JP4659575B2 - Optical compensation sheet, polarizing plate, liquid crystal display device, and method for producing optical compensation sheet - Google Patents

Description

  The present invention relates to an optical functional material, in particular, an optical compensation sheet having a large viewing angle compensation ability and a method for producing the optical functional material. Furthermore, the present invention relates to a polarizing plate using the optical compensation sheet and a liquid crystal display device having the polarizing plate.

A liquid crystal display device is generally composed of a liquid crystal cell, a polarizing plate and an optical compensation sheet (retardation plate), and is roughly classified into a transmission type liquid crystal display device and a reflection type liquid crystal display device.
In a transmissive liquid crystal display device, two polarizing plates are attached to both sides of a liquid crystal cell, and one or two optical compensation sheets are disposed between the liquid crystal cell and the polarizing plate. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, one optical compensation sheet, and one polarizing plate are arranged in this order.
A liquid crystal cell usually comprises a rod-like liquid crystalline molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. Various display modes have been proposed for liquid crystal cells depending on the alignment state of rod-like liquid crystalline molecules. Transmission types include TN (Twisted Nematic), IPS (In-Plane Switching), and FLC (Ferro electric Liquid Crystal). As for reflection types such as OCB (Optically Compensatory Bend), STN (Supper Twisted Nematic), and VA (Vertically Aligned), HAN (Hybrid Aligned Nematic) has been proposed.
A polarizing plate generally comprises a polarizing film and a transparent protective film. The polarizing film is generally obtained by impregnating polyvinyl alcohol with an aqueous solution of iodine or a dichroic dye and further uniaxially stretching the film. The polarizing plate has a configuration in which two transparent protective films are attached to both sides of the polarizing film.

  Optical compensation sheets are used in various liquid crystal display devices in order to eliminate image coloring and expand the viewing angle. As an optical compensation sheet, it has been proposed to use an optical compensation sheet having an optically anisotropic layer formed from liquid crystalline molecules (particularly discotic liquid crystalline molecules) on a transparent support. The optically anisotropic layer is formed by aligning liquid crystalline molecules and fixing the alignment state. In general, the alignment state is fixed by a polymerization reaction using liquid crystalline molecules having a polymerizable group. Liquid crystalline molecules have a large birefringence. The liquid crystal molecules have various alignment forms. By using liquid crystalline molecules, it has become possible to realize optical properties that cannot be obtained with conventional stretched birefringent films.

The optical properties of the optical compensation sheet are determined according to the optical properties of the liquid crystal cell, specifically, the difference in the display mode. When liquid crystalline molecules, particularly discotic liquid crystalline molecules are used for the optical compensation sheet, optical compensation sheets having various optical properties corresponding to various display modes of the liquid crystal cell can be produced.
Optical compensation sheets using discotic liquid crystalline molecules have already been proposed for various display modes.

In the optical compensation sheet, by controlling the orientation of the liquid crystal molecules, it is possible to control the optical properties optimum for the liquid crystal cell to be applied. Specifically, it can be controlled by the intrinsic birefringence of the liquid crystalline molecules, the film thickness, and the orientation mode (optically uniaxial orientation, hybrid orientation, tilt angle distribution in that case, etc.).
In addition, the alignment control is greatly affected by the difference in hydrophilicity / hydrophobicity between the air interface side and the alignment film interface side of the liquid crystal layer. be able to. Conventionally, a polymer used for an alignment film, for example, a polyvinyl alcohol compound is modified with a functional group, and then the alignment film is applied to control the hydrophilicity / hydrophobicity on the alignment film side. It has been possible to control the hydrophilicity / hydrophobicity on the air interface side by adding an alignment control agent, a chiral agent or the like.

  When producing an optical compensation sheet having an optically anisotropic layer in which the orientation of liquid crystalline molecules is fixed on a transparent support, an alignment film is provided between the transparent support and the optically anisotropic layer. In this case, adhesion between the transparent support (usually a cellulose acetate film) and the alignment film is required. The alignment film is aligned by rubbing, electric field application, magnetic field application, light irradiation, or the like. However, adhesion of minute dust or the like on the alignment film impairs alignment uniformity. In particular, in the rubbing process, countermeasures against static electricity generation are required to rub the film surface. For this reason, a water-soluble resin cured film is usually used as the alignment film, and in particular, a cured film made of a hydroxyl group-containing resin such as polyvinyl alcohol and a curing agent is used.

Usually, since the cellulose acetate film used as a transparent support is hydrophobic, it has poor affinity with a water-soluble resin cured film, and in order to eliminate this, an undercoat layer such as gelatin is provided as an adhesive layer (for example, Patent Document 1) or an alkali saponification treatment on the surface of a transparent support (particularly, cellulose acetate film) to provide adhesion to the support surface to provide an alignment film (see, for example, Patent Document 2) A method is disclosed. However, when the gelatin undercoat layer is provided, there is a problem that uniform coating cannot be performed due to the influence of a coating solvent contained in the undercoat layer when the thickness of the support is reduced.
For the alignment film formed of the water-soluble resin cured film coated as described above, rapid curing reaction, dependency on humidity resistance after film formation, and the like are important. For example, a method of applying and curing a coating solution in which an acid compound is used in combination with a polyvinyl alcohol resin and a bifunctional aldehyde compound (see Patent Document 3), a coating solution under acidic conditions by adding acid to the modified polyvinyl alcohol and the curing agent A method of applying and curing (see paragraph No. [0148] of Patent Document 4) has been proposed.
Japanese Patent Laid-Open No. 11-248940 JP 2002-302561 A JP-A-10-2188938 JP 2000-155216 A

However, when these techniques are used, optical defects (for example, white spots etc.) are likely to occur, and particularly when a long film is manufactured, the yield for obtaining a performance that can be practically used is significantly reduced. There are challenges and it is not enough.
In particular, in recent years, as an optical compensation sheet that can be applied to various liquid crystal display devices as described above, a sheet having excellent optical characteristics and a thin film thickness is strongly desired.

Accordingly, an object of the present invention is to provide an optical functional material (particularly, an optical compensation sheet) that achieves both adhesion and good viewing angle characteristics.
Still another object of the present invention is to provide a polarizing plate in which the optical compensation sheet is disposed on at least one of polarizing films, and a liquid crystal display device having a high display quality provided with the optical compensation sheet.

The above object of the present invention is achieved by an optical compensation sheet having the following constitution, a polarizing plate using the optical compensation sheet, a liquid crystal display device having the optical compensation sheet, and a method for producing the optical compensation sheet.
<1>
In an optical compensation sheet formed by forming an alignment film on a support and then applying an optically anisotropic layer coating liquid containing a discotic liquid crystalline compound on the alignment film to form an optically anisotropic layer. An optical compensation sheet formed by performing plasma treatment on the film in the afterglow region of glow discharge plasma and then applying an optically anisotropic layer coating liquid.
<2>
<1> The optical compensation sheet according to <1>, wherein the alignment film is a cured film formed by applying and drying an alignment film forming composition containing polyvinyl alcohol and / or modified polyvinyl alcohol as a main component.
<3>
<1> The optical compensation sheet according to <1>, wherein the alignment film contains polyimide as a main component.
< 4 >
The optical compensation sheet according to any one of <1> to <3>, wherein a reaction gas in the plasma treatment is a substance containing halogen.
< 5 >
A polarizing plate, wherein a transparent protective film, a polarizing film, and the optical compensation sheet according to any one of <1> to < 4 > are laminated in this order.
< 6 >
In a liquid crystal display device comprising a polarizing film and polarizing plates comprising two transparent protective films disposed on both sides of the polarizing film, the two sheets disposed between the liquid crystal cell and the polarizing film. At least one of the transparent protective films is the optical compensation sheet according to any one of <1> to < 4 >.
< 7 >
A method for producing an optical compensation sheet comprising forming an optically anisotropic layer by applying an optically anisotropic layer coating liquid containing a discotic liquid crystalline compound on the alignment film after forming the oriented film on the support A method for producing an optical compensation sheet, comprising: forming an alignment film on a support and then performing a plasma treatment on the alignment film in an afterglow region of glow discharge plasma .
< 8 >
< 7 > The method for producing an optical compensation sheet according to < 7 >, wherein the plasma treatment step is performed after the rubbing treatment step of the support provided with the alignment film.
< 9 >
The method for producing an optical compensation sheet according to < 7 > or < 8 >, wherein the support is a film, and the plasma treatment is continuously performed in a longitudinal direction.
In addition, although this invention is related to said <1>-< 9 >, the other matter (For example, the matter described in following (1)-(12) etc.) was described for reference.

(1) In an optical functional material formed by forming a liquid crystal layer by applying a liquid crystal layer coating liquid containing a liquid crystalline compound after forming an alignment film on a support, a vapor phase method is used on the alignment film. An optical functional material formed by applying a liquid crystal layer coating liquid after a surface treatment.
(2) The alignment film according to (1), wherein the alignment film is a cured film formed by applying and drying an alignment film forming composition containing polyvinyl alcohol and / or modified polyvinyl alcohol as a main component. Optical functional material.
(3) The optical functional material as described in (1) above, wherein the alignment film contains polyimide as a main component.
(4) The optical functional material according to any one of (1) to (3), wherein the surface treatment by the vapor phase method is a plasma treatment.
(5) The optical functional material as described in (4) above, wherein the reaction gas in the plasma treatment is a substance containing halogen.

(6) The optical functional material as described in any one of (1) to (5) above, wherein the surface treatment by the vapor phase method is performed in an after glow region of glow discharge plasma.
(7) An optical functional sheet according to any one of (1) to (6), wherein the optical compensation sheet compensates for birefringence.
(8) A polarizing plate, wherein a transparent protective film, a polarizing film, and the optical compensation sheet according to (7) are laminated in this order.
(9) In a liquid crystal display device in which a polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof is disposed on both sides of the liquid crystal cell, the polarizing film is disposed between the liquid crystal cell and the polarizing film. A liquid crystal display device, wherein at least one of the two transparent protective films is the optical compensation sheet according to (7).
(10) A method for producing an optical functional material, wherein after forming an alignment film on a support, a liquid crystal layer coating liquid containing a liquid crystalline compound is applied thereon to form an optically anisotropic layer, A method for producing an optical functional material, comprising: forming an alignment film on a support; and performing a surface treatment on the alignment film by a vapor phase method.
(11) The optical functional material according to (10), wherein the surface treatment step by the vapor phase method is performed after the rubbing treatment step of the support having the alignment film applied thereto. Manufacturing method.
(12) The optical function according to (10) or (11), wherein the support is a film, and is subjected to surface treatment by the gas phase method continuously in the longitudinal direction. Material manufacturing method.

