JPS6321683A - Developing device - Google Patents

Abstract

PURPOSE:To reduce the return amount of toner which is scattered once from a toner conveyance surface member to an electrostatic latent image carrier and to obtain an image having no fog by providing a 3rd magnetic pole at the position where the toner conveyance surface member and electrostatic latent image carrier are closest to each other. CONSTITUTION:Single-component magnetic toner which is charged triboelectrically through the rotation of a developing sleeve 1 and covers uniformly the surface of the sleeve 1 by a toner control blade 4 and a toner conveyance control magnet 6 is carried to a development area 10, where the toner is scattered to stick on the dark part of a photosensitive body 5. Toner remaining on the sleeve is carried and recovered in a toner container 3 according to the rotation of the sleeve 1. The magnetic force of a 2nd developing pole magnet 8 is made large and a magnet 11 having the 3rd magnetic pole with the same polarity is provided on the side of the magnet 8 to generate magnetic force repelling the magnetic pole of the 3rd magnet 11. Consequently toner sticking on the surface of the photosensitive body 5 is held and the amount of toner which is attracted back is reduced to obtain the image having no fog.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention is applicable to an electrostatic latent image carrier (a typical example is a photoreceptor drum of an electrostatic copying machine), such as an electrostatic copying machine or an electrostatic recording machine. The present invention relates to a developing device used for the developing step in an image forming apparatus that includes a step of developing an electrostatic latent image formed thereon with toner.

[Background of the invention]

Conventionally, this type of developing device has a toner conveying surface member made of a non-magnetic material (a typical example is a cylindrical sweep shape).
The charged one-component magnetic toner layer on the surface of the developing sleeve (commonly referred to as a developing sleeve) is conveyed to a developing area including the position closest to the electrostatic latent image carrier by movement of the toner conveying surface member, and in the developing area. Under the influence of an electric field applied between the electrostatic latent image carrier and the toner transport surface member and a magnetic field generated by a magnetic pole arranged on the back side of the toner transport surface member, the -component magnetic toner is converted into an electrostatic latent image. A type of developing device is known that performs development by flying and adhering an electrostatic latent image onto the surface of a carrier.

In this type of developing device, as an improvement to obtain a clearer image, the magnetic hole that generates the magnetic field that affects the toner in the developing area is composed of two magnetic poles of different polarity,
A structure has been proposed in which the closest position between the toner transport surface member and the electrostatic latent image carrier is located between these two magnetic poles. However, although the developing device with this configuration has the advantage of preventing toner from adhering to the non-image area (bright area) of the electrostatic latent image carrier and does not cause fogging, the toner that has flown away from the toner transport surface member Since the toner is not sufficiently attached to the image area (dark area) of the electrostatic latent image carrier and is pulled back to the toner transport surface member by the electric field force or the magnetic force of the second polarity magnetic pole, the developing efficiency decreases and the image density decreases. It is an object of the present invention to provide a developing device capable of sufficiently adhering one-component magnetic toner only to an image area, with no toner adhering to a non-image area, and capable of obtaining a clear image with sufficient image density.

(Summary of the Invention) The present invention provides a method for applying a charged one-component magnetic toner layer on the surface of a toner conveying surface member made of a non-magnetic material to a developing area including a position closest to an electrostatic latent image carrier on the toner conveying surface. The one-component magnetic toner is transported by the movement of the member, and is transferred to the surface of the electrostatic latent image carrier under the influence of a magnetic field and an electric field applied between the electrostatic latent image carrier and the toner transport surface member in the development region. In a type of developing device that performs development by flying and adhering an electrostatic latent image, a magnetic pole that generates a magnetic field that affects the toner in the development area is located between the toner conveying surface member and the electrostatic latent image carrier. two magnetic poles of mutually different polarity arranged on the back side of the toner conveying surface member with the contact position in between; The arrangement is shown on the front side of the toner conveying surface member. 1 is a cylindrical toner conveying surface member (developing sleeve) made of a non-magnetic material;
It rotates in the direction of the arrow and is in contact with the one-component magnetic toner 2 in the toner container 3 . 4 is a toner regulating blade made of a magnetic material attached to the outlet end of the toner container 3 in order to uniformly coat the surface of the developing sleeve 10 with toner; 5 is an electrostatic latent image support (photoconductive) that rotates in the direction of the arrow; 6 is a toner transport regulating magnet facing the toner regulating blade; 7 and 8 are developing pole magnets with mutually different polarities; 9 is a toner transport magnet facing the inside of the toner container 3; be. A shaded area 10 indicates a developing area where toner flies and adheres, including the closest position between the developing sleeve 1 and the photoreceptor 5.

The closest position between the developing sleeve and the photoreceptor is between the positions of the maximum magnetic flux densities of the developing pole magnets 7 and 8. The magnets 6.7, 8.9 mentioned above are placed inside the developing sleeve 1. Reference numeral 11 denotes a third magnet disposed outside the developing sleeve 1 on the downstream side of the closest position between the developing sleeve 1 and the photoreceptor, and is close to the downstream magnetic pole 8 of the developing pole magnets 7°8. One side has a magnetic pole having the same polarity as the developing pole magnet.

