JP2002365915A - Development roller, production thereof, development machine, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing roller that reduces a magnetic force irregularity in a development magnetic pole, thereby obtaining a satisfactory development characteristics and to provide the production method of the development roller, a development machine, and an imaging device. SOLUTION: One of the lengthwise surfaces of a magnet block 48 made of a rare-earth magnetic powder is a sheared surface and the other is constituted of a formed surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., a developing device mounted on the image forming apparatus, a developing roller and a method of manufacturing the same.

[0002]

2. Description of the Related Art In an electrophotographic system, magnetic brush development using a two-component developer is well known and widely used in image forming apparatuses. In this magnetic brush development, a magnetic brush is formed by magnetically adsorbing the developer on the outer peripheral surface of the developing roller, and the electrostatic brush is formed in a developing area (an area where a developable electric field is secured between the developing roller and the image carrier). By an electric field between the image carrier on which the latent image is formed and the sleeve to which the electric bias is applied, the toner is selectively supplied and adhered to the latent image surface of the opposed image carrier from the magnetic brush, Development takes place.

The developing roller at this time is usually formed as a cylindrical sleeve (developing sleeve), and a magnet body (magnet roller) for forming a magnetic field so as to cause the developer to spike on the sleeve surface. Provided inside. When the ears are raised, the carrier is raised on the sleeve so as to follow the lines of magnetic force generated by the magnet roller, and the charged toner is attached to the carrier related to the raised ears. The magnet roller has a plurality of magnetic poles, and the magnets forming the respective magnetic poles are formed in a rod shape or the like. In particular, the developing roller is provided with a developing main magnetic pole for starting up a developer in a developing region on the sleeve surface. By moving at least one of the sleeve and the magnet roller, the developer that has raised ears on the sleeve surface moves, and the developer conveyed to the developing area moves along the magnetic force lines generated from the developing main magnetic pole. The chains of the developer contact the surface of the image carrier so as to bend, and the chain of the contacted developer rubs against the electrostatic latent image based on the relative linear velocity difference with the image carrier. While supplying the toner.

In the conventional magnetic brush developing device, the developing condition for increasing the image density and the developing condition for obtaining a good contrast image are incompatible, and both the high density portion and the low density portion are simultaneously used. It is difficult to improve. That is, the developing conditions for increasing the image density include (i) reducing the developing gap, which is the distance between the image carrier and the developing sleeve, or (ii) increasing the developing area width. . On the other hand, developing conditions for obtaining a low-contrast image favorably include (i ′) widening the developing gap or (ii ′) narrowing the developing area width. That is, both developing conditions are opposite and incompatible, and it is generally difficult to satisfy both conditions and obtain a good quality image over the entire density range.

For example, when emphasis is placed on a low-contrast image, a so-called "back-end blank area" in which a blank portion occurs at a cross portion of a solid line, a black solid area, or a rear end of a half-tone solid image.
An abnormal image called “image” easily occurs. Further, such a phenomenon that a horizontal line of a grid image formed with the same width becomes thinner than a vertical line, and a small point image such as one dot is not developed has occurred.

[0006] The developing conditions for increasing the image density and the developing conditions for obtaining a low-contrast image, which have been problems in the related art, are satisfied at a high point in time, and a high-quality image can be obtained over the entire density range. The applicant of the present application has previously proposed a developing method and a developing device for obtaining the same (Japanese Patent Application 200
0-29637).

[0007]

However, in the developing device proposed by the applicant of the present invention, since the angle between the main poles of the developing roller is narrower than that of the conventional developing roller, it is difficult to use magnet material. High magnetic properties are required.
In addition, the accuracy of the main pole portion is required to be higher than that of the conventional developing roller (ie, ± 1 ° with respect to the conventional ± 2 °).

[0008] In order to achieve these requirements, it is difficult to implement the conventional materials and roller configurations and manufacturing methods. In particular, with respect to the magnet material, sufficient magnetic properties cannot be obtained with a generally used ferrite-based magnet, which is difficult to achieve, and a rare-earth magnet must be used. In addition, since the cost of the rare earth magnet is high, it is desirable to use a rare earth magnet only for the developing pole requiring high magnetic characteristics and a ferrite magnet for the other poles as a practical roller magnet configuration.

Here, a method of manufacturing a conventional developing roller will be described. Manufacturing method A: As shown in FIG. 7, a method of attaching ferrite and rare earth magnets 62 and 63 to a holder 61 integrated with a cored bar 60. As a merit, the position accuracy of the magnetic pole is good, but as a disadvantage, a part to which the magnet is attached. Cost and man-hours increase.

