JP2002103361A - Casting die, solution film-making method, and polarizing plate, etc. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a skinning preventing means for improving productivity which does not affect a cast film and does not need the periodic washing of a peeling residue which is generated by the lack of drying at an end part peeling point from a support. SOLUTION: A casting die for solution film-making in which the angle θmade by a lip surface and a lip side in the cross-sectional shape of both end part of a lip tip is at least 120 deg. is used. A film manufactured from a solution with the use of the casting die is suitable for a polarizing plate and can be used for a liquid crystal display, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting die for preventing skinning at both ends in the width direction of a casting die in a solution casting, a solution casting method using the casting die, and a solution casting method using the casting die. The present invention relates to a polarizing plate and the like using a film with a film.

[0002]

2. Description of the Related Art Generally, a part of a support film such as cellulose acetate, polycarbonate and cellophane is produced by a solution casting method. FIG. 20 shows a state in which a polymer solution (dope) is cast from the die 1 by this solution casting method.
FIG. 21 shows an end shape of the slot 13 which is a dope discharge port of the die 1. As shown in FIG. 21, the end of the slot 13 has a right angle at the corner.
In most cases, drying of the dope at both ends of the casting die lip causes skinning 23 as shown in FIG. This skinning grows in a icy manner at both ends of the lip tip, disturbs the flow of the dope from the lip, and inhibits stable film formation.

[0003] When skinning occurs, the casting speed must be reduced to a speed at which the casting film is not cut off even if the casting film becomes unstable due to disturbance, and the skinning must be removed, which significantly reduces productivity. Was causing it.

Conventionally, as a countermeasure against this, there has been known a method of preventing the above by blowing a solvent-saturated gas into both ends of a die lip or flowing a solvent which is soluble in a dope.

For example, Japanese Patent Application Laid-Open No. Hei 2-276607 discloses a casting die having a shape such that the discharge amount per unit width near the side edge is smaller than the average discharge amount at the center. This die addresses the tendency of the film cast from the die to generally have a thicker side portion of the casting width in the casting film forming method. As means for reducing the discharge amount in the vicinity of the side edge, means for narrowing the packing and means for narrowing the gap between the die slots are disclosed. In the latter case, the portion which narrows the gap between the slots is about 2 times the slot width. Doubled.

On the other hand, Japanese Patent Application Laid-Open No. 2-208650 discloses that a solvent flow path is provided inside both ends of a die for casting a cellulose triacetate solution, and a solvent such as methylene chloride is supplied from the solvent flow path to prevent the formation of a film. A method of preventing this is disclosed. The lower end of this flow path joins at the solution discharge end, and the solvent is discharged together with the solution.

Also, Japanese Patent No. 2687260 discloses that
A method of preventing the formation of a film by supplying a solvent such as methylene chloride so that the solution such as cellulose triacetate is placed on both ends of the dope cast slightly inside the dope discharge ends at both ends of the die where the solution is cast. Is disclosed.

[0008]

However, these methods are susceptible to the influence of the wind speed around the die lip, temperature conditions, and the like, and it is difficult to control the gas concentration and the solvent flowing position. It was not something that could be reliably suppressed. That is, if the gas concentration is low, skinning occurs, and even if the saturated concentration is maintained, dew condensation occurs due to fluctuations in the die ambient temperature, and a failure in the appearance of the film occurs. Further, under the flow of the solvent, the solvent is rather excessive because it spreads in the width direction at the dope discharge portion at the tip of the lip. If a peeling residue occurs on the support, the casting speed must be reduced and the support must be washed, which significantly reduces productivity.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art in solution casting, and to eliminate a peeling residue generated due to insufficient drying at an end peeling point from a support without adversely affecting a casting membrane. An object of the present invention is to provide a means for preventing skinning, which does not require periodic cleaning and improves production efficiency.

Another object of the present invention is to provide a solution film forming method of a film having excellent optical characteristics by adding various additives to a cellulose acylate solution and using the casting die. is there.

Further, another object of the present invention is to provide a polarizing plate protective film, a polarizing plate, and the like having excellent optical characteristics using the film.
An object is to provide an optical functional film and a liquid crystal display device.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a solution in which an angle θ between a lip surface and a lip side surface in a cross-sectional shape of both ends of a lip tip is 120 degrees or more. This object has been achieved by a casting die for film formation.

As shown in FIG. 21, the cross-sectional shape of both ends of the conventional lip tip is rectangular, and the angle θ between the lip surface 18 and the lip side surface 19 is 90 degrees. The present inventors have found that skinning at both ends of the tip of the lip occurs due to a small dope flow rate at the corners and the dope surface is easily dried. In order to eliminate such a portion where the flow rate of the dope is reduced, it is necessary to minimize the angle in the cross-sectional shape of both ends of the lip tip. In other words, it is effective to increase the angle between the lip surface and the lip side surface as much as possible. However, if the angle is too large at the end, a sharp portion is formed on the lip side surface, and the occurrence of skinning increases. This is the opposite effect. Therefore, the lip side surface section preferably has a smooth curve.

The present invention includes a solution casting method using the casting die. In the solution casting method, it is preferable to use a cellulose acylate solution. Further, the solvent of the cellulose acylate solution comprises methyl acetate, ketones and alcohols, and the solvent ratio is 20 to 90% by weight of methyl acetate, 0 to 60% by weight of ketones, and 5 to 30% by weight of alcohols. %.

The cellulose acylate solution contains at least one plasticizer in an amount of 0.1% to the cellulose acylate.
It is preferable to contain 1 to 20% by weight. It is preferable that the cellulose acylate solution contains at least one ultraviolet absorber in an amount of 0.001 to 5% by weight based on the weight of the cellulose acylate. Further, it is preferable that the cellulose acylate solution contains at least one kind of fine particle powder in an amount of 0.001 to 5% by weight based on the cellulose acylate. Further, it is preferable that the cellulose acylate solution contains at least one release agent in an amount of 0.002 to 2% by weight based on the weight of the cellulose acylate. Further, the cellulose acylate solution preferably contains at least one fluorine-based surfactant in an amount of 0.001 to 2% by weight based on the weight of the cellulose acylate.

