JPH11307340A - Magnet roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high magnetic performance magnet roll which is most suitable for reproducing a precise copy image, the magnet roll being attached to an electrophotography developing apparatus with a dry developer. SOLUTION: A roll-shaped magnet 6 is injection-molded into an injection die, in which a shaft 6a is placed with a composite resin magnet material component which uses two alloyed ethylene-ethylene acrylate copolymer resins with different molecular weights of 16,000 and 29,000 components as a matrix, and a shaft inserted magnet roll with high magnetic performance is obtained at a low coat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet roll used in an electrophotographic developing device such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In general, a magnet roll used for magnetic brush development in an electrophotographic developing apparatus is a roll having a cylindrical non-magnetic sleeve and a plurality of magnetic poles on the surface inside the non-magnetic sleeve. The main part of the roll-shaped magnet, a flange or an integrated bearing for rotating at least one of the non-magnetic sleeve and the roll-shaped magnet, so as to hold the shaft portion at both ends of the roll-shaped magnet. It is fixed to both ends of the non-magnetic sleeve.

In an electrophotographic developing apparatus, at least one of the above-mentioned non-magnetic sleeve and a roll-shaped magnet is rotated to adsorb and transport a developer made of magnetic powder on the non-magnetic sleeve, and to charge the photosensitive material. A magnetic brush developing method is used in which an electrostatic latent image formed on the surface is transferred and visualized.

Hereinafter, a conventional magnet roll for developing a magnetic brush will be described with reference to a sectional view of FIG. According to the figure, the magnet roll is configured to relatively rotate the roll magnet 6 in the non-magnetic sleeve 5, but bearings 7 a and 7 b and bearings 7 a and 7 b are provided at both ends of the non-magnetic sleeve 5. A bearing portion formed of flanges 8a and 8b for holding the metal magnet 7b and preventing foreign matter from entering the non-magnetic sleeve 5 from both ends is formed, and the roll-shaped magnet 6 and the non-magnetic sleeve 5 are minimized. The flanges 8a and 8b are adhered and fixed to the non-magnetic sleeve 5 with an adhesive in such a dimensional relationship that the interval 9 is provided and the rotational load is not increased.

A shaft 6a for rotating or fixing the roll-shaped magnet 6 is drawn out of one flange 8b, but a system in which the roll-shaped magnet 6 is fixed and the non-magnetic sleeve 5 is rotated is mainly used. A reference surface such as a D-cut is provided at the end of the shaft 6a in order to regulate the positional relationship between the magnetization pattern and the photoconductor. The shaft 6a is made of a conductive metal material for the purpose of forming an electric path for giving specific electric characteristics to the surface of the nonmagnetic sleeve 5.

[0006] The roll-shaped magnet 6 fixed to the outside of the metal shaft 6a has conventionally been formed using cylindrical sintered ferrite, but in recent years, nylon (nylon 6, nylon 6) has been used.
Nylon 12, etc.), polypropylene, polyethylene,
It is made of a composite resin magnet material using a thermoplastic resin such as chlorinated polyethylene or vinyl acetate as a binder.

Conventionally, composite resin magnet materials have been improved in magnetic properties by a method of orienting the axis of easy magnetization of ferrite powder, which is a ferromagnetic powder, in a fixed direction by mechanical means, and a method of orienting by a magnetic field. It is planned.

[0008] A method of orienting the easy axis of ferrite powder in a certain direction by using mechanical means is as shown in FIG. 5 (a).
1 to form a sheet magnet 13 in which the axis of easy magnetization 12 of the ferrite powder is oriented in a direction perpendicular to the sheet surface, and then, as shown in FIG. It is wound around a shaft 6a to form a roll, and then magnetized to form a roll magnet 6.

As another method, as shown in FIG.
In order to increase the orientation efficiency, after stacking several sheet-shaped magnets 13, as shown in FIG. 5D, the fan-shaped pressure-formed piece 6 b is turned into a metal shaft 6 a as shown in FIG. There is also a device in which the outer periphery of the lamination is cut adjacent to the center and formed into a roll shape, and magnetized to form a roll magnet 6.

