JP2002137237A - Method for producing cellulose ester film - Google Patents

Abstract

(57) [Summary] [Problem] In a solution casting method of a cellulose ester film, even if the discharge amount from a casting die is changed in order to change a product type, a large number of foreign substances are mixed in the formed film. Don't do it. SOLUTION: The dope in a stock tank 3 is sent to a continuous filtration device 5 by a metering pump 4 for filtration. At this time, the flow rate sent to the continuous filtration device 5 by the metering pump 4 is the maximum flow rate discharged from the casting die 7 (the flow rate used when forming a thicker film). In this state, a part of the dope sent out from the continuous filtration device 5 is sent back to the stock tank 3 through the reverse feed pipe 8 by the reverse feed pump 9, and another dope is sent to the casting die 7. At this time,
The flow rate of the dope reversely fed by the reverse feed pump 9 is set so that the flow rate sent to the casting die 7 is a flow rate for forming a thinner film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a cellulose ester film produced by a solution casting method.
More specifically, the present invention relates to a method for producing a cellulose ester film used as a protective film of a polarizing plate.

[0002]

2. Description of the Related Art A cellulose triacetate film used as a protective film of a polarizing plate is manufactured by a solution casting method. Specifically, a cellulose dope in which cellulose triacetate and various additives are dissolved in a solvent is cast. The product is cast from a die onto a drum or an endless band, dried to a certain extent, peeled off, and further dried to obtain a product.

In general, a dope contains many impurities and undissolved gels which are not dissolved in a solvent when simply dissolved, so that if the film is formed as it is, a large number of foreign substances are mixed in the completed film and cannot be used as a product. is there. Therefore, conventionally, the dope was subjected to filtration at least once before casting to remove foreign matter from the dope and then cast.

In general, when a film is produced by a solution casting method, a variety of varieties having different thicknesses, widths and grades are produced using the same film forming apparatus. Since there is a difference, a difference in product width, and a difference in film forming speed, the amount of dope discharged from the casting die differs for each product type.

[0005] Incidentally, among the solution casting devices, there is a continuous casting device arranged in series upstream of a casting die for continuous filtration in-line. The film is formed with the flow rate of the dope passing through the filtration device equal to the flow rate discharged from the casting die. Therefore, in a solution casting apparatus in which a continuous filtration device is arranged in series with a casting die, the flow rate passing through the continuous filtration device is also changed according to the discharge amount from the casting die as the product type changes.

[0006]

However, when the flow rate of the dope passing through the continuous filtration device is changed, foreign substances increase in the dope after filtration, and as a result, the number of foreign substances in the produced film increases. In particular, when the flow rate was increased, the amount of foreign matters increased. This foreign matter decreases after a certain period of time and returns to the level before the flow rate was changed. However, until the flow returns to the level before the flow rate change, the formed film has many foreign substances, significantly reducing the value of the product, or causing an unacceptable level of the product and causing a large production loss. is there.

[0007] The present invention solves the above problems, and prevents a large number of foreign substances from being mixed in a formed film even when the discharge amount from a casting die is changed in order to change the product type. As a result, it is an object of the present invention to provide a solution casting method for a cellulose ester film of high quality and low production loss.

[0008]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies in order to achieve the above object, and has found the cause of an increase in foreign matter. That is, the filter medium captures foreign substances contained in the dope passing therethrough on the surface or inside thereof, but the retention force is not perfect. Therefore, even if captured once under certain conditions, when the conditions are changed, capture and retention can no longer be completed and released, and may flow out to the downstream side of the filter medium. In particular, changing the type from a thinner type to a thicker type, changing the type from a narrower type to a wider type, or changing from a type with the same thickness and width to a type with a lower film forming speed to a higher type. Due to the change of varieties to different varieties, the flow rate of the dope discharged from the casting die increases, and accordingly, the flow rate of filtration increases from a low flow rate to a high flow rate. As a result, the shearing force against foreign matter trapped on or in the furnace material increases. As a result, the trapped foreign matter flows out downstream along with the dope, resulting in an increase in foreign matter in the formed film.

The present invention has been made on the basis of the above-mentioned findings, and is provided by providing a facility for back-feeding a part of the filtered dope to the upstream side of the filtration and changing the flow rate of the back-feed.
Even when the dope flow rate discharged from the casting die is changed, the filtration flow rate can be kept constant.

That is, the method for producing a cellulose triacetate film according to the present invention is directed to a method for producing a cellulose ester film having a casting die and a continuous filtration device arranged in series upstream of the casting die. Providing a recirculation path for recirculating a part of the filtered dope upstream of the continuous filtration device between the casting die and the casting die, by changing the recirculation flow rate, the dope flow rate passing through the continuous filtration device is reduced. It is characterized in that the discharge flow rate from the casting die is changed while always being kept constant.

In the method for producing a cellulose ester film of the present invention, the dope that has passed through the continuous filtration device is:
Since the flow flows separately on the casting die side and the reverse feeding side, by adjusting the flow rates of both, the discharge flow rate of the casting die can be changed while keeping the filtration flow rate constant.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is necessary to ensure at least the maximum value of the dope flow rate discharged from the casting die in the dope flow rate passing through the continuous filtration device, but it is necessary to make the dope flow rate maximum value. Is preferred. By setting the flow rate of the dope higher than the maximum value, a part of the filtered dope is always returned and filtered by the continuous filtration device, so that the removal of foreign substances in the dope is more complete. The flow rate of the dope which is always reversely fed is preferably 10% or more, more preferably 20% or more, and most preferably 25% or more of the total flow rate of the dope passing through the continuous filtration device.

[0013] The continuous filtration device can be used alone or when a plurality of filters are arranged in series. When a plurality of filters are arranged, it is preferable that the dope that has passed through the most downstream continuous filtration device is sent back, but the dope that has passed through any one or all of the continuous filtration devices can be sent back.

In some cases, the continuous filtration device is installed between a mixing tank for adjusting the dope and a stock tank.
The dope that has passed can be returned to the mixing tank. In this way, the foreign matter in the dope can be more reliably removed.

As the continuous filtration device, various filtration devices and filter media that can be used for producing a cellulose ester film can be used. For example, a filter press can be used as the filtration device, and a filter cloth can be used as the filter material. , Filter paper, metal mesh, metal fiber, non-woven fabric and the like can be used.

In the film produced by the method for producing a cellulose ester film according to the present invention, the number of foreign matters having a diameter of 30 μm or more is preferably 20 or less per 1000 m, and more preferably 10 or less. Diameter 3
When the number of foreign substances having a particle size of 0 μm or more exceeds 20 per 1000 m, when a polarizing plate is formed using a formed film as a protective film, a bright spot defect occurs, and the quality of the polarizing plate is deteriorated.

Representative examples of the cellulose ester include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate). A lower fatty acid means a fatty acid having 6 or less carbon atoms. Cellulose acetate includes cellulose triacetate (TAC) and cellulose diacetate (DAC).

Examples of organic solvents for dissolving the cellulose ester include hydrocarbons (eg, benzene, toluene), halogenated hydrocarbons (eg, methylene chloride, chlorobenzene), alcohols (eg, methanol, ethanol, diethylene glycol), ketones (Eg, acetone), esters (eg, methyl acetate, ethyl acetate, propyl acetate) and ethers (eg, tetrahydrofuran, methyl cellosolve) and the like.

Halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and methylene chloride is most preferably used. From the viewpoint of the physical properties such as the solubility of the cellulose ester, the peeling property from the support, the mechanical strength of the film, and other optical properties, the number of carbon atoms is 1 in addition to methylene chloride.
It is preferable to mix one to several kinds of alcohols of (1) to (5). The content of alcohol is 2 to 2 with respect to the entire solvent.
It is preferably 25% by mass, more preferably 5 to 20% by mass. Specific examples of alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like.
-Butanol or a mixture thereof is preferably used.

The solvent ratio of methyl acetate, ketones and alcohol is 20 to 90% by mass of methyl acetate, 5 to 60% by mass of ketones and 5 to 3% of alcohol.
It is preferable to use a solvent that is 0% by mass.

Recently, a solvent composition not using methylene chloride has been proposed in order to minimize the influence on the environment. For this purpose, the number of carbon atoms is between 3 and 12
Ether, ketone having 3 to 12 carbon atoms, and ester having 3 to 12 carbon atoms are preferable, and these are appropriately mixed and used. These ethers, ketones and esters may have a cyclic structure. Compounds having two or more functional groups of ether, ketone and ester (that is, -O-, -CO- and -COO-) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group.
In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the range specified for the compound having any one of the functional groups.

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

In a system that cannot be easily dissolved at room temperature and a system in which a large amount of insoluble matter is present, a good cellulose ester solution can be prepared by using cooling or heating or a combination of the two during dissolution. In the cooling dissolution method, the dissolution is promoted by allowing the solvent to rapidly and effectively penetrate into the polymer. Effective temperature conditions are -100 to -10 ° C, and a cellulose ester solution having better solubility can be obtained by heating to room temperature to 200 ° C after cooling.

In the dope (cellulose ester solution) used in the solution casting method of the present invention, various additives (for example, a plasticizer, an ultraviolet absorber, a deterioration inhibitor, a fine particle powder) depending on the use in each preparation step are included. , A release agent, an optical property adjusting agent, and a fluorine-based surfactant). The timing of the addition may be any in the cellulose ester solution preparation step, but may be added to the final preparation step of the cellulose ester solution preparation step by adding an additive.

A phosphoric acid ester or a carboxylic acid ester is used as the plasticizer. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP), cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like. Is raised. Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DB
P), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include:
O-acetyl triethyl citrate (OACTE) and O
-Acetyl tributyl citrate (OACTB), acetyl triethyl citrate, acetyl tributyl citrate.

Examples of other carboxylic esters include trimellitic esters such as butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and trimethyl trimellitate. Examples of glycolic acid esters include triacetin, tributyrin, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate, butylphthalylbutyl glycolate and the like.

Among the plasticizers exemplified above, triphenyl phosphate, biphenyl diphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, It is preferable to use diethylhexyl phthalate, triacetin, ethyl phthalyl ethyl glycolate, trimethyl trimellitate and the like. Particularly, triphenyl phosphate, biphenyl diphenyl phosphate, diethyl phthalate, ethyl phthalyl ethyl glycolate, and trimethyl trimellitate are preferred.

The above plasticizers may be used alone or in combination of two or more. The amount of the plasticizer added is preferably 0.1 to 20% by mass relative to the cellulose ester, and
5 mass% is more preferable. If the addition amount is less than 0.1% by mass, the effect of addition cannot be sufficiently exhibited, and the addition amount is 2%.
If it exceeds 0% by mass, bleeding out may occur on the film surface.

In the present invention, as a plasticizer for reducing the optical anisotropy, JP-A-11-12444 is used.
5, (di) pentaerythritol esters, glycerol esters described in JP-A-11-246704, diglycerol esters described in JP-A-2000-63560, citrate esters described in JP-A-11-92574, Substituted phenyl phosphates described in JP-A-11-90946 are preferably used.

The UV absorber may be of any type depending on the purpose. Examples of the UV absorber include salicylic acid ester type, benzophenone type, benzotriazole type, benzoate type, cyanoacrylate type, and nickel complex type. Although benzophenone-based, benzotriazole-based, and salicylate-based are preferred. Examples of benzophenone-based ultraviolet absorbers include 2,4.
-Dihydroxybenzophenone, 2-hydroxy-4-
Acetoxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-di-hydroxy-4-
Methoxybenzophenone, 2,2'-di-hydroxy-
4,4'-methoxybenzophenone, 2-hydroxy-
4-n-octoxybenzophenone, 2-hydroxy-
4-dodecyloxybenzophenone, 2-hydroxy-
4- (2-hydroxy-3-methacryloxy) propoxybenzophenone and the like. As a benzotriazole-based ultraviolet absorber, 2 (2'-hydroxy-3'-tert-butyl-5'-methylphenyl)
-5-chlorobenzotriazole, 2 (2'-hydroxy-5'-tert-butylphenyl) benzotriazole, 2 (2'-hydroxy-3 ', 5'-di-ter
t-amylphenyl) benzotriazole, 2 (2'-
Hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2 (2'-hydroxy-5'-tert-octylphenyl) benzotriazole and the like. Examples of salicylate esters include phenyl salicylate, p-octylphenyl salicylate, p-tert-butylphenyl salicylate and the like. Among these exemplified UV absorbers, in particular, 2-hydroxy-4-methoxybenzophenone, 2,2′-di-hydroxy-4,
4'-methoxybenzophenone, 2 (2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-
5-chlorobenzotriazole, 2 (2'-hydroxy-5'-tert-butylphenyl) benzotriazole, 2 (2'-hydroxy-3 ', 5'-di-tert
-Amylphenyl) benzotriazole, 2 (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole is particularly preferred.

As the ultraviolet absorber, it is preferable to use a plurality of absorbers having different absorption wavelengths in combination since a high blocking effect can be obtained in a wide wavelength range. The UV absorber for liquid crystal has a wavelength of 370 nm from the viewpoint of preventing deterioration of the liquid crystal.
From the standpoint of liquid crystal display properties, those having excellent ultraviolet absorbing ability and little absorption of visible light having a wavelength of 400 nm or more are preferred. For example, oxybenzophenone compounds,
Examples include benzotriazole-based compounds, salicylic acid ester-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, nickel complex salt-based compounds, and the like. Particularly preferred ultraviolet absorbers are benzotriazole-based compounds and benzophenone-based compounds. Above all, a benzotriazole-based compound is preferable because unnecessary coloring of the cellulose ester is small.

As for the UV absorber, see JP-A-6
0-235852, JP-A-3-199201, 5
-1907073, 5-194789, 5-2
No. 71471, No. 6-107854, No. 6-1182
No. 33, No. 6-148430, No. 7-11056,
7-11055, 7-11056, 8-29
Nos. 619 and 8-239509, JP-A-2000-20
It is described in each publication of No. 4173.

The amount of the ultraviolet absorber added is preferably 0.001 to 5% by mass relative to the cellulose ester, and is preferably 0.01 to 5% by mass.
１1% by mass is more preferred. 0.001% by mass
When the amount is less than 5%, the effect of addition cannot be sufficiently exerted. When the amount exceeds 5% by mass, the ultraviolet absorbent may bleed out to the film surface.

