CN1788971B - Manufacturing method of optical film - Google Patents

Abstract

The present invention provides a method for manufacturing an optical film having a phase difference function and a viewing angle expansion function used in a liquid crystal display device (LCD). And achieve the distribution of orientation angle with desired precision, the manufacturing method of an optical film whose orientation angle is uniform in the width direction (TD direction) and has excellent phase difference compensation performance and viewing angle expansion function. The manufacturing method of the optical film of the present invention is characterized in that, when the optical film is formed into a film, according to the orientation angle of the manufactured optical film, the roller axis arrangement direction of one or more conveying rollers in the film forming line Adjust to an angle range of more than 0° and less than 5° with respect to the direction perpendicular to the film conveyance direction.

Description

Manufacturing method of optical film

technical field

The present invention relates to a method for producing an optical film having a retardation function and a viewing angle expansion function used in a liquid crystal display (LCD) or the like. the

Background technique

The basic configuration of a general liquid crystal display device is to provide polarizers on both sides of a liquid crystal element. The polarizer can only pass polarized light in a certain direction, so in the liquid crystal display device, it plays an important role in visualizing the orientation change of the liquid crystal caused by the electric field. The performance of the liquid crystal display device is largely affected by the performance of the polarizer. the

In the production method of an optical film, it is roughly divided into a solution casting film forming method and a melt casting film forming method. The former is a method of dissolving a polymer in a solvent, casting the solution on a support, evaporating the solvent, and stretching the film as needed. It is widely used in view of excellent film thickness uniformity, but there are problems such as increasing the size of equipment for drying the solvent. The latter is a method in which the polymer is heated and melted, cast on a support, cooled and solidified, and then stretched to form a film as needed. Since there is no need to dry the solvent, it has the advantage of relatively compact equipment, but there is a problem of poor film thickness uniformity. . the

In the past, cellulose ester films with excellent transparency and adhesiveness have been widely used as polarizer protective films due to their low birefringence characteristics. Because cellulose ester films have optical compensation functions, liquid crystal display devices The manufacturing process can be shortened, and the occurrence of defects can also be suppressed. Here, when a cellulose ester film is used as an optical compensation sheet, it may also serve as a polarizer protective film. the

The production of such a film is carried out as follows by using a solution casting film-forming method using a triacetate cellulose (TAC) film as an example. the

That is, first dissolving cellulose triacetate in a good solvent of cellulose triacetate such as methylene chloride, and a mixed solvent of weak solvents of cellulose triacetate such as methanol, ethanol, butanol or cyclohexane, Add a plasticizer, an ultraviolet absorber, and particles for improving the sliding properties of the film to prepare a cellulose triacetate solution (hereinafter referred to as a slurry), and rotate the slurry endlessly on a mirror-finished surface. Drive a metal support (for example, an endless belt or drum made of stainless steel), and uniformly cast it from a casting die to obtain a slurry film (hereinafter referred to as a coil), after drying it on the support, peel it off with a peeling roller It is peeled off, and the end of the film is equipped with a conveying roller with a control force to convey the coiled material. Before or after the roller is conveyed, the coiled material is stretched in the width direction with a tenter, and it is wound with a winding machine after drying. Made into a cellulose ester film. the

As a method for imparting an optical compensation function to such a cellulose ester film, the methods described in the following prior patent documents are known. the

[Patent Document 1] Japanese Unexamined Patent Publication No. 2002-71957 In this patent document 1, an optical film using a cellulose ester containing an acetyl group and a propionyl group or a butyryl group is disclosed. In the method described in this patent document 1, in order to exhibit the desired high retardation (retardation), the produced film is placed in the same direction as the film conveying direction, that is, the machine direction (MD direction) or a direction perpendicular to the conveying direction. That is, stretching is performed in the width direction (TD direction). the

As a method of stretching a film after peeling from a support, methods described in the following conventional patent documents are known. the

[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2-191904. This Patent Document 2 discloses a technology for producing a retardation film that is longitudinally uniaxially (free width) stretched in the machine direction. the

[Patent Document 3] Japanese Unexamined Patent Application Publication No. 5-127019. This Patent Document 3 discloses a technology for producing a phase difference plate in which lateral uniaxial stretching and sequential biaxial stretching are performed. the

Contents of the invention

However, in the stretching method of longitudinal uniaxial stretching described in the above-mentioned Patent Document 2, it is difficult to keep the heating temperature between the stretching rolls uniform, and there is a problem in the controllability of the retardation. When stretching in the MD direction, the shrinkage in the TD direction is controlled. The force hardly works, and since it shrinks almost freely, streaky film thickness unevenness related to the MD direction, and streaky retardation unevenness in the MD direction (shade under cross Nicol) is likely to occur There was a problem. In addition, the shrinkage ratio in the width direction of the film is different between the vicinity of the roll and the center of the roll, and the optical slow axis becomes non-uniform in the width direction of the film (substrate). Axis deviation easily occurs, and it is very difficult to control the axis deviation. shortcoming. the

In addition, the horizontal uniaxial stretching described in the above-mentioned Patent Document 3, which is generally widely used, is excellent in temperature controllability, but stress occurs in a direction perpendicular to the stretching direction, and axial misalignment called the bow phenomenon inevitably occurs. the

In addition, in the method of shrinking in the MD direction by the heat treatment described in Patent Document 3, there is a problem that a desired amount of shrinkage cannot be obtained depending on the type of resin. the

Here, various methods for obtaining appropriate retardation by shrinking in the MD direction after once stretching the film in the lateral direction are disclosed in the following patent documents. the

[Patent Document 4] JP-A-6-160623 Gazette

[Patent Document 5] JP-A-6-160624 Gazette

[Patent Document 6] Japanese Unexamined Patent Application Publication No. 6-300917 discloses in these Patent Documents 4 to 6 a phase difference plate manufacturing technique in which a wave buffer is provided in a tenter nip to maintain width and shrink in the MD direction. the

However, in the methods described in these Patent Documents 4 to 6, creases are likely to be generated during cutting, and the risk of breakage in the tenter and subsequent transportation increases. In addition, there is also a problem that the film shrinks in the MD direction. Difficulty in rate control. the

In recent years, a film for phase difference correction is generally used in a liquid crystal display device having an enlarged viewing angle. Due to the large-screen and high-definition, the quality requirements of the retardation film are strict, especially the retardation film with a large in-plane retardation is used, and the direction (orientation angle) of the retardation axis (orientation axis) of the retardation is strict. , the accuracy is required to be below ±1° in the entire area of the film, preferably around ±0.3° to 0.5°. the

Therefore, the film production line of the optical film should be made as symmetrical as possible, but the orientation angle of the above-mentioned film is required to be close to the limit of mechanical precision, so it is difficult to meet the above-mentioned requirements. the

In the manufacture of optical films, attention should be paid to the deviation of the film thickness during the transfer line, heating/drying equipment, and casting, so that it can be as uniform as possible in the width direction. However, due to repeated thermal strain and friction on the sliding part etc., the orientation angle of the film also changes with time due to the time-dependent deterioration of the machine-left and right unevenness of the production line. the

In addition, the film made by the solution casting film method is stretched on-line, and when the optical film is manufactured, the transported film is soft because it contains a solvent, so it is more affected by the unevenness of the transported film from left to right, and the orientation angle of the film tends to be in the A distribution is generated in the width direction. the

On the other hand, when the film produced by the melt casting film method is stretched online to produce an optical film, the transported film is cast on a cooling drum at a high temperature of 250° C., and then peeled off and mixed with the solution. Compared with the film produced by the cast film method, the film is soft at high temperature, so it is more affected by the unevenness of the transported film, and the orientation angle of the film tends to be distributed in the width direction. the

In addition, in the film after peeling from the support, the width direction distribution of the optical characteristics occurs due to unevenness in film thickness or unevenness in the width direction of drying. the

These distributions in the width direction become more remarkable especially when the film forming speed is increased in order to improve productivity. the

High-precision optical films are required, especially in the manufacture of retardation films, and it is important to maintain the necessary accuracy in the distribution of such orientation angles in the width direction. the

In the viewing angle expansion film, there is a problem of axis shift (orientation angle inclination), and it must be controlled with high precision (0.1 to 0.2°). the

The method for controlling the axis deviation of the film has previously disclosed a variety of methods for making the film inclined at an orientation angle of 45° by stretching, but there is no method that is at right angles (90°) to the film conveying direction and maintains accuracy when it is horizontal. the

The known technology is to reduce the punching loss of the polarizer for TN (the liquid crystal element is twisted nematic) by making the orientation angle (direction of the optical slow axis) to 15 to 45° to the film (substrate) conveying direction. There is no technology to uniformly control the orientation angle in the width direction (TD direction) of the stretching machine technology. the

The object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method for manufacturing an optical film whose orientation angle is uniform in the width direction (TD direction) in approximately the entire area of the film and has excellent retardation compensation performance and viewing angle expansion function. . the

As a result of careful research by the inventors in view of the above-mentioned problems, it has been found that in the optical film production line, a so-called torsion force is given to the conveyed film to control the orientation angle. Wrinkles and other faults, and achieve the desired precision of the orientation angle distribution, to manufacture an orientation angle in approximately the entire area of the film, uniform in the width direction (TD direction), and have excellent phase difference compensation performance and viewing angle expansion function. Thin film, complete the present invention.

