JP3387343B2 - Magnetic developer - Google Patents

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, it relates to an insulating magnetic developer capable of preventing characteristic deterioration in a low temperature and low humidity environment.

[0002]

2. Description of the Related Art Among developing methods applied to electrophotography or electrostatic recording, a two-component developing method using a two-component developing agent prepared by mixing a non-magnetic toner and a magnetic carrier is relatively stable. The obtained image is obtained and has excellent characteristics, but on the other hand, it has drawbacks such as carrier deterioration and toner concentration fluctuation. 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 copying machines and printers,
Alternatively, an insulating magnetic developer (also referred to as a 1.5-component developer) obtained by mixing a magnetic toner and a magnetic powder-dispersed resin carrier (hereinafter abbreviated as a resin carrier) has been widely used.

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 dispersion type resin carrier (hereinafter abbreviated as resin carrier) is a magnetic toner and a developer carrier ( (Hereinafter abbreviated as “sleeve”), a layer thickness regulating blade and / or a resin carrier is applied to the magnetic toner by frictional electrification, and the electrostatic latent image is visualized by the magnetic toner. Magnetic toner is attached to the electrostatic latent image formed on the photoconductor or the electrostatic recording medium to form a magnetic toner image. The magnetic toner image is transferred onto a transfer paper and then fixed to form a copy. On the other hand, the magnetic toner remaining on the photoconductor or the electrostatic recording body without being transferred is cleaned in preparation for the next copying process. These 1-component developer or 1.5-component developer are
Although it has excellent properties in terms of space saving and energy saving, the charging property is unstable as compared with the two-component developer, and stabilization of the charging property has been desired conventionally.

Therefore, various studies have been attempted in order to ensure good charging characteristics of the toner. For example, Japanese Patent Publication No. 52-32256 discloses a method in which chargeable fine particles are added to a toner as a charging auxiliary agent, as disclosed in JP-A-56-643.
No. 52 discloses a method of adding fine resin powder having a polarity opposite to that of the toner, and Japanese Patent Laid-Open No. 61-160760 proposes a method of adding a fluorinated compound to the toner. However, in the case of the above method, it is not easy to uniformly disperse the additive on the toner surface, and it is unavoidable that the additives that cannot adhere to the toner particles become 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 triboelectric charge amount of the toner becomes unstable, the image density is not constant, and the image has a lot of fog, or when a large number of copies are made, the content of the charging auxiliary agent changes, There are various problems such as the inability to maintain the initial image quality.

Japanese Patent Publication No. 2-3172 and Japanese Patent Publication No. 4
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, although these resin fine powders have a large triboelectric charging ability, they have poor hydrophilicity on the surface. Therefore, when copying a large number of sheets under low temperature and low humidity, the charge amount of the toner mixed with the resin fine powders becomes large. However, there is a problem in that the image density is lowered due to excessive flow. Further, under low temperature and low humidity, the charge amount of the resin fine powder becomes too large, so that the resin fine powder tends to agglomerate and the mixing property is lowered, or the resin fine powder easily adheres to the carrier, This is one of the causes of poor friction with the toner, and as a result, the charge state becomes unstable, causing fog (toner flying to the non-image area,
There is a problem that the quality of the copied image is deteriorated, such as an increase in the phenomenon of adhesion).

[0006]

The present invention has been made in view of such circumstances, and the charge amount of the magnetic toner is stable for a long period of time even when the environment changes, and the magnetic toner is charged especially in an environment of low temperature and low humidity. An object of the present invention is to provide an insulative magnetic developer in which the decrease in image density and the increase in fog are prevented by suppressing the increase.

[0007]

The first invention comprises 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. A magnetic developer formed by mixing, wherein the fine powder (b) is a fine powder obtained by multi-stage polymerization by suspension polymerization, and the alkyl acrylate and / or methacrylic acid is used in the polymerization in the stage before the final stage. Polymerization or copolymerization of acid alkyl ester, resulting in addition-polymerizable unsaturated in the final stage polymerization
After the aliphatic monocarboxylic acid was polymerized, addition polymerization
Carboxylic acid derived from saturated aliphatic monocarboxylic acid as a salt
It is a magnetic developer characterized by being a fine powder of

A second aspect of the present invention is a magnetic resin particle (a) containing magnetic powder and a binder resin, and an average particle size of 0.05 to 5 μm.
A magnetic developer obtained by mixing fine powder (b) which is a magnetic powder and a resin carrier (c) containing a magnetic powder and a binder resin, wherein the fine powder (b) is suspended. It is a fine powder obtained by multi-stage polymerization by polymerization, and in the polymerization of the stage before the final stage, it polymerizes or copolymerizes alkyl acrylate and / or alkyl methacrylate.
In the final stage of polymerization, addition-polymerizable unsaturated fat
Addition-polymerizable unsaturation after polymerization of aromatic monocarboxylic acids
The carboxylic acid derived from an aliphatic Monokaru Bonn acid as salt
The magnetic developer is a fine powder .

