JP2008013640A - Magnetic polymer particle, method for producing the same and aqueous dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide magnetic polymer particles dispersing magnetic powder in a polymer of ethylenically unsaturated monomers at high concentration and having good water dispersibility, to provide an aqueous dispersion using the particles and to provide a method for producing the magnetic polymer particles by which even a post-treatment of a polymerization reaction can easily be carried out and aggregation of the mutual particles can be inhibited to afford the desired particles in good yield even when the magnetic polymer particles are obtained by suspension polymerization in an aqueous medium. <P>SOLUTION: The magnetic polymer particles are composed of the magnetic powder and the polymer of the ethylenically unsaturated monomers and has the content of the magnetic powder is within the range of 2.5-50 mass%. The ethylenically unsaturated monomers contain a monomer having a hydroxy group, a monomer having a carboxy group and a hydrophobic monomer free of the hydroxy group and carboxy group. In the magnetic polymer particles, the content of the hydroxy group in the polymer without containing the magnetic powder is within the range of 0.3-5.0 mmol/g and the content of the carboxy group in the polymer is within the range of 0.005-0.5 mmol/g. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to magnetic polymer particles, a method for producing the same, and an aqueous dispersion, and more particularly, an image forming material, a magnetic fluid, a diagnostic agent and a pharmaceutical carrier, a viscosity modifier, and a resin molding, which are used particularly as an aqueous dispersion. The present invention relates to magnetic polymer particles that can be suitably used for applications such as materials, paint additives, crosslinking / curing agents, and cosmetic additives, a method for producing the same, and an aqueous dispersion.

  As the magnetic polymer particles, magnetic toners for electrostatic charge development in electrophotography are known. In addition, as a production method thereof, a method of dispersing a lipophilic magnetic powder in a polymerizable monomer and subjecting the polymerizable monomer to suspension polymerization using a hardly water-soluble inorganic powder as a suspension protective agent. (For example, refer to Patent Document 1) Or, a method of obtaining magnetic polymer particles by dispersing magnetic powder subjected to magnetization treatment and oleophilic treatment in a polymerizable monomer, and subjecting the polymerizable monomer to suspension polymerization (for example, Patent Document 2) is known. However, these methods are intended to produce a dry toner, and the obtained particles are highly hydrophobic and difficult to use as an aqueous dispersion. Furthermore, when trying to produce small particles having a number average particle size of 0.5 to 5.0 μm, the particles during polymerization are more likely to aggregate with each other. There was a problem that the dispersibility of the magnetic powder was poor.

  On the other hand, as magnetic polymer particles utilized as an aqueous dispersion, physiologically active substance fixing particles are known. For example, a magnetic powder dispersed in a hydrocarbon oil is dispersed in an organic phase containing a vinyl aromatic monomer, and this dispersion is homogeneously dispersed in an aqueous phase using a homogenizer and then polymerized. A method for obtaining magnetic polymer particles having a small particle size is disclosed (for example, see Patent Document 3). However, it is necessary to disperse nano-order magnetic particles in hydrocarbon oil in advance, and the process is complicated and expensive.

  Further, by depositing an iron compound in the presence of porous polymer particles having a specific functional group and oxidizing the iron compound, magnetic powder is introduced into the porous polymer particles, and the particle diameter is 2 μm or more. Although a method for obtaining magnetic polymer particles having a uniform diameter has been disclosed (see, for example, Patent Document 4), this method has a complicated manufacturing process and uses a large amount of a crosslinking agent such as glycidyl methacrylate. The obtained particles are highly crosslinked and cannot be applied to image forming materials that require fixing properties to paper or film.

  Also, a lipophilic-treated magnetic powder is dispersed in a hydrophobic monomer such as (meth) acrylic acid ester and styrene to prepare a monomer composition, and this monomer composition is emulsified in an aqueous phase. A suspension is obtained by dispersing, and a magnetic monomer is polymerized after adding a hydrophilic monomer such as methyl methacrylate and a hydrophilic monomer having a carboxyl group such as acrylic acid to the resulting suspension. A method for producing particles is disclosed (for example, see Patent Document 5). However, magnetic polymer particles produced by this method are limited to small particles having a particle size of 0.2 to 0.3 μm, and it has been extremely difficult to produce particles having a particle size of 0.5 μm or more. That is, in this method, since a water-soluble hydrophilic monomer is post-added in water, a hydrophilic monomer such as methacrylic acid or 2-hydroxyethyl methacrylate is used regardless of a monomer having low hydrophilicity such as methyl methacrylate. When highly hydrophilic monomers are used as the hydrophilic monomers, it is difficult for these monomers to enter the polymer particles efficiently. For this reason, particles having a particle size of 0.5 μm or more are difficult to obtain. It is difficult to obtain magnetic polymer particles having high water dispersibility because not only can not be obtained but also it is virtually impossible to introduce carboxyl groups or hydroxyl groups into the particles.

  Further, particles having a carboxyl group are known as magnetic polymer particles for fixing physiologically active substances. For example, particles obtained by suspension polymerization of a mixture of an unsaturated carboxylic acid such as (meth) acrylic acid and magnetic powder are treated with an organic base or a water-soluble solvent to increase the surface charge. A technique for fixing active substance particles is disclosed (for example, see Patent Documents 6 and 7). In this method, it is essential to treat the obtained base particles with an organic base such as ammonia or amine, but it is difficult to remove the organic base that has penetrated into the particles in the washing step after the treatment. There was a problem. Furthermore, as a result of the penetration of an organic base such as amine into the particles, the glass transition temperature (Tg) of the particles is lowered, the particles tend to aggregate, resulting in a decrease in yield, and particularly in the case of non-crosslinked particles. It was a big problem.

  Moreover, magnetic particles of immunoassay particles in which a magnetic powder such as iron oxide of 1 to 30 nm is encapsulated in a crosslinked polymer composed of styrene and glycidyl methacrylate are disclosed (for example, see Patent Document 8). These particles are obtained by emulsion polymerization using a water-soluble polymerization initiator such as potassium persulfate (KPS) and simultaneously oxidizing iron chloride in the same aqueous solution to produce iron oxide. However, the magnetic polymer particles obtained by this method are limited to small particles having a particle size of 0.05 to 0.5 μm, and it is extremely difficult to produce particles having a particle size of 0.5 μm or more.

On the other hand, a method of using a polymer having a carboxyl group as a binder resin as a magnetic paint for producing a magnetic tape is known. For example, a magnetic coating material is disclosed in which a vinyl chloride copolymer having a specific proportion of hydroxyl groups and carboxylic acid groups is used as a binder resin for magnetic powder (see, for example, Patent Document 9), but the binder resin is dissolved. Therefore, an organic solvent is required, and the coating film formed after removing the solvent is hydrophobic. Therefore, it has been difficult to produce particles with high water dispersibility using this technique.
JP-A-57-102666 JP 59-221302 A Japanese Patent Publication No. 4-3088 Japanese Patent Publication No. 5-10808 JP-A-9-208788 Japanese Patent Laid-Open No. 10-87711 JP 10-270233 A JP 2004-331953 A Japanese Patent Publication No. 4-34578

The object of the present invention is to solve the above-mentioned problems of the prior art.
That is, the present invention provides a magnetic polymer particle in which a magnetic powder is dispersed at a high concentration in a polymer of an ethylenically unsaturated monomer and has good water dispersibility, and an aqueous dispersion using the same. Objective. In addition, even when the magnetic polymer particles are obtained by suspension polymerization in an aqueous medium, the present invention allows easy post-treatment of the polymerization reaction, can suppress aggregation of the particles, and achieves desired particles with a good yield. It is an object of the present invention to provide a method for producing magnetic polymer particles capable of obtaining the above.

The above-described problems are achieved by the present invention described below. That is, the present invention
<1> Consists of magnetic powder and a polymer of ethylenically unsaturated monomer, the content of the magnetic powder is in the range of 2.5 to 50% by mass, and the ethylenically unsaturated monomer The polymer contains a monomer having a hydroxyl group, a monomer having a carboxyl group, and a hydrophobic monomer having no hydroxyl group and no carboxyl group, and the polymer does not contain magnetic powder and the amount of hydroxyl group in the polymer is 0. The magnetic polymer particles have a carboxyl group content in the range of 0.005 to 0.5 mmol / g.

<2> The magnetic polymer particle according to <1>, wherein a part or all of the carboxyl group forms a salt structure.

<3> An aqueous dispersion containing the magnetic polymer particles according to <1>.

<4> A monomer having a hydroxyl group of A part by mass, a monomer having a carboxyl group of B part by mass, and a hydrophobic monomer having no hydroxyl group and carboxyl group of C part by mass (A + B) < Disperse a mixture containing an ethylenically unsaturated monomer that satisfies the relationship C, a polymerization initiator, and a magnetic powder having a hydrophobic surface treated in an aqueous medium in which a salt is dissolved and a dispersion stabilizer is added. And a method for producing magnetic polymer particles having a step of suspension polymerization.

