JPH10221957A - Magnet roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain reduction in cost and the sure application of a bias voltage by providing a specific cylindrical ferrite magnet and a specific coating layer formed on the surface of the ferrite magnet with vapor deposition plating. SOLUTION: A developing roll 4 is provided with the cylindrical ferrite magnet 6 constituted so that magnetic poles being different from each other in polarity are arranged on the surface supported by a conductive shaft 5, at regular intervals in a circumferential direction, the pitch between the magnetic poles is 1-3mm and a surface magnetic flux density is within the range of 200-700G. Then, the developing roll 4 is provided with a conductive covering layer which is formed on the surface of the ferrite magnet 6 by the vapor deposition plating, consists essentially of a nonmagnetic metal or its alloy or compound and has a thickness of 0.5-5μm and a volume resistivity of <=10<5> Ω.cm. Since the surface of the ferrite magnet 6 has the vapor deposition plating in the above-mentioned manner, a covering layer having conductivity can be comparatively easily formed on the surface of a magnet. Thus, a prescribed bias voltage can be stably applied to a magnetic developer attracted to the surface of the magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnet roll used for developing an electrostatic image formed on the surface of an image carrier.

[0002]

2. Description of the Related Art In an image forming method utilizing electrophotography or electrostatic recording, an electrostatic charge image formed on a surface of an image carrier made of a photoconductor or a dielectric is transferred to a toner held on a developing roll. Development is performed using a magnetic brush formed of a magnetic developer containing, and a final image is obtained by transferring and fixing the obtained toner image onto plain paper or another transfer member.

[0003] The developing roll includes a developer supporting member or sleeve formed of a non-magnetic material, and a permanent magnet member (a permanent magnet with a shaft) having a plurality of magnetic poles on its surface disposed therein. And a sleeve is disposed opposite to the surface of the image carrier at a predetermined distance so as to form a development area between the sleeve and the surface of the image carrier. Due to the relative rotation of the sleeve and the permanent magnet member, the magnetic developer held on the sleeve is transported to the developing area, and the toner contained in the magnetic developer adheres to the electrostatic image to obtain a toner image.

On the other hand, in an electrophotographic apparatus represented by a copying machine or a printer, it is desired to reduce the price and size of the apparatus, and the structure of a developing roll has been changed to meet this demand. For example, the sleeve constituting the developing roll is omitted,
It has been proposed that a magnetic developer is directly adsorbed on the surface of a permanent magnet member and the magnetic developer is conveyed to a development area by rotation of the permanent magnet member (for example, Japanese Patent Application Laid-Open No. 62-20146).
No. 3).

[0005]

When an electrostatic image is developed by holding a magnetic developer on a magnet roll, a bias voltage is applied to the developer to prevent background fog or to perform reversal development. Is done. In the sleeved magnet roll, since the sleeve is formed of a conductor such as aluminum alloy or stainless steel, a bias voltage can be applied to the developer by applying a bias voltage to the sleeve.

On the other hand, a sleeveless type magnet roll has a structure in which a shaft is fixed to, for example, a cylindrical ferrite magnet, and this ferrite magnet has a resistance of 10 ⁸ to 10 ⁹ Ω.
Since it has a volume resistivity of about cm, the effective bias voltage applied to the magnetic developer held on the surface of the ferrite magnet is extremely small even if the shaft is formed of a conductor and connected to a bias voltage source.

Therefore, it has been proposed to form a conductor layer by plating the surface of a cylindrical ferrite magnet. However, in the prior art, the process of forming the conductor layer is complicated or the conductor layer and the ferrite are not formed. There is a problem that the adhesion to the magnet is not sufficient.

Accordingly, an object of the present invention is to provide a sleeveless type magnet roll which is inexpensive and in which the conductive layer is hard to peel off.

