JPS59114548A - Carrier used for electrophotographic magnetic brush developer - Google Patents

Abstract

PURPOSE:To obtain a magnetic brush developing carrier high in abrasion and impact resistance, and prevented from attachment of toner particles to the surface of the carrier by using spherical lithium silicate particles contg. magnetic powder within a specified proportion. CONSTITUTION:A slurry of magnetic powder and an aq. soln. of lithium silicate is subjected to spray drying to obtain spherical particles of 20-40mum and heat- treated in an N2 atm. to obtain lithium silicate spherical particles contg. 50- 90wt% magnetic powder having <=5mum particle diameter. These particles are used as a carrier for a developer together with a toner. The toner to be used is not specified, and the carrier thus obtained is long in life and it can form an always sharp image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developer, particularly a carrier in a two-component developer consisting of a toner and a carrier.

In electrophotography, the dry developer used when developing an electrostatic image formed on a photoreceptor by a magnetic brush method is a two-component system consisting of toner and carrier. This developer typically consists of a mixture of relatively fine toner particles and relatively large carrier particles, and the toner particles are held on the surface of the carrier particles by electrostatic forces of opposite polarity created by the contact of the particles. and,
When this developer comes into contact with the electrostatic charge image on the photoreceptor, toner particles are attracted to the electrostatic charge image to form an image. In this case, the toner particles must have the correct chargeability and charge magnitude to ensure that they are preferentially attracted to the desired image areas on the photoreceptor.

By the way, in the conventional dry type developer used in electrophotography, a portion of the toner particles are exposed to the surface of the carrier particles due to repeated contact and collision between the carrier particles and the toner particles, and between the developer and the mechanical part of the developing machine. It has the property of adhering to 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, so-called background smear development 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.

Therefore, it is necessary to select a material for the carrier particles that gives an appropriate amount of charge to the toner particles.
It is required to have mechanical strength as well as surface properties that prevent the accumulation of toner particles. Furthermore, it also needs to have an appropriate specific gravity.

Currently, irregularly formed or spherical iron powder, ferrite, or those coated with resin are used as carrier particles, but these do not necessarily satisfy the above-mentioned characteristics. For example, when irregularly shaped iron powder is used as carrier particles, toner particles accumulate in the recesses when used repeatedly.
On the other hand, when coating this with resin, even if adhesion of toner particles can be prevented, the resin itself does not have sufficient adhesion to the iron powder, which is the core material, and is susceptible to friction and impact. It also has the disadvantage that it cannot withstand long-term use because it lacks mechanical strength.

The present invention provides a carrier for electrophotographic magnetic brush developer which eliminates the above-mentioned drawbacks.

That is, the carrier of the present invention is a spherical carrier in which a specific amount of fine magnetic powder is contained and dispersed in lithium silicate, which is an inorganic binder, and is a new carrier for a two-component magnetic brush developer, which is different from the conventional iron powder carrier. Examples of the magnetic powder used in the present invention, which is a carrier that can provide high-quality copy images with improved density compared to when using iron powder, magnetite (Fe304), gamma powder, etc. -Iron oxide (γ-F
e20s) and ferrite, and it is preferable to use fine particles with a particle size of 5 microns or less.

Furthermore, the lithium silicate used in the present invention is n5
It is expressed in the form i02.LiO,2, and those with n in the range of 3.5 to 7°5, which are usually commercially available as aqueous solutions, are used.

The content of fine magnetic powder contained in this lithium silicate as an inorganic binder is 50 to 90% by weight,
Preferably it is 60 to 80% by weight. If the magnetic powder content exceeds 90% by weight, the strength of the carrier particles becomes weak and cannot withstand long-term use, and the magnetic flux density force of the carrier particles becomes too large, causing the magnetic brush to have long ears. Since the image becomes relatively rough, high-quality copies cannot be obtained.Furthermore, if it is less than 50% by weight, the magnetic flux density of the carrier particles decreases more than necessary, resulting in the inconvenience that the carrier particles fly out of the magnetic brush developer.

In other words, if the content of magnetic powder is within the range of 5-0 to 90% by weight, the magnetic flux density of the carrier particles will be in the appropriate range for shortening and denser the ears of the magnetic brush, resulting in high image quality. You can get a copy.

Furthermore, since the specific gravity of the carrier particles is smaller than that of conventional iron powder or resin-coated particles, the stress on the toner can be reduced and the life of the developer can be extended.

A preferred method for producing the carrier particles of the present invention is as follows, but is not necessarily limited thereto.

That is, after preparing a slurry of a lithium silicate aqueous solution of magnetic powder by sufficiently stirring and mixing the previously finely divided magnetic powder in a lithium silicate aqueous solution with a solid content concentration of 40 to 70% by weight using a ball mill or attritor, etc. Then, the magnetic powder slurry is spray-dried using a spray dryer to obtain spherical particles. The particle size of the spherical particles is usually about 10 to 100 microns. Next, the carrier particles of the present invention can be obtained by heat-treating these spherical particles at a temperature of 7.0.0.degree. C. or higher using an electric furnace or the like. Furthermore, the surface of the particles may be coated with a resin or the like for use, if necessary.

The toner to be used in combination with the carrier of the present invention is not particularly limited, and includes those produced by dispersing various well-known dyes and pigments in a wide range of materials including natural resins and improved materials that combine natural and synthetic resins.

Further, the developer using the carrier of the present invention can also be used to form an electrostatic image formed on a photoconductive photoconductor using known selenium, zinc oxide, cadmium sulfide, polyvinyl carbazole, etc. as a photoconductor, or a photoconductor. This invention can be applied to any electrostatic 4:'ql 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 0.6 microns, shape: cubic) 15 kg and lithium silicate aqueous solution (Lithium silicate 35 manufactured by Nissan Chemical ■, solid content 22.
9% by weight) was dispersed and mixed for 6 hours using an attritor to prepare a magnetite lithium silicate aqueous solution slurry.

The slurry described above was spray-dried using a spray dryer to obtain spherical particles of 20 to 40 microns. Next, the spherical particles were heat-treated at 800° C. for 1 hour in a nitrogen atmosphere to obtain a carrier of the present invention.

A developer was prepared by stirring and mixing the above carrier with a commercially available magnetic brush developing toner (toner for Toshiba MBD7501), and an electrostatic latent image on a selenium photoconductor was developed. No significant change in image quality was observed even after multiple development cycles.

Example 2 Styrene acrylic resin (Himer SBM-600 manufactured by Sanyo Chemical Co., Ltd.) was added to 2 kg of the carrier of the present invention obtained in Example 1.
) was spray-coated with 500 g of methyl ethyl ketone solution (resin content: 4%) to obtain a resin-coated carrier.

A developer was prepared by stirring and mixing the above resin-coated carrier with a commercially available magnetic brush developing toner (toner for 5F750 manufactured by Sharp), and an electrostatic latent image on an organic photoreceptor was developed. A clear image with improved image quality and density compared to the previous case was obtained. Furthermore, no significant change in image quality was observed even after 70,000 times of development.

Example 3 Fine iron powder by pulverization method (average particle size 4 microns, shape;
15 kg of lithium silicate aqueous solution (lithium silicate 75 manufactured by Nissan Chemical, solid content 21)
．． A slurry of an aqueous lithium silicate solution of iron powder was prepared by dispersing the iron powder in 37.5 kg (3% by weight) for 5 minutes using a high-speed stirrer.

The slurry was spray-dried using a spray dryer to obtain spherical particles of 20 to 40 microns. Next, the spherical particles were heat-treated at 800° C. for 1 hour in a nitrogen atmosphere to obtain a carrier of the present invention.

A developer was prepared by stirring and mixing the above carrier with a commercially available magnetic brush developing toy (toner for Toshiba's BD7501), and when the electrostatic latent image on the selenium photoreceptor was developed, a clear image was obtained. Even after 70,000 times of development, the initial clear image was maintained.

Example 4 Fe103 64.5%, Zn019.5%, Ni01
A mixed powder of metal oxides having a blending composition of 0.3% CuO and 5.1% CuO was fired at 1200°C to obtain a powder having a ferrite composition. 15 kg of this ferrite powder and 14 liters of lithium silicate aqueous solution similar to that used in Example 1.
kg was pulverized and mixed in an attritor for 18 hours to prepare a ferrite lithium silicate aqueous solution slurry.

The slurry was spray-dried using a spray dryer to obtain spherical particles of 20 to 40 microns. Next, the spherical particles were heat-treated at 800° C. for 1 hour in a nitrogen atmosphere to obtain a carrier of the present invention.

The above carrier of the present invention was coated with G styrene acrylic resin in the same manner as in Example 2 to obtain a resin coated carrier.

The resin-coated carrier was stirred and mixed with a commercially available magnetic brush developing toner (toner for Toshiba BD3504) to prepare a developer, and an electrostatic latent image on a selenium photoreceptor was developed. A clear image with improved image quality and edge curvature was obtained compared to the case where the In addition, the image maintained clear image quality even after 80,000 times of development.

Procedural amendment (method) April 1980 158 1. Indication of the case Patent Application No. 1987-2'25419 2. Name of the invention Carrier for electrophotographic magnetic brush developer 3. Interaction between the person making the amendment and the case. Patent application Person Kanto Denka Kogyo Co., Ltd. 4, Agent 601 Pacific Nogizaka, 6-29 Akasaka 9-chome, Minato-ku, Tokyo

Claims (1)

[Claims] (A carrier for an electrophotographic magnetic brush developer, characterized in that it consists of lithium silicate spherical particles containing 1150 to 90% by weight of magnetic powder. (2) The particle size of the magnetic powder is 5 microns. The following carrier for electrophotographic magnetic brush developer according to claim 1):