JP2012048214A - Method for manufacturing optical film, and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film showing little increase in haze in a forced deterioration test that repeats high temperature and low temperature conditions.SOLUTION: The method for manufacturing an optical film aims to manufacture an optical film containing cellulose acylate and a matting agent. A web containing cellulose acylate having a calcium content of 50 ppm or less and a polyester-based additive represented by a general formula (1): B-(G-A)n-G-B is stretched by 5% to 50% magnification of stretching at a temperature of 180°C or higher and 230°C or lower. Thereby, the optical film after stretched is controlled to have an in-plane retardation Re in the range from 0 to 10 nm and a retardation Rth in a thickness direction in the range from -5 to 20 nm, measured at a wavelength of 590 nm in an environment of 23°C and 55% RH.

Description

  The present invention relates to a method for producing an optical film and a polarizing plate, and more particularly to a method for producing an optical film with little change in haze with time and a polarizing plate having a high contrast.

  In recent years, the demand for liquid crystal display devices (hereinafter also referred to as LCDs) is vigorous due to the widespread use of liquid crystal displays mounted on automobiles, large liquid crystal television displays, mobile phones, notebook computers, and the like. In such LCDs, various optical films such as a polarizing film and a retardation film are used.

  The demand for LCDs is increasing, and there is a demand for thinner, lighter, and more productive polarizing plates that are used in line with this demand. Furthermore, along with the increase in the screen size of LCDs, the optical film as a member is also required to be thinned and widened with high production, and studies to improve film properties centering on mechanical strength properties are also being promoted. Yes.

  However, when the film thickness is reduced, the moisture permeability of the optical film increases. Therefore, when the optical film is used as a polarizing plate protective film or the like, the polarizer is liable to deteriorate under high temperature and high humidity conditions. Therefore, the technique which tries to suppress moisture permeability by adding a plasticizer in an optical film is disclosed (for example, refer patent documents 1-3).

  When such an optical film is manufactured, in order to adjust the optical properties and flatness, and further the film thickness and width of the obtained optical film, the film is generally adjusted by stretching with a tenter after film formation.

  When the optical film is stretched at a high magnification in order to make it wider and thinner, especially when producing a wide optical film exceeding 1.6 m, the above-mentioned technology for improving moisture permeability is insufficient, under conditions of high temperature and high humidity. Then, it was found that polarizer deterioration, plasticizer volatilization, and bleeding are likely to occur, and the haze change of the optical film is large.

  A cellulose ester film having a thickness of 10 to 50 μm and containing 20 ppm or less of calcium (Ca) is disclosed (see, for example, Patent Document 4). Haze changes under high-temperature and high-humidity conditions for the purpose of suppressing deterioration (scratches, foreign matter) during storage, and suppressing scratches when the film is processed into a polarizing plate after storage or transportation There is no attention at all.

JP 2008-69225 A JP 2008-88292 A JP 2008-115221 A JP 2004-189288 A

  An object of the present invention is to use an optical film produced by a method for producing an optical film with little haze rise and a method for producing the optical film in a repeated forced deterioration test at high and low temperatures even when stretched at a high magnification. The object is to provide a polarizing plate with high contrast.

  The above object of the present invention can be achieved by the following configuration.

  1. A method for producing an optical film comprising cellulose acylate and a matting agent, wherein a web containing cellulose acylate having a calcium content of 50 ppm or less and a polyester-based additive represented by the following general formula (1): By stretching at a draw ratio of 5% to 50% at 180 ° C. to 230 ° C., the in-plane retardation Re measured at a wavelength of 590 nm in a 23 ° C./55% RH environment of the stretched optical film is 0. A method for producing an optical film, wherein the retardation Rth in the thickness direction is adjusted within a range of −5 to 20 nm within a range of −10 nm.

General formula (1) B- (GA) n-GB
In the formula, B is a monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A is This represents a dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, n represents an integer of 0 or more, and includes a configuration of BGB.

  2. 2. The method for producing an optical film as described in 1 above, wherein the polyester-based additive has a number average molecular weight of 300 to 700.

  3. 3. The method for producing an optical film as described in 1 or 2 above, wherein the dicarboxylic acid of the polyester-based additive is a mixture of at least one aliphatic dicarboxylic acid and at least one aromatic dicarboxylic acid.

  4). 4. The method for producing an optical film as described in any one of 1 to 3 above, wherein the terminal blocking group represented by B in the general formula (1) is an aromatic group.

  5. A polarizing plate using an optical film produced by the method for producing an optical film described in any one of 1 to 4 above.

  According to the present invention, even when stretched at a high magnification, in a repeated forced deterioration test at high temperature and low temperature, an optical film produced by the method for producing an optical film with little haze rise, and an optical film produced by the method for producing the optical film are used. A polarizing plate with high contrast can be provided.

  The method for producing an optical film of the present invention provides a method for producing an optical film in which haze increase is suppressed in a repeated forced deterioration test at high and low temperatures. As a result of repeated studies, the present inventor has found that the haze increase of the optical film is caused by aggregation of calcium and matting agent due to heat shock in the cellulose acylate film, and the haze increases. As a result, in order to suppress haze rise, the amount of calcium in the cellulose acylate that causes aggregation is suppressed to a low value, and stretched in the presence of the polyester-based additive according to the present invention as an environment that hardly aggregates The inventors have found that it is important to keep the in-plane and thickness direction retardation values low, and have made the present invention.

  In addition, it was found that the polyester additive coats around the matting agent and calcium and is less likely to aggregate by stretching at a high temperature of 180 to 230 ° C. and a stretching ratio of 5% to 50%. .

  Furthermore, since the resin is arranged isotropically by keeping the retardation value low, the matting agent and calcium are difficult to move between the resins. By these combinations, haze increase can be suppressed. Since the optical film manufactured by the method for manufacturing an optical film of the present invention is an optical film excellent in haze, a polarizing plate having a high panel contrast can be provided by the present invention.

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

《Polyester additive》
In order to obtain the effects of the present invention, the optical film according to the present invention contains a polyester-based additive represented by the following general formula (1), while maintaining haze low, in-plane and thickness direction retardation. Is required to adjust within the scope of the present invention.

General formula (1) B- (GA) n-GB
In the formula, B is a monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A is This represents a dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, n represents an integer of 0 or more, and includes a configuration of BGB.

  In the general formula (1), a monocarboxylic acid residue represented by B and an alkylene glycol residue, an oxyalkylene glycol residue or an aryl glycol residue represented by G, a dicarboxylic acid residue or an aryl dicarboxylic acid residue represented by A And obtained by the same reaction as that of a normal polyester-based additive.

  Examples of the monocarboxylic acid component of the polyester-based additive used in the present invention include, for example, acetic acid, benzoic acid, para-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, normal There are propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component having 2 to 12 carbon atoms of the polyester-based additive that can be used in the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1, 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neo Pentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3propanediol (3,3-dimethylolheptane) 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-penta Diol, 2-ethyl 1,3-hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, and the like. It is used as one kind or a mixture of two or more kinds. In particular, alkylene glycols having 2 to 12 carbon atoms are particularly preferable because of excellent compatibility with cellulose acylate.

