JPH06102708A - Magnetic particles and method for producing the same - 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 incorporating a magnetic powder bonded with high polymer chains with a coupling agent on the surface of particles. CONSTITUTION:This magnetic powder contains a magnetic powder bonded with high polymer chains with a coupling agent on its surface. Namely, the magnetic powder is treated with a coupling agent having functional groups in the molecule to introduce the functional groups into the surface, and then a polymn. initiator having functional groups to be bonded with the functional groups is allowed to react to bond the polymn. initiator to the surface of the magnetic powder. 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 with the coupling agent containing functional groups, hydrophilic groups on the surface of the magnetic powder are masked and the magnetic powder is made hydrophobic, which improves dispersibility and dispersion stability of the magnetic powder with the monomer phase. The excess amt. of the coupling agent is further polymerized in the succeeding process. Thereby, the obtd. magnetic particles have excellent heat resistance, wear resistance, etc., and binder-type magnetic particles which are hard and hardly cracked can be obtd.

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 characterized in that they contain magnetic powder having polymer chains bonded to the surface thereof via a coupling agent. Further, the method for producing magnetic particles of the present invention comprises treating a magnetic powder with a coupling agent having a functional group in the molecule (hereinafter referred to as “functional group-containing coupling agent”) to introduce a functional group on the surface, After reacting a polymerization initiator having a functional group that bonds with a functional group to bond the polymerization initiator to the surface of the magnetic powder, a monomer phase containing the magnetic powder and a vinyl monomer is placed in a dispersion medium. It is characterized in that it is polymerized while being dispersed in a droplet form.

In the present invention having the above constitution, when the magnetic powder is treated with a functional group-containing coupling agent, hydrophilic groups (hydroxyl group, sulfuric acid group, nitric acid group, etc.) on the surface of the magnetic powder are treated by the coupling agent. Since the magnetic powder is masked to make it hydrophobic, the dispersibility and dispersion stability of the magnetic powder in the monomer phase are improved. In addition, the functional group of the functional group-containing coupling agent introduced on the surface of the magnetic powder, the polymerization initiator is bound in the subsequent step, and the polymerizable monomer is further bound in the suspension polymerization step to form the graft chain. Is generated 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 characteristics non-uniform. It is also possible to prevent the produced magnetic particles from cracking or the magnetic powder from falling off. The grafting reaction proceeds between the magnetic powder having the polymerization initiator introduced on the surface by the two-step treatment and the polymerizable vinyl monomer, so that the grafting rate is extremely high. Further, the functional group-containing coupling agent used for the treatment of the magnetic powder has a polymerization initiator bound to the functional group in the subsequent step even if an excessive amount is generated, and the monomer is further polymerized in the suspension polymerization step. As a result, the polymer does not exist in the magnetic particles with a low molecular weight. Therefore, the produced magnetic particles have excellent heat resistance, wear resistance, etc.,
It is hard and hard to break.

In addition, as described above, since the polymer is not generated in the preceding stage up to the suspension polymerization step, the viscosity of the monomer phase used in the suspension polymerization is low, and the liquid phase in the dispersion medium is low. It becomes easy to disperse in a drop shape. Therefore, the produced magnetic particles have a small particle size and a narrow particle size distribution,
The particle size will be uniform. The present invention will be described below according to the steps of the manufacturing method.

First, the magnetic powder is treated with the functional group-containing coupling agent to introduce a functional group onto the surface of the magnetic powder. Since the reaction between the magnetic powder and the functional group-containing coupling agent proceeds at a relatively low temperature of about room temperature as in the case of a normal coupling agent, the above treatment can be performed by, for example, a predetermined amount of magnetic powder and the coupling agent. It suffices to put and into a suitable solvent and mix.

As the functional group-containing coupling agent used for treating the magnetic powder, various compounds containing a coupling agent portion and a functional group such as a glycidoxy group or an isocyanate group in one molecule should be used. You can Examples of the functional group-containing coupling agent include various silane coupling agents represented by the formulas (1) to (8).

[0019]

[Chemical 1]

[0020]

[Chemical 2]

The amount of the functional group-containing coupling agent used is not particularly limited, but is 0.1 per 100 parts by weight of the magnetic powder.
The range of 10 to 10 parts by weight is preferable, and the range of 1 to 5 parts by weight is more preferable. If the amount of the functional group-containing coupling agent used is less than the above range, the magnetic powder may not be sufficiently hydrophobized, and the dispersibility and dispersion stability may decrease, and the grafting ratio may decrease. , The affinity with the binder resin is deteriorated to cause cracking or detachment of magnetic powder, or the grafting ratio is reduced, heat resistance, wear resistance, etc. are deteriorated, and the magnetic particles are soft and easily cracked. There is a risk of becoming.

On the other hand, when the amount of the functional group-containing coupling agent used exceeds the above range, a free coupling agent which is not coupled to the magnetic powder remains in the particles or is added in the next step. The required amount of the polymerization initiator increases, and as a result, the moisture resistance and charge stability of the toner, and further the life of the carrier and the magnetic toner are adversely affected. The functional group-containing coupling agent can be used alone or in combination of two or more.

Treated with a functional group-containing coupling agent
The type of magnetic powder to be used is not particularly limited. Starting
In the clear, metals that exhibit ferromagnetism and their alloys,
Or containing no ferromagnetism elements,
Currently known, such as alloys that exhibit ferromagnetism by heat treatment
Use powders of all types of magnetic materials
You can Ferromagnetic metals include iron, cobalt,
Nickel and the like are included, and as described above, these metals are not included.
It is also possible to use the alloys with. As ferrite
Is, for example, ferric oxide (Fe₃O_Four), Ferric oxide (γ
−Fe₂O₃), Zinc oxide (ZnFe₂O_Four), Iron oxide
Thorium (Y₃Fe_FiveO₁₂), Iron cadmium oxide (CdFe₂
O_Four), Iron gadolinium oxide (Gd₃Fe_FiveO_Four),iron oxide
Copper (CuFe ₂O_Four), Iron oxide lead (PbFe₁₂O₁₉), Iron oxide
Ojim (NdFeO₃), Iron oxide barium (BaFe₁₂O₁₉),
Magnesium iron oxide (MgFe₂O_Four), Iron manganese oxide
(MnFe₂O_Four), Lanthanum iron oxide (LaFeO₃) Etc.
To be Also, as an alloy that exhibits ferromagnetism by heat treatment
Is, for example, manganese-copper-aluminum or manganese.
-Heusler compound containing manganese and copper, such as copper-tin
Money can be given. These are used alone and 2 types
The above can also be used together. Regarding the particle size of magnetic powder
No particular limitation, used for ordinary binder type carrier
The same level as that, that is, about 0.01 to 5 μm is preferable.
Good If the particle size of the magnetic powder falls below the above range, the saturation magnetization
Decrease, or the viscosity of the monomer phase increases,
And the magnetic particles with a uniform particle size may not be obtained.
is there. If the particle size of the magnetic powder exceeds the above range, even if
Dispersion even when treated with a functional group-containing coupling agent
Property and dispersion stability become insufficient, and from droplets during suspension polymerization
Magnetic particles with uniform magnetic properties, such as magnetic powder falling off,
There is a risk that it will not be obtained.

As the solvent used for the treatment, various non-aqueous solvents can be used. Then, to the treatment liquid, when a polymerization initiator having a functional group capable of binding to the functional group of the functional group-containing coupling agent introduced on the surface of the magnetic powder is added, the functional group introduced on the surface of the magnetic powder is added. The functional group of the polymerization initiator is bonded, and the polymerization initiator is bonded to the surface of the magnetic powder via the coupling agent.

As the above-mentioned polymerization initiator, a functional group capable of binding to the functional group of the functional group-containing coupling agent in one molecule,
Various compounds including a part of the polymerization initiator can be used. When the functional group capable of binding to the functional group of the functional group-containing coupling agent is a glycidoxy group or an isocyanate group as described above, as the functional group on the polymerization initiator side,
A carboxylic acid group and the like which can be bonded to the glycidoxy group and the like under relatively low temperature conditions such as room temperature are preferable. Further, as a part of the polymerization initiator, an azo which does not react with the above-mentioned carboxylic acid group or glycidoxy group at room temperature, and moreover, generates a radical by heating or the like to initiate the polymerization reaction of the polymerizable vinyl monomer. A group and the like are preferable.

Specific examples of the above polymerization initiator include 4,4'-azobis (4-cyanovaleric acid),
2,2'-azobis (2-cyanopropionic acid), 2,
2'-azobis (2-methylpropionic acid), 4,4 '
-Azobis (4-methylvaleric acid) and the like. The amount of the polymerization initiator used is not particularly limited, but it is desirable to set the amount used so that the functional group equivalent of the polymerization initiator is equal to or more than the functional group equivalent of the functional group-containing coupling agent. When the functional group equivalent of the polymerization initiator is less than the functional group equivalent of the functional group-containing coupling agent, the functional group-containing coupling agent in which the polymerization initiator is not bonded remains on the surface of the magnetic powder. , The magnetic powder exhibits hydrophilicity due to its functional group, which may adversely affect the weather resistance, especially the moisture resistance, of the magnetic particles to be produced. Without being polymerized by the initiator, it may remain in the magnetic particles with a low molecular weight, and heat resistance, abrasion resistance, etc. may be deteriorated, or the magnetic particles may be soft and easily cracked.

The polymerization initiator may be used alone, or
Two or more kinds can be used in combination. After the above treatment, in the production method of the present invention, the treated magnetic powder is mixed with a vinyl monomer or 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.

The polymerization initiator bound to the surface of the magnetic powder produces free radicals in both the portion remaining on the magnetic powder side and the portion separated from the magnetic powder when cut by heat or the like. It is not necessary to intentionally add a polymerization initiator to the monomer phase. However, in order to ensure the formation of the binder resin and to control the molecular weight of the formed binder resin, a polymerization initiator may be supplementarily added.

Examples of vinyl monomers include monovinyl aromatic monomers, acrylic monomers, vinyl ester monomers, vinyl ether monomers, diolefin monomers, monoolefin monomers. Various conventionally known vinyl-based monomers such as halogenated olefin-based monomers and polyvinyl-based monomers can be used. As the monovinyl aromatic monomer, the following general formula (9):

[0030]

[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.

As the acrylic monomer, the following general formula (1
0):

[0033]

[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, tricyanurate and the like. 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 blending ratio of the vinyl monomer and the magnetic powder having a polymerization initiator bonded on the surface varies depending on the use of the magnetic particles, but in the case of a binder type carrier, the total amount of the vinyl monomer. 10 parts by weight of magnetic powder to 100 parts by weight
It is preferable to blend in a proportion of 0 to 250 parts by weight, preferably 150 to 200 parts by weight. As the auxiliary 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, and each of the above compounds are surface-treated. 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 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 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 the colorant, various conventionally known colorants such as carbon black, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green, and rose bengal are used. 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 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 can be easily dispersed in the dispersion medium in the form of droplets. is there. Therefore, in the case of carrier, 50 to 70
It is possible to produce magnetic particles having a uniform particle size of less than μm, 5 to 10 μm in the case of a magnetic toner, and having an extremely narrow particle size distribution.

Since the magnetic powder is hydrophobized by the functional group-containing coupling agent, it has excellent dispersibility and dispersion stability when dispersed in the monomer phase and does not re-aggregate. The magnetic particles are almost uniformly dispersed in the produced magnetic particles, and the magnetic particles have excellent magnetic properties. Further, at the time of the polymerization reaction, the vinyl monomer is polymerized to the polymerization initiator 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 magnetic particles. The magnetic powder and the binder resin are integrated into a state in which they are almost uniformly mixed. For this reason, there is no possibility that cracks will occur at the interface between the two and the magnetic powder will not fall off from the magnetic particles, and the manufactured magnetic particles will have excellent durability.

Moreover, in the above reaction process, a low molecular weight polymer and unreacted components which deteriorate the physical properties of the magnetic particles are hardly formed, so that the magnetic particles are excellent in heat resistance and abrasion resistance and hard. And it becomes difficult to break. As described above, the magnetic particles of the present invention can be used as a carrier that constitutes a two-component developer together with a chargeable toner, and also can be used as a magnetic toner as a one-component developer or in various magnetic displays. Can be used in the field of.

[0051]

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 0.7 parts by weight of 3-glycidoxypropyltrimethoxysilane represented by the formula (7) as a group-containing coupling agent was added to 500 parts by weight of acetone, and the mixture was stirred and mixed for 5 minutes. Processed.

Then, 4,4'-azobis (4-cyanovaleric acid) 1.2 as a polymerization initiator was added to the above treatment solution.
After adding a part by weight, stirring and mixing for a further 5 minutes, the mixture was treated, and then acetone was removed by a reduced pressure drying method to recover the treated ferric tetroxide powder. Next, the above-mentioned iron oxide black powder 2
0.019 parts by weight was mixed with each component shown below to prepare a paste-like monomer phase.

Component weight parts Vinyl monomer: Styrene 70 Butyl methacrylate 20 Crosslinker: Divinylbenzene 2 Diethylene glycol dimethacrylate 8 Polymerization initiator: 2,2′-Azobis- (2,4-dimethylvaleronitrile) 6 Next, after dissolving 40 parts by weight of tricalcium phosphate as a suspension stabilizer and 0.5 parts by weight of sodium dodecylbenzenesulfonate in 600 parts by weight of distilled water as a dispersion medium, the above monomer phase was added, A monomer phase of TK homomixer [made by Tokushu Kika Kogyo Co., Ltd.] was suspended by stirring for 12 minutes at a rotation speed of 7,000 rpm using a mixer with modified legs for high viscosity.

Next, this suspension was transferred into a separable flask and heated to 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. Example 2 As a functional group-containing coupling agent, 0.7 parts by weight of 3-glycidoxypropylmethyldiethoxysilane represented by the above formula (4) was used instead of 3-glycidoxypropyltrimethoxysilane. Magnetic particles were obtained in the same manner as in Example 1 except for the above.

Comparative Example 1 Tetratrioxide not treated with 3-glycidoxypropyltrimethoxysilane as a functional group-containing coupling agent and 4,4'-azobis (4-cyanovalerianic acid) as a polymerization initiator. Iron powder (product number BL- manufactured by Titanium Industry Co., Ltd.
A monomer phase was prepared in the same manner as in Example 1 except that 100 parts by weight of 100) and 100 parts by weight of iron trioxide powder (product number BL-200 manufactured by Titanium Industry Co., Ltd.) were used. Since the iron particles have low wettability with respect to the monomer, a homogeneous monomer phase could not be obtained. And
An attempt was made to suspend the monomer phase in the dispersion medium under the same conditions as in Example 1, but the monomer phase could not be formed into droplets.

Comparative Example 2 Instead of 3-glycidoxypropyltrimethoxysilane as a functional group-containing coupling agent, a normal silane coupling agent having no functional group (Product No. SH6020 manufactured by Toray Silicone Co., Ltd.) 0.7 Magnetic particles were obtained in the same manner as in Example 1 except that parts by weight were used.

Example 3 As a functional group-containing coupling agent, 0.8 parts by weight of 3-isocyanatopropyltriethoxysilane represented by the above formula (1) was used in place of 3-glycidoxypropyltrimethoxysilane. Magnetic particles were obtained in the same manner as in Example 1 except for the above.

The following tests were carried out on the above Examples and Comparative Examples to evaluate the characteristics. Average particle size measurement The volume-based median diameter D ₅₀ of the particle size distribution of the magnetic particles produced in each Example and Comparative Example was measured using a laser diffraction particle size measuring device (Model No. LA-700 manufactured by Horiba Ltd.). To obtain the average particle size. 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.

[0059]

[Table 1]

From the results in Table 1 above, all of the magnetic particles of Examples 1 to 3 have a smaller D ₅₀ than the magnetic particles of Comparative Example 2, so that the average particle size is small, and D ₂₅ / D ₇₅ is Since it was small, it was found that the width of the particle size distribution was narrow and the particle size was uniform. From this fact, it was confirmed that according to the production method of the present invention, the viscosity of the monomer phase can be lowered, and therefore the monomer phase can be easily dispersed in the dispersion medium as fine droplets.

Practical Test Using the magnetic particles produced in each of the Examples and Comparative Examples 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 was 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), 2,000th sheet, 6,000th 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 Fog Density The density of the blank area of the first image formed (initial stage), the 2,000th sheet, the 6,000th sheet, and the 10,000th image formed was measured using the reflection densitometer. Blow-off charge amount measurement The charge amount of the developer before continuous copying (initial stage) of 10,000 sheets, after copying 2,000 sheets, after copying 6,000 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.

[0065]

[Table 2]

[0066]

[Table 3]

[0067]

[Table 4]

From the results of the above-mentioned 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, fog was observed on the entire surface of the 2,000th image and fog was observed on the entire surface of the 6,000th 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 each of Examples 1 to 3, 1
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 to 3 had excellent durability.

[0070]

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 front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display area C08F 2/44 MCQ 7442-4J 4/02 MEF 7242-4J G03G 9/083

Claims (2)

[Claims] 1. A magnetic particle comprising a surface on which magnetic powder having a polymer chain bound thereto via a coupling agent is contained. 2. A magnetic powder is treated with a coupling agent having a functional group in the molecule to introduce a functional group on the surface, and a polymerization initiator having a functional group that binds to this functional group is reacted to obtain magnetic properties. After binding the polymerization initiator to the surface of powder, the monomer phase containing the magnetic powder and the vinyl monomer is polymerized while being dispersed in a dispersion medium in the form of droplets. Method.