JPH03196168A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the earlier deterioration of a developer and the increment of driving torque of a developing device by setting the sleeve plane of a developing roller facing a magnet cleaning roller as a homopolar magnetizing part. CONSTITUTION:A two-component developer 18 supplied to the developing rollers 11, 12 is carried and supplied to a photosensitive material 1 by rotating the developing rollers 11, 12, and is used in developing, and after that, it is further carried backward. Homopolar parts are provided at backward planes of sleeves 15, 16, and 17, and the repulsion magnetic field of the homopolar part is provided with the magnetic field of the developer 18 carried to the backward of the developing rollers 11, 12, and functions so as to separate magnetically the carrier and toner attracted and held with the developing roller from the planes of the sleeves 15, 16, and 17. Furthermore, the magnet cleaning roller 21 is provided at the backward of the developing rollers 11, 12, and its magnetic function is also applied so as to separate magnetically the carrier of the developer 18 and the toner from the developing roller and to transfer them, and also, they are carried from a transfer part. In such a way, it is possible to prevent the increment of the driving torque of a developing apparatus and the deterioration of the developer.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a laser beam printer. The present invention relates to a developing device that develops a latent image.

(Prior Art) This type of developing device uses a developing roller having a magnet inside a sleeve. The two-component developer consists of toner and carrier, and is conveyed while being stirred and supplied to the developing roller. Toner is contact-electrified by this agitation, and is usually considered an insulator. Conventionally, non-magnetic toner was the mainstream, but recently it has been said that magnetic restraint of toner can be increased to prevent toner plumes. Magnetic toner is also used.

The developing roller carries the supplied developer on the surface of the sleeve by the action of a magnet, and conveys and supplies it to the photoreceptor by rotation of the sleeve or magnet, thereby developing the electrostatic latent image formed on the photoreceptor. .

In order to temporarily separate the developer on the developing roller after being subjected to this development and to stabilize the amount of developer on the developing roller and replace it, for example, a developing roller facing the photoreceptor of the developing roller is used. A homopolar magnetized part (hereinafter simply referred to as the homopolar part) in which the same magnetic poles are lined up is provided on the sleeve surface on the side opposite to the position, and the developer is separated from the developing roller by a repulsive magnetic field formed between the same magnetic poles. The particles fall into the developing device and are reduced.

However, since the carrier is a magnetic material, it is susceptible to the attraction effect of the magnet in the developing roller and the bias voltage of the developing roller, and it goes around the repelling magnetic field, especially at both ends of the developing roller, and is attracted and held onto the sleeve of the developing roller. It may continue to occur. When this occurs, the toner ratio of the developer on the developing roller decreases, and carrier excess occurs, resulting in insufficient density and carrier adhesion to the white background portion of the image. Furthermore, there is a possibility that developer clogging may occur at the end of the developing roller. Also, when magnetic toner is used, due to its own magnetism, it is more likely to remain attached to the sleeve of the developing roller than non-magnetic toner, which is simply a charged toner (in a so-called sleeve development state). When sleeve development occurs, so-called capri occurs, in which toner adheres to the white background portion of the image.

Conventionally, to deal with this problem, a scraper or fur brush was used to forcefully scrape off the developer on the sleeve surface of the developing roller, or the bias voltage of the developing roller was kept low to prevent carrier and toner from adhering. ing.

(Problem to be solved by the invention) However, if the removal method is forcible using a scraper or fur brush, the stress exerted on the developer is large, leading to early deterioration of the developer, and the driving torque of the developing device increases. do. Further, if the developing bias voltage is limited, it becomes difficult to set the developing conditions, and it becomes difficult to deal with various cases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can solve the above-mentioned problems by improving the structure for collecting developer from a developing roller.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a developing device using a two-component developer, in which a sleeve is provided behind the developing roller that conveys and supplies the developer to the photoreceptor. A magnetic cleaning roller having a built-in magnet and capable of transporting the developer is provided, and the sleeve surface of the developing roller facing the magnetic cleaning roller is a homopolar part where identical magnetic poles are lined up, The developing device may use a two-component developer in which the toner is a magnetic toner.