In the solution casting method, it is preferable that two or more types of cellulose acylate solutions containing at least one type of cellulose acylate are co-cast in the casting step.

The film formed by the solution casting method of the present invention is preferably used as a protective film for a polarizing plate, a polarizing plate, an optical functional film, and a liquid crystal display. In this case, a product having excellent durability can be obtained.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION [Polymer] Polymers that can be used for preparing a dope in the solution casting method of the present invention include cellulose esters, polycarbonates and the like. Typical examples of the cellulose ester include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). A lower fatty acid means a fatty acid having 6 or less carbon atoms. Cellulose acetate includes cellulose triacetate (TAC) and cellulose diacetate (DAC). In particular, in the present invention, it is preferable to form a dope composed of a cellulose acylate solution, and it is more preferable that the cellulose acylate is cellulose triacetate.

[Solvent] As a solvent for the above polymer, a chloride of a lower aliphatic hydrocarbon or a lower aliphatic alcohol is generally used. Examples of chlorides of lower aliphatic hydrocarbons include methylene chloride. Examples of lower aliphatic alcohols include methanol, ethanol,
Includes n-propyl alcohol, isopropyl alcohol and n-butanol. Examples of other solvents include substantially no halogenated hydrocarbons, acetone, and ketones having 4 to 12 carbon atoms include, for example, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone, and methylcyclohexanone. Examples of the ester having 3 to 12 atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, 2-ethoxy-ethyl acetate, and the like. Examples of the alcohols from to 6 include methanol, ethanol, propanol, iso-propanol, 1-butanol, t-butanol, 2-methyl-2-butanol, 2-methoxyethanol and 2-methoxyethanol.
Butoxyethanol, etc., containing 3 to 1 carbon atoms
The ethers up to 2 include, for example, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole, phenetole and the like, and cyclic carbons having 5 to 8 carbon atoms. Hydrogens include cyclopentane, cyclohexane, cycloheptane, cyclooctane and the like.

As the solvent, methylene chloride is particularly preferred. Other solvents may be mixed with methylene chloride and used. However, the mixing ratio of methylene chloride is 7
It is preferably at least 0% by weight. Particularly preferred mixing rates are 75 to 93% by weight of methylene chloride and 7 to 25% by weight of other solvents. The solvent is removed in forming the cellulose ester film. The residual amount of solvent is generally less than 5% by weight. Residual amount is 1% by weight
Is preferably less than 0.5% by weight, and more preferably less than 0.5% by weight.

In consideration of the effects on the human body and the environment, it is preferable to use a solvent that does not use methylene chloride. In this case, it is preferable to use a mixed solvent of methyl acetate and the aforementioned ketones and alcohols. In particular, when cellulose acylate is selected as the polymer for preparing the dope, it is preferable to use methyl acetate as a main solvent from the viewpoint of solubility. Also,
In order to improve the solubility of the polymer, methyl acetate may be mixed with a solvent such as a ketone or an alcohol. In this case, the component ratio of each solvent is as follows.
It is preferred that the content is from 90 to 90% by weight, from 0 to 60% by weight of ketones and from 5 to 30% by weight of alcohols.

[Additives] Additives such as plasticizers, ultraviolet absorbers and deterioration inhibitors may be added to the dope. Hereinafter, each of these additives will be described in detail.

(Plasticizer) The plasticizer that can be used in the present invention is not particularly limited, but in the case of a phosphate ester type, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl Phthalates such as phosphate, trioctyl phosphate, tributyl phosphate, etc.
In glycolic acid esters such as dimethoxyethyl phthalate, dimethyl phthalate and dioctyl phthalate,
It is preferable to use triacetin, tributyrin, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate, butylphthalylbutyl glycolate or the like alone or in combination.
Further, JP-A-11-80381 and JP-A-11-12
Plasticizers described in JP-A Nos. 4445 and 11-248940 can also be added. These plasticizers are 0.1 to 20% by weight based on cellulose acylate.
Is desirably mixed in the dope so as to contain

(Ultraviolet absorber) An ultraviolet absorber can be added to the dope. In particular, it is preferable to contain one or more ultraviolet absorbers. It is preferable that the UV absorber for liquid crystal is excellent in absorbing ability of UV light having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal, and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display property. For example, oxybenzophenone compounds, benzotriazole compounds, salicylate compounds, benzophenone compounds,
Examples include a cyanoacrylate compound and a nickel complex compound. Particularly preferred ultraviolet absorbers are benzotriazole-based compounds and benzophenone-based compounds. Above all, a benzotriazole-based compound is preferable because unnecessary coloring of the cellulose ester is small. Further, a benzotriazole-based ultraviolet absorber described in JP-A-8-29619 or an ultraviolet absorber described in JP-A-8-239509 can also be added. In addition, a known ultraviolet absorber may be added. These ultraviolet absorbers are desirably mixed in the dope so as to contain 0.001 to 5% by weight with respect to cellulose acylate. For example, a benzotriazole-based ultraviolet absorber described in JP-A-8-29619 or 8-239509
An ultraviolet absorber described in JP-A No. 2000-216, can also be added.

Preferred UV inhibitors include 2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], Triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3
5-di-tert-butyl-4-hydroxyphenyl)
Propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-
Butylanilino) -1,3,5-triazine, 2,2-
Thio-diethylenebis [3- (3,5-di-tert-
Butyl-4-hydroxyphenyl) propionate],
Octadecyl-3- (3,5-di-tert-butyl-
4-hydroxyphenyl) propionate, N, N'-
Hexamethylene bis (3,5-di-tert-butyl-
4-hydroxy-hydrocinnamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert)
-Butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate and the like. In particular,
2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-te
rt-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-te
rt-butyl-5-methyl-4-hydroxyphenyl)
Propionate] is most preferred. Also, for example, N, N
'-Bis [3- (3,5-di-tert-butyl-4-
[Hydroxyphenyl) propionyl] hydrazine compounds such as hydrazine-based metal deactivators and tris (2,4-
A phosphorus-based processing stabilizer such as di-tert-butylphenyl) phosphite may be used in combination. The amount of addition of these compounds is 0.001 to cellulose acylate.
Preferably, it is contained at 5% by weight.