[0009]

A third aspect of the invention is that the fine powder (b) is a fine powder in which a carboxylic acid derived from an addition-polymerizable unsaturated aliphatic monocarboxylic acid is converted to a divalent metal salt after the final stage polymerization. The magnetic developer according to the first invention or the second invention, characterized in that

A fourth invention is the magnetic developer according to any one of the first to third inventions, characterized in that the magnetic resin particles (a) contain 10 to 55% by weight of magnetic powder.

A fifth aspect of the present invention is a magnetic resin particle (a) 100.
The magnetic powder according to any one of the first to fourth inventions, characterized in that the fine powder (b) is mixed in an amount of 0.01 to 10 parts by weight with respect to parts by weight.

A sixth invention is the magnetic developer according to any one of the second to fifth inventions, wherein the magnetic powder-dispersed resin carrier (c) contains 60 to 95% by weight of the magnetic powder. Is.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic powder used in the present invention has a pH of 6.5 to 8, and more preferably a pH of 7 to 7.5. The pH of the magnetic powder is less than 6.5,
If it is greater than 8, the magnetic powder dispersed in the binder resin and exposed on the surface of the magnetic resin particles (a) is greatly affected by environmental humidity, and the charging property becomes unstable, so the magnetic powder is constant regardless of the environment. And a good image without fog cannot be obtained. pH
For the measurement of, 5 g of the sample (magnetic powder) is weighed, and ion-exchanged water 1
After adding 00 cc and gently boiling for 5 minutes, the reduced volume is added with decarbonated deionized water and the mixture is left to cool to room temperature. After cooling, the sample solution is filtered and measured with a commercially available pH meter.

Further, in the present invention, the fine powder (b) used as an external additive is a fine powder obtained by multistage polymerization by suspension polymerization, and addition polymerization in the final stage polymerization.
Addition after polymerizing unsaturated unsaturated aliphatic monocarboxylic acid
Carvone derived from polymerizable unsaturated aliphatic monocarboxylic acid
It is important that the fine powder is a salt of an acid. That is, since the surface of the fine powder (b) is covered with a layer containing a carboxylate having a relatively high hydrophilicity, the carboxylate absorbs and retains a suitable amount of water, so It is possible to prevent excessive charge-up of fine powder and magnetic developer under low humidity, and to suppress / prevent image density decrease and fog generation under low temperature and low humidity, and decrease triboelectric chargeability under high temperature and high humidity. It is considered that the increase in fogging can be suppressed by suppressing the above.

The fine powder (b) used in the present invention is a fine powder obtained by multistage polymerization by so-called suspension polymerization,
For example, in the case of two-step polymerization, a dispersion liquid containing the fine powder is obtained by the following method. (1) A dispersion liquid of fine particles of a polymer of acrylic acid ester and / or an alkyl methacrylic acid ester or a dispersion liquid of fine particles of a copolymer (hereinafter abbreviated as the first-stage dispersion liquid) is obtained by the first-stage polymerization. Then, as the second-stage polymerization, an addition-polymerizable unsaturated aliphatic monocarboxylic acid monomer is added or dropped to the dispersion liquid of the first stage to carry out suspension polymerization. (2) In the method of (1), after completion of the second-stage polymerization, a carboxyl group derived from an addition-polymerizable unsaturated aliphatic monocarboxylic acid existing near the surface of the dispersed particles is used as a salt. the above
(1) and (2) have been described for the case of two-stage polymerization, but also in the case of multi-stage polymerization of more than two stages, similarly, in the final stage polymerization of multi-stage polymerization, addition-polymerizable unsaturated fat
The group monocarboxylic acid may be polymerized, and the polymerization or copolymerization of the acrylic acid ester and / or the methacrylic acid alkyl ester may be any one of the steps before the final step. It is not limited to the last stage.

