JP4586617B2 - Manufacturing method of optical film - 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 using them, and a liquid crystal display device. More specifically, the optical film has less coloring and has excellent haze and tear strength. The present invention relates to a film, a method for producing an optical film, a polarizing plate protective film, a retardation film, a polarizing plate using them, and a liquid crystal display device.

  Polyester such as PET, and general-purpose resin films such as polyethylene (PE) and polypropylene (PP) are formed by melt extrusion molding. However, it is used as a cellulose ester-based optical film (polarizing plate protective film) such as TAC (triacetyl cellulose). Is not yet available for melt extrusion.

  Cellulose ester films are usually formed by the solution casting method, but due to the solubility of cellulose esters, a large amount of halogen-based solvent such as methylene chloride is used as a solvent, and there is a problem that the environmental load is large. It has become.

  On the other hand, since the melt casting method does not use a solvent, there is a high possibility that the environmental load is small, the width is wide, and the film forming speed can be increased, and the productivity can be improved.

  However, since triacetyl cellulose (TAC), which is a raw material for optical films, is a polymer having a melting start temperature higher than the decomposition starting temperature, it has not been achieved to obtain an optical film using the melt casting method.

  On the other hand, a technique for obtaining a cellulose ester film applicable to a photographic support by a melt casting method by substituting not only acetyl groups but also propionyl groups at a specific ratio has been disclosed (for example, patents). Reference 1).

  Patent Document 2 discloses that a polarizer protective film, a polarizer, and a liquid crystal display device having good dimensional stability can be obtained by using a fatty acid cellulose ester such as an acetyl group, a propionyl group, and a butyryl group by a melt casting method. Is disclosed.

  As a supply form of the cellulose ester-based raw material polymer, there are those supplied in powder or flake form. When this powder or flaky raw material polymer is directly melt-extruded, it is colored by drying immediately before melting, soars when supplied to the extruder, or deposited and deposited on the raw material supply part of the extruder. There was a problem that the handling was inferior due to contamination.

  In addition, when powder or flakes are directly melt-extruded, deterioration will increase when the set temperature of the extruder is increased. Therefore, it is necessary to extrude at the lowest possible temperature. There is a problem that an insufficient one becomes a bright spot foreign matter, and there is a problem that an appropriate temperature range is narrow.

On the other hand, some cellulose ester-based raw materials are supplied in the form of pellets of 2 to 3 mm. This is a cellulose ester prepared from pulp or cotton in a solution system, then dried, heat-melted and formed into pellets. Since it has already been heated once during pellet formation, it is further melt-cast When heated again during film formation, the cellulose ester deteriorates by heat, and the molecular weight tends to decrease or yellow, which is not preferable.
Japanese National Patent Publication No. 6-501040 JP 2000-352620 A

  Accordingly, an object of the present invention is to provide an optical film for display having good optical properties by a melt casting method using a raw material polymer of cellulose ester, and a method for producing the optical film. Another object of the present invention is to provide an optical film for a display that is excellent in haze and tear strength, without using a halogen-based solvent that has a high environmental impact, and has a good haze and tear strength. It is providing the polarizing plate and liquid crystal display device which were used as a phase difference film.

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

( 1 )
In a method for producing an optical film comprising at least one stabilizer, at least one plasticizer, and cellulose resin powder, the cellulose resin powder and the at least one stabilizer are powdered at a temperature Tmix. A method for producing an optical film, characterized in that a film constituent material mixed and then dried at a drying temperature Tdry having the following relationship is formed into a film by a melt casting method.

Tmix <Tm−a ≦ Tdry <Tg
(Wherein, Tmix is the temperature during powder mixing of the cellulose resin powder and at least one stabilizer, Tm-a is the melting point of the stabilizer, Tdry is the drying temperature of the powder mixture, and Tg is the cellulose resin. Represents the glass transition temperature of.
( 2 )
The molecular weight retention rate of the being film formation by melt-casting method film, on the molecular weight of the resin is not heated, production of optical film according to 1 you being a range of 90% to 100% Method.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a display optical film having good optical properties by a melt casting method using a cellulose ester raw polymer and a method for producing the optical film. In addition, it is possible to provide an optical film for display with little coloration, excellent haze and tear strength, and a method for producing the optical film without using a halogen-based solvent with a high environmental load. A polarizing plate and a liquid crystal display device used as a phase difference film can be provided.

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

  The method for producing an optical film of the present invention is the method for producing an optical film comprising at least one stabilizer, at least one plasticizer, and cellulose resin powder, wherein the cellulose resin powder and the at least one kind are prepared. The stabilizer is mixed with powder at a temperature Tmix, and the film constituent material dried at a drying temperature Tdry having the following relationship is formed into a film by a melt casting method.

Tmix <Tm−a ≦ Tdry <Tg
(Wherein, Tmix is the temperature during powder mixing of the cellulose resin powder and at least one stabilizer, Tm-a is the melting point of the stabilizer, Tdry is the drying temperature of the powder mixture, and Tg is the cellulose resin. Represents the glass transition temperature of.
While the present inventors are examining a method of adding a stabilizer to the cellulose ester resin, the cellulose resin powder and at least one stabilizer are powder-mixed at the temperature Tmix, and then stabilized. It is found that the stabilizer can be melted in the process and uniformly mixed with the cellulose resin powder by drying at a drying temperature equal to or higher than the melting point of the agent and less than Tg of the cellulose resin. It is found that an optical film having a high molecular weight retention and excellent coloration, haze, and tearing strength can be obtained by producing an optical film by the melt casting method using the above-described film constituent materials. It is up to.

  That is, in the present invention, the following relationship is essential for the materials used and the temperature conditions during production.

  (1) The melting point of the stabilizer is a temperature lower than the Tg of the cellulose resin. In the first place, if the melting point of the stabilizer is higher than the Tg of the cellulose resin, the stabilizer cannot be melted and mixed uniformly with the cellulose resin powder, so that the effect aimed at by the present invention cannot be obtained.

  (2) The heating temperature for drying the cellulose resin is lower than the Tg of the cellulose resin. Since the feature of the present invention is that the cellulose resin is dried as a powder, the drying temperature is set to Tg or less.

  (3) The heating temperature for drying the cellulose resin is equal to or higher than the melting point of the stabilizer. This is an essential condition for obtaining the effects of the present invention. In consideration of production speed and finish uniformity, drying is preferably performed at a temperature exceeding the melting point of the stabilizer.

  Hereinafter, the present invention will be described in detail for each element.

[Melt casting method]
The present invention is characterized in that a cellulose resin film formed by a melt casting method is used as an optical film. In the present invention, melting and casting a film constituent material without using a solvent generally used for solution casting is defined as a melt casting method.

  More specifically, the heating and melting molding method can be classified into a melt extrusion molding method, a press molding method, an inflation method, an injection molding method, a blow molding method, a stretch molding method, and the like. Among these, in order to obtain an optical film excellent in mechanical strength and surface accuracy, the melt extrusion method is excellent.

  Here, a method of extruding a film constituting material onto the drum or the endless belt after the film constituent material is heated to express its fluidity is also included in the melt casting method of the present invention as a melt casting film forming method.

(Cellulose resin)
The cellulose resin according to the present invention (hereinafter also referred to as a cellulose ester) shows the structure of a cellulose ester, and includes at least one of fatty acid acyl groups and substituted or unsubstituted aromatic acyl groups. Single or mixed acid ester.

  The cellulose ester constituting the optical film of the present invention is at least one selected from cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. It is preferable that

  Among these, particularly preferable cellulose esters include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate.

  As the degree of substitution of the mixed fatty acid ester, the lower fatty acid ester such as cellulose acetate propionate and cellulose acetate butyrate mentioned as the preferred cellulose ester has an acyl group having 2 to 4 carbon atoms as a substituent, When the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, it is preferably a cellulose resin containing a cellulose ester that simultaneously satisfies the following formulas (I) and (II).

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 not substituted with the acyl group is usually present as a hydroxyl group. These can be synthesized by known methods.

  Furthermore, the cellulose ester used in the present invention preferably has a weight average molecular weight Mw / number average molecular weight Mn ratio of 1.5 to 5.5, particularly preferably 2.0 to 5.0, Preferably it is 2.5-5.0, More preferably, the cellulose ester of 3.0-5.0 is used preferably.

[Raw material cellulose]
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 releasability 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.