The ultraviolet absorber may be added simultaneously with dissolution of the cellulose ester, or may be added to the dissolved cellulose ester solution. In particular, a mode in which a UV absorber solution is added to the cellulose ester solution immediately before casting using a static mixer or the like is preferable because the spectral absorption characteristics can be easily adjusted.

The above-mentioned deterioration preventing agent can prevent cellulose triacetate and the like from being deteriorated and decomposed. Examples of the deterioration inhibitor include butylamine, hindered amine compounds (Japanese Patent Application Laid-Open No. 8-325537), guanidine compounds (Japanese Patent Application Laid-Open No. 5-271471), benzotriazole UV absorbers (Japanese Patent Application Laid-Open No. 6-235819), and benzophenone type. UV absorber (JP-A-6-118)
No. 233).

Of these, examples of the hindered amine compound include t-butylamine, triphenylamine, tribenzylamine and the like. Examples of the guanidine derivative include compounds represented by the following formulas (1a) and (1b).

[0037]

Embedded image

The amount of the deterioration inhibitor added is 0.001 to 5%
Is preferable, and 0.01 to 1% is more preferable. If the addition amount is less than 0.001%, the effect of addition is small, and if the addition amount exceeds 5%, the raw material cost increases, which is disadvantageous.

As the fine particle powder, silica, kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, alumina and the like can be arbitrarily used according to the purpose. Before adding these fine particle powders to the cellulose ester solution, it is preferable to disperse them in the binder solution by an arbitrary means such as a high-speed mixer, a ball mill, an attritor, and an ultrasonic disperser. As the binder, a cellulose ester is preferable. It is also preferable to carry out dispersion with other additives such as an ultraviolet absorber. The dispersion solvent is optional, but preferably has a composition close to that of the cellulose ester solution solvent.

The number average particle diameter of the fine particle powder is 0.01 to 10
0 μm is preferred, and 0.1 to 10 μm is particularly preferred.
The above dispersion may be added to the cellulose ester dissolving step at the same time or may be added to the cellulose ester solution in an optional step, but it is preferably added just before casting using a static mixer or the like as in the case of the ultraviolet absorbent.

The content of the fine particle powder is preferably from 0.001 to 5% by mass, more preferably from 0.01 to 1% by mass, based on the cellulose ester. When the addition amount is less than 0.001% by mass, the effect of addition cannot be sufficiently exhibited, and when the addition amount exceeds 5% by mass, the appearance and surface condition may be deteriorated.

As the release agent, a surfactant is effective and is not particularly limited, such as phosphoric acid type, sulfonic acid type, carboxylic acid type, nonionic type and cationic type. They are,
For example, it is described in JP-A-61-243837. The amount of the release agent added is preferably 0.001 to 2% by mass, and more preferably 0.01 to 1% by mass based on the cellulose ester.
Is more preferred. If the addition amount is less than 0.001% by mass, the effect of addition cannot be sufficiently exhibited, and the addition amount is 2%.
If the amount is more than mass%, precipitation or insoluble matter may occur.

The nonionic surfactant is a surfactant having a nonionic hydrophilic group of polyoxyethylene, polyoxypropylene, polyoxybutylene, polyglycidyl or sorbitan, and specifically, polyoxyethylene alkyl. Ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene glycol, polyhydric alcohol fatty acid partial ester, polyoxyethylene polyhydric alcohol fatty acid partial ester, polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, fatty acid diethanolamide, Triethanolamine fatty acid partial esters can be mentioned.

The anionic surfactants include carboxylate, sulfate, sulfonate and phosphate ester salts. Representative examples are fatty acid salt, alkylbenzene sulfonate, alkylnaphthalene sulfonate,
Alkyl sulfonate, α-olefin sulfonate, dialkyl sulfosuccinate, α-sulfonated fatty acid salt, N-methyl-N-oleyltaurine, petroleum sulfonate, alkyl sulfate, sulfated oil, polyoxyethylene alkyl Ether sulfate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate,
And naphthalene sulfonate formaldehyde condensate.

As the cationic surfactant, an amine salt,
Examples thereof include quaternary ammonium salts, pyridum salts and the like, and primary to tertiary fatty amine salts, quaternary ammonium salts (tetraalkylammonium salts, trialkylbenzylammonium salts, alkylpyridium salts, alkylimidazolium salts and the like) ). Examples of the amphoteric surfactant include carboxybetaine and sulfobetaine, such as N-trialkyl-N-carboxymethylammonium betaine and N-trialkyl-N-sulfoalkyleneammonium betaine.

By adding the above-mentioned fluorine-based surfactant, an antistatic effect can be exhibited. The addition amount of the fluorinated surfactant is preferably from 0.002 to 2% by mass, more preferably from 0.01 to 0.5% by mass, based on the cellulose ester. If the addition amount is less than 0.002% by mass, the effect of addition cannot be sufficiently exerted. If the addition amount exceeds 2% by mass, precipitation or insoluble matter may be generated.

In the present invention, a retardation increasing agent (optical property adjusting agent) can be added. The optical anisotropy can be controlled by adding a retardation increasing agent. As the retardation increasing agent, it is preferable to use an aromatic compound having at least two aromatic rings in order to adjust the retardation of the cellulose ester film. The aromatic compound is used in an amount of 0.0
Used in the range of 1 to 20 parts by mass. The aromatic compound is used in an amount of 0.05 to 100 parts by mass of cellulose acetate.
Preferably used in the range of 15 parts by mass, 0.1 to
More preferably, it is used in the range of 10 parts by mass. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

The aromatic hydrocarbon ring is a six-membered ring (ie,
Benzene ring). Aromatic heterocycles are generally unsaturated heterocycles. The aromatic hetero ring is preferably a 5-, 6-, or 7-membered ring, more preferably a 5- or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring include a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, an isoxazole ring, a thiazole ring, an isothiazole ring, an imidazole ring, a pyrazole ring, a furazane ring, a triazole ring, a pyran ring, and a pyridine ring. , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring.

In the present invention, a coloring agent can be added. Addition of a coloring agent can prevent light piping when used for a photosensitive material support or the like. The amount of the colorant to be added is preferably 10 to 1000 ppm by mass relative to the cellulose ester, and 50 to
500 ppm is more preferred.

The cellulose ester solution of the present invention contains a heat stabilizer such as a salt of an alkaline earth metal such as ruthenium and magnesium, an antistatic agent, a flame retardant, a lubricant,
An oil agent or the like can be appropriately added as needed.

The optical properties of the film produced by the solution casting method of the present invention will be described. First, the in-plane retardation (Re) of the film is described by using an ellipsometer (Ellipsometer AEP-100: manufactured by Shimadzu Corporation) in a longitudinal and transverse direction at a wavelength of 632.8 nm. Is multiplied by the film thickness of the film, and is obtained by the following equation. Re = (nx−ny) × d nx: refractive index in the horizontal direction ny: refractive index in the vertical direction

The smaller the retardation (Re), the lower the optical anisotropy in the in-plane direction.
It is used depending on the application within the range of m. Further, the retardation (Rth) in the thickness direction of the film is also important,
It is obtained by multiplying the birefringence in the thickness direction at a wavelength of 632.8 nm by the film thickness, and is obtained by the following equation. Rth = {(nx + ny) / 2−nz} × d nx: refractive index in the horizontal direction ny: refractive index in the vertical direction nz: refractive index in the thickness direction

The smaller the refractive index in the thickness direction, the lower the optical anisotropy in the thickness direction. The preferable range is determined depending on the intended use. Generally, Rth of the cellulose ester film produced according to the present invention is 100 μm.
0 nm to 600 nm per m, furthermore 0 nm
Used at ~ 400 nm.

