JP5206554B2 - Optical film manufacturing method, optical film, and optical film manufacturing apparatus - Google Patents

Description

  The present invention relates to an optical film manufacturing method, an optical film, and an optical film manufacturing apparatus.

  Conventionally, as a method for producing an optical film having optical properties, it is desired that a film-forming process for forming a thin film from a heat-melted thermoplastic resin is followed by a stretching process for stretching the film in the longitudinal direction. There is known a method of forming an optical film having a thickness and optical properties (see, for example, Patent Documents 1 to 3).

  In the above film forming process, generally, a thermoplastic resin extruded into a thin film is cooled by a cast roller or the like to form a long film, or a thermoplastic resin dissolved in a solvent is applied to a belt drum or the like. A solution casting method is used in which the solvent is evaporated after casting and a long film is formed. Among them, the melt casting method can form a film that is less likely to break than the solution casting method, and enables high-speed stretching and further thinning in the stretching step.

  Further, in the stretching process, in general, the film formed in the film forming process is heated between these rollers while being transported by a plurality of rollers so as to go from a roller having a low peripheral speed to a roller having a high peripheral speed. The film is stretched in the transport direction.

Japanese Patent Publication No. 2003-315551 Japanese Patent Publication No. 2008-302581 Patent Publication 2008-296478

However, in the above method, longitudinal wrinkles and distortion in the longitudinal direction may occur in the film as follows.
In the above film forming process, when the thermoplastic resin is extruded into a thin film shape, a pulling force acts on the thermoplastic resin in the width center direction, and a film having thickened both ends is formed (neck-in phenomenon). As a result of the thick film at both ends being transported by a plurality of guide rollers or the like, the transport tension is concentrated on the film thickness portions at both ends, and as a result, the film is pulled toward the center of the width (force to narrow the width of the film). It has been found that since stress acts to generate stress, longitudinal wrinkles in the longitudinal direction and minute strains that cannot be visually confirmed occur.

  Further, when the film is stretched in the transport direction in the stretching process, the above vertical wrinkles and distortion are emphasized. In particular, when the film is further stretched to a thin film or stretched at a high speed, minute vertical wrinkles and distortion are likely to occur.

  Although the above vertical wrinkles and distortions are hardly observed visually, they affect the optical properties when used as an optical film, especially for protective films such as liquid crystals, for optical phase difference compensation or for field expansion, etc. It has been found that the production of these optical films has a non-negligible effect on these functions and performance.

  The present invention has been made in view of the above circumstances, and it is an object to provide an optical film manufacturing method, an optical film manufacturing apparatus, and an optical film thereby capable of suppressing the occurrence of longitudinal wrinkles and distortion in the longitudinal direction. To do.

According to a first aspect of the present invention, in a method for producing an optical film comprising a film forming step of forming a thin film from a thermoplastic resin, and a stretching step of stretching the formed film in the longitudinal direction,
After the film forming step and before the stretching step,
A temperature T satisfying the following formula (1) at least a part of the film within a range of 10% of the total width from both ends in the width direction of the film and having an average film thickness equal to or less than the average film thickness of the range. It is characterized by comprising a heating step of heating to.
80 ≦ T ≦ Tg + 50 [° C.] (1)
(However, Tg: Glass transition temperature of the thermoplastic resin [° C.])

In this optical film manufacturing method,
After the heating step and before the stretching step,
It is preferable to include a cutting step of cutting and removing at least a part of the film portion heated in the heating step in the longitudinal direction of the film.

Moreover, in the manufacturing method of this optical film,
The thermoplastic resin is preferably cellulose acylate.

According to the second aspect of the present invention, in the optical film,
It is manufactured by the method for manufacturing an optical film of the present invention.

According to a third aspect of the present invention, in an optical film manufacturing apparatus comprising: a film forming means for forming a thin film from a thermoplastic resin; and a stretching means for extending the formed film in the longitudinal direction.
With respect to the film after being formed by the film forming means and before being stretched by the stretching means, it is within the range of 10% of the total width from both ends in the width direction of the film, and the average of the range A heating means for heating at least a part of the film portion having a film thickness equal to or less than the film thickness to a temperature T satisfying the following expression (1) is provided.
80 ≦ T ≦ Tg + 50 [° C.] (1)
(However, Tg: Glass transition temperature of the thermoplastic resin [° C.])

According to the present invention, since the film before being stretched in the longitudinal direction is heated at least partially within a predetermined range from both ends in the width direction of the film, longitudinal wrinkles and distortion in the longitudinal direction are emphasized by stretching. Before being applied, the portion where the conveying tension stronger than the inner side in the width direction is thermally deformed can effectively relieve the stress that causes vertical wrinkles and distortion.
At this time, it is only necessary to heat at least a part within a range of 10% of the total width from both ends in the width direction of the film, and it is not necessary to heat the entire film. It does not cause stretching or changes in optical properties, or cause vertical wrinkles or distortion on the inner side of the film outside the above range, thereby reducing the effective width of the finished optical film.
Further, since at least a part of the film part having a film thickness equal to or less than the average film thickness in the above range is heated, that is, the endmost part of the film which is formed to be the thickest and to which the transport tension acts most strongly is not heated. Thereby, the fracture | rupture of the said film by the said outermost part being heated and a film extending | stretching partially can be prevented.
In addition, since at least a part of the film portion is heated to a temperature T that satisfies 80 ≦ T ≦ Tg + 50 [° C.] (Tg: glass transition temperature of the thermoplastic resin [° C.]), it is sufficient to prevent melting of the heated portion. It is possible to reliably relieve stress that causes vertical wrinkles and distortion.
As described above, the occurrence of longitudinal wrinkles and distortion in the longitudinal direction can be suppressed.

It is a whole block diagram of the manufacturing apparatus of the optical film which concerns on this invention. 1 is an overall configuration diagram of a longitudinal stretching machine. It is a graph which shows the film thickness distribution of a film. It is a graph for demonstrating the film part heated at a heating process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[1 Optical film manufacturing equipment]
First, an optical film manufacturing apparatus (hereinafter referred to as manufacturing apparatus) 1 according to the present invention will be described.
FIG. 1 is an overall configuration diagram of the manufacturing apparatus 1, and FIG. 2 is an overall configuration diagram of a longitudinal stretching machine 4 to be described later.

  The manufacturing apparatus 1 is an apparatus that forms an optical film M having optical characteristics from a thermoplastic resin R. In the present embodiment, the manufacturing apparatus 1 forms an optical film M as a protective film used for a polarizing plate of a liquid crystal display device. is there.

