JP2001142065A - Reflection type color liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type color liquid crystal display device in which the lightness can be improved without decreasing the chroma and a bright image with good color contrast can be obtained. SOLUTION: The reflection type color liquid crystal display device using a cholesteric liquid crystal color filter layer is provided with a light-absorbing body 10 having 5 to 50% reflectance for visible rays (400 to 700 nm) in the proximity of the cholesteric liquid crystal color filter layer. The light-absorbing body 10 preferably has 7 to 30% reflectance for visible rays (400 to 700 nm) and consists of a coating film 104 of a gray coating material formed on a substrate 102.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type color liquid crystal display device, and more particularly to a reflection type liquid crystal display device having a cholesteric color filter layer, which is suitable for increasing brightness without impairing color purity. The present invention relates to a color liquid crystal display device.

[0002]

2. Description of the Related Art In general, a color filter used in a color liquid crystal display has red (R), green (G), and blue (B) pixels and a black matrix for the purpose of improving display contrast in a gap between the pixels. It is configured. Conventionally, such color filters are mainly those in which a pigment is dispersed in a resin or dyed with a dye.However, as the performance of the color filter, high transmittance and high color purity are required. In recent years, in color filters using dyes, the type of dye and dyeing resin have been optimized, and in color filters using pigments, the transmittance and color purity have been improved by using finely dispersed pigments. Has been planned.

However, in recent years, liquid crystal displays (L
Demands on the transmittance and color purity of a color filter in a CD) panel are extremely high. In particular, in color filters for reflective LCDs, it is difficult to achieve both the white display of paper white, contrast, and color reproducibility, but a color filter manufactured by dyeing a dye in a conventional resin or dispersing a pigment. Are all light-absorbing color filters, and the improvement in color purity by further improving the transmittance has reached its limit.

[0004] A polarization-based color filter comprising a cholesteric liquid crystal as a main component, a polymerizable monomer, a polymerization initiator, and the like mixed with such a light absorption type color filter and patterning to form a fine pattern,
Since an image is displayed by reflecting and transmitting a certain amount of light, the light use efficiency is high and the transmittance and the color purity have more excellent performance than the light absorption type color filter.

In this type of color filter, a black absorbing layer is generally provided on the back side of the color filter layer with respect to the light incident surface, so that the color of image display is clear or the contrast is high. However, in this absorption layer, since the light absorption rate is high, the brightness of the color filter is low, and a bright image with good color contrast cannot be obtained.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection type color liquid crystal display device which can obtain a bright and high-contrast image without deteriorating color purity.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reflective color liquid crystal display device using a cholesteric liquid crystal color filter layer, which is provided near a surface of the cholesteric liquid crystal color filter layer opposite to a light incident surface. This is achieved by a reflective type color liquid crystal display device, wherein a light absorber having a reflectance of light (400 to 700 nm) of 5 to 50% is provided. The light absorber is made of visible light (400
(700 nm) is preferably 7 to 30%, and the light absorber includes a glass substrate, a metal plate, or a plastic substrate and a coating layer laminated on any of them. Or a metal plate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. FIG. 1 is a sectional view schematically showing a main part of a preferred embodiment of the present invention. In the figure, 10 is a light absorber, 12 is a cholesteric color filter layer, 14 is a retardation film, 16 is a liquid crystal layer, 18 is a liquid crystal alignment film, 20 is an electrode, and 22 is a polarizing plate <24 substrate.

The light absorber 10 comprises a glass substrate 102 and a gray paint coating layer 104. Gray paint coating film 104
Has a reflectivity of visible light (400 to 700 nm) of the coating film itself of 5 to 50%, preferably visible light (400 to 70 nm).
0 nm) is 7 to 30%. The value of the reflectance is a value obtained by measuring the regular reflection angle under the condition that the incident angle and the reflection angle of the gray paint coating film 104 itself are 5 degrees, and the reflectance is 5%.
If it is less than 1, the desired brightness of the color filter of the present invention cannot be obtained. On the other hand, when the reflectance exceeds 50%, the brightness of the color filter increases, but the color purity of the color filter decreases, and an image with good color contrast cannot be obtained.

