JP2005060479A - Production method for highly monodisperse fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing highly monodisperse crosslinked fine particles having a uniform particle size and excellent in dynamic strength, by a simple polymerization reaction. <P>SOLUTION: The production method comprises causing seed particles dispersed in an aqueous dispersion medium to adsorb an ethylenically unsaturated monomer and polymerizing the monomer in the presence of an oil-soluble polymerization initiator. In the method, the ethylenically unsaturated monomer is caused to contain at least 15 wt.% monomer having at least two ethylenically unsaturated groups, then finely dispersed in water together with the oil-soluble polymerization initiator, adsorbed by the seed particles, and polymerized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing highly monodispersed fine particles having a uniform particle size by seed polymerization.

Polymer fine particles used for liquid crystal panel spacers, chromatographic fillers, diagnostic reagents and the like are required to have a uniform particle size.
Conventionally, as a method for obtaining fine particles having a uniform particle size, a method of classifying fine particles mainly obtained by suspension polymerization using a dry or wet classifier can be mentioned.
However, in such a method, the yield is remarkably lowered and the uniformity of the particle size is not sufficient.

  Furthermore, in the emulsion polymerization, it is difficult to synthesize micron order fine particles, and in the dispersion polymerization, micron order monodisperse fine particles are obtained, but it is difficult to obtain crosslinked fine particles.

  As methods for producing micron-order monodisperse crosslinked fine particles, for example, Japanese Patent Publication No. 57-24369 discloses a two-stage swelling seed polymerization method, and Japanese Patent Publication No. 5-64964 uses a nonionic compound. An improved swollen seed polymerization process has been disclosed. However, all of these methods produce uncrosslinked or crosslinked fine particles by polymerizing the monomer after diffusing the monomer into the seed particles using an auxiliary agent that promotes the movement of the monomer. However, particularly in the production of crosslinkable fine particles, there is a problem that the auxiliary agent bleeds out during the polymerization to generate porous fine particles.

Further, for example, Patent Document 1 and Patent Document 2 disclose a method of polymerizing by absorbing a monomer or an organic compound having a volume 20 to 500 times that of a low molecular weight seed latex. However, the obtained fine particles have poor particle size accuracy, and when the molecular structure of the seed latex and the absorbed material is different, phase separation occurs between each other, and voids and cracks are generated inside as the polymerization proceeds, resulting in the generated fine particles There was a problem that the mechanical strength of the material was significantly reduced.
Japanese Patent Publication No. 63-32500 Japanese Examined Patent Publication No. 4-71921

  In view of the above problems, an object of the present invention is to provide a method for producing highly monodispersed fine particles having a uniform particle size and excellent mechanical strength by a simple polymerization reaction.

  The method for producing highly monodispersed fine particles of the present invention comprises adsorbing an ethylenically unsaturated monomer on seed particles dispersed in an aqueous dispersion medium, and polymerizing in the presence of an oil-soluble polymerization initiator. As an unsaturated monomer, an ethylenically unsaturated monomer containing 15% by weight or more of a monomer having two or more ethylenically unsaturated groups in the molecule is finely dispersed in water together with an oil-soluble polymerization initiator. Then, it is absorbed into seed particles and polymerized.

  As the seed particles, polymers containing 50% by weight or more of styrene and derivatives thereof are used. In this seed particle, when the ratio of styrene and its derivative decreases, the mechanical strength of the resulting crosslinked fine particles undergoes phase separation with a monomer having two or more ethylenically unsaturated groups in the molecule added later. Is significantly reduced.

Examples of the styrene derivative include p-methylstyrene, p-chlorostyrene, p-chloromethylstyrene, and p-methoxystyrene. These may be used alone or in combination of two or more.
As components other than the styrene and derivatives thereof, (meth) acrylic acid, (meth) acrylic acid ester, butadiene and the like are used.

  When the weight average molecular weight of the seed particle is small, fine particles are likely to coalesce, and monodisperse spherical particles are not formed. When the weight average molecular weight is large, a single particle having two or more ethylenically unsaturated groups is added in a molecule added later. 10,000 to 30,000 is preferable because it causes phase separation from the monomer and mechanical strength of the resulting crosslinked fine particles is significantly reduced.

  In order to control the weight average molecular weight of the seed particles within a preferable range, a chain transfer agent may be used. The chain transfer agent is not particularly limited, and a chain transfer agent generally used in the polymerization may be used, but the chain transfer constant at 60 ° C. with respect to the monomer is 1 or less, preferably 0.5. Hereinafter, more preferably 0.2 or less is used. As a chain transfer agent used suitably, 1-methyl-4-isopropylidene-cyclohexane is mentioned, for example. The amount of the chain transfer agent is appropriately determined depending on the weight average molecular weight of the seed particles, the kind of the monomer, and the like, but usually 1 to 20 parts by weight is used with respect to 100 parts by weight of the monomer.

