JP2519083B2 - Method for producing polymer particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing hydrophobic polymer particles having a particle size of 1 to 20 μm and having a monodisperse particle size distribution.

(Prior Art) Polymer particles having a particle size of about 1 to 100 μm and having a uniform particle size are difficult to manufacture although there are many demands for column packing materials, various spacers, diagnostic drug carriers, etc. Met.

Conventionally, as a method for obtaining polymer particles having such a particle diameter, a fine particle polymer having a particle size of about 2 μm or less can be obtained by carefully performing a seed emulsion polymerization method. The seed emulsion polymerization method has a very slow reaction rate and is difficult to practically manufacture. Therefore, in general, when it is desired to obtain particles having a particle size of 2 μm or more, polymer particles having a particle size distribution are obtained by a suspension polymerization method, and then classified to a certain degree to narrow the particle size distribution. However, it is almost impossible to completely monodisperse the particle size by this method. Further, this method has a drawback that the yield is not good although the process is complicated and laborious. Another method for producing polymer particles having a relatively large particle size and a uniform particle size distribution is disclosed in JP-A-54-12.
There are methods disclosed in Japanese Patent No. 6288 or Japanese Patent Application Laid-Open No. 61-215604. In both of these methods, a swelling aid is absorbed in seed particles, and then a monomer component is absorbed to perform polymerization, whereby a large particle size is obtained. It is the one to get united. Both of these methods
When the polymer particles obtained contain a swelling aid and are used for various purposes, they become impurities, which is not preferable. Further, although these methods are relatively easy to obtain monodisperse large-sized fine particles, there is a problem that the steps are complicated because the seed particles have a swelling aid and a monomer and two absorption steps. There are also points.

Moreover, in recent years, a dispersion polymer (Dispersion Polymerzatio)
n. For example, see CAN.J.CHEM.vol.63,209-216 (1985))
Has been proposed to produce relatively mono-separated large-sized polymer fine particles. Generally, in the dispersion polymerization method,
A solvent as a dispersion medium, a water-soluble polymer as a dispersion stabilizer, a monomer, and a polymerization initiator soluble in the solvent are essential components. In the dispersion polymerization method, it is necessary for these mixtures to be a homogeneous solution before the initiation of polymerization. After the mixture is added to the polymerization reactor, the polymerization reactor is heated to a predetermined reaction temperature to start the polymerization reaction. The reaction system within a few minutes after the start of the reaction becomes a heterogeneous system in which a homogeneous transparent state is changed to a cloudy state. That is, precipitation of a particulate polymer occurs. After that, the precipitated polymer particles continue to grow as particles until there is no monomer in the reaction system. Although the mechanism of this dispersion polymerization has not been sufficiently clarified yet, the water-soluble polymer in the system causes hydrogen abstraction by radicals derived from the polymerization initiator generated by heat, It is considered that a polymer is precipitated by causing a graft reaction with. Therefore, the obtained particle surface is covered with the used dispersion stabilizer, and the particle surface becomes a hydrophilic surface. For example, after polymerizing a hydrophobic monomer using polyacrylic acid as a water-soluble polymer, sufficiently separating the polymer particles separated by centrifugation, and conducting conductivity titration on the polymer particles A considerable amount of carboxylic acid was detected on the surface, and the surface of the hydrophobic polymer particles became a considerable hydrophilic surface. Therefore, when the particles are applied to, for example, electrophotographic toner particles, the charge amount decreases due to the hydrophilicity of the particle surface, and the obtained image becomes thin.

(Problems to be Solved by the Invention) The inventors of the present invention have earnestly studied to obtain a hydrophobic polymer particle in which the surface of the particle is not hydrophilic by dispersion polymerization, and as a result, polymethacrylic acid was used as a dispersion stabilizer. Having a particle size of 1 μm to 20 μm and a monodisperse particle size distribution (weight average particle size / number average particle size <1.2) by polymerizing a polymerizable monomer and washing the obtained polymer particles. It was found that a hydrophobic polymer particle having the above can be obtained, and the present invention has been completed based on this finding.

