JPH05100495A - Production of magnetic particles - Google Patents

Abstract

PURPOSE:To produce magnetic particles having excellent durability, electrostatic chargeability, moisture resistance and environmental resistance and capable of providing a satisfactory image. CONSTITUTION:When magnetic particles are produced by dispersing magnetic powder in resin particles, a compsn. contg. a radical polymerizable monomer, magnetic powder and a peroxide type radical polymn. initiator is suspended in an aq. medium and a water soluble reducing agent is added to the resulting suspension at a temp. below the temp. at which the polymn. initiator is reduced by half in 10hr. The polymerizable monomer present on the surfaces of liq. particles is then polymerized and this polymn. is completed by further heating.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing magnetic particles in which magnetic powder is dispersed in resin particles, and more specifically,
The present invention relates to a method for producing a binder type carrier used as a developer for developing an electrostatic latent image or a magnetic latent image in electrophotography, electrostatic recording, electrostatic printing and the like.

[0002]

2. Description of the Related Art Generally, in electrophotography or electrostatic recording, coloring is performed in order to develop an electrostatic latent image formed on a latent image carrier made of a photoconductive photoconductor or a dielectric. A two-component developer composed of fine powder toner and carrier is widely used.

This two-component developer rubs the toner and the carrier by stirring to charge the toner to a specific polarity, and utilizes the electrostatic attraction between the electrostatic charge forming the electrostatic latent image and the toner. Develop by adhering to the latent image carrier.
This two-component developer is characterized in that it is possible to form a sharp visible image because the triboelectric charge control of the toner is relatively easy and the developer can be provided with sufficiently high fluidity.

The properties required for the carrier used in the two-component developer are charging property, impact resistance, abrasion resistance and spent resistance, and the binder resin is required to satisfy these properties. Binder type carriers of small particle size in which magnetic powder is dispersed in particles have been proposed. Furthermore, in order to improve durability, JP-A-58-59457
JP-A-58-121046, JP-A-63-228
174, JP-A 1-2292667, JP-A 63-
235958-62, JP-A-62-295074-6
Carrier coated with a core material obtained by the kneading method described in JP-A No. 63-58359 or the like, a binder resin described in JP-A No. 61-120158, and this binder. There has been proposed a carrier in which a core material having magnetic powder dispersed in a resin and an outer wall containing a hard resin as a main component are coated.

[0005]

However, when the carrier is repeatedly used, peeling occurs between the core particles and the coat layer, resulting in poor durability and charging characteristics. Further, since one of the coating materials of the carrier is water-soluble, there is a problem in moisture resistance and environment resistance.

The present invention is intended to solve the above-mentioned drawbacks, and an object thereof is to produce magnetic particles which are excellent in durability, charging property, moisture resistance and environment resistance and can provide good images. To provide a method.

[0007]

The method for producing magnetic particles according to the present invention is a method of suspending a composition containing a radical-polymerizable monomer, magnetic powder, and a peroxide-based radical polymerization initiator in an aqueous medium. A step of granulating, a step of adding a water-soluble reducing agent to the suspension at a temperature not higher than the 10-hour half-life temperature of the polymerization initiator to polymerize the radical-polymerizable monomer present on the droplet surface, and The step of warming to complete the polymerization of the radically polymerizable monomer is included, whereby the above object can be achieved.

Next, the invention will be described in detail.

Examples of the radically polymerizable monomer used in the present invention include styrenes such as styrene, chlorostyrene and vinylstyrene; monoolefins such as ethylene, propylene, butylene and isobutylene: vinyl acetate, propylene vinyl, Vinyl esters such as vinyl benzoate and vinyl butyrate; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate. Α-methylene aliphatic monocarboxylic acid esters such as; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether;
Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone are preferred. These compounds may be used alone or in combination of two or more.

The magnetic powder used in the present invention is a substance which is extremely strongly magnetized in that direction by a magnetic field, for example,
Metals such as iron, cobalt, nickel: Alloys or compounds containing ferromagnetism elements such as ferrite, magnetite, hematite, etc. such as ferrite, magnetite, hematite: Proper heat treatment without containing ferromagnetic elements An alloy exhibiting ferromagnetism, for example, manganese-
Heusler alloys containing manganese such as copper-aluminum or manganese-copper-tin and copper are listed.
These compounds may be used alone or in combination of two or more.

The amount of the magnetic powder used is preferably 50 to 300 parts by weight based on 100 parts by weight of the polymerizable monomer.
When the amount of the magnetic powder used is less than 50 parts by weight, the magnetic attraction force of the developing sleeve is weakened, and carrier adhesion to the photoconductor and developer spillage from the developing machine are likely to occur. On the other hand, when the content of the magnetic powder exceeds 300 parts by weight, the binding effect of the resin cannot be sufficiently obtained and the carrier is cracked. In addition, the dispersion of the contained powder such as magnetic powder may be deteriorated, and a homogeneous resin may not be obtained.

The particle size of the magnetic powder is 0.01-5.
μm is preferred. If the particle size of the magnetic powder is less than 0.01 μm, the saturation magnetization may be reduced, or the viscosity of the composition may increase, making it impossible to obtain carrier particles having a uniform particle size. On the other hand, when the particle size of the magnetic powder exceeds 5 μm,
It may not be possible to obtain homogeneous magnetic particles, and the magnetic powder may drop out of the droplets during suspension granulation.

Examples of the peroxide type radical polymerization initiator include benzoyl peroxide, lauroyl peroxide, acetyl peroxide, t-butyl peroxide, cumene hydroperoxide and the like. These compounds may be used alone or in combination of two or more. The amount of the peroxide radical polymerization initiator used is preferably 1 to 10 parts by weight with respect to 100 parts by weight of the radical polymerizable monomer.

In addition to the radical-polymerizable monomer, the magnetic powder, and the peroxide-based radical polymerization initiator, the composition may contain a crosslinking agent, a colorant, and a charge control agent.

Examples of the cross-linking agent include divinyl compounds, diallyl compounds, triallyl compounds, diacrylate compounds, triacrylate compounds, dimethacrylate compounds and trimethacrylate compounds.

As the colorant, carbon black,
Aniline Blue, Calco Oil Blue, Chrome Yellow, Ultramarine Blue, DuPont Oil Red, Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue, Malachite Green, Lamp Black,
Examples include rose bengal. These colorants may be used alone or in combination of two or more.

Examples of the charge control agent include Fett Schwarz HBN having a positive triboelectric charging property described in JP-B No. 41-2427, nigrosine soluble in alcohol, Sudan Chief Schwarz BB, Solvent Black 3, Brilliant. Examples thereof include Spirit Schwartz TN, Zavon Schwarz X, quaternary ammonium compounds, Ceres Schwarz (R) G, which has a negative frictional charging property, Chromogen Syubalz ETOO, Azo Oil Black (R), Spiron Black, and Bontron. These charge control agents may be used alone or in combination of two or more.

When the magnetic particles produced according to the present invention are used as a one-component developer for electrophotography, it is particularly effective to add the colorant and the charge control agent to the composition.

In the production method of the present invention, first, a composition containing the above-mentioned radical-polymerizable monomer, the above-mentioned magnetic powder and a peroxide-based radical polymerization initiator is dispersed in an aqueous solvent for suspension granulation. .. As a granulation method, suspension granulation using stirring with a mixer or the like is easy, and the temperature at this time is preferably a low temperature, at least 10 hours half temperature or lower of the peroxide polymerization initiator.

The above-mentioned aqueous solvent is usually water containing a small amount of a suspension stabilizer, and examples thereof include mixed solvents with alcohols and glycols.

After the above suspension granulation, a water-soluble reducing agent is added to this suspension to redox polymerize the radically polymerizable monomer present on the droplet surface. This redox polymerization reaction occurs promptly due to the presence of the peroxide-based polymerization initiator in the droplets when the surface of the droplets generated by the suspension granulation encounters the water-soluble reducing agent present in the aqueous medium. It is a reaction.

Examples of the water-soluble reducing agent include inorganic reducing agents (Fe ²⁺ salt, NaHSO ₃ etc.) and organic reducing agents (polyamine, alcohol etc.). These compounds may be used alone or in combination of two or more. The amount of the water-soluble reducing agent used is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the aqueous medium.

The temperature of this redox polymerization reaction is
It is necessary that the temperature is not higher than the 10-hour half-life temperature of the polymerization initiator, and preferably 20 to 40 ° C. When this temperature exceeds the 10-hour half-life temperature of the polymerization initiator, thermal decomposition of the polymerization initiator is likely to occur, and therefore only the surface of the droplet cannot be polymerized first.

A suspension stabilizer may be used if necessary during the above-mentioned suspension granulation, and examples thereof include an ionic surfactant, a water-soluble polymer, and a nonionic surfactant.

In the above-mentioned polymerization reaction, a redox polymerization reaction first produces a polymer on the surface of the liquid droplets, so that aggregation of particles in a usual radical polymerization reaction can be reduced. Therefore, the amount of the suspension stabilizer used can be reduced, and the amount of the suspension stabilizer used is 1
The amount may be 5 parts by weight or less with respect to 00 parts by weight.

After the completion of the redox polymerization reaction, the suspension is further heated to complete the polymerization reaction of the radically polymerizable monomer present inside the droplets.

The temperature of this polymerization reaction is preferably 60 to 100 ° C. which is the decomposition temperature of the peroxide type polymerization initiator.

The particle size of the magnetic particles obtained by the production method of the present invention is 30 to 30 when used as a carrier.
150 μm, 5 to 10 when used as a magnetic toner
μm is preferred.

In the present invention, since the magnetic particles are produced by the suspension polymerization method, the production efficiency is higher than that of the melt-kneading method, and magnetic particles having a uniform particle size and a spherical shape can be obtained.

