JP4530735B2 - Cellulose acylate film and method for producing the same - Google Patents

Description

The present invention relates to a cellulose acylate film having a negative retardation in the film thickness direction, a retardation plate, a polarizing plate and a liquid crystal display device using the same.

The cellulose ester film is used for a support of a halogenated photographic light-sensitive material, a retardation plate, a support of a retardation plate, a protective film for a polarizing plate, and a liquid crystal display device.
Among the cellulose ester films, the most commonly used cellulose acetate film for optical applications such as image display devices mainly employs the solution casting film forming method to produce a good film with high flatness. ing. The retardation (Rth) in the film thickness direction of this film usually shows a positive value, but cellulose acetate significantly lowers the Rth by increasing the degree of acetylation, and at the same time the solubility in organic solvents. Therefore, Rth is expected to be negative in a cellulose acetate film having a very high acetylation degree, but it can be sufficiently dissolved even after stirring in a halogen-based organic solvent and stirring at a temperature close to room temperature. It was not possible to form a film for optical use having an excellent surface shape. On the other hand, Non-Patent Document 1 and Patent Document 1 show that the solubility in a solvent can be improved by using cellulose acetate as a mixed fatty acid ester.
When a cellulose ester film having negative Rth is produced, the film can be used as it is as a retardation plate of an IPS mode liquid crystal display device to improve the visibility of the panel, or a cellulose ester film having positive Rth is bonded. Accordingly, it is possible to manufacture a retardation plate in which Rth, which is generally not easily controlled, is adjusted freely. Therefore, it is anxious to produce a cellulose ester film having negative Rth. A film having negative Rth can be produced by a complicated method as disclosed in Patent Document 2, but the productivity is not sufficient.

JP-A-8-231761 JP2000-231616 Ind. Eng. Chem. 43, 688, 1951

When the cellulose ester film is used for optical applications such as a retardation plate, a support for the retardation plate, a protective film for a polarizing plate, and a liquid crystal display device, the control of the optical anisotropy is very important. In general, the cellulose ester film is easy to control the retardation (Re) in the in-plane direction, but is difficult to control the retardation (Rth) in the thickness direction. Especially in the solution casting film forming method, since a compressive force is inevitably applied in the film thickness direction during the film forming process, it is very difficult to produce a cellulose ester film so that the retardation in the thickness direction becomes a low value. It was difficult.

On the other hand, in a display device using a cellulose ester film as an optical material, the retardation value of the cellulose ester film is a very important parameter that determines the performance (for example, visibility) of the display device. For example, in an IPS mode liquid crystal display device, by inserting a film having a negative Rth as a retardation plate, the color and contrast can be improved, and a panel with excellent image quality can be obtained.

An object of the present invention is to provide a cellulose acylate film having a negative retardation value in the film thickness direction, which is used as a retardation plate, a support for a retardation plate, a protective film for a polarizing plate, and an excellent liquid crystal It is to provide a display device.

The present invention provides a method for producing a cellulose acylate film of the following (1) to a cellulose acylate film (5), contact and following (9) to (12). It also describes the retardation plates (6) and (7) below and the polarizing plate (8) below.

(1) acyl substitution degree is represented by the following formula to the hydroxyl group of cellulose (I) ~ a cellulose ester satisfies all of (III), and an organic solvent having a boiling point of 80 ° C. or less, A having a boiling point of not lower than 95 ° C. Ruko le 1 Swelled at -10 to 35 ° C. in a solvent containing ˜5 % by mass , the mixture is stirred and dissolved at 0 to 35 ° C., and is subjected to casting from a solution obtained through filtration. A cellulose acylate film having a retardation value in the film thickness direction of -50 to -1 nm .
(I) 2.80 ≦ SA + SP <2.87
(II) 0 ≦ SA ≦ 1.0
(III) 1.8 ≦ SP <2.87
(In the formula, SA and SP represent the substitution degree of the acyl group substituted by the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SP is the substitution degree of the propionyl group. )
(2) The solvent contains two or more kinds of alcohols, and the two or more kinds of alcohols comprise at least one kind of alcohol having a boiling point of 95 ° C. or higher and at least one kind of alcohol having a boiling point of less than 95 ° C. The cellulose acylate film as described in ( 1) above, wherein
(3) The cellulose acylate film as described in (2) above, wherein 10 to 30% by mass of the solvent is alcohol.
(4) The above-mentioned characteristic, wherein the change with humidity between the retardation value in the film thickness direction at 25 ° C. and 10% RH and the retardation value in the film thickness direction at 25 ° C. and 80% RH is 20 nm or less. The cellulose acylate film according to any one of 1) to (3) .
(5) The cellulose acylate film according to any one of the above (1) to (4) , wherein the film thickness is 60 to 180 μm.

(6) A laminated phase difference plate comprising the cellulose acylate film according to any one of (1) to (5) above and a cellulose acylate film having a positive retardation value in the film thickness direction. .
(7) A retardation film comprising at least one cellulose acylate film according to any one of (1) to (5) .

(8) A polarizing plate comprising a polarizing film and two transparent plastic films provided on both sides thereof, wherein one transparent plastic film is at least one of the above (1) to (5) A polarizing plate comprising a cellulose acylate film.

(9) An acyl substitution degree is represented by the following formula to the hydroxyl group of cellulose (I) ~ a cellulose ester satisfies all of (III), and an organic solvent having a boiling point of 80 ° C. or less, A having a boiling point of not lower than 95 ° C. Ruko le 1 swollen with solvent -10～35 ° C. containing a 5% by weight, that the mixture dissolved by stirring at 0 to 35 ° C., to a solution or al casting film obtained through the step of filtering A method for producing a cellulose acylate film having a retardation value in the film thickness direction of -50 to -1 nm .
(I) 2.80 ≦ SA + SP <2.87
(II) 0 ≦ SA ≦ 1.0
(III) 1.8 ≦ SP <2.87
(In the formula, SA and SP represent the substitution degree of the acyl group substituted by the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SP is the substitution degree of the propionyl group. )
(10) The solvent contains two or more kinds of alcohols, and the two or more kinds of alcohols comprise at least one kind of alcohol having a boiling point of 95 ° C. or more and at least one kind of alcohol having a boiling point of less than 95 ° C. The method for producing a cellulose acylate film as described in (9) above.
(11) The method for producing a cellulose acylate film as described in (10) above, wherein 10 to 30% by mass of the solvent is alcohol.
(12) The method for producing a cellulose acylate film according to any one of (9) to (11) , wherein the organic solvent having a boiling point of 80 ° C. or less is a halogenated hydrocarbon.
Although this invention is invention which concerns on said (1)- (5) and (9)-(12) , below, other matters are also described.