  Specifically, as shown in FIG. 1, the manufacturing apparatus 1 includes a film forming unit 2 that forms a thin film F from a thermoplastic resin R, a heating unit 3 that heats the formed film F, and a molding. A longitudinal stretching machine 4 that stretches the heated film F in the longitudinal direction and a winding unit 5 that winds up the film F that has been stretched to become the optical film M are provided.

  Among these, the film forming section 2 includes a uniaxial extruder 21 that melts and extrudes the thermoplastic resin R at a predetermined temperature, a gear pump 22 that sends out the extruded thermoplastic resin R, and the thermoplastic resin R that is sent out. Filter 23 for filtering, T die 24 for extruding molten thermoplastic resin R from a slit having a predetermined shape to form a thin film, and elasticity for feeding thin film thermoplastic resin R extruded from T die 24 while cooling A touch roller 25 and a cast roller 26 and take-up rollers 27 and 27 for feeding the thermoplastic resin R while further cooling are provided. In the film forming section 2, the thermoplastic resin R is cooled and solidified into a thin film shape and formed as a film F by these configurations.

  The heating unit 3 includes an inline film thickness meter 31 that measures the thickness of the film F formed by the film forming unit 2, a heat gun 32 that heats the film F, and an end of the film F in the width direction. A rotary cutter 33 that removes the film F, a feed roller 34 that feeds the film F whose end is cut off, and a plurality of guide rollers 35 that are driven rollers that support the film F at each part.

Here, the heat gun 32 is an industrial dryer that heats the film F with hot air. Although not shown, one heat gun 32 is provided near each end of the film F in the width direction. In addition, the heat gun 32 has at least a part of the film portion within the range of 10% of the entire width from both ends in the width direction of the film F and having a film thickness equal to or less than the average film thickness in the range (1 It can be heated to a temperature T that satisfies the equation (1).
80 ≦ T ≦ Tg + 50 [° C.] (1)
However, Tg is the glass transition temperature [° C.] of the thermoplastic resin R.

  As shown in FIG. 2, the longitudinal stretching machine 4 is formed between a first roller to a ninth roller 41 to 49, and a sixth roller 46 and a seventh roller 47, in which the film F can be stretched in this order. An IR (Infrared Rays) heater 40 that heats the film F stretched between the guide roller 35 and a guide roller 35 that supports the film F entering the first roller 41 and the film F exiting the ninth roller 49, respectively. Yes. Among these, the first to ninth rollers 41 to 49 are configured to be able to heat the temperature of the peripheral surface so that the temperature of the stretched film F can be changed, and can be driven at independent rotation speeds. It is configured to be variable.

  As shown in FIG. 1, a guide roller 35 that supports a film F that has been stretched to a predetermined thickness by a longitudinal stretching machine 4 to become an optical film M and is sent from the guide roller 35 to the winding unit 5. A winder 51 for winding the optical film M is provided.

  The manufacturing apparatus 1 further includes a control unit (not shown). The control unit controls the rotational speed of various rollers, the temperature of each unit, and the like. An output adjustment is performed.

[2 Thermoplastic resin]
Then, the thermoplastic resin R which is a material of the optical film M (film F) is demonstrated.
The thermoplastic resin R is cellulose acylate in the present embodiment.

[2.1 Cellulose acylate]
Cellulose acylate is suitably used as the thermoplastic resin R for producing the optical film M because of its excellent optical properties and moldability.
The cellulose as the cellulose acylate raw material is not particularly limited, and examples thereof include cotton linter, wood pulp, and kefna. Moreover, you may mix and use the raw material cellulose obtained from these in arbitrary ratios. The cellulose acylate is preferably a cellulose acylate having an acetyl group or an acyl group having 3 to 22 carbon atoms. Examples of the acyl group having 3 to 22 carbon atoms, propionyl _{(C 2 H 5 CO -)} , n- butyryl (C ₃ H ₇ CO-), isobutyryl, valeryl (C ₄ H ₉ CO-), isovaleryl, Includes sec-valeryl, tert-valeryl, octanoyl, dodecanoyl, octadecanoyl and oleoloyl. Propionyl and butyryl are preferred. As the cellulose acylate, cellulose acetate is preferable, and cellulose triacetate is particularly preferable. When the acylating agent for the acyl group is an acid anhydride or acid chloride, an organic acid (eg, acetic acid) or methylene chloride is used as the organic solvent as the reaction solvent. In the cellulose acylate, the substitution degree of the hydroxyl group of cellulose is preferably 2.6 to 3.0. The degree of polymerization (average viscosity) of cellulose acylate is preferably 200 to 700, and particularly preferably 250 to 550. These cellulose acylates are marketed by Daicel Chemical Industries, Ltd., Courtles, Hoechst, and Eastman Kodak. Photographic grade cellulose acylate is preferably used. The water content of cellulose acylate is preferably 2% by mass or less.

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with acetic acid or other acids. The degree of acyl substitution means the proportion of cellulose esterified at each of the 2-position, 3-position and 6-position (100% esterification is 1.00).

  The cellulose acylate used in the present embodiment is a cellulose acylate having a total acyl substitution degree of 2-position and 3-position of 1.70 to 1.95 and an acyl substitution degree of 6-position of 0.88 or more. It is obtained by blending cellulose acylate having a total acyl substitution degree at the 2-position and the 3-position of 1.70 to 1.95 and an acyl substitution degree at the 6-position of less than 0.88. When the total of the 2- and 3-position acyl substitutions is 1.70 or less, the film is likely to absorb moisture and is susceptible to hydrolysis, so the durability of the film is lowered. In addition, the dimensional change due to humidity or the like becomes large. On the other hand, if it exceeds 1.95, the organicity of cellulose acylate increases, so the affinity with the solvent increases and the viscosity of the dope increases. Accordingly, the total of the 2- and 3-position acyl substitutions is preferably 1.70 to 1.95, and more preferably 1.75 to 1.88.

  By the way, since the hydroxyl group at the 6-position is a primary hydroxyl group, unlike the hydroxyl groups at the 2- and 3-positions, it has been found that hydrogen bonding of the hydroxyl group is extremely likely to occur. Therefore, by setting the acyl substitution degree at the 6-position to 0.88 or more, the solubility in a solvent is remarkably improved, and it is possible to obtain a dope that is preferable in terms of casting suitability. The range of the degree of acyl substitution at the 6-position is preferably from 0.88 to 0.99, more preferably from 0.89 to 0.98 in view of synthesis suitability and the like. However, when the degree of acyl substitution at the 6-position is improved, there is a problem that the film strength is lowered, and it is difficult to achieve both. On the other hand, if the acyl substitution degree is less than 0.88, the solubility in a solvent is remarkably lowered, which is not preferable.

