JP5018398B2 - Magnetic polymer particles for liquid magnetography and developer for liquid magnetography - Google Patents

Description

  The present invention relates to a magnetic polymer particle for liquid magnetography and a developer for liquid magnetography using the same.

  2. Description of the Related Art A magnetic printing apparatus that can print a required number of copies by forming a latent image once is known. In this magnetic printing apparatus, a magnetic latent image magnetically formed is held on a magnetic recording medium (magnetic latent image holding member), and magnetic toner is supplied to the magnetic recording medium in a developing region to convert the magnetic latent image into toner. It is visualized as an image, a recording medium such as paper is pressed against the magnetic recording medium in the transfer area, the visualized toner image is transferred to the recording medium, and the transferred recording medium is transported to the fixing area and fixed. The print is completed by processing. This method is generally called magnetography.

In the above, the magnetization state in the magnetic recording medium is maintained semi-permanently, so once a latent image is formed, a very large number of copies can be obtained simply by repeating the development and transfer processes. In addition, since it is not necessary to re-record the latent image to obtain a multi-copy, it is possible to cope with high speed. Further, unlike static electricity, magnetism is stable to the environment, and an image with high resolution can be obtained.
On the other hand, the magnetic latent image can be easily formed and erased magnetically, and a printing plate is not required, so that the cost can be reduced.

As a specific process of the magnetography, for example, magnetic toner is supplied by a supply roller disposed at a distance from the magnetic recording medium. The supply roller holds the magnetic toner layer on the peripheral surface thereof, brings the magnetic toner layer into contact with the magnetic recording medium, and supplies and adheres the magnetic toner to the magnetic latent image of the magnetic recording medium.
As an image forming apparatus using the above process, there is a so-called dry type image forming apparatus using magnetic powder toner, but an image forming apparatus using a liquid developer in which magnetic toner is dispersed in a liquid (so-called “liquid”). (See, for example, Patent Documents 1 and 2), since toner is contained in the liquid in this process, even if the toner particle size is reduced, the toner cloud is reduced. There is an advantage that such a problem does not occur.

  As the liquid developer, as a developer used in a technique for visualizing an electrostatic latent image, toner particles containing a coloring material in a water-insoluble hydrophobic resin are dispersed in an aqueous medium mainly containing water. Toner particles coated with a colorant with a water-based developer and a film-forming thermoplastic resin having a hydrophilic group (for example, see Patent Documents 3 and 4) were dispersed in a carrier liquid containing water as a main component. An aqueous liquid developer (see, for example, Patent Document 5) has been proposed.

On the other hand, as a liquid developer for visualizing a magnetic latent image, a developer composed of liquid ink and resin particles containing magnetic powder dispersed in the ink has been proposed (for example, Patent Document 6). In this technique, a developer containing liquid ink and resin particles is supplied to the magnetic latent image, and only the liquid ink is transferred to the recording paper to obtain an image with excellent color reproducibility. .
Japanese Patent Publication No. 5-87834 Japanese Patent Laid-Open No. 5-18827 Japanese Patent Laid-Open No. 10-10802 Japanese Patent Laid-Open No. 11-24410 JP-A-11-24324 JP 11-38671 A

  However, with respect to a developer used for liquid magnetography, it is extremely difficult to stably cause toner particles containing particles having a relatively large particle diameter and a large specific gravity, such as magnetic powder, to exist in water. Further, from the viewpoint of simplification of the process, it is desirable that the toner transferred to the recording medium can be fixed by non-heating instead of the conventional fixing by heating.

  The present invention has been made in view of the above-described circumstances, has excellent water dispersibility and dispersion stability, and enables high-resolution image formation and non-heat fixing to a recording medium such as paper in liquid magnetography. It is an object of the present invention to provide magnetic polymer particles for liquid magnetography and a developer for liquid magnetography using the same.

The above-described problems are achieved by the present invention described below.
That is, the invention according to claim 1 is a magnetic polymer particle for liquid magnetography comprising at least a water absorbent resin and magnetic powder.

  The invention according to claim 2 is the magnetic polymer particle for liquid magnetography according to claim 1, wherein the water absorption rate of the water absorbent resin is 200% or more and 5000% or less.

  The invention according to claim 3 is the magnetic polymer particle for liquid magnetography according to claim 1 or 2, wherein the volume average particle size in water is 0.5 μm or more and 20 μm or less.

  The invention according to claim 4 is the liquid magneto according to any one of claims 1 to 3, wherein the water-absorbent resin has an acidic group, and a part or all of the acidic group forms a salt structure. Magnetic polymer particles for graphics.

  The invention according to claim 5 is a developer for liquid magnetography comprising the magnetic polymer particles for liquid magnetography according to any one of claims 1 to 4 and an aqueous medium.

According to the first aspect of the present invention, a liquid magnet having good water dispersibility and dispersion stability and capable of high-resolution image formation and non-heat-fixing on a recording medium such as paper in liquid magnetography. Graphic polymer particles are provided.
According to the second aspect of the invention, magnetic polymer particles for liquid magnetography having better non-heat fixing can be obtained without adversely affecting the developability and transferability.
According to the third aspect of the present invention, magnetic polymer particles for liquid magnetography having better non-heat fixing can be obtained without adversely affecting the developability and transferability.
According to the fourth aspect of the present invention, magnetic polymer particles for liquid magnetography that are excellent in liquid absorption and easily swell can be obtained.
According to the fifth aspect of the present invention, there is provided a developer for liquid magnetography capable of forming a high-resolution image and performing non-heat fixing on a recording medium such as paper in liquid magnetography.

Hereinafter, embodiments of the present invention will be described in detail.
<Magnetic polymer particles for liquid magnetography>
The magnetic polymer particles for liquid magnetography of the present embodiment (hereinafter sometimes simply referred to as “magnetic polymer particles” or “toner”) include at least a water-absorbing resin and magnetic powder. And a particulate magnetic polymer used in the developer for liquid magnetography. Therefore, it is possible to suppress (uniformly) dispersion in an aqueous medium such as water while maintaining a certain magnetic force.
The “magnetic polymer particles” are composed of magnetic powder dispersed particles in which magnetic powder is dispersed in a polymer.

  When a magnetic latent image is visualized with a liquid developer containing magnetic polymer particles and image formation is performed by transferring the toner image to a recording medium, the image composed of the magnetic polymer particles is fixed on the recording medium. There is a need. In general, heat fixing is used for the fixing. However, from the viewpoint of simplification of the process and energy saving, it is desirable that the fixing can be performed by a non-heating method such as pressure fixing.

In this embodiment, at least a water-absorbing resin is used as a resin component constituting the toner, and magnetic polymer particles are mixed with magnetic powder. The toner image is dispersed in a liquid containing water and absorbed. It was found that the toner image can be transferred to a recording medium such as paper and the toner image can be fixed to the recording medium without heating.
Here, the “water-absorbing resin” means a resin having a water absorption rate of 100% or more in water absorption measurement according to JIS K7209 (1984) described later.

That is, the water-absorbent resin absorbs water in an aqueous medium mainly composed of water and expands to form gel-like particles. However, the water-absorbent resin in a state in which part or all of the resin component constituting the toner is absorbed. When the toner is transferred from the latent image holding member (or from the latent image holding member through an intermediate transfer member or the like) to a recording medium such as paper, the fixing resin is used simultaneously with the transfer or from the fixing member after the transfer. It was found that the image was fixed to the recording medium as it was without being heated by the pressure contact.
In addition, in the aqueous medium, since the toner absorbs water and becomes hydrophilic, the toner is excellent in dispersibility and dispersion stability. Therefore, a high-quality image can be formed by using it in liquid magnetography.

Hereinafter, the structure of the magnetic polymer particle of this embodiment is demonstrated with the manufacturing method.
(Water absorbent resin)
The water-absorbing resin used in the toner of the present embodiment is softened and swollen in the liquid because the liquid component absorbed (for example, water, aqueous solvent) acts as a kind of resin (polymer) plasticizer. Non-heat fixability of toner onto a recording medium is improved.

  On the other hand, when the liquid is excessively absorbed and highly swollen, the image quality is deteriorated and the fixing property is deteriorated. In this embodiment, the liquid absorbency of the magnetic polymer particles is grasped by the “water absorption rate” of the water-absorbing resin contained in the magnetic polymer particles, so that the fixability when the magnetic polymer particles are used as a toner is sufficient. It was found that it can be controlled. Specifically, in the present embodiment, the water absorption rate of the water absorbent resin is desirably 200% or more and 5000% or less, and more preferably 400% or more and 3000% or less.

