JPH10207105A - Magnetic developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the charge amount of a toner for a long period of time even due to environmental changes, and to prevent a decrease in image density and an increase in fog by suppressing charge-up of the toner particularly in a low-temperature and low-humidity environment. It is intended to provide a developer. A magnetic developer comprising a mixture of magnetic resin particles (a) containing magnetic powder and a binder resin and fine powder (b) having an average particle size of 0.05 to 5 μm, The fine powder (b) is a fine powder obtained by multi-stage polymerization by emulsion polymerization, wherein the alkyl acrylate and / or the alkyl methacrylate are polymerized or copolymerized in the polymerization at a stage prior to the final stage. A magnetic developer, which is a fine powder obtained by polymerizing a polymerizable carboxylic acid or a polymerizable carboxylate in the polymerization of (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic developer, and more particularly to an insulative magnetic developer capable of preventing deterioration in characteristics under a low-temperature and low-humidity environment.

[0002]

2. Description of the Related Art Among development methods applied to electrophotography or electrostatic recording, a two-component development method using a two-component developer obtained by mixing a non-magnetic toner and a magnetic carrier is relatively stable. The resulting image has excellent characteristics, but has disadvantages such as deterioration of carrier and fluctuation of toner concentration. On the other hand, in response to recent market needs such as energy saving and space saving, magnetic toner alone (also referred to as one-component developer) for copiers and printers,
Alternatively, an insulating magnetic developer (also referred to as a 1.5-component developer) formed by mixing a magnetic toner and a magnetic powder-dispersed resin carrier (hereinafter abbreviated as a resin carrier) has been widely used.

[0003] A developing method using an insulating magnetic developer composed of a magnetic toner alone, or a mixture of a magnetic toner and a magnetic powder-dispersed resin carrier (hereinafter abbreviated as a resin carrier) has been proposed. This is a method in which a charge is applied to a magnetic toner by frictional charging between a layer thickness regulating blade and / or a resin carrier, and an electrostatic latent image is visualized by the magnetic toner. A magnetic toner is attached to an electrostatic latent image formed on a photoconductor or an electrostatic recording medium to form a magnetic toner image. After the magnetic toner image is transferred to a transfer sheet, it is fixed to form a copy. On the other hand, the magnetic toner remaining on the photoconductor or the electrostatic recording medium without being transferred is cleaned in preparation for the next copying process. These one-component developer, or 1.5-component developer,
Although it has excellent characteristics such as space saving and energy saving, the charging property is unstable as compared with the two-component developer, and it has been desired to stabilize the charging property conventionally.

[0004] Therefore, various studies have been made to secure good charging characteristics of the toner. For example, Japanese Patent Publication No. 52-32256 discloses a method of adding chargeable fine particles to a toner as a charge assisting agent.
No. 52 proposes a method of adding a resin fine powder having a polarity opposite to that of the toner, and Japanese Patent Application Laid-Open No. 61-160760 proposes a method of adding a fluorinated compound to the toner. However, in the case of the above-described method, it is not easy to uniformly disperse the additive on the toner surface, and it is difficult to avoid that the additives that cannot completely adhere to the toner particles form aggregates. This tendency becomes more remarkable as the triboelectric charging ability of the charging aid increases and as the particle size decreases. In such a case, the amount of frictional charge of the toner becomes unstable, the image density is not constant, the image becomes fogged, or the content of the charging auxiliary agent changes when a large number of copies are made, There are various problems such as that the image quality at the initial stage cannot be maintained.

