JPH07319282A - Magnet roll - Google Patents

Abstract

PURPOSE:To secure the width of a magnetic brush in a circumferential direction, to increase the drop amount of flux density between peaks in flux density distribution and to improve the reproducibility of halftone by forming the flux density distribution having plural peaks in the same polarity in a magnet piece constituting a developing pale. CONSTITUTION:A recessed groove 5 extended in an axial direction is provided at the specified magnetic pole part of a permanent magnet member 1 formed to be extended in the axial direction on an outer peripheral surface so that plural magnetic poles may appear in the circumferential direction, and the magnet piece 4 formed so that the flux density distribution having plural peaks in the same polarity may appear is fixed in the recessed groove, whereby the developing pole is constituted. The recessed part 6 in the longitudinal direction of the magnet piece 4 is provided in the center part of the circumferential direction of the outer periphery of the magnet piece 4 and a magnet piece 7 is fixed in the recessed part. Or the outer peripheral surface of the magnet piece 7 and the outer peripheral surface of the permanent magnet 1 are formed to be the same surface in substance. Or the outer peripheral surface of the magnet piece 7 is projected further than the outer peripheral surface of the permanent magnet 1. Furthermore, the magnet member 1 and the magnet piece 7 are formed of an isotropic or anisotropic permanent magnet.

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 as a developing roll in electrophotography, electrostatic recording, etc., and has a plurality of magnetic poles extending in the axial direction on the outer peripheral surface and circumferentially. The present invention relates to a magnet roll configured such that a specific magnetic pole of a permanent magnet member formed so as to appear as a developing pole and a magnetic flux density distribution having a plurality of peaks of the same polarity appear at the developing pole.

[0002]

2. Description of the Related Art Conventionally, as a magnet roll used for a developing roll in electrophotography, electrostatic recording, etc., a magnet roll having a structure as shown in FIG. Figure 4
In the above, the permanent magnet member 1 is integrally formed into a cylindrical shape by using a sintered powder magnet material such as hard ferrite or a material composed of a mixture of a ferromagnetic powder material and a binding material. Magnetic poles S ₁ , S ₂ , N ₁ , N ₂ , N ₃ extending in the axial direction are provided on the outer peripheral surface of the permanent magnet member 1, and these are arranged at equal or unequal intervals in the circumferential direction. The permanent magnet member 1 is often formed to have an outer diameter of 14 mm to 50 mm and a length of 100 mm to 650 mm. A shaft 2 is coaxially fixed to the center of the permanent magnet member, and support members are rotatably mounted on both ends of the shaft 2 via bearings (none of which is shown). The support member is a hollow cylinder. The sleeve 3 formed in a shape is fitted.

With the above structure, for example, a specific magnetic pole (for example, N ₂ pole) of the permanent magnet member 1 is fixed so as to be opposed to the electrostatic image carrier, and the sleeve 3 is rotated so that the permanent magnet member 1 has a magnetic property. A developer having magnetism is adsorbed and conveyed to the outer peripheral surface of the sleeve 3 by a suction force to form a magnetic brush (not shown), and a predetermined developing operation is performed.

On the other hand, it is effective to increase the contact width in the circumferential direction between the magnetic brush and the surface of the electrostatic image carrier in order to improve the developing efficiency in the above-mentioned developing work. There is a proposal of forming at least one recess on the magnetic pole surface of the magnetic pole portion of the permanent magnet member 1 forming the magnetic pole portion on the side facing the electrostatic charge image carrier.
(See Japanese Patent Publication No. 62-55149) FIG. 3 is an explanatory view showing an example of the magnet roll according to the above proposal. (A) is a cross-section of a main part, (b) is a circumferential direction generated by a magnet piece in (a). Shows the magnetic flux density distribution of
(C) is an enlarged view of the portion A of the magnetic flux density distribution of (b), and the same portions are denoted by the same reference numerals as those in FIG. Figure 3 (a)
In, the concave groove 5 is provided along the axial direction at a position corresponding to the developing pole. Next, the magnet piece 4 is formed in a block shape from, for example, an anisotropic ferrite sintered magnet material, and a concave portion 6 is provided on the outer peripheral surface along the longitudinal direction, and is fixed in the concave groove 5 with an adhesive, for example. It Next, in FIG. 3B, the horizontal axis represents the position in the circumferential direction, and the vertical axis represents the magnetic flux density. That is, as shown in FIG. 3A, the recess 6 is formed in the magnet piece 4.
By providing the magnetic flux density distribution as shown in FIG. 3 (b), two magnetic flux density distributions (P _3a , P _3b ) are formed, and the magnetic flux density distribution is formed by a magnetic field rather than the conventional one. The contact width of the magnetic brush in the circumferential direction with respect to the electrostatic image carrier can be increased. As a result, it is said that development efficiency can be improved and development unevenness and bleeding can be prevented.