(Fine particle powder) As the dope, a matting agent which is a fine particle powder can be used in order to improve the slipperiness of the film and the adhesion resistance under high humidity. The average height of the projections on the surface of the matting agent is preferably 0.005 to 10 μm, more preferably 0.01 to 5 μm. The better the number of the protrusions on the surface, the better. As the matting agent used, both inorganic compounds and organic compounds can be used. Barium sulfate, manganese colloid,
There are fine powders of inorganic substances such as titanium dioxide, strontium barium sulfate, silicon dioxide, aluminum oxide, tin oxide, zinc oxide, calcium carbonate, barium sulfate, talc, kaolin, and calcium sulfate. And silicon dioxide such as synthetic silica obtained by chemical conversion, and titanium dioxide (rutile type or anatase type) generated by titanium slag and sulfuric acid. It can also be obtained by pulverizing an inorganic substance having a relatively large particle size, for example, 20 μm or more, and then performing classification (vibration filtration, wind classification, etc.). As organic compounds, polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin,
Pulverized and classified organic polymer compounds such as melamine-based resin, polyolefin-based powder, polyester-based resin, polyamide-based resin, polyimide-based resin, polyfluoroethylene-based resin, and starch are also included. Alternatively, a polymer compound synthesized by a suspension polymerization method, a spherical polymer compound by a spray drying method, a dispersion method, or the like, or an inorganic compound can be used. Further, if the fine particle powder is added in an excessively large amount, adverse effects such as impairment of the flexibility of the film may occur.
Preferably, it is contained in an amount of about 5% by weight.

(Release Agent) A release agent for facilitating the release operation can be added to the dope. Release agents include high melting point waxes, higher fatty acids and their salts and esters, silicone oil, polyvinyl alcohol,
Examples include, but are not limited to, low molecular weight polyethylene, vegetable protein derivatives, and the like. Since the amount of the release agent added affects the gloss and smoothness of the film surface, it is preferably contained in an amount of 0.002 to 2% by weight based on the cellulose acylate.

(Fluorine-based surfactant) Dope includes
An elementary surfactant can also be added. Fluorine interface
Activator has surface activity with hydrophobic group of fluorocarbon chain
Agent in organic solvents to significantly reduce surface tension
And as an antistatic agent. Fluorine
As the surfactant, C₈F₁₇CH_TwoCH_TwoO- (CH
_TwoCH_TwoO)_Ten-OSO_ThreeNa, C₈F₁₇SO_TwoN (C
_ThreeH₇) (CH_TwoCH_TwoO)₁₆-H, C₈F₁₇SO_TwoN
(C_ThreeH₇) CH_TwoCOOK, C₇F_FifteenCOONH_Four,
C₈F₁₇SO_TwoN (C_ThreeH₇) (CH_TwoCH_TwoO)_Four−
(CH_Two)_Four-SO_ThreeNa, C₈F₁₇SO_TwoN (C_ThreeH
₇) (CH_Two)_Three-N⁺(CH_Three)_Three・ I^-, C₈F₁₇
SO_TwoN (C_ThreeH₇) CH_TwoCH_TwoCH_TwoN⁺(C
H_Three)_Two-CH_TwoCOO^-, C₈F₁₇CH_TwoCH_TwoO
(CH_TwoCH_TwoO)₁₆-H, C₈F₁₇CH_TwoCH_TwoO
(CH_Two) _Three-N⁺(CH_Three)_Three・ I^-, H (CF_Two)
₈-CH_TwoCH_TwoOCOCH_TwoCH (SO_Three) COOC
H_TwoCH_TwoCH_TwoCH_Two− (CF_Two)₈-H, H (CF
_Two) ₆CH_TwoCH_TwoO (CH_TwoCH_TwoO)₁₆-H, H
(CF_Two)₈CH_TwoCH_TwoO (CH_Two)_Three-N⁺(CH
_Three)_Three・ I^-, H (CF_Two)₈CH_TwoCH_TwoOCOCH
_TwoCH (SO_Three) COOCH_TwoCH_TwoCH_TwoCH_TwoC₈
F₁₇, C₉F₁₇-C₆H _Four-SO_TwoN (C_ThreeH₇) (C
H_TwoCH_TwoO)₁₆-H, C₉F₁₇-C₆H_Four-CSO_Two
N (C_ThreeH₇) (CH_Two)_Three-N⁺(CH_Three)_Three・ I^-
And the like, but are not limited to these.
The amount of the fluorosurfactant to be added is cellulose acylate.
0.001 to 2% by weight with respect to
New

Further, if necessary, various additives may be added to the dope at any stage before or after the preparation of the solution. Heat stabilizers such as salts of alkaline earth metals such as calcium and magnesium; antistatic agents; flame retardants; lubricants;

[Preparation of Dope] (Swelling Step) First, a swelling step of mixing the cellulose acylate particles with a solvent and swelling the cellulose acylate particles with the solvent is performed. The temperature of the swelling process is
It is preferably −10 to 55 ° C. It is usually performed at room temperature. The ratio between the cellulose acylate and the solvent is determined according to the concentration of the finally obtained solution. Generally, the amount of cellulose acylate in the mixture is between 5 and 30% by weight.
Is more preferably 8 to 20% by weight, and most preferably 10 to 15% by weight. The mixture of the solvent and the cellulose acylate is preferably stirred until the cellulose acylate is sufficiently swollen. Further, in the swelling step, components other than the solvent and cellulose acylate, for example, a plasticizer, a deterioration inhibitor,
A dye or an ultraviolet absorber may be added.

(Heating Step) Next, the above dope is heated to 130 ° C.
The heating step of heating is performed as described above. Heating temperature is 130 ° C
Or more, preferably 160 ° C. or more, most preferably 180 ° C.
° C or higher. However, when the temperature exceeds 250 ° C., the cellulose acylate in the dope is decomposed, which deteriorates the quality of the film, which is not preferable. In this case, the heating rate is preferably 1 ° C./min or more, more preferably 2 ° C./min or more, further preferably 4 ° C./min or more, and 8 ° C./min or more. Is most preferred. The heating rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
C / sec is a technical upper limit, and 100 C / sec is a practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from the start of heating to the final heating temperature. The heating method may be any method such as an autoclave method, a multi-tube heat exchanger, a screw extruder, and a static mixer.

