JPH096138A - Developing magnet member and developing device - Google Patents

Abstract

(57) [Abstract] [Purpose] A developing magnet member capable of preventing bending of a shaft due to expansion of a resin magnet by fixing a non-magnetic resin to at least a part of a shaft portion to which a resin magnet is not fixed. I will provide a. In a developing magnet member, which is used by being built in a developing sleeve 30 and in which a resin magnet 32 in which magnetic powder is dispersed is fixed to a shaft 31, a portion of the shaft where the resin magnet is not fixed. Resin 33, which is non-magnetic and has substantially the same coefficient of thermal expansion and / or expansion coefficient with respect to humidity as that of the resin magnet, was fixed to part or all of the above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and a developing magnet member used in the developing device.

[0002]

2. Description of the Related Art Conventionally, in this main developing device, a permanent magnet is provided in a developing sleeve as a non-magnetic cylinder, and a magnetic developer is carried on the developing sleeve by magnetic force from the permanent magnet extending over the developing sleeve. And is used for development. As the permanent magnet, in addition to sintered ferrite, magnetic powder is kneaded with rubber (see, for example, Japanese Utility Model Publication No. 59-121660), and magnetic powder is kneaded with plastic (for example, Japanese Patent Publication No. 57-28928). Is also widely used.

[0003]

When the above sintered ferrite is used, in order to reduce the diameter of the developing sleeve, if the ferrite is cut into small pieces and used for each pole in the sleeve, the magnet per piece becomes thin. It becomes too easy to crack. In order to solve this drawback, a magnet in which magnetic powder is dispersed in a resin such as nylon (hereinafter referred to as "plamag") is widely used as a small-diameter sleeve.
For example, when it is desired to form the sleeve 10 having the magnetic flux density distribution as shown in FIG. 1 with this plastic mug, the plastic mug 12 must be attached only to the photoconductor side on the shaft 11 as shown in FIG. Even if the same magnetization is performed after the plastic magnet 12 is provided over the entire circumference of the shaft 11, an unnecessary magnetic force remains in the portion a of FIG. 1 and causes various problems. This is because. Further, when a mag roller provided with a plastic magnet around the entire circumference of the shaft is used in a developing device using a plurality of sleeves 20 and 30 with built-in mag rollers as shown in FIG. 3, for example, magnetic parts which are not magnetized are adjacent to each other. This is because the magnetic line of force from the roller is pulled in and distorted, which makes designing difficult.

However, if the plamag is attached to only one side of the shaft in this way, the shaft (metal) and the plamag material, such as nylon, have different thermal expansion coefficients and expansion coefficients with respect to humidity. Therefore, 1) the sleeve shaft bends, The gap between the photoconductor and the developing sleeve may be widened or, on the contrary, narrowed. 2) Also, as shown in FIG. 4A, for example, it was confirmed that the shaft and the plastic magnet may bend and come into contact with the inner surface of the sleeve (aluminum cylinder) to cause a serious problem such as the sleeve not rotating. . In order to solve this problem, for example, the plastic mag and the sleeve shaft are bonded with a rubber-based adhesive to absorb the difference in thermal expansion coefficient between the shaft and the plastic mag, or a resin having a small expansion coefficient is used. I also examined the methods, but neither was enough.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing magnet member capable of preventing bending of a shaft or the like due to expansion of a resin magnet.
And to provide a developing device.

[0006]

In order to achieve the above object, the developing magnet member according to claim 1 is a developing magnet member in which a resin magnet in which magnetic powder is dispersed is fixed to a shaft. A resin, which is non-magnetic and has substantially the same coefficient of thermal expansion and / or expansion coefficient with respect to humidity as that of the resin magnet, is fixed to a part or all of the portion of the shaft where the resin magnet is not fixed. It is a feature.

According to a second aspect of the present invention, there is provided the developing magnet member according to the first aspect, wherein the same resin as the resin magnet is used, and a resin having the same quality as that of the resin magnet is used. To do. Here, as the resin of the same quality as the resin of the resin magnet, the base resin itself in which the magnetic material of the resin magnet is mixed is most suitable.

According to a third aspect of the present invention, in the developing device, a non-magnetic cylinder is provided.
In a developing device in which a developing magnet member having a resin magnet in which magnetic powder is dispersed is fixed to a shaft is provided, and a magnetic developer is adsorbed and conveyed on the surface of the non-magnetic cylinder, as the developing magnet member, The developing magnet member according to claim 1 or 2 is used.