[Raw polymer shape]
<Particle size / size distribution>
The shape of the raw material polymer including the cellulose resin is a powder, and the particle size is preferably in the range of 1 to 10 mm. This is when the average particle size is between 1 and 10 mm when the particle size distribution is measured. Yes, and 90% by mass or more of particles are in the range of 1 to 10 mm. The particle size distribution can be measured using, for example, a particle size distribution measuring device such as Nikkiso Co., Ltd. particle size distribution measuring device Microtrac MT3000, Shimadzu Corporation SALD-2000A.

  Further, the measurement can be performed by dispersing a raw material polymer in water and then taking a microphotograph and analyzing the image.

<Bulk specific gravity>
The bulk specific gravity of the raw material polymer including the cellulose resin can be determined by measuring the mass of the powder filled in a container having a known volume. For example, Tsutsui Rika Instruments Co., Ltd. B. By using a dedicated measuring device such as a D powder characteristic measuring device, it is possible to measure easily and accurately.

  In the present invention, the bulk specific gravity is preferably in the range of 0.1 to 1.0. B. It means that the loosely packed bulk specific gravity measured using the D powder characteristic measuring device takes a value between 0.1 and 1.0.

  If the bulk specific gravity is less than 0.1, it becomes fluffy, and handling such as transportation and weighing is extremely bad. If it is larger than 1.0, it will be in a compacted state at the bottom of the storage silo, causing problems such as being unable to bridge and discharge. Therefore, it is preferable to be within the above range.

[Drying: Removal of volatile components]
Film casting by the melt casting method is significantly different from the solution casting method. When volatile components are present in the material to be cast, the flatness and transparency of the film are ensured in order to utilize the function as a film or retardation film. From the point of view, it is not preferable. This is because transparency deteriorates when volatile components are mixed into the formed film, and when a film is formed by extrusion from a die-slit, the film surface becomes a factor that causes streaking and induces deterioration in flatness. There are things to do. Therefore, when a film constituent material is formed into a film, it is not preferable that a component that volatilizes exists in a region lower than the melting temperature for film formation from the viewpoint of avoiding generation of a volatile component during heating and melting.

  Examples of the volatile component include moisture absorbed by any of the film constituent materials, or a solvent mixed before the material is purchased or at the time of synthesis, and includes volatilization caused by evaporation, sublimation, or decomposition by heating. The solvent here is different from the solvent for preparing the resin as a solution as a solution casting, and is contained in a trace amount in the film constituting material. Therefore, selection of the film constituent material is important in avoiding the generation of volatile components.

  It is preferable that the film constituent material used in the melt casting method of the present invention removes volatile components typified by the moisture and the solvent before film formation or during heating. For this removal, a so-called known drying method can be applied, and it can be performed by a method such as a heating method, a decompression method, a heating decompression method, etc., or even in an atmosphere where nitrogen is selected as an inert gas. Good. 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 water or solvent remaining after removal in the drying step is 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably, with respect to the total mass of the film constituting material. Is 1% by mass or less.

  The drying temperature at this time is intended to reduce the generation of volatile components by drying before film formation, but as described above, the drying temperature is set to a temperature satisfying the following relationship.

Tmix <Tm−a ≦ Tdry <Tg
(In the formula, Tmix represents the temperature during powder mixing, Tm-a represents the melting point of the stabilizer, Tdry represents the drying temperature of the powder mixture, and Tg represents the glass transition temperature of the cellulose resin.)
A specifically preferable drying temperature is preferably 100 ° C. or higher and lower than Tg of the cellulose resin. Including the viewpoint of avoiding fusion between materials, the drying temperature is more preferably 100 ° C. or more and (Tg−5) ° C. or less. Further, the drying is performed at a temperature equal to or higher than the melting point of at least one stabilizer, preferably at a higher temperature.

  A preferable drying time is 0.5 to 24 hours, more preferably 1 to 18 hours, and still more preferably 1.5 to 12 hours. Below these ranges, the removal rate of volatile components may be low or it may take too long to dry, and when Tg is present in the material to be dried, heating to a drying temperature higher than Tg will cause the material to It may be difficult to handle due to fusion.

  The drying process may be separated in two or more stages. For example, the film may be formed through storage of the material in the preliminary drying process and a previous drying process performed immediately before film formation to one week before film formation.

  In order to obtain the effect of the present invention, the molecular weight retention of the film formed by the melt casting method is in the range of 90% to 100% with respect to the molecular weight of the unheated resin. preferable. If it is less than 90%, the tear strength is deteriorated and breakage failure is likely to occur. In order to keep the molecular weight retention within a preferable range, it can be achieved by adjusting a preferable drying temperature, a preferable drying time, a drying process, and the like of the above-described film constituent materials. The molecular weight retention is defined below.

(Molecular weight retention)
Molecular weight retention: The weight average molecular weight Mw0 of the raw material polymer before being supplied to the melt extruder and the weight average molecular weight Mw1 of the polymer after melt extrusion were measured by gel permeation chromatography (GPC), and Mw1 / Mw0 × 100. (%) Is defined as the molecular weight retention.

<Granulation>
In the present invention, the film constituent material can be granulated before the optical film is produced by the melt casting method using the dried film constituent material. The term “granulation” as used herein refers to a method of extruding and cutting from a screen having a desired shape while applying pressure as it is in a powder form, extruding from a screen having a desired shape by kneading with a biaxial rotor or the like at a temperature equal to or lower than the melting point. Say method.

  The shape of the granulated body is not particularly limited, such as a cylindrical shape, a spherical shape, a rectangular parallelepiped shape, and an indefinite shape. Although it depends on the granulation mechanism of the granulator, when measuring the particle size of the granulated material, the total of those smaller than 1 mm and larger than 10 mm is preferably less than 10% by mass, and the screw diameter of the extruder, etc. The size is determined accordingly.

  When granulating, it is also preferable to perform granulation by applying a certain pressure or by applying a temperature below the melting point of the polymer.

  When granulating, additives such as a plasticizer, an antioxidant, a heat stabilizer, a slipping agent, etc., which will be described later, can be mixed and granulated.

  As a granulator, a commercially available thing can be used, for example, Fuji Paudal Co., Ltd. disk pelleter F-5-440, Nippon Steel Works Co., Ltd. large granulator CMP, CIM each series, Examples include press pelleters FMP-180N to 800N manufactured by Chiyoda Giken Co., Ltd., and cylindrical granulators FG-250 to 600 manufactured by Fukae Powtex Co., Ltd.

(Additive)
Additives are added before or during the heat melting of the cellulose resin of the present invention.

  Examples of additives include plasticizers, antioxidants, acid scavengers, light stabilizers, peroxide decomposers, radical scavengers, metal deactivators, ultraviolet absorbers, matting agents, dyes, and pigments. . Moreover, if it has the said function, the additive which is not classified into this is also used.

  Of these, stabilizers such as antioxidants, acid scavengers, and light stabilizers play an important role in terms of function together with the plasticizer. It is a feature of the present invention that at least one of these stabilizers is dried together with the cellulose resin before heating and melting.

  In the present invention, the oxidation of the film constituent materials, the capture of the acid generated by decomposition, the suppression of or prohibition of the decomposition reaction of radical species caused by light or heat, etc. The above-mentioned stabilizer is used in order to impart a function of suppressing generation of volatile components due to alteration such as degradation and decomposition of materials.

  On the other hand, when the film constituent material is heated and melted, the decomposition reaction becomes remarkable, and this decomposition reaction may be accompanied by strength deterioration of the constituent material due to coloring or molecular weight reduction. Moreover, generation | occurrence | production of an unfavorable volatile component may occur by the decomposition reaction of a film constituent material.

  When the film constituent material is heated and melted, the presence of the above-mentioned stabilizer is excellent in terms of suppressing the deterioration of the strength based on the deterioration and decomposition of the material, or maintaining the inherent strength of the material. From the viewpoint of producing the optical film of the invention, it is necessary that at least one stabilizer described above is present.

  Further, the presence of the above-mentioned stabilizer is preferable as an optical film such as transmittance and haze value generated by suppressing the formation of colored substances in the visible light region at the time of heating and melting or by mixing volatile components in the film. Excellent in that it can suppress or eliminate performance.

  In the present invention, the display image of the liquid crystal display device has an influence when the haze value exceeds 2% when the optical film of the present invention is used. Therefore, the haze value is preferably less than 1%, more preferably less than 0.5%. is there. As an index of colorability, yellowness (yellow index, YI) can be used, preferably 3.0 or less, more preferably 1.0 or less. The optical film for display of the present invention preferably has a transmittance of 85% or more.