The heating time is preferably from 20 seconds to 4 hours. If the heating time is less than 20 seconds, insolubles remain in the heated dope, and a high-quality film cannot be produced. Further, even when the insoluble matter is removed by filtration, the filtration life is extremely short, which is disadvantageous. The beginning of the heating time is measured from when the target temperature is reached, and the end is when cooling is started from the target temperature. The cooling of the device may be natural cooling or forced cooling.

(Pressurizing Step) In the heating step, the dope is preferably heated to a temperature not lower than the boiling point of the solvent at atmospheric pressure under a pressure adjusted so that the solution does not boil. By applying pressure, foaming of the dope can be prevented, and a uniform dope can be obtained. At this time, the pressure to be applied is determined by the relationship between the heating temperature and the boiling point of the solvent.

(Cooling Step) It is also effective to carry out a cooling step of cooling the above-mentioned dope to -100 to -10 ° C. before the heating step, in order to obtain a film having good optical properties. In a system that cannot be easily dissolved at room temperature and a system that contains many insolubles, a good dope can be prepared by using cooling or heating or a combination of both. By cooling, the solvent can be quickly and effectively penetrated into the cellulose acylate, and the dissolution is promoted. Effective temperature conditions are -100 to -10C. In the cooling step, it is desirable to use an airtight container in order to avoid water contamination due to dew condensation during cooling. If the pressure is reduced during cooling, the cooling time can be shortened. In order to reduce the pressure, it is desirable to use a pressure-resistant container. Also,
It is effective in the present invention that the cooling step is performed after the heating step. If the dissolution is insufficient, the steps from the cooling step to the heating step may be repeated. Whether the dissolution is sufficient can be determined by visually observing the appearance of the solution.

[Film Forming] The dope obtained as described above is poured into a mixing tank and stirred by a stirring blade to form a uniform solution. At this time, additives such as a hydrophobic plasticizer and an ultraviolet absorber can be mixed with the dope. The dope is sent to a filtration device by a pump to remove impurities. A solution casting method is performed using this dope, and typical methods are classified into a method using a casting band and a method using a casting drum.

[Casting Die] First, a method using a casting band will be described. FIG. 4 shows an example of a band type solution casting apparatus.
Shown in In this apparatus, an endless belt 2 having a mirror-finished surface is wound around a pair of rotating drums 3 (only one is shown). 1 of this rotating drum 3
The casting die 1 is provided slightly away from the peripheral surface. A decompression chamber 6 is provided behind the casting die 1, that is, on the right side of the drawing, and the decompression chamber 6 is sucked by a suction blower 9 via a suction duct 7 and a buffer chamber 8. Dope is the casting die 1
As shown in FIG. 2 or FIG. 3, it is extruded and cast on a casting band 2 running to the left in the drawing, solidified during running, and stripped off by a stripping roller 5 after approximately one round. It is sent to a tenter stretching machine (not shown). Some devices do not have the above-mentioned vacuum chamber.

The film is stretched and dried while being conveyed by a tenter stretching machine. The film that has exited the tenter stretching machine is sent to a drying zone, dried while being conveyed by a plurality of rollers, then passed through a cooling zone, cooled to room temperature, and wound up by a winder. It is preferred that knurling or trimming be performed before winding. However, in the present invention, the film may be dried by any known method.

The apparatus shown in FIG. 6 uses a casting drum 4 instead of the casting band 2.

The casting die 1 is shown in FIGS.
8, one shown in FIG. 19 can be used.

The casting die shown in FIG. 17 is used for forming a single-layer film, and the casting die 1 has one manifold 11 formed therein. The casting die in FIG. 18 is a multi-manifold type co-casting die, and the co-casting die 1 includes three manifolds 111, 112, and 113.
Is formed, and a three-layer film can be formed. The manifold 11 has a coat hanger shape, and a dope supply port 12 is provided at a central portion thereof. The lower side of the manifold 11 is a slot 13 from which the dope is extruded into a film. Die 1
Are closed by side plates 15 via packings 14 on both sides. The casting die shown in FIG. 19 is a feed-block type co-casting die. The co-casting die 1 has a manifold 1 formed thereon, a feed block 22 provided therein, and a plurality of merged portions in the feed block 22. The dope in the layer (three layers in FIG. 19) is cast. In the above-mentioned casting die, a coat hanger die is used. However, the present invention is not limited to this, and a die having another shape such as a T die may be used.

The die lip clearance in the solution casting method is usually set in the range of 0.2 mm to 3 mm, preferably in the range of 0.5 mm to 2.5 mm, but is not limited to this. Absent.

The distance between the casting die and the support (casting band or casting die) is usually set in the range of 1 mm to 10 mm, and preferably in the range of 1.5 mm to 6 mm. It is not limited to this.

The present invention is characterized by the shape of both ends of the tip of the die lip. That is, in the related art, the angle between the lip surface, that is, the surface in the longitudinal direction of the slot, and the side surface of the lip, that is, the end surface of the slot, is a right angle. In the present invention, the angle is set to 120 degrees or more, preferably 150 degrees or more, and more preferably, the tangent from the lip side surface and the lip surface coincide with each other to form an arc without a bent portion. In any case, it is preferable that the lip side surface section has a smooth curved shape having a minimum radius of curvature d / 10 or more with respect to the lip clearance d. In addition, the ratio w / d of the distance w between the lip clearance d and the distance w between the connection point between the lip surface and the lip side surface, that is, the base point where the straight line on the lip surface starts changing toward the center and the innermost portion of the lip side surface is 1. .5
Below, it is preferable to make it 1.0 or less, more preferably 0.8 or less. The lower limit of w / d is
Although not particularly limited, it is, for example, 0.1. The cross-sectional shape of the lip side surface is typically an arc shape, but is not limited to this. For example, in the cross-sectional shape of FIG. Is also good. The shape of the both ends may be symmetric unless there is a special purpose.

