JPS60458A - Carrier for electrophotography - Google Patents

Abstract

PURPOSE:To obtain a carrier which charges electrostatically always surely a toner, obviates sticking of the toner to the carrier and has excellent durability by combining the carrier formed by using spherical magnetite (Fe3O4) as a core and coating the surface thereof with a resin with the toner. CONSTITUTION:A slurry prepd. by dispersing Fe3O4 fined to about 0.6mu average grain size in an aq. soln. contg. PVA is made into spherical particles of 20-100mu by a spray drying method, etc. The particles are calcined at >=1,000 deg.C in an N2 atmosphere and cooled, then an acrylic resin soln. is spray-coated thereon to manufacture a resin-coated carrier. The carrier is mixed with a toner for magnetic brush development to prepare a developer. The carrier has the specific gravity smaller than the specific gravity of an iron powder carrier, is spherical to permit easy agitation and mixing, contributes to the sure electrostatic charging of the toner and yields always a good image without sticking of the toner to the carrier particles.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developer for a dry copying machine, that is, a carrier in a two-component dry developer consisting of a toner and a carrier.

In dry copying, ie, electrophotography, a two-component dry developer consisting of toner and carrier is used to develop an electrostatically charged image formed on a photoreceptor by a magnetic brush method. This developer is usually a mixture of a toner consisting of fine particles and a carrier consisting of relatively large particles. Particles with a particle size of 30 to 250 microns are used. The toner generally used is a particle size of 5 to 20 microns, which is made by dispersing a pigment such as carbon blank or a dye such as nigrosine dye in a natural or synthetic resin, and if necessary, a charge control agent, a mold release agent, etc. .

The role of the carrier during development is to provide the toner with the correct triboelectric properties and appropriate charge so that it is preferentially and selectively attracted to the electrostatic charge image formed on the photoreceptor and adheres to the image area. The purpose is to electrostatically attract and remove the toner again, forming a clear image.

By the way, in conventional dry developers generally used for electrophotography, when stirring, some of the toner particles are caused by the stirring resistance caused by repetition, contact, and collision between carrier particles and toner particles and between mechanical parts of the developing machine. It has the property of adhering to the surface of particles and forming a film. In such a situation, a film of toner material (toner particles) gradually accumulates on the surface of the carrier particles, and the frictional charging between the carrier particles and toner particles changes to the frictional charging between the toner materials, which damages the entire developer. The triboelectric charging properties of the toner are deteriorated, and as a result, a so-called background smudge phenomenon occurs in which a large number of toner particles adhere to the background portion of the copied image, resulting in a reduction in the quality of the copied image.

In this way, film formation due to toner material adhesion on the surface of carrier particles results in a shortened lifespan of the developer.

In order to prevent this, it is necessary for the carrier particles to be selected from a substance that imparts an appropriate amount of charge to the toner particles, and to have surface characteristics that can prevent the formation of a film due to adhesion of the toner material. Furthermore, the formation of a film due to the adhesion of the toner material to the carrier particles is largely affected by the stirring resistance during development and mixing, and as the stirring resistance increases, the contact pressure between the carrier particles and toner particles increases, causing
- It is necessary to reduce the stirring resistance because toner adhesion is likely to occur.

Carrier particle factors that affect stirring resistance include specific gravity, particle shape, and particle size.

That is, as the specific gravity of the carrier particles increases, the stirring resistance increases, and as the carrier shape approaches a spherical shape, the fluidity of the carrier improves and the stirring resistance decreases. Furthermore, when the carrier particle size becomes fine, fluidity decreases and stirring resistance increases.

Hitherto, amorphous or spherical iron powder or particles coated with resin have been used as carrier particles, but the life of the developer has not been satisfied. The reason for this is that the iron powder carrier has a large specific gravity and a large stirring resistance when stirring the developer.

