JP2009208476A - Cellulose ester film, its manufacturing method, and protective film for polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellulose ester film which cannot be easily torn when a polarizing plate is removed from a glass base as a thin film, and excels in moisture and thermal resistance, transparency, and optical isotropy, and also to provide a protective film for a polarizing plate. <P>SOLUTION: The method of manufacturing a cellulose ester film comprises: making a mixture of a cellulose ester having the substitution degree of an acyl group of 2.6-3.0, a polyester ether or polyester with an organic solvent not substantially containing a chlorine based solvent as a dope; casting the obtained dope in a film shape on a support; peeling a casted film not being fully dried on the support to be dried; and manufacturing a monolayer film having the film thickness of 20-60 μm and having the tear strength by a right angled tear method of 3.5 N-7.0 N when the film thickness is converted into the thickness of 40 μm. The cellulose ester film and the protective film for a polarizing plate are also disclosed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a cellulose ester film useful for a protective film for a polarizing plate and a cellulose ester film. In particular, the present invention relates to a protective film for a polarizing plate having good peelability from a glass substrate even if it is thinned.

  At present, cellulose triacetate films are preferably used in silver halide photographic light-sensitive materials and liquid crystal image display devices because of their transparency and characteristics free from optical defects. In particular, it is used as a protective film for polarizing plates in liquid crystal image display devices. The liquid crystal image display device is configured by attaching polarizing plates to both sides of a glass substrate in which a liquid crystal element is incorporated. In the polarizing plate, both sides of a polarizer made of polyvinyl alcohol or the like are sandwiched between protective films, and the thickness of the protective film is generally about 80 μm. Accordingly, four protective films are used in one liquid crystal display device, and the total thickness is about 320 μm. In recent years, improvement in portability of liquid crystal display devices has been demanded, and thinning the protective film for polarizing plates is considered to be an effective means for this requirement.

  However, when the polarizing plate protective film is thinned, there is a problem that the productivity of the liquid crystal display device is lowered. In other words, when assembling a liquid crystal display device, a polarizing plate is attached to a glass substrate in which a liquid crystal element is incorporated, but at this time, a defective product such as a small amount of dust or a misalignment is likely to occur. . For this reason, it is inevitable to peel off the polarizing plate from the glass substrate and re-stretch it. However, if the protective film for the polarizing plate is made thin, the strength of the polarizing plate cannot withstand the peeling force between the glass substrate and the polarizing plate. It is difficult to peel off the polarizing plate from the glass substrate.

  In order to improve such releasability, it was thought that the tear strength of the protective film for polarizing plates should be improved.

  As a method for improving the tear strength of a cellulose triacetate film, for example, Japanese Patent Publication No. 44-32672 proposes a method of blending a methylene chloride-soluble polyurethane resin. Moreover, the method of blending polyester-urethane resin is disclosed (for example, refer patent document 1).

  However, according to these methods, the tear strength is certainly improved, but the above-mentioned peelability is not necessarily improved, and there is no correlation between the tear strength and the peelability.

  Therefore, the present situation is that the cellulose ester film with improved peelability has not yet been put into practical use.

Japanese Patent Publication No. 47-760

  An object of the present invention is to provide a cellulose ester film that is not easily torn when a polarizing plate is peeled off from a glass substrate even as a thin film. In particular, it is excellent in wet heat resistance, transparency, optical isotropy, and from the glass substrate. It is providing the protective film for polarizing plates which consists of a cellulose-ester film which is hard to tear when peeling a polarizing plate.

  The above object of the present invention can be achieved by the following configuration.

1. A mixture of a cellulose ester having an acyl group substitution degree of 2.6 to 3.0, a polyester ether or a polyester, and an organic solvent substantially free of a chlorinated solvent,
(1) A method in which the organic solvent has a boiling point or higher at normal pressure and is dissolved and made into a dope under pressure conditions that do not foam,
(2) After cooling to −100 ° C. to −10 ° C., heating the cooled product to 0 ° C. to 120 ° C. to make a dope, or
(3) A method of forming a dope by pressurizing to 50 atm or more and 2,000 atm or less,
The dope obtained by any of the above methods is cast on a support in the form of a film, the raw film cast on the support is peeled off and dried to obtain a film thickness of 20 to 60 μm. A method for producing a cellulose ester film, comprising producing a single-layer film having a tear strength of 3.5 N to 7.0 N by a right-angled tearing method when the thickness is converted to a thickness of 40 μm.

  2. 2. The method for producing a cellulose ester film as described in 1 above, wherein the organic solvent contains 50% or more of methyl acetate.

  3. Content of the said polyester ether or polyester is 5-30 mass% with respect to a cellulose ester, The manufacturing method of the said 1 or 2 characterized by the above-mentioned.

  4). 4. The method for producing a cellulose ester film according to any one of 1 to 3, wherein the cellulose ester has a number average molecular weight of 70,000 to 300,000.

  5). A cellulose ester film produced by the method according to any one of 1 to 4 above.

