JP4792954B2 - Manufacturing method of optical film - Google Patents

Description

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

  In general, the basic configuration of a liquid crystal display device 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 liquid crystal display device. The performance of the liquid crystal display device depends on the performance of the polarizing plate. Is greatly affected.

  Optical film production methods are roughly classified into a solution casting film forming method and a melt casting film forming method. The former is a method in which a polymer is dissolved in a solvent, the solution is cast on a support, the solvent is evaporated, and further, if necessary, stretched to form a film. Although it has been widely adopted from the viewpoint of excellent film thickness uniformity, it has a problem such as an increase in size of equipment due to drying of the solvent. The latter is a method in which a polymer is heated and melted and cast on a support, cooled and solidified, and further stretched as necessary to form a film. Since it is not necessary to dry the solvent, the equipment can be made relatively compact. However, there is a problem that the uniformity of the film thickness is inferior.

  Conventionally, cellulose ester films excellent in transparency and adhesiveness have been widely used as polarizing plate protective films in recent years due to their low birefringence properties. By providing cellulose ester films with an optical compensation function, liquid crystal The manufacturing process of the display device can be shortened and occurrence of defects can be suppressed. Here, when a cellulose ester film is used as an optical compensation sheet, it can also serve as a polarizing plate protective film.

  Taking such a cellulose triacetate (TAC) film as an example, the production of such a film is performed by the solution casting film forming method as follows.

  That is, first, cellulose triacetate is dissolved in a mixed solvent obtained by adding a good solvent for cellulose triacetate such as methylene chloride and a poor solvent for cellulose triacetate such as methanol, ethanol, butanol, or cyclohexane, and the like. A cellulose triacetate solution (hereinafter referred to as “dope”) is prepared by adding ultraviolet absorbers and fine particles for improving film slipperiness, and the dope is made of an endless rotationally driven metal having a mirror-finished surface. A dope film (hereinafter referred to as a web) is obtained by uniformly casting from a casting die on a support (for example, a stainless steel endless belt or drum), dried on the support, and then peeled off. The transport roller is peeled off with a regulating force at the film edge. Conveying the web by Le, before or after the roll conveying the, by stretching the web in the width direction at a tenter, by winding in a winder after drying, had been producing a cellulose ester film.

As a method for imparting an optical compensation function to such a cellulose ester film, those described in the following prior patent documents are known.
JP-A-2002-71957 discloses an optical film using a cellulose ester containing an acetyl group and a propionyl group or a butyl group. In the method described in Patent Document 1, in order to develop a desired high retardation, the film formed in the same direction as the film transport direction, that is, the machine direction (MD direction), or the direction orthogonal to the transport direction, that is, the width direction. Stretching is performed in the (TD direction).

As a method of stretching the film after peeling from the support, those described in the following prior patent documents are known.
JP-A-2-191904 discloses a technique for manufacturing a retardation film that performs longitudinal uniaxial (free width) stretching in the machine direction. Japanese Patent Application Laid-Open No. 5-1207019 discloses a technique for manufacturing a retardation plate that performs lateral uniaxial stretching and sequential biaxial stretching.

  However, in the stretching method by longitudinal uniaxial stretching described in Patent Document 2, it is difficult to keep the heating temperature uniform between the stretching rolls, and there is a problem in the controllability of the retardation, and the stretching is performed in the MD direction. At this time, the force that regulates the shrinkage in the TD direction is hardly applied, and the film shrinks almost freely. Therefore, the unevenness of the stripe-like film thickness connected to the MD direction and the unevenness of the stripe-like retardation in the MD direction (under crossed Nicols) There was a problem that the light and darkness) was likely to occur. Also, the shrinkage rate in the width direction of the film is different between the vicinity of the roll and the center of the roll, and it is easy to generate an axial shift in which the optical slow axis is nonuniform in the width direction of the film (base). Has the disadvantage of being very difficult.

  In addition, the transverse uniaxial stretching described in Patent Document 3 that is widely used is excellent in temperature controllability, but stress is generated in a direction orthogonal to the stretching direction, and it is difficult to avoid axial misalignment called bowing. There was a problem.

  Further, the method of contracting in the MD direction by the heat treatment described in Patent Document 3 has a problem that a desired contraction amount cannot be obtained depending on the type of resin.

Thus, various methods are disclosed in the following patent documents for obtaining an appropriate retardation by contracting in the MD direction once the film has been subjected to lateral uniaxial stretching.
JP-A-6-160623 JP-A-6-160624 Japanese Patent Application Laid-Open No. 6-300917 These Patent Documents 4 to 6 disclose a technology for manufacturing a phase difference plate in which a tenter clip portion is provided with a wave-shaped slack portion, is held in width, and contracts in the MD direction. .

  However, in the methods described in Patent Documents 4 to 6, there is a problem that wrinkles are likely to be close at the time of clipping, and there is a large risk of breakage in the tenter and during subsequent transport, and control of the shrinkage rate in the MD direction of the film. There was a problem that was difficult.

  In recent years, it is common to use a retardation correction film in a liquid crystal display device having a wide viewing angle. The quality required for retardation films has become stricter due to the larger screen and higher definition. Especially for retardation films with a large in-plane retardation, the direction of the retardation slow axis (orientation axis) (orientation angle). ) Is severe, and an accuracy of ± 1 ° or less, desirably about ± 0.3 to 0.5 ° is required over the entire area of the film.

  By the way, although the film-forming line of an optical film is made as symmetrical as possible as much as possible, the demand for the orientation angle of the film is close to the limit of mechanical accuracy, and it is difficult to satisfy the demand.

  In the production of optical films, care should be taken to ensure that film thickness unevenness during transport lines, heating / drying facilities, and casting is as uniform as possible in the width direction. Due to wear or the like, the mechanical left and right non-uniformity of the production line deteriorates with time, so the orientation angle of the film also changes with time.

  In addition, when an optical film is produced by stretching a film created by the solution casting film formation method in-line, the film to be transported is soft and contains a solvent. It is strongly received and tends to cause a lateral distribution of the orientation angle of the film.

  On the other hand, when an optical film is produced by in-line stretching of a film produced by the melt casting film forming method, the film to be conveyed is at a high temperature of, for example, 250 ° C. in the casting die portion. Even after being peeled and then peeled off, it is softer at a higher temperature than the film made by the solution casting film forming method, so it is more affected by unevenness of the left and right of the transfer line, and the width of the orientation angle of the film Hand direction distribution is likely to occur.

  Furthermore, the film after peeling from the support has a lateral distribution of optical characteristics due to uneven film thickness and uneven lateral width of drying.

  These widthwise distributions are particularly noticeable when the film forming speed is increased in order to improve productivity.

  In the production of optical films that require high precision, particularly retardation films, it is important to maintain such a distribution in the width direction of the orientation angle with the necessary precision.

  In the viewing angle widening film, axial misalignment (inclination of the orientation angle) becomes a problem, and control with very high accuracy (0.1 to 0.2 °) is necessary.

