JP2001206981A - Method for preparing cellulose ester solution, method for producing cellulose ester film, cellulose ester film and polarizing plate using the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a cellulose ester film having a reduced retardation value (Rt value) in the thickness direction by preparing a cellulose ester solution without using a chlorine-based solvent. SOLUTION: This method for preparing a cellulose ester solution is characterized in that a mixture containing a cellulose ester and bromopropane is dissolved in the whole organic solvents used at a temperature equal to or higher than the boiling point of an organic solvent having the lowest boiling point under normal pressure among the whole organic solvents used and under a pressure condition not to cause bubbling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preparing a cellulose ester solution dissolved by a novel organic solvent, a method for producing a cellulose ester film useful for a polarizing plate used in a liquid crystal display, a cellulose ester film and a polarizing plate.

[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 cellulose ester solution (hereinafter sometimes referred to as a 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.
Japanese Patent No. 21379 proposes a method of mixing cellulose triacetate with acetone and applying a pressure of 980 to 490000 kPa.

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

The retardation value (Rt value) in the thickness direction
Is represented by Rt value = [{(nx + ny) / 2} −nz] × d, where nx is the refractive index of the film in the casting direction of the film, and ny is the refractive index of the film in the transverse direction (width direction). Refractive index, nz represents the refractive index of the film in the thickness direction, and d represents the thickness (nm) of the film.

When the Rt value increases, the STN, TFT, T
In various types of liquid crystal display devices such as N, 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, JP-A-11-92574
In JP-A-124445 and JP-A-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 solution is prepared by a cooling dissolution method, and the solution is cast. A method of reducing the Rt value of a film by forming a film has been proposed.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preparing a cellulose ester solution without using a chlorinated solvent to obtain a cellulose ester film having a reduced retardation value (Rt value) in the thickness direction. Is to provide.

[0010]

The present invention has the following constitution.

(1) dissolving a mixture containing a cellulose ester and bromopropane at a temperature not lower than the boiling point of the organic solvent having the lowest boiling point at normal pressure among all the organic solvents to be used, and under pressure conditions which do not cause foaming; A method for preparing a cellulose ester solution, comprising:

(2) After cooling a mixture containing a cellulose ester and bromopropane to -100 to -10 ° C, the mixture is heated to 0 to 120 ° C to dissolve the cellulose ester solution. Preparation method.

(3) A method for preparing a cellulose ester solution, comprising dissolving a mixture containing a cellulose ester and bromopropane at a pressure of 50 to 2000 atm.

(4) The cellulose ester solution according to (1) to (3), wherein the alcohol having 1 to 4 carbon atoms is contained in an amount of 2 to 40% by mass based on the total solvent of the solution. Preparation method.

(5) pyrrolidone, imidazolidinone,
The cellulose ester according to any one of (1) to (4), wherein at least one selected from methyl acetoacetate, dioxolane, and fluoroalcohol is contained in an amount of 1 to 40% by mass based on the total solvent of the solution. How to prepare the solution.

(6) The method for preparing a cellulose ester solution according to any one of (1) to (5), wherein the plasticizer is contained in an amount of 1 to 30% by mass based on the cellulose ester.

(7) The cellulose ester has a substituent having an acyl group having 2 to 3 carbon atoms, and the degree of substitution of the acyl group is 2.45 to 3.0. The method for preparing a cellulose ester solution according to any one of (1) to (6).

(8) The cellulose ester according to any one of (1) to (7), wherein the cellulose ester has an acetyl group as a substituent, and the degree of substitution of the acetyl group is 1.4 to 3.0. The method for preparing a cellulose ester solution according to claim 1.

(9) 70,00 cellulose ester
The method for preparing a cellulose ester solution according to any one of (1) to (8), having a number average molecular weight of 0 to 300,000.

(10) A cellulose ester film formed by a solution casting method using a cellulose ester solution prepared by the method according to any one of (1) to (9). Manufacturing method.

(11) A cellulose ester film obtained by the method according to (10).

(12) A polarizing plate, wherein the cellulose ester film according to (11) is attached to at least one surface of a polarizer.