The processing of the shape of both ends of the die lip may be performed on the lip itself, or may be performed on the side plate packing or the side plate itself which is a member of the lip side surface portion. A packing may be inserted into the casing and the packing may be formed into a predetermined shape. Figure 8 shows an example of processing
To FIG.

The die shown in FIG. 8 is an example in which processing is performed on an integrated and seamless lip 16, and the dies shown in FIGS. 9 and 10 are examples in which processing is performed on a lip 16 having a seam. Further, the die of FIG. 11 is an example in which a thick material is used for the side plate packing 14 and processing is performed thereon, and the die of FIG. 12 is an example in which a thick material is used for the die side plate 15 and processing is performed there. . The die shown in FIG. 13 is an example in which the packing 20 is inserted into the end of the die lip and processed.

FIGS. 14 to 16 show side views of an example in which packing is inserted into the end of the die lip and processed.
As shown in these figures, the packing 20 has a constant slot width in the liquid flow direction inside the die (FIG. 14),
The outlet width may be wide (FIG. 15). The die shown in FIG. 16 is an example in which a solvent supply pipe 24 for preventing skinning is provided at the end of the lip. As the solvent, methylene chloride or the like is used, and details thereof are described in Japanese Patent No. 2687260 or the like.

The degree of decompression p of the decompression chamber is usually -50.
Set in the range of 0 to -10 Pa, preferably -400 to
It is preferable to set at -20 Pa, but it is not limited to this.

The casting speed v is usually 3 m / min to 150 m /
Minutes, preferably from 10 m / min to 100 m / min.
It is preferable to set the time in the range of minutes, but it is not limited to this.

The thickness t of the film is preferably 20 to 500 μm, more preferably 30 to 300 μm, and more preferably 35 to 2 μm.
00 μm is most preferable, but is not limited to this.

[Product] The obtained film can be used as a protective film for a polarizing plate. By attaching this polarizing plate protective film to both surfaces of a polarizing film formed of polyvinyl alcohol or the like, a polarizing plate can be formed. further,
It can also be used as an optical compensation film in which an optical compensation sheet is adhered on a film, or as an optical functional film such as an antireflection film in which an antiglare layer is laminated on the film. From these products, it is also possible to constitute a part of a liquid crystal display device.

[Co-casting] The solution casting method of the present invention is also applicable to a solution casting method by preparing two or more kinds of dopes and simultaneously coating the layers. For example, when a film is formed by simultaneous three-layer coating, a relatively large amount of cellulose acylate is contained in the dope for the inner layer, and a relatively large amount of cellulose acylate is contained in the dope for the outer layer formed on the front and back surfaces of the inner layer. Include a small amount. A film formed by simultaneously applying three layers of these dopes by the co-casting method has good flatness, transparency or moldability. However, the co-casting method in the solution casting method of the present invention is not limited to this embodiment.

[0052]

EXAMPLES The raw materials used in the solution casting process are as follows. Cellulose triacetate 100 parts by weight Triphenyl phosphate 10 parts by weight Biphenyl diphenyl phosphate 5 parts by weight Methylene chloride 315 parts by weight Methanol 60 parts by weight n-butanol 10 parts by weight Product thickness after drying 40,80 μm Decompression chamber pressure reduction degree 0 to 500 Pa Side dope composition during casting Cellulose triacetate 100 parts by weight Triphenyl phosphate 10 parts by weight Biphenyl diphenyl phosphate 5 parts by weight Methylene chloride 400 parts by weight Methanol 75 parts by weight n-butanol 13 parts by weight Total product thickness after drying 80 μm Main flow thickness 76 μm Side flow thickness (upper and lower layers) 2 μm each Die lip clearance d = 1.0 mm Casting speed 50 m / min

No solvent gas or solvent flow for preventing skinning was used. Under each condition of the examples, the time and extent of skinning at both ends of the lip and the remaining stains on the support were evaluated.

Example 1 A single layer was cast under the following conditions. At the end of the lip, a packing having a cross-sectional shape processed into a curve was inserted. 1) Angle θ between the lip surface and the lip side surface = 120 degrees 2) Minimum radius of curvature of the lip side surface = 0.5 mm Skinning occurred in 2 minutes. The amount of generation was small, as the skinning did not easily grow in the form of icicles. There was almost no residual stain on the support.

Example 2 A single layer was cast under the following conditions. At the end of the lip, a packing having a cross-sectional shape processed into a curve was inserted. 1) The angle θ between the lip surface and the lip side surface = 150 degrees 2) The minimum radius of curvature of the lip side surface = 0.5 mm Skinning occurred in 20 minutes. The amount of generation was small, as the skinning did not easily grow in the form of icicles. There was almost no residual stain on the support.

Example 3 A single layer was cast under the following conditions. The lip itself was curved. 1) The tangent line from the lip side surface and the lip surface coincide, forming a smooth curve with no step. 2) The minimum radius of curvature of the lip side surface = 0.5 mm No skinning occurred even after 60 minutes. There was almost no residual stain on the support.

Example 4 Co-casting was performed under the conditions of Example 3. As a result, no skinning occurred even after 60 minutes. There was almost no residual stain on the support.

Example 5 A single layer was cast under the following conditions. At the end of the lip, a packing having a cross-sectional shape processed into a curve was inserted. 1) The angle θ between the lip surface and the lip side surface = 150 degrees 2) The minimum radius of curvature of the lip side surface = 0.5 mm 3) The solvent was allowed to flow down at both ends of the lip at 0.1 ml / min. The solvent composition is 50 parts by weight of methylene chloride and 50 parts by weight of methanol. Even after 60 minutes, no skinning occurred. Residual stains on the support occurred.

Example 6 A single layer was cast according to the following dope recipe. The lip itself was curved. Cellulose triacetate 100 parts by weight Triphenyl phosphate 10 parts by weight Biphenyl diphenyl phosphate 5 parts by weight Methyl acetate 315 parts by weight Ethanol 60 parts by weight n-butanol 10 parts by weight The cellulose triacetate is swollen with a solvent for 30 minutes, and the cellulose triacetate solution is screwed. The liquid was fed by an extruder and passed through a cooling part so as to be maintained at -70 ° C for 3 minutes. Cooling was carried out with a refrigerator at −80 ° C. (Novac FC-77 manufactured by 3M or HF).
E-7100). Then, the solution obtained by cooling was transferred to a stainless steel container and stirred at 50 ° C. for 2 hours. Then, filtration was performed with a filter paper (# 63, manufactured by Toyo Roshi Kaisha, Ltd.) having an absolute filtration accuracy of 0.01 mm.

