JPH0749502A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve the contrast of the liquid crystal display element oriented and dispersed with liquid crystals and high-polymer particles and to improve the visibility thereof by display of a paper white tone. CONSTITUTION:This liquid crystal display element is constituted by orienting and dispersing the liquid crystals 106 contg. dichromatic dyestuff and the high- polymers 105 having refractive index anisotropy with each other and holding these liquid crystals and high polymers between two sheets of substrates 101, 110 which have pixel electrodes 103 and wirings for transmitting electric signals to these pixel electrodes 103 and at least one of which are transparent. A spacing holding material 107 for holding the specified spacing between the substrates 101 and 110 consist of a light absorptive insulator material or are formed by patterning a photosensitive org. insulating material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element which constitutes a display portion of information equipment terminals, televisions, home electric appliances and the like.

[0002]

2. Description of the Related Art In recent years, with the increasing demand for miniaturization and portability of information equipment, a reflective liquid crystal display element is indispensable from the viewpoint of power saving required for displays in this field. The TN method has been widely used for wrist watches, calculators and the like, and the STN method has been used for large capacity display as a reflection type liquid crystal display device for notebook personal computers, word processors and the like. Furthermore, on the reflective liquid crystal display device,
Applications for combining an information input device such as a tablet are expanding, and a reflective liquid crystal display element is required to have good brightness and visibility. Recently, in such a field, a liquid crystal display device using a polymer-dispersed liquid crystal in which a liquid crystal and a polymer are mutually dispersed without using a polarizing plate has attracted attention.

The principle of operation of this liquid crystal display element utilizes the difference in the refractive index between the liquid crystal and the polymer, and when the refractive index of the liquid crystal and that of the polymer match due to the application of an electric field, a transmissive state is exhibited.
This is because when the refractive index changes due to the removal of the electric field, a scattering state is exhibited. NCAP (invention of Ferguson et al .: Japanese Patent Publication No. 58-501631), LCPC (Asahi Glass Co., Ltd .:
US Patent 4,818,070), PDLC (Kent State University: US Patent 4,685,771), PNL
C (Dainippon Ink and Chemicals, Inc .: European open patent E
PAs 313 and 053) are based on the above operation principle. On the other hand, a liquid crystal display device using a polymer dispersed liquid crystal of a reverse mode (hereinafter referred to as a reverse type) that transmits when no electric field is applied and scatters when an electric field is applied (Kent State University: US Pat. No. 4,994,204, Philips: published in Europe). Patent EP 0451905 A1) is also disclosed.

[0004]

However, in the liquid crystal display element of the TN type and the STN type using the conventional polarizing plate, since the utilization efficiency of light is low, it is dark when it is a reflection type, and it is difficult to use as an information input device such as a tablet. When combined, it became a very dark display, which was a problem. Also, in the TN method and the STN method, since the reflector is arranged over the polarizing plate on the back surface of the substrate on the back side, there is a double image of the display,
Small letters were hard to see, and visibility was a problem. On the other hand, according to the technique of European Patent Publication EP0488116A2, when a dichroic dye is contained in the liquid crystal, light absorption without application of an electric field and switching of white turbid light scattering with application of an electric field are possible, resulting in a bright reflective type. It was possible to manufacture a display. Furthermore, when the light reflecting surface is also used as the pixel electrode, a bright reflective display without a double image of the display was possible.

However, although this conventional technique can solve the problems of the conventional display method using a polarizing plate,
When the space holding material (spacer) for holding the space between the substrates of the display section of the liquid crystal display device constant is made of a plastic ball, silica, or the like that transmits light, light leakage occurs from the spacer. Therefore, when the black dichroic dye is added to the liquid crystal, there is a problem that the black state floats and the contrast is lowered. When the addition amount of the dichroic dye is increased in order to prevent the floating of the display in the off state, the light resistance is deteriorated, the dye is deposited, and the specific resistance value of the liquid crystal is lowered. There was a problem that caused it. Furthermore, when the pixel electrode is used as a reflective surface, even if a voltage is applied to cause a cloudy scattering state, light that is less affected by the scattering from the spacer of the pixel portion causes a metallic color tone affected by the reflective surface. There was a point.