<5> Furthermore, it is a manufacturing method of the magnetic polymer particle as described in <4> which has the process of processing the particle | grains obtained by the said suspension polymerization with a basic compound.

<6> The magnetic polymer according to <4>, wherein the content of the hydrophobic monomer having no hydroxyl group or carboxyl group is in the range of 50.0 to 90.0% by mass in all monomer components. A method for producing particles.

<7> The method for producing magnetic polymer particles according to <4>, wherein the hydrophobizing treatment is a surface coating treatment with a coupling agent.

<8> The method for producing magnetic polymer particles according to <4>, wherein the salt is an inorganic salt.

<9> The method for producing magnetic polymer particles according to <4>, wherein the dispersion stabilizer is an inorganic powder.

  According to the present invention, it is possible to provide magnetic polymer particles in which magnetic powder is dispersed at a high concentration in a polymer of an ethylenically unsaturated monomer and has good water dispersibility, and an aqueous dispersion using the same. it can. In addition, even when the magnetic polymer particles are obtained by suspension polymerization in an aqueous medium, the present invention allows easy post-treatment of the polymerization reaction, can suppress aggregation of the particles, and achieves desired particles with a good yield. It is possible to provide a method for producing magnetic polymer particles capable of obtaining the above.

Hereinafter, the present invention will be described in detail.
<Magnetic polymer particles>
The magnetic polymer particle of the present invention comprises magnetic powder and a polymer of an ethylenically unsaturated monomer, and the content of the magnetic powder is in the range of 2.5 to 50% by mass, The ethylenically unsaturated monomer includes a monomer having a hydroxyl group, a monomer having a carboxyl group, and a hydrophobic monomer having no hydroxyl group and a carboxyl group, and the above-described heavy polymer containing no magnetic powder. The amount of hydroxyl groups in the coalescence is 0.3 to 5.0 mmol / g, and the amount of carboxyl groups is in the range of 0.005 to 0.5 mmol / g.

  The magnetic polymer particles of the present invention are particulate magnetic polymers used mainly in aqueous dispersions such as magnetic printing inks. Therefore, it can be uniformly dispersed in an aqueous medium such as water while maintaining a certain magnetic force.

  In order to obtain good dispersibility in the aqueous medium, it is effective to have a hydroxyl group and a carboxyl group on the particle surface. On the other hand, in order to improve the dispersibility of the magnetic powder in the particles, it is desirable that carboxyl groups exist in the particles. For this reason, it is preferable that the constituent components of the polymer constituting the particles have a hydroxyl group and a carboxyl group. For example, when polyester is used as the polymer, the polymer is hydrolyzed in water. Therefore, it is not appropriate.

  In the present invention, a polymer of an ethylenically unsaturated monomer is used as the polymer, and the dispersibility in an aqueous medium is determined by the copolymerization ratio of the monomer having a hydroxyl group and the monomer having a carboxyl group contained therein. From the viewpoint of the stability of the polymer particles, the optimum range of the amount of hydroxyl groups and carboxyl groups was examined. Furthermore, in the present invention, the polymer particles contain a certain amount of magnetic powder, and the range in which the hydroxyl group amount and carboxyl group amount are optimal is found from the relationship between the dispersibility in the particles and the content of the magnetic powder. It was.

  The hydroxyl group amount and carboxyl group amount in the magnetic polymer particles of the present invention vary depending on the content of the magnetic powder, and are therefore defined as the hydroxyl group amount and carboxyl group amount of the polymer component excluding the magnetic powder. It is necessary that the amount of hydroxyl group of the polymer not containing selenium is in the range of 0.3 to 5.0 mmol / g and the amount of carboxyl group is in the range of 0.005 to 0.5 mmol / g.

When the amount of the hydroxyl group is less than 0.3 mmol / g, the dispersibility of the polymer particles in the aqueous medium is deteriorated. If it exceeds 5.0 mmol / g, the swellability of the polymer particles in water increases and the operability deteriorates.
The amount of hydroxyl groups is preferably in the range of 0.4 to 4.0 mmol / g, and more preferably in the range of 0.5 to 3.0 mmol / g.

On the other hand, if the amount of carboxyl groups is less than 0.005 mmol / g, dispersibility in an aqueous medium will deteriorate even if the amount of hydroxyl groups in the polymer particles is increased. When it exceeds 0.5 mmol / g, the swellability of the polymer particles in water increases and the operability deteriorates.
The amount of carboxyl groups is preferably in the range of 0.008 to 0.3 mmol / g, and more preferably in the range of 0.01 to 0.1 mmol / g.

  The hydroxyl group amount can be determined by a general titration method. For example, a certain amount of a reagent such as pyridine solution of acetic anhydride is added to the above polymer, heated, hydrolyzed by adding water, separated into particles and supernatant by a centrifuge, and the supernatant is divided into phenolphthalein and the like. The amount of the hydroxyl group can be determined by titrating with an ethanolic potassium hydroxide solution or the like using an indicator.

On the other hand, the amount of carboxyl groups can also be determined by a general titration method. For example, a certain amount of a reagent such as an ethanol solution of potassium hydroxide is added to the above polymer to carry out a neutralization reaction, and it is separated into particles and supernatant by a centrifuge, and the supernatant containing excess potassium hydroxide is automatically titrated. The amount of carboxyl groups can be determined by titrating with an isopropanol hydrochloric acid solution or the like using an apparatus.
When the carboxyl group forms a salt structure (-COO ^- Y ⁺ : where Y ⁺ represents an alkali metal ion, an alkaline earth metal ion, or an organic cation such as ammonium), an acid such as hydrochloric acid After converting the salt into carboxylic acid, the above titration can be performed to determine the amount of carboxyl groups.
That is, the amount of carboxyl groups in the present invention refers to the amount of carboxyl groups including the carboxyl groups contributing to the salt structure when the carboxyl group forms a salt structure.

The content of the magnetic powder in the magnetic polymer particles of the present invention is in the range of 2.5 to 50% by mass, preferably in the range of 3.0 to 40% by mass, and 5.0 to 30% by mass. % Is more preferable.
If the content is less than 2.5% by mass, the necessary magnetic force may not be obtained. If it exceeds 50% by mass, uniform dispersion in the magnetic powder particles and dispersion stability of the polymer particles may not be obtained.

  In the present invention, it is preferable that the magnetic powder is uniformly dispersed in the magnetic polymer particles. In this case, it is preferable that the particle size dependence of the magnetic powder content is small (the magnetic powder content does not vary greatly depending on the particle size). Specifically, the ratio of the magnetic powder content (P mass%) of magnetic polymer particles having a number average particle diameter of 2 μm to the magnetic powder content (Q mass%) of 5 μm magnetic polymer particles (P / Q) is preferably 0.5 or more, more preferably in the range of 0.6 to 1.0. By making the content of the magnetic powder almost constant regardless of the particle size, there is an advantage that, for example, when the magnetic polymer particles are used for magnetography or the like, it becomes easier to control the developability.

  In addition, the presence state of the magnetic powder on the particle surface can be confirmed by observing the surface with an electron microscope, and in the magnetic polymer particle of the present invention, the magnetic powder protruding to the surface of all the observed polymer particles is observed. Preferably not. Also from this viewpoint, in the magnetic polymer particles in the present application, it is effectively contributed that the polymer has a carboxyl group that is effective in improving the dispersibility of the magnetic powder in addition to the hydroxyl group.

The hydroxyl group-containing polymer of the present invention is particulate, but the number average particle size is preferably 0.5 μm or more. Specifically, the range of 0.5 to 5 μm is more preferable, and the range of 1.0 to 4.0 μm is more preferable.
If the number average particle size is less than 0.5 μm, it may be difficult to handle because the particle size is too small, hydroxyl groups cannot be effectively introduced by the production method as described later, or magnetic powder may be contained. It may not be possible. Moreover, when it exceeds 5 micrometers, when it is set as an aqueous dispersion, sedimentation becomes too early and may cause inconvenience in handling. For example, when used as an image forming material, high image quality may not be obtained.

  The above number average particle diameter is obtained by taking a photograph of dry particles with an optical microscope or an electron microscope, measuring the particle diameters of 100 to 200 particles randomly selected from them, and summing them up. The value divided by the number.

The magnetic polymer particles of the present invention are excellent in water dispersibility. The water dispersibility can be evaluated by observing the particle state when the magnetic polymer particles are introduced into about 20 times the amount of water of the polymer particle mass and stirred. In this case, a glass container having an opening area of about 1 to 10 cm ² is used as the container for storing the water. In this evaluation, the magnetic polymer of the present invention is preferably well dispersed in water without stirring so that the polymer particles do not float on the water surface or deposit on the wall of the container after stirring.

