JPS6030946B2 - developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to a developing device applied to an electrophotographic copying machine, and more particularly to an improvement in a magnetic brush developing device.

Development devices conventionally applied to electrophotographic copying machines include those based on the powder cloud method, cascade method, and magnetic brush method, but each of these has different characteristics. It is put into practical use in various fields.

Among these methods, in the case of the powder cloud method and the cascade method, the developing toner is concentrated in the area where the electric field intensity of the static latent image on the surface of the photoconductor is large, that is, in the discontinuous area of the original image density, and the reproduced image in this area is emphasized. This method has an advantage in reproducibility of office document copying because of the occurrence of so-called peripheral effects. However, this appears to be a disadvantage when it comes to reproducing general tone images, that is, reproducing parts of an original image where the density changes continuously. Further, in both the powder cloud method and the cascade method, since the developing area needs to be widened, the capacity of the developing device itself is also large. On the other hand, in the case of the magnetic rigidity method, a developer consisting of a mixture of iron powder and developer toner is attracted to a magnet, and the developer is formed into a brush shape at the magnetic pole portion, and the static latent image on the photoreceptor is rubbed. The image is developed and reproduced by washing.

At this time, since the iron powder itself is softened and acts as a developing electrode, it is possible to attach developing toner in proportion to the charge density of the electrostatic latent image, which is suitable for reproducing tone images. . Furthermore, the phenomenon device itself has the feature that it can be configured into a 4-type. As a further improvement of this magnetic brush development system, the magnetic poles are sequentially arranged in opposite polarities in the circumferential direction of the magnet bar, a non-magnetic material is provided on the outer periphery, and the two are moved relative to each other. A method is also known in which a magnetic brush is formed on a portion of the body surface that corresponds to the magnetic pole, and the surface to be developed is gently rubbed and developed using this brush.

The relationship between the amount of charge of the electrostatic latent image on the surface to be developed and the amount of developing toner attached thereto in this method is as shown by line a in FIG. 1A.

In other words, the relationship between the amount of electric charge and the amount of adhered toner is proportional, and if this relationship is expressed by the original image density Do - copied image density Dc characteristic of the copied image, as shown in the opening of Figure 1, the image of density Do At a certain concentration, the concentration Pc becomes saturated. For this reason, the tone image cannot be identified in the image density portion of Do above the certain density. This indicates that after the toner adhering to the copying material covers the surface to be developed by one or two layers, the density Dc of the copied image does not change even if the toner layer increases further. gives the impression of an extremely high-contrast image.

In order to soften the impression of this image, the amount of toner adhering to the surface to be developed must have the characteristics shown by line b in Figure 1A, but in this case, it is said that the reproducibility of the character image will deteriorate. produce defects. It is an object of the present invention to provide a new developing device that has all the advantages of the above-mentioned conventional developing methods and also provides new effects.

That is, the developing device of the present invention includes a magnetic field generating means having a plurality of magnetic poles fixed to a positioning layer, and a non-magnetic section provided so as to surround the magnetic field generating means and rotate. , the developer is held on the surface of the non-magnetic member by the magnetic action formed by the magnetic field generating means on the surface of the non-magnetic member, and the developer is supplied to the surface to be developed on which the latent image is formed by rotating the non-magnetic member. A developing device that performs development using a magnetic field generating means, in which magnetic poles that are close to the surface to be developed and that are adjacent to each other among a plurality of magnetic poles of the magnetic field generating means have the same polarity to form a repulsive magnetic field, and the same magnetic poles are close to the surface to be developed. This is a developing device that performs development by moving the non-magnetic member and the surface to be developed in the same direction at a position. DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrophotographic developing device of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a structural diagram showing an example in which the developing device of the present invention is applied to a transfer type electrophotographic copying machine.

In the figure, 1 is a drum-type electrophotographic photoreceptor having an insulating layer, a photoconductive layer, and a conductive support layer, and the entire surface of the photoreceptor is uniformly charged to a desired polarity by a primary corona discharger 2. Next, a secondary corona discharge simultaneous image exposure device 3 generates a DC corona discharge with a polarity opposite to that of the primary charging polarity, or an AC
Image exposure is performed simultaneously with corona discharge. Then, if necessary, the entire surface is exposed by the entire surface exposure section 4, and a high-contrast electrostatic latent image is formed on the surface of the photoreceptor. The electrostatic latent image is then turned into a head image by the developing device 5 of the present invention, and the developed image is transferred to the transfer material P by the transfer corona charger 6 under the action of a transfer electric field, and separated from the photosensitive drum. After that, the fixing roller 7 heats and fixes the image. The untransferred toner powder in the transfer process is removed by a cleaning device 8.
After being scraped off by the cleaning blade 9 inside the photosensitive drum, the toner is transported to the end of the photosensitive drum in the rotational axis direction by the transport screw 10, passes through a toner collection duct 11 provided in contact with the end, and is transferred to the developing device. 5 and will be collected for reuse.

