JP2009298094A - Optical film and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film in which generation of a surface defect and thickness unevenness is sufficiently prevented and a method and an apparatus for manufacturing the optical film by melting casting film making method. <P>SOLUTION: In the method for manufacturing the optical film in which the optical film is manufactured by discharging a film constituting material containing a molten thermoplastic resin onto a cooling roll in a film shape from the lip portions 41a, 41b of a casting die cooling and solidifying the same, volatile matters vaporized from the molten matter 42 are deposited on the surface of cooling devices 43a, 43b whose surface temperature is held under the boiling point of the volatile matters and recovered, and the optical film manufactured by the method is also disclosed. In the apparatus for manufacturing the optical film in which the optical film is manufactured by discharging the film constituting material containing the molten thermoplastic resin onto the cooling roll in the film shape from the lip portions of the casting die and cooling and solidifying the same, the apparatus includes the cooling devices 43a, 43b whose surface temperature is held under the boiling point of the volatile matters vaporized from the molten matters 42, the volatile matter is deposited on the surface of the cooling devices and recovered. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film and a method for producing the same.

  A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, various optical films such as a polarizing plate protective film, a retardation film, and a viewing angle widening film are used. In addition, optical films such as an antireflection film, an antiglare film, and a protective form are also used in plasma displays, organic EL displays, and the like.

  These optical films are required to have a uniform thickness. In particular, as the size of monitors and TVs increases and the definition becomes higher, the required quality is becoming stricter.

  The optical film production methods are roughly classified into a melt casting film forming method and a solution casting film forming method. The former is a method in which a polymer is heated and dissolved, cast on a support, cooled and solidified, and further stretched as necessary to form a film. The latter is a method in which a polymer is dissolved in a solvent, the solution is cast on a support, the solvent is evaporated, and further stretched as necessary to form a film. In any film forming method, the molten polymer or polymer solution is cooled and solidified on the support. And after peeling from a support body, processes, such as drying and extending | stretching, are made | formed, while a polymer film is conveyed using a some conveyance roll.

  The solution casting film forming method has a problem in that productivity is low because equipment and energy for recovering the solvent are required rather than using a large amount of the solvent. On the other hand, since the melt casting film forming method does not use a solvent, an improvement in productivity can be expected. The melt casting film forming method is preferable from the viewpoint of productivity, but the film cast by melt casting has a problem that the thickness unevenness is larger than that of the solution casting film forming method. Also, in the melt casting film forming method, volatiles volatilized from the melt adhere to the opening of the lip portion of the casting die that discharges the melt, and surface defects caused by the deposit become die lines to form the film surface. There is also the problem of appearing in

Therefore, after the thermoplastic resin is melted by an extruder, as shown in FIG. 5, the molten resin 101 is discharged from the die 102 onto a support 103 that runs or rotates and is cooled and solidified by being cooled and solidified. In the method of manufacturing a thermoplastic film for forming a film, a method of manufacturing a thermoplastic film is proposed in which low molecular components that volatilize from the molten resin discharged from the die 102 are sucked and removed by suction means 104a and 104b. (Patent Document 1).
JP 2006-335050 A

  In the above method, although surface defects such as die lines are prevented, the melt vibrates in order to suck and collect volatiles in the vicinity of the discharged melt. When the vibrating melt was grounded on the support and cooled and solidified, the film had uneven thickness. In particular, in a system in which the discharged film-like melt is pressed by a touch roll on a support (cooling roll), since the tension is generated in the melt by the touch roll, vibration of the melt causes resonance, Thickness unevenness occurred remarkably.

  An object of the present invention is to provide an optical film in which occurrence of surface defects and thickness unevenness is sufficiently prevented, and a method and apparatus for producing the optical film by a melt casting film forming method.

The present invention
A method for producing an optical film by discharging a film-constituting material containing a molten thermoplastic resin from a lip portion of a casting die onto a cooling roll in the form of a film, and cooling and solidifying the film.
A method for producing an optical film characterized by depositing and recovering volatiles volatilized from a melt on the surface of a cooling device whose surface temperature is kept below the boiling point of the volatiles, and produced by the method The present invention relates to an optical film.

The present invention also provides
An apparatus for producing an optical film by discharging a film constituent material containing a molten thermoplastic resin from a lip portion of a casting die onto a cooling roll in the form of a film and cooling and solidifying,
A cooling device in which the surface temperature is kept below the boiling point of the volatiles volatilized from the melt,
The present invention relates to an optical film manufacturing apparatus which deposits and collects volatiles on the surface of the cooling device.

  According to the present invention, since the volatiles are forcibly cooled and deposited, the volatiles are recovered without causing vibration in the melt. As a result, an optical film in which occurrence of surface defects and thickness unevenness is sufficiently prevented can be obtained. Such an effect can be effectively obtained even when the discharged film-like melt is pressed on the cooling roll by the touch roll.

[Optical Film Manufacturing Method and Manufacturing Apparatus]
An optical film manufacturing method and manufacturing apparatus according to the present invention is based on a so-called melt casting method, that is, a film-constituting material containing a molten thermoplastic resin is formed into a film from a lip portion of a casting die in a cooling roll. An optical film is manufactured by discharging and cooling to solidify.

  In detail, the method for producing an optical film according to the present invention includes a melt extrusion step, and usually further includes a stretching / winding step. Hereafter, each process is demonstrated in detail using FIGS. 1-3. FIG. 1 is a schematic configuration diagram of an example of an apparatus for carrying out the method for producing an optical film of the present invention. 2 to 3 are enlarged views of main parts of one embodiment from the casting die to the cooling roll in FIG. 1-3, the common code | symbol shall show the same member.

