JP2006069049A - Method for producing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film by a solution casting method which can prevent the occurrence of bubbles even without using a special method such as carbon dioxide gas displacement so that the optical film almost free from the occurrence of a bubble failure and excellent in appearance quality can be produced. <P>SOLUTION: In the method for producing the optical film, a resin and a solvent are mixed/agitated to prepare a resin solution, the solution is cast from a casting die on a support, and the cast film is peeled off from the support and dried. The temperature of the solvent when it is mixed is adjusted at a temperature lower by at least 10°C than the boiling point of the solvent. After the mixing and before the casting on the support, the temperature of the solution, after being raised temporarily to the boiling point of the solvent or above, is kept at a temperature below the boiling point. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a resin film by a solution casting method. In particular, the present invention relates to a method for producing an optical film free from bubble failure.

  In general, an optical film such as a polarizing plate protective film or a retardation film used for a liquid crystal display device or the like is formed by a solution casting method because of excellent flatness.

  The solution casting method is a manufacturing method in which a resin is dissolved in a solvent, cast on a support, and the solvent is evaporated to separate. However, in this method, when the resin and the solvent are stirred and mixed, air is taken into the resin solution to generate fine bubbles, and foaming occurs when the resin solution cast on the support is dried. was there.

In the past, removal of bubbles in resin solutions has been carried out, but due to the increase in size and definition of liquid crystal display devices, high quality is also required for optical films, which highly prevent foaming. A method was desired. Various methods for defoaming a solution using an organic solvent as a solvent have been proposed mainly for low-viscosity solutions for coating. For example, the following patent documents are known.
Japanese Patent Application Laid-Open No. 7-289983 discloses a method for stably applying an organic solvent-based coating solution in a thin layer to a multilayer and thin film material such as a photographic film. Describes a vacuum degassing method in which a coating solution containing an organic solvent as a main solvent is degassed under reduced pressure. Japanese Patent Laid-Open No. 1-224077 discloses a liquid coating composition (coating liquid) on a long flexible support (referred to as a web) that runs continuously in the production of photographic photosensitive materials such as photographic film and photographic paper. ) Is disclosed, and the coating method uses a porous polymer film. JP-A-11-47508 discloses a defoaming method for removing bubbles in a liquid from a bubble-containing liquid containing bubbles. Various recording material coating liquids such as photographic photosensitive materials are stirred and mixed at the time of preparation, and thus contain a large amount of bubbles in the liquid, but if used as they are, pinholes and streaky irregularities can be formed on the coating film. End up. For this reason, the coating liquid is used after removing bubbles in the liquid. Patent Document 3 describes a method in which a coating liquid is degassed under reduced pressure and further passed through a filter medium. JP-A-9-76257 discloses a method for producing a resin film by a solution casting method (solution casting film forming method). A method for removing bubbles in a resin solution by a solution casting method Describes a method of mixing and stirring a resin and a solvent in an atmosphere of carbon dioxide gas. Japanese Patent Laid-Open No. 2003-200445 discloses a solution casting method capable of obtaining a film having good flatness that does not generate pinholes and the like. Specifically, the amount of dissolved air is less than a predetermined value. A solution casting film-forming method using a high-concentration cellulose acylate solution is disclosed. In the solution-casting film-forming method according to Patent Document 5, a high-concentration cellulose acylate before casting on a casting support is disclosed. By degassing the solution to 90% or less of the amount of saturated dissolved air under 1 atmosphere, bubbles are prevented from being generated during casting.

  However, the method of applying an organic solvent-based coating solution disclosed in Patent Documents 1 to 3 has not been effective for a solution having a high solution viscosity, such as a resin solution used in a solution casting method.

  On the other hand, in the method of removing bubbles in the resin solution in the solution casting method disclosed in Patent Document 4, there is a problem that the cost of carbon dioxide gas or recovery equipment is required. In the case of a resin solution with a high viscosity as in the disclosed solution casting method, it is difficult to sufficiently deaerate in a short time. Rather, there is an effect of side effects such as a change in the concentration of the resin solution or the formation of a dry film. There was a problem of being big.

  An object of the present invention is to solve the above-described problems of the prior art and to provide a method for producing an optical film which does not cause foaming without using a special method such as carbon dioxide replacement.