  Furthermore, the film F made of cellulose acylate having a total acyl substitution degree of 2-position and 3-position of 1.70 to 1.95 and an acyl substitution degree of 6-position of 0.88 or more, or 2-position, In the optical film M in which a thin film is formed on a film F made of cellulose acylate having a total 3-position acyl substitution degree of 1.70 to 1.95 and a 6-position acyl substitution degree of less than 0.88, Deterioration of flatness such as wrinkles and dents is likely to occur during storage in a roll state, and further, there is a problem that the formed metal oxide layer is liable to crack and uneven film thickness is likely to occur.

  It has been found that these problems can be solved by blending cellulose acylate. In addition, cellulose acylate having an acyl substitution degree at the 6-position of 0.88 or more desirably has a smaller number of carbon atoms in the acyl substituent from the viewpoint of film strength, and is preferably all acetyl groups. In JP-A-11-5851, the total of acetyl substituents at the 2nd, 3rd and 6th positions is 2.67 or more, and the total of the acetyl substituents at the 2nd and 3rd positions is 1.97 or less. Although cellulose acetate is described, the range in which the sum of the 2nd and 3rd positions exceeds 1.90 describes the preferred range from the optical suitability of the optical film. The range described is more preferable.

  The basic principle of the method for synthesizing cellulose acylate is described in Wood Chemistry, pages 180-190 (Umeda et al., Kyoritsu Shuppan, 1968). A typical synthesis method is a liquid phase acetylation method using an acetic anhydride-acetic acid-sulfuric acid catalyst. Specifically, a cellulose raw material such as wood pulp is pretreated with an appropriate amount of an organic acid, and then it is esterified by adding it to a pre-cooled acylated mixture to complete cellulose acylate (2nd, 3rd and 6th positions). The total degree of acyl substitution is approximately 3.00). The acylated mixed solution generally contains an organic acid as a solvent, an anhydrous organic acid as an esterifying agent, and sulfuric acid as a catalyst. The organic anhydride is usually used in a stoichiometric excess over the sum of the cellulose that reacts with it and the water present in the system. After completion of the acylation reaction, a neutralizing agent (for example, calcium, magnesium, iron, aluminum or zinc) is used for hydrolysis of excess organic anhydride remaining in the system and neutralization of a part of the esterification catalyst. Of carbonate, acetate or oxide). Next, the obtained complete cellulose acylate is saponified and aged by keeping it at 50 to 90 ° C. in the presence of a small amount of acetylation reaction catalyst (generally, remaining sulfuric acid), and the desired acyl substitution degree and The cellulose acylate having a polymerization degree is changed. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized with the neutralizing agent as described above, or water or dilute sulfuric acid without neutralization. A cellulose acylate solution is introduced into the cellulose acylate solution (or water or dilute sulfuric acid is introduced into the cellulose acylate solution) to separate the cellulose acylate, and the cellulose acylate is obtained by washing and stabilizing treatment.

  In an ordinary cellulose acylate synthesis method, the acyl substitution degree at the 2-position or the 3-position is higher than the acyl substitution degree at the 6-position. Therefore, in order to make the total acyl substitution degree at the 2nd and 3rd positions 1.95 or less and the acyl substitution degree at the 6th position 0.88 or more, the above reaction conditions need to be specifically adjusted. . As specific reaction conditions, it is preferable to reduce the amount of the sulfuric acid catalyst and lengthen the time of the acylation reaction. When the amount of the sulfuric acid catalyst is large, the acylation reaction proceeds faster, but a sulfuric ester is formed between the cellulose and the cellulose according to the amount of the catalyst, and is released at the end of the reaction to form a residual hydroxyl group. Sulfate esters are more produced at the 6-position, which is highly reactive. Therefore, when there is much sulfuric acid catalyst, the acyl substitution degree of 6-position will become small. Therefore, in order to synthesize the cellulose acylate used in this embodiment, it is necessary to extend the reaction time in order to reduce the amount of the sulfuric acid catalyst as much as possible and compensate for the reduced reaction rate.

[2.2 Plasticizer]
Examples of the plasticizer added to the thermoplastic resin R of the present embodiment include the following plasticizers.
An ester plasticizer comprising a polyhydric alcohol and a monovalent carboxylic acid, and an ester plasticizer comprising a polyvalent carboxylic acid and a monohydric alcohol are preferred because of their high affinity with the cellulose ester.

  An ethylene glycol ester plasticizer that is one of polyhydric alcohol esters: specifically, ethylene glycol alkyl ester plasticizers such as ethylene glycol diacetate and ethylene glycol dibutyrate, ethylene glycol dicyclopropylcarboxylate And ethylene glycol cycloalkyl ester plasticizers such as ethylene glycol dicyclohexylcarboxylate, and ethylene glycol aryl ester plasticizers such as ethylene glycol dibenzoate and ethylene glycol di4-methylbenzoate. These alkylate groups, cycloalkylate groups, and arylate groups may be the same or different, and may be further substituted. Further, it may be a mix of alkylate group, cycloalkylate group and arylate group, and these substituents may be covalently bonded. Further, the ethylene glycol part may be substituted, and the ethylene glycol ester partial structure may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber, etc. It may be introduced into a part of the molecular structure of the additive.

  Glycerin ester plasticizer that is one of polyhydric alcohol esters: Specifically, glycerol alkyl esters such as triacetin, tributyrin, glycerol diacetate caprylate, glycerol oleate propionate, glycerol tricyclopropylcarboxylate, glycerol Glycerin cycloalkyl esters such as tricyclohexylcarboxylate, glycerol aryl esters such as glycerol tribenzoate and glycerol 4-methylbenzoate, diglycerol tetraacetylate, diglycerol tetrapropionate, diglycerol acetate tricaprylate, diglycerol tetralaur Diglycerin alkyl ester such as rate, diglycerin tetracyclobutylcarboxylate, diglycerin tetracyclo Diglycerol cycloalkyl esters such as emissions chill carboxylate, diglycerin tetrabenzoate, diglycerin aryl ester such as diglycerin 3-methylbenzoate or the like. These alkylate groups, cycloalkylcarboxylate groups, and arylate groups may be the same or different, and may be further substituted. Further, it may be a mixture of alkylate group, cycloalkylcarboxylate group, and arylate group, and these substituents may be bonded by a covalent bond. Furthermore, the glycerin and diglycerin part may be substituted, the partial structure of the glycerin ester and the diglycerin ester may be part of the polymer or regularly pendant, and the antioxidant, acid scavenger, You may introduce | transduce into a part of molecular structure of additives, such as a ultraviolet absorber.