The shape of the lip end portion is as follows: 1) The tangent line from the lip side surface matches the lip surface, and the lip has a smooth curve without a step. 2) The minimum radius of curvature of the lip side surface = 0.5 mm No skinning occurred even after 60 minutes. There was almost no residual stain on the support.

Comparative Example 1 Casting was performed under the following conditions. 1) The angle θ between the lip surface and the lip side surface = 90 degrees Skinning occurred within 10 seconds even after removal. The amount of generation was very large, with the skinning growing like a icicle. There was almost no residual stain on the support.

Example 7 Co-casting was carried out using the dope of Example 5 with the following dope as a substream. Cellulose triacetate (degree of substitution 2.83, viscosity average degree of polymerization 320, water content 0.4% by weight, viscosity 6% by weight in methylene chloride solution 305 mPa · s) 25 parts by weight Methyl acetate 75 parts by weight Cyclopentanone 10 parts by weight Acetone 5 parts by weight Methanol 5 parts by weight Ethanol 5 parts by weight Plasticizer A (dipentaerythritol hexaacetate) 1 part by weight Plasticizer B (triphenyl phosphate) 1 part by weight Fine particles (silica (particle diameter: 20 nm)) 0.1 part by weight Part UV agent a: (2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5-triazine 0.1 part by weight UV agent b: 0.1% by weight of 2 (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole UV agent c: 2 (2'-hydroxy-3 ', 5'-di -tert- amyl phenyl) - 5-chloro-benzotriazole 0.1 part by weight _{C 12 H 25 OCH 2 CH 2} O-P (= O) -(OK) ₂ 0.05 parts by weight

Further, in addition to the lip end shape of the fifth embodiment,
The solvent was allowed to flow down at both ends of the lip at a rate of 0.1 ml / min. The solvent composition is 90 parts by weight of methyl acetate and 10 parts by weight of acetone. As a result, no skinning occurred even after 60 minutes. There was almost no residual stain on the support.

Further, an antireflection film by coating was prepared by the following procedure using the films of Examples 6 and 7 which were cast by the above method.

(Preparation of Coating Solution A for Antiglare Layer) 125 g of a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (DPHA, manufactured by Nippon Kayaku Co., Ltd.), bis (4-methacryloylthiophenyl) sulfide ( MPSMA, manufactured by Sumitomo Seika Co., Ltd.)
125 g was dissolved in 439 g of a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50% by weight. A solution prepared by dissolving 5.0 g of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) and 3.0 g of a photosensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 49 g of methyl ethyl ketone was added to the obtained solution. added. The refractive index of the coating film obtained by applying this solution and curing with ultraviolet light is 1.60.
Met. Further, 10 g of crosslinked polystyrene particles having an average particle size of 2 μm (trade name: SX-200H, manufactured by Soken Chemical Co., Ltd.) was added to this solution, and 500 g of high-speed disperser was used.
After stirring and dispersing at 0 rpm for 1 hour, the mixture was filtered through a polypropylene filter having a pore size of 30 μm, and the coating liquid A for the antiglare layer was applied.
Was prepared.

(Preparation of Coating Solution B for Antiglare Layer) A hard coat coating solution containing a zirconium oxide dispersion (Desolite KZ-7) was mixed with a mixed solvent of 104.1 g of cyclohexanone and 61.3 g of methyl ethyl ketone while stirring with an air disper.
886A (manufactured by JSR Corporation) 217.0 g. The refractive index of the coating film obtained by applying this solution and curing with ultraviolet light was 1.61. In addition, the solution has an average particle size of 2
μm crosslinked polystyrene particles (trade name: SX-200)
H, manufactured by Soken Chemical Co., Ltd.), and the mixture was stirred and dispersed at 5000 rpm for 1 hour with a high-speed disperser.
The solution was filtered through a 0 μm polypropylene filter to prepare a coating solution B for the antiglare layer.

(Preparation of Coating Solution C for Antiglare Layer) 91 g of a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (DPHA, manufactured by Nippon Kayaku Co., Ltd.), a hard coat coating solution containing a zirconium oxide dispersion ( Desolite KZ-7115, JSR
199 g) and a hard coat coating solution containing zirconium oxide dispersion (Desolite KZ-7161, J
19 g of SR (manufactured by SR Corporation) was dissolved in 52 g of a mixed solvent of methyl ethyl ketone / cyclohexanone = 54/46% by weight. To the resulting solution was added 10 g of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy). The refractive index of the coating film obtained by applying this solution and curing with ultraviolet light is 1.6.
It was one. Further, 20 g of crosslinked polystyrene particles having an average particle size of 2 μm (trade name: SX-200H, manufactured by Soken Chemical Co., Ltd.) were added to this solution in 80 g of a mixed solvent of methyl ethyl ketone / cyclohexanone = 54/46% by weight at 5000 rpm by high-speed disper. Dispersion liquid 2 with stirring and dispersion for 1 hour
After adding 9 g and stirring, the mixture was filtered through a polypropylene filter having a pore size of 30 μm to prepare a coating solution C for the antiglare layer.

(Preparation of Coating Solution D for Hard Coat Layer) An ultraviolet-curable hard coat composition (Desolite KZ-768)
A solution prepared by dissolving 250 g of 9,72% by weight (manufactured by JSR Corporation) in 62 g of methyl ethyl ketone and 88 g of cyclohexanone was added. The refractive index of the coating film obtained by applying this solution and curing with ultraviolet light was 1.53. The solution was further filtered through a polypropylene filter having a pore size of 30 μm to prepare a coating solution D for the hard coat layer.

