JPH0438124B2 - - Google Patents

Description

[Detailed description of the invention] (a) Purpose of the invention [Field of industrial application] This invention is mainly applicable to copying machines, facsimile machines,
This invention relates to a magnet roll for a magnetic brush in electrostatic recording such as a printer.

[Prior art]

In an electrostatic recording device, a magnet roll for a magnetic brush is normally fixed concentrically in a rotating cylindrical sleeve made of non-magnetic material, and a developer containing a mixture of toner and carrier is delivered to this roll from a hopper or the like. supplied to the surface of the sleeve. This developer is attracted to the surface of the sleeve by the magnetic force of the magnet roll, and when it comes to the development position where it comes into contact with the photoreceptor drum due to the rotation of the sleeve, it stands up like a brush to form a so-called magnetic brush. . This magnetic brush
The brush comes into sliding contact with the electrostatic latent image formed on the photoreceptor drum, and a portion of the toner in the brush adheres thereto to be developed. Then, developer consisting of remaining toner and carrier (developer with reduced toner concentration)
The toner is once removed from the sleeve, refilled with new toner to maintain a constant toner concentration, and then magnetically attached to the sleeve again for repeated use. However, if the developer with a reduced toner concentration is not sufficiently removed from the sleeve, the developer with a reduced toner concentration remains attached to the sleeve surface and cannot be mixed with the developer with a normal toner concentration. Instead, a problem occurs, and the toner density of the developer during the next development is lower than the previous one, and if this is repeated many times, the copy density decreases, making it impossible to obtain accurate copying performance.

Conventionally, a sintered magnet having a structure in which a notch communicating from the outer circumferential surface to the inner circumferential surface is formed in the widest part between the magnetic poles along the axial direction is used as a means for removing the developer whose toner concentration has decreased from above the sleeve. Rolls have been proposed (Special Publication No. 57-33685, etc.). However, when such notches are formed in a resin magnet roll made of magnetic powder and a synthetic resin binder, the symmetry of the stress distribution in the cross section is lost, stress is concentrated in a part, and the temperature during manufacturing and use increases. The roll itself may break or crack due to changes, etc.
There are problems such as deformation and failure to maintain dimensional accuracy.

Therefore, the inventor of this invention went back to the origin once again and carefully examined the resin magnet roll before forming the notches. It was found that this caused the developer to remain adsorbed on the sleeve surface and not fall. Also,
It was found that the new different poles had a stronger magnetic force at both ends of the roll than at other parts.

Based on these facts, the inventor of the present invention demagnetized or demagnetized the magnetic force due to the new different polarity to reduce it as much as possible, and formed a groove at the end of the roll. It was discovered that almost the same effect as forming a notch can be obtained by
This invention was completed.

The main object of the present invention is to provide a magnetic brush magnet roll that is made of plastic magnets, has a wide non-magnetic zone, and has excellent resistance to temperature changes and aging.

(B) Structure of the Invention According to the present invention, there is provided a roll that is made of magnetic powder and a synthetic resin binder and has an integral structure of a plastic magnet having a plurality of magnetic poles around the periphery and a metal core, and the roll has an integral structure with a metal core. A demagnetizing groove is formed on the circumferential surface of the core and is parallel to the core body and is open at the end face, and the plastic magnet between the demagnetizing grooves at both ends is demagnetized or demagnetized. A magnet roll for a magnetic brush is provided.

One of the features of the structure of this invention is that instead of forming a notch over the entire length of the roll as in conventional rolls, local grooves for demagnetization are provided in a part of both ends of the roll. .

The cross-sectional shape of this demagnetizing groove is preferably U-shaped, but is not necessarily limited to this. In addition, the depth of this groove from the outer peripheral surface toward the core is approximately 1/3 to 2/3 times the thickness of the plastic magnet layer, and the width of the groove is at least equal to the magnetic flux of the adjacent same polarity. The length that reaches the area, and its depth is 1/4 to 1 of this groove width.
It has been experimentally confirmed that if the magnetic force is about twice as large, the magnetic force at the end of the roll can be demagnetized to a practical range.

The new demagnetization or demagnetization of the different polarities of the plastic magnet between the demagnetization grooves is performed by a known demagnetization or demagnetization device.

Known magnetic powders can be used as the magnetic powder in the above configuration, and specific examples thereof include barium ferrite, strontium ferrite, and lead ferrite.

Specific examples of the synthetic resin binder include thermosetting resins such as phenol resins, epoxy resins, and unsaturated polyester resins, thermoplastic resins such as polyamide resins, polyethylene resins, polyethylene terephthalate resins, ABS resins, and ethylene-vinyl acetate copolymers. Examples include resin.

