JPH08101380A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE: To expand the visual field angle of a reflection type liquid crystal display device by having a layer contg. a disk-shaped compd. on a supporting body, which is at least optically negative and uniaxial, of an optical phase compensation plate. CONSTITUTION: This reflection type liquid crystal display device has a liquid crystal cell formed by holding twist-oriented nematic liquid crystals between a pair of substrates having electrodes and at least one layer of substrates having an optical phase compensation function and a pair of polarizing plates arranged to hold these substrates therebetween and has further a light reflection plate. The optical phase compensation plate of the reflection type liquid crystal display device has the layer contg. the disk-shaped compd. on a supporting body, which is at least optically negative and uniaxial.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a direct-view backlight used for office automation (OA) equipment such as word processors and notebook computers with improved viewing angles, and various video equipment and game equipment. Related to a reflection type liquid crystal display device

[0002]

2. Description of the Related Art In recent years, application of liquid crystal display devices to OA equipment such as word processors and laptop personal computers, and video equipment such as portable televisions called pocket televisions has been rapidly expanding. Among these liquid crystal display devices, the reflection type liquid crystal display device that reflects light incident from the outside to perform display does not require a backlight as a light source, and thus can reduce power consumption, be thin and be lightweight. And, it is especially noticeable.

In a liquid crystal display device, a plurality of opposed stripe-shaped electrodes are arranged so as to intersect each other through a liquid crystal having a twist angle of 90 ° or more in a molecular arrangement, and pixels are arranged at the intersecting portions. A simple matrix type to be formed, and a pixel electrode having a non-linear active element of a three-terminal system or a two-terminal system using a thin layer transistor or a diode with a twist angle of 90 ° in the arrangement of liquid crystal molecules,
An active matrix type in which a pixel is formed by this pixel electrode and a counter electrode has been proposed. Among these liquid crystal display devices, a display device such as a word processor, a personal computer, or a TV monitor has a high image quality and a high response speed among the liquid crystal display devices which are thin, lightweight, and have low power consumption from a mainstream CRT. It is being converted to a fast active matrix type.

The active matrix type is basically a twisted nematic type (hereinafter, referred to as TN) liquid crystal cell using a nematic liquid crystal having a twist angle of 90 °, and has a three-terminal type as a non-linear element. Currently, TFT-LCDs that use thin-layer transistors and MIM-LCDs that use two-terminal type MIM elements are in the mainstream.

The TFT-LCD and MIM-LCD are at least a driving TFT or a MIN for each pixel.
A TN liquid crystal cell having an element, a polarizer arranged so that its transmission axis is orthogonal or parallel to the rubbing direction of the light incident side substrate of the liquid crystal cell, and the rubbing of the light emitting side substrate of the liquid crystal cell. It is composed of an analyzer arranged parallel or orthogonal to the direction, and has a fast response speed (tens of milliseconds) and high display contrast. It is a method. However, since these liquid crystal display devices use a nematic liquid crystal having a twist angle of 90 °, there is a big problem that the contrast is lowered depending on the viewing angle due to the principle of the display system.

On the other hand, JP-A-4-229828,
As seen in JP-A-4-258923,
A method has been proposed in which a retardation plate is arranged between a pair of polarizing plates and a TN type liquid crystal cell to increase the viewing angle. The retardation plate proposed in the above patent publication has almost no retardation in the direction perpendicular to the liquid crystal cell, and does not exert any optical effect from the front, but when tilted, A phase difference is developed and the phase difference developed in the liquid crystal cell is compensated. However, this method cannot improve the viewing angle, in particular, the decrease in contrast when tilted vertically or horizontally from the screen normal direction, which is a practical problem.

JP-A-4-366808, JP-A-4-3
In Japanese Patent No. 66809, a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis is used as a retardation plate to improve the viewing angle. However, the two-layer liquid crystal system is costly, heavy, and power-saving. It is far from that. Further, in Japanese Patent Laid-Open No. 6-75116 and Japanese Patent Laid-Open No. 6-214116 by the present inventors, by using a retardation plate which exhibits optically negative uniaxiality and whose optical axis is inclined, , TN LCDs have been proposed to improve the viewing angle characteristics. According to this method, the viewing angle was significantly improved as compared with the conventional one. However, when considering CRT substitution, it was necessary to further improve the viewing angle. These drawbacks are the same problems when the above liquid crystal display device is used as a reflection type liquid crystal display device, but they have not been improved yet.