  6). 6. A protective film for a polarizing plate, wherein the cellulose ester film as described in 5 above is used.

  According to the present invention, a cellulose ester film that is difficult to tear when peeling a polarizing plate from a glass substrate as a thin film is obtained. Particularly, when the polarizing plate is peeled from a glass substrate, it is excellent in heat and moisture resistance, transparency, and optical isotropy. The protective film for polarizing plates which consists of a cellulose-ester film which cannot be easily broken was able to be provided.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The present invention is described in more detail below. The cellulose ester film of the present invention has a tear strength by a right-angled tearing method converted to 40 μm of 3.5N to 7.0N, and more preferably 4.0N or more. The higher the value of tear strength by the right-angled tearing method, the better. However, 7.0 N is the upper limit. The tear strength by the right-angled tearing method is determined by performing the test speed condition by the A method according to JIS K7128-1991 C method and dividing the maximum tear load by the thickness of the test piece. It is obtained by converting the tear strength into a thickness of 40 μm. It is preferable that the film is measured in the casting direction and the direction perpendicular thereto, and both satisfy the above conditions.

  As a method for testing the tear strength of a film, there are A method (trouser tear method), B method (Elmendorf tear method), and C method (right angle tear method) as described in JIS K7128-1991. As an optical film, a cellulose ester film has been used for a long time as a photographic film support. In this case, it was important that tears from defective parts of the perforation part do not propagate to the photographing part. Under the conditions, the Elmendorf tearing method of Method B, which is a method for measuring the force required to transmit tearing to a specified distance from the slit, has been widely adopted as an index of film strength. The tear strengths described in Japanese Patent Publication No. 44-32672 and Japanese Patent Publication No. 47-760 are also measured by this Elmendorf tear method. The value of tear strength described in these publications is about several g to several tens g when converted to 40 μm.

  However, when the force required to peel the polarizing plate from the glass substrate was examined, it was found that a force of about 1 kg was required. In other words, there is a large discrepancy between the force required for peeling and the value of tear strength by the Elmendorf tear method, and the technology that improves the tear strength by the conventional Elmendorf tear method is a film tear when peeling the polarizing plate from the glass substrate. It is not possible to improve the peelability. As described above, the relationship between the peelability and the tear strength obtained by the right-angled tear method was first found by the author.

  The cellulose ester film having a high tear strength by the right-angled tearing method as described above is manufactured by a conventional solution casting method in which a dope in which cellulose triacetate is dissolved in methylene chloride is formed by a solution casting method. However, it can be manufactured for the first time by a manufacturing method described later.

  The film thickness of the cellulose ester film of the present invention is 20 to 60 μm. If it is too thin, the stiffness of the film becomes too weak and it becomes difficult to bond the polarizing plate and the film. If it is thicker than this range, the superiority over the conventional protective film for polarizing plate is lowered.

The characteristic values of the cellulose ester film of the present invention are as follows: water vapor permeability is 500 g / m ² · 24H or less, dynamic friction coefficient is 0.5 or less, haze is 0.6% or less, and elastic modulus is 2.45 GPa or more. The absolute value (Re) of the retardation value with respect to the incident light in the vertical direction is 0 to 10 nm, the absolute value of the retardation value with respect to the incident light in the oblique direction 45 degrees from the surface is 0 to 30 nm, and the absolute value of the retardation value in the thickness direction is 0. It is preferably ˜70 nm. When these characteristic values are within the above range, good characteristics as a polarizing plate protective film are exhibited.

  The water vapor transmission rate is measured under the conditions of 25 ° C. and 90% RH according to JIS Z0208-76.

  The cellulose ester constituting the cellulose ester film of the present invention is a cellulose ester having a C2-C3 acyl group as a substituent, such as cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose propionate, etc. Is mentioned. It may contain an acyl group having 4 or more carbon atoms, such as cellulose acetate butyrate and cellulose acetate propionate butyrate. Of these, those consisting only of an acyl group having 2 to 3 carbon atoms are preferred, and cellulose triacetate and cellulose acetate propionate are particularly preferred. The substitution degree of the acyl group is preferably 2.6 to 3.0. By setting the degree of substitution within this range, a film having good resistance to high temperature and high humidity can be obtained. If the degree of substitution of the acetyl group is too small, the breaking strength of the film may be too low, so it is preferably 1.4 or more.

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

  The cellulose ester synthesis method of the present invention can be synthesized by an ordinary method. For example, it can be synthesized by the method described in JP-A-10-45804.

  The cellulose as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively. Cellulose esters obtained from cotton linters are preferred because they have particularly good releasability from the support during film formation.

  The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 70,000 to 300,000 because the mechanical strength when molded is strong. Furthermore, 80,000-200,000 are preferable.

  The polyester ether used in the present invention is an aromatic dicarboxylic acid or alicyclic dicarboxylic acid having 8 to 12 carbon atoms (for example, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid), carbon atom 2 To 10 aliphatic glycols or cycloaliphatic glycols (eg, ethylene diol, propylene diol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol and 1, 5-pentanediol), polyether glycols having 2 to 4 carbon atoms between the ether units (for example, polytetramethylene ether glycol, especially 1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol and polytetramethylene). Copolyester ethers as components ether glycol) is preferable.

