JP5072385B2 - Transparent polymer film, production method thereof, retardation film using the same, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to a transparent polymer film having optical anisotropy and capable of being directly bonded to a polarizing film, and a method for producing the transparent polymer film, and a retardation film, a polarizing plate and a liquid crystal using the transparent polymer film The present invention relates to a 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 ester film having an appropriate moisture permeability can be directly bonded on-line with the most common polarizing film made of polyvinyl alcohol (PVA) / iodine. For this reason, cellulose acylate, particularly cellulose acetate, has been widely adopted as a protective film for polarizing plates.

  On the other hand, when the transparent polymer film is used for a retardation film, a retardation film support, 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. Along with the recent demand for wide viewing angle of liquid crystal display devices, it is required to improve the compensation of retardation, and the in-plane direction letter of the retardation film disposed between the polarizing film and the liquid crystal cell. It is possible to appropriately control the retardation value (Re; hereinafter simply referred to as “Re”) and the retardation value in the film thickness direction (Rth; hereinafter referred to simply as “Rth”). It is requested. Among these, since a transparent polymer film that exhibits negative Rth and satisfies Rth / Re ≧ −0.39 is not easy to manufacture, it is required to be manufactured easily.

  As a method for producing a transparent polymer film exhibiting negative Rth, a method of forming a vertically aligned liquid crystal layer using an isotropic transparent polymer film as a support is disclosed (for example, see Patent Document 1). The manufacturing process is complicated and the yield of orientation is a problem.

  Further, as a method for producing a transparent polymer film exhibiting negative Rth, a method using a cellulose ester film having a high degree of acetyl substitution is disclosed (for example, see Patent Document 2). According to this method, a film having an appropriate moisture permeability can be obtained, but there are problems that the energy required for dissolving the polymer is large and that Re is not sufficiently developed.

Furthermore, as a method for producing a transparent polymer film exhibiting Rth / Re ≧ −0.5, a continuous production method in which a heat-shrinkable film is bonded to the transparent polymer film and subjected to a heat stretching treatment is disclosed (for example, (See Patent Document 3 and Patent Document 4). However, when this method is carried out, a large amount of heat-shrinkable film is consumed, and the quality of the obtained film varies. This problem was particularly noticeable with polymers having a high elastic modulus such as cellulose esters.
JP-A-6-331826 JP 2005-120352 A JP-A-5-157911 Japanese Patent Laid-Open No. 2000-23310

  An object of the present invention is to provide an optically uniform transparent polymer film having an appropriate moisture permeability, exhibiting negative Rth, exhibiting Rth / Re ≧ −0.39, and a method for producing the same. . In addition, the object of the present invention is to provide a retardation film using the transparent polymer film of the present invention, and to directly polarize the transparent polymer film of the present invention as a retardation film, a support for the retardation film, or a protective film for a polarizing plate. Another object is to provide a polarizing plate that can be bonded to a film and exhibit excellent optical performance. Another object of the present invention is to provide a highly reliable liquid crystal display device using the same.

The above-mentioned problem is solved by the following means.
(1) A method for producing a transparent polymer film, comprising a step of stretching a polymer film having Rth <0 to satisfy ΔRth> 0.
ΔRth = [Rth after stretching] − [Rth before stretching]
[In the formula, Rth represents a retardation value in the film thickness direction (unit: nm). ]
(2) The method for producing a transparent polymer film according to (1), wherein the stretched polymer film has a moisture permeability of 100 g / (m ² · day) or more at 40 ° C. and 90% relative humidity. .
(3) The transparent polymer film according to (1) or (2), wherein the stretching is performed at a cooling temperature or higher after the polymer film is cooled by heat treatment at (Tg + 50) ° C. or higher. Method (where Tg is the glass transition temperature of the polymer film). (4) The method for producing a transparent polymer film according to any one of (1) to (3), wherein the polymer film is a cellulose acylate film.
(5) The method for producing a transparent polymer film according to (4), wherein the stretching is carried out at a cooling temperature or higher after the film is heat-treated at 200 ° C. or higher and cooled.

(6) The method for producing a transparent polymer film according to (3) or (5), wherein a difference between the heat treatment temperature and the stretching temperature is 1 ° C. or more.
(7) The method for producing a transparent polymer film according to (3), (5) or (6), wherein the stretching temperature is lower than the heat treatment temperature.
(8) Any one of (3) or (5) to (7), wherein the heat treatment is a heat treatment performed while heating between two or more apparatuses that hold the film in the transport direction. The manufacturing method of the transparent polymer film of description.
(9) The method for producing a transparent polymer film according to any one of (3) and (5) to (8), wherein the cooling temperature is lower by 50 ° C. or more than the heat treatment temperature.
(10) The method for producing a transparent polymer film according to any one of (3) and (5) to (9), wherein the polymer film before the heat treatment satisfies −1000 ≦ Rth <50.
[In the formula, Rth represents a retardation value in the film thickness direction (unit: nm). ]
(11) The method for producing a transparent polymer film according to any one of (1) to (10), wherein the stretching is tenter stretching.