[0005] Japanese Patent Publication No. 2-3172, Japanese Patent Publication No.
No. 9299 discloses that the toner has an average particle size of 0.05 to 5
A method of mixing resin fine particles of μm has been proposed. However, these resin fine powders have high triboelectric charging ability, but have poor hydrophilicity on the surface, so that when a large number of copies are made under low temperature and low humidity, the charge amount of the toner obtained by mixing the resin fine powders increases. And there is a problem that the image density is reduced. Further, under low temperature and low humidity, the charge amount of the resin fine powder becomes too large, so that the resin fine powder is easily aggregated, the mixing property is reduced, or the resin fine powder is easily attached to the carrier, and This is one of the causes of poor friction with the toner, and as a result, the charging state becomes unstable, and fog (toner flies to non-image areas,
However, there is a problem that the quality of a copied image is deteriorated, for example, the phenomenon of adhesion is increased.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the charge amount of a magnetic toner is stable for a long period of time due to environmental changes. An object of the present invention is to provide an insulative magnetic developer in which a decrease in image density and an increase in fog are prevented by suppressing the increase.

[0007]

According to a first aspect of the invention, a magnetic resin particle (a) containing a magnetic powder and a binder resin and a fine powder (b) having an average particle size of 0.05 to 5 μm are used. A mixed magnetic developer, wherein the fine powder (b) is a fine powder obtained by multi-stage polymerization by emulsion polymerization, and the acrylate alkyl ester and / or methacrylic acid is used in the polymerization at a stage prior to the final stage. A magnetic developer characterized in that it is a fine powder obtained by polymerizing or copolymerizing an alkyl ester and polymerizing a polymerizable carboxylic acid or a polymerizable carboxylate in the final stage of polymerization.

[0008] A second invention is a magnetic recording medium comprising: a magnetic resin particle (a) containing a magnetic powder and a binder resin;
And a magnetic powder-dispersed resin carrier (c) containing a magnetic powder and a binder resin, wherein the fine powder (b) is emulsion polymerized. Is a fine powder obtained by multi-stage polymerization according to (1), wherein an alkyl acrylate and / or an alkyl methacrylate is polymerized or copolymerized in a polymerization in a stage prior to the final stage, and a polymerizable carboxylic acid or A magnetic developer characterized by being a fine powder obtained by polymerizing a carboxylic acid salt.

A third invention is the first invention or the first invention, wherein the fine powder (b) is a fine powder comprising a salt of a carboxylic acid derived from a polymerizable carboxylic acid after polymerization in the final stage. 2 is a magnetic developer according to the invention.

[0010] A fourth invention is the magnetic developer according to the first invention or the second invention, wherein the polymerizable carboxylate is a divalent metal salt of a polymerizable carboxylic acid.

A fifth invention is characterized in that the fine powder (b) is a fine powder comprising a carboxylic acid derived from a polymerizable carboxylic acid as a divalent metal salt after polymerization in the final step. The magnetic developer according to the invention.

A sixth invention is the magnetic developer according to any one of the first to fifth inventions, wherein the magnetic resin particles (a) contain 10 to 55% by weight of magnetic powder.

A seventh aspect of the present invention is a magnetic resin particle (a) 100
The magnetic developer according to any one of the first to sixth inventions, wherein 0.01 to 10 parts by weight of the fine powder (b) is mixed with respect to parts by weight.

An eighth invention is the magnetic developer according to any one of the second to seventh inventions, wherein the magnetic powder-dispersed resin carrier (c) contains 60 to 95% by weight of the magnetic powder. It is.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the fine powder (b) used as an external additive is a fine powder obtained by multi-stage polymerization by emulsion polymerization. It is important that the powder is a fine powder obtained by polymerizing an acidic carboxylate. That is, the surface of the fine powder (b) is covered with a layer containing a carboxylic acid or a carboxylate having relatively high hydrophilicity, so that the carboxylic acid or the carboxylate adsorbs a suitable amount of water. In addition, it is possible to prevent excessive charge-up of the fine powder and the magnetic developer under low temperature and low humidity, and to suppress / prevent a decrease in image density and generation of fog under low temperature and low humidity. It is considered that the lowering of the triboelectric chargeability was suppressed below, and the increase in fog could be suppressed.

