JPS6312370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a magnet roll used mainly in a magnetic brush developing device and a magnetic brush cleaning device of an electrostatic copying machine.

Isotropic or anisotropic sintered ferrite magnets are generally used as magnet rolls for magnetic brush development, but these magnets have many problems when formed into rolls, such as the following.

(1) Compression molding of ferrite powder into a roll shape with a length larger than its diameter is difficult with normal equipment, and special molding equipment must be used.

(2) The compression-molded product obtained in (1) is extremely susceptible to chipping and brittle until it is fired, so great care must be taken when handling it.

(3) Because it shrinks significantly during firing and has poor dimensional accuracy, post-processing is required to improve accuracy.

(4) The sintered ferrite magnet itself is hard;
Since it is brittle, processing to improve dimensional accuracy must be performed by grinding or the like, and productivity is poor because the cutting depth of the grinding wheel cannot be increased.

On the other hand, in order to eliminate the drawbacks of the above-mentioned sintered ferrite magnet rolls, it has been proposed to use rubber magnets or plastic magnets in which ferrite powder is blended with a polymer in the form of a roll. It has not yet been put to practical use as a developing magnetic roll. This is because rubber magnet rolls and plastic magnet rolls have a lower ferrite density due to the high molecular weight contained therein than the ferrite magnet rolls produced by the sintering method described above, and are therefore magnetically weaker, making them suitable for magnetic brush development. This is because it is not suitable for

Therefore, in order to improve this, attempts have been made to make the rubber or plastic magnet roll anisotropic to increase the magnetic flux density. The method is to form a rubber magnet into a thin sheet 5 as shown in Figure 1.
A rubber magnet sheet 5, in which the easy magnetization axis 4 is mechanically oriented perpendicular to the sheet surface by utilizing the shape of the ferrite particles 6, is wound around the shaft 1 as shown in FIG. A method of forming and magnetizing a magnet roll (see JP-A No. 53-94940), and a rubber magnet whose axis of easy magnetization is first oriented in a direction perpendicular to the sheet surface as shown in Figure 3-a. Solid roll sample 1 by rolling the sheet into a roll
0, and then, as shown in Figure 3-b, this solid roll 10 is glued around the shaft (support shaft) 1 in a number corresponding to the number of magnetized rolls, and then from the outer peripheral surface. A method of hydrostatically compressing in the radial direction to form a rubber magnet roll 9 as shown in Fig. 3-c, and magnetizing it so that the magnetic pole is disposed at the center of each solid roll sample (Unexamined Japanese Patent Publication No. (See No. 1983-27995).

In the magnet roll manufactured by the former method, the direction of the magnetic flux lines inside the magnet roll and the direction of the axis of easy magnetization do not completely match, and there are parts where the directions are completely opposite depending on the location. Therefore, the magnetic flux density does not improve that much.

If the latter method is used, the orientation will almost match the magnetic flux lines, but the manufacturing process will be complicated, and
It is not possible to obtain a roll that is magnetically homogeneous and has good dimensional accuracy.

The present invention eliminates these conventional drawbacks and provides a method for manufacturing a magnetic brush developing roll that is magnetically homogeneous, has good dimensional accuracy, has high magnetic flux density, and has extremely low demagnetization. be.

Generally, a magnet roll for magnetic brush development or magnetic brush cleaning has a structure in which a magnet material 2 is fixed around a shaft 1, as shown in Figure 4-b (front sectional view), and a magnet material 2 is fixed around a shaft 1. It is used by being magnetized with multiple poles in the radial direction as shown in Figure 4-a (plan sectional view). At this time, the magnetic flux lines passing through the magnet are as shown in 3. Therefore, this magnetic flux line 3
If the axis of easy magnetization of ferrite can be oriented in the same direction, stronger magnetic properties can be obtained.

The present inventors believe that it is sufficient as a magnet roll for magnetic brush development if the axis of easy magnetization is oriented in the direction of the magnetic flux lines, especially in a region with high magnetic flux line density, and that We have discovered that it is not necessary to anisotropicize the entire roll. That is, in a magnet roll for magnetic brush development or cleaning, the easy magnetization axis of the magnetic material constituting the magnet roll is at least in the high-density region of the magnetic flux lines passing inside the roll between adjacent magnetized poles. Based on the fact that it is sufficient to be oriented in the direction of the magnetic flux lines, we have succeeded in producing for the first time an integrally molded anisotropic magnet roll for electrostatic copying magnetic brushes with the axis of easy magnetization oriented in the direction of the magnetic flux lines. It is.

The integrally molded magnetic roll of the present invention kneads a mixture substantially composed of a magnetic material and a polymer compound, and forms the kneaded product into a roll or pipe shape while pressurizing the magnetic material of the forming roll. It can be created by applying a magnetic field corresponding to the magnetization pattern from the outside so that the axis of easy magnetization is oriented in the direction of the lines of magnetic flux passing between the magnetization poles. For example, after uniformly kneading a composition consisting essentially of ferrite powder and a polymer, a strong magnetic field is generated using an electromagnet, etc., and the magnetic force causes the axis of easy magnetization of the ferrite particles to change. Injection molding or extrusion molding is performed while oriented in the same direction as the magnetic flux lines to obtain a roll-shaped or pipe-shaped molded product having a shaft. The molded product obtained in this way remains in a magnetized state even when the magnetic field is removed, and in Fig. 6 (hysteresis loop of a permanent magnet) it is located at a point corresponding to the Br point in the state of magnetic field H = 0 ( In an actual magnet, it is at the Bd point, not the Br point.)
After cooling the molded product in such a state, a reverse magnetic field with a smaller absolute value than during molding is applied.
The molded product is demagnetized by applying _BHC .
However, at this time, the axis of easy magnetization of the magnetic material constituting the magnet roll remains oriented in the direction of the magnetic flux lines during molding. After demagnetization, a magnetic field is applied to the molded product as required for each magnetic pole to obtain the intended magnetic roll. That is, each of the steps a, b, and c in FIG. 5 can be performed in one mold.