(12) All the following formulas (I) to (III) are satisfied, and the moisture permeability at 40 ° C. and relative humidity 90% is 100 to 2000 g / (m ² · day), and Rth is increased by 8 nm or more A transparent polymer film characterized by not containing an additive composition.
Formula (I): Rth / Re ≧ −0.39
Formula (II): Re> 0
Formula (III): Rth <0
[In the formula, Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction. ]

(13) A transparent polymer film that satisfies all of the following formulas (I) to (III) and has a moisture permeability of 100 to 2000 g / (m ² · day) at 40 ° C. and a relative humidity of 90%. , and Rth (Rth ₀₎ of the transparent polymer film, a transparent polymer film was immersed in methanol at 25 ° C., 3 hours and ultrasonic extraction, further 80 ° C. at was measured after drying 10 min Rth (Rth ₁ ) (Rth ₀ -Rth ₁ ) is less than 8 nm.
Formula (I): Rth / Re ≧ −0.39
Formula (II): Re> 0
Formula (III): Rth <0
[In the formula, Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction. ]

(14) The transparent polymer film according to (12) or (13), which is produced by the production method according to any one of (1) to (11).
(15) The transparent polymer film according to any one of (12) to (14), wherein the fluctuation range of the direction of the slow axis is less than 5 °.
(16) The transparent polymer film according to any one of (12) to (15), which has a single-layer structure.
(17) The transparent polymer film according to any one of (12) to (16), wherein the polymer as a main component is cellulose acylate.
(18) The transparent polymer film as described in (17), wherein the cellulose acylate is cellulose acetate.

(19) A retardation film comprising at least one transparent polymer film according to any one of (12) to (18).
(20) A polarizing plate comprising at least one transparent polymer film according to any one of (12) to (18).
(21) The polarizing plate according to (20), wherein the transparent polymer film is directly bonded to a polarizing film.
(22) At least one sheet of the transparent polymer film according to any one of (12) to (18), the retardation film according to (19), or the polarizing plate according to (20) or (21). A liquid crystal display device comprising:

  According to the present invention, it is possible to provide an optically uniform transparent polymer film having an appropriate moisture permeability, negative Rth, and Rth / Re ≧ −0.39, and a method for producing the same. An excellent retardation film can be provided. Moreover, since the transparent polymer film of this invention has moderate moisture permeability, it can be bonded together with a polarizing film on-line, and can provide the polarizing plate excellent in visibility with sufficient productivity. Furthermore, a highly reliable liquid crystal display device can be provided.

  Below, the transparent polymer film of this invention, its manufacturing method, retardation film, a polarizing plate, and a liquid crystal display device 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.

<Transparent polymer film>
[Retardation]
The transparent polymer film of the present invention satisfies all of the following formulas (I) to (III).
Formula (I): Rth / Re ≧ −0.39
Formula (II): Re> 0
Formula (III): Rth <0
[In the formula, Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction when the measurement wavelength is 632.8 nm, respectively. ]

First, each retardation in the present invention will be described. 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, and a He-Ne laser of 632.8 nm was used at 25 ° C. and 60% relative humidity. The average refractive index (n) represented by the following formula (a) is used.
Formula (a): 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. ]

Subsequently, using a birefringence measuring apparatus (ABR-10A: manufactured by UNIOPT Co., Ltd.), the humidity-controlled film was perpendicular to the sample film surface and in the film plane at 25 ° C. and a relative humidity of 60%. Measure the direction of the slow axis and the retardation value using a 632.8 nm He-Ne laser from the direction tilted ± 40 ° from the normal to the film surface with the slow axis as the tilt axis (rotation axis), and Using the average refractive index obtained above, nx, ny, and nz were calculated, respectively, and the in-plane retardation value (Re) and the film thickness direction represented by the following formulas (b) and (c), respectively. The retardation value (Rth) is calculated.
Formula (b): Re = (nx−ny) × d
Formula (c): Rth = {(nx + ny) / 2−nz} × d
[Wherein nx is the refractive index in the slow axis (x) direction in the film plane, ny is the refractive index in the direction perpendicular to the x direction in the film plane, and nz is the film thickness direction of the film (film (Surface normal direction) and d is the film thickness (nm). The slow axis is the direction in which the refractive index is maximum in the film plane. ]

The retardation value of the transparent polymer film of the present invention satisfies all of the above formulas (I) to (III). Moreover, it is preferable that the transparent polymer film of the present invention that satisfies all of the formulas (I) to (III) satisfies all of the following formulas (Ia) to (IIIa).
Formula (Ia): Rth / Re ≧ −0.30
Formula (IIa): Re ≧ 15
Formula (IIIa): −300 ≦ Rth <0

More preferably, the transparent polymer film of the present invention satisfies all of the following formulas (Ib) to (IIIb).
Formula (Ib): Rth / Re ≧ −0.20
Formula (IIb): 30 ≦ Re ≦ 350
Formula (IIIb): −200 ≦ Rth <0

The transparent polymer film of the present invention most preferably satisfies all of the following formulas (Ic) to (IIIc).
Formula (Ic): Rth / Re ≧ −0.10
Formula (IIc): 40 <Re ≦ 300
Formula (IIIc): −100 ≦ Rth <0

  The angle θ formed between the transport direction of the present invention and the slow axis of Re of the film is preferably 0 ± 10 ° or 90 ± 10 °, more preferably 0 ± 5 ° or 90 ± 5 °, More preferably, it is 0 ± 3 ° or 90 ± 3 °, and in some cases, 0 ± 1 ° or 90 ± 1 ° is preferred, and 90 ± 1 ° is most preferred. Further, the fluctuation range of the direction of the slow axis is preferably less than 5 °, more preferably less than 3 °, still more preferably less than 1 °, most preferably less than 0.5 °, and in some cases, 0.1 ° Less than is more preferred.

[Film thickness]
The film thickness of the transparent polymer film of the present invention is preferably 20 μm to 180 μm, more preferably 40 μm to 160 μm, and further preferably 60 μm to 140 μm. When the film thickness is thinner than 20 μm, handling property and curling of the polarizing plate when processing into a polarizing plate or the like are not preferable. The film thickness unevenness of the transparent polymer 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%. Particularly preferred.

[Moisture permeability]
Next, moisture permeability will be described. In the present invention, “moisture permeability” refers to a case where a cup containing calcium chloride is covered with each film sample and sealed, and left for 24 hours at 40 ° C. and 90% relative humidity. It is the value evaluated from the mass change (g / (m ² · day)) before and after humidity control.
The moisture permeability increases as the temperature increases and increases as the humidity increases, but the magnitude relationship of moisture permeability between the films remains unchanged 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.

