JP4622677B2 - Optical film, method for producing optical film, polarizing plate protective film, retardation film, polarizing plate, and display device - Google Patents

Description

  The present invention relates to an optical film, a method for producing an optical film, a polarizing plate protective film, a retardation film, a polarizing plate, and a display device.

  Cellulose ester films are widely used because they are optically and physically useful as protective films for polarizing plates, but general-purpose resin films such as polyesters such as PET, polyethylene (PE), and polypropylene (PP) are commonly used. The film is formed by melt extrusion molding, but the melt extrusion molding method is not yet available for cellulose ester-based optical films such as TAC (cellulose triacetate film).

  That is, as an optical film, for example, a cellulose triacetate film is generally produced by a solution casting film forming method. This cellulose triacetate film is produced by first dissolving cellulose triacetate 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. A cellulose triacetate solution (dope) is prepared by adding a plasticizer or an ultraviolet absorber to this, and an endless metal support (for example, a belt or drum, below) having a mirror-finished surface. (Also referred to as a support), cast uniformly from a casting die on the support, evaporate the solvent on the support, and after the dope film (web) has solidified, it is peeled off by a peeling roll, and the film after peeling During the drying process, the optical properties of the film (birefringence) To adjust the thickness and improve the flatness, the tenter (film width direction stretching device) holds the peeled film at both ends in the width direction of the film to maintain the film width, stretch the film width direction, and relax While performing a process, a film is dried and a cellulose triacetate film is obtained.

  However, since the film production method is a production method based on a casting film production method using a halogen-based solvent, the cost required for solvent recovery has been a very heavy burden. For this reason, a variety of solvents other than halogen-based solvents were tested, but there was no substitute with satisfactory solubility. In addition to the alternative solvent, a new dissolution method such as a cooling method described in JP-A-10-95861 has been tried, but industrial realization is difficult and further investigation is required.

On the other hand, Patent Document 1 proposed a melt extrusion molding method focusing on the problem of the solution casting film forming method having a great influence on environmental pollution. However, the film thickness variation at the time of melt extrusion is large, and the control method is difficult. It was.
JP 2000-352620 A

  The present invention has been made in view of the above circumstances, and its purpose is to provide an optical film that is optically and physically excellent without using a solvent, and particularly has excellent dimensional stability. The object is to provide a technique for stabilizing the change and to improve the instability of the film thickness obtained by the melt casting method.

  In addition, in this invention, an optical film is a functional film used for various display apparatuses, such as a liquid crystal display, a plasma display, and an organic EL display, and especially a polarizing plate protective film, retardation film, antireflection film, brightness | luminance Includes enhancement films, optical compensation films for viewing angle expansion, etc. In particular, it is to provide a polarizing plate using the optical film of the present invention as a polarizing plate protective film and a liquid crystal display device equipped with the polarizing plate.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
Viscosity change at 250 ° C. is Ri range der of 0.001poise / ℃ ~0.06poise / ℃, 1 ) a weight average molecular weight of weight average molecular weight is smallest cellulose ester A large cellulose ester in the second relative to the B is A cellulose ester mixture raw material containing 60% by mass or more of a mixture having a mass ratio of A to B of 1: 1 or more and less than 1000 times A and at least 1: 1. 2) The weight average molecular weight of the side chain group is 10% or more. Two or more different cellulose ester raw materials and 3) a cellulose ester composition using at least one selected from cellulose ester raw materials having at least one crosslinkable group are melt- formed at 120 ° C. or higher and lower than 250 ° C. An optical film characterized by being manufactured.
(Claim 2)
The optical film according to claim 1, wherein the raw material is a mixture of two or more cellulose esters having different primary structures.
(Claim 3)
The viscosity change at 250 ° C. is in the range of 0.001 poise / ° C. to 0.06 poise / ° C., and 1) the weight average molecular weight of the second largest cellulose ester B based on the cellulose ester A having the smallest weight average molecular weight is A 2 to 1000 times, and at least 60% by mass of a mixture of A and B having a mass ratio of 1: 1, and 2) The weight average molecular weight of the side chain group differs by 10% or more. Melting and forming a cellulose ester composition using at least one selected from two or more cellulose ester raw materials and 3) a cellulose ester raw material having at least one crosslinkable group at 120 ° C. or higher and lower than 250 ° C. A method for producing an optical film.
(Claim 4)
A polarizing plate protective film using the optical film according to claim 1.
(Claim 5)
A retardation film using the optical film according to claim 1.
(Claim 6)
A polarizing plate using the polarizing plate protective film according to claim 4 or the retardation film according to claim 5.
(Claim 7)
A display device using the polarizing plate according to claim 6.

  According to the present invention, in providing an optical film that is optically and physically excellent without using a solvent, and particularly excellent in dimensional stability, a technique for stabilizing a viscosity change at the time of melt extrusion is provided. The instability of the film thickness obtained by the method can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The present invention was made to investigate a method for forming a film without using a solvent in the use of an optical film (hereinafter also referred to as a cellulose ester film). In order to produce a cellulose ester film, it may be formed by melting and casting a cellulose ester adjusted to an optimum composition at an optimum temperature, and if the viscosity change caused by the temperature change during film formation is stabilized. The present invention has been achieved based on the knowledge that the change in film thickness can be reduced. And the cellulose ester film obtained by this method is optically and physically excellent, and in particular, it has been found that the film has excellent optical properties such as film thickness uniformity and retardation. As a result, as a protective film having those characteristics It came to obtain the employ | adopted polarizing plate and a display apparatus.

  The present invention is described in detail below. The optical film of the present invention is a cellulose ester film formed by melt casting.

  The melt casting in the present invention means that the cellulose ester is heated and melted to a temperature showing fluidity without using a solvent, and then the fluid cellulose ester is extruded onto an endless belt or drum to form a film.

  The flowable cellulose ester, which may contain various additives used for casting, contains almost no volatile solvent, while a solvent may be used in part of the process for preparing the molten cellulose ester.

(Cellulose ester)
The cellulose ester raw material cellulose used in the present invention may be wood pulp or cotton linter, and the wood pulp may be softwood or hardwood, but softwood is more preferred. A cotton linter is preferably used from the viewpoint of peelability during film formation. The cellulose ester made from these can be mixed suitably or can be used independently.

  For example, the ratio of cellulose ester derived from cellulose linter: cellulose ester derived from wood pulp (coniferous): cellulose ester derived from wood pulp (hardwood) is 100: 0: 0, 90: 10: 0, 85: 15: 0, 50:50: 0, 20: 80: 0, 10: 90: 0, 0: 100: 0, 0: 0: 100, 80:10:10, 85: 0: 15, 40:30:30.

  The cellulose ester of the present invention is preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. For example, cellulose acetate, cellulose propionate, cellulose butyrate and the like are preferable as the lower fatty acid ester of cellulose. In addition, mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate can be used. The most preferable lower fatty acid ester of cellulose has an acyl group having 2 to 4 carbon atoms as a substituent, and when the substitution degree of acetyl group is X and the substitution degree of propionyl group or butyryl group is Y, the following formula ( It is a cellulose ester containing the cellulose ester which satisfy | fills I) and (II) simultaneously.