A substrate 24 used for a color filter;
The light-transmitting substrate 102 may be a known light-transmitting substrate, and specific examples thereof include a glass plate, a soda glass plate having a silicon oxide film formed on a surface thereof, and a polymer film. It is preferable that an alignment film is formed on the surface of the various substrates, or an alignment treatment, preferably a rubbing treatment, is performed by a conventional method. The rubbing angle and the like during the rubbing process are set in advance, but are not particularly limited.

It is preferable that the surface of the light absorber 10 reduce the scattering of light as much as possible. In view of this, a transparent and smooth surface substrate such as glass or the like, or a substrate such as glass It is desirable to apply a gray paint to the transparent and smooth surface of the base material, and the applied surface may be formed on the surface of the cholesteric color filter layer 12 side as shown in FIG. It may be formed on the surface opposite to the filter layer 12 side. Further, the light absorber may be prepared such that the glass substrate 10 itself has the above-mentioned reflectance. Also,
A gray paint coating film may be formed on the surface of the polymer film, or the polymer filter itself may be prepared to have the above-mentioned reflectance. Further, a gray metal plate having a smooth surface may be used.

Cholesteric color filter layer 12
Is composed of a cholesteric liquid crystal layer that reflects circularly polarized light in a predetermined direction of light of a specific wavelength and transmits circularly polarized light in the opposite direction to the predetermined direction and has no electric field application means for display control.
It is formed as three types of repeating stripe patterns or mosaic patterns corresponding to the primary colors.

The cholesteric liquid crystal layer in such a cholesteric color filter layer 12 contains a cholesteric liquid crystal material, a chiral compound, and a polymerizable monomer. If necessary, a photopolymerization initiator, a binder resin, a surfactant, Agents, thermal polymerization inhibitors, thickeners, dyes, pigments, ultraviolet absorbers, gelling agents, solvents and the like.

The cholesteric liquid crystal material is characterized in that its liquid crystal phase is fixed below the liquid crystal transition temperature, and has a refractive index anisotropy Δn of 0.10 to 0.10.
It can be appropriately selected from a liquid crystal material of 0.40, a polymer liquid crystal material, and a polymerizable liquid crystal material. While in the liquid crystal state at the time of melting, it can be used as a solid phase by, for example, aligning by using an alignment substrate that has been subjected to an alignment treatment such as rubbing treatment, and then fixing it by cooling or the like. Among the above, the cholesteric liquid crystal material is preferably a cholesteric liquid crystal compound having a polymerizable group in the molecule, from the viewpoint of ensuring sufficient curability.

Examples of the chiral compound include compounds such as isomanide, catechin, isosorbide, fencon and carvone from the viewpoint of improving the hue and color purity of the liquid crystal compound.

Examples of the polymerizable monomer include monomers having an ethylenically unsaturated bond, and examples include polyfunctional monomers such as pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate.

Further, in order to fix the helical pitch of the liquid crystal molecules in the cholesteric liquid crystal layer having the cholesteric liquid crystal layer formed on the substrate, and to improve the film strength of the cholesteric liquid crystal layer, the photopolymerization initiator is added. Can also. The photopolymerization initiator can be appropriately selected from known ones. For example, p-methoxyphenyl-2,4-bis (trichloromethyl) -s-triazine, 2- (p-butoxystyryl)- 5-trichloromethyl 1,3,4-oxadiazole, 9-phenylacridine, 9,10-dimethylbenzphenazine, benzophenone / Michler's ketone, hexaarylbiimidazole / mercaptobenzimidazole, benzyldimethyl ketal, thioxanthone / amine and the like. Can be

Examples of the binder resin include polystyrene compounds such as polystyrene and poly-α-methylstyrene, cellulose resins such as methyl cellulose, ethyl cellulose and acetyl cellulose, acidic cellulose derivatives having a carboxyl group in the side chain, polyvinyl formal, Acetal resins such as polyvinyl butyral, JP-A-59-44615, JP-B-54-34327,
JP-B-58-12577, JP-B-54-25957
JP-A-59-53836, JP-A-59-7104
No. 8, methacrylic acid copolymer, acrylic acid copolymer, itaconic acid copolymer, crotonic acid copolymer, maleic acid copolymer, partially esterified maleic acid copolymer and the like.