  In order to achieve the above object, an optical film manufacturing method according to the invention of claim 1 is a method of preparing a resin solution by stirring and mixing a resin and a solvent, and flowing the resin solution from a casting die onto a support. In a method for producing an optical film in which the cast film is peeled off from the support and dried, the temperature of the solvent at the time of mixing is 10 ° C. or more lower than the boiling point of the solvent.

  The method for producing an optical film according to the invention of claim 2 is the method for producing an optical film according to claim 1, wherein the resin solution and the solvent are stirred and mixed until the resin solution is cast on a support. Thus, the resin solution is once brought to a temperature not lower than the boiling point of the solvent after being brought to a temperature not lower than the boiling point of the solvent.

  The method for producing an optical film according to the invention of claim 3 is the method for producing an optical film according to claim 1, wherein the resin is a powder excluding gas.

  An optical film manufacturing method according to a fourth aspect of the present invention is the optical film manufacturing method according to the first aspect, wherein the concentration of the solvent vapor, carbon dioxide gas or helium in the atmosphere of the container for adjusting the resin solution is 80 volumes. % Or more.

  An optical film manufacturing method according to the invention of claim 5 is the optical film manufacturing method according to claim 1, wherein the solvent is a solvent containing 60% by weight or more of methylene chloride or methyl acetate. .

  The method for producing an optical film according to the invention of claim 6 is the method for producing an optical film according to claim 1, wherein the resin is a cellulose ester.

  The method for producing an optical film according to the invention of claim 7 is the method for producing an optical film according to claim 1, wherein the solvent contains 60% by weight or more of methylene chloride, and the temperature of the solvent at the time of mixing. Is 0 to 25 ° C.

  The method for producing an optical film according to the invention of claim 8 is the method for producing an optical film according to claim 1, wherein the temperature of the resin solution during casting is at least 5 ° C. higher than the temperature of the solvent during mixing. It is characterized by being less than the boiling point of the solvent.

  The present invention relates to a method for producing an optical film by a solution casting method. In preparing a resin solution by stirring and mixing a resin and a solvent, the temperature of the solvent at the time of mixing is 10 ° C. or more lower than the boiling point of the solvent. Therefore, by lowering the temperature of the solvent when mixing in this way, the amount of dissolved air brought into the solvent can be reduced, and the permeability to the resin is further improved. Generation of bubbles in the optical film can be prevented by the combined effect of reducing air left inside. Therefore, according to the present invention, the occurrence of bubble failure can be prevented without depending on a special method, and an optical film having a high appearance quality can be provided. This optical film has the effect that it can be used for optical films that require high quality, such as polarizing plate protective films and retardation films.

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

  The polymer used in the method for producing an optical film of the present invention is not particularly limited as long as it can be formed by a solution casting method. Examples thereof include polycarbonate, alicyclic structure-containing polymer, polyvinyl alcohol, polyamide, polyimide, cellulose ester and the like. In particular, alicyclic structure-containing polymers and cellulose esters are characterized by a small photoelastic coefficient, and can be preferably used for optical films. The alicyclic structure-containing polymer is a polymer having an alicyclic structure in the repeating unit, and the alicyclic structure may be in either the main chain or the side chain. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, but a cycloalkane structure is preferable because of excellent thermal stability.

  The alicyclic structure-containing polymer is a monomer containing a norbornene ring structure, a monocyclic olefin, a cyclic conjugated diene, a vinyl aromatic compound, a vinyl alicyclic hydrocarbon compound, or the like, such as metathesis ring-opening polymerization or addition polymerization. It can superpose | polymerize by a well-known polymerization method and can obtain by hydrogenating a carbon-carbon unsaturated bond as needed.

  The alicyclic structure-containing polymer used in the present invention has a polyisoprene or polystyrene equivalent weight average molecular weight (Mw) of 25 measured by gel permeation chromatography of a cyclohexane solution (or a toluene solution when the polymer is not dissolved). 5,000 to 50,000, more preferably 30,000 to 45,000. The molecular weight distribution (Mw / Mn) is preferably 1.2 to 3.5, more preferably 1.5 to 3.0. The glass transition temperature (Tg) is preferably 80 to 170 ° C. By setting the characteristics of the alicyclic structure-containing polymer within the above range, good heat resistance and moldability can be obtained.