If the water absorption rate is less than 200%, even when toner particles are dispersed in an aqueous medium, the toner does not swell sufficiently and cannot be fixed to the recording medium without heating. If it exceeds 5000%, not only will the toner particles expand too much, the image quality after fixing will deteriorate, but also the adhesiveness of the toner will increase, and the transferability and the like may decrease.
In addition, the water absorption rate in this embodiment is measured according to JIS K7209 (1984). Details will be described later.

  The water-absorbing resin in the present embodiment is composed of, for example, a homopolymer of a hydrophilic monomer, or a copolymer composed of both a hydrophilic monomer and a hydrophobic monomer. However, from the above viewpoint, the water-absorbing resin in the present embodiment is desirably a so-called weak water-absorbing resin that is saturated with a certain amount of water absorption (liquid absorption). The copolymer is preferred. In addition, not only the monomer but also a graft copolymer or block copolymer in which other units such as a polymer / oligomer structure are copolymerized as a start may be used. Here, the “hydrophilic monomer” includes a monomer that is itself hydrophobic but can be easily hydrophilized after polymerization.

Here, as a hydrophilic monomer, -OH, -EO unit (ethylene oxide group), -COOM (M is alkali metal, such as hydrogen, Na, Li, and K, ammonia, organic amines, etc.). ), - _SO 3 M (M is, for example, hydrogen, Na, Li, alkali metals K, etc., ammonia, organic amines, etc.), - _NR 3 (R is, for example, H, alkyl, phenyl, etc.). - NR ₄ X (R is, for example, H, alkyl, phenyl, etc., and X is, for example, halogen, sulfate radical, acid anions such as carboxylic acid, BF ₄ , etc.) and the like. It is done. Specific examples include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, acrylamide, acrylic acid, methacrylic acid, unsaturated carboxylic acid, crotonic acid, maleic acid, and the like. Examples of hydrophilic units or monomers include cellulose derivatives such as cellulose, ethyl cellulose, carboxymethyl cellulose, starch derivatives, monosaccharide / polysaccharide derivatives, vinyl sulfonic acid, styrene sulfonic acid, acrylic acid, methacrylic acid, (anhydrous) Polymeric carboxylic acids such as maleic acid, (partially) neutralized salts thereof, vinyl alcohols, vinyl pyrrolidone, vinyl pyridine, derivatives such as amino (meth) acrylate and dimethylamino (meth) acrylate, and oniums thereof Salts, amides such as acrylamide and isopropylacrylamide, polyethylene oxide chain-containing vinyl compounds, hydroxyl group-containing vinyl compounds, polyesters composed of polyfunctional carboxylic acids and polyhydric alcohols, especially trimellitic acid Branched polyester containing a large amount of content and terminal carboxylic acid or hydroxyl functionality more acid as a constituent component, a polyester containing polyethylene glycol structure, etc. may be mentioned.

Among these, a monomer having an acidic group is desirable. Specifically, using a monomer having a carboxyl group and forming a salt structure by a neutralization reaction after polymerization provides good water absorption. In view of this, it is particularly desirable to use an ethylenically unsaturated monomer having a carboxyl group.
Examples of the monomer having a carboxyl group used in the present embodiment include acrylic acid, methacrylic acid, methacryloyloxyethyl monophthalate, methacryloyloxyethyl monohexahydrophthalate, methacryloyloxyethyl monomaleate, and methacryloyloxyethyl monosuccinate. Acryloyloxyethyl monophthalate, acryloyloxyethyl monohexahydrophthalate, acryloyloxyethyl monomaleate and acryloyloxyethyl monosuccinate.
Among these, it is preferable to use methacryloyloxyethyl monophthalate 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, and the like. .

  Examples of the hydrophobic monomer include monomers having a hydrophobic group. Specifically, for example, olefin (ethylene, butadiene, etc.), styrene, α-methylstyrene, α-ethylstyrene, methyl methacrylate. , Ethyl methacrylate, butyl methacrylate, acrylonitrile, vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, lauryl methacrylate, and the like. Hydrophobic units or monomers include styrene derivatives such as styrene, α-methylstyrene, vinyltoluene, vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylate esters, phenyl acrylate esters, alkyl methacrylate esters, methacrylic acid Examples also include phenyl esters, cycloalkyl methacrylates, alkyl esters of crotonic acid, dialkyl esters of itaconic acid, dialkyl maleates, polyolefins such as polyethylene, ethylene / vinyl acetate and polypropylene, and derivatives thereof.

  Specific examples of the water-absorbent resin comprising a copolymer of such a hydrophilic monomer and a hydrophobic monomer include, for example, (meth) acrylic acid esters / methacryloyloxyethyl monophthalate copolymer, Styrene / methacryloyloxyethyl monophthalate copolymer, styrene / (meth) acrylic acid / (anhydrous) maleic acid copolymers, olefin polymers such as ethylene / propylene (or modified products thereof, or introduction of carboxylic acid units by copolymerization) And branched polyesters and polyamides whose acid value is improved with trimellitic acid and the like.

  Further, the water-absorbing resin preferably has the acidic group, and part or all of the acidic group preferably forms a salt structure after polymerization. That is, for example, a (meth) acrylic acid ester / methacryloyloxyethyl monophthalate copolymer or a styrene / methacryloyloxyethyl monophthalate copolymer carboxylic acid is neutralized with a base such as NaOH to obtain a salt (neutralized salt) In the case of the structure, the liquid absorbency is remarkably improved as compared with the resin before neutralization.

  In this case, it is desirable that the water-absorbent resin in the present embodiment has a structural unit represented by the following structural formula (I) in terms of affinity with other resins and magnetic powder.

In the structural formula (I), R represents hydrogen or a methyl group, n represents an integer of 1 to 18, and X ⁺ represents any one of an alkali metal ion, an alkaline earth metal ion, and a quaternary ammonium ion.

  In the water-absorbent resin used in the present embodiment, the molar ratio (hydrophilic unit) between the hydrophilic unit (part composed of hydrophilic monomer) and the hydrophobic unit (part composed of hydrophobic monomer). (Mer: hydrophobic monomer) is preferably in the range of 5:95 to 90:10, more preferably in the range of 7:93 to 80:20, and still more preferably in the range of 10:90 to 70:30. . By setting the amount of the hydrophilic monomer within the above range, it is possible to achieve both the improvement in the liquid absorption rate when the magnetic polymer particles absorb the aqueous medium, the balance between the improvement in the liquid absorption amount and the fixability. .

  The water-absorbent resin having the structural unit represented by the structural formula (I) is a copolymer including the structural units (A), (B), and (C) represented by the following structural formula (II). It is desirable from the viewpoint of image storability after fixing and drying.

In the structural formula (II), R, n, and X ⁺ are the same as those described in the structural formula (I). R ¹ represents any one of alkyl groups having 1 to 18 carbon atoms. The structural unit (A) represented by the structural formula (II) corresponds to that based on the hydrophilic monomer, and the structural units (B) and (C) correspond to those based on the hydrophobic monomer. To do.
Further, when the above three structural units are included, the molar ratio of each structural unit (A), (B), (C) is 10 mol% or more and 90 mol% or less, 5 mol% or more and 80 mol% or less, 5 It is desirable to set it as mol% or more and 80 mol% or less.

Further, the water-absorbent resin in the present embodiment may have a linear structure or a branched structure. In other words, the liquid-absorbing resin may be a linear random copolymer or block copolymer, but a branched polymer (including branched random copolymers, block copolymers, and graft copolymers). Can also be suitably used.
Further, the water absorbent resin may contain a crosslinked structure. By including a crosslinked structure in the resin, the liquid absorption amount may be constant and excessive swelling may be suppressed. Such a cross-linked structure can be synthesized by adding a small amount of a so-called cross-linking agent such as divinylbenzene or di (meth) acrylate during synthesis, or by adding a large amount of an initiator together with the cross-linking agent.

As the crosslinking agent to be used, a known crosslinking agent can be selected and used. Examples of suitable crosslinking agents 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.
The addition amount of the cross-linking agent is preferably 0 to 5 parts by mass, more preferably 0 to 3 parts by mass with respect to 100 parts by mass of all monomer components. is there.