Homopolymers of alkyl acrylates and homopolymers of alkyl methacrylates are also mentioned. In these, alkyl groups are methyl, ethyl, n-propyl, n-butyl, iso-
-Butyl group, n-hexyl group, cyclohexyl group, 2-
Examples thereof include an ethylhexyl group. In addition, a polymer having a hydroxyl group to which an acid anhydride is added, a benzyl (meth) acrylate / (homopolymer of methacrylic acid) acrylic acid copolymer or benzyl (meth) acrylate / (meth) acrylic acid / other monomer And the like.

Examples of the polymerization inhibitor added for improving the storage stability include hydroquinone, hydroquinone monomethyl ether, phenothiazine, benzoquinone, and derivatives thereof.

Each of the above components is dissolved in an appropriate solvent to prepare a coating liquid solution, and this coating liquid is applied on a substrate described later by a desired coating method to form a cholesteric liquid crystal layer. it can.

In the cholesteric color filter layer, as a light source used for photopolymerization by light irradiation, an ultra-high pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, various laser light sources, etc., among which an ultra high pressure mercury lamp is preferable. The irradiation amount of the actinic ray is 0.1 to 1000.
Preferably ^{mj / cm 2, 0.2~500mj / cm} 2 is more preferable. If the irradiation amount is less than 0.1 mj / cm ² , the curing reaction may not be sufficiently performed,
If it exceeds 000 mj / cm ² , the working efficiency may decrease.

For the purpose of aging the alignment and promoting uniform alignment, and to develop a hue excellent in transmittance and color purity, a heat treatment can be performed (color formation treatment). The coloring process may be performed simultaneously with the curing process, or may be performed before performing the curing process. In the case of forming a full-color color filter, the curing treatment is performed by using a red, green, or blue transfer material whose selective reflection wavelength belongs to the visible wavelength region. After the forming step, it may be performed at any time during the curing process,
After completing the image forming processes for all three colors, the processes may be performed collectively.

In the present invention, heat treatment can be performed for the purpose of adjusting the helical pitch of the cholesteric liquid crystal layer by heating. The heat treatment may be provided at any time during the image forming step, after the image forming step is completed, or during the curing processing.

The retardation film 14 is made of a film having a predetermined retardation over the entire visible light range, such as polyvinyl alcohol, and the liquid crystal layer 16 is arranged in a matrix and has application means consisting of a transparent electrode. These retardation films 14
The liquid crystal film 16 forms a birefringent layer.

The liquid crystal layer 16 is made of a twisted nematic (T
N) Using a liquid crystal layer, a super twisted nematic (STN) liquid crystal layer having a large helix angle of liquid crystal molecules, or a combination of these liquid crystal layers and an active matrix element or an active matrix substrate such as a so-called TFT or MIM. Can be.

A liquid crystal alignment film is provided between the cholesteric color filter layer 12 and the light absorber 10, the surface of the alignment film is subjected to an alignment treatment by a known method such as rubbing, and a cholesteric liquid crystal layer is provided on the surface. Thereby, the liquid crystal molecules can be oriented so as to have a predetermined orientation promoted by the orientation treatment, and in this state, by cooling and fixing, it is possible to develop a desired hue having excellent transparency and high color purity. it can.

Materials usable for forming the liquid crystal alignment film include, for example, polyvinyl alcohol (PVA), polyimide, polyamide, nylon, polystyrene, polyethylene, polyethylene terephthalate (PET), polybutyl terephthalate (PBT), polyester, Examples include polycyclohexyl methacrylate, polyvinyl cinnamate, polybrene, polyacetal, and the like.

The polarizing plate 22 selectively transmits light in accordance with the polarization of output light due to reflection, and a linear polarizing plate, a circular polarizing plate, or the like is used.

In the above embodiment, the short-pitch cholesteric liquid crystal reflects light of a predetermined direction with respect to light of a wavelength selected by the helical pitch, transmits light of a predetermined direction, and transmits light of another wavelength range. Since it does not affect the light, when the cholesteric liquid crystal of the cholesteric color filter layer 14 is rotated clockwise red, the right circularly polarized light of the red light is transmitted, and the left circularly polarized light is reflected. Light of other color wavelengths is blocked and absorbed by the light absorber 10. In this case, since the light absorber 10 has a visible light reflectance of 5 to 50%, the reflectance of the left circularly polarized light increases, and the red left circularly polarized light passes through the phase difference film and the liquid crystal layer. The light reaches the polarizing plate 22. If the cholesteric color filter layer 14 is a clockwise or counterclockwise laminate, most of the red light is reflected and reaches the polarizing plate 22. Since the birefringent layer is adjusted for retardation, the phase advances by π depending on the presence or absence of an electric field, or the retardation is broken. Therefore, when there is no electric field in the polarizing plate 22, for example, the display color is achromatic (black). ),
When an electric field is applied, the light is transmitted and the display color becomes red.

