JP6696451B2 - Optical film manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an optical film used in a liquid crystal display device or the like.

  Various optical films (for example, a transparent protective film for protecting a polarizing element of a polarizing plate) are arranged in the image display area of the liquid crystal display device.

  As such an optical film, a resin film having excellent transparency such as a cellulose ester film is used. Such an optical film is often manufactured as a long resin film by, for example, a solution casting (film forming) method.

  Specifically, the solution casting method is obtained by casting a resin solution (dope) in which a transparent resin, which is a raw material resin, is dissolved in a solvent onto a running support and drying it to a peelable degree. By peeling the formed web (also referred to as a dope film or cast film) from the support and performing drying or stretching while conveying the peeled web with a conveying roller, a long resin film is formed. is there.

  In this way, when producing an optical film by the solution casting method, the dope is continuously cast on a rotating support to peel off and form a film, but when the factory is operating for a long time, it gradually becomes on the support. Dirt such as peeling residue accumulates. In this case, conventionally, there was a problem that the production efficiency was poor because it was necessary to manually clean the belt after stopping. Further, in recent years, there is a tendency that the width of the film is increased and the support itself is also widened, and the cleaning area is further expanded, and the load is increased in the manual cleaning.

  With respect to such a problem of stains on the support, some means have conventionally been considered as a method for cleaning the support.

  For example, by selecting a cleaning cloth to be used at the time of wiping work, studies have been made to increase the occurrence of scratches during wiping and the stain removal rate (Patent Document 1).

  In addition, a method of identifying a main component of dirt as Ca salt and selecting a material having a low Ca concentration that does not easily generate it (Patent Document 2), and a process condition (Patent Document 3) in which Ca salt / Mg salt hardly precipitates Is being considered.

  Alternatively, a method of spraying a dry ice cleaning gas onto the support after peeling (Patent Document 4), or a method of decomposing / removing organic substances adhering to the surface of the support by supplying oxygen radicals (Patent Document 5) Proposed. Further, a method of improving peelability by adding an acrylic compound called a cleaning agent to the dope to suppress the generation of stains (Patent Document 6) and a method of defining the peeling stability condition of the gel film (Patent Document 7). Has also been reported so far.

JP, 2011-24567, A JP, 2006-199029, A JP, 2006-95971, A JP, 2007-269013, A JP, 2008-265313, A JP, 2009-34946, A JP, 2004-98513, A JP, 2004-291448, A

  However, according to the method described in Patent Document 1, although the efficiency of the cleaning operation itself is certainly improved, the device that had been operating is stopped, so that a time loss for that purpose still occurs. According to the method of Patent Document 2 or 3, the precipitation of Ca salt or Mg salt is suppressed and the continuous production time is extended, but if the accumulated amount increases, eventually it is necessary to perform cleaning after the stoppage, which results in time loss. Will occur. Both of the methods of Patent Documents 4 and 5 enable online cleaning work, but there is a problem in that remodeling costs due to new equipment are required. Although the cleaning agent in the method described in Patent Document 6 has good compatibility with the cellulose ester, it may cause a problem depending on the additive, which causes a restriction on the dope formulation. According to the technique described in Patent Document 7, dirt can be suppressed by taking the peeling stability condition, but complete suppression cannot be achieved. Therefore, when dirt is accumulated, cleaning work is also required after the stop.

  The present invention has been made in view of such circumstances, and provides a manufacturing method for efficiently removing stains on a support by a solution casting method to obtain a high-quality thin film with excellent productivity. To aim.

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

  The method for producing an optical film according to an aspect of the present invention is a method for producing an optical film by a solution casting film forming method, and at least a cast dope, which is a raw material solution of the optical film, is cast on a support, A casting process of forming a web (cast film) on a support, a peeling process of peeling the web from the support, a drying process of drying the peeled web to obtain a film, and a winding process of winding the film. And a cleaning step of cleaning the surface of the support at least during the peeling step, and in the cleaning step, the same dope as in the production of the product is cast to form a web on the support. Then, the residual solvent ratio Z of the web represented by the following formula when peeling the web from the support is adjusted to a range of Z = 30 to 70%, and the web is removed from the support in the cleaning step. Peel off Peel force which is required for the, being greater than the peeling force necessary upon the release of the web from the support in the release step during product production, method for producing an optical film.

Residual solvent ratio Z (%) = {(W-V) / V} × 100
(In the formula, W represents the mass of the web containing the solvent, and V represents the mass when W is dried at 120 ° C. for 2 hours)
With such a configuration, it is possible to efficiently remove the stain on the support without stopping the equipment of the factory such as the manufacturing apparatus, and it is possible to improve the production efficiency of the film.

  Further, the peeling force required to peel the web from the support in the cleaning step is 1.15 to 5.00 times the peeling force required to peel the web from the support in the peeling step. Is preferred. Thereby, the above-mentioned effect can be obtained more reliably.

  Further, in the above-mentioned method for producing an optical film, it is preferable that the film is wound up by 1000 m or more in the cleaning step. This makes it possible to remove the stains on the support more reliably.

  According to the present invention, stains on a support can be efficiently removed without stopping the factory equipment such as a manufacturing apparatus, and thus an optical film can be manufactured with high production efficiency.

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

  In the solution casting method, it is known that the peeling load changes depending on the web residual solvent ratio (%) at the time of peeling the web from the support, and the low residual solvent (Z = 0 to 40% residual solvent). It is reported that there is a peak (peeling peak) where the peeling load becomes high between the ratio; Z is as described later) and the high residual solvent (Z = 65 to 120% residual solvent ratio) (Patent Document). 8).

  As a result of intensive studies by the present inventors, the peak of the peeling (residual solvent ratio region where the peeling force is high), which was conventionally considered to promote peeling residue on the support, is certainly long time. It has been found that, if the peeling is continued at the peak, stains are accumulated, but if the peeling force is short, the peeling force can be used to remove the stains adhering to the surface of the support. Furthermore, in the method that uses this peeling force, the product can be brought to the so-called “belt cleaning state” by simply changing the peeling residual solvent ratio from the product manufacturing conditions, so cleaning can be performed by flowing the web for a very short time. It was found that it is possible to quickly return to normal production conditions after completing the above. Based on these findings, further research was conducted to complete the present invention.

That is, the method for producing an optical film according to an aspect of the present invention is a method for producing an optical film by a solution casting film forming method, in which at least a dope, which is a raw material solution for an optical film, is cast on a support, A casting process of forming a web (cast film) on a support, a peeling process of peeling the web from the support, a drying process of drying the peeled web to obtain a film, and a winding process of winding the film. It has a taking step and a cleaning step of cleaning the surface of the support, and in the cleaning step, the same dope as in the production of the product is cast to form a web on the support, and the web is formed from the support. It is necessary to adjust the residual solvent ratio Z of the web represented by the following formula at the time of peeling to the range of Z = 30 to 70%, and to peel the web from the support in the cleaning step. The peeling force is larger than the peeling force required for peeling the web from the support in the peeling step.
Residual solvent ratio Z (%) = {(W-V) / V} × 100
(In the formula, W represents the mass of the web containing the solvent, and V represents the mass when W is dried at 120 ° C. for 2 hours)

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

[Method for producing optical film]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus used in this embodiment. The method for producing an optical film of the present embodiment uses a solution casting method in which a dope containing a polymer and a solvent is cast from a casting die on a running support and then peeled as a film.

