.

  Among these, preferable aliphatic dicarboxylic acids are malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, and 1,4-cyclohexanedicarboxylic acid. Particularly preferably, the aliphatic dicarboxylic acid component is succinic acid, glutaric acid, or adipic acid.

  The diol utilized for the high molecular weight additive is selected from, for example, an aliphatic diol having 2 to 20 carbon atoms and an alkyl ether diol having 4 to 20 carbon atoms.

  Examples of the aliphatic diol having 2 to 20 carbon atoms include alkyl diols and alicyclic diols, such as ethane diol, 1,2-propanediol, 1,3-propanediol, and 1,2-butane. Diol, 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-1,3-propanediol (3,3-dimethylolheptane), 3 -Methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl 1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. Used as a mixture of two or more.

  Preferred aliphatic diols include ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1 , 4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, particularly preferred Is ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6- Hexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol.

  Preferred examples of the alkyl ether diol having 4 to 20 carbon atoms include polytetramethylene ether glycol, polyethylene ether glycol and polypropylene ether glycol, and combinations thereof. The average degree of polymerization is not particularly limited, but is preferably 2 to 20, more preferably 2 to 10, further 2 to 5, and particularly preferably 2 to 4. As examples of these, commercially useful polyether glycols typically include Carbowax, Pluronics and Niax resins.

In the present invention, a high molecular weight additive whose end is sealed with an alkyl group or an aromatic group is particularly preferable. This is because the terminal is protected with a hydrophobic functional group, which is effective against deterioration with time at high temperature and high humidity, and is due to the role of delaying hydrolysis of the ester group.
It is preferable to protect with a monoalcohol residue or a monocarboxylic acid residue so that both ends of the polyester additive are not carboxylic acid or OH group.
In this case, the monoalcohol is preferably a substituted or unsubstituted monoalcohol having 1 to 30 carbon atoms, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol. , Octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, aliphatic alcohol such as dodecaoctanol, allyl alcohol, oleyl alcohol, benzyl alcohol, 3-phenyl Examples thereof include substituted alcohols such as propanol.

  End-capping alcohols that can be preferably used are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol, isooctanol, 2-ethylhexyl alcohol, isononyl alcohol, oleyl alcohol Benzyl alcohol, in particular methanol, ethanol, propanol, isobutanol, cyclohexyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol, benzyl alcohol.

  Moreover, when sealing with a monocarboxylic acid residue, the monocarboxylic acid used as a monocarboxylic acid residue is preferably a substituted or unsubstituted monocarboxylic acid having 1 to 30 carbon atoms. These may be aliphatic monocarboxylic acids or aromatic ring-containing carboxylic acids. Preferred aliphatic monocarboxylic acids are described, for example, acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid, and examples of the aromatic ring-containing monocarboxylic acid include Benzoic acid, p-tert-butylbenzoic acid, p-tert-amylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc. Yes, these can be used alone or in combination of two or more.

  The synthesis of the high molecular weight additive may be a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the aliphatic dicarboxylic acid and a diol and / or a monocarboxylic acid or monoalcohol for end-capping by a conventional method. Alternatively, it can be easily synthesized by any of the interfacial condensation methods of acid chlorides of these acids and glycols. These polyester-based additives are described in detail in Koichi Murai, “Additives, Theory and Application” (Kokaibo Co., Ltd., first edition published on March 1, 1973). In addition, Japanese Patent Laid-Open Nos. 05-155809, 05-155810, Japanese Patent Laid-Open Nos. 05-97073, 2006-259494, 07-330670, 2006-342227, 2007-003679. The materials described in each publication can also be used.

The aromatic polyester polymer is obtained by copolymerizing a monomer having an aromatic ring with the polyester polymer. The monomer having an aromatic ring is at least one monomer selected from aromatic dicarboxylic acids having 8 to 20 carbon atoms and aromatic diols having 6 to 20 carbon atoms.
Examples of the aromatic dicarboxylic acid having 8 to 20 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,8- There are naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid. Among these, preferable aromatic dicarboxylic acids are phthalic acid, terephthalic acid, and isophthalic acid.

  Examples of the aromatic diol having 6 to 20 carbon atoms include, but are not limited to, bisphenol A, 1,2-hydroxybenzene, 1,3-hydroxybenzene, 1,4-hydroxybenzene, and 1,4-benzenedimethanol. Bisphenol A, 1,4-hydroxybenzene and 1,4-benzenedimethanol are preferred.

  The aromatic polyester polymer is used in combination with at least one kind of aromatic dicarboxylic acid or aromatic diol with the above-mentioned polyester, but the combination is not particularly limited, and several kinds of respective components are combined. There is no problem. In the present invention, as described above, a high molecular weight additive whose end is sealed with an alkyl group or an aromatic group is particularly preferable, and the above-described method can be used for sealing.

  As Rth control agents other than the non-phosphate ester compounds, for example, phosphate ester compounds and compounds other than ester esters known as additives for cellulose acylate films can be widely employed.

  The polymer Rth reducing agent is selected from phosphoric acid polyester polymers, styrene polymers, acrylic polymers, and copolymers thereof, and acrylic polymers and styrene polymers are preferred. Moreover, it is preferable that at least one polymer having negative intrinsic birefringence, such as a styrene polymer and an acrylic polymer, is included.

  Examples of the low molecular weight Rth reducing agent that is a compound other than the non-phosphate ester-based compound include the following. These may be solid or oily. That is, the melting point and boiling point are not particularly limited. For example, mixing of an ultraviolet absorbing material at 20 ° C. or lower and 20 ° C. or higher, and a mixture of deterioration preventing agents are also possible. Furthermore, infrared absorbing dyes are described, for example, in JP-A No. 2001-194522. Moreover, the addition time may be added at any time in the cellulose acetate solution (dope) preparation step, but may be added by adding an additive to the final preparation step of the dope preparation step. Furthermore, the amount of each material added is not particularly limited as long as the function is manifested.

  Although it does not specifically limit as a low molecular weight Rth reducing agent which is compounds other than a non-phosphate ester type | system | group, The detail is described in Unexamined-Japanese-Patent No. 2007-272177 [0066]-[0085].

The compound described as the general formula (1) in [0066] to [0085] of JP-A-2007-272177 can be prepared by the following method.
The compound of the general formula (1) of the publication can be obtained by a condensation reaction between a sulfonyl chloride derivative and an amine derivative.

  JP, 2007-272177, A The compound of general formula (2) is a dehydration condensation reaction of carboxylic acids and amines using a condensing agent (for example, dicyclohexylcarbodiimide (DCC) etc.), or a carboxylic acid chloride derivative, It can be obtained by a substitution reaction with an amine derivative.