  In addition, examples of the oxyalkylene glycol component having 4 to 12 carbon atoms of the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. It can be used as a seed or a mixture of two or more.

  Examples of the dicarboxylic acid component having 4 to 12 carbon atoms of the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Each is used as one or a mixture of two or more. Examples of the aryl dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and the like.

  It is particularly preferred that the dicarboxylic acid is a mixture of at least one aliphatic dicarboxylic acid and at least one aromatic dicarboxylic acid. When the aliphatic dicarboxylic acid and the aromatic dicarboxylic acid are contained, the ratio of the aliphatic dicarboxylic acid and the aromatic dicarboxylic acid is preferably 55:45 to 99: 1, and preferably 60:40 to 90:10. Is more preferable.

  The number average molecular weight of the polyester-based additive according to the present invention is preferably in the range of 300 to 700, more preferably in the range of 300 to 500. When the number average molecular weight is in this range, the polyester additive is coated around the matting agent and calcium and is less likely to agglomerate when stretched at the temperature and draw ratio according to the present invention. An optical film with little haze rise can be obtained. The number average molecular weight is measured using the following gel permeation chromatography.

  The number average molecular weight of the polyester-based additive can be adjusted by adjusting the reaction time of condensation or polycondensation.

  The polyester additive according to the present invention has an acid value of 0.5 mgKOH / g or less, a hydroxyl value of 25 mgKOH / g or less, more preferably an acid value of 0.3 mgKOH / g or less, and a hydroxyl value of 15 mgKOH / g or less. preferable.

  The polyester additive according to the present invention can be synthesized by a conventional method, a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the dicarboxylic acid and a diol and / or a monocarboxylic acid for end-capping, or these acids. It can be easily synthesized by any of the interfacial condensation methods of acid chlorides and glycols. These polyester-based additives are described in detail in Koichi Murai, “Additives, Theory and Application” (Kokaibo Co., Ltd., first edition published on March 1, 1973). In addition, Japanese Patent Laid-Open Nos. 05-155809, 05-155810, Japanese Patent Laid-Open Nos. 05-97073, 2006-259494, 07-330670, 2006-342227, 2007-003679. The materials described in each publication can also be used.

  Hereinafter, synthesis examples of aromatic terminal ester plasticizers that can be used in the present invention will be shown.

<Sample No. 1-1 (Aromatic Terminal Ester Sample)>
In a reaction vessel, 410 parts of phthalic acid and adipic acid in a mixing ratio of 5: 5, 610 parts of benzoic acid, 737 parts of 1,2 propanediol and ethylene glycol in a mixing ratio of 5: 5, and tetraisopropyl titanate as a catalyst 0 .40 parts are charged all at once, while stirring in a nitrogen stream, a reflux condenser is attached to reflux excess monohydric alcohol, and heating is continued at 130 to 250 ° C. until the acid value becomes 2 or less. Water was removed continuously. Next, the distillate is removed under reduced pressure at 200 to 230 ° C. under a reduced pressure of 1.33 × 10 ⁴ Pa to 4 × 10 ² Pa or less, and then filtered to remove an aromatic terminal ester plastic having the following properties: An agent was obtained.

Number average molecular weight (Mn): 350
<Sample No. 2 (Aromatic terminal ester sample)>
In a reaction vessel, 410 parts of terephthalic acid and succinic acid in a mixing ratio of 5: 5, 610 parts of benzoic acid, 341 parts of 1,2 propanediol and ethylene glycol in a mixing ratio of 5: 5, and tetraisopropyl titanate as a catalyst Sample No. was used except 0.35 parts. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.

Number average molecular weight (Mn): 310
<Sample No. 3 (Aromatic terminal ester sample)>
In a reaction vessel, 410 parts of isophthalic acid and succinic acid at a mixing ratio of 5: 5, 610 parts of p-troyl acid, 418 parts of 1,3 propanediol and ethylene glycol at a mixing ratio of 5: 5, and tetra as a catalyst. Sample No. 1 was used except 0.35 parts of isopropyl titanate. In the same manner as in No. 1, an aromatic terminal ester having the following properties was obtained.

Number average molecular weight (Mn): 400
<Sample No. 4 (Ester sample)>
Sample No. 4 was used except that 410 parts of terephthalic acid and maleic acid were mixed in a reaction vessel in a 5: 5 ratio, 610 parts of p-troyl acid, 418 parts of ethylene glycol, and 0.35 part of tetraisopropyl titanate as a catalyst. An ester having the following properties was obtained in the same manner as in Example 1.

Number average molecular weight (Mn): 350
<Sample No. 1-2 to 1-8, 5-9>
Sample No. The synthesis was performed using the raw materials shown in Table 1 in the same manner as in 1-1. 1-2 to 1-8 were synthesized in the same manner as 1-1 by adjusting the reaction time.

  Here, the notation of 1,2-propanediol and ethylene glycol = 5,5 means that 1,2-propanediol and ethylene glycol were mixed at a ratio of 5 to 5. The same applies to other similar notations.

[Method for measuring number average molecular weight (Mn) of polyester-based additive]
Using a gel permeation chromatography (GPC) measuring device (“HLC-8330” manufactured by Tosoh Corporation), the number average molecular weight (Mn) in terms of standard polystyrene of the ester compound was measured under the following measurement conditions.
Column: “TSK gel SuperHZM-M” × 2 and “TSK gel SuperHZ-2000” × 2 Guard column: “TSK superH-H”
Developing solvent: Tetrahydrofuran Flow rate: 0.35 ml / min

  It is preferable that the said compound contains 1-35 mass% in an optical film, especially 5-30 mass%. Within this range, it is preferable that the excellent effects of the present invention are exhibited and there is no bleeding out during storage of the raw material.

  Moreover, another plasticizer can be contained as needed. The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or an acrylic plasticizer. Selected from agents and the like. Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer. Examples of the polyhydric alcohol ester compounds include paragraphs (0218) to (0170) of JP 2010-32655 A.

《Cellulose acylate》
The cellulose acylate used in the optical film according to the present invention is preferably a carboxylic acid ester having about 2 to 22 carbon atoms, and particularly preferably a lower fatty acid ester of cellulose. The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. The acyl group bonded to the hydroxyl group may be linear or branched or may form a ring. Furthermore, another substituent may be substituted. When the degree of substitution is the same, birefringence decreases when the number of carbon atoms is large, and therefore, the number of carbon atoms is preferably selected from acyl groups having 2 to 6 carbon atoms.