  As the cellulose ester, cellulose diacetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate are preferable. The degree of substitution of the acetyl group of the cellulose ester is preferably at least 1.5 or more because the resulting film has excellent dimensional stability. As a measuring method of the substitution degree of the acyl group of a cellulose ester, it can implement according to ASTM-D-817-91. The molecular weight of the cellulose ester is preferably 50,000 to 300,000, particularly 60,000 to 200,000 as the number average molecular weight because the mechanical strength of the resulting film can be increased.

  The method for synthesizing the cellulose ester is not particularly limited. For example, cellulose such as linter pulp, wood pulp, and kenaf pulp is used, and an acid corresponding to an ester such as acetic anhydride, propionic anhydride or butyric anhydride is reacted with cellulose by a conventional method. Can be obtained. The synthesized cellulose ester is used in the form of flakes, powders, chips or pellets, but the handleability and solubility can be improved by forming the particle size to a size of 0.1 to 5.0 mm. Therefore, it is preferable.

  The optical film of the present invention may contain additives such as a plasticizer, an ultraviolet absorber, an antioxidant, and a matting agent for various purposes. Examples of the plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixyl phosphate, arylene bis (diaryl phosphate) Phosphate ester plasticizers such as esters, tricresyl phosphate, phthalate plasticizers such as diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate and di-2-ethylhexyl phthalate, triacetin, tributyrin, butyl Phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycol Glycolate ester plasticizers such as butyl phthalyl butyl glycolate, citric acid plasticizers such as tributyl acetyl citrate, dipropylene glycol benzoate, tripropylene glycol dibenzoate, 1,3-dibutylene glycol dibenzoate, Examples include polyhydric alcohol ester plasticizers such as tetraethylene glycol dibenzoate, trimethylolpropane triacetate, and trimethylolpropane tribenzoate, and trimellitic acid tris (2-ethylhexyl). You may use together 2 or more types of plasticizers among the above as needed.

  By adding these plasticizers, the moisture content of the film can be lowered and the water barrier property can be improved. The amount of plasticizer added to the film weight is preferably 0.5 to 30%, particularly preferably 2 to 15%.

  In addition, it is preferable to contain an ultraviolet absorber in the optical film, and as the ultraviolet absorber, a wavelength of 400 nm or more is preferable from the viewpoint of excellent liquid crystal display property and excellent absorption of ultraviolet rays having a wavelength of 370 nm or less for preventing deterioration of the liquid crystal. Those that absorb as little visible light as possible are preferred. In particular, the transmittance at a wavelength of 370 nm needs to be 10% or less, preferably 5% or less, more preferably 2% or less. Specific examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Triazole compounds are preferred. Preferred commercially available UV absorbers based on benzotriazole include Tinuvin 109, Tinuvin 171, Tinuvin 326, Tinuvin 327, Tinuvin 328 and the like manufactured by Ciba Specialty Chemicals Co., Ltd. Two or more kinds of ultraviolet absorbers may be used. The ultraviolet absorber may be added to the dope after the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, methyl acetate, and dioxolane, or may be added directly into the dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and the resin to be dispersed, and then added to the dope. The usage-amount of a ultraviolet absorber can be added at 0.5-20% with respect to a film weight, 0.6-5.0% is preferable and 0.6-2.0% is especially preferable.

  It is preferable to contain an antioxidant in the optical film. As the antioxidant, hindered phenol compounds are suitable. Specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [ 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadec -3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy Benzyl) benzene and tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and 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. The amount of these compounds added is preferably 1 ppm to 1.0%, particularly preferably 10 to 1000 ppm, based on the film weight.