The present invention has been made to solve the above problems, and an object thereof is to prevent light leakage from a spacer for holding two substrates at a constant interval. By doing so, it is possible to provide a paper-white reflection type liquid crystal display device that suppresses the floating of the display when it is off, has a high contrast ratio.

[0007]

In order to solve the above problems, the liquid crystal display device of the present invention has the following constitution.

(1) A liquid crystal containing a dichroic dye and a refractive index anisotropy are provided between two substrates, at least one of which has a pixel electrode and a wiring for transmitting an electric signal to the pixel electrode and at least one of which is transparent. In the liquid crystal display device in which the polymers having the above are orientated and dispersed with each other and sandwiched, the space holding material for holding the substrates at a constant interval is a light absorbing insulating material.

(2) In the liquid crystal display device, the space holding material for holding the substrates at a constant interval is formed by patterning a photosensitive organic insulating material.

(3) One of the pixel electrodes on the substrate is formed of a reflective material.

(4) A nonlinear element is formed on at least one of the substrates.

(5) The non-linear element is a two-terminal element.

(6) The non-linear element is a three-terminal element.

[0014]

【Example】

(Embodiment 1) Hereinafter, in this embodiment, a structure using a reflection type liquid crystal display element in which a silica ball subjected to a light absorption treatment is used as a space holding material and a two-terminal element (MIM element) is formed on one substrate Indicates. FIG. 1 shows a cross-sectional view of the liquid crystal display element of this example. The substrate 110 on the back side is a MIM facing substrate, and an alloy of aluminum and magnesium is formed on the glass substrate by sputtering to form about 2000 angstroms, and then patterned to form a stripe-shaped reflective electrode 10.
It was set to 9. Polyimide was formed as an alignment film 108 on this substrate and subjected to rubbing treatment. On the substrate 101,
The MIM element 102, the ITO pixel electrode 103, and the signal wiring are formed, and after forming polyimide as the alignment film 104 on the surface, rubbing treatment is performed. The rubbing angle was 90 ° between the upper and lower substrates.

Next, as the space holding material 107, light absorbing black silica balls (made by Tokuyama Soda Co., Ltd.) in which porous silica is impregnated with carbon are used, and one substrate has about 100 pieces per square mm. Sprinkled so that further,
A sealant for adhering and fixing the substrate was printed on the other substrate around the substrate, and both substrates were adhered and fixed. Glass fibers were mixed in the sealant so that the distance between the substrates was about 5 μm, and the diameters of the glass fibers and silica balls were selected. In addition, black paper was adhered to the back surface of the substrate 110 as the light absorption layer 111 in order to prevent light leakage from between the pixel electrodes.

Next, the liquid crystal and polymer precursor mixture sealed between the substrates will be described. TL- as liquid crystal
202 (manufactured by Merck) and BL-007 (manufactured by Merck) were mixed and used at 7: 3, and R1 as a chiral component was added thereto.
011 (manufactured by Merck) was mixed in an amount of 0.5% by weight. Further, as dichroic dyes, M361, SI512, M3
4 (all manufactured by Mitsui Toatsu Dye Co., Ltd.) were mixed with the above liquid crystal at 1.5% by weight, 1.75% by weight, and 0.43% by weight, respectively. Biphenyl methacrylate was used as a polymer precursor in an amount of 8% by weight based on the above liquid crystal mixture. The above was mixed by heating and vacuum-sealed in the empty panel described above. Then, while maintaining the panel at 50 ° C,
Ultraviolet rays of mW (350 nm) were irradiated for 10 minutes to precipitate a polymer from the liquid crystal, thus completing the liquid crystal display device of this example.