In the magnetic polymer particles of the present invention, it is preferable that a part or all of the carboxyl groups present on the surface and inside of the particles form a salt structure. In the case of particles having a small amount of hydroxyl groups, the formation of a salt structure is particularly effective for water dispersibility.
Here, the salt structure means that carboxyl group hydrogen is substituted with an organic cation such as an alkali metal ion, an alkaline earth metal ion, or ammonium to form a carboxylate. In the present invention, some of the carboxyl groups in the magnetic polymer particles may form a salt structure, or all may form a salt structure, but all may form a salt structure. More preferred.

Specific contents of the magnetic powder and ethylenically unsaturated monomer used in the present invention will be described in the method for producing magnetic polymer particles of the present invention described later.
The method for producing the magnetic polymer particles of the present invention is not particularly limited, and may be produced by a dry melt-kneading pulverization method or by various wet production methods. It is preferable to produce the polymer particles by a method for producing polymer particles from the viewpoint of obtaining uniform polymer particles.

<Method for producing magnetic polymer particles>
The method for producing magnetic polymer particles of the present invention includes a monomer having a hydroxyl group of A part by mass, a monomer having a carboxyl group of B part by mass, and a hydrophobicity having no hydroxyl group and carboxyl group of C part by mass. A mixture containing an ethylenically unsaturated monomer containing a monomer satisfying the relationship of (A + B) <C, a polymerization initiator and a magnetic powder having a hydrophobic surface is dissolved in a salt and dispersed stably. Characterized in that it comprises a step of suspension polymerization in an aqueous medium to which an agent is added.

  In order to obtain the above-described magnetic polymer particles of the present invention, the present inventors have studied the production method, and as a result, mixed a hydrophobic monomer, a monomer having a hydroxyl group, and a monomer having a carboxyl group. In the case of suspension polymerization in water, it was found that the particles tend to aggregate during the polymerization, and it is difficult to obtain a polymer having a desired copolymerization ratio. The reason is that the monomer having a hydroxyl group or the monomer having a carboxyl group diffuses into water from oil droplets dispersed as a monomer mixture in water and polymerizes in water other than oil droplets. Because of that.

  When the polymer contains a hydrophobic component, the magnetic powder surface is relatively hydrophilic, so that the magnetic particles are less likely to be contained in the polymer particles. When the monomer polymerization component and the hydrophilic monomer polymerization component are phase-separated, the dispersibility of the magnetic powder tends to become non-uniform accordingly. In addition, when the amount of hydroxyl groups in the particles is small, the redispersibility of the obtained polymer particles in water tends to decrease.

  In order to solve the above problems, the present inventors have (1) the presence of the monomer mixture in the aqueous medium as stable and uniform suspended particles, and (2) the dispersibility of the magnetic powder in the monomer mixture. Improvement was attempted from four viewpoints of (3) preventing these particles from agglomerating during polymerization, and (4) suppressing aggregation of the obtained magnetic polymer particles.

  First, for (1) above, with respect to the mixing amount of the monomer, a monomer having a hydroxyl group of A part by mass, a monomer having a carboxyl group of B part by mass, a hydroxyl group of C part by mass and When using a hydrophobic monomer having no carboxyl group, it is possible to form stable suspended particles in an aqueous medium by mixing them so as to satisfy the relationship (A + B) <C. I understood it.

  In addition, (2) can be dealt with by hydrophobizing the surface of the magnetic powder. Since the surface of the magnetic powder is basically hydrophilic as described above, the affinity for the hydrophobic monomer can be increased by performing the hydrophobization treatment, and the dispersion uniformity in the particles of the magnetic powder and The content could be increased.

  Furthermore, even in the above case, in order to prevent the diffusion of the monomer (some of which may include magnetic powder) from the suspended particles into the aqueous medium, the salt is dissolved in the aqueous medium, and the salting-out effect makes it hydrophilic. The monomer mixture containing the polymerizable monomer could be preferentially arranged in the oil layer of the suspension polymerization system.

  On the other hand, for (3), it can be said that the dissolution of the salt in the aqueous medium suppresses the occurrence of emulsion polymerization that occurs during suspension polymerization, and at the same time, it has an effect on the aggregation of particles. Furthermore, it has been found that the addition of a dispersion stabilizer in the aqueous medium can suppress the aggregation of particles.

  Then, magnetic polymer particles having desired performance can be obtained only by the above (1) to (3). Further, as (4), the magnetic polymer particles obtained after polymerization are treated with a base, By converting a part or all of the carboxyl groups present in the coalesced particles into a salt structure, even when the polymer particles have a small amount of hydroxyl groups, the polymer particles after polymerization have good dispersibility in water and agglomerate. Was found to be more suppressed.

That is, in the present invention, in the ethylenically unsaturated monomer, the monomer having a hydroxyl group, the adjustment of the mixing amount of the monomer having a carboxyl group and the hydrophobic monomer, the hydrophobic treatment on the surface of the magnetic powder, the aqueous Only when the four conditions of dissolution of the salt in the medium and addition of the dispersion stabilizer are satisfied, the effects (1) to (3) are exhibited, and the hydrophilic monomer, the hydrophobic monomer, and the magnetic powder. Stable polymerization reaction in suspended particles containing H 2 O in a uniform state became possible. Furthermore, it became possible to significantly improve the dispersibility in water by treating the obtained polymer particles with a base.
By doing so, it was possible to easily and magnetically produce magnetic polymer particles in which magnetic powder was uniformly dispersed at a desired content.

  Hereinafter, the production method of the hydroxyl group-containing magnetic polymer particles of the present invention will be described in detail. In addition, the ethylenically unsaturated monomer in this invention means the monomer which has ethylenically unsaturated groups, such as a vinyl group. And the monomer which has the following hydroxyl group, the monomer which has a carboxyl group, and the hydrophobic monomer which does not have a hydroxyl group and a carboxyl group are contained in the ethylenically unsaturated monomer in this invention.

(Process for mixing monomers, etc.)
-Monomer having a hydroxyl group-
Examples of the monomer having a hydroxyl group used in the present invention include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, glycerin di (meth) acrylate, 1 , 6-bis (3-acryloxy-2-hydroxypropyl) -hexyl ether, pentaerythritol tri (meth) acrylate, tris- (2-hydroxyethyl) isocyanuric acid ester (meth) acrylate, polyethylene glycol (meth) acrylate, etc. Can be mentioned.
Here, the (meth) acrylate is an expression representing acrylate or methacrylate, and the same applies hereinafter.

  Among these, it is possible to use at least one selected from 2-hydroxyethyl (meth) acrylate and polyethylene glycol (meth) acrylate, to control the copolymerization ratio with the hydrophobic monomer described later, and to control the polymerization reaction From the viewpoint of properties and the like.

-Monomer having a carboxyl group-
Examples of the monomer having a carboxyl group used in the present invention include acrylic acid, methacrylic acid, methacryloxyethyl monophthalate, methacryloxyethyl monomaleate, and methacryloxyethyl monosuccinate. .
Among these, methacrylooxyethyl monophthalate is used from the viewpoints of control of the copolymerization ratio with the hydrophobic monomer described later, dispersion of magnetic powder in the polymer particles, controllability of the polymerization reaction, etc. preferable.

-Hydrophobic monomer without hydroxyl and carboxyl groups-
Examples of the hydrophobic monomer having no hydroxyl group and carboxyl group include aromatic vinyl monomers such as styrene and α-methylstyrene; an alkyl group having 1 to 18 carbon atoms (more preferably 2 to 16), or (Meth) acrylic acid alkyl ester having an aralkyl group (for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth)) Acrylate, lauryl (meth) acrylate, benzyl (meth) acrylate, etc.); (meth) acrylic acid alkoxyalkyl ester having an alkylene group having 1 to 12 carbon atoms (more preferably 2 to 10) (for example, methoxymethyl (meth) ) Acrylate, methoxyethyl ( Acrylate), ethoxymethyl (meth) acrylate, ethoxyethyl (meth) acrylate, ethoxybutyl (meth) acrylate, n-butoxymethyl (meth) acrylate, n-butoxyethyl (meth) acrylate, etc.); amino group-containing (meta ) Acrylic acid ester (eg, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, etc.); acrylonitrile, ethylene, vinyl chloride, vinyl acetate and the like.

  Among these, styrene, methyl (meth) acrylate, butyl (meth) acrylate 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, ethoxybutyl (meth) acrylate, benzyl (meth) acrylate, and diethylaminoethyl (meth) acrylate Further, styrene, methyl (meth) acrylate, and butyl (meth) acrylate are particularly preferable.

The content of the monomer having a hydroxyl group and the hydrophobic monomer copolymerizable with the monomer having a carboxyl group is preferably in the range of 20 to 99% by mass in all monomer components. More preferably, it is in the range of 50 to 90% by mass.
When the content is less than 20% by mass, the amount of hydroxyl groups and carboxyl groups in the polymer is excessively increased, and uniform polymerization may not be possible even by the technique of the present invention. The hydrophilic effect due to the hydroxyl group and carboxyl group may not be obtained.

