JPH04306684A - Flexible magnet and magnet roll using the same - Google Patents

Abstract

PURPOSE:To obtain a magnet roll for direct contact type electron photograph developing, from which no adhesion problem is not generated between a metal blade for regulating the amount of toner carriage and toner powder itself by obtaining a flexible magnet of excellent processing feature and non-adhesive characteristic, and by using the flexible magnet. CONSTITUTION:A flexible magnet is composed of total 60-35 volume % of prior amount of polyethylene chlorinated resin and inferior amount of olefin/ vinylester copolymer, and 40-65 volume % of hard ferrite powder, while the amount of vinylester in the olefin/vinylester copolymer of the flexible magnet is defined 20-40 volume %, and the flexible magnet is arranged around a shaft axis, and a magnet roller is thus formed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to copying machines, facsimiles,
Furthermore, regarding magnet rolls used in electrophotographic developing devices such as laser printers and flexible magnets used for producing the magnet rolls, more specifically, we will discuss so-called direct magnet rolls in which the developer is brought into direct contact with the surface of the magnet roll without using an exterior sleeve. The present invention relates to a magnet roll used in a contact electrophotographic development method and a flexible magnet used for producing the magnet roll.

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 development method uses a magnet roll, which has a rubber magnet placed around the outer periphery of a cylindrical or cylindrical metal shaft, and a hemispherical floating electrode with a smooth metal surface placed on the outside. . Recently, this type of magnet roll has been further improved, and the floating electrode on the outermost layer has been removed, and the magnet has been adhesively fixed around the shaft axis, and the magnet roll has been finished with a fine surface texture. A so-called direct contact electrophotographic developing method has been proposed in which the toner is directly magnetically attached to the surface of the magnetic roll and transported. 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 press-fitted on the surface of the rubber magnet roll for the purpose of regulating the amount of toner conveyed by the magnet roll. Such magnet 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.

0003

[Problems to be Solved by the Invention] Such rubber-based magnet rolls have the following problems, and solutions to these problems have been sought.

[0004] During cross-linking for rubber magnet modification or high-temperature pressing for adhering rubber magnets to shafts, cracks may occur in the magnet layer, and gaps may occur due to poor adhesion between the shaft and magnet roll. In addition, if the press pressure is partially insufficient, bubbles are formed due to the gas generated during vulcanization and crosslinking, resulting in uneven areas, and for these reasons, the magnetic roll properties such as magnetic field strength may be affected. There is a problem in that local changes occur, resulting in uneven shading in the developed image transferred to paper. In addition, in the direct contact electrophotographic development method, the magnetic roll itself is charged, so its charging characteristics are important; Variation in characteristics becomes a problem.

■Rubber has a high viscosity during processing, so when fillers such as ferrite powder are mixed in, the viscosity increases even more.
Processing becomes difficult. This tendency is particularly noticeable when using ferrite powder with a small average particle size, so ferrite powder with a large particle size is used to improve workability; This makes it difficult to obtain the desired fine surface texture, and the quality is unstable.

[0006] Regardless of the particle size of the ferrite powder, it is difficult to uniformly disperse the ferrite powder in rubber processing because the rubber raw material is in the form of crumbs. Therefore, the ferrite content in each part of the molded magnet is Non-uniformity is likely to occur, and uniformity of magnetization is likely to be impaired.

As a result of extensive research, the present inventors have discovered that these difficulties can be solved at once by using a thermoplastic resin instead of rubber. However, it has been found that new problems arise when thermoplastic resin is used instead of rubber. In other words, in order to obtain a flexible magnet with strong magnetic field strength, it is necessary to increase the amount of magnet powder blended, but in thermoplastic resin-based flexible magnets, even when filled with a large amount of inorganic magnet powder, mechanical Resins that can ensure strength are limited to chlorinated polyethylene resin and vinyl chloride resin containing plasticizer. However,
Plasticizer-containing vinyl chloride resin has a problem in that the plasticizer bleeds during long-term use and transfers or sticks to objects that come into contact with the magnet. On the other hand, although chlorinated polyethylene resins are advantageous because they do not have such problems, chlorinated polyethylene resins have a limit in thermoplastic moldability due to thermal decomposition. In order to improve the thermoplastic moldability of chlorinated polyethylene resin, it is possible to lower the melt viscosity during thermoforming by using an olefin/vinyl ester copolymer together, but it is possible to improve the compatibility with chlorinated polyethylene resin. This requires the use of olefin/vinyl ester copolymers with a relatively high vinyl ester content. However, such olefins/
Vinyl ester copolymers have the problem of extremely strong adhesiveness and stickiness. Olefin/vinyl ester copolymers themselves have strong adhesiveness and stickiness, as can be seen from the fact that they are commonly used as raw materials for paints and adhesives, but those with a high vinyl ester content have strong adhesiveness and stickiness. is even stronger, and when a magnet roll for direct contact electrophotographic development is made from a flexible magnet using such a binder resin, this magnet roll has a metal blade for regulating the amount of toner conveyed, and toner particles are attached to the surface of the magnet roll. There was a problem that the adhesive would stick and cause problems.

The present invention has been made in view of the current situation, and aims to improve the moldability of a thermoplastic resin used as a binder, and also to improve the tackiness that normally occurs when adding an olefin/vinyl ester copolymer. In addition, by using the flexible magnet obtained in this way, we aim to create a magnetic roll for direct contact electrophotographic development that does not cause adhesion problems with the metal blade for regulating the amount of toner conveyance or with the toner particles themselves. This is what we intend to provide.

[0009]

[Means for Solving the Problems] The present invention has been achieved as a result of intensive research to solve the above problems. The flexible magnet of the present invention solves the above problems,
A flexible magnet comprising a dominant amount of chlorinated polyethylene resin and a minor amount of olefin/vinyl ester copolymer, totaling 60 to 35% by volume, and 40 to 65% by volume of hard ferrite powder, the olefin/vinyl ester copolymer comprising: Vinyl ester content during coalescence is 20-40% by weight
It is characterized by having a melt index of 5.
It is preferable to use an olefin/vinyl ester copolymer having a molecular weight of 0 or more. The magnet roll of the present invention is constructed by disposing this flexible magnet around the shaft axis.

0010

EXAMPLES Next, details of the present invention will be explained based on examples. The feature of the present invention is that the processability of a ferrite-based flexible magnet using a binder resin mainly composed of chlorinated polyethylene resin is improved when the vinyl ester content is 20 to 40%.
% by weight of olefin/vinyl ester copolymer is used as a minor component of the binder to prevent the development of tackiness. When the vinyl ester component exceeds 40% by weight, tackiness is observed, and when it is less than 20% by weight, compatibility with the chlorinated polyethylene resin is poor and flexibility is impaired. The vinyl ester content is particularly preferably in the range of 20 to 30% by weight. Those in this range are usually used as raw materials for hot melt adhesives, and exhibit good adhesion to metals and the like during hot melt molding, and exhibit no tackiness when solidified by cooling. Therefore, when coating a metal shaft or the like as a thermoplastic resin binder component, it is particularly suitable since it also has the effect of increasing adhesiveness to the shaft. Furthermore, the purpose of adding the olefin/vinyl ester copolymer is to improve the moldability of the chlorinated polyethylene resin, and this function is extremely important. From this point of view, in order to enhance the effect of addition, it is preferable to use an olefin/vinyl ester copolymer having a melt index of 50 or more, and it is particularly preferable to use one having a melt index of 100 or more. A typical example of the olefin/vinyl ester copolymer used in the present invention is ethylene/vinyl acetate copolymer (EVA). It is important that the olefin/vinyl ester copolymer be in the form of a powder so that it can be well dispersed in the flexible magnet.

[0011] Such chlorinated polyethylene and olefin/
A flexible magnet made by blending 60-35% by volume of a vinyl ester copolymer mixture as a binder resin and 40-65% by volume of hard ferrite powder not only provides a suitable magnet that is easy to mold and has low adhesive strength. This magnet also has excellent thermal adhesion to metal shafts, etc.

[0012] If a magnet roll is manufactured using the flexible magnet of the present invention obtained in this manner, it is possible to easily manufacture the magnetic roll and to obtain a magnet roll of extremely excellent quality. That is, by using a thermoplastic resin as the binder resin, it becomes possible to employ ordinary covering injection molding or covering extrusion molding, and a press method becomes unnecessary. By using a coated injection molding method or a coated extrusion molding method, it is possible to obtain a magnet roll that is homogeneous throughout and has good adhesion to the shaft.Furthermore, by forming an adhesive layer on the shaft surface, it is possible to obtain a magnet roll that is homogeneous throughout and has good adhesion to the shaft. This makes it possible to further improve the properties of rubber magnets, and eliminates the problems associated with conventional rubber magnets, such as the generation of air bubbles inside the magnet and the generation of gaps between the magnet and the shaft.

[0013] Furthermore, since it uses a thermoplastic resin, it has excellent moldability, and is stable even when using ferrite powder that has a small average particle size of about 0.8 to 1.3 μm and does not contain coarse particles. Since it can be molded, a magnet roll with fine surface roughness can be obtained. Furthermore, it is easy to uniformly disperse ferrite powder in thermoplastic resin, and a magnet roll with uniform material properties throughout can be obtained, so even fine-pitch magnetization can be achieved with a uniform magnetization state. Multi-pole magnetization of about 50 to 50 poles is also easy. Since the magnetic roll according to the present invention has a low surface adhesiveness, there is no problem of adhesion with metal blades or toner particles.

The ferrite used in the present invention is Ba ferrite or Sr ferrite, which is used as a permanent magnet material. Particularly suitable is anisotropic ferrite powder that does not contain coarse particles and has a uniform and fine particle size, with an average particle size of 0.8.
Although the average particle diameter of ferrite is preferably 1.3 μm, the average particle diameter of the ferrite is not limited to the above range, and even if it is outside the above range, it can be used as long as it is close to the above range and does not contain coarse particles. Anisotropic ferrite powder is suitable because it is more pulverized than normal isotropic ferrite powder and contains fewer coarse particles. The ferrite content in the magnet layer is preferably 40 to 65% by volume. 40
If it is less than 65% by volume, the magnetic properties required for the magnet roll will be insufficient, and if it exceeds 65% by volume, the processing properties will deteriorate and the adhesion and homogeneity of the molded product will be slightly impaired.

Next, a comparative test conducted to confirm the effects of the present invention will be described. Anisotropic grade Ba ferrite with an average particle diameter of 1.3 μm was used as the ferrite powder, chlorinated polyethylene resin and ethylene/vinyl acetate copolymer (EVA) were used as the thermoplastic resin, and these were used as a stabilizer and coupling agent. The mixture was mixed with the agent in a mixer using an extruder at 130°C to form pellets, and the pellets were coated on the surface of an iron shaft with a diameter of 18 mm and a length of 240 mm using an extruder at a temperature of 130°C. A magnetic layer-coated molded article having a diameter of 20.2 mm was obtained. Next, this was finished by cutting to a diameter of 20 mm using a lathe, and then magnetized to 50 poles to obtain a target magnet roll as an example of the present invention. The surface magnetic field was magnetized to approximately 300 Gauss on the surface of the magnet roll. The adhesive strength of the magnet is determined by applying a stainless steel plate to the longitudinal direction of the magnetic roll surface, applying a load of 100g, and heating it at 23°C.
After leaving it for 168 hours, it was determined whether the pressed stainless steel plate part was sticky or not. The moldability was evaluated by observing the surface condition of the molded article and determining whether the surface was uniform and smooth, and by observing and evaluating the condition of the magnet surface after cutting and finishing. Each of these tests was conducted by varying the EVA content and the vinyl acetate content in the EVA resin.

