JP2001163995A - Cellulose ester film and its manufacturing method and protective film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of cellulose ester films having a reduced retardation value (Rt value) in the thickness direction by preparing a cellulose ester dope without using a chlorine-based solvent. SOLUTION: The cellulose ester films comprise at least one member of aliphatic dibasic acid diesters, trimellitic tri-esters, and phosphoric triesters. The manufacturing method and protective films for a polarizing plate are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a cellulose ester film useful as a protective film for a polarizing plate, and a cellulose ester film.

[0002]

2. Description of the Related Art At present, cellulose triacetate films are preferably used for silver halide photographic materials and liquid crystal image display devices because of their transparency and properties free from optical defects, and the required quality is increasing year by year. .

On the other hand, chlorinated hydrocarbon solvents such as methylene chloride, which is a good solvent for cellulose esters represented by cellulose triacetate, tend to be environmentally restricted in their use. There is a demand for a manufacturing method that does not.
However, it is difficult to obtain a good quality dope by replacing the solvent for the cellulose ester with a non-chlorine organic solvent.

The following proposals have been made in response to the above requirements. For example, Japanese Patent Application Laid-Open Nos. 9-95544 and 9-95557 propose a cooling dissolution method using an organic solvent consisting essentially of acetone, or using methyl acetate or acetone and another non-chlorine organic solvent. ing. JP-A-9-95538 discloses a method of dissolving by cooling using an organic solvent selected from ethers, ketones or esters other than acetone.
JP-21379 proposes a method of mixing cellulose triacetate with acetone and applying a pressure of 0.98 to 490 MPa.

However, it has been found that a film obtained by using such a method has a problem that the retardation value in the thickness direction of the film is increased.

[0006] Retardation value (Rth value) in the thickness direction
Is represented by the following equation. Rth value = ((nx + ny) / 2−nz) × d (nx is the refractive index of the film in the casting direction of the film, ny
Represents the refractive index of the film in the direction perpendicular to the casting direction (width direction), nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film. When the Rth value is increased, in liquid crystal display devices of various types such as STN, TFT, TN, etc., there is a problem that the contrast when viewed from an oblique direction is reduced and the viewing angle is narrowed.

JP-A-11-92574 and JP-A-11-12
In Nos. 4445 and 11-246704, a lower fatty acid ester of cellulose and a specific compound are mixed with an organic solvent containing 50% by mass or more of acetone or methyl acetate,
A method of reducing the Rth value of a film by preparing a solution by a cooling dissolution method and casting the film has been proposed, but it is not yet sufficient.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for preparing a cellulose ester dope without using a chlorine-based solvent to obtain a cellulose ester film having a reduced retardation value (Rth value) in a thickness direction. Is to provide.

[0009]

The above objects of the present invention have been attained by the following constitutions.

(1) A cellulose ester film comprising at least one compound represented by the following general formula (1).

Formula (1) R—OOC (CH ₂ ) _n COO—R In the formula, R represents an alkyl group having 1 to 10 carbon atoms, and n represents 4
Represents an integer of 10 to 10.

(2) A cellulose ester film comprising at least one compound represented by the following general formula (2).

[0013]

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In the formula, R ₁ represents an alkyl group having 1 to 8 carbon atoms. (3) A cellulose ester film comprising at least one compound represented by the following general formula (3).

[0015]

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In the formula, R ₂ represents an alkyl group having 1 to 4 carbon atoms. (4) The cellulose ester film as described in any one of (1) to (3) above, wherein the cellulose ester is a lower fatty acid ester of cellulose.

(5) The cellulose ester is 70,00
The cellulose ester film according to any one of the above items 1 to 4, having a number average molecular weight of 0 to 300,000.

(6) A cellulose ester and at least one of the compounds represented by the above general formula (1) are added to an organic solvent substantially free of a chlorinated solvent at a boiling point of the organic solvent at normal pressure or higher. A method for producing a cellulose ester film, comprising: casting a dope obtained by dissolving under pressure conditions under which foaming does not occur, onto a support, peeling off the raw dry film cast on the support, and drying.

(7) A cellulose ester and at least one of the compounds represented by the general formula (2) are added to an organic solvent substantially free of a chlorine-based solvent at a boiling point of the organic solvent at normal pressure or higher. A method for producing a cellulose ester film, comprising: casting a dope obtained by dissolving under pressure conditions under which foaming does not occur, onto a support, peeling off the raw dry film cast on the support, and drying.

(8) A cellulose ester and at least one of the compounds represented by the general formula (3) are added to an organic solvent substantially free of a chlorine-based solvent at a temperature not lower than the boiling point of the organic solvent at normal pressure. A method for producing a cellulose ester film, comprising: casting a dope obtained by dissolving under pressure conditions under which foaming does not occur, onto a support, peeling off the raw dry film cast on the support, and drying.