Formula (I) 2.6 ≦ X + Y ≦ 3.0
Formula (II) 0 ≦ X ≦ 2.5
Of these, cellulose acetate propionate is particularly preferably used. Among them, 1.9 ≦ X ≦ 2.5 and 0.1 ≦ Y ≦ 0.9 are preferable. The portion that is not substituted with an acyl group is usually present as a hydroxyl group. These can be synthesized by known methods.

  If the characteristic of one structure of the cellulose ester used in the present invention is described, it is preferable to use the lower fatty acid ester of the cellulose, but the known cellulose ester described in JP-A-2000-352620 is used in a single composition. In such a case, a modified cellulose ester in which the object of the present invention cannot be sufficiently achieved and the viscosity change at 250 ° C. is in the range of 0.001 poise / ° C. to 0.06 poise / ° C. is preferable.

  The following method is a method for preparing a modified cellulose ester, which was discovered by chance in the course of the inventors' investigation of additives such as plasticizers in order to achieve the object of the present invention, and therefore achieves the object of the present invention. If possible, a modified cellulose ester having a viscosity change at 250 ° C. in the range of 0.001 poise / ° C. to 0.06 poise / ° C. may be used other than the method described herein, and the method described here particularly limits the invention. It is not a thing.

(Method A) Modified cellulose in which two or more types of cellulose esters having different primary structure characteristics are mixed. (Method B) The weight average molecular weight of the second largest cellulose ester B based on the cellulose ester A having the smallest weight average molecular weight is A. Modified cellulose ester containing 20% by mass or more of a mixture in which the mass ratio of A and B is 1: 1, and the weight average molecular weight of the side chain groups is different by 10% or more. Modified cellulose ester mixed with the above cellulose ester (Method D) Cellulose ester having at least one kind of crosslinkable group The molecular weight distribution of a single composition polymer statistically has one peak. In the present invention, when a modified cellulose ester having a molecular weight distribution not found in a polymer having a single composition was used, a surprising effect was confirmed. Although the relationship between the distribution form and the effect of the present invention is unclear, the above methods A, B, and C describe specific means for achieving them.

  Method D is a method that was found by chance when a modified cellulose ester having a side chain group having a crosslinkable group was used in the study of various methods, and is effective even if only one peak in the molecular weight distribution is present. However, in order to achieve the object of the present invention, the crosslinking density needs to be 0.5% or more, and if it is 1% or more, the effect of the present invention can be confirmed without depending on the type of the side chain group. If the crosslink density exceeds 30%, the effect of the present invention can be confirmed, but the film becomes fragile, which is not preferable. In addition to the effect of the present invention, less than 20% is preferable. Considering the load on the motor accompanying the increase in viscosity at the time of melt extrusion, less than 15% is suitable. However, the present invention does not particularly limit the crosslinking density as long as an optical film can be produced by melt extrusion.

  Melt extrusion is usually preferably performed at a temperature lower than 250 ° C., but the temperature is not particularly limited in the present invention. However, since discoloration becomes a problem when considering the application of the film, it is recommended not to exceed 300 ° C. in the entire process. It is preferable that the temperature in the entire process from the raw material to the film can be controlled to less than 250 ° C.

  In consideration of the load on the motor of the melt extruder, a modified cellulose ester containing at least one stabilizer and having a viscosity at 250 ° C. of less than 2800 poise is suitable for reducing the influence of shearing force on the raw material. More preferably, the viscosity at 250 ° C. is less than 2500 poise, and if the viscosity at 250 ° C. is less than 2000 poise, a good film can be produced. However, if the viscosity is too low, it is difficult to control the film thickness distribution and the object of the present invention cannot be achieved. Therefore, the viscosity at 250 ° C. is preferably 100 poise or more, more preferably 500 poise or more.

  In general polymer materials, the relationship between viscosity and molecular weight is known, and the molecular weight of cellulose ester, which is a raw material used to achieve the object of the present invention, is exemplified by weight average molecular weight Mw / number average molecular weight Mn ratio. Of 1.5 to 5.5 is preferably used, particularly preferably 2.0 to 5.0, more preferably 2.5 to 5.0, and still more preferably 3.0 to 5. Zero cellulose ester is preferably used. However, if the object of the present invention can be achieved even if the molecular weight distribution is outside the exemplified range, this is not excluded, and the range of viscosity is emphasized as a means for achieving the object of the invention rather than the molecular weight.

  The optical film of the present invention may contain a plasticizer, an ultraviolet absorber, a plasticizer, a slipping agent, a matting agent and the like as desired in addition to the cellulose ester.

  Examples of the plasticizer include phosphorous such as triphenyl phosphate, tricresyl phosphate, cresyl phenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixylyl phosphate, tris ortho-biphenyl phosphate. Acid ester plasticizers, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, and other phthalate ester plasticizers, triacetin, tributyrin, butyl phthalyl butyl glycolate, Ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycol Glycolic acid ester based plasticizers such as over bets, and the like. Of these, phthalate ester and glycolate ester plasticizers are preferred because they hardly cause hydrolysis of cellulose esters. Further, it is preferable that a plasticizer having a freezing point of 20 ° C. or lower is included. Examples of such plasticizers include tricresyl phosphate, cresyl phenyl phosphate, tributyl phosphate, diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, and ethyl phthalyl ethyl glycolate. It is done.

In particular, among the plasticizers, those having non-volatility are preferably used. The non-volatile plasticizer is a compound having a vapor pressure at 200 ° C. of 1.33 × 10 ³ Pa or less, having a very low vapor pressure and a low volatility. Preferably it is 6.65 * 10 < ² > Pa or less, More preferably, it is 1.33 * 10 < ² > Pa or less. Specific examples include non-volatile phosphate esters described in JP-A-6-501040. For example, arylene bis (diaryl phosphate) esters are preferred.

  From the viewpoint of dimensional stability, the content of the above plasticizer is preferably 0.1 to 30% by mass, particularly preferably 0.5 to 15% by mass with respect to the cellulose ester.

  In addition, the softness | flexibility of a cellulose-ester film is improved, and the workability of a film (it is a slit process or a punching process, and when these processability is bad, a cut surface will become a saw shape and a chip will be generated. When these debris adheres to the film, the liquid crystal display performance is deteriorated). Therefore, it is preferable that the plasticizer has a freezing point of 20 ° C. or less, particularly 14 ° C. or less.

  As the ultraviolet absorber, those which are excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal and have little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties are preferable. For example, “Latest Technology of Polymer Additives”, page 100 (1987) published by CMC Corporation includes benzophenone, benzotriazole, acrylate, salicylate, oxanilide, hindered amine, nickel, and the like. . Preferred are benzophenone and benzotriazole.

  Although the specific example of an ultraviolet absorber is given to the following, 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) -5-chlorobenzotriazole UV-8: 2- (2H-benzotriazol-2-yl) -6 (Linear and side chain dodecyl) -4-methylphenol (TINUVIN 171: 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- Mixture of 4-hydroxy-5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate (TINUVIN109: manufactured by Ciba Specialty Chemicals)
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 the present invention, the ultraviolet absorber is preferably added in an amount of 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and further preferably 1 to 5% by mass.

  Since it is often preferable to use two or more of these in combination, it is preferable to search for an optimal combination as appropriate depending on the production conditions, use conditions, and the like. The usage-amount is 0.01-10 mass% with respect to a cellulose ester, Preferably it is 0.1-5 mass% from the point of coloring. The ultraviolet absorber is preferably one having high heat stability.

