JP5915655B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention can be used, for example, 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, and an antireflection film used for a plasma display. The present invention relates to a method for producing an optical film.

  In recent years, liquid crystal display devices such as notebook computers, televisions, and large monitors have been developed to be thinner and lighter, larger screens, and higher definition. Along with this, there is an increasing demand for thinner, wider and higher quality protective films for liquid crystal polarizing plates. Further, as the cost of optical films is reduced, a technique for increasing the film forming speed is required.

  Recently, liquid crystal display devices have been increasingly used for high transmittance and high contrast (CR). In a high CR liquid crystal display device, it is necessary to suppress a decrease in contrast due to light scattering in the film, more than required for a conventional liquid crystal display device.

  Optical films are required to be more uniform with respect to thickness in order to develop a predetermined optical function. This is because the uniformity of the thickness of the optical film has become an even more important factor for liquid crystal display devices such as a liquid crystal television set toward higher brightness and larger screen.

  Further, the optical film is required to have no optical defect and uniform retardation. In particular, the required quality is becoming stricter as monitors and TVs are becoming larger and higher definition.

  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.

  In Patent Document 1, in a film stretching method in which both ends in the width direction of a film (web) are gripped and the film is stretched in the width direction, the film thickness in the film width direction is from both ends of the film. A film having a film thickness profile that becomes gradually thinner toward the center part is stretched in the width direction, resulting in difficulty in stretching at both ends of the film at the time of stretching, and occurs from the both ends of the film toward the center part. The increasing distribution of the in-plane retardation (Ro) before and after stretching, which is gradually increased, is offset by the variation distribution of the in-plane retardation (Ro) that gradually decreases from the both ends of the film toward the center due to the thickness profile. Therefore, desired in-plane retardation (Ro) while suppressing variation of in-plane retardation (Ro) in the width direction. Method of stretching imparted to the film and the solution casting method for efficiently producing a film having a uniform in-plane retardation (Ro) is disclosed.

  According to the method described in Patent Document 1, it is disclosed that variation in in-plane retardation (Ro) in the film width direction can be improved by adjusting the film thickness in the film width direction.

  Further, in Patent Document 2, air is blown by a blowing means in the vicinity of a casting film formed by casting a dope on a traveling support, and the web is peeled off from the support. In the solution casting method for drying, a method using a guide member for preventing the drying air from flowing in the direction intersecting the web conveyance direction on the support is disclosed.

  According to Patent Document 2, it is disclosed that a polymer film in which striped thickness unevenness in an oblique direction is suppressed can be manufactured.

JP 2009-96183 A JP 2007-223307 A

  The object of the present invention is not only to improve the variation in in-plane retardation (Ro) in the width direction of the film, but also to improve the variation in retardation (Rt) in the thickness direction, and to generate optical defects. A method for producing an optical film that sufficiently suppresses the above, has uniform retardation, and can meet the strict quality requirements of high transmittance and high contrast (CR) due to the increase in size and definition of monitors and TVs. It is to provide.

  One aspect of the present invention is to prepare a dope in which a resin film raw material is dissolved in a solvent, cast the dope from a casting die onto a traveling support, and form a web on the support. In the method for producing an optical film by a solution casting film forming method, the web is dried on a support, the web is peeled off from the support, the peeled web is stretched, dried and wound up. During the step of drying the web on the support, 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, in the width direction of the web The method for producing an optical film is characterized in that, using a blower capable of changing a drying speed, drying conditions at both ends in the width direction of the web are made stronger than those in the width direction center of the web.

  Objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a schematic flow sheet showing an example of an apparatus for performing an optical film manufacturing method according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing a specific example of the web drying step in the method for producing an optical film according to the embodiment of the present invention. FIG. 3 is a schematic cross-sectional view schematically showing another specific example of the web drying step.

  According to the inventor's study, in the method described in Patent Document 1, in consideration of retardation in the thickness direction (Rt), in addition to the film thickness, the amount of residual solvent during stretching must be controlled, There was a problem that retardation (Rt) unevenness in the thickness direction was likely to occur.

  Further, according to the study of the present inventor, the method described in Patent Document 2 described above is insufficient in the effect of suppressing the occurrence of optical defects.

  From the above, it is required to further suppress the occurrence of optical defects.

  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. In this case, by making the drying conditions at both ends in the web width direction stronger than the center portion in the web width direction, the expression of the retardation (Rt) in the thickness direction is improved, and the retardation (Rt) in the thickness direction is improved. The present inventors have found that an optical film that can improve variation, sufficiently suppress the occurrence of optical defects, and has uniform retardation can be manufactured, and the present invention has been completed.

  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 an apparatus for producing an optical film by a solution casting film forming method according to an embodiment of the present invention.

  Referring to the figure, an optical film manufacturing method using a solution casting method is prepared by preparing a dope (resin solution) in which a resin film raw material is dissolved in a solvent, and applying the dope from a casting die (2) to a rotationally driven metal. The film is cast on an endless belt made of a metal or a rotating drive metal drum (support) (1) to form a cast film (web) (10) on the support (1), and on the support (1). The web (10) is dried, the web (10) is peeled from the support (1), the peeled web (10) is stretched, dried, and the film (F) is wound up. It is by law.

