JP5857922B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention relates to an optical film manufacturing method for manufacturing an optical film by a solution casting film forming method.

  In an image display device such as a liquid crystal display device, various optical films including a protective film for a polarizing plate are used. As such an optical film, for example, a film having excellent transparency such as a cellulose ester film is used.

  The optical film is manufactured by, for example, a solution casting film forming method. The solution casting film forming method is a method in which a resin solution (dope) obtained by dissolving a transparent resin, which is a raw material resin, in a solvent is cast on a traveling support to form a casting film and is peelable. This is a technique for obtaining a long optical film by drying and peeling from a support, and stretching and drying the peeled cast film.

  In recent years, in optical films applied to polarizing plates, techniques for further improving the viewing angle and color by adding an optical compensation function to the protective function of polarizing plates have been studied. Is being considered. Therefore, a cellulose triacetate resin in which retardation is less likely to occur and a cellulose acetate resin having a substitution degree of acetyl group of 2.0 to 2.6, which is more likely to cause retardation due to stretching treatment than cellulose acetate propionate resin. The use of (cellulose diacetate resin) has been studied.

  However, when a cellulose diacetate resin is used, the peelability from the support becomes a problem during film formation by the solution casting film formation method. That is, the cellulose diacetate resin contains a hydroxyl group, and this hydroxyl group is strongly bonded to the metal. For this reason, the dope which has cellulose diacetate resin as a main component has strong adhesiveness with the support body which consists of metals, and a big tension | tensile_strength is required when peeling a cast film from a support body.

  When the cast film is peeled off with a large tension, the cast film extends in the transport direction (MD direction) at the time of peeling, and the resin is oriented in the MD direction. Therefore, when the cast film after peeling is stretched in the width direction (TD direction) with a tenter, a desired optical value can be obtained unless the stretching ratio in the TD direction is made larger than usual. become unable. However, when the draw ratio is increased, the haze of the film increases and the transparency tends to decrease. As a result, when the produced film is applied to a polarizing plate of a liquid crystal display device to perform black display, light leakage occurs and the contrast is lowered.

  Therefore, in order to suppress the above-described contrast reduction in the liquid crystal display device, in the production of an optical film containing a cellulose acetate resin having a low degree of substitution, the casting film is removed from the support while suppressing the elongation when the casting film is peeled off. It would be desirable to be able to peel easily (with low tension).

  Various methods have been proposed for peeling the cast film from the support. For example, in Patent Document 1, both ends of the casting film in the width direction are subjected to an activation treatment by irradiation with atmospheric pressure plasma or excimer UV (ultraviolet light) on the surface of the support in contact with both ends of the casting film in the width direction. The fluttering of the part is suppressed to improve the adhesion (wettedness) with the surface of the support, and the peeling from the support is performed more stably. Moreover, in patent document 2, it peels only in the part (width direction center part) used as a product by peeling only the width direction both ends of a casting film from a support body first, and pulling both ends with a pin after that in a conveyance direction. The cast film is peeled off from the support with almost no tension.

  The methods of Patent Documents 1 and 2 described above are effective in that the cast film can be easily peeled off from the support, but are not desirable in the following points.

  In the technique of Patent Document 1, when the optical film is manufactured at a high speed by increasing the transport speed of the casting film on the support, the output in the activation process (for example, the voltage applied between the counter electrodes in the atmospheric pressure plasma) In the case of excimer UV, it is necessary to increase the amount of ultraviolet light), and for this purpose, it is necessary to enlarge the apparatus for generating atmospheric pressure plasma and excimer UV. Such a large apparatus is narrower in the vicinity of the support than the casting position of the dope (for example, between the casting die for casting the dope and the peeling roll for peeling the casting film from the support). In practice, it is difficult to arrange in a space unless the length of the support or the casting position of the dope is changed. For this reason, the method of patent document 1 cannot respond easily to the high-speed conveyance of a casting film.

  In the method of Patent Document 2, since both ends of the casting film are peeled off before the center part, a difference in the amount of residual solvent occurs between the both ends and the center part of the casting film, which also causes a difference in film thickness. Will occur. As a result, there is a concern that the cast film breaks at the boundary between both end portions and the central portion.

JP 2011-115969 A (refer to claim 1, paragraphs [0022] to [0028], etc.)

JP 2010-274583 A (refer to claim 1, paragraphs [0022], [0052] to [0065], FIGS. 3 to 8 etc.)

  In view of the above circumstances, an object of the present invention is to easily peel off a casting film while suppressing elongation at the time of peeling of the casting film in the production of an optical film containing a cellulose acetate resin having a low substitution degree. Another object of the present invention is to provide a method for producing an optical film that can easily cope with high-speed conveyance of a cast film and can suppress breakage of the cast film.

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

1. A method for producing an optical film comprising a cellulose acetate resin having an acetyl group substitution degree of 2.0 to 2.6,
A casting step of casting a dope containing the cellulose acetate resin and a solvent on a support to form a casting film;
A peeling conveyance step of peeling the casting film from the support at the same time in the width direction center and both ends in the width direction, and conveying it to the take-up roll;
A take-up step of taking up the cast film by the take-up roll;
In the peeling / conveying step, the tension provided in the high residual solvent amount conveying region where the residual solvent amount of the casting film is 45% by mass or more in the conveying region from the peeling position of the casting film to the take-off roll. The manufacturing method of the optical film characterized by providing a tension | tensile_strength in a conveyance direction with respect to the width direction both ends of the said cast film with a provision roll.

  2. In the high residual solvent amount conveyance region, tension is applied in the conveyance direction to the both end portions of the casting film by the tension applying rolls provided at a plurality of locations in the conveyance direction of the casting film. The method for producing an optical film as described in 1 above.

  3. Among the tension applying rolls provided at two different places in the transport direction of the casting film, the tension applied to the both end portions of the casting film by the tension applying roll located on the upstream side in the transport direction is the transport direction. 3. The method for producing an optical film as described in 2 above, wherein the tension is not higher than the tension applied to the both end portions of the cast film by a tension applying roll located on the downstream side.

4). The high residual solvent amount conveyance area,
A first conveying region in which tension is applied to the both end portions of the cast film by the tension applying roll;
When divided into a second transport area located downstream of the first transport area in the transport direction,
In the second transport area, the cast film is transported with a tension smaller than a tension applied by a tension applying roll on the most downstream side of the first transport area. The manufacturing method of the optical film in any one.

  5. Any one of 1 to 4 above, wherein an elongation in the conveyance direction of the casting film is + 1.0% or less with respect to a conveyance length of the casting film in the high residual solvent amount conveyance region. The manufacturing method of the optical film of description.

  6). In the peeling and conveying step, the peeling position of the cast film is monitored, and the tension applied to the both end portions of the cast film by the tension applying roll is controlled based on the monitoring result. To 5. The method for producing an optical film according to any one of 5 to 5.

  7). In the peeling and conveying step, the tension applied to the both end portions of the casting film by the tension applying roll is controlled so that the peeling position of the casting film falls within a certain range. The manufacturing method of the optical film of description.

  8). The optical film according to any one of 1 to 7 above, wherein a tension is applied by using a nip roll that is driven in the conveying direction while pressing both ends of the casting film as the tension applying roll. Production method.

  9. The optical film as described in any one of 1 to 7 above, wherein a tension roll is applied as the tension applying roll by using a suction roll that is driven in the conveying direction while sucking the both ends of the cast film. Manufacturing method.

  10. The take-up roll is provided in a conveyance region where the residual solvent amount of the casting film is 15% by mass or less, and the casting film is provided with tension in the conveyance direction in a region including the both ends of the casting film. 10. The method for producing an optical film as described in any one of 1 to 9 above, wherein the film is taken up.

  11. 11. The production of an optical film as described in any one of 1 to 10 above, further comprising a stretching / drying step in which the cast film taken by the take-up roll is stretched and dried to form an optical film. Method.

12 When the retardation in the in-plane direction of the optical film is Ro and the retardation in the film thickness direction is Rth,
25 nm ≦ Ro ≦ 100 nm
And
50 nm ≦ Rth ≦ 300 nm
12. The method for producing an optical film as described in 11 above, wherein

  13. 13. The method for producing an optical film as described in 11 or 12 above, wherein the film thickness of the optical film is from 15 to 60 μm.

  According to the above production method, in the production of an optical film containing a cellulose acetate resin having a low degree of substitution, it is provided in the high residual solvent amount conveyance area when the cast film is peeled off from the support and conveyed to the take-up roll. The tension applying rolls apply tension for assisting peeling to both ends in the width direction of the cast film. Thus, while suppressing the elongation at the time of peeling of the casting film by peeling the casting film by applying tension to the local positions of both ends instead of the entire width direction of the casting film. The cast film can be easily peeled off. In addition, by providing tension applying rolls that apply tension to both ends, the film surface is used as an optical film even in the case where the tension applying roll is brought into contact with the web under a high residual solvent (center portion). The deterioration of the surface shape can be suppressed. Both end portions of the optical film are gripped by gripping means such as a tenter clip at the time of the subsequent stretching in the width direction, and thereafter removed by a slitter or used as an area to be embossed to prevent sticking. Therefore, there is no problem even if the surface shape is deteriorated.

