JPS633292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electro-optical device, and particularly to a liquid crystal display device using a nematic liquid crystal having positive dielectric anisotropy.

It is known that nematic liquid crystals (abbreviated as N-liquid crystals) can be used for optical modulation, etc. by making use of changes in optical properties caused by the application of electric fields, magnetic fields, ultrasonic waves, etc. This usually consists of two panels, at least one of which is transparent, that are placed facing each other with an interval of about 50μ or less.
It has an N-liquid crystal sandwiched between two substrates, and uses changes in molecular arrangement due to the application of electric fields, magnetic fields, ultrasonic waves, etc. for optical modulation. When an electric field is applied, an electrode plate is used as the substrate, which is a support plate such as a glass plate, and one surface of which is coated with a thin conductive coating.

The compounds forming the above-mentioned N-liquid crystals can be divided into two types based on the relationship between molecular structure and dielectric properties. One is the type where the molecular axis and the electric dipole are almost perpendicular (this is called Nn), and the other is the type where they are almost parallel (this is called Np). Nn has a negative dielectric anisotropy. It means an N-liquid crystal with anisotropy, and Np means an N-liquid crystal with a positive dielectric anisotropy.
A conventional Np-liquid crystal electro-optical device generally used has a structure in which an Np-liquid crystal is sandwiched between two opposing electrode plates. In this case, the molecular axes of the Np-liquid crystal are parallel to the electrode plates, and the molecular axes are aligned in almost the same direction on the same plane parallel to the electrode plates, and the electrode plates are perpendicular to each other between adjacent surfaces. Arrange in a continuous twisted direction. Such orientation of the molecular axes can be achieved by polishing the electrode surface in one direction with cloth, paper, etc., and injecting liquid crystal between the two sheets stacked so that the polishing directions cross each other. It is known that near the electrode surface, the molecular axes are aligned in the polishing direction, but within the liquid crystal layer, the molecular axes are continuously twisted.

However, this method has the disadvantage that the orientation is not uniform and that the orientation is lost within a short time. Furthermore, it is known that orientation destruction occurs under heating.

As a method to solve these problems, it is known to use a certain kind of surfactant in combination to rub the electrode plate in one direction, but surfactant causes deterioration of the liquid crystal and makes it difficult to apply voltage. If this continues, the surfactant may be decomposed or altered by the electric field, and its orientation may be destroyed. As another method, it is known to coat the surface of an electrode plate with a certain type of polymer such as polyimide or polyamideimide, and to orient the coated polymer layer.
However, polyimide films formed by dehydration and ring closure of polyamic acid solutions using polar solvents such as dimethylacetamide have excellent heat resistance and orientation, but the processing temperature is high at 250°C to 300°C or higher, and the solvent At present, they are highly toxic polar solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide, and N-methylpyrrolidone, so they must be handled with care. On the other hand, polyvinyl alcohol is a water-soluble resin that uses water as a solvent, and is not toxic like the solvents mentioned above and is easy to handle. It has the disadvantage of lacking in character.

An object of the present invention is to provide a liquid crystal display device that has improved the above-mentioned points, and particularly to provide a liquid crystal display device that has improved alignment stability against heat and stability over time.

It is an object of the present invention to provide an electro-optical device with an electrode plate in which the surface of the group provided with the conductive film is covered with a film of polyvinyl alcohol resin having a hardened acetoacetate ester group, and the surface is subjected to orientation treatment. In particular, this can be achieved by using it as an electrode plate constituting a liquid crystal display device.

The polyvinyl alcohol resin having an acetoacetate group used in the present invention can be obtained by adding diketene to a polyvinyl alcohol resin or transesterifying acetoacetate. In addition, polyvinyl alcohol resin is
In addition to partially or completely saponified polyvinyl esters such as polyvinyl acetate, monomers mainly composed of vinyl acetate and copolymerizable with this, such as unsaturated carboxylic acids or partially or completely esters thereof,
salt, anhydride, amide, nitrile, unsaturated sulfonic acid or its salt, α-olefin having 2 to 30 carbon atoms,
"Copolymerized modified" polyvinyl alcohol obtained by saponifying a copolymer with vinyl ether or the like, and "post-modified" polyvinyl alcohol obtained by acetalizing, urethanizing, etherifying, grafting, phosphoric acid esterifying, etc. polyvinyl alcohol can also be used.

The content of acetoacetate groups in the polyvinyl alcohol resin in the present invention can be 0.05 mol% or more, up to the maximum within the range of water solubility, but is usually 0.1 to 40 mol%, preferably 0.2 to 20 mol%. % range.

This polyvinyl alcohol resin is produced by, for example, water being dissolved in alcohol (methanol, ethanol, isopropyl alcohol, etc.), and ammonium dichromate added to this solution as a water-resistant insolubilizing agent.
After magnesium chloride and dimethylolated melamine are added with compounds having two or more active groups, such as dialdehydes, they can be cured under predetermined curing conditions. Examples of the dialdehydes mentioned above include glyoxal, malondialdehyde, succindialdehyde, glutardialdehyde, maleic dialdehyde, phthalaldehyde, isophthalaldehyde, and terephthalaldehyde, but glyoxal and glutardialdehyde are preferred. Glyoxal is particularly preferred.

