JP2010069646A - Optical film, method for producing the same, polarizing plate and liquid crystal display using optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film formable at high speed, excellent in flatness without unevenness of film thickness, high in production efficiency, and excellent in quality, without foaming of the film by involvement of air (carrier air) accompanying a base in a thin film state during flow casting of a dope even when a production rate of the film is increased, and a method for producing the same, in the method for producing the optical film by a solution flow casting film forming method. <P>SOLUTION: In the method for producing the optical film, a readily soluble gas supply device 4 for supplying a readily soluble gas to the dope near a surface of a base 7 directly front of a flow casting die 3, is provided, and the readily soluble gas is sprayed to a dope flow casting part during flow casting of the dope from the flow casting die. An exhauster 5 is further provided near the surface of the base 7 in an upper stream side of the readily soluble gas supply device 4, and the readily soluble gas is preferably sprayed to the dope casting part of the base 7, after exhausting the carrier air on the base 7 with the exhauster 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention can be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used for a plasma display. The present invention relates to a film, a manufacturing method thereof, a polarizing plate using an optical film, and a liquid crystal display device.

  Conventionally, a liquid crystal display device (LCD) can be directly connected to an IC circuit with low voltage and low power consumption, and can be thinned, so that it is widely used as a display device for a word processor, a personal computer or the like. .

  By the way, the basic structure of this LCD is one in which polarizing plates are provided on both sides of a liquid crystal cell. Since the polarizing plate allows only light with a polarization plane in a certain direction to pass, it plays an important role in visualizing changes in the orientation of the liquid crystal due to the electric field in the LCD, and the performance of the polarizing plate greatly depends on the performance of the polarizing plate. The A polarizing plate consists of a polarizer and a protective film laminated on both sides of the polarizer. And as a protective film of such a polarizing plate, the cellulose-ester film (henceforth only a film) is widely used. In addition to the polarizing plate protective film, it is known to use an optical film such as a retardation film, a viewing angle widening film, an antireflection film, or the like for a liquid crystal display device. Optical films are used. As materials for the optical film, materials other than cellulose ester are also known.

  These optical films have been produced exclusively by a solution casting method. When manufacturing an optical film with a solution casting film forming apparatus, there are roughly two dope casting methods. One is a belt casting method in which an endless belt as a support is wound between a pair of drums, and the other is a drum casting method in which the rotating drum itself is a support.

  The present invention relates to an optical film manufacturing method using both the belt casting method and the drum casting method.

  With the recent enlargement of the screen, there is a demand for a film film having a wide film width and a long winding length. Conventionally, a method for producing an optical film by a solution casting film forming method is such that a dope of a thermoplastic resin is cast from an endless die on an endless support, and a dope film (web) is formed. Is peeled off from the support, the peeled web is transported and dried, and the resulting film is wound up.

  In the method for producing an optical film by this solution casting film forming method, the film forming speed is slow, and methods for increasing the speed are disclosed in various patent publications, etc., but even if the speed is increased using these methods, There has been a problem of the quality of optical films made of cellulose triacetate film and the like, in particular, entrainment of entrained air.

  For example, Patent Documents 1 and 2 describe a method of blocking an accompanying wind by installing a wind shield or a wind shield plate upstream of a casting die.

Patent Document 3 describes a method for reducing entrained air by improving the decompression chamber structure.
JP 2004-114328 A Japanese Patent Laid-Open No. 2006-281772 JP 2006-123500 A

  However, as described in Patent Documents 1 and 2, even if it is possible to block the entrained air by placing a wind shield or a wind shield plate, the amount of entrained air increases with the speed. There were limits.

  Further, as described in Patent Document 3, there is a countermeasure by improving the decompression chamber. However, if the degree of decompression is excessively increased, there is a problem that film thickness unevenness due to pressure pulsation may occur.

  Thus, in the formation of an optical film such as a cellulose triacetate film, foaming due to entrainment of air entrained in a dope film formed by casting from a casting die, lowering of adhesion, peeling deterioration or film Various defects such as the occurrence of thickness unevenness or failures that cause a reduction in work efficiency often occur in normal production. These defects hinder the improvement in productivity of optical films, and it has been desired to reduce them as much as possible.

  The object of the present invention is to solve the above-mentioned problems of the prior art. First, even if the production rate of the optical film is increased, the air (which is entrained in a thin film state on the metal support during casting of the dope ( The film is not foamed due to entrainment of entrained air, and secondly, an optical film having excellent flatness without film thickness unevenness can be produced, and thirdly, the web is peeled off from the support. It is an object of the present invention to provide an optical film that can be easily formed, has high production efficiency, and is excellent in quality, and that can be formed at high speed, a manufacturing method thereof, a polarizing plate using the optical film, and a liquid crystal display device.

  As a result of intensive studies in view of the above points, the present inventor has obtained a thin film state on the metal support immediately before the dope is cast on the metal support in the continuous production of the optical film by the solution casting film forming method. The dope and the metal support when casting the dope on the metal support by replacing the entrained air (entrained air) with a gas that is easily dissolved in the dope, or by making the casting part an easily soluble gas atmosphere. Eliminates air trapped between the body and enables film formation in the high-speed range compared to the current situation, and improves production by expanding film production conditions, and film formation in the high-speed range Therefore, even if the liquid contact angle between the dope discharged from the casting die and the metal support is reduced, entrained air is not entrained, and the film thickness unevenness in the film transport direction can be reduced. The present invention has been completed by finding that an excellent film can be produced, and that it is possible to meet the demand for higher quality optical films and that stable production of optical films is possible. .