  As a method for controlling the axial misalignment of the film, a number of methods for forming an orientation angle of 45 ° obliquely to the film by stretching have been disclosed. However, the method is perpendicular to the film conveyance direction (90 °) and horizontal. There is no way to keep the accuracy in case.

  The known technique reduces the punching loss of the polarizing plate for TN (liquid crystal cell is Twisted Nematic mode) by setting the orientation angle (direction of optical slow axis) to 15 to 45 ° with respect to the film (base) transport direction. This is a technique related to a tenter stretching machine for controlling the width, and is not a technique for uniformly controlling the orientation angle in the width direction (TD direction).

  An object of the present invention is to solve the above-mentioned problems of the prior art, and an optical film having an alignment angle uniform in the width direction (TD direction) and an excellent phase difference compensation performance and a viewing angle expansion function over substantially the entire area of the film. It is in providing the manufacturing method of.

  As a result of intensive studies in view of the above points, the present inventor has given a so-called torsional force to the film transported in the film-forming line of the optical film to control the orientation angle. By adjusting the axis of the roll, it is possible to achieve an orientation angle distribution with desired accuracy without wrinkles and the like, and the orientation angle is uniform and excellent in the width direction (TD direction) over almost the entire area of the film. The present inventors have found that an optical film having a retardation compensation performance and a viewing angle widening function can be manufactured, and completed the present invention.

  In order to achieve the above object, the invention of the method for producing an optical film according to claim 1 measures a plurality of orientation angles in the width direction of the finished optical film, and produces an optical film according to the measured value. The film is characterized in that the arrangement direction of the roll shaft of one or a plurality of transport rolls is adjusted in the range of an angle greater than 0 ° and 5 ° or less with respect to a direction perpendicular to the film transport direction. .

  Next, in the invention of the optical film manufacturing method according to claim 2, the optical film is formed by a solution casting film forming method, and the residual solvent amount in the film is in the range of 10 to 70% by mass. It is characterized in that the arrangement direction of the roll shafts of one or a plurality of transport rolls is adjusted in a range of an angle greater than 0 ° and 5 ° or less with respect to a direction perpendicular to the film transport direction. In this case, it is preferable that the atmospheric temperature at which the film is conveyed and dried is in the range of 30 to 140 ° C.

  In the invention of the method for producing an optical film according to claim 3, the optical film is formed by a melt casting method, and is greater than 0 ° and less than or equal to 5 ° with respect to a direction perpendicular to the optical film conveyance direction. It is characterized by adjusting within a range of angles.

  Further, the invention of 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 the completion is performed on-line in the production of the optical film. The orientation angle of the film is measured, and the arrangement direction of the roll axis of the transport roll is adjusted according to the result.

  In the method for producing an optical film according to claim 1 of the present invention, depending on the orientation angle of the finished film, the arrangement direction of the roll shafts of one or more conveyance rolls in the film production line is defined as the film conveyance direction. By adjusting the range of the angle of 0 ° to 5 ° with respect to the vertical direction, the optical film manufacturing method solves the above-mentioned problems of the prior art, and the orientation angle is wide over substantially the entire area of the film. It is possible to provide a method for producing an optical film that is uniform in the hand direction (TD direction) and has excellent retardation compensation performance and a viewing angle widening function.

  The invention of the method for producing an optical film according to claim 2 of the present invention is a method for controlling the orientation angle by applying a so-called torsional force to the film conveyed in the film production line of the optical film. In the film method, by appropriately selecting the range of residual solvent amount in the film and the atmospheric drying temperature and adjusting the roll axis of the transport roll, that is, an optical made of a cellulose ester resin film by a solution casting film forming method In film formation, the amount of residual solvent in the film is in the range of 10 to 70% by mass, and the roll axis of one or a plurality of transport rolls according to the positive or negative of the width average value of the orientation angle of the finished film By adjusting the arrangement direction of the film within an angle range of greater than 0 ° and less than 5 ° with respect to the direction perpendicular to the film conveyance direction, the film has a desired accuracy without wrinkles and other troubles. The orientation angle distribution can be achieved, and the orientation angle is uniform in the width direction (TD direction) over almost the entire area of the film, and an optical film having excellent retardation compensation performance and a viewing angle expansion function can be manufactured. There is an effect.

  Next, the invention of the method for producing an optical film according to claim 3 is a method for controlling the orientation angle by giving a so-called torsional force to the film conveyed in the optical film production line. In the production of an optical film by the casting film-forming method, after the casting of the molten resin and the peeling of the film, the orientation angle of the finished film is within the range of the glass temperature (Tg) ± 30 ° C. of the film. According to the positive / negative of the average width of the roll, the arrangement direction of the roll shaft of one or a plurality of transport rolls is adjusted in the range of an angle greater than 0 ° and less than 5 ° with respect to the direction perpendicular to the film transport direction By doing so, there is an effect that a highly accurate orientation angle distribution can be achieved.

  Moreover, invention of Claim 4 is a manufacturing method of the optical film of any one of the said Claims 1-3, Comprising: In film forming of an optical film, the orientation angle of a film is measured online, As a result, the orientation of the roll axis of the transport roll is adjusted. While measuring the orientation angle during film formation online, the orientation angle can be adjusted immediately based on the information. There is an effect that it is excellent in productivity.

  Next, an embodiment of the present invention will be described.

  First, when the method for producing an optical film according to the present invention is performed by a solution casting film forming method, a cellulose ester-based resin is preferably used as a target resin, and cellulose triacetate or cellulose is used as the cellulose ester-based resin. Acetate propionate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate butyrate and the like are preferably used. In the case of cellulose triacetate, cellulose triacetate having a polymerization degree of 250 to 400 and a bound acetic acid amount of 54 to 62.5% is particularly preferable.

  As the cellulose ester, either cellulose ester synthesized from cotton linter or cellulose ester synthesized from wood pulp can be used alone or in combination.

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

  If the number average molecular weight of the cellulose ester is too low, the strength will be low, and if it is too high, the viscosity of the solution may be too high, so it is preferably 70000-300000, more preferably 80000-200000.

  It is preferable to use a large amount of cellulose ester synthesized from a cotton linter that has good releasability from a rotationally driven metal support made of an endless belt or a drum because of high productivity efficiency. Moreover, in order for the effect of peeling to become remarkable, it is preferable that the ratio of the cellulose ester synthesize | combined from the cotton linter is 60 mass% or more, More preferably, it is 85 mass% or more, Furthermore, it uses independently. Most preferred.

  In particular, a cellulose ester film having a total acyl group substitution degree of less than 2.85 is preferred because the dimensional change can be reduced, and a cellulose ester film having a total acyl group substitution degree of less than 2.75 is preferred. A remarkable effect is observed with a cellulose ester film of less than 70.

  In the present invention, the optical film made of a cellulose ester resin film preferably contains an ultraviolet absorber from the viewpoint of preventing deterioration when placed outdoors as a liquid crystal display device. As the ultraviolet absorber, one that is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and has little absorption of visible light having 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 less than 10%, and particularly preferably less than 5%.

  Examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and doriadine compounds. However, it is not limited to these.