  In the present invention, the addition of the above-mentioned stabilizer is to suppress the deterioration of the strength of the film constituting material or to maintain the strength inherent to the material in the step of producing a film or providing retardation. . If the film constituent material becomes brittle due to significant deterioration, breakage is likely to occur in the stretching step, and the retardation value may not be controlled.

  In the above-described film constituent material storage or film formation process, deterioration reactions due to oxygen or moisture in the air may occur simultaneously. In this case, in addition to the stabilizing action of the stabilizer, reducing the humidity and oxygen concentration in the air can be preferably used in combination for realizing the present invention. This includes the use of nitrogen or argon as an inert gas as a known technique, a degassing operation under reduced pressure to vacuum, and an operation under a sealed environment, and at least one of these three methods includes the above stabilizer. It can be used in combination with the method. By reducing the probability that the film constituent material comes into contact with oxygen in the air, deterioration of the material can be suppressed, which is preferable for the purpose of the present invention.

  In addition, since the optical film of the present invention is used as a polarizing plate protective film, it is described above in the film constituting material from the viewpoint of improving the storage stability with time with respect to the polarizing plate of the present invention and the polarizer constituting the polarizing plate. The presence of additives plays an important role.

  In the liquid crystal display device using the polarizing plate of the present invention, when the above-mentioned stabilizer is present in the optical film of the present invention, the storage stability of the optical film over time can be improved from the viewpoint of suppressing the above-mentioned deterioration and deterioration, and the liquid crystal Also in improving the display quality of the display device, the optical compensation design is excellent in that the function can be expressed over a long period of time.

  Hereinafter, the additive will be described in more detail.

(Plasticizer)
In the present invention, at least one plasticizer is included.

  It is preferable to add a compound known as a plasticizer to the optical film of the present invention from the viewpoint of film modification such as improvement of mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability. Further, in the melt casting method carried out in the present invention, the purpose of lowering the melting temperature of the film constituting material by adding a plasticizer rather than the glass transition temperature of the cellulose ester used alone, or the plasticizer than the cellulose ester at the same heating temperature. It has the objective that the viscosity of the film constituent material containing can be reduced.

  Here, in the present invention, the melting temperature of the film constituent material means a heating temperature at which the material is heated and exhibits fluidity.

  If the cellulose ester alone is lower than the glass transition temperature, the fluidity for forming a film is not exhibited. However, the cellulose ester has a lower elastic modulus or viscosity due to the absorption of heat at a glass transition temperature or higher, and exhibits fluidity. In order to melt the film constituent material, the plasticizer to be added preferably has a melting point or glass transition temperature lower than the glass transition temperature of the cellulose ester in order to satisfy the above object.

  As the plasticizer used in the present invention, for example, phosphate ester derivatives and carboxylic acid ester derivatives are preferably used. Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of 500 to 10,000 described in JP-A-2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or cyclohexyl An acrylic polymer having a group in the side chain is also preferably used.

  Specific plasticizers include phosphate ester plasticizers, ethylene glycol ester plasticizers, glycerin ester plasticizers, diglycerin ester plasticizers (fatty acid esters), polyhydric alcohol ester plasticizers, dicarboxylic acid esters. System plasticizers, polycarboxylic acid ester plasticizers, polymer plasticizers, and the like. Of these, polyhydric alcohol ester plasticizers, dicarboxylic acid ester plasticizers and polycarboxylic acid ester plasticizers are preferred. Further, the plasticizer may be a liquid or a solid, and is preferably colorless due to restrictions on the composition. Thermally, it is preferably stable at a higher temperature, and the decomposition start temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher. The addition amount may be as long as it does not adversely affect the optical properties and mechanical properties, and the blending amount is appropriately selected within the range not impairing the object of the present invention, and preferably 0.001 with respect to 100 parts by mass of the cellulose resin according to the present invention. -50 mass parts, More preferably, it is 0.01-30 mass parts. 0.1-15 mass% is especially preferable.

  Hereinafter, the plasticizer used in the present invention will be described. Specific examples are not limited to these examples.

  Phosphate ester plasticizers: specifically, phosphoric acid alkyl esters such as triacetyl phosphate and tributyl phosphate, phosphoric acid cycloalkyl esters such as tricyclobenthyl phosphate and cyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate And phosphoric acid aryl esters such as cresylphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixylyl phosphate, tris ortho-biphenyl phosphate. These substituents may be the same or different, and may be further substituted. Moreover, the mix of an alkyl group, a cycloalkyl group, and an aryl group may be sufficient, and substituents may couple | bond together by the covalent bond.

  Also alkylene bis (dialkyl phosphate) such as ethylene bis (dimethyl phosphate), butylene bis (diethyl phosphate), alkylene bis (diaryl phosphate) such as ethylene bis (diphenyl phosphate), propylene bis (dinaphthyl phosphate), phenylene bis (dibutyl phosphate) ), Arylene bis (dialkyl phosphate) such as biphenylene bis (dioctyl phosphate), phosphate esters such as arylene bis (diaryl phosphate) such as phenylene bis (diphenyl phosphate) and naphthylene bis (ditoluyl phosphate). These substituents may be the same or different, and may be further substituted. Moreover, the mix of an alkyl group, a cycloalkyl group, and an aryl group may be sufficient, and substituents may couple | bond together by the covalent bond.

  Furthermore, the partial structure of phosphate ester may be part of the polymer, or may be regularly pendant, and also introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, UV absorbers, etc. May be. Among the above-mentioned compounds, phosphoric acid aryl ester and arylene bis (diaryl phosphate) are preferable, and specifically, triphenyl phosphate and phenylene bis (diphenyl phosphate) are preferable.

  Ethylene glycol ester plasticizer: Specifically, ethylene glycol alkyl ester plasticizers such as ethylene glycol diacetate and ethylene glycol dibutyrate, ethylene glycol dicyclopropyl carboxylate, ethylene glycol dicyclohexyl carboxylate and the like Examples include ethylene glycol cycloalkyl ester plasticizers and ethylene glycol aryl ester plasticizers such as ethylene glycol dibenzoate and ethylene glycol di4-methylbenzoate. These alkylate groups, cycloalkylate groups, and arylate groups may be the same or different, and may be further substituted. Further, it may be a mix of alkylate group, cycloalkylate group and arylate group, and these substituents may be covalently bonded. Further, the ethylene glycol part may be substituted, and the ethylene glycol ester partial structure may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber, etc. It may be introduced into a part of the molecular structure of the additive.

  Glycerin ester plasticizers: Specifically, glycerol alkyl esters such as triacetin, tributyrin, glycerol diacetate caprylate, glycerol oleate propionate, and glycerin cycloalkyl esters such as glycerol tricyclopropyl carboxylate and glycerol tricyclohexyl carboxylate Glyceryl aryl esters such as glycerin tribenzoate and glycerin 4-methylbenzoate, diglycerin tetraacetylate, diglycerin tetrapropionate, diglycerin acetate tricaprylate, diglycerin alkyl esters such as diglycerin tetralaurate, di Diglycerides such as glycerin tetracyclobutylcarboxylate and diglycerin tetracyclopentylcarboxylate Emissions cycloalkyl esters, diglycerin tetrabenzoate, diglycerin aryl ester such as diglycerin 3-methylbenzoate or the like. These alkylate groups, cycloalkylcarboxylate groups, and arylate groups may be the same or different, and may be further substituted. Further, it may be a mixture of alkylate group, cycloalkylcarboxylate group, and arylate group, and these substituents may be bonded by a covalent bond. Furthermore, the glycerin and diglycerin part may be substituted, and the partial structure of the glycerin ester and diglycerin ester may be part of the polymer or regularly pendant, and may be an antioxidant or an acid scavenger. Or may be introduced into a part of the molecular structure of an additive such as an ultraviolet absorber.

  Polyhydric alcohol ester plasticizer: Specific examples include polyhydric alcohol ester plasticizers described in paragraphs [30] to [33] of JP-A No. 2003-12823.

  These alkylate groups, cycloalkylcarboxylate groups, and arylate groups may be the same or different, and may be further substituted. Further, it may be a mixture of alkylate group, cycloalkylcarboxylate group, and arylate group, and these substituents may be bonded by a covalent bond. Furthermore, the polyhydric alcohol part may be substituted, and the partial structure of the polyhydric alcohol may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber. May be introduced into a part of the molecular structure of the additive.