  To the cellulose ester in the present invention, fine particles such as a matting agent can be added in order to impart slipperiness. The fine particles include inorganic compound fine particles and organic compound fine particles.

  Inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. More preferred is an inorganic compound containing silicon or zirconium oxide, and silicon dioxide is particularly preferably used.

  As the silicon dioxide fine particles, for example, commercially available products such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  As the fine particles of zirconium oxide, for example, commercially available products such as Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) can be used.

  As the organic compound, for example, polymers such as silicone resin, fluorine resin, and acrylic resin are preferable, and among them, silicone resin is preferably used.

  Among the above silicone resins, those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (above, manufactured by Toshiba Silicones Co., Ltd.) Commercial products having a trade name such as can be used.

  The primary average particle diameter of the fine particles according to the present invention is preferably 20 nm or less, more preferably 16 to 5 nm, and particularly preferably 12 to 5 nm, from the viewpoint of keeping the haze low.

  The primary average particle diameter of the fine particles according to the present invention is measured by observing particles with a transmission electron microscope (magnification of 500,000 to 2,000,000 times), observing 100 particles, and using the average value, the primary average particle size is measured. The diameter.

  These fine particles can be added by kneading by a conventional method. Particularly preferably, the fine particles dispersed in a solvent in advance are mixed with a cellulose ester and / or a plasticizer and / or an ultraviolet absorber, and then the solvent is added. It is preferable that the solid is made to be volatilized and used in the process of producing the cellulose ester melt in that a uniform melt is obtained.

(Melt casting process)
The optical film of the present invention is formed by melt casting.

  The method for producing the optical film of the present invention conforms to the melt film-forming method described in JP-A-2000-352620, but the present invention is not limited thereto.

  As described above, the molding method by melt casting that is heated and melted without using the solvent (for example, methylene chloride, etc.) used in the solution casting method is the melt extrusion molding method, the press molding method, the inflation method, and the injection molding method. And can be classified into blow molding, stretch molding and the like. Among these, in order to obtain a polarizer protective film having excellent mechanical strength and surface accuracy, the melt extrusion method is excellent.

  The winding length of the optical film of the present invention is preferably 500 to 5000 m, and more preferably 1000 to 5000 m. It is also preferable to wind up by providing a knurling with a height of 0 to 25% of the film thickness at both ends of the width.

  In order to stably produce such a very long film, it is important how the molecular weight is not reduced during melt film formation. When the molecular weight is lowered, the film becomes brittle and breakage tends to occur, and it is difficult to obtain a film having the above length. In order to prevent a decrease in molecular weight, not only the above-mentioned stabilizers are added, but also the solvent, impurities, oxygen and moisture mixed before the material purchase or synthesis are removed as much as possible before the melting process. It is important to keep it. Film formation by the melt casting method has a significantly higher temperature at the time of film formation compared to the solution casting method. Therefore, if oxygen, moisture, or chemically active impurities are mixed, the cellulose ester is decomposed. This is because it will be promoted. Even if it is not an impurity / contaminant that promotes the decomposition of cellulose ester, if there are volatile components in the material to be cast, those additives will volatilize during film formation and adhere to the film forming apparatus. This causes fluctuations in the film thickness of the film to be formed and causes various failures, which is not preferable from the viewpoint of ensuring the flatness and transparency of the film for utilizing the function as a film or a polarizer protective film. In particular, when it adheres to the die, it may cause a streak on the film surface and induce flatness deterioration. Therefore, when a film constituent material is formed into a film, it is not preferable that a component that volatilizes at a temperature lower than the melting temperature for film formation is present from the viewpoint of avoiding generation of a volatile component during heating and melting. It is preferable to use a material having a 1% mass reduction temperature Td (1.0) of 250 ° C. or higher as the material added to the optical film of the present invention.

  It is preferable that volatile components such as moisture and impurities are removed before film formation or before melting. A method by drying can be applied to this removal method, and a method such as a heating method, a reduced pressure method, or a heated reduced pressure method can be used. Drying may be performed in air or in an atmosphere in which an inert gas such as nitrogen or argon is selected as the inert gas. These inert gases preferably have a low water or oxygen content. The oxygen concentration is preferably 0.1% or less, and the dew point of the gas is preferably −30 ° C. or less. Most preferably, it does not contain substantially. When these known drying methods are performed, it is preferable in terms of film quality to be performed in a temperature range where the film constituting material does not decompose. For example, the moisture or solvent remaining after removal in the drying step is preferably 1% by mass or less, more preferably 0.5% by mass or less, based on the total mass of the film constituent materials. It is.

  In particular, the moisture content of the cellulose ester resin is preferably less than 0.3% by mass. These characteristic values can be measured by ASTM-D817-96. The cellulose ester is preferably used as 0.1 to 1000 ppm by further reducing the moisture by heat treatment.

  The amount of residual organic solvent can be measured by a headspace gas chromatography method. That is, a known amount of the optical film is heated in a sealed container at 120 ° C. for 20 minutes, and the organic solvent contained in the gas phase in the sealed container is quantified by gas chromatography. From this result, the residual organic solvent amount (%) can be calculated.

  The film constituent material can reduce the generation of volatile components by drying before film formation, and the resin alone or at least one mixture or compatible material other than the resin among the resin and the film constituent material. It can be divided and dried. The preferable drying temperature is preferably 80 ° C. or higher and the Tg or melting point of the material to be dried. Including the viewpoint of avoiding fusion between materials, the drying temperature is more preferably 100 to (Tg-5) ° C, and still more preferably 110 to (Tg-20) ° C. A preferable drying time is 0.5 to 24 hours, more preferably 1 to 18 hours, and further preferably 1.5 to 12 hours. Below these ranges, the removal rate of volatile components may be low, or drying may take too long, and when Tg is present in the material to be dried, heating to a drying temperature higher than Tg will cause the material to be removed. May be difficult to handle due to fusion. Drying is preferably performed at 1 atm or less, and particularly preferably performed while reducing the pressure from vacuum to 1/2 atm. Drying is preferably performed while appropriately stirring the material such as resin, and the fluidized bed system in which drying air or dry nitrogen is fed from the lower part in the drying container can perform necessary drying in a shorter time. This is preferable because it is possible.

  The drying process may be separated into two or more stages. For example, the material may be formed using a material that has been subjected to storage of the material in the preliminary drying process and drying immediately before film formation to immediately before a week. .

  After removing volatile components such as moisture and impurities in the film-forming material by the drying process, the film-forming material is individually or pre-mixed / pelleted and sent to a heated barrel to melt and flow After being formed, it is extruded into a sheet shape by a T-die, and brought into close contact with a cooling drum or an endless belt by an electrostatic application method or the like, and cooled and solidified to be solidified into a sheet shape to obtain an unstretched sheet. These processes are called casting processes.

  In view of the physical properties of the obtained cellulose ester film, the melting temperature (temperature in the barrel) is preferably in the range of 120 to 250 ° C, more preferably 180 to 250 ° C, and particularly preferably 220 ° C to 250 ° C. . The temperature of the cooling drum is preferably maintained at 90 to 150 ° C. If the temperature of the drum is 90 ° C. or lower, the sheet extruded from the die is rapidly cooled, and the structure in the film may become uneven or brittle in the film thickness direction. It is preferable. On the other hand, when the temperature is 150 ° C. or higher, the cooling rate of the unstretched sheet becomes slow and the productivity is lowered, which is not preferable.