  The cellulose acylate may be an acyl group derived from a mixed acid, and particularly preferably an acyl group having 2 and 3 carbon atoms or 2 and 4 carbon atoms. In the present invention, a mixed fatty acid ester of cellulose to which a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, or cellulose acetate propionate butyrate can be used. The butyryl group forming butyrate may be linear or branched. In the present invention, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cellulose acetate phthalate are particularly preferably used.

  The retardation value can be appropriately controlled depending on the kind of the acyl group of cellulose acylate, the degree of substitution of the acyl group on the pyranose ring of the cellulose resin skeleton, and the like.

  Preferred cellulose acylates for the present invention are those that simultaneously satisfy the following formulas (1) and (2).

Formula (1) 2.0 <= X + Y <= 3.0
Formula (2) 0 ≦ Y ≦ 1.5
In the formula, X is the degree of substitution of the acetyl group, and Y is the degree of substitution of the propionyl group or butyryl group. Those satisfying the above two formulas can obtain a film exhibiting excellent physical properties and optical properties that meet the object of the present invention.

  Of these, triacetyl cellulose and cellulose acetate propionate are particularly preferably used. In cellulose acetate propionate, 1.0 ≦ X ≦ 2.5, preferably 0.1 ≦ Y ≦ 1.5, and 2.0 ≦ X + Y ≦ 3.0. The measuring method of the substitution degree of an acyl group can be measured according to ASTM-D817-96.

  If the substitution degree of the acyl group is too low, there will be more unreacted parts with respect to the hydroxyl groups of the pyranose ring that constitutes the skeleton of the cellulose resin, and a large amount of the hydroxyl groups will remain, so that the humidity change of the retardation and the polarizing plate protective film As a result, the ability to protect the polarizer may decrease, which is not preferable.

  The value of the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the cellulose acylate according to the present invention is preferably 1.4 to 3.0. In the present invention, the cellulose acylate film may contain, as a material, cellulose acylate having a Mw / Mn value of 1.4 to 3.0, but the cellulose acylate contained in the film (preferably Is a cellulose triacetate or cellulose acetate propionate) The Mw / Mn value of the whole is more preferably in the range of 1.4 to 3.0. More preferably, it is 1.7-2.2.

  In the case of acetylcellulose, it is necessary to extend the time for the acetylation reaction in order to increase the acetylation rate. However, if the reaction time is too long, the decomposition proceeds at the same time, and the polymer chain is broken and the acetyl group is decomposed, resulting in undesirable results. Therefore, it is necessary to set the reaction time within a certain range in order to increase the degree of acetylation and suppress decomposition to some extent. It is not appropriate to define the reaction time because the reaction conditions are various and greatly change depending on the reaction apparatus, equipment and other conditions. As the decomposition of the polymer proceeds, the molecular weight distribution becomes wider. Therefore, in the case of cellulose acylate, the degree of decomposition can be defined by the value of weight average molecular weight (Mw) / number average molecular weight (Mn) that is usually used. In other words, in the process of acetylation of cellulose triacetate, the weight average molecular weight used as one index of the reaction degree for allowing the acetylation reaction to be carried out for a sufficient time for acetylation without being excessively decomposed too much. The value of (Mw) / number average molecular weight (Mn) can be used.

  The molecular weight of cellulose acylate used in the optical film according to the present invention is preferably a number average molecular weight (Mn) of 80000-200000. More preferred are 100,000 to 200,000, particularly preferably 150,000 to 200,000.

  The average molecular weight and molecular weight distribution of cellulose acylate can be measured by a known method using high performance liquid chromatography. Using this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

  Measured by high performance liquid chromatography under the following conditions.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (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 Corporation) Mw = 100000 to 500 calibration curves with 13 samples were used. Thirteen samples are used at approximately equal intervals.

  The optical film according to the present invention is characterized by using cellulose acylate having a calcium content of 50 ppm or less, and can effectively suppress an increase in haze over time.

  In order to bring the calcium content in the cellulose acylate into the above-mentioned range, it largely depends on the raw material of cellulose acylate and the production method.

  The calcium content in the cellulose acylate according to the present invention is 50 ppm or less, and preferably in the range of 10 to 50 ppm from the viewpoint of production and cost.

  Wood pulp (coniferous pulp, hardwood pulp), cotton linter, etc. can be used as the cellulose of the cellulose acylate used in the present invention. The Mw of cellulose acylate can be controlled by the type of cellulose and the use of a plurality of raw material celluloses. For example, when esterification is performed using a hardwood pre-hydrolyzed kraft pulp, Mw of cellulose acylate is increased, and when softwood sulfite pulp is used, Mw tends to be decreased. Therefore, cellulose may be used singly or in combination of two or more. For example, softwood pulp and cotton linter or hardwood pulp may be used in combination. As cellulose, usually pulp (particularly softwood pulp) is often used. In addition, the α-cellulose content (% by mass) of cellulose is usually from 94 to 99 (for example, 95 to 99), preferably from about 96 to 98.5 (for example, 97.3 to 98). .

(Calcium content of pulp)
In the present invention, it is preferable to use a pulp having a low calcium content as the raw material pulp. By using a pulp having a low calcium content, the amount of calcium contained in cellulose acylate can be reduced. For example, the calcium content of a suitable pulp is 20 ppm or less (for example, 0.01 to 18 ppm), preferably 15 ppm or less (for example, 0.01 to 15 ppm), more preferably 10 ppm or less (for example, 0.05 to 10 ppm). In particular, it is 5 ppm or less (for example, 0.1 to 5 ppm). The calcium content in the dissolving pulp is preferably as small as possible from the viewpoint of optical quality.

  In the study by the present inventors, for example, in the case of kraft pulp, a dissolved pulp having a calcium content of about 3 ppm can be obtained by switching sodium hydroxide used in the cooking process from a recovered and regenerated product to a virgin product. It was. As a method of reducing the amount of calcium in raw pulp, (1) a method of limiting the types of cellulose sources (crude linters and wood chips) that are originally low in calcium components, and (2) that calcium is not mixed in the pulp cooking process. And (3) a method of combining the methods (1) and (2). These methods can reduce the calcium content in the pulp.

  In the method (2), the pulp cooking step is a step in the production of dissolving pulp. Various methods for producing dissolving pulp have been proposed. Industrially, two types of methods are used: a sulfite method and a kraft method. Regarding the method for producing these dissolving pulps, for example, the method described in detail in “Wood Chemistry” (written by E. Sjostrom, translated by Tamio Kondo, published by Kodansha, published in 1986, pages 104 to 147) and the like are used. it can. The cooking process is carried out by any method, and its main purpose is to remove lignin contained in pulp raw materials (wood chips and the like). In the sulfite method, an aqueous solution containing sulfite and bisulfite is used as the cooking solution. As the base of bisulfite, for example, calcium, sodium, magnesium or ammonium is used, but industrially, calcium is mainly used. Therefore, in the sulfite method, since alkaline earth metals, especially calcium are often mixed, the calcium content can be reduced by not using calcium salts as bisulfites.