The optical functional material of the present invention has a layer structure in which a support, an alignment film, and a liquid crystal layer are laminated in this order. In particular, when the optical functional material is used as an optical compensatory sheet, the liquid crystal layer functions as an optically anisotropic layer, and the transparent support, the alignment film, and the optically anisotropic layer that have been subjected to adhesion treatment in advance are used in this manner. It has the layer structure laminated | stacked in order.
The optical functional material and the optical compensation sheet of the present invention are characterized in that a non-contact (gas phase) surface treatment is performed on the alignment film, thereby controlling the range of liquid crystal alignment of the upper liquid crystal layer. Can be enlarged.
Non-contact surface treatment is applied to the alignment film coated on the support, and the hydrophobicity of the alignment film surface can be improved by, for example, modification with fluorine, and the tilt angle of the liquid crystal layer on the alignment film side is increased. Can be made. Since it is a treatment after the alignment film is applied, when the alignment film is prepared by a coating method, it can be applied with an alignment film composition having good coatability, and the physical properties can be changed by the subsequent surface treatment. Can be mentioned.

  The optical compensation sheet of the present invention is suitably used for polarizing plates and liquid crystal displays, and can provide a wider viewing angle characteristic. In addition, the manufacturing method of the present invention makes it possible to control the tilt angle of the liquid crystal layer more widely and to create a novel optical functional material.

  Hereinafter, the optical functional material of the present invention, the production method thereof, the optical compensation sheet, the polarizing plate using the optical compensation sheet, and the liquid crystal display device having the polarizing plate will be described in detail.

  First, an optical functional material and a manufacturing method thereof will be described. As described above, the optical functional material of the present invention has a layer structure in which a support, an alignment film, and a liquid crystal layer are laminated in this order. The optical compensation sheet is an embodiment of an optical functional material obtained by using a transparent support and controlling the retardation characteristics of the transparent support and the orientation of the liquid crystal layer.

[Support]
The support of the present invention may be any material such as glass, polymer film, metal band, metal drum, and metal oxide as long as it has a smooth coating surface. When used without peeling off the coating layer and the support after coating, it is preferably a transparent support, in which case it is preferably a transparent material such as glass or a polymer film, and its light transmittance is It is preferably 70% or more, more preferably 80% or more. When used as an optical compensation sheet, the light transmittance is 80% or more, preferably 90% or more.
Examples of the polymer constituting the polymer film include cellulose esters (eg, cellulose mono- or triacylate), and norbornene-based polymers such as ARTON and ZEONEX (both are trade names). Moreover, even if it is a conventionally known polymer such as polycarbonate or polysulfone that easily develops birefringence, it is possible to develop birefringence by modifying the molecule as described in International Publication No. 00/26705 pamphlet. Can be used as a support for the optical functional material of the present invention.
As the polymer film of the present invention, a cellulose ester film is preferable, and a cellulose acetate film is more preferable.
The thickness of the support is preferably 20 to 500 μm, more preferably 30 to 200 μm, and most preferably 40 to 90 μm.

When the polymer film is used as a support in the optical compensation sheet, the polymer film preferably has a desired retardation value.
In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at a wavelength λ, respectively. Re (λ) is measured by making light with a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH (manufactured by Oji Scientific Instruments). Rth (λ) is the light of wavelength λnm from the direction inclined by + 40 ° with respect to the normal direction of the film, with Re (λ) and the in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis And a retardation value measured by making light of wavelength λ nm incident from a direction inclined by −40 ° with respect to the film normal direction with the in-plane slow axis as the tilt axis (rotation axis). KOBRA 21ADH calculates based on the retardation value measured in three directions, the assumed value of the average refractive index, and the input film thickness value. Here, as the assumed value of the average refractive index, the values in the polymer handbook (JOHN WILEY & SONS, INC) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH calculates nx, ny, and nz by inputting these assumed values of average refractive index and film thickness.
The retardation value of the polymer film varies in a preferred range depending on the liquid crystal display device in which the optical compensation sheet is used and the method of use thereof. Usually, the Re retardation value is 0 to 200 nm, and the Rth retardation value is 70 to It is preferable to adjust to the 400 nm range.

When two optical compensation sheets are used in the liquid crystal display device, the Rth retardation value of the polymer film is preferably in the range of 70 to 250 nm. When one optical compensation sheet is used in the liquid crystal display device, the Rth retardation value of the polymer film is preferably in the range of 150 to 400 nm.
The birefringence (Δn: nx−ny) of the polymer film is preferably in the range of 0.00028 to 0.020. The birefringence {(nx + ny) / 2−nz} in the thickness direction of the polymer film is preferably in the range of 0.001 to 0.04.
In order to adjust the retardation value of the polymer film, a method of applying an external force such as stretching is generally used. As another method, a retardation increasing agent for adjusting optical anisotropy is optionally added. The

As the cellulose ester used in the present invention, it is preferable to use a lower fatty acid ester of cellulose. Lower fatty acid means a fatty acid having 6 or less carbon atoms. A cellulose acylate having 2 to 4 carbon atoms is preferred. Cellulose acetate is particularly preferred. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used.
The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more. Cellulose acetate preferably has a narrow molecular weight distribution of Mw / Mn (Mw is mass average molecular weight and Mn is number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 4.0.
In the present invention, it is preferable to use cellulose acetate having an acetylation degree of 55.0 to 62.5%. The acetylation degree is more preferably 57.0 to 62.0%, and particularly preferably 59.0 to 61.5%. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation is determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

In cellulose acetate, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not evenly substituted, but the substitution degree at the 6-position tends to be small. In the cellulose acetate used in the present invention, it is preferable that the degree of substitution at the 6-position of cellulose is the same or greater than that at the 2- and 3-positions.
The ratio of the substitution degree at the 6-position to the total substitution degree at the 2-position, the 3-position, and the 6-position is preferably 30 to 40%, more preferably 31 to 40%, and more preferably 32 to 40%. Most preferably it is. The substitution degree at the 6-position is preferably 0.88 or more.

As described above, the retardation increasing agent can be used to increase the retardation in the thickness direction of the transparent support. As the retardation increasing agent, a compound having at least two aromatic rings and a molecular structure that does not sterically hinder the conformation of the two aromatic rings can be used. The aromatic compound is used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of the cellulose ester. The aromatic compound is preferably used in the range of 0.05 to 15 parts by mass, more preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the cellulose ester. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.
Examples of the retardation increasing agent include compounds described in European Patent 0911656A2, JP-A Nos. 2000-1111914, 2000-275434 and the like.

It is preferable to add fine particles to the cellulose ester film in order to maintain good scratch resistance and film transportability.
They are conventionally used as matting agents, antiblocking agents, or anti-kissing agents. Although they are not particularly limited as long as they are materials exhibiting the above-mentioned functions, preferred specific examples of these matting agents include compounds containing silicon, silicon dioxide, titanium oxide, zinc oxide, aluminum oxide, oxidation as inorganic compounds. Barium, zirconium oxide, strontium oxide, antimony oxide, tin oxide, tin oxide / antimony, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, etc. More preferred is an inorganic compound containing silicon or zirconium oxide, but silicon dioxide is particularly preferred because the turbidity of the cellulose ester film can be reduced.
Further, the surface-treated inorganic fine particles are also preferable because of good dispersibility in the cellulose ester. Examples of the treatment method include the method described in JP-A No. 54-57562. Examples of the particles include those described in JP-A No. 2001-151936.
As the organic compound, for example, polymers such as cross-linked polystyrene, silicone resin, fluororesin and acrylic resin are preferable, and among them, silicone resin is preferably used. Among silicone resins, those having a three-dimensional network structure are particularly preferable.

  A plasticizer can be added to the cellulose ester film in order to improve mechanical properties or increase the drying speed. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Specifically, the content described in detail on page 16 of the Japan Society for Invention and Innovation Technical Report (Technology Number 2001-1745, Invention Association issued on March 15, 2001) is preferably used. The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of the cellulose ester.

Further deterioration inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) and UV inhibitors may be added to the cellulose ester film. . Examples of the deterioration inhibitor include compounds described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. As a particularly preferred example of the deterioration preventing agent, butylated hydroxytoluene (BHT) can be mentioned. Examples of the ultraviolet light inhibitor include compounds described in JP-A-7-11055 and JP-A-7-11056.
Further, for these details, materials described in detail on pages 17 to 22 of the above-mentioned public technical number 2001-1745 are preferably used.

Furthermore, the hygroscopic expansion coefficient of the cellulose ester film used in the optical compensation sheet of the present invention is preferably 30 × 10 ⁻⁵ /% RH or less. The hygroscopic expansion coefficient is preferably 15 × 10 ⁻⁵ /% RH or less, and more preferably 10 × 10 ⁻⁵ /% RH or less. Further, the hygroscopic expansion coefficient is preferably small, but usually a value of 1.0 × 10 ⁻⁵ /% RH or more. The hygroscopic expansion coefficient indicates the amount of change in the length of the sample when the relative humidity is changed at a constant temperature.
By adjusting the hygroscopic expansion coefficient, it is possible to prevent frame-like transmittance increase, that is, light leakage due to distortion, while maintaining the optical compensation function of the optical compensation sheet.

The method for measuring the hygroscopic expansion coefficient is shown below. A sample having a width of 5 mm and a length of 20 mm was cut out from the produced cellulose ester film, and one end was fixed and hung in an atmosphere of 25 ° C. and 20% RH (R0). A weight of 0.5 g was hung from the other end and left for 10 minutes to measure the length (L0). Next, the length (L1) was measured while maintaining the temperature at 25 ° C. and the humidity at 80% RH (R1). The hygroscopic expansion coefficient was calculated by the following equation. The measurement was performed 10 samples for the same sample, and the average value was adopted.
Hygroscopic expansion coefficient [/% RH] = {(L1-L0) / L0} / (R1-R0)
In order to reduce the dimensional change due to moisture absorption of the produced cellulose ester film, it is preferable to add a compound having a hydrophobic group or fine particles. As the compound having a hydrophobic group, a material corresponding to a plasticizer or a degradation inhibitor having a hydrophobic group such as an aliphatic group or an aromatic group in the molecule is particularly preferably used. The amount of these compounds added is preferably in the range of 0.01 to 10% by mass with respect to the solution (dope) to be adjusted. In addition, the free volume in the cellulose ester film may be reduced. Specifically, the smaller the amount of residual solvent during film formation by the solvent casting method described later, the lower the free deposition. It is preferable to dry under the condition that the residual solvent amount with respect to the cellulose ester film is in the range of 0.01 to 1.00% by mass.

[Method for producing transparent support]
In this invention, it is preferable to manufacture a cellulose acetate film by the solvent cast method, and a film is manufactured using the solution (dope) which melt | dissolved the cellulose acetate in the organic solvent.
Examples of the organic solvent to be used include conventionally known organic solvents. For example, those having a solubility parameter in the range of 17 to 22 are preferable. Lower aliphatic hydrocarbon chloride, lower aliphatic alcohol, ketone having 3 to 12 carbon atoms, ester having 3 to 12 carbon atoms, ether having 3 to 12 carbon atoms, fat having 5 to 8 carbon atoms Group hydrocarbons and aromatic hydrocarbons having 6 to 12 carbon atoms.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.
Specifically, for example, detailed compounds can be mentioned on pages 12 to 16 of the aforementioned technical number 2001-1745.