The film produced by the solution casting method of the present invention includes, for example, a polarizing plate protective film, an optical compensation sheet, AR,
Optical films such as support films for LR and AG films,
It can also be used as a support film for photographic light-sensitive materials.

When a film produced by the solution casting method of the present invention is used as an optical compensation sheet, the film itself can be used as the optical compensation sheet. When using the film itself as the optical compensation sheet,
It is preferable to arrange the transmission axis of the polarizing plate and the slow axis of the optical compensation sheet so as to be substantially parallel or perpendicular.
The arrangement of such a polarizing plate and an optical compensation sheet is described in JP-A-10-48420. The liquid crystal display device has a liquid crystal cell holding liquid crystal between two electrode substrates, two polarizing plates disposed on both sides thereof, and at least one sheet between the liquid crystal cell and the polarizing plate. It has a configuration in which an optical compensation sheet is arranged.

The liquid crystal layer of the liquid crystal cell is usually formed by enclosing a liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on a substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer or an undercoat layer (used for bonding the transparent electrode layer). These layers are usually provided on a substrate. The substrate of the liquid crystal cell generally has a thickness of 50 μm to 2 mm.

The optical compensation sheet has birefringence and is used for the purpose of removing coloring of the display screen of the liquid crystal display device and improving the viewing angle characteristics. The cellulose ester film itself according to the present invention can be used as an optical compensation sheet. Further anti-reflection layer, anti-glare layer,
A function may be imparted as a λ / 4 layer or a biaxially stretched cellulose ester film. Further, in order to improve the viewing angle of the liquid crystal display device, a cellulose ester film of the present technology and a film exhibiting the opposite birefringence (positive / negative relationship) may be used as an optical compensation sheet.

An optical compensatory sheet in which an optically anisotropic layer containing a liquid crystal compound (particularly discotic liquid crystal molecules) is provided on a support has also been proposed (JP-A-3-93).
No. 25, No. 6-148429, No. 8-50206,
No. 9-26572). The film produced by the solution casting method of the present invention can also be used as a support for such an optical compensation sheet.

The polarizing element of the polarizing plate includes an iodine-based polarizing film, a dye-based polarizing film using a dichroic dye, and a polyene-based polarizing film. Each polarizing element is generally manufactured using a polyvinyl alcohol-based film. The protective film of the polarizing plate preferably has a thickness of 25 to 350 μm,
More preferably, it has a thickness of 40 to 200 μm. The liquid crystal display device may be provided with a surface treatment film. The functions of the surface treatment film include a hard coat, an anti-fog treatment, an anti-glare treatment and an anti-reflection treatment.

It is preferable that the optically anisotropic layer is a layer containing discotic liquid crystal molecules having negative uniaxiality and being obliquely aligned. The layer containing discotic liquid crystalline molecules may be in a hybrid orientation in which the angle between the disc surface and the support surface changes in the depth direction of the optically anisotropic layer, or the disc surface may be parallel to the support surface. Homeotropic orientation, homogeneous orientation in which the disk surface is perpendicular to the support surface,
Alternatively, the disk surface may have a twist orientation twisted in the depth direction of the optically anisotropic layer. In addition, an orientation in which these orientations are mixed (for example, hybrid orientation + twist orientation) may be used. Among them, hybrid orientation is preferred. The optical axis of each discotic liquid crystalline molecule exists in the direction normal to the disk surface. However, the optical axis does not exist in the entire layer in which the discotic liquid crystal molecules are hybrid-aligned.

The film produced by the solution casting method of the present invention can be used for liquid crystal cells of various display modes. TN (Twisted Nematic), I
PS (In-Plane Switching), FL
C (Ferroelectric Liquid Cry
stal), AFLC (Anti-ferroelec)
tric Liquid Crystal), OCB (O
optically Compensatory Ben
d), STN (Super Twisted Nema)
tic), VA (Vertically Align)
d) and HAN (Hybrid Aligned Nem)
atic). In addition, a display mode in which the above-mentioned display mode is orientation-divided has been proposed. The cellulose ester film is effective in a liquid crystal display device of any display mode.
Further, the present invention is effective in any of the transmissive, reflective, and transflective liquid crystal display devices.

The film produced by the solution casting method of the present invention may be used as a support for an optical compensation sheet of a TN type liquid crystal display device having a TN mode liquid crystal cell. TN mode liquid crystal cells and TN type liquid crystal display devices have been well known for a long time. Regarding the optical compensation sheet used for the TN type liquid crystal display device, see JP-A-3-9325,
148429, 8-50206, 9-265
No. 72 is described in each publication. Also, Mori
Other articles (Jpn. J. Appl. Phys. Vol.
36 (1997) p. 143 and Jpn. J. App
l. Phys. Vol. 36 (1997) p. 106
8). The TN type liquid crystal display device is described in JP-A-10-123478, WO98848320, and Japanese Patent No. 30222477.

The film produced by the solution casting method of the present invention may be used as a support for an optical compensation sheet of an STN type liquid crystal display having an STN mode liquid crystal cell. Generally, in an STN-type liquid crystal display device, rod-like liquid crystal molecules in a liquid crystal cell are twisted in the range of 90 to 360 degrees, and the refractive index anisotropy (Δn) of the rod-like liquid crystal molecules and the cell gap (d) (Δnd) is in the range of 300 to 1500 nm. The optical compensation sheet used for the STN liquid crystal display device is described in JP-A-2000-105316.

The film produced by the solution casting method of the present invention may be used as a support for an optical compensation sheet of a VA type liquid crystal display device having a VA mode liquid crystal cell. In the optical compensation sheet used for the VA-mode liquid crystal display device, it is preferable that the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensation sheet nor in the normal direction. The optical properties of the optical compensation sheet used for the VA liquid crystal display device are as follows:
It is determined by the optical properties of the optically anisotropic layer, the optical properties of the support, and the arrangement of the optically anisotropic layer and the support. V
When two optical compensatory sheets are used in the A-type liquid crystal display device, the in-plane retardation of the optical compensatory sheet is -5n.
It is preferable to set it in the range of m to 5 nm. Therefore, the absolute value of the in-plane retardation of each of the two optical compensation sheets is preferably set to 0 to 5. When one optical compensatory sheet is used for a VA liquid crystal display device, the in-plane retardation of the optical compensatory sheet is set to -10 nm to 1 nm.
It is preferable to set it within the range of 0 nm.