The moisture permeability of the transparent polymer film of the present invention is 100 g / (m ² · day) or more. By using a film having a moisture permeability of 100 g / (m ² · day) or more, the film can be directly bonded to the polarizing film. As the moisture ^{permeability, 100~1500g / (m 2 · day} ) are ^{preferred, 300~1000g / (m 2 · day} ) , more ^{preferably, 400~800g / (m 2 · day} ) is more preferred.
When the transparent polymer 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 transparent polymer film of the present invention is 500 g / (m ² · day). preferably) less than a ^{is, 50~450g / (m 2 · day} ) , more ^{preferably, 100~400g / (m 2 · day} ) are more ^{preferred, 150~300g / (m 2 · day} ) are 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.

In order to prepare the film of the present invention having a moisture permeability of 100 g / (m ² · day) or more in terms of 80 μm, it is preferable to appropriately control the hydrophilicity / hydrophobicity of the polymer or to reduce the density of the film. The former method includes, for example, a method of appropriately controlling the hydrophilicity / hydrophobicity of the polymer main chain and further introducing a hydrophobic or hydrophilic side chain. The latter method includes, for example, a side chain in the polymer main chain. And the like, selecting the type of solvent used during film formation, and controlling the drying rate during film formation.

[Tg]
20 mg of the sample 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 cooled to −30 ° C./min to 30 ° C. did. Thereafter, the temperature was raised again from 30 ° C. to 250 ° C., and the temperature at which the baseline started to deviate from the low temperature side was defined as Tg of the film.

[polymer]
Examples of the polymer that is a constituent element of the transparent polymer film of the present invention include cellulose ester, polyester, polycarbonate, cycloolefin polymer, vinyl polymer, polyamide, and polyimide. The polymer preferably has a hydrophilic structure such as a hydroxyl group, amide, imide or ester in the main chain or side chain in order to achieve appropriate moisture permeability. As the polymer, cellulose ester is more preferable.
As said polymer, a powder or a particulate thing can be used, and the pelletized thing can also be used.
The water content of the polymer 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 polymer is not within the preferred range, it is preferable to use the polymer after drying it by heating or the like.
These polymers may be used alone or in combination of two or more polymers.

Examples of the cellulose ester include a cellulose ester compound and a compound having an ester-substituted cellulose skeleton obtained by introducing a functional group biologically or chemically from cellulose as a raw material. Among them, cellulose acylate is particularly preferable.
In addition, as a polymer as a main component of the transparent polymer film of this invention, it is preferable to use the above-mentioned cellulose acylate. Here, the “polymer as the main component” indicates a polymer when it is composed of a single polymer, and when it is composed of a plurality of polymers, it is the most mass fraction of the constituent polymers. Indicates a high polymer.

The cellulose ester is an ester of cellulose and acid. As the acid constituting the ester, an organic acid is preferable, a carboxylic acid is more preferable, a fatty acid having 2 to 22 carbon atoms is further preferable, and a lower fatty acid having 2 to 4 carbon atoms is most preferable.
The 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. Examples of the acyl group include, for example, acetyl, propionyl, butyryl, isobutyryl, pivaloyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, cyclohexanecarbonyl, oleoyl, Examples include benzoyl, naphthylcarbonyl, and cinnamoyl. As the acyl group, acetyl, propionyl, butyryl, dodecanoyl, octadecanoyl, pivaloyl, oleoyl, benzoyl, naphthylcarbonyl, and cinnamoyl are preferable, and acetyl, propionyl, and butyryl are most preferable.
The cellulose ester may be an ester of cellulose and a plurality of acids. Cellulose acylate may be substituted with a plurality of acyl groups.

  In the transparent polymer film of the present invention, cellulose acetate which is cellulose acylate having an ester with acetic acid is particularly preferable. From the viewpoint of solubility in a solvent, cellulose acetate having a degree of acetyl substitution of 2.70 to 2.87 is preferable. More preferred is cellulose acetate of 2.80 to 2.86, most preferred.

  The basic principle of the cellulose acylate synthesis method is described in Nobuhiko Umeda et al., Wood Chemistry, 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method of cellulose acylate 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 a suitable amount of carboxylic acid such as acetic acid, and then esterified by introducing into a pre-cooled acylated mixture to 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 stoichiometrically excessive amount with respect 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 components 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 raw material cotton of cellulose ester and the synthesis method are also described in pages 7 to 12 of the Japan Society of Invention Disclosure (Public Technical Number 2001-1745, published on March 15, 2001, Japan Society of Invention).

[Preparation of transparent polymer film]
The transparent polymer film of the present invention can be produced from a polymer solution containing a polymer and various additives by a solution casting film forming method. In addition, when the melting point of the polymer of the present invention 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 described later, the film is formed by a melt film forming method. Can also be made. The transparent polymer film of the present invention can also be formed by a melt film forming method, and the melt film forming method is described in JP-A No. 2000-352620.

[Polymer solution]
(solvent)
The transparent polymer film of the present invention can be produced, for example, by forming a polymer solution containing a polymer and, if necessary, various additives by a solution casting film forming method or the like.
As a main solvent of a polymer solution (preferably a cellulose ester solution) used for production of the transparent polymer film 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.

  Examples of such a main solvent include halogenated hydrocarbons, esters, ketones, ethers, alcohols and hydrocarbons, which may have a branched structure or a cyclic structure. 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 polymer solution (preferably cellulose ester solution) used for preparation of the transparent polymer film of the present invention is composed of a single solvent, it indicates that solvent, and is composed of a plurality of solvents. In the case, it indicates a solvent having the highest mass fraction among the constituent solvents.