(Function) The two-component developer supplied to the developing roller is conveyed and supplied to the photoreceptor by the rotation of the developing roller, subjected to development, and then further conveyed to the rear. There is a homopolar part on the sleeve surface behind this, and the repulsive magnetic field formed between the magnetic poles of the same polar part attracts the magnetic developer, which is conveyed behind the developing roller, to the developing roller. In addition to working to magnetically separate the held carrier and the toner that is not electrostatically charged or magnetically attracted and held by the carrier and the developing roller from the sleeve surface, there is also a mechanism behind the developing roller. There is a magnetic cleaning roller opposite thereto, the magnetic action of which also works to magnetically separate and transfer the developer carrier and toner conveyed behind the developer roller from the developer roller, and transport them from the transfer area. Therefore, not only charged toner but also magnetic carrier and toner can be reliably separated from the developing roller, held, and conveyed to other places by the two magnetic separating effects.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIGS. 1 and 2 are a sectional view of the vicinity of a photoreceptor and an enlarged sectional view of a main part of a developing device of an image forming apparatus showing a first embodiment of the present invention. As shown in FIG. 1, the photosensitive drum 1 is surrounded by a charging charger 2, an image exposure section 3 in a copying machine or laser beam printer, a developing device 4, transfer/separation chargers 5, 6, separation claws 7, cleaning/separation claws 7, etc. A blade 8 and an eraser lamp 9 are sequentially arranged in the rotational direction of the photosensitive drum 1. As a result, the photosensitive drum 1 transfers the photosensitive surface uniformly charged by the charger 2 to the image exposure section 3.
An electrostatic latent image is formed on the surface. This electrostatic latent image is developed by the next developing device 4, and the developed image is placed on the register roller 2 so that its leading edge coincides with the developed image.
3, the transfer sheet is transferred by a transfer charger 5. The surface of the photosensitive drum 1 after the transfer is cleaned of residual toner by a cleaning blade 8, and is then static-eliminated by an eraser lamp 9. After being charged by the charger 2, it is subjected to the next exposure.

As shown in FIG. 2, the developing device 4 has two developing rollers 1 and 12 disposed in a housing 10 close to the photosensitive drum 1. A replenishment roller 13 is provided behind the developing rollers 11 and 12, and a bucket roller 14 is provided behind the replenishment roller 13, respectively.

The developer roller 11.12 and the replenishment roller 13 are both mounted with a fixed magnet N in a rotationally driven sleeve 15.16.17.
, has S. In FIGS. 1 and 2, straight lines radially shown in the magnet portions of the developing roller 11, 12, the replenishing roller 13, and the magnet cleaning roller 21 (described later) indicate the direction of magnetism from the center of the roller to the periphery, respectively. It shows. In addition, M is a drive motor of the developer replenishment system, 24 is its transmission gear, M2 is a drive motor of the developing rollers 11 and 12, and 25 is its transmission gear.

The development conditions are, for example, Photosensitive layer of photosensitive drum: Se Photosensitive drum surface potential: +900V Development bias voltage: +400V It is said that

When development is performed in the conventional manner with the above settings, the developer 18 in the housing 10 is conveyed while being stirred and mixed by the packet roller 4 and supplied to the replenishment roller 13. The developer 8 supplied onto the supply roller 13 is conveyed and transferred to the upper developing roller 11 while being regulated to a constant layer thickness by a developer regulating blade 19 . The developer transferred to the upper developing roller 11 is conveyed and supplied to the photosensitive drum 1 to develop the static tjIWJ image on the photosensitive drum 1.

The developer 18 that has been subjected to development on the upper developing roller 11 is further conveyed and transferred to the upper developing roller 12 to develop the electrostatic latent image on the photosensitive drum 1 again.