The polymer 105 and the liquid crystal 106 are provided between the substrates.
Had a structure in which they were oriented and dispersed with each other, and black display was obtained by absorption of the dichroic dye when the voltage was off. Also,
When a sufficient voltage was applied, the liquid crystal 106 was oriented in the direction of the electric field, and a discontinuity in the refractive index occurred in the medium, resulting in a light scattering state. At this time, since the absorption of the dichroic dye was very small, white display was obtained.

When the liquid crystal display device thus obtained was driven by MIM, the contrast ratio was 12 according to the brightness ratio under diffused illumination. In this example, the visibility was significantly improved as compared with the conventional liquid crystal display element (contrast 8) in which the light absorbing material was not arranged in the gap holding material. Further, since the non-scattered light from the void-holding material portion was drastically reduced when an electric field was applied, the metallic impression was diminished and a paper-white display was obtained. Furthermore, when the surface of this liquid crystal display element was subjected to a non-glare treatment and a non-reflective coating, the reflection of the scenery was reduced and the visibility was significantly improved.

In this embodiment, as the two-terminal non-linear element, besides the MIM element, a lateral type MIM element, a back-to-back type MIM element, an MSI element, a diode ring element, a varistor element or the like can be used. Also, 3
The non-linear element of the terminal can be used in the same way.
T element, amorphous silicon TFT element, Cd-Se
A TFT element or the like can be used.

The material used for the substrate is soda glass,
Quartz, non-alkali glass, silicon single crystal, sapphire substrate, thermosetting polymer, thermoplastic polymer and the like are preferably used. The polymer material is not particularly limited as long as it does not adversely affect the liquid crystal and the polymer sandwiched between the substrates, and PET, polyether sulfone, epoxy curing resin, phenoxy resin, polyallyl ether, etc. are preferably used. It

Although the reflective electrode is a mixture of Al-Mg, simple metals such as Al, Cr, Mg, Ag, Au and Pt, or a mixture thereof can be used. In particular, a mixture of Al-Mg is preferable in terms of stability and reflectance, and M
The amount of g added is preferably 0.1 to 10% by weight.

The light absorbing layer for preventing light leakage from between the pixel electrodes is black paper adhered to the back surface of the substrate in this embodiment, but a light absorbing material may be applied directly to the substrate. . Furthermore, an organic color resist may be applied on the substrate electrode side and patterned to form a light absorbing layer between the electrodes.
The absorption wavelength of the light absorption layer between the pixel electrodes is the entire visible light (black)
However, it may be combined with the absorption region of the dichroic dye used. Further, instead of the light absorption layer, light may be shielded by a metal material.

A polyimide film was used as the alignment film.
An iO oblique vapor deposition film, polyvinyl alcohol, or the like can be used. The liquid crystal and the polymer precursor sandwiched between the substrates only need to be aligned when irradiated with ultraviolet rays, and the substrate surface may be rubbed as it is without forming an alignment film. The rubbing angle is not limited to this embodiment.

As the light-absorbing void-holding material, a material obtained by impregnating porous silica with carbon was used, but the light-absorbing ability may be imparted by, for example, dyeing in addition to the impregnation. Any material may be used as long as it has a high insulating property and a uniform diameter. Further, the number of particles scattered on the surface of the substrate is not limited to this embodiment.

As the liquid crystal, those used in ordinary liquid crystal display elements can be preferably used, but in order to improve the scattering degree, the birefringence anisotropy Δn of the liquid crystal should be 0.15 or more. desirable. Further, in order to drive with a non-linear element, the specific resistance value of the liquid crystal alone is 1.0 × 10 ⁹ Ω · cm to 1.0 ×.
10 ¹⁰ Ω · cm or more, more preferably 1 × 10 ¹² Ω
-A cm or more is desirable for maintaining a high retention rate and improving display quality.

