JP2009119808A - Cellulose acylate film, method of producing the same, retardation film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a cellulose acylate film which has large retardation value (Re), is hard to crack, has a galvanized sheet-like form and has no wrinkle using a cellulose acylate film. <P>SOLUTION: The method of producing the cellulose acylate film includes: stretching in a span of 0.01-2 times of the width of the film before stretching in the transporting direction at a temperature T (unit; °C) satisfying a condition expressed by relation (I); Tc+10≤T<Tm<SB>0</SB>(in the relation, Tc expresses the crystallization temperature (unit; °C) of the cellulose acylate film before a heat treatment and Tm<SB>0</SB>expresses the melting point (unit; °C) of the cellulose acylate film before the heat treatment). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cellulose acylate film that has optical anisotropy, is difficult to break, and can be directly bonded to a polarizing film, and a method for producing the same, and a retardation film using the cellulose acylate film The present invention relates to a polarizing plate and a liquid crystal display device.

  Polymer films represented by cellulose ester, polyester, polycarbonate, cycloolefin polymer vinyl polymer, polyimide, and the like are used for silver halide photographic light-sensitive materials, retardation films, polarizing plates, and image display devices. From these polymers, films that are more excellent in terms of flatness and uniformity can be produced, and are therefore widely used as films for optical applications.

  Among these, a cellulose acylate film having an appropriate moisture permeability can be directly bonded on-line with the most common polarizing film made of polyvinyl alcohol (PVA) / iodine. Therefore, in particular, cellulose acetate has been widely adopted as a protective film for polarizing plates, and various production methods thereof have been studied (for example, see Patent Documents 1 and 2).

On the other hand, when the cellulose acylate film is used for a retardation film, a support for a retardation film, a protective film for a polarizing plate, and an optical application such as a liquid crystal display device, the control of the optical anisotropy is This is a very important factor in determining the performance (for example, visibility) of the display device. With the recent demand for wider viewing angle of liquid crystal display devices, it is required to improve the compensation of retardation, and the retardation value in the in-plane direction of the retardation film disposed between the polarizing film and the liquid crystal cell. (Re; hereinafter simply referred to as “Re”) and the retardation value in the film thickness direction (Rth; hereinafter referred to simply as “Rth”) are required to be appropriately controlled. . In particular, it is required to easily produce a film having a large Re and a film having | Rth | / Re of around 0.5. As a method for producing such a film, various methods for uniaxially stretching the film at the free end have been studied (see, for example, Patent Document 3).
JP 2001-188128 A JP 2000-352620 A JP 2005-264022 A

However, when a cellulose acylate film is stretched to produce a film with a large Re, the resulting film is liable to break, or there is a problem that a tin plate-like wrinkle enters the film. Became clear. When such a film is used for a polarizing plate or a liquid crystal display device, for example, the base is broken during the production of the cellulose acylate film, or the obtained polarizing plate is easily broken.
Therefore, in order to solve the problems of the prior art, the present inventors have used a cellulose acylate film to produce a cellulose acylate film having a large Re, hardly cracked, and free of tin plate-like wrinkles. As a purpose of the present invention, studies have been made to provide the above.

  As a result of intensive studies, the inventors of the present invention solved the problems of the prior art by stretching a cellulose acylate film in the conveying direction within a predetermined temperature range with an apparatus in which the span between the film width was narrowed. I found out. That is, the following present invention has been provided as means for solving the problems.

(1) Cellulose reed that is stretched in the conveying direction at a temperature T (unit: ° C) that satisfies the following formula (I) between 0.01 to 2 times the span of the film width before stretching A method for producing a rate film.
Formula (I): Tc + 10 ≦ T <Tm ₀
[Wherein, Tc represents a crystallization temperature (unit: ° C.) of the cellulose acylate film before stretching, and Tm ₀ represents a melting point (unit: ° C.) of the cellulose acylate film before stretching. ]
(2) Stretching in a direction in which the sound wave propagation speed is maximized at a temperature T (unit: ° C.) satisfying the above formula (I) between spans of 0.01 to 2 times the film width before stretching. A method for producing a cellulose acylate film, comprising:
(3) The film before stretching was formed by a production method including a step of casting a cellulose acylate solution on a support and stripping the residual solvent from the support in a state of 10 to 100% by mass. It is a cellulose acylate film, The manufacturing method of the cellulose acylate film as described in (1) or (2) characterized by the above-mentioned.
(4) A cellulose acylate film satisfying the following formula (II) and having a wave height of 0 to 5 mm.
Formula (II): 0.4 ≦ | Rth | /Re≦0.6
[In the formula, Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction. (5) The cellulose acylate film according to (4), wherein the tear strength is 5 g or more.
(6) The cellulose acylate film according to (4) or (5), wherein the retardation value in the in-plane direction is 50 nm or more.
(7) The cellulose acylate film according to any one of (4) to (6), which is produced by the production method according to any one of (1) to (3).
(8) A retardation film comprising at least one cellulose acylate film according to any one of (4) to (7).
(9) A polarizing plate comprising at least one cellulose acylate film according to any one of (4) to (7).
(10) Having at least one sheet of the cellulose acylate film according to any one of (4) to (7), the retardation film according to (8), or the polarizing plate according to (9). A characteristic liquid crystal display device.

  The cellulose acylate film of the present invention has a large Re, is difficult to break, has no tin plate-like wrinkles, and is excellent in flatness. Moreover, the retardation film, polarizing plate, and liquid crystal display device manufactured using the cellulose acylate film of the present invention exhibit excellent optical properties.

  Below, the manufacturing method of the cellulose acylate film of this invention, etc. are demonstrated in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

<< Method for Producing Cellulose Acylate Film >>
[Cellulose acylate]
First, the cellulose acylate that can be used in the method for producing a cellulose acylate film of the present invention will be described.
The cellulose acylate film heat-treated by the production method of the present invention is a film in which the polymer as a main component constituting the film is cellulose acylate. Here, the “polymer as the main component” means a polymer when the film is composed of a single polymer, and when the film is composed of a plurality of polymers, the most mass fraction of the constituting polymers. This indicates a high polymer.

Cellulose acylate is an ester of cellulose and carboxylic acid. In the cellulose acylate, all or part of the hydrogen atoms of the hydroxyl groups present at the 2-position, 3-position and 6-position of the glucose unit constituting the cellulose are substituted with acyl groups. The number of carbon atoms in the acyl group is preferably 2 to 22, and more preferably 2 to 4. Examples of the acyl group include, for example, acetyl group, propionyl group, butyryl group, isobutyryl group, pivaloyl group, heptanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, and hexadecanoyl group. Examples include a noyl group, an octadecanoyl group, a cyclohexanecarbonyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group. As the acyl group, an acetyl group, a propionyl group, a butyryl group, a dodecanoyl group, an octadecanoyl group, a pivaloyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group are preferable, and an acetyl group, a propionyl group, and A butyryl group is most preferred.
The cellulose acylate may be an ester of cellulose and a plurality of carboxylic acids. That is, the cellulose acylate may be substituted with a plurality of acyl groups.

When the substitution degree of the acetyl group (carbon number 2) substituted on the hydroxyl group of cellulose of cellulose acylate is SA and the substitution degree of the acyl group of 3 or more carbon atoms substituted on the hydroxyl group of cellulose is SB, By adjusting SA and SB, the expression of retardation of the cellulose acylate film produced by the production method of the present invention and the humidity dependence of the retardation can be adjusted. In addition, Tc can be adjusted, whereby the heat treatment temperature can be adjusted. The humidity dependency of retardation is a change in retardation due to humidity.
SA + SB is appropriately adjusted depending on the optical properties required for the cellulose acylate film produced by the production method of the present invention, which is the film of the present invention, but preferably 2.70 <SA + SB ≦ 3.00. Preferably 2.88 ≦ SA + SB ≦ 3.00, more preferably 2.89 ≦ SA + SB ≦ 2.99, still more preferably 2.90 ≦ SA + SB ≦ 2.98, particularly preferably 2.2. It is 92 <= SA + SB <= 2.97. By increasing SA + SB, Re obtained after heat treatment can be increased, and the humidity dependency of retardation can also be improved.
Moreover, the humidity dependence of the retardation of the cellulose acylate film produced by the production method of the present invention can be adjusted by adjusting SB. By increasing SB, the humidity dependency of retardation can be reduced, and the melting point is lowered. In consideration of the humidity dependence of retardation and the balance of the melting point reduction, the range of SB is preferably 0 ≦ SB ≦ 2.0, more preferably 0.1 <SB ≦ 1.0, and still more preferably 0.8. 2 <SB ≦ 0.7. In addition, when all the hydroxyl groups of cellulose are substituted, said substitution degree will be 3.

Cellulose acylate can be synthesized by a known method.
For example, the basic principle of the cellulose acylate synthesis method is described in Nobuhiko Ueda et al., Wood Chemistry pages 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method of cellulose acylate includes a liquid phase acylation method using a carboxylic acid anhydride-carboxylic acid-sulfuric acid catalyst. Specifically, first, 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 to be esterified, and complete cellulose acylate (2 The total degree of acyl substitution at the 3rd, 6th and 6th positions is approximately 3.00). The acylated mixed solution generally contains a carboxylic acid as a solvent, a carboxylic acid anhydride as an esterifying agent, and sulfuric acid as a catalyst. In addition, the carboxylic acid anhydride is usually used in a stoichiometric excess amount relative to the total amount of cellulose reacting with the carboxylic acid anhydride and moisture present in the system.

  Subsequently, 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. Further, in order to partially neutralize the esterification catalyst, an aqueous solution containing a neutralizing agent (for example, calcium, magnesium, iron, aluminum or zinc carbonate, acetate, hydroxide or oxide) is added. Also good. Furthermore, 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 degree of polymerization. Change to cellulose acylate. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized using the neutralizing agent or the like, or water or dilute acetic acid without neutralizing the catalyst. Cellulose acylate solution is added into the solution (or water or dilute acetic acid is added into the cellulose acylate solution) to separate the cellulose acylate, and the desired cellulose acylate is obtained by washing and stabilizing treatment. Can do.

  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 the description of Uda et al.'S intrinsic viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Science, Vol. 18, No. 1, pages 105-120, 1962). The method for measuring the viscosity average degree of polymerization is also described in JP-A-9-95538.

In addition, cellulose acylate having 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. Such a cellulose acylate having a small amount of low molecular components can be obtained by removing the low molecular components from cellulose acylate synthesized by an ordinary 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 obtained by synthesis. When synthesizing 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 within the above range, cellulose acylate that is preferable in terms of molecular weight distribution (uniform molecular weight distribution) can be synthesized. The degree of polymerization and molecular weight distribution of cellulose acylate can be measured by gel permeation chromatography (GPC) or the like.
The raw material cotton of cellulose ester and the synthesis method are also described in pages 7 to 12 of the Japan Society for Invention and Innovation (public technical number 2001-1745, published on March 15, 2001, Japan Institute of Invention).

As a cellulose acylate used as a raw material when producing a cellulose acylate film, a powder or a particulate material can be used, and a pelletized one can also be used. The water content of cellulose acylate when used as a raw material is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and most preferably 0.5% by mass or less. . Moreover, it is preferable that the said moisture content is 0.2 mass% or less depending on the case. When the water content of the cellulose acylate is not within the preferred range, it is preferable to use the cellulose acylate after drying it by drying air or heating.
When producing a cellulose acylate film, a single type of polymer may be used, or a plurality of types of polymers may be used.

[Cellulose acylate solution]
The cellulose acylate film used in the production method of the present invention (hereinafter, also referred to as “cellulose acylate film before heat treatment” in the specification) is, for example, a cellulose acylate solution containing the cellulose acylate and various additives. Can be produced by a solution casting film forming method. Hereinafter, a cellulose acylate solution that can be used in the solution casting film forming method will be described.

(solvent)
As the main solvent of the cellulose acylate solution used for producing the cellulose acylate film used in the production method of the present invention, an organic solvent which is a good solvent for the polymer can be preferably used. As such an organic solvent, an organic solvent having a boiling point of 80 ° C. or lower is more preferable from the viewpoint of reducing the drying load. The boiling point of the organic solvent is more preferably 10 to 80 ° C, and particularly preferably 20 to 60 ° C. Moreover, the organic solvent whose boiling point is 30-45 degreeC depending on the case can also be used suitably as said main solvent.

  As such a main solvent, halogenated hydrocarbons can be particularly preferably mentioned, and in some cases, esters, ketones, ethers, alcohols and hydrocarbons can also be mentioned, and these have a branched structure or a cyclic structure. It may be. The main solvent may have two or more functional groups of esters, ketones, ethers and alcohols (that is, —O—, —CO—, —COO—, —OH). Furthermore, 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, when the main solvent of the cellulose acylate solution used for the production of the “cellulose acylate film used in the production method of the present invention” is composed of a single solvent, it indicates that solvent. In this case, the solvent having the highest mass fraction among the constituent solvents is shown. Preferred examples of the main solvent include halogenated hydrocarbons.

As said halogenated hydrocarbon, a chlorinated hydrocarbon is more preferable, for example, a dichloromethane, chloroform, etc. are mentioned, A dichloromethane is further more preferable.
Examples of the ester include methyl formate, ethyl formate, methyl acetate, and ethyl acetate.
Examples of the ketone include acetone and methyl ethyl ketone.
Examples of the ether include diethyl ether, methyl tert-butyl ether, diisopropyl ether, dimethoxymethane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, 1,4-dioxane and the like.
As said alcohol, methanol, ethanol, 2-propanol etc. are mentioned, for example.
Examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, benzene, and toluene.