  Examples of the Rth reducing agent include acrylic polymers and styrene polymers, and low molecular compounds represented by general formulas (3) to (7) of JP-A-2007-272177. Among them, acrylic polymers and styrene polymers. Are preferred, and acrylic polymers are more preferred.

The Rth control agent is preferably added at a ratio of 0.01 to 30% by mass with respect to cellulose acetate.
By making the said addition amount 30 mass% or less, compatibility with a cellulose resin can be improved and whitening can be suppressed. When two or more types of Rth control agents are used, the total amount is preferably within the above range.

  From the viewpoint of further reducing the haze of the resulting film, the Rth control agent is more preferably added at a rate of 10 to 30% by mass relative to cellulose acetate, and may be added at a rate of 15 to 30% by mass. Particularly preferred.

(B) Inorganic fine particles The film of the present invention preferably contains inorganic fine particles in at least one outermost layer.

It is preferable to add inorganic fine particles (mat agent) to the film of the present invention. Examples of inorganic fine particles used in the present invention include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Mention may be made of magnesium silicate and calcium phosphate. Inorganic fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable. The silicon dioxide fine particles preferably have a primary average particle size of 20 nm or less and an apparent specific gravity of 70 g / liter or more. A primary particle having an average diameter of 5 to 30 nm is more preferable from the viewpoint of controlling the total haze of the film within the range of the present invention. The apparent specific gravity is preferably 10 to 100 g / liter or more, and more preferably 30 to 80 g / liter or more.
When the film of the present invention has a laminated structure of two layers, the inorganic fine particles are contained in at least one outermost layer. Moreover, when the film of this invention is a laminated structure of 3 or more layers, it is preferable that the said inorganic fine particle is contained in both the said surface layers.

  These fine particles usually form secondary particles having an average particle diameter of 0.1 to 3.0 μm, and these fine particles are present as aggregates of primary particles in the film, and 0.1 to 0.1 μm on the film surface. An unevenness of 3.0 μm is formed. The secondary average particle diameter is preferably 0.2 μm to 1.5 μm, more preferably 0.4 μm to 1.2 μm, and most preferably 0.6 μm to 1.1 μm. The primary and secondary particle diameters were determined by observing the particles in the film with a scanning electron microscope and determining the diameter of a circle circumscribing the particles as the particle size. In addition, 200 particles were observed at different locations, and the average value was taken as the average particle size.

As fine particles of silicon dioxide, for example, commercially available products such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (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.
Among these, Aerosil R972 is particularly preferable from the viewpoint of cohesiveness when preparing an inorganic fine particle dispersion.

  In order to obtain a film having particles having a small secondary average particle size in the present invention, several methods are conceivable when preparing a dispersion of fine particles. For example, there is a method in which a fine particle dispersion prepared by stirring and mixing a solvent and fine particles is prepared in advance, and this fine particle dispersion is added to a small amount of a separately prepared cellulose acetate solution, stirred and dissolved, and further mixed with the main cellulose acetate dope solution. . This method is a preferable preparation method in that the dispersibility of the silicon dioxide fine particles is good and the silicon dioxide fine particles are more difficult to reaggregate. In addition, after adding a small amount of cellulose ester to the solvent and dissolving with stirring, add the fine particles to this and disperse with a disperser. There is also a method of mixing. The present invention is not limited to these methods, but the concentration of silicon dioxide when the silicon dioxide fine particles are mixed and dispersed with a solvent or the like is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and 15 to 20%. Mass% is most preferred. A higher dispersion concentration is preferable because the liquid turbidity with respect to the added amount is lowered, and haze and aggregates are improved.

  The solvent used is preferably lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like. Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film forming of a cellulose ester.

(C) Plasticizer As the plasticizer used in the present invention, many compounds known as a plasticizer for cellulose acylate can also be used effectively. As the plasticizer, phosphate ester compounds or carboxylic acid esters are used. Examples of the phosphate ester-based compound include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethyl hexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.

(D) Re enhancer The film of the present invention can develop a retardation in a desired in-plane direction even if it does not contain a Re enhancer, but further contains a Re enhancer. Also good. By adopting a Re enhancer, high Re developability can be obtained at a low draw ratio. The type of Re enhancer is not particularly defined, and examples thereof include those composed of rod-like or discotic compounds, and compounds exhibiting Re developability among the non-phosphate ester compounds. As the rod-like or discotic compound, a compound having at least two aromatic rings can be preferably used as the Re enhancer.
Two or more types of Re enhancers may be used in combination.
The Re enhancer preferably has maximum absorption in the wavelength region of 250 to 400 nm, and preferably has substantially no absorption in the visible region.

As the Re enhancer, for example, compounds described in JP-A-2004-50516 and JP-A-2007-86748 can be used, but the present invention is not limited thereto.
Examples of the discotic compound include a compound described in European Patent Application No. 0911656A2, a triazine compound described in Japanese Patent Application Laid-Open No. 2003-344655, and Japanese Patent Application Laid-Open No. 2008-150592 [0097] to [0108]. The triphenylene compound to be used can also be preferably used.

  The discotic compound can be synthesized by a known method such as a method described in JP-A No. 2003-344655 and a method described in JP-A No. 2005-134484.

  In addition to the aforementioned discotic compound, a rod-shaped compound having a linear molecular structure can also be preferably used. For example, the rod-shaped compounds described in JP 2008-150592 A [0110] to [0127] are preferably used. it can.

Two or more rod-shaped compounds having a maximum absorption wavelength (λmax) longer than 250 nm in the ultraviolet absorption spectrum of the solution may be used in combination.
The rod-like compound can be synthesized with reference to methods described in literature. References include Mol. Cryst. Liq. Cryst., 53, 229 (1979), 89, 93 (1982), 145, 111 (1987), 170, 43. Page (1989), J. Am. Chem. Soc., 113, 1349 (1991), 118, 5346 (1996), 92, 1582 (1970), J. Org. Chem., 40, 420 (1975), Tetrahedron, 48, 16, 3437 (1992).

The Re enhancer is more preferably added at a rate of 0.2 to 10% by mass, more preferably 0.5 to 5% by mass, more preferably 1 to 4% by mass with respect to cellulose acetate. It is particularly preferable to add at a ratio of
Furthermore, the Re enhancer is preferably used in combination with the Rth control agent from the viewpoint of producing a cellulose acetate film having a low haze while controlling Re and Rth within a preferable range.

(Manufacture of dope)
In the production method of the present invention, the dope can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. The dope can be prepared by stirring cellulose acetate and a solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, cellulose acetate and a solvent are put in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 110 ° C.

  Each component may be roughly mixed in advance and then placed in a container (tank or the like). Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.