(Melting extrusion process)
In this step, film constituent materials including a thermoplastic resin are mixed, melted using the extruder 1, and then passed through the filter 2 and the static mixer 3 as required, so that the lip 41a, The melt 42 is extruded into a film form from 41b. Hereinafter, the case where the film-like melt 42 is pressed by the touch roll 6 on the first cooling roll 5 as shown in FIGS. 1 to 3 will be described, but the first cooling is not limited thereto. After being discharged onto the outer peripheral surface of the roll 5, it may be conveyed to the next step without being pressed by the touch roll 6. Moreover, in FIGS. 1-3, although the film-form melt 42 is discharged and pressed directly on the opposing part 47 of the 1st cooling roll 5 and the touch roll 6, it is not restrict | limited to this, For example, After being discharged onto the outer peripheral surface of the first cooling roll 5 and conveyed by the rotation of the first cooling roll 5, it may be sandwiched between the facing portions 47. When the touch roll 6 is used, the touch roll 6 and the first cooling roll 5 form a pair of rotating rolls, and the melt is sandwiched and pressed between the facing portions 47. The facing portion 47 is a portion where the first cooling roll 5 and the touch roll 6 are opposed to each other, and the first cooling roll 5 and the touch roll 6 are brought into contact with the melt when the melt 42 is sandwiched between the rolls. It is a part which contacts indirectly through 42.

  In the present invention, the volatiles volatilized from the melt 42 are forcibly cooled to precipitate and recovered. Specifically, volatiles are deposited on the surface of the cooling device and collected. As a result, since volatiles can be recovered without causing vibration in the melt, an optical film in which occurrence of surface defects and thickness unevenness can be sufficiently prevented can be obtained.

  In this specification, precipitation is a phenomenon in which gaseous volatiles appear in the solid state (sublimation (solidification)), appear in the liquid state (condensation), and once appear in the liquid state, then become solid. It is meant to include phenomena.

  The cooling device is such that the surface temperature is kept below the boiling point of the volatile matter, preferably below the melting point. Therefore, the volatiles are cooled and deposited on the surface of the cooling device, so that the volatiles can be recovered and removed. Specifically, the surface temperature of the cooling device is set to Tb-5 (° C.) or less, particularly Tb-5 to Tb-120 (° C.), preferably Tb-50, where the boiling point of the volatile material is Tb (° C.). It is set to ~ Tb-120 (° C), more preferably Tb-80 to TB-100 (° C). The surface temperature can be measured by a non-contact thermometer, for example, TX series (manufactured by Hayashi Electric Works).

  Specifically, the surface temperature of the cooling device is usually set to 150 ° C. or less, particularly 3 to 50 ° C., and preferably 3 to 10 ° C.

  Examples of volatiles that volatilize from the melt 42 include, for example, low-molecular components that are inevitably contained in the thermoplastic resin described later, and stabilizers, plasticizers, ultraviolet absorbers, matting agents, and retardation control agents. Agents. Examples of the low molecular components that are necessarily contained in the thermoplastic resin include monomers and oligomers used in the production of the thermoplastic resin. The boiling point Tb of the volatile matter described above means the boiling point of the compound having the lowest boiling point among the low molecular component and the additive contained in the thermoplastic resin used.

  Since the volatile matter is mainly generated when the melt 42 is discharged from the lip portions 41a and 41b of the casting die 4 and released to the atmosphere, the cooling device is disposed in the vicinity of the lip portions 41a and 41b. It is preferable.

  The cooling device is not particularly limited as long as the surface temperature can be maintained within a predetermined range, and examples thereof include a fixed cooling device and a movable cooling device.

  The fixed cooling device is a cooling device in which the deposition surface of the volatile matter is fixed without moving. For example, a fixed cooling device represented by 43a and 43b in FIG. 2 can be used. The fixed cooling device 43a (43b) is formed by circulating a cooling medium 432a (432b) inside the pipe-shaped member 431a (431b). The cooling medium 432a (432b) is Then, it is cooled to the same temperature as the predetermined surface temperature and is circulated. As a result, the volatile matter is recovered as precipitates 49 on the outer peripheral surface of the pipe-like member 431a (431b) of the fixed cooling device 43a (43b).

  The fixed cooling device 43 a (43 b) is installed so that the axial direction of the pipe-shaped member 431 a (431 b) is substantially parallel to the axial direction of the cooling roll 5. The fixed cooling device 43a (43b) is installed on both sides of the discharged melt 42 in FIG. 2, but is not limited to this, and may be installed on either side. Preferably, it is installed on both sides of the discharge melt 42. The distance from the lip portion 41a (41b) and the discharge melt 42 of the fixed cooling device 43a (43b) is not particularly limited as long as the object of the present invention is achieved, and is preferably a cross section perpendicular to the axial direction of the cooling roll 5 The distance from the lip portion 41a (41b) is 1 to 100 mm, and the distance from the discharge melt 42 is 1 to 100 mm.

  The cooling medium 432a (432b) is not particularly limited as long as it can be controlled to the same temperature as the above-described predetermined surface temperature, and for example, water, silicone oil, carbon dioxide, liquid nitrogen, or the like can be used. The flow rate of the cooling medium is not particularly limited as long as the object of the present invention is achieved, and for example, 1 to 100 L / min is preferable.

  The constituent material of the pipe-shaped member 431a (431b) is not particularly limited as long as the temperature of the cooling medium flowing through the pipe-shaped member 431a (431b) can be conducted to the outer peripheral surface. For example, a material having a relatively large specific heat is preferably used. Specific examples of such a material include SUS and the like. The thickness (thickness), inner diameter, outer diameter, and other dimensions of the pipe-shaped member 431a (431b) are not particularly limited as long as the object of the present invention is achieved, and preferably the thickness (thickness) is 1 to 5 mm, the inner diameter. Is 2 to 30 mm, and the outer diameter is 4 to 40 mm. The axial length of the pipe-shaped member is usually longer than the total length of the lip portions 41a, 41b in the same direction. The cross-sectional shape of the pipe-shaped member 431a (431b) is not particularly limited as long as the cooling medium is circulated therein, and examples thereof include a circular shape, a rectangular shape, other polygonal shapes, and an elliptical shape.