The blending ratio of water-resistant insolubilizer to polyvinyl alcohol resin is 100% polyvinyl alcohol resin.
The water-resistant insolubilizing agent can be added in an amount of 0.1 part by weight to 100 parts by weight, preferably 1 part by weight to 50 parts by weight.

The aforementioned polyvinyl alcohol resins containing ammonium dichromate can be cured by suitable light irradiation, especially ultraviolet irradiation, and the aforementioned polyvinyl alcohol resins containing dialdehydes and dimethylolated melamine can be cured by suitable light irradiation, especially ultraviolet irradiation. It can be cured by heating at a temperature of, for example, (180 to 200°C).

Methods for applying the polyvinyl alcohol resin used in the present invention on the electrode plate include a brush coating method, a dip coating method, a spinner coating method using a solution prepared by adding water-resistant insolubilizing agents such as ammonium dichromate and glyoxal to an aqueous polyvinyl alcohol solution. After being applied to the electrode plate by a spray coating method or a bar coating method, and dried, a polyvinyl alcohol resin film is formed which is cured under predetermined curing conditions.

This cured polyvinyl alcohol resin film can be removed with a chromic acid (CrO ₃ ) aqueous solution, so it can be removed, for example, when it is formed on the terminal part of the electrode plate and the seal spacer forming part during the process of manufacturing a display device. The polyvinyl alcohol coating can be removed by using a conventional photolithography process and an aqueous chromic acid solution. In particular, use of this chromic acid aqueous solution can prevent contamination of the seal spacer.

The polyvinyl alcohol resin film treated with the water-resistant insolubilizing agent is subjected to a homogeneous alignment treatment, for example, a rubbing treatment, in one direction using a cloth or the like. This orientation-treated polyvinyl alcohol resin film can improve stability and stabilize orientation over time.

The electrode plate used in the liquid crystal display device of the present invention is a substrate on which at least one side is provided with a transparent conductive film (for example, indium oxide, tin oxide, indium oxide-tin oxide (tin oxide: 0.1 to 40% by weight), etc.) (glass, plastic, etc.) is preferably used. Furthermore, examples of the opaque conductive film used in the present invention include aluminum, gold, silver, copper, and lead.

The liquid crystal sealed in the display device of the present invention is not particularly limited, and various types can be used as appropriate. In particular, nematic liquid crystals with positive dielectric anisotropy, such as "ZLI-1216", "ZLI-1253", "ZLI-" manufactured by Merck & Co., Ltd.
1285”, “ZLI−1414”, “ZLI−1565” and “ZLI−
1694" etc. can be used. These liquid crystals can be used alone or in combination.

Hereinafter, a liquid crystal display device will be described as an example of the electro-optical device of the present invention, but the present invention is not limited thereto.

FIG. 1 is a sectional view of a display device of the present invention.
In FIG. 1, reference numerals 11 and 12 indicate substrates such as glass plates and plastic plates. Segment electrodes 13 patterned into a predetermined shape are formed on the inner surface of the substrate 11, and further covered with a film 15 of a cured polyvinyl alcohol resin having an acetoacetate group. On this occasion,
The segment electrodes 13 can be formed from a transparent conductive film such as indium oxide or tin oxide.

The portion 17 of the coating 15 that covers the segment electrodes 13 is dyed by an appropriate method so that it can be identified by displaying half of it. The coating 15 is
When alignment treatment is performed by rubbing in mutually intersecting directions with one of the insulating films 14 provided on the opposing common electrodes 16, the liquid crystal 18 disposed between them becomes
Twisted orientation at a 90° angle. As the liquid crystal 18 used in this case, a nematic liquid crystal (hereinafter referred to as Np liquid crystal) having positive dielectric anisotropy is used.

Polarizing plates 10 and 19 in a crossed nicol state are arranged outside the liquid crystal cell having such a structure.

In this liquid crystal display device, when a voltage is applied between the segment electrode 13 and the common electrode 16 shown in FIG. 1, for example, the molecular axis of the Np liquid crystal 18 is aligned in the direction of the electric field, so that incident light is blocked between crossed nicols. This can be seen as a black display 22 in a liquid crystal display device 21 as shown in FIG. 2, and this black display 22 can be distinguished from a half display 23 that looks like a dyed color.

In the liquid crystal display device shown in FIGS. 1 and 2,
By using colored, gray, red, etc. colored polarizing plates as the polarizing plates 10 and 19, the color tone effect in this device can be enhanced. or,
A reflecting plate (not shown) having light diffusing properties can be placed behind the polarizing plate 10.