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, toluene and the like.

  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.
Examples of the hydrocarbon include n-pentane, cyclohexane, n-hexane, benzene, toluene, xylene and the like.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, 2-butoxyethanol, and methyl acetoacetate.

When the polymer which comprises the transparent polymer film of this invention contains a cellulose acylate, 5-30 mass% in all the solvents, More preferably, 7-25 mass%, More preferably, it contains 10-20 mass% alcohol. It is preferable from the viewpoint of reducing the peeling load from the band.
Further, from the viewpoint of reducing Rth, the polymer solution used for the production of the transparent polymer film of the present invention has a small proportion of volatilizing with the halogenated hydrocarbon at the initial stage of the drying process, and the boiling point gradually concentrated is 95 ° C. or higher. And it is preferable to contain the organic solvent which is a poor solvent of a cellulose ester 1-15 mass%, More preferably, it is 1.5-13 mass%, More preferably, it is 2-10 mass%.

  Although the example of the combination of the organic solvent preferably used as a solvent of the polymer solution used for preparation of the transparent polymer film of this invention is given below, this 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 = 85/15
(26) Dichloromethane / methanol = 92/8
(27) Dichloromethane / methanol = 90/10
(28) Dichloromethane / methanol = 87/13
(29) Dichloromethane / ethanol = 90/10

  In addition, the detailed description in the case of using a non-halogen organic solvent as the main solvent is described in the Japan Society for Invention and Innovation (Publication No. 2001-1745, published on March 15, 2001, Japan Institute of Invention), and used as appropriate. can do.

(Solution concentration)
The polymer concentration in the polymer 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 polymer concentration can be adjusted to a predetermined concentration at the stage of dissolving the polymer in the 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 concentration of the polymer can be lowered by adding an additive.

(Additive)
The said polymer solution used for preparation of the transparent polymer film of this invention can contain the various liquid or solid additive according to a use in each preparation process. 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 plasticizer and the optical anisotropy controlling agent are organic compounds 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, when these compounds are used in combination with cellulose acylate particularly preferably used in the present invention, the hydrophobicity of the film can be improved and the change in humidity of retardation can be reduced. Moreover, the wavelength dependence of retardation can be effectively controlled by using the ultraviolet absorber or the infrared absorber in combination. The additives used for the transparent polymer film of the present invention are preferably those that are substantially free of volatilization during the drying process.

Of the plasticizer and the optical anisotropy control agent, the additive used in the present invention is not particularly limited. However, the plasticizer and the optical anisotropy have the effect of increasing Rth beyond 8 nm by the following measurement method. It is preferable not to add a sex control agent.
The kind, amount, concentration, and the like of such a compound are not particularly limited, and can be evaluated by the following method.

In the present invention, the Rth value (unit: nm) raised by the additive is evaluated as the difference between the Rth of the film formed with the additive and the Rth of the film formed without the additive. can do.
Further, in the present invention, an additive having an effect of increasing Rth means that the film is immersed in a solvent in which the additive is soluble at 25 ° C. and the film is insoluble, such as methanol or tetrahydrofuran. Sign of difference (Rth ₀ -Rth ₁ ) between Rth (Rth ₁ ) measured after ultrasonic extraction for a period of time and further drying the film at 80 ° C. for 10 minutes and Rth (Rth ₀ ) before treatment with the solvent Is an additive that is positive. In the film of the present invention, Rth ₀ -Rth ₁ is preferably less than 8 nm, more preferably from −100 to less than 8 nm, further preferably from −50 to 5 nm, and from −30 to 3 nm. Is most preferred. If an additive is added such that Rth ₀ -Rth ₁ falls within the above preferred range, the fluctuation range of the direction of the slow axis of the produced film can be reduced.

  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 is increased, the glass transition temperature (Tg) of the polymer film is decreased, and the additive is added in the film production process. It becomes easy to cause the volatilization problem of the agent. Therefore, when the 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 0.01 to 30% by mass, more preferably 2 to 30% by mass with respect to the polymer. Preferably, 5 to 20% by mass is more preferable.

  A plasticizer that can be suitably used when cellulose acylate is used as the polymer constituting the transparent polymer film of the present invention is described in JP-A No. 2001-151901. 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.

(Preparation of polymer solution)
The polymer solution can be prepared by, for example, JP-A-58-127737, JP-A-61-106628, JP-A-2-276830, JP-A-4-259511, JP-A-5-163301, and 9- No. 95544, No. 10-45950, No. 10-95854, No. 11-71463, No. 11-302388, No. 11-322946, No. 11-322947, No. 11-323017 No. 2000, JP-A-2000-53784, JP-A-2000-273184, and JP-A-2000-273239. 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 polymer solution.

[Casting, drying]
The transparent polymer film of the present invention can be produced using a conventional solution casting film forming apparatus according to a conventional solution casting film forming method. Specifically, the dope (polymer solution) prepared in a dissolving machine (kettle) can be filtered and then temporarily stored in a storage kettle, and the foam contained in the dope can be defoamed for final preparation. The dope is kept at 30 ° C., and is sent from the dope discharge port to the pressure die through a pressure metering gear pump capable of delivering a constant amount of liquid with high accuracy, for example, by the rotational speed, and the dope runs endlessly from the die (slit) of the pressure die. It casts uniformly on the metal support body of the cast part currently cast (casting process). Next, the dope film (also referred to as web) is peeled off from the metal support at the peeling point where the metal support has almost gone around, and then transported to the drying zone, and drying is completed while being transported by a roll group. In the present invention, a metal belt is preferable as the metal support.

