JP3397938B2 - Magnet roll - Google Patents

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 in particular, it has a supporting shaft at its axial center and an axial line on its outer peripheral surface. Direction, and a specific magnetic pole of a permanent magnet member formed so that a plurality of magnetic poles appear in the circumferential direction is used as a developing pole, and a magnetic flux density distribution having a plurality of peaks of the same polarity appears in this developing pole. It relates to a magnet roll.

[0002]

2. Description of the Related Art Conventionally, a magnet roll used as a developing roll in electrophotography, electrostatic recording and the like is most commonly constructed as shown in FIG. Figure 5
1 is a permanent magnet member, which is integrally molded into a cylindrical shape with 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, and has a shaft 2 at the center thereof. Are fixed coaxially.

Magnetic poles S ₁ , S ₂ , N ₁ and N ₂ 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. Next, a support member is rotatably mounted on both ends of the shaft 2 via bearings (none of which is shown), and a hollow cylindrical sleeve 3 is fitted on the support member. The support member and the sleeve 3 are made of a non-magnetic material such as aluminum alloy or stainless steel. The outer diameter of the permanent magnet member 1 is 16 to 60 mm, and the length is 150 to 450.
Often formed to mm.

With the above structure, for example, the permanent magnet member 1
By fixing a specific magnetic pole (for example, N ₂ ) facing the electrostatic image carrier and rotating the sleeve 3, the outer peripheral surface of the sleeve 3 has magnetism due to the magnetic attraction force of the permanent magnet member 1. The developer is adsorbed and conveyed to form a so-called magnetic brush (not shown), and a predetermined developing operation is performed.

On the other hand, in order to improve the developing efficiency in the above-mentioned developing operation, it is effective to increase the contact width in the circumferential direction between the magnetic brush and the surface of the electrostatic charge image carrier. Permanent magnet member 1 forming a brush
There is also a proposal of forming at least one recess on the magnetic pole surface of the magnetic pole portion on the side facing the electrostatic image carrier (see Japanese Patent Publication No. 62-55149).

4A and 4B are explanatory views showing an example of the magnet roll proposed above, FIG. 4A shows an end face of a main portion, and FIG. 4B shows a magnetic flux density distribution in the circumferential direction generated by the magnet pieces in FIG. 4A. The same parts are designated by the same reference numerals as those in FIG. In FIG. 4A, a groove 5 is provided along the axial direction at a portion corresponding to the developing pole. Next, reference numeral 4 denotes a magnet piece, which is formed in a block shape from, for example, an anisotropic ferrite sintered magnet material, and is provided with a recessed portion 6 along the longitudinal direction on the outer surface thereof. It is fixed.

Next, in FIG. 4B, the horizontal axis represents the position in the circumferential direction, and the vertical axis represents the magnetic flux density. That is, FIG.
By providing the magnet piece 4 with the concave portion 6 as shown in FIG. 4A, the magnetic flux density distribution has two peaks as shown in FIG. The contact width of the magnetic brush formed by the magnetic field in the circumferential direction with respect to the electrostatic charge 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.

[0008]

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 in that the magnetic flux density at both ends of the magnet roll in the axial direction is insufficient, and a so-called white spot in the image portion occurs.

FIG. 3 is a diagram showing the relationship between the longitudinal position of the magnet piece 4 in FIG. 4 (a) and the magnetic flux density. Curves b ₁ and b ₂ partially shown by broken lines are respectively shown in FIG. 4 (b). Mountain c
It corresponds to ₁ and valley c ₂ . In FIG. 3, the curve b ₁ has a relatively high magnetic flux density even at the end of the magnet piece 4 (see FIG. 4A), but the curve b ₂ has a gentle gradient at the end of the magnet piece 4. , The magnetic flux density remains low. That is, it is presumed that as a result of the height of the brush of the magnetic brush corresponding to this portion becoming small, the degree of contact of the magnetic brush with the electrostatic charge image carrier becomes small, resulting in uneven development or defective development (white spots). It