  As described above, in the present invention, a monomer having a hydroxyl group of A part by mass, a monomer having a carboxyl group of B part by mass, and a hydrophobic monomer having no hydroxyl group and carboxyl group of C part by mass When using the body, it is necessary to mix them so as to satisfy the relationship of (A + B) <C. Specifically, when the amount of the hydrophobic monomer having no hydroxyl group and no carboxyl group is 100 parts by mass (C part by mass), A + B is preferably in the range of 5 to 50 parts by mass, More preferably, the range is 30 parts by mass.

  Further, the ratio (A / B) of the amount of monomer having a hydroxyl group (A part by mass) and the amount of monomer having a carboxyl group (B part by mass) should be in the range of 1000/1 to 10/1. Preferably, the range is 1000/5 to 100/1.

-Other monomers-
If necessary, a crosslinking agent can be mixed in the reactive mixture (containing the ethylenically unsaturated monomer and the like) dispersed in the aqueous medium described later. By controlling the amount of the crosslinking agent added to the monomer mixture, the swellability with respect to water caused by hydroxyl groups and carboxyl groups can be controlled.

As a crosslinking agent to be used, a known crosslinking agent can be appropriately selected and used. Preferred examples include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, methylene bis (meth) acrylamide, Examples thereof include glycidyl (meth) acrylate and 2-([1′-methylpropylideneamino] carboxyamino) ethyl methacrylate. Among these, divinylbenzene, ethylene glycol di (meth) acrylate, and diethylene glycol di (meth) acrylate are more preferable, and divinylbenzene is particularly preferable.
As addition amount of a crosslinking agent, it is preferable that it is 0.1-100 mass parts with respect to 100 mass parts of all the monomer components, and it is more preferable that it is 0.5-50 mass parts.

  Other ethylenically unsaturated monomers include, for example, acrylamides, glycidyl (meth) acrylates, and the like. These also include monomers having a hydroxyl group and a monomer having a carboxyl group, if necessary. And can be used in addition to hydrophobic monomers.

-Magnetic powder-
As the magnetic powder, magnetite, ferrite, or the like represented by a general formula of MO · Fe ₂ O ₃ or M · Fe ₂ O ₄ exhibiting magnetism can be preferably used. Here, M is a divalent or monovalent metal ion (Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, etc.), and M can be a single metal or a plurality of metals. Examples thereof include iron-based oxides such as magnetite, γ iron oxide, Mn—Zn-based ferrite, Ni—Zn-based ferrite, Mn—Mg-based ferrite, Li-based ferrite, and Cu—Zn-based ferrite. Among these, inexpensive magnetite can be used more preferably.

Other metal oxides include Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, and Sn. Nonmagnetic metal oxides using a single metal or a plurality of metals such as Ba, Pb, and the like, and metal oxides exhibiting the above magnetism can be used. For example, as non-magnetic metal oxides, Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , V ₂ O ₅ , CrO ₂ , MnO ₂ , Fe ₂ O ₃ , CoO, NiO, CuO, ZnO, SrO, Y ₂ O ₃ , ZrO _{2 and the} like can be used.

  The average primary particle diameter of the magnetic powder before the hydrophobization treatment described later is preferably in the range of 0.02 to 2.0 μm. If the average primary particle diameter of the magnetic powder is not within the above range, the magnetic powder tends to aggregate and it may be difficult to uniformly disperse it in the polymerizable monomer.

  In the present invention, the surface of the magnetic powder needs to be hydrophobized. The method for the hydrophobizing treatment is not particularly limited, and can be performed by coating the surface of the magnetic powder with a hydrophobizing agent such as various coupling agents, silicone oils, and resins. It is preferable to perform a surface coating treatment with an agent.

Examples of the coupling agent include a silane coupling agent and a titanium coupling agent. A silane coupling agent is more preferably used, and a silane compound having a structure represented by the following general formula (1) is particularly preferable.
General formula (1): RmSiYn
(In the above formula, R represents an alkoxy group, m represents an integer of 1 to 3, Y represents a hydrocarbon group such as an alkyl group, vinyl group, glycidoxy group, and methacryl group, and n represents an integer of 1 to 3. Is shown.)

  Specifically, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, Examples include dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, phenethyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane.

_{Particularly, C p H 2p + 1 -Si-} (OC q H 2q + 1) 3 ( wherein, p represents an integer of 2 to 20, q represents. An integer of 1 to 3) alkyltrialkoxysilane coupling represented by _agents, aralkyl _{C 6 H 5 -C r H 2r} -Si- (OC s H 2s + 1) 3 ( wherein, r is an integer of 2 to 20, s is represents an integer of 1-3.) represented by It is preferable to hydrophobize the magnetic powder using a trialkoxysilane coupling agent. As used herein, “aralkyl” means a hydrocarbon group having both an aromatic structure and an aliphatic structure. That is, a substituted or unsubstituted aryl group is substituted for the hydrogen atom of the alkyl group. Examples of the aralkyl group include benzyl group, phenethyl group, α-mesityl group and the like.

When p and r in each of the above formulas are smaller than 2, the hydrophobization treatment is easy, but it is difficult to sufficiently impart hydrophobicity, and it is difficult to suppress the exposure of the magnetic powder from the polymer particles. There is a case. On the other hand, when p and r are larger than 20, the hydrophobicity is sufficient, but the coalescence between the magnetic powders increases, and it may be difficult to sufficiently disperse the magnetic powders in the polymer particles.
On the other hand, when q and s are larger than 3, the reactivity of the silane coupling agent is lowered and the hydrophobicity is not sufficiently performed.

Among the above, in particular, the use of an alkyltrialkoxysilane coupling agent represented by C _p H _{2p + 1} —Si— (OC _q H _{2q + 1} ) ₃ has improved dispersibility in the polymerizable monomer. It is preferable in obtaining.

  For example, in the case of silane coupling agent treatment, the hydrophobization treatment of the magnetic powder is a dry treatment in which the vaporized silane coupling agent is reacted with the clouded magnetic powder, or the magnetic powder in a solvent. Or by adding a silane coupling agent in a solvent and evaporating the solvent in a distillation apparatus such as a rotary evaporator. The adhering magnetic powder can be treated by a generally known method such as a method of heat treatment. Moreover, the said hydrophobization process can be used together suitably.

  The treatment amount of the hydrophobizing agent with respect to the magnetic powder in the hydrophobization treatment in the present invention is preferably in the range of 0.05 to 20 parts by mass, and in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the magnetic powder. More preferably.

  The hydrophobized magnetic powder is mixed with a mixture of the polymerizable monomer and the like as described later. The content of the magnetic powder is determined by the required magnetic force. In the present invention, the content is preferably in the range of 2.5 to 50% by mass with respect to the total amount of the polymer particle constituents, and 5 to 30. More preferably, it is in the range of mass%. When the content is less than 2.5% by mass, a sufficient magnetic force may not be obtained. When the content is more than 50% by mass, when the polymer particles are dispersed in an aqueous medium, the settling is quick in water. May get worse.

-Polymerization initiator-
Preferred examples of the polymerization initiator used in the present invention include azo polymerization initiators and peroxide initiators. Among them, oil-soluble initiators are preferable.
Examples of oil-soluble azo initiators include azobisisobutyronitrile (AIBN), 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl Examples include 2,2′-azobis (2-methylpropionate), 1,1′-azobiscyclohexane-1-carbonitrile and the like. Examples of the oil-soluble peroxide-based initiator include benzoyl peroxide, acetyl peroxide, decanoyl peroxide, lauroyl peroxide, o-methoxybenzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, Diisopropyl peroxide, di-2-ethylhexyl peroxide, acetylcyclohexylsulfonyl peroxide, t-butyl perisobutyrate, t-butyl perbivalate, t-butyl per-2-ethylhexanoate, t-butyl peroxide , T-butyl cumyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, t-butyl hydroperoxide and the like. Etc.

  Although the said polymerization initiator can be used in arbitrary quantity, it is preferable that it is the range of 0.05-10 mass parts with respect to 100 mass parts of all the monomer components, Furthermore, 0.1-5 masses Part.

-Other additives-
If necessary, an organic solvent can be added to the monomer mixture of the present invention. As the organic solvent, all organic solvents can be used in principle as long as they are hardly soluble in water and have a boiling point higher than the reaction temperature during polymerization and do not inhibit the polymerization. Examples include hydrocarbons, alcohols, ketones, ethers and the like, but are not limited thereto.
Examples of the hydrocarbons include aliphatic hydrocarbons and aromatic hydrocarbons. Aliphatic hydrocarbons include hexane, heptane, octane, dodecane, cyclohexane, decahydronaphthalene, petroleum hydrocarbons, naphthenic hydrocarbons, etc., and aromatic hydrocarbons include toluene, xylene, diethylbenzene, And dodecylbenzene.