The retardation value of the cellulose ester film is 25 ° C. using an automatic birefringence meter (for example, KOBRA-21ADH: manufactured by Oji Scientific Instruments) after conditioning the film at 25 ° C. and 60% RH for 24 hours. At 60% RH, the retardation value at a wavelength of 590 nm was measured from the direction perpendicular to the sample film surface and the direction inclined by ± 40 ° from the normal to the film surface, and expressed by the following formulas (1) and (2), respectively. The in-plane retardation value (Re) and the retardation value (Rth) in the film thickness direction are calculated.

(1) Re = (nx−ny) × d
(2) Rth = {(nx + ny) / 2−nz} × d
In the formula, nx is the refractive index in the slow axis (x) direction in the film plane, ny is the refractive index in the fast axis (y) direction in the film plane, and nz is the film thickness direction (film surface). And d is the thickness (nm) of the film. The slow axis is the direction in which the refractive index is maximum in the film plane, and the fast axis is the direction in which the refractive index is minimum in the film plane.

Changes in the retardation value with humidity are Re and Rth calculated by conditioning the film at 25 ° C. and 10% RH (represented as Re (10%) and Rth (10%), respectively). And Re and Rth (represented as Re (80%) and Rth (80%), respectively) calculated after conditioning at 25 ° C. and 80% RH, the following formulas (3) and (4) The humidity dependency (ΔRe) of Re and the humidity dependency (ΔRth) of Rth, which are respectively represented by the above, are calculated.
(3) ΔRe = | Re (10%) − Re (80%) |
(4) ΔRth = | Rth (10%) − Rth (80%) |

The cellulose acylate film of the present invention characterized by the above-mentioned substituted ester group structure is a cellulose ester film in which Rth is a negative value, and the Rth ranges from −50 to −1 nm, particularly from −40 to 40 nm. Rth in a practically valuable range of −5 nm, and further −30 to −10 nm can be obtained. If the humidity dependence of Rth is 20 nm or less, there is no practical problem. However, the cellulose acylate film according to the present invention is more preferably 18 nm or less, and further shows a stable humidity dependence of 15 nm or less.
In general, it is very difficult to largely control the retardation (Rth) in the thickness direction of the cellulose ester film by adjusting the manufacturing process conditions such as stretching, but the cellulose ester of the present invention in which Rth is a negative value. If there is a film, it can be used as it is as a retardation plate for an IPS (In-Plane Switching) mode liquid crystal display device. In addition, Rth can be easily controlled by bonding a conventionally known cellulose ester film having a positive Rth value and the cellulose ester film of the present invention.

In addition, since the cellulose ester used as a raw material of the film of the present invention is very excellent in solubility in a solvent, the cellulose ester film obtained by the present invention has a feature that there are very few foreign substances, and is used in optical applications. It can be suitably used as a film.
In addition, as a polymer film in which Rth has a negative value, a polycarbonate film manufactured by a complicated method is well known. However, this film is not sufficiently productive due to the complicated manufacturing method, and polycarbonate films and cellulose ester films have physical properties such as expansion coefficient, optical properties such as refractive index, and moisture permeability. Because the coefficients are different, when a polycarbonate film and a cellulose ester film are laminated, problems due to differences in physical properties (for example, curls due to differences in expansion coefficients depending on the environment) and problems due to differences in optical properties (for example, , A decrease in transmittance due to reflection at the bonding interface, etc. occurs, and when used as a polarizing plate protective film having a retardation plate function, there is a problem due to a low moisture permeability coefficient (for example, water (A decrease in the degree of polarization due to the fact that the polarizer containing) does not dry.
By using the cellulose ester film with a small amount of foreign matter, in which Rth is a negative value obtained by the present invention, it becomes possible to freely control the Rth of the retardation plate and the polarizing plate without causing the above problems. It was. A highly reliable image display device can be obtained by using these retardation plates or polarizing plates.

The cellulose acylate film of the present invention is a film containing a cellulose ester compound and a compound having an ester-substituted cellulose skeleton obtained by introducing a functional group biologically or chemically using cellulose as a raw material. Among them, the acid constituting the ester is acetic acid and / or propionic acid, which is a carboxylic acid having 2 and / or 3 carbon atoms. In cellulose acylate composed of a carboxylic acid having 4 or more carbon atoms, the side chain is flexible because the side chain lies in the plane by the compressive force during film formation, and functions to increase Rth. In addition, a cellulose acylate film having a large negative value in the film thickness direction cannot be produced.

The substitution degree of the cellulose ester satisfies all of the following formulas (I) to (III),
(I) 2.80 ≦ SA + SP <2.87
(II) 0 ≦ SA ≦ 1.1
(III) 1.8 ≦ SP <2.87
(In the formula, SA and SP represent the substitution degree of the acyl group substituted with the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SP is the substitution degree of the propionyl group.)
Is preferred,
(I) 2.81 ≦ SA + SP ≦ 2.86
(II) 0 ≦ SA ≦ 0.9
(III) 2.0 ≦ SP ≦ 2.85
Is more preferred,
(I) 2.82 ≦ SA + SP ≦ 2.86
(II) 0 ≦ SA ≦ 0.7
(III) 2.2 ≦ SP ≦ 2.85
Is more preferable.

In the cellulose acetate propionate and cellulose propionate according to the present invention, a film having a negative Rth value is achieved by setting the total substitution degree represented by the above formula (I) to 2.8 or more. The total substitution degree is preferably high, but if the total substitution degree exceeds 2.87, the problem that the film is whitened during the drying process occurs. Further, by increasing the degree of substitution of propionyl represented by the above formula (III), it is possible to reduce Rth as compared to cellulose acetate, and to reduce the humidity dependency of Rth, and at the same time improve the solubility in a solvent. It is possible to obtain a well-dissolved dope solution just by stirring near room temperature, and it is possible to produce a good film with excellent surface shape without consuming a great deal of energy during production. It becomes.

