JP2005283997A - Cellulose ether acetate optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diminish unreacted cellulose which becomes a problem as an optical foreign substance in an optical film, that is, an insoluble component or a less soluble minute foreign substance. <P>SOLUTION: The optical film comprising a cellulose ether acetate is provided. The cellulose ether ester forming the film is prepared by carrying out etherification as a first step and acetylation as a second step, whereby acetylation proceeds uniformly and an optical foreign substance is diminished. Solubility in a halogen-free organic solvent is also improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure of a liquid crystal display device such as a polarizing plate protective film and an optical film of cellulose ether acetate suitable as a base film for photographic materials. Furthermore, the present invention relates to a cellulose ether acetate solution used for the production of these optical films and a method for producing an optical film of cellulose ether acetate.

Cellulose acetate film is used as a film in various photographic materials and optical materials because of its toughness and flame retardancy. For example, cellulose acetate film is a typical support for photographic light-sensitive materials. Cellulose acetate films are also used in liquid crystal display devices whose market is expanding in recent years due to their optical isotropy. Of these cellulose acetate films, the present invention relates to a cellulose acetate film used for optical film applications. The optical film referred to in the present invention is 1) a transparent film used as a photographic material or a base film of an optical material, and preferably 2) can be used as a component (element) of a liquid crystal display device. It is a film. Specific examples of the use of the liquid crystal display device described above include a polarizing plate protective film and a color filter, a retardation film, an optical compensation sheet, a scattering film, a viewing angle widening film, a surface protective film, and the like. Is.

  Such an optical film of cellulose acetate is required to have high optical characteristics because its use is optical. For example, the yellowness index (hereinafter abbreviated as YI) and haze are low, the birefringence is low, the transparency is high, and furthermore there are few optical defects that affect light transmission. Is required. And if it is the use of the conventional cellulose-ester film, even if it is a fine surface unevenness | corrugation and a flaw, or an optical defect which does not have a quality problem, it will become a problem in these optical films. In particular, when an optical film is used as a component of the liquid crystal display device of 2) above, a so-called bright spot foreign matter that abnormally refracts transmitted light even if it is transparent becomes an optical defect. It becomes a quality problem.

  In recent years, these liquid crystal display devices have been used not only as display devices for personal computers but also as display devices for television receivers, DVDs, etc., or display devices for mobile phones and PDAs (mobile terminals). There is a demand for less. That is, in recent years, display devices for personal computers, television receivers, and computer games have become larger and the number of image forming elements (so-called dot number) has increased, and the area per image forming element has become very small. .

  Accordingly, it is required to provide a film having less optical defects per unit area as an optical film of a polarizing plate protective film or an antireflection film used in a liquid crystal display device. An object of this invention is to provide the optical film which can be used suitably for such a liquid crystal display device.

As described above, these optical defects include black foreign matter and bright spot foreign matter. The black foreign matter is caused by impurities and the like, and the bright spot foreign matter is mainly caused by cellulose acetate having a different degree of acetylation and a refractive index is different and transmitted light is abnormally refracted. Black foreign matter is a defect that does not transmit light in the film. On the other hand, bright spot foreign matter can be observed as light leakage when a film is disposed between two polarizing plates arranged so that the polarization directions are orthogonal. Both of these two optical defects impair the performance of the liquid crystal display device.
In order to reduce black foreign substances and bright spot foreign substances as described above, a solution (dope) in which cellulose acetate is dissolved is used during filtration of the optical film. The opening is becoming smaller and the productivity and usage rate of optical films are decreasing.

  The problem of black foreign matters is due to the contamination of impurities during the production of cellulose acetate and in the cellulose acetate dissolution process. Moreover, the cause of the bright spot foreign matter is due to cellulose acetate having a different degree of acetylation. That is, the part that is not sufficiently acetylated in the acetylation process during the production of cellulose acetate partially remains as cellulose acetate having a low degree of acetylation (unreacted cellulose), and these unreacted cellulose is ordinary vinegar. Since it has a refractive index different from that of cellulose acetate, it is recognized as a bright spot foreign material. Unreacted cellulose remains as an insoluble component when cellulose acetate is dissolved to form a solution (dope). That is, since this unreacted cellulose has a very low degree of acetylation, its solubility is close to that of cellulose and does not dissolve in organic solvents that are used as ordinary cellulose acetate solvents. Therefore, unreacted cellulose becomes a filtration residue, Depending on the size and shape of the unreacted cellulose lump, it may pass through the filter medium. Since the refractive index thereof is different from that of ordinary cellulose acetate, those passing through such a filter medium cause bright spot foreign matter in the product of the optical film, thereby degrading the quality of the optical film.

The applicant of the present application already stated in Japanese Patent Application No. 2001-571778 that the main cause of these bright spot foreign substances is a fine fragment in which the cellulose fiber with insufficient reaction has collapsed, and the fine fragment is reduced by not entering the acetylation reaction system. We have filed a patent application to find out what we can do.
However, the pulp, which is the raw material for cellulose acetate, contains a cellulose portion that is poorly reactive due to high crystallization, etc., and this undergoes non-uniform acetylation and a substitution degree different from that of ordinary triacetate. In other words, the phenomenon existing in the cellulose acetate film as unreacted cellulose was an unsolved problem.
On the other hand, a cellulose acetate film is generally produced by a solvent cast method. In the solvent cast method, a solution (dope) in which cellulose acetate is dissolved in a solvent is cast on a support, and the solvent is evaporated to form a film.

The solvent cast method is described in many documents. In the recent solvent casting method, it is a problem to improve the productivity of the film forming process by shortening the time required from casting the dope onto the support to peeling off the formed film on the support. It has become. For example, Japanese Patent Publication No. 5-17844 proposes that a high concentration dope is cast on a cooling drum to shorten the time until stripping after casting.
As described above, the solvent used in the solvent casting method requires not only simply dissolving cellulose acetate but also various conditions. That is, in order to economically and efficiently produce a film having excellent flatness and uniform thickness, it is necessary to prepare a solution (dope) having an appropriate viscosity and polymer concentration and excellent in storage stability. The dope is required to be easily gelled and easily peeled from the support. In order to prepare such a dope, cellulose acetate having good solubility is required. Furthermore, it is preferable to be able to form a high concentration dope for improving the productivity of the cellulose acetate optical film.

Various organic solvents have been proposed as a solvent for cellulose acetate, but the ones that have been used since the past have been substantially limited to those mainly composed of methylene chloride. In other words, solvents other than methylene chloride are hardly practically used. However, in recent years, the use of halogenated hydrocarbons such as methylene chloride is in the direction of being significantly restricted from the viewpoint of protecting the global environment. Moreover, since methylene chloride has a low boiling point (41 ° C.), there is a problem that it easily evaporates in the production process.
On the other hand, acetone (boiling point: 56 ° C.) and methyl acetate (boiling point: 57 ° C.), which are general-purpose organic solvents, have an appropriate boiling point, and the drying load is not so large. In addition, the human body and the global environment are less problematic than chlorinated organic solvents. However, acetone and methyl acetate have low solubility in cellulose acetate. In particular, cellulose triacetate having a substitution degree of 2.80 (acetylation degree: 60.1%) or more swells in acetone or methyl acetate and hardly dissolves. For this reason, from the viewpoint of the human body and the global environment, a cellulose acetate solution that is highly soluble in organic solvents other than halogenated hydrocarbons such as methylene chloride, forms a stable dope, and dissolves at a high concentration. There is a need for optical films formed by the process.

C. J. et al. Malm et al. (Ind. Enig. Chem. 43, 688, 1951) states that cellulose propionate and cellulose butyrate have a wider range of solvent choices than cellulose acetate. Has been. Cellulose propionate and cellulose butyrate also dissolve in ketones and esters that cannot dissolve cellulose acetate. However, a film produced from cellulose propionate or cellulose butyrate is inferior to cellulose acetate film in mechanical strength and durability.
Japanese National Publication No. 6-501040 proposes using a melt extrusion method, that is, a melt cast method, instead of the solvent cast method having the above problems. However, the melt casting method has a problem that the melting point of cellulose triacetate is higher than the decomposition temperature. That is, cellulose triacetate having a high substitution degree of acetyl group is decomposed before being melted when heated. In order to solve this problem, in the invention described in the publication, the substitution degree of the acetyl group in the cellulose acetate is adjusted to 1.9 to 2.6.
The publication also discloses cellulose acetate propionate. However, the level of optical defects of these was not satisfactory.
The present applicants have already disclosed a technique relating to a solution comprising a mixed ester of an acetyl group and an acyl group and a method for producing this mixed ester film in JP-A-08-231761. In addition, the present applicant discloses a mixed fatty acid ester production method in which an amorphous degree is defined in JP-A-10-45803, and further in JP-A-10-45804, a method for producing a mixed fatty acid ester in which a specific degree of substitution is defined. Is disclosed. These mixed fatty acid esters of cellulose are easily dissolved in a general-purpose non-halogen organic solvent and have excellent crystallinity. Therefore, a molded article having excellent mechanical characteristics and optical characteristics can be produced without using a halogen-based solvent with few problems. However, the cellulose mixed fatty acid ester has a problem that the molecular weight tends to decrease, and furthermore, it has not been able to provide a sufficient solution for unreacted cellulose, which is an insoluble component, which causes bright spot foreign matter.

In addition, the cellulose ester reaction is described in detail in “Mitsubishi Wadano” published by Tokyo Maruzen Co., Ltd. “Acetic acid fiber-its production and use-”, but the organic acid used is a diluent, which reacts with anhydrous organic Depending on the type of organic acid anhydride, the reaction rate is only about 50% at most, and the remainder is combined with moisture to obtain the organic acid as a by-product. Therefore, these organic acids are recovered and reused in an industrial cellulose ester production method. However, these cellulose esters are esterified products of mixed fatty acids of cellulose, and the recovered acid in the esterification step becomes a mixed organic acid, which requires separation and production, and has a problem of high energy consumption.
In addition, in order to ensure solubility, it is necessary to introduce an acyl group other than an acetyl group in a certain ratio or more, and there is a problem that retardation (Rth) in the thickness direction is likely to vary. As described above, in order to increase the productivity of the optical film, it is necessary to increase the concentration of the cellulose acetate solution. However, in such a case, the above-described problems are particularly likely to occur.

  As a solution other than the cellulose mixed fatty acid ester as described above, an attempt has been made to improve the solubility by making the substitution degree distribution in the glucose ring specific with cellulose ester, particularly cellulose acetate. That is, Japanese Patent Laid-Open No. 11-5851 discloses a technique for dissolving in a solvent other than methylene chloride by setting the substitution degree of the 2-position, 3-position and 6-position of cellulose acetate within a specific range. Has been.

  However, these are those in which a total acetylation degree of 2.97 or less is dissolved in a mixed solvent of methyl acetate and ethanol. Moreover, it is the same technique of Unexamined-Japanese-Patent No. 2002-338601, and melt | dissolves a thing with a total acetylation degree of 2.925 or less in a mixed solvent. Even in the above two techniques, there is a characteristic that the stability of the solution that has been cooled and dissolved becomes worse as the total degree of acetylation increases. For this reason, since the solubility is not sufficient, a high concentration dope could not be formed.

  And this cellulose acetate with limited degree of substitution at 6-position is soluble in non-halogen solvents in the cooled state, but difficult to dissolve at room temperature, and the technology to dissolve at room temperature in a single solvent other than methylene chloride is disclosed Was not.

Japanese Patent Laid-Open No. 2002-212338 discloses a cellulose mixed fatty acid ester in which the substitution degree of the 2-position, 3-position and 6-position of the cellulose acylate is within a specific range, and the total acetylation degree is at most 2.90 or less. Although this is also a cellulose mixed fatty acid ester, there is a problem of the recovered acid. Furthermore, if the solvent used for cooling dissolution in the patent is a non-chlorine solvent, it becomes a complex mixed solvent of 3 or more types, and when the solvent is recovered in the drying process of the solvent cast method, this is a large amount for separation and purification. There was a problem that energy was required and the environmental load was high. In addition, a technique for dissolving in a single solvent other than methylene chloride at room temperature has not been disclosed, and the problem of bright spot foreign matter caused by unreacted cellulose has not been solved.
Japanese Patent Application No. 2001-571778 Japanese Patent Publication No. 5-17844 Japanese National Patent Publication No. 6-501040 JP-A-8-231761 Japanese Patent Laid-Open No. 10-45803 Japanese Patent Laid-Open No. 10-45804 Japanese Patent Laid-Open No. 11-5851 JP 2002-338601 A JP 2002-212338 A Ind. Enig. Chem. 43, 688, 1951

An object of the present invention is to provide an optical film of cellulose ether acetate. In addition, there is little variation in the acetylation degree between molecules, that is, cellulose ether acetate optical film with less unreacted cellulose, that is, insoluble components and acetyl cellulose with insufficient reaction level, that is, less bright spot foreign matter. It is to be. Furthermore, the objective of this invention is providing the optical film which consists of a cellulose ether acetate which can be manufactured using the manufacturing equipment of the existing cellulose acetate, without a collection | recovery acid becoming a mixed acid. Still another object of the present invention is to provide a high-concentration cellulose ether acetate solution having good solubility and stability, which can be prepared at room temperature using various kinds of organic solvents, preferably with a single solvent. Furthermore, an object of the present invention is to provide an optical film having less unreacted cellulose, that is, insoluble components and less bright spot foreign matter, by using these cellulose ether acetate solutions. Still another object of the present invention is to provide a method for producing an optical film of cellulose ether acetate having a high total acetylation and excellent moisture resistance.

  As a result of studies to solve the above problems, the present inventor has used existing cellulose acetate production equipment by acetylating a modified cellulose in which a substituent is introduced by an ether bond into a part of the hydroxyl groups of cellulose. The inventors have found that cellulose ether acetates having any degree of acetyl substitution can be obtained, and have reached the present invention. Further, the obtained cellulose ether acetate is a cellulose ether acetate which can be formed into a film by a melt cast method, more preferably a solvent cast method.

Furthermore, the obtained cellulose ether acetate was found to be well dissolved in an organic solvent such as methyl acetate at room temperature even when the total degree of acetyl group substitution was high, forming a stable solution, and having excellent solubility. Furthermore, even when a conventionally known cooling dissolution is applied, it is possible to dissolve the cellulose derivative more satisfactorily (that is, a cellulose derivative having a high degree of substitution or a higher concentration if the degree of substitution is the same). This eliminates the need for dissolution using a chlorinated solvent such as methylene chloride. And since the cellulose ether acetate film obtained from these solutions has few insoluble components, there are few bright spot foreign materials, and the film suitable for using for the structure of liquid crystal display devices, such as said polarizing plate protective film, should be obtained. And reached the present invention.
In addition, the cellulose ether acetate as used in the field of this invention points out the cellulose derivative obtained by acetylating the modified cellulose modified by etherifying cellulose.