  Specific examples of the other polyhydric alcohol ester plasticizer include polyhydric alcohol ester plasticizers described in paragraphs [0030] to [0033] of JP-A-2003-12823. The alkylate group, cycloalkylcarboxylate group, and arylate group contained therein may be the same or different, and may be further substituted. Further, it may be a mixture of alkylate group, cycloalkylcarboxylate group, and arylate group, and these substituents may be bonded by a covalent bond. Furthermore, the polyhydric alcohol part may be substituted, and the partial structure of the polyhydric alcohol may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber. May be introduced into a part of the molecular structure of the additive.

  Among the ester plasticizers composed of the polyhydric alcohol and the monovalent carboxylic acid, alkyl polyhydric alcohol aryl esters are preferred. Specifically, the above-mentioned ethylene glycol dibenzoate, glycerin tribenzoate, diglycerin tetrabenzoate, Exemplified compound 16 described in paragraph 32 of Kokai 2003-12823 can be mentioned.

  Dicarboxylic acid ester plasticizer that is one of polyvalent carboxylic acid esters: Specifically, alkyl dicarboxylic acid alkyl such as didodecyl malonate (C1), dioctyl adipate (C4), dibutyl sebacate (C8), etc. Ester plasticizers, 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, Cycloalkyl dicarboxylic acid alkyl ester plasticizers such as dihexyl-1,4-cyclohexanedicarboxylate and didecylbicyclo [2.2.1] heptane-2,3-dicarboxylate, dicyclohexyl-1,2-cyclobutane Dicarbo Cycloalkyl dicarboxylic acid cycloalkyl ester plasticizers such as sylate and dicyclopropyl-1,2-cyclohexyl dicarboxylate, diphenyl-1,1-cyclopropyl dicarboxylate, di2-naphthyl-1,4-cyclohexane Cycloalkyldicarboxylic acid aryl ester plasticizers such as dicarboxylate, aryl dicarboxylic acid alkyl ester plasticizers such as diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, and di-2-ethylhexyl phthalate, dicyclopropyl phthalate Aryl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclohexyl phthalate, and aryl dicarboxylic acid aryl esters such as diphenyl phthalate and di 4-methylphenyl phthalate. Ether-based plasticizers. These alkoxy groups and cycloalkoxy groups may be the same or different, may be mono-substituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, and these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. Also, the partial structure of phthalate ester may be part of the polymer or regularly pendant to the polymer, and it may be part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. It may be introduced.

  Examples of other polycarboxylic acid ester plasticizers include alkyl polycarboxylic acid alkyl esters such as tridodecyl tricarbarate and tributyl-meso-butane-1,2,3,4-tetracarboxylate. Plasticizers, alkylpolycarboxylic acid cycloalkyl ester plasticizers such as tricyclohexyltricarbarate, tricyclopropyl-2-hydroxy-1,2,3-propanetricarboxylate, triphenyl 2-hydroxy- Alkyl polyvalent carboxylic acid aryl ester plasticizers such as 1,2,3-propanetricarboxylate, tetra-3-methylphenyltetrahydrofuran-2,3,4,5-tetracarboxylate, tetrahexyl-1,2, 3,4-cyclobutanetetracarboxylate, tetrabu Cycloalkyl polycarboxylic acid alkyl ester plasticizers such as ru-1,2,3,4-cyclopentanetetracarboxylate, tetracyclopropyl-1,2,3,4-cyclobutanetetracarboxylate, tricyclohexyl- Cycloalkyl polycarboxylic acid cycloalkyl ester plasticizers such as 1,3,5-cyclohexyl tricarboxylate, triphenyl-1,3,5-cyclohexyl tricarboxylate, hexa-4-methylphenyl-1,2, Cycloalkyl polycarboxylic acid aryl ester plasticizers such as 3,4,5,6-cyclohexylhexacarboxylate, tridodecylbenzene-1,2,4-tricarboxylate, tetraoctylbenzene-1,2,4 , 5-tetracarboxylate and other aryl polyvalent Rubinoic acid alkyl ester plasticizers, tricyclopentylbenzene-1,3,5-tricarboxylate, tetracyclohexylbenzene-1,2,3,5-tetracarboxylate and other aryl polyvalent carboxylic acid cycloalkyl esters Plasticizers of aryl polyvalent carboxylic acid aryl esters such as triphenylbenzene-1,3,5-tetracartoxylate and hexa-4-methylphenylbenzene-1,2,3,4,5,6-hexacarboxylate A plasticizer is mentioned. These alkoxy groups and cycloalkoxy groups may be the same or different, and may be mono-substituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, and these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. Also, the partial structure of phthalate ester may be part of the polymer or regularly pendant into the polymer, and introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, UV absorbers, etc. May be.

  Among the ester plasticizers composed of the polyvalent carboxylic acid and the monohydric alcohol, dialkyl carboxylic acid alkyl esters are preferable, and specific examples include the dioctyl adipate and tridecyl tricarbalate.

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

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

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

  Next, the carbohydrate ester plasticizer will be described. The carbohydrate means a monosaccharide, disaccharide or trisaccharide in which the saccharide is present in the form of pyranose or furanose (6-membered ring or 5-membered ring). Non-limiting examples of carbohydrates include glucose, saccharose, lactose, cellobiose, mannose, xylose, ribose, galactose, arabinose, fructose, sorbose, cellotriose and raffinose. The carbohydrate ester refers to an ester compound formed by dehydration condensation of a carbohydrate hydroxyl group and a carboxylic acid, and specifically means an aliphatic carboxylic acid ester or an aromatic carboxylic acid ester of a carbohydrate. Examples of the aliphatic carboxylic acid include acetic acid and propionic acid, and examples of the aromatic carboxylic acid include benzoic acid, toluic acid, and anisic acid. Carbohydrates have a number of hydroxyl groups depending on the type, but even if a part of the hydroxyl group reacts with the carboxylic acid to form an ester compound, the whole hydroxyl group reacts with the carboxylic acid to form an ester compound. Also good. In this embodiment, it is preferable that all of the hydroxyl groups react with the carboxylic acid to form an ester compound.

  Specific examples of the carbohydrate ester plasticizer include glucose pentaacetate, glucose pentapropionate, glucose pentabtylate, saccharose octaacetate, saccharose octabenzoate, and of these, saccharose octaacetate is more preferable. preferable.

  Polymer plasticizer: Specifically, aliphatic hydrocarbon polymer, alicyclic hydrocarbon polymer, polyethyl acrylate, polymethyl methacrylate, copolymer of methyl methacrylate and 2-hydroxyethyl methacrylate (For example, an arbitrary ratio between copolymer ratios 1:99 to 99: 1), vinyl polymers such as polyvinyl isobutyl ether, poly N-vinyl pyrrolidone, polystyrene, poly 4-hydroxystyrene, etc. Examples thereof include styrene-based polymers, polybutylene succinates, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyethers such as polyethylene oxide and polypropylene oxide, polyamides, polyurethanes, and polyureas. 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 arises in volatility, and if it exceeds 500000, the plasticizing ability is lowered, and the mechanical properties of the cellulose ester film 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.