[0009]

According to the present invention, the resin magnet of the shaft is fixed to a part or the whole of the portion where the resin magnet is not fixed and is non-magnetic and has substantially the same coefficient of thermal expansion and / or expansion coefficient with respect to humidity as the resin magnet. The resin or the like suppresses bending due to various differences in expansion coefficient between the shaft and the resin magnet.

[0010]

FIG. 2 is a sectional view of a developing sleeve accommodating a mag roller as a developing magnet member according to the embodiment, and FIG. 3 is a schematic configuration diagram of a developing device using the developing sleeve.
In FIG. 3, in the developing device of this copying machine, two developing sleeves 20 and 30 are used. A first sleeve 20 on the upstream side in the surface moving direction of the photoconductor 1 and a second sleeve 20 on the downstream side in the same direction.
The sleeve 30 is composed of an aluminum cylinder (non-magnetic cylinder) that rotates around the axis of the developing sleeve and a non-rotatable mag-roller using a pragmag. The mag roller generates a magnetic field on the outer peripheral surface of the sleeve, and the developer is conveyed along the lines of magnetic force. A groove of 1 mm pitch is cut in the aluminum cylinder in order to carry the developer efficiently (to prevent the developer from slipping). The sleeve diameter is 20φ for both the first and second sleeves. The drum diameter of the photoconductor 1 is 100φ,
The gap between the drum and the sleeve is 0.75 mm for both the first and second sleeves, the gap between the doctor 2 and the first sleeve 20 is 0.65 mm, and the linear velocity ratio between each sleeve and the drum is 2: 1. .

In the above structure, the toner replenishing roller 3
The toner replenished from the toner is dispersed in the developer by the elliptical plate 4 and the paddle 5, is supplied to the first sleeve 20 by the paddle 5, is squeezed by the doctor blade 2, and is electrically raised to the first sleeve. 20 is regulated to a constant layer thickness. The developer on the first sleeve 20 is conveyed to the area on the photoconductor side by the rotation of the sleeve, and
It is delivered to the sleeve 30. The developer conveyed by the second sleeve 30 and returned to the inside of the developing device is the second sleeve 3
At the point where no magnetic force is present on 0, it falls from the sleeve and is agitated by the paddle 5. It is formed on the photoconductor drum 1 by charging and exposure by a charging device or an exposure device (not shown) using the developer conveyed in the area facing the photoconductor 1 by the first and second sleeves 20 and 30. The latent image is developed at the developing position of the sleeves 20 and 30 (on the main pole).

Here, the mag roller in the first sleeve is
In addition to the main pole magnetized to 95 mT (millitesla) with the N pole (the pole at the development position facing the photoconductor), it has four magnetic poles for carrying the developer, and the pragmag also extends over the entire circumference ( It has a cylindrical shape). On the other hand, the magnet roller in the second sleeve is magnetized to 100 mT (millitesla) at the S pole, has two poles for developer transport in addition to the main pole, and all three poles are close to one side of the shaft. If the mag roller in the second sleeve is magnetized into a cylindrical plamag with only 3 poles and the plamag is simply attached to one side of the shaft as shown in FIG. 1, the amount of deformation of the sleeve shaft due to temperature changes. Is 0.1 mm /
There are also about deg. Considering that the photoconductor sleeve gap of this embodiment is 0.75 mm, this change amount cannot be ignored. In addition, an unnecessary magnetic force remains in the portion a of FIG. 1, the developer is hard to separate from the sleeve, and is entangled with the developer, and the developer not passing through the gap between the doctor 2 and the first sleeve 20 is removed. It is conveyed from the space between the first and second sleeves to the photoconductor 1 side. The developer conveyed to the side of the photoconductor does not pass through the doctor sleeve gap, and the toner contained in the developer is insufficiently charged, so that fog (toner adhesion to the background) occurs. There is a fear.

Therefore, in the present embodiment, as the mag roller in the second sleeve 20, as shown in FIG. 2, a non-magnetic resin (nylon) 33 embedded in the clearance portion in FIG. 1 is used. Since the embedded resin 33 is non-magnetic, no extra magnetic force remains in the portion a shown in FIG. Further, since the pla-mag 32 is nylon kneaded with magnetic powder and is the same as the non-magnetic resin 33, no axial deformation due to a difference in coefficient of thermal expansion occurs.
In this embodiment, when the magnetized plastic magnet portion 32 and the non-magnetic resin portion 33 are combined, the resin is fixed over the entire circumference of the shaft 31, but this non-magnetic resin is used. The fixing range may be only a part of the shaft to which the plastic mag is not fixed, as long as the resin that cancels the expansion of the plastic mag can be fixed. Further, it is possible to use a material other than resin as long as the expansion coefficients are almost the same (preferably the same).