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. The Rth of the film (raw material) after drying is preferably −1000 nm or more and less than 50 nm, more preferably −100 to 45 nm, and further preferably −50 to 40 nm. Moreover, the preferable width | variety of a film is 0.5-5 m, More preferably, it is 0.7-3 m.
This film may be conveyed to a stretching zone or a heat treatment zone as it is, or may be stretched or heat treated off-line after winding the film. 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.

[Stretching]
In the production method of the present invention, in order to achieve the target Re and Rth, the polymer film is stretched to increase Rth. Rth of the film before stretching is less than 0 nm, preferably −1000 to −10 nm, more preferably −500 to −20 nm, further preferably −300 to −30 nm, most preferably −200 to −40 nm, and in some cases— 150 to -50 nm is still more preferable. Such a film can be obtained, for example, by a heat treatment described later, and the Rth / Re value can be increased by stretching the obtained film to increase the film density and increasing Rth.

(Stretching method)
The stretching may be, for example, longitudinal stretching performed in the transport direction between two or more devices (for example, nip rolls or suction drums) that hold the film whose peripheral speed on the outlet side is increased in the transport direction, but preferably stretched. The direction is transverse stretching performed by extending in the direction orthogonal to the transport direction, and for example, tenter stretching is preferably performed in an apparatus having a heating zone by holding both ends of the film with a tenter clip. The draw ratio can be appropriately set according to the retardation required for the film, preferably 1 to 500%, more preferably 3 to 400%, still more preferably 5 to 300%, and particularly preferably 10 to 100%. These stretching operations may be performed in one stage or in multiple stages. Here, “stretch ratio (%)” means that obtained using the following formula.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / Length before stretching The stretching speed in the stretching is preferably 10 to 10,000% / min, more preferably 20 It is -1000% / min, More preferably, it is 30-800% / min.

[Heat treatment]
In the present invention, in order to achieve the target Re and Rth, it is preferable to use a step of heat-treating the formed transparent polymer film in addition to the stretching step. The heat treatment step is preferably performed before the stretching step, and it is preferable that the film is once cooled after the heat treatment, and further moved to the stretching step.

(temperature)
The heat treatment temperature is preferably (Tg + 50) ° C. or more, more preferably (Tg + 60) ° C. or more, still more preferably (Tg + 60) to (Tg + 180) ° C., and even more preferably (Tg + 65) to (Tg + 150). ° C, particularly preferably (Tg + 70) to (Tg + 100) ° C. This temperature is preferably 200 ° C. or higher, more preferably 200 to 280 ° C., further preferably 210 to 270 ° C., particularly when the polymer that is the main component of the polymer film is cellulose acylate. Preferably it is 220-250 degreeC.
The cooling temperature is preferably 50 ° C. or more lower than the heat treatment temperature, more preferably 100 to 300 ° C., and further preferably 150 to 250 ° C.
The difference between the heat treatment temperature and the stretching temperature is preferably 1 ° C. or more, more preferably 10 to 200 ° C., further preferably 30 to 150 ° C., particularly preferably 50 to 100 ° C., and the stretching temperature is the heat treatment temperature. Lower is preferred. By appropriately setting the temperature difference, the Rth / Re value can be controlled.

(Heat treatment method)
The heat treatment is preferably carried out while transporting the film into a heating zone maintained at the temperature. In this case, it is preferably performed while heating between two or more apparatuses (for example, nip rolls or suction drums) held in the transport direction, and may be performed in an apparatus having a heating zone between nip rolls, for example.
In addition, it may be carried out without giving a difference in the peripheral speed between the inlet side and the outlet side, and when the peripheral speed is given a difference, the elongation of the film is controlled to 3 to 500%. It is preferably 5 to 100%, more preferably 10 to 80%, and particularly preferably 20 to 60%. The “elongation (%) of the film” here means a value obtained by using the following formula.
Elongation of film (%) = 100 × {(length after heat treatment) − (length before heat treatment)} / length before heat treatment

  The transparent polymer film of the present invention 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 polymer 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 transparent polymer film of the present invention can be improved in adhesion with each functional layer (for example, an undercoat layer, a back layer, and an optically anisotropic layer) by appropriately performing a surface treatment. 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) can be provided on the transparent polymer 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 transparent polymer film of the present invention is described in pages 32 to 45 of the Japan Society of Invention Disclosure Technical Bulletin (Public Technical Number 2001-1745, published on March 15, 2001, Japan Society of Invention). Yes, those described here can be used as appropriate.

<Phase difference film>
The transparent polymer 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 transparent polymer film of the present invention, a retardation film in which the Re value and the Rth value are freely controlled can be easily produced. For example, a film satisfying Re ≧ 30 nm and | Rth | ≦ 15 nm can be preferably produced as a retardation film whose retardation does not change regardless of the tilt angle in the slow axis direction, and Re ≧ 50 nm and | Rth | A film satisfying ≦ 10 nm can be more preferably produced.

  The transparent polymer film of the present invention can be used as a retardation film as it is. In addition, a plurality of the transparent polymer films of the present invention can be laminated, or the transparent polymer film of the present invention and a film outside of the present invention can be laminated to appropriately adjust Re and Rth to be used as a retardation film. . Lamination of the film can be performed using a pressure-sensitive adhesive or an adhesive.

In some cases, the transparent polymer 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 or may be formed from a polymer film having birefringence.
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 crystalline compound that can be used as the liquid crystalline 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 Chemical Society of Japan, Quarterly Chemical Review, No. 22, Chemistry of Liquid Crystal, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm. , 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 rod-like liquid crystalline compounds 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 include, for example, Makromol. Chem., 190, 2255 (1989), Advanced Materials, 5, 107 (1993), US Pat. Nos. 683,327, 5,622,648, 5,770,107, WO 95/22586, 95/24455, 97/00600, 98/23580 pamphlet, 98/52905 pamphlet, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, and JP-A-2001-328773. Compounds described in publications and the like are included.