In particular, in the present invention, the solvent is preferably used by mixing two or more kinds of organic solvents, and particularly preferred organic solvents are three or more kinds of mixed solvents different from each other, and the first solvent has the number of carbon atoms. A ketone having 3 to 4 carbon atoms and an ester having 3 to 4 carbon atoms, or a mixture thereof, and the second solvent is selected from ketones having 5 to 7 carbon atoms or acetoacetic acid ester; It is preferably selected from alcohol having a boiling point of 30 to 170 ° C or hydrocarbon having a boiling point of 30 to 170 ° C.
In particular, it is preferable from the viewpoint of the solubility of cellulose acetate to use 20 to 90% by mass of acetate, 5 to 60% by mass of ketones, and 5 to 30% by mass of alcohols.

Further, non-halogen organic solvent systems that do not contain halogenated hydrocarbons are particularly preferred.
Technically, halogenated hydrocarbons such as methylene chloride can be used without problems, but from the viewpoint of the global environment and working environment, it is preferable that the organic solvent is substantially free of halogenated hydrocarbons. “Substantially free” means that the proportion of halogenated hydrocarbon in the organic solvent is less than 5% by mass (preferably less than 2% by mass). Further, it is preferable that no halogenated hydrocarbon such as methylene chloride is detected from the produced cellulose acetate film.

  Specific examples of the organic solvent used in the present invention include paragraph numbers [0021] to [0025] in JP-A No. 2002-146043 and paragraph numbers [0016] to [0021] in JP-A No. 2002-146045. ] Examples of the solvent system described in the above.

  On the other hand, in addition to the organic solvent of the present invention, the dope used in the present invention may contain fluoroalcohol and methylene chloride in an amount of 10% by mass or less, more preferably 5% by mass or less of the total organic solvent amount of the present invention. It is preferable for improving the transparency of the resin and for increasing the solubility. The fluoroalcohol has a boiling point of 165 ° C or lower, preferably 111 ° C or lower, and more preferably 80 ° C or lower. The fluoroalcohol has about 2 to 10 carbon atoms, preferably about 2 to 8 carbon atoms. The fluoroalcohol is a fluorine atom-containing aliphatic alcohol, which may or may not have a substituent. As the substituent, an aliphatic substituent or an aromatic substituent containing or not containing a fluorine atom is preferable.

  Examples of the fluoroalcohol include compounds described in paragraph No. [0020] in JP-A-8-143709, paragraph No. [0037] in JP-A-11-60807, and the like. These fluoroalcohols may be used alone or in combination.

  When preparing the cellulose acetate solution, the container may be filled with an inert gas such as nitrogen gas. The viscosity of the cellulose triacetate solution immediately before film formation may be within a range that allows casting, and is usually adjusted to a range of 10 ps · s to 2000 ps · s, particularly 30 ps · s to 400 ps. -S is preferable.

  Regarding the preparation of the cellulose acetate solution (dope) according to the present invention, the dissolution method is not particularly limited, and may be a room temperature dissolution method, a cooling dissolution method or a high temperature dissolution method, or a combination thereof. Regarding these, for example, JP-A-5-163301, JP-A-61-106628, JP-A-58-127737, JP-A-9-95544, JP-A-10-95854, JP-A-10-45950, JP-A-2000-53784, Kaihei 11-322946, JP-A-11-322947, JP-A-2-276830, JP-A-2000-273239, JP-A-11-71463, JP-A-04-259511, JP-A-2000-273184, JP-A-11-323017, JP-A-11-323017 11-302388 etc. and the preparation method of the cellulose acylate solution is mentioned. The above-described method for dissolving cellulose acylate in an organic solvent is applicable to the present invention as long as it is within the scope of the present invention. Further, the dope solution of cellulose acetate is usually subjected to concentration and filtration of the solution, and is also described in detail on page 25 of the aforementioned technical number 2001-1745. In addition, when it melt | dissolves at high temperature, it is the case where it is more than the boiling point of the organic solvent to be used, and in that case, it uses in a pressurized state.

  Next, in the present invention, a method for producing a film using a cellulose acylate solution will be described. As a method and equipment for producing a cellulose acylate film, a conventionally known solution casting film forming method and solution casting film forming apparatus called a drum method or a band method used for producing a cellulose triacetate film are used. The film forming process will be described by taking the band method as an example. The dope (cellulose acylate solution) prepared from the dissolving machine (kettle) is temporarily stored in the storage kettle, and the bubbles contained in the dope are defoamed to finish. Prepare. The prepared dope is fed 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 is run endlessly from the die (slit) of the pressure die. The dope film (also referred to as a web) is peeled off from the metal support at the peeling point where the metal support is almost cast around the metal support. Both ends of the obtained web are sandwiched between clips, transported by a tenter while keeping the width, dried, then transported by a roll group of a drying device, dried, and wound up to a predetermined length by a winder. The combination of the tenter and the roll group dryer varies depending on the purpose. Each of these manufacturing processes (casting (including co-casting), metal support, drying, peeling, stretching, etc.) is described in detail on pages 25 to 30 of the aforementioned technical number 2001-1745. The contents made are mentioned. In the casting step, one type of cellulose acylate solution may be cast as a single layer, or two or more types of cellulose acylate solutions may be cast simultaneously and / or sequentially.

  Further, the cellulose acetate solution of the present invention can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorbing layer, a polarizing layer).

  In the conventional monolayer liquid, it is necessary to extrude a cellulose acetate solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In many cases, the problem occurs, such as a failure or flatness. As a solution to this, by casting a plurality of cellulose acetate solutions from the casting port, a highly viscous solution can be simultaneously extruded onto the support, and the planarity is improved and an excellent planar film can be produced. In addition, by using a concentrated cellulose acetate solution, it is possible to reduce the drying load and increase the production speed of the film.

[Method of imparting adhesion of transparent support]
When the alignment support is provided by the coating method, the transparent support of the present invention provides adhesion to the surface of the transparent support and is subjected to a surface treatment so that the alignment film coating solution is uniformly applied. Is preferred.
Examples of the surface treatment method include a method of providing an undercoat layer of the alignment film. Adheres well to a polymer film as a first layer of a single layer method in which an undercoat layer described in JP-A-7-333433 or a resin layer such as gelatin containing both a hydrophobic group and a hydrophilic group is applied alone. A so-called multi-layer in which a layer (hereinafter abbreviated as the undercoat first layer) is provided and a hydrophilic resin layer such as gelatin (hereinafter abbreviated as the undercoat second layer) is applied thereon as the second layer. The contents of the law (for example, described in JP-A-11-248940) can be mentioned.
Examples of other surface treatment include a method of modifying the film surface by corona discharge treatment, glow discharge treatment, ultraviolet irradiation treatment, flame treatment, ozone treatment, acid treatment, alkali treatment, and the like. Details of these are described in detail on pages 30 to 32 of the aforementioned public technical number 2001-1745. Among these, alkali saponification treatment is particularly preferable, and it is extremely effective as the surface treatment of the cellulose acetate film.

[Alkaline saponification]
The alkali saponification treatment is performed by immersing, spraying or coating an alkali solution on a transparent support. Preferably, a saponification treatment is preferably performed by coating, and examples of the coating method include a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E-type coating method.

[Alkaline solution]
The alkaline solution of the present invention is preferably an alkaline solution having a pH of 11 or more. More preferably, the pH is 12-14.
Examples of the alkaline agent used in the alkaline solution include inorganic alkaline agents such as sodium hydroxide, potassium and lithium, diethanolamine, triethanolamine, DBU (1,8-diazabicyclo [5,4,0] -7. -Undecene), DBN (1,5-diazabicyclo [4,3,0] -5-nonene), tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, triethylbutylammonium Organic alkali agents such as hydroxide are also used. These alkali agents can be used alone or in combination of two or more, and a part of them may be added, for example, in the form of a halogenated salt.
Among these alkali agents, sodium hydroxide or potassium hydroxide is preferable because the pH can be adjusted in a wide pH range by adjusting these amounts.

  The concentration of the alkaline solution is determined according to the type of alkaline agent used, the reaction temperature, and the reaction time. The content of the alkaline agent is preferably 0.1 to 5 mol / Kg in the alkaline solution, 0.5 ˜3 mol / Kg is more preferred.

The solvent of the alkaline solution of the present invention preferably comprises a mixed solution of water and a water-soluble organic solvent. Any organic solvent miscible with water can be used as the organic solvent, but those having a boiling point of 120 ° C. or lower, more preferably 100 ° C. or lower are preferable.
Among them, preferred organic solvents are those having an inorganic / organic value (I / O value) of 0.5 or more and a solubility parameter in the range of 16 to 40 [mJ / m ³ ] ^1/2 . More preferably, the I / O value is 0.6 to 10, and the solubility parameter is 18 to 31 [mJ / m ³ ] ^1/2 . If the I / O value is more inorganic than this range or the solubility parameter is low, the alkali saponification rate decreases and the overall uniformity of the saponification degree is unsatisfactory. On the other hand, if the I / O value is on the organic side of the above range or the solubility parameter is highly soluble, the saponification rate is fast, but haze is likely to occur. Dissatisfied.
In addition, when an organic solvent, particularly an organic solvent in each of the above-mentioned organic and soluble ranges, is used in combination with a surfactant, a compatibilizing agent, etc. described later, a high saponification rate is maintained and the saponification degree is uniform over the entire surface. Improve.

  Examples of the organic solvent having preferable characteristic values include those described in “Synthetic Organic Chemistry Association”, “New Edition Solvent Pocket Book” (Ohm Co., Ltd., published in 1994) and the like. (In addition, the inorganic / organic value (I / O value) of the organic solvent is described in, for example, Yoshio Tanaka, Organic Conceptual Diagram) Sankyo Publishing Co., Ltd., 1983, pages 1-31).

  Specifically, monohydric aliphatic alcohols (eg, methanol, ethanol, propanol, butanol, pentanol, hexanol, etc.), alicyclic alkanols (eg, cyclohexanol, methylcyclohexanol, methoxycyclohexanol, cyclohexylmethanol, Cyclohexylethanol, cyclohexylpropanol, etc.), phenylalkanols (eg, benzyl alcohol, phenylethanol, phenylpropanol, phenoxyethanol, methoxybenzyl alcohol, benzyloxyethanol, etc.), heterocyclic alkanols (furfuryl alcohol, tetrahydrofurfuryl alcohol) Etc.), monoethers of glycol compounds (methyl cellosolve, ethyl cellosolve, propyl cellosolve, methoxymethoxyethane) Butyl cell sorb, hexyl cell sorb, methyl carbitol, ethyl carbitol, propyl carbitol, butyl carbitol, methoxy triglycol, ethoxy triglycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl Ethers, etc.) ketones (eg, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), amides (eg, N, N-dimethylformamide, dimethylformamide, N-methyl-2-pyrrolidone, 1,3 dimethylimidazolidinone, etc.) , Sulfoxides (eg, dimethyl sulfoxide) and ethers (eg, tetrahydrofuran, pyran, dioxane, trioxane, dimethylcellosolve, diethylcellosolve, dipro Ruserusorubu, methyl ethyl cellosolve, dimethyl carbitol, dimethyl carbitol, methyl ethyl carbitol, etc.) and the like. The organic solvent to be used may be used alone or in combination of two or more.

