JPH0990761A - Magnet roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnet roll in which a magnetic flux density distribution having plural peaks can be easily formed at a developing magnetic pole portion. SOLUTION: A magnetic roll is equipped with a sleeve 1 and a cylindrical permanent magnet member 4 which has plural magnetic poles including a developing magnetic pole disposed therein. The developing magnetic pole has two peaks the magnetic flux density of which is 800G or more on the sleeve 1, and has such a magnetic flux density distribution that difference between the average value of the peak values and a valley value stays in the range of 45 to 80% of the average value of the peak values and the angles of the peak values stay in the range of 10 to 35 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet roll that constitutes a developing section in an electrophotographic device, an electrostatic recording device or the like.

[0002]

2. Description of the Related Art In an electrophotographic apparatus or an electrostatic recording apparatus, an electrostatic latent image formed on the surface of an image carrier (photoreceptor or dielectric) is developed and the resulting toner image is directly fixed or The final image is obtained by transferring and fixing the toner image onto a transfer member such as plain paper. A developing device used in this type of device includes a sleeve made of a non-magnetic material for holding a magnetic developer (hereinafter simply referred to as a sleeve), and a permanent magnet body having a plurality of magnetic poles arranged inside the sleeve. A magnetic brush developing device provided with a magnet roll having the above is widely used. The magnetic developer includes, for example, a one-component magnetic toner or magnetic carrier (iron powder, soft ferrite powder, etc.) consisting of a binder resin and toner particles containing ferromagnetic powder as an essential component, a binder resin and a colorant. A two-component developer, which is a powder powder mixed with toner particles (magnetic or non-magnetic), is generally used.

In the above magnetic brush developing device,
As a developer conveying method, a method of fixing a permanent magnet member so that one magnetic pole faces the image carrier and rotating a sleeve is often adopted. This is because the structure of the developing device is simple, the carrying force of the developer is strong, and since the magnetic poles are stationary, uneven development due to the magnetic pole pitch does not occur. On the other hand, in the sleeve rotation type developing device, the spikes of the developer on the sleeve are more easily affected by the value of the magnetic flux density on the sleeve and its distribution as compared with the case where the magnet is rotated, and variations in the magnetic flux density and Even if the magnetic flux density distribution is slightly disturbed, the image quality may be significantly reduced. Therefore, conventionally, the image quality is improved by setting the optimum magnetic flux density distribution in consideration of the developing conditions.

For example, Japanese Patent Publication No. 62-55149 discloses
A magnet disposed in the sleeve, a magnetic pole portion at a position facing the image carrier, at least one depression is formed in the magnetic pole surface,
It is described that the magnetic roll is configured so that the magnetic pole portion generates a magnetic field strength distribution having a plurality of peaks.

FIG. 5 shows a specific structure of this magnet roll.
This will be described below. In FIG. 5, reference numeral 1 denotes a sleeve made of a non-magnetic material, in which a permanent magnet member 4 having a cylindrical permanent magnet 2 (for example, an isotropic sintered ferrite magnet) and a shaft 3 supporting the same is arranged. Has been done. A concave groove 21 is provided along the axial direction at a portion of the permanent magnet 2 facing the developing pole, and in the concave groove 21, a magnet piece 23 having a concave portion 22 along the longitudinal direction on the outer surface (for example, anisotropic). Sintered ferrite magnet) is fixed. According to this magnet roll, since the magnet piece is provided with the concave portion, a magnetic flux density distribution having two peaks as shown by a solid line in the drawing is formed in the developing magnetic pole portion. When the magnetic flux density distribution as described above is formed in the developing magnetic pole portion, the contact width of the magnetic brush with the image carrier is widened, thereby improving the developing efficiency and preventing uneven development and bleeding, especially at high speed. It is advantageous for development.

[0006]

In the magnet roll having the above structure, in order to form the magnet piece 23, it is necessary to form the recess 22 in the block magnet made of, for example, an anisotropic sintered ferrite magnet by machining. . However, since such a sintered magnet material is hard, the recess 2
There is a problem that it takes a long time for the machining of item 2. Further, when the magnet piece 23 is fixed to the concave groove 21 of the permanent magnet 2, a positional deviation may occur due to a dimensional error between the two.

On the other hand, when the magnet piece 23 is formed of a resin magnet material, for example, by extrusion molding or injection molding,
It is possible to form the concave portion 22 during the molding of the magnet piece, and there is an advantage that the number of manufacturing steps can be reduced as compared with the case where the concave portion 22 is formed of the sintered magnet material. However, since the magnet piece made of the resin magnet material has a lower magnetic force than that made of the sintered magnet material, the magnet piece 23 must be made large in order to obtain the magnetic force required for the developing magnetic pole. There is a problem that it is difficult to apply to a magnet roll having a diameter.

Therefore, an object of the present invention is to solve the problems existing in the prior art and to provide a magnet roll capable of easily forming a magnetic flux density distribution having a plurality of peaks in the developing magnetic pole portion.

[0009]

In order to achieve the above object, the present invention provides a cylindrical permanent magnet having a sleeve made of a non-magnetic material and a plurality of magnetic poles including a developing magnetic pole arranged in the sleeve. In a magnet roll having a member, the developing magnetic pole has two peaks having a magnetic flux density of 800 G or more on the sleeve, and a difference between an average value of the peak values and a valley value therebetween is the peak. The technical means was adopted that the magnetic flux density distribution is in the range of more than 45% and less than 80% of the average value and the magnetic pole angle between the peaks is in the range of 10 to 35 °. In the above invention, it is desirable that the developing magnetic pole and the other magnetic pole are formed at the same time.

With the above construction, that is, the developing magnetic pole has a difference between the two peak values of the same polarity and the value of the valley between them in a specific range, so that the soft magnetic brush is not accompanied by defective conveyance of the developer. It is possible to form a developing pole having a large peak value because the peak position is within a specific range while improving the reproducibility of halftone and preventing fog. .

[0011]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a magnet roll according to an embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIG. In FIG. 1, reference numeral 1 denotes a cylindrical sleeve made of a non-magnetic material such as aluminum alloy or austenitic stainless steel, and a permanent magnet member having a cylindrical permanent magnet 2 and a shaft 3 supporting the cylindrical permanent magnet 2 therein. 4 are arranged. A plurality of magnetic poles including developing magnetic poles (indicated by N ₁ and N ₂ in the drawing) are provided on the surface of the cylindrical permanent magnet 2. The permanent magnet 2 is, for example, one or more of ferrite powder [M: Ba, Sr, Pb,
n = 5-6)] is formed into a cylindrical shape by a rubber press or extrusion molding method, and after sintering, the outer peripheral surface is subjected to grinding processing (Japanese Patent Publication No. 55-6).
907). Alternatively, a mixture composed mainly of a ferromagnetic powder (the above-mentioned ferrite powder or rare earth magnet powder) and a resin is heated and kneaded, and then molded in a mold having a cylindrical molding space (for example, injection molding, extrusion molding). Or compression molding), and the surface of the molded body is magnetized in the same manner as described above. The resin magnet is not limited to the one molded in a cylindrical shape, but a plurality of magnet pieces (for example, a fan shape) may be prepared, and these may be bonded in a cylindrical shape around the shaft. Alternatively, the entire permanent magnet member 4 may be made of a permanent magnet material (that is, the shaft may be made of a permanent magnet).

The cylindrical permanent magnet shown in FIG.
It is magnetized by setting it in the magnetizing yoke shown in. In FIG. 2, reference numeral 10 denotes a magnetizing yoke, which is formed of a ferromagnetic material such as soft iron into a hollow cylindrical shape, and has protrusions 11 ₁ to 11 ₁ to at portions corresponding to the magnetic poles of the cylindrical permanent magnet 2.
A plurality of grooves 1 along the axial direction to form 11 ₅
2 _{1 to} 12 ₄ are provided. Magnetizing coils 13 _{1 to} 13 ₅ are wound around these grooves so as to surround each protruding portion. In particular, a spacer 14 made of a magnetic material is provided between the magnetizing coils 13 ₁ and 13 ₂ facing the developing magnetic pole. According to the above-mentioned magnetizing yoke, the magnetizing coil is connected to a capacitor-type magnetizing power source (not shown), and a direct current voltage of several hundred volts is instantaneously applied to the magnetizing coil so that the developing magnetic poles have the same polarity. It is possible to have a magnetic flux density distribution having two peaks.

FIG. 3 is a diagram showing the magnetic flux density distribution in the radial direction of the developing magnetic pole portion in the magnet roll of the present invention.
In FIG. 3, the peak values of the magnetic flux density are B ₁ (G), B
₂ (G), the valley value is B ₃ (G), and the amount of depression is ΔB [=
((B ₁ + B ₂ ) / 2) −B ₃ ], and the angle between B ₁ and B ₂ (the magnetic pole angle between peaks) is θ, B ₁ and B ₂ are 800
G (more preferably 900 G) or more, and ΔB is greater than 45% of (B ₁ + B ₂ ) / 2 (= B ₄ ) and 80
% Or less, and θ is required to be in the range of 10 to 35 °. △ B is (B ₁ + B ₂ ) / 2 45
% Is less than 80% of (B ₁ + B ₂ ) / 2 because the soft magnetic brush is hard to be formed on the sleeve, the halftone reproducibility is not improved, and the background fog increases. If it becomes large, the developer may not be conveyed properly on the sleeve, and good development cannot be performed in any case. The preferable range of the above ratio is 55 to 75%. θ is 10
If it is smaller than 50 °, it will be difficult to form a winding on the magnetizing yoke. On the other hand, if θ is larger than 35 °, the values of B ₁ and B ₂ will be low, and high image density cannot be obtained. In addition, the preferable range of (theta) is 20-35 degrees.

