JPH07333434A - Optical compensating sheet and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To industrially obtain an optical compensating sheet capable of considerably widening the angle of the field of view of a TN type liquid crystal display device and to prevent the electrification of a transparent-polymer film so that the sheet is obtd. CONSTITUTION:At least an oriented film is formed on a transparent polymer film and a discoid compd. is preferentially oriented so that the normal direction of the discoid face of the discoid compd. coincides with a direction inclined from the normal direction of the polymer film by 5-85 deg.. An antistatic agent is contained in the resultant optical compensating sheet.

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 viewing angle characteristics of contrast and display color of a TN type liquid crystal display device.

[0002]

2. Description of the Related Art CRTs, which are the mainstream display devices for office automation equipment such as Japanese word processors and desktop personal computers
Have been converted into liquid crystal display elements which have the great advantages of thinness, light weight, and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) which are currently popular use twisted nematic liquid crystals. The display method using such a liquid crystal can be roughly classified into a birefringence mode and an optical rotation mode.

An LCD using a birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics. Therefore, a simple matrix is provided without active elements (thin film transistors or diodes). A large-capacity display can be obtained by time-divisional driving with the electrode structure. But,
An LCD using this birefringence mode has a drawback that the response speed is slow (several hundreds of milliseconds) and gradation display is difficult. Therefore, a liquid crystal display element (TFT-LCD, MIM-LCD, etc.) using an active element is used. The display performance of) is exceeded.

For the TFT-LCD and MIM-LCD, a display system (TN type liquid crystal display element) of optical rotation mode in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most effective method for high image quality compared with other LCDs because it has a fast response speed (tens of milliseconds), white display is easily obtained, and high display contrast is exhibited. is there. However, since the twisted nematic liquid crystal is used, there is a problem in view angle characteristics that the display color and the display contrast are changed depending on the viewing direction due to the principle of the display system, and the display performance of the CRT cannot be exceeded.

Japanese Unexamined Patent Publication No. 4-229828 and Japanese Unexamined Patent Publication No. 4-2
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-mentioned patent publication has a retardation of almost zero in the direction perpendicular to the liquid crystal cell, and does not exert any optical action from the front.
A phase difference appears when tilted, and the phase difference that appears in the liquid crystal cell is compensated. However, even with these methods, the viewing angle of LCD is still insufficient, and further improvement is desired. In particular, when considered as a vehicle-mounted type or as a substitute for a CRT, the current viewing angle cannot cope with the situation.

Further, 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. It is a two-layer liquid crystal system, which is expensive and very heavy. Further, in JP-A-4-113301 and JP-A-5-80323,
For liquid crystal cells, a method of using a retardation film whose optical axis is inclined has been proposed, but since a uniaxial polycarbonate is used by obliquely slicing, a large area retardation film is provided at low cost. There was a problem that it was difficult to obtain. Further, JP-A-5-157913 and EP057630.
4A1 proposes a method of using a retardation film having an optical axis inclined by specially stretching a polycarbonate, but it is still difficult to obtain a large area retardation film at low cost. .

Further, in Japanese Patent Laid-Open No. 215921/1993, there is proposed a plan for optically compensating an LCD with a birefringent plate in which a rod-shaped compound exhibiting liquid crystal properties at the time of curing is sandwiched between a pair of aligned substrates. However, this plan is no different from the so-called double-cell type compensator that has been proposed in the past, and it causes a great increase in cost and is practically unsuitable for mass production. Further, as long as a rod-shaped compound is used, the birefringent plate is TN for the optical reason described later.
It is impossible to improve the omnidirectional viewing angle of the type LCD. Further, in Japanese Patent Laid-Open Nos. 3-9326 and 3-291601, there is described a plan to apply a polymer liquid crystal to a film-shaped substrate on which an alignment film is provided to form an optical compensator for LCD. However, since it is impossible to orient molecules obliquely with this method, TN-type LCDs are also used.
It is impossible to improve the omnidirectional viewing angle.