  In addition, since the cellulose acylate in this embodiment will affect as an optical use when it colors, preferably yellowness (yellow index, YI) is 3.0 or less, More preferably, it is 1.0 or less. Yellowness can be measured based on JIS-K7103.

  It is preferable that the plasticizer removes impurities such as residual acids, inorganic salts, organic low molecules, etc. that are carried over from the time of manufacture or generated during storage, and more preferably has a purity of 99% or more. is there. The residual acid and water are preferably from 0.01 to 100 ppm, and when melt-forming the cellulose resin, thermal deterioration can be suppressed, and film-forming stability, optical properties of the film F, and mechanical properties are improved. To do.

[2.3 Antioxidant]
In the cellulose acylate of this embodiment, an antioxidant is used as a stabilizer because cellulose ester is decomposed not only by heat but also by oxygen in a high temperature environment where melt film formation is performed. Is preferred.
The antioxidant useful in the present embodiment can be used without limitation as long as it is a compound that suppresses deterioration of the melt-molded material due to oxygen. Among them, as the useful antioxidant, phenolic compounds, hindered amine compounds , Phosphorus compounds, sulfur compounds, heat-resistant processing stabilizers, oxygen scavengers and the like. Among these, phenol compounds, hindered amine compounds, phosphorus compounds, and lactone compounds are particularly preferable.

The hindered amine compound (HALS) is described, for example, in columns 5 to 11 of US Pat. No. 4,619,956 and columns 3 to 5 of US Pat. No. 4,839,405. Thus, 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds are preferred. As a commercial item, LA52 (made by Asahi Denka Co., Ltd.) can be mentioned.
As the lactone compound, compounds described in JP-A-7-233160 and JP-A-7-247278 are preferable.

  These stabilizers can be used singly or in combination of two or more, and the blending amount thereof is appropriately selected within the range not impairing the purpose of the present embodiment, but is usually based on 100 parts by mass of the cellulose ester. 0.001 to 10.0 parts by mass, preferably 0.01 to 5.0 parts by mass, and more preferably 0.1 to 3.0 parts by mass.

By blending these compounds, it is possible to prevent coloration or strength reduction of the molded product due to heat or thermal oxidation deterioration during melt molding without reducing transparency, heat resistance, and the like.
The addition amount of the antioxidant is usually 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the cellulose ester.

[2.4 Acid Scavenger]
The acid scavenger is an agent that plays a role of trapping an acid (protonic acid) remaining in the cellulose ester brought in from the production. Further, when the cellulose ester is melted, the hydrolysis of the side chain is promoted by moisture and heat in the polymer, and if it is CAP, acetic acid and propionic acid are generated. A compound having an epoxy structure, a tertiary amine, an ether structure, or the like may be used as long as it can be chemically bonded to an acid, but is not limited thereto.

  Specifically, it is preferable to comprise an epoxy compound as an acid scavenger described in US Pat. No. 4,137,201. Epoxy compounds as such acid scavengers are known in the art and are derived by condensation of diglycidyl ethers of various polyglycols, particularly about 8-40 moles of ethylene oxide per mole of polyglycol. Metal glycol compounds such as polyglycols, diglycidyl ethers of glycerol (eg, those conventionally used in and together with vinyl chloride polymer compositions), epoxidized ether condensation products, bisphenol A Diglycidyl ether (ie, 4,4'-dihydroxydiphenyldimethylmethane), epoxidized unsaturated fatty acid ester (especially an ester of an alkyl of about 2 to 2 carbon atoms of a fatty acid of 2 to 22 carbon atoms (e.g. Butyl epoxy stearate ), And various epoxidized long chain fatty acid triglycerides and the like (e.g., epoxidized vegetable oils and other unsaturated natural oils, which may be represented and exemplified by compositions such as epoxidized soybean oil, sometimes epoxidized natural) These are referred to as glycerides or unsaturated fatty acids, which generally contain 12 to 22 carbon atoms)).

[2.5 UV absorber]
As an ultraviolet absorber, from the viewpoint of preventing deterioration of a polarizer or 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, absorption of visible light having a wavelength of 400 nm or more is absorbed. Less is preferred.
For example, salicylic acid ultraviolet absorbers (phenyl salicylate, p-tert-butyl salicylate, etc.) or benzophenone ultraviolet absorbers (2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, etc.), Benzotriazole UV absorber (2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′, 5′-di) -Tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-3'-dodecyl- 5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-te t-butyl-5 '-(2-octyloxycarbonylethyl) -phenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3'-(1-methyl-1-phenylethyl) -5'- (1,1,3,3-tetramethylbutyl) -phenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di- (1-methyl-1-phenylethyl) -phenyl) benzotriazole ), Cyanoacrylate ultraviolet absorbers (2′-ethylhexyl-2-cyano-3,3-diphenyl acrylate, ethyl-2-cyano-3- (3 ′, 4′-methylenedioxyphenyl) -acrylate, etc.) , Triazine-based ultraviolet absorbers, or compounds described in JP-A Nos. 58-185777 and 59-149350, nickel complex compounds, inorganic powders And the like.

  As the UV absorber of this embodiment, a benzotriazole UV absorber and a triazine UV absorber that are highly transparent and excellent in preventing the deterioration of the polarizing plate and the liquid crystal element are preferable, and the spectral absorption spectrum is more appropriate. Benzotriazole ultraviolet absorbers are particularly preferred.

  The conventionally known benzotriazole-based ultraviolet absorber particularly preferably used together with the ultraviolet absorber of this embodiment may be bisified, for example, 6,6′-methylenebis (2- (2H-benzo [d ] [1,2,3] triazol-2-yl))-4- (2,4,4-trimethylpentan-2-yl) phenol, 6,6'-methylenebis (2- (2H-benzo [d] And [1,2,3] triazol-2-yl))-4- (2-hydroxyethyl) phenol.

  Moreover, in this embodiment, it can also be used in combination with a conventionally well-known ultraviolet absorbing polymer. Although it does not specifically limit as a conventionally well-known ultraviolet absorbing polymer, For example, the polymer which homopolymerized RUVA-93 (made by Otsuka Chemical Co., Ltd.), the polymer which copolymerized RUVA-93, and another monomer, etc. are mentioned. It is done. Specific examples include PUVA-30M obtained by copolymerization of RUVA-93 and methyl methacrylate at a ratio (mass ratio) of 3: 7, and PUVA-50M obtained by copolymerization at a ratio of 5: 5 (mass ratio). It is done. Furthermore, the polymer etc. which are described in Unexamined-Japanese-Patent No. 2003-113317 are mentioned.

