JPS63228174A - Magnetic carrier and its manufacture - Google Patents

Abstract

PURPOSE:To uniformize characteristics in the surface of a carrier and to ensure superior chargeability are free from scattering by forming a resin film on the surfaces of magnetic particles composed of a binder resin and fine magnetic powder dispersed into the binder. CONSTITUTION:The magnetic particles composed of a binder resin containing the fine magnetic particles dispersed into the binder is prepared by kneading the binder resin and the fine magnetic powder, pulverizing the mixture after solidifying it, and the magnetic carrier is obtained by mixing these magnetic particles with the resin powder smaller in average particle diameter then them, stirring the mixture to electrostatically attach the resin powder to the magnetic particles, and melting the attached powder by an impact force to form the resin film, thus permitting the obtained magnetic carrier to be enhanced in the uniformity of the surface state, uniformly charged electrically, and good images to be formed for a long period.

Description

[Detailed Description of the Invention] [Summary] As a magnetic carrier for a two-component magnetic developer used in electrophotography, etc., this is applied to the surface of an amorphous or spherical binder resin containing dispersed magnetic fine powder. A resin coating is formed by fusing amorphous or spherical resin powder with a small average particle size.

[Industrial application field]

The present invention relates to a magnetic brush developer used in electrophotography, and more particularly to a magnetic carrier used in a two-component magnetic developer.

[Prior art and problems]

As for electrophotography, the method described in U.S. Pat. An electrical latent image is formed by irradiating a light image onto this electrostatic latent image carrier, and then this latent image is developed and visualized using colored fine powder called toner, and if necessary, it is printed on paper, etc. After the toner image is transferred to the paper, it is fixed using pressure, heat, light, etc. to obtain a printed matter.

The developing method using the toner is particularly described in U.S. Patent No. 2
The magnetic brush development method described in No. 786439 and the like has been widely put into practical use. In detail, this magnetic brush development method uses a magnetic developer in which a magnetic carrier and toner are mixed and stirred and frictionally charged to opposite polarities, and a brush-like spike holding this magnetic developer on a magnet is used. By rubbing the previously formed electrostatic latent image on the carrier surface, only the toner is separated and adhered by electrical attraction, and the electrostatic latent image is developed. Generally, a so-called two-component magnetic developer is used as a magnetic developer, and more specifically, magnetic powder such as iron powder, ferrite powder, magnetite powder, etc. with an average particle size of about 100 μm, or a resin-coated powder of these magnetic powders is used as the carrier. As a toner, a non-magnetic insulating powder is used in which a coloring agent and the like are dispersed in a binder resin made of a natural or synthetic polymeric substance and finely pulverized to an average particle size of about 10 μm.

When conventional two-component magnetic developers are used, only non-magnetic insulating toner is developed, resulting in excellent transfer and fixing properties.However, in order to obtain good images, the mixing ratio of carrier and toner is The so-called tolerable range of toner density is very narrow. For this reason, it is necessary to maintain a constant toner concentration by constantly replenishing consumed toner appropriately, and a toner concentration control mechanism that accurately detects and controls toner concentration automatically replenishes toner in small amounts at the appropriate time according to the control level. A complicated and expensive mechanism such as a toner replenishment mechanism must be provided.

The following method is known as a means of alleviating the above-mentioned problems and widening the toner density tolerance range.

The method of dispersing magnetic fine powder in an insulating resin reduces the particle size of the carrier and makes it easier to control electrical resistance and chargeability. There were problems such as non-uniform surface characteristics, which caused variations in charging properties, and the photocon drum was easily damaged by magnetic powder appearing on the surface.

On the other hand, when magnetic powders such as iron powder, ferrite powder, magnetite powder, etc. are reduced in particle size as they are, it becomes difficult to form a resin coating, which is commonly used to control electrical resistance and chargeability. Therefore, sufficient effects are not obtained. In order to form a resin film on the surface of magnetic powder, methods such as spray drying are used to spray a resin dissolved in a solvent, but since a solvent is used, the chargeability of the carrier may deteriorate. However, there were problems such as difficulty in controlling the film thickness and the tendency for resin-coated magnetic carriers to aggregate with each other.