  Examples of the organic solvent used in combination with these main solvents include halogenated hydrocarbons, esters, ketones, ethers, alcohols and hydrocarbons, which may have a branched structure or a cyclic structure. The organic solvent may have any two or more of ester, ketone, ether and alcohol functional groups (that is, —O—, —CO—, —COO—, —OH). Furthermore, 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 said halogenated hydrocarbon, a chlorinated hydrocarbon is more preferable, for example, a dichloromethane, chloroform, etc. are mentioned, A dichloromethane is further 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 the ether include diethyl ether, methyl tert-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, and phenetole. Etc.
Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, cyclohexanol, and 2-fluoro. Examples include ethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol. Preferred is an alcohol having 1 to 4 carbon atoms, more preferred is methanol, ethanol or butanol, and most preferred is methanol or butanol.
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 types of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, 2-butoxyethanol, and methyl acetoacetate.

Since the polymer constituting the cellulose acylate film of the present invention contains a hydrogen bonding functional group such as a hydroxyl group, an ester, or a ketone, it is 5 to 30% by mass in the total solvent, more preferably 7 to 25% by mass, It is preferable to contain 10-20 mass% alcohol from a viewpoint of the peeling load reduction from a casting support body preferably.
By adjusting the alcohol content, it is possible to easily adjust the expression of Re and Rth of the cellulose acylate film produced by the production method of the present invention. Specifically, by increasing the alcohol content, the heat treatment temperature can be set relatively low, and the reach range of Re and Rth can be increased.
In addition, the cellulose acylate solution used in the production of the cellulose acylate film used in the production method of the present invention has a small proportion of volatilization with the halogenated hydrocarbon in the initial stage of the drying process, and the boiling point gradually concentrated is 95 ° C. or higher. In addition, an organic solvent which is a poor solvent for cellulose ester may be contained in an amount of 1 to 15% by mass, more preferably 1.5 to 13% by mass, and still more preferably 2 to 10% by mass. In the present invention, the addition of a small amount of water in the cellulose acylate solution is also effective for increasing the solution viscosity and the film strength in the wet film state during drying, or for increasing the dope strength during casting by the drum method. For example, it may be contained in an amount of 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, and particularly 0.2 to 2% by mass. Also good.

Although the example of the combination of the organic solvent preferably used as a solvent of the cellulose acylate solution used for preparation of the cellulose acylate film used for the manufacturing method of the present invention is given below, the present invention is not limited to these. In addition, the numerical value of a ratio means a mass part.
(1) Dichloromethane / methanol / ethanol / butanol = 80/10/5/5
(2) Dichloromethane / methanol / ethanol / butanol = 80/5/5/10
(3) Dichloromethane / isobutyl alcohol = 90/10
(4) Dichloromethane / acetone / methanol / propanol = 80/5/5/10
(5) Dichloromethane / methanol / butanol / cyclohexane = 80/8/10/2
(6) Dichloromethane / methyl ethyl ketone / methanol / butanol = 80/10/5/5
(7) Dichloromethane / butanol = 90/10
(8) Dichloromethane / acetone / methyl ethyl ketone / ethanol / butanol = 68/10/10/7/5
(9) Dichloromethane / cyclopentanone / methanol / pentanol = 80/2/15/3
(10) Dichloromethane / methyl acetate / ethanol / butanol = 70/12/15/3
(11) Dichloromethane / methyl ethyl ketone / methanol / butanol = 80/5/5/10
(12) Dichloromethane / methyl ethyl ketone / acetone / methanol / pentanol = 50/20/15/5/10
(13) Dichloromethane / 1,3-dioxolane / methanol / butanol = 70/15/5/10
(14) Dichloromethane / dioxane / acetone / methanol / butanol = 75/5/10/5/5
(15) Dichloromethane / acetone / cyclopentanone / ethanol / isobutyl alcohol / cyclohexane = 60/18/3/10/7/2
(16) Dichloromethane / methyl ethyl ketone / acetone / isobutyl alcohol = 70/10/10/10
(17) Dichloromethane / acetone / ethyl acetate / butanol / hexane = 69/10/10/10/1
(18) Dichloromethane / methyl acetate / methanol / isobutyl alcohol = 65/15/10/10
(19) Dichloromethane / cyclopentanone / ethanol / butanol = 85/7/3/5
(20) Dichloromethane / methanol / butanol = 83/15/2
(21) Dichloromethane = 100
(22) Acetone / ethanol / butanol = 80/15/5
(23) Methyl acetate / acetone / methanol / butanol = 75/10/10/5
(24) 1,3-dioxolane = 100
(25) Dichloromethane / methanol / butanol / water = 85/18 / 1.5 / 0.5
(26) Dichloromethane / acetone / methanol / butanol / water = 87/5/5 / 2.5 / 0.5
(27) Dichloromethane / methanol = 92/8
(28) Dichloromethane / methanol = 90/10
(29) Dichloromethane / methanol = 87/13
(30) Dichloromethane / ethanol = 90/10

  In some cases, a non-halogen organic solvent can be used as the main solvent, and the detailed description can be found in the Japan Institute of Invention Publication (Publication No. 2001-1745, published on March 15, 2001, Invention Association). is there.

(Solution concentration)
The cellulose acylate concentration in the cellulose acylate solution to be prepared is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and most preferably 15 to 30% by mass.
The cellulose acylate concentration can be adjusted to a predetermined concentration at the stage of dissolving the cellulose acylate in a solvent. Further, after preparing a solution with a low concentration (for example, 4 to 14% by mass) in advance, the solution may be concentrated by evaporating the solvent or the like. Furthermore, after preparing a high concentration solution in advance, it may be diluted. Moreover, the density | concentration of a cellulose acylate can also be reduced by adding an additive.

(Additive)
The said polymer solution used for preparation of the polymer film used for the manufacturing method of this invention can contain the various liquid or solid additive according to a use in each preparation process. Additives preferably used in the cellulose acylate film of the present invention is an additive having a molecular weight of 3000 or less, and for the purpose of reducing the humidity dependence of retardation and adjusting the balance between Re and Rth, as appropriate. Can be used. Examples of the additive include a plasticizer (preferable addition amount is 0.01 to 10% by mass based on the polymer, the same applies hereinafter), an ultraviolet absorber (0.001 to 1% by mass), and an average particle size of 5 to 5. 3000 nm fine particle powder (0.001 to 1% by mass), fluorosurfactant (0.001 to 1% by mass), release agent (0.0001 to 1% by mass), deterioration inhibitor (0.0001 -1 mass%), an optical anisotropy control agent (0.01-10 mass%), and an infrared absorber (0.001-1 mass%).

  The optical anisotropy controlling agent is an organic compound having a molecular weight of 3000 or less, preferably a compound having both a hydrophobic part and a hydrophilic part. These compounds change the retardation value by orienting between polymer chains. Furthermore, these compounds can improve the hydrophobicity of the film and reduce the humidity change of the retardation when used in combination with the cellulose acylate particularly preferably used in the present invention. Moreover, the wavelength dependence of retardation can also be controlled effectively by using the ultraviolet absorber or the infrared absorber in combination. Any additive used in the cellulose acylate film of the present invention is preferably substantially free of volatilization during the drying process.

  Depending on the intended Re and Rth values, an optical anisotropy control agent having an effect of not changing or decreasing the Rth of the film before the heat treatment can be preferably used. By adding such an additive, the mobility of the polymer molecules during the heat treatment can be improved, so that the expression of Re and Rth of the cellulose acylate film produced by the production method of the present invention is further adjusted. Therefore, the heat treatment temperature can be set relatively low, and the reach range of Re and Rth can be increased.

  From the viewpoint of reducing the humidity change of the retardation, it is preferable that the amount of these additives to be added is large. However, as the amount of addition increases, the glass transition temperature (Tg) of the polymer film decreases and the additive in the film production process It becomes easy to cause volatilization problem. Therefore, when cellulose acetate used more preferably in the present invention is used as a polymer, the amount of the additive having a molecular weight of 3000 or less is preferably 30% by mass or less, and 0.1 to 30% by mass with respect to the cellulose acylate. More preferably, 2-20 mass% is further more preferable.

From the viewpoint of increasing the Rth / Re value, specifically, a compound having one or more aromatic rings is preferable, 2 to 15 is more preferable, and 3 to 10 is more preferable. The atoms other than the aromatic ring in the compound are preferably arranged in the same plane as the aromatic ring, and in the case of having a plurality of aromatic rings, the aromatic rings may be arranged in the same plane. preferable. Further, in order to selectively increase Rth, the presence state of the additive in the film is preferably such that the aromatic ring plane is in a direction parallel to the film surface.
The said additive may be used independently and may be used in combination of 2 or more types of additive.

Additives that can be suitably used when cellulose acylate is used as the polymer in the present invention are described in JP-A-2005-104148. Moreover, about an infrared absorber, Unexamined-Japanese-Patent No. 2001-194522 has description. The timing of adding the additive can be appropriately determined according to the type of the additive.
In the present invention, the following polymeric plasticizers can also be preferably used as additives.

(Polymer plasticizer)
Here, the polymer plasticizer in the present invention is characterized by having a repeating unit portion in the compound. The polymer plasticizer of the present invention has a number average molecular weight of 500 to 3000, preferably a number average molecular weight of 600 to 2800, more preferably a number average molecular weight of 700 to 2500, and particularly preferably a number average molecular weight. 700-2000. However, the high-molecular plasticizer in the present invention is not limited to the compound having only such a repeating unit portion, and may be a mixture with a compound having no repeating unit.

The polymer plasticizer of the present invention may be a liquid or a solid under the ambient temperature or humidity used (generally room temperature conditions, so-called 25 ° C., relative humidity 60%). Further, the smaller the color, the better, and it is particularly preferable that the color is colorless. Thermally, it is preferably stable at a higher temperature, and the decomposition start temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher.
Hereinafter, the polymer plasticizer used in the present invention will be described in detail with specific examples, but the polymer plasticizer that can be used in the present invention is not limited thereto.

(Type of polymer plasticizer)
The polymer plasticizer that can be used in the polymer film of the present invention is not particularly limited, but is a polyester plasticizer, a polyether plasticizer, a polyurethane plasticizer, a polyester polyurethane plasticizer, or a polyester polyether plasticizer. The number average molecular weight of at least one selected from an agent, a polyether polyurethane plasticizer, a polyamide plasticizer, a polysulfone plasticizer, a polysulfonamide plasticizer, and other polymer plasticizers described later is 500 or more Preferable plasticizers can be mentioned.

  At least one of them is polyester plasticizer, polyether plasticizer, polyurethane plasticizer, polyester polyurethane plasticizer, polyester polyether plasticizer, polyether polyurethane plasticizer, polyamide plasticizer, polysulfone More preferred are plasticizers and polysulfonamide plasticizers, and particularly preferred are polyester plasticizers, polyester polyurethane plasticizers, and polyester polyether plasticizers. Hereinafter, the polymeric plasticizers preferably used in the present invention will be described by type.

(Polyester plasticizer)
First, the polyester plasticizer used in the present invention will be described. A preferable polyester plasticizer is not particularly limited, and is obtained by reaction of dicarboxylic acid and glycol. Both ends of the reaction product may remain as the reaction product, but a monocarboxylic acid or monoalcohol is further reacted. So-called end sealing may be performed. It is effective in terms of storage stability that the end capping is performed in order not to contain a free carboxylic acid. The dicarboxylic acid used in the polyester plasticizer of the present invention is preferably an aliphatic dicarboxylic acid residue having 4 to 12 carbon atoms or an aromatic dicarboxylic acid residue having 8 to 12 carbon atoms.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms of the polyester plasticizer preferably used in the present invention include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. 1,4-cyclohexanedicarboxylic acid and the like. Examples of the arylene dicarboxylic acid component having 8 to 12 carbon atoms include phthalic acid, terephthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and the like. These are used as one kind or a mixture of two or more kinds, respectively. Next, the glycol used for the polyester plasticizer will be described as an aliphatic or alicyclic glycol residue having 2 to 12 carbon atoms and an aromatic glycol residue having 6 to 12 carbon atoms.

  Examples of aliphatic glycols or alicyclic glycols having 2 to 12 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1 , 3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentanediol 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol There are 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are used as one kind or a mixture of two or more kinds. Be done

  Moreover, it is preferable to protect with a monoalcohol residue or a monocarboxylic acid residue so that both ends of the polyester plasticizer of the present invention do not become carboxylic acid. In this case, the monoalcohol residue is preferably a substituted or unsubstituted monoalcohol residue having 1 to 30 carbon atoms, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isopropanol. Hexanol, cyclohexyl alcohol, octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, dodecaoctanol, allyl alcohol, oleyl alcohol and other aliphatic alcohols, benzyl alcohol And substituted alcohols such as 3-phenylpropanol.

  The end-capping alcohol residues that can be preferably used are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol, isooctanol, 2-ethylhexyl alcohol, isononyl alcohol, Oleyl alcohol and benzyl alcohol, especially methanol, ethanol, propanol, isobutanol, cyclohexyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol and benzyl alcohol.

  Moreover, when sealing with a monocarboxylic acid residue, the monocarboxylic acid used as a monocarboxylic acid residue is preferably a substituted or unsubstituted monocarboxylic acid having 1 to 30 carbon atoms. These may be aliphatic monocarboxylic acids or aromatic carboxylic acids. First, preferred aliphatic monocarboxylic acids are described. Examples include acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, and oleic acid. Examples of aromatic monocarboxylic acids include benzoic acid. Acid, p-tert-butylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, etc., each of which is one or two It can be used as a mixture of seeds or more.