  The optical film preferably contains a particulate matting agent. Specific examples of the particulate matting agent include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, and calcined silicic acid. Mention may be made of inorganic fine particles such as calcium, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Of these, silicon dioxide is preferable because it can reduce the haze of the film. The average particle size of the secondary particles of the fine particles is 0.01 to 1.0 μm, and the content is preferably 0.005 to 0.3% with respect to the film weight. In many cases, fine particles such as silicon dioxide are surface-treated with an organic substance, but such particles are preferable because they can reduce the haze of the film. Preferable organic substances in the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like. The larger the average particle size of the fine particles, the larger the mat effect, and on the contrary, the smaller the average particle size, the better the transparency. Therefore, the preferable average particle size of the primary particles is 5 to 50 nm, more preferably. 7 to 14 nm. The fine particles are usually present as aggregates in the cellulose ester film, and it is preferable to generate irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film. Preferable examples of commercially available silicon dioxide fine particles include AEROSIL 200, 200V, 300, R972, R972V, R974, R202, R812, OX50 and TT600 manufactured by Aerosil Co., Ltd., particularly preferably AEROSIL 200V, R972. , R972V, R974, R202 and R812. Two or more types of matting agents may be used in combination, and when two or more types of matting agents are used in combination, they can be mixed and used at an arbitrary ratio. At this time, matting agents having different average particle sizes and materials, for example, AEROSIL 200V and R972V can be used in a weight ratio of 0.1: 99.9 to 99.9 to 0.1.

  The film may contain a dye or the like. The amount of these compounds added is preferably 1 ppm to 1.0%, particularly preferably 10 to 1000 ppm, based on the film weight. In addition, an antistatic agent, a flame retardant, a lubricant and an oil agent may be added to the film. These additives may be added together with the resin and the solvent during the preparation of the resin solution, or may be added during or after the solution preparation.

  The solvent used in the present invention is not particularly limited as long as the drying load is small and the resin can be dissolved. For example, methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3 -Dioxolane, 4-methyl-1,3-dioxolane, 1,4-dioxane, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro- 2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2, 3,3,3-pentafluoro-1-propanol, nitroethane, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2- Midazorijinon, and methylene chloride and bromo propane. Of these, methyl acetate, acetone or methylene chloride, which has excellent solubility and a boiling point which is not too high, is preferred, and methylene chloride and methyl acetate are particularly preferred. In the method for producing an optical film according to the present invention, the solvent is preferably a solvent containing 60% by weight or more of methylene chloride or methyl acetate.

  Further, it is preferable that the solution contains a lower alcohol such as methanol, ethanol, and butanol because the solubility of the resin in an organic solvent can be improved and the viscosity of the solution can be reduced. Of these, ethanol having a low boiling point and low toxicity is preferable. The amount of the lower alcohol used for such a purpose is preferably 2 to 50%, more preferably 4 to 30%, based on the amount of the solvent.

  The present invention is characterized in that, when a resin solution is prepared by stirring and mixing a resin and a solvent, the temperature of the solvent at the time of mixing is at least 10 ° C. lower than the boiling point of the solvent. By lowering the temperature of the solvent during mixing in this way, the amount of dissolved air brought into the solvent can be reduced, and the permeability to the resin is further improved. As a result, the air left in the resin during dissolution It is considered that the generation of bubbles in the optical film can be prevented by the combined effect of the reduction of the thickness. More preferably, the solvent temperature is 15 ° C. or more lower than the boiling point of the solvent. The lower the temperature of the solvent, the better. However, if the temperature is too low, there is a practical problem such as an increase in the size of the cooling equipment, so it may be set appropriately in consideration of the effect. For example, when the solvent is methylene chloride A temperature of 0 ° C. to 25 ° C. is particularly preferable.

  In the method for producing an optical film according to the present invention, the solvent contains 60% by weight or more of methylene chloride, and the temperature of the solvent during mixing is preferably 0 ° C to 25 ° C.

  Moreover, the resin powder at the time of mixing is also preferable because the generation of bubbles in the optical film can be highly prevented by eliminating the gas in advance. Since the resin used in the solution casting method increases the dissolution rate, a powder form having an average flow diameter of about 0.1 to 5 mm is preferably used. The method for removing the gas from the resin is not particularly limited, but it can be performed by a method such as compression molding such as a roller compactor, or removal under reduced pressure or vacuum.