  When the optical film of the present invention is used as a protective film for polarizing plates, the thickness of the protective film is preferably 10 to 500 μm. 10-100 micrometers is especially preferable, 20-80 micrometers is preferable, Especially preferably, it is 30-60 micrometers. If the optical film is thicker than the above region, for example, when used as a polarizer protective film, the polarizing plate after polarizing plate processing becomes too thick, especially in liquid crystal displays used for notebook computers and mobile electronic devices It is not suitable for the purpose. On the other hand, if the thickness is smaller than the above region, the film has high moisture permeability, and the ability to protect the polarizer from humidity decreases, which is not preferable. Moreover, in the retardation film, since it becomes difficult to express retardation, it is not preferable.

  In the solution casting method, when the film thickness is increased, the drying load is remarkably increased. However, in the present invention, since a drying step is not required, a thick film can be produced with high productivity. Therefore, there is an advantage that it is easier than ever to increase the thickness of the film in accordance with the purpose of providing a necessary phase difference or reducing moisture permeability. Further, even when a thin film is obtained, it has an effect that it can be produced with high productivity by stretching such a thick film. In addition, the film thickness of the film at the time of extending | stretching becomes thin in inverse proportion to the draw ratio. For example, when the unstretched sheet is 200 μm, a 100 μm film can be obtained by stretching twice.

  The film thickness variation of the optical film support is preferably ± 3%, more preferably ± 1%, and still more preferably ± 0.1%. These film thickness fluctuations can be reduced by stretching.

  In view of the recent increase in the size of liquid crystal displays, the width of the polarizer protective film is preferably 1 m or more. On the other hand, if it exceeds 4 m, the apparatus becomes large and difficult to convey, so the width of the optical film of the present invention is preferably 1 to 4 m, particularly preferably 1.4 to 2 m. Since it is difficult to uniformly extrude the cellulose ester flowing from the barrel from the die to a width of 1.4 m or more, it is difficult to obtain a film having a width of 1.4 m or more unless it is laterally stretched. is there.

(Stretching process)
Next, the stretching process will be described.

  Since the optical film using the cellulose ester of the present invention is produced with an optimum melt viscosity, a film having high flatness can be obtained without performing post-treatment such as stretching.

  However, in order to further improve the flatness and the productivity, the film discharged from the die and cooled and solidified is disclosed in lateral stretching, longitudinal stretching, or Japanese Patent Application Laid-Open No. 2004-226465. It is preferable to perform stretching in an oblique direction. By performing the stretching operation, the birefringence value can be controlled, the flatness can be improved, and the production rate can be improved. These stretching operations may be performed a plurality of times, and when performing the stretching a plurality of times, they may be performed simultaneously or sequentially. When stretching is performed a plurality of times, the product of all the stretching ratios becomes the final stretching ratio. For example, if 2 times of stretching is performed twice, the final stretching ratio is 4 times.

  The cellulose ester of the present invention can be processed into a film with higher planarity by stretching, because not only a melt-formed film with high planarity can be obtained even when unstretched, but also high magnification stretching is possible. The mechanical properties of the film can be improved and productivity can be increased. Therefore, a high-quality optical film can be manufactured with high productivity.

  The cellulose ester has a refractive index that increases in the stretched direction, and forms a slow axis. Therefore, the stretching operation is performed within the range of the optical properties that the finally obtained film should satisfy.

  When it is desired to reduce the retardation value in the film plane (hereinafter sometimes referred to as Ro) as much as possible, biaxial stretching is preferred. By stretching at the same magnification in the direction perpendicular to the first stretching axis, the occurrence of birefringence due to the first stretching is canceled, and an optically isotropic film can be obtained.

  On the other hand, when obtaining a retardation film that has the effect of expanding the viewing angle of the liquid crystal display, the ratio of the first stretching and the second stretching is changed, and one of the stretching ratios is the other stretching An optically anisotropic film can be obtained by stretching so as to be larger than the magnification. In this case, the draw ratio between the width direction and the longitudinal direction is preferably 1.1 to 2.0, more preferably 1.2 to 1.5.

  When stretching a plurality of times, the film may be stretched from the longitudinal direction or from the width direction, but after the stretching process in the width direction, the transport width of the film becomes large, and the transport device Therefore, it is preferable to perform stretching in the width direction after stretching in the longitudinal direction.

  The final draw ratio of the optical film is preferably 1.5 to 4.0 times. If it is less than 1.5 times, the flatness of the resulting film may not be sufficient. On the other hand, stretching more than 4.0 times is difficult even if the cellulose ester of the present invention is used, and it is not preferable because there is a high possibility that fracture occurs in the stretching process. More preferably, it is stretched 1.5 to 3.0 times. In the present invention, the final draw ratio means the product of the draw ratios in the longitudinal direction and the width direction.

  First, the stretching method in the longitudinal direction (MD) will be described.

  After being extruded from the barrel and brought into close contact with the cooling drum, the film peeled off from the cooling drum is heated again in the longitudinal direction through one or more roll groups and / or a heating device such as an infrared heater. Single-stage or multistage MD stretching may be performed.

  When stretching, assuming that the glass transition temperature of the film of the present invention is Tg, it is heated in the range of (Tg-30) to (Tg + 100) ° C., more preferably (Tg-20) to (Tg + 80) ° C. It is preferable to stretch in the (longitudinal direction; MD) or width direction (TD). It is preferable to perform transverse stretching within the temperature range of (Tg-20) to (Tg + 20) ° C. and then heat-set. It is also preferable to perform relaxation treatment after the stretching step.

  The Tg of the optical film can be controlled by the material type constituting the film and the ratio of the constituting materials. In the application of the present invention, the Tg when the film is dried is preferably 110 ° C. or higher, more preferably 120 ° C. or higher. This is because when the optical film of the present invention is used for a liquid crystal display device, if the Tg of the film is lower than the above, the temperature and humidity of the use environment and the influence of the heat of the backlight cause the molecules fixed inside the film. The orientation state is affected, and there is a high possibility that the retardation value and the dimensional stability and shape as a film are greatly changed. In addition, the shape of the film may not be maintained. Conversely, if the Tg of the film is too high, it becomes difficult to produce because it approaches the decomposition temperature of the film constituting material, and the presence of a volatile component or coloring may occur due to the decomposition of the material itself used when forming a film. Accordingly, the glass transition temperature is preferably 180 ° C. or lower, more preferably 150 ° C. or lower. At this time, the Tg of the film can be determined by the method described in JIS K7121.

  Next, the extending | stretching method of a lateral direction (TD) is demonstrated.

  In the case of TD stretching, it is preferable to perform transverse stretching while sequentially raising the temperature difference in the range of 1 to 50 ° C. in a stretching region divided into two or more, because the distribution of physical properties in the width direction can be reduced. Further, after transverse stretching, it is preferable that the film is held at a temperature not higher than the final TD stretching temperature and not lower than Tg−40 ° C. for 0.01 to 5 minutes because the distribution of physical properties in the width direction can be further reduced.