[0008]

SUMMARY OF THE INVENTION The present invention provides a reflection type liquid crystal display device which solves the above-mentioned problems, that is, high definition, high contrast, high display quality, and less viewing angle dependence of contrast. With the goal.

[0009]

Therefore, the inventors of the present invention have disclosed in Japanese Patent Application No. 6-126521 that the optical anisotropy is optically uniaxial and the optical axis thereof is inclined from the normal direction of the film. It was found that the viewing angle characteristics of the TN LCD are remarkably improved by the retardation plate having the characteristics of the element and the optically anisotropic element whose optical axis is in the normal direction of the film and whose optical axis is optically negative uniaxial. As a result of detailed examination of the effect of improving the viewing angle for the reflective liquid crystal display device, the present invention has been achieved.
That is, (1) a liquid crystal cell in which a nematic liquid crystal having a twisted orientation is sandwiched between a pair of substrates provided with electrodes, a substrate having at least one layer of an optical phase compensation function, and a pair of substrates arranged so as to sandwich them. In a reflective liquid crystal display device further comprising a polarizing plate of (1) and a light reflecting plate on one surface of the polarizing plate, the optical phase compensating plate has at least a layer containing a discotic compound on a support. Characteristic reflection type liquid crystal display device. (2) The reflective liquid crystal display device according to (1), wherein the optical axis of the layer containing the discotic compound is tilted by 5 ° to 50 ° from the normal direction of the film. (3) When the main refractive index in the plane of the support is N1, N2, the main refractive index in the thickness direction is N3, and the thickness of the support is d, 0 ≦ ((N1 + N2) / 2−N3) × d ≦ 300 (n
m) The reflective liquid crystal display device according to the above (1) or (2). (4) The reflective liquid crystal as described in (1), (2) or (3) above, wherein the support is optically negative uniaxial and the optical axis is in the direction normal to the support. Display device. Achieved by

Negative uniaxiality in the present invention means a relationship of N1 <N2 = N3, where N1, N2, and N3 are the refractive indices of the sheet having optical anisotropy in the triaxial directions in ascending order. I have. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However, it is not necessary that the values of N2 and N3 are exactly equal, and it is sufficient if they are almost equal.

The discotic compound of the present invention means a discotic liquid crystal such as those listed below, or a reaction product of a discotic liquid crystal which no longer exhibits liquid crystallinity due to a reaction with other low molecular weight compounds or polymers. And the like mean all compounds having a molecule itself having optically negative uniaxiality.

Typical discotic liquid crystals include, for example, C.I. Report of Destrade et al., Mo
l. Cryst. Liq. Cryst. Volume 71, 111
Page (1981), benzene derivatives,
Triphenylene derivatives, truxene derivatives, phthalocyanine derivatives, B.I. Report of Kohne et al., Ange
w. Chem. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. J. Lehn et al. Chem. Soc. Chem. Commu
n. , Pp. 1794 (1985), J. Research report by Zhang et al. Am. Chem. Soc. 116 volumes, 2
Examples thereof include azacrown-based and phenylacetylene-based macrocycles described on page 655 (1994). Other than those listed below, if the molecule itself has negative uniaxial optical anisotropy and the optical axis is obliquely oriented with respect to the substrate surface by the oblique alignment film, It is not limited to the substance.

[0013]

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[0014]

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[0015]

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[0016]

[Chemical 4]

In the case where the discotic compound in the present invention is a discotic liquid crystal, the layer containing them is oriented so as to have an optically negative uniaxial axis and an optical axis inclined by 5 ° to 50 ° from the normal direction of the film. The following processing is required for this. Specifically, a discotic liquid crystal is applied to a substrate on which a rubbing-treated organic alignment film or inorganic alignment film is formed, and then the temperature is raised to a liquid crystal phase, more preferably a disconematic phase formation temperature. As a result, the liquid crystal is obliquely aligned, and remains in the solid state at room temperature while maintaining the alignment by subsequent cooling. Further, the discotic nematic liquid crystal phase forming temperature is unique to the discotic liquid crystal, but can be arbitrarily adjusted by mixing two or more different types. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystal used in the present invention is preferably 70 ° C. or higher and 300 ° C. or lower, and particularly preferably 70 ° C. or higher and 170 ° C. or lower.