When at least one organic solvent is used alone or in combination of two or more organic solvents, those having high solubility in water are preferable. The solubility of water in the organic solvent is preferably 50% by mass or more, and more preferably freely mixed with water. Thereby, an alkali solution having sufficient solubility in an alkali agent, a salt of a fatty acid by-produced by a saponification treatment, a salt of carbonic acid generated by absorbing carbon dioxide in the air, and the like can be prepared.
The use ratio of the organic solvent in the solvent is determined according to the type of solvent, miscibility with water (solubility), reaction temperature and reaction time.
The mixing ratio of water and organic solvent is preferably 3/97 to 85/15 mass ratio. More preferably, it is 5 / 95-60 / 40 mass ratio, More preferably, it is 15 / 85-40 / 60 mass ratio. In this range, the entire film surface can be easily saponified uniformly without impairing the optical properties of the acylate film.

  As the organic solvent contained in the alkaline solution used in the present invention, an organic solvent (for example, fluorinated alcohol) different from the organic solvent having the above-mentioned preferable I / O value is used as a dissolution aid for the surfactant and compatibilizer described later. You may use together as an agent. The content is preferably 0.1 to 5% by mass relative to the total weight of the liquid used.

  The alkaline solution used in the present invention preferably contains a surfactant. By adding a surfactant, the surface tension can be lowered to facilitate coating, and the uniformity of the coating film can be increased to prevent cissing failure, and haze that tends to occur in the presence of an organic solvent is suppressed. Progress evenly. The effect becomes particularly remarkable by the coexistence of a compatibilizer described later. There is no restriction | limiting in particular in surfactant to be used, Any of anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, a fluorine-type surfactant, etc. may be sufficient.

Specifically, for example, Tokiyuki Yoshida “Surfactant Handbook (new edition)” (Engineering Book, published in 1987), “Functional Creation / Material Development / Applied Technology of Surfactant”, Volume 1 (Technical Education Publishing) , Published in 2000) and the like.
Among these surfactants, quaternary ammonium salts as cationic surfactants, various polyalkylene glycol derivatives as nonionic surfactants, polyethylene oxide derivatives such as various polyethylene oxide adducts, Betaine type compounds as amphoteric surfactants are preferred.
It is preferable to use a nonionic activator and an anionic activator or a nonionic activator and a cationic activator together in the alkaline solution because the effect of the present invention is enhanced.

  The amount of these surfactants added to the alkaline solution is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass.

  The alkaline solution used in the present invention preferably contains a compatibilizing agent. In the present invention, the “compatibilizer” refers to a hydrophilic compound having a water solubility of 50 g or more with respect to 100 g of the compatibilizer at a temperature of 25 ° C. The solubility of the water of the compatibilizing agent is preferably 80 g or more, more preferably 100 g or more with respect to 100 g of the compatibilizing agent. When the compatibilizer is a liquid compound, the boiling point is preferably 100 ° C. or higher, and more preferably 120 ° C. or higher.

  The compatibilizing agent has an action of preventing drying of the alkaline solution attached to a wall surface such as a bath for storing the alkaline solution, suppressing fixation, and stably holding the alkaline solution. Also, after applying the alkali solution to the surface of the transparent support and holding it for a certain period of time, until the saponification treatment is stopped, the applied alkali solution thin film is dried, causing precipitation of solids, and the water washing step It has the effect of preventing difficulty in washing out the solid matter in Furthermore, phase separation between water as a solvent and the organic solvent is prevented. In particular, the coexistence of the surfactant, the organic solvent, and the compatibilizer described above allows the treated transparent support to have a low haze and be stable and uniform even in the case of a long continuous saponification treatment. The degree of saponification.

The compatibilizing agent is not particularly limited as long as it is a material that satisfies the above-mentioned conditions. For example, a water-soluble polymer containing a repeating unit having a hydroxyl group and / or an amide group such as a polyol compound or a saccharide is preferable. .
As the polyol compound, any of a low molecular compound, an oligomer compound, and a high molecular compound can be used.
Examples of aliphatic polyols include alkanediols having 2 to 8 carbon atoms (for example, ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, glycerin monomethyl ether, glycerin monoethyl ether, cyclohexanediol, cyclohexanedimethanol). , Diethylene glycol, dipropylene glycol, etc.), C3-C18 alkanes containing 3 or more hydroxyl groups (for example, glycerin, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, diglycerin) , Dipentaerythritol, inositol, etc.).
As the polyalkyleneoxy polyols, the same alkylene diols as described above may be bonded to each other, or different alkylene diols may be bonded to each other, but a polyalkylene polyol in which the same alkylene diols are bonded to each other is more preferable. . In any case, the number of bonds is preferably 3 to 100, and more preferably 3 to 50. Specific examples include polyethylene glycol, polypropylene glycol, and poly (oxyethylene-oxypropylene).

Examples of sugars include “Natural Polymers” Chapter 2 (published by Kyoritsu Shuppan Co., Ltd., published in 1984) edited by the Society of Polymer Science, Japan, “The Modern Industrial Chemistry 22, Natural Products Industrial Chemistry” II "(Asakura Shoten Co., Ltd., published in 1967) and the like. Among these, saccharides that do not have a free aldehyde group and a ketone group and do not exhibit reducibility are preferable.
Saccharides are generally classified into glucose, sucrose, trehalose type oligosaccharides in which reducing groups are bonded to each other, glycosides in which a reducing group of saccharides and non-saccharides are combined, and sugar alcohols reduced by hydrogenation of saccharides. Both are suitably used in the present invention.
For example, saccharose, trehalose, alkyl glycoside, phenol glycoside, mustard oil glycoside, D, L-arabit, rebit, xylit, D, L-sorbit, D, L-mannit, D, L-exit , D, L-Tallit, Zulsicit, Allozulcit, and reduced water candy. These saccharides can be used alone or in combination of two or more.

Examples of the water-soluble polymer having a repeating unit having a hydroxyl group and / or an amide group include natural gums (for example, gum arabic, guar gum, tragand gum, etc.), polyvinyl pyrrolidone, dihydroxypropyl acrylate polymers, celluloses. Alternatively, addition reactants of chitosans and epoxy compounds (ethylene oxide or propylene oxide) can be mentioned.
Of these, polyol compounds such as alkylene polyols, polyalkyleneoxy polyols and sugar alcohols are preferred.

  The content of the compatibilizer is preferably 0.5 to 25% by mass and more preferably 1 to 20% by mass with respect to the alkaline solution.

  The alkaline solution used in the present invention can contain other additives. Examples of other additives include known additives such as antifoaming agents, alkaline solution stabilizers, pH buffering agents, preservatives, and antibacterial agents.

[Alkaline saponification method]
The surface treatment method of the cellulose acetate film using the above alkaline solution may be any conventionally known method, but the coating method is preferred particularly when only one surface of the film is uniformly saponified without unevenness. As a coating method, a conventionally known coating method [for example, die coater (extrusion coater, slide coater), roll coater (forward roll coater, reverse roll coater, gravure coater), rod coater, blade coater, etc.] is preferable. Available.
The saponification treatment is preferably performed at a treatment temperature in a range not exceeding 120 ° C. at which deformation of the film to be treated, alteration of the treatment liquid, and the like do not occur. Further, the temperature is preferably 10 ° C. or higher and 100 ° C. or lower. In particular, a temperature of 20 to 80 degrees is preferable.
The time for the saponification treatment is determined by appropriately adjusting the alkali solution and the treatment temperature, but it is preferably performed in the range of 1 second to 60 seconds.

A step of saponifying the cellulose acetate film with an alkaline solution at a surface temperature of at least 10 ° C., a step of maintaining the temperature of the cellulose acetate film at least at 10 ° C., and a step of washing the alkaline solution from the cellulose acetate film; It is preferable to carry out an alkali saponification treatment.
For saponification treatment of cellulose acetate film with an alkaline solution at a predetermined temperature, a step of adjusting the temperature to a predetermined temperature before coating, a step of adjusting an alkaline solution to a predetermined temperature in advance, or a combination thereof The process etc. are mentioned. It is preferable to combine with a step of adjusting to a predetermined temperature before coating.
After the saponification reaction, it is preferable to wash and remove the alkaline solution and the saponification treatment reaction product from the film surface by washing with water, neutralizing and washing with water.
Specifically, for example, the contents described in International Publication No. 02/46809 pamphlet and the like can be mentioned.

[Alignment film]
The alignment film of the present invention is preferably an alignment film formed by applying an organic compound (preferably polymer) coating solution. A cured polymer film is preferred from the viewpoint of the strength of the alignment film itself and the adhesion to the optically anisotropic layer as the lower layer or the upper layer. The alignment film is provided in order to define the alignment direction of the liquid crystal compound provided thereon. Examples of the orientation regulating method include conventionally known rubbing, application of a magnetic field or electric field, and light irradiation.

The alignment film used in the present invention can correspond to the type of display mode of the liquid crystal cell.
In display modes (eg, VA, OCB, HAN) in which many rod-like liquid crystal molecules in the liquid crystal cell are aligned substantially vertically, the liquid crystal molecules in the optically anisotropic layer are aligned substantially horizontally. It has a function to make it. In a display mode in which many rod-like liquid crystal molecules in the liquid crystal cell are aligned substantially horizontally (eg, STN), the liquid crystal molecules of the optically anisotropic layer have a function of aligning substantially vertically. . In a display mode in which many rod-like liquid crystal molecules in the liquid crystal cell are substantially obliquely aligned (for example, TN), the liquid crystal molecules of the optically anisotropic layer have a function of substantially obliquely aligning. .

Specific types of polymers used in the alignment film of the present invention are described in the literature on optical compensation sheets using discotic liquid crystalline molecules corresponding to the various display modes described above.
As the polymer used for the alignment film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used, and a plurality of combinations thereof can be used. Examples of the polymer include compounds described in paragraph [0022] of JP-A-8-338913. Preferable examples include water-soluble polymers (for example, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol). Among these, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol are more preferable, and polyvinyl alcohol and modified polyvinyl alcohol. Polyvinyl alcohol is most preferred.
The polymer used for the alignment film preferably contains polyvinyl alcohol and / or modified polyvinyl alcohol as a main component, preferably 40% by mass or more, more preferably 75% by mass or more of the alignment film-forming polymer component.
Moreover, as a polymer used for the alignment film, it is also possible to use polyimide as a main component (preferably 40 mass% or more, more preferably 75 mass% or more of the alignment film forming polymer component).

  The saponification degree of polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and most preferably 85 to 95%. The degree of polymerization of polyvinyl alcohol is preferably 100 to 3000.