(9) A cellulose ester, at least one of the compounds represented by the above general formula (1), and an organic solvent substantially free of a chlorine solvent are used at a temperature of -100 ° C to -10 ° C.
After cooling to 0 ° C. to 120 ° C., the obtained dope is cast on a support, and the undried film cast on the support is peeled off and dried. A method for producing a cellulose ester film.

(10) A mixture of a cellulose ester and at least one of the compounds represented by the above general formula (1) and an organic solvent containing substantially no chlorine-based solvent is applied to a pressure of 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting a solution obtained by pressing on a support, peeling off the raw dry film cast on the support, and drying.

(11) A cellulose ester, at least one of the compounds represented by the above general formula (2), and an organic solvent substantially free from a chlorine-based solvent are used at a temperature of -100 ° C to -10 ° C.
After cooling to 0 ° C., the cooled product is heated to 0 ° C. to 120 ° C., and the obtained dope is cast on a support, and the raw dry film cast on the support is peeled off and dried. Of producing a cellulose ester film.

(12) A mixture of a cellulose ester, at least one of the compounds represented by the above general formula (2), and an organic solvent substantially free of a chlorine-based solvent is applied to a pressure of 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting a solution obtained by pressing on a support, peeling off the raw dry film cast on the support, and drying.

(13) A cellulose ester, at least one of the compounds represented by the above general formula (3), and an organic solvent substantially free from a chlorine-based solvent are used at a temperature of -100 ° C to -10 ° C.
After cooling to 0 ° C., the cooled product is heated to 0 ° C. to 120 ° C., and the obtained dope is cast on a support, and the raw dry film cast on the support is peeled off and dried. Of producing a cellulose ester film.

(14) A mixture of a cellulose ester, at least one of the compounds represented by the general formula (3), and an organic solvent substantially free of a chlorine-based solvent is applied to a pressure of 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting a solution obtained by pressing on a support, peeling off the raw dry film cast on the support, and drying.

(15) The organic solvent is 50% methyl acetate
The method for producing a cellulose ester film according to any one of the above items 6 to 14, comprising:

(16) The above-mentioned item (6), wherein the cellulose ester is a lower fatty acid ester of cellulose.
16. The method for producing a cellulose ester film according to any one of items 15 to 15.

(17) 70,0 cellulose ester
The method for producing a cellulose ester film according to any one of the above items 6 to 16, wherein the cellulose ester film has a number average molecular weight of 00 to 300,000.

(18) A polarizing plate protective film, comprising using the cellulose ester film according to any one of the above (1) to (5).

Hereinafter, the present invention will be described in more detail. The cellulose ester constituting the cellulose ester film of the present invention is a cellulose ester having an acyl group having 2 to 3 carbon atoms as a substituent, such as cellulose triacetate, cellulose diacetate, cellulose acetate propionate, and cellulose propionate. Is mentioned. An acyl group having 4 or more carbon atoms, such as cellulose acetate butyrate and cellulose acetate propionate butyrate, may be contained. Among them, those comprising only an acyl group having 2 to 3 carbon atoms are preferable, and cellulose triacetate and cellulose acetate propionate are particularly preferable. The degree of substitution of the acyl group is
It is preferably from 2.6 to 3.0. By setting the substitution degree 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. Therefore, the degree of substitution of the acetyl group is preferably 1.4 or more.

The method for measuring the degree of substitution of the acyl group is ASTM-
It can be measured according to D817-96.

The cellulose ester of the present invention can be synthesized by a usual method. For example, JP-A-10-45
It can be synthesized by the method described in JP-A-804.

The cellulose as a raw material of the cellulose ester is not particularly limited, but examples thereof include cotton linter, wood pulp, and kenaf. Cellulose esters obtained therefrom can be mixed and used at an arbitrary ratio. Cellulose esters obtained from cotton linters are particularly preferred because of their excellent 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 of the film is strong. Further 80,
000 to 200,000 is preferred.

The amount of free acid in the cellulose ester used in the present invention is preferably 1.0 mol or less, more preferably 0.3 mol or less, and most preferably 0.1 mol or less per 1 kg of the cellulose ester. preferable. Further, the amount of bound sulfuric acid in the cellulose ester is preferably 0.1 g or less, more preferably 0.05 g or less, particularly preferably 0.03 g or less, per kg of the cellulose ester as a sulfur atom. When the amount of free acid and the amount of bound sulfuric acid in the cellulose ester are within the above ranges, excellent heat and moisture resistance as a polarizing plate protective film or a photographic support can be imparted. The moist heat resistance required for a polarizing plate protective film or a photographic support is defined as the most severe conditions in which they are used, for example, decomposition or coloring even after being put at 80 ° C. and 90% RH for 1,000 hours. Is not deteriorated.
The amount of free acid and the amount of bound sulfuric acid in the cellulose ester can be measured by ASTM-D817-96.

The cellulose ester film of the present invention comprises
It is characterized by containing at least one compound represented by the above general formulas (1) to (3).