Hereinafter, the present invention will be described in detail. The cellulose ester used in the present invention is a cellulose ester having an acyl group having 2 to 4 carbon atoms as a substituent, such as cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and acetate propionate butyrate. Is mentioned.
Further, a substituent or an alkyl group constituting an inorganic ester such as a nitro group 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 2.45 to
It is preferably 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, and 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 the releasability of the web from the support during the solution casting of the film is particularly good.

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 high. 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, and particularly preferably 0.03 g or less as sulfur atoms in 1 kg of the cellulose ester. When the amount of free acid and the amount of bound sulfuric acid in the cellulose ester are in the above ranges, excellent heat and moisture resistance as a polarizing plate or a photographic support can be imparted. The moist heat resistance required for a polarizing plate or a photographic support is defined as the most severe conditions in which they are used, for example, 80 ° C., 90% R
No degradation such as decomposition or coloring occurs even after 1000 hours under H. The amount of free acid and the amount of bound sulfuric acid in the cellulose ester can be measured by ASTM-D817-96.

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

Dissolution step: This is a step of dissolving the cellulose ester in an organic solvent mainly containing a good solvent for the cellulose ester while stirring to form a dope.

The present invention is characterized in that a novel bromopropane is contained in the dope as an organic solvent which is a good solvent for the cellulose ester. Examples of bromopropane include 1-bromopropane and 2-bromopropane,
Particularly, 1-bromopropane is preferable. The amount of bromopropane in the total organic solvent in the dope is preferably at least 10% by mass, more preferably at least 50% by mass, based on the total organic solvent. Of course, bromopropane alone may be used. The retardation value in the thickness direction of the cellulose ester film obtained by using the bromopropane solvent can be reduced as compared with the case of using the conventional methylene chloride solvent, and the content of bromopropane in the total organic solvent is high. Can be made smaller.

The method of preparing the dope of the present invention is carried out at a temperature not lower than the boiling point of the organic solvent having the lowest boiling point at normal pressure in all the organic solvents in the dope and at a pressure not boiling (hereinafter, referred to as (Referred to as a high-temperature dissolution method), cooling the cellulose ester and the organic solvent to -100 to -10C, or mixing the cellulose ester with an organic solvent at -100 to -10C, and then heating to 0 to 120C. Method (hereinafter referred to as cooling dissolution method), the cellulose ester and the organic solvent are 50 to
Pressurizing to 2000 atm (hereinafter referred to as high pressure melting method)
Is mentioned.

In the high-temperature dissolution method, for example, when the organic solvent having the lowest boiling point at normal pressure among the organic solvents used is 1-bromopropane (boiling point 70.97 ° C.), the temperature is 70. 97 ° C. to 150 ° C. is preferable, and 7
1 ° 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 cooling dissolution method is described in JP-A-9-955.
No. 38, No. 9-95544, No. 9-95557, etc., by changing the solvent to bromopropane.

As for the high-pressure melting method, see 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 bromopropane can be similarly used.

In the present invention, an organic solvent other than bromopropane may be used in combination. The organic solvent used is preferably a non-chlorine solvent. Useful non-chlorinated organic solvents include esters such as ethyl formate, methyl acetate, ethyl acetate, amyl acetate and nitroethane; ketones such as acetone and cyclohexanone; and ethers such as 1,3-dioxolane. , 2-methyl-1,3-dioxolan, 4-methyl-1,3-dioxolan, 2-
Ethyl-1,3-dioxolan, 4-ethyl-1,3-
Examples of fluoroalcohols such as dioxolan and 1,4-dioxane include 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,
1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro -1-propanol and pyrrolidones include 2-
Examples of pyrrolidone, N-methyl-2-pyrrolidone, and imidazolidinones include 1,3-dimethyl-2-imidazolidinone, and methyl acetoacetate. In particular, when a dioxolane, a fluoroalcohol, a pyrrolidone, an imidazolidinone, and methyl acetoacetate are contained in the cellulose ester solution, the retardation value in the thickness direction can be further reduced.
It is preferable that the ratio of these organic solvents to the total organic solvent in the solution is 1 to 40% by mass.