In order to solve the above-mentioned drawbacks, it is conceivable to form the magnet roll in a large axial length and use only the intermediate portion. However, in this case, the size of the developing device in the longitudinal direction is increased. In addition to increasing the size, the overall size of the image forming apparatus also becomes large, which hinders the downsizing and downsizing of the apparatus, which has become increasingly demanded in recent years.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems existing in the above-mentioned prior art, to improve the developing efficiency, to eliminate the defective development at both ends, and to provide a magnet roll which can be miniaturized. And

[0012]

In order to achieve the above object, in the present invention, a shaft for supporting is provided in the axial center portion, and a plurality of magnetic poles extending in the axial direction on the outer peripheral surface and in the circumferential direction. Is formed so that a magnetic pole portion of a permanent magnet member formed so that the magnetic flux density distribution that has a plurality of peaks of the same polarity appears in the concave groove. In a magnet roll that is firmly fixed to form a developing pole, a recess having a U-shaped cross section is provided along the longitudinal direction of the magnet piece at the outer circumferential center of the magnet piece. A technical means was adopted in which plate-like chips made of a magnetic material and having inclined surfaces on a part of the outer periphery are made to face each other and are attached to each other.

In the present invention, both ends of the recess of the magnet piece can be filled with a unit member formed by sandwiching a filling material made of a non-magnetic material between the chips. In the present invention, as the magnetic material forming the chip, simple metals such as iron, cobalt and nickel as well as alloys or compounds thereof can be used. It is also possible to use a mixture of a powder of the above metal or alloy, ferrite, magnetite or other permanent magnet material and a thermoplastic resin or a thermosetting resin. In this case, the content of the magnetic material powder is preferably 50 to 95% by weight.

As the non-magnetic material constituting the filler, aluminum, copper and other simple metals, alloys thereof, and resin materials can be used. In the present invention, the permanent magnet member can be formed by an isotropic or anisotropic permanent magnet, and the magnet piece can be formed by an anisotropic permanent magnet. As these permanent magnets, metal magnets such as alnico magnets, ferrite magnets and rare earth magnets can be used, and sintered magnets, plastic magnets and the like can be used.

Next, it is preferable that the cross-sectional contour of the permanent magnet member is circular, but a plurality of block-shaped permanent magnets may be fixed to the outer periphery of the supporting shaft.

[0016]

With the above construction, the magnetic flux density distribution having a plurality of peaks of the same polarity is formed in the magnet piece constituting the developing pole, so that the circumferential width of the magnetic brush is ensured and both ends of the magnet piece are secured. It is possible to make the rising of the magnetic flux density distribution in the longitudinal direction in the portion sharp, and it is possible to eliminate the development failure in this portion.

[0017]

FIG. 1 is an enlarged explanatory view showing an embodiment of the present invention. (A) is an end face of a main part, (b) is AA in (a).
A line cross section is shown, and the same portions are denoted by the same reference numerals as those in FIG. In FIG. 1, 7 is a chip, which is formed of, for example, an iron plate, and is attached so as to face the inner side surfaces of both ends of the recess 6. Reference numeral 8 denotes an inclined surface, which is provided on a part of the outer periphery of the chip 7, that is, on the outer periphery opposite to the end. The dimensions in FIG. 1 are expressed in mm.

In this case, the permanent magnet member 1 is an isotropic ferrite magnet (YBM-3 made by Hitachi Metals) and has an outer diameter of 38.
3mm, inner diameter 16mm, length 618mm, SUS30
The shaft made of 3 is fitted and adhered. Also the magnet piece 4
Is formed by an anisotropic ferrite magnet (YBM-2B made by Hitachi Metals), and is fixed in the groove 5 with an adhesive. After that, the chip 7 was attached to the inside of the recess 6 as described above, and then the outer peripheral surfaces of the permanent magnet member 1, the magnet piece 4 and the chip 7 were ground and subjected to predetermined magnetization.

A sleeve made of SUS304 having an outer diameter of 40 mm was fitted into the permanent magnet member 1 and the magnetic flux density distribution generated by the magnet pieces 4 on this sleeve was measured. The results are also shown in FIG. Curves a ₁ and a ₂ shown by solid lines in FIG. 3 correspond to the curves b ₁ and b ₂ , respectively. That is, the curve a ₁ (corresponding to the crest c ₁ in FIG. 4B) is near the end of the magnet piece 4 (see FIG. 1).
Although the magnetic flux density is slightly decreased, the rising edge of the magnetic flux density distribution at the end is steep.