  The manufacturing method of the present embodiment includes at least the casting process, the peeling process, the drying process, the winding process, and the cleaning process as described above. Hereinafter, each step of the manufacturing method of the present embodiment will be described in more detail.

  As shown in FIG. 1, first, in a casting step, a resin such as cellulose ester is dissolved in a mixed solvent of a good solvent and a poor solvent in a dissolution pot 1 and a plasticizer, an ultraviolet absorber, etc. are added to this. The agent is added to prepare a resin solution (dope). The good solvent and the poor solvent will be described later.

  Then, the dope adjusted in the melting tank 1 is sent to the casting die 3 by a conduit through the pressurization type constant quantity gear pump 2 and is cast on a support body 6 made of a rotary drive stainless steel endless belt for endless transfer. At a position, the dope is cast from the casting die 3 to form a web 9 as a casting film on the support 6. At this time, a decompression chamber (decompression chamber) 4 is arranged upstream of the casting die 3 in the moving direction of the traveling support 6, and the decompression chamber 4 allows the decompression chamber 4 to be located upstream (especially The dope is cast from the casting die 3 onto the support 6 while depressurizing the space on the upstream side of the casting ribbon from the casting die 3 to the support 6.

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

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

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

  The belt temperature during film formation when an endless belt is used as the support 6 is a temperature of 0 ° C. to a temperature lower than the boiling point of the solvent in a general temperature range, but a temperature lower than the boiling point of the solvent having the lowest boiling point in the mixed solvent. And more preferably in the range of 5 ° C to the solvent boiling point-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity to be higher than the dew point. The moving speed of the support 6 under the production conditions is preferably 80 m / min to 200 m / min.

  In the dope cast on the support 6 in this manner, the strength of the gel film (film strength) also increases due to the acceleration of the drying until the stripping.

  On the support 6, the web 9 is dried and solidified until the film strength is such that it can be peeled from the support 6 by the peeling roll 8.

  Next, in the peeling step, the web 9 is peeled from the support 6. The total residual solvent amount of the web 9 when the web 9 is peeled off from the support 6 is the releasability from the support, the amount of residual solvent at the time of peeling, the transportability after peeling, the physical properties of the film formed after transporting and drying, Can be appropriately set in consideration of the above. For example, in the case of a cellulose ester film, 70% by mass to 170% by mass is preferable. Further, the ratio of the good solvent amount to the total residual solvent amount, the peelability of the web from the belt support, the residual solvent amount at the time of peeling, the transportability after peeling, the physical properties of the cellulose ester film produced after transport and drying, etc. Considering the above, 10% to 70% is preferable. It is preferably 5% to 60%, more preferably 5% to 30%.

In addition, in this embodiment, the residual solvent ratio Z is represented by the following formula.
Residual solvent ratio Z (%) = {(W-V) / V} × 100
(In the formula, W represents the mass of the web containing the solvent, and V represents the mass when W is dried at 120 ° C. for 2 hours)

  The web temperature when peeling the web 9 from the support 6 is preferably 0 to 30 ° C. Immediately after the web 9 is peeled from the support 6, the temperature of the web 9 is rapidly lowered by evaporation of the solvent from the contact surface side with the support 6, and volatile components such as water vapor and solvent vapor in the atmosphere easily condense. Therefore, the web temperature at the time of peeling is more preferably 5 to 30 ° C.

  The web 9 formed by the dope cast on the support 6 is heated on the support 6 to evaporate the solvent from the support 6 by the peeling roll 8 until the web can be peeled.

  To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the support 6 by a liquid, a method of transferring heat from the front and back sides by radiant heat, and the like, which may be used alone or in combination. Good.

  The peeling tension at the time of peeling the support 6 and the web 9 by the peeling roll 8 is larger than the peeling force obtained by the peeling force measurement such as JIS Z 0237, but this is because the peeling tension is set to JIS in high speed film formation. If the peeling force obtained by the measuring method is made equal, the peeling position may be brought to the downstream side, so the temperature is set higher for stabilization. It is also confirmed that even if the film is formed with the same peeling tension in the process, the variation in the crossed Nicol transmittance (CNT) of the film is significantly reduced when the peeling force according to the JIS measurement method is reduced.

  The peeling tension value in the step is usually 20 to 400 N / m, but in the optical film made thinner than the conventional one, the residual solvent amount of the web 9 is large at the time of peeling, and it easily extends in the transport direction. Therefore, the film tends to shrink in the width direction, and when drying and shrinkage overlap, curls occur at the ends, and wrinkles easily occur. Therefore, the peeling tension is preferably from the lowest peelable tension to 300 N / m, more preferably from the lowest tension to 200 N / m.

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

  After being dried and solidified on the support 6 until the web 9 has a peelable film strength, the web 9 is peeled off by a peeling roll 8 and, if necessary, the web 9 is stretched in a tenter 10 in a stretching step. May be.

  In the stretching step, as a film for a liquid crystal display device, a tenter system in which both side edges of the web 9 are fixed with clips or the like is preferable in order to improve flatness and dimensional stability of the film.

  The amount of residual solvent in the web 9 immediately before entering the tenter 10 in the stretching step is preferably 5 to 50% by mass, and more preferably 10 to 35% by mass. The stretching ratio of the web in the tenter 10 in the stretching step is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%.

  Further, the temperature of the warm air blown out from the warm air blowing slit port in the tenter 10 is 70 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  After the tenter 10 in the stretching process, the drying process is performed by the drying device 11. In the drying device 11, the web 9 is meandered by a plurality of transport rolls arranged in a zigzag shape when viewed from the side, and the web 9 is dried in the meantime. Further, the film transport tension in the drying device 11 is affected by the physical properties of the dope, the amount of residual solvent in peeling and in the film transport step, the drying temperature, etc., but the film transport tension during drying is 10 to 400 N / m. The width is 20 to 300 N / m, and the width is more preferable.

  The means for drying the web 9 is not particularly limited, and generally hot air, infrared rays, heating rolls, microwaves or the like are used. It is preferable to dry with hot air from the viewpoint of simplicity. For example, the web 9 can be dried by blowing the drying air 12 through the warm air inlet of the drying device 11 and discharging the exhaust air through the outlet of the drying device 11 to form the optical film F. The temperature of the dry air 12 is preferably 40 to 160 ° C., and more preferably 50 to 160 ° C. in order to improve flatness and dimensional stability.

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

  Before the introduction to the next winding step, the end of the optical film F is prevented in order to prevent winding deviation or blocking (sticking of the films) in the winding step before the optical film F that has been subjected to the transport and drying step. It is preferable to form an embossed portion having many irregularities on the portion.

