JP2013126728A - Method of manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method of manufacturing an optical film and the optical film obtained by the same.SOLUTION: A method of manufacturing an optical film includes: a casting step of casting a dope including a cellulose acetate resin whose substitution degree of acetyl is 2.0-2.6 and a solvent on a casting support to form a casting film; a peeling step of peeling the casting film from the support; and a drying step of drying the peeled casting film. The casting step includes a step of cooling the end of the casting film on the casting support to form dew condensation. When a moisture content in the center of the casting film is W, and the moisture content at the end of the casting film is Wat a point where the casting film is peeled from the casting support, Wand Wsatisfy the formula (1) in which 5≤W-W≤20, the end of the casting film indicates a region 100 mm from both ends in the cross direction to the inside, and the center of the casting film indicates a region other than the region above.

Description

  The present invention can be used for optical films such as protective films for polarizing plates used in liquid crystal display devices (LCDs), retardation films, viewing angle widening films, anti-reflection films used in plasma displays, and other functional films. The present invention relates to a film manufacturing method.

  Various optical films such as a transparent protective film for protecting the polarizing element of the polarizing plate are disposed in the image display region of the liquid crystal display device. As such an optical film, for example, an optical film excellent in transparency such as a cellulose ester film is used.

  Moreover, such an optical film is often manufactured as a long optical film by, for example, a solution casting film forming method. Specifically, the solution casting film forming method is a method in which a resin solution (dope) in which a transparent resin as a raw material resin is dissolved in a solvent is cast on a traveling support and dried to a peelable extent. This is a method for producing a long optical film by peeling off the film obtained from the support, and drying and stretching while carrying the peeled film with a carrying roller.

  In addition, a technique for improving the viewing angle and color by adding an optical compensation function of a polarizer and a liquid crystal cell to an optical film for protecting the polarizing element as described above has been studied. Giving a phase difference is under consideration. Therefore, a cellulose acetate resin (cellulose diacetate resin) having a degree of substitution of acetyl groups of 2.0 to 2.6, which is likely to generate a retardation by stretching treatment, with respect to a cellulose triacetate resin which does not easily generate a retardation. Use is also being considered.

  However, the optical film dope mainly composed of cellulose acetate resin having a low degree of substitution with an acetyl group substitution degree of 2.0 to 2.6 has strong adhesion to the support and a large tension during peeling. Is required. For this reason, the cast film extends in the transport direction due to peeling, and the resin is oriented in that direction, causing a phenomenon that a phase difference having a large refractive index occurs in the stretching direction. As a result, in order to generate a phase difference having a large refractive index in the width direction by stretching in the width direction and to control the magnitude of the phase difference, it is necessary to stretch the film at a larger magnification than usual. There is a problem that haze is generated and transparency is lowered.

  On the other hand, as a method for improving the peeling of the cast film in the solution casting method, a polymer and a solvent are placed on an annular belt that has been wound around a pair of rotating rollers and conveyed so as to circulate. In a solution casting method for producing a polymer film by casting a dope containing a film to form a cast film, peeling the cast film as a film, and drying the cast film, upstream of the first rotating roller and the stripping position The casting film on the belt toward the first rotating roller is cooled by the cooling means provided on the belt, and the temperature of the casting film to be peeled off is adjusted by adjusting the cooling section to the peeling position at the position of the cooling means. A solution casting method (Patent Document 1) characterized in that the temperature is lower than 6 ° C. has been reported.

Japanese Patent No. 2006-306059

  However, in the technique described in Patent Document 1, since the entire width of the casting film is cooled, there may be a problem in the flatness / transparency of the film such as condensation marks due to condensation.

  The present invention has been made in view of such circumstances, and provides a method for efficiently producing a high-quality optical film excellent in transparency with high productivity while achieving a desired phase difference and haze. Objective.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by a method for producing an optical film having the following configuration, and have further completed the present invention based on such findings.

