JP2000191706A - Production of flat fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method enabling a flat fine particle in a micron order to be produced by an easy operation. SOLUTION: This method for producing a flat fine particle comprises allowing a crosslinking monomer and a polymerization initiator to be absorbed in a polymer seed particle dispersed in water, and having 10,000-300,000 weight average molecular weight, and polymerizing the crosslinking monomer to form a polymer having different composition from the polymer seed particle. The polymer seed particle is produced by a soap-free polymerization or a dispersion polymerization. The crosslinking monomer and the polymerization initiator is added into water as an emulsion to allow the polymer seed particle to absorb them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing flat fine particles used for a spacer for a liquid crystal display device or a filler for chromatography.

[0002]

2. Description of the Related Art Fine particles having a uniform diameter on the order of microns are used as spacers for liquid crystal display elements or fillers for chromatography, and are high value-added fine particles. Conventionally, as a method for obtaining such fine particles, a method in which fine particles obtained by suspension polymerization are sieved using a dry and wet classifier has been the mainstream.

Further, Japanese Patent Publication No. 57-24369 and Japanese Patent Publication No. 5-64964 disclose a method for producing monodispersed fine particles which does not require classification. These methods are related to seed polymerization in which a relatively small particle is made to absorb a polymerizable monomer and swelled to a micron-order size, followed by polymerization, and the fine particles obtained by such a polymerization method are: In order to polymerize in the presence of oil droplets of polymerizable monomer in water, it is normal to make it spherical due to its surface tension

On the other hand, in the case of fine particles on the order of submicrons, irregularly shaped particles due to phase separation in emulsion polymerization are known, and particles such as daruma, leek, confetti, and hollow have been reported by the group of Okubo et al. [Polymer
36, P651 (1987), 8th Polymer Microsphere Symposium Lecture Abstracts P95].

[0005] These particles have characteristics such as a large surface area, a change in fluidity, a change in light reflectivity, and the like as compared with particles having a smooth surface due to their shapes. Application fields are expected to expand. But,
These particles are submicron-order particles obtained by emulsion seed polymerization, and few examples have reported micron-order particles.

[0006]

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a method capable of producing flat micron-order fine particles by an easy operation.

[0007]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object, and as a result, have found that the weight average molecular weight of the polymer seed particles to be produced is controlled and the crosslinkable monomer capable of absorbing is obtained. It has been found that by selecting the composition of the monomer, fine particles having a flat shape on the order of microns can be produced, and the present invention has been completed.

That is, according to the present invention, after a crosslinkable monomer and a polymerization initiator are absorbed in polymer seed particles having a weight average molecular weight of 300,000 or more dispersed in water, the crosslinkable monomer is polymerized, A method for producing flat fine particles, wherein a polymer having a composition different from that of the polymer seed particles is formed. Hereinafter, the present invention will be described in detail.

In the present invention, a polymer seed particle having a weight average molecular weight of 300,000 or more is used. When the weight average molecular weight is less than 300,000, phase separation with a crosslinking component to be added later does not occur, resulting in mere uniform spherical fine particles, or phase separation with the crosslinking component in some portions. Occurs, and furthermore, polymerization shrinkage occurs at that portion, resulting in porous fine particles.

The monomer used for the production of the polymer seed particles is not particularly restricted but includes, for example, styrene, α
Styrene derivatives such as -methylstyrene, p-methylstyrene, p-chlorostyrene and chloromethylstyrene; vinyl esters such as vinyl chloride, vinyl acetate and vinyl propionate; unsaturated nitriles such as acrylonitrile;
Methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylic acid
2-ethylhexyl, stearyl (meth) acrylate,
(Meth) acrylic acid ester derivatives such as ethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, pentafluoropropyl (meth) acrylate, and cyclohexyl (meth) acrylate are exemplified. These monomers may be used alone,
More than one species may be used in combination.

The above-mentioned polymer seed particles can be produced by soap-free polymerization, dispersion polymerization, emulsion polymerization, suspension polymerization, and the like. It is desirable to produce by polymerization. In these polymerization methods, it is possible to produce polymer seed particles having a CV value of a particle size distribution of 5% or less. Therefore, the flat fine particles finally produced can also be made to have high monodispersibility.

The CV value is defined by the following equation (1); CV value (%) = (σ / Dn) × 100 (1) (where σ represents the standard deviation of the particle diameter) , Dn represent the number average particle diameter). The standard deviation and the number average particle diameter are numerical values obtained by observing 300 fine particles with an electron microscope.