In the dope prepared in the present invention, in addition to bromopropane, an alcohol having 1 to 4 carbon atoms, which is a poor solvent for 1 to 30% by mass (based on the total amount of organic solvent) of cellulose ester, is used. Is preferably contained. By using such a poor solvent alcohol in combination, after the dope is cast on the casting support, as the solvent evaporates, the ratio of the alcohol in the solution increases, and the web (the dope becomes a film). Is gelled, and the effect is obtained that the web becomes strong and easy to peel off from the casting support. 1-4 carbon atoms
Examples of alcohols include methanol, ethanol, and n-
Examples thereof include propanol, iso-propanol, n-butanol, sec-butanol and tert-butanol. Of these, ethanol is most preferred because of its relatively low solution stability, good boiling point, good drying properties and no toxicity.

The concentration of the solid content of the dope is usually preferably 10 to 40% by mass, and it is preferable to adjust the dope viscosity in the range of 100 to 500P from the viewpoint of obtaining good flatness of the film.

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

In the dope, a plasticizer, a matting agent, an ultraviolet absorber, an antioxidant, a dye and the like may be added. In particular, it is preferable to add a plasticizer.

For example, examples of the plasticizer include alkylphthalylalkyl glycolates, phosphate esters and aromatic carboxylate esters, and the plasticizer helps to improve the moisture resistance of the film. Examples of the alkylphthalylalkyl glycolates include methylphthalylmethyl glycolate, ethylphthalylethyl glycolate, propylphthalylpropyl glycolate, butylphthalylbutyl glycolate, octylphthalyloctyl glycolate, and methylphthalylethyl. 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 Rate, butylphthalylethyl glycolate, propylphthalylbutyl glycolate, butylphthalylpropyl glycolate, methylphthalyloctyl glycolate, ethylphthalyl Chi le glycolate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate, and the like. 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, octyl phthalyl octyl glycolate is preferable, and ethyl phthalyl ethyl glycolate is particularly 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, particularly preferably from 2 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 dope, or may be added during or after the preparation of the dope.

A dye may be added to the dope 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, unlike a photographic support, there is no need to prevent light piping, so the content may be reduced, and the mass ratio to the cellulose ester may be 1 to 100.
ppm is preferable, and 2 to 50 ppm is more preferable. Some cellulose esters are slightly yellowish,
Blue or purple dyes are 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 poor handling. In this case,
Mats of 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, and crosslinked polymers It is preferable to include an agent. Among them, silicon dioxide is preferred because it reduces 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 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 a polarizing plate with a function of cutting off ultraviolet rays. For this purpose, the cellulose ester film preferably contains an ultraviolet absorber, but an ultraviolet absorber having no absorption in the visible light region is preferable. Examples of such an ultraviolet absorber include a benzotriazole-based compound, a benzophenone-based compound, and a salicylic acid-based compound. 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 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.

In order to improve 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,
0-1000 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. The amount of the alkaline earth metal is preferably from 1 to 100 ppm based on the cellulose ester.

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 installed on the upper surface. The surface of the casting support is a mirror surface. Other casting methods include a doctor blade method in which the thickness of the cast dope film is adjusted with a blade or a reverse roll coater method in which the dope film is adjusted with a counter-rotating roll, but the slit shape of the die is adjusted. A pressure die that can be formed and has a uniform 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 doping amount may be divided to form a plurality of layers.

Solvent evaporation step: This is a step in which the web formed by casting the dope into a film is heated on a 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.

As a method for increasing the film forming speed, a gel casting method (gel casting) capable of peeling off at most the residual solvent.
There is. 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 web, 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 device that alternately transports the web through rolls arranged in a staggered manner and / or a tenter device 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 to 250 ° C, preferably 70 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 off from the surface of the casting support, 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 residual solvent amount of the web is 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.

The residual solvent amount can be represented by the following equation: residual solvent amount (% by mass) = {(M−N) / N} × 100. Where M is the mass of the web at any time, N
Is the mass when M is dried at 110 ° C. for 3 hours.