  Next, the film on which the embossed portion has been formed is wound by the winding device 13 to obtain the original roll 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.

  The winding method of the film in the winding step of the present embodiment, a generally used winder may be used, the constant torque method, constant tension method, taper tension method, tension such as a program tension control method of constant internal stress There are ways to control, and you can use them properly. The film may be bonded to the take-up core (roll core) with either a double-sided adhesive tape or a single-sided adhesive tape. The width of the optical film F after winding is preferably 1000 to 2500 mm.

  Next, the cleaning process, which is a major feature of this embodiment, will be described. The cleaning step of this embodiment is a step of cleaning the surface of the support, and is performed at least during the above-described peeling step. Specifically, in the above peeling step, the same dope as in the production of the product is cast to form a web on a support, and the residual of the web represented by the above formula when the web is peeled from the support. The solvent ratio Z is adjusted in the range of Z = 30 to 70% for peeling, and the peeling force required when peeling the web from the support in this cleaning step is peeled off during product manufacturing. It is characterized in that it is made larger than the peeling force required for peeling the web from the support in the step.

  That is, in the manufacturing method of the present embodiment, when the manufacturing mode is switched to the cleaning mode, the residual solvent ratio and the peeling force of the web at the time of peeling in the peeling step are adjusted as described above to remain on the support. It is possible to remove stains.

  Means for adjusting the residual solvent ratio within the above range at the time of peeling in the cleaning step is not particularly limited.

  Specifically, for example, a method of adjusting by the flow rate of the dope, a method of adjusting by the drying temperature of the web, a method of adjusting by the traveling speed of the support and the like can be mentioned.

  In the method of adjusting by the flow rate of the dope, the film thickness deviation of the width becomes large and it may take time to restore to the production condition.Therefore, the method of adjusting by the traveling speed of the support or the drying temperature of the web The method is preferred.

  In the method of adjusting the drying temperature of the web, the residual solvent ratio can be controlled by adjusting the temperature to adjust the amount of solvent drying (volatilization). However, if the web temperature is raised too high, the boiling point of the solvent may be exceeded and foaming may occur as described above, and the unevenness of the drying temperature also increases. Therefore, it is necessary to adjust within a range where these do not pose a problem.

  In the method of adjusting by the traveling speed of the support, when the speed is changed, the drying time (residence time on the support) of the web and the film thickness (the same flow rate dope is stretched to become thinner as the speed of the support increases) change simultaneously. Therefore, it is necessary to take this into consideration. Regarding the above, since the contribution of the film thickness is usually large, the film thickness is made thin by increasing the speed and the residual solvent ratio is shifted to a lower side for adjustment.

  The residual solvent ratio Z of the web in the cleaning step of the present embodiment is slightly different depending on the main component of the dope used. For example, when a cyclic polyolefin resin is used as the main component, the residual solvent ratio Z is 70%. May exceed.

  Preferably, the peeling force required when peeling the web from the support in the cleaning step is 1.15 of the peeling force required when peeling the web from the support in the peeling step during product manufacturing. It is preferable to adjust it so that it will be up to 5.00 times. In this way, if the peeling force ratio at the time of manufacturing and cleaning is about 1.15 times, the cleaning effect can be more reliably obtained. However, if the peel force ratio becomes too large, the risk of dirt accumulation increases, so it is preferably 5.00 times or less. More preferably, the peeling force ratio is adjusted to 1.20 to 2.50 times.

  Such peeling force can be adjusted by adjusting the residual solvent ratio Z in the dope at the time of peeling.

  The cleaning step of the present embodiment can be performed for a time that provides an appropriate cleaning effect, but it is preferable that the cleaning step is performed for about 1000 m or more. Therefore, it is considered that the dirt on the support can be cleaned more reliably. There is no particular upper limit on the length of the cleaning step, but if the cleaning step is carried out for too long, the cleaning effect may decrease, so it is preferable that the film is wound up to about 50,000 m. This is because, if the cleaning process is performed for a long time, a peeling residue tends to occur when the state of high peeling force continues for a long time.

  The cleaning process of the present embodiment can be continuously performed after the film winding process described above in product manufacturing. Therefore, unlike the conventional cleaning of the support, it is not necessary to stop the device once to perform the cleaning, and the cleaning can be performed very efficiently. In addition, after the cleaning step is performed, the web separated in the cleaning step is dried and wound up, and subsequently, the casting step for manufacturing the product is performed, and the film can be continuously manufactured again.

  The film thickness after drying of the optical film obtained by the production method of the present embodiment is preferably in the range of 5 to 30 μm as a finished film from the viewpoint of thinning 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.

  In the method for producing an optical film by the solution casting film forming method of the present embodiment, in a resin solution (dope) containing a resin such as a cellulose ester as a main material, a plasticizer, a retardation modifier, an ultraviolet absorber, fine particles, and It is preferable that at least one substance selected from low molecular weight substances and a solvent are contained. Hereinafter, these materials will be described.

  In the present embodiment, various resins can be used as the film material, but among them, cellulose ester or cyclic polyolefin is preferably used.

  The cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylate such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among them, cellulose triacetate, cellulose acetate butyrate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. The cellulose ester used in the method of the present invention may contain other substituents.

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

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

  The number average molecular weight of the cellulose ester is preferably in the range of 20,000 to 300,000 because the resulting film has high mechanical strength. Further, 40,000 to 200,000 is preferable. Various additives can be added to the cellulose ester.

  In the method for producing an optical film according to the present embodiment, it is preferable to use a dope composition containing a cellulose ester and an additive that reduces the thickness direction retardation (Rt).

  Reducing the thickness direction retardation (Rt) of the cellulose ester film is important in the sense of widening the viewing angle of the liquid crystal display device operating in the IPS mode, but such an additive reducing the thickness direction retardation (Rt). The following may be mentioned as examples.

  Generally, the retardation of the cellulose ester film appears as the sum of the retardation derived from the cellulose ester and the retardation derived from the additive. Therefore, as the additive for reducing the retardation of the cellulose ester, the additive that disturbs the orientation of the cellulose ester and is difficult to orient itself and / or has a small polarizability anisotropy has a retardation (Rt) in the thickness direction. It is a compound that effectively reduces. Therefore, as an additive for disturbing the orientation of the cellulose ester, an aliphatic compound is preferable to an aromatic compound.

Here, specific retardation reducing agents include, for example, polyesters represented by the following general formula (1) or (2).
General formula (1) B1- (GA-) mG-B1
General formula (2) B2- (GA-) nG-B2
In the above formula, B1 represents a monocarboxylic acid component, B2 represents a monoalcohol component, G represents a divalent alcohol component, and A represents a dibasic acid component, which means that they are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

  The monocarboxylic acid component represented by B1 is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids and the like can be used.

  Examples of preferable monocarboxylic acid include the followings, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 12 carbon atoms. When acetic acid is contained, compatibility with cellulose ester is increased, which is preferable, and it is also preferable to use acetic acid and another monocarboxylic acid as a mixture.

