JPH04321075A - Thin dielectric roll and production thereof - Google Patents

Abstract

PURPOSE:To eliminate the surface defects liable to arise in a bonded magnet layer and to stabilize the magnetization state and surface texture of the bonded magnet layer. CONSTITUTION:The magnetoplumbite type ferrite powder of the thin dielectric roll constituted by laminating the thin bonded magnet layer consisting of the above-mentioned ferrite powder and an org. high-polymer binder on a conductive base body is the powder which is subjected to wet pulverization at <=1.5mum average particle size and is passed through a <=24mesh sieve.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a developing roll used in electrophotographic developing devices such as copying machines, facsimile machines, and laser printers, and more specifically, the present invention relates to a developing roll used in electrophotographic developing devices such as copying machines, facsimile machines, and laser printers. The present invention relates to a dielectric developing roll having magnetism suitable for contact electrophotographic development.

0002

[Prior Art] One method of electrophotographic developing devices such as copying machines and facsimiles uses a dielectric material in which a rubber magnet is arranged around the outer periphery of a cylindrical or cylindrical metal shaft, and the surface of the magnet is finished with a fine surface texture. A direct contact developing method has been proposed in which a developing roll (hereinafter referred to as a dielectric roll) is used and toner is directly magnetically attached to the surface of the dielectric roll. For example, in the developing device described in Japanese Patent Application Laid-Open No. 63-223675, a developer conveying member disposed close to a latent image carrier made of a photoreceptor and carrying one-component magnetic toner while conveying it to a developing area is installed on the outer periphery. A thin layer of toner is formed on the surface of the magnet by using a magnet with magnetic force and frictionally charging the toner collected on the surface of the magnet in the gap between the charging member and the thin layer of toner. A toner is used that conveys toner to a photoreceptor by rotating and moving the toner. The magnet layer formed around the shaft axis of such a magnet roll is formed from a rubber magnet in which isotropic Ba ferrite is dispersed in a rubber binder, and the layer thickness is set to about 1 mm. A hard blade is pressed onto the surface of the rubber dielectric roll for the purpose of regulating the amount of toner conveyed by the roll.

[0003] Such a magnetic dielectric roll is made by kneading a rubber raw material with a compound such as ferrite to form a sheet, which is wound around a metal shaft, then press-formed at high temperature, and then the surface is polished. manufactured by the method.

0004

[Problems to be Solved by the Invention] Such rubber-based dielectric rolls have the following problems, and solutions to these problems have been sought. ■During cross-linking to modify rubber magnets or high-temperature pressing to bond rubber magnets to shafts, cracks may occur in the magnet layer or gaps may occur due to poor adhesion between the shaft and magnet. Also, if the press pressure is partially insufficient, bubbles are formed due to the gas generated during vulcanization and crosslinking, resulting in uneven areas, and due to these reasons, the properties of the dielectric roll such as magnetic field strength may partially change. This causes a problem in that unevenness in density occurs in the developed image transferred to the paper. In addition, in the direct contact electrophotographic development method, since the dielectric roll itself is charged,
The charging characteristics are important, but fluctuations in the charging characteristics due to the presence of residues of chemicals for vulcanization and crosslinking of rubber and other impurities pose a problem. ■Rubber has a high viscosity during processing, so when fillers such as ferrite powder are mixed in, the viscosity increases even more, making processing difficult. This tendency is particularly noticeable when using ferrite powder with a small average particle size.
Ferrite powder with a large particle size is used to improve processability, but there is a problem that using ferrite powder with a large particle size deteriorates the surface roughness of the magnet roll. If ferrite powder with a small particle size (anisotropic ferrite powder satisfies this condition) is used to improve the process, the molding properties deteriorate and there are limitations in processing, such as increased torque during processing. ■In rubber processing, the rubber raw material is crumb (
Since the ferrite powder is in the form of lumps, it is difficult to uniformly disperse the ferrite powder, which requires a large amount of man-hours, and the ferrite content tends to be uneven in each part of the molded magnet, impairing the uniformity of magnetization. It's easy to get lost. ■Although polishing etc. are performed to obtain a certain surface roughness, since ferrite powder with relatively large average particles is used, there are many coarse particles mixed in, making it difficult to obtain the desired fine surface texture, resulting in poor quality. It was not stable and the developed image was non-uniform. ■ Pinhole-like defects occasionally occur on the surface of the magnet layer, which impairs the uniformity of magnetization and the uniformity of the surface texture of the magnet layer.

The inventors of the present invention found that most of these difficulties could be solved at once by using thermoplastic resin instead of rubber. As a magnet composition that can secure strength, ■ prevent the transfer of magnetic components or adhesion problems to objects that come into contact with the magnet, and ■ have low melt viscosity during thermoforming and good moldability, vinyl A ferritic flexible magnet composition has already been proposed in which the binder is a mixture of an olefin/vinyl ester copolymer and chlorinated polyethylene having an ester content of 20 to 40% by weight and a melt index of 50 or more.

However, although many of the above problems have been improved by using thermoplastic resin, it has not been possible to completely suppress the occasional occurrence of pinhole-like defects on the surface of the dielectric magnet layer. Ta. Therefore, it has not been possible to completely eliminate non-uniform magnetization and non-uniform surface texture due to the presence of pinhole-like defects. The present invention has been made in view of the current situation,
The purpose is to eliminate pinhole-like surface defects that tend to occur on the surface of a magnet layer, and to stabilize the magnetization and surface texture of the surface of the magnet layer.

[0007]

[Means for solving the problem] In order to solve the problem of the conventional technology, as a result of intensive research on factors that affect the surface defects of dielectric rolls, the generation of pinhole-like surface defects was found to be They discovered that ferrite was the cause, and arrived at the present invention. That is, the ferrite powder conventionally used is only subjected to dry pulverization or wet pulverization and then passing through a sieve of about 10 mesh to remove extremely coarse giant particles. The reason why conventional sieving processes only use a coarse sieve of about 10 mesh is because ferrite powder has poor powder fluidity and the efficiency of the sieving process is low. It was found that there was a large amount of coarse particles mixed in, which had a large adverse effect on the surface roughness of the dielectric roll.

[0008] As a result of research into what kind of ferrite is suitable, the present invention was completed. That is, the present invention provides a thin dielectric roll formed by laminating a thin bonded magnet layer made of magnetoplumbite type ferrite powder and an organic polymer binder on a conductive substrate, wherein the ferrite powder has an average particle diameter of 1.5 μm. wet pulverized as below, and 2
It is characterized by having passed through a sieve of 4 mesh or less. The organic polymer binder is preferably a thermoplastic resin, and the bonded magnet layer can be coated by injection molding or extrusion.

[0009]

EXAMPLES Next, details of the present invention will be explained based on examples. Basically, in order to reduce the coarse particles of ferrite, the present invention first pulverizes the ferrite so that the average particle size is 1.5 μm or less, and then sieves it through a sieve of 24 mesh or less, more preferably 32 mesh or less. This is based on the discovery that the instability of the surface condition can be significantly improved by using only the material that has passed through this sieve. Furthermore, 64
If it passes through a sieve with a mesh size or smaller, it is more complete.

[0010] Fine pulverization methods include a wet method and a dry method, but the wet method is more preferable because it provides a stronger degree of pulverization and leaves fewer coarse particles remaining. The decrease in sieving efficiency caused by using a fine mesh can be alleviated by applying centrifugal force or the like to sieve. The ferrite used is magnetoplumbite type ferrite, but barium ferrite and strontium ferrite are preferred, and whether barium ferrite or strontium ferrite is used can be selected as appropriate depending on the level of electrical resistivity required. .

In the present invention, the binder for the ferrite powder is appropriately selected from organic polymer compounds. Rubber materials can also be used, but because of the various problems mentioned above,
Thermoplastic resins are preferred. When a flexible material is required, examples include chlorinated polyethylene, ethylene/vinyl acetate copolymer, uncrosslinked ethylene propylene terpolymer, etc. When using these binders, extrusion molding is a suitable processing method. be. When a hard material is required, examples include polyamide, polypropylene, linear saturated polyester, etc. In this case, injection molding is preferred. Additionally, various additives may be added to improve processability, thermal stability, mechanical strength, etc.
It can be adopted as long as it does not impair the roller properties of the present invention. Examples of additives include surface treatment agents such as coupling agents, plasticizers, stabilizers, lubricants, cross-sulfurizing agents or cross-linking agents,
There are fillers, etc.

Next, specific examples carried out to confirm the effects of the present invention will be described. Examples 1 to 3 40 parts of a resin mixture consisting of 100 parts by weight of chlorinated polyethylene with a chlorine content of 30% by weight and 3 parts by weight of tribasic lead sulfate
Ba ferrite with volume% and maximum grain boundary diameter of approximately 0.5 μm was wet-pulverized in water, adjusted to an average particle size of 1.2 μm, and passed through 24 mesh, 32 mesh, and 64 mesh sieves, respectively. The resulting mixture was mixed with 60% by volume of the isotropic barium ferrite powder obtained using a high-speed rotary blade mixer, then kneaded at 120°C with a heated roll mill and cut to obtain three types of plastic resin magnet kneaded products for molding. This was coated on a stainless steel shaft with a diameter of 18 mm and a length of 240 mm using an extruder equipped with a crosshead die at 140° C. to a thickness of 1.2 mm. The molded product was precisely cut using a lathe to a diameter of 20 mm, and the resin magnet layer, which is a magnetic dielectric layer, had a thickness of 1 mm, and 100 rolls were produced for each kneaded product. The surface of this roll was observed with a lighting magnifying glass, and the number of pinhole defects with a size of 0.2 mm or more was counted. The results are shown in Table 1.

Comparative Example 100 rolls were prepared in the same manner as in Examples 1 to 3, except that ferrite powder that had passed through a 12-mesh sieve was used, and evaluation was conducted in the same manner. Table 1 shows the results.
It was shown to.

[0014]

[Table 1]

As is clear from Table 1, the number of pinholes observed in the comparative example using a 12-mesh sieve was higher in Examples 1 to 3 using a sieve with a finer mesh than 24 mesh. The number of pinholes observed was significantly smaller, indicating that the present invention has a significant improvement effect on surface defects in the bonded magnet layer. It can also be seen that the finer the mesh, the greater the improvement effect.

[0016]

According to the present invention, surface defects caused by coarse particles in ferrite, which were a problem in conventional magnetic thin dielectric rolls, can be significantly reduced. Therefore, it becomes possible to stably mass-produce thin dielectric rolls that have a stable magnetized state and a uniform surface texture and are suitable for direct contact electrophotographic development.

Claims (5)

[Claims] 1. A thin dielectric roll comprising a thin bonded magnet layer made of magnetoplumbite type ferrite powder and an organic polymer binder laminated on a conductive substrate, wherein the ferrite powder has an average particle diameter of 1.5 μm or less. A thin dielectric roll characterized in that it has been wet-pulverized and passed through a sieve of 24 mesh or less. 2. The dielectric roll according to claim 1, wherein the organic polymer binder is a thermoplastic resin. 3. A method for manufacturing a thin dielectric roll in which a thin bonded magnet layer made of magnetoplumbite type ferrite powder and an organic polymer binder is laminated on a conductive substrate, wherein the ferrite powder has an average particle diameter of 1. .5μ
1. A method for producing a thin dielectric roll, characterized in that the roll is wet-pulverized to a size of 24 mesh or less and passed through a sieve of 24 mesh or less. 4. The method for manufacturing a thin dielectric roll according to claim 3, wherein the bonded magnet layer is coated by injection molding. 5. The method for manufacturing a thin dielectric roll according to claim 3, wherein the bonded magnet layer is coated by extrusion molding.