JP6889416B2 - Optical film manufacturing method - Google Patents

Description

The present invention relates to a method for producing an optical film containing a polyimide resin, a polyarylate resin or a cycloolefin resin.

Various optical films (for example, a transparent protective film for protecting the polarizing element of the polarizing plate) are arranged in the image display area of the liquid crystal display device. In particular, a transparent resin film containing a polyimide resin, a polyarylate resin, a cycloolefin resin or the like is used for an optical film, mainly an optical compensation film for a liquid crystal display device. Such an optical film is often produced as a long resin film by, for example, a solution casting (film forming) method.

However, resins such as polyimide resins, polyarylate resins, and cycloolefin resins are synthetic polymers and contain residual monomers, antioxidants, catalysts, and the like as impurities during production. The presence of such residual monomers may cause process contamination during drying. In addition, impurities (antioxidants, catalysts, etc.) in the resin remain in the film, which causes a problem that the internal haze increases.

Removing unnecessary substances from a dope for an optical film has also been conventionally performed in the production of a cellulose film. For example, in a dope containing a cellulose resin, an unnecessary substance is deposited and a chelating agent is added to the dope. A method for removing sediment has been reported (Patent Document 1).

However, in the conventional method using a chelating agent, the dope may be discharged at the same time because it is precipitated by forming a complex between the impurities of the resin and the chelating agent.

The present invention has been made in view of such circumstances, and a high-quality polyimide resin, polyarylate resin or cycloolefin resin which can efficiently remove doping impurities and has a low internal haze without using a chelating agent can be obtained. It is an object of the present invention to provide a method for producing an optical film containing the mixture.

Japanese Patent No. 5729233

As a result of diligent studies, the present inventor has found that the above-mentioned problems can be solved by a method for producing an optical film having the following structure, and has completed the present invention by conducting further studies based on such findings.

That is, in the method for producing an optical film according to one aspect of the present invention, in the solution casting film forming method, a polyimide resin, a polyarylate resin or a cycloolefin resin, at least one alcohol solvent, and at least one with respect to the resin are used. A dope containing a good solvent of any kind was prepared, the optical dope was cast on the support, a web (casting film) was formed on the support, the web was peeled from the support, and then peeled off. A method for producing an optical film by winding and drying a web is characterized by including a step of adjusting the dope and then further adding a good solvent to the dope, and then a step of removing the good solvent. And.

FIG. 1 is a schematic view showing a basic configuration of an optical film manufacturing apparatus by a solution casting method using an endless belt support.

Hereinafter, embodiments according to the present invention will be described, but the present invention is not limited thereto.

In the method for producing an optical film according to the present embodiment, in a solution casting film forming method, a polyimide resin, a polyarylate resin or a cycloolefin resin, at least one alcohol solvent, and a good solvent for at least one resin are used. The dope containing the solvent is adjusted, the optical dope is cast on the support, a web (casting film) is formed on the support, the web is peeled from the support, and then the peeled web is wound up. The method for producing an optical film by drying is characterized by including a step of adjusting the dope and then further adding a good solvent to the dope, and then a step of removing the good solvent.

According to the above configuration, by removing the impurities of the doping without using a chelating agent, an optical film containing a high-quality polyimide resin, polyarylate resin or cycloolefin resin having a low internal haze can be efficiently produced. A method can be provided.

In the present embodiment, the dope is a resin solution that is a raw material for a film, and a solution that gels after casting on a support and has hardness as a film is referred to as a web (casting film). That is, the film in the drying process up to the finished optical film is referred to as a web. However, it should be noted that the boundary between the dope-formed dome membrane, the web and the film is not exactly defined.

Hereinafter, the solution casting film forming method will be described first.

[Solution casting film forming method]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus used in the present embodiment. In the method for producing an optical film of the present embodiment, a dope containing a polymer (polyimide resin, polyarylate resin or cycloolefin resin) and a solvent is cast on a running support from a casting die, and then as a film. The solution casting method for peeling is used. In addition, in FIG. 1, each reference numeral means the following. 1: Melting pot 2: Pump 3: Casting die 4: Decompression chamber 5: Front and rear winding drum, 6: Endless belt for casting (support), 7: Peeling roll, 8: Web, 9: Tenter, 10: Roll transport drying device, 11: Warm air (dry air), 12: Transport roll, 13: Winder, F: Film.

The outline of the solution casting method will be described with reference to FIG. First, in the dissolution kettle 1, for example, a polyimide resin, a polyarylate resin, or a cycloolefin resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and if necessary, additives such as a matting agent and an ultraviolet absorber are added. To prepare a resin solution (dope). The preparation method of each dope and the good solvent and the poor solvent will be described later.

The dope preferably removes insoluble matter, foreign matter, and the like by filtration. The filter medium to be used may be one that can satisfactorily remove insoluble matter and the like without causing clogging. For example, a filter medium having an absolute filtration accuracy of 0.008 mm or less, preferably 0.003 to 0.006 mm is used. It is preferable to use it.

Then, the dope adjusted in the melting pot 1 is sent to the casting die 3 by a conduit through the pressure type metering gear pump 2 and transferred indefinitely on the support 6 made of a rotary drive stainless steel endless belt. At the position, the dope is cast from the casting die 3 to form a web 8 as a casting film on the support 6.

For the casting of the dope by the casting die 3, the doctor blade method of adjusting the film thickness of the cast web with a blade, the method of adjusting the film thickness of the cast web with a reverse rotating roll, and the reverse roll coater method are added. There is a method using a pressure die and the like. Among them, a method using a pressure die is preferable because the slit shape of the base portion can be adjusted and the film thickness can be easily made uniform. The pressure die includes a coat hanger die, a T die, and the like, and any of them can be preferably used.

The support 6 is held by a pair of front and rear drums 5.5 and a plurality of intermediate rolls (not shown). One or both of the drums 5 and 5 is provided with a drive device (not shown) that applies tension to the support 6, whereby the support 6 is used in a tensioned state.

The width of the support 6 is preferably about 1000 to 4000 mm, and the width of the film after winding is preferably about 1000 to 2500 mm. As a result, a wide optical film for a liquid crystal display device can be manufactured by the metal support method.

