JP2006219615A - Optical film, polarizing plate and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellulose ester formable to a film by melt-forming at a low temperature not to cause the thermal degradation and having sufficiently high wet-heat resistance, an optical film having good optical properties, and excellent flatness and wet-heat resistance and produced by using the cellulose ester, and a polarizing plate and a liquid crystal display device produced by using the optical film and further provide an optical film having high performance and produced without using a halogen-base solvent having high environmental load. <P>SOLUTION: The optical film is produced by the melt film-forming of a composition composed mainly of a cellulose ester, the cellulose ester is an ester substituted with acetic acid and an alicyclic carboxylic acid, and the alicyclic carboxylic acid has a substitution degree of ≥0.3 and ≤1.5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical film, a polarizing plate, and a liquid crystal display device that are formed by melting cellulose ester.

  Cellulose ester film is a film that protects photographic negative film supports and polarizers used in liquid crystal displays because of its high transparency, low birefringence, and easy adhesion to polarizers. Has been used.

  Due to the thinness and lightness of the liquid crystal display, the production volume has increased greatly in recent years, and the demand for liquid crystal displays has increased. In addition, TVs using liquid crystal displays are thin and light, and large-scale TVs that have not been achieved with TVs using Brown 菅 are now being produced. The demand for polarizers and polarizer protective films is also increasing.

  Until now, these cellulose ester films have been produced exclusively by the solution casting method. The solution casting method is a film forming method in which a solution obtained by dissolving cellulose ester in a solvent is cast to obtain a film shape, and then the solvent is evaporated and dried to obtain a film. Since a film formed by the solution casting method has high flatness and uniformity, a high-quality liquid crystal display without unevenness can be obtained using this film.

  However, the solution casting method is not self-supporting until the solvent used for dissolving the cellulose ester is volatilized to some extent, so a drying process is essential before it is discharged from the die and peeled off and wound. Since the drying process requires a certain amount of time, the production speed cannot be increased, and it has become difficult to meet the demand for increased production in the market. In addition, since an organic solvent is used in the solution casting method, a large environmental load has been a problem. In particular, cellulose ester films are formed using halogen-based solvents with high environmental impact due to their dissolution characteristics, so reduction of solvent usage is required, and production of cellulose ester films is increased by solution casting film formation. It has become difficult to do.

  In recent years, attempts have been made to melt film-form cellulose esters for silver salt photography (for example, see Patent Document 1) or polarizer protective films (for example, see Patent Document 2). Since the melt casting method does not use a solvent, the drying process is not required, so the production speed can be improved, and the production line such as a drying line and a solvent recovery / regeneration device is not required. This is a preferable manufacturing method because it can be easily increased in size and the environmental load can be greatly reduced.

  However, triacetyl cellulose, a cellulose ester that has been used for silver salt photography and polarizer protective films, is a polymer that has a melting temperature higher than the decomposition start temperature. The film obtained is not obtained by melt casting.

  On the other hand, in the cellulose ester for melt molding used for melt molding of toothbrushes and the like, cellulose esters mainly using propionic acid or butyric acid (CAP482-20 or CAB381-20 manufactured by Eastman Chemical Co., Ltd.) are used as organic acids for replacing cellulose. Etc.) are used.

  Such a cellulose ester has a glass transition temperature significantly lower than that of triacetyl cellulose, so that it can be melt-molded. On the other hand, the thermal deformation temperature and the wet heat deformation temperature are lowered, and a polarizer protective film for a liquid crystal display. As a result, the necessary physical properties cannot be obtained.

  As described above, it is known that the thermal properties of cellulose esters vary greatly depending on the type and degree of substitution of the organic acid that replaces cellulose (see, for example, Non-Patent Document 1).

  However, as a result of investigation by the inventors of the present invention, in the case of a combination of acetic acid and propionic acid or acetic acid and butyric acid, the cellulose ester having a low melting temperature does not reach the wet heat deformation temperature at which film deformation or the like is observed at high temperature and high humidity. On the other hand, the cellulose ester having a sufficient wet heat deformation temperature has a high melting temperature and melt viscosity, and the load on the apparatus is high, the flatness of the resulting film is inferior, the thermal decomposition occurs, and the coloring and film It has been found that a cellulose ester having an appropriate degree of substitution cannot be obtained due to the problem of embrittlement of the resin.

  Above all, the flatness of the film is a big problem of the melt film-forming process itself, and even for polymers other than cellulose esters, films used for optics are formed by solution film-forming. This is because in the melt film-forming process, the time from when the fluid polymer is discharged from the die to solidification is short, so the time for the film to level is short. Furthermore, the cellulose ester has a problem that its melt viscosity is high, and a melt-formed cellulose ester film having a quality that can be used for optics by melt film formation has not been obtained.

  In Patent Document 1, stretching is performed about 2 to 4 times to obtain a melt-formed cellulose ester film. However, cellulose ester is a polymer that is difficult to stretch, and is usually disclosed in the same publication. As described above, it is possible to stretch only about 20% to 40% at room temperature, and it was difficult to perform high-strength stretching such as 2 to 4 times with high productivity even at high temperatures.

As the alicyclic cellulose ester, in paragraph No. 126 of Patent Document 3, acetic acid-alicyclic carboxylic acid cellulose ester having a degree of substitution with acetic acid of 2.43 and a degree of substitution with adamantanecarboxylic acid of 0.22 is listed. Although examples are disclosed, the acetic acid-alicyclic carboxylic acid cellulose ester is mixed with about 1% to 4% with respect to triacetyl cellulose, thereby improving the peelability when forming a film by solution casting. There is no description about the melt film-forming property of the cellulose ester with acetic acid-alicyclic carboxylic acid.
Japanese National Patent Publication No. 6-501040 JP 2000-352620 A JP 2004-315756 A Industrial and Engineering Chemistry, vol. 34-4 (1942), p430-435

  Therefore, an object of the present invention is to provide a cellulose ester that can be melt-formed at a low temperature at which thermal decomposition does not occur and has sufficiently high moisture and heat resistance, and by using such a cellulose ester, good optical properties, excellent Another object of the present invention is to provide an optical film having flatness and moisture and heat resistance, a polarizing plate using the optical film, and a liquid crystal display device. Another object of the present invention is to provide a high-performance optical film manufactured without using a halogen-based solvent having a high environmental load.

  When the present inventor diligently studied the above problem, a cellulose ester having a low melting temperature and a sufficient wet heat deformation temperature is obtained by using a cellulose ester in which alicyclic carboxylic acid and acetic acid are substituted at a specific ratio. I found that I can do it. Surprisingly, the cellulose ester has a low melt viscosity and is relatively excellent in flatness even with an unstretched film. Thus, a cellulose ester film can be obtained that can be used as an optical film even at low magnification stretching that can be stably stretched. As a result, the present invention has been completed. That is, the said subject of this invention is achieved by the following structures.

(Claim 1)
An optical film formed by melting a composition mainly comprising cellulose ester, wherein the cellulose ester is a cellulose ester substituted with acetic acid and an alicyclic carboxylic acid, and the alicyclic carboxylic acid is substituted. An optical film having a degree of 0.3 to 1.5.

(Claim 2)
2. The optical film according to claim 1, wherein the total degree of substitution of the cellulose ester (the sum of the degree of substitution by acetic acid and the degree of substitution by alicyclic carboxylic acid) is 2.4 or more and 2.8 or less.

(Claim 3)
The optical film according to claim 1, wherein the alicyclic carboxylic acid is cyclohexane carboxylic acid.

(Claim 4)
The optical film according to any one of claims 1 to 3, wherein the cellulose ester has a weight average molecular weight of 150,000 or more.

(Claim 5)
5. The optical film according to claim 1, wherein a temperature at which the composition mainly comprising the cellulose ester is melted to form a film is 180 ° C. or higher and 230 ° C. or lower.

(Claim 6)
The optical film according to claim 1, wherein the optical film formed by melting is stretched 1.1 to 2.0 times in at least one direction.

(Claim 7)
The optical film according to any one of claims 1 to 6, wherein the composition contains 5 to 13% by mass of a polyhydric alcohol ester plasticizer.

(Claim 8)
The optical film according to any one of claims 1 to 7, wherein the composition contains 0.1 to 5% by mass of a hindered phenol-based antioxidant.