  Hereinafter, although the specific example of a ultraviolet absorber is given, this invention is not limited to these.

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- (linear And side chain dodecyl) -4-methylphenol (TINUVIN171: manufactured by Ciba Specialty Chemicals)
UV-9: Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl -4-Hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and mixture (TINUVIN 109: manufactured by Ciba Specialty Chemicals)
UV-10: 2,4-dihydroxybenzophenone UV-11: 2,2'-di-hydroxy-4-methoxybenzophenone UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone UV-13: bis (2 -Methoxy-4-hydroxy-5-benzoylphenylmethane)
In the present invention, for the optical film, a benzotriazole-based UV absorber and a benzophenone-based UV absorber, which are highly transparent as UV absorbers and have an excellent effect of preventing the deterioration of polarizing plates and liquid crystals, can be preferably used. Particularly preferred are benzotriazole-based UV absorbers with less unnecessary coloration. The ultraviolet absorber is preferably one that does not bleed out or volatilize in the film forming process.

  As the UV absorber, a polymer UV absorber can be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  In this invention, it is preferable that 0.1-10 mass% is added with respect to a resin component, and, as for an ultraviolet absorber, it is especially preferable that 0.5-5 mass% is added.

  Moreover, in this invention, these ultraviolet absorbers may be used independently and may be used by mixing 2 or more types from which it differs.

  As a method for adding the ultraviolet absorber, the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, dioxosilane and the like, and then added to the dope, or may be added directly into the dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  In the present invention, if necessary, fine particles such as silicon dioxide can be added to the optical film as a matting agent. Fine particles such as silicon dioxide are preferably surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazanes, and siloxanes. The larger the average particle size of the fine particles, the greater the mat effect, and the smaller the average particle size, the better the transparency. Therefore, the preferable average particle size of the primary particles is 5 to 50 nm, more preferably 7 to 14 nm. is there.

  Examples of the silicon dioxide fine particles used in the present invention include AEROSIL-200, 200V, 300, R972, R972V, R974, R202, R812, OX50, and TT600 manufactured by Aerosil Co., preferably AEROSIL-200. 200V, R972, R972V, R974, R202, R812, and the like.

  In the present invention, the fine particles are added in an amount of 0.04 to 0.4 mass%, preferably 0.05 to 0.3 mass%, more preferably 0.05 to 0.2 mass%, based on the resin. used.

  In the method of the present invention, the solvent used for dissolving the resin may be used alone or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in terms of increasing production efficiency. This is preferable in terms of the solubility of the film and the amount of film foreign matter due to minute insoluble matter. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 30 to 2% by mass for the poor solvent.

  Here, the good solvent and the poor solvent used in the present invention define a good solvent that dissolves the resin used alone, and a poor solvent that swells or does not dissolve alone.

  The good solvent used in the present invention is not particularly limited. For example, when the resin is cellulose triacetate, an organic halogen compound such as methylene chloride or dioxolane, and when the resin is cellulose acetate propionate, methylene chloride, acetone, methyl acetate are used. Etc. Moreover, it is although it does not specifically limit as a poor solvent, For example, methanol, ethanol, i-propyl alcohol, n-butanol, cyclohexane, acetone, cyclohexanone etc. are used preferably.

  For example, U.S. Pat. Nos. 2,492,978, 2,739,070, 2,739,069, and 2, can be used for producing an optical film comprising a cellulose ester resin film by a solution casting method. No. 492,977, No. 2,336,310, No. 2,367,603, No. 2,607,704, British Patent No. 64,071, No. 735,892, No. 45-9074 49-4554, 49-5614, 60-27562, 61-39890, 62-4208 and the like can be referred to.

  In the method for producing an optical film of the present invention, it is preferable to add a plasticizer to the optical film in view of mechanical strength, dimensional stability, and the like. As the addition amount, for example, when the optical film is a cellulose ester film, the cellulose ester film or the cellulose ester film obtained by acylating cellulose with an acetyl group and an acyl group having 3 to 4 carbon atoms is 3 to 30% by mass. It is preferable to set it as the mass%, 10-30 mass% is more preferable, 15-25 mass% is especially preferable. In general, when the amount of plasticizer added increases, the dimensional change is likely to occur. However, according to the method of the present invention, the dimensional change rate can be remarkably reduced.

  Although it does not specifically limit as a plasticizer which can be used by this invention, Phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer Citric acid ester plasticizers, polyester plasticizers, and the like can be preferably used.

  Here, in the phosphoric acid ester system, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like can be preferably used. In the phthalic acid ester system, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate and the like can be preferably used. As the trimellitic acid plasticizer, tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate and the like can be preferably used. In the pyromellitic acid ester plasticizer, tetrabutyl pyromellitate, tetraphenyl pyromellitate, tetraethyl pyromellitate and the like can be preferably used. In the glycolic acid ester system, triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate and the like can be preferably used. As the citrate plasticizer, triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n- (2-ethylhexyl) citrate, etc. are preferably used. Can do. In the polyester plasticizer, a copolymer of a dibasic acid such as an aliphatic dibasic acid, an alicyclic dibasic acid, or an aromatic dibasic acid and a glycol can be used. The aliphatic dibasic acid is not particularly limited, and adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyl dicarboxylic acid and the like can be used. As the glycol, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, or the like may be used. it can. These dibasic acids and glycols 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 terms of weight average molecular weight from the viewpoint of compatibility with the cellulose resin.

  In the method of the present invention, it is particularly preferable to use a plasticizer having a vapor pressure of less than 1333 Pa at 200 ° C., more preferably a plasticizer having a vapor pressure of 666 Pa or less, and more preferably 1 to 133 Pa. Although the plasticizer which has non-volatility is not specifically limited, For example, arylene bis (diaryl phosphate) ester, tricresyl phosphate, trimellitic acid tri (2-ethylhexyl) etc. are mentioned. These plasticizers can be used alone or in combination of two or more.

  In the method for producing an optical film according to the present invention, when the optical film is a cellulose ester film, the solid content concentration of the dope that is a cellulose ester solution is usually about 10 to 40% by mass, and the dope at the time of casting in the casting step The viscosity is adjusted in the range of 1 to 200 poise.

  Here, first, dissolution of the cellulose ester is usually performed by means such as a stirring dissolution method, a heating dissolution method, and an ultrasonic dissolution method in a dissolution vessel, and the pressure is higher than the boiling point of the solvent at normal pressure. In addition, a method of heating at a temperature where the solvent does not boil and dissolving with stirring is more preferable in order to prevent the formation of a bulk undissolved material called gel or mamako. Further, a cooling dissolution method described in JP-A-9-95538 or a method of dissolving under high pressure described in JP-A-11-21379 may be used.

  A method in which the cellulose ester is mixed with a poor solvent and wetted or swollen, and then mixed with a good solvent and dissolved is also preferably used. At this time, an apparatus for mixing or dissolving cellulose ester with a poor solvent and an apparatus for mixing and dissolving with a good solvent may be separately provided.