  The heat setting is performed at a temperature higher than the final TD stretching temperature and usually within 0.5 to 300 seconds within a temperature range of Tg-20 ° C. or less. Under the present circumstances, it is preferable to heat-fix, heating up sequentially in the range from which a temperature difference is set to 1-100 degreeC in the area | region divided into 2 or more.

  The heat-set film is usually cooled to Tg or less, and clip holding portions at both ends of the film are cut and wound. At this time, it is preferable to perform a relaxation treatment of 0.1 to 10% in the lateral direction and / or the longitudinal direction within a temperature range of not more than the final heat setting temperature and not less than Tg. In addition, it is preferable that the cooling is gradually performed from the final heat setting temperature to Tg at a cooling rate of 100 ° C. or less per second. Means for cooling and relaxation treatment are not particularly limited, and can be performed by a conventionally known means. In particular, it is preferable to carry out these treatments while sequentially cooling in a plurality of temperature ranges from the viewpoint of improving the dimensional stability of the film. The cooling rate is a value obtained by (T1-Tg) / t, where T1 is the final heat setting temperature and t is the time until the film reaches Tg from the final heat setting temperature.

  More optimal conditions of these heat setting conditions, cooling, and relaxation treatment conditions vary depending on the type of additives such as cellulose ester and plasticizer constituting the film, so the physical properties of the obtained biaxially stretched film are measured and preferable characteristics are obtained. What is necessary is just to determine by adjusting suitably so that it may have.

  The in-plane retardation value (Ro) and the retardation value (Rth) in the thickness direction of the optical film according to the present invention are preferably 0 ≦ Ro and Rth ≦ 70 nm when used as a polarizer protective film. More preferably, 0 ≦ Ro ≦ 20 nm and 0 ≦ Rth ≦ 50 nm, and more preferably 0 ≦ Ro ≦ 10 nm and 0 ≦ Rth ≦ 30 nm. When used as a retardation film for a VA mode liquid crystal panel (when two films are used on both sides of the liquid crystal panel), 30 ≦ Ro ≦ 100 nm and 70 ≦ Rth ≦ 400 nm, more preferably 35 ≦ Ro ≦ 65 nm. And 90 ≦ Rth ≦ 180 nm. In the case where the phase difference is earned only with the film on one side of the liquid crystal panel, it is preferable that the phase difference is double this.

  Further, the variation of Rth and the width of distribution are preferably less than ± 10%, more preferably less than ± 5%. More preferably, it is less than ± 1%, and most preferably, there is no fluctuation of Rth.

  The retardation values Ro and Rth can be obtained by the following equations.

Ro = (nx−ny) × d
Rth = ((nx + ny) / 2−nz) × d
Here, d is the thickness (nm) of the film, the refractive index nx (also referred to as the maximum refractive index in the plane of the film, the refractive index in the slow axis direction), ny (in the direction perpendicular to the slow axis in the film plane). ) (Refractive index of the film in the thickness direction).

  The retardation values (Ro) and (Rth) can be measured using an automatic birefringence meter. For example, it can be obtained at a wavelength of 590 nm using KOBRA-21ADH (Oji Scientific Instruments) under an environment of 23 ° C. and 55% RH.

  The slow axis is preferably in the width direction ± 1 ° or the longitudinal direction ± 1 ° of the film. More preferably, it is ± 0.7 ° with respect to the width direction or the longitudinal direction, and further preferably ± 0.5 ° with respect to the width direction or the longitudinal direction. By setting it as such a range, the contrast of the liquid crystal display obtained can be raised.

  Since the optical film of the present invention does not substantially use a solvent in the film forming process, the amount of residual organic solvent contained in the optical film wound up after film formation is stably less than 0.1% by mass. Thus, it is possible to provide an optical film having more stable flatness and Rth than before. In particular, it is possible to provide an optical film having stable flatness and Rth even in a long roll of 100 m or more. The optical film is not particularly limited with respect to the winding length, and is preferably used even if it is 1500 m, 2500 m, or 5000 m.

  It is difficult to reduce the residual organic solvent amount (%) of the cellulose ester film produced by the solution casting method to 0.1% by mass or less, and this requires a long drying step. For example, a cellulose ester film having a very low residual organic solvent content can be obtained at low cost, and a cellulose ester film having excellent characteristics as an optical film can be obtained.

  In the film forming process, the clip gripping portions at both ends of the cut film are pulverized or granulated as necessary, and then used as a raw material for the same type of film or for different types of film. It may be reused as a raw material.

(Functional layer)
In producing the optical film of the present invention, before and / or after stretching, the antistatic layer, the transparent conductive layer, the hard coat layer, the antireflection layer, the antifouling layer, the slippery layer, the easy adhesion layer, the easy saponification layer, and the smoothness. A functional layer such as a lightening layer, an antiglare layer, a gas barrier layer, or an optical compensation layer may be provided. In particular, it is preferable to provide at least one layer selected from an antistatic layer, a hard coat layer, an antireflection layer, an easy adhesion layer, an antiglare layer, and an optical compensation layer. At this time, various surface treatments such as corona discharge treatment, plasma treatment, and chemical treatment can be performed as necessary. The chemical treatment includes not only chemically active chemicals, but also operations such as simply applying an organic solvent to dissolve or swell the surface of the cellulose ester film to improve planarity.

  Further, in the optical film according to the present invention, the types of cellulose ester and / or additives may be coextruded layers having different contents to form an optical film having a laminated structure.

  For example, a cellulose ester film having a structure of skin layer / core layer / skin layer can be produced. For example, fine particles such as a matting agent can be contained in the skin layer in a large amount or only in the skin layer. In addition, a melt-extruded layer of diacetyl cellulose that can be easily saponified may be formed on the skin layer. Melt extrusion of diacetylcellulose can be achieved according to known methods. Further, a low-volatile plasticizer and / or an ultraviolet absorber may be included in the skin layer, and a plasticizer having excellent plasticity or an ultraviolet absorber having excellent ultraviolet absorbability may be added to the core layer. The glass transition temperature of the skin layer and the core layer may be different, and the glass transition temperature of the core layer may be lower than the glass transition temperature of the skin layer. Also, the viscosity of the melt containing the cellulose ester at the time of melt casting may be different between the skin layer and the core layer, and the viscosity of the skin layer> the viscosity of the core layer or the viscosity of the core layer ≧ the viscosity of the skin layer may be When the viscosity of the thinner layer (usually the skin layer) is higher, a laminate having a uniform film thickness can be obtained.

(Polarizer)
The polarizing plate of the present invention and the liquid crystal display device of the present invention using the polarizing plate will be described.