  As for the compounding quantity of polyester ether, 5-30 mass% is preferable with respect to a cellulose ester. By setting the blending amount within this range, a cellulose ester film exhibiting good peelability can be obtained.

  In the present invention, polyester-urethane can be used. The polyester-urethane that can be used in the present invention is a polyester-urethane obtained by a reaction between polyester and diisocyanate, and has a repeating unit represented by the following general formula (1).

  In the formula, l represents 2, 3 or 4, m represents 2, 3 or 4, and n represents 1 to 100. R represents the structural unit shown below.

  As polyester, the glycol component is ethylene glycol, 1,3-propanediol, or 1,4-butanediol, and the dibasic acid component is a hydroxyl group at both ends consisting of succinic acid, glutaric acid, or adipic acid. The degree of polymerization n is 1-100. A polyester having a molecular weight of 1,000 to 4,500 is particularly desirable.

  Diisocyanate components include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, polymethylene isocyanate such as hexamethylene diisocyanate, p-phenylene diisocyanate, tolylene diisocyanate, p, p Examples thereof include aromatic diisocyanates such as' -diphenylmethane diisocyanate and 1,5-naphthylene diisocyanate, and m-xylylene diisocyanate. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are preferable because they are excellent in compatibility with cellulose ester.

  The molecular weight of the polyester-urethane is preferably 2,000 to 50,000, more preferably 5,000 to 15,000. The synthesis of the polyester-urethane can be easily obtained by a conventional synthesis method in which the above polyester and diisocyanate are mixed and heated with stirring. In addition, the raw material polyester can be obtained by a conventional method, a corresponding dibasic acid, or a hot melt condensation method using a polyesterification reaction or transesterification reaction between these alkyl esters and glycols, or an acid chloride of these acids. It can be easily synthesized by appropriately adjusting the terminal group to be a hydroxyl group by any method of interfacial condensation with glycols.

  As for the compounding quantity of polyester-urethane, 5-30 mass% is preferable with respect to a cellulose ester. By setting the blending amount within this range, a cellulose ester film exhibiting good peelability can be obtained.

The polyester of the present invention is a polyester composed of polyethylene glycol and an aliphatic dibasic acid, and the average molecular weight is preferably 700 to 10,000. The general formula of polyethylene glycol is represented by HO— (CH ₂ CH ₂ —O) _n —H (n is an integer). n is preferably 4 or less. Aliphatic dibasic acids are oxalic acid, malonic acid, succinic acid, adipic acid, etc. whose general formula is represented by HOOC-R-COOH (R is an aliphatic divalent hydrocarbon group), and has 9 or less carbon atoms Is preferred. The polyester is synthesized by a conventional method, a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the dibasic acid or an alkyl ester thereof and a glycol, or an interface between an acid chloride of the acid and a glycol. It can be easily synthesized by any of the condensation methods.

  As for the compounding quantity of polyester, 5-30 mass% is preferable with respect to a cellulose ester. By setting the blending amount within this range, a cellulose ester film exhibiting good peelability can be obtained.

  A method for forming a cellulose ester film by the solution casting method according to the present invention will be described.

  1. Dissolution step: a step of dissolving the flakes in an organic solvent mainly composed of a good solvent for the flakes of cellulose ester in a dissolution vessel while stirring to form a dope.

  The dissolution method useful in the present invention is a method performed at a temperature not lower than the boiling point of the main solvent and under a pressure that does not boil (hereinafter referred to as a high temperature dissolution method), cooling the cellulose ester and the organic solvent to −100 ° C. to −10 ° C. Or after mixing the cellulose ester with an organic solvent at −100 ° C. to −10 ° C. and then heating to 0 ° C. to 120 ° C. (hereinafter referred to as cooling dissolution method), the cellulose ester and the organic solvent at 50 atm. Examples include a method of pressurizing to 2,000 atmospheres (hereinafter referred to as a high-pressure dissolution method).

  For example, in the case of using methyl acetate (boiling point 56.32 ° C.) as the main solvent in the high temperature dissolution method, the temperature is preferably 56.32 ° C. to 120 ° C., more preferably 60 ° C. to 90 ° C. At this time, the pressure that does not boil may be about 2 atm or more, and there is no particular upper limit, but the effect is saturated at about 50 atm, so 2 to 50 atm is preferable. Further, 2 to 10 atm is preferable.

  The cellulose ester used for this invention has a C2-C3 acyl group as a substituent, and the substitution degree of an acyl group is 2.6-3.0. When the substitution degree of the acetyl group is 2.5 or more, it is preferable to use a cooling dissolution method or a high pressure dissolution method.

  For the cooling dissolution method, a method of forming a dope using a solvent such as acetone, methyl acetate, ethyl formate described in JP-A Nos. 9-95538, 9-95544, and 9-95557 is used. I can do it.

