JPH0451067A - Developing device for housing magnetic developer - Google Patents

Abstract

PURPOSE:To make a magnetic developer scratched off from a doctor flow without being stagnated and to prevent the reduction in electrifying efficiency by providing a magnetic body plate. CONSTITUTION:This developing device is provided with the magnetic body plate 10 arranged apart form a developing roller 6 and almost perpendicular to the surface of the developing roller 6, on the upstream side of the doctor 9. The magnetic body plate 10 is magnetized by the magnetic force of the developing roller 6, and in this magnetization, a polarity is repeatedly replaced by the rotation of the developing roller 6. On the other hand, the developer scratched off by the doctor 9 is returned to the side of the magnetic body plate 10, and moved in a direction where it is separated from the developing roller along the downstream side surface of the plate 10. When the scratched off developer 10 reaches the end part of the magnetic body plate, it is moved in the direction of the developing roller 6 along the upstream side surface, joined to the napping of the surface of the developing roller 6, and used for developing processing. Thus, the developer scratched off by the doctor 9 is prevented from being stagnated on the upstream side of the doctor and the reduction in the electrifying efficiency of toner can be prevented, as well.

Description

Detailed Description of the Invention fal Industrial Application Field This invention forms spikes of magnetic developer (magnetic toner and magnetic carrier) on the surface of a developing roller having a magnetic roller, and brings the spikes into contact with a photoreceptor. The present invention relates to a developing device that supplies developer to a photoreceptor by causing the developer to reach the photoreceptor.

(b) Prior Art Some developing devices included in electrophotographic image forming apparatuses perform developing processing using a two-component developer consisting of magnetic toner and magnetic carrier. This developing device includes a toner hopper that stores magnetic toner, and a developer tank that is equipped with a developing roller, stores a magnetic carrier, and is supplied with the magnetic toner from the toner hopper. The developing roller is composed of a magnet roller having magnets arranged radially inside thereof, and a sleeve provided outside the magnet roller, and the magnetic force of the magnet roller forms spikes of magnetic carrier and magnetic toner on the surface of the sleeve. The magnetic nod roller and the sleeve are rotated in opposite directions, and the state of the spikes formed on the sleeve surface changes. As a result, the magnetic toner and the magnetic carrier are frictionally charged to opposite polarities.

Toner is replenished to the photoconductor by the spikes facing the photoconductor. At this time, if the height of the spikes varies from time to time, the amount of toner supplied changes, causing uneven image density. arise. Therefore, the height of the spikes is generally regulated by a doctor placed opposite the developing roller before contacting the photoreceptor.

(C) Problems to be Solved by the Invention However, as described above, when the height of the spikes on the developing roller is regulated by the doctor, the scraped developer may become stagnant on the upstream side of the doctor. In other words, in conventional developing devices, there is nothing in the developing tank other than the developing roller that can stir the developer, and the fluidity of the developer that is scraped off by the doctor and separated from the developing roller surface is extremely reduced. However, it was stuck upstream of the doctor. If the developer stagnates upstream of the doctor in this way, the developer
In particular, there was a problem in that the magnetic carrier could not be used effectively, resulting in a decrease in the rise of the charging potential. In the developer tank, toner is replenished one after another, but carrier is not replenished, so if carrier stagnates upstream of the doctor, the amount of carrier in the developer decreases extremely, and the replenished toner becomes electrically charged. It becomes difficult. The initial developer stagnation leads to subsequent developer stagnation, making it impossible to effectively utilize the magnetic carrier and magnetic toner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that prevents developer scraped off by a doctor from stagnation upstream of the doctor to prevent a decrease in toner charging efficiency.

(61 Means for Solving the Problems) This invention forms spikes of magnetic developer on the surface of a developing roller, and scrapes off the developer on the upper portion of the spikes with a doctor placed opposite to the developing roller. The developing device for regulating the height of the spikes is characterized in that a magnetic plate is provided on the upstream side of the doctor at a distance from the developing roller and arranged substantially perpendicular to the surface of the developing roller.

(e) Function In the present invention, the magnetic plate arranged substantially perpendicular to the surface of the developing roller is magnetized by the magnetic force of the developing roller. As the developing roller rotates, the polarity of this magnetization changes repeatedly, while the developer scraped off by the doctor returns to the magnetic plate, is attracted to the magnetized magnetic plate, and moves along the magnetic plate. and move on. First, it moves in a direction away from the developing roller along the downstream side of the magnetic plate, and when it reaches the end of the magnetic plate, it is then moved toward the developing roller along the upstream side of the magnetic plate. Then, it joins the spikes on the surface of the developing roller and is used for the developing process.

(f) Embodiment FIG. 3 shows a schematic structure of a developing device which is an embodiment of the present invention.

