JP2013067074A - Method for manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film which can cope with a requirement of a thin, broad and high-quality protective film for a liquid crystal polarizing plate and a high deposition speed, improve flatness of a film, suppress a dispersion in phase difference, and reduce unevenness in phase difference in a width direction of the film.SOLUTION: In the method for manufacturing the optical film by a solution casting production method, air supply and exhaust of a dried wind capable of vaporizing a part of a solvent contained in a web by spraying the web 10 on a support 1 with drying air and changing the velocity of the dried wind at the center and both ends in a width direction of the web are used. The exhaust velocity of the dried air spraying on both the ends in the web width direction is made smaller than the exhaust velocity of the dried air spraying on the center in the web width direction and the air supply velocity of the dried air spraying on both the ends in the web width direction is made larger than the air supply velocity of the dried air spraying on the center in the web width direction.

Description

 The present invention can also be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, an antireflection film used for a plasma display, and the like. The present invention relates to a method for producing an optical film.

  In general, the basic configuration of a liquid crystal display device is one in which polarizing plates are provided on both sides of a liquid crystal cell. Since the polarizing plate allows only light with a polarization plane in a certain direction to pass, it plays an important role in visualizing changes in the orientation of the liquid crystal due to the electric field in the liquid crystal display device. The performance of the liquid crystal display device depends on the performance of the polarizing plate. Is greatly affected.

 In recent years, demand for display quality of thin-film liquid crystal display devices has increased, and various liquid crystal display methods such as VA (vertical alignment mode), OCB, and IPS have been proposed. In a liquid crystal display device with a wide viewing angle, it is common to use a retardation correction film. The quality required for optical films has become stricter due to the larger screen and higher definition, and the uniformity of the film retardation value in the width direction and the longitudinal direction is required.

 In addition, the development of thinner, lighter, larger screens and higher definition liquid crystal display devices such as TVs and large monitors has progressed, and accordingly, protective films for liquid crystal polarizing plates have become increasingly thinner, wider, and higher quality. The demand for computerization is getting stronger. Further, as the cost of optical films is reduced, a technique for increasing the film forming speed is required.

 Optical films are generally prepared by preparing a dope (resin solution) in which a resin film raw material is dissolved in a solvent, and casting the dope from a casting die onto a rotationally driven metal endless belt or a rotationally driven metal drum (support). Then, a cast film (web) is formed on the support, the web is dried on the support, the web is peeled off from the support, the peeled web is stretched, dried, and wound up. Manufactured by the casting film forming method.

 Conventionally, in order to increase the production speed of the optical film, the web is positively dried on the support, for example, drying air (drying air) is directly blown onto the web on the support. Yes.

 In addition, in Patent Document 1 below, when a dope (cellulose ester solution) is cast on an endless belt (band), it is substantially windless for a period of 10 seconds to 90 seconds in the first half of drying before peeling. The manufacturing method of the cellulose-ester film which performs the process of drying is disclosed. Here, “drying before peeling” refers to drying from when the dope is applied on the endless belt to when it is peeled off as a film. In addition, the “first half” refers to a process before half of the total time required from dope application to stripping. “Substantially no wind” is defined as no wind speed of 0.5 m / s or more detected at a distance within 200 mm from the endless belt surface.

Japanese Patent No. 4330400

 However, when the drying air is blown directly onto the web on the support as in the conventional method described above, the surface property of the film is impaired by the drying air because the web contains a lot of solvent components. was there.

 Also, in recent high-resolution televisions, slight retardation variations in retardation films affect visibility. Conventionally, large ducts have been used when drying on a support in the solution casting film forming method. Because of this, there was a difference in air volume in the width direction of the web. Conventionally, there has been known a technique for making drying and shrinkage uniform by changing the temperature in the width direction of the web. There is a problem that the light transmittance is reduced because the speed difference occurs and the density in the minute region is changed due to the deviation of the orientation of the resin.

 Furthermore, according to the method for producing a cellulose ester film described in Patent Document 1, when casting a dope on an endless belt, a step of drying with substantially no air for a predetermined time in the first half of drying before peeling is performed. Therefore, the turbulent flow on the web due to the drying wind does not occur, but there is a problem that the drying speed becomes slow in order to obtain a substantially windless state.

 The object of the present invention is to solve the above-mentioned problems of the prior art, and to suppress variation in retardation in the width direction of the film, and to suppress minute retardation unevenness, and to achieve flatness of the film. In addition, the web can be quickly dried on the support, and the protective film for the liquid crystal polarizing plate can be made thinner, wider and higher in quality, and the film forming speed can be increased. An object of the present invention is to provide a method for manufacturing an optical film.

  As a result of intensive studies in view of the above points, the inventor of the present invention, in the production of an optical film by the solution casting film forming method, blows drying air (drying air) onto the web on the support to dry the web. The present inventors have found that by providing an air supply port, the direction of the drying air can be aligned and the flatness of the film can be improved, and the present invention has been completed.

  In order to achieve the above object, the invention of claim 1 prepares a dope (resin solution) in which a resin film raw material is dissolved in a solvent, casts the dope from a casting die onto a support, and supports it. Production of an optical film by a solution casting film forming method in which a web (also referred to as a casting film) is formed on a body, the web is dried on a support, the web is peeled off from the support, dried and wound up In the method, drying air is blown onto the web on the support to evaporate a part of the solvent contained in the web, and at this time, the wind speed of the drying air is changed at the center and both ends in the width direction of the web. It is characterized by using dry air supply and / or exhaust.

Here, the “end portion” in the “both ends” in the web width direction means a range of 10 to 30% from one end in the web width direction, and the central portion in the web width direction means the web width center. The invention according to claim 2 is the method for producing an optical film according to claim 1, wherein when the drying air is blown onto the web formed on the support, The exhaust air speed of the dry air blown to both ends in the web width direction is made smaller than the exhaust air speed of the dry air blown to the center portion in the width direction.

 Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: When spraying dry air on the web formed on the support body, it is the dry wind sprayed on the center part of a web width direction. Compared to the air supply air speed, the air supply air speed of the dry air blown to both ends in the width direction of the web is increased.

 Invention of Claim 4 is a manufacturing method of the optical film as described in any one of Claims 1-3, Comprising: When blowing dry air on the web formed on the support body, it is the width direction of a web. Compared to the exhaust air speed of the dry air blown to the center portion, the exhaust air speed of the dry air blown to both ends in the width direction of the web is reduced in the range of 2% to 40%.

 Invention of Claim 5 is a manufacturing method of the optical film as described in any one of Claims 1-4, Comprising: When blowing dry air on the web formed on the support body, it is the width direction of a web. Compared with the supply air speed of the dry air blown to the center, the supply air speed of the dry air blown to both ends in the width direction of the web is increased in the range of 2% to 40%.

 The invention according to claim 6 is the method for producing an optical film according to claim 1, wherein when the drying air is blown onto the web formed on the support, the wind speed of the drying air is higher on the exhaust side than on the supply side. 1 to 30% more.

 Invention of Claim 7 is a manufacturing method of the optical film as described in any one of Claims 1-6, Comprising: An in-plane retardation value (Ro) manufactures the optical film which is 60 nm or less. It is said.

Invention of Claim 8 is a manufacturing method of the optical film as described in any one of Claims 1-7, Comprising: Film thickness (X) is,
20μm ≦ X ≦ 50μm
It is characterized by manufacturing an optical film in the range of.

Invention of Claim 9 is a manufacturing method of the optical film as described in any one of Claims 1-8, Comprising: The conveyance speed (S) of the web on a support body is,
30 m / min ≦ S ≦ 150 m / min
It is characterized by being in the range of.

Invention of Claim 10 is a manufacturing method of the optical film as described in any one of Claims 1-8, Comprising: Product width (D) is,
1500mm ≦ D
It is characterized by manufacturing an optical film.