  As said alcohol, C8-C24 (preferably 12-22) aliphatic alcohol etc. can be used, Any of acyclic aliphatic alcohol and alicyclic alcohol may be sufficient. Further, any of natural alcohol and synthetic alcohol (Ziegler alcohol, oxo alcohol, etc.) may be used. Further, the alkyl group portion may be linear or branched.

  As the acyclic aliphatic alcohol, a saturated aliphatic alcohol and an unsaturated aliphatic alcohol are used. Examples of the acyclic saturated aliphatic alcohol include isoamyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, dodecyl alcohol (lauryl alcohol), tridecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol , Nonadecyl alcohol, tetracocenyl alcohol and the like. Examples of the acyclic unsaturated aliphatic alcohol include octenyl alcohol, decenyl alcohol, dodecenyl alcohol, tridecenyl alcohol, pentadecenyl alcohol, oleyl alcohol, tetracocenyl alcohol, Examples thereof include gadreyl alcohol and linoleyl alcohol.

  As the alicyclic alcohol, monocyclic aliphatic alcohols and polycyclic aliphatic alcohols are used. Examples of monocyclic aliphatic alcohols include ethyl cyclohexyl alcohol, propyl cyclohexyl alcohol, octyl cyclohexyl alcohol, nonyl cyclohexyl alcohol, and stearyl cyclohexyl alcohol. Examples of the polycyclic aliphatic alcohol include adamantyl alcohol and dicyclohexyl alcohol.

As said ketones, a C6-C22 (preferably 7-12) aliphatic ketone, an aromatic ketone, etc. can be used, and any of an acyclic aliphatic ketone and an alicyclic ketone may be sufficient as an aliphatic ketone. . The alkyl group moiety may be linear or branched. For example, dipropyl ketone, methyl amyl ketone, methyl hexyl ketone, diisobutyl ketone and the like can be mentioned.
As the ethers, aliphatic ethers and aromatic ethers having 6 to 22 (preferably 7 to 12) carbon atoms can be used, and aliphatic ethers may be either acyclic aliphatic ethers or alicyclic ethers. . The alkyl group moiety may be linear or branched. Examples thereof include ethylene glycol dibutyl ether, methyl phenyl ether, butyl phenyl ether, diethylene glycol dibutyl ether and the like. These solvents can be used alone or in combination of several kinds.

  The magnetic polymer particles of the present invention can further contain dyes, pigments, carbon black and the like for the purpose of coloring the polymer. In that case, the additives can be included in a mixture of the monomer and the like in which the magnetic powder is dispersed, or the magnetic powder is dispersed in advance in the mixture of the magnetic powder and the monomer. And each additive dispersion treatment can be performed simultaneously.

As a mixture containing each monomer as described above, a monomer mixture is first prepared by mixing the ethylenically unsaturated monomer, the polymerization initiator, and other necessary components. The mixing method is not particularly limited.
A known method can be applied to the dispersion of the magnetic powder in the monomer mixture. That is, a dispersing machine such as a ball mill, a sand mill, an attritor, or a roll mill can be used. In the case where the monomer component is separately polymerized in advance and the magnetic powder is dispersed in the obtained polymer, a kneader such as a kneader, a Banbury mixer, or an extruder can be used.

(Step of suspending the mixture in an aqueous medium)
-Aqueous medium-
As the aqueous medium in the present invention, water or a solution obtained by adding a water-soluble organic solvent such as methanol or ethanol to water is preferably used, and water alone is particularly preferable among them. The amount of water-soluble organic solvent to be added depends on the properties of the monomer to be suspended, but is preferably 30% by mass or less, particularly preferably 10% by mass or less, based on the total solvent. When the addition amount is 30% by mass or less, the dispersion stability may be kept good in some cases.

-Salt-
In the present invention, it is an essential requirement to dissolve a salt in the aqueous medium. The reaction of emulsion polymerization is suppressed by the salting out effect, the dispersion stability of the suspended particles is obtained, and a good yield can be realized.

  As the salt to be dissolved, water-soluble inorganic or organic salts can be used. In particular, inorganic salts are preferable because the salting-out effect can be effectively exhibited. Examples of the inorganic salts include sodium chloride, potassium chloride, potassium carbonate, calcium chloride, ammonium chloride, sodium sulfate, sodium acetate, ammonium sulfate, magnesium chloride, magnesium sulfate and the like. Among these, sodium chloride, potassium chloride Potassium carbonate and calcium chloride are more preferable, and sodium chloride is particularly preferable.

The addition amount of the salt is preferably 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more with respect to the aqueous medium from the viewpoint of dispersion stability.
If the dissolution amount is less than 5% by mass, the salting-out effect may not be sufficiently obtained, and emulsion polymerization may easily occur.

-Dispersion stabilizer-
In the present invention, it is further essential that a dispersion stabilizer is present in the aqueous medium. As the dispersion stabilizer, known dispersion stabilizers can be used, but using an inorganic powder such as calcium carbonate and calcium phosphate is effective in enhancing the dispersibility of the suspended particles in the present invention, and the particles are This is preferable because aggregation of the resin can be suppressed. Moreover, it is preferable that the surface of the inorganic powder is coated with a surface modifier from the viewpoint of improving the stability of the dispersed particles. Furthermore, in addition to the inorganic powder, a surfactant such as an anionic emulsifier, a nonionic emulsifier, or a cationic emulsifier can be used in combination. However, when a surfactant is used in combination, addition of less than the critical micelle concentration is preferable.

  Although the said dispersion stabilizer can be used in arbitrary quantity, it is preferable that it is the range of 1-100 mass parts with respect to 100 mass parts of mixtures containing the said monomer, magnetic powder, etc., 2-90 masses. More preferred is the range of parts. By being 1 part by mass or more, a good dispersion state can be obtained, while by being 100 parts by mass or less, derivation of fine particles can be suppressed and the particle size distribution of suspended particles can be sharpened. There is an advantage.

A thickener may be added to the aqueous medium in the present invention for the purpose of adjusting the particle size of the suspended particles. As the thickener, polycarboxylates such as sodium carboxymethylcellulose, sodium alginate, sodium polyacrylate and the like can be added.
When these thickeners are used, the viscosity of the aqueous medium is preferably in the range of 100 to 10,000 mPa · s.

The mixture containing the monomer and the like can be suspended in an aqueous medium containing the salt and the like (hereinafter sometimes referred to as “dispersion medium”) as follows.
That is, in an aqueous medium in which the salt is dissolved and a dispersion stabilizer is present, a mixture in which a hydrophilic monomer, a hydrophobic monomer, a magnetic powder, a polymerization initiator, a crosslinking agent and the like are added, Suspend. As a suspension method, a known suspension method can be used. For example, like a mixer, a special stirring blade is rotated at a high speed to suspend monomers and the like in an aqueous medium, a method of suspending with a rotor-stator shear force known as a homogenizer, and suspension by ultrasonic waves. And mechanical suspension methods such as

In addition, it is also possible to prepare a liquid to which the above-described monomer or the like is added and suspend it using an emulsification method known as a membrane emulsification method in which the liquid is extruded from a porous membrane into an aqueous medium.
The mixing mass ratio (mixture / dispersion medium) of the suspended mixture and the dispersion medium is preferably in the range of 10/100 to 100/100, and the number average particle diameter of the suspended particles is 0. It is preferable to make it into the range of 5-5.0 micrometers.

(Process for polymerizing suspended particles)
In the present invention, polymer particles are obtained by suspension polymerization of particles containing the suspended monomer and magnetic powder. The polymerization reaction can be carried out not only in the air but also under pressure, but these other reaction conditions are applied as required and are not particularly limited.

  As the reaction conditions, for example, it is possible to carry out the reaction at a reaction temperature of 40 to 100 ° C. for 1 to 24 hours while stirring the suspension in which the suspended particles are dispersed under atmospheric pressure, in a high yield. It is preferable from the viewpoint of obtaining particles.

  Polymer particles containing magnetic powder can be obtained by the method described above. In such a production method of the present invention, an aqueous medium in which a salt is dissolved and a dispersion stabilizer mainly composed of inorganic powder is added. By dispersing the monomer mixture inside, the generation of dispersed droplets less than 0.5 μm is suppressed, so that particles with a small particle size less than 0.5 μm are hardly formed. . For this reason, the method for producing magnetic polymer particles of the present invention has not only the ease of control of the amount of hydroxyl groups and the amount of carboxyl groups, but also the number average particle size preferred as the magnetic polymer particles of the present invention is 0.00. It is also excellent in that it can be easily obtained having a thickness of 5 μm or more.

(Processing with basic compound)
The polymer particles obtained in this manner may be washed and dried as they are after removing the dispersion stabilizer, but in the present invention, the polymer particles are preferably further treated with a basic compound as described above. Thereby, the carboxyl group in a polymer particle is changed into a salt structure.

  As a method for forming a salt structure, magnetic polymer particles may be treated with a basic compound in the presence of water, a mixed solution of water and a water-soluble organic solvent, or an organic solvent. In the present invention, the treatment may be performed by adding a basic compound to the aqueous dispersion of magnetic polymer particles, or by mixing the magnetic polymer particles in an aqueous solution in which the basic compound is dissolved. good.