  In addition, since the casting film can be easily peeled off, it is not necessary to improve the adhesion to the casting film by performing an activation treatment on both ends of the support to facilitate the peeling as in the prior art. . This eliminates the need to consider the arrangement of the apparatus for performing the activation process when transporting the casting film at a high speed, and thus can easily cope with the high-speed transport of the casting film.

  In the peeling conveyance process, since the casting film is peeled from the support at the center and both ends in the width direction, there is a difference in the amount of residual solvent and film thickness between the center and both ends of the casting film. It does not occur, and the casting film can be prevented from breaking at the boundary between the central portion and both end portions.

It is explanatory drawing which shows the structure of the outline of the manufacturing apparatus which enforces the manufacturing method of the optical film which concerns on embodiment of this invention. It is a perspective view which shows an example of the tension | tensile_strength provision roll with which the said manufacturing apparatus is provided. In the said manufacturing apparatus, it is a block diagram which shows the structure relevant to the drive of the said tension provision roll. It is explanatory drawing which shows the fluctuation | variation of the peeling position of a casting film in the said manufacturing apparatus. It is a perspective view which shows the other example of the said tension | tensile_strength provision roll.

  Hereinafter, although an embodiment of the present invention is described, the present invention is not limited to the following embodiment.

  The manufacturing method of the optical film of this embodiment is a method of manufacturing an optical film by a solution casting film forming method using a resin solution (dope). First, the dope used in this embodiment will be described.

[About Dope]
The dope used in the present embodiment is obtained by dissolving a transparent resin in a solvent. Cellulose acetate resin is used as the transparent resin.

<Cellulose acetate>
The cellulose acetate used in the present embodiment can be produced at low cost, has high retardation, and can be made into a thin film even when it is a retardation film having a high retardation, and has a high retardation. Even if it is expressed, it is preferable to use cellulose acetate having a degree of substitution of acetyl group of 2.0 to 2.6 from the viewpoint that the draw ratio can be kept low and failure such as breakage can be avoided.

  When the substitution degree of the acetyl group of cellulose acetate is less than 2.0, deterioration of film surface quality due to an increase in dope viscosity, haze-up due to an increase in stretching tension, and the like may occur. Further, when the substitution degree of the acetyl group is larger than 2.6, it is difficult to obtain a necessary phase difference. The method for measuring the degree of substitution of the acetyl group can be carried out according to D-817-91, which is one of the standards formulated and published by ASTM (American Society for Testing and Materials). The substitution degree of the acetyl group is more preferably 2.2 to 2.45.

  The number average molecular weight (Mn) of cellulose acetate is preferably in the range of 30,000 to 300,000 from the viewpoint of strong mechanical strength of the resulting film, and more preferably 50,000 to 200,000.

  The ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of cellulose acetate is preferably 1.4 to 3.0.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) of cellulose acetate were measured using gel permeation chromatography (GPC). The measurement conditions are as follows.
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.

  There are no particular limitations on cellulose as the raw material for cellulose acetate, but cotton linters, wood pulp (from conifers and hardwoods), kenaf, and the like can be mentioned, and cellulose acetates obtained from them can be mixed in any proportion. Can also be used.

  The cellulose acetate of this embodiment can be produced by a known method. Specifically, it can be synthesized with reference to the methods described in JP-A Nos. 10-45804 and 2009-161701. Moreover, as a commercial item, Daicel Corporation L20, L30, L40, L50, Ca398-3, Ca398-6, Ca398-10, Ca398-30, Ca394-60S, etc. of Eastman Chemical Co. can be used.

  The dope in the present embodiment is mainly composed of the cellulose acetate resin as described above, but may further contain the following composition.

<Sugar ester compound>
The optical film (dope) in this embodiment may contain a compound represented by the following general formula (1) (hereinafter also referred to as a sugar ester compound).

The average degree of substitution of the compound represented by the general formula (1) is preferably 3.0 to 6.0. Here, the degree of substitution of the compound represented by the general formula (1) represents the number of substituents other than hydrogen among the eight hydroxyl groups contained in the general formula (1). among R ₁ to R ₈ of formula (1) represents the number containing a group other than hydrogen. Accordingly, when all of R _{1 to} R ₈ are substituted with a substituent other than hydrogen, the degree of substitution is 8.0, which is the maximum value, and when all of R _{1 to} R ₈ are hydrogen atoms, the degree of substitution is Becomes 0.0.

  In the present embodiment, the average substitution degree of the compound represented by the general formula (1) needs to be 3.0 to 6.0. In the compound having the structure represented by the general formula (1), it is difficult to synthesize a single kind of compound in which the number of hydroxyl groups and the number of OR groups are fixed. Since it is known that it becomes a compound in which several different components are mixed, it is appropriate to use the average degree of substitution as the degree of substitution in the general formula (1). The average substitution degree can be measured from the area ratio of the chart showing the substitution degree distribution by high performance liquid chromatography by a conventional method.

In the general formula (1), R _{1 to} R ₈ represent a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group, and R _{1 to} R ₈ may be the same or different. It may be.

  Examples of the sugar as a raw material for synthesizing the sugar ester compound according to the present embodiment include the following, but the present invention is not limited thereto.

  Glucose, galactose, mannose, fructose, xylose or arabinose, lactose, sucrose, nystose, 1F-fructosyl nystose, stachyose, maltitol, lactitol, lactulose, cellobiose, maltose, cellotriose, maltotriose, raffinose or kestose . In addition, gentiobiose, gentiotriose, gentiotetraose, xylotriose, galactosyl sucrose, and the like are also included.

  There is no restriction | limiting in particular as monocarboxylic acid used at the time of the synthesis | combination of the sugar ester compound which concerns on this embodiment, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. . The carboxylic acid used may be one type or a mixture of two or more types.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, Saturated lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, and laxaric acid Examples thereof include unsaturated fatty acids such as fatty acids, undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferable aromatic monocarboxylic acids include aromatic monocarboxylic acids having 1 to 5 alkyl groups or alkoxy groups introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, cinnamic acid, benzylic acid, An aromatic monocarboxylic acid having two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, tetralin carboxylic acid, or a derivative thereof can be exemplified, and benzoic acid is particularly preferable.

Some specific examples of the sugar ester compound according to this embodiment are shown below. These are cases where R _{1 to} R ₈ are all the same substituent R, but the present invention is not limited thereto.

  The sugar ester compound according to the present embodiment can be produced by reacting a sugar ester with an acylating agent. The acylating agent is also called an esterifying agent, and is composed of, for example, an acid halide of acetyl chloride, an anhydride such as acetic anhydride. The distribution of the degree of substitution is formed by adjusting the amount of acylating agent, the timing of addition, and the esterification reaction time, but it is a mixture of sugar ester compounds with different degrees of substitution or purely isolated compounds with different degrees of substitution. Thus, the desired average degree of substitution can be obtained, and components having a degree of substitution of 4 or less can be adjusted.

  (Synthesis example of sugar ester compound)

Four-headed Kolben equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube was charged with 34.2 g (0.1 mol) of sucrose, 180.8 g (0.8 mol) of benzoic anhydride, 379. 7 g (4.8 mol) was charged, the temperature was raised while bubbling nitrogen gas from a nitrogen gas introduction tube with stirring, and an esterification reaction was carried out at 70 ° C. for 5 hours. Next, the inside of the Kolben was depressurized to 4 × 10 ² Pa or less, and after excess pyridine was distilled off at 60 ° C., the inside of the Kolben was depressurized to 1.3 × 10 Pa or less and the temperature was raised to 120 ° C. Most of the acid and benzoic acid formed were distilled off. Then, 1 L of toluene and 300 g of a 0.5% by mass aqueous sodium carbonate solution were added, and the mixture was stirred at 50 ° C. for 30 minutes and then allowed to stand to separate a toluene layer. Finally, 100 g of water is added to the collected toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer is separated, and the toluene is distilled off at 60 ° C. under reduced pressure (4 × 10 ² Pa or less). A mixture of A-1, A-2, A-3, A-4 and A-5 was obtained.

  When the obtained mixture was analyzed by HPLC and LC-MASS, A-1 was 1.2% by mass, A-2 was 13.2% by mass, A-3 was 14.2% by mass, and A-4 was 35%. The mass% and A-5 were 40.0 mass%. The average degree of substitution was 5.2.