  And the method which concerns on this embodiment sprays drying air (dry wind) on the web (10) on a support body (1) in the case of the drying process of the web (10) on a support body (1). A part of the solvent contained in the web (10) is evaporated, and at that time, using the blower (11) capable of changing the drying speed in the width direction of the web (10), the central portion ( It is characterized in that the drying conditions at both ends (10a) and (10b) in the web width direction are stronger than those in 10c).

  Here, the both end portions are regions that occupy 3% of the length in the width direction of the web from the respective ends in the width direction of the web. Further, the central portion here is a region other than the both end portions.

  Further, to increase the drying condition is to increase the drying speed by the blower. In other words, the solvent contained in the web is easily evaporated. Specific examples include a method of increasing the wind speed of the drying air to be blown, a method of increasing the temperature of the drying air, and the like as described later.

  In the method for producing an optical film according to the present embodiment, the web (film) (10) before stretching after drying on the support (1) has the film thickness of the width direction both ends (10a) (10b). It is preferable that the thickness is larger than the film thickness of the central portion (10c) in the width direction.

  In this case, for example, as shown in the specific example of FIG. 2, only the film thicknesses of the both ends (10a) and (10b) in the width direction of the web (10) are center portions (10c) in the width direction of the web (10). May be larger than the film thickness of other web portions including the web width, or, for example, as shown in the specific example of FIG. The film thickness may be sequentially increased toward both ends (10a) and (10b) in the direction.

  In the method for producing an optical film according to the present embodiment, when the drying air is blown onto the web (10) formed on the support (1), for example, as shown by the arrows in FIGS. 2 and 3, the web (10) It is preferable to increase the wind speed of the drying air blown to both ends of the web (10) in the width direction compared to the wind speed of the drying air blown to the center portion (10c) in the width direction. Here, the wind speed of the drying air blown on the central portion and the wind speed of the drying air blown on both ends mean the average wind speed of the drying air at the interface between the film and the air in each region.

  Moreover, in the manufacturing method of the optical film which concerns on this embodiment, when spraying dry wind on the web (10) formed on the support body (1), the temperature of the dry wind sprayed on the center part (10c) of a web width direction It is preferable to raise the temperature of the drying air sprayed on both ends (10a) and (10b) in the width direction of the web. Here, the temperature of the drying air blown to the central portion and the temperature of the drying air blown to both ends mean the average temperature of the drying air at the interface between the film and air in each region.

  According to the method for producing an optical film according to the present embodiment, the drying air (drying air) is applied to the web (10) on the support (1) during the drying step of the web (10) on the support (1). ) To evaporate a part of the solvent contained in the web (10), and at that time, using the blower (11) capable of changing the drying speed in the width direction of the web (10), the width direction of the web Since the drying conditions at the both ends (10a) and (10b) in the width direction of the web are stronger than the center portion (10c) of the web, the remaining at both ends (10a) and (10b) in the width direction of the web (10) The amount of solvent can be adjusted, and after the web (10) is dried on the support (1), the residual solvent amount of the web (10) before stretching can be reduced, and the surface in the width direction of the film Improves dispersion of internal retardation (Ro) In addition to improving variation in retardation (Rt) in the thickness direction, that is, it is possible to prevent the occurrence of retardation (Rt) unevenness in the thickness direction, sufficiently suppressing the occurrence of optical defects, and retardation. Can be produced, and an optical film that satisfies the strict quality requirements for high transmittance and high contrast (CR) accompanying the increase in size and definition of monitors and TVs can be produced.

  In the method for producing an optical film according to this embodiment, a suction port (not shown) is provided on the downstream side in the transport direction of the air supply port of the blower (11) that blows dry air on the web (10) formed on the support (1). ) Is preferably controlled to reduce the unevenness of drying in the width direction of the web (10).

  In the method for producing an optical film according to the present embodiment, when the drying air is blown onto the web (10) formed on the support (1), a shielding plate (in the vicinity of both ends in the width direction of the support (1) ( It is preferable to control the flow of the drying air by providing (not shown).

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

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

  In the method according to the present embodiment, as a resin that is preferably used, for example, a cellulose ester-based resin having a substitution degree of acyl groups of 1.8 to 2.80, such as cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate, Polymerization of cellulose ether resins such as cellulose methyl ether, cellulose ethyl ether, cellulose propyl ether and the like having a degree of alkyl group substitution of 2.0 to 2.80, cycloolefin resins, norbornene resins, polycarbonate resins, and alkylene dicarboxylic acids and diamines. Polyamide resins, polymers of alkylene dicarboxylic acid and diol, polymers of alkylene diol and dicarboxylic acid, polymers of cyclohexane dicarboxylic acid and diol, cyclohexane diol and dicarbo Polyester resin such as polymer of acid, polymer of aromatic dicarboxylic acid and diol, vinyl acetate resin such as polyvinyl acetate and vinyl acetate copolymer, polyvinyl acetal resin such as polyvinyl acetal and polyvinyl butyral, epoxy Examples thereof include polyurethane resins such as resins, ketone resins, and linear polymers of alkylene diisocyanate and alkylene diol, and it is preferable to 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 other resins preferably used in the present embodiment include homopolymers and copolymers 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, taking cellulose ester as an example, embodiments according to the present invention will be described.

  In this embodiment, a cellulose ester solution containing a cellulose ester and an organic solvent is referred to as a dope, and this is used to form a solution casting film 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.

  Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester used by this embodiment, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  In the present embodiment, the number average molecular weight of the cellulose ester is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable.

  In the present embodiment, 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 embodiment, 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.

  In this embodiment, examples of the ultraviolet absorber that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. However, 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 this embodiment include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butyl). Phenyl) 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 -Tert-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- ( And a mixture of 5-chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like, but is 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 embodiment, the plasticizer and the ultraviolet absorber described above 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 embodiment, 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 0.1% 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 0.1% 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 the 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 embodiment is an apparatus that creates special conditions such as high shear and high-pressure conditions 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 / second or more and those having a heat transfer speed of 100 kcal / hour 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 other manton gorin type high-pressure dispersing devices such as those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  In the method for producing a cellulose ester film according to the present embodiment, a dope (resin solution) containing a cellulose ester and an additive (retardation reducing additive) for reducing thickness direction retardation (Rt) is used as a metal rotating drum or metal. A casting process in which a web is formed by casting on a rotating endless belt (support), a stretching process in which the web peeled from the support is stretched by a tenter device, a drying process in which the web is dried after stretching, and drying. A winding process for winding the film.

  The manufacturing method of the optical film by this embodiment comprises a dope preparation process (dissolution process), a casting process, a drying process, and a winding process.

  In the method for producing an optical film according to the present embodiment, 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 stirring and dissolving in a dissolution vessel, heating and dissolving, ultrasonic A method such as a dissolution method is usually used, and a method in which the solution is heated 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 and dissolved while stirring is a lump called gel or mamaco In order to prevent generation | occurrence | production of an undissolved substance, 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 and stirred and dissolved for 30 minutes or more.

  In the method according to the present embodiment, 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 according to this embodiment, the cellulose ester dope is filtered to remove foreign matters, particularly foreign matters that are mistakenly recognized as images in the 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 according to this embodiment, 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, after the two liquids are merged, they are transferred to the next step while being sufficiently mixed by a mixer such as an in-line mixer.

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

Referring to FIG. 1 showing an example of an apparatus for producing an optical film by a solution casting film forming method, the optical film producing method according to the present embodiment uses, for example, a dope which is a raw material solution of a cellulose ester film as a support (1 The dope casting die (dope casting means) (2) cast on the support (1) and the web (10) formed on the support (1) by the dope casting die (2) A peeling roll (peeling means) (3) to be peeled from the substrate, a drying means for drying the web (10) peeled from the support (1) by the peeling roll (3), and a film after drying ( F) a winder (winding means) (13) for winding.

  Here, first, the 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 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 manufacturing method of the optical film according to the present embodiment, drying air (drying air) is blown onto the web (10) on the support (1) during the drying process of the web (10) on the support (1). Then, by evaporating a part of the solvent contained in the web (10), using the blower (11) capable of changing the drying speed in the width direction of the web (10), the web (10) width direction The drying condition at the both ends in the width direction of the web (10) is stronger than the central portion (10c).

  Here, when the drying air is blown to the web (10) formed on the support (1), the web (10) is compared with the wind speed of the drying air blown to the central portion (10c) in the width direction of the web (10). It is preferable to increase the wind speed of the drying air blown to both ends in the width direction.

In particular, when blowing dry air to the web (10) formed on the support (1), the wind speed of the dry air at the widthwise ends (10a) (10b) of the web (10) and the web (10) It is preferable that the ratio of the width direction central portion (10c) to the wind speed of the drying air satisfies the following formula.
THE / THc × 0.5 ≦ Ve / Vc ≦ (THe / THc−1) × 20 + 1
In the formula, THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, Ve is the wind speed of the drying air at both ends in the width direction of the web, and Vc. Means the wind speed of the drying wind at the center in the width direction of the web. It is assumed that THe / THc ≧ 1.

  Here, the ratio of the wind speed of the dry wind at the widthwise ends (10a) and (10b) of the web (10) to the wind speed of the dry wind at the widthwise center (10c) of the web (10): Ve / If the value of Vc is THe / THc × 0.5 or more, the amount of residual solvent at the widthwise ends (10a) and (10b) of the web (10) can be sufficiently adjusted, and the retardation in the thickness direction can be adjusted. (Rt) It is preferable because unevenness can be further prevented. Moreover, if the value of Ve / Vc is (THe / THc-1) × 20 + 1 or less, it is preferable because drying unevenness in the web width direction can be further suppressed.

  Moreover, in the manufacturing method of the optical film which concerns on this embodiment, when drying air is sprayed on the web (10) formed on the support body (1), it sprays on the center part (10c) of the width direction of a web (10). It is preferable that the temperature of the drying air sprayed on both ends (10a) and (10b) in the width direction of the web (10) is higher than the temperature of the drying air.

In particular, when the drying air is blown onto the web formed on the support, the ratio between the drying air temperature at both ends in the width direction of the web and the drying air temperature at the center in the width direction of the web satisfies the following formula: Is preferred.
THE / THc × 0.5 ≦ Te / Tc ≦ (THe / THc−1) × 20 + 1
In the formula, THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, Te is the drying air temperature at both ends in the width direction of the web, and Tc is It means the drying air temperature at the center in the width direction of the web. It is assumed that THe / THc ≧ 1.