  In order to achieve the above object, the invention of claim 1 is characterized in that a dope of a thermoplastic resin is cast from an endless support on which an endless transition of a thermoplastic resin dope is carried out by a solution casting film forming method. ), The web is peeled off from the support, the peeled web is transported and dried, and the resulting film is wound up. There is an easy-dissolving gas supply device that supplies an easily-dissolving gas to the dope nearby. When casting the dope from the casting die, the dope casting point is easier than the easily-dissolving gas supply device. It is characterized by spraying soluble gas.

  The invention according to claim 2 is the method for producing an optical film according to claim 1, wherein the easily soluble gas is carbon dioxide, ethane, or acetylene.

  Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: The exhaust apparatus is further provided near the support body surface upstream from an easily soluble gas supply apparatus, and it supports by an exhaust apparatus. After the air entrained on the body is exhausted, an easily soluble gas is sprayed from an easily soluble gas supply device to the dope casting portion of the support.

  The invention of an optical film according to claim 4 is characterized by being manufactured by the method for manufacturing an optical film according to any one of claims 1 to 3.

  The invention of a polarizing plate according to claim 5 is characterized in that the optical film according to claim 4 is used as a protective film for a polarizing plate and is provided on at least one surface of both surfaces of the polarizing film.

  The invention of a liquid crystal display device according to claim 6 is characterized in that the polarizing plate according to claim 5 is provided on at least one surface of the liquid crystal cell.

  The invention of claim 1 is a method for producing an optical film by a solution casting film forming method, wherein an easily soluble gas for supplying an easily soluble gas to the dope near the support surface immediately before the casting die. A supply device is provided, and when the dope is cast from the casting die, an easily soluble gas is sprayed from the easily soluble gas supply device to the dope casting portion. In the continuous production of optical films by the casting method, the air (entrained air) entrained in a thin film state on the metal support immediately before the dope is cast on the metal support is easily dissolved in the dope. By replacing or making the casting part into an easily dissolving gas atmosphere, when the dope is cast on the metal support, the air trapped between the dope and the metal support is eliminated, and the high speed region is compared with the current one. Enables film formation at As the production conditions of the film expand, the productivity improves, and even if the liquid contact angle between the dope discharged from the casting die and the metal support is reduced by forming the film in a high speed region, the entrainment is accompanied. It is possible to produce a film with good smoothness, which can reduce film thickness unevenness in the film transport direction without involving air, and in response to the demand for higher quality optical films and stable optical films. There is an effect that high productivity can be achieved.

  Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: The easily soluble gas is a carbon dioxide, ethane, or acetylene, According to invention of Claim 2, metal When casting the dope onto the metal support by replacing the air entrained in a thin film state on the support (entrained air) with these easily-dissolved gases of dope, or by setting the casting site to an easily-dissolvable gas atmosphere. Eliminates the air trapped between the dope and the metal support, enables film formation in a high-speed region compared to the current one, and increases the production conditions of the film, thereby improving productivity. Also, by forming a film in the high-speed region, even if the liquid contact angle between the dope discharged from the casting die and the metal support is reduced, entrained air is not entrained, and film thickness unevenness in the film transport direction is prevented. Low It can be an effect that it is possible to produce a good film smoothness.

  Invention of Claim 3 is a manufacturing method of the optical film of Claim 1 or 2, Comprising: The exhaust apparatus is further provided near the support body surface upstream from an easily soluble gas supply apparatus, and it supports by an exhaust apparatus. After exhausting the entrained air on the body, the easily soluble gas is sprayed from the easily soluble gas supply device onto the dope casting portion of the support. According to the invention of claim 3, the exhaust device The entrained air is exhausted in advance, and then the easily soluble gas is sprayed from the easily soluble gas supply device to the dope casting portion of the support, so that the accompanying air is surely replaced with these easily dissolved dope gases. Alternatively, the casting part can be surely made into an easily dissolved gas atmosphere, and the above effect can be surely achieved.

  Invention of Claim 4 was manufactured by the manufacturing method of the optical film as described in any one of Claims 1-3, The invention of Optical film of Claim 4 According to the present invention, the film thickness unevenness in the transport direction is reduced and the smoothness is good, thereby producing an effect that it is possible to meet the demand for higher quality of the optical film.

  The invention of the polarizing plate according to claim 5 is characterized in that the optical film according to claim 4 is used as a protective film for a polarizing plate and has on at least one of both surfaces of the polarizing film. According to the invention of the polarizing plate of item 5, since the thickness unevenness is reduced and the optical film having good smoothness is used as the polarizing plate protective film, it is provided on at least one surface of the polarizing film. When this polarizing plate is incorporated in a liquid crystal panel, the liquid crystal panel does not cause a decrease in contrast or uneven density, and has an effect of excellent visibility.

  Since the invention of the liquid crystal display device of claim 6 uses the polarizing plate comprising the optical film having the excellent optical characteristics of claim 5, the invention of the liquid crystal display device of claim 6 is used. For example, the liquid crystal panel does not cause a decrease in contrast or uneven density, and has an effect of excellent visibility.

