JP2747789B2 - Optical compensation sheet and liquid crystal display device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensatory sheet, and more particularly to an optical compensatory sheet useful for improving the contrast and the viewing angle characteristics of display colors of a TN type liquid crystal display device.

[0002]

2. Description of the Related Art A CRT which is a mainstream display device of OA equipment such as a Japanese word processor and a desktop personal computer.
Has been converted to a liquid crystal display element having great advantages such as thin and light weight and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) that are currently widely used use twisted nematic liquid crystals. Display methods using such a liquid crystal can be roughly classified into two methods, a birefringence mode and an optical rotation mode.

An LCD using a birefringence mode has a liquid crystal molecule arrangement in which the twist angle is twisted by 90 ° or more and has a steep electro-optical characteristic. Therefore, a simple matrix without an active element (thin film transistor or diode) is used. A large-capacity display can be obtained by time-sharing driving with a rectangular electrode structure. But,
LCDs using this birefringence mode have the disadvantage that response speed is slow (several hundred milliseconds) and that gray scale display is difficult. Therefore, liquid crystal display devices using active elements (TFT-LCD, MIM-LCD, etc.) It does not reach the point where the display performance of ()) is exceeded.

In the TFT-LCD and the MIM-LCD, an optical rotation mode display mode (TN type liquid crystal display element) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method has a fast response speed (several tens of milliseconds), can easily obtain a white display, and has a high display contrast. Therefore, this display method is the most effective method for improving the image quality as compared with LCDs of other methods. is there. However, since the twisted nematic liquid crystal is used, there is a problem in viewing angle characteristics such that a display color and a display contrast change depending on a viewing direction due to a principle of a display method, and the display performance of a CRT cannot be exceeded.

JP-A-4-229828, JP-A-4-2-2
As disclosed in Japanese Patent No. 58923, a method has been proposed in which a viewing angle is increased by disposing a retardation film between a pair of polarizing plates and a TN type liquid crystal cell. The retardation film proposed in the above patent gazette has a phase difference of almost zero in a direction perpendicular to the liquid crystal cell, and has no optical effect from directly in front of the liquid crystal cell.
A phase difference is developed when tilted, and the phase difference developed in the liquid crystal cell is to be compensated. However, even with these methods, the viewing angle of the LCD is still insufficient, and further improvement is desired. In particular, when it is considered as an in-vehicle type or as a substitute for a CRT, the current viewing angle cannot be used at all.

In JP-A-4-366808 and JP-A-4-366809, a viewing angle is improved by using a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis as a retardation film. This is a two-layer liquid crystal system, which is expensive and very heavy. Further, JP-A-4-113301 and JP-A-5-80323 disclose
For liquid crystal cells, a method of using a retardation film whose optical axis is inclined has been proposed, but since uniaxial polycarbonate is sliced obliquely, a large-area retardation film can be used at low cost. There was a problem that it was difficult to obtain. JP-A-5-157913, EP 057630
4A1 proposes a method of using a retardation film whose optical axis is inclined by performing special stretching on polycarbonate, but it is still difficult to obtain a large-area retardation film at low cost. .

Japanese Patent Application Laid-Open No. Hei 5-215921 proposes a method of optically compensating an LCD by using a birefringent plate in which a pair of alignment-treated substrates is sandwiched with a rod-like compound exhibiting liquid crystallinity when cured. However, this proposal is no different from the so-called double-cell type compensator proposed in the past, which greatly increases the cost and is not suitable for mass production. Further, as long as the rod-shaped compound is used, the birefringent plate has TN for the optical reason described later.
It is impossible to improve the omnidirectional viewing angle of the LCD. Also, JP-A-3-9326 and JP-A-3-291601 describe a method of applying an optical compensator for an LCD by applying a polymer liquid crystal to a film-like substrate provided with an alignment film. However, since it is impossible to align molecules obliquely with this method, TN-type LCDs
It is impossible to improve the omnidirectional viewing angle.

