JPH04316304A - Magnet composition small in composition scattering - Google Patents

Abstract

PURPOSE:To equalize the composition without causing inconvenience such as the change, etc., of electric properties resulting from the thermal deterioration of resin or bringing about the drop of production efficiency by seeing that all resin materials consist of the powder in rough surface conditions. CONSTITUTION:In the magnet composition consisting of thermoplastic resin and hard ferrite powder, all the resin material consist of the powder in rough surface conditions. And it is to be desired that the resin material particles should be all 1mm or less in diameter. For example, Ba ferrite of anisotropic grade 1.3mum in average particle diameter, as ferrite powder, accounting for 45 volume%, and chlorinated polyethylene resin, as thermoplastic resin, and ethylene/vinyl acetate copolymer being frozen and crushed to be as far as 0.5mm in particle diameter together with a stabilizer and a coupling agent, accounting for 55vol.%, are mixed with a high-speed rotary blade mixer so as to be get a uniform mixture. And the mixture is kneaded and made into pellets at 130 deg.C, using a kneader.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to copying machines, facsimiles,
The present invention further relates to a magnetic composition suitable for a magnet roll used in an electrophotographic developing device such as a laser printer, and more specifically to a magnetic composition suitable for a magnetic roll for a developing system in which a developer is brought into direct contact with the surface of the magnetic roll.

0001

[Prior Art] One method of electrophotographic developing devices such as copying machines and facsimiles is a magnet roll 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 the toner is directly magnetically attached to the surface of the magnetic 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 press-fitted on the surface of the rubber magnet roll for the purpose of regulating the amount of toner conveyed by the magnet roll.

[0002] 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.

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. ■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 roll. 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 magnetic roll properties 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, 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, making processing 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 poses a problem of deteriorating the surface roughness of the magnet roll, and on the other hand, if ferrite powder with a small particle size is used to improve the surface roughness (anisotropic ferrite powder satisfies this condition), the molding characteristics will deteriorate. There were limitations in machining, such as increased torque during machining. ■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, and for this reason, the ferrite content is uneven in each part of the molded magnet. is likely to occur, and the uniformity of magnetization is likely to be impaired. ■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.

[0004] The inventors of the present invention have found that these difficulties can be solved all at once by using thermoplastic resin instead of rubber. ■ No transfer of magnetic components or adhesion problems to objects that come into contact with the magnet, and ■ Low melt viscosity during thermoforming and good moldability as a magnetic composition containing vinyl ester. amount is 2
0 to 40% by weight and a melt index of 50
A ferrite-based flexible magnet composition using a mixture of the above olefin/vinyl ester copolymer and chlorinated polyethylene as a binder has already been proposed.

However, since the olefin/vinyl ester copolymer raw material, which is one of the raw materials for the magnetic roll, is usually in the form of particles with a diameter of about 5 mm, there are the following problems. Further, such a problem is a general problem faced by thermoplastic resins in magnet compositions made of thermoplastic resins and hard ferrite powder. ■When the compound is put into the raw material hopper of the kneading extruder during kneading and pelletizing, the olefin/vinyl ester copolymer with low density is unevenly distributed in the upper layer due to stirring in the hopper and other factors, so the extruded product is There will be a bias in the composition between the first one and the last one. ■Furthermore, some of the pellets made from the extrusion product have a very high content of olefin/vinyl ester copolymer, and the composition of the magnet roll using these pellets is partially changed. Variations occur, resulting in uneven shading in the developed image. ■When ferrite powder, which is a fine powder, is mixed with large resin particles, the ferrite segregates because of the large density difference between them. Further, even if there is no segregation as described above, in order to uniformly knead and disperse large granular resin, it is necessary to knead with strong force at high temperatures, which causes problems such as thermal deterioration of the resin.

[0006] The only way to solve this problem is to repeat the kneading/pelletizing process several times to improve the uniformity of the composition, or to knead at high temperatures, for long periods of time, and with high shear force. In addition to significantly reducing efficiency, there was a problem in that each component was subjected to a history of high temperature and high shear force for a long period of time, and the electrical characteristics changed due to thermal deterioration of chlorinated polyethylene in particular. The present invention has been made in view of the current situation, and it is possible to change the composition of a magnet composition without causing problems such as changes in electrical properties due to thermal deterioration of the resin, and without causing a decrease in production efficiency. The purpose is to achieve uniformity.

[0007]

[Means for Solving the Problems] The present invention has been achieved as a result of intensive research to solve the above problems. The present invention, which has achieved the above object, is characterized in that, in a magnet composition made of a thermoplastic resin and hard ferrite powder, all the resin raw materials are made of powder with a rough surface. All of the resin raw material powders have a particle size of 1m.
It is preferable that it is below m.

[0008]

[Example] A more detailed explanation will be given below. A feature of the present invention is that in a magnet composition consisting of a thermoplastic resin and hard ferrite powder, all the resin raw materials are powders with a rough surface, which reduces compositional variations during kneading and pelletizing, and reduces the possibility of variations in composition after molding. The objective is to suppress local compositional variations in the magnet roll. More specifically, by pulverizing the resin raw material, the friction between different types of resins is increased, and a magnet with a uniform composition can be obtained while maintaining a good mixing state using a blender. In other words, by turning the resin raw material into a powder with a rough surface, the composition can be made uniform in a microscopic area, and by making the surface condition of the raw material particles rough, it is possible to increase the friction between the raw material powders. This is because it is possible to suppress separation phenomena due to density differences that tend to occur during handling (stirring and transportation) of blended materials before being kneaded.

[0009] If the surface of the raw material powder is smooth, separation of the blend due to the difference in density is likely to occur, and the rougher the surface of the raw material powder, the easier it is to achieve uniform composition. In addition, by further pulverizing the raw materials, two types of binder resins with different compatibility can be uniformly dispersed without intensive kneading. Further, the raw material ferrite powder is easily held by the intertwined structure of the resin powders having a rough surface, and the uniformity of dispersion of the ferrite powder can be easily ensured. These provide the effect of stabilizing both electrical and magnetic properties. Moreover, if the particle size of the resin raw material powder is larger than 1 mm, there will be large compositional variations during kneading and pelletizing, and the occurrence of local compositional variations will be confirmed when a magnet roll is produced. Therefore, it is preferable that the particle size of the resin raw material is 1 mm or less in order to avoid such compositional variations. However, the particle size of the raw material is 1 mm.
Even if it is below, in spherical and smooth surfaces like granulated products, there is less friction between the raw material powders and the composition tends to vary widely, so in order to suppress the composition variation, it is necessary to , particle shape and surface roughness are most important.

[0010] The main purpose of the present invention is that all resin raw materials are composed of powder with a rough surface in a magnet composition composed of a thermoplastic resin and hard ferrite powder. In a magnet composition consisting of a total of 60 to 35 volume % of a chlorinated polyethylene resin, a minor amount of an olefin/vinyl ester copolymer, and 40 to 65 volume % of hard ferrite powder, all the resin raw materials have a rough surface condition. This is when it is made into a powder. Although the following description will be based on this thermoplastic resin, it is also possible to use other thermoplastic resins.

The raw material powder used in the present invention is pulverized by pulverization and has a non-spherical shape. Regarding the method of pulverizing the raw material, since the olefin/vinyl ester copolymer exhibits rubber-like properties, it cannot be pulverized by ordinary pulverizing methods. Freeze pulverization is considered to be the most appropriate method for pulverizing materials exhibiting such properties. In the present invention, a method is used in which the powder is pulverized while being cooled using liquid nitrogen. Naturally, chlorinated polyethylene is also pulverized in a similar manner.

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 to 1.
．． 3 μm is preferred. Anisotropic ferrite powder is preferable 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. If it is less than 40%, the magnetic properties required for a 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.

[0013] If necessary, the composition of the present invention may contain various additives that are generally added to synthetic resins for the purpose of surface treatment of ferrite, stabilization of heat resistance, improvement of processability, and other purposes. . The magnet roll, in which the molded product of the magnet composition obtained in this manner is arranged on a metal shaft, has extremely small variations in surface magnetic properties and electrical properties, and is suitable for use in a development method in which the developer comes into direct contact with the surface of the magnet roll. It meets the strict quality requirements of magnetic rolls and produces good developed images.

Next, specific examples carried out to confirm the effects of the present invention will be described. Example 1-1 45% by volume of anisotropic grade Ba ferrite with an average particle size of 1.3 μm as ferrite powder, chlorinated polyethylene resin as thermoplastic resin, and ethylene/vinyl acetate freeze-pulverized to a particle size of 0.5 mm. The copolymer was mixed with a stabilizer and a coupling agent at a concentration of 55% by volume using a high-speed rotary blade mixer to obtain a homogeneous mixture. As the stabilizer, Tribase manufactured by Shin Nippon Rika was used, and as the coupling agent, PlainAct TTS manufactured by Ajinomoto was used. The resulting mixture was kneaded into pellets at 130° C. using a PCM45 kneader manufactured by Ikegai Iron Works. How the amount of ferrite contained in each pellet changes depending on whether the pellets are made from the first ejected material or the last ejected material. was investigated by thermal analysis. Five samples (n=5) were sampled for each sample, and the average value was calculated. The results are shown in Table 1.

[0014] In addition, when evaluating the uniformity of kneading and dispersion of resin raw particles of chlorinated polyethylene and ethylene/vinyl acetate copolymer, it is possible to determine in which part of the magnet small composition variations exist from surface observation. Since this is difficult and difficult to analyze, we focused on the fact that compositional fluctuations in the resin raw material are sensitively reflected in the electromagnetic properties, and used a magnet roll made from this magnet composition to evaluate images of electrostatic development copying. (Especially for image unevenness). Since variations in the composition of the resin raw material affect the ferrite content in each part of the magnet roll, variations in the ferrite content indirectly suggest non-uniformity of the resin.

[0015] The pellets obtained by the above procedure were
13 mm using an extruder on an iron shaft with a length of 240 mm.
Covering molding was performed at 0° C. to obtain a magnetic layer-covered molded product having a diameter of 20.5 mm. Next, this was machined on a lathe to a diameter of 20 mm.
A magnetic roll was obtained by cutting and finishing. When this magnetic roll was attached to an electrostatic photographic development type copying machine and a test chart was copied, the obtained developed image was good and had no unevenness.

Example 2-1 Pellets were prepared in the same manner as in Example 1-1, except that the ethylene/vinyl acetate copolymer was freeze-pulverized to a particle size of 1 mm. As in Example 1-1, thermal analysis was conducted to examine how the amount of ferrite contained in the pellets changes depending on the discharged material. The results are shown in Table 1. Furthermore, when a copy image of a magnet roll produced using the present magnet composition was evaluated in the same manner as in Example 1-1, the obtained copy image was good and free of defects.

Comparative Example 1-1 Ethylene/vinyl acetate copolymer was not crushed at all and the particle size was 5 m.
Pellets were produced in the same manner as in Example 1-1, except that m was used as is, and the amount of ferrite contained in the pellets was determined by thermal analysis for the first and last discharged products. Examined. The results are shown in Table 1.

Comparative Example 2-1 An ethylene/vinyl acetate copolymer was freeze-pulverized to an average particle size of 30 μm, and then granulated to a diameter of 1 mm. Pellets were prepared in the same manner as in Example 1-1 using this granulated product of ethylene/vinyl acetate copolymer, and the ferrite contained in the pellets was determined for the first discharged product and the last discharged product. The amount was determined by thermal analysis. The results are shown in Table 1.

[0019] Furthermore, the quality of the copied images was examined in the same manner as in Example 1-1 for the magnet rolls obtained by molding the magnetic compositions obtained in Comparative Example 1-1 and Comparative Example 2-1. In both cases, 0.5 to 0.8 mm is included in the copied image.
Some patchy uneven density of the image was observed, indicating that the uniformity of the dispersion was insufficient.

[0020]

[Table 1]

Example 1-2 The process of mixing the pellets produced in Example 1-1 again and kneading them into pellets under the same conditions was repeated 3 and 5 times. Five samples (n=5) were randomly taken from the produced pellets, and the ferrite content of each sample was examined by thermal analysis. The results are shown in Table 2.

Example 2-2 The process of mixing the pellets produced in Example 2-1 again and kneading them into pellets under the same conditions was repeated 3 and 5 times. Five samples (n=5) were randomly taken from the produced pellets, and the ferrite content of each sample was examined by thermal analysis. The results are shown in Table 2.

Comparative Example 1-2 The pellets prepared in Comparative Example 1-1 were mixed again and the process of kneading and pelletizing them again under the same conditions was repeated 3 and 5 times. Five samples (n=5) were randomly taken from the produced pellets, and the ferrite content of each sample was examined by thermal analysis. The results are shown in Table 2.

Comparative Example 2-2 The process of mixing the pellets produced in Comparative Example 2-1 again and kneading them into pellets under the same conditions was repeated three and five times. Five samples (n=5) were randomly taken from the produced pellets, and the ferrite content of each sample was examined by thermal analysis. The results are shown in Table 2.

[0025]

[Table 2]

Example 1-3 The pellets produced in Example 1-1 were coated and molded onto an iron shaft with a diameter of 18 mm and a length of 240 mm at 130° C. using an extruder to form a magnetic layer with a diameter of 20.5 mm. I got a body. Next, this was finished by cutting to a diameter of 20 mm using a lathe to obtain a magnet roll. The magnet layer of the obtained magnet roll was randomly cut into 1 mm square pieces, and 10 samples (n=10) were randomly taken from the pieces. The collected sample was further adjusted to a size of 10 mg, and the ferrite content was examined using a thermograph for thermal analysis. The results are shown in Table 3.

Example 2-3 Example 1-3 using the pellets produced in Example 2-1
A magnet roll was produced in the same manner as above, and sampling was conducted in the same manner to examine the ferrite content. The results are shown in Table 3.

Comparative Example 1-3 Example 1-3 was prepared using the pellets produced in Comparative Example 1-1.
A magnet roll was produced in the same manner as above, and sampling was conducted in the same manner to examine the ferrite content. The results are shown in Table 3.

Comparative Example 2-3 Example 1-3 was prepared using the pellets produced in Comparative Example 2-1.
A magnet roll was produced in the same manner as above, and sampling was conducted in the same manner to examine the ferrite content. The results are shown in Table 3.

[0030]

[Table 3]

As shown in Table 1, in the examples of the present invention, the difference in the ferrite content in the pellets at the beginning and end of kneading/pelletization was small, and variations in composition were suppressed. I can see that it is being done. On the other hand, when using the granulated ethylene/vinyl acetate copolymer shown as Comparative Example 2-1, the particle size was 1 m, the same as in Example 2-1.
Even in the case where the ferrite content is m, the amount of variation tends to increase, indicating that the surface condition, shape, etc. of the pulverized product affect the variation in ferrite content. In addition, as shown in Table 2, in Comparative Examples 1-2 and 2-2, which used resin raw materials with large particle sizes or granulated resin raw materials, when the number of times of kneading was one, the variation was very large; It can be seen that the variation cannot be reduced unless the kneading is repeated three times to three times, whereas in the examples of the present invention, the variation can be suppressed to a small level even when the kneading is repeated once. This shows that in the magnet composition of the present invention, it is possible to significantly improve the efficiency of kneading and pelletizing to make the composition uniform. Furthermore, as shown in Table 3, it can be seen that even when the examples of the present invention are formed into magnetic rolls, local composition variations are extremely small.

In all Examples and Comparative Examples, the obtained magnetic compositions were made into magnetic rolls in the same manner as in Example 1-1, and the copied images were evaluated. However, in each of the comparative examples, spot-like image density unevenness was observed, and this tendency was particularly noticeable in completely black images.

As described above, the present invention has made it possible to obtain a magnet composition with small compositional variations without significantly reducing production efficiency. By using this magnet composition, it is possible to supply a stable magnet roll with no local compositional variations and almost no density unevenness on the developed image, and to obtain a magnet roll suitable for direct contact development. Can be done.

[0034]

Effects of the Invention The present invention makes it possible to create magnetic compositions with small compositional variations without significantly reducing production efficiency by making all of the resin raw materials into powders with rough surface conditions in magnetic compositions with specific compositions. It became possible to obtain. Further, by using the magnet composition of the present invention, it is possible to supply a stable magnet roll with little local variation in composition and almost no density unevenness on developed images.

Claims (2)

[Claims] 1. A magnet composition comprising a thermoplastic resin and a hard ferrite powder, characterized in that all the resin raw materials are powders with a rough surface, and the composition has small variations. 2. The magnetic composition with small compositional variations according to claim 1, wherein all of the resin raw material powders have a particle size of 1 mm or less.