  When using a fixed cooling device, the precipitate collected on the outer peripheral surface of the pipe-shaped member may be periodically cleaned.

  The movable cooling device is a cooling device in which the deposition surface of the volatile matter is movable, for example, a belt is stretched around at least two rotatable support rolls, and the inside of at least one of the support rolls The one in which a cooling medium is circulated can be used. As a specific example, for example, a movable cooling device represented by 44a and 44b in FIG. 3 can be used. The movable cooling device 44a (44b) includes a belt 443a (443b) stretched between two rotatable support rolls 441a (441b) and 442a (442b), and the inside of the support roll 441a (441b) is cooled. The medium 444a (444b) is distributed. The cooling medium 444a (444b) is cooled to a temperature similar to the above-described predetermined surface temperature by a cooling means (not shown), and is used in a circulating manner. Accordingly, the cooling medium not only cools the support roll 441a (441b) but also cools the contact portion of the belt 443a (443b) with the support roll 441a (441b). As a result, the volatile matter is collected as precipitates 49 on the outer peripheral surface of the belt 443a (443b) at the contact portion.

  In the movable cooling device 44a (44b), the axial direction of the support roll is substantially parallel to the axial direction of the cooling roll 5, and the support roll in which the cooling medium is flowed is disposed in the vicinity of the lip portion. Installed. Although the movable cooling device 44a (44b) is installed on both sides of the discharged melt 42 in FIG. 3, the movable cooling device 44a (44b) is not limited to this and may be installed on either side. Preferably, it is installed on both sides of the discharge melt 42. The distance from the lip 41a (41b) and the discharge melt 42 of the movable cooling device 44a (44b) is not particularly limited as long as the object of the present invention is achieved, and is preferably a vertical cross section with respect to the axial direction of the cooling roll 5 The distance x from the lip portion 41a (41b) is 1 to 100 mm, and the distance y from the discharge melt 42 is 1 to 100 mm.

  The cooling medium 444a (444b) and its flow rate, and the cooling means (not shown) are the same as the cooling medium 432a (432b) and its flow rate and cooling means in the above-described fixed cooling device, respectively.

  Of the support rolls 441a (441b) and 442a (442b), at least the support roll 441a (441b) that can be rotated with a belt stretched and can circulate a cooling medium therein is used. As a constituent material of such a support roll, the same material as that of the pipe-like member 431a (431b) of the above-described fixed cooling device can be used, and the thickness (thickness), inner diameter and outer diameter, and axial direction of the support roll. Dimensions such as length are the same as those of the pipe-shaped member.

  The constituent material of the belt 443a (443b) is not particularly limited as long as the temperature of the cooling medium can be conducted to the outer peripheral surface. For example, a material having a relatively large specific heat of about 0.3 to 0.7 is preferably used. . Specific examples of such a material include a fluorine resin and an acrylic resin. The thickness of the belt is not particularly limited, and is preferably 1 to 5 mm. The length of the belt in the support roll axial direction is usually longer than the total length of the lip portions 41a and 41b in the same direction.

  When the movable cooling device is used, the precipitate collected on the outer peripheral surface of the belt can be conveyed by rotating the support roll, so that the precipitate can be easily cleaned.

  In the movable cooling device, as shown in FIG. 3, the deposit 49 can be more easily cleaned by providing the cleaning member 445 a (445 b).

  The cleaning member 445a (445b) is not particularly limited as long as the precipitate can be separated and removed from the belt surface. For example, the cleaning member 445a (445b) may have a rotatable brush roll shape as shown in FIG. Alternatively, it may have a blade shape. Usually, a storage tank 446a (446b) for storing the removed precipitate is further provided.

  When the cleaning member 445a (445b) is used, it is preferable to circulate the heating medium 447a (447b) inside the support roll 442a (442b). This facilitates separation / removal of the precipitate 49 from the belt surface. The heating medium 447a (447b) is heated and recirculated by a heating means (not shown). The heating medium not only heats the support roll 442a (442b), but also heats the contact portion of the belt 443a (443b) with the support roll 442a (442b). As a result, the precipitate 49 is separated and removed from the outer peripheral surface of the belt 443a (443b) at the contact portion.

  The temperature of the heating medium 447a (447b) is controlled to, for example, Tm + 5 to Tm + 50 ° C., preferably Tm + 10 to Tm + 30 ° C. Here, Tm is the melting point of the precipitate. The temperature of the heating medium is usually specifically 120 to 200 ° C, preferably 150 to 200 ° C. The heating medium is not particularly limited as long as such temperature control is possible. For example, water, silicone oil, or the like can be used. The flow rate of the heating medium is not particularly limited, and is preferably 1 to 100 L / min, for example.

  In the movable cooling device 44a (44b), the belt 443a (443b) and the cleaning member 445a (445b) may be continuously driven or periodically driven while the optical film manufacturing apparatus is driven. May be.

  The common items will be described below regardless of what kind of cooling device is used.

  The distance until the molten material is discharged from the lip portion of the casting die and comes into contact with the rotating roll is not particularly limited, and is, for example, 10 to 300 mm, preferably 50 to 150 mm.

  Preferred materials for the first cooling roll 5 and the touch roll 6 include carbon steel, stainless steel, resin, and the like. The surface accuracy is preferably increased, and the surface roughness is set to 0.3 S or less, more preferably 0.01 S or less. The touch roll 6 is preferably pressed against the first cooling roll 5 by pressing means. The linear pressure at which the touch roll 6 presses the film can be adjusted by a pneumatic piston or the like, and is preferably 0.1 to 100 kN / m, more preferably 1 to 50 kN / m.

  The surface temperature of the first cooling roll 5 and the touch roll 6 is not particularly limited. Usually, the first cooling roll 5 is 80 to 150 ° C., particularly 100 to 130 ° C., and the touch roll 6 is 80 to 150 ° C., particularly 100 to 100 ° C. The temperature is preferably set to 130 ° C.