  The modifying group of the modified polyvinyl alcohol can be introduced by copolymerization modification, chain transfer modification or block polymerization modification. Examples of modifying groups include hydrophilic groups (carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, amino groups, ammonium groups, amide groups, thiol groups, etc.), hydrocarbon groups having 10 to 100 carbon atoms, fluorine atoms Substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy) and the like can be mentioned. Specific examples of these modified polyvinyl alcohol compounds include, for example, paragraph number [0074] in JP-A 2000-56310, paragraph numbers [0022] to [0145] in JP-A 2000-155216, Examples described in paragraphs [0018] to [022] in the specification of JP-A-2002-62426 are included.

  When the alignment is performed by light irradiation, a photo-alignment group that exhibits a photo-alignment function is included in the molecule. Examples of these photo-alignment groups include those described in “Liquid Crystal, Vol. 3 (1) 3-16 (1999)” written by Masaki Hasegawa, and have a photo-alignment function by a photodimerization reaction having a C═C bond. Photo-alignment group that develops photo-alignment function (for example, polyene group, stilbene group, stilbazole group, stilbazolium group, cinnamoyl group, hemithioindigo group, chalcone group, etc.) Group (for example, a group having a structure such as a benzophenone group or a coumarin group). Specific examples include those described in paragraphs [0021] of JP-A Nos. 2000-122069 and 2002-317013.

  Examples of cross-linking agents for polymers (preferably water-soluble polymers, more preferably polyvinyl alcohol or modified polyvinyl alcohol) used in the alignment film include aldehydes, N-methylol compounds, dioxane derivatives, and carboxyl groups by activating them. Compounds that act, active vinyl compounds, active halogen compounds, isoxazoles and dialdehyde starches are included. Two or more kinds of crosslinking agents may be used in combination. Specific examples include compounds described in paragraphs [0023] to [0024] in JP-A-2002-62426. Aldehydes having high reaction activity, particularly glutaraldehyde are preferred.

  The addition amount of the crosslinking agent is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass with respect to the polymer. The amount of the unreacted crosslinking agent remaining in the alignment film is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. If the crosslinking agent remains in the alignment film in an amount exceeding 1.0% by mass, sufficient durability cannot be obtained. When such an alignment film is used in a liquid crystal display device, reticulation may occur when used for a long time or when left in a high temperature and high humidity atmosphere for a long time.

  The alignment film is basically formed by applying a coating solution containing the polymer, which is a composition for forming an alignment film, and a crosslinking agent on a transparent support, followed by drying by heating (crosslinking) and performing an alignment treatment. It is a cured film that can be used. As described above, the crosslinking reaction may be performed at an arbitrary time after coating on the transparent support. When a water-soluble polymer such as polyvinyl alcohol is used as the alignment film forming composition, the coating solution is preferably a mixed solvent of an organic solvent (eg, methanol) having defoaming action and water. The ratio of water: methanol is preferably 0: 100 to 99: 1, and more preferably 0: 100 to 91: 9. Thereby, generation | occurrence | production of a bubble is suppressed and the defect of the layer surface of an orientation film and also an optically anisotropic layer reduces remarkably.

  The alignment film is preferably applied by spin coating, dip coating, curtain coating, extrusion coating, rod coating, or roll coating. A rod coating method is particularly preferable. Further, the film thickness after drying is preferably 0.1 to 10 μm, more preferably 0.3 to 5 μm, and particularly preferably 0.4 to 2 μm. When a water-soluble polymer such as polyvinyl alcohol is used as the composition for forming an alignment film, the heat drying can be performed at 20 ° C to 110 ° C. In order to form sufficient cross-linking, 60 ° C to 100 ° C is preferable, and 80 ° C to 100 ° C is particularly preferable. The drying time can be 1 minute to 36 hours, preferably 1 minute to 30 minutes. In the case of a polymer such as polyimide, polyamide, or polyamic acid, a higher temperature is generally used, and any known method may be used. However, taking into consideration the heat resistance of the support, it is preferable to dry it at a temperature lower than the heat resistance temperature of the support.

Furthermore, the coating liquid containing the composition for forming an alignment film of the present invention is applied to a support, dried, and aligned by an aligning means, and then applied when the coating liquid for an optically anisotropic layer is applied. It is preferable that the surface of the membrane be maintained in the range of pH 2.0 to 6.9. Furthermore, pH 2.5-5.0 is more preferable.
Further, when applying the coating liquid for the optically anisotropic layer, it is preferable that the fluctuation range ΔpH of the pH of the alignment film surface in the coating width direction is within a range of ± 0.30. More preferably, ΔpH is in the range of ± 0.15.
An optical compensation sheet coated with an optically anisotropic layer in this range is preferable because optical defects are remarkably reduced.

The method for measuring the pH value of the alignment film surface is to leave the sample coated with the alignment film in an environment of (temperature 25 ° C./humidity 65% RH) for 1 day, and then place 10 ml of pure water in a nitrogen atmosphere. Immediately read the pH value with a pH meter.
In order to specify the pH value of the alignment film surface of the present invention and to control the ΔpH in the coating width direction, it is achieved by coating by the rod coating method described above. Furthermore, it is also effective to adjust the drying temperature of the film surface, the air volume when using the drying air, the wind direction, and the like.

  The alignment film is provided on the transparent support or the undercoat layer. The alignment film can be obtained by rubbing the surface after crosslinking the polymer layer as described above.

[Surface treatment of alignment film]
The surface treatment of the alignment film by the vapor phase method of the present invention is performed after forming the alignment film on the support, and may be performed before or after the rubbing process on the alignment film surface. It is preferable to perform a surface treatment by a vapor phase method after the rubbing treatment. In the conventional method, the molecular structure in the vicinity of the surface layer is disturbed by rubbing, and thus the above functional group could not be effectively affected. This is because the functional group can be modified on the surface of the alignment film.

  For the surface treatment of the alignment film by the vapor phase method of the present invention, any method may be used as long as it can modify the chemical structure of the main chain and / or side chain in the vicinity of the alignment film surface. For example, in addition to plasma treatment exemplified in corona discharge treatment, vacuum glow discharge treatment, atmospheric pressure glow discharge treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, flame treatment, ozone treatment or acid mist treatment, alkali mist treatment, etc. A method used for alignment treatment of a substrate alignment film of a liquid crystal panel used in a liquid crystal display device, such as a method for modifying the film surface, is preferred, particularly plasma treatment is preferred, and vacuum or atmospheric pressure glow discharge treatment is most preferred. . The plasma is described in detail, for example, in Yoshida Nagata, “Low Temperature Plasma Material Chemistry” (Industry Books, 1994).

[Alignment film surface treatment with plasma]
In order to control the hydrophilicity / hydrophobicity of the alignment film surface, it is preferable to modify the alignment film surface with a polar functional group. For this reason, it is preferable to use a gas that generates radicals that can modify the alignment film as a reactive gas during the plasma treatment. When it is desired to make the surface hydrophobic, a gas that generates fluorine radicals is preferably used, for example, NF ₃ , CF ₄ , SF ₆ , C ₂ F _4, etc. NF ₃ that generates fluorine radicals is preferably used. When it is desired to make the alignment film surface hydrophilic, it is preferable to use a gas containing a hydrophilic group or oxygen. In particular, the use of oxygen or water is preferably used because there is no possibility of contaminating the alignment film.
In order to induce glow discharge plasma, the equipment may be a batch type or a continuous conveyance type, but the continuous conveyance type is particularly preferable from the viewpoint of productivity. Although any known apparatus may be used, the conditions for generating plasma uniformly may involve trial and error. For example, there is a method using an apparatus as exemplified in Japanese Patent Laid-Open No. 2000-82223.

Plasma discharge is the generation of a plasma state by discharge. There are several types of plasma, but glow discharge plasma is a kind of non-equilibrium plasma, in which high kinetic energy electrons and low kinetic energy chemical species (molecules, atoms, radicals, ions) exist. It is a feature. In order to induce a glow discharge into a plasma state, there is a method of inducing capacitively coupled plasma by applying a high-frequency AC voltage to at least two opposing electrodes. There is a method of inducing inductively coupled plasma by flowing an alternating current.
Hereinafter, a method for inducing capacitively coupled plasma by applying a high-frequency AC voltage to at least two opposing electrodes will be described with reference to the drawings.
FIG. 1 is an example of a schematic diagram of a plasma reaction facility.
In order to induce plasma, an inert gas is used as a base gas, which is particularly preferable in the case of vacuum glow discharge. For example, helium, argon, xenon, krypton, etc. are used, and argon gas is particularly preferably used. The reactive gas is sequentially added to the induced plasma or mixed with the illustrated inert base gas before being introduced into the reaction chamber.
Although depending on the electrode arrangement of the apparatus, a higher applied voltage is preferable because the processing speed can be increased. On the other hand, the alignment film surface is strongly exposed to plasma, and polymerization or dissociation of the alignment film composition occurs. The preferred conditions must be determined by experiment.
As a method of damaging the alignment film as much as possible, an active chemical species (fluorine radical, oxygen radical, etc.) is produced in the plasma, but the alignment film, which is a non-treated material, is arranged away from the plasma. It is preferably used in the invention. That is, an alignment film is disposed in a so-called afterglow region. In this method, by changing the gas flow to the direction of voltage application electrode ⇒ installation electrode ⇒ alignment film surface, the generated active chemical species can be efficiently attacked on the alignment film surface, and the surface is efficiently modified. The In addition, since this method can treat only one surface of the alignment film, it is not necessary to change the physical properties of the support, and for example, it affects the bonding with an adhesive when used as an optical compensation sheet. It is preferable.

For the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment process of LCD can be applied. That is, a method of obtaining the orientation by rubbing the surface of the orientation film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like can be used. Generally, it is carried out by rubbing several times using a cloth or the like in which fibers having a uniform length and thickness are planted on average.
In the case of photo-alignment by light irradiation, the light source as the light irradiation device can be an ultra-high pressure mercury lamp, xenon lamp, fluorescent lamp, laser, etc. Are combined with a polarizing film (through the polarizing film) to convert the ultraviolet light into linearly polarized light and irradiate the photo-alignment film. As the polarizing film, stretch dyed PVA is mainly used. As this linearly polarized ultraviolet irradiation device, for example, the one disclosed in JP-A-10-90684 can be used.

[Liquid crystal layer]
The liquid crystal layer of the present invention is formed as a composition mainly composed of liquid crystal molecules. In order to produce an optical compensation sheet, this layer is designed to function as an optically anisotropic layer.
As the liquid crystal molecule, a rod-like liquid crystal molecule or a discotic liquid crystal molecule is preferable, and a discotic liquid crystal molecule is particularly preferable.
As rod-like liquid crystalline molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used. These low-molecular liquid crystal compounds preferably have a polymerizable group in the molecule (for example, described in paragraph number [0016] of JP-A No. 2000-304932). In addition to the above low-molecular liquid crystalline molecules, high-molecular liquid crystalline molecules can also be used. The high molecular liquid crystalline molecule is a polymer having a side chain corresponding to the above low molecular liquid crystalline molecule. Examples of the optical compensation sheet using polymer liquid crystalline molecules include compounds described in JP-A-5-53016.

