JPH11264966A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display element which has a low driving voltage and high contrast by using microcapsuled nematic liquid crystals. SOLUTION: A liquid crystal display element has a liquid crystal layer 20 sandwiched between transparent substrates 11 and 12 provided with transparent electrodes 13 and 14. The liquid crystal layer 20 is formed by putting chiral nematic liquid crystal compositions or nematic liquid crystal compositions 22a, which show a cholesteric phase at a room temperature by adding a chiral material to nematic liquid crystal components, in capsules 21 consisting of macromolecule films and dispersing the capsules 21 in a chiral nematic liquid crystal composition or nematic liquid crystal composition 22b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using a liquid crystal exhibiting a cholesteric phase at room temperature.

[0002]

2. Description of the Related Art In recent years, various researches have been made on liquid crystal display devices using a chiral nematic liquid crystal which shows a cholesteric phase at room temperature by adding a chiral material to the nematic liquid crystal. In this element, display is performed by switching the liquid crystal between the planar state and the focal conic state according to the magnitude of the applied voltage.

However, in a device in which a chiral nematic liquid crystal is merely sandwiched between a pair of substrates, there is a concern about the long-term bistability of the liquid crystal molecular arrangement. Therefore, a network type in which a network-like composite film made of a liquid crystal material and a resin material is formed has been proposed. However, it is difficult to form a uniform network, and the problem that characteristics such as reflectance vary locally cannot be solved.

Accordingly, the present inventors have studied a microencapsulation method in which a liquid crystal is enclosed in a capsule made of a polymer film as a basic structure replacing the network type. However, merely holding the spherical microcapsules between the substrates or dispersing them in a polymer such as polyvinyl alcohol increases the driving voltage and lowers the display contrast.

An object of the present invention is to provide a liquid crystal display device using a microencapsulated nematic liquid crystal, which has a low driving voltage and a high contrast.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, a liquid crystal display device according to the present invention is characterized in that a liquid crystal layer sandwiched between a pair of transparent substrates has a cholesteric phase at room temperature. The composition or the nematic liquid crystal composition is surrounded by a capsule made of a polymer film, and the capsule is dispersed in the chiral nematic liquid crystal composition or the nematic liquid crystal composition.

In the present invention, the chiral nematic liquid crystal composition or the capsule surrounding the nematic liquid crystal composition is dispersed in the chiral nematic liquid crystal composition or the nematic liquid crystal composition.
The coloring state switches and stabilizes. Moreover, high contrast can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described with reference to the accompanying drawings.

(Configuration and Display Operation of Liquid Crystal Display Element) FIG.
1 schematically shows a cross section of the liquid crystal display element according to the first embodiment of the present invention. In FIG. 1, transparent substrates 11 and 12 have transparent electrodes 13 and 14 formed on the respective surfaces in a matrix. An insulating thin film or an alignment film may be formed on the electrodes 13 and 14.

As the substrates 11 and 12, besides glass,
Flexible substrates such as polycarbonate, polyethersulfone, and polyethylene terephthalate can be used.

The electrodes 13 and 14 are made of ITO (Indium).
A transparent conductive film typified by Tin Oxide, a metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon or BSO (Bismuth Silicon Oxide) can be used. In order to form the electrodes 13 and 14 in a matrix, for example, an ITO film may be formed on the substrates 11 and 12 by a sputtering method and then patterned by a photolithography method.

Reference numeral 20 denotes a liquid crystal layer, in which a capsule 21 surrounding a chiral nematic liquid crystal composition 22a is dispersed in a chiral nematic liquid crystal composition 22b. Chiral nematic liquid crystal composition 22 surrounded by capsule 21
“a” is obtained by adding a chiral material to a nematic liquid crystal component so as to exhibit a cholesteric phase at room temperature, and the selective reflection wavelength can be adjusted depending on the amount of the chiral material added.
As the nematic liquid crystal, a liquid crystal compound having a positive dielectric anisotropy such as a liquid crystal tolan compound, a liquid crystal pyrimidine compound, a liquid crystal ester compound, or a liquid crystal cyanobiphenyl compound is preferable. Further, a dye may be added.

The capsule 21 is made of a polymer material such as a polyurea resin, a polyurethane resin, a polyester resin, a polyamide resin, a polysulfonamide resin, an epoxy resin, a polysulfonate resin, and a polycarbonate resin. The particle size of the capsule 21 is 10 μm or less, preferably 1 μm.
About 10 μm. The dispersion medium in which the capsules 21 are dispersed is a chiral nematic liquid crystal composition in which a chiral material is added to a nematic liquid crystal component. As the encapsulation method, conventionally known various methods can be used. For example, a chemical encapsulation method such as an interfacial polymerization method, an in-situ polymerization method, or a method combining these methods can be used. it can.

In order to accurately maintain the distance between the substrates 11 and 12, a spherical spacer or a columnar structure made of resin or inorganic oxide may be interposed between the substrates 11 and 12. The distance between the substrates can be set to 20 μm or less, more preferably 10 μm or less. A lower limit of about 1 μm is appropriate.

In the liquid crystal display device shown in FIG. 1, the display is switched by applying an appropriate voltage to the electrodes 13 and 14 from the power supply 25. That is, when a relatively high voltage is applied, the liquid crystal enters a planar state, and selectively reflects light in a specific wavelength range, thereby exhibiting a high reflectance. By applying a relatively low voltage, the liquid crystal becomes a focal conic state, that is, transparent, and exhibits a low reflectance.

As a second embodiment of the present invention, there is a liquid crystal display device using a nematic liquid crystal alone instead of a chiral nematic liquid crystal as a liquid crystal component used in a capsule and a dispersion medium of the capsule. Such a liquid crystal display element does not have a memory property as in the first embodiment, and when an electric field is not applied or the applied electric field is small, the incident light is scattered by a random arrangement of liquid crystals. When a sufficiently large electric field is applied, the liquid crystal is arranged in the direction of the electric field, so that scattering of incident light is reduced and the liquid crystal becomes transparent.

As the chiral material to be added, various known chiral materials such as an ester compound, a pyrimidine compound, an azoxy compound and a tolan compound can be used.

Experimental Example 1 15 g of a chiral nematic liquid crystal obtained by adding a chiral material S811 (manufactured by Merck) to a nematic liquid crystal MN1000 (manufactured by Chisso) having a liquid crystalline trans compound as a main component, 6 g of ethyl acetate and xylylene diisocyanate 1.5 g of an adduct of 3 mol and 1 mol of trimethylolpropane were added and kept at room temperature. Further, 5 g of a 2.5% aqueous solution of diethylenetriamine was added to 30 g of a 4% aqueous solution of polyvinyl alcohol to prepare a water-soluble solvent, which was kept at room temperature. Further, 10 g of a solution obtained by dissolving 3 g of a reactive surfactant (New Frontier N177E, manufactured by Daiichi Kogyo Seiyaku) in 97 g of pure water was taken.
The two solutions were mixed and emulsified and dispersed at room temperature with a laboratory homogenizer to obtain an oil-in-water emulsion.
About 10 minutes after the preparation of this emulsion, 6.7 g of a 5% aqueous solution of diethylenetriamine was gradually added dropwise.
The mixture was mechanically stirred for 3 hours in a water bath set at 60 ° C. to complete the encapsulation reaction.

The solution after the encapsulation reaction was completed was centrifuged, and only the capsule was taken out. The capsule was dried in a dryer at about 40 ° C. for 4 hours to remove water. A nematic liquid crystal MN1000 containing a liquid crystalline tolan compound as a main component was added to 5 g of the capsule thus obtained.
A coating liquid was prepared by adding 11 g of a chiral nematic liquid crystal prepared by adding a chiral material S811 (manufactured by Merck) to a (Chisso Corporation) dispersion medium.

The coating solution was applied to a substrate with an ITO electrode by a blade method, and was sandwiched between another substrate with an ITO electrode. The gap between the substrates is 5 μm.

In such a liquid crystal display element, a voltage of 35 V was applied between the electrodes to make the liquid crystal transparent by the focal conic arrangement, and the Y value was measured.
The Y value was 5. When a voltage of 75 V was applied to change the liquid crystal to a green display state by the planar arrangement, and the Y value was measured, the Y value was 16. That is, a large contrast was shown according to the magnitude of the applied voltage. The Y value (luminous reflectance) was measured using a spectrophotometer CM-3700d (manufactured by Minolta). The same applies to the following experimental examples and comparative examples.

(Comparative Example 1) The above Experimental Example 1 was repeated except that a 15% aqueous solution of polyvinyl alcohol was used as the dispersion medium of the capsule instead of the chiral nematic liquid crystal composition.
A liquid crystal display device was manufactured by the same substance and in the same process.

In such a liquid crystal display device, when a voltage of 350 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured, the Y value was 12. Further, when a voltage of 500 V was applied to make a green display state by the liquid crystal planar arrangement, and the Y value was measured, the Y value was 14. That is, the contrast was reduced and the driving voltage was significantly increased.

(Experimental Example 2) As a liquid crystal composition, a chiral nematic prepared by adding a chiral material CN (manufactured by Merck) to a nematic liquid crystal GR-63 (manufactured by Chisso) having a liquid crystalline cyanobiphenyl compound as a main component. The liquid crystal was used, and the other substances were the same as those in the experimental example 1, and a liquid crystal display device was manufactured in the same process.

In such a liquid crystal display element, a voltage of 45 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured.
The Y value was 4. Further, when a voltage of 85 V was applied to bring the liquid crystal into a green display state by the planar arrangement of the liquid crystal, and the Y value was measured, the Y value was 15. That is, a large contrast was shown according to the magnitude of the applied voltage.

(Comparative Example 2) Experimental Example 2 except that a 15% aqueous solution of polyvinyl alcohol was used instead of the chiral nematic liquid crystal composition as the dispersion medium of the capsule.
A liquid crystal display device was manufactured by the same substance and in the same process.

In such a liquid crystal display device, when a voltage of 380 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured, the Y value was 11. When a voltage of 550 V was applied to make a green display state by the liquid crystal planar arrangement, and the Y value was measured, the Y value was 13. That is, the contrast was reduced and the driving voltage was significantly increased.

Experimental Example 3 A liquid crystal composition was prepared by adding a chiral material C-15 (Merck) to a nematic liquid crystal E-31LV (Merck) mainly containing a liquid crystalline cyanobiphenyl compound. A chiral nematic liquid crystal was used, and the other substances were the same as those in Experimental Example 1, and a liquid crystal display device was manufactured in the same process.

In such a liquid crystal display element, a voltage of 40 V was applied to the electrode side to make the liquid crystal transparent by the focal conic arrangement, and the Y value was measured.
The Y value was 6. Further, when a voltage of 80 V was applied to bring the liquid crystal into a green display state by the planar arrangement of the liquid crystal, and the Y value was measured, the Y value was 17. That is, a large contrast was shown according to the magnitude of the applied voltage.

Comparative Example 3 The above Experimental Example 3 was repeated except that a 15% aqueous solution of polyvinyl alcohol was used instead of the chiral nematic liquid crystal composition as the dispersion medium for the capsule.
A liquid crystal display device was manufactured by the same substance and in the same process.

In such a liquid crystal display device, when a voltage of 380 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured, the Y value was 10. When a voltage of 580 V was applied to make a green display state by the liquid crystal planar arrangement, and the Y value was measured, the Y value was 13. That is, the contrast was reduced and the driving voltage was significantly increased.

(Experimental Example 4) A liquid crystal composition was prepared by adding a chiral material C-15 (manufactured by Merck) to a nematic liquid crystal E-7 (manufactured by Merck) having a liquid crystalline cyanobiphenyl compound as a main component. A chiral nematic liquid crystal was used, and the other substances were the same as those in Experimental Example 1, and a liquid crystal display device was manufactured in the same process.