[0010] The method of orienting by the action of a magnetic field is called magnetic field injection molding, in which a strong magnetic field is applied to a plastic composite magnet material in a mold at the time of injection molding.
As shown in FIG. 6, a magnetic pole piece 6b having a fan-shaped cross section and a fan-shaped circular arc portion and oriented to the fan-shaped side surface and the inner circumference was obtained as a roll-shaped magnet in which the easy axis of ferrite powder was oriented in the direction of the magnetic flux lines. Then, a plurality of magnetic pole pieces 6b are joined to a metal shaft 6a using an adhesive or the like to form a roll-shaped magnet 6, and a composite resin magnet material in a plastic state during injection molding as shown in FIG. Is a coil 16a and a yoke 16 arranged around a cavity 15 in a mold 14.
There is a type in which the easy axis of the ferrite powder is oriented in the direction of the magnetic flux lines by receiving the action of a magnetic field from the oriented magnet 16 made of b, and a roll-shaped magnet is formed only by molding.

In any case, the base resin of the composite resin magnet material is determined with emphasis on the orientation characteristics and molding characteristics of the ferrite powder, and a modified polyethylene resin or a rubber-based elastomer is used in the method of obtaining a sheet-like magnet by mechanical orientation. Then, after forming an oriented piece for each pole by magnetic field injection molding, nylon 6 or nylon 12 is used in a type in which the piece is fixed to a metal shaft with an adhesive or the like. Shaft 6a
In the type of insert molding, a single ethylene / ethyl acrylate copolymer resin is used as a base resin in order to absorb a difference in expansion coefficient between the metal shaft 6a and the composite resin magnet material.

[0012]

In general, an electrophotographic developing apparatus using a dry developing agent forms a latent image by applying an electrostatic attraction effect to image information such as a latent image formed by charging and exposing a photosensitive member. In this configuration, a roll-shaped magnet having a high magnetic force for the purpose of agitating and charging and attracting and transporting the developer is received by a flange via a bearing, and is incorporated in a non-magnetic sleeve.

Then, the magnet portion is fixed, the flange is driven to rotate the non-magnetic sleeve, and the developer is transferred along the magnetic field distribution on the surface of the non-magnetic sleeve.
For this reason, the function of each magnetic pole of the developing magnet roll composed of a plurality of poles is determined according to the configuration of the developing unit and the relationship with the photoreceptor, and an optimal magnetic field line distribution is required for the function. Is done.

That is, the distribution of the lines of magnetic force generated from the roll-shaped magnet has an important role in determining the image characteristics.
It is required that a plurality of configured magnetic poles can be individually designed and a complicated magnetized pattern can be realized by an easy process.

Further, the metal shaft of the fixed magnet portion is formed by processing a metal material having conductivity in order to impart certain electric characteristics to the surface of the non-magnetic sleeve.

The base resin of the composite resin magnet material is effective if the ferromagnetic powder, which is indispensable for improving the efficiency as a magnet, can be easily oriented and the fixation after orientation can be stably and quickly performed. In this respect, nylon 6 and nylon 12 in the magnetic field injection molding are optimal, but the type in which a metal shaft is insert-molded cannot be used immediately after molding or in a reliability test due to cracks in the diameter direction in a reliability test.

On the other hand, the system using a single material of ethylene / ethyl acrylate resin as a base material, which is used in the conventional shaft insert molding type, has a molecular weight of 29000 component level, and the product characteristic assurance temperature range of the magnet roll due to the viscoelasticity of the resin. It can be used without deformation and cracking at -40 ° C to 100 ° C. However, fluidity during magnetic field orientation molding due to viscoelastic properties is adversely affected and orientation efficiency is low, and there is a limit to product development due to magnetic properties. .