As discotic liquid crystalline molecules, various documents (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); , Liquid Crystal Chemistry, 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)). As for the polymerization of discotic liquid crystalline molecules, the description in JP-A-8-27284 can be mentioned.
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. A compound in which the discotic core and the polymerizable group are bonded via a linking group is preferable, whereby the alignment state can be maintained even in the polymerization reaction. Examples thereof include compounds described in paragraph numbers [0151] to [0168] in JP-A-2000-155216.
In order to optically compensate a liquid crystal cell in which rod-like liquid crystalline molecules such as STN mode are twisted, it is preferable that the discotic liquid crystalline molecules are also twisted. When an asymmetric carbon atom is introduced into the linking group, the discotic liquid crystal molecules can be twisted and aligned in a spiral shape. Further, even when an optically active compound containing an asymmetric carbon atom (chiral agent) is added to the optically anisotropic layer, the discotic liquid crystal molecules can be twisted and aligned in a helical manner.

Two or more kinds of discotic liquid crystal molecules may be used in combination. For example, a polymerizable discotic liquid crystalline molecule and a non-polymerizable discotic liquid crystalline molecule as described above can be used in combination.
The non-polymerizable discotic liquid crystalline molecule is preferably a compound obtained by changing the polymerizable group of the polymerizable discotic liquid crystalline molecule described above to a hydrogen atom or an alkyl group. That is, examples of the non-polymerizable discotic liquid crystalline molecule include compounds described in Japanese Patent No. 2640083.

[Other compositions of optically anisotropic layer]
Along with the above liquid crystal molecules, a plasticizer, a surfactant, a polymerizable monomer, a polymer, or the like can be used in combination to improve the uniformity of the coating film, the strength of the film, the orientation of the liquid crystal molecules, and the like. It is preferable that the compound has compatibility with the liquid crystal molecules and can change the tilt angle of the liquid crystal molecules or does not inhibit the alignment.

  Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Preferably, it is a polyfunctional radically polymerizable monomer and is preferably copolymerizable with the above-described polymerizable group-containing liquid crystal compound. Examples thereof include those described in paragraph numbers [0018] to [0020] in JP-A No. 2002-296423. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline molecules.

Examples of the surfactant include conventionally known compounds, and fluorine compounds are particularly preferable. Specific examples include compounds described in paragraph numbers [0028] to [0056] in JP-A-2001-330725.
The polymer used together with the discotic liquid crystalline molecule is preferably capable of changing the tilt angle of the discotic liquid crystalline molecule.
A cellulose ester can be mentioned as an example of a polymer. Preferable examples of the cellulose ester include those described in paragraph [0178] of JP-A No. 2000-155216. The addition amount of the polymer is preferably in the range of 0.1 to 10% by mass, and in the range of 0.1 to 3% by mass with respect to the liquid crystal compound so as not to disturb the alignment of the liquid crystal molecules. It is more preferable.
The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystal molecules is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

The optically anisotropic layer is a liquid crystalline molecule, or the following polymerizable initiator or any additive (eg, plasticizer, polymerizable monomer, surfactant, cellulose ester, 1,3,5-triazine compound, chiral It is formed by applying a coating solution containing an agent on the alignment film.
As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Of these, alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.
The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

[Fixing the alignment state of liquid crystalline molecules]
The liquid crystalline molecules are preferably substantially uniformly aligned, more preferably fixed in a substantially uniformly aligned state, and the liquid crystalline molecules are fixed by a polymerization reaction. Is most preferred. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).
The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight, based on the solid content of the coating solution.
Light irradiation for polymerization of discotic liquid crystalline molecules is preferably performed using ultraviolet rays.
The irradiation energy is preferably 20 mJ / cm ^{2 to} 50 J / cm ² , and more preferably 100 to 800 mJ / cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. Further, in order to accelerate the polymerization reaction, light irradiation may be performed with the oxygen partial pressure lowered, such as in a nitrogen atmosphere.

The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and most preferably 0.7 to 5 μm. However, depending on the mode of the liquid crystal cell, the optically anisotropic layer may be thickened (3 to 10 μm) in order to obtain high optical anisotropy.
As described above, the alignment state of the liquid crystalline molecules in the optically anisotropic layer is determined according to the type of display mode of the liquid crystal cell. Specifically, the alignment state of liquid crystalline molecules is controlled by the type of liquid crystalline molecules, the type of alignment film, and the use of additives (eg, plasticizers, polymers, surfactants) in the optically anisotropic layer. The

In an optically anisotropic layer in which a discotic compound or rod-shaped compound is oriented, the tilt angle on one surface of the optically anisotropic layer (the physical target axis of the discotic compound or rod-shaped compound is the interface of the optically anisotropic layer) It is difficult to directly and accurately measure θ1 and the tilt angle θ2 of the other surface. Therefore, in this specification, θ1 and θ2 are calculated by the following method. Although this method does not accurately represent the actual orientation state of the present invention, it is effective as a means for expressing the relative relationship of some optical properties of the optical film.
In this method, in order to facilitate calculation, the following two points are assumed and the tilt angle at the two interfaces of the optically anisotropic layer is used.
1. The optically anisotropic layer is assumed to be a multilayer body composed of layers containing a discotic compound or a rod-like compound. Further, it is assumed that the minimum unit layer (assuming that the tilt angle of the discotic compound or rod-shaped compound is uniform in the layer) is optically uniaxial.
2. It is assumed that the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer.
The specific calculation method is as follows.
(1) In a plane in which the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer, the incident angle of the measurement light to the optically anisotropic layer is changed, and three or more The retardation value is measured at the measurement angle. In order to simplify measurement and calculation, it is preferable to measure the retardation value at three measurement angles of −40 °, 0 °, and + 40 °, with the normal direction to the optically anisotropic layer being 0 °. Such measurements include KOBRA-21ADH and KOBRA-WR (manufactured by Oji Scientific Instruments), transmission ellipsometer AEP-100 (manufactured by Shimadzu Corporation), M150 and M520 (manufactured by JASCO Corporation) ), ABR10A (manufactured by UNIOPT Co., Ltd.).
(2) In the above model, the refractive index of ordinary light in each layer is no, the refractive index of extraordinary light is ne (ne is the same value in all layers, and no is the same), and the thickness of the entire multilayer body is d And Further, based on the assumption that the tilt direction of each layer and the uniaxial optical axis direction of the layer coincide with each other, the calculation of the angular dependence of the retardation value of the optically anisotropic layer agrees with the measured value. Fitting is performed using the tilt angle θ1 on one surface of the isotropic layer and the tilt angle θ2 on the other surface as variables, and θ1 and θ2 are calculated.
Here, known values such as literature values and catalog values can be used for no and ne. If the value is unknown, it can also be measured using an Abbe refractometer. The thickness of the optically anisotropic layer can be measured by an optical interference film thickness meter, a cross-sectional photograph of a scanning electron microscope, or the like.

As described above, the optical functional material of the present invention is manufactured. As described above, by using a transparent support and selecting an appropriate formulation within the scope of the present invention, it is possible to produce the optical compensation sheet of the present invention that compensates for birefringence. As described above, the compensation sheet has a layer structure in which a transparent support, an alignment film, and an optically anisotropic layer are laminated in this order.
The optical compensation sheet of the present invention can be used for a liquid crystal display device by remarkably exhibiting its function by being bonded to a polarizing plate or used as a protective film for a polarizing plate.
Hereinafter, the polarizing plate and its production will be described in detail.

<Polarizing plate>
A polarizing plate usually comprises a polarizing film and transparent protective films on both sides thereof. That the protective film is transparent means that the light transmittance is 80% or more. As the transparent protective film, generally a cellulose ester film, preferably an acetyl cellulose film is used. The cellulose ester film is preferably formed by the solvent cast method described in the transparent support. The thickness of the transparent protective film is preferably 20 to 200 μm, and more preferably 30 to 100 μm. Especially preferably, it is 30-80 micrometers.

  In the present invention, the optical compensation sheet of the present invention is used instead of the transparent protective film on one side of the polarizing plate. That is, in the polarizing plate of the present invention, a transparent protective film, a polarizing film, and the optical compensation sheet are laminated in this order. When the polarizing plate according to the present invention is attached to a liquid crystal display device, a liquid crystal display device having excellent optical characteristics and high display quality can be obtained.

[Surface treatment of optical compensation sheet]
When the optical compensation sheet is used instead of the transparent protective film of the polarizing plate, adhesion between the optical compensation sheet and the polarizing film may be a problem. In the present invention, it is preferable to improve the adhesion between the optical compensation sheet and the polarizing film by subjecting the surface of the optical compensation sheet on the side of the polarizing film (that is, the support surface). Examples of the surface treatment include corona discharge treatment, glow discharge treatment, flame treatment, ultraviolet irradiation treatment, ozone treatment, acid treatment, and alkali treatment.
Examples of the treatment method such as corona discharge treatment, glow discharge treatment, flame treatment, ultraviolet irradiation treatment, ozone treatment, acid treatment, and alkali treatment include the contents described in pages 30 to 31 of the aforementioned public technical number 2001-1745. Can be mentioned. In the present invention, it is preferable to perform an alkali treatment, and examples thereof include the same contents as described in the saponification treatment of the above-described film.

[Polarizing film]
The polarizing film used in the present invention is usually preferably a coating type polarizing film represented by Optiva Inc., or a polarizing film comprising a binder and iodine or a dichroic dye. The iodine and the dichroic dye in the polarizing film develop polarizing performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal.
Currently, a commercially available polarizing film is produced by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing iodine or dichroic dye to penetrate into the binder. Is common.
The commercially available polarizing film has iodine or dichroic dye distributed about 4 μm (about 8 μm on both sides) from the polymer surface, and a thickness of at least 10 μm is necessary to obtain sufficient polarizing performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably not more than a commercially available polarizing plate (about 30 μm), preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

The binder of the polarizing film may be cross-linked.
As the crosslinked binder, a polymer that can be crosslinked per se can be used. A polarizing film can be formed by reacting a polymer having a functional group or a binder obtained by introducing a functional group into a polymer between the binders by light, heat, or pH change.
Moreover, you may introduce | transduce a crosslinked structure into a polymer with a crosslinking agent.
Crosslinking is generally carried out by applying a coating liquid containing a polymer or a mixture of a polymer and a crosslinking agent on a transparent support and then heating. Since it is only necessary to ensure durability at the stage of the final product, the crosslinking treatment may be performed at any stage until the final polarizing plate is obtained.