Manufacturing method B: As shown in FIG.
Ferrite block 6 with ferrite magnet block 64 and rare earth magnet block 65 adhered to it
6 has a merit that the cost of the core metal is lower than that of the manufacturing method A, but has the disadvantage that the magnetic pole position accuracy is not high and that the number of man-hours and the manufacturing cost are high as in the manufacturing method A. Have.

Manufacturing method C: As shown in FIG. 9, a method of attaching a rare earth magnet 68 to a ferrite magnet molded product 67 has the advantage of a small number of steps, but requires high precision in the complicated shape of the main pole. Has the disadvantage of

As a method of manufacturing the rare earth magnet block used for the main pole, sintering, injection molding, extrusion molding, and powder filling are conceivable. As a matter of fact,
Limited to extrusion or injection molding.

However, in the injection magnetic field molding, there is a problem that the density differs between the gate portion and the other portions, and as a result, the magnetic force varies in the axial direction. On the other hand, as a conventional method, as described in Japanese Patent Application Laid-Open No. H10-256068, there is a method in which rare-earth magnet powder is extruded from one end in the axial direction and molded. However, even with this method, there is a problem that the rare-earth magnet powder has poor fluidity, does not have a uniform density in the axial direction, and consequently cannot obtain a uniform magnetic force.

The present invention solves the above-mentioned conventional problems,
It is an object of the present invention to provide a developing roller capable of reducing uneven magnetic force of a developing pole to obtain good developing characteristics, a method of manufacturing the same, a developing device, and an image forming apparatus.

[0015]

Means for Solving the Problems To solve the above problems, the developing roller of the present invention has at least a portion corresponding to a developing pole of a magnet roll formed by dispersing a magnetic powder in a polymer compound and having a cylindrical shape. In the developing roller provided with a groove-shaped storage portion of one or more poles, and in the storage portion, a rare-earth magnet powder formed in a block shape having a higher magnetic force than the magnet roll is disposed, the block-shaped rare-earth magnet powder is , Characterized in that one surface in the longitudinal direction is a shear surface and the other surface is a molding surface.

Further, in order to solve the above-mentioned problems, a method of manufacturing a developing roller according to the present invention is characterized in that a magnetic powder is dispersed in a polymer compound, and at least one portion is formed at a portion corresponding to a developing pole of a magnet roll formed in a cylindrical shape. The method for manufacturing a developing roller, wherein a rare earth magnet powder formed in a block shape having a magnetic force higher than that of the magnet roll is provided in the storage portion having a groove-shaped storage part having more than poles, wherein the block-shaped rare earth magnet is provided. The powder is molded by a mold in which a gate is disposed over substantially the entire length in the longitudinal direction, and after molding, the gate side is cut to form one longitudinal surface as a shear surface, and is disposed in the storage portion. It is characterized by.

Further, in order to solve the above-mentioned problems, a developing device of the present invention uses the developing roller according to the first aspect. Furthermore, in order to solve the above problem, an image forming apparatus according to the present invention uses the developing device according to the third aspect.

[0018]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, an image forming unit of an image forming apparatus using a developing roller according to the present invention will be described with reference to FIG.

In FIG. 1, a charging device 2 for charging the surface of a photosensitive drum 1, which is an electrostatic latent image carrier, forms a latent image on a uniformly charged surface. A developing device 4 for forming a toner image by attaching a charged toner to a latent image on the drum surface, a transfer device 5 for transferring the toner image formed on the drum to recording paper, A cleaning device 7 for removing the residual toner on the drum and a charge removing lamp 8 for removing the residual potential on the drum are sequentially arranged.

In such a configuration, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2 is
The exposure 3 forms an electrostatic latent image, and the developing device 4 forms a toner image. The toner image is transferred from the surface of the photosensitive drum 1 to a transfer material conveyed from a paper feed tray (not shown) by a transfer device 5 including a transfer belt or the like. At the time of this transfer, the transfer material electrostatically attached to the photosensitive drum is separated from the photosensitive drum 1 by the separation claw. When the transfer material carrying the unfixed toner image passes through the fixing device 9, the transfer material is fixed to the transfer material under the action of heat, pressure, and the like. On the other hand, the toner remaining on the photosensitive drum 1 without being transferred is removed and collected by the cleaning device 7. The photosensitive drum 1 from which the residual toner has been removed is initialized by the charge removing lamp 8, and is used for the next image forming process. Reference numeral 6 denotes a registration roller for feeding a transfer material from a paper feed tray (not shown) in synchronization with a toner image on the photosensitive drum 1.