In the present invention, the crosslinkable monomer and the polymerization initiator are absorbed in the polymer seed particles dispersed in water, and then the crosslinkable monomer is polymerized. The crosslinkable monomer to be absorbed by the polymer seed particles is not particularly limited. For example, divinylbenzene, divinylbiphenyl, divinylnaphthalene, polyethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, Neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylol methane tri (meth) acrylate, tetramethylolpropane tetra (meth) acrylate, diallyl phthalate and its isomers, triallyl isocyanurate and its derivatives And the like. The crosslinkable monomer may be used alone,
Two or more kinds may be used in combination.

As the crosslinkable monomer to be absorbed by the polymer seed particles, in addition to the above crosslinkable monomer, for example, a monofunctional monomer or the like used in the production of the above polymer seed particles may be used. The crosslinkable monomer and the monofunctional monomer may be used in combination. However, in the production of flat fine particles, since it is necessary that phase separation and polymerization shrinkage occur, it is necessary to synthesize a polymer having a different composition from the polymer constituting the polymer seed particles. It is preferable that the crosslinkable monomer is blended in an amount of 50% by weight or more based on all monomers.

The above-mentioned polymerization initiator is not particularly limited.
For example, benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2-ethylhexanoate, di-t- Organic peroxides such as butyl peroxide;
Examples include azo compounds such as azobisisobutyronitrile, azobiscyclohexacarbonitrile, and azobis (2,4-dimethylvaleronitrile). The amount of the polymerization initiator is based on 100 parts by weight of the crosslinkable monomer.
0.1 to 10 parts by weight is preferred.

The polymer seed particles dispersed in water are:
When absorbing the crosslinking monomer and the polymerization initiator,
It is preferable that the crosslinkable monomer and the polymerization initiator are added to water as an emulsion and absorbed by the polymer seed particles. When preparing the emulsion, to the crosslinking monomer and the polymerization initiator, water and an emulsifier are added in advance, and the mixture is treated with a homogenizer, or subjected to ultrasonic treatment, or What is necessary is just to emulsify with a fine emulsifier, such as a Nanomizer.

In order to absorb the crosslinkable monomer and the polymerization initiator into the polymer seed particles, the emulsion may be mixed with an aqueous dispersion of the polymer seed particles and stirred for 1 to 24 hours. The end of the absorption can be confirmed by observing with an optical microscope.

In the above method for producing flat fine particles, a dispersion stabilizer may be used if necessary. As the dispersion stabilizer, those that are soluble in a medium can be used. As these dispersion stabilizers, for example, polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, ethyl cellulose, polyacrylic acid, polyacrylamide,
Examples thereof include a polymer soluble in a medium such as polyethylene oxide, a nonionic surfactant, and an ionic surfactant.

The amount of the crosslinkable monomer to be added during the seed polymerization is preferably 20 to 100 parts by weight based on 1 part by weight of the seed particles. If the amount of the crosslinking monomer is less than 20 parts by weight, the breaking strength of the produced crosslinked fine particles is not sufficient,
If the amount exceeds 100 parts by weight, the particle size distribution is broadened due to coalescence of the particles during seed polymerization, which is not preferable.

There are two technical points in the method for producing flat fine particles of the present invention described above. One is phase separation that occurs during seed polymerization, and the other is polymerization shrinkage that occurs when the crosslinkable monomer is polymerized.

When the composition of the polymer seed particles and the polymer of the crosslinkable monomer to be subsequently absorbed are different, phase separation occurs as the seed polymerization proceeds. The degree of the phase separation is affected by the molecular weights of the two polymers, and the larger the molecular weight of the polymer seed particles, the more significant the phase separation occurs.

When the molecular weight of the polymer seed particles is 300,000 or more, phase separation within the polymer seed particles becomes remarkable,
The phase-separated polymer gathers in one place, and the polymerization shrinkage also concentrates in one place, so that the particles become flat fine particles in which some of the particles are dented. Such flat fine particles are less likely to roll as particles, so that an improvement in adhesion can be expected, and further, when mixed into a sheet or film or dispersed in a paint, diffused light reflectance can be increased.

The molecular weight of the polymer seed particles is from 10,000 to
If it is about 300,000, phase separation occurs in some parts of the particles, and polymerization shrinkage occurs in those parts, resulting in porous fine particles having pores everywhere, and the molecular weight of the polymer seed particles is less than 10,000. In this case, phase separation does not occur between the polymer and a polymer to be formed later, resulting in true spherical particles.