As the binder of the polarizing film, either a polymer that can be crosslinked per se or a polymer that is crosslinked by a crosslinking agent can be used. Examples of the polymer include the same polymers as those described for the alignment film.
Most preferred are polyvinyl alcohol and modified polyvinyl alcohol.
The modified polyvinyl alcohol is described in JP-A-8-338913, JP-A-9-152509 and JP-A-9-316127.
Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

The addition amount of the crosslinking agent in the binder is preferably 0.1 to 20% by mass with respect to the binder. The orientation of the polarizing element and the wet heat resistance of the polarizing film are improved.
The alignment film contains a certain amount of a crosslinking agent that has not reacted even after the crosslinking reaction has been completed. However, the amount of the remaining crosslinking agent is preferably 1.0% by mass or less and more preferably 0.5% by mass or less in the alignment film. In this way, even if the polarizing film is incorporated in a liquid crystal display device and used for a long time or left in a high temperature and high humidity atmosphere for a long time, the degree of polarization does not decrease.
About a crosslinking agent, the description of US reissue patent 23297 is mentioned. Boron compounds (eg, boric acid, borax) can also be used as a crosslinking agent.

As the dichroic dye, an azo dye, stilbene dye, pyrazolone dye, triphenylmethane dye, quinoline dye, oxazine dye, thiazine dye or anthraquinone dye is used. The dichroic dye is preferably water-soluble. The dichroic dye preferably has a hydrophilic substituent (eg, sulfo, amino, hydroxyl).
Examples of the dichroic dye include compounds described in JIII Journal of Technical Disclosure No. 2001-1745, page 58 (issued on March 15, 2001).

  In order to increase the contrast ratio of the liquid crystal display device, the transmittance of the polarizing plate is preferably higher and the degree of polarization is preferably higher. The transmittance of the polarizing plate is preferably in the range of 30 to 50%, more preferably in the range of 35 to 50%, and most preferably in the range of 40 to 50% with respect to light having a wavelength of 550 nm. . The degree of polarization is preferably in the range of 90 to 100%, more preferably in the range of 95 to 100%, and most preferably in the range of 99 to 100% in light having a wavelength of 550 nm.

  When the polarizing film and the optical compensation sheet are arranged via an adhesive, the adhesive may be a polyvinyl alcohol resin (including a modified polyvinyl alcohol with an acetoacetyl group, a sulfonic acid group, a carboxyl group, or an oxyalkylene group) or a boron compound aqueous solution. Can be used. A polyvinyl alcohol resin is preferred. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

[Production of polarizing plate]
From the viewpoint of yield, the polarizing film is stretched by tilting the binder at an angle of 10 to 80 degrees with respect to the longitudinal direction (MD direction) of the polarizing film (stretching method) or rubbed (rubbing method). It is preferable to dye with a dichroic dye. The tilt angle is preferably stretched so as to match the angle formed between the transmission axis of the two polarizing plates bonded to both sides of the liquid crystal cell constituting the LCD and the vertical or horizontal direction of the liquid crystal cell.
A normal inclination angle is 45 °. Recently, however, devices that are not necessarily 45 ° have been developed for transmissive, reflective, and transflective LCDs, and it is preferable that the stretching direction can be arbitrarily adjusted in accordance with the design of the LCD.

In the stretching method, the stretching ratio is preferably 2.5 to 30.0 times, and more preferably 3.0 to 10.0 times. Stretching can be performed by dry stretching in air. Moreover, you may implement wet extending | stretching in the state immersed in water. The stretch ratio of dry stretching is preferably 2.5 to 5.0 times, and the stretch ratio of wet stretching is preferably 3.0 to 10.0 times. The stretching step may be performed in several steps including oblique stretching. By dividing into several times, it is possible to stretch more uniformly even at high magnification. Before the diagonal stretching, a slight stretching may be performed horizontally or vertically (to the extent that shrinkage in the width direction is prevented).
Stretching can be performed by performing tenter stretching in biaxial stretching in different steps. The biaxial stretching is the same as the stretching method performed in normal film formation. In biaxial stretching, stretching is performed at different speeds on the left and right, so that the thickness of the binder film before stretching needs to be different on the left and right. In casting film formation, the flow rate of the binder solution can be differentiated between the left and right sides by tapering the die.
As described above, a binder film that is obliquely stretched by 10 to 80 degrees with respect to the MD direction of the polarizing film is manufactured.

In the rubbing method, a rubbing treatment method widely adopted as a liquid crystal alignment treatment process of LCD can be applied. That is, the orientation is obtained by rubbing the surface of the film in a certain direction using paper, gauze, felt, rubber, nylon, or polyester fiber. Generally, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are planted on average.
The roll itself is preferably carried out using a rubbing roll whose roundness, cylindricity, and deflection (eccentricity) are all 30 μm or less. The wrap angle of the film on the rubbing roll is preferably 0.1 to 90 °. However, as described in JP-A-8-160430, a stable rubbing treatment can be obtained by winding 360 ° or more.
When rubbing a long film, the film is preferably transported at a speed of 1 to 100 m / min in a constant tension state by a transport device. The rubbing roll is preferably rotatable in the horizontal direction with respect to the film traveling direction for setting an arbitrary rubbing angle. It is preferable to select an appropriate rubbing angle in the range of 0 to 60 °. When used in a liquid crystal display device, the angle is preferably 40 to 50 °. 45 ° is particularly preferred.

The transparent protective film is preferably disposed on the surface of the polarizing film opposite to the optical compensation sheet (arrangement of optical compensation sheet / polarizing film / transparent protective film).
It is also preferred that the transparent protective film is provided with an antireflection film having an outermost surface having antifouling properties and scratch resistance. Any conventionally known antireflection film can be used.

As described above, the polarizing plate of the present invention is produced.
The optical compensation sheet of the present invention or the polarizing plate using the optical compensation sheet is advantageously used in a liquid crystal display device, particularly a transmissive liquid crystal display device.
Hereinafter, a liquid crystal display device, particularly a transmissive liquid crystal display device and its manufacture will be described in detail.

"Liquid Crystal Display"
The transmissive liquid crystal display device of the present invention comprises a liquid crystal cell and two polarizing plates arranged on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates.
One optical compensation sheet is disposed between the liquid crystal cell and one polarizing film, or two optical compensation sheets are disposed between the liquid crystal cell and both polarizing films.
A preferred form of the optically anisotropic layer in each liquid crystal mode will be described below.
In a preferable form of the optically anisotropic layer in each liquid crystal mode, the optical compensation sheet of the present invention or the polarizing plate using the optical compensation sheet can be optically compensated advantageously.

(TN mode liquid crystal display)
The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and many publications are cited. The alignment state in the liquid crystal cell in the TN mode black display is an alignment state in which the rod-like liquid crystalline molecules rise at the center of the cell and the rod-like liquid crystalline molecules lie in the vicinity of the cell substrate.

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

(VA mode liquid crystal display device)
In a VA mode liquid crystal cell, rod-like liquid crystal molecules are aligned substantially vertically when no voltage is applied.
The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625) (2) Liquid crystal cell (SID97, Digest of tech. Papers (Preliminary Proceed) 28 (1997) 845 in which the VA mode is made into a multi-domain (MVA mode) for widening the viewing angle ), (3) Liquid crystal cell in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (1998)) and (4) SURVAVAL mode liquid crystal cells (announced at LCD International 98).

(Other liquid crystal display devices)
For IPS mode, ECB mode, and STN mode liquid crystal display devices, optical compensation can be made in the same manner as described above.

Specific examples of the optical functional material, optical compensation sheet, polarizing plate, and liquid crystal display device of the present invention are described below, but the present invention is not limited to these.
[Example 1]
(Preparation of optical compensation sheet 1) (Invention)

(Preparation of cellulose acylate film)
The following composition was put into a mixing tank and stirred while heating to 30 ° C. to dissolve each component to prepare a cellulose acetate solution.

(Cellulose acetate solution composition)
Cellulose acetate solution composition (parts by mass) Inner layer Outer layer Cellulose acetate with an acetylation degree of 60.9% 100 100
Triphenyl phosphate (plasticizer) 7.8 7.8
Biphenyl diphenyl phosphate (plasticizer) 3.9 3.9
Methylene chloride (first solvent) 293 314
Methanol (second solvent) 71 76
1-butanol (third solvent) 1.5 1.6
Silica fine particles (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.)
0 0.8
The following retardation increasing agent 1.50

Retardation raising agent

The obtained inner layer dope and outer layer dope were cast on a drum cooled to 0 ° C. using a three-layer co-casting die. The film having a residual solvent amount of 70% by mass was peeled off from the drum, both ends were fixed with a pin tenter, and the film was dried at 80 ° C. while transporting at a draw ratio of 110% in the transport direction, resulting in a residual solvent amount of 10%. By the way, it was dried at 110 ° C. Thereafter, it was dried at a temperature of 140 ° C. for 30 minutes to prepare a cellulose acylate film 1 (outer layer: 3 μm, inner layer: 74 μm, outer layer: 3 μm) having a residual solvent of 0.3 mass%. The obtained cellulose acylate film had a width of 180 mm and a thickness of 80 μm.
Re (630) of the obtained cellulose acylate film was 8 nm (slow axis in the casting direction), and Rth (630) was 80 nm.

(Saponification treatment)
After passing a dielectric heating roll having a temperature of 60 ° C. on one side of the roll film and raising the film surface temperature to 40 ° C., an alkaline solution having the following composition was applied using a bar coater to 14 ml / m ² , 110 After being kept for 10 seconds under a steam far infrared heater (manufactured by Noritake Co., Ltd.) heated to 0 ° C., 3 ml / m ^{2 of} pure water was applied using the same bar coater. The film temperature at this time was 40 degreeC. Next, washing with a fountain coater and draining with an air knife were repeated three times, and then the film was retained in a drying zone at 70 ° C. for 2 seconds to be dried.

(Alkaline solution composition)
Potassium hydroxide 4.7 parts by weight Water 15.7 parts by weight Isopropanol 64.8 parts by weight Propylene glycol 14.9 parts by weight C ₁₆ H ₃₃ O (CH ₂ CH ₂ O) ₁₀ H (surfactant) 1.0 part by weight Part

Thereafter, a coating solution having the following composition was further applied at 28 mL / m ² with a # 16 wire bar coater. Drying was performed with warm air of 60 ° C. for 60 seconds, and further with warm air of 90 ° C. for 150 seconds.

(Orientation film coating solution composition)
The following modified polyvinyl alcohol 20 parts by mass Water 360 parts by mass Methanol 120 parts by mass Glutaraldehyde (crosslinking agent) 1.0 part by mass

Modified polyvinyl alcohol (average polymerization degree: 4000)

(Surface treatment of alignment film)
Next, the formed film was subjected to plasma treatment. This was performed continuously in the longitudinal direction in the apparatus schematically shown in FIG. In a plasma reaction chamber with a base pressure of 10 Pa due to differential evacuation, a plate punch metal-shaped application electrode 40 μm wide × 1 m long (pores are opened in 10 mm steps from above, from which a source gas (reaction gas + Inert gas) is blown out), a 40 cm wide × 1 m long plate mesh ground electrode, and a transparent support coated with a transported alignment film, in this order in parallel at intervals of about 25 cm (Ie, there is an alignment film in the afterglow region).
When argon gas and NF ₃ gas were introduced from the application electrode side of the reaction chamber so as to be 9: 1, the vacuum degree was kept at 50 Pa, and a high frequency AC voltage of 13.56 MHz was applied between both electrodes, glow discharge occurred. As a result, reddish purple light emission occurred. The applied power at this time was 250W.
The alignment film surface after the treatment was colorless and transparent.
Next, the formed film was rubbed so as to be oriented in a direction parallel to the casting direction of the cellulose acylate film (that is, the rubbing axis was parallel to the casting direction of the cellulose acylate film). .