It is important that these compounds have excellent compatibility with cellulose esters and excellent volatility when formed into a film.

Compounds represented by the general formula (1) include, for example, bis (2-ethylhexyl) azelate, bis (2-ethylhexyl) adipate, diisononyl adipate, di-n-hexyl adipate, di-n-adipate -Octyl, di-n-decyl adipate, diisodecyl adipate, diisobutyl adipate, dibutyl sebacate,
Bis (2-ethylhexyl) sebacate, bis (2-ethylhexyl) dodecandioate and the like are preferably used, and among them, bis (2-ethylhexyl) azelate,
Bis (2-ethylhexyl) adipate, bis (2-ethylhexyl) sebacate and bis (2-ethylhexyl) dodecane diacid are particularly preferred.

The compound represented by the general formula (2) is, for example, tris (2-ethylhexyl) trimellitate.

The compound represented by the general formula (3) is, for example, trimethyl phosphate, triethyl phosphate, tributyl phosphate and the like.

The above compounds are compounds mainly known as plasticizers for vinyl chloride and rubber. The present inventor has found that the Rth value of the film can be reduced by producing the film by adding these compounds to a cellulose ester solution containing substantially no chlorine-based solvent.

These compounds are commercially available from a plurality of manufacturers, and they can be preferably used. Two or more of the above compounds may be used in combination.

The content of the above compound in the cellulose ester film is preferably 0.5 to 30% by mass,
More preferably, it is 0% by mass. If the content is too small, the effect of reducing the Rth value may not be obtained, and if it is too large, bleed out may occur.

Conventionally, triphenyl phosphate and diethyl phthalate are well known as plasticizers for cellulose esters. However, even if these plasticizers are contained, the effect of reducing the Rth value is not recognized. .

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

Dissolving step: This is a step of dissolving the flakes in an organic solvent mainly containing a good solvent for the cellulose ester flakes in a dissolving vessel with stirring to form a dope.

The dissolving method useful in the present invention is a method of conducting at a temperature not lower than the boiling point of the main solvent and under a pressure that does not cause boiling (hereinafter referred to as a high-temperature dissolving method). Cooling to 0 ° C. or mixing the cellulose ester with an organic solvent at −100 ° C. to −10 ° C., followed by heating to 0 ° C. to 120 ° C. (hereinafter referred to as cooling dissolution method). 50 atm
A method of pressurizing to 2,000 atm (hereinafter referred to as a high-pressure dissolution method) can be given.

In the high-temperature dissolution method, for example, when methyl acetate (boiling point: 56.32 ° C.) is used as a main solvent, the temperature is preferably 56.32 ° C. to 120 ° C., and more preferably 6 ° C. to 120 ° C.
0 ° C to 90 ° C is preferred. The pressure that does not boil at this time may be about 2 atm or more. There is no particular upper limit, but the effect is saturated at about 50 atm. 2-10 more
Atmospheric pressure is preferred.

The cellulose ester used in the present invention has an acyl group having 2 to 3 carbon atoms as a substituent, and the degree of substitution of the acyl group is preferably 2.6 to 3.0.
At this time, when the degree of substitution of the acetyl group is 2.5 or more, it is preferable to use the above-described cooling dissolution method or high-pressure dissolution method because good solubility in a non-chlorine solvent can be obtained.

The cooling dissolution method is described in JP-A-9-955.
No. 38, No. 9-95544, and No. 9-95557, and a method of forming a dope using a solvent such as acetone, methyl acetate, and ethyl formate can be used.

The high-pressure melting method is described in JP-A-11-21.
The high-pressure dissolution method described in JP-A-379-379 can be used. In the publication, acetone is used as an organic solvent, but the same can be carried out with methyl acetate.

The non-chlorine organic solvents useful in the present invention include methyl acetate, ethyl acetate, amyl acetate, acetone,
Tetrahydrofuran, 1,3-dioxolan, 1,4-
Dioxane, cyclohexanone, ethyl formate, 2,2,2
2-trifluoroethanol, 2,2,3,3-tetrafluoro-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,
Examples thereof include nitroethane, and methyl acetate, ethyl acetate, and 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 all the organic solvents. Further, it is preferable to use 5 to 30% by mass of acetone based on the total organic solvent in combination with methyl acetate, because the viscosity of the dope can be reduced.

In the present invention, the phrase "contains substantially no chlorine-based solvent" means that the chlorine-based solvent is 10% by mass or less, preferably 5% by mass or less, and most preferably contains no chlorine-based solvent, based on the total amount of the organic solvent.

The cellulose ester dope preferably contains 0.1 to 30% by mass (based on the total amount of the organic solvent) of an alcohol having 1 to 4 carbon atoms in addition to the above-mentioned non-chlorinated organic solvent. . By using the alcohol which is a poor solvent of the cellulose ester in this way, when the dope is cast on a casting support, as the solvent evaporates, the ratio of the alcohol in the dope increases, and the web The effect is obtained that the (dope film) is gelled to make the web strong and easy to peel off from the casting support. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol and t-butanol.
tert-butanol. Among these, the stability of the dope, the boiling point is relatively low, the drying property is good,
Ethanol is most preferred because it has no toxicity.