The present invention can be carried out in the following modes (1) to (28).
However, in the following description of the mode, MSether represents the average number of molecular weights of the denaturing agent ether-bonded per anhydroglucose unit constituting cellulose. DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. Furthermore, Ds2 shows the average substitution degree of the acetyl group couple | bonded with 2-position of the anhydroglucose ring which comprises a cellulose ether acetate.
Ds3 represents the average degree of substitution of the acetyl group bonded to the 3-position of the anhydroglucose ring constituting the cellulose ether acetate.
Moreover, the average substitution degree of the acetyl group couple | bonded with the 6-position of the anhydroglucose ring which comprises Ds6 cellulose ether acetate is shown.

(1) An optical film made of cellulose ether acetate that satisfies the following formulas (I) and (II):
(I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0

(2) An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (III):
(I) 0.01 ≦ MSether ≦ 3.00
(III) 2.6 ≦ DSester ≦ 3.0

(3) An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (IV):
(I) 0.01 ≦ MSether ≦ 3.00
(IV) 1.3 ≦ DSester <2.6

(4) The optical film according to the aspect (3) comprising cellulose ether acetate satisfying the following formulas (V) and (VI):
(V) 0.50 ≦ MSether ≦ 3.00
(VI) 1.3 ≦ DSester <2.2

(5) The optical film as described in the aspect (3) manufactured by the solvent cast method which consists of a cellulose ether acetate which contains a plasticizer as an essential component and satisfy | fills the following formula (I) and (IV).
(I) 0.01 ≦ MSether ≦ 3.00
(IV) 1.3 ≦ DSester <2.6

(6) The solvent is composed of cellulose ether acetate whose substituents bonded to the anhydroglucose ring constituting the cellulose are the following (a), (b), (c) and (d), and contains a plasticizer as an essential component. The optical film as described in aspect (1) made by the casting method.

(A) OR ₁ —OH (where R ₁ represents any organic group)
(B) O-COCH ₃
(C) OR ₂ —O—COCH ₃ (wherein R ₂ represents an arbitrary organic group, and R ₁ and R ₂ may be the same)
(D) OH

(7) An optical film made of cellulose ether acetate whose insoluble matter amount measured by the following measurement method is 0.014 wt% or less.
(Measuring method)
A solution obtained by dissolving cellulose ether acetate in a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio) to a concentration of 2 wt% solid content is filtered using a glass filter (pore diameter: 5 to 10 μm). Thereafter, the dope adhering to the filtration residue is washed with a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio). The filtration residue is dried together with the glass filter until a constant weight is obtained. The weight of the glass filter before and after filtration is measured, and the amount of insoluble matter is calculated from the following formula.
Insoluble matter amount (wt%) = [glass filter weight after filtration (g) −glass filter weight before filtration (g)] / weight of cellulose ether acetate (g) × 100

(8) The following formulas (I) and (III) are satisfied, and the acetyl group substitution degree at the 2-position, 3-position and 6-position of the anhydrous glucose ring of the cellulose ether acetate satisfies the following formulas (i) and (ii) An optical film made of cellulose ether acetate.
(I) 0.01 ≦ MSether ≦ 3.00
(III) 2.6 ≦ DSester ≦ 3.0

(I) Ds2 + Ds3 ≧ −Ds6 + 2.67
(Ii) Ds2 + Ds3 ≦ 1.97 (

(9) The optical film according to any one of modes (1) to (6), comprising cellulose ether acetate dissolved in a non-halogen organic solvent having a melting temperature of 25 ° C. at a concentration of 10% by weight or more.
The present invention can be further implemented by the following production methods (10) to (11).

(10) A step of mixing cellulose ether acetate satisfying the following formulas (I) and (II) with an organic solvent to swell the cellulose ether acetate in the organic solvent; Cooling step; heating the cooled mixture to 0 to 200 ° C. to prepare a cellulose ether acetate solution in which the cellulose ether acetate is dissolved in an organic solvent; flowing the prepared cellulose ether acetate solution on the support And the method for producing an optical film according to the embodiment (1) comprising the step of evaporating the organic solvent to form a cellulose ether acetate film (I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0

(11) The following formulas (I) and (III) are satisfied, and the degree of acetyl group substitution at the 2-position, 3-position and 6-position of the anhydrous glucose ring of the cellulose ether acetate is A step of mixing cellulose ether acetate to be filled with an organic solvent to swell the cellulose ether acetate in the organic solvent; cooling the swollen mixture to −100 to −10 ° C .; adding the cooled mixture to 0 to 200 ° C. Warming and preparing a cellulose acetate solution in which cellulose acetate is dissolved in an organic solvent; casting the prepared cellulose acetate solution on a support; and evaporating the organic solvent to form a cellulose acetate film Process for producing optical film of mode (8) comprising steps (I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0
(I) Ds2 + Ds3 ≧ −Ds6 + 2.67
(Ii) Ds2 + Ds3 ≦ 1.97
(Iii) Ds2 + Ds3 <Ds6 × 4-1.70

The present invention can be preferably implemented in the following modes.

(12) An optical film made of cellulose ether acetate that satisfies the following formulas (VII) and (VIII):
(VII) 0.02 ≦ MSether ≦ 2.00
(VIII) 1.5 ≦ DSester ≦ 3.0

(13) An optical film comprising cellulose ether acetate that satisfies the following formulas (VII) and (IX):
(VII) 0.02 ≦ MSether ≦ 2.00
(IX) 2.0 ≦ DSester ≦ 3.0

(14) An optical film comprising cellulose ether acetate satisfying the following formulas (VII) and (VIII) and having an insoluble matter amount measured by the following measuring method of 0.014 wt% or less.
(Measuring method)
A solution obtained by dissolving cellulose ether acetate in a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio) to a concentration of 2 wt% solid content is filtered using a glass filter (pore diameter: 5 to 10 μm). Thereafter, the dope adhering to the filtration residue is washed with a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio). The filtration residue is dried together with the glass filter until a constant weight is obtained. The weight of the glass filter before and after filtration is measured, and the amount of insoluble matter is calculated from the following formula.
Insoluble matter amount (wt%) = [glass filter weight after filtration (g) −glass filter weight before filtration (g)] / weight of cellulose ether acetate (g) × 100

(VII) 0.02 ≦ MSether ≦ 2.00
(VIII) 1.5 ≦ DSester ≦ 3.0

(15) The optical film according to the aspect (1), which is produced by a solvent cast method comprising a cellulose ether acetate containing a plasticizer as an essential component and satisfying the following formulas (X) and (VIII):
(X) 0.01 ≦ MSether ≦ 0.7
(VIII) 1.5 ≦ DSester ≦ 3.0

(16) The optical film according to the aspect (15), wherein the plasticizer contained in the optical film is a phosphate ester or a carboxylic acid ester.

(17) The optical film according to the aspect (1), wherein the in-plane retardation value (Re550) at a wavelength of 550 nm is 20 to 300 nm.

(18) The optical film as described in the aspect (3), wherein the retardation value (Rth550) in the thickness direction at a wavelength of 550 nm is 200 to 400 nm.

(19) The optical film according to the aspect (1), wherein the bright spot foreign matter having a thickness of 20 μm or more per 80 μm of the film thickness measured by the following method for measuring bright spot foreign matters is 0.1 pieces / mm ² or less of cellulose ether acetate.
(Measurement method of bright spot foreign matter)
Cellulose ether acetate is dissolved in a mixed solvent of methylene chloride / methanol = 9/1 (weight ratio) to obtain a 15 weight (solid content concentration) solution. This solution is cast and dried on a slide glass to obtain a film sample having a thickness of about 100 μm on the slide glass. This sample was observed with a polarizing microscope under a dark field, and the number of bright spot foreign matters having a maximum length of 20 μm or more within an area of 20 mm ² was counted, corrected with an accurate film thickness measured separately, and a unit area per 80 μm thickness ( The number of foreign matters per 1 mm ² ) is obtained. The same measurement is performed on three films formed from different solutions of the same sample, and an average value thereof is calculated as the number of bright spot foreign matters.
The number of bright spot foreign matter may be counted by taking an image observed by a suitable image processing apparatus and performing binarization processing.

(20) The mode (14) according to the mode (14), wherein the bright spot foreign matter having a thickness of 20 μm or more per 80 μm of the film thickness measured by the method for measuring a bright spot foreign matter in the mode (19) is 0.06 pieces / mm ² or less. Optical film.

(21) Molar ratio determined from total sulfuric acid (A) [unit is mol] remaining in 1 g of cellulose ether acetate and total amount of calcium (B) [unit is mol] contained in 1 g of cellulose ether acetate The optical film according to the aspect (1) comprising cellulose ether acetate satisfying the following formula: 0.5 <(B) / (A) <1.5

(22) At least selected from hardwood pulp having a carboxyl group content of 1 meq / 100 g or less, softwood pulp having a carboxyl group content of 1.5 meq / 100 g or less, and cotton linter pulp having a carboxyl group content of 1 meq / 100 g or less The optical film according to aspect (1), comprising cellulose ether acetate prepared by acetylating modified cellulose obtained by etherifying one type of cellulose

(23) The optical film according to the aspect (1), comprising cellulose ether acetate prepared by acetylating cellulose ether obtained by etherifying cellulose prepared from cellulose having a hemicellulose component of less than 3 mol%.

(23) at least one acid selected from at least one acid having an acid dissociation index pka of 1.93 to 4.50 in an aqueous solution, an alkali metal salt of the acid, and an alkaline earth metal salt of the acid; The optical film according to aspect (1), comprising cellulose ether acetate.

(24) The optical film according to the aspect (1), comprising cellulose ether acetate in which the ratio of mannose and xylose contained in the neutral constituent sugar component is the former / the latter = 0.35 to 3.0 (molar ratio). .

(24) The optical film according to the aspect (9), wherein the organic solvent for dissolving the modified cellulose ester is methyl acetate or ethyl acetate.

(25) A solution obtained by dissolving cellulose ether acetate satisfying the following formulas (I) and (II) in a non-halogen organic solvent.
(I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0
The present invention can be particularly preferably carried out in the following modes (26) to (27).

(26) An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (XI):
(I) 0.01 ≦ DSester ≦ 3.00
(XI) 0.02 ≦ MSether ≦ 0.5

(27) An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (XII):
(I) 0.01 ≦ DSester ≦ 3.00
(XII) 0.02 ≦ MSether ≦ 0.1
The present invention can be particularly preferably carried out in the following mode (28).

(28) An optical film comprising cellulose ether acetate that satisfies the following formulas (XII) and (XIII):
(XII) 0.02 ≦ MSether ≦ 0.1
(XIII) 2.80 ≦ DSester ≦ 3.00

  The problem to be solved has an advantage that unreacted cellulose that is a problem as an optical foreign substance in the optical film, that is, an insoluble component or a minute foreign substance having poor solubility can be suppressed. That is, it is clear that these undissolved substances, that is, unreacted cellulose, are produced by the reaction proceeding without sufficiently relaxing the crystalline region of cellulose because the acetylation reaction for acetylating cellulose is fast. As a solution, there is an advantage that the cellulose crystal region is relaxed by etherifying cellulose in advance, the reaction proceeds uniformly by acetylation, and a cellulose derivative suitable for use as an optical film can be obtained.

In addition, when mixed acid is generated during the production of cellulose ester, a large energy cost is required for separation and purification. However, in the cellulose ether acetate of the present invention, mixed fatty acid is not generated by ester, thus saving energy cost. There are advantages that can be made.
Furthermore, there is an advantage that a cellulose derivative that dissolves well in a non-halogen solvent can be obtained, which is useful in the environment.

  Furthermore, when it is made into a film, there is an advantage that it is possible to provide an optical film made of a cellulose ether ester which is excellent in optical properties and mechanical properties comparable to cellulose acetate.

The ether acetate for obtaining the optical film of this invention and the solution for manufacturing an optical film can be manufactured by passing through the following 1st process and 2nd process. The first step is a step for obtaining modified cellulose, and the second step is a step for acetylating the obtained modified cellulose.

[Production of modified cellulose]
In the present invention, the first step is to introduce a substituent group into a part of the hydroxyl group of cellulose through an ether bond. That is, to obtain cellulose ethers. The cellulose ethers may be alkyl celluloses, hydroxyalkyl ethers, carboxyalkyl celluloses, or cyanoalkyl ethers. That is, alkali cellulose can be prepared by treating with various reagents such as halogenated, sulfated, alkyl or aryl, alkene oxide, and unsaturated compounds activated with an electron withdrawing group. By such modification, a raw material for the cellulose ether acetate of the present invention is obtained.

As the cellulose to be modified, various known cellulose sources can be used. Cellulose esters are usually produced by esterifying cellulose such as wood pulp (conifer pulp, hardwood pulp) and cotton linter pulp. These pulps usually contain foreign components such as hemicellulose. Accordingly, in the present specification, the term “cellulose” is used in the sense that it also contains a different component such as hemicellulose.
Examples of these include cotton, cotton linter, wood pulp and the like. The best source of cellulose is linter pulp consisting of cotton linter, but this is limited in availability and expensive. Of course, linter pulp can be used as the cellulose source of the present invention, but wood pulp can be preferably used.

As the wood pulp, at least one selected from hardwood pulp or softwood pulp can be used, and linter pulp and wood pulp may be used in combination.
The α-cellulose content, which is an indicator of the purity of the pulp, can be selected from a range of, for example, about 90 to 100% by weight, and is usually about 92 to 98% by weight for wood pulp. In the present invention, a low-purity pulp, for example, a pulp having an α-cellulose content of 90 to 97% by weight, particularly 92 to 96% by weight, more preferably 93 to 95% by weight can be used, but preferably a high-purity pulp can be used. .

  That is, preferably, the α-cellulose content is 95% by weight or more, in other words, the minor component such as hemicellulose is less than 5% by weight. More preferably, the α-cellulose content is 97% by weight or more, that is, a minor component such as hemicellulose is less than 3% by weight.

  It is known that cellulose as a raw material usually contains some carboxyl groups in a state of being bonded to cellulose molecules and / or hemicellulose molecules. The carboxyl group content (concentration) can be quantified by various methods such as TAPPI Standard T237 om-83. The carboxyl group content in the pulp (cellulose) defined in the present invention is a value determined by TAPPI Standard T237 om-83.

  The cellulose used in the present invention is not particularly limited to the carboxyl group content, but as a more preferred form, cellulose having a low carboxyl group content is used, and the cellulose ester in the cellulose ester after the completion of acetylation in the second step is used. The carboxyl group content (concentration) can also be reduced. In this case, the carboxyl group content of cellulose is 1 meq / 100 g or less (for example, 0 to 1 meq / 100 g, particularly 0.001 to 1 meq / 100 g), preferably 0.8 meq / 100 g or less (for example, for hardwood pulp) 0.001 to 0.8 meq / 100 g), more preferably about 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g).

    The carboxyl group content of the softwood pulp is 1.5 meq / 100 g or less (for example, 0 to 1.5 meq / 100 g, particularly 0.001 to 1.5 meq / 100 g), preferably 1 meq / 100 g or less (for example, 0.001 to 0.001). 1 meq / 100 g), more preferably 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g).

  The carboxyl group content of cotton linter pulp is 1 meq / 100 g or less (for example, 0 to 1 meq / 100 g, particularly 0.001 to 1 meq / 100 g), preferably 0.7 meq / 100 g or less (for example, 0.001 to 0.7 meq). / 100 g), more preferably 0.4 meq / 100 g or less (for example, 0.001 to 0.4 meq / 100 g).