  Dicarboxylic acid ester plasticizers: Specifically, alkyldocarboxylic acid alkyl ester plasticizers such as didodecyl malonate (C1), dioctyl adipate (C4), dibutyl sebacate (C8), dicyclopentyl succinate, Alkyl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclohexyl adipate, diphenyl succinate, alkyl dicarboxylic acid aryl ester plasticizers such as di4-methylphenyl glutarate, dihexyl-1,4-cyclohexanedicarboxylate, Cycloalkyldicarboxylic acid alkyl ester plasticizers such as didecylbicyclo [2.2.1] heptane-2,3-dicarboxylate, dicyclohexyl-1,2-cyclobutanedicarboxylate, dicyclopropyl-1,2 Cycloalkyldicarboxylic acid cycloalkyl ester plasticizers such as cyclohexyl dicarboxylate, aryl cycloalkyldicarboxylates such as diphenyl-1,1-cyclopropyldicarboxylate, di2-naphthyl-1,4-cyclohexanedicarboxylate Ester plasticizers, aryl dicarboxylic acid alkyl ester plasticizers such as diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, and di-2-ethylhexyl phthalate, and aryl dicarboxylic acid cycloalkyls such as dicyclopropyl phthalate and dicyclohexyl phthalate Examples include ester plasticizers and aryl dicarboxylic acid aryl ester plasticizers such as diphenyl phthalate and di4-methylphenyl phthalate. These alkoxy groups and cycloalkoxy groups may be the same or different, may be mono-substituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, and these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. Also, the partial structure of phthalate ester may be part of the polymer or regularly pendant to the polymer, and it may be part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. It may be introduced.

  Polycarboxylic acid ester plasticizers: Specifically, alkyl polycarboxylic acid alkyl ester plastics such as tridodecyl tricarbarate and tributyl-meso-butane-1,2,3,4-tetracarboxylate Agents, alkyl polyvalent carboxylic acid cycloalkyl ester type plasticizers such as tricyclohexyl tricarbarate, tricyclopropyl-2-hydroxy-1,2,3-propanetricarboxylate, triphenyl 2-hydroxy-1,2 Alkyl polycarboxylic acid aryl ester plasticizers such as 1,3-propanetricarboxylate, tetra-3-methylphenyltetrahydrofuran-2,3,4,5-tetracarboxylate, tetrahexyl-1,2,3,4 -Cyclobutane tetracarboxylate, tetrabutyl-1,2, 1,4-cyclopentanetetracarboxylate and other cycloalkyl polycarboxylic acid alkyl ester plasticizers, tetracyclopropyl-1,2,3,4-cyclobutanetetracarboxylate, tricyclohexyl-1,3,5-cyclohexyl Cycloalkyl polycarboxylic acid cycloalkyl ester plasticizers such as tricarboxylate, triphenyl-1,3,5-cyclohexyl tricarboxylate, hexa-4-methylphenyl-1,2,3,4,5,6 -Cycloalkyl polycarboxylic acid aryl ester plasticizers such as cyclohexyl hexacarboxylate, tridodecylbenzene-1,2,4-tricarboxylate, tetraoctylbenzene-1,2,4,5-tetracarboxylate, etc. Aryl polycarboxylic acid Lester ester plasticizer, aryl polyvalent carboxylic acid cycloalkyl ester plasticizer tri such as tricyclopentylbenzene-1,3,5-tricarboxylate, tetracyclohexylbenzene-1,2,3,5-tetracarboxylate Aryl polycarboxylic acid aryl ester-based plasticizers such as phenylbenzene-1,3,5-tetracartoxylate and hexa-4-methylphenylbenzene-1,2,3,4,5,6-hexacarboxylate Can be mentioned. These alkoxy groups and cycloalkoxy groups may be the same or different, may be mono-substituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, and these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. Also, the partial structure of phthalate ester may be part of the polymer or regularly pendant to the polymer, and it may be part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. It may be introduced.

  Polymer plasticizer: Specifically, aliphatic hydrocarbon polymer, alicyclic hydrocarbon polymer, acrylic polymer such as polyethyl acrylate and polymethyl methacrylate, polyvinyl isobutyl ether, poly N-vinyl pyrrolidone, etc. Examples include vinyl polymers, polystyrene, styrene polymers such as poly-4-hydroxystyrene, polybutylene succinate, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyethers such as polyethylene oxide and polypropylene oxide, polyamides, polyurethanes, and polyureas. It is done. The number average molecular weight is preferably about 1,000 to 500,000, particularly preferably 5,000 to 200,000. If it is 1,000 or less, a problem arises in volatility, and if it exceeds 500,000, the plasticizing ability is lowered, which adversely affects the mechanical properties of the cellulose ester derivative composition. These polymer plasticizers may be a homopolymer composed of one type of repeating unit or a copolymer having a plurality of repeating structures. Two or more of the above polymers may be used in combination, and other plasticizers, antioxidants, acid scavengers, ultraviolet absorbers, slip agents, matting agents, and the like may be included.

  The addition amount of these compounds is preferably used in the range of 0.5% by mass to less than 50% by mass, more preferably 1% by mass to 30% by mass with respect to the resin in which the plasticizer constitutes the film. %, More preferably in the range of 1% by mass to less than 11% by mass. The addition amount of these compounds can be adjusted from the viewpoint of the above purpose.

  Among the plasticizers, it is preferable that no volatile component is generated during heat melting. Specific examples include nonvolatile phosphate esters described in JP-A-6-501040. For example, among arylene bis (diaryl phosphate) esters and the above exemplified compounds, trimethylolpropane tribenzoate is preferable. It is not limited to.

  If the volatile component is generated by thermal decomposition of the plasticizer, the temperature at which the mass of the plasticizer is reduced by 1.0 mass% due to heat is defined as the thermal decomposition temperature Td-p (1.0). The thermal decomposition temperature Td-p (1.0) is required to be higher than the melting temperature of the film constituent material. This is because the amount of the plasticizer added to the cellulose ester is larger than that of other film constituent materials, and if a volatile component is present in the plasticizer, the film quality is greatly affected. The thermal decomposition temperature Td-p (1.0) can be measured with a commercially available differential thermogravimetric analysis (TG-DTA) apparatus.

  Furthermore, the same applies to stabilizers such as antioxidants, acid scavengers, and light stabilizers, which will be described later, and satisfying the following relationships with the film constituent materials to satisfy the physical properties of the obtained optical film. preferable. As a matter of course, when the melting temperature exceeds the decomposition temperature of the plasticizer and stabilizer, the physical properties of the obtained optical film are lowered.

Tm <Td-p (1.0)
Tm <Td-a (1.0)
(In the formula, Tm is a melting temperature of a film constituting material formed at a temperature of 120 ° C. or more and 250 ° C. or less, Td-p (1.0) is a temperature when 1.0% by mass of the plasticizer is reduced, Td− a (1.0) represents the decomposition temperature when the stabilizer is reduced by 1.0 mass%.)
(Antioxidant)
The antioxidant which is a stabilizer used in the present invention will be described.

  Antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, heat-resistant processing stabilizers, oxygen scavengers, etc. Among them, phenolic antioxidants, particularly alkyl-substituted phenolic compounds Antioxidants are preferred. By blending these antioxidants, it is possible to prevent coloration and strength reduction of the molded product due to heat during molding or oxidative degradation without lowering transparency, heat resistance and the like. These antioxidants can be used singly or in combination of two or more, and the blending amount thereof is appropriately selected within a range not impairing the object of the present invention, but the cellulose resin 100 according to the present invention. Preferably it is 0.001-5 mass parts with respect to a mass part, More preferably, it is 0.01-1 mass part.

  The hindered phenolic antioxidant compound is a known compound, and is described in, for example, columns 12 to 14 of U.S. Pat. No. 4,839,405, and includes a 2,6-dialkylphenol derivative compound. It is.