(Claim 9)
The optical film according to any one of claims 1 to 8, wherein the composition contains 0.1 to 5% by mass of a hindered amine light stabilizer.

(Claim 10)
The optical film according to any one of claims 1 to 9, wherein the composition contains 0.1 to 5% by mass of an epoxy-based acid scavenger.

(Claim 11)
The optical film according to any one of claims 1 to 10, wherein the composition contains 0.1 to 5% by mass of a benzotriazole-based ultraviolet absorber.

(Claim 12)
A polarizing plate using the optical film according to claim 1 as a protective film for a polarizing plate.

(Claim 13)
A liquid crystal display device using the optical film according to claim 1.

(Claim 14)
A liquid crystal display device using the polarizing plate according to claim 12.

According to the present invention, a cellulose ester that can be melt-formed at a low temperature at which thermal decomposition does not occur and has a sufficiently high moisture and heat resistance is provided. By using such a cellulose ester, good optical properties and excellent flatness are provided. In addition, an optical film having heat-and-moisture resistance, a polarizing plate using the same, and a liquid crystal display device can be provided. In addition, it is possible to provide a high-performance optical film manufactured without using a halogen-based solvent having a high environmental load.

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

  Conventionally, when a film is produced using a cellulose ester resin as a material for a polarizer protective film, a solution in which the resin is dissolved in a solvent is cast, and then the solvent is evaporated and dried to form a film, so-called solution casting. The law is being done. In the solution casting method, the self-supporting property of the film cannot be obtained until the dope discharged from the die is dried to some extent, so there is a limit in improving the production rate, and the solvent used is a solvent with a high environmental load. In addition, since facilities such as solvent recovery are necessary, it is necessary to make capital investment that is higher than the production volume, making it difficult to meet the demand for increased production from the market.

  Therefore, if there is no solvent to be evaporated and dried at the time of film formation, it can be expected that the problems encountered in the solution casting method can be avoided.

  The present invention was made in order to investigate a method for forming a film by heating and melting a cellulose ester, and is a specific cellulose that can be formed into a film at a low temperature at which thermal decomposition does not occur and has sufficient moisture and heat resistance. By melting and casting the ester at an optimum temperature to form a film, it is possible to provide an optical film having good optical characteristics, excellent flatness, and heat and humidity resistance, and using these as an optical compensation film, It has been found that a liquid crystal display device with improved display quality can be provided by forming a polarizing plate using it as a polarizer protective film.

  The present invention is described in detail below.

  The present invention is characterized by using a cellulose ester film formed by melt casting as an optical film. In the present invention, it is defined as melt casting that the film constituent material is cast in a flowable state by heating without dissolving in the solvent as in the solution casting.

  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 having excellent mechanical strength and surface accuracy, the melt extrusion molding method is excellent.

(Cellulose ester)
The optical film of the present invention is characterized by being formed using a film-forming material containing the cellulose ester according to the present invention described below, and the cellulose ester is contained in an amount of 80 to 99% by mass in the film-forming material. Preferably it is.

  The cellulose ester used in the present invention is a cellulose ester satisfying the following formula (1) when the substitution degree with acetic acid is X and the substitution degree with alicyclic carboxylic acid is Y.

Formula (1) 0.3 <= Y <= 1.5
(Y represents the degree of substitution with alicyclic carboxylic acid)
When the degree of substitution with the alicyclic carboxylic acid is 0.3 or more, the glass transition temperature of the cellulose ester is lowered to the extent that it can be melted, and when it is 1.5 or less, it is sufficient for use as an optical film. It is possible to impart wet heat resistance.

  The heat and humidity resistance means that the film is softened even under high temperature and high humidity conditions, and the shape of the film does not change, or the physical properties such as the birefringence value and flatness of the film do not change.

  Cellulose ester is a hydrophilic polymer, and although it can be rendered hydrophobic by substitution with a hydrophobic organic acid, it absorbs 1 to 10% of moisture under high humidity conditions. As a result, the glass transition temperature is lower than in dry conditions, and the shape and physical properties of the film are likely to change.

  In this invention, it discovered that meltability and heat-and-moisture resistance could be provided by using alicyclic carboxylic acid as a substituent of a cellulose ester, and came to complete this invention. Although details are unknown, the cycloaliphatic carboxylic acid provides moderate hydrophobicity and reduces the glass transition temperature, maintaining film shape and physical properties even under high-temperature and high-humidity conditions while maintaining melt suitability. Is presumed to be possible.

  In addition, since it is difficult to measure the glass transition temperature under high humidity conditions, in the present invention, it is determined whether the glass transition temperature is exceeded under the temperature and humidity conditions by the deformation amount under certain high temperature and high humidity conditions described later. is doing.

  Furthermore, it is preferable that the cellulose ester of this invention satisfy | fills following formula (2).

Formula (2) 2.4 <= X + Y <= 2.8
(X represents the degree of substitution with acetic acid, Y represents the degree of substitution with alicyclic carboxylic acid, and X + Y represents the total degree of substitution)
Since the hygroscopicity / glass transition temperature of the cellulose ester is affected by the total substitution degree of the cellulose ester, the cellulose ester is more preferably in the above range.

  When the total degree of substitution (X + Y) is less than 2.4, the hydrophilicity of the cellulose ester is increased, and physical properties are likely to change under high humidity conditions. Further, the glass transition temperature becomes high, and the meltability is lowered. On the other hand, when the total substitution degree exceeds 2.8, the glass transition temperature becomes high, and the meltability deteriorates. In general, the melting point of the cellulose ester is considered to be the lowest in the range where the total degree of substitution is 2.4 to 2.8 (see Non-Patent Document 1, for example).

  The alicyclic carboxylic acid that can be used in the cellulose ester of the present invention can be used without limitation as long as it is composed of carbon, oxygen, and hydrogen and has an alicyclic structure. Cyclopropanecarboxylic acid, cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, oxirane-2-carboxylic acid, oxetane-2-carboxylic acid, tetrahydrofuran-2-carboxylic acid, 1,2-dioxolane- 4-carboxylic acid, tetrahydropyran-2-carboxylic acid, 1,4-dioxane-2-carboxylic acid, 4-methylcyclohexanecarboxylic acid, 1-adamantaneacetic acid, 1-adamantanecarboxylic acid, 2-adamantanecarboxylic acid, cyclopentylacetic acid , Cyclohexylacetic acid 3-cyclopentyl propionic acid, 3-cyclohexyl propionic acid, 5-norbornene-2-carboxylic acid, 2-norbornane acetic acid, camphanic acid. Among these, a carboxylic acid having a 5-membered or 6-membered alicyclic structure is preferable. A 3-membered ring or a 4-membered ring has a large ring strain and may cause a ring-opening reaction due to overheating at the time of melting. Therefore, a 5-membered ring having a stable ring structure is preferable. Moreover, since the fall of a glass transition temperature is large at 7-membered ring or more and the heat resistance of the film obtained may be low, 6-membered ring or less is preferable. Among these, cyclohexanecarboxylic acid is preferable because it is thermally stable, excellent in meltability, and capable of obtaining a cellulose ester film having good heat and heat resistance.

  With the cellulose ester having the structure as described above, a cellulose ester film having excellent melt film-forming properties and good film heat and moisture resistance can be obtained.

  The melt film-forming property refers to the ease of melting a composition containing a cellulose ester by heating and shaping on a film, specifically, the molecular weight of the cellulose ester does not decrease during melting, This means that the viscosity at the time of melting is low and the load on the extruder is small.

  In general, cellulose ester is a polymer that is difficult to melt, and is because the melting temperature is higher than the decomposition start temperature and the melt viscosity is nearly two orders of magnitude higher than that of general polymers. Cellulose ester does not depend on the substituent, but starts to decrease in molecular weight from around 200 ° C. When the molecular weight is below a certain level, it becomes a fragile and brittle film. Such a film is not preferable because the film frequently breaks during production, and the productivity is significantly impaired. In order to maintain the mechanical strength and toughness of the resulting film, the weight average molecular weight of the cellulose ester constituting the film (after undergoing the melting process) is preferably 150,000 or more. If it is less than 150,000, the film may frequently break during production as described above. More preferably, it is 180,000 or more, more preferably 200,000 or more. The weight average molecular weight can be measured by commercially available gel permeation chromatography (GPC).