In the method for producing an optical film according to one aspect of the present invention, a dope containing a cellulose acetate resin having a substitution degree of acetyl group of 2.0 to 2.6 and a solvent is cast on a casting support. A casting process for forming a casting film; a peeling process for peeling the casting film from the support; and a drying process for drying the peeled casting film. said method comprising to condensation by cooling the Ueno casting film end, at a point where the casting film is peeled off from the casting support, the water content and W ₁ in the casting film center portion, the casting film end the water content in the case of the _{W 2} in, _{W 1} and _{W 2} is represented by the following formula (1):
5 ≦ W ₂ −W ₁ ≦ 20 (1)
And the end portion of the cast film indicates an area of 100 mm inward from both ends of the width, and the center part of the cast film indicates the other area.

  According to such a structure, since only the edge part of a casting film has a high moisture content in a peeling point, the adhesive force between the support body and film in a casting film edge part is relieve | moderated. Therefore, the tension required for film peeling can be reduced, the unnecessary orientation of the resin in the transport direction at the time of peeling from the support can be reduced, and a phase difference is generated by stretching in the width direction. Since it becomes possible to keep a draw ratio low, the optical film excellent in transparency can be provided. In particular, since the production method according to the present invention can achieve both retardation and haze, it is suitable for producing a retardation film for a VA liquid crystal display device that requires a high retardation.

  Furthermore, when the substitution degree of the acetyl group of the cellulose acetate resin is 2.0 to 2.6, the degree of adhesion between the cast film and the support is increased, so that the effect of the production method can be further exhibited. .

  Moreover, in the said manufacturing method, it is preferable to cut off a film width | variety edge part at least once after peeling a cast film and the final winding process of a film. Since the end portion of the casting film is rich in water, a higher quality film can be obtained by cutting off the region.

  In the said manufacturing method, even if the moving speed of a casting support body is as high as 80-150 m / min in the said casting process, a highly transparent high quality film can be manufactured.

  Moreover, in the said manufacturing method, in the said peeling process, the tension | tensile_strength required for peeling is about 50-120 N / m, and it can peel sufficiently with such tension | tensile_strength.

  Moreover, the optical film which concerns on another one aspect | mode of this invention is obtained by the manufacturing method of the said optical film, It is characterized by the above-mentioned. According to such a configuration, a high-quality optical film with high transparency can be obtained.

  The optical film has a haze value of 0.10 to 0.40%, and is very high quality as a retardation film.

  According to the present invention, a high-quality optical film that is excellent in transparency and can maintain a desired retardation and haze can be efficiently produced.

FIG. 1 is a schematic diagram showing a basic configuration of an optical film manufacturing apparatus by a solution casting method using an endless belt support 8. FIG. 2 is a schematic view showing the periphery of the peeling roller 4 according to the embodiment of the present invention (note that the endless belt support 8 is omitted in FIG. 2).

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The method for producing an optical film according to the present embodiment includes a casting step of casting a dope containing a cellulose acetate resin and a solvent on a casting support to form a casting film; and This is a production method by a so-called solution casting film forming method, comprising a peeling step for peeling from the support and a drying step for drying the peeled cast film. For example, it is performed by an optical film manufacturing apparatus using a solution casting film forming method as shown in FIG. In addition, as an optical film manufacturing apparatus, it is not limited to what is shown in FIG. 1, The thing of another structure may be sufficient.

  FIG. 1 is a schematic view showing a basic configuration of an optical film manufacturing apparatus by a solution casting method using an endless belt support 8.

  The optical film manufacturing apparatus according to this embodiment includes an endless belt support 8, a casting die 1, a peeling roller 4, and the like. The casting die 1 casts a dope (resin solution) 2 in which a transparent resin is dissolved onto the surface of the endless belt support 8. The endless belt support 8 is supported to be drivable by a conveying roller 3 (a pair of driving roller and driven roller), and forms a casting film made of the dope 2 cast from the casting die 1 while being conveyed. dry. Then, the peeling roller 4 peels the dried casting film 5 from the endless belt support 8. The peeled casting film 5 is further dried by a drying device or the like (not shown), and the dried casting film is wound as an optical film by the winding device or the like (not shown).

  As shown in FIG. 1, the endless belt support 8 is an endless metal belt having a mirror surface and infinite transition. As the belt, for example, a belt made of stainless steel or the like is preferably used from the viewpoint of peelability of the casting film 5. From the viewpoint of effectively utilizing the width of the endless belt support 8, the width of the casting film 5 cast by the casting die 1 is set to 80 to 99% with respect to the width of the endless belt support 8. preferable. And in order to finally obtain an optical film with a width of 1000 to 2500 mm, the width of the endless belt support 8 is preferably 1200 to 3200 mm. Further, instead of the endless belt support, a rotating metal drum having a mirror surface (endless drum support) or the like may be used.

