JPH08211369A - Liquid crystal display element - Google Patents

Abstract

PURPOSE: To make it possible to control light absorption without depending on the dyestuff in liquid crystals and light molecules, to enhance reliability to light and to make display with good visibility by forming a light absorption layer on an electrode surface. CONSTITUTION: The reflection electrode 108 is formed by sputtering Cr and patterning its film on a lower substrate 109 of a liquid crystal display element. The light absorption layer 107 is formed by spin coating the organic resist on the front surface of the reflection electrode 108. Transparent electrodes 102 are formed by ITO on an upper substrate 101. The liquid crystals 105 are injected between the substrates formed in such a manner, by which the liquid crystal display panel is formed. Black display is obtd. with this panel by absorption of the light absorption layer 107 when voltage is off. The liquid crystals 105 orient in an electric field direction and generate the discontinuous points of the refractive index within the medium when the sufficient voltage is impressed thereon and, therefore, a light scattering state is attained. Consequently, the light scattering layer is formed just before the light absorption layer 107 and, therefore, the white display is obtd.

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, information devices have become smaller and lighter,
The display mounted on it is also required to save power. A liquid crystal display element in the TN mode has been put into practical use for a small display capacitance device and a liquid crystal display element in the FTN mode for a medium display capacitance device as a reflective display. further,
Applications for combining an information input device such as a tablet on a reflective display are also expanding, and the reflective liquid crystal display element is required to have good brightness and visibility. Recently, bright reflective displays that do not use polarizing plates are being developed in such fields. For example, a polymer-dispersed liquid crystal in which a liquid crystal and a polymer are dispersed, a liquid crystal display element (such as JP-B-58-501631) that is transparent when an electric field is applied and controls light scattering when no electric field is applied, or a liquid crystal display element that scatters when an electric field is applied. A liquid crystal display element that is transparent or controls light absorption without application of an electric field (European published patent EPO488116A
2, JP-A-4-227684, JP-A-5-119302
Etc.) are being developed.

[0003]

However, in the liquid crystal display element of the TN type and the FTN 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. Further, in the TN method and the FTN method, since the reflection plate 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,
The small letters were unclear, and visibility was a problem. On the other hand, since the liquid crystal display device using polymer dispersed liquid crystal does not use a polarizing plate, it is possible to manufacture a bright reflective display. Furthermore, when the light reflecting surface is also used as a pixel electrode, a double image of the display is obtained. Not a bright reflective display was possible.

However, although the prior art disclosed regarding the polymer-dispersed liquid crystal can solve the problem of the liquid crystal display device using the polarizing plate, the liquid crystal and / or the polymer in which a dye is added to control the light absorption is used. When using, there were the following problems.

(1) The dye is easily damaged by light, the time constant is reduced, and the display quality due to driving the active element is deteriorated.

(2) Since the dye absorbs a part of the scattered light, the maximum reflectance is lowered.

If the dye cannot be added sufficiently due to the above problems, (3) the light absorption is insufficient, the surrounding scenery is reflected, and the visibility is deteriorated.

The present invention has been made in order to solve such a problem, and an object of the present invention is to control light absorption by a light absorption layer provided on an electrode surface, thereby improving the optical reliability. The purpose of the present invention is to provide a reflective liquid crystal display element which is highly visible, bright, and has good visibility.

[0009]

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

(1) A liquid crystal and a polymer have a refractive index anisotropy between two transparent substrates, at least one of which is provided with a pixel electrode and a wiring for transmitting an electric signal to the pixel electrode. In a liquid crystal display element sandwiched in a state of being oriented and dispersed with each other, a light absorption layer is formed on the electrode surface.

(2) Further, the liquid crystal and / or polymer is characterized by not containing a dichroic dye.

(3) Further, one of the pixel electrodes is formed of a reflective material.

(4) Further, it is characterized in that an active element is formed for each pixel electrode.

(5) Further, the surface is subjected to a non-glare treatment and / or an antireflection treatment.

(6) Further, the above-mentioned light absorbing layer is formed by a color filter.

[0016]

In the liquid crystal display device of the present invention, since the light absorption layer is formed on the electrode surface, the light absorption can be controlled without relying on the dye contained in the liquid crystal and / or the polymer. It is possible to perform display with high light reliability, high brightness, and good visibility.

[0017]

【Example】

(Embodiment 1) In this embodiment, a structure in which a light absorption layer is arranged on the surface of a reflective electrode will be described below.