  The polarizing plate can be produced by a general method. The back side of the optical film of the present invention is subjected to alkali saponification treatment, and the treated optical film is bonded to at least one surface of a polarizer produced by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. It is preferable. The optical film of the present invention may be used on the other surface, or another polarizing plate protective film may be used. With respect to the optical film of the present invention, a commercially available cellulose ester film (polarizing plate protective film, retardation film) can be used as the polarizing plate protective film used on the other surface. For example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto Co., Ltd.) are preferable. Used. Alternatively, it is also preferable to use a polarizing plate protective film that also serves as an optical compensation film having an optical anisotropic layer formed by aligning liquid crystal compounds such as discotic liquid crystal, rod-shaped liquid crystal, and cholesteric liquid crystal. For example, the optically anisotropic layer can be formed by the method described in JP-A-2003-98348. By using in combination with the optical film of the present invention, a polarizing plate having excellent flatness and a stable viewing angle expansion effect can be obtained. Or you may use films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate, as a polarizing plate protective film of the other surface. In this case, since the suitability for saponification is low, it is preferable to perform adhesion processing to the polarizing plate through an appropriate adhesive layer.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed. As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxially stretching or dyed, or uniaxially stretched after dyeing, and then preferably subjected to a durability treatment with a boron compound. The thickness of the polarizing film is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. On the surface of the polarizing film, one side of the optical film of the present invention is bonded to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Further, in the case of a resin film other than a cellulose ester film having low saponification suitability, it can be bonded to the polarizing plate through an appropriate adhesive layer.

  Since the polarizer is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction perpendicular to the stretching (usually the width direction) ) Will grow. As the thickness of the polarizing plate protective film becomes thinner, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizing film increases. Normally, the stretching direction of the polarizing film is bonded to the casting direction (MD direction) of the polarizing plate protective film. Therefore, when thinning the polarizing plate protective film, it is particularly important to suppress the stretch rate in the casting direction. It is. Since the optical film of the present invention is excellent in dimensional stability, it is suitably used as such a polarizing plate protective film.

  The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the other surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. Moreover, a separate film is used in order to cover the contact bonding layer bonded to a liquid crystal board, and is used for the surface side which bonds a polarizing plate to a liquid crystal cell.

(Liquid crystal display device)
In a liquid crystal display device, a substrate containing liquid crystal is usually disposed between two polarizing plates. A polarizing plate protective film and a retardation film to which the optical film of the present invention is applied have high flatness and retardation uniformity. Therefore, excellent display properties can be obtained regardless of the location. A polarizing plate protective film provided with a clear hard coat layer, an antiglare layer, an antireflection layer, or the like is preferably used for this portion of the polarizing plate protective film on the outermost display side of the liquid crystal display device. In addition, in the case of a retardation film provided with an optical compensation layer, or a retardation film provided with an appropriate optical compensation capability by itself such as stretching operation, excellent display properties can be obtained by placing it at a site in contact with the liquid crystal cell. Is obtained. In particular, the use of the present invention for a multi-domain type liquid crystal display device, more preferably a multi-domain type liquid crystal display device with a birefringence mode, can further exhibit the effects of the present invention.

  Multi-domain is a method of dividing a liquid crystal cell that constitutes one pixel into a plurality of parts, and is also suitable for improving viewing angle dependency and improving symmetry of image display. Various methods have been reported. “Okita, Yamauchi: Liquid Crystal, 6 (3), 303 (2002)”. The liquid crystal display cell is also shown in “Yamada, Yamabara: Liquid Crystal, 7 (2), 184 (2003)”, but is not limited thereto.

  The display quality of the display cell is preferably symmetrical with respect to human observation. Therefore, when the display cell is a liquid crystal display cell, the domains can be multiplied substantially giving priority to the symmetry on the observation side. A known method can be used to divide the domain, and can be determined by taking into account the properties of the known liquid crystal mode by a two-division method, more preferably a four-division method.

  The polarizing plate of the present invention includes an MVA (Multi-domain Vertical Alignment) mode represented by a vertical alignment mode, in particular, an MVA mode divided into four, a known PVA (Patterned Vertical Alignment) mode and an electrode multi-domained by electrode arrangement. It can be effectively used in a CPA (Continuous Pinwheel Alignment) mode in which arrangement and chiral ability are fused. In addition, a proposal of an optically biaxial film in the adaptation to the OCB (Optical Compensated Bend) mode has been disclosed, and “T. Miyashita, T. Uchida: J. SID, 3 (1), 29 ( 1995) ", the polarizing plate of the present invention can also exhibit the effect of the present invention in display quality. If the effect of this invention can be expressed by using the polarizing plate of this invention, arrangement | positioning of a liquid crystal mode and a polarizing plate will not be limited.

  Since the liquid crystal display device has high performance as a device for colorization and moving image display, the display quality of the liquid crystal display device using the optical film of the present invention, particularly a large-sized liquid crystal display device is less fatigued and faithful. Display is possible.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this. In addition, the following "part" represents a "mass part".

(Method for preparing modified cellulose)
The modified cellulose ester used in the present invention may be a combination of commercially available products, or a new cellulose esterified by a known method, or a polysaccharide or a special cellulose derived from a polysaccharide. Any one may be used. The following specific examples do not limit the present invention.

(Manufacture of optical film (cellulose ester film))
<Example 1>
(1) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, hydroxyethyl cellulose having a weight average molecular weight of about 800,000 and a hydroxyethyl group substitution degree of 1.8 (HEC-QP4400, manufactured by Union Carbide) 50 g, 88 g of 88% isopropyl alcohol and 3.5 g of 48% aqueous sodium hydroxide were added to prepare a slurry, which was stirred at room temperature for 30 minutes in a nitrogen atmosphere. To this was added 5.4 g of stearyl glycidyl ether, and the mixture was reacted at 80 ° C. for 8 hours for hydrophobicity. After completion of the hydrophobic reaction, the reaction solution was neutralized with acetic acid, and the reaction product was filtered off. The reaction product was washed twice with 500 g of 80% acetone and then twice with 500 g of acetone, and dried under reduced pressure at 70 ° C. for one day to obtain 49.4 g of a hydrophobized hydroxyethyl cellulose derivative A.

  (2) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, hydroxyethyl cellulose having a weight average molecular weight of about 800,000 and a hydroxyethyl group substitution degree of 1.8 (HEC-QP4400, manufactured by Union Carbide) 50 g, 88 g of 88% isopropyl alcohol and 3.5 g of 48% aqueous sodium hydroxide were added to prepare a slurry, which was stirred at room temperature for 30 minutes in a nitrogen atmosphere. To this, 8.5 g of palmityl glycidyl ether was added and reacted at 80 ° C. for 9 hours for hydrophobicity. After completion of the hydrophobic reaction, the reaction solution was neutralized with acetic acid, and the reaction product was filtered off. The reaction product was washed twice with 500 g of 80% acetone and then twice with 500 g of acetone and dried under reduced pressure at 70 ° C. for one day to obtain 50.3 g of a hydrophobized hydroxyethyl cellulose derivative B.

  (3) 1 kg of a 1: 1 mixture of hydroxyethylcellulose derivative A and hydroxyethylcellulose derivative B and 2 kg of cellulose acetate (CA-398-3 manufactured by Eastman Chemical Co., Ltd.) are mixed in the form of a powder using a V-type powder mixer, and modified cellulose ester C.

  Using this modified cellulose ester C, an 80 μm film was produced by the following melt film-forming method to obtain cellulose ester film 1.