  As described above, specific preferred polyester plasticizers include poly (ethylene glycol / adipic acid) ester, poly (propylene glycol / adipic acid) ester, poly (1,3-butanediol / adipic acid) ester, and poly (propylene). Glycol / sebatic acid) ester, poly (1,3-butanediol / sebatic acid) ester, poly (1,6-hexanediol / adipic acid) ester, poly (propylene glycol / phthalic acid) ester, poly (1,3 -Both ends of butanediol / phthalic acid ester, poly (propylene glycol / terephthalic acid) ester, poly (propylene glycol / 1,5-naphthalene-dicarboxylic acid) ester, poly (propylene glycol / terephthalic acid) ester are 2- Ethyl-hexyl alcohol Examples thereof include 2-ethyl-hexyl alcohol ester and acetylated poly (butanediol / adipic acid) ester at both ends of steal / poly (propylene glycol, adipic acid) ester.

Such polyesters can be synthesized by conventional methods, such as a hot melt condensation method using a polyesterification reaction or transesterification reaction between the dibasic acid or an alkyl ester thereof and a glycol, or an acid chloride of these acids and a glycol. It can be easily synthesized by any of the interfacial condensation methods. These polyester-based plasticizers are described in detail in Koichi Murai, “Plasticizers Theory and Applications” (Kobo Publishing Co., Ltd., first edition published on March 1, 1973). In addition, Japanese Patent Laid-Open Nos. 05-155809, 05-155810, Japanese Patent Laid-Open Nos. 05-97073, 2006-259494, 07-330670, 2006-342227, 2007-003679. The materials described in each publication can also be used.

  In addition, as a product, ADEKA Co., Ltd. can use Adeka Sizer (various Adeka Sizer P series and Adeka Sizer PN series) as described in DIARY 2007, pages 55-27 as a polyester plasticizer. Kogyo Co., Ltd. “Polymer-related Product List 2007” on page 25, various products of Polylite, Dainippon Ink and Chemicals, Inc. “DIC Polymer Modifier” (issued 2004.4.1.000VIII) 2-5 Various types of polysizers described in the above can be used. Furthermore, it is available as Plasthall P series made by CP HALL, USA. Benzoyl functionalized polyethers are commercially available from Velsicol Chemicals, Rosemont, Ill. Under the trade name BENZOFLEX (eg, BENZOFLEX 400, polypropylene glycol dibenzoate).

(Polyester polyether plasticizer)
Next, the polyester polyether plasticizer used in the present invention will be described. The polyester polyether plasticizer of the present invention refers to a condensation polymer of dicarboxylic acid and polyether diol. As the dicarboxylic acid, an aliphatic dicarboxylic acid residue having 4 to 12 carbon atoms or an aromatic dicarboxylic acid residue having 8 to 12 carbon atoms described in the polyester plasticizer is used as it is.

  Next, examples of the polyethers having an aliphatic glycol having 2 to 12 carbon atoms include polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol, and combinations thereof. Typical useful commercially available polyether glycols include Carbowax resin, Pluronics resin and Niax resin. In the production of the polyester polyether plasticizer used in the present invention, a commonly used polymerization method known to those skilled in the art can be used.

  Examples of these polyester ether plasticizers include polyester polyether plasticizers described in US Pat. No. 4,349,469. Basically, it is a polyester polyether plasticizer synthesized from, for example, 1,4-cyclohexanedicarboxylic acid as dicarboxylic acid and 1,4-cyclohexanedimethanol and polytetramethylene ether glycol as polyether. Other useful polyester polyether plasticizers include commercially available resins such as DuPont's Hytrel copolyesters and copolymers such as GAF's Galflex polymer. For these, the materials described in JP-A-5-197073 can be used. It is commercially available as ADEKA Sizer RS series from ADEKA Corporation. Polyester ether plasticizers that are alkyl-functionalized polyalkylene oxides are commercially available from ICI Chemicals, Wilmington, Del., Under the trade name PYCAL (eg, PYCAL 94, a phenyl ester of polyethylene oxide). ).

(Polyester polyurethane plasticizer)
Further, the polyester polyurethane plasticizer used in the present invention will be described. The plasticizer can be obtained by condensation of a polyester and an isocyanate compound. First, as the polyester, the polyester plasticizer before sealing both ends can be used as it is, and the materials described above for the polyester plasticizer can be preferably used.

Examples of the diisocyanate component forming the polyurethane structure include OCN (CH ₂ ) _p NCO (p = 2) represented by ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate and the like. -8) Polymethylene isocyanate and aromatic diisocyanates such as p-phenylene diisocyanate, tolylene diisocyanate, p, p'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, Although m-xylylene diisocyanate or the like is used, it is not limited thereto. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are particularly preferable.

  In the present invention, the polyester polyurethane plasticizer can be easily synthesized by a conventional synthesis method in which the raw material polyester diol and diisocyanate are mixed and heated with stirring. For these, the materials described in JP-A-5-197073, JP-A-2001-122979, JP-A-2004-175971, JP-A-2004-175972 and the like can be used.

(Other polymer plasticizers)
In the present invention, not only the polyester plasticizer, polyester polyether plasticizer and polyester polyurethane plasticizer described above, but also other polymer plasticizers can be used. Examples of the polymer plasticizer include aliphatic hydrocarbon polymers, alicyclic hydrocarbon polymers, acrylic polymers such as polyacrylic acid esters and polymethacrylic acid esters (the ester groups include methyl groups, ethyl groups, Propyl, butyl, isobutyl, pentyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, nonyl, isononyl, tert-nonyl, dodecyl, tridecyl, stearyl, oleyl, benzyl Group, phenyl group, etc.), vinyl polymers such as polyvinyl isobutyl ether and poly N-vinyl pyrrolidone, styrene polymers such as polystyrene and poly 4-hydroxystyrene, polyethers such as polyethylene oxide and polypropylene oxide, polyamides, polyurethanes and polyureas Phenol - formaldehyde condensate, urea - formaldehyde condensate, vinyl acetate, and the like.

  These polymer plasticizers may be a homopolymer composed of one type of repeating unit or a copolymer having a plurality of repeating structures. Two or more of the above polymers may be used in combination. These high molecular weight plasticizers may be used singly, or the same effect can be obtained by using them in combination. Among these, a polyacrylic acid ester, a polymethacrylic acid ester, or a copolymer with another vinyl monomer is preferable, and in particular, an acrylic polymer such as polyacrylic acid ester and polymethacrylic acid ester (the ester group is methyl Group, ethyl group, propyl group, butyl group, hexyl group, cyclohexyl group, 2-ethylhexyl group, isononyl group, oleyl group).

(Example of specific polymer plasticizer)
Specific examples of preferred polymer plasticizers are described below, but the polymer plasticizers that can be used in the present invention are not limited to these.
PP-1: Condensation product with ethanediol / succinic acid (1/1 molar ratio) (number average molecular weight 2500)
PP-2: Condensate with 1,3-propanediol / glutaric acid (1/1 molar ratio) (number average molecular weight 1500)
PP-3: Condensate with 1,3-propanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1300)
PP-4: Condensate with 1,3-propanediol / ethylene glycol / adipic acid (1/1/2 molar ratio) (number average molecular weight 1500)
PP-5: Condensation product with 2-methyl-1,3-propanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1200)
PP-6: Condensate with 1,4-butanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1500)
PP-7: Condensate with 1,4-cyclohexanediol / succinic acid (1/1 molar ratio) (number average molecular weight 800)

PP-8: butyl esterified product (number average molecular weight 1300) at both ends of the condensate with 1,3-propanediol / succinic acid (1/1 molar ratio)
PP-9: Cyclohexyl esterified compound (number average molecular weight 1500) at both ends of the condensate with 1,3-propanediol / glutaric acid (1/1 molar ratio)
PP-10: 2-ethylhexyl esterified product (number average molecular weight 3000) at both ends of the condensate with ethanediol / succinic acid (1/1 molar ratio)
PP-11: isononyl esterified product (number average molecular weight 1500) at both ends of the condensate with 1,3-propanediol / ethylene glycol / adipic acid (1/1/2 molar ratio)
PP-12: Propyl ester of both ends of the condensate with 2-methyl-1,3-propanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1300)
PP-13: 2-ethylhexyl esterified compound (number average molecular weight 1300) at both ends of the condensate with 2-methyl-1,3-propanediol / adipic acid (1/1 molar ratio)
PP-14: Isononyl esterified product (number average molecular weight 1300) at both ends of the condensate with 2-methyl-1,3-propanediol / adipic acid (1/1 molar ratio)
PP-15: butyl esterified product (number average molecular weight 1800) at both ends of the condensate with 1,4-butanediol / adipic acid (1/1 molar ratio)

PP-16: Condensate with ethanediol / terephthalic acid (1/1 molar ratio) (number average molecular weight 2000)
PP-17: Condensation product with 1,3-propanediol / 1,5-naphthalenedicarboxylic acid (1/1 molar ratio) (number average molecular weight 1500)
PP-18: Condensation product with 2-methyl-1,3-propanediol / isophthalic acid (1/1 molar ratio) (number average molecular weight 1200)
PP-19: Condensate with 1,3-propanediol / terephthalic acid (1/1 molar ratio) benzyl esterified compound at both ends (number average molecular weight 1500)
PP-20: 1,3-propanediol / 1,5-naphthalenedicarboxylic acid condensate (1/1 molar ratio) with propyl esterified compounds (1/1 molar ratio) (number average molecular weight 1500)
PP-21: Condensation product of 2-methyl-1,3-propanediol / isophthalic acid (1/1 molar ratio) at both ends butyl esterified product (number average molecular weight 1200)

PP-22 poly (average polymerization degree 5) condensate with propylene ether glycol / succinic acid (1/1 molar ratio) (number average molecular weight 1800)
PP-23: Condensation product (number average molecular weight 1600) with poly (average polymerization degree 3) ethylene ether glycol / glutaric acid (1/1 molar ratio)
PP-24: Condensation product (number average molecular weight 2200) with poly (average polymerization degree 4) propylene ether glycol / adipic acid (1/1 molar ratio)
PP-25: Condensation product (number average molecular weight 1500) with poly (average polymerization degree 4) propylene ether glycol / phthalic acid (1/1 molar ratio)

PP-26: Poly (average polymerization degree 5) propylene ether glycol / succinic acid (1/1 molar ratio) condensate at both ends butyl esterified product (number average molecular weight 1900)
PP-27: Condensation product of poly (average polymerization degree 3) ethylene ether glycol / glutaric acid (1/1 molar ratio) 2-ethylhexyl esterified compound (number average molecular weight 1700) at both ends
PP-28: tert-nonyl esterified product (number average molecular weight 1300) at both ends of the condensate with poly (average polymerization degree 4) propylene ether glycol / adipic acid (1/1 molar ratio)
PP-29: Condensation product of poly (average polymerization degree 4) propylene ether glycol / phthalic acid (1/1 molar ratio) at both ends with propyl esterified compound (number average molecular weight 1600)
PP-30: Condensate with ethanediol / adipic acid (1/1 molar ratio) (number average molecular weight 1000)

PP-31: a polyester urethane compound obtained by condensing a condensate (number average molecular weight 1500) with 1,3-propanediol / succinic acid (1/1 molar ratio) with trimethylene diisocyanate (1 mol),
PP-32: Polyester-urethane compound PP-33 obtained by condensing a condensate (number average molecular weight 1200) with 1,3-propanediol / glutaric acid (1/1 molar ratio) with tetramethylene diisocyanate (1 mol). : Polyester-urethane compound PP-34 obtained by condensing a condensate (number average molecular weight 1000) with 1,3-propanediol / adipic acid (1/1 molar ratio) with p-phenylene diisocyanate (1 mol): 1 Polyester-urethane compound PP-35 obtained by condensing a condensate (number average molecular weight 1500) with 1,3-propanediol / ethylene glycol / adipic acid (1/1/2 molar ratio) with tolylene diisocyanate (1 mol): A condensate (number average molecular weight 1200) with 2-methyl-1,3-propanediol / adipic acid (1/1 molar ratio) Polyester-urethane compound PP-36 condensed with m-xylylene diisocyanate (1 mol): a condensate (number average molecular weight 1500) with 1,4-butanediol / adipic acid (1/1 molar ratio) is tetramethylene. Polyester-urethane compound condensed with diisocyanate (1 mole)

PP-37: Polyisopropyl acrylate (number average molecular weight 1300)
PP-38: Polybutyl acrylate (number average molecular weight 1300)
PP-39: Polyisopropyl methacrylate (number average molecular weight 1200)
PP-40: Poly (methyl methacrylate / butyl methacrylate (molar ratio 8/2, number average molecular weight 1600)
PP-41: poly (methyl methacrylate / 2-ethylhexyl methacrylate (molar ratio 9/1, number average molecular weight 1600)
PP-42: Poly (vinyl acetate (number average molecular weight 2400)

(Preparation of cellulose acylate solution)
The cellulose acylate solution is prepared, for example, in JP-A-58-127737, JP-A-61-106628, JP-A-2-276830, JP-A-4-259511, and JP-A-5-163301. No. 9-95544, No. 10-45950, No. 10-95854, No. 11-71463, No. 11-302388, No. 11-322946, No. 11-322947, No. 11 No.-323017, JP-A 2000-53784, 2000-273184, 2000-273239, and the like. Specifically, the polymer and the solvent are mixed and stirred to swell, and optionally cooled or heated to dissolve and then filtered to obtain a cellulose acylate solution.

In this invention, in order to improve the solubility to the solvent of a polymer, it is preferable to include the process of cooling and / or heating the mixture of a polymer and a solvent.
When a halogenated organic solvent is used as the solvent and the mixture of the cellulose acylate and the solvent is cooled, it is preferable to include a step of cooling the mixture to −100 to 10 ° C. Moreover, it is preferable to include the process swollen at -10-39 degreeC in the process before a cooling process, and the process heated to 0-39 degreeC in the process after cooling.