As the basic compound, either an inorganic basic compound or an organic basic compound can be used. Specifically, inorganic basic compounds such as sodium hydroxide, potassium hydroxide and ammonia; organic basic compounds such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; other basic trimethylamines, diethylamine, triethylamine, trimethylamine Alkylamines such as propylamine and tributylamine; alkanolamines such as monoethanolamine, methylethanolamine, diethanolamine, diisopropanolamine, triethanolamine, dimethylaminoethanol and morpholine;
These basic compounds may be used alone or in combination of two or more. Moreover, it is preferable to use an inorganic basic compound from the ease of removal of the basic compound after a process.

  In the present invention, the amount of the basic compound used is preferably in the range of 0.1 to 20% by mass of the aqueous dispersion of magnetic polymer particles. As described above, in the magnetic polymer particles obtained by this treatment step, it is preferable that all the carboxyl groups form a salt structure. Usually, in the range of the amount used, the basic compound is a polymer particle. It is set to be excessive with respect to the amount of carboxyl groups.

  At this time, the pH of the aqueous dispersion of magnetic polymer particles needs to be 9 or more, preferably 11 or more. Although there is no restriction | limiting in particular in process temperature, you may heat to about 50 to 80 degreeC. Although there is no restriction | limiting in processing time, Usually, it is 0.5 to 5 hours. Further, the concentration of the magnetic polymer particles during the treatment is not particularly limited, but is usually in the range of 1 to 50% by mass. When the magnetic polymer particles settle during the treatment time, it is preferable to perform moderate stirring. After the treatment, the basic compound is removed by washing with water.

  The magnetic polymer particles obtained as described above are polymerized or treated, and in some cases, diluted and dispersed in a solvent such as methanol, filtered, and further washed with water and / or solvent, followed by spray drying, reduced pressure. It can be isolated as a powder by ordinary means such as drying and freeze-drying.

The hydroxyl group amount, carboxyl group amount, and number average particle diameter in the obtained magnetic polymer particles can be determined by the same method as described above. The preferred hydroxyl group amount, carboxyl group amount, and number average particle size of the polymer particles obtained by the method for producing hydroxyl group-containing magnetic polymer particles of the present invention are the same as those described for the hydroxyl group-containing magnetic polymer particles of the present invention. is there.
In the measurement of the number average particle diameter, it is preferable that no agglomerated particles (one in which a plurality of particles are aggregated or one in which fine particles are attached to one particle and become deformed) are found.

  Moreover, although the molecular weight (number average molecular weight) of the hydroxyl group-containing magnetic polymer particles in the present invention varies depending on the application, in the case where no cross-linking agent is added in the polymerization step, a range of 5000 to 1000000 is preferable. The range of 500,000 is more preferable.

  The number average molecular weight was measured using gel permeation chromatography (GPC). GPC uses HLC-8120GPC, SC-8020 (manufactured by Tosoh Corporation), and column uses two TSKgel and SuperHM-H (manufactured by Tosoh Corporation, 6.0 mm ID × 15 cm). As THF (tetrahydrofuran).

<Water dispersion>
The aqueous dispersion of the present invention is a particle dispersion in which the magnetic polymer particles of the present invention are dispersed in an aqueous medium such as water. In the magnetic polymer particles of the present invention, since the magnetic powder is uniformly dispersed in the particles as described above, there is almost no magnetic powder on the particle surface. Moreover, since it has a hydroxyl group and a carboxyl group on the surface, it shows good water dispersibility. For this reason, the aqueous dispersion of the present invention is used for various applications in which dispersed particle characteristics as described later are reflected uniformly or efficiently.

As an aqueous medium, the thing similar to what was demonstrated at the said suspension process can be used.
In the production of an aqueous dispersion, various auxiliary materials that can be used in an ordinary aqueous dispersion, such as a dispersant, an emulsifier, a surfactant, a stabilizer, a wetting agent, a thickener, a foaming agent, a foaming agent, and the like. Foaming agent, coagulant, gelling agent, anti-settling agent, charge control agent, antistatic agent, anti-aging agent, softener, plasticizer, filler, coloring agent, flavoring agent, anti-sticking agent, release agent, etc. May be used in combination.
The water dispersibility of the magnetic polymer particles can be evaluated by the same method as described above, and the preferable water dispersibility of the magnetic polymer particles obtained by the present invention is described in the magnetic polymer particles of the present invention. It is the same as the contents.

The dispersed particle size in the aqueous dispersion of the present invention can be in the range of about 0.5 to 5 μm as an average particle size, but is preferably in the range of 1 to 4 μm.
The solid content concentration of the aqueous dispersion is not particularly limited, but is preferably in the range of 1 to 50% by mass, and more preferably in the range of 5 to 30% by mass.

  As described above, the magnetic polymer particles, the production method thereof, and the aqueous dispersion of the present invention have been described in detail. However, the magnetic polymer particles obtained by the present invention and the aqueous dispersion thereof can be used for image forming materials, magnetic fluids, diagnosis, It can be suitably used for applications such as drugs and pharmaceutical carriers, viscosity modifiers, resin molding materials, paint additives, cross-linking / curing agents and cosmetic additives. In particular, in the magnetic polymer particles, a certain amount or more of the magnetic powder is uniformly dispersed, and since the surface is excellent in dispersibility in an aqueous medium due to hydroxyl groups, image formation for magnetic ink and wet image forming methods is used. It can be suitably used as a material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these. In the examples, “part” and “%” represent “part by mass” and “% by mass”, respectively, unless otherwise specified.

<Preparation of surface-treated magnetic powder>
(Magnetic powder 1)
150 parts of magnetic powder (product name: MTS-010, average particle size: 0.13 μm) is added to 150 parts of dried ethanol, and 2.5 parts of a silane coupling agent (manufactured by Chisso Corporation) , Trade name: phenethyltrimethoxysilane), and the magnetic powder was dispersed with ultrasonic waves. This dispersion was distilled with ethanol using a rotary evaporator to dry the magnetic powder, and then heat-treated at 150 ° C. for 5 hours. The magnetic powder thus treated did not conform to water (a small amount was mixed with water and stirred to float on the water surface and did not settle, the same applies hereinafter), and the surface was hydrophobized. This was designated as magnetic powder 1.

(Magnetic powder 2)
To 600 parts of magnetic powder (made by Toda Kogyo Co., Ltd., trade name: MTS-010) is added 400 parts of styrene acrylic resin (trade name: S-LEC P-SE-0020, manufactured by Sekisui Chemical Co., Ltd.) and kneaded with a pressure kneader. The magnetic powder 2 whose surface was resin-coated was obtained.

<Example 1>
(Manufacture of magnetic polymer particles)
20 parts of hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 2 parts of methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich), 75 parts of styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd.), and divinyl After 1 part of benzene (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed, 1:30 parts of the magnetic powder was added and dispersed for 48 hours with a ball mill. To 90 parts of the magnetic powder dispersion, 5 parts of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added to prepare a mixture containing the monomer and the magnetic powder.

  In an aqueous solution obtained by dissolving 28 parts of sodium chloride in 160 parts of ion-exchanged water, 30 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Luminous) and carboxymethyl cellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (Product name: Serogen) 3.5 parts was added and dispersed for 24 hours with a ball mill to obtain a dispersion medium. The mixture was charged into 200 parts of this dispersion medium, and emulsified at 8000 rpm for 3 minutes with an emulsifying device (manufactured by SMT Co., Ltd., HIGH-FLEX HOMOGENIZER) to obtain a suspension. The number average particle size of the suspended particles at this time was about 2.0 μm.

  On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a good dispersion, and no agglomerates could be confirmed during polymerization. A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1000 parts of ion-exchanged water and then passed through a sieve having an opening of 100 μm. The passed dispersion was adjusted to pH 12 with 0.5N sodium hydroxide and stirred at room temperature for 1 hour. After the treatment, it was washed with 1000 parts of ion-exchanged water, and further washed with 500 parts of ethanol and ion-exchanged water to obtain magnetic polymer particles A.

  After the magnetic polymer particles A were oven dried at 60 ° C., the yield of the magnetic polymer particles was measured and found to be 82 parts and the yield was 86%.

(Characteristic evaluation of magnetic polymer particles)
-Magnetic powder content-
The magnetic polymer particles A were passed through a 1 μm nylon sieve and fractionated into a particle group A1 having an average particle diameter of 1 μm and a particle group A2 having an average particle diameter of 3 μm.
About these, when the content of magnetic powder in the particles was calculated from the weight loss due to heating by thermogravimetric analysis (TGA), it was 23% by mass for A1 and 20% by mass for A2, which was generally consistent. The TGA measurement was performed under the condition that the temperature was raised to 600 ° C. at a temperature raising rate of 10 ° C./min and held at 600 ° C. for 10 minutes.