In such a liquid crystal display device, a voltage of 45 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured.
The Y value was 5. Further, when a voltage of 85 V was applied to bring the liquid crystal into a green display state by the planar arrangement of the liquid crystal, and the Y value was measured, the Y value was 15. That is, a large contrast was shown according to the magnitude of the applied voltage.

(Comparative Example 4) The above Experimental Example 4 was repeated except that a 15% aqueous solution of polyvinyl alcohol was used instead of the chiral nematic liquid crystal composition as the dispersion medium of the capsule.
A liquid crystal display device was manufactured by the same substance and in the same process.

In such a liquid crystal display element, when a voltage of 420 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured, the Y value was 9. Further, a voltage of 580 V is applied to make a green display state by the planar arrangement of the liquid crystal.
When the value was measured, the Y value was 12. That is, the contrast was reduced and the driving voltage was significantly increased.

(Experimental Example 5) As a chiral nematic liquid crystal composition as a dispersion medium of a capsule, a nematic liquid crystal E-63 containing a liquid crystalline cyanobiphenyl compound as a main component was used.
A chiral nematic liquid crystal prepared by adding a chiral material CN (manufactured by Merck) to (manufactured by Merck) is used. Was manufactured.

In such a liquid crystal display element, when a voltage of 25 V was applied between the electrodes to make the liquid crystal transparent by the focal conic alignment, and the Y value was measured.
The Y value was 4. Further, when a voltage of 85 V was applied to make a green display state by the planar arrangement of the liquid crystal, and the Y value was measured, the Y value was 13. That is, a large contrast was shown according to the magnitude of the applied voltage.

(Comparative Example 5) A liquid crystal display device was manufactured in the same manner as in Experimental Example 5 except that a 15% aqueous solution of polyvinyl alcohol was used instead of the chiral nematic liquid crystal composition as a dispersion medium for the capsule. did.

In such a liquid crystal display device, when a voltage of 405 V was applied between the electrodes to make the liquid crystal transparent by the focal conic arrangement, and the Y value was measured, the Y value was 8. Further, a voltage of 590 V is applied to make a green display state by the planar arrangement of the liquid crystal.
When the value was measured, the Y value was 11. That is, the contrast was reduced and the driving voltage was significantly increased.

(Experimental Example 6) A nematic liquid crystal MN1000 (manufactured by Chisso Corporation) containing a liquid crystalline trans compound as a main component was used alone instead of the chiral nematic liquid crystal as a capsule and a liquid crystal used as a dispersion medium of the capsule. A liquid crystal display device was manufactured using the same materials and the same process as in Experimental Example 1 except for the above.

In such a liquid crystal display device, the transmittance was measured by a spectrophotometer while a voltage of 10 V was applied between the electrodes. As a result, the transmittance was 1.5%.
When the transmittance was measured while applying a voltage of 19 V, the transmittance was 83%. That is, a large contrast was shown according to the magnitude of the applied voltage.

(Comparative Example 6) A liquid crystal display device was manufactured in the same manner as in Experimental Example 6, except that a 15% aqueous solution of polyvinyl alcohol was used instead of the nematic liquid crystal composition as a dispersion medium for the capsule. .

In such a liquid crystal display device, when the transmittance was measured with a voltage of 25 V applied between the electrodes, the transmittance was 3%. When the transmittance was measured while applying a voltage of 55 V, the transmittance was 10%.
Met. That is, the contrast was greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cross section of a first embodiment of a liquid crystal display device according to the present invention.

[Explanation of symbols]

 11, 12 ... substrate 13, 14 ... electrode 20 ... liquid crystal layer 21 ... capsule 22a, 22b ... liquid crystal composition

Claims (2)

[Claims] 1. A liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of transparent substrates, at least one of which is formed of a chiral nematic liquid crystal composition or a nematic liquid crystal composition exhibiting a cholesteric phase at room temperature. A liquid crystal display device surrounded by a capsule made of a film, wherein the capsule is dispersed in a chiral nematic liquid crystal composition or a nematic liquid crystal composition. 2. The liquid crystal display device according to claim 1, wherein the capsule has a particle size of 10 μm or less, and the distance between the substrates is 10 μm or less.