FIG. 1 shows a simple partial cross-sectional view of the liquid crystal display element in this embodiment. Cr on the lower substrate 109
Is formed to a thickness of about 2000 angstrom by sputtering, and then patterned to form the reflective electrode 108. Furthermore, as the organic resist (black), color mosaic CK (manufactured by Fuji Hunt Co., Ltd.) is formed on the surface of the reflective electrode.
The light absorption layer 107 is formed by coating with a spin coater at about 3000 angstroms. Upper substrate 1
01 on ITO by sputtering about 1500
After forming angstrom, patterned transparent electrode 1
02 is formed. Polyimide is formed as a liquid crystal alignment film on both of these substrates, and alignment films 106 and 103 are formed by rubbing treatment. The two substrates are bonded and fixed around the substrates with a gap of 12 μm. The rubbing direction is set to 270 ° of liquid crystal right twist.

Next, the liquid crystal and polymer precursor mixture sealed between the substrates will be described. TL-2 as liquid crystal
02 (manufactured by Merck) and MJ92786 (manufactured by Merck) were mixed at a ratio of 7: 3 (hereinafter referred to as liquid crystal A), and R1011 (manufactured by Merck) as a chiral component was added to 0.2
weight%. Biphenyl methacrylate was used as a polymer precursor in an amount of 7% by weight based on the liquid crystal mixture. However, no dichroic dye was used. After the above components were heated and mixed to form a liquid crystal state, they were vacuum-sealed in the empty panel described above.

The liquid crystalline mixed material enclosed in the panel was twisted to the right from the rubbing axis of the upper substrate 101 to the rubbing axis of the lower substrate 109 by 270 °. Then, while maintaining the panel at 50 ° C, 5 mW / cm2 (350 nm)
Was irradiated with the ultraviolet rays for 8 minutes to precipitate a polymer from the liquid crystal, and the liquid crystal display element of this example was completed. The liquid crystal shows an alignment state before ultraviolet irradiation, and the polymer 10 is present between the substrates.
4 and the liquid crystal 105 were oriented with respect to each other and had a dispersed structure.

FIG. 2 shows the electro-optical characteristics of the liquid crystal display device obtained in this example. The electro-optical characteristics showed a threshold characteristic and a normally black characteristic in which the reflectance increased by applying a voltage was obtained. That is, black display is obtained by absorption of the light absorption layer 107 when the voltage is off, and when a sufficient voltage is applied, the liquid crystal 105 is oriented in the direction of the electric field, and a discontinuity of the refractive index occurs in the medium. In order to do so, it became a light scattering state. At this time, a thick light scattering layer is formed in front of the light absorption layer 107, so that white display is obtained.

Next, the electro-optical characteristics of the liquid crystal display device of this embodiment will be described. The electro-optical characteristics of a liquid crystal display device are 10% by using a xenon lamp / ring light source.
Applying a rectangular wave of 0 Hz, incident angle 3 from the normal direction of the device
Response reflected light in the normal direction of the 0 ° omnidirectional incident light was detected. The reflectance of 100% was standardized by the brightness of the surface of the standard white plate.

The liquid crystal display device of this example had a maximum reflectance of 83%, which is an index of brightness, and was brighter than the liquid crystal display device of Comparative Example 1. In addition, the visibility of the surrounding landscape has been reduced, improving visibility. Furthermore, visible light is integrated with a xenon lamp at an integrated light intensity of 850 MJ /
The time constant after irradiation up to m2 (measured with a pyranometer) hardly decreased from the initial value.

In this embodiment, a specific structure has been illustrated, but the present invention is not limited to this.

The light absorbing layer can be used as long as it has absorption in the visible light region. In this embodiment, black is particularly preferable because of the combination with the metal used for the reflective electrode. Also,
The thickness of the light absorption layer is not limited to this, and the reflective electrode material,
It can be set in consideration of the liquid crystalline mixed material, the gap between the substrates, and the like. If the thickness of the light absorption layer is too thick, the white display becomes dark, and if it is too thin, sufficient black display cannot be performed.

The reflective electrode is made of Al, Cr, Mg, Ag, A.
A simple metal such as u or Pt or a mixture thereof can be used. In particular, from the viewpoint of stability and reflectance, Cr or a mixture of Al-Mg is preferable, and the addition amount of Mg is
0.1 to 10% by weight is desirable. Further, the method of forming these reflective electrodes is not limited to sputtering. For example, vapor deposition, plating, etc. can also be used.