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

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

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

In the present invention, since the compounds of the general formulas (1) to (3) also serve as a plasticizer, it is not necessary to add a plasticizer again, but the plasticizer may be added for another purpose. Is also good.

For example, for the purpose of improving the moisture resistance of the film, there may be mentioned alkylphthalylalkylglycolates, phosphate esters other than the general formula (3), aromatic carboxylate esters and citrate esters.

As the alkylphthalylalkyl glycolates, for example, methylphthalylmethyl glycolate,
Ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl Phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalate Propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate,
Octylphthalylmethyl glycolate, octylphthalylethyl glycolate and the like can be mentioned. Examples of the phosphate ester include triphenyl phosphate, tricresyl phosphate, phenyldiphenyl phosphate and the like. Examples of the aromatic carboxylic acid ester include phthalic acid ester and citrate ester, and examples of the phthalic acid ester include dimethyl phthalate, diethyl phosphate, dioctyl phthalate and diethylhexyl phthalate, and the like. Acetyl tributyl citrate can be mentioned.

Among them, methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate and octyl phthalyl octyl glycolate are preferred, and ethyl phthalyl ethyl glycolate is particularly preferred. It is preferably used. Further, two or more of these alkylphthalylalkyl glycolates may be used in combination.

The amount of the plasticizer used for this purpose is preferably from 1 to 30% by mass relative to the cellulose ester, and more preferably from 2 to 30% by mass.
13 mass% is preferred.

These compounds may be added together with the cellulose ester and the solvent when preparing the cellulose ester solution, or may be added during or after the solution is prepared.

A dye is added for the purpose of improving the yellowness of the film. It is preferable that the color can be colored in gray as seen in a usual photographic support. However, as a polarizing plate protective film, unlike a photographic support, there is no need to prevent light piping, so the content may be small,
1 to 100 pp in mass ratio to cellulose ester
m is preferable and 2 ppm to 50 ppm is more preferable.
Since the cellulose ester has a slightly yellow tint, a blue or purple dye is preferably used. A plurality of dyes may be appropriately combined so as to be gray.

If the film is not slippery, the films may be blocked with each other, resulting in inferior handleability. 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. Among them, silicon dioxide is preferable because the haze of the film can be reduced. 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 has an average particle size of 0.01 to 1.0 μm,
Content is 0.005 to cellulose ester
0.3 mass% is preferred.

Since the liquid crystal display device is frequently used outdoors, it is also important to provide the polarizing plate protective film with a function of cutting off 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 amount of the ultraviolet absorber added is preferably in the range of 0.5 to 20% by mass based on the cellulose ester.
The range of 0.6 to 5% by mass is more preferable.

For the purpose of improving the wet heat resistance of the film,
Hindered phenol compounds are preferably used,
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-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,
5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamide), 1,3,5- Trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate and the like. Particularly, 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]. Also, for example, a hydrazine-based metal deactivator such as N, N'-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine or tris (2,4-di-t A phosphorus-based processing stabilizer such as (-butylphenyl) phosphite may be used in combination. The addition amount of these compounds is preferably 1 ppm to 1.0% by mass relative to the cellulose ester,
0 to 1,000 ppm is more preferred. In addition,
A heat stabilizer such as a salt of an alkaline earth metal such as calcium and 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 appropriately added. Casting step: The dope is fed to a pressurized die through a pressurized metering gear pump and, at the casting position, an endless metal belt or a rotating metal drum for infinitely transferring (hereinafter simply referred to as a support). This is a step of casting a dope from a pressure die. The surface of the casting support is a mirror surface. Other casting methods include a doctor blade method for adjusting the film thickness of the cast dope film with a blade, and a reverse roll coater method for adjusting the film with a counter-rotating roll. It is preferable to use a pressure die which can make the film thickness uniform. 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 doping amount may be divided to form a plurality of layers.

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

Peeling step: This is a step of peeling the web from which the solvent has evaporated on the support at the peeling position. The peeled web is sent to the next step. If the residual solvent amount (the following formula) of the web at the time of peeling is too large, the web is difficult to peel, or conversely, if the web is sufficiently dried on the support and then peeled, a part of the web is peeled off in the middle.

The amount of the residual solvent can be expressed by the following equation. Residual solvent amount (% by mass) = {(M−N) / N} × 100 where M is the mass of the web at any time, and N is M
The mass when dried at 0 ° C. for 3 hours.