  As for the high-pressure dissolution method, the high-pressure dissolution method described in JP-A No. 11-21379 can be used. In the publication, acetone is used as the organic solvent, but the same can be applied to methyl acetate.

  Thus, by dissolving the cellulose ester having a specific substituent and the above-described polyester ether, polyester-urethane, and polyester in a substantially non-chlorine organic solvent by a method different from usual, the right angle tearing method is used. The tear strength can be increased.

  Non-chlorine organic solvents useful in the present invention include methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trimethyl. Fluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane and the like, and methyl acetate, ethyl acetate Acetone can be preferably used. In particular, it is preferable that methyl acetate is contained in an amount of 50% by mass or more based on the total organic solvent. It is preferable to use 5 to 30% by mass of acetone with methyl acetate based on the total organic solvent because the viscosity of the dope can be reduced.

  The phrase “substantially free of chlorinated solvent” in the present invention means that the chlorinated solvent is 10% by mass or less, preferably 5% by mass or less, and most preferably not contained at all, with respect to the total amount of organic solvent.

  In addition to the non-chlorine organic solvent, the cellulose ester dope preferably contains 0.1 to 30% by mass of an alcohol having 1 to 4 carbon atoms. As a result, after the dope is cast on the casting support, the solvent starts to evaporate, and when the proportion of alcohol increases, the web (dope film) gels, making the web strong and peeling from the casting support. Further, it is possible to obtain an effect of promoting the dissolution of the cellulose ester of the non-chlorine organic solvent. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is most preferable because of the stability of the dope, the boiling point is relatively low, the drying property is good, and there is no toxicity.

  The solid content concentration of the dope is usually preferably 10 to 40% by mass, and the dope viscosity is preferably adjusted to a range of 100 to 500 poise from the viewpoint of obtaining good film flatness.

  The dope prepared as described above is filtered with a filter medium, defoamed, and sent to the next process with a pump.

  In the dope, a plasticizer, a matting agent, an ultraviolet absorber, an antioxidant, a dye, and the like may be added.

  In the present invention, the polyester ether, polyester-urethane, and polyester blended with the cellulose ester exhibit an effect as a plasticizer, so that sufficient film characteristics can be obtained without adding other plasticizers. A plasticizer may be added.

  For example, for the purpose of improving the moisture permeability of the film, alkylphthalylalkyl glycolates, phosphate esters, carboxylic acid esters and the like can be mentioned.

  Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycol Butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl Chi le glycolate, octyl phthalyl methyl glycolate, and the like octyl phthalyl ethyl glycolate. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like. Examples of the carboxylic acid ester include phthalic acid ester and citric acid ester. Examples of the phthalic acid ester include dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethyl hexyl phthalate. Mention may be made of acetyltributyl. Other examples include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and triacetin.

  Among them, methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate and octyl phthalyl octyl glycolate are preferable, and ethyl phthalyl ethyl glycolate is particularly preferable. . These alkyl phthalyl alkyl glycolates may be used in combination of two or more.

  The amount of the plasticizer used for this purpose is preferably 1 to 30% by mass, particularly 4 to 13% by mass, based on the cellulose ester.

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

  A dye is added for the purpose of improving the yellowness of the film. The tint is preferably one that can be colored gray as seen on a normal photographic support. However, unlike the photographic support, it is not necessary to prevent light piping, so the content may be small, and the mass ratio to the cellulose ester is preferably 1 to 100 ppm, more preferably 2 ppm to 50 ppm. Since the cellulose ester is slightly yellowish, a blue or purple dye is preferably used. A plurality of dyes may be appropriately combined so as to become gray.

  If the film is difficult to slip, the films may block and handleability may be poor. In this case, inorganic fine particles such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. It is preferable to include a matting agent such as a molecule. Of these, silicon dioxide is preferable because it can reduce the haze of the film. The matting agent is preferably blended so that the haze of the film is 0.6% or less and the dynamic friction coefficient is 0.5 or less. The matting agent used for this purpose preferably has an average particle size of 0.01 to 1.0 μm and a content of 0.005 to 0.3% by mass with respect to the cellulose ester.

  Liquid crystal display devices are often used outdoors, and it is important to provide a protective film for polarizing plates with a function of cutting ultraviolet rays. The ultraviolet absorber used for this purpose preferably has no absorption in the visible light region, and examples thereof include benzotriazole compounds, benzophenone compounds, and salicylic acid compounds. For example, 2- (2′-hydroxy-5-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy- 3'-di-t-butyl-5'-methylphenyl) benzotriazole, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 4-dodecyloxy 2-hydroxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, phenyl salicylate, methyl salicylate, and the like.

  The addition amount of the ultraviolet absorber is preferably in the range of 0.5 to 20% by mass, more preferably in the range of 0.6 to 5% by mass with respect to the cellulose ester.

  For the purpose of improving the heat and heat resistance of the film, hindered phenol compounds are preferably used, and 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1 , 3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1,000 ppm in terms of mass ratio with respect to the cellulose ester. In addition, a heat stabilizer such as a salt of an alkaline earth metal such as calcium or magnesium may be added.