When using a halogen-based organic solvent as a solvent and heating a mixture of cellulose acylate and solvent, the method includes dissolving cellulose acylate in the solvent by one or more methods selected from the following (a) or (b): It is preferable.
(A) Swell at −10 to 39 ° C. and warm the resulting mixture to 0 to 39 ° C.
(B) Swell at −10 to 39 ° C., heat the resulting mixture to 40 to 240 ° C. at 0.2 to 30 MPa, and cool the heated mixture to 0 to 39 ° C.
Furthermore, when using a non-halogen organic solvent as the solvent and cooling the mixture of cellulose acylate and the solvent, it is preferable to include a step of cooling the mixture to −100 to −10 ° C. Moreover, it is preferable to include the process of swelling at -10-55 degreeC in the process before a cooling process, and the process heated to 0-57 degreeC in the process after cooling.

When using a halogen-based organic solvent as a solvent and heating a mixture of cellulose acylate and solvent, the method includes dissolving cellulose acylate in the solvent by one or more methods selected from the following (c) or (d) It is preferable.
(C) Swell at −10 to 55 ° C. and warm the resulting mixture to 0 to 57 ° C.
(D) Swell at −10 to 55 ° C., heat the obtained mixture to 40 to 240 ° C. at 0.2 to 30 MPa, and cool the heated mixture to 0 to 57 ° C.

[Film Formation of Cellulose Acylate Film Used for Production Method of the Present Invention]
The cellulose acylate film used in the production method of the present invention can be produced by the solution casting film formation method using the above cellulose acylate solution. In carrying out the solution casting film forming method, a conventional apparatus can be used in accordance with a conventional method. Specifically, the dope (cellulose acylate solution) prepared in a dissolving machine (kettle) is filtered, and then temporarily stored in a storage kettle, and the foam contained in the dope is defoamed and finally prepared. it can. 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. It casts uniformly on the metal support body of the cast part currently cast (casting process). Next, the raw dry dope film (also referred to as a web) is peeled from the metal support at the peeling point where the metal support has almost gone around, and then transported to the drying zone, and drying is completed while being transported by a roll group. Details of the casting process and the drying process of the solution casting film forming method are also described in pages 120 to 146 of JP-A-2005-104148, and can be applied to the present invention as appropriate.

  Moreover, the cellulose acylate film used for the production method of the present invention can be produced by a melt casting film production method without using the cellulose acylate solution. The melt casting film forming method is a method in which a polymer melted by heating is cast on a support and cooled to form a film. If the melting point of the polymer or the melting point of the mixture of the polymer and various additives is lower than the decomposition temperature and higher than the stretching temperature, it is possible to employ a melt casting film forming method. The melt casting film forming method is described in JP-A No. 2000-352620.

  In the present invention, a metal band or a metal drum can be used as the metal support used in forming the cellulose acylate film before the heat treatment, and a metal band is more preferable. When a cellulose acylate film formed using a metal band is used, there is a tendency that Rth of the film after heat treatment tends to be low, and depending on factors such as the above-mentioned additives and other retardation adjusting factors, Rth A film having / Re of −0.6 to −0.4 can be produced. In addition, when a cellulose acylate film formed using a metal drum is used, there is a tendency that the Rth of the film after heat treatment tends to be high, and it depends on other retardation adjusting elements such as the additive. A film having Rth / Re of 0.4 to 0.6 can be produced. The difference in Rth after the heat treatment of the cellulose acylate film used in the production method of the present invention is due to the fact that the external force applied to the web is different during the film formation process, and thus the cellulose acylate polymer chain present in the film before the heat treatment This is presumed to be caused by the difference in the plane orientation state.

When a cellulose acylate film before heat treatment is formed using a metal band, after the cellulose acylate solution is cast on the metal support, the dope film (web) Is also peeled from the metal support, and then transported to the drying zone, and the drying is completed while being transported by a roll group.
In this invention, when peeling a web from a metal support body, it is preferable that the residual solvent amount in a web (mixture containing a cellulose acylate and a solvent) is 10-100 mass%, and is 20-90 mass%. More preferably, it is more preferably 30 to 80% by mass. The residual solvent amount in the cellulose acylate web in the present invention is calculated based on the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
[In the formula, M represents the mass of the cellulose acylate web sampled immediately after peeling from the support, and the mass when this film is dried at 110 ° C. for 3 hours is N. ]
By doing in this way, Rth of the film after heat processing can be made lower, and a favorable planar cellulose acylate film can be obtained. Here, the ratio (v ₂ / v ₁ ) between the support speed (v ₁ ) and the film winding speed (v ₂ ) is preferably 0.90 to 1.20, preferably 0.96 to 1 .15 is more preferable, and 1.02 to 1.10.

When controlling the retardation of the cellulose acylate film produced by the production method of the present invention, the mechanical history applied to the cellulose acylate film before the heat treatment, that is, the external force applied to the cellulose acylate web during the film formation process is determined. It is also preferable to control. Specifically, the cellulose acylate web can be stretched by 0.1% or more and less than 15%, preferably 0.5 to 10%, more preferably 1 to 8%. In addition, when producing while conveying the cellulose acylate film before heat processing, it is preferable to extend | stretch in the said conveyance direction. The residual solvent amount of the cellulose acylate web at the time of stretching is calculated based on the following formula and is 5 to 1000%. The amount of residual solvent is preferably 10 to 200%, more preferably 30 to 150%, and still more preferably 40 to 100%.
Residual solvent amount (% by mass) = {(MN) / N} × 100
[Wherein, M is the mass of the cellulose acylate film just before being inserted into the stretching zone, and N is the mass when the cellulose acylate film just before being inserted into the stretching zone is dried at 110 ° C. for 3 hours. To express]
In some cases, the cellulose acylate web can be stretched by 15 to 300%, preferably 18 to 200%, more preferably 20 to 100%. In addition, when producing while conveying the cellulose acylate film before heat processing, it is preferable to extend | stretch in the said conveyance direction. The residual solvent amount of the cellulose acylate web at the time of stretching is calculated based on the above formula and is 5 to 1000%. The residual solvent amount is preferably 30 to 500%, more preferably 50 to 300%, and still more preferably 80 to 250%.
The stretch ratio (elongation) of the cellulose acylate web during the stretching can be achieved by the difference in peripheral speed between the metal support speed and the stripping speed (stripping roll draw). By performing such stretching, the expression of retardation can be adjusted.

  When stretched in a state where the residual solvent amount is 5% or more, haze is hardly increased, and when stretched in a state where the residual solvent amount is 1000% or less, external force applied to the cellulose acylate polymer chain is easily transmitted, and the solvent is contained. There exists a tendency for the effect of retardation expression adjustment by the cellulose acylate web extending | stretching implemented in a state to become large. The residual solvent amount of the cellulose acylate web is appropriately determined by changing the concentration of the cellulose acylate solution, the temperature and speed of the metal support, the temperature and air volume of the drying air, the concentration of the solvent gas in the drying atmosphere, and the like. Can be adjusted.

  The cellulose acylate web that has been subjected to the stretching process in this manner is then conveyed to a drying zone, and drying is terminated while both ends are clipped by a tenter or conveyed by a roll group.

  The amount of residual solvent in the film thus dried is preferably 0 to 2% by mass, and more preferably 0 to 1% by mass. This film may be conveyed to the heat treatment zone as it is, or may be heat treated offline after the film is wound. The preferable width | variety of the cellulose acylate film before heat processing is 0.5-5 m, More preferably, it is 0.7-3 m. Moreover, when winding up a film once, preferable winding length is 300-30000m, More preferably, it is 500-10000m, More preferably, it is 1000-7000m.

The moisture permeability in terms of film thickness of 80 μm of the cellulose acylate film used in the production method of the present invention is preferably 100 g / (m ² · day) or more, and is 100 to 1500 g / (m ² · day). more preferably in, more preferably from ^{200~1000g / (m 2 · day)} , particularly preferably ^{300~800g / (m 2 · day)} .
The moisture permeability in the present invention refers to the change in mass before and after humidity control when a lid is sealed with a film for evaluating a cup containing calcium chloride and left for 24 hours at 40 ° C. and 90% relative humidity. g / (m ² · day)). The moisture permeability increases with increasing temperature and also increases with increasing humidity, but the magnitude relationship of moisture permeability between films is not changed regardless of the conditions. Therefore, in the present invention, the value of the mass change at 40 ° C. and 90% relative humidity is used as a reference. In addition, since the moisture permeability decreases as the film thickness increases and increases as the film thickness decreases, the measured moisture permeability is first multiplied by the actually measured film thickness and divided by 80 in the present invention. The water vapor transmission rate in terms of thickness of 80 μm ”.

(Preliminary stretching)
In the present invention, the formed cellulose acylate film can be stretched before stretching described below (hereinafter, the stretching is also referred to as “preliminary stretching”). By performing the preliminary stretching, the expression of Re and Rth in the stretching process can be further adjusted. Specifically, within the range described below, by reducing the stretching temperature or increasing the stretching ratio, the stretching temperature can be set relatively low, or the reach range of Re or Rth can be increased. It becomes possible. Moreover, within the range which does not deviate from the meaning of this invention, another process may be included between the preliminary extending process and the extending process.

In the production method of the present invention, pre-stretching is performed at (Tg-20) to (Tg + 50) ° C., where Tg (unit: ° C.) is the glass transition temperature of the cellulose acylate film used in the production method of the present invention. Is preferred. The pre-stretching temperature is more preferably (Tg-10) to (Tg + 45) ° C., further preferably Tg to (Tg + 40) ° C., and most preferably (Tg + 5) to (Tg + 35) ° C. However, the preliminary stretching temperature does not exceed the stretching temperature described later. The preliminary stretching temperature is preferably 5 ° C or more lower than the stretching temperature, more preferably 10 ° C or more lower than the stretching temperature, and 15 ° C or more lower than the stretching temperature. Is more preferable, and it is particularly preferable to carry out at a temperature lower by 20 ° C. or more than the stretching temperature, and it is most preferable to carry out at a temperature lower by 35 ° C. or more than the stretching temperature.
In the present invention, the glass transition temperature is a boundary temperature at which the mobility of the polymer constituting the cellulose acylate film of the present invention changes greatly. As for the glass transition temperature in the present invention, 20 mg of a cellulose acylate film used in the production method of the present invention is placed in a measurement pan of a differential scanning calorimeter (DSC), and this is 30 ° C. to 120 ° C. at 10 ° C./min in a nitrogen stream. The temperature is raised to 30 ° C., held for 15 minutes, cooled to −30 ° C./min to 30 ° C., and then heated again from 30 ° C. to 250 ° C., where the baseline starts to deviate from the low temperature side. .
The production method of the present invention is estimated to grow the structure observed by X-ray diffraction and adjust the retardation by stretching the cellulose acylate film used in the production method of the present invention at (Tc + 10 ° C.) or higher. However, by preliminarily stretching the film in advance as described above, the polymer can be arranged to some extent in the prestretching direction. Therefore, in the stretching step described later, the structure observed by X-ray diffraction can be efficiently used. And it can grow anisotropically. In addition, by making the preliminary stretching temperature lower than the stretching temperature, the cellulose acylate polymer can be oriented without growing the structure observed by X-ray diffraction. There is an advantage that a structure observed by X-ray diffraction can be grown. Therefore, it is more preferable that the stretching direction in the preliminary stretching coincides with the stretching direction or the transporting direction at the time of stretching described later from the viewpoint of reducing the heat treatment temperature and extending the reach range of Re and Rth. Conversely, if these directions do not match, the reach range of Re and Rth can be reduced and the Rth / Re value can be adjusted.

The direction of the preliminary stretching is not particularly limited, and when the cellulose acylate film before stretching is being transported, even if it is longitudinal stretching that is stretched in the transport direction, Although it may be stretched, in order to be preferably used as an IPS mode or VA mode liquid crystal panel application, it is preferable to extend the slow axis in the film plane in the width direction (direction perpendicular to the transport direction). It is preferable that For the longitudinal stretching and lateral stretching methods and preferred embodiments, reference can be made to the section of stretching described later. The prestretch ratio is preferably 1 to 500%, more preferably 3 to 400%, further preferably 5 to 300%, and particularly preferably 10 to 100%. These preliminary stretchings may be performed in one stage or in multiple stages. Here, “preliminary draw ratio (%)” means that obtained by the following formula.
Pre-stretch ratio (%) = 100 × {(length after stretching) − (length before stretching)} / length before stretching The stretching speed in the pre-stretching is preferably 10 to 10,000% / min, more preferably. Is 20 to 1000% / min, more preferably 30 to 800% / min.

[Stretching]
The method for producing a cellulose acylate film of the present invention is performed under the condition of the following formula (I) while applying a tension in the film conveying direction between the span of 0.01 to 2 times the film width before stretching. It includes a step (sometimes referred to as a heat treatment or a heat treatment step) of stretching the cellulose acylate film at least in the transport direction at a temperature T (unit: ° C.) that satisfies the above.
Formula (I): Tc + 10 ≦ T <Tm ₀
In the formula (I), Tc represents the crystallization temperature of the cellulose acylate film before stretching, and the unit is ° C. In the present invention, the crystallization temperature indicates a temperature at which the polymer constituting the cellulose acylate film forms a regular periodic structure, and when this temperature is exceeded, a structure observed by X-ray diffraction grows. The crystallization temperature in the present invention is that after 20 mg of cellulose acylate film before heat treatment is placed in a DSC measurement pan, and this is heated from 30 ° C. to 120 ° C. at 10 ° C./min and held for 15 minutes. This is the starting temperature of the exothermic peak observed when the temperature was cooled to 30 ° C. at −20 ° C./min and then heated again from 30 ° C. to 300 ° C. Tc usually appears on the higher temperature side than the glass transition temperature (Tg). For example, the crystallization temperature of a cellulose triacetate film having a total degree of substitution of 2.85 varies depending on additives and film forming conditions, but is about 190 ° C., and the crystallization temperature of a cellulose triacetate film having a total degree of substitution of 2.92 is increased. The temperature is about 170 ° C.
In the formula (I), Tm ₀ represents the melting point of the cellulose acylate film before stretching, and the unit is ° C. In the present invention, the melting point of the cellulose acylate film 20 mg before stretching was put in a DSC measurement pan, and this was heated from 30 ° C. to 120 ° C. at 10 ° C./min in a nitrogen stream and held for 15 minutes. This is the end temperature of the endothermic peak observed when the temperature is cooled to -20 ° C / min to ℃, and then heated again from 30 ℃ to 300 ℃. Tm ₀ usually appears on the higher temperature side than the above-mentioned crystallization temperature (Tc). For example, the melting point of a cellulose triacetate film having a total degree of substitution of 2.85 slightly varies depending on the additives and film forming conditions, but is about 285 ° C., and the melting point of a cellulose triacetate film having a total degree of substitution of 2.92 is about 290 ° C.

