JPH10226512A - Resin-coated silica particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve melt sticking property at a low temp., solvent resistance, liquid crystallinity resistance and dispersion stability by treating silica fine particles with a vinyl silane coupling agent and then coating the particles with a vinyl polymer coating film and a polymer having siloxane bonds. SOLUTION: Silica particles having 0.5 to 15μm average particle size with <=2% coefft. of variation in the particle size distribution are dispersed in an alcohol solvent to obtain a dispersion liquid, to which ammonia water and a vinyl silane coupling agent are added to treat the surface of particles to introduce vinyl groups into the surface of the silica fine particles. The silica fine particles are dispersed in a polar solvent to obtain a dispersion liquid, to which a unifunctlonal vinyl monomer is added and polymerized to form a vinyl polymer coating film on the surface of the silica fine particles. Then the silica fine particles are dispersed in a polar solvent, to which a radical polymn. initiator and a vinyl silane coupling agent are added to form a coupling agent polymer layer. The coupling agent polymer layer is then hydrolyzed to form a polymer coating layer having siloxane bonds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to resin-coated silica fine particles and a method for producing the same. More specifically, the present invention relates to resin-coated silica fine particles suitable as spacer particles for controlling the thickness of liquid crystal of a liquid crystal display device, and a method for efficiently producing the fine particles.

[0002]

2. Description of the Related Art Liquid crystal display devices are typical of flat panel displays. Due to their low power consumption and low voltage drive, they are used as display devices for various devices such as electronic desktop computers, televisions, computers and word processors. Widely used. The display panel of this liquid crystal display device forms a liquid crystal cell by bonding two transparent substrates provided with predetermined members such as a transparent electrode and an alignment film with a sealing material while maintaining a predetermined interval. It is formed by enclosing liquid crystal in a liquid crystal cell. At this time, the interval (cell gap) between the two transparent substrates is set to a predetermined value by, for example, wet spraying on a predetermined surface of one of the two transparent substrates (the surface that becomes the inner wall of the liquid crystal cell). Spacers for forming a liquid crystal layer having a desired thickness while maintaining the predetermined thickness are dispersed in advance.

In order to obtain a liquid crystal display device having good display characteristics, it is necessary to prevent the liquid crystal from being adversely affected by components eluted from the spacer.
It is necessary to prevent local variations in the distance between the transparent substrates.

As a spacer material which can satisfy such requirements, silica fine particles obtained by hydrolyzing and polycondensing silicon alkoxide to form seed particles, and then growing the seed particles by a predetermined method. . Since the silica fine particles have a high purity, even if they come into contact with the liquid crystal, the elution components hardly affect the liquid crystal. In addition, the particle size accuracy of individual silica fine particles is high, and the coefficient of variation (CV) of the particle size of the silica fine particles manufactured under the same conditions is high.
Value), the spacing between the two transparent substrates can be kept substantially uniform when used as a spacer. However, in the conventional spacer made of fine silica particles, a part of the fine silica particles is moved in the process of injecting the liquid crystal into the liquid crystal cell, and the alignment film may be damaged at the time of the movement, resulting in uneven alignment. In addition, the liquid crystal adhered to the periphery of the liquid crystal cell during the injection of the liquid crystal is generally removed by ultrasonic cleaning. During the ultrasonic cleaning, some of the silica fine particles move, and the movement damages the alignment film. May cause uneven alignment. Therefore, in order to manufacture a liquid crystal display device having high display characteristics with high productivity, it is necessary to substantially prevent the movement of the spacer during liquid crystal injection or ultrasonic cleaning performed after the liquid crystal cell is formed. There is a need.

In particular, in recent years, ferroelectric liquid crystal materials which enable a large screen, high-definition display, and a wide viewing angle of an LCD have been used. This liquid crystal has lower fluidity than the conventional TN liquid crystal, and it takes time to inject the liquid crystal after forming the liquid crystal cell.
The injection is promoted by physical force such as ultrasonic waves.
However, if the fixation (adhesion) between the spacer and the alignment film is weak during the injection, the spacer is moved by the pressure of the injected liquid crystal, and a liquid crystal cell having a uniform thickness cannot be manufactured. There is a point.

As a spacer which does not substantially move after the formation of the liquid crystal cell, there is a spacer in which the surface of silica fine particles is coated with a commercially available synthetic resin powder. Specifically, after a commercially available synthetic resin powder is adsorbed on the surface of the silica fine particles by electrostatic force, an impact force is applied thereto, and a part of the synthetic resin is melted by heat generated at that time, thereby synthesizing the synthetic resin powder. There is known a method in which powders are joined together and a synthetic resin powder is fixed to silica fine particles (JP-A-63-9463).
224). In this spacer, the synthetic resin powder covering the silica fine particles is melted by heat applied when two transparent substrates are bonded together with a sealant to form a liquid crystal cell. For this reason, the spacer is fixed to each transparent substrate,
As a result, the spacer does not substantially move after the liquid crystal cell is formed. However,
The surface of the silica fine particles is coated with a commercially available synthetic resin powder.Since the spacer has insufficient bonding force between the synthetic resin powder and the silica fine particles, the resin layer adhered to the surface of the silica fine particles easily peels off, The peeled resin layer may damage the liquid crystal material.

Japanese Patent Application Laid-Open No. 1-294702 (Japanese Patent Publication No. 6-96605) discloses that a nuclear material is dissolved or dispersed in a predetermined solution, and then a hydroxide and a strong acid are added to the dispersion system. As a result, oil droplets composed of an oil-soluble substance such as a monomer and a polymerization initiator are formed around the core substance, and the monomers in the oil droplets are selectively polymerized to produce polymer particles having a monodisperse particle size distribution. A method for doing so is disclosed.
This publication discloses polymer fine particles produced using silica fine particles as a nucleus substance.When this polymer particle is used as a spacer for a liquid crystal display device, it is not disclosed in the publication. Although it is an effect, it is presumed that it is hard to cause movement after the liquid crystal cell is formed. However, in the method described in this publication, the particle size distribution of the generated fine particles has a considerable range, and the monodispersity (CV value of 2% or less) of the particle size distribution required for the spacer for the liquid crystal display device is required.
The one that satisfies is not obtained. In order to obtain a material satisfying the above monodispersity, a classification operation by means such as a sieve after the production is required.

When silica fine particles are used as a core material, the average particle diameter of the silica fine particles before coating is 0.02 μm.
However, applying the coating has a disadvantage that the average particle diameter eventually increases to 10.3 μm, and the coating thickness cannot be controlled. In order to make the coating thickness about 0.05 to 1 μm suitable as a spacer, it is necessary to lower the monomer concentration. However, when the monomer concentration is low, the polymerizable functional groups on the surface of the silica fine particles are small, so that a uniform coating is required. Cannot be applied.

Further, JP-A-5-232480 discloses that the surface of a crosslinked polymer particle having a predetermined active hydrogen is
After introducing an i-H group, converting the Si-H group into a glycidyl group, and further converting the glycidyl group into a vinyl group, the surface of the crosslinked polymer particle having the introduced vinyl group is graft-polymerized, A liquid crystal spacer formed by forming an adhesion layer made of a thermoplastic resin is disclosed. In the liquid crystal spacer disclosed in this publication, the adhesion layer and the base material of the crosslinked polymer particles are bonded by covalent bonds, so that the adhesion layer hardly peels off, and the adhesion layer is softened by heating. Shows good adhesion to the alignment substrate. For this reason, it is presumed that the liquid crystal spacer hardly moves after the liquid crystal cell is formed.

However, according to the method described in this publication, no dispersion stabilizer is used, and the resin-coated particles tend to aggregate during the production process, and monodisperse resin-coated particles having a uniform resin film on the surface are produced. It is difficult to do. In particular, the LCD spacer is required to have high cell gap accuracy, and the aggregated particles cannot sufficiently fulfill the role of the spacer for keeping the cell gap at a constant interval. Further, there is a problem that the process until the vinyl group is introduced on the surface of the crosslinked polymer particle is complicated, and the production cost is increased.