The basic principle of the cellulose acylate synthesis method is described in Nobuhiko Umeda et al., Wood Chemistry, 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method of cellulose acylate is a liquid phase acylation method using a carboxylic acid anhydride-carboxylic acid-sulfuric acid catalyst. Specifically, cellulose raw materials such as cotton linter and wood pulp are pretreated with an appropriate amount of carboxylic acid such as acetic acid, and then put into a precooled acylated mixture for esterification, and complete cellulose acylate (2nd, The total degree of acyl substitution at the 3rd and 6th positions is approximately 3.00). The acylated mixed solution generally contains a carboxylic acid as a solvent, a carboxylic anhydride as an esterifying agent, and sulfuric acid as a catalyst. The carboxylic anhydride is usually used in a stoichiometric excess over the total of the cellulose that reacts with it and the water present in the system.

After completion of the acylation reaction, water or hydrous acetic acid is added in order to hydrolyze the excess carboxylic anhydride remaining in the system. In order to partially neutralize the esterification catalyst, an aqueous solution of a neutralizing agent (eg, calcium, magnesium, iron, aluminum or zinc carbonate, acetate, hydroxide or oxide) may be added. Next, the obtained complete cellulose acylate is saponified and aged by maintaining it at 20 to 90 ° C. in the presence of a small amount of acylation reaction catalyst (generally, remaining sulfuric acid) to obtain the desired degree of acyl substitution and polymerization. The cellulose acylate having a degree is changed. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized with a neutralizing agent as described above, or in water or dilute acetic acid without neutralization. The cellulose acylate solution is added (or water or dilute acetic acid is added into the cellulose acylate solution) to separate the cellulose acylate, and the cellulose acylate is obtained by washing and stabilizing treatment.

The degree of polymerization of the cellulose acylate is preferably from 150 to 500, more preferably from 200 to 400, and even more preferably from 220 to 350 in terms of viscosity average degree of polymerization. The viscosity average degree of polymerization can be measured according to Uda et al.'S limiting viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Science, Vol. 18, No. 1, pages 105-120, 1962). A method for measuring the viscosity average degree of polymerization is also described in JP-A-9-95538.

Cellulose acylate with a small amount of low molecular components has a high average molecular weight (degree of polymerization), but its viscosity is lower than that of ordinary cellulose acylate. Cellulose acylate having a small amount of low molecular components can be obtained by removing low molecular components from cellulose acylate synthesized by a usual method. The removal of the low molecular component can be performed by washing the cellulose acylate with an appropriate organic solvent. In addition, cellulose acylate having a small amount of low molecular components can be synthesized. When producing a cellulose acylate having a small amount of low molecular components, the amount of sulfuric acid catalyst in the acylation reaction is preferably adjusted to 0.5 to 25 parts by mass with respect to 100 parts by mass of cellulose. When the amount of the sulfuric acid catalyst is in the above range, cellulose acylate that is preferable in terms of molecular weight distribution (uniform molecular weight distribution) can be synthesized.
The cellulose acylate raw material cotton and the synthesis method are also described in pages 7 to 12 of published technical bulletin 2001-1745 (issued on March 15, 2001, Invention Association).

In the cellulose acylate film, the polymer component constituting the film is preferably substantially composed of cellulose acylate. “Substantially” means 55% by mass or more (preferably 70% by mass or more, more preferably 80% by mass or more) of the polymer component. Two or more types of cellulose acylate may be used in combination with the cellulose acylate film.

As a raw material of the cellulose ester solution, it is preferable to use cellulose acylate particles. 90% by mass or more of the particles used preferably have a particle size of 0.2 to 5 mm. Further, it is preferable that 50% by mass or more of the particles to be used have a particle diameter of 0.4 to 4 mm. The cellulose acylate particles preferably have a shape as close to a sphere as possible.

The cellulose acylate used for preparing the cellulose ester solution preferably has a moisture content of 1.5% by mass or less, more preferably 1% by mass or less, and most preferably 0.7% by mass or less. preferable. Cellulose acylate generally has a moisture content of 1.8-5% by weight. Therefore, it is preferable to use the cellulose acylate after drying it.

In the cellulose ester solution, various additives (for example, plasticizers, modifiers, UV inhibitors, optical anisotropy control agents, fine particles, release agents, infrared absorbers) depending on the application in each preparation step. Can be added. About a plasticizer, Unexamined-Japanese-Patent No. 2001-151901 has description. About an infrared absorber, Unexamined-Japanese-Patent No. 2001-194522 has description. The timing for adding the additive is determined according to the type of the additive.
When the cellulose ester film has a multilayer structure, the kind and amount of additives in each layer may be different (for example, described in JP-A No. 2001-151902).
The additives for cellulose ester film are also described in pages 16 to 22 of published technical report No. 2001-1745 (issued on March 15, 2001, Invention Association).

The main solvent of the cellulose ester solution is preferably an organic solvent having a boiling point of 80 ° C. or less from the viewpoint of reducing the drying load, more preferably 10-80 ° C., more preferably 20-60 ° C. Further, it is more preferable that the boiling point is 30 to 45 ° C. Examples of such a main solvent include halogenated hydrocarbons, esters, ketones, ethers, alcohols and hydrocarbons, and they may have a branched structure or a cyclic structure. Moreover, you may have any two or more of the functional groups (namely, -O-, -CO-, -COO-, -OH) of ester, ketone, ether, and alcohol. Further, the hydrogen atom in the hydrocarbon portion of the ester, ketone, ether and alcohol may be substituted with a halogen atom (particularly a fluorine atom). In addition, the main solvent of the cellulose ester solution indicates that solvent when it is composed of a single solvent, and when it is composed of a plurality of solvents, it is the solvent having the highest weight fraction among the constituent solvents. It shows that.

As the halogenated hydrocarbon, a chlorinated hydrocarbon is more preferable, and examples thereof include dichloromethane and chloroform, and dichloromethane is more preferable.
Examples of the ester include methyl formate, ethyl formate, methyl acetate, ethyl acetate and the like.
Examples of the ketone include acetone and methyl ethyl ketone.
Examples of ethers include diethyl ether, methyl-t-butyl ether, diisopropyl ether, dimethoxymethane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, and methyltetrahydrofuran.
Examples of the alcohol include methanol, ethanol, 2-propanol and the like.
Examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, and benzene.

Examples of the organic solvent used in combination with these include halogenated hydrocarbons, esters, ketones, ethers, alcohols and hydrocarbons, and they may have a branched structure or a cyclic structure. Moreover, you may have any two or more of the functional groups (namely, -O-, -CO-, -COO-, -OH) of ester, ketone, ether, and alcohol. Further, the hydrogen atom in the hydrocarbon portion of the ester, ketone, ether and alcohol may be substituted with a halogen atom (particularly a fluorine atom).