As a method for increasing the film forming speed (the film forming speed can be increased because the film is peeled while the amount of the residual solvent is as large as possible), there is a gel casting method in which the film can be peeled even when the amount of the residual solvent is large. . Examples of the method include a method in which a poor solvent for the cellulose ester is added to the dope, gelling is performed after casting the dope, and a method in which the temperature of the support is lowered to gelate. There is also a method of adding a metal salt to the dope. By gelling on the support and strengthening the film, peeling can be accelerated and the film forming speed can be increased. If the residual solvent amount is greater at the time of peeling, if the web is too soft, the flatness at the time of peeling may be impaired, or shear or vertical stripes may easily occur due to peeling tension, and the amount of the residual solvent may be reduced in consideration of economic speed and quality. I can decide.

Drying step: This is a step of drying the web using a drying apparatus that alternately transports the web through rolls arranged in a staggered manner and / or a tenter apparatus that transports the web by clipping both ends of the web with clips. In general, hot air is blown to both sides of the web as a drying means, but there is also a method of heating by applying a microwave instead of the wind. Too fast drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed when the residual solvent is about 8% by mass or less. Throughout, the drying temperature is usually 40 ° C to 250 ° C, preferably 70 ° C to 180 ° C.
The drying temperature, the amount of drying air, and the drying time vary 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. The quicker it dries at higher temperatures, the greater the shrinkage. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the resulting film. From this viewpoint, for example, Japanese Patent Application Laid-Open No. 62-4662.
The method of drying all the steps or a part of the steps as described in Japanese Patent Publication No. 5 (tenter method) while holding both ends of the width of the web with a clip in the width direction is preferable.

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

To adjust the film thickness of the cellulose ester film, the dope concentration, the amount of liquid sent from the pump, the slit gap of the die cap, the extrusion pressure of the die, and the thickness of the casting support are adjusted so as to obtain the desired thickness. It is good to control speed etc. In addition, as means for making the film thickness uniform, it is preferable to use a film thickness detecting means to feed back and adjust the programmed feedback information to each of the above-described devices.

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

The cellulose ester film obtained as described above is laminated on both sides of the polarizer via an adhesive such as acrylic if necessary to form a polarizing plate. There is no particular limitation on the type of polarizer, and iodine or a dichroic dye may be added to a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene-vinyl acetate copolymer-based partially saponified film. An oriented and stretched polyene film or a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dechlorinated polyvinyl chloride product is used. The polarizing plate using the cellulose ester film of the present invention has a high degree of polarization, for example, STN, TFT, T
By combining with various liquid crystal cells such as N, FCL, and SH, a liquid crystal display device having excellent viewing angle characteristics can be obtained.

When the cellulose ester film of the present invention is used as a protective film for a polarizing plate, the film thickness is preferably from 20 to 200 μm, particularly preferably from 30 to 90 μm.
m is preferred. The water vapor transmission rate of the film is 500 g /
m ² · 24H or less, preferably 300g / m ² · 24H,
The coefficient of dynamic friction of the film surface is 0.5 or less, the haze of the film is 0.6% or less, and the elastic modulus of the film is 2.4.
The absolute value (Re) of the retardation value with respect to incident light in a direction perpendicular to the film surface of 5 GPa or more is 0 to 10 nm,
It is preferable that the absolute value of the retardation value with respect to the incident light in an oblique direction at 45 degrees from the film surface is 0 to 30 nm, and the absolute value of the retardation value in the thickness direction is 0 to 70 nm. When these characteristic values are in the above ranges, good characteristics as a polarizing plate protective film are exhibited.

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

Hereinafter, the present invention will be described in detail with reference to examples, but embodiments of the present invention are not limited thereto.

[0084]

EXAMPLES Each measurement and evaluation method in the examples was carried out by the following methods.

<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 of 4: 1).
A predetermined 1N aqueous sodium hydroxide solution is added, and saponification is performed 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 in the same manner as described above. Further dilute the supernatant of the solution after the titration,
The composition of the organic acid is measured by a conventional method using an ion chromatograph. Then, the degree of substitution (%) is calculated as follows.

TA = (Q−P) × F / (1000 × W) DSace = (162.14 × TA) / ｛1-42.1
4 × TA + (1-56.06 × TA) × (AL / A
C)｝ DSacy = Ssce × (AL / AC) where P is the amount of 1N sulfuric acid (ml) required for titration of the sample, Q
Is the amount of 1N sulfuric acid required for the blank test (ml), F is 1
N sulfuric acid titer, W is sample mass (g), TA is total organic acid amount (mol / g), AL / AC is acetic acid (AC) and other organic acid (AL) measured by ion chromatography. The molar ratio, DSace, indicates the degree of substitution of the acetyl group, and DSacy indicates the degree of substitution of the acyl group having 3 or 4 carbon atoms.

<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 W / v% Flow rate: 1.0 ml / min Sample injection volume: 300 μl Standard sample: polystyrene Temperature: 23 ° C. <Film The retardation value (Re value) and the thickness direction retardation value (Rth) for incident light in the direction perpendicular to the surface
Value)> Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), a three-dimensional refractive index measurement was performed at 23 ° C. and 55% RH at a wavelength of 590 nm, and the refractive index nx , Ny and nz were determined. According to the following formula, each of the retardation values (Re
Value, Rth value).