  Similarly, 158.2 g (0.7 mol) of benzoic anhydride, 146.9 g (0.65 mol), 135.6 g (0.6 mol), 124.3 g (0.55 mol) and equimolar pyridine. To obtain sugar esters of components as shown in Table 1.

  Then, by purifying a part of the obtained mixture by column chromatography using silica gel, each of A-1, A-2, A-3, A-4, A-5, etc. with 100% purity was obtained. Obtained.

  A-5 or the like means a mixture of all components having a substitution degree of 4 or less, that is, compounds having substitution degrees of 4, 3, 2, 1. The average substitution degree was calculated with A-5 and the like being the substitution degree 4.

  In this embodiment, the average substitution degree was adjusted by adding a sugar ester close to the desired average substitution degree and the isolated A-1 to A-5 in combination.

(Measurement conditions for HPLC-MS)
1) LC section Device: JASCO CO., LTD. Column oven (JASCO CO-965), detector (JASCO UV-970-240 nm), pump (JASCO PU-980), degasser (JASCO DG-980-50)
Column: Inertsil ODS-3 Particle size 5 μm 4.6 × 250 mm (manufactured by GL Sciences Inc.)
Column temperature: 40 ° C
Flow rate: 1 ml / min
Mobile phase: THF (1% acetic acid): H ₂ O (50:50)
Injection volume: 3 μl
2) MS unit Device: LCQ DECA (manufactured by Thermo Quest Co., Ltd.)
Ionization method: Electrospray ionization (ESI) method Spray Voltage: 5 kV
Capillary temperature: 180 ° C
Vaporizer temperature: 450 ° C

  The average substitution degree of the compound represented by the general formula (1) added to the optical film of the present embodiment is preferably 4.5 to 6.0, and the distribution range of the substitution degree is 4.0 to 8. 0.0 is preferred. Furthermore, it is preferable that the content ratio of the component having a substitution degree of 8.0 is 2% or less.

  The distribution of the degree of substitution is formed by adjusting the esterification reaction time, but may be adjusted to the target average degree of substitution by mixing compounds with different degrees of substitution.

  The optical film of the present embodiment preferably contains 1 to 20% by mass, particularly 3 to 15% by mass of the sugar ester compound in the ester film. Within this range, the excellent effects of the present embodiment are exhibited, and there is no bleed out during storage of the original fabric, which is preferable.

<Ester compound represented by general formula (2)>
Furthermore, the dope forming the optical film according to the present embodiment may contain an ester compound represented by the following general formula (2) from the viewpoint of retardation stability particularly in the environmental change of the polarizing plate.

General formula (2) B- (GA) n-GB
However, in the formula, B is a hydroxy group or carboxylic 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. The group A represents an alkylene 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 1 or more.

  In the general formula (2), the alkylene glycol component having 2 to 12 carbon atoms includes 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 (neopentyl glycol), 2 , 2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl- 1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1, -Hexanediol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are one kind or two kinds or more Used as a mixture.

  In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with cellulose acetate.

  Examples of the aryl glycol component having 6 to 12 carbon atoms include hydroquinone, resorcin, bisphenol A, bisphenol F, bisphenol and the like, and these glycols can be used as one kind or a mixture of two or more kinds.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. These glycols may be used alone or in combination of two or more. Can be used as a mixture.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and the like. Used as a mixture of two or more. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5 naphthalene dicarboxylic acid, 1,4 naphthalene dicarboxylic acid, and 2,6-naphthalene dicarboxylic acid.

  Although the specific compound of the ester compound represented by General formula (2) used for this embodiment below is shown, this invention is not limited to these.

<Other additives>
(Plasticizer)
In the present embodiment, the optical film has a general formula (
A plasticizer may be contained in addition to the compound represented by 2).

  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 ester plasticizer. Agent, acrylic plasticizer and the like.

  Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol preferably used in the present embodiment is represented by the following general formula (a).

Formula _{(a) R 11 - (OH} ) n
R ₁₁ represents an n-valent organic group, n represents a positive integer of 2 or more, and the OH group represents an alcoholic and / or phenolic hydroxyl group.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like.

  In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferable in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with cellulose acetate is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as an alkyl group, a methoxy group or an ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid or toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose acetate.

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

  Below, the specific compound of a polyhydric alcohol ester is illustrated.

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

  Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (b).

Formula (b) R ₁₂ (COOH) _m1 (OH) _n1
In the formula, R ₁₂ represents an (m1 + n1) -valent organic group, m1 represents a positive integer of 2 or more, n1 represents an integer of 0 or more, a COOH group represents a carboxyl group, and an OH group represents an alcoholic or phenolic hydroxyl group.

  Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited to these.

  Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for the polyhydric carboxylic acid ester compound which can be used for this embodiment, Well-known alcohol and phenols can be used.

  For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenyl carboxylic acid, naphthalene carboxylic acid, and tetralin carboxylic acid. The aromatic monocarboxylic acid which has, or those derivatives can be mentioned. Particularly preferred are acetic acid, propionic acid, and benzoic acid.

  The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improvement in retention, and the smaller one is preferable in terms of moisture permeability and compatibility with cellulose acetate.

  One kind of alcohol may be used for the polyvalent carboxylic acid ester of the present embodiment, or a mixture of two or more kinds may be used.

  The acid value of the polyvalent carboxylic acid ester compound of this embodiment is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. By setting the acid value within the above range, the environmental fluctuation of retardation is also suppressed, which is preferable.

  In addition, an acid value means the milligram number of potassium hydroxide required in order to neutralize the acid (carboxyl group which exists in a sample) contained in 1g of samples. The acid value is measured in accordance with JIS K0070, which is one of the standards of JIS (Japanese Industrial Standards Committee).

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto.

  For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

(UV absorber)
The optical film of this embodiment can also contain 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 this embodiment is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex salts, inorganic Examples thereof include powders.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, and the like. In addition, there are tinuvins such as tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, and tinuvin 328. These are all commercial products manufactured by BASF Japan and can be preferably used.

  The UV absorbers preferably used in this embodiment are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, and particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. is there. In addition, a discotic compound such as a compound having a 1,3,5 triazine ring is also preferably used as the ultraviolet absorber.

  It is preferable that the polarizing plate protective film concerning this embodiment contains 2 or more types of ultraviolet 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 of adding the UV absorber can be added 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 acetate 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 operating conditions, and the like. However, when the dry film thickness of the polarizing plate protective film is about 30 to 200 μm, the amount of the UV absorbing agent is 0. 5-10 mass% is preferable and 0.6-4 mass% is still more preferable.

(Antioxidant)
The antioxidant is also referred to as a deterioration preventing agent, and has a role of delaying or preventing the film from decomposing due to, for example, halogen as a residual solvent in the film or phosphoric acid as a phosphoric acid plasticizer. For this reason, it is preferable that the optical film of this embodiment contains antioxidant.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

  The amount of these compounds added is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to cellulose acylate.

(Fine particles)
In the optical film of the present embodiment, for example, silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate are used to improve handling. It is preferable to contain inorganic fine particles such as magnesium silicate and calcium phosphate and fine particles such as a crosslinked polymer. Among these, silicon dioxide is preferable because it can reduce the haze of the film.

  The primary average particle diameter of the fine particles is preferably 20 nm or less, more preferably 5 to 16 nm, and particularly preferably 5 to 12 nm.

  These fine particles preferably form secondary particles having a particle size of 0.1 to 5 μm and are contained in the optical film, and the preferable average particle size is 0.1 to 2 μm, more preferably 0.1 to 0. .6 μm. Thereby, the unevenness | corrugation about 0.1-1.0 micrometer high can be formed in the film surface, and this can give appropriate slipperiness to the film surface.

  Measurement of the primary average particle diameter of the fine particles used in the present embodiment is performed by observing the particles with a transmission electron microscope (magnification of 500,000 to 2,000,000 times), observing 100 particles, measuring the particle diameter, The average value was taken as the primary average particle size.

  The apparent specific gravity of the fine particles is preferably 70 g / liter or more, more preferably 90 to 200 g / liter, and particularly preferably 100 to 200 g / liter. A larger apparent specific gravity makes it possible to produce a high-concentration dispersion, which improves haze and agglomerates, and is particularly preferred when preparing a dope having a high solid content concentration. .

  Silicon dioxide fine particles having an average primary particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more are, for example, a mixture of vaporized silicon tetrachloride and hydrogen burned in air at 1000 to 1200 ° C. Can be obtained. Further, for example, those commercially available under the trade names of Aerosil 200V and Aerosil R972V (manufactured by Nippon Aerosil Co., Ltd.) can be used as the fine particles.