When an endless belt is used as the support 6, the belt temperature during film formation is -50 ° C to less than the boiling point of the solvent in the general temperature range, but less than the boiling point of the solvent having the lowest boiling point in the mixed solvent. The temperature is preferably in the range of 5 ° C to 70 ° C, more preferably in the range of 5 to 40 ° C. At this time, it is necessary to control the ambient humidity above the dew point. The moving speed of the support 6 under production conditions is preferably 5 m / min or more, preferably 10 to 180 m / min, and more preferably 80 m / min to 150 m / min.

The dope cast on the support 6 in this way also increases the strength of the gel film (film strength) by promoting drying until stripping.

The web 8 formed by the dope cast on the support 6 is heated on the support 6 and the solvent is evaporated from the support 6 until the web can be peeled off by the peeling roll 7.

To evaporate the solvent and dry the web, there are a method of blowing wind from the web side, a method of transferring heat from the back surface of the support with a liquid, a method of transferring heat from the front and back surfaces by radiant heat, etc. The method is preferable because it has good drying efficiency. In addition, a method of combining them is also preferably used. It is preferable to dry the web on the support after casting in an atmosphere of 30 to 100 ° C. on the support. In order to maintain the atmosphere at 30 to 100 ° C., it is preferable to blow warm air at this temperature on the upper surface of the web or heat it by means such as infrared rays.

From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 180 seconds.

The web temperature at the time of peeling the web 8 from the support 6 is preferably −50 to 60 ° C., more preferably 10 to 40 ° C., and more preferably 11 to 30 ° C.

The amount of residual solvent of the web on the metal support at the time of peeling is preferably in the range of 15 to 100% by mass. The amount of residual solvent is preferably controlled by the drying temperature and drying time in the solvent evaporation step.

The amount of residual solvent in the web or film is defined by the following formula (Z).

Equation (Z)
Residual solvent amount (%) = (mass before heat treatment of web or film-mass after heat treatment of web or film) / (mass after heat treatment of web or film) × 100
The heat treatment for measuring the amount of residual solvent means that the heat treatment is performed at 115 ° C. for 1 hour.

The peeling tension when the support 6 and the web 8 are peeled off by the peeling roll 7 is larger than the peeling force obtained by the peeling force measurement such as JIS Z 0237, which means that the peeling tension is JIS at the time of high-speed film forming. If it is made equal to the peeling force obtained by the measuring method, the peeling position may be moved to the downstream side, so the peeling force is set higher for stabilization. It has also been confirmed that even if the film is formed with the same peeling tension in the process, the variation in the cross Nicol transmittance (CNT) of the film is greatly reduced when the peeling force by the JIS measurement method is reduced.

The peeling tension value in the process is usually 20 to 400 N / m, but in the optical film produced by making the film thinner than before, the amount of residual solvent in the web 8 is large at the time of peeling, and the film easily stretches in the transport direction. Therefore, the film tends to shrink in the width direction, and when drying and shrinking overlap, the end portion is curled and folds, so that wrinkles are likely to occur. Therefore, the peeling tension is preferably the minimum tension that can be peeled off to 190 N / m.

Although a belt-shaped support is illustrated as the support in FIG. 1, the support of the present embodiment is not limited to the belt-shaped one, and for example, a drum-shaped support may be used. ..

After the web 8 is dried and solidified on the support 6 until the film strength is such that the web 8 can be peeled off, the web 8 is peeled off by a peeling roll 7, and then the web 8 is stretched in the tenter 9 of the stretching step.

In addition, the production method of the present embodiment may include a stretching step of stretching the obtained web. By performing the stretching treatment with a low stretching ratio under a specific residual solvent amount in the stretching device (tenter 9), it is possible to suppress the generation of minute crazes near the film surface and promote the uniform distribution of the matting agent. it can. Further, by controlling the orientation of the molecules in the film, it is possible to obtain a target phase difference value Ro in the in-plane direction and a phase difference value Rt in the thickness direction.

In the stretching step, a tenter method in which both side edges of the web 8 are fixed with clips or the like and stretched is preferable in order to improve the flatness and dimensional stability of the film.

In the present embodiment, in the step of stretching the film, the amount of residual solvent at the start of stretching is preferably 1% by mass or more and less than 25% by mass. More preferably, it is in the range of 5 to 20% by mass.

The optical film of the present embodiment is preferably stretched in the longitudinal direction (also referred to as MD direction and spreading direction) and / or in the width direction (also referred to as TD direction), and at least in the width direction by a stretching device. It is preferably produced by stretching.

The stretching operation may be performed in multiple stages. Further, when biaxial stretching is performed, simultaneous biaxial stretching may be performed, or biaxial stretching may be performed step by step. In this case, the term “stepwise” means, for example, that stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any of the steps. Is also possible.

The stretching temperature and stretching ratio can be appropriately set according to the resin to be used and the desired film characteristics.

After the tenter 9 in the stretching step, the stretched film is heated and dried in the drying device 10. In the drying device 10, the web 8 is meandered by a plurality of transport rolls 12 arranged in a staggered pattern when viewed from the side surface, and the web 8 is dried between them.

The means for drying the web 8 is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. From the viewpoint of convenience, it is preferable to dry with hot air. For example, the web 8 can be dried by blowing the drying air 11 from the hot air inlet of the drying device 10 and discharging the exhaust air from the outlet of the drying device 10 to obtain the optical film F. The temperature of the drying air 11 is preferably 40 to 350 ° C., and the drying time is preferably about 5 seconds to 30 minutes.

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

Next, the dried film is wound by the winding device 13 to obtain the original winding of the optical film F. By setting the residual solvent amount of the film at the end of drying to 0.5% by mass or less, preferably 0.1% by mass or less, a film having good dimensional stability can be obtained.

As a film winding method, a commonly used winder may be used, and there are methods for controlling tension such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method with a constant internal stress. You can use it properly. The film may be bonded to the take-up core (winding core) with either double-sided adhesive tape or single-sided adhesive tape. The width of the optical film F after winding is preferably 1000 to 2500 mm.

The film thickness (final film thickness) of the optical film of the present embodiment after drying is preferably in the range of 5 to 40 μm as the finished film from the viewpoint of reducing the thickness of the liquid crystal display device. Here, the film thickness after drying refers to a film in which the amount of residual solvent in the film is 0.5% by mass or less.

Next, the characteristic portion of the manufacturing method of the present embodiment will be described in more detail.

In the method for producing an optical film according to the present embodiment, in the solution casting film forming method as described above, as a dope, a polyimide resin, a polyarylate resin or a cycloolefin resin, at least one alcohol solvent, and the resin are used. A major feature is that it includes a step of preparing a dope containing at least one kind of good solvent, a step of further adding a good solvent to the dope after adjusting the dope, and a step of removing the good solvent. It is one of.

The dope preparation of the present embodiment can be performed using a known dope production apparatus. Specifically, for example, a dope manufacturing apparatus having a supply port for charging the material in the upper part, a mixing pot provided with a rotating body for mixing the material, and a discharge port for taking out the mixed sample in the lower part is used. Prepare the dope.

The dope preparation can be prepared by mixing the materials and then preparing by a high temperature melting method or the like. In the high temperature melting method, the mixed solution is heated to a range of 30 to 200 ° C. under a pressure in the range of 0.2 to 30 MPa. The temperature range is preferably in the range of 40 to 150 ° C, more preferably in the range of 40 to 100 ° C. As the heating method, for example, high-pressure steam may be used, or an electric heat source may be used. When preparing the dope by the high temperature melting method, the mixing pot is preferably a pressure resistant tank that can be pressurized.

The alcohol solvent used for the doping of the present embodiment is not particularly limited, and examples thereof include methanol, ethanol, isopropanol, n-butanol, and 2-butanol. Of these, selection from methanol, ethanol and butanol is preferable from the viewpoint of improving peelability and enabling high-speed casting. In particular, it is preferable to use methanol or ethanol.

The concentration of the alcohol solvent when adjusting the dope is preferably about 2 to 30% by mass with respect to the total amount of the solvent. When the ratio of the alcohol solvent in the solvent contained in the dope is in the above range, the web is appropriately gelled to facilitate peeling from the metal support, and the resin and other compounds are dissolved in the organic solvent. It is considered to promote moderately. The ratio of the more preferable alcohol solvent in the total solvent is about 2 to 20% by mass.

Next, the good solvent used when preparing the dope of the present embodiment is not particularly limited as long as it is a solvent that is easily solvated with respect to the polymer (resin). Specifically, in the present embodiment, the good solvent means a solvent that is transparent in a state where the resin constituting the dope is dissolved in the solvent in an amount of 10% by mass or more. Further, "transparent" means that Δ haze (dope-filled haze-quartz cell haze) <3.0, which is the dope haze when the quartz cell is filled with dope and measured with a haze meter.

More specific good solvents include, for example, dichloromethane, tetrachloromethane and the like as chlorine-based organic solvents, and methyl acetate, ethyl acetate, amyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, 1, as non-chlorine-based organic solvents. 3-Dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 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 Examples thereof include 3-pentafluoro-1-propanol, nitroethane, methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, etc., among which the resin is polyarylate or cycloolefin. Is preferably dichloromethane, and when the resin is polyimide, it is preferably tetrachloromethane. The good solvent used for the dope is preferably 55% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, based on the total amount of the solvent contained in the dope.

In the production method of the present embodiment, a dope is prepared using a mixed solvent containing at least one alcohol solvent and at least one good solvent as described above, and after the dope is prepared, a good solvent is further added. Examples of the good solvent to be added include the same as the above-mentioned good solvent. The good solvent used at the time of preparing the dope and the good solvent added after the preparation may be the same solvent or may be different.

The method of adding the good solvent to the dope after the preparation is not particularly limited, but the good solvent prepared separately after the dope preparation may be added as it is, or the good solvent in the dope volatilized by heating at the time of the dope preparation may be added. It is also possible to cool it back into droplets and add it by dropping it. The timing at which the good solvent is added is not particularly limited, but since the dope may volatilize even if it is added while the dope is at a high temperature, the dope is supported after the dope temperature falls below the boiling point of the good solvent. It is preferably added before spreading to the body.

The amount of the good solvent added after the dope preparation is preferably about 1 to 50% by mass with respect to the total amount of the dope. When the amount of the good solvent added is within this range, the removal rate of impurities is increased, so that the quality of the produced film can be ensured, the doping loss due to the solvent removal is reduced, and the time is shortened, which is preferable. A more preferable addition amount is about 2 to 10% by mass with respect to the total amount of dope.

The production method of the present embodiment further includes a step of removing the good solvent after adding the good solvent. The means for removing the good solvent is not particularly limited, and the good solvent can be removed by a conventionally known method. Specifically, for example, it may be taken out from the discharge port of the above-mentioned dope production apparatus, or the good solvent may be removed by branching the liquid feeding pipe and reusing / discarding only the solvent.

The timing for removing the good solvent is also not particularly limited, but it is preferable to remove the good solvent before the start of the liquid feeding or during the change of the liquid feeding pot, for example.

The amount of the good solvent to be removed is preferably 80 to 100% by mass of the amount of the good solvent to be added. When the amount of good solvent removed is within this range, the removal rate of impurities increases, so that film quality can be ensured. A more preferable amount of the good solvent removed is about 90 to 100% by mass with respect to the amount of the good solvent to be added.

According to the production method as described above, it is possible to provide a method for producing an optical film containing high-quality polyimide resin, polyarylate resin or cycloolefin resin which can efficiently remove dope impurities and has low internal haze. it can.

[Dope]
(Dope for polyimide film)
The dope used in the polyimide resin-containing optical film in the present embodiment contains polyamic acid or polyimide as a main material.

Although not particularly limited, it is preferable to use a polyamic acid or polyimide having a weight average molecular weight of 30,000 to 1,000,000. More specifically, for example, a polyamic acid or polyimide as described in JP-A-2016-64642 can be used.

As the mixed solvent for dissolving the polyamic acid or the polyimide, as described above, a mixed solvent containing at least one alcohol solvent and at least one good solvent is used. Above all, it is preferable to use a solvent containing 50% by mass or more of tetrachloromethane as a good solvent.