When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. It is preferable to dissolve each component in a solvent in the container. The prepared dope is preferably taken out of the container after cooling, or after taking out, it is preferably cooled using a heat exchanger or the like.

The dope can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved in a solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acetate with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method.
In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent with stirring at room temperature. The amount of cellulose acetate is preferably adjusted so as to be contained in the mixture in an amount of 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass.
The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acetate and organic solvent solidifies.

The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling to the final cooling temperature.
Further, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acetate is dissolved in the organic solvent. The temperature may be increased by simply leaving it at room temperature or in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is the value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. is there.

A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution by visual observation.
In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
In addition, according to differential scanning calorimetry (DSC), a 20% by mass solution of cellulose acetate (total acetyl substitution degree: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by the cooling dissolution method is There is a quasi-phase transition point between a sol state and a gel state in the vicinity of 33 ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the total acetyl substitution degree, viscosity average polymerization degree, solution concentration, and organic solvent used in cellulose acetate.

  In the present invention, preferably, cellulose acetate is dried in advance by a silo and then mixed with the solvent to prepare a dope. More preferably, the additive to be added to the dope is also dried in advance with a silo and then mixed with the solvent or cellulose acetate to prepare the dope.

<Film forming process and peeling process>
In the production method of the present invention, a cellulose acetate having a total substitution degree of 2.0 to 2.7, a solvent, and 0.01 mass% to 20 mass% of the following (1) on the metal support. ) To (3) a solution containing an organic acid and a step of casting a dope film to form a dope film (hereinafter also referred to as a film forming process), and a step of peeling the dope film from the support ( Hereinafter, it is also referred to as a peeling step). That is, in the present invention, a cellulose acylate film can be produced from the prepared dope by a solvent cast method.
Furthermore, it is preferable that the manufacturing method of this invention is a strip | belt-shaped support body to which the said metal support body moves.
Further, in the manufacturing method of the present invention, it is preferable to control the residual solvent amount when the dope film is peeled off to 100% or less, and in the region where the dope film of the support is peeled off, the dope film of the support body It is also preferable to bring a cooling body having a surface temperature of 10 ° C. or less into contact with the surface opposite to the peeling side.
Hereinafter, a preferable aspect is demonstrated about the said film forming process and the said peeling process in the manufacturing method of this invention.

The equipment used in the film-forming step in the method for producing the cellulose acetate film of the present invention having a low acyl substitution degree is the same as the solution casting film-forming method and solution casting film-forming apparatus used for the conventional cellulose triacetate film production. Is used. In the production method of the present invention, for example, a production apparatus described in JP-A No. 2004-359379 can be preferably used.
As for casting in the solvent casting method and the drying method described later, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-115035.
Further, JP-A Nos. 2000-301555, 2000-301558, 7-032391, JP-A 3-193316, JP-A-5-086212, JP-A-62-237113, JP-A-2-276607. The cellulose acylate film forming techniques described in JP-A-55-014201, JP-A-2-111511, and JP-A-2-208650 can be applied in the present invention.
Hereinafter, more specifically, a preferable aspect is demonstrated about the said film forming process and the said peeling process.

It is preferable that the dope (cellulose acetate solution) prepared from the dissolving machine (kettle) is temporarily stored in a storage kettle, and the foam contained in the dope is defoamed for final preparation.
In the production method of the present invention, the prepared dope is preferably cast on a moving belt-like support. The prepared dope is preferably sent from the dope discharge port to a pressure die through a pressure metering gear pump that can be metered with high accuracy by, for example, the number of rotations, and is cast on the moving belt-like support. .
The moving belt-like support is not particularly limited, but is preferably in the form of a band or a belt, and more preferably an endless band or belt. By using such an endless support, the dope can be moved endlessly. Further, the belt-like support may be moved in any manner, but is particularly preferably an endless belt that is stretched between two or more rolls (drums).
Further, the material of the belt-like support is not particularly limited except that it is made of metal, but is preferably made of SUS (for example, SUS 316).
The specific heat of the belt-like support is preferably 0.1 to 1.0 J / (m ³ · K).
The width of the belt-like support is preferably 1 to 3 m, more preferably 1.5 to 3 m, and particularly preferably about 2 m. In addition, about 2 m here means a range of 2 m ± 30 cm.
The length of the belt-like support (so-called band length) is preferably 80 to 100 m.
The surface roughness (Ra value) of the belt-like support is preferably 0.01 μm or less. The surface of the belt-like support is preferably finished in a mirror state. The mirror finish means that the surface of the band is smoothed by repeating polishing. Furthermore, it is more preferable that the surface of the band is finished to a so-called super mirror surface having higher thickness accuracy in the width direction.
The thickness of the belt-like support is preferably 1.5 to 2 mm.
The strip-shaped support has a surface opposite to the peeling side in contact with the cooling body in the dope film peeling region. The shape of the cooling body is not particularly limited, and may be a cooling plate or a cooling curved surface body. Among them, a cylindrical cooling body is preferable. Furthermore, it is preferable that the cooling body is a drive roll or a driven roll, and the belt-like support body is wound around any one of these rolls. The diameter of the roll is preferably 2 to 3 m. Further, when there are a plurality of the rolls, it is preferable that at least one of the rolls is a drive roll that can positively rotate the belt-like support by a motor. In addition, the roll around which the other band-shaped support body is wound may be a drive roll or a driven roll that rotates around the drive roll.
It is preferable that the moving speed of the belt-like support driven by the drive roll is 15 to 80 m / s.

In the production method of the present invention, after the dope is uniformly cast on the metal support (preferably a belt-like support), the dope film is formed on the metal while controlling to a specific condition. It is preferable to peel off from the support. In the production method of the present invention, the region where the dope is peeled off (hereinafter also referred to as a peeling point) is not particularly limited, but the residual solvent amount when peeling off the dope film is controlled to 100% or less, and In the region where the dope film is peeled off from the metal support, it is preferable that a cooling body having a surface temperature of 10 ° C. or less is brought into contact with the surface opposite to the dope film peeling side of the metal support. Thus, after evaporating the solvent on the metal support (preferably a belt-shaped support), the dope film (also referred to as a web) to be dried is preferably the metal support (the belt-shaped support). Is preferable from the viewpoint of improving the peelability.
As a specific aspect, when the belt-like support is an endless belt, it is preferable that the point of travel is a little less than one turn as the peeling point.