The water absorbent resin is desirably an amorphous resin, and the glass transition temperature (Tg) thereof is preferably 0 ° C. or higher and 100 ° C. or lower, more preferably 20 ° C. or higher and 80 ° C. or lower. By setting the glass transition temperature in the above range, it is possible to improve the storability of the image after fixing, and to make it easy to pulverize the fused particles in the production of the magnetic polymer particles described later.
In addition, the glass transition temperature was calculated | required from the main body maximum peak measured based on ASTMD3418-8. DSC-7 manufactured by Perkin Elmer Co. can be used for measurement of the main maximum peak. The temperature correction of the detection part of this apparatus uses the melting point of indium and zinc, and the correction of heat quantity uses the heat of fusion of indium. As the sample, an aluminum pan was used, an empty pan was set as a control, and the measurement was performed at a heating rate of 10 ° C./min.

  Further, the weight average molecular weight of the water-absorbent resin is preferably from 1,000 to 1,000,000, more preferably from 5,000 to 500,000. By setting the weight average molecular weight within the above range, it is possible to realize both a quick liquid absorption and good fixing without heating and an image strength after fixing. The weight average molecular weight was measured under the following conditions. For example, GPC uses “HLC-8120GPC, SC-8020 (manufactured by Tosoh Corporation)” apparatus, and two columns are “TSKgel, SuperHM-H (6.0 mm ID × 15 cm, manufactured by Tosoh Corporation)”. And THF (tetrahydrofuran) was used as the eluent. As experimental conditions, the sample concentration was 0.5%, and the flow rate was 0.6 ml / min. The experiment was conducted using a sample injection amount of 10 μl, a measurement temperature of 40 ° C., and an IR detector. The calibration curve is “polystylen standard sample TSK standard” manufactured by Tosoh Corporation: “A-500”, “F-1”, “F-10”, “F-80”, “F-380”, “A-2500”. ”,“ F-4 ”,“ F-40 ”,“ F-128 ”, and“ F-700 ”.

  Furthermore, the acid value of the water-absorbent resin is 50 mgKOH / g or more and 1000 mgKOH / g or less, more preferably 150 mgKOH / g or more and 500 mgKOH / g or less, more preferably 100 mgKOH / g, in terms of carboxylic acid group (—COOH). It is 300 mgKOH / g or less. By controlling the acid value within the above range, it becomes possible to control the handling properties, water absorption and fixing properties of the particles. The acid value in terms of this carboxylic acid group (—COOH) was measured as follows.

  The acid value was measured according to JIS K0070 and using a neutralization titration method. That is, an appropriate amount of a sample is taken, 100 ml of a solvent (diethyl ether / ethanol mixed solution) and a few drops of an indicator (phenolphthalein solution) are added, and shaken sufficiently until the sample is completely dissolved in a water bath. This was titrated with a 0.1 mol / l potassium hydroxide ethanol solution, and the end point was when the indicator was light red for 30 seconds. When the acid value is A, the sample amount is S (g), the 0.1 mol / l potassium hydroxide ethanol solution used for the titration is B (ml), and f is the factor of the 0.1 mol / l potassium hydroxide ethanol solution. , A = (B × f × 56.11) / S.

(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 suitably 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 suitably.

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 size of the magnetic powder before the hydrophobization treatment described later is preferably in the range of 0.02 μm to 2.0 μm. When the average primary particle diameter of the magnetic powder is in the above range, the magnetic powder is less likely to aggregate, and uniform dispersion in the polymerizable monomer is facilitated.

  In the present embodiment, the surface of the magnetic powder is preferably subjected to a hydrophobic treatment. 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, or 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 An aralkyl represented by an agent, C ₆ H ₅ —C _r H _2r —Si— (OC _s H _{2s + 1} ) ₃ (wherein r represents an integer of 2 to 20 and s represents an integer of 1 to 3). 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 the above formulas are in the above ranges, desired hydrophobicity can be imparted while avoiding coalescence of the magnetic powders, and the magnetic powders can be uniformly dispersed in the polymer particles. . Moreover, when q and s are in the above ranges, the reactivity of the silane coupling agent is good and desired hydrophobicity can be achieved.

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. Desirable to obtain.

  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. The above hydrophobization treatment can also be used in combination.

  The treatment amount of the hydrophobizing agent with respect to the magnetic powder in the hydrophobization treatment is desirably in the range of 0.05 part by mass or more and 20 parts by mass or less, and 0.1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the magnetic powder. The following range is more preferable.

  The content of the magnetic powder is determined by the required magnetic force, but in the present embodiment, the content should be in the range of 2.5% by mass to 50% by mass with respect to the total amount of the magnetic polymer particle constituent components. Desirably, the range of 5% by mass to 30% by mass is more preferable. By setting the content in the above range, a sufficient magnetic force can be obtained, and the dispersion stability of the polymer particles in an aqueous medium can be enhanced.

(Other ingredients)
The magnetic polymer particles of the present embodiment can further contain a dye for the purpose of coloring the polymer, an organic pigment, a colorant such as carbon black, titanium oxide, and the like. In that case, the additives can be directly mixed in the mixture of the monomer and the like in which the magnetic powder is dispersed, or the magnetic powder is dispersed in advance in the magnetic powder and the mixture of the monomer and the like. The treatment and the dispersion treatment of the respective additives can be performed simultaneously.

  Examples of the colorant include carbon black, chrome yellow, hansa yellow, benzidine yellow, sren yellow, quinoline yellow, permanent yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliant carmine 3B, Brilliant Carmine 6B, DuPont Oil Red, Pyrazolone Red, Risor Red, Rhodamine B Lake, Lake Red C, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Phthalocyanine Green, Malachite Green Oxalate, etc. Various pigments: acridine, xanthene, azo, benzoquinone, azine, anne Rakinon, dioxazine, thiazine, azomethine, indigo, thioindigo, phthalocyanine, triphenylmethane dyes, diphenylmethane dyes, thiazine, thiazole, and the like various dyes, such as xanthene. These colorants may be used alone or in combination of two or more.

The magnetic polymer particles of the present embodiment can further contain other resin components. After non-heat-fixing, if necessary, treatment with external energy such as heating, electromagnetic waves, or solvent vapor can be performed to melt the resin component to further improve the image storability.
Examples of the resin component include plastic binder resins. Specifically, homopolymers or copolymers (styrene-based resins) of styrenes such as styrene, parachlorostyrene, and α-methylstyrene; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) Homopolymers or copolymers of vinyl group esters such as lauryl acrylate (vinyl resin); Homopolymers or copolymers of vinyl nitriles such as acrylonitrile and methacrylonitrile (vinyl resin); Homopolymers or copolymers of vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether (vinyl resins); vinyl Homopolymers or copolymers of vinyl ketones such as tilketone, vinyl ethyl ketone, and vinyl isopropenyl ketone (vinyl resins); Homopolymers or copolymers of olefins such as ethylene, propylene, butadiene, and isoprene (olefins) Resin); non-vinyl condensation resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and graft polymers of these non-vinyl condensation resins and vinyl monomers. Can be mentioned. These resins may be used alone or in combination of two or more. Among these resins, styrene resins, vinyl resins, polyester resins, and olefin resins are preferable, copolymers of styrene and n-butyl (meth) acrylate, n-butyl (meth) acrylate, bisphenol A. -A fumaric acid copolymer and a copolymer of styrene and olefin are particularly preferred.

  The magnetic polymer particles of the present embodiment may further contain components such as a release agent, inorganic particles, lubricant, and abrasive depending on the purpose. Examples of the release agent used herein include low molecular weight polyolefins such as polyethylene, polypropylene, and polybutene; silicones having a softening point upon heating; fatty acids such as oleic acid amide, erucic acid amide, ricinoleic acid amide, and stearic acid amide Amides; Long-chain aliphatic alcohols such as lauryl alcohol, stearyl alcohol, and behenyl alcohol; plant waxes such as carnauba wax, rice wax, candelilla wax, tree wax, jojoba oil; animal waxes such as beeswax; montan wax And mineral / petroleum waxes such as ozokerite, ceresin, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax; and modified products thereof.

Next, the manufacturing method of the magnetic polymer particle of this embodiment is demonstrated.
As a result of examining the production method for obtaining the above-mentioned magnetic polymer particles by the present inventors, the reason is not clear, but a hydrophobic monomer and a monomer having an acidic group are mixed in water. In the case of suspension polymerization, it has been found that the particles tend to aggregate during the polymerization, and it is difficult to form particles in which the magnetic powder is uniformly incorporated.