As the material of the substrate, 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,
PET, polyether sulfone, epoxy curing resin, phenoxy resin, polyallyl ether and the like are preferably used.

The gap between the substrates is not limited to this. If the gap width is too narrow, scattered light of sufficient whiteness cannot be obtained, and conversely, if it is too wide, the driving voltage becomes high.

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 or more, preferably 1.0 × 10 ^ 10 Ω · cm or more, but the retention rate is kept high and the display quality is high. Is desirable in order to improve.

The chiral component need not be added,
It is added to improve the stability of orientation, the steepness of electro-optical response, and the degree of scattering, and is added in an optimum amount to obtain a predetermined liquid crystal twist angle. As the chiral agent, the materials used for ordinary TN and STN can be preferably used as they are. The amount added is not limited to this, and the twist angle is preferably d / p of 2 or less. If the voltage is higher than this, the driving voltage becomes high, and it cannot be driven by a normal nonlinear element. In addition, hysteresis occurs in the electro-optical response. In this embodiment, the twist is 270 °,
It is not limited to this. Steepness of electro-optical response,
The optimum twist angle can be freely set in consideration of the drive voltage and the viewing angle characteristics. The direction of the twist angle due to the chiral component may be left or right.

The polymer precursor may be any one as long as it exhibits a refractive index anisotropy after polymerization and exhibits alignment dispersion with the liquid crystal, but an ultraviolet-curable monomer is preferable from the viewpoint of 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. In particular, a material having a biphenyl, terphenyl or quarter phenyl skeleton is preferably used. These monomers may be substituted with fluorine or the like. These monomers include
It 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.

(Comparative Example 1) In this comparative example, a structure in which a light absorption layer is not formed on the surface of the reflective electrode and a dichroic dye is added to the liquid crystal will be exemplified.

In the liquid crystal display element of this comparative example, the light absorption layer 107 of Example 1 is not formed. Instead, M361, SI512, and M137 (all manufactured by Mitsui Toatsu Dyes Co., Ltd.) as dichroic dyes were added to the liquid crystal A in Example 1 at 0.8% by weight, 1.0% by weight, and 0% by weight, respectively. 0.2% by weight, and a chiral component and a polymer precursor were mixed and used in the same manner as in Example 1. Other conditions were exactly the same as in Example 1.

The liquid crystal display element of this comparative example had a maximum reflectance of 77%, which is an index of brightness. Further, when the visible light was irradiated with a xenon lamp to an integrated light amount of 850 MJ / m2, the time constant decreased to 30% of the initial value.

(Embodiment 2) In this embodiment, a two-terminal element (MIM) is formed for each pixel electrode and a light absorption layer is arranged on the surface of the reflection electrode.

A simple partial cross-sectional view of the liquid crystal display device of this embodiment is shown in FIG. The lower substrate is a MIM substrate manufactured by the two-photo process. The substrate process is T
After a is sputtered, it is patterned into a desired shape (first photo step), and then Ta is anodized to form an insulating film Ta on the Ta surface. Subsequently, Cr is sputtered and then patterned into a desired shape (second photo step) to form the MIM element 310 and the reflective electrode 308. Furthermore, as the organic resist (black), color mosaic CK (manufactured by Fuji Hunt Co., Ltd.) is formed on the surface of the reflective electrode.
The light absorption layer 307 is formed by coating with a spin coater at about 3000 angstroms. On the other hand, the upper substrate 3
On 01, ITO is sputtered and patterned in stripes to form transparent electrodes 302. Subsequently, polyimide was formed as a liquid crystal alignment layer on both substrates, and a rotary rubbing treatment was performed to form alignment films 303 and 306. The two substrates thus obtained were bonded together at their peripheries with a gap of 12 μm and fixed to produce an empty panel. The rubbing direction is 270
It is set in °.

Subsequently, a liquid crystal mixture material composed of the same liquid crystal and polymer precursor as in Example 1 was vacuum-injected into the above empty panel. The liquid crystal mixed material sealed in the panel is moved from the rubbing axis of the upper substrate 301 to the lower substrate 30 as in the first embodiment.
A right twist of 270 ° was taken to the rubbing axis of No. 9.
Then, while maintaining the panel at 50 ° C, 5 mW / cm2
Ultraviolet rays of (350 nm) were irradiated for 8 minutes to precipitate a polymer from the liquid crystal, thus completing the liquid crystal display device of this example.

