JPH04358181A - Magnetic roll consisting of crystalline thermoplastic resin composite material and production thereof - Google Patents

Abstract

PURPOSE:To provide the magnetic roll suitable for turning by a precision lathe and to minimize a material escape by forming a thin magnet layer consisting of a crystalline hard thermoplastic resin and hard ferrite powder on the surface of a shaft core. CONSTITUTION:The magnet layer A consisting of the crystalline hard thermoplastic resin and the hard ferrite powder is formed on the surface of the shaft core B. More particularly the crystalline hard thermoplastic resin is preferably >=1 kinds selected from linear polyester, linear polyamide and polyphenylene sulfide. Further, the content of the hard ferrite powder is preferably <60vol.%. The ferrite powder is barium ferrite or strontium ferrite and the particle size thereof is preferably <=1.3mum. The magnet layer A of this magnetic roll is produced by injection molding, extrusion molding, etc. Particularly the insertion molding with the shaft core is preferable. This material is turned by the precision lathe, by which the magnetic roll for development having the excellent surface smoothness is obtd.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a developing roll used in electrophotographic developing devices such as copying machines, facsimile machines, and laser printers, and particularly to a direct contact type developing roll that does not use a metal sleeve, in which the developer comes into direct contact with the surface of the developing roll. The present invention relates to a magnetic roll for development suitable for electrophotographic development.

0002

2. Description of the Related Art Magnetic rolls are used in electrophotographic developing devices such as copying machines and facsimile machines as a device for conveying toner to a photoreceptor. Conventionally, for example, a magnet roll made of a cylindrical magnet body with a metal shaft inserted through it is covered with a non-magnetic sleeve in a non-contact manner, and this sleeve is rotated relative to the magnet roll. The mainstream method was to transfer toner magnetically attached to the surface of a sleeve onto a photoreceptor disposed close to each other in a non-contact manner, but in recent years, developing methods that eliminate this sleeve have become popular. This developing method uses a developing roll with a rubber magnet arranged around the outer periphery of a cylindrical or cylindrical metal shaft, and a hemispherical floating electrode with a smoothed metal surface arranged on the outside. . Recently, this type of developing roll has been further improved by removing the floating electrode on the outermost layer, forming a magnetic layer around the shaft that also serves as a dielectric, and creating a fine surface texture on the surface. A so-called direct contact electrophotographic developing method has been proposed in which a finished magnetic dielectric developing roll is constructed and toner is directly magnetically attached to the surface of the developing roll to transport the toner. 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 magnetized dielectric developing roll is formed from a rubber magnet in which isotropic Ba ferrite is dispersed in a rubber binder. A hard blade is pressed onto the surface of the rubber magnetic roll for the purpose of regulating the amount of toner conveyed by the roll.

[0003] Such magnetic rolls are manufactured by kneading a rubber raw material with a compound such as ferrite to form a sheet, winding it around a metal shaft, press-forming it at high temperature, and then polishing the surface. ing.

[0004] In such a rubber-based developing roll,
There were the following problems that needed to be solved. ■Due to the manufacturing method of rubber magnets, there are problems such as cracks occurring in the magnet layer during high-temperature pressing for crosslinking and adhesion, and gaps occurring due to poor adhesion between the shaft and magnet. The gas creates bubbles, which cause local non-uniformity in the magnetic layer, causing uneven shading in the developed image. ■Changes in electrical properties due to residues of chemicals for cross-sulfurization and cross-linking of rubber and other impurities are a problem. ■Since magnetization is performed at minute intervals, non-uniform magnetization occurs due to non-uniformity of the material. ■Due to limitations in rubber processing, ferrite powder with a relatively large average particle size is used, making it difficult to obtain the desired fine surface and resulting in unstable quality. ■Since the raw rubber is in the form of crumbs, uniform dispersion of ferrite is difficult and requires a large number of man-hours.

The inventors of the present invention have found that these difficulties can be solved all at once by using thermoplastic resin instead of rubber. Ferrite that uses a specific thermoplastic resin as a binder is a magnetic composition that can be used as a magnet composition that has: ■ no problems with component migration or adhesion to objects that come into contact with the magnet; and ■ low melt viscosity during thermoforming and good moldability. A flexible magnet composition has already been proposed. Although the various problems faced by rubber magnets were solved at once by employing flexible thermoplastic resin magnets, it was found that new problems arose due to the use of thermoplastic resins. In other words, when surface finishing is done by polishing in the same way as when using rubber, the polished thermoplastic resin magnet material fills the gaps in the grinding wheel, causing severe clogging and making it impossible to reuse the grinding wheel. In addition, it was found that a method that relies only on polishing for surface finishing cannot be adopted industrially because the amount of polishing per step is small when polishing alone is used. Therefore, in order to solve this difficulty, the present inventors found that it is effective to use turning with a precision lathe alone or in combination with polishing, and the present inventors decided to perform turning with a precision lathe instead of polishing or It has already been proposed to perform turning before polishing.

[0006]

[Problems to be Solved by the Invention] However, although the idea of finishing the surface of the roll by turning with a precision lathe is extremely effective industrially, the use of a flexible thermoplastic resin as a binder makes turning the surface difficult. At times, resin magnet materials tend to deform due to the pressure from lathe blades, and a new problem has arisen: machining speeds cannot be increased to achieve sufficient precision, resulting in low productivity.

[0007]

[Means for Solving the Problems] The present invention has been achieved as a result of intensive research to solve the above problems. The magnetic roll used in the direct contact development method requires a surface roughness that is approximately the same as or smaller than the toner particle diameter, and also minimizes core runout and waviness on the roll surface to the extent that these can be ignored. It is necessary to finish strictly. Resin molding alone cannot achieve such a level of surface roughness and prevent run-out and waviness on the roll surface. Therefore, it is essential to surface finish the roll obtained by molding. As mentioned above, turning with a precision lathe is most effective for surface finishing. The purpose of the present invention is to provide a roll using a thermoplastic resin binder suitable for turning with such a precision lathe, and more specifically, to provide a roll using a flexible material as the thermoplastic resin. It is an object of the present invention to provide a roll that can minimize the so-called "material escape" that occurs when the roll is heated. In order to achieve this objective, basically it is sufficient to increase the elastic modulus of the thermoplastic resin which is the binder for the ferrite. However, when an amorphous high modulus thermoplastic resin such as polystyrene or polyphenylene oxide is used, the retention of ferrite powder is poor, and many pinhole-like defects occur during turning. The inventors of the present invention have conducted intensive research to solve these problems, and have found that the above problems can be solved by using a crystalline thermoplastic resin as a binder and keeping the ferrite content below a specific range. This discovery led to the present invention.

The present invention is a magnetic roll made of a crystalline thermoplastic resin composite material, in which a thin magnet layer A made of a crystalline hard thermoplastic resin and hard ferrite powder is formed on the surface of a shaft core B, as shown in FIG. In particular, it is preferable that the crystalline hard thermoplastic resin is one or more selected from linear polyester, linear polyamide, and polyphenylene sulfide, and the content of hard ferrite powder is less than 60% by volume. is preferred.

The thermoplastic resin used in the present invention is a crystalline resin. A crystalline resin has a property of having a low viscosity in a molten state, and therefore can be easily thermoplastically molded in a state containing a large amount of ferrite powder. Moreover, in the cooled and solidified state, mechanical strength can be maintained using the crystalline parts as nodes, so even if a large amount of inorganic material such as ferrite powder is filled, it can withstand post-processing and handling. Furthermore, since the melt viscosity is low, it is easy to form a thin magnet layer of 1 to 2 mm or less on the axis, and from this point of view as well, crystalline thermoplastic resins are suitable. However, even among crystalline thermoplastic resins, resins with a low glass transition temperature of the main chain such as polyolefins such as polyethylene and polypropylene, and polyacetal have too low hardness or a crystalline melting point that is too low for the purpose of the present invention. not compatible. As the crystalline thermoplastic resin used in the present invention, a hard crystalline thermoplastic resin whose crystal melting point exceeds 100°C is suitable, and is commonly referred to as engineering plastics such as polyamide, linear polyester, and polyphenylene sulfide. Examples include:

The ferrite powder used in the magnetic roll of the present invention is barium ferrite or strontium ferrite. The particle size is preferably 1.3 μm or less, and preferably does not contain coarse particles. The content of ferrite is preferably 60% by volume or less. If it exceeds 60% by volume, the molding characteristics of a thin magnetic layer will be slightly degraded, and the suitability for molding a thin magnetic layer may be lost. If it is less than 40% by volume, the necessary magnetic properties cannot be obtained.