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

  FIG. 1 is a flow sheet showing a first embodiment of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. Note that the implementation of the present invention is not limited to the process of the drawings shown below.

  In the figure, first, in a melting pot (1), a thermoplastic resin made of, for example, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and an additive such as a plasticizer or an ultraviolet absorber is added thereto. Is added to prepare a resin solution (dope).

  Next, a support comprising an endless belt made of, for example, a rotationally driven stainless steel, in which the dope adjusted in the melting pot is fed to the casting die (3) by a conduit through, for example, a pressurized metering gear pump (2) and transferred infinitely. (7) The dope is cast from the casting die (3) to the upper casting position.

  As shown in detail in FIG. 3, in the method for producing an optical film according to the present invention, an easily soluble gas is supplied to the dope near the surface of the support (7) immediately before the casting die (3). A gas supply device (4) is provided, and when the dope is cast from the casting die (3), an easily soluble gas is sprayed from the easily soluble gas supply device (4) to the dope casting portion.

  According to the method for producing an optical film of the present invention, a gas having a high solubility in the dope casting is replaced by blowing a gas having a high solubility with respect to the dope or a gas atmosphere around the casting portion. Thus, even when the production rate is increased, a film without foaming can be obtained without entraining entrained air. Moreover, even if the liquid contact angle between the dope discharged from the casting die (3) and the metal support (7) is reduced by forming the film in a high-speed region, entrained air is not involved and the film is conveyed. The film thickness unevenness in the direction can be reduced, and a film with good surface smoothness can be obtained.

  Carbon dioxide (carbon dioxide), ethane gas, and acetylene gas are effective as specific gases having high solubility in the dope.

  Moreover, the supply amount (gas flow rate) of the easily soluble gas is preferably 20 to 1000 L / min, more preferably 40 to 500 L / min per 1 m of the effective film width.

  Further, as shown in detail in FIG. 3, in the present invention, an exhaust device (5) is further provided near the surface of the support (7) on the upstream side from the easily soluble gas supply device (4). After the entrained air on the support (7) is exhausted by 5), it is preferable to spray an easily soluble gas from the easily soluble gas supply device (4) onto the dope casting portion of the support (7).

  Thereby, the entrained air on the support (7) is exhausted in advance by the exhaust device (5), and then easily dissolved in the dope casting portion of the support (7) from the easily soluble gas supply device (4). Since the gas is blown, the entrained air can be surely replaced with these easily dissolved dope gases, or the casting site can be surely made into an easily soluble gas atmosphere, and the above-mentioned effects can be surely achieved. .

  The dope casting by the casting die (3) includes a doctor blade method in which the film thickness of the cast web is adjusted with a blade, or a reverse roll coater method in which the web is adjusted with a reverse rotating roll. A method using a pressure die that can adjust the slit shape of the die part and easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. Here, as the casting die (3), a pressure die that can adjust the slit shape of the die portion and easily make the film thickness uniform is preferable.

  By the way, when using, for example, cellulose ester as the thermoplastic resin solution (dope), the solid content concentration of the cellulose ester solution is preferably 15 to 30% by weight. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by weight, sufficient drying cannot be performed on the support (7), and a part of the dope film remains on the support (7) during peeling. This is not preferable because it leads to belt contamination. Moreover, when the solid content concentration exceeds 30%, the dope viscosity is increased, filter clogging is accelerated in the dope adjustment process, or pressure is increased during casting on the support (7), and it is not preferable to extrude. Absent.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the support (7), the belt support (7) is held by a pair of front and rear drums (15) (15) and a plurality of intermediate rolls (not shown). Has been.

  One or both of the drums (15) and (15) at both ends of the rotary drive endless belt support (7) are provided with a drive device for applying tension (not shown) to the belt support (7). Thus, the belt support (7) is used in a tensioned state.

  The width of the metal support (7) is preferably 1700 to 2500 mm, the casting width of the cellulose ester solution is preferably 1600 to 2400 mm, and the width of the film after winding is preferably 1400 to 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  When an endless belt is used as the support (7), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and a mixed solvent having a temperature lower than the boiling point of the lowest boiling solvent. The range of 5 ° C. to the boiling point of the solvent −5 ° C. is more preferable. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  In addition, it is preferable that the peripheral speed (conveyance speed) of a support body (7) is 40-200 m / min. And it is preferable that the liquid contact angle (theta) with respect to the support body (7) surface of casting dope at this time is 10 degrees-50 degrees.

  The dope cast on the surface of the support (7) as described above also increases the strength of the gel film (film strength) by promoting the drying until peeling.

  In the system using an endless belt as the metal support (7), the film strength on which the web (10) can be peeled from the metal support (7) by the peeling roll (8) on the metal support (7). In order to dry and solidify until it becomes, it is preferable to dry to 60 to 160 weight% of residual solvent amount in a web (10), and 80 to 130 weight% is more preferable. Moreover, as for the web temperature when peeling a web (10) from a metal support body (7), 0-30 degreeC is preferable. Further, immediately after the web (10) is peeled off from the metal support (7), the temperature once decreases rapidly due to the solvent evaporation from the metal support (7) contact surface side, and water vapor or solvent vapor in the atmosphere. For example, the web temperature at the time of peeling is more preferably 5 to 30 ° C. because volatile components are easily condensed.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M is the weight of the web at an arbitrary time point, and N is the weight when a weight M is dried at a temperature of 110 ° C. for 3 hours.