Examples of the polymer used as the above organic alignment film include polyimide and polystyrene derivatives, and examples of the water-soluble polymer include gelatin, polyvinyl alcohol, carboxymethyl cellulose and the like.
By subjecting all of them to rubbing treatment, the discotic liquid crystal can be oriented obliquely. Of these, alkyl-modified polyvinyl alcohol is particularly preferable,
The present inventors have discovered that the discotic liquid crystal has an excellent ability to be uniformly aligned. It is speculated that this is due to the strong interaction between the alkyl chain on the surface of the alignment film and the alkyl side chain of the discotic liquid crystal. The alkyl-modified polyvinyl alcohol has an alkyl group at the terminal as listed below, and has a saponification degree of 80% or more,
The degree of polymerization is preferably 200 or more. Further, polyvinyl alcohol having an alkyl group in a side chain can also be used effectively. As commercial products, MP103, MP20 manufactured by Kuraray
3, R1130 and the like are available.

A polyimide film, which is widely used as an alignment film for LCDs, is also preferable as an organic alignment film, and it is a polyamic acid (for example, LQ / LX series manufactured by Hitachi Chemical Co., SE series manufactured by Nissan Chemical Co., Ltd.) on the substrate surface. It is obtained by applying and rubbing after baking at 100 to 300 ° C. for 0.5 to 1 hour.

Further, the rubbing treatment is the same as the widely used liquid crystal orientation treatment step for LCD, and the surface of the orientation film is made of paper, gauze, felt, rubber, nylon, polyester fiber or the like. It is a method of obtaining orientation by rubbing in a certain direction. In general, rubbing is performed several times using a cloth or the like in which fibers of uniform length and thickness are evenly flocked.

Further, as a vapor deposition substance for the inorganic oblique vapor deposition film, metal oxides such as TiO ₂ , MgF ₂ and ZnO ₂ and fluorides, and metals such as Au and Al can be cited as a representative of SiO.
The metal oxide can be used as the oblique vapor deposition material as long as it has a high dielectric constant, and is not limited to the above. Both a fixed substrate type method and a continuous vapor deposition type method on a film can be used to form a vapor deposition film.
For example, when the vapor deposition angle α is about 65 to 88 °, the discotic liquid crystal is uniformly aligned in a direction whose optical axis is substantially perpendicular to the direction of the vapor deposition particle column.

The above-mentioned alignment film has a function of determining the alignment direction of the discotic liquid crystal molecules coated thereon, but since the alignment property of the discotic liquid crystal depends on the alignment film, its combination is optimized. There is a need. Further, the uniformly aligned discotic liquid crystal molecules are aligned at an angle with the normal line of the film, but the tilt angle does not change much depending on the alignment film and often takes a value specific to the discotic liquid crystal molecules. When two or more discotic liquid crystals are mixed or a compound similar to the discotic liquid crystal is mixed, the tilt angle can be adjusted by the mixing ratio. Therefore, a method of selecting or mixing discotic liquid crystals is more effective for controlling the tilt angle of the oblique alignment.

As another method for orienting the discotic liquid crystal obliquely, magnetic field orientation or electric field orientation can be mentioned. In this case, it is necessary to apply a magnetic field or an electric field at a desired angle while heating the substrate coated with the discotic liquid crystal. Diagonal orientation of the discotic compound thus obtained can be maintained at high temperature and high humidity, in advance, the discotic compound, a polymerizable unsaturated group, an epoxy group, a hydroxyl group, an amino group, a carboxyl group. Having a functional group such as a group, heat or a photopolymerization initiator, radical polymerization of a polymerizable unsaturated group, or a ring-opening polymerization of an epoxy group by a photoacid generator, a polyvalent isocyanate,
It is preferable to crosslink the discotic compound itself by a crosslinking reaction with a polyvalent epoxy compound. At this time, another compound having the same functional group may be contained.

The optically anisotropic element according to the present invention is
It can also be obtained by subjecting at least a step of applying a shearing force to both sides of the transparent film. Specifically, it can be obtained by sandwiching a film made of a thermoplastic resin and having a light transmitting property between two rolls having different peripheral speeds and applying a shearing force to the film. The thermoplastic resin used here has no problem as long as it has a light transmittance of 70%, more preferably 85%, and is not particularly limited. Specifically, polycarbonate, polyarylate,
Polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyethylene ether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose polymer, Polyacrylonitrile, polystyrene, various binary and ternary polymers, graft copolymers, blends and the like are preferably used.

Further, the optically anisotropic element of the present invention can be obtained by irradiating a photoisomerizable substance with polarized light. Here, the photoisomerizable substance is one that causes stereoisomerization or structural isomerization by light, and preferably,
The reverse isomerization is caused by light or heat of another wavelength. Generally, as these compounds, those accompanied by structural change and color tone change in the visible region are often well known as photochromic compounds,
Examples thereof include azobenzene compounds, benzaldoxime compounds, azomethine compounds, fulgide compounds, diarylethene compounds, cinnamic acid compounds, retinal compounds and hemithioindigo compounds.

