JPH09101525A - Resin coated silica fine particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain silica fine particles having high hardness and strength as a whole which can function as a spacer for a long time when the particles are used as a spacer for a liquid crystal display device by applying a vinyl silane coupling agent on the surface of calcined silica fine particles and then forming a thermoplastic resin coating film having a single layer or multilayer structure thereon. SOLUTION: The resin-coated silica fine particles are produced by applying a silane coupling agent having vinyl groups on the surface of calcined silica fine particles and then forming a thermoplastic resin film having a single layer or multilayer structure thereon. The production method of the resin-coated silica fine particles includes the following processes (A) and (B). In the process (A), calcined silica fine particles are subjected to surface treatment with a silane coupling agent having vinyl groups so as to introduce vinyl groups to the surface of silica fine particles. In the process (B), unifunctional vinyl monomers are dispersed and polymerized in a polar solvent in the presence of a dispersion stabilizer, radical polymn. initiator and chain-moving agent to form a thermoplastic resin coating film on the surface of silica fine particles after the surface treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to resin-coated silica fine particles which can be used as spacer particles for controlling the thickness of liquid crystal of a liquid crystal display device and a method for producing the same.

[0002]

2. Description of the Related Art Liquid crystal display devices are typical of flat panel displays, and due to their low power consumption and low voltage driveability, they are used in various devices such as electronic desk calculators, televisions, computers and word processors. Widely used as a display device. 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 predetermined surface (the surface which becomes the inner wall of the liquid crystal cell) of one of the two transparent substrates is, for example, wet-spreaded to
Spacers for forming a liquid crystal layer of a desired thickness are dispersed and arranged in advance while keeping the distance (cell gap) between the transparent substrates to a predetermined value.

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 meet such requirements, there are 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, since the silica fine particle spacers disclosed in this publication are all unfired, there is a problem that they are cracked by heating or pressurizing when the sealant is cured. Furthermore, when the silica fine particles are used as a spacer for a liquid crystal display device, some of the silica fine particles move during the process of injecting liquid crystal into the liquid crystal cell, and during this movement, the alignment film is damaged and the alignment film is aligned. Spots may occur. 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 that does not substantially move after the liquid crystal cell is formed, there is a silica fine particle whose surface 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. Therefore, 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 adhesive layer and the cross-linked polymer particles that are the base material thereof are bonded by a covalent bond, so that peeling of the adhesive layer does not easily occur, and the adhesive layer is softened by heating. And shows good adhesion to the alignment substrate. Therefore, it is presumed that the liquid crystal spacer does not easily move after the liquid crystal cell is formed.

In this publication, there is an example in which unfired silica fine particles are used as the base material particles for forming the adhesion layer. In this case, since the silica fine particles themselves are not fired, the compression strength of the silica fine particles themselves is weak and the liquid crystal It is inconvenient to use as a spacer for a display device. Further, in the method described in this publication,
It is difficult to produce monodisperse resin-coated particles having a uniform resin coating on the surface without using a dispersion stabilizer and the resin-coated particles are easily aggregated in the production process.
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 in that the process for introducing the vinyl group on the surface of the crosslinked polymer particles is complicated and the manufacturing cost becomes high.

[0011]

The object of the present invention is (i)
Hardness and strength as a whole are high, and when used as a spacer for a liquid crystal display device, the function as a spacer of keeping a cell gap at a predetermined interval can be achieved for a long period of time. (Ii) By ultrasonic vibration Peeling of the resin film does not substantially occur even when dispersed in a spray liquid (alcohol aqueous solution). (Iii) It has good adhesion to the alignment substrate for liquid crystal display devices, and not only the liquid crystal itself but also the liquid crystal It is an object of the present invention to provide a resin-coated silica fine particle and a method for producing the same, which has an advantage that it does not substantially affect the orientation of the resin.

[0012]

The resin-coated silica fine particles of the present invention are thermoplastic resins having a single-layer structure or a multi-layer structure formed on the surface of calcined silica particles through a silane coupling agent having a vinyl group. It is characterized by having a coating.

Further, in the method for producing resin-coated silica fine particles of the present invention which achieves the above object, the calcined silica fine particles are surface-treated with a silane coupling agent having a vinyl group to introduce a vinyl group on the surface of the silica fine particles. Step (A); and dispersion polymerization of a monofunctional vinyl monomer in the presence of a dispersion stabilizer, a radical polymerization initiator, and a chain transfer agent in a polar solvent to form a thermoplastic resin coating on the surface of the silica fine particles surface-treated. It is characterized by including the step (B) of forming.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
What constitutes the resin-coated silica fine particles of the present invention are the baked silica fine particles, the vinyl-based silane coupling agent, and the thermoplastic resin coating. Among them, the calcined silica fine particles are the base material forming the core portion, and calcined the raw silica fine particles (uncalcined silica fine particles) obtained by the hydrolysis and polycondensation reaction of the silicon alkoxide by the so-called sol-gel method. It is obtained by The production method and properties of the calcined silica fine particles will be described in detail in the method for producing resin-coated silica fine 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 fired silica fine particles and the thermoplastic resin coating described below to form a thermoplastic resin coating having excellent adhesion on the surface of the fired silica fine particles. Explaining this point in detail, the silane portion of the vinyl-based silane coupling agent reacts with the silanol group on the surface of the fired silica fine particles to form a chemical bond, and at the same time, the vinyl group of the vinyl-based silane coupling agent changes to the thermoplastic resin coating. When the polymerization monomer is polymerized, it reacts with the unsaturated double bond in the monomer to form a chemical bond, resulting in excellent adhesion to the surface of the fine silica particles through a vinyl-based silane coupling agent as a linking agent. A thermoplastic resin coating is formed.

In the resin-coated silica fine particles of the present invention, the vinyl-based silane coupling agent, which is 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-based silane coupling agent,
A vinyl group having a silane moiety (for example, an alkoxysilane group, a halogenosilane group, an acetoxysilane group, etc.) having reactivity with a silanol group on the surface of silica fine particles and having reactivity with a monomer for forming a thermoplastic resin film is formed. Any thing can be used as long as it has it. 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 vinyl-based silane coupling agent, 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 can be mentioned.

In the resin-coated silica fine particles of the present invention,
The thermoplastic resin film constitutes an outer layer formed on the surface of the fired silica fine particles via a vinyl-based silane coupling agent. Various types of thermoplastic resin coatings can be selected depending on the purpose and application of the resin-coated silica fine particles, but the following conditions (a) have one polymerizable carbon-carbon double bond. (B) It has a functional group capable of reacting with the vinyl group of the vinyl-based silane coupling agent. It is necessary that the monofunctional monomer satisfying the above conditions is mainly obtained by polymerization. The type of monofunctional vinyl monomer will be described later.

Since it is obtained by polymerizing a monofunctional vinyl monomer, the resin coating is composed of the thermoplastic resin as described above. The thermoplastic resin here basically means a resin obtained by polymerizing only a monofunctional vinyl monomer as a monomer component, but the polyfunctional vinyl monomer is substantially crosslinked with the monofunctional vinyl monomer. Resins obtained by polymerizing a monomer mixture added to the extent not present (for example, in an amount of less than 0.5 mol% based on all monomers) are also included.

When the thermoplastic resin coating has a multi-layer structure, these plural layers may be made of the same kind of resin or different kinds of resins. Further, even when the same kind of resin is used, the composition of the vinyl monomer which is a raw material of the resin may be different.

The resin-coated silica fine particles of the present invention have the following advantages. (I) Since the core portion (base material) is formed of fine silica particles, it has high strength and hardness, and when used as a spacer for a liquid crystal display device, functions as a spacer that keeps the cell gap at a predetermined interval. Can be achieved over a long period of time.

(Ii) Since the thermoplastic resin coating is formed on the surface of the fired silica fine particles via the vinyl silane coupling agent, the adhesion between the surface of the fired silica fine particles and the resin coating 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 coating formed on the surface of the silica fine particles has a hardness lower than that of the base silica fine particles 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.

Next, preferable numerical conditions for 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.

When 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 diameter, it is necessary to use those having a large average particle diameter as the base silica particles. 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. Therefore, the upper limit of the average particle size of the resin-coated silica fine particles of the present invention is also 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 17 μm.
About.

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 thereof is preferably 1.0 to 12 μm, and particularly 1.2 to
It is preferably 10 μm.

The coefficient of variation of the particle size distribution (hereinafter referred to as "CV value") of 2% or less means that the so-called monodispersity, which is sufficient to function as a spacer for a liquid crystal display device, is satisfied. 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 resin coating in the resin-coated silica fine particles of the present invention depends on the particle diameter of the resin-coated silica fine particles, but is preferably in the range of 0.01 to 0.5 μm. If the thickness of the resin coating is less than 0.01 μm, it is difficult to obtain resin-coated silica fine particles having sufficient adhesion to the alignment substrate for the liquid crystal display device. On the other hand, when the thickness of the resin coating exceeds 0.5 μm, the resin-coated silica fine particles are likely to be fused with each other, and it becomes difficult to obtain fine particles having a CV value of 2% or less. The preferable thickness of the resin coating is 0 .. when the particle diameter of the silica fine particles is approximately 4 μm or less.
The particle size of the silica fine particles is 4
When it is more than μm, it is about 0.02 to 0.5 μm.

Next, a method for producing the resin-coated silica fine particles of the present invention will be described. The method for producing resin-coated silica fine particles of the present invention comprises a step (A) of surface-treating calcined silica fine particles with a vinyl-based silane coupling agent to introduce vinyl groups on the surfaces of the silica fine particles; and a dispersion stabilizer in a polar solvent. In the presence of a radical polymerization initiator and a chain transfer agent, the step (B) of dispersion-polymerizing a monofunctional vinyl monomer to form a thermoplastic resin film on the surface of silica fine particles is included. Hereinafter, each step will be described in detail.

Step (A) The step (A) is a step of introducing molecules (vinyl-based silane coupling agent) for connecting the fired silica fine particles and the thermoplastic resin film formed on the surface thereof to the surface of the fired silica fine particles. Is.

The calcined silica microparticles which are the base material of the resin-coated silica microparticles are substantially spherical microparticles as long as the particles are not substantially agglomerated with each other. It may be quality. In the present specification, the calcined silica fine particles have a particle strength of 7 by calcining.
It refers to one that has become 0 kgf / mm ² or more.

For the particle strength, a compressive fracture load was obtained using a micro compression tester (MCTE-200) manufactured by Shimadzu Corporation, and the volume of the mining industry of Japan was 81, 1024, 1024 (196).
It is the 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 fracture load (kgf) d: particle size (mm)

The resin-coated silica fine particles using uncalcined silica fine particles (raw silica fine particles obtained by the sol-gel method) as a base material have a particle strength of about 50 k.
It is about gf / mm ² , and the particle strength is insufficient for use as a spacer for a liquid crystal display device. That is, when resin-coated silica fine particles containing unburned silica fine particles are used as a spacer for a liquid crystal display device, deformation may occur due to pressure applied when forming a liquid crystal cell, and a uniform cell gap cannot be obtained. Inappropriate.

The average particle size of the fine particles of calcined silica as the base material may be any size as long as the desired resin-coated silica fine particles can be obtained. Although it differs depending on the case, specifically, it is 0.5 to 15 μm, preferably 0.8 to 12 μm.
m, particularly preferably in the range of 1.0 to 10 μm.
The CV value is preferably 2% or less, and particularly preferably 1.5% or less. 0.5 to 15 μm as the average particle diameter of silica fine particles
The reason why the range is preferable is that it becomes difficult to obtain resin-coated silica fine particles having a target particle diameter when the average particle diameter deviates from the above range. The reason why the CV value of the silica fine particles is preferably 2% or less is that the CV value is 2%.
When the silica fine particles exceeding the above are used as the base material (core substance), the resin-coated silica fine particles substantially satisfying the monodispersity of the particle size distribution (variability of 2% or less) required for the spacer for the liquid crystal display device are substantially used. Because you cannot get it.

The calcined silica fine particles which are the base material of the resin-coated silica fine particles of the present invention may be obtained by any method as long as they satisfy the above requirements.
Silica fine particles before firing (fine silica fine particles) are obtained by a so-called sol-gel method, and specific examples thereof include the following (a) and (b).

(A) Seed particles having a monodisperse particle size distribution are produced by the hydrolysis and polycondensation reaction 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) Silica seed particles are dispersed in a mixed solvent of alcohol and aqueous ammonia, and a silicon alkoxide is added to the dispersion to hydrolyze it, whereby silica seed particles are grown and silica particles are obtained. . At that time, the ratio So / Vo of the total surface area So of all silica seed particles in the dispersion liquid before the addition of the silicon alkoxide to the total volume Vo of the solution components in the dispersion liquid was 300 cm ² / cm ^3.
In addition to the above, the ratio S / V of the total surface area S of all the grown silica particles in the dispersion after addition of the silicon alkoxide to the total volume V of the solution components in the dispersion is 30.
0 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 silica fine particles are produced by means such as hydrolysis and dehydration / polycondensation of a silicon alkoxide in a mixed solution of water, ammonia and alcohol as described above. The unfired silica fine particles obtained as described above have silanol groups (Si-OH).
Therefore, it is relatively easy to introduce the polymerizable functional group into the surface of the silica fine particles by the silane coupling agent. However, organic substances, water, and ammonia are considerably left, and the strength and hardness are low as described above. When the unfired silica fine particles are fired at 500 to 1200 ° C., organic substances and water are volatilized, silanol groups are condensed with each other to increase siloxane bonds (Si—O—Si), and strength and hardness are increased. 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 firing temperature of silica fine particles, time, surface area of particles and the like has a wide range. 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 calcination and a reduced amount of silanol groups, which are reaction active points, are treated as they are with the vinyl-based silane coupling agent, a sufficient amount of vinyl groups are provided on the silica fine particle surface. Therefore, silica fine particles having a uniform resin coating 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 to the silica fine particle surfaces due to the reaction of the vinyl-based silane coupling agent is insufficient). , A silicon alkoxide or a partial hydrolyzate thereof is reacted with the calcined silica fine particles to introduce a silanol group on the surface of the calcined silica fine particles, thereby increasing the reaction active point with the vinyl-based silane coupling agent and increasing the required amount of vinyl. It is preferred to introduce a group. That is, by treating the fired silica fine particles having a high degree of firing with silicon alkoxide or a partial hydrolyzate thereof, it is possible to obtain a high strength / high hardness which cannot be used as a base material of a spacer for a liquid crystal display device. Pyrogenic silica fine particles can now be used advantageously as a base material.

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

Si (OR) ₄ + 4H ₂ O → Si (OH) ₄ + 4ROH Si (OH) ₄ → SiO ₂ + 2H ₂ O

The surface of the calcined silica fine particles having many siloxane bonds and the tetrahydroxysilane produced by the above hydrolysis are essentially the same component and cannot be distinguished from each other. 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 that can be used in the present invention is not particularly limited as long as it can introduce silanol groups onto the surface of the fine silica 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.

Examples of the partial hydrolyzate of silicon alkoxide include those obtained by partially hydrolyzing 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. ) Can be performed simultaneously with and / or before the surface treatment of the fired silica fine particles with a vinyl-based silane coupling agent (hereinafter referred to as “coupling agent treatment”) (that is, 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 the treatment of silicon alkoxide is
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-based silane coupling agent used in the treatment of the coupling agent in the step (A) of the method for producing resin-coated silica fine particles of the present invention means the silanol group on the surface of the silica fine particles as described above. Any reactive silane moiety (eg, alkoxysilane group, halogenosilane group, acetoxysilane group, etc.) and vinyl group reactive with the resin film forming monomer can be used. Can be used. Here, the vinyl group is understood 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 vinyl-based silane coupling agent include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, Examples thereof include vinyltris (β-methoxy) silane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, vinyltriacetoxysilane, and γ-methacryloxypropylmethyldimethoxysilane.

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

The amount of the vinyl-based silane coupling agent used is preferably 0.5 to 5 mmol / m ² per unit surface area of the fine silica particles, and more preferably 1 to 3 mmol / m ^2. preferable.

In the method for producing resin-coated silica fine particles of the present invention, the step (A) of surface-treating the silica fine particles described above with a vinyl-based silane coupling agent is first carried out. This step (A) is, for example, It can be done as follows. First, using ultrasonic vibration or the like, the calcined silica fine particles are dispersed in an alcohol solvent such as methanol, ethanol, or 2-propanol to obtain a desired dispersion liquid. The solvent at this time may be a single type of alcohol or a mixture of a plurality of types of alcohols. The weight of the alcohol solvent is preferably 5 to 30 times the weight of the fine silica particles. 2 to 30 times the weight of the calcined silica particles was added to the dispersion liquid thus obtained.
Ammonia water of 5 to 30% is added, and a vinyl-based silane coupling agent is further added. The liquid temperature of the dispersion liquid is 20 to
Stir for 1 to 24 hours while maintaining at 80 ° C. This allows
The calcined silica fine particles are surface-treated with a vinyl-based silane coupling agent, and vinyl groups are introduced on the surfaces of the calcined silica fine particles.

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

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

In the step (B), the step (A) is carried out as described above, and the fine silica particles having a vinyl group introduced on the surface are dispersed in a polar solvent by using a dispersion stabilizer.
Monofunctional vinyl monomer was added to this dispersion and dissolved,
By polymerizing the vinyl monomer in the presence of a radical polymerization initiator and a chain transfer agent, a resin film is formed on the surface of silica fine particles having a vinyl group introduced on the surface to form resin-coated silica fine particles in the reaction solution. Let Since the monofunctional vinyl monomer is basically used, the resin coating obtained is made of a thermoplastic resin.

The thermoplastic resin coating formed on the surface of the fired fine particles in the step (B) is a resin that does not elute the components even when it comes into contact with liquid crystals of nematic type, super twisted nematic (STN) type, ferroelectric type, etc. Consists of. Further, it is a monodisperse film having a substantially uniform film thickness and no aggregation of resins. Therefore, the resin-coated silica fine particles of the present invention do not adversely affect the liquid crystal itself and its orientation even when it is used as a spacer for a liquid crystal display device, so that it does not substantially cause a liquid crystal display defect.

When the resin-coated silica fine particles as described above are used as spacers for a liquid crystal display device, the resin film adheres to the substrate surface (alignment film surface) by heating. Even in the case, it does not substantially move.

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, Propylmethacrylate, butylmethacrylate, hexylmethacrylate, 2-ethylhexylmethacrylate, cyclohexylmethacrylate, β-hydroxyethylmethacrylate, β-aminoethylmethacrylate, N, N-dimethylaminoethylmethacrylate, γ-hydroxypropylmethacrylate, glycidylmethacrylate, etc., and Vinylsilane (vinyltrimethoxysilane, vinyltriethoxysilane Vinyltrimethylsilane, γ-methacryloxypropyltrimethoxysilane, etc.), and a resin made of a thermoplastic resin such as a styrene resin, an acrylic resin, or a methacrylic resin by polymerizing these monofunctional vinyl monomers. A film is formed.

As described above, the polyfunctional vinyl monomer can be used together with the monofunctional vinyl monomer in the range where crosslinking is not substantially caused.

In step (B), it is essential that dispersion polymerization is carried out in the presence of a dispersion stabilizer. By the addition of the dispersion stabilizer, silica fine particles after the resin film is formed,
That is, the coalescence of the resin-coated silica fine particles can be substantially prevented, and the polymerization of the resin coating on the surface of the silica fine particles suitably proceeds.

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

The polymerization is carried out in the presence of a so-called polar solvent or an organic solvent miscible with the polar solvent in any proportion. 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. Of these, those which dissolve the vinyl monomer but do not dissolve the resin which is a polymer thereof are appropriately selected according to the vinyl monomer to be used, and one or a plurality of them are mixed and used.

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 thermoplastic resin particles precipitated in the solvent becomes smaller, and when the resin particles adhere to the silica surface to form a film, the film should be formed in a more uniform and dense state. You can

A particularly preferable combination of polar solvents and their mixing ratio for obtaining the monodisperse resin-coated silica fine particles which is the object of the present invention are, for example, ethylene glycol: water: methanol = 20-60% by weight: 20-40.
% By weight: 20 to 40% by weight.

There is no particular limitation on the method for dispersing the surface-treated silica fine particles in a polar solvent by using a dispersion stabilizer, but for example, the desired dispersion can be obtained by the following method (a) or (b). You can

(A) First, a dispersion stabilizer is dissolved in a polar solvent to prepare a solution having a dispersion stabilizer concentration of 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 1 to 5% by weight with respect to the polar solvent.

(B) First, the silica fine particles after the surface treatment are added to the polar solvent, and the silica fine particles are dispersed by utilizing ultrasonic vibration or the like. The amount of the silica fine particles added at this time is such that the proportion of the silica fine particles in the finally obtained dispersion becomes 1 to 5% by weight with respect to the polar solvent. 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
The proportion of the dispersion stabilizer in the finally obtained dispersion is 2 to 15% by weight based on 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 dispersed in a polar solvent using the dispersion stabilizer as described above, and then the vinyl monomer and the radical polymerization are added to the dispersion. The monomer mixture is polymerized in the presence of an 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 addition amount of the radical polymerization initiator is preferably 1 to 50 mol%, particularly preferably 10 to 30 mol% with respect to the addition amount of the monomer mixture.

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

The reason why the addition of the chain transfer agent reduces the coalescence / aggregation of the resin-coated silica fine particles with each other is as follows.
(Polymer (thermoplastic resin) for the polar solvent used
Basically, the addition of a chain transfer agent shortens the polymer chain of the polymer and reduces the particle size of the precipitated thermoplastic resin. It is considered that this is because the film is formed on the surface of the silica particles in a uniform and dense state.

When the chain transfer agent is added, the number of repeating units of vinyl monomer molecules constituting the polymer chain is reduced and the length of the polymer chain is shortened. Therefore, even silica fine particles having a relatively small particle diameter can be uniformly dispersed. Various resin coatings are possible.

On the other hand, when the resin coating is applied to the silica fine particles having a relatively small particle diameter of about 3 μm or less without adding the chain transfer agent, the resin coating is not uniformly formed on the surface of the silica fine particles. Part of the coating is thick and thin. This is because the polymer obtained by polymerizing a 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. It is thought that this is because it cannot be covered.

By the way, 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 spacer at a temperature at which there is no risk of damaging the alignment film. It can be surely 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-, which are 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 step (B) is carried out after the radical polymerization initiator and the chain transfer agent are added to the polar solvent dispersion containing the silica fine particles after the coupling agent treatment and the dispersion stabilizer. The radical polymerization initiator and the chain transfer agent may be added at the same time.

The polymerization of the monofunctional vinyl monomer in the step (B) is carried out by increasing the temperature of the dispersion liquid to 20 after the addition of the monofunctional vinyl monomer, the radical polymerization initiator and the chain transfer agent.
It can be carried out by stirring the dispersion for 1 to 24 hours while maintaining at -80 ° C. By this polymerization, a desired thermoplastic resin film is formed on the surface of the silica fine particles that have been surface-treated with the above-mentioned vinyl silane coupling agent, and resin-coated silica fine particles are generated in the reaction liquid.

The thickness of the resin film formed by the polymerization reaction in 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.

Along with the polymerization of the vinyl monomer in 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 produced as a by-product in the reaction solution are removed by washing to separate the resin-coated silica fine particles of the present invention.

The desired resin-coated silica fine particles can be isolated by removing the resin fine particles as described above, replacing the washing solution with water, and then freeze-drying.

The resin-coated silica fine particles obtained by carrying out the steps (A) and (B) are as follows:
The resin film constituting this has a single-layer structure (hereinafter, referred to as “single-layer resin-coated silica fine particles”). The resin coating may have a single-layer structure or a multi-layer structure as described above. For the resin-coated silica fine particles having a resin coating having a structure of two or more layers, for example, the following step (C) is performed. Can be obtained by doing.

Step (C) First, the single-layer resin-coated silica fine particles are collected as described above, and then the single-layer resin-coated silica fine particles are dispersed in a polar solvent by using a dispersion stabilizer. A monofunctional vinyl monomer is added to the liquid and dissolved. Next, by further polymerizing the monofunctional vinyl 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 a new two-layer structure is formed in the reaction solution. Generating resin-coated silica fine particles having a resin coating on the eyes.

Then, in the same manner as described above, resin fine particles by-produced in the reaction solution are removed by washing, and new two-layer resin-coated silica fine particles are collected. As a result, it is possible to obtain the resin-coated silica fine particles having the desired thermoplastic resin coating having a multi-layer structure.

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 in forming the resin film of the first layer. 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 the step (C), when a polyhydric alcohol is used as the polar solvent, the thermoplastic resin film can be effectively formed.

Similarly, by forming a new resin coating on the outer side of the outermost thermoplastic resin coating by the dispersion polymerization method, it is possible to obtain resin-coated silica fine particles having a thermoplastic resin coating having a three-layer structure or more. .

The resin-coated silica fine particles of the present invention isolated as described above can be directly used as a spacer for a liquid crystal display device without performing a classification operation with a sieve or the like, and a filler for a resin for encapsulating a semiconductor. It can also be preferably used as a filling material for a dental material resin.

[0093]

Example 1 (1) Surface Treatment of Silica Fine Particles with Vinyl Silane Coupling Agent Monodisperse silica fine particles fired at a firing temperature of 500 ° C. (average particle size 1.80 μm, CV value 1.35%, particle strength) 98k
200 g of gf / mm ² ) was placed in a flask having an internal volume of 5 liters, and 1260 g of isopropyl alcohol was added thereto, and then silica fine particles were uniformly dispersed by utilizing ultrasonic vibration. 1260 g of methanol and 25
1000 g of wt% ammonia water was added, and the mixture was stirred at a liquid temperature of 30 ° C. for 30 minutes. In this mixed solution, 86 g (0.35 mol) of γ-methacryloxypropyltrimethoxysilane which is a vinyl-based silane coupling agent and 11.2 g (0.054) of tetraethoxysilane which is an alkoxysilane.
Mol) was added over 15 minutes. After the addition was completed, the liquid temperature of the obtained solution was raised to 60 ° C., and the surface treatment of the silica fine particles was performed while stirring the solution for 10 hours. After the completion of the surface treatment, the solution was allowed to stand to precipitate the silica particles, and the supernatant was removed to obtain precipitated particles (silica particles after the surface treatment). The particles were washed by repeating precipitation and decantation in methanol. After removing methanol, the obtained surface-treated silica particles were dried in an oven at 150 ° C. for 1 hour.
Thus, silica fine particles having a vinyl group introduced on the surface were obtained.

(2) Production of resin-coated silica fine particles 17 g of polyvinylpyrrolidone K-90 (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 400,000) which is a dispersion stabilizer, was used as a polar solvent in ethylene glycol: methanol: water = 6: 2: 2
It was dissolved in 500 ml of the mixed solution (weight ratio). To this solution, surface-treated silica fine particles 1 obtained in (1) above
0 g was added, and the silica fine particles were uniformly dispersed by utilizing ultrasonic vibration. To this dispersion liquid, 1.0 g (6.1 mmol) of 2,2-azobisisobutyronitrile was added and well stirred. 5.0 g (50.0 mmol) of methyl methacrylate, which is a monofunctional vinyl monomer, and 0.12 g (1.3 mmol) of mercaptoacetic acid, which is a chain transfer agent, were added thereto, and polymerization was carried out at 65 ° C. with stirring. It was 8
After a lapse of time, the reaction liquid was changed to water: methanol = 8: 2 (volume ratio).
The polymerization reaction was terminated by pouring the mixture into 500 ml of the above mixture.

The above mixed solution was allowed to stand as it was, to precipitate silica fine particles having a thermoplastic polymethamethyl acrylate (PMMA) coating layer on the surface. After settling, the supernatant was removed, and 500 ml of a mixed solution of methanol: water = 2: 8 (volume ratio) was added thereto, and the mixture was stirred to disperse the particles. Then, a series of operations of sedimentation of PMMA-coated silica fine particles and removal of the supernatant liquid was repeated 7 times to obtain P
The MMA-coated silica fine particles were washed to remove PMMA resin particles. After replacing the washing solvent with water, lyophilization was performed. When the PMMA-coated silica fine particles thus obtained are observed with a scanning electron microscope, there is no coalescence between individual particles, and the particle size is 1.92 μm (CV of particle size distribution).
(Value: 1.65%), PMMA uniformly coated the silica particles with a thickness of 0.06 μm.

Further, the P coating the silica particles
The number average molecular weight (Mn) of the MMA resin was 13,000 according to GPC measurement.

(3) Liquid crystal resistance test of PMMA-coated silica fine particles 1 g of PMMA-coated silica fine particles obtained in the above (2) was
STN type liquid crystal (Merck, ZLI-5150-07
5, specific resistance: 2.1 × 10 ¹¹ Ωcm) mixed with 2 cc,
The container containing this was sealed, heat-treated by leaving it in an oven at 90 ° C. for 3 days, and 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, the original specific resistance of STN type liquid crystal 2.1 × 1
Almost no change from 0 ¹¹ Ωcm. From this, it is understood that the PMMA-coated silica fine particles have resistance to the liquid crystal, and do not substantially elute a component harmful to the liquid crystal, such as an ion, when contacted with the liquid crystal.

(4) Coating durability test of PMMA-coated silica fine particles The durability of the PMMA-coated silica fine particles obtained in (2) above to ultrasonic vibration treatment was examined as follows. First, 1 g of PMMA-coated silica fine particles and 100 cc of dispersion medium were placed in a flask having an internal volume of 200 cc, and this was placed at
Cleaning tank (internal size: 50 mm) of an ultrasonic cleaner (VS150 manufactured by Inai Seieidou Co., Ltd.) with 0 kHz and an output of 150 W
It was immersed in (vertical) × 200 mm (horizontal) × 100 mm (depth)). After this, 1 at output condition of 50kHz, 150W
Ultrasonic treatment was performed for 5 minutes. 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. Further, water was filled in the cleaning tank of the ultrasonic cleaning machine to a height of 2/3 of the cleaning tank.

After the ultrasonic treatment, a predetermined number of PMMA-coated silica fine particles were randomly extracted and observed with a scanning electron microscope. As a result, no matter which dispersion medium was used, P
No change such as peeling of the PMMA coating was observed on the MMA-coated silica fine particles.

(5) Adhesion performance test on oriented substrate PMMA-coated silica fine particles obtained in the above (2) 0.02
Using a dry sprayer, g was sprayed on two glass plates which were previously coated with a polyimide alignment film.
One glass plate was heat-treated in an oven at 150 ° C. for 2 hours, and the other glass plate was allowed to stand at room temperature as a comparative control. These two glass plates are attached to a dedicated stand, the nitrogen gas blowing nozzle is fixed at a position of 1 cm above the glass plate at an angle of 45 degrees, and nitrogen gas is directed toward the glass plate at a pressure of 3 kg / cm ² . For 30 seconds. After the spraying, the number of PMMA-coated silica fine particles on the glass plate before and after spraying nitrogen gas was counted by an optical microscope, and the particle residual rate was calculated by the following formula.

Particle residual rate (%) = (number of particles after spraying nitrogen gas / number of particles before spraying nitrogen gas) × 100

As a result, it was found that the particle residual ratio of the heat-treated glass plate was 100%, and the PMMA-coated silica fine particles were completely fixed to the oriented substrate. On the other hand, in the comparative glass plate, the particle residual rate was 0%, and the PMMA-coated silica fine particles were not fixed at all.

Example 2 (1) Surface Treatment of Silica Fine Particles with Vinyl Silane Coupling Agent Average particle size 5.70 μm, C
Surface-treated silica fine particles having a vinyl group introduced on the surface were obtained in the same manner as in (1) of Example 1 except that monodispersed silica fine particles having a V value of 1.01% and a particle strength of 97 kgf / mm ² were used.

(2) Production of resin-coated silica fine particles 17 g of polyvinylpyrrolidone K-90 (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 400,000) which is a dispersion stabilizer, is used as a polar solvent in ethylene glycol: methanol: water = 2: 4: 4
It was dissolved in 750 ml of the mixed solution (weight ratio). To this solution, the surface-treated silica fine particles 2 obtained in (1) above
5 g was added, and the silica fine particles were uniformly dispersed by utilizing ultrasonic vibration. To this dispersion, 1.0 g of 2,2-azobisisobutyronitrile which is a radical polymerization initiator
(6.1 mmol) was added and well stirred. 8.0 g of methyl methacrylate, which is a monofunctional vinyl monomer
(85.0 mmol) and 0.18 g (1.95 mmol) of chain transfer agent mercaptoacetic acid were added, and 65
Polymerization was carried out while stirring at ℃. After 8 hours, the reaction solution was
500 ml of a mixture of water: methanol = 8: 2 (volume ratio)
It poured into the inside and the polymerization reaction was completed.

The above mixed solution was allowed to stand as it was, to precipitate fine silica particles having a thermoplastic polymethamethyl acrylate (PMMA) coating layer on the surface. After settling, the supernatant was removed, and 500 ml of a mixed solution of methanol: water = 2: 8 (volume ratio) was added thereto, and the mixture was stirred to disperse the particles. Then, a series of operations of sedimentation of PMMA-coated silica fine particles and removal of the supernatant liquid was repeated 7 times to obtain P
The MMA-coated silica fine particles were washed to remove PMMA resin particles. After replacing the washing solvent with water, lyophilization was performed. When the PMMA-coated silica particles thus obtained are observed by a scanning electron microscope, there is no coalescence between the individual particles and the particle diameter is 5.94 μm (CV of particle size distribution).
(Value: 1.65%), PMMA uniformly coated the silica particles with a thickness of 0.12 μm.

Further, the number average molecular weight (Mn) of the PMMA resin coating the silica fine particles was 15,000 according to GPC measurement.

(3) Liquid Crystal Resistance Test The PMMA-coated silica fine particles obtained in (2) above were subjected to a liquid crystal resistance test in the same manner as in Example 1 (3). As a result, the specific resistance of the liquid crystal after heat treatment was 1.9 ×
A 10 ¹¹ [Omega] cm, this value was hardly changed from the original specific resistance value 2.1 × 10 ¹¹ Ωcm of the STN-type liquid crystal. From this, it is understood that the PMMA-coated silica fine particles have resistance to the liquid crystal and substantially do not cause the elution of harmful components such as ions even when contacting with the liquid crystal.

(4) Coating durability test PM obtained in (2) above
A coating durability test was conducted on the MA-coated silica fine particles in the same manner as in Example 1 (4). As a result, PMMA
The particle diameter of the coated silica fine particles was 5.91 μm, the peeling of the PMMA coating due to ultrasonic irradiation was not observed, and it was revealed that the coating layer has excellent durability.

(5) Adhesion Test on Oriented Substrate The PMMA-coated silica fine particles obtained in (2) above were subjected to an adhesion test on an oriented substrate in the same manner as in (5) of Example 1. As a result, it was found that the particle residual ratio of the heat-treated glass plate was 100%, and the PMMA-coated silica fine particles were completely fixed to the oriented substrate.
On the other hand, in the comparative glass plate, the particle residual rate was 0%, and the PMMA-coated silica fine particles were not fixed at all.

Example 3 Formation of Resin Coating of Second Layer 17 g of polyvinylpyrrolidone K-90 (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 400,000) which is a dispersion stabilizer, was mixed with ethylene glycol: methanol: water as a polar solvent. = 6: 2: 2
It was dissolved in 500 ml of the mixed solution (weight ratio). To this solution, 10 g of the silica fine particles after the surface treatment obtained in (2) of Example 1 were added, and the silica fine particles were uniformly dispersed by utilizing ultrasonic vibration. To this dispersion liquid, 1.0 g (6.1 mmol) of 2,2-azobisisobutyronitrile was added and well stirred. 5.0 g (50.0 mmol) of methyl methacrylate, which is a monofunctional vinyl monomer, and 0.12 g (1.3 g) of mercaptoacetic acid, which is a chain transfer agent.
Was added and the polymerization was carried out at 65 ° C. with stirring. After 8 hours, the reaction solution was poured into 500 ml of a mixed solution of water: methanol = 8: 2 (volume ratio) to terminate the polymerization reaction.

The above mixed solution was allowed to stand as it was, to precipitate silica fine particles having a thermoplastic polymethamethyl acrylate (PMMA) coating layer on the surface. After settling, the supernatant was removed, and 500 ml of a mixed solution of methanol: water = 2: 8 (volume ratio) was added thereto, and the mixture was stirred to disperse the particles. Then, a series of operations of sedimentation of PMMA-coated silica fine particles and removal of the supernatant liquid was repeated 7 times to obtain P
The MMA-coated silica fine particles were washed to remove PMMA resin particles. After replacing the washing solvent with water, lyophilization was performed. When the PMMA-coated silica fine particles thus obtained are observed with a scanning electron microscope, there is no coalescence between the individual particles, and the particle size is 2.02 μm (CV of particle size distribution).
At a value of 1.76%), PMMA uniformly coated the silica particles with the PMMA coating of the first layer at a thickness of 0.05 μm.

Comparative Example 1 No Use of Vinyl Silane Coupling Agent In place of the vinyl silane coupling agent, methyl triethoxysilane, which is a silane coupling agent having no vinyl group, was used in place of (1) of Example 1. The surface-treated silica fine particles were prepared in the same manner as in (1). Using the obtained surface-treated silica fine particles, an attempt was made to produce PMMA-coated silica fine particles in the same manner as in Example 1 (2). When the PMMA resin coating was carried out without introducing a vinyl group on the surface of the silica fine particles, the obtained silica fine particles had an average particle size of 1.8 μm as observed by a scanning electron microscope. It was confirmed that PMMA was not coated at all.

Comparative Example 2 : No Dispersion Stabilizer [0113] In the same manner as in (1) of Example 1, 10 g of silica fine particles having a vinyl group introduced on the surface, a radical polymerization initiator 2,
2-azobisisobutyronitrile 1.0 g (6.1 mmol) and dioxane 200 g were charged into a reaction vessel,
The reaction was carried out at 70 ° C for 1.5 hours. Then, a vinyl monomer and a chain transfer agent were added dropwise to the above reaction solution in the same manner as in (2) of Example 1 except that the dispersion stabilizer was not added, and a polymerization reaction was tried. At this time, the viscosity of the reaction liquid became abnormally high 30 minutes after the dropping of the vinyl monomer and the chain transfer agent, and the reaction liquid became gel-like after 1 hour.

After polymerizing for 1 hour, the gelled reaction solution was put into a large amount of dioxane to separate the PMMA-coated silica fine particles. It had no usable monodispersity.

It is understood that when the polymerization reaction is carried out without adding the dispersion stabilizer, the particles are coalesced and agglomerated with each other, and monodisperse resin-coated silica fine particles cannot be obtained.

Comparative Example 3 : No use of chain transfer agent P was prepared in the same manner as in Example 1 except that no chain transfer agent was used.
MMA-coated silica fine particles were obtained. According to the scanning electron microscope observation, the PMMA-coated silica fine particles thus obtained have a large amount of coalescence and aggregation, and are 10% of the total number of particles.
Only some particles were observed. The particle size of the individual particles was 1.94 μm (CV value 2.41%), and the monodispersity was extremely low. The number average molecular weight (Mn) of the PMMA resin coating the silica fine particles was 144,000 as measured by GPC.

Further, the single particles were subjected to the adhesion test with respect to the oriented substrate in the same manner as in (5) of Example 1.
As a result, the residual rate of particles on the heat-treated glass plate is 80%.
It can be seen that the adhesiveness to the alignment substrate is lower than that of the PMMA-coated silica fine particles obtained in (2) of Example 1.

[0118]

The resin-coated silica fine particles of the present invention have high strength and hardness as a whole, and when used as spacers for liquid crystal display devices, they can function as spacers for a long time. Further, even when dispersed in a dispersion medium by ultrasonic vibration, peeling of the thermoplastic resin coating does not substantially occur. That is, it has durability against ultrasonic vibration. Further, it has good adhesion to the alignment substrate for the liquid crystal display device and does not substantially affect the liquid crystal itself and its alignment.

The resin-coated silica fine particles of the invention satisfy the monodispersibility of the average particle size and the particle size distribution required for the spacers for liquid crystal display devices. By producing by a method, coalescence and agglomeration of particles can be prevented from being produced as a by-product, so that there is a clear economic advantage such as an improvement in yield.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Norihiro Nakayama 2-1-1 Yabuda Nishi, Gifu City, Gifu Ube Nitto Kasei Co., Ltd. Gifu Research Institute (72) Inventor Tatsuhiko Adachi 2-1, Yabuta Nishi, Gifu City, Gifu Prefecture 1 Ube Nitto Kasei Co., Ltd. Gifu Research Center

Claims (9)

[Claims] 1. A resin-coated silica fine particle having a thermoplastic resin coating having a single-layer structure or a multi-layer structure formed on the surface of the calcined silica fine particle via a vinyl-based silane coupling agent. 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 calcined silica fine particles are surface-treated with a silicon alkoxide or a partial hydrolyzate thereof. 4. The resin-coated silica fine particles according to claim 1, wherein the resin coating formed on the surface of the silica fine particles has a thickness of 0.05 to 1 μm. 5. A step (A) of surface-treating the calcined silica fine particles with a vinyl-based silane coupling agent to introduce vinyl groups on the surface of the silica fine particles; and a dispersion stabilizer, a radical polymerization initiator and a chain in a polar solvent. In the presence of a transfer agent,
A process for producing resin-coated silica fine particles, which comprises a step (B) of forming a thermoplastic resin coating on the surface of the surface-treated silica fine particles by dispersion-polymerizing a monofunctional vinyl monomer. 6. The method according to claim 5, wherein the calcined silica fine particles are reacted with the silicon alkoxide or a partial hydrolyzate thereof at the same time and / or before the surface treatment with the vinyl-based silane coupling agent. . 7. The method according to claim 6, wherein a polyhydric alcohol is present as a polar solvent in the dispersion polymerization system. 8. The resin-coated silica fine particles produced by the method according to claim 5 or 6, wherein a monofunctional vinyl monomer is dispersed in a polar solvent in the presence of a dispersion stabilizer, a radical polymerization initiator and a chain transfer agent. A method for producing resin-coated silica fine particles having a multi-layer structure, which comprises performing step (C) of polymerizing to form a thermoplastic resin coating on the surface of the thermoplastic resin coating at least once. 9. The method according to claim 8, wherein a polyhydric alcohol is present as a polar solvent in the dispersion polymerization system.