[0024]

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

Example 1 Preparation of polymer seed particles A 90 parts by weight of ion-exchanged water, 10 parts by weight of styrene, and NaC
0.1 part by weight was placed in a separable flask, and a cooling tube, a stirring blade and a nitrogen introducing tube were attached to the container, and nitrogen was supplied for 1 hour to replace the polymerization atmosphere with nitrogen. Next, the stirring blade was rotated, the temperature was raised to 70 ° C., and the atmosphere was replaced with nitrogen for 1 hour. Subsequently, it was dissolved in a small amount of water.
One part by weight of potassium persulfate was poured into the system using a syringe.

Thereafter, the reaction was continued at 70 ° C. for 24 hours, and then the temperature was lowered to room temperature to stop the reaction. At the end of the reaction, the polymerization conversion was 80%. The resulting polymerization liquid was subjected to centrifugation to perform solid-liquid separation on the polymerization medium and the polymer seed particles A. Subsequently, the polymer seed particles A were washed and centrifuged twice each in the order of ethanol, a mixed medium of ethanol and water, and water to remove excess polymerization initiator, monomer, and chain transfer agent. .

Measurement of Particle Diameter The washed polymer seed particles A were dispersed in a suitable medium and deposited and fixed on a collodion film supported by a metal mesh.
This was observed using a transmission electron microscope, and a photograph of the polymer seed particles A was taken. The particle diameter of 200 to 500 arbitrary particles in the photographed photograph was measured, and the average particle diameter and the particle diameter distribution were determined. As a result, the average particle diameter Dn = 0.97
μm, CV value = 2.8%. When the molecular weight was measured using gel permeation chromatography (GPC), the weight average molecular weight Mw was 69500.
It was 0.

Preparation of Crosslinked Fine Particles 50 parts by weight of ion-exchanged water and 0.05 parts by weight of sodium lauryl sulfate were added to 0.5 parts by weight of the obtained polymer seed particles A, and the resulting mixture was uniformly dispersed. As a dispersion, 20 parts by weight of a 3% by weight aqueous solution of polyvinyl alcohol was added, and the dispersion was placed in a separable flask. Next, 5 parts by weight of divinylbenzene and benzoyl peroxide (2
0.25 parts by weight of water (containing 5% by weight), 50 parts by weight of ion-exchanged water, and 0.1 part by weight of sodium lauryl sulfate were mixed and finely dispersed and emulsified by a homogenizer. This emulsion was added to the dispersion liquid of the polymer seed particles A, and the mixture was added at 25 ° C and 100 rpm.
And the mixture was stirred for 24 hours to absorb the emulsion into the polymer seed particles A. Next, nitrogen was introduced into the system for 1 hour to perform nitrogen substitution, and then polymerization was performed at 70 ° C. for 24 hours while stirring at 200 rpm to obtain crosslinked fine particles.

After the completion of the polymerization, the polymerization liquid was subjected to centrifugal separation to perform solid-liquid separation into a polymerization medium and crosslinked fine particles. Subsequently, the crosslinked fine particles were washed and centrifuged twice each in the order of ethanol, a mixed medium of ethanol and water, and water to remove excess polymerization initiator, monomer, and surfactant. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in the case of the polymer seed particles A, and then the particle diameter and the particle distribution were measured. The results are shown in Table 1. The particle size and particle distribution of the flat particles are calculated from the observation photograph obtained using a transmission electron microscope, image analysis is performed to determine the cross-sectional area of the particles, and the average value when the particles are assumed to be true spheres. The particle size and particle size distribution were determined. 1 and 2 show photographs of the obtained crosslinked fine particles observed by a scanning electron microscope and a transmission electron microscope.

Example 2 The preparation composition of the polymer seed particles B was as follows: 90 parts by weight of ion-exchanged water and styrene 10
Parts by weight, 0.5 parts by weight of n-dodecyl mercaptan and Na
Polymer seed particles B were obtained in the same manner as in Example 1 except that Cl was 0.1 part by weight. Obtained polymer seed particles B
Means average particle diameter Dn = 0.76 μm, CV value = 3.8
%, Weight average molecular weight Mw = 354000.

Preparation of Crosslinked Fine Particles Crosslinked fine particles were obtained in the same manner as in Example 1 except that polymer seed particles B were used. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1,
The particle size and particle size distribution were measured. The results are shown in Table 1.