The mixing ratio of the magnetic powder and the synthetic resin binder is 75 to 95% by weight of the magnetic powder and 25 to 5% by weight of the synthetic resin binder, and a plasticizer, a lubricant, and other additives are added as necessary.

Further, the roll of the present invention may be integrally formed with a synthetic resin cushion layer interposed between a plastic magnet layer made of magnetic powder and a synthetic resin binder and a metal core.

In this case, the synthetic resin of the cushion layer is a synthetic resin with a lower melting point than the synthetic resin binder, or a synthetic resin with greater ductility. It is sufficient if at least one of the conditions is satisfied, but it is even better if it has a low melting point and high ductility. As a specific example, if the synthetic resin binder is polypropylene, then polyethylene resin may be used for the cushion layer. If the synthetic resin binder is a polyamide resin, the cushion layer may be made of, for example, polyethylene resin, polypropylene resin, polyvinyl chloride resin, ABS resin or polystyrene resin.

The thickness of the cushion layer is preferably in the range of 0.1 mm to 10 mm, and 5 to 50% by weight, preferably 10 to 30% by weight of glass fiber may be mixed into the cushion layer.

The method for manufacturing the magnet roll for magnetic brushes of the present invention can be carried out by injection molding or extrusion molding a mixture of magnetic powder and synthetic resin binder onto the surface of a metal core. Alternatively, press molding or the like may be used.

When a roll having a cushion layer is formed, the cushion layer is first formed on the surface of a metal core, and then a plastic magnet is formed on the surface of the cushion layer. The cushion layer can be formed by injection molding on the surface of a metal core, extrusion molding on the surface of a metal core,
Any method may be used, such as forming a cushion layer singly in advance by extrusion molding or the like, and pressing or bonding the cushion layer and the metal core, but is not particularly limited.

Note that the magnet roll is magnetized simultaneously with the molding of the magnet layer by a magnetizing device provided in the molding die.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings. Note that this invention is not limited to this.

Reference numeral 1 shown in FIG. 1 is a magnet roll for a magnetic brush, and FIG. 2 shows a sectional view taken along line A--A. The metal core 5 has a diameter of 8 mm and a length of 273 mm.
Made of stainless steel. This shaft 5
was inserted into a mold capable of obtaining a product with an outer diameter of 22 mm and a length of 22 mm, and polypropylene mixed with 30% by weight of glass fiber was injection molded to form the cushion layer 4. Next, the shaft 5 with the cushion layer 4 formed thereon is inserted into a mold that yields a product with an outer diameter of 35.4 mm and a length of 220 mm, having grooves 2 and 2' for demagnetization on the outer peripheral surface at both ends. , barium ferrite 83
% by weight and 17% by weight of 6-nylon is injection molded to form the plastic magnet 3. In addition,
The demagnetizing grooves 2, 2' have a depth of 4 mm from the roll surface and a width at an angle centered on the roll core 5.
The angle is 60° and the depth is 20mm. By the way, the mold for the plastic magnet mentioned above is equipped with a magnetizing device, and a magnetic field is applied while the synthetic resin binder (6-nylon) is not solidified, so barium is absorbed in the magnetic field formed by the magnetic poles. The ferrite particles are oriented in the same direction and are anisotropic, and the plastic magnet 3 is magnetized at the same time as it is formed. Arrow N ₁ in Figure 1,
N ₂ indicates the magnetized part of the N pole by arrows S ₁ , S ₂ ,
S ₃ indicates the magnetized location of the S pole. _N1
is a main magnetic pole for development forming a magnetic brush, and the other magnetic poles are auxiliary magnetic poles for conveying the developer and adjusting the height of the ears of the magnetic brush. The non-magnetized zone for releasing the developer is provided between the widest S ₂ and S ₃ between the magnetic poles in the auxiliary pole, and the demagnetizing zone is provided at both ends of the center between these magnetized points. The grooves 2 and 2' are positioned in such a way that the grooves 2 and 2' are positioned. The magnetic brush magnet roll, which was magnetized at the same time as molding as described above, was taken out of the mold, and then a decompression coil was wound around the non-magnetized portion, that is, the center of magnetic poles S ₂ and S ₃ . A demagnetizing yoke (S-pole generation yoke) is attached, a predetermined half-wave pulse current is conducted to the demagnetizing coil, demagnetizing processing is performed, and the fabrication is completed.

This magnetic brush magnet roll has an outer diameter of 38mm and a thickness of
It is used by being inserted into a 0.5 mm aluminum cylindrical sleeve, and Fig. 3 shows an example of the results of actually measuring the magnetic flux density around the circumference on the surface of the sleeve. The solid line shows the magnetic flux density at the end of the magnet roll, and the broken line shows the magnetic flux density at the center.