(Preparation of Coating Solution for Low Refractive Index Layer) Refractive index
42 heat-crosslinkable fluoropolymers (TN-049, JS
R (manufactured by R Corporation) in MEK-ST (average particle size: 1)
8 g of a MEK dispersion of SiO2 sol having a solid content concentration of 30% by weight (0 to 20 nm, 8 g of Nissan Chemical Co., Ltd.) and 100 g of methyl ethyl ketone were added. After stirring, the mixture was filtered through a polypropylene filter having a pore size of 1 μm to obtain a low refractive index. A coating solution for a rate layer was prepared.

The triacetyl cellulose film having a thickness of 80 μm prepared in Example 6 and the above coating solution D for a hard coat layer were applied by a bar coater, dried at 120 ° C., and then air-cooled with a 160 W / cm metal halide lamp. (Eye Graphics Co., Ltd.) using an illuminance of 400 mW /
cm ^2, and an irradiation dose of 300 mJ / cm ² to cure the coating layer, to form a hard coat layer having a thickness of 2.5 [mu] m. The anti-glare layer coating solution A was applied thereon using a bar coater, dried and cured under the same conditions as the hard coat layer to form an anti-glare layer having a thickness of about 1.5 μm. The coating solution for a low refractive index layer was coated thereon with a bar coater, dried at 80 ° C., and further dried at 120 ° C. for 1 hour.
Thermal crosslinking was performed for 0 minutes to form a low refractive index layer having a thickness of 0.096 μm.

Next, using the film of Example 6, an antireflection film was prepared in which the coating liquid A for the antiglare layer was replaced with the coating liquid B for the antiglare layer, and the other conditions were the same. Further, an antireflection film was prepared in which the coating liquid A for the antiglare layer was replaced with the coating liquid C for the antiglare layer, and the other conditions were the same.

Further, from the film of Example 7, the above-described antireflection film was prepared under the same conditions by using the coating solutions A, B and C for the antiglare layer one by one.

[Evaluation of Antireflection Film] The film was formed from the film of Example 6 (anti-glare layers A, B, and C) and the film of Example 7 (anti-glare layers A, B, and C) by the above-described method. 6
The following items were evaluated for the various types of antireflection films.
Table 1 summarizes the results obtained from the following evaluation methods.

(Evaluation of Antireflection Film) The obtained film was evaluated for the following items.

(1) Specular reflectivity and tint An adapter ARV-474 was attached to a spectrophotometer V-550 (manufactured by JASCO Corporation), and emission was performed at an incident angle of 5 ° in a wavelength range of 380 to 780 nm. The specular reflectance at an angle of -5 degrees was measured, the average reflectance at 450 to 650 nm was calculated, and the antireflection property was evaluated. Further, from the measured reflection spectrum, CIE1976L * a representing the color of specularly reflected light with respect to the incident light of 5 degrees of the CIE standard light source D65 from the CIE standard light source D65.
The L * value, a * value, and b * value of the * b * color space were calculated, and the tint of the reflected light was evaluated.

(2) Integrated Reflectance An adapter ILV-471 was attached to a spectrophotometer V-550 (manufactured by JASCO Corporation), and the integrated reflectance at an incident angle of 5 ° in a wavelength range of 380 to 780 nm was measured. It measured and calculated the average reflectance of 450-650 nm.

(3) Haze The haze of the obtained film was measured with a haze meter MODEL.
It measured using 1001DP (made by Nippon Denshoku Industries Co., Ltd.).

(4) Evaluation of Pencil Hardness Pencil hardness evaluation described in JIS K 5400 was performed as an index of scratch resistance. Antireflection film at a temperature of 25 ° C and a humidity of 60
% RH for 2 hours, using a 3H test pencil specified in JIS S 6006, with a load of 1 kg, and no scratches are observed in the evaluation of n = 5: ○ In the evaluation of n = 5 1 or 2 scratches: Δ 3 or more scratches in the evaluation of n = 5: ×

(5) Measurement of Contact Angle As an index of stain resistance of the surface, the optical material was heated at a temperature of 25 ° C.
After conditioning for 2 hours at a humidity of 60% RH, the contact angle with water was measured and used as an index for fingerprint adhesion.

(6) Measurement of dynamic friction coefficient The dynamic friction coefficient was evaluated as an index of the surface slip property. The coefficient of kinetic friction was adjusted at 25 ° C. and a relative humidity of 60% for 2 hours, and then 5 mmφ using a HEIDON-14 kinetic friction measuring instrument.
Stainless steel ball, load 100g, speed 60cm / min
The value measured in was used.

(7) Evaluation of anti-glare property Exposed fluorescence without louver on the prepared anti-glare film
Light (8000 cd / m ^Two) And the reflection image is blurred
The degree was evaluated according to the following criteria. The outline of the fluorescent lamp is not known at all: ◎ The outline of the fluorescent lamp is slightly recognized: ○ The fluorescent lamp is blurred, but the outline can be identified: △ The fluorescent lamp is hardly blurred: ×

[0082]

[Table 1]

The anti-reflection films formed from the films of Examples 6 and 7 are all excellent in anti-glare properties and anti-reflection properties, have low tint, and have pencil hardness, fingerprint adhesion and dynamic friction coefficient. Evaluation results reflecting the physical properties of the film were also good.

Next, an antiglare antireflection polarizing plate was prepared using the film of Example 7. When a liquid crystal display device in which an antireflection layer was disposed on the outermost layer was prepared using this polarizing plate, an excellent contrast was obtained because there was no reflection of external light, and a reflection image was inconspicuous due to antiglare properties. It had visibility and fingerprints were good.

Further, the composition ratio of the mixed solvent for preparing the dope is changed in the above-described Example 6 and Example 7. In Example 6, methyl acetate was 82% by weight, ketones were 0% by weight, and alcohols (ethanol, n-butanol) were 1%.
It was 8% by weight. In Example 7, methyl acetate 7
5% by weight, ketones (cyclopentanone, acetone) 1
5% by weight, alcohols (methanol, ethanol) 1
It was 0% by weight. Thus, in the present invention, a dope can be prepared from a solvent in which the mixing ratio of methyl acetate, ketones, and alcohols is changed.

[0086]

According to the present invention, the occurrence of skinning at the end of the casting die lip can be reliably suppressed.