Specific methods for preparing a dope in which polyamic acid or polyimide is dissolved in a mixed solvent containing 50% by mass or more of tetrachloromethane include the following methods (i) to (iii). , Not limited to these methods.

(I) An aromatic, aliphatic or alicyclic tetracarboxylic acid or a derivative thereof is preferably added to a solution of a diamine or a derivative thereof, or a solution of an aromatic, aliphatic or alicyclic tetracarboxylic acid component is preferable. Diamine or a derivative thereof is added thereto, and the mixture is kept at a temperature of preferably 80 ° C. or lower (more preferably 30 ° C. or lower) for 0.5 to 3 hours to obtain a polyamic acid solution. As the solvent used here, the above-mentioned polymerization solvent is used.

The dope according to the present invention can be obtained by substituting the polymerization solvent in the obtained polyamic acid solution with a mixed solvent containing the tetrachloromethane and an alcohol solvent.

(Ii) A polyimide solution can be obtained by dehydrating the polyamic acid solution obtained in (i) above. In this case, it is preferable to add the dehydrating agent and the ring closure catalyst. Further, it is preferable to add a solvent such as toluene or xylene that azeotropes with water to the polyamic acid solution, and carry out the dehydration reaction while removing the generated water from the system by azeotrope. The reaction temperature is preferably in the temperature range of -20 to 50 ° C. when the ring closure catalyst is added, and preferably in the temperature range of 80 to 300 ° C. when the ring closure catalyst is not added. ..

When the ring closure reaction is allowed to proceed in the solution in this way, by-products of the dehydrating agent and residual monomers can be removed, which is preferable.

The dope according to the present invention can be obtained by substituting the polymerization solvent in the polyimide solution obtained by any of the above methods with a mixed solvent containing the tetrachloromethane and an alcohol solvent.

(Iii) A dehydrating agent such as acetic anhydride is added to the polyamic acid solution obtained in (i) above, imidized by heating or addition of a ring-closing catalyst, and then a solvent such as methanol having poor solubility in polyimide is added. To precipitate the polyimide. The dope according to the present invention can be obtained by separating it as a solid by filtering, washing and drying, and then dissolving it in the above-mentioned mixed solvent.

The concentration of polyamic acid or polyimide in the dope prepared as described above is preferably 1 to 50% by mass, more preferably 10 to 40% by mass. When it is 50% by mass or less, the surface flatness of the obtained polyimide film is good.

The viscosity of the dope is preferably 1000 to 100,000 cp, preferably 1000 to 50,000 cp, as measured by a Brookfield viscometer, because stable liquid feeding is possible.

Various additives can be added to the dope containing polyamic acid or polyimide, if necessary. Additives that can be used include inorganic fillers, surfactants, antioxidants, and other various functional materials (eg, conductive materials such as carbon nanotubes and nanometal materials, and ferroelectric materials such as barium titanate. _{, ZnS: Ag, ZnS: Cu} , Y 2 O 2 S: phosphor such as Eu, ultraviolet absorbers, etc.), flame retardants, and the like.

When a web is formed using polyamic acid, a polyimide film can be produced by subjecting the obtained film to an imidization treatment.

When the film is subjected to appropriate heat treatment, imidization within the polymer chain molecules and between the polymer chain molecules progresses to improve the mechanical properties, but the more the heat treatment is applied, the darker the polyimide film changes with the change in absorption wavelength. .. In particular, in a thin polyimide film of 4.0 to 15.0 μm, the higher the L * value, the lighter the color as a whole, so that horizontal unevenness due to thickness unevenness is hard to see and the appearance is good, but imidization Since the progress is not sufficient, the mechanical properties such as bending resistance and breaking strength of the polyimide film deteriorate. On the other hand, if the L * value is too low, the color contrast due to the uneven thickness becomes clear and the horizontal unevenness worsens, and the polyimide film becomes partially carbonized and fragile, and the mechanical properties of the film become remarkable. fall back. For the above reasons, in the method for producing a polyimide film of the present invention, an L * value of 30 to 55 is good for maintaining good mechanical properties, and more preferably an L * value of 38 to 54. Is good.

The L * value of the film was measured using SM-7-CH manufactured by Suga Test Instruments. For each sample divided into five in the film width direction, a range of 30 mm × 30 mm centered on the center position in the width direction was cut out and measured, and the average value was taken over the five points. The L * value becomes one sheet for a film having a film thickness of 50 μm or more and 50 μm or more for a film having a film thickness of less than 50 μm because the sensitivity of the detector becomes dull and an appropriate evaluation cannot be made when the film thickness becomes thin. It is a value measured by stacking the minimum number of sheets.

Regarding the method of heat treatment for obtaining a film having an L * value of the film of 30 to 55, for example, a method of adjusting the amount of heat treatment using a known means such as hot air or an electric heater (for example, an infrared heater). Can be mentioned.

In the method for producing a polyimide film of the present embodiment, a solution of a polyamic acid containing no ring-closing catalyst is cast to form a film, heat-dried on a support, the film is peeled off from the support, and the temperature is further increased. A thermal imidization method for imidization by dry heat treatment underneath can be used. In the case of this method, the reaction rate of imidization can be improved by containing a dehydrating agent in the polyamic acid solution, but it is preferable not to contain the dehydrating agent. By not containing the dehydrating agent, it is possible to suppress a decrease in the durability of the polyimide film due to the residual dehydrating agent. In the thermal imidization method, heat treatment can be performed by using, for example, an infrared heater.

Further, a solution of polyamic acid containing a ring-closing catalyst and a dehydrating agent is cast to form a film, and imidization is partially promoted on the support to form a film, and then the film is peeled off from the support. It is also possible to use a chemical imidization method in which heat-drying / imidization and heat treatment are performed. As the ring closure catalyst, the above-mentioned tertiary amine or the like can be used. In the case of this method, by adding a dehydrating agent to the polyamic acid solution, imidization can proceed at a low temperature, so that a decrease in durability of the polyimide film can be suppressed.

Any of the above ring-closing methods may be adopted in the method for producing a polyimide film, but the chemical imidization method requires equipment for containing a ring-closing catalyst and a dehydrating agent in a polyamic acid solution, but provides self-supporting property. It can be said that it is a more preferable method in that the film to be held can be obtained in a short time.