  In the case of an anisotropic film, it is preferable that the cellulose acylate film be conveyed in a direction in which the sound wave propagation speed (sound speed) is maximized. Specifically, the angle formed between the direction in which the sound wave propagation speed becomes maximum and the conveyance direction is preferably 10 ° or less, more preferably 3 ° or less, and even more preferably 1 ° or less, Most preferably, it is 0 °. In the present invention, the direction in which the speed of sound wave propagation becomes maximum is that the film is conditioned at 25 ° C. and a relative humidity of 60% for 24 hours, and then an orientation measuring machine (SST-2500: manufactured by Nomura Corporation) is used. This is the direction in which the propagation speed of the longitudinal wave vibration of the ultrasonic pulse is maximized. However, the sound velocity ratio, which is the ratio of the sound wave propagation velocity in the direction where the sound wave propagation velocity is maximum and the sound wave propagation velocity in the direction orthogonal to that direction (maximum sound wave propagation velocity / sonic wave propagation velocity in the direction orthogonal), is 1. For an isotropic film of 03 or less, it is preferable that the direction in which the sound wave propagation speed is maximized is not the transport direction.

The expression of retardation of the cellulose acylate film is adjusted by stretching the cellulose acylate film at a temperature T satisfying the formula (I) between 0.01 to 2 times the span of the film width before stretching. be able to. In particular, a film satisfying | Rth | / Re of 0.4 to 0.6 can be produced. By stretching under such conditions, Re usually increases by 15 nm or more than before stretching, but preferably increases by 25 nm or more, more preferably by 50 nm or more. The increasing range of Re can be controlled by the above-described pre-stretching conditions (temperature and magnification), stretching conditions (temperature and magnification), and the like. The stretching temperature in the production method of the present invention preferably satisfies the following formula (1a), more preferably satisfies the following formula (1b), and further preferably satisfies the following formula (1c). By selecting a temperature that satisfies these formulas, there are advantages that the Re expression is increased, and in some cases, the stretching direction and the direction of the slow axis are orthogonal to each other.
Formula (1a): Tc + 15 ≦ T <Tm
Formula (1b): Tc + 20 ≦ T <Tm ₀ −5
Formula (1c): Tc + 25 ≦ T <Tm ₀ −10
The time (heat treatment time) for the conveyed cellulose acylate film to pass through the zone of temperature T is usually 0.01 to 60 minutes, preferably 0.03 to 10 minutes, and more preferably 0.05. ~ 5 minutes. By setting it as the said range, it is excellent in the expression of retardation and coloring of a film can be suppressed.

When the film is stretched at a temperature T satisfying Tc + 10 ≦ T <Tm ₀ according to the production method of the present invention, the mobility of the cellulose acylate polymer chain can be improved. Rise) and cutting of the film can be prevented. Moreover, the balance between the aggregation and orientation of the cellulose acylate polymer chains and the simultaneous thermal relaxation can be appropriately controlled by adjusting the stretching speed and the stretching ratio as described later. Therefore, by following the production method of the present invention, the cellulose acylate polymer chains in the film can be highly aggregated and arranged, and the cellulose acylate having a large elastic modulus, small humidity dimensional change, and appropriate moisture permeability. A rate film can be produced.

  Moreover, the span (L) with respect to the film width (W) before stretching in the production method of the present invention is 0.01 to 2 times, preferably 0.1 to 1.5 times, It is more preferable that it is -1.3 times, and it is further more preferable that it is 0.5-1 times. The term “between spans” as used herein refers to a device that applies tension to the film during stretching, preferably a pair of or more nip rolls or suction drums, and more preferably a distance between the pair of nip rolls. As is conventionally known, when a film satisfying | Rth | / Re of 0.4 to 0.6 is required, it is necessary to use a uniaxial stretching condition at the free end. The ratio (sometimes referred to as the aspect ratio (L / W)) between 2 and 50 or less, preferably 3 to 40, more preferably 4 to 20, In the film produced in (1), there were problems such as easy cracking and tin plate-like wrinkles. Further, since it is necessary to take a long span, there is a problem that uneven stretching is likely to occur due to fluctuations in external force (heating air and gravity) applied to the film during stretching. In the production method of the present invention, by appropriately adjusting the stretching temperature and the L / W ratio, the | Rth | / Re value, which was not easy to produce conventionally, is 0.4 to 0.6. In addition, it has become possible to stably produce a cellulose acylate film that is hard to break and has no wrinkles.

The stretching in the production method of the present invention can be performed, for example, using a tenter that performs simultaneous biaxial stretching shown in FIG. In FIG. 1, “between spans” represents a distance from a position where the film is fixed to the clip 10 to a position where the film is released.
FIG. 1 shows a mode in which the conveyed film 3 is stretched in the tenter 2. First, the film 3 is installed at a tenter inlet 16, and the film 3 is installed on a film mounting portion 27 below the tenter. Thereafter, the film is fixed to the clip 10 by chucking both ends with the film fixing portion 29. By moving the clip 10 along the rails 5 and 6, stretching in the width direction (direction perpendicular to the transport direction) is performed simultaneously with the film transport direction. At this time, the stretching ratio in the transport direction can be adjusted by controlling the interval and moving speed of the clip 10, and the stretching ratio in the width direction can be adjusted by changing the rail width. Thereafter, the clip 10 is removed by the opening members 23 and 24, and the film 3 is finally conveyed to the outside of the tenter through the tenter outlet 17.
FIGS. 2 and 3 show a side view of a mode in which the tenter of FIG. 1 has a film placed on the mounting portion 27 and a mode in which the film is chucked. By using such a tenter, the film of the present invention can be easily produced.

  The conveyance speed is usually 1 to 500 m / min, preferably 5 to 300 m / min, more preferably 10 to 200 m / min, and still more preferably 20 to 100 m / min. If the conveyance speed is 1 m / min or more, which is the above lower limit value, there is a tendency that it is preferable in that sufficient productivity can be secured industrially. If the conveying speed is increased, the coloring of the film tends to be suppressed. It is preferable to keep the transport speed during stretching (the speed of devices such as nip rolls and suction drums that determine the transport speed) constant.

As a heating method at the time of stretching in the production method of the present invention, for example, a method of passing a cellulose acylate film through a zone at a temperature T while conveying a cellulose acylate film, a method of applying hot air to a cellulose acylate film being conveyed, Examples thereof include a method of irradiating the cellulose acylate film with heat rays and a method of bringing the cellulose acylate film into contact with a heated roll.
A method of passing the cellulose acylate film through the zone of the temperature T while applying hot air is preferable. This method has an advantage that the cellulose acylate film can be heated uniformly. The temperature in the zone can be maintained at the temperature T by controlling it to a constant temperature with a heater while monitoring it with a temperature sensor, for example.
A draw ratio is 0.8-100 times normally, Preferably it is 1.0-10 times, More preferably, it is 1.2-5 times. In addition, the ratio of Re and Rth can be further adjusted by optionally stretching the cellulose acylate film in a direction orthogonal to the transport direction.
The stretching speed in the stretching is preferably 20 to 10000% / min, more preferably 40 to 1000% / min, and still more preferably 50 to 500% / min.

The step of stretching the cellulose acylate film may be performed only once or a plurality of times in the production method of the present invention. Performing a plurality of times means that the temperature is once lowered to less than (Tc + 10 ° C.) after the previous stretching is completed, and then stretching is performed while transporting again while setting the temperature to (Tc + 10) or more and below Tm _0. . In the case where the stretching is performed a plurality of times, it is preferable to satisfy the above-mentioned range of the stretching ratio when all the stretching is completed. The stretching in the production method of the present invention is preferably 3 times or less, more preferably 2 times or less.

[Cooling after heat treatment]
The polymer film after the heat treatment is cooled to a temperature lower than Tc. At this time, the humidity dependency of the retardation (particularly Re) of the cellulose acylate film finally obtained can be effectively reduced by cooling while transporting at a transport tension of 0.1 to 500 N / m. . The conveyance tension during cooling is preferably 1 to 400 N / m, more preferably 10 to 300 N / m, and still more preferably 50 to 200 N / m. By setting the transport tension to 0.1 N / m or more, there is a tendency that the humidity dependency of retardation is reduced and the surface shape is also easily improved. Further, by setting the transport tension to 500 N / m or less, there is a tendency that the humidity dependency of retardation is reduced and the absolute value of Re is easily increased.

The conveyance tension is controlled by, for example, arranging at least a pair of tension control devices (for example, nip rolls, suction drums, etc.) immediately before the cooling zone and behind the cooling zone, and adjusting the respective rotation speeds. Can do. Specifically, when the ratio (v ₂ / v ₁ ) between the feeding speed (v ₁ ) and the winding speed (v ₂ ) of the pair of tension control devices is decreased, the transport tension is decreased, and when the ratio is increased, the transport tension is decreased. To rise.

The cooling rate during cooling is not particularly limited, but is preferably 100 to 1,000,000 ° C./min, more preferably 1,000 to 100,000 ° C./min, and further preferably 3,000 to 50. Cool the film at 1,000 ° C / min. The temperature range for cooling the film at such a cooling rate is preferably 50 ° C. or more, more preferably 100 to 300 ° C., further preferably 150 to 280 ° C., and 180 to 250 ° C. It is particularly preferred.
Thus, by adjusting a cooling rate, the expression property of the retardation of the cellulose acylate film obtained can be further adjusted. Specifically, the retardation can be improved by increasing the cooling rate. Moreover, the distribution of the orientation of polymer chains in the thickness direction in the cellulose acylate film can be reduced, and the humidity curl of the film can be suppressed. Such an effect can be obtained more sufficiently by controlling the temperature range for cooling at a relatively high cooling rate within the above-mentioned preferable range.

  For the cooling rate, after the heating zone, a cooling zone maintained at a temperature lower than the heating zone is provided, and the cellulose acylate film is sequentially conveyed to these zones, the cooling roll is brought into contact with the film, Control can be performed by blowing cooling air onto the film or immersing the film in a cooled liquid. The cooling rate is not always required to be constant during the cooling step, and the cooling rate may be reduced at the beginning and the end of the cooling step, and the cooling rate may be increased in the meantime. The cooling rate can be determined by measuring the temperature at a plurality of points with a thermocouple arranged on the film membrane surface as described in the examples described later.

[Stretching after heat treatment (re-stretching)]
In the production method of the present invention, in some cases, stretching may be performed after the stretching (referred to as “re-stretching” in order to distinguish from other stretching). Thereby, the humidity dependency of retardation (particularly Re) of the finally obtained transparent film can also be reduced. The re-stretching temperature can be appropriately set according to the target Re and Rth values, but is preferably (the stretching temperature−20) to (the stretching temperature + 20) ° C., and (the stretching temperature− 10) to (the stretching temperature + 10) ° C. is more preferable, and (the stretching temperature−5) to (the stretching temperature + 5) ° C. is more preferable. Here, Tg represents the glass transition temperature (unit: ° C.) of the cellulose acylate film before heat treatment.
By carrying out the redrawing, it is considered that the oriented amorphous part can be reduced without largely moving the crystalline part. Therefore, ΔRe can be reduced. Such re-stretching is preferably re-stretching in a direction orthogonal to the stretching direction in the stretching step, from the viewpoint of efficiently reducing the oriented amorphous portion, and generally in the transverse direction in the width direction. More preferably.

  The re-stretching may be performed after the cellulose acylate film is cooled to a temperature lower than Tc after the heat treatment, or may be performed without being cooled while maintaining the heat treatment temperature.

  As the re-stretching method, the method described in the explanation of the stretching during the heat treatment can be employed. Re-stretching may be performed in one stage or in multiple stages. Preferable are a method of stretching in the transport direction by changing the rotational speed of the nip roll and a method of stretching by gripping both ends of the polymer film with tenter clips and spreading them in a direction perpendicular to the transport direction. Particularly preferred is a mode in which after stretching the film is re-stretched by holding both ends of the polymer film with a tenter clip and spreading it in a direction perpendicular to the conveying direction.

  The draw ratio of redrawing can be appropriately set according to the retardation required for the cellulose acylate film, preferably 1 to 500%, more preferably 3 to 400%, still more preferably 5 to 300%, and more preferably 10 to 100%. % Is particularly preferred. The redrawing speed is preferably 10 to 10000% / min, more preferably 20 to 1000% / min, and further preferably 30 to 800% / min.

By performing re-stretching after the stretching, Re and Rth of the obtained transparent film can be adjusted. For example, by increasing the stretching temperature for re-stretching, Rth can be lowered without changing Re much. Moreover, Re can be reduced and Rth can be increased by increasing the draw ratio of re-stretching. Since these show a substantially linear correlation, it becomes easy to achieve the intended Re and Rth by appropriately selecting the stretching conditions for re-stretching.
After the heat treatment is finished, Re and Rth of the cellulose acylate film in a state before re-stretching are not particularly limited.

