JPH0344675A - Developing device - Google Patents

Abstract

PURPOSE:To stabilize the electrostatic charging quantity of toner to form an image with sufficient density even when a developing bias is low by making the rotary axis of a sleeve eccentric with the rotary axis of a magnet roller. CONSTITUTION:A developer conveyance body 7 is constituted by arranging a magnet roller 8 eccentrically in a sleeve 9 across a gap. The toner 11 is held on the conveyance body 7 with magnetic flux produced by the roller 8 and conveyed to a developing gap part 16 to form a development nip. In the gap 16, the toner 1 is used for development on a carrier 1 according to an electrostatic latent image and developing bias applying means 13. At this time, there is a part where a magnetic force is intense and a part where the magnetic force is weak at the gap part 16, so the development is performed by a sufficient quantity at the weak part and the toner is scraped off at the intense part. Therefore, the electrostatic charging quantity of the toner becomes stable and the sufficient image density is obtained even when the developing bias is low.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing device that performs development using a -component magnetic toner.

[Prior Art] A conventional developing device is a rotatable non-magnetic roller that coaxially houses a cylindrical magnetic roller with a plurality of magnetic poles magnetized in the axial direction, as known as the one-component magnetic brush developing method. Toner is conveyed by a cylindrical sleeve while forming a magnetic brush according to the magnetic field generated by a magnet roller, and development is performed according to the electrostatic latent image on the latent image carrier.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, as the magnetic field of the magnet roller is strengthened, the scraping force increases, and in order to ensure a sufficient developing temperature, the developing bias must be increased. . In addition, if the magnetic field of the magnet roller is weakened, the scraping force will be weakened, causing problems such as background smudges and lower resolution.The power to agitate the toner in the developing device will also be weakened, which will reduce the amount of charge on the toner. The problem was that there was a shortage of.

The present invention is intended to solve these problems, and its purpose is to provide an image in which the toner charge amount is stable and an image with sufficient density can be formed even when the developing bias is low. The purpose is to provide a forming device.

Another object of the present invention is to provide a high-resolution image forming apparatus by optimizing the magnetic force distribution in the development gap.

[Means for Solving the Problems] The developing device of the present invention includes a latent image carrier that forms an electrostatic latent image, a non-magnetic cylindrical sleeve, and a developer conveying member having a cylindrical magnetic roller inside the sleeve. are arranged so as to maintain a constant set interval, and toner containing magnetic particles, which is an image forming body, is supported on the surface of the developer conveying body by magnetic force, and a constant setting is maintained with respect to the developer conveying body. The conveyance amount is regulated by conveyance amount regulating members arranged to maintain the interval,
In a developing device that conveys the toner to a developing area where the latent image carrier and the developer conveying body are close to each other and performs development, the rotational axis of the sleeve and the rotational axis of the magnetic roller are not coaxial. It is characterized by Further, the magnetic roller is made of a rare earth magnet.

[Function] According to the above-described structure of the invention, the magnetic force is weak at the portion in contact with the latent image carrier, and the magnetic force can be strong within the developing unit. By changing the distance between the sleeve and the rotation axis of the magnetic roller, it is possible to set the magnetic force that will provide a sufficient amount of development with an appropriate development bias, and since the magnetic force is strong inside the developing device, it is possible to agitate a large amount of toner and create a sufficient amount of toner. It has the effect of being able to provide electrical charge. Furthermore, by creating an angle θ between a straight line connecting the rotational axis of the latent image carrier and the sleeve and a straight line connecting the rotational axis of the sleeve and the rotational axis of the magnetic roller, it is possible to create a gradient in the magnetic force at the developing gear part. I can do it. In other words, when the electrostatic latent image on the latent image carrier reaches the development gap, at first it attracts and holds the carried toner with a weak magnetic force, and as it progresses to the latter half of the development gap, the magnetic force increases. The force becomes stronger and can have the effect of scraping some of the toner that has been developed back into the sleeve. That is, it is possible to strengthen the scraping force and form a high-resolution image without reducing the amount of development.

Hereinafter, the present invention will be explained in detail with reference to Examples.

[Embodiment] FIG. 1 is a cross-sectional schematic diagram of an image forming apparatus including a developing device in an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a latent image carrier, which has a photoconductive layer 3 coated on a conductive support 2. After the photosensitive layer 3 is charged with a charger 4 to a predetermined potential, the light emitted from a light source 5 such as a laser is scanned using a rotating polygon mirror (not shown), and an imaging optical system 6 scans the light emitted from a light source 5 such as a laser. An electrostatic latent image is formed on the latent image carrier 1 by forming an image on the photosensitive layer 3 to obtain a potential contrast. On the other hand, numeral 12 in the figure is a developing device, which charges the toner 11 which is an image forming body and transports it by the developer transporting member 7. In the developer conveying body 7, a cylindrical magnet roller 8, which is a magnetic field generating means, is eccentrically arranged inside a cylindrical non-magnetic sleeve 9 with a gap interposed therebetween. Adjacent to the developer transport body 7, an electrically conductive flat blade 10, which is a transport amount regulating member, is disposed. The toner 11 is held on the developer conveying body 7 by the magnetic flux generated by the magnet roller 8, and the amount of conveyance is regulated by the blade 10.
The toner is conveyed to the developing gap portion 16 adjacent to which the developer conveying body 7 is located, forming a developing nip. In the development gap section 16, the toner 11 forms an electrostatic latent image and a development bias applying means 13.
(which is connected between the conductive support part 2 and the sleeve 9) is developed on the latent image carrier 1. The visualized image is electrostatically transferred to a recording paper 15 or the like by a transfer device 14, and fixed by means such as pressure or heating to obtain a desired image.