  The method for producing cellulose having a low carboxyl group content as described above is not particularly limited. For example, a method for suppressing oxidation by a bleaching agent in a pulp bleaching step (for example, bleaching under mild conditions), a specific linter pulp is used. Obtained by a method of selecting, a method of reducing the content of hemicellulose, a method of extracting a carboxyl group-containing component in the pulp bleaching step, a method of producing pulp using raw materials with low carboxyl groups (wood tree species, linter species, etc.), etc. Can do.

In addition, when the carboxyl group content of cellulose for cellulose acetate is measured by the measurement method, for example, it is 1.1 to 1.6 meq / 100 g for hardwood pulp and 1.8 to 2.8 meq / 100 g for softwood pulp. The literature (A. Isogai et al., Textile Society Journal, 48 (11), 649 (1992); Okada et al., Papa-Pagi Technical Journal, 28 (2), 59 (1974)) contains 1.4 meq. A linter pulp having a carboxyl group content of / 100 g is described.

        The carboxyl group content of the cellulose ester obtained using cellulose having a low carboxyl group content is 1 meq / 100 g or less (for example, 0 to 1 meq / 100 g, particularly 0.001 to 1 meq / 100 g), preferably 0 in terms of cellulose. It is about 8 meq / 100 g or less (for example, 0.001 to 0.8 meq / 100 g), more preferably about 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g).

  Further, the carboxyl group content in the cellulose ester necessary for improving the film peelability and / or spinnability can be classified by the mannose content or the ratio of the xylose content to the mannose content.

  That is, the carboxyl group content of the cellulose ester is 1.1 meq / 100 g or less (for example, 0.001 to 1.1 meq / 100 g) in terms of cellulose when the mannose content is 0.4 mol% or more, preferably Is 0.8 meq / 100 g or less (for example, 0.001 to 0.8 meq / 100 g), more preferably 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g).

  When the mannose content is more than 0.1 mol% and less than 0.4 mol%, the carboxyl group content of the cellulose ester is 0.8 meq / 100 g or less (for example, 0.001 to 0.8 meq in terms of cellulose). / 100 g), preferably 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g), more preferably 0.5 meq / 100 g or less (for example, 0.001 to 0.5 meq / 100 g). is there.

  When the mannose content is 0.1 mol% or less, the carboxyl group content of the cellulose ester is 1.1 meq / 100 g or less (for example, 0.001 to 1.1 meq / 100 g) in terms of cellulose, preferably 0.8. It is about 7 meq / 100 g or less (for example, 0.001 to 0.7 meq / 100 g), more preferably about 0.4 meq / 100 g or less (for example, 0.001 to 0.4 meq / 100 g).

  In addition, when the ratio of the xylose content to the mannose content (molar ratio) is less than 3, the carboxyl group content of the cellulose ester is 1.1 meq / 100 g or less (for example, 0.001 to 1.1 meq / 100 g), preferably 0.8 meq / 100 g or less (for example, 0.001 to 0.8 meq / 100 g), more preferably 0.6 meq / 100 g or less (for example, 0.001 to 0.6 meq / 100 g). .

  In general, cellulose acetate using hardwood pulp as a raw material is inferior in film peelability by casting, and cellulose acetate using softwood pulp as a raw material is generally inferior in optical properties such as transparency.

  In the present invention, cellulose ether obtained by modifying cellulose obtained by modifying cellulose having a reduced carboxyl group using wood pulp as a raw material, and using the modified cellulose as an acetate ester In the case of acetate, in particular, it is a raw material for optical films having good characteristics for use in optical applications such as transparency and peelability.

Next, the modifying agent for producing the modified cellulose will be described. As the modifying agent that can be used in the first step of the present invention, modifying agents having various organic groups capable of substituting the substituent of cellulose with an ether bond can be used. That is, the modifying agent in the first step in the present invention is an etherifying agent. The substituent introduced by the etherifying agent into the hydroxyl group of cellulose is a group based on a hydrocarbon and optionally containing a hetero atom. More specifically, (1) a linear or branched alkyl group having 1 to 6 carbon atoms,
(2) aryl, alkylaryl and arylalkyl groups,
(3) An alkyl group such as carboxyl, nitrile or hydroxyl group can be used.

  Examples of specific organic groups that can be used in the present invention include hydroxyalkyl such as methyl, ethyl, propyl, benzyl, hydroxypropyl, hydroxyethyl, carboxymethyl, cyanoethyl, sulfoethyl. Most preferred is an alkyl group containing at least one hydroxyl function. Further preferred are alkyl groups containing one hydroxyl function. The cellulose of the present invention can contain a plurality of substitution organic groups having different properties.

Epoxy compounds are suitably used as etherifying agents for introducing such substitution organic groups. Examples of the epoxy compound that can be used in the present invention include monoepoxy compounds such as ethylene oxide, propylene oxide, butylene oxide, epoxy alkane, styrene oxide, cyclohexane monooxide, epichlorohydrin, butyl glycidyl ether, allyl glycidyl ether, phenyl glycidyl ether, Examples include cresyl glycidyl ether, glycidyl methacrylate, glycidyl acrylate, epoxidized soybean oil, epoxidized flax oil, and epoxy stearate.
Among these, epoxide is preferable, and examples thereof include ethylene oxide, butylene oxide, and propylene oxide. Among these, propylene oxide is particularly preferable.
These etherifications may be carried out by known methods, and are described in JP-A-52-23186, JP-T 2000-513042 and the like.

  In general, in the case of cellulose acetate, the physical properties of the obtained cellulose acetate differ depending on the degree of substitution of three hydroxyl functional groups present in the cellulose. That is, in cellulose acetate, the acetyl group appears in a direction substantially perpendicular to the main chain. And when it forms into a film by the solvent cast method by presence of this acetyl group, even if it orientates, the birefringence (Re) of a film front direction is very small. If the film is used for optical applications, it is necessary that the birefringence is small. For this reason, cellulose acetate having a high degree of acetyl group substitution, ie triacetate, is used as an optical film. Therefore, in the present invention, it is preferable to select a substituent that makes MSether as small as possible or does not increase the birefringence.

  For this reason, the degree of substitution (MSether) by the organic group for substitution in the first step of the present invention needs to be 0.02 or more and 2 or less. Preferably it is 0.02 or more and 1.5 or less, More preferably, it is 0.02 or more and 1.0 or less, More preferably, it is 0.02 or more and 1.0 or less, More preferably, it is 0.02 or more and 0.5 or less Furthermore, it is 0.02 or more and 0.30 or less. It is particularly preferably 0.02 or more and less than 0.10, particularly preferably 0.02 or more and 0.08 or less.

  When MSether becomes large, the molecular chain interaction of cellulose ester becomes weak, and the mechanical strength (elastic modulus, folding strength) of the film to be produced decreases. In addition, the optical characteristics may change greatly. Also, if MSether becomes too small, if the degree of substitution of the acetyl group in the second step is 2.5 or more, the solubility in organic solvents decreases, and the decrease in bright spot foreign matter caused by unreacted cellulose, that is, insoluble components The effect is not satisfactory.

  However, as described above, in the first step of the present invention, the degree of substitution (MSether) in the etherification reaction does not need to be so high. MSether is preferably as small as possible as long as the following relational expression is satisfied. Even when MSether is low, it is suitable as the modified cellulose which is the product of the first step of the present invention.

  When the etherification reaction is performed as the first step of the present invention, it is preferably performed in the presence of an alkali. A particularly preferred method is preferably carried out in the pulp during pulp production as part of the bleaching of the starting cellulose and the alkaline refining chain. That is, by adding an etherifying agent while an active base (eg, about 1-12% by weight caustic soda or other alkali or alkaline earth metal hydroxide) is being added during pulp refining. One step can be performed. The reaction temperature can be appropriately determined, for example, at about 10 to 120 ° C. in consideration of the reactivity of the etherifying agent, MSether value, reaction rate, and safety. The reaction pressure can be appropriately determined in consideration of the stability and reaction efficiency of the etherifying agent and the desired product. The reaction time of the etherification reaction varies depending on the reaction amount and the like, but is about 10 to 3 hours, for example.

In the first step of the present invention, it is not necessary to carry out the reaction until a uniform dope is obtained as in the case of reaction with ordinary cellulose ether. Even a heterogeneous etherified product can be sufficiently used as a modified cellulose which is a product of the first step of the present invention.
One of the purposes of the first step of the present invention is to maintain the crystal structure relaxation effect by relaxing the crystal structure of cellulose and introducing a substituent. As a result, the modified cellulose, which is the product of the first step, has a reduced crystallinity. The crystal structure of at least a certain portion of the remaining crystal part is converted from cellulose I type to cellulose II type.
In the present invention, as the reaction form in the cellulose crystalline region and the amorphous region of the etherification reaction in the first step, naturally, the reaction first occurs in the amorphous region and then gradually proceeds to the crystalline region, Etherification has a slow reaction rate, the rate of reaction is limited, and the reaction proceeds uniformly in the crystalline region. As a result, the reaction proceeds almost uniformly in both the amorphous region and the crystalline region, and the crystal structure of cellulose is relaxed.

  In the case of normal cellulose, there is a portion having a crystal structure highly in cellulose I type, and this portion is difficult to proceed in the acetylation step. The reason for this is that, in the acetylation reaction of cellulose, the diffusion rate of acid into the cellulose crystal region of the acetylating agent is slower than the reaction rate, so that the diffusion rate becomes rate limiting, and the reaction proceeds non-uniformly in the crystal region. Cellulose II type crystal structure can be acetylated more easily than cellulose I type crystal structure.

  For this reason, when the 2nd process (acetylation) is performed using the product of the 1st process of the present invention, the reaction progresses uniformly, and the low acetylation degree fiber whose reaction is not sufficient decreases. That is, unreacted cellulose, that is, insoluble components are reduced. Therefore, cellulose ether acetate with uniform properties can be obtained, the dope obtained by dissolving this modified cellulose ester exhibits good filterability, and the optical film obtained from this modified cellulose solution is unreacted cellulose. That is, optical defects due to insoluble components are small, that is, bright spot foreign matter is reduced, and excellent quality and properties are exhibited when used in recent large-screen liquid crystal display devices.

  Furthermore, as an effect of etherification in the first step of the present invention, due to the introduced substituent, the modified cellulose ester after the second step is more than normal cellulose ester if the degree of substitution (DSester) is the same. Excellent solvent solubility. If the same solubility is acceptable, the degree of substitution (DSester) can naturally be increased.

  Of course, the acetylation can be carried out after the degree of etherification has been advanced to some extent in the same manner as in the ordinary etherification reaction. In that case, since the birefringence index in the thickness direction becomes large, it is unsuitable for use in a product for a part of the use of the optical film 2) (for example, a polarizing plate protective film). How much the degree of etherification proceeds can be selected according to the use and purpose of the optical film.

  The crystallinity of the modified cellulose thus obtained varies depending on the type of pulp as a raw material, but is 10% or more and 60% or less, preferably 10% or more, 55 when measured by X-ray diffraction. % Or less, more preferably 15% or more and 50% or less, further preferably 15% or more and 40% or less, particularly preferably 15% or more and 35% or less, and most preferably 20% or more and 30% or less.

In the case of ordinary cellulose acetate, the crystallinity measured by the X-ray diffraction method is in the case of cellulose acetate using softwood pulp, and the crystallinity is about 60%. The X-ray scattering method described in the present invention indicates small-angle X-ray scattering, and the measurement method is described in “Polymer Analysis Handbook” published by Asakura Shoten, edited by the Japan Analytical Chemical Society. The outline of the method carried out in is described in the Examples.
The modified cellulose crystals in the first step measured by X-ray diffractometry are usually cellulose I-type crystals, while the modified cellulose of the present invention is mainly cellulose II-type crystals. The form is shown. Details of the structure of cellulose type I and cellulose type II are described in the literature (Kolpac et al., 1978, Polymer, 19, 123-131).

[Acetylation process]
The second step of the present invention is a modified cellulose acetylation step.
For the modified cellulose ester of the present invention, a conventional method of cellulose ester using the modified cellulose which is the product of the first step of the present invention, for example, a method such as a sulfuric acid catalyst method, an acetic acid method, a methylene chloride method, etc. Can be manufactured. Below, the acetic acid method by a sulfuric acid catalyst is illustrated.

  As the cellulose acetate, pulp (cellulose) is usually used, but in the present invention, the modified cellulose produced in the first step is used instead of ordinary cellulose. The modified cellulose is activated with acetic acid or the like as necessary (activation step), and then triacetate is prepared with acetic anhydride using a sulfuric acid catalyst (acetylation step), then saponified (hydrolyzed) and ripened with vinegar. It can be produced by adjusting the degree of conversion (saponification / aging process). In this method, the activation step can be performed by treating the modified pulp (cellulose) by spraying acetic acid or hydrous acetic acid, immersing in acetic acid or hydrous acetic acid, and the amount of acetic acid used is The amount of the first step product is 10 to 100 parts by weight, preferably 20 to 80 parts by weight, and more preferably about 30 to 60 parts by weight with respect to 100 parts by weight of the modified pulp (modified cellulose).

  The amount of acetic anhydride used in the acetylation step (acetylation step, ie, acetic esterification step) can be selected within the range of the acetylation degree, for example, 230 to 700 weights per 100 parts by weight of the modified pulp (modified cellulose). Parts, preferably 240 to 300 parts by weight, more preferably about 250 to 280 parts by weight. In the acetylation step, acetic acid is usually used as a solvent. The amount of acetic acid used is, for example, 200 to 1000 parts by weight, preferably 300 to 600 parts by weight, and more preferably about 350 to 500 parts by weight with respect to 100 parts by weight of the modified pulp (modified cellulose).

As the esterification or aging catalyst, sulfuric acid is usually used. The usage-amount of a sulfuric acid is 1-20 weight part normally with respect to 100 weight part of modified cellulose, Preferably it is 1-15 weight part, Especially about 5-10 weight part. The saponification / ripening can be performed at a temperature of about 50 to 70 ° C., for example.
In the cellulose ether acetate of the present invention, the average degree of substitution of acetyl groups, that is, DSester can be selected from the range of about 2.0 to 3.0 depending on the intended use and characteristics.

  The degree of acetyl substitution (DSester) in the present invention is usually DSester = 2.63 to 3.00 in order to improve dimensional stability, moisture resistance, heat resistance, etc., and to maintain the current optical properties. , Preferably 2.70 to 2.95, more preferably 2.79 to 2.95, and particularly preferably 2.83 to 2.92). If DSester, which is the degree of acetyl group substitution, is improved, the birefringence in the width direction and length direction of the obtained film will be reduced, especially for polarizing plate protective film, anti-scattering film, surface protective film, photographic film, etc. An optical film suitable for is obtained.