  In the Kraft method, a mixed solution of sodium hydroxide and sodium sulfide is used as a cooking solution, and sodium sulfide reacts with lignin to produce thiolignin and solubilize lignin. The digested pulp cleaning liquid contains thiolignin, excess sodium sulfide and sodium hydroxide. Furthermore, this cleaning liquid containing impurities such as lignin is burned in a reducing atmosphere, and the sulfur content becomes sodium sulfide. On the other hand, the other sodium component is sodium carbonate. Sodium sulfide and sodium carbonate are recovered as a residue left in the furnace and dissolved in water. Next, calcium oxide or calcium hydroxide obtained by dissolving calcium oxide in water is added to the residue solution.

  By this operation, sodium carbonate is causticized to become sodium hydroxide and calcium carbonate, and the residual solution becomes a solution containing sodium sulfide, sodium hydroxide and calcium carbonate. At this stage, the calcium carbonate precipitates for the portion exceeding the solubility limit and is separated from the solution in the filtration process. That is, when calcium carbonate is precipitated and filtered, sodium hydroxide used for cooking is recovered and calcium carbonate and sodium hydroxide are separated. However, in the filtration process of this precipitate, since both cannot be separated industrially completely, it was conventionally allowed to mix a small amount of calcium carbonate into the cooking liquid. For this reason, it is a manufacturing process by a normal kraft method that a trace amount of calcium carbonate is mixed in the sodium hydroxide solution added in the process of delignification.

  Therefore, as a method of reducing calcium in the Kraft method, (1) a method that does not use recovered (regenerated) products for sodium hydroxide and sodium sulfide used, and (2) a recovery that uses sodium hydroxide and sodium sulfide. (Regeneration) Method to reduce the usage rate of the product, (3) In the separation of calcium carbonate and the solution containing sodium sulfide and sodium hydroxide, the solid and liquid are completely separated by filtration using a membrane filter etc. (4) In the filtration of calcium carbonate and a solution containing sodium sulfide and sodium hydroxide, a method of industrially filtering by installing a filtration step in multiple stages can be used, but it is not limited to these methods. .

  In addition, when using these methods, it is not necessary to restrict | limit the kind of wood chip used as a raw material of a pulp in order to obtain the pulp which reduced calcium. For this reason, it is not influenced by the raw material of the pulp, and is suitable because it can be applied to pulp for obtaining cellulose acylate having the optimum physical properties for the target film based on conventional knowledge.

[Measurement method of calcium content in pulp]
The calcium content in the pulp is measured by the atomic absorption method. The following method is used as a specific measurement pretreatment procedure.

  (1) A magnetic crucible having a capacity of 50 ml that has been washed is immersed in a 2N aqueous nitric acid solution overnight.

  (2) The magnetic crucible soaked in 2N nitric acid is washed with pure water, rinsed with ultrapure water, and dried in a drier.

  (3) Weigh accurately 2 g of sample into a magnetic crucible.

  (4) Carbonize the sample in the magnetic crucible on the electric heater.

  (5) The magnetic crucible is put into an electric furnace and incinerated at 500 ° C. for about 1 hour and at 600 ° C. for about 1.5 hours.

  (6) When the ash is completely white, stop the electric furnace and let it cool in the furnace.

  (7) 10 ml of 0.5N hydrochloric acid aqueous solution is put in a magnetic crucible and dissolved by heating on a sand bath.

  (8) The solution is allowed to cool and then transferred to a 50 ml volumetric flask using a washed funnel, and the magnetic crucible is rinsed with ultrapure water to make up the volume (hydrochloric acid concentration: 0.1 N).

  (9) As a standard solution, a calcium standard solution having a concentration of 1000 ppm is diluted with a 0.1N hydrochloric acid aqueous solution and prepared at concentrations of 0.1 ppm, 0.75 ppm, and 1.5 ppm.

  (10) Measured by flame atomic absorption.

  The calibration curve was created by the following method. The standard solution for the calibration curve was prepared by diluting a commercially available standard solution for atomic absorption with 0.1N hydrochloric acid solution to concentrations of 0.1, 0.75, and 1.5 ppm. The used atomic absorption device is a product name “AA-680” manufactured by Shimadzu Corporation.

  Cellulose acylate also contains other metal ions, which are related to the water used in the manufacturing process. It is preferable that the number of components that can become insoluble nuclei is small, and metal ions other than calcium, such as iron and magnesium, are insoluble by forming a salt with a polymer decomposition product that may contain an organic acidic group. It is preferable that the amount is small. The iron (Fe) component is preferably 1 ppm or less.

  The magnesium (Mg) component is preferably in the range of 0 to 70 ppm, particularly preferably 0 to 20 ppm, since too much will cause insoluble matter. Metal components such as iron (Fe) content, magnesium (Mg) content, etc. are subjected to pretreatment of completely dried cellulose acylate with a micro digest wet cracking device (sulfuric acid decomposition) and alkali melting, then ICP- Analysis can be performed using AES (Inductively Coupled Plasma Atomic Emission Spectrometer).

In the cellulose acylate according to the present invention, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as acetic acid or an organic solvent such as methylene chloride is used. The reaction is carried out using a protic catalyst such as sulfuric acid. When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

  The average substitution degree of the acyl group at the 6-position of the glucose unit of the cellulose acylate used in the present invention is preferably 0.5 to 0.9.

  Unlike the 2nd and 3rd positions, the glucose unit constituting the cellulose acylate has a highly reactive primary hydroxyl group, which is a process for producing cellulose acylate using sulfuric acid as a catalyst. To preferentially form sulfate esters. Therefore, by increasing the amount of catalytic sulfuric acid in the esterification reaction of cellulose, it is possible to increase the average degree of substitution at the 2nd and 3rd positions rather than the 6th position of the glucose unit as compared with normal cellulose acylate. Furthermore, if the cellulose is tritylated as necessary, the hydroxyl group at the 6-position of the glucose unit can be selectively protected. Therefore, the trityl group protects the hydroxyl group at the 6-position, and after esterification, the trityl group (protection) The average substitution degree at the 2nd and 3rd positions can be increased from the 6th position of the glucose unit. Specifically, cellulose acylate produced by the method described in JP-A No. 2005-281645 can also be preferably used.

  An example of a method for producing cellulose acylate is shown below. 100 parts by weight of a cotton linter was crushed as a cellulose raw material, 40 parts by weight of acetic acid was added, and pretreatment activation was performed at 36 ° C. for 20 minutes. Thereafter, 8 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride and 350 parts by mass of acetic acid were added, and esterification was performed at 36 ° C. for 120 minutes. After neutralization with 11 parts by mass of a 24% magnesium acetate aqueous solution, saponification aging was carried out at 63 ° C. for 35 minutes to obtain acetylcellulose. This was stirred for 160 minutes at room temperature using a 10-fold acetic acid aqueous solution (acetic acid: water = 1: 1 (mass ratio)), then filtered and dried to obtain purified acetylcellulose having an acetyl substitution degree of 2.75. . This acetylcellulose had Mn of 92000, Mw of 156000, and Mw / Mn of 1.7. Similarly, cellulose acylates having different degrees of substitution and Mw / Mn ratios can be synthesized by adjusting the esterification conditions (temperature, time, stirring) and hydrolysis conditions of cellulose acylate.