  In the present invention, the type of the pressure vessel used for dissolving the cellulose ester is not particularly limited as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. In addition, instruments such as a pressure gauge and a thermometer are appropriately disposed in the pressurized container. The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature after adding the solvent is higher than the boiling point of the solvent to be used. In the case of two or more mixed solvents, the heating temperature is higher than the boiling point of the lower boiling solvent and the solvent does not boil. Is preferred. If the heating temperature is too high, the required pressure increases and productivity decreases. The range of preferable heating temperature is 20-120 degreeC, 30-100 degreeC is more preferable, The range of 40-80 degreeC is further more preferable. The pressure is adjusted so that the solvent does not boil at the set temperature.

  In addition to cellulose ester and solvent, additives such as necessary plasticizers and UV absorbers can be mixed with the solvent in advance, dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester. It may be put into the dope.

  After dissolving the cellulose ester, take it out from the container while cooling, or remove it from the container with a pump and cool it with a heat exchanger, etc., and use the resulting cellulose ester dope for film formation. The temperature may be cooled to room temperature.

  The mixture of the cellulose ester raw material and the solvent is dissolved by a dissolving apparatus having a stirrer, and at this time, the peripheral speed of the stirring blade is preferably at least 0.5 m / second and stirred and dissolved for 30 minutes or more.

  In the method of the present invention, the cellulose ester dope is filtered to remove foreign matters, particularly foreign matters that are mistakenly recognized as images in a liquid crystal display device. It may be said that the quality as an optical film is determined by this filtration.

  Filter media used for filtration preferably have low absolute filtration accuracy. However, if the absolute filtration accuracy is too low, the filter media is likely to be clogged, and the filter media must be replaced frequently, resulting in reduced productivity. There is a problem of making it.

  For this reason, in the method of the present invention, the filter medium used for the cellulose ester dope preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and 0.003 to 0.006 mm. A filter medium in the range of is more preferable.

  There are no particular restrictions on the material of the filter medium, and normal filter media can be used. However, plastic fiber filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel fibers are used to remove fibers. This is preferable.

  In the method of the present invention, filtration of the cellulose ester dope can be performed by a normal method, but a method of filtering while heating under pressure at a temperature not lower than the boiling point at normal pressure of the solvent and in a range where the solvent does not boil, The increase in the differential pressure before and after the filter medium (hereinafter sometimes referred to as filtration pressure) is small and preferable.

  The range of preferable filtration temperature is 45-120 degreeC, 45-70 degreeC is more preferable, and it is more preferable that it is the range of 45-55 degreeC.

  The filtration pressure is preferably 3500 kPa or less, more preferably 3000 kPa or less, and even more preferably 2500 kPa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

  If the cellulose of the raw material contains an acyl group unsubstituted or low-substituted cellulose ester, foreign matter failure (hereinafter sometimes referred to as bright spot or bright spot foreign matter) may occur. The bright spot is a normal cellulose ester film when a cellulose ester film is placed between two polarizing plates in an orthogonal state (crossed Nicols), irradiated with light from one side and observed with an optical microscope (50 times) from the opposite side. If this is the case, the light is blocked, black, and nothing can be seen, but if there is a foreign object, the light leaks from it and appears to shine like a spot. The larger the bright spot diameter, the greater the actual damage in the liquid crystal display device. The bright spot diameter is preferably 50 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. The diameter of the bright spot means a diameter measured by approximating the bright spot to a perfect circle.

As long as the bright spot foreign matter has a diameter of 400 / cm ² or less, there is no practical problem, but 300 / cm ² or less is preferable, and 200 / cm ² or less is more preferable. In order to reduce the number and size of such bright spot foreign matters, it is necessary to sufficiently filter fine foreign matters.

  In addition, for example, as described in JP-A-2000-137115, a pulverized product of a cellulose ester film once formed is re-added at a certain ratio in a dope, and used as a raw material for cellulose ester and its additive Can be preferably used because it can reduce bright spot foreign matter.

  Next, to produce an optical film by the method of the present invention, 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 poor solvent, A cellulose ester solution (dope) is prepared by adding a plasticizer and an ultraviolet absorber.

  The belt temperature during film formation can be cast in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and can be cast in a range of 5 ° C. to the boiling point of the solvent −5 ° C. However, it is more preferable to cast on a 5-30 degreeC support body. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  In addition, a dope adjusted to have a dope viscosity of 1 to 200 poise is cast from the casting die so as to have a substantially uniform film thickness, and the amount of residual solvent in the casting film is solid. When the partial mass is 200% or more, the casting film (web) is dried with drying air so that the casting film temperature is below the boiling point of the solvent and from 200% or less to peeling up to the boiling point of the solvent + 20 ° C. .

  On the support, in order to dry and solidify the web until the film has a peelable film strength, the residual solvent amount in the web is preferably dried to 150% by mass or less, more preferably 50 to 120%.

  The web temperature when peeling the web from the support is preferably 0 to 30 ° C. In addition, immediately after the web is peeled off from the support, the temperature once drops rapidly due to solvent evaporation from the support close-contact surface side, and volatile components such as water vapor and solvent vapor in the atmosphere tend to condense. The web temperature is more preferably 5 to 30 ° C.

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

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

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

  The web after peeling is introduced into a primary drying apparatus, for example. In the primary drying device, the web is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, while the web is blown from the ceiling of the drying device and discharged from the bottom portion of the drying device. Dried by.

  The web is then introduced into a tenter dryer. Therefore, the side edges of the web are gripped with a clip and stretched, and the web is dried.

  As a liquid crystal display member, a tenter method in which both side edges of a web are fixed with a clip or the like and stretched is known, which is preferable for improving flatness and dimensional stability.

  In particular, in the drying process after peeling from the support, the web tends to shrink in the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point, for example, a method / tenter method in which all or part of the drying process as shown in JP-A-62-46625 is performed while holding the width at both ends of the web with a clip in the width direction. Is preferred.

  Gripping / stretching with a tenter can be performed anywhere from 50 to 150% by mass of the residual solvent of the film immediately after peeling to 0% by mass of the residual residual solvent immediately before winding. It is as described in the present invention that is preferably performed in the range of 5 to 30%.

  It is also common to divide the tenter into several temperature zones in the direction of travel of the base. The temperature during stretching is selected so that desired physical properties and planarity can be obtained, but the temperature in the drying zone before and after the tenter is also selected from a temperature different from the temperature during stretching for various reasons. Sometimes. For example, if the atmospheric temperature in the drying zone before the tenter is different from the temperature in the tenter, the temperature in the zone near the tenter entrance is set to an intermediate temperature between the temperature in the drying zone before the tenter and the temperature in the center of the tenter. It is generally done. Similarly, when the temperature in the tenter is different from that in the tenter, the temperature in the zone near the tenter outlet is set to an intermediate temperature between the temperature after the tenter and the temperature in the tenter. The temperature of the drying zone before and after the tenter is generally 30 to 120 ° C., preferably 50 to 100 ° C., and the temperature of the stretching portion in the tenter is 50 to 180 ° C., preferably 80 to 140 ° C. The temperature is appropriately selected from intermediate temperatures thereof.