One of the optical suitability required for the optical film as in the present invention is retardation. Retardation is the product of birefringence and film thickness, i direction (i is any direction selected from the direction of film width direction (x), forming axis direction (y), film thickness direction (z)) ) And the film thickness d (nm).
Re (front): | nx−ny | × d
Rth (thickness): | (nx + ny) / 2−nz | × d
Among these, the retardation in the front direction (Re) is preferably as small as possible in the optical film, and the retardation in the thickness direction (Rth) may be preferably larger for the use of the optical film, and may be smaller. . (Cellulose Commun. Vol.5, No.2 (1998) 101-104)

Therefore, when DSester, which is the degree of acetyl group substitution, is increased, the retardation in the thickness direction is decreased, which is suitable for use in a polarizing plate protective film. On the other hand, those in which DSester, which is the degree of acetyl group substitution, is decreased to less than 2.63 are optical films suitable for use in viewing angle widening films and retardation films. The technique which can obtain the optical film which improved the retardation of the thickness direction by cooling and melt | dissolving what reduced DSester of the above cellulose acetate to less than 2.63 is disclosed. (JP 2000-154261 A)
According to the present technology, an optical film having a retardation value in the thickness direction (Rth550) of 200 to 400 nm at a wavelength of 550 nm is obtained as a retardation film using cellulose acetate having a DSester of 2.41 to 2.63. When the cellulose ether acetate of the present invention is used, a lower retardation value in the thickness direction can be obtained even in such a use, and it can be suitably used.

[Acetylation process with controlled distribution of substitution degree of acetyl group in glucose ring]
As the second step of the present invention, an acetylation step in which the substitution degree distribution of the acetyl group in the glucose ring is controlled may be employed. That is, the solubility of cellulose acetate usually becomes poorer as the substitution degree of acetyl groups increases. And when it becomes a cellulose triacetate, as above-mentioned, only a methylene chloride will actually exist as a solvent. Among these cellulose triacetates, cellulose acetates in which the substitution degree distribution of acetyl groups in the glucose ring is controlled have been proposed. That is, it is a technique that dissolves in a cooled state in a solvent other than methylene chloride by paying attention to the degree of substitution at positions 2, 3, 6 of cellulose acetate. (Japanese Patent Laid-Open Nos. 11-5851 and 2002-338601)

  However, even in these cases, when the total acetylation degree exceeds 2.95, there is a problem that the solubility and the stability of the dissolved solution are deteriorated even by cooling dissolution. On the other hand, considering the optical properties and hygroscopicity of cellulose acetate, the degree of substitution is preferably as high as possible. When the cellulose acetate step having a high degree of substitution at the 6-position is used in the second step of the present invention, it can be dissolved in a solvent other than methylene chloride at room temperature even when MSether is small and DSester is high. Further, a cellulose ether acetate having a smaller Rth and a more preferable cellulose ether acetate can be obtained when used for an optical film for applications such as a polarizing plate protective film.

  Details are described below. In the conventional method for producing cellulose acetate, the obtained cellulose acetate is saponified and aged by maintaining it at 50 to 90 ° C. in the presence of a small amount of an acetylation reaction catalyst (generally, remaining sulfuric acid). The cellulose acetate has a degree of acetyl substitution and a degree of polymerization. When the desired cellulose acetate is obtained, the catalyst remaining in the system is completely neutralized with the neutralizing agent as described above, or water or Cellulose acetate solution was put into acetic acid (or water or dilute acetic acid was put into cellulose acetate solution) to separate cellulose acetate, and cellulose acetate was obtained by washing and stabilization treatment.

  Japanese Patent Application Laid-Open No. 11-5851 discloses that cellulose acetate having a relatively high degree of substitution at the 6-position can be obtained by selecting a small amount of sulfuric acid in the acetylation reaction. In general, when acetylation is performed under sulfuric acid conditions, the cellulose raw material as a solid phase undergoes acetylation and proceeds while gradually being dissolved. In the reaction under low sulfuric acid conditions, a qualitative difference occurs between the part dissolved first and the part dissolved later, and as a result, heterogeneous cellulose acetate is produced. For this reason, the produced cellulose ester solution causes white turbidity or poor solubility.

In the second step of the present invention, such cellulose ether acetate produced under low sulfuric acid conditions may cause problems such as white turbidity or poor solubility in the above cellulose ether acetate solution. Less. That is, when the cellulose ether acetate of the present invention is used, cellulose is etherified in the first step. For this reason, even in the crystal part of cellulose (especially cellulose type I crystal part) where acetylation is most difficult to proceed during the acetylation process, the crystal structure is relaxed to some extent before acetylation and is fixed in that state. . Therefore, as a whole, a uniform reaction easily proceeds in the acetylation step.
As a technique employed in the above process, it is preferable to use a technique disclosed in Japanese Patent Application Laid-Open No. 2002-338601 filed by the present applicants. That is, in the second step of the present invention, in the presence of 0.1 to 10 mol% (0.1 mol% or more and less than 10 mol%) of water or an alcohol and a catalyst, the acetyl group donor. Upon aging, the acetyl substitution degree at the 2-position, 3-position and 6-position can be adjusted easily and appropriately.

When this technique adjusts the degree of acetyl substitution continuously with the synthesis reaction of cellulose acetate, 0.1 mol% or more of water or alcohol is necessary for the decomposition of sulfate ester. When adjusting the degree of acetyl substitution, the fact that water or alcohol may not be present is utilized. The acetyl group donor has an acetyl group (—COCH ₃ ) in the molecule, and can donate an acetyl group to an unreacted hydroxyl group (—OH) of cellulose acetate by a transesterification reaction or an ester formation reaction in the presence of a catalyst. When the amount of water or alcohol is 10 mol% or more of the acetyl group donor, the degree of substitution is high (the total degree of acetyl substitution at the 2-position, 3-position and 6-position is 2.70 or more). ) In cellulose acetate, the acetyl group is easily released. Conversely, when the amount of water or alcohol is reduced to less than 10 mol% (preferably less than 7 mol%) of the acetyl group donor, the acetylation reaction of the free hydroxyl group (especially the hydroxyl group at the 6-position) is eliminated. Dominate against.

The above technique can also be used in the modified cellulose that is the product of the first step of the present invention. Therefore, the acetyl substitution degree at the 2-position, 3-position and 6-position can be effectively adjusted.
When the above technique is used, an acid or a metal (eg, titanium, tin) ion is preferable as the catalyst in the aging step of the second step of the present invention. As the acid, not only a normal proton acid but also a Lewis acid is effective. When the aging reaction is carried out in an acetic acid ester (acetyl group donor) -alcohol (solvent) system, a metal alkoxide or an organic base (eg, dialkylaminopyridine, N-methylimidazole) can also be used as a catalyst. The most preferred catalyst is an acid. The acid catalyst is preferably a strong acid (eg, sulfonic acid, perchloric acid, sulfuric acid, boron trifluoride, tetrafluoroboric acid). In consideration of various properties such as availability, stability, toxicity, and corrosivity, sulfuric acid is most preferable.

  In addition, under the reaction conditions of 100 ° C. or higher, acetic acid as an acetyl group donor can be used as an acid catalyst. An embodiment in which acetic acid serves as both an acetyl group donor and a catalyst is also included in the present invention. The amount of catalyst used is determined in consideration of the catalyst function (acidity in the case of an acid catalyst) and the reaction temperature. In the normal ripening reaction of cellulose ester, it was usual to carry out in an acetic acid (acetyl group donor) -water (solvent) system. However, the conventional ripening reaction was performed under conditions where water was present in an amount of 10 mol% or more based on acetic acid. Under such conditions, only the decomposition reaction of the ester bond of cellulose ether acetate proceeds, and the degree of substitution decreases. Therefore, in such an aging reaction, the degree of acetyl substitution at the 2-position, 3-position and 6-position could not be adjusted. As a desirable aging reaction in the second step of the present invention, by limiting the amount of water or alcohol to less than 10 mol% (preferably less than 7 mol%) of the acetyl group donor, the 2-position, 3-position and 6-position Adjust the degree of acetyl substitution. In the step of synthesizing cellulose ether acetate, an excess amount of acetic anhydride is generally used. However, before the aging step, excess acetic anhydride is hydrolyzed to acetic acid (no acetic anhydride is present in the aging step). It is preferable.

In order to appropriately adjust the equilibrium reaction between the acetyl group donor and cellulose ether acetate, the reaction history parameter (R) defined by the following formula is set to a value exceeding 20 in the aging process. It is preferable to adjust to. R is more preferably a value exceeding 30, and most preferably a value exceeding 40.
R = ∫YZ / Xdt
In the formula, X is the molar ratio of water or alcohol in the reaction system to the acetyl group donor; Y is the molar ratio of the catalyst in the reaction system to the acetyl group donor; Z is a temperature conversion factor ( 3 ^{(T-30) / 20} : T is the reaction temperature (° C.); and t is the reaction time.

  In addition, when X is less than 0.1 mol%, it calculates as 0.1. By adopting the above production method, it becomes a preferable step as the second step of the present invention, and it is possible to synthesize cellulose ether acetate in which the degree of acetyl substitution at the 2-position, 3-position and 6-position is appropriately adjusted. . In the present invention, when MSether is 0.7 or less (less than) and DSester is 2.0 or more, the sum of the 2- and 3-position substitutions is obtained by subtracting the 6-position substitution value from 2.67. Or less. Furthermore, in view of the acetylation process, a glucose ring substitution degree distribution satisfying the formulas (iii) and (iv) is preferable.

The degree of acetyl substitution at the 2-position, 3-position and 6-position of cellulose ether acetate can be determined by measuring 13 C-NMR after propionylating the cellulose acetate. Details of the measurement method are described in Tezuka et al. (Carbohydr. Res. 273 (1995) 83-91).
On the other hand, a film produced using a cellulose ether acetate having DSester = 2.3 to 2.6 has a high birefringence in the thickness direction. Accordingly, the thickness direction retardation (Rth) increases. When such a solution of cellulose ether acetate is obtained, if a cooling dissolution method is further used, a film having a larger birefringence in the thickness direction than a birefringence in the film plane direction, that is, an optical film having a large Rth can be obtained. And such an optical film becomes a film suitable for a viewing angle expansion film.
As described above, in the present invention, the DSester value can be adjusted so as to obtain an optical property suitable for the intended use between 2.3 and 3.0 in the DSester.

As described above, the second step of the present invention is an acetylation step. In this step, the cellulose is treated with acetic acid as described in Japanese Patent Application No. 2000-86998, and the pretreated cellulose is treated with vinegar. In the cellulose acetate manufacturing process including the cotton feeding process and the acetylation reaction process, the pretreated cellulose adhering to the cotton feeding path of the cotton feeding process is mixed with acetic acid or acetic acid and acetic anhydride prior to the start of the acetylation reaction. The method for producing cellulose acetate, which is characterized by being washed into the acetylation reaction system, can be suitably used as the second step of the present invention. That is, since the modified cellulose is acetylated in the second step of the present invention, it is a product that reacts more uniformly compared to normal cellulose acetylation, but at the end of acetylation and the mainland. There is a possibility that unreacted cellulose adhering to the inner wall of the reaction apparatus will fall into the reaction system at the stage where the process is completed. The technique described in Japanese Patent Application No. 2000-86998 is effective for reducing unreacted cellulose due to cellulose falling into the reaction system after the reaction in the acetylation process has progressed and cellulose having a significantly low reaction level. Can be used.

[Heat-resistant treatment]
In the production process of cellulose ether acetate, which is a raw material for the optical film of the present invention, it is desirable to perform heat resistance treatment at the final stage of the production process. That is, in general, the cellulose ester production method uses acetic acid as a solvent and a cellulose raw material to react with an acid such as acetic anhydride. At this time, a strong acid having a dehydrating action is used as a catalyst. Although sulfuric acid is generally used, this sulfuric acid not only acts as a catalyst, but also causes a reaction to become cellulose sulfate. As a result, depending on the reaction, this sulfate group also remains in the reaction product.
That is, cellulose acetate usually undergoes hydrolysis in an environment where heat and moisture are present. Even the cellulose ether acetate of the present invention similarly undergoes hydrolysis in the presence of heat and moisture to produce acetic acid.

Therefore, a general cellulose acetate usually has a stabilizer such as an alkali metal (lithium, potassium, sodium, etc.) or a salt thereof, a compound thereof, an alkaline earth metal (in order to improve heat stability and wet heat stability. Calcium, magnesium, strontium, barium, etc.) or a salt or compound thereof is contained in a large excess. Thereby, stability is imparted without making the sulfate group free.
Thus, it is arbitrary that the alkali acetate or alkaline earth metal is contained in the cellulose acetate, and the purpose thereof is to improve the heat resistance and wet heat stability as mentioned above. It has also been clarified that metals and alkaline earth metals affect the peelability and spinnability from a metal support (metal band) in the solution casting film forming method, that is, the solvent casting method. (Japanese Patent Laid-Open No. 10-316701)
And when the addition amount of alkaline-earth metal was reduced, it was inferior to stability and the heat-and-moisture stability was not satisfactory.
As described above, the alkali metals and alkaline earth metals added by the heat-resistant treatment have an adverse effect on the peelability of the metal metal band at the time of solvent casting of the optical film, and as a result, in the thickness direction of the optical film of the present invention. In order to increase the retardation (Rth), it is necessary to pay close attention to the amount added.

In the present invention, the total sulfuric acid (A) remaining in 1 g of cellulose ether acetate (unit is mol) and the total amount of calcium contained in 1 g of cellulose ether acetate (B) [unit is mol] When the ratio satisfies the following formula, it is possible to satisfy the mold release system and heat resistance stability for the metal.
0.5 <(B) / (A) <1.5
These relational expressions are preferably 0.5 <(B) / (A) <1.2.
More preferably 0.6 <(B) / (A) <1.0
It is. Furthermore, as the amount of calcium, the total amount of calcium (B) [unit is mol] contained in 1 g of cellulose ether acetate satisfies the following formula, but cellulose ether acetate is preferred.
5 × 10 ⁻⁷ <(B) <20 × 10 ⁻⁷
More preferably, the relational expression of the amount of calcium is 8 × 10 ⁻⁷ <(B) <15 × 10 ^−7.
It is.

An optical film made of cellulose ether acetate that has been subjected to heat treatment satisfying these relational expressions can provide a cellulose ether acetate optical film that is excellent in releasability and optical properties, and also excellent in wet heat stability. . In the present invention, (B) / (A) is a “Ca / SO4 ratio”, and the “Ca / SO4 ratio” is calculated based on the alkaline earth metal content and the sulfuric acid content obtained by the following method. Can be determined.
First, the dried cellulose ether acetate was completely burned, and then pretreated by dissolving ash in hydrochloric acid, and then measured by an atomic absorption method. The measured values are obtained in units of ppm as the content of each alkaline earth metal in 1 g of completely dry cellulose ether acetate.
The amount of sulfuric acid can be determined as follows.
The dried cellulose ether acetate is baked in an electric furnace at 1300 ° C., and the sublimated sulfurous acid gas is trapped in a 10% hydrogen peroxide solution and titrated with a normal sodium hydroxide aqueous solution. The obtained value is the amount of SO42-converted. The measured value is obtained in ppm as the sulfuric acid content in 1 g of the completely dry cellulose ester.