An object of the present invention is to provide an inexpensive shaft insert type magnet roll for developing a magnetic brush having high magnetic force characteristics, with the object of solving the above-mentioned conflicting problems.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a composite resin magnet material having a high productivity and a roll-shaped magnet having high productivity obtained by insert molding with a metal shaft. Has a molecular weight of 1600
Two types of ethylene / ethyl acrylate copolymer resins having different components 0 and 29000 are alloyed and used as a base resin.

According to the above configuration, unlike the conventional composite resin magnet material, it is possible to manufacture a magnet roll excellent in high magnetic force characteristics at a low cost by a shaft insert type manufacturing method excellent in productivity. Things.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION
A mixture mainly composed of a ferromagnetic powder material and a polymer compound material is melt-injected by setting a metal shaft in a mold in which a plurality of oriented magnets for generating an orientation magnetic field are arranged, and the outer peripheral surface of the molded body In a magnet roll that forms a plurality of magnetic poles, two types of ethylene / ethyl acrylate copolymer resins with different molecular weights are alloyed and used as a base material resin. And a magnet roll excellent in high magnetic force characteristics.

The second aspect of the present invention is the first aspect.
By setting the optimum alloying ratio of the mixture mainly composed of the ferromagnetic powder material and the polymer compound material described in 1 to 1: 9 to 5: 5 in a molecular weight of 16,000 components: 29000 components, the fluidity during molding can be improved. And stabilizes the linearity of the orientation magnetic characteristics.

The third aspect of the present invention is the first aspect of the present invention.
By containing 80 to 95% by weight of the ferromagnetic powder material described in 1 above, the properties of the magnet roll can be further improved.

Next, prior to the description of the embodiment of the present invention, a general manufacturing method of the present invention will be described.

The mixture mainly composed of a ferromagnetic powder material and a polymer compound material used for molding has a molecular weight of 1600.
Alloying two kinds of ethylene-ethyl acrylate copolymer resins having different 0 component and 29000 component to make a base resin, hard ferrite powder such as barium ferrite and strontium ferrite, and rare earth magnetic powder such as titanium or silane And surface-treated with a coupling agent, and kneaded at a content of 80 to 95% by weight.

The alloying ratio of the base resin is 1600 molecular weight.
0 component: 1: 9 to 5: 5 in 29000 molecular weight component
The effective range is that the low molecular weight component acts as a plasticizer for the high molecular weight component to improve the orientation efficiency of the ferromagnetic powder in magnetic field injection molding. This is because a problem occurs in reliability.

The molecular weight of the two kinds of ethylene / ethyl acrylate copolymer resins is from 14,000 to 17000 and the molecular weight is 2900.
The zero component can obtain the effects of the present invention when the molecular weight is between 28,000 and 31,000 components.

The developing magnet roll produced by such a manufacturing method has an orienting magnet arranged around a molding die cavity in order to impart optimum characteristics to each required magnetic pole. It is important that the strength and the positional relationship between the orienting magnets are designed to be optimal according to the magnetization pattern required for each product.

An embodiment of the magnet roll of the present invention will be described below with reference to FIGS.

FIG. 1 is a cross-sectional view of an orientation mold used for magnetic field injection molding of a magnet roll of the present invention, FIG. 2 is a cross-sectional view around the gate portion, and FIG. 3 shows an example of a magnetized pattern. Things.

According to FIG. 1, reference numeral 1 denotes a non-magnetic base made of stainless steel, and the periphery of the cavity 2 in the non-magnetic base 1 corresponds to the number of poles and pole positions of the magnet roll to be obtained. And the orientation magnet 3 is arranged.
The oriented magnet 3 is configured by integrating a permanent magnet 3a with a front yoke 3b and a base yoke 3c made of a soft magnetic material.

The intervals between adjacent oriented magnets 3, that is, the so-called pole angles θ1, θ2, θ3, θ4 are determined according to the product specifications. The magnetic strength and the size of the permanent magnet 3a and the tip size of the front yoke 3b are determined by the product. The permanent magnet 3a is designed based on the specifications, especially the magnetic force and the half width.
Rare earth cobalt magnets with 0G and IHC of 10700 Oe are used and magnetized in the diameter direction.