  In addition, the synthesized cellulose acylate is preferably purified to remove low molecular weight components or to remove unacetylated or low acetylated components by filtration.

  In the case of mixed acid cellulose acylate, it can be obtained by the method described in JP-A-10-45804.

(Acrylic copolymer)
The optical film according to the present invention preferably contains an acrylic copolymer (hereinafter also referred to as an acrylic polymer).

  In order to exert an effect on retardation stability, the acrylic polymer preferably contains an acrylic polymer having a weight average molecular weight of 500 or more and 30000 or less. Among them, an ethylenic polymer having no aromatic ring and no hydrophilic group in the molecule. A polymer having a weight average molecular weight of 5,000 to 30,000 obtained by copolymerization of a saturated monomer and an ethylenically unsaturated monomer having a hydrophilic group and having no aromatic ring in the molecule, more preferably an aromatic ring in the molecule And a polymer having a weight average molecular weight of 5,000 to 30,000 obtained by copolymerizing an ethylenically unsaturated monomer having no hydrophilic group and an ethylenically unsaturated monomer having no aromatic ring in the molecule and having a hydrophilic group And a polymer having a weight average molecular weight of 500 or more and 3000 or less obtained by polymerizing an ethylenically unsaturated monomer having no aromatic ring. Preferably contains a chromatography.

(UV absorber)
The optical film according to the present invention preferably contains an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body.

  The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

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

  The method for adding the UV absorber is to add the UV absorber to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane, or a mixed solvent thereof. Or you may add directly in dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose acylate to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the use conditions, etc., but when the dry film thickness of the optical film is 30 to 200 μm, it is 0.5 to 10% by mass relative to the optical film. Is preferable, and 0.6-4 mass% is still more preferable.

(Matting agent)
The optical film according to the present invention contains a matting agent (fine particles). By containing the matting agent, slipperiness and storage stability are improved.

  As fine particles, examples of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate. And calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable. The content of these fine particles in the optical film is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass. In the case of an optical film having a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available under the trade names of, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the haze of the optical film low. In the optical film according to the present invention, the dynamic friction coefficient of at least one surface is preferably 0.2 to 1.0.

(dye)
A dye may be added to the optical film according to the present invention for color adjustment. For example, a blue dye may be added to suppress the yellowness of the film. Preferred examples of the dye include anthraquinone dyes.

  The anthraquinone dye may have an arbitrary substituent at an arbitrary position from the 1st position to the 8th position of the anthraquinone. Preferred substituents include an anilino group, hydroxyl group, amino group, nitro group, or hydrogen atom. In particular, it is preferable to contain a blue dye described in JP-A-2001-154017, particularly an anthraquinone dye.

  Various additives may be batch-added to the dope that is a cellulose acylate-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, it is preferable to add a part or all of the fine particles in-line in order to reduce the load on the filter medium.

  When the additive solution is added in-line, it is preferably dissolved in a small amount of cellulose acylate in order to improve mixing with the dope. A preferable amount of cellulose acylate is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

(Optical film manufacturing method)
Next, the manufacturing method of the optical film of this invention is demonstrated.

  The method for producing an optical film of the present invention is a method for producing an optical film containing cellulose acylate and a matting agent, and is represented by cellulose acylate having a calcium content of 50 ppm or less and the general formula (1). By stretching a web containing a polyester-based additive at a stretch ratio of 5% to 50% at 180 ° C. or higher and 230 ° C. or lower, the optical film after stretching has a wavelength of 590 nm in a 23 ° C./55% RH environment. The measured in-plane retardation Re is adjusted within the range of 0 to 10 nm, and the retardation Rth in the thickness direction is adjusted within the range of −5 to 20 nm.

  Here, the web refers to a film formed by casting the following dope from a casting die onto a support made of a stainless steel endless belt.

  The optical film according to the present invention can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

  Production of the optical film according to the present invention by a solution casting method is a step of preparing a dope by dissolving cellulose acylate and the additive in a solvent, and casting the dope onto an endless metal support that moves indefinitely. It is carried out by a step, a step of drying the cast dope as a web, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. The concentration of cellulose acylate in the dope is preferably higher because the drying load after casting on the metal support can be reduced, but if the concentration of cellulose acylate is too high, the load during filtration increases and the filtration accuracy Becomes worse. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  The solvent used in the dope may be used alone or in combination of two or more. However, it is preferable in terms of production efficiency that a good solvent and a poor solvent of cellulose acylate are mixed and used. A larger amount is preferable from the viewpoint of the solubility of cellulose acylate. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose acylate to be used independently is defined as a good solvent, and what poorly swells or does not melt | dissolve is defined as a poor solvent. Therefore, depending on the average degree of acetylation (acetyl group substitution degree) of cellulose acylate, the good solvent and the poor solvent change. For example, when acetone is used as the solvent, cellulose acylate acetate (acetyl group substitution degree 2.4) Cellulose acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent.

  The good solvent is not particularly limited, and examples thereof include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although a poor solvent is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope. Moreover, the solvent used for melt | dissolution of a cellulose acylate collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again. The recovered solvent may contain trace amounts of additives added to cellulose acylate, such as plasticizers, UV absorbers, polymers, and monomer components. Can be purified and reused if necessary.

  As a method for dissolving cellulose acylate when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos. In addition, a method in which cellulose acylate is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  A higher heating temperature with the addition of a solvent is preferable from the viewpoint of the solubility of cellulose acylate, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 ° C to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used, whereby cellulose acylate can be dissolved in a solvent such as methyl acetate.

  Next, this cellulose acylate solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose acylate by filtration.

A bright spot foreign object is placed when two polarizing plates are placed in a crossed Nicols state, an optical film is placed between them, light is applied from one polarizing plate, and the opposite is observed when observed from the other polarizing plate. It is a point (foreign matter) where light from the side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less. More preferably, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

  The dope can be filtered by a normal method, but the method of filtering while heating at a temperature not lower than the boiling point of the solvent at normal pressure and in a range where the solvent does not boil under pressure is the filtration pressure before and after filtration. The increase in the difference (referred to as differential pressure) is small and preferable. A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

  A smaller filtration pressure is preferred. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and further preferably 1.0 MPa or less.

  Here, the dope casting will be described.