Of the above alkaline earth metal content, the Ca / SO4 ratio is calculated from the calcium content and the sulfuric acid content. The Ca / SO4 ratio is a molar ratio. That is, by dividing the amount of sulfuric acid by 96, 1) the sulfuric acid content in 1 g of cellulose ester can be obtained in mol. Similarly, 2) Calcium content in 1 g of cellulose ester can be obtained in units of mol by dividing calcium content by 40.1 out of the alkaline earth metal content. By dividing 2) by 1), the “Ca / SO4 ratio” can be obtained.
With wet heat stability, the amount of free acetic acid when boiled in a boiling water bath for 7 hours is used as a measure for estimating long-term hydrolysis stability. As a specific measurement method, the method described later is followed.

[Degree of substitution]
The degree of substitution DSester and MSether can be determined according to a conventional method. In other words, it can be measured by NMR or IR using a calibration curve made of an appropriate standard substance. Considering the accuracy of the substitution degree, it is preferable to obtain MSether and DSester by NMR.

[Degree of polymerization]
Furthermore, the polymerization degree of the cellulose ether acetate forming the optical film of the present invention is a viscosity average polymerization degree of 200 to 400, preferably 250 to 400, more preferably about 270 to 400 (for example, 290 to 400). The viscosity average degree of polymerization is about 270 to 350. The average degree of polymerization can be measured by the intrinsic viscosity method of Uda et al. (Kazuo Uda, Hideo Saito, Journal of Textile Society, Vol. 18, No. 1, pp. 105-120, 1962). In that case, a solvent can be selected suitably. For example, a modified cellulose triacetate or an optical film made thereof is dissolved in a mixed solution of methylene chloride / methanol = 9/1 (weight ratio) to prepare a solution having a predetermined concentration c (2.00 g / L). This solution is poured into an Ostwald viscometer, and the time (second) t during which the solution passes between the markings of the viscometer at 25 ° C. is measured. In the case of an optical film, since an additive is generally contained, the viscosity is measured after dissolving in a poor solvent of cellulose ether acetate and eluting the additive. On the other hand, for the mixed solvent alone, the passage time (seconds) t ₀ is measured in the same manner as described above, and the viscosity average polymerization degree can be calculated according to the following formula.

η rel = t / t ₀
[Η] = (lnη rel) / c
DP = [η] / (6 × 10 - 4)
(Where t is the solution passage time (second), t0 is the solvent passage time (second), c is the modified cellulose triacetate concentration (g / L) of the solution, η rel is the relative viscosity, and [η] is the limiting viscosity. DSester indicates the average degree of polymerization). Further, when a mixed solvent of methylene chloride / methanol = 9/1 (weight ratio) is used, the 6% by weight solution viscosity of the modified cellulose triacetate is, for example, 150 to 700 cps, preferably 200 to 600 cps, particularly about 250 to 500 cps. It is.

[Molecular weight distribution]
In the present invention, the molecular weight distribution, that is, the ratio of the number average molecular weight to the weight average molecular weight is also important.
That is, the cellulose ether acetate used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.4 to 5.0, more preferably 1.6 to 4.5, and more preferably 1.8 to 3.5. It is particularly preferably 1.9 to 3.2, and most preferably 2.0 to 3.0. In general, in acetylation of cellulose, it is considered that an acetylation reaction and cellulose depolymerization occur in parallel. Cellulose depolymerization is thought to follow the most probable distribution.

  Therefore, when the acetylation reaction is sufficiently performed, the molecular weight distribution of cellulose acetate seems to approach 2 according to the most probable distribution. Since cellulose is a natural product, cellulose acetate having a distribution of 4.5 or more can be obtained by selecting the molecular weight distribution of cellulose used as a raw material for cellulose acetate and using cellulose having a large molecular weight distribution. Cellulose acetate is not preferred for use in optical films. That is, when the value of Mw / Mn exceeds 4.5, the dope viscosity in which cellulose ether acetate is dissolved becomes too large, and the flatness of the film may be lowered. Cellulose acetate having a Mw / Mn value of 1.0 to 1.4 is generally difficult to produce. Even if it is going to obtain the cellulose acetate of the value of this range, only what has a remarkably low molecular weight is actually obtained. Therefore, the film produced from such cellulose acetate often deteriorates the mechanical properties of the film due to a decrease in molecular weight.

  In addition, as a method for obtaining the molecular weight distribution from the optical film of the present invention, size exclusion chromatography (Gel Permeation chromatography GPC) can be used. That is, after dissolving the optical film in an appropriate solvent, GPC measurement is performed, and it is confirmed from the peak width after confirming that the collected sample is cellulose ether acetate with an appropriate analyzer such as FT-IR or NMR. Molecular weight distribution can be determined. Since additives are often low molecular weight components, they can be separated at the GPC peak. Of course, in order to protect the GPC column, a plasticizer may be extracted from the optical film in advance using a poor solvent of cellulose ether acetate, and only the cellulose ether acetate may be measured by GPC.

As a preferable method for measuring the molecular weight distribution of cellulose ether acetate, the following measuring method can be used.
That is, a high performance liquid chromatography system (GPC-: SYSTEM-21, detector RI: detector RI-71, manufactured by Tosoh Corporation) in which a detector for detecting refractive index and light scattering is connected to a gel filtration column is used. The measurement conditions for GPC are as follows.

Solvent: Acetone column: TSKgel GMX _XL x2 (manufactured by Tosoh Corporation), sample concentration with guard column: 0.2 W / v%
Flow rate: 1.0ml / min
Sample injection volume: 300 μl
Standard sample: polymethyl methacrylate (Mw = 188,200)
Column temperature: 23 ° C
Next, the weight average molecular weight of cellulose ether acetate is measured under the same measurement conditions as described above. The molecular weight distribution may be calculated according to the following formula from the weight average molecular weight and number average molecular weight obtained from the measurement results.

Dp = Mw / Mn
Dp: molecular weight distribution Mw: weight average molecular weight Mn: number average molecular weight

[Moist heat stability]
The wet heat stability of the cellulose ether acetate film of the present invention can be determined by the following method.
First, the dried cellulose ester is pulverized, and about 2.0 g is weighed into a Pyrex (registered trademark) test tube, 2 ml of distilled water is added, and then sealed and immersed in a boiling water bath for 7 hours. After cooling, the contents are washed out on the filter paper with boiling water, and the filtrate is combined to 150 ml. This solution is titrated with 0.01N NaOH solution using phenolphthalein as an indicator. At the same time, a blank test using only the water used is performed, and the wet heat stability is calculated by the following formula.

Wet heat stability (%) = (A−B) × F × 0.06 ÷ sample weight (gr.)
(However, A: 0.01N-NaOH solution titration (ml) B: 0.01N-NaOH solution titration in blank test (ml) F: 0.01N-NaOH solution factor)

  Wet heat stability is an index of the difficulty of hydrolysis of the cellulose ester when it is exposed to high temperatures with sufficient water content. If it is 0.08% or less, the stability is evaluated. That is, when a film is obtained by the above method using the obtained cellulose acetate, the cellulose ester even when kept for a long time (for example, 1000 hours) under the condition of high temperature and high humidity (for example, 40 ° C. × 90 RH%). Difficult to cause problems with hydrolysis of

[Cellulose ester solution]
Cellulose ether acetate is dissolved in a solvent to prepare a cellulose ether acetate solution. As the solvent, an organic solvent is preferably used. As described above, the cellulose ether acetate solution of the present invention has an effect that it can be prepared using various kinds of organic solvents. That is, not only is it excellent in solubility in an organic solvent containing a halogen atom such as methylene chloride, but a solution can be prepared without using an organic solvent containing a halogen atom. However, of course, the solution may be prepared using methylene chloride. The proportion of the organic solvent containing halogen atoms in all the solvents is preferably 50% by weight or less, more preferably less than 5% by weight, and further preferably less than 2% by weight. Moreover, it is particularly preferable not to use it at all.

  An organic solvent not containing a halogen atom selected from ketones, esters and ethers is preferably used. Of these, ketones and esters are more preferable. Ketones, esters and ethers may have a cyclic structure. The boiling point of the organic solvent is preferably less than 140 ° C, more preferably less than 100 ° C, and most preferably less than 70 ° C.

  Examples of organic solvents include acetone (boiling point: 56 ° C.), N-methylpyrrolidone (boiling point: 202 ° C.), tetrahydrofuran (boiling point: 65.4 ° C.), 1,4-dioxane (boiling point: 101.1 ° C.), Examples include methyl acetate (boiling point: 57.8 ° C.), ethyl formate (boiling point: 54 ° C.), and 2-methoxyethanol (boiling point: 124 ° C.). Acetone and methyl acetate are particularly preferred. Two or more organic solvents may be used in combination. However, it can also be dissolved in a single solvent of methyl acetate. When two or more organic solvents are used in combination, the good solvent exemplified above and the other poor solvent may be used in combination. Examples of the poor solvent include lower alcohols having 1 to 4 carbon atoms (eg, methanol, n-butanol) and cyclohexane. When a good solvent and a poor solvent are used in combination, the proportion of the good solvent is preferably 50% by weight or more. More preferably, it is 70% by weight or more, and particularly preferably 90% by weight or more.

The cellulose ether acetate solution of the present invention can be prepared using a dope preparation method and apparatus in a general solvent cast method. A relatively low concentration solution can be obtained by stirring at room temperature. In the case of a high-concentration solution, it is preferably prepared by stirring under pressure and heating conditions. Specifically, cellulose ether acetate and a solvent are placed in a pressure vessel, sealed, and stirred under heating to a temperature not lower than the boiling point of the solvent at room temperature and in a range where the solvent does not boil. The heating temperature is usually 60 ° C. or higher, preferably 80 ° C. to 110 ° C.
Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. If necessary, an inert gas such as nitrogen gas can be injected to pressurize the container. 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. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like. The concentration of cellulose ether acetate in the solution to be prepared is determined according to the use of the solution. The concentration in the solution is generally 5 to 50% by weight, preferably 10 to 40% by weight. When the cellulose ether acetate solution is used for film production, the viscosity of the solution is preferably in the range of 10,000 to 1,000,000 cP. Preparation of these cellulose ester solutions is described in JP-A-08-231761.

[Cooling dissolution method of cellulose ether acetate with controlled substitution degree distribution of acetyl group in glucose ring]
As the second step of the present invention, a particularly preferred modified cellulose ester film and solution can be obtained when an acetylation step in which the substitution degree distribution of acetyl groups in the glucose ring is controlled is employed. That is, in the cellulose acetate step of the second step of the present invention, when a production method in which the substitution degree at the 6-position is specified among the three types of substituents of cellulose acetate, DSester is obtained by cooling and dissolving. Can be dissolved even when it is as high as 2.9 or more.

  When cellulose acetate is used for a constituent film of a liquid crystal display device such as a polarizing plate protective film or a retardation film, it is generally preferable that the birefringence is low. However, when a solvent other than methylene chloride is used as the solvent for these cellulose acetates, cellulose acetate having a high total acetylation degree, that is, a high DSester cannot be used. For this reason, in Japanese Patent Application Laid-Open No. 2002-338601 and Japanese Patent Application Laid-Open No. 2002-212338, those having a total acetylation degree of 2.97 or less are dissolved in a mixed solvent of methyl acetate and ethanol using the cooling dissolution method, or the total acetylation degree is 2.925 or less. Is dissolved in a mixed solvent.

  However, since the cellulose ether acetate of the present invention is excellent in solubility, even if the total acetylation degree, that is, DSester is 2.95 to 3.00, it can be dissolved by cooling if the 6-position substitution degree is high. is there. Furthermore, since there is little variation in the degree of substitution between molecules and within the molecule, the stability of the dissolved solution is also excellent. If the degree of substitution is less than 2.9, it can be dissolved in a solvent other than methylene chloride at room temperature. Various solvents can be used as the solvent for dissolving the cellulose ether acetate of the present invention having a substitution degree of less than 2.9, and examples thereof include methyl acetate and ethyl acetate. In particular, methyl acetate exhibits good solubility at room temperature.

The case where the cellulose ether acetate of the present invention having a high substitution degree at the 6-position and a total acetylation degree of 2.9 or more is dissolved by a cooling dissolution method is described below.
In the case where the optical film of the present invention is formed into a sex film by a solvent cast method from a solution dissolved by a cooling dissolution method, the organic solvent used for preparing the solution (dope) is preferably a substantially non-chlorine solvent. . “Substantially non-chlorine” means that a solvent containing at least one chlorine atom in the structural formula (eg, dichloromethane, dichloroethane, chlorobenzene) is not arbitrarily added, and the content thereof is 5 vol% or less. It is preferable that it is 1 vol% or less, and it is most preferable that it is less than 0 vol%. The non-chlorine solvent is preferably composed of a compound having 3 to 12 carbon atoms, and more preferably selected from the group consisting of esters, ethers, ketones and alcohols.

The ester, ether, ketone and alcohol may have a linear structure, a branched structure or a cyclic structure. A compound having any two or more functional groups of an ester, an ether, a ketone, and an alcohol (that is, —COO—, —O—, —CO—, and —OH) can also be used as a solvent. Examples of esters include methyl formate, ethyl formate, propyl formate, methyl acetate and ethyl acetate. Methyl formate, ethyl formate and methyl acetate are preferred, and methyl acetate is more preferred. Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclopentanone and cyclohexanone. Acetone, cyclopentanone and cyclohexanone are preferred, and acetone and cyclopentanone are more preferred.

  The esters and ketones preferably have a solubility parameter of 19-21. Further, two or more kinds of solvents may be mixed and used. It is preferable to use a mixture of an ester having a solubility parameter of 19 to 21 and a ketone having a solubility parameter of 19 to 21. Moreover, it is preferable to mix alcohol in addition to ester and ketone. As a combination of solvents, methyl acetate / cyclopentanone / acetone / methanol / ethanol (60/15/15/5/5, parts by mass), methyl acetate / acetone / methanol / ethanol (75/15/5/5, Parts by weight), methyl acetate / cyclohexanone / methanol / 1-butanol (70/20/5/5, parts by weight) and methyl formate 50 / methyl ethyl ketone / acetone / methanol / ethanol (50/20/20/5/5, weight) Methyl acetate / acetone / methanol / ethanol (75/15/5/5, parts by mass), methyl acetate / cyclopentanone / methanol / ethanol (80/10/5/5, parts by mass) preferable.

  In order to prepare a cellulose ether acetate solution (dope), the cellulose ether acetate is first swollen by adding the cellulose ether acetate while stirring the solvent in the tank at room temperature. The swelling time is required to be at least 10 minutes, and insoluble materials remain after 10 minutes. Moreover, in order to fully swell cellulose ether acetate, the temperature of the solvent is preferably 0 to 40 ° C. If the temperature is 0 ° C. or lower, the swelling speed tends to decrease and insoluble matter tends to remain. If the temperature is 40 ° C. or higher, the swelling rapidly occurs and the central portion does not swell sufficiently. In order to dissolve cellulose ether acetate after the swelling step, it is preferable to use a cooling dissolution method or both a cooling dissolution method and a high temperature dissolution method. In the cooling dissolution method, first, cellulose ether acetate is gradually added to an organic solvent with stirring at a temperature around room temperature (−10 to 40 ° C.).