(Means for Solving the Problems) Thus, according to the present invention, a hydrophobic monomer and polymethacrylic acid of 1 to 40 wt% of all monomers are dissolved in these,
The resulting polymer is dissolved in a solvent that does not dissolve, polymerization is carried out using a radical initiator soluble in the solvent to produce a particulate polymer, and the separated polymer particles are dissolved in polymethacrylic acid, A method for producing polymer particles having a particle size of 1 to 20 μm and having a monodispersed particle size is provided, which comprises washing with a solvent that does not dissolve the polymer.

The hydrophobic monomer used in the present invention means a monomer having a solubility in water of less than 1% by weight, such as styrene and α-.
Aromatic vinyl monomers such as methylstyrene, p-methylstyrene, chloromethylstyrene, halogenated styrene, and sivinylbenzene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl ( Examples are (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth) acrylic acid ester such as ethylene glycol di (meth) acrylate, and conjugated diolefins such as butadiene and isoprene. Moreover, vinyl pyridine, chrysidyl (meth) acrylate, etc. can also be used. These monomers are used alone or in combination so that the resulting polymer has a glass transition temperature of room temperature or higher.

As the organic solvent used in the present invention, a solvent that dissolves each of the polymerization components used and does not dissolve the polymer particles obtained is used. Such solvents include methyl alcohol, ethyl alcohol, propyl alcohols,
Lower alcohols such as butyl alcohol, acetone,
Ketones such as methyl ethyl ketone, heterocyclic compounds such as pyridine, pyrrole and terrahydrofuran, hydrocarbons such as n-hexane and cyclohexane, aromatic hydrocarbons such as benzene and toluene, halogenated carbonization such as methylene chloride and chloroform. Hydrogen can be illustrated. These organic solvents can be used alone or in combination of two or more. In addition, water may be optionally mixed. Lower alcohols are preferred.

As the polymerization initiator used in the present invention, a usual radical polymerization initiator soluble in the solvent used is used.
Usually, a peroxide such as benzoyl peroxide or an azo initiator such as azobisisobutyronitrile is used, but the invention is not limited thereto.

In the present invention, the polymerization reaction temperature varies depending on the kind of the polymerization initiator used, but it is usually in the range of 20 ° C to 100 ° C.

The greatest feature of the present invention is that polymethacrylic acid is used as a water-soluble polymer that is a dispersion stabilizer to carry out dispersion polymerization. Polymethacrylic acid may be obtained by polymerizing a methacrylic acid monomer prior to adding a hydrophobic monomer to the polymerization system, or by adding a prepolymerized polymethacrylic acid at the same time as the polymerization. The reaction may proceed. In the dispersion polymerization of the present invention, the mechanism of generation of polymer particles is currently unknown, but it is considered to be different from the above mechanism. That is, there is no hydrogen at the α-position, which is usually considered as the grafting point, in polymethacrylic acid. Therefore, the polymethacrylic acid and the hydrophobic monomer are not graft-copolymerized, and the polymethacrylic acid and the hydrophobic polymer particles can be separated by performing purification such as centrifugation. The surface of the polymer particles easily changes from a hydrophilic surface to a hydrophobic surface.

When a methacrylic acid monomer is polymerized to produce polymethacrylic acid prior to the polymerization of a hydrophobic monomer in the polymerization system, the time required for the polymerization depends on the amount of the monomer used, the type of the polymerization initiator and Although it depends on the amount used or the reaction temperature, it is usually 1 to 24 hours. The amount of methacrylic acid used is in the range such that the polymethacrylic acid produced is 1 to 40% by weight of the total amount of hydrophobic monomers. If it is less than 1% by weight, the polymerization stability during polymerization is deteriorated and a large amount of coagulated product is generated. If it exceeds 40% by weight, the particle size becomes small. Preferred is 5 to 30% by weight. Also, when polymethacrylic acid is added to the polymerization system at the same time as the hydrophobic monomer, the usage ratio of polymethacrylic acid is the same as above. Furthermore, in both cases, the degree of polymerization of polymethacrylic acid is
Clay measured with a B-type viscometer of a 20 wt% aqueous solution of polymethacrylic acid is in the range of 100 to 500,000 cps. Monodisperse polymer particles (weight average particle diameter / number average particle diameter <1.2
That is preferable). More preferably,
It is 50,000 to 150,000 cps.