First, the casting process will be described in detail. In the present embodiment, in the casting step, the casting film end on the casting support is condensed by cooling, and the casting film center at the point where the casting film is peeled off from the casting support. the water content and W ₁ in section, the water content in the casting film ends when the W _2, W ₁ and W ₂ is represented by the following formula (1):
5 ≦ W ₂ −W ₁ ≦ 20 (1)
And the end portion of the cast film indicates an area of 100 mm inward from both ends of the width, and the center part of the cast film indicates the other area.

  According to such a method for producing an optical film, the end of the casting film on the casting support is condensed to cause condensation, and the moisture content at the end is increased. The adhesion between the films is relaxed. Therefore, since the tension required for film peeling can be reduced, an optical film excellent in transparency can be provided. Moreover, when the moisture content of the casting film central portion increases, the transparency of the resulting film may be lowered, but by increasing the moisture content only at the end of the casting membrane as in the production method according to the present invention. The water content in the central portion is not high, and it is considered that a film having further excellent transparency can be obtained.

  In order to increase the moisture content at the end of the casting membrane, it is preferable to use means for directly spraying water on the end, which increases the humidity of the entire room and causes stain-like condensation at the center of the width. Absent. If the end portion is condensed by cooling as in the manufacturing method according to the present invention, the moisture content of the end portion increases, but it does not affect indoor humidity and the like, so that a high-quality film is obtained very efficiently. It becomes possible.

  In the present embodiment, the moisture content is defined by (moisture content at the peeling point / casting film mass at the peeling point) × 100 (%).

  When the difference between the moisture content W2 at the end of the casting membrane and the moisture content W1 at the center of the casting membrane is less than 5% in that the casting membrane is peeled off from the casting support. The effect of relieving the adhesion between the support and the dope cannot be obtained, and if it exceeds 20%, the dope film may remain on the support.

  The moisture content of the casting film end and the casting film center at the peeling point of the casting film is, for example, a small amount of the casting film sampled at the peeling point, and the temperature using a CA-20 model manufactured by Mitsubishi Chemical Corporation. After drying and vaporizing water at 150 ° C., it can be quantitatively measured by the Karl Fischer method.

  As a method of condensing the casting film end on the casting support by cooling, the moisture content at the casting film end and the moisture content at the center at the casting film peeling point satisfy the relational expression as described above. The method is not particularly limited as long as it is a related method. Specifically, for example, as shown in FIG. 1, the end cooling roller 6 is brought into contact with the support from the back surface of the support, or FIG. As shown, a method of blowing cold air to the end surface of the cast film by the end cold air header 7 is mentioned.

  The surface to be cooled may be on the support side or on the film side.

  As a more specific example, when a cooling roller is used, for example, the end of the casting film is cooled by bringing a roller whose surface temperature is cooled to about −10 ° C. to 10 ° C. into contact with the back surface of the support. Can do.

  In the case of blowing cool air, for example, as the cool air, the dew point is 0 ° C. or less and the temperature is −5 ° C. or more and 5 ° C. or less and the air is blown to the film side in the range of 2 m / sec to 30 m / sec. By doing so, the casting film edge part can be cooled.

  Thus, by casting and condensing the casting film end, the casting film can be easily peeled off from the support and the casting film (web) 5 can be wound up.

  In addition, as a position where the cooling means as described above is provided, a position where the moisture content of the casting film end portion and the moisture content of the central portion at the casting film peeling point satisfy the relational expression as described above. If it is, there will be no limitation in particular, However, It is thought that it is easier to adjust a moisture content to cool at the position near a peeling point as much as possible.

  Preferably, the cooling means is provided, for example, within 2 to 5 m upstream of the casting film peeling point. If the cooling means is at a position 5 m or more upstream from the peeling point, the water may dry before peeling. Furthermore, when the cooling means is located at a position less than 2 m upstream from the peeling point, the moisture condensed by cooling is not sufficiently penetrated into the film, and there is a possibility that the effect of reducing the adhesion between the support and the casting film is small.