  The first cooling roll 5 or the touch roll 6 can be made thin in diameter at both ends of the roll or have a flexible roll surface in order to improve the uniformity of adhesion with the film.

  The material constituting the optical film of the present invention contains at least a thermoplastic resin and usually contains a plasticizer. If necessary, a matting agent and a retardation control agent may be contained as a stabilizer, an ultraviolet absorber, and a slipping agent. These materials are appropriately selected depending on the required characteristics of the target optical film.

  As the thermoplastic resin, a resin conventionally used in the field of optical films can be used. For example, a cellulose resin is preferably used. The cellulose resin has a cellulose ester structure and is preferably a single or mixed acid ester of cellulose having at least one group selected from a fatty acid acyl group and a substituted or unsubstituted aromatic acyl group. is there.

  Specific examples of the cellulose resin include, for example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. Among these, particularly preferable cellulose resins include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate. A cellulose resin may be used individually by 1 type, or may be used in combination of 2 or more type.

  Cellulose acetate propionate and cellulose acetate butyrate which are mixed fatty acid esters have an acyl group having 2 to 4 carbon atoms as a substituent, the substitution degree of acetyl group is X, and the substitution degree of propionyl group or butyryl group When Y represents Y, those satisfying the following formulas (I) and (II) are preferable. The degree of substitution is defined as a numerical value indicating the number of hydroxyl groups substituted by an acyl group in glucose units.

Formula (I) 2.6 ≦ X + Y ≦ 3.0
Formula (II) 0 ≦ X ≦ 2.5

  In particular, cellulose acetate propionate is preferably used. Among them, 1.9 ≦ X ≦ 2.5 and 0.1 ≦ Y ≦ 0.9 are preferable. The portion not substituted with the acyl group usually exists as a hydroxyl group.

The cellulose resin can be synthesized by a known method.
The raw material cellulose of the cellulose resin used in the present invention may be wood pulp or cotton linter, and the wood pulp may be softwood or hardwood, but softwood is more preferable. A cotton linter is preferably used from the viewpoint of peelability during film formation. Cellulose resins made from these can be used in appropriate mixture or independently.

  The molecular weight of the cellulose resin is not particularly limited. For example, the number average molecular weight is preferably 60,000 to 200,000, particularly preferably 70,000 to 120,000.

  In order to remove foreign substances in the cellulose resin, the melt of the film constituent material can be filtered with the filter 2.

  As the material of the filter 2, conventionally known materials such as glass fibers, cellulose fibers, filter paper, and fluororesins such as tetrafluoroethylene resin are preferably used, and ceramics, metals and the like are particularly preferably used. The absolute filtration accuracy is 50 μm or less, preferably 30 μm or less, more preferably 10 μm or less, and still more preferably 5 μm or less. These can be used in combination as appropriate. The filter can be either a surface type or a depth type, but the depth type is preferable because it is relatively less clogged.

  Additives such as stabilizers, plasticizers, ultraviolet absorbers, matting agents, retardation control agents, etc., which may be contained in the film constituent materials, are those conventionally used as additives in the field of optical films. It can be used.

  The stabilizer suppresses generation of volatile components and deterioration of strength based on alteration or decomposition of the film constituent material. Examples of such stabilizers include hindered phenol antioxidants, acid scavengers, hindered amine light stabilizers, peroxide decomposers, radical scavengers, metal deactivators, amines, and the like.

As the hindered phenol antioxidant, for example, those described in columns 12-14 of US Pat. No. 4,839,405 can be used. Specific examples include 2,6-dialkylphenol derivative compounds.
Hindered phenol antioxidants are available, for example, from Ciba Specialty Chemicals under the trade names “Irganox 1076” and “Irganox 1010”.

  Examples of the acid scavenger include epoxy compounds described in US Pat. No. 4,137,201.

  Examples of hindered amine light stabilizers include those described in US Pat. No. 4,619,956, columns 5-11 and US Pat. No. 4,839,405, columns 3-5. Can be used. Specific examples include 2,2,6,6-tetraalkylpiperidine compounds, acid addition salts thereof, or complexes of these with metal compounds.

  The addition amount of the stabilizer is preferably 0.001% by weight or more and 5% by weight or less, more preferably 0.005% by weight or more and 3% by weight or less, and further preferably 0.01% by weight with respect to the thermoplastic resin. The content is 0.8% by weight or less. Two or more kinds of stabilizers may be used as a mixture, and in that case, the total amount thereof may be within the above range.

  The plasticizer is preferably used in terms of film modification such as improvement of mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability. Further, by adding a plasticizer, the melting temperature of the film constituent material can be lowered, or the melt viscosity of the film constituent material containing the plasticizer can be lowered at the same heating temperature as compared with the thermoplastic resin alone. it can.

  As the plasticizer, for example, phosphate ester derivatives and carboxylic acid ester derivatives are preferably used. Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of 500 to 10,000 described in JP-A-2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or cyclohexyl An acrylic polymer having a group in the side chain is also preferably used.

Examples of phosphate ester derivatives include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like.
Examples of carboxylic acid ester derivatives include phthalic acid esters and citric acid esters. Examples of the phthalic acid ester derivative include dimethyl phthalate, diethyl phthalate, dicyclohexyl phthalate, dioctyl phthalate, and diethyl hexyl phthalate. Citric acid esters include acetyl triethyl citrate and acetyl tributyl citrate.

  In addition, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, trimethylolpropane tribenzoate, and the like can also be mentioned. 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 Cholate, octyl phthalyl methyl glycolate, and an octyl phthalyl ethyl glycolate, and the like.

  The addition amount of the plasticizer is preferably 0.5% by weight or more and less than 20% by weight, more preferably 1% by weight or more and less than 11% by weight with respect to the thermoplastic resin. Two or more kinds of plasticizers may be used in combination, and in that case, the total amount thereof may be within the above range.