Further, in the present invention, after the completion of the polymerization, a radical polymerization initiator and a solvent may be added to the reaction system, if necessary, to restart the polymerization. In this case, it is preferable to add 150% by weight or less of the monomer based on the amount of particles obtained by the polymerization. If it is added more than that, the added monomer forms new particles and the monodispersity of the particle diameter is impaired. More preferably, it is 100% by weight or less. The newly added monomer may be the same as or different from the previously polymerized monomer, as long as it is soluble in the solvent used.

The polymer particles thus produced are separated from the reaction system, washed with a polymethacrylic acid-soluble solvent and purified.

The washing is to remove polymethacrylic acid on the surface of the polymer particles. The solvent used is not particularly limited as long as it is a polymethacrylic acid-soluble solvent, but it is preferable to use water or an aqueous alkali solution. After washing, it is purified by a usual fine particle purification method such as centrifugal separation, dialysis using a semipermeable membrane, and ultrafiltration. In order to completely remove polymethacrylic acid, it is preferable to use a centrifugal separation method after washing. Further, in the case of performing the centrifugation method, in order to improve the solubility of polymethacrylic acid in water, it is also possible to add a base such as NaOH to the particle suspension and perform it on the alkali side.

(Effect of the invention) Thus, according to the present invention, compared with the conventionally known method for producing polymer particles having a particle size of 1 to 20 μm and having a particle size of monodisperse, a water-soluble polymer and a swelling aid 1 μm-without including impurities such as
Polymer particles having a particle size of 20 μm and a monodisperse particle size distribution can be obtained.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples. The parts and percentages in the examples are on a weight basis unless otherwise specified.

Example 1 A 2 liter reactor equipped with a stirring blade, a cooling condenser, a nitrogen gas introducing tube, and a thermometer was previously replaced with nitrogen. In this reaction vessel, ethanol 840g, distilled water 360g, methacrylic acid 1
3.3 g and 2,5-isobisisobutyronitrile (0.95 g) were added, and the mixture was stirred until a homogeneous system was obtained. Then, after bubbling with nitrogen, the reactor was heated to 70 ° C. to start the reaction and kept as it was for 6 hours. Then, 66.7 g of styrene was added to the reaction vessel, and the reaction was continued for another 16 hours. The polymerization conversion rate was 98.3% by gravimetric method. Then the reactor was cooled to room temperature. The obtained suspension was centrifuged to precipitate polymer particles, and decantation was performed to collect the polymer particles. The polymer particles were put into distilled water, sufficiently stirred, and then centrifuged. Do this twice,
The polymer particles were washed and purified. The obtained polymer particles have a particle diameter measured by Coulter Multisizer (manufactured by Coulter Co.) of 2.05 μm in weight average and 2.01 μm in number average.
The particles were spherical particles having a monodisperse particle size distribution of Also, 0.1N NaOH solution was added to 50 g of the obtained polymer particles suspended in distilled water (solid content 2 g) until the pH reached 12, and the mixture was stirred for 6 minutes, and then 0.1 N HCl solution was added to 0.5 cm ³ Conduct conductivity titration by adding every 30 seconds (Kyoto Denshi CM-117 conductivity meter),
The amount of acid on the particle surface was measured, but no acid was detected on the particle surface, and it was found that the particle surface was polystyrene and the hydrophobic surface was maintained.