  According to the first aspect of the present invention, a dope (resin solution) in which a resin film raw material is dissolved in a solvent is prepared, and the dope is flowed from a casting die onto a rotationally driven metal endless belt or a rotationally driven metal drum (support). And forming a cast film (web) on the support, drying the web on the support, peeling the web from the support, stretching the peeled web, drying and winding up, In the method for producing an optical film by the solution casting film forming method, drying air (drying air) is blown onto the web on the support to evaporate a part of the solvent contained in the web, and in that case, the width direction of the web According to the invention of claim 1, in the width direction of the film, the air supply and / or exhaust of the dry air that can change the wind speed of the dry air at the center and both ends of the film is used. Suppressing phase difference variation In addition to being able to suppress minute phase difference unevenness, the flatness of the film can be improved, the web drying speed on the support is fast, and the film forming speed can be increased. There is an effect that can be.

 Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: When blowing dry air on the web formed on the support body, the exhaust wind speed of the dry wind sprayed on the center part of a web width direction Compared to the above, the exhaust air velocity of the dry air blown to both ends in the width direction of the web is made smaller. According to the invention of claim 2, the effect of reducing the wind leaking to both ends of the web Play.

 Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: When spraying dry air on the web formed on the support body, it is the dry wind sprayed on the center part of a web width direction. Compared to the air supply air speed, the air supply air speed of the dry air blown to both ends in the width direction of the web is increased. The effect is to reduce.

 Invention of Claim 4 is a manufacturing method of the optical film as described in any one of Claims 1-3, Comprising: When blowing dry air on the web formed on the support body, it is the width direction of a web. Compared to the exhaust air velocity of the dry air blown to the center portion, the exhaust air velocity of the dry air blown to both ends in the width direction of the web is reduced in the range of 2% or more and 40% or less. According to invention of claim | item 4, there exists an effect that the nonuniformity of the wind on a web does not generate | occur | produce.

 Invention of Claim 5 is a manufacturing method of the optical film as described in any one of Claims 1-4, Comprising: When blowing dry air on the web formed on the support body, it is the width direction of a web. Compared to the supply air velocity of the dry air blown to the center, the supply air velocity of the dry air blown to both ends in the width direction of the web is increased in the range of 2% to 40%. According to the invention of claim 5, there is an effect that the unevenness of the wind on the web does not occur.

 The invention according to claim 6 is the method for producing an optical film according to claim 1, wherein when the drying air is blown onto the web formed on the support, the wind speed of the drying air is higher on the exhaust side than on the supply side. According to the invention of claim 6, it is possible to suppress variations in retardation in the width direction of the film and to suppress minute retardation differences. In addition, the flatness of the film can be improved, the web can be quickly dried on the support, and the film forming speed can be increased.

 Invention of Claim 7 is a manufacturing method of the optical film as described in any one of Claims 1-6, Comprising: An in-plane retardation value (Ro) manufactures the optical film which is 60 nm or less. Therefore, according to the invention of claim 7, it is possible to suppress variations in retardation in the width direction of the film, and to suppress minute retardation differences, and to improve the flatness of the film. In addition, the speed of drying the web on the support is fast, and there is an effect that it is possible to meet the demand for higher quality of the protective film for a liquid crystal polarizing plate and the higher film forming speed.

Invention of Claim 8 is a manufacturing method of the optical film as described in any one of Claims 1-7, Comprising: Film thickness (X) is,
20μm ≦ X ≦ 50μm
According to the invention of claim 8, it is possible to suppress variations in retardation in the width direction of the film, and to prevent minute retardation unevenness. It can be suppressed, the flatness of the film can be improved, and the drying speed of the web on the support is fast, which makes it necessary to reduce the thickness of the protective film for liquid crystal polarizing plates and increase the film forming speed. Also has the effect of being able to respond.

Invention of Claim 9 is a manufacturing method of the optical film as described in any one of Claims 1-8, Comprising: The conveyance speed (S) of the web on a support body is,
30 m / min ≦ S ≦ 150 m / min
According to the invention of claim 9, it is possible to suppress variation in retardation in the width direction of the film and to suppress minute retardation unevenness. In addition, the flatness of the film can be improved, and the web can be quickly dried on the support, and the film forming speed can be increased.

Invention of Claim 10 is a manufacturing method of the optical film as described in any one of Claims 1-9, Comprising: Product width (D) is,
1500mm ≦ D
According to the invention of claim 10, it is possible to suppress variation in retardation in the width direction of the film, and to suppress minute retardation unevenness. It is possible to improve the flatness of the film, and the web drying speed is fast on the support, and it can respond to the demand for widening the protective film for liquid crystal polarizing plates and the high film forming speed. There is an effect that can be done.

It is a general | schematic flow sheet which shows an example of the apparatus which enforces the manufacturing method of the optical film of this invention.

 Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

 FIG. 1 shows an example of a solution casting film forming apparatus for producing an optical film by the method of the present invention.

 Referring to the figure, the method for producing an optical film according to the present invention prepares a dope (resin solution) in which a resin film raw material is dissolved in a solvent, and converts the dope from a casting die (2) to a rotationally driven metal endless belt Cast on the support (1) to form a cast film (web) (10) on the support (1), dry the web (10) on the support (1), (1) The web (10) is peeled off from above, the peeled web (10) is stretched, dried, and the optical film (F) is wound up.

 In the method of the present invention, drying air (drying air) is blown to the web on the support to evaporate a part of the solvent contained in the web. It is characterized by using dry air supply and / or exhaust, which can change the wind speed of the dry air in the section.

 Here, when the drying air is blown onto the web formed on the support, the exhaust air speed of the drying air blown to both ends in the web width direction is compared with the exhaust air speed of the drying air blown to the center portion in the width direction of the web. Is preferably reduced. At this time, in particular, the exhaust air speed of the dry air blown to both ends in the width direction of the web is smaller in the range of 2% or more and 40% or less than the exhaust air speed of the dry air blown to the center portion in the width direction of the web. It is preferable to do. More preferably, the exhaust air velocity of the dry air blown to both ends in the web width direction is made smaller in the range of 10% or more and 30% or less than the exhaust air velocity of the dry air blown to the center portion in the web width direction. It is preferable.

 Here, if the exhaust air velocity of the drying air blown to both ends in the width direction of the web, which is smaller than the exhaust air velocity of the drying air blown to the center portion in the width direction of the web, is less than 2%, it leaks to both ends of the web. Since wind is generated, it is not preferable. Further, when the exhaust air velocity of the dry air blown to both ends in the web width direction, which is smaller than the exhaust air velocity of the dry air blown on the center portion in the web width direction, exceeds 40%, the width direction on the web This is not preferable because of uneven wind.

 Alternatively, when the drying air is blown onto the web formed on the support, the supply air speed of the drying air blown to both ends in the width direction of the web is compared with the supply speed of the drying air blown to the center portion in the width direction of the web. It is preferable to make this larger. In this case, in particular, the air supply speed of the dry air blown to both ends in the web width direction is in the range of 2% or more and 40% or less, compared with the supply air speed of the dry air blown to the central part in the web width direction. It is preferable to make it larger. More preferably, the air supply speed of the dry air blown to both ends in the web width direction is in the range of 10% or more and 30% or less as compared with the supply air speed of the dry air blown to the center part in the web width direction. It is preferable to enlarge it.

 Here, if the supply air velocity of the dry air blown to both ends in the web width direction, which is larger than the supply air velocity of the dry air blown to the center portion in the web width direction, is less than 2%, both ends of the web This is not preferable because a wind leaking into the water is generated. Further, when the supply air speed of the dry air blown to both ends in the width direction of the web, which is larger than the supply air speed of the dry air blown to the center portion in the width direction of the web, exceeds 40%, the width on the web This is not preferable because of uneven wind in the hand direction.