  In addition to the above, an antistatic agent, a flame retardant, a lubricant, an oil agent, and the like may be added as appropriate.

  2. Casting process: a dope is fed to a pressure die through a pressurized metering gear pump, and an endless metal belt for infinite transfer or a rotating metal drum casting support at the casting position (hereinafter simply referred to as a support). It may be a step of casting a dope from a pressure die on the top. The surface of the casting support is a mirror surface. Other casting methods include a doctor blade method in which the film thickness of the cast dope film is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll, but the slit shape of the die part is adjusted. A pressure die that is easy to make uniform in film thickness is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more pressure dies may be provided on the casting support, and the dope amount may be divided and stacked.

  3. Solvent evaporation step: This is a step of evaporating the solvent by heating the web (the dope film after the dope is cast on the casting support is referred to as the web) on the casting support. In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. The drying efficiency is good and preferable. A method of combining them is also preferable.

  4). Peeling step: A step in which the web in which the solvent has evaporated on the support is peeled off at the peeling position. The peeled web is sent to the next process. If the residual solvent amount (the following formula) of the web at the time of peeling is too large, peeling is difficult, or conversely, if it is peeled off after sufficiently drying on the support, part of the web is peeled off.

  As a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled off while the residual solvent amount is as large as possible), there is a gel casting method (gel casting) in which even a large amount of residual solvent can be removed. For example, a poor solvent for the cellulose ester is added to the dope, and after the dope is cast, the gel is formed, and the temperature of the support is lowered to form a gel. There is also a method of adding a metal salt in the dope. By gelling on the support and strengthening the film, it is possible to speed up the peeling and increase the film forming speed. When peeling at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be impaired, or slippage and vertical stripes due to peeling tension are likely to occur, and the amount of residual solvent that is peeled off is a balance between economic speed and quality. It is decided.

  5). Drying step: a step of drying the web using a drying device that alternately conveys the web through rolls arranged in a staggered pattern and / or a tenter device that clips and conveys both ends of the web with a clip. As a drying means, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. Too much drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout, the drying temperature is usually 40 to 250 ° C, preferably 70 to 180 ° C. The drying temperature, the amount of drying air, and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used.

  In the drying step after peeling from the casting support surface, the web tends to shrink in the width direction due to evaporation of the solvent. Shrinkage increases as the temperature rapidly dries. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point of view, for example, a method of drying the entire drying process or a part of the process as shown in Japanese Patent Application Laid-Open No. 62-46625 while holding the width at both ends of the web with a clip in the width direction (tenter method) ) Is preferred.

  6). Winding step: The step of winding the web as a film after the residual solvent amount becomes 2% by mass or less. By setting the residual solvent amount to 0.4% by mass or less, a film having good dimensional stability can be obtained. As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  The amount of residual solvent can be expressed by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at any point, and N is the mass when M is dried at 110 ° C. for 3 hours.

  To adjust the film thickness of the cellulose ester film, adjust the dope concentration, the pumping amount, the slit gap of the die base, the extrusion pressure of the die, the speed of the casting support, etc. It is good to control. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

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

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this.

Each measurement and evaluation method in an Example was performed with the following method.
<Degree of substitution of cellulose ester>
The degree of substitution is measured by a saponification method. The dried cellulose acylate is precisely weighed and dissolved in a mixed solvent of acetone and dimethyl sulfoxide (volume ratio 4: 1), and then a predetermined 1N aqueous sodium hydroxide solution is added and saponified at 25 ° C. for 2 hours. Phenolphthalein is added as an indicator and excess sodium hydroxide is titrated with 1N sulfuric acid. A blank test is performed by the same method as described above. Further, the supernatant of the solution after titration is diluted, and the composition of the organic acid is measured by an ordinary method using an ion chromatograph. Then, the degree of substitution (%) is calculated according to the following.

TA = (Q−P) × F / (1,000 × W)
DSace = (162.14 × TA) / {1−42.14 ×
TA + (1−56.06 × TP) × (AL / AC)}
DSacy = Ssce × (AL / AC)
In the formula, P is the amount of 1N sulfuric acid required for titration of the sample (ml), Q is the amount of 1N sulfuric acid required for the blank test (ml), F is the titer of 1N sulfuric acid, W is the mass of the sample, TA is the total organic acid amount ( mol / g), AL / AC is the molar ratio of acetic acid (AC) and other organic acid (AL) measured by ion chromatography, DSace is the substitution degree of acetyl group, DSacy is an acyl group having 3 or 4 carbon atoms Indicates the degree of substitution.
<Number average molecular weight of cellulose ester>
Measured by high performance liquid chromatography under the following conditions.
Solvent: Methylene chloride Column: MPW × 1 (manufactured by Tosoh Corporation)
Sample concentration: 0.2% by mass
Flow rate: 1.0 ml / min Sample injection amount: 300 μl
Standard sample: polystyrene temperature: 23 ° C.
<Tear strength of film>
It measured according to JIS K7128-1991. The measurement result was converted into a thickness of 40 μm and displayed.
<Peelability>
The obtained film is used as a protective film for a polarizing plate, and a polarizing plate is produced by laminating on both sides of a polarizing film made of polyvinyl alcohol. The obtained polarizing plate is punched into a size of 100 × 100 mm and bonded to a glass substrate. The polarizing plate is peeled off from the glass substrate a little from one corner, and the peeled polarizing plate is grasped and pressed in the diagonal direction while holding the glass substrate. The same operation was performed on each of 10 samples, and when 10 sheets were completely peeled, ◎ when only one piece was left partially peeled, ○, 2 to 5 pieces were left unseparated The case where the peeling occurred was Δ, and the case where 6 or more peeling residue was generated was marked X. Practically, it is preferable that it is more than rank (circle).

