JPH09288384A - Magnetic carrier for electrophotographic developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure stable physical properties of a developer over a long period of time, to form a high density image free from fog without scattering a toner and to transfer the toner with high efficiency by specifying the ratio of the extent of saturation electrostatic charge of the toner with a resin coated carrier to that of the toner with only the magnetic core particles of the carrier. SOLUTION: This magnetic carrier is used in combination with a toner and consists of magnetic core particles and resin coating layers formed on the surfaces of the core particles. The ratio of the extent of saturation electrostatic charge of the toner with this resin coated carrier to that of the toner with only the magnetic core particles is 0.78-1.1, especially 0.8-1.05. The resin coating layers are preferably formed from a resin compsn. based on a thermosetting resin and contg. a thermoplastic resin or wax having a low m.p. or a low softening point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic carrier for an electrophotographic developer which has stable developer physical properties for a long period of time and is capable of forming a stable and high quality image for a long period of time.

[0002]

2. Description of the Related Art Conventionally, in electrophotography, a magnetic brush developing method has been widely used for developing an electrostatic latent image, and one type of a developer used for the method is a mixture of a magnetic carrier and a toner. Component developers are also widely used.

A problem with this two-component developer is the generation of so-called spent toner in which the toner is fused to the surface of the carrier, which lowers the charge imparting ability of the carrier.
It is known that image density is reduced and fog is generated.

In order to solve this problem, resin-coated carriers obtained by coating the surface of magnetic carrier particles with various resins have been used as the magnetic carrier for the developer.
The carrier has a high resistance, the charge amount is too high, the image density becomes low, and the coating resin peels off, which impairs the image quality.

The surface of the magnetic carrier particles has unevenness to some extent, and some proposals have already been made for providing a resin or a partial resin coating so as to fill the recesses.

For example, Japanese Unexamined Patent Publication No. 54-78138 (Ricoh) proposes to fill the holes or recesses of the magnetic core having a large surface roughness with fine powder of an electrically insulating resin.

In Japanese Patent Laid-Open No. 58-216260 (Ricoh), a resin is coated on the entire surface of magnetic core particles,
After that, it is described that the convex portion is exposed by scraping off the resin layer of the convex portion.

Japanese Unexamined Patent Publication (Kokai) No. 61-158339 (Minolta) describes that carrier particles having recesses on the surface are filled with resin powder and then the carrier particles are heated to fuse the resin powder. Has been done.

Japanese Unexamined Patent Publication (Kokai) No. 4-93954 (Tomokawa) describes a developer using a magnetic carrier in which fine spherical spherical ferrite particles having a small apparent density are coated with a resin so that the convex portions are exposed. ing.

Japanese Unexamined Patent Publication (Kokai) No. 8-44118 (Mita) discloses a resin coating layer mainly composed of a thermosetting resin on the surface of magnetic core particles and containing a small amount of a thermoplastic resin or wax having a low melting point or low softening point. It is described that by providing the core particles, at least the concave portions are filled, and the partial coating layer having a coating area ratio of 0.1 to 60% is provided.

Japanese Patent Publication No. 7-72810 (Canon)
In the formula, the toner, the resin-coated carrier and the carrier core satisfy the following condition: 0.18 ≦ T ₁ / T ₂ ≦ 0.77, where T ₂ is a triboelectric charge amount between the carrier core and the toner,
Its absolute value is 15.1 to 30.2 μC / g, and T
₂ is the triboelectric charge amount of the resin-coated carrier, which is lower than the triboelectric charge amount T ₁ by an absolute value of 3.5 μC / g or more, and the polarities of T ₁ and T ₂ are the same. Component developers are described.

[0012]

The above-mentioned prior art is somewhat satisfactory in that the coating resin is embedded in the recesses of the magnetic core particles to prevent the generation of spent toner in the recesses. Although the properties are satisfactory, the developer properties after long-term use have not been sufficiently satisfied.

That is, in the case of the conventional resin-coated carrier, the coating resin is inevitably peeled off during long-term use, and the physical properties of the developer change, so that there is a drawback that the durability is poor. Also, with a carrier in which resin is embedded only in the recess,
Since the core part and the resin coating part have different charging ability,
After all, there was a problem that stable developer properties could not be obtained.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, to obtain stable developer physical properties for a long period of time, to form a high-concentration image free from fogging of toner, and to prevent fog. Another object of the present invention is to provide a magnetic carrier for an electrophotographic developer that can be transferred with high efficiency.