  Preferred monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid. , Myristic acid, pentadecylic acid, palmitic acid, heptadecyl acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, melissic acid, saturated fatty acids such as lacceric acid, undecic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  The monoalcohol component represented by B2 is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or an aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1 to 20 carbon atoms, and particularly preferably 1 to 12 carbon atoms.

  Examples of the dihydric alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned, and among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 , 2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol and triethylene glycol are preferable, and 1,3-propylene glycol and 1,4-butylene glycol are more preferable. , 1,6-hexanediol and diethylene glycol are preferably used.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid, and examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, and the like. Particularly, as the aliphatic carboxylic acid, one having 4 to 12 carbon atoms, or at least one selected from these is used. To do. That is, two or more dibasic acids may be used in combination.

  The number of repetitions m and n in the above general formula (1) or (2) is preferably 1 or more and 170 or less.

  The mass average molecular weight of the polyester is preferably 20,000 or less, more preferably 10,000 or less. In particular, a polyester having a mass average molecular weight of 500 to 10,000 has good compatibility with cellulose ester, and neither evaporation nor volatilization occurs during film formation.

  Polycondensation of polyester is carried out by a conventional method. For example, a hot melt condensation method by a direct reaction between the above dibasic acid and glycol, a polyesterification reaction or a transesterification reaction between the above dibasic acid or an alkyl ester thereof, for example, a methyl ester of the dibasic acid and glycol, or Although it can be easily prepared by any method of dehydrohalogenation reaction of acid chloride of these acids and glycol, it is preferable that polyester having a not so large mass average molecular weight is directly reacted. Polyester, which has a high distribution on the low molecular weight side, has a very good compatibility with cellulose ester, and after the film formation, it is possible to obtain a highly transparent cellulose ester film having low moisture permeability.

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, depending on the polymerization conditions, it can be controlled by a method of blocking the molecular end with a monovalent acid or a monovalent alcohol, and the amount added of these monovalent ones. In this case, a monovalent acid is preferable because of the stability of the polymer. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but when they are stopped by removing such monovalent acid outside the reaction system during the polycondensation reaction, they are not distilled off outside the system. Those that are easy to remove are selected. You may mix and use these. In the case of a direct reaction, the mass average molecular weight can be adjusted by measuring the timing of stopping the reaction depending on the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid charged, or can be adjusted by controlling the reaction temperature.

  The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by mass based on the cellulose ester. It is particularly preferable to contain 5 to 15 mass%.

  Examples of the additive that reduces the retardation (Rt) in the thickness direction further include the following.

  The dope used in the production of the optical film of the present embodiment is mainly a cellulose ester, a polymer as an additive for reducing retardation (Rt) (a polymer obtained by polymerizing an ethylenically unsaturated monomer, an acrylic polymer). , And an organic solvent.

  In order to synthesize a polymer as an additive for reducing the retardation (Rt) in the thickness direction, it is difficult to control the molecular weight by ordinary polymerization, and it is desirable to use a method that can make the molecular weight uniform as much as possible without increasing the molecular weight too much. . As such a polymerization method, a method using a peroxide polymerization initiator such as cumene peroxide or t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than usual polymerization, and a mercapto compound in addition to the polymerization initiator And a method of using a chain transfer agent such as carbon tetrachloride, a method of using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and further, JP-A-2000-128911 or 2000-344823. Examples thereof include a compound having one thiol group and a secondary hydroxyl group as described in the publication, or a method of bulk polymerization using a polymerization catalyst in which the compound and an organometallic compound are used in combination, and both are preferably used. However, the method described in the publication is particularly preferable.

  Examples of the monomer as a monomer unit constituting the polymer as an additive for reducing the useful thickness-direction retardation (Rt) are shown below, but are not limited thereto.

  The ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the retardation in the thickness direction (Rt) obtained by polymerizing the ethylenically unsaturated monomer is first a vinyl ester such as vinyl acetate or propionic acid. Vinyl, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, Examples thereof include vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate and the like.

  Next, as the acrylate ester, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those changed to methacrylic acid esters.

  Furthermore, examples of unsaturated acids include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, and itaconic acid.

  The polymer composed of the above monomers may be a copolymer or a homopolymer, and is preferably a homopolymer of vinyl ester, a copolymer of vinyl ester, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester.

  The term “acrylic polymer” (simply referred to as “acrylic polymer”) refers to a homopolymer or copolymer of acrylic acid or methacrylic acid alkyl ester having no monomer unit having an aromatic ring or a cyclohexyl group.

  Examples of the acrylate ester monomer having no aromatic ring and cyclohexyl group include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-). , Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid 2-methoxy-ethyl), acrylic acid (2-ethoxyethyl), or the acrylic acid ester may include those obtained by changing the methacrylic acid ester.

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30 mass% or more, and the methacrylic acid methyl ester monomer unit has 40 mass% or more. Preferably. A homopolymer of methyl acrylate or methyl methacrylate is particularly preferable.

  Polymers obtained by polymerizing the above-mentioned ethylenically unsaturated monomers, acrylic polymers are both excellent in compatibility with cellulose ester, excellent in productivity without evaporation or volatilization, and retainability as a protective film for polarizing plate. Good, low moisture permeability, and excellent dimensional stability.

  In the case of an acrylic acid or methacrylic acid ester monomer having a hydroxyl group, it is a constituent unit of a copolymer, not a homopolymer. In this case, it is preferable that the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is contained in the acrylic polymer in an amount of 2 to 20% by mass.

  In the method for producing an optical film of the present embodiment, the dope composition contains a cellulose ester and an acrylic polymer having a mass average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). Preferably.

  Further, in the present embodiment, it is preferable that the dope composition contains a cellulose ester and an acrylic polymer having a mass average molecular weight of 5,000 or more and 30,000 or less as an additive that reduces retardation (Rt) in the thickness direction.

  Compatibility with cellulose ester if the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or if the weight average molecular weight of the polymer is 5000 or more and 30000 or less. Is good, and neither evaporation nor volatilization occurs during film formation. Further, the formed cellulose ester film has excellent transparency and extremely low moisture permeability, and exhibits excellent performance as a protective film for a polarizing plate.

  As an additive for reducing the retardation in the thickness direction (Rt), a polymer having a hydroxyl group in the side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the above-mentioned monomer, but acrylic acid or methacrylic acid ester is preferable, and for example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids Those substituted with methacrylic acid can be mentioned, and 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate are preferable. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by mass, more preferably 2 to 10% by mass.

  The polymer containing 2 to 20% by mass of the above-mentioned hydroxyl group-containing monomer unit is, of course, not only excellent in compatibility with cellulose ester, retention, and dimensional stability, but also low in moisture permeability, The adhesiveness to a polarizer as a protective film for a polarizing plate is particularly excellent, and it has the effect of improving the durability of the polarizing plate.