In order to achieve the above object, the invention of the optical film manufacturing method described in claim 1 of the present invention is characterized in that the width direction orientation angle of the manufactured optical film is measured at multiple points, and based on the measured value, the When forming a film, the direction of arrangement of the roller axes of one or more conveying rollers is adjusted to an angle range of greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction. the

Next, the method for producing an optical thin film according to claim 2 is characterized in that the optical thin film is formed by a solution casting method, the amount of residual solvent in the film is in the range of 10 to 70% by weight, and one or more The arrangement direction of the roller axis of the root conveying roller is adjusted to an angle range of greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction. At this time, it is preferable that the atmospheric temperature of film transfer drying is implemented in the range of 30-140 degreeC. the

The manufacturing method of the optical film described in claim 3 is characterized in that, the film forming of the optical film is carried out by the melt casting film forming method, and the roller axis arrangement direction of one or more conveying rollers is adjusted to be opposite to the film conveying direction. The vertical direction is greater than the angle range of 0° and below 5°. the

In addition, the method for producing an optical film according to claim 4 is the method for producing an optical film according to any one of claims 1 to 3, wherein in the method for producing an optical film, online measurement of the production completion According to the orientation angle of the optical film, adjust the roller axis arrangement direction of the conveying roller according to the positive or negative of the average value. the

Invention effect

In the manufacturing method of the optical film described in the aspect 1 of the present invention, according to the orientation angle of the optical film that has been manufactured, the roller axis arrangement direction of one or more conveying rollers in the film production line is relative to the film conveying direction. The angle range of the perpendicular direction is greater than 0° and less than 5°. Through the manufacturing method of the optical thin film characterized by these, the above-mentioned problems of the prior art can be solved, and the orientation angle in almost all regions of the film can be provided. The production direction of an optical film that is uniform in the width direction (TD direction) and has excellent retardation compensation performance and viewing angle expansion function. the

According to the invention of the optical thin film manufacturing method described in the second aspect of the present invention, by imparting a so-called torsion force to the film conveyed in the optical thin film production line to control the orientation angle, in the solution casting film forming method, the residues in the film The range of the amount of solvent and the temperature of the atmosphere for conveying and drying the film are appropriately selected, and the roll axis of the conveying roller is adjusted, that is, in the optical film forming of a cellulose ester resin film using the solution casting film forming method, the film The amount of residual solvent in the film is in the range of 10 to 70% by weight. According to the positive and negative of the widthwise average value of the orientation angle of the manufactured film, the roller axis arrangement direction of one or more conveying rollers is adjusted to be relative to the film conveying roller. The direction perpendicular to the direction is greater than the angle range of 0° and 5°, and the orientation angle distribution that does not cause defects such as wrinkles and achieves the desired accuracy can be manufactured. The orientation angle in the approximate entire area of the film is in the width direction (TD Direction) uniform optical film with excellent phase difference compensation performance and viewing angle expansion function. the

The invention of the optical film production method described in claim 3 is also characterized in that the method of imparting so-called torsion to control the orientation angle to the film conveyed in the film production line of the optical film is applied to the optical film production method using the melt casting film production method. In this method, after the casting of molten resin and film peeling, the film temperature is within the range of the glass transition temperature (Tg) of the film ± 30°C, depending on the positive or negative of the average value of the orientation angle of the manufactured film in the width direction. The arrangement direction of the roller axis of one or more conveying rollers is adjusted to an angle range greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction, so as to achieve high-precision orientation angle distribution. the

In addition, the invention described in claim 4 is the optical film manufacturing method described in any one of the above-mentioned claims 1 to 3, wherein in the film formation of the optical film, the orientation angle of the film is measured online, and the angle of the conveying roll is adjusted based on the result. The direction of the roll axis is arranged, and the orientation angle during film production is measured online, and the adjustment of the orientation angle is performed in real time based on the information, so the productivity is excellent. the

Description of drawings

Figure 1 is a diagram defining orientation angles. the

Figure 2 is a diagram defining orientation angles. the

FIG. 3 is a diagram showing a method of controlling an orientation angle. the

FIG. 4 is a diagram showing a method of controlling an orientation angle. the

FIG. 5 is a diagram showing a method of controlling an orientation angle. the

FIG. 6 is a diagram showing a method of controlling an orientation angle. the

Description of attached numbers in the figure

F: film

θ: orientation angle

φ: Angle of the roller axis

Detailed ways

Embodiments of the present invention are described below. the

First of all, when the manufacturing method of the optical film of the present invention is carried out by solution casting film forming method, as the target resin, preferably cellulose ester resin, as the cellulose resin, preferably adopt cellulose triacetate, cellulose acetate propionate, etc. Vegan ester, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate butyrate, etc. When cellulose triacetate is used, especially cellulose triacetate with a degree of polymerization of 250-400 and a bound acetic acid content of 54-62.5% is preferred. the

Any of cellulose esters, cellulose esters synthesized from cotton linters and cellulose esters synthesized from wood pulp may be used alone or in combination. the

A specific method for producing cellulose ester preferably used in the present invention can be synthesized by, for example, the method described in JP-A-10-45804. the

When the number average molecular weight of the cellulose ester is too low, the strength becomes low, and when it is too high, the viscosity of the solution becomes too high, so it is preferably 70,000 to 300,000, and more preferably 80,000 to 200,000. the

Cellulose ester synthesized from cotton linters excellent in detachability on a rotationally driven metal support composed of an endless belt or a roller is widely used, and its production efficiency is high, so it is preferable. In addition, in order to make the releasable effect remarkable, the proportion of cellulose ester synthesized from cotton linters is preferably 60% by weight or more, more preferably 85% by weight or more, and it is most preferably used alone. the

In particular, cellulose ester films with a total acyl substitution degree of less than 2.85 are preferred due to small dimensional changes, while cellulose ester films with a total acyl substitution degree of less than 2.75 are more preferred, especially cellulose esters with a total acyl substitution degree of less than 2.70 Ester film, confirmed to have a significant effect. the

In the present invention, the optical film composed of a cellulose ester film is preferably one containing an ultraviolet absorber from the viewpoint of preventing aging when it is placed outdoors as a liquid crystal display device. As the ultraviolet absorber, those having excellent ultraviolet absorbing ability with a wavelength of 370 nm or less and little absorption of visible light with a wavelength of 400 nm or more can be preferably used. For example, the transmittance at a wavelength of 380 nm is preferably 20%, more preferably lower than 10%, particularly preferably lower than 5%. the

Examples of ultraviolet absorbers include hydroxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, and nickel complex salts. compounds, triazine compounds, etc., but the present invention is not limited thereto. the

UV-1: 2(2′-Hydroxy-5′-methylphenyl)benzotriazole

UV-2: 2(2'-Hydroxy-3',5'-di-tert-butylphenyl)benzotriazole

UV-3: 2(2'-Hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole

UV-4: 2(2'-Hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole

UV-5: 2(2'-Hydroxy-3'(3", 4", 5", 6"-tetrahydrophthalimidomethyl)-5'-methylphenyl)benzotriazole

UV-6: 2,2 methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol

UV-7: 2(2′-Hydroxy-3′-tert-butyl-5′-methylphenyl)chlorobenzotriazole

UV-8: 2-(2H-benzotriazol-2-yl)-6-(straight chain and side chain dodecyl)-4-methylphenol (TINUVIN 171: manufactured by Chiba Special Chemicals Co., Ltd.)

UV-9: Octyl-3-[3-tert-butyl-4-hydroxy-5-(chloro-2H-benzotriazol-2-yl)phenyl]propionate and 2-ethylbenzyl- Mixture of 3-[3-tert-butyl-4-hydroxy-5-(chloro-2H-benzotriazol-2-yl)phenyl]propionate (TINUVIN109: manufactured by Chiba Special Chemicals Co., Ltd.)