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

  The film stretching pattern, that is, the trajectory of the gripping clip, is selected from the optical properties and flatness of the film as well as the temperature, and varies. A pattern held in width is often used. In the vicinity of the end of clip holding near the tenter exit, the width is generally relaxed to suppress base vibration by releasing the grip.

  The drawing pattern is also related to the drawing speed, but the drawing speed is generally 10 to 1000 (% / min), preferably 100 to 500 (% / min). This stretching speed is not constant when the clip trajectory is a curve, and gradually changes in the base traveling direction.

  Further, the web (film) after drying by the tenter method is introduced into a secondary drying apparatus. In the secondary drying device, the web is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, while the web is blown from the ceiling of the secondary drying device, and at the bottom of the secondary drying device. It is dried by the warm air discharged from the part, and wound up on a winder as a cellulose ester film.

  In the method for producing an optical film comprising the cellulose ester resin film of the present invention, the means for drying the web 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 in terms of simplicity. The drying temperature is preferably 40 to 150 ° C., and more preferably 80 to 130 ° C. in order to improve the flatness and dimensional stability.

  Thus, in the web drying step, the web peeled from the support is further dried, and finally the residual solvent amount is 3% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less. It is preferable for obtaining a film having good 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.

  In addition, it is preferable to perform the process which forms emboss in the both-sides edge part of an optical film with the embossing apparatus in the front | former stage introduce | transduced into a winding process with respect to the optical film which finished the conveyance drying process. As the embossing apparatus, for example, an apparatus described in JP-A-63-74850 can be used.

  In the method of the present invention, the winder related to the production of the optical film may be one generally used, such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, etc. It can be wound up by a winding method.

  In the method of the present invention, the film thickness of the optical film after winding varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 30 to 200 μm, which is 40 for the recent thin tendency. The range of ˜120 μm is preferable, particularly 80 μm or less, preferably 20 to 60 μm, and more preferably 30 to 50 μm.

  The method for producing an optical film according to the present invention is a method for controlling the orientation angle by applying a so-called torsional force to a film conveyed in a film production line of the optical film. That is, in the formation of an optical film made of a cellulose ester resin by a solution casting film forming method, the amount of residual solvent in the film is in the range of 10 to 70% by mass, and the width of the orientation angle of the finished film is According to the positive / negative of the hand average value, the arrangement direction of the roll shaft of one or a plurality of transport rolls is adjusted within an angle range of 0 ° to 5 ° with respect to the direction perpendicular to the film transport direction. It is. In this case, it is preferable that the ambient temperature at which the film is conveyed and dried is in the range of 30 to 140 ° C.

  According to the present invention, in the solution casting film forming method, by appropriately selecting the range of the residual solvent amount in the film and the film temperature and adjusting the roll axis, there is no trouble such as wrinkles, An optical film capable of achieving a highly accurate orientation angle distribution of a film, having an orientation angle uniform in the width direction (TD direction) over substantially the entire area of the film, and having excellent phase difference compensation performance and a viewing angle expansion function. Can be manufactured.

  Here, the orientation angle referred to in the present invention represents the direction of the slow axis in the surface of the thermoplastic resin film (the angle with respect to the width direction during casting film formation), and the measurement of the orientation angle is performed automatically. This is done using a refractometer KOBRA-21ADH. The orientation angle is measured at 3 to 10 cm intervals in the width direction of the film, for example, at 5 points, and all orientation angles are preferably ± 1.7 °, within ± 1.5 °. Is more preferable, and within ± 1.0 ° is more preferable.

  A specific control method will be described with reference to the drawings. The orientation angle is defined by the direction of the slow axis of the in-plane retardation of the film. As shown in FIG. 1, when the direction of the slow axis is substantially 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. When the direction of the slow axis is substantially parallel to the film transport direction, the transport direction is defined as 0 ° and the counterclockwise direction is defined as positive as shown in FIG.

  The orientation angle of the width of the finished film is measured at a plurality of points based on the above definition, and the orientation angle is brought close to the desired value of 0 ° by changing the roll angle according to the sign of the average value. Is possible. In the roll arrangement as shown in FIG. 3, when the average value of the orientation angle measured from the upper surface of the film (upper side of the paper) is positive, the path length of the film on the right side in the traveling direction as viewed from the orientation angle measurement surface is long as shown in FIG. The average value of the orientation angles can be brought close to 0 by changing the arrangement direction of the roll axes so as to be. As the arrangement direction of the roll axis to be changed, as long as the path length on the same side of the film is increased, the vertical direction as shown in FIG. 5 or the direction shown in FIG. Such an oblique direction may be used, and although not shown, a plurality of roll shaft arrangement directions may be changed simultaneously. When changing the arrangement direction of a plurality of roll shafts, a continuous roll may be used, or the arrangement directions of a plurality of roll shafts at separate positions may be changed.

  If the roll axis is adjusted to be too small, there is no effect of correcting the orientation angle. If the roll axis is too large, the transported film is distorted or wrinkled, and therefore there is an appropriate value range. It is desirable to adjust the roll shaft arrangement direction to an angle in the range of greater than 0 ° and less than or equal to 5 ° with respect to the direction perpendicular to the film transport direction.

  In order to maximize the effect of correcting the orientation angle, it is desirable that the residual solvent amount of the film is 10 to 70% by mass in the case of solution casting as described above. If the amount of residual solvent is too small, the effect of correcting the orientation angle is small, and if the amount of residual solvent is too large, the film is wrinkled when the arrangement direction of the roll shaft is changed.

  In the production of an optical film, there may be provided a stretching facility for stretching the film forming line in the film transport direction or a direction perpendicular to the transport direction, but the present invention is effective regardless of the presence or absence of the stretching facility. When there is a stretching facility, the arrangement direction of the roll shaft before the stretching facility may be changed, or the arrangement direction of the roll shaft after the stretching facility may be changed. Further, the arrangement direction of the roll shaft before and after the stretching equipment may be changed simultaneously.

  Next, the manufacturing method of the optical film of the present invention may be based on a melt casting film forming method. Here, as the melt casting film forming method, a method using a T-die that can reduce film thickness unevenness and retardation unevenness is preferable. In the extrusion method using a T die, the polymer is melted at a temperature at which it can be melted, and a film-like (sheet-like) molten resin is extruded from the T die onto a cooling drum (support). Subsequently, the film-like (sheet-like) molten resin is cooled and solidified by the cooling drum, and the resin film is peeled off from the cooling drum.

  Next, when the method for producing an optical film according to the present invention is performed by a melt casting film forming method, the target thermoplastic resin is not particularly limited as long as it can be formed by the melt casting film forming method.

  For example, polycarbonate (glass transition temperature Tg: about 150 ° C.), alicyclic structure-containing polymer, polyvinyl alcohol, polyamide, polyimide, cellulose ester resin and the like can be mentioned. Of these, cellulose esters and alicyclic structure-containing polymers are preferred because of their small photoelastic coefficient.

