JPH04321074A - Thin dielectric roll and production thereof - Google Patents

Abstract

PURPOSE:To obtain the thin dielectric roll which suppresses a change in the electric characteristics of a dielectric layer arising from a change in humidity environment and lapse of a long period of time and has the stable electric characteristics. CONSTITUTION:The magnetoplumbite type ferrite of the thin dielectric roll constituted by laminating a thin bonded magnet layer consisting of the above- mentioned ferrite and an org. high-polymer binder on a conductive base body is the ferrite powder produced by a wet pulverization method.

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 barium 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. ■The electrical characteristics of the magnetic layer change as the humidity conditions of the usage environment change and over time, and the image density is affected by humidity and the passage of time, making it unstable.

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, even when a thermoplastic resin is used in this manner, changes in the electrical characteristics of the magnet layer due to changes in humidity or over a long period of time have not been significantly improved. The present invention aims to improve the stability of such electrical properties.

[0007]

[Means for Solving the Problems] In order to solve the problems of the conventional technology, we conducted extensive research into the factors that affect the electrical properties of dielectric rolls.We found that the electrical properties of dielectric rolls are unstable due to the ferrite used in the past. The present invention was achieved by discovering that there is a cause for this. That is, in ferrite,
Ionic components and various additives present in the iron oxide raw material used when firing the ferrite remain as residues, and as humidity increases, this residue increases electrical conductivity and deteriorates electrical properties. It was found that this was the main cause of variation. And this residue was found to be large when dry grinding method was used. Based on these facts, the reason why the electrical properties of conventional ferrite powder were not stable was because dry pulverization was used as a means of obtaining ferrite powder, and electrically conductive components remained as they were during firing. It was found that the largest factor was

[0008]Although there is no direct relationship with electrical properties, there is a limit to the degree of pulverization in dry pulverization, and the particles obtained by pulverization have a relatively large average particle size, resulting in the possibility of contamination with coarse particles. It was also found that many of them also have an adverse effect on the surface roughness of the developing roller.

[0009] The present invention uses ferrite powder with a small amount of residual electrically conductive components to form a bonded magnet layer, so that it can be used even when the amount of moisture absorbed increases due to increased atmospheric humidity or long-term use. It is an object of the present invention to provide a thin dielectric roll having stable electrical characteristics with little variation in electrical characteristics, and also to improve the surface roughness of the thin dielectric roll.

[0010] As a result of researching what kind of ferrite is suitable, it was found that the object of the present invention can be achieved by using ferrite powder produced by wet pulverization. The average particle size of ferrite powder is 1.5μm
The ferrite to be wet-pulverized is preferably isotropic ferrite, which is an aggregate of microcrystals with a crystal size of less than 1 μm.

[0011] The reason why ferrite subjected to wet pulverization is preferable is that it can be pulverized more finely than the dry method, and there are significantly fewer coarse particles, and because it is a wet method, the above-mentioned ionic electrically conductive residue is not pulverized. It is presumed that this is due to two reasons: it is washed away with water, which is a medium.

By the way, the so-called anisotropic ferrite powder is usually wet-pulverized, so it meets the purpose of the present invention from the viewpoint of the average particle size, but the anisotropic ferrite powder During the manufacturing process, various crystal growth promoters and other additives are added and fired in order to make the powder anisotropic, so there is a large amount of electrically conductive components remaining in the ferrite powder, which is not very desirable. In comparison, microcrystalline isotropic ferrite is produced without adding such additives, and therefore is more suitable since it basically leaves less electrically conductive material. Furthermore, when anisotropic ferrite powder is used and molded into a thin wall, partial orientation of the ferrite particles occurs due to shear stress during molding, causing slight fluctuations in magnetic properties, but microcrystalline isotropic Ferrite powder has the advantage that such problems do not occur at all.

For the above reasons, the present invention uses ferrite powder produced by a wet pulverization method, particularly microcrystalline isotropic ferrite pulverized to an average particle size of 1.5 μm or less by a wet pulverization method. .

Next, details of the present invention will be explained based on examples. The present invention is characterized in that it uses ferrite powder produced by a wet pulverization method. The ferrite used is a magnetoplumbite type ferrite, but barium ferrite and strontium ferrite are preferred, and whether barium ferrite or strontium ferrite is used depends on the level of electrical resistivity required by the dielectric roll to be manufactured. It may be selected accordingly. but,
Since barium ferrite is industrially easily available as isotropic ferrite, it is industrially advantageous to use barium ferrite.

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. Example 1 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
Barium ferrite with volume% and maximum grain boundary diameter of approximately 0.5 μm was wet-pulverized in water to obtain an average particle size of 1.2 μm.
60% by volume of isotropic barium ferrite powder adjusted to m
After mixing with a high-speed rotary blade mixer, the mixture was kneaded at 120° C. with a hot roll mill and cut to obtain a plastic resin magnet kneaded product for molding. This has a diameter of 18 mm and a length of 240 m.
Using an extruder equipped with a crosshead die on a stainless steel shaft, the shaft surface was coated 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, the resin magnet layer, which is a magnetic dielectric layer, had a thickness of 1 mm, and this dielectric roll was cut in an environment of 20°C and 50% humidity (50% RH). Conditions were adjusted for 24 hours, and the volume resistivity was measured under the same conditions. Next, this roll was subjected to humidification treatment at 40° C. and 90% RH for 24 hours, and the volume resistivity was measured after conditioning under the same conditions as before. The results are shown in Table 1.

Example 2 A roll-shaped product was prepared in exactly the same manner as in Example 1, except that wet-pulverized anisotropic barium ferrite powder having an average particle diameter of 1.0 μm was used, and evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example A roll-shaped product was prepared in the same manner as in Example 1 except that dry-pulverized isotropic barium ferrite powder having an average particle diameter of 1.7 μm was used as the ferrite powder. Similarly evaluated. The results are shown in Table 1.

[0019]

[Table 1]

As is clear from Table 1, in the comparative example using dry finely pulverized ferrite, the volume resistivity before and after humidification was 7.
While there was a significant change in resistance value of 0%, in Examples 1 and 2 using wet-pulverized ferrite, the change was only around 20% at most, indicating that the present invention is stable against changes in the humidity environment. It can be seen that it has very good electrical characteristics. Further, in a comparison between Example 1 and Example 2, the resistance change was smaller in Example 2, which used finer ferrite powder. Furthermore, as a result of observing the appearance of the obtained roll, a large number of pinhole-like defects were found on the roll surface of the comparative example, whereas in Examples 1 and 2, there were no defects on the cut magnetic layer surface. A roll having a fine surface roughness and a uniform surface texture was obtained.

[0021]

Effects of the Invention According to the present invention, it is possible to significantly suppress changes in electrical properties caused by changes in the humidity environment and changes over time, which have been a problem with magnetic thin dielectric rolls, and also to reduce surface defects. To obtain a thin dielectric roll suitable for direct contact electrophotographic development with a fine surface roughness and to stably mass-produce such a thin dielectric roll with stable electrical properties and surface condition. becomes possible.

Claims (6)

[Claims] 1. A thin dielectric roll comprising a thin bonded magnet layer made of magnetoplumbite ferrite and an organic polymer binder laminated on a conductive substrate, comprising:
A thin dielectric roll characterized in that the ferrite is ferrite powder produced by a wet pulverization method. 2. The thin dielectric roll according to claim 1, wherein the magnetoplumbite type ferrite is wet-pulverized isotropic ferrite powder having an average particle size of 1.5 μm or less. 3. The thin dielectric roll according to claim 1 or 2, wherein the organic polymer binder is a thermoplastic resin. 4. A thin dielectric roll comprising a thin bonded magnet layer made of magnetoplumbite ferrite and an organic polymer binder laminated on a conductive substrate,
A method for manufacturing a thin dielectric roll by manufacturing the ferrite by a wet pulverization method. 5. The method for producing a thin dielectric roll according to claim 4, wherein the bonded magnet layer is coated by injection molding. 6. The method for producing a thin dielectric roll according to claim 4, wherein the bonded magnet layer is coated by extrusion molding.