As a method for controlling the amount of residual solvent when the dope film is peeled off to 100% or less, for example, there is a description in Japanese Patent Publication No. 5-17844, and the dope is cast on the belt-like support. The method of drying for 2 seconds or more from the wind can be mentioned. Moreover, the method etc. which make the surface temperature of the said strip | belt-shaped support body 10 to 40 degreeC in the area | region which controls the amount of residual solvents until it reaches the peeling point vicinity are mentioned.
The residual solvent amount can be expressed by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the web of which M is measured is dried at 110 ° C. for 3 hours.
The amount of residual solvent when the dope film is peeled off is more preferably controlled to 50% by mass or less, particularly preferably 45% by mass or less, and particularly preferably less than 45% by mass. The amount of residual solvent when the dope film is peeled off is preferably 30% by mass or more from the viewpoint of more expressing Rth of the film.

In the production method of the present invention, in a region where the dope film is peeled off from the metal support, it is preferable to contact a cooling body having a surface temperature of 10 ° C. or less on the surface opposite to the dope film peeling side of the metal support. . It is preferable that the cooling body also serves as a roll capable of rotating the moving belt-like support. As a method for controlling the surface temperature of the cooling body, for example, the surface temperature is 10 ° C. or less (upper limit is preferably 5 ° C. or less, more preferably 0 ° C. or less, particularly preferably 10 ° C. or less). Preferably, it can be set to −5 ° C. or lower. The surface temperature of the roll closest to the stripping region is more preferably -25 ° C to 5 ° C, particularly preferably -25 ° C to 0 ° C, and preferably -20 ° C to -5 ° C. More particularly preferred.
By controlling the surface temperature of the cooling body within such a temperature range and controlling the residual solvent amount of the dope within the range, the dope can be gelled at the surface temperature of the belt-like support during casting. In addition, the releasability of the cellulose acetate web having a low acyl substitution degree can be remarkably improved.

  On the other hand, in the region where the dope film is peeled off from the metal support, the surface temperature of the metal support on the side of the dope film peeling side is not necessarily 10 ° C. or less, but preferably 10 ° C. or less. The more preferable range is the same as the preferable range of the surface temperature of the cooling body.

  The solid content concentration contained in the dope to be cast is preferably controlled to 15% to 25% from the viewpoint of the film surface after drying, more preferably 16% to 23%, and more preferably 17% to 23%. It is particularly preferable to control to 22%.

An embodiment of the band casting apparatus preferably used in the production method of the present invention is shown in FIG.
FIG. 1 shows an example of a continuous cellulose acetate film production machine using a single metal endless belt 101 that has been subjected to ultra-mirror finishing with high thickness accuracy in the belt width direction. In this continuous film production machine, for example, the metal endless belt 101 is made of stainless steel, the thickness is about 1.5 mm, the belt width is about 3 m, the belt speed is 2 to 100 m / min, and the product thickness is 10 μm or less. It is preferable that Depending on the apparatus, it can be applied to thicker films and sheets. The metal endless belt 101 is stretched over a driven roll 102 on the product transfer side and a drive roll 103 on the raw material resin supply side, and can be actively rotated by the drive roll 103.

  In the illustrated continuous film production machine, cellulose acetate dope is supplied in a fixed amount from a high-precision gear pump 104 to the upper surface of the belt on the drive roll 103 side, and is extruded with a required width via a specially designed T-die 105. While being transported on the belt 101 to the driven roll side, the residual solvent amount control device 108 performs three stages of heating. After that, it passes through the belt turning portion on the driven roll 102 side and is transferred to the driving roll 103 side while being carried on the lower surface of the belt 101 as the endless belt 101 rotates, and the dope film is peeled off in the peeling region 107. It is peeled from the endless belt 101, and is wound around a winding unit (not shown) via a take-up roll group 106 arranged on the outside of the drive roll 103 from the endless belt 101. Here, the driving roll 103 is provided with a cooling device 109, and the surface temperature of the driving roll 103, that is, the cooling body is controlled in a specific range in the peeling area 107. In addition, it is more preferable that the operating part of the belt meandering prevention device 110 is arranged on the driven roll 102 side.

<Drying process>
A method for drying a web that has been dried and peeled on the belt-like support will be described. The web peeled at the peeling position immediately before the belt-shaped support makes one round is conveyed alternately through a group of rolls arranged in a staggered manner, or both ends of the peeled web are gripped by clips or the like Then, it is transported by a non-contact transport method or the like. Drying is performed by a method of applying wind at a predetermined temperature to both sides of the web (film) being conveyed or a method using a heating means such as a microwave. Since rapid drying may impair the flatness of the film to be formed, it is preferable to dry at a temperature at which the solvent does not foam in the initial stage of drying, and to dry at a high temperature after the drying proceeds. In the drying process after peeling from the support, the film tends to shrink in the longitudinal direction or the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point, for example, as shown in Japanese Patent Laid-Open No. 62-46625, a method in which all or part of the drying process is performed while holding the width at both ends of the web with clips or pins in the width direction. (Tenter method) is preferable. It is preferable that the drying temperature in the said drying process is 100-145 degreeC. Although the drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, it may be appropriately selected according to the type and combination of the solvents used. It is also possible to evaporate the residual solvent by drying with high-temperature air with different temperatures.

<Extension process>
The production method of the present invention preferably includes a step of stretching the web (film) peeled from the metal support at a temperature satisfying the following formula (1) from the viewpoint of achieving both optical expression and suppression of film whitening. .
160-Numerical value when the amount of residual solvent is expressed in mass% ≤ Stretching temperature (° C) ≤ 190-Numerical value when the amount of residual solvent is expressed in mass% (1)
The residual solvent amount can be expressed by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the web of which M is measured is dried at 110 ° C. for 3 hours. If the amount of residual solvent in the web is too large, the effect of stretching cannot be obtained, and if it is too small, stretching becomes extremely difficult and the web may break. The more preferable range of the residual solvent amount in the web is 10% by mass to 50% by mass, and most preferably 12% by mass to 30% by mass. Further, if the stretching ratio is too small, a sufficient phase difference cannot be obtained, and if it is too large, stretching may become difficult and breakage may occur.
In the present invention, a solution cast film-formed web can be stretched without being heated to a high temperature as long as the residual solvent amount is in a specific range. However, if drying and stretching are combined, it is preferable because the process can be shortened. . However, since the plasticizer volatilizes when the temperature of the web is too high, a range of room temperature (15 ° C) to 145 ° C or less is preferable. Further, stretching in the biaxial directions perpendicular to each other is an effective method for bringing the refractive indexes Nx, Ny, and Nz of the film within the scope of the present invention. For example, when stretching in the casting direction, if the shrinkage in the width direction is too large, the value of Nz becomes too large. In this case, it can be improved by suppressing the width shrinkage of the film or stretching in the width direction. When stretching in the width direction, the refractive index may be distributed with a width. This is sometimes seen when using, for example, the tenter method, but it is a phenomenon that occurs when the film is stretched in the width direction and contraction force is generated at the center of the film and the end is fixed. It is thought to be called the bowing phenomenon. Even in this case, by stretching in the casting direction, it is possible to suppress the bowing phenomenon and to improve the distribution of the width retardation. Furthermore, the film thickness fluctuation | variation of the film obtained by extending | stretching to the biaxial direction orthogonal to each other can be reduced. If the film thickness variation of the optical film is too large, the retardation will be uneven. 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 ratios in the biaxial directions orthogonal to each other are 1.2 to 2.0 times and 0.7 to 1.0, respectively. It is preferable that the range be doubled. Here, stretching to 1.2 to 2.0 times in one direction and making the other orthogonal to 0.7 to 1.0 times is the distance between clips and pins supporting the film. Is in the range of 0.7 to 1.0 times the interval before stretching.

