JPH06102707A - Magnetic particle and its production - Google Patents

Abstract

PURPOSE:To obtain magnetic particles having good dispersibility, disperson stability and affinity to a binder resin and improved in heat resistance and wear resistance by polymerizing vinyl monomers in the presence of a magnetic powder to which vinyl groups are introduced to the surface. CONSTITUTION:The magnetic particles consist of polymers obtd. by polymerizing vinyl monomers in the presence of a magnetic powder treated with vinyl monomers containing isocyanate groups to introduce vinyl groups to the surface of powder particles. Namely, after treating the magnetic powder with vinyl monomers containing isocyanate groups to introduce vinyl groups to the particle surface, a monomer phase containing this magnetic powder and vinyl monomers is prepared and dispersed in a dispersion medium in a dropping state to effect polymn. By treating the magnetic powder by this method, active hydrogen of hydrophilic groups on the surface of the magnetic powder and the isocyanate groups of vinyl monomers containing isocyanate groups are allowed to react with each other to introduce vinyl groups into the surface of the magnetic powder. Thus, the magnetic powder is made hydrophobic, and dispersibility and dispersion stability of the magnetic powder with the monomer phase is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier which constitutes a two-component developer together with a chargeable toner in an image forming apparatus utilizing an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like, The present invention relates to magnetic particles used not only as a magnetic toner as a one-component developer but also for magnetic displays and the like, and a method for producing the same by suspension polymerization.

[0002]

2. Description of the Related Art Heretofore, as the magnetic particles, ferrite particles whose surfaces are coated with a resin are generally used. However, when the above ferrite particles are used in an image forming apparatus as a carrier of a two-component developer, for example, it is the current situation that it is not possible to sufficiently meet the recent demand for higher image quality.

In a developing section of an image forming apparatus using a two-component developer composed of a carrier and a toner, the developer is first agitated and mixed to charge the toner, and the toner is attached around the carrier particles, and then the magnet is magnetized. A magnetic brush is formed by magnetically adhering a carrier to the surface of the developing sleeve containing the carrier. Then, when the magnetic brush is brought close to or in contact with the surface of the photoconductor on which the electrostatic latent image is formed, the toner in the magnetic brush electrostatically adheres to the electrostatic latent image, and the electrostatic latent image is formed. The toner image is visualized.

However, when ferrite particles are used as the carrier, due to the weight of the ferrite particles, the magnetic brush greatly expands due to the centrifugal force generated when the developing sleeve rotates, and the surface of the photoconductor is damaged by inertial force. The toner electrostatically adhered to the surface of the photoconductor is scraped off or the adhering position is shifted to deteriorate the quality of the formed image.

Another cause of deterioration in the quality of the formed image is that it is difficult to reduce the particle size because the carrier composed of the above-mentioned ferrite particles is manufactured by sintering ferrite powder, and that the carrier has a perfect spherical shape. There is also the fact that it is not possible to form it and the fluidity is poor. Therefore, in recent years, in order to solve the problems of the carrier made of the ferrite particles and to improve the quality of the formed image, a lightweight carrier in which magnetic powder is dispersed in the particles made of a binder resin, that is, a so-called binder type carrier is used. Research and development on carriers are being actively conducted.

Since this binder type carrier is lighter than the ferrite particles, the magnetic brush does not greatly expand due to centrifugal force, and the inertial force is small, so that the surface of the photoconductor is damaged or the surface of the photoconductor is static. It does not scrape off the toner that has been electro-deposited or shift the attachment position. The binder type carrier can also be produced by melt-kneading a binder resin such as styrene-acrylic resin, magnetic powder such as ferrite powder and other additives, and then pulverizing and classifying. However, such a pulverized type carrier has a problem that the particle size distribution is wide, the particle size is large, and the carrier is not completely spherical.

Therefore, it has been studied to produce the above binder type carrier by utilizing the suspension polymerization method. This method is a radical polymerizable vinyl monomer that is the basis of the binder resin, and a liquid monomer phase containing magnetic powder and other additives is heated while being dispersed in a dispersion medium in a droplet form, It is a method of polymerizing a vinyl monomer. The binder type carrier obtained by such a method has a narrow particle size distribution,
In addition, since it is possible to reduce the particle size and to obtain a particle close to a perfect sphere, it is possible to improve the quality of the formed image as compared with the case where a carrier made of ferrite particles is used.

[0008]

However, the magnetic powder such as magnetite powder has a hydrophilic surface, a specific gravity remarkably larger than that of the vinyl monomer, and a large amount (volume ratio by volume) relative to the vinyl monomer. It is difficult to disperse it uniformly in the monomer phase due to the fact that it needs to be mixed in about 2: 1), and so on, so that the dispersion state of the magnetic powder in the produced carrier becomes uneven. Therefore, the magnetic properties and electrical properties of the carrier may become non-uniform. Further, in the manufactured carrier, the affinity between the magnetic powder and the binder resin of the carrier is low and the two are not sufficiently bonded, so that carrier cracking occurs at the interface between the two and the magnetic powder is It may fall off from the toner, contaminate the formed image, and deteriorate the performance of the developer.