UV-10: 2,4-dihydroxybenzophenone

UV-11: 2,2′-dihydroxy-4-methoxybenzophenone

UV-12: 2-Hydroxy-4-methoxy-5-sulfobenzophenone

UV-13: bis(2-methoxy-4-hydroxy-5-benzoylphenylmethane)

In the optical film of the present invention, it is preferable to use a benzotriazole-based ultraviolet absorber and a benzophenone-based ultraviolet absorber that have high transparency and excellent effects of preventing polarizers or liquid crystals from aging as the ultraviolet absorber. Among them, A benzotriazole-based ultraviolet absorber with little unnecessary coloration is particularly preferable. It is preferable that the ultraviolet absorber has no bleeding or no volatilization in the film forming process. the

In addition, it is also preferable to use a polymer ultraviolet absorber as the ultraviolet absorber, and it is particularly preferable to use a polymer type ultraviolet absorber described in JP-A-6-148430. the

In the present invention, it is preferable to add the ultraviolet absorber to the resin component in an amount of 0.1 to 10% by weight, and it is particularly preferable to add it in an amount of 0.5 to 5% by weight. the

In the present invention, these ultraviolet absorbers may be used alone or in combination of two or more different kinds. the

The method of adding the ultraviolet absorber can dissolve the ultraviolet absorber in organic solvents such as ethanol, dichloromethane, and dioxolane, and then add it to the slurry, or directly add it to the composition of the slurry. Inorganic powders are insoluble in organic solvents, so they are dispersed in organic solvents and cellulose esters with a dissolver or sand mill and then added to the slurry. the

In addition, in the optical film of the present invention, if necessary, fine particles such as silica may be added as a matting agent. Surface treatment of organic matter for fine particles such as silica is preferable because the size of the film can be reduced. Examples of organic substances preferable for surface treatment include halosilanes, alkoxysilanes, silazanes, and siloxanes. The particles with a large average particle size have a good roughening effect, and those with a small average particle size have excellent transparency. Therefore, the average primary particle size of the fine particles is preferably 5 to 50 nm, more preferably 7 to 14 nm. the

In the present invention, examples of silica fine particles used include AEROSIL-200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600, etc. manufactured by Aerosil Corporation, preferably AEROSIL-200 and 200V. , R972, R972V, R974, R202, R812, etc. the

In the present invention, the fine particles are added to the resin in an amount of 0.04 to 0.4% by weight, preferably 0.05 to 0.3% by weight, and more preferably 0.05 to 0.2% by weight. the

In the method of the present invention, the solvent for dissolving the resin can be used alone or in combination, but after mixing the good solvent and the weak solvent, it is preferable to improve the production efficiency. The more good solvents, the better. It is preferable in view of the solubility of cellulose ester and less film impurities due to fine insoluble matter. A preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by weight of the good solvent and 30 to 2% by weight of the poor solvent. the

The so-called good solvent and weak solvent used in the present invention are defined as good solvents that can dissolve the resin used alone, and defined as weak solvents that can be swollen or insoluble alone. the

As the good solvent used in the present invention, it is not particularly limited. For example, when the resin is cellulose triacetate, organic halides such as methylene chloride or dioxolanes can be mentioned, and when it is cellulose acetate propionate In this case, dichloromethane, acetone, methyl acetate, etc. are mentioned. Moreover, although it does not specifically limit as a weak solvent, For example, methanol, ethanol, isopropanol, n-propanol, cyclohexane, acetone, cyclohexanone, etc. can be used preferably. the

For the production method of an optical film made of cellulose ester by solution casting, for example, U.S. Patent No. 2,492,978, U.S. Patent No. 2,739,070, U.S. Patent 2,739,069, U.S. Patent 2,492,977, U.S. Patent No. Patent No. 2367603, US Patent No. 2607704; British Patent No. 64071, British Patent No. 735892; -39890, the method recorded in the Japanese Patent Publication No. 62-4208, as a reference. the

In the method for producing an optical film composed of a cellulose ester resin film of the present invention, it is preferable to add a plasticizer to the optical film from the viewpoint of mechanical strength, dimensional stability, and the like. As its addition amount, for example, when the optical film is a cellulose ester, the weight % of the cellulose ester film acylated with an acetyl group and an acyl group with 3 to 4 carbon atoms to the cellulose ester film or cellulose reaches 3 -30% by weight is preferred, 10-30% by weight is more preferred, and 15-25% by weight is especially preferred. Generally, when the amount of plasticizer added increases, the size tends to change, but according to the method of the present invention, the rate of dimensional change can be significantly reduced. the

The plasticizers that can be used in the present invention are not particularly limited, but preferably phosphate plasticizers, phthalate plasticizers, trimellitate plasticizers, pyromellitic acid plasticizers , glycolate plasticizers, citrate plasticizers, polyester plasticizers. the

Phosphate ester plasticizers here are preferably triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tri-octyl phosphate Butyl ester etc. And phthalates, preferably dibutyl phthalate, ethyl dimethoxy phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethyl phthalate Esters, benzyl butylphthalate, etc. As the trimellitic acid plasticizer, tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate, etc. are preferably used. As the pyromellitic acid plasticizer, tetrabutyl pyromellitate, tetraphenyl pyromellitate, tetraethyl pyromellitate and the like are preferably used. Glycolic acid ester plasticizers, preferably triacetin, tributyrin, ethyl phthaloethyl glycolate, methyl phthaloethyl glycolate, butyl phthaloethyl glycolate wait. Citrate plasticizer, preferably use triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl citrate tri-normal (2- Ethylhexyl) ester, etc. As the polyester plasticizer, copolymers of dibasic acids such as aliphatic dibasic acids, alicyclic dibasic acids, and aromatic dibasic acids and diols are preferably used. The aliphatic dibasic acid is not particularly limited, and adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, and the like can be used. In addition, as diols, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, diol, etc. These dibasic acids and diols may be used alone or in combination of two or more. The molecular weight of the polyester is preferably in the range of 500 to 2000 in weight average molecular weight from the viewpoint of compatibility with the cellulose resin. the

In addition, in the method of the present invention, it is preferable to use a plasticizer whose vapor pressure is lower than 1333Pa at 200°C, more preferably a plasticizer whose vapor pressure is lower than 666Pa, and especially preferably a plasticizer whose vapor pressure is lower than 133Pa. The non-volatile plasticizer is not particularly limited, and examples thereof include arylene bis(diaryl phosphate) ester, tricresyl phosphate, tris(2-ethylhexyl trimellitate), and the like. These plasticizers can be used alone or in combination of two or more. the

In the production method of the optical film of the present invention, when the optical film is a cellulose ester resin film, the solid content concentration in the cellulose ester solution slurry is usually about 10 to 40% by weight. The viscosity of the slurry during casting is adjusted within the range of 1 to 200 poise. the

First of all, for the dissolution of cellulose ester, methods such as stirring and dissolving methods in a dissolving tank, heating and dissolving methods, and ultrasonic dissolving methods are commonly used. The method of heating at a certain temperature and dissolving while stirring is more preferable because it can prevent the generation of gel or block-shaped insolubles called mother nuclei. In addition, the cooling dissolution method described in JP-A-9-95538 or the high-pressure dissolution method described in JP-A-11-21379 can also be used. the

A method of dissolving the cellulose ester by mixing it with a weak solvent to moisten or swell it and then mixing it with a good solvent can also be preferably used. In this case, a device for mixing the cellulose ester with a weak solvent to moisten or swell and a device for mixing and dissolving the cellulose ester with a good solvent may be provided separately. the

In the present invention, the type of pressurized vessel used for dissolving cellulose ester is not particularly limited, as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. Additional gauges such as pressure gauges and thermometers may be appropriately installed on the pressurized container. Pressurization can be performed by injecting an inert gas such as nitrogen or by heating to increase the vapor pressure of the solvent. Heating from the outside is preferable, and for example, a jacket-type device is preferable because it is easy to control the temperature. the

The heating temperature after adding the solvent is above the boiling point of the solvent used, and when two or more mixed solvents are used, it is preferable to heat to a temperature above the boiling point of the solvent with a lower boiling point and the temperature in the range where the solvent does not boil. When the heating temperature is too high, the pressure must be increased, and the production efficiency becomes poor. A preferable heating temperature range is 20-120°C, more preferably 30-100°C, especially preferably 40-80°C. And the pressure can be adjusted at the set temperature so that the solvent does not boil. the