  The ultraviolet absorber is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the polarizer and the display device with respect to ultraviolet rays, and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. Those are preferred. Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Less benzotriazole compounds are preferred. Moreover, you may use the ultraviolet absorber of Unexamined-Japanese-Patent No. 10-182621, Unexamined-Japanese-Patent No. 8-337574, and the polymeric ultraviolet absorber of Unexamined-Japanese-Patent No. 6-148430.

  Ultraviolet absorbers are available, for example, as commercially available TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals).

  The addition amount of the ultraviolet absorber is 0.1 to 20% by weight, preferably 0.5 to 10% by weight, and more preferably 1 to 5% by weight with respect to the thermoplastic resin. Two or more kinds of ultraviolet absorbers may be used in combination, and in that case, the total amount thereof may be within the above range.

  The matting agent improves the slipperiness, transportability, winding property and strength of the film. The matting agent is preferably as fine as possible. Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include inorganic fine particles such as magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because it can reduce the haze of the film. In many cases, fine particles such as silicon dioxide are surface-treated with an organic material, but such a material is preferable because it can reduce the haze of the film.

  Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazane, siloxane and the like. The larger the average particle size of the fine particles, the greater the sliding effect, and the smaller the average particle size, the better the transparency. The average particle size of the secondary particles of the fine particles is in the range of 0.005 to 1.0 μm. The average particle size of the secondary particles of preferable fine particles is 5 to 50 nm, more preferably 7 to 14 nm. These fine particles are preferably used for generating irregularities of 0.01 to 1.0 μm on the film surface. The content of the fine particles is preferably 0.005 to 0.3% by weight with respect to the thermoplastic resin.

  Examples of the fine particles of silicon dioxide include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600, etc. manufactured by Nippon Aerosil Co., preferably Aerosil 200V, R972, R972V, R974, R202, and R812. Two or more kinds of these fine particles may be used in combination.

  It is preferable that the matting agent is added before the film constituent material is melted or is previously contained in the film constituent material. For example, after mixing and dispersing fine particles previously dispersed in a solvent and cellulose resin and / or other additives such as a plasticizer and an ultraviolet absorber, the solvent is volatilized or the matting agent is preliminarily formed into a film by a precipitation method. Included in the material. By using such a film constituent material, the matting agent can be uniformly dispersed in the thermoplastic resin.

  The retardation control agent is preferably used particularly as an optical film, for example, when producing a retardation film. As the retardation control agent, an aromatic compound having two or more aromatic rings as described in European Patent No. 911,656A2 can be used. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. Particularly preferred is an aromatic heterocycle, and the aromatic heterocycle is generally an unsaturated heterocycle. Of these, a 1,3,5-triazine ring is particularly preferred.

  When a stabilizer, a plasticizer, and the above-mentioned other additives are added to the thermoplastic resin, the total amount of additives including them is 1% by weight or more and 30% by weight or less, preferably 5 to 5%. 20% by weight.

  As the film constituent material, a polymer material other than cellulose resin or an oligomer may be appropriately selected and mixed. Such a polymer material or oligomer preferably has excellent compatibility with the cellulose resin, and the transmittance is 80% or more, preferably 90% or more, more preferably over the entire visible region (400 nm to 800 nm) when formed into a film. Is 92% or more. The purpose of mixing at least one of polymer materials and oligomers other than the cellulose resin includes meanings for viscosity control at the time of heating and melting and for improving film physical properties after film processing.

  In the present invention, it is preferable to mix the thermoplastic resin and other additives such as a stabilizer added as necessary before melting. Mixing may be performed by a mixer or the like, or may be mixed in the cellulose resin preparation process as described above. When a mixer is used, a general mixer such as a V-type mixer, a conical screw type mixer, a horizontal cylindrical type mixer, or the like can be used.

  After mixing the film constituent materials, the mixture may be directly melted using the extruder 1 to form a film, but once the film constituent materials are pelletized, the pellets are melted by the extruder 1 Then, the film may be formed. When the film constituent material includes a plurality of materials having different melting points, a so-called braided semi-melt is once produced at a temperature at which only the material having a low melting point is melted, and the semi-melt is supplied to the extruder 1. It is also possible to form a film by introducing it. If the film component contains a material that is easily pyrolyzed, in order to reduce the number of times of melting, a method of directly forming a film without producing pellets, or after making a paste-like semi-molten material as described above A method of forming a film is preferred.

  The melt extrusion by the extruder 1 can be performed under the same conditions as those used for other thermoplastic resins such as polyester. The material is preferably dried beforehand. It is desirable to dry the moisture to 1000 ppm or less, preferably 200 ppm or less, using a vacuum or reduced pressure dryer or a dehumidifying hot air dryer. For example, a thermoplastic resin dried under hot air, vacuum, or reduced pressure is melted at an extrusion temperature of about 200 to 300 ° C. using the extruder 1, and filtered through a leaf disk type filter 2 to remove foreign matters.

When introducing into the extruder 1 from a supply hopper (not shown), it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere.
When additives such as a plasticizer are not mixed in advance, they may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer 3.

  As the extruder 1, what is generally available as a plastic extruder is used, and various extruders available on the market can be used. However, a melt-kneading extruder is preferable, and a single-screw extruder or a twin-screw extruder is also used. An extruder may be used. When forming a film directly without producing pellets from film constituent materials, it is preferable to use a twin-screw extruder because an appropriate degree of kneading is required. However, even with a single-screw extruder, the screw shape is a Maddock type. By changing to a kneading type screw such as a unimelt type or a dull mage, moderate kneading can be obtained, so that it can be used. When a pellet or braided semi-melt is once used as a film constituent material, it can be used in either a single screw extruder or a twin screw extruder. In the extruder, it is preferable to lower the oxygen concentration by replacing with an inert gas such as nitrogen gas or by reducing the pressure.