As a method for dyeing the portion 17 covering the segment electrode 13, for example, a coating 15 is formed on a substrate having a transparent conductive coating patterned into a predetermined shape, and a coating of photoresist material is further formed on this coating 15. After that, the area other than the aforementioned electrode area is subjected to prescribed exposure and development so as to serve as a mask, and then immersed in a staining solution (for example, 2% ammonia solution of "Sumix Super Brilliant Red 3BF" manufactured by Sumitomo Chemical Co., Ltd.). An example of this method is to dye the portion of the film 15 covering the electrode, and then remove the mask.

Hereinafter, the present invention will be explained according to examples.

Example 1 Ammonium dichromate and glyoxal (ammonium dichromate: glyoxal = 1:1) were added to a 5% aqueous solution of polyvinyl alcohol having an acetoacetic acid ester group ("Gocephaimer Z200" manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.). It was added at a rate of 5% by weight based on the solid content of polyvinyl alcohol. This solution was applied onto the electrode plate for 10 seconds using a spinner coating machine rotating at 3000 rpm to form a film of 1500 Å, and then dried by heating at a temperature of 200° C. for 30 minutes.

Next, in order to remove the coating on the terminal part and seal spacer forming part of this electrode plate, a normal photolithography process is used to form a mask on the part excluding the terminal part and seal spacer forming part, and then this electrode plate is removed. was immersed in a 10% chromic acid (CrO ₃ ) aqueous solution for 10 minutes to remove the film formed on the non-mask areas.
Thereafter, the resist was peeled off and reheated at 180° for 15 minutes.

Next, the pair of electrode plates provided with the polyvinyl alcohol coating were rubbed in one direction with a cloth to align them.
After that, the cells are assembled so that the rubbing directions are perpendicular to each other, and a nematic liquid crystal with positive dielectric anisotropy ("ZLI-1253" manufactured by Merck & Co., Ltd. in West Germany) is sealed, and then a polarizing film is applied to both outside surfaces of the cell. A display device was prepared by laminating the polarizing films so that the polarization directions of the polarizing films were parallel to the rubbing direction of the adjacent substrates (this will be referred to as sample No. 1).

On the other hand, as a comparative sample, instead of the polyvinyl alcohol used when creating the display device of sample No. 1 mentioned above, polyvinyl alcohol without acetoacetate was used as "NL-05" manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd. A display device was created in the same manner as described above, except that `` was used.

These samples were heated to a temperature of 85°C and a relative temperature of 85%.
100 hours, 200 hours, 300 hours under the conditions, respectively.
A forced aging test was performed on each sample by storing it at 400, 500 and 1000 hour intervals and measuring the increase in current in the liquid crystal display at each aging time. As a result, the sample of the present invention
No. 1 has an increase in current of 10 even after 1000 hours.
% or less, and sufficient liquid crystal display ability was observed, but the comparison sample had a current increase of 10% after 1000 hours.
% or more. In addition, sufficient display ability was observed in this comparative sample even after 500 hours had passed.

Example 2 A display device was prepared in the same manner as in Example 1, except that dimethylolated melamine was used as the water-resistant insolubilizing agent used when preparing Sample No. 1 of Example 1 (Sample No. 2).

When sample No. 2 was subjected to a forced aging test in the same manner as in Example 1, the current increase was less than 10% even after 1000 hours, and sufficient liquid crystal display ability was observed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention, and FIG. 2 is a plan view thereof. 11, 12...Substrate, 13...Segment electrode, 14...Insulating film, 15...Coating of cured polyvinyl alcohol resin having acetoacetate group, 16...Common electrode, 17...Segment electrode 13 Part of the insulating film to cover (dyed part), 18...Liquid crystal, 10, 19...Polarizing plate, 2
1...Liquid crystal display device, 22...Display by driving,
23...Half display.

Claims (1)

[Scope of Claims] 1. In an electro-optical device comprising a liquid crystal layer sandwiched between two substrates each having a transparent conductive coating on at least one of the substrates, at least one of the electrode plates has a hardened surface. An electro-optical device comprising a polyvinyl alcohol resin coating having an acetoacetate group, and the coating is subjected to an orientation treatment. 2. The electro-optical device according to claim 1, wherein the liquid crystal is a nematic liquid crystal having positive dielectric anisotropy. 3. The electro-optic according to claim 1, wherein the cured polyvinyl alcohol resin having acetoacetate groups is cured under predetermined curing conditions in the presence of a water-resistant insolubilizer having at least two active groups. Device. 4. The electro-optical device according to claim 3, wherein the water-resistant insolubilizer is at least one compound selected from the group of compounds consisting of ammonium dichromate, magnesium chloride, dialdehydes, and dimethylolated melamine. 5. The electro-optical device according to claim 4, wherein the water-resistant insolubilizer is glyoxal. 6. The electro-optical device according to claim 1, wherein the alignment treatment is a rubbing treatment. 7. The electro-optical device according to claim 1, wherein the polyvinyl alcohol resin coating is colored at a portion of the conductive coating forming the segment electrode.