  Specific examples of the hindered phenol compound include n-octadecyl = 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, n-octadecyl = 3- (3,5-di-t- Butyl-4-hydroxyphenyl) -acetate, n-octadecyl = 3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl = 3,5-di-t-butyl-4-hydroxyphenylbenzoate, n -Dodecyl = 3,5-di-tert-butyl-4-hydroxyphenylbenzoate, neo-dodecyl = 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, dodecyl = β (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate, ethyl = α- (4-hydroxy-3,5-di-t-butylphenyl) isobuty Rate, octadecyl = α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl = α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n-octylthio) ethyl = 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (n-octylthio) ethyl = 3,5-di-t-butyl-4-hydroxy-phenylacetate 2- (n-octadecylthio) ethyl = 3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl = 3,5-di-t-butyl-4-hydroxy -Benzoate, 2- (2-hydroxyethylthio) ethyl = 3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol = bi Su- (3,5-di-tert-butyl-4-hydroxy-phenyl) propionate, 2- (n-octadecylthio) ethyl = 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate , Stearamide-N, N-bis- [ethylene = 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino-N, N-bis- [ethylene = 3- (3 , 5-di-tert-butyl-4-hydroxyphenyl) propionate], 2- (2-stearoyloxyethylthio) ethyl = 3,5-di-tert-butyl-4-hydroxybenzoate, 2- (2-stearoyl) Oxyethylthio) ethyl = 7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,2-propylene glycol = bis- 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], ethylene glycol = bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], neopentyl Glycol = bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], ethylene glycol = bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), glycerin -Ln-octadecanoate-2,3-bis- (3,5-di-t-butyl-4-hydroxyphenylacetate), pentaerythritol-tetrakis- [3- (3 ', 5'-di -T-butyl-4'-hydroxyphenyl) propionate], 1,1,1-trimethylolethane-tris- [3- (3,5-di-t-butyl) -4-hydroxyphenyl) propionate], sorbitol hexa- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl = 7- (3-methyl-5-t- Butyl-4-hydroxyphenyl) propionate, 2-stearoyloxyethyl = 7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol-bis [(3 ′, 5'-di-tert-butyl-4-hydroxyphenyl) propionate], pentaerythritol-tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate). Hindered phenolic antioxidants of the above type are commercially available from Ciba Specialty Chemicals under the trade names “Irganox 1076” and “Irganox 1010”, for example.

  Specific examples of other antioxidants include phosphorus antioxidants such as trisnonylphenyl phosphite, triphenyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, and dilauryl-3. , 3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, pentaerythrityltetrakis (3-laurylthiopropionate), etc. System antioxidant, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy-3,5- Di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenyl acrylate 3,4-dihydro-2H-1-benzopyran compound, 3,3′-spirodichroman compound, 1,1-spiroindane compound, morpholine, thiomorpholine, thiomorpholine oxide, described in JP-B-08-27508, Examples include thiomorpholine dioxide, compounds having a piperazine skeleton in the partial structure, oxygen scavengers such as dialkoxybenzene compounds described in JP-A-3-174150, and the like. These antioxidant partial structures may be part of the polymer or regularly pendant to the polymer.

(Acid scavenger)
Since cellulose ester is also decomposed by an acid at a high temperature, the optical film of the present invention preferably contains an acid scavenger as a stabilizer.

  Any acid scavenger useful in the present invention can be used without limitation as long as it is a compound that reacts with an acid to inactivate the acid, and is described in U.S. Pat. No. 4,137,201. Compounds having an epoxy group are preferred. Epoxy compounds as such acid scavengers are known in the art and are derived by condensation of various polyglycol diglycidyl ethers, particularly about 8-40 moles of ethylene oxide per mole of polyglycol. Glycol, diglycidyl ether of glycerol, metal epoxy compounds (such as those conventionally used in and together with vinyl chloride polymer compositions), epoxidized ether condensation products, diphenols of bisphenol A Glycidyl ether (i.e., 4,4'-dihydroxydiphenyldimethylmethane), epoxidized unsaturated fatty acid ester (especially an ester of an alkyl of about 4 to 2 carbon atoms of a fatty acid of 2 to 22 carbon atoms (e.g. butyl Epoxy stearate And epoxidized vegetable oils and other unsaturated natural oils (sometimes these are epoxidized natural glycerides, which can be represented and exemplified by compositions of various epoxidized long chain fatty acid triglycerides and the like (eg, epoxidized soybean oil and the like) Or unsaturated fatty acids, which generally contain 12 to 22 carbon atoms). Moreover, EPON 815C can also be preferably used as a commercially available epoxy group-containing epoxide resin compound.

  Furthermore, examples of acid scavengers that can be used other than the above include oxetane compounds, oxazoline compounds, organic earth salts of alkaline earth metals and acetylacetonate complexes, and paragraphs 68 to 105 of JP-A-5-194788. Is included.

  In addition, although an acid scavenger may be called an acid scavenger, an acid scavenger, an acid catcher, etc., in this invention, it can use without a difference by these names.

(Light stabilizer)
In the present invention, as a stabilizer for external light exposed as a polarizer protective film after production or light from the backlight of a liquid crystal display, a hindered amine light stabilizer (HALS) compound can be mentioned, which is a known compound, For example, as described in US Pat. No. 4,619,956, columns 5-11 and US Pat. No. 4,839,405, columns 3-5, 2,2,6 , 6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds.

  Specific examples of hindered amine light stabilizer compounds include 4-hydroxy-2,2,6,6-tetramethylpiperidine, 1-allyl-4-hydroxy-2,2,6,6-tetramethylpiperidine, 1-benzyl. -4-hydroxy-2,2,6,6-tetramethylpiperidine, 1- (4-t-butyl-2-butenyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine, 4-stearoyl Oxy-2,2,6,6-tetramethylpiperidine, 1-ethyl-4-salicyloyloxy-2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-1,2,2,6 6-pentamethylpiperidine, 1,2,2,6,6-pentamethylpiperidin-4-yl-β (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, -Benzyl-2,2,6,6-tetramethyl-4-piperidinyl maleate, (di-2,2,6,6-tetramethylpiperidin-4-yl) -adipate, (di- 2,2,6,6-tetramethylpiperidin-4-yl) -sebacate, (di-1,2,3,6-tetramethyl-2,6-diethyl-piperidin-4-yl) -sebacate, (di -1-allyl-2,2,6,6-tetramethyl-piperidin-4-yl) -phthalate, 1-acetyl-2,2,6,6-tetramethylpiperidin-4-yl-acetate, trimellitic acid- Tri- (2,2,6,6-tetramethylpiperidin-4-yl) ester, 1-acryloyl-4-benzyloxy-2,2,6,6-tetramethylpiperidine, dibutyl-malonic acid-di -(1,2,2,6,6-pentamethyl-piperidin-4-yl) -ester, dibenzyl-malonic acid-di- (1,2,3,6-tetramethyl-2,6-diethyl-piperidine- 4-yl) -ester, dimethyl-bis- (2,2,6,6-tetramethylpiperidine-4-oxy) -silane, tris- (1-propyl-2,2,6,6-tetramethylpiperidine- 4-yl) -phosphite, tris- (1-propyl-2,2,6,6-tetramethylpiperidin-4-yl) -phosphate, N, N′-bis- (2,2,6,6- Tetramethylpiperidin-4-yl) -hexamethylene-1,6-diamine, N, N'-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -hexamethylene-1,6- Diacetamide, 1-acetyl -4- (N-cyclohexylacetamide) -2,2,6,6-tetramethyl-piperidine, 4-benzylamino-2,2,6,6-tetramethylpiperidine, N, N'-bis- (2, 2,6,6-tetramethylpiperidin-4-yl) -N, N'-dibutyl-adipamide, N, N'-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -N , N'-dicyclohexyl- (2-hydroxypropylene), N, N'-bis- (2,2,6,6-tetramethylpiperidin-4-yl) -p-xylylene-diamine, 4- (bis-2 -Hydroxyethyl) -amino-1,2,2,6,6-pentamethylpiperidine, 4-methacrylamide-1,2,2,6,6-pentamethylpiperidine, α-cyano-β-methyl-β- [N- (2,2 6,6-tetramethyl-piperidin-4-yl)] - amino - and methyl acrylate and the like.

  At least one or more kinds of stabilizers in the film constituting material used in the present invention can be selected. The amount to be added is 0.001% by mass or more with respect to the mass of the cellulose ester. The content is preferably not more than mass%, more preferably not less than 0.005 mass% and not more than 3 mass%, and still more preferably not less than 0.01 mass% and not more than 0.8 mass%.