-Hydroxyl amount-
The magnetic polymer particles A are weighed and placed in a capped test tube, and a predetermined amount of a pre-prepared acetic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) pyridine (manufactured by Wako Pure Chemical Industries, Ltd.) solution is added. Heated for 24 hours under temperature conditions.
Further, distilled water was added to hydrolyze acetic anhydride in the test tube, and then centrifuged at 3000 rpm for 5 minutes to separate into particles and supernatant. The particles are further washed by repeated ultrasonic dispersion and centrifugation with ethanol (Wako Pure Chemical Industries, Ltd.), and the supernatant and the cleaning solution are collected in a conical beaker. Phenolphthalein (Wako Pure Chemical Industries, Ltd.) is used as an indicator. The solution was titrated with a 0.1M ethanolic potassium hydroxide solution (Wako Pure Chemical Industries, Ltd.).

A blank experiment without using magnetic polymer particles was also performed, and the amount of hydroxyl group (mmol / g) was calculated from the difference according to the following formula (1).
Hydroxyl group amount = ((B−C) × 0.1 × f) / (w− (w × D / 100)) (1)
In the above formula (1), B is the dripping amount (ml) in the blank experiment, C is the dripping amount (ml) of the sample, f is the factor of the potassium hydroxide solution, w is the weight (g) of the particle, D is the particle It is a magnetic powder content rate (%).
As a result, the amount of hydroxyl groups in the magnetic polymer particles A was 1.2 mmol / g.

-Amount of carboxyl group-
The magnetic polymer particles A were redispersed in 10 times the amount of ion-exchanged water, and 1N hydrochloric acid was added to adjust the pH to 3. Stirring was continued for 1 hour at room temperature, and after filtration, the mixture was repeatedly washed with 10 times the amount of ion-exchanged water. After centrifugation, it was lyophilized at 60 ° C. The obtained polymer particles were weighed and placed in a capped test tube, a fixed amount of 0.1 M ethanolic potassium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was reacted at room temperature for 3 hours.
This was centrifuged at 3000 rpm for 5 minutes and separated into particles and supernatant, and then the particles were further subjected to ultrasonic dispersion and centrifugation repeatedly with ethanol (manufactured by Wako Pure Chemical Industries, Ltd.), and the supernatant and washing liquid were conical. The sample was collected in a beaker and titrated with a 0.1 M 2-propanolic hydrochloric acid solution (Wako Pure Chemical Industries, Ltd.) using methyl orange (Wako Pure Chemical Industries, Ltd.) as an indicator.

A blank experiment without using magnetic polymer particles was also performed, and the carboxyl group amount (mmol / g) was calculated from the difference according to the following formula (2).
Carboxyl group amount = ((E−F) × 0.1 × f) / (x− (xx × G / 100)) (2)
In the above formula (2), E is the dripping amount (ml) in the blank experiment, F is the dripping amount (ml) of the sample, f is the factor of the potassium hydroxide solution, x is the weight (g) of the particle, and G is the particle It is a magnetic powder content rate (%).
As a result, the amount of carboxyl groups in the magnetic polymer particles A was 0.04 mmol / g.

-Number average particle size and particle shape-
As described above, the number average particle diameter of the magnetic polymer particles A was determined from a photograph of the dried particles observed with an electron microscope and found to be 2.0 μm. In the photograph, no agglomerated particles were observed.

-Presence of magnetic powder on particle surface-
The presence state of the magnetic powder on the surface of the magnetic polymer particle A was confirmed by a scanning electron microscope (SEM). Specifically, when the surface state was confirmed for 100 particles at a magnification of 10,000, no state in which magnetic powder protruded from the surface of all particles was observed.

(Production and characteristics of water dispersion)
1 part of the dried magnetic polymer particles A was taken and placed in 20 parts of pure water contained in a glass container having an opening area of 4 cm ² and stirred to obtain an aqueous dispersion. In this water dispersion, the entire particles were redispersed well in water without floating on the water surface or depositing on the container wall.
Moreover, when the dispersed particle diameter of the particle | grains in an aqueous dispersion was measured with the laser diffraction type particle size distribution measuring apparatus (Horiba Ltd. make, LA-700), the average particle diameter was 3.4 micrometers.

<Example 2>
(Manufacture of magnetic polymer particles)
15 parts hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 2 parts methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich), 57 parts styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd.), 30 cyclohexanone Part and divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part were mixed, and then the magnetic powder 2:40 parts (magnetic powder content: 60%) was added and dispersed with a ball mill for 48 hours. To 120 parts of the magnetic powder dispersion, 5 parts of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added as a polymerization initiator to prepare a mixture containing the monomer and the magnetic powder.

  In an aqueous solution obtained by dissolving 56 parts of sodium chloride in 320 parts of ion-exchanged water, 60 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Luminous) and carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (Product name: Serogen) 7 parts were added and dispersed for 24 hours with a ball mill to obtain a dispersion medium. The mixture was charged into 400 parts of this dispersion medium and emulsified at 8000 rpm for 3 minutes with an emulsifying apparatus (manufactured by SMT Co., Ltd., HIGH-FLEX HOMOGENIZER) to obtain a suspension. The number average particle size of the suspended particles at this time was about 2.0 μm.

On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a good dispersion, and no agglomerates could be confirmed during polymerization. A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1000 parts of ion exchange water, then repeatedly washed with 1000 parts of ethanol, and then replaced with 1000 parts of ion exchange water again. The pH was adjusted to 12 with 0.5N sodium hydroxide, and the mixture was stirred at room temperature for 1 hour. After the treatment, it was washed with ion exchange water, and further washed with 500 parts of ethanol and ion exchange water to obtain magnetic polymer particles B.
After the magnetic polymer particles B were oven dried at 60 ° C., the yield of the magnetic polymer particles was measured and found to be 83 parts and the yield was 89%.

(Characteristic evaluation of magnetic polymer particles)
-Magnetic powder content-
As in Example 1, this magnetic polymer particle B was passed through a 1 μm nylon sieve and fractionated into a particle group B1 having an average particle diameter of 1 μm and a particle group B2 having an average particle diameter of 3 μm. When the magnetic powder content was calculated, it was 21% by mass for B1 and 19% by mass for B2, which was almost the same.

-Number average particle size and particle shape-
As in Example 1, the number average particle size of the polymer particles was determined from a photograph of the dried particles observed with an electron microscope and found to be 2.2 μm. In the photograph, no agglomerated particles were observed.

-Hydroxyl group content, carboxyl group content, surface condition-
When the hydroxyl group content of the magnetic polymer particles B was measured in the same manner as in Example 1, the hydroxyl group content of the particles was 1.2 mmol / g. Similarly, the carboxyl group amount was 0.02 mmol / g.
Next, the presence state of the magnetic powder on the particle surface was also confirmed in the same manner as in Example 1. Similarly, no magnetic powder jumping out on the particle surface was observed.

(Production and characteristics of water dispersion)
In the same manner as in Example 1, an aqueous dispersion was prepared using the dried magnetic polymer particles B. In this water dispersion, the entire particles were redispersed well in water without floating on the water surface or depositing on the container wall.
Moreover, when the dispersed particle diameter of the particle | grains in an aqueous dispersion was measured with the laser diffraction type particle size distribution measuring apparatus (the Horiba make, LA-700), the average particle diameter was 3.2 micrometers.

<Example 3>
(Manufacture of magnetic polymer particles)
20 parts of polyethylene glycol methacrylate (Nippon Yushi Co., Ltd., Bremer PE200), 1 part of methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich), 70 parts of styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part of divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed, 2:40 parts of the magnetic powder (magnetic powder content: 60%) was added, and dispersed for 48 hours with a ball mill. To 90 parts of the magnetic powder dispersion, 5 parts of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added to prepare a mixture containing the monomer and the magnetic powder.

  In an aqueous solution obtained by dissolving 28 parts of sodium chloride in 160 parts of ion-exchanged water, 30 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Luminous) and carboxymethyl cellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (Product name: Serogen) 3.5 parts was added and dispersed for 24 hours with a ball mill to obtain a dispersion medium. The mixture was charged into 200 parts of this dispersion medium, and emulsified at 8000 rpm for 3 minutes with an emulsifying device (manufactured by SMT Co., Ltd., HIGH-FLEX HOMOGENIZER) to obtain a suspension. The number average particle size of the suspended particles at this time was about 1.9 μm.

On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a good dispersion, and no agglomerates could be confirmed during polymerization. A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1000 parts of ion-exchanged water, adjusted to pH 12 with 0.5N sodium hydroxide, and stirred at room temperature for 1 hour. After the treatment, it was washed with 1000 parts of ion exchange water, and further washed with 500 parts of ethanol and ion exchange water to obtain magnetic polymer particles C.
The magnetic polymer particles C were freeze-dried at 40 ° C., and the yield of the magnetic polymer particles was measured to be 80 parts and the yield was 86%.