  The seed particles are preferably non-crosslinked particles having an average particle size of 0.1 to 10 μm and a Cv value [(standard particle size deviation / average particle size) × 100] of 10 or less. These seed particles are produced using, for example, soap-free polymerization or dispersion polymerization, but are not limited to these methods, and known techniques can be applied.

  Examples of the ethylenically unsaturated monomers include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and chloromethylstyrene; vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate. ; Unsaturated nitriles such as acrylonitrile; (meth) such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate Acrylic ester derivatives; monofunctional monomers such as conjugated dienes such as butadiene and isoprene may be mentioned, and these may be used alone or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having two or more ethylenically unsaturated groups in the molecule include divinylbenzene, ethylene oxide di (meth) acrylate, tetraethylene oxide di (meth) acrylate, and 1,6-hexanediol. Polyfunctional monomers such as diacrylate, neopentyl glycol diacrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane triacrylate, tetramethylolpropane tetra (meth) acrylate, and the like are used alone. Or two or more of them may be used in combination.

  Among the ethylenically unsaturated monomers, the proportion of the ethylenically unsaturated monomer having two or more ethylenically unsaturated groups in the molecule decreases the mechanical strength of the fine particles as it decreases. It is preferably 15% by weight or more, more preferably 30% by weight or more.

  The amount of the ethylenically unsaturated monomer added is insufficient for the cross-linking component to be reduced, resulting in insufficient mechanical strength of the generated fine particles. It is 1-20 weight part with respect to a weight part.

  Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2- Organic peroxides such as ethyl hexanoate and di-t-butyl peroxide; azobisisobutyronitrile, azobiscyclohexacarbonitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), etc. Examples include azo compounds.

  In the production method of the present invention, the above-mentioned ethylenically unsaturated monomer is finely dispersed in water together with an oil-soluble polymerization initiator to form a finely dispersed emulsion, and then seed particles dispersed in the finely dispersed emulsion and an aqueous dispersion medium ( Seed particle dispersion) is mixed, and the ethylenically unsaturated monomer and the oil-soluble polymerization initiator are adsorbed on the seed particles for polymerization.

In the polymerization step, a method in which the ethylenically unsaturated monomer is finely dispersed in water together with an oil-soluble polymerization initiator and then adsorbed onto seed particles is preferable. In order to finely disperse the ethylenically unsaturated monomer and the oil-soluble polymerization initiator, they may be finely dispersed by a homogenizer or the like, or may be finely dispersed by ultrasonic treatment, a nanomizer or a mount gaurine type fine emulsifier. .
In addition, in order to obtain a finely dispersed emulsion of both components, both components may be mixed and finely dispersed in advance, or both components may be mixed after finely dispersing each component separately.

  The particle size of the finely dispersed emulsion is preferably smaller than the particle size of the seed particles. By selecting such a particle size, the speed at which the ethylenically unsaturated monomer and the oil-soluble polymerization initiator are dissolved in water and diffused into the seed particles can be increased. When this diffusion rate becomes slow, the particle size distribution accuracy of the fine particles to be produced deteriorates.

  In order to adsorb the finely dispersed emulsion to the seed particles, the seed particle dispersion and the finely dispersed emulsion are mixed and stirred at room temperature for 1 to 12 hours, but by heating to 30 to 50 ° C. Adsorption can be promoted.

The degree of swelling of the seed particles by adsorption of the finely dispersed emulsion can be arbitrarily selected by adjusting the mixing ratio of the seed particle dispersion and the finely dispersed emulsion. Double swelling is preferred.
The degree of swelling here is defined by the volume ratio of the fine particles after swelling to the seed particles before swelling. The end of adsorption is determined by confirming the enlargement of the particle diameter by observation with an optical microscope.

In the polymerization step, the seed particles are polymerized with the finely dispersed emulsion adsorbed on the seed particles. The polymerization temperature can be appropriately selected depending on the type of ethylenically unsaturated monomer and oil-soluble polymerization initiator used, but is usually preferably 25 to 100 ° C, more preferably 50 to 90 ° C. .
The polymerization is preferably started after the ethylenically unsaturated monomer and the oil-soluble polymerization initiator are completely adsorbed on the seed particles.

  In the polymerization step, a surfactant or a polymer dispersion stabilizer may be added in order to improve the dispersion stability of the polymer fine particles. Examples of such surfactants include anionic surfactants such as sodium lauryl sulfate and sodium lauryl benzene sulfonate; and polymer dispersion stabilizers such as polyvinyl pyrrolidone, gelatin, starch, hydroxyethyl cellulose, polyvinyl ether, and polyvinyl alcohol. These may be used alone or in combination of two or more.