The specific gravity of iron powder used as carrier particles is generally determined by the apparent specific gravity including the shape factor, and its value is 2.
5 to 4.5 g/cc, and the apparent specific gravity increases as the shape approaches from amorphous to spherical. As mentioned above, in order to reduce the stirring resistance, it is preferable to reduce the specific gravity of the carrier and make the shape closer to a spherical shape. However, in the case of iron powder, if the shape is closer to a spherical shape, the fluidity improves, but on the other hand, the apparent Since the specific gravity increases, the overall stirring resistance is not improved much. Furthermore, if the shape of the iron powder is made irregular and the apparent specific gravity is reduced, the fluidity will decrease and the overall stirring resistance will not be improved much.

Furthermore, when iron powder is coated with a resin to prevent toner particles from adhering to the surface of the carrier particles, even if it is possible to prevent toner material from adhering, the resin itself does not have sufficient adhesion to the iron powder, which is the core material. Additionally, it lacks mechanical strength, making it vulnerable to friction and street strikes. Furthermore, since the core material is iron powder, it has a large specific gravity and a high stirring resistance, so it has the disadvantage that it cannot withstand long-term use.

The present invention provides an electrophotographic carrier that eliminates these drawbacks.

That is, the carrier for electrophotography of the present invention is a lightweight spherical coated carrier in which fine magnetite (Fe304) particles are granulated into a spherical shape, and the surface thereof is coated with a resin using spherical magnetite (Fe304) particles as a core material. , is a new two-component magnetic brush development carrier that has significantly improved developer life compared to when conventional iron powder carriers are used. Furthermore, the carrier of the present invention is a carrier that can provide high-quality copy images with improved density compared to when conventional iron powder carriers are used.

Magnetite (Fe304) is a magnetic iron oxide with a specific gravity of approximately 5 g/cc, and the specific gravity of metallic iron (7.6 g/cc).
This is about two-thirds of the total.

The fine magnetite particles used for granulating the spherical magnetite (Fe304) particles according to the present invention preferably have a particle size of 5μ or less and a purity of 95% or more. By granulating, the spherical magnetite according to the present invention, which is lighter than spherical iron powder (apparent specific gravity of about 4.5 g/cc), has an apparent specific gravity of 2.0 to 2.5, and has good fluidity is obtained.

As a result, the stirring resistance during developer stirring is significantly lower than that of conventional iron powder carriers. Furthermore, in the present invention, in order to provide a carrier resistance suitable for a carrier for two-component magnetic brush development and to more completely prevent toner adhesion to the carrier surface, the particles are used as a core material and coated with a resin, thereby improving the carrier resistance of the conventional iron powder carrier. 1M is a carrier that exhibits high quality copying with a dramatically improved lifespan compared to the 1M carrier.

As mentioned above, when the resin used for coating is coated on a carrier with high stirring resistance, such as iron powder,
Although it does not have enough mechanical strength to be used for a long time, when coated on the lightweight spherical carrier used in the present invention, it is lightweight and has extremely good fluidity, so the stirring resistance is greatly reduced. Breakage of the resin film is greatly reduced, and the durability of conventional resins is improved.

A preferred method for producing the carrier particles of the present invention is as follows, but is not necessarily limited thereto. Namely, finely divided magnetite (Fe304) is prepared in a ball mill or an attritor until the solid content concentration is 40 to 70%. After stirring and mixing in a suitable solvent, the magnetite slurry is spray-dried with a spray dryer to a size of 20 to 100 μm.
spherical particles. Outside this range, compatibility in terms of fluidity is somewhat lacking. Next, the spherical particles are heat-treated in an electric furnace or the like in a nitrogen atmosphere at a temperature of 1000°C or higher to have sufficient mechanical strength, and then the surfaces of the particles are coated with a resin by a known method. Obtain carrier particles of the present invention. Further, in the present invention, when obtaining the magnetite slurry, appropriate dispersants, binders, etc. may be added as necessary.

The resin to be coated on the particle surface of the present invention may be any resin that exhibits appropriate charging characteristics for the toner, but it is preferable that the resin has good adhesion to the particle surface. Coating resins used in the present invention include thermoplastic resins containing polyolefins, such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polyvinyl and polyvinylidene, such as polystyrene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate; polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone;
Vinyl chloride-vinyl acetate polymers, styrene-acrylic copolymers, silicone resins; fluorocarbons such as polytetrafluoroethylene, polyvinyl fluoride, polyvinyldene fluoride, polychlorotrifluoroethylene; polyamide resins; polyesters such as polyethylene terecrate; polyurethanes; polycarbonates; Examples of amino resins include urea-bormaldehyde; epoxy resins, and the like. Particularly preferred are acrylic resins, silicone resins, and fluorine resins.

The amount of coating on the particles is sufficient as long as it forms a continuous film on at least the surface of the particles, but it is generally 0.04 to 4% by weight, preferably 0.05 to 3% by weight.
is good.

The toner to be used in combination with the carrier particles of the present invention is not particularly limited, and may be manufactured by dispersing various well-known dyes and pigments in a wide range of materials, including natural resins and modified materials that combine natural and synthetic resins. Can be mentioned.

In addition, the developer using the carrier of the present invention can be used to form an electrostatic charge image formed on a photoconductive photoreceptor using known selenium, zinc oxide, cadmium sulfide, polyvinyl carbazole, or the like as a photoconductor, or to develop photosensitivity. The present invention can be applied to any electrostatic image formed on an electrostatic recording sheet.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Wet method magnetite (average particle size 0.6μ, shape two cubes) 15Kg and polyvinyl alcohol (Nippon Goseibu, G
H17) 22 kg of an aqueous solution containing 150 g was dispersed and mixed in an attritor for 8 hours to cleave the magnetite polyvinyl aqueous solution slurry.

The above slurry was spray-dried using a spray dryer to obtain spherical particles of 20 to 40μ (apparent specific gravity 2.2).
. The spherical particles are then sintered under a nitrogen atmosphere at a temperature of about 1200° C. for about 2 hours, and then cooled.

2.5 kg of a methyl ethyl ketone solution (resin content: 4%) of an acrylic resin (manufactured by Mitsubishi Rayon, BPO4) was spray coated on 10 kg of the obtained sintered particles to form the carrier of the present invention.

A developer was prepared by combining the above resin-coated carrier with a commercially available magnetic brush developing toner (BD45 November toner manufactured by Toshiba), and when the electrostatic latent image on the selenium photoreceptor was developed, a clear image was obtained. No significant change in image quality was observed even after 120,000 times of development.

Example 2 Wet method magnetite (average particle size 0.6μ, shape: cubic) 15Kg and polyvinyl alcohol (Japan Synthesis Department, G
6 kg of an aqueous solution containing 150 g of H17) was dispersed and mixed in an attrike for 8 hours to prepare a magnetite polyvinyl aqueous solution slurry.

The above slurry was spray-dried using a spray dryer to obtain spherical particles of 40 to 100 μm (apparent specific gravity: 2.1
). The spherical particles were then heated at approximately 1200°C under a nitrogen atmosphere.
After sintering at a temperature of about 2 hours, it is cooled.

2.5 kg of a methyl ethyl ketone solution (resin content: 4%) of an acrylic resin (manufactured by Mitsubishi Rayon, ER83) was spray coated on 10 kg of the obtained sintered particles to obtain a carrier of the present invention.

A developer was prepared by combining the above resin-coated carrier with a commercially available magnetic brush developing toner (toner for BD4511 manufactured by Toshiba), and when the electrostatic latent image on the selenium photoreceptor was developed, a clear image was obtained. No major change in image quality was observed even after 120,000 times of development.

Example 3 To 10 kg of the sintered spherical particles obtained in Example 1, a toluene solution (resin content: 4
%) 2.5 kg was spray coated to obtain the carrier of the present invention.

A developer was prepared by stirring and mixing the above resin-coated carrier with a commercially available magnetic brush developing toner (manufactured by Xerox, 2830), and when the electrostatic latent image on the selenium photoreceptor was developed, a clear image was obtained. No significant change in image quality was observed even after multiple development cycles.

Example 4 10 kg of the sintered spherical particles obtained in Example 1 were spray-coated with 1 g of a methyl ethyl ketone solution (resin content: 4%) of a fluororesin (manufactured by DuPont, Teflon 5954-101) to obtain the carrier of the present invention. Ta.

A developer was prepared by stirring and mixing the resin-coated carrier with a commercially available magnetic brush developing toner (manufactured by Sharp, 5F750), and when the electrostatic latent image on the organic photoreceptor was developed, a clear image was obtained. No significant change in image quality was observed even after 10,000 times of development.

Comparative Example 1 After spray-coating 1.25 kg of a methyl ethyl ketone solution (resin content 4%) of an acrylic resin (manufactured by Mitsubishi Rayon, BPO4) on 5 kg of 20-40μ spherical iron powder (apparent specific gravity 4.5), commercially available Toner for magnetic brush development (manufactured by Toshiba, toner for BD4511) When a developer was prepared by combining color toners and the electrostatic latent image on the selenium photoreceptor was developed, a clear image was initially obtained, but 4 After 10,000 times of development, the image density was low and the image became unclear with a lot of fog.

Comparative Example 2 Amorphous iron powder of 20 to 40μ (apparent specific gravity 2.8) 5K
gnia'/ +7 /lzukinFj (threet L/
After spray-coating 1.25 kg of methyl ethyl ketone solution (resin content: 4%) of BPO4 (manufactured by A.Y.), a developer was prepared by combining the color toner of a commercially available magnetic brush developing toner (manufactured by Toshiba, toner for BD4511). However, when the electrostatic latent image on the selenium photoreceptor was developed, an alcohol image with some streaks was obtained, and after 60,000 times of development, the image density was low (an unclear image with a lot of fog).

Procedural amendment 1. Description of the case Japanese Patent Application No. 58-103379 2 Title of the invention Electrophotographic carrier 3 Person making the amendment Relationship to the case Patent applicant Kanto Denka Kogyo Co., Ltd. 4 Agent 9-6 Akasaka, Minato-ku, Tokyo No. 29 Pacific Nogizaka No. 601 ■ 107 I03 (479) 2531 Voluntary amendment (amendment within 1 year and 3 months from filing of the application) 7. Contents of amendment (1) Amend the scope of claims as attached.

(2) Delete 1 (apparent specific gravity 2.2) J on page 11, lines 4-5.

(3) Next to "to cool" on page 11, line 7, add [(apparent specific gravity of particles is 2.2) J.

(4) Delete [(apparent specific gravity 2.1)j in lines 5-6 on page 12.

(5) Next to "to cool" on page 12, line 8, add [(apparent specific gravity of particles is 2.1) J.

(6) Corrected r2830J on page 13, line 5 to read “toner for r2830.”

(7) rsF750j on page 13, page 15 was corrected to "rSF750 toner" color toner (8) "Alcohol" on page 14, lines 16-17 was corrected to "yes".

2. Claims +11 An electrophotographic carrier characterized in that the core material is composed of spherical magnetite (Fe304) particles, and the spherical magnetite (Fe304) particles are coated with a resin.

(2) The electrophotographic carrier according to claim 11, wherein the spherical magnetite particles have a diameter of 20 to 100 μm.

(3) The electrophotographic carrier according to claim 11, wherein the spherical magnetite particles are produced by granulating fine magnetite and then firing at 1000° C. or higher.

Claims (2)

[Claims] (1) An electrophotographic carrier characterized in that the core material is composed of spherical magnetite (Pe304) particles, and the spherical magnetite (Fe30a) particles are coated with a resin. (2) The carrier for electrophotography according to claim (1), wherein the spherical magnetite particles have a diameter of 20 to 100 μm. (3) The carrier for electrophotography according to claim (1), wherein the spherical magnetite particles are produced by granulating fine magnetite and then firing at 100° C. or higher.