The present inventors have invented an optical compensatory sheet in which a layer containing a discotic compound is oriented on an orientation film provided on a plane-oriented transparent film, and is disclosed in Japanese Patent Application No. 5-236.
No. 539. In this optical compensatory sheet, a monodomain structure in which the discotic compound has a tilted orientation has a negative uniaxial optical property in which the optical axis is tilted, and the optical axis is in the normal direction due to the plane orientation of the transparent film. Due to the synergistic effect with the negative uniaxial optical characteristic described above, there is no optical axis as a whole, but there is a minimum value of the absolute value of the retardation, and the direction is tilted from the normal direction of the optical compensation sheet. It has characteristics and can further improve the viewing angle in all directions as compared with the conventionally proposed optical compensation sheet for TFT. However, when the optical compensation film is used as an optically anisotropic element in a liquid crystal display device, there has been a problem that peeling or cracking occurs due to poor adhesion between the alignment film and the transparent polymer film.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to industrially provide an optical compensatory sheet capable of significantly widening the viewing angle of a TN type LCD. The purpose is to improve the adhesion between the film.

[0010]

According to the present invention, the in-plane principal refractive indexes nx and ny and the principal refractive index nz in the thickness direction are represented by the following formula (1): 10 ≦ {(nx + ny) / 2−nz} d ≦ 600 --- (1) (where d represents a film thickness (unit: nm)), after performing a surface activation treatment on a transparent polymer film or installing an adhesion improving layer, An alignment film is formed on the surface, and then a discotic compound is placed on the alignment film in a range of 5 ° to 85 ° from the normal direction of the transparent polymer film.
(4) An optical compensatory sheet comprising a layer formed by preferentially orienting the discotic compound so that the normal direction of the disc surface of the discotic compound is in the inclined direction. The present invention provides a liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, two polarizing plates disposed on both sides thereof, and at least one polarizing plate between the liquid crystal cell and the polarizing plate. A liquid crystal display device comprising the above optical compensation sheet, wherein the optical compensation sheet is the above-mentioned optical compensation sheet. In the optical compensation sheet, the intrinsic birefringence of the transparent polymer film is preferably 0.05 or less.

Hereinafter, the usefulness of the present invention will be described. First,
The optical utility will be described using a TN type LCD as an example with reference to the drawings. 1 and 2 show the polarization state of light propagating through the liquid crystal cell when a sufficient voltage equal to or higher than the threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light when a voltage is applied particularly greatly contributes to the viewing angle characteristics of the contrast, the description will be made by taking a voltage application as an example. FIG. 1 is a diagram illustrating a polarization state of light when the light is vertically incident on the liquid crystal cell. When the natural light L0 is perpendicularly incident on the polarizing plate A having the polarizing axis PA, the light transmitted through the polarizing plate PA becomes linearly polarized light L1.

When the arrangement state of the liquid crystal molecules when a sufficient voltage is applied to the TN type liquid crystal cell is schematically represented by one liquid crystal molecule, LC in the schematic diagram is obtained. When modeled by liquid crystal molecules in a liquid crystal cell, if the molecular long axis of LC in the schematic diagram is parallel to the path of light, a difference in refractive index occurs on the incident surface (in a plane perpendicular to the path of light). Therefore, even when the light passes through the liquid crystal cell, it propagates as linearly polarized light. Polarization axis P of polarizing plate B
When B is set perpendicular to the polarization axis PA of the polarizing plate A, the linearly polarized light L2 that has passed through the liquid crystal cell cannot pass through the polarizing plate B and is in a dark state.

FIG. 2 is a diagram showing the polarization state of light when the light is obliquely incident on the liquid crystal cell. Natural light L of incident light
When 0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes substantially linearly polarized light. (In practice, it becomes elliptically polarized light due to the characteristics of the polarizing plate). In this case, the refractive index anisotropy of the liquid crystal causes a difference in the refractive index on the incident surface of the liquid crystal cell, and the light L2 transmitted through the liquid crystal cell is elliptically polarized and is not completely blocked by the polarizing plate B. As described above, in the oblique incidence, the blocking of light in the dark state becomes insufficient, and the contrast is greatly reduced, which is not preferable.