In addition to the cellulose ester and the solvent, the necessary plasticizer, ultraviolet absorber and other additives are mixed with the solvent in advance. After dissolving or dispersing, the solvent before the cellulose ester is dissolved, and the solvent after the cellulose ester is dissolved can also be added. in slurry. the

After the cellulose ester is dissolved, take it out of the container while cooling it, or pump it out from the container, cool it with a heat exchanger, etc., and supply the obtained cellulose ester slurry to film formation. The cooling temperature at this time may be cooled to room temperature. the

The mixture of the cellulose ester raw material and the solvent is dissolved with a dissolving device equipped with a stirrer. At this time, it is preferable to dissolve the mixture with the stirring blade at a peripheral speed of at least 0.5 m/sec and stir for 30 minutes or more. the

In the method of the present invention, the cellulose ester slurry must be removed by filtering it so that impurities, especially impurities in the gap between the liquid crystal display device and the image recognition, must be removed. The quality as an optical film depends on this filtering. the

For the filter material used in filtration, the one with small absolute filtration precision is preferred. When the absolute filtration precision is too small, the filter material is prone to clogging, and the filter material must be replaced frequently. the

Therefore, in the method of the present invention, the filter material that cellulose ester slurry uses, the material of absolute filtration accuracy below 0.008mm is preferred, the scope of 0.001～0.008mm is more preferred, the filter material of 0.003～0.006mm scope is more preferable. the

The material of the filter material is not particularly limited, and ordinary filter materials can be used, but filter materials made of plastic fibers such as polypropylene and Teflon (registered trademark) or metal filters such as stainless steel fibers do not shed fibers etc. are preferred. the

In the method of the present invention, the filtration of the cellulose ester slurry is carried out by a usual method, heating at a temperature above the boiling point of the solvent under normal pressure and at a temperature in the non-boiling range of the solvent, and filtering while heating, before and after the filter material The rise of the differential pressure (sometimes referred to as filter pressure below) is small, so it is more preferable. the

The preferred filtration temperature range is 45-120°C, more preferably 45-70°C, especially preferably 45-55°C. the

Filtration pressure is preferably below 3500kPa, more preferably below 3000kPa, especially preferably below 2500kPa. In addition, the filter pressure can be properly selected and controlled through the filter flow rate and filter area. the

When raw cellulose contains unsubstituted acyl groups or cellulose esters with a low degree of substitution, impurity solidification (hereinafter sometimes referred to as bright spot or bright spot impurity) may occur. The bright spot refers to a normal fiber when a cellulose ester film is placed between two polarizers in a vertical state (crossed Nicol), and light is irradiated from one side and observed from the opposite side with a fiber optic microscope (50 times). If the film is made of plain ester, the light is blocked, it is black, and nothing can be seen. When there are impurities, light leaks from here, and the phenomenon of speckled light can be seen. The larger the diameter of the bright spot, the more harmful it is to the liquid crystal display device. The diameter of the bright spot is preferably 50 μm or less, more preferably 10 μm or less, and especially preferably 8 μm or less. Also, the so-called diameter of the bright spot refers to the diameter measured by the bright spot approximating a true circle. the

Bright spot impurities, such as impurities with the above-mentioned diameter of 400 particles/cm ² or less, are practically no problem, but 300 particles/cm ² or less are preferable, and 200 particles/cm ² or less are more preferable. In order to reduce the number and size of such bright point impurities, it is necessary to fully filter the fine impurities.

In addition, for example, the cellulose ester film pulverized product of the primary film production described in the Japanese publication No. 2000-137115 is added to the slurry in a certain proportion, and the method of using cellulose ester and its additives as raw materials can reduce the brightness point. Impurities can be preferably used. the

In addition, when using the method of the present invention to manufacture an optical film, when the optical film is a cellulose ester resin film, first, the cellulose ester is dissolved in a mixed solvent of a good solvent and a weak solvent, and the above-mentioned plasticizer is added thereto. agent and UV absorber to make cellulose ester solution (slurry). the

The belt temperature during film making is generally cast in the temperature range of 0°C to lower than the boiling point of the solvent, and cast in the range of 5°C to the boiling point of the solvent -5°C, but cast on a support of 5 to 30°C is more preferable. At this time, the ambient air temperature must be controlled above the dew point. the

In addition, the viscosity of the slurry is adjusted to 1-200 poise, and the slurry is cast from the casting die to the support to achieve a uniform film thickness. The amount of residual solvent in the casting film is more than 20% relative to the solid content, such as Cast film temperature is below the boiling point of the solvent, then it is below 200% ~ peeling, and the casting film (coil) is dried with dry air to reach the range below the boiling point of the solvent + 20°C. the

On the support, the web is dried and cured so that the film strength can be peeled off from the support. The amount of residual solvent in the web is preferably 150% by weight or less, more preferably 50 to 120%. the

It is preferable that the temperature of the web at the time of peeling the web from the support reaches 0 to 30°C. In addition, after the coil is peeled from the support, once the solvent evaporation temperature on the adhesive side of the support drops rapidly, volatile components such as water vapor or solvent vapor in the atmosphere are likely to condense, so the coil temperature at the time of peeling It is more preferable to reach 5 to 30°C. the

The amount of residual solvent here can be expressed by the following formula:

Amount of residual solvent (weight%) = {(M-N)/N}×100

In the formula, M is the weight of the coil at any point in time, and N is the weight of a sample of weight M when it is dried at 110°C for 3 hours. the

In the drying process of the web (or film), a method of drying while conveying the web is generally adopted by a roll hanging method, a pin tenter method, or a clip tenter method. the

The stripped coil is, for example, introduced into a primary drying device. In the primary drying device, the coil is meandered by a plurality of conveying rollers arranged in a thousand-island shape when viewed from the side, and the hot air is blown in from the top of the coil drying device and discharged from the bottom of the drying device for drying. the

Then, the web is led into a tenter drying unit. Here, the both side edges of the coil are fixed with clips, and the coil is dried while being stretched. the

As a liquid crystal display component, a tenter method in which both side edges of a roll are fixed with clips or the like and then stretched is known, and it is preferable because planarity and dimensional stability can be improved. the

In particular, the web shrinks in the width direction due to evaporation of the solvent in the drying step after peeling off from the support. The more dry it is at high temperature, the greater the shrinkage. It is preferable to dry while suppressing such shrinkage as much as possible because the planarity of the formed film is good. From this point of view, for example, in the whole drying process or a part of the drying process shown in JP-A-62-46625, the method of drying while clamping the width of the coil to both ends with clips in the width direction/tenter method is preferred. the

Clipping and stretching with a tenter can be carried out after the residual solvent content of the film reaches 50 to 150% by weight after peeling, and the residual solvent content of the film before winding reaches 0% by weight. However, the residual solvent content It is preferable to carry out in the range of 5 to 10%, and the present invention is described below. the

Generally, the tenter is divided into several temperature zones in the moving direction of the substrate. The temperature during stretching is selected to obtain desired physical properties or planarity, but the temperature in the drying zone before and after the tenter is also selected to be different from the temperature during stretching for various reasons. For example, when the air temperature in the drying area before the tenter is different from the temperature inside the tenter, the temperature in the area near the entrance of the tenter is generally set at the same temperature as the temperature in the drying area before the tenter. It is carried out at the middle temperature of the central part temperature. When the temperature behind the stenter is different from that inside the stenter, the temperature in the area near the entrance of the stenter is also set at an intermediate temperature between the back of the stenter and the temperature inside the stenter. The temperature of the drying zone before and after the tenter is generally 30-120°C, preferably 50-100°C, and the temperature of the stretching part in the tenter is 50-180°C, preferably 80-140°C. The temperature of the part is appropriately selected from these intermediate temperatures. the

The stretching ratio of the film can be selected so that desired physical properties and planarity can be obtained. For example, in the case of a cellulose ester resin, it is 0 to 150%, preferably 0 to 50%. the

Stretching pattern is the trajectory of holding. Like temperature, it can be selected from various optical physical properties and planarity of the film. The deviation after holding starts is a certain width, then stretches, and then maintains a certain width after the end of stretching The pattern can also be adopted. In the vicinity of the end of the grip near the exit of the tenter, the vibration of the substrate can be suppressed by releasing the grip, and the width is generally relaxed. the

The stretching pattern is also related to the stretching speed, and the stretching speed is generally 10-1000 (%/min), preferably 100-500 (%/min). When the gripping trajectory is a curve, the stretching speed is not constant, and the moving direction of the substrate changes slowly. the