(Formation of optically anisotropic layer)
On the alignment film using a cellulose acylate film, the following coating solution is rotated in the same direction as the film conveyance direction by rotating the # 4 wire bar at 764 rotations, and the roll film being conveyed at 24 m / min. It applied continuously to the alignment film surface. The solvent is dried in a process of continuously heating from room temperature to 100 ° C., and then the film surface wind speed corresponding to the discotic liquid crystal compound layer is 1.0 m parallel to the film conveying direction in the drying zone supplied to 130 ° C. / Sec and heated for about 120 seconds to align the discotic liquid crystal compound. Next, the film is transported to a drying zone supplied at 80 ° C., and an ultraviolet ray irradiation device (ultraviolet lamp: output 160 W / cm) is irradiated with ultraviolet rays having an illuminance of 600 mW for 4 seconds while the surface temperature of the film is about 95 ° C. Irradiation allowed the crosslinking reaction to proceed and the discotic liquid crystal compound was fixed in its orientation. Thereafter, the mixture was allowed to cool to room temperature and wound into a cylindrical shape to form a roll. Thus, an optical compensation sheet 1 was produced.

(Coating solution composition of optically anisotropic layer)
The following composition was dissolved in 107 parts by mass of methyl ethyl ketone to prepare a coating solution.
The following discotic liquid crystalline compound (1) 41.01 parts by mass Ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) 4.06 parts by mass Cellulose acetate butyrate (CAB551-0.2) 0.9 parts by mass Cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemicals Co., Ltd.) 0.21 parts by mass Fluoro aliphatic group-containing polymer (Megafac F780, Dainippon Ink Co., Ltd.) 0.14 parts by mass Photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.35 parts by mass Sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 parts by mass

Discotic liquid crystalline compounds (1)

(Preparation of optical compensation sheet 2) (Invention)
An optical compensation sheet 2 was produced in the same manner as the optical compensation sheet 1 except that plasma treatment on the alignment film was performed after rubbing.

(Preparation of optical compensation sheet 3) (Invention)
An optical compensation sheet 3 was produced in the same manner as the optical compensation sheet 2 except that the plasma treatment on the alignment film was performed by batch treatment. Since it was a batch process, the degree of vacuum in the plasma reaction chamber could be improved as compared with the case where the compensation sheet 2 was produced, and the base pressure was 1 Pa.

(Preparation of optical compensation sheet 4) (Invention)
An optical compensation sheet 4 was produced in the same manner as the optical compensation sheet 2 except that atmospheric pressure glow discharge was used instead of vacuum glow discharge in the plasma treatment on the alignment film.
In producing this sheet, the reaction outer chamber 8 was removed from the apparatus schematic diagram shown in FIG. 1 in the plasma treatment step. The applied power was pulsed, the rise time and fall time of the pulse electric field were both 80 ns, and the intensity of the pulse electric field was 30 kV / cm. The formation time of the pulse electric field was an average of 50 ms. The electrode was provided with a solid dielectric made of sintered ceramics on the opposing surface side, and the specific resistance was 10 ⁹ Ω · cm.

(Preparation of optical compensation sheet 5) (Invention)
In the plasma treatment on the alignment film, an optical compensation sheet 5 was produced in the same manner as the optical compensation sheet 2 except that CF ₄ was used as a reactive gas and the applied power was 300 W.

(Preparation of optical compensation sheet 6) (Comparative example)
An optical compensation sheet 6 was produced in the same manner as the optical compensation sheet 1 except that the plasma treatment was not performed on the alignment film.

(Preparation of optical compensation sheet 7) (Comparative example)
As a composition of the alignment film, 1.5 parts by mass of the following fluoroaliphatic group-containing polymer 1 (surfactant) is added to the composition used in the optical compensation sheet 1, and then the alignment film is converted into the optical compensation sheet 1. It was coated in the same way. Moreover, the optical compensation sheet 7 was produced without performing plasma treatment.
However, after the alignment film was applied, the dried alignment surface was observed, and repellency failures occurred frequently. When the liquid crystal layer was applied, unevenness and repellency occurred on the entire surface. It was bad.

(Preparation of optical compensation sheet 8) (present invention)
The optical compensation sheet 8 was created by changing the following points in the method of creating the optical compensation sheet 2. 1) The alignment film coating solution was a mixed solution of 4.8 parts by mass of polyimide-based low-temperature processing type alignment film Optomer AL3046 (manufactured by JSR Corporation) and 8.0 parts by mass of γ-butyllactone. 2) Drying after coating is performed with warm air of 60 ° C. for 90 seconds, warm air of 90 ° C. for 150 seconds, and further with warm air of 130 ° C. for 10 minutes. This was done by drying for a total of 40 minutes. The subsequent steps are the same as the method for producing the optical compensation sheet 2.

The discotic liquid crystalline compound of the optically anisotropic layer was hybrid-aligned so that the angle formed by the disk surface and the support surface increased with increasing distance from the support.
When the polarizing plates are arranged in a crossed Nicol arrangement and the unevenness of the obtained optical compensation sheets 1 to 8 is observed, the optical compensation sheets 1 to 6 and 8 are viewed from the front side and the direction inclined from the normal to 60 degrees. However, no unevenness was detected. As described above, the optical compensation sheet 7 of the comparative example had unevenness, repellency, and poor alignment on the entire surface.

(Measurement of tilt angle of optically anisotropic layer of optical compensation sheet)
In the optically anisotropic layer made of the discotic liquid crystalline compound of each optical compensation sheet, the tilt angles (θ1 and θ2) of the liquid crystal compound were calculated by the optical method described in this specification. In the discotic liquid crystal molecules, the angle (tilt angle) formed by the disk surface and the alignment film plane was hybrid aligned from the film surface toward the optical air interface. The results are shown in Table 1. Note that none of the samples had a uniform tilt angle in the depth direction, and had variations that were assumed to be caused by thermal and physical fluctuations. The results in Table 1 show average results.

(Preparation of polarizing plate)
A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by immersing it in an aqueous iodine solution having an iodine concentration of 0.05% by mass at 30 ° C. for 60 seconds, and then in an aqueous boric acid solution having a boric acid concentration of 4% by mass. The film was vertically stretched to 5 times the original length while being immersed for 2 seconds, and then dried at 50 ° C. for 4 minutes to obtain a polarizing film having a thickness of 20 μm.
The optical compensation sheets 1 to 8 were immersed in an aqueous sodium hydroxide solution at 55 ° C. at 1.5 mol / L, and then the sodium hydroxide was sufficiently washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at 35 ° C. for 1 minute at 0.005 mol / L, the diluted sulfuric acid aqueous solution was sufficiently washed away by immersion in water. Finally, the sample was thoroughly dried at 120 ° C.
At this time, the film surface of the optical compensation sheet 7 was peeled off, making it impossible to produce a polarizing plate.
Using the polyvinyl alcohol-based adhesive so that the optical compensation sheets 1 to 6 and 8 subjected to the saponification treatment as described above are combined with the commercially available cellulose acylate film subjected to the same saponification treatment so as to sandwich the polarizing film. Bonded polarizing plates 1 to 6 and 8 were obtained. Here, Fujitac TF80UL (Fuji Photo Film Co., Ltd.) was used as a commercially available cellulose acylate film. At this time, since the polarizing film and the protective films on both sides of the polarizing film are produced in a roll form, the longitudinal directions of the roll films are parallel to each other and are continuously bonded. Therefore, the optical compensation sheet roll lengthwise direction was parallel to the polarizer absorption axis.

(Evaluation with TN liquid crystal cell)
A pair of polarizing plates provided in a liquid crystal display device using a TN type liquid crystal cell (Syncmaster 172X, manufactured by Samsung Electronics Co., Ltd.) is peeled off. Instead, the above-prepared polarizing plate is replaced with an optical compensation sheet on the liquid crystal cell side. It stuck on the observer side and the backlight side through the adhesive so that it might become. The transmission axis of the polarizing plate on the viewer side and the transmission axis of the polarizing plate on the backlight side were arranged to be in the O mode.
About the produced liquid crystal display device, the viewing angle was measured from black display (L1) to white display (L8) using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM). On the left and right, an area having a contrast ratio (white transmittance / black transmittance) of 10 or more was determined as a viewing angle. The measurement results are shown in Table 2.

It is a schematic diagram of the plasma reaction equipment preferably used in the present invention.

Explanation of symbols

1: RF power supply
2: Film-like support provided with an alignment film
3: RF electrode
4: Raw material gas (reaction gas + inert gas mixture)
5: Mesh ground electrode
6: Glow discharge plasma
7: Plasma reaction chamber
8: Plasma reaction outer chamber
9: Earth
10: Transport roller

Claims (9)

In an optical compensation sheet formed by forming an alignment film on a support and then applying an optically anisotropic layer coating liquid containing a discotic liquid crystalline compound on the alignment film to form an optically anisotropic layer. An optical compensation sheet formed by performing plasma treatment on the film in the afterglow region of glow discharge plasma and then applying an optically anisotropic layer coating liquid.   2. The optical compensation sheet according to claim 1, wherein the alignment film is a cured film formed by applying and drying an alignment film forming composition containing polyvinyl alcohol and / or modified polyvinyl alcohol as a main component.   The optical compensation sheet according to claim 1, wherein the alignment film contains polyimide as a main component. The optical compensation sheet according to claim 1, wherein a reaction gas in the plasma treatment is a substance containing halogen. A polarizing plate, wherein a transparent protective film, a polarizing film, and the optical compensation sheet according to any one of claims 1 to 4 are laminated in this order. In a liquid crystal display device comprising a polarizing film and polarizing plates comprising two transparent protective films disposed on both sides of the polarizing film, the two sheets disposed between the liquid crystal cell and the polarizing film. A liquid crystal display device, wherein at least one of the transparent protective films is the optical compensation sheet according to any one of claims 1 to 4 . A method for producing an optical compensation sheet comprising forming an optically anisotropic layer by applying an optically anisotropic layer coating liquid containing a discotic liquid crystalline compound on the alignment film after forming the oriented film on the support A method for producing an optical compensation sheet, comprising: forming an alignment film on a support and then performing a plasma treatment on the alignment film in an afterglow region of glow discharge plasma . 8. The method of manufacturing an optical compensation sheet according to claim 7 , wherein the plasma treatment step is performed after the rubbing treatment step of the support having the alignment film applied thereto. The method of manufacturing an optical compensation sheet according to claim 7 or 8 , wherein the support is a film, and the plasma treatment is continuously performed in a longitudinal direction.

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