The apparent specific gravity described above is calculated by the following equation by taking a certain amount of silicon dioxide fine particles in a graduated cylinder and measuring the weight at this time.
Apparent specific gravity (g / liter) = silicon dioxide mass (g) / volume of silicon dioxide (liter)

  Examples of the method for preparing the fine particle dispersion used in the present embodiment include the following three types.

<< Preparation Method A >>
After stirring and mixing the solvent and fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the dope solution and stirred.

<< Preparation Method B >>
After stirring and mixing the solvent and fine particles, dispersion is performed with a disperser. This is a fine particle dispersion. Separately, a small amount of cellulose acylate is added to the solvent and dissolved by stirring. The fine particle dispersion is added to this and stirred. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.

<< Preparation Method C >>
Add a small amount of cellulose acylate to the solvent and stir to dissolve. Fine particles are added to this and dispersed by a disperser. This is a fine particle addition solution. The fine particle additive solution is sufficiently mixed with the dope solution using an in-line mixer.

  Preparation method A is excellent in dispersibility of silicon dioxide fine particles, and preparation method C is excellent in that silicon dioxide fine particles are difficult to re-aggregate. Among them, the preparation method B described above is a preferable preparation method that is excellent in both dispersibility of the silicon dioxide fine particles and difficulty in reaggregation of the silicon dioxide fine particles.

《Distribution method》
The concentration of silicon dioxide when the silicon dioxide fine particles are mixed with a solvent and dispersed is preferably 5% by mass to 30% by mass, more preferably 10% by mass to 25% by mass, and most preferably 15% by mass to 20% by mass. A higher dispersion concentration is preferable because liquid turbidity with respect to the added amount tends to be low, and haze and aggregates are improved.

  The solvent used preferably includes lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. The solvent other than the lower alcohol is not particularly limited, but it is preferable to use a solvent used at the time of film formation of cellulose acetate.

  The amount of silicon dioxide fine particles added to cellulose acetate is preferably 0.01 parts by mass to 5.0 parts by mass, and 0.05 parts by mass to 1.0 parts by mass with respect to 100 parts by mass of cellulose acetate. More preferred is 0.1 to 0.5 parts by mass. The larger the amount of silicon dioxide fine particles added, the better the dynamic friction coefficient, and the smaller the amount added, the less aggregate.

  As the disperser, a normal disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. It is preferable to use a medialess disperser for dispersing the silicon dioxide fine particles because of low haze. Examples of the media disperser include a ball mill, a sand mill, and a dyno mill.

  Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type. In this embodiment, a high pressure disperser is preferable. The high pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

  When processing with a high-pressure dispersion apparatus, for example, the maximum pressure condition inside the apparatus is preferably 10 MPa or more, more preferably 20 MPa or more in a thin tube having a tube diameter of 1 to 2000 μm. At that time, it is preferable that the maximum reaching speed reaches 100 m / second or more, and the heat transfer speed reaches 420 kJ / hour or more.

  Examples of the high-pressure dispersion apparatus include an ultrahigh-pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersion apparatuses such as homogenizer manufactured by Izumi Food Machinery. UHN-01 manufactured by Sanwa Machinery Co., Ltd.

  In addition, casting a dope containing fine particles so as to be in direct contact with the casting support is preferable because a film having high slip properties and low haze can be obtained.

  Moreover, functional thin films, such as a hard-coat layer and an antireflection layer, are provided with respect to the optical film which peeled after casting and was dried and wound up in roll shape. In addition, until the optical film is processed or shipped, the optical film is usually packaged to protect the product from dirt, static electricity, and the like.

  The packaging material is not particularly limited as long as the above purpose can be achieved, but a material that does not hinder volatilization of the residual solvent from the film is preferable. Specific examples include polyethylene, polyester, polypropylene, nylon, polystyrene, paper, various non-woven fabrics, and the like. Those in which the fibers are mesh cloth are more preferably used.

<Preparation of dope>
The concentration of cellulose acetate in the dope is preferably higher because the drying load after casting on the metal support can be reduced. However, if the concentration of cellulose acetate is too high, the load during filtration increases and the filtration accuracy increases. Deteriorate. 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 to use a mixture of a good solvent and a poor solvent of cellulose acetate in terms of production efficiency, and there are many good solvents. This is preferable from the viewpoint of solubility of cellulose acetate. The good solvent refers to a solvent that dissolves the cellulose acetate used alone, and the poor solvent refers to a solvent that does not dissolve the cellulose acetate used alone or a solvent that swells. 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. In addition, a good solvent and a poor solvent change with the average acetylation degree (acetyl group substitution degree) of a cellulose acetate.

  Although the good solvent used by this embodiment is not specifically limited, Organic halogen compounds, such as a methylene chloride, dioxolanes, acetone, methyl acetate, methyl acetoacetate, etc. are mentioned. Particularly preferred is methylene chloride or methyl acetate.

  Moreover, although the poor solvent used by this embodiment 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, it is preferable to collect | recover the solvent removed from the film by the drying in a film forming process, and to recycle this into the solvent used for melt | dissolution of a cellulose acetate. The recovered solvent may contain a small amount of additives (for example, plasticizer, ultraviolet absorber, polymer, monomer component, etc.) added to cellulose acetate, but it is preferable that these are included. It can be reused, and can be purified and reused if necessary.

  As a method for dissolving cellulose acetate 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.

  Further, a method in which cellulose acetate is mixed with a poor solvent (poor solvent) and wetted or swollen, and then a good solvent (good solvent) is further 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 acetate, 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.

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

  Next, this cellulose acetate 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. However, if the absolute filtration accuracy is too small, there is a problem that the filter medium is easily clogged. 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 acetate by filtration. Bright spot foreign matter means that when two polarizing plates are placed in a crossed Nicol state, an optical film or the like is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite 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, the number of bright spots is 100 / cm ² or less, more preferably 50 / cm ² or less, and further preferably 0 to 10 / 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. Further, the filtration pressure is preferably small. More specifically, 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.

[Method for producing optical film]
Next, a method for producing an optical film by the solution casting film forming method using the above-described dope will be described. FIG. 1 is an explanatory diagram illustrating a schematic configuration of a manufacturing apparatus that performs the method for manufacturing an optical film of the present embodiment. The manufacturing apparatus includes a casting die 1, a support 2, a peeling roll 3, a transport unit 4, a take-up roll 5, a stretching unit 6, a drying unit 7, and a winding unit 8. It is configured.

  The casting die 1 casts a dope 11 in which a transparent resin is dissolved on the surface of the support 2. In the present embodiment, the dope 11 includes a cellulose acetate resin having a low substitution degree (acetyl substitution degree of 2.0 to 2.6) and a solvent as described above.

  The support body 2 is composed of a metal endless belt made of, for example, stainless steel (SUS), and is stretched by rolls 2a and 2a made of a pair of drive rolls and driven rolls so as to be able to run. In addition, the support body 2 may be comprised with the rotating metal drum (endless drum) whose surface is a mirror surface. The support 2 supports the dope 11 cast from the casting die 1 and is dried while being transported to form a casting film (web) 12.

  From the viewpoint of effectively utilizing the width of the support 2, the width of the dope 11 or the cast film 12 cast by the casting die 1 is preferably 80 to 99% with respect to the width of the support 2. And in order to finally obtain an optical film with a width | variety of 1000-2500 mm, it is preferable that the width | variety of the support body 2 is 1200-3200 mm.

  The peeling roll 3 is a roll for peeling the casting film 12 dried on the support 2 from the support 2 at the center 12a in the width direction and both ends 12b and 12b (see FIG. 2) at the same time. In the roll shape, the diameter is constant in the rotation axis direction and longer than the casting film 12 in the width direction. Here, in the casting film 12, the end portions 12b and 12b are regions that are cut in the future and are not used as products (optical films), and the remaining regions sandwiched between the end portions 12b and 12b on both sides are The central portion 12a can be used as a product.

  The distance between the support 2 and the peeling roll 3 is preferably 1 to 100 mm. Using the peeling roll 3 as a fulcrum, the cast film 12 can be peeled from the support 2 by pulling the dried cast film 12 under tension. The peeling tension (conveying tension) when peeling the casting film 12 from the support 2 is, for example, about 50 to 200 N / m. Adjusting the peeling tension by adjusting the nip roll pressure and rotation speed of the tension applying roll 21 (to be described later) of the transport unit 4, the suction force and rotation speed of the feed roll with suction, and the take-up tension of the take-up roll 5. Can do.

Residual solvent amount (residual solvent ratio) at the time of peeling the casting film 12 is 80 to 200% by mass in consideration of transportability after peeling, physical properties of the optical film formed after transporting and drying, and the like. In this embodiment, it is set to 80% by mass. The residual solvent amount is represented by the following formula.
Residual solvent amount (% by mass) = {(M1-M2) / M2} × 100
However, M1 shows the mass in the arbitrary time points of a cast film, M2 shows the mass after drying the cast film which measured M1 at 115 degreeC for 1 hour. Further, since the residual solvent amount of the casting film 12 is slightly different between the film surface and in the film, the residual solvent amount hereinafter refers to the average value of the residual solvent amount in the film thickness direction.