To adjust the film thickness of the cellulose ester film, the dope concentration, the amount of liquid supplied by the pump, the slit gap of the die cap, the extrusion pressure of the die, the pressure of the casting support, and the like 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 immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, but 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 bonded to at least one side, preferably both sides, of the polarizer via an adhesive of a polyvinyl alcohol-based liquid, if necessary, to form a polarizing plate. Is configured. 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. Polarizing plate using the cellulose ester film of the present invention,
High degree of polarization, for example, STN, TFT, TN, FCL,
By combining with various liquid crystal cells such as 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 polarizing plate, the thickness of the film is from 20 to
200 μm is preferable, and particularly preferably 30 to 90 μm. The water vapor transmission rate of the film is 500 g / m ² · 24
H, preferably 300 g / m ² · 24H, the coefficient of dynamic friction on 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 2.45 GP.
a, the absolute value of the retardation value (Re) with respect to the incident light in the direction perpendicular to the film surface is 0 to 10 nm, the absolute value of the retardation value with respect to the incident light at an angle of 45 degrees from the film surface is 0 to 30 nm, and the thickness. The absolute value of the retardation value in the direction is preferably from 0 to 70 nm. When these characteristic values are within the above ranges, the polarizing plate exhibits good characteristics.

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

[0059]

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

Each measurement and evaluation method in the examples was performed 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: 4: 1), and then a predetermined 1N aqueous sodium hydroxide solution is added thereto, followed by saponification at 25 ° C. for 2 hours. Add phenolphthalein as an indicator and add 1N
Titrate excess sodium hydroxide with sulfuric acid. A blank test is performed in the same manner as described above. Further, the supernatant of the solution after completion of the 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 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 = DSace × (AL / AC) where P is the amount of 1 mol / l sulfuric acid (ml) required for titration of the sample, Q is the amount of 1 mol / l sulfuric acid (ml) required for the blank test, and F is 1mol / l sulfuric acid titer, W is sample mass (g), TA is total organic acid amount (mol / g), A
L / AC is acetic acid (A) measured by ion chromatography.
The molar ratio between C) and another organic acid (AL), DSace indicates the degree of substitution of an acetyl group, and DSacy indicates the degree of substitution of an acyl group having 3 or 4 carbon atoms.

<Number average molecular weight of cellulose ester> Measured under the following conditions of high performance liquid chromatography.

Solvent: methylene chloride Column: MPW × 1 (manufactured by Tosoh Corporation) Sample concentration: 0.2 (mass / volume)% Flow rate: 1.0 ml / min Sample injection volume: 300 μl Standard sample: polystyrene Temperature: 23 ° C <Retardation value (Re value) for incident light in the direction perpendicular to the film surface and retardation value (Rt
Value)> Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), a three-dimensional refractive index was measured at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH, and the refractive index nx , Ny, nz. According to the following formula, Re value = | nx−ny | × d Rt value = [{(nx + ny) / 2} −nz] × d Each retardation value (Re value,
Rt value) was calculated. Here, nx is the refractive index of the film in a direction parallel to the film forming direction, ny is the refractive index of the film in a direction perpendicular to the film forming direction, nz is the refractive index of the film in the thickness direction, and d is Each represents the thickness (nm) of the film.

<Degree of Polarization> Two polarizing plates were stacked, and the transmittance at a wavelength of 550 nm was measured using a spectrophotometer. At this time, the transmittance when the polarization axes of the two polarizing plates are parallel is Tp, and the transmittance when the polarization axes are orthogonal to each other is Tc, and P (%) = ｛(Tp−Tc) / ( Tp-Tc)｝ ^1/2 ×
100 The degree of polarization P was determined. P is 9 from the practicality as a polarizing plate
9.0% or more is preferable.

Example 1 100 parts by mass of cellulose triacetate having a degree of acetyl substitution of 2.88 (number average molecular weight: 150,000), Tinuvin 326 (manufactured by Ciba Specialty Chemicals)
0.5 parts by mass, Tinuvin 171 (manufactured by Ciba Specialty Chemicals) 0.5 parts by mass, Aerosil 200V
0.1 part by mass (manufactured by Nippon Aerosil Co., Ltd.), 2 parts by mass of ethylphthalylethyl glycolate, and 10 parts by mass of trimethyl phosphate were mixed in a mixed solvent of 450 parts by mass of 1-bromopropane and 50 parts by mass of ethanol. Next, the mixture was placed in a double-structured closed container, 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 pressure in the container was 1.5 atm. The temperature was lowered to 60 ° C. with 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, 15 μm, and 5 μm in this order) with a filtration pressure of 9.8 kPa.