An object of the present invention is to industrially provide an optical compensatory sheet capable of preventing such a decrease in contrast at oblique incidence and improving viewing angle characteristics. FIG. 3 shows a usage example of the optical compensation sheet manufactured according to the present invention. Between the polarizing plate A and the liquid crystal cell TNC, an optical compensation sheet RF1 having a minimum value of the absolute value of the retardation in a direction inclined from the normal direction of the liquid crystal cell is disposed. The optical compensatory sheet RF1 is a birefringent body whose phase difference increases as the angle of incidence of light with respect to this direction increases. Further, an optical compensation sheet RF2 having the same optical characteristics as the optical compensation sheet RF1 is disposed between the polarizing plate B and the liquid crystal cell TNC. When the natural light L0 is obliquely incident on the liquid crystal display device having such a configuration as in the case of FIG. 2, the optical modulation described below occurs. First, the light is converted into linearly polarized light L1 by the polarizing plate A, and is modulated into elliptically polarized light L3 by a phase delay effect when transmitted through the optically anisotropic element RF1. Next, when the light passes through the liquid crystal cell TNC, the light is modulated into the elliptically polarized light L4 having the opposite phase. When the light passes through the optically anisotropic element RF2, the light is returned to the original linearly polarized light L5 by the phase delay effect. By such an operation, the same transmittance of the natural light L0 can be obtained even at various oblique incidences, and a liquid crystal display device capable of high-quality display without dependence on viewing angle can be obtained.

It is estimated that the viewing angle of the liquid crystal display device can be greatly improved by the optical compensatory sheet of the present invention as follows. Many TN-LCDs employ a normally white mode. In this mode, as the viewing angle is increased, the transmittance of light from the black display section is significantly increased, resulting in a sharp decrease in contrast. The black display is a state when a voltage is applied. At this time, the liquid crystal molecules in the TN liquid crystal cell are arranged as shown in the model of FIG. When the arrangement of the liquid crystal molecules is approximated by a plurality of refractive index ellipsoids having substantially the same triaxial refractive index, the result is as shown in FIG. 4B. In the TN liquid crystal cell, the optical axis is slightly inclined from the direction normal to the cell surface. It can be considered as a laminate of four positive uniaxial optically anisotropic bodies and two positive uniaxial optically anisotropic bodies whose normal axis and the optical axis are in the same direction.

If the liquid crystal cell can be regarded as a laminated body of four positive uniaxial optically anisotropic bodies, in order to compensate for it, a negative uniaxial optical element having the same combination of the optical axis inclination angles as that of the laminated body is used. It is preferable to use four anisotropic bodies. In the case of the present invention,
The disc-shaped compound layer acts as a negative uniaxial optical anisotropic body whose optical axis is slightly inclined from the normal direction to the cell surface, and the negative optical axis is oriented in the same direction as the normal direction to the cell surface. The plane-oriented base film acts as a uniaxial optically anisotropic body. For these reasons, it is presumed that the viewing angle characteristics were significantly improved by the negative uniaxial optically anisotropic laminate in the present invention.

If a specific discotic liquid crystal is selected as the discotic compound, and the discotic liquid crystal phase is solidified in the aligned state, its structure is maintained below the discotic liquid crystal phase / solid phase transition temperature. The optically anisotropic body is thermally stable.

The discotic liquid crystal in the present invention is as listed below, but the molecules themselves have negative uniaxiality and the optical axis is oriented obliquely to the substrate surface by the oblique orientation film. If so, it is not particularly limited to the following substances.

[0019]

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[0020]

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[0021]

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[0022]

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The negative uniaxial discotic liquid crystal layer in the present invention, the 3 axial refractive index of the liquid crystal layer, when the n _1, n _2, n ₃ in order that the value is less, n ₁ <n ₂ = n ₃
It has the following relationship. Therefore, it has the characteristic that the refractive index in the optical axis direction is the smallest. However,
The values of n ₂ and n ₃ need not be exactly equal, but need only be approximately equal. Specifically, there is no practical problem if | n ₂ −n ₃ | / | n ₂ −n ₁ | ≦ 0.2. Further, as conditions for greatly improving the viewing angle characteristics of the TFT and TN type liquid crystal cells, it is preferable that the optical axis of the liquid crystal layer has an inclination β from the normal direction of the sheet surface of 5 to 50 degrees, 10 degrees to 40 degrees is more preferable. Further, when the thickness of the liquid crystal layer is a, it is preferable to satisfy the following condition: 50 ≦ Δn ′ · a ≦ 300 (nm). Where Δn ′ = (n
₂ + n ₃₎ is / 2-n _1.

Next, the alignment film of the present invention will be described. Discotic liquid crystal that can obtain an effective alignment simply by rubbing the substrate surface and applying it on it
Although there are combinations of substrates, the most versatile method is to use an alignment film. As the alignment film, an inorganic oblique deposition film or an alignment film obtained by rubbing a specific organic polymer film corresponds to this. Further, L made of an azobenzene derivative
This also applies to a thin film in which molecules are isomerized by light and molecules are uniformly arranged with directionality, such as a B film. A typical example of the organic alignment film is a polyimide film. In this method, a polyamic acid (for example, SE-7210 manufactured by Nissan Chemical Co., Ltd.) is applied to the substrate surface and the temperature is increased from 100 ° C. to 300
By rubbing after baking at a temperature of ° C., the discotic compound can be oriented. Further, alkyl chain-modified poval (for example, MP203 and R1130 manufactured by Kuraray Co., Ltd.)
Etc.), baking is not required, and the orientation ability can be imparted only by rubbing. In addition, most organic polymer films that form a hydrophobic surface, such as polyvinyl butyral and polymethyl methacrylate, can impart alignment ability by rubbing the surface.

The above-mentioned alignment film has the function of determining the alignment direction when the discotic compound applied thereon forms a discotic liquid crystal. However, since the orientation of the discotic liquid crystal also depends on the primary structure of the discotic compound, it is necessary to optimize the combination. Next, once aligned discotic liquid crystal molecules are oriented at a certain angle θ with respect to the substrate surface, the angle of oblique alignment does not change much depending on the type of alignment film in the one-component system, and the value specific to discotic liquid crystal molecules is changed. Often taken. When two or more discotic liquid crystal molecules are mixed, the tilt angle can be adjusted within a certain range by the mixing ratio. Therefore, to control the tilt angle of the tilt alignment, selection of the discotic liquid crystal type, and
A method of mixing at least three or more discotic liquid crystal molecules is effective.

The polymer film used for the optical compensatory sheet of the present invention has good light transmittance, and in addition to the formula (1)
It is necessary to have a retardation of the plane orientation. Equation (1) is a state that satisfies 10 ≦ {(nx + ny) / 2−nz} × d ≦ 600 (nm). Here, nx and ny are the main refractive indexes orthogonal to each other in the film plane, and nz is the main refractive index in the thickness direction of the film. nx = ny is preferred, but nx and n
The values of y need not be exactly equal, but it is sufficient if they are approximately equal. Specifically, there is no practical problem if | nx-ny | / | nx-nz | ≦ 0.2. It is more preferable that the condition (2) satisfy 20 ≦ {(nx + ny) / 2−nz} × d ≦ 300 (nm). The polymer film is formed by a solution casting method or a melt extrusion method. In general, in the solution casting method, plane orientation occurs due to evaporation of a solvent in a state where the width and length are regulated, and in the melt extrusion method, stretching is performed. Plane orientation occurs. As shown in the formulas (1) and (2), a material having an intrinsic birefringence value of 0.05 or less is required for industrially controlling a relatively low retardation. Specifically, a film formed from a material sold under a trade name such as ZEONEX (Zeon Corporation of Japan), ARTON (Japan Synthetic Rubber), or FUJITAC (Fuji Photo Film) is preferable.

Next, the adhesion improving treatment of the present invention will be described. In order to improve the adhesion between the polymer film and the alignment film, (1) were then treated for surface activation, directly alignment film coating
A method of forming to obtain adhesion Ri, (2) once the surface treatment, or without the surface treatment, a subbing layer is provided, and <br/> Ru method to form a coating an alignment film on the There are two methods, for example, Dr. K. Keller
Editing Science and Technology
(VCH, 1993) describes various methods. Various modifications have also been made to the structure of the undercoat layer (adhesion improving layer). A layer (hereinafter, abbreviated as the first undercoat layer) that adheres well to the polymer film is provided as the first layer. A so-called multi-layer method in which a hydrophilic resin layer (hereinafter, abbreviated as a second undercoat layer) that adheres well to the alignment film as a second layer is formed by coating, and a resin containing both a hydrophobic group and a hydrophilic group. There is a single-layer method in which a single layer is formed by coating.