Comparative Example 1 In the same reaction vessel as in Example 1, 840 g of ethanol and distilled water
360 g, acrylic acid 13.3 g, and 2,2-isobisisobutyronitrile 0.95 g were added, and the mixture was stirred until it became a homogeneous system. Then, after bubbling with nitrogen, the reactor was heated to 70 ° C. to start the reaction and kept as it was for 6 hours. Then, 66.7 g of styrene was added to the reaction vessel, and the reaction was continued for another 16 hours. The polymerization conversion rate was 98.3% by gravimetric method.
Then the reactor was cooled to room temperature. The obtained suspension was centrifuged to precipitate polymer particles, and the polymer particles were recovered by decantation. The polymer particles were put into distilled water, sufficiently stirred, and then centrifuged. This operation was performed twice to purify the polymer particles. The obtained polymer particles were spherical particles having a monodisperse particle size distribution with a weight average of 1.87 μm and a number average of 1.80 μm measured with a Coulter Multisizer (manufactured by Coulter). Also, a liquid obtained by suspending the obtained polymer particles in distilled water.
To 50g (solid content 2g), add 0.1N NaOH solution to pH 12 and stir for 6 minutes, then add 0.1N HCl solution 0.5cm ³ every 30 seconds to conduct conductivity titration (Kyoto Denshi). (CM-117 conductivity meter), the amount of acid on the surface of the particle was measured, and the acid on the surface of the particle was 1.18 meq / g of polymer. Therefore, when acrylic acid was used as the dispersion stabilizer, it was confirmed that the surface of the particles was considerably hydrophilic even when hydrophobic polystyrene particles were prepared.

Example 2 In the reaction vessel of Example 1, ethanol 1140 g, polymethacrylic acid aqueous solution (AC30H manufactured by Nippon Pure Chemical Co., solid content 20%) 30.0
g, styrene 66.7g, 2,2-azobisisobutyronitrile
0.95 g was added, and the mixture was stirred until it became a homogeneous system. Then, after bubbling with nitrogen, the reactor was heated to 70 ° C. to start the reaction, and the reaction was continued for 16 hours. The polymerization conversion rate was 96.2%. Then, the reactor was cooled to room temperature to obtain purified polymer particles. Polymer particles have a particle size
The spherical particles had a monodisperse particle size distribution with a weight average of 5.54 μm and a number average of 5.35 μm. Further, the amount of acid on the particle surface was measured by conductivity titration, but no acid was detected on the particle surface, and it was found that the particle surface was hydrophobic polystyrene.

Example 3 The system in which the polymerization was completed in Example 2 was further supplemented with 66.7 styrene.
g, 2,2-azobisisobutyronitrile 0.95 g, 1
Polymerization was continued for 0 hours. The polymerization conversion rate was 97.8%. Purified polymer particles were obtained by the same procedure as in the example. The polymer particles were spherical particles having a monodisperse particle size distribution with a weight average of 6.95 μm and a number average of 6.72 μm. Further, the amount of acid on the particle surface was measured by conductivity titration, but no acid was detected on the particle surface, and it was found that the particle surface was hydrophobic polystyrene.

Example 4 The system in which the polymerization was completed in Example 2 was further supplemented with styrene at 10.0.
g, divinylbenzene (Wako Pure Chemical Industries, purity 55%) 10.0 g,
0.50 g of 2,2-azobisisobutyronitrile was added and the polymerization reaction was continued for 10 hours. The polymerization conversion rate was 94.8%. The purified polymer particles obtained in the same manner as in Example 1 were spherical particles having a monodisperse particle size distribution with a weight average of 6.02 μm and a number average of 5.78 μm. Also, the amount of acid on the particle surface was measured by conductivity titration, but no acid was detected on the particle surface,
The particle surface was found to be hydrophobic polystyrene.
When the obtained particles were dropped into a toluene solvent, the solution became cloudy and the particles were insoluble in the toluene solvent, which confirmed that a crosslinked structure was introduced into the particles.

Claims (1)

(57) [Claims] 1. A hydrophobic monomer and 1 to 40% by weight of all monomers.
The polymethacrylic acid is dissolved in a solvent that does not dissolve the resulting polymer, and polymerization is performed using a radical initiator that is soluble in the solvent to produce a particulate polymer, which is then separated. A method for producing polymer particles having a particle size of 1 to 20 μm and having a monodisperse particle size distribution, characterized in that the polymer particles are dissolved in polymethacrylic acid and washed with a solvent that does not dissolve the polymer. .