Therefore, in order to improve the dispersibility and dispersion stability of the magnetic powder and the affinity for the binder resin, a coupling agent such as a titanate coupling agent, a silane coupling agent, and an aluminum coupling agent. It has been proposed to use magnetic powder whose surface has been hydrophobized by treatment with JP-A-56-51755 and JP-A-5-51755.
9-224102, JP-A-60-254054, JP-A-61-53653, etc.). However, in order to obtain a sufficient treatment effect, it is necessary to treat the magnetic powder with an excess amount of the coupling agent, and since the excess coupling agent exists in a low molecular weight state in the produced carrier, the carrier produced Has poor heat resistance and wear resistance, and has low hardness and softness.

In the case of a binder type carrier, if the hardness is low, it tends to agglomerate, and for example, it is clogged in a portion such as a cutting plate (a member for adjusting the thickness of the magnetic brush) in the developing section,
The magnetic brush is not formed only in the clogged portion, which causes a problem that white streaks occur in the image. Further, a carrier having a low hardness is likely to be cracked, and the magnetic powder dropped from the cracked carrier may contaminate the formed image.

Monomers of a mono- or bis-organic phosphate compound that can be adsorbed on the surface of the magnetic powder and other polymerizable monomers are polymerized in the presence of water to encapsulate the surface of the magnetic powder with the polymer. It has also been proposed (see JP-A-63-281409). However, as the degree of polymerization of the polymer increases, the properties of the other polymerizable monomers become more pronounced, and the adsorption effect of the mono- or bis-organophosphate compound on the magnetic powder surface diminishes. The degree of polymerization of the polymer cannot be increased so much in order to secure the adsorptivity to the polymer. For this reason, the manufactured carrier is also inferior in heat resistance and wear resistance, and has low hardness and softness, which causes the various problems mentioned above.

Further, since the magnetic powder which has been subjected to the above treatment contains a large amount of the polymer having a low molecular weight as described above, the viscosity of the monomer phase becomes high and it is difficult to disperse it in the dispersion medium in the form of droplets. Therefore, there arises a problem that a carrier having a small particle size of about 50 to 70 μm or less cannot be obtained, and the particle size distribution of the carrier is widened. The present invention has been made in view of the above circumstances, dispersibility of magnetic powder, dispersion stability,
Magnetic particles that have good affinity with the binder resin, have a small particle size and a narrow particle size distribution range, and are excellent in heat resistance, wear resistance, etc., hard and difficult to crack, and that are suitable for use as carriers, etc., It aims at providing the manufacturing method by the polymerization method.

[0013]

Means and Actions for Solving the Problems The magnetic particles of the present invention for solving the above problems are obtained in the presence of a magnetic powder treated with an isocyanate group-containing vinyl monomer and having a vinyl group introduced on the surface thereof. And is made of a polymer obtained by polymerizing a vinyl monomer. The first aspect of the present invention
The method for producing is that the magnetic powder is treated with an isocyanate group-containing vinyl monomer to introduce a vinyl group on the surface, and then a monomer phase containing the magnetic powder and the vinyl monomer is formed into a droplet in a dispersion medium. It is characterized by polymerizing while being dispersed.

Further, in the second production method of the present invention, the magnetic powder is treated with an isocyanate group-containing vinyl monomer to introduce a vinyl group on the surface, and the magnetic powder and the vinyl monomer are polymerized to graft. After the polymerization, the grafted magnetic powder and a monomer phase containing a vinyl monomer which is the same as or different from the vinyl monomer are polymerized while being dispersed in a droplet form in a dispersion medium. .

In the present invention having the above constitution, when the magnetic powder is treated with an isocyanate group-containing vinyl monomer, the active hydrogen of the hydrophilic groups (hydroxyl group, sulfuric acid group, nitric acid group, etc.) on the surface of the magnetic powder and the isocyanate are The vinyl group is introduced on the surface of the magnetic powder by reacting with the isocyanate group of the group-containing vinyl monomer, and the magnetic powder is hydrophobized, so that the dispersibility in the monomer phase of the magnetic powder and the dispersion stability are improved. . Further, the vinyl group introduced on the surface of the magnetic powder is polymerized with a polymerizable monomer in a subsequent step to form a graft chain, and the magnetic powder is grafted.

Therefore, according to the present invention, the dispersibility of the magnetic powder, the dispersion stability, and the affinity with the binder resin are improved, so that the magnetic powder dispersed in the monomer phase is re-aggregated to make the magnetic properties non-uniform. It is also possible to prevent the produced magnetic particles from cracking or the magnetic powder from falling off. Since the reaction between the magnetic powder and the isocyanate group-containing vinyl monomer proceeds at a relatively low temperature of about room temperature, at this stage, even if other vinyl monomer is present in the system, it may Very little free polymer is generated as product. Further, the grafting reaction proceeds between the magnetic powder having a vinyl group introduced on the surface by the above treatment and the polymerizable vinyl monomer, so that the grafting rate is remarkably high, and free grafting as a by-product. The formation of the polymer is remarkably suppressed. Further, the isocyanate group-containing vinyl monomer used for the treatment of the magnetic powder is polymerized with other monomers in the subsequent polymerization step even if an excessive amount is generated, so that it remains in the magnetic particles with a low molecular weight. It never exists. Therefore, the produced magnetic particles are excellent in heat resistance, wear resistance, etc., and are hard and hard to break.

Moreover, as described above, no free polymer is generated as a by-product during the reaction between the magnetic powder and the vinyl monomer containing an isocyanate group or during the grafting reaction. The viscosity of the monomer phase is low, and it becomes easy to disperse it in the form of droplets in the dispersion medium. Therefore, the produced magnetic particles have a small particle size, a narrow particle size distribution, and a uniform particle size.

The present invention will be described below according to the steps of the manufacturing method. First, the magnetic powder is treated with a vinyl monomer containing an isocyanate group to introduce a vinyl group on the surface of the magnetic powder. Since the reaction between the magnetic powder and the isocyanate group-containing vinyl monomer proceeds at a relatively low temperature of about room temperature as described above, in order to perform the above treatment, for example, a predetermined amount of the magnetic powder and the isocyanate group-containing vinyl monomer are used. All that is required is to put the body in a suitable solvent and mix. Since the isocyanate group of the isocyanate group-containing vinyl monomer easily reacts with water, the above treatment is preferably performed in a dry atmosphere.

As the isocyanate group-containing vinyl monomer used for treating the magnetic powder, various compounds containing an isocyanate group and a vinyl group in one molecule can be used. As the isocyanate group-containing vinyl monomer,
For example, general formula (1):

[0020]

[Chemical 1]

Examples thereof include an acryloyl isocyanate derivative represented by the formula [wherein R ¹ represents a hydrogen atom or an alkyl group]. Specific examples of the acryloyl isocyanate derivative include compounds represented by the formula (1a):

[0022]

[Chemical 2]

Methacryloyl isocyanate represented by is preferably used. The amount of the isocyanate group-containing vinyl monomer used is not particularly limited, but is preferably in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder.
It is more preferably in the range of 5 parts by weight. When the amount of the isocyanate group-containing vinyl monomer used is less than the above range, the amount of vinyl groups introduced to the surface of the magnetic powder is insufficient, the magnetic powder is not sufficiently hydrophobized, and the dispersibility, In addition to the possibility of lowering the dispersion stability, the grafting rate decreases, so that the affinity with the binder resin deteriorates and cracks and magnetic powder fall off, or the grafting rate decreases. As the production of free polymer as product is increased,
There is a possibility that heat resistance, abrasion resistance, etc. may deteriorate, and that the magnetic particles may become soft and easily crack.

On the other hand, when the amount of the isocyanate group-containing vinyl monomer used exceeds the above range, since the isocyanate group-containing vinyl monomer is hydrophilic, the magnetic particles produced have weather resistance, particularly moisture resistance. In addition to the possibility of adversely affecting the properties, the isocyanate group-containing vinyl monomer is slightly inferior to other vinyl monomers in terms of polymerizability, so that the low molecular weight remaining in the magnetic particles does not participate in the polymerization reaction. There is a possibility that heat resistance, abrasion resistance, etc. may be deteriorated due to an increase in the components, and the magnetic particles may be soft and easily cracked.

The isocyanate group-containing vinyl monomer may be used alone or in combination of two or more. The type of magnetic powder treated with the isocyanate group-containing vinyl monomer is not particularly limited. The present invention does not contain a metal exhibiting ferromagnetism or an alloy thereof, various ferrites, or an element exhibiting ferromagnetism, but an alloy exhibiting ferromagnetism by appropriately heat-treating, etc. Powders of material can be used. Ferromagnetic metals include iron, cobalt,
Examples thereof include nickel and the like, and alloys containing these metals as described above can also be used. Examples of the ferrite include ferrosoferric oxide (Fe ₃ O ₄ ), ferric sesquioxide (γ
-Fe ₂ O _3), iron oxide, zinc (ZnFe ₂ O _4), iron oxide, yttrium _{(Y 3 Fe 5 O 12)} , iron oxide cadmium (CDFE ₂
O ₄ ), iron gadolinium oxide (Gd ₃ Fe ₅ O ₄ ), iron oxide copper (CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), iron neodymium oxide (NdFeO ₃ ), iron oxide barium oxide (BaFe ₁₂ O ₁₉ ),
Examples thereof include iron magnesium oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), and lanthanum iron oxide (LaFeO ₃ ). Examples of alloys exhibiting ferromagnetism by heat treatment include Heusler alloys containing manganese and copper, such as manganese-copper-aluminum and manganese-copper-tin. These may be used alone or in combination of two or more. The particle size of the magnetic powder is not particularly limited, and is preferably about the same as that used for a usual binder type carrier, that is, about 0.01 to 5 μm. If the particle size of the magnetic powder is less than the above range, the saturation magnetization may be lowered, or the viscosity of the monomer phase may increase, so that it is not possible to obtain magnetic particles having a minute and uniform particle size. If the particle size of the magnetic powder exceeds the above range, the dispersibility and dispersion stability will be insufficient even if treated with an isocyanate group-containing vinyl monomer, and the magnetic powder will fall out of the droplets during suspension polymerization. Therefore, there is a possibility that magnetic particles having uniform magnetic properties cannot be obtained.

As the solvent used for the treatment, various non-aqueous solvents can be used. In particular, the above treatment is carried out under a relatively low temperature condition of about room temperature, and as described above, other vinyl monomers are used. Even if it is present in the system, a free polymer is not generated as a by-product, so it is preferable to use the same vinyl monomer as that used in the subsequent polymerization step as a solvent. In this case, since the step of removing the solvent can be omitted when shifting to the next step, there is an advantage that the production efficiency is improved.

After the above treatment, in the first production method of the present invention, the treated magnetic powder is mixed with a vinyl monomer, a polymerization initiator and the like to prepare a monomer phase for suspension polymerization. Then, the monomer phase is polymerized while being dispersed in a suitable dispersion medium in the form of droplets, whereby the magnetic particles of the present invention are produced. Examples of vinyl monomers include monovinyl aromatic monomers, acrylic monomers, vinyl ester monomers,
Vinyl ether type monomer, diolefin type monomer, monoolefin type monomer, halogenated olefin type monomer,
Various conventionally known vinyl monomers such as polyvinyl monomers can be used.

The monovinyl aromatic monomer has the following general formula (2):

[0029]

[Chemical 3]

[In the formula, R ² represents a hydrogen atom, a lower alkyl group or a halogen atom, and R ³ represents a hydrogen atom, a lower alkyl group, a halogen atom, an alkoxy group, an amino group, a nitro group, a vinyl group, a sulfo group, or sodium. Indicates a sulfonate group, a potassium sulfonate group, or a carboxyl group. ), For example, styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, o, m, p
-Chlorostyrene, p-ethylstyrene, sodium styrenesulfonate, etc. may be mentioned.

The acrylic monomer has the following general formula
(3):

[0032]

[Chemical 4]

[In the formula, R ⁴ represents a hydrogen atom or a lower alkyl group, and R ⁵ represents a hydrogen atom, a hydrocarbon group having up to 12 carbon atoms, a hydroxyalkyl group, a vinyl ester group or an aminoalkyl group. ) A compound represented by, for example, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, acrylonitrile, methyl methacrylate, Butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, β-hydroxy acrylate, γ-hydroxy acrylate, δ-hydroxy butyl acrylate, β-hydroxy methacrylate, γ-amino propyl acrylate, Examples include γ-N, N-diethylaminoacrylic acid propyl ester, ethylene glycol dimethacrylic acid ester, and tetraethylene glycol dimethacrylic acid ester.

Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate and the like. Examples of vinyl ether-based monomers include vinyl methyl ether, vinyl ethyl ether, vinyl-n-butyl ether, vinyl phenyl ether, vinyl cyclohexel ether and the like.

Examples of the diolefin-based monomer include butadiene, isoprene, chloroprene and the like. Examples of the monoolefin-based monomer include ethylene, propylene, butene-1, pentene-1,4-methylpentene-1 and the like. Examples of the halogenated olefin-based monomer include vinyl chloride and vinylidene chloride.

Further, examples of the polyvinyl monomer include divinylbenzene, diallyl phthalate and tricyanurate. These can be used alone or in combination of two or more. For example, when magnetic particles containing the most common styrene-acrylic binder resin are produced, styrene and an acrylic monomer may be used in combination as the vinyl monomer.

The mixing ratio of the above vinyl monomer and the magnetic powder treated with the isocyanate group-containing vinyl monomer varies depending on the use of the magnetic particles, but in the case of a binder type carrier, the total amount of vinyl monomer is 100 to 250 parts by weight, preferably 15 to 100 parts by weight of magnetic powder
It is preferably blended in a proportion of 0 to 200 parts by weight. As the polymerization initiator, those which are insoluble in the dispersion medium and compatible with the vinyl monomer are preferable, and examples thereof include azobisisobutyronitrile and 2,2'-azobis- (2,4-dimethylvaleronitrile). ), 2,2′-azobis- (4-
Methoxy-2,4-dimethylvaleronitrile), 2,
2'-azobis- (2-cyclopropylpropionitrile), 2,2'-azobis- (2-methylpropionitrile), 2,2'-azobis- (2-methylbutyronitrile), 1,1 ′ -Azobis- (cyclohexane-1-
Carbonitrile), 2-phenylazo-4-methoxy-
2,4-dimethylvaleronitrile, dimethyl-2,2 '
-Azo compounds such as azobis (2-methylpropionate); peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, benzoyl peroxide and lauroyl peroxide are used In addition, a conventionally known photopolymerization initiator can be used when the polymerization is carried out by irradiation with ultraviolet rays or visible rays. These may be used alone or in combination of two or more.

The amount of the polymerization initiator used is 10
The amount is 0.001 to 10 parts by weight, preferably 0.01 to 6 parts by weight, based on 0 parts by weight. It is also possible to initiate the polymerization using γ-rays, accelerated electron beams, etc. In this case, it is not necessary to use a polymerization initiator. Further, the polymerization may be initiated by combining ultraviolet rays and various photosensitizers.

If necessary, in addition to the above components,
Various additives, such as a charge control agent, an offset preventing agent (release agent), and a cross-linking agent, may be added. The charge control agent is blended when the magnetic particles are used as a carrier of a two-component developer or a magnetic toner as a one-component developer. Depending on the charging polarity, the charge control agent can be used for positive charge control or negative charge control. There are two types of charge control agents.

As the charge control agent for controlling the positive charge, an organic compound having a basic nitrogen atom, such as a basic dye, an aminopyrine, a pyrimidine compound, a polynuclear polyamino compound, an aminosilane, or the like, is surface-treated with each of the above compounds. Examples include fillers. Examples of the charge control agent for controlling the negative charge include oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), Bontron S, and Spiron Black; charge control resins such as styrene-styrene sulfonic acid copolymers; Examples thereof include compounds having a carboxy group (for example, metal chelate of alkylsalicylic acid), metal complex dyes, fatty acid metal soaps, resin acid soaps, naphthenic acid metal salts and the like.

The charge control agent is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the vinyl monomer. The offset preventing agent is for preventing aggregation of magnetic particles, and examples thereof include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Among them, the weight average molecular weight is 1000-
About 10,000 aliphatic hydrocarbons are preferred. Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like is suitable.

The offset preventive agent is a vinyl monomer 100.
0.1 to 10 parts by weight, preferably 0.5
Used at a rate of ~ 8 parts by weight. The cross-linking agent is compounded to cross-link the binder resin or the graft chain of the magnetic powder to improve the mechanical or thermal characteristics of the magnetic particles and to further firmly integrate the magnetic powder and the binder resin. Divinyl compounds such as divinylbenzene; diallyl phthalate, diallyl isophthalate, diallyl adipate, diallyl glycolate, diallyl maleate, diallyl sebacate and other diallyl compounds; triallyl phosphate, triallyl aconitate, triary Triallyl compounds such as lucyanurate, trimellitic acid allyl ester, pyromellitic acid allyl ester; 1,6
-Hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, butylene glycol diacrylate, pentaerythritol diacrylate, 1,4-butanediol diacrylate, etc. Diacrylate compound; trimethylolpropane triacrylate, pentaerythritol triacrylate and other triacrylate compounds; 1,6-hexanediol dimethacrylate,
Dimethacrylate compounds such as neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, butylene glycol dimethacrylate; trimethacrylate compounds such as trimethylolpropane trimethacrylate; dipentaerythritol hexa Acrylate, tetramethylolmethane tetraacrylate, poly (meth) acrylate compounds such as acrylic acid ester of N, N, N ', N'-tetrakis (β-hydroxyethyl) ethylenediamine; allyl-acrylic compounds such as allyl acrylate and allyl methacrylate Compound; N, N'-methylenebisacrylamide, N,
Acrylamide compounds such as N′-methylenebismethacrylamide; prepolymers such as polyurethane acrylate, epoxy acrylate, polyether acrylate, polyester acrylate and the like.

The crosslinking agent is used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the vinyl monomer. When the magnetic particles of the present invention are used as a carrier, the crosslinking agent may be blended in a higher proportion. When the magnetic particles of the present invention are used as a magnetic toner, a colorant may be further added. As colorants, carbon black, aniline blue, chalco oil blue, chrome yellow,
Various conventionally known colorants such as ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green, and rose bengal can be used. The colorant is used in an amount of 1 to 15 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the vinyl monomer.

The dispersion medium in which the monomer phase composed of the above components is dispersed does not dissolve the raw material components such as vinyl monomers and the magnetic particles after polymerization at all, or hardly dissolves them, and an inert solvent. Is used. Suitable dispersion media include, for example, water or water-based solvents. In order to obtain a good dispersion state, it is preferable to add a suspension stabilizer to the dispersion medium.

As the suspension stabilizer, various conventionally known suspension stabilizers can be used, but the desired particle size of the magnetic particles is
Considering that the carrier has a particle size of 50 to 70 μm or less and the magnetic toner has a particle size of 5 to 10 μm or less, it is necessary to have an excellent suspending and dispersing ability, and in order not to affect the characteristics of the magnetic particles after production. Must be easy to remove from the magnetic particles. Examples of suspension stabilizers preferably used in the present invention which satisfy the above requirements include a combination of a calcium phosphate such as tricalcium phosphate and sodium dodecylbenzenesulfonate.

A monomer phase containing each of the above components is added to the above dispersion medium, and for example, 10 ² to 10 ⁸ dynes / cm ² is added.
When the mixture is stirred with a shearing force of a certain degree, the monomer phase is suspended in the dispersion medium and granulated into a spherical shape. In this state, -30 to 90
When the polymerization is carried out at a temperature of 30 ° C., particularly 30 to 80 ° C. for about 0.1 to 50 hours, the vinyl monomer is polymerized to obtain spherical magnetic particles. At this time, it is preferable to replace the inside of the reaction system with an inert gas in order to suppress the termination reaction of the polymerization due to oxygen. In order to obtain a high-resolution image, the magnetic particles thus obtained have a volume average particle size of 50 to 70 μm or less in the case of a carrier and 5 to 1 in the case of a magnetic toner as described above.
It is preferably 0 μm or less.

According to the above-mentioned first production method of the present invention, since each component contained in the monomer phase has a low molecular weight, the monomer phase has a low viscosity and is dispersed in the dispersion medium in the form of droplets. Is easy. Therefore, 50 for carriers
It is possible to produce magnetic particles having a uniform particle size of ˜70 μm or less, and in the case of a magnetic toner, 5 to 10 μm or less and an extremely narrow particle size distribution. In addition, since the magnetic powder has a vinyl group introduced on the surface to make it hydrophobic, it has excellent dispersibility and dispersion stability when dispersed in the monomer phase, and does not re-aggregate. Further, the magnetic particles are dispersed almost uniformly in the magnetic particles, and the magnetic particles have excellent magnetic properties.

Further, during the polymerization reaction, the vinyl monomer is polymerized on the vinyl group on the surface of the magnetic powder to be grafted with high efficiency, so that the polymer grafted on the magnetic powder and the binder resin of the magnetic particles are separated from each other. The magnetic powder and the binder resin are integrated in a state where they are mixed almost uniformly in the magnetic particles. For this reason,
There is no risk of cracking from the interface between the two and the magnetic powder falling off from the magnetic particles, and the manufactured magnetic particles have excellent durability.

In addition, in the above reaction process, since a low molecular weight polymer and unreacted components which deteriorate the physical properties of the magnetic particles are hardly formed, the magnetic particles are excellent in heat resistance and abrasion resistance and hard. And it becomes difficult to break. On the other hand, in the second production method of the present invention, the magnetic powder treated with the isocyanate group-containing vinyl monomer is first mixed with the vinyl monomer and polymerized to obtain a grafted magnetic powder.

The vinyl monomer is the same vinyl monomer as the binder resin produced by the polymerization of the vinyl monomer in the suspension polymerization step of the next step from among the various vinyl monomers exemplified above. Alternatively, it is most preferable to use the same combination of vinyl monomers, but if a graft chain having excellent compatibility with the binder resin can be formed, the vinyl monomer constituting the binder resin or a combination thereof is used. It is also possible to use vinyl monomers different from or in combination with. However, vinyl monomers that adversely affect the physical properties of the magnetic particles are not desirable for use in grafting, even if they have excellent compatibility with the binder resin.

For example, in the case of producing magnetic particles containing the most common styrene-acrylic binder resin, as a vinyl monomer for grafting and a vinyl monomer for suspension polymerization, It is most desirable to use styrene and an acrylic monomer together, but it is also possible to use styrene alone in one of the steps and use the acrylic monomer alone in the other step.

The amount of the vinyl monomer used is preferably about 10 to 50 parts by weight with respect to 100 parts by weight of the magnetic powder. When the amount of the vinyl monomer used is less than the above range, the molecular weight of the grafted polymer is too small, so that the magnetic particles produced are inferior in heat resistance and abrasion resistance, and have low hardness and softness. There is a risk.

On the contrary, when the amount of the vinyl monomer used exceeds the above range, the molecular weight of the grafted polymer is too high and the viscosity of the monomer phase becomes high, so that the droplets are dispersed in the dispersion medium. , It becomes difficult to disperse the particles into small particles, magnetic particles having a small particle size cannot be obtained, and the particle size distribution of the magnetic particles becomes wide,
May cause problems such as Further, excess vinyl monomer may form a free polymer, and the magnetic particles produced may have poor heat resistance and abrasion resistance, and may have low hardness and softness.

Although the above grafting reaction may proceed only by heating, it is still preferable to add a polymerization initiator. Further, similarly to the above, it is also possible to start the polymerization using γ-rays, accelerated electron beams, or the like, or to start the polymerization by combining ultraviolet rays and various photosensitizers,
In this case, the polymerization initiator may not be used. The polymerization initiator used in the grafting reaction may be any one having excellent solubility in the vinyl monomer, and the solubility with the dispersion medium is taken into consideration like the polymerization initiator used in the suspension polymerization. No need. However, in consideration of the moisture resistance of the obtained magnetic particles, it is preferable to use a water-insoluble polymerization initiator as in the suspension polymerization.

The amount of the polymerization initiator added is 10
It is preferably 0.001 to 5 parts by weight, and particularly preferably 0.01 to 1 part by weight, relative to 0 parts by weight.
The grafting reaction may be carried out in an appropriate solvent, but considering that the step of removing the solvent is omitted, the vinyl monomer used for the grafting also serves as the solvent without using the solvent. Is preferred.

Next, the reaction solution after the grafting is completed,
Further, a vinyl monomer, a polymerization initiator, a charge control agent, an anti-offset agent, a cross-linking agent, etc. are added to prepare a monomer phase for suspension polymerization. Then, the monomer phase is polymerized while being dispersed in a suitable dispersion medium in the form of droplets, whereby the magnetic particles of the present invention are produced. The vinyl monomer added to the monomer phase constitutes the binder resin as described above, and is a vinyl monomer that can form a binder resin having excellent compatibility with the polymer grafted on the magnetic powder. It is desirable to use a polymer. The amount of the magnetic powder may be 100 to 250 parts by weight, preferably 150 to 200 parts by weight, based on 100 parts by weight of the total amount of the vinyl monomer used for grafting. Good.

Regarding the polymerization initiator and other additives, the same amount as that used in the first production method can be used in the same amount. Further, as the dispersion medium and the suspension stabilizer, the same ones as mentioned in the first production method can be used. According to the second production method of the present invention, since the vinyl monomer is polymerized on the vinyl group on the surface of the magnetic powder to be grafted with high efficiency, the grafting rate is remarkably high and a by-product is obtained. The formation of free polymer of is significantly suppressed.

Further, since the polymerization step is carried out twice, the isocyanate group-containing vinyl monomer and the vinyl monomer rarely remain in a low molecular weight, and a low molecular weight component such as a coupling agent is not used. In combination with this, there is no low molecular weight component that affects the physical properties of the magnetic particles produced. Therefore, the magnetic particles produced are excellent in heat resistance, wear resistance, etc.,
It is hard and hard to break.

In the grafting reaction as described above, the grafting ratio is remarkably improved, and the formation of a free polymer as a by-product is remarkably suppressed, so that the monomer phase has a low viscosity and is dispersed in the dispersion medium. It is easy to disperse in droplets. Therefore, in the case of a carrier, 50 to 70 μm or less,
In the case of a magnetic toner, it is possible to produce magnetic particles having a uniform particle size of 5 to 10 μm or less and an extremely narrow particle size distribution.

Further, the grafted magnetic powder has improved dispersibility in the monomer phase and dispersion stability as compared with the untreated magnetic powder, and a vinyl monomer polymer produced in the suspension polymerization step. The binding resin and the polymer grafted on the magnetic powder are mixed almost uniformly in the magnetic particles, and the magnetic powder and the binding resin are integrated. For this reason,
There is no risk of cracking from the interface between the two and the magnetic powder falling off from the magnetic particles, and the manufactured magnetic particles have excellent durability.

As described above, the magnetic particles of the present invention can be used as a carrier for forming a two-component developer together with a chargeable toner, as well as a magnetic toner or a magnetic display as a one-component developer. It can be used in various fields such as.

[0062]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Example 1 100 parts by weight of triiron tetraoxide powder (product number BL-100 manufactured by Titanium Industry Co., Ltd.) and 100 parts by weight of iron trioxide powder (product number BL-200 manufactured by Titanium Industry Co., Ltd.) in a dry atmosphere 10 parts by weight of methacryloyl isocyanate represented by the formula (1a) was added to 60 parts by weight of styrene, and the mixture was stirred and mixed for 5 minutes for treatment.

Next, the above treatment liquid was mixed with the following components to prepare a monomer phase. Component weight parts-Vinyl monomer: butyl methacrylate 20-Crosslinking agent: divinylbenzene 2 Diethylene glycol dimethacrylate 8-Polymerization initiator: 2,2'-azobis- (2,4-dimethylvaleronitrile) 6 Next, dispersion After dissolving 40 parts by weight of tricalcium phosphate as a suspension stabilizer and 0.5 part by weight of sodium dodecylbenzenesulfonate in 600 parts by weight of distilled water as a medium, the above monomer phase was added to the mixture, and a TK homomixer [special Kika Kogyo Co., Ltd.] was stirred and suspended for 12 minutes at a rotation speed of 6500 rpm with a mixer with modified high viscosity legs to make the monomer phase into droplets.

Next, this suspension was transferred into a separable flask and heated to 80 ° C. under nitrogen atmosphere while stirring at a rotation speed of 250 rpm to carry out a polymerization reaction for 5 hours. Then, the polymer particles were separated by filtration, washed with dilute acid, washed with water and dried to obtain magnetic particles. Comparative Example 1 Except that the methacryloyl isocyanate was not added to the first treatment liquid and the amount of styrene used was 70 parts by weight.
When a monomer phase was prepared in the same manner as in Example 1 above, a homogeneous monomer phase could not be obtained because the iron trioxide particles had low wettability with respect to the monomer. Then, the monomer phase was put into a dispersion medium and an attempt was made to suspend it under the same conditions as in Example 1, but the monomer phase could not be formed into droplets.

Comparative Example 2 Instead of methacryloyl isocyanate, 10 parts by weight of a silane coupling agent (product number S manufactured by Toray Silicone Co., Ltd. was used.
Magnetic particles were obtained in the same manner as in Example 1 except that H6026) was used. Example 2 100 parts by weight of triiron tetraoxide powder (product number BL-100 manufactured by Titanium Industry Co., Ltd.) and 100 parts by weight of iron trioxide powder (product number BL-200 manufactured by Titanium Industry Co., Ltd.) in a dry atmosphere, and Methacryloyl isocyanate 2.0 represented by formula (1a)
Parts by weight, 20 parts by weight of butyl methacrylate, and 0.02 parts by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile) as a polymerization initiator were added to 60 parts by weight of styrene, Mixed and treated with ferric oxide powder. Next, the above treatment liquid is heated to 60 ° C. under stirring to
After reacting for a period of time, a slurry containing the grafted triiron tetraoxide powder was obtained.

Next, the above slurry was mixed with the following components to prepare a monomer phase. Component parts by weight Vinyl monomer: Butyl methacrylate 8.0 2-Ethylhexyl methacrylate 7.0 Crosslinking agent: Divinylbenzene 2.0 Diethylene glycol dimethacrylate 8.0 Polymerization initiator: 2,2'-Azobis- ( 2,4-dimethylvaleronitrile) 6.0 Next, to 600 parts by weight of distilled water as a dispersion medium, 40 parts by weight of tricalcium phosphate as a suspension stabilizer and 0.5 part by weight of sodium dodecylbenzenesulfonate are added. After dissolution, the above monomer phase was added, and the mixture was suspended by stirring for 12 minutes at a rotation speed of 7,000 rpm using a mixer in which the legs for high viscosity of TK homomixer [made by Tokushu Kika Kogyo Co., Ltd.] were modified. The monomer phase was made into droplets.

Next, this suspension was transferred into a separable flask and heated at 80 ° C. under nitrogen atmosphere with stirring at a rotation speed of 250 rpm to carry out a polymerization reaction for 5 hours. Then, the polymer particles were separated by filtration, washed with dilute acid, washed with water and dried to obtain magnetic particles. The following tests were carried out on the above-mentioned respective Examples and Comparative Examples to evaluate the characteristics.

Measurement of Average Particle Size The volume-based median diameter D ₅₀ of the particle size distribution of the magnetic particles produced in each of the examples and comparative examples was measured by a laser diffraction type particle size measuring device (model number LA-700 manufactured by Horiba Ltd.). The average particle diameter was measured by using the above. Also, 25% residual diameter D ₂₅ and 75
The ratio D ₂₅ / D ₇₅ to the% residual diameter D ₇₅ was determined to evaluate the width of the particle size distribution. The results are shown in Table 1.

[0069]

[Table 1]

From the results in Table 1 above, the magnetic particles of Examples 1 and 2 have a small D ₅₀ to the same extent as the magnetic particles of Comparative Example 2 and therefore have a small average particle size and a small D ₂₅ / D _75. From this, it was found that the width of the particle size distribution was narrow and the particle sizes were uniform. From this fact, according to the first and second production methods of the present invention, the viscosity of the monomer phase can be reduced in any case by the generation of the by-product free polymer, and therefore, It was confirmed that it becomes easy to disperse the monomer phase in the dispersion medium as fine droplets.

Further, comparing Examples 1 and 2, Example 1 has a smaller average particle size and a narrower particle size distribution.
From this, it is better to mix the magnetic powder treated with the isocyanate group-containing vinyl monomer in the monomer phase as the preceding step than to mix the grafted magnetic powder in the monomer phase, because the viscosity of the monomer phase is further improved. I found that it can be lowered.

Practical Test Using the magnetic particles produced in each Example and Comparative Example as a carrier, a toner having an average particle size of 10 μm (for DC2585 manufactured by Mita Kogyo Co., Ltd.) and a toner concentration of 8% were used. A two-component developer was prepared by blending, and the following measurements were performed to evaluate the characteristics.

Image Density Measurement Each developer is treated with a plain paper copying machine (model No. D) manufactured by Mita Industry Co., Ltd.
C2585) as a starting developer, and using the same toner as the developer as a replenishing toner, 10,000 black and white originals were continuously copied.
Image formation 1st sheet (initial), 1st sheet, 4th sheet and 1st
The image density in the tenth sheet of the formed image was measured using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.).

Measurement of Fogging Density The density of the blank portion of the formed images of the first (first), 1,000th, 4,000th, and 10,000th sheets of image formation was measured using the reflection densitometer. Blow-off charge amount measurement The charge amount of the developer before continuous copying of 10,000 sheets (initial), after copying 1,000 sheets, after copying 4,000 sheets, and after copying 10,000 sheets was measured by blow-off charge amount manufactured by Toshiba Chemical Co. It measured using the instrument.

The image density measurement results are shown in Table 2, the fog density measurement results are shown in Table 3, and the blow-off charge amount measurement results are shown in Table 4.

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[Table 2]

[0077]

[Table 3]

[0078]

[Table 4]

From the results shown in the above tables, the developer containing the magnetic particles of Comparative Example 2 as a carrier had a lower image density and an increased fog density as the number of copies increased, and the blow-off charge amount also decreased. did. Further, when the formed image was observed, fogging was observed on the entire surface of the 1000th image, fogging was observed on the entire surface of the 4000th image, and many white streaks were generated. Therefore, when continuous copying was stopped and the developing section of the copying machine was inspected, it was observed that the carriers were aggregated and clogged in the part of the cutting board of the developing section.

On the other hand, in the first and second embodiments,
Even after continuous copying of ten thousand sheets, almost no change was observed in each characteristic, and the formed image was good. From this, it was confirmed that the magnetic particles of Examples 1 and 2 were excellent in durability.

[0081]

As described in detail above, according to the present invention,
Good dispersibility of magnetic powder, dispersion stability, good affinity with binder resin, small particle size and narrow particle size distribution, and heat resistance,
It is possible to obtain binder type magnetic particles which are excellent in abrasion resistance and are hard and hard to break.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08F 2/44 MCQ 7442-4J G03G 9/083

Claims (3)

[Claims] 1. A magnetic material comprising a polymer obtained by polymerizing a vinyl monomer in the presence of a magnetic powder having a vinyl group introduced on the surface thereof, which is treated with an isocyanate group-containing vinyl monomer. particle. 2. A magnetic powder is treated with a vinyl monomer containing an isocyanate group to introduce a vinyl group on the surface, and then a monomer phase containing the magnetic powder and the vinyl monomer is made into droplets in a dispersion medium. A method for producing magnetic particles, which comprises polymerizing while dispersing. 3. A magnetic powder is treated with a vinyl monomer containing an isocyanate group to introduce a vinyl group on the surface, the magnetic powder and the vinyl monomer are polymerized and grafted, and then the grafted magnetic A method for producing magnetic particles, characterized in that a monomer phase containing a powder and a vinyl monomer that is the same as or different from the vinyl monomer is dispersed in a dispersion medium in the form of droplets for polymerization.