In the examples, Kenreact TTS (manufactured by Ajinomoto Co., Ltd.) was used as the titanate coupling agent, and Tribase (manufactured by Shin Nihon Rika Co., Ltd.) was used as the stabilizer. Table 1 shows the formulation of the magnet composition, and Table 2 shows the characteristics and usage amount of the EVA resin. The content of EVA in the binder resin is superior to that of the chlorinated polyethylene resin, and the EV
Those in which the content of vinyl acetate in A was 20 to 40% by weight were shown as Examples 1 to 5, and those outside the above range were shown as Comparative Examples 1 to 4. The results are shown in Table 3.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

As shown in Table 3, Examples 1 to 5 of the present invention
In Comparative Example 3, which used EVA with a small vinyl acetate content, unevenness occurred on the surface of the molded product, and Comparative Example 4, which did not use EVA, had good moldability and the surface of the molded product was smooth. In this case, the surface of the molded product became shark skin-like. Formability is EV
It was found that as the amount of A added increases, the performance becomes better. . Moreover, Comparative Examples 3 and 4 showed a tendency for the motor current during extrusion molding to be high. Regarding adhesion, Comparative Example 1, which had a high vinyl acetate content, adhered strongly to the stainless steel plate, and when it was peeled off, the magnetic layer was broken and a large amount remained on the stainless steel plate. In addition, in Comparative Example 2 using a binder resin that has a low vinyl acetate content but a superior EVA content to chlorinated polyethylene resin (CPE),
Adhesion to the stainless steel plate was observed, and when it was peeled off, traces of the magnet were transferred onto the stainless steel plate. On the other hand, in Examples 1 to 5 of the present invention and Comparative Examples 3 and 4, no adhesion was observed at all. The surface after cutting is the same as Example 1.
Although the results were good for all of the results in Comparative Examples 3 and 4, the surface texture was rough, which was inconvenient. The adhesion between the shaft and the magnet layer was good in Examples 1 to 5 and Comparative Examples 1 and 2, and no swelling of the magnet surface was observed, but in Comparative Example 3 and EV, which used EVA with a low vinyl acetate content,
In Comparative Example 4 in which A was not used, blisters were observed at the ends and part of the center of the magnet roll, and the magnet had peeled off from the shaft in those areas. In addition, poor adhesion between the shaft and the magnet layer and the presence of gaps, which frequently occur in conventional rubber magnets, were not found in all of Examples 1 to 5 and Comparative Examples 1 to 4, both of which used thermoplastic resin.

As mentioned above, since the flexible magnet of the present invention uses a thermoplastic resin as a binder resin, it has good adhesion to the circumference of the shaft by thermal coating molding such as coating injection molding or coating extrusion molding. A magnetic layer can be formed, and since the thermoplastic resin contains an olefin/vinyl ester copolymer with a vinyl ester content set within a specific range, tackiness can be suppressed. Therefore, a magnet roll produced using the flexible magnet has excellent non-adhesive properties and does not have the problem of adhesion with metal blades or toner, and can be used as a magnet roll for direct contact electrophotographic development.

[0022]

EFFECTS OF THE INVENTION According to the present invention, a suitable flexible magnet can be obtained which has good thermoplastic processability, low adhesive strength, and also has good adhesive strength when thermally coated. Magnet rolls using this magnet can eliminate the cracks and bubbles that frequently occur in magnet rolls made using conventional rubber binders, and there is no gap between the magnet and the shaft. A magnet roll with good adhesion between the magnet and the shaft can be provided. Furthermore, since the material properties of this magnet roll are homogeneous throughout, it is possible to perform magnetization at minute intervals, and the surface roughness can also be made fine.
A magnet roll suitable for direct contact electrophotographic development can be obtained.

Claims (3)

[Claims] [Claim 1] Predominant amount of chlorinated polyethylene resin and minor amount of olefin/vinyl ester copolymer, totaling 60
35% by volume of hard ferrite powder and 40 to 65% by volume of hard ferrite powder, the flexible magnet having a vinyl ester content of 20 to 40% by weight in the olefin/vinyl ester copolymer. 2. The flexible magnet according to claim 1, wherein the olefin/vinyl ester copolymer has a melt index of 50 or more. 3. A magnet roll comprising the flexible magnet according to claim 1 or 2 arranged around a shaft axis.