  Further, it is preferable that at least one end of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the terminal of the main chain is not particularly limited as long as it has a hydroxyl group at the terminal of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ionic polymerization, A compound having one thiol group and a secondary hydroxyl group as described in JP 2000-128911 A or JP 2000-344823 A, or a bulk using a polymerization catalyst in which the compound and an organometallic compound are used in combination. It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Actflow Series manufactured by Soken Chemical Industry Co., Ltd. and can be preferably used.

  The above-mentioned polymer having a hydroxyl group at the terminal and / or a polymer having a hydroxyl group at the side chain has an advantage of significantly improving the compatibility and transparency of the polymer with the cellulose ester.

  As a useful additive for reducing the retardation in the thickness direction (Rt), in addition to the above, for example, an ester compound of a diglycerin-based polyhydric alcohol and a fatty acid described in JP-A-2000-63560, JP-A-2001-247717. Ester or ether compound of sugar alcohol of hexose described in JP-A No. 2004-315613, tri-aliphatic phosphate ester compound described in JP-A 2004-315613, and compound represented by general formula (1) described in JP-A 2005-41911. , A phosphoric acid ester compound described in JP-A-2004-315605, a styrene oligomer described in JP-A-2005-105139, and a polymer of a styrene-based monomer described in JP-A-2005-105140.

  In the method for producing an optical film according to the present embodiment, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and also exhibits a main effect on the dissolution, in which the organic solvent used in large amounts is mainly used. It is called an (organic) solvent or a main (organic) solvent.

  Examples of the good solvent include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, ethers such as 1,2-dimethoxyethane, and formic acid. In addition to esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, etc., methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide, sulfolane, nitroethane, methylene chloride. , 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferred.

  In addition to the above organic solvent, the dope preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms. These are gels that, after casting the dope on the support, cause the solvent to start to evaporate and increase the proportion of alcohol, thereby gelling the web, making the web strong, and easily peeling it from the support. It also has the role of being used as a solubilizing solvent, or promoting the dissolution of the cellulose derivative of the non-chlorine organic solvent when the proportion of these is small.

  Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol and propylene glycol monomethyl ether. Of these, ethanol is preferable because it is excellent in stability of the dope, has a relatively low boiling point, has good drying property, and has no toxicity. These organic solvents alone have no solubility in the cellulose derivative and are called poor solvents.

  The most preferable solvent for dissolving the cellulose derivative, which is a preferable polymer compound satisfying such conditions, in a high concentration is a mixed solvent having a methylene chloride: ethyl alcohol ratio of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

  In the present embodiment, the optical film includes a plasticizer which imparts processability, flexibility and moisture resistance to the film, fine particles (matting agent) which imparts slipperiness to the film, an ultraviolet absorber which imparts an ultraviolet absorbing function, You may contain antioxidant etc. which prevent deterioration of a film.

  The plasticizer used in the solution casting film-forming method is not particularly limited, but it is a cellulose derivative or a reactive compound capable of hydrolytic polycondensation so that haze is generated in the film or bleeding out or volatilization from the film is prevented. It preferably has a functional group capable of interacting with a polycondensate of a metal compound by a hydrogen bond or the like.

  Such functional groups include hydroxyl group, ether group, carbonyl group, ester group, carboxylic acid residue, amino group, imino group, amide group, imide group, cyano group, nitro group, sulfonyl group, sulfonic acid residue, Examples thereof include a phosphonyl group and a phosphonic acid residue, but a carbonyl group, an ester group and a phosphonyl group are preferable.

  Examples of such plasticizers include phosphoric acid ester plasticizers, phthalic acid ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester-based plasticizers, fatty acid ester-based plasticizers, carboxylic acid ester-based plasticizers, polyester-based plasticizers and the like can be preferably used, but polyhydric alcohol ester-based plasticizers and glycolate-based plasticizers are particularly preferable. And non-phosphoric acid ester plasticizers such as polyhydric carboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of an aliphatic polyhydric alcohol having a valence of 2 or more and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

The polyhydric alcohol used in this embodiment is represented by the following general formula (1).
General formula (1) R1- (OH) n
(However, R1 is an n-valent organic group, and n is a positive integer of 2 or more.)

  Examples of preferable polyhydric alcohols include the followings, but the present invention is not limited thereto.

  Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gas Lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like can be mentioned. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane and xylitol are preferable.

  The monocarboxylic acid used for the polyhydric alcohol ester is not particularly limited, and known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. It is preferable to use an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid in terms of improving moisture permeability and retention.

  Examples of preferable monocarboxylic acid include the followings, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a linear or side chain fatty acid having 1 to 32 carbon atoms can be preferably used. The carbon number is more preferably 1 to 20, and particularly preferably 1 to 10. It is preferable to contain acetic acid because the compatibility with the cellulose derivative is increased, and it is also preferable to use acetic acid and another monocarboxylic acid as a mixture.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Saturated fatty acids such as tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecyl acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, melicinic acid, lacceric acid, and undecylene. Examples thereof include unsaturated fatty acids such as acids, oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  Examples of preferable alicyclic monocarboxylic acid include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

  Examples of preferable aromatic monocarboxylic acid include benzoic acid, toluic acid and other benzoic acid having an alkyl group introduced into the benzene ring, biphenylcarboxylic acid, naphthalenecarboxylic acid, tetralincarboxylic acid and the like having two or more benzene rings. Examples thereof include aromatic monocarboxylic acids or derivatives thereof, and benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, more preferably 350 to 750. A higher molecular weight is preferable because it is less likely to volatilize, and a lower molecular weight is preferable in terms of moisture permeability and compatibility with the cellulose derivative.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Further, all the OH groups in the polyhydric alcohol may be esterified, or a part thereof may be left as it is.

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. Preferred glycolate plasticizers include, for example, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate and the like.

  Phosphate ester plasticizers include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc.Phthalate ester plasticizers include diethyl phthalate and dimethoxy Although ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate and the like can be used, it is preferable that the phosphoric acid ester plasticizer is not substantially contained.

  Here, the phrase "substantially free from" means that the content of the phosphoric acid ester plasticizer is less than 1% by mass, preferably 0.1% by mass, and particularly preferably no addition.

  These plasticizers can be used alone or in combination of two or more.

  The amount of the plasticizer used is preferably 1 to 20% by mass. It is more preferably 6 to 16% by mass, and particularly preferably 8 to 13% by mass. If the amount of the plasticizer used is less than 1% by mass relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so it is not preferable. If it exceeds 20% by mass, the plasticizer bleeds out from the film, Is not preferable because the physical properties of are deteriorated.

  It is preferable to add fine particles such as a matting agent to the cellulose derivative in the present embodiment in order to impart slipperiness. Examples of the fine particles include fine particles of an inorganic compound and fine particles of an organic compound.

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

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

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

  The average particle size of the fine particles refers to the average value of the lengths of the particles in the long axis direction at the observation location of the film when the cellulose ester film is observed with an electron microscope or an optical microscope. The particles observed in the film may be primary particles or secondary particles obtained by aggregating the primary particles, but most of the particles usually observed are secondary particles.