As the halogenated hydrocarbon, a chlorinated hydrocarbon is more preferable, and examples thereof include dichloromethane and chloroform, and dichloromethane is more preferable.
Examples of the ester include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate.
Examples of the ketone include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone.
Examples of ethers include diethyl ether, methyl t-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, phenetole and the like. It is done.
Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol, cyclohexanol, 2-fluoroethanol, 2 , 2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, and the like.
Examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, benzene, toluene, xylene and the like.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, 2-butoxyethanol, and methyl acetoacetate.

Among these, it is preferable from the viewpoint of reducing the peeling load from the band that at least 10 to 30% by mass, more preferably 11 to 30% by mass, and still more preferably 12 to 25% by mass of alcohol is contained in the total solvent.
In addition, from the viewpoint of reducing Rth, the organic solvent which is a poor solvent for cellulose ester having a small proportion of volatilization with the halogenated hydrocarbon at the initial stage of the drying process and having a boiling point of 95 ° C. or higher is gradually concentrated. More preferably, it is contained in an amount of 1.5 to 5 mass%, more preferably 2 to 5 mass%.
The organic solvent having a boiling point of 95 ° C. or higher is preferably an alcohol from the viewpoint of reducing the peeling load from the band and reducing Rth, and the alcohol is composed of two or more alcohols from the viewpoint of improving productivity by reducing the drying load. The mixture preferably comprises an alcohol having a boiling point of 95 ° C. or higher and an alcohol having a boiling point of less than 95 ° C.

Although the example of the combination of the organic solvent preferably used in this invention is given below, it is not limited to these. The numerical value of a ratio is a mass part.

(1) Dichloromethane / methanol / ethanol / butanol = 80/10/5/5
(2) Dichloromethane / acetone / methanol / propanol = 80/10/5/5
(3) Dichloromethane / methanol / butanol / cyclohexane = 80/10/5/5
(4) Dichloromethane / methyl ethyl ketone / methanol / butanol = 80/10/5/5

(5) Dichloromethane / acetone / methyl ethyl ketone / ethanol / butanol = 68/10/10/7/5
(6) Dichloromethane / cyclopentanone / methanol / pentanol = 80/2/15/3
(7) Dichloromethane / methyl acetate / ethanol / butanol = 70/12/15/3
(8) Dichloromethane / cyclohexanone / methanol / pentanol = 80/2/15/3

(9) Dichloromethane / methyl ethyl ketone / acetone / methanol / pentanol = 50/20/20/5/5
(10) Dichloromethane / 1,3-dioxolane / methanol / butanol = 70/20/5/5
(11) Dichloromethane / dioxane / acetone / methanol / butanol = 80/2/10/5/3
(12) Dichloromethane / acetone / cyclopentanone / ethanol / isobutanol / cyclohexane = 60/18/3/15/2/2

(13) Dichloromethane / methyl ethyl ketone / acetone / methanol / isobutanol = 70/10/10/5/5
(14) Dichloromethane / acetone / ethyl acetate / ethanol / butanol / hexane = 69/10/10/5/5/1
(15) Dichloromethane / methyl acetate / methanol / isobutanol = 65/20/10/5
(16) Dichloromethane / cyclopentanone / ethanol / butanol = 86/2/10/2
(17) Acetone / ethanol / butanol = 82/15/3
(18) Methyl acetate / acetone / methanol / butanol = 77/10/11/2

The concentration of the cellulose ester solution to be prepared is preferably 10 to 40% by mass, more preferably 13 to 35% by mass, and most preferably 15 to 30% by mass.
The cellulose ester can be adjusted to a predetermined concentration at the stage of dissolution in a solvent. Alternatively, a solution having a low concentration (for example, 9 to 14% by mass) may be concentrated after preparation, but from the viewpoint of energy efficiency, it is swollen in a solvent containing a halogenated hydrocarbon at room temperature or −10 to 35 ° C. Most preferably, the mixture is stirred and dissolved at room temperature or 0-35 ° C. Furthermore, a high concentration solution may be diluted after preparation. By adding an additive, the concentration of the cellulose ester can be reduced.

The cellulose ester solution can contain various liquid or solid additives. Examples of the additive include a plasticizer (preferred addition amount is 0.1 to 20% by mass with respect to the cellulose ester, the same applies hereinafter), a modifier (0.1 to 20% by mass), an ultraviolet absorber (0. 001-5 mass%), fine particle powder (0.001-5 mass%) having an average particle size of 5-3000 nm, fluorine-based surfactant (0.001-2 mass%), release agent (0.0001 ˜2 mass%), deterioration inhibitor (0.0001-2 mass%), optical anisotropy control agent (0.1-15 mass%), infrared absorber (0.1-5 mass%). It may be.

Regarding the method for preparing the cellulose ester solution, JP-A-58-127737, JP-A-61-106628, JP-A-2-276830, JP-A-4-259511, JP-A-5-163301, JP-A-9-95544, 45950, 10-95854, 11-71463, 11-302388, 11-322946, 11-322947, 11-323017, JP 2000-53784, 2000- 273184 and 2000-273239. In the step of preparing the cellulose ester solution of the present invention, it is not necessary to actively cool or heat.

The cellulose ester solution preferably has a viscosity at 30 ° C. of 1 to 400 Pa · s, and more preferably 10 to 200 Pa · s.
Viscosity and dynamic storage elastic modulus are measured using a rheometer (CLS500, manufactured by TA Instruments) by putting 1 mL of the sample solution into a container (STEEL CONE, manufactured by TA Instruments) having a diameter of 4 cm and a cone angle of 2 °. The measurement conditions were measured using the conditions (Oscillation Step / Temperature Ramp) attached to the apparatus. Measurement is started after the sample solution is kept warm at the measurement start temperature until the liquid temperature becomes constant.

The cellulose ester film can be produced using a conventional solution casting film forming apparatus according to a conventional solution casting film forming method. The dope (cellulose ester solution) prepared in the dissolving machine (kettle) is filtered and then temporarily stored in a storage kettle, and the foam contained in the dope is defoamed for final preparation. The dope is kept at 30 ° C., and is sent from the dope discharge port to the pressure die through a pressure metering gear pump capable of delivering a constant amount of liquid with high accuracy, for example, by the number of rotations. The cast film is uniformly cast on the metal support of the cast portion, and the dough film (also referred to as web) is peeled off from the metal support at the peeling point where the metal support has almost gone around.
In the casting step, two or more types of cellulose ester solutions may be cast simultaneously or sequentially.
Two or more types of cellulose ester solutions may have exactly the same composition. If the composition is different, the type of solvent or additive can be changed from solution to solution. Two or more types of solutions may have different concentrations. Two or more types of solutions may have different aggregate molecular weights of cellulose esters. Two or more solutions may be held at different temperatures.