On the other hand, the curve a ₂ (corresponding to the valley c ₂ in FIG. 4B) also has a steep rise in the magnetic flux density distribution at the end of the magnet piece 4, and the curve b ₂ in the conventional case is shown.
It can be seen that there is a significant improvement from those with a gentle gradient such as. The above-mentioned improvement of the magnetic flux density distribution is due to the magnetic flux concentration action by the chip 7 attached so as to face the inner side surfaces of both ends of the recess 6, and this action is achieved.
It has been clarified experimentally that the one in which the inclined surface 8 is provided on a part of the outer periphery of is more effective than the one lacking it.

FIG. 2 is an enlarged end view of an essential part showing another embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIG. In FIG. 2, 9 is a filler, which is formed in a block shape with a non-magnetic material such as an aluminum alloy and is filled between the chips 7, 7. In this case, the filler 9
It is preferable that the chips 7 and 7 are attached to both side surfaces of the magnet to form a unit member, and the unit member is filled and fixed to both ends of the recess 6 of the magnet piece 4 because workability is improved.

The magnetic flux density distribution on the sleeve having the above-described structure also becomes like the curves a ₁ and a ₂ in FIG. 3, and it has been confirmed that the rising edges at both ends of the magnet piece 4 are steep.

[0023]

EFFECTS OF THE INVENTION Since the present invention has the structure and operation as described above, the following effects can be obtained.

(1) A magnetic flux density distribution having a plurality of peaks of the same polarity can be easily formed on the developing pole, and the contact width between the magnetic brush and the surface of the electrostatic image carrier can be increased, and It is possible to improve efficiency.

(2) By sticking plate-like chips made of a magnetic material so as to face the inner surfaces of both ends of the recess of the magnet piece, the rising of the magnetic flux density distribution at both ends of the magnet piece is made sharp. It is possible to prevent development failure at both ends.

(3) The chips are adhered to both side surfaces of a block-shaped filler made of a non-magnetic material to form a unit member, whereby workability for fixing the chips is improved and manufacturing cost is improved. Can be reduced.

(4) The length of the magnet pieces constituting the permanent magnet member can be effectively utilized, and the developing device and the image forming apparatus can be downsized.

[Brief description of drawings]

FIG. 1 is an enlarged explanatory view showing an embodiment of the present invention,
(A) shows an end face of a main part, and (b) shows a cross section taken along the line AA in (a).

FIG. 2 is an enlarged end view of essential parts showing another embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a longitudinal position of a magnet piece 4 and a magnetic flux density.

FIG. 4 is an explanatory view showing an example of a magnet roll according to a conventional improvement proposal, in which (a) is an end face of a main part and (b) is (a).
3 shows the magnetic flux density distribution in the circumferential direction generated by the magnet pieces in FIG.

FIG. 5 is a cross-sectional view showing an example of a conventional magnet roll.

[Explanation of symbols] 1 Permanent magnet member 4 magnet pieces 7 chips 9 Filling material

─────────────────────────────────────────────────── ─── Continuation of front page (72) Nobuyasu Hirayama 3-7-1, Fuchu, Iwatsuki-shi, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Works (72) Yoshifumi Ozaki 3-7-1, Fuchu, Iwatsuki, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Works (56) Reference JP-A-7-29726 (JP, A) JP-A-3-46203 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/08 G03G 15/09

Claims (2)

(57) [Claims] 1. A specific magnetic pole portion of a permanent magnet member which is provided with a supporting shaft at its axial center portion and is formed so that a plurality of magnetic poles appear in the outer circumferential surface in the axial direction and in the circumferential direction. In a magnet roll in which a developing groove 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 in this groove, A recess having a U-shaped cross section is provided along the longitudinal direction of the magnet piece at the center of the outer circumference in the circumferential direction, and the inner surface of both ends of the recess is made of a magnetic material and is inclined to a part of the outer circumference. A magnet roll, characterized in that plate-shaped chips each having a surface are opposed to each other and attached. 2. The magnet roll according to claim 1, wherein a unit member formed by sandwiching a filler made of a non-magnetic material between the chips is filled in both ends of the recess of the magnet piece.