  The web (10) formed by the dope cast on the support (7) is heated on the support (7) to evaporate the solvent until the web is peelable from the support (7).

  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 (7) with a liquid, a method of transferring heat from the front and back by radiant heat, and the like. Can be used.

  The residual solvent amount of the web (10) when the web (10) is peeled from the support (7) is preferably 60 to 160% by weight.

  The web (10) on the support (7) is dried and solidified to a peelable film strength, and then the web (10) is peeled off from the support (7). In 11) the web (10) is stretched.

  FIG. 2 is a flow sheet showing a second embodiment of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. As a support, for example, stainless steel having a surface subjected to hard chrome plating treatment The case where the made rotational drive drum (6) is used is illustrated.

  The other points of the optical film manufacturing apparatus in FIG. 2 are the same as those of the optical film manufacturing apparatus in FIG.

  In the method for producing an optical film by the solution casting film forming method of the present embodiment, various resins can be used as the film material, and among them, cellulose ester is preferable.

  A cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present invention are not impaired.

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

  The cellulose used as a raw material for 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 arbitrary ratios, respectively.

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

  In the present embodiment, various additives can be added to the cellulose ester.

  In the method for producing an optical film according to the present embodiment, a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt) can be used.

  When the cellulose ester film is used for widening the viewing angle of a liquid crystal display device operating in the IPS mode, it is important to reduce the thickness direction retardation (Rt), but such thickness direction retardation (Rt) is reduced. The following are mentioned as an additive.

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

  Here, as a specific retardation reducing agent, for example, a polyester represented by the following general formula (1) or (2) may be mentioned.

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, A represents a dibasic acid component, and these are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

  There is no restriction | limiting in particular as a monocarboxylic acid component represented by B1, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used.

  Examples of preferred monocarboxylic acids include the following, 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. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  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 , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecinic 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 aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12.

  Examples of the divalent 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. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferred, and 1,3-propylene glycol, 1,4-butylene glycol Lumpur, 1,6-hexanediol, diethylene glycol is preferably used.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. 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, in particular, aliphatic carboxylic acid having 4 to 12 carbon atoms, at least one selected from these 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 weight average molecular weight of the polyester is preferably 20000 or less, and more preferably 10,000 or less. In particular, polyesters having a weight average molecular weight of 500 to 10,000 have good compatibility with cellulose esters, and neither evaporation nor volatilization occurs during film formation.

  Polycondensation of polyester is carried out by a conventional method. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, it is preferable that polyester having a weight average molecular weight not so large is by direct reaction. Polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester, and after forming the film, a moisture permeability is small, and a cellulose ester film rich in transparency can be obtained.

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent compounds can be controlled by a method of blocking the molecular ends with a monovalent acid or monovalent alcohol. In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but during the polycondensation reaction, it is not distilled out of the system, but is stopped and such monovalent acid is removed from the reaction system. The one that is easy to accumulate is selected. These may be used in combination. In the case of direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction by 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 to be 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 weight based on the cellulose ester. It is particularly preferable to contain 5 to 15% by weight.

  Examples of the additive for reducing the thickness direction retardation (Rt) include the following.

In order to synthesize a polymer as an additive that reduces the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can align the molecular weight as much as possible without increasing the molecular weight. . Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. compound and a one thiol group and secondary hydroxyl group, such as in Japanese, or by using a combination with a polymerization catalyst to the compound and an organic metal compound can be exemplified a method in which bulk polymerization, both present Although preferably used in the form , the method described in the publication is particularly preferable.

  Although the monomer as a monomer unit which comprises the polymer as an additive which reduces useful thickness direction retardation (Rt) is mentioned below, it is not limited to this.

  As the ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the thickness direction retardation (Rt) obtained by polymerizing an ethylenically unsaturated monomer, first, as a vinyl ester, for example, vinyl acetate, propionic acid, etc. 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 include vinyl crotonate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate.

  Next, as 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 the unsaturated acid include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, and the like.

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

  In this specification, the 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 monomer having no aromatic ring and cyclohexyl group include, 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-), 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% by weight or more, and the methacrylic acid methyl ester monomer unit has 40% by weight or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both highly compatible with cellulose ester, excellent in productivity without evaporation and volatilization, and retainability as a protective film for polarizing plates The moisture permeability is small, and the dimensional stability is excellent.

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

  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 weight average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). It is preferable.

  Moreover, in the manufacturing method of the optical film of this embodiment, the dope composition contains cellulose ester and an acrylic polymer having a weight average molecular weight of 5000 or more and 30000 or less as an additive for reducing thickness direction retardation (Rt). It is preferable to contain.

  In this embodiment, 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 polymer has a weight average molecular weight of 5000 or more and 30000 or less, cellulose Good compatibility with esters, and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester film after film formation is excellent, the moisture permeability is extremely low, and it exhibits excellent performance as a protective film for polarizing plates.

