JPH1152344A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device formed with such silica based films so that the formation of insulating films having a specific dielectric constant as small as <=3 and an excellent adhesion property to a surface to be coated, mechanical strength and chemical resistance, such as alkali resistance, and excellent crack resistance and the planatarization of the ruggedness of the surface to be coated at a high degree are possible. SOLUTION: This liquid crystal display device has the silica based films of <=3 in the specific dielectric constant which are formed by using a coating liquid for forming the low-dielectric constant silica based films contg. a reaction product of (i) fine silica particles and (ii) the alkoxysilane expressed by Xn Si(OR)4-n or the hydrolyzate of the silane halide expressed by formula Xn SiX'4-n . In the equation, X denotes a hydrogen atom, fluorine atom, 1 to 8C alkyl group, aryl group or vinyl group, R denotes a hydrogen atom, 1 to 8C alkyl group, aryl group or vinyl group, X' denotes a chlorine atom or bromine atom, (n) denotes an integer from 0 to 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an insulating material having a small relative dielectric constant of 3 or less and having excellent chemical resistance such as adhesion to a surface to be coated, mechanical strength and alkali resistance, and at the same time excellent crack resistance. The present invention relates to a liquid crystal display device on which a silica-based coating capable of forming a film and highly flattening irregularities on a surface to be coated is formed.

[0002]

BACKGROUND OF THE INVENTION As a color liquid crystal display device, an electrode plate comprising a TFT (thin film transistor) element and an ITO pixel electrode on a glass substrate, and a color filter and a transparent electrode are sequentially formed on the glass substrate. There is known a matrix type color liquid crystal display device having a counter electrode plate and a liquid crystal display cell in which a liquid crystal layer is filled between the electrode plate and the counter electrode plate. In the liquid crystal display cell as described above, the aperture ratio of the pixel is being increased in order to increase the definition of the display, and an overlapping structure of the pixel electrode and the TFT element has been proposed.

In such a liquid crystal display cell, the electric field becomes non-uniform due to crosstalk between the pixel electrode and the TFT element or a step on the surface of the pixel electrode, and the orientation of the liquid crystal material sealed in the liquid crystal display cell is disturbed. In addition, there is a tendency that pixel unevenness such as color unevenness easily occurs in a display image.

For this reason, it is required to provide a flattening film having a relative dielectric constant of 3 or less between a TFT element and an ITO pixel electrode to prevent alignment disorder of a liquid crystal material. The flattening film used for such a purpose is generally a plasma CV
It is formed on a substrate by using a vapor deposition method such as a D method or a sputtering method or a coating liquid for forming a film. However, in a vapor phase growth method such as a plasma CVD method, it is said that the relative permittivity of the obtained film is limited to 3.5 of a fluorine-doped silica film, and it is difficult to form a film of 3 or less.

[0005] Further, a film formed by using a coating solution composed of a fluorine-added polyimide resin or a fluorine-based resin has a relative dielectric constant of about 2, but has poor adhesion to a surface to be coated and has a fine processing property. There are also drawbacks such as poor adhesion to the resist material used for the above, poor chemical resistance, and poor oxygen plasma resistance.

Further, even when a coating is formed using a silica-based coating forming solution containing a partial hydrolyzate of an alkoxysilane which has been conventionally used, a coating having a relative dielectric constant of about 2.5 can be obtained. However, there is a disadvantage that adhesion to the surface to be coated is poor.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems in the prior art, and has a relative permittivity as small as 3 or less, and furthermore, the adhesiveness to the surface to be coated, the mechanical strength, and the like. Provided is a liquid crystal display device which has excellent chemical resistance such as alkali resistance, can form an insulating film having excellent crack resistance, and has a silica-based coating formed thereon, which can highly flatten irregularities on a surface to be coated. It is intended to be.

[0008]

SUMMARY OF THE INVENTION A liquid crystal display device according to the present invention comprises (i) silica fine particles and (ii) an alkoxysilane represented by the following general formula [1] or a halogenated silane represented by the following general formula [2]. Characterized in that it has a silica-based coating having a relative dielectric constant of 3 or less formed using a coating solution for forming a low-dielectric-constant silica-based coating containing a reaction product with a hydrolyzate.

[0009] X _n Si (OR) in _{4-n ... [1] X} n SiX '4-n ... [2] formula, X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, an aryl group, or Represents a vinyl group, R is a hydrogen atom,
X ′ represents an alkyl group, an aryl group or a vinyl group having 1 to 8 carbon atoms, X ′ represents a chlorine atom or a bromine atom, and n represents 0 to
It is an integer of 3.

[0010] The coating liquid for forming a low dielectric constant silica-based coating film comprises (i) silica fine particles and (ii) a hydrolyzate of the above-mentioned alkoxysilane or halogenated silane at a temperature of 10 to 80 ° C for 0.5 minute. It preferably contains a reactant obtained by reacting for up to 20 hours.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the liquid crystal display device according to the present invention will be specifically described. The liquid crystal display device according to the present invention comprises a reaction product of (i) silica fine particles and (ii) a hydrolyzate of an alkoxysilane represented by the formula [1] or a halogenated silane represented by the formula [2]. It has a silica-based coating having a relative dielectric constant of 3 or less, formed by using the coating solution for forming a low-dielectric-constant silica-based coating contained therein.

Silica Fine Particles The silica fine particles used in the present invention comprise one or more alkoxysilanes represented by the following general formula [1]:
It can be obtained by hydrolysis in the presence of water, an organic solvent and a catalyst.

X _n Si (OR) _4-n ... [1] In the formula, X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group, R represents a hydrogen atom,
It represents an alkyl group, an aryl group or a vinyl group having 1 to 8 carbon atoms, and n is an integer of 0 to 3.

Specific examples of the alkoxysilane represented by the general formula [1] include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraoctylsilane, methyltrimethoxysilane, and methyltriethoxysilane. Silane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, octyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, phenyl Triethoxysilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, dimethyldimethoxysilane, dimethyl Distearate silane, diethyl dimethoxy silane, diethyl diethoxy silane, dimethoxy silane, di-silane, difluoromethyl dimethoxysilane, difluoro diethoxy silane, trifluoromethyl trimethoxy silane, trifluoromethyl triethoxy silane.

Examples of the organic solvent include alcohols, ketones, ethers, esters and the like. Examples thereof include alcohols such as methanol, ethanol, propanol and butanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, methyl cellosolve, and the like. Glycol ethers such as ethyl cellosolve and propylene glycol monopropyl ether, glycols such as ethylene glycol, propylene glycol and hexylene glycol, and esters such as methyl acetate, ethyl acetate, methyl lactate and ethyl lactate are used.

Examples of the catalyst include inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid; organic acids such as acetic acid, oxalic acid and toluenesulfonic acid; compounds which are acidic in aqueous solution such as metal soap; ammonia, amines and alkali metal hydrides; 4th
Basic compounds such as secondary ammonium compounds and amine-based coupling agents are used.

Such silica fine particles are obtained, for example, by stirring a water-alcohol mixed solvent, adding a catalyst such as alkoxysilane and aqueous ammonia to the mixed solvent, and subjecting the alkoxysilane to a hydrolysis reaction. At this time, it is desirable that water is contained in the mixed solvent in an amount of 0.5 to 50 mol, preferably 1 to 25 mol per 1 mol of the Si-OR group constituting the alkoxysilane. It is desirable that the catalyst is added in an amount of 0.01 to 1 mol, preferably 0.5 to 0.8 mol, per 1 mol of the alkoxysilane.

The hydrolysis of the alkoxysilane is preferably carried out at a temperature lower than the boiling point of the solvent, preferably at a temperature lower by 5 to 10 ° C. than the boiling point. When hydrolysis is performed under such conditions, polycondensation of the alkoxysilane proceeds three-dimensionally, and silica fine particles are generated and grown. Further, the obtained silica fine particles may be aged at the same temperature as the hydrolysis temperature or at a higher temperature.

The above-mentioned hydrolysis temperature and aging temperature are desirably higher, because the polycondensation of alkoxysilane is further promoted and the inside of the silica fine particles becomes denser. Therefore, use a pressure vessel such as an autoclave to
As described above, the hydrolysis and aging are preferably performed at a temperature of 200 ° C. or higher. The silica fine particles thus obtained are dense, have low hygroscopicity of the particles themselves, have few residual functional groups on the surface of the particles, and have a film formed by blending with the coating solution having a specific dielectric constant with time. No change,
Excellent heat resistance.

Alternatively, a high-boiling solvent such as ethylene glycol may be added to a water-alcohol mixed solvent to hydrolyze the alkoxysilane to produce fine silica particles. If such a high-boiling solvent is added during the hydrolysis of alkoxysilane, transesterification of the alkoxy group occurs, the high-boiling solvent is taken into the silica fine particles, and porous silica fine particles having a low density are obtained. .

The silica fine particles thus obtained are:
The dispersion medium may be replaced with water, and deionization treatment may be performed with an ion exchange resin. By such a deionization treatment, the reactivity between the silica fine particles and a silane compound described below can be increased.

In the present invention, silica fine particles are
Silica sol obtained by ion exchange or hydrolysis of an alkali metal silicate or the like can be used. Further, as the silica fine particles, fine particles made of a porous zeolite obtained by removing aluminum from a zeolite made of an aluminosilicate can also be used.

The shape of the silica fine particles used in the present invention is not particularly limited, and may be spherical, fibrous, scaly or the like. For example, in the case of spherical silica fine particles, those having a particle size in the range of 30 to 1000 °, preferably 50 to 500 ° are desirable. Further, in the short fibrous silica fine particles, the average diameter (D) is 100 to
300Å, preferably 100-200Å, length (L) 300-1000
Å, preferably 300-600Å, and the aspect ratio (L / D) is 3
Those in the range of 10 to 10, preferably 3 to 5 are desirable. When such silica fine particles are used, a film having a low dielectric constant and few defects during processing can be formed.

Alkoxysilane or halogenated silane
In the present invention, a hydrolyzate of an alkoxysilane represented by the following general formula [1] or a halogenated silane represented by the following general formula [2] is used.

[0025] X _n Si (OR) in _{4-n ... [1] X} n SiX '4-n ... [2] formula, X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, an aryl group, or Represents a vinyl group, R is a hydrogen atom,
X ′ represents an alkyl group, an aryl group or a vinyl group having 1 to 8 carbon atoms, X ′ represents a chlorine atom or a bromine atom, and n represents 0 to
It is an integer of 3.

As the alkoxysilane represented by the general formula [1], the same as those described above can be mentioned. In addition,
The alkoxysilane used as the silane compound may be the same as or different from the one used for preparing the silica fine particles.

The halogenated silane represented by the general formula [2] includes trichlorosilane, tribromosilane, dichlorosilane, fluorotrichlorosilane, fluorotribromosilane and the like.

Such a hydrolyzate of an alkoxysilane or a halogenated silane can be obtained by converting the alkoxysilane represented by the general formula [1] or the halogenated silane represented by the general formula [2] to water, an organic solvent. And hydrolysis and polycondensation in the presence of a catalyst. Such hydrolysis
Examples of the polycondensation method include conventionally known methods, and examples of the organic solvent and the catalyst include the same ones as described above.

The amount of water required for the hydrolysis is usually 0.1 to 5 mol, preferably 1 mol, per mol of the Si-OR group constituting the alkoxysilane or the Si-X 'group constituting the halogenated silane. Desirably, the amount is 0.1 to 2 moles. The catalyst is usually used in an amount of 0.001 to 1 mol per mol of alkoxysilane or halogenated silane.

The thus obtained hydrolyzate has a number average molecular weight of 1,000 to 50,000, preferably 200 to 50,000.
Desirably, it is 0 to 20,000 (molecular weight in terms of polystyrene).

When such a hydrolyzate of an alkoxysilane or a halogenated silane is used, aggregation and gelation of silica fine particles hardly occur, and a stable coating solution can be obtained.

The coating liquid for forming a low dielectric constant silica-based film The coating liquid for forming a low dielectric constant silica-based film used in the present invention contains a reaction product of the silica fine particles and the hydrolyzate. This reaction product is considered to be a product in which the hydrolyzate is bonded to at least a part of the surface of the silica fine particles.

Such a coating solution for forming a low dielectric constant silica-based film is prepared by mixing a dispersion of silica fine particles and the hydrolyzate, and then at a temperature of 10 to 80 ° C. for 0.5 to 20 hours.
It is preferably obtained by performing a heat treatment at a temperature of 20 to 60 ° C. for 0.5 to 10 hours, more preferably at a temperature of 40 to 60 ° C. for 3 to 8 hours.

The amount of time hydrolyzate may be an amount sufficient to at least a portion of the surface of the silica fine particles to bind to the hydrolyzate, in particularly in terms of SiO _2, the silica microparticles 1 It is desirable that the amount is 0.01 parts by weight or more, preferably 0.02 parts by weight or more, per part by weight. When the amount of the hydrolyzate is less than 0.01 part by weight, the obtained silica-based coating becomes porous containing a large number of grain boundary voids of the silica fine particles, and the adhesion to the coated surface, mechanical strength, alkali resistance, etc. Poor chemical resistance, crack resistance and flattening performance of the surface to be coated may be deteriorated.

Further, since the hydrolyzate also has a function as a binder for forming a film, a hydrolyzate that has not been reacted with silica fine particles may be present in the coating solution. However, when these amounts are increased, the resulting coating is filled with the hydrolyzate in the grain boundary voids of the silica fine particles, and the relative dielectric constant of the coating does not decrease. Therefore, the amount of the hydrolyzate is 1 part by weight of the silica fine particles. Per part, preferably less than 10 parts by weight, preferably less than 1 part by weight.

In preparing the coating solution for forming a low dielectric constant silica-based film, it is desirable that the dispersion liquid of the silica fine particles is previously solvent-replaced with an organic solvent containing no water by ultrafiltration or the like. . Examples of the organic solvent used include the same organic solvents as those used in the hydrolysis of the alkoxysilane.

By the above-mentioned heat treatment, the silica fine particles react with the hydrolyzate. In such a reaction, the growth of silica fine particles or the generation of new silica fine particles does not occur, and the surface of the silica fine particles does not occur. It is considered that a surface reaction between the silica fine particles and the hydrolyzate has occurred.

Further, from the coating solution after the heat treatment, alcohol and water generated by a rotary evaporator may be completely removed, if necessary. The solid content concentration in the coating liquid for forming a low dielectric constant silica-based film thus prepared is desirably 5 to 40% by weight, preferably 10 to 30% by weight.

When a silica-based coating is formed using such a coating liquid for forming a low-dielectric-constant silica-based coating, the hydrolyzate component in the reaction product prevents water from re-adsorbing to the voids. It is possible to form a silica-based film having excellent properties, low relative dielectric constant, and little change with time.

Such a coating solution is applied on a substrate, and calcined at 400 ° C. in an oxygen-containing gas atmosphere (for example, 1000 rpm oxygen-containing nitrogen gas). After measuring the FT-IR spectrum,
No peak attributable to the H group is measured, and therefore, the relative dielectric constant value of the obtained coating does not increase.

Liquid Crystal Display The liquid crystal display according to the present invention is characterized in that a silica-based coating having a relative dielectric constant of 3 or less is formed between the TFT element and the ITO pixel electrode by using the low-dielectric-constant silica-based coating liquid. Is formed.

Such a silica-based coating can be formed by applying the coating solution for forming a low-dielectric-constant silica-based coating and then heating the coating. Examples of the method for applying such a coating liquid include a spray method, a spin coating method, a dip coating method, a roll coating method, and a transfer printing method. The heating temperature after coating is usually 200 to 4
The temperature may be 50 ° C, preferably 200 to 400 ° C. The thickness of the silica-based coating thus formed is usually 5000
３０30000Å.

In the heat-curing treatment of the coating film, a curing treatment of the coating film by ultraviolet irradiation or electron beam irradiation, plasma treatment or the like may be used in combination.

[0044]

According to the present invention, the relative dielectric constant is as small as 3 or less, and it has excellent chemical resistance such as adhesion to the surface to be coated, mechanical strength and alkali resistance, and also has excellent crack resistance. A liquid crystal display device having a planarizing insulating film can be obtained. That is, since the planarization insulating film having a low dielectric constant is used, the aperture ratio of the pixel can be increased for higher definition of the display, and the overlapping structure of the pixel electrode and the TFT element can be formed. it can. In addition, since the cross talk between the pixel electrode and the TFT element and the level difference on the surface of the pixel electrode can be reduced, the orientation of the liquid crystal material sealed in the liquid crystal display cell is disturbed, and the pixel unevenness such as color unevenness in a display image is suppressed. High quality display characteristics can be exhibited.

[0045]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the examples.

[0046]

[Production Example] 1. Preparation of silica fine particles (1) A mixed solvent of 139.1 g of pure water and 169.9 g of methanol was kept at 60 ° C., and tetraethoxysilane (ethyl silicate-28, manufactured by Tama Chemical Industry) was added thereto. Water-methanol solution (532.5 g of tetraethoxysilane dissolved in 2450 g of a mixed solvent of water / methanol (weight ratio 2/8)) 2982.
5 g and 596.4 g of 0.25% aqueous ammonia were simultaneously added over 52 hours. After the addition was completed, the mixture was further aged at this temperature for 3 hours. Then, after removing unreacted tetraethoxysilane, methanol, and ammonia by ultrafiltration, pure water was added at the same time to adjust the silica concentration to 5% by weight. , Amphoteric ion exchange resin (AG-501, Bio-Ra
silica fine particles with an average particle size of 300 mm
(A) was obtained.

(2) 139.1 g of pure water and 140 g of methanol
Preparation was carried out under the same conditions as for the silica fine particles (A) except that a mixed solvent of 29.9 g of ethylene glycol was used to obtain porous silica fine particles (B) having an average particle size of 250 °. 2. Hydrolysis of alkoxysilane and halogenated silane
Preparation of digest (1) 250 g of triethoxysilane was mixed with 750 g of methyl isobutyl ketone, and a 0.01% by weight aqueous solution of hydrochloric acid (1) was added.
000 g was added and reacted at 50 ° C. for 1 hour with stirring. After standing, the methyl isobutyl ketone solution in the upper layer was separated to obtain a hydrolyzate (C).

(2) Trichlorosilane was hydrolyzed according to the method described in JP-B-6-41518, and the obtained hydrogensilsesquioxane was dissolved with methyl isobutyl ketone to obtain a hydrolyzate (D). 3. Preparation of Coating Solution for Forming Film From the dispersion of silica fine particles (A) and (B) obtained as described above, water and alcohol were distilled off using a rotary evaporator, and the solvent was added to methyl isobutyl ketone. Replaced. The obtained fine particle dispersion, the hydrolyzates (C) and (D) were mixed at the ratio shown in Table 1, and the mixture was mixed at 50 ° C for 1 hour.
Heated for hours. Then, after completely removing the alcohol and moisture generated by the heat treatment using a rotary evaporator, the solvent was replaced again with methyl isobutyl ketone, and the silica concentration was adjusted to 20% by weight. Was prepared.

[0049]

[Table 1]

[0050]

Examples 1-4, Comparative Examples 1 and 2 The coating liquid for film formation prepared in the example of manufacturing a color liquid crystal display device was coated on a glass substrate on which a TFT element was formed, and then heated to give a silica-based film. Was formed. After that, ITO pixel electrode on the upper layer,
A polyimide alignment film was formed and bonded to a counter electrode plate on which a color filter, a transparent electrode, and a polyimide alignment film were sequentially formed on a glass substrate. Then, a liquid crystal layer was filled in the meantime to prepare a matrix type color liquid crystal display device having a liquid crystal display cell.

The flatness characteristics of the silica-based film of the color liquid crystal display device thus obtained, the presence or absence of crosstalk,
The display characteristics were evaluated. Table 2 shows the results. The flattening characteristics were observed with an SEM-type electron microscope, the presence or absence of crosstalk was visually observed, and the display characteristics were determined by luminance and contrast ratio.

[0052]

[Table 2]

As shown in Table 2, the liquid crystal display device according to the present invention
There is no crosstalk, and it has excellent flattening characteristics and display characteristics.

Claims (2)

[Claims] 1. A reaction product of (i) silica fine particles and (ii) a hydrolyzate of an alkoxysilane represented by the following general formula [1] or a halogenated silane represented by the following general formula [2]: A liquid crystal display device comprising a silica-based coating having a relative dielectric constant of 3 or less formed using a coating solution for forming a low-dielectric-constant silica-based coating containing the same. _{X n Si (OR) 4-} n ... [1] X n SiX '4-n ... [2] ( wherein, X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group R represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group, X ′ represents a chlorine atom or a bromine atom, and n represents 0
-3. ) 2. A coating solution for forming a silica film having a low dielectric constant, comprising: (i) silica fine particles; and (ii) a hydrolyzate of the above alkoxysilane or halogenated silane at a temperature of 10 to 80 ° C. The liquid crystal display device according to claim 1, comprising a reaction product obtained by reacting for 5 to 20 hours.