The liquid crystal display device thus obtained was
When MIM driving was performed at 0 duty, the maximum reflectance was 66% under the measurement conditions of Example 1, and a bright liquid crystal display element was obtained as compared with the liquid crystal display element of Comparative Example 2.
In addition, the visibility of the surrounding landscape has been reduced, improving visibility. In addition, the visible light accumulated by the xenon lamp is 85
No decrease in display quality due to a decrease in time constant after irradiation up to 0 MJ / m2 was observed.

In this embodiment, a specific structure has been illustrated, but the present invention is not limited to this.

The light absorbing layer can be used as long as it has absorption in the visible light region. In this embodiment, black is particularly preferable because of the combination with the metal used for the reflective electrode. Also,
The thickness of the light absorption layer is not limited to this, and the reflective electrode material,
It can be set in consideration of the liquid crystalline mixed material, the gap between the substrates, and the like. If the thickness of the light absorption layer is too thick, the white display becomes dark, and if it is too thin, sufficient black display cannot be performed.

The reflective electrode is made of Al, Cr, Mg, Ag, A.
A simple metal such as u or Pt or a mixture thereof can be used. In particular, from the viewpoint of stability and reflectance, Cr or a mixture of Al-Mg is preferable, and the addition amount of Mg is
0.1 to 10% by weight is desirable. Further, the method of forming these reflective electrodes is not limited to sputtering. For example, vapor deposition, plating, etc. can also be used.

As the material of the substrate, 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,
PET, polyether sulfone, epoxy curing resin, phenoxy resin, polyallyl ether and the like are preferably used.

The gap between the substrates is not limited to this. If the gap width is too narrow, scattered light of sufficient whiteness cannot be obtained, and conversely, if it is too wide, the driving voltage becomes high.

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 or more, preferably 1.0 × 10 ^ 10 Ω · cm or more, but the retention rate is kept high and the display quality is high. Is desirable in order to improve.

The chiral component need not be added,
It is added to improve the stability of orientation, the steepness of electro-optical response, and the degree of scattering, and is added in an optimum amount to obtain a predetermined liquid crystal twist angle. As the chiral agent, the materials used for ordinary TN and STN can be preferably used as they are. The amount added is not limited to this, and the twist angle is preferably d / p of 2 or less. If the voltage is higher than this, the driving voltage becomes high, and it cannot be driven by a normal nonlinear element. In addition, hysteresis occurs in the electro-optical response. In this embodiment, the twist is 270 °,
It is not limited to this. Steepness of electro-optical response,
The optimum twist angle can be freely set in consideration of the drive voltage and the viewing angle characteristics. The direction of the twist angle due to the chiral component may be left or right.

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. In particular, a material having a biphenyl, terphenyl or quarter phenyl skeleton is preferably used. These monomers may be substituted with fluorine or the like. These monomers include
It 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.

As the two-terminal non-linear element, in addition to the MIM element, a lateral MIM element and a back-to-back MI
M element, MSI element, diode ring element, varistor element, etc. can be used. Also, a 3-terminal non-linear element can of course be used, and as the 3-terminal non-linear element, a polysilicon TFT element, an amorphous silicon TFT element, C
A d-SeTFT element or the like can be used.

Further, in this embodiment, the reflective electrode and the light absorption layer are formed on the MIM substrate, but they can be formed on the counter substrate side.

Comparative Example 2 Hereinafter, in this comparative example, a two-terminal element (MIM) was formed for each pixel electrode, a light absorbing layer was not formed on the surface of the reflective electrode, and a dichroic dye was added to the liquid crystal. The configuration will be exemplified.

In the liquid crystal display element of this comparative example, the light absorption layer 307 of Example 2 is not formed. Instead, M361, SI512, and M137 (all manufactured by Mitsui Toatsu Dyes Co., Ltd.) as dichroic dyes were added to the liquid crystal A in Example 2 at 0.8% by weight, 1.0% by weight, and 0% by weight, respectively. 0.2% by weight, and a chiral component and a polymer precursor were mixed and used in the same manner as in Example 2. The other conditions were exactly the same as in Example 2.

The liquid crystal display device thus obtained was
When MIM driving was performed at 0 duty, the maximum reflectance was 61% under the measurement conditions of Example 1. Further, when the visible light was applied to the integrated light amount of 850 MJ / m2 with the xenon lamp, the contrast ratio was decreased to the initial ratio of 30% due to the decrease of the time constant.

(Embodiment 3) In this embodiment, the structure of Embodiment 2 in which the surface of the upper substrate is subjected to antireflection treatment and antiglare treatment will be exemplified.

In the liquid crystal display element of this embodiment, the liquid crystal mixed material consisting of the liquid crystal and polymer precursor of the second embodiment is sealed in the panel having the structure of the second embodiment, and the ultraviolet rays are irradiated in the same manner as in the second embodiment. Irradiation was performed to precipitate a polymer from the liquid crystal. Subsequently, a non-glare film subjected to antireflection treatment was attached to the surface of the upper substrate to complete the liquid crystal display element of this example.

The liquid crystal display device thus obtained was
When MIM driving was performed at 0 duty, a bright liquid crystal display device was obtained under the measurement conditions of Example 1 as compared with the liquid crystal display device of Comparative Example 2. Furthermore, as compared with the liquid crystal display element of Example 2, the reflection of the surrounding scenery was reduced and the visibility was improved. Further, no deterioration in display quality due to a decrease in time constant after irradiation of visible light with a xenon lamp up to an integrated light amount of 850 MJ / m 2 was observed.

(Embodiment 4) In this embodiment, the structure in which the light absorption layer is formed of a color filter will be described below.

FIG. 4 shows a simple partial sectional view of the liquid crystal display element of this embodiment. The liquid crystal display element in this embodiment is
A liquid crystal mixed material composed of the liquid crystal and polymer precursor of Example 2 is enclosed in a panel having a structure in which the light absorption layer of Example 2 is formed by a color filter 407, and ultraviolet rays are irradiated in the same manner as in Example 2. Then, a polymer was deposited from the liquid crystal to complete the liquid crystal display device of this example.

The liquid crystal display device thus obtained was
When MIM driving was performed at 0 duty, a bright, highly visible color display with good light resistance was obtained. The colors of the color filter are not limited to red, blue and green, and any primary color that can reproduce a natural color may be used.

[0058]

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, it is possible to solve the problems of low light reliability, low brightness, and glare of scenery due to the dichroic dye, which have been a problem in the past, by the arrangement of the light absorption layer on the electrode surface. became. As described above, according to the present invention, it is possible to manufacture a liquid crystal display element having high reliability, brightness, and good visibility.

[Brief description of drawings]

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

FIG. 2 is a diagram showing electro-optical characteristics of the liquid crystal display element of Example 1 of the present invention.

FIG. 3 is a partial cross-sectional view of a liquid crystal display element of Example 2 of the present invention.

FIG. 4 is a partial cross-sectional view of a liquid crystal display element of Example 4 of the present invention.

[Explanation of symbols]

 101 substrate 102 transparent electrode 103 alignment film 104 polymer 105 liquid crystal 106 alignment film 107 light absorption layer 108 reflection electrode 109 substrate 301 substrate 302 transparent electrode 303 alignment film 304 polymer 305 liquid crystal 306 alignment film 307 light absorption layer 308 reflection electrode 309 substrate 310 MIM element 401 Substrate 402 Transparent electrode 403 Alignment film 404 Polymer 405 Liquid crystal 406 Alignment film 407 Color filter 408 Reflective electrode 409 Substrate 410 MIM element

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Yazaki, Masayuki Yazaki, 3-3-5 Yamato, Suwa, Nagano Seiko Epson Co., Ltd. (72) Hidehito Iizaka, 3-5, Yamato, Suwa, Nagano Prefecture Seiko Epson Incorporated (72) Inventor Shuhei Yamada 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (6)

[Claims] 1. A liquid crystal and a polymer have a refractive index anisotropy between two substrates, at least one of which is transparent, on which a pixel electrode and a wiring for transmitting an electric signal to the pixel electrode are formed. A liquid crystal display element sandwiched in a state of being oriented and dispersed, wherein a light absorbing layer is formed on the electrode surface. 2. The liquid crystal display element according to claim 1, wherein the liquid crystal and / or polymer does not contain a dichroic dye. 3. The liquid crystal display element according to claim 1, wherein one of the pixel electrodes is formed of a reflective material. 4. The liquid crystal display element according to claim 1, wherein an active element is formed for each pixel electrode. 5. A liquid crystal display device according to claim 1, wherein the surface is subjected to a non-glare treatment and / or an antireflection treatment. 6. The liquid crystal display device according to claim 1, wherein the light absorption layer is formed of a color filter.