The magnet roll composition used in the method of the present invention includes 70 to 95% by weight of magnetic material particles having a large magnetic anisotropy constant, such as ferrite powder or rare earth magnet powder containing at least one of barium, strontium, and lead;
5 to 30% by weight of a polymer compound consisting of a highly fluid thermoplastic resin such as polyethylene, polystyrene, chlorinated polyethylene, polyamide, polypropylene, etc.
It consists of 0-10% by weight of solid plasticizer and/or liquid plasticizer, 1-3% by weight of lubricant, and other additives as required. After kneading and blending these compositions using a roll, kneader, banbury, etc., the above compositions are compression molded in a magnetic field corresponding to the magnetization pattern for a magnetic brush roll for electrostatic copying to produce a resin with high magnetic flux density. You can get a magnet roll. In the present invention, it is not preferable to use a rubber-based polymer as the polymer compound because it hinders fluidization when kneading and blending with other compositions and when forming into a roll or pipe.

Here, a magnet particle with a large magnetic anisotropy constant has an axis of easy magnetization 4 as shown in FIG. When a magnetic field is applied to a magnet from the outside, lines of magnetic flux are generated within the magnet, but if the magnet particles are in a state where they can move easily, their axis of easy magnetization 4 will be oriented in the same direction as the lines of magnetic flux.

Since the resin magnet roll of the present invention can be easily and efficiently manufactured by injection molding or extrusion molding, the above-mentioned properties can be utilized at that time. For example, the above kneaded composition is extruded into a mold 7 consisting of a non-magnetic region and a magnetic region as shown in FIG. 8-a (plan sectional view) and FIG. 8-b (front sectional view), and then When molding into a pipe shape, a magnetic field is applied from the outside using an electromagnet 13 or the like to the same location as the pole to be magnetized as a magnet roll for a magnetic brush to generate lines of magnetic flux, and the magnetic flux blended into the resin in the molten state is The easy axis of magnetization of the particles can be oriented in the direction of the magnetic flux lines.

The magnet roll obtained in this way has the following features.

(1) Excellent productivity as it can be magnetized and oriented during roll forming. In particular, it can be manufactured as a single piece by injection molding or extrusion molding,
Compared to manufacturing methods for sintered magnet rolls and conventional resin magnet rolls, this method has superior mass productivity and can be produced at extremely low cost.

(2) Compared to anisotropic magnet rolls in which the axis of easy magnetization is oriented in the radial direction, the easy axis of magnetization is oriented in the same direction as the lines of magnetic flux passing through the magnet, so it has superior magnetic properties.

(3) Because it is flexible, it does not easily crack or chip, and is impact resistant.

(4) Since it is molded using a mold, dimensional accuracy is high;
No post-processing required.

(5) It has a lower density than sintered magnets, so it can be made lighter.

(6) Plastic magnets and rubber magnets have less demagnetization than sintered ferrite magnets.

(7) The circumferential surface of the magnet roll can be selectively magnetized and the magnetic strength of the magnetic poles can be adjusted arbitrarily.

[Brief explanation of the drawing]

Figures 1, 2, 3-a, 3-b, and 3-c are explanatory diagrams regarding anisotropy of conventional rubber magnet rolls, and Figures 4-a and 4-b The figures are a plan sectional view and a front sectional view showing the structure and magnetization pattern of a normal magnetic brush developing magnet roll, FIGS. 5 a to 5 c show the manufacturing process of the magnet roll of the present invention, and FIG. shows the hysteresis loop of the permanent magnet. Figure 7 shows the easy axis of magnetization of magnet particles with a large magnetic anisotropy constant, and Figure 8-a
FIG. 8 and FIG. 8-b are a plan sectional view and a front sectional view of a mold used when carrying out the method of the present invention. Codes in the figure: 1...shaft; 2...magnetic material; 3...
Lines of magnetic flux; 4... Axis of easy magnetization; 5... Magnet sheet; 6...
Magnet particles; 7... Mold; 9... Magnet roll; 10... Solid roll; 11... Non-magnetic material; 12... Magnetic material; 13
…electromagnet.

Claims (1)

[Claims] 1. Injection molding a mixture containing a magnetic material and a polymer compound under pressure into a roll or pipe shape,
When injection molding is performed in a method for manufacturing a magnet roll having a plurality of magnetized poles on the circumferential surface, (a) a constant external magnetic field is applied so that the axis of easy magnetization of the magnetic material of the forming roll is oriented in the direction of the magnetic flux lines passing between the magnetized poles; (b) Next, applying a magnetic field opposite to that during forming to demagnetize the magnetic force of the magnet roll, and (c) Finally, re-magnetizing the roll. A method for manufacturing a magnet roll for a magnetic brush, characterized in that the step of reapplying a magnetic field so as to selectively obtain the magnetic strength of the magnetic poles is carried out in one mold.