  Moreover, as a commercial item, TINUVIN 109, TINUVIN 171, TINUVIN 360, TINUVIN 900, TINUVIN 900, TINUVIN 928 (all manufactured by Ciba Specialty Chemicals), LA-31 (Manufactured by Asahi Denka Co., Ltd.) and RUVA-100 (manufactured by Otsuka Chemical Co., Ltd.) 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-benzoylphenylmethane) and the like, but are not limited thereto.

  In this embodiment, it is preferable to add 0.1-20 mass% of ultraviolet absorbers, it is preferable to add 0.5-10 mass% further, and it is preferable to add 1-5 mass% further. Two or more of these may be used in combination.

[2.6 Viscosity reducing agent]
In the present embodiment, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity. The hydrogen bonding solvent is J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” between a hydrogen atom covalently bonded to an electronegative atom, ie, a bond having a large bond moment and containing hydrogen, such as O—H (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), and organic solvent that can arrange adjacent molecules by including F—H (fluorine hydrogen bond). These have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin, and in the melt casting method performed in this embodiment, from the glass transition temperature of the cellulose resin alone used. However, it is possible to lower the melting temperature of the cellulose resin composition by adding a hydrogen bonding solvent, or to lower the melt viscosity of the cellulose resin composition containing the hydrogen bonding solvent than the cellulose resin at the same melting temperature. it can.

  Examples of the hydrogen bonding solvent include alcohols: for example, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, t-butanol, 2-ethylhexanol, heptanol, octanol, nonanol, dodecanol, ethylene glycol, Propylene glycol, hexylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, hexyl cellosolve, glycerin, etc., ketones: acetone, methyl ethyl ketone, etc., carboxylic acids: eg formic acid, acetic acid, propionic acid, Butyric acid, etc., ethers: eg, diethyl ether, tetrahydrofuran, dioxane, etc., Pyrrolidones: eg, N-methyl Pyrrolidone, etc., amines: for example, can be exemplified trimethylamine, pyridine, etc., and the like. These hydrogen bonding solvents can be used alone or in admixture of two or more. Among these, alcohol, ketone, and ether are preferable, and methanol, ethanol, propanol, isopropanol, octanol, dodecanol, ethylene glycol, glycerin, acetone, and tetrahydrofuran are particularly preferable. Furthermore, water-soluble solvents such as methanol, ethanol, propanol, isopropanol, ethylene glycol, glycerin, acetone, and tetrahydrofuran are particularly preferable. Here, water-soluble means that the solubility in 100 g of water is 10 g or more.

[2.7 Retardation control agent]
In the film F of this embodiment, an alignment film may be formed to provide a liquid crystal layer, and polarizing plate processing may be performed in which the film F and retardation derived from the liquid crystal layer are combined to provide optical compensation ability. As the compound to be added for controlling the retardation, an aromatic compound having two or more aromatic rings as described in EP 911,656A2 can be used as a retardation control agent. . Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. An aromatic heterocyclic ring is particularly preferred, and the aromatic heterocyclic ring is generally an unsaturated heterocyclic ring. Of these, compounds having a 1,3,5-triazine ring are particularly preferred.

[2.8 Matting Agent]
To the cellulose acylate of this embodiment, fine particles such as a matting agent can be added in order to impart slipperiness, and examples of the fine particles include inorganic compound fine particles and organic compound fine particles. The matting agent is preferably as fine as possible. Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include inorganic fine particles such as magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because the haze of the film F can be lowered. In many cases, fine particles such as silicon dioxide are surface-treated with an organic material, but such particles are preferable because the haze of the film F can be reduced.

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

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

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

[2.9 Polymer material]
In the cellulose acylate of the present embodiment, a polymer material other than cellulose ester or an oligomer may be appropriately selected and mixed. The polymer materials and oligomers described above are preferably those having excellent compatibility with the cellulose ester, and the transmittance when formed into a film F is 80% or more, more preferably 90% or more, more preferably 92% or more. . The purpose of mixing at least one of polymer materials and oligomers other than cellulose ester includes meaning to be performed in order to improve viscosity control at the time of heating and melting and film physical properties after film formation.

[3 Optical Film Manufacturing Method]
Then, the manufacturing method of the optical film M which concerns on this invention is demonstrated.

First, a thin film F is formed from the thermoplastic resin R in the film forming section 2 (film forming process).
In the film forming process of the present embodiment, the film F is formed using a melt casting method. Specifically, first, the pellet-shaped thermoplastic resin R is melted by the single screw extruder 21. Then, the molten thermoplastic resin R is sent out by the gear pump 22 and is extruded from the slit of the T die 24 through the filter 23 to be formed into a thin film. The thin film-like thermoplastic resin R is extruded between the elastic touch roller 25 and the cast roller 26 at a predetermined temperature to be sent to the take-up rollers 27 and 27 while being cooled, and further heated by the take-up rollers 27 and 27 while being cooled. Send to part 3. Thus, the film F is formed by cooling and solidifying the thermoplastic resin R into a thin film.

Next, the formed film F is heated by the heating unit 3 (heating step).
In this heating step, first, the film thickness of the film F is measured by the in-line film thickness meter 31. Thereby, for example, as shown in FIG. 3, the film thickness in which both ends in the width direction are formed thicker than the inside is measured. Note that the film thickness at both ends in the width direction is increased in this way because a force pulling the thermoplastic resin R toward the center of the width acts when the thermoplastic resin R is pushed out from the slit of the T die 24. This is due to the so-called neck-in phenomenon.

  Then, the film F whose film thickness is measured is heated with the heat gun 32. At this time, as shown in FIG. 4, an average film thickness t in a range of 10% of the width from the width direction both ends of the film F is calculated by a control unit (not shown) based on the film thickness measurement result. The heat gun 32 is set so as to heat at least a part of the film portion H within the range and having a film thickness equal to or less than the average film thickness t. At the same time, the output of the heat gun 32 is adjusted so that the temperature T of at least a part of the heated film portion H becomes 80 ≦ T ≦ Tg + 50 [° C.] (Tg: glass transition temperature of the thermoplastic resin [° C.]). The

  This heating is for relaxing the stress generated at both ends of the film F by thermal deformation. More specifically, as a result of the concentration of the conveyance tension at the ends of the film F formed by the above-mentioned neck-in phenomenon at the time of conveyance by a plurality of rollers, the force (T A force that reduces the width of the film F acts to generate stress. The above heating is for relieving this stress. As a result, it is possible to suppress the occurrence of longitudinal wrinkles in the longitudinal direction (conveying direction) due to this stress and minute distortions that cannot be visually confirmed. This effect acts more remarkably in the process of transporting the unstretched film F for a long time due to the above-mentioned stress generation factors.