<Melting method>
90 parts by weight of the above modified cellulose ester C, 10 parts by weight of Aldrich pentaerythritol tetrabenzoate as a plasticizer, 1.0 part by weight of Tinuvin 360 from Ciba Specialty Chemicals as an ultraviolet absorber, and epoxidized tar as a heat stabilizer Oil 0.6% by mass, para-tert-butylphenol 0.4% by mass, neopentylphenyl phosphite 0.07% by mass, strontium naphthoate 0.02% by mass and silicon dioxide fine particles (Aerosil R972V) 0.05% by mass Were mixed in powder form and fed to a twin screw extruder. The screw rotation speed was 100 rpm, the temperature in the barrel (melting temperature) was set to 230 ° C., the material was melted, and the fluidized cellulose ester composition was cast on a cooling drum maintained at 130 ° C. The cellulose ester film 1 having a film thickness of 80 μm was prepared by stretching 25% in the flow direction (MD) and 25% in the width direction (TD) (final draw ratio was 1.56 times).

  The obtained cellulose ester film 1 was cut into a disk shape having a diameter of 1 cm, and the temperature dispersion of dynamic viscoelasticity up to 270 ° C. was performed using the ARES viscoelasticity measurement system of Rheometric Scientific F.E. It was measured. The viscosity at 250 ° C. obtained from this evaluation was 2020 poise, and the viscosity change at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.05 poise / ° C. Moreover, it was 0.7% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

  The film thickness deviation is a value (%) obtained by dividing the difference between the maximum value and the minimum value of the film thickness by the average value of the film thickness and multiplying by 100.

<Example 2>
(1) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, methyl cellulose having a weight average molecular weight of about 400,000 and a methyl group substitution degree of 1.8 (Metroses SM-800, manufactured by Shin-Etsu Chemical Co., Ltd.) 50 g, 400 g of isopropyl alcohol and 4.5 g of 48% aqueous sodium hydroxide solution were added, and the mixture was stirred at room temperature for 30 minutes under a nitrogen atmosphere. To this, 6.0 g of stearyl glycidyl ether was added and reacted at 80 ° C. for 8 hours for hydrophobicity. After completion of the hydrophobic reaction, the reaction solution was neutralized with acetic acid, and the reaction product was filtered off. The reaction product was washed twice with 500 g of 80% acetone and then twice with 500 g of acetone, and dried under reduced pressure at 70 ° C. for one day to obtain 48.5 g of hydrophobized methylcellulose D.

  (2) 1 kg of a 1: 1 mixture of this methyl cellulose D and the hydroxyethyl cellulose derivative A obtained in Example 1 and 2 kg of cellulose acetate (CA-398-3 manufactured by Eastman Chemical Co.) are used in a V-type powder mixer. This was mixed to obtain modified cellulose ester E.

  Using this modified cellulose ester E, a cellulose ester film 2 was produced in the same manner as in Example 1.

  Subsequently, the temperature dispersion up to 270 ° C. of the dynamic viscoelasticity of the cellulose ester film 2 was measured in the same manner as in Example 1. The viscosity at 250 ° C. obtained from this evaluation was 1800 poise, and the viscosity change at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.03 poise / ° C. Moreover, it was 0.5% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

<Example 3>
(1) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, hydroxyethyl cellulose (HEC-QP100M, Union Carbide Corporation) having a weight average molecular weight of about 1,500,000 and a hydroxyethyl group substitution degree of 1.8 50 g, 88 g isopropyl alcohol 400 g and 48% sodium hydroxide aqueous solution 3 g were added to prepare a slurry, and the mixture was stirred at room temperature for 30 minutes in a nitrogen atmosphere. To this, 1.5 g of octadecyl glycidyl ether was added and reacted at 80 ° C. for 7 hours for hydrophobization. After completion of the hydrophobization reaction, the reaction solution was neutralized with hydrochloric acid, and the reaction product was filtered. This reaction product was washed twice with 500 g of 80% acetone, then twice with 500 g of acetone, and dried under reduced pressure at 70 ° C. for one day to obtain 44.3 g of a hydrophobized hydroxyethyl cellulose derivative F.

  (2) 1 kg of a 1: 1 mixture of the hydroxyethylcellulose derivative F and the hydroxyethylcellulose derivative A obtained in Example 1 and 2 kg of cellulose acetate (CA-398-3 manufactured by Eastman Chemical Co.) are mixed in a V-type powder as powder. The modified cellulose ester G was obtained by mixing with a machine.

  Using this modified cellulose ester G, a cellulose ester film 3 was produced in the same manner as in Example 1.

  In the same manner as in Example 1, the temperature dispersion up to 270 ° C. of the dynamic viscoelasticity of the cellulose ester film 3 was measured. The viscosity at 250 ° C. obtained from this evaluation was 1950 poise, and the viscosity change at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.05 poise / ° C. Moreover, it was 0.2% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

<Example 4>
(1) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, hydroxyethyl cellulose (HEC-QP100M, Union Carbide Co., Ltd.) having a weight average molecular weight of about 1,500,000 and a hydroxyethyl group substitution degree of 1.8 50 g, 88 g isopropyl alcohol 400 g and 48% sodium hydroxide aqueous solution 3 g were added to prepare a slurry, and the mixture was stirred at room temperature for 30 minutes in a nitrogen atmosphere. To this, 1.0 g of octadecyl glycidyl ether was added and reacted at 80 ° C. for 7 hours for hydrophobization. After completion of the hydrophobization reaction, the reaction solution was neutralized with hydrochloric acid, and the reaction product was filtered. This reaction product was washed twice with 500 g of 80% acetone and then twice with 500 g of acetone and dried under reduced pressure at 70 ° C. for one day to obtain 45.1 g of a hydrophobized hydroxyethylcellulose derivative H.

  (2) 0.5 kg of a 1: 1 mixture of this hydroxyethylcellulose derivative H and the hydroxyethylcellulose derivative A obtained in Example 1 and 2.5 kg of cellulose acetate (CA-398-3 manufactured by Eastman Chemical Co.) remain in powder form A modified cellulose ester I was obtained by mixing with a V-type powder mixer.

  Using this modified cellulose ester I, a cellulose ester film 4 was produced in the same manner as in Example 1.

  In the same manner as in Example 1, the temperature dispersion up to 270 ° C. of the dynamic viscoelasticity of the cellulose ester film 4 was measured. The viscosity at 250 ° C. obtained from this evaluation was 2000 poise, and the viscosity change at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.04 poise / ° C. Moreover, it was 0.3% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

<Example 5>
(1) In a 1000 ml glass separable reaction vessel equipped with a stirrer, a thermometer and a cooling tube, a hydroxyethyl cellulose having a weight average molecular weight of about 1.5 million and a hydroxyethyl group substitution degree of 1.8 (HEC-QP100M, manufactured by Union Carbide Corporation) 50 g, 88 g of 88% isopropyl alcohol and 3.5 g of 48% aqueous sodium hydroxide were added to prepare a slurry, which was stirred at room temperature for 30 minutes in a nitrogen atmosphere. To this, 2.2 g of 1,2-epoxyoctadecane was added and reacted at 80 ° C. for 8 hours for hydrophobization. After completion of the hydrophobic reaction, the reaction solution was neutralized with acetic acid, and the reaction product was filtered off. The reaction product was washed twice with 500 g of 80% acetone and then twice with 500 g of acetone, and dried under reduced pressure at 70 ° C. for one day to obtain 49.4 g of a hydrophobized hydroxyethyl cellulose derivative J.