In the present invention, the polymer or copolymer produced in the step before the final step includes a polymer of acrylic acid alkyl ester monomer, a polymer of methacrylic acid alkyl ester monomer, an acrylic acid alkyl ester monomer and A copolymer of a methacrylic acid alkyl ester monomer, or a copolymer containing an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer in an amount of 50% by weight or more and one or more other copolymerizable monomers is available. Can be mentioned.

Examples of the acrylic acid alkyl ester monomer and methacrylic acid alkyl ester monomer used in the present invention include esterification products of acrylic acid or methacrylic acid with alcohols such as alkyl alcohol, alkoxy alcohol, aralkyl alcohol and alkenyl alcohol. An alkyl alcohol such as methyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, dodecyl alcohol, tetradecyl alcohol, or 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 copolymerizable with the above-mentioned acrylic acid alkyl ester monomer and methacrylic acid alkyl ester monomer include amides and nitriles such as acrylonitrile, acrylamide, methacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide. , Vinyl acetates, vinyl ethers; nitrogen-containing vinyl compounds such as vinylcarbazole, vinylpyridine, vinylpyrrolide; aliphatic monoolefins such as ethylene, propylene, butene, isobutylene; vinyl chloride, vinyl bromide, 1,2-dichloroethylene , 1,2-Dibromoethylene, isopropenyl chloride, isopropenyl bromide, allyl chloride, allyl bromide, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other halogenated aliphatic olefins; Ene, 1,3-pentadiene, 2
-Conjugated diene-based aliphatic olefins such as methyl-1,3-butadiene; styrenes such as styrene and α-methylstyrene.

[0020]

The addition polymerizable unsaturated aliphatic monocarboxylic acid used in the final polymerization step is acrylic acid,
Methacrylic acid, α-ethylacrylic acid, crotonic acid,
Examples thereof include α-methylcrotonic acid, α-ethylcrotonic acid, isocrotonic acid, tiglic acid, and ungeric acid, and one or more of these can be used, with acrylic acid and methacrylic acid being preferred.

Addition-polymerizable unsaturated fat before or after polymerization
Examples of the salt forming agent used for forming a salt of a group monocarboxylic acid include Na, Mg, K, Li, NH ₄ , Ca, Ba and Z.
Examples thereof include hydroxides, oxides, inorganic acid salts and organic acid salts of n, Fe, Cu, Al, Ni, Co and Cr.
Preferred are hydroxides, oxides, inorganic acid salts and organic acid salts of divalent metals such as g, Ca, Ba, Zn, Fe, Ni and Co, and further hydroxides of Mg, Ca, Ba and Zn. , Oxides, inorganic acid salts and organic acid salts are preferable, and hydroxides, oxides, inorganic acid salts and organic acid salts of Zn are most preferable. Examples of the organic acid include formic acid, acetic acid, propionic acid and the like. The amount of these salt-forming agents added is preferably an equivalent amount 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 with respect to charging ability under low temperature and low humidity.
Further, even if added in an equivalent amount or more, there is no problem since the excess portion can be removed by performing a water washing step later.

The addition polymerizable unsaturated aliphatic monocarboxylic acid is preferably used in an amount of 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 parts by weight, even if the produced fine powder is added to magnetic resin particles as a toner, the effect of improving the image density under low temperature and low humidity is poor, and if it exceeds 20 parts by weight, the hydrophilicity of the surface of the fine powder is reduced. Since it becomes large and the moisture absorption effect of water becomes too large, the triboelectrification capacity tends to decrease.

Examples of the polymerization initiator used in the polymerization of the fine powder (b) used in the present invention include peroxide type initiators and azobis type initiators. Examples of the peroxide type initiator include benzoyl peroxide, and examples of the azobis type initiator include 2,2′-azobisisobutyronitrile and 2,2′-azobisvaleronitrile. You can

As the emulsifier used in the suspension polymerization of the fine powder (b) used in the present invention, sodium higher alcohol sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylbenzene sulfonate, dialkyl sulfosuccinate is used. Anionic emulsifiers such as sodium, fatty acid sodium or potassium, alkyl (or alkylphenyl) ether, sodium sulfate, or ammonium sulfate: alkylphenol ethylene oxide adduct, higher alcohol ethylene oxide adduct, polypropylene glycol ethylene oxide adduct Nonionic emulsifiers such as; cationic emulsifiers such as quaternary ammonium salts and the like, and water-soluble polymers such as polyvinyl alcohol are also used. You can

Fine powder (b) used in the present invention
Is added after polymerization or after polymerization using the above salt forming agent.
After the polymerizable unsaturated aliphatic monocarboxylic acid is made into a salt, water may be removed from the aqueous dispersion to give a powder. As a means for removing water, various drying methods and crushing / grinding methods usually used in powder production can be applied, but after the aqueous dispersion is spray-dried, the dried product is crushed / crushed. Preferably.

The fine powder (b) used in the present invention is obtained by polymerizing or after polymerizing the carboxylic acid on the surface with the above salt-forming agent to form a salt, which is then removed from the aqueous dispersion by a cross-flow filtration method. It is also possible to remove emulsifiers and the like.
For example, the emulsifier and unreacted substances can be removed by putting the aqueous dispersion in a table-top emulsion filter (manufactured by Soken Chemical Industry Co., Ltd.) and flushing the aqueous dispersion with water. After washing, water may be removed by the above method to obtain fine powder.

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

In the magnetic developer of the present invention, the above-mentioned fine powder (b) is added to and mixed with the magnetic resin particles (a), or the above-mentioned fine powder (b), magnetic resin particles (a) and magnetic powder are added. Dispersion type resin carrier (c) (hereinafter, resin carrier (c)
And abbreviated) are added and mixed. In the latter case,
First, it is preferable to 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 latter case, that is, when a resin carrier is used, the fine powder (b) is mixed with the magnetic resin particles (a).
The one added and mixed with is sometimes called a magnetic toner.
The magnetic resin particles (a) used in the present invention contain a binder resin and a magnetic powder, and examples of the binder resin used include styrenes such as styrene, chlorostyrene and vinylstyrene, ethylene, propylene. , Vinylene such as butylene, isobutylene, vinyl acetate, vinyl bromionate, vinyl benzoate, vinyl butyrate, etc., methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, acrylic acid Acrylic alkyl esters and methacrylic acid alkyl esters 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 and vinyl Examples include homopolymers or copolymers of vinyl ketones such as silketone and vinyl isopropenyl ketone, and particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene- Examples thereof include methacrylic acid alkyl ester copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, wax can be mentioned. Further, one or more of the resins and waxes listed above 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 magnetite, maghemite and ferrite such as iron, cobalt, nickel and manganese. A compound containing zinc or the like is preferable, but carbon black or the like may be added if necessary to obtain a practically sufficient blackness. The amount of magnetic powder in the magnetic resin particles (a) used in the present invention is preferably 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.
Is. When the resin carrier (c) described below is used,
The amount of magnetic powder in the magnetic resin particles (a) is 10 to 30% by weight.
Is preferable, and more preferably 15 to 25% by weight. If the amount of magnetic powder is less than 10% by weight, the magnetic restraining force is weakened to cause toner scattering, and if it is more than 55% by weight, the triboelectric charge amount is reduced, and the magnetic restraining force is too strong, and the image density is lowered. Furthermore, a charge control agent may be added to the magnetic resin particles (a). Examples thereof include nigrosine dye, quaternary ammonium salt, metal-containing azo dye, salicylic acid derivative metal complex and the like.

The magnetic resin particles (a) used in the present invention are used by subjecting a binder resin, magnetic powder and the like to melt kneading, cooling, pulverizing, classifying and the like according to a conventional method. The average particle size of the magnetic resin particles (a) used is preferably smaller than about 30 μm, more preferably 3 to 20 μm. In the magnetic developer (a) of the present invention, it is preferable to add 0.01 to 10 parts by weight of the above-mentioned fine powder (b) to 100 parts by weight of the magnetic resin particles, and
It is more preferable to add 5 to 3.0 parts by weight.

The magnetic developer of the present invention is added to the surface.
In addition to the fine powder (b) containing a salt of a polymerizable unsaturated aliphatic monocarboxylic acid , various additives may be added to the magnetic resin particles (a). For example, silica, titania, and alumina each fine particle surface is subjected to a hydrophobic treatment, a lubricant typified by polyvinylidene fluoride, an abrasive typified by tungsten carbide,
A conductive fine powder and the like can be used in combination with the above fine powder.

The resin carrier (c) used in the present invention is obtained by dispersing magnetic powder in a binder resin as in the case of the above-mentioned magnetic resin particles (a), and the magnetic powder is contained in an amount of 60 to 95% by weight. %, More preferably 70 to 85% by weight. If the magnetic powder is less than 60% by weight, the magnetic binding force on the sleeve is weak and carrier spills are likely to occur, and if it is more than 95% by weight, the binder resin becomes relatively small and the carrier does not solidify. I can not use it. The binder resin for the resin carrier (c) is preferably a styrene-acrylic resin, a polyester resin, or the like among those mentioned above. The average particle size of the resin carrier (c) is the same as the above-mentioned magnetic resin particles (a).
And the average particle size is the same, that is, about 3 to 30 μm to 200
The thickness is preferably up to μm, and the surface of these resin carriers (c) may be further coated 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 photoconductor or an electrostatic recording material. That is, selenium, zinc oxide, cadmium sulfide, an inorganic photoconductive material such as amorphous silicon, a phthalocyanine pigment, an electrostatic latent image is formed electrophotographically on a photoreceptor made of an organic photoconductive material such as bisazo facials, or An electrostatic latent image is formed on an electrostatic recording material having a dielectric material such as polyethylene terephthalate by a needle-stick electrode or the like, and the electrostatic latent image is formed by a developing method such as a magnetic brush method, a cascade method or a touchdown method. A toner image is formed with the toner attached. 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 photoconductor or the like is cleaned. As the cleaning method, various methods such as a blade method, a brush method, a web method, and a roll method can be used.

[0035]

【Example】

[Production Example 1] 100 parts of methyl methacrylate, 200 parts of distilled water, 0.4 parts of benzoyl peroxide were placed in a 1 L four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a reflux condenser.
Parts, 4 parts of polyoxyethylene nonylphenol, 1 part of sodium lauryl sulphate, and 8 in a nitrogen stream
Suspension polymerization was carried out at 0 ° C for 4 hours. After 4 hours, 3 parts of acrylic acid was 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 reaction solution is filtered and washed using a desktop emulsion filter (Soken Chemical Co., Ltd .: cross flow filtration device), dried with a spray dryer, and crushed with a jet mill to obtain an average particle size. A fine powder (b1) of 0.3 μm was obtained. The 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 (b2 having an average particle size of 0.4 μm) was produced in the same manner as in Production Example 1 except that 0.4 part of azobisisobutyronitrile was used instead of 0.4 part of potassium persulfate. )
Got

[0037]

[Production Example 5] 100 parts of methyl methacrylate, 200 parts of distilled water, 0.4 parts of benzoyl peroxide were placed in a 1 L four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a reflux condenser.
Parts, 4 parts of polyoxyethylene nonylphenol, 1 part of sodium lauryl sulphate, and 8 in a nitrogen stream
Suspension polymerization was carried out at 0 ° C for 4 hours. After completion of the polymerization, the reaction solution was cooled to 20 ° C., and the reaction solution was 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 diameter of 0.3 μm. . As in Production Example 1, the particles were substantially spherical particles.

[0038]

Example 1 Copolymer of styrene and n-butyl methacrylate (binder resin) 76 parts Charge control agent (Spiron Black TRH: Hodogaya Kagaku) 2 parts Wax 4 parts Carbon black 3 parts Magnetic powder (magnetite) , PH 7.
2) 15 parts were premixed with a Henschel mixer, melt-kneaded with an extruder, cooled, coarsely crushed with a hammer mill, then finely pulverized with an air jet mill pulverizer, classified, and a magnetic resin having an average particle diameter of 10 μm. Particles (a1)
Got A magnetic toner was obtained by mixing 100 parts of the obtained magnetic resin particles (a1) with 0.5 part of the fine powder (b1) obtained in Production Example 1 as an external additive. Magnetic powder (magnetite) 75
25 parts of styrene resin was dispersed and mixed, melt-kneaded with an extruder, and crushed to obtain a resin carrier (c1) having an average particle size of 50 μm. Related resin carrier (c1) 89
11 parts of the magnetic toner was mixed with 1 part to obtain a magnetic developer. A continuous copying test of 50,000 sheets was conducted using a commercially available copying machine using this magnetic developer, and it was found that the charge amount and image density under low temperature and low humidity were almost at the beginning of copying and after the continuous copying test of 50,000 sheets. It didn't change.
In addition, fogging was hardly generated under low temperature and low humidity and high temperature and high humidity.

[0039]

Example 2 A magnetic developer was obtained in the same manner as in Example 1 except that the fine powder (b2) obtained in Production Example 2 was used, and the same evaluation was carried out. There was no increase, and a good image was obtained with the image density unchanged from the initial stage of copying.

[0040]

[Comparative Example 1] The procedure of Example 1 was repeated except that the fine powder (b5) obtained in Production Example 5 was used. As a result, the density was reduced under low temperature and low humidity, and fog occurred.

[0041]

[Comparative Examples 2 to 3] The same procedure as in Example 1 was carried out except that the magnetites having pH 5 and pH 9 were used in Example 1, respectively, and the electrification amount was decreased under high temperature and high humidity, and fog occurred.

[0042]

The effects obtained by the present invention are as follows. 1. Magnetic resin particles containing magnetic powder of a specific pH and fine powder coated with carboxylic acid or its salt even when a large number of copies are made in a low temperature and low humidity environment that can prevent image density deterioration at low temperature and low humidity. Since these magnetic powders and fine powders retain a suitable amount of water and suppress excessive charge-up, as a result, it is possible to maintain a suitable charge amount, and to maintain a large number of sheets in a low temperature and low humidity environment. Even if copying is performed, it is possible to prevent a decrease in image density. 2. It is possible to prevent an increase in fogging at high temperature and high humidity. Even if a large number of copies are made in a high temperature and high humidity environment, since magnetic resin particles containing magnetic powder of a specific pH and fine powder coated with carboxylic acid or its salt are used, these magnetic powder and fine powder Holds a suitable amount of water and suppresses the reduction of the triboelectric chargeability, so that a suitable amount of charge is maintained, and it is possible to prevent an increase in fogging even when copying a large number of sheets.

Continuation of the front page (56) Reference JP 60-192959 (JP, A) JP 59-86062 (JP, A) JP 8-328301 (JP, A) JP 8-320592 (JP , A) JP 7-209904 (JP, A) JP 6-118686 (JP, A) JP 6-11883 (JP, A) JP 5-333585 (JP, A) JP 5-323659 (JP, A) JP-A-5-150558 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 9/08

Claims (6)

(57) [Claims] 1. Magnetic resin particles (a) containing magnetic powder having a pH of 6.5 to 8 and a binder resin, and an average particle diameter of 0.05 to 5
A magnetic developer prepared by mixing with a fine powder (b) having a particle size of μm, wherein the fine powder (b) is a fine powder obtained by multi-stage polymerization by suspension polymerization, In the polymerization, an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester is polymerized or copolymerized ,
Addition-polymerizable unsaturated aliphatic monocarbonate in the final stage of polymerization
After polymerization of rubonic acid, addition-polymerizable unsaturated aliphatic
Fine powder formed from carboxylic acid derived from nocarboxylic acid as a salt
Magnetic developer, which is a powder. 2. Magnetic resin particles (a) containing magnetic powder having a pH of 6.5 to 8 and a binder resin, and an average particle diameter of 0.05 to 5
A magnetic developer obtained by mixing a fine powder (b) having a diameter of μm and a magnetic powder-dispersed resin carrier (c) containing a magnetic powder and a binder resin, wherein the fine powder (b) is suspended. It is a fine powder obtained by multi-stage polymerization by turbidity polymerization, in which alkyl acrylate and / or methacrylic acid alkyl ester is polymerized or copolymerized in the polymerization in the stage before the final stage, and the addition-polymerizable Saturation
After the aliphatic monocarboxylic acid was polymerized, addition polymerization
Carboxylic acid derived from saturated aliphatic monocarboxylic acid as a salt
A magnetic developer characterized by being a fine powder of 3. A fine powder (b) is obtained after the final stage of polymerization,
The magnetic developer according to claim 1 or 2, which is a fine powder containing a carboxylic acid derived from an addition-polymerizable unsaturated aliphatic monocarboxylic acid as a divalent metal salt. 4. The magnetic resin particles (a) contain 10 to 5 magnetic powder.
The magnetic developer according to any one of claims 1 to 3, wherein the content is 5% by weight. 5. 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). . 6. The magnetic developer according to claim 2, wherein the magnetic powder-dispersed resin carrier (c) contains 60 to 95% by weight of magnetic powder.