In general, when a biaxial stretching tenter is used to stretch in the width direction so as to have an interval of 1.2 to 2.0 times, a contracting force acts in the longitudinal direction, which is the perpendicular direction.
Therefore, if the force is applied in only one direction and the stretching is continued, the width in the perpendicular direction is reduced, but this means that the amount of shrinkage is suppressed with respect to the amount that shrinks without restricting the width. This means that the interval between the clip or pin whose width is restricted is restricted to a range of 0.7 to 1.0 times that before stretching. At this time, in the longitudinal direction, a force is exerted to shrink the film by stretching in the width direction. By taking the interval between the clips or pins in the longitudinal direction, an excessive tension is not applied in the longitudinal direction. There is no particular limitation on the method of stretching the web. For example, a method in which a difference in peripheral speed is applied to a plurality of rolls, and the roll peripheral speed difference is used to stretch in the longitudinal direction, the both ends of the web are fixed with clips and pins, and the interval between the clips and pins is increased in the traveling direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by a linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.
The film stretch ratio (sometimes referred to as stretch ratio) in the stretching step is preferably 1.2 to 2.0 times, and more preferably 1.3 to 1.5 times.

  Even when the film containing the residual solvent is stretched by setting the stretching temperature defined by the above formula (1), the dimensional change rate when the obtained film is aged in a moist heat environment is remarkable. Can be improved. Although not bound by any theory, it is a case where a film containing a residual solvent is stretched by correcting the stretching temperature by the above formula (1) in consideration of the influence of the residual solvent. Surprisingly, however, the dimensional change rate is significantly improved.

  Examples of the method of stretching in the direction perpendicular to the film conveying direction include, for example, JP-A-62-115035, JP-A-4-152125, JP-A-4284221, JP-A-4-298310, and JP-A-11-48271. It is described in the publication. In the case of stretching in the film transport direction (longitudinal direction), for example, the film is stretched by adjusting the speed of the film transport roll to make the film winding speed faster than the film stripping speed. In the case of stretching in the direction perpendicular to the film transport direction, the film can also be stretched by transporting the film while holding the film with a tenter and gradually widening the tenter. After the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine).

  When using an optical film as a protective film for a polarizer, the transmission axis of the polarizer and the slow axis in the plane of the optical film are placed in parallel to suppress light leakage when the polarizing plate is viewed from an oblique direction. There is a need to. Since the transmission axis of the roll film-shaped polarizer produced continuously is generally parallel to the width direction of the roll film, the protective film comprising the roll film-shaped polarizer and the roll film-shaped optical film. In order to continuously bond the film, the in-plane slow axis of the roll film-like protective film needs to be parallel to the width direction of the film. Therefore, it is preferable to stretch more in the width direction. In addition, the stretching treatment may be performed during the film forming process, or the raw film that has been formed and wound may be stretched, but in the production method of the present invention, the stretching is performed in a state containing a residual solvent. In order to carry out, it is preferable to extend | stretch in the middle of a film forming process.

<Heat treatment process>
The film production method of the present invention is preferably provided with a heat treatment step after the drying step. The heat treatment in the heat treatment step may be performed after completion of the drying step, and may be performed immediately after the stretching / drying step, or may be separately provided only after the winding process is performed by a method described later after the completion of the drying step. . In the present invention, it is preferable to provide the heat treatment step again after the drying step is once cooled to room temperature to 100 ° C. or less. This is because a film having better thermal dimensional stability can be obtained. For the same reason, it is preferable that the amount of residual solvent is dried to less than 2% by mass, preferably less than 0.4% by mass immediately before the heat treatment step.
Although the reason why the shrinkage rate of the film can be reduced by such treatment is not clear, in the film that has undergone the treatment to be stretched in the stretching process, the residual stress in the stretching direction is large, so the residual stress is eliminated by heat treatment. Thus, it is presumed that the shrinkage force in the region below the heat treatment temperature is reduced.

The heat treatment is performed by a method of applying a wind at a predetermined temperature to the film being conveyed or a method using a heating means such as a microwave.
The heat treatment is preferably performed at a temperature of 150 to 200 ° C., more preferably 160 to 180 ° C. The heat treatment is preferably performed for 1 to 20 minutes, more preferably 5 to 10 minutes.
When the heat treatment temperature exceeds 200 ° C. for a long time, it may cause a problem because the amount of the plasticizer scattered in the film increases.
In the heat treatment step, the film tends to shrink in the longitudinal direction or the width direction. It is preferable to heat-treat while suppressing the shrinkage as much as possible in order to improve the flatness of the finished film, and a method in which the width ends of the web are held with clips or pins in the width direction (tenter method). Is preferred. Furthermore, it is preferable to extend | stretch 0.9 to 1.5 times in the width direction and conveyance direction of a film, respectively.

<Winding process>
Further, it is preferable that both ends of the obtained web are sandwiched between clips, transported by a tenter and dried, then transported by a roll group of a drying device, dried, and wound up to a predetermined length by a winder. The combination of the tenter and the roll group drying apparatus can be changed depending on the purpose.

  As a winder for winding the obtained film, a commonly used winder can be used, such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, etc. It can be wound up by the winding method. In the optical film roll obtained as described above, the slow axis direction of the film is preferably ± 2 ° with respect to the winding direction (longitudinal direction of the film), and further within the range of ± 1 °. Preferably there is. Alternatively, it is preferably ± 2 degrees with respect to the direction perpendicular to the winding direction (film width direction), and more preferably within a range of ± 1 degree. In particular, the slow axis direction of the film is preferably within ± 0.1 degrees with respect to the winding direction (longitudinal direction of the film). Alternatively, it is preferably within ± 0.1 degrees with respect to the width direction of the film.

  The film thickness may be adjusted by adjusting the solid content concentration contained in the dope, the slit gap of the die base, the extrusion pressure from the die, the metal support speed, and the like so as to obtain a desired thickness.