  As an example of the measuring method, 10 vertical cross-section photographs are randomly taken for each film, and the number of particles in 100 μm 2 having a major axis length in the range of 0.05 to 5 μm is taken for each cross-sectional photograph. To count. The average value of the major axis lengths of the particles counted at this time is calculated, and the average value of 10 points is taken as the average particle diameter.

  In the case of fine particles, the primary particle diameter, the particle diameter after being dispersed in a solvent, and the particle diameter added to the film often change. What is important is that the final particles in the film are complexed with cellulose ester and aggregated. The purpose is to control the particle size formed by.

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

  The above fine particles are used by adding 0.04 to 0.8 mass% to cellulose ester. It is preferably used by adding 0.05 to 0.5% by mass, more preferably 0.05 to 0.35% by mass. When the amount of the fine particles added is 0.04% by mass or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of the fine particles added exceeds 0.5% by mass, the coefficient of friction of the film surface will be too low and winding misalignment will occur at the time of winding, or the transparency of the film will be low and haze will be high, so for liquid crystal display devices. The above range is essential because it has no value as a film.

  The fine particles are preferably dispersed by treating the composition obtained by mixing the fine particles and the solvent with a high-pressure dispersing device. The high-pressure dispersion device used in the solution casting film formation method is a device that creates special conditions such as high shear and high-pressure conditions by passing a composition obtained by mixing fine particles and a solvent through a thin tube at high speed.

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

  Examples of the high-pressure disperser as described above include an ultra-high-pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or Nanomizer manufactured by Nanomizer, and other manton-gorin type high-pressure dispersers, for example, manufactured by Izumi Food Machinery. Homogenizer etc. are mentioned.

  In the solution casting film formation method, the fine particles are dispersed in a solvent containing 25 to 100% by mass of a lower alcohol, and then mixed with a dope prepared by dissolving a cellulose ester (cellulose derivative) in the solvent to support the mixed solution. A cellulose ester film is obtained which is cast on a body, dried and formed into a film.

  Here, the content ratio of the lower alcohol is preferably 25 to 100% by mass, more preferably 50 to 100% by mass.

  In addition, examples of lower alcohols include preferably methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  The solvent other than the lower alcohol is not particularly limited, but it is preferable to use the solvent used when forming the cellulose ester film.

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by mass. Dispersion at a concentration higher than this is not preferable because the viscosity rapidly increases. The concentration of fine particles in the dispersion liquid is preferably 5 to 25% by mass, more preferably 10 to 20% by mass.

  The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on the film made of the cellulose derivative.

  Examples of the ultraviolet absorber that can be used in the solution casting film formation method include oxybenzophenone compounds, benzotriazole compounds, salicylate compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex salt compounds, and the like. However, a benzotriazole-based compound that is less colored is preferable. Further, the ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574, and the polymer ultraviolet absorber described in JP-A-6-148430 are also preferably used.

  As the ultraviolet absorber, those having excellent absorption ability for ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the polarizer and liquid crystal, and having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display property are available. preferable.

  Specific examples of useful UV absorbers include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole and 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzo. Triazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5- Chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-Tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl)- 5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3- [3-tert-butyl-4-hydroxy- 5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) ) Phenyl] propionate mixture and the like can be mentioned, but not limited thereto.

  Further, as commercially available ultraviolet absorbers, TINUVIN 928, TINUVIN 109, TINUVIN 171, and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Further, specific examples of the benzophenone-based compound that is the ultraviolet absorber that can be used in the present embodiment include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-methoxy-5. -Sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane) and the like can be mentioned, but the invention is not limited thereto.

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, based on the cellulose ester (cellulose derivative). If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient, and if the amount of the ultraviolet absorber used is too large, the transparency of the film may deteriorate, which is not preferable. It is preferable that the ultraviolet absorber has high heat stability.

  Further, the ultraviolet absorber that can be used in the optical film of the present embodiment is preferably the high molecular ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357. Can be used. Particularly, it is represented by the general formula (1) or the general formula (2) described in JP-A-6-148430, or the general formulas (3), (6) and (7) described in JP-A-2002-47357. A polymeric UV absorber is preferably used.

  The antioxidant, which is generally referred to as a deterioration inhibitor, is preferably contained in the cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid-based plasticizer, so it is preferable to include it in the film. .

  As such an antioxidant, a hindered phenol-based compound is preferably used, and examples thereof include 2,6-di-t-butyl-p-cresol and 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-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-2,4 , 6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate and the like can be mentioned. . In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-Butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N'-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t). A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  The addition amount of these compounds is preferably 1 ppm to 1.0% by mass and more preferably 10 to 1000 ppm in terms of mass ratio with respect to the cellulose derivative.

  Next, for the dope containing mainly the cyclic polyolefin resin, in an organic solvent mainly containing a good solvent for the cyclic polyolefin resin, the cyclic polyolefin resin in a dissolution pot, in some cases, a plasticizer or various function expressing agents ( For example, an antioxidant, a light stabilizer, an ultraviolet absorber, a retardation adjuster, a peeling accelerator, an infrared absorber, a matting agent, etc.) can be dissolved with stirring to obtain a dope.

  When producing the cyclic polyolefin film of the present embodiment, the organic solvent useful for preparing the dope can be used without limitation as long as it can dissolve the cyclic polyolefin resin and other compounds at the same time.

  For example, the chlorine-based organic solvent is dichloromethane, and the non-chlorine-based organic solvent is methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2 , 2,2-Trifluoroethanol, 2,2,3,3-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 and the like can be mentioned. For example, dichloromethane, methyl acetate, ethyl acetate, acetone can be preferably used as a main solvent, and dichloromethane or ethyl acetate is particularly preferable.

  In addition to the above organic solvent, the dope preferably contains a linear or branched aliphatic alcohol having 1 to 4 carbon atoms in the range of 1 to 40% by mass. When the proportion of alcohol in the dope is high, the web is gelled, which facilitates peeling from the metal endless support, and when the proportion of alcohol is low, cyclic polyolefin and other polyolefins in a chlorine-free organic solvent system. It also has the role of promoting dissolution of the compound. In forming the cyclic polyolefin film of the present invention, a method of forming a film using a dope having an alcohol concentration in the range of 0.5 to 15.0 mass% from the viewpoint of enhancing the flatness of the obtained cyclic polyolefin film. Can be applied.

  In particular, a dope composition in which a cyclic polyolefin and other compounds are dissolved in a total amount of 15 to 45% by mass in a solvent containing dichloromethane and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. Is preferred.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol and tert-butanol. Of these, methanol and ethanol are preferable because the dope is stable, the boiling point is relatively low, and the drying property is good.