In contrast, FIGS. 4 and 5 show the results of measuring the magnetic flux density on the sleeve of a magnet roll that was subjected to magnetic field forming as described above without providing the demagnetizing grooves 2 and 2'. There is. FIG. 4 shows the measurement results before the above demagnetization process, and FIG. 5 shows the measurement results after the demagnetization process.

As shown in Figure 4, in order to provide a non-magnetized zone between the magnetic poles S _{2 and} S ₃ , the distance between the poles _is set wide.
A part of the magnetic flux passes through and an apparent N pole N ₀ is generated, and the magnetic flux density of N ₀ also exceeds 100 Gauss at the center of the magnet roll and 250 Gauss at the ends. ing.

At N ₀ in Figure 5, the center of the magnet roll (dashed line)
A demagnetizing effect is seen at the edge (solid line)
is hardly demagnetized. this is,
The lines of magnetic force entering the end surface of the magnet roll from the end surface to the end surface cannot be reduced by the demagnetization treatment described above, and because the demagnetization grooves are not provided, these lines of force appear largely on the sleeve. It is.

In addition, since the magnetic flux at this end is demagnetized, even if a stronger reverse polarity magnetic field is applied during the demagnetization process, it will not have much effect on the magnetic flux from the end face of the magnet roll, and the center part of the magnet roll will be reversed. This results in the poles being over-magnetized. Therefore, it is not easy to provide a wide non-magnetized zone over the entire length of the magnet roll just by demagnetizing it.

However, it has been practically confirmed that in order to function as a non-magnetized zone, the magnetic flux density in that area must be 50 Gauss or less. In Figure 3, as seen between the magnetic poles S ₂ and S ₃ ,
It can be seen that N ₀ is demagnetized to 50 Gauss or less at both the center and end portions of the magnet roll, forming a practical non-magnetized zone. That is, FIG. 3 shows that the demagnetizing grooves provided at both ends of the magnet roll function effectively to prevent the magnetic flux from the end faces from exiting to the sleeve surface.

FIG. 6 is a graph showing the distribution of the magnetic flux density of N ₀ at the center of the magnetic poles S ₂ and S ₃ in FIG. 3 measured in the axial direction of the roll and corresponding to the length of the roll. Even with this, the magnetic flux density of the non-magnetized belt does not exceed 50 Gauss over the entire length of the roll, and the effect of the demagnetizing grooves is particularly noticeable at both ends.

(c) Effects According to the present invention, local demagnetizing grooves are formed at both ends of the magnet roll, and the magnets between the grooves are demagnetized or demagnetized. A practically sufficient non-magnetized zone can be obtained, and developer with reduced toner concentration can be more reliably removed. Moreover, a magnetic brush magnet roll having excellent resistance to temperature changes and aging can be obtained.

[Brief explanation of drawings]

FIG. 1 is a side view showing one embodiment of the present invention, FIG. 2 is a sectional view of FIG. 1, FIG. 3 is a graph showing the magnetic flux density of one embodiment of the present invention, and FIG.
5 is a graph showing the magnetic flux density of a magnet roll without a groove for demagnetization, and FIG. 6 is a graph showing the magnetic flux density in the axial direction of an embodiment according to the present invention. 1... Magnet roll for magnetic brush, 2, 2'...
Concave groove for demagnetization, 3...Plastic magnet, 4...Cushion layer, 5...Metal core.

Claims (1)

[Scope of Claims] 1. A roll that is made of magnetic powder and a synthetic resin binder and has an integral structure of a plastic magnet having a plurality of magnetic poles around the periphery and a metal core, which A demagnetizing groove is formed parallel to the core body and opened at the end face, and the plastic magnet between the demagnetizing grooves at both ends is demagnetized or demagnetized. Magnet roll for magnetic brushes. 2. The magnet roll for a magnetic brush according to claim 1, wherein a demagnetizing groove is formed in the center between adjacent magnetic poles of the same polarity. 3. Claims in which the roll is made of magnetic powder and a synthetic resin binder and is integrally formed between a plastic magnet having a plurality of magnetic poles around the periphery and a metal core with a synthetic resin cushion layer interposed therebetween. The magnet roll for a magnetic brush according to item 1 or 2. 4. The demagnetizing groove is a U-shaped groove, and (i) the depth from the outer peripheral surface toward the core is 1/3 to 2/3 times the thickness of the plastic magnet layer, and (ii) ) The groove width is long enough to reach at least adjacent magnetic flux regions of the same polarity, and (iii) the depth is 1/4 to 1 times the groove width. A magnet roll for a magnetic brush according to any one of the items.