  In order to set the weight average molecular weight after the melting process to 150,000 or more, the cellulose ester as the raw material (before the melting process) needs to have a weight average molecular weight of 200,000 or more, preferably 250,000 or more. More preferably, it is 300,000 or more. There is no particular upper limit, but it is usually in the range of 1 million or less. If it is 500,000 or more, the viscosity at the time of melting becomes too high, and the burden on the extrusion molding machine may be increased. The molecular weight reduction during the melting process can be improved by adding a plasticizer to reduce the melting temperature or by using an antioxidant, a hindered amine light stabilizer, an acid scavenger, etc. described later.

  However, even when these additives are used, it is difficult to make the molecular weight 150,000 or more even when using an antioxidant or the like at 250 ° C. or higher. Therefore, the temperature during melt film formation is preferably 250 ° C. or lower. More preferably, it is 230 degreeC, More preferably, it is 220 degrees C or less. On the other hand, if the temperature during melt film formation is too low, non-uniform dissolution occurs or foaming is observed in the film. Therefore, it is preferable to melt at a temperature of 150 ° C or higher. More preferably, it is 180 degreeC or more, More preferably, it is 190 degreeC or more.

  The cellulose ester having the structure and molecular weight as described above can be synthesized by a known method.

  The positions where cellulose is substituted with organic acid are the 2nd, 3rd and 6th positions of the glucose unit, the 2nd and 3rd positions are secondary hydroxyl groups, and the 6th position is a primary hydroxyl group. Depending on which position the carboxylic acid substitutes, the higher order structure and physical properties of the cellulose ester may slightly change, but in the optical film of the present invention, the cellulose ester in which the alicyclic carboxylic acid is in any substitution position is preferable. Can be used.

  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 in the film-forming material is preferably in the range of 80% by mass to 99% by mass, but 1 to 20% by mass as the other material constituting the film, stabilizers, plasticizers and ultraviolet absorbers described later. By containing an agent, it is possible to suppress a decrease in melt viscosity and melting temperature and a decrease in molecular weight during the melting process, and to impart excellent performance as an optical film. If the cellulose ester content is 80% by mass or less, the additive will bleed out, which is not preferable. Further, when the amount of other additives necessary as an optical film is 1.0% by mass or less (the content of cellulose ester is 99% or more), it is difficult to satisfy the required physical properties. More preferably, the cellulose ester content is 85 to 95% by mass, and still more preferably 88 to 92% by mass.

(Plasticizer)
In forming the optical film by melt casting according to the present invention, it is preferable to add at least one plasticizer in the film forming material.

  Generally, a plasticizer is an additive having an effect of improving brittleness or imparting flexibility by adding it to a polymer. In the present invention, a plasticizer is melted. Used as an additive that lowers the temperature or as an additive that lowers the viscosity of the film-forming material at the same melting temperature. By lowering the melting temperature or melt viscosity, deterioration of the cellulose ester during the melting process can be suppressed. Therefore, in the present invention, any material having such an effect can be used as a plasticizer without any limitation. Such a melting point lowering effect / viscosity reduction lowering can be more easily obtained when a plasticizer to be added has a melting point or glass transition temperature lower than the glass transition temperature of the cellulose ester.

  In addition, the addition of a plasticizer may improve the mechanical properties of the cellulose ester film, improve the tear strength, impart water resistance, reduce moisture permeability, etc. More preferably, it is used as a plasticizer.

  In addition, the plasticizer also has an effect of suppressing degradation in the hot melt process of the cellulose ester by adding as described above, but the effect is due to a physical effect and not due to a chemical effect. In the present invention, it is not classified as a stabilizer.

  Examples of plasticizers that satisfy the above conditions and are used in the present invention include phosphate ester plasticizers, polyhydric alcohol ester plasticizers (ethylene glycol ester plasticizers, glycerin ester plasticizers, diglycerin). Ester plasticizers), polycarboxylic acid ester plasticizers, polymer plasticizers, phosphazene plasticizers, siloxane plasticizers, and the like. Of these, polyhydric alcohol ester plasticizers and polycarboxylic acid ester plasticizers are preferred, and polyhydric alcohol ester plasticizers are more preferred. Further, the plasticizer may be a liquid or a solid, and is preferably colorless due to restrictions on the composition. It is preferably thermally stable at higher temperatures and does not volatilize, and the 1% mass reduction temperature Td (1.0) in dry air is 200 ° C. or higher, more preferably 230 ° C. or higher, and particularly preferably 250 ° C. or higher. The 1% mass reduction temperature Td (1.0) under dry air can be measured with a commercially available differential thermogravimetric analysis (TG-DTA) apparatus.

  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 a range not impairing the object of the present invention, and is preferably 1 to 20 parts by mass in the film composition according to the present invention. Is 5 to 13 parts by mass. 8-12 mass parts is especially preferable.

  Hereinafter, although the plasticizer used for this invention is demonstrated to a specific example, this invention is not limited to these.

  Polyhydric alcohol ester plasticizer: In the present invention, a compound in which a compound having a plurality of hydroxyl groups in one molecule and a plurality of monovalent organic acids are condensed is referred to as a polyhydric alcohol ester plasticizer.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,2,4-trimethylpentane- 1,3-diol, 1,6-hexanediol, 1,2,3-hexanetriol, 1,2,6-hexanetriol, glycerin, diglycerin, erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, galactite Le, glucose, cellobiose, inositol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, diethylene glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol are preferable.

  Examples of preferable organic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, pivalic acid, acrylic acid, methacrylic acid, cyclohexanecarboxylic acid, benzoic acid, naphthoic acid, and the like. It is preferable that the polyhydric alcohol ester is formed of an unsaturated carboxylic acid having a high effect of reducing.

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

  Among specific examples of such polyhydric alcohol ester plasticizers, for example, ethylene glycol plasticizers include ethylene glycol alkyl ester plasticizers such as ethylene glycol diacetate and ethylene glycol dibutyrate, and ethylene glycol dibutylate. Examples thereof include ethylene glycol cycloalkyl ester plasticizers such as cyclopropylcarboxylate and ethylene glycol dicyclohexylcarboxylate, ethylene glycol dibenzoate, and ethylene glycol di4-methylbenzoate.

  Specific examples of glycerin ester plasticizers include glycerin alkyl esters such as triacetin, tributyrin, glycerin diacetate caprylate, glycerin oleate propionate, and glycerin cycloesters such as glycerin tricyclopropyl carboxylate and glycerin tricyclohexyl carboxylate. Diglycerol alkyl esters such as alkyl esters, glycerol aryl esters such as glycerol tribenzoate, glycerol 4-methylbenzoate, diglycerol tetraacetylate, diglycerol tetrapropionate, diglycerol acetate tricaprylate, diglycerol tetralaurate, etc. , Diglycerin tetracyclobutylcarboxylate, diglycerin tetracyclopentylcarboxylate, etc. Diglycerol cycloalkyl esters, diglycerin tetrabenzoate, diglycerin 3-methylbenzoate or the like.

  Specific examples of polyhydric alcohol ester plasticizers other than those described above include the compounds described in paragraph Nos. [30 to 33] of JP-A No. 2003-12823, or the chemical formulas 2 to 12 of Japanese Patent Application No. 2004-356546. Compounds.

  The plasticizer listed above may be further substituted with an alkyl group, an alkoxy group, an acyl group, an oxycarbonyl group, a carbonyloxy group or the like in both the polyhydric alcohol part or the organic acid part. They may be bonded by a covalent bond. Alternatively, these structures may be part of the polymer, or may be regularly pendant, and are introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. May be.

  Polycarboxylic acid ester plasticizer: In the present invention, a compound obtained by condensing a compound having a plurality of carboxylic acid groups in one molecule and a plurality of monovalent alcohols or phenols is a polyvalent carboxylic acid ester It is called a plasticizer.