In order to prevent toner crosslinking within the collection duct YII, a duct striking member (elastic material) 12 is attached to the duct member. Further, a driving pin 13 of a striking member is attached to the end of the photosensitive drum, and untransferred toner is reliably collected into the developing device by the vibration action of the driving pin and the striking member. The above-mentioned developing device is equipped with a toner concentration detection device in the developer using a carrier toner breakdown voltage change detection method in order to measure the developing ability of the developer. The concrete developer is replenished from the hopper 14.

The concrete developer contains carrier in a weight ratio of 40 to 50%, and the carrier that has increased in the developing device due to replenishment of the concrete developer overflows and is discharged from the developing device. In this method, the new carrier in the replenisher and the old carrier in the developing device always exist in a mixed state, and regeneration continues in a stable state over a long period of time. Furthermore, this developing device is equipped with a new toner scattering prevention device, eliminating the need for a suction blower and toner filter to collect scattered toner, which were essential in conventional dry copying machines. As a result, it is possible to design a compact dry copying machine.

Next, the specific configuration of the developing device of the present invention will be described in detail.

FIG. 3 is a sectional view of the developing device of the present invention. Developer container D
A fixed magnetic roller 15 and a rotating non-magnetic sleeve 16 that rotates in the direction of the arrow are housed in C. The magnetic pole arrangement of the magnetic roller 15 consists of a developer conveying magnetic pole N1, developer pumping magnetic poles S2, N3, and developing magnetic poles S4, S5. In particular, as shown in the drawing, the magnetic pole is located at the developing position relative to the photosensitive drum 17. It is characterized in that it consists of magnetic rollers that are magnetized so that S4 and S5 have the same polarity. In the above configuration, the developer transported by the magnetic pole NI and pumped up in S2 and S3 is regulated to a certain amount of developer thickness to 2 to 3 sails by the doctor blade 18, and then is rubbed against the photosensitive drum surface. .

The positional shape of the doctor blade and the strength of the magnetic flux at the regulating position have characteristics that determine the stable regulation of the developer around the sleeve and the magnitude of the driving torque of the sleeve. In this device, developer regulation is performed using a knife-edge shaped doctor blade 18 near the pumping magnetic pole, and the sleeve surface is knurled to limit the magnetic flux strength at the regulation position. By achieving stable conveyance and pumping, it became possible to develop a low-drive torque developing device, which is necessary for high-speed copying and developing devices. At the rear of the developing agent pumping magnetic poles S2 and S3, developing magnetic poles S4 and S5 are arranged, and these adjacent same poles form a repulsive magnetic field (see Fig. 3 for details on the magnetic field and magnetic force). A, see mouth), its S4, S5
The strength of the magnetic force is almost 0 at approximately the center.

Therefore, when the developer drawn up by the magnetic poles S2 and N3 reaches S4 due to the rotation of the non-magnetic body in the direction of the arrow, the developer is pushed onto the surface of the non-magnetic cylinder due to the action of the repelling magnetic field and the centrifugal force of the sleeve. On the other hand, the particles are repelled in the vertical direction, dispersed and separated from the surface of the non-magnetic cylinder, and collide with the photosensitive drum surface with the developing electrode effect substantially weakened to develop the electrostatic latent image. This is a phenomenon in which the dispersed developer moves on the surface of the photoreceptor and develops the electrostatic latent image, just like in the cascade development method. At this time, since the photosensitive drum 17 is moving in the direction of the arrow, the developer that collided with the photosensitive drum surface is then attracted to the non-magnetic material surface again when S5 approaches, and the developer is moved on the non-magnetic material again. The laying is done. When the developer reaches S5 from S4, the magnetic flux strength is substantially 0 to 0 between the non-magnetic material and the photosensitive drum in the central part of both magnetic poles, that is, the developer moves in a state where almost no magnetic force acts. will be carried out. At this time, as a result of the mutual attraction between carrier particles being weakened, a powder cloud state is generated due to the action of the centrifugal force of the magnetic sleeve and the repulsive magnetic field. Furthermore, by rotating the photosensitive drum and the non-magnetic cylinder in the same direction at the developing position where the same magnetic poles S4 and S5 face the photosensitive drum, the existence of the repulsive magnetic field and the rotation in the same direction cause the developer to develop. The developer moves on the surface of the photosensitive drum in cooperation with the developer conveyance force that draws the developer into the position, resulting in so-called cascade or powder cloud legal imaging. In this way, by aligning the magnetic poles of the magnets with the same polarity as S4 and S5 in the developing section to form a repulsive magnetic field, and by utilizing the same direction movement of the non-magnetic cylinder and the photoreceptor, we are able to overcome the conventional magnetic storm U In addition to the advantages of development, the cascade-like powder cloud development phenomenon that weakens the effect of the dispersed toner development electrode as described above adds the advantages of both, resulting in character reproducibility and tone image reproduction even in high image density areas. A developed image with extremely good quality can be obtained.