(UV absorber)
When the optical film of the present invention is used as a polarizer protective film used on the outer side with respect to the liquid crystal cell, it is preferable to further contain an ultraviolet absorber. The ultraviolet absorber is a material having an effect of preventing the material constituting the film from being decomposed by ultraviolet rays in an environment used after production. Cellulose ester itself is a material that is relatively resistant to ultraviolet rays, but other additives may be compounds that are weak against ultraviolet rays, and polarizers and liquid crystal cells are also vulnerable to ultraviolet rays. In addition, it is preferable that at least the polarizer protective film on the side exposed to external light and the polarizer protective film on the side on which the backlight of the liquid crystal display is incident contain an ultraviolet absorber.

  As such an ultraviolet absorber, from the viewpoint of preventing deterioration of a polarizer or a liquid crystal display device with respect to ultraviolet rays, the ultraviolet absorber has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, visible light having a wavelength of 400 nm or more. Those that absorb less light are preferred. Examples include oxybenzophenone compounds, benzotriazole compounds, triazine compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Triazole compounds are preferable, and benzotriazole compounds are particularly preferable. Moreover, you may use the ultraviolet absorber of Unexamined-Japanese-Patent No. 10-182621, Unexamined-Japanese-Patent No. 8-337574, and the polymeric ultraviolet absorber of Unexamined-Japanese-Patent No. 6-148430.

  Specific examples of useful benzotriazole ultraviolet absorbers include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl). ) Benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl)- 5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydro Cis-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy Examples include, but are not limited to, a mixture of -5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

  As commercially available products, TINUVIN 109, TINUVIN 171, TINUVIN 234, and TINUVIN 360 (all manufactured by Ciba Specialty Chemicals) can also be used.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenyl) methane and the like can be mentioned, but are not limited thereto.

  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. Two or more of these may be used in combination.

(Matting agent)
In the optical film of the present invention, fine particles such as a matting agent can be added in order to impart slipperiness. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound. The matting agent is preferably as fine as possible. Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include inorganic fine particles such as magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because it can reduce the haze of the film. In many cases, fine particles such as silicon dioxide are surface-treated with an organic substance, but such particles are preferred because they can reduce the haze of the film.

  Preferred organic substances for the surface treatment include halosilanes, alkoxysilanes, silazane, siloxane and the like. The larger the average particle size of the fine particles, the greater the sliding effect, and the smaller the average particle size, the better the transparency. The average particle size of the secondary particles of the fine particles is in the range of 0.05 to 1.0 μm. The average particle size of secondary particles of the fine particles is preferably 5 to 50 nm, more preferably 7 to 14 nm. These fine particles are preferably used in the cellulose ester film in order to generate irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film. The content of the fine particles in the cellulose ester is preferably 0.005 to 0.3% by mass with respect to the cellulose ester.

  Examples of the fine particles of silicon dioxide include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600 manufactured by Nippon Aerosil Co., Ltd., preferably Aerosil 200V, R972. , R972V, R974, R202, R812. Two or more kinds of these fine particles may be used in combination. When using 2 or more types together, it can mix and use in arbitrary ratios. In this case, fine particles having different average particle sizes and materials, for example, Aerosil 200V and R972V can be used in a mass ratio of 0.1: 99.9 to 99.9: 0.1.

  The presence of fine particles in the film used as the matting agent can be used for another purpose to improve the strength of the film. The presence of the fine particles in the film can also improve the orientation of the cellulose ester itself constituting the optical film of the present invention.

(Retardation control agent)
The optical film of the present invention is provided with a liquid crystal layer by forming an alignment film, providing an optical compensation ability by combining the optical film itself and the retardation derived from the liquid crystal layer, and improving the liquid crystal display quality. Can be used for polarizing plate processing. As the compound to be added for adjusting the retardation, an aromatic compound having two or more aromatic rings as described in EP 911,656A2 may be used as a retardation control agent. I can do it. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. Particularly preferred is an aromatic heterocycle, and the aromatic heterocycle is generally an unsaturated heterocycle. Of these, a 1,3,5-triazine ring is particularly preferred.

(Other additives)
Examples of other additives include dyes, pigments, phosphors, refractive index adjusters, and gas permeation inhibitors. Moreover, the additive which is not classified into this can be used if it has the said function.

  Then, as a method of incorporating these additives into the cellulose resin, the respective materials are mixed as solid or liquid, heated and melted and kneaded to form a uniform melt, and then cast to form an optical film. Even in this method, after dissolving all the materials in advance using a solvent or the like to obtain a uniform solution, the solvent is removed to form a mixture of the additive and the cellulose resin, and this is heated and melted. The optical film may be formed by casting.

(Film formation)
Examples of the optical film of the present invention include U.S. Pat. Nos. 2,492,978, 2,739,070, 2,739,069, 2,492,977, and 2,336. 310, No. 2,367,603, No. 2,607,704, British Patent Nos. 64,071, 735,892, No. 45-9074, No. 49-4554, The film can be formed by referring to the methods described in JP 49-5614, JP 60-27562, JP 61-39890, and 62-4208.

  For example, the cellulose ester and additive mixture of the present invention can be hot-air dried or vacuum dried, melt extruded, extruded into a film form from a T-die, and taken up by a roll adjusted to 50 to 150 ° C. . At this time, nipping with two rolls is preferable from the viewpoint of improving flatness.

  For melt extrusion, a single screw extruder, a twin screw extruder, or a single screw extruder may be connected downstream of the twin screw extruder, but a twin screw extruder is used from the viewpoint of uniformly dispersing the aforementioned additives. It is preferable. Furthermore, it is preferable to replace or depressurize the raw material supply and melting processes such as the raw material tank, the raw material charging section, and the inside of the extruder with an inert gas such as nitrogen gas.

  The temperature during the melt extrusion of the present invention is preferably in the range of Tg or more and Tg + 100 ° C. or less. Furthermore, it is preferable that it is the range of Tg + 10 degreeC or more and Tg + 90 degreeC or less.

  When a polarizing plate is produced using the optical film of the present invention as a polarizing plate protective film, the cellulose ester film is particularly preferably a film stretched in the width direction or the film forming direction.

  The unstretched film peeled from the cooling roll described above is brought into the glass transition temperature (Tg) -50 ° C. to Tg + 100 ° C. of the cellulose ester via a plurality of roll groups and / or a heating device such as an infrared heater. It is preferable to heat and stretch in one or more stages. Next, it is preferable that the cellulose ester film stretched in the longitudinal direction obtained as described above is transversely stretched within a temperature range of Tg-50 ° C to Tg + 100 ° C and then heat-set.

  In the case of transverse 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 the transverse stretching, it is preferable that the film is held at a temperature of Tg-40 ° C. or higher at a temperature equal to or lower than the final transverse stretching temperature for 0.01 to 5 minutes because the distribution of physical properties in the width direction can be further reduced.

  In the heat setting, heat setting is usually performed for 0.5 to 300 seconds at a temperature higher than the final transverse stretching temperature and within a temperature range of Tg-20 ° C. At this time, it is preferable to heat-fix while sequentially raising the temperature difference in the range of 1 to 100 ° C. in the region divided into two 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 cellulose ester constituting the film, so the physical properties of the obtained biaxially stretched film should be measured and adjusted appropriately to have desirable characteristics. It may be determined by.

(Functional layer)
When the optical film of the present invention is used as a polarizing plate protective film, an antistatic layer, a transparent conductive layer, a hard coat layer, an antireflection layer, an antifouling layer, an easy-sliding layer are produced before and / or after stretching in the production of the optical film. Functional layers such as an adhesive layer, an easy adhesion layer, an antiglare layer, a gas barrier layer, and 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.

  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 film material of the same product type or as a film material of a different product type. It may be reused.

  A cellulose ester film having a laminated structure can also be produced by co-extruding compositions containing cellulose resins having different additive concentrations such as the above-mentioned plasticizer, ultraviolet absorber and matting agent. For example, a cellulose ester film having a structure of skin layer / core layer / skin layer can be produced. For example, the matting agent can be contained in the skin layer in a large amount or only in the skin layer. More plasticizers and UV absorbers can be added to the core layer than the skin layer, and may be added only to the core layer. In addition, the type of plasticizer and UV absorber can be changed between the core layer and the skin layer. For example, the skin layer contains a low volatility plasticizer and / or UV absorber, and the core layer has excellent plasticity. It is also possible to add a plasticizer or an ultraviolet absorber excellent in ultraviolet absorption. The Tg of the skin layer and the core layer may be different, and the Tg of the core layer is preferably lower than the Tg of the skin layer. Further, the viscosity of the melt containing the cellulose ester during 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 used.