 According to the method for producing an optical film of the present invention, it is possible to suppress variations in retardation in the width direction of the film and to suppress minute retardation unevenness and to improve the flatness of the film. In addition, the web drying speed is fast on the support, and it is possible to meet the demands for thinning, widening, and high quality of the protective film for the liquid crystal polarizing plate, and high film forming speed. .

 Moreover, in the manufacturing method of the optical film of this invention, when blowing dry air on the web formed on the support body, it is preferable to increase the wind speed of dry air in 30% or less of range. For example, it is preferable to increase by 1 to 30%.

 It is preferable to produce an optical film having an in-plane retardation value (Ro) of 60 nm or less by the method for producing an optical film of the present invention.

Moreover, the film thickness (X) is determined by the method for producing an optical film of the present invention.
20μm ≦ X ≦ 50μm
It is preferable to produce an optical film in the range.

In the method for producing an optical film of the present invention, the web conveyance speed (S) on the support is:
30 m / min ≦ S ≦ 150 m / min
It is preferable that it exists in the range.

  Here, when the conveyance speed of the web on the support is less than 30 m / min, sufficient drying can be performed without controlling the drying air in the width direction, and the width is changed in the width direction. This is not preferable because there is no difference. Further, if the web conveyance speed on the support exceeds 150 m / min, the variation in the wind speed caused by the movement of the belt is so great that the wind cannot be controlled in the width direction.

By the method for producing an optical film of the present invention, the product width (D) is
1500 mm ≦ D, preferably 2000 mm ≦ D ≦ 4000 mm
It is preferable to produce an optical film.

 Here, when the casting width of the web on the support is less than 1500 mm, it is possible to dry sufficiently even without controlling the drying air in the width direction, and when the width is changed in the width direction. Since a difference does not arise, it is not preferable.

  The method for producing an optical film according to the present invention is carried out by a solution casting method, which will be described in detail below.

  In the method for producing an optical film according to the present invention, various resins can be used as a film material.

  Examples of the resin preferably used in the method of the present invention include cellulose ester resins having a substitution degree of acyl groups of 1.8 to 2.80, such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate, and cellulose. Cellulose ether resins having a degree of alkyl group substitution of 2.0 to 2.80, such as methyl ether, cellulose ethyl ether, and cellulose propyl ether, cycloolefin resins, norbornene resins, polycarbonate resins, and polymers of alkylene dicarboxylic acids and diamines Polyamide resin, polymer of alkylene dicarboxylic acid and diol, polymer of alkylene diol and dicarboxylic acid, polymer of cyclohexane dicarboxylic acid and diol, cyclohexane diol and dicarboxylic acid Compounds, polyester resins such as polymers of aromatic dicarboxylic acids and diols, vinyl acetate resins such as polyvinyl acetate and vinyl acetate copolymers, polyvinyl acetal resins such as polyvinyl acetal and polyvinyl butyral, epoxy resins and ketones Examples thereof include polyurethane resins such as resins, linear polymers of alkylene diisocyanates and alkylene diols, and preferably contain at least one selected from these.

  Among these, cellulose ester resins such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate, cycloolefin resins, norbornene resins, and polycarbonate resins are particularly preferable. In addition, two or more compatible polymers may be blended and dope dissolution described later may be performed, but the present invention is not limited to these.

  Examples of the other resin preferably used in the present invention include a homopolymer or a copolymer having an ethylenically unsaturated monomer unit. More preferably, poly (methyl acrylate), poly (ethyl acrylate), poly (propyl acrylate), poly (cyclohexyl acrylate), copolymers of alkyl acrylate, poly (methyl methacrylate), poly (ethyl methacrylate), poly (cyclohexyl methacrylate), alkyl methacrylate (s). Examples include homopolymers or copolymers of acrylic acid or methacrylic acid esters such as ester copolymers. Furthermore, since acrylic acid or methacrylic acid esters are excellent in transparency and compatibility, homopolymers or copolymers having acrylic acid ester or methacrylic acid ester units, particularly homopolymers having acrylic acid or methyl methacrylate units. Polymers or copolymers are preferred. Specifically, polymethyl methacrylate is preferable. Preferred are alicyclic alkyl esters of acrylic acid or methacrylic acid such as polyacrylic acid or polymethacrylic acid cyclohexane, which have advantages such as high heat resistance, low hygroscopicity, and low birefringence. .

  Hereinafter, the present invention will be described by taking cellulose ester as an example.

  In the present invention, a cellulose ester solution containing a cellulose ester and an organic solvent is referred to as a dope, which is used for solution casting to form a cellulose ester film.

  A cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present invention are not impaired.

  As an example of cellulose triacetate, the substitution degree of acetyl groups is preferably 2.0 or more and 3.0 or less. By making the degree of substitution within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

  The cellulose used as a raw material for the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  In the present invention, the number average molecular weight of the cellulose ester is preferably in the range of 60000 to 300000, since the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable.

  In the present invention, various additives can be added to the cellulose ester.

  The solvent of the cellulose ester is not particularly limited as long as it is a solvent that can dissolve the cellulose ester, but even a solvent that cannot be dissolved alone can be used if it can be dissolved by mixing with other solvents. Can do. In general, a mixed solvent composed of a good solvent, methylene chloride and a poor solvent of cellulose ester, is used, and the mixed solvent preferably contains 4 to 30% by weight of the poor solvent.

  In addition, examples of good solvents that can be used include methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2- Trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2- Examples include propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like, such as methylene chloride. Of organic halogen compounds, dioxolane derivatives, methyl acetate, ethyl acetate, acetone and the like are preferred organic solvents (ie Mentioned as good solvent). The use of methyl acetate is particularly preferred because the resulting film has less curl.

  Examples of the poor solvent for cellulose ester include alcohols having 1 to 8 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, methyl ethyl ketone, methyl isobutyl ketone, and acetic acid. Examples thereof include ethyl, propyl acetate, monochlorobenzene, benzene, cyclohexane, tetrahydrofuran, methyl cellosolve, and ethylene glycol monomethyl ether. These poor solvents can be used alone or in combination of two or more.

  In the present invention, it is preferable to add a so-called plasticizer in order to improve dimensional stability under wet heat. It has not been known so far that a plasticizer has an effect of improving dimensional stability under wet heat. As the plasticizer, conventionally known plasticizers for cellulose esters can be preferably used. In particular, those having excellent compatibility are preferred, and for example, phosphate esters and carboxylic acid esters are preferred. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like. Examples of the carboxylic acid ester include phthalic acid ester and citric acid ester. Examples of the phthalic acid ester include dimethyl phthalate, diethyl phthalate, dioctyl phthalate and diethyl hexyl phthalate. Mention may be made of tributyl. In addition, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, and the like are also included. Alkylphthalylalkyl glycolates are also preferably used for this purpose. The alkyl in the alkylphthalylalkyl glycolate is an alkyl group having 1 to 8 carbon atoms. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl glycolate, Ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl Phthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl Collate, octyl phthalyl methyl glycolate, octyl phthalyl ethyl glycolate and the like can be mentioned, such as 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. A plasticizer having a large molecular weight is preferable because it can suppress volatilization during extrusion. Examples of these include aliphatic polyesters composed of glycol and dibasic acids such as polyethylene adipate, polybutylene adipate, polyethylene succinate and polybutylene succinate, and fats composed of oxycarboxylic acids such as polylactic acid and polyglycolic acid. Aliphatic polyesters composed of lactones such as aromatic polyesters, polycaprolactone, polypropiolactone and polyvalerolactone, and vinyl polymers such as polyvinylpyrrolidone. These plasticizers can be used alone or in combination.

  It is preferable to contain 1-30 weight% of content of the plasticizer mentioned above with respect to a cellulose ester. By containing the plasticizer in this range, the dimensional stability of the cellulose ester film under wet heat can be improved.