  Here, if the ratio of the drying air temperature at both ends in the width direction of the web and the drying air temperature at the center in the width direction of the web: Te / Tc is equal to or greater than THe / THc × 0.5, This is preferable because the amount of residual solvent at both ends in the width direction of the web can be adjusted sufficiently and the occurrence of retardation (Rt) unevenness in the thickness direction can be prevented. Moreover, it is preferable if the value of Te / Tc is (THe / THc-1) × 20 + 1 or less because drying unevenness in the width direction of the web can be sufficiently suppressed.

  In the method for producing an optical film according to the present embodiment, the web (film) (10) before stretching after drying on the support (1) has the film thickness of the width direction both ends (10a) (10b). It is preferable that the thickness is larger than the film thickness of the central portion (10c) in the width direction.

  In this case, for example, as shown in the specific example of FIG. 2, only the film thickness of the widthwise ends (10a) and (10b) of the web (10) is the width direction central portion (10c) of the web (10). It may be larger than the film thickness of the other web portion to be included, or alternatively, as shown in the specific example of FIG. 3, both ends in the width direction of the web (10c) from the width direction center (10c). The film thickness may be gradually increased as it reaches 10a) and 10b).

Furthermore, specifically, it is preferable that the web (film) before drying after drying on the support (1) has a film thickness represented by the following formula a and the following formula b.
1.02 ≦ THe / THc ≦ 1.04 (a)
THE-THc ≦ 3 μm (b)
In the formula, THe means the average film thickness at both ends in the width direction of the web, and THc means the average film thickness at the center in the width direction of the web.

  According to the method for producing an optical film according to the present embodiment, the drying air (drying air) is applied to the web (10) on the support (1) during the drying step of the web (10) on the support (1). ) To evaporate a part of the solvent contained in the web (10), and at that time, using the blower (11) capable of changing the drying speed in the width direction of the web (10), the width direction of the web Since the drying conditions at both ends in the width direction of the web are stronger than the center portion of the web, the amount of residual solvent at both ends (10a) and (10b) in the width direction of the web (10) can be adjusted. After drying of the web (10) on the support (1), the residual solvent amount of the web (10) before stretching can be reduced, and the variation in in-plane retardation (Ro) in the width direction of the film is improved. As well as the thickness direction Can also improve the dispersion of the film (Rt), that is, can prevent the occurrence of retardation (Rt) unevenness in the thickness direction, sufficiently suppress the generation of optical defects, the retardation is uniform, An optical film can be manufactured that satisfies the strict quality requirements for high transmittance and high contrast (CR) as TVs become larger and have higher definition.

  Moreover, in the manufacturing method of the optical film which concerns on this embodiment, a suction port (at the downstream of the conveyance direction of the air supply port of the air blower (11) which blows dry air on the web (10) formed on the support body (1) ( By providing an unillustrated), it is preferable to control the air flow and reduce drying unevenness in the width direction of the web (10). Thereby, there exists an advantage that the flow of dry air can be controlled.

  Furthermore, in the method for producing an optical film according to this embodiment, when dry air is blown onto the web (10) formed on the support (1), a shielding plate is provided in the vicinity of the end in the width direction of the support (1). It is preferable to control the flow of the drying air by providing (not shown). Thereby, there exists an advantage that the flow of dry air can be controlled.

  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.

  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 to a product width by the slitter (12) and cut off, and then wound by the winder (13).

  The winder (13) related to the production of the cellulose ester film may be one generally used, such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, or the like. 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 this embodiment is 30 to 200 μm, and for the recent thin tendency, the range of 40 to 120 μm is preferable, especially 40 A range of ˜100 μm is preferred. 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 cellulose ester film produced by the method according to this embodiment is preferably used for a liquid crystal display member, specifically, a polarizing plate protective film. In particular, the cellulose ester film according to the present embodiment is preferably used in a polarizing plate protective film that has strict requirements for 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 according to the present embodiment as a retardation film, and the cellulose ester film according to the present embodiment also serves as a retardation film and a protective film. Alternatively, it may be produced by directly bonding to a polarizing film. 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 stretched in the longitudinal direction and treated with a dichroic dye and the long retardation film according to the present embodiment. 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.

  The polarizing plate thus obtained is provided on one side or both sides of the liquid crystal cell, and the liquid crystal display device according to this embodiment 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 according to this embodiment can also be used as a base material for an antireflection film or an optical compensation film.
As described above, the present specification discloses various modes of technology, of which the main technologies are summarized below.

  One aspect of the present invention is to prepare a dope in which a resin film raw material is dissolved in a solvent, cast the dope from a casting die onto a traveling support, and form a web on the support. In the method for producing an optical film by a solution casting film forming method, the web is dried on a support, the web is peeled off from the support, the peeled web is stretched, dried and wound up. During the step of drying the web on the support, 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, in the width direction of the web The method for producing an optical film is characterized in that, using a blower capable of changing a drying speed, drying conditions at both ends in the width direction of the web are made stronger than those in the width direction center of the web.

  According to such a configuration, not only the variation in in-plane retardation (Ro) in the film width direction is improved, but also the variation in retardation (Rt) in the thickness direction is improved, that is, retardation in the thickness direction (Rt). Unevenness can be prevented, the occurrence of optical defects is sufficiently suppressed, the retardation is uniform, and the high transmittance and high contrast (CR) associated with the increase in size and definition of monitors and TVs. The optical film satisfying the demanded quality requirements can be produced.