  The optical film of the present invention is preferably used as a polarizing plate protective film. When using as a polarizing plate protective film, the manufacturing method of a polarizing plate is not specifically limited, It can manufacture by a general method. The obtained optical film is alkali-treated, and a polarizer protective film is bonded to both sides of the polarizer using a completely saponified polyvinyl alcohol aqueous solution on both sides of the polarizer produced by immersing and stretching the polyvinyl alcohol film in an iodine solution. There is a method, and it is preferable that an optical film which is a polarizing plate protective film of the present invention is directly bonded to a polarizer on at least one side.

  Further, instead of the alkali treatment, easy-adhesion processing as described in JP-A-6-94915 and JP-A-6-118232 may be applied to perform polarizing plate processing.

  The polarizing plate is composed of a polarizer and a protective film for protecting both surfaces of the polarizer, and can further be constructed by laminating a protective film on one surface of the polarizing plate and a separate film on the opposite 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.

(Stretching operation, refractive index control)
The optical film of the present invention can be optimally controlled in refractive index by a stretching operation, and is preferably used as a retardation film. The obtained retardation film is preferably a polarizing plate bonded to at least one surface of the polarizing plate and having a wide viewing angle.

  As the stretching operation, the refractive index is controlled within a preferable range by stretching 1.0 to 2.0 times in one direction of the cellulose ester and 1.01 to 2.5 times in the direction perpendicular to the film plane. I can do it. 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 either one of the stretching ratios is more than the other stretching ratio. An optically anisotropic film can be obtained by stretching the film so as to increase.

  For example, the film can be stretched sequentially or simultaneously in the longitudinal direction of the film and the direction perpendicular to the longitudinal direction of the film, that is, the width direction. At this time, if the stretching ratio in at least one direction is too small, a sufficient phase difference cannot be obtained, and if it is too large, stretching becomes difficult and breakage may occur.

  For example, when the film is stretched in the direction of melting and casting, if the contraction in the width direction is too large, the refractive index in the thickness direction of the film becomes too large. In this case, the width shrinkage of the film can be suppressed or improved by stretching in the width direction. When stretching in the width direction, the refractive index may be distributed with a width. This is sometimes seen when the tenter method is used, but it is a phenomenon that occurs when the film is stretched in the width direction, causing contraction force at the center of the film and the ends being fixed. It is thought to be called a phenomenon. Even in this case, by stretching in the casting direction, the bowing phenomenon can be suppressed and the distribution of the width retardation can be reduced.

  Furthermore, the film thickness fluctuation | variation of the film obtained can be reduced by extending | stretching in the biaxial direction orthogonal to each other. If the variation in the film thickness of the optical film is too large, the retardation will be uneven, and unevenness such as coloring may be a problem when used in a liquid crystal display.

  The film thickness variation of the cellulose ester film support is preferably in the range of ± 3%, more preferably ± 1%. For the purposes as described above, the method of stretching in the biaxial directions perpendicular to each other is effective, and the stretching ratio in the biaxial directions perpendicular to each other is finally 1.0 to 2.0 times in the casting direction. The width direction is preferably 1.01 to 2.5 times, the casting direction is 1.01 to 1.5 times, and the width direction is 1.05 to 2.0 times. preferable.

  When cellulose ester that obtains positive birefringence with respect to stress is used, the slow axis of the optical film can be provided in the width direction by stretching in the width direction. In this case, in the present invention, in order to improve display quality, the slow axis of the optical film is preferably in the width direction, and satisfies (stretch ratio in the width direction)> (stretch ratio in the casting direction). It is necessary.

  There is no particular limitation on the method of stretching the web. For example, a method in which a circumferential speed difference is applied to a plurality of rolls, and the roll circumferential speed difference is used to stretch the rolls in the longitudinal direction. And a method of stretching in the vertical direction, a method of stretching in the horizontal direction and stretching in the horizontal direction, a method of stretching in the vertical and horizontal directions and stretching in both the vertical and horizontal directions, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  It is preferable to perform the width maintenance or the transverse stretching in the film forming process by a tenter, and it may be a pin tenter or a clip tenter.

  The in-plane retardation value (Ro) and thickness direction retardation value (Rth) of the optical film according to the present invention are preferably 0 ≦ Ro and Rth ≦ 70 nm when used as a polarizing plate 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, 30 ≦ Ro ≦ 100 nm and 70 ≦ Rth ≦ 400 nm, and more preferably 35 ≦ Ro ≦ 65 nm and 90 ≦ Rth ≦ 180 nm. 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.

Formula (i) Ro = (nx−ny) × d
Formula (ii) 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 optical film of the present invention preferably has a surface roughness Ra of 1 μm or less. When Ra is larger than 1 μm, when the above-described various functional layers are provided, the surface may become uneven or remain as convex defects, and smoothness and gloss may be impaired. In order to reduce Ra to 1 μm or less, the surface of the take-up roll and the drawing roll immediately after melt extrusion is made into a mirror surface, or the surface of the take-up roll immediately after being taken by the roll is nipped between the mirror surface rolls, This is achieved by appropriately selecting the magnification and the stretching speed. It is also effective to reduce Ra by sharpening the lip edge of the melt-extrusion die or mirroring the surface in contact with the molten resin inside the die.

  When the optical film of the present invention is a polarizing plate protective film or a retardation film, the thickness of the film is preferably 10 to 500 μm. In particular, it is preferably 20 μm or more, and more preferably 35 μm or more. Moreover, 150 micrometers or less, Furthermore 120 micrometers or less are preferable. Most preferably, it is 25 or more and 90 micrometers. If the optical film is thicker than the above region, the polarizing plate after polarizing plate processing becomes too thick, so that it is not suitable for the purpose of thin and light in liquid crystal displays used for notebook personal computers and mobile electronic devices. On the other hand, if it is thinner than the above-mentioned region, it is not preferable because it becomes difficult to develop retardation, the moisture permeability of the film becomes high, and the ability to protect the polarizer from humidity decreases.

  The slow axis or the fast axis of the optical film of the present invention is present in the film plane, and θ1 is preferably −1 ° or more and + 1 ° or less, assuming that the angle formed with the film forming direction is θ1. More preferably, it is 5 ° or more and + 0.5 ° or less. This θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-21ADH (Oji Scientific Instruments). Each of θ1 satisfying the above relationship can contribute to obtaining high luminance in a display image, suppressing or preventing light leakage, and contributing to obtaining faithful color reproduction in a color liquid crystal display device.

(Liquid crystal display device)
In a liquid crystal display device, a substrate containing liquid crystal is usually disposed between two polarizing plates. However, a polarizing plate protective film to which the optical film of the present invention is applied can provide excellent display properties regardless of the location. . In particular, since a clear hard coat layer, an antiglare layer, an antireflection layer, and the like are provided on the polarizing plate protective film on the display side outermost surface of the liquid crystal display device, the polarizing plate protective film is preferably used in this portion. In addition, in the case of a polarizer protective film provided with an optical compensation layer or a retardation film imparted with an appropriate optical compensation ability by itself, such as stretching operation, an excellent display can be obtained by placing it at a site in contact with the liquid crystal cell. Sex is obtained.

  When the optical film of the present invention is used as a polarizing plate protective film or a retardation film, it can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. . A VA (MVA, PVA) type liquid crystal display device is preferable. In particular, it can be preferably used for a large-screen liquid crystal display device having a 30-inch or larger screen.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

  The following cellulose ester was used as a raw material polymer.

<Cellulose ester>
C-1: cellulose acetate propionate (acetyl group substitution degree 1.8, propionyl group substitution degree 0.8, molecular weight Mn = 70000, molecular weight Mw = 220,000, Mw / Mn = 3)
<Plasticizer>
P-1: Trimethylolpropane tribenzoate <Antioxidant (stabilizer)>
A-1: IRGANOX-1076 (melting point (Tm-a): 55 ° C., manufactured by Ciba Specialty Chemicals)
A-2: IRGANOX-565 (melting point: 97 ° C., manufactured by Ciba Specialty Chemicals)
A-3: IRGANOX-1010 (melting point: 115 ° C., manufactured by Ciba Specialty Chemicals)
A-4: IRGANOX-3114 (melting point: 217 ° C., manufactured by Ciba Specialty Chemicals)
Example 1
<< Production of optical film >>
Cellulose ester C-1 was adjusted so as to have an average particle diameter of 0.2 mm by pulverizing with a pulverizer manufactured by Horai Co., Ltd. and pulverizing, and passing through a classification sieve. To this, 0.5 mass% of antioxidant A-1 was added with respect to the cellulose ester, and the mixture was mixed with a V-type mixer at a mixing temperature (Tmix) shown in Table 1 for 30 minutes.