The fine powder (b) used in the present invention is a fine powder obtained by multi-stage polymerization by so-called emulsion polymerization.
For example, in the case of two-stage polymerization, a dispersion containing the fine powder is obtained by the following method. (1) By the first-stage emulsion polymerization, a dispersion of fine particles of a polymer of an acrylic acid ester and / or an alkyl methacrylate or a dispersion of fine particles of a copolymer (hereinafter abbreviated as a first-stage dispersion). Then, as a second stage emulsion polymerization, a polymerizable carboxylic acid monomer is added or dropped into the first stage dispersion to carry out emulsion polymerization. (2) In the method of (1), after completion of the second-stage emulsion polymerization, a carboxyl group derived from a polymerizable carboxylic acid present near the surface of the dispersed particles is converted into a salt. (3) In the second stage emulsion polymerization in the method of (1), the first
Emulsion polymerization is carried out by adding or dropping a salt of a polymerizable carboxylic acid to the dispersion liquid in place of the polymerizable carboxylic acid monomer. Although the above (1) to (3) have been described for the case of two-stage polymerization, similarly, in the case of multi-stage polymerization exceeding two stages, the polymerizable carboxylic acid or polymerizable The carboxylate may be polymerized, and the polymerization or copolymerization of the acrylate and / or the alkyl methacrylate may be any one of the stages prior to the final stage, and may be performed immediately before the final stage. Is not limited to this stage.

In the present invention, the polymer or copolymer produced in the step before the final step includes a polymer of an alkyl acrylate monomer, a polymer of an alkyl methacrylate monomer, an alkyl acrylate monomer and A copolymer of an alkyl methacrylate monomer or a copolymer containing at least 50% by weight of an alkyl acrylate monomer or an alkyl methacrylate monomer and containing one or more other copolymerizable monomers is provided. No.

The alkyl acrylate monomer and alkyl methacrylate monomer used in the present invention include esterified products of acrylic acid or methacrylic acid with alcohols such as alkyl alcohols, alkoxy alcohols, aralkyl alcohols and alkenyl alcohols. Examples of the alcohol include methyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, dodecyl alcohol, tetradecyl alcohol, alkyl alcohols such as hexadecyl alcohol; methoxyethyl alcohol, Alkoxy such as ethoxyethyl alcohol, methoxypropyl alcohol, ethoxypropyl alcohol Alcohol; benzyl alcohol, phenylethyl alcohol, such aralkyl alcohols phenylpropyl alcohol; allyl alcohol, include such alkenyl alcohols crotonyl alcohol, methyl acrylate, methyl methacrylate is preferable.

Other monomers which can be copolymerized with the above-mentioned alkyl acrylate monomer and alkyl methacrylate monomer include amides such as acrylonitrile, acrylamide, methacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide and nitriles. , Vinyl acetates, vinyl ethers; nitrogen-containing vinyl compounds such as vinyl carbazole, vinyl pyridine, and vinyl pyrrolide; aliphatic monoolefins such as ethylene, propylene, butene, and isobutylene; vinyl chloride, vinyl bromide, and 1,2-dichloroethylene 1,3-dibromoethylene, halogenated aliphatic olefins such as isopropenyl chloride, isopropenyl bromide, allyl chloride, allyl bromide, vinylidene chloride, vinyl fluoride and vinylidene fluoride; Ene, 1,3-pentadiene, 2
Conjugated diene-based aliphatic olefins such as -methyl-1,3-butadiene; and styrenes such as styrene and α-methylstyrene.

Fine powder (b) used in the present invention
As described above, the polymerizable carboxylic acid may be polymerized in the final polymerization step, or the polymerizable carboxylic acid salt may be polymerized in the final polymerization step.