  Although the preferable conditions for the melting temperature of the film constituent material in the extruder 1 vary depending on the viscosity and discharge amount of the film constituent material, the thickness of the sheet to be manufactured, etc., in general, with respect to the glass transition temperature (Tg) of the film Tg or more and Tg + 100 ° C. or less, preferably Tg + 10 ° C. or more and Tg + 90 ° C. or less. The melt viscosity at the time of extrusion is 10 to 100,000 poise, preferably 100 to 10,000 poise. The residence time of the film constituent material in the extruder 1 is preferably shorter, and is within 5 minutes, preferably within 3 minutes, more preferably within 2 minutes. Although the residence time depends on the type of the extruder 1 and the extrusion conditions, it can be shortened by adjusting the material supply amount, L / D, screw rotation speed, screw groove depth, etc. It is.

  The shape, rotation speed, and the like of the screw of the extruder 1 are appropriately selected depending on the viscosity, the discharge amount, and the like of the film constituent material. In the present invention, the shear rate in the extruder 1 is 1 / second to 10000 / second, preferably 5 / second to 1000 / second, more preferably 10 / second to 100 / second.

  The film constituent material extruded from the extruder 1 is sent to the casting die 4 and extruded from the casting die 4 into a film shape.

The casting die 4 to which the melt discharged from the extruder 1 is supplied is not particularly limited as long as it is used for producing a sheet or a film. The material of the casting die 4 is sprayed or plated with hard chromium, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide), etc. Processing includes buffing, lapping using a # 1000 or higher whetstone, flat cutting using a # 1000 or higher diamond whetstone (the cutting direction is perpendicular to the resin flow direction), electrolytic polishing, and electrolytic composite polishing. And so on.
A preferred material for the lip portion of the casting die 4 is the same as that of the casting die 4.

  The film-like melt pressed by the pair of rotary rolls 5 and 6 is further cooled and solidified while being sequentially circumscribed and conveyed to the second cooling roll 7 and the third cooling roll 8, and the unstretched film 10 is formed. can get.

(Stretching and winding process)
In this step, the unstretched film 10 peeled off from the third cooling roll 8 by the peeling roll 9 is guided to a stretching machine 12 through a dancer roll (film tension adjusting roll) 11, where the film 10 is stretched and then wound. Winding is performed by the take-up device 16. The molecules in the film are oriented by stretching.

  In the stretching process, stretching in the width direction of the film is usually performed. Not only the width direction but also the conveyance direction (also referred to as the longitudinal direction or MD direction) can be stretched.

  As a method of stretching the film in the width direction, a known tenter or the like can be preferably used. In particular, it is preferable to set the stretching direction to the width direction because lamination with the polarizing film can be performed in a roll form. By stretching in the width direction, the slow axis of the optical film obtained in the present invention is in the width direction.

  The stretching in the conveying direction is preferably performed in one or more longitudinal stages via one or a plurality of roll groups and / or a heating device such as an infrared heater. When extending | stretching to both the conveyance direction and the width direction, extending | stretching can be performed sequentially or simultaneously, for example with respect to the conveyance direction and the width direction of a film. Assuming that the glass transition temperature of the film of the present invention is Tg, a film stretched in the conveying direction within a temperature range of (Tg-30) ° C. or more and (Tg + 100) ° C. is (Tg-20) ° C. or more and (Tg + 20) ° C. It is preferable to stretch in the width direction within the following temperature range and then heat-set.

  The draw ratio in the biaxial direction is preferably in the range of 1.0 to 2.0 times in the transport direction and 1.01 to 2.5 times in the width direction, respectively. It is more preferable to obtain a retardation value required to be performed in a range of 01 to 1.5 times and 1.05 to 2.0 times in the width direction.

  In the stretching step, a known heat setting treatment, cooling treatment and relaxation treatment may be performed, and it may be appropriately adjusted so as to have the characteristics required for the target optical film.

  After stretching, after slitting the edge of the film to a product width by the slitter 13, the film is subjected to knurling (embossing) on both ends of the film by a knurling device comprising an embossing ring 14 and a back roll 15. By winding with the winder 16, sticking in the optical film (original winding) F and generation of scratches are prevented. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing. In addition, since the grip part of the clip of the both ends of a film is deform | transforming normally and cannot be used as a film product, it is cut out and reused as a raw material.

[Optical film]
In the optical film obtained in the present invention, thickness unevenness in the width direction and the conveyance direction is sufficiently prevented.
For example, for the unstretched film 10 obtained immediately before the stretching step, the film thickness variation in the width direction and the transport direction is within ± 1.5%, preferably within ± 1.0%, more than the average film thickness. Preferably, it is within ± 0.5%. Film thickness fluctuations are measured with an online film thickness meter at 10 points in the width direction every 1 m in the transport direction (total of 500 points), and expressed as a ratio of the maximum fluctuation width to the average film thickness. It is a thing. “Average film thickness” means the average value of all measured values.

  The thickness of the optical film obtained in the present invention may be appropriately selected depending on the application. For example, when the optical film of the present invention is used as a retardation film or a polarizing plate protective film, the thickness is preferably 10 to 500 μm after drying. In particular, the lower limit is 20 μm or more, preferably 35 μm or more. The upper limit is 150 μm or less, preferably 120 μm or less. A particularly preferable range is 25 to 90 μm.

  The Tg of the optical film is not particularly limited. However, when the optical film is used as a retardation film or a polarizing plate protective film, the Tg after drying is used from the viewpoint of preventing change in the molecular orientation state in the use environment. Is 120 ° C. or higher, preferably 135 ° C. or higher. From the viewpoint of reducing energy consumption during film production and preventing coloration, Tg is preferably 250 ° C. or lower. The Tg of the film can be controlled by changing the material type constituting the film and the ratio of the constituting material.

  The optical film according to the present invention is useful as a functional film used in various displays such as a liquid crystal display, a plasma display, and an organic EL display, particularly a liquid crystal display. Among them, a polarizing plate protective film, a retardation film, and an antireflection film are used. It is particularly suitable as a film, a brightness enhancement film, an optical compensation film for expanding the viewing angle, and the like.