[0009]

In order to achieve the above object, according to the present invention, a conductive shaft and magnetic poles having different polarities are provided at equal intervals along a circumferential direction on a surface supported by the conductive shaft. A cylindrical ferrite magnet arranged and having a magnetic pole pitch of 1 to 3 mm and a surface magnetic flux density in a range of 200 to 700 G, and a nonmagnetic metal, an alloy thereof, or a nonmagnetic metal formed on the surface of the cylindrical ferrite magnet by vapor deposition plating The technical means of using the compound as a main component and having a conductive coating layer having a thickness of 0.5 to ⁵ μm and a volume resistivity of 10 ⁵ Ω · cm or less was employed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a developing device provided with a magnet roll according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of AA in FIG. 1, and FIG. 1 and 2
The developing device 1 includes a developer tank 3 containing a magnetic developer 2 composed of a magnetic carrier and a toner, and a developing roll 4.
And The developing rolls 4 are arranged at equal intervals so that a conductive shaft 5 made of, for example, a metal material and N poles and S poles fixed to the shaft 5 alternately appear on the surface along the circumferential direction. A cylindrical ferrite magnet 6 having a plurality of magnetic poles; and a coating layer 7 formed by vapor deposition plating on the surface of the ferrite magnet 6 and having a thickness of 0.5 to ⁵ μm and a volume resistivity of 10 ⁵ Ω · cm or less. And

The developing roll 4 has both ends of a shaft 5 supported by a pair of side plates 8 via bearings 9, and the shaft 5 is connected to a bias voltage source 10. The developing roll 4 faces the photosensitive drum 20 rotating in the direction of the arrow Z, and a developing area is formed between the two. Photoconductor drum 2
0 has a conductive substrate 20a and a photoconductive layer 20b. A doctor member 11 for regulating the thickness of the magnetic developer 2 adsorbed on the surface of the developing roll 4 is mounted on the developer tank 3.

With the above configuration, when the developing roll 4 is rotated, for example, in the direction of arrow X, the magnetic developer 2 in the developer tank 3 is attracted to the surface of the developing roll 4 to form a magnetic brush. Conveyed in the same direction. The magnetic brush passes through a doctor gap (a gap between the distal end of the doctor member and the developing roll) and is conveyed to a developing area, and after passing through a developing gap (a gap between the photosensitive drum and the developing roll at the closest position). The developer is collected in the developer tank 3. Here, in the development area, toner charged to a predetermined polarity due to contact with a doctor blade or a carrier adheres to the electrostatic image to perform development.

Details of each part of the developing roll 4 are as follows. The cylindrical ferrite magnet 6 is obtained by hydrostatically pressing a raw material obtained by dry mixing ferrite particles [MO · nFe ₂ O ₃ (M = Ba, Sr, Pb, at least one, n = 5 to 6)] and a binder such as PVA. It is formed by forming into a cylindrical shape with a press and processing after sintering. As another method, a raw material obtained by sufficiently mixing ferrite particles, water and alcohol may be extruded from a mold, formed into a hollow cylinder, cut into a predetermined length, dried, and then sintered. After sintering, the ferrite magnet is finished to a predetermined length in the axial direction, and then machined (for example, centerless ground) on the outer peripheral surface to be finished to a predetermined size. The surface of the ferrite magnet is
The surface is processed to have a surface roughness of 5 to 30 μm [ten-point average roughness (Rz) defined in JIS B 0601].

The shaft 5 is fixed to the inner diameter of the cylindrical ferrite magnet 6, and a coating layer 7 is formed on the surface thereof in accordance with the following procedure. That is, the ferrite magnet is degreased with a neutral detergent, trichlene, fluon or the like, etched with an inorganic acid mixed solution in order to enhance the adhesion, then neutralized with 5% caustic soda, and subjected to vapor deposition plating by the apparatus shown in FIG. That is, the cylindrical ferrite magnet is vacuum-evaporated
After setting the degree of vacuum to about 2 × 10 ⁻⁴ mm / Hg by a vacuum pump (not shown),
By applying a DC voltage of, for example, 200 V to the filament 32 via 1, the plating material 33 is heated and evaporated, and steam is applied to the magnet surface to attach the plating. Here, plating is performed in a vacuum because, when the metal is heated in air or another gas, the metal is oxidized or combined with the gas, and even when an inert gas is used, the vapor of the metal is released. This is because it becomes difficult or becomes granular. As the metal, Al, Ni, Cu, Ag, or the like can be used, but Al is most advantageous in terms of cost.