[0030]

[Function] A composition containing a radical-polymerizable monomer, magnetic powder and a peroxide-based radical polymerization initiator is suspended and granulated in an aqueous solvent to form droplets. Then, when a water-soluble reducing agent is added to this suspension at a temperature not higher than the 10-hour half-life temperature of the above-mentioned polymerization initiator, the redox polymerization reaction causes the radical-polymerizable monomer existing only on the surface of the droplets to be dissolved. The polymerization reaction proceeds and a polymer is formed. Then, when heated, the radical polymerization reaction causes the polymerization reaction of the radically polymerizable monomer present inside the droplets to proceed to form a polymer. At this time, because the covalent bond or the copolymerization occurs between the polymer on the surface of the droplets generated by the redox polymerization and the polymer generated by the radical polymerization, and the composition is the same, the surface of the obtained magnetic particles Layer separation does not occur,
Therefore, the durability and the charging property are excellent.

Further, since the polymer film is first formed on the surface of the droplets, the aggregation of particles during the suspension polymerization can be reduced, so that the amount of the suspension stabilizer used can be reduced. Therefore, the moisture resistance and environment resistance of the obtained magnetic particles can be improved.

[0032]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples.

Styrene 70 parts by weight Butyl methacrylate 20 parts by weight Divinylbenzene 2 parts by weight Diethylene glycol dimethacrylate 8 parts by weight Iron trioxide (BL-100 titanium industrial product) 100 parts by weight Iron trioxide (BL-200 titanium industrial product) 100 parts by weight Titanate coupling agent (KR-TTS manufactured by Ajinomoto) 0.5 parts by weight Benzoyl peroxide 5 parts by weight The above compositions were mixed. Next, 0.8 parts by weight of sodium dodecylbenzene sulfonate was dissolved in 600 parts by weight of distilled water, and the above mixture was added to this solution to prepare a mixer with modified TK homomixer (manufactured by Tokushu Kika Kogyo) for high viscosity. A suspension was obtained by stirring at a rotation speed of 6000 to 10000 rpm for 12 minutes. This suspension was transferred to a separable flask, and a 2.5% aqueous solution of 10 parts by weight of ammonium thiocyanate was added dropwise with stirring under a nitrogen atmosphere at a temperature of 40 ° C. and a rotation speed of 250 rpm, and the mixture was reacted for 1 hour. Polymerization was completed by raising the temperature to 80 ° C. and reacting for 3 hours. Then, the polymer was filtered, washed with water, and dried to obtain binder type carrier particles.

Example 2 A binder type carrier was obtained in the same manner as in Example 1 except that sodium hydrogen sulfite was used instead of ammonium thiocyanate of Example 1.

Example 3 Binder type was prepared in the same manner as in Example 1 except that ferrous chloride was used in place of ammonium thiocyanate in Example 1 and 1.0 part by weight of sodium dodecylbenzenesulfonate was used. Got a career.

Comparative Example 1 A polymerization reaction was carried out in the same manner as in Example 1 except that ammonium thiocyanate of Example 1 was not used and that the suspension was immediately heated to 80 ° C. for polymerization. However, aggregation of suspended particles occurred 1 hour after the initiation of the polymerization, and the carrier particles could not be obtained.

Comparative Example 2 2,2'-azobis- was used without using ammonium thiocyanate of Example 1 and in place of benzoyl peroxide.
A binder type carrier was obtained in the same manner as in Example 1 except that 6 parts by weight of (2,4-dimethylvaleronitrile) was used.

92 parts by weight of the binder type carriers obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were mixed with 8 parts by weight of a toner for DC-2585 (manufactured by Mita Kogyo Co., Ltd.) to prepare a developer. Evaluation was performed using a copier DC-2585 (manufactured by Mita Kogyo). The results are shown in Table 1.

[0039]

[Table 1]

It can be seen from Table 1 that the developers using the binder type carriers obtained in Examples 1 and 2 are excellent in durability and chargeability and form good images.

[0041]

As is clear from the above description, according to the method for producing magnetic particles of the present invention, it is possible to provide magnetic particles excellent in durability and chargeability, and to provide a good image. You can Moreover, since the amount of the suspension stabilizer used can be reduced, the moisture resistance and environment resistance of the obtained magnetic particles are improved.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Nobuhiro Hirano 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd. (72) Toshiro Tokuno 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Engineering Co., Ltd. (72) Inventor Shigeo Yabe 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Engineering Co., Ltd.

Claims (1)

[Claims] 1. A method for producing magnetic particles comprising magnetic particles dispersed in resin particles, wherein a composition containing a radical polymerizable monomer, magnetic powder and a peroxide radical polymerization initiator is added to an aqueous medium. In the step of suspension granulation, a water-soluble reducing agent is added to the suspension to polymerize the radical-polymerizable monomer present on the droplet surface at a temperature not higher than the 10-hour half-life temperature of the polymerization initiator. And a step of further heating to complete the polymerization of the radical-polymerizable monomer.