  In the present embodiment, as an additive for reducing the thickness direction retardation (Rt), a polymer having a hydroxyl group in a side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. 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. The thing replaced by methacrylic acid can be mentioned, Preferably, it is 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. 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 weight, more preferably 2 to 10% by weight.

  The polymer as described above containing 2 to 20% by weight of the monomer unit having the above hydroxyl group, of course, is excellent in compatibility with cellulose ester, retention, dimensional stability, and low moisture permeability. It is particularly excellent in adhesion with a polarizer as a protective film for a polarizing plate, and has an effect of improving the durability of the polarizing plate.

  Moreover, in this embodiment, it is preferable to have a hydroxyl group at least at one terminal of the main chain of the polymer. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end 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 ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. 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 Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

  The polymer having a hydroxyl group at the terminal and / or the polymer having a hydroxyl group in a side chain has an advantage of significantly improving the compatibility and transparency of the polymer with respect to the cellulose ester in this embodiment.

  In the present embodiment, as an additive for reducing useful thickness direction retardation (Rt), in addition to the above, for example, an ester compound of a diglycerin polyhydric alcohol and a fatty acid described in JP-A No. 2000-63560, An ester or ether compound of a hexose sugar alcohol described in JP-A No. 2001-247717, a trialiphatic alcohol phosphate compound described in JP-A No. 2004-315613, and a general formula (1) described in JP-A No. 2005-41911 ), A phosphate ester compound described in JP-A No. 2004-315605, a styrene oligomer described in JP-A No. 2005-105139, and a polymer of a styrene monomer described in JP-A No. 2005-105140. It is done.

  The content of the additive for reducing the thickness direction retardation (Rt) described above is preferably 5 to 25% by weight based on the cellulose ester resin. If the content of the additive for reducing the thickness direction retardation (Rt) is less than 5% by weight, the effect of reducing the thickness direction retardation (Rt) of the film is not manifested. On the other hand, if the content of the additive for reducing the thickness direction retardation (Rt) exceeds 25% by weight, so-called bleed-out occurs and the stability in the film decreases, which is not preferable.

  In the method for producing an optical film according to the present embodiment, an organic solvent having good solubility for the cellulose derivative is referred to as a good solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. These are gels that, after casting the dope onto the support, the solvent begins to evaporate and the proportion of alcohol increases, making the web gel, making the web strong and easy to peel off from the support When used as a solvating solvent, or when the proportion of these is small, it also has a role of promoting dissolution of a cellulose derivative of a non-chlorine organic solvent.

  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 preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

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

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

  The plasticizer used in the present embodiment is not particularly limited, but is a cellulose derivative or a reactive metal compound capable of hydrolysis polycondensation so as not to generate haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the polycondensate by hydrogen bonding or the like.

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

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol 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 (3).

Formula ^{(3) R 1 - (OH} ) n
In the formula, R ¹ represents an n-valent organic group, and n represents a positive integer of 2 or more.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  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, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this embodiment, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

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

  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, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and 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, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

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

  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. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, and the like can be used. In this embodiment, it is preferable that the phosphate ester plasticizer is not substantially contained.

  Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by weight, preferably 0.1% by weight, and particularly preferably not added.

  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 weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film This is not preferable because the physical properties of the resin deteriorate.

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

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

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

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

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

  As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for one film, and the number of particles in 100 μm 2 whose major axis length is in the range of 0.05 to 5 μm is taken for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film to aggregate. And controlling the particle size formed.

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

  The fine particles are used by adding 0.04 to 0.5% by weight to the cellulose ester. Preferably, 0.05 to 0.3% by weight, more preferably 0.05 to 0.25% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. A high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

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

  Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name, Microfluidizer) manufactured by Microfluidics Corporation, or a nanomizer manufactured by Nanomizer, and other examples include Manton Gorin type high-pressure dispersing devices such as Izumi Food Machinery. Examples thereof include a homogenizer.

  In this embodiment, the fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is placed on a support. A cellulose ester film is obtained which is cast and dried to form a film.

  Here, the content ratio of the lower alcohol is preferably 50 to 100% by weight, more preferably 75 to 100% by weight.

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

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

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

  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 a film made of the cellulose derivative.

  In this embodiment, examples of the ultraviolet absorber that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. However, a benzotriazole-based compound with little coloring is preferable. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

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

  In this embodiment, specific examples of useful UV absorbers include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert). -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butyl Phenyl) -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'-hydro Cis-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 Examples include, but are not limited to, a mixture of -5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

  Further, as commercially available ultraviolet absorbers, 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 an 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 are not limited thereto.

  In the present embodiment, the blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight with respect to the cellulose ester (cellulose derivative). If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

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

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a 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 plasticizer, so that it is preferably contained in the film. .

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-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-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-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-hydroxy Benzyl) -isocyanurate and the like. 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 amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1000 ppm by weight with respect to the cellulose derivative.

  In addition, in the apparatus which implements the manufacturing method of the optical film of this embodiment shown in FIG. 1 and FIG. 2, the stretching step clips the both side edges of the web (or film) (10) as a film for a liquid crystal display device. A tenter method in which the film is fixed and stretched with the like is preferable in order to improve the flatness and dimensional stability of the film.

  It is preferable that the residual solvent amount of the web (film) (10) immediately before entering the tenter (11) in the stretching step is 10 to 35% by weight.