  Examples of ultraviolet absorbers that can be used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574, and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used. As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred.

  Specific examples of UV absorbers useful in the present invention include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) Benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy-3'- ert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5 -Chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight, based on the cellulose ester. If the amount used is too small, the UV absorption effect may be insufficient, and if it is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  In the present invention, the above-mentioned plasticizer and ultraviolet absorber may also have a role as an additive for reducing the thickness direction retardation (Rt).

  When the substitution degree of the acetyl group of the cellulose ester is low, the heat resistance may be lowered. In this case, it is effective to add an antioxidant.

  As the antioxidant, a hindered phenol compound is preferably used, and 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl- 4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-tert-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 -Di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl -2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, etc. Can be mentioned. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  In order to impart slipperiness to the cellulose derivative in the present invention, it is preferable to add fine particles such as a matting agent. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

  Examples of the organic compound fine particles include fine particles such as acrylic resin, silicone resin, fluorine compound resin, and urethane resin.

  The primary particle size of the fine particles is not particularly limited, but the average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1-1.0 micrometer.

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for each film, and the number of particles in 100 μm ² whose major axis length is in the range of 0.05 to 5 μm for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size after being added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film. And controlling the particle size formed by aggregation.

  When the average particle diameter of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or it may cause a failure in a wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 1.0% by weight to the cellulose ester. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth, and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present invention is an apparatus that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. Further, at that time, those having a maximum reaching speed of 100 m / sec or more and those having a heat transfer speed of 100 kcal / hr or more are preferable.

  Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, or a nanomizer manufactured by Nanomizer, and also a Manton Gorin type high-pressure dispersing device such as Izumi Food Machinery. A homogenizer etc. are mentioned.

  The method for producing a cellulose ester film according to the present invention comprises a dope (resin solution) containing a cellulose ester and an additive (retardation reducing additive) for reducing thickness direction retardation (Rt), a metal rotating drum or a metal rotating drum. A casting step of casting on an endless belt (support) to form a web, a stretching step of stretching the web peeled from the support by a tenter device, a drying step of drying the web after stretching, and a drying It has a winding-up process of winding up a film.

  The method for producing an optical film according to the present invention comprises a dope preparation step (dissolution step), a casting step, a drying step, and a winding step.

  In the method for producing an optical film according to the present invention, taking the case where the optical film is a cellulose ester film as an example, the dissolution of the cellulose ester is first performed by a stirring dissolution method, a heating dissolution method, an ultrasonic dissolution in a dissolution vessel. A method such as a method is usually used, and a method of heating under stirring at a temperature not lower than the boiling point of the solvent at a normal pressure and in a range where the solvent does not boil, and dissolving with stirring is not a lump that is called a gel or mamako. In order to prevent generation | occurrence | production of a melt, it is more preferable. Further, a cooling dissolution method described in JP-A-9-95538 or a method of dissolving under high pressure described in JP-A-11-21379 may be used.

  A method in which the cellulose ester is mixed with a poor solvent and wetted or swollen, and then mixed with a good solvent and dissolved is also preferably used. At this time, an apparatus for mixing or dissolving cellulose ester with a poor solvent and an apparatus for mixing and dissolving with a good solvent may be separately provided.

  The type of the pressure vessel used for dissolving the cellulose ester is not particularly limited as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. In addition, instruments such as a pressure gauge and a thermometer are appropriately disposed in the pressurized container. The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature after adding the solvent is higher than the boiling point of the solvent to be used. In the case of two or more mixed solvents, the heating temperature is higher than the boiling point of the lower boiling solvent and the solvent does not boil. Is preferred. If the heating temperature is too high, the required pressure increases and productivity decreases. The range of preferable heating temperature is 20-120 degreeC, 30-100 degreeC is more preferable, The range of 40-80 degreeC is further more preferable. The pressure is adjusted so that the solvent does not boil at the set temperature.

  In addition to cellulose ester and solvent, additives such as necessary plasticizers and UV absorbers can be mixed with the solvent in advance, dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester. It may be put into the dope.

  After dissolving the cellulose ester, it is taken out from the container while cooling, or it is taken out from the container with a pump or the like and cooled with a heat exchanger or the like, and the resulting polymer dope is used for film formation. May be cooled to room temperature.

  The particle size d of the cellulose ester as a raw material is such that particles having a size of 0.1 mm ≦ d ≦ 20 mm are constituted at a ratio of 60% by weight or more, so that good solubility can be obtained without generating an aggregate of cellulose ester. Desirable to get.

  The mixture of the raw material cellulose ester and the solvent is dissolved in a dissolving kettle having a stirrer, and at this time, the peripheral speed of the stirring blade is preferably at least 0.5 m / second or more and stirred and dissolved for 30 minutes or more.

  In the method of the present invention, the cellulose ester dope dissolved in the dissolution vessel is sent to a filter by a pump and filtered in the filter. This filtration can be performed by a normal method, but the method of filtering while heating under pressure at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil is the differential pressure before and after the filter medium (hereinafter referred to as the pressure difference). The increase in the pressure may be small, which is preferable.

  In the method of the present invention, the cellulose ester dope is filtered to remove foreign matters, particularly foreign matters that are mistakenly recognized as images in a liquid crystal image display device. It may be said that the quality of the protective film for polarizing plates is determined by this filtration.

  Filter media used for filtration preferably have a low absolute filtration accuracy. However, if the absolute filtration accuracy is too low, the filter media is likely to be clogged, and the filter media must be frequently replaced, resulting in increased productivity. There is a problem of lowering.

  For this reason, in the method of the present invention, the filter medium used for the cellulose ester dope preferably has an absolute filtration accuracy of 0.020 mm or less. As the filter paper, for example, No. of Azumi Filter Paper Co., Ltd., a commercially available product. 244, 277, etc. can be mentioned and used preferably.

  There are no particular restrictions on the material of the filter medium, and normal filter media can be used. However, plastic fiber filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel fibers are used to remove fibers. This is preferable.

  The preferable temperature range of dope filtration is 45-120 degreeC, 45-70 degreeC is more preferable, and it is further more preferable that it is the range of 45-55 degreeC.

  The filtration pressure is preferably 3500 kPa or less, more preferably 3000 kPa or less, and even more preferably 2500 kPa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area. The dope thus obtained is stored in a stock tank, defoamed and then used for casting.

  Thus, when the dope is prepared by previously mixing the domain forming material, the cellulose ester and the solvent in the dissolution vessel, it is usually unnecessary to add the domain forming material in-line. However, if necessary, all or part of the domain forming material can be mixed in-line.

  For example, an amorphous particle dispersion mixed or dispersed in a suitable solvent in a dissolution vessel is sent to a filter by a pump and filtered in the filter. The obtained dope is stored in the second stock tank and defoamed.

  Cellulose ester solution (or may be referred to as dope stock solution) transferred from the first stock tank through the conduit by the pump, and domain-forming material solution transferred from the second stock tank by the pump (the amorphous particle dispersion). Is merged with a merge pipe.

  A filter is arranged immediately before the junction tube, and for example, lump and large foreign matter generated from the path due to exchange of filter media etc. can be removed from the amorphous particle dispersion or dope stock solution being fed. . Here, a metal filter having solvent resistance is preferably used.

  The filter medium is preferably a metal, particularly stainless steel, from the viewpoint of durability. From the viewpoint of clogging, it is preferable to have a porosity of 60 to 80%. Most preferably, the filtration is performed with a metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80%, so that coarse foreign substances can be reliably removed over a long period of time. preferable. Examples of the metal filter medium having an absolute filtration accuracy of 30 to 60 μm and a porosity of 60 to 80% include NF-10, NF-12, and NF-13 of Finepore NF series manufactured by Nippon Seisen Co., Ltd. be able to.