  After mixing the resin and the solvent, it is preferable from the viewpoint of preventing the generation of bubbles in the optical film, that the air in the atmosphere inside the adjustment kettle is removed. As a method of removing air, there is a method of replacing the air in the atmosphere by allowing the air in the adjustment kettle to escape and filling the atmosphere with solvent vapor. Substitution with helium or carbon dioxide gas is also effective in preventing the generation of bubbles in the optical film. In this case, it is preferable that the atmosphere concentration in the adjustment kettle of solvent vapor, helium, and carbon dioxide is 80% or more. Of course, complete substitution is most preferable.

  Next, the resin is dissolved in the solvent while stirring. As a method for dissolving the resin solution, a known method may be used, for example, a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, a method performed using the cooling dissolution method, In addition, there is a method performed at a high pressure as disclosed in JP-A-11-21379.

  In the present invention, when the resin is dissolved in the solvent while stirring, it is preferable that the resin solution is once brought to a temperature not lower than the boiling point of the solvent and then lower than the boiling point of the solvent. By doing in this way, it can prevent that the undissolved substance of resin remains, and can prevent generation | occurrence | production of the bubble in a resin solution. In addition, when a solvent is a mixed solvent, it means the boiling point of the main solvent. When the main solvent is methylene chloride (boiling point 39.95 ° C.), the resin solution is preferably heated once to 50 ° C. to 80 ° C. and then cooled to 20 ° C. to 39 ° C.

  After dissolution, the solution is filtered with a filter medium, allowed to stand, defoamed, and sent to the next step with a pump. The resin concentration in the solution is about 10 to 35%, preferably 15 to 25%.

The filter medium used for filtering the resin solution should preferably have a low absolute filtration accuracy. However, if the absolute filtration accuracy is too low, the filter medium is likely to be clogged, and the filter medium must be replaced frequently. There is a problem of reducing the sex. For this reason, the filter medium used for the solution preferably has an absolute filtration accuracy of 0.001 to 0.008 mm, and particularly preferably 0.003 to 0.006 mm. As the filter medium, ordinary ones can be used, but those made of plastic fibers such as polypropylene and Teflon (registered trademark) and those made of metal such as stainless steel fibers are preferable because they do not drop off. Filtration of the solution 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 a normal pressure and in a range where the solvent does not boil is a differential pressure before and after the filtration (hereinafter, , Which is called “filtering pressure”). A preferable temperature range is 45 to 120 ° C, more preferably 45 to 70 ° C, and particularly preferably 45 to 55 ° C. The filtration pressure is preferably 1.6 × 10 ⁶ Pa or less, more preferably 1.2 × 10 ⁶ Pa or less, and particularly preferably 1.0 × 10 ⁶ Pa or less.

  The resin solution thus adjusted is cast on a support such as a drive metal endless belt or drum. The temperature of the resin solution at the time of casting is preferably 5 ° C. or more higher than the solvent temperature to be mixed at the time of preparing the resin solution to a temperature lower than the boiling point of the solvent because it is possible to prevent generation of bubbles.

  As a method of casting the resin solution, a method of casting from an extrusion die using a quantitative gear pump is preferable because the film thickness is easily uniformed. The extrusion die includes a coat hanger die and a T die, and any of them can be preferably used. The extrusion die may be a single layer or a multilayer. Alternatively, two or more extrusion dies may be used for multi-layer casting. In order to adjust the film thickness, the solution concentration, pumping amount, slit gap of the die of the casting die, extrusion pressure of the casting die, and the moving speed of the support are controlled so as to obtain the desired thickness. Can be adjusted.

  Then, the solvent in the solution cast on the support is evaporated, and the film is peeled when it becomes peelable. Alternatively, the solution cast on the support is cooled to be gelled and peeled off. In order to evaporate the solvent, there are a method of sending warm air from the side where the solution is cast and the back side of the support, a method of heating with a heating liquid from the back side of the support, a method of heating by radiant heat, a method of combining these, etc. is there.

  The position where the film is peeled off from the support is called the peeling point, and the roll that assists peeling is called the peeling roll. The residual solvent amount of the film at the peeling point is usually 20 to 300%. The residual solvent amount is obtained by dividing the loss on drying when the sample is dried at 110 ° C. for 3 hours by the weight of the sample after drying.

  The film peeled from the support is dried while being transported by a plurality of transport rolls. If necessary, during or after drying, the film is stretched or shrunk using a tenter, a roll stretching machine, or the like in the lateral direction, the longitudinal direction, or an arbitrary oblique direction to obtain an optical film having desired optical properties.