  The metal support in the casting (casting) step preferably has a mirror-finished surface. As the metal support, a stainless steel belt or a drum whose surface is plated with a casting is preferably used. The cast width can be 1 to 4 m. Since the width of the optical film according to the present invention is preferably 1.6 to 4 m, the cast width is inevitably wide. The surface temperature of the metal support in the casting step is −50 ° C. to a temperature lower than the boiling point of the solvent, and a higher temperature is preferable because the web can be dried faster. May deteriorate. A preferable support body temperature is 0-40 degreeC, and 5-30 degreeC is still more preferable. Alternatively, it is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent. The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing hot air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short. When warm air is used, wind at a temperature higher than the target temperature may be used.

  In order for the optical film to exhibit good flatness, the residual solvent amount when peeling the web from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass. Yes, particularly preferably 20 to 30% by mass or 70 to 120% by mass.

  In the present invention, the amount of residual solvent is defined by the following formula.

Residual solvent amount (% by mass) = {(MN) / N} × 100
M is the mass of a sample collected during or after the production of the web or film, and N is the mass after heating M at 115 ° C. for 1 hour.

  Further, in the optical film drying step, the web is peeled off from the metal support and further dried, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.1% by mass or less, particularly Preferably it is 0-0.01 mass% or less.

  In the film drying process, generally, a roll drying method (a method in which a plurality of rolls arranged on the upper and lower sides are alternately passed through and dried) or a method of drying while transporting the web by a tenter method is adopted.

  In order to produce the optical film according to the present invention, it is preferable to stretch in the longitudinal direction (MD direction) where the residual solvent amount of the web immediately after peeling from the metal support is large.

  In order to stretch in the MD direction immediately after peeling, it is preferable to peel at a peeling tension of 210 N / m or more, particularly preferably 220 to 300 N / m.

  The means for drying the web is not particularly limited, and can be generally performed with hot air, infrared rays, a heating roll, microwave, or the like, but it is preferably performed with hot air in terms of simplicity.

  The drying temperature in the web drying step is preferably 90 ° C to 200 ° C, more preferably 110 ° C to 160 ° C. The drying temperature is preferably increased stepwise.

  Although preferable drying time is based also on drying temperature, 5 minutes-60 minutes are preferable and 10 minutes-30 minutes are more preferable.

  Although the film thickness of an optical film is not specifically limited, 10-200 micrometers is used. In particular, the film thickness is particularly preferably 20 to 100 μm. More preferably, it is 20-60 micrometers.

  The optical film according to the present invention has a width of 1 to 4 m. From the viewpoint of productivity, those having a width of 1.6 to 4 m are preferably used, and particularly preferably 1.8 to 3.6 m. If it exceeds 4 m, conveyance becomes difficult.

(Stretching operation)
The optical film according to the present invention takes the configuration of the present invention and preferably performs the following stretching operation.

  The stretching operation can be sequentially or simultaneously stretched in the MD direction (casting direction or longitudinal direction) and the TD direction (width direction) of the film. The stretching ratio in the biaxial direction perpendicular to each other is 0 to 20% in the MD direction and 5 to 50% in the TD direction.

  Particularly in the present invention, the film is stretched 5 to 50% in the TD direction, the temperature at the time of stretching is 180 ° C. or more and 230 ° C. or less, the in-plane retardation Re after stretching is 0 to 10 nm, and the retardation Rth in the thickness direction is When adjusted to the range of -5 to 20 nm, the haze stability is remarkably improved.

  In particular, when the polyester additive is stretched at a relatively high temperature of 180 ° C. or higher and 230 ° C. or lower, which is higher than before in the presence of the polyester additive, the polyester additive coats around the matting agent and calcium, resulting in more aggregation. It becomes difficult to get up. At this time, the surface coating ability is higher when the molecular weight of the polyester-based additive is smaller, and the coating ability is higher when the dicarboxylic acid group is a mixture of an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid.

  Furthermore, it is preferable to keep the residual solvent at less than 5% by mass at the start of stretching because the in-plane retardations Re and Rth can be easily adjusted to the preferred ranges and the effect on haze of the present invention can be further improved. The measurement of the residual solvent is as described above, and here, at the start of stretching, for example, if it is a tenter, it means the residual solvent in the web immediately before the stretching is actually started by gripping the edge of the web with a clip. . In order to keep the residual solvent at the start of stretching below 5% by mass, it is preferable to provide the drying step and evaporate the solvent in the process of peeling the web from the metal support and carrying it. When stretching is carried out while retaining a residual solvent of 5% by mass or more as in the prior art, it is difficult to adjust the in-plane retardations Re and Rth to the preferred ranges, and the haze is likely to increase. The preferred residual solvent is 4% by mass or less, more preferably 2% by mass or less, and particularly preferably 1% by mass or less. This operation is preferably performed online considering productivity.

  There is no particular limitation on the method of stretching the web. For example, a method in which peripheral speed differences are applied to a plurality of rolls and a roll peripheral speed difference is used to stretch in the MD direction, both ends of the web are fixed with clips and pins, and the distance between the clips and pins is increased in the traveling direction. And a method of stretching in the MD direction, a method of stretching in the transverse direction and stretching in the TD direction, a method of stretching in the MD / TD direction simultaneously and stretching in both the MD / TD directions, and the like. Of course, these methods may be used in combination. In the case of the so-called tenter method, driving the clip portion by the linear drive method is preferable because smooth stretching can be performed and the risk of breakage and the like can be reduced.

  These width maintenance or width direction stretching in the film forming step is preferably performed by a tenter, and may be a pin tenter or a clip tenter.

  The film transport tension in the film forming process such as in the tenter depends on the temperature, but is preferably 120 N / m to 200 N / m, and more preferably 140 N / m to 200 N / m. 140 N / m to 160 N / m is most preferable.

  The elastic modulus of the optical film according to the present invention measured in a 23 ° C. and 55% RH environment is 3.4 GPA or more and 7.0 GPA or less in both the film longitudinal direction (MD) and the film width direction (TD). / MD elastic modulus is adjusted to be 1.05 to 2.0. In order to avoid the stability of stretching operation, breakage, and the like, the elastic modulus is preferably adjusted by the material type constituting the film and the ratio of the constituting materials in the range of 3.4 GPA or more and 4.5 GPA or less.

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

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

  More optimal conditions of these heat setting conditions, cooling, and relaxation treatment conditions vary depending on the additive species such as cellulose acylate and plasticizer constituting the film, so the physical properties of the obtained stretched film are measured, and preferable characteristics are obtained. It may be determined by adjusting as appropriate.

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

<Physical properties, optical properties>
Moisture permeability of the optical film according to the present invention, 40 ° C., of preferably 10~1200g ^/ m 2 · 24h at 90% RH, further 20~1000g ^/ m 2 · 24h are preferred, 20~850g ^/ m 2 · 24h Particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

  The breaking elongation of the optical film according to the present invention is preferably 10 to 80%, more preferably 20 to 50%.

  The optical film according to the present invention preferably has a visible light transmittance of 90% or more, and more preferably 93% or more.

  The haze of the optical film according to the present invention is preferably less than 1%, particularly preferably 0 to 0.1%.