  One of the preferred embodiments for achieving the above-described effect is a method for producing the optical film, wherein when the dry air is blown onto the web formed on the support, the width of the web is increased. It can be mentioned that the wind speed of the drying air blown to both ends in the width direction of the web is made larger than the wind speed of the drying wind blown to the center in the direction.

  One of the preferred embodiments for achieving the above-described effect is a method for producing the optical film, wherein when the dry air is blown onto the web formed on the support, the width of the web is increased. It can be mentioned that the temperature of the drying air blown to both ends of the web in the width direction is made higher than the temperature of the drying air blown to the center portion in the direction.

Further, in the method for producing the optical film, when the drying air is blown onto the web formed on the support, the wind speed of the drying air blown to both ends in the width direction of the web, and the width direction of the web It is preferable that the ratio of the wind speed of the drying air blown to the center portion satisfies the following formula.
THE / THc × 0.5 ≦ Ve / Vc ≦ (THe / THc−1) × 20 + 1
In the formula, THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, Ve is the wind speed of the drying wind blown at both ends in the width direction of the web, Vc means the wind speed of the dry wind sprayed on the center in the width direction of the web. It is assumed that THe / THc ≧ 1.

  According to such a configuration, the above-described effects of the present invention can be obtained particularly preferably.

Further, in the method for producing the optical film, when the drying air is blown onto the web formed on the support, the temperature of the drying air blown to both ends in the width direction of the web, and the width direction of the web It is preferable that the ratio of the temperature of the drying air blown to the center portion satisfies the following formula.
THE / THc × 0.5 ≦ Te / Tc ≦ (THe / THc−1) × 20 + 1
In the formula, THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, Te is the drying air temperature at both ends in the width direction of the web, and Tc is It means the drying air temperature at the center in the width direction of the web. It is assumed that THe / THc ≧ 1.

  According to such a configuration, the above-described effects of the present invention can be obtained particularly preferably.

  Further, in the method for manufacturing the optical film, the air flow is controlled by providing a suction port on the downstream side in the transport direction of the air supply port of the blower that blows the dry air on the web formed on the support. Is preferred.

  According to such a configuration, it becomes possible to control the airflow of the dry air, and thus it is possible to further improve the uniformity of retardation.

  Further, in the method for producing the optical film, when the drying air is blown onto the web formed on the support, a shielding plate is provided in the vicinity of the widthwise end portion of the support to It is preferable to control the flow.

  According to such a configuration, it becomes possible to control the airflow of the dry air, and thus it is possible to further improve the uniformity of retardation.

  Further, in the method for producing the optical film, after the web is dried on the support, the thickness of the web before stretching is set to the width of the web with respect to the thickness of the central portion in the width direction of the web. It is preferable to increase the film thickness at both ends in the hand direction to 1.02 times to 1.30 times.

  According to such a configuration, the above-described effects of the present invention can be obtained particularly preferably.

  Moreover, it is a manufacturing method of the said optical film, Comprising: It is preferable that the said support body is a rotation drive metal endless belt or a rotation drive metal drum.

  According to such a configuration, the optical film can be easily manufactured.

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

Examples 1-12
(Preparation of dope)
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 prepared.

(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.

(Production of optical film)
Next, using the solution casting film forming apparatus shown in FIG. 1, the temperature of the dope prepared as described above is maintained at 35 ° C., and the casting die (2) is made of a mirror-finished stainless steel endless belt at 25 ° C. The web (dope film) (10) was formed by casting uniformly on a support (1) having a width of 2400 mm and a width of 2200 mm. The running speed of the support (1) was 100 m / min.

  And in the method which concerns on this embodiment, in the drying process of the web (10) on a support body (1), the air for drying (dry wind) is sprayed on the web (10) on a support body (1). Then, a part of the solvent contained in the web (10) was evaporated. At that time, using the blower (11) capable of changing the drying speed in the width direction of the web (10), the web (10) at the both ends in the width direction of the web (10) rather than the center portion in the width direction. Increased drying conditions.

  In Table 1 below, in each example, when blowing dry air to the web (10) formed on the support (1), the wind speed and temperature of the dry air blown to the web width direction center (10c), and The wind speed and temperature of the drying air blown to the both ends (10a) and (10b) in the width direction of the web are described.

  Here, in Examples 1 to 5, when the drying air is blown onto the web (10) formed on the support (1), the wind speed of the drying air blown to the web width direction center portion (10c), and the web width The temperature was made the same by changing the speed of the drying air blown to both ends (10a) and (10b) in the hand direction.

  On the other hand, in Examples 6-11, when blowing dry air to the web (10) formed on the support body (1), the temperature of the dry air blown to the web width direction center part (10c), and the web The temperature of the drying air blown to both ends (10a) and (10b) in the width direction was changed, and the wind speed was the same.

  Moreover, in Example 12, when blowing dry air on the web (10) formed on the support (1), the wind speed and temperature of the dry air blown on the web width direction center (10c), and the web width. Both the wind speed and temperature of the drying air blown to the direction both ends (10a) and (10b) were changed.