  Specific examples of dicarboxylic acid ester plasticizers composed of divalent carboxylic acids include alkyl dicarboxylic acid alkyl ester plastics such as didodecyl malonate (C1), dioctyl adipate (C4), and dibutyl sebacate (C8). Agents, alkyl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclopentyl succinate and dicyclohexyl adipate, alkyl dicarboxylic acid aryl ester plasticizers such as diphenyl succinate and di4-methylphenyl glutarate, dihexyl-1, Cycloalkyl dicarboxylic acid alkyl ester plasticizers such as 4-cyclohexanedicarboxylate and didecylbicyclo [2.2.1] heptane-2,3-dicarboxylate, dicyclohexyl-1,2-cyclobutanedicarboxylate , Cycloalkyl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclopropyl-1,2-cyclohexyl dicarboxylate, diphenyl-1,1-cyclopropyl dicarboxylate, di-2-naphthyl-1,4-cyclohexanedi Cycloalkyl dicarboxylic acid aryl ester plasticizers such as carboxylate, aryl dicarboxylic acid alkyl ester plasticizers such as diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclopropyl phthalate, Aryl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclohexyl phthalate, and aryl dicarboxylic acid aryl ester systems such as diphenyl phthalate and di-4-methylphenyl phthalate Plasticizers.

Specific examples of the plasticizer comprising a trivalent or higher carboxylic acid include alkyl polyvalent carboxylic acid alkyl esters such as tridodecyl tricarbarate and tributyl-meso-butane-1,2,3,4-tetracarboxylate. Plasticizers, alkyl polyvalent carboxylic acid cycloalkyl ester plasticizers such as tricyclohexyl tricarbarate, tricyclopropyl-2-hydroxy-1,2,3-propanetricarboxylate, triphenyl 2-hydroxy-1, Alkyl polyvalent carboxylic acid aryl ester plasticizers such as 2,3-propanetricarboxylate and tetra-3-methylphenyltetrahydrofuran-2,3,4,5-tetracarboxylate, tetrahexyl-1,2,3, 4-cyclobutanetetracarboxylate, tetrabutyl-1 Cycloalkyl polycarboxylic acid alkyl ester plasticizers such as 2,3,4-cyclopentanetetracarboxylate, tetracyclopropyl-1,2,3,4-cyclobutanetetracarboxylate, tricyclohexyl-1,3, Cycloalkyl polycarboxylic acid cycloalkyl ester plasticizers such as 5-cyclohexyl tricarboxylate, triphenyl-1,3,5-cyclohexyl tricarboxylate, hexa-4-methylphenyl-1,2,3,4, Cycloalkyl polycarboxylic acid aryl ester plasticizers such as 5,6-cyclohexylhexacarboxylate, tridodecylbenzene-1,2,4-tricarboxylate, tetraoctylbenzene-1,2,4,5-tetra Aryl polyvalent carboxylic such as carboxylate Alkyl ester plasticizers, aryl polyvalent carboxylic acid cycloalkyl ester plasticizers such as tricyclopentylbenzene-1,3,5-tricarboxylate, tetracyclohexylbenzene-1,2,3,5-tetracarboxylate Aryl polycarboxylic acid aryl ester based plasticizers such as triphenylbenzene-1,3,5-tetracartoxylate, hexa-4-methylphenylbenzene-1,2,3,4,5,6-hexacarboxylate Is mentioned.
The alkoxy group and cycloalkoxy group in the above plasticizer 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. Further, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. In addition, the partial structure of phthalate ester may be part of the polymer or may be regularly pendant to the polymer, and introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, UV absorbers, etc. May be.

  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. Further, it may be a mix of an alkyl group, a cycloalkyl group, and an aryl group, and the substituents may be covalently bonded.

  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) ), Biphenylene bis (arylene bis (dialkyl phosphate) such as dioctyl phosphate, phenylene bis (diphenyl phosphate) such as ADK STAB PFR manufactured by Asahi Denka), phenylene bis (dixylenyl phosphate) such as ADK STAB FP500 manufactured by Asahi Denka, Asahi Denka Arylene bis (di-diyl phosphate) such as bisphenol A diphenyl phosphate such as ADK STAB FP600 Phosphoric acid esters of the reel phosphate) and the like. 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 phosphate ester partial structure may be part of the polymer or regularly pendant, and may be introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. 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.

  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 1000 or less, a problem occurs in volatility, and if it exceeds 500,000, the plasticizing ability is lowered, and the mechanical properties of the cellulose ester derivative composition are adversely affected. 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.

  Among the plasticizers, it is preferable that no volatile component is generated during heat melting.

(Stabilizer)
In the present invention, the stabilizer refers to a material that suppresses decomposition of a polymer by heat, oxygen, moisture, acid, or the like by a chemical action. Since the optical film of the present invention is molded at a high temperature of about 150 to 250 ° C., it is a system in which the polymer is easily decomposed and deteriorated, and a stabilizer is preferably contained in the film forming material.

  Addition of a stabilizer to the film-forming material prevents oxidation / thermal deterioration of the film-forming material due to radical species, acids, alkalis, etc. generated by heat, oxygen, light, etc. It can capture low molecules such as acids, and can prevent deterioration of the properties such as coloring and molecular weight reduction, process contamination due to material decomposition, and deterioration of physical properties of the resulting film.

  Examples of stabilizers include, but are not limited to, antioxidants, acid scavengers, hindered amine light stabilizers, ultraviolet absorbers, peroxide decomposers, radical scavengers, metal deactivators, and the like. Not. These are described in JP-A-3-199201, JP-A-5-1907073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, and the like. Among these, for the purpose of the present invention, it is preferable that at least one of an antioxidant, a hindered amine light stabilizer, and an acid scavenger is included in the film forming material as a stabilizer.

  At least one or more stabilizers in the film-forming material used in the present invention can be selected, and the added amount is 0.01% by mass or more and 5% by mass with respect to the mass of the cellulose ester. % Or less, more preferably 0.1% by mass or more and 3% by mass or less, and further preferably 0.3% by mass or more and 2% by mass or less.

  If the addition amount of the stabilizer is less than the range of the above addition amount, the stabilizing effect of the material at the time of heat melting is low, so the effect of the stabilizer cannot be obtained, and if the addition amount is more than the above range of the addition amount From the viewpoint of compatibility with the resin, it is not preferable because it may cause a decrease in transparency as an optical film or the film may become brittle.

  These stabilizers are preferably thermally stable at higher temperatures. When the 1% mass reduction temperature Td (1.0) of the stabilizer is Td (1.0), the Td (1.0) is 200 ° C. In addition, 230 ° C. or higher, particularly 250 ° C. or higher is preferable.

  A film-forming material can be stored as one or more kinds of pellets by mixing a plurality of materials prior to film formation for the purpose of avoiding material alteration and moisture absorption and simplifying the film formation process. . Pelletization may improve the mixing or compatibility of the melt during heating, or may ensure the optical uniformity of the resulting film. Moreover, the design of the barrel can be simplified.

  Even when the film forming material is pelletized prior to film formation, it can be pelletized by heating and melting. Even when pelletizing, the presence of the above-mentioned stabilizer is excellent from the viewpoint of suppressing the strength and degradation of optical transparency based on the degradation and decomposition of the material, or maintaining the inherent strength of the material. Yes.

  If the film constituting material is significantly deteriorated by heating, coloring may occur and the film may not be used as an optical film. Moreover, when using the optical film of the present invention as an optical compensation film, the retardation imparting step (stretching step) is performed next to the casting step. However, when the film constituent material is significantly deteriorated by heating and the molecular weight is lowered. In some cases, the formed film becomes brittle and breakage is likely to occur in the stretching process, or the retardation value of the target optical compensation film cannot be expressed.

  Therefore, the presence of the above-mentioned stabilizer suppresses the generation of colored substances in the visible light region at the time of heating and melting, or the transmittance and haze value caused by volatile components generated by decomposition of the material constituting the film. It is also excellent in that it is possible to suppress or eliminate deterioration that is undesirable as an optical film, such as a decrease in temperature.

  In the present invention, the display image of the liquid crystal display device is affected when the haze value of the optical film used exceeds 1%. Therefore, the haze value is preferably less than 1%, more preferably less than 0.5%. The haze value can be measured based on JIS-K7136. As an index of colorability, yellowness (yellow index, YI) can be used, preferably 3.0 or less, more preferably 1.0 or less. Yellowness can be measured based on JIS-K7103.

  In the above-described film forming material storage or film forming 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 polarizer protective film, the above-mentioned in the film constituting material is also used from the viewpoint of improving storage stability with respect to the polarizing plate of the present invention and the polarizer constituting the polarizing plate. The presence of stabilizers 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.