Therefore, the inventors of the present invention invented an optical compensation sheet in which a layer containing a discotic compound is oriented on an orientation film provided on a plane orientation transparent film, and Japanese Patent Application No. Hei 5-236.
Filed in No. 539. In this optical compensatory sheet, a negative uniaxial optical property in which the optical axis is tilted due to the monodomain structure in which the discotic compound is tilted and oriented, 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 property of the above, there is an optical axis as a whole, but there is a minimum value for the absolute value of the retardation, and the direction is tilted from the normal direction of the optical compensation sheet. Since it has characteristics, the viewing angle can be further improved in all directions as compared with the conventionally proposed TFT optical compensation sheet. However, in the production of the optical compensation film, there are problems such as dust attachment and explosion proof due to charging when rubbing the alignment film.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to industrially provide an optical compensation sheet capable of significantly widening the viewing angle of a TN type LCD, and for that purpose, charging of a transparent polymer film. Is to prevent.

[0010]

Means for Solving the Problems The above-mentioned problems are as follows: (1) After forming at least an alignment film on a transparent polymer film, a discotic compound is formed in a direction inclined by 5 ° to 85 ° from the normal direction of the film. An optical compensation sheet in which the discotic compound is preferentially oriented so that the disc surface has a normal direction,
An optical compensation sheet, wherein the optical compensation sheet contains an antistatic agent. (2) The transparent polymer film has an intrinsic birefringence value of 0.05
The optical compensatory sheet according to claim 1, which is made of the following materials and has in-plane principal refractive indices nx and ny and a thickness-wise principal refractive index nz represented by the formula (1). Formula (1) 10 ≦ {(nx + ny) / 2−nz} × d ≦ 600 (nm) (3) A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates and arranged on both sides of the liquid crystal cell. Two polarizing plates and at least 1 between the liquid crystal cell and the polarizing plate.
A liquid crystal display device comprising a sheet of optical compensation sheet, wherein the optical compensation sheet is the optical compensation sheet of (1) or (2). Achieved by

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

When a sufficient voltage is applied to the TN type liquid crystal cell, the alignment state of the liquid crystal molecules is schematically shown as a model with one liquid crystal molecule, which is represented by LC in the schematic diagram. Modeling the liquid crystal molecules in a liquid crystal cell, when the LC major axis in the schematic diagram is parallel to the light path, a difference in refractive index occurs on the incident surface (in the plane perpendicular to the light path). Since it does not exist, linearly polarized light propagates even when it passes through the liquid crystal cell. Polarization axis P of polarizing plate B
When B is set to be 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 a polarization state of light when the light obliquely enters the liquid crystal cell. Natural light of incident light L
When 0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes almost linearly polarized light. (In the actual case, it becomes elliptically polarized 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 light and is not completely blocked by the polarizing plate B. As described above, in the case of oblique incidence, blocking of light in a dark state becomes insufficient, which causes a large reduction in contrast, which is not preferable.

The present invention is intended to industrially provide an optical compensatory sheet capable of preventing such a decrease in contrast due to oblique incidence and improving viewing angle characteristics. FIG. 3 shows an example of using the optical compensation sheet manufactured by the present invention. Between the polarizing plate A and the liquid crystal cell TNC, an optical compensation sheet RF1 having a minimum absolute value of retardation is arranged in a direction inclined from the normal direction of the liquid crystal cell. The optical compensatory sheet RF1 is a birefringent body in which the phase difference increases as the angle of incidence of light in this direction increases. Further, an optical compensation sheet RF2 having the same optical characteristics as the optical compensation sheet RF1 is arranged 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 structure as in the case of FIG. 2, the optical modulation described below occurs. First, it is converted into linearly polarized light L1 by the polarizing plate A, and is modulated into elliptically polarized light L3 by the phase delay action when passing through the optically anisotropic element RF1.
Next, when it passes through the liquid crystal cell TNC, it is modulated into elliptically polarized light L4 having an opposite phase, and when it further passes through the optically anisotropic element RF2, it is returned to the original linearly polarized light L5 by the phase delaying action. With such an effect, the natural light L0 can obtain the same transmittance even under various oblique incidences, and it is possible to obtain a liquid crystal display element capable of high-quality display without viewing angle dependence.