(Characteristic evaluation of magnetic polymer particles)
-Magnetic powder content-
As in Example 1, this magnetic polymer particle C was passed through a 1 μm nylon sieve and fractionated into a particle group C1 having an average particle diameter of 1 μm and a particle group C2 having an average particle diameter of 3 μm. When the magnetic powder content was calculated, it was 18% by mass for C1 and 14% by mass for C2, which was almost the same.

-Number average particle size and particle shape-
As in Example 1, the number average particle diameter of the polymer particles was determined from a photograph of the dried particles observed with an electron microscope and found to be 2.0 μm. In the photograph, no agglomerated particles were observed.

-Hydroxyl group content, carboxyl group content, surface condition-
When the hydroxyl group content of the magnetic polymer particles C was measured by the same method as in Example 1, the hydroxyl group content of the particles was 0.6 mmol / g. Similarly, the amount of carboxyl groups was 0.03 mmol / g.
Next, the presence state of the magnetic powder on the particle surface was also confirmed in the same manner as in Example 1. Similarly, no magnetic powder jumping out on the particle surface was observed.

(Production and characteristics of water dispersion)
In the same manner as in Example 1, an aqueous dispersion was prepared using the dried magnetic polymer particles C. In this water dispersion, the entire particles were redispersed well in water without floating on the water surface or depositing on the container wall.
Moreover, when the dispersed particle diameter of the particle | grains in an aqueous dispersion was measured with the laser diffraction type particle size distribution measuring apparatus (the Horiba make, LA-700), the average particle diameter was 3.2 micrometers.

<Comparative Example 1>
In the production of the magnetic polymer particles of Example 2, suspension polymerization was carried out with the same formulation except that 2 parts of methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich Co.) was changed to 2 parts of styrene. Particle D was obtained. After the magnetic polymer particles D were oven-dried at 60 ° C., the yield of the magnetic polymer particles was measured and found to be 83 parts and a good yield of 89%.
Further, when the number average particle diameter of the polymer particles was determined from the photograph of the dried particles observed with an electron microscope in the same manner as in Example 1, it was 2.2 μm and no agglomerated particles were found at all.

However, in the same manner as in Example 1, the magnetic polymer particles D were fractionated into a particle group D1 having an average particle diameter of 1 μm and a particle group D2 having an average particle diameter of 3 μm, and the content of magnetic powder in the particles was calculated. As a result, D1 was 22% by mass and D2 was 10% by mass, and the particle size dependence of the magnetic powder content was large.
When the amount of hydroxyl groups in the magnetic polymer particles D was measured by the same method as in Example 1, the amount of hydroxyl groups in the particles was 1.2 mmol / g, but the amount of carboxyl groups was 0.001 mmol / g. .

<Comparative example 2>
In the production of the magnetic polymer particles of Example 1, suspension polymerization was performed in the same manner except that 20 parts of hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) was changed to 20 parts of styrene, and magnetic polymer particles E Got. After the magnetic polymer particles E were oven-dried at 60 ° C., the yield of the magnetic polymer particles was measured and found to be 63 parts. The yield decreased to 66%.

In the same manner as in Example 1, the number average particle diameter of the polymer particles was determined from the photograph of the dried particles observed with an electron microscope, and found to be 2.5 μm. Aggregated particles were scattered. Further, in the same manner as in Example 1, the magnetic polymer particles D were fractionated into a particle group E1 having an average particle diameter of 1 μm and a particle group E2 having an average particle diameter of 3 μm, and the magnetic powder content in the particles was calculated. However, E1 was 23 mass% and E2 was 10 mass%, and the particle size dependence of the magnetic powder content was large.
The hydroxyl group content of the magnetic polymer particles E was measured by the same method as in Example 1. As a result, the hydroxyl group content of the particles was 0.01 mmol / g and the carboxyl group content was 0.04 mmol / g.

  Next, when the presence state of the magnetic powder on the particle surface was observed by SEM in the same manner as in Example 1, a portion where the magnetic powder protruded on the particle surface was observed. In addition, an attempt was made to produce an aqueous dispersion in the same manner as in Example 1, but the magnetic polymer particles obtained did not redisperse well in water because they became lumps (particles solidified) on the water surface. E was difficult to adjust to water.

<Comparative Example 3>
In the production of the magnetic polymer particles of Example 1, 20 parts of hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) is 75 parts, and 2 parts of methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich Co., Ltd.) is changed. First, suspension polymerization was performed in the same manner except that 75 parts of styrene monomer was changed to 20 parts, and magnetic polymer particles F were obtained. After the magnetic polymer particles F were oven-dried at 60 ° C., the yield of the magnetic polymer particles was measured and found to be 24 parts, and the yield was greatly reduced to 25%.

When the number average particle diameter of the polymer particles was determined from the photograph of the dried particles observed with an electron microscope in the same manner as in Example 1, it was 30 μm and there were many aggregated particles. Further, in the same manner as in Example 1, an attempt was made to fractionate the magnetic polymer particles F into a particle group F1 having an average particle diameter of 1 μm and a particle group F2 having an average particle diameter of 3 μm, but could not be separated.
The hydroxyl group content of the magnetic polymer particles E was measured by the same method as in Example 1. As a result, the hydroxyl group content of the particles was 4.6 mmol / g and the carboxyl group content was 0.1 mmol / g.

<Comparative Example 4>
In the production of the magnetic polymer particles of Example 1, the mixture containing the monomer and the magnetic powder was suspended by performing the same treatment as in Example 1 except that sodium chloride was not added at the time of preparing the dispersion medium, and the polymerization was performed. As a result, white fine particles passing through a filter paper (ADVANTEC, No. 5C, retained particle size: 1 μm) were observed in the washing step with ion-exchanged water. This confirmed that the emulsion polymerization was derived in the dispersion medium. When the yield of the obtained magnetic polymer particles G was measured, it was 38 parts and the yield was reduced to 40%.

  When the hydroxyl group content of the magnetic polymer particles G was measured by the same method as in Example 1, the hydroxyl group content of the particles was as low as 0.03 mmol / g. Further, when these polymer particles were observed with a microscope, there was a large variation in particle diameter, but the number average particle diameter was 2.0 μm. A considerable number of aggregated particles were observed.

<Comparative Example 5>
In the production of the magnetic polymer particles of Example 1, the mixture containing the monomer and the magnetic powder is suspended by performing the same treatment as in Example 1 except that calcium carbonate is not added at the time of preparing the dispersion medium. Attempts were made, but the mixture could not be well suspended in the dispersion medium and became a dumpling mass upon polymerization.

  As described above, according to the method for producing magnetic polymer particles of the present invention of the examples, since the suspended particles at the time of polymerization are stable, there is no aggregation and the magnetic powder is uniformly dispersed at a high concentration. Magnetic polymer particles excellent in water dispersibility can be obtained. On the other hand, in the comparative example in which even one of the production conditions in the present invention is insufficient, some problem occurred in yield, particle state, and the like.

Claims (9)

  It comprises a magnetic powder and a polymer of an ethylenically unsaturated monomer, the content of the magnetic powder is in the range of 2.5 to 50% by mass, and the ethylenically unsaturated monomer is a hydroxyl group. A polymer having a hydroxyl group, a monomer having a carboxyl group, a hydrophobic monomer having no hydroxyl group and no carboxyl group, and the amount of hydroxyl group of the polymer not containing magnetic powder is 0.3 to Magnetic polymer particles characterized by being 5.0 mmol / g and having a carboxyl group content in the range of 0.005 to 0.5 mmol / g.   2. The magnetic polymer particle according to claim 1, wherein a part or all of the carboxyl group forms a salt structure.   An aqueous dispersion comprising the magnetic polymer particles according to claim 1.   (A + B) <C relationship between a monomer having a hydroxyl group of A part by mass, a monomer having a carboxyl group of B part by mass, and a hydrophobic monomer having no hydroxyl group and carboxyl group of C part by mass A mixture containing an ethylenically unsaturated monomer, a polymerization initiator, and a magnetic powder having a hydrophobic surface is dispersed in an aqueous medium in which a salt is dissolved and a dispersion stabilizer is added. A method for producing magnetic polymer particles, comprising a step of suspension polymerization.   Furthermore, the manufacturing method of the magnetic polymer particle of Claim 4 which has the process of processing the particle | grains obtained by the said suspension polymerization with a basic compound.   5. The magnetic property according to claim 4, wherein the content of the hydrophobic monomer having no hydroxyl group or carboxyl group is in the range of 50.0 to 90.0% by mass in all monomer components. Production method of polymer particles.   The method for producing magnetic polymer particles according to claim 4, wherein the hydrophobizing treatment is a surface coating treatment with a coupling agent.   The method for producing magnetic polymer particles according to claim 4, wherein the salt is an inorganic salt.   The method for producing magnetic polymer particles according to claim 4, wherein the dispersion stabilizer is an inorganic powder.