[0015]

According to the present invention, a magnetic carrier for an electrophotographic developer, which is used in combination with a toner and comprises magnetic core particles and a resin coating layer provided on the surfaces of the core particles. In the above, the ratio of the saturated charge amount of the resin-coated carrier and the toner per the saturated charge amount of the magnetic core particles alone and the toner is in the range of 0.78 to 1.1, particularly 0.8 to 1.05. A magnetic carrier characterized by the above is provided.

In the present invention, it is preferable that the resin coat layer is composed of a resin composition mainly containing a thermosetting resin and containing a thermoplastic resin or wax having a low melting point or a low softening point.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a magnetic carrier for an electrophotographic developer comprising magnetic core particles and a resin coating layer provided on the surface of the core particles. It is a remarkable feature that the ratio of saturated charge amount of the resin-coated carrier and the toner per hit is set to a specific range of 0.78 to 1.1, particularly 0.8 to 1.05. Even if the coating resin peels off during long-term use, stable developer physical properties can always be obtained, a high-density fog-free image can be formed without toner scattering, and toner transfer is also performed with high efficiency. It was

Conventionally, the purpose of using a resin-coated carrier as a magnetic carrier of a two-component developer is, of course, to prevent the generation of toner spent, but at the same time, to control the charge amount and polarity of the toner. Also has a significant significance, and as it is seen in Japanese Examined Patent Publication No. 7-72810, a resin-coated carrier coated so as to have a saturation charge amount that is considerably different from the saturation charge amount of the carrier core. I was using it.

On the other hand, in the present invention, the ratio of the charge amount,
That is By using a magnetic carrier coated with a resin so that the value is 1 or close to 1, even if the coating resin is peeled off during long-term use, a constant charge amount can be obtained and the physical properties of the developer are always stable. . Further, there is an advantage that a stable charge amount can be obtained even with a carrier in which the resin is filled only in the concave portion of the surface of the charging means.

In the resin-coated carrier, if the ratio of the amount of charge is less than the above range, or if the resin-coated carrier deteriorates due to resin peeling or the like, the amount of highly charged toner in the developer increases and the image density tends to decrease. On the contrary, when the ratio of the charge amount exceeds the above range, when the resin-coated carrier is deteriorated due to resin peeling or the like, the low-charged toner is increased in the developer, and the fog density is increased or the toner is easily scattered.

In the present invention, the ratio of the charge amounts is of course influenced by the saturation charge amount (q ₁ ) of the magnetic core particles alone and the toner, and the saturation charge amount (q ₁ ) is
It depends on the chemical composition of the magnetic core particles, the particle size, the particle shape, the surface state of the particles, and the like. The charge amount (q ₂ ) of the resin-coated carrier is, in addition to the saturated charge amount-dependent factor of the magnetic core particles, the chemical composition of the coating resin, the physical properties including the triboelectrification tendency,
Depends on the amount of coating, distribution of coating, etc. By selecting and combining these various factors, a predetermined charge amount ratio can be obtained.

[Magnetic Core Particles] The magnetic core particles used in the present invention are generally made of a known magnetic material such as sintered ferrite, magnetite or iron powder, but may be spherical or sintered spheres close to spherical. preferable.
The magnetic core particles may have a smooth surface or may have irregularities on the surface. According to the present invention, stable charging performance can be obtained for a long time even if the magnetic core particles have irregularities on the surface. That is also one of the features.

Saturated charge amount of the magnetic core particles and the toner (q
₁ ) is an absolute value, generally 5 to 35 μC / g,
In particular, it is preferable to be in the range of 10 to 30 μC / g.

The particle size of the magnetic core particles is generally 30 to 200 μm, especially 50 as expressed by the particle size by electron microscopy.
It is generally from 1 to 150 μm. In addition, in the case of having a concave portion, the size of the concave portion is represented by the maximum diameter of the concave portion and is 0.
It is about 0.1 to 20 μm.