It is presumed as follows that the viewing angle of the liquid crystal display device was significantly improved by the optical compensation sheet of the present invention. Most TN-LCDs adopt a normally white mode. In this mode, the transmittance of light from the black display portion is significantly increased as the viewing angle is increased, resulting in a sharp drop in contrast. The black display is the state when a voltage is applied. At this time, the liquid crystal molecules in the TN liquid crystal cell are aligned as 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, it becomes as shown in FIG. 4B, and the optical axis of the TN liquid crystal cell is slightly tilted from the direction normal to the cell surface. It can be regarded as a laminated body of four positive uniaxial optical anisotropic bodies and two positive uniaxial optical anisotropic bodies whose optical axes are in the same direction as the normal direction.

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

If a particular discotic liquid crystal is selected as the discotic compound, the structure is kept stable below the discotic liquid crystal phase / solid phase transition temperature when the discotic liquid crystal phase is solidified in the aligned state. The optically anisotropic substance is also thermally stable.

The discotic liquid crystals in the present invention are those 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 it is, it is not particularly limited to the following substances.

[0019]

[Chemical 1]

[0020]

[Chemical 2]

[0021]

[Chemical 3]

[0022]

[Chemical 4]

Negative uniaxiality of the discotic liquid crystal layer in the present invention means that n ₁ <n when the refractive indices in the triaxial direction of the liquid crystal layer are n ₁ , n ₂ and n _{3 in the} order of decreasing values. ₂ = n ₃
Have a relationship of. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However,
The values of n ₂ and n ₃ do not have to be exactly equal, they need to be approximately equal. Specifically, if | n ₂ −n ₃ | / | n ₂ −n ₁ | ≦ 0.2, there is no practical problem. Further, as a condition for greatly improving the viewing angle characteristics of the TFT or TN type liquid crystal cell, it is preferable that the optical axis of the liquid crystal layer has an inclination β of 5 ° to 50 ° from the normal direction of the sheet surface, It is more preferably 10 degrees to 40 degrees. Further, when the thickness of the liquid crystal layer is a, it is preferable that the condition of 50 ≦ Δn ′ · a ≦ 300 (nm) is satisfied. However, Δn ′ = (n
₂ + n ₃₎ is / 2-n _1.

Next, the alignment film in the present invention will be described. A discotic liquid crystal that can be effectively aligned by simply rubbing the surface of the substrate and coating 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 vapor deposition film or an alignment film obtained by rubbing a specific organic polymer film corresponds to this. In addition, L consisting of an azobenzene derivative
This also applies to a thin film, such as the B film, which undergoes isomerization by light and in which the molecules are oriented and uniformly arranged. A polyimide film is a typical organic alignment film. This is a coating of polyamic acid (for example, SE-7210 manufactured by Nissan Kagaku Co., Ltd.) on the surface of the substrate, and the temperature is 100 ° C.
The discotic compound can be oriented by rubbing after firing at ℃. In addition, an alkyl chain-modified Poval (for example, MP203 and R1130 manufactured by Kuraray Co., Ltd.)
No coating is required for the coating film of (1), and the orientation ability can be imparted only by rubbing. In addition, almost any organic polymer film such as polyvinyl butyral or polymethyl methacrylate that forms a hydrophobic surface can be provided with an orientation ability by rubbing the surface.

The above-mentioned alignment film has the function of determining the alignment direction when the discotic compound coated thereon forms a discotic liquid crystal. However, since the orientation of the discotic liquid crystal depends on the primary structure of the discotic compound, it is necessary to optimize the combination. Next, the discotic liquid crystal molecules that have once been oriented are oriented at an angle θ with respect to the substrate surface, but in the one-component system, the angle of oblique orientation does not change much depending on the type of the alignment film, and the value specific to the discotic liquid crystal molecules is changed. I often take it. 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 oblique alignment, select the discotic liquid crystal type, and
A method of mixing at least one discotic liquid crystal molecule is effective.

The polymer film used in the optical compensation sheet of the present invention has good light transmittance and also has the formula (1)
It is necessary to have the plane orientation retardation of. (1) A state in which 10 ≦ {(nx + ny) / 2−nz} × d ≦ 600 (nm) is satisfied. However, nx and ny are main refractive indices that are orthogonal to each other in the film plane, and nz is a main refractive index in the thickness direction of the film. nx = ny is preferable, but nx and n
The values of y need not be exactly equal, but nearly equal is sufficient. Specifically, if | nx-ny | / | nx-nz | ≦ 0.2, there is no practical problem. Further, it is more preferable that (2) 20 ≦ {(nx + ny) / 2−nz} × d ≦ 300 (nm) is satisfied. The polymer film is formed by a solution casting method or a melt extrusion method. Generally, in the solution casting method, surface orientation occurs due to solvent evaporation in a state where the width and length are regulated, and in the melt extrusion method, stretching is performed. This causes plane orientation. As in 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 the trade name of Zeonex (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fuji Photo Film Co., Ltd.) or the like is preferable.

Next, in the present invention which describes the antistatic agent according to the present invention, the conductive material preferably used is crystalline metal oxide particles, and those containing oxygen defects, and
Those containing a small amount of different atoms forming a donor with respect to the metal oxide used are generally preferred because they have high conductivity. Examples of metal oxides include ZnO and TiO
₂ , SnO ₂ , Al ₂ O ₃ , In ₂ O ₃ , SiO ₂ , MgO,
BaO, MoO ₃ , V ₂ O _5, etc., or a composite oxide of these is preferable, and particularly ZnO, In ₂ O ₃ , V ₂ O ₅ , and Sn.
O ₂ is preferred. As an example containing a hetero atom, for example, Z
Addition of Al, In, etc. to nO, addition of Sb, Nb, P, halogen element, etc. to SnO ₂ , TiO
_{For 2} , the addition of Nb, Ta, etc. is effective. The amount of addition of these hetero atoms is 0.01 mol% to 30 mo.
The range of 1% is preferable, but 0.1-10 mol% is particularly preferable. Furthermore, in order to improve the dispersibility of fine particles and the transparency, a silicon compound may be added during the formation of fine particles. The metal oxide fine particles of the present invention have conductivity, and their volume resistivity is 10 ⁷ Ω-cm or less, particularly 10 ⁵ Ω-cm or less.

Regarding these oxides, JP-A-56-1
43431, 56-120519, 58-62.
No. 647, etc. Furthermore, Japanese Patent Publication Sho 59
As described in No. 6235, a conductive material obtained by adhering the above metal oxide to other crystalline metal oxide particles or fibrous substances (for example, titanium oxide) may be used. The usable primary particle size is preferably 0.0001 to 1 μm, but when it is 0.001 to 0.5 μm, stability after dispersion is good and easy to use. Further, it is very preferable to use conductive particles of 0.001 to 0.3 μm in order to reduce the light scattering property as much as possible because the transparency is increased. These particles are usually secondary agglomerates in which several or more primary particles are aggregated in the dispersion liquid and the coating film, and the particle size is 0.3 to 0.
It is 01 μm, preferably 0.2 to 0.03 μm. When the conductive material is needle-like or fibrous, the length is preferably 30 μm or less and the diameter is 1 μm or less, and particularly preferably, the length is 10 μm or less and the diameter is 0.3 μm or less. Is 3 or more.

These conductive metal oxides of the present invention may be coated from a coating solution without a binder, and the preferable coating amount is 1 g / m 2, more preferably 0.0
009 to 0.5 g / m 2, particularly preferably 0.0012
Is about 0.3 g / m ² . In that case, it is preferable to further apply a binder thereon. Further, the metal oxide of the present invention is more preferably coated with a binder.
The binder is not particularly limited, but the above-mentioned binders and the like can be used. For example, a water-soluble binder such as gelatin, dextran, polyacrylamide, starch, or polyvinyl alcohol may be used, or poly (meth) acrylic acid ester, poly Synthetic polymer binders such as vinyl acetate, polyurethane, polyvinyl chloride, polyvinylidene chloride, styrene / butadiene copolymer, polystyrene, polyester, polyethylene, polyethylene oxide, polypropylene and polycarbonate may be used as the organic solvent, and further, these may be used. The polymeric binder may be used in the form of an aqueous dispersion.

These metal oxides may be used as a mixture of spherical and fibrous ones. The content of the metal oxide of the present invention is 0.0005 g / m ² or more,
The amount is more preferably 0.0009 to 0.5 g / m ² , and particularly preferably 0.0012 to 0.3 g / m ² . Further, a heat-resistant agent, a weather-resistant agent, inorganic particles, a water-soluble resin, an emulsion, etc. may be added to the layer made of the metal oxide of the present invention for matting and improving the film quality within a range that does not impair the effects of the present invention. good. For example, inorganic fine particles may be added to the layer made of the metal oxide of the present invention. Examples of the inorganic fine particles to be added include silica, colloidal silica, alumina, alumina sol, kaolin, talc, mica, calcium carbonate and the like. Fine particles have an average particle diameter of 0.01 to 1
0 μm is preferable, more preferably 0.01 to 5 μm,
The weight ratio to the solid content in the coating agent is preferably 0.05 to 10 parts, and particularly preferably 0.1 to 5 parts.

Further, various organic or inorganic curing agents may be added to the coating agent of these conductive agents. These curing agents may be low molecular weight compounds or high molecular weight compounds, and these may be used alone or in combination.

As the low-molecular curing agent, for example, tea
"The Theory of the Photographic Process" by TH James
y of the Photographic Process) ", 4th edition, p. 77-
The low-molecular curing agent described on page 88 is used, among which vinyl sulfonic acid, aziridine group, epoxy group,
Those having a triazine ring are preferable, and especially JP-A-53-53.
-421221 and the low molecular weight compounds described in JP-A-60-225143 are preferable.

The polymer hardening agent is preferably a compound having a molecular weight of 2000 or more and having at least two groups which react with a hydrophilic colloid such as gelatin in the same molecule and which reacts with a hydrophilic colloid such as gelatin. Examples of the group include an aldehyde group, an epoxy group, an active halide (dichlorotriazine, chloromethylstyryl group, chloroethylsulfonyl group, etc.), an active vinyl group, an active ester group and the like. Examples of the polymer curing agent used in the present invention include polymers having an aldehyde group such as dialdecit starch, polyacrolein and acrolein copolymers described in US Pat. No. 3,396,029, and US Pat. No. 3,623. , 878, Polymers with Epoxy Groups, Research Disclosure 1733
3 (1978) and the like having a dichlorotriazine group, a polymer having an active ester group described in JP-A-56-66841, and JP-A-5-
6-142524, U.S. Pat. No. 4,161,407.
Polymers having an active vinyl group or a group serving as a precursor thereof described in JP-A-54-65033, Research Disclosure 16725 (1978) and the like are preferable, and JP-A-56-142524 is particularly preferable. Preference is given to active vinyl groups or groups which are the precursors thereof being linked to the polymer main chain by means of long spacers, as described.

The conductive polymer or latex preferably used in the invention will be described below. The conductive polymer used is not particularly limited, and may be anionic, cationic,
Either betaine or nonionic may be used, but among them, anionic and cationic are preferable. More preferred are anionic sulfonic acid-based, carboxylic acid-based, and phosphoric acid-based polymers or latexes, and tertiary amine-based, quaternary ammonium-based, and phosphonium-based polymers. These conductive polymers are disclosed, for example, in Japanese Examined Patent Publication No.
25251, JP-A-51-29923, JP-B-60
-48024 described anionic polymer or latex, JP-B-57-18176 and 57-56059.
Nos. 58-56856, US Pat. No. 4,118,231 and the like, and cationic polymers or latexes can be mentioned.

Specific examples of these conductive polymers or latices will be described below, but the present invention is not limited thereto.

[0036]

[Chemical 5]

These conductive polymers or latices of the present invention may be coated from a coating solution without a binder, in which case it is preferable to further coat a binder thereon. The conductive polymer or latex of the present technology may be co-coated with a binder. The content of the conductive polymer or terax of the present invention is 0.005 to 5 g / m ² , and preferably 0.01 to 5.
3 g / m ^2, more preferably from 0.02 to 1 g / m ^2. Further, the binder is 0.005 to 5 g / m ² ,
It is preferably 0.01 to 3 g / m ² , and particularly preferably 0.01 to ² g / m ² . The weight ratio of conductive polymer or latex to binder is 99: 1 to 1
It is 0:90, preferably 95: 5 to 15:85, and particularly preferably 90:10 to 20:80. The additive layer of the conductive metal oxide, polymer and latex used as the antistatic agent of the present invention is not particularly limited. An antistatic layer containing an antistatic agent may be provided, or it may be used as an alignment film layer, a discotic compound layer or a protective layer, an undercoat layer, a back layer, a back protective layer, etc. which are provided as necessary. Among these, an undercoat layer and a back layer are preferable. The conductivity of the antistatic layer produced as described above is preferably as low as possible, and is 10 ¹³ or less at 25 ° C. and relative humidity, more preferably 10 ¹² or less, and particularly preferably 10 ¹¹ or less.

[0038]

EXAMPLES The present invention will be described in detail below based on examples. Example 1 Triacetyl cellulose manufactured by Fuji Photo Film Co., Ltd. (thickness 100 μm, {(nx + ny) / 2−nz} × d = 70)
gelatin layer (0..nm) on one side of the roll film.
1 μm) was coated, the compound shown by P-5 was coated on the opposite surface, and diacetyl cellulose containing silica having a particle size of 0.1 μm was coated thereon to obtain a roll film. Next, a long-chain alkyl-modified Poval (MP-203 manufactured by Kuraray Co., Ltd.) was applied onto the applied gelatin layer, dried with hot air at 110 ° C. for 30 seconds, and then rubbed to form an alignment film. . The discotic compound TE-8 was formed on the alignment film.
Is 10 wt% and Irgacure 907 (trade name, manufactured by Ciba-Geigy Co., Ltd.) is 0.1 wt%, and a solution prepared by dissolving in methyl ethyl ketone is applied at 3200 rpm by a spin coater to contain a 1 μ-thick discotic compound. A film with layers was made. This film 15
After being placed in a constant temperature bath set at 0 ° C for 5 minutes to form a discotic liquid crystal and aged, the mercury lamp (400 watt) is continuously irradiated for 2 minutes under the condition of 150 ° C, and allowed to cool to room temperature. An optical compensation sheet was obtained.

Example 2 Polycarbonate manufactured by Mitsubishi Gas Chemical Co., Inc .: Iupilon (thickness 100 μm, {(nx + ny) / 2−nz} × d =
Both sides of the roll film (34 nm) were subjected to glow discharge treatment (denoted as G) by the method described below. In the glow discharge treatment, first, columnar rod-shaped electrodes having a diameter of 2 cm and a length of 40 cm were fixed on four insulating plates at intervals of 10 cm. This electrode plate is fixed in a vacuum tank, and 15c from this electrode surface
At a distance of m, the film having a width of 30 cm was run so as to face the electrode surface so that the surface treatment was performed for 2 seconds. Just before the film passes through the electrodes, the film has a diameter of 50c.
Place the heating roll so that it makes 3/4 round contact with the heating roll with a temperature controller of m, and further bring the film surface temperature to 115 ° C. by bringing a thermocouple thermometer into contact with the film surface between the heating roll and the electrode zone. Controlled. The pressure in the vacuum chamber was 0.15 Torr, and the partial pressure of H ₂ O in the atmospheric gas was 80%. Discharge frequency is 30KH
z, output 2500 W, processing intensity 0.5 KV · A · min /
It was carried out at m ² . The vacuum glow discharge electrode is Japanese Patent Application No. 5-147.
The method described in 864 was followed. After the discharge treatment, the diameter of the support should be 50 so that the surface temperature becomes 30 ° C before the support is wound up.
It was wound in contact with a cooling roll having a temperature controller of cm.