The film produced by the solution casting method of the present invention may be used as an OCB type liquid crystal display device having an OCB mode liquid crystal cell or a HAN having a HAN mode liquid crystal cell.
May be used as a support for an optical compensation sheet of a liquid crystal display device. In the optical compensatory sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, it is preferable that the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensatory sheet nor in the normal direction. The optical properties of the optical compensatory sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device also include the optical properties of the optically anisotropic layer, the optical properties of the support, and the optically anisotropic layer and the support. Is determined by the arrangement. The optical compensation sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device is described in JP-A-9-197397. Also, a paper by Mori et al. (Jpn. J. App.)
l. Phys. Vol. 38 (1999) p. 283
7).

The film produced by the solution casting method of the present invention was converted to ASM (Axially Symmetric Al).
It may be used as a support of an optical compensation sheet of an ASM type liquid crystal display device having a liquid crystal cell of an ignited microcell mode. The ASM mode liquid crystal cell is characterized in that the thickness of the cell is maintained by a resin spacer whose position can be adjusted. Other properties are similar to those of the TN mode liquid crystal cell. ASM mode liquid crystal cell and AS
Regarding the M-type liquid crystal display device, a paper by Kume et al. (Kume et al., SID 98 Digest)
1089 (1998)).

FIG. 1 shows a first embodiment of a production apparatus for carrying out the method for producing a cellulose ester film according to the present invention.
This will be described with reference to FIG. FIG. 1 is a schematic view of an apparatus for producing a cellulose ester film. In this figure, reference numeral 1 denotes a mixing tank for preparing a dope. The mixing tank 1 is connected to a stock tank 3 via a transfer pump 2. This stock tank 3 has a metering pump 4
The continuous filtration device 5 is connected to a casting die 7 by a liquid feed pipe 6.

A reverse feed pipe 8 as a reverse feed path is connected to the liquid feed pipe 6 at an intermediate branch point A, and the other end of the reverse feed pipe 8 is connected to the stock tank 3. Is provided with a reverse pump 9.

A casting band 10 is provided below the casting die 7.
In addition, a drying unit 11 composed of a group of guide rolls is disposed adjacent to the belt 10, and a winding roll 12 for winding the film is provided. And between the drying part 11 and the winding roll 12,
An on-line defect detection device 13 for detecting foreign matter mixed in the film is provided.

A method for forming two types of films having different thicknesses with the above-described apparatus for producing a cellulose ester film will be described.

First, the dope prepared in the mixing tank 1 is sent to the stock tank 3 by the transfer pump 2,
The dope is stored in the stock tank 3.

Then, the dope in the stock tank 3 is sent to the continuous filtration device 5 by the metering pump 4 to be filtered. At this time, the flow rate sent to the continuous filtration device 5 by the metering pump 4 is
The maximum flow rate (flow rate used when forming a thicker film) discharged from the casting die 7 is used. In this state, a part of the dope sent out from the continuous filtration device 5 is
The stock tank 3 is passed through the reverse feed pipe 8 by the reverse feed pump 9.
And the other dope is sent to the casting die 7. At this time, the flow rate of the dope reversely fed by the reverse feed pump 9 is set so as to be a flow rate for forming a thinner film sent to the casting die 7.

That is, assuming that the flow rate used when forming the thicker film is a and the flow rate used when forming the thinner film is a1, the flow is sent to the continuous filtration device 5 by the metering pump 4. The flow rate is set to a, and the flow rate to be reversely fed by the reverse feed pump 9 is set to a2 (a-a1). Then, at the branch point A, the dope sent out from the continuous filtration device 5 is sent to the casting die 7 by the flow rate a1 to form a thinner film.

Next, in order to switch to the formation of a thicker film, the reverse feed pump 9 is gradually squeezed. Then, since the flow rate of the metering pump 4 does not change, it flows into the casting die 7 by the reduced flow rate of the reverse pump 9, and when the reverse pump 9 is finally stopped, the metering pump is 4, the entire flow rate a flows, and a thicker film can be formed.

The dope cast on the casting band 10 is dried to a certain extent, peeled off from the casting band 10, further dried in the drying unit 11, and taken up by the take-up roll 12. At this time, the film defect is counted by the online defect detection device 13 immediately before the winding roll 12.

FIG. 2 is a schematic view of a second embodiment of the apparatus for producing a cellulose ester film. The second embodiment of the apparatus for manufacturing a cellulose ester film shown in FIG. 2 removes the reverse pump 9 in the first embodiment,
Instead, a casting die pump 14 is provided in the liquid sending pipe 6 between the branch point A and the casting die 7. Other configurations are the same as those of the first embodiment.

In this embodiment, by adjusting the flow rate of the casting die pump 14 to the flow rate discharged from the casting die 7, it is possible to change the reverse feeding flow rate and maintain the filtration flow rate constant. Is available.

FIG. 3 is a schematic diagram of a third embodiment of the apparatus for producing a cellulose ester film. In the third embodiment of the apparatus for producing a cellulose ester film shown in FIG. 3, a reverse pump 1 is connected to a reverse pipe 8 in the same manner as the first embodiment.
5, and a casting die pump 16 is provided in the liquid feed pipe 6 between the branch point A and the casting die 7 as in the second embodiment. Other configurations are the same as those of the first embodiment.

In this embodiment, the reverse feed pump 15
The filtration flow rate can be maintained constant by controlling the sum of the flow rates of the casting die pump 16 and the flow rate of the casting die 16 to be constant.

[0080]

EXAMPLES Example 1 Two types of cellulose triacetate films having different thicknesses were formed using the cellulose ester film manufacturing apparatus shown in FIG. The continuous filtration apparatus is a filter press, and the filter medium is No. 63 filter papers were used.

<Dope> Cellulose triacetate 16.0 parts by weight Triphenyl phosphate 1.3 parts by weight Biphenyl diphenyl phosphate 0.7 parts by weight Methylene chloride 76.0 parts by weight Methanol 6.0 parts by weight Total 100.0 parts by weight The above-mentioned raw materials were put into the mixing tank 1 and dissolved by stirring to obtain a dope.

<Film Production of 40 μm Type> First, the flow rate of the metering pump 4 is adjusted so that the thickness of the film becomes 80 μm. Thereafter, the reverse pump 9 is operated without changing the flow rate of the metering pump 4 to reduce the amount of dope sent to the casting die 7, and further, the flow rate of the reverse pump 9 is adjusted to adjust the flow rate of the wound film. The thickness was adjusted to 40 μm, and a 40 μm variety was formed as it was for 3 days.

<Film formation of 80 μm type> The flow rate of the reverse feed pump 9 is gradually reduced, and finally stopped. Thereby, the thickness of the wound film was set to 80 μm. In this state, an 80 μm product was continuously formed.

Comparative Example 1 The apparatus for producing a cellulose ester film shown in FIG. 1 was used, but the reverse feed pump 9 was not used.

<Dope> The same as in the first embodiment.

<Film formation of 40 μm type> The flow rate of the metering pump 4 is adjusted without operating the reverse feed pump 9 from the beginning so that the thickness of the wound film is adjusted to 40 μm. In this state, a 40 μm product was formed into a film for 3 days.

<Film Production of 80 μm Variety> The flow rate of the metering pump 4 was gradually increased, and the flow rate of the metering pump 4 was adjusted so that the thickness of the wound film finally became 80 μm. In this state, 80 μm varieties were continuously manufactured.

[Comparative Results] The number of defects per 1000 m of the completed film was detected by an on-line defect detector and compared. Table 1 shows the results.