Therefore, the present inventors have proposed that (i) when used as a spacer for a liquid crystal display device as a whole, have a high hardness and strength and, as a spacer, maintain the cell gap at a predetermined interval as a spacer for a long period of time. Can be fulfilled across,
(ii) peeling of the resin film does not substantially occur even when dispersed in a spray liquid (aqueous alcohol solution) by ultrasonic vibration; (iii) it has good adhesion to an alignment substrate for a liquid crystal display device and Research has been conducted to develop resin-coated silica fine particles that have substantially no adverse effect not only on the liquid crystal itself but also on the orientation of the liquid crystal. A resin-coated silica fine particle having a thermoplastic resin film having a single-layer structure or a multi-layer structure formed via a coupling agent has been found (Japanese Patent Application No. 7-260185).

The resin-coated silica fine particles are
It satisfies the properties of (i), (ii) and (iii) and has good performance as spacer particles for a liquid crystal display device.

By the way, recently, in the field of liquid crystal display devices, organic substances are often used in liquid crystal members such as film liquid crystal, and accordingly, it is required to lower the temperature of heat treatment in the manufacturing process of liquid crystal display devices. It has become Therefore, it is necessary to fix the spacer particles at a lower temperature. As a fixing component,
Generally, a thermoplastic resin is used. However, in order to fix the resin at a lower temperature, it is necessary to reduce the molecular weight or use a resin having a low softening temperature. However, such resins generally have a drawback that they have poor durability against organic solvents and liquid crystals. For this reason, in wet spraying,
If the particles coated with such a resin are immersed in a dispersion solvent for a long time, aggregation of the particles occurs, so that the particle dispersion must be used in a short time, or the composition of the spraying solvent is reduced. There were problems such as being limited.

[0014]

Under such circumstances, the present invention sufficiently satisfies the above-mentioned properties (i), (ii), and iii), melts and fixes at a low temperature, and furthermore, disperses a solvent. And to provide resin-coated silica fine particles having excellent durability against liquid crystals, hardly aggregating even after being dispersed in a dispersion solvent for a long time, having good dispersion stability, and suitable as a spacer for liquid crystal display devices. It is intended for.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies to develop resin-coated silica fine particles having the above-mentioned excellent functions, and as a result, have found that a vinyl-based polymer coated with a polymer having siloxane bonds has been obtained. The resin-coated silica fine particles provided with the coalesced film on the surface of the silica fine particles via the vinyl-based silane coupling agent can meet the purpose, and the resin-coated silica fine particles are subjected to a surface treatment step of the silica fine particles. Forming a vinyl-based polymer film on the surface of the surface-treated silica fine particles, forming a coating layer of a coupling agent polymer on the vinyl-based polymer film, and sequentially performing a hydrolysis treatment process. As a result, the present inventors have found that they can be efficiently obtained, and have completed the present invention based on this finding.

That is, the present invention provides a vinyl-based polymer film having a single-layer structure or a multi-layer structure formed on the surface of silica fine particles via a vinyl-based silane coupling agent.
Furthermore, the present invention provides resin-coated silica fine particles characterized by being coated with a polymer having a siloxane bond.

Further, according to the present invention, the resin-coated silica fine particles may be obtained by a step (A) of treating the silica fine particles with a vinyl silane coupling agent to introduce a vinyl group into the surface of the silica fine particles; (B) forming a vinyl-based polymer film on the surface of the surface-treated silica fine particles by dispersing and polymerizing the system-based monomer, and polymerizing the vinyl-based silane coupling agent to form the vinyl formed on the surface of the silica fine particles. (C) forming a coating layer made of a coupling agent polymer on the polymer film, and hydrolyzing the coating layer made of the coupling agent polymer formed on the vinyl polymer film, It can be manufactured by sequentially performing the step (D) of forming a coating layer made of a polymer having a siloxane bond.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resin-coated silica fine particles of the present invention are a coating layer comprising silica fine particles, a vinyl-based silane coupling agent, a vinyl-based polymer film, and a polymer having a siloxane bond.

In the resin-coated silica fine particles of the present invention,
The silica fine particles may be a base material forming a core portion, and may be raw silica fine particles obtained by hydrolyzing and polycondensing silicon alkoxide by a so-called sol-gel method, or calcined silica obtained by calcining the raw silica fine particles. Fine particles may be used. The production method and properties of the raw silica particles and the calcined silica particles will be described in detail in the method of producing the resin-coated silica particles of the present invention described later.

In the resin-coated silica fine particles of the present invention,
The vinyl-based silane coupling agent is interposed between the silica fine particles and a vinyl-based polymer film described below to form a vinyl-based polymer film having excellent adhesion on the surface of the silica fine particles. In detail, the silane portion of the vinyl silane coupling agent reacts with silanol groups on the surface of the silica fine particles to form a chemical bond, and at the same time, the vinyl group of the vinyl silane coupling agent forms a vinyl polymer film. By reacting with the unsaturated double bond in the monomer during the polymerization of the monomer for forming to form a chemical bond, the surface of the silica fine particles has excellent adhesion through a vinyl silane coupling agent as a linking agent. A vinyl polymer coating is formed.

In the resin-coated silica fine particles of the present invention, the vinyl silane coupling agent as a linking agent is
It is clear from the above description that the vinyl group and the silane moiety, which are reactive groups, are present in a reacted form.

As the vinyl silane coupling agent,
A vinyl group having a silane moiety (e.g., an alkoxysilane group, a halogenosilane group, an acetoxysilane group, etc.) having a reactivity with a silanol group on the surface of silica fine particles, and having a reactivity with a monomer for forming a vinyl polymer film. Any material can be used as long as it has the following. Here, the vinyl group is interpreted in the broadest sense and includes an acryloyl group, a methacryloyl group, an allyl group and the like in addition to the vinyl group itself. Specific examples of the above-mentioned vinyl silane coupling agent include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltris (β -Methoxy) silane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, vinyltriacetoxysilane, γ-methacryloxypropylmethyldimethoxysilane, and the like.

In the resin-coated silica fine particles of the present invention,
The vinyl polymer coating is formed on the surface of the silica fine particles via a vinyl silane coupling agent. The vinyl polymer film can be selected from various types according to the purpose and application of the resin-coated silica fine particles. The following conditions (a) having one polymerizable carbon-carbon double bond:
(B) It must be obtained by mainly polymerizing a monofunctional vinyl monomer satisfying that it has a functional group capable of reacting with the vinyl group of the vinyl silane coupling agent. The type of the monofunctional vinyl monomer will be described later.

Since the resin film is obtained by polymerization of a monofunctional vinyl monomer, the resin film is composed of a vinyl polymer as described above. Here, the vinyl polymer basically means a polymer obtained by polymerizing only a monofunctional vinyl monomer as a monomer component, and a polyfunctional vinyl monomer is substantially added to the monofunctional vinyl monomer. Resins obtained by polymerizing a monomer mixture added within a range that does not cause cross-linking (for example, in an amount of less than 0.5 mol% based on all monomers) are also included.

When the vinyl polymer film has a multilayer structure,
These multiple layers may be composed of the same type of polymer or different types of polymers. In addition, even when composed of the same type of polymer,
The composition of the vinyl monomer which is a raw material of the polymer may be different.

In the resin-coated silica fine particles of the present invention,
The coating layer made of a polymer having a siloxane bond constitutes an outer layer formed on the vinyl polymer film.

The coating layer made of a polymer having a siloxane bond can be formed as follows, as described in the method for producing resin-coated silica fine particles of the present invention described below. First, a vinyl-based silane coupling agent polymer is radically polymerized to form a coating layer made of the coupling-agent polymer on the vinyl-based polymer film, and then subjected to hydrolysis treatment. For example, an alkoxyl group portion therein is hydrolyzed and condensed to form a coating layer made of a polymer having a network-like siloxane bond on the vinyl polymer film.

In the radical polymerization of the vinyl-based silane coupling agent, the vinyl-based silane coupling agent is grafted onto the remaining vinyl groups in the vinyl-based polymer film to form a carbon-carbon bond. It is considered that the adhesion between the coating layer made of a polymer having a siloxane bond and the vinyl polymer film becomes excellent.

The vinyl silane coupling agent used here is not particularly limited as long as it has a vinyl group and a silane moiety. The vinyl silane coupling agent provided on the surface of the silica fine particles is not limited. The same ones as exemplified in the description can be given.

The length of the polymer chain of the polymer having a siloxane bond and the amount of the siloxane bond are preferably set to such an extent as not to affect the melting and fixing of the vinyl polymer film during heating.

The resin-coated silica fine particles of the present invention have the following advantages.

(I) Since the core portion (base material) is formed of silica fine particles, the strength and hardness are high, and when used as a spacer for a liquid crystal display device, the cell gap is maintained at a predetermined interval. Can be performed over a long period of time.

(Ii) Since the vinyl polymer film is formed on the surface of the silica fine particles via the vinyl silane coupling agent, the adhesion between the surface of the silica fine particles and the resin film is excellent. Therefore, even when dispersed in a spray liquid (aqueous alcohol solution) by ultrasonic vibration, peeling of the resin film from the silica fine particles hardly occurs. That is, the resin coating has durability to the ultrasonic treatment.

(Iii) The resin film formed on the surface of the silica fine particles has lower hardness than the silica fine particles of the base material, and has appropriate elasticity, flexibility and thermoplasticity. Therefore,
When the resin-coated silica fine particles of the present invention are used as a spacer for a liquid crystal display, the resin coating adheres to the surface of the substrate (the surface of the alignment film) by moderate heating. Absent. Further, since the particles are not coalesced or aggregated, the workability of spraying on the substrate surface is improved, and the risk of liquid crystal display failure due to the aggregated particles acting as foreign matter can be reduced. Further, since there is substantially no adverse effect on the liquid crystal due to elution of the components from the resin film, display failure due to disorder in the alignment of the liquid crystal does not substantially occur.

(Iv) In the manufacturing process of the liquid crystal display device, even if a vinyl-based polymer film having a low softening point is used as the resin film in order to fix the spacer particles at a lower temperature, the surface has siloxane bonds. Since the coating layer made of the polymer is formed, the durability to the dispersing solvent and the liquid crystal does not decrease, and aggregation does not easily occur even when dispersed in the dispersing solvent for a long time.

Next, preferable numerical conditions of the resin-coated silica fine particles of the present invention will be described.

The resin-coated silica fine particles of the present invention preferably have an average particle size of 0.6 to 17 μm and a coefficient of variation (CV value) of the particle size distribution of 2% or less.

If the average particle size of the resin-coated silica fine particles is within the above range, it is suitable for use as a spacer for a liquid crystal display device. The reason why the lower limit of the average particle diameter is preferably 0.6 μm is that the lower limit of the cell gap of the liquid crystal display device is approximately 0.6 μm. On the other hand, the average particle size is 17 μm.
The reason why m or less is preferable is as follows. In order to obtain resin-coated silica fine particles having a large average particle size, it is necessary to use silica fine particles having a large average particle size also as a base material. However, when the silica fine particles having a large particle diameter are sedimented in a solution when the resin-coated silica fine particles are obtained by the method of the present invention described later, they are apt to coalesce with each other. Will be difficult to obtain. For this reason, the upper limit of the average particle size of the resin-coated silica fine particles of the present invention is defined according to the upper limit of the average particle size of the silica fine particles used as the base material, and the value is about 17 μm.

When the resin-coated silica fine particles of the present invention are used as a spacer for a liquid crystal display device, the average particle size is preferably from 1.0 to 12 μm, particularly preferably from 1.2 to 12 μm.
It is preferably 10 μm.

A coefficient of variation of the particle size distribution (hereinafter, referred to as “CV value”) of 2% or less means that the material satisfies so-called monodispersity, which can function as a spacer for a liquid crystal display device. The reason why the CV value is preferably 2% or less is as follows.
If the CV value exceeds 2%, the driving voltage of the liquid crystal changes, resulting in a decrease in contrast and non-uniform display colors, which is unsuitable for use as a spacer for a liquid crystal display device.

The CV value is calculated by the following equation.

CV value (%) = (standard deviation of particle size) ÷ (average particle size) × 100 The thickness of the vinyl polymer film in the resin-coated silica fine particles of the present invention is determined by the particle size of the resin-coated silica fine particles. Although it depends, it is preferable that it is generally in the range of 0.01 to 0.5 μm. If the thickness of the resin film is less than 0.01 μm, it is difficult to obtain resin-coated silica fine particles having a sufficient adhesive force to an alignment substrate for a liquid crystal display device. on the other hand,
When the thickness of the resin coating exceeds 0.5 μm, coalescence of the vinyl polymer-coated silica fine particles tends to occur, and C
It becomes difficult to obtain fine particles having a V value of 2% or less. The preferred thickness of the vinyl polymer coating is such that the particle size of the silica fine particles is approximately 4%.
When the particle size of the silica fine particles is 4 μm or more, it is about 0.02 to 0.2 μm.
It is about 5 μm.

The thickness of the coating layer comprising a polymer having a siloxane bond in the resin-coated silica fine particles of the present invention depends on the length of the polymer chain of the polymer and the amount of the siloxane bond. It is preferably in the range of 0.2 μm. When the thickness is less than 0.005 μm, when a vinyl polymer film having a low softening point is used, the durability to the dispersion solvent and the liquid crystal and the dispersion stability in the dispersion solvent may be reduced. .2μ
If it exceeds m, it becomes difficult to fix at the intended heating temperature.

Next, a method for producing the resin-coated silica fine particles of the present invention will be described.

In the method for producing resin-coated silica fine particles of the present invention, the step (A) of treating the silica fine particles with a vinyl silane coupling agent to introduce a vinyl group into the surface of the silica fine particles comprises the steps of: Dispersion polymerization,
Step (B) of forming a vinyl-based polymer film on the surface of the surface-treated silica fine particles, polymerizing a vinyl-based silane coupling agent, and coupling onto the vinyl-based polymer film formed on the surface of the silica fine particles. (C) forming a coating layer made of an agent polymer, and hydrolyzing the coating layer made of the coupling agent polymer formed on the vinyl-based polymer film to form a polymer having a siloxane bond. The step (D) of forming a coating layer is sequentially performed.

Hereinafter, each step will be described in detail.

Step (A) Step (A) is a step of introducing a molecule (vinyl-based silane coupling agent) for linking the fine silica particles with the vinyl polymer film formed on the surface of the fine silica particles to the surface of the fine silica particles. is there.

The silica fine particles serving as the base material of the resin-coated silica fine particles are substantially spherical fine particles, and may be those in which the particles are not substantially coalesced. The silica fine particles are porous. There may be. Raw silica fine particles or calcined silica fine particles may be used. In the present specification, the baked silica fine particles refer to particles having a particle strength of 70 kgf / mm ² or more by calcination of raw silica fine particles.

The particle strength was determined by using a micro compression tester (MCTE-200) manufactured by Shimadzu Corporation, and the compressive breaking load was calculated.
It is a numerical value replaced with the particle strength (St) by the following equation described in 5).

Particle strength St (kgf / mm ² ) = 2.8 P / πd ² P: compressive breaking load (kgf) d: particle size (mm) The average particle size of the silica fine particles serving as the base material depends on the purpose. Any size can be used as long as the resin-coated silica fine particles to be obtained can be obtained. The average particle size of the resin-coated silica fine particles, the thickness of the resin coating, the thickness of the coating layer made of a polymer having a siloxane bond, and the like vary. However, specifically, 0.5 to 1
5 μm, preferably 0.8 to 12 μm, particularly preferably 1.0 to 10 μm. CV value is 2%
Or less, particularly preferably 1.5% or less. The reason that the average particle diameter of the silica fine particles is preferably in the range of 0.5 to 15 μm is that if the average particle diameter is out of the above range, it becomes difficult to obtain resin-coated silica fine particles having a target particle diameter. The reason why the CV value of the silica fine particles is preferably 2% or less is that if silica fine particles having a CV value exceeding 2% are used as a base material (core material), the particle size distribution required for a spacer for a liquid crystal display device is reduced. This is because substantially no resin-coated silica fine particles satisfying the monodispersity (variation rate of 2% or less) can be obtained.

The silica fine particles serving as a base material of the resin-coated silica fine particles of the present invention may be obtained by any method as long as the above-mentioned requirements are satisfied. Raw silica fine particles are obtained by the so-called sol-gel method,
Specific examples thereof include the following (a) and (b).

(A) Monodispersed seed particles having a particle size distribution are produced by hydrolysis and polycondensation of silicon alkoxide. Next, a silicon alkoxide is added to the dispersion liquid of the seed particles in the presence of a catalyst to grow the seed particles to increase the particle size. By carrying out a plurality of times while maintaining the distribution to be monodisperse, silica fine particles are obtained.

(B) Silicon alkoxide is added to a dispersion obtained by dispersing silica seed particles in a mixed solvent of alcohol and aqueous ammonia and hydrolyzed, whereby silica seed particles are grown and silica particles are grown. obtain. At that time, the ratio So / Vo of the total surface area So of all the silica seed particles in the dispersion before adding the silicon alkoxide to the total volume Vo of the solution components in the dispersion is 300 cm ² / c.
m ³ or more, and the ratio S / V of the total surface area S of all the grown silica particles in the dispersion after adding the silicon alkoxide to the total volume V of the solution components in the dispersion is 300 to 1200 cm ^2. / Cm ³ or more. In this way, after obtaining silica fine particles having two kinds of particle size distributions whose distributions do not overlap with each other, one of the silica fine particles is obtained by classification (see JP-A-6-48720).

The raw silica fine particles are produced by means such as hydrolysis, dehydration and polycondensation of a silicon alkoxide in a mixture of water, ammonia and alcohol as described above. The raw silica fine particles obtained as described above contain a large amount of silanol groups (Si-OH), so that it is relatively easy to introduce a polymerizable functional group onto the surface of the silica fine particles using a silane coupling agent, In some cases, water and ammonia remain, and strength and hardness may be low. In such a case, when the raw silica fine particles are fired at about 500 to 1200 ° C., organic substances and water are volatilized, and silanol groups are condensed to increase siloxane bonds (Si—O—Si), thereby increasing strength and strength. Hardness increases. Therefore, although the strength and hardness are improved by firing, the silanol groups present on the surface of the silica fine particles, which are active sites for reaction with the vinyl-based silane coupling agent, are consumed for condensation and considerably reduced. The reaction with the ring agent hardly progresses or does not progress at all.

The amount of silanol groups lost depending on conditions such as the firing temperature, time, and surface area of the silica fine particles varies considerably. For example, in the case of calcined silica fine particles having a low calcining degree and a relatively large amount of silanol groups on the surface,
Since the introduction of the vinyl group by the reaction with the vinyl-based silane coupling agent proceeds relatively easily, the calcined silica fine particles can be directly surface-treated with the vinyl-based silane coupling agent.

However, even if the calcined silica fine particles having a high degree of calcining and having a reduced amount of silanol groups, which are the reactive sites, are treated with a vinyl silane coupling agent as they are, a sufficient amount of vinyl groups will be formed on the surface of the silica fine particles. Therefore, silica fine particles having a uniform resin film cannot be obtained.

Therefore, when the silanol groups on the surface of the calcined silica fine particles are insufficient (that is, when the amount of vinyl groups introduced into the surface of the silica fine particles by the reaction of the vinyl silane coupling agent becomes insufficient). By reacting silicon alkoxide or a partial hydrolyzate thereof with calcined silica fine particles to introduce silanol groups on the surface of the calcined silica fine particles, it is possible to increase the number of active sites for reaction with the vinyl-based silane coupling agent to increase the required amount of vinyl. It is preferred to introduce groups. That is, by performing a treatment with a silicon alkoxide or a partial hydrolyzate thereof on a calcined silica fine particle having a high calcining degree, a high-strength and high-hardness which could not be conventionally used as a base material of a spacer for a liquid crystal display device was obtained. The calcined silica fine particles can be advantageously used as a base material. Of course, the raw silica fine particles may be surface-treated with silicon alkoxide or a partial hydrolyzate thereof in order to introduce silanol groups on the surface.

Under alkaline conditions, silicon alkoxide is hydrolyzed as shown by the following reaction formula, and is gradually dehydrated and condensed.

Si (OR) ₄ + 4H ₂ O → Si (OH) ₄ + 4ROH Si (OH) ₄ → SiO ₂ + 2H ₂ O The surface of baked silica fine particles having a large number of siloxane bonds and tetrahydroxy Silanes are essentially homogeneous components and are indistinguishable. Therefore, the tetrahydroxysilane generated as described above is integrated with the surface of the calcined silica fine particles, so that a thin film of tetrahydroxysilane is formed on the surface of the calcined silica fine particles. The vinyl silane coupling agent reacts with the silanol groups in the tetrahydroxysilane thin film formed on the surfaces of the baked silica fine particles, and the vinyl groups are introduced into the surfaces of the silica fine particles.

The silicon alkoxide or its partial hydrolyzate which can be used in the present invention is not particularly limited as long as it can introduce a silanol group on the surface of the silica fine particles. The silicon alkoxide that can be used herein is represented by the general formula Si (OR ¹ ) ₄ or Si (R ² ) _n (OR ¹ ) _4-n (wherein R ¹ and R ² are an alkyl group or an acyl group, especially An alkyl group having 1 to 5 carbon atoms or an acyl group having 2 to 6 carbon atoms, and n is an integer of 1 to 3). Specific examples thereof include tetramethoxysilane and tetramethoxysilane. Ethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like can be mentioned.

The partial hydrolyzate of silicon alkoxide is obtained by hydrolyzing a part of a plurality of alkoxy groups (OR ₁ ) or (OR ₂ ) in the silicon alkoxide represented by the above general formula.

Reaction with silicon alkoxide or its partial hydrolyzate (hereinafter referred to as “silicon alkoxide treatment”)
That. ) Is a surface treatment of silica fine particles with a vinyl silane coupling agent (hereinafter referred to as “coupling agent treatment”).
That. ) (Ie, step (A))) and / or before the step (A)). That is, the silicon alkoxide treatment may be performed before the coupling agent treatment, simultaneously with the coupling agent treatment, or both.

The amount of silicon alkoxide or its partial hydrolyzate used for silicon alkoxide treatment is as follows:
The molar ratio to the amount of the vinyl silane coupling agent used is preferably 0.5 or less, and particularly preferably 0.25 or less.

In the present invention, the vinyl silane coupling agent used in the coupling agent treatment in the step (A) of the method for producing the resin-coated silica fine particles of the present invention is, as described above, a silanol group on the surface of the silica fine particles. Having a reactive silane moiety (e.g., an alkoxysilane group, a halogenosilane group, an acetoxysilane group, etc.) and a vinyl group having a reactivity with a vinyl polymer film-forming monomer. Anything can be used. Here, the vinyl group is understood in the broadest sense, and in addition to the vinyl group itself, an acryloyl group, a methacryloyl group,
It shall include an allyl group and the like.

Specific examples of the above-mentioned vinyl silane coupling agent include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, Vinyl tris (β-methoxy) silane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, vinyltriacetoxysilane, γ-methacryloxypropylmethyldimethoxysilane, and the like.

The vinyl silane coupling agent may be used alone or in combination of two or more.

The amount of the vinyl silane coupling agent to be used is preferably an amount corresponding to 0.5 to 5 mmol / m ² , more preferably an amount corresponding to 1 to 3 mmol / m ² per unit surface area of the silica fine particles. .

In the method for producing resin-coated silica fine particles of the present invention, the step (A) of surface-treating the above-mentioned silica fine particles with a vinyl-based silane coupling agent is first carried out. This can be done as follows. First, silica fine particles are dispersed in an alcohol solvent such as methanol, ethanol, or 2-propanol using ultrasonic vibration or the like to obtain a desired dispersion. The solvent at this time may be one kind of alcohol,
It may be a mixture of a plurality of alcohols. The weight of the alcohol solvent is preferably 5 to 30 times the weight of the silica fine particles. In the dispersion obtained in this manner, 25 to 30% by weight of 2 to 30 times the weight of the silica fine particles.
Aqueous ammonia water is added at a moderate concentration, and a vinyl silane coupling agent is further added. When the temperature of the dispersion is 20
Stir for about 1 to 24 hours while maintaining the temperature at about 80 ° C. As a result, the silica fine particles are surface-treated with the vinyl-based silane coupling agent, and a vinyl group is introduced into the surface of the silica fine particles.

As described above, a small amount of silicon alkoxide (0.5 or less in terms of a molar ratio to the vinyl silane coupling agent) can be added as needed during the surface treatment with the vinyl silane coupling agent. By coexisting a vinyl silane coupling agent and a silicon alkoxide having a high hydrolysis rate, it is possible to introduce a sufficient amount of vinyl groups to form a uniform resin film on the surface of the silica fine particles.

Step (B) Next, the step (B) of forming a vinyl polymer film on the surface of the silica fine particles will be described.

In the step (B), the step (A) is carried out as described above, and a monofunctional vinyl monomer is dispersed and polymerized in the presence of the silica fine particles having a vinyl group introduced on the surface. In this dispersion polymerization, usually, while dispersing silica fine particles in a polar solvent using a dispersion stabilizer, a monofunctional vinyl monomer is added to this dispersion and dissolved, and the presence of a radical polymerization initiator and a chain transfer agent is present. A method of polymerizing the vinyl monomer below is used. As a result, a vinyl-based polymer film is formed on the surface of the silica fine particles having a vinyl group introduced into the surface.

The monofunctional vinyl monomer which can be used in the step (B) is a monomer having one carbon-carbon unsaturated double bond, and specific examples thereof include vinyl aromatic hydrocarbons (styrene, α -Methylstyrene, vinyltoluene, α-chlorostyrene, o-chlorostyrene, m
-Chlorostyrene, p-chlorostyrene, p-ethylstyrene, etc.), acrylic acid, esters of acrylic acid (methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate,
2-ethylhexyl acrylate, cyclohexyl acrylate, β-hydroxyethyl acrylate, β-aminoethyl acrylate, N, N-dimethylaminoethyl acrylate, γ-hydroxypropyl acrylate, etc.), methacrylic acid, esters of methacrylic acid (methyl methacrylate, ethyl methacrylate) Propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, β-hydroxyethyl methacrylate, β-aminoethyl methacrylate, N, N-dimethylaminoethyl methacrylate, γ-hydroxypropyl methacrylate, glycidyl methacrylate, etc.), And vinylsilane (vinyltrimethoxysilane, vinyltriethoxysila Vinyl trimethyl silane, .gamma.-methacryloxypropyl trimethoxysilane) are exemplified by polymerizing these monofunctional vinyl monomers, styrene resins, acrylic resins,
A resin film made of a vinyl polymer such as a methacrylic resin is formed.

As described above, a polyfunctional vinyl monomer can be used together with a monofunctional vinyl monomer as long as crosslinking is not substantially caused.

In step (B), the dispersion polymerization is advantageously carried out in the presence of a dispersion stabilizer. By the addition of the dispersion stabilizer, it is possible to substantially prevent coalescence between the silica fine particles after the resin film is formed, that is, the resin-coated silica fine particles, and the polymerization of the resin film on the surface of the silica fine particles is preferably performed. proceed.

Specific examples of the dispersion stabilizer used in the step (B) include polyvinyl pyrrolidone, polyvinyl methyl ether, polyethylene imine, polyacrylic acid, polyvinyl alcohol, ethyl cellulose, hydroxypropyl cellulose and the like.

The polymerization is usually carried out in the presence of a so-called polar solvent or an organic solvent miscible with the polar solvent in any ratio. In the present invention, the “polar solvent” is a broad concept including not only a so-called polar solvent but also a polar solvent-miscible organic solvent. Specific examples of the polar solvent include, for example, water, lower alcohols such as methanol, ethanol, 2-propanol, butanol, amyl alcohol, and benzyl alcohol, and polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, and triethylene glycol. Examples thereof include alcohols, esters such as ethyl acetate, ketones such as acetone and methyl ethyl ketone, nitriles such as acetonitrile, amides such as formamide and dimethylformamide, and ethers such as tetrahydrofuran. Specific examples of the polar solvent-miscible organic solvent include ethers such as dioxane and tetrahydrofuran. Among them, those which dissolve the vinyl monomer but do not dissolve the polymer are appropriately selected according to the vinyl monomer to be used, and are used alone or in combination of a plurality thereof.

When a polyhydric alcohol is used as the polar solvent, the viscosity of the solvent increases and the solubility of the polymer decreases. As a result, the particle size of the vinyl polymer particles precipitated in the solvent decreases, and when the resin particles adhere to the silica surface to form a film, the film is formed in a more uniform and dense state. be able to.

Particularly preferred combinations of polar solvents and the mixing ratio thereof for obtaining the monodispersed resin-coated silica fine particles which are the object of the present invention are, for example, ethylene glycol: water: methanol = 20 to 60% by weight: 20 to 40%.
% By weight: 20 to 40% by weight.

The method for dispersing the silica fine particles after the surface treatment in a polar solvent using a dispersion stabilizer is not particularly limited. For example, a desired dispersion may be obtained by the following method (a) or (b). Can be.

(A) First, a dispersion stabilizer is dissolved in a polar solvent to prepare a solution having a concentration of the dispersion stabilizer of about 2 to 15% by weight. Next, the silica fine particles after the surface treatment are added to this solution, and the silica fine particles are dispersed using ultrasonic vibration or the like to obtain a target dispersion. At this time, the addition amount of the silica fine particles is preferably 1 to 5% by weight based on the polar solvent.

(B) First, silica particles after surface treatment are added to a polar solvent, and the silica particles are dispersed using ultrasonic vibration or the like. At this time, the addition amount of the silica fine particles is preferably such that the ratio of the silica fine particles in the finally obtained dispersion is 1 to 5% by weight with respect to the polar solvent.
Amount. Separately, a solution in which a dispersion stabilizer is dissolved in a polar solvent is prepared. The concentration of the dispersion stabilizer in this solution is such that the proportion of the dispersion stabilizer in the finally obtained dispersion is preferably 2 to 15% by weight with respect to the polar solvent. Then, a polar solvent in which the silica fine particles are dispersed and a polar solvent in which the dispersion stabilizer is dissolved are mixed to obtain a target dispersion.

In the step (B), the silica fine particles after the surface treatment in the step (A) are usually dispersed in a polar solvent using a dispersion stabilizer as described above. The monomer mixture is polymerized in the presence of a radical polymerization initiator and a chain transfer agent. Specific examples of the radical polymerization initiator used at this time include an azo polymerization initiator such as 2,2'-azobisisobutyronitrile and a peroxide such as benzoyl peroxide.

The amount of the radical polymerization initiator to be added is preferably from 1 to 50 mol%, more preferably from 10 to 30 mol%, based on the amount of the monomer mixture.

In step (B), the dispersion polymerization is advantageously carried out in the presence of a chain transfer agent. By the addition of the chain transfer agent, it is possible to substantially prevent coalescence between the silica fine particles after the resin coating is formed, that is, the resin-coated silica fine particles, and to polymerize the monofunctional vinyl monomer on the surface of the silica fine particles. The formation of the resin film by the process suitably proceeds.

The reason why the addition of the chain transfer agent reduces the coalescence and aggregation of the resin-coated silica fine particles is as follows.
(Although it is also affected by the solubility of the vinyl polymer in the polar solvent used.) Basically, the addition of a chain transfer agent shortens the polymer chain of the polymer and causes the vinyl polymer to precipitate. Because the particle size of
It is considered that the film is formed on the surface of a single silica particle in a uniform and dense state.

When a chain transfer agent is added, the number of repeating units of the vinyl monomer molecule constituting the polymer chain is reduced, and the length of the polymer chain is shortened. Uniform resin coating becomes possible.

On the other hand, when a resin coating is applied to silica fine particles having a relatively small particle size of about 3 μm or less without adding a chain transfer agent, the resin coating is not uniformly formed on the surface of the silica fine particles. Some parts of the coating are thick and some parts are thin. This is because the polymer obtained by polymerizing the monofunctional vinyl monomer is a linear polymer, and the particle size of the silica fine particles to be coated is too small with respect to the length of the polymer chain. This is probably because the particles cannot be coated.

In the case of silica fine particles having a relatively large particle diameter exceeding about 3 μm, a resin film having a relatively uniform film thickness can be formed without adding a chain transfer agent. . However, since a resin film formed without using a chain transfer agent is made of a polymer having a long molecular chain and a high softening temperature, silica fine particles coated with a resin made of such a high softening point polymer are used for a liquid crystal display device. When used as a spacer, heat treatment must be performed at a high temperature in order to securely attach the spacer to the alignment film substrate, and there is a risk that the alignment film may be damaged by heat.

On the other hand, the polymer constituting the resin film formed by using the chain transfer agent has a short molecular chain, a relatively low softening temperature, and a temperature at which there is no risk of damaging the alignment film. It can be reliably attached to the alignment film substrate.

Specific examples of the chain transfer agent used in the step (B) include, for example, isopropyl mercaptan, n-butyl mercaptan, and n-butyl mercaptan generally used in radical polymerization.
Mercaptans such as dodecyl mercaptan, 3-ethoxypropane thiol, bis-2-aminodiphenyl disulfide, bis-2-benzothiazoyl disulfide, ethyl thioglycolate, amyl mercaptan, mercaptoacetic acid; carbon tetrachloride And halogenated carbons such as bromine tetrachloride; hydrocarbons such as diphenylmethane and triphenylmethane; and triethylamine.

The addition of the monofunctional vinyl monomer in the step (B) is performed after the addition of the radical polymerization initiator and the chain transfer agent to the polar solvent dispersion containing the silica fine particles and the dispersion stabilizer after the treatment with the coupling agent. And the addition may be simultaneously with the addition of the radical polymerization initiator and the chain transfer agent.

In the polymerization of the monofunctional vinyl monomer in the step (B), the liquid temperature of the dispersion after the addition of the monofunctional vinyl monomer, the radical polymerization initiator and the chain transfer agent is maintained at about 20 to 80 ° C. The dispersion can be performed by stirring the dispersion for about 1 to 24 hours. By this polymerization, a desired vinyl-based polymer film is formed on the surface of the silica fine particles after the surface treatment with the above-mentioned vinyl-based silane coupling agent, and resin-coated silica fine particles are generated in the reaction solution.

The thickness of the resin film formed by the polymerization reaction in the step (B) is preferably 0.01 to 0.5 μm. The thickness of the resin coating depends on the concentration of the monomer mixture in the dispersion, the concentration of the radical polymerization initiator and the chain transfer agent,
It can be controlled by appropriately changing the polymerization time and the like.

With the polymerization of the vinyl monomer in the step (B), a large number of resin fine particles are by-produced in the reaction solution. These resin fine particles are significantly smaller than the resin-coated silica fine particles, and are present in a suspended state together with the resin-coated silica fine particles in the reaction solution. Therefore, after the completion of the polymerization reaction in the step (B), the resin fine particles by-produced in the reaction solution can be easily removed by washing.

After removing the resin fine particles as described above, the resin-coated silica fine particles are directly used in the next step (C).
If necessary, for example, the washing solution may be replaced with water, and then isolated by drying using a freeze-drying method or the like, and used in the step (C).

The resin-coated silica fine particles obtained by performing the above steps (A) and (B)
The resin film constituting this has a single-layer structure (hereinafter, referred to as “single-layer resin-coated silica fine particles”). The resin film may have a single-layer structure or a multi-layer structure as described above. To make the resin film have a structure of two or more layers, for example, the following method may be used. .

First, the single-layer resin-coated silica fine particles are fractionated as described above, and the single-layer resin-coated silica fine particles are dispersed in a polar solvent using a dispersion stabilizer. A vinyl monomer is added and dissolved.
Next, by polymerizing the monofunctional vinyl-based monomer in the presence of a radical polymerization initiator and a chain transfer agent, a resin film is further formed on the surface of the single-layer resin-coated silica fine particles, and new 2 A resin-coated silica fine particle having a resin coating layer is generated.

Next, as described above, the resin fine particles by-produced in the reaction solution are removed by washing, and then new two-layer resin-coated silica fine particles are collected. As a result, a desired vinyl polymer film having a multilayer structure is formed.

The dispersion stabilizer, polar solvent, monofunctional vinyl monomer, radical polymerization initiator and chain transfer agent used at this time may be the same as those used when forming the first resin coating. It may be different. These specific examples are as described above. The method of dispersing the single-layer resin-coated silica fine particles in a polar solvent using a dispersion stabilizer conforms to the method in the step (B). And
The procedure after this also conforms to the procedure for obtaining single-layer resin-coated silica fine particles. Also in this case, when a polyhydric alcohol is used as the polar solvent, the vinyl polymer film can be effectively formed.

In the same manner, a new resin film is formed on the surface of the vinyl polymer film by a dispersion polymerization method, whereby resin-coated silica fine particles having a vinyl polymer film having a three-layer structure or more can be obtained.

Step (C) In the step (C), the step (B) is performed as described above.
This is a step of forming a coating layer made of a vinyl-based silane coupling agent polymer on the vinyl-based polymer film formed on the surface of the silica fine particles.

The vinyl silane coupling agent used in the step (C) is not particularly limited as long as it has a vinyl group and a silane moiety. For example, the vinyl silane coupling agent used in the step (A) can be used. The same ones as those exemplified as the ring agent can be exemplified. These vinyl silane coupling agents may be used alone or in combination of two or more.

As a polymerization method of the vinyl-based silane coupling agent, for example, after dispersing silica fine particles having a vinyl-based polymer film obtained in the step (B) in a polar solvent, radical polymerization is started. For example, a method of adding an agent and a vinyl silane coupling agent to perform polymerization may be used. At this time, if necessary, a dispersion stabilizer may be used.

The polar solvent, radical polymerization initiator and dispersion stabilizer used in this step (C) can be the same as those exemplified in the description of step (B). The method of dispersing the silica fine particles having a vinyl polymer coating in a polar solvent is the same as in the case of the step B. The amount of the radical polymerization initiator to be added is preferably from 1 to 500 mol%, more preferably from 1 to 300 mol%, based on the amount of the monomer mixture.

The polymerization of the vinyl silane coupling agent in the step (C) is generally carried out by stirring for about 1 to 24 hours while maintaining the temperature at about 20 to 80 ° C.

Thus, a coating layer made of the vinyl silane coupling agent polymer is formed on the vinyl polymer coating. At this time, as described above, it is considered that the vinyl-based silane coupling agent is grafted to the vinyl group remaining in the vinyl-based polymer film to form a carbon-carbon bond. The thickness of the coating layer made of the coupling agent polymer is appropriately selected depending on the desired thickness of the coating layer made of the polymer having a siloxane bond formed in the next step (D). It can be controlled by appropriately changing the concentration of the vinyl silane coupling agent, the concentration of the radical polymerization initiator, the polymerization time, and the like.

Step (D) In the step (D), the step (C) is performed as described above.
This is a step of hydrolyzing the coating layer formed of the coupling agent polymer formed on the vinyl polymer film. By this hydrolysis treatment, a hydrophilic substituent (eg, an alkoxyl group) in the coupling agent polymer is hydrolyzed, and a network-like siloxane bond is formed by a dehydration / condensation reaction. The coating layer formed of the union becomes a coating layer formed of a polymer having a siloxane bond. At this time, it is not necessary that all of the hydrophilic substituents in the coating layer made of the coupling agent polymer are hydrolyzed to form a siloxane bond, and even if only a part thereof is hydrolyzed to form a siloxane bond. Good.

The hydrolysis treatment in the step (D) is usually performed on the resin-coated silica fine particles having a coating layer made of the coupling agent polymer obtained in the step (C) using aqueous ammonia. , A hydrolysis treatment with a dilute aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, or the like, and then a condensation reaction is promoted with aqueous ammonia to form a siloxane bond. The amount of ammonia used for the hydrolysis is usually 10 to 5000% by weight based on the coupling agent polymer,
Preferably it is in the range of 50 to 2000% by weight. Also,
The hydrolysis, dehydration / condensation reaction is usually performed at 0 to 70 ° C, preferably 5 to 60 ° C, particularly preferably 10 to 40 ° C, and the reaction time is usually 0.1 to 50 hours, preferably 1 to 50 hours. The range is 30 hours.

After completion of the reaction, the particles were recovered according to a conventional method.
After sufficient washing, the resin-coated silica fine particles of the present invention are subjected to a drying treatment by a freeze-drying method or the like, that is, a single-layer structure or a multi-layer structure formed on the surface of the silica fine particles via a vinyl-based silane coupling agent. Resin-coated silica fine particles having a coating layer of a polymer having a siloxane bond on a vinyl polymer coating of

The resin-coated silica fine particles of the present invention thus obtained can be used as a spacer for a liquid crystal display device without performing a classification operation using a sieve or the like. It can also be suitably used as a filler for the material resin.

[0111]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 (1) Preparation of Resin-Coated Particles As spherical particles serving as cores, MPTMS (γ-methacryloxypropyltrimethoxysilane) -treated silica fine particles having a vinyl group introduced to the surface (average particle size: 5.80 μm, Coefficient of variation for particle size (hereinafter abbreviated as "CV value")
(0.9%) 30 g was prepared. The MPTMS-treated silica fine particles are subjected to a surface treatment using MPTMS and tetraethoxysilane having a molar ratio of 0.15 with respect to the MPTMS in a mixed liquid state.
It was obtained by drying for hours.

As a dispersion medium for obtaining a dispersion of the above-mentioned MPTMS-treated silica fine particles, methanol 840 is used.
of polyvinylpyrrolidone (average molecular weight 36) as a dispersion stabilizer in a mixed solution of ethylene glycol and ethylene glycol 1560 ml.
A solution in which 120 g was dissolved was prepared. Then, the above-mentioned MPTMS-treated silica fine particles were added to the above-described dispersion medium, and the mixture was dispersed well by applying ultrasonic vibration to obtain a dispersion.

6 g of 2-2'-azobisisobutyronitrile, 27 g of styrene and 0.85 g of mercaptoacetic acid were added to this dispersion, and polymerization was carried out at 65 ° with stirring. After 8 hours, 500 ml of a mixture of water and methanol (water: methanol = 8: 2 (volume ratio)) was poured into the reaction solution, and the mixture was allowed to cool. By this polymerization, a polystyrene layer was formed on the surface of the MPTMS-treated silica fine particles, and resin-coated particles were generated. Polystyrene fine particles were also generated in the system. After cooling, the resin-coated particles (MPTMS-treated silica fine particles having a polystyrene layer formed on the surface) were allowed to settle, and the upper polystyrene fine particles were removed by decantation.

400 ml of water was added to the solution after decantation.
And a mixture of methanol and 400 ml of methanol. The mixture was stirred until the settled particles were uniformly dispersed, and then the resin-coated particles were settled again. At this time, the classification was performed by a series of operations of removing the upper polystyrene fine particles by decantation. Was repeated 5 times or more. Thereafter, the dispersion medium was replaced with water, and lyophilization was performed to obtain 31 g of resin-coated particles obtained by coating the surfaces of MPTMS-treated silica fine particles with a polystyrene layer.

A scanning electron micrograph was taken of the resin-coated particles, and the particle diameter was measured from the photograph. As a result, the average particle diameter was 5.88 μm, the CV value was 1.0%, and the resin-coated particles were obtained. The particles maintained the monodispersibility of the MPTMS-treated silica fine particles used as the material. No coalescence between the particles was observed, and it was confirmed that a substantially uniform polystyrene layer was formed on each resin-coated particle. The number average molecular weight of the polystyrene forming the polystyrene layer is 5500 in terms of polystyrene by GPC (gel permeation chromatography).
Met.

(2) Preparation of resin-coated particles having a coating layer made of a polymer having a siloxane bond on the outermost layer Polyvinylpyrrolidone (trade name: K, manufactured by Wako Pure Chemical Industries, Ltd.) as a dispersion stabilizer in 750 g of methanol 15 g of the resin-coated particles prepared in the above (1) was dispersed in a solution in which 45 g of (−90, molecular weight 400,000) was dissolved using ultrasonic vibration. To this dispersion, 2,2-azobis (4-methoxy-
After adding and dissolving 15 g of (2,4-dimethylvaleronitrile), γ-methacryloxypropyltrimethoxysilane, which is a vinyl silane coupling agent, is added.
5 g was added, and the mixture was stirred at 30 ° C. for about 12 hours to perform radical polymerization.

After the completion of the reaction, 500 ml of methanol was added, and the mixture was allowed to stand still to settle resin-coated particles having a coating layer formed of a coupling agent polymer on the surface (hereinafter referred to as surface-treated resin-coated particles). Was. After sedimentation, the supernatant was removed, 300 ml of methanol was added, and the mixture was stirred to disperse the particles. Next, a series of operations of sedimentation of the surface-treated resin-coated particles and removal of the supernatant were repeated seven times to wash the surface-treated resin-coated particles.

Next, after replacing the washing solvent with 450 ml of a mixed solvent of water / methanol (5/5 by volume), 15 ml of 25% by weight aqueous ammonia was added, and the mixture was stirred at room temperature for about 10 hours to obtain a resin-coated particle surface. Was subjected to hydrolysis and condensation of the alkoxyl group in the coating layer formed of the coupling agent polymer formed in the above.

After the completion of the reaction, the particles were washed in the same manner as described above, and then lyophilized to obtain 15.5 g of resin-coated particles having a coating layer made of a polymer having a siloxane bond in the outermost layer. Was.

A scanning electron microscope photograph was taken of the resin-coated particles, and the particle diameter was measured from the photograph. As a result, the average particle diameter was 5.9 μm and the CV value was 1.0%. The thickness of the coating layer made of a polymer having a siloxane bond was 0.01 μm.

(3) Evaluation The following test was carried out on the resin-coated particles having the outermost layer obtained by the above (2) and having a coating layer comprising a polymer having a siloxane bond formed thereon, and evaluated.

(I) Liquid crystal resistance test 1 g of the resin-coated particles obtained in the above (2) was mixed with an STN type liquid crystal (ZLI-5150-075, manufactured by Merck, specific resistance:
2.1 × 10 ¹¹ Ωcm), and the container containing the mixture was sealed and left to stand in an oven at 90 ° C. for 3 days for heat treatment. Then, the specific resistance of the liquid crystal was measured. as a result,
The specific resistance of the liquid crystal after the heat treatment is 2 × 10 ¹¹ Ωcm,
There was almost no change from the original specific resistance of the STN type liquid crystal of 2.1 × 10 ¹¹ Ωcm. This indicates that the resin-coated particles have resistance to the liquid crystal and do not substantially elute components harmful to the liquid crystal, such as ions, even when in contact with the liquid crystal.

(Ii) Durability test The durability of the resin-coated particles obtained in the above (2) to the ultrasonic vibration treatment was examined as follows. First, the internal volume 2
In a 00 cc flask, 1 g of the resin-coated particles and the dispersion medium 10
0cc, put this into 50kHz frequency, 150W output
Cleaning tank (inside dimensions: 50 mm (length) x 200 mm (width) x 1) of the ultrasonic cleaner (VS150 manufactured by Inuchi Seieido Co., Ltd.)
00 mm (depth)). After this, 50kHz,
Ultrasonic treatment was performed for 15 minutes under an output condition of 150 W. At this time, a mixed solvent of a lower alcohol of methanol or 2-propanol and pure water or pure water was used as the dispersion medium, and the test was carried out by changing the dispersion medium variously. Also, the cleaning tank of the ultrasonic cleaning machine has two thirds of the cleaning tank.
Water to the height of

After the completion of the ultrasonic treatment, a predetermined number of resin-coated particles were randomly extracted and observed by a scanning electron microscope. No change was noted.

(Iii) Adhesion performance test 0.02 g of the resin-coated particles obtained in the above (2) was placed on two glass plates which had been coated with a polyimide alignment film using a dry sprayer. Sprayed. One glass plate was heat-treated in an oven at 120 ° C. for 2 hours, and the other glass plate was allowed to stand at room temperature as a control. These two glass plates were mounted on a special stand, and a nitrogen gas spray nozzle was fixed at a position of 1 cm above the upper surface of the glass plate at an angle of 45 degrees and nitrogen gas was directed toward the glass plate.
It was sprayed at a pressure of kg / cm ² for 30 seconds. After the spraying, the number of resin-coated particles on the glass plate before and after spraying with nitrogen gas was counted by an optical microscope, and the particle remaining ratio was calculated by the following equation.

Particle Residual Rate (%) = (Number of Particles after Spraying with Nitrogen Gas / Number of Particles before Spraying with Nitrogen Gas) × 100 As a result, the particle remaining rate of the heat-treated glass plate is 100
%, Which indicates that the resin-coated particles are completely fixed to the alignment substrate. On the other hand, in the glass plate of the comparative example, the particle residual ratio was 0%, and the resin-coated particles were not fixed at all.

(Iv) Evaluation in a liquid crystal cell A glass substrate (30 × 24 × 1.1 mm) with an ITO film was prepared, and a polyimide intermediate was printed on the ITO film to obtain a film.
By baking at 0 ° C. for 90 minutes, a polyimide alignment film was formed. Next, rubbing was performed on the upper and lower substrates so that the liquid crystal was twisted 240 °. An in-plane spacer (particles obtained in the present invention) is sprayed on one substrate coated with the alignment film, and the other substrate contains a one-liquid type containing a sealant (Ube Nitto Kasei Co., Ltd .: High Pressica). After printing an epoxy-based curing agent (manufactured by Mitsui Toatsu Chemicals: Struct Bond), the upper and lower substrates were bonded together. Next, this was put in an oven and the epoxy-based curing agent was cured by heating at 120 ° C. for 120 minutes. An STN liquid crystal cell was prepared by injecting a liquid crystal into the obtained cell. When the liquid crystal was injected, no movement of the in-plane spacer was observed. A liquid crystal display device using the obtained liquid crystal cell is shown in FIG.
As shown in the electron micrograph (magnification: 300 times) at the time of the lighting operation, no light leakage due to the abnormal alignment of the liquid crystal molecules at the interface between the liquid crystal molecules and the spacer for the liquid crystal display element was observed at the time of the lighting operation.

(V) Dispersibility test 0.2 g of the resin-coated particles obtained in the above (2) was ultrasonically dispersed in 20 ml of a methanol / water mixed solvent (5/5 by volume), and then stirred with a magnetic stirrer. After 30 minutes, 1 hour, and 3 hours, the dispersibility of the particles was confirmed by an optical microscope. As a result, even after stirring for 3 hours in the dispersion solvent, one particle and one particle were well dispersed, and no aggregation or the like was confirmed.

Comparative Example Resin-coated particles (MPTMS-treated silica fine particles having a polystyrene layer on the surface) were prepared in the same manner as in Example 1. When the particles were evaluated in the same manner as in Example 1,
Regarding (i) the liquid crystal resistance test and (iii) the adhesion performance test, the same results as in Example 1 were obtained without any problem, but (ii) the durability test, (iv) the evaluation in the liquid crystal cell, and (v) the dispersion In the sex test, the following results were obtained.

(Ii) Durability Test Evaluation was performed in the same manner as in Example 1, and the observation with a scanning electron microscope showed that when a dispersion medium having a high alcohol mixing ratio was used, peeling of the resin layer was partially observed. .

(Iv) Evaluation in liquid crystal cell When the liquid crystal cell was evaluated in the same manner as in Example 1, no movement of the spacer was observed at the time of injecting the liquid crystal. (Magnification: 300
As shown in (2), during the lighting operation, light leakage observed due to swelling (dissolution) of the coating resin was observed around the spacer.

(V) Dispersibility test A dispersibility test was conducted in the same manner as in Example 1. As a result, it was observed that a part of the resin-coated particles was aggregated after stirring for 3 hours in a dispersion solvent.

[0134]

The resin-coated silica fine particles of the present invention have the following excellent properties, and are suitably used as spacer particles for liquid crystal display devices. That is, in the manufacturing process of the liquid crystal display device, a coating layer made of a polymer having a siloxane bond is formed on the surface thereof even if a resin film having a low softening point is used in order to fix the spacer particles at a lower temperature. Therefore, the durability to the dispersing solvent and the liquid crystal does not decrease, and aggregation does not easily occur even when dispersed in the dispersing solvent for a long time. Furthermore, since a silanol group is present on the surface of the resin film, it is possible to introduce a functional substituent for preventing abnormal orientation, for example, starting from the silanol group.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of a liquid crystal display device obtained by using the resin-coated silica particles of the present invention obtained in Example 1 as a spacer during a lighting operation.

FIG. 2 is an electron micrograph of a liquid crystal display device obtained by using a resin-coated particle of a comparative example as a spacer.

Claims (8)

[Claims] 1. A method in which a silica polymer film having a single-layer structure or a multi-layer structure formed on a surface of a silica fine particle via a vinyl-silane coupling agent is further coated with a polymer having a siloxane bond. Characteristic resin-coated silica fine particles. 2. The resin-coated silica fine particles according to claim 1, having an average particle size of 0.6 to 17 μm and a coefficient of variation of the particle size distribution of 2% or less. 3. The resin-coated silica fine particles according to claim 1, wherein the silica fine particles are surface-treated with silicon alkoxide or a partial hydrolyzate thereof. 4. The thickness of the vinyl polymer film formed on the surface of the silica fine particles is 0.05 to 1 μm.
4. The resin-coated silica fine particles according to any one of items 1 to 3. 5. A step of surface-treating silica fine particles with a vinyl-based silane coupling agent to introduce a vinyl group onto the surface of the silica fine particles, and dispersing and polymerizing a monofunctional vinyl-based monomer to obtain surface-treated silica. Step (B) of forming a vinyl polymer film on the surface of the fine particles, comprising polymerizing the vinyl silane coupling agent to form a coupling agent polymer on the vinyl polymer film formed on the surface of the silica fine particles. A step (C) of forming a coating layer, and a step of subjecting the coating layer of a coupling agent polymer formed on the vinyl polymer coating to a hydrolysis treatment to form a coating layer of a polymer having a siloxane bond. The method for producing resin-coated silica fine particles according to any one of claims 1 to 4, wherein (D) is sequentially applied. 6. The process according to claim 5, wherein in the step (A), the calcined silica fine particles are reacted with a silicon alkoxide or a partial hydrolyzate thereof simultaneously with and / or before the surface treatment with a vinyl silane coupling agent. Method. 7. In the step (B), the dispersion polymerization of the monofunctional vinyl monomer is carried out in a polar solvent in the presence of a dispersion stabilizer, a radical polymerization initiator and a chain transfer agent.
Or the method of 6. 8. The step (B) is performed once or twice or more,
The method according to claim 5, 6 or 7, wherein a vinyl polymer film having a single-layer structure or a multi-layer structure is formed.