(2) With respect to the undercoating method, the first undercoating layer in the multilayer method is, for example, a single layer selected from vinyl chloride, vinylidene chloride, butadiene, methacrylic acid, acrylic acid, itaconic acid, maleic anhydride and the like. Starting from copolymers starting from monomers, polyethyleneimine, epoxy resin, grafted gelatin, nitrocellulose, polyvinylbromide, polyvinylfluoride, polyvinylacetate, chlorinated polyethylene, chlorinated polypropylene, brominated Polyethylene, chloride rubber, vinyl chloride-ethylene copolymer, vinyl chloride-propylene copolymer, vinyl chloride-styrene copolymer, isobutylene chloride copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-styrene-anhydrous Maleic acid terpolymer, vinyl chloride-styrene-acrylonitrile Polymer, vinyl chloride-butadiene copolymer, vinyl chloride-isoprene copolymer, vinyl chloride-chlorinated propylene copolymer, vinyl chloride-vinylidene chloride-vinyl acetate terpolymer, vinyl chloride-acrylate copolymer Polymer, vinyl chloride-maleic acid ester copolymer, vinyl chloride methacrylic acid ester copolymer, vinyl chloride-acrylonitrile copolymer, internally plasticized polyvinyl chloride, vinyl chloride-vinyl acetate copolymer,
Halogen containing polyvinylidene chloride, vinylidene chloride-methacrylic acid ester copolymer, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-acrylic acid ester copolymer, chloroethyl vinyl ether-acrylic acid ester copolymer, polychloroprene, etc. Α-olefin copolymers such as synthetic resins, polyethylene, polypropylene, polybutene, poly-3-methylbutene, poly-1,2-butadiene, etc., ethylene-propylene copolymers, ethylene-vinyl ether copolymers, ethylene-
Propylene-1,4-hexadiene copolymer, ethylene-vinyl acetate copolymer, butene-1-propylene copolymer, butadiene-acrylonitrile copolymer, and blends of these copolymers with halogen-containing resins, acrylic Acid methyl ester-acrylonitrile copolymer, acrylic acid ethyl ester-styrene copolymer, methacrylic acid methyl ester-acrylonitrile copolymer, polymethacrylic acid methyl ester, methacrylic acid methyl ester-styrene copolymer, methacrylic acid butyl ester- Styrene copolymer, polymethyl acrylate, poly-α
-Methyl chloroacrylate, methoxyethyl acrylate, glycidyl polyacrylate, butyl acrylate, methyl acrylate, ethyl acrylate, acrylate-butyl acrylate copolymer, acrylate- Acrylic resin such as butadiene-styrene copolymer, methacrylate-butadiene-styrene copolymer,
Polystyrene, poly-α-methylstyrene, styrene-
Dimethyl fumarate copolymer, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, styrene-
Butadiene-acrylonitrile copolymer, poly-2,6
-Dimethylphenylene oxide, styrene-acrylonitrile copolymer, polyvinylcarbazole, poly-p
-Xylylene, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl phthalate, cellulose triacetate, cellulose butyrate, cellulose butyrate, cellulose phthalate, nylon 6, nylon 6
6, nylon 12, methoxymethyl-6-nylon, nylon 6, 10 polycapramide, poly-N-butyl-nylon-6 polyethylene sebacate, polybutylene glutarate, polyhexamethylene adipate, polybutylene isophthalate, polyethylene terephthalate, polyethylene Adipate, polyethylene adipate terephthalate, polyethylene-2,6-naphthalate, polydiethylene glycol terephthalate, polyethylene oxybenzoate, bisphenol A-isophthalate,
Polyacrylonitrile, bisphenol A-adipate, polyhexamethylene-m-benzenedisulfonamide, polytetramethylenehexamethylene carbonate,
Polydimethylsiloxane, polyethylene methylene bis-
There are oligomers and polymers such as 4-phenylene carbonate and bisphenol A-polycarbonate (for these, EHImmergut "Polymer Handboo"
k "IV187-231, Intersciense Pub. New York 19
In the second subbing layer (e.g., No. 66 etc.), its properties have mainly been studied for gelatin.