(Dope for polyarylate film)

The dope used in the polyarylate resin-containing optical film in the present embodiment contains polyarylate as a main material. Polyarylate contains at least an aromatic dialcohol component unit and an aromatic dicarboxylic acid component unit. More specifically, for example, a polyarylate as described in JP-A-2016-112773 can be used.

The glass transition temperature of the polyarylate used in the present embodiment is preferably 260 ° C. or higher and 350 ° C. or lower, more preferably 265 ° C. or higher and lower than 300 ° C., and further preferably 270 ° C. or higher and lower than 300 ° C. preferable. The glass transition temperature of polyarylate can be measured according to JIS K7121 (1987). Specifically, using a DSC6220 manufactured by Seiko Instruments Inc. as a measuring device, measurement can be performed under the conditions of a polyarylate sample of 10 mg and a heating rate of 20 ° C./min.

The glass transition temperature of polyarylate can be adjusted by the type of aromatic dialcohol component constituting polyarylate and the like. In order to raise the glass transition temperature, for example, it is preferable to include "a unit derived from bisphenols containing a sulfur atom in the main chain" as an aromatic dialcohol component unit.

The intrinsic viscosity of the polyarylate used in the present embodiment is preferably 0.3 to 1.0 dl / g, more preferably 0.4 to 0.9 dl / g, and 0.45 to 0.8 dl / g. Is even more preferable, and 0.5 to 0.7 dl / g is even more preferable. When the intrinsic viscosity of polyarylate is 0.3 dl / g or more, the molecular weight of the resin composition tends to be constant or higher, and a film having sufficient mechanical properties and heat resistance can be easily obtained. When the intrinsic viscosity of polyarylate is 1.0 dl / g or less, it is possible to suppress an excessive increase in the viscosity of the solution during film formation.

Intrinsic viscosity can be measured according to ISO 1628-1. Specifically, a solution prepared by dissolving a polyarylate sample in 1,1,2,2-tetrachloroethane so as to have a concentration of 1 g / dl is prepared. The intrinsic viscosity of this solution at 25 ° C. is measured using an Ubbelohde viscous tube.

The method for producing the polyarylate may be a known method, preferably an interface in which an aromatic dicarboxylic acid halide dissolved in an organic solvent incompatible with water and an aromatic dialcohol dissolved in an alkaline aqueous solution are mixed. It may be a polymerization method (WM EARECKSON, J. Poly. Sci. XL399, 1959, Japanese Patent Publication No. 40-1959).

The dope containing the polyarylate may contain other resins other than the polyarylate, a heat stabilizer, an antioxidant, a light stabilizer, a colorant, an antistatic agent, a lubricant, a mold release agent, and an ultraviolet absorbing agent, if necessary. Additives such as agents may be further included.

As described above, the polyarylate as described above is dissolved in a mixed solvent containing at least one alcohol solvent and at least one good solvent to obtain a dope.

The concentration of polyarylate in the dope is preferably 10% by mass or more, preferably about 10 to 30% by mass.

(Dope for cycloolefin film)

The dope used in the cycloolefin resin-containing optical film in the present embodiment contains cycloolefin as a main material.

As the cycloolefin used in the present embodiment, the cycloolefin resin may be used alone or in combination of two or more. The preferred molecular weight of the cycloolefin resin used in the present embodiment, 0.2~5cm ³ / g in intrinsic viscosity [η] inh, more preferably 0.3~3cm ³ / g, particularly preferably 0.4 to It is 1.5 cm ³ / g, and the polystyrene-equivalent number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 8000 to 10000, more preferably 1000 to 80000, and particularly preferably 12000 to 50000. The weight average molecular weight (Mw) is in the range of 20000 to 300,000, more preferably 30,000 to 250,000, and particularly preferably 50,000 to 200,000.

When the intrinsic viscosity [η] inh, the number average molecular weight and the weight average molecular weight are within the above ranges, the heat resistance, water resistance, chemical resistance and mechanical properties of the cycloolefin resin and the molding process as the optical film of the present invention are obtained. The property becomes good.

The glass transition temperature (Tg) of the cycloolefin resin used in the present embodiment is preferably 130 ° C. or higher, preferably 130 to 350 ° C., more preferably 130 to 250 ° C., and particularly preferably 130 to 220 ° C. ℃. A case where Tg is 130 ° C. or higher is preferable because deformation is unlikely to occur due to use under high temperature conditions or secondary processing such as coating and printing.

On the other hand, when the Tg is 350 ° C. or lower, it is possible to avoid the case where the molding process becomes difficult and suppress the possibility that the resin is deteriorated by the heat during the molding process.

As the cycloolefin resin, commercially available products can be preferably used, and examples of the commercially available products include Arton (Arton: registered trademark) G series, Arton F series, Arton R series, and Arton RX series from JSR Corporation. Zeon Corporation (Zeonor: registered trademark) ZF14, ZF16, 1420R, 1020R, 1060R, 1420R, etc., Zeonex (registered trademark) 250, 280, 480, 480R , E48R, F52R, 330R, RS420 and the like are commercially available, and these can be appropriately selected and used according to the intended use.

The dope containing cycloolefin includes resins other than cycloolefin resin, heat stabilizers, antioxidants, light stabilizers, colorants, antistatic agents, lubricants, mold release agents, and ultraviolet rays, if necessary. Additives such as absorbents may be further included.

As described above, the cycloolefin as described above is dissolved in a mixed solvent containing at least one alcohol solvent and at least one good solvent to obtain a dope.

The cycloolefin resin is dissolved at normal pressure, below the boiling point of the main solvent, and pressurized above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557. , Or a method of performing by a cooling dissolution method as described in JP-A-9-95538, a method of performing at high pressure as described in JP-A-11-21379, and various other melting methods can be used. A method of pressurizing above the boiling point of the solvent is preferable.

The concentration of the cycloolefin resin in the dope is preferably in the range of 10 to 40% by mass.

The optical film produced by the production method of the present embodiment is useful as a functional film used for various displays such as liquid crystal displays, plasma displays, and organic EL displays, particularly liquid crystal displays, and is useful as a polarizing plate protective film, a retardation film, and the like. It can also be used as an antireflection film, a brightness improving film, an optical compensation film for expanding the viewing angle, and the like.