The obtained dope was cast from a die onto a stainless steel belt. 65 ° 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 25 ° C., further contacting 25 ° C. cold water on the back surface of the stainless steel belt and holding for 15 seconds,
Peeled 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 150 ° C. for 10 minutes while fixing both ends of the peeled film to obtain a film having a thickness of 80 μm. The obtained film was placed in a 2 mol / l sodium hydroxide aqueous solution at 60 ° C. for 2 hours.
For 10 minutes, washed with water, and dried 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. Next, a polyvinyl alcohol film having a thickness of 120 μm was coated with iodine 1
It was immersed in 100 parts by mass of an aqueous solution containing 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 measurement results.

Example 2 100 parts by mass of cellulose triacetate (number average molecular weight 170,000) having an acetyl substitution degree of 2.92, Tinuvin 109 (manufactured by Ciba Specialty Chemicals)
0.5 parts by mass, 1.0 part by mass of Tinuvin 171 (manufactured by Ciba Specialty Chemicals), Aerosil 200V
0.1 parts by mass (manufactured by Nippon Aerosil Co., Ltd.), 6 parts by mass of ethylphthalylethyl glycolate, and 5 parts by mass of trimethyl phosphate were mixed in a mixed solvent of 450 parts by mass of 1-bromopropane and 50 parts by mass of ethanol. 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. After filtration using 244, the mixture was allowed to stand overnight and defoamed. Next, Finemet NM (absolute filtration accuracy 100 μm) and Finepore NF (absolute filtration accuracy 50 μm, 15 μm, 5 μm) manufactured by Nippon Seisen Co., Ltd.
m in order of m) and filtered at a filtration pressure of 9.8 kPa for membrane formation. Using the obtained dope, a film having a thickness of 80 μm was produced in the same manner as in Example 1, and then a polarizing plate was produced. Table 1 shows the measurement results.

Example 3 In Example 1, N-methyl-2 was further used as an organic solvent.
-A cellulose ester film having a thickness of 80 µm was prepared in the same manner except that 50 parts by mass of pyrrolidone was added, and then a polarizing plate was prepared. Table 1 shows the measurement results.

Example 4 The procedure of Example 1 was repeated, except that 50 parts by mass of 1,3-dioxolane was further added as an organic solvent.
A μm cellulose ester film was prepared, and a polarizing plate sample 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 50 parts by mass of 2,2,2-trifluoroethanol was further added as an organic solvent. Was prepared. Table 1 shows the evaluation results.

Example 6 The procedure of Example 1 was repeated, except that 50 parts by mass of methyl acetoacetate was further added as an organic solvent.
Was produced, and then a polarizing plate was produced. The measurement results are shown in Table 1.

Example 7 100 parts by mass of cellulose acetate propionate having a degree of substitution of acetyl group of 2.00, a degree of substitution of propionyl group of 0.80 and a number average molecular weight of 100,000, 10 parts by mass of trimethyl phosphate, tinuvin 326 ( 0.5 parts by mass, Tinuvin 1 by Ciba Specialty Chemicals
71 (manufactured by Ciba Specialty Chemicals) 0.5
Parts by mass, Aerosil 200V (Nippon Aerosil Co., Ltd.)
0.1 parts by mass, 350 parts by mass of 1-bromopropane,
50 parts by mass of ethanol was put into a pressure-closed container,
The cellulose ester was completely dissolved with stirring to obtain a dope. The temperature of the dope was lowered to 60 ° C. and 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. Then Nippon Seisen Co., Ltd.
Finemet NM (absolute filtration accuracy 100 μm),
Fine pore NF (absolute filtration accuracy 50 μm, 15 μm,
The filtration was performed at a filtration pressure of 9.8 kPa using 5 μm in order of increasing the filtration accuracy and used for membrane formation. Using the obtained dope, a film having a thickness of 80 μm was produced in the same manner as in Example 1, and then a polarizing plate was produced. Table 1 shows the measurement results.