The thickness of the plating layer that can be formed by one evaporation plating is as thin as about 0.1 μm. If the thickness of the coating layer is too thick, the number of evaporation plating increases and the cost increases. The thickness of the coating layer is preferably 5 μm or less (preferably 3 μm or less). However, if the thickness of the coating layer is too thin, it is likely to peel off during use or the magnet surface will be partially exposed, so that the thickness is preferably 0.5 μm or more (preferably 1 μm or more).

Finally, the surface of the developing roll is subjected to multipolar magnetization to obtain the magnet roll of the present invention. The magnet roll preferably has a magnetic pole pitch (P) of 1 to 3 mm and a surface magnetic flux density (Bo) of 200 to 700G.
That is, if P is less than 1 mm, Bo is reduced and the magnetic brush formed on the roll surface is reduced, so that ground fog is easily generated and the image density is reduced. P is 3m
If m exceeds m, the developer thickness between the magnetic poles and on the magnetic poles becomes extremely different, and image density unevenness tends to occur. Also Bo
If Bo is less than 200 G, the developer tends to be scattered from the developing roll, and if Bo exceeds 700 G, the developability decreases.

The magnetic developer used in the present invention may contain only a magnetic toner or may contain a magnetic toner or a non-magnetic toner and a magnetic carrier. The toner has an average particle diameter of 5 to 10 μm (preferably 6 μm).
-9 μm), a volume resistivity of 10 ¹⁴ Ω · cm / or more, and a triboelectric charge of 5 μc / g or more in absolute value. The toner composition contains a binder resin and a colorant as essential components, and contains (internally and / or externally) magnetic powder, a charge control agent, a release agent, and a fluidizing agent as optional components. it can.

As the magnetic carrier, magnetic particles such as iron powder, soft ferrite or magnetite may be used as they are, particles having at least a part of their surface coated with a resin, or binder-type particles in which the magnetic powder is dispersed in the resin. Can be used. The carrier has an average particle size of 1
0 to 70 μm, volume resistivity is 10 ³ to 10 ¹³ Ω · c
m, those having a saturation magnetization of 20 emu / g or more are preferable.

The measuring methods of the above various physical properties are as follows. The average particle size (based on volume) of the toner is measured using a commercially available particle size analyzer (Coulter Counter Model TA-II manufactured by Coulter Electronics Co., Ltd.).
The value of the volume resistivity was determined by weighing an appropriate amount of the sample (several ten mg), filling it into a Teflon (registered trademark) cylinder with an inner diameter of 3.05 mm and an improved dial gauge,
Under the load of D. An electric field of C4 KV / cm is applied. C100 V / cm electric field was applied, and 4329 manufactured by Yokogawa Hewlett-Packard Company was applied.
It was measured using an A-type insulation resistance meter. The triboelectric charge amount is determined by mixing a standard carrier (KBN-100 manufactured by Hitachi Metals) and a toner (toner concentration: 5% by weight), blowing the toner at a blowing pressure of 1.0 kg · f / cm, and charging the blow-off powder. Quantity measuring device (TB-20 manufactured by Toshiba Chemical Corporation)
0).

When developing the electrostatic charge image by supplying the above magnetic developer onto the magnet roll of the present invention, it is desirable to carry out development under the following conditions. Magnet roll (peripheral speed:
The direction of rotation (V ₂ mm / sec) may be either the same direction (with mode) as the image carrier (peripheral speed: V ₁ mm / sec) or the opposite direction (counter mode) in the developing area, but the image quality is poor. setting the speed ratio (V ₂ / V ₁₎ as follows from desirable. V in the mode
₂ / V ₁ is preferably in the range of ₁ to 3. If V ₂ / V ₁ is less than ₁ , the image density is reduced, and if V ₂ / V ₁ is more than 3, density unevenness becomes conspicuous. The most preferable condition is V ₂ /
V ₁ = 1 to 2.5, g ₁ (doctor gap) = g
₂ (development gap). Under this condition, the image density is high, and fog and density unevenness hardly occur. In the counter mode, if V ₂ / V ₁ is 1 or more, density unevenness does not occur, but 3 or more is preferable from the viewpoint of image density. However, since ground fog is likely to occur with the V ₂ / V ₁ is large, V ₂
/ V ₁ is preferably 5 or less.