[0005]

The use of the magnet roll having the above structure is expected to improve the developing efficiency.
On the other hand, there is a problem that the reproducibility of halftone is not good. It is considered that this is due to the small amount of drop in the magnetic flux density between the peaks of the magnetic flux density distribution. That is, the amount of depression d ₃ in FIG. 3B is small. The drop amount d ₃ of the magnetic flux density can be adjusted to some extent by the width dimension and the depth dimension of the concave portion 6 provided in the magnet piece 4 shown in FIG.
The width dimension and the thickness (height) dimension of the magnet piece 4 are usually small values, and when the diameter of the permanent magnet member 1 is small, the dimension is inevitably smaller, as shown in FIG. ) Drop amount d ₃ (P _3a or P _3b , whichever is larger, and V 3
It is almost impossible to adjust the difference) with a wide range. Further, as shown in FIG. 3C, if the diameter is small, a slight width dimension error (± 0.1 mm) of the concave portion 6 provided in the magnet piece 4
The magnetic flux density distribution changes from curve a to curve b, and the bipolar difference (peak difference) also increases from ΔB (= P _3a −P _3b ) to ΔB ′ (= P _3a −P ′ _3b ). However, the effect of widening the circumferential contact width of the magnetic brush with respect to the electrostatic image carrier cannot be expected. SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnet roll that solves the above-mentioned problems existing in the prior art, can improve the developing efficiency, and can improve the reproducibility of halftone.

[0006]

In order to achieve the above object, in the present invention, a specific permanent magnet member formed so as to extend in the axial direction on the outer peripheral surface and have a plurality of magnetic poles appearing in the circumferential direction is specified. A magnet roll in which a magnetic pole is provided with a groove extending in the axial direction, and a magnet piece formed so that a magnetic flux density distribution having a plurality of peaks of the same polarity appears in the groove is fixed to form a developing pole. A technical means was adopted in which a recess is provided along the longitudinal direction of the magnet piece in the circumferential center of the outer circumference of the magnet piece, and the magnet piece is fixed in the recess. In the present invention, the outer peripheral surface of the magnet piece may be formed to be substantially the same as the outer peripheral surface of the magnet piece, or may be formed to project from the outer peripheral surface of the magnet piece. As the magnet piece, a metal sintered magnet obtained by sintering magnetic powder, a bond magnet obtained by hardening magnetic powder with plastic or rubber as a binder, and the like can be used. The cross-sectional shape of the permanent magnet member is preferably circular, but a plurality of block-shaped permanent magnets may be fixed to the outer circumference of the supporting shaft. The cross-sectional shape of the recess may be a short shape, a trapezoidal shape, a D-shape, or any other geometrical shape. As the permanent magnet, a metal magnet such as an alnico magnet, a ferrite magnet, a rare earth magnet can be used, and a sintered magnet, a plastic magnet, a rubber magnet, or the like can be used.

[0007]

With the above construction, the magnetic flux density distribution having a plurality of peaks of the same polarity is formed on the magnet piece constituting the developing pole, so that the circumferential width of the magnetic brush can be secured and the magnetic flux density distribution The amount of decrease in the magnetic flux density between the peaks can be increased, and the reproducibility of halftone can be improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing an embodiment of the present invention, in which (a) shows a transverse cross section and (b) shows a magnetic flux density distribution in the circumferential direction generated by a magnet piece in (a). The parts are designated by the same reference numerals as in FIG. In FIG. 1, the permanent magnet member 1 is formed by an isotropic ferrite magnet (YBM-3 made by Hitachi Metals) with an outer diameter of 18 mm and an inner diameter of 6 mm.
A shaft 2 made of brushed steel bar (SUM) is fitted in the inner diameter portion of 6 mm. Next, a concave groove 5 is formed in the permanent magnet member 1 to a position 6 mm wide and 4 mm away from the shaft center by, for example, machining. The magnet piece 4 is made of an anisotropic ferrite magnet (YBM-2B made by Hitachi Metals), and the magnet piece 4 having a width of 6 mm and a height of 6 mm is bonded and fixed in the groove 5. In this state, the outer peripheries of the permanent magnet member 1 and the magnet piece 4 are polished to finish the outer diameter to 15 mm. Furthermore, a concave groove 6 having a width of 2 mm and a depth of 2 mm is formed in the central portion of the magnet piece, a predetermined magnetizing is performed, and the concave groove 6 of the magnet piece 4 is magnetized in advance in the height direction (rubber piece). The magnet) 7 is fixed.