The developing device 4 has a developing roller 41 opposed to the photosensitive drum 1 so as to be close to the photosensitive drum 1, and a portion where the developing roller faces the photosensitive drum is a developing area. Reference numeral 42 denotes a doctor blade that regulates the height of the developer chain, that is, the amount of the developer on the developing sleeve, reference numeral 43 denotes an inlet seal member, and reference numeral 44 denotes a developer while stirring the developer in the developing device casing. This is a screw for pumping to the roller 41.

As shown in FIG. 2, the developing roller 41 has a cylindrical developing sleeve 45 made of a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin.
The developing sleeve 45 is rotated clockwise in the figure by a rotation driving mechanism (not shown). In the developing sleeve 45, a magnet roller 46 for generating a magnetic field so as to cause the developer to spike on the peripheral surface is fixedly arranged. The magnet roller 46 includes a developing pole 47 that causes the developer to spike in the developing area, a transport pole that transports the pumped developer to the developing area, and a transport that transports the developer in the developed area. With poles. In the present embodiment, the developing pole 47 is constituted by three magnet blocks 48 having opposite polarities.
May be composed of one magnet block 48,
It can also be constituted by a magnet block 48 having two or four or more poles.

As described above, when the developing pole 47 is composed of three magnet blocks 48, the half width of the developing pole is 25 ° or less, and the attenuation rate of the magnetic flux density in the normal direction of the developing pole is 40% or less. . Note that the half-value width is an angular width of a portion indicating a half value of the highest normal magnetic force (apex) of the magnetic force distribution curve in the normal direction of the developing main magnetic pole. Maximum normal magnetic force is 1
In the case of 20 mT (millistera), it is the angular width of a portion indicating a value of 60 mT. Further, the attenuation rate of the magnetic flux density in the normal direction of the developing magnetic pole is defined as the magnetic flux density y in the normal direction at a portion 1 mm away from the surface of the developing roller with respect to the magnetic flux density x in the normal direction.
(X−y) ÷ x × 10 representing how much the signal has attenuated
For example, when the magnetic flux density in the normal direction on the surface of the developing roller is 100 mT, and the magnetic flux density in the normal direction at a portion 1 mm away from the surface of the developing roller is 80 mT, the attenuation factor is 20%.

The developing roller 41 includes a magnet roller 46.
Is a portion where the transport poles other than the developing pole 47 are formed, and are manufactured by injection molding and extrusion molding.
As a raw material of the magnet roller 46, a plastic magnet or a rubber magnet in which a polymer compound is mixed with magnetic powder of Sr ferrite or Ba ferrite is often used. Examples of the polymer compound include PA materials such as 6PA and 12PA, ethylene compounds such as EEA (ethylene / ethyl copolymer) and EVA (ethylene / vinyl copolymer), and chlorine compounds such as CPE (chlorinated polyethylene). Rubber materials such as a base material and NBR can be used.

The magnet block 48 used for the developing pole 47 has a width of Br>
It is desirable to use a material of 0.5T, and most of the materials are Ne-based (Ne-Fe-B or the like) or Sm-based (Sm-Co,
-Fe-N or the like, or a plastic magnet or a rubber magnet in which these magnet powders are mixed with the same polymer compound as described above. Furthermore, in the case of the developing electrode having the above-mentioned half-value width of 25 ° or less, for example, the diameter is 16 mm to 20 mm.
When the developing roller is of the order of magnitude, a magnetic flux density of 80 to 90 mT is required on the surface of the sleeve.
It needs to be small. Note that the length differs depending on the maximum image forming size of the device used, but is generally the horizontal width of A3 (= vertical width of A4).

By the way, the magnet block 48
Is manufactured by injection molding, but it is quite difficult to make the density of the magnet powder in the longitudinal direction uniform if the cross section is small and the length is long with a material with poor fluidity such as rare earth magnet powder. .

Therefore, in the present embodiment, a mold is used in which one surface corresponding to the surface in the longitudinal direction of the magnet block 48 is a gate portion over the entire surface, and after molding, the runner portion formed on the gate portion side is cut. And magnet block 4
8 are formed. Since the magnet block 48 formed in this way is a gate portion on one entire surface in the longitudinal direction, it is easy to uniformly fill the magnet powder, and the runner portion where the packing density tends to vary is cut off. The variation of the magnetic force in the axial direction is small. In the obtained magnet block 48, one surface in the longitudinal direction has a shear surface, the other surface is a transfer molding surface, and the shear surface has a larger surface roughness than the other surfaces.