Next, the developing gap (g ₂ ) is set in accordance with the surface potential of the image carrier, its moving speed (process speed), and the like, and is preferably in the range of 0.15 to 0.4 mm. If the developing gap is too narrow, the contact state between the magnetic brush and the image carrier changes even with a slight deflection of the magnet roll,
If image unevenness is likely to occur and the developing gap is too wide,
High image density cannot be obtained. Doctor gap (g
₁ ) is set to be equal to the developing gap (g ₂ ), but it is necessary to consider the height of the magnetic brush, and normally, g ₁ = g ₂
What is necessary is just to make it fall within the range of ± 0.1 mm.

[0022]

Next, the present invention will be described in more detail with reference to the following examples. A shaft made of SUS303 is fixed to an isotropic ferrite magnet (YBM-3 manufactured by Hitachi Metals) having an outer diameter of 20 mm, a length of 214 mm, and a surface roughness of about Rz = 15 μm, and thereafter, a coating layer is formed by performing Al vapor deposition plating according to the above process. Then, a magnet roll of Bo = 450 G was produced by performing 16-pole symmetrical magnetization. Here, the thickness (t) of the coating layer
Different types of magnet rolls (roll A: t =
0.3 μm, Roll B: t = 1.4 μm, Roll C: t
= 2.0 μm, Roll D: t = 3.0 μm, Roll E:
t = 5 μm).

The magnetic developer includes an iron powder carrier (average particle size (weight basis) 50 μm, volume specific resistance 10 ⁷ Ω · cm, σs 190 emu / g) coated with a silicone resin and toner (volume average particle size 9 μm, volume specific Resistance 10 ¹⁵ Ω · cm,
And triboelectric charge amount of −22 μc / g) in a weight ratio of 60:40. This toner is styrene-n
85 parts by weight of a butyl methacrylate copolymer (Mw: about 200,000, Mn: about 16,000), 10 parts by weight of carbon black (Mitsubishi Kasei's # 55) and 3 parts by weight of polypropylene (TP-32 from Sanyo Chemical) 2 parts by weight of a charge control agent (Bontron S34 manufactured by Orient Chemical Co., Ltd.) are dry-mixed, heated and kneaded, cooled and solidified, pulverized and classified, and then 0.5 parts by weight of hydrophobic silica (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) is added to the surface. Was added.

The above-mentioned magnet roll was incorporated in the developing device shown in FIG. 1, and the above-mentioned developer was charged into the developing device to perform development under the following conditions. OPC photoreceptor (peripheral speed 60m
m / sec) electrostatic latent image on the surface (surface potential -600 V)
Is formed, the developing gap is set to 0.4 mm, the doctor gap is set to 0.3 mm, and the magnet roll is set to 120 m.
Rotate at a peripheral speed of m / sec and put -45 on the magnet roll.
Reversal development was performed by applying a DC voltage of 0V.

The resulting images were of good quality with all magnet rolls having an image density of 1.35 to 1.40, little background fog, and no dust or uneven fine line width.
In the image after continuous copying of 100,000 sheets, rolls B to E were good, but in roll A, the plating layer was partially peeled off, and whitening was recognized. Also, the roll E is somewhat disadvantageous in cost.

[0026]

According to the present invention, a conductive coating layer is formed on the surface of a ferrite magnet relatively easily by directly depositing a plating on the surface of the ferrite magnet. A predetermined bias voltage can be stably applied to the agent.

[Brief description of the drawings]

FIG. 1 is a sectional view of a developing device provided with a magnet roll according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view showing a vacuum evaporation apparatus.

[Explanation of symbols]

Reference Signs List 1 magnet roll, 5 shaft, 6 ferrite magnet, 7 coating layer, 10 bias voltage source

Claims (1)

[Claims] An electroconductive shaft and magnetic poles of different polarities supported on the electroconductive shaft are arranged on the surface at equal intervals in the circumferential direction, the pitch between the magnetic poles is 1 to 3 mm, and the surface magnetic flux density is 200 to 200 mm. A cylindrical ferrite magnet in the range of 700G, and a non-magnetic metal, its alloy or its compound mainly formed by vapor deposition plating on the surface of the ferrite magnet, having a thickness of 0.5 to 5 µm and a volume resistivity. Is 10 ⁵
A magnet layer having a coating layer of Ω · cm or less.