The both ends of the web obtained by peeling from the metal support are sandwiched between clips, transported by a tenter while holding the width, dried, then transported by a roll group of a drying apparatus, dried and finished with a winder. Wind up to length. The combination of the tenter and the roll group dryer varies depending on the purpose.
Here, as in the present invention, in order to obtain a film having a low Rth, a method of widening the distance between the polymer main chains of cellulose acylate is effective. Therefore, a method of containing an organic solvent which is a poor solvent for cellulose ester having a high boiling point as described above is effective, and when the film is cooled after completion of drying, the film temperature is the glass transition temperature (Tg). It is effective to rapidly cool from a state where the main chain interval is wide and to quench while the main chain interval is wide. Therefore, it is usually cooled at about 100 ° C./min, but by blowing dehumidified air of about −30 to 10 ° C., it is 110 to 600 ° C./min, more preferably 120 to 350 ° C./min, more preferably It is preferable to cool at 150 to 300 ° C./min.
The residual solvent in the film thus dried is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and still more preferably 0 to 1% by mass. After drying, trim both ends and wind up. A preferable width is 0.5 to 5 m, more preferably 0.7 to 3 m, and still more preferably 1 to 2 m. A preferable winding length is 300 to 30000 m, more preferably 500 to 10000 m, and still more preferably 1000 to 7000 m.

In order to adjust Re and Rth, the cellulose acylate film can be stretched. Stretching may be performed in an undried state during film formation (for example, after peeling from the support after casting and after completion of drying), or may be performed after completion of drying. These stretching operations may be performed on-line during the film-forming process, or may be performed off-line after winding up once after film-forming is completed.
The stretching is preferably performed at Tg or more and Tg + 50 ° C or less, more preferably Tg + 1 ° C or more and Tg + 30 ° C or less, and further preferably Tg + 2 ° C or more and Tg + 20 ° C or less. A preferred draw ratio is 1% to 500%, more preferably 3% to 400%, and still more preferably 5% to 300%. These stretching operations may be performed in one stage or in multiple stages. The draw ratio here is determined using the following equation.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / Length before stretching Such stretching is performed by using two or more pairs of nip rolls having a higher peripheral speed on the outlet side. The film may be stretched in the longitudinal direction (longitudinal stretching), or both ends of the film may be held by a chuck and spread in the orthogonal direction (perpendicular to the longitudinal direction) (lateral stretching). In any case, Rth can be increased by increasing the draw ratio. Further, Re can be increased by increasing the difference between the ratios of longitudinal stretching and lateral stretching.

Further, the ratio of Re and Rth can be freely controlled by controlling the value (aspect ratio) obtained by dividing the space between nip rolls by the film width in the case of longitudinal stretching. That is, the Rth / Re ratio can be increased by reducing the aspect ratio. In the case of lateral stretching, it can be controlled by stretching in the orthogonal direction and simultaneously stretching in the longitudinal direction, or conversely relaxing. That is, the Rth / Re ratio can be increased by stretching in the vertical direction, and the Rth / Re ratio can be decreased by relaxing in the vertical direction.
Such stretching speed is preferably 10 to 10000% / min, more preferably 20 to 1000% / min, and further preferably 30 to 800% / min.
Further, the angle θ formed by the film forming direction (longitudinal direction) and the slow axis of Re of the film is preferably 0 ± 3 °, + 90 ± 3 ° or −90 ± 3 °, preferably 0 ± 2 °, +90 It is more preferably ± 2 ° or −90 ± 2 °, and further preferably 0 ± 1 °, + 90 ± 1 ° or −90 ± 1 °.

The thickness of the cellulose acylate film of the present invention is preferably 60 to 180 μm or less, more preferably 60 to 150 μm, and even more preferably 65 to 120 μm. When the film thickness is less than 60 μm, handling properties and curling of the polarizer when processing into a polarizing plate or the like are not preferable. When the film thickness is greater than 180 μm, it takes a long time to dry to a volatile content that can be peeled off. Therefore, it is not preferable from the viewpoint of productivity. The film thickness unevenness is preferably 0 to 2% in both the film thickness direction and the width direction, both unstretched and after stretching, more preferably 0 to 1.5%, and still more preferably 0 to 1%.

The cellulose acylate film of the present invention that has not been stretched and has been stretched may be appropriately surface treated to improve adhesion between the cellulose acylate film and each functional layer (for example, an undercoat layer or a back layer). It becomes possible. The surface treatment includes glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, saponification treatment (acid saponification treatment, alkali saponification treatment), and glow discharge treatment and alkali saponification treatment are particularly preferable.
The glow discharge treatment includes a low temperature plasma treatment performed under a low pressure gas of 10 ^{−3 to} 20 Torr. Plasma treatment under atmospheric pressure is also a preferable glow discharge treatment. As the plasma exciting gas, argon, helium, neon, krypton, xenon, nitrogen, carbon dioxide, chlorofluorocarbon (eg, tetrafluoromethane) and a mixture thereof are used. The plasma treatment at atmospheric pressure is preferably performed at 10 to 1000 Kev, more preferably 30 to 500 Kev. The irradiation energy is preferably 20 to 500 kGy, more preferably 20 to 300 kGy. The glow discharge treatment is described in published technical bulletin 2001-1745 (issued March 15, 2001, Invention Association), pages 30-32.

The alkali saponification treatment is carried out by applying a saponification solution to the film or immersing the film in the saponification solution.
As a coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method or an E-type coating method can be adopted. The solvent of the coating solution has good wettability to the film, and it is desirable to keep the surface state good without forming irregularities on the film surface. Specifically, the solvent is preferably alcohol, and isopropyl alcohol is particularly preferable. Further, water (preferably an aqueous solution of a surfactant) can be used as a solvent. The alkali is preferably an alkali metal hydroxide, and more preferably KOH and NaOH. The pH of the saponification coating solution is preferably 10 or more, and more preferably 12 or more. The reaction conditions during alkali saponification are preferably 1 second to 5 minutes at room temperature, more preferably 5 seconds to 5 minutes, and most preferably 20 seconds to 3 minutes. After the alkali saponification reaction, it is preferable to wash the surface to which the saponification solution is applied, or after washing with an acid. Further, the coating-type saponification treatment and the alignment film uncoating described later can be performed continuously, and the number of steps can be reduced. Specific examples of these saponification methods are described in JP-A-2002-82226 and WO02 / 46809.