  The length of the optical film obtained as described above is preferably wound at 100 to 10,000 m per roll, more preferably 500 to 7000 m, and further preferably 1000 to 6000 m. The width of the optical film is preferably 0.5 to 5.0 m, more preferably 1.0 to 3.0 m, and still more preferably 1.0 to 2.5 m. When winding, it is preferable to give knurling to at least one end, the knurling width is preferably 3 mm to 50 mm, more preferably 5 mm to 30 mm, and the height is preferably 0.5 to 500 μm, more preferably 1 to 200 μm. is there. This may be a single push or a double push.

  In general, in a large-screen display device, since the contrast reduction and coloration in an oblique direction become remarkable, the film of the present invention is particularly suitable for use in a large-screen liquid crystal display device. When used as an optical compensation film for a large-screen liquid crystal display device, for example, the film width is preferably set to 1470 mm or more. In addition, the optical compensation film of the present invention is produced not only in the form of a film piece cut into a size that can be incorporated into a liquid crystal display device as it is, but also in a long shape by continuous production, and in a roll shape. The film of the aspect wound up by this is also included. The optical compensation film of the latter mode is stored and transported in that state, and is cut into a desired size and used when actually incorporated into a liquid crystal display device or bonded to a polarizer or the like. Similarly, it is cut into a desired size when it is actually incorporated into a liquid crystal display device after being bonded to a polarizer or the like made of a polyvinyl alcohol film or the like that has been made into a long shape. Used. As one mode of the optical compensation film wound up in a roll shape, a mode in which the roll length is rolled up to 2500 m or more can be mentioned.

  In the solution casting film forming method used for the functional protective film for electronic displays, in addition to the solution casting film forming apparatus, surface processing on films such as an undercoat layer, an antistatic layer, an antihalation layer, a protective layer, etc. Therefore, a coating device is often added.

[Cellulose acetate film]
(Retardation)
The film of the present invention is produced by the method for producing a cellulose acetate film of the present invention, and has a retardation value Rth in the film thickness direction measured at a wavelength of 590 nm of 80 nm or more. Further, Rth preferably satisfies 80 nm ≦ Rth ≦ 300 nm, and more preferably satisfies 80 nm ≦ Rth ≦ 150 nm. By using such Rth, a VA retardation film with less color shift can be produced.

The film of the present invention preferably has a retardation value Re in the in-plane direction of the film measured at a wavelength of 590 nm of 30 to 100 nm.
Re is preferably 35 nm ≦ Re ≦ 80 nm, and more preferably 40 nm ≦ Re ≦ 60 nm.

In this specification, Re (λ) and Rth (λ) respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. In the present specification, the wavelength λ is 590 nm unless otherwise specified. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). In selecting the measurement wavelength λnm, the wavelength selection filter can be exchanged manually, or the measurement value can be converted by a program or the like.
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (in the absence of the slow axis, any in-plane value) The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Rth can also be calculated from the following formula (A) and formula (B) based on the value, the assumed value of the average refractive index, and the input film thickness value.

上記のＲｅ（θ）は法線方向から角度θ傾斜した方向におけるレターデーション値をあらわす。
式（Ａ）におけるｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表す。ｄは膜厚である。
式（Ｂ）：
Ｒｔｈ＝｛（ｎｘ＋ｎｙ）／２−ｎｚ｝ｘｄ
測定されるフィルムが１軸や２軸の屈折率楕円体で表現できないもの、いわゆる光学軸（ｏｐｔｉｃ ａｘｉｓ）がないフィルムの場合には、以下の方法によりＲｔｈ（λ）は算出される。
Ｒｔｈ（λ）は前記Ｒｅ（λ）を、面内の遅相軸（ＫＯＢＲＡ ２１ＡＤＨまたはＷＲにより判断される）を傾斜軸（回転軸）としてフィルム法線方向に対して−５０度から＋５０度まで１０度ステップで各々その傾斜した方向から波長λｎｍの光を入射させて１１点測定し、その測定されたレターデーション値と平均屈折率の仮定値及び入力された膜厚値を基にＫＯＢＲＡ ２１ＡＤＨまたはＷＲが算出する。
上記の測定において、平均屈折率の仮定値はポリマーハンドブック（ＪＯＨＮ ＷＩＬＥＹ＆ＳＯＮＳ, ＩＮＣ）、各種光学フィルムのカタログの値を使用することができる。平均屈折率の値が既知でないものについてはアッベ屈折計で測定することができる。主な光学フィルムの平均屈折率の値を以下に例示する：セルロースアシレート（１．４８）、シクロオレフィンポリマー（１．５２）、ポリカーボネート（１．５９）、ポリメチルメタクリレート（１．４９）、ポリスチレン（１．５９）である。これら平均屈折率の仮定値と膜厚を入力することで、ＫＯＢＲＡ ２１ＡＤＨまたはＷＲはｎｘ、ｎｙ、ｎｚを算出する。この算出されたｎｘ、ｎｙ、ｎｚよりＮｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）が更に算出される。 Formula (A):

The above Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction.
In formula (A), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny. . d is the film thickness.
Formula (B):
Rth = {(nx + ny) / 2−nz} xd
In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is the above-mentioned Re (λ), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) from −50 degrees to +50 degrees with respect to the film normal direction. The light of wavelength λ nm is incident from each inclined direction in 10 degree steps and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or WR is calculated.
In the above measurement, the assumed value of the average refractive index may be a value in a polymer handbook (John Wiley & Sons, Inc.) or a catalog of various optical films. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). By inputting these assumed values of average refractive index and film thickness, KOBRA 21ADH or WR calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

(Film thickness)
The thickness of the film of the present invention can be appropriately determined depending on the type of polarizing plate used and the like, but is preferably 30 to 60 μm, and more preferably 35 to 55 μm. It is preferable that the thickness of the film be 60 μm or less because the cost can be reduced.

(Haze)
The film of the present invention preferably has a haze of 1% or less, more preferably 0.8% or less, particularly preferably less than 0.5%, and preferably 0.3% or less. More particularly preferred.

(Polarizer)
The polarizing plate of the present invention comprises a polarizer and at least one cellulose acetate film of the present invention.
The cellulose acetate film of the present invention is suitable for a protective film for a polarizing plate. The polarizing plate is formed by laminating and laminating a protective film on at least one surface of the polarizer. A conventionally known polarizer can be used. For example, a hydrophilic polymer film such as a polyvinyl alcohol film is treated with a dichroic dye such as iodine and stretched. The bonding of the cellulose acetate film and the polarizer is not particularly limited, but can be performed with an adhesive made of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution.