  The two liquids that have joined together as described above migrate in a layered manner in the conduit and are difficult to mix as they are. Therefore, the two liquids are merged and then transferred to the next step while being sufficiently mixed by a mixer (19) such as an in-line mixer.

  As an in-line mixer that can be used in the present invention, for example, a static mixer SWJ (Toray static type in-pipe mixer, Hi-Mixer, manufactured by Toray Engineering) is preferable.

  FIG. 1 shows an example of an apparatus for producing an optical film by the solution casting method of the present invention.

  Referring to the figure, an apparatus for producing an optical film by the method of the present invention is based on a solution casting film forming method.

  First, for example, a dope which is a raw material solution of a cellulose ester film is cast on a support (1) by a dope casting die (dope casting means) (2) and a support (1) by a dope casting die (2). ) A peeling roll (peeling means) (3) for peeling the web (10) formed thereon from the support (1), and a web (10) peeled from the support (1) by the peeling roll (3). ) Is dried while being conveyed, and a winder (winding means) (15) for winding the dried film (F) is provided.

    In FIG. 1, first, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and the above plasticizer and ultraviolet absorber are added thereto to prepare a resin solution (dope). The dope is fed to the casting die (2) through, for example, a pressurized metering gear pump, and the dope is cast from the casting die (2) onto the stainless steel endless belt support (1) at the casting position. The belt temperature during film formation can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, and more preferably in the range of 5 ° C. to the boiling point of the solvent −5 ° C. At this time, it is necessary to control the ambient atmosphere temperature to be higher than the dew point.

    In order to cast the dope by the casting die (2), there is a doctor blade method in which the film thickness of the cast dope film (web) is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. However, a pressure die that can adjust the slit shape of the die portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

    When casting the dope onto the support (1), the temperature is controlled below the boiling point of the solvent used for dissolving the raw resin, and below the boiling point of the solvent having the lowest boiling point in the mixed solvent. The temperature can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, but is more preferably cast on a support (1) at 5 to 30 ° C.

    In the illustrated film forming apparatus comprising a rotationally driven endless belt as the support (1), the belt support (1) is disposed between a pair of drums and the upper transition portion of the endless belt support (1). And a plurality of rolls each supporting the lower transition portion from the back side. In addition, one or both of the drums wound at both ends of the rotationally driven endless belt support (1) are provided with a drive device that applies tension to the belt support (1), whereby the belt support (1). Is used under tension and tension.

    Then, the dope adjusted to have a dope viscosity of 1 to 200 poise is cast from the casting die (2) onto the support (1) so as to have a substantially uniform film thickness. When the amount of residual solvent in the casting film is 200% or more by weight of the solid content, the casting film temperature is below the boiling point of the solvent, and when the amount of residual solvent is 100 to 200% of the weight of the solid content, The casting film (web) is dried by drying air so that the boiling point is + 10 ° C. or less and the residual solvent amount is 100% or less to peeling until the solvent boiling point is + 20 ° C. or less.

The product width (D) of the optical film manufactured by the optical film manufacturing method of the present invention is:
1500 mm ≦ D, preferably 2000 mm ≦ D ≦ 4000 mm
It is preferable that

  The dope is cast from a casting die (2) onto a stainless steel endless belt support (1) having a mirror-finished surface to obtain a dope film (web) (10).

In the method for producing an optical film of the present invention, the conveyance speed (S) of the web (10) on the support (1) is:
30 m / min ≦ S ≦ 150 m / min
It is preferable that it exists in the range.

 And in the manufacturing method of the optical film of the present invention, a part of the solvent contained in the web (10) is evaporated by blowing drying air (dry air) onto the web (10) on the support (1), At this time, the supply and / or exhaust of the drying air that can change the wind speed of the drying air at the center and both ends in the width direction of the web (10) is used.

 Here, when the drying air is blown onto the web (10) formed on the support (1), the drying is blown to both ends in the width direction of the web as compared with the exhaust air velocity of the drying air blown to the center portion in the width direction of the web. It is preferable to reduce the wind exhaust velocity. At this time, in particular, the exhaust air speed of the dry air blown to both ends in the width direction of the web is smaller in the range of 2% or more and 40% or less than the exhaust air speed of the dry air blown to the center portion in the width direction of the web. It is preferable to do.

 As a result, the problem that the drying speed in the web width direction is different due to the lower solvent concentration at the edge in the web width direction and the quality is not uniform in the web width direction is improved. There is an advantage that the drying in the hand direction becomes uniform and the film quality becomes uniform.

 Alternatively, when dry air is blown onto the web (10) formed on the support (1), it is blown to both ends in the web width direction compared to the supply air velocity of the dry wind blown to the center portion in the web width direction. It is preferable to increase the air supply speed of the dry air. In this case, in particular, the air supply speed of the dry air blown to both ends in the web width direction is in the range of 2% or more and 40% or less, compared with the supply air speed of the dry air blown to the central part in the web width direction. It is preferable to make it larger.

 As a result, the problem that the drying speed in the web width direction is different due to the lower solvent concentration at the edge in the web width direction and the quality is not uniform in the web width direction is improved. There is an advantage that the drying in the hand direction becomes uniform and the film quality becomes uniform.

 According to the method for producing an optical film of the present invention, it is possible to suppress variations in retardation in the width direction of the film and to suppress minute retardation unevenness and to improve the flatness of the film. In addition, the web (10) can be quickly dried on the support (1), and the protective film for the liquid crystal polarizing plate is required to be thinned, widened and improved in quality, and the film forming speed is increased. Can also respond.

 Moreover, in the manufacturing method of the optical film of this invention, when blowing dry air on the web (10) formed on the support body (1), the direction of exhaust gas is 30% or less rather than the supply amount of dry air. It is preferable to increase it.

  Thus, the web (10) dried on the support is peeled off by the peeling roll (3) when the web (10) moves approximately 3/4 rounds by the rotation of the endless belt support (1).

    Since the web (10) is dried and solidified on the support (1) until the web (10) has a peelable film strength, generally the residual solvent amount in the web (10) is 150% by weight. It is preferable to dry to below, and 80 to 120 weight% is more preferable.

    Moreover, generally the temperature of the web (10) when peeling a web (10) from a support body (1) has preferable 0-30 degreeC. Further, immediately after the web (10) is peeled off from the support (1), the temperature is once lowered rapidly by the solvent catalyst from the contact surface side of the support (1), and volatile components such as water vapor and solvent vapor in the atmosphere are removed. Since it is easy to condense, 5-30 degreeC is more preferable as the web temperature at the time of peeling.

    Here, the residual solvent amount can be expressed by the following equation.

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

    Peeling is usually performed at a peeling tension of 20 to 25 kg / m when peeling the support (1) and the web (10), but peeling is preferably performed at a minimum tension of 17 kg / m. More preferably, peeling is performed with a minimum tension of -14 kg / m.

In the present invention,
The web (10) is then introduced into the tenter dryer (4). Therefore, the side edges of the web (10) are gripped with a clip and stretched, and the web (10) is dried. In the tenter drying device (4), the web (10) is blown from the front portion of the bottom of the tenter drying device (4) and dried by warm air discharged from the rear portion of the ceiling of the tenter drying device (4). Is done.

    In the tenter drying apparatus (4), drying is performed using warm air, but the means for drying the film is not particularly limited, and is performed by hot air as described above, or also by infrared rays, heating rolls, microwaves, or the like. It is preferable to carry out with hot air in terms of simplicity. The drying temperature is preferably in the range of 40 ° C. to 150 ° C. and divided into 3 to 5 steps, and the temperature is preferably increased step by step. In order to improve the dimensional stability, it is preferable to carry out in the range of 80 ° C. to 140 ° C. preferable.