The polymerizable carboxylic acid used in the final polymerization step includes acrylic acid, methacrylic acid, α-
Ethyl acrylic acid, crotonic acid, α-methyl crotonic acid, α-ethyl crotonic acid, isocrotonic acid, tiglic acid, addition-polymerizable unsaturated aliphatic monocarboxylic acid such as ungeric acid, or maleic acid, fumaric acid, itaconic acid, Examples include addition-polymerizable unsaturated aliphatic dicarboxylic acids such as citraconic acid, mesaconic acid, glutaconic acid, and dihydromuconic acid. One or more of these can be used, and acrylic acid and methacrylic acid are preferred. As the polymerizable carboxylic acid salt used in the final polymerization step, various salts of the above-mentioned polymerizable carboxylic acid are used.

Salts used for forming carboxylic acid salts before or after polymerization include Na, Mg, K, Li, N
H ₄ , Ca, Ba, Zn, Fe, Cu, Al, Ni, C
hydroxides, oxides, inorganic acid salts, organic acid salts such as o, Cr, etc., among which Mg, Ca, Ba, Zn, Fe, N
Hydroxides, oxides, inorganic acid salts and organic acid salts of divalent metals such as i and Co are preferable, and Mg, Ca, Ba,
The hydroxide, oxide, inorganic acid salt and organic acid salt of Zn are preferable, and the hydroxide, oxide, inorganic acid salt and organic acid salt of Zn are most preferable. Organic acids include formic acid, acetic acid, propionic acid and the like. It is preferable to add these salt-forming agents in an amount equivalent to the carboxyl group of the used or used polymerizable carboxylic acid. Even if it is less than the equivalent, it is effective for improving the stability to the charging ability under low temperature and low humidity. Even if it is added in an equivalent amount or more, there is no problem because the excess portion can be removed by performing a water washing step later.

The amount of the polymerizable carboxylic acid or the polymerizable carboxylate used is preferably 0.05 to 20 parts by weight based on 100 parts by weight of the total amount of the monomers used up to the polymerization step before the final step. If the amount is less than 0.05 part by weight, the produced fine powder is added to the magnetic resin particles to form a toner, and the effect of improving the image density under low temperature and low humidity is poor. The triboelectrification ability tends to decrease because the water-absorbing action of water becomes too large.

The polymerization initiator used in the emulsion polymerization of the fine powder (b) used in the present invention includes a persulfate initiator, a redox initiator comprising a persulfate and a sulfoxy compound, and a water-soluble initiator. An azo-based initiator may, for example, be mentioned. Examples of the persulfate initiator include potassium persulfate and sodium persulfate. Examples of the Redox initiator composed of a persulfate and a sulfoxy compound include the above-described persulfate and potassium thiosulfate or sodium thiosulfate. Furthermore, azobiscyanovaleric acid is used as a water-soluble azo initiator,
2,2′-azobis (2-amidinopropane) hydrochloride,
2,2′-azobis (2-amidinopropane) acetate,
2,2′-azobis (N, N′-dimethyleneisobutylamidine) dihydrochloride and the like can be exemplified.

The emulsifier used in the emulsion polymerization of the fine powder (b) used in the present invention includes sodium higher alcohol sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylbenzene sulfonate and sodium dialkyl sulfosuccinate. Anionic emulsifiers such as sodium or potassium fatty acids, alkyl (or alkylphenyl) ethers, sodium or ammonium sulfates: alkylphenol ethylene oxide adducts, higher alcohol ethylene oxide adducts, polypropylene glycol ethylene oxide adducts, etc. Nonionic emulsifiers; cationic emulsifiers such as quaternary ammonium salts; and water-soluble polymers such as polyvinyl alcohol. Can be

Fine powder (b) used in the present invention
After the emulsion polymerization or after the emulsion polymerization, the carboxylic acid on the surface is converted into a salt using the above-mentioned salt-forming agent, and then water is removed from the aqueous dispersion to form a powder. As a means for removing water, various drying methods and pulverization methods / pulverization methods usually used for powder production can be applied. After spray-drying the aqueous dispersion, the dried product is pulverized / pulverized. Is preferred.

The fine powder (b) used in the present invention is prepared by subjecting the carboxylic acid on the surface to a salt after emulsion polymerization or after the emulsion polymerization by using the above-mentioned salt-forming agent, and then subjecting the aqueous dispersion to cross-flow filtration. Emulsifiers and the like can also be removed from the liquid. For example, the emulsifier, unreacted substances and the like can be removed by placing the aqueous dispersion in a tabletop emulsion filter (manufactured by Soken Chemical Co., Ltd.), washing the aqueous dispersion by flowing water. After washing, water may be removed by the above method to obtain fine powder.

Fine powder (b) used in the present invention
Is obtained by various methods as described above, but preferably has an average particle size of 0.05 to 5 μm, and 0.1 to 2 μm.
Those having an average particle size of m are more desirable. 0.05
If it is less than μm, aggregation easily occurs under low temperature and low humidity,
The aggregates are liberated, and it is difficult to suppress or prevent a decrease in image density under low temperature and low humidity. On the other hand, if it exceeds 5 μm, the dispersion becomes non-uniform or it is difficult to integrate with the magnetic resin particles, so it is difficult to suppress and prevent the charge-up of the toner under low temperature and low humidity, and to suppress the decrease in image density under low temperature and low humidity.・ It tends to be difficult to prevent. If the fine powder has a large number of sharp corners, the photoreceptor may be damaged. Therefore, the shape of the fine powder is preferably as small as possible with sharp edges and as round as possible, for example, spherical.

The magnetic developer of the present invention may be prepared by adding and mixing the above-mentioned fine powder (b) with the magnetic resin particles (a) or by mixing the above-mentioned fine powder (b) with the magnetic resin particles (a) and the magnetic powder. Dispersion type resin carrier (c) (hereinafter, resin carrier (c)
Abbreviated as)), and in the latter case,
It is preferable to first add and mix the above-mentioned fine powder (b) to the magnetic resin particles (a) and then add and mix the magnetic powder-dispersed resin carrier (c). In the case of using the latter, ie, a resin carrier, the fine powder (b) is replaced with the magnetic resin particles (a).
The toner added and mixed with the toner may be referred to as a magnetic toner.
The magnetic resin particles (a) used in the present invention contain a binder resin and a magnetic powder. Examples of the binder resin used include styrenes such as styrene, chlorostyrene and vinylstyrene, ethylene, and propylene. , Butylene, isobutylene and other monoolefins, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and other vinyl esters, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, acrylic acid Alkyl acrylates and alkyl methacrylates such as phenyl, methyl methacrylate, ethyl methacrylate, butyl methacrylate and dodecyl methacrylate; vinyl ethers such as vinyl ethyl ether and vinyl butyl ether; vinyl methyl ketone; Examples thereof include homopolymers or copolymers of vinyl ketones such as silketone and vinyl isopropenyl ketone. Particularly typical binder resins include polystyrene, styrene-alkyl acrylate copolymer, and styrene- Examples thereof include a methacrylic acid alkyl ester copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene copolymer, a styrene-maleic anhydride copolymer, polyethylene, and polypropylene. Further examples include polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and waxes. Further, one or more of the above-mentioned resins and waxes can be used in combination.

The magnetic powder for obtaining the magnetic resin particles (a) used in the present invention includes ferromagnetic elements and alloys and compounds containing them, such as iron, cobalt, nickel, manganese such as magnetite, maghemite, and ferrite. A compound containing zinc or the like is preferable, but carbon black or the like may be added as needed to obtain a practically sufficient blackness. The amount of the magnetic powder in the magnetic resin particles (a) used in the present invention is preferably from 10 to 55% by weight. When the resin carrier (c) is not used, the amount of the magnetic powder in the magnetic resin particles (a) is preferably 30 to 55% by weight, more preferably 35 to 45% by weight.
It is. When a resin carrier (c) described later is used,
The amount of the magnetic powder in the magnetic resin particles (a) is 10 to 30% by weight.
And more preferably 15 to 25% by weight. If the amount of the magnetic powder is less than 10% by weight, the magnetic restraining force is weakened and toner scattering occurs. If the magnetic powder is more than 55% by weight, the triboelectric charge is reduced, and the magnetic restraining force is too strong and the image density is reduced. Furthermore, you may mix | blend a charge control agent with the magnetic resin particle (a). Examples include nigrosine dyes, quaternary ammonium salts, metal-containing azo dyes, salicylic acid derivative metal complexes, and the like.

The magnetic resin particles (a) used in the present invention are used after melt-kneading, cooling, pulverizing, classifying, etc. the binder resin, magnetic powder and the like in a conventional manner. The magnetic resin particles (a) used preferably have an average particle size of less than about 30 μm, and more preferably an average particle size of 3 to 20 μm. In the magnetic developer (a) of the present invention, the fine powder (b) is preferably added in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the magnetic resin particles.
It is more preferable to add 5 to 3.0 parts by weight.

The magnetic developer of the present invention is obtained by adding various additives to the magnetic resin particles (a) in addition to the fine powder (b) having a carboxylic acid or a salt thereof on the surface. You may. For example, silica, titania, and alumina each having a fine particle surface subjected to a hydrophobic treatment, a lubricant represented by polyvinylidene fluoride, an abrasive represented by tungsten carbide, a conductive fine powder, etc. Can be used in combination with powder.

The resin carrier (c) used in the present invention is obtained by dispersing a magnetic powder in a binder resin as in the case of the magnetic resin particles (a) described above. %, More preferably 70 to 85% by weight. When the amount of the magnetic powder is less than 60% by weight, the magnetic binding force to the sleeve is weak and "carrier spill" is likely to occur. Can no longer be used. As the binder resin for the resin carrier (c), a styrene-acrylic resin, a polyester resin, or the like is preferable among those described above. The average particle size of the resin carrier (c) is preferably the same as that of the magnetic resin particles (a), that is, from about 3 to 30 μm to 200 μm. May be covered with a coating agent such as a fluorine resin, an acrylic resin, or a silicone resin.

The magnetic developer of the present invention can develop an electrostatic latent image formed on a photoreceptor or an electrostatic recording medium. That is, selenium, zinc oxide, cadmium sulfide, an inorganic photoconductive material such as amorphous silicon, phthalocyanine pigment, an electrophotographic electrostatic latent image formed on a photoreceptor made of an organic photoconductive material such as bisazo face, or An electrostatic latent image is formed on an electrostatic recording medium having a dielectric material such as polyethylene terephthalate using a needle electrode or the like, and the electrostatic latent image is formed on the electrostatic latent image by a developing method such as a magnetic brush method, a cascade method, or a touch-down method. A toner image is formed to adhere the toner. This toner image is transferred to a transfer material such as paper and then fixed to form a copy, and the toner remaining on the surface of the photoreceptor or the like is cleaned. Various methods such as a blade method, a brush method, a web method, and a roll method can be used as the cleaning method.

[0035]

【Example】

Production Example 1 100 parts of methyl methacrylate, 200 parts of distilled water, 0.4 part of potassium persulfate were placed in a 1 L four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser.
Parts, 4 parts of polyoxyethylene nonylphenol and 1 part of sodium lauryl sulfate.
Emulsion polymerization was performed at 0 ° C. for 4 hours. After 4 hours, 3 parts of acrylic acid were added, and the polymerization was further continued for 1 hour. After completion of the polymerization, the reaction solution was cooled to 20 ° C., and 3 parts of zinc acetate was added to form a salt. The obtained emulsion is filtered and washed using a desktop emulsion filter (manufactured by Soken Chemical Co., Ltd .: Crossflow filtration device), dried using a spray drier, and crushed with a jet mill to obtain an average particle size. A fine powder (b1) of 0.3 μm was obtained. Fine powder (b) thus obtained
When 1) was observed with a scanning electron microscope (SEM),
It was almost spherical.

[0036]

Production Example 2 Fine powder having an average particle diameter of 0.4 μm (b2) was prepared in the same manner as in Production Example 1 except that 0.4 parts of azobiscyanovaleric acid was used instead of 0.4 part of potassium persulfate.
I got

[0037]

[Production Example 3] Production Example 1 except that salt formation is not performed with 2 parts of zinc acetate.
In the same manner as in the above, a fine powder (b3) having an average particle size of 0.4 μm was obtained.

[0038]

Production Example 4 Fine powder having an average particle diameter of 0.4 μm (b4) in the same manner as in Production Example 1 except that 5 parts of sodium methacrylate was used instead of 3 parts of acrylic acid, and no salt was formed after polymerization. I got

[0039]

Production Example 5 100 parts of methyl methacrylate, 200 parts of distilled water, 0.4 parts of potassium persulfate were placed in a 1 L four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a reflux condenser.
Parts, 2 parts of polyoxyethylene nonylphenol and 0.5 part of sodium lauryl sulfate, and reacted at 80 ° C. for 4 hours in a nitrogen stream. After completion of the polymerization, the reaction solution was cooled to 20 ° C., filtered and washed with a cross-flow filtration device in the same manner as in Production Example 1, dried and pulverized to obtain fine particles (b5) having an average particle size of 0.3 μm. . As in Production Example 1, the particles were substantially spherical.

[0040]

Example 1 Copolymer of styrene and n-butyl methacrylate (binder resin) 76 parts Charge control agent (Spiron Black TRH: Hodogaya Chemical) 2 parts Wax 4 parts Carbon black 3 parts Magnetic powder (magnetite) 15 parts were premixed with a Henschel mixer, melt-kneaded with an extruder, cooled, crushed with a hammer mill,
Then finely pulverized with an air jet mill pulverizer, classified,
Magnetic resin particles (a1) having an average particle size of 10 μm were obtained. To 100 parts of the obtained magnetic resin particles (a1), 0.5 part of the fine powder (b1) obtained in Production Example 1 was mixed as an external additive to obtain a magnetic toner. 75 parts of magnetic powder (magnetite) is dispersed and mixed in 25 parts of a styrene resin, melt-kneaded with an extruder, and crushed to obtain a resin carrier (c) having an average particle size of 50 μm.
1) was obtained. For 89 parts of the resin carrier (c1),
11 parts of the magnetic toner were mixed to obtain a magnetic developer. A continuous copy test of 50,000 sheets was performed using a commercially available copying machine using this magnetic developer. The charge amount and image density under low temperature and low humidity were almost the same both at the beginning of copying and after the continuous copy test of 50,000 sheets. It did not change. In addition, fog hardly occurred under low temperature, low humidity and high temperature, high humidity.

[0041]

Example 2 A magnetic developer was obtained and evaluated in the same manner as in Example 1 except that the fine powder (b2) obtained in Production Example 2 was used. There was no increase, and a good image was obtained without changing the image density from the initial copy.

[0042]

Example 3 Magnetic resin particles (a2) were obtained by changing the charge control agent used in Example 1 to a nigrosine dye. To 100 parts by weight of the magnetic resin particles (a2), 2.0 parts of the fine powder (b3) obtained in Production Example 3 was added to obtain a magnetic toner, and otherwise a magnetic developer was obtained in the same manner as in Example 1. The evaluation was performed using a commercially available printer. As a result, there was no charge-up of the charge amount under low temperature and low humidity, and a good image was obtained without changing the image density as in the initial stage of copying. In addition, fog hardly occurred under low temperature, low humidity and high temperature, high humidity.

[0043]

Example 4 Polyester resin (binder resin) 56 parts Charge control agent (Spiron Black TRH: Hodogaya Chemical) 2 parts Wax 4 parts Magnetic powder (magnetite) 38 parts were premixed with a Henschel mixer and extruder Melt-kneaded in, crushed with a hammer mill after cooling,
Then finely pulverized with an air jet mill pulverizer, classified,
Magnetic resin particles (a3) having an average particle size of 10 μm were obtained. To 100 parts of the obtained magnetic resin particles (a3), 0.5 part of the fine powder (b4) obtained in Production Example 4 was mixed as an external additive to obtain a magnetic developer. Using this magnetic developer, a continuous copying test of 30,000 sheets was conducted by a commercially available one-component developing printer. Did not change much. Further, there was no decrease in the charge amount under high temperature and high humidity, and almost no fogging occurred.

[0044]

Comparative Examples 1 to 3 The same procedures as in Examples 1, 3 and 4 were carried out except that the fine powder (b5) obtained in Production Example 5 was used. did.

[0045]

The effects obtained by the present invention are as follows. 1. It is possible to prevent a decrease in image density at low temperature and low humidity. Even if a large number of copies are made in a low-temperature and low-humidity environment, the fine powder coated with the carboxylic acid or its salt added to the magnetic resin particles retains a suitable amount of water and suppresses excessive charge-up. As a result, a suitable charge amount can be maintained, and even if a large number of copies are made in a low-temperature and low-humidity environment, a decrease in image density can be prevented. 2. An increase in fog at high temperature and high humidity can be prevented. Even when a large number of copies are made in a high-temperature and high-humidity environment, the fine powder coated with the carboxylic acid or its salt added to the magnetic resin particles adsorbs a suitable amount of water and suppresses a decrease in triboelectricity. By doing so, a suitable charge amount is maintained, and even when a large number of copies are made, an increase in fog can be prevented.

Claims (8)

[Claims] 1. A magnetic developer comprising a mixture of magnetic resin particles (a) containing a magnetic powder and a binder resin and a fine powder (b) having an average particle size of 0.05 to 5 μm. Wherein the fine powder (b) is a fine powder obtained by multi-stage polymerization by emulsion polymerization, wherein the alkyl acrylate and / or alkyl methacrylate is polymerized or copolymerized in the polymerization at a stage prior to the final stage. A magnetic developer, which is a fine powder obtained by polymerizing a polymerizable carboxylic acid or a polymerizable carboxylate in the polymerization in a step. 2. A magnetic resin particle (a) containing a magnetic powder and a binder resin, a fine powder (b) having an average particle size of 0.05 to 5 μm, and a magnetic powder and a binder resin. A magnetic developer obtained by mixing a magnetic powder-dispersed resin carrier (c), wherein the fine powder (b) is a fine powder obtained by multi-stage polymerization by emulsion polymerization, A magnetic powder characterized in that it is a fine powder obtained by polymerizing or copolymerizing an alkyl acrylate and / or an alkyl methacrylate in polymerization and polymerizing a polymerizable carboxylic acid or a polymerizable carboxylate in the final stage of polymerization. Developer. 3. The fine powder (b) is, after the final stage of polymerization,
3. The magnetic developer according to claim 1, which is a fine powder of a carboxylic acid derived from a polymerizable carboxylic acid as a salt. 4. The magnetic developer according to claim 1, wherein the polymerizable carboxylic acid salt is a divalent metal salt of a polymerizable carboxylic acid. 5. The fine powder (b) is, after the final stage polymerization,
4. The magnetic developer according to claim 3, which is a fine powder of a carboxylic acid derived from a polymerizable carboxylic acid as a divalent metal salt. 6. The magnetic resin particles (a) contain the magnetic powder in an amount of 10 to 5 particles.
The magnetic developer according to any one of claims 1 to 5, wherein the content is 5% by weight. 7. The magnetic developer according to claim 1, wherein 0.01 to 10 parts by weight of the fine powder (b) is mixed with 100 parts by weight of the magnetic resin particles (a). . 8. The magnetic developer according to claim 2, wherein the magnetic powder-dispersed resin carrier (c) contains 60 to 95% by weight of magnetic powder.