  As the cellulose ester resin, cellulose acetate propionate (glass transition temperature Tg: about 170 ° C.), cellulose acetate butyrate and cellulose acetate propionate butyrate are preferable. The degree of substitution of the acetyl group of the cellulose ester is preferably at least 1.5 or more because the resulting film has excellent dimensional stability. As a measuring method of the substitution degree of the acyl group of a cellulose ester, it can implement according to ASTM-D-817-91. The molecular weight of the cellulose ester is preferably 50,000 to 300,000, particularly 60,000 to 200,000 as the number average molecular weight because the mechanical strength of the resulting film can be increased.

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

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

  The cycloaliphatic structure-containing polymer used in the present invention has a polyisoprene or polystyrene equivalent weight average molecular weight (Mw) measured by gel permeation chromatography of a cyclohexane solution (or a toluene solution when the polymer is not dissolved) of 25000. It is preferably ˜50000, and more preferably 30000-45000. The molecular weight distribution (Mw / Mn) is preferably 1.2 to 3.5, more preferably 1.5 to 3.0. Moreover, it is preferable that a glass transition temperature (Tg) is 80-200 degreeC. By setting the characteristics of the alicyclic structure-containing polymer within the above range, good heat resistance and moldability can be obtained.

  The thermoplastic resin of the present invention may contain additives such as a plasticizer, an ultraviolet absorber, an antioxidant, a matting agent, an antistatic agent, a flame retardant, a dye and an oil agent for various purposes.

  As the plasticizer, those used in the method for producing an optical film by the above-mentioned solution casting film-forming method and those substantially the same can be used.

  As the antioxidant, hindered phenol compounds are suitable. Specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [ 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadec -3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy Benzyl) benzene and tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. In order to obtain the effect, the amount of these compounds added is preferably from 1 ppm to 1.0%, particularly preferably from 10 to 1000 ppm, by mass relative to the thermoplastic resin.

  When the method for producing an optical film of the present invention is based on the melt casting film forming method, usable ultraviolet absorbers include those used in the method for producing an optical film by the above solution casting film forming method, Similar ones can be used.

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass with respect to the thermoplastic resin. If the amount used is too small, the UV absorption effect may be insufficient, and conversely if too large, the transparency of the film may deteriorate. The ultraviolet absorber is preferably one having high heat stability.

  In the present invention, it is preferable to add fine particles in order to impart slipperiness of the film. The fine particles used in the present invention may be either an inorganic compound or an organic compound as long as it has heat resistance during melting. Examples of the inorganic compound include a compound containing silicon, silicon dioxide, aluminum oxide, zirconium oxide, and calcium carbonate. Talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like are preferred, and silicon-containing inorganic compounds and zirconium oxide are more preferred. Among them, silicon dioxide is particularly preferably used because haze can be suppressed to a small value. Even when the method for producing an optical film of the present invention is carried out by a melt casting film forming method, the solution casting film forming method is used. The same matting agent as that used in the method for producing an optical film can be used.

  When the optical film production method of the present invention is carried out by the melt casting film forming method, the melt casting film forming method includes a melt extrusion method such as a method using a T-die or an inflation method, a calendar method, and a hot press. And injection molding methods. Among these, a method using a T-die that is small in thickness unevenness, can be easily processed to a thickness of about 50 to 500 μm, and can reduce film thickness unevenness and retardation unevenness is preferable. The extrusion method using a T die is a method in which the above-described polymer is melted at a meltable temperature, extruded from the T die into a film (sheet shape) on a cooling drum, solidified by cooling, and peeled off from the cooling drum. The resulting film has excellent thickness accuracy and can be preferably used in the present invention.

  The conditions for melt extrusion can be carried out in the same manner as those used for other thermoplastic resins such as polyester. For example, the cellulose ester dried under hot air, vacuum, or reduced pressure is melted at an extrusion temperature of about 200-300 ° C using a single-screw or twin-screw extruder, and filtered through a leaf disk type filter to remove foreign matter. Then, the film is cast from the T die into a film (sheet) and solidified on a cooling drum. When introducing into the extruder from the supply hopper, it is preferable to prevent oxidative decomposition or the like under reduced pressure or in an inert gas atmosphere.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances. A stainless steel fiber sintered filter is an integrated stainless steel fiber body that is intricately entangled and then compressed and sintered at the contact point. The density is changed according to the thickness of the fiber and the amount of compression, and the filtration accuracy is improved. Can be adjusted. It is preferable to use a multilayer body in which the filtration accuracy is repeated coarsely and densely a plurality of times. In addition, it is preferable to adopt a configuration in which the filtration accuracy is sequentially increased or a method in which coarse and dense filtration accuracy is repeated, so that the filtration life of the filter can be extended and the trapping accuracy of foreign matters and gels can be improved.

  If flaws or foreign matter adhere to the die, streaky defects may occur. Such a defect is called a die line, but in order to reduce surface defects such as the die line, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip. Since the volatile component may be deposited from the resin around the die and cause a die line, it is preferable to suck the atmosphere containing the volatile component. Moreover, since it may precipitate also in apparatuses, such as an electrostatic application, it is preferable to apply alternating current or to prevent precipitation with another heating means.

  Additives such as plasticizers may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

  The temperature of the cooling drum is preferably equal to or lower than the glass transition temperature of the thermoplastic resin. In order to bring the resin into close contact with the cooling drum, it is preferable to use a method in which the resin is brought into contact by electrostatic application, a method in which the resin is brought into contact by wind pressure, a method in which the full width or the end is brought into contact with nip, a method in which the resin is brought into contact with reduced pressure.

  Unlike the resin sheet formed by the solution casting film forming method, the thermoplastic resin sheet formed by such a melt casting film forming method has a feature that the thickness direction retardation (Rt) is small. There may be a case where stretching conditions different from the film-forming method are required. In order to obtain desired optical properties, depending on the case, both stretching in the direction of travel of the film and stretching in the width direction of the film may be performed simultaneously or sequentially. Moreover, depending on the case, it may be only extending | stretching of a film width direction. By this stretching operation, the molecules are oriented and the film is adjusted to the necessary retardation value.

  The stretching method is not particularly limited, but a known pin tenter or clip type tenter can be preferably used. The stretching direction can be a length direction, a width direction, or an arbitrary direction (an oblique direction). However, by setting the stretching direction to the width direction, lamination with a polarizing film can be preferably performed. 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 usually in the width direction. A good viewing angle can be obtained by incorporating a polarizing plate in which the transmission axis of the polarizing film and the slow axis of the optical film are parallel to each other into the liquid crystal display device.

  As the stretching conditions, the temperature and magnification can be selected so that desired retardation characteristics can be obtained. Usually, the draw ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually the glass transition temperature (Tg) of the resin constituting the sheet−50 ° C. to Tg + 50. It is carried out in the temperature range of ° C, preferably Tg-40 ° C to Tg + 40 ° C. If the draw ratio is too small, the desired retardation may not be obtained. Conversely, if it is too large, it may break. If the stretching temperature is too low, it will break, and if it is too high, the desired retardation may not be obtained.