The transparent film provided with the discotic compound of the present invention preferably has good light transmittance. Specifically, the light transmittance is preferably 80% or more, more preferably 90% or more. Therefore, a support formed of a material having a small intrinsic birefringence value, which is sold under the trade name of Zeonex (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fuji Film), or the like is preferable. But,
Polycarbonate, polyacrylate, polysulfone,
Even if it is a material with a large intrinsic birefringence value such as polyether sulfone, it is possible to form an optically isotropic support by controlling the molecular orientation during film formation, and these are also suitably used. To be done. Specifically, when the plane orientation main refractive index of the support is N1, N2, the thickness direction main refractive index is N3, and the thickness is d, the range of the plane orientation Re value represented by the following formula (1) is: 0 nm to 300 nm, more preferably 30
nm to 150 nm. By satisfying the condition of this plane orientation, a remarkable effect is obtained in improving the viewing angle characteristics.

Formula (1) Re = ((N1 + N2) / 2-N3) × d

When the optical compensation sheet of the present invention is produced, a step for obtaining a uniform oblique orientation is required in the production process. Specifically, the step of uniformly rubbing a long film coated with an alignment film, the step of applying a discotic liquid crystal, and the step of raising the temperature to the discotic liquid crystal formation temperature include UV light irradiation in the case of a crosslinkable molecule. This is a step of performing a crosslinking treatment and cooling. As a result, the liquid crystal has a uniform oblique orientation and becomes a solid at room temperature without breaking the orientation. The temperature at which the discotic liquid crystal used in the present invention takes a discotic liquid crystal phase is preferably 90 ° C. or higher and 300 ° C. or lower, particularly preferably 90 ° C. or higher and 1
It is 50 ° C or lower.

As a method other than the above method for obliquely aligning the discotic liquid crystal coated on the substrate, there are magnetic field orientation and electric field orientation as methods other than the orientation film. In this method, after the discotic liquid crystal is applied to the substrate, a zone for applying a magnetic field or an electric field at a desired angle is required, but the zone itself needs to be adjusted to a temperature at which the discotic liquid crystal is formed. .

The optical compensation sheet thus obtained is arranged on one or both sides of the liquid crystal cell used for the reflection type. In the case of a TN type liquid crystal cell, it is preferable to arrange the rubbing direction of the glass substrate of the liquid crystal cell on the side in contact with the optical compensation sheet and the rubbing direction of the optical compensation sheet within ± 10 ° as shown in FIG.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. Example 1 A long-chain alkyl-modified poval (MP203) was formed on a 100 μm thick film of triacetyl cellulose (manufactured by Fuji Photo Film Co., Ltd.) coated with a gelatin thin film (0.1 μm).
: Trade name (manufactured by Kuraray Co., Ltd.) was applied and dried with hot air at 40 ° C., followed by rubbing treatment to form an alignment film. The main in-plane refractive index is nx ', ny', and the refractive index in the thickness direction is n.
z ', where d'is the thickness, the triacetyl cellulose film has | nx-ny' | xd '= 3 nm, {(nx'
+ Ny ′) / 2−nz ′} × d ′ = 70 nm, which was almost negative uniaxial, and the optical axis was almost in the film normal direction.

On this alignment film, 0.4 g of the above-mentioned discotic liquid crystal TE-8 (m = 4), 0.04 g of trimethylolpropane triacrylate and 0.004 g of Irgacure 907 were dissolved in 1.6 g of methyl ethyl ketone. The coating solution is applied with a spin coater (rotation speed 150 rpm / 2 minutes) and attached to a metal frame 145
After heating for 5 minutes in a high temperature bath at ℃, aligning the discotic liquid crystal, UV irradiation for 1 minute at 145 ℃ using a high pressure mercury lamp, and letting it cool to room temperature, it has a layer containing a discotic compound. The retardation plate A of the present invention was produced. The thickness of the layer containing the discotic compound is approximately 2.3 μm, and when the main refractive index of this layer is set to n1, n2, and n3 in the ascending order, the relationship of n1 <n2 = n3 has a negative value. It was uniaxial. Further, the optical axis was inclined by 30 ° from the film normal direction. When the layer thickness is d, (n2-n1)
-D = 150 nm.