  Since the optical film obtained by the method of the present invention has no optical defect of bubble failure, it is a member of a liquid crystal display device, for example, a polarizing plate protective film, a retardation plate, a reflector, an optical compensation film, and a viewing angle improvement. It can be suitably used for a film, an antiglare film, an antireflective film, and an antistatic film.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
(Preparation of dope solution)
The following materials were charged into a regulating container equipped with a stirrer. In addition, methylene chloride (boiling point 39.95 ° C.) used was kept at 25 ° C. in advance. The powder of the resin material used was a gas that had been removed in advance in a sealed container under a reduced pressure of 100 mmHg.

Cellulose triacetate 100 parts by weight (acetyl substitution degree 2.88, number average molecular weight 140000)
Triphenyl phosphate (melting point: 47.5) 10 parts by weight Tinuvin 326 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 414 parts by weight Ethanol 36 parts by weight Wait for 10 minutes in this state, and the atmosphere inside the adjustment vessel is solvent vapor I was satisfied. Subsequently, the temperature was gradually raised, and the mixture was dissolved at 80 ° C. for 30 minutes, and then cooled to 35 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and allowed to stand at 35 ° C. for 5 hours.

  This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 35 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, the number of the bubbles of 50 micrometers or more in the range of 25 cm x 40 cm was investigated, and it ranked by the following evaluation criteria. The results are shown in Table 1.

(Evaluation criteria for bubble failure)
Rank Number of bubbles below 50-100 μm Number of bubbles above 100 μm A 0 0
B 1-2 0
C 2-6 0
D 7 or more 0
E-One or more comparative example 1
The following materials were charged into a regulating container equipped with a stirrer. In addition, the methylene chloride used was kept at 35 ° C. in advance. The resin material powder was used as it was without any gas removal treatment.

Cellulose triacetate 100 parts by weight (acetyl substitution degree 2.88, number average molecular weight 150,000)
Triphenyl phosphate (melting point: 47.5) 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 414 parts by weight Ethanol 36 parts by weight Immediately after heating And dissolved at 80 ° C. for 30 minutes, and then cooled to 40 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and allowed to stand at 35 ° C. for 5 hours.

  This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 35 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, it carried out similarly to Example 1, investigated the number of bubbles, and ranked. The results are shown in Table 1.

Example 2
The following materials were charged into a regulating container equipped with a stirrer. In addition, the methylene chloride used was kept at 15 ° C. in advance. The powder of the resin material was previously removed from the gas in a sealed container under a reduced pressure of 100 mmHg.

Cellulose acetate propionate 100 parts by weight (acetyl substitution degree 1.95, propionyl substitution degree 0.7,
And number average molecular weight 70,000)
Triphenyl phosphate (melting point: 47.5) 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 1 part by weight AEROSIL 972V 0.1 part by weight Methylene chloride 336 parts by weight Ethanol 64 parts by weight Wait for 10 minutes in this state and adjust The atmosphere inside the container was filled with solvent vapor. Then, the temperature was gradually raised and dissolved at 70 ° C. for 30 minutes, and then cooled to 38 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and allowed to stand at 35 ° C. for 5 hours.

  This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 35 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, it carried out similarly to Example 1, investigated the number of bubbles, and ranked. The results are shown in Table 1.

Example 3
The following materials were charged into a regulating container equipped with a stirrer. In addition, methyl acetate (boiling point 57.5 ° C.) used was kept at 30 ° C. in advance. The powder of the resin material was previously removed from the gas in a sealed container under a reduced pressure of 100 mmHg.

Cellulose acetate propionate 100 parts by weight (acetyl substitution degree 1.95, propionyl substitution degree 0.7,
And number average molecular weight 70,000)
Triphenyl phosphate (melting point: 47.5) 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 1 part by weight AEROSIL 972V 0.1 part by weight Methyl acetate 280 parts by weight Ethanol 120 parts by weight Wait for 20 minutes in this state and adjust The atmosphere inside the container was filled with solvent vapor. Next, the temperature was gradually raised, and the mixture was dissolved at 80 ° C. for 30 minutes, and then cooled to 55 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and left at 55 ° C. for 5 hours.