(Optically anisotropic layer made of polymer film)
The optically anisotropic layer may be formed from a polymer film. The polymer film can be formed from a polymer that can exhibit optical anisotropy. Examples of the polymer that can exhibit the optical anisotropy include polyolefin (eg, polyethylene, polypropylene, norbornene-based polymer), polycarbonate, polyarylate, polysulfone, polyvinyl alcohol, polymethacrylic acid ester, polyacrylic acid ester, and Cellulose esters (eg, cellulose triacetate, cellulose diacetate) are included. Moreover, as the polymer, a copolymer or polymer mixture of these polymers may be used.

"Polarizer"
The transparent polymer film or retardation film of the present invention can be used as a protective film for a polarizing plate (polarizing plate of the present invention). The polarizing plate of the present invention comprises a polarizing film and two polarizing plate protective films (transparent polymer films) that protect both surfaces thereof, and the transparent polymer film or retardation film of the present invention is used as at least one polarizing plate protective film. be able to.
When the transparent polymer film of the present invention is used as the polarizing plate protective film, the transparent polymer film of the present invention is subjected to the surface treatment (also described in JP-A-6-94915 and JP-A-6-118232) to make it hydrophilic. For example, it is preferable to perform glow discharge treatment, corona discharge treatment, or alkali saponification treatment. In particular, when the polymer constituting the transparent polymer film of the present invention is cellulose acylate, alkali saponification treatment is most preferably used as the surface treatment.

  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 transparent polymer 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 transparent polymer film is directly bonded to the polarizing film as described above. As the adhesive, an aqueous solution of polyvinyl alcohol or polyvinyl acetal (eg, polyvinyl butyral) or a latex of a vinyl polymer (eg, polybutyl acrylate) can be used. A particularly preferred adhesive is an aqueous solution of fully saponified polyvinyl alcohol.

  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 transparent polymer film of the present invention may be used for any of the four polarizing plate protective films, but the transparent polymer film of the present invention is disposed 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. Further, the protective film disposed on the opposite side of the transparent polymer film of the present invention across the polarizing film can be provided with a transparent hard coat layer, an antiglare layer, an antireflection layer, etc. It is preferably used as a polarizing plate protective film on the outermost surface of the display side.

<Liquid crystal display device>
The transparent polymer 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 transparent polymer 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 transparent polymer 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 transparent polymer 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 transparent polymer 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 transparent polymer 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 transparent polymer film of the present invention is particularly advantageous 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. Used for. In these modes, the liquid crystal material is aligned substantially in parallel during black display, and black is displayed by aligning liquid crystal molecules in parallel with the substrate surface in the absence of applied voltage. In these embodiments, the polarizing plate using the transparent polymer 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 transparent polymer 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 retardation is minimum does not exist in the plane of the retardation film and 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. It is also described in Mori et al. (Jpn. J. Appl. Phys. Vol. 38 (1999) p. 2837).

(Reflective liquid crystal display)
The transparent polymer film of the present invention is also advantageously used as a retardation film of a reflective liquid crystal display device of TN type, STN type, HAN type, and GH (Guest-Host) type. 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 transparent polymer 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 an ASM (Axially Symmetric Aligned Microcell) mode liquid crystal cell. 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 Kume et al. (Kume et al., SID 98 Digest 1089 (1998)).

(Hard coat film, antiglare film, antireflection film)
The transparent polymer film of the present invention may be applied to a hard coat film, an antiglare film and an antireflection film depending on circumstances. 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 transparent polymer film of the present invention. can do. Preferred embodiments of such an antiglare film and antireflection film are described in detail on pages 54 to 57 of the Japan Society for Invention and Innovation (Publication No. 2001-1745, published on March 15, 2001, Japan Society of Invention and Innovation). It can be preferably used also in the transparent polymer film of the present invention.

<Measurement method>
First, the measurement method and evaluation method of characteristics used in this example are shown below.

[Retardation]
5 points in the width direction (center part, end part (position of 5% of the total width from both ends), and two intermediate parts between the center part and the end part) are sampled every 100 m in the longitudinal direction, and the size is 2 cm □ The samples were taken out, and the average value of each point evaluated according to the above-described method was obtained and set as Re and Rth. In addition, the difference between the maximum value and the minimum value of the deviation of the slow axis direction at each position from the conveyance direction or a direction perpendicular thereto (unit: possible values of °, −45 to + 45 °) is delayed. The variation range of the direction of the phase axis was used.

[Moisture permeability]
The value evaluated according to the method described above was defined as moisture permeability.

[Tg]
The value evaluated according to the above-mentioned method was defined as Tg of the film.

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

  The features of the present invention will be described more specifically with reference to examples and comparative 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.

[Examples 101 to 111, Comparative examples 101 to 105]
(Preparation of polymer solution)
1) Polymer In each example and comparative example, the following polymer A was used. Polymer A was heated to 120 ° C. and dried, and after the water content was adjusted to 0.5% by mass or less, 20 parts by mass was used.

-Polymer A:
Cellulose acetate powder having a substitution degree of 2.85 was used as polymer A. Polymer A 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 0.2 mass. %, 6% by mass Viscosity in dichloromethane solution is 305 mPa · s, residual acetic acid content is 0.1% by mass or less, Ca content is 65 ppm, Mg content is 26 ppm, iron content is 0.8 ppm, sulfate ion content Was 18 ppm, the yellow index was 1.9, and the amount of free acetic acid was 47 ppm. The average particle diameter of the powder was 1.5 mm, and the standard deviation was 0.5 mm.