The Δn · d of the retardation plate of the present invention thus obtained from all directions was measured by an ellipsometer (AEP-100) manufactured by Shimadzu Corporation. As a result, a direction inclined by 21 ° from the normal line direction of the film was obtained. The absolute value of Δn · d was the minimum when measured from, and the minimum value was 17 nm. Further, the direction in which the direction in which the absolute value of Δn · d was the minimum was orthographically projected on the film surface was the same as the direction in which the optical axis of the discotic liquid crystal layer was orthographically projected on the film surface.

Example 2 Two retardation plates used in Example 1 were mounted in the same arrangement as in FIG. 1 so as to sandwich the TN type liquid crystal cell. After that, the two polarizing plates were attached so as to be orthogonal to each other so as to sandwich the whole on the outermost side, and the reflection type liquid crystal display device of the present invention was produced. With this device, white display and black display were performed, and the contrast ratio was measured in all directions. The result is shown in Figure 2.
Shown in

Example 3 In the TN type liquid crystal cell, as shown in FIG. 3, the two retardation plates used in Example 1 were mounted between the reflector and the TN type liquid crystal cell. 1 more
A quarter-wave plate was arranged between the polarizing plate on the opposite side of the cell and a reflective liquid crystal display device of the present invention was prepared. With this device, white display and black display were performed, and the contrast ratio was measured in all directions. FIG. 4 shows the results.

Example 4 Two phase difference plates used in Example 1 were mounted between the TN type liquid crystal cell and the reflector in the arrangement shown in FIG. After that, the two polarizing plates were attached so as to be orthogonal to each other so as to sandwich the whole on the outermost side, and the reflection type liquid crystal display device of the present invention was produced. With this device, white display and black display were performed, and the contrast ratio was measured in all directions. The result is shown in FIG.

Comparative Example 1 To the TN type liquid crystal cell used in Example 2, two sheets of the same polarizing plate used in Example 2 were attached so as to sandwich the liquid crystal cell so as to be orthogonal to each other. About this LCD
White display and black display were performed, and the contrast ratio was measured in all directions. FIG. 7 shows the result.

As is apparent from FIGS. 2, 4, 6 and 7, Examples 2, 3 and 4 are significantly improved in viewing angle from the contrast in black and white display, as compared with Comparative Example 1. You can see that

[0039]

According to the present invention, a reflective liquid crystal display device having a TN type liquid crystal cell, in particular, a liquid crystal display device having a non-linear active element such as a TFT has improved viewing angle characteristics and is excellent in visibility. The liquid crystal display device can be provided. Needless to say, even if the present invention is applied to an active matrix liquid crystal display device using a three-terminal element such as MIM and a two-terminal element such as TFD, excellent effects can be obtained.

[Brief description of drawings]

FIG. 1 shows a configuration of a TN type reflective liquid crystal display device of the present invention.

FIG. 2 shows the results of measuring the contrast ratio when the reflective liquid crystal display device in Example 2 is viewed from all directions.

FIG. 3 shows a configuration of a TN type reflective liquid crystal display device used in Example 3.

FIG. 4 shows the result of measuring the contrast ratio when the reflective liquid crystal display device in Example 3 is viewed from all directions.

FIG. 5 shows a structure of a TN type reflective liquid crystal display device used in Example 4.

FIG. 6 shows the results of measuring the contrast ratio when the reflective liquid crystal display device in Example 4 is viewed from all directions.

FIG. 7 shows a contrast ratio measurement result when the reflective liquid crystal display device in Comparative Example 1 is viewed from all directions.

Claims (4)

[Claims] 1. A liquid crystal cell in which a nematic liquid crystal having a twisted orientation is sandwiched between a pair of substrates provided with electrodes, at least one substrate having an optical phase compensation function, and a pair arranged so as to sandwich these substrates. A reflective liquid crystal display device comprising the polarizing plate of 1. and further comprising a light reflection plate, wherein the optical phase compensation plate has at least a layer containing a discotic compound on a support. 2. A reflection type liquid crystal display device, wherein the optical axis of the layer containing the discotic compound is tilted by 5 ° to 50 ° from the normal direction of the film. 3. The main in-plane refractive index of the support is N1, N2,
When the main refractive index in the thickness direction is N3 and the thickness of the support is d, 0 ≦ ((N1 + N2) / 2−N3) × d ≦ 300 (n
The reflective liquid crystal display device according to claim 1 or 2, characterized in that 4. The reflection type liquid crystal display device according to claim 1, wherein the support is optically negative uniaxial and the optical axis is in the direction normal to the support. .