  The cellulose acetate film of the present invention is a protective film for polarizing plate / polarizer / protective film for polarizing plate / liquid crystal cell / cellulose acetate film / polarizer / protective film for polarizing plate of the present invention, or a protective film for polarizing plate. / Polarizer / cellulose acetate film of the present invention / liquid crystal cell / protective film for polarizing plate of the present invention / polarizer / protective film for polarizing plate can be preferably used. In particular, when used by being attached to a liquid crystal cell such as a TN type, a VA type, or an OCB type, it is possible to provide a display device that is excellent in viewing angle and visibility with little coloring. Moreover, the polarizing plate using the cellulose acetate film of the present invention has little deterioration under high temperature and high humidity conditions, and can maintain stable performance for a long time.

The aspect of the polarizing plate of the present invention is produced not only in the form of a film piece cut into a size that can be incorporated into a liquid crystal display device as it is, but also in a long shape by continuous production, and in a roll shape. A polarizing plate in a rolled up mode (for example, a roll length of 2500 m or longer or 3900 m or longer) is also included. In order to use for a large-screen liquid crystal display device, the width of the polarizing plate is preferably 1470 mm or more as described above.
The specific configuration of the polarizing plate of the present invention is not particularly limited, and a known configuration can be employed. For example, the configuration described in FIG. 6 of JP-A-2008-262161 can be employed.

(Liquid crystal display device)
The liquid crystal display device of the present invention includes the cellulose acetate film of the present invention.
The film of the present invention can be applied to a liquid crystal display device having the polarizing plate of the present invention.
The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal cell and a pair of polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate of the present invention. An IPS, OCB or VA mode liquid crystal display device is preferable.
A specific configuration of the liquid crystal display device of the present invention is not particularly limited, and a known configuration can be adopted. Further, the configuration described in FIG. 2 of JP-A-2008-262161 can also be preferably employed.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

In the present invention, measurement was performed by the following measurement method.
(Peelability)
In each Example and Comparative Example, the fluctuation range of the peeling point when the cast film was peeled off from the support as a wet film (peeling before stretching) was measured, and the stripping suitability was evaluated.
(Double-circle): The fluctuation range of a peeling point It does not fluctuate at 0 mm (very light).
○: Fluctuation width of the peeling point More than 0 mm, it fluctuates within 2 mm (light).
▲: Fluctuation width of the peeling point More than 2 mm and fluctuating within 5 mm (slightly heavy).
X: Fluctuation width of peeling point More than 5 mm, fluctuating at 10 mm or more (heavy)
XX: Fluctuation range of peeling point Fluctuates over 10 mm (very heavy)
According to the above evaluation, stripping suitability was evaluated, and the obtained results are shown in Tables 6 and 7 below. In Comparative Examples 1 and 3, the stripping suitability was not evaluated.

(Re, Rth)
Re and Rth were measured at a wavelength of 590 nm by KOBRA 21ADH (manufactured by Oji Scientific Instruments) by the above method. The results are shown in Tables 6 and 7 below.

(Haze)
The haze was measured according to JIS K-6714 using a haze meter (HGM-2DP, Suga Test Instruments) with a film sample of 40 mm × 80 mm of the present invention at 25 ° C. and a relative humidity of 60%. The results are shown in Tables 6 and 7 below.

(Corrosion evaluation of organic acids: SUS corrosion)
In each of the examples and comparative examples, 20 g of the prepared dope was weighed in an autoclave, and a SUS316 test piece having a thickness of 0.5 cm, cut into a width of 2 cm and a length of 3 cm was immersed therein. The autoclave was sealed, and after aging at 90 ° C. for 72 hours, the lid of the autoclave was opened, and the corrosion of the SUS316 test piece and the change in the dope due to this were observed and evaluated according to the following criteria.
A: There is no change in the smoothness of the test piece surface, and the organic acid solution is colorless and transparent.
○: The change in smoothness of the surface of the test piece is small, but the organic acid solution is colored yellow.
X: The surface of the test piece is rough, and the organic acid solution is brown and cloudy.
According to the above evaluation, the corrosivity of the organic acid was evaluated, and the obtained results are shown in Tables 6 and 7 below.

[Examples 1 to 57, Comparative Examples 1 to 8: Film formation of cellulose acetate film]
(1) Preparation of Cellulose Acetate Dope Cellulose acetates having the acyl substitution degree shown in Tables 6 and 7 were prepared. Sulfuric acid (7.8 parts by mass with respect to 100 parts by mass of cellulose) was added as a catalyst, carboxylic acid was added, and an acylation reaction was performed at 40 ° C. Thereafter, the total substitution degree and the 6-position substitution degree were adjusted by adjusting the amount of sulfuric acid catalyst, the amount of water and the aging time. The aging temperature was 40 ° C. Furthermore, the low molecular weight component of the cellulose acetate was removed by washing with acetone.

(Cellulose acetate solution)
The cellulose acetate and dichloromethane described in Table 6 and Table 7 below, and the alcohol described in Table 6 and Table 7 below were put into a mixing tank, stirred to dissolve each component, and further heated at 90 ° C. for about 10 minutes. The solution was filtered through a filter paper having an average pore diameter of 34 μm and a sintered metal filter having an average pore diameter of 10 μm. Inorganic fine particles and each additive described in Table 6 and Table 7 below were further added to prepare the following cellulose acetate solution. The inorganic fine particles were prepared by adding them to a disperser, and each additive was dissolved by stirring while heating. The composition of the dope of Example 1 is shown below.

――――――――――――――――――――――――――――――――――
Example) Dope of Example 1 ――――――――――――――――――――――――――――――――――
Cellulose acetate (substitution degree 2.10) 100.0 parts by mass Compound B (Rth control agent) 19.0 parts by mass Inorganic fine particles (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by mass Methylene chloride 365.5 parts by mass / ethanol 54.6 parts by mass ―――――――――――――――――――――――――――――――――

を、ＡＢは、

を、ＡＣは、

をそれぞれ示している。 (Each additive)
Here, the addition amounts of the Rth control agent and the Re enhancer (additive 2) are as shown in Tables 6 and 7, and are expressed in mass% with respect to cellulose acetate. In Table 7, AA is

AB is

AC

Respectively.

添加剤Ｂ〜Ｈについては下記表５に記載のものである。なお、下記表５中、ＥＧはエチレングリコールを、ＰＧはプロピレングリコールを、ＢＧはブチレングリコールを、ＴＰＡはテレフタル酸を、ＰＡはフタル酸を、ＡＡはアジピン酸を、ＳＡはコハク酸をそれぞれ示している。
また、前記添加剤の添加量は、ドープ中に含まれる熱可塑性樹脂に対する質量％である。 Additive A is compound D-1 of JP-A-2009-222994. The structure of the additive A will be described below.