In order to improve adhesion between the film and the functional layer, an undercoat layer (adhesive layer) can be provided in addition to or in place of the surface treatment. The undercoat layer is described in published technical bulletin No. 2001-1745 (issued on March 15, 2001, Invention Association), page 32, and these can be used as appropriate.

The functional layer provided on the cellulose ester film is described in Published Technical Bulletin No. 2001-1745 (issued on March 15, 2001, Invention Association), pages 32 to 45, and these can be used as appropriate.

The cellulose ester film having a negative retardation value in the thickness direction can be used as it is as a protective film for a retardation plate or a polarizing plate having the function of a retardation plate. By laminating with a cellulose ester film having a positive value, it can be used as a retardation plate whose retardation value in the thickness direction is freely controlled.
Cellulose ester film having a negative retardation value in the thickness direction, or a retardation film in which a plurality of the retardation films are laminated, or a film in which a cellulose ester film having a positive retardation value in the thickness direction is laminated. Can be used as a retardation plate as it is, or as a polarizing plate protective film. In addition, a retardation plate can be produced by using the cellulose ester film and the retardation plate as a support, and providing an optically anisotropic layer (for example, a layer formed of liquid crystalline molecules) thereon.

When used as a polarizing plate protective film, the cellulose ester film is preferably subjected to alkali saponification treatment. In the case of using a polarizing film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution, the alkali saponification surface of the cellulose ester film can be bonded to both surfaces of the polarizing film using an adhesive. As the adhesive, an aqueous solution of polyvinyl alcohol or polyvinyl acetal (eg, polyvinyl butyral) or a latex of a vinyl polymer (eg, polybutyl acrylate) can be used. A particularly preferred adhesive is an aqueous solution of fully saponified polyvinyl alcohol.
Surface treatment other than the alkali saponification treatment (described in JP-A-6-94915 and JP-A-6-118232) may be performed.
After the polarizing plate is manufactured, before use, an external protective film is bonded to one surface of the polarizing plate, and a separate film is bonded to the opposite surface. The external protective film and the separate film are used for the purpose of protecting the polarizing plate in shipping of the polarizing plate and product inspection. The external protective film is used on the side opposite to the side where the polarizing plate is bonded to the liquid crystal cell. The separate film is used for the purpose of covering an adhesive layer for bonding the polarizing plate to the liquid crystal cell. In general, a liquid crystal display device is provided with a liquid crystal cell between two polarizing plates. In general, a liquid crystal cell is injected between two substrates. Therefore, a normal liquid crystal display device has four polarizing plate protective films. The cellulose ester film according to the present invention may be used for any of the four polarizing plate protective films. However, it can be used particularly advantageously as a plastic film disposed between a polarizer and a liquid crystal layer in a liquid crystal display device.

The cellulose ester film of the present invention, and the retardation plate and polarizing plate using the same can be used in liquid crystal display devices of various display modes. Each liquid crystal mode in which these films are used will be described below. These liquid crystal display devices may be any of a transmissive type, a reflective type, and a transflective type.
(TN mode liquid crystal display)
It is most frequently used as a color TFT liquid crystal display device and is described in many documents. In the TN (Twisted Nematic) mode black display, the alignment state in the liquid crystal cell is an alignment state in which the rod-like liquid crystalline molecules rise at the center of the cell and the rod-like liquid crystalline molecules lie in the vicinity of the cell substrate.

(OCB mode liquid crystal display)
This is a bend alignment mode liquid crystal cell in which rod-like liquid crystal molecules are aligned in a substantially opposite direction (symmetrically) between the upper part and the lower part of the liquid crystal cell. Liquid crystal display devices using a bend alignment mode liquid crystal cell are disclosed in US Pat. Nos. 4,583,825 and 5,410,422. Since the rod-like liquid crystal molecules are symmetrically aligned at the upper and lower portions of the liquid crystal cell, the bend alignment mode liquid crystal cell has a self-optical compensation function. For this reason, this liquid crystal mode is also called an OCB (Optically Compensatory Bend) liquid crystal mode.
Similarly to the TN mode, the liquid crystal cell in the OCB mode is in a black display, and the alignment state in the liquid crystal cell is an alignment state in which the rod-like liquid crystal molecules rise at the center of the cell and the rod-like liquid crystal molecules lie near the cell substrate. .

(VA mode liquid crystal display device)
The feature is that the rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied. In the VA (Vertically Aligned) mode liquid crystal cell, (1) the rod-like liquid crystalline molecules are substantially not applied when no voltage is applied. In addition to a narrowly defined VA mode liquid crystal cell (described in JP-A-2-176625) that is aligned vertically to a voltage and substantially horizontally aligned when a voltage is applied, (2) in order to expand the viewing angle, the VA mode is Domained (MVA mode) liquid crystal cell (SID97, Digest of tech. Papers (preliminary report) 28 (1997) 845), (3) A rod-like liquid crystal molecule is substantially vertically aligned when no voltage is applied. Liquid crystal cell with twisted multi-domain alignment (n-ASM mode) when applied (Preliminary Proc. 58-59 (1998) of the Japanese Liquid Crystal Society) ) And (4) SURVAVAL mode liquid crystal cells (announced at LCD International 98).

(IPS mode liquid crystal display)
The feature is that the rod-like liquid crystalline molecules are aligned substantially horizontally in the plane when no voltage is applied, and this is characterized by switching by changing the orientation direction of the liquid crystal with or without voltage application. Specifically, those described in JP-A Nos. 2004-365941, 2004-12731, 2004-215620, 2002-221726, 2002-55341, and 2003-195333 can be used.
(Other liquid crystal display devices)
The ECB mode and the STN mode can be optically compensated based on the same concept as described above.

The measurement method and evaluation method of characteristics used in the examples are shown below.
[Retardation]
Three points in the width direction (center, end (5% of the total width from both ends)) are sampled three times every 10 m in the longitudinal direction, and nine 3 cm-square samples are taken out according to the following method. The average value of the obtained points was obtained.
After adjusting the cellulose ester film at 25 ° C. and 60% RH for 24 hours, the surface of the sample film at 25 ° C. and 60% RH using an automatic birefringence meter (KOBRA-21ADH: manufactured by Oji Scientific Instruments) The retardation value at a wavelength of 590 nm was measured from the direction perpendicular to the film and the direction inclined by ± 40 ° from the normal to the film surface, and the in-plane retardation values (Re) represented by the following formulas (1) and (2), respectively. And the retardation value (Rth) in the film thickness direction were calculated.