  For this reason, the magnetic polymer particles of this embodiment form resin fine particles containing a water-absorbing resin precursor in advance by emulsion polymerization or the like, mix magnetic powder, etc., and granulate in an aqueous medium, and then perform a neutralization reaction. To obtain water-absorbing resin composite particles containing magnetic powder, or by previously forming resin fine particles containing a water-absorbing resin by emulsion polymerization or the like and mixing this with magnetic powder etc. It is desirable to fuse and then pulverize the resulting fusion. By this method, magnetic polymer particles in which the water-absorbent resin and the magnetic powder are combined can be obtained by a simple process.

  The resin fine particles can be easily obtained by an emulsion polymerization method or a nonuniform dispersion polymerization method similar thereto. In addition, a polymer that has been uniformly polymerized by a solution polymerization method, a bulk polymerization method, or the like in advance can be obtained by an arbitrary method such as a method in which a polymer is added to a solvent in which the polymer is not dissolved together with a stabilizer and mechanically mixed and dispersed Can do.

  For example, in the case of a vinyl monomer (ethylenically unsaturated monomer), an emulsion polymerization is performed using an ionic surfactant or the like according to the production method to prepare a resin fine particle dispersion. Can do. In the case of other resins, if the resin is soluble in oil and has a relatively low solubility in water, the resin is dissolved in those solvents and the water is homogenized with an ionic surfactant or polymer electrolyte. A dispersion of resin fine particles can be prepared by dispersing fine particles in water with a disperser such as the above, and then heating or depressurizing to evaporate the solvent.

  Examples of the surfactant include anionic surfactants such as sulfate ester sulfonates, phosphate esters and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; polyethylene glycols Nonionic surfactants such as alkylphenol ethylene oxide adduct system, alkyl alcohol ethylene oxide adduct system, polyhydric alcohol system, and various graft polymers can be exemplified, but are not particularly limited.

  When preparing a resin fine particle dispersion by emulsion polymerization, a protective colloid layer can be formed with a small amount of unsaturated acid such as acrylic acid, methacrylic acid, maleic acid, styrene sulfonic acid, etc. Is particularly preferable.

As the polymerization initiator used in the present embodiment, azo polymerization initiators, peroxide initiators and the like can be mentioned as preferable ones, and among them, a water-soluble initiator is desirable.
Water-soluble azo initiators include 2,2′-azobis [N- (2-hydroxyethyl) -2-methyl-propionamidine] dihydrochloride, 2,2′-azobis (2-amidinopropane) dihydrochloride 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 4,4 ′ -Azobis (4-cyanovaleric acid) etc. are mentioned.
Examples of the water-soluble peroxide initiator include ammonium persulfate, potassium persulfate, and hydrogen peroxide.

  The addition amount of the polymerization initiator is not particularly limited, but is preferably in the range of 0.05 to 10 parts by mass with respect to 100 parts by mass of all monomer components, and is 0.1 to 5 parts by mass. It is more preferable that the amount is not more than part.

The polymerization reaction can be carried out not only in the air but also under pressure, but these other reaction conditions are applied as necessary and are not particularly limited.
As the reaction conditions, for example, a reaction at a reaction temperature of 40 ° C. to 100 ° C. for 1 to 24 hours while stirring the emulsion in which the emulsified particles are dispersed is performed at atmospheric pressure, and a high yield of about 80% or more is obtained. From the standpoint of obtaining polymer particles at a high rate.

  The particle size of the resin fine particles (polymer particles) in the resin fine particle dispersion is desirably 1 μm or less in terms of volume average particle size, and more preferably in the range of 100 nm to 800 nm. If the volume average particle size exceeds 1 μm, it may be difficult to uniformly disperse the magnetic powder during fusion, which will be described later, or free particles may be generated, leading to a reduction in the final toner yield. If the thickness is less than 100 nm, it may take time to coagulate and grow the resin fine particles and the magnetic powder, which may not be industrially suitable. If the thickness exceeds 800 nm, the dispersion of the magnetic powder becomes non-uniform and the colorant or the like When these are used, their dispersibility may be non-uniform.

In addition, the acidic group amount of the polymer particles in the present embodiment is desirably in the range of 1.0 mmol / g to 3.5 mmol / g, and in the range of 1.5 mmol / g to 3.0 mmol / g. More desirable.
If the amount of acidic groups is less than 1.0 mmol / g, sufficient liquid absorbency may not be obtained for non-heat-fixing even if these have a salt structure. If it exceeds 3.5 mmol / g, the liquid absorbency becomes too large, and it may be difficult to handle as particles used for liquid magnetography, and the image quality may be lowered.

  As described above, the magnetic polymer particles of the present embodiment are obtained by (Method 1) forming resin fine particles containing a water-absorbing resin precursor in advance by emulsion polymerization or the like, mixing magnetic powder and the like and granulating them in an aqueous medium. Or a neutralized reaction to obtain water-absorbing resin composite particles containing magnetic powder, or (Method 2) forming resin fine particles containing a water-absorbing resin in advance by emulsion polymerization or the like, It is desirable to fuse the resin fine particles and the magnetic powder by mixing, and then pulverize the resulting fusion product.

In the case of (Method 1), magnetic powder, resin fine particles containing a water-absorbing resin precursor, the other resin, and if necessary, a colorant and other additives are dissolved and dispersed in an organic solvent such as ethyl acetate. Is emulsified in an aqueous medium containing a dispersant stabilizer by using an emulsifier or a disperser to form an oil-in-water type aqueous suspension, and then the solvent is removed to remove the magnetic resin composite particles. Is obtained. The in-liquid drying method is preferable from the viewpoint that a toner containing a resin that melts at a low temperature can be easily produced, and that a release agent (such as wax) can be contained in the toner. The magnetic polymer composite particles obtained by the in-liquid drying method are neutralized with a basic compound in the presence of water or a mixture of water and a water-soluble organic solvent to obtain the magnetic polymer particles of this embodiment. be able to.
In the present embodiment, the treatment may be performed by adding a basic compound to the aqueous dispersion of the magnetic resin composite particles, or by mixing the magnetic resin composite particles in the aqueous solution in which the basic compound is dissolved. May be. It is preferable to mix and disperse the magnetic powder with the other resin components in advance to form a so-called masterbatch because it can cause a high degree of dispersion of the magnetic powder in the resin and a hydrophobic treatment of the magnetic powder. The neutralization treatment can be performed in the same manner as described later (Method 2).

In the case of (Method 2), some or all of the acidic groups in the water-absorbent resin contained in the resin fine particles prepared in advance by emulsion polymerization or the like have a salt structure. It is desirable to neutralize by. This is because the carboxyl group in the resin has a salt structure, the water absorbability of the water-absorbent resin is increased, the resin is easily swollen, and the fusion with the magnetic powder is promoted.
In the same manner as described above, for example, the resin fine particles may be treated with a basic compound in the presence of water or a mixed liquid of water and a water-soluble organic solvent. In this embodiment, the treatment may be performed by adding a basic compound to the aqueous dispersion of resin fine particles, or the resin fine particles may be mixed and treated in an aqueous solution in which the basic compound is dissolved.

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 desirable to use an inorganic basic compound from the viewpoint of easy removal of the basic compound after the treatment.

  In the present embodiment, the amount of the basic compound used is desirably in the range of 0.1% by mass or more and 20% by mass or less of the aqueous dispersion of resin fine particles. Further, in the resin fine particles obtained by the treatment with the basic compound, it is desirable that all the carboxyl groups form a salt structure. Usually, in the range of the use amount, the basic compound is a carboxyl group of the resin fine particles. It is set to be excessive with respect to the amount.

  At this time, the pH of the aqueous dispersion of resin fine particles is preferably 9 or more, and 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 resin fine particles during the treatment is not particularly limited, but is usually in the range of 1% by mass to 50% by mass. When the resin fine 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.

Next, the resin fine particles containing the produced water-absorbing resin and the magnetic powder are mixed and fused.
For the fusion, for example, a predetermined amount of magnetic powder and other components such as a colorant are added and mixed in the aqueous dispersion of resin fine particles subjected to the neutralization treatment. The mixing method is not particularly limited, but a known mixing method can be used. For example, like a mixer, rotating a special stirring blade at high speed to mix resin fine particles and magnetic powder in an aqueous medium, mixing by the shearing force of a rotor / stator known as a homogenizer, suspension by ultrasonic waves And mechanical mixing methods such as

In the fusion, normal fine particles of non-crosslinked resin may be mixed as the fine resin particles used in addition to the fine particles of the water absorbent resin.
As said non-crosslinked resin, what was illustrated by the above-mentioned other resin can be utilized suitably.

