JPS622313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device for developing an electrostatic image, and more specifically, the present invention relates to a developing device for developing an electrostatic image. The present invention relates to a developing device that forms a brush and performs development using the brush.

Taking an image forming apparatus such as an electrophotographic copying machine as an example, conventionally known developing devices applied to these copying machines include those based on the powder cloud method, cascade method, and magnetic brush method. They have different characteristics and are put into practical use in various fields depending on their characteristics.

In the case of the powder cloud method and the cascade method, the developing toner is concentrated in the area where the electric field gradient of the electrostatic latent image on the surface of the latent image carrier such as a photoreceptor is large, that is, in the discontinuous area of the original image density. This method has an advantage in the reproducibility of office document copying, that is, in line copying, because of the occurrence of so-called peripheral effects in which a reproduced image of a portion is emphasized. However, this is a general tone image (image containing halftone density)
This appears as a disadvantage in the reproduction of parts of the original image where the density changes continuously.

In addition, in both the powder cloud method and the cascade method, it is necessary to widen the area in which the developer acts on the surface of the latent image carrier, so that the capacity of the developing device itself becomes large.

On the other hand, in the case of the magnetic brush method, a developer consisting of a mixture of an iron powder carrier and a developer toner is attracted to a magnet, and the developer is formed into a brush shape at the magnetic pole portion, and the electrostatic potential on the latent image carrier is The image is developed and reproduced by rubbing the image. At this time, since the iron powder itself acts as a soft developing electrode, it is possible to attach the developing toner in proportion to the charge density of the electrostatic latent image, that is, it is suitable for reproducing tone images.

Further, the developing device itself has the feature that it can be constructed in a small size.

As a further improvement of this magnetic brush developing device, for example, in the dry developing process of an electrophotographic copying device, a plurality of magnetic poles are arranged in a cylindrical shape, close to the outer periphery, and a non-magnetic sleeve is rotated. , a developer having a magnetic carrier and a toner,
The developer is conveyed from the developer reservoir to a developing magnetic pole located opposite to an electrostatic image holding member such as a photoreceptor, and the developer is made to stand up like a brush at this developing magnetic pole, thereby forming an electrostatic image on the electrostatic image holding member. A sleeve developing method in which development is performed by lightly rubbing the sleeve is widely used. In a developing device employing the sleeve developing method described above, the developer separated from the sleeve after development is once stirred and sent to a developer reservoir installed near the bottom of the sleeve. Then, in order to hold and transport the developer from the developer reservoir to the developing magnetic pole position on the sleeve, a magnetic field is created by the magnetic pole inside the sleeve between the developing magnetic pole and the developer reservoir, and the magnetic field is applied to the developing magnetic pole. A method is used in which the developer is attached to a sleeve and transported.

In such conventional sleeve developing methods, when the potential of the electrostatic image is low or when the speed of the electrostatic image holding member is high, one sleeve is not necessarily sufficient for development. Therefore, it is necessary to use two or more sleeves in parallel to lengthen the development zone and extend the development time. In addition, when the electrostatic image holding member moves at a fast speed, when the sleeve rotates in the same direction as the electrostatic image holding member, uneven development may occur in the solid black area, where the developing section is uneven as shown in Figure 1A. appears more easily, and therefore the sharpness of the developed line also tends to decrease. If the sleeve rotates in the opposite direction to the electrostatic image holding member, please refer to Figure 1B.
As shown in the figure, uneven development tends to occur, with white areas appearing