Then, in the same manner as in Example 1, a gelatin layer (0.1 μm) was coated on one side of the roll film, and the compound represented by P-5 was coated on the opposite side, and the layer was coated on the gelatin layer. A roll film coated with diacetyl cellulose having a particle size of 0.1 μm was obtained. Next, a long-chain alkyl-modified Poval (MP-manufactured by Kuraray Co., Ltd.) was applied on the applied gelatin layer.
203) was applied and dried with hot air at 110 ° C. for 30 seconds, and then rubbing treatment was performed to form an alignment film. A mixture of the discotic compounds TE-8 and TE-8 mixed at a weight ratio of 4: 1 was applied (1.0 μm) on the alignment film, and then 1
The temperature was raised to 45 ° C., heat treatment was performed to form a discotic liquid crystal, the mixture was aged, and then rapidly cooled to room temperature to obtain an optical compensation sheet.

Comparative Example 1 An optical compensation sheet was obtained in the same manner as in Example 1 except that nothing was coated on the side opposite to the gelatin layer.

Comparative Example 2 An optical compensation sheet was obtained in the same manner as in Example 2 except that nothing was coated on the side opposite to the gelatin layer.

The product of the difference in refractive index between 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 compensation sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were mounted on a TN type liquid crystal cell at 0 ° as shown in FIG. 5, and the transmittance (T) at a 40 Hz rectangular wave of 0 V to 5 V was measured with respect to the liquid crystal cell. The angle dependence of) was measured by LCD-5000 manufactured by Otsuka Electronics. 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 was defined as the viewing angle, and the viewing angle in the vertical and horizontal directions was obtained. Here, the measurement of only the TN type liquid crystal cell without any optical compensation sheet was set as Comparative Example 3. In FIG. 5, arrows indicate the rubbing direction in the optical compensation sheet and the rubbing direction in the liquid crystal cell. In FIG. 5, both discotic liquid crystal layers of the optical compensation sheet are present on the liquid crystal cell side. The optical compensation sheets of Examples 1 and 2 were able to significantly widen the viewing angle of the TN type liquid crystal cell, and no problems occurred in the manufacturing process. On the other hand, the optical compensatory sheets of Comparative Examples 1 and 2 had a problem with dust, which is considered to be caused by static generated in the rubbing process, and the yield was very poor. Further, the optical compensation sheets of Example 1 and Comparative Example 1 using the film having the plane orientation retardation satisfying the formula (1) are more effective in improving the viewing angle than the optical compensation sheets of Example 2 and Comparative Example 2. It was great.

[0044]

According to the present invention, charging can be prevented,
It has been possible to industrially provide an optical compensation sheet with a high yield, which can significantly widen the viewing angle of a TN type LCD.

[Brief description of drawings]

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

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

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

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

FIG. 5 is a diagram showing a relationship among 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 measuring viewing angle characteristics 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 a sufficient voltage is applied to the electrodes RF1, RF2: Optical compensation sheet BL: Backlight R1, R2: Rubbing direction of the optical compensation sheet

Claims (3)

[Claims] 1. At least an alignment film is formed on a transparent polymer film, and a normal direction of the disc surface of the discotic compound is in a direction inclined by 5 ° to 85 ° from the normal direction of the film. An optical compensatory sheet in which the discotic compound is preferentially oriented, wherein the optical compensatory sheet contains an antistatic agent. 2. The transparent polymer film is made of a material having an intrinsic birefringence value of 0.05 or less and has an in-plane principal refractive index n.
2. The optical compensatory sheet according to claim 1, wherein x, ny, and the main refractive index nz in the thickness direction are represented by the formula (1). Formula (1) 10 ≦ {(nx + ny) / 2−nz} × d ≦ 600 (nm) 3. A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, two polarizing plates arranged on both sides of the liquid crystal cell, and at least one optical element between the liquid crystal cell and the polarizing plate. A liquid crystal display element comprising a compensation sheet, wherein the optical compensation sheet is the optical compensation sheet according to claim 1.