  Next, the web (10) dried on the support (1) is peeled off from the support (1) with a residual solvent amount of 80% by weight, and the both ends of the web are clipped using a tenter device (4). A cellulose acetate propionate film was produced by stretching in the width direction (TD direction) of the film while gripping with.

In addition, the film thickness of the web (film) before extending | stretching after drying on a support body (1) had a film thickness ratio of a following formula.
THE / THc = 1.025
In the formula, THe means the average film thickness at both ends in the width direction of the web, and THc means the average film thickness at the center in the width direction of the web.

  The stretch ratio of the web (film) by the tenter device (4) was 1.2 times. The produced cellulose acetate propionate film was dried at 120 ° C.

  Then, after drying processing with a roll transport drying device (5) in which 500 mirror surface transport rolls (7) (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 wound up by a winder (13), and finally a cellulose acetate propionate film (F) having a film thickness of 42.0 μm was obtained.

Comparative Examples 1-3
For comparison, a cellulose acetate propionate film is prepared in the same manner as in Example 1. However, as shown in Table 1 below, Comparative Example 1 is different from Example 1 above. When dry air is blown onto the web (10) formed on the support (1), the wind speed of the dry air blown to the widthwise center (10c) of the web (10) and both widthwise ends (10a) The speed of the drying air blown on (10b) is the same, and the temperature of the drying air blown on the widthwise center (10c) of the web (10) and the drying blown on the widthwise ends (10a) (10b). The point is that the temperature of the wind is the same. In Comparative Example 2, when the drying air is blown onto the web (10) formed on the support (1), the width direction is higher than the wind speed of the drying air blown to the width direction center (10c) of the web (10). The temperature of the drying air blown to the width direction center part (10c) of the web (10) and the width direction both ends (10a) (10a) ( The temperature of the drying air blown to 10b) is the same. In Comparative Example 3, when the drying air is blown onto the web (10) formed on the support (1), the wind speed of the drying air blown to the center portion (10c) in the width direction of the web (10), and both ends in the width direction. The both ends in the width direction (10a) (10a) (10a) (the same as the wind speed of the drying wind blown to the parts (10a) and (10b)) The temperature of the drying air blown to 10b) is made small.

<Evaluation of optical properties of film>
Next, for the cellulose acetate propionate films obtained in Examples 1 to 12 and Comparative Examples 1 to 3, the retardation value (Rt) in the thickness direction of each film is evaluated in order to evaluate the optical properties of the films. Using an automatic birefringence meter measuring device (KOBRA-WIS / RT, manufactured by Oji Scientific Instruments), the wavelength was measured at 590 nm in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

  And the retardation value (Rt) of the thickness direction of 20 points | pieces of each film was measured, and while calculating the average value (Rtav), the variation of the retardation value (Rt) of the thickness direction with respect to an average value was calculated, and the following Evaluation was made according to the criteria.

  Here, RtX is expressed by the following formula, where W1 is the width of the region where the measured value of retardation Rt in the thickness direction satisfies the following formula, and W0 is the width of the film.

W1: | Rt−Rtav | /Rtav≦0.07
RtX = W0 / W1
The measurement results and evaluation results of the variation in thickness direction retardation (RtX) obtained are shown in Table 1 below.

Evaluation criteria for optical properties of film ◎: RtX is 95% or more, the best level ○: RtX is 90% or more, practically good level Δ: RtX is 80% or more, practically no problem level X: RtX is less than 80%, problematic level

(Preparation of polarizing film)
Next, in order to produce a liquid crystal display device using the cellulose acetate propionate film obtained in Examples 1 to 12 and Comparative Examples 1 to 3, a polarizing film was first 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 acetate propionate film (polarizing plate protective film) prepared in Examples 1 to 12 and Comparative Examples 1 to 3 was formed on both surfaces of the polarizing film. And a commercially available retardation film were bonded together to produce a polarizing plate.

  Step 1: The polarizing plate protective film and the commercially available retardation film are immersed in a 1 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 60 seconds, then washed with water and dried, and the side to be bonded to the polarizing film is bonded. A saponified polarizing plate protective film and a commercially available retardation film were obtained.

  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 and a commercially available retardation film were laminated on both sides of the polarizing film.

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

  Step 5: A sample in which the polarizing film prepared in Step 4 and a commercially available retardation film and polarizing plate protective film 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 T2 film of the VA mode type liquid crystal television (Sony TV “BRAVIA KDL-40NX800”) is peeled off, and the viewing-side polarizing plate bonded in advance is peeled off so that the absorption axes of the polarizing plates match. The VA mode type liquid crystal display device was produced by pasting on the glass surface of the liquid crystal cell so that the optical compensation film of each polarizing plate produced in the above was on the liquid crystal cell side.

<Evaluation of color stability>
About each produced said VA mode type liquid crystal display device, color measurement was performed by the method shown below, the stability of color was evaluated, and the obtained result was described according to Table 1 below.

Measuring method of color
About each VA mode type liquid crystal display device, the color measurement at the time of black display was performed with the color measuring device (Topcon company make, SR-3A). At this time, the hue was measured between the front and an oblique angle (azimuth angle 45 degrees) with a tilt angle of 60 ° (front reference), and the values of the following formulas were calculated and evaluated.
[(Xx ′) ² + (y−y ′) ² ] ^1/2
In the formula, front: (x, y), diagonal: (x ′, y ′).