Additives B to H are listed in Table 5 below. In Table 5, EG is ethylene glycol, PG is propylene glycol, BG is butylene glycol, TPA is terephthalic acid, PA is phthalic acid, AA is adipic acid, and SA is succinic acid. ing.
Moreover, the addition amount of the said additive is the mass% with respect to the thermoplastic resin contained in dope.

Furthermore, in Comparative Example 5, citric acid ethyl ester (monoester 40%, diester 40%, triester 10%) was used as a peeling accelerator, and in Comparative Example 6, citric acid (manufactured by Tokyo Chemical Industry) was used. 7 was mixed to prepare a dope for film formation. The final addition ratios of cellulose acetate, each solvent, and each additive were as shown in Table 6 and Table 7 below.
The cellulose acetate and various additives used as the dope raw material were dried in advance at 120 ° C. for 2 hours using a silo manufactured by Nara Machinery Co., Ltd.
Moreover, the solid content concentration contained in the dope at this time was measured and listed in Tables 6 and 7 below.

(2) Casting and stripping The above-mentioned dope was cast using a band casting machine having the configuration shown in FIG. The band is made of SUS 316, the band width is about 2 m, the band is an endless belt, the band length is about 80 m, the surface roughness Ra value is 0.01 μm, and the thickness of the band is about 1. It was 5 to 2 mm, and was super-mirror finished. The endless metal belt of the band casting machine is wound around two rolls and has a diameter of about 2.5 m. The roll on the side where the dope film is peeled is provided with a cooling device. The cooling device can cool the roll using a branler, and the surface temperature of the roll is controlled to the surface temperature described as the roll temperature in Tables 6 and 7 below using the roll as a cooling body. The moving speed of the endless metal belt was 40 m / s.
Residual solvent amounts described in Tables 6 and 7 below in the stripping region by a residual solvent amount control device that can be appropriately controlled in the range of the supply air temperature on the band of 80 ° C to 130 ° C (exhaust temperature is 75 ° C to 120 ° C). After drying so that, the dope film was peeled off from the band.
In Table 6 and Table 7, “37 → post-drying 0” in Example 56 means that the film was removed without being stretched (without going through the stretching zone) after peeling off at the time when the solvent residual amount was 37%. It means that the film is dried at 30 ° C. for 30 minutes and then stretched to form a dried film. In the same manner as in Example 56, Example 57 was also performed on a film that was a dry film.

(3) Stretching The obtained web (film) was peeled off from the band, sandwiched between clips, and the amount of residual solvent relative to the total mass of the film was listed in Tables 6 and 7 below (however, Examples 56 and 57 were still left) In the condition of fixed end uniaxial stretching when the amount of solvent is 0% after drying), at the stretching temperature described in Table 6 and Table 7 below, using a tenter at a stretching ratio of 1.3 times and orthogonal to the film transport direction Stretched in the direction (transverse direction).
Thereafter, the clip was removed from the film and dried at 130 ° C. for 20 minutes. At this time, the cast film thickness was adjusted so that the film thickness after stretching became the film thickness (unit: μm) described in Tables 6 and 7. For the purpose of producing cellulose acetate films of Examples and Comparative Examples having the characteristics shown in Tables 6 and 7 by such a method, and judging the suitability for production, rolls having a roll width of 1280 mm and a roll length of 2600 mm were subjected to the above conditions. A minimum of 24 rolls were produced. About 1 roll in 24 rolls manufactured continuously, a 1-m long sample (width 1280 mm) was cut out at intervals of 100 m, and each measurement was performed.

From Table 6 and Table 7, according to the present invention, a cellulose acetate film that is easy to peel off from a metal support when cast by a solution, has good corrosiveness in manufacturing equipment, and has good Rth expression. I found that I could provide it.
On the other hand, Comparative Examples 1 and 3 are those in which the total acyl substitution degree of the cellulose acetate used was lower than the range of the present invention, and the obtained film was poorly peelable and could not measure optical properties and haze. It was. In Comparative Examples 2 and 4, the total acyl substitution degree of the cellulose acetate used was higher than the range of the present invention, and the resulting film had poor Rth expression. Comparative Examples 5 and 6 are comparative examples using citric acid ethyl ester and citric acid, which are organic acids that do not satisfy the requirements (1) to (3), respectively, as peeling accelerators. I found it bad. Comparative Example 7 is a comparative example in which an organic acid that satisfies the requirements (1) to (3) was added in excess of the upper limit of the amount specified in the present invention, and the resulting film had poor Rth expression. . Comparative Example 8 was a comparative example in which no peeling accelerator such as an organic acid was added, and the peelability was poor.

101 metal endless belt 102 driven roll 103 driving roll (cooling body)
104 Gear pump 105 T die 106 Take-off roll group 107 Stripping area 108 Residual solvent amount control device 109 Roll cooling device 110 Belt meandering prevention device

Claims (10)

Cellulose acetate having a total substitution degree of 2.0 to 2.7, a solvent, and an organic acid satisfying the following requirements (1) to (3) of 0.01% by mass to 20% by mass with respect to the cellulose acetate: Casting a solution containing the solution on a metal support;
And a step of stripping the dope film from the metal support.
(1) Includes a structure in which a polyhydric alcohol and a polycarboxylic acid are bonded by forming an ester bond.
(2) The total number of molecules of the polyhydric alcohol and polycarboxylic acid forming the compound is 3 or more.
(3) It has at least one unsubstituted carboxyl group derived from a polyvalent carboxylic acid.   The method for producing a cellulose acetate film according to claim 1, wherein 15% by mass or more of the solvent is an alcohol, and the alcohol has an average carbon number of 1.5 to 4.   The method for producing a cellulose acetate film according to claim 2, wherein ethanol is contained as the alcohol. The metal support is a moving belt-like support;
The cooling body having a surface temperature of 10 ° C. or less is brought into contact with the surface of the metal support opposite to the side where the dope film is peeled off in the region where the doped film is peeled off. 4. The method for producing a cellulose acetate film according to any one of 3 above.   The method for producing a cellulose acetate film according to any one of claims 1 to 4, wherein a retardation Rth control agent in the film thickness direction is contained in the dope. Manufactured by the method for producing a cellulose acetate film according to any one of claims 1 to 5,
A cellulose acetate film having a retardation value Rth in the film thickness direction measured at a wavelength of 590 nm of 80 nm or more.   The cellulose acetate film according to claim 6, wherein the haze is less than 0.5%.   The cellulose acetate film according to claim 6 or 7, wherein the retardation value Re in the in-plane direction of the film measured at a wavelength of 590 nm is 30 to 100 nm.   A polarizing plate comprising a polarizer and at least one cellulose acetate film according to claim 6.   A liquid crystal display device comprising the cellulose acetate film according to claim 6.

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