(Antioxidant)
Since the cellulose ester is decomposed not only by heat but also by oxygen at high temperatures, the optical film of the present invention preferably contains an antioxidant as a stabilizer. The antioxidant useful in the present invention can be used without limitation as long as it is a compound that suppresses the deterioration of the film-forming material due to oxygen. Among them, useful antioxidants include phenolic antioxidants and phosphorus-based antioxidants. Antioxidants, sulfur-based antioxidants, heat-resistant processing stabilizers, oxygen scavengers and the like can be mentioned. Among these, phenol-based antioxidants, particularly hindered phenol-based antioxidants are preferable. By blending these antioxidants, it is possible to prevent coloring and strength reduction of the molded product due to heat during heat molding or thermal oxidative degradation without lowering transparency and heat resistance. These antioxidants can be used alone or in combination of two or more thereof, and the blending amount thereof is appropriately selected within a range that does not impair the object of the present invention, but in the optical film according to the present invention. Is preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass.

  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. Among such compounds, preferred compounds are those represented by the following general formula (1).

  In the above formula, R 1, R 2 and R 3 represent a further substituted or unsubstituted alkyl substituent. 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.

(Hindered amine light stabilizer)
In the present invention, a hindered amine light stabilizer (HALS) is used as a stabilizer at the time of melting the film constituting material, and as a stabilizer against external light exposed as a polarizer protective film after production or light from a backlight of a liquid crystal display. Compounds, which are known compounds, such as columns 5-11 of US Pat. No. 4,619,956 and columns 3-5 of US Pat. No. 4,839,405. 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds, as described in. Examples of such a compound include compounds represented by the following general formula (2).

  In the above formula, R1 and R2 are H or a substituent. 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 - acrylic acid methyl ester. Examples of preferred hindered amine light stabilizers include the following HALS-1 and HALS-2.

In addition, among the hindered amine light stabilizers, Tinuvin 144 (manufactured by Ciba Specialty Chemicals) having a hindered phenol structure in the same molecule is also commercially available, and such a complex type stabilizer is also preferable. It is an example of a stabilizer.

(Acid scavenger)
Cellulose ester is preferably decomposed by an acid at high temperatures, and therefore 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, but is described in US Pat. No. 4,137,201. A compound having an epoxy group is 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). Further, as a commercially available epoxy group-containing epoxide resin compound, EPON 815C and other epoxidized ether oligomer condensation products of the following general formula (3) can also be preferably used.

  In the above formula, n represents 0-12.

  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 capture agent, an acid catcher, etc., in this invention, it can use without a difference by these names.

(UV absorber)
When the optical film of the present invention is used as a polarizer protective film used on the outside of the liquid crystal cell, it is preferable to further contain an ultraviolet absorber as a stabilizer. 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 relatively resistant to ultraviolet rays, but other additives may be compounds that are weak against ultraviolet rays, and polarizers and liquid crystal cells also contain compounds that are sensitive to ultraviolet rays. Therefore, 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 and a 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 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 and triazine 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 5% by mass, more preferably 0.3 to 3% by mass, and further preferably 0.5 to 2% by mass. Two or more of these may be used in combination in order to interpolate the transmission of ultraviolet light by the absorption waveform.

(Matting agent)
A matting agent can be added to the cellulose ester film of the present invention in order to impart slipperiness, optical and mechanical functions. Examples of the matting agent include inorganic compound fine particles and organic compound fine particles.

  The shape of the matting agent is preferably a spherical shape, a rod shape, a needle shape, a layer shape, a flat shape or the like. Examples of the matting agent include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Examples thereof include inorganic fine particles such as oxides, phosphates, silicates, carbonates, and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because it can reduce the haze of the film. These fine particles are preferably surface-treated with an organic substance because the haze of the film can be reduced.

  The surface treatment is preferably performed with halosilanes, alkoxysilanes, silazane, siloxane, or 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 primary particle size of the fine particles is in the range of 0.01 to 1.0 μm. The average particle size of the primary particles of preferable fine particles is preferably 5 to 50 nm, more preferably 7 to 14 nm. These fine particles are preferably used for generating irregularities of 0.01 to 1.0 μm on the surface of the cellulose ester film.

  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. 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.

  These matting agents are preferably added by kneading. Further, as another form, after mixing and dispersing a matting agent previously dispersed in a solvent and a cellulose ester and / or a plasticizer and / or an ultraviolet absorber, a solid material obtained by volatilizing or precipitating the solvent is obtained. It is preferable to use it in the production process of the ester melt from the viewpoint that the matting agent can be uniformly dispersed in the cellulose resin.

  The matting agent can be added to improve the mechanical, electrical and optical properties of the film.

  The slipperiness of the resulting cellulose ester film improves as the fine particles are added, but the haze increases as the fine particles are added. Therefore, the content is preferably 0.001 to 5% by mass, more preferably 0. 0.005 to 1% by mass, and more preferably 0.01 to 0.5% by mass.

(Other additives)
In the present invention, the cellulose ester can contain various additives in addition to the plasticizer, the stabilizer and the matting agent.

  For example, fillers, inorganic compounds such as silica and silicate, organic polymers, dyes, pigments, phosphors, dichroic dyes, retardation control agents, infrared absorbers, refractive index regulators, gas permeation inhibitors, antibacterial agents Agents, biodegradability imparting agents, anti-gelling agents, viscosity modifiers and the like. 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 ester, each material is mixed in a solid or liquid state, 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 ester, and this is heated and melted. It may be cast to form an optical film.

[Melt casting film formation]
The cellulose ester film of the present invention is preferably formed by melt casting.

  The molding method by melt casting, which is heated and melted without using the solvent used in the solution casting method (for example, methylene chloride, etc.), more specifically, melt extrusion molding method, press molding method, inflation method, injection molding method , Blow molding method, stretch molding method and the like. Among these, in order to obtain a polarizing plate protective film having excellent mechanical strength and surface accuracy, the melt extrusion method is excellent. In view of the physical properties of the obtained cellulose ester film, the melting temperature is preferably in the range of 150 to 250 ° C, more preferably 180 ° C to 230 ° C, and further preferably 190 ° C to 220 ° C.

  That is, after the film forming material containing cellulose ester formed into powder or pellets is dried with hot air or vacuum, it is heated and melted together with other film constituent materials to express its fluidity. Then, it is melt extruded, extruded into a sheet form from 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 obtain an unstretched sheet. The temperature of the cooling drum is preferably maintained at 90 to 150 ° C.

  The film obtained by peeling from the cooling drum may be heated again through one or a plurality of roll groups and / or a heating device such as an infrared heater and stretched in one or more stages in the longitudinal direction. By stretching, the productivity of the optical film can be increased, and when the ratio of longitudinal stretching to lateral stretching is nonuniform, an optical compensation film or retardation film can be obtained.

  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 cellulose ester 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 120 ° C. or higher, and more preferably 135 ° C. or higher. This is because when the cellulose ester film of the present invention is used in a liquid crystal display device, if the Tg of the film is lower than the above, molecules fixed inside the film due to the influence of the temperature and humidity of the use environment and the heat of the backlight. The orientation state of the film is affected, and there is a high possibility that the retardation value and the dimensional stability and shape of the film will greatly change. 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.

  In the transverse stretching width direction (TD), it is preferable to perform transverse stretching while sequentially raising the temperature difference in the range of 1 to 50 ° C. in the 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 or lower. 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 perform 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 preferred stretch ratio of the cellulose ester film is that stretched by 1.01 to 3.00 in both the longitudinal direction and the width direction. More preferably, the film is stretched 1.1 to 2.0 times, and more preferably 1.4 to 1.8 times. Thereby, while being able to obtain a cellulose-ester film with favorable flatness, productivity can be improved significantly. 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.

  In the case of obtaining a retardation film, by changing the stretching ratio in the longitudinal direction and the width direction and stretching so that one of the stretching ratios is larger than the other stretching ratio, optical anisotropy is achieved. A film can be obtained. 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 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. When the cellulose ester film is thicker than the above region, for example, when used as a polarizing plate protective film, the polarizing plate after polarizing plate processing becomes too thick, and is particularly thin in liquid crystal displays used for notebook computers and mobile electronic devices. Not suitable for lightweight purposes. 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 necessary, a film having a large film thickness 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. Moreover, even if it is a film with a thin film thickness, it has the effect that it can be produced with high productivity by extending | stretching such a thick film.