  In the present embodiment, it is preferable that a small amount of toluene is contained in the organic solvent, and the content of toluene in the dope is within the range of 0.001 to 0.1% by mass by adding other organic solvents and additives. It is preferable to adjust The inclusion of toluene increases the solubility of foreign matter due to the resin in the dope, and the effect of reducing foreign matter failure becomes remarkable. It is assumed that the cycloolefin resin has a high solubility in toluene and dissolves a poorly synthesized component generated during resin synthesis, so that the amount of foreign matter is significantly reduced.

  As the toluene, commercially available purified toluene can be used, and the purity is preferably 99.0% or more.

  Plasticizers and various function expressing agents that can be added to the dope containing the cyclic polyolefin resin (for example, antioxidants, light stabilizers, ultraviolet absorbers, retardation adjusters, peeling accelerators, infrared absorbers, mats) As the agent, etc., the same ones as those added to the above-mentioned cellulose ester dope can be used.

  The optical film targeted by the present invention is a functional film used for various displays such as a liquid crystal display, a plasma display, an organic EL display, and particularly a liquid crystal display, and is a polarizing plate protective film, a retardation film, an antireflection film, It includes a brightness enhancement film and an optical compensation film for expanding the viewing angle.

  By using the protective film for a polarizing plate comprising the optical film of the present embodiment, it is possible to provide a polarizing plate that is thin and has excellent durability, dimensional stability, and optical isotropy.

  Further, by using the polarizing plate provided with the optical film of the present embodiment, it is possible to realize a liquid crystal display device with high image quality.

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

(Test Example 1: TAC film)
[Example 1]
An optical film was manufactured by the method described below.
(Dope composition)
Cellulose triacetate 100 parts by mass (Mn = 148000, Mw = 310000, Mw / Mn = 2.1)
Triphenyl phosphate 8 parts by mass Ethylphthalylethyl glycolate 2 parts by mass Methylene chloride 440 parts by mass Ethanol 40 parts by mass Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.5 parts by mass Tinuvin 171 (Ciba Specialty Chemicals) 0.5 parts by mass Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by mass The above materials were placed in a closed container, heated, completely dissolved with stirring, and filtered to adjust the dope.

(Manufacture of optical film)
A cellulose triacetate film was produced by the solution casting film forming apparatus shown in FIG.

  The filtered dope was uniformly cast on a support maintained at a temperature of 25 ° C. In Example 1, the width of the support was 1850 mm, the casting width of the dope was 1600 mm, and the running speed of the support was 80 m / min.

  On the support, the solvent was evaporated until the residual solvent amount became 100% by mass, and the web (film) was peeled from the support. Then, the web was stretched 1.06 times in the width direction using a tenter.

  Then, it was dried by a drying device with a drying air of 100 ° C. The dried film was wound up by a winding device to finally obtain a cellulose triacetate film having a film thickness of 40 μm and a film width of 1300 mm.

  After that, the film is continuously manufactured for 50 hours, and the number of belt cycle failures (dirt) in that state is used as a reference, and then the cleaning process is performed, the film manufacturing condition is restored again, and the number of belt cycle failures (dirt) is restarted. Was evaluated. The results are shown in Table 1.

  The cleaning step was performed until the film was wound up to 5000 m while peeling with a residual solvent ratio Z of the web at the time of peeling of 30% and a peeling force of 1.15 times the peeling force at the time of film production. The residual solvent ratio Z was adjusted by adjusting the support temperature, the support transport speed, and the dope flow rate.

In addition, the specific evaluation is the belt cycle when the film is continuously produced under the production conditions for 50 hours, the number of belt cycle failures on the film in that state is used as a reference, and the cleaning step is performed and then the film production conditions are restored. The number of failures (dirt) was evaluated. The criteria are as follows:
×: The number of belt cycle failures is equal to or greater than the standard (more than 0.9 times) Δ: The number of belt cycle failures is 0.6 to 0.9 times the standard ○: The number of belt cycle failures is 0.4 to 0.6 of the standard Double: The number of belt cycle failures is 0.4 times or less than the standard

[Examples 2-8 and Comparative Examples 1-2]
The residual solvent ratio Z of the web at the time of peeling in the cleaning step and the ratio of the peeling force at the time of the cleaning step to the peeling force at the time of film production are shown in Table 1 by adjusting the support temperature, the support transport speed and the dope flow rate. A cellulose triacetate film was produced in the same manner as in Example 1 except that the cleaning step was carried out as shown in Table 1, and the length of the cleaning step (film winding length) was also changed as shown in Table 1. The number of periodic failures was evaluated.

  The results are shown in Table 1.

(Test Example 2: COP film)
[Example 9]
The following cyclic polyolefin film was produced with reference to the description of Japanese Patent No. 485947.

<Synthesis of Cyclic Polyolefin Polymer P-1>
100 parts by mass of purified toluene and 100 parts by mass of norbornene carboxylic acid methyl ester were charged into a reaction kettle. Then, ethylhexanoate-Ni 25 mmol% (relative to the monomer mass) dissolved in toluene, tri (pentafluorophenyl) boron 0.225 mol% (relative to the monomer mass) and triethylaluminum 0.25 mol% (relative to the monomer mass) dissolved in toluene. ) Was charged into the reaction kettle. The reaction was carried out for 18 hours while stirring at room temperature. After completion of the reaction, the reaction mixture was put into excess ethanol to generate a polymer precipitate. The polymer (P-1) obtained by purifying the precipitate was dried at 65 ° C. for 24 hours by vacuum drying.

<Preparation of dope>
The following composition was put into a mixing tank, stirred to dissolve each component, and then filtered through a filter paper having an average pore diameter of 34 μm and a sintered metal filter having an average pore diameter of 10 μm to prepare a dope.
Cyclic polyolefin polymer P-1 150 parts by mass Dichloromethane 380 parts by mass Methanol 70 parts by mass

Next, the following composition containing the cyclic polyolefin solution (dope) produced by the above method was charged into a disperser to prepare a fine particle dispersion (M-1).
Fine particles (Aerosil R812: manufactured by Nippon Aerosil Co., Ltd.,
Primary average particle diameter: 7 nm, apparent specific gravity 50 g / L) 4 parts by mass Dichloromethane 76 parts by mass Methanol 10 parts by mass Cyclic polyolefin solution (dope) 10 parts by mass

  100 parts by mass of the cyclic polyolefin solution (dope) and 0.75 parts by mass of the fine particle dispersion (M-1) were mixed to prepare a dope for film formation. The dope was cast on a film forming line, dried on a metal support until the dope was self-supporting, then stripped off as a web, and introduced into a tenter.

  The residual solvent of the web when introduced into the tenter was 5 to 15% by mass. The stretching rate was 0% with a tenter, the temperature inside the tenter was 140 ° C., and the film was conveyed without stretching in the width direction. Immediately after leaving the tenter, the roll was conveyed with a tension of 100 N / m, further dried at 140 ° C., and the film was wound up at a winding length of 4000 m to produce a cyclic polyolefin film. The dry thickness of the film at this time was 40 μm.