  In addition, the dope 2 is cast by the casting die 1 by a method in which the resin is heated and the molten resin pressurized by a screw is extruded from a die, or the resin is dissolved in a solvent to improve fluidity. There is a solution casting method in which the dope is cast on a metal drum or belt and the solvent is evaporated through a drying process.In this embodiment, the optical film has optical properties such as optical properties, strength, and smoothness. From the viewpoint of performance, it is preferable to cast using a solution casting method.

  Further, in the method for producing an optical film of the present invention, since the casting film can be easily peeled off from the support, it is possible to cope with an increase in the film forming speed. The speed can be, for example, about 80 to 150 m / min.

  Furthermore, since the tension required for peeling the cast film from the support can be less than usual, it can be peeled with a tension of about 50 to 120 N / m.

  The casting film (web) 5 formed on the endless belt support 8 in the casting process as described above is peeled off by the peeling roller 4, a drying device (not shown), a winding device (not shown), or the like. An optical film can be manufactured by a process or a drying process. The process described below is not particularly limited and can be adopted as long as it is a general process. Specifically, for example, the following steps can be used, but the present invention is not limited to the following steps.

  First, the solvent in the casting film 5 is dried while the formed casting film 5 is conveyed by the endless belt support 8. The drying is performed by, for example, heating the endless belt support 8 or blowing heated air on the web. At that time, although the temperature of the cast film varies depending on the dope solution, the range of −5 ° C. to 70 ° C. is preferable in consideration of the transport speed accompanying the evaporation time of the solvent, the degree of dispersion of fine particles, productivity, and the like. The range of 0 ° C to 60 ° C is more preferable. The higher the temperature of the web, the faster the solvent can be dried. However, when the temperature is too high, the web tends to foam or the flatness tends to deteriorate.

  When heating the endless belt support 8, for example, a method of heating the web on the endless belt support 8 with an infrared heater, a method of heating the front and back surfaces of the endless belt support 8 with an infrared heater, the endless Examples include a method of heating by heating air on the back surface of the belt support 8, and the method can be appropriately selected as necessary.

  When the heated air is blown, the wind pressure of the heated air is preferably 50 to 5000 Pa in consideration of the uniformity of solvent evaporation, the degree of dispersion of fine particles, and the like. The temperature of the heating air may be dried at a constant temperature, or may be supplied in several steps in the running direction of the endless belt support 8.

  The time from casting the dope 2 onto the endless belt support 8 to peeling the cast film (web) 5 from the endless belt support 8 is the film thickness of the optical film to be produced, Although it varies depending on the solvent to be used, it is preferably in the range of 0.5 to 5 minutes in consideration of peelability from the endless belt support 8.

  As described above, the traveling speed of the endless belt support 8 is preferably about 80 to 150 m / min.

  The peeling roller 4 is disposed in the vicinity of the surface of the endless belt support 8 on the side on which the dope 2 is cast, and the distance between the endless belt support 8 and the peeling roller 4 is 1 to 100 mm. It is preferable. The dried casting film (web) 5 is peeled off as a film by pulling the dried casting film (web) 5 under tension using the peeling roller 4 as a fulcrum. When the film is peeled from the endless belt support 8, the film is stretched in the film transport direction (Machine Direction: MD direction) by the peeling tension and the subsequent transport tension. In this respect, in this embodiment, since the tension required for peeling is small as described above, the peeling tension and the conveyance tension when peeling the film from the endless belt support 8 are about 50 to 120 N / m. .

  The residual solvent ratio of the film when the film is peeled off from the endless belt support 8 takes into consideration the transportability after peeling from the endless belt support 8 and the physical characteristics of the optical film formed after transport and drying. 30 to 200% by mass is preferable. The residual solvent ratio of the film is defined by the following formula (I).

Residual solvent ratio (mass%) = {(M ₁ −M ₂ ) / M ₂ } × 100 (I)
Here, M ₁ is shows the mass at any point in the film, M ₂ shows the mass after drying for 1 hour at 115 ° C. The film was measured M _1.