As described above, this specification discloses various aspects of technology, of which the main technologies are summarized below.

A method for producing an optical film according to one aspect of the present invention is a solution casting film forming method in which a polyimide resin, a polyarylate resin or a cycloolefin resin, at least one alcohol solvent, and at least one kind of the resin are produced. The dope containing a good solvent is adjusted, the dope is optically cast on the support, a web (casting film) is formed on the support, the web is peeled from the support, and then the peeled web is peeled off. A method for producing an optical film by winding and drying comprises a step of adjusting the dope and then further adding a good solvent to the dope, and then a step of removing the good solvent. ..

With such a configuration, it is possible to produce an optical film containing a high-quality polyimide resin, polyarylate resin or cycloolefin resin having a low internal haze by removing impurities of the doping without using a chelating agent. it can.

Further, in the method for producing an optical film, it is preferable that the good solvent is dichloromethane or tetrachloromethane. Thereby, the above-mentioned effect can be obtained more reliably.

Further, in the method for producing an optical film, the amount of good solvent to be added is preferably 1 to 50% by mass with respect to the total amount of doping. Thereby, the above-mentioned effect can be obtained more reliably.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to any examples.

[Example 1]
A polyarylate film was produced by the method shown below.

(Synthesis of polyarylate 1)
After adding 2514 parts by weight of water to a reaction vessel equipped with a stirrer, 22.7 parts by weight of sodium hydroxide and 9,9-bis (3,5-dimethyl-4-hydroxyphenyl) as an aromatic dialcohol component. ) Fluorene (BCF) 35.6 parts by weight, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane (TMBPA) 18.5 parts by weight, p-tert-butylphenol (PTBP) as a molecular weight modifier 0.049 parts by weight was dissolved, 0.34 parts by weight of a polymerization catalyst (tributylbenzylammonium chloride) was added, and the mixture was stirred.

On the other hand, 26.8 parts by weight of an equal amount mixture of terephthalic acid chloride and isophthalic acid chloride as an aromatic dicarboxylic acid component was weighed and dissolved in 945 parts by weight of methylene chloride. This methylene chloride solution was added to the alkaline aqueous solution prepared above under stirring to initiate polymerization. The polymerization reaction temperature was adjusted to be 15 ° C. or higher and 20 ° C. or lower. The polymerization was carried out for 2 hours, and then acetic acid was added into the system to stop the polymerization reaction, and the organic phase and the aqueous phase were separated.

The operation of separating the obtained organic phase into an organic phase and an aqueous phase was repeated after washing with twice the amount of ion-exchanged water as the organic phase in each washing. The washing was completed when the electrical conductivity of the washing water became less than 50 μS / cm. The washed organic phase was put into a warm water tank equipped with a homomixer at 50 ° C. to evaporate methylene chloride to obtain a powdery polymer. Further dehydration and drying were performed to obtain polyarylate 1.

(Preparation of dope)
(Composition of main dope)
Dichloromethane 360 parts by mass Ethanol 40 parts by mass Polyallylate 1 100 parts by mass Particles: Nippon Aerodil Co., Ltd. R812 (primary particle size 7 nm) 0.1 parts by mass

A main dope having the above composition was prepared. First, dichloromethane (MC) and ethanol (ETOH) were added as mixed solvents to the pressure dissolution tank. The content of alcohol in the mixed solvent was 10% by mass. The polyarylate 1 prepared above was put into a pressurized dissolution tank containing the mixed solvent with stirring. This is heated and completely dissolved while stirring, and this is Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After filtering using 244, the remaining components were added and stirred to dissolve to prepare the main dope.

Then, dichloromethane volatilized during heating and stirring was agglomerated using a cooling facility to form a liquid, which was added dropwise to the dope so that the amount added to the total amount of the dope was 50% by mass.

(Hypersalivation process)
Then, using an endless belt casting device, the dope was uniformly cast on the stainless belt support at a temperature of 30 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled to 30 ° C.

(Peeling process)
The solvent was evaporated on the stainless belt support until the amount of residual solvent in the cast film reached 75%, and then the solvent was peeled from the stainless belt support at a peeling tension of 180 N / m.

(Drying process)
The peeled web having a residual solvent ratio of 25% by mass is dried on a transport roll at a drying temperature at a transport tension of 100 N / m and a drying time of 15 minutes so that the amount of residual solvent is less than 0.1% by mass, and the drying film thickness is 25 μm. I got the film. The resulting film was wound up.

(Heating process)
The wound film was heat-treated at 300 ° C. for 5 minutes with an infrared heater to obtain a polyimide film 1.

[Example 2]
In the preparation of the dope, the same as in Example 1 except that dichloromethane volatilized during heating and stirring was aggregated into a liquid using a cooling facility and added to the dope so that the amount added to the total amount of the dope was 30% by mass. A polyarylate film 2 was obtained.

[Example 3]
In the preparation of the dope, the same as in Example 1 except that dichloromethane volatilized during heating and stirring was aggregated into a liquid using a cooling facility and added to the dope so that the amount added to the total amount of the dope was 10% by mass. Obtained a polyarylate film 3.

[Example 4]
In the preparation of the dope, the same as in Example 1 except that dichloromethane volatilized during heating and stirring was aggregated into a liquid using a cooling facility and added to the dope so that the amount added to the total amount of the dope was 1% by mass. A polyarylate film 4 was obtained.

[Example 5]
In the preparation of the dope, a polyarylate film 5 was obtained in the same manner as in Example 3 except that the content of alcohol in the mixed solvent was 2% by mass.

[Example 6]
In the preparation of the dope, a polyarylate film 6 was obtained in the same manner as in Example 3 except that the content of alcohol in the mixed solvent was 30% by mass.

[Example 7]
In the preparation of the dope, a polyarylate film 7 was obtained in the same manner as in Example 3 except that the alcohol in the mixed solvent was methanol.

[Example 8]
In the preparation of the dope, a polyarylate film 8 was obtained in the same manner as in Example 3 except that the alcohol in the mixed solvent was butanol.