In the single-layer method, good adhesion is achieved by expanding the polymer film and mixing it with the hydrophilic undercoat polymer at the interface. Examples of the hydrophilic undercoat polymer used in the present invention include a water-soluble polymer, a cellulose ester, a latex polymer, and a water-soluble polyester. Examples of the water-soluble polymer include gelatin, gelatin derivatives, casein, agar, sodium alginate, starch, polyvinyl alcohol, polyacrylic acid copolymer, and maleic anhydride copolymer.Examples of cellulose esters include carboxymethyl cellulose and hydroxyethyl cellulose. And so on. Latex polymers include vinyl chloride-containing copolymers, vinylidene chloride-containing copolymers, acrylate-containing copolymers, vinyl acetate-containing copolymers, butadiene-containing copolymers, and the like. Among these, gelatin is most preferred. As gelatin, so-called lime-processed gelatin, acid-processed gelatin,
Any of those generally used in the art, such as enzyme-treated gelatin, gelatin derivatives, and modified gelatin, can be used. Among these gelatins, lime-treated gelatin and acid-treated gelatin are most preferably used. These gelatins contain various impurities in the preparation process, for example, metals (Na, K, Li, Rb, Ca, Mg, Ba, Ce, F, 0.01 to 20,000 ppm).
e, Sn, Pb, Al, Si, Ti, Au, Ag, Z
Metals such as n and Ni, and ions thereof, and ions (F, Cl, Br, I, sulfate ions, nitrate ions, acetate ions, ammonium ions, etc.) may be contained. Particularly in lime-processed gelatin, it is common knowledge in the art that Ca and Mg ions are contained.
It is very wide as 0 to 3000 ppm, but is preferably 1000 ppm or less, more preferably 500 ppm, in terms of undercoat coating performance.
ppm or less. Specific examples of the compound used in the adhesion improving layer of the present invention are shown below.

[0030]

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In addition, various additives can be contained in the undercoat liquid, if necessary. For example, surfactants,
Antistatic agents, pigments, coating aids and the like. Various known gelatin hardeners can be used for the undercoat layer of the present invention. Examples of gelatin hardeners include chromium salts (chromium alum, etc.), aldehydes (formaldehyde, glutaraldehyde, etc.), isocyanates, epichlorohydrin resins, polyamide-epichlorohydrin resins (JP-B-49-26580, JP-A-51-3619). , Cyanuric chloride compounds (for example, JP-A-47-6151)
No. 47-33380, No. 54-25411, compounds described in JP-A-56-130740), vinyl sulfone or sulfonyl compounds (for example, Japanese Patent Publication No. Sho 4).
Nos. 7-24259 and 50-35807,
No. 24435, No. 53-41221, No. 59-18
No. 944), carbamoyl ammonium salt compounds (for example, JP-B-56-12853, JP-B-58-32699, JP-A-49-51945, and JP-A-49-51945).
1-59625 and 61-9641), amidinium salt-based compounds (for example,
No. 225148), carbodiimide compounds (for example, JP-A-51-126125 and JP-A-52-4).
No. 8311), pyridinium salt compounds (for example, JP-B-58-50699, JP-A-52-5)
No. 4427, JP-A-57-44140 and JP-A-57-46140.
No. 538), and other Bergi Patent No. 82.
No. 5,726, U.S. Pat. No. 3,321,313, JP-A-50-38540, JP-A-52-93470, and JP-A-56-93470.
And compounds described in JP-A-43353 and JP-A-58-113929.

The undercoat layer of the present invention may contain inorganic or organic fine particles as a matting agent to such an extent that transparency is not substantially impaired. Silica (SiO ₂ ), titanium dioxide (Ti)
O ₂ ), calcium carbonate, magnesium carbonate and the like can be used. Organic fine particle matting agents include polymethyl methacrylate, cellulose acetate propionate, polystyrene, and US Pat. No. 4,142,89.
No. 4, the processing solution soluble polymer described in U.S. Pat. No. 4,396,706 and the like can be used. The average particle size of these fine particle matting agents is preferably 0.01 to 10 μm. More preferably, it is 0.05 to 5 μm. The content is preferably 0.5 to 600 mg / m2, more preferably 1 to 400 mg / m2.

The undercoating liquid according to the present invention can be applied by a well-known coating method such as a dip coating method, an air-knife coating method, a curtain coating method, a roller coating method, and a wire coating method. The coating can be performed by a bar coating method, a gravure coating method, a slide coating method, or an extrusion coating method using a hopper described in U.S. Pat. No. 2,681,294. . If desired, U.S. Pat. Nos. 2,761,791, 3,508,947, 2,941,898 and 3,526,528, Yuji Harazaki, "Coating Engineering" 253 Two or more layers can be applied simultaneously by the method described in the page (1973, published by Asakura Shoten).