  The stretch ratio of the web in the tenter (11) in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%. Moreover, the temperature of the warm air blown from the warm air blowing slit port in the tenter (11) is 100 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  It is preferable to provide a drying device (12) after the tenter (11) in the stretching step. In the drying device (12), the web (10) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web (10) is dried in the meantime. Moreover, although the film conveyance tension | tensile_strength in a drying apparatus (10) is influenced by the physical property of dope, the amount of residual solvents at the time of peeling and a film conveyance process, drying temperature, etc., the film conveyance tension | tensile_strength at the time of drying is 30-300N. / M width, and 40 to 270 N / m width is more preferable.

  The means for drying the web (film) (10) is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the drying air (14) blown from the hot air inlet at the front portion of the bottom of the drying device (12), and is dried on the ceiling of the drying device (12). It is dried by exhaust air being discharged from the outlet of the rear portion. The temperature of the drying air (14) is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve the flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or in 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.

  For example, a cellulose ester film that has finished the transport drying process is generally processed to form an emboss on the film by an embossing apparatus before the introduction to the winding process.

  Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. For example, when the film thickness is 40 μm, the emboss height h 1 + h 2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The film after drying is wound up by a winding device (13) to obtain the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film to be dried to 0.5% by weight or less, preferably 0.1% by weight or less.

  The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. You can use it properly.

  The film may be bonded to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  In the optical film according to the present invention, the width of the film after winding is preferably 1200 to 2500 mm.

  In the present invention, the film thickness after drying of the optical film is preferably in the range of 20 to 150 μm, and more preferably in the range of 30 to 80 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 weight or less.

  As described above, in the method for producing an optical film according to the present invention, an easily soluble gas supply device for supplying an easily soluble gas to the dope near the surface of the support (7) immediately before the casting die (3). (4), and when the dope is cast from the casting die (3), the easily soluble gas is sprayed from the easily soluble gas supply device (4) to the dope casting portion. The optical film manufactured by the method for manufacturing an optical film preferably has a film thickness deviation (Δh μm) of 0.05 to 0.2 μm, and more preferably 0.05 to 0.15 μm.

  In addition, when the film thickness of the cellulose-ester film after winding is too thin, the intensity | strength required as a protective film for polarizing plates may not be obtained, for example. If the film thickness is too thick, the advantage of thinning the film becomes less than the conventional cellulose ester film. In order to adjust the film thickness, the dope concentration, the pumping amount, the slit gap of the die of the casting die, the extrusion pressure of the casting die, the speed of the support, etc. are controlled so as to obtain the desired thickness. Is good. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film-forming method to drying, the atmosphere in the drying apparatus may be air, but may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

  In the present embodiment, the cellulose ester film preferably has a moisture content of 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

  In the present embodiment, the cellulose ester film desirably has a transmittance of 90% or more, more preferably 92% or more, and further preferably 93% or more.

  Moreover, the optical film manufactured by the method of the present embodiment has a haze of 0.3 to 2.0 when three sheets are stacked, has a very low haze, and has transparency and flatness. It has excellent optical characteristics.

  Here, the haze of the optical film may be measured using, for example, a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS K6714.

  In addition, the tensile modulus in the machine direction (MD direction) of the cellulose ester film produced by the method for producing an optical film according to the present embodiment is 1500 MPa to 3500 MPa, and the tensile modulus in the direction perpendicular to the machine direction (TD direction). It is preferably 3000 MPa to 4500 MPa, and the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the film is preferably 1.40 to 1.90.

  Here, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the optical film is less than 1.40, the sag of the central portion becomes large in winding a film having a width exceeding 1650 mm, and Since sticking increases, it is not preferable. Further, when the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage after overheating in the polarizing plate occurs, or the backlight is heated by the heat of the backlight when incorporated in a liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

  As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JIS K7217 can be mentioned.

  That is, using a tensile tester (TG-2KN, manufactured by Minebea Co., Ltd.), a sample was set at a chucking pressure: 0.25 MPa, a distance between marked lines: 100 ± 10 mm, and a pulling speed: 100 ± 10 mm / min. Pull on. As a result, from the obtained tensile stress-strain curve, the elastic modulus calculation start point is 10N, the end point is 30N, and the tangent line drawn between them is extrapolated to calculate the elastic modulus.

  In the optical film of this embodiment, the in-plane retardation (Ro) defined by the following formula is 30 to 300 nm under the conditions of a temperature of 23 ° C. and a humidity of 55% RH, and the thickness direction retardation (Rt) is a temperature of 23 ° C. It is preferably 70 to 400 nm under the condition of humidity 55% RH.

Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d
In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the film. (Refractive index is measured at a wavelength of 590 nm), d represents the thickness (nm) of the film.

  The retardation values Ro and Rt can be measured using an automatic birefringence meter. For example, using KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the wavelength can be obtained at 590 nm in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

  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, and an organic EL display, particularly a liquid crystal display. A polarizing plate protective film, a retardation film, an antireflection film, It includes an optical compensation film such as a brightness enhancement film and a viewing angle expansion.

  The optical film according to the present invention is preferably used for a liquid crystal display member, specifically, a protective film for a polarizing plate. In particular, in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability, the optical film produced by the method of the present invention is preferably used.