Reference example 1
A polyester-urethane having an average molecular weight of 7,300 was obtained from dihydroxy polyester having an average molecular weight of 2,125 consisting of adipic acid and ethylene glycol and tolylene diisocyanate by a conventional method (this compound is referred to as P1). 30 parts by mass of the obtained compound (P1), 100 parts by mass of cellulose triacetate (number average molecular weight 200,000) having an acetylation degree of 60.9%, 10 parts by mass of triphenyl phosphate, 350 parts by mass of methyl acetate and 125 parts by mass of acetone And swollen in a mixed solvent consisting of 25 parts by mass of ethanol and 25 parts by mass of ethanol. Next, this mixture was put into a double-structured closed container, and the refrigerant was introduced into the outer jacket while slowly stirring the mixture. This cooled the mixture in the inner container to -70 ° C. Cooled for 30 minutes until the mixture was cooled uniformly. The refrigerant in the jacket outside the sealed container is discharged, and hot water is introduced into the jacket instead. The contents were subsequently stirred and raised to 80 ° C. over 40 minutes. The inside of the container was 2 atm. While stirring, the temperature was lowered to 50 ° C. and the pressure was returned to normal pressure. This dope was added to Azumi Filter Paper No. It filtered using 244 and used for film forming.

  The obtained dope was cast on a stainless steel belt from a die. After drying for 1 minute on a stainless steel belt whose temperature is controlled by contacting hot water at a temperature of 35 ° C. from the back surface of the stainless steel belt, 15 ° C. cold water is brought into contact with the back surface of the stainless steel belt and held for 15 seconds. Removed from the stainless steel belt.

Next, the film was dried at 130 ° C. for 10 minutes while fixing both ends of the peeled film to obtain a film having a thickness of 40 μm. The obtained film had a water vapor transmission rate of 400 g / m ² · 24 h, a haze of 0.4%, an elastic modulus of 3.00 GPa, an in-plane retardation value of 5 nm, a thickness direction retardation value of 20 nm, and a dynamic friction coefficient of 0. .5, the tear strength by the Elmendorf method was 0.10 N, and the tear strength by the right angle tear method was 3.5 N. The film casting direction (MD) and the direction perpendicular to the film casting direction (TD) were measured by the Elmendorf method and the right-angled tearing method. In each case, the same numerical value was shown. The following Reference Examples 2 to 10 and Comparative Examples 1 and 2 were similarly the same numerical values in MD and TD. Ten sheets of polarizing plates were prepared using the obtained film as a protective film for polarizing plates, and the peelability from the glass substrate was evaluated. As a result, peeling residue occurred on one sheet (peelability: rank ○). The results are shown in Table 1.

Reference example 2
100 parts by mass of cellulose triacetate (number average molecular weight 200,000) having a substitution degree of acetyl group of 2.85, 30 parts by mass of the above compound (P1), 350 parts by mass of methyl acetate, and 150 parts by mass of acetone were put into a pressure sealed container. A pressure of 1,000 atmospheres was applied for 30 minutes. Thereafter, the pressure was released to normal pressure. This operation was repeated three times to obtain a dope. The dope temperature was allowed to stand overnight at 40 ° C., and after defoaming operation, the solution was added to Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. It filtered using 244 and used for film forming.

Using the obtained dope, a film having a film thickness of 40 μm was obtained in the same manner as in Reference Example 1. The obtained film had a water vapor transmission rate of 450 g / m ² · 24 h, a haze of 0.3%, an elastic modulus of 3.10 GPa, an in-plane retardation value of 3 nm, a thickness direction retardation value of 30 nm, and a dynamic friction coefficient of 0. .4, the tear strength by the Elmendorf method was 0.11 N, and the tear strength by the right-angled tear method was 3.8 N. Ten sheets of polarizing plates were prepared using the obtained film as a protective film for polarizing plates, and the peelability from the glass substrate was evaluated. As a result, peeling residue occurred on one sheet (peelability: rank ○). The results are shown in Table 1.