(1) Re = (nx−ny) × d
(2) Rth = {(nx + ny) / 2−nz} × d
In the formula, nx is the refractive index in the slow axis (x) direction in the film plane, ny is the refractive index in the fast axis (y) direction in the film plane, and nz is the film thickness direction (film surface). And d is the thickness (nm) of the film. The slow axis is the direction in which the refractive index is maximum in the film plane, and the fast axis is the direction in which the refractive index is minimum in the film plane.

Changes in the retardation value with humidity were Re, Rth (represented as Re (10%) and Rth (10%), respectively) calculated by adjusting the humidity of the film at 25 ° C. and 10% RH, and From Re and Rth (represented as Re (80%) and Rth (80%), respectively) calculated by conditioning and measuring at 25 ° C. and 80% RH, the following expressions (3) and (4) are used respectively. The humidity dependency (ΔRe) of Re and the humidity dependency (ΔRth) of Rth are calculated.
(3) ΔRe = | Re (10%) − Re (80%) |
(4) ΔRth = | Rth (10%) − Rth (80%) |

[Substitution degree of cellulose acylate]
The degree of acyl substitution of cellulose acylate is described in Carbohydr. Res. Was determined by ¹³ C-NMR according to the method described in 273 (1995) 83-91 (Tezuka et al.).

Although the specific embodiment about the cellulose acylate film of this invention is described below, it is not limited to these.
Example 1
(Preparation of cellulose acylate)
Cellulose acylates having different acyl group types and substitution degrees as shown in Table 1 were prepared. That is, a mixture of sulfuric acid as a catalyst (7.8 parts by mass with respect to 100 parts by mass of cellulose) and carboxylic anhydride is added to cellulose derived from pulp after cooling to -20 ° C, and acylation is performed at 40 ° C. went. At this time, the kind of acyl group and its substitution ratio were adjusted by adjusting the kind and amount of carboxylic anhydride. After acylation, aging was performed at 40 ° C. to adjust the total substitution degree. The degree of polymerization of the cellulose acylate thus obtained was determined by the following method and listed in Table 1.
[Method of measuring degree of polymerization]
About 0.2 g of completely dried cellulose acylate was precisely weighed and dissolved in 100 mL of a mixed solvent of dichloromethane: ethanol = 9: 1 (mass ratio). This was measured with an Ostwald viscometer at 25 ° C. for the number of seconds to drop, and the degree of polymerization DP was determined by the following equation.
ηrel = T / T0 T: Seconds of measurement sample falling [η] = 1n (ηrel) / C T0: Seconds of fall of solvent alone
DP = [η] / Km C: concentration (g / L)
Km: 6 × 10-4

(Preparation of cellulose acylate solution)
1) Cellulose acylate The cellulose acylate prepared was heated to 120 ° C. and dried to adjust the water content to 0.5% by mass or less, and then 30 parts by mass was mixed with a solvent. However, in Comparative Examples 2 and 9, since it was necessary to reduce the cellulose acylate concentration from the viewpoint of solubility, the cellulose acylate was mixed with a solvent at 18 parts by mass.
In addition, the cellulose acylate used in Comparative Example 1 was purchased from Eastman Chemical Japan Co., Ltd. CAP482-20, and the cellulose acylate used in Comparative Example 9 was manufactured by Daicel Chemical Industries, Ltd. LT-35, both of which were synthesized from pulp-derived cellulose.

2) Solvents Selected from the following solvents and listed in Table 1.
Solvent 1: dichloromethane / methanol / butanol (81/15/4 parts by mass)
Solvent 2: dichloromethane / methanol / butanol (83/15/2 parts by mass)
Solvent 3: dichloromethane / methanol / 1-propanol (81/15/4 parts by mass)
Solvent 4: dichloromethane / methanol (97/3 parts by mass)
Solvent 5: dichloromethane / methanol (60/40 parts by mass)
The water content of these solvents was 0.2% by mass or less.

3) Additives In preparing all solutions except Example 7, 0.9 parts by weight of trimethylolpropane triacetate (referred to as Additive 1 in Table 1) was added. In addition, 0.25% by mass of silicon dioxide fine particles (particle diameter 20 nm, Mohs hardness about 7) was added in preparing all solutions.

4) The cellulose acylate was gradually added to the 400 liter stainless steel dissolution tank having swelling and dissolution stirring blades and circulating cooling water around the outer periphery, while stirring and dispersing the solvent and additives. . After completion of the addition, the mixture was stirred at room temperature for 2 hours, swollen for 3 hours, and then stirred again to obtain a cellulose acylate solution.
For stirring, a dissolver type eccentric stirring shaft that stirs at a peripheral speed of 15 m / sec (shear stress 5 × 10 ⁴ kgf / m / sec ² ) and an anchor blade on the central axis and a peripheral speed of 1 m / sec. A stirring shaft that stirs at a sec (shear stress of 1 × 10 ⁴ kgf / m / sec ² ) was used. Swelling was carried out with the high speed stirring shaft stopped and the peripheral speed of the stirring shaft having anchor blades set at 0.5 m / sec.

5) Filtration The cellulose acylate solution obtained above was filtered with a filter paper (# 63, manufactured by Toyo Filter Paper Co., Ltd.) having an absolute filtration accuracy of 0.01 mm, and further a filter paper (FH025, Poll) having an absolute filtration accuracy of 2.5 μm. To obtain a cellulose acylate solution.

(Preparation of cellulose acylate film)
The cellulose acylate solution was heated to 30 ° C., and cast on a mirror surface stainless steel support having a band length of 60 m set at 15 ° C. through a casting Giesser (described in JP-A-11-314233). The casting speed was 15 m / min and the coating width was 200 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose acylate film that had been cast and rotated 50 cm before the end point of the casting part was peeled off from the band, and 45 ° C. dry air was blown. Next, after drying at 110 ° C. for 5 minutes and further at 140 ° C. for 10 minutes, the film was cooled to room temperature in 30 seconds to obtain a cellulose acylate film. The obtained film was cut at 3 cm at both ends, further provided with a knurling with a height of 125 μm at a portion 2 to 10 mm from the end, and wound into a 3000 m roll.