FIG. 4 shows an example of a developing device using the magnet roll of the present invention. In FIG. 4, reference numeral 5 denotes a developing device, which is arranged close to the photosensitive drum 6 rotating in the direction of the arrow in the drawing, and has a magnet roll 20 having a sleeve 1 and a permanent magnet member 4 provided therein. A developer container 8 for containing the magnetic developer 7 and a doctor member 9 for regulating the thickness of the developer adsorbed on the sleeve 1 are provided. The developing magnetic poles (N ₁ , N ₂ ) are provided such that their centers are located on a line connecting the center a of the photosensitive drum 6 and the center b of the magnet roll. According to the above-described developing device, the magnetic developer 7 adsorbed on the sleeve 1 is formed at the closest position between the sleeve 1 and the photosensitive drum 7 and in the vicinity thereof by rotating the sleeve 1 in the direction of the arrow in the figure. The electrostatic latent image (not shown) is developed by being conveyed to the developed area and the surface of the photosensitive drum 7 being rubbed by the magnetic brush formed in the developing area.

[0015]

Next, the present invention will be described more specifically with reference to examples. In FIG. 4, the surface of a drum (outer diameter 30 mm) having an opc photoconductor rotating at a peripheral speed of 180 mm / sec was uniformly charged to -500 V and then exposed to form an electrostatic latent image. Then, the developing gap is set to 0.6 mm, the doctor gap is set to 0.5 mm, and the SUS 304 sleeve 1 to which a DC bias voltage of -450 V is applied is rotated at 260 rpm to develop the electrostatic latent image, and the toner is developed. The final image was obtained by corona transferring the image onto plain paper and hot roll fixing. The magnetic developer is 85 parts by weight of a styrene-acrylic copolymer (Mn = 210,000, Mn = 14,000).
10 parts by weight of carbon black (# 50 manufactured by Mitsubishi Kasei),
Charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) 2
Parts by weight and polypropylene (TP32 manufactured by Sanyo Chemical Co., Ltd.) 3
Toner (volume average particle size 10 μm) in which 0.5 part by weight of hydrophobic silica (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) is added to the surface of toner particles consisting of parts by weight and ferrite carrier (KBN100 manufactured by Hitachi Metals, average particle size 50 μm)
Was used so that the toner concentration was 3.5% by weight.

As the permanent magnet member, the magnetizing yoke shown in FIG. 2 was used, and the magnetizing conditions were changed to prepare seven kinds of members having different magnetic flux density distributions. Table 1 shows the image evaluation results when each permanent magnet member was used. The image densities in the table are the values measured by a Macbeth densitometer, and the background fog is the value measured by the color difference meter between the whiteness before and after passing the white paper. Is 0.2 or less, there is no practical problem.

[0017]

[Table 1]

From Table 1 it can be seen that high quality images are obtained with the magnet rolls (Examples 1 to 4) having a magnetic flux density distribution according to the present invention. However, when the amount of drop is small (Examples 5 to 7), a good quality image cannot be obtained. It was confirmed that when the amount of drop (ΔB) was extremely large, the developer was not conveyed properly, resulting in an image with a lot of unevenness.

[0019]

As described above, according to the present invention, it is possible to form a magnetic flux density distribution having a plurality of peaks of the same polarity on a developing magnetic pole without forming a concave portion, and a specific peak value and a peak. Since the angle is between, a high quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a magnet roll according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a magnetizing yoke used for manufacturing the magnet roll of the present invention.

FIG. 3 is a diagram showing a magnetic flux density distribution of a developing magnetic pole in FIG.

FIG. 4 is a sectional view showing an example of a developing device having a magnet roll of the present invention.

FIG. 5 is a sectional view of a conventional magnet roll.

[Explanation of symbols]

1 sleeve, 2 cylindrical permanent magnet, 3 shaft, 4 permanent magnet member

Claims (3)

[Claims] 1. A magnet roll having a sleeve made of a non-magnetic material and a cylindrical permanent magnet member having a plurality of magnetic poles arranged in the sleeve, the developing magnetic pole being on the sleeve. A magnetic flux density at 800 G or more has two peaks, and the difference between the average value of the peak values and the value of the valley between them is greater than 45% and not more than 80% of the average value of the peak values. And a magnetic flux density distribution in which the magnetic pole angle between the peaks is in the range of 10 to 35 °. 2. The magnet roll according to claim 1, wherein the magnetic poles are formed at the same time. 3. The magnet roll according to claim 1, wherein the cylindrical permanent magnet material is an isotropic ferrite magnet.