  By using the protective film for a polarizing plate comprising the optical film of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning.

  By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

  The polarizing plate may be prepared by laminating the optical film produced by the method of the present invention as a retardation film, and the optical film produced by the method of the present invention is a retardation film and a protective film. Alternatively, it may be produced by directly bonding to a polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of the present invention. . A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

  The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. Is preferred.

  By the way, a polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is immersed and stretched in an iodine solution and bonded to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. is there. The alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness.

  The optical film produced by the method of the present invention includes a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optical anisotropic layer, a liquid crystal layer, an alignment layer, an adhesive layer, Various functional layers such as an adhesive layer and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or plasma treatment.

  Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and a liquid crystal display device is obtained using this.

  By using the protective film for polarizing plates made of the optical film produced by the method of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

  The optical film produced by the method of the present invention can also be used as a base material for an antireflection film or an optical compensation film.

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

Example 1
(Preparation of dope)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 4 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxyphenyl) -2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Aerosil R972V 0.1 part by weight (Preparation of cellulose triacetate film)
Using the above dope, a cellulose triacetate film was produced as follows.

  Film formation was performed using the manufacturing apparatus shown in FIGS. Referring to the figure, the filtered dope is uniformly flown from a casting die (3) made of a coat hanger die on a support (7) made of SUS316 endless belt at a temperature of 20 ° C. at a dope temperature of 35 ° C. To form a cast film (web) (10).

  As shown in detail in FIG. 3, in this embodiment, carbon dioxide (carbon dioxide) is supplied as an easily soluble gas to the dope near the surface of the support (7) immediately before the casting die (3). An easily soluble gas supply device (4) is provided.

On the other hand, in this embodiment, an exhaust device (5) is further installed near the surface of the support (7) upstream from the easily soluble gas supply device (4), and the support (7) is provided by the exhaust device (5). After the upper entrained air was exhausted at an exhaust rate of 10 m ³ / min, carbon dioxide was added to the dope casting portion of the support (7) as an easily soluble gas from the easily soluble gas supply device (4) by 10 m. It sprayed with the air supply amount of ³ / min.

  The liquid contact angle with respect to the surface of the support (7) of the casting dope: θ was measured and found to be 10 (°). The film thickness deviation (Δh μm) was measured and found to be 0.05 μm. The obtained results are shown in Table 1 below.

  Thereafter, the temperature of the drying air on the support (7) is kept constant at 30 ° C., and the residual solvent amount of the web (10) at the time of peeling is set to 80 weight by appropriately adjusting the conveyance speed of the support (7). % Was adjusted.

  After peeling the web (10) from the support (7) with the peeling roll (8), the web (10) is dried while being conveyed with the conveying roll (9), and when the residual solvent amount is 10% with the tenter (11), the temperature is 100 ° C. In this atmosphere, the web (10) was stretched 1.06 times in the width direction, the width retention was released, and the drying was finished in the drying zone (12) at a temperature of 125 ° C. while being conveyed by rolls. A knurling process having a width of 10 mm and a height of 8 μm was applied to produce a cellulose triacetate film having a thickness of 40 μm. The film width was 1300 mm, and the winding length was 1500 m.

  The cellulose triacetate film was wound up by a winder (13) with the final residual solvent amount being 0.2% by weight.

Examples 2 and 3
As in the case of Example 1 above, carbon dioxide was sprayed as an easily soluble gas from the easily soluble gas supply device (4) to the dope casting portion of the support (7) to cast the dope. A cellulose triacetate film having a film thickness of 40 μm is produced. The difference from the case of Example 1 is that the liquid contact angle with the surface of the support (7) of the casting dope is 25 ° in Example 2, and Example 3 Then, in each Example, it carried out by changing the conveyance speed of a support body (7) so that it might be set to 50 degrees.

  And the film thickness deviation ((DELTA) hmicrometer) in each Example at this time was measured, and the obtained result was combined with following Table 1, and was shown.

Examples 4-6
A cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1 above, but the difference from Example 1 is that ethane gas is used as the easily soluble gas. Then, in each example, the liquid contact angle with respect to the surface of the support (7) of the casting dope is 10 ° in Example 4, 25 ° in Example 5, and 50 ° in Example 6. It was carried out by changing the transport speed of 7).

  And the film thickness deviation ((DELTA) hmicrometer) in each Example at this time was measured, and the obtained result was combined with following Table 1, and was shown.

Comparative Examples 1-3
A cellulose triacetate film having a film thickness of 40 μm is produced in the same manner as in Example 1, but the difference from Example 1 is that it is carried out without using an easily soluble gas and an exhaust device. It is in the point. In each example, the liquid contact angle with respect to the surface of the support (7) of the casting dope is 10 ° in Comparative Example 1, 25 ° in Comparative Example 2, and 50 ° in Comparative Example 3. It was carried out by changing the transport speed of 7).

  And the film thickness deviation ((DELTA) hmicrometer) in each Example at this time was measured, and the obtained result was combined with following Table 1, and was shown.

(Evaluation of film)
For the films produced in Examples 1 to 6 and Comparative Examples 1 to 3, in order to evaluate the performance of the film, the presence or absence of foam generation of the film and “film” evaluation were performed, and the obtained evaluation results were obtained. The results are shown in Table 1 below.

(Evaluation method for film bubble generation)
The cellulose triacetate film samples prepared in Examples 1 to 6 and Comparative Examples 1 to 3 of the present invention were cut out to a length of 1 m in the longitudinal direction with the full width, and the film surface was visually checked for the presence or absence of bubbles on the film surface. It was evaluated by.

(Evaluation of presence of bubbles)
“No”: No bubble generation “Yes (small)”: Little bubble generation “Yes (large)”: Many bubble generation (film evaluation)
The cellulose triacetate film samples prepared in Examples 1 to 6 and Comparative Examples 1 to 3 of the present invention were evaluated according to the following criteria.

◎: No bubble generation and small film thickness deviation ○: No bubble generation but slightly large film thickness deviation ×: Bubble generation

  As is clear from the results in Table 1 above, according to the cellulose triacetate films produced in Examples 1 to 6 using the easily soluble gas of the present invention, generation of bubbles on the film surface could be eliminated. And generation | occurrence | production of the bubble was not seen even if the contact angle was made small to 10 degree | times in order to make the film thickness deviation of a film small.

  Next, using the cellulose triacetate films prepared in Examples 1 to 6 and Comparative Examples 1 to 3 as protective films for polarizing plates, various polarizing plates were prepared by the following methods and evaluated.

(Preparation of polarizing film)
A long polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a long polarizing film.

(Preparation of polarizing plate)
Subsequently, according to the following processes 1-5, the polarizing film and the cellulose triacetate film optical film produced in Examples 1-6 and Comparative Examples 1-3 were bonded together, and the polarizing plate was produced.

  Step 1: The cellulose triacetate films prepared in Examples 1 to 15 and Comparative Examples 1 to 4 were immersed in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, and then Washed with water and dried.

  On the other hand, a commercially available long cellulose ester film was immersed in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, then washed with water and dried.

  Process 2: Said long polarizing film was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excessive adhesive adhered to the polarizing film in Step 2 was lightly removed, and the long cellulose triacetate films of Examples 1 to 6 and Comparative Examples 1 to 3 that were alkali-treated in Step 1 were commercially available. The sample was sandwiched between and placed in a scale with a cellulose ester film.

Process 4: These films were laminated together at a speed of about 2 m / min at a pressure of ^{20 to} 30 N / cm ² with two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The film sample produced in Step 4 was dried for 2 minutes in a dryer at 80 ° C. to produce a polarizing plate.

(Production of liquid crystal display panel)
Carefully peel off the polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD1525J, model name LA-1529HM), and paste the various polarizing plates prepared above in accordance with the polarization direction. A liquid crystal display panel was produced.

(Visual evaluation of polarizing plate)
About each liquid crystal display panel produced as mentioned above, the color unevenness which looks whitish when it sees from the front and diagonally by several evaluators was observed, and it was set as evaluation of a polarizing plate.

  As a result, in the liquid crystal display panel using the cellulose triacetate film prepared in Examples 1 to 6 as a protective film for polarizing plate, no evaluator can see any color unevenness, and the polarizing plate has excellent performance. Met. On the other hand, in the liquid crystal display panel using the cellulose triacetate film produced in Comparative Examples 1 to 3 as a protective film for a polarizing plate, many evaluators can confirm color unevenness and cannot be used as a polarizing plate product. there were.

It is a schematic flow sheet which shows 1st Embodiment of the apparatus which enforces the manufacturing method of the optical film of this invention. It is a schematic flow sheet which shows the 2nd embodiment. It is a principal part expanded side view of the apparatus of FIG.

Explanation of symbols

1: Melting pot 2: Pump 3: Casting die 4: Easily soluble gas supply device 5: Entrained air exhaust device 6: Rotating drive drum (support)
7: Endless belt (support)
8: Web transport roll 9: Web transport roll 10: Web 11: Tenter 12: Roll transport dryer 13: Winder 14: Hot air (dry air)
15: Front and rear winding drum

Claims (6)

  The dope of the thermoplastic resin is cast from a casting die on an endless support that moves infinitely by a solution casting film forming method, a dope film (hereinafter also referred to as a web) is formed, and then the web is peeled off from the support. Then, the peeled web is transported and dried, and the obtained film is wound up, which is a method for producing an optical film, which is a gas that is easily soluble in the dope near the support surface immediately before the casting die. An easily dissolvable gas supply device, and when the dope is cast from the casting die, the easily dissolvable gas is sprayed from the easily dissolvable gas supply device to the dope casting portion. A method for producing a film.   The method for producing an optical film according to claim 1, wherein the easily soluble gas is carbon dioxide, ethane, or acetylene.   An exhaust device is further provided near the surface of the support upstream from the easily soluble gas supply device, and after the entrained air on the support is exhausted by the exhaust device, the easily soluble gas is supplied to the dope casting portion of the support The method for producing an optical film according to claim 1, wherein an easily soluble gas is sprayed from the apparatus.   The optical film manufactured by the manufacturing method of the optical film as described in any one of Claims 1-3.   A polarizing plate comprising the optical film according to claim 4 as a protective film for a polarizing plate, on at least one of both surfaces of the polarizing film.   A liquid crystal display device comprising the polarizing plate according to claim 5 on at least one surface of a liquid crystal cell.

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