  In addition, the smaller number represents that the color is stable.

Evaluation rank of color taste ◎: 0.00 or more and less than 0.01 ○: 0.01 or more and less than 0.03 Δ: 0.03 or more and less than 0.07 ×: 0.07 or more

  As is clear from the results of Table 1 above, in the cellulose acetate propionate films obtained in Examples 1 to 12 according to the present embodiment, the evaluation result of variation in thickness direction retardation (RtX) is a problem in practical use. There was no problem or the best level, and there was no problem at all as a polarizing plate protective film.

  Moreover, in the evaluation of the color stability by the liquid crystal display device produced using the cellulose acetate propionate film obtained in Examples 1 to 12, the numerical values indicating the color are all small, The taste was stable.

  Thus, according to the method according to the present embodiment, variation in retardation (Rt) in the thickness direction of the cellulose acetate propionate film can be improved, sufficiently suppressing the occurrence of optical defects, The retardation was uniform, and the required quality required for high transmittance and high contrast (CR) with the increase in size and definition of monitors and TVs could be satisfied.

  On the other hand, in the cellulose acetate propionate films obtained in Comparative Examples 1 to 3, the evaluation result of the variation in the thickness direction retardation (RtX) is a practically problematic level and is used as a polarizing plate protective film. There was a problem. Moreover, in the evaluation of the color stability by the liquid crystal display device produced using the cellulose acetate propionate film obtained in Comparative Examples 1 to 3, the numerical value indicating the color is large, and the color is stable. I did not.

  Next, in the method for producing an optical film according to the present embodiment, the web width direction is determined by using a blower that can change the drying speed in the width direction of the web during the drying process of the web on the support. The drying condition at both ends in the width direction of the web is stronger than that at the center of the web. Specifically, when the drying air is blown onto the web formed on the support, the width of the web is Compared to the wind speed of the drying air blown to the center of the direction, the method of increasing the wind speed of the drying wind blown to both ends in the width direction of the web, and the web width when blowing the drying air to the web formed on the support There is a method in which the temperature of the drying air blown to both ends in the web width direction is made higher than the temperature of the drying air blown to the center portion in the hand direction.

  However, in reality, when the drying of the web is controlled only by the wind speed of the drying air, the web surface roughness is different in the width direction of the web, and uneven surface roughness tends to occur. On the other hand, if it is attempted to control the drying of the web only by the temperature of the drying air, the vibration of the support (belt) (1) increases due to the temperature unevenness of the support in the width direction of the web, and the horizontal stage generated during casting. Tend to be wrinkled.

  In order to verify this point, for the cellulose acetate propionate film obtained in Examples 3, 9, and 12, the surface roughness was measured, and the surface roughness unevenness in the film width direction was evaluated, Each film was evaluated for a lateral failure of the cast (longitudinal unevenness).

<Evaluation of surface roughness unevenness in the width direction of the film>
The surface roughness Ra (nm) of the cellulose acetate propionate films obtained in Examples 3, 9, and 12 was measured. In this embodiment, the surface roughness Ra of the film after the winding process is used as the surface roughness Ra of the film. About each said film, it measured on condition of the following using the surface roughness measuring device (New View5000, product made from ZYGO).

  Measurement conditions: Objective lens magnification: Photographed at 50 × and 2.0 × zoom. The measured values were processed by applying an FFT Fixed type High Pass filter.

  And about each film, the surface roughness Ra nonuniformity of the film width direction was computed and evaluated, and the obtained result was described in following Table 2.

Evaluation rank of surface roughness Ra unevenness in the film width direction ○: Surface roughness Ra unevenness in the film width direction within ± 0.05 nm Δ: Surface roughness Ra unevenness in the film width direction less than ± 0.1 nm ×: Film Surface roughness Ra unevenness in the width direction ± 0.1 nm or more

<Evaluation of cast lateral failure (longitudinal unevenness)>
Next, with respect to the cellulose acetate propionate films obtained in Examples 3, 9, and 12, the cast lateral failure (longitudinal unevenness) was evaluated by the following method.

  From the cellulose acetate propionate film obtained in Examples 3, 9, and 12, a sample having a length of 3 m (full width) was taken out and allowed to stand on a black base plate. On the other hand, an illumination plate in which eight 40 W fluorescent lamps were arranged at intervals of 10 cm was prepared. This lighting plate was placed 1.5 m above the film that was allowed to stand, the flatness of the film was observed, and cast lateral failure (longitudinal unevenness) was evaluated with the following rank. The results of cast lateral failure (longitudinal unevenness) of the obtained cellulose acetate propionate film are shown in Table 2 below.

Evaluation rank of cast lateral stage failure (longitudinal unevenness) ○: No unevenness Δ: There are about 10 weak unevennesses ×: There are many regular strong irregularities

  As can be seen from the results in Table 2 above, as in Example 3 according to the present embodiment, during the drying process of the web on the support, the drying of the web is controlled only by the wind speed of the drying wind. When the temperature was kept constant, the measurement result of the surface roughness unevenness of the obtained cellulose acetate propionate film was at a level of no practical problem, but was slightly unpreferable.

  On the other hand, as in Example 9 according to this embodiment, when the web drying process is controlled only by the temperature of the drying air during the web drying process on the support, and the wind speed of the drying air is constant. The measurement result of the cast lateral failure of the obtained cellulose acetate propionate film was at a level not causing any practical problems, but was slightly unpreferable.