Stabilizers, plasticizers, lubricants, ferrite powder surface treatment agents, etc. may be added to the mixture of ferrite powder and crystalline hard thermoplastic resin.

The magnetic layer of the magnetic roll of the present invention is manufactured by injection molding, extrusion molding, or compression molding. In particular, it is preferable to insert and mold the shaft core. Compression molding is not a preferred molding method because it takes time to heat and melt the resin, and it is not necessarily easy to uniformly cover and mold a magnetic layer around a long axis. In addition, in extrusion molding, a crosshead die is usually used to coat and mold a magnetic layer around the axis, but when molding crystalline resin, the viscosity of the resin coated and discharged from the die is low, and it takes a long time until it cools and solidifies. Since the magnetic layer coated and molded flows slightly, causing uneven thickness in the molded product, it is necessary to consider the molding conditions. In injection molding, the shaft core is mounted and fixed in a mold, and molten resin is coated and molded around the shaft core, which is the most preferable method for molding a magnet layer using crystalline thermoplastic resin.

[0013] The roll obtained by the present invention is free-cutting in lathe machining, has sufficient strength of the resin binder, has few surface defects due to traces of ferrite particles falling off from the magnet layer, and is free from "material escape" during lathe machining. Because it is small, it is eccentric,
It is possible to obtain a satisfactory magnetic developing roll with small waviness, and since lathe processing can be performed at high speed, productivity is also high.

[0014]

EXAMPLES Next, examples of the present invention will be described based on comparative tests conducted to confirm the effects of the invention. Diameter 18mm,
A molded magnetic roll was obtained by coating a stainless steel shaft with a length of 240 mm with a resin magnet compound consisting of 50% by volume of 12 polyamide resin and 50% by volume of Ba ferrite by Isert injection molding to a thickness of 1.1 mm. As a comparative example, the resin was replaced with amorphous chlorinated polyethylene, insert extrusion molding was performed using a crosshead die, and a molded magnetic roll was obtained by coating to a thickness of 1.1 mm. Rotate these rolls on a lathe at a rotation speed of 1500 rpm.
Turning was carried out under the conditions of a feed rate of the cutting tool of 0.05 mm/rotation. After turning, the roll of the comparative example had a surface roughness Rz = 7 μm, waviness 4.2 μm, and center runout 22 μm, whereas the roll of the example of the present invention had a surface roughness Rz = 7 μm.
= 3 μm, waviness 0.9 μm, center runout 12 μm,
It was confirmed that the rolls of the examples of the present invention were able to achieve extremely good values in terms of surface roughness, waviness, and runout. It was also confirmed that in the case of the roll of the present invention, the same level of surface precision could be maintained even when the rotational speed of the lathe was set to 2000 rpm, confirming the excellent productivity of the examples of the present invention. As described above, according to the present invention, it is possible to stably provide a magnetic roll with a smooth surface while maintaining high productivity.

[0015]

[Effects of the Invention] According to the present invention, a magnetic roll suitable for turning can be obtained, and by turning with a precision lathe, a surface condition that is satisfactory in terms of surface roughness, waviness, and center runout can be obtained. This makes it possible to obtain a developing magnetic roll suitable for direct contact electrophotographic development that has excellent surface smoothness. Moreover, when the magnetic roll of the present invention is turned, there is extremely little occurrence of "material escape" caused by the pressing force of the turning blade, so high-speed turning can be performed and productivity is excellent.

[Brief explanation of drawings]

FIG. 1 shows the configuration of a magnetic roll of the present invention, (a) is an axial sectional view, and (b) is a radial sectional view.

[Explanation of symbols]

A Magnet layer B Axis core

Claims (4)

[Claims] 1. A magnetic roll made of a crystalline thermoplastic resin composite material, in which a thin magnet layer made of a crystalline hard thermoplastic resin and hard ferrite powder is formed on the surface of the shaft core. 2. Claim 1, wherein the crystalline hard thermoplastic resin is made of at least one of linear polyester, polyamide, and polyphenylene sulfide.
A magnetic roll made of the crystalline thermoplastic resin composite material described above. 3. A magnetic roll made of a crystalline thermoplastic resin composite material according to claim 1 or 2, wherein the content of hard ferrite powder is less than 60% by volume. 4. A method for manufacturing a magnetic roll made of a crystalline thermoplastic resin composite material, comprising injection molding a thin composite material composition made of a crystalline hard thermoplastic resin and hard ferrite powder onto the shaft core surface. .