In the above embodiment, the red color of the cholesteric color filter layer 14 has been particularly described as an example, but the same applies to other green and blue colors. In the present embodiment, light of a specific wavelength range is effectively used, and an electric field is not applied to a liquid crystal utilizing wavelength selectivity. High-time-division driving display that is available and has good color contrast due to the light reflection effect of the light absorber 10 can be performed.

[0032]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to this embodiment. (Example 1) A polyimide alignment film coating solution was applied on a glass substrate by a spin coater, dried in a 100 ° C oven for 5 minutes, and then baked in a 250 ° C oven for 1 hour to form an alignment film. The surface was rubbed and subjected to an orientation treatment to obtain a glass substrate with an orientation film. Further, a coating solution prepared according to the following formulation was spin-coated on the alignment film,
After drying in an oven at 0 ° C. for 2 minutes, a blue cholesteric color filter was provided. <Coating solution for cholesteric color filter>-81% by weight of compound (a) having the following structure-11% by weight of compound (b) having the following structure-5% by weight of dipentaerythritol hexaacrylate-2,4-trichloromethyl- (4 ') -Methoxystyryl) -6-triazine 3% by weight

[0033]

Embedded image

Further, polyethylene terephthalate was laminated on the cholesteric color filter layer. This glass substrate is placed on a hot plate at a temperature of 110 ° C. for 5 minutes.
The cholesteric color filter layer was developed for ² minutes by an ultra-high pressure mercury lamp (500 w / cm ² ) from the distance of 60 cm to the cholesteric color filter layer.
Exposure was performed for 5 seconds. (Irradiation energy: 100 mj /
cm ² ) After exposure, the substrate was cooled to room temperature, and then polyethylene terephthalate was peeled off at the interface with the cholesteric color filter layer. This substrate was placed on a paper coated with a gray paint having a reflectance of 20% with respect to visible light, λ / 4 sheets were further placed thereon with a polarizing plate, and X was measured using a colorimeter manufactured by Minolta Co., Ltd.
The lightness Y and chroma in the YZ color system were measured. as a result,
Lightness Y was 36 and chroma was 70%. By the way, the brightness Y is increased by 25% compared with the following comparative example, and the saturation is
It was slightly smaller.

(Comparative Example 1) Lightness Y and chroma were measured in the same manner as in Example 1 except that paper coated with black paint was used instead of paper coated with gray paint having a reflectance of 20%. However, lightness Y was 29 and chroma was 73%.

[0036]

As described above, according to the reflective color liquid crystal display device of the present invention, the brightness can be improved without deteriorating the chroma, and a bright image with good color contrast can be obtained. .

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram showing a preferred embodiment of a reflective type color liquid crystal display device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light absorber 12 Cholesteric color filter layer 14 Retardation film 16 Liquid crystal layer 20 Electrode 22 Polarizer 24 Base

Claims (4)

[Claims] 1. A reflection type color liquid crystal display device using a cholesteric liquid crystal color filter layer, wherein the reflectance of visible light (400 to 700 nm) is located close to the surface of the cholesteric liquid crystal color filter layer opposite to the light incident surface. A reflective color liquid crystal display device, wherein a light absorber of 5 to 50% is provided. 2. The method according to claim 1, wherein the light absorber is a visible light (400 to 70).
The reflective color liquid crystal display device according to claim 1, wherein a reflectance of the reflective color liquid crystal display device is 7 to 30%. 3. The method according to claim 2, wherein the light absorber is a glass substrate, a metal plate,
The reflective color liquid crystal display device according to claim 1, comprising a plastic substrate and a coating layer laminated on any of the plastic substrates. 4. The reflective color liquid crystal display device according to claim 1, wherein said light absorber is made of a metal plate.