[0089]

[Table 1]

The on-line defect detection apparatus is designed so that a laser beam passes through a film so as to scan in the width direction and receives light from the opposite side. If there is a defect in the film being transported, the laser beam is scattered or cut off, and the received light is disturbed. A defect is detected by detecting the disturbance.
As a result, foreign substances having a size of about 30 μm or more can be detected.

In Example 1, the foreign matter level settled in a short time after the change, but in Comparative Example 1, the foreign matter increased after the change and it took time to settle to the steady level.

Further, the number of defects during manufacture of a 40 μm product was smaller in Example 1 than in Comparative Example 1. This is because the reversely fed dope is again filtered through the filtration device, so that the filtration is strengthened as a whole.

Example 2 Two types of cellulose triacetate films having different thicknesses were formed using the cellulose ester film manufacturing apparatus shown in FIG. The continuous filtration apparatus is a filter press, and the filter medium is No. 63 filter papers were used.

<Dope> Cellulose triacetate 16.0 parts by weight Triphenyl phosphate 1.3 parts by weight Biphenyl diphenyl phosphate 0.7 parts by weight Methyl acetate 73.8 parts by weight Ethanol 8.2 parts by weight Total 100.0 parts by weight The above-mentioned raw material was put into the mixing tank 1, and after the solid content was swollen in the solvent, the mixture was cooled to -75 ° C and dissolved by stirring, and further heated to 120 ° C to completely dissolve to obtain a dope.

<Film formation of 40 μm type> Same as in the first embodiment.

<Film formation of 80 μm type> Same as in the first embodiment.

Comparative Example 2 <Dope> The same as in Example 2.

<Film formation of 40 μm type> Same as Comparative Example 1.

<Film formation of 80 μm type> Same as Comparative Example 1.

[Comparative Results] The number of defects per 1000 m of the completed film was detected by an on-line defect detector and compared. Table 2 shows the results.

[0101]

[Table 2]

In Example 2, the foreign matter level settled in a short time after the change, whereas in Comparative Example 2, the foreign matter increased after the change and it took time to settle to the steady level.

As in the case of the first embodiment, the number of defects during manufacture of a 40 μm product was smaller in the second embodiment than in the second comparative example.

Example 3 Film formation of two types of cellulose triacetate films having different thicknesses using an apparatus similar to the apparatus for manufacturing a cellulose ester film shown in FIG. 1 (a filtration apparatus is composed of two stages). Was done. As the filtration device, a filter paper having an absolute filtration accuracy of 0.01 mm (“# 63” manufactured by Toyo Roshi Kaisha, Ltd.) and an absolute filtration accuracy of 0.002
5 mm filter paper ("FH025", manufactured by Pall Corporation) was used.

<Preparation of Cellulose Triacetate Solution>
A cellulose triacetate powder (average size: 2 mm) was gradually added to a stainless steel dissolution tank having stirring blades while stirring well in the following solvent mixed solution, and charged. After the addition, the mixture was left at room temperature (25 ° C.) for 3 hours at 25 ° C. to swell the cellulose triacetate. In addition,
Solvents methyl acetate and cyclopentanone, acetone,
Methanol and ethanol all have a water content of 0.1.
Those having 2% by mass or less were used.

Cellulose triacetate 16 parts by mass (degree of substitution 2.83, viscosity-average degree of polymerization 320, water content 0.4% by mass, viscosity of 6% by mass in methylene chloride solution 305 mPa · s) Methyl acetate 53 parts by mass Cyclopentane 10 Parts by mass acetone 5 parts by mass methanol 5 parts by mass ethanol 5 parts by mass plasticizer A (dipentaerythritol hexaacetate) 3 parts by mass plasticizer B (triphenyl phosphate) 3 parts by mass fine particle powder (silica (particle size: 20 nm)) 0.1 parts by mass UV absorber a 0.1 parts by mass (2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5 -Triazine) UV absorber b 0.1 parts by mass (2 (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) 5-chlorobenzotriazole) UV absorber c 0.1 part by weight (2 (2'-hydroxy-3 ', 5'-di -tert- amyl phenyl) - 5-chloro-benzotriazole C ₁₂ H ₂₅ OCH ₂ CH ₂ OP (= O)-(OK) ₂ 0.05 mass part

The viscosity of this solution obtained by the cooling dissolution method described later was 160 Pa · S (45 ° C.).

<Cooling Dissolution of Cellulose Triacetate Solution> The above-described cellulose triacetate solution was fed by a screw extruder, and passed through a cooled portion at −70 ° C. for 3 minutes. The cooling was performed with a refrigerator.
The test was performed using a refrigerant at 0 ° C. (“Fluorinert” manufactured by 3M). Then, the solution obtained by cooling is heated to 120 ° C. by a heat exchanger equipped with a static mixer, kept for 3 minutes, cooled, transferred to a stainless steel container at 50 ° C., and transferred to a stainless steel container at 50 ° C. The mixture was stirred for 2 hours to remove bubbles. The cellulose triacetate solution prepared in this manner is passed through a filter paper having an absolute filtration accuracy of 0.01 mm (Toyo Roshi Kaisha, Ltd.)
, “# 63”), and filtered with an absolute filtration accuracy of 0.
0025mm filter paper (FH025, manufactured by Pall)
To obtain a dope.

<Film formation of 40 μm type> This is the same as in the first embodiment.

<Formation of 80 μm Product> This is the same as in the first embodiment. In the film formation of 40 μm and 80 μm, the temperature of the cellulose triacetate solution was 50 ° C., the temperature of the casting band was 10 ° C., the casting speed was 40 m / min, and the coating width was 100 cm. In addition, drying air was blown at 120 ° C. Two minutes after casting, the film was peeled off from the casting band, and then at 110 ° C. for 10 minutes, and further at 150 ° C.
After drying for a minute, a cellulose triacetate film was obtained.

[Comparative Example 3] As in Comparative Example 1, the flow rate of the metering pump was adjusted without operating the liquid feed pump. Other conditions are the same as those of the third embodiment.

[Evaluation of Number of Defects] Defects (foreign matter) per 1000 m of completed film in the same manner as in Example 1.
The number was detected.

In Example 3, the number of defects was all 18 pieces / 1000 m or less up to 36 hours after the type change, whereas in Comparative Example 3, after the type change, the maximum number of foreign particles was 180 pieces / 1000 m. It has reached 1000m. In addition, in Example 3, the increase in foreign matters was small and the level immediately fell to a steady level, but in Comparative Example 3, it took time to reduce the number of foreign matters.

<Preparation of Polarizing Plate a> A polarizing element was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the above cellulose triacetate film (thickness: 40 μm) was formed using a polyvinyl alcohol-based adhesive.
It was attached to both sides such that its slow axis was parallel to the transmission axis of the polarizing element.

<Evaluation of Polarization> The polarizing plate a was heated at 80 ° C. and 90 °
Exposure was performed for 500 hours in an atmosphere of RH, and the degree of polarization was measured. The degree of polarization was 99.6% or more, and sufficient durability was recognized. The degree of polarization was determined by determining the parallel transmittance (Yp) and the orthogonal transmittance (Yc) in the visible region using a spectrophotometer, and determining the degree of polarization P based on the following equation.