  Further, in the vicinity of the peeling roll 3, a peeling position detection sensor 3a for detecting the peeling position of the casting film 12 from the support 12 is provided. In this embodiment, the drive of each tension | tensile_strengthening roll 21 mentioned later is controlled based on the peeling position detected by the peeling position detection sensor 3a.

  The transport unit 4 transports the casting film 12 peeled off by the peeling roll 3 to the take-up roll 5 by a plurality of rolls. The plurality of rolls include a tension applying roll 21 (for example, a nip roll or a suction roll), details of which will be described later.

  The take-up roll 5 is a roll for taking up the casting film 12 transported by the transport section 4 with a predetermined tension, and is composed of a pair of nip rolls 5a and 5b arranged to face each other. In the present embodiment, the take-up roll 5 is configured to take up the casting film 12 while applying tension in the transport direction (Machine Direction: MD direction) to a region including the end portions 12b and 12b of the casting film 12. Yes. That is, the take-up roll 5 applies the tension in the transport direction to a region wider in the width direction including the region where the tension is applied by the tension applying roll 21 of the transport unit 4 and pulls the casting film 12. The take-up roll 5 may be configured to take up the casting film 12 by applying tension in the transport direction to the entire width direction of the casting film 12.

  The take-up roll 5 is provided in a conveyance region where the residual solvent amount of the casting film 12 is 15% by mass or less. That is, the residual solvent amount of the casting film 12 gradually decreases due to drying as it goes from the peeling position by the peeling roll 3 toward the take-up roll 5.

  As described above, the take-up roll 5 is provided in the conveyance area where the residual solvent amount of the casting film 12 is low, so that the take-up roll 5 includes the end portions 12b and 12b of the casting film 12 and more than this. Even if tension is applied to a wide area and the casting film 12 is conveyed, the casting film 12 can be conveyed without roughening the surface in contact with the take-up roll 5. Accordingly, the contact area between the take-up roll 5 and the casting film 12 is increased and the casting film 12 is stably conveyed as compared with the case where only the end portions 12b and 12b of the casting film 12 are nipped and pulled. It becomes possible.

  The stretching unit 6 is a tenter that stretches the cast film 12 taken by the take-up roll 5 in a direction (Transverse Direction: TD direction) orthogonal to the transport direction of the cast film 12. The casting film 12 can be stretched in the TD direction by fixing both ends of the casting film 12 with clips or pins.

  The drying unit 7 dries the casting film 12 stretched by the stretching unit 6 and discharges it as an optical film. The casting film 12 may be dried by using heated air or infrared light alone or in combination, but it is preferable to use heated air from the viewpoint of simplicity. The amount of the residual solvent of the optical film after drying in the drying unit 7 is preferably 0.001 to 5% by mass in consideration of the load of the drying process, dimensional stability during storage, stretching rate, and the like.

  The winding unit 8 is a unit that winds the optical film having a predetermined residual solvent amount on the winding core in the drying unit 7. For example, a constant tension method, a constant torque method, a taper tension method, a program with constant internal stress. It can be constituted by a winder that winds up an optical film using a tension control method or the like.

  In the above configuration, when the dope 11 is cast from the casting die 1 to the support 2, the dope 11 is dried on the support 2 to become a casting film 12 (casting step). Drying on the support 2 can be performed by heating the support 2 or by blowing heated air. At that time, the temperature of the casting film 12 varies depending on the solution of the dope 11, but in the range of −5 ° C. to 70 ° C. in consideration of the transport speed accompanying the evaporation time of the solvent, the degree of dispersion of fine particles, productivity, and the like. Is preferable, and the range of 0 ° C. to 60 ° C. is more preferable. The higher the temperature of the casting film 12, the higher the drying speed of the solvent, which is preferable. However, when the temperature is too high, foaming or flatness tends to deteriorate.

  Subsequently, the casting film 12 is simultaneously peeled off from the support 2 at the center portion 12a and the end portions 12b and 12b in the width direction by the peeling roll 3 and the conveying portion 4 and conveyed to the take-up roll 5 (peeling conveyance). Process). The time from casting the dope 11 on the support 2 to peeling off the casting film 12 varies depending on the film thickness of the optical film to be produced and the solvent used, but the peelability from the support 2 is considered. And it is preferable that it is the range for 0.5 to 5 minutes.

  The cast film 12 transported to the take-up roll 5 by the transport unit 4 is taken up by the take-up roll 5 (take-off process), then stretched in the TD direction by the stretching unit 6 and dried by the drying unit 7. An optical film is used (stretch drying process). The optical film after drying is wound up by the winding unit 8.

  In addition, after the casting film 12 is peeled off from the support 2, both ends in the width direction are cut at least once before being wound up by the winding unit 8 as an optical film. That is, the optical film is used as a product after both end portions in the width direction are cut. At this time, the positions at which both ends of the optical film are cut are at least either between the take-up roll 5 and the stretching unit 6, between the stretching unit 6 and the drying unit 7, or between the drying unit 7 and the winding unit 8. Any position is acceptable. The end portions 12b and 12b of the casting film 12 are included in a region that is cut before being wound as an optical film, and are not used as a product.

[About the transport unit]
Next, the detail of the above-mentioned conveyance part 4 is demonstrated. The transport unit 4 has a tension applying roll 21 in the high residual solvent amount transport region S. Here, first, the high residual solvent amount conveyance area S will be described.

  The high residual solvent amount conveyance area S is a conveyance area where the residual solvent amount of the casting film 12 is 45 mass% or more in the conveyance area from the peeling position where the casting film 12 is peeled off from the support 2 to the take-up roll 5. It is an area. In the present embodiment, the high residual solvent amount conveyance area S is further divided into a high tension conveyance area S1 (first conveyance area) and a low tension conveyance area S2 (second conveyance area). In addition, the high residual solvent amount conveyance area | region S may be comprised only in the high tension | tensile_strength conveyance area S1.

  The high tension conveyance area S <b> 1 is an area in which the casting film 12 is conveyed while applying tension in the conveyance direction by the tension applying roll 21. On the other hand, the low-tension conveyance area S2 is an area that is located downstream of the high-tensile conveyance area S1 in the conveyance direction and that conveys the casting film 12 further downstream by the conveyance roll 31.

  The conveyance roll 31 is not a nip roll (a pair of rolls) that sandwiches the casting film 12 but a single roll that conveys the casting film 12 only by contact with the peripheral surface. Thereby, the conveyance tension | tensile_strength provided to the casting film 12 by the conveyance roll 31 becomes lower than the tension | tensile_strength provided to the casting film 12 by the tension | tensile_strength provision roll 21 located in the most downstream side in the high tension | tensile_strength conveyance area | region S1. Yes. Here, the tension refers to the tension applied to both ends (ends 12b and 12b) in the width direction of the casting film 12 because the tension applying roll 21 is provided in the high-tension conveyance area S1. To do. In FIG. 1, two transport rolls 31 are provided in the low-tension transport area S <b> 2, but at least one transport roll 31 may be provided.

  In the high tension conveyance area S1, a tension applying roll 21 is provided in order to realize conveyance of the casting film 12 with high tension. In addition, at least one transport roll 22 for guiding the cast film 12 peeled off by the peeling roll 3 to the tension applying roll 21 is provided.

  The tension applying roll 21 conveys the casting film 12 while applying tension in the conveying direction to the end portions 12 b and 12 b of the casting film 12. FIG. 2 is a perspective view showing an example of the tension applying roll 21. Although the casting film 12 is conveyed while being bent by the tension applying roll 21 as shown in FIG. 1 (changing the conveying direction), in FIG. 2, for convenience, the casting film 12 is unidirectionally (linearly shaped). To). Of course, as shown in FIG. 2, the cast film 12 may be conveyed without being bent by the tension applying roll 21.

  As shown in FIG. 2, the tension applying roll 21 includes nip rolls 21 a and 21 b that press both end portions of the casting film 12. The nip rolls 21a and 21b are made of a resin such as NBR (Nitrile butadiene rubber). The length of one nip roll 21b in the axial direction is longer than the length of the casting film 12 in the width direction. Two nip rolls 21a are provided so as to correspond to the end portions 12b and 12b of the casting film 12, respectively. Therefore, when the casting film 12 is transported to the tension applying roll 21, only the end portions 12b and 12b of the casting film 12 are pressed by the nip rolls 21a and 21b, and driven in the transporting direction so that the end portions 12b and 12b are moved. Only the tension is applied in the transport direction.