    Next, the cellulose-ester film (web) (10) after extending | stretching is introduce | transduced into a roll conveyance drying apparatus (5) through intermediate rolls (6) (8). In the roll transport drying device (5), the web (10) is meandered by 50 to 1000 transport rolls (7), while the web (10) is, for example, in front of the bottom of the roll transport drying device (5). It is blown from the near part and dried by the warm air discharged from the rear part of the ceiling of the roll transport drying device (5).

    Both ends in the width direction of the film dried by the roll conveyance drying device (5) are slit into a product width by the slitter (12) and cut off, and then wound by the winder (15).

    The winder (15) related to the production of the cellulose ester film may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. It can be wound up by the method.

    These steps from casting to post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. In the case of an air atmosphere, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the evaporation solvent.

    The film thickness of the optical film varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 30 to 200 μm, and the recent thin tendency is preferably 40 to 120 μm, particularly 40 to A range of 100 μm is preferred.

Moreover, the optical film manufactured by the manufacturing method of the optical film of the present invention has a film thickness (X),
20μm ≦ X ≦ 50μm
It is preferable that it exists in the range.

  The average film thickness of the film can be adjusted by controlling the extrusion flow rate, the gap of the casting port of the casting die (2), the speed of the endless belt support (1), and the like so as to obtain a desired thickness.

 The optical film produced by the method for producing an optical film of the present invention preferably has an in-plane retardation value (Ro) of 60 nm or less.

  Here, the retardation value of the film is measured using a three-dimensional refractive index at a wavelength of 590 nm using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), and the obtained refractive indexes Nx, Ny, It can be calculated from Nz.

In-plane retardation (Ro) = (Nx−Ny) × d
Thickness direction retardation (Rt) = [(Nx + Ny) / 2−Nz] × d
In the formula, Nx, Ny, and Nz represent the refractive indexes in the principal axes x, y, and z directions of the refractive index ellipsoid, respectively, Nx, Ny represent the refractive index in the film in-plane direction, and Nz represents the film thickness direction. Refractive index. Further, Nx ≧ Ny, and d represents the thickness (nm) of the film.

  The cellulose ester film produced by the method of the present invention is preferably used for a liquid crystal display member, specifically, a protective film for a polarizing plate. The cellulose ester film of the present invention is preferably used in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability.

    By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

    The polarizing plate may be prepared by laminating the cellulose ester film of the present invention as a retardation film, and the cellulose ester film of the present invention serves as both a retardation film and a protective film, and is a direct polarizing film. And may be produced by pasting together. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film which has been stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film of the present invention. A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

    The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. Is preferred.

    By the way, a polarizing plate can be produced by a general method. For example, there is a method in which a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is immersed and stretched in an iodine solution, and bonded to both surfaces using a completely saponified polyvinyl alcohol aqueous solution. The alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness.

    For cellulose ester film, hard coat layer, antiglare layer, antireflection layer, antifouling layer, antistatic layer, conductive layer, optically anisotropic layer, liquid crystal layer, alignment layer, adhesive layer, adhesive layer, subbing layer, etc. Various functional layers can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

    Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and the liquid crystal display device of this invention is obtained using this.

    By using a protective film for a polarizing plate made of a cellulose ester film, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

    The cellulose ester film produced by the method of the present invention can also be used as a base material for an antireflection film or an optical compensation film.

    EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1
(Dope composition)
Using cellulose acetate propionate having a total acyl group substitution degree of 2.50, an acetyl substitution degree of 1.59, and a propionyl substitution degree (substitution degree of acyl groups having 3 or more carbon atoms) of 0.91 The dope was adjusted.

(Dope formulation)
Cellulose acetate propionate 100 parts by weight plasticizer (triphenyl phosphate) 7 parts by weight plasticizer (ethylphthalylethyl glycolate) 2 parts by weight Solvent: 300 parts by weight of methylene chloride: 60 parts by weight of ethanol The above cellulose acetate propio The formulation of the nate was mixed and completely dissolved with stirring, and then filtered using a filter paper having a filtration accuracy of 0.005 mm. By allowing this to stand overnight, the bubbles in the dope were degassed.

 Next, using the solution casting film-forming apparatus shown in FIG. 1, a dope having a temperature of 30 ° C. is uniformly flowed from a casting die (2) onto a stainless steel endless belt (1) having a width of 2400 mm with a width of 2200 mm. Extended. The traveling speed of the endless belt (1) was 100 m / min.

 In Example 1, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction is 12 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 16.7%. Further, the supply air speed of the dry air blown to the central portion in the web width direction was set to 10 m / sec, and the supply air speed of the dry air blown to both ends in the web width direction was set to 10 m / sec.

  On the stainless steel endless belt support (1), the solvent was evaporated until the residual solvent amount reached a predetermined amount, and the web (film) (10) was peeled from the stainless steel endless belt support (1). Subsequently, the both ends of the width direction of the web (10) were hold | gripped with the tenter (4), and it extended | stretched.

Then, after drying treatment with a roll conveyance drying device (5) in which 500 mirror surface conveyance rolls (surface length 2200 mm, diameter 110 mm) having a surface roughness (Rmax) of 0.8 μm are installed, both ends of the film are slitted (12). The film (F) was removed by a winder (15) to obtain a cellulose ester film having a product width of 2100 mm and a film thickness of 40 μm.

<Evaluation of optical properties of film>
Next, for the cellulose ester film obtained in Example 1, in order to evaluate the optical properties of the film, the retardation (Rt) and in-plane retardation (Ro) in the thickness direction of the cellulose ester film were determined by automatic birefringence. Using a measuring instrument (KOBRA-WIS / RT, manufactured by Oji Scientific Instruments), measurement was performed at a wavelength of 590 nm under an environment of a temperature of 23 ° C. and a humidity of 55% RH.

 Here, 20 thickness direction retardation values (Rt) of the cellulose ester film obtained in Example 1 were measured, the average value (Rtav) was calculated, and the thickness direction retardation value (Rtv) relative to the average value was calculated. ) Was calculated and evaluated by the following method.

 That is, when the variation of the measured value of retardation Rt in the thickness direction of the cellulose ester film obtained in Example 1 is W1, the width of the region satisfying the following formula is W1, and the width of the film is W0, the following formula is used. RtX (%) was calculated by evaluating the ratio of the region width in the range in which the variation in the measured Rt measurement value in the thickness direction is within a preferable range.

W1: | Rt−Rtav | /Rtav≦0.07
RtX (%) = W1 / W0 × 100
The width (W0) of the cellulose ester film obtained in Example 1 was 2100 mm, and the region width (W1) in which the variation in retardation Rt measurement value in the thickness direction was in a preferable range was 1900 mm.

 Accordingly, the ratio of the region width RtX (%) in which the variation in the retardation Rt measurement value in the thickness direction of the cellulose ester film is in a preferable range was 90%.

 Table 1 below shows the evaluation result of RtX (%) thus obtained, and the exhaust air velocity (m / sec) of the dry air blown to the center in the width direction of the web on the support (1) in Example 1. The exhaust air velocity (m / sec) of the drying air blown to both ends of the web width direction, the supply air velocity (m / sec) of the drying air blown to the center portion of the web width direction, and both ends of the web width direction The supply air velocity (m / sec) of the dry air to be blown is shown.

 In addition, the in-plane retardation (Ro) value of the cellulose ester film obtained in Example 1 was 60 nm or less.

Examples 2-14
A cellulose ester film is produced in the same manner as in Example 1 above, but in Examples 2 to 14, drying air (drying air) is applied to the web (10) on the support (1) by the method of the present invention. To evaporate a part of the solvent contained in the web (10), and at that time, the dry air supply can change the wind speed of the web (10) at the center and both ends in the width direction. And / or exhaust was used.