19 and 2 in the figure are the developer transport and light screws placed in pairs across the developer partition plate 21, and the developer is transported in the back direction from the screw 201.
The developer is passed to the screw 19 through a reversing screw provided at the rear end of the screw 20 and a developer transfer hole provided at the end of the partition plate 21, and is conveyed to the front side by the screw 19. Conveying screw 1
When using configurations 9 and 20, screws 19 and 2
If the transport capacity ratio of 0 is selected to be 6:10 to 8:10, it is possible to distribute the developer extremely uniformly in all directions along the longitudinal axis of the sleeve. Next, FIG. 4 shows another embodiment of the developing device of the present invention.

Components indicated with the same reference numerals as in FIG. 2 refer to the same components. Third
In the figure, below the developing magnetic brush rotating body shown in FIG. A developer recovery rotating body having a doctor blade 24 is provided. The magnetic pole arrangement of the fixed magnetic bar is as shown in the figure, and the developer (containing some carrier) attached to the surface of the photoreceptor after being developed by the developing magnetic seat U-element rotating body, and the developing magnetic The developer on the surface of the brush rotor is attracted by the magnetic force of the developer recovery rotor and drawn onto the non-magnetic cylinder. Thereafter, it is removed by a blade 24 that is slid on the surface of the non-magnetic cylinder, and is again subjected to development. Application of this developer recovery rotating body can remove excess developer toner and unnecessary carriers adhering to the surface of the photoreceptor, thereby preventing fogging on the background of copied images and damaging the photoreceptor surface caused by carriers, etc. prevention,
This brings about great effects such as saving on developer. Next, the fifth
Figures A, C, C and 2 show various magnetized arrangements of the fixed magnetic rods of the magnetic brush rotor for development, and the developing unit explained in the embodiment in Figure 2 is used in the developing unit for the photoreceptor. Other magnetic pole arrangements are also applicable.

The developing device of the present invention has been described above with reference to FIGS. 1 to 5. The improvements made by the present invention not only improve the quality of tone images produced by conventional magnetic brush development, but also reduce the cascade-like powder cloud that occurs in the repulsive magnetic field area. It is possible to achieve extremely ideal development that also provides excellent character reproducibility due to standard development.

[Brief explanation of drawings]

Figure 1A is a graph showing the relationship between the amount of charge and the amount of adhered toner.
Figure 1 is a graph showing the relationship between original image density and copied image density, Figure 2 is a configuration diagram showing an example in which the developing device of the present invention is applied to an electrophotographic copying machine, Figures 3, 4, and FIG. 5 is a structural explanatory diagram showing various embodiments of the developing device of the present invention. In the figure, 15 is a fixed magnetic bar, 16 is a rotating non-magnetic cylinder, 17 is a photosensitive drum, and 18 is a doctor blade.
Umzu Diagram 2 Diagram 3 Chrysanthemum 4 Diagram Chrysanthemum S Diagram

Claims (1)

[Claims] 1 Comprising a magnetic field generating means having a plurality of magnetic poles fixed at a fixed position, and a non-magnetic member provided so as to surround and rotate the magnetic field generating means, the magnetic field generating means is a non-magnetic member. A developing device that holds developer on the surface of a non-magnetic member by magnetic action formed on the surface of the non-magnetic member, and performs development by rotating the non-magnetic member and supplying the developer to the surface to be developed on which a latent image is formed. Among the plurality of magnetic poles of the magnetic field generating means, mutually adjacent magnetic poles that are close to the surface to be developed are set to have the same polarity to form a repulsive magnetic field, and these same magnetic poles interact with the non-magnetic member at a position close to the surface to be developed. A developing device characterized by performing development by moving a developing surface in the same direction.