In addition, the dried web (film) using the above-mentioned tenter system is then introduced into a secondary drying device. In this secondary drying device, a plurality of conveyor rollers arranged in a thousand-island shape viewed from the side are used to make the coil meander, and the hot air blown in between from the top of the secondary drying device and discharged from the bottom of the secondary drying device is used for drying. Wound on a winder as a cellulose ester film. the

In the production method of the optical film composed of the cellulose ester resin film of the present invention, the method of drying the web is not particularly limited, but generally hot air, infrared rays, heating rollers, microwaves, etc. are used. In view of simplicity, drying with hot air is preferable. The drying temperature is preferably 40 to 150°C, and more preferably 80 to 130°C in order to obtain good planarity and dimensional stability. the

Therefore, in the drying process of the coil, the coil peeled off from the support is dried again, and the final residual solvent amount is less than 3% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, from which Membranes with good dimensional stability are considered to be preferred. the

The steps from these castings to post-drying may be performed under an air atmosphere or an inert atmosphere such as nitrogen. At this time, of course, a dry atmosphere should be used in consideration of the explosive limit concentration of the solvent. the

Also, it is preferable to emboss the optical film on both sides of the optical film using an embossing device before the transfer and drying step is introduced into the winding step. As an embossing apparatus, for example, the apparatus described in Unexamined-Japanese-Patent No. 63-74850 can be used. the

In the method of the present invention, the winding machine involved in the manufacture of the optical film can be either a general one, or a constant tension method, a constant torque method, an oblique tension method, a program tension control method with a constant internal stress, etc. method to wrap. the

In the method of the present invention, the film thickness of the optical film after winding varies depending on the purpose of use. As the final processed film, the film thickness used in the present invention ranges from 30 to 200 μm. For the recent thin-walled tendency, The range of 40-120 μm is preferable, especially 80 μm or less, preferably 20-60 μm, more preferably 30-50 μm. the

In the manufacturing method of the optical film of the present invention, the method of imparting torsion to the film conveyed in the optical film production line to control the orientation angle is to properly adjust the temperature and the roller axis of the conveying roller, that is, when the film is formed by solution casting In the production of an optical film made of a cellulose ester resin film according to the method, the amount of residual solvent in the film is in the range of 10 to 70% by weight. According to the positive or negative of the widthwise average value of the orientation angle of the finished film, one Or the arrangement direction of the roller axes of the plurality of conveying rollers is adjusted within an angle range of more than 0° and less than 5° relative to the direction perpendicular to the film conveying direction. At this time, it is preferable to perform the film transfer drying at an atmospheric temperature in the range of 30 to 140°C. the

According to the present invention, in the solution casting film-making method, the range of the residual solvent amount in the film and the film temperature are appropriately adjusted, and the adjustment of the roll axis is carried out, so that no faults such as crepes occur and the orientation angle distribution of the desired precision is achieved. An optical film that has an orientation angle in approximately the entire area, is uniform in the width direction (TD direction), and has excellent retardation compensation performance and viewing angle expansion function can be manufactured. the

Here, the orientation angle of the present invention means the direction of the slow axis (the angle to the width direction at the time of cast film formation) in the thermoplastic resin film plane, and the measurement of the orientation angle is carried out with an automatic birefringence meter KOBRA-21ADH. The method of measuring the orientation angle is to measure, for example, 5 points at intervals of 3 to 10 cm in the width direction of the film, and it is preferable that all orientation angles are within ±1.7°. More preferably within ±1.5°, most preferably within ±1.0°. the

A specific control method will be described using the diagram. The orientation angle is defined by the orientation of the slow axis of retardation in the film plane. As shown in FIG. 1 , when the orientation of the slow axis is almost perpendicular to the film transport direction, the direction perpendicular to the transport direction is defined as 0°, and the counterclockwise direction is defined as a positive value. Also, when the orientation of the slow axis is almost parallel to the film transport direction, as shown in FIG. 2 , the transport direction is defined as 0°, and the counterclockwise direction is defined as positive. the

Based on the above definition, it is possible to measure the orientation angle in the width direction of the manufactured film at multiple points, and to change the angle of the roll according to the positive or negative of these average values, so that the orientation angle is close to the desired value of 0°. In the roller arrangement as shown in Figure 3, when the average value of the orientation angle measured from the film surface (top of the paper surface) is positive, as shown in Figure 4, viewed from the orientation angle measurement surface, by making the film on the right side of the advancing direction The average value of the orientation angle can be brought close to zero by changing the arrangement direction of the roll axes so that the roll nip length becomes long. As changing the arrangement direction of the roll shaft, there is a configuration that the length of the roll gap on the same side of the film becomes longer. In addition to the horizontal direction as shown in Figure 4, there are also vertical directions as shown in Figure 5 or oblique directions as shown in Figure 6, etc., although there is no However, it is also possible to change the arrangement direction of multiple roller shafts at the same time. When the arrangement direction of the plurality of rollers is changed, the continuous rollers may be used, or the arrangement direction of the plurality of rollers separated by a certain distance may be changed. the

If the adjustment of the roller axis arrangement direction is too small, there will be no effect of correcting the orientation angle, and if it is too large, misalignment or wrinkles will occur in the film being conveyed, so it should be within an appropriate value range. Preferably, the roller axis arrangement direction is adjusted to an angle greater than 0° and not more than 5° with respect to the direction perpendicular to the film conveyance direction. the

In addition, in order to maximize the correction effect of the orientation angle, as mentioned above, it is preferable that the residual solvent amount of the film is 10 to 70% by weight at the time of solution casting. If the amount of residual solvent is too small, the effect of correcting the orientation angle will be small, and if the amount of residual solvent is too large, wrinkles will be generated in the film when the roll axis arrangement direction is changed. the

In the manufacture of optical films, stretching equipment such as stretching can be installed in the film conveying direction of the film production line or in a direction perpendicular to the conveying direction, and the present invention is effective regardless of the presence or absence of the stretching equipment. of. If there is a stretching device, the direction of the roller shaft arrangement can be changed before the stretching device, or the direction of the roller shaft arrangement can be changed after the stretching device. Also, it is also possible to change the arrangement direction of the roll shafts simultaneously before and after the stretching equipment. the

The method for producing the optical film of the present invention can adopt a melt casting film forming method. Here, as the melt casting film forming method, it is preferable to use a T-die method with small film thickness unevenness and retardation unevenness. In the extrusion method using a T-die, the above-mentioned polymer is melted at a melting temperature, and the film-shaped (sheet-shaped) molten resin is extruded from the T-shaped die onto a cooling drum (support). Next, the film-like (sheet-like) molten resin is cooled and solidified by cooling, and the resin film is peeled off from the cooling drum. the

When the method for producing an optical film of the present invention is performed by melt casting, the thermoplastic resin to be used is not particularly limited as long as it can be formed by melt casting. the

For example, polycarbonate (glass transition temperature Tg: about 150 degreeC), polymer containing an alicyclic structure, polyvinyl alcohol, polyamide, polyimide, cellulose ester resin etc. are mentioned. Among them, cellulose esters or polymers containing an alicyclic structure are preferable from the viewpoint of a small photoelastic coefficient. the

As the cellulose ester resin, cellulose acetate propionate (glass transition temperature Tg: about 170° C.), cellulose acetate butyrate, and cellulose acetate propionate are preferable. It is preferable that the degree of acetyl substitution of the cellulose ester is at least 1.5 or more because the obtained dimensional stability is excellent. As a measuring method of the acetyl substitution degree of cellulose ester, it can follow D-817-91 of ASTM. The molecular weight of the cellulose ester is preferably a number average molecular weight of 50,000 to 300,000, especially 60,000 to 200,000, since the obtained mechanical strength is large, so it is preferable. the

The so-called alicyclic structure-containing polymer refers to a polymer having an alicyclic structure in a repeating unit, and the alicyclic structure may be in the main chain or in the side chain. Examples of the alicyclic structure include a cycloalkane structure, a cycloalkene structure, and the like, and a cycloalkane structure is preferable because of excellent thermal stability. the

As a polymer containing an alicyclic structure, monomers such as norbornene ring monomers, monocyclic olefins, cyclic conjugated dienes, vinyl aromatic compounds, and vinyl alicyclic hydrocarbon compounds are synthesized by metathesis It can be obtained by performing polymerization by a known polymerization method such as ring-opening polymerization or addition polymerization, and hydrogenating a carbon-carbon unsaturated bond if necessary. the