  The obtained mixture was granulated with Fuji Powder Co., Ltd. disk pelleter F-5. The obtained granulated body had an average particle diameter of 2.0 mm and a cylindrical shape with a particle size distribution of 6% by mass obtained by adding particles less than 1 mm and greater than 10 mm. The pellets were dried at a temperature (Tdry) shown in Table 1 by a dehumidifying hot air dryer (Matsui Seisakusho DMZ2). Then, it supplied to the technobel Co., Ltd. twin-screw extruder, melt-extruded, and shape | molded into the film. In addition, the schematic diagram of a twin-screw extruder is shown in FIG.

  The set temperature of the extruder was 230 ° C. from the raw material hopper 1 toward the barrel tip, and the T die was 240 ° C. The T-die was a coat hanger type with a gap of 300 μm. The gap can be adjusted by push-pull bolts according to the thickness of the film formed.

  From the opening of the additive hopper 2 provided in the middle part of the extruder, the plasticizer P-1 is continuously 8% by mass, and the silica particles (particle size 2 μm) as the slip agent are continuously added to 0.05% of the extrusion amount. Added by a formula feeder. Similarly, a UV absorber (TINUVIN 360) was added so as to be 0.5 mass% of the extrusion amount from the opening. The melt-extruded film is dropped between two chrome-plated mirror rolls adjusted to 120 ° C. and passed between the three rolls, and the resulting film has a roll temperature of Tg−5 ° C. and a length of 1.05 in the longitudinal direction. The film is stretched and then relaxed after stretching by 1.10 times at a temperature of Tg + 3 ° C. of the film obtained by using a tenter in the width direction, wound at a temperature lower than the Tg of the obtained film, and slitted at the winder. Rolled up. The extrusion amount and the rotation speed of the take-up roll were adjusted so that the wound film had a thickness of 80 μm.

  The film obtained as described above was designated as an optical film 101.

  Subsequently, as shown in Table 1, the antioxidants A-2 to A-4 were used, and the optical films 102 to 117 were produced in the same manner as the optical film 101 as the mixing temperature (Tmix) and the drying temperature (Tdry). .

<Evaluation>
(Measure haze)
According to ASTM-D1003-52, it measured using T-2600DA by Tokyo Denshoku Industries Co., Ltd. One sample was stacked and measured. If it is 3.0% or less, there is no practical problem, but it is preferably 2.0% or less, and more preferably 1.0% or less.

(Yellow Index: YI)
The yellow index (yellowness) is obtained by the method described in JIS standard K7105-6.3. The yellow index in the present invention is obtained by using the spectrophotometer U-3200 manufactured by Hitachi, Ltd. and the attached saturation calculation program, etc., to determine the tristimulus values X, Y, and Z of the color, and obtaining the yellow index according to the following formula: I can do it.

Yellow index = 100 (1.28X-1.06Z) / Y
(Molecular weight retention)
Molecular weight retention: The weight average molecular weight Mw0 of the raw material polymer before being supplied to the melt extruder and the weight average molecular weight Mw1 of the polymer after melt extrusion were measured by gel permeation chromatography (GPC), and Mw1 / Mw0 × 100. (%) Was defined as the molecular weight retention.

(Tear strength)
The tear strength of the Elmendorf method was measured with a light load tear device manufactured by Toyo Seiki Co., Ltd. according to JIS K 7128-1991.

  The above evaluation results are summarized in Table 1.

  From the above table, optical films 101, 103, 104, 112 to 116 at a level in which the relationship between the temperature of mixing and drying of the cellulose resin and the stabilizer, Tmix, Tm-a, Tdry, and Tg is within the scope of the present invention. Is clearly an optical film excellent in haze, YI, molecular weight retention, and tear strength.

Example 2
(Preparation of polarizing plate)
A 120 μm-thick polyvinyl alcohol film was immersed in an aqueous solution containing 1 part by mass of iodine, 2 parts by mass of potassium iodide, and 4 parts by mass of boric acid, and stretched 4 times at 50 ° C. to produce a polarizer. The optical films 101 to 117 of Example 1 were alkali-treated with a 2.5 M / L-sodium hydroxide aqueous solution at 40 ° C. for 60 seconds, further washed with water and dried to alkali-treat the surface.

  Polarizing plates 101 to 117 each having a protective film formed thereon were bonded to both sides of the polarizer by bonding the alkali-treated surface of the optical film of Example 1 from both sides using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. Two copies were made.

<Evaluation>
When the same two polarizing plates were perpendicular to the transmission axis and observed from the front through illumination, the optical films 101, 103, 104, and 112 to 116 of the present invention showed no light leakage and became a black display. In the polarizing plate using the optical film, light leakage was recognized based on scattering due to haze, and it could not be used for display applications.

Example 3
An optical film 118 of the present invention was prepared in the same manner as in the production of the optical film 104 of Example 1, except that the draw ratio in the width direction was changed to 1.3.

  The maximum refractive index of the optical film 118 coincided with the width direction, and the retardation values obtained from the following formulas were Ro = 43 nm and Rt = 132 nm.

  The measurement was carried out using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). Measurement of foundation was performed. The average refractive index and film thickness d (nm) of the film constituent material measured with an Abbe refractometer were input, and in-plane retardation (Ro) and thickness direction retardation (Rth) were obtained. Further, the values of the three-dimensional refractive indexes nx, ny and nz are calculated by the above device.

Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = {(nx + ny) / 2−nz} × d
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is Represents film thickness (nm).)
Next, a polarizing plate was prepared. The optical films 101 to 118 and Konica Minolta Tack KC8UCR-3 (manufactured by Konica Minolta Opto Co., Ltd., referred to as UCR-3 in Table 2) were used in FIG. Polarizing plates 6a-101 to 118 and polarizing plates 6b-101 to 118 having the configurations shown in Table 2 were prepared for the polarizing plates 6a and 6b shown.

(Characteristic evaluation as a liquid crystal display device)
The polarizing plates on both sides of the 15-inch display VL-150SD manufactured by Fujitsu were previously peeled off, and the above-prepared polarizing plates 6a-101 to 118 and polarizing plates 6b-101 to 118 were adjusted to the size of the liquid crystal cell. And cut and bonded to the glass surface.

  As shown in FIG. 2, the two produced polarizing plates were attached so as to be orthogonal to each other so that the polarizing axes of the polarizing plates did not change, and liquid crystal display devices 101 to 118 were produced.

  The liquid crystal display devices 101, 103, 104, 112 to 116 and 118 using the polarizing plate of the present invention had high contrast and showed excellent display properties. Thereby, it was confirmed that it is excellent as a polarizing plate for image display apparatuses, such as a liquid crystal display.

The schematic diagram of a twin-screw extruder is shown. It is the schematic of the liquid crystal display device used in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material hopper 2 Additive hopper 1a Protective film 1b Protective film 2a Phase difference film 2b Phase difference film 5a, 5b Polarizer 3a, 3b Film slow axis direction 4a, 4b Polarizer transmission axis direction 6a, 6b Polarizer 7 Liquid crystal cell 9 Liquid crystal display device

Claims (2)

In a method for producing an optical film comprising at least one stabilizer, at least one plasticizer, and cellulose resin powder, the cellulose resin powder and the at least one stabilizer are powdered at a temperature Tmix. A method for producing an optical film, characterized in that a film constituent material mixed and then dried at a drying temperature Tdry having the following relationship is formed into a film by a melt casting method.
Tmix <Tm−a ≦ Tdry <Tg
(Wherein, Tmix is the temperature during powder mixing of the cellulose resin powder and at least one stabilizer, Tm-a is the melting point of the stabilizer, Tdry is the drying temperature of the powder mixture, and Tg is the cellulose resin. Represents the glass transition temperature of. 2. The optical film according to claim 1, wherein the film formed by the melt casting method has a molecular weight retention of 90% to 100% with respect to a molecular weight of an unheated resin. Production method.

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