Among these, in particular, when polyester is used to form a non-crosslinked polymer, it is effective for heat fixing. As the polyester, for example, a linear polyester resin made of a polycondensate containing bisphenol A and a polyvalent aromatic carboxylic acid as main monomer components can be preferably used.
Styrene-alkyl acrylate copolymers and styrene-alkyl methacrylate copolymers are also preferably used because they can easily control physical properties and can be easily mixed and dispersed with a magnetic powder described later.

In this embodiment, the mixture such as stirring is mixed and then freeze-dried or the like as it is to obtain a fusion product of resin fine particles and magnetic powder. However, if necessary, the mixture is heated and mixed during the mixing. You may let them.
The fusion product can be obtained through a solid-liquid separation process such as filtration, and a washing process and a drying process as necessary. As the drying step, an arbitrary method such as a normal vibration type fluidized drying method, a spray drying method, a freeze drying method, or a flash jet method can be adopted. At this point, from the viewpoint of facilitating pulverization, it is desirable to adjust the moisture content of the fusion product after drying to 5% by mass or less.

Since the fusion product is obtained by agglomerating and fusing resin fine particles containing a water-absorbing resin from a gel state in water, the fusion product is often obtained as a lump rather than a particle. Therefore, in order to obtain magnetic polymer particles having a desired particle size, it is necessary to grind the massive fusion product.
The pulverization method is not particularly limited, and can be carried out using a pulverization means known per se, such as a mortar, ball mill, jet mill or the like.

The magnetic polymer particles after pulverization are in the form of particles, but the number average particle size is preferably 0.4 μm or more and 16 μm or less, and more preferably 0.8 μm or more and 8 μm or less.
If the number average particle diameter is less than 0.4 μm, the content of the magnetic powder varies, and the number of particles that do not contain the magnetic powder may increase and the image quality may deteriorate. If it exceeds 16 μm, the particle size may become too large when dispersed in an aqueous medium as a developer described later, and the image quality may deteriorate.

  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. The value divided by the number.

  The magnetic polymer particles of the present embodiment contain a water-absorbing resin in the resin, and the water-absorbing resin has an acidic group as described above, so that the liquid-absorbing resin has a large structure and easily swells. In this case, examples of the acidic group include a carboxyl group, a sulfone group, a phosphoric acid group, and a formyl group, and the carboxyl group is most desirable as described above.

In the present embodiment, the amount of acidic groups in the magnetic polymer particles varies greatly depending on the content of the magnetic powder, and thus is defined as the amount of acidic groups with respect to 1 g of all resin components (including color materials) excluding the magnetic powder. Is preferably in the range of 0.5 mmol / g to 3.0 mmol / g, and more preferably in the range of 1.0 mmol / g to 2.5 mmol / g.
If the amount of acidic groups is less than 0.5 mmol / g, sufficient liquid absorbency may not be obtained for non-heat-fixing even if these have a salt structure. When it exceeds 3.0 mmol / g, the liquid absorbency becomes too large, and it may be difficult to handle as particles used in liquid magnetography or the image quality may be deteriorated.

  The amount of the acidic group can be determined by a general titration method as will be described later. For example, a certain amount of a reagent such as an ethanol solution of potassium hydroxide is added to the polymer particles to carry out a neutralization reaction, and the particles and supernatant are separated by a centrifuge, and the supernatant containing excess potassium hydroxide is automatically removed. The amount of carboxyl groups can be determined by titrating with an isopropanol hydrochloric acid solution or the like using a titration apparatus.

For example, when the acidic group is a carboxyl group and a salt structure (-COO ^- Y ⁺ : where Y ⁺ represents an organic cation such as an alkali metal ion, an alkaline earth metal ion, or ammonium) is formed. Can convert the salt into a carboxylic acid with an acid such as hydrochloric acid and then titrate as described above to determine the amount of carboxyl groups.
That is, the carboxyl group amount (acidic group amount) in the present embodiment means the carboxyl group amount including the carboxyl group contributing to the salt structure when the carboxyl group forms a salt structure.

The volume average particle diameter of the magnetic polymer particles having the above characteristics in water is desirably 0.5 μm or more and 20 μm or less, and more preferably 1.0 μm or more and 10 μm or less.
If the volume average particle size in water is less than 0.5 μm, swelling due to liquid absorption is not sufficient, and good non-heat fixing may not be performed. If it exceeds 20 μm, the particle size is too large for liquid magnetography, and the image quality may be deteriorated or the handling as a developer may be hindered.

  The volume average particle size of the magnetic polymer particles in the water is measured by Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.) after dispersing the magnetic polymer particles in distilled water and leaving them at 23 ° C. for 24 hours. can do.

Since the magnetic polymer particles in the present embodiment contain a water-absorbing resin, the particle surface becomes hydrophilic in the aqueous medium and has excellent dispersibility. The dispersibility can be evaluated by water dispersibility (dispersibility in pure water). Specifically, it can be carried out by observing the particle state when the magnetic polymer particles are added to 20 times the amount of water of the polymer particles 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, it is desirable that the magnetic polymer particles are well dispersed in water without stirring so that the polymer particles do not float on the water surface or deposit on the wall surface of the container after stirring.

<Developer for liquid magnetography>
The developer for liquid magnetography in the present embodiment (hereinafter sometimes simply referred to as “liquid developer”) is a particle dispersion in which the magnetic polymer particles are dispersed in an aqueous medium such as water.
As the aqueous medium, water or water added with a water-soluble organic solvent such as methanol or ethanol is suitably used. Among these, water alone is particularly preferable. The amount of water-soluble organic solvent to be added depends on the properties of the magnetic polymer particles to be dispersed, but is preferably 30% by mass or less, more preferably 10% by mass or less, based on the total solvent.

In the production of a liquid developer, various auxiliary materials that can be used in ordinary aqueous particle dispersions, such as dispersants, emulsifiers, surfactants, stabilizers, wetting agents, thickeners, foaming agents. Antifoaming agent, coagulant, gelling agent, anti-settling agent, charge control agent, antistatic agent, anti-aging agent, softening agent, plasticizer, filler, coloring agent, flavoring agent, anti-adhesive agent, mold release An agent or the like may be used in combination.
Specifically, as the surfactant, any known surfactant such as an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. In addition, silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers; splicrisporic acid and rhamnolipid, And biosurfactants such as lysolecithin.

  As the dispersant, any polymer having a hydrophilic structure portion and a hydrophobic structure portion can be used effectively. For example, styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer. Polymer, vinyl naphthalene-acrylic acid copolymer, acrylic acid alkyl ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid, styrene-methacrylic acid alkyl ester-methacrylic acid copolymer, styrene-acrylic acid alkyl ester -Acrylic acid copolymer, styrene-methacrylic acid phenyl ester-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, etc., and these copolymers are random, block and graft copolymer Coalescence It may be in any of the structure.

In the present embodiment, a water-soluble organic solvent can be used for the purpose of controlling evaporation and interface characteristics. The water-soluble organic solvent is an organic solvent that does not separate into two phases when added to water, and examples thereof include mono- or polyhydric alcohols, nitrogen-containing solvents, sulfur-containing solvents, and other derivatives thereof.
Furthermore, for the purpose of adjusting conductivity and pH in an aqueous medium, compounds of alkali metals such as potassium hydroxide, sodium hydroxide and lithium hydroxide, ammonium hydroxide, triethanolamine, diethanolamine, ethanolamine, 2- Addition of nitrogen-containing compounds such as amino-2-methyl-1-propanol, alkaline earth metal compounds such as calcium hydroxide, acids such as sulfuric acid, hydrochloric acid and nitric acid, strong acids such as ammonium sulfate, and weak alkali salts Is possible.

  In addition, benzoic acid, dichlorophen, hexachlorophene, sorbic acid, and the like may be added as necessary for the purpose of mold prevention, antiseptic, rust prevention, and the like. Moreover, you may add antioxidant, a viscosity modifier, a electrically conductive agent, a ultraviolet absorber, a chelating agent, etc.

  In this embodiment, the dispersed particle diameter of the magnetic polymer particles in the liquid developer is preferably 0.5 μm or more and 20 μm or less in terms of volume average particle diameter, and is preferably in the range of 1 μm or more and 8 μm or less. The dispersion average particle diameter of the magnetic polymer particles is a volume average particle diameter determined by a Coulter Counter Multisizer 3 (manufactured by Beckman-Coulter).