  An auxiliary solvent (eg, alcohol) may be added after cellulose ether acetate is added to the main solvent (eg, ester, ketone). Further, the main solvent may be added after the cellulose ether acetate is previously moistened with an auxiliary solvent (eg, alcohol). The amount of cellulose ether acetate is preferably adjusted so as to be contained in the mixture at 10 to 40% by mass. Furthermore, the amount of cellulose ether acetate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture. The mixture is then cooled to -100 to -10 ° C, more preferably -80 to -10 ° C, more preferably -50 to -20 ° C, and 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.). The cooling rate is preferably as high as possible, and is preferably 100 ° C./second or more. Also, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling.

After cooling, heating to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.) provides a solution in which cellulose ether acetate is dissolved in an organic solvent. . Heating may be performed only at room temperature.
The cooled mixture may also be warmed in a warm bath. 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. The cooling and heating operations may be repeated twice or more. The viscosity of the cellulose ether acetate solution immediately before film formation is adjusted within a range that allows casting. The viscosity is preferably in the range of 10 Pa · s to 2000 Pa · s, and more preferably 30 Pa · s to 4030 Pa · s. In addition, it is preferable that it is -5-70 degreeC, and, as for the temperature at the time of casting, it is more preferable that it is -5-55 degreeC. The concentration of the cellulose ether acetate solution is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass.

In the cellulose ether acetate solution, additives (eg, plasticizers, deterioration inhibitors, UV inhibitors) may be added depending on the application. These additives are plasticizers, UV inhibitors and deterioration inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines).
It is common to add a plasticizer to the cellulose ether acetate film in order to improve the mechanical properties or to increase the drying speed.
Examples of plasticizers include triphenyl phosphate (TPP), diphenyl biphenyl phosphate, tricresyl phosphate (TCP), dioctyl phthalate (DOP), tributyl O-acetylcitrate (OACTB), and acetyltriethyl citrate. .

As plasticizers for reducing optical anisotropy, (di) pentaerythritol esters (described in JP-A-11-124445), glycerol esters (described in JP-A-11-246704), diglycerol esters (special JP-A 2000-63560), citric acid ester (described in JP-A-11-92574) or substituted phenyl phosphates (described in JP-A-11-90946) may be used. Two or more plasticizers may be used in combination. The addition amount of the plasticizer is preferably 5 to 30% by mass, more preferably 8 to 16% by mass with respect to the cellulose ether acetate.
Regarding the deterioration preventing agent and the ultraviolet ray preventing agent, JP-A-60-235852, JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, 6-118233, 6-148430, 7-11056, 7-11055, 7-11056, 8-29619, 8-239509, and JP-A-2000-204173. There is a description.

Examples of the deterioration preventing agent include butylated hydroxytoluene (BHT). The ultraviolet absorber is preferably a compound that has the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and has little absorption of visible light having a wavelength of 400 nm or more. Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, and nickel complex compounds. Benzotriazole compounds and benzophenone compounds are preferred. The addition amount of the deterioration inhibitor and the ultraviolet light inhibitor is preferably 1 ppm to 10000 ppm, more preferably 10 to 1000 ppm in terms of mass ratio with respect to cellulose ether acetate.
The cellulose ether acetate of the present invention has an advantage that a small amount of plasticizer may be added as compared with the conventional cellulose acetate. For this reason, even if the amount of the plasticizer is 15% by weight or less, the effect of the plasticizer can be obtained. Examples of the deterioration inhibitor that can be added to the cellulose ester solution (dope) or the cellulose ester film include a peroxide decomposer, a radical inhibitor, a metal deactivator, and an acid scavenger. The deterioration preventing agent is described in JP-A-5-1973. Further, the ultraviolet ray preventing agent is described in JP-A-7-156.

  The in-plane retardation (Re) of the cellulose ether acetate film is preferably in the range of 0 to 300 nm. The retardation (Rth) in the thickness direction of the film is preferably from 0 nm to 600 nm, more preferably from 0 nm to 400 nm, and most preferably from 0 nm to 250 nm per 100 μm thickness.

[paint remover]
As described in the aspect (23), the optical film of the present invention has at least one acid having an acid dissociation index pka in an aqueous solution of 1.93 to 4.50, an alkali metal salt of the acid, and the acid. At least one selected from alkaline earth metal salts can be included as a release agent.
The release agent can be added before casting the cellulose ether acetate solution. The release agent may be contained in cellulose ether ester which is a raw material of the optical film of the present invention.

The release agent is preferably an acid having an acid dissociation index (pKa) in an aqueous solution of 1.93 to 4.50, an alkali metal salt or an alkaline earth metal salt thereof. As the acid, either an inorganic acid or an organic acid can be used. Examples of inorganic acids include HClO ₂ (2.31), HOCN (3.48), molybdic acid (H ₂ MoO ₄ , 3.62), HNO ₂ (3.15), phosphoric acid (H ₃ PO ₄ 2.15), triphosphoric acid (H ₅ P ₃ O ₁₀ , 2.0) and vanadic acid (H ₃ VO ₄ , 3.78). The numerical value in parentheses is the acid dissociation index (pKa) in an aqueous solution (the same applies to the following acids). Typical organic acids are carboxylic acid, sulfonic acid and phosphoric acid.

  Carboxylic acids include aliphatic monocarboxylic acids, aliphatic polycarboxylic acids, oxycarboxylic acids, aldehyde acids, ketone acids, aromatic monocarboxylic acids, aromatic polycarboxylic acids, heterocyclic monocarboxylic acids, heterocyclic rings Formula polycarboxylic acids and amino acids are included. Examples of aliphatic monocarboxylic acids include formic acid (3.55), oxaloacetic acid (2.27), cyanoacetic acid (2.47), phenylacetic acid (4.10), phenoxyacetic acid (2.99), fluoro Acetic acid (2.59), chloroacetic acid (2.68), bromoacetic acid (2.72), iodoacetic acid (2.98), mercaptoacetic acid (3.43), vinylacetic acid (4.12), chloropropionic acid (2.71-3.92), 4-aminobutyric acid (4.03) and acrylic acid (4.26). Ten examples of aliphatic polycarboxylic acids include malonic acid (2.65), succinic acid (4.00), glutaric acid (4.13), adipic acid (4.26), pimelic acid (4.31). ), Azelaic acid (4.39), and fumaric acid (2.85). Examples of oxycarboxylic acids include glycolic acid (3.63), lactic acid (3.66), malic acid (3.24), tartaric acid (2.82-2.99) and citric acid (2.87), Examples of aldehyde acids include glyoxylic acid (3.18). Examples of ketonic acid include pyruvic acid (2.26) and levulinic acid (4.44).

  Examples of aromatic monocarboxylic acids include aniline sulfonic acid (3.74-3.23), benzoic acid (4.20), aminobenzoic acid (2.02-3.12), chlorobenzoic acid (2. 92-3.99), cyanobenzoic acid (3.60-3.55), nitrobenzoic acid (2.17-3.45), hydroxybenzoic acid (4.08-4.58), anisic acid (4 .09-4.48), fluorobenzoic acid (3.27-4.14), chlorobenzoic acid, bromobenzoic acid (2.85-4.00), iodobenzoic acid (2.86-4.00) Salicylic acid (2.81), naphthoic acid (3.70-4.16), cinnamic acid (3.88) and mandelic acid (3.19). Examples of aromatic polycarboxylic acids include phthalic acid (2.75), isophthalic acid (3.50) and terephthalic acid (3.54). Examples of heterocyclic monocarboxylic acids include nicotinic acid (2.05) and 2-furan carboxylic acid (2.97). Examples of the heterocyclic polyvalent carboxylic acid include 2,6-pyridinedicarboxylic acid (2.09).

  In addition to normal amino acids, amino acids include amino acid derivatives (amino acids having substituents and oligopeptides. Examples of amino acids include asparagine (2.14), aspartic acid (1.93), and adenine (4 .07), alanine (2.30), β-alanine (3.53), arginine (2.05), isoleucine (2.32), glycine (2.36), glutamine (2.17), glutamic acid ( 2.18), serine (2.13), tyrosine (2.17), tryptophan (2.35), threonine (2.21), norleucine (2.30), valine (2.26), phenylalanine 50 ( 2.26), methionine (2.15), lysine (2.04), leucine (2.35), adenosine (3.50), adenosine triphosphate (4.06), ade Sinphosphate (3.65-3.80), L-alanyl-L-alanine (3.20), L-alanylglycine (3.10), β-alanylglycine (3.18), L-alani Luglycylglycine (3.24), β-alanylglycylglycine (3.19), L-alanylglycylglycylglycine (3.18), glycyl-L-alanine (3.07), glycyl-β- Alanine (3.91), glycylglycyl-L-alanine (3.18), glycylglycylglycine (3.20), glycylglycylglycylglycine (3.18), glycylglycyl-L-histidine (2.72) Glycylglycylglycyl-L-histidine (2.90), glycyl-DL-histidylglycine (3.26), glycyl-L-histidine (2.54), glycy Ru-L-leucine (3.09), γ-L-glutamyl-L-cysteinylglycine (2.03), N-methylglycine (sarcosine, 2.20), N, N-dimethylglycine (2. 08), citrulline (2.43), 3,4-dihydroxyphenylalanine (2.31), L-histidylglycine (2.84), L-phenylalanylglycine (3.02), L-prolyl. Glycine (3.07) and L-Leucyl-L-tyrosine (3.15) are included.

Moreover, sulfonic acid and phosphoric acid can also be used as a release agent. A surfactant (described in JP-A-61-243837) can also be used as a release agent. Examples of surfactants used as release agents include C ₁₂ H ₂₅ O—P (═O) — (OK) ₂ , C ₁₂ H ₂₅ OCH ₂ CH ₂ O—P (═O) — (OK) _2. and _{(iso-C 9 H 19)} 2 -C 6 H 3 -O- (CH 2 CH 2 O) 3 - (CH 2) include ₄ SO ₃ Na.
The total content of the acid or metal salt is determined within a range where the peelability and transparency are not impaired. Content per cellulose ether acetate 1 g, 1 × 10 ^- is preferably ⁵ mol ^{- 9 ~3} × 10.

[Fine particles]
Fine film (matting agent) can be added to prevent film stagnation. The fine particles are preferably made of an inorganic substance. Examples of inorganic materials include silica, kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, alumina, manganese colloid, titanium dioxide, strontium barium sulfate, silicon dioxide, alkaline earth metals (eg, calcium , Magnesium) salts. The average height of the protrusions on the film surface by adding fine particles is preferably 0.005 to 10 μm, and more preferably 0.01 to 5 μm. The shape of the fine particles is preferably spherical or irregular. The content of fine particles in the film is preferably 0.5 to 600 mg / m <2>, more preferably 1 to 400 mg / m <2>.

It is preferable to remove foreign matters (eg, undissolved matter, dust, impurities) from the solution before casting using an appropriate filter medium (eg, wire mesh, paper, flannel). The absolute filtration accuracy of the filter used for solution filtration is preferably 0.05 to 100 μm, and more preferably 0.5 to 10 μm. The filtration pressure is preferably 16 kg / cm 2 or less, more preferably 12 kg / cm 2 or less, further preferably 10 kg / cm 2 or less, and most preferably 2 kg / cm 2 or less.
[Production of cellulose ether acetate film]
As a method and equipment for producing a cellulose ether acetate film, a solution casting film forming method and a solution casting film forming apparatus for use in conventional cellulose triacetate film production can be used.

  The dope (cellulose ether acetate solution) prepared from the dissolution tank (pot) is temporarily stored in a stock tank, and the foam contained in the dope is defoamed or finally prepared. The dope is sent from the dope discharge port to the pressure die through a pressure metering gear pump capable of delivering a constant amount of liquid with high accuracy, for example, by the number of rotations, and the dope is run endlessly from the die (slit) of the pressure die. The dry-dried dope film (also referred to as a web) is peeled from the support at a peeling point that is uniformly cast on the support and has substantially gone around the support. Both ends of the obtained web are sandwiched between clips, transported by a tenter while keeping the width, 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 dryer varies depending on the purpose. In the solution casting film forming method used for silver halide photographic light-sensitive materials and functional protective films for electronic displays, in addition to the solution casting film forming apparatus, various layers (undercoat layer, antistatic layer, antihalation layer) In order to provide a protective layer on the support, a coating apparatus is often added.

  The obtained cellulose ether acetate solution is cast on a smooth band or drum as a support. Two or more cellulose ether acetate films may be produced by sequentially casting or co-casting a plurality of cellulose ether acetate liquids. For example, when casting a plurality of cellulose ether acetate solutions, a film is produced while casting and laminating a solution containing cellulose ether acetate from a plurality of casting openings provided at intervals in the direction of travel of the support. It is also possible (described in JP-A-11-198285). Also, a method of forming a film by casting a cellulose ether acetate solution from two casting ports (described in JP-A-6-134933) can be carried out. Also, a cellulose ether acetate film casting method in which a flow of a high viscosity cellulose ether acetate solution is wrapped with a low viscosity cellulose ether acetate solution and the high and low viscosity cellulose ether acetate solution is simultaneously extruded (Japanese Patent Laid-Open No. Sho 56-162617). (Publication publication).

  By performing such co-casting, as described above, since the smoothing in the drying of the surface proceeds, a significant improvement in the surface shape can be expected. In the case of co-casting, the thickness of each layer is not particularly limited, but preferably the outer layer is preferably thinner than the inner layer. In this case, the thickness of the outer layer is preferably 1 to 50 μm, particularly preferably 1 to 30 μm. Here, the surface layer indicates a layer that is not a band surface (drum surface) in the case of two layers, and a layer on both surface sides of the completed film in the case of three or more layers. The inner layer is a band surface (drum surface) in the case of two layers. In the case of three or more layers, a layer located inside the surface layer is shown. The cellulose ether acetate solution can be cast simultaneously with other functional layers (eg, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorption layer, and a polarizing layer).

  30-250 degreeC is preferable and the drying temperature in a drying process has more preferable 40-180 degreeC. The drying process is described in JP-B-5-17844. A method of actively stretching the film in the width direction (described in JP-A-62-115035, JP-A-4-152125, JP-A-4284221, JP-A-4-298310, and JP-A-11-48271) May be adopted. Uniaxial stretching or biaxial stretching can be employed for stretching the film. The stretching ratio of the film (the ratio of the increase due to stretching relative to the original length) is preferably 10 to 30%.

  The thickness of the finished cellulose ether acetate film (after drying) varies depending on the purpose of use, but is usually in the range of 5 to 500 μm, more preferably in the range of 20 to 250 μm, and most preferably in the range of 30 to 180 μm. In addition, as an optical use, the range of 30-110 micrometers is especially preferable. The thickness of the film 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, and the support speed so as to obtain a desired thickness.