[Example 9]
In the preparation of the dope, a polyarylate film 9 was obtained in the same manner as in Example 3 except that dichloromethane prepared separately was added after the dope preparation so that the addition amount was 10% by mass with respect to the total amount of the dope.

[Example 10]
In the preparation of the dope, a polyarylate film 10 was obtained in the same manner as in Example 3 except that after the dope preparation, chloroform prepared separately was added so that the amount added was 10% by mass with respect to the total amount of the dope.

[Example 11]
In the preparation of the dope, a polyarylate film 11 was obtained in the same manner as in Example 3 except that tetrahydrofuran (THF) prepared separately was added so that the addition amount was 10% by mass with respect to the total amount of the dope after the dope preparation.

[Example 12]
In the preparation of the dope, the good solvent of the main dope was methyl ethyl ketone (MEK), and the MEK volatilized during heating and stirring was cooled and added to the dope so that the amount added to the total amount of the dope was 10% by mass. The polyarylate film 12 was obtained in the same manner as above.

[Example 13]
A cycloolefin film was produced by the method shown below.

(Cycloolefin)
The cycloolefin resin (COP) was dope-adjusted using a commercially available ARTON G7810 (manufactured by JSR Corporation, weight average molecular weight (Mw) = 140000). The cycloolefin resin is a resin having a glass transition temperature of 178 ° C. and an alkoxycarbonyl group as a polar group.

(Preparation of dope)
(Composition of main dope)
Dichloromethane 198 parts by mass Ethanol 22 parts by mass 100.0 parts by mass of the above cycloolefin resin Particles: Nippon Aerodil Co., Ltd. R812 (primary particle size 7 nm) 0.1 parts by mass

A main dope having the above composition was prepared. First, dichloromethane (MC) and ethanol (ETOH) were added as mixed solvents to the pressure dissolution tank. The content of alcohol in the mixed solvent was 10% by mass. The polyimide A prepared above was put into a pressure dissolution tank containing the mixed solvent with stirring. This is heated and completely dissolved while stirring, and this is Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After filtering using 244, the remaining components were added and stirred to dissolve to prepare the main dope.

Then, the dichloromethane volatilized during heating and stirring was cooled, and the dichloromethane was added dropwise to the dope so that the amount added to the total amount of the dope was 10% by mass.

(Hypersalivation process)
Then, using an endless belt casting device, the dope was uniformly cast on the stainless belt support at a temperature of 30 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled to 30 ° C.

(Peeling process)
The solvent was evaporated on the stainless belt support until the amount of residual solvent in the cast film reached 30%, and then the solvent was peeled from the stainless belt support at a peeling tension of 180 N / m.

(Drying process)
The peeled web having a residual solvent ratio of 10% by mass was dried on a transport roll at a drying temperature at a transport tension of 100 N / m and a drying time of 15 minutes so that the amount of residual solvent was less than 0.1% by mass, and the drying film thickness was 25 μm. I got the film. The resulting film was wound up.

(Heating process)
The wound film was heat-treated at 100 ° C. for 5 minutes with an infrared heater to obtain a cycloolefin film 1.

[Example 14]
The dope was adjusted in the same manner as in Example 13 except that a commercially available RX4500: ARTON-RX4500 (manufactured by JSR Corporation, weight average molecular weight (Mw) = 63000) was used as the cycloolefin resin (COP). Film 14 was obtained.

[Example 15]
A polyimide film was produced by the method shown below.

(Synthesis of Polyimide A)
100 g (0.31 mol) of 2,2'-bis (trifluoromethyl) benzidine, 500 g of hexafluoroisopropyl alcohol, (2.5% Pt-2.5% Pd /) in a 1 L volume autoclave with a stirrer. C) 17 g of the supported catalyst was added.

After the inside of the reactor was replaced with hydrogen in the state where stirring was stopped, the bath temperature was gradually raised, and the reduction reaction was carried out at a hydrogen pressure of 1.0 MPa while adjusting the internal temperature to around 100 ° C. Since the absorption of hydrogen was almost completed in 2 hours, the reactor was ice-cooled and the hydrogen in the reactor was gradually purged. When the reaction solution was filtered to remove the catalyst (2.5% Pt-2.5% Pd / C) and then the product was isolated by distillation, about 22 g of diamine was obtained (yield 21. 6%).

1.18 g (3.54 mmol) of the synthesized diamine, 1.57 g (3.54 mmol) of 4,4'-(hexafluoroisopropyridene) diphthalic anhydride, N- in a 300 ml three-necked flask equipped with a stirrer. 13.4 ml of methyl-2-pyrrolidone was added, and the mixture was stirred at 80 ° C. for 3 hours under a nitrogen stream. The obtained reaction solution was allowed to cool to room temperature and then poured into methanol / water (1/1 volume%) to precipitate a polymer. After recovery by filtration, the mixture was dried under reduced pressure at 35 ° C. to obtain 2.61 g of white powder polyamic acid A represented by the following formula (yield 95%).

54 g of the polyamic acid A repeatedly synthesized as described above was weighed and dissolved in dimethylacetamide. Next, after developing on a clean glass plate, heat treatment was performed at 200 ° C. for 1 hour and 310 ° C. for 1 hour under a nitrogen stream to obtain 47 g of polyimide A represented by the following formula as a transparent polyimide (yield). Rate 92%).

(Preparation of dope)
(Composition of main dope)
Tetrachloromethane 396 parts by mass Ethanol 4 parts by mass Polyimide A (weight average molecular weight: 203000, imidization rate: 100%)
100.0 parts by mass Particles: Nippon Aerosil Co., Ltd. R812 (primary particle size 7 nm) 0.1 parts by mass

A main dope having the above composition was prepared. First, tetrachloromethane and ethanol (ETOH) were added as a mixed solvent to the pressurized dissolution tank. The content of alcohol in the mixed solvent was 10% by mass. The polyimide A prepared above was put into a pressure dissolution tank containing the mixed solvent with stirring. This is heated and completely dissolved while stirring, and this is Azumi Filter Paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. After filtering using 244, the remaining components were added and stirred to dissolve to prepare the main dope.

Then, tetrachloromethane volatilized during heating and stirring was agglomerated using a cooling facility to form a liquid, which was added dropwise to the dope so that the amount added to the total amount of the dope was 10% by mass.