When magnetic polymer particles suitably designed for the present embodiment are used as the magnetic toner in the liquid developer, the magnetic powder is uniformly dispersed in the particles as described above. There is almost no magnetic powder on the particle surface. Moreover, since the particles contain a water-absorbing resin, they exhibit good dispersibility in an aqueous medium.
For this reason, when the above liquid developer is used, there is no variation in micro surface tension in the liquid, and the mobility of particles with respect to the magnetic force during development is small among the particles. Effective for improving image quality (density uniformity, fine line reproducibility, etc.).

The production of the developer for liquid magnetography can be carried out by the following procedure, but is not limited thereto.
First, a dispersion medium containing water as a main solvent and the respective additives is prepared using a magnetic stirrer or the like, and the magnetic polymer particles are dispersed in the dispersion medium. A known method can be applied to the dispersion. That is, a dispersing machine such as a ball mill, a sand mill, an attritor, or a roll mill can be used. Further, as a mixer, a method of rotating a special stirring blade at high speed to disperse, a method of dispersing by the shearing force of a rotor / stator known as a homogenizer, a method of dispersing by ultrasonic waves, and the like can be mentioned.

  It was confirmed by microscopic observation of the dispersion liquid that the magnetic polymer particles were in a single dispersion state in the liquid, and then it was confirmed that the additive was dissolved by adding additives such as preservatives. Thereafter, the obtained dispersion liquid is filtered using, for example, a membrane filter having a pore diameter of 100 μm, and dust and coarse particles are removed to obtain a liquid developer as an image forming recording liquid.

  The viscosity of the liquid developer in the exemplary embodiment is preferably 1 mPa · s or more and 500 mPa · s or less, although it depends on the image forming system used. When the viscosity of the liquid developer is less than 1 mPa · s, a sufficient image density may not be obtained because the amount of the magnetic polymer particles and the amount of the additive are not sufficient. On the other hand, when the viscosity of the liquid developer is greater than 500 mPa · s, handling may be difficult or developability may be deteriorated because the viscosity is too high.

Next, a process in which a developer for liquid magnetography containing magnetic polymer particles is used will be described.
The image forming process to which the liquid developer of the present embodiment is applied includes a so-called electrophotographic process, a process of forming an electrostatic latent image with ions or the like on a dielectric (ionography), and a thermal head on a charged dielectric. It is a process that forms a toner image by forming a magnetic latent image on an image carrier, not using an electrostatic latent image, such as a process of forming an electrostatic latent image according to image information by heat. The configuration is not particularly limited except that a liquid developer containing an aqueous medium is used as the developer.
In the following, an image forming apparatus using a magnetic development process using the developer for liquid magnetography in the present embodiment will be briefly described.

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus employing a liquid magnetography method that can be used in the present embodiment. The image forming apparatus 100 includes a magnetic drum (magnetic latent image holder) 10, a magnetic head (magnetic latent image forming means) 12, a developing device (developer storage means and developer supply means) 14, and an intermediate transfer body (transfer means). 16, a cleaner 18, a demagnetizer (demagnetizer) 20, and a transfer fixing roller (transferr) 28. The magnetic drum 10 has a cylindrical shape, and a magnetic head 12, a developing device 14, an intermediate transfer member 16, a cleaner 18 and a demagnetizing device 20 are sequentially provided on the outer periphery of the magnetic drum 10.
The operation of the image forming apparatus 100 will be briefly described below.

First, the magnetic head 12 is connected to an information device (not shown), for example, and receives binarized image data sent from the information device. The magnetic head 12 forms a magnetic latent image 22 on the magnetic drum 10 by emitting lines of magnetic force while scanning the side surface of the magnetic drum 10. In FIG. 1, the magnetic latent image 22 is indicated by a hatched portion in the magnetic drum 10.
The developing device 14 includes a developing roller (developer supply means) 14a and a developer storage container (developer storage means) 14b. The developing roller 14a is provided so that a part thereof is immersed in the liquid developer 24 stored in the developer storage container 14b.

The liquid developer 24 includes an aqueous medium and toner particles. The toner particles are a magnetic toner including a magnetic material. Details of the aqueous medium and toner particles are as described above.
In the liquid developer 24, the toner particles are uniformly dispersed. For example, the liquid developer 24 is further stirred by a stirring member provided in the developer storage container 14 b at a predetermined rotation speed, so that the liquid The positional variation in the concentration of toner particles in the developer 24 is reduced. Thus, the liquid developer 24 with reduced toner particle density variation is supplied to the developing roller 14a rotating in the direction of arrow A in the figure.

  The liquid developer 24 supplied to the developing roller 14a is transported to the magnetic drum 10 in a state where the liquid developer 24 is limited to a constant supply amount by a regulating member described later, and the developing roller 14a and the magnetic drum 10 come close (or contact). The magnetic latent image 22 is supplied at the position. As a result, the magnetic latent image 22 is visualized and becomes a toner image 26.

The developed toner image 26 is transported to a magnetic drum 10 that rotates in the direction of arrow B in the figure and transferred to a sheet (recording medium) 30. In this image forming apparatus, before being transferred to the sheet 30, the magnetic image is magnetically transferred. In order to improve the transfer efficiency to the recording medium including the separation efficiency of the toner image from the drum 10 and to perform fixing simultaneously with the transfer to the recording medium, the toner image is once transferred to the intermediate transfer body 16.
Transfer to the intermediate transfer member 16 is preferably performed by shearing transfer (non-electric field transfer) because the toner particles have almost no charge. Specifically, the magnetic drum 10 rotating in the direction of arrow B and the intermediate transfer member 16 rotating in the direction of arrow C are brought into contact with each other with a certain nip (contact surface having a contact width in the moving direction), and a toner image 26 is obtained. On the other hand, the toner image 26 is transferred onto the intermediate transfer member by an attractive force greater than the magnetic force with the magnetic drum 10. At this time, a peripheral speed difference may be provided between the magnetic drum 10 and the intermediate transfer member 16.

Next, the toner image conveyed in the direction of arrow C by the intermediate transfer member 16 is transferred to the paper 30 at a position where it contacts the transfer and fixing roller 28 and is simultaneously fixed.
The transfer fixing roller 28 sandwiches the paper 30 with the intermediate transfer member 16, and brings the toner image on the intermediate transfer member 16 into close contact with the paper 30. As a result, the toner image can be transferred to the paper 30 and simultaneously fixed on the paper. The toner image can be fixed only by pressure without heating because the developer for liquid magnetography of this embodiment is used as the developer. In this case, the pressing force applied to the intermediate transfer member 16 by the transfer fixing roller 28 is preferably 0.05 MPa or more and 10 MPa or less. Unlike this embodiment, when a separate fixing device is provided, for example, the pressing force between the fixing rollers is preferably set to the same level as described above.

On the other hand, in the magnetic drum 10 in which the toner image 26 is transferred to the intermediate transfer member 16, the transfer residual toner is conveyed to a contact position with the cleaner 18 and collected by the cleaner 18. After cleaning, the magnetic drum 10 rotates and moves to the demagnetization position while holding the magnetic latent image 22.
The degaussing device 20 erases the magnetic latent image 22 formed on the magnetic drum 10. The cleaner 18 and the degaussing device 20 return the magnetic drum 10 to a state in which there is no variation in the magnetization state of the magnetic layer before image formation. By repeating the above operation, images successively sent from the information device are continuously formed in a short time. The magnetic head 12, the developing device 14, the intermediate transfer member 16, the transfer fixing roller 28, the cleaner 18, and the demagnetizing device 20 provided in the image forming apparatus 100 are all operated in synchronization with the rotation speed of the magnetic drum 10. ing.

In the image forming apparatus, it is desirable to use the magnetic drum 10 having water repellency as the image carrier. Here, water repellency means the property of repelling water, and specifically means that the contact angle with pure water is 70 degrees or more.
The contact angle of the surface of the magnetic drum 10 was measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd .: CA-X) under the environment of 25 ° C. and 50% RH with pure water on the surface of the magnetic drum 10. 3.1 μl was dropped and the contact angle after 15 seconds was determined.

  That is, an aqueous medium is used as a dispersion medium in the liquid developer, but since water has a large surface tension due to hydrogen bonding, the liquid developer is imaged during development by combining with a water repellent image carrier. Even when it comes into contact with the holding body, the liquid as the dispersion medium hardly transfers to the image holding body, and the toner image can be transferred to the recording medium without leaving the liquid on the image holding body. Accordingly, a squeeze roller or the like for removing the residual solvent on the image holding member is unnecessary, and the recording medium on which the toner image is transferred hardly needs to be dried.

  Furthermore, during development, an aqueous medium having a large surface tension hardly wets and spreads on the surface of the image carrier. On the other hand, a magnetic toner having high mobility and being uniformly dispersed in the developer is At the same time as the contact with the holder, only the magnetic latent image is transferred by magnetic force, so that a developing environment in which image fog is hardly generated is created.

  In the image forming apparatus employing the liquid magnetography method exemplified above, the developer for liquid magnetography of this embodiment in which magnetic polymer particles containing a water-absorbing resin are uniformly dispersed in an aqueous medium containing water is used for image formation. When used as a developer, not only a high-quality image excellent in non-heat-fixing property is obtained, but also the work environment is not contaminated by a non-aqueous solvent.

  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.

<Measurement method for each characteristic value>
First, a method for measuring each characteristic value shown in the following examples will be described. Note that the measurement methods already described are omitted.
(Water absorption rate)
The water absorption was measured as follows according to JIS K7209 (1984).
First, the dried resin particles are put into a beaker. Ion exchange water is put here, and it is immersed at 23 ° C. for 24 hours. This particle dispersion is transferred to a centrifuge tube and centrifuged to sediment the particles. Remove the separated scum and absorb excess water remaining on the cake with filter paper. The mass M2 (mg) of the centrifuge tube at this time is weighed and then vacuum-dried at 40 ° C. for 24 hours, and the mass M1 (mg) of the centrifuge tube after drying is weighed. From these measured values, the water absorption C (%) was calculated according to the following formula (1).
Water absorption C (%) = [(M2-M1) / (M1-M3)] × 100 Formula (1)
(Here, M3 is the mass (mg) of the centrifuge tube.)

  The above measurement is for the case where the resin particle is a water-absorbent resin alone. However, when the water-absorbent resin is contained in the magnetic polymer particle, the magnetic powder content is determined by a vibrating sample magnetometer (VSM) or The water absorption rate can be determined by the above method by quantifying with a thermogravimetric analyzer (TG) and calculating the value by subtracting the amount of magnetic powder.

(Amount of acidic group)
-In the case of polymer particles-
First, polymer particles were weighed and placed in a capped test tube, 5 ml of DMF was added, and the mixture was dispersed for 1 hour using an ultrasonic stirrer. The total amount of the dispersion was collected in a conical beaker, and 0.1M ethanolic potassium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise using phenolphthalein (manufactured by Wako Pure Chemical Industries, Ltd.) as an indicator.
Moreover, the blank experiment which does not use a polymer particle was also performed, and the acidic group amount (mmol / g) was computed from the difference according to the following Formula (2).

Acid group content = ((FE) × 0.1 × f) / W (2)
In the above formula (2), E is the potassium hydroxide solution dropping amount (ml) in the blank experiment, F is the sample potassium hydroxide solution dropping amount (ml), f is the factor of the potassium hydroxide solution, W is the polymer Each represents the weight (g) of the particles.

-In the case of magnetic polymer particles-
The magnetic polymer particles were redispersed in 10 times the amount of ion exchange 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 using no magnetic polymer particles was also performed, and the carboxyl group amount (mmol / g) was calculated from the difference according to the following formula (2 ′).
Amount of carboxyl groups = ((BA) × 0.1 × f) / (x− (xx × C / 100)) (2)
In the above formula (2 ′), B is the amount of potassium hydroxide solution dropped in the blank experiment (ml), A is the amount of sample potassium hydroxide solution dropped (ml), f is the factor of the potassium hydroxide solution, x is magnetic The weight (g) of polymer particles, C is the magnetic powder content (%) in the particles.

<Example 1>
(Manufacture of magnetic polymer particles)
In a 2 L three-necked flask equipped with a cooling tube, a nitrogen introduction tube, and a thermometer, 1000 parts of ion-exchanged water was added. To this, 6.0 parts of a surfactant (manufactured by Kao Corporation, Perex CS, solid content concentration: 75%) and 1.5 parts of a polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., potassium persulfate) are added. Dissolved. After making the inside of the system into a nitrogen atmosphere, 4.5 parts of styrene (Wako Pure Chemical Industries, Ltd.), 18.5 parts of butyl methacrylate (Wako Pure Chemical Industries, Ltd.), mono-2-phthalic acid mono (methacryloyloxy) ) Ethyl (Mitsubishi Rayon Co., Ltd., Acryester PA) 72.0 parts and divinylbenzene (Wako Pure Chemical Industries, Ltd., purity: 55%) 1.1 parts were mixed, and this mixture was charged.

  Thereafter, the system was heated to 60 ° C. and reacted for 8 hours. After completion of the reaction, the reaction solution was passed through a sieve having an opening of 20 μm. However, no aggregates of 20 μm or more remained on the sieve, and the whole amount passed. A part of the reaction product was taken and observed with a scanning electron microscope (manufactured by Keyence Corporation, VE7800). As a result, it was monodisperse polymer particles having an average particle diameter of 0.4 μm. After the obtained polymer particles were washed by centrifugation, a part thereof was collected and dried in a vacuum, and the amount of acidic groups was measured to find 2.3 mmol / g.

  Further, 600 parts of a 2% aqueous sodium hydroxide solution was added to the polymer particle slurry washed by centrifugation, and stirred at room temperature for 1 hour to neutralize carboxyl groups. The neutralized polymer particles were washed again by centrifugation, and a part of the polymer particles was collected and vacuum-dried. The water absorption was measured and found to be 500%.

Next, an aqueous dispersion with a solid content of 70% is prepared using the neutralized polymer particles, and 30 parts of magnetic powder (manufactured by Toda Kogyo Co., Ltd., MTS010) is added to the nanomizer (manufactured by Nanomizer). ) And then lyophilized.
The obtained magnetic powder mixture (fusion) was put in a ball mill pot, pulverized with zirconia balls having a diameter of 10 mm, and classified to obtain magnetic polymer particles having a number average particle diameter of 3 μm. The amount of acidic groups of the magnetic polymer particles was 2.1 mmol / g.

(Preparation of liquid developer)
In addition to 100 parts of pure water with respect to 5 parts of the magnetic particles, a developer for liquid magnetography was obtained. In this liquid developer preparation, the particles were redispersed in water well without dislodging the particles on the water surface or depositing on the container wall surface, and the dispersibility was good.

  After preparation of the liquid developer, the mixture was stirred for 1 hour, and then the dispersed particle diameter of the magnetic polymer particles in the developer (in water) was measured. For the measurement, 0.1 ml of liquid developer was sampled, dispersed in 100 ml of a measurement solution Isoton (manufactured by Beckman Coulter, Inc.), and volume averaged particles using Coulter Counter Multisizer 3 (manufactured by Beckman Coulter, Inc.). It measured as a diameter (dispersion average particle diameter). As a result, the volume average particle size was 5 μm. Further, when this measurement was performed after 30 days from the preparation of the liquid developer, the volume average particle diameter was 5 μm.

(Evaluation of actual machine characteristics)
An image forming apparatus 100 having the configuration shown in FIG. 1 was prepared, and the liquid developer was used as a developer to evaluate developability and fixability.
As the magnetic drum 10, Ni—P was plated as an underlayer to a thickness of 15 μm and Co—Ni—P as a magnetic recording layer to a thickness of 0.8 μm on an aluminum drum. Fluorine lubrication plating with -P-PTFE fine particles was performed to form a protective layer having a thickness of 1.5 μm. The magnetic recording layer had a coercive force of 400 Oe and a residual magnetic flux density of 7000 G.
The contact angle of pure water with this magnetic drum 10 surface at 25 ° C. and 50% RH was 110 degrees.

  As the magnetic head 12, a 4-channel full-line magnetic head capable of forming a pixel equivalent to 600 dpi made of Mn—Zn ferrite was prepared.

  The developing device 14 includes, as a developing roller 14a, a magnet roll in which cylindrical permanent magnets are concentrically arranged in a nonmagnetic sleeve made of aluminum, and stirring the liquid developer inside the developer storage container 14b. A developing device 14 provided with a wing was used. The liquid developer was charged into the developer storage container 14b, and the developing device 14 was arranged so that the gap between the nonmagnetic sleeve surface and the magnetic drum 10 surface was 50 μm.

  As the intermediate transfer member 16, an aluminum intermediate transfer drum having a silicone rubber layer having a thickness of 7.5 mm on the surface and rotating at the same peripheral speed as the magnetic drum 10 was used. As the transfer and fixing roller 28, an elastic roll in which a silicone rubber layer and a fluororubber layer are coated in this order on the outer periphery of a stainless steel core material was used.