  The optical film of the present invention has a retardation value Re represented by the following formula of 0 to 10 nm and Rth of −5 to 20 nm.

Formula (i) Re = (nx−ny) × d
Formula (ii) Rth = ((nx + ny) / 2−nz) × d
(In the formula, Re is the retardation value in the film plane, Rth is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is (The refractive index in the thickness direction of the film, d represents the thickness (nm) of the film.)
The refractive index is obtained at a wavelength of 590 nm under an environment of 23 ° C. and 55% RH using, for example, KOBRA-21ADH or KOBRA-WR (Oji Scientific Instruments).

  Furthermore, the retardation value Re is preferably in the range of 0 to 5 nm, and Rth is preferably in the range of 0 to 15 nm in order to enhance the effect of the present invention.

  In order to obtain the retardation values Re and Rth, it is preferable that the optical film has the configuration of the present invention and the refractive index is controlled under more preferable stretching operation conditions.

(Functional layer)
In the production of the optical film according to the present invention, before and / or after stretching, an antistatic layer, a hard coat layer, a back coat layer, a slippery layer, an adhesive layer, a barrier layer, an antiglare layer, an antireflection layer, optical A functional layer such as a compensation layer may be provided.

<< Polarizing plate, liquid crystal display >>
The polarizing plate of the present invention and a liquid crystal display device using the same will be described.

(Polarizer)
The polarizing plate of the present invention is a polarizing plate formed by sandwiching at least one surface of a polarizer with the optical film according to the present invention.

  The polarizing plate can be produced by a general method. The optical film according to the present invention is preferably bonded to at least one surface of a polarizer prepared by subjecting the polarizer side of the optical film to alkali saponification treatment and immersion drawing in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. The optical film may be used on the other surface, or another optical film may be used. Commercially available cellulose acylate films (for example, Konica Minoltak KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, KC8UY-HA, C8UY-HA, C8UY KC4UE, KC4HR-1, KC4KR-1, KC4UA, KC6UA or more manufactured by Konica Minolta Opto Co., Ltd.) are also preferably used.

  When the optical film according to the present invention is the optical film A, the optical film used on the opposite side through the polarizer has an in-plane retardation Re measured at a wavelength of 590 nm of 20 to 100 nm and Rth = 70 to 300 nm. It is preferable that it is an optical film which has.

  The optical film having the retardation function is not particularly limited, and these films can be produced by, for example, methods described in JP-A Nos. 2005-196149 and 2005-275104. It is also preferable to use an optical film that also serves as an optical compensation film having an optically anisotropic layer formed by aligning a liquid crystal compound such as a discotic liquid crystal. For example, the optically anisotropic layer can be formed by the method described in JP-A-2005-275083. By using the optical film in combination with the optical film according to the present invention, a liquid crystal display device having a stable viewing angle expansion effect can be obtained.

  A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5 to 30 μm, particularly preferably 10 to 20 μm.

  Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is also preferably used. Among them, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used. The difference in hot water cutting temperature between two points 5 cm away in the TD direction of the film is more preferably 1 ° C. or less in order to reduce color spots, and two points separated 1 cm in the TD direction of the film. In order to reduce color spots, it is more preferable that the difference in the hot water cutting temperature is 0.5 ° C. or less.

  A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarization performance and durability, and has few color spots, and is particularly preferably used for a large-sized liquid crystal display device.

  The polarizer obtained as described above is usually used as a polarizing plate with a protective film bonded to both sides or one side. Examples of the adhesive used for pasting include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferably used.

(Liquid crystal display device)
By incorporating the polarizing plate of the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. The optical film according to the present invention can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), and IPS. Particularly preferred are VA (MVA, PVA) type and IPS type liquid crystal display devices.

  In particular, a polarizing plate using the optical film according to the present invention can impart excellent front contrast when used in a large-screen liquid crystal display device.

  In a large-screen liquid crystal display device with a 17-inch or larger screen, especially a 30-inch or larger screen, there is no distortion such as color unevenness and wavy unevenness in addition to the effects of the present invention, so eyes are not tired even during long-time viewing. There was an effect.

  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
<Production of cellulose acylate>
50 parts by mass of acetic acid was added to raw pulp (α cellulose 93% or more, water content 8.5%, calcium content in pulp 25 ppm: manufactured by Nippon Paper Industries Co., Ltd.), and an activation treatment was performed for 1 hour.

  The above acetic acid-containing pulp was put into a reactor, and further 500 parts by mass of acetic anhydride and 12 parts by mass of sulfuric acid were added to the reactor, the temperature was gradually increased from room temperature to 40 ° C., and kept at 40 ° C. for 1 hour, The esterification reaction was allowed to proceed.

  Next, after neutralizing by adding 250 parts of 30% aqueous acetic acid solution in the primary neutralization step, and neutralizing sulfuric acid to neutralize the sulfuric acid to stop the reaction, In order to hydrolyze the carboxylic anhydrides remaining in the aging step, 150 parts by mass of an 80% by mass aqueous acetic acid solution was added, maintained at 60 ° C., and stirred for 1 hour.

  Thereafter, 15 parts by mass of a 30% by mass aqueous magnesium acetate solution was added to neutralize the sulfuric acid to stop the reaction.

  Hydrophilic silica particles having an average particle size of 30 μm having a hydrophilic group were added to the dope after termination of the ripening reaction, and the mixture was stirred for 5 minutes, and then the acetic acid dope was filtered with a glass filter in a filtration step.

  Next, the cellulose acylate precipitated in the precipitation step is separated by filtration, washed 5 times with hot water at 50 ° C., and the remaining acetic acid aqueous solution is eluted, followed by drying at 70 ° C. for 3 hours. 89, triacetyl cellulose having a total acyl group substitution degree of 2.89 was obtained. The weight average molecular weight (Mw) was 190,000 as a result of measurement using the following measurement method.

(Measurement of weight average molecular weight (Mw))
The weight average molecular weight Mw was measured using commercially available gel permeation chromatography (GPC).

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three products manufactured by Showa Denko KK)
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 Corporation) Mw = 100000 to 500 calibration curves with 13 samples are used. Thirteen samples are used at approximately equal intervals.

(Calcium content)
3.0 g of the cellulose acylate sample prepared above is taken in a crucible and carbonized on an electric heater, and then put into an electric furnace and incinerated at 800 ± 10 ° C. for about 2 hours. After cooling with a lid, add 25 ml of 0.07% hydrochloric acid solution and dissolve by heating on a hot plate. After standing to cool, the solution is transferred to a 200 ml Nalgel flask. Wash the crucible with distilled water, transfer the liquid to a Nalgel flask, and pour distilled water up to the marked line.

  Using this as a test solution, the absorbance was measured using an atomic absorption photometer to determine the amount of Ca in the sample. As a result, the calcium content was 25 ppm.

  Similarly, raw material pulps having different calcium contents, types and amounts of additives, esterification reaction conditions, and water quality were adjusted, and triacetyl celluloses having different calcium contents shown in Tables 2 and 3 were prepared.