A main body (frame) 1 of the developing device consists of a developer tank 2 portion and a toner hopper 3 portion. The toner hopper 3 stores magnetic toner. Further, a magnetic carrier is stored in the developer tank 2, and magnetic toner is supplied from a toner hopper 3. A partition plate 4 is arranged between the toner hopper 3 and the developer tank 2. The partition plate 4 does not completely separate the developer tank 2 and the toner hopper 3, but forms a slit-shaped toner supply port 4a along the front-rear direction in the figure.

The toner in the hopper 3 is supplied to the developer tank 2 from this toner supply port 4a.
supplied to

A toner conveying member 5 is disposed in the toner hopper 3 near the toner supply port 4a. The toner conveying member 5 is connected to a drive system (not shown) on the back side, and rotates counterclockwise as indicated by an arrow in the figure to feed the magnetic toner in the toner hopper 3 into the developer tank 2. A developing roller 6 is provided within the developing tank 2 . FIG. 2 shows the structure of the developing ports 6 to 6.

The developing roller 6 has a cylindrical sleeve 6a and a magnet roller 6b housed within the sleeve 6a. The magnet roller 6b has magnets 61 to 66 arranged radially outward. This magnet group 61
.about.66 generate lines of magnetic force on the surface of the sleeve 6a. The magnetic carrier and magnetic toner in the developer tank 2 form spikes 6C along these lines of magnetic force as shown in the figure, and the spikes contact the photoreceptor 7, and the toner among them electrostatically adheres to the photoreceptor 7. do.

The sleeve 6a is rotated clockwise, and the magnet roller 6b is rotated counterclockwise in the opposite direction to the sleeve 6a. As described above, spikes of magnetic carrier and magnetic toner are formed on the surface of the sleeve 6a, but when the sleeve 6a and the magnet roller 6b rotate in opposite directions like this, the state of the magnetic lines of force changes every moment. The magnetic carrier and the magnetic toner are sufficiently stirred, and both are triboelectrically charged to opposite polarities.

In FIG. 3, an opening 2a is formed on the right side of the developer tank 2, and the developing roller 6 faces the photoreceptor 7 at this opening 2a. The photoreceptor 7 has photoconductivity so that it acts as an insulator when it is not irradiated with light, and when it is irradiated with light, the portion that is irradiated with the light acts as a conductor. The photoreceptor 7 rotates counterclockwise as shown by an arrow in the figure, and is provided with a charging device 7a, a transfer device fi7b, a charging device 70, etc. around the photoreceptor 7. Further, a polygon mirror 7d, which is irradiated with laser light from a laser oscillation device (not shown), is placed on the surface of the photoreceptor 7 at a position between the charging device 7a and the developing device 1 (exposure section PI).
When forming an image guided via a mirror 7e etc., the photoreceptor 7
is first charged by the charging device 7a, and then the exposed portion P
1, it is exposed to laser light from a laser oscillation device. Then, since the aIIt property resides in the area irradiated with the light, the charge in that area is canceled, and a contrast in charge occurs between the area irradiated with the laser light and the area not irradiated (electrostatic latent image). Note that the light emitted from the laser oscillation device is light corresponding to the characters and patterns on the screen, and a latent image is formed on the photoreceptor 7 in which the charge of the character 1 pattern part is canceled. On the other hand, the photoreceptor 7 is grounded, and a voltage having the same polarity as the charging polarity of the magnetic toner is applied to the developing roller 2. For example, when the charging bag W7a is for charging the photoreceptor 7, a magnetic toner that can be sufficiently frictionally charged is used as the magnetic toner. The photoreceptor is grounded to oV, and a scraping voltage is applied to the developing roller 6. Then, the positively charged toner electrostatically adheres to the OV region where the voltage is lower, that is, the region where the charge on the photoreceptor has been canceled. As a result, the electrostatic latent image on the photoreceptor is visualized (reversal development).

Thereafter, paper is fed to the photoreceptor 7 by transport rollers 8a, 8b, etc. from a paper feeding section (not shown), and the toner image is transferred onto the paper.

In the developing device configured in this manner, the toner conveying member 5 rotates so as to feed sufficient toner to the developer tank 2 for the image to be formed. FIG. 4 is a timing chart showing the driving timing of the toner conveying member 5. As shown in FIG.

FIG. 2A shows processing performed when the main body of the image forming apparatus is powered on. When the power of the image forming apparatus main body is turned on, the main motor is turned on and the developing roller 6 and photoreceptor 7 are turned on.
Rotation and operation checks are performed. Further, the static eliminator around the photoconductor sufficiently removes residual toner and residual charge on the photoconductor, and the heater of the fixing device is turned on to start raising the temperature. However, at this time, the toner conveying member 5 of the toner hopper does not operate, and the toner in the toner hopper 3 is not sent to the developer tank 2.

CB) to CB (D) in the same figure show operations during image forming processing. The printing area in the figure is the size of the formed image, for example, B5 size, A4 size, etc. When printing is performed in this printing area, the laser oscillation device is turned on and the photoreceptor is exposed to laser light. The on-time of the laser oscillation device corresponds to the amount of printing. As described above, this image forming apparatus converts the two character designs into laser light and irradiates the laser light, so toner adheres to the portion of the photoreceptor that is irradiated with the laser light. Therefore, in this device, the on-time of the laser oscillation device is taken as the printing amount, and the toner conveying member 5 is driven in proportion to the on-time. Furthermore, in this device, the amount of toner used when the laser oscillation device is turned on one unit and the amount of toner conveyed to the developer tank 2 when the toner conveying member 5 is driven one unit are almost the same. The on-time of the laser oscillation device and the on-time of the toner conveying member 5 almost match, as shown in FIGS.

In this manner, when the laser oscillation device irradiates laser light, by operating the toner conveying member 5 in accordance with the ON time of the laser beam, only the necessary and sufficient toner can be sent to the developer tank 2. In the case of an image forming apparatus that does not use a laser oscillation device, such as a copying machine that forms a latent image using light reflected from an original, the amount of light reflected from the original is detected, and the amount of printing is determined based on the amount of light reflected from the original. In general copying machines, toner adheres to areas of the photoreceptor that are not exposed to light, so as the amount of detected light increases, the amount of printing decreases and the amount of drive of the toner conveying member decreases.

On the other hand, FIG. 1 is a diagram showing the flow of toner and carrier. Arrows in the figure indicate the flow of toner and carrier within the developing device. First, toner is supplied to the developing roller 6 from the toner hopper 3 by the toner conveying member 5 . The supplied toner and the carrier in the developing tank form spikes on the sleeve 6a, and are conveyed toward the photoreceptor 7 by the rotation of the sleeve 6a as shown by the arrow in the figure. A doctor 9 having an acute-angled tip is disposed upstream of the portion where the developing roller 6 faces the photoreceptor 7 (in the flow direction of toner and carrier). The doctor 9 scrapes off the upper part of the spikes of magnetic carrier and magnetic toner on the developing roller 6 to regulate the height of the spikes.

Further upstream of the doctor 9, a magnetic plate 10 is arranged. The magnetic plate 10 is provided so as to be slightly inclined in a direction along the toner flow direction rather than perpendicular to the surface of the developing roller 6. Further, the distance of the magnetic plate 10 from the surface of the developing roller 6 is set longer than the distance between the doctor 9 and the surface of the developing roller 6. The magnetic plate 10 is magnetized when facing the magnet roller 6b, and the direction of its magnetization polarity is reversed by rotation of the magnet roller 6b. Therefore, the magnetic carrier and magnetic toner scraped off by the doctor 9 are carried along the magnetic plate 10 as indicated by the arrow in the figure by the magnetic force of the magnetic plate 0, and are again deposited on the surface of the developing roller 6. It is used for image forming processing. By providing the magnetic plate 10 in this way, the toner and carrier scraped off by the doctor 9 can be fully utilized, and in particular, the carrier that is not normally replenished in the developing tank 2 is not stagnated behind the doctor 9. You will no longer have to worry about
Since it is fully involved in the triboelectric charging process, it is possible to prevent a decrease in charging efficiency.

(Effects of the Phantom Invention As described above, according to this invention, the magnetic developer scraped off from the doctor is made to flow without stagnation with a simple structure that only requires the provision of a magnetic plate, and is allowed to flow back into the spikes for development processing. In other words, the magnetic carrier content in the developer can be prevented from decreasing and can be used effectively, and the rise of the charging potential will not deteriorate.

FIG. 2 is a diagram showing the configuration of the developing roller, FIG. 3 is a diagram showing the configuration of the vicinity of the developing device, and FIGS. 4(A) to (D) are diagrams showing the toner conveying member. FIG. 2 is a diagram showing drive timing, in which (A) shows the operating state of the main body of the image forming apparatus during a warm amplifier, and (B) to (D) show the operating state during image formation.

1-Developing device main body, 2-Developer tank, 3-toner hopper, 4
- partition plate, 4a - toner supply port, 5 - toner transport member, 6 - developing roller, 6a - three-flow b - magnet roller, 6c - spike stand, 7 - photoreceptor, 9 - doctor, 10 magnetic plate.

Claims (1)

[Claims] (1) Form spikes of magnetic developer on the surface of the developing roller,
In a developing device that regulates the height of the spikes by scraping off the developer in the upper part of the spikes with a doctor disposed opposite to the developing roller, there is a developing device located upstream of the doctor and spaced apart from the developing roller. A developing device containing a magnetic developer, characterized in that a magnetic plate is arranged substantially perpendicularly to the surface of a roller.