FIG. 2 is a sectional view showing a gate portion of a mold. For example, a shaft end portion is formed at both ends of a cavity having a diameter of 17.4 mm, and a sprue and a runner connected to a nozzle port are provided at one end A. Are connected, the conical attachment 4 is inserted into one end of the shaft 6a to form a ring gate, and the composite resin magnet material is uniformly injection-molded on the outer peripheral surface of the shaft 6a.

In the injection molding, the composition of the composite resin magnet roll composed of various base resins shown in (Table 1) was previously mixed by a super mixer, and then pelletized by using a twin-screw kneading extruder. The conical attachment 4 was mounted in a mold by inserting the iron shaft 6a thus obtained, and the roll-shaped magnet 6 was integrally formed.

[0035]

[Table 1]

Next, the following comparative test was conducted. First, a heat resistance test and a cold resistance test in which the rolled magnet 6 is left for 100 hours in a constant temperature bath at 100 ° C. and −40 ° C.
A heat shock test was performed for 10 cycles from room temperature to room temperature to 60 ° C., and the external shape was confirmed and the surface magnetic flux density was measured with a Gauss meter.

In the measurement, in order to be used as a magnet roll, a Hall element of a Gauss meter was incorporated into a sleeve having an outer diameter of 20 mm, and the Hall element of the Gauss meter was brought into contact with the surface of the sleeve to evaluate the peak magnetic force characteristic at the center in the longitudinal direction. went.

The results of confirming the above external appearance are shown in Table 2.
Table 3 shows the measurement results of the surface magnetic flux density.

[0039]

[Table 2]

[0040]

[Table 3]

As is apparent from the above results, the molecular weight is 1
A composite resin magnet material obtained by alloying two kinds of ethylene / ethyl acrylate copolymer resins having different 6000 components and 29000 components into a matrix resin and a metal shaft 6a by insert molding in a mold in which an orientation magnetic field is formed. By integrally forming the roll-shaped magnet 6, a magnet roll having high magnetic properties can be provided at low cost by a method of insert molding a metal shaft.

In the above embodiment, the optimum composition should be determined in accordance with a wide range of product characteristics such as magnetic properties and mechanical properties, and the detailed composition ratio is not limited to the above embodiment. Absent.

[0043]

As described above, the magnet roll of the present invention is a composite resin magnet material composition comprising a base material obtained by alloying two kinds of ethylene / ethyl acrylate copolymer resins having different molecular weights of 16,000 and 29000 components. Thus, a shaft insert type magnet roll having high magnetic properties and realizing high quality image properties can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold for manufacturing a magnet roll according to an embodiment of the present invention.

FIG. 2 is a sectional view of a gate portion of the mold for manufacturing the magnet roll.

FIG. 3 is a diagram illustrating a magnetization pattern according to an embodiment;

FIG. 4 is a sectional view of a conventional magnet roll.

FIG. 5 is an explanatory view of a conventional magnet roll manufacturing process.

FIG. 6 is a perspective view of another conventional magnet roll.

FIG. 7 is a sectional view of a molding die for forming another conventional magnet roll by injection molding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-magnetic base 2 Cavity 3 Oriented magnet 4 Conical attachment 6 Roll magnet 6a Shaft

Claims (3)

[Claims] A mixture mainly composed of a ferromagnetic powder material and a polymer compound material is melt-injected by setting a metal shaft in a mold in which a plurality of oriented magnets for generating an orientation magnetic field are arranged, A magnet roll comprising a plurality of magnetic poles formed on an outer peripheral surface of a molded body, wherein two kinds of ethylene / ethyl acrylate copolymer resins having different molecular weights are alloyed and used as a base resin. 2. The magnet roll according to claim 1, wherein the alloying ratio of the two kinds of ethylene / ethyl acrylate copolymer resins is 1: 9 to 5: 5 in a molecular weight of 16,000 components and a molecular weight of 29000 components. 3. The magnet roll according to claim 1, comprising 80 to 95% by weight of the ferromagnetic powder material.