The chiral component need not be added,
Normal TN, ST added to improve scattering
The material used for N can be preferably used as it is. The amount added is 0.01 to 10% by weight, preferably 0.1 to 5% by weight. If it is 0.01% by weight or less, the effect is small, and if it is 10% by weight or more, the driving voltage becomes high, and it cannot be driven by a normal nonlinear element.

As the dichroic dye, azo-type, anthraquinone-type, naphthoquinone-type, perylene-type, quinophthalone-type, azomethine-type, and the like which are used in a normal GH display system are preferably used. Among them, anthraquinone-based compounds alone or, if necessary, mixed with other dyes are particularly preferable from the viewpoint of light resistance. These dichroic dyes are mixed and used depending on the required color.

The polymer precursor may be any one as long as it exhibits a refractive index anisotropy after polymerization and is aligned and dispersed with a liquid crystal, but an ultraviolet-curable monomer is preferable from the viewpoint of simplicity of liquid crystal display device production. As the UV-curable monomer, monofunctional methacrylate, bifunctional methacrylate or polyfunctional methacrylate is preferably used. In order to improve the degree of scattering, it is desirable that these monomers contain at least one benzene ring in their molecular structure. These monomers may contain a chiral component. Moreover, these monomers may be polymerized by irradiating with ultraviolet rays after they are used alone or mixed with other monomers.

In this embodiment, the reflection electrode is arranged on the counter substrate side of the MIM substrate, but the same effect can be obtained by arranging the reflection electrode on the MIM element substrate side. Furthermore, the configuration of the present invention has exactly the same effect even in the simple matrix system. (Embodiment 2) Hereinafter, in the present embodiment, a space holding material for holding the substrates at a constant interval is formed by patterning a photosensitive organic insulating material, and one substrate is provided with a three-terminal element (polysilicon) as a non-linear element. 1 shows a configuration of a reflective liquid crystal display element on which a TFT element) is formed. FIG. 2 shows a cross-sectional view of the liquid crystal display element of this example. Backside substrate 213
Is a TFT substrate, a TFT element 212 and a signal line are formed on a quartz substrate, and a reflective pixel electrode 210 is formed via an insulating layer 211. For the reflective pixel electrode, an alloy of aluminum and magnesium is sputtered to about 10
00 angstroms formed, T in contact hole
It is connected to FT. The reflective electrode 2 is formed on the counter substrate 201.
In order to prevent light leakage from between 08, a light shielding layer (black stripe) 202 of chromium is formed, and the protective film 20
The ITO electrode 204 is formed via the electrode 3.

Next, a method for producing the void retaining material will be described. On the above-mentioned TFT substrate 213, the photosensitive polyimide P
I-440 (manufactured by Ube Industries, Ltd.) with a spin coater
Apply at 1200 rpm for 60 seconds at 65 ° C, 6
It was prebaked under the condition of 0 minutes and cooled to room temperature. Next, exposure was performed with an integrated light amount of 1000 mJ per 1 cm 2. In the photomask, the pattern corresponding to the space holding material has a size of 10 μm × 15 μm, and 1 pattern is used for 100 pixels.
The pattern is provided so as to be located between the pixel electrodes at a ratio of individual pieces. Then, after developing and rinsing, 160
Post-baking was performed at 50 ° C. for 50 minutes, and finally peeling was performed. The film thickness of the obtained void retaining material is 5 μm ± 0.1 μm
Met.

Polyimide was formed as the alignment films 209 and 205 on the TFT substrate and the counter substrate in which the space holding material 208 was thus formed between the reflective pixel electrodes, and the rubbing treatment was performed. The rubbing angle was 90 ° between the upper and lower substrates. Subsequently, a sealant for sticking and fixing the substrates to one of the substrates was printed around the substrates, and the both substrates were stuck and fixed. Glass fibers were mixed in the sealant and the diameter of the glass fibers was selected so that the distance between the substrates was about 5 μm. Further, black paper was adhered to the back surface of the substrate 213 as the light absorption layer 214 in order to prevent light leakage from between the pixel electrodes.