In the developing roller having such a configuration, the magnet block 48 used for the developing pole 47 has a small variation in magnetic force in the axial direction and is substantially uniform, so that the developing conditions for increasing the image density and the low contrast image are excellent. The developing roller is optimal for a developing method capable of satisfying the developing conditions for obtaining the toner at a high point in time.

Next, a specific example of the method of manufacturing the magnet block will be described. FIG. 3 shows a mold for molding the magnet block 48 of the present invention. In FIG.
Reference numeral 50 denotes a cavity, 51 denotes a core plate, 52 denotes a movable side insert, and 53 and 54 denote ejector pins. The rare earth magnet powder is filled in the direction of the arrow, and when the filling is completed, the cavity 50 is removed as shown in FIG. The filled rare earth magnet powder has a shape in which a runner portion 55 is connected to a magnet block 48 portion. Then, as shown in FIG.
The rare earth magnet block is taken out of the core plate 51 by 3 and 54.

The removed rare earth magnet block is
For example, the runner portion is cut by a cutting machine as shown in FIG. This cutting machine comprises a die 60 for fixing a rare-earth magnet block, a ruler 61, a stripper 62, a knockout 63 for supporting a runner portion 55 for cutting and removing, a punch 64 for cutting the runner portion 55, and a backup plate 65 for guiding the punch 64. Have been.

The removed rare earth magnet block is set in a cutting machine while being fixed by a die 60 and a ruler 61 and supported by a knockout 63. After setting, the rare earth magnet block is pressed by the stripper 62 and the punch 64 is lowered to cut the runner portion 55.

Thus, a magnet block 48 having a shear surface on one surface in the longitudinal direction and having a substantially uniform magnetic force in the axial direction can be manufactured.

【The invention's effect】

As described above, according to the developing roller of the present invention, since the magnet block having little variation in the axial direction is arranged, it is possible to obtain a developing characteristic compatible with a high image density and a good low contrast image. .

Further, it is possible to easily manufacture a rare earth magnet block having little variation in the axial direction.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram illustrating a developing roller.

FIG. 3 is an explanatory view showing a mold for manufacturing a magnet block.

FIG. 4 is an explanatory view showing a manufacturing process of the magnet block using the mold shown in FIG. 3;

FIG. 5 is an explanatory view showing a manufacturing process of the magnet block using the mold shown in FIG. 3;

FIG. 6 is an explanatory view showing a cutting machine used for manufacturing a magnet block.

FIG. 7 is a configuration diagram illustrating a developing roller according to a conventional manufacturing method.

FIG. 8 is a configuration diagram illustrating a developing roller according to another conventional manufacturing method.

FIG. 9 is a configuration diagram illustrating a developing roller according to still another conventional manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (latent image carrier) 2 Developing device 41 Developing roller 46 Developing sleeve 48 Magnet block

Continued on front page F term (reference) 2H031 AB02 AC08 AC11 AC14 AC18 AC19 AC20 AC30 AD01 BA04 3J103 FA10 GA02 GA57 GA58 GA60 HA16 HA41 4F202 AB13 AH81 CA11 CB01 CK02 CK06 CM02

Claims (4)

[Claims] 1. A magnet roll formed by dispersing magnetic powder in a polymer compound and having a cylindrical shape and having a groove-shaped housing portion having at least one pole at a portion corresponding to a developing pole, wherein the magnet portion is provided at the housing portion. In the developing roller provided with a rare earth magnet powder formed in a block shape having a higher magnetic force than the roll, the block-shaped rare earth magnet powder has a shear surface on one surface in the longitudinal direction and a molded surface on the other surface. A developing roller, which is a surface. 2. A magnet roll formed by dispersing magnetic powder in a polymer compound and having a cylindrical shape and having a groove-shaped housing portion having at least one pole in a portion corresponding to a developing pole, wherein the magnet portion is provided in the housing portion. A method of manufacturing a developing roller in which a rare earth magnet powder formed in a block shape having a higher magnetic force than a roll is disposed, wherein the block-shaped rare earth magnet powder is provided with a gate disposed over substantially the entire length in the longitudinal direction. Molded by
A method of manufacturing a developing roller, comprising cutting the gate side after molding, making one surface in the longitudinal direction into a shear surface, and disposing the shear surface in the housing portion. 3. A developing device using the developing roller according to claim 1. 4. An image forming apparatus using the developing device according to claim 3.