  On the other hand, as in Example 12 according to the present embodiment, when the drying of the web is controlled by both the wind speed and the temperature of the drying air during the drying process of the web on the support, it is obtained. The measurement results of the surface roughness unevenness of the cellulose acetate propionate film and the measurement results of the cast horizontal step failure were both good.

  According to the present invention, not only the variation in in-plane retardation (Ro) in the width direction of the film but also the variation in retardation (Rt) in the thickness direction is improved, that is, the retardation (Rt) in the thickness direction is uneven. The generation of optical defects is sufficiently suppressed, the retardation is uniform, and the high transmittance and high contrast (CR) due to the increase in size and definition of monitors and TVs. An optical film manufacturing method capable of manufacturing an optical film satisfying strict required quality is provided.

Claims (6)

A dope prepared by dissolving a resin film raw material in a solvent is prepared, the dope is cast from a casting die onto a traveling support, a web is formed on the support, and the web is formed on the support. In the method for producing an optical film by a solution casting film forming method, drying, peeling the web from the support, stretching the peeled web, drying and winding up,
During the step of drying the web on the support, a drying air is blown onto the web on the support to evaporate a part of the solvent contained in the web, and in this case, the width direction of the web Using a blower that can change the drying speed in the above, the drying condition at both ends in the width direction of the web is stronger than the width direction center of the web ,
When the drying air is blown onto the web formed on the support, the wind speed of the drying air blown to both ends of the web in the width direction is compared with the wind speed of the drying air blown to the widthwise center of the web. An optical film characterized in that the ratio of the wind speed of the drying air blown to both ends in the width direction of the web and the wind speed of the drying wind blown to the center portion in the width direction of the web satisfies the following formula : Production method.
THE / THc × 0.5 ≦ Ve / Vc ≦ (THe / THc−1) × 20 + 1
[Where THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, and Ve is the wind speed of the drying wind blown at both ends in the width direction of the web. , Vc means the wind speed of the drying air blown to the center in the width direction of the web. It is assumed that THe / THc ≧ 1. ] A dope prepared by dissolving a resin film raw material in a solvent is prepared, the dope is cast from a casting die onto a traveling support, a web is formed on the support, and the web is formed on the support. In the method for producing an optical film by a solution casting film forming method, drying, peeling the web from the support, stretching the peeled web, drying and winding up,
During the step of drying the web on the support, a drying air is blown onto the web on the support to evaporate a part of the solvent contained in the web, and in this case, the width direction of the web Using a blower that can change the drying speed in the above, the drying condition at both ends in the width direction of the web is stronger than the width direction center of the web,
When blowing the drying air on the web formed on the support, the temperature of the drying air blowing on both ends of the web in the width direction is compared to the temperature of the drying air blowing on the widthwise center of the web. The ratio of the temperature of the drying air blown to the both ends in the width direction of the web and the temperature of the drying air blown to the center portion in the width direction of the web satisfies the following formula: Production method.
THE / THc × 0.5 ≦ Te / Tc ≦ (THe / THc−1) × 20 + 1
[Where THe is the average film thickness at both ends in the width direction of the web, THc is the average film thickness at the center in the width direction of the web, Te is the drying air temperature at both ends in the width direction of the web, Tc Means the drying air temperature at the center in the width direction of the web. It is assumed that THe / THc ≧ 1. ] A dope prepared by dissolving a resin film raw material in a solvent is prepared, the dope is cast from a casting die onto a traveling support, a web is formed on the support, and the web is formed on the support. In the method for producing an optical film by a solution casting film forming method, drying, peeling the web from the support, stretching the peeled web, drying and winding up,
During the step of drying the web on the support, a drying air is blown onto the web on the support to evaporate a part of the solvent contained in the web, and in this case, the width direction of the web Using a blower that can change the drying speed in the above, the drying condition at both ends in the width direction of the web is stronger than the width direction center of the web,
A method for producing an optical film, characterized in that an air flow is controlled by providing a suction port on a downstream side in a conveying direction of an air supply port of a blower that blows the dry air on a web formed on the support. A dope prepared by dissolving a resin film raw material in a solvent is prepared, the dope is cast from a casting die onto a traveling support, a web is formed on the support, and the web is formed on the support. In the method for producing an optical film by a solution casting film forming method, drying, peeling the web from the support, stretching the peeled web, drying and winding up,
During the step of drying the web on the support, a drying air is blown onto the web on the support to evaporate a part of the solvent contained in the web, and in this case, the width direction of the web Using a blower that can change the drying speed in the above, the drying condition at both ends in the width direction of the web is stronger than the width direction center of the web,
An optical film characterized by controlling the flow of drying air by providing a shielding plate in the vicinity of an end in the width direction of the support when the drying air is blown onto the web formed on the support. Production method. After the web is dried on the support, the thickness of the web before stretching is 1.02 times the thickness of the web in the widthwise direction relative to the thickness of the web in the widthwise center. The method for producing an optical film according to any one of claims 1 to 4 , wherein the optical film is enlarged to -1.30 times. The method for producing an optical film according to any one of claims 1 to 5 , wherein the support is a rotationally driven metal endless belt or a rotationally driven metal drum.

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