  When using the optical film of this invention as a functional film of a liquid crystal display, the liquid crystal display element of a structure as shown in FIG. 4 can be manufactured, for example.

  In FIG. 4, 21a and 21b are protective films, 22a and 22b are retardation films, 25a and 25b are polarizers, 23a and 23b are slow axis directions of the film, 24a and 24b are transmission axis directions of the polarizer, and 27 is A liquid crystal cell 29 is a liquid crystal display device. Reference numerals 26a and 26b denote polarizing plates, which include a protective film, a retardation film, and a polarizer.

  In such a liquid crystal display element, the optical film of the present invention may be used as the protective films 21a and 21b, or may be used as the retardation films 22a and 22b.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
<Example 1>
(Pellet creation)
100 parts by mass of cellulose acetate propionate (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, number average molecular weight 75000, dried at 100 ° C. for 5 hours, glass transition temperature Tg ₁ = 136 ° C.)
Trimethylolpropane tris (3,4,5-trimethoxybenzoate)
10 parts by mass IRGANOX-1010 (manufactured by Ciba Specialty Chemicals) 1 part by mass Sumitizer GP (manufactured by Sumitomo Chemical) 1 part by mass

  To the above material, 0.05 part by mass of silica particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.)) as a matting agent and 0.5 part by mass of TINUVIN 360 (produced by Ciba Specialty Chemicals) as an ultraviolet absorber are added, and nitrogen gas is added. After mixing for 30 minutes in a V-type mixer containing bismuth, it was melted at 240 ° C. using a twin-screw extruder (PCM30, Ikegai Co., Ltd.) equipped with a strand die, and a cylindrical shape with a length of 4 mm and a diameter of 3 mm A pellet was prepared. The shear rate at this time was set to 25 (/ s).

(Film production)
The film was manufactured with the manufacturing apparatus shown in FIGS.

The apparatus conditions will be specifically described below.
Cooling devices 43a, 43b (FIG. 2); surface temperature 5 ° C., distance 10 mm from lip portions 41a, 41b, distance 10 mm from discharge melt 42.
Pipe-shaped members 431a and 431b; stainless steel, thickness (wall thickness) 2 mm, inner diameter 10 mm, outer diameter 14 mm.
Cooling media 432a and 432b; water was used and controlled to the same temperature as the surface temperature. Flow rate 10 L / min.

A casting die having a lip clearance of 1.0 mm and an average surface roughness Ra of 0.01 μm was used. The temperature of the lip portion of the casting die was controlled at 250 ° C. Silica fine particles were added as a slip agent from the hopper opening in the middle of the extruder so as to be 0.1 part by mass.
The first cooling roll and the second cooling roll were made of stainless steel having a diameter of 40 cm, and the surface was hard chrome plated. In addition, temperature adjusting oil (cooling fluid) was circulated inside to control the roll surface temperature.
The elastic touch roll had a diameter of 30 cm, the inner cylinder and the outer cylinder were made of stainless steel, and the outer cylinder surface was hard chrome plated. The wall thickness of the outer cylinder is 2 mm, and the surface temperature of the elastic touch roll is controlled by circulating temperature adjusting oil (cooling fluid) in the space between the inner cylinder and the outer cylinder. The surface temperature of the first cooling roll was 100 ° C., and the surface temperature of the second cooling roll was 30 ° C. The surface temperature of each roll of the elastic touch roll, the first cooling roll, and the second cooling roll is determined by measuring the temperature of the roll surface at a position 90 ° before the rotation direction from the position where the film first contacts the roll. The average value obtained by measuring 10 points in the width direction using was used as the surface temperature of each roll.
The film forming speed was 20 m / min.
After the melt was discharged from the lip portion of the casting die, the distance until it contacted the rotating roll was 100 mm.

The operation method will be specifically described below.
The obtained pellets (water content 50 ppm) were melted in a single screw extruder and subjected to pressure filtration using a leaf disk type metal filter. The film-like melt was directly extruded and pressed between the first cooling roll and the touch roll from the lip portion of the casting die to obtain a cast film having a draw ratio of 10 and a film thickness of 100 μm.

At the time of pressing, the film was pressed on the first cooling roll with an elastic touch roll having a 2 mm thick metal surface at a linear pressure of 10 kg / cm.
The film temperature on the touch roll side during pressing was 180 ° C. ± 1 ° C. The film temperature on the touch roll side at the time of pressing here is a state in which there is no touch roll when the touch roll on the first cooling roll is in contact with the touch roll using a non-contact thermometer. The average value of the film surface temperature measured 10 points in the width direction from a position 50 cm away. The glass transition temperature Tg of this film was 136 ° C. Tg measured the glass transition temperature of the film extruded from the die by DSC method (in nitrogen, temperature rising temperature 10 ° C./min) using “DSC6200” manufactured by Seiko Co., Ltd.

  The obtained film is introduced into a tenter having a preheating zone, a stretching zone, a holding zone, and a cooling zone (there is also a neutral zone for ensuring thermal insulation between the zones), and 160 ° C. in the width direction. After stretching 1.3 times, cool down to 70 ° C while relaxing 2% in the width direction, and then release from the clip. And a film F-1 having a thickness of 80 μm slit to a width of 1430 mm was obtained. At this time, the preheating temperature and the holding temperature were adjusted to prevent the bowing phenomenon due to stretching.

<Example 2>
A film was produced in the same manner as in Example 1 except that the following apparatus conditions were employed.
Cooling devices 43a and 43b (FIG. 2); surface temperature 5 ° C., distance 30 mm from lip portions 41a and 41b, distance 30 mm from discharge melt 42.

<Comparative Example 1>
A film was produced in the same manner as in Example 1 except that the volatiles were sucked and exhausted using the suction devices 104a and 104b shown in FIG. 5 without using the cooling devices 43a and 43b.
Suction devices 104a and 104b (FIG. 5); Suction speed 180 L / min. The distance from the lip portions 41 a and 41 b is 10 mm, and the distance from the discharge melt 42 is 10 mm.