  In addition, this heating can be effectively suppressed from occurrence of the above-mentioned vertical wrinkles and distortions by performing it before the stretching process described later. This is because vertical wrinkles and distortion are emphasized by stretching in the longitudinal direction of the film F in the stretching step. Furthermore, this heating is desirably performed immediately after the thermoplastic resin R is cooled and solidified by the elastic touch roller 25, the cast roller 26, and the take-up rollers 27 and 27.

  Moreover, the temperature T of the film F by this heating is less than 80 degreeC, there is little thermal deformation of the film F, the effect which relieve | moderates stress is insufficient, and when higher than Tg + 50 degreeC, the heating location of the film F May melt and the film F may adhere to the roller or break in the transport direction. Therefore, by setting the temperature T to 80 ≦ T ≦ Tg + 50 [° C.], the film F can be sufficiently thermally deformed while preventing melting of the heated portion. However, the temperature T is more preferably 80 ≦ T ≦ Tg + 30 [° C.], and further preferably 100 ≦ T ≦ Tg + 10 [° C.].

Next, at least a part of the heated film portion H is cut and removed (cutting step).
More specifically, the portion from the heated portion of the film portion H to the end of the film F is removed by cutting in the longitudinal direction of the film F with the rotary cutter 33 of the heating portion 3. By removing both ends of the film F in this cutting step, it is possible to prevent the occurrence of stress at both ends due to the subsequent conveyance, and thus it is possible to more reliably suppress the occurrence of vertical wrinkles and distortion. In this cutting step, only the heated portion of the film portion H may be removed, or the entire film portion H may be removed. Further, this cutting step may not be performed.

Next, the formed and heated film F is stretched in the longitudinal direction by the longitudinal stretching machine 4 (stretching step).
In this stretching process, the film F is conveyed by the first to ninth rollers 41 to 49 which are driven so as to gradually increase the peripheral speed in order while the film F is heated by the IR heater 40. Is stretched in the longitudinal direction (conveying direction). At this time, the first to ninth rollers 41 to 49 are driven so that the difference in the peripheral speed between the sixth roller 46 and the seventh roller 47 where the film F is heated by the IR heater 40 is the largest. .

Next, the film F that has been stretched to become the optical film M is wound up by the winder 51 of the winding unit 5.
Thus, the rolled optical film M wound up by the winder 51 is completed.

According to the manufacturing method of the above optical film M, since at least a part within the predetermined range is heated from both ends in the width direction of the film F with respect to the film F before being stretched in the longitudinal direction, Before the vertical wrinkles and distortion are emphasized by stretching, the part where the conveyance tension is stronger than the inner side in the width direction is thermally deformed to effectively relieve the stress that causes vertical wrinkles and distortion. Can do.
At this time, since at least a part within the range of 10% of the total width is heated from both ends in the width direction of the film F, the entire film F is heated to cause unnecessary stretching and changes in optical characteristics due to the conveyance tension. And the effective width of the optical film M, which is a finished product, is not reduced by causing vertical wrinkles or distortions inside the film F outside the above range.
Further, since at least a part of the film portion H having a film thickness equal to or less than the average film thickness t in the above range is heated, that is, the endmost portion of the film F that is formed to be the thickest and has the strongest transport tension acts. Do not heat. Thereby, the fracture | rupture of the said film F by the said extreme end part being heated and the film F partially extending | stretching can be prevented.
Further, since at least a part of the film portion H is heated to a temperature T that satisfies 80 ≦ T ≦ Tg + 50 [° C.] (Tg: glass transition temperature [° C.] of the thermoplastic resin R), melting of the heated portion is prevented. However, it can be sufficiently thermally deformed to reliably relieve stress that causes vertical wrinkles and distortion.
As described above, the occurrence of longitudinal wrinkles and distortion in the longitudinal direction can be suppressed.

  It should be noted that the present invention should not be construed as being limited to the above-described embodiments, and of course can be modified or improved as appropriate.

For example, in the above embodiment, the melt casting method is used in the film forming process, but the solution casting method may be used.
In the stretching step, the film F is stretched only in the longitudinal direction (conveying direction), but a tenter is provided in the downstream of the longitudinal stretching machine 4 and the film F is stretched in the width direction by the tenter. Good.

The in-line film thickness meter 31 may be either a contact type or a non-contact type, but it is a non-contact type using a laser or X-ray from the viewpoint of easy measurement in the line. Is preferable.
The heat gun 32 may not be one that heats the film F with hot air, but may be one that heats the film F while being in contact with a heat roller, or one that is heated by irradiation with an IR heater or the like.
Further, the rotary cutter 33 may not be a rotary type, and may be a fixed type such as a single-edged cutter.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(1) Production of Sample As an example and a comparative example of the present invention, a sample of the optical film M was produced under the following conditions.

(1.1) Example 1
<Thermoplastic resin>
As thermoplastic resin R, the raw materials of the following formulation are mixed thoroughly and dried, melted and extruded into strands at 240 ° C. in a twin screw extruder, cooled and solidified with pure water at room temperature, and cut with a cutter. A pellet having a diameter of 1 to 2 mm and a length of 2 to 3 mm was formed.

<Raw material of thermoplastic resin>
Cellulose acetate propionate (acetylation degree 0.15, propionylation degree 2.63, total acyl substitution degree 2.78, number average molecular weight 55800 (number average polymerization degree DPn = 177), mass average molecular weight 13900 (mass average polymerization) Degree DPw = 440), residual sulfuric acid content 61 ppm (S sulfur content 21 ppm), magnesium content 20 ppm, calcium content 7 ppm, sodium content 1 ppm, potassium content 1 ppm, iron content 2 ppm): 100 parts by mass,
Stabilizer (Sumilyzer GP: manufactured by Sumitomo Chemical Co., Ltd.): 0.1 parts by mass,
Stabilizer (ADK STAB AO-60: manufactured by Asahi Denka Kogyo Co., Ltd.): 0.3 part by mass,
Ultraviolet absorber (ADK STAB LA-31: manufactured by Asahi Denka Kogyo Co., Ltd.): 1.1 parts by mass.

<Film forming process>
The pellet-shaped thermoplastic resin R was dried to a water content of 100 ppm or less with dry air, and then melted at 250 ° C. with a single screw extruder 21. This thermoplastic resin R is sent out by the gear pump 22, and is passed between the elastic touch roller 25 and the cast roller 26 that are each kept at 120 ° C. through the filter 23 through the slits of the T die 24 (interval 1 mm, width 1500 mm). Extruded. Then, the thermoplastic resin R was passed through two take-up rollers 27 and 27 kept at 100 ° C. and 80 ° C. in the order of conveyance direction, thereby forming a film F having a total width of about 1400 mm. At this time, the extrusion amount of the thermoplastic resin R from the single screw extruder 21 was 220 kg / hr, and the winding speed (peripheral speed) of each roller was 20 m / min.