<Preparation of polyester additive represented by general formula (1)>
The polyester additives listed in Table 1 were used. No. For No. 1, the reaction time was adjusted and No. 1 with different number average molecular weights. 1-1 to 1-8 polyester additives were prepared. The number average molecular weight was measured using the gel permeation chromatography (GPC) described above.

<Preparation of optical film T1>
(Silicon dioxide dispersion)
Aerosil R812 (Nippon Aerosil Co., Ltd.) 10 parts by mass Ethanol 90 parts by mass The above was stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. 88 parts by mass of methylene chloride was added to the silicon dioxide dispersion while stirring, and the mixture was stirred and mixed for 30 minutes with a dissolver to prepare a silicon dioxide dispersion dilution. It filtered with the fine particle dispersion | distribution dilution liquid filter (Advantech Toyo Co., Ltd .: Polypropylene wind cartridge filter TCW-PPS-1N).

(Preparation of dope of cellulose acylate)
TAC: Triacetyl cellulose (acetyl group substitution degree 2.89, Mw = 19000, Ca content 25 ppm) 100 parts by mass Tinuvin 928 (manufactured by BASF Japan Ltd.) 3 parts by mass Polyester represented by the general formula (1) Additives, additive no. 1-1
10 parts by mass Methylene chloride 700 parts by mass Ethanol 40 parts by mass The above was put into a sealed container, heated, stirred and completely dissolved, and filtered. To this, 4 parts by mass of the silicon dioxide dispersion dilution was added with stirring, and the mixture was further stirred for 30 minutes.

(Film formation / stretching / drying)
Next, using a belt casting apparatus, a cellulose acylate dope was uniformly cast on a stainless steel band support at a temperature of 35 ° C. and a width of 2 m. With the stainless steel band support, the solvent was evaporated until the residual solvent amount reached 100% by mass, and the stainless steel band support was peeled off. The web of the peeled optical film is conveyed while being dried at 50 ° C., slitted, and then stretched at a stretching ratio of 10% in a TD direction (direction perpendicular to the film conveying direction) at 190 ° C. And dried at a drying temperature of 160 ° C. At this time, the residual solvent amount when starting stretching with a tenter was 4.5%. Thereafter, the film was dried for 15 minutes while being transported in a drying apparatus at 120 ° C. with a number of rolls, slitted, knurled with a width of 15 mm and a height of 10 μm at both ends of the film, wound around a core, and optical film T1 Got. The residual solvent amount of the film was less than 0.1%, the film thickness was 60 μm, the width was 2 m, and the winding length was 6000 m.

  In addition, the draw ratio of MD direction computed from the rotational speed of a stainless steel band support body and the driving speed of a tenter was 1.05 times.

<Production of optical films T2 to T36>
Tables 2 and 3 are the same as those of the optical film T1, except that the cellulose acylate, the polyester additive, the stretching condition (magnification, temperature), and the film thickness are adjusted by changing the raw material pulp. Optical films T2 to T36 described in 1 were produced. The film thickness and product width were adjusted appropriately so that the width and film thickness during casting were adjusted to the set values.

(Additives other than polyester additives)
BzSc: Sugar ester compound, benzyl saccharose EPEG: Ethyl phthalyl ethyl glycolate TPP: Triphenyl phosphate BDP: Biphenyl diphenyl phosphate In Tables 2 and 3, the description “TPP, BDP = 5, 5” And 5 parts by mass of BDP are added to the dope.

  In Tables 2 and 3, the haze after throwing is the haze value after 100 cycles after leaving the environment at −35 ° C. for 30 minutes and 90 ° C. for 30 minutes, and Δhaze is the haze value around 100 cycles. Is the difference.

<Preparation of polarizing plate>
The polarizing plate was produced by a general method. The polarizer side of the optical films T1 to T36 prepared above was subjected to alkali saponification treatment, and was bonded to both surfaces of the polarizer prepared by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution.

  In Tables 2 and 3, the panel contrast means that the above-prepared polarizing plate is peeled off from the polarizing plate on the front side of the panel of the 40-inch display BRAVIA X1 manufactured by SONY, and the prepared polarizing plate is used as a liquid crystal cell. Bonded to the front of the glass surface.

  The backlight of the liquid crystal display device was lit continuously for 1 hour in an environment of 23 ° C. and 55% RH, and then the front contrast of the panel was measured. For measurement, Konica Minolta Sensing Co., Ltd. Spectral Luminance Colorimeter CS-2000 was used to measure the luminance from the normal direction of the display screen of white display and black display on the liquid crystal display device, and the ratio was determined as the front contrast. did.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The front contrast of any 5 points of the liquid crystal display device was measured and averaged.

  As is clear from Tables 2 and 3, it can be seen that the optical film according to the present invention is an excellent optical film with little haze deterioration due to forced deterioration. Further, since the haze is improved, it can be seen that the panel contrast is excellent when used for a polarizing plate.

  The number average molecular weight of the polyester-based additive is preferably in the range of 300 to 700, more preferably in the range of 300 to 500.

Example 2
In the same manner as in Example 1, polarizing plates H1 to H8 were manufactured in the combinations shown in Table 4 using the manufactured optical film as a polarizer protective film. KC8UX, KC4UY, KC4UA, and KC6UA are all Konica Minolta Tac (manufactured by Konica Minolta Opto).

  The polarizing plate obtained by the above method was cut into a square of 500 mm, crossed Nicol on a light box, and the polarization degree unevenness was visually evaluated. It was shown to.

  It can be seen from Table 4 that none of the polarizing plates using the optical film according to the present invention is uneven.

Claims (5)

A method for producing an optical film comprising cellulose acylate and a matting agent, wherein a web containing cellulose acylate having a calcium content of 50 ppm or less and a polyester-based additive represented by the following general formula (1): By stretching at a draw ratio of 5% to 50% at 180 ° C. to 230 ° C., the in-plane retardation Re measured at a wavelength of 590 nm in a 23 ° C./55% RH environment of the stretched optical film is 0. A method for producing an optical film, wherein the retardation Rth in the thickness direction is adjusted within a range of −5 to 20 nm within a range of −10 nm.
General formula (1) B- (GA) n-GB
In the formula, B is a monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A is This represents a dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, n represents an integer of 0 or more, and includes a configuration of BGB.   The method for producing an optical film according to claim 1, wherein the polyester-based additive has a number average molecular weight of 300 to 700.   The method for producing an optical film according to claim 1 or 2, wherein the dicarboxylic acid of the polyester-based additive is a mixture of at least one aliphatic dicarboxylic acid and at least one aromatic dicarboxylic acid.   The method for producing an optical film according to claim 1, wherein the end-capping group represented by B in the general formula (1) is an aromatic group.   The polarizing plate using the optical film manufactured by the manufacturing method of the optical film of any one of Claims 1-4.