JPH07333909A - Electrophotographic developer and image forming method - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic developer in which fracture of a magnetic resin carrier due to collision or friction between two kinds of carriers or a spent ferromagnetic carrier due to fine particles produced by the fracture is avoided and drop out of magnetic particles is prevented by incorporating a first carrier comprising a magnetic resin carrier coated with a resin and a second carrier comprising ferromagnetic particles coated with a resin. CONSTITUTION:This magnetic electrophotographic developer contains magnetic particles as a first carrier and a second carrier. The first carrier is a magnetic resin carrier which contains magnetic particles dispersed in a binder resin and is coated with a resin. The second carrier consists of ferromagnetic particles coated with a resin. By coating both of two kinds of carriers with resin, energy of collision can be decreased in the resin layer to prevent breaking of the magnetic resin carrier. More preferably, both of the resins for the first carrier and the second carrier are silicone resin. Or, a more significant effect is obtd. when the difference of electrification between the first carrier and the second carrier is <=10muc/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer used for developing an electric latent image or a magnetic latent image in electrophotography, electrostatic printing or the like.

[0002]

2. Description of the Related Art Attempts have been made for a long time to improve the performance of a developer by mixing two types of carriers.
For example, there is JP-A-59-192262. This is a combination of a binder type magnetic carrier and a ferromagnetic particle carrier to form soft ears and achieve both high image quality and prevention of carrier aggregation and carrier pulling. But,
As can be seen in the combination of the binder type magnetic carrier using styrene-acrylic resin and the ferrite particles mentioned in the examples, this technique uses two carriers because the two carriers have different specific gravities and different charging properties. There is a problem that electric charges are easily generated due to friction between the toner particles, and as a result, triboelectric charging between the toner particles and the carrier is impaired. This problem causes fogging on the image and lowers the resolution, resulting in extremely poor image quality.

This phenomenon is particularly caused by developing the latent image on the latent image carrier to form a toner image, transferring the formed toner image from the latent image carrier, and cleaning the latent image carrier after transfer. This is a big problem in a system (hereinafter referred to as a toner recycling system) in which the toner on the latent image carrier is collected and the collected toner is supplied to a developing device to be used in the developing process. On the other hand, the collected toner generally has a different charging property from the replenishment toner due to a change in the particle size distribution and shape, and the embedding / separation of the external additive, and therefore two types of toner having different charging properties are replenished to the developing device. This is because the influence of charging between the two types of carriers is amplified.

Japanese Patent Application Laid-Open No. 5-323674 also uses a magnetic resin carrier and a ferromagnetic carrier and combines them with an abrasive magnetic toner to achieve both good chargeability and carrier pulling / toner spent prevention. However, even this technology has the same problem, and it is the present situation that it cannot be used in a system such as a toner recycling system which has a strict charge amount control.

There is another big problem in the combination of the magnetic resin carrier and the ferromagnetic carrier.
When a substance with a large specific gravity such as ferrite is used, its own weight becomes relatively large, and as a result, the ferromagnetic carrier collides with the magnetic resin carrier, which has a relatively low mechanical strength.
This is a problem that the corner of the magnetic resin carrier is broken by rubbing and the fine powder is spent on the ferromagnetic carrier. This spent deteriorates the chargeability and electric resistance of the ferromagnetic carrier. Further, detachment of the magnetic particles from the surface of the magnetic resin carrier is also likely to occur, resulting in problems such as fog and reduction in resolution.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to destroy a magnetic resin carrier due to collision / friction between two types of carriers and at least fine particles which are destroyed in a carrier which is a combination of at least a magnetic resin carrier and a ferromagnetic carrier. It is an object of the present invention to provide a developer having no spent on the ferromagnetic carrier and no desorption of magnetic particles.

Another object of the present invention is to provide a developing agent which makes the chargeability of toner particles uniform by minimizing the electric charge due to friction between two types of carriers.

A third object of the present invention is to provide a developer and an image forming method which provide a uniform charging property even in a toner recycling system and do not cause fog or deterioration in resolution even when used for a long period of time.

[0009]

The above object of the present invention is to provide a developer for electrophotography comprising magnetic particles and a toner, wherein the magnetic particles are magnetic particles in which at least (a) magnetic particles are dispersed in a binder resin. This is achieved by an electrophotographic developer comprising a resin-coated first carrier coated with a resin and (b) a second carrier coated with a ferromagnetic magnetic material particle with a resin.

Preferably, the coating resins for the first carrier and the second carrier are both silicone type resins.

Further, when the difference in chargeability between the first carrier and the second carrier is 10 μC / g or less, a more remarkable effect is exhibited.

Further, the first carrier is preferably a magnetic resin carrier produced by a polymerization method and coated with a silicone resin, and the latent image on the latent image carrier is developed to form a toner image. Then, the formed toner image is transferred from the latent image bearing member, the latent image bearing member after the transfer is cleaned to collect the toner on the latent image bearing member, and the collected toner is supplied to the developing device to perform the developing process. It is preferable to use the electrophotographic developer in the system used for.

As another aspect of the present invention, at least (a) a first carrier obtained by coating a magnetic resin carrier obtained by a polymerization method with a silicone-based resin and (b) a ferromagnetic resin particle with a silicone-based resin. The electrophotographic developer containing the second carrier coated with (c) toner is used to develop the latent image on the latent image carrier to form a toner image, and the formed toner image is formed on the latent image carrier. , The latent image carrier after the transfer is cleaned to collect the toner on the latent image carrier,
This is achieved by an image forming method characterized in that the collected toner is supplied to a developing device and used in a developing process.

That is, the two types of carriers perform a well-balanced interaction while maintaining common effects and different functions in both. In other words, by coating both types of carriers with resin, the energy due to collision is relaxed by the resin layer, and the magnetic resin carrier is prevented from being destroyed. By coating the surface with a resin having a small surface energy, it is possible to prevent the spent of fine powder due to the destruction.

Further, the resin for coating the two types of carriers is not particularly limited, but it is particularly preferable to select a cross-linking type silicone resin having a low surface energy to increase the film forming strength and to reduce the surface area. Since it is energy, it is possible to prevent the magnetic resin carrier fine powder generated by destruction from being spent on the ferromagnetic carrier.

The silicone resin used in the coating layer of the carrier of the present invention is not particularly limited, but for example, condensation reaction type silicone resins which are cured by the reactions shown in the following 1) and 2) are particularly preferably used.

[0017]

[Chemical 1]

In the formula, R ₁ , R ₂ , R ₃ and R ₄ each represent a substituent such as an alkyl group, a hydrogen atom, a methoxy group, a halogen group and a phenyl group, and OX represents an alkoxy group, a ketoxime group and an acetoxy group. Group, aminoxy group and the like. In such condensation reaction type silicone resin, a particularly preferred substituent is a methyl group. The coating layer obtained by the condensation reaction type silicone resin having a methyl group as a substituent has a dense structure, and is particularly suitable for forming a magnetic resin carrier. In addition, the carrier has good water repellency and moisture resistance.

The silicone resin used for the carrier coating layer may be either a heat-curable silicone resin or a room temperature curable silicone resin. When a room temperature curable silicone resin is used, it is necessary to heat it to a high temperature. The carrier can be easily manufactured because there is no such a problem.

When using a thermosetting silicone resin, it is necessary to heat at 180 to 300 ° C. Even a room temperature curable silicone resin does not require a high temperature, but may be heated within a range of 100 to 250 ° C. to accelerate curing.
Further, upon drying, metal soap such as lead such as octylic acid and naphthenic acid, iron, cobalt, tin, manganese and zinc may be used as a drying accelerator. Further, organic amines such as ethanolamine can also be effectively used as a drying accelerator.

The coverage of the resin is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, based on the core material particles. The reason is that if it is less than 0.01% by weight, the surface of the magnetic particles is significantly exposed, which is not preferable. On the other hand, if it exceeds 10% by weight, the film strength is weakened, which is not preferable.

As the method for producing the resin-coated carrier of the present invention, a wet method such as a dipping method, a spray drying method, a fluidized bed method or a mechanical impact force is applied to fix and coat resin fine particles on the surface of the magnetic material. And the dry method.

The magnetic resin carrier coated with a resin can be manufactured, for example, by the following method.

(1) Melt and mix magnetic fine particles and insulating binder resin, then cool and pulverize. (2) Melt spray dry method of spraying a molten mixture of magnetic fine particles and insulating binder resin (3 ) A method of producing a magnetic resin carrier in which magnetic fine particles are dispersed in a condensation type binder by reacting and curing a monomer or pre-monomer in an aqueous medium in the presence of magnetic fine particles, among which magnetic In order to improve the breaking strength of the resin carrier, those manufactured by a polymerization method are particularly preferable.

Since the carrier obtained by the polymerization method allows the magnetic particles to be present inside the polymer, there is no detachment of the magnetic particles and the shape can be controlled according to the purpose. The distribution itself can be controlled sharply.

As a method for obtaining a carrier in these polymerization methods, for example, magnetic particles and a radical-polymerizable monomer are mixed, suspended in water and then radical-polymerized to form a carrier, or in an aqueous medium. Formed by a method of reacting phenols and aldehydes in the presence of magnetic particles, a basic catalyst, and a suspension stabilizer to obtain composite particles, or a microencapsulation method such as an interfacial polymerization method or an in-situ polymerization method. The method of doing so can be mentioned.

Radical polymerizable monomers for obtaining a carrier by the suspension polymerization method include styrene, o-methylstyrene,
m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pt-butylstyrene, pn -Hexyl styrene, p-
Styrenes or styrene derivatives such as n-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, methacryl Acid t-butyl, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, methacrylic acid ester derivatives such as dimethylaminoethyl methacrylate, methyl acrylate, Ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lacrylate acrylate Lil, phenyl acrylate, dimethylaminoethyl acrylate, acrylic acid ester derivatives such as diethylaminoethyl acrylate ethyl can be mentioned as a monomer constituting the specific resins, these can be used alone or in combination.
Furthermore, olefins such as ethylene, propylene and isobutylene, vinyl chloride, vinylidene chloride, vinyl bromide,
Halogen vinyl such as vinyl fluoride, vinyl propionate, vinyl acetate, vinyl benzoate and other vinyl esters, vinyl methyl ether, vinyl ethyl ether and other vinyl ethers, vinyl methyl ketone, vinyl ethyl ketone, vinyl hexyl ketone, etc. Vinyl ketones, N-
N-vinyl compounds such as vinylcarbazole, N-vinylindole, N-vinylpyrrolidone, vinylnaphthalene, vinyl compounds such as vinylpyridine, acrylonitrile, methacrylonitrile, acrylamide, N-butylacrylamide, N, N-dibutylacrylamide, Examples thereof include acrylic acid or methacrylic acid derivatives such as methacrylamide, N-butyl methacrylamide, and N-octadecyl acrylamide. Further, a cross-linking agent may be used as a polymerization method carrier in order to increase hardness. Examples of this include divinylbenzene, ethylene glycol diacrylate,
Diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, etc. may be mentioned. The amount of the cross-linking agent used is appropriately adjusted depending on the required degree of cross-linking. Generally, it is used in an amount of 0.1 to 5% by weight based on the vinyl monomer. Examples of the radical polymerization initiator include peroxides such as benzoyl peroxide and lauryl peroxide, and azo initiators such as azobisisobutyronitrile and azobisisovaleronitrile. The amount used is generally 0.1 to 2.0% by weight of the radical-polymerizable monomer. Examples of suspension stabilizers for suspension in water include inorganic suspension stabilizers such as tricalcium phosphate, sodium dodecylbenzene sulfonate, polyvinyl alcohol, gelatin and the like.

When synthesized by the interfacial polymerization method, urethane or urea microcapsules formed by the reaction of an isocyanate compound and an amine compound are preferable.

The carrier used in the polymerization method is preferably spherical in practical use.

Polymerization method In the carrier, the method of surface-treating the surface of the magnetic particles with a titanium coupling agent or a silane coupling agent is also a preferable method. That is, since these magnetic particles themselves are inorganic compounds, they have low wettability with respect to monomers and the like. Therefore, when adding a large amount, it is necessary to improve the wettability with respect to the monomer by subjecting the surface to a hydrophobic treatment.

As a method of dispersing the magnetic particles in the monomer, there are a method of mixing with magnetic beads and the like, a method of dispersing and mixing with a sand grinder, and a method of dispersing with a ball mill or the like.

Further, since the polymerization method carrier forms a resin by a polymerization reaction, unlike the pulverization method, the surface can be uniformly coated with the resin, and as a result, the magnetic particles are not exposed on the surface. In addition, since the shape of the carrier is also relatively spherical, using a substance with a large specific gravity such as ferrite causes its own weight to become relatively large, and as a result, the ferromagnetic carrier collides and rubs, causing the corners of the magnetic resin carrier to collide. Does not occur, and the problem that the fine powder is spent on the ferromagnetic carrier does not occur.

The second carrier coated with the ferromagnetic magnetic particles in the resin aids the mixing property of the first carrier coated in the resin with the magnetic resin carrier, efficiently imparts charge, and improves the fluidity and transportability of the developer. Improve. This function is the most important in implementing the toner recycling system.

That is, when the magnetic resin carrier is used alone as the resin-coated first carrier, the specific gravity is small and the electric charge per unit weight is large, but the magnetization is comparatively weak, so that conveyance failure, scattering, carrier development, etc. Cause

Further, since the difference in specific gravity from the toner becomes small, the mixing with the toner to be replenished becomes insufficient, and toner scattering and image defects are likely to occur. Therefore, in order to make full use of the characteristics while compensating for the drawbacks of the first carrier coated with resin on the magnetic resin carrier, the second carrier coated with resin of ferromagnetic magnetic particles is necessary.

If the second carrier is an uncoated magnetic particle, the triboelectric charging with the toner is slow, and a charging difference with the first carrier is generated, resulting in non-uniform charging property. Further, the toner is likely to be spent on the surface of the carrier, which causes scattering in the machine and background fog.

Therefore, by coating the ferromagnetic magnetic particles with a resin, the toner to be replenished can be rapidly mixed while being sufficiently charged, and the toner scattering in the machine and the background fog can be prevented.

By coating the ferromagnetic magnetic particles with a resin, the problem that the coating material is worn or peeled off due to repeated use is caused by mixing the magnetic resin carrier having a small true specific gravity with the resin-coated first carrier. It is a great improvement over the one used in.

As the ferromagnetic magnetic particles, iron, magnetite, light metal ferrite and the like can be preferably used. These are very preferable even considering the environment.

The average particle size of the first carrier obtained by coating the magnetic resin carrier used in the present invention with resin is preferably 30 to 80 μm, and particularly preferably 40 to 70 μm. If the average particle size of the first carrier is smaller than 30 μm, even if the second carrier is mixed, the particle size is close to the particle size of the toner, so that the particles are developed together with the toner, and the mixing property is not uniform, which is not preferable. If the average particle size exceeds 80 μm, the particles are easily scattered by the centrifugal force generated by the rotation of the magnetic brush.

The average particle size of the second carrier having the ferromagnetic magnetic particles coated with a resin is preferably 50 to 100 μm, particularly preferably 60 to 80 μm. If it is less than 50 μm, the magnetic binding force becomes small even if the first carrier is mixed, and carrier adhesion to the photoconductor occurs, which is not preferable. Further, when the average particle size exceeds 100 μm, the spikes of the magnetic brush formed by mixing become coarse, and defects such as sweeps due to the carrier occur in the image, and the self-weight per carrier increases, resulting in This is not preferable because the impact force on the first carrier becomes large. This particle size is [HELO
S] (manufactured by SYMPATIC) is a volume average particle diameter.

The preferred saturation magnetization of the carrier of the present invention is in the range of 20 to 80 emu / g for the first carrier and 3 for the second carrier.
It is preferably in the range of 0 to 100 emu / g. When the saturation magnetization is high, the formed magnetic brush becomes rough and uneven density or sweeping due to carriers occurs in the image, which is not preferable.
Further, the higher the magnetization is, the harder the ears become, and the stronger they are, which leads to deterioration of the carrier, which is not preferable. Further, when the magnetization becomes small, the magnetic binding force also becomes small and carrier scattering and the like occur, which is not preferable.

Further, by controlling the difference in chargeability between the two types of carriers by changing the resin coating of the same composition or the film thickness of the coating layer, etc., the charge is kept below 10 μC / g to prevent excessive charging between the carriers. However, it is possible to realize uniform charging with the toner, and to provide a high-resolution image without fogging for a long period of time even in a system in which charging control is difficult such as a toner recycling system.

The charging property was measured under the following conditions.

Carrier: 18.8 g; Toner: 1.2 g
(Toner concentration of about 6 wt%) was put in a 20 ml glass sample tube, left at 20 ° C. and 50% RH for 2 hours or more, and then shaken for 5 minutes with a shaker (Yayoi type: NEW YS-1). Blow-off method (Toshiba Chemical Co., Ltd .: TB200)
To measure.

The measurement conditions were as follows: pressure: 1.0 kg / cm ² ; time: 30 sec; Mesh: # 400; measurement amount: about 0.5 g.

The carrier of the present invention comprises a magnetic resin carrier coated with a resin and a ferromagnetic magnetic particle coated with a second carrier in a mixing ratio of 15:85 to 85:15, preferably 25:75. By mixing and using at ~ 75: 25, it is possible to realize a developer having higher durability and higher image quality than conventional ones. If the two types of carriers are out of this range, the two types of advantages cannot be fully utilized, which is not preferable.

The toner used in the present invention is not particularly limited. Conventionally used as toner resin for this kind of application, specifically, styrene resin, styrene /
Acrylic resins, polyester resins and the like can be used.
Further, the colorant is not particularly limited, and carbon blacks, pigments and dyes of this kind can be used. If necessary, a charge control agent and wax may be added. Further, as the external additive, it is desirable that an inorganic oxide, for example, silica, titania, alumina or the like is added after being hydrophobized.

The volume average particle diameter of the toner is 3 μm.
The range is preferably from 15 to 15 μm, and more preferably from 5 to 10 μm from the viewpoint of image quality.

Details of the present invention will be described below based on examples.

[0051]

EXAMPLE As a toner to be mixed with the carrier of the present invention, 8.5 parts of carbon black and 3 parts of wax (polypropylene) were premixed with 100 parts of styrene / acrylic resin, and then kneaded, pulverized and classified to obtain a volume average. Grain size 8.5
A toner of μm was obtained.

To this toner, 0.5 part of hydrophobic silica as an external additive was added and mixed to obtain a developing toner.

<First Carrier> Carrier Production Example 1 According to the method described in JP-A-6-3863, phenol and formalin, ammonia water, calcium fluoride, water,
A cationic surfactant and spherical magnetite having a volume average primary particle diameter of 0.23 μm are charged with stirring to dissolve and disperse. The reaction solution is gradually heated under stirring to agglomerate and bind a large number of magnetite particles with a matrix of cured and cured phenolic resin as a result of a synthetic and curing reaction, resulting in a spherical resin dispersion type with a volume average particle size of 52 μm. Got a career. This carrier was coated with 2.5% by weight of monomethyl silicone resin and dried and cured to obtain magnetic particles.
These magnetic particles are used as carrier 1.

Carrier Production Example 2 As magnetic fine particles, 100 parts of magnetic fine particles (magnetite) having a volume average primary particle diameter of 0.21 μm were treated with 3 parts of a titanium coupling agent. Then, 20 parts of styrene monomer and 30 parts of methyl methacrylate monomer were mixed and mixed with a sand stirrer for 20 minutes to disperse magnetic fine particles (magnetite). Then, 0.5 part of benzoyl peroxide was added as a radical polymerization initiator. This dispersion was dispersed with 2 parts of tricalcium phosphate and 300 parts of water to which 0.01 part of sodium dodecylbenzenesulfonate was added using a TK homogenizer. The particle size of the oil phase at the time of dispersion was about 45 μm by microscopic observation. Then, the temperature was raised to 75 ° C. and the reaction was carried out for 6 hours to polymerize the monomer. Then, after cooling, hydrochloric acid was added to remove the dispersion stabilizer, followed by washing with water and drying to obtain a carrier for the polymerization method. The volume average particle size of the obtained carrier was 48 μm. This carrier is called carrier 2.

The carrier 2 was coated with 1.5 wt% of monomethyl silicone resin and dried and cured to obtain magnetic particles. This carrier is called carrier 3.

The carrier 2 is coated with 2.4 wt% of methyl methacrylate / styrene (MMA / St) resin fine particles by a mechanical impact force to obtain a carrier 4.

Carrier Production Example 3 Using 100 parts of the magnetic fine particles used in Carrier Production Example 2, 50 parts of styrene monomer and 5 parts of diphenylmethane diisocyanate were added and dispersed for 20 minutes with a sand stirrer. Then, 0.5 part of benzoyl peroxide was added as a radical polymerization initiator. This dispersion was dispersed with 2 parts of tricalcium phosphate and 300 parts of water to which 0.01 part of sodium dodecylbenzenesulfonate was added using a TK homogenizer. The particle size of the oil phase at the time of dispersion was about 45 μm by microscopic observation. Then, 5 parts of xylenediamine was dropped into water and reacted for 2 hours to form microcapsules having a urea film by an interfacial polymerization method. After that, the temperature is raised to 75 ° C. and reacted for 6 hours,
The monomer was polymerized. Then, after cooling, hydrochloric acid was added to remove the dispersion stabilizer and then washed with water and dried to obtain a microcapsule type carrier. The volume average particle size of the obtained carrier was 45 μm.

The particles were coated with 1.5 wt% of epoxy-modified silicone resin, dried and cured to obtain a carrier. This is carrier 5.

Carrier Production Example 4 Styrene / acrylic copolymer resin, Hymer 73 (trade name:
Sanyo Kasei) 100 parts by weight, magnetic powder, RB-BL (trade name: made by Titanium Industry) 200 parts by weight, carbon black 4
Part by weight is mixed with a ball mill for 20 hours, thoroughly mixed with a three-roll mill, allowed to cool, coarsely pulverized with a feather mill to a size of 5 mm or less, finely pulverized with a jet mill, and then classified to obtain an average particle size. A magnetic resin carrier having a diameter of 37 μm was obtained. This is carrier 6.

<Second Carrier> Carrier 7 After dissolving the monomethyl silicone resin in a solvent, magnetic particles (magnetite) having a volume average particle diameter of 60 μm are applied on a circulating fluidized bed, dried, and then sintered. did.

Carrier 8 An epoxy-modified silicone resin was dissolved in a solvent, magnetic particles (magnetite) having a volume average particle size of 63 μm were applied on a circulating fluidized drying bed, dried, and then sintered.

Carrier 9 Magnetite particles having a volume average particle diameter of 82 μm were used, and 100 parts of the magnetite particles were used to prepare an MMA / St copolymer resin.
A resin-coated carrier was prepared by coating 1.6 parts.

Carrier 10 Ferrite particles having a volume average particle size of 65 μm.

To each carrier, a developing toner was charged to a toner concentration of 6 wt% and shaken for 5 minutes, and each charge amount was measured. The results are shown in Table 1 below.

[0065]

[Table 1]

The evaluation method was as follows. A developing toner was mixed in a carrier mixed in the following ratio so as to have a toner concentration of 6.0 wt%, and the carriers of Examples 1, 2 and 3 were Ko
nica4145 machine equipped with toner recycling system (developing the latent image on the latent image carrier to form a toner image, transferring the formed toner image from the latent image carrier, and cleaning the latent image carrier after the transfer. To recover the toner on the latent image carrier and reconvert it to a developing device or a system used for the developing process by supplying it to a replenishment toner hopper.
Images of opy (50,000 sheets) (hereinafter referred to as Kcopy or Kc) were printed, and changes in charge amount and image fogging were evaluated. The carrier of each of Examples 4, 5, 6 and 7 was prepared by mixing the developing toner with the carrier mixed in the following ratio.
Mix so that it becomes 6.0wt%, and make an image with Konica 4145 at 50k.
Copying was performed to evaluate changes in charge amount and image fogging.

(Development conditions at this time were changed to VH = 500V and Vbias = 100V for image formation.) Mixing ratio of carriers used in Examples Example 1: Carrier 1 and carrier 7 were 50:50 in weight. Mixing ratio: Example 2: Mixing carrier 1 and carrier 8 in a weight ratio of 35:65 Example 3: Mixing carrier 3 and carrier 7 in a weight ratio of 60:40 Example 4: Carrier 5 and carrier 7 25 Example 5: Carrier 3 and carrier 8 were mixed at a weight ratio of 15:85 Example 6: Carrier 1 and carrier 9 were mixed at a weight ratio of 65:35 Example 7: Carrier 4 Carrier 7 is mixed at a weight ratio of 50:50 Mixing ratio of carriers used in Comparative Example Comparative Example 9: Carrier 1 and Carrier 10 are mixed at a weight ratio of 50:50 Comparative Example 10: Carrier 2 and Carrier 9 are 95: Mixing in a weight ratio of 5 Comparative Example 11: Carrier 6 and carrier 7 in a weight ratio of 50:50 Comparative Example 12: Carrier 6 and Carrier 10 were mixed at a weight ratio of 35:65 Comparative Example 13: Carrier 4 and Carrier 10 were mixed at a weight ratio of 35:65.

The evaluation results are shown in Table 2.

[0069]

[Table 2]

The change in the charge amount depends on the initial charge amount and 50 Kcopy.
The subsequent charge amount difference (ΔQ / M) is shown.

The image cast is Start, 5Kc, 10Kc, 20Kc,
The white paper portions of the images of 30Kc, 40Kc, and 50Kc were measured, and the relative density when the density of the paper was set to 0 was measured with a reflection densitometer RD918 (manufactured by Macbeth). The measurement was carried out at 10 points respectively, and the average concentration was 0.005 or less as O, and 0.005 or more as X.

From Table 2, the present invention provides uniform chargeability,
It can be seen that fog and resolution are not deteriorated even when used for a long period of time, and the toner recycling system is also excellent.

[0073]

According to the present invention, in a carrier formed by combining at least a magnetic resin carrier and a ferromagnetic carrier, the magnetic resin carrier is destroyed by collision / friction between two types of carriers and the finely divided ferromagnetic carrier is obtained. It is possible to provide a developer that does not have spent of magnetic particles and desorption of magnetic particles. Further, by minimizing the charge due to friction between two types of carriers, the chargeability with toner particles can be made uniform. It was possible to provide a developing agent that does.

Further, even in the toner recycling system, it is possible to provide a developer and an image forming method which give uniform charging property and are free from fogging and deterioration in resolution even when used for a long period of time.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 9/113 15/08 112 15/09 Z 21/10 G03G 9/10 331 351 352 21/00 326 (72) Inventor Masafumi Uchida 2970 Ishikawacho, Hachioji City, Tokyo Konica Stock Company

Claims (6)

[Claims] 1. An electrophotographic developer comprising magnetic particles and a toner, wherein the magnetic particles are at least (a) a magnetic resin carrier in which magnetic particles are dispersed in a binder resin, and a first carrier coated with the resin. (B) A developer for electrophotography, comprising a second carrier in which ferromagnetic magnetic particles are coated with a resin. 2. The electrophotographic developer according to claim 1, wherein both the coating resin of the first carrier and the coating resin of the second carrier are silicone resins. 3. The electrophotographic developer according to claim 1, wherein a difference in chargeability between the first carrier and the second carrier is 10 μC / g or less. 4. The electrophotographic developer according to claim 1, 2 or 3, wherein the first carrier is a magnetic resin carrier obtained by a polymerization method and coated with a silicone resin. 5. A latent image is formed by developing the latent image on the latent image carrier to form a toner image, transferring the formed toner image from the latent image carrier, and cleaning the latent image carrier after the transfer. 5. The electrophotographic developer according to claim 1, which is used in a system in which the toner on the carrier is collected and the collected toner is supplied to a developing device to be used in a developing process. 6. A first carrier in which at least (a) a magnetic resin carrier obtained by a polymerization method is coated with a silicone resin, and (b) a second carrier in which ferromagnetic magnetic particles are coated with a silicone resin (c). ) Using an electrophotographic developer containing toner, the latent image on the latent image carrier is developed to form a toner image, and the formed toner image is transferred from the latent image carrier,
An image forming method characterized in that the latent image carrier after transfer is cleaned to recover the toner on the latent image carrier, and the recovered toner is supplied to a developing device for use in a developing step.