  As a drying apparatus for drying the dope on the support, for example, an apparatus provided with a plurality of transport rollers and drying the film while transporting the film between the rollers can be used. In that case, you may dry using heating air, infrared rays, etc. independently, and you may dry using heating air and infrared rays together. It is preferable to use heated air from the viewpoint of simplicity. The drying temperature varies depending on the amount of residual solvent in the film. That's fine. Moreover, it may be dried at a constant temperature, or may be divided into two to four stages of temperature, and may be divided into several stages of temperature. Further, the film can be stretched in the MD direction while being transported in the drying device 14.

  The residual solvent ratio of the film after the drying treatment in the drying apparatus is preferably 0.001 to 5% by mass in consideration of the load of the drying process, the dimensional stability expansion / contraction ratio during storage, and the like. In the present embodiment, the film in which the solvent is gradually removed in the drying step and the total residual solvent amount is 15% by mass or less is referred to as an optical film.

  As the winding device, any device can be used without particular limitation as long as it is a device that winds the optical film having a predetermined residual solvent ratio on a winding core to a required length. In addition, it is preferable that the temperature at the time of winding is cooled to room temperature in order to prevent abrasion, loosening, and the like due to shrinkage after winding. The winder to be used can be used without particular limitation, and may be a commonly used one. Specifically, for example, it can be wound using a winder using a constant tension method, a constant torque method, a taper tension method, a program tension controller method with a constant internal stress, or the like.

  In addition, the manufacturing apparatus of an optical film is not limited to the thing of said structure, For example, you may provide the extending | stretching apparatus etc. separately. Examples of the stretching device include a stretching device that stretches the film peeled from the endless belt support 8 in a direction (Transverse Direction: TD direction) orthogonal to the film transport direction.

  Hereinafter, the composition of the dope (resin solution) used in the present embodiment will be described.

  The dope used in the present embodiment is obtained by dissolving a transparent resin in a solvent. As the transparent resin, a cellulose acetate resin is used.

<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. Cellulose acetate having a degree of acetyl group substitution of 2.0 to 2.6 is preferred from the viewpoint that even if it is expressed, the draw ratio can be kept low and failures such as breakage can be avoided.

  When the acetyl group substitution degree of cellulose acetate is less than 2.0, deterioration of film surface quality due to an increase in dope viscosity, haze increase due to an increase in stretching tension, and the like may occur. Moreover, when the acetyl group substitution degree is larger than 2.6, it is difficult to obtain a necessary phase difference. The method for measuring the degree of acetyl group substitution can be carried out according to ASTM D-817-91, and the preferred degree of acetyl group substitution is 2.2 to 2.45.

  The number average molecular weight (Mn) of cellulose acetate is preferred because the mechanical strength of the film from which a range of 30000-300000 is obtained is strong. Furthermore, the thing of 50000-200000 is used preferably.

  The value of the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the 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.

  The cellulose as a raw material for cellulose acetate is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from conifers and hardwoods), kenaf and the like. Moreover, the cellulose acetate obtained from them can be mixed and used in arbitrary ratios, respectively.

  The cellulose acetate according to the present invention can be produced by a known method. Specifically, it can be synthesized with reference to the methods described in JP-A-10-45804 and JP-A-2009-161701.

  Commercially available products include Daicel Corporation L20, L30, L40, L50, Eastman Chemical Co. Ca398-3, Ca398-6, Ca398-10, Ca398-30, Ca394-60S, and the like.

  The dope in the present embodiment is mainly composed of the cellulose acetate resin as described above, but may further include 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 substitution degree of the compound represented by the general formula (1) is 3.0 to 6.0.

The degree of substitution of the compound represented by the general formula (1) represents the number substituted with a substituent other than hydrogen among the eight hydroxyl groups contained in the general formula (1). It represents the number including groups other than hydrogen among R _{1 to} R _{8 in} 1). Therefore, 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 R _{1 to} R ₈ are all hydrogen atoms, 0.0 It becomes.

  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 of the general formula (1) in the present invention. The average substitution degree can be measured from the area ratio of the chart showing the substitution degree distribution.

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 are the same or different. 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, 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, melicic acid,
Saturated fatty acids such as laccellic acid, and unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid and octenoic acid can be used.

  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 according to the present invention are shown below, but these are cases where R _{1 to} R ₈ are all the same substituent R, and the present invention is not limited thereto.