  After that, the film is continuously manufactured for 50 hours, and the number of belt cycle failures (dirt) in that state is used as a reference, and then the cleaning process is performed, the film manufacturing condition is restored again, and the number of belt cycle failures (dirt) is restarted. Was evaluated. The results are shown in Table 2.

  The cleaning step was performed until the film was wound up to 5000 m while peeling with a residual solvent ratio Z of the web at the time of peeling of 30% and a peeling force of 1.3 times the peeling force at the time of film production. The residual solvent ratio Z was adjusted by adjusting the support temperature, the support transport speed, and the dope flow rate.

[Examples 10 to 12 and Comparative Example 3]
Table 2 shows the residual solvent ratio Z of the web at the time of peeling in the cleaning step, and the ratio of the peeling force at the time of the cleaning step to the peeling force at the time of film production, by adjusting the support temperature, the support transport speed and the dope flow rate. A cyclic polyolefin film was produced in the same manner as in Example 8 except that the cleaning step was changed as shown in Table 2 and the length of the cleaning step was changed as shown in Table 2. The number of periodic failures was evaluated.

  The results are shown in Table 2.

(Test Example 3: CAB film)
[Example 13]
<Particle dispersion liquid 1>
Fine particles (Aerosil R812 manufactured by Nippon Aerosil Co., Ltd.) 11 parts by mass Ethanol 89 parts by mass The above components were stirred and mixed with a dissolver for 50 minutes, and then dispersed with manton-goline to prepare a fine particle dispersion liquid 1.

<Particle addition liquid 1>
The fine particle dispersion liquid 1 was slowly added to the dissolution tank containing methylene chloride with sufficient stirring. Further, dispersion was performed using an attritor so that the particle size of the secondary particles would be a predetermined size. This was filtered through Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive liquid 1.
Methylene chloride 99 parts by weight Fine particle dispersion 1 5 parts by weight

<Preparation of dope>
Next, methylene chloride and ethanol were added to the pressure dissolution tank. Then, a cellulose acetate butyrate having a total acyl group substitution degree of 2.4 was put into a pressure dissolution tank containing a solvent while stirring. This was heated and completely dissolved with stirring, and this was mixed with Azumi filter paper No. A. The main dope was prepared by filtration using 244. Then, the following materials were placed in a closed melting pot and dissolved with stirring to prepare a dope.

<< Dope composition >>
Methylene chloride 365 parts by mass Ethanol 50 parts by mass Cellulose ester-based resin (cellulose acetate butyrate, acetyl group substitution degree 2.0, butyryl group substitution degree 0.4, total acyl group substitution degree 2.4) 100 parts by mass Nitrogen-containing complex Ring compound A (Exemplary compound 1, carbazole-based compound) 4 parts by mass Sugar ester S 10 parts by mass Polycondensation ester 1-15 2 parts by mass Fine particle addition liquid 1 1 part by mass In addition, as the sugar ester S, BzSc (benzyl) Sucrose: A sugar residue was B-2, the substituent was a mixture of a1 to a4 described in Chemical formula 11, average degree of ester substitution = 5.5).

<Film formation>
Next, the solvent was evaporated on the stainless belt support until the amount of residual solvent in the web formed by the cast dope became 75% by mass, and then the peeling tension was 130 N / m and the stainless belt support was used. The web was peeled off from the body. Then, the peeled web was stretched in the width direction by 30% using a tenter. The residual solvent at the start of stretching was 15%. The stretching temperature in the tenter was 160 ° C.

  Next, the drying was completed while being conveyed by a large number of rollers in the drying zone. The drying temperature after stretching was 100 ° C., and the drying time was 5 minutes. As described above, a cellulose acetate butyrate film having a dry film thickness of 60 μm was obtained.

  After that, the film is continuously manufactured for 50 hours, and the number of belt cycle failures (dirt) in that state is used as a reference, and then the cleaning process is performed, the film manufacturing condition is restored again, and the number of belt cycle failures (dirt) is restarted. Was evaluated. The results are shown in Table 3.

  The cleaning step was performed until the film was wound up to 5000 m while peeling with a residual solvent ratio Z of the web at the time of peeling of 30% and a peeling force 2.5 times the peeling force at the time of film production. The residual solvent ratio Z was adjusted by adjusting the support temperature, the support transport speed, and the dope flow rate.

[Examples 14 to 16 and Comparative Examples 4 to 5]
The residual solvent ratio Z of the web at the time of peeling in the cleaning step, the ratio of the peeling force at the time of the cleaning step to the peeling force at the time of film production were adjusted by adjusting the support temperature, the support transport speed and the dope flow rate, and shown in Table 3. A cellulose acetate butyrate film was produced in the same manner as in Example 12, except that the cleaning process was performed as shown in Table 3 and the length of the cleaning process was changed as shown in Table 3. The number of belt cycle failures was evaluated.

  The results are shown in Table 3.

[Discussion]
As can be seen from Tables 1 to 3, according to the production method of the present invention, it was found that the number of failures due to stains was small and the cleaning effect was excellent. Further, from the results of Examples 2 to 3 and the like, the peeling force ratio at the time of manufacturing and cleaning is about 1.2 to 2.5 times more exerting the cleaning effect, and Examples 4 and 7 From the result, it can be seen that it is preferable to perform the cleaning process in an appropriate period.

  On the other hand, when the residual solvent ratio in the cleaning step deviates from the range of the present invention, or when the ratio of the peeling force under the manufacturing conditions and the peeling force during the cleaning is insufficient, the cleaning effect is exhibited. It was shown not to.

1: Melting pot 2: Pump 3: Casting die 4: Decompression chamber 5: Front-rear winding drum 6: Stainless steel endless belt for casting (support)
7: Casting rotary drive stainless steel drum (support)
8: peeling roll 9: web 10: tenter 11: roll conveying / drying device 12: warm air (dry air)
13: Winding machine F: Film

Claims (3)

In the method for producing an optical film by the solution casting film forming method, at least,
A casting step of casting a dope, which is a raw material solution for an optical film, on a support to form a web (cast film) on the support;
A peeling step of peeling the web from the support,
A drying step of drying the peeled web to obtain a film,
Having a winding step of winding the film,
And a cleaning step of cleaning the surface of the support during at least the peeling step,
In the cleaning step, the same dope as in the production of the product is cast to form a web on a support, and when the web is peeled from the support, the residual solvent ratio Z of the web represented by the following formula is Z: = 30 to 70%, and
The peeling force required for peeling the web from the support in the cleaning step is larger than the peeling force required for peeling the web from the support in the peeling step during product production. , A method for producing an optical film.
Residual solvent ratio Z (%) = {(W-V) / V} × 100
(In the formula, W represents the mass of the web containing the solvent, and V represents the mass when W is dried at 120 ° C. for 2 hours)   The peeling force required to peel the web from the support in the cleaning step is 1.15 to 5.00 times the peeling force required to peel the web from the support in the peeling step. A method for producing an optical film according to claim 1.   The method for producing an optical film according to claim 1, wherein the film is wound up for 1000 m or more in the cleaning step.

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