Here, the back portion of the upper and lower developing rollers 11 and 12 opposite to the side facing the photosensitive drum 1 is a homopolar portion 1 in which magnets with the same polarity are lined up.
1a and 12a, and the developer transported by the repulsive magnetic field formed between the same poles is transferred to each sleeve 1.
5.16 It is designed to be pulled off from above. Further, a same-polarity portion 13a is provided at the back of the replenishment roller 13 past the portion facing the upper developing roller 11, so that the developer 18 after being supplied from the replenishment roller 13 to the upper developing roller 11 is further transported. When the developer 18 reaches the homopolar portion 13a, the developer 18 is separated from the sleeve 17.

The developer separated from the developing rollers 11, 12 and the supply roller 13 falls into the housing 10 and is collected. The collected developer is remixed with other developer in the housing 10, stirred, and restored to a predetermined toner concentration before being reused.

By the way, the surface potential of the white background portion of the electrostatic latent image formed on the photosensitive drum 1 is +1.
oov and a solid white area uniformly lower than the developing bias voltage +400■, and the toner is electrostatically attracted to the developing rollers 11 and 12 between the developing rollers 11 and 12. This solid white part exists over a wide area, and its presence ratio and frequency are high, so
While the developing roller L12 is repeatedly used, the toner of the developer 18 that was not consumed during development remains attached to the surface of the sleeves 1516, and even if it reaches the same polar parts 11a and 12a behind them. The repelling magnetic field does not pull it away from the sleeve 15,16. This phenomenon appears strongly because the toner is a magnetic toner,
Even after passing through the homopolar parts 11a, 12a of the sleeve 15, 16, it tends to remain attached to the surface, a phenomenon called sleeve development.

In such a sleeve development state, the development potential by the development bias voltage is lowered due to the negative charge that the toner has, and fogging occurs in solid white areas. Further, even if the toner is not a magnetic toner and does not easily cause sleeve development, the carrier may flow around to the photosensitive drum 1 side, resulting in a decrease in toner density or adhesion of the carrier to the blank white area.

Conventionally, to prevent these things, each sleeve 15.1
6, a scrubber or fur brush is used. However, since the particle size of the toner is extremely small, around IOμ, the toner may slip through a scraper or the like, and the stress caused at that time may cause the toner to fuse to the sleeve 15, 16.

In addition, the driving torque of the motor M2 increases along with this, and mechanical stress also increases.

To solve this problem, in this embodiment, a magnetic cleaning roller 21 is provided behind each developing roller 11, 12. This magnet cleaning roller 21 has magnets N and S provided inside a rotationally driven sleeve 22, and has a gap of 0.2 to 0.6 with respect to each developing roller 11 and 12.
It is set to about the level of the throat. The sleeve 22 is rotated at a much lower rotational speed than the developing roller 1112 by the transmission gear 25.

Here, the magnets in the lower developing roller 11 are S, N, S,
Five magnets are arranged in the order of N and S, and the first and last magnets S and S form a homopolar portion 11a on the surface of the sleeve 15 behind the developing roller 11.

Further, the magnets in the lower developing roller 12 are N, S, N, S from the upstream side to the downstream side of the developing section facing the photosensitive drum 1.
, N, and the first and last magnets N and N
has the same polarity 1 on the surface of the sleeve 16 behind the developing roller 12.
2a is formed.

Further, the magnet in the magnet cleaning roller 21 has a magnet N facing the substantially central part of the same polar part 11a behind the upper developing roller 11, and a magnet N facing the substantially central part of the same polar part 12a behind the lower developing roller 12. This S and another S on the almost opposite side form a same polar part on the surface of the sleeve 22 at the back of the magnet cleaning roller 21 facing toward the packet roller 6 in the device housing 10. 2fa is formed. Therefore, three magnets are provided.

The seven magnets in the replenishment roller 13 are arranged in the order of S, N, S, N, S, N, S from the lower part of the replenishment roller 13 on the packet roller 14 side to the lower part on the developing roller 11.12 side.

Moreover, as a result of the above, the magnet N of the replenishment roller 13 and the magnet S of the upper developing roller 11 are opposed to each other, and the upper and lower developing rollers 11
, work 2 is such that the magnets S and N face each other.

The flow of the developer 18 during development in this case will be explained.

The developer 18 supplied to the replenishment roller 13 is regulated by the developer regulating blade 19 in the same way as in the previous case, and is made into a constant layer thickness, and is then conveyed to the upper developing roller 11, where it is transferred to the upper developing roller 11, and is then regulated by the developer regulating blade 19. The magnetic field is transferred to the upper developing roller 11 by the attractive magnetic field formed between the opposing magnets N and S. The developer 18 transferred onto the lower developing roller 11 is conveyed to the photosensitive drum 1 and subjected to development. Thereafter, the developer 18 is further conveyed to the lower developing roller 12, and is transferred to the lower developing roller 12 by an attractive magnetic field formed between the opposing magnets S and N of the upper and lower developing rollers 11, 12. The developer 18 transferred onto the lower developing roller 12 is conveyed to the photosensitive drum 1 and subjected to development.

Thereafter, the developer 18 is further conveyed to the rear side.

In the above flow of the developer 18, a part of the developer 18 on the lower developing roller 11 is transferred to the lower developing roller 12 due to the solid white portion, the carrier of the developer 18, and the magnetic influence of the toner. Therefore, even if it goes around to the same polarity portion 11a behind the lower developing roller 11, it is not separated yet and tends to go around to the photosensitive drum l side again.

Further, in the lower developing roller 12 as well, the developer after being subjected to development tends to tend to flow around to the photosensitive drum 1 side without being separated from the lower developing roller 12 at the same polar portion 12a behind the lower developing roller 12.

However, each homopolar portion 11 behind each developing roller 11, 12
The magnets N and S of the magnet cleaning roller 21 face the magnets a and 12a, and exert an attractive action toward the roller 21 side. Therefore, the same polarity 11 of each developing roller 11.12
In a and 12a, the developer is separated by the repulsive magnetic field generated between the same poles, and the magnet of the magnetic cleaning roller 21 is attracted to the roller 21 side. This causes the photosensitive drum 1 to pass over each of the developing rollers 11 and 12 over their same polar portions 11a and 12a.
Even if there is a developer 8 that tries to turn to the side, it is removed by the magnet cleaning roller 2 at the same polar portions 11a and 12a.
The developer 18 can be reliably transferred to the photosensitive drum 1 side in a non-contact state and transported from that position to the other side. This eliminates the problem of being served on a regular basis.

According to experiments conducted by the present inventor, no change was observed in the development characteristics even after 100,000 copies were made, and good images without fogging could be obtained. In addition, since the rotation speed of the magnet cleaning roller 21 can be significantly lower than that of the developing roller, the torque required to rotate the sleeve is small, and since it does not apply much stress to the developer, it is possible to prevent toner deterioration. .

FIG. 3 shows a second embodiment of the present invention, which differs in that the magnetic cleaning roller 21 is placed close to each developing roller 11, 12 and the replenishing roller 13 with a gap of 0.2 to 0.6 cm. ing.

Note that the part of the magnet cleaning roller 21 facing the replenishment roller 13 is the midpoint between the adjacent magnets N and 3 that are far apart, and the part of the magnet cleaning roller 21 of the replenishment roller 13
A magnet S is positioned in a portion facing 1.

As a result, the developer 18 collected by the magnet cleaning roller 21 from each developing roller 11. Since there is no magnet on the side and the magnet N is on the replenishment roller 13 side, the magnet is transferred to the replenishment roller 13 side to some extent.

According to this embodiment, the toner of the developer 18 collected by the magnetic cleaning roller 21 has a particle size of 10 μm.
Even if it reaches the same polar part 21a behind the magnet cleaning roller 21, it may not be completely separated from the magnet cleaning roller 21 and remain attached. By planning the transition in advance, the same polar portion 2 of the magnet cleaning roller 21
The developer 18 can be reliably dropped at the position 1a, and the magnet cleaning roller 21 can be prevented from becoming dirty and the developing rollers 11 and 12 can be prevented from being contaminated thereby.

Although each of the above embodiments shows only the case where there are two developing rollers, the number of developing rollers can be changed as appropriate.
The structure for replenishing the developer to the developing roller is not limited to the above embodiments, and any system may be adopted.

4 and 5 show a third embodiment of the present invention, in which a collection guide 31 for collecting the developer 18 into the device housing 2 is provided around the outer periphery of the magnetic cleaning roller 21. In this case, the magnet cleaning roller 21 is attached to the sleeve 22.
There are fixed and magnet-rotating types, and the collection guide 3 is made of a non-magnetic, thin, flexible polyester film with a thickness of 100 μ, for example, or a non-magnetic stainless steel belt with a thickness of 100 μ, as shown in Figure 5. As clearly shown in , both ends 31a and 31b of the collection guide 31 along the outer periphery of the magnetic cleaning roller 21 extend downward. Four magnets, S, N, S, and N, are provided within the sleeve 22 at equal intervals.

As a result, the developer 18 after being subjected to development in the developing rollers 11 and 12 is transferred to the same polar portion 1 of the developing rollers Il and 12.
1a, 12a, the magnetic cleaning roller 2
Magnet cleaning roller 21 by rotating magnet 1
It is attracted to the side and transferred onto the collection guide 31. The transferred developer 18 is conveyed to the packet roller 14 side on the collection guide 31 by the rotation of the magnet.

The transported developer 18 is collected at the end 31 of the collection guide 31.
a and 31b extend downward and gradually move away from the magnetic cleaning roller 21 without turning around, and are released from the magnetic holding force after the time when the influence of the magnet of the magnetic cleaning roller 21 disappears. and everything will fall.

Therefore, in the case of this embodiment, the magnet cleaning roller 2
1, it is possible to reliably ensure that the developer falls in one day.

FIG. 6 shows a fourth embodiment of the present invention, which differs from the third embodiment in that the sleeve 22 of the magnet cleaning roller 21 is also used as a recovery guide. This embodiment is more advantageous than the third embodiment in that the number of parts is reduced, and other effects remain the same.

(Effects of the Invention) According to the present invention, the two-component developer supplied to the developing roller is conveyed and supplied to the photoreceptor by the rotation of the developing roller, subjected to development, and then further conveyed to the rear. When,
The repulsive magnetic field formed between the magnetic poles of the same polarity on the rear sleeve surface causes the magnetic carrier of the developer to be attracted and held by the developing roller, and the carrier that is not charged or has magnetism to be held by the developing roller. In addition to working to magnetically separate the toner that is attracted and held by the sleeve from the sleeve surface, the magnetic action of a magnetic cleaning roller that faces the back of the developing roller in a non-contact manner also causes the toner to be transported behind the developing roller. It works to magnetically separate the developer carrier and toner from the developing roller, so not only charged toner but also magnetic carrier and toner can be developed by the two magnetic separation actions. The carrier can be reliably separated from the roller and transported to another location, without increasing the developer drive torque or deteriorating the developer due to stress, which is the case when using a scraper or fur brush. Stable development characteristics without adhesion to solid white areas or capri can be guaranteed over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the vicinity of a photosensitive drum of an image forming apparatus showing a first embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view showing main parts of a developing device, and FIG. FIG. 4 is an enlarged sectional view of the main parts of the developing device showing a fourth embodiment of the present invention, FIG. 5 is an enlarged sectional view of the magnet cleaning roller section, FIG. 6 is an enlarged sectional view of a magnet cleaning roller section showing a fifth embodiment of the present invention. ■・−・−・・−・−−−−−−・・−・Photosensitive drum 11.12・−・・−・−・−・−−−−−−−・
Developing rollers 11a, 12a-- Same polar portion

Claims (2)

[Claims] (1) In a developing device that uses a two-component developer, a magnetic cleaning roller capable of conveying the developer is provided near the developing roller that conveys and supplies the developer to the photoreceptor, and is opposed to the magnetic cleaning roller of the developing roller. The sleeve surface is
A developing device characterized by having a homopolar magnetized section in which identical magnetic poles are lined up. (2) The developing device according to claim 1, wherein a two-component developer in which the toner is a magnetic toner is used.