  The sugar ester compound according to this embodiment can be produced by reacting a sugar ester with an acylating agent (also referred to as an esterifying agent, for example, an acid halide of acetyl chloride, an anhydride such as acetic anhydride). The distribution of the degree of substitution is made by adjusting the amount of acylating agent, the timing of addition, and the esterification reaction time, but it is possible to mix sugar ester compounds with different degrees of substitution, or purely isolated degrees of substitution. By mixing the compounds, it is possible to adjust a component having a target average substitution degree and a substitution degree of 4 or less.

  (Synthesis Example: Synthesis of Compound According to the Present Invention)

A four-headed colben equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was mixed 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 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.

  Next, a part of the obtained mixture is purified by column chromatography using silica gel to obtain 100% pure A-1, A-2, A-3, A-4, A-5, etc., respectively. 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 the present invention, the average degree of substitution was adjusted by combining and adding sugar esters close to the desired degree of average substitution, isolated A-1 to A-5, and the like by the method prepared here.

<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 in the present invention is preferably 4.5 to 6.0, and the distribution range of the substitution degree is 4.0 to 8. 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 made by adjusting the esterification reaction time, but may be adjusted to the target average degree of substitution by mixing compounds having different degrees of substitution.

  The optical film of the present invention 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, it is preferable that the excellent effects of the present invention are exhibited and there is no bleeding out during storage of the raw material.

<Ester compound represented by general formula (2)>
Furthermore, the optical film (dope) 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
(Wherein 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) , 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, and 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, it is not limited to this.

<Other additives>
(Plasticizer)
In the present embodiment, the optical film can contain a plasticizer in addition to the compound represented by the general formula (2) as necessary to obtain the effects of the present invention.

  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 invention is represented by the following general formula (a).

Formula _{(a) R 11 - (OH} ) n
However, 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 preferred 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. The inclusion of acetic acid is preferred because the compatibility with cellulose acetate increases, and it is also preferred to use a mixture of acetic acid and other monocarboxylic acids.

  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, and 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 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.

  The alcohol used for the polyvalent carboxylic acid ester that can be used in the present invention may be one kind or a mixture of two or more kinds.

  The acid value of the polyvalent carboxylic acid ester compound that can be used in the present invention 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, retardation fluctuations are 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 according to JIS K0070.

  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, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, etc. These are commercially available products made by BASF Japan and can be preferably used.

  The UV absorbers preferably used in the present 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, etc., but when the dry film thickness of the polarizing plate protective film is 30 to 200 μm, it is 0.5 with respect to the polarizing plate protective film. -10 mass% is preferable, and 0.6-4 mass% is still more preferable.

(Antioxidant)
Antioxidants are also called anti-degradation agents. For example, they have the role of delaying or preventing the film from decomposing due to the residual solvent halogen in the film or phosphoric acid of the phosphoric acid plasticizer. preferable.

  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. Of 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. For example, it is marketed with the brand name of Aerosil 200V and Aerosil R972V (above, Nippon Aerosil Co., Ltd. product), and can use them.

  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, 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 invention 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 is preferably lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like. Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose acetate.

  The amount of silicon dioxide fine particles added to cellulose acetate is preferably 0.01 parts by weight to 5.0 parts by weight, and more preferably 0.05 parts by weight to 1.0 parts by weight with respect to 100 parts by weight of cellulose acetate. Preferably, 0.1 mass part-0.5 mass part is the most preferable. The larger the added amount, the better the dynamic friction coefficient, and the smaller the added amount, the less aggregates.

  As the disperser, a normal disperser can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. For dispersing silicon dioxide fine particles, a medialess disperser is preferred because of its 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 the present invention, 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 9.807 MPa or more in a thin tube having a tube diameter of 1 to 2000 μm.

  More preferably, it is 19.613 MPa or more. Further, at that time, those having a maximum reaching speed of 100 m / second or more and those having a heat transfer speed of 420 kJ / hour or more are preferable.

  Examples of the high-pressure dispersing apparatus include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing apparatuses such as a 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, after peeling and drying after casting and winding up into a roller shape, functional thin films such as a hard coat layer and an antireflection layer are provided. Until processing or shipment, packaging is usually performed in order 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 is poor. Become. 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 preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by mass for the good solvent and 2 to 30% by mass for the poor solvent. With a good solvent and a poor solvent, what dissolve | melts the cellulose acetate to be used independently is defined as a good solvent, and what swells or does not melt | dissolve independently is defined as a poor solvent.