  In the present embodiment, as shown in FIG. 1, the tension applying rolls 21 are provided at seven locations in the transport direction of the casting film 12, and are transported to both ends of the casting film 12 by each tension applying roll 21. Directional tension is applied. In FIG. 1, for the purpose of clearly distinguishing the nip rolls 21a and 21b constituting the tension applying roll 21 on the drawing, only the nip roll 21a is hatched (the roll without hatching is a nip roll 21b). is there). The tension applying roll 21 may be provided in at least one place in the transport direction of the casting film 12.

  The tension applied to the casting film 12 by the tension applying roll 21 can be adjusted by adjusting the nip pressures of the nip rolls 21a and 21b by a drive unit 10 (see FIG. 3) described later. In the present embodiment, the tension applied by each tension applying roll 21 provided at seven locations in the transport direction is a1 (N / m), a2 (N / m) in order from the upstream side of the casting film 12 in the transport direction. ),..., A7 (N / m), a1 ≦ a2 ≦. That is, of the tension applying rolls 21 and 21 provided at two different locations in the transport direction of the casting film 12, the tension applying roll 21 positioned on the upstream side in the transport direction is applied to both ends of the casting film 12. When the tension is A1 (N / m) and the tension applied to both ends of the casting film 12 by the tension applying roll 21 located on the downstream side in the transport direction is A2 (N / m), which two tensions The granting rolls 21 and 21 also satisfy A1 ≦ A2.

  When the casting film 12 is peeled off from the support 2 and transported to the take-up roll 5 by the above-described configuration of the transport unit 4, tension is provided in the high residual solvent transport region S (particularly, the high-tensile transport region S 1). The roll 21 applies tension to the both end portions of the casting film 12 in the transport direction. Since the applied tension works as a tension that assists the peeling of the casting film 12 with the peeling roll 3 as a fulcrum, peeling of the casting film 12 becomes easy. In addition, since tension is applied to the casting film 12 not at the entire width direction but at local positions at both ends, it is not necessary to apply extra tension to the casting film 12 as tension for assisting the peeling. In other words, it is possible to suppress elongation in the transport direction when the casting film 12 is peeled off.

In this way, the casting film 12 can be easily peeled off, and the elongation of the casting film 12 can be suppressed. Therefore, even if the peeled casting film 12 is stretched at a low stretching ratio by the stretching portion 6, it is dried after that. When an optical film is obtained, desired optical characteristics can be obtained. For example, in an optical film having a film thickness of 15 to 60 μm, the haze is 0.005 to 0.015, and the film thickness deviation (film thickness variation) in both the longitudinal direction and the width direction is 0.05 to 0.7 μm. An optical film can be realized. Further, when the retardation in the in-plane direction of the optical film is Ro (nm) and the retardation in the film thickness direction is Rth (nm),
25 nm ≦ Ro ≦ 100 nm
And
50 nm ≦ Rth ≦ 300 nm
The optical film can also be realized. As a result, when the manufactured optical film is applied to a polarizing plate of a liquid crystal display device to perform black display, light leakage can be reduced and contrast can be improved.

  In particular, the thinner the optical film to be manufactured, the easier it is to stretch the casting film 12 in the transport direction when tension is applied by the tension applying roll 21 during manufacturing. The manufacturing method of this embodiment to suppress becomes more effective. Therefore, the manufacturing method of this embodiment becomes very effective when manufacturing an optical film with a film thickness of 15 to 60 μm.

  Moreover, since the peeling of the casting film 12 is facilitated by providing the tension applying roll 21, as in Patent Document 1, in order to facilitate the peeling, the both ends of the support are subjected to activation treatment to be cast. There is no need to improve the adhesion to the film. For this reason, it is not necessary to consider the arrangement of the apparatus for performing the activation process when the casting film is conveyed at a high speed, and the layout before the peeling position (the length of the support, the casting position of the dope) is eliminated. It is not necessary to change the peeling position. Thereby, it is possible to easily cope with high-speed conveyance of the cast film.

  Moreover, since the peeling of the casting film 12 is facilitated by providing the tension applying roll 21, when the casting film is peeled as in Patent Document 2, the center portion and both end portions in the width direction are shifted in time. Therefore, it is possible to peel the central portion and both end portions of the cast film from the support at the same time as in this embodiment. Thereby, there is no difference in the amount of residual solvent and the film thickness between the central part and both end parts of the casting film, and the casting film can be prevented from breaking at the boundary between the central part and both end parts. .

  Furthermore, as in Patent Document 2, in the configuration in which both ends of the casting film are peeled off from the support body before the center, and then both ends are pulled in the transport direction by pins, and the center is peeled off. Due to the shrinkage in the width direction after peeling off, both ends are not covered with the pin, and the central part may not be peeled off. However, in this embodiment, the both end portions and the central portion of the casting film are peeled off at the same time, so that only the central portion cannot be peeled due to the shrinkage in the width direction of the both end portions.

  Further, in the present embodiment, in the high residual solvent amount conveyance region S, tension in the conveyance direction is applied to both ends of the casting film 12 by the tension applying rolls 21 provided at a plurality of locations in the conveyance direction of the casting film 12. Has been granted. By providing the tension applying rolls 21 at a plurality of locations in the transport direction, the tension applied to both ends of the casting film 12 can be dispersed at a plurality of locations in the transport direction. Thereby, the elongation of the casting film 12 in the conveyance direction can be suppressed as much as possible.

  In addition, the relationship between the tension A1 (N / m) of the tension applying roll 21 located on the upstream side in the transport direction and the tension A2 (N / m) of the tension applying roll 21 located on the downstream side in the transport direction is related to which two Even if the tension applying rolls 21 and 21 are selected, A1 ≦ A2. That is, in the high residual solvent amount conveyance area S, the tension applied to the casting film 12 in a state where the residual solvent amount is higher is the tension applied to the casting film 12 in the state where the residual solvent amount is lower. It is the same or smaller. In the state where the amount of residual solvent of the casting film 12 is high, the casting film 12 becomes easier to stretch when pulled in the transport direction than in the state where the amount of residual solvent is low. Therefore, by setting A1 ≦ A2, the residual solvent It is possible to further suppress the casting film 12 from extending in the transport direction in a high amount state.

  Further, in the low tension conveyance area S2, the casting film 12 is conveyed by the conveyance roll 31 with a tension smaller than the tension applied by the tension applying roll 21 on the most downstream side of the high tension conveyance area S1, so that the high tension is high. Even if the casting film 12 may once extend in the transport direction due to the application of tension in the transporting area S1, the casting film 12 is transported at a low tension in the low tension transporting area S2, thereby transporting the casting film 12 The film can be shrunk in the direction, whereby the elongation of the casting film 12 in the entire high residual solvent amount conveyance area S can be minimized. For example, the transport of the casting film 12 with respect to the transport length of the casting film 12 in the high residual solvent amount transport region S (the length in which the casting film 12 is actually transported in the high residual solvent amount transport region S). The elongation in the direction can be suppressed to + 1.0% or less. As described above, as a result of minimizing the elongation of the casting film 12 in the conveying direction, the peeled casting film 12 is stretched at a low stretching ratio by the stretching section 6 to obtain desired optical characteristics. It becomes possible to obtain reliably.

  In the present embodiment, nip rolls 21 a and 21 b are used as the tension applying roll 21. The nip pressure of the nip rolls 21a and 21b can be easily adjusted by reducing the distance between the axes of each roll, and is applied to both ends of the casting film 12 by changing the driving force (rotational speed) in the transport direction. The tension can be easily adjusted.

[About drive control of tension applying roll]
Next, drive control of the tension applying roll 21 based on the detection of the peeling position will be described. FIG. 3 is a block diagram illustrating a configuration related to driving of the tension applying roll 21 in the optical film manufacturing apparatus described above. The manufacturing apparatus further includes a control unit 9 and a drive unit 10 in addition to the peeling position detection sensor 3a and the tension applying roll 21 described above.

  The drive unit 10 is for driving the tension applying roll 21, and includes a motor, a gear, and the like, and is provided corresponding to each of the plurality of tension applying rolls 21. The drive unit 10 also has a function of adjusting the nip pressure and the nip roll rotation speed of the nip rolls 21a and 21b constituting the tension applying roll 21 and adjusting the inter-axis distance of the nip rolls 21a and 21b.

  The control unit 9 controls the driving unit 10 based on the detection result of the peeling position of the casting film 12 by the peeling position detection sensor 3a, and adjusts the nip pressure and the nip roll rotation speed of the tension applying roll 21, thereby the casting film. The tension applied to 12 is controlled.