  The film thickness variation of the cellulose ester film support is preferably ± 3%, more preferably ± 1%, and still more preferably ± 0.1%.

  The width of the cellulose ester film of the present invention is preferably 1 to 4 m, and particularly preferably 1.4 to 4 m.

  In the cellulose ester film using the cellulose ester of the present invention, the melting temperature can be kept low and the molecular weight reduction of the cellulose ester can be suppressed. And since the optical film excellent in planarity is obtained, a cellulose-ester film can be manufactured with sufficient productivity. In particular, those having a width of 1.4 to 4 m are preferably used, and particularly preferably 1.4 to 2 m. If it exceeds 4 m, the apparatus becomes large and the conveyance becomes difficult.

  As the winding length of the film obtained by the cellulose ester of the present invention, 500 to 5000 m is preferable, and 1000 to 5000 m is more preferable. 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 decreases, the film tends to break, and it is difficult to obtain a film having the above length. It is also important that volatile components are not mixed in the material to be cast. Film formation by the melt casting method differs significantly from the solution casting method in the temperature at the time of film formation, and if there are volatile components in the material to be cast, these additives volatilize and adhere to the film forming apparatus at the time of film formation. However, since it causes various failures, it is not preferable from the viewpoint of ensuring the flatness and transparency of the film for utilizing the function as a film or a polarizing plate 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.

  Examples of the volatile component include moisture absorbed by any of the film constituent materials, gas such as oxygen and nitrogen mixed therein, or solvent and impurities mixed before the material is purchased or synthesized. Evaporation by sublimation, sublimation or volatilization by decomposition. The solvent here is different from the solvent for adjusting 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.

  In the present invention, the film constituent material used for melt casting is preferably removed before film formation or heating, when the volatile components typified by the moisture and the solvent are formed. A method by drying can be applied to this removal method, and it can be performed by a method such as a heating method, a reduced pressure method, or a heated reduced pressure method. 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 content of water or oxygen, and preferably do not substantially contain them. 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 mass of the entire film constituent material. 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 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 still more 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. It 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. .

  The in-plane retardation value (Ro) and thickness direction retardation value (Rt) of the cellulose ester film according to the present invention are preferably 0 ≦ Ro and Rt ≦ 70 nm when used as a polarizer protective film. More preferably, 0 ≦ Ro ≦ 20 nm and 0 ≦ Rt ≦ 50 nm, and more preferably 0 ≦ Ro ≦ 10 nm and 0 ≦ Rt ≦ 30 nm. When used as an optical compensation film (retardation film), 30 ≦ Ro ≦ 100 nm and 70 ≦ Rt ≦ 400 nm, and more preferably 35 ≦ Ro ≦ 65 nm and 90 ≦ Rt ≦ 180 nm. Further, the variation of Rt 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 Rt.

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

Ro = (nx−ny) × d
Rt = ((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 (Rt) 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.

  Since the cellulose ester film of the present invention does not substantially use a solvent in the film forming step, the amount of residual organic solvent contained in the cellulose ester film wound up after film formation is stably less than 0.1% by mass. Accordingly, it is possible to provide a cellulose ester film having more stable flatness and Rt than before. In particular, it has become possible to provide a cellulose ester film having stable planarity and Rt even in a long roll of 100 m or longer. The cellulose ester film is not particularly limited as to the winding length, and is preferably used even if it is 1500 m, 2500 m, or 5000 m.

  The amount of residual organic solvent can be measured by the headspace gas chromatography method. That is, a known amount of cellulose ester 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.

  Moreover, when a film contains a water | moisture content, the moisture content (g) further contained in the cellulose-ester film is calculated | required by another method, and the mass of a water | moisture content from the mass difference (g) of the cellulose-ester film before and behind the said heat processing. The residual organic solvent content (%) can be obtained from the value obtained by subtracting (g).

  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.

  In the cellulose ester film of the present invention, the cellulose ester film or the additive may be co-extruded layers having different contents to form a cellulose ester 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 can be contained in the skin layer, and a plasticizer having excellent plasticity or an ultraviolet absorber having excellent ultraviolet absorption can 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 skin layer) is higher, a laminate having a uniform film thickness can be obtained.

(Polarizer)
When forming and using a polarizing plate using the cellulose ester film of the present invention as a polarizing plate protective film for a liquid crystal display device, the polarizing plate on at least one surface is preferably the polarizing plate of the present invention, and both surfaces are polarizing plates of the present invention. It is more preferable that

  In addition, as a conventional polarizing plate protective film, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC8UCR-3, KC8UCR-4, KC12UR, KC8UXW-H, KC8UYW-HA, KC8UX-RHA Cellulose ester films such as those manufactured by KK) are used.

  The production method of the polarizing plate of the present invention is not particularly limited, and can be produced by a general method. The obtained polarizing plate protective film was treated with an alkali, and a polyvinyl alcohol film was immersed and stretched in an iodine solution, using a completely saponified polyvinyl alcohol aqueous solution on both sides of the polarizer, and polarizing plate protective films on both sides of the polarizer. Can be pasted together. This method is preferable in that the polarizing plate protective film of the present invention can be 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 when the polarizing plate is shipped or transported. 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 cell. The separate film is used for the purpose of covering the adhesive layer.

(Liquid crystal display device)
In a liquid crystal display device, a substrate containing liquid crystal is usually disposed between two polarizing plates. However, a polarizer protective film to which the optical film of the present invention is applied has high dimensional stability, so it can be disposed at any position. Excellent display properties can be obtained. A polarizer protective film provided with a clear hard coat layer, an antiglare layer, an antireflection layer, or the like is preferably used for this part of the polarizer protective film on the outermost display side of the liquid crystal display device. In addition, in the case of a polarizer protective film provided with an optical compensation layer, or a polarizer protective film provided with an appropriate optical compensation capability by itself, such as stretching operation, it is excellent in being disposed at a site in contact with the liquid crystal cell. Displayability 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 suitable for improving the viewing angle dependency and the 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 faithful with less eye fatigue. A moving image can be displayed.

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

Example 1
《Synthesis of cellulose ester》
Polymers for Advanced Technologies, vol. 14 (2003), p478, various cellulose esters were synthesized.

<Cellulose ester a1>
100 parts by mass (100 parts by mol) of cellulose, 420 parts by mass (1600 parts by mol) of lithium chloride, 26 parts by mass (70 parts by mol) of acetic acid, 182 parts by mass (230 parts by mol) of cyclohexanecarboxylic acid, To a solution mixed with 1000 parts by mass (10 times by volume) of acetamide, 380 parts by mass (300 parts by mol) of dicyclohexylcarbodiimide (DCC), 130 parts by mass (170 parts by mol) of dimethylaminopyridine, and dimethylaminopyridine-tosylate 130 parts by weight (70 moles) was added at room temperature and stirred for 24 hours until the DCC was completely consumed. After completion of the reaction, a white precipitate formed by adding 5000 parts by mass of distilled water was filtered off. The solid matter separated by filtration was washed several times with pure water, then subjected to Soxhlet extraction with methanol for 24 hours, and finally dried in vacuo at 70 ° C. to obtain cellulose ester a1. The substitution degree and molecular weight of the obtained cellulose ester were carried out according to the measurement method described later, and the measurement results are shown in Table 1.

<Cellulose ester a2>
The same as cellulose ester a1 except that 26 parts by mass (70 parts by mol) of acetic acid was changed to 48 parts by mass (130 parts by mol) and 182 parts by mass (230 parts by mol) of cyclohexanecarboxylic acid were changed to 134 parts by mass (170 parts by mol). Synthesis was performed to obtain cellulose ester a2.

<Cellulose ester a3>
The same as cellulose ester a1 except that 26 parts by mass (70 mols) of acetic acid was changed to 78 parts by mass (210 parts by mol) and 182 parts by mass (230 mols) of cyclohexanecarboxylic acid were changed to 71 parts by mass (90 parts by mol). Then, synthesis was carried out to obtain cellulose ester a3.

<Cellulose ester a4>
The same as cellulose ester a1 except that 26 parts by mass (70 parts by mol) of acetic acid was changed to 93 parts by mass (250 parts by mol) and 182 parts by mass (230 parts by mol) of cyclohexanecarboxylic acid were changed to 40 parts by mass (50 parts by mol). Synthesis was performed to obtain cellulose ester a4.