The printing conditions were set as follows by the image forming apparatus 100 having the above configuration.
Magnetic drum linear velocity: 100 mm / second.
Developing roller peripheral speed / magnetic drum peripheral speed ratio: 1.2.
Transfer conditions (intermediate transfer): The pressing force of the intermediate transfer member to the magnetic drum is set to 0.147 MPa (1.5 kgf / cm ² ).
Transfer fixing condition: The pressing force of the transfer fixing roller against the intermediate transfer member is set to 0.245 MPa (2.5 kgf / cm ² ).

Under the above conditions, a magnetic latent image equivalent to a solid image of 20 mm × 50 mm and a magnetic latent image of 42 μm / line are formed on the magnetic drum 10 by the magnetic head 12, and liquid development is performed on the magnetic latent image by the developing roller. Development was carried out in contact with the agent. When the striped pattern image after development was checked for fine line reproducibility using an ultra-deep laser microscope, the line width of the developed toner for each latent image line was 42 μm on average, and the magnetic latent image However, it had sufficient developability and resolution.
Further, when the fixability of the solid image portion was evaluated by a crease method or a scratch method, it was confirmed that the solid image portion had a sufficient fixability.

<Example 2>
(Manufacture of magnetic polymer particles)
The polymer particles produced in Example 1 were lyophilized without neutralization. On the other hand, 200 parts of styrene acrylic resin (manufactured by Sekisui Chemical Co., Ltd., trade name: S-LEC P-SE-0020) is added to 200 parts of magnetic powder (manufactured by Toda Kogyo Co., Ltd., MTS010), and melt kneaded with a pressure kneader. A magnetic powder master batch (magnetic powder content: 50%) in which magnetic powder was primarily dispersed was prepared.

  To 30 parts of the polymer particles and 60 parts of the magnetic powder masterbatch, 180 parts of ethyl acetate was added and dispersed and dissolved in a ball mill for 24 hours to prepare an oil phase composed of the magnetic powder dispersion. To 200 parts of ion-exchanged water, 40 parts of calcium carbonate (Luminous manufactured by Maruo Calcium Co., Ltd.) and 10.0 parts of carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Cellogen) are added as a dispersion stabilizer. The dispersion medium was dispersed for 24 hours. Into 200 parts of the dispersion medium, 145 parts of the mixture was added, and emulsified at 10,000 rpm for 1 minute with an emulsifying apparatus (manufactured by IKA, Ultra Tarrax) to obtain a suspension. The number average particle size of the suspended particles at this time was 5.0 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 added thereto, and the solvent was removed while flowing nitrogen at 60 ° C. for 3 hours. 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 subjected to a classification operation to obtain magnetic polymer particles having a number average particle size of 5 μm. The amount of acidic groups of the magnetic polymer particles was 1.2 mmol / g. Further, 600 parts of a 2% aqueous sodium hydroxide solution was added to the magnetic polymer particle slurry and stirred at room temperature for 1 hour to neutralize carboxyl groups. The neutralized polymer particles were washed again by centrifugation to obtain magnetic polymer particles of this example. A part of the particles was collected and dried in a vacuum, and the water absorption was measured and found to be 300%.

(Preparation of liquid developer)
A liquid magnetography developer was obtained in the same manner as in Example 1 with respect to 5 parts of the magnetic particles. In this liquid developer preparation, the particles were redispersed in water well without dislodging the particles on the water surface or depositing on the container wall surface, and the dispersibility was good.

  After preparation of the liquid developer, the dispersed particle diameter of the magnetic polymer particles was measured in the same manner as in Example 1. As a result, the volume average particle diameter was 6 μm. Further, when this measurement was carried out after 30 days from the preparation of the liquid developer, the volume average particle diameter was 6 μm and there was no change.

<Example 3>
(Manufacture of magnetic polymer particles)
In the production of the magnetic polymer particles of Example 1, polymer particles were obtained in the same manner except that 1.1 parts of divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., purity: 55%) was 2.0 parts. . The polymer group had an acidic group content of 2.0 mmol / g and a water absorption of 120%.
Further, after neutralization in the same manner as in Example 1, mixing, fusion and pulverization with magnetic powder were similarly performed to obtain magnetic polymer particles having a number average particle diameter of 5 μm. The amount of acidic groups of the magnetic polymer particles was 1.8 mmol / g.

(Production of liquid developer, evaluation of actual machine characteristics)
A liquid developer was prepared in the same manner as in Example 1 using the obtained magnetic polymer particles. The volume average particle size of the magnetic polymer particles in the developer at this time was 6 μm after the production, and 6 μm after being left for 30 days after the production of the developer.

  Next, in the same manner as in Example 1, when image formation was performed by the image forming apparatus shown in FIG. 1, the developability and resolution were good, but the fixability was in Example 1 for both the crease method and the scratch method. It was slightly lower than the case.

<Example 4>
(Manufacture of magnetic polymer particles)
In the production of the magnetic polymer particles of Example 1, polymer particles were obtained in the same manner as in Example 1 except that divinylbenzene was not used. The amount of acidic groups of the polymer particles was 2.5 mmol / g, and the water absorption was 6000%.
Further, after neutralization treatment in the same manner as in Example 1, mixing, fusion and pulverization with magnetic powder were similarly performed to obtain magnetic polymer particles having a number average particle diameter of 3 μm. The amount of acidic groups in the magnetic polymer particles was 2.5 mmol / g.

(Production of liquid developer, evaluation of actual machine characteristics)
A liquid developer was prepared in the same manner as in Example 1 using the obtained magnetic polymer particles. The volume average particle diameter of the magnetic polymer particles in the liquid developer at this time was 12 μm after the production, and 15 μm after being left for 30 days after the production of the developer.

  Next, image formation was performed by the image forming apparatus shown in FIG. 1 in the same manner as in Example 1. As a result, the developability and resolution decreased slightly as the particle size increased, but the fixability was good. there were.

<Comparative Example 1>
(Manufacture of magnetic polymer particles)
In the production of the magnetic polymer particles of Example 1, 23.5 parts of styrene, 24.0 parts of butyl methacrylate, 47.0 parts of mono-2- (methacryloyloxy) ethyl phthalate, divinylbenzene 2.2 Polymer particles were obtained in the same manner as in Example 1 except for changing to parts. The amount of acidic groups of the polymer particles was 0.89 mmol / g, and the water absorption was 90%.
Further, after neutralization in the same manner as in Example 1, mixing, fusion and pulverization with magnetic powder were similarly performed to obtain magnetic polymer particles having a number average particle diameter of 5 μm. The amount of acidic groups of the magnetic polymer particles was 0.82 mmol / g.

(Production of liquid developer, evaluation of actual machine characteristics)
A liquid developer was prepared in the same manner as in Example 1 using the obtained magnetic polymer particles. The volume average particle size of the magnetic polymer particles in the developer at this time was 5 μm after the production, and 5 μm after being left for 30 days after the production of the developer.

  Next, in the same manner as in Example 1, when image formation was performed by the image forming apparatus shown in FIG. 1, the developability and the resolution were good, but the fixability was lowered in both the crease method and the scratch method. Almost never settled.

  As described above, in the embodiment, magnetic polymer particles and a liquid developer that are excellent in water dispersibility and exhibit good fixability when not heated can be obtained. On the other hand, in the comparative example using the magnetic polymer particles not containing the water-absorbing resin, some problem occurred in the fixing property.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus used in the present embodiment.

Explanation of symbols

10 Magnetic drum (magnetic latent image holder)
12 Magnetic head (magnetic latent image forming means)
13 Restricting member 14 Developing device (developer supply means)
15 Stirring member 16 Intermediate transfer member 18 Cleaner 20 Demagnetizing device (demagnetizing means)
22 Magnetic latent image 24 Liquid developer 26 Toner image 28 Transfer fixing roller (transfer means)
29 Fixed image 30 Recording medium

Claims (5)

  A magnetic polymer particle for liquid magnetography, comprising at least a water-absorbent resin and magnetic powder.   2. The magnetic polymer particle for liquid magnetography according to claim 1, wherein the water absorption rate of the water absorbent resin is 200% or more and 5000% or less.   3. The magnetic polymer particle for liquid magnetography according to claim 1, wherein the volume average particle size in water is 0.5 μm or more and 20 μm or less.   The magnetism for liquid magnetography according to any one of claims 1 to 3, wherein the water-absorbent resin has an acidic group, and a part or all of the acidic group forms a salt structure. Polymer particles.   A liquid magnetography developer comprising the magnetic polymer particles for liquid magnetography according to any one of claims 1 to 4 and an aqueous medium.

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