The same liquid crystal and polymer precursor mixture as in Example 1 was vacuum-sealed between the substrates, and ultraviolet rays were irradiated in the same manner as in Example 1 to precipitate the polymer, and the liquid crystal display of this example was displayed. The device was obtained.

When the liquid crystal display device thus obtained was driven by TFT, the contrast ratio was 14 according to the brightness ratio under diffused illumination. In this example, the visibility was significantly improved as compared with the conventional liquid crystal display element (contrast 8) in which the spacers were scattered without forming the gap holding material between the pixel electrodes. Further, when the electric field was applied, the non-scattered light from the void-holding material portion of the pixel portion disappeared, so that the metallic impression faded and a paper-white display was obtained. Furthermore, when the surface of this liquid crystal display element was subjected to a non-glare treatment and a non-reflective coating, the reflection of the scenery was reduced and the visibility was significantly improved.

In this embodiment, as the three-terminal non-linear element, an amorphous silicon TFT element, a Cd-SeTFT element, etc. can be used in addition to the polysilicon TFT element.

Similarly, a two-terminal non-linear element can be used, and an MIM element, a lateral type MIM element, a back-to-back type MIM element, an MSI element, a diode ring element, a varistor element or the like can be used.

The material used for the substrate is soda glass,
Quartz, non-alkali glass, silicon single crystal, sapphire substrate, thermosetting polymer, thermoplastic polymer and the like are preferably used. The polymer material is not particularly limited as long as it does not adversely affect the liquid crystal and the polymer sandwiched between the substrates, and PET, polyether sulfone, epoxy curing resin, phenoxy resin, polyallyl ether, etc. are preferably used. It

Although the reflective electrode is a mixture of Al-Mg, a simple metal such as Al, Cr, Mg, Ag, Au and Pt, or a mixture thereof can be used. In particular, a mixture of Al-Mg is preferable in terms of stability and reflectance, and M
The amount of g added is preferably 0.1 to 10% by weight.

As the light absorption layer for preventing light leakage from between the pixel electrodes, black paper is brought into close contact with the back surface of the substrate in this embodiment, but a light absorbing material may be applied directly to the substrate. . Furthermore, an organic color resist may be applied on the substrate electrode side and patterned to form a light absorbing layer between the electrodes.
The absorption wavelength of the light absorption layer between the pixel electrodes is the entire visible light (black)
However, it may be combined with the absorption region of the dichroic dye used. Further, instead of the light absorption layer, light may be shielded by a metal material. However, when the TFT is formed from the silicon single crystal substrate, it is not necessary to provide means for preventing light leakage from between pixels.

A polyimide film was used as the alignment film.
An iO oblique vapor deposition film, polyvinyl alcohol, or the like can be used. The liquid crystal and the polymer precursor sandwiched between the substrates only need to be aligned when irradiated with ultraviolet rays, and the substrate surface may be rubbed as it is without forming an alignment film. The rubbing angle is not limited to this embodiment.

A photosensitive organic insulating material can be used as the void-holding material formed by patterning.
A photosensitive polyimide is particularly preferably used because of its simplicity in the production process such as film uniformity and thickness tolerance. The number of void-holding materials formed on the surface of the substrate is determined by the size of the liquid crystal display element, and is not limited to this embodiment. Also, either substrate may be formed.

As the liquid crystal, those used in ordinary liquid crystal display devices can be preferably used, but in order to improve the scattering degree, the birefringence anisotropy Δn of the liquid crystal should be 0.15 or more. desirable. Further, in order to drive with a non-linear element, the specific resistance value of the liquid crystal alone is 1.0 × 10 ⁹ Ω · cm to 1.0 ×.
10 ¹⁰ Ω · cm or more, more preferably 1 × 10 ¹² Ω
-A cm or more is desirable for maintaining a high retention rate and improving display quality.