Reference example 3
Acetyl group substitution degree 2.00, propionyl group substitution degree 0.80, number average molecular weight 100,000 cellulose ester 100 parts by mass, compound (P1) 30 parts by mass, methyl acetate 210 parts by mass, ethanol 90 parts by mass Was put in a pressure sealed container, heated to 80 ° C. to set the pressure in the container to 5 atm, and the cellulose ester was completely dissolved while stirring to obtain a dope. The dope temperature was lowered to 40 ° C. and allowed to stand overnight, and after defoaming operation, the solution was added to Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. It filtered using 244 and used for film forming.

Using the obtained dope, a film having a film thickness of 40 μm was obtained in the same manner as in Reference Example 1. The obtained film had a water vapor transmission rate of 350 g / m ² · 24 h, a haze of 0.3%, an elastic modulus of 2.80 GPa, an in-plane retardation value of 2 nm, a thickness direction retardation value of 60 nm, and a dynamic friction coefficient of 0. .3, the tear strength by the Elmendorf method was 0.15 N, and the tear strength by the right-angled tear method was 5.0 N. Using the obtained film as a protective film for a polarizing plate, 10 polarizing plates were produced and evaluated for peelability from the glass substrate. As a result, no peeling residue occurred in all 10 sheets, and good peelability (rank ◎). Indicated. The results are shown in Table 1.

Reference example 4
A film having a thickness of 40 μm was obtained in the same manner as in Reference Example 3 except that the amount of the compound (P1) added in Reference Example 3 was changed from 30 parts by mass to 10 parts by mass. The obtained film had a water vapor transmission rate of 360 g / m ² · 24 h, a haze of 0.2%, an elastic modulus of 2.95 GPa, an in-plane retardation value of 2 nm, a thickness direction retardation value of 40 nm, and a dynamic friction coefficient of 0. .4, the tear strength by the Elmendorf method was 0.11 N, and the tear strength by the right-angled tear method was 5.5 N. Using the obtained film as a protective film for a polarizing plate, 10 polarizing plates were produced and evaluated for peelability from the glass substrate. As a result, no peeling residue occurred in all 10 sheets, and good peelability (rank ◎). Indicated. The results are shown in Table 1.

Comparative Example 1
30 parts by mass of the compound (P1), 100 parts by mass of cellulose triacetate (number average molecular weight 200,000) having an acetylation degree of 60.9%, 10 parts by mass of triphenyl phosphate, 475 parts by mass of methylene chloride and 25 parts by mass of methanol The dope was obtained while being stirred at 35 ° C. while being put in a pressure sealed container. The solution was allowed to stand overnight and subjected to a defoaming operation, and then the solution was obtained from Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. It filtered using 244 and used for film forming.

Using the obtained dope, a film having a film thickness of 40 μm was obtained in the same manner as in Reference Example 1. The obtained film had a water vapor transmission rate of 400 g / m ² · 24 h, a haze of 0.7%, an elastic modulus of 2.50 GPa, an in-plane retardation value of 5 nm, a thickness direction retardation value of 20 nm, and a dynamic friction coefficient of 0. .6, the tear strength by the Elmendorf method was 0.09 N, and the tear strength by the right angle tear method was 2.0 N. Ten sheets of polarizing plates were prepared using the obtained film as a protective film for polarizing plates, and the peelability from the glass substrate was evaluated. As a result, all of the 10 sheets were unsatisfactory in peelability (rank x). . The results are shown in Table 1.

Comparative Example 2
100 parts by mass of cellulose triacetate (number average molecular weight 200,000) having an acetylation degree of 60.9%, 10 parts by mass of triphenyl phosphate, 475 parts by mass of methylene chloride, and 25 parts by mass of methanol were put into a pressure-sealed container, and 35 A dope was obtained with stirring at ° C. The solution was allowed to stand overnight and subjected to a defoaming operation, and then the solution was obtained from Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. It filtered using 244 and used for film forming.

Using the obtained dope, a film having a film thickness of 40 μm was obtained in the same manner as in Reference Example 1. The obtained film had a water vapor transmission rate of 550 g / m ² · 24 h, a haze of 0.6%, an elastic modulus of 2.90 GPa, an in-plane retardation value of 5 nm, a thickness direction retardation value of 20 nm, and a dynamic friction coefficient of 0. .6, the tear strength by the Elmendorf method was 0.05 N, and the tear strength by the right-angled tear method was 2.3 N. Ten sheets of polarizing plates were prepared using the obtained film as a protective film for polarizing plates, and the peelability from the glass substrate was evaluated. As a result, all of the 10 sheets were unsatisfactory in peelability (rank x). . The results are shown in Table 1.

Example 5
Polyester ether consisting of 100 mol% 1,4-cyclohexanedicarboxylic acid having a trans isomer content of at least 70%, 91 mol% 1,4-cyclohexanedimethanol, 9 mol% polytetramethylene ether glycol having a molecular weight of 1,000 Was obtained by a conventional method (referred to as compound P2). The following procedure was performed using compound (P2).