<Cellulose ester a5>
The same as cellulose ester a1 except that 26 parts by mass (70 parts by mol) of acetic acid was changed to 104 parts by mass (280 parts by mol) and 182 parts by mass (230 parts by mol) of cyclohexanecarboxylic acid were changed to 16 parts by mass (20 parts by mol). Then, synthesis was carried out to obtain cellulose ester a5.

<Cellulose ester b1>
Synthesis was carried out in the same manner as cellulose ester a3 except that 78 parts by mass (210 parts by mol) of acetic acid was changed to 63 parts by mass (170 parts by mol) to obtain cellulose ester b1.

<Cellulose ester b2>
Synthesis was carried out in the same manner as cellulose ester a3 except that 78 parts by mass (210 parts by mol) of acetic acid was changed to 70 parts by mass (190 parts by mol) to obtain cellulose ester b2.

<Cellulose ester b3>
Synthesis was performed in the same manner as cellulose ester a3 except that 78 parts by mass (210 parts by mol) of acetic acid was changed to 85 parts by mass (230 parts by mol) to obtain cellulose ester b3.

<Cellulose ester b4>
Synthesis was carried out in the same manner as cellulose ester a3 except that 78 parts by mass (210 parts by mol) of acetic acid was changed to 93 parts by mass (250 parts by mol) to obtain cellulose ester b4.

<Cellulose ester c1>
Synthesis was performed in the same manner as the cellulose ester a3 except that 182 parts by mass (230 mols) of cyclohexanecarboxylic acid was changed to 162 parts by mass (230 mols) of cyclopentanecarboxylic acid to obtain cellulose ester c1.

<Cellulose ester c2>
Synthesis was performed in the same manner as cellulose ester a3 except that 182 parts by mass (230 mols) of cyclohexanecarboxylic acid was changed to 162 parts by mass (230 mols) of tetrahydrofuran-2-carboxylic acid to obtain cellulose ester c2.

<Cellulose ester d1>
The cellulose ester d1 was obtained by synthesizing by the method described in Section 8 Example B of Patent Document 1 referred to in the section of the prior art. Cellulose ester d1 was used for production of optical films D1 and D2.

<Cellulose ester d2>
Eastman Chemical cellulose acetate propionate, CAP482-20 was used.

<Cellulose ester d3>
Eastman Chemical Cellulose Acetate Butyrate, CAB171-15 was used.

<Cellulose ester d4>
Eastman Chemical Cellulose Acetate Butyrate, CAB381-20 was used.

  Each cellulose ester obtained by the above synthesis example was measured for molecular weight and substitution degree by the following method.

(Measurement of molecular weight of cellulose ester)
Since the average molecular weight and molecular weight distribution of a cellulose ester can be measured using high performance liquid chromatography, the weight average molecular weight (Mw) can be calculated using this.

  The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803 (used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

(Measurement of substitution degree of cellulose ester)
Based on ASTM D817-96, substitution degree DS was calculated | required as follows.

  1.90 g of the dried cellulose ester was precisely weighed, 70 ml of acetone and 30 ml of dimethyl sulfoxide were added and dissolved, and then 50 ml of acetone was further added. While stirring, 30 ml of 1 mol / L sodium hydroxide aqueous solution was added and saponified for 2 hours. After adding 100 ml of hot water and washing the sides of the flask, titration was performed with 0.5 mol / L sulfuric acid using phenolphthalein as an indicator. Separately, a blank test was performed in the same manner as the sample. The supernatant of the solution after titration was diluted 100 times, and the composition of the organic acid was measured by an ordinary method using an ion chromatograph. From the measurement result and the acid composition analysis result by ion chromatography, the substitution degree was calculated by the following formula.

TA = (B−A) × F / (1000 × W)
X = (162.14 * TA) / {1-42.14 * TA + (1-SA * TA) * (Y / X)}
Y = X × (Y / X)
DS = X + Y
A: Sample titration (ml)
B: Blank test titration (ml)
F: Potency of 0.5 mol / L sulfuric acid W: Mass of sample (g)
TA: Total organic acid amount (mol / g)
Y / X: molar ratio of acetic acid to acid other than acetic acid measured by ion chromatography X: degree of substitution with acetic acid Y: degree of substitution with acid other than acetic acid SA: 96.12 when Y is cyclopentanecarboxylic acid, cyclohexane 110.15 for carboxylic acid, 98.10 for 2-tetrahydrofurancarboxylic acid, 56.06 for propionic acid, 70.09 for butyric acid
<Film forming method>
90 parts by mass of cellulose esters (a1 to a5, b1 to b4, c1 to c2, and d1 to d4) prepared in Synthesis Examples, 10 parts by mass of the following plasticizer, and 1.0 part by mass of an ultraviolet absorber After mixing with powder, it was fed to a twin screw extruder. The screw rotation speed was 100 rpm, and the temperature (melting temperature) in the barrel was selected as the lowest temperature at which a transparent film was obtained. The film was formed so that the film thickness was 80 μm.

  The various additives used and their 1% mass reduction temperature Td (1.0) are shown below. About 1% mass reduction | decrease temperature Td (1.0), it measured with the temperature increase rate of 10 degree-C / min and dry air (dew point -30 degreeC) with the Seiko Instruments differential thermal-thermal mass simultaneous measurement apparatus and EXSTAR6000TG / DTA.

-Plasticizer:-TMPTB manufactured by Asahi Denka: trimethylolpropane tribenzoate (262 ° C)
・ The following phosphate plasticizer di-TPP (275 ° C)
<Synthesis of Phosphate Plasticizer Di-TPP>
Synthesis was performed with reference to Example A on page 8 of Patent Document 1.

  Under nitrogen, 32.7 g of hydroquinone was dissolved in 500 ml of pyridine, and then cooled to 5 ° C. To this solution, 200 g of diphenyl chlorophosphate was added, and after completion of the dropwise addition, the reaction vessel was warmed to room temperature and kept for a whole day and night. After this solution was mixed with 200 ml of water, this solution was put into a 3 L water container to obtain a white precipitate. The white precipitate was collected by filtration and then recrystallized from methanol to obtain a white solid. The yield was 90% and the melting point was 107 ° C.

UV absorber: Tinuvin 360 (323 ° C) manufactured by Ciba Specialty Chemicals
The following evaluations were performed on optical films A1 to A5, B1 to B4, C1 to C2, and D1 to D5 obtained based on the formulations in Table 1, and the results are also shown in Table 1.

(Evaluation)
<Measurement of molecular weight after film formation>
The obtained optical film was sampled, and the molecular weight was measured by GPC in the same manner as described above. Moreover, the value divided by the molecular weight before film formation was defined as the molecular weight retention rate.

<Moisture and heat resistance>
The film sample was stored in an environmental chamber at 23 ° C. and 55% RH for 24 hours, and then cut into a size of 50 mm in the width direction and 150 mm in the longitudinal direction. A 5 g weight is hung on the side of the short axis direction of the obtained rectangular sample, stored in an environmental room at 80 ° C. and 90% RH for 48 hours, and then stored again in an environmental room at 23 ° C. and 55% RH for 24 hours. After humidity conditioning, the amount of deformation of the film and the presence or absence of additive bleed out were evaluated.

◎: There is no bleed out of the additive, and the change in the length in the long axis direction after removal from the environmental chamber is 1% or less. Change in length in direction is 3% or less △: No additive bleed-out, and change in length in the major axis direction after removal from the environmental chamber is 10% or less ×: Additive bleed-out is observed And, the change in length in the major axis direction after taking out from the environmental chamber is 10% or more <Evaluation of stretchability>
Ten film samples cut to 10 cm × 10 cm were prepared and biaxially stretched. First, 20% MD (casting direction during film formation) was stretched, and then 20% TD (direction perpendicular to the casting direction during film formation) was stretched (final stretch ratio was 44% = 1.44 times). ). The stretching temperature was 120 ° C., and the stretching speed was 100% per minute.

  Such stretching operation was performed on 10 films, and the number of films that could be biaxially stretched without breaking was evaluated.