《Cellulose acylate film》
(Characteristics of the cellulose acylate film of the present invention)
According to the production method of the present invention described above, it is possible to obtain a cellulose acylate film having improved ease of cracking and galvanized film-like wrinkles, and | Rth | / Re of 0.4 to 0.6.

(Retardation)
In this specification, Re and Rth (unit: nm) are determined according to the following method. First, the film was conditioned at 25 ° C. and 60% relative humidity for 24 hours, and then a prism coupler (MODEL2010 Prism Coupler: manufactured by Metricon) was used. At 25 ° C. and 60% relative humidity, the following formula was used: The average refractive index (n) represented by (2) is obtained.
Formula (2): n = (n _TE × 2 + n _TM ) / 3
[ _Where n _TE is a refractive index measured with polarized light in the film plane direction, and n _TM is a refractive index measured with polarized light in the film surface normal direction. ]

In this specification, Re (λnm) and Rth (λnm) represent in-plane retardation and retardation in the thickness direction at a wavelength λ (unit: nm), respectively. Re (λnm) is measured by making light having a wavelength of λnm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λnm) is calculated by the following method.
Rth (λnm) is Re (λnm), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) (if there is no slow axis, any in-plane film The light is incident at a wavelength of λ nm in 10 ° steps from the normal direction to 50 ° on one side with respect to the normal direction of the film (with the direction of the rotation axis as the rotation axis), and a total of 6 points are measured. KOBRA 21ADH or WR calculates based on the measured retardation value, average refractive index, and input film thickness value.
In the above, there is no description about λ, and when only Re and Rth are described, it represents a value measured using light having a wavelength of 590 nm. In addition, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the slow axis in the plane from the normal direction as the rotation axis, the retardation value at a tilt angle larger than the tilt angle is After changing the sign to negative, KOBRA 21ADH or WR calculates.
In addition, the retardation value is measured from two arbitrary inclined directions with the slow axis as the tilt axis (rotation axis) (in the case where there is no slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the average refractive index, and the input film thickness value, Rth can also be calculated from the following equations (3) and (4).

Formula (3)

［式中、Ｒｅ（θ）は法線方向から角度θ傾斜した方向におけるレタ−デーション値を表す。また、ｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘおよびｎｙに直交する厚み方向の屈折率を表し、ｄはフィルムの膜厚を表す。］
式（４）： Ｒｔｈ＝(（ｎｘ＋ｎｙ）／２−ｎｚ)×ｄ
測定されるフィルムが一軸や二軸の屈折率楕円体で表現できないもの、いわゆる光学軸（ｏｐｔｉｃ ａｘｉｓ）がないフィルムの場合には、以下の方法によりＲｔｈ（λｎｍ）は算出される。
Ｒｔｈ（λｎｍ）は前記Ｒｅ（λｎｍ）を、面内の遅相軸（ＫＯＢＲＡ ２１ＡＤＨまたはＷＲにより判断される）を傾斜軸（回転軸）としてフィルム法線方向に対して−５０度から＋５０度まで１０度ステップで各々その傾斜した方向から波長λｎｍの光を入射させて１１点測定し、その測定されたレタデーション値と平均屈折率および入力された膜厚値を基にＫＯＢＲＡ ２１ＡＤＨまたはＷＲが算出する。これら平均屈折率と膜厚を入力することで、ＫＯＢＲＡ ２１ＡＤＨまたはＷＲはｎｘ、ｎｙ、ｎｚを算出する。この算出されたｎｘ、ｎｙ、ｎｚよりＮｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）がさらに算出される。

[In the formula, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. Further, nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, nz represents the refractive index in the thickness direction perpendicular to nx and ny, and d Represents the film thickness of the film. ]
Formula (4): Rth = ((nx + ny) / 2−nz) × d
When the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film without a so-called optical axis, Rth (λnm) is calculated by the following method.
Rth (λnm) is from -50 degrees to +50 degrees with respect to the normal direction of the film, with Re (λnm) being the slow axis (indicated by KOBRA 21ADH or WR) as the tilt axis (rotation axis). In 11 degrees, light of wavelength λ nm is incident from each inclined direction and measured at 11 points, and KOBRA 21ADH or WR is calculated based on the measured retardation value, average refractive index, and input film thickness value. . By inputting these average refractive index and film thickness, KOBRA 21ADH or WR calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

The cellulose acylate film used in the production method of the present invention satisfies the following formula (II).
Formula (II): 0.4 ≦ | Rth | /Re≦0.6
Moreover, it is preferable that the cellulose acylate film used in the production method of the present invention satisfies the following formula (IIa).
Formula (IIa): 0.43 ≦ | Rth | /Re≦0.57
Furthermore, the cellulose acylate film used in the production method of the present invention more preferably satisfies the following formula (IIa).
Formula (IIb): 0.46 ≦ | Rth | /Re≦0.54

  In the cellulose acylate film produced by the production method of the present invention, the Re is preferably 50 nm or more. Moreover, Re of the cellulose acylate film of the present invention is more preferably 60 to 400 nm, and further preferably 80 to 300 nm.

(Humidity dependency)
In the present invention, the humidity dependence (ΔRe) of Re and the humidity dependence (ΔRth) of Rth are the retardation values in the in-plane direction and the film thickness direction when the relative humidity is H (unit:%): Re (H %) And Rth (H%) based on the following formula.
ΔRe = Re (10%) − Re (80%)
ΔRth = Rth (10%) − Rth (80%)
Re (H%) and Rth (H%) are relative humidity H% in the same manner as described above at 25 ° C. and relative humidity H% after conditioning the film for 24 hours at 25 ° C. and relative humidity H%. The retardation value when the measurement wavelength is 590 nm is measured and calculated. In addition, when only Re is described without specifying the relative humidity, it is a value measured at a relative humidity of 60%.
The retardation value when the humidity of the cellulose acylate film of the present invention is changed preferably satisfies the following relational expression.
| ΔRe / Re | <0.5, and
| ΔRth | <50
It is more preferable to satisfy the following relational expression.
| ΔRe / Re | <0.3, and
| ΔRth | <40
It is more preferable to satisfy the following relational expression.
| ΔRe / Re | <0.2 and
| ΔRth | <30

Moreover, it is preferable that the retardation value at the time of changing the humidity of the cellulose acylate film of the present invention also satisfies the following relational expression.
| ΔRe | <50
It is more preferable to satisfy the following relational expression.
| ΔRe | <40
It is more preferable to satisfy the following relational expression.
| ΔRe | <30
It is most preferable that the following relational expression is satisfied.
| ΔRe | <20
By controlling the retardation value when the humidity is changed, the retardation change when the external environment changes can be reduced, and a highly reliable liquid crystal display device can be provided.

(Slow axis)
In the cellulose acylate film of the present invention, the angle θ formed between the transport direction during production and the slow axis of Re of the film is preferably 0 ± 10 ° or 90 ± 10 °, and preferably 0 ± 5 ° or 90 ±. 5 ° is more preferable, 0 ± 3 ° or 90 ± 3 ° is further preferable, and in some cases, 0 ± 1 ° or 90 ± 1 ° is preferable, and 90 ± 1 ° is preferable. Is most preferred.

(Tear strength)
In the present invention, the tear strength (Elmendorf tear method) is determined by cutting out a sample of 64 mm × 50 mm, with the direction parallel to the slow axis of the film and the direction perpendicular thereto as the longitudinal direction, respectively, at 25 ° C. and 60% relative humidity After adjusting the humidity for 2 hours, it was measured using a light load tear strength tester, and the smaller value was taken as the tear strength of the film.
The tear strength of the cellulose acylate film of the present invention is preferably 5 g or more, more preferably 8 to 50 g, still more preferably 10 to 40 g, and particularly preferably 12 to 30 g.

(Wavy height)
In the present invention, the wavy height refers to the height of a wavy ridge (distance from the base to the film) due to poor flatness by placing a sample cut out on a horizontal and smooth base by cutting the film into 30 cm × 30 cm. ) Was measured using a vernier caliper, and the maximum value was the wave height of the film.
The wavy height of the cellulose acylate film of the present invention is 0 to 5 mm, preferably 0 to 3 mm, and more preferably 0 to 2 mm.

(Haze)
In the present invention, the haze of the cellulose acylate film was measured using a haze meter (NDH 2000: manufactured by Nippon Denshoku Industries Co., Ltd.) after conditioning the film for 24 hours at 25 ° C. and a relative humidity of 60%.
In the present invention, the haze of the cellulose acylate film after heat treatment is preferably small, preferably 1.0% or less, more preferably 0.7% or less, further preferably 0.5% or less, and 0.3% or less. Most preferred.
In the present invention, the haze of the cellulose acylate film after pre-stretching and before heat treatment is preferably 0.5 to 20%, more preferably 1.0 to 10%, and more preferably 1.5 to More preferably, it is 6.0%. If the haze before the heat treatment is less than 0.5%, retardation developability tends to decrease, and if it exceeds 20%, the film tends to become brittle.

(Film thickness)
The film thickness of the cellulose acylate film of the present invention is preferably 20 μm to 180 μm, more preferably 30 μm to 160 μm, and still more preferably 40 μm to 120 μm. A film thickness of 20 μm or more is preferable from the viewpoint of handling properties when processing into a polarizing plate and curling of the polarizing plate. Further, the film thickness unevenness of the cellulose acylate film of the present invention is preferably 0 to 2% in both the transport direction and the width direction, more preferably 0 to 1.5%, and 0 to 1%. Is particularly preferred.

(Moisture permeability)
The moisture permeability of the cellulose acylate film of the present invention is preferably 100 g / (m ² · day) or more in terms of 80 μm. By using a film having a moisture permeability of 100 μm / (m ² · day) or more in terms of 80 μm, it becomes easy to bond directly to the polarizing film. The moisture permeability of the 80μm ^{terms, 100~1500g / (m 2 · day} ) , more ^{preferably, 200~1000g / (m 2 · day} ) , and even more preferably 300~800g / (m ² · day) .
Further, when the cellulose acylate film of the present invention is used as an outer protective film that is not disposed between the polarizing film and the liquid crystal cell as described later, the moisture permeability of the cellulose acylate film of the present invention is 500 g / in terms of 80 μm. preferably (m ² · day) is less ^{than, 100~450g / (m 2 · day} ) , more ^{preferably, 100~400g / (m 2 · day} ) are more preferred, 150~300g / (m ² · day ) Is most preferred. By doing in this way, durability of the polarizing plate with respect to humidity or wet heat improves, and a highly reliable liquid crystal display device can be provided.

(Configuration of cellulose acylate film)
The cellulose acylate film of the present invention may have a single layer structure or a plurality of layers, but preferably has a single layer structure. Here, the “single layer structure” film does not mean that a plurality of film materials are bonded together, but means a single polymer film. And it includes the case where a single polymer film is produced from a plurality of cellulose acylate solutions using a sequential casting method or a co-casting method. In this case, a polymer film having a distribution in the thickness direction can be obtained by appropriately adjusting the type and blending amount of the additive, the molecular weight distribution of the polymer, the type of polymer, and the like. Moreover, what has various functional parts, such as an optical anisotropy part, a glare-proof part, a gas barrier part, and a moisture-resistant part, in those one film is also included.

(surface treatment)
The cellulose acylate film of the present invention can be appropriately surface-treated to improve adhesion with each functional layer (for example, an undercoat layer, a back layer, and an optically anisotropic layer). 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” here is a treatment for subjecting the film surface to a plasma treatment in the presence of a plasma-excitable gas. The details of these surface treatment methods are described in the Japan Institute of Invention Disclosure Technical Bulletin (Public Technical No. 2001-1745, issued on March 15, 2001, Japan Institute of Invention) and can be used as appropriate.

  In order to improve the adhesion between the film surface and the functional layer, an undercoat layer (adhesive layer) may be provided on the cellulose acylate film of the present invention in addition to or in place of the surface treatment. About the said undercoat, it describes in an invention association public technical bulletin (public technical number 2001-1745, March 15, 2001 issue, invention association) 32 pages, These can be used suitably. In addition, the functional layer provided on the cellulose acylate film is described in Invention Technical Disclosure Bulletin (Public Technical No. 2001-1745, published on March 15, 2001, Invention Association), pages 32 to 45. Those described in (2) can be appropriately used on the cellulose acylate film of the present invention.

<Phase difference film>
The cellulose acylate film of the present invention can be used as a retardation film. The “retardation film” is generally used for a display device such as a liquid crystal display device, and means an optical material having optical anisotropy, and is synonymous with a retardation plate, an optical compensation film, an optical compensation sheet, and the like. It is. In a liquid crystal display device, a retardation film is used for the purpose of improving the contrast of a display screen or improving viewing angle characteristics and color.
By using the cellulose acylate film of the present invention, a retardation film in which the Re value and the Rth value are freely controlled can be easily produced.

  In addition, a plurality of the cellulose acylate films of the present invention are laminated, or the cellulose acylate film of the present invention and a film other than the present invention are laminated, and Re and Rth are appropriately adjusted and used as a retardation film. You can also. Lamination of the film can be performed using a pressure-sensitive adhesive or an adhesive.

In some cases, the cellulose acylate film of the present invention may be used as a support for a retardation film, and an optically anisotropic layer made of liquid crystal or the like may be provided thereon to be used as a retardation film. The optically anisotropic layer applied to the retardation film of the present invention may be formed from, for example, a composition containing a liquid crystal compound, a polymer film having birefringence, You may form from the cellulose acylate film of invention.
The liquid crystal compound is preferably a discotic liquid crystal compound or a rod-like liquid crystal compound.