  (2) 0.5 kg of a 1: 1 mixture of the hydroxyethylcellulose derivative J and the derivative D obtained in Example 2 and 2.5 kg of cellulose acetate (Eastman Chemical Co., CA-398-3) are used in the form of powder V The mixture was mixed with a powder mixer to obtain modified cellulose ester K.

  Using this modified cellulose ester K, a cellulose ester film 5 was produced in the same manner as in Example 1.

  In the same manner as in Example 1, the temperature dispersion up to 270 ° C. of the dynamic viscoelasticity of the cellulose ester film 5 was measured. The viscosity at 250 ° C. obtained from this evaluation was 2100 poise, and the change in viscosity at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.03 poise / ° C. Moreover, it was 0.05% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

<Comparative example 1>
Cellulose acetate (CAP-482-0.5) was dissolved using methylene chloride, a solution casting film forming method using a solvent was employed to produce a film having a thickness of 80 μm, and a cellulose ester film was obtained. The cellulose ester film used ethylphthalyl ethyl glycolate as a plasticizer.

  Similar to Example 1, the temperature dispersion of dynamic viscoelasticity up to 270 ° C. was measured. The viscosity at 250 ° C. obtained from this evaluation was 1900 poise, and the viscosity change at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.10 poise / ° C. Moreover, it was 5.3% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

<Comparative example 2>
A 80 μm film was produced under the same conditions as in Example 1 using cellulose acetate (CA-398-3 manufactured by Eastman Chemical Co., Ltd.) to obtain a cellulose ester film.

  Similar to Example 1, the temperature dispersion of dynamic viscoelasticity up to 270 ° C. was measured. The viscosity at 250 ° C. obtained from this evaluation was 3000 poise, and the change in viscosity at 250 ° C. obtained from the slope of the derivative of the curve drawn by temperature dispersion was 0.09 poise / ° C. Moreover, it was 6.2% when the film thickness deviation in arbitrary 10 points | pieces of 20 cm square was measured.

  From the above, it can be seen that the instability of the film thickness is significantly improved in the cellulose ester films of Examples 1 to 5, which are optical films according to the present invention.

  Furthermore, the following dimensional stability was evaluated using the produced cellulose ester film.

(Dimensional stability)
Dimensional stability is expressed in terms of heat shrinkage. Three test pieces each having a width of 30 mm and a length of 120 mm are collected from the longitudinal direction and the lateral direction of the produced cellulose ester film sample. Holes of 6 mmφ are punched at 100 mm intervals on both ends of the test piece. This is conditioned for at least 3 hours in a room at 23 ± 3 ° C. and a relative temperature of 65 ± 5%. Using an automatic pin gauge (manufactured by Shinto Kagaku Co., Ltd.), the original dimension (L1) of the punch interval is measured to the minimum scale / 1000 mm. Next, the test piece was suspended in an incubator at 80 ° C. ± 1 ° C. and heat-treated for 3 hours, adjusted to a humidity of 23 ± 3 ° C. and a relative humidity of 65 ± 5% for 3 hours or more, and then subjected to heat treatment with an automatic pin gauge. The punch spacing dimension (L2) is measured. And the thermal contraction rate is calculated by the following formula.

Thermal contraction rate = (L1-L2 / L1) × 100
Evaluation is less than 0.02% for heat shrinkage, ◯ for less than 0.02 to 0.05%, △ for less than 0.05 to 0.08, x for less than 0.08 to 0.11%, 0.11% or more was defined as xx.

  As a result, the cellulose ester films of Examples 1 to 5 were evaluated as ◎, but Comparative Examples 1 and 2 were evaluated as × to Δ, and the cellulose ester films of the examples were excellent in dimensional stability. I understood.

(Preparation of polarizing plate)
A polyvinyl alcohol film having a thickness of 50 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a polarizer.

  Subsequently, according to the following processes 1-5, the polarizing plate was produced using the polarizer and the cellulose ester films of Examples 1-5 and Comparative Examples 1 and 2 produced above. On the opposite side of the polarizer, when the cellulose ester film of Example 1 was produced, the film was stretched 25% in the flow direction (MD) and 50% in the width direction (TD) (the final stretch ratio was 1). Each of the retardation films produced in the same manner as in Example 1 was used except that (.88 times) was performed. The retardation value of this retardation film was Ro = 45 nm and Rt = 136 nm.

  Step 1: The optical film was immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to saponify the side to be bonded to the polarizer.

  Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped, and this was placed on each cellulose ester film treated in Step 1 and laminated.

  Step 4: The cellulose ester film and the polarizer laminated in Step 3 were bonded at a pressure of 20 to 30 N / cm 2 and a conveyance speed of about 2 m / min.

  Step 5: A sample in which the cellulose ester film prepared in Step 4 and the polarizer were bonded together in a dryer at 80 ° C. was dried for 2 minutes to prepare a polarizing plate.

(Production of liquid crystal display device)
The polarizing plate of a commercially available 30-inch color liquid crystal television, which is a VA type liquid crystal display device, was peeled off, and each polarizing plate produced above was cut according to the size of the liquid crystal cell. Two polarizing plates were attached so as to sandwich the liquid crystal cell so that the polarizing axes of the polarizing plates were not perpendicular to each other so as to be orthogonal to each other, a 30-inch color liquid crystal television was produced, and the properties as a polarizing plate were evaluated. However, the polarizing plates according to the present invention using the cellulose ester films of Examples 1 to 5 had high contrast and exhibited excellent display properties. Thereby, it was confirmed that it was useful as a polarizing plate for image display apparatuses, such as a liquid crystal display, and can provide the visibility which was excellent as a liquid crystal display apparatus.

Claims (7)

Viscosity change at 250 ° C. is Ri range der of 0.001poise / ℃ ~0.06poise / ℃, 1 ) a weight average molecular weight of weight average molecular weight is smallest cellulose ester A large cellulose ester in the second relative to the B is A cellulose ester mixture raw material containing 60% by mass or more of a mixture in which the mass ratio of A to B is 1: 1 or more and less than 1000 times A and 2) The weight average molecular weight of the side chain group is 10% or more Two or more different cellulose ester raw materials and 3) a cellulose ester composition using at least one selected from cellulose ester raw materials having at least one crosslinkable group are melt- formed at 120 ° C. or higher and lower than 250 ° C. An optical film characterized by being manufactured. The optical film according to claim 1, wherein the raw material is a mixture of two or more cellulose esters having different primary structures. The viscosity change at 250 ° C. is in the range of 0.001 poise / ° C. to 0.06 poise / ° C., and 1) the weight average molecular weight of the second largest cellulose ester B based on the cellulose ester A having the smallest weight average molecular weight is A 2 to 1000 times, and at least 60% by mass of a mixture of A and B having a mass ratio of 1: 1. A cellulose ester mixture raw material. 2) The weight average molecular weight of the side chain group differs by 10% or more. Melting and forming a cellulose ester composition using at least one cellulose ester raw material having at least one selected from two or more types of cellulose ester raw materials and 3) a cellulose ester raw material having at least one crosslinkable group at 120 ° C. or higher and lower than 250 ° C. A method for producing an optical film. A polarizing plate protective film using the optical film according to claim 1. A retardation film using the optical film according to claim 1. A polarizing plate using the polarizing plate protective film according to claim 4 or the retardation film according to claim 5. A display device comprising the polarizing plate according to claim 6.