<Comparative Example 2>
A film was produced in the same manner as in Comparative Example 1 except that the following apparatus conditions were employed.
Suction devices 104a and 104b (FIG. 5); Suction speed 180 L / min. The distance from the lip portions 41a and 41b is 30 mm, and the distance from the discharge melt 42 is 30 mm.

<Example 3>
A film was produced in the same manner as in Example 1 except that the touch roll 6 was not used.

<Example 4>
A film was produced in the same manner as in Example 2 except that the touch roll 6 was not used.

<Comparative Example 3>
A film was produced in the same manner as in Comparative Example 1 except that the touch roll 6 was not used.

<Comparative example 4>
A film was produced in the same manner as in Comparative Example 2 except that the touch roll 6 was not used.

<Example 5>
A film was produced in the same manner as in Example 1 except that the following apparatus conditions were adopted using the production apparatus shown in FIGS.
Cooling devices 44a, 44b (FIG. 3); distance 10 mm from lip portions 41a, 41b, distance 10mm from discharge melt 42.
Support rolls 441a, 441b, 442a, 442b; stainless steel, thickness (thickness) 2 mm, inner diameter 10 mm, outer diameter 14 mm.
Cooling media 444a and 444b; water was used and the temperature was controlled at 5 ° C. Flow rate 10 L / min.
Heating media 447a and 447b; silicone oil was used and controlled at 150 ° C. Flow rate 10 L / min.
Belts 443a and 443b (glass cloth coated with fluororesin). Conveyance speed 5m / min.
Cleaning members 445a and 445b; nylon brush rollers. The peripheral speed is 5m / min.
The belts 443a and 443b and the cleaning members 445a and 445b were continuously driven at the above speed during driving of the optical film manufacturing apparatus.

<Comparative Example 5>
A film was produced in the same manner as in Example 1 except that the cooling devices 44a and 44b were not used.

<Evaluation>
An optical film was continuously produced by the above method for 6 hours.

-Film thickness fluctuation | variation The film thickness fluctuation | variation of the width direction and conveyance direction of the unstretched film obtained just before the extending process was evaluated. The film thickness variation was expressed as a ratio of the maximum variation width to the average film thickness based on the value measured by the above-described method using an online film thickness meter (Z5FM-200B; manufactured by OMRON). Within ± 1.5% of the film thickness variation, “acceptable (accepted)” was set, “good” was set within ± 1.0%, and “excellent” was set within 0.5%.

-Die line The unstretched film obtained immediately before the stretching process was visually observed over the entire length in the transport direction, and the die line as a surface defect caused by the deposit on the lip portion of the casting die was evaluated.
None; no die line occurred;
Existence: Die line was generated and there was a problem in practical use.

It is a schematic block diagram of an example of the apparatus which enforces the manufacturing method of the optical film which concerns on this invention. It is a principal part enlarged view of one Embodiment from the casting die in FIG. 1 to a cooling roll. It is a principal part enlarged view of one Embodiment from the casting die in FIG. 1 to a cooling roll. It is a disassembled perspective view which shows the outline of the block diagram of a liquid crystal display device. It is a principal part enlarged view from the casting die in a prior art to a cooling roll.

Explanation of symbols

  1: Extruder, 2: Filter, 3: Static mixer, 4: Casting die, 5: First cooling roll, 6: Touch roll, 7: Second cooling roll, 8: Third cooling roll, 9:11 : 13:14:15: Conveying roll, 10: Unstretched film, 12: Stretching machine, 16: Winding device, 21a: 21b: Protective film, 22a: 22b: Retardation film, 23a: 23b: Slow phase of film Axis direction, 24a: 24b: Transmission axis direction of polarizer, 25a: 25b: Polarizer, 26a: 26b: Polarizing plate, 27: Liquid crystal cell, 29: Liquid crystal display device, 41a: 41b: Lip part, 42: Melt 43a: 43b: cooling device, 44a: 44b: cooling device, 47: opposite part, 49: precipitate, 431a: 431b: pipe-like member, 432a: 432b: cooling medium, 441a: 441b: 4 2a: 442b: support roll, 443a: 443b: belt, 444a: 444b: cooling medium, 445a: 445b: cleaning member, 446a: 446b: storage tank, 447a: 447b: heating medium, 104a: 104b: suction means (suction device) ).

Claims (8)

A method for producing an optical film by discharging a film-constituting material containing a molten thermoplastic resin from a lip portion of a casting die onto a cooling roll in the form of a film, and cooling and solidifying the film.
A method for producing an optical film, comprising: collecting and recovering volatiles volatilized from a melt on the surface of a cooling device whose surface temperature is kept below the boiling point of the volatiles. The boiling point of the volatiles is Tb (° C.)
The manufacturing method of the optical film of Claim 1 whose surface temperature of a cooling device is Tb-5-Tb-120 (degreeC).   The method for producing an optical film according to claim 1, wherein the discharged film-like melt is pressed on a cooling roll by a touch roll.   An optical film manufactured by the manufacturing method according to claim 1. An apparatus for producing an optical film by discharging a film constituent material containing a molten thermoplastic resin from a lip portion of a casting die onto a cooling roll in the form of a film and cooling and solidifying,
A cooling device in which the surface temperature is kept below the boiling point of the volatiles volatilized from the melt,
An apparatus for producing an optical film, wherein volatiles are deposited on the surface of the cooling device and collected.   The optical film manufacturing apparatus according to claim 5, wherein the cooling device is disposed in the vicinity of the lip portion.   The apparatus for producing an optical film according to claim 5 or 6, wherein the cooling device circulates a cooling medium whose temperature is controlled below the boiling point of the volatile matter inside the pipe-shaped member.   A cooling device has a belt stretched around at least two rotatable support rolls, and a cooling medium whose temperature is controlled below the boiling point of volatile substances is circulated inside at least one of the support rolls. The apparatus for producing an optical film according to claim 5 or 6.

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