Due to the rotation of the developing sleeve, the sleeve 1 is charged by friction and is charged by the toner regulating blade 4 and the toner transport regulating magnet 6.
The toner uniformly coated on the surface of the photoreceptor 5 is transported to the development area 10, and within this area, the toner flies and adheres to the dark area of the photoreceptor 5. The toner remaining on the sleeve 1 after passing through this area is carried into the toner container 3 and collected as the sleeve 1 rotates. The toner is stirred and transported again by the transport magnet 9 located inside the toner container 3, and is again subjected to development.

If all the toner that flew to the photoreceptor from the vicinity of the first development pole magnet 7 in the development area 10 adheres to the dark part of the photoreceptor, efficient development will be performed, but if the third magnetic pole 11 is not present, The electric field force between the sleeve 1 and the photoreceptor 5 and the first. Some of the toner ejected by the second developing pole magnets 7 and 8 is pulled back into the sleeve 1 again. The amount of toner drawn back into the sleeve is influenced by the strength of the second developing pole magnet 8 located on the downstream side. If the magnetic force of the second developing pole magnet 8 is strong, the amount of toner that is pulled back is large, and the developing efficiency is poor, but an image with less fogging can be obtained. The reason for this is that in the magnetic pole arrangement and magnetic pole strength of the two developing pole magnets 7.8 in the developing area, the resultant force 5 of the magnetic force component Gx in the radial direction of the sleeve and the magnetic force component Gy in the rotational direction of the sleeve is This is because, by acting on the toner, a stronger magnetic force acts on the toner, strongly suppressing the toner that is about to fly away, and also having the effect of forcing the toner that is pulled back out of the development area. Furthermore, if the magnetic force of the second developing pole magnet 8 is weak, the amount of toner that is pulled back is small, and although the developing efficiency is good, the image becomes foggy.

Therefore, in the embodiment of the present invention, in order to obtain an image without overlapping, the magnetic force of the second developing pole magnet is strengthened, and a magnet 11 having a third magnetic pole having the same polarity as that of the second developing pole magnet is installed on the side of the second developing pole magnet. By applying repulsive magnetic force between the magnetic pole of the second developing pole magnet and the third magnetic pole to the toner that is about to be drawn back into the sleeve, the toner remains attached to the surface of the multiphotoreceptor, resulting in high development efficiency. I'm trying to get an image without any turnips. The preferred strength of the magnetic force due to each magnetic pole in the diagram used in this example is as follows. N1 pole (6):
700~900 Gauss, S1 pole (7): 800~
900 Gauss, N2 pole (s): s o ~ 900
Gauss, third magnetic pole (term 8 of magnet 11): SOO~90
0 Gauss, S2 pole (9): 600-800 Gauss.

FIG. 2 shows another embodiment of the present invention, in which a third magnet 11 having a magnetic pole of the same polarity as the second developing magnet 8 is fixed in a rotatable cylindrical non-magnetic member 11'. Oh dear,
The toner adhering to the rotating member 11' is scraped off by a scraper 12.

Note that the polarity of the magnetic poles shown in the above figures may be reversed.

In the present invention, when the latent image carrier and the toner conveying surface member move in the same direction in the development area, the magnetic pole of the third magnet is at a distance t2 from the surface of the surface member. tl
It is preferable that O is larger because it does not disturb the development. For these distances t1 and t2, tl is 211E or more 5u+
Hereinafter, stability and concentration improvement could be achieved optimally within the range of tl of 1 day or more and 5 days or less.

(Effects of the Invention) According to the present invention, the amount of toner that has once flown from the toner conveying surface member to the electrostatic latent image bearing member returns is near the closest position between the toner conveying surface member and the electrostatic latent image bearing member. By providing the third magnetic pole, the amount of dust is reduced, development efficiency is increased, and an image with high image density without fogging can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views showing other embodiments of the present invention.

Claims (1)

[Claims] A charged one-component magnetic toner layer on the surface of a toner conveying surface member made of a non-magnetic material is conveyed to a development area including a position closest to the electrostatic latent image carrier by movement of the toner conveying surface member, and the developing Under the influence of a magnetic field and an electric field applied between the electrostatic latent image carrier and the toner transport surface member in the region, the one-component magnetic toner flies to the surface of the electrostatic latent image carrier in response to the electrostatic latent image. In a developing device of the type that performs development by adhesion, a magnetic pole that generates a magnetic field that affects the toner in the development region is placed between the toner transport surface member and the electrostatic latent image carrier at a position closest to the toner transport surface member. two magnetic poles of mutually different polarities arranged on the back surface side of the toner conveying surface member, and a magnetic pole located near one of the two magnetic poles and having the same polarity as that and located on the surface side of the toner conveying surface member in the vicinity of the closest position. A developing device comprising a third magnetic pole arranged.