[Discotic liquid crystalline compounds]
Examples of the discotic liquid crystal compound that can be used as the liquid crystal compound in the present invention include various documents (for example, C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 ( 1981); edited by The Chemical Society of Japan, Quarterly Review, No. 22, Chemistry of Liquid Crystal, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. , Page 1794 (1985); J. Zhang et al., J. Am. Chem. Soc., Vol. 116, page 2655 (1994)).

  In the optically anisotropic layer, the discotic liquid crystalline molecules are preferably fixed in an aligned state, and most preferably fixed by a polymerization reaction. Further, the polymerization of discotic liquid crystalline molecules is described in JP-A-8-27284. In order to fix the discotic liquid crystalline molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline molecules. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Discotic liquid crystalline molecules having a polymerizable group are disclosed in JP-A No. 2001-4387.

[Bar-shaped liquid crystalline compound]
Examples of the rod-like liquid crystalline compound that can be used as the liquid crystalline compound in the present invention include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane. , Cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles. Further, as the rod-like liquid crystal compound, not only the above low molecular liquid crystal compound but also a polymer liquid crystal compound can be used.

  In the optically anisotropic layer, the rod-like liquid crystalline molecules are preferably fixed in an aligned state, and most preferably fixed by a polymerization reaction. Examples of polymerizable rod-like liquid crystalline compounds that can be used in the present invention are described in, for example, Makromol. Chem. 190, 2255 (1989), Advanced Materials 5, 107 (1993), U.S. Pat. Nos. 4,683,327, 5,622,648, 5,770, No. 107 specification, International Publication No. 95/22586 pamphlet, No. 95/24455 pamphlet, No. 97/00600 pamphlet, No. 98/23580 pamphlet, No. 98/52905 pamphlet, JP-A-1-272551, The compounds described in JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, JP-A-2001-328773, and the like are included.

"Polarizer"
The cellulose acylate film or retardation film of the present invention can be used as a protective film for a polarizing plate (the polarizing plate of the present invention). The polarizing plate of the present invention comprises a polarizing film and two polarizing plate protective films (cellulose acylate film) protecting both surfaces thereof, and the cellulose acylate film or retardation film of the present invention is at least one polarizing plate protective film. Can be used as
When the cellulose acylate film of the present invention is used as the polarizing plate protective film, the cellulose acylate film of the present invention is subjected to the surface treatment (also described in JP-A-6-94915 and JP-A-6-118232). For example, glow discharge treatment, corona discharge treatment, or alkali saponification treatment is preferably performed. As the surface treatment, alkali saponification treatment is most preferably used.

  As the polarizing film, for example, a film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution can be used. When using a polarizing film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution, the surface-treated surface of the cellulose acylate film of the present invention can be directly bonded to both surfaces of the polarizing film using an adhesive. In the production method of the present invention, it is preferable that the cellulose acylate film is directly bonded to the polarizing film as described above. As the adhesive, an aqueous solution of polyvinyl alcohol or polyvinyl acetal (for example, polyvinyl butyral) or a latex of vinyl polymer (for example, polybutyl acrylate) can be used. A particularly preferred adhesive is an aqueous solution of fully saponified polyvinyl alcohol.

  In general, a liquid crystal display device includes four polarizing plate protective films because a liquid crystal cell is provided between two polarizing plates. The cellulose acylate film of the present invention may be used for any of the four polarizing plate protective films, but the cellulose acylate film of the present invention is provided between the polarizing film and the liquid crystal layer (liquid crystal cell) in the liquid crystal display device. It can be used particularly advantageously as a protective film disposed on the substrate. Further, the protective film disposed on the opposite side of the cellulose acylate film of the present invention across the polarizing film can be provided with a transparent hard coat layer, an antiglare layer, an antireflection layer, and the like, particularly a liquid crystal display device. It is preferably used as a polarizing plate protective film on the outermost surface of the display side.

<Liquid crystal display device>
The cellulose acylate film, retardation film and polarizing plate of the present invention can be used for liquid crystal display devices in various display modes. Each liquid crystal mode in which these films are used will be described below. Among these modes, the cellulose acylate film, retardation film and polarizing plate of the present invention are particularly preferably used for VA mode and IPS mode liquid crystal display devices. These liquid crystal display devices may be any of a transmissive type, a reflective type, and a transflective type.

(TN type liquid crystal display device)
The cellulose acylate film of the present invention may be used as a support for a retardation film of a TN type liquid crystal display device having a TN mode liquid crystal cell. TN mode liquid crystal cells and TN type liquid crystal display devices have been well known for a long time. Regarding the retardation film used in the TN type liquid crystal display device, each of JP-A-3-9325, JP-A-6-148429, JP-A-8-50206, and JP-A-9-26572, and Mori. It is described in other papers (Jpn. J. Appl. Phys. Vol. 36 (1997) p. 143 and Jpn. J. Appl. Phys. Vol. 36 (1997) p. 1068).

(STN type liquid crystal display device)
The cellulose acylate film of the present invention may be used as a support for a retardation film of an STN type liquid crystal display device having an STN mode liquid crystal cell. In general, in a STN type liquid crystal display device, rod-like liquid crystalline molecules in a liquid crystal cell are twisted in the range of 90 to 360 degrees, and the refractive index anisotropy (Δn) and cell gap (d) of the rod-like liquid crystalline molecules. Product (Δnd) is in the range of 300 to 1500 nm. The retardation film used in the STN type liquid crystal display device is described in JP-A No. 2000-105316.

(VA type liquid crystal display device)
The cellulose acylate film of the present invention is particularly advantageously used as a retardation film or a support for a retardation film in a VA liquid crystal display device having a VA mode liquid crystal cell. The VA-type liquid crystal display device may be an alignment-divided system as described in, for example, JP-A-10-123576. In these embodiments, the polarizing plate using the cellulose acylate film of the present invention contributes to widening the viewing angle and improving the contrast.

(IPS liquid crystal display device and ECB liquid crystal display device)
The cellulose acylate film of the present invention is particularly used as a retardation film or a support for a retardation film of an IPS liquid crystal display device and an ECB liquid crystal display device having IPS mode and ECB mode liquid crystal cells, or as a protective film for a polarizing plate. It is advantageously used. In these modes, the liquid crystal material is aligned substantially in parallel during black display, and black is displayed by aligning liquid crystal molecules parallel to the substrate surface in the absence of voltage. In these embodiments, the polarizing plate using the cellulose acylate film of the present invention contributes to widening the viewing angle and improving the contrast.

(OCB type liquid crystal display device and HAN type liquid crystal display device)
The cellulose acylate film of the present invention is also advantageously used as a support for a retardation film of an OCB type liquid crystal display device having an OCB mode liquid crystal cell or a HAN type liquid crystal display device having a HAN mode liquid crystal cell. In the retardation film used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, it is preferable that the direction in which the absolute value of the retardation is minimum does not exist in the plane of the retardation film or in the normal direction. The optical properties of the retardation film used in the OCB type liquid crystal display device or the HAN type liquid crystal display device are the same as the optical properties of the optical anisotropic layer, the optical properties of the support, and the optical anisotropic layer and the support. Is determined by the arrangement of A retardation film used for an OCB type liquid crystal display device or a HAN type liquid crystal display device is described in JP-A-9-197397. Further, it is described in a paper by Mori et al. (Jpn. J. Appl. Phys. Vol. 38 (1999) p. 2837).

(Reflective liquid crystal display)
The cellulose acylate film of the present invention is also advantageously used as a retardation film of a TN type, STN type, HAN type, GH (Guest-Host) type reflective liquid crystal display device. These display modes have been well known since ancient times. The TN type reflective liquid crystal display device is described in JP-A-10-123478, WO98 / 48320 pamphlet, and Japanese Patent No. 3022477. The retardation film used in the reflective liquid crystal display device is described in International Publication No. 00/65384 pamphlet.

(Other liquid crystal display devices)
The cellulose acylate film of the present invention is also advantageously used as a support for a retardation film of an ASM type liquid crystal display device having a liquid crystal cell in an ASM (axially aligned microcell) mode. The ASM mode liquid crystal cell is characterized in that the thickness of the cell is maintained by a resin spacer whose position can be adjusted. Other properties are the same as those of the TN mode liquid crystal cell. The ASM mode liquid crystal cell and the ASM type liquid crystal display device are described in a paper by Kume et al. (Kume et al., SID 98 Digest 1089 (1998)).

(Hard coat film, antiglare film, antireflection film)
In some cases, the cellulose acylate film of the present invention may be applied to a hard coat film, an antiglare film, and an antireflection film. For the purpose of improving the visibility of flat panel displays such as LCD, PDP, CRT, EL, etc., any or all of a hard coat layer, an antiglare layer and an antireflection layer are provided on one or both sides of the cellulose acylate film of the present invention. Can be granted. Preferred embodiments of such an antiglare film and antireflection film are described in detail on pages 54 to 57 of the Japan Institute of Invention and Technology (Publication No. 2001-1745, published on March 15, 2001, Japan Society of Invention). It can be preferably used also in the cellulose acylate film of the present invention.

  The features of the present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

"1" assay First, methods of measuring and evaluating the characteristics below.

[Glass transition point (Tg)]
20 mg of cellulose acylate film before heat treatment was placed in a DSC measurement pan, and this was heated from 30 ° C. to 120 ° C. at 10 ° C./min in a nitrogen stream and held for 15 minutes, and then −20 ° C./30° C. Cooled in minutes. Thereafter, the temperature was raised again from 30 ° C. to 250 ° C., and the temperature at which the baseline began to deviate from the low temperature side was taken as the glass transition point of the film.

[Melting point (Tm ₀ )]
20 mg of cellulose acylate film before heat treatment was placed in a DSC measurement pan, and this was heated from 30 ° C. to 120 ° C. at 10 ° C./min in a nitrogen stream and held for 15 minutes, and then −20 ° C./30° C. Cooled in minutes. Then, the temperature at the top of the endothermic peak that appeared when the temperature was raised again from 30 ° C. to 300 ° C. was taken as the melting point of the film.

[Crystallization temperature (Tc)]
20 mg of a cellulose acylate film before heat treatment was put in a DSC measurement pan, and this was heated from 30 ° C. to 120 ° C. at 10 ° C./min in a nitrogen stream, held for 15 minutes, and then kept at −20 ° C./30° C. After cooling in minutes, the starting temperature of the exothermic peak that appeared when the temperature was raised again from 30 ° C. to 300 ° C. was taken as the crystallization temperature of the film.

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

[Tear strength]
With the direction parallel to the slow axis of the film and the direction perpendicular to the longitudinal direction as the longitudinal direction, a sample of 64 mm × 50 mm was cut from each film, and the value evaluated according to the above-mentioned method was taken as the tear strength.

[Wavy height]
The film was cut into 30 cm × 30 cm, conditioned for 24 hours at 25 ° C. and 60% relative humidity, and the value evaluated according to the above-mentioned method was taken as the undulation height.

[Retardation]
5 points in the width direction of the film (the central part and the end part of the film (positions at 5% of the total width from both ends) and the middle part of the center part and the end part) are sampled every 100 m in the longitudinal direction. Samples with a size of □ were taken out, the average value of each point evaluated according to the above-described method was calculated, and Re, Rth, ΔRe, ΔRth, and the direction of the in-plane slow axis were obtained.

[Haze]
The same sampling as that at the time of retardation measurement was performed, the sample was conditioned at 25 ° C. and 60% relative humidity for 24 hours, and then measured using a haze meter (NDH 2000: manufactured by Nippon Denshoku Industries Co., Ltd.). The haze.

[Degree of polarization]
The transmittance (Tp) when the produced two polarizing plates are superposed in parallel with the absorption axis and the transmissivity (Tc ′) when the absorption axes are superposed with each other perpendicular to each other are measured. (P) was calculated.
Polarization degree P = ((Tp−Tc ′) / (Tp + Tc ′)) ^0.5

<< 2 >> 150 g of cellulose acetate propionate synthetic cellulose (hardwood pulp) and 75 g of acetic acid were placed in a 5 L separable flask equipped with a reflux apparatus as a reaction vessel and heated in an oil bath adjusted to 60 ° C., Stir vigorously for 2 hours. The cellulose subjected to such pretreatment was swollen and crushed to form a fluff shape. The reaction vessel was placed in an ice water bath at 2 ° C. for 30 minutes and cooled.
Separately, a mixture of 1545 g of propionic acid anhydride and 10.5 g of sulfuric acid was prepared as an acylating agent, cooled to −30 ° C., and then added to the reaction vessel containing the above-treated cellulose at once. After 30 minutes, the external temperature was gradually increased, and the internal temperature was adjusted to 25 ° C. after 2 hours from the addition of the acylating agent. The reaction vessel was cooled in an ice water bath at 5 ° C., the internal temperature was adjusted to 10 ° C. 0.5 hours after addition of the acylating agent, and the internal temperature was 23 ° C. after 2 hours, and the internal temperature was 23 ° C. The mixture was further stirred for 3 hours. The reaction vessel was cooled in an ice water bath at 5 ° C., and 120 g of 25% by mass hydrous acetic acid cooled to 5 ° C. was added over 1 hour. The internal temperature was raised to 40 ° C. and stirred for 1.5 hours. Next, a solution obtained by dissolving magnesium acetate tetrahydrate in 2-fold mol of sulfuric acid in 50% by mass aqueous acetic acid was added to the reaction vessel, and the mixture was stirred for 30 minutes. Cellulose acetate propionate was precipitated by adding 1 L of 25% by mass hydrous acetic acid, 500 mL of 33% by mass hydrous acetic acid, 1 L of 50% by mass hydrous acetic acid and 1 L of water in this order. The obtained cellulose acetate propionate precipitate was washed with warm water. By changing the washing conditions at this time, cellulose acetate propionate in which the amount of residual sulfate radicals is changed can be obtained. The sulfate radical content can be measured according to ASTM D-817-96. After washing, the mixture was stirred in a 0.005 mass% calcium hydroxide aqueous solution at 20 ° C. for 0.5 hour, further washed with water until the pH of the washing solution became 7, and then vacuum dried at 70 ° C.
According to ¹ H-NMR and GPC measurement, the obtained cellulose acetate propionate had an acetylation degree of 0.30, a propionylation degree of 2.63, and a polymerization degree of 320.
Other cellulose acylates that can be used in the present invention were produced by the same method.