The apparent density of the magnetic core particles is generally 2.60 to 3.00 g / cm ³ , especially 2.70 to 2, though it varies depending on the composition of the magnetic material, the surface structure, the particle size and the like. It is in the range of 0.90 g / cm ³ . Furthermore,
The saturation magnetization of the magnetic core particles is 40 to 70 Am ² / kg,
In particular, it is preferably in the range of 45 to 65 Am ² / kg.

The magnetic core particles are generally obtained by granulating a magnetic material having a fine particle size of submicron into substantially spherical particles by means such as spray granulation and then sintering the granules by means such as firing. To be If the surface of the magnetic core particles may be smooth, or if the surface thereof has recesses or wrinkles that are recognized as the primary particles still retaining their outer shape or due to contraction during sintering. There is also.

As the magnetic powder used in the production of the magnetic core particles, any of magnetic powders known per se can be used, and examples thereof include iron trioxide (Fe ₃ O ₄ ) and iron sesquioxide ( ferromagnetic iron oxides such as γ-Fe ₂ O ₃ ),
Zinc iron oxide (ZnFe ₂ O ₄ ), yttrium iron oxide (Y
₃ Fe ₅ O ₁₂ ), cadmium oxide (CdFe ₂ O ₄ ),
Iron oxide gadolinium (Gd ₃ Fe ₅ O ₁₂ ), iron oxide copper (C
uFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), iron oxide neodymium (NdFeO ₃ ), iron oxide barium (BaFe ₁₂
O ₁₉ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), ferrites such as composites thereof, iron powder (Fe), cobalt powder (Co),
Ferromagnetic metals or alloys such as nickel powder (Ni) can be used alone or in combination. The particle shape of the magnetic material is not particularly limited, and may be any shape such as spherical shape, cubic shape, and amorphous shape.

The electric resistance of the magnetic core may be high resistance or low resistance, and generally the volume resistivity is 10 or less.
^{5 to} 10 ¹⁰ Ω · cm, especially 10 ^{7 to} 10 ⁹ Ω · cm
Is used.

[Resin Coat Layer] As the resin coat layer used in the present invention, any resin can be used as long as it provides the above-mentioned charge amount ratio (q ₂ / q ₁ ). A resin coat composed of a thermosetting resin as a main component and a resin composition having a low melting point of a thermoplastic resin or a small amount of wax is particularly useful in setting the ratio of the amount of charge within the range specified in the present invention.

As the thermosetting resin, all thermosetting resins conventionally used for the production of coated magnetic carriers can be used, but modified or unmodified silicone resin, thermosetting acrylic or acryl-styrene resin, phenol. A resin made of at least one of resin, urethane resin, thermosetting polyester resin, epoxy resin and amino resin is preferable.

Thermosetting resins include heat resistance, durability,
From the viewpoint of abrasion resistance and the like, a thermosetting resin having a gel fraction measured with tetrahydrofuran as a solvent of 55% or more, particularly 65% or more is suitable. The gel fraction means a value given by the following formula.

The functional group in the thermosetting resin used not only affects the curing performance of the resin but also greatly affects the charging polarity of the magnetic carrier. That is, nitrogen-containing resins such as amino groups are generally positively chargeable, while oxygen-containing resins such as hydroxyl groups and carboxyl groups are generally negatively chargeable. Examples of positively chargeable ones include amino resins and amino group-containing acrylic resins, and examples of negatively chargeable ones include silicon resins, carboxyl group-containing acrylic resins and phenol resins. Thus, by selecting the combination of the functional groups of the thermosetting resin, appropriate curing performance and charging performance can be obtained.

A modified silicone resin can be mentioned as a particularly preferable thermosetting resin. This modified silicone resin is obtained by modifying polyorganosiloxane with an acrylic resin, a phenol resin, an epoxy resin, an amino resin, or the like, and imparting a curing performance and an appropriate charging property.

On the other hand, as the thermoplastic resin or wax having a low melting point or a low softening point, a thermoplastic resin or wax having a melting point or a softening point lower than the thermosetting temperature of the thermosetting resin to be used, particularly a melting point of 150 ° C. or lower. Or, a thermoplastic resin or wax having a softening point is used. In the present specification, the melting point or softening point means the melting point uniquely when the resin or wax to be used has a melting point, and the softening point when it does not show a definite melting point.

The thermoplastic resin or wax having a low melting point or a low softening point should have a certain degree of compatibility or dispersibility with the thermosetting resin, and can be applied uniformly in the state of paint. It should behave as if it were repelled from the thermosetting resin during thermosetting to form a partial coating. In this sense, the thermoplastic resin or wax used preferably has a polar group in the resin.

As the polar group, ester, amide, imide group, carboxyl group, acid anhydride group, keto group, hydroxyl group,
Amino groups, ether groups, epoxy groups and the like can be mentioned, and these polar groups are contained in the resin in an amount of 1 to 1200 mmol / 100 g, particularly 10 to 1000 mmol / 100 g.
It is preferable to contain it at a concentration of.

Suitable examples thereof include thermoplastic acrylic or acrylic styrene resin, ethylene copolymer resin, low melting point polyamide resin or low melting point polyester resin.

In the present invention, as the thermoplastic acrylic resin, an acrylic acid ester or a methacrylic acid ester is mainly used, and a comonomer having a functional group such as a carboxyl group, a hydroxyl group, an amino group or an epoxy group is optionally copolymerized. The resin used is used.

Examples of acrylic acid and methacrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl (meth) acrylate. , (Meth) acrylic acid n-amyl, (meth) acrylic acid isoamyl, (meth) acrylic acid n-hexyl,
Examples include 2-ethylhexyl (meth) acrylate and n-octyl (meth) acrylate. However, the above-mentioned (meth) acrylic acid means acrylic acid or methacrylic acid.

Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids or anhydrides thereof, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, maleic anhydride, and anhydrous. Itaconic acid and the like. Examples of the hydroxyl group-containing monomer include γ-hydroxypropyl ester of acrylic acid and methacrylic acid, β-hydroxyethyl ester, and hydroxymethylol compound of acrylamide. Examples of the amino group-containing monomer include γ-aminopropyl ester of acrylic acid and methacrylic acid, β-aminoethyl ester, N-2.
-Aminoethyl-aminoethyl ester and the like. Examples of the epoxy group-containing monomer include glycidyl esters of acrylic acid and methacrylic acid and allyl glycidyl ether. Examples of other comonomers copolymerized with these monomers include styrene, vinyltoluene, acrylonitrile and methacrylonitrile.
The acrylic resin used should have a molecular weight sufficient to form a film.

As the ethylene copolymer resin or wax, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid ester copolymer, acid-modified polyethylene such as maleic anhydride graft polyethylene, ionomer, polyethylene oxide wax. , Acid-modified polyethylene wax, and the like.

As the low-melting polyamide resin, a copolymer amide resin having a low melting point or a low softening point obtained by copolymerizing a plurality of kinds of ω-aminocarboxylic acid or diamine / dicarboxylic acid salt is used, and generally nylon 6 or nylon 6 is used. , 6 types,
Copolymers of ω-aminocarboxylic acids having 10 or more carbon atoms such as dimer acid and ω-aminolauric acid, and diamine / dicarboxylic acid salts having 10 or more carbon atoms such as dodecanediamine and dodecanedicarboxylic acid are used. .

As the low melting point polyester resin, a low melting point or low softening point copolymerized polyester resin obtained by copolymerizing a plurality of kinds of ω-hydroxycarboxylic acid or diol / dicarboxylic acid is used, and generally ethylene glycol and terephthalic acid are used. Polyethylene glycols such as diethylene glycol, diols such as bisphenol, aliphatic dicarboxylic acids such as adipic acid, and copolymers of isophthalic acid are used.

The thermoplastic resin or wax used in the present invention may have a function as a polymer charge control agent, and in addition to the thermosetting resin and the thermoplastic resin or wax, a usual charge control agent may be used. Agents may be added.

In the coating resin composition, the compounding ratio of the thermosetting resin to the low melting point thermoplastic resin or wax is generally 99.5: 0.5 to 51:49, and particularly 99: 1 to 90:10. the weight ratio, the ratio of the charge amount (q ₂ / q ₁₎
Is selected within the above range.

[Coated magnetic carrier and its manufacturing method]
In the clear, the above resin composition was charged on the surface of the magnetic core particles and charged.
Ratio of quantities (q_Two/ Q ₁) Is within the above range.
Form a cover layer.

To this end, a solution or dispersion of a resin composition containing a thermosetting resin and a low melting point thermoplastic resin in the above weight ratio is applied to the magnetic core particles to give a resin composition on the surface of the magnetic core particles. Form a coating layer.

As the organic solvent for the coating solution, aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; cyclic ethers such as tetrahydrofuran and dioxane; ethanol, Alcohol solvents such as propanol and butanol; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide;
Species or two or more can be used. The concentration of the resin component in the raw material solution is generally in the range of 0.001 to 50% by weight, preferably 0.01 to 30% by weight.

Amount of resin coating layer with respect to magnetic core particles
Is a solid content of 0.001 to 2.0% by weight, particularly
From the range of 0.01 to 1.0% by weight, the charge amount ratio (q
_Two/ Q ₁) Is within the above range.

The resin may be applied to the magnetic core particles by dip coating, spray coating, spray coating using a moving bed or fluidized bed, and the like.

Next, the resin composition on the surface of the magnetic core particles is heated to a temperature not lower than the melting point of the thermoplastic resin and not lower than the thermosetting temperature of the thermosetting resin. At this stage, the curing of the thermosetting resin proceeds and the final coating state is determined.

Hot air drying is generally used to cure the resin coating layer on the surface of the magnetic core particles, but stirring heating, infrared heating, heat transfer heating, and fluidized bed heating may also be used.

The heating temperature is generally 100 to 300 ° C., and heating for about 5 to 300 minutes is suitable. If necessary, the obtained coated core is crushed to a degree that loosens agglomerates, classified, and cooled to obtain a product.

[Two-Component Developer] The magnetic carrier of the present invention is used in combination with a toner known per se as a two-component developer for developing an electrostatic latent image. The toner for a two-component developer is a toner in which a colorant, a charge control agent, a release agent and the like are dispersed in a binder resin to be granulated, and a fluidity improver is externally added if desired.

As the binder resin which is a toner component, a thermoplastic resin or a thermosetting resin of an uncured or an initial condensation product is used. Suitable examples thereof include, in order of importance, vinyl aromatic resins such as polystyrene, styrene-acrylic copolymer resins, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenol resins, petroleum resins, olefin resins, etc. Is.

In order to control the toner charge, a charge control agent, for example, an oil-soluble dye such as nigrosine base (CI 50415), oil black (CI 26150) or spirone black, a metal complex dye, a metal naphthenate, a fatty acid is used. Metal soap, resin acid soap, etc. are used as necessary.

It is also possible to give the minimum charge control action required for development by the charge control action of the resin. That is, a copolymer resin or a resin composition having an anionic or cationic polar group can be used as at least a part of the fixing resin medium in the toner to be used. , Second
Basic or nitrogen-containing groups such as secondary or tertiary amino group, quaternary ammonium group, amide group, imino group, imide group, hydrazino group, guanidino group and amidino group, and anionic groups include carboxyl group and sulfone group. Group, phosphone group and the like. Examples of the resin include resins obtained by polymerizing a cationic or anionic polar group-containing monomer with another monomer or resin by means of random copolymerization, block copolymerization, graft copolymerization or the like.

As the colorant to be contained in the resin, for example, the following inorganic or organic pigments and dyes are used alone or in combination of two or more kinds, but of course the present invention is not limited thereto. Carbon black such as furnace black and channel black; iron black such as ferrosoferric oxide; titanium dioxide such as rutile type or anatase type; phthalocyanine blue; phthalocyanine green; cadmium yellow; molybdenum orange; pyrazolone red; fast violet B etc. The colorant is used in an amount of 5 to 20 parts by weight, particularly 10 to 15 parts by weight, based on 100 parts by weight of the fixing resin medium.

The above resin may contain various waxes and low molecular weight olefinic resins as a releasing agent for heat fixing. The olefinic resin has a number average molecular weight (M
n) is 1000 to 10000, especially 2000 to 60
Those in the range of 00 are preferable. As the olefin resin, polypropylene, polyethylene, and a propylene-ethylene copolymer are used, and polypropylene is particularly preferable.

The toner particles have an average particle diameter of 5 to 1
It is preferable to use toner of 5 μm, especially 7 to 12 μm. The particle shape may be an amorphous one produced by a melt-kneading / pulverization method, or a spherical one produced by a dispersion or suspension polymerization method.

The toner can be produced by a method known per se such as a pulverizing and classifying method, a melt granulating method, a spray granulating method and a polymerization method, but the pulverizing and classifying method is generally used. These respective toner components are pre-mixed with a mixer such as a Henschel mixer and then kneaded with a kneading device such as a twin-screw extruder, and the kneaded composition is cooled, pulverized and classified to obtain a toner. To do.

Hydrophobic silica is generally used as an external additive for the toner. Use of such an external additive is
It is preferable from the viewpoint of improving the image density while preventing the fogging on the white paper exposed portion.

The hydrophobic silica used as the external additive is vapor phase silica, that is, fine silica obtained by the high temperature (flame) hydrolysis method of silicon chloride, and silanes such as dimethyldichlorosilane and trimethylchlorsilane. It is obtained by treating with an organosilicon compound and blocking silanol on the surface with an organosilane.

Further, in order to peel off the deteriorated thin layer on the surface of the photoreceptor, a toner to which an abrasive or a polishing agent is externally added can be used. As the polishing agent or polishing agent, among the polishing agents or polishing agents known per se, those having an average particle size of 0.1 to 5 μm, particularly 0.15 to 1 μm are preferably used. Generally, these abrasives or polishes preferably have a Mohs hardness of 5 to 10.

Suitable examples of abrasives or polishes include, but are not limited to, alumina (Al ₂ O ₃ ), zirconia.
(ZrO ₂ ), mullite (3Al ₂ O ₃ · 2SiO ₂ ),
Cordierite (2MgO / 2Al ₂ O ₃ / 5Si
O ₂ ), titania (TiO ₂ ), steatite (MgO
₂ · SiO ₂ ), oxide ceramics such as silica and silica-alumina; carbide ceramics such as silicon carbide (SiO ₂ ), tungsten carbide (WC), zirconium carbide (ZrC); boron nitride (BN), titanium nitride (TiN) ,
Nitride ceramics such as silicon nitride (Si ₃ B ₄ ); zirconium boride (ZrB ₂ ), titanium boride (Ti
B ₂ ) and other boride ceramics; tungsten silicide (WSi ₂ ), molybdenum silicide (MoSi ₂ ) and other silicide ceramics, diamond, corundum, chromium oxide, cerium oxide and the like.

The amount of the external additive added to the toner differs depending on the type and cannot be specified unconditionally, but generally it is determined within the range of 0.01 to 10% by weight, particularly 0.1 to 5% by weight, per toner. Good.

The mixing ratio of the coated magnetic carrier of the present invention and the toner is generally 98: 2 to 90:10 by weight, and particularly preferably 97: 3 to 94: 6 by weight.

In the electrostatographic copying method using the two-component developer of the present invention, the electrostatic latent image can be formed by any method known per se, for example, by forming a photoconductive layer on a conductive substrate. After being uniformly charged, it can be imagewise exposed to form an electrostatic latent image. Development of the electrostatic image is easily performed by bringing a magnetic brush of a two-component magnetic developer into contact with the photoconductor. The toner image formed by the development is transferred onto copy paper, and the toner image is fixed by bringing the toner image into contact with a heating roll. After the transfer, the photosensitive member is cleaned by rubbing the residual toner with a blade or the like.
The above process is reapplied.

[0069]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following examples.

Example 1 Production of Carrier As magnetic core particles, 1000 parts by weight of spherical ferrite particles having an average particle size of 100 μm were mixed with a coating agent comprising the following components using a heating and stirring device, and then the solvent was dried. Then, heat treatment was performed at 200 ° C. for 1 hour to manufacture a carrier for electrophotography. (Coating agent) Acrylic modified silicone resin: 4.5 parts by weight Styrene acrylic resin (softening point 108 ° C.): 0.5 parts by weight Solvent (toluene): 200 parts by weight

Example 2 Acrylic modified silicone resin 0.95 as a coating agent
The same procedure as in Example 1 was repeated except that the amount of styrene-acrylic resin was changed to 0.05 part by weight.

Example 3 Example 1 was repeated except that the coating agent was changed to 9.0 parts by weight of acrylic modified silicone resin and 1.0 part by weight of styrene acrylic resin.

Comparative Example 1 The procedure of Example 1 was repeated except that the acrylic modified silicone resin as the coating agent was changed to 10 parts by weight.