[Degree of substitution]
The acyl substitution degree of cellulose acylate was determined by ¹³ C-NMR by the method described in Carbohydr. Res. 273 (1995) 83-91 (Tezuka et al.).
[Degree of polymerization]
After the produced cellulose acylate was absolutely dried, about 0.2 g was precisely weighed and dissolved in 100 mL of a mixed solvent of dichloromethane: ethanol = 9: 1 (mass ratio). This was measured with an Ostwald viscometer at 25 ° C. for the number of seconds to drop, and the degree of polymerization DP was determined by the following equation.
η _rel = T / T ₀
[Η] = ln (η _rel ) / C
DP = [η] / Km
[In the formula, T is the number of seconds that the sample is dropped, T ₀ is the number of seconds that the solvent is dropped, ln is the natural logarithm, C is the concentration (g / L), and Km is 6 × 10 ⁻⁴ . ]

2) Solvent In each Example and Comparative Example, the following mixed solvent was used (see Table 1). The water content of the solvent was 0.2% by mass or less.
Solvent A:
Dichloromethane / methanol / butanol (83/15/2 parts by mass)
Solvent B:
Dichloromethane / methanol (90/10 parts by mass)

3) Additive In each of the examples and comparative examples, any one of additive compositions A to B having the following composition was used according to Table 1 below.

Additive composition A:
Silicon dioxide fine particles (particle size 20 nm, Mohs hardness about 7) (0.08 parts by mass)
Additive composition B:
Triphenyl phosphate (1.6 parts by mass)
Biphenyl diphenyl phosphate (0.8 parts by mass)
Silicon dioxide fine particles (particle size 20 nm, Mohs hardness about 7) (0.08 parts by mass)
Additive composition C:
Triphenyl phosphate (1.6 parts by mass)
Biphenyl diphenyl phosphate (0.8 parts by mass)
Retardation increasing agent having the following structure (0.6 parts by mass)

二酸化ケイ素微粒子（粒子サイズ２０ｎｍ、モース硬度 約７）（０．０８質量部）

Silicon dioxide fine particles (particle size 20 nm, Mohs hardness about 7) (0.08 parts by mass)

4) Swelling and dissolution In each of the examples and comparative examples, the solvent and additive were added to a 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery, while stirring and dispersing. The polymer was added gradually. 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 polymer 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 be completely dissolved. 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 polymer solution.

5) Filtration The obtained polymer 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, manufactured by Pall) with an absolute filtration accuracy of 2.5 μm. To obtain a polymer solution.

(Production of film)
The polymer 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. And the polymer film which was cast and rotated 50 cm before the end point part of the casting part was peeled off from the band, and 45 ° C. drying air 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.
Tack A is a commercially available Fuji Tac T80UZ (manufactured by Fuji Film Co., Ltd.), which is used as it is.

(Heat treatment)
The resulting film was heat treated using an apparatus having a heating zone between two nip rolls. The aspect ratio (distance between nip rolls / base width) was adjusted to 3.3, the heating zone was set to the temperature shown in Table 1, and after passing through the two nip rolls, the film was cooled to the temperature shown in Table 1. . Further, the elongation of the film was determined from the following formula by placing marked lines at regular intervals in a direction orthogonal to the film transport direction, measuring the intervals before and after the heat treatment.
Elongation of film (%) = 100 × (Interval between marked lines after heat treatment−Interval between marked lines before heat treatment) / Interval between marked lines before heat treatment

(Stretching)
Subsequently, both ends of the heat-treated film were held with tenter clips, and then stretched in a direction perpendicular to the transport direction in the heating zone. The heating zone was set to the temperature shown in Table 1, and the draw ratio was determined from the following formula by placing marked lines at regular intervals in a direction parallel to the film transport direction, measuring the intervals before and after stretching.
Stretch ratio (%) = 100 × (interval between marked lines after stretching−interval between marked lines before stretching) / interval between marked lines before stretching

(Evaluation of transparent polymer film)
Each transparent polymer film obtained was evaluated. The results are shown in Table 1 below. In addition, Rth after cooling of Example 102 and Comparative Example 102 is evaluated in-line.
The slow axis of Re of the film after stretching is observed in the direction orthogonal to the film transport direction in Examples 101 to 109 and Comparative Examples 101 to 103, and parallel to the film transport direction in Comparative Example 104 and Comparative Example 105. It was observed in various directions. In addition, the Re and Rth variations (variations in measured values at five points) evaluated based on the above-described method were Re within ± 1 nm and Rth within ± 2 nm for all samples.

  As shown in Table 1, by following the method of the present invention, it was possible to produce an optically uniform film satisfying all of Rth / Re ≧ −0.39, Re> 0, and Rth <0. . On the other hand, when the stretching temperature or the heat treatment temperature is not appropriate or the additive is not appropriate, a film having the desired retardation could not be produced.

The above-prepared film was immersed in methanol at 25 ° C., subjected to ultrasonic extraction for 3 hours, and further Rth (Rth ₁ ) measured after drying the film at 80 ° C. for 10 minutes, and Rth (Rth ₀ ) before methanol treatment. (Rth ₀ -Rth ₁ ) is 1 nm when the additive composition A is added, 5 nm when the additive composition B is added, and 72 nm when the additive composition C is added. It was 6 nm.

[Comparative Example 106]
A 50 μm cellulose acetate film was produced in the same manner as in Example 105, and a birefringent film was obtained using this film in accordance with Example 5 of JP-A-5-157911. The fluctuation range of the direction of the slow axis of this film was as large as 8 °, and the variation in Re and Rth (the variation in measured values at 5 points) was as large as ± 25 nm for Re and ± 43 nm for Rth.