  When correcting the retardation of the thermoplastic resin film produced by the above method to a desired value, the film may be stretched or shrunk in the length direction or the width direction. To shrink in the length direction, for example, a method of shrinking the film by temporarily clipping out the width stretching and relaxing in the length direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine. There is. The latter method can be performed by using a general simultaneous biaxial stretching machine and by using a pantograph method or a linear drive method to drive the clip portion in a smooth and gradually narrowing interval between adjacent clips in the longitudinal direction. it can.

  A heat treatment zone may be provided for the purpose of flatness correction, dimensional stability improvement and the like after stretching and before winding. For example, for a period of several tens of seconds to several tens of minutes, a glass transition temperature (Tg) of a resin constituting the sheet is maintained at a temperature of -30 ° C. to Tg, and a zone for transporting between staggered rolls is provided. There is also.

  The film thickness of the optical film varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 30 to 200 μm, and the recent thin tendency is preferably 40 to 120 μm, particularly 40 to A range of 100 μm is preferred. The film thickness can be adjusted by controlling the extrusion flow rate, the slit gap of the die base, the speed of the cooling drum, and the like so as to obtain a desired thickness. 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.

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

  The method for producing an optical film according to the present invention is a method for controlling the orientation angle by applying a so-called torsional force to a film conveyed in a film production line of the optical film. In other words, in the production of an optical film made of a cellulose ester resin by a melt casting film forming method, after casting of the molten resin and peeling of the film, the film temperature is the glass transition temperature (Tg) of the film. In the range of ± 30 ° C., depending on whether the width average value of the orientation angle of the finished film is positive or negative, the direction of the roll axis of one or more transport rolls is perpendicular to the film transport direction. Adjustment is made within an angle range of 0 ° to 5 °.

  In the case of the melt casting film forming method, the film temperature is desirably in the range of the glass transition point ± 30 ° C. of the film. When the film temperature is too low, the effect of correcting the orientation angle is small, and when the film temperature is too high, the film is wrinkled when the roll shaft arrangement direction is changed.

  Here, the glass transition temperature (Tg) of the film means the glass transition temperature (Tg) of the film composition containing a resin, an additive, and a solvent which are the main materials of the film.

  The glass transition temperature (Tg) is measured using a generally known thermomechanical analyzer (TMA), differential scanning calorimeter (DSC), differential thermal analyzer (DTA), dynamic viscoelasticity measuring device (DMA), etc. Can be measured.

  According to such the present invention, in the melt casting film forming method, after peeling, by appropriately selecting the range of the film temperature during conveyance, by adjusting the roll axis of the conveyance roll, without trouble such as wrinkles, An optical film capable of achieving a highly accurate orientation angle distribution of a film, having an orientation angle uniform in the width direction (TD direction) over substantially the entire area of the film, and having excellent phase difference compensation performance and a viewing angle expansion function. It can be manufactured.

  Furthermore, in the present invention, in the production of an optical film by any one of the above optical film production methods, the orientation angle of the film is measured online, and the installation direction of the roll axis of the transport roll is adjusted according to the result. Is.

  According to the present invention as described above, the orientation angle can be adjusted on the basis of the information while measuring the orientation angle during film formation online, and the productivity is excellent.

  The optical film manufactured by the method of the present invention can be formed into an elliptically polarizing plate by being bonded to at least one surface of a polarizing film.

  The polarizing film is a film that has been conventionally stretched by treating with a dichroic dye such as iodine a stretchable film such as a polyvinyl alcohol film. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose triacetate film having no anisotropy as a protective film to both sides thereof.

  The polarizing plate may be produced by laminating the optical film according to the present invention on the polarizing film, or may be produced by directly laminating the optical film of the present invention as a protective film.

  Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the length direction and treated with a dichroic dye and a long optical film 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 of the present invention 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.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Examples 1-9, Comparative Examples 1-8
By the method of the present invention, an optical film made of cellulose acetate propionate resin by a solution casting film forming method was produced.

(Preparation of dope)
First, a dope of cellulose acetate propionate was prepared as follows.

Cellulose acetate propionate 100 parts by mass (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7)
Triphenyl phosphate 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by weight AEROSIL 200V (manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by weight Methylene chloride 300 parts by weight Ethanol 40 parts by weight Part The above materials are sequentially put into a sealed container, the temperature in the container is raised from 20 ° C. to 80 ° C., and the mixture is stirred for 3 hours while maintaining the temperature at 80 ° C. to obtain cellulose acetate propionate. Dissolved completely. Then, stirring was stopped and the liquid temperature was lowered to 43 ° C. The dope was filtered using a filter paper (Azumi filter paper No. 244, manufactured by Azumi Filter Paper Co., Ltd.) to obtain a dope.

  The dope prepared as described above is cast through a casting die kept at 30 ° C. onto a 30 ° C. support made of a stainless steel endless belt to form a web (dope film), and finally After drying on the support until the residual solvent amount in the web reached 80% by mass, the web was peeled from the support with a peeling roll.

  The web is then dried in a staggered roll transport drying process, subsequently introduced into a stretching machine consisting of a tenter, sandwiched between the ends of the web by clips, and under conditions where residual solvent is present, the width is substantially reduced. The film was stretched in the hand direction and dried by applying dry air.

  Furthermore, the web (film) was dried in a roll conveyance drying process arranged in a staggered manner, wound up by a winder, and finally a cellulose acetate propionate film having a film thickness of 60 μm was produced.

  In this embodiment, a heating chamber having a temperature of 60 ° C. is installed in front of the stretching machine, and two conveyance rolls that can adjust the arrangement angle of the roll axis are installed therein, and the arrangement angle of the roll axis of each conveyance roll is appropriately set. Adjustment was performed to stretch the cellulose acetate propionate film. Here, the arrangement angle of the roll shaft is an angle indicated by φ in FIG. 4, and is an angle measured in the direction of increasing counterclockwise with the film transport direction being 0 °. The arrangement angle of the roll axis of each transport roll was adjusted to 90 ° -2 °, that is, 88 °, and the cellulose acetate propionate film was stretched.

  In Examples 1 to 9, the roll axis arrangement angle that is within the scope of the present invention was set to 85 ° or more and less than 90 °, and the residual solvent amount of the film was changed to 10 to 70%. In Comparative Examples 1 to 11, the roll shaft arrangement angle and the residual solvent amount were out of the scope of the present invention.

  Thus, the orientation angle of the cellulose acetate propionate film thus obtained was measured at five points in the width direction with the Oji measuring instrument KOBRA-21ADH. The obtained results are shown in Table 1 below.

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

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

  B: Although the absolute value of the average orientation angle is 1.0 ° or less, the difference between the maximum orientation angle and the minimum orientation angle is 1.5 ° or more, and the orientation angle distribution is large, but the average orientation angle is suppressed. Therefore, it was sufficiently usable as a retardation film or a viewing angle widening film.

  C: Although 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 less, and the average orientation angle is large, but the orientation angle distribution is suppressed. In practical use, it could be used as a retardation film or a viewing angle widening film.

  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 the orientation angle distribution are large, a retardation film or a visual field It was difficult to use as a corner enlargement film.