The surfactant or the polymer dispersion stabilizer may be added after the ethylenically unsaturated monomer and the polymerization initiator are absorbed in the seed particles, or the ethylenically unsaturated monomer and the polymerization start may be added. It may be added when the agent is finely dispersed.
By addition during fine dispersion, both stabilization during fine dispersion and dispersion stabilization during polymerization can be obtained.

  The particle diameter of the highly monodispersed fine particles obtained by the polymerization method can be freely designed according to the particle diameter of the seed particles used and the mixing ratio of the ethylenically unsaturated monomer and the seed particles. The method is suitable for producing highly monodispersed crosslinked fine particles having a particle diameter of 1 to 10 μm and a Cv value of 5 or less.

  The fine particles after polymerization can be isolated by drying after centrifugation to remove the aqueous phase, washing with water and a solvent.

  The structure of the method for producing highly monodispersed crosslinked fine particles of the present invention is as described above, and high monodispersed fine particles having a uniform particle diameter and high mechanical strength are obtained in a high yield by a simple polymerization reaction. be able to.

Next, examples of the present invention will be described.
Production of seed particles (1) Seed particles (A)
1.2 parts by weight of polyvinylpyrrolidone (weight average molecular weight 30,000), 0.57 parts by weight of an anionic surfactant (“Aerosol OT” manufactured by Wako Pure Chemical Industries, Ltd.) and 1.43 parts by weight of azobisisobutyronitrile The solution dissolved in 83.8 parts by weight was charged with 14 parts by weight of styrene under a nitrogen stream while stirring, and the temperature was raised to 70 ° C. to conduct a polymerization reaction for 24 hours to obtain a seed particle (A) dispersion. . The obtained seed particles (A) had an average particle size of 1.63 μm, a Cv value of 2.2, a weight average molecular weight (Mw) = 5,000, and a number average molecular weight (Mn) of 2,400.

(2) Seed particles (B)
In the synthesis of seed particles (A), seed particles (B) were obtained by polymerization in the same manner as seed particles (A) except that the amount of azoisobutyronitrile used was changed to 0.45 parts by weight. The obtained seed particles (B) had an average particle size of 1.6 μm, a Cv value of 2.31, Mw = 18,000, and Mn = 7,500.

(3) Seed particles (C)
In the synthesis of seed particles (A), polymerization was performed in the same manner as seed particles (A) except that the amount of azoisobutyronitrile used was changed to 2.9 parts by weight to obtain seed particles (C). The seed particles (C) thus obtained had an average particle size of 1.88 μm, a Cv value of 2.4, Mw = 2,100, and Mn = 800.

(4) Seed particles (D)
In the synthesis of seed particles (A), polymerization was performed in the same manner as seed particles (A) except that 7 parts by weight of styrene, 6 parts by weight of p-methylstyrene and 1 part by weight of acrylic acid were used instead of styrene. Seed particles (D) were obtained.
The obtained seed particles (D) had an average particle diameter of 1.65 μm, a Cv value of 2.4, Mw = 5,200, and Mn = 2,100.

(5) Seed particles (E)
In the synthesis of seed particles (A), seed particles (E) were obtained by polymerization in the same manner as seed particles (A) except that the amount of azoisobutyronitrile used was changed to 0.23 parts by weight. The obtained seed particles (E) had an average particle size of 1.58 μm, a Cv value of 2.34, Mw = 39,000, and Mn = 17,600.

(6) Seed particles (F)
In the synthesis of seed particles (A), polymerization was carried out in the same manner as seed particles (A) except that the amount of azoisobutyronitrile used was changed to 11.2 parts by weight to obtain seed particles (F). The obtained seed particles (F) had a flat particle and an average particle size could not be measured, and the Cv value was polydisperse, Mw = 800, Mn = 350.

(7) Seed particles (G)
In the synthesis of seed particles (A), seed particles (G) were obtained by polymerization in the same manner as seed particles (A) except that methyl methacrylate was used instead of styrene. The obtained seed particles (G) had an average particle diameter of 1.66 μm, a Cv value of 2.25, Mw = 5,200, and Mn = 2,100.

(7) Seed particles (H)
In the synthesis of seed particles (A), polymerization was carried out in the same manner as seed particles (A) except that 0.2 parts by weight of azoisobutyronitrile was added and 2 parts by weight of 1-methyl 4-isopropylidenecyclohexane was added. Seed particles (H) were obtained. The obtained seed particles (H) had an average particle size of 1.61 μm, a Cv value of 2.28, Mw = 26,000, and Mn = 1,200.