  Therefore, the good solvent and the poor solvent change depending on the average acetylation degree (acetyl group substitution degree) of cellulose acetate.

  Although the good solvent used for this invention 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 for this invention is not specifically limited, For example, methanol, ethanol, n-butanol, cyclohexane, cyclohexanone, etc. are used preferably. Moreover, it is preferable that 0.01-2 mass% of water contains in dope.

  Moreover, the solvent used for melt | dissolution of a cellulose acetate collect | recovers the solvent removed from the film by drying at the film-forming process, and uses this again.

  The recovery solvent may contain trace amounts of additives added to cellulose acetate, such as plasticizers, UV absorbers, polymers, monomer components, etc., but these are preferably reused even if they are included. 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 mamaco.

  Further, a method in which cellulose acetate is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

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

  The heating temperature with the addition of a solvent is preferably higher 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.

  Alternatively, 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, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small.

  For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable.

  It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose 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, it is 100 pieces / cm < ² > or less, More preferably, it is 50 pieces / m < ² > or less, More preferably, it is 0-10 pieces / cm < ² > or less. Further, it is preferable that the number of bright spots of 0.01 mm or less is small.

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

  A preferred temperature is 45 to 120 ° C, more preferably 45 to 70 ° C, and still more preferably 45 to 55 ° C.

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

  According to the manufacturing method according to the present embodiment as described above, the tension required for peeling the cast film from the support can be reduced, and a high-quality optical film excellent in transparency can be obtained.

  In addition, according to the manufacturing method which concerns on this embodiment, an optical film with a haze value of 0.10-0.40% can be obtained. Such an optical film is very useful as a retardation film.

  In addition, it is preferable that the width | variety of the optical film obtained here is 1000-2500 mm from the point of the use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency.

  Moreover, it is preferable that the film thickness of an optical film is 20-70 micrometers from points, such as a viewpoint of thickness reduction of a liquid crystal display device, and production stabilization of an optical film. Here, the film thickness means an average film thickness, and 20 to 200 locations in the width direction of the optical film are measured with a contact-type film thickness meter manufactured by Mitutoyo Corporation, and the average value of the measured values. Is shown as the film thickness.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

[Example 1]
An optical film was produced by the following method.

(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 2.35) 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. by a casting die comprising a coat hanger die on the endless belt support at a temperature of 25 ° C. Casting was performed at a casting speed (running speed of the support) of 90 m / min to form a casting film.

  Then, when the point at which the casting film is peeled off from the casting support is used as a reference point, the casting film ends on the casting support (at both ends of the casting film at the width 3 m upstream from the reference point) Cold air was blown onto the film side (opposite side to the support) by a cold air header on the area from the inside to 100 mm. In addition, as a cold wind, the dew point was 1 degreeC and the cold air whose temperature is 3 degreeC was ventilated in the range of 10 m / sec of wind speeds.

  The peel tension of the cast film was 80 N / m, and the final optical film thickness was 40 μm.

In addition, a small amount of the cast film was sampled at the peeling point, and after moisture was dried and vaporized at a temperature of 150 ° C. using a CA-20 model manufactured by Mitsubishi Chemical Corporation, the peeling point was determined by quantification by the Karl Fischer method. When the moisture content of the casting membrane was measured, the moisture content (W ₁ ) at the center of the casting membrane was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 10%.

[Example 2]
Except that the end of the casting film on the casting support is dewed by bringing a cooling roller having a surface temperature of 4 ° C. into contact with the back of the support at 2 m upstream from the point where the casting film is peeled off (reference point). Produced a cellulose acetate film in the same manner as in Example 1. The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 10%.

[Example 3]
A cellulose acetate film was produced in the same manner as in Example 2 except that the cooling roller was brought into contact 4 m upstream of the point where the cast film was peeled off (reference point). The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 3%, and the moisture content (W ₂ ) at the end of the casting membrane was 8%.

[Example 4]
A cellulose acetate film was produced in the same manner as in Example 2 except that the cooling roller was brought into contact 5 m upstream of the point where the cast film was peeled off (reference point). The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 7%.

[Example 5]
A cellulose acetate film was produced in the same manner as in Example 1 except that cold air having a temperature of 0 ° C. was blown 2 m upstream from the point (reference point) where the cast film was peeled off. The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 22%.