In FIG. 1, the potential of each part is O[V] for the conductive support part 2 of the latent image carrier 1, and -400[V] for the sleeve 9.
V], and the gaps between each part are set to 0.2 [mm] between the latent image carrier 1 and the developer transport member 7, and 0.15 [mm] between the developer transport member 7 and the blade 10. When set to did it.

Note that the configuration shown in FIG. 1 does not limit the present invention, and similarly, the above-mentioned numerical values do not limit the present invention.

FIG. 2 is a cross-sectional schematic view of a developing device according to another embodiment of the present invention, and members having the same names and functions as those in FIG. 1 are indicated by common numbers. In this embodiment, an angle θ=20 ['' This is an example using a developing device with a magnetic force of 1. A gradient is created in the magnetic force at the development gap, and sufficient image density is obtained in the first half of the electrostatic latent image at the development gap due to the weak magnetic force (development inhibiting force). The latent image is developed with toner until the latent image is covered, and in the latter half, some of the toner is returned to the latent image carrier to obtain sufficient resolution.

FIG. 3 is a diagram showing the magnetic flux density distribution on the surface of a sleeve arranged not coaxially with the built-in magnet roller.

Figure 3 shows that when the magnetic roller is rotated,
This is the time-averaged magnetic flux density distribution in the direction perpendicular to the surface. It is thought that the magnetic flux density distribution in the direction parallel to the surface has a similar distribution. As is clear from FIG. 3, the magnetic flux density distribution on the sleeve surface can be made non-uniform.

In particular, the magnetic roller 8 contains 14 kinds of rare earth elements (Nd, Pr,
When a rare earth magnet is formed by adding resin, etc. to a 3dJ transfer metal such as Fe, Ni, or CO to a molded magnet, it is effective because even a thin-walled magnet can generate a large magnetic field. be. If there is a distance between the inner surface of the sleeve and the surface of the magnet roller, 6m will leak from the sleeve surface.
Although the number of lines of force is reduced, by using rare earth magnets,
Enough 42 lines of force can be secured.In addition, the use of this rare earth 6B stone is particularly effective as it can be made smaller and lighter.

More detailed examples will be shown below.

Example 1 In the developing device shown in FIG. 1, the outer diameter of the sleeve was set to 24 [
mm], the outer diameter of the magnetic roller is 16 [mm]
], the distance between the rotation axis of the sleeve and the magnetic roller is 2 [mm], and the angle θ in the direction in which the axis is eccentric is O [0
] is an example. A toner containing styrene-acrylic magnetic powder of 40% by weight was used, and an average optical normality on the paper surface of 1.45 was ensured, resulting in an image of good quality.

Example 2 This is an example in which the developing device shown in FIG. 2 is incorporated into the image forming apparatus shown in FIG. Optical density on paper is at least 1.4
3 was secured, and a good image was obtained in which no background fogging or sweeping lines could be visually confirmed.

Example 3 This is an example in which a samarium-cobalt-based magnet manufactured by extrusion molding is used for the magnetic roller in the image forming apparatus of Example 1. In this example as well, a sufficient amount of toner conveyance was ensured, and an image with good image density and resolution was obtained.

The present invention can be widely used as an electrophotographic developing device, and can be applied to copying machines, printers, facsimile machines, displays, etc.

[Effects of the Invention] As described above, according to the above structure of the present invention, the amount of charge of the toner is stable and sufficient image density can be obtained even when the developing bias is low, thereby providing an image forming apparatus with low power consumption. It has the effect of being able to do things.

In addition, the development gap has areas with strong magnetic force and areas with weak magnetic force, allowing a sufficient amount of development to occur in the areas with weak magnetic force, and scraping off toner in the areas with strong magnetic force to ensure sufficient image density. However, it has the effect of realizing a high-resolution image forming apparatus without background fog or sweeping marks.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional schematic diagram of an image forming apparatus including a developing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional schematic view of a developing device in another embodiment of the present invention. FIG. 3 is a diagram showing the magnetic flux density distribution on the surface of a sleeve arranged not coaxially with the built-in magnet roller. 0 1 3 Latent image carrier Toner conveyor Sleeve Magnet roller blade Toner development bias applying means

Claims (2)

[Claims] (1) A latent image carrier that forms an electrostatic latent image, a non-magnetic cylindrical sleeve, and a developer conveyor having a cylindrical magnet roller inside are arranged so as to maintain a fixed interval. and a conveyance amount regulating member that supports toner containing magnetic particles as an image forming body on the surface of the developer conveyance body by magnetic force, and is disposed so as to maintain a predetermined interval with respect to the developer conveyance body. In a developing device that regulates the conveyance amount by a rotation shaft of the sleeve and the magnetic roller, and conveys the toner to a developing area where the latent image carrier and the developer conveying body are close to each other, and performs development. A developing device characterized in that the rotation axes of the two are not coaxial. (2) The developing device according to claim 1, wherein the magnet roller is made of a rare earth magnet.