(Example 1)
To 5 parts by weight of the seed particles (A), 200 parts by weight of ion exchange water and 0.13 parts by weight of sodium lauryl sulfate were added and dispersed uniformly to obtain a seed particle dispersion.
Separately, 0.6 parts by weight of benzoyl peroxide was added to 40 parts by weight of an ethylenically unsaturated monomer mixture consisting of 50% by weight of styrene and 50% by weight of divinylbenzene, and the mixture was roughly dispersed with a homogenizer, and then averaged by ultrasonic treatment. It was finely dispersed and emulsified to a particle size of 0.2 μm. When the obtained emulsion was added to the seed particle dispersion and stirred at 25 ° C. and 200 rpm for 3 hours, the monomer mixture was completely absorbed by the seed particles.
Next, after adding 100 parts by weight of a 3% by weight aqueous solution of polyvinyl alcohol (“GH-17” manufactured by Nippon Synthetic Chemical Co., Ltd., saponification degree: 88 mol%) to this dispersion, 70 ° C. under nitrogen with stirring at 200 rpm. Polymerization was carried out for 12 hours to obtain a dispersion of polymer fine particles. The resulting dispersion is centrifuged to remove the polymer fine particles, washed with ion-exchanged water and ethanol three times, and then dried to obtain highly monodispersed crosslinked fine particles (yield 98%, average particle size 3.19 μm, Cv The value 2.14) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope (Olympus Optical Co., Ltd. “BX-40”) at a magnification of 1,000 times, the structure was uniform.

(Example 2)
Except that the seed particles (B) were used in place of the seed particles (A), the same as in Example 1, highly monocrosslinked fine particles (yield 98%, average particle size 3.16 μm, Cv value) 2.25) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

(Example 3)
Highly monodisperse crosslinked fine particles (yield 98%, average particle size 3.3 μm, Cv value 2) in the same manner as in Example 1 except that seed particles (C) were used instead of seed particles (A). .32) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

Example 4
Highly monodisperse crosslinked fine particles (yield 98%, average particle size 3.28 μm, Cv value 2) in the same manner as in Example 1 except that seed particles (D) were used instead of seed particles (A). .3) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

(Example 5)
Except that the amount of the ethylenically unsaturated monomer mixture composed of 50% by weight of styrene and 50% by weight of divinylbenzene was changed to 10 parts by weight, it was the same as in Example 1 except that the highly monocrosslinked fine particles (yield) 99%, average particle size 2.33 μm, Cv value 2.2). When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

(Example 6)
Highly monodisperse crosslinked fine particles (yield 97), except that the amount of the ethylenically unsaturated monomer mixture composed of 50% by weight of styrene and 50% by weight of divinylbenzene was changed to 80 parts by weight. %, Average particle size 4.1 μm, Cv value 2.09). When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

(Example 7)
Highly monodisperse crosslinked fine particles (yield 98%, average particle size 3.22 μm, Cv value 2) in the same manner as in Example 1 except that seed particles (H) were used instead of seed particles (A). .31) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, the structure was uniform.

(Comparative Example 1)
Highly monodisperse crosslinked fine particles (yield 98%, average particle size 3.14 μm, Cv value 2) in the same manner as in Example 1 except that seed particles (E) were used instead of seed particles (A). .38) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, many voids were observed.

(Comparative Example 2)
High monodisperse crosslinked fine particles were obtained in the same manner as in Example 1 except that seed particles (F) were used in place of the seed particles (A). Was not obtained.

(Comparative Example 3)
Highly monodisperse crosslinked fine particles (yield 98%, average particle size 3.23 μm, Cv value 2) in the same manner as in Example 1 except that seed particles (G) were used instead of seed particles (A). .45) was obtained. When the highly monodispersed crosslinked fine particles were observed with an optical microscope, many voids were observed.

(Comparative Example 4)
Highly monodisperse crosslinked fine particles (yield 99) in the same manner as in Example 1 except that the amount of the ethylenically unsaturated monomer mixture composed of 50% by weight of styrene and 50% by weight of divinylbenzene was changed to 4 parts by weight. %, Average particle size 1.98 μm, Cv value 2.2). When the highly monodispersed crosslinked fine particles were observed with an optical microscope, many voids were observed.

(Comparative Example 5)
Highly monodisperse crosslinked fine particles (yield 97), except that the amount of the ethylenically unsaturated monomer mixture composed of 50% by weight of styrene and 50% by weight of divinylbenzene was changed to 200 parts by weight. %, Average particle size 5.21 μm, Cv value polydispersion).

Claims (1)

  An ethylenically unsaturated monomer is adsorbed on seed particles containing 50% by weight or more of styrene having a weight average molecular weight of 1,000 to 30,000 and a derivative thereof dispersed in an aqueous dispersion medium. When polymerizing in the presence, an ethylenically unsaturated monomer containing 15% by weight or more of a monomer having two or more ethylenically unsaturated groups in the molecule is used as the ethylenically unsaturated monomer And 100 parts by weight of the ethylenically unsaturated monomer is finely dispersed in water together with an oil-soluble polymerization initiator, and then absorbed and polymerized in 5 to 100 parts by weight of seed particles. Production method.