[Example 201]
(Preparation of laminated retardation film)
The cellulose ester film of the present invention can be used as it is as a retardation film satisfying all of Rth / Re ≧ −0.39, Re> 0, and Rth <0. Here, the film is formed using an adhesive. A retardation film with a controlled Rth / Re ratio was produced by laminating by roll-to-roll.
Fujitac T80UZ (manufactured by FUJIFILM Corporation) and Example 106 were bonded to each other by roll-to-roll using an adhesive, and Re and Rth were measured by the method described above. Re = 150 nm, Rth = 0 nm . Further, the slow axis of Re of this retardation film was observed in the width direction of the film.

[Examples 301 to 310, Comparative examples 301 to 307]
(Preparation of polarizing plate)
The obtained film was saponified to produce a polarizing plate.

1) Saponification of Films Films A and B shown in Table 2 below were immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) adjusted to 55 ° C. for 2 minutes, and then washed with water. After being immersed in a 0.05 mol / L sulfuric acid aqueous solution for 30 seconds, it was further 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 Layer 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 layer having a thickness of 20 μm.

3) Bonding Two films were selected from the polarizing layer thus obtained and the saponified film (referred to as film A and film B, respectively), and the combinations in each example and comparative example are shown in Table 2 below. ), The saponified surface of the film is disposed on the polarizing film side, and the polarizing layer is sandwiched between them. Bonding was performed so that the directions were orthogonal.
In the following Table 2, “Tack B” means Fujitac TD80UF (manufactured by FUJIFILM Corporation; moisture permeability at 40 ° C. and 90% relative humidity = 430 g / (m ² · day)), and “polycarbonate”. And Panlite C1400 (manufactured by Teijin Chemicals Ltd .; moisture permeability at 40 ° C. and 90% relative humidity = 25 g / (m ² · day)). “COP1” is an Arton film (film thickness of 80 μm, JSR Co., Ltd .; moisture permeability at 40 ° C. and 90% relative humidity = 30 g / (m ² · day)). “COP2” indicates a ZEONOR film (film thickness: 100 μm, manufactured by Nippon Zeon; moisture permeability at 40 ° C. and 90% relative humidity = 0 g / (m ² · day)).
In Comparative Example 304, the film surface treatment was changed to a corona treatment, and bonding was performed.

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

[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%, and the degree of polarization after standing (time-dependent polarization degree) was calculated by the method described above. The results are shown in Table 2 below.

[Time polarization 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 the conditions of 90 ° C. and relative humidity of 0%, 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.

(Evaluation of mounting on IPS liquid crystal display)
The polarizing plate of Example 301, Example 305, and Example 307 was replaced with the polarizing plate incorporated in the IPS type | mold liquid crystal display device (32V type high-vision liquid crystal television monitor (W32-L7000), Hitachi Ltd. make). As a result, the viewing angle characteristics were improved and display unevenness was improved. On the other hand, when the polarizing plates of Comparative Examples 304 to 307 were incorporated, the viewing angle characteristics were not improved or even improved.

  According to the present invention, it is possible to provide a transparent polymer film having an appropriate moisture permeability and satisfying all of Rth / Re ≧ −0.39, Re> 0, Rth <0, and an excellent retardation film. Can be provided. Moreover, since the transparent polymer film of this invention has moderate moisture permeability, it can be bonded together with a polarizing film on-line, and can provide the polarizing plate excellent in visibility with sufficient productivity. Furthermore, a highly reliable liquid crystal display device can be provided. Therefore, the present invention has high industrial applicability.

Claims (13)

A method for producing a transparent cellulose acylate film comprising a step of heat-treating a cellulose acylate film having Rth <0 at (Tg + 50) ° C. or higher and then cooling to a temperature equal to or higher than a cooling temperature to make ΔRth> 0 ,
Production of a transparent cellulose acylate film in which the stretched cellulose acylate film satisfies the following formulas (I) to (III) and has a moisture permeability of 100 g / (m ² · day) or more at 40 ° C. and 90% relative humidity: Method.
ΔRth = [Rth after stretching] − [Rth before stretching]
Formula (I): Rth / Re ≧ −0.39
Formula (II): Re> 0
Formula (III): Rth <0
[Tg represents the glass transition temperature of the cellulose acylate film. Re and Rth represent retardation values (unit: nm) in the in-plane direction and the film thickness direction, respectively. ] The method for producing a transparent cellulose acylate film according to claim 1 , wherein the stretching is carried out at a cooling temperature or higher after the film is cooled by heat treatment at 200 ° C or higher. The method for producing a transparent cellulose acylate film according to claim 1 or 2, wherein the difference between the stretching temperature and the heat treatment temperature is more than 1 ° C.. The method for producing a transparent cellulose acylate film according to any one of claims 1 to 3, wherein the stretching temperature is lower than the heat treatment temperature. The transparent cellulose acylate film according to any one of claims 1 to 4 , wherein the heat treatment is a heat treatment performed while heating between two or more apparatuses that hold the film in the transport direction. Production method. The said cooling temperature is 50 degreeC or more lower than heat processing temperature, The manufacturing method of the transparent cellulose acylate film as described in any one of Claims 1-5 characterized by the above-mentioned. The method for producing a transparent cellulose acylate film according to claim 1 , wherein the cellulose acylate film before the heat treatment satisfies −1000 ≦ Rth <50.
[In the formula, Rth represents a retardation value in the film thickness direction (unit: nm). ] The method for producing a transparent cellulose acylate film according to any one of claims 1 to 7, wherein the stretching is a tenter stretching. Transparent cellulose acylate film characterized by being manufactured by the manufacturing method according to any one of claims 1-8. A retardation film comprising at least one transparent cellulose acylate film according to claim 9 . A polarizing plate comprising at least one transparent cellulose acylate film according to claim 9 . The polarizing plate according to claim 11 , wherein the transparent cellulose acylate film is directly bonded to a polarizing film. A liquid crystal display device comprising at least one transparent cellulose acylate film according to claim 9 , a retardation film according to claim 10 , or a polarizing plate according to claim 11 or 12 .