<Heating process>
The film thickness of the film F was measured with a laser-type inline film thickness meter 31. In the obtained film thickness distribution, the film thickness at the extreme end of the film F was about 200 μm, and the average film thickness t in the range of 10% of the entire width from both ends was 129 μm on the OS side and 126 μm on the DS side. The film thickness on the inner side in the width direction from the above range was 112 to 116 μm. The OS side refers to the left side (the back side in FIG. 1) when the film F is viewed in the transport direction, and the DS side refers to the right side (the near side in FIG. 1).

  From the measurement results of the above film thickness, as the film portion H having an average film thickness t or less, the OS side is heated in the range of 50 to 140 mm, and the DS side is heated in the range of 1260 to 1360 mm. Within each range, the OS side was heated at a position of 60 mm, and the DS side was heated at a position of 1340 mm with a heat gun 32 having a blower opening of φ30 mm so as to be 110 ° C., respectively. Note that the numerical values of the above range and position are the distances from the film side on the OS side. The glass transition temperature Tg of the thermoplastic resin R is 135 ° C.

<Extension process>
In the longitudinal stretching machine 4, the peripheral speed of the first roller 41 (entry speed of the film F) is 20 m / min, the peripheral speed of the ninth roller 49 (the feeding speed of the film F) is 40 m / min (double stretching), The film F was heated to 200 ° C. with an IR heater 40 and stretched. At this time, the peripheral surfaces of the first to sixth rollers 41 to 46 are kept at 60, 70, 80, 90, 120, and 120 ° C., respectively, and the peripheral surfaces of the seventh to ninth rollers 47 to 49 are 120 respectively. , 90, 70 ° C.
The optical film M produced under the above conditions was used as a sample of “Example 1”.

(1.2) Example 2
After the heating process of Example 1, a cutting process of cutting and removing the film portion H with the rotary cutter 33 was performed. The film F after the cutting step was stretched in the same manner as in Example 1 to obtain a sample of “Example 2”.

(1.3) Comparative Example A sample of “Comparative Example” was prepared without performing the heating step of Example 1.

(2) Evaluation of samples For each of the prepared samples, the following three evaluation methods were used to evaluate the occurrence of vertical wrinkles at the three positions of the head portion, the center portion, and the tail portion in the longitudinal direction of the optical film M. The results shown in Table 1 were obtained.

(2.1) Evaluation by transmitted light A white screen, a sample, and a metal halide lamp are arranged in this order with an interval of 1 m and 0.5 m, and the transmitted light of the metal halide lamp transmitted from the sample is enlarged on the screen. The generation of vertical wrinkles was evaluated by visual inspection and visual inspection. When the occurrence of vertical wrinkles could not be confirmed, two samples of the same kind were stacked and evaluated in the same manner. The criteria for evaluation are as follows.

A: Vertical wrinkles cannot be confirmed even when two samples are stacked.
○: Vertically wrinkled unevenness can be confirmed when two samples are stacked.
Δ: Slight vertical wrinkle-like unevenness can be confirmed even with one sample.

(2.2) Evaluation by reflected light Generation of vertical wrinkles was evaluated by visually confirming the reflected light of the fluorescent light reflected by the sample under a daylight fluorescent light. The criteria for evaluation are as follows.

A: Vertical wrinkles cannot be confirmed at all.
○: Slight vertical wrinkle-like unevenness can be confirmed, but the position of this vertical wrinkle cannot be specified.
Δ: Slight vertical wrinkle-like unevenness can be confirmed, and the position of this vertical wrinkle can be specified.

(2.3) Evaluation by light leakage The sample was sandwiched between two polarizing plates (polarization directions were perpendicular to each other), and the occurrence of vertical wrinkles was evaluated by confirming light leakage on the Schaukasten. The light leakage was confirmed at an angle with the least amount of light leaking when the film F was rotated. The criteria for evaluation are as follows.

A: Light leakage cannot be confirmed.
○: Slight vertical wrinkle-like light leakage can be confirmed, but the position of this vertical wrinkle cannot be specified.
Δ: Slight vertical wrinkle-like light leakage can be confirmed, and the position of this vertical wrinkle can be specified.

(3) Summary From the results of Example 1 and Comparative Example in Table 1, it can be seen that by performing the heating step, the occurrence of minute vertical wrinkles (distortions) difficult to confirm by direct visual inspection can be suppressed. . Moreover, it turns out that generation | occurrence | production of a vertical wrinkle can be further suppressed by removing the film part H from the result of Example 1 and Example 2. FIG.

1 Manufacturing equipment (Optical film manufacturing equipment)
2 Film forming part (film forming means)
4 Longitudinal stretching machine (stretching means)
32 Heat gun (heating means)
F film H film portion M optical film R thermoplastic resin T temperature Tg glass transition temperature t of thermoplastic resin average film thickness

Claims (5)

In a method for producing an optical film comprising a film forming step of forming a thin film from a thermoplastic resin and a stretching step of stretching the formed film in the longitudinal direction,
After the film forming step and before the stretching step,
A temperature T satisfying the following formula (1) at least a part of the film within a range of 10% of the total width from both ends in the width direction of the film and having an average film thickness equal to or less than the average film thickness of the range. The manufacturing method of the optical film characterized by including the heating process heated to.
80 ≦ T ≦ Tg + 50 [° C.] (1)
(However, Tg: Glass transition temperature of the thermoplastic resin [° C.]) In the manufacturing method of the optical film of Claim 1,
After the heating step and before the stretching step,
A method for producing an optical film, comprising: a cutting step of cutting and removing at least a part of the film portion heated in the heating step in a longitudinal direction of the film. In the manufacturing method of the optical film of Claim 1 or 2,
The method for producing an optical film, wherein the thermoplastic resin is cellulose acylate.   The optical film manufactured by the manufacturing method of the optical film as described in any one of Claims 1-3. In an optical film manufacturing apparatus comprising: a film forming means for forming a thin film from a thermoplastic resin; and a stretching means for stretching the formed film in the longitudinal direction.
With respect to the film after being formed by the film forming means and before being stretched by the stretching means, it is within the range of 10% of the total width from both ends in the width direction of the film, and the average of the range An apparatus for producing an optical film, comprising heating means for heating at least a part of a film portion having a film thickness equal to or less than the film thickness to a temperature T satisfying the following expression (1).
80 ≦ T ≦ Tg + 50 [° C.] (1)
(However, Tg: Glass transition temperature of the thermoplastic resin [° C.])

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