Re value = | nx−ny | Rth value = ((nx + ny) / 2−nz) × d (nx is the refractive index of the film in a direction parallel to the film forming direction, and ny is the film forming direction) (The refractive index of the film in the vertical direction, nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film.) <Polarization degree> Two polarizing plates are stacked and a spectrophotometer is used. Was used to measure the transmittance at a wavelength of 550 nm. At this time, the transmittance was Tp when the polarization axes of the two polarizing plates were parallel, and Tc was the transmittance when they were orthogonal to each other, and the degree of polarization P was determined by the following equation.

P (%) = ｛(Tp−Tc) / (Tp−T)
c)｝ ^1/2 × 100 P is preferably 99.0% or more from the practicality as a polarizing plate.

Example 1 100 parts by mass of cellulose acetate having a degree of acetyl substitution of 2.88 (number average molecular weight 170,000), tinuvin 32
6, 0.5 parts by mass of Tinuvin 109 (manufactured by Ciba Specialty Chemicals), 0.5 parts by mass of Tinuvin 171 (manufactured by Ciba Specialty Chemicals), Aerosil 200V (manufactured by Nippon Aerosil Co., Ltd.), 2 parts by weight of ethylphthalylethyl glycolate, 10 parts by weight of trimethyl phosphate, 450 parts by weight of methyl acetate and 5 parts of acetone
It was mixed with 0 parts by mass of a mixed solvent to swell. Next, the mixture was placed in a closed container having a double structure, and a refrigerant was introduced into the outer jacket while slowly stirring the mixture. This allowed the mixture in the inner vessel to cool to -70 ° C. The mixture was cooled for 30 minutes until it was cooled uniformly. The refrigerant in the jacket outside the sealed container is discharged, and warm water is introduced into the jacket instead. The contents were subsequently stirred and raised to 100 ° C. over 40 minutes. The inside of the container became 2.5 atm.
The temperature was lowered to 50 ° C. while stirring and returned to normal pressure, and the mixture was left overnight to obtain a dope. This dope was prepared using Azumi Filter Paper No. After filtration using Nippon Seisen Co., Ltd., Finemet NM (absolute filtration accuracy 100 μm) and Finepore NF (absolute filtration accuracy 50)
, 15 μm, and 5 μm in this order with increasing filtration accuracy) at a filtration pressure of 0.98 MPa and subjected to membrane formation.

The obtained dope was cast from a die onto a stainless steel belt. 35 ° C from the back of the stainless steel belt
After drying for 1 minute on a temperature-controlled stainless steel belt by contacting hot water at a temperature of 15 ° C., further contacting 15 ° C. cold water on the back surface of the stainless steel belt and holding for 15 seconds,
Removed from stainless steel belt. The residual solvent amount in the film at the time of peeling was 40% by mass.

Next, the film was dried at 130 ° C. for 10 minutes while fixing both ends of the peeled-off film to obtain a film having a thickness of 80 μm. The obtained film was immersed in a 2N aqueous solution of sodium hydroxide at 60 ° C for 2 minutes, washed with water, and heated at 100 ° C.
For 10 minutes to obtain an alkali-treated sample film. The retardation value (Re value) and the thickness direction retardation value (Rt value) with respect to the incident light in the direction perpendicular to the film surface were measured. The results are shown in Table 1.

Next, a polyvinyl alcohol film having a thickness of 120 μm was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 4 times at 50 ° C. to form a polarizing film. The alkali-treated sample film was bonded to both surfaces of the polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive to prepare a polarizing plate. The degree of polarization was measured using the obtained polarizing plate. Table 1 shows the evaluation results.

Example 2 100 parts by mass of cellulose acetate having a degree of acetyl substitution of 2.88 (number average molecular weight 170,000), tinuvin 32
6, 0.5 parts by mass of Tinuvin 109 (manufactured by Ciba Specialty Chemicals), 0.5 parts by mass of Tinuvin 171 (manufactured by Ciba Specialty Chemicals), Aerosil 200V (manufactured by Nippon Aerosil Co., Ltd.), 2 parts by weight of ethylphthalylethyl glycolate, 10 parts by weight of trimethyl phosphate, 450 parts by weight of methyl acetate and 5 parts of acetone
It was mixed with 0 parts by mass of a mixed solvent to swell. Next, the mixture was put into a pressure-sealed container, and a pressure of 1,000 atm was applied for 30 minutes. Thereafter, the pressure was released to normal pressure. This operation was repeated three times to obtain a dope.

This dope was prepared using Azumi Filter Paper No. manufactured by Azumi Filter Paper Co., Ltd. After filtration using 244, the mixture was allowed to stand overnight and defoamed. Then, using Nippon Seisen Co., Ltd. Finemet NM (absolute filtration accuracy: 100 μm) and Finepore NF (absolute filtration accuracy: 50 μm, 15 μm, 5 μm, in order of increasing filtration accuracy, using a filtration pressure of 0.98 MPa) , And used for film formation.