[0116]

(Equation 1)

<Preparation of Polarizing Plate b> A polarizing element was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the above-mentioned cellulose triacetate film (thickness: 80 μm) was prepared using a polyvinyl alcohol-based adhesive.
Affixed to one side so that its slow axis is parallel to the transmission axis of the polarizing film, saponified the cellulose triacetate film, and affixed to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. Was. further,
An optical compensation sheet (Fuji Photo Film Co., Ltd., “WV film”) is placed on the cellulose triacetate film side.
A polarizing plate was attached by using an adhesive so that the slow axes were parallel to each other, and an optical compensation sheet was attached.

<Evaluation in Liquid Crystal Display> The polarizing plates a and b were mounted on a TFT (thin film transistor) type liquid crystal display. As a result, a good viewing angle and a good contrast could be obtained.

Example 4 An apparatus similar to the apparatus for producing a cellulose ester film shown in FIG. 1 (there are three dope feeding systems, a three-layer casting die, and a filtration die) The apparatus was configured in two stages) to form two types of cellulose triacetate films having different thicknesses. Absolute filtration accuracy is 0.
01mm filter paper (manufactured by Toyo Roshi Kaisha, Ltd., "# 63")
Filter paper with an absolute filtration accuracy of 0.0025 mm (manufactured by Pall Corporation,
“FH 025”).

<Preparation of Cellulose Triacetate Solution for Inner Layer> Into a stainless dissolution tank having stirring blades, cellulose triacetate powder (average size: 2 mm) was gradually added while stirring well into the following solvent mixed solution. . After the addition, the mixture was left at room temperature (25 ° C.) for 3 hours to swell the cellulose triacetate. The solvents methyl acetate and cyclopentanone, acetone, methanol and ethanol all have a water content of 0.2% by mass.
The following were used.

Cellulose triacetate 16 parts by mass (degree of substitution 2.83, viscosity average degree of polymerization 320, water content 0.4% by mass, viscosity of 6% by mass in methylene chloride solution 305 mPa · s) Methyl acetate 53 parts by mass Cyclopentane 10 Parts by mass acetone 5 parts by mass methanol 5 parts by mass ethanol 5 parts by mass plasticizer A (dipentaerythritol hexaacetate) 3 parts by mass plasticizer B (triphenyl phosphate) 3 parts by mass fine particle powder (silica (particle size: 20 nm)) 0.1 parts by mass UV absorber a 0.1 parts by mass (2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5 -Triazine) UV absorber b 0.1 parts by mass (2 (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) 5-chlorobenzotriazole) UV absorber c 0.1 part by weight (2 (2'-hydroxy-3 ', 5'-di -tert- amyl phenyl) - 5-chloro-benzotriazole C ₁₂ H ₂₅ OCH ₂ CH ₂ OP (= O)-(OK) ₂ 0.05 mass part

The viscosity of the solution obtained by the cooling dissolution method was 60 Pa · S (45 ° C.).

<Cooling and dissolving of cellulose triacetate solution for inner layer> The above-mentioned cellulose triacetate solution was fed by a screw extruder, and passed through a cooled portion at -70 ° C for 3 minutes. Cooling was performed using a refrigerant (-Fluorinert, manufactured by 3M) cooled at −80 ° C. by a refrigerator. Then, the temperature of the solution obtained by cooling is raised to 120 ° C. by a heat exchanger equipped with a static mixer, held for 3 minutes, and then cooled to 50 ° C. and transferred to a stainless steel container. The mixture was stirred for 2 hours to remove bubbles. This cellulose triacetate solution was filtered with a filter paper having an absolute filtration accuracy of 0.01 mm (# 6 manufactured by Toyo Roshi Kaisha, Ltd.).
3 "), and the absolute filtration accuracy is 0.0025m
Then, the mixture was filtered with a filter paper (Mf. Pf, "FH025").

<Preparation of Cellulose Triacetate Solution for Outer Layer> The same procedure was carried out except that the cellulose triacetate solution for the inner layer was changed to 19 parts by mass and the methyl acetate to 44 parts by mass.
The viscosity of this solution obtained by the cooling dissolution method was 25 Pa
-It was S (45 degreeC).

<Cooling and dissolving of cellulose triacetate solution for outer layer> The above-described cellulose triacetate solution was fed by a screw extruder, and passed through a cooled portion at -70 ° C for 3 minutes. Cooling was performed using a refrigerant (-Fluorinert, manufactured by 3M) cooled at −80 ° C. by a refrigerator. Then, the temperature of the solution obtained by cooling is raised to 120 ° C. by a heat exchanger equipped with a static mixer, held for 3 minutes, and then cooled to 50 ° C. and transferred to a stainless steel container. The mixture was stirred for 2 hours to remove bubbles. This cellulose triacetate solution was filtered with a filter paper having an absolute filtration accuracy of 0.01 mm (# 6 manufactured by Toyo Roshi Kaisha, Ltd.).
3 "), and the absolute filtration accuracy is 0.0025m
Then, the mixture was filtered with a filter paper (Mf. Pf, "FH025").

<Preparation of Cellulose Triacetate Film> The above-described cellulose triacetate solution was arranged using a three-layer co-casting die such that the cellulose triacetate solution for the inner layer was on the inside and the cellulose triacetate solution for the outer layer was on both sides. After being simultaneously discharged onto a casting support made of metal and subjected to multi-layer casting, the casting film is peeled off from the casting support, dried, and a three-layered cellulose triacetate film laminate (inner layer thickness: 80 μm) (Thickness of each surface layer: 2 μm).

The dope in the stock tank is a gear pump for primary pressure increase, and the primary pressure of the high precision gear pump is 0.8.
Feedback control was performed by an inverter motor so as to obtain Mpa. The high-precision gear pump had a volumetric efficiency of 99.2% and a discharge rate fluctuation rate of 0.5% or less. The discharge pressure was 1.5 MPa.

The die is equipped with a feed block adjusted for co-casting.
A film having a layer structure was formed. The flow rate was adjusted so that the dry film became 2 μm, 80 μm, and 2 μm, respectively.

The dope to be supplied to the outer layer is taken out of the stock tank, the additive and the solvent are mixed through a static mixer, and the feed block is adjusted to a predetermined flow rate using a primary pressure increasing gear pump and a high precision gear pump. Supplied.
Using a UV absorption analyzer, measure the concentration of the UV absorber in the pipe, adjust the flow rate of the UV additive based on the result,
The specified UV absorption performance was realized.

The die, feed block, and piping are all 5
It was kept at 0 ° C. The die is a coat hanger type die, provided with thickness adjustment bolts at a pitch of 20 mm, and equipped with an automatic thickness adjustment mechanism using heat bolts. This heat bolt can set a profile according to the liquid feed rate of the high-precision gear pump by a preset program, and also performs feedback control by an adjustment program based on the profile of the infrared thickness gauge installed in the film forming process. It is possible. Usually, the thickness difference between any two points 50 mm apart in the film excluding the casting edge portion 20 mm was within 1 μm, and the difference between the maximum and minimum values in the width direction was adjusted to 3 μm / m or less.

The average thickness accuracy of each layer was ± 2 for both outer layers.
%, The mainstream is controlled to ± 1% or less, and the total thickness is ±
It was adjusted to 1.5% or less.