 First, in Examples 2 to 5, when the drying air is blown onto the web (10) formed on the support (1), the web width direction is larger than the exhaust air speed of the drying air blown to the center in the web width direction. The exhaust air velocity of the dry air blown to both ends of the web is reduced as follows, the supply air velocity of the dry air blown to the central portion of the web width direction is 10 m / sec, and the both ends of the web width direction are The supply air speed of the dry air to be blown was set to 10 m / sec, and all were the same.

 In Example 2, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction is 10.1 m / sec, the web width direction. The exhaust air speed of the dry air blown to both ends of the web was set to 10 m / sec, and the exhaust air speed of the dry air blown to both ends in the width direction of the web was reduced by 1%.

 In Example 3, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction is 10.2 m / sec, the web width direction. The exhaust air speed of the dry air blown to both ends of the web was set to 10 m / sec, and the exhaust air speed of the dry air blown to both ends in the width direction of the web was reduced by 2%.

 In Example 4, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central part in the web width direction is 14 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 28.6%.

 In Example 5, when blowing dry air to the web (10) formed on the support (1), the exhaust air velocity of the dry air blown to the central part in the web width direction is 15 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 33.3%.

 Next, in Examples 6 to 10, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air speed of the drying air blown to the central portion in the width direction of the web is 10 m / sec. The exhaust air velocity of the dry air blown to both ends in the width direction was set to 10 m / sec, and all were the same. On the other hand, as compared with the supply air speed of the dry air blown to the central part in the web width direction, the supply air speed of the dry air blown to both ends in the web width direction was increased as follows.

 In Example 6, when blowing dry air to the web (10) formed on the support (1), the supply air speed of the dry air blown to the central part in the web width direction was 9 m / sec, and the web width direction was The supply air velocity of the dry air blown to both ends is set to 10 m / sec, and the supply air velocity of the dry air blown to both ends in the width direction of the web is compared with the supply air velocity of the dry air blown to the center portion in the width direction of the web. Was increased by 11.1%.

 In Example 7, the supply air speed of the dry air blown to the center part in the web width direction was 9.9 m / sec, the supply air speed of the dry air blown to both ends in the web width direction was 10 m / sec, and the web width Compared to the supply air speed of the dry air blown to the center in the hand direction, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 1%.

 In Example 8, the supply air speed of the dry air blown to the central part in the web width direction was 9.8 m / sec, the supply air speed of the dry air blown to both ends in the web width direction was 10 m / sec, and the web width Compared to the supply air speed of the dry air blown to the center in the hand direction, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 2%.

 In Example 9, the supply air speed of the drying air blown to the center in the width direction of the web was 6.4 m / sec, the supply air speed of the drying air blown to both ends in the width direction of the web was 10 m / sec, Compared to the supply air speed of the dry air blown to the center in the hand direction, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 56.2%.

 In Example 10, the supply air speed of the dry air blown to the center in the web width direction is 6.5 m / sec, the supply air speed of the dry air blown to both ends in the web width direction is 10 m / sec, Compared to the supply air velocity of the dry air blown to the center in the hand direction, the supply air velocity of the dry air blown to both ends in the width direction of the web was increased by 53.8%.

 In Example 11, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction and the both ends in the web width direction are blown. The exhaust air speed of the dry air was set to zero. Then, the air supply speed of the dry air blown to the central part in the web width direction is 9 m / sec, and the air supply speed of the dry air blown to both ends in the web width direction is 10 m / sec. Compared to the supply air speed of the dry air blown to the web, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 11.1%.

 In Examples 12 to 14, when the drying air is blown onto the web (10) formed on the support (1), both ends in the web width direction are compared with the exhaust air velocity of the drying air blown to the center in the web width direction. Compared with the supply air speed of the drying air blown to the center part in the width direction of the web, the exhaust air speed of the drying air blown to the web part is made smaller. Increased.

 In Example 12, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the center in the web width direction is 12 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 16.7%. Further, the air supply speed of the dry air blown to the central part in the web width direction is 10 m / sec, and the air supply speed of the dry air blown to both ends in the web width direction is 12 m / sec. Compared to the supply air speed of the dry air blown to the web, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 20.0%.

 In Example 13, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction is 12 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 16.7%. Moreover, the supply air speed of the dry air blown to the center part of the web width direction is 6.5 m / sec, and the supply air speed of the dry air blown to both ends of the web width direction is 10 m / sec. Compared to the supply air velocity of the dry air blown to the center, the supply air velocity of the dry air blown to both ends in the width direction of the web was increased by 53.8%.

 In Example 14, when the drying air is blown onto the web (10) formed on the support (1), the exhaust air velocity of the drying air blown to the central portion in the web width direction is 12 m / sec, both ends in the web width direction. The exhaust wind speed of the dry wind sprayed on the part was 10 m / sec, and the exhaust wind speed of the dry wind sprayed on both ends in the width direction of the web was reduced by 16.7%. Further, the air supply speed of the dry air blown to the central part in the web width direction is 9 m / sec, and the air supply speed of the dry air blown to both ends in the web width direction is 10 m / sec. Compared to the supply air speed of the dry air blown to the web, the supply air speed of the dry air blown to both ends in the width direction of the web was increased by 11.1%.

 Next, in order to evaluate the optical properties of the cellulose ester films obtained in Examples 2 to 14, in the same manner as in Example 1 above, retardation in the thickness direction of the cellulose ester film (Rt). And in-plane retardation (Ro) was measured.

 And about the cellulose-ester film obtained in Examples 2-14, similarly to the case of the said Example 1, the ratio of the area | region width | variety: RtX (%) which has the variation in the retardation Rt measured value of a thickness direction in a preferable range. Calculated.

 In Table 1 below, the evaluation results of RtX (%) of Examples 2 to 14 obtained in this way and the dry wind blown to the center in the web width direction on the support (1) in Examples 2 to 14 Exhaust air velocity (m / sec), exhaust air velocity (m / sec) of dry air blown to both ends in the width direction of the web, supply air velocity (m / sec) of dry air blown to the center portion in the width direction of the web, and The supply air velocity (m / sec) of the dry air blown to both ends in the web width direction is also shown.

 In addition, all of the in-plane retardation (Ro) values of the cellulose ester films obtained in Examples 2 to 14 were 60 nm or less.

Comparative Examples 1-4
For comparison, a cellulose ester film is prepared in the same manner as in Example 1, but the points different from Example 1 are as follows.

 In Comparative Example 1, the exhaust air velocity of 10 m / sec of the dry air blown to the central portion in the web width direction when the dry air is blown onto the web (10) formed on the support (1), both end portions in the web width direction The exhaust air velocity of the dry air blown on the air was set to 10 m / sec and the same. Further, the supply air speed of dry air blown to the central part in the web width direction was set to 10 m / sec, and the supply air speed of dry air blown to both ends in the web width direction was set to 10 m / sec.

  In Comparative Example 1, the exhaust air velocity of the drying air blown to the central portion in the web width direction when blowing the drying air to the web (10) formed on the support (1) was 10 m / sec, both ends in the web width direction. The exhaust air velocity of the dry air blown to the part was set to 10 m / sec and the same. Further, the supply air speed of dry air blown to the central part in the web width direction was set to 10 m / sec, and the supply air speed of dry air blown to both ends in the web width direction was set to 10 m / sec.

 In Comparative Example 2, the exhaust air velocity of the dry air blown to the central portion in the web width direction when the dry air is blown onto the web (10) formed on the support (1), and the both ends in the web width direction are blown. The exhaust air speed of the dry air was set to zero. Further, the supply air speed of dry air blown to the central part in the web width direction was set to 10 m / sec, and the supply air speed of dry air blown to both ends in the web width direction was set to 10 m / sec.