Further, according to the present invention, cellulose acylate could be efficiently dissolved by a mixed solvent of methyl acetate, ketones and alcohols. A film obtained from the cellulose acylate solution by a solution casting method has excellent optical properties and physical properties.

Further, a polarizing plate protective film, a polarizing plate, an optical function film, and a liquid crystal display device made from this film have excellent optical properties and physical properties and also have excellent durability.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing the shape of an opening at the end of the lip of a casting die according to an embodiment of the present invention.

FIG. 2 is a side view showing a state where the casting is performed by using the casting die of FIG. 1;

FIG. 3 is a side view showing a state where a decompression chamber is provided in FIG. 2;

FIG. 4 is a partial side view showing a main configuration of a casting device of a casting band type using the casting die of FIG. 1;

FIG. 5 is a plan view of a main part of the belt-type casting apparatus shown in FIG. 1;

FIG. 6 is a partial side view showing an example in which the casting die of FIG. 1 is applied to a casting device of a casting drum type.

FIG. 7 is a plan view of a main part of the application example shown in FIG. 6;

FIG. 8 is a partial sectional view of an end portion of a lip tip of an example of a casting die according to the present invention.

FIG. 9 is a partial sectional view of an end portion of a lip tip of another example of a casting die according to the present invention.

FIG. 10 is a partial sectional view of an end portion of a lip tip of another example of a casting die according to the present invention.

FIG. 11 is a partial sectional view of an end portion of a lip tip of another example of a casting die according to the present invention.

FIG. 12 is a partial sectional view of an end portion of a lip tip of another example of the casting die according to the present invention.

FIG. 13 is a partial sectional view of an end portion of a lip tip of another example of a casting die according to the present invention.

FIG. 14 is a partial side view showing the structure of an example of the casting die of the present invention.

FIG. 15 is a partial side view showing the structure of another example of the casting die of the present invention.

FIG. 16 is a partial side view showing the structure of another example of the casting die of the present invention.

FIG. 17 is a longitudinal sectional view of an example of a casting die to which the present invention is applied.

FIG. 18 is a longitudinal sectional view of another example of a casting die to which the present invention is applied.

FIG. 19 is a longitudinal sectional view of another example of a casting die to which the present invention is applied.

FIG. 20 is a side view showing a state in which casting is performed using a conventional casting die.

FIG. 21 is a partial cross-sectional view showing an end opening shape of the tip of the die lip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casting die 2 Casting band 3 Rotating drum 4 Casting drum 5 Peeling roller 6 Pressure reducing chamber 7 Suction duct 8 Buffer chamber 9 Suction blower 10 Casting dope 11 Manifold 12 Dope supply port 13 Slot 14 Side plate packing 15 Side plate 16 Die lip 17 Lip tip 18 Lip face 19 Lip side face 20 Packing 21 Dope flow path 22 Feed block 23 Skinning 24 Solvent supply pipe d Lip clearance w Curved width of lip side face θ Angle between lip face and lip side face

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B29L 7:00 B29L 7:00 11:00 11:00 C08L 1:10 C08L 1:10 (72) Inventor Takao Kumazawa 210 Nakanuma, Minamiashigara-shi, Kanagawa Prefecture Fuji Photo Film F-term (reference) AG24 AH73 AM32 CA07 CB02 CD08 4F205 AA49L AC05 AG01 AG23 AG24 AH73 AM32 GA07 GB02 GC06 GF24

Claims (18)

[Claims] In the cross-sectional shape of both ends of the lip tip,
A casting die for solution casting, wherein the angle θ between the lip surface and the lip side surface is 120 degrees or more. 2. A ratio w / a ratio of a distance w between a connection portion of the lip side surface to the lip surface and the lip side surface and a lip clearance d.
The casting die according to claim 1, wherein d is 1.5 or less. 3. The casting die according to claim 1, wherein the minimum radius of curvature in the cross-sectional shape of both ends of the lip tip is d / 10 or more. 4. The casting die according to claim 1, wherein the lip side surface is formed by packing or side plate packing. 5. The lip side surface is formed by a die side plate.
The casting die described in (1). 6. A solution casting method using the casting die according to any one of claims 1 to 5. 7. The solution casting method according to claim 6, wherein a cellulose acylate solution is used. 8. The solvent of the cellulose acylate solution comprises methyl acetate, ketones and alcohols, and the solvent ratio is 20 to 90% by weight for methyl acetate, 0 to 60% by weight for ketones, and 5 for alcohols. The solution casting method according to claim 7, wherein the content is from 30 to 30% by weight. 9. The solution according to claim 7, wherein the cellulose acylate solution contains at least one plasticizer in an amount of 0.1 to 20% by weight based on the weight of the cellulose acylate. Membrane method. 10. The method according to claim 7, wherein the cellulose acylate solution contains at least one ultraviolet absorber in an amount of 0.001 to 5% by weight based on the weight of the cellulose acylate. 5. The solution casting method according to any one of the above. 11. The cellulose acylate solution according to claim 7, wherein the cellulose acylate solution contains at least one kind of fine particle powder in an amount of 0.001 to 5% by weight based on the cellulose acylate. 5. The solution casting method according to any one of the above. 12. The cellulose acylate solution according to claim 7, wherein the cellulose acylate solution contains at least one release agent in an amount of 0.002 to 2% by weight based on the weight of the cellulose acylate. 5. The solution casting method according to any one of the above. 13. The method according to claim 7, wherein the cellulose acylate solution contains at least one fluorine-based surfactant in an amount of 0.001 to 2% by weight based on the weight of the cellulose acylate. The solution casting method according to any one of the first to third aspects. 14. The solution casting method according to claim 7, wherein two or more types of cellulose acylate solutions containing at least one type of cellulose acylate are co-cast in the casting step. The solution casting method according to any one of the first to third aspects. 15. A polarizing plate protective film comprising a film formed by the solution film forming method according to any one of claims 7 to 14. 16. A polarizing plate comprising a film formed by the solution casting method according to any one of claims 7 to 14. 17. An optically functional film comprising a film formed by the solution casting method according to claim 7. Description: 18. A liquid crystal display device comprising a film formed by the solution film forming method according to claim 7. Description: