JP2001188236A - Liquid crystal spacer and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal spacer having high adhesion strength with a coating resin layer, hardly causing the peeling of the coating resin layer and having high mechanical strength. SOLUTION: The liquid crystal spacer consists of spherical silica particles having 1 to 20 μm average particle diameter, <=1.5 geometric standard deviation σof the grain size distribution expressed by a formula σ=(D1/D2)0.5, wherein D1 is the particle diameter at 84 cumulative wt.% and D2 is the particle diameter at 16 cumulative wt.%, and >=6 μmol/g silanol groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to particles suitable as spacer particles for controlling the thickness of a liquid crystal of a liquid crystal display device and a method for producing the same.

[0002]

2. Description of the Related Art In a liquid crystal display panel, a liquid crystal material is usually sealed in a gap between two substrates. However, the interval between the two substrates must be kept uniform on the order of μm. Particles of silica, hard plastic, or the like formed into spherical particles of a uniform size or finely ground glass fibers have been used as spacers. However, these spacers are effective in maintaining a gap in the direction of compressing the liquid crystal, that is, the compressive force from the outside of the two substrates, but expand the liquid crystal because they do not have adhesiveness to the substrates. Direction, that is, weak against the force from the inside of the substrate,
Large screen LCD panels do not have the effect of reinforcing the overall flexure or distortion, and the spacers move due to external shocks or ultrasonic cleaning, causing them to be biased in the LCD screen or to move. In this case, there is a problem that the hard spacer may damage an alignment film, a protective film, a color filter, an electric element, and the like formed on the liquid crystal substrate.

As a countermeasure against these problems, it has been proposed to provide a resin layer on the surface of the silica spacer to prevent the liquid crystal substrate from being damaged, or to reinforce the opposing liquid crystal substrate by bonding by point bonding. However, the adhesive strength between the silica and the adhesive layer, which are different kinds of materials, is low, and the resin layer may peel off from the silica and damage the liquid crystal material. Therefore,
Japanese Patent Application Laid-Open No. 9-101528 discloses a method of increasing the adhesion to a resin by subjecting a calcined silica particle to a surface treatment with a vinyl silane coupling agent. However, since the calcined silica has few silanol groups capable of forming a chemical bond with the coupling agent, the added coupling agent only crosslinks with each other in the resin layer and has an effect of increasing the adhesion at the interface with the silica. poor. Attempts have been made to treat the surface of the baked silica with an acid or alkali, or to form a silica gel coating by coating with an alkyl silicate to provide silanol groups on the silica surface. Dissolves but does not produce stable silanol groups. When a silica coating was applied to the surface, it was easily peeled off because no chemical bond was formed. On the other hand, unfired silica, which is generally called silica gel, has a large number of silanol groups that can be chemically bonded to a coupling agent.However, it is also described in the publication that silica gel itself cannot be used as a liquid crystal spacer because the silica gel itself is very easily broken. ing.

[0004]

The conventional silica used as a liquid crystal spacer for maintaining the distance between liquid crystal substrates has insufficient adhesion to a resin layer, and is not suitable for use with a silane coupling agent. Also, since the calcined silica had almost no silanol groups, the adhesion was not sufficiently improved.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the amount of silanol groups was 6 μm.
We found that silica that had been heat-treated under precise temperature control so that it remained at mol / g or more, or that which had been treated with a silane coupling agent, had extremely high adhesion to the resin layer and could be used preferably as a liquid crystal spacer. Was.

In a conventional manufacturing technique of a spherical silica spacer for a liquid crystal, spherical silica having a uniform particle size is synthesized by hydrolyzing alkoxysilane in alcohol by one kind of a wet method called a steeper method. However, it is common knowledge that this method produces porous, highly water-absorbing, low-strength silica gel, which is not suitable for electronic materials. ing. This is what is called calcined silica. Silica gel generated by the wet method is generally rich in silanol groups, not limited to the steamer method.Since sintering of silanol groups progresses to several ppm or less by firing at 1200 ° C., so-called silane coupling agent is used for so-called calcined silica. It could hardly be expected that a chemical bond would be produced directly by the reaction with. On the other hand, the present inventors have found a method for producing spherical silica having a certain amount of silanol groups by suppressing the decrease in silanol groups while improving the mechanical strength of the spherical silica, and the adhesiveness of the resin layer has been found. The invention of a liquid crystal spacer in which the above was improved was completed. That is, the present invention is a spherical silica having an average particle diameter of 1 to 20 μm, a geometric standard deviation σ of a particle size distribution represented by the following formula of 1.5 or less, and having a silanol group of 6 μmol / g or more. Liquid crystal spacer.

[0007]

## EQU2 ## σ = (D ₁ / D ₂ ) ^0.5 D ₁ : Particle size at a cumulative weight of 84% by weight D ₂ : Particle size at a cumulative value of 16% by weight

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The silica for a liquid crystal spacer of the present invention is manufactured by firing silica gel synthesized by a wet method at a constant temperature under precise temperature control. Examples of the method for producing silica gel by a wet method include the following methods, and all methods are known. Specifically, an aqueous solution of an alkali metal silicate such as water glass or sodium silicate is mixed with an inorganic acid such as sulfuric acid, nitric acid, phosphoric acid, or hydrochloric acid, or an ammonium salt of an inorganic acid such as ammonium sulfate, ammonium nitrate, ammonium phosphate, or ammonium chloride. It can be produced by a method of neutralizing with an aqueous solution, or a method of hydrolyzing an alkyl silicate such as methyl silicate, ethyl silicate or isopropyl silicate with water in the presence of an acid such as hydrochloric acid or acetic acid or a base such as aqueous ammonia. However, when it is used as a liquid crystal spacer, it is preferable to use sodium silicate, which causes corrosion of copper wiring, or an alkyl silicate, which has a low content of impurities that may adversely affect the liquid crystal material, as a raw material. Even when an aqueous solution of a metal silicate is used as a raw material, impurities in the silica that has been formed can be reduced by repeatedly washing silica gel or purifying the raw material solution by ion exchange or the like.

The shape of the liquid crystal spacer is preferably a true spherical shape without anisotropy in order to keep the gap between the two liquid crystal substrates constant in the order of μm, and a sharp distribution form having a narrow particle size distribution. It is preferred to have
More specifically, those having a geometric standard deviation σ of the particle size distribution represented by the following formula of 1.5 or less are preferably used.

[0010]

Σ = (D ₁ / D ₂ ) ^0.5 D ₁ : Particle size at a cumulative weight of 84% by weight D ₂ : Particle size at a cumulative value of 16% by weight

As a method for producing silica particles having such a shape and particle size, a method called an emulsion method is preferably used in addition to the steiba method. The emulsion method utilizes the particle shape in liquid of an emulsion such as a water-in-oil type, an oil-in-water type, and an oil-in-oil type, for example, in the case of a water-in-oil type, under conditions such that silica gel is formed in water particles. This is a method of obtaining spherical silica gel by causing a sol-gel reaction.

In addition to the wet method, a method of producing silica called a dry method is also known. For example, a method in which a natural or synthetic bulk silica is pulverized and exposed to a high temperature in a flame or the like to melt a corner to form a quasi-spherical fused silica, or to react a silicon source such as silicon chloride, alkyl silicate or metallic silicon at a high temperature. and so on. These are collectively referred to as dry process silica, but all methods are common in that they are high-temperature processes, and the silica obtained in contrast to the wet process is nonporous, and impurities within the silica are reduced. It has the advantage that it does not easily come out, but the silanol group does not remain, so even if a silane coupling agent is used in combination, there is almost no reaction between silica and the silane coupling agent, improving the adhesion at the interface. There was a disadvantage that it did not.

Since wet-process silica goes through a wet process, the synthesized silica is usually obtained as a slurry.
By performing steps such as separation, drying, and calcination of silica from the slurry, spherical silica with few impurities can be produced. For separation and drying, for example, there is a method of filtering a slurry, repeatedly washing with a solvent that dissolves the organic solvent used in the synthesis, such as alcohol or acetone, and heating at less than 1000 ° C. for several hours. Since organic components are decomposed by firing at a high temperature, separation and washing can be omitted. Many processes are industrially performed for processes such as separation and drying, and any of these processes can be preferably used.

It is known that silica synthesized by a wet method has a large amount of silanol groups. However, when the silica is calcined, the silanol groups are dehydrated and condensed. It has long been said that the strength of the silica itself increases due to the occurrence. In the present invention, by precisely controlling the firing temperature, sufficient silica strength and a sufficient amount of silanol groups to react with the silane coupling agent and increase the adhesion of the interface are simultaneously realized. It is spherical silica.

As a method of firing to leave silanol groups of 6 μmol / g or more, a method of performing temperature control precisely at a temperature of 1050 ° C. or less and firing for a fixed time, and a method of performing a heat treatment at a higher temperature for a short time Both methods can be preferably used.However, in the method of high temperature and short time, the effect of the heat treatment time on the amount of silanol groups is large, and when an industrial process is considered, the temperature inside a certain amount of powder is not sufficient. Since problems such as uniformity and excessive sintering of the retained powder are likely to occur, it is preferable to perform firing at a temperature of 1050 ° C. or lower.

Regarding the apparatus used for firing, any apparatus may be used as long as it can maintain a temperature of less than 1050 ° C., and the heat source may be Joule heat by electricity or combustion heat of oil or gas. Specifically, a device such as a rotary kiln or a shuttle furnace is used. These furnaces are preferably provided with some temperature control method.

The preferable calcination conditions are that the calcination temperature is 300 ° C. or higher in order to obtain the minimum strength of silica, and 1050 ° C. or lower in order to leave silanol groups of 6 μmol / g or more. preferable. More preferably 70
It is in the range of 0 ° C or more and 1000 ° C or less. The firing time at this temperature is preferably 10 minutes or more in order to reach a uniform temperature to the inside of a certain amount of powder, and is 24 hours or less for economic reasons. More preferably, it is 1 hour or more and 8 hours or less. If the rate of temperature rise until reaching this temperature is too rapid, stress cracking may be caused. On the other hand, if it is too slow, it is not economical, so 1 ° C./min to 100 ° C./min, and further 5 ° C./min to 20 ° C. C./min or less is preferred. The temperature may be lowered from 0.1 ° C./min to 40 ° C./min. The temperature rise and fall are not necessarily required to be continuous and uniform, and a stepwise change in temperature is also possible. In this case, the temperature rise and fall can be carried out preferably at a rate other than the above temperature rise and fall rates.

The amount of the silanol group of the calcined silica can be measured from a measuring device such as infrared absorption spectroscopy, a neutralization titration method, a reaction amount with a silane coupling agent, and the like. Specifically, for example, the absorption / resonance of silanol groups contained in silica is measured by an infrared absorption spectrometer, a near infrared absorption spectrometer, a nuclear magnetic resonance analyzer, or the like, or an acid using a titration indicator or a potentiometric electrode is used. Base titration, a method in which silica is dispersed in a non-polar solvent such as benzene in which a silane coupling agent is dissolved, and the amount is determined from a change in the concentration of the silane coupling agent by gas chromatography or the like, and any method can be preferably used. By this measuring method, the amount of silanol groups of the fired silica can be confirmed, and the silica during the firing process is taken out and measured, and when the target amount of silanol groups is reached, the process management such as stopping the firing is performed. It can also be used for

The preferable amount of the silanol group in the spherical silica thus obtained is preferably large because the silanol group reacts with the resin itself or with the silane coupling agent to form a chemical bond and enhance the adhesiveness of the interface. The value is at least 6 μmol / g. On the other hand, if the density of the silanol group is too high, silanol groups that cannot be completely reacted even if reacted with a resin or a silane coupling agent remain, and the hygroscopicity of the resin composition itself increases, which is preferable as an electronic material. May not be. The preferable value of the amount of the silanol group is from 6 μmol / g to 5 mmol / g, more preferably from 10 μmol / g to 1 mmol / g.

The silanol group of the spherical silica itself can react with a resin such as a polyester resin or an epoxy resin, and also reacts with an interface modifier such as a silane coupling agent to increase the adhesion at the interface. Can be. When a silane coupling agent is used, known ones can be used.
For example, when it is desired to provide an epoxy resin-based resin layer on silica, the functional group of the silane coupling agent is preferably an epoxy-based, amino-based, chloropropyl-based, or mercapto-based, and particularly preferably an epoxy-based or amino-based. In addition, a known method can be used for selecting a preferable silane coupling agent such as a vinyl resin for the polyolefin resin. In addition to the silane coupling agent, a method of directly providing a silicone coating by a condensation reaction with a silicone having a silanol group can also be performed.

The method of treating the spherical silica and the silane coupling agent includes an integral blending method in which the silane coupling agent is simultaneously added and mixed when the resin and the silica are mixed, and a method in which the silica is preliminarily treated before mixing with the resin. However, an arbitrary method can be selected.
In order to easily obtain the effect of the coupling treatment, the pretreatment method is more preferable. The treatment amount may be equal to or more than the equivalent of the silanol group, but if added in excess, aggregation may occur.
Good times.

The coating resin used in the present invention may be any resin that can be generally used, such as an epoxy resin, a nylon resin, a polyester resin, a polyolefin resin, and a silicone resin. Resins and the like are preferred. These resin layers may have a multilayer structure or may be used as a mixture. For example, for epoxy resins, curing agents, curing accelerators, flame retardants, low stress agents, waxes, fatty acids such as stearic acid and their metal salts, pigments such as carbon black, dyes, antioxidants, ion scavengers, and other additives An agent can be blended. The amount of these additives can be a usual amount as long as the effects of the present invention are not impaired.
Other resin systems are used together with various mixtures, but the composition and conditions are not particularly limited according to a usual method.

In the case of using a spherical silica provided with a resin layer,
The thickness is 10 nm or more and 30 μm or less, more preferably 5 nm or less.
It is not less than 0 nm and not more than 5 μm. Of course, it is possible to use it without a resin layer.However, when a resin layer is provided and used for point bonding between opposing liquid crystal substrates, if it is too thin, the adhesive strength of the resin layer cannot be sufficiently exhibited, and conversely, it is too thick However, it is not preferable because the deformation rate of the coated particles becomes high and the gap between the liquid crystal substrates cannot be fixed as designed. However, this is not the case when it is used for special applications where the particle size does not matter, and the resin layer can be used with a resin layer thickness suitable for the application.

As a method of covering the outside of the spherical silica with a resin layer, a resin fine powder or a resin diluted with a solvent is adhered to the surface of the silica, and then the resin is melted and formed into a film so that the particles do not aggregate. Or silanol groups on the silica surface,
Alternatively, a method of grafting a resin to a silane coupling agent or the like reacted with a silanol group or the like can also be used. As a method of adsorbing the resin fine powder on the surface of silica and forming a melt film, a normal method such as a Henschel mixer, a super mixer, a raii device, a ribbon mixer, a tumbler, a vibration dryer, a flash dryer, and a spray dryer is used. Can be used.

[0025]

The present invention will be specifically described below with reference to examples. Example 1 A 200 L reactor was charged with 90 kg of xylene, 0.8 kg of an emulsifier (SPAN-80), 30 kg of pure water and 0.1 kg of hydrochloric acid, and tetramethoxy was added while stirring at 100 rpm while maintaining the liquid temperature at 45 ° C. 27 kg of the silane oligomer was supplied over 60 minutes. Thereafter, the temperature was maintained at 45 ° C. for 2 hours, and then heated to 110 ° C. Then, the reaction solution is filtered, put into a shuttle furnace, heated to 600 ° C. at 3 ° C./min, kept at 600 ° C. ± 20 ° C. for 4 hours, and then returned to room temperature at 4 ° C./min to remove the white powder. Obtained. Observation of the powder with a scanning electron microscope revealed that each powder had an independent true spherical shape.

When this powder was dispersed in pure water and the particle size distribution was measured by a laser diffraction type particle size distribution analyzer, the average particle size was 5.7 μm and σ was 1.37.
When the amount of the silanol group was measured by T-NIR (diffuse reflection method), it was 1.4 mmol / g. The particle strength is a numerical value obtained by calculating the compressive breaking load using a micro-compression tester and substituting the particle strength (St) by the following equation described in the Japan Industrial Association, Vol. 81, No. 10, page 1024 (1965).

[0027]

Equation 4] Particle strength St (MPa) = 27.4P / πd 2 P: compression breaking load (N) d: particle size (mm)

Next, this powder was put into a Henschel mixer, and 3-methacryloxypropyltrimethoxysilane equivalent to a silanol group was added thereto while stirring at room temperature, followed by stirring for 20 minutes, and then a methyl methacrylate resin powder having a particle size of 0.2 μm was obtained. Was added to the silica surface by stirring, and the resin was melt-film-formed by increasing the internal temperature of the mixer to 140 ° C. while stirring, and the outer layer of silica was coated with a thickness of 0%. A 1 μm resin layer was formed.

Example 2 Silica was produced in the same manner as in Example 1 except that the firing temperature was 980 ° C. Table 1 shows values of the silanol group amount, the average particle size and the like of the silica. Further, in the same manner as in Example 1, the outer layer of silica was
A resin layer of m was formed to produce resin-coated silica.

Comparative Example 1 Silica was produced in the same manner as in Example 1 except that the sintering temperature was 200 ° C. Table 1 shows the amount of silanol groups, the average particle size, and the σ value of this silica. Since it was found that the silica was not suitable for a liquid crystal spacer because the strength was too low, it was excluded from subsequent evaluations.

Comparative Example 2 Silica was produced in the same manner as in Example 1 except that the sintering temperature was 1200 ° C. Table 1 shows the amount of silanol groups, the average particle size, and the σ value of this silica. Since the amount of the silanol group was not detected, the amount of the silane coupling agent to be treated on the obtained silica was 1.4 mmol / g.
A methyl methacrylate resin layer having a thickness of 0.1 μm was formed in the same manner as in Example 1 except for the above.

[0032]

[Table 1]

[Fixing performance on imide substrate] A, B,
0.1 g of each particle of D was dispersed in 5 g of Freon, and after 10 minutes of ultrasonic dispersion, the particles were sprayed on a liquid crystal imide substrate at an air pressure of 0.29 MPa. The substrate was baked under the condition of 180 ° C. × 10 minutes, and the adhesion was evaluated by measuring the residual ratio of silica beads by two methods, an air blow method using a nitrogen gas pressure of 0.29 MPa and a pressure-sensitive adhesive tape peeling method. The results are shown in Tables 2 and 3.

[0034]

[Table 2]

[0035]

[Table 3]

The adhesion of the example was higher than that of the comparative example.

When the surface of the imide substrate for liquid crystal after the pressure-sensitive adhesive tape peeling test was observed with a microscope, it was found that the resin-coated silica particles of Examples 1 and 2 were considered to be traces of particles peeled off on the substrate. However, in the case of the comparative example, a large number of fragments remaining on the substrate, which seemed to have caused the silica resin coating layer to peel off, remained. This indicates that the adhesion at the interface between the silica particles and the coating resin is different, and that the use of the liquid crystal spacer of the present invention improves the adhesion at the interface.

[0038]

The spherical silica according to the present invention is perfectly spherical and has a uniform particle size, so that it is suitably used as a spacer for liquid crystal. In addition, since the adhesive force with the coating resin layer is high, the coating resin layer can be peeled off. It is excellent in that it hardly occurs and has high mechanical strength.

Claims (3)

[Claims] (1) a spherical particle having an average particle diameter of 1 to 20 μm;
A liquid crystal spacer comprising spherical silica having a geometric standard deviation σ of a particle size distribution represented by the following formula of 1.5 or less and having a silanol group of 6 μmol / g or more. Σ = (D ₁ / D ₂ ) ^0.5 D ₁ : Particle size at a cumulative weight of 84% by weight D ₂ : Particle size at a cumulative value of 16% by weight 2. A liquid crystal spacer, wherein the spherical silica according to claim 1 is subjected to a surface treatment with a silane coupling agent, and then a resin layer is provided on the surface of the spherical silica. 3. A method for producing a liquid crystal spacer comprising spherical silica, wherein the spherical silica obtained by a wet method is calcined at 300 ° C. or more and less than 1050 ° C. to reduce the silanol groups of the spherical silica to 6 μmol / g or more and 5 mmol / g or less. A method for producing a liquid crystal spacer.