(Hypersalivation process)
Then, using an endless belt casting device, the dope was uniformly cast on the stainless belt support at a temperature of 30 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled to 30 ° C.

(Peeling process)
The solvent was evaporated on the stainless belt support until the amount of residual solvent in the cast film reached 75%, and then the solvent was peeled from the stainless belt support at a peeling tension of 180 N / m.

(Drying process)
The peeled web having a residual solvent ratio of 30% by mass was dried on a transfer roll at a drying temperature at a transfer tension of 100 N / m and a drying time of 15 minutes at a drying temperature at which the amount of residual solvent was less than 0.1% by mass, and the drying film thickness was 25 μm. I got the film. The resulting film was wound up.

(Heating process)
The wound film was heat-treated at 300 ° C. for 5 minutes with an infrared heater to obtain a polyimide film 1.

[Comparative Example 1]
In the preparation of the dope, the polyarylate film was added in the same manner as in Example 3 except that pure ethanol, which was different from the ethanol prepared as the main dope component, was added to the dope so that the amount added to the total amount of the dope was 10% by mass. I got 13.

[Comparative Example 2]
In the preparation of the dope, a polyarylate film 14 was obtained in the same manner as in Example 3 except that the main dope was changed to the following dope.

(Composition of main dope)
Dichloromethane 400 parts by mass Polyarylate 1 100 parts by mass Particles: Nippon Aerodil Co., Ltd. R812 (primary particle size 7 nm) 0.1 parts by mass

[Reference example]
(Composition of main dope)
Dichloromethane 440 parts by mass Ethanol 40 parts by mass Cellulose triacetate (vinegarization degree 61.0%, Mn = 148,000, Mw = 310,000, Mw / Mn = 2.1)
100 parts by mass Particles: Nippon Aerosil Co., Ltd. R812 (primary particle size 7 nm) 0.1 parts by mass

An attempt was made to produce a cellulose triacylate film in the same manner as in Example 3 except that the above main dope was used, but the film could not be produced.

It is considered that this is because the cellulose dope and dichloromethane have a high affinity, and the dope is partially diluted by the solvent added afterwards, resulting in uneven concentration.

<Evaluation>
The following evaluation tests were performed on each of the films (Examples 1 to 15 and Comparative Examples 1 and 2) obtained as described above.

[Scatterability evaluation]
The obtained optical film was placed between two polarizing plates in an orthogonal (cross-nicol) state, illuminated from one polarizing plate side, and visually observed from the other polarizing plate side. The number of bright spot foreign substances (pieces / m ² ) was measured. At that time, a plurality of locations such as the central portion and the end portion in the width direction were observed within a range of 100 m in length of the optical film.

Then, when the number of bright spot foreign substances was 1/2 or less of the film produced by the normal process, it was evaluated as "⊚", the equivalent to 1/2 was evaluated as "◯", and the deteriorated one was evaluated as "x".

[Internal haze]
For each film, the internal haze of the film was measured according to the following method. First, a glass slide glass that had been thoroughly washed was used, and the glass / glycerin / film / glycerin / glass was laminated in this order. Glycerin was added dropwise (0.05 ml), being careful not to allow air bubbles to enter. After that, using an internal haze measuring device (haze meter (turbidity meter) (model: NDH 2000, manufactured by Japanese Industrial Standards Co., Ltd.)), the light source is a 5V9W halogen bulb and the light receiving part is a silicon photocell (luminous efficiency filter). The internal haze (%) was measured according to JIS K-7136.

Slide glass used: MICRO SLIDE GLASS S9213 MATSUNAMI, cover glass: Matsunami cover glass 24 x 50 mm (KN3321827), glycerin: Kanto Kagaku Co., Ltd. deer special grade (purity> 99.0%), refractive index 1.47. ..

The evaluation criteria are as follows:
×: 0.2 or more with actual damage Δ: more than 0.15 to less than 0.2 No actual damage ○: 0.1 to 0.15 Good ⊚: less than 0.1 Excellent results are shown in Table 1.

[Discussion]
As can be seen from Table 1, in Examples 1 to 13 obtained by the production method of the present invention, it was shown that the impurities of the doping could be efficiently removed and a high-quality optical film having a low internal haze could be produced.

On the other hand, in Comparative Example 1 in which a good solvent was not added after the dope preparation, a bright spot foreign substance was observed and the internal haze was also high. It is considered that this is because the impurities in the dope could not be removed.

Further, even in Comparative Example 2 in which alcohol was not added as the solvent for the main dope, a bright spot foreign substance was observed, and the internal haze was slightly increased. It is considered that this is because the dope and dichloromethane are compatible with each other, so that the effect of removing impurities in the dope could not be obtained only by diluting the dope.

On the other hand, from the results of Examples 1 and 2, it was also found that the larger the amount of the good solvent added after the dope preparation, the more the impurities can be removed, and the better the evaluation of the scattering property and the internal haze.

This application is based on Japanese Patent Application No. 2016-200596 filed on October 12, 2016, the contents of which are included in the present application.

In order to express the present invention, the present invention has been appropriately and sufficiently described through the embodiments with reference to specific examples and the like, but those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that it can be done. Therefore, unless the modified or improved form implemented by a person skilled in the art is at a level that deviates from the scope of rights of the claims stated in the claims, the modified form or the improved form is the scope of rights of the claims. It is interpreted as being comprehensively included in.

The present invention has a wide range of industrial applicability in the technical field relating to optical films and methods for producing the same.

Claims (3)

In the solution casting film forming method, a polyimide resin, a polyarylate resin or a cycloolefin resin, and at least one alcohol solvent, to prepare a dope containing at least one good solvent for said resin, before on a support In a method for producing an optical film by casting a dope, forming a web (casting film) on a support, peeling the web from the support, and then winding the peeled web and drying it. ,
A method for producing an optical film, comprising a step of further adding a good solvent to the dope after preparing the dope, and then a step of removing the good solvent before casting the dope on the support. The method for producing an optical film according to claim 1, wherein the good solvent is dichloromethane or tetrachloromethane. The method for producing an optical film according to claim 1 or 2, wherein the amount of the good solvent to be added is 1 to 50% by mass with respect to the total amount of the doping.

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