The amount of deformation between the conventional developing sleeve in which the pragmag is fixed to one side of the shaft as shown in FIG. 1 and the developing sleeve in which nylon is fixed to the part without the plamag as in this embodiment The comparison is shown in FIG. FIG. 5 (a)
As shown in FIG. 4B, the developing sleeve (total length of the shaft 3
(85 mm), one end of which is fixed and the temperature is increased in a constant temperature bath, the deformation amount h (mm) of the other end is shown. In the conventional example, the deformation amount is about 0.1 mm / deg, whereas in the embodiment, the deformation amount is not. FIG. 5B shows a sleeve 90.
Degree of deformation when left in ° C hot water. In order to see the amount of deformation due to humidification, this amount of deformation uses a value obtained by subtracting the amount of deformation due to heat when it is similarly left in a constant temperature bath at 90 ° C. 0.15 mm when the conventional example is left for 150 hours
In contrast to the deformation, there is no deformation in the embodiment. That is,
In the mag roller of this embodiment, since the non-magnetic resin having the same expansion coefficient with respect to heat and humidity is fixed to the non-fixed portion of the plastic magnet, there is no problem due to an extra magnetic force, and the sleeve is not deformed. Does not occur.

[0015]

According to the first and second aspects of the present invention, the non-magnetic and thermal expansion coefficient and / or the expansion coefficient with respect to humidity are fixed to a part or all of the portion of the shaft where the resin magnet is not fixed. Since a resin or the like that is substantially the same as the resin magnet suppresses bending due to various expansion coefficients of the shaft and the resin magnet, it is possible to prevent the shaft from bending due to expansion of the resin magnet. A member can be provided.

In particular, according to the second aspect of the invention, since the same resin as that used for the resin magnet is used as the resin substantially the same as the resin magnet, the coefficient of thermal expansion and the expansion with respect to humidity are used. The ratio is the same, the design is easy, and the deformation of the sleeve can be almost completely prevented.

According to the third aspect of the invention, since the developing magnet member of the first or second aspect is used as the developing magnet member provided in the non-magnetic cylinder, a shaft or the like due to expansion of the resin magnet of this member is used. A developing device that can prevent bending can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory view of a developing magnet member according to a conventional example.

FIG. 2 is a sectional view of a developing sleeve accommodating a mag roller as a developing magnet member according to the embodiment.

FIG. 3 is a schematic configuration diagram of a copying machine adopting a developing device using the developing sleeve.

FIG. 4A is an explanatory diagram of a defect of a conventional example. FIG. 6B is an explanatory diagram of a method for measuring the deformation of the developing sleeve.

FIG. 5A is a graph showing temperature deformation characteristics of the developing sleeve and a developing sleeve according to a conventional example. 6B is a graph showing the deformation characteristics of the developing sleeve and the developing sleeve according to the conventional example due to humidification.

[Explanation of symbols]

 1 Photoreceptor 30 Sleeve Cylinder 31 Shaft 32 Plamag (Resin Magnet) 33 Non-Magnetic Resin

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[Procedure amendment]

[Submission date] September 30, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Developing magnet member and developing device

Claims (3)

[Claims] 1. A developing magnet member in which a resin magnet in which magnetic powder is dispersed is fixed to a shaft, wherein a part or all of a portion of the shaft where the resin magnet is not fixed is made nonmagnetic. Further, a developing magnet member is characterized in that a resin or the like having a thermal expansion coefficient and / or an expansion coefficient with respect to humidity which is substantially the same as that of the resin magnet is fixed. 2. The developing magnet member according to claim 1, wherein a resin having substantially the same quality as that of the resin magnet is used as substantially the same resin as the resin magnet. 3. A non-magnetic cylinder is provided with a developing magnet member in which a resin magnet in which magnetic powder is dispersed is fixed to a shaft, and a magnetic developer is adsorbed and conveyed on the surface of the non-magnetic cylinder. A developing device, wherein the developing magnet member according to claim 1 or 2 is used as the developing magnet member.