Using the obtained dope, a film having a thickness of 80 μm was prepared in the same manner as in Example 1, and a polarizing plate sample was prepared. Table 1 shows the evaluation results.

Example 3 A cellulose ester film having a thickness of 80 μm was prepared in the same manner as in Example 1 except that 10 parts by mass of bis (2-ethylhexyl) azelate was used instead of trimethyl phosphate. Was prepared. Table 1 shows the evaluation results.

Example 4 A cellulose ester film having a thickness of 80 μm was prepared in the same manner as in Example 2 except that 10 parts by mass of bis (2-ethylhexyl) azelate was used instead of trimethyl phosphate. Was prepared. Table 1 shows the evaluation results.

Example 5 A cellulose ester film having a thickness of 80 μm was prepared in the same manner as in Example 1, except that 10 parts by mass of tris (2-ethylhexyl) trimellitate was used instead of trimethyl phosphate. A sample was prepared. Table 1 shows the evaluation results.

Example 6 A cellulose ester film having a thickness of 80 μm was prepared in the same manner as in Example 2, except that 10 parts by mass of tris (2-ethylhexyl) trimellitate was used instead of trimethyl phosphate. A sample was prepared. Table 1 shows the evaluation results.

Comparative Example 1 In Example 1, the raw material used was the acetyl substitution degree 2.
85 cellulose acetate (number average molecular weight 170,0
00) 100 parts by mass, 2- (2'-hydroxy-3 ',
5'-di-t-butylphenyl) benzotriazole 1
In the same manner as in Example 1 except that parts by mass, 10 parts by mass of triphenyl phosphate, 2 parts by mass of diethyl phthalate, 450 parts by mass of methyl acetate, and 50 parts by mass of ethanol were used.
A μm cellulose ester film was prepared, and a polarizing plate sample was further prepared. Table 1 shows the evaluation results.

Example 7 A substitution degree of acetyl group of 2.00, a substitution degree of propionyl group of 0.80, 100 parts by mass of cellulose ester having a number average molecular weight of 100,000, 10 parts by mass of trimethyl phosphate, tinuvin 326 (Ciba Specialty Co., Ltd.) 0.5 parts by mass of Chemicals, 0.5 parts by mass of Tinuvin 109 (manufactured by Ciba Specialty Chemicals), and 0.5 parts by mass of Tinuvin 171 (manufactured by Ciba Specialty Chemicals).
5 parts by mass, Aerosil 200V (Nippon Aerosil Co., Ltd.)
), 210 parts by mass of methyl acetate and 90 parts by mass of ethanol were charged into a pressure-closed container, heated to 80 ° C., the pressure in the container was set to 5 atm, and the cellulose ester was completely dissolved with stirring to obtain a dope. Was. The temperature of the dope was lowered to 50 ° C., the mixture was allowed to stand overnight, and this dope was subjected to Azumi Filter Paper No. After filtration using 244, the mixture was allowed to stand overnight to remove bubbles. Next, Nippon Seisen Co., Ltd. Finemet N
M (absolute filtration accuracy 100 μm), fine pore NF (absolute filtration accuracy 50 μm, 15 μm, 5 μm in order to increase the filtration accuracy in order) using a filtration pressure of 0.98 MPa
, And used for film formation.

Using the obtained dope, a film having a thickness of 80 μm was prepared in the same manner as in Example 1, and a polarizing plate sample was prepared. Table 1 shows the evaluation results.

Example 8 A film having a thickness of 80 μm was prepared in the same manner as in Example 7, except that 10 parts by mass of bis (2-ethylhexyl) azelate was used instead of trimethyl phosphate. A plate sample was prepared. Table 1 shows the evaluation results.

Example 9 A film having a thickness of 80 μm was obtained in the same manner as in Example 7 except that trimethyl phosphate was replaced by 10 parts by mass of tris (2-ethylhexyl) trimellitate.
Was prepared, and a polarizing plate sample was prepared. Table 1 shows the evaluation results.

Comparative Example 2 In Example 7, 15 parts by mass of diethyl phthalate and 450 parts of methyl acetate were used in place of trimethyl phosphate.
A cellulose ester film having a thickness of 80 μm was prepared in the same manner except that the mass parts and ethanol were changed to 50 parts by mass, and a polarizing plate sample was further prepared. Table 1 shows the evaluation results.

[0108]

[Table 1]

Table 1 shows that the retardation in the thickness direction of the cellulose ester film according to the present invention is lower than that of the conventional method shown in Comparative Example, and that the polarizing plate is excellent in the degree of polarization.