Example 3 Production of Polymer Seed Particle C Polyvinylpyrrolidone (weight average molecular weight: 30,000)
4 parts by weight, 0.6 parts by weight of aerosol OT (anionic surfactant manufactured by Wako Pure Chemical Industries, Ltd.), and 2,2′-azobis-2,4-dimethylvaleronitrile (V-Pure, manufactured by Wako Pure Chemical Industries, Ltd.) 65) 0.05 part by weight was dissolved in a mixture of 84 parts by weight of methanol, and 14 parts by weight of styrene was added dropwise while stirring the liquid under a nitrogen stream. After that, the system
C. and the reaction was carried out for 24 hours. After completion of the reaction, the polymer seed particles C were separated by a centrifugal separator, and washed several times with methanol. Obtained polymer seed particles C
Means average particle diameter Dn = 1.5 μm, CV value = 3.0%,
The weight average molecular weight Mw was 322,000.

Preparation of Crosslinked Fine Particles Crosslinked fine particles were obtained in the same manner as in Example 1 except that polymer seed particles C were used. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1,
The particle size and particle size distribution were measured. The results are shown in Table 1.

Example 4 The polymer seed particles A obtained in Example 1 were used as the polymer seed particles. Then, crosslinked fine particles were produced in the same manner as in Example 1 except that 3 parts by weight of divinylbenzene and 2 parts by weight of styrene were used as the crosslinkable monomer. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1, and the particle diameter and the particle distribution were measured. The results are shown in Table 1.

Example 5 Preparation of polymer seed particles D Polymer seed particles D were obtained in the same manner as in Example 1 except that 10 parts by weight of methyl methacrylate was used instead of 10 parts by weight of styrene. Obtained polymer seed particles D
Means average particle diameter Dn = 0.82 μm, CV value = 4.8
%, Weight average molecular weight Mw = 722000.

Preparation of Crosslinked Fine Particles Using polymer seed particles D, ethylene glycol methacrylate (EDM) was used instead of 5 parts by weight of divinylbenzene.
A) Crosslinked fine particles were obtained in the same manner as in Example 1 except that 5 parts by weight was used. About the obtained crosslinked fine particles, Example 1
Observation was performed using a transmission electron microscope in the same manner as in Example 2 to measure the particle size and the particle size distribution. The results are shown in Table 1.

Comparative Example 1 The preparation composition of the polymer seed particles E was as follows: 90 parts by weight of ion-exchanged water and styrene 10
Polymer seed particles F were obtained in the same manner as in Example 1 except that the parts by weight, 0.1 parts by weight of NaCl, and 0.3 parts by weight of octyl mercaptan were used. The obtained polymer seed particles F
The average particle diameter Dn was 0.74 μm, the CV value was 4.0%, and the weight average molecular weight Mw was 55,000.

Preparation of Crosslinked Fine Particles Crosslinked fine particles were obtained in the same manner as in Example 1 except that the polymer seed particles E were used. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1,
The particle size and particle size distribution were measured. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2 The composition prepared for preparing polymer seed particles F was as follows: 90 parts by weight of ion-exchanged water and styrene 10
Polymer seed particles F were obtained in the same manner as in Example 1 except that the parts by weight, 0.1 parts by weight of NaCl, and 3.0 parts by weight of octyl mercaptan were used. The obtained polymer seed particles F
The average particle diameter Dn was 0.78 μm, the CV value was 4.0%, and the weight average molecular weight Mw was 3000.

Preparation of Crosslinked Fine Particles Crosslinked fine particles were obtained in the same manner as in Example 1 except that polymer seed particles F were used. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1,
The particle size and particle size distribution were measured. The results are shown in Table 1.

Comparative Example 3 The polymer seed particles A obtained in Example 1 were used as the polymer seed particles. Then, crosslinked fine particles were produced in the same manner as in Example 1 except that 5 parts by weight of styrene was used as the crosslinkable monomer. The obtained crosslinked fine particles were observed using a transmission electron microscope in the same manner as in Example 1, and the particle diameter and the particle distribution were measured. The results are shown in Table 1.

[0042]

[Table 1]

[0043]

According to the method for producing flat fine particles of the present invention having the above-described structure, flat fine particles on the order of microns can be produced by an easy operation.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of the crosslinked fine particles obtained in Example 1.

FIG. 2 is a transmission electron micrograph of the crosslinked fine particles obtained in Example 1.

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Claims (3)

[Claims] A polymer seed particle having a weight-average molecular weight of 300,000 or more dispersed in water absorbs a crosslinkable monomer and a polymerization initiator, and then polymerizes the crosslinkable monomer. A method for producing flat fine particles, comprising forming a polymer having a different composition from particles. 2. The method for producing flat fine particles according to claim 1, wherein the polymer seed particles are produced by soap-free polymerization or dispersion polymerization. 3. The method for producing flat fine particles according to claim 1, wherein the crosslinkable monomer and the polymerization initiator are added to water as an emulsion and absorbed by the polymer seed particles.