Comparative Example 1 100 parts by mass of cellulose triacetate having a degree of acetyl substitution of 2.88 (number average molecular weight: 150,000), Tinuvin 326 (manufactured by Ciba Specialty Chemicals)
1.0 part by mass and 13 parts by mass of trimethyl phosphate were mixed in a mixed solvent of 475 parts by mass of methylene chloride and 25 parts by mass of methanol. Put into a pressurized airtight container,
The solution was heated to 0 ° C., the pressure in the vessel was set to 1.2 atm, and the cellulose ester was completely dissolved with stirring to obtain a dope.
The temperature of the dope was lowered to 35 ° C. and the mixture was allowed to stand overnight. This dope was subjected to Azumi Filter Paper No. After filtration using 244, the mixture was allowed to stand overnight to remove bubbles. Then, Nippon Seisen Co., Ltd. Finemet NM (absolute filtration accuracy 100μ)
m), fine pore NF (absolute filtration accuracy 50 μm, 15
(in order of increasing the filtration accuracy in the order of μm and 5 μm) at a filtration pressure of 9.8 kPa and subjected to membrane formation. Using the obtained dope, a thickness of 80
A μm film was prepared, and then a polarizing plate was prepared. Table 1 shows the measurement results.

[0074]

[Table 1]

(Results) According to Table 1, the retardation in the thickness direction of the cellulose ester film using bromopropane according to the present invention was lower than that of the conventional method shown in the comparative example. It turns out that it is excellent.

[0076]

According to the present invention, a cellulose ester film formed using bromopropane, an organic solvent capable of dissolving a novel cellulose ester, has a retardation value in the thickness direction, and provides an excellent polarizing plate for use in a liquid crystal image display device. I can do it.

Continued on the front page F-term (reference) 2H049 BA02 BA26 BA42 BB33 BB49 BC01 BC03 BC22 2H091 FA08X FA08Z FB02 FC01 FD15 GA16 KA02 4F071 AA09 AA81 AB18 AB26 AC03 AC10 AC15 AE04 AE11 AE19 AH16 BA02 BB02 ACO1 4 GE24 GF02 GF24 4J002 AB021 EB046 EC037 EC038 ED027 EE037 EH037 EH149 EL107 EU027 EU107 EW049 FD029 GP00 HA05

Claims (12)

[Claims] 1. Dissolving a mixture containing a cellulose ester and bromopropane at a pressure higher than the boiling point of the organic solvent having the lowest boiling point at normal pressure among all the organic solvents used, and under pressure conditions that do not cause foaming. A method for preparing a characteristic cellulose ester solution. 2. A method for preparing a cellulose ester solution, comprising cooling a mixture containing a cellulose ester and bromopropane to -100 to -10 ° C., and then heating the mixture to 0 to 120 ° C. to dissolve the mixture. Method. 3. A method for preparing a cellulose ester solution, comprising dissolving a mixture containing a cellulose ester and bromopropane at a pressure of 50 to 2000 atm. 4. The method for preparing a cellulose ester solution according to claim 1, wherein the alcohol having 1 to 4 carbon atoms is contained in an amount of 2 to 40% by mass based on the total solvent of the solution. 5. The method according to claim 1, wherein at least one selected from pyrrolidone, imidazolidinone, methyl acetoacetate, dioxolane and fluoroalcohol is added to the total solvent of the solution.
The method for preparing a cellulose ester solution according to any one of claims 1 to 4, wherein the content of the cellulose ester is in the range of from about 40 to about 40% by mass. 6. The plasticizer is added to the cellulose ester in an amount of 1: 1.
The method for preparing a cellulose ester solution according to any one of claims 1 to 5, wherein the content thereof is from 30 to 30% by mass. 7. The cellulose ester having 2 to 3 carbon atoms.
The cellulose ester solution according to any one of claims 1 to 6, wherein the cellulose ester solution has an acyl group as a substituent, and the degree of substitution of the acyl group is 2.45 to 3.0. Preparation method. 8. The cellulose ester has an acetyl group as a substituent, and the degree of substitution of the acetyl group is 1.4 to 10.
The method for preparing a cellulose ester solution according to any one of claims 1 to 7, wherein the value is 3.0. 9. A cellulose ester comprising 70,000 to 3%.
The method for preparing a cellulose ester solution according to any one of claims 1 to 8, wherein the cellulose ester solution has a number average molecular weight of 000. 10. A method for producing a cellulose ester film, comprising forming a film by a solution casting method using the cellulose ester solution prepared by the method according to claim 1. Description: . 11. A cellulose ester film obtained by the method according to claim 10. 12. A polarizing plate, wherein the cellulose ester film according to claim 11 is adhered to at least one surface of a polarizer.