The polymer containing the alicyclic structure used in the present invention is measured by gel permeation chromatography in cyclohexane solution (toluene solution when the polymer is insoluble), converted into the weight average molecular weight of polyisobutylene or polystyrene (Mw) is preferably 25,000 to 50,000, more preferably 30,000 to 45,000. The molecular weight distribution (Mw/Mn) is preferably 1.2 to 3.5, more preferably 1.5 to 3.0. In addition, the glass transition temperature (Tg) is preferably 80 to 200°C. When the properties of the alicyclic structure-containing polymer are within the above-mentioned ranges, good heat resistance and molding processability can be obtained. the

The thermoplastic resin of the present invention may contain additives such as plasticizers, ultraviolet absorbers, antioxidants, matting agents, antistatic agents, flame retardants, dyes, and oils according to various purposes. the

As the plasticizer, those used in the production method of the optical film by the above-mentioned solution casting method can be used, and they can be used almost in the same manner. the

As an antioxidant, hindered phenolic compounds are suitable. As specific examples, 2,6-di-tert-butyl-p-cresol, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4 -hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol- [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert Butylanilino)-1,3,5-triazine, 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tri(3,5-di-tert Butyl-4-hydroxybenzyl)benzene and tris(3,5-di-tert-butyl-4-hydroxybenzyl)-isocyanurate, etc. Especially 2,6-di-tert-butyl-p-cresol, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3 -(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] is preferred. In addition, such as N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine and other hydrazine metal deactivators or tris(2,4-di-tert-butyl Phosphorous processing stabilizers such as phenyl)phosphides can also be used in combination. In order to obtain this effect, the addition amount of these compounds is preferably 1 ppm to 1.0% by weight of the thermoplastic resin, and particularly preferably 10 to 1000 ppm. the

When the optical film production method of the present invention is performed by the melt casting method, the ultraviolet absorber is almost the same as that used in the above-mentioned optical film production method by the solution casting method. the

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 thermoplastic resin. When the amount used is too small, the effect of the ultraviolet absorber cannot be fully exhibited, and when it is too large, the transparency of the film may deteriorate. Those with high thermal stability of the ultraviolet absorber are preferable. the

In the present invention, it is preferable to add fine particles in order to impart slipperiness to the film. The microparticles used in the present invention may be any of inorganic compounds or organic compounds having heat resistance when melted. For example, as inorganic compounds, silicon-containing compounds, silica, alumina, oxide Zirconium, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate, more preferably silicon-containing inorganic compounds or zirconia. Among them, silicon dioxide is particularly preferred in terms of suppressing the mist to a small value. The optical film manufacturing method of the present invention, when implemented by the melt casting film method, can adopt the optical film method of the solution casting film method. Almost the same matting agent used in thin film manufacturing methods. the

When the method for producing the optical film of the present invention is carried out by a melt casting film forming method, examples of the melt casting film forming method include a melt extrusion method such as a T-die method or an expansion method, a calender method, and a hot press method. , injection molding, etc. Among them, the T-die method is preferable in view of small thickness variation, easy processing to a thickness of about 50 to 500 μm, and small film thickness variation and retardation variation. The extrusion method using a T-shaped die is a method in which the above-mentioned polymer is melted at a temperature that can be melted, extruded from a T-shaped die onto a film-shaped (sheet-shaped) cooling drum, cooled and solidified, and peeled off from the cooling drum. The obtained film has excellent thickness accuracy and can be preferably used in the present invention. the

The conditions for melt extrusion can be performed in the same manner as those used for thermoplastic resins such as other polyesters. For example, melt the cellulose ester dried by hot air or vacuum or reduced pressure with a single-screw or twin-screw extruder at an extrusion temperature of about 200-300°C, and filter it with a thin disc filter, etc. 1. After removing impurities, it is cast from a T-shaped mold into a film (sheet), and cooled and solidified on a cooling drum. When leading from the supply hopper to the extruder, it is preferable to carry out under reduced pressure or in an inert gas atmosphere to prevent oxidative decomposition and the like. the

It is preferable that the flow rate of extrusion and introduction into a gear pump etc. can be performed stably. In addition, as a filter for removing impurities, it is preferable to use a stainless steel fiber sintered filter. The stainless steel fiber sintered filter is made of stainless steel fiber into a complex twisted state and then compressed, and the contact part is sintered into a whole. The density can be changed by the thickness, thickness and compression of the fiber, and the filtration accuracy can be adjusted. It is preferable to make a multi-layered body with coarse, dense and continuous filtration accuracy. In addition, it is preferable to adopt a structure in which the filtration precision is sequentially increased or a method in which the filtration precision is repeated coarsely and densely, so that the filtration life of the filter is extended and the precision of replenishing impurities, gel, etc. is also improved. the

When the mold is damaged or impurities are attached, streaky defects sometimes occur. This kind of defect is called die line, and in order to reduce the die line defect on the surface, it is preferable to adopt a structure in which the stagnation portion of the resin is extremely small in the piping from the extruder to the die. On the inside or edge of the mold, it is preferable to use as little contact as possible. Components volatilized from the resin are precipitated around the mold, which may cause mold lines, so it is preferable to suck an atmosphere containing volatile components. In addition, since deposition may also occur on devices that apply static electricity, etc., application of alternating current or other heating means can prevent deposition, which is preferable. the

Additives such as plasticizers can be pre-mixed with the resin or added in the middle of the extruder. In order to make the addition uniform, it is preferable to use a mixing device such as a static mixer. the

It is preferable that the temperature of the cooling drum is below the glass transition temperature of the thermoplastic resin. In order to make the resin adhere to the cooling drum, it is preferable to adopt the method of applying electrostatic bonding, the method of bonding with air pressure, the method of bonding by clamping the entire width or the end, and the method of bonding with reduced pressure. . the

The thermoplastic resin sheet formed by this melt casting film method is different from the resin sheet formed by the solution casting film method, and has the characteristics of small retardation (Rt) in the thickness direction. different stretching conditions. In order to obtain desired optical properties, stretching of the film in the advancing direction and stretching of the film in the width direction may be performed simultaneously or sequentially in some cases. In addition, depending on the occasion, stretching may be performed only in the width direction of the film. Molecules are oriented by this stretching operation, and the film is adjusted to a necessary retardation value. the

The stretching method is not particularly limited, and it is preferable to use a known pin tenter type or clip type tenter or the like. The stretching direction may be in the longitudinal direction, the width direction, or any direction (oblique direction). It is preferable to form a roll by laminating the polarizing film with the stretching direction as the width direction. By stretching in the width direction, the slow axis of the optical film made of the thermoplastic resin film becomes the width direction. On the other hand, the transmission axis of the polarizing film is also in the normal width direction. A good viewing angle can be obtained by installing the laminated polarizer in the liquid crystal display device so that the transmission axis of the polarizing film is parallel to the slow axis of the optical film. the

As stretching conditions, temperature and magnification can be selected such that desired retardation characteristics can be obtained. The usual stretch ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the stretching temperature is usually the glass transition temperature (Tg) of the resin constituting the sheet (Tg)-50°C to Tg+50°C, preferably at Tg-40°C to The temperature range of Tg+40°C is carried out. When the draw ratio is too small, desired retardation characteristics may not be obtained, and when it is too large, cracking may occur. When the stretching temperature is too low, cracking occurs, and when it is too high, desired retardation characteristics may not be obtained. the

When the retardation characteristic of the thermoplastic resin film produced by the above method is corrected to the target value, the film may be stretched or shrunk in the longitudinal direction or the width direction. For shrinking in the longitudinal direction, for example, the clips stretched in the width direction are temporarily stopped to relax in the longitudinal direction, or the film is shrunk by gradually reducing the distance between adjacent clips of the stretching machine in the width direction. The latter method generally uses a biaxial stretching machine at the same time, and the interval between vertically adjacent clips is smoothly and slowly narrowed, for example, by using a pantograph method or a linear drive type to drive the holding part. the

After stretching, before winding, a heat treatment zone may be provided for the purpose of flatness correction, improvement of dimensional stability, and the like. For example, it is held for tens of seconds to tens of minutes to make the resin constituting the sheet at a temperature of glass transition temperature (Tg) -30°C to Tg, and a transfer zone may be provided between rollers arranged in thousand islands. the