When the glow discharge treatment is used, a sufficient adhesion between the support and the emulsion layer can be obtained without using an etching solvent such as parachlorophenol or resorcin in the undercoating liquid in a single layer system. If it is an organic solvent system,
A composition mainly composed of a solvent having a low boiling point such as methanol may be used, and if there is no problem in drying load, an aqueous system may be used.

[0035]

EXAMPLES Example 1 A roll film of triacetyl cellulose manufactured by Fuji Photo Film Co., Ltd. (thickness: 100 μm, Δ (nx + ny) /
2-nz｝ d = 70 nm), a gelatin layer (0.1 μm) was applied on one side, and a layer of the compound indicated by P-5 was applied on the other side, and the particle size was A layer of diacetylcellulose containing 0.1 μm silica was applied. Then, an alkyl-modified polyvinyl alcohol solution (manufactured by Kuraray Co., Ltd., Poval MP-20) was placed on the gelatin layer.
After 3) was applied and dried with hot air of 110 ° C. for 30 seconds, rubbing treatment was performed to obtain an alignment film. On the above-mentioned alignment film, a disc-shaped compound (the above-mentioned TE-8) is 10w.
t%, a solution of Irgacure 907 (trade name, manufactured by Nippon Ciba Geigy Co., Ltd.) dissolved in methyl ethyl ketone so as to have a concentration of 0.1 wt.
pm to form a 1 μm thick layer containing the discotic compound. The film having the layer formed as described above is
After placing in a thermostat set at 0 ° C. for 5 minutes to form a discotic liquid crystal layer, aging, and then aging at 150 ° C.
Under the conditions described above, light from a mercury lamp (400 watts) was irradiated for 2 minutes and allowed to cool to room temperature to obtain an optical compensation sheet.

Example 2 Polycarbonate manufactured by Mitsubishi Gas Chemical Co., Ltd .: Iupilon (100 μm thick, {(nx + ny) / 2-nz} × d =
Glow discharge treatment (shown as G) was performed on both sides of a roll film of 34 nm in the following manner. In the glow discharge treatment, first, four rod-shaped electrodes having a cross section of 2 cm in diameter and a length of 40 cm were fixed on the insulating plate at intervals of 10 cm. This electrode plate was fixed in a vacuum tank, and 15c from this electrode surface.
The film having a width of 30 cm was run so as to be subjected to a surface treatment for 2 seconds so as to face the electrode surface at a distance of m. Immediately before the film passes the electrode, the film has a diameter of 50c.
The heating roll is arranged so as to make 3/4 circumference contact with the heating roll with a temperature controller of m, and the thermocouple thermometer is brought into contact with the film surface between the heating roll and the electrode zone to reduce the film surface temperature to 115 ° C. Controlled. The pressure in the vacuum chamber was 0.15 Torr, and the partial pressure of H ₂ O in the atmosphere gas was 80%. Discharge frequency is 30KH
z, output 2500W, processing intensity 0.5KV · A · min /
It was carried out in m ^2. The vacuum glow discharge electrode is disclosed in Japanese Patent Application No. 5-147.
864. The diameter of the support is adjusted so that the surface temperature becomes 30 ° C. before winding the support after the discharge treatment.
cm and contacted with a cooling roll equipped with a temperature controller and wound up.

Next, in the same manner as in Example 1, a gelatin layer (0.1 μm) was applied on one side of the roll film, and a compound indicated by P-5 was applied on the other side, and the granules were placed thereon. Diameter 0.1
A roll film coated with diacetylcellulose containing μm silica was obtained. Next, a long-chain alkyl-modified poval (MP-203 manufactured by Kuraray Co., Ltd.) is applied on the gelatin layer coated.
And dried with hot air of 110 ° C. for 30 seconds, followed by rubbing treatment to form an alignment film. The discotic compounds TE-8 and TE-8 were put on this alignment film in a weight ratio of 4: 1.
145 ° C after coating (1.0 µm)
After heating and heat-treating to form a discotic liquid crystal and aging, it was rapidly cooled to room temperature to obtain an optical compensation sheet.

Comparative Example 1 An optical compensatory sheet was obtained in the same manner as in Example 1 except that the gelatin layer was not provided and the alignment film was provided directly on triacetyl cellulose.