[0110]

According to the present invention, it is possible to provide a method for preparing a cellulose ester dope without using a chlorine-based solvent and obtaining a cellulose ester film having a reduced retardation value (Rt value) in a thickness direction. Was.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (reference) // B29K 1:00 B29K 1:00 F term (reference) 2H023 FA01 FA13 2H049 BB33 4F071 AA09 AA81 AC05 AC07 AC10 AC12 AC15 AC19 AE19 BB02 4F205 AA01 AB19 AB22 AG01 AH42 GA07 GB02 GC07 GE02 GE03 GE22 GF02 GF24 GN22 GN29 4J002 AB021 EH096 EH146 EW046 GP00 HA05

Claims (18)

[Claims] 1. A cellulose ester film comprising at least one compound represented by the following general formula (1). General formula (1) R-OOC (CH ₂ ) _n COO-R [wherein, R represents an alkyl group having 1 to 10 carbon atoms, and n represents an integer of 4 to 10. ] 2. A cellulose ester film comprising at least one compound represented by the following general formula (2). Embedded image [In the formula, R ₁ represents an alkyl group having 1 to 8 carbon atoms. ] 3. A cellulose ester film comprising at least one compound represented by the following general formula (3). Embedded image [Wherein, R ₂ represents an alkyl group having 1 to 4 carbon atoms. ] 4. The cellulose ester film according to claim 1, wherein the cellulose ester is a lower fatty acid ester of cellulose. 5. A cellulose ester comprising 70,000 to 3
The cellulose ester film according to any one of claims 1 to 4, having a number average molecular weight of 000. 6. A cellulose ester and the above general formula (1)
A dope obtained by dissolving at least one compound represented by the formula (1) in an organic solvent substantially free of a chlorine-based solvent, at a boiling point of the organic solvent at normal pressure or higher, and under pressure conditions under which foaming does not occur. A method for producing a cellulose ester film, comprising: casting a film on a support; removing a dry film cast on the support; and drying the film. 7. A cellulose ester and the above-mentioned general formula (2)
A dope obtained by dissolving at least one compound represented by the formula (1) in an organic solvent substantially free of a chlorine-based solvent, at a boiling point of the organic solvent at normal pressure or higher, and under pressure conditions under which foaming does not occur. A method for producing a cellulose ester film, comprising: casting a film on a support; removing a dry film cast on the support; and drying the film. 8. A cellulose ester and the above-mentioned general formula (3)
A dope obtained by dissolving at least one compound represented by the formula (1) in an organic solvent substantially free of a chlorine-based solvent, at a boiling point of the organic solvent at normal pressure or higher, and under pressure conditions under which foaming does not occur. A method for producing a cellulose ester film, comprising: casting a film on a support; removing a dry film cast on the support; and drying the film. 9. A cellulose ester and the above-mentioned general formula (1)
After cooling at least one of the compounds represented by and an organic solvent substantially free of a chlorine-based solvent to -100 ° C to -10 ° C, the cooled product can be heated to 0 ° C to 120 ° C. A method for producing a cellulose ester film, comprising casting a dope on a support, peeling off the raw dry film cast on the support, and drying. 10. A mixture of a cellulose ester, at least one of the compounds represented by the above general formula (1), and an organic solvent containing substantially no chlorine-based solvent is pressurized to 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting the obtained solution on a support, peeling off the raw dry film cast on the support, and drying. 11. A cellulose ester, at least one of the compounds represented by the above general formula (2), and an organic solvent substantially free of a chlorine-based solvent, at -100 ° C. to -10 ° C.
After cooling to 0 ° C. to 120 ° C., the obtained dope is cast on a support, and the undried film cast on the support is peeled off and dried. A method for producing a cellulose ester film. 12. A mixture of a cellulose ester, at least one compound represented by the above general formula (2), and an organic solvent substantially free of a chlorine-based solvent is pressurized to 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting the obtained solution on a support, peeling off the raw dry film cast on the support, and drying. 13. A cellulose ester, at least one of the compounds represented by the general formula (3), and an organic solvent substantially free from a chlorine-based solvent, at -100 ° C. to -10 ° C.
After cooling to 0 ° C. to 120 ° C., the obtained dope is cast on a support, and the undried film cast on the support is peeled off and dried. A method for producing a cellulose ester film. 14. A mixture of a cellulose ester, at least one compound represented by the above general formula (3), and an organic solvent substantially free of a chlorine-based solvent is pressurized to 50 to 2,000 atm. A method for producing a cellulose ester film, comprising casting the obtained solution on a support, peeling off the raw dry film cast on the support, and drying. 15. The method for producing a cellulose ester film according to claim 6, wherein the organic solvent contains 50% or more of methyl acetate. 16. The cellulose ester according to claim 6, wherein the cellulose ester is a lower fatty acid ester of cellulose.
6. The method for producing a cellulose ester film according to any one of items 5 to 5. 17. A cellulose ester having a molecular weight of 70,000 to 70,000.
The method for producing a cellulose ester film according to any one of claims 6 to 16, wherein the cellulose ester film has a number average molecular weight of 300,000. 18. A polarizing plate protective film using the cellulose ester film according to claim 1. Description: