JPH04337607A - Magnetized dielectric roll and its manufacture - Google Patents

Abstract

PURPOSE:To provide a magnetized dielectric roll which satisfies all of surface condition, mechanical property, electrical property and magnetic property and is suitable for both direct contacting electrophotographic development and mass production. CONSTITUTION:The magnetized dielectric material consisting of a thermoplastic resin (60-35, volume percentage) and hard ferrite powder (40-65, volume percentage) with dielectric constant 9 or more is cylindrically formed and arranged with constant thickness around the shaft, and a lot of magnetic poles are set with narrow spacings on the surface of the thin magnetized conductor layer, constituting the features of the roll.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art Magnetized dielectric 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 magnetic dielectric roll made of a cylindrical magnet body with a metal shaft penetrated therein is covered with a non-magnetic sleeve in a non-contact manner, and this sleeve is placed relative to the magnetic dielectric roll. The mainstream was to rotate the sleeve to transfer the toner magnetically attached to the sleeve surface to a photoreceptor placed 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 magnetized dielectric roll with a rubber magnet arranged around the outer periphery of a cylindrical or cylindrical metal shaft, and a hemispherical metal floating electrode with a smoothed surface arranged on the outside of the rubber magnet. ing. Recently, this type of magnetized dielectric roll has been further improved by removing the floating electrode on the outermost layer, adhering and fixing a magnetized dielectric layer made of rubber magnet around the shaft axis, and fixing the magnetized dielectric layer on the surface of the magnet. A magnetized dielectric roll with a fine surface texture is constructed, and the toner is directly magnetically attached to the surface of the magnetized dielectric roll to transport the toner.
A so-called direct contact electrophotographic development method has been proposed. For example, in the developing device described in Japanese Patent Application Laid-Open No. 63-223675, one
A magnetic body having magnetic force on the outer periphery is used as a developer conveying member that carries component magnetic toner while conveying it to the development area.
The toner collected on the surface of the magnet is charged by friction in the gap between the charging member and a thin layer of toner is formed on the surface of the magnet, and the thin layer of toner is moved along with the rotation of the magnet to remove the toner. A device that conveys the image to the photoreceptor is used.

The magnet layer formed around the shaft axis of such a magnetized dielectric roll is made of a rubber magnet in which isotropic Ba ferrite is dispersed in a rubber binder, and the layer thickness is set to around 1 mm. has been done. A hard blade is pressed onto the surface of the rubber magnetized dielectric roll for the purpose of regulating the amount of toner conveyed by the magnetized dielectric roll.

[0004] Such a magnetized dielectric roll is produced 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. Manufactured.

[0005]

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

[0006] ■During cross-linking for rubber magnet modification or high-temperature pressing for adhering rubber magnets to shafts, cracks may occur in the magnetic dielectric layer, or due to poor adhesion between the shaft and the magnetic dielectric layer. Gaps may occur, and 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 field strength etc. There is a problem in that local changes occur in the characteristics of the magnetic dielectric roll, resulting in uneven shading in the developed image transferred to the paper. In addition, in the direct contact electrophotographic development method, the magnetic dielectric roll itself is charged, so its charging characteristics are important; Fluctuations in charging characteristics are 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 magnetized dielectric 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 deterioration and 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. (2) Since ferrite powder with relatively large average particles was used, there was a large amount of coarse particles mixed in, making it difficult to obtain the desired fine surface texture, resulting in unstable quality and non-uniformity of developed images. ■ Pinhole-like defects occasionally occur on the surface of the magnetic dielectric layer, which impairs the uniformity of magnetization.
The uniformity of the surface texture of the magnetic dielectric layer is impaired. (2) Since the rubber sheet is wrapped around the shaft and pressure-molded, the fusion of the seams of the wrapped sheet is incomplete, resulting in uneven magnetic and electrical properties, and the developed image becomes disordered.

The inventors of the present invention have found that most of these difficulties can be solved 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. As a result, we were able to obtain a magnetized dielectric roll with much superior properties compared to conventional rubber-based magnetized dielectric rolls, but even with this magnetized dielectric roll, we were able to completely eliminate problems such as uneven density of developed images. The problem could not be resolved, and further improvements were desired. In particular, the presence of the sheet seam shown as ■ causes magnetic and electrical non-uniformity in the area, which is one of the causes of image unevenness, but it is difficult to eliminate this with conventional manufacturing methods. Improvement was desired.

The present invention has been made in view of the current situation, and the surface state,
The present invention aims to provide a magnetized dielectric roll that satisfies all mechanical, electrical, and magnetic properties, is suitable for use in direct contact electrophotographic development, and is also suitable for mass production.

[0009]

[Means for Solving the Problems] The present invention has been completed as a result of intensive research by the present inventors in order to solve the above problems. The present invention solves these problems by combining 60 to 35% by volume of thermoplastic resin and 40 to 6% by volume of hard ferrite powder.
A magnetic dielectric material consisting of 5% by volume and having a relative dielectric constant of 9 or more is molded and arranged in a cylindrical shape with a uniform thickness around the outer periphery of a magnetic metal shaft, and the surface roughness is 5 μm or less when molded. It is characterized in that a thin magnetic dielectric layer with virtually no seams is formed, and a large number of magnetic poles are provided at small intervals on the surface of the magnetic dielectric layer. Such a magnetic dielectric roll is produced by coating the surface of the metal shaft with a thermally fused magnetic dielectric material when forming the magnetic dielectric layer on the surface of the metal shaft. By adopting this manufacturing method, it is possible to completely fuse the joints (weld parts) that exist when covering and molding, making it possible to virtually eliminate the joints and magnetically spread over the entire surface. It is possible to provide a magnetized dielectric roll suitable for direct contact electrophotographic development that has uniform physical and electrical properties.

[0010] The electric properties of the magnetized dielectric roll change due to moisture absorption, which also causes poor development, but from the viewpoint of preventing this, it is preferable to use wet-pulverized hard ferrite powder. Furthermore, in order to prevent pinhole-like defects caused by the inclusion of coarse particles, wet-pulverized hard ferrite powder with an average particle diameter of 1.3 μm or less is passed through a sieve with a mesh finer than 24 mesh. It is desirable to use only those that have passed the test.

In addition, since the hard plate-shaped blade is in pressure contact, there is a concern that the magnetic dielectric layer may deform during the use process, but from the viewpoint of preventing this, compression permanent thermoplastic resin is used. It is preferable to use one with low distortion.

[0012] In addition, uneven distribution of ferrite powder during kneading of magnetizable dielectric materials can cause variations in electrical properties, but from the perspective of preventing this, thermoplastic resin with a rough surface can be used. It is preferable to use a powder having

Further, in the present invention, the surface roughness of the magnetic dielectric layer is set to 5 μm or less, but such smoothing processing does not rely solely on polishing, but may be performed by turning processing or by turning processing. It is desirable to perform this in combination with polishing and polishing.

Furthermore, since the magnetic dielectric layer and the metal shaft have poor affinity, in order to increase the adhesion strength between the magnetic dielectric layer and the metal shaft, a A thin layer of adhesive is interposed between the two to bond them together.

[0015] The magnetic dielectric roll, which has no seams on the surface and has excellent adhesion strength between the magnetic dielectric layer and the metal shaft, is made of magnetic dielectric material in a thermally molten state as described above. It is manufactured by coating and molding it on the surface of a metal shaft, but specifically methods include extruding and molding a molten magnetic dielectric material onto the surface of the shaft, or insert molding using injection molding, and then cooling and solidifying it. be done.

[0016]

[Example] The present invention applies a magnetic dielectric material consisting of 60 to 35 volume % of thermoplastic resin and 40 to 65 volume % of hard ferrite powder and having a relative permittivity of 9 or more to the outer circumference of a magnetic metal shaft and uniformly over the entire length. A thin magnetic dielectric layer having a surface roughness of 5 μm or less is formed by molding and disposing the thin magnetic dielectric layer in a cylindrical shape so as to have a thickness of 5 μm or less, and a specific molding method is adopted when molding the magnetic dielectric layer. It is characterized in that there is virtually no seam on the surface of the magnetic dielectric layer, and that a large number of magnetic poles are magnetized at small intervals on the surface of the magnetic dielectric layer.

The present invention will be explained below based on specific examples. Regarding the thermoplastic resin, various thermoplastic resins are selected and used depending on the purpose of use as the thermoplastic resin used in the present invention. Commonly used examples thereof include polypropylene, ethylene/vinyl acetate copolymer, 6-polyamide, 12-polyamide, plasticized vinyl chloride resin, chlorinated polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, and the like.

When considering the thermoplastic resin to be used as a binder, the inventors first came up with the idea of reducing the compression set rate in order to suppress the deformation of the magnetic dielectric layer due to the blade in pressure contact. Chlorinated polyethylene resin (hereinafter referred to as CPE) is generally used as a thermoplastic binder resin for flexible magnets having rubber elasticity. Since these CPEs are uniformly chlorinated over the entire polyethylene chain, there are no parts that bind the polymer chains when cooled and solidified, so they suffer from a large degree of permanent deformation if stress is continuously applied. there were. Of course, increasing the degree of chlorination will reduce the degree of permanent deformation, but in this case processing becomes extremely difficult and is not practical.

[0019] As a result of various studies by the present inventors on measures to reduce permanent set without deteriorating processability, we have developed a partially chlorinated polyethylene resin in which polyethylene chains are partially chlorinated to leave a crystalline portion of polyethylene. It has been discovered that when used as a binder resin for ferrite, a flexible magnet with low compression set while maintaining good processability can be obtained. This is presumed to be because the remaining crystalline polyethylene portion crystallizes after molding and solidification to provide nodal points, producing an effect similar to that of a vulcanized portion of rubber. When the crystallinity of partially chlorinated CPE is less than 10%, the permanent deformation is large; on the other hand, when the crystallinity is less than 2%,
Partially chlorinated C
The crystallinity of PE is preferably set within the range of 10% to 20%.

60 to 35% by volume of such partially chlorinated CPE as a binder resin and 40% by volume of hard ferrite powder.
The magnetic dielectric material produced by blending ~65% by volume is easy to mold, and when a magnetic dielectric roll is formed, it has a small compression set and is not deformed by the blade in pressure contact, making it a suitable magnetic dielectric material. You can get a body roll. The reason why the ferrite content is set to 40 to 65% by volume is that if it is less than 40% volume, the magnetic properties and dielectric constant required for a magnetized dielectric roll will be insufficient, and the volume resistivity value will be excessive, and if it exceeds 65% by volume. This is because the processing characteristics deteriorate and the adhesion and homogeneity of the molded product are slightly impaired. Although CPE has been mainly described here, a magnetic dielectric layer having excellent non-adhesive properties can be obtained using other thermoplastic resins as long as they have a small compression set.

When considering a thermoplastic resin as a binder, as with the compression set rate mentioned above, an important issue is to provide a thermoplastic resin that can prevent uneven distribution of ferrite powder. That is, when the thermoplastic resin as a binder is a mixed resin consisting of multiple types of resins, there are the following problems. ■When the compound is put into the raw material hopper of the kneading extruder during kneading and pelletizing, the resin with low density is unevenly distributed in the upper layer due to stirring in the hopper and other factors. In the case of the last one, the composition will be biased. ■When ferrite powder, which is a fine powder, is mixed with large resin particles, a phenomenon occurs in which ferrite segregates due to the large density difference between them. In order to eliminate such segregation and uniformly knead and disperse large granular resin, it is necessary to knead with strong force at high temperatures or repeat the kneading process multiple times, but in this case, thermal deterioration of the resin etc. There are problems and problems with reduced production efficiency.

[0022] When kneaded at high temperature, for a long time, and with high shear force,
There was a problem in that each component was exposed to high temperature and high shear stress for a long period of time, and in particular, the electrical properties changed due to thermal deterioration of the resin. In order to prevent changes in electrical properties and decreases in production efficiency due to thermal deterioration of resin, we discovered that it is sufficient to use thermoplastic resins made of powder with a rough surface as the raw material for all resins. Ta. It is particularly preferable that all of the resin raw material powders have a particle size of 1 mm or less.

If the surface of the raw material powder is smooth, separation of the blend is likely to occur due to the density difference, but the present inventor has found that by pulverizing the resin raw material and roughening the surface of the raw material powder, the composition can be made uniform. We found that it is possible to achieve this. That is, by pulverizing resin raw materials, the friction between different types of resins is increased, and a magnet with a uniform composition is obtained while maintaining a good mixing state with a blender.
By turning the resin raw material into a powder with a rough surface, the composition can be made uniform in minute areas, and by making the surface condition of the raw material particles rougher, it is possible to increase the friction between the raw material powders, so it is possible to increase the friction between the raw material powders until they are kneaded. This is intended to suppress the separation phenomenon due to density differences that tends to occur during handling (stirring and transportation) of blended products.

By pulverizing the raw material, two types of binder resins with different compatibility can be uniformly dispersed without strong kneading, and the raw ferrite powder has a rough surface that allows it to be held by the interlocking structure between the resin powders. This makes it easier to ensure uniform dispersion of the ferrite powder. These provide the effect of stabilizing both electrical and magnetic properties. Furthermore, 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 magnetized dielectric 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, even if the particle size of the raw material is 1 mm or less, in spherical and smooth surfaces such as granulated products, there is little friction between the raw material powders and the composition tends to vary widely. In order to suppress compositional variations, particle shape and surface roughness are most important.

Regarding Ferrite Powder The ferrite used in the present invention is Ba ferrite and Sr ferrite, which are used as permanent magnet materials. In particular, anisotropic ferrite powder that does not contain coarse particles and has a uniform and fine particle size is suitable, and the average particle size is preferably 0.8 to 1.3 μm. Anisotropic ferrite powder is preferable because it is more pulverized than normal isotropic ferrite powder and contains fewer coarse particles.

By the way, even when a thermoplastic resin is used as a binder, pinhole-like defects may occasionally occur on the surface of the magnetic dielectric layer, just as when a rubber binder is used. As a result, the uniformity of magnetization may be impaired or the uniformity of the surface texture of the magnetic dielectric layer may be impaired.

As a result of intensive research into factors that affect surface defects in dielectric rolls, the present inventors have found that the occurrence of pinhole-like surface defects is caused by the ferrite that has been used in the past. In other words, the conventionally used ferrite powder is dry-pulverized or wet-pulverized.
Only extremely coarse and large particles are removed using a sieve of around 10 mesh. 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.

[0028] As a result of researching what kind of ferrite is suitable, we found that it is ferrite powder that has been wet-pulverized to an average particle size of 1.3 μm or less, and that has passed through a sieve of 24 mesh or less. It was found to be suitable. By using such finely pulverized ferrite powder, it has become possible to eliminate pinhole-like defects and to significantly suppress changes in electrical characteristics caused by changes in the humidity environment and changes over time.

The magnetic dielectric layer in the magnetic dielectric roll of the present invention is prepared by kneading 60 to 35% by volume of the above-mentioned thermoplastic resin and 40 to 65% of hard ferrite powder. As mentioned above, the reason why the ferrite content in the magnetic dielectric layer is set to 40 to 65 volume % is because if it is less than 40%, the magnetic properties required for the magnetic dielectric roll will be insufficient.
This is because if it exceeds 100%, the processing properties will deteriorate and the adhesion and homogeneity of the molded product will be slightly impaired. Further, the dielectric constant of the magnetic dielectric layer needs to be 9 or more. This has a relative permittivity of 9
This is because if it is less than that, the image will be too thin.

Regarding molding, the above-mentioned thermoplastic resin, especially a thermoplastic resin with a small compression set, and a magnetic dielectric material made of ferrite powder have excellent non-adhesive properties, so when molded onto a metal shaft, a magnetic dielectric layer is formed. There is a problem in that the adhesion to the metal shaft is reduced. This decrease in adhesion tends to cause destruction at the interface between the magnetic dielectric layer and the surface of the metal shaft. Rolls with poor adhesion between the magnetizable dielectric layer and the metal shaft are often used during post-processing stages such as cutting the outer periphery using a lathe after forming and polishing for surface finishing. Adhesion defects such as peeling between the shafts may occur. Also, when used by incorporating it into a copying machine, etc.
At the moment when rotational force is applied to the shaft, shear stress is generated between the magnetic dielectric layer and the metal shaft, and the magnetic dielectric layer may peel off. Furthermore, since the surface of the magnetic dielectric layer is pressurized by a doctor blade, such a phenomenon is likely to occur. If the magnetic dielectric layer peels off in this way, the magnetized pattern will shift when used in a copying machine or the like, resulting in uneven density on the developed image. In order to avoid such inconveniences, we have found that it is preferable to form a thin uniform adhesive layer on the surface of the metal shaft to improve the adhesion with the magnetic dielectric layer as the magnetic dielectric layer. However, in the roll of the present invention, since the magnetic dielectric layer is used as the magnetic dielectric, it is important to stabilize electrical properties such as relative dielectric constant and volume resistivity, and bonding is required between the metal shaft and the magnetic dielectric layer. There is a problem in that the electrical properties change significantly due to the presence of the agent layer. To avoid this, reduce the thickness of the adhesive layer to reduce the effect on the electrical properties, and make the thickness of the adhesive layer uniform to suppress local variations in electrical properties. This is effective. In this way, it is possible to improve adhesiveness and stabilize electrical properties.

The adhesive used here is preferably a solution-diluted adhesive such as vinyl chloride, acrylic, or nitrile rubber, which can be easily processed into a thin film uniformly. However, it goes without saying that other types of adhesives, such as hot-melt adhesives, can also be used if uniform thin film processing is possible. Although the coating thickness of the adhesive depends on the thickness of the magnetic dielectric layer, it is preferably 100 μm or less in consideration of the influence on electrical characteristics. Furthermore, if the film thickness exceeds this value, it becomes difficult to make the thickness uniform, and local variations in electrical characteristics become large. There are no restrictions on the adhesive application method as long as the adhesive can be uniformly applied in a thin film, but the easiest methods include a roller method, spray method, brush coating, and dipping method. In the present invention, since a thermoplastic resin is used as the binder, it is possible to employ ordinary covering injection molding or covering extrusion molding. By employing a coating injection molding method or a coating extrusion molding method, it is possible to obtain a magnetized dielectric roll that is uniform throughout and has good adhesion to the shaft, and it is also possible to form an adhesive layer on the shaft surface. This makes it possible to further improve adhesion, and eliminates the problem of gaps occurring between the magnet and the shaft.

In addition, since thermoplastic resin is used, 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 magnetized dielectric roll with fine surface roughness can be obtained. Furthermore, uniform dispersion of ferrite powder into thermoplastic resin is easy, and a magnetized dielectric roll with uniform material properties throughout can be obtained, so even fine-pitch magnetization can be achieved as described below. The desired multipole magnetization of about 40 to 50 poles is also easy.

By the way, the insertion molding method (covering molding method) can be used to arrange the magnetic dielectric layer around the outer periphery of the shaft, but it is possible to use the insertion molding method (cover molding method) to increase the adhesion strength between the shaft and the magnetic dielectric layer. For this purpose, forming notches or uneven surfaces on the shaft surface, or applying epoxy or other hardening adhesives to the shaft surface and curing it after insertion, as described above, can be considered, but such molding methods However, this is not necessarily a satisfactory method as it requires a lot of cost and effort.In particular, since the magnetic roller is long, the adhesive method itself is difficult.

In order to avoid this, composite molding and molten thermal bonding can be achieved by inserting and molding a shaft with a thin layer of thermoplastic adhesive on its surface and a molten thermoplastic resin magnet composition and then cooling and solidifying it. It is effective to do both at the same time.

[0035] The melting temperature of the thermoplastic adhesive is lower than the melt-molding temperature of the thermoplastic resin magnet composition. After being applied, it is dried, and a metal or other shaft having a thin layer of thermoplastic adhesive on its surface is preheated to a temperature below and near the melting temperature of the thermoplastic adhesive before being subjected to insertion molding. thing,
The thickness of the thin thermoplastic adhesive layer formed on the shaft surface is 1
It is more preferable to set it to 00 μm or less. Moreover, such bonding and simultaneous insertion molding can be performed by extrusion molding using a crosshead die or injection molding using a mold having a shaft holding mechanism.

Various additives may be used in the resin composition of the present invention. For example, silane-based or titanate-based coupling agents are used to improve the adhesion between ferrite powder and resin, lubricants and plasticizers are used to improve molding characteristics or add flexibility, and deterioration during molding Stabilizers are used to prevent this.

The thermoplastic adhesive used here includes polyvinyl acetate, polyvinyl formal, polyvinyl butyral, ethylene/vinyl acetate copolymer, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate,
Examples include vinyl chloride/butyl acrylate copolymer and soluble nylon. Of course, a so-called composite adhesive consisting mainly of a thermoplastic adhesive and a minor amount of a thermosetting adhesive can also be used. The thermoplasticization temperature of these thermoplastic adhesives is preferably below the thermoforming temperature of the magnet composition used in the present invention. That is, during thermoforming, the thermoplastic adhesive on the shaft is heated and melted to near the temperature of the magnet composition, and by cooling and solidifying it, the shaft and the adhesive and the adhesive and the magnet composition are bonded.
Melt heat bonding and composite molding can be performed at the same time.

[0038] When forming an adhesive layer on the shaft, if it is too thick, the heat resistance strength may decrease, so it is preferably a thin layer, approximately 100 μm thick.
m or less is suitable. Furthermore, when forming an adhesive layer with a thickness of about 100 μm or more by, for example, a solution coating method, there are disadvantages such as a high solution viscosity and a large number of coatings. Also,
If the thickness of the adhesive layer is several micrometers or more, sufficient adhesive strength will be exhibited, so there is no need to make it excessive. As a method for providing such a thin adhesive layer on the shaft, hot melt deposition is not preferable because it results in excessive thickness, and emulsion coating or solution coating is suitable. For emulsion application,
The solution coating method is most preferable because it may be undesirable due to the presence of impurities such as dispersants and emulsifiers, or the presence of pinholes, and it tends to result in a slightly thicker coating film. The solution application may be carried out by a conventional method, and an adhesive solution of a predetermined concentration may be applied onto the shaft and dried.

In the thermal welding and simultaneous composite molding method of the present invention,
It is preferable to preheat the shaft to be inserted and molded prior to molding. Although the temperature of the molten magnetic dielectric material is high, it contacts the shaft surface during molding and instantaneously causes partial cooling, which may not reach the temperature that sufficiently melts the thermoplastic adhesive, resulting in insufficient adhesion. Sometimes all you can get is strength. Therefore, this problem can be solved by preheating the shaft coated with the adhesive to a temperature close to the melting temperature of the adhesive, which is extremely preferable. Preheating is not particularly necessary when the molding temperature of the magnetic dielectric material is 100° C. or more higher than the melting temperature of the adhesive, but it is particularly effective when the molding temperature is close to the adhesive. Further, when the shaft has a large volume and a large heat capacity, preheating is effective because the temperature of the adhesive layer on the shaft surface is difficult to rise.

The heat melt adhesion simultaneous composite molding method shown here can be applied to various thermoplastic molding methods. Although it can naturally be applied to hot compression molding, the efficiency of insertion hot compression molding itself is not good, and the manufacturing method of the present invention is suitable for high-productivity molding methods such as extrusion molding and injection molding. In the extrusion molding method, it is preferable to use a crosshead die in order to perform composite insertion molding efficiently. By inserting the shaft with an adhesive layer formed on its surface into the opening of the die from the direction perpendicular to the extruder, the magnetic dielectric material melted and supplied from the extruder is continuously coated and adhesively molded onto the shaft. In injection molding, a shaft with an adhesive layer formed on it is held at a specified position in a mold, and after the mold is closed, molten magnetic dielectric material is injected into the mold and cooled for a certain period of time. By taking out the post-molded body, it is possible to obtain an object in which the shaft and the magnetic dielectric layer are firmly bonded.

Regarding surface treatment, the surface of the magnetic dielectric layer formed as described above must be smoothed so that the surface roughness is 5 μm or less. When the present inventors performed surface finishing processing by polishing in the same way as when using rubber, the polished thermoplastic resin magnet material filled the gaps in the grinding wheel, causing strong clogging and causing the grinding wheel to become clogged. It was found that it cannot be used industrially because it cannot be reused and the amount of polishing per process is small if only polishing is performed.

[0042] Therefore, the present inventors came up with the idea of employing turning processing as a method of smoothing the surface of the magnetic dielectric layer. In particular, it is preferable to perform the turning process in two stages: rough machining and finishing machining. A more preferred embodiment is to further perform surface polishing after turning, and it is further preferred that the polishing material used for this polishing is sandpaper.

[0043] In surface turning with a lathe, if there is vibration from the lathe itself or surrounding vibration sources or vibration due to dimensional variations in the magnet roll itself, variations will occur in the machined surface, so these vibrations will affect the lathe work. It is necessary to make improvements to prevent this from happening.

That is, if the magnet roll having the ferrite resin magnet layer on the surface is turned using a vibration-suppressed lathe, the surface can be improved by adjusting the shape and feed rate of the cutting tool of the lathe used. Smooth with a roughness of several μm or less,
A surface with little runout or waviness can be obtained. However, it has been found that when a magnetic roll used for turning has a large core runout, a portion having a partially rough surface sometimes occurs. After intensive investigation into the cause of this problem, it was discovered that the main cause is likely to occur when the core run-out or waviness of the magnetic roll used for turning is large. Therefore, in order to obtain a magnet roll with a stable and smooth surface, it was found that the surface of the magnet roll should be rough-turned prior to the finishing turning process to minimize core run-out and waviness. .

Furthermore, it has been found that the above-mentioned partial roughness of the surface can be prevented by subsequently performing a finishing turning process. Also, in this case, a good surface can be obtained even if polishing is performed instead of turning in the finishing process, and since the main parts have been removed by turning in advance, the consumption of abrasive material is entirely reduced by polishing. It is much less expensive than the case where it is carried out, and it can be carried out industrially. In particular, when using sandpaper as the abrasive material, the cost of the abrasive material consumed is low, and if the polishing process is performed while gradually feeding out long and wide sandpaper, it can be performed at high speed and without the problem of deterioration of the abrasive material. It is possible. It is more preferable to carry out preliminary turning followed by finish turning to obtain good surface properties, and then to perform further polishing, since even better surface properties can be achieved.

Regarding magnetization, the roll-formed body produced as described above needs to be magnetized at fine intervals because it is necessary to magnetize the toner uniformly on the roll surface. Furthermore, since the triboelectrically charged toner is transferred to the latent image on the surface of the photoreceptor by electrostatic force, it is essential to apply a potential directly to the surface of the roll, but if the magnetic dielectric layer is thick, the developed image will be poor. Therefore, the layer thickness cannot be increased. On the other hand, the dielectric layer must also ensure the function as a permanent magnet for toner magnetization;
If the thickness is reduced, it becomes difficult to obtain the surface magnetic field necessary for toner magnetic attachment. The inventors have discovered that this contradiction can be avoided by making the layer thickness of the magnetic dielectric layer specific in relation to the magnetization spacing.

[0047] In the first place, the properties of a material as a dielectric are unique to that material and cannot be changed by devising the surrounding structure. For example, it is necessary to reset all the dielectric properties of surrounding materials, which is not practical. Therefore, in order to achieve the purpose of the present invention, it is necessary to research how to exhibit magnet performance to a higher degree. The simplest method is to increase the ferrite content in the magnetic dielectric layer, but increasing the ferrite content increases the dielectric constant of the layer and decreases the electrical resistivity, making it difficult to develop the developing device. This is not appropriate as it would require a complete redesign of the design and materials including toner. The next possible method is to make the ferrite powder anisotropic and use an orientation means to make the developing roll radially anisotropic to improve magnetic performance. One of the means of imparting anisotropy in the radial direction is radial magnetic field orientation molding, but because the roll has an elongated structure, it has a side surface area that is much larger than its cross-sectional area, causing magnetic field orientation. cannot be used because the necessary radial magnetic field cannot be obtained. Another method is to use mechanically oriented ferrite powder and roll it into a thin sheet.The shear force during the forming process will orient the ferrite powder in the thickness direction, creating a sheet with anisotropy in the thickness direction. By wrapping this around a round shaft, a radially anisotropic roll is created. However, with this method, the degree of anisotropy varies greatly due to variations in the properties of the ferrite powder used, the viscoelastic properties of the binder resin or rubber, and slight variations in processing conditions, resulting in large variations in magnetic properties. I understand. On the other hand, since the developing roll of the direct contact electrophotographic developing method, which is the object of the present invention, utilizes a magnetic field on its surface, variations in the magnetic properties of the material greatly affect the magnetic adhesion of the toner. Although rolls obtained by the above manufacturing method can be used, they are not suitable.

In the present invention, the latent magnetic properties of the magnetic dielectric layer can be effectively exhibited without changing the electrical properties such as dielectric and electrical resistance properties, that is, without changing the material of the magnetic dielectric layer. We conducted intensive research with a focus on the magnetic circuit of this roll in order to bring out the latent characteristics of the magnet. As a result, when the thickness of the magnetic dielectric layer was set to 50% to 100% of the magnetization interval, a magnetic dielectric roll that could satisfy both electrical and magnetic properties could be obtained.

When a sufficiently thick magnet is magnetized with multiple poles, N and S poles appear alternately on the surface of the magnet, and a magnetic circuit is formed in the shape of a horseshoe inside the magnet, so that magnetic circuits from each pole are formed in a horseshoe shape. The generated magnetic field is used effectively. However, if the thickness is thin, penetration magnetization will occur on the back side of the magnetized surface, for example, an S pole will occur exactly on the back side of the N pole part on the front surface, and the magnetic field generated from the N pole on the front surface. is canceled out by the magnetic field from the south pole on the back surface, and as a result it only acts as a weak north pole. Since the magnetic dielectric layer of the roll to which the present invention is applied is thin, similarly, if the shaft core is made of a non-magnetic material such as aluminum, non-magnetic stainless steel, synthetic resin, etc., only a weak and insufficient surface magnetic field can be obtained.