  For example, when the adhesion of the casting film 12 to the support 2 is high, the casting film 12 is peeled off from the support 2 after exceeding the normal peeling position, as shown by the broken line path in FIG. There is a case. When the casting film 12 is peeled in this way, the casting film 12 is bent, so that there is a risk of streaking in the width direction leading to a product defect.

  Therefore, in such a case, the control unit 9 controls the drive unit 10 to increase the nip pressure and the nip roll rotation speed of the tension applying roll 21, and the conveyance applied to the casting film 12 by the tension applying roll 21. Increase directional tension. Thereby, it becomes possible to return the peeling position of the casting film 12 to the regular position close to the peeling roll 3, and to suppress the occurrence of product defects.

  On the contrary, when the tension by the tension applying roll 21 is too large and the peeling position of the casting film 12 fluctuates upstream from the normal position, the nip pressure of the tension applying roll 21 is set by the drive unit 10. By lowering and decreasing the tension by the tension applying roll 21, the peeling position of the casting film 12 can be returned to the normal position.

  In addition, the tension | tensile_strength of the tension | tensile_strength provision roll 21 may be controlled so that the width | variety may be given to the regular peeling position of the casting film 12, and the peeling position may be settled in a predetermined range.

  As described above, the peeling position of the casting film 12 is monitored by the peeling position detection sensor 3a, and the tension of the tension applying roll 21 is controlled based on the result, thereby suppressing fluctuations in the peeling position of the casting film 12. be able to. In particular, the occurrence of product defects can be suppressed by controlling the tension of the tension applying roll 21 so that the peeling position of the casting film 12 falls within a certain range.

  Incidentally, FIG. 5 is a perspective view showing another configuration example of the tension applying roll 21. The tension applying roll 21 may be composed of a suction roll 23. The suction roll 23 is a roll that conveys the casting film 12 while sucking both end portions (12b, 12b) in the width direction of the casting film 12. A plurality of suction holes 23 a are formed side by side on the outer peripheral surface of the suction roll 23. In at least the region of the outer peripheral surface that is in contact with the end portions 12b and 12b of the casting film 12, the suction roll 23 is rotated while sucking air through the suction holes 23a, thereby conveying the end portions 12b and 12b in the conveying direction. A tension can be applied to the. Therefore, even if the tension applying roll 21 is constituted by such a suction roll 23, the same effect as in the present embodiment can be obtained.

  The suction holes 23 a may be formed in the entire axial direction on the outer peripheral surface of the suction roll 23, or may be formed only in a region in contact with the end portions 12 b and 12 b of the casting film 12. However, if the suction holes 23a are formed in the whole area of the suction roll 23 in the axial direction, it is possible to easily cope with various settings of the widths of the end portions 12b and 12b by adjusting the width of the suction area in the axial direction. This is preferable because it is possible.

〔Example〕
Examples of the present invention will be described below, but the present invention is not limited to the following examples. For comparison with the examples of the present invention, comparative examples will also be described.

<Example 1>
The optical film was manufactured by the method shown below.

(Preparation of dope)
The following materials were put into a sealed container, heated at 80 ° C., completely dissolved with stirring, and filtered to prepare a dope.

Cellulose diacetate (acetyl substitution degree 2.40) 100 parts by mass Sugar ester compound (benzyl saccharose having an average substitution degree of 5.5) 10 parts by mass Plasticizer (ethylphthalylethyl glycolate) 3 parts by mass UV absorber (Tinuvin 326) 1 part by mass Inorganic fine particles (Aerosil 200V, manufactured by Nippon Aerosil Co., Ltd.) 0.5 part by mass Methylene chloride 340 parts by mass Ethanol 64 parts by mass

(Manufacture of cellulose acetate film)
First, by using an endless belt support made of SUS316, the dope obtained as described above was cast at a dope temperature of 35 ° C. and a cast hanger die on an endless belt support at a temperature of 25 ° C. Casting was performed at a casting speed (running speed of the support) of 100 m / min to form a casting film. And the casting film was peeled with the peeling roll, and it conveyed, providing tension | tensile_strength in a conveyance direction with the tension | tensile_strength provision roll with respect to the width direction both ends of a casting film. At this time, the residual solvent amount at the time of peeling the cast film from the endless belt support was 85% by mass.

  The cast film transported by the tension applying roll was transported further downstream by the transport roll and taken up by the take-up roll. At this time, the take-up tension with the take-up roll was 120 N / m. Then, the drawn cast film was stretched at a stretching portion in a TD direction at a predetermined stretching ratio (see Table 2) and dried, and then the obtained optical film was wound up by a winding portion. Thus, a retardation film having a thickness of 30 μm, an in-plane retardation Ro of 50 nm, and a retardation Rth of 120 nm in the film thickness direction was produced as an optical film.

  One nip roll (material: NBR, manufactured by Kakkuri Roller Mfg. Co., Ltd., EC200 series) was used as the tension applying roll for assisting the peeling of the cast film. Then, a nip roll is disposed at a position where the residual solvent amount is 65% by mass in the high residual solvent amount conveyance region, and tension is applied to both ends of the cast film, and this tension is applied to the peeling tension (120N / same as the take-up tension). added to m). Further, the nip pressure and roll rotation speed of the nip roll were arbitrarily followed in accordance with the change in the peeling position detected by the peeling position detection sensor so that the peeling position was within a certain range.

<Example 2>
Example 2 is the same as Example 1 except that a nip roll is disposed at a position where the residual solvent amount becomes 55% by mass after the casting film is peeled off, and tension is applied to both ends of the casting film. .

<Example 3>
Example 3 is the same as Example 1 except that after the casting film is peeled off, a nip roll is disposed at a position where the residual solvent amount is 45% by mass and tension is applied to both ends of the casting film. .

<Example 4>
In Example 4, two nip rolls were used, and after the casting film was peeled off, each nip roll was placed at a position where the residual solvent amount was 65% by mass and 62% by mass. Example 1 is the same as Example 1 except that tension is applied to both ends. However, when the nip pressure of each nip roll was set to P1 (Pa) and P2 (Pa) from the upstream side, control was performed so that P1 ≦ P2.

<Example 5>
In Example 5, three nip rolls were used, and after peeling off the cast film, each nip roll was placed at a position where the residual solvent amount was 65% by mass, 62% by mass, and 60% by mass. The same as Example 1 except that tension was applied to both ends of the cast film. However, when the nip pressure of each nip roll was P1 (Pa), P2 (Pa), and P3 (Pa) from the upstream side, control was performed so that P1 ≦ P2 ≦ P3.

<Comparative Example 1>
In Comparative Example 1, no nip roll was provided between the cast film peeling position and the take-up roll. The rest is the same as in the first embodiment.

<Comparative Example 2>
Comparative Example 2 is the same as Example 1 except that after the casting film is peeled, a nip roll is disposed at a position where the residual solvent amount is 40% by mass and tension is applied to both ends of the casting film. .

<Comparative Example 3>
In Comparative Example 3, after the casting film was peeled off, a nip roll was disposed at a position where the residual solvent amount was 80% by mass, and the tension was applied in the transport direction to the entire width direction of the casting film. Similar to Example 1.

<Comparative Example 4>
In Comparative Example 4, after the casting film was peeled off, a nip roll was disposed at a position where the residual solvent amount was 45% by mass, and the tension was applied in the transport direction to the entire width direction of the casting film. Similar to Example 1.

<Comparative Example 5>
In Comparative Example 5, two nip rolls were used, and after the cast film was peeled off, each nip roll was disposed at a position where the residual solvent amount was 65 mass% and 62 mass%. The upstream nip roll applies tension in the transport direction to both ends of the casting film in the width direction, and the downstream nip roll applies tension in the transport direction to the entire width of the casting film. . The rest is the same as in the first embodiment.

<Comparative Example 6>
In Comparative Example 6, two nip rolls were used, and after the casting film was peeled off, each nip roll was disposed at a position where the residual solvent amount was 65 mass% and 62 mass%. Then, tension is applied in the transport direction to the entire width direction of the casting film by the nip roll on the upstream side, and tension is applied in the transport direction to both ends in the width direction of the casting film by the nip roll on the downstream side. . The rest is the same as in the first embodiment.

<Evaluation method>
In each example and each comparative example, evaluation was made on the internal haze (Hz) and flatness (wrinkles in MD direction / pressed failure) of the manufactured optical film, and comprehensive evaluation based on these evaluations.