The film thickness of the optical film varies depending on the purpose of use. As the final processed film, the film thickness used in the present invention ranges from 30 to 200 μm. For the recent thin-walled tendency, the range of 40 to 120 μm is preferable, and 40 to 100 μm is preferred. A range of 100 μm is particularly preferred. The film thickness can be adjusted by controlling the extrusion flow rate, the slit clearance of the die nozzle, the speed of the cooling drum, etc., so as to achieve the desired thickness. In addition, as a measure to make the film thickness uniform, a film thickness detection device can be used, and it is preferable to feed back programmed feedback information to the above-mentioned device for adjustment. the

The thermoplastic resin film stretched in the width direction obtained by the above method has a certain retardation because the molecules are oriented by stretching. the

In the manufacturing method of the optical film of the present invention, the film conveyed in the optical film production line is given the method of controlling the orientation angle by so-called torsion, and the appropriate temperature and the roller axis of the conveying roller are adjusted, that is, in the melt casting film production method In the production of optical films made of cellulose ester films, the film temperature is within the range of the glass transition temperature (Tg) of the film ± 30°C after the casting of the molten resin and the film is peeled off. The positive and negative of the width-wise average value of the orientation angle is adjusted to adjust the roller axis arrangement direction of one or more conveying rollers to an angle range greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction. the

In the melt casting film forming method, the film temperature is preferably in the range of ±30° C. from the glass transition point of the film. When the film temperature is too low, the correction effect of the orientation angle is small, and when the film temperature is too high, changing the direction of the roll axis arrangement will cause wrinkles in the film. the

Here, the glass transition temperature (Tg) of a film means the glass transition temperature (Tg) of a film composition including a main material resin of the film, an additive, and a solvent. the

The mensuration of glass transition temperature (Tg) can adopt generally known thermomechanical analysis device (TMA), differential scanning calorimeter (DSC), differential thermal analysis device (DTA), dynamic viscoelasticity measuring device (DMA) ) etc. to measure. the

According to the present invention, in the melt casting film forming method, by properly selecting the temperature range of the conveying film after peeling and adjusting the roll axis of the conveying roller, high-precision film orientation can be obtained without causing troubles such as wrinkles. The angular distribution, the orientation angle is uniform in the width direction (TD direction) over substantially the entire area of the film, and an optical film having excellent retardation compensation performance and viewing angle expansion function can be produced. the

In addition, in the present invention, in the production of an optical film using any one of the above optical film production methods, the orientation angle of the film is measured online, and the position of the roller axis of the conveying roller is adjusted based on the result. the

According to the present invention, the orientation angle is measured in-line during film formation, and the orientation angle is adjusted in real time based on the information, which is excellent in productivity. the

The optical film produced by the method of the present invention can be made into an elliptical polarizer by pasting on at least one surface of a polarizing film. the

As for the polarizing film, a stretchable orientable film such as a polyvinyl alcohol film that has been used before is treated with a dichroic dye such as bromine and then stretched longitudinally. Since the polarizing film itself does not have sufficient strength and durability, a non-anisotropic cellulose triacetate film is generally bonded on both sides as a protective film to form a polarizing plate. the

The polarizing plate can also be produced by pasting the optical film of the present invention on the above-mentioned polarizing film, and the optical film of the present invention can also be used as a protective film and directly pasted on the polarizing film. the

In addition, by stretching in the longitudinal direction, a long polarizing film can be obtained by bonding the long polarizing film treated with the dichroic dye to the long optical film of the present invention. The polarizer can be laminated with a pressure-sensitive adhesive layer (such as an acrylic pressure-sensitive adhesive layer, etc.) on one or both sides of the polarizer, or it can be laminated as a peelable sheet (by peeling and peeling). sheet, can be easily pasted on the liquid crystal cell). the

The polarizing plate of the present invention thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA-type liquid crystal element in which liquid crystal molecules are substantially vertically oriented when no voltage is applied, or a TN-type liquid crystal element in which liquid crystal molecules are substantially horizontally twisted when no voltage is applied is preferred. the

Example

The present invention will be specifically described below through examples, but the present invention is not limited thereto. the

Embodiment 1～9, comparative example 1～8

According to the method of the present invention, the optical film made of cellulose acetate propionate resin is produced by solution casting film forming method. the

(preparation of slurry)

First, a cellulose acetate propionate slurry was produced as follows. the

Cellulose acetate propionate 100 parts by weight

(The degree of substitution of acetyl group is 1.95, the degree of substitution of propionyl group is 0.7) 

Triphenyl Phosphate 10 parts by weight

Ethyl phthaloyl ethyl glycol ester 2 parts by weight

チヌビン 326 (manufactured by Chiba Special Chemicals Co., Ltd.) 1 part by weight

AEROSIL 200V (manufactured by Japan Aerosil Corporation) 0.1 parts by weight

Dichloroethane 300 parts by weight

Ethanol 40 parts by weight

The above-mentioned materials were put into a closed container in turn, and after the temperature inside the container was raised from 20°C to 80°C, it was kept at 80°C and stirred for 3 hours to completely dissolve the cellulose acetate propionate. Then, the stirring was stopped, and the liquid temperature was lowered to 43°C. Filtration was performed with filter paper (Azumi Filter Paper Co., Ltd., Azumi Filter Paper No. 244) to obtain a slurry. the

Pass the slurry prepared above into a casting mold that is kept warm at 30°C, and cast on a 30°C support made of a stainless steel endless belt to form a coil (slurry film), and finally, on the support After drying, the amount of residual solvent in the slurry was adjusted to 80% by weight, and the coil was peeled from the support by a peeling roller. the

Next, the coil is dried in a roller transfer drying process arranged in a thousand-island shape, and then introduced into a stretching device composed of a tenter, clamping both ends of the coil with clips, and in the presence of a residual solvent, substantially Stretch in the width direction and dry with dry air. the

In addition, the web (film) was dried in a roll transfer drying process arranged in a thousand islands shape, and wound up with a winder to obtain a cellulose acetate propionate film with a final film thickness of 60 μm. the

In this embodiment, a heating chamber with a temperature of 60° C. is set in front of the stretching machine, and 2 conveying rollers that can adjust the disposition angle of the roller shafts are arranged in it, and the disposition angles of each conveying roller shafts are adjusted appropriately. The plain ester film is stretched. Here, the arrangement angle of the roller shafts is an angle shown by φ in FIG. 4 , and is an angle measured in a counterclockwise increasing direction with the film transport direction as 0°. The roller axis arrangement angle of each conveying roller is adjusted to the range of 90°-2°, that is, adjusted to 88° to stretch the cellulose acetate propionate film. the

In Examples 1 to 9, the roller shaft arrangement angle within the scope of the present invention was set to 85° or more and less than 90°, and the amount of residual solvent in the film was varied from 10 to 70%. In Comparative Examples 1 to 11, the roller shaft arrangement angle and the residual solvent amount were outside the range of the present invention. the

Therefore, the orientation angle of the produced cellulose acetate propionate film was measured at 5 points in the width direction of the film using Oji Scientific Instruments KOBRA-21ADH. The results obtained are shown in Table 1 below. the

Also, in Table 1, the uniformity of the film orientation angle was evaluated according to the following criteria. the

A: The absolute value of the average orientation angle is 1.0° or less and the difference between the maximum orientation angle and the minimum orientation angle is 1.5° or less. The orientation angle characteristics are very excellent, and it is very suitable as a retardation film or a viewing angle expansion film. the

B: The absolute value of the average orientation angle is less than 1.0°, but the difference between the maximum orientation angle and the minimum orientation angle is more than 1.5°, the orientation angle distribution is large, and the average orientation angle is suppressed. It can be used as a retardation film or a viewing angle expansion film. . the

C: The absolute value of the average orientation angle is more than 1.0°, but the difference between the maximum orientation angle and the minimum orientation angle is less than 1.5, the average orientation angle is large, and the distribution of the orientation angle is suppressed. It can be used as a retardation film or a viewing angle expansion film in practice. use. the

D: The absolute value of the average orientation angle is 1.0° or more, the difference between the maximum orientation angle and the minimum orientation angle is 1.5° or more, the average orientation angle and orientation angle distribution are large, and it is difficult to use as a retardation film or a viewing angle expansion film. the

E: Wrinkles occurred during production, and the orientation angle could not be measured. As a result, the produced film could not be used as a retardation film or a viewing angle expansion film. the

The measurement results and evaluation results of the orientation angles of the obtained films are shown in Table 1 below. the

Table 1 angle Residual solvent amount (%) Maximum and minimum difference average evaluate Comparative example 1 90 40 3.1 +1.8 D. Example 1 89 40 1.7 +0.9 B Example 2 87 40 1.1 +0.3 A Example 3 85 40 1.2 -1.2 C Comparative example 2 84 40 (unable to measure) (unable to measure) E. Comparative example 3 90 70 3.1 +1.8 D. Example 4 89 70 1.3 +1.2 C Example 5 87 70 1.2 -0.1 A Example 6 85 70 1.4 -1.6 C Comparative example 4 84 70 (unable to measure) (unable to measure) E. Comparative Example 5 90 10 3.1 +1.8 D.