A film having a thickness of 40 μm was obtained in the same manner as in Reference Example 3 except that the compound (P1) of Reference Example 3 and the addition amount of 30 parts by mass were changed to the compound (P2) and the addition amount of 10 parts by mass. The obtained film had a water vapor transmission rate of 400 g / m ² · 24 h, a haze of 0.5%, an elastic modulus of 2.70 GPa, an in-plane retardation value of 5 nm, a thickness direction retardation value of 60 nm, and a dynamic friction coefficient of 0. .5, the tear strength by the Elmendorf method was 0.08 N, and the tear strength by the right-angled tear method was 4.0 N. Using the obtained film as a protective film for a polarizing plate, 10 polarizing plates were produced and evaluated for peelability from the glass substrate. As a result, no peeling residue occurred in all 10 sheets, and good peelability (rank ◎). Indicated. The results are shown in Table 1.

Example 6
A polyester having an average molecular weight of 2,500 was obtained from triethylene glycol and adipic acid by a conventional method (referred to as compound P3). The following was performed using compound (P3).

A film having a thickness of 40 μm was obtained in the same manner as in Reference Example 3 except that the compound (P1) of Reference Example 3 and the addition amount of 30 parts by mass were changed to the compound (P3) and the addition amount of 10 parts by mass. The obtained film had a water vapor transmission rate of 450 g / m ² · 24 h, a haze of 0.5%, an elastic modulus of 2.65 GPa, an in-plane retardation value of 6 nm, a thickness direction retardation value of 65 nm, and a dynamic friction coefficient of 0. .5, the tear strength by the Elmendorf method was 0.08 N, and the tear strength by the right-angled tear method was 4.0 N. Using the obtained film as a protective film for a polarizing plate, 10 polarizing plates were produced and evaluated for peelability from the glass substrate. As a result, no peeling residue occurred in all 10 sheets, and good peelability (rank ◎). Indicated. The results are shown in Table 1.

Example 7
Acetyl group substitution degree 2.00, propionyl group substitution degree 0.80, number average molecular weight 100,000 cellulose ester 100 parts by mass, compound (P2) 30 parts by mass, methyl acetate 210 parts by mass, ethanol 90 parts by mass A film having a thickness of 40 μm was obtained in the same manner as in Reference Example 1 except that was used. Table 1 shows the measured values of the Elmendorf method and the right-angled tear method, and the peelability from the glass substrate.

Example 8
Acetyl group substitution degree 2.00, propionyl group substitution degree 0.80, number average molecular weight 100,000 cellulose ester 100 parts by mass, compound (P2) 30 parts by mass, methyl acetate 210 parts by mass, ethanol 90 parts by mass A film having a thickness of 40 μm was obtained in the same manner as in Reference Example 2 except that was used. Table 1 shows the measured values of the Elmendorf method and the right-angled tear method, and the peelability from the glass substrate.

Example 9
A film having a thickness of 40 μm was obtained in the same manner as in Example 7 except that the compound (P3) was used instead of the compound (P2). Table 1 shows the measured values of the Elmendorf method and the right-angled tear method, and the peelability from the glass substrate.

Example 10
A film having a thickness of 40 μm was obtained in the same manner as in Example 8 except that the compound (P3) was used instead of the compound (P2). Table 1 shows the measured values of the Elmendorf method and the right-angled tear method, and the peelability from the glass substrate.

  It can be seen from Table 1 that good peelability is exhibited when the tear strength by the right-angled tearing method is 3.5 N or more, particularly 4.0 N or more. According to the method for producing a cellulose ester of the present invention, it can be seen that a cellulose ester film showing good peelability can be obtained when a protective film for a polarizing plate is obtained.

Claims (6)

A mixture of a cellulose ester having an acyl group substitution degree of 2.6 to 3.0, a polyester ether or a polyester, and an organic solvent substantially free of a chlorinated solvent,
(1) A method in which the organic solvent has a boiling point or higher at normal pressure and is dissolved and made into a dope under pressure conditions that do not foam,
(2) After cooling to −100 ° C. to −10 ° C., heating the cooled product to 0 ° C. to 120 ° C. to make a dope, or
(3) A method of forming a dope by pressurizing to 50 atm or more and 2,000 atm or less,
The dope obtained by any of the above methods is cast on a support in the form of a film, the raw film cast on the support is peeled off and dried to obtain a film thickness of 20 to 60 μm. A method for producing a cellulose ester film, comprising producing a single-layer film having a tear strength of 3.5 N to 7.0 N by a right-angled tearing method when the thickness is converted to a thickness of 40 μm.   The method for producing a cellulose ester film according to claim 1, wherein the organic solvent contains 50% or more of methyl acetate.   Content of the said polyester ether or polyester is 5-30 mass% with respect to a cellulose ester, The manufacturing method of the cellulose-ester film of Claim 1 or 2 characterized by the above-mentioned.   The method for producing a cellulose ester film according to claim 1, wherein the cellulose ester has a number average molecular weight of 70,000 to 300,000.   A cellulose ester film produced by the method according to claim 1.   The protective film for polarizing plates characterized by using the cellulose-ester film of Claim 5.