Therefore, in the present invention, the shaft on which the magnetic dielectric layer is provided is made of a magnetic material. There are two effects of using magnetic material. The first is that when magnetizing, the magnetic field generated from the magnetizing yoke magnetizes the shaft, making it appear as if there are two sides on the front and back.
This has the same effect as when magnetizing by arranging a set of magnetizing magnetic fields, and the effective magnetizing magnetic field is stronger than when the yoke is used alone, and as a result, it penetrates to the back side of the magnetic dielectric layer, This is because it can be strongly magnetized over the entire thickness. The second effect of using a magnetic shaft is that the above-mentioned problem of surface magnetic field drop that occurs when the back surface of a thin magnetic dielectric layer is magnetized is eliminated, and the magnetic energy due to the penetration magnetization is reduced. This is because it can be used effectively and the surface magnetic field increases. This is because the magnetic field from the reverse magnetic pole generated on the magnetized back surface in contact with the axis of the magnetic dielectric layer flows through the inside of the axis as a magnetic circuit, forming a horseshoe-shaped magnet that is thicker than the magnetic dielectric layer. This is because they behave similarly.

[0051]

As described above, according to the present invention, a magnetic dielectric layer having uniform and stable electrical and magnetic properties and a smooth surface is used in a direct contact electrophotographic developing method. It is possible to obtain a magnetized dielectric roll suitable for. Since a thermoplastic resin is used as the magnetic dielectric material, it is possible to provide a magnetic dielectric roll that is easy to mold and has excellent mass productivity.

[0052] Furthermore, when wet-pulverized hard ferrite powder with an average particle diameter of 1.3 μm or less, or sieved with a mesh finer than 24 mesh, is used, it is difficult to resist changes in the humidity environment and changes over time. It becomes possible to significantly suppress changes in electrical properties and surface defects caused by this.

[0053] Furthermore, when a thermoplastic resin having a small compression set is used, the non-adhesiveness of the surface can be reduced, and it is possible to provide a magnetic dielectric layer that is not deformed even by a blade in a press-contact state. Can be done.

When powder having a rough surface is used as the thermoplastic resin, it becomes possible to uniformly disperse the ferrite powder in the binder, and the electrical and magnetic properties become more stable.

When the surface of the magnetic dielectric layer is smoothed by turning or a combination of turning and polishing, a magnetic dielectric roll having excellent surface smoothness can be obtained industrially and stably. be able to.

[0056] When the magnetic dielectric layer and the metal shaft are bonded with a thin layer of adhesive, there is no gap between the magnetic dielectric layer and the shaft, and the adhesion between the magnetic dielectric layer and the shaft is improved. A good magnetized dielectric roll can be provided.

Claims (9)

[Claims] Claim 1: A magnetic dielectric material consisting of 60 to 35 volume % of thermoplastic resin and 40 to 65 volume % of hard ferrite powder and having a relative dielectric constant of 9 or more is coated in a cylinder with a uniform thickness around the outer periphery of a magnetic metal shaft. The surface roughness is 5μ.
A thin magnetic dielectric layer with a diameter of less than m and virtually no seams on the surface during molding is formed on the outer periphery of the shaft, and a large number of magnetic poles are provided at small intervals on the surface of the thin magnetic dielectric layer. Features a magnetic dielectric roll. 2. The magnetic dielectric roll according to claim 1, wherein the hard ferrite powder is wet-pulverized and has an average particle diameter of 1.3 μm or less. 3. The magnetic dielectric roll according to claim 1, wherein the hard ferrite powder is sieved with a mesh finer than 24 mesh. 4. The magnetic dielectric roll according to claim 1, wherein the thermoplastic resin has a small compression set. 5. The magnetic dielectric roll according to claim 1, wherein a powder having a rough surface is used as the thermoplastic resin. 6. Claim 1, wherein the surface of the magnetic dielectric layer is smoothed by turning or a combination of turning and polishing.
The magnetized dielectric roll described above. 7. The magnetic dielectric roll according to claim 1, wherein the magnetic dielectric layer and the metal shaft are bonded together with a thin layer of adhesive. 8. The magnetized dielectric roll according to claim 1, wherein the shaft is formed by inserting and molding the shaft into a magnetized dielectric material. 9. A heat-molten magnetized dielectric material having a relative dielectric constant of 9 or more and consisting of 60 to 35 volume % of thermoplastic resin and 40 to 65 volume % of hard ferrite powder is uniformly distributed around the outer circumference of the magnetic metal shaft. By coating and molding into a cylindrical shape with a thickness, a thin magnetic dielectric layer with a surface roughness of 5 μm or less and no seams on the surface during molding is formed on the outer periphery of the shaft, and the magnetic dielectric layer A method for manufacturing a magnetized dielectric roll by magnetizing a large number of magnetic poles at small intervals on the surface of the roll.