  The surface treatment of the cellulose ether acetate film may improve the adhesion between the cellulose ether acetate film and each functional layer (for example, the undercoat layer and the back layer). Surface treatment includes glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, acid or alkali treatment. Acid or alkali treatment is preferred, and alkali treatment is more preferred. The acid or alkali treatment functions as a saponification treatment for the cellulose ether acetate film. The alkali saponification treatment is preferably performed by a procedure of immersing the film surface in an alkali solution, neutralizing with an acidic solution, washing with water and drying. Examples of the alkaline solution include a potassium hydroxide solution and a sodium hydroxide solution, and the prescribed concentration of hydroxide ions is preferably 0.1N to 3.0N, and more preferably 0.5N to 2.0N. The alkaline solution temperature is preferably room temperature to 90 ° C, more preferably 30 ° C to 70 ° C. Next, it is generally washed with water, and then passed through an acidic aqueous solution, followed by washing with water to obtain a surface-treated cellulose ether acetate film. At this time, the acid is hydrochloric acid, nitric acid, sulfuric acid, acetic acid, formic acid, chloroacetic acid, oxalic acid or the like, and the concentration is preferably 0.01N to 3.0N, more preferably 0.05N to 2.0N. In order to achieve adhesion between the cellulose ether acetate film support and the functional layer, it is also preferable to provide an undercoat layer (adhesive layer) and apply the functional layer thereon.

[Elements of liquid crystal display devices]
In the constitution of the protective film for polarizing plate, it is preferable that an antistatic layer is provided on at least one layer of the cellulose ether acetate film or a hydrophilic binder layer for adhering to the polarizer is provided. As the conductive material, a conductive metal oxide or a conductive polymer is preferable. A transparent conductive film by vapor deposition or sputtering may be used. The conductive layer may be the outermost layer or the inner layer without any problem.

Regarding the power transmission performance of the conductive layer, the resistance is preferably 10 ⁰ to 10 ¹² Ω, and more preferably 10 ⁰ to 10 ¹⁰ Ω. The power transmission layer of the conductive layer is preferably a metal oxide. Examples of metal oxides include _{ZnO, TiO 2, SnO 2,} Al 2 O 3, In 2 O 3, SiO 2, MgO, BaO, is MoO _2, V ₂ O ₅ and a composite oxide. ZnO, SnO ₂ and V ₂ O ₅ are preferred. Examples of the conductive ionic polymer compound include an ionene type polymer having a dissociating group in the main chain and a cationic pendant polymer having a cationic dissociating group in the side chain. As the conductive material, an organic electron conductive material is preferable. Examples of organic electron conductive materials include polyaniline derivatives, polythiophene derivatives, polypyrrole derivatives, and polyacetylene derivatives.

  A surfactant can be preferably added to any functional layer of the cellulose ether acetate film of the present invention. Nonionic surfactants, cationic surfactants and betaine surfactants are preferred. A fluorine-based surfactant can also be used. The surfactant can function as a coating agent or an antistatic agent in an organic solvent. Moreover, it is preferable to contain a slipping agent in any layer on the cellulose ether acetate film of the present invention.

  Examples of the slip agent include polyorganosiloxane (described in Japanese Patent Publication No. 53-292), higher fatty acid amide (described in US Pat. No. 4,275,146), higher fatty acid ester (British Patent 927446, Japanese Patent Publication No. 58-33541). And JP-A 55-126238 and 58-90633). The higher fatty acid ester is an ester of a fatty acid having 10 to 24 carbon atoms and an alcohol having 10 to 24 carbon atoms.

The optical film formed from the cellulose ether acetate solution of the present invention can be used in various optical applications, but is particularly effective when used as an optical compensation sheet for a liquid crystal display device.
In the cellulose ether acetate film of the present invention, the film itself can be used as an optical compensation sheet. When the film itself is used as an optical compensation sheet, the transmission axis of the polarizing element (described later) and the slow axis of the optical compensation sheet made of cellulose ether acetate film are arranged so as to be substantially parallel or perpendicular. It is preferable. Such an arrangement of the polarizing element and the optical compensation sheet is described in JP-A-10-48420. The liquid crystal display device includes a liquid crystal cell having a liquid crystal supported between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one sheet between the liquid crystal cell and the polarizing element. An optical compensation sheet is arranged. The liquid crystal layer of the liquid crystal cell is usually formed by sealing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on the substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer, or an undercoat layer (used for adhesion of the transparent electrode layer). These layers are usually provided on the substrate. The substrate of the liquid crystal cell generally has a thickness of 80 to 500 μm.

  The retardation film is also called an optical compensation sheet, and is a birefringence film for removing the color of the liquid crystal screen. The cellulose ether acetate film can be used as an optical compensation sheet. Further, the function may be imparted as an antireflection layer, an antiglare layer, a λ / 4 layer or a biaxially stretched cellulose ether acetate film. In order to improve the viewing angle of the liquid crystal display device, a cellulose ether acetate film and a film showing birefringence (positive / negative relationship) opposite to that may be used as an optical compensation sheet. These films have also been demonstrated as viewing angle widening films. The range of the thickness of the optical compensation sheet is the same as the preferable thickness of the above-described film. Examples of the polarizing film of the polarizing element include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. Any polarizing film is generally produced using a polyvinyl alcohol film. The protective film of the polarizing plate preferably has a thickness of 25 to 350 μm, and more preferably 30 to 200 μm. The liquid crystal display device may be provided with a surface treatment film. The functions of the surface treatment film include hard coat, anti-fogging treatment, anti-glare treatment and antireflection treatment. As described above, there has also been proposed an optical compensation sheet in which an optically anisotropic layer containing a liquid crystal (particularly a discotic liquid crystalline molecule) is provided on a support (Japanese Patent Application Laid-Open Nos. 3-9325 and 6-148429). Nos. 8-50206 and 9-26572). The cellulose ether acetate film can also be used as a support for such an optical compensation sheet.

  Furthermore, the cellulose ether acetate film of the present invention has a support for an optical compensation sheet of a VA type liquid crystal display device having a VA mode liquid crystal cell, an OCB type liquid crystal display device having an OCB mode liquid crystal cell, or a HAN mode liquid crystal cell. It is preferably used as a support for an optical compensation sheet of a HAN type liquid crystal display device and an optical compensation sheet for an ASM type liquid crystal display device having ASM (Axially Symmetric Aligned Microcell) mode liquid crystal cells.

Furthermore, a polarizing plate on which a polarizing element film that serves as a light shutter is laminated is provided on the surface of a display body such as a liquid crystal display. However, since the polarizing plate itself has poor scratch resistance, It is protected by a transparent protective substrate such as a transparent plastic plate or a transparent plastic film. Since a transparent protective substrate made of a plastic such as a transparent plastic plate or a transparent plastic film is easily damaged, in recent years, it has been developed to treat the surface of the polarizing plate with high mechanical strength. As such a technique, for example, there is a technique described in JP-A-1-105738. The cellulose ether acetate film of the present invention is also preferably used as such a transparent protective substrate.
JP-A-6-157791 discloses a triacetyl cellulose film having an antireflection effect in addition to the above-mentioned purpose, a polarizing plate using the film, and a method for producing a triacetyl cellulose film having excellent scratch resistance. Yes. The cellulose ether acetate film of the present invention can also be suitably used as an antireflection film having such an antireflection effect.

In each example, the chemical and physical properties of cellulose ether acetate, solution and film were measured and calculated as follows.

(1) Degree of Substitution of Cellulose Ether Acetate In the present invention, DSester (acetyl substitution degree) and MSether (degree of ether substitution) of the optical film of the present invention or cellulose ether acetate which is a raw material of the optical film are 13C-NMR (nuclear). It can be measured by a magnetic resonance method. At this time, for example, deuterated methyl sulfoxide (DMSO-d6) can be used as a measurement solvent. If the sample is a film of the present invention, it contains plasticizers and additives, so that these plasticizers can be extracted as much as possible with an appropriate organic solvent and analyzed by the same method as described above. .

(2) Solubility in non-halogen solvent To 85 parts by weight of a predetermined non-halogen solvent, 15 parts by weight of a cellulose ether acetate sample or a cellulose acetate sample is added and stirred at room temperature (23 ° C.). Observation was conducted for days, and the dissolution state was determined silently.
◯: Transparent, uniformly dissolved, maintained even after 1 day, indicating a stable solution state.
(Triangle | delta): Although transparent and melt | dissolves uniformly, after 1 day progress, a non-uniform | heterogenous slurry state is shown.
X: Even if it stirs, it forms only a non-uniform slurry and does not show a transparent uniform solution state.

(3) Method for measuring crystallinity of modified cellulose First, a sample of modified cellulose, which is a product of the first step of the present invention, or a pulp sample as a raw material is used as an X-ray generator as a rotating counter-cathode type as an X-ray source. Using Cu Kα line, the tube voltage is 40 kV and the tube current is 30 mA. The goniometer is operated at a rotational angular velocity of 2 ° (2θ) / min, and an X-ray diffraction intensity is obtained in a range of 2θ = 3 ° to 30 ° by a symmetrical reflection method. The obtained X-ray diffraction curve is not subjected to air scattering, Lorentz / polarization factor correction, or the like, and is separated into a crystalline diffraction peak and an amorphous background by a multiple peak separation method. The sum of the integrated intensities of the crystalline diffraction peaks was calculated, and the sum of the integrated intensities in the same measurement angle range was expressed as a percentage to determine the crystallinity.

(4) Hemicellulose content Cellulose ether acetate is hydrolyzed by being diluted with 72% by weight sulfuric acid in an ice water bath for 4 hours, then diluted to 6% by weight sulfuric acid and treated at 110 ° C. for 3 hours. After neutralizing this with barium carbonate, the filtrate obtained by filtration was subjected to liquid chromatography analysis using a sugar analysis system manufactured by Dionex, and the ratio of the total amount of mannose and xylose to the total amount of mannose, xylose and glucose (mol %).

(5) Haze of solution, YI
[Haze]
12.0 g of the dried modified cellulose is accurately weighed and 88.0 g of a solvent (mixed solvent of methylene chloride / methanol = 9/1 (weight ratio)) is added and completely dissolved (12 wt% sample solution). Using a turbidimeter (manufactured by Nippon Denshoku Industries Co., Ltd.) and using a glass cell (width 45 mm, height 45 mm, optical path length 10 mm), measurement is performed as follows. The solvent is placed in a glass cell and set in a turbidimeter, and zero point alignment and standard alignment are performed. Next, a 12 wt% sample solution is put in a glass cell, set in a turbidimeter, and the numerical value is read.
[Yellowness Index (YI)]
12.0 g of dried cellulose ether acetate is accurately weighed, and 88.0 g of a solvent (mixed solvent of methylene chloride / methanol = 9/1 (weight ratio)) is added and completely dissolved (12 wt% sample solution). Using a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., color difference meter Σ90) and a glass cell (width 45 mm, height 45 mm, optical path length 10 mm), YI is calculated by the following formula. YI = YI2 -YI1 (where YI1 represents the YI value of the solvent and YI2 represents the YI value of the 12 wt% sample solution).

(6) Insoluble component amount (measurement method)
A solution obtained by dissolving cellulose ether acetate in a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio) to a concentration of 2 wt% solid content is filtered using a glass filter (pore diameter: 5 to 10 μm). As a glass filter, G-4 manufactured by Mutual Science Glass Co., Ltd. was used. Thereafter, the dope adhering to the filtration residue is washed with a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio). The filtration residue is dried together with the glass filter until a constant weight is obtained. The weight of the glass filter before and after filtration is measured, and the amount of insoluble matter is calculated from the following formula.
Insoluble matter amount (wt%) = [glass filter weight after filtration (g) −glass filter weight before filtration (g)] / weight of cellulose ether acetate (g) × 100

(7) Measurement of bright spot foreign matter The bright spot foreign substance of the film prepared using the cellulose ether acetate of the present invention is obtained by the following method.
Two polarizing plates are placed in an orthogonal state (crossed Nicols), the sample is placed between them, an image is captured per 20 mm ² (4 mm x 5 mm) using a microscope with a CCD camera, and binarized by image conversion software. . Since bright spot foreign matter appears white, the number of foreign matters having a diameter of 10 μm or more that appears white is counted. This operation was repeated 20 times. That is, bright spot foreign matter was measured at 20 locations. These average values were determined. At this time, the microscope was equipped with a CCD camera and was a transmission light source at a magnification of 30 times.
In addition, the polarizing plate used in order to measure a bright spot foreign material was a product made from glass.
The average value of the obtained bright spot foreign matter was divided by 20 mm ² which is the area where the image was taken in, and the number of bright spot foreign matters per 1 mm ² was calculated.
The following synthesis examples were carried out using hardwood kraft pulp or conifer sulfite pulp described in Table 1 below.

Synthesis example 1
(First Step) Synthesis of Modified Cellulose 140 parts by weight of 5% aqueous sodium hydroxide solution was added to 100 parts by weight of hardwood kraft pulp of Table 1 and mixed. Next, 800 parts by weight of propylene oxide was added and kept at a temperature of 0 to 5 ° C. with stirring for about 1 hour, and then heated to 30 to 40 ° C. and reacted for 6 hours. The contents were filtered off to remove the precipitate, and warm water was added thereto. After neutralizing with 1% phosphoric acid aqueous solution, the reaction product was precipitated by dropwise addition into acetone. The product was separated by filtration, washed several times with acetone / water (9: 1), and vacuum-dried at 60 ° C. to obtain hydroxypropylcellulose, which is the modified cellulose of the present invention. The degree of substitution (MSether) of the product with propylene oxide was 1.1 as a result of measurement by NMR.

(Second step) Acetylation of modified cellulose After applying 50 parts by weight of acetic acid to 100 parts by weight of the modified cellulose obtained in the first step and activating pretreatment, 470 parts by weight of glacial acetic acid and 265 parts by weight of acetic anhydride. A mixture of 8.3 parts by weight and 8.3 parts by weight of sulfuric acid was added and esterification was carried out by a conventional method. Thereafter, hydrolysis is carried out, and a heat resistance stabilizer (calcium acetate and magnesium acetate) is added, whereby acetyl substitution degree (DSester) = 2.91, substitution degree with propylene oxide (MSether) = 1.1, viscosity average polymerization A cellulose ether acetate having a degree of 289 was obtained. The obtained cellulose ether acetate had a YI of 3.2 and a haze of 1.7. Further, it was uniformly dissolved in methyl acetate and acetone at a concentration of 10% by weight at room temperature.

Synthesis example 2
(First Step) Synthesis of Modified Cellulose 140 parts by weight of 5% aqueous sodium hydroxide solution was added to 100 parts by weight of hardwood kraft pulp of Table 1 and mixed. Next, 100 parts by weight of propylene oxide was added and kept at a temperature of 0 to 5 ° C. with stirring for about 1 hour, and then heated to 30 to 40 ° C. and reacted for 4 hours. The contents were separated by filtration to remove the precipitate, neutralized with a 1% phosphoric acid aqueous solution to which warm water was added, and then dropped into acetone to precipitate a reaction product. The product was separated by filtration, washed several times with acetone / water (9: 1), and vacuum-dried at 60 ° C. to obtain hydroxypropylcellulose, which is the modified cellulose of the present invention. The degree of substitution of the product with propylene oxide (MSether) was 0.10.