[Problem that the invention seeks to solve]

A magnetic carrier made of a binder resin containing dispersed magnetic fine powder has disadvantages such as exposing the magnetic fine powder on the surface, impairing the uniformity of charging, and having a narrow tolerance range for toner concentration. With the resin coating method used for magnetic particles, it was difficult to control the film thickness.

[Means for Solving the Problems] The above problems are solved by a magnetic carrier characterized in that magnetic particles made of a binder resin containing dispersed magnetic fine powder have a resin coating on their surfaces; After the binder resin is kneaded with magnetic fine powder, it is mixed, crushed, and dispersed to form magnetic particles, and the magnetic particles are mixed with a resin powder whose average particle size is smaller than the magnetic particles, and the mixture is stirred. The problem is solved by a manufacturing method for magnetic carriers, which is characterized by electrostatically attaching resin powder to the surface of magnetic particles and fusing the attached resin powder to the magnetic particles by impact force to form a resin film. be able to.

[For production]

Magnetic particles made of binder resin containing dispersed magnetic fine powder are coated with resin on the surface to make the characteristics uniform on the carrier surface, eliminating variations in charging performance and achieving excellent charging characteristics. Since magnetic powder does not appear on the surface, the photocon drum is less likely to be damaged. Further, by making the magnetic particles spherical, the resin powder can be uniformly fused to the surface of the particles, thereby making the surface even more uniform.

As the binder resin for dispersing the magnetic fine powder, for example,
Homopolymers such as polystyrene, polyacrylate, polymethacrylate, polyacrylonitrile, polyether, polyvinyl chloride, thermoplastic polyester, vinyl resins, copolymer resins combining two or more of these heptads, or mixtures thereof. In addition to thermoplastic resins, polyurethane resins, modified acrylic resins, phenolic resins, melamine resins, etc. can also be used.

Examples of the magnetic fine powder include all materials exhibiting magnetism. For example, metals such as iron and nickel, metal oxides, alloys, etc. Frequently used materials include triiron tetroxide, iron sesquioxide, ferrite, and fine nickel powder.

Examples of resin powder for film formation include polyethylene,
polyacrylic ester, polymethyl methacrylate,
Examples include polystyrene, epoxy resin, coumaron resin, maleic acid resin, carbonic acid resin, and fluororesin. These resin powders can be of any shape such as amorphous, spherical, or flat, but it is advantageous to have a spherical shape, and the average particle size of the resin powder must be smaller than the average particle size of the carrier. However, those having a particle size of preferably 0.01 to 5 μm, more preferably 0.1 to 2 μm give good results. If it is smaller than 0.01 μm, there is a problem that the film thickness becomes non-uniform during film formation, and if it is larger than 5 μm, the film thickness becomes thick and the particle size of the carrier becomes too large. In addition, the particle size distribution of the resin powder is 0.5 of the average particle size.
It is preferable that particles in the range of 1.5 times to 1.5 times are 70% of the grain size. In this way, when spherical resin powder with a narrow particle size distribution is used, the individual resin powders have almost uniform charging properties with respect to the magnetic particles, so they can be uniformly electrostatically attached to the magnetic particles. It is possible to eliminate variations in the thickness of the film, and achieve better charging performance.

This benefit is not achieved if the particle size distribution is greater than 70% by weight. In addition, since the resin is fused without using a solvent,
There is no deterioration in chargeability due to solvents, and no aggregation of carriers is observed, allowing excellent characteristics to be exhibited.

〔Example〕

Fruit 1" 0 = Styrene-acrylic resin (Himer S8M-600, Sanyo Chemical Industries) 57 parts by weight fine iron powder (particle size 2 μm, magnetization at 1 kOe 93 emu
/g, Kanto Denka) 40 parts by weight of carbon black (Black Pe5rls 2000+ manufactured by Capot) were melt-kneaded and then pulverized and classified to obtain amorphous magnetic particles with an average particle size of 20 μm.

Next, 10 parts by weight of amorphous polymethyl methacrylate having an average particle size of 0.4 μm and a particle size distribution in the range of 0.2 to 0.6 μm accounts for 70% by weight as resin powder, and 100 parts by weight of the magnetic particles were added. Mixing and stirring was performed using a Henschel mixer (FM-10B type, Mitsui Miike Seisakusho Engineering) to electrostatically adhere the resin powder to the surface of the magnetic particles. Next, this mixture was mixed in a centrifugal mixer (Mechanomill M
MIO1 (Okada Seiko) was mixed, and the resin powder was caused to collide with plates arranged in the radial direction in the mixer to fuse the resin powder to the surface of the magnetic particles to form a resin film, producing a magnetic carrier. .

On the other hand, the toner was manufactured by melting and kneading 95 parts by weight of polyester resin (NE2150, manufactured by Kao), 2 parts by weight of azo dye (Bontron 5-34, manufactured by Orient Chemical Co., Ltd.), and 3 parts by weight of carbon black (Black Pe5rls L, manufactured by Cabot). Thereafter, the mixture was pulverized and classified to obtain an irregularly shaped insulating toner having an average particle size of 12 μm.

The thus produced magnetic carrier and insulating toner were mixed and stirred in a ball mill to prepare a magnetic developer.

The obtained magnetic developer exhibited very excellent charging properties, with a toner specific charge of -10 to -15 μc/g in a toner concentration range of 5 to 40% by weight. Furthermore, as a result of printing tests conducted using a commercially available copying machine using a hot roll fixing method, good images were obtained with less fogging and carrier adhesion in the image background at toner concentrations in the range of 5 to 40% by weight. It could be made very wide. However, when the toner concentration was less than 5% by weight, the image density decreased, and when the toner concentration was higher than 40% by weight, toner scattering increased.

Next, the initial toner concentration was set to 30% by weight, and 20,000 sheets of printing were performed while replenishing 4 g of toner every 100 sheets of printing, but the image remained the same as the initial image.

As a resin powder, the average particle size is 0.5 μm and the particle size distribution is 0.2.
A magnetic carrier was obtained in exactly the same manner as in Example 1 except that an amorphous styrene-acrylic resin having a size of 70% by weight in the range of 5 to 0.75 μm was used, and mixed and stirred with the same toner as in Example 1 to form a magnetic developer. was prepared. The charging property of the obtained magnetic developer was almost the same as that of the magnetic developer of Example 1. Furthermore, when printing was evaluated in the same manner as in Example 1, good images with little fogging or carrier adhesion in the image background were obtained at toner concentrations in the range of 5 to 40% by weight. Furthermore, the toner transferability and fixing performance were good.

Comparison (2) A magnetic carrier was obtained in exactly the same manner as in Example 1, except that no resin coating was applied to the surface of the clay magnetic particles, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer had a toner specific charge of -5 to -15 μc/g at a toner concentration of 5 to 30% by weight, and the dependence of the toner specific charge on the toner concentration was stronger than in Example 1. Due to variations in chargeability, when a printing test was conducted after preparing a magnetic developer with a toner concentration of 20% by weight using the same insulating toner as in Example 1, significant carrier adhesion and fogging occurred.

Comparison Example 5 A magnetic carrier was obtained in exactly the same manner as in Example 1, except that a spray drying method was used to form the resin film, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer has a toner specific charge of -5 to -15 μc/g at a toner concentration of 5 to 30% by weight, which is lower than that of Example 1. When a printing test was carried out after preparing a magnetic developer with a toner concentration of 20% by weight, significant carrier adhesion and fogging occurred.

1. After melting and kneading a mixture of low-cost styrene-acrylic resin, fine iron powder, and carbon black, the amorphous particles obtained by pulverization and classification are transformed into spherical magnetic particles by hot air treatment in a fluidized granulator. Other than this, a magnetic carrier was manufactured using an amorphous resin powder in the same manner as in Example 1, and an insulating toner was manufactured in the same manner as in Example 1.

The thus produced magnetic carrier and insulating toner were mixed and stirred in a ball mill to prepare a magnetic developer.

The obtained magnetic developer exhibited very excellent charging properties with a toner specific charge of -10 to -15 μc/g at a toner concentration of 5 to 50% by weight. Furthermore, as a result of a printing test using a commercially available copying machine using a heat roll fixing method, good images with little fogging or carrier adhesion in the image background were obtained at toner concentrations in the range of 5 to 50% by weight, and the toner density tolerance range was greatly exceeded. was able to expand to. However, when the toner concentration was less than 5% by weight, the image density decreased, and when the toner concentration was higher than 50% by weight, toner scattering increased.

Next, the initial toner concentration was set to 35% by weight, and 20,000 sheets of printing were performed while replenishing 4 g of toner every 100 sheets of printing, but the image remained the same as the initial image.

A magnetic carrier was obtained in exactly the same manner as in Example 3, except that the amorphous resin powder of Example 2 was used, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The charging property of the obtained magnetic developer was almost the same as that of the magnetic developer of Example 1. Furthermore, when printing was evaluated in the same manner as in Example 3, a good image was obtained with a toner concentration in the range of 5 to 50% by weight with less gagginess and less carrier adhesion in the background of the image.

Furthermore, the toner transferability and fixing performance were good.

Example 3 except that no resin coating was applied to the surface of the soil plate main carrier.
A magnetic carrier was obtained in exactly the same manner as in Example 1, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer has a toner specific charge of -5 to -15 μC/g in a toner concentration range of 5 to 30% by weight, and the dependence of the toner specific charge on the toner concentration is stronger than in Example 3. Since the charging properties vary depending on the individual developer, a magnetic developer with a toner concentration of 20% by weight was prepared using the same insulating toner as in Example 3, and then a printing test was conducted, and significant carrier adhesion and fogging occurred. .

A magnetic carrier was obtained in exactly the same manner as in Example 3, except that a spray drying method was used to form the resin coating, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer has a toner specific charge of -5 to -15 μc/g at a toner concentration of 5 to 30% by weight, which is lower than that of Example 3. When a printing test was carried out after preparing a magnetic developer with a toner concentration of 20% by weight, significant carrier adhesion and fogging occurred.

1. As a clay engineering resin powder, the average particle size is 0.4 μm and the particle size distribution is 0.
．． A magnetic carrier was manufactured using irregularly shaped magnetic particles in the same manner as in Example 1, except that spherical polymethyl methacrylate having a particle diameter of 2 to 0.6 μm accounted for 70% by weight was used to form an insulating toner. was produced in exactly the same manner as in Example 1.

The thus produced magnetic carrier and insulating toner were mixed and stirred in a ball mill to prepare a magnetic developer.

The obtained magnetic developer exhibited very excellent charging properties with a toner specific charge of -10 to -15 μc/g at a toner concentration of 5 to 50% by weight. Furthermore, as a result of a printing test using a commercially available copying machine using a heat roll fixing method, good images with little fogging or carrier adhesion in the image background were obtained at toner concentrations in the range of 5 to 50% by weight, and the toner density tolerance range was greatly exceeded. was able to expand to. However, even though 20,000 sheets of printing were performed while replenishing 4 g of toner for every 5 layers of toner density, the image remained the same as the initial image.

Example 111 A magnetic carrier was obtained in the same manner as in Example 5, except that the styrene-acrylic resin was used as a spherical resin powder, and Example 1 was obtained.
A magnetic developer was prepared by mixing and stirring with the same toner. The charging property of the obtained magnetic developer was almost the same as that of the magnetic developer of Example 5. Furthermore, when printing was evaluated in the same manner as in Example 5, good images with little fogging and carrier adhesion in the image background were obtained at toner concentrations in the range of 5 to 50% by weight. Furthermore, the toner transferability and fixing performance were good.

Comparison 1 A magnetic carrier was obtained in exactly the same manner as in Example 5, except that no resin coating was applied to the surface of the magnetic particles, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer had a toner specific charge of -5 to -15 μc/g at a toner concentration of 5 to 30% by weight, and the dependence of the toner specific charge on the toner concentration was stronger compared to Example 5. Due to variations in chargeability, when a magnetic developer with a toner concentration of 20% by weight was prepared using the same non-magnetic toner as in Example 5 and then subjected to a printing test, significant carrier adhesion and fogging occurred.

A magnetic carrier was obtained in exactly the same manner as in Example 5, except that the spray drying method was used to form the Kitakasa Madarako resin film, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer has a toner specific charge of -5 to -15 μc/g at a toner concentration range of 5 to 30% by weight, which is lower than that of Example 5. When a printing test was carried out after preparing a magnetic developer with a toner concentration of 20% by weight, significant carrier adhesion and fogging occurred.

Implementation ■1 A magnetic carrier was produced in the same manner as in Example 1, except that the spherical magnetic particles of Example 3 and the spherical resin powder of Example 5 were used, and the insulating toner was the same as that of Example 1. It was manufactured in exactly the same manner.

The thus produced magnetic carrier and insulating toner were mixed and stirred in a ball mill to prepare a magnetic developer.

The obtained magnetic developer exhibited very excellent charging properties, with a toner specific charge of -10 to -15 μc/g in a toner concentration range of 5 to 55% by weight. Furthermore, as a result of printing tests using a commercially available copying machine using a heat roll fixing method, good images with little fogging or carrier adhesion in the image background were obtained at toner concentrations in the range of 5 to 55% by weight. was able to expand to. However, even though 20,000 sheets were printed by setting the initial toner concentration to 35% by weight and replenishing 4 g of toner every 100 sheets, the image remained the same as the initial image.

A magnetic carrier was obtained in exactly the same manner as in Example 7, except that the spherical resin powder of Example 6 was used, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The charging property of the obtained magnetic developer was almost the same as that of the magnetic developer of Example 7. Furthermore, when printing was evaluated in the same manner, good images were obtained with less fogging and less carrier adhesion in the image background at toner concentrations in the range of 5 to 55% by weight. Furthermore, the toner transferability and fixing performance were good.

Soil comparison Example 7 except that no resin coating was applied to the surface of the carrier
A magnetic carrier was obtained in exactly the same manner as in Example 1, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer had a toner specific charge of -5 to -15 μC/g at a toner concentration of 5 to 30% by weight, and the dependence of the toner specific charge on the toner concentration was stronger compared to Example 7. Due to variations in chargeability, when a printing test was conducted after preparing a magnetic developer with a toner concentration of 20% by weight using the same insulating toner as in Example 1, significant carrier adhesion and fogging occurred.

, Comparison Side - A magnetic carrier was obtained in exactly the same manner as in Example 7 except that a spray drying method was used to form a resin film, and mixed and stirred with the same toner as in Example 1 to prepare a magnetic developer. The obtained developer has a toner specific charge of -5 to -15 μc/g at a toner concentration of 5 to 30% by weight, which is lower than that of Example 7, and the same insulating toner as Example 1 was used. When a printing test was carried out after preparing a magnetic developer with a toner concentration of 20% by weight, significant carrier adhesion and fogging occurred.

〔Effect of the invention〕

The magnetic carrier of the present invention has an excellent surface uniformity, so it is not only able to charge uniformly and maintain good images over a long period of time, but also has a wide tolerable range of toner density, so it can be used for printing. Easy to operate.

Claims (1)

[Scope of Claims] 1. A magnetic carrier characterized in that magnetic particles made of a binder resin containing dispersed magnetic fine powder have a resin coating on their surfaces. 2. The magnetic carrier according to claim 1, wherein the magnetic particles have an amorphous shape. 3. The magnetic carrier according to claim 1, wherein the magnetic particles are spherical. 4. After kneading the binder resin with magnetic fine powder, solidify it, crush it, and disperse it to form magnetic particles, and mix the magnetic particles with resin powder whose average particle size is smaller than the magnetic particles and stir. A method for producing a magnetic carrier, which comprises: electrostatically adhering resin powder to the surface of magnetic particles; and fusing the adhering resin powder to the magnetic particles by impact force to form a resin film. 5. The manufacturing method according to claim 4, wherein the magnetic particles have an amorphous shape. 6. The manufacturing method according to claim 4, wherein the magnetic particles are spherical. 7. The manufacturing method according to claim 4, wherein the resin powder has an amorphous shape. 8. The manufacturing method according to claim 4, wherein the resin powder is spherical. 9. The manufacturing method according to claim 8, wherein the resin powder has an average particle size of 0.01 to 5 μm. 10. The resin powder has an average particle size x 0.5 to an average particle size x 1.
10. The method according to claim 9, wherein the amount of particles in the range No. 5 is 70% by weight or more.