◎: All 10 sheets could be stretched ○: 8 sheets or more could be stretched △: 5 sheets or more could be stretched ×: Less than 5 sheets could be stretched XX: 1 sheet could not be stretched <Evaluation of flatness>
The flatness (sag) of the film surface produced by the above stretching operation was evaluated by the degree of reflection of the fluorescent lamp.

◎: Fluorescent lamps appear straight and fine irregularities are hardly seen ○: Fluorescent lamps appear straight and very slight irregularities are seen △: Fluorescent lamps appear slightly distorted ×: Fluorescent lamps are considerably distorted <Measurement of in-plane birefringence Ro>
Measured using an automatic birefringence meter KOBRA-21ADH manufactured by Oji Scientific Instruments Co., Ltd. under an environment of 23 ° C. and 55% RH, and the thickness is 80 μm due to the difference in refractive index between the X and Y directions in the plane of each transparent film. The value multiplied by assuming that is expressed as birefringence (nm).

  As is clear from Table 1, in comparative films D1 to D5 using known cellulose esters, a film having flatness that is acceptable as a polarizer protective film is obtained at a draw ratio at which cellulose esters can be stably stretched. You can't do it.

  On the other hand, in the cellulose ester films A2 to A4 having the degree of substitution with cyclohexanecarboxylic acid within the scope of the present invention, it can be seen that both the heat and moisture resistance and the meltability are compatible. Moreover, even if it extended | stretched, it was a film which has a low birefringence value and can be used as a polarizer protective film. On the other hand, the cellulose ester film (A1) having a degree of substitution with an alicyclic carboxylic acid larger than the range of the present invention lacks heat and moisture resistance, and the cellulose ester film (A5) smaller than the range of the present invention increases the melting temperature, It can be seen that the molecular weight of the cellulose ester after film formation is too low, and the film cannot be stretched stably.

  Moreover, when film B1-B4 is compared, melt film forming property also changes with the total substitution degree by an acetic acid and alicyclic carboxylic acid, and it is set as the stable stretchability by setting it as the cellulose ester of the total substitution degree of the range of this invention. It can be seen that a film having excellent flatness and low birefringence can be obtained.

  Cellulose ester films C1 and C2 can also use cycloaliphatic carboxylic acid such as cyclopentane carboxylic acid and tetrahydrofuran-2-carboxylic acid instead of cyclohexane carboxylic acid, and also have excellent melt suitability and moisture and heat resistance. Although an ester film is obtained, it can be seen that a film made of a cellulose ester using cyclohexanecarboxylic acid can obtain an optical film having the lowest low birefringence.

Example 2
Cellulose ester used for melt film formation is fixed to cellulose ester a3 (substitution degree 1.9 with acetic acid, substitution degree 0.7 with cyclohexanecarboxylic acid, molecular weight before film formation 223000), and additives such as plasticizer and ultraviolet absorber The film was formed by changing the thickness. Melting conditions were a barrel temperature of 220 ° C., a screw rotation speed of 100 rpm, and the types of additives are shown in Table 2.

  The abbreviations in Table 2 represent the following compounds.

・ PFR: Asahi Denka Co., Ltd. ADK STAB PFR
-I1010: Irganox 1010 manufactured by Ciba Specialty Chemicals, hindered phenol antioxidant-LP63P: Asahi Denka, hindered amine light stabilizer-T144: Tinuvin 144 manufactured by Ciba Specialty Chemicals, hindered phenol-hindered amine combined antioxidant Agent V7190: Atofina Bicoflex 7190, acid scavenger MBHMB: Aldrich 5,5'-methylenebis (2-hydroxy-4methoxybenzophenone), benzophenone UV absorber The addition amount of each additive is as follows: The plasticizer is 10%, and the antioxidant, acid scavenger, and ultraviolet absorber are all 1.0%.

  The obtained films E1 to E6 were evaluated in the same manner as in Example 1 for molecular weight retention, wet heat resistance, and yellowness. Moreover, the light resistance test was also carried out according to the following method.

<Light resistance evaluation>
The produced cellulose ester film was put into a light resistance evaluation tester manufactured by Suga Corporation for 500 hours, the light transmittance at 380 nm before and after the feeding was measured, and the attenuation rate ΔT (%) was evaluated.

A: Change rate of less than 2% (a level that does not cause a problem as a polarizer protective film)
○: degree of change 2% or more and less than 10% (a level that does not cause a problem as a polarizer protective film)
Δ: degree of change 10% or more and less than 20% (a level that can be managed as a polarizer protective film)
×: Change of 20% or more (problem level as a polarizer protective film)

  When the film A3 of Example 1 and the film E1 of Example 2 are compared, the degradation of the cellulose ester is less when the polyhydric alcohol ester plasticizer is used as the plasticizer, and the resulting film has a higher molecular weight retention. I understand. As a result, a film excellent in stretchability can be obtained by using a polyhydric alcohol ester compound as a plasticizer.

  Moreover, it turns out that molecular weight retention can be raised by adding an antioxidant and an acid scavenger like films E2-E5, and a film can be stretched stably.

  In addition, the film E6 using a benzophenone-based compound as an ultraviolet absorber has low light resistance and its ultraviolet absorption ability is deteriorated by a light resistance test. Therefore, it should be used only for an inner polarizer protective film that is not exposed to external light. It was an optical film.

Example 3
The optical films obtained in Examples 1 and 2 were bonded to both surfaces of a polarizer according to the following procedure to produce a polarizing plate.

<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.

  Examples or Comparative Films A1 to E6 were alkali-treated with a 2.0 M / L-sodium hydroxide aqueous solution at 90 ° C. for 120 seconds, further washed with water and dried to be alkali-treated.

  Polarizers A1 to A1 having protective films formed on both surfaces of the polarizer by bonding the alkali-treated surfaces of Examples or Comparative Films A1 to E6 from both surfaces with a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive. E6 was produced.

(Characteristic evaluation as a liquid crystal display device)
The polarizing plate of 15-type TFT color liquid crystal television LA-1529HM (manufactured by NEC) was peeled off, and each polarizing plate produced above was cut according to the size of the liquid crystal cell. The two polarizing plates prepared as described above were bonded so that the polarizing axes of the polarizing plates were not perpendicular to each other so as to sandwich the liquid crystal cell, so that a 15-inch TFT color liquid crystal display was prepared, and the polarization of the cellulose ester film When the characteristics as a plate were evaluated, the polarizing plates A2 to A4, B1 to B4, C1 to C2, and E1 to E6 of the present invention had high contrast and exhibited 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.

Claims (14)

An optical film formed by melting a composition mainly comprising cellulose ester, wherein the cellulose ester is a cellulose ester substituted with acetic acid and an alicyclic carboxylic acid, and the alicyclic carboxylic acid is substituted. An optical film having a degree of 0.3 to 1.5. 2. The optical film according to claim 1, wherein the total degree of substitution of the cellulose ester (the sum of the degree of substitution by acetic acid and the degree of substitution by alicyclic carboxylic acid) is 2.4 or more and 2.8 or less. The optical film according to claim 1, wherein the alicyclic carboxylic acid is cyclohexane carboxylic acid. The optical film according to any one of claims 1 to 3, wherein the cellulose ester has a weight average molecular weight of 150,000 or more. 5. The optical film according to claim 1, wherein a temperature at which the composition mainly comprising the cellulose ester is melted to form a film is 180 ° C. or higher and 230 ° C. or lower. The optical film according to claim 1, wherein the optical film formed by melting is stretched 1.1 to 2.0 times in at least one direction. The optical film according to any one of claims 1 to 6, wherein the composition contains 5 to 13% by mass of a polyhydric alcohol ester plasticizer. The optical film according to any one of claims 1 to 7, wherein the composition contains 0.1 to 5% by mass of a hindered phenol-based antioxidant. The optical film according to any one of claims 1 to 8, wherein the composition contains 0.1 to 5% by mass of a hindered amine light stabilizer. The optical film according to any one of claims 1 to 9, wherein the composition contains 0.1 to 5% by mass of an epoxy-based acid scavenger. The optical film according to any one of claims 1 to 10, wherein the composition contains 0.1 to 5% by mass of a benzotriazole-based ultraviolet absorber. A polarizing plate using the optical film according to claim 1 as a protective film for a polarizing plate. A liquid crystal display device using the optical film according to claim 1. A liquid crystal display device using the polarizing plate according to claim 12.