Comparative Example 2 The procedure of Example 1 was repeated except that the acrylic modified silicone resin as the coating agent was changed to 5 parts by weight.

Comparative Example 3 The magnetic core particles used in Example 1 were used as a carrier for electrophotography.

Manufacture of toner Toner precursor 1 was prepared by mixing the following components, melt-kneading, cooling, pulverizing and classifying the mixture to obtain an average particle size of 10 μm.
A surface treatment was performed with 0.2 parts by weight of hydrophobic silica based on 100 parts by weight to prepare a toner. (Toner) Fixing resin (styrene-acrylic copolymer): 100 parts by weight Carbon black: 10 parts by weight Release agent (polypropylene wax): 3 parts by weight

Preparation of Developer 96.5 parts by weight of the carrier of Examples and Comparative Examples and 3.5 parts by weight of the above toner were used in a ball mill 7 using a 3 L poly container.
The mixture was stirred and mixed at 5 min ⁻¹ for 1 hour to prepare a two-component developer.

Evaluation method An electrostatic copying machine (model number DC manufactured by Mita Kogyo Co., Ltd.
-4585) was used as a starting agent and the same toner was used as a replenishing toner, and continuous copying of 100,000 sheets was performed and evaluated.

Measurement of Coverage Area The carrier particles were photographed by an electron microscope, the area of the carrier particles and the area of the resin coated on the carrier surface were measured with an image analyzer, and the ratio of the area was calculated as the coverage area ratio. Calculated as (%).

Measurement of Charge Amount of Developer The blow-off charge amount (μC / g) of the developer was measured using a blow-off manufactured by Toshiba Chemical Corporation.

Image Density Measurement Using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.),
The image density (ID) of the black solid portion of the copied image was measured.

Measurement of Fog Density Using the reflection densitometer, the density of the non-image portion of the copied image was measured, and the difference from the base paper (the density of the paper before copying) was defined as the fog density (FD). did.

Transfer Efficiency The amount of toner in the toner hopper before copying and the amount in the toner hopper after copying a predetermined number of sheets were measured, and the toner consumption amount was calculated from the difference. On the other hand, the amount of toner collected in the cleaning process after copying a predetermined number of sheets was measured to obtain the amount of toner collected. From these values, the transfer efficiency of toner was calculated by the following formula.

Toner scattering The toner scattering inside the copying machine at the end of copying 100,000 sheets was visually observed and evaluated according to the following criteria. ○: No toner scattering ×: Toner scattering

The obtained results are shown in Table 1 below.

[0086]

[Table 1]

[0087]

EFFECTS OF THE INVENTION The conventional resin-coated carrier has a drawback that the coating resin is inevitably peeled off during long-term use and the physical properties of the developer are changed, resulting in poor durability.
In the carrier in which the resin is embedded only in the concave portion, there is a problem that stable physical properties of the developer cannot be obtained because the charge imparting ability is different between the core portion and the resin coating portion. However, according to the present invention, the magnetic core By setting the ratio of the saturated charge amount of the resin-coated carrier and the toner per saturated charge amount of the particles alone and the toner within the range of 0.78 to 1.1, the above-mentioned drawbacks of the prior art are solved. It is possible to obtain stable developer properties for a long period of time, to form a high-concentration image without fog without toner scattering, and to transfer the toner with high efficiency.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiichi Tamura 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd.

Claims (4)

[Claims] 1. A magnetic carrier for an electrophotographic developer, comprising a magnetic core particle and a resin coating layer provided on the surface of the core particle, which is used in combination with a toner,
The ratio of the saturated charge amount of the resin-coated carrier and the toner per saturated charge amount of the magnetic core particles alone and the toner is 0.
A magnetic carrier characterized by being in the range of 78 to 1.1. 2. The ratio of the saturated charge amount is 0.8 to 1.0.
The magnetic carrier according to claim 1, wherein the magnetic carrier is in the range of 5. 3. The magnetic carrier according to claim 1, wherein the magnetic core particles are magnetic core particles having concave portions on the surface thereof, and the concave portions are filled with a resin. 4. The magnetic carrier according to claim 1, wherein the resin coating layer is composed of a resin composition mainly containing a thermosetting resin and containing a thermoplastic resin or wax having a low melting point or a low softening point. .