  This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 55 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, it carried out similarly to Example 1, investigated the number of bubbles, and ranked. The results are shown in Table 1.

Example 4
The following materials were charged into a regulating container equipped with a stirrer. In addition, methylene chloride (boiling point 39.95 ° C.) used was kept at 20 ° C. in advance. The powder of the resin material was previously removed from the gas in a sealed container under a reduced pressure of 100 mmHg.

100 parts by weight of hydrogenated norbornene ring-opening polymer (Nippon Zeon Co., Ltd., ZEONOR 1420R, glass transition temperature 140 ° C.)
AEROSIL 972V 0.1 weight part Methylene chloride 300 weight part It waited for 5 minutes in this state, and it was made to fill the atmosphere inside the adjustment container with solvent vapor | steam. Then, the temperature was gradually raised and dissolved at 80 ° C. for 30 minutes, and then cooled to 35 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and allowed to stand at 35 ° C. for 5 hours.

  This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 35 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, it carried out similarly to Example 1, investigated the number of bubbles, and ranked. The results are shown in Table 1.

Example 5
The following materials were put into a control vessel equipped with a stirrer that was previously filled with helium gas. In addition, methylene chloride (boiling point 39.95 ° C.) used was kept at 25 ° C. in advance. The powder of the resin material was previously removed from the gas in a sealed container under a reduced pressure of 100 mmHg.

Cellulose triacetate 100 parts by weight (acetyl substitution degree 2.88, number average molecular weight 140000)
Triphenyl phosphate (melting point: 47.5) 10 parts by weight Tinuvin 326 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 414 parts by weight Ethanol 36 parts by weight Then, the temperature was gradually raised and dissolved at 80 ° C. for 30 minutes. Cooled to 35 ° C. Further, the solution was filtered using a filter paper having an absolute filtration accuracy of 0.005 mm, filtered at a filtration flow rate of 300 l / m ² · hour, and a filtration pressure of 1.0 × 10 ⁻⁶ Pa, and allowed to stand at 35 ° C. for 5 hours.

This solution was cast from a casting die onto a rotationally driven stainless steel support, dried at 35 ° C. for 10 minutes, and the resin film was peeled from the support. About the obtained resin film, it carried out similarly to Example 1, investigated the number of bubbles, and ranked. The results are shown in Table 1.

  As is clear from the results in Table 1, according to Examples 1 to 5 of the present invention, the generation of bubbles in the resin film can be prevented without using a special method. The resin films obtained in No. 1 had almost no bubble failure, had a high appearance quality, and were suitable as optical films. In contrast, the resin film obtained in Comparative Example 1 had a bubble failure and was inferior in quality as an optical film.

Claims (8)

  In the method for producing an optical film in which a resin and a solvent are stirred and mixed to prepare a resin solution, the resin solution is cast on a support from a casting die, and the casting film is peeled off from the support and dried. A method for producing an optical film, characterized in that the temperature of the solvent at the time of mixing is lower than the boiling point of the solvent by 10 ° C or more.   After stirring and mixing the resin and solvent, until the resin solution is cast on the support, the resin solution is once brought to a temperature not lower than the boiling point of the solvent after being brought to a temperature not lower than the boiling point of the solvent. The manufacturing method of the optical film of Claim 1 characterized by the above-mentioned.   The method for producing an optical film according to claim 1, wherein the resin is a powder excluding gas.   2. The method for producing an optical film according to claim 1, wherein the concentration of the solvent vapor, carbon dioxide gas or helium in the atmosphere of the container for adjusting the resin solution is 80% by volume or more.   The method for producing an optical film according to claim 1, wherein the solvent is a solvent containing 60% by weight or more of methylene chloride or methyl acetate.   The method for producing an optical film according to claim 1, wherein the resin is a cellulose ester.   The method for producing an optical film according to claim 1, wherein the solvent contains methylene chloride in an amount of 60% by weight or more, and the temperature of the solvent at the time of mixing is 0 ° C to 25 ° C. The method for producing an optical film according to claim 1, wherein the temperature of the resin solution at the time of casting is at least 5 ° C higher than the temperature of the solvent at the time of mixing and less than the boiling point of the solvent.