Comparative Example 2 An optical compensatory sheet was obtained in the same manner as in Example 2 except that the glow discharge treatment and the gelatin layer (0.1 μm) were not applied.

The product of the difference between the refractive index of the extraordinary light and the ordinary light of the liquid crystal and the gap size of the liquid crystal cell is 480 nm and the twist angle is 90.
The optical compensatory sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were attached to the TN type liquid crystal cell of 図 as shown in FIG. 5, and the transmittance (T at 40 V rectangular wave of 0 V to 5 V to the liquid crystal cell (T ) Was measured by Otsuka Electronics LCD-5000. The angle from the direction normal to the surface of the liquid crystal cell to the position where the contrast ratio (T _1V / T _5V ) shows 10 is defined as the viewing angle, the upper, lower, left and right viewing angles are determined, and the TN type without any optical compensation sheet is used. The liquid crystal cell was compared for comparison. In FIG. 5, the arrows indicate the rubbing direction in the optical compensation sheet and the rubbing direction in the liquid crystal cell. In FIG. 5, both disc-shaped compound layers of the optical compensation sheet exist on the liquid crystal cell side. Example 1,
The optical compensatory sheet No. 2 was able to greatly widen the viewing angle of the TN type liquid crystal cell, and no peeling or cracking occurred in a heat test at 80 ° C. for 500 hours. In contrast,
The optical compensation sheets of Comparative Examples 1 and 2 were peeled and cracked in a heat test at 80 ° C. for 500 hours. Further, the optical compensation sheets of Example 1 and Comparative Example 1 using a film having a retardation of the plane orientation satisfying the formula (1) have a better viewing angle improvement effect than the optical compensation sheets of Example 2 and Comparative Example 2. It was big.

[0041]

Industrial Applicability According to the present invention, there is provided an optical compensatory sheet capable of improving the adhesion between a transparent polymer film and an alignment film and extending the viewing angle of a TN type LCD industrially. Was completed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a polarization state of light when the light is vertically incident on a liquid crystal cell.

FIG. 2 is a diagram showing a polarization state of light when light is obliquely incident on a liquid crystal cell.

FIG. 3 is a diagram illustrating an example of use of an optical compensation sheet.

FIG. 4 is a diagram showing a liquid crystal molecule arrangement model when a voltage is applied to a TN liquid crystal cell, and a diagram in which the optical characteristics thereof are approximated.

FIG. 5 is a diagram showing a relationship between a polarization axis of a polarizing plate, a rubbing direction of a liquid crystal cell, and a rubbing direction of an optical compensation sheet alignment film when viewing angle characteristics are measured in Examples and Comparative Examples.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: polarizing plate PA, PB: polarization axis L0: natural light L1, L5: linearly polarized light L2: modulated light after passing through the liquid crystal cell L3, L4: elliptically polarized light LC: TN type liquid crystal cell State of liquid crystal molecules when voltage is sufficiently applied to RF1, RF2: optical compensation sheet BL: backlight R1, R2: rubbing direction of optical compensation sheet

Claims (3)

(57) [Claims] 1. The in-plane principal refractive indexes nx and ny and the principal refractive index nz in the thickness direction are represented by the following formula: 10 ≦ {(nx + ny) / 2−nz} d ≦ 600 (where d is the film thickness) (Representing the unit: nm)) After performing a surface activation treatment on a transparent polymer film satisfying the following, or installing an adhesion improving layer, an alignment film is formed on the surface thereof, and then the alignment film is formed on the alignment film. The discotic compound is placed at 5 ° to 85 ° from the normal direction of the transparent polymer film.
(4) An optical compensation sheet provided with a layer formed by preferentially orienting the discotic compound so that the normal direction of the disc surface of the discotic compound is in the inclined direction. 2. The optical compensation sheet according to claim 1, wherein the transparent polymer film has an intrinsic birefringence value of 0.05 or less. 3. A liquid crystal cell comprising a twisted nematic liquid crystal sandwiched between two electrode substrates, two polarizing plates disposed on both sides thereof, and at least one polarizing plate between the liquid crystal cell and the polarizing plate. A liquid crystal display device comprising a plurality of optical compensation sheets, wherein the optical compensation sheet is the optical compensation sheet according to claim 1 or 2.