JP2555704B2 - Electrophotographic carrier - Google Patents

Description

The present invention relates to a component of a two-component developer that develops an electrostatic latent image or a magnetic latent image in electrophotography, electrostatic recording, electrostatic printing, etc. And more specifically, it relates to a magnetic substance dispersion type carrier.

2. Description of the Related Art In electrophotography, a photoconductive substance such as selenium is used as a photoconductor, an electrostatic latent image is formed by various means, and a magnetic brush developing method or the like is applied to the electrostatic latent image to obtain a toner. A method of adhering and visualizing is generally adopted.

In this developing step, carrier particles called carriers are used in order to give a proper amount of positive or negative electric charge to the toner. Various types of carriers have been developed and put into practical use.

Problems to be Solved by the Invention There are various properties required for a carrier, but as particularly important properties, suitable charging property, impact resistance, abrasion resistance, developability, developer life, etc. may be mentioned. it can.

Considering the above required characteristics, the conventionally used carriers still have problems to be improved, and no sufficiently satisfactory carriers are known. For example, a conductive carrier such as iron oxide powder is excellent in solid developability but inferior in fine line reproducibility, and it is necessary to add a special charge control agent to the toner in order to extend the life. On the other hand, the coated insulating carrier has a long life, fine line reproducibility, etc., but has poor solid reproducibility. For the purpose of improving these drawbacks, a small particle size carrier in which magnetic particles are dispersed in a binder resin, a so-called microtoning carrier has been proposed and put into practical use. Adhesion to the surface, changes in the amount of charge at high humidity and low humidity due to magnetic particles released on the surface, and carrier surface treatment are difficult, so that the life cannot be drastically extended.

Accordingly, it is an object of the present invention to provide a novel magnetic brush developing carrier used for developing an electrostatic latent image in electrophotography and electrostatic recording.

Another object of the present invention is to provide a magnetic brush developing carrier which can provide excellent image quality and also has excellent developer life and high-speed developing property.

Means for Solving the Problems The present invention is characterized in that a resin coating layer containing titanium dioxide powder is provided on the surface of a carrier core containing magnetic powder and a binder resin as essential components.

As the binder resin for the carrier core used in the present invention, all common thermoplastic resins can be used, but specifically, styrenes such as styrene and chlorostyrene;
Mono-olefins such as ethylene, propylene, butylene, isobutylene; vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and other vinyl esters; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, Α-Methylene aliphatic monocarboxylic acid esters such as phenyl acrylate, ethyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; vinyl methyl ketone, vinyl Hexyl ketone, vinyl ketone homopolymers such as vinyl isopropenyl ketone, or copolymers can be exemplified.
Particularly typical examples of the binder resin include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. Examples thereof include polymers, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin and waxes can be mentioned. In the carrier core of the present invention, the magnetic fine particles used by being dispersed in the binder resin can be any fine particles of a ferromagnetic material that are usually used,
Specific examples thereof include ferrosoferric oxide, γ-iron sesquioxide, various ferrites, chromium oxide, and various metal powders.

The content of the magnetic particles is usually 30 to 30 with respect to the total amount of the binder resin.
Amounts of about 95% by weight, preferably 45-90% by weight, give good results.

In addition to the binder resin and the magnetic fine particles, the carrier core of the present invention contains a resin, a charge control agent, a coupling agent, a filler, and other materials for the purpose of charge control, dispersion improvement, strength reinforcement, fluidity improvement, and other purposes. Fine powder and the like can be added.

The carrier core is generally manufactured by a method in which the magnetic powder, the binder resin and other additives are heated and melted and kneaded by a kneader, roll mill, Banbury mixer, etc., and the kneaded product is cooled and then classified. . Alternatively, the melt-kneaded product can be produced by spray cooling with a nozzle-type or disc-type atomizing device and solidifying.

The average particle size of the carrier core of the present invention is 20 in terms of the balance between the developer life and the adhesion of the carrier to the photoreceptor and the image quality.
.About.400 .mu.m, more preferably 30 to 200 .mu.m.

Next, the resin coating layer provided on the surface of the carrier core will be described.

As the material used for the resin coating layer in the present invention, any general plastic resin can be used. Specifically, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; methyl acrylate and acrylic acid. Α-methylene aliphatic monocarboxylic acid esters such as ethyl, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, ethyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl methyl ether, vinyl Vinyl ethers such as ethyl ether and vinyl butyl ether; homopolymers or copolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone, etc. can be exemplified, and particularly representative resins The resin for coating layer,
Examples thereof include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene and polypropylene. it can.

Furthermore, polyester, polyurethane, epoxy resin,
Silicone resin, polyamide, modified rosin, paraffin,
Waxes can be used.

Further, a halogen-containing polymer can be mentioned, and specifically, olefin chloride, a monomer containing fluorine in the main chain, for example, tetrafluoroethylene, vinylidene fluoride,
Homopolymers or copolymers of monofluoroethylene, hexafluoropropylene, etc., and these monomers and ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, and other copolymerizable unsaturated bond-containing monomers The copolymer of

In addition, a compound containing fluorine in the side chain is also suitable as a monomer, and particularly, a fluoroalkyl acrylate and a fluorinated alkyl methacrylate are mentioned as typical monomers.

Furthermore, a fluorinated epoxy resin, a fluorinated polyester resin, a fluorinated silicon resin, or the like can be used.

These coating materials are used alone or in combination of two or more.

The titanium dioxide powder used in the present invention preferably has a particle size of 2 μm or less, more preferably 1 μm or less. The resistance value is 10 ¹² Ωcm or less, more preferably 10 ¹² Ωcm or less.
^{A value of 10} Ωcm or less is suitable. The amount of titanium dioxide powder added is appropriately 1 to 100% by weight, more preferably 5 to 70% by weight, based on the resin of the resin coating layer.

Further, if necessary, a resin, a charge control agent, a coupling agent, a filler, and other fine powder may be added to the coating resin for the purposes of charge control, dispersion improvement, strength reinforcement, fluidity improvement, and other purposes. it can.

The coating layer is a resin for resin coating on the surface of the carrier core,
Titanium dioxide powder and, if necessary, other additives are added to a solvent that does not dissolve the binder resin of the carrier core, and the resulting dispersion is applied, and the solvent is removed. The titanium dioxide powder can be dispersed by using an attritor, a disperser, a sand mill, a ball mill or the like. Further, as the coating device, a fluidized bed, a spray dryer, a kneader coder, and other ordinary coating devices can be used.

The thickness of the resin coating layer of the carrier of the present invention is 0.01 to 5 μm.
m, more preferably 0.1 to 1.0 μm.

The carrier of the present invention thus obtained is mixed with toner and used as a magnetic brush developer for developing an electrostatic latent image.

As the toner, any chargeable toner in which a colorant is dispersed in a binder resin and used in a usual electrophotographic method can be used.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
However, the present invention is not limited to these examples. In the following examples, parts represent parts by weight.

Example 1 Magnetic powder (EPT-1000, manufactured by Toda Kogyo Co., Ltd.) 70 parts Polyethylene (Mitsui High Wax 400p, manufactured by Mitsui Petrochemical Co., Ltd.) 30 parts The above components were heated and melted and kneaded by a pressure kneader. After sufficient kneading, the mixture was cooled and solidified using a disk-type spraying device, and then classified to obtain a spherical magnetic particle-dispersed carrier core having an average particle size of 100 μm.

To 100 parts of the obtained carrier core, 1 part of methyl methacrylate and titanium dioxide powder (particle size 0.5 μm) 0.1
Parts were dispersed in 10 parts of toluene for 12 hours using a ball mill, and coated using a fluidized bed coating apparatus,
A spherical carrier having a resin coating layer was obtained.

Comparative Example 1 A 100% part of the carrier core of Example 1 was treated with a 10% toluene solution containing 1 part of methyl methacrylate, and Example 1 was used.
A coating operation was performed in the same manner as in 1. to obtain a carrier.

Example 2 Magnetic powder (EPT-1000, manufactured by Toda Kogyo Co., Ltd.) Styrene-methyl methacrylate 70 parts Copolymer (copolymerization ratio 8: 2) 30 parts The above components were heated and melt-kneaded with a pressure kneader. After sufficiently kneading, it was cooled, pulverized and classified to obtain a carrier core having an average particle size of 50 μm.

With respect to 100 parts of the obtained carrier core, vinylidene fluoride-tetrafluoroethylene copolymer (copolymerization ratio 80: 2
0) 1 part and 0.1 part of titanium dioxide powder (particle size 0.5 μm) were dispersed in 10 parts of a solvent (Daiflon Solvent S-3, manufactured by Daikin Industries, Ltd.) for 12 hours using a ball mill, and a solution was added. The same coating operation as in Example 1 was performed to obtain a dispersion type carrier having a resin coating layer.

Comparative Example 2 Vinylidene fluoride-tetrafluoroethylene copolymer (copolymerization ratio 80: 2 was added to 100 parts of the carrier core of Example 2).
0) A 10% solution of Daiflon Solvent S-3 containing 1 part was added, and a coating operation was performed in the same manner as in Example 1 to obtain a carrier.

Using the carriers of Examples 1 and 2 and Comparative Examples 1 and 2, evaluation was performed as a developer. As the toner, a toner having an average particle diameter of 11 μm, which is composed of 100 parts of styrene-n-butylmethacrylate copolymer and 10 parts of carbon black, is mixed with a carrier at a concentration of 3% by weight to obtain a developer. .

The developer using the carrier of Example 1 and Comparative Example 1 is
An electrophotographic copying machine (FX4790, manufactured by Fuji Xerox Co., Ltd.) and a developer using the carrier of Example 2 and Comparative Example 2 are electrophotographic copying machines (FX7700, manufactured by Fuji Xerox Co., Ltd.).
Initial charge amount, solid image density, background stain,
Fine line reproducibility, charge amount when running 100,000 sheets, solid image density, background stain, fine line reproducibility, etc. were evaluated, and high temperature and high humidity (30 ℃, 80% RH) and low temperature and low humidity (10 ℃, 30 % R
H) Tested under environmental conditions. The results are shown in Table 1.

Effects of the Invention Since the electrophotographic carrier of the present invention contains the titanium dioxide powder in the resin coating layer, the following effects are produced.
First, by adding titanium dioxide powder, the electric resistance of the carrier is appropriately reduced, and a high quality image having excellent reproducibility is obtained in both the fine line portion and the solid portion. In addition, the addition of titanium dioxide powder has less effect on the charging property as compared with conventional conductive materials such as carbon black and magnetic powder, so that the life of the developer is prolonged, the charging property is stabilized, and the environment It is possible to achieve a reduction in change in charge amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayoshi Aoki 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Zerox Co., Ltd. Takematsu Plant (56) References JP-A-58-59457 (JP, A) JP-A-61- 9660 (JP, A) JP 60-12558 (JP, A) JP 55-155363 (JP, A)

Claims (1)

(57) [Claims] 1. A carrier for electrophotography, comprising a carrier core containing magnetic powder and a binder resin as essential components, and a resin coating layer containing titanium dioxide powder provided on the surface of the carrier core.