The magnet roll having the above-mentioned structure has an outer diameter of 18 mm.
As a result of measuring the magnetic flux density distribution on the sleeve by inserting the magnetic flux density distribution into the SUS304 sleeve, the magnetic flux density distribution as shown in FIG. 1B is obtained, and the peak value P _1a = 760.
G, dip amount d ₁ = 150 G, bipolar difference ΔB (P _1a −P
_1b ) = 10G. As a comparative example, the magnet roll shown in FIG. 3 (a) was manufactured under the same conditions as above except that the magnet piece was removed, and as a result, the magnetic flux density drop d ₃ in FIG. 3 (b) was as low as 80G. . When an image evaluation (magnetic brush phenomenon using a two-component developer consisting of toner and iron powder carrier) was carried out with the above magnet roll, the one shown in FIG. However, the magnet roll shown in FIG. 1 has a higher image density than that of FIG. 3 (a), no background fog occurs, and the halftone reproducibility is good. Was confirmed.

2A and 2B are explanatory views showing another embodiment of the present invention. FIG. 2A is a cross section, FIG. 2B is a magnetic flux density distribution in the circumferential direction generated by the magnet pieces in FIG. c)
Shows an enlarged view of part B in (a), and the same portions corresponding to those in FIG. 1 are designated by the same reference numerals as those in FIG. 2 (a) and 2 (c), the outer peripheral surface of the magnet piece (rubber magnet) is configured to protrude from the outer peripheral surface of the magnet piece 4 by 0.6 mm. Other configurations and dimensions are shown in FIG.
It is similar to that shown in (a). In the magnetic flux density distribution of FIG. 2B, peak values P _2a = 760G, P _2b = 750
G, dip amount d ₂ = 320 G, bipolar difference ΔB = 760−
A result of 750 = 10 G was obtained. When the image was evaluated under the same conditions as described above using the magnet roll of this structure, it was confirmed that the reproducibility of the halftone was further improved as compared with the one shown in FIG.

Next, in the magnet roll shown in FIG. 3 (a), when the position of the concave portion 6 is displaced by about 0.2 mm in the circumferential direction, the magnetic flux density distribution becomes a curve b in FIG. 3 (c), and P _{3a = 760G, P '3b =} 640G, bipolar difference △ B'
= 120G. In this magnet roll,
Fix the magnet piece 7 to the groove 6 (projection amount 0.3 mm)
After making the structure similar to that of FIG. 2 (a), the magnetic flux density distribution was measured to find that P _3a = 760G and P ′ _3b = 750G, and it was confirmed that the bipolar difference ΔB ′ can be suppressed to an extremely small value such as 10G. It was Therefore, by fixing the magnet piece 7 in the concave groove 6, it is possible to obtain the effect that the bipolar difference caused by the width dimension error of the concave portion of the magnet piece can be reduced.

[0012]

According to the present invention, the following effects can be obtained by the configuration and operation as described above. (1) A magnetic flux density distribution having a plurality of peaks of the same polarity can be easily formed on the developing electrode, and the contact width between the magnetic brush and the image carrier surface can be increased. (2) The development efficiency can be improved by the action of the item (1). (3) The difference (fall amount) between the two peaks of the magnetic flux density distribution can be increased. (4) The reproducibility of halftone can be improved by the action of the items (3). (5) It is possible to reduce the bipolar difference caused by the width dimension error of the recess of the magnet piece.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, in which (a) is a cross section and (b) is a magnetic flux density distribution in the circumferential direction in (a).

FIG. 2 is an explanatory view showing another embodiment of the present invention,
(A) is a cross section, (b) shows the magnetic flux density distribution in the circumferential direction in (a), and (c) shows an enlarged view of part B of (a).

3A and 3B are explanatory views showing an example of a magnet roll according to a conventional improvement proposal, where FIG. 3A is a cross section, FIG. 3B is a magnetic flux density distribution in the circumferential direction in FIG. 3A, and FIG. (B)
The enlarged view of A part of the magnetic flux density distribution is shown.

FIG. 4 is a cross-sectional view showing an example of a conventional magnet roll.

[Explanation of symbols]

1 ... Permanent magnet member, 2 ... Shaft, 3 ... Sleeve, 4 ...
Magnet piece, 5 ... Groove, 6 ... Recess, 7 ... Magnet piece (rubber magnet)

Claims (4)

[Claims] 1. A groove extending in the axial direction is provided in a specific magnetic pole portion of a permanent magnet member formed on the outer peripheral surface so as to extend in the axial direction and a plurality of magnetic poles appear in the circumferential direction. In a magnet roll in which a developing pole is formed by fixing a magnet piece formed so that a magnetic flux density distribution having a plurality of peaks of the same polarity appears, the longitudinal direction of the magnet piece is at the outer circumferential center of the magnet piece. Along with a recess along the
A magnet roll having a magnet piece fixed in the recess. 2. The magnet roll according to claim 1, wherein the outer peripheral surface of the magnet piece and the outer peripheral surface of the permanent magnet are formed to be substantially flush with each other. 3. The magnet roll according to claim 1, wherein the outer peripheral surface of the magnet piece is projected from the outer peripheral surface of the permanent magnet. 4. The magnet roll according to claim 1, wherein the permanent magnet member and the fixing magnet piece are formed by an isotropic or anisotropic permanent magnet.