The chiral component need not be added,
Normal TN, ST added to improve scattering
The material used for N can be preferably used as it is. The amount added is 0.01 to 10% by weight, preferably 0.1 to 5% by weight. If it is 0.01% by weight or less, the effect is small, and if it is 10% by weight or more, the driving voltage becomes high, and it cannot be driven by a normal nonlinear element.

As the dichroic dye, azo type, anthraquinone type, naphthoquinone type, perylene type, quinophthalone type, azomethine type and the like which are used in a usual GH display system are preferably used. Among them, anthraquinone-based compounds alone or, if necessary, mixed with other dyes are particularly preferable from the viewpoint of light resistance. These dichroic dyes are mixed and used depending on the required color.

The polymer precursor may be any one as long as it exhibits a refractive index anisotropy after polymerization and is aligned and dispersed with the liquid crystal, but an ultraviolet-curable monomer is preferable from the viewpoint of the ease of manufacturing a liquid crystal display device. As the UV-curable monomer, monofunctional methacrylate, bifunctional methacrylate or polyfunctional methacrylate is preferably used. In order to improve the degree of scattering, it is desirable that these monomers contain at least one benzene ring in their molecular structure. These monomers may contain a chiral component. Moreover, these monomers may be polymerized by irradiating with ultraviolet rays after they are used alone or mixed with other monomers.

In this embodiment, the reflective electrode layer is arranged on the TFT element substrate, but the structure of this embodiment is particularly desirable because the substrate aperture ratio can be increased. Furthermore, the configuration of the present invention has exactly the same effect even in the simple matrix system.

[0046]

As described above, the liquid crystal display element of the present invention can provide a bright liquid crystal display element which does not require a polarizing plate and has no double image. In particular, by suppressing the light leakage from the air gap holding material of the display pixel portion, which has been a problem in the past, by a light absorbing air gap holding material or a simple method of disposing the air gap holding material between pixel electrodes, It was possible to provide a liquid crystal display device with significantly improved characteristics. Further, since the non-scattered light from the electric field application pixel portion disappears, it is possible to display a paper white tone. Furthermore, since the addition amount of the dichroic dye can be reduced by the present invention, a liquid crystal display element having excellent light resistance and reliability can be provided, and active matrix driving provides a reflective large-capacity display with excellent visibility. Can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display element of Example 1 of the present invention.

FIG. 2 is a sectional view of a liquid crystal display element of Example 2 of the present invention.

[Explanation of symbols]

 101 substrate 102 MIM element 103 ITO pixel electrode 104 alignment film 105 polymer 106 liquid crystal 107 void holding material 108 alignment film 109 reflective electrode 110 substrate 111 light absorption layer 201 substrate 202 black stripe 203 protective film 204 ITO electrode 205 alignment film 206 polymer 207 Liquid crystal 208 Gap holding material 209 Alignment film 210 Reflective electrode 211 Insulating layer 212 TFT element 213 Substrate 214 Light absorbing layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hidehito Iizaka 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (6)

[Claims] 1. A liquid crystal containing a dichroic dye and a refractive index anisotropy are provided between two substrates, at least one of which has a pixel electrode and a wiring for transmitting an electric signal to the pixel electrode and at least one of which is transparent. In a liquid crystal display element in which the polymers contained therein are oriented and dispersed with each other and sandwiched, a space holding material for holding the substrates at a constant interval is a light absorbing insulating material. element. 2. The liquid crystal display element according to claim 1, wherein a space holding material for holding the substrates at a constant interval is formed by patterning a photosensitive organic insulating material. 3. The pixel electrode on one side of the substrate is formed of a reflective material.
The liquid crystal display element described. 4. The liquid crystal display element according to claim 1, wherein a nonlinear element is formed on at least one of the substrates. 5. The liquid crystal display element according to claim 1, wherein the non-linear element is a two-terminal element. 6. The liquid crystal display element according to claim 1, wherein the non-linear element is a three-terminal element.