(Evaluation of cellulose acylate film)
[Surface shape]
The film surface condition was visually evaluated on the following evaluation scale.
Good: No irregularities or irregularities are observed on the film.
Whitening: The film is completely whitened and cannot be applied as an optical film.
Unevenness: Many irregularities and horizontal unevenness on the film surface are recognized and cannot be applied as an optical film.
Unpeelable: The dope on the support cannot be sufficiently dried, resulting in significant peeling on the support that cannot be peeled off.

[Retardation]
The retardation value in the film thickness direction of the cellulose acylate film and its humidity dependency were measured by the method described above.

[curl]
The cellulose acylate film was immersed in a 1.5 N NaOH aqueous solution (saponification solution) adjusted to 60 ° C. for 2 minutes, then immersed in a 0.1 N sulfuric acid aqueous solution for 30 seconds, and further saponified through a water washing bath.
According to Example 1 of Japanese Patent Laid-Open No. 2001-141926, a circumferential speed difference is given between two pairs of nip rolls, and a Fujitac (TD-80UF) is provided on one surface with respect to a polarizing layer having a thickness of 20 μm produced by stretching in the longitudinal direction. Then, the cellulose acylate film of the present invention saponified on the other side was bonded to a PVA (PVA-117H manufactured by Kuraray Co., Ltd.) 3% aqueous solution as an adhesive to produce a polarizing plate.
The resulting polarizing plate was conditioned at 25 ° C. and 10% RH for 24 hours, conditioned at 25 ° C. and 80% RH for 24 hours, and further conditioned at 25 ° C. and 10% RH for 24 hours. The curl was visually confirmed and evaluated in the following three stages.
Yu: The curl is hardly confirmed.
Good: Slight curling was confirmed, but there was no problem for use in optical applications.
Inferior: Curling or waviness on the surface is remarkable and cannot be applied as an optical application.

In Table 1, in Examples 1 to 8, good films having a residual solvent amount of less than 1% by mass were obtained. When these films were observed visually and with an optical microscope and a polarizing microscope, the number of foreign matters was very good at 0 pieces / cm ^{2. After the} films were laminated with an adhesive as required to obtain the intended Rth, When used in the IPS type liquid crystal display device described in FIG. 11 of Open 2004-12731, a good liquid crystal display device was obtained.

On the other hand, when cellulose acylate having an acyl substitution degree that is too low as in Comparative Example 1 is used, Rth increases and becomes a positive value. When Comparative Example 2 has a low propionyl substitution degree, As Rth increases, the humidity dependence of Rth increases. When the degree of propionyl substitution was low as in Comparative Example 8 and the degree of total substitution was high, it could not be sufficiently dissolved and the unevenness of the film became large.
When the cellulose acylate having a too high total substitution degree is used as in Comparative Example 3 or when the amount of alcohol in the solvent is too large as in Comparative Example 5, the number of foreign matters increases or the drying process The film turned white.
When the amount of alcohol in the solvent was too small as in Comparative Example 4, the peeling load at the time of peeling from the band became high, and the unevenness of the film became large.
Therefore, when the film of these comparative examples was used, a favorable phase difference plate, a polarizing plate, and a highly reliable liquid crystal display device were not obtained.

Further , when the film thickness was too thin as in Example 9 , a good film was obtained, and the film was greatly curled when a polarizing plate was prepared and conditioned.
Conversely, as in Comparative Example 7, when an attempt was made to produce a sample having a thicker film thickness, the dope on the band was not sufficiently dried, resulting in unpeeled portions, which could not be produced.

Claims (9)

Acyl substitution degree is represented by the following formula to the hydroxyl group of cellulose (I) ~ (III) of the cellulose ester to satisfy all, and an organic solvent having a boiling point of 80 ° C. or lower and a boiling point of more than 95 ° C. A Ruko le 1 to 5 mass The film thickness is formed by casting from a solution obtained through a step of causing the mixture to swell at −10 to 35 ° C. and stirring and dissolving the mixture at 0 to 35 ° C. and filtering. A cellulose acylate film having a direction retardation value of -50 to -1 nm .
(I) 2.80 ≦ SA + SP <2.87
(II) 0 ≦ SA ≦ 1.0
(III) 1.8 ≦ SP <2.87
(In the formula, SA and SP represent the substitution degree of the acyl group substituted with the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SP is the substitution degree of the propionyl group.) The solvent contains two or more kinds of alcohols, and the two or more kinds of alcohols comprise at least one kind of alcohol having a boiling point of 95 ° C. or more and at least one kind of alcohol having a boiling point of less than 95 ° C. The cellulose acylate film according to claim 1 . The cellulose acylate film according to claim 2, wherein 10 to 30% by mass of the solvent is alcohol. 25 ° C., the retardation value in the thickness direction and 25 ° C. in 10% RH, according to claim 1-3 to change with the humidity of the retardation value in the thickness direction of 80% RH is equal to or is 20nm or less The cellulose acylate film according to any one of the above. The cellulose acylate film according to any one of claims 1 to 4, wherein the film thickness is 60 to 180 µm. Acyl substitution degree is represented by the following formula to the hydroxyl group of cellulose (I) ~ (III) of the cellulose ester to satisfy all, and an organic solvent having a boiling point of 80 ° C. or lower and a boiling point of more than 95 ° C. A Ruko le 1 to 5 mass In a solvent containing 10 % to 35 ° C., and the mixture is stirred and dissolved at 0 to 35 ° C., followed by casting to form a film from a solution obtained through filtration. The manufacturing method of the cellulose acylate film whose retardation value of a film thickness direction is -50--1 nm .
(I) 2.80 ≦ SA + SP <2.87
(II) 0 ≦ SA ≦ 1.0
(III) 1.8 ≦ SP <2.87
(In the formula, SA and SP represent the substitution degree of the acyl group substituted with the hydroxyl group of cellulose, SA is the substitution degree of the acetyl group, and SP is the substitution degree of the propionyl group.) The solvent contains two or more kinds of alcohols, and the two or more kinds of alcohols comprise at least one kind of alcohol having a boiling point of 95 ° C. or more and at least one kind of alcohol having a boiling point of less than 95 ° C. The method for producing a cellulose acylate film according to claim 6 .   The method for producing a cellulose acylate film according to claim 7, wherein 10 to 30% by mass of the solvent is alcohol. The method for producing a cellulose acylate film according to any one of claims 6 to 8, wherein the organic solvent having a boiling point of 80 ° C or less is a halogenated hydrocarbon.