Example 7 89 10 1.4 +1.5 C Example 8 87 10 1.5 +0.7 B Example 9 85 10 1.8 -0.4 B Comparative example 6 84 10 1.6 -1.1 D Comparative Example 7 87 8 2.5 +1.7 D Comparative example 8 87 80 (unable to determine) (unable to determine) E

As can be seen from the results in Table 1, in Examples 1 to 9 of the present invention, in the optical film forming of cellulose acetate propionate resin using the solution casting film forming method, the amount of residual solvent in the film is within the specified range of the present invention. Within the range, and in the heating chamber at a specific temperature, adjust the roller axis of the conveying roller to the specific range of the present invention, stretch, and achieve high-precision film orientation angle distribution. The optical film made of the cellulose acetate propionate resin obtained in this way has broad application prospects, especially as a phase difference and viewing angle expansion film. the

Conversely, the amount of residual solvent during stretching of the cellulose acetate propionate film and the setting angle of the roller axis of the conveying roller in a heating chamber at a specific temperature were used as cellulose acetate propionate in Comparative Examples 1 to 4 outside the scope of the present invention, respectively. For ester films, the orientation angle of the film cannot be uniformly distributed, so it cannot be used as a phase difference and viewing angle expansion film. the

Embodiments 1 to 9 and comparative examples 1 to 8 are at right angles (90°) to the film conveying direction as known roll axis configuration angle φ in comparative example 1 and the prior art, and the average value of the orientation angle is positive ( +1.8°), when the roll axis arrangement direction φ is smaller than 90°, a good orientation angle result is obtained. On the other hand, when the roll axis arrangement angle φ was 90° and the average value of the orientation angles was negative, good results were also obtained when the roll axis arrangement angle φ was changed to be larger than 90°. Also, the same results can be obtained when other resins such as polycarbonate or cycloolefin, polyimide, etc. are used. the

Embodiment 10～18, comparative example 9～16

According to the method of the present invention, an optical film made of cellulose acetate propionate resin by melt casting film forming method is produced. the

Cellulose acetate propionate 100 parts by weight

(The degree of substitution of acetyl group is 1.95, the degree of substitution of propionyl group is 0.7, the glass transition temperature: about 170℃)

Plasticizer: dibutyl phthalate 10 parts by weight

Antioxidant: 2,6-di-tert-butyl-p-cresol 0.07 parts by weight

チヌビン 326 (manufactured by Chiba Special Chemicals Co., Ltd.) 1 part by weight

AEROSIL 200V (manufactured by Japan アェロジル Corporation) 0.1 parts by weight

Melt and mix the mixture of materials containing the above-mentioned cellulose acetate propionate resin with a twin-screw extruder at 240°C, filter through a metal filter, and extrude from a T-shaped die with a gear pump into a film (sheet) , The film-like resin is bonded to a cooling drum at 150°C and solidified while being transported, and the film is peeled off with a peeling roller. This film was stretched with a stretching machine heated to 150°C. A heating chamber is installed at the front of the stretching machine, and two conveying rollers that can adjust the arrangement angle of the roller shafts are installed in it. With respect to the glass transition temperature (Tg: about 140°C) of the cellulose acetate propionate resin film, the atmosphere temperature of the heating chamber is set at 105°C to 175°C, and the roller axis arrangement angle of each conveying roller is 90° The range of -96° was changed, and the same evaluation as in Examples 1-9 and Comparative Examples 1-8 was performed. the

The orientation angle of the cellulose acetate propionate resin film thus obtained was measured in the same manner as in Example 1 above, and the results obtained are shown in Table 2 below. the

Table 2 angle T-Tg(°C) Maximum and minimum difference average evaluate Comparative Example 9 90 0 4.2 -2.1 D.

Example 10 91 0 2.2 -1.3 C Example 11 93 0 1.4 -0.8 A Example 12 95 0 1.6 +0.5 B Comparative Example 10 96 0 (unable to determine) (unable to determine) E Comparative example 11 90 25 4.2 -2.1 D Example 13 91 25 1.6 -0.9 B Example 14 93 25 1.1 +0.1 A Example 15 95 25 1.4 +1.2 C Comparative example 12 96 25 (unable to determine) (unable to determine) E Comparative Example 13 90 -25 4.2 -2.1 D Example 16 91 -25 1.5 -1.8 C Example 17 93 -25 1.4 -1.6 C Example 18 95 -25 1.1 -1.3 C Comparative Example 14 96 -25 2.3 -1.4 D Comparative Example 15 93 -35 4 -1.8 D Comparative Example 16 93 35 (unable to determine) (unable to determine) E

As can be seen from the results in Table 2, in Examples 10 to 18 of the present invention, in the film formation of an optical film made of cellulose acetate propionate resin using the melt casting film forming method, the casting of the molten resin, the film After peeling, make the temperature of the film within the specified range of the present invention, and use a heating chamber with a specific temperature to adjust the roller shaft setting angle of the conveying roller to within the specific range of the present invention for stretching, so that a high-precision film orientation angle can be achieved distributed. An optical film made of the cellulose acetate propionate resin thus obtained can be used particularly as a retardation film and a viewing angle expansion film. the

In Examples 10 to 18, although cellulose acetate propionate resin was exemplified by melt casting method for film formation, other cellulose esters, polycarbonates, cycloolefins, polyesters, polyethylenes, polystyrenes, Any resin having an appropriate melting point such as polymethyl methacrylate can also be used, and good results can also be obtained by selecting the temperature range of the present invention with respect to the glass transition temperature of each raw material. the

Embodiment 19, comparative example 17

The same method as Comparative Example 1 was used to manufacture the optical film made of cellulose acetate propionate resin by solution casting film-making method, after the stretching machine, before winding, the device (Oji gauge) was set to measure the phase difference of the film in the production line. KOBRA-WI, manufactured by Measekiki Co., Ltd.), measures the retardation of the film being conveyed online. the

In Example 19, 100 film rolls were produced over 3 days while changing the arrangement direction of the roll axis based on the orientation angle of the film measured online. In Comparative Example 17, the roll axis arrangement direction was fixed at 90° as in Comparative Example 1, and 100 film rolls were produced in the same manner. The above-described evaluation of the uniformity of the orientation angle was performed using the film produced in this way. the

As a result, in the evaluation of 100 film rolls, A=98%, B=2%, and C=D=E=0% in Example 19. In contrast, in Comparative Example 17, A=B=0%, C=3%, D=97%, and E=0%. It can be seen that a very good high-quality product rate is obtained in the embodiment of the present invention. the

Claims (4)

1. A manufacturing method of an optical film, characterized in that, when the optical film is formed into a film, the roller shafts of one or more conveying rollers in the film production line are arranged according to the orientation angle of the manufactured optical film The direction is adjusted to an angle range greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction, and the optical thin film is formed by a solution casting film forming method, and the amount of residual solvent in the film is 10 to 70% by weight According to the positive and negative of the width-wise average value of the orientation angle of the finished optical film, adjust the roller axis arrangement direction of one or more conveying rollers to be greater than 0° relative to the direction perpendicular to the film conveying direction, Angle range below 5°. 2. The method for producing an optical film according to claim 1, wherein in the method for producing an optical film, the orientation angle of the finished optical film is measured online, and the conveying roller is adjusted according to the positive or negative value of the average value. The roller axis configuration direction. 3. A method for manufacturing an optical film, characterized in that, when the optical film is formed, the roller shafts of one or more conveying rollers in the film production line are arranged according to the orientation angle of the manufactured optical film The direction is adjusted to an angle range greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction, and the optical film is formed by the melt casting film forming method. After the casting of the molten resin and the film peeling, the film temperature Within the range of the glass transition temperature (Tg) of the film ± 30°C, according to the positive or negative of the widthwise average value of the orientation angle of the finished optical film, adjust the direction of the roller axis arrangement of one or more conveying rollers To the angle range of greater than 0° and less than 5° relative to the direction perpendicular to the film conveying direction. 4. The method for producing an optical film according to claim 3, wherein in the method for producing an optical film, the orientation angle of the finished optical film is measured online, and the conveying roller is adjusted according to the positive or negative value of the average value. The roller axis configuration direction.

Images