  E: Wrinkles were generated during production, and the orientation angle could not be measured. The resulting film could not be used as a retardation film or a viewing angle widening film.

  Table 1 shows the measurement results and evaluation results of the orientation angles of the films thus obtained.

  From the results of Table 1, in Examples 1 to 9 of the present invention, in the formation of an optical film made of cellulose acetate propionate resin by the solution casting film forming method, the amount of residual solvent in the film is specified as the specific amount of the present invention. By adjusting the installation angle of the roll axis of the transport roll in the heating chamber at a specific temperature within the specified range of the present invention and stretching, a film having excellent orientation angle characteristics can be achieved. It was. The optical film made of cellulose acetate propionate resin thus obtained was sufficiently usable particularly as a retardation film and a viewing angle widening film.

  On the other hand, according to Comparative Examples 1 to 4, the residual solvent amount during stretching of the cellulose acetate propionate film and the installation angle of the roll shaft of the transport roll in the heating chamber at a specific temperature were out of the scope of the present invention. In the cellulose acetate propionate film, a uniform distribution of the film orientation angle cannot be obtained, and it cannot be used as a retardation film or a viewing angle widening film.

  In Examples 1-9 and Comparative Examples 1-8, as can be seen in Comparative Example 1, when the roll shaft arrangement angle φ is set to a right angle (90 °) in the same film transport direction as in the prior art, the average of the orientation angles This is an example in which the value is positive (+ 1.8 °), and a favorable orientation angle result is obtained when the roll axis arrangement direction φ is smaller than 90 °. On the other hand, when the roll shaft arrangement angle φ is 90 ° and the average value of the orientation angle is negative, a good result is obtained when the roll shaft arrangement angle φ is changed more than 90 °. . Similar results were obtained when other resins, polycarbonate, cycloolefin, polyimide, and the like were used.

Examples 10-18, Comparative Examples 9-16
By the method of the present invention, an optical film made of cellulose acetate propionate resin by a melt casting method was produced.

Cellulose acetate propionate 100 parts by mass (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, glass transition temperature: about 170 ° C.)
Plasticizer: 10 parts by weight of dibutyl phthalate Antioxidant: 0.07 parts by weight of 2,6-di-t-butyl-p-cresol 1 part by weight of TINUVE 326 (manufactured by Ciba Specialty Chemicals) AEROSIL 200V (Nippon Aerosil) 0.1 parts by mass Melting and mixing a mixture of materials containing the above cellulose acetate propionate resin at 240 ° C. using a twin screw extruder, filtering with a metal filter, and then forming a film from a T die with a gear pump Extruded into a (sheet form), the film-like resin was brought into close contact with a 130 ° C. cooling drum and solidified while being conveyed, and the film was peeled off with a peeling roll. This film was stretched with a stretching machine heated to 140 ° C. to prepare a film. A heating chamber was installed in front of the stretching machine, and two transport rolls capable of adjusting the arrangement angle of the roll shaft were installed there. The atmospheric temperature of the heating chamber is set to 105 ° C. to 175 ° C. with respect to the glass transition temperature (Tg: about 140 ° C.) of the cellulose acetate propionate resin film, and the arrangement angle of the roll shaft of each transport roll is set to 90 °. The temperature was changed in the range of 0 to 96 °, and the same measurements and evaluations as in Examples 1 to 9 and Comparative Examples 1 to 8 were performed.

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

  From the results of Table 2, in Examples 10 to 18 of the present invention, in the formation of an optical film made of cellulose acetate propionate resin by the melt casting film forming method, after casting of the molten resin and peeling of the film, the film By having the temperature within the specific range of the present invention and adjusting the installation angle of the roll axis of the transport roll in the heating chamber at the specific temperature within the specific range of the present invention, it has excellent orientation angle characteristics. A film could be achieved. The optical film made of cellulose acetate propionate resin thus obtained was sufficiently usable particularly as a retardation film and a viewing angle widening film.

  In Examples 10-18, film formation by melt casting of cellulose acetate propionate resin was exemplified, but in addition, cellulose ester, polycarbonate, cycloolefin, polyester, polyethylene, polystyrene, polymethyl methacrylate, etc. Any resin having a melting point can be used, and similarly good results were obtained by selecting the temperature range of the present invention for the glass transition temperature of each material.

Example 19 and Comparative Example 17
An optical film made of cellulose acetate propionate resin by a solution casting film forming method was manufactured in the same manner as in Comparative Example 1, but after the tenter stretching machine, the phase difference of the film in the line was measured before winding. A means (KOBRA-WI, manufactured by Oji Scientific Instruments Co., Ltd.) was installed, and the phase difference of the film being conveyed was measured online.

  In Example 19, 100 film rolls were produced over a period of 3 days while changing the orientation of the roll axis based on the orientation angle of the film measured online. In Comparative Example 17, 100 film rolls were produced in the same manner while the roll shaft was fixed at 90 ° as in Comparative Example 1. Using the film thus produced, the uniformity of the orientation angle was evaluated.

  As a result, in evaluation of 100 film rolls, Example 19 had A = 98%, B = 2%, and C = D = E = 0%. On the other hand, in Comparative Example 17, A = B = 0%, C = 3%, D = 97%, and E = 0%, and a very good yield rate was obtained in the examples of the present invention.

It is the figure which defined the orientation angle. It is the figure which defined the orientation angle. It is the figure which showed the method of controlling an orientation angle. It is the figure which showed the method of controlling an orientation angle. It is the figure which showed the method of controlling an orientation angle. It is the figure which showed the method of controlling an orientation angle.

Explanation of symbols

F film θ orientation angle φ roll axis angle

Claims (4)

When forming an optical film, depending on the orientation angle of the finished optical film, the arrangement direction of the roll axis of one or more transport rolls in the film forming line is set to a direction perpendicular to the film transport direction. A method for producing an optical film, wherein the adjustment is performed within an angle range of 0 ° to 5 °. Film formation of the optical film is performed by a solution casting film formation method, and the amount of residual solvent in the film is in the range of 10 to 70% by mass, depending on whether the width average value of the orientation angle of the finished optical film is positive or negative. The roll shaft arrangement direction of one or a plurality of transport rolls is adjusted in a range of an angle greater than 0 ° and less than or equal to 5 ° with respect to a direction perpendicular to the film transport direction. The manufacturing method of the optical film of description. The optical film is formed by a melt casting method, and after the casting of the molten resin and the peeling of the film, the film temperature is within the range of the glass transition temperature (Tg) ± 30 ° C. Depending on whether the width average value of the orientation angle of the optical film is positive or negative, the arrangement direction of the roll shaft of one or a plurality of transport rolls is greater than 0 ° and less than 5 ° with respect to the direction perpendicular to the film transport direction. It adjusts in the range of an angle, The manufacturing method of the optical film of Claim 1 characterized by the above-mentioned. In the manufacturing method of the said optical film, the orientation angle of the said completed optical film is measured online, The arrangement direction of the roll axis | shaft of a conveyance roll is adjusted with the positive / negative of the average value, The characterized by the above-mentioned. The manufacturing method of the optical film of any one.