[Example 6]
A cellulose acetate film was produced in the same manner as in Example 1 except that cold air having a temperature of 0 ° C. was blown at 3 m upstream from the point (reference point) where the cast film was peeled off. The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 1%, and the moisture content (W ₂ ) at the end of the casting membrane was 17%.

[Example 7]
A cellulose acetate film was produced in the same manner as in Example 1 except that cold air was blown at 1 m upstream of the point where the cast film was peeled off (reference point). The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 3%, and the moisture content (W ₂ ) at the end of the casting membrane was 10%.

[Comparative Example 1]
A cellulose acetate film was produced in the same manner as in Example 1 except that cold air having a dew point of 4 ° C. and a temperature of 10 ° C. was blown at a wind speed of 5 m / sec. The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 2%.

[Comparative Example 2]
A cellulose acetate film was produced in the same manner as in Example 1 except that cold air having a dew point of 4 ° C. and a temperature of 0 ° C. was blown at a wind speed of 20 m / sec. The moisture content (W ₁ ) at the center of the casting membrane at the peeling point was 2%, and the moisture content (W ₂ ) at the end of the casting membrane was 27%.

(Evaluation)
The following evaluation tests were performed on the optical films (Examples 1 to 7 and Comparative Examples 1 and 2) obtained as described above.

(Haze)
The film sample was measured according to JIS-K7136 using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.
The evaluation criteria are as follows.
○ Haze 0.10 to 0.40; Quality that is not problematic as a retardation film for VA × Haze 0.41 or more; Quality that is problematic as a retardation film for VA

(Peeling residue)
Immediately after the cast film was peeled from the support, it was visually evaluated whether or not the dope film remained on the support.
The evaluation criteria are as follows.
○ The film can be confirmed on the support by visual observation. Table 2 shows the results where the film cannot be confirmed on the support by visual observation.

[Discussion]
As can be seen from Table 2, the water content W ₁ in the casting film central portion of the separation point, also the water content in the casting film end of the separation point in the case of the W _2, the value of W ₂ -W ₁ is In the optical films produced in Examples 1 to 7 having 5 or more and 20 or less, the haze is suppressed even though the running speed of the support is 90 m / min and the casting film peeling tension is 80 N / m. There was no peeling residue.

On the other hand, the optical film produced in Comparative Example 1 in which the value of W ₂ -W ₁ is less than 5 has a high haze, and the Comparative Example in which the value of W ₂ -W ₁ exceeds 20 In the optical film produced in 2, a peeling residue occurred.

  From the above, it was shown that according to the method for producing an optical film according to the present embodiment, no peeling residue occurs and a high-quality optical film excellent in transparency can be obtained.

1 Casting die 2 Dope (resin solution)
3 Conveying roller 4 Peeling roller 5 Casting film (web)
6 Cooling roller 7 Cold air header 8 Endless belt support

Claims (6)

A casting step of casting a dope containing a cellulose acetate resin having a substitution degree of acetyl group of 2.0 to 2.6 and a solvent on a casting support to form a casting film; A peeling step of peeling the membrane from the support, and a drying step of drying the peeled cast membrane,
In the casting step, comprising condensing the end of the casting film on the casting support by cooling;
At the point where the casting film is peeled off from the casting support, the water content and W ₁ in the casting film center portion, the water content in the casting film ends when the W _2, W ₁ and W ₂ Is the following formula (1):
5 ≦ W ₂ −W ₁ ≦ 20 (1)
And the casting film end portion indicates an area of 100 mm inward from both ends of the width, and the casting film center portion indicates the other area.   2. The method for producing an optical film according to claim 1, wherein the film width end portion is cut off at least once after the casting film is peeled off until the final winding step of the film.   The method for producing an optical film according to claim 1, wherein in the casting step, the moving speed of the casting support is 80 to 150 m / min.   In the said peeling process, the tension | tensile_strength required for peeling is 50-120 N / m, The optical film manufacturing method in any one of Claims 1-3 characterized by the above-mentioned.   It is obtained by the manufacturing method of the optical film in any one of Claims 1-4, The optical film characterized by the above-mentioned. The optical film according to claim 5, having a haze value of 0.10 to 0.40%.

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