A chamber for reducing the pressure was provided on the primary side of the die. The degree of decompression of the decompression chamber is such that a pressure difference of 1 to 1000 mPa can be applied before and after the casting bead, and can be adjusted according to the casting die bead. Desirable conditions are that the bead length is 5 to 40.
mm. Further, a mechanism capable of setting the temperature of the chamber higher than the condensation temperature of the gas around the casting part is provided.

[Comparative Example 4] As in Comparative Example 1, the flow rate of the metering pump was adjusted without operating the liquid feed pump. Other conditions are the same as in the fourth embodiment.

[Evaluation of Number of Defects] Defects (foreign matter) per 1000 m of completed film in the same manner as in Example 1.
The number was detected.

In Example 4, the number of defects was all 18 pieces / 1000 m or less up to 36 hours after the type change, whereas in Comparative Example 4, after the type change, the maximum number of foreign matters was 155/1000 m. It has reached 1000m. In Example 4, the increase in the amount of foreign matter was small, and the level immediately fell to a steady level. In Comparative Example 4, however, it took time to reduce the number of foreign matter.

The film peeled off from the casting support was dried while being conveyed by a tenter.
After drying at 130 ° C. for 5 minutes, the mixture was dried stepwise at 150 ° C. for 10 minutes and the solvent was evaporated to obtain a cellulose triacetate film.

<Preparation of Polarizing Plate c> A polarizing element was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the above cellulose triacetate film was coated with a polyvinyl alcohol-based adhesive. Pasted on both sides so as to be parallel to the transmission axis.

<Evaluation of Polarizing Property> The polarizing plate c was heated at 80 ° C. and 90 °
After exposure for 500 hours in an atmosphere of RH, the degree of polarization was measured by the method described above. The degree of polarization was 99.6% or more, and sufficient durability was recognized.

<Preparation of Polarizing Plate d> A polarizing element was prepared by adsorbing iodine on a stretched polyvinyl alcohol film, and the above cellulose triacetate film was treated with a polyvinyl alcohol-based adhesive. The film was attached to one side so as to be parallel to the transmission axis, the cellulose triacetate film was subjected to a saponification treatment, and attached to the opposite side of the polarizing element using a polyvinyl alcohol-based adhesive. Further, an optical compensation sheet ("WV film", manufactured by Fuji Photo Film Co., Ltd.) is attached to the cellulose triacetate film side using an adhesive so that the slow axes are parallel to each other, and the optical compensation sheet is attached. A combined polarizing plate was produced.

<Evaluation in Liquid Crystal Display> The polarizing plates c and d were mounted on a TFT (thin film transistor) type liquid crystal display. As a result, a good viewing angle and a good contrast could be obtained.

[0141]

According to the present invention, when the type of the cellulose ester film to be produced is changed, it is possible to suppress an increase in foreign substances, and to produce a cellulose ester film of high quality and small production loss. . In addition, since the dope sent back is passed through the filtering device again and the filtration is repeated, foreign substances in a steady state can be reduced during the backward feeding.

[Brief description of the drawings]

FIG. 1 is a schematic view of a first embodiment of a manufacturing apparatus for performing a method for manufacturing a cellulose ester film according to the present invention.

FIG. 2 is a schematic view of a second embodiment of a manufacturing apparatus for performing the method for manufacturing a cellulose ester film according to the present invention.

FIG. 3 is a schematic view of a third embodiment of a manufacturing apparatus for performing the method for manufacturing a cellulose ester film according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mixing tank 2 ... Transfer pump 3 ... Stock tank 4 ... Metering pump 5 ... Continuous filtration device 6 ... Liquid sending pipe 7 ... Casting die 8 ... Reverse feeding pipe 9 ... Reverse feeding pump 10 ... Casting band 11 ... Drying part 12 ... take-up roll 13 ... online defect detection device 14 ... casting die pump 15 ... reverse feed pump

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C08L 1/10 C08L 1/10 G02B 5/30 G02B 5/30 G02F 1/1335 510 G02F 1/1335 510 / / B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 F term (reference) 2H049 BA07 BA25 BA27 BB13 BB33 BB43 BB51 BB65 BC14 BC22 2H091 FA08X FA08Z FB02 FC01 GA16 LA12 4F071 AA09 AB18 AB21 AB24 AC10 AC14 AC15 AE04 AE05 AE10 AH19 BA02 BB02 BC01 4F205 AA01 AB07 AB10 AB11 AB14 AC05 AG01 AH73 AR14 GA07 GB02 GC07 GF24 GF41 GF47 4J002 AB021 CH022 DE138 DE148 DE238 DG048 DJ008 DJ018 DJ038 DJ048 EE037 EH0106 EEV0EVE 139 FD057 FD162 FD169 FD200 FD208 FD312 FD319 GP00

Claims (12)

[Claims] 1. A method for producing a cellulose ester film having a casting die and a continuous filtration device arranged in series upstream of the casting die, wherein the filtration is performed between the continuous filtration device and the casting die. By providing a reverse feed path for feeding a part of the dope back to the upstream side of the continuous filtration device and changing the reverse flow rate, the dope flow rate through the continuous filtration device is always kept constant, and A method for producing a cellulose ester film, comprising changing a discharge flow rate. 2. A flow rate of the dope passing through the continuous filtration apparatus is set to a value larger than a maximum value of a flow rate of the dope discharged from the casting die, and a part of the filtered dope is always supplied to the upstream side of the continuous filtration apparatus through the reverse feed path. The method for producing a cellulose ester film according to claim 1, wherein 3. The solvent of the dope comprises methyl acetate, ketone and alcohol, and the solvent ratio is 20 to 90% by mass of methyl acetate, 5 to 60% by mass of ketone and 5 to 30% by mass of alcohol. Item 3. The method for producing a cellulose ester film according to Item 1 or 2. 4. The method for producing a cellulose ester film according to claim 1, wherein the dope contains at least one plasticizer in an amount of 0.1 to 20% by mass based on the cellulose ester. 5. The method for producing a cellulose ester film according to claim 1, wherein the dope contains at least one ultraviolet absorber in an amount of 0.001 to 5% by mass based on the cellulose ester. 6. The solution casting method according to claim 1, wherein the dope contains at least one kind of fine particle powder in an amount of 0.001 to 5% by mass with respect to the cellulose ester. 7. The cellulose ester film according to claim 1, wherein the dope contains at least one release agent in an amount of 0.001 to 2% by mass based on the cellulose ester. Manufacturing method. 8. The dope contains at least one fluorine-based surfactant in an amount of 0.002 to cellulose ester.
1, 2, 3, 4, 5, 6.
Or a method for producing a cellulose ester film according to 7. 9. The number of foreign substances having a diameter of 30 μm or more is 100.
The method for producing a cellulose ester film according to Claim 1, 2, 3, 4, 5, 6, 7, or 8, which produces 20 or less films per 0 m. 10. The method of claim 1, 2, 3, 4, 5, 6, 7,
10. A polarizing plate protective film produced by the method for producing a cellulose ester film according to 8 or 9. 11. A polarizing plate comprising the polarizing plate protective film according to claim 10. 12. A liquid crystal display device using the polarizing plate according to claim 11.