(Internal haze)
About internal haze, a glass plate (MICRO SLIDE GLASS) with a thickness of 1.3 mm was dropped by dropping a few drops of glycerin (Kanto Chemical deer special grade (purity> 99.0%) refractive index 1.47) on both sides of the obtained film. A value obtained by subtracting the haze measured in a state where a few drops of glycerin were dropped between two glasses from a haze value measured in a state of being sandwiched from both sides by two pieces (product number S9213, manufactured by MATSUNAMI) was measured. The haze meter is model type: NDH 2000, manufactured by Nippon Denshoku Industries Co., Ltd., the light source is a 5V9W halogen bulb, and the light receiving part is measured according to JIS K-7136 using a silicon photocell (with a relative visibility filter). Evaluation was made based on the following criteria. The optical film was conditioned at 23 ° C. and 55% RH for 5 hours or more, and a measurement sample was prepared. All the above haze measurements were performed at 23 ° C. and 55% RH.
A: Haze is 0.01 or less.
○: Haze is 0.01 to 0.015.
X: Haze is larger than 0.015.

(Flatness)
As for wrinkles and pressed failures in the MD direction of the optical film, the optical film immediately after being rolled up as a product is expanded and observed obliquely under room lighting, and visually observed for wrinkles and pressed failures in the MD direction. did. And the flatness of the optical film was evaluated based on the following criteria.
○: No wrinkles / push in MD direction.
X: Wrinkles / pressed in the MD direction and a failure has occurred.

  Note that wrinkles in the MD direction indicate streaky irregularities in the film conveyance direction. Such wrinkles are glaring when the film is viewed obliquely under room lighting. In addition, when two polarizing plates are placed in a crossed Nicol state, an optical film is placed between them, light is applied from one polarizing plate side, and light is streaked when observed from the other polarizing plate side. Therefore, white streaks are visible. Further, the pressed failure refers to a failure in which the film is locally recessed. If there is a failure when pressed against the film, the light appears locally white under crossed nicols, and therefore appears white.

(Comprehensive evaluation)
Based on the evaluation of the internal haze and flatness (MD direction wrinkles / pressed failure), the obtained optical film was comprehensively evaluated based on the following criteria.
○: There is no problem as a product.
×: There is a problem as a product.

  Table 2 shows the results of the above evaluations.

  As in Comparative Example 1, when the nip roll was not disposed between the peeling position of the casting film and the take-up roll, and even when the nip roll was disposed as in Comparative Example 2, after peeling the casting film, When the nip roll is disposed at a position where the residual solvent amount is 40% by mass, the internal haze of the optical film is larger than 0.015, and it cannot be said that the transparency is good. Also, the flatness of the optical film is wrinkled in the MD direction and cannot be said to be good. As a result, the overall evaluation is x.

  Further, even when the nip roll is disposed at a position where the residual solvent amount is 45% by mass or more, as in Comparative Examples 3 to 6, at least one nip roll nips the entire width direction of the cast film, When the tension in the conveying direction is applied to the optical film, although the internal haze and MD wrinkles of the optical film are improved, the optical film is pushed and causes a failure, so that an optical film with good flatness can be obtained. Can not.

  On the other hand, as in Examples 1 to 5, at least one nip roll is disposed at a position where the residual solvent amount is 45% by mass or more, and the nip roll nips only both ends in the width direction of the cast film. It can be seen that good results were obtained for both internal haze and flatness (MD wrinkles / pressed failure) by applying tension in the conveying direction only to both ends. Thereby, when the manufactured optical film is applied to the polarizing plate of a liquid crystal display device and black display is performed, light leakage can be reduced and contrast can be improved.

  In particular, as in Examples 1, 4, and 5, by niping both ends of the casting film at a relatively high position where the residual solvent amount is 65% by mass, and applying tension in the transport direction to both ends, The effect of reducing internal haze can be further increased. Thereby, when the manufactured optical film is applied to the polarizing plate of a liquid crystal display device, contrast can be further improved.

  In addition, although the manufacturing method of the optical film as a protective film for polarizing plates of a liquid crystal display device was demonstrated above, the manufacturing method mentioned above is used for the phase difference film, viewing angle expansion film, and plasma display which are used for a liquid crystal display device. The present invention can also be applied to the production of various functional films such as antireflection films used.

  The present invention can be used, for example, for the production of various functional films such as a protective film for a polarizing plate used in a liquid crystal display device, a retardation film, a viewing angle widening film, and an antireflection film used in a plasma display.

DESCRIPTION OF SYMBOLS 2 Support body 5 Take-up roll 11 Dope 12 Casting film 12a Center part 12b End part 21 Tension applying roll 21a Nip roll 21b Nip roll 23 Suction roll S High residual solvent amount conveyance area S1 High tension conveyance area (1st conveyance area)
S2 Low tension conveyance area (second conveyance area)

Claims (11)

A method for producing an optical film comprising a cellulose acetate resin having an acetyl group substitution degree of 2.0 to 2.6,
A casting step of casting a dope containing the cellulose acetate resin and a solvent on a support to form a casting film;
A peeling conveyance step of peeling the casting film from the support at the same time in the width direction center and both ends in the width direction, and conveying it to the take-up roll;
A take-up step of taking up the cast film by the take-up roll;
In the peeling / conveying step, the tension provided in the high residual solvent amount conveying region where the residual solvent amount of the casting film is 45% by mass or more in the conveying region from the peeling position of the casting film to the take-off roll. With the application roll, tension is applied in the transport direction to both ends in the width direction of the cast film ,
In the high residual solvent amount conveyance area, the tension applying rolls provided at a plurality of locations in the conveyance direction of the casting film impart tension to the both end portions of the casting film in the conveyance direction,
Among the tension applying rolls provided at two different places in the transport direction of the casting film, the tension applied to the both end portions of the casting film by the tension applying roll located on the upstream side in the transport direction is the transport direction. The method for producing an optical film, wherein the tension is not more than the tension applied to the both end portions of the cast film by a tension applying roll located on the downstream side. A method for producing an optical film comprising a cellulose acetate resin having an acetyl group substitution degree of 2.0 to 2.6,
A casting step of casting a dope containing the cellulose acetate resin and a solvent on a support to form a casting film;
A peeling conveyance step of peeling the casting film from the support at the same time in the width direction center and both ends in the width direction,
A take-up step of taking up the cast film by the take-up roll;
In the peeling / conveying step, the tension provided in the high residual solvent amount conveying region where the residual solvent amount of the casting film is 45% by mass or more in the conveying region from the peeling position of the casting film to the take-off roll. With the application roll, tension is applied in the transport direction to both ends in the width direction of the cast film,
The high residual solvent amount conveyance area,
A first conveying region in which tension is applied to the both end portions of the cast film by the tension applying roll;
When divided into a second transport area located downstream of the first transport area in the transport direction,
In the second transport area, the casting film is transported with a tension smaller than the tension applied by the tension applying roll on the most downstream side of the first transport area. . The elongation in the conveyance direction of the casting film is + 1.0% or less with respect to the conveyance length of the casting film in the high residual solvent amount conveyance region. Manufacturing method of the optical film. A method for producing an optical film comprising a cellulose acetate resin having an acetyl group substitution degree of 2.0 to 2.6,
A casting step of casting a dope containing the cellulose acetate resin and a solvent on a support to form a casting film;
A peeling conveyance step of peeling the casting film from the support at the same time in the width direction center and both ends in the width direction,
A take-up step of taking up the cast film by the take-up roll;
In the peeling / conveying step, the tension provided in the high residual solvent amount conveying region where the residual solvent amount of the casting film is 45% by mass or more in the conveying region from the peeling position of the casting film to the take-off roll. With the application roll, tension is applied in the transport direction to both ends in the width direction of the cast film,
In the peeling and conveying step, the peeling position of the casting film is monitored, and the tension applied to the both end portions of the casting film by the tension applying roll is controlled based on the result. Manufacturing method. The tension applied to the both end portions of the casting film by the tension applying roll is controlled so that the peeling position of the casting film is within a certain range in the peeling conveyance step. 4. A method for producing an optical film as described in 4. The method for producing an optical film according to any one of claims 1 to 5, wherein a nip roll that is driven by itself in the conveying direction while pressing both ends of the cast film is used as the tension applying roll. The method for producing an optical film according to any one of claims 1 to 5, wherein a suction roll that is driven in the conveying direction while sucking the both end portions of the cast film is used as the tension applying roll. The take-up roll is provided in a conveyance region where the residual solvent amount of the casting film is 15% by mass or less, and the casting film is provided with tension in the conveyance direction in a region including the both ends of the casting film. The method for producing an optical film according to claim 1, wherein the film is taken up. The optical film according to any one of claims 1 to 8, further comprising a stretching and drying step in which the cast film taken up by the take-up roll is stretched and dried to form an optical film. Production method. When the retardation in the in-plane direction of the optical film is Ro and the retardation in the film thickness direction is Rth,
25 nm ≦ Ro ≦ 100 nm
And
50 nm ≦ Rth ≦ 300 nm
The method for producing an optical film according to claim 9, wherein: The film thickness of the said optical film is 15-60 micrometers, The manufacturing method of the optical film of Claim 9 or 10 characterized by the above-mentioned.

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