 In Comparative Example 3, the exhaust air speed of 10 m / sec of the dry air blown to the central portion in the web width direction when the dry air is blown on the web (10) formed on the support (1), both end portions in the web width direction The exhaust air velocity of the dry air sprayed on the was set to zero. Further, the supply air speed of dry air blown to the central part in the web width direction was set to 10 m / sec, and the supply air speed of dry air blown to both ends in the web width direction was set to 10 m / sec.

 In Comparative Example 4, the exhaust air velocity of the drying air blown to the central portion in the web width direction when blowing the drying air to the web (10) formed on the support (1) was 10 m / sec, both ends in the web width direction. The exhaust air velocity of the dry air blown to the part was set to 10 m / sec and the same. Further, the supply air speed of the dry air blown to the central portion in the web width direction was set to 10 m / sec, and the supply air speed of the dry air blown to both ends in the web width direction was set to zero.

 Next, in order to evaluate the optical properties of the cellulose ester films obtained in Comparative Examples 1 to 4, in the same manner as in Example 1 above, retardation in the thickness direction of the cellulose ester film (Rt). And in-plane retardation (Ro) was measured.

 And about the cellulose-ester film obtained by Comparative Examples 1-4, similarly to the case of the said Example 1, the ratio of the area | region width | variety: RtX (%) which has the variation in the retardation Rt measured value of a thickness direction in a preferable range. Calculated.

 In Table 1 below, the evaluation results of RtX (%) of Comparative Examples 1 to 4 thus obtained and the dry wind blown to the center in the width direction of the web on the support (1) in Comparative Examples 1 to 4 Exhaust air velocity (m / sec), exhaust air velocity (m / sec) of dry air blown to both ends in the width direction of the web, supply air velocity (m / sec) of dry air blown to the center portion in the width direction of the web, and The supply air velocity (m / sec) of the dry air blown to both ends in the web width direction is also shown.

(Preparation of polarizing film)
Next, in order to produce a liquid crystal display device using the cellulose ester films according to Examples 1 to 14 and Comparative Examples 1 to 4, first, a polarizing film was produced. That is, a polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched at a temperature of 110 ° C. and a stretch ratio of 5 times. This was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizing film.

(Preparation of polarizing plate)
Then, according to the following Step 1 to Step 5, the 40 μm-thick cellulose ester film (polarizing plate protective film) prepared in Examples 1 to 14 and Comparative Examples 1 to 4 was bonded to both surfaces of the polarizing film. A polarizing plate was produced.

  Step 1: The polarizing plate protective film obtained by immersing the polarizing plate protective film in a 1 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 60 seconds, then washing with water and drying, and saponifying the side to be bonded to the polarizing film. Got.

  Step 2: The polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by weight for 1 to 2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was gently wiped off, and a polarizing plate protective film saponified in Step 1 was laminated and disposed on both sides of the polarizing film.

Step 4: a polarizing film laminated in step 3, the laminate of the polarizing plate protective film, a pressure 20-30 N / cm ^2, the conveyance speed was pasted at approximately 2m / min.

  Step 5: The sample on which the polarizing film and the polarizing plate protective film prepared in Step 4 were bonded together was dried in a dryer at 80 ° C. for 2 minutes to prepare a polarizing plate.

(Production of liquid crystal display device)
Next, the polarizing plate of a commercially available VA type liquid crystal television Sony “BRAVIA KDL-40NX800” was peeled off, and each of the produced polarizing plates was bonded to the glass surface of the liquid crystal cell to produce a liquid crystal display device.

  At that time, the direction of bonding of the polarizing plate was performed so that the absorption axis was in the same direction as the polarizing plate that had been bonded in advance.

(Visibility evaluation)
In order to evaluate the visibility performance of each of the liquid crystal display devices prepared using the cellulose ester films according to Examples 1 to 14 and Comparative Examples 1 to 4, the liquid crystal display device was set at a temperature of 23 ° C. and a humidity of 55% RH. In this environment, after the backlight of the liquid crystal display device of the liquid crystal display device is turned on and left as it is for 30 minutes, the visibility of whether or not there is fine optical unevenness in the display device is determined according to the following criteria: The results obtained are shown in Table 1 below.

Visibility evaluation standard ○: No unevenness △: Several weak unevennesses ×: Strong irregularity with regularity

 As is clear from the results of Table 1 above, according to the cellulose ester films prepared in Examples 1 to 14 of the present invention, the ratio of the region width in which the variation in the retardation Rt measurement value in the thickness direction is within a preferable range: RtX ( %) Was high and the film had uniform optical characteristics in the width direction. Therefore, it is possible to suppress variations in retardation in the width direction of the film, to suppress minute retardation differences, to improve the flatness of the film, and on the support (1). The web (10) had a fast drying speed and could cope with an increase in the film forming speed.

 On the other hand, according to the cellulose ester films prepared in Comparative Examples 1 to 4, the ratio of the region width in which the variation of the retardation Rt measurement value in the thickness direction is in a preferable range: RtX (%) is low, and the width direction It was a film with non-uniform optical characteristics. Moreover, in the liquid crystal display device produced using the cellulose-ester film of the said Comparative Examples 1-4, there existed a regular and strong unevenness in evaluation of visibility, and there was a problem in use.

1: Stainless steel endless belt support 2: Casting die 3: Peeling roll 4: Tenter dryer 5: Roll transport dryer 6: Transport roll 7: Transport roll 8: Transport roll 10: Web 12: Slitter 15: Winding Remover F: Cellulose ester film

Claims (10)

  A dope (resin solution) in which a resin film raw material is dissolved in a solvent is prepared, and the dope is cast from a casting die onto a rotationally driven metal endless belt or a rotationally driven metal drum (support), on the support A casting film (hereinafter also referred to as a web), the web is dried on the support, the web is peeled off from the support, the peeled web is stretched, and dried and wound up. In the method for producing an optical film by a film forming method, drying air (drying air) is blown onto the web on the support to evaporate a part of the solvent contained in the web. And a dry air supply and / or exhaust air that can change the speed of the dry air at both ends.   When blowing dry air to the web formed on the support, the exhaust air velocity of the dry air blown to both ends in the width direction of the web is made smaller than the exhaust air velocity of the dry air blown to the center portion in the width direction of the web. The manufacturing method of the optical film of Claim 1 characterized by the above-mentioned.  When blowing dry air to the web formed on the support, the supply air speed of the dry air blown to both ends in the width direction of the web is compared to the supply air speed of the dry wind blown to the center portion in the width direction of the web. The method for producing an optical film according to claim 1, wherein the optical film is enlarged.   When blowing dry air to the web formed on the support, the exhaust air velocity of the dry air blown to both ends in the width direction of the web is 2% of the exhaust air velocity of the dry air blown to the center portion in the width direction of the web. The method for producing an optical film according to any one of claims 1 to 3, wherein the thickness is reduced in the range of 40% or less.  When blowing dry air to the web formed on the support, the supply air speed of the dry air blown to both ends in the width direction of the web is compared to the supply air speed of the dry wind blown to the center portion in the width direction of the web. The method for producing an optical film according to any one of claims 1 to 4, wherein the size is increased within a range of 2% or more and 40% or less.  When blowing dry air on the web formed on the support, the wind speed of the dry air is 1 to 30% higher on the exhaust side than on the supply side. The manufacturing method of the optical film of one term.   The method for producing an optical film according to any one of claims 1 to 6, wherein an optical film having an in-plane retardation value (Ro) of 60 nm or less is produced. Film thickness (X) is 20 μm ≦ X ≦ 50 μm
The manufacturing method of the optical film as described in any one of Claims 1-7 characterized by manufacturing the optical film in the range of these. The web transport speed (S) on the support is
80 m / min ≦ S ≦ 150 m / min
It exists in the range of this, The manufacturing method of the optical film as described in any one of Claims 1-8 characterized by the above-mentioned. Product width (D) is 1500mm ≦ D
The method for producing an optical film according to claim 1, wherein an optical film is produced.

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