<< 3 >> Manufacture and evaluation of cellulose acylate film (preparation of polymer solution)
1) Cellulose acylate Among the following cellulose acylates A to D, those listed in Table 1 were selected and used. Each cellulose acylate was heated to 120 ° C. and dried to adjust the water content to 0.5% by mass or less, and then 20 parts by mass was used.
Cellulose acylate A:
A cellulose acetate powder having a substitution degree of 2.94 was used. Cellulose acylate A had a viscosity average degree of polymerization of 300 and a 6-position acetyl group substitution degree of 0.94.
Cellulose acylate B:
A cellulose acetate propionate powder having an acetyl substitution degree of 2.28 and a propionyl substitution degree of 0.70 was used. Cellulose acylate B had a viscosity average polymerization degree of 280.
Cellulose acylate C:
A cellulose acetate powder having a substitution degree of 2.86 was used. Cellulose acylate C has a viscosity average degree of polymerization of 300, an acetyl group substitution degree at the 6-position of 0.89, an acetone extract of 7% by mass, a mass average molecular weight / number average molecular weight ratio of 2.3, and a water content of 0.3. Viscosity in 2 mass% and 6 mass% dichloromethane solutions is 305 mPa · s, residual acetic acid content is 0.1 mass% or less, Ca content is 65 ppm, Mg content is 26 ppm, iron content is 0.8 ppm, sulfate ion The content was 18 ppm, the yellow index was 1.9, and the amount of free acetic acid was 47 ppm. The average particle size of the powder was 1.5 mm, and the standard deviation was 0.5 mm.
Cellulose acylate D:
A cellulose acetate powder having a substitution degree of 2.70 was used. Cellulose acylate D had a viscosity average degree of polymerization of 250 and a 6-position acetyl group substitution degree of 0.84.

2) Solvent The following solvent A or B was used. The water content of each solvent was 0.2% by mass or less.
・ Solvent A
Dichloromethane / methanol = 90/10 parts by mass / solvent B
Dichloromethane / methanol / butanol = 83/15/2 parts by mass

3) Additives The additives listed in Table 1 were selected from the following additives A or B and used.
・ Additive A
Silicon dioxide fine particles (particle size 20 nm, Mohs hardness about 7) (0.08 parts by mass)
・ Additive B
PP-30 (2.4 parts by mass)
Silicon dioxide fine particles (particle size 20 nm, Mohs hardness about 7) (0.08 parts by mass)

4) Dissolution In each of the examples and comparative examples, swelling and dissolution were carried out by selecting and using those described in Table 1 from the following dissolution steps A or B.
・ Dissolution process A
The cellulose acylate was gradually added to the 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery, while stirring and dispersing the solvent and additive. 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 the 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 [4.9 × 10 ⁵ N / m / sec ² ]). And an agitation shaft having an anchor blade on the central axis and stirring at a peripheral speed of 1 m / sec (shear stress 1 × 10 ⁴ kgf / m / sec ² [9.8 × 10 ⁴ N / m / sec ² ]) It was. 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.
The swollen solution was heated from a tank to 50 ° C. with a jacketed pipe, and further heated to 90 ° C. under a pressure of 2 MPa to completely dissolve. The heating time was 15 minutes. At this time, filters, housings, and pipes that were exposed to high temperature were made of Hastelloy alloy and had excellent corrosion resistance, and those having a jacket for circulating a heat medium for heat retention and heating were used.
Next, the temperature was lowered to 36 ° C. to obtain a cellulose acylate solution.
・ Dissolution process B
The cellulose acylate was gradually added to the 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery, while stirring and dispersing the solvent and additive. 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 mixture.
For the 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 [4.9 × 10 ⁵ N / m / sec ² ]). And an agitation shaft having an anchor blade on the central axis and stirring at a peripheral speed of 1 m / sec (shear stress 1 × 10 ⁴ kgf / m / sec ² [9.8 × 10 ⁴ N / m / sec ² ]) It was. 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.
The swollen mixture was fed from a tank by a screw pump whose center part was heated to 30 ° C., cooled from the outer periphery of the screw, and passed through the cooling part at −70 ° C. for 3 minutes. Cooling was performed using a -75 ° C refrigerant cooled by a refrigerator. The mixture obtained by cooling was heated to 30 ° C. in the liquid feed column with a screw pump and transferred to a stainless steel container.
Next, it stirred at 30 degreeC for 2 hours, and obtained the cellulose acylate solution.

5) Filtration The obtained cellulose acylate solution was filtered with a filter paper (# 63, manufactured by Toyo Roshi Kaisha, Ltd.) having an absolute filtration accuracy of 10 μm, and further a sintered metal filter (FH025, Pole Corporation) having an absolute filtration accuracy of 2.5 μm. To obtain a polymer solution.

(Production of film)
The one described in Table 1 was selected from the following film forming steps A or B and used.
・ Film formation process A
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 50 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, the film was dried at 110 ° C. for 5 minutes and further at 140 ° C. for 10 minutes to obtain a transparent film of cellulose acylate having a thickness of 80 μm.
・ Film forming process B
The polymer solution was heated to 30 ° C., and cast on a mirror surface stainless steel support, which was a drum having a diameter of 3 m, through a casting Giuser. The temperature of the support was set to −5 ° C., the casting speed was 100 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 which had been cast and rotated 50 cm before the end point of the casting part was peeled off from the drum, and both ends were clipped with a pin tenter. The cellulose acylate film held by the pin tenter was conveyed to the drying zone. In the initial drying, a drying air of 45 ° C. was blown. Next, it was dried at 110 ° C. for 5 minutes and further at 140 ° C. for 10 minutes to obtain a transparent film of cellulose acylate having a thickness of 80 μm.

(Stretching)
Selected from the following stretching steps A or B and listed in Table 1.

・ Extension process A
The resulting film was heat treated using an apparatus having a heating zone between two nip rolls. The distance between nip rolls is adjusted so that the aspect ratio (distance between nip rolls / base inlet width) is the value shown in Table 1, the base temperature before entering the heating zone is 25 ° C., and the heating zone is as shown in Table 1. It was temperature. The speed ratio (v ₁₁ / v ₁₀ ) between the speed of the feeding nip roll (v ₁₀ ) and the speed of the take-up nip roll (v ₁₁ ) was the value shown in Table 1. The dimensional change rate in the width direction obtained according to the above-described method is shown in Table 1.

・ Extension process B
After gripping both ends of the obtained film with a tenter clip of a simultaneous biaxial stretching machine shown in FIG. 1, the film was stretched by the magnification described in Table 1 in the transport direction. The temperature in the stretching zone was the temperature shown in Table 1.

(Evaluation of manufactured cellulose acylate film)
Each obtained cellulose acylate film was evaluated. The results are shown in Table 1 below.

As shown in Table 1, in the cellulose acylate film produced according to the production method of the present invention, | Rth | / Re is appropriately adjusted, it is difficult to break, there is no tin plate-like wrinkle, and the flatness is excellent. Was low. In addition, the film of the present invention has a small humidity dependency of Re. In addition, according to the manufacturing method of the present invention, the shrinkage rate in the width direction in the manufacturing process is suppressed, so that a wide product width can be secured.
On the other hand, the cellulose acylate film produced according to the production method other than the present invention had an inadequate | Rth | / Re, the film was liable to break, or the tin plate-like wrinkles were severe. Further, the film of Comparative Example 104 was severely colored during stretching and was crushed in the tenter.
In all Examples and Comparative Examples, the direction in which the sound wave propagation speed (sound speed) of the film after the film forming process and before the stretching process was maximized was substantially the same as the film transport direction. The sound speed ratio was 1.01 to 1.02 in Examples 101 to 114, Examples 117 to 119, and Comparative Examples 101 to 106, and 1.35 to 1.45 in Examples 115 to 116. It was.

<< 4 >> Preparation and evaluation of polarizing plate (Preparation of polarizing plate)
1) Saponification of Film Each film prepared in Examples and Comparative Examples and Fujitac TF80UL (manufactured by FUJIFILM Corporation: hereinafter referred to as “Tack A”) were adjusted to 55 ° C. with a 1.5 mol / L NaOH aqueous solution (saponification). The film was washed with water for 2 minutes, then immersed in a 0.05 mol / L sulfuric acid aqueous solution for 30 seconds, and then passed through a washing bath. Then, draining with an air knife was repeated three times, and after dropping the water, the film was retained in a drying zone at 70 ° C. for 15 seconds and dried to produce a saponified film.

2) Production of Polarizing Film According to Example 1 of Japanese Patent Application Laid-Open No. 2001-141926, a circumferential speed difference was given between two pairs of nip rolls and stretched in the longitudinal direction to prepare a polarizing film having a thickness of 20 μm.

3) Bonding Two films were selected from the polarizing film thus obtained and the saponified film (referred to as film A and film B, respectively, and combinations are described in Table 2 below), and the saponified surface of the film was selected. After being arranged on the polarizing film side and sandwiching the polarizing film between them, the polarizing axis and the longitudinal direction of the film are orthogonal to each other using PVA (manufactured by Kuraray Co., Ltd., PVA-117H) 3% aqueous solution as an adhesive. A polarizing plate was prepared by laminating by roll-to-roll.

(Evaluation of yield)
In the laminating step, when each of the rolls of Examples and Comparative Examples was processed by 50 rolls, when the film A was broken once or twice, it was evaluated as Δ, and the film A was broken three times or more. The case was evaluated as x and the case where there was no breakage of the film A was evaluated as ◯, and is shown in Table 2 below.

(Evaluation of polarizing plate)
1) Initial polarization degree The polarization degree of the polarizing plate was calculated by the method described above. The results are shown in Table 2 below.

2) Time polarization 1
The film A side of the polarizing plate was bonded to a glass plate with an adhesive, and allowed to stand for 500 hours at 60 ° C. and a relative humidity of 95%. The results are shown in Table 2 below.

3) Polarization degree with time 2
The film A side of the polarizing plate was bonded to a glass plate with an adhesive, and allowed to stand for 500 hours under conditions of 90 ° C. and 0% relative humidity, and the degree of polarization after standing (degree of polarization with time) was calculated by the method described above. The results are shown in Table 2 below.

  As shown in Table 2, all the polarizing plates exhibited good performance with a polarization degree of 99.9%.

<< 5 >> Mounting on IPS liquid crystal display Evaluation of polarizing plate in Example 304 in place of polarizing plate incorporated in IPS liquid crystal display (37-inch high-definition liquid crystal television monitor (37Z2000), manufactured by Toshiba Corporation) As a result, it was confirmed that sufficient viewing angle compensation was achieved and good visibility could be secured. On the other hand, when the polarizing plates of Comparative Examples 303 to 305 were incorporated, viewing angle compensation was insufficient.

It is the plane schematic diagram of the tenter which performs simultaneous biaxial stretching in the present invention. FIG. 2 is a schematic side view showing a state before the tenter of FIG. 1 chucks the film. It is the side surface schematic diagram which shows the state after the tenter of FIG. 1 chucked the film.

Explanation of symbols

2 Tenter 3 Film 5, 6 Rail 7, 8 Endless chain 10 Clip 11, 12 Drive sprocket 13, 14 Driven sprocket 16 Direction B Film width direction

Claims (10)

At least the cellulose acylate film is conveyed at a temperature T (unit: ° C) that satisfies the following formula (I) while applying tension in the film conveyance direction between spans of 0.01 to 2 times the film width before stretching. The manufacturing method of the cellulose acylate film characterized by including the process extended | stretched to a direction.
Formula (I): Tc + 10 ≦ T <Tm ₀
[Wherein, Tc represents a crystallization temperature (unit: ° C.) of the cellulose acylate film before stretching, and Tm ₀ represents a melting point (unit: ° C.) of the cellulose acylate film before stretching. ]   2. The method for producing a cellulose acylate film according to claim 1, wherein the film conveyance direction is a direction in which a sound wave propagation speed of the cellulose acylate film before stretching is maximized. 3.   The cellulose acylate formed by the production method including the step of casting the cellulose acylate solution on the support, and peeling the film from the support in a state where the residual solvent amount is 10 to 100% by mass. It is a film, The manufacturing method of the cellulose acylate film of Claim 1 or 2 characterized by the above-mentioned. A cellulose acylate film satisfying the following formula (II) and having a wave height of 0 to 5 mm.
Formula (II): 0.4 ≦ | Rth | /Re≦0.6
[In the formula, Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction. ]   The cellulose acylate film according to claim 4, wherein the tear strength is 5 g or more.   The cellulose acylate film according to claim 4 or 5, wherein a retardation value in an in-plane direction is 50 nm or more.   The cellulose acylate film according to any one of claims 4 to 6, wherein the cellulose acylate film is produced by the production method according to any one of claims 1 to 3.   A retardation film comprising at least one cellulose acylate film according to any one of claims 4 to 7.   A polarizing plate comprising at least one sheet of the cellulose acylate film according to claim 4.   A liquid crystal display comprising at least one of the cellulose acylate film according to any one of claims 4 to 7, the retardation film according to claim 8, or the polarizing plate according to claim 9. apparatus.

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