(Second step) Acetylation of modified cellulose After applying 50 parts by weight of acetic acid to 100 parts by weight of the modified cellulose obtained in the first step and activating pretreatment, 470 parts by weight of glacial acetic acid and 265 parts by weight of acetic anhydride. A mixture of 8.3 parts by weight and 8.3 parts by weight of sulfuric acid was added and esterification was carried out by a conventional method. Thereafter, hydrolysis is carried out, and a heat resistance stabilizer (calcium acetate and magnesium acetate) is added, whereby acetyl substitution degree (DSester) = 2.89, substitution degree with propylene oxide (MSether) = 0.1, viscosity average polymerization A cellulose ether acetate having a degree of 304 was obtained. The obtained cellulose ether acetate had a YI of 3.7 and a haze of 1.8. Further, it was uniformly dissolved in methyl acetate at a concentration of 10% by weight at room temperature. The crystallinity of the softwood sulfite pulp used in this synthesis example was 59%. On the other hand, the crystallinity of the modified cellulose in the synthesis example was 27%.

Synthesis example 3
(First Step) Synthesis of Modified Cellulose 140 parts by weight of 5% aqueous sodium hydroxide solution was added to 100 parts by weight of hardwood kraft pulp of Table 1 and mixed. Next, 50 parts by weight of propylene oxide was added, and the mixture was maintained at a temperature of 0 to 5 ° C. for about 1 hour with stirring, and then heated to 30 to 40 ° C. and reacted for 4 hours. The contents were separated by filtration to remove the precipitate, neutralized with a 1% phosphoric acid aqueous solution to which warm water was added, and then dropped into acetone to precipitate a reaction product. The product was separated by filtration, washed several times with acetone / water (9: 1), and vacuum-dried at 60 ° C. to obtain hydroxypropylcellulose, which is the modified cellulose of the present invention. The degree of substitution of the product with propylene oxide (MSether) was 0.05.
(Second step) Acetylation of modified cellulose

[Acetylation process]
30 parts by weight of glacial acetic acid was uniformly sprayed on 100 parts by weight of the modified cellulose obtained in the first step and stirred, and then allowed to stand at room temperature for 90 minutes. The pulp was charged and mixed in a precooled mixed solution of 270 parts by weight of acetic anhydride, 380 parts by weight of acetic acid and 7 parts by weight of 98% sulfuric acid. The reaction temperature was increased linearly to 37 ° C. 60 minutes after 0 ° C. at the start of the reaction by external cooling / heating, and maintained at 37 ° C. for 90 minutes. In this way, cellulose ether acetate was synthesized.

[Aging process]
Acetic acid aqueous solution was added to the synthesized cellulose acetate dope, the temperature was raised to 54 ° C., and maintained for 115 minutes to age the cellulose acetate. The mixing ratio was 1930 parts by weight of acetic acid (acetyl group donor), 64 parts by weight of water, and 21 parts by weight of sulfuric acid (catalyst) with respect to 499 parts by weight of cellulose acetate. Therefore, the amount of water relative to acetic acid (acetyl group donor) was 11 mol%. The obtained solution was kept at 30 ° C. for 3 hours to age the cellulose acetate.
After completion of aging, an aqueous magnesium acetate solution was added and stirred. The obtained solution was added to a 10% by weight acetic acid aqueous solution, and the resulting precipitate was divided into two parts, and then filtered, washed with running pure water and drained, and the resulting sample was deuterated with chloroform. And the spectrum of carbon 13 is measured. The signal of the carbonyl carbon of the acetyl group appears in the region of 169 ppm to 171 ppm, the signals of the carbonyl carbon of the propionyl group appear in the same order in the region of 172 ppm to 174 ppm from the high magnetic field in the 2nd, 3rd and 6th positions. The distribution of acetyl groups in the original cellulose acetate can be determined from the abundance ratio of acetyl and propionyl at the corresponding positions. As a result of analysis by this method, 6DSester was 0.901, 2DSester was 0.945, and 3DSester was 0.941. The degree of polymerization was 284. A cellulose ether acetate having an acetyl substitution degree (DSester) = 2.79, a substitution degree with propylene oxide (MSether) = 0.05, and a viscosity average polymerization degree 304 was obtained.

Synthesis example 4
(First step) Synthesis of modified cellulose The procedure was the same as in Synthesis Example 2 except that the softwood sulfa pulp of Table 1 was used as the cellulose raw material. The degree of substitution of the product with propylene oxide (MSether) was 0.10.
(Second Step) Acetylation of Modified Cellulose The modified cellulose was acetylated in the same manner as in Synthesis Example 2. The obtained cellulose ether acetate had an acetyl substitution degree (DSester) = 2.88, a substitution degree with propylene oxide (MSether) = 0.10, and a viscosity average polymerization degree 290. The obtained cellulose ether acetate had a YI of 2.5 and a haze of 2.2. Further, it was uniformly dissolved in methyl acetate at a concentration of 10% by weight at room temperature.
Comparative example

Reference example 1
For comparison, the second step of Synthesis Example 2 was performed using the hardwood pulp of Table 1 used in the first step of Synthesis Example 1. The degree of substitution of the obtained cellulose acetate was 2.87. The cellulose acetate had a YI of 8.8 and a haze of 4.0. In addition, it was hardly dissolved in methyl acetate at a concentration of 10% by weight at room temperature.
Reference example 2
For comparison, the second step of Synthesis Example 3 was performed using the hardwood pulp of Table 1 used in the first step of Synthesis Example 1. The degree of substitution of the obtained cellulose acetate was 2.79. The cellulose acetate had a YI of 7.7 and a haze of 3.7. In addition, it was hardly dissolved in methyl acetate at a concentration of 10% by weight at room temperature.
Reference example 3
For comparison, the second step of Synthesis Example 1 was performed using the softwood pulp used in the first step of Synthesis Example 4. The degree of substitution of the obtained cellulose acetate was 2.87. The cellulose acetate had a YI of 4.0 and a haze of 4.5. In addition, it was hardly dissolved in methyl acetate at a concentration of 10% by weight at room temperature.
The synthesis results are shown in Table 2.

Examples 1-4, Comparative Examples 1-3
(1) Production of solution The cellulose ether acetate and cellulose acetate of Synthesis Examples 1 to 4 and Reference Examples 1 to 3 were dissolved in a methylene chloride solvent to prepare a solution (dope), and the haze and YI of this solution were measured. The results were summarized. Further, the solubility in methyl acetate, which is a non-halogen solvent, was measured. Furthermore, the amount of insoluble components was measured. The results are shown in Table 3.

(2) Production of Film (1-1) Cellulose Ether Acetate A cellulose ether acetate solution was prepared by the following two dissolution methods. For the solvent compositions of the present invention and comparative examples, a methyl acetate solution was used for the cellulose ether acetate of the present invention. About the dissolution conditions, about the comparative example 2 which does not melt | dissolve at normal temperature, melt | dissolution was performed under cooling. Since Comparative Examples 1 and 3 did not dissolve even when cooled, no film was formed.

  Silica particles (particle size 20 nm), triphenyl phosphate / biphenyl diphenyl phosphate (1/2), 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di- tert-Butylanilino) -1,3,5-triazine was added in an amount of 10% by mass of cellulose ether acetate.

(1-1a) Cooling dissolution method In a solvent, while stirring well, the cellulose ether acetate or cellulose acetate described in Table 1 is adjusted to a cellulose ether acetate concentration of 20 wt%, methyl acetate 80 wt%, cyclohexanone 15 wt%, The mixture was gradually added to a mixed solvent of 5 wt% of methanol and left to swell for 3 hours at room temperature (23 ° C.). The obtained swollen mixture was slowly cooled to −30 ° C. at −8 ° C./min while slowly stirring, and after 6 hours, the temperature was increased at + 8 ° C./min and the content was solated to some extent. Stirring of the product started. The dope was obtained by heating to 50 ° C.

(1-1b) Room temperature dissolution method The cellulose ether acetate or cellulose acetate described in Table 1 was gradually added to the solvent while stirring well, and the mixture was stirred and dissolved at room temperature (23 ° C).

  (1-2) The filter (dope) obtained in the above (1-1a) and (1-1b) at 50 ° C. and having an absolute filtration accuracy of 0.01 mm (manufactured by Toyo Filter Paper Co., Ltd., # 63) And further filtered with a filter paper having an absolute filtration accuracy of 0.0025 mm (FH025, manufactured by Pall). In Comparative Examples 1 and 3, since a stable solution could not be formed with methyl acetate, it was not possible to proceed to the following step (1-3).

(1-3) A solution of (1-2) is cast using a casting machine, dried in an environment of 120 ° C. for 30 minutes, the solvent is evaporated, and a cellulose ether acetate film or cellulose having a film thickness of about 80 μm An acetate film was obtained.
(3) Measurement of bright spot foreign matter The bright spot foreign matter was measured for the cellulose ether acetate film and cellulose acetate film of the comparative example of Example obtained in (2) above. Table 4 below shows the number of measured bright spot foreign substances in these films.

In the cellulose ether acetate solution and film of the present invention, no particular problem was observed in the solution stability, the mechanical properties of the film, and the optical properties. On the other hand, in the comparative example, a problem was recognized in the surface shape of the obtained film. The cellulose ether acetate film thus obtained contains the liquid crystal display device described in Example 1 of JP-A-10-48420 and the discotic liquid crystal molecules described in Example 1 of JP-A-9-26572. An optically anisotropic layer, an alignment film coated with polyvinyl alcohol, a VA liquid crystal display device described in FIGS. 2 to 9 of JP-A-2000-154261, and FIGS. 10 to 15 of JP-A-2000-154261 When used in the OCB type liquid crystal display device, good performance was obtained. Furthermore, when used as a polarizing plate described in JP-A No. 54-016575, good performance was obtained.

Claims (13)

An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (II):
(I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. An optical film comprising cellulose ether acetate that satisfies the following formulas (I) and (III):
(I) 0.01 ≦ MSether ≦ 3.00
(III) 2.6 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. An optical film comprising cellulose ether acetate satisfying the following formulas (I) and (IV):
(I) 0.01 ≦ MSether ≦ 3.00
(IV) 1.3 ≦ DSester <2.6
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. The optical film according to claim 3, comprising cellulose ether acetate satisfying the following formulas (V) and (VI).
(V) 0.50 ≦ MSether ≦ 3.00
(VI) 1.3 ≦ DSester <2.2
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. The optical film according to any one of claims 1 to 3, wherein the optical film is produced by a solvent cast method comprising a cellulose ether acetate containing a plasticizer as an essential component and satisfying the following formulas (I) and (IV):
(I) 0.01 ≦ MSether ≦ 3.00
(IV) 1.3 ≦ DSester <2.6
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. Solvent cast comprising cellulose ether acetate whose substituents bonded to the anhydroglucose ring constituting cellulose are the following (a), (b), (c) and (d), containing a plasticizer as an essential component, and The optical film according to claim 1, which is made by a method.
(A) OR ₁ —OH (where R ₁ represents any organic group)
(B) O-COCH ₃
(C) OR ₂ —O—COCH ₃ (wherein R ₂ represents an arbitrary organic group, and R ₁ and R ₂ may be the same)
(D) OH An optical film made of cellulose ether acetate whose insoluble matter amount measured by the following measurement method is 0.014 wt% or less.
(Measuring method)
A solution obtained by dissolving cellulose ether acetate in a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio) to a concentration of 2 wt% solid content is filtered using a glass filter (pore diameter: 5 to 10 μm). Thereafter, the dope adhering to the filtration residue is washed with a mixed solvent of methylene chloride: methanol = 9: 1 (weight ratio). The filtration residue is dried together with the glass filter until a constant weight is obtained. The weight of the glass filter before and after filtration is measured, and the amount of insoluble matter is calculated from the following formula.
Insoluble matter amount (wt%) = [glass filter weight after filtration (g) −glass filter weight before filtration (g)] / weight of cellulose ether acetate (g) × 100 Cellulose ether acetate satisfying the following formulas (I) and (III), and satisfying the following formulas (i) and (ii) in the degree of substitution of acetyl groups at the 2-position, 3-position and 6-position of the anhydrous glucose ring of the cellulose ether acetate An optical film comprising:
(I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose.
* POH 11-5851 Claim 1
(I) Ds2 + Ds3 ≧ −Ds6 + 2.67
(Ii) Ds2 + Ds3 ≦ 1.97
However, Ds2 shows the average substitution degree of the substituent couple | bonded with 2-position of the anhydroglucose ring which comprises a cellulose ether acetate.
Ds3 represents the average degree of substitution of substituents bonded to the 3-position of the anhydroglucose ring constituting cellulose ether acetate.
Moreover, the average substitution degree of the substituent couple | bonded with the anhydroglucose ring 6th position which comprises Ds6 cellulose ether acetate is shown. The optical film according to any one of claims 1 to 6, comprising cellulose ether acetate which is dissolved in a non-halogen organic solvent having a dissolution temperature of 25 ° C at a concentration of 10% by weight or more. A step of mixing cellulose ether acetate satisfying the following formulas (I) and (II) with an organic solvent to swell the cellulose ether acetate in the organic solvent; cooling the swollen mixture to −100 to −10 ° C. Heating the cooled mixture to 0 to 200 ° C. to prepare a cellulose ether acetate solution in which cellulose ether acetate is dissolved in an organic solvent; casting the prepared cellulose ether acetate solution on a support And (1) 0.01 ≦ MSether ≦ 3.00, wherein the organic solvent is evaporated to form a cellulose ether acetate film.
(II) 0.01 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. Cellulose ether satisfying the following formulas (I) and (III), and the substitution degree of acetyl groups at the 2-position, 3-position and 6-position of the anhydrous glucose ring of the cellulose ether acetate satisfying the following formulas (i) to (iii) Mixing cellulose acetate with an organic solvent to swell the cellulose ether acetate in the organic solvent; cooling the swollen mixture to −100 to −10 ° C .; heating the cooled mixture to 0 to 200 ° C .; A step of preparing a cellulose acetate solution in which cellulose acetate is dissolved in an organic solvent; a step of casting the prepared cellulose acetate solution on a support; and a step of evaporating the organic solvent to form a cellulose acetate film The method for producing an optical film according to claim 8 (I) 0.01≤MSether≤3.00
(III) 2.6 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose.
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose.
(I) Ds2 + Ds3 ≧ −Ds6 + 2.67
(Ii) Ds2 + Ds3 ≦ 1.97
(Iii) Ds2 + Ds3 <Ds6 × 4-1.70

However, Ds2 shows the average substitution degree of the substituent couple | bonded with 2-position of the anhydroglucose ring which comprises a cellulose ether acetate.
Ds3 represents the average degree of substitution of substituents bonded to the 3-position of the anhydroglucose ring constituting cellulose ether acetate.
Moreover, the average substitution degree of the substituent couple | bonded with the anhydroglucose ring 6th position which comprises Ds6 cellulose ether acetate is shown. A solution obtained by dissolving cellulose ether acetate satisfying the following formulas (I) and (II) in a non-halogen organic solvent.
(I) 0.01 ≦ MSether ≦ 3.00
(II) 0.01 ≦ DSester ≦ 3.0
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose. .
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose. A solution obtained by dissolving cellulose ether acetate satisfying the following formulas (XX) and (XXI) in a non-halogen organic solvent.
(XX) 0.01 ≦ MSether ≦ 1.00
(XXI) 2.80 ≦ DSester ≦ 3.00
However, MSether indicates the average number of modifiers ether-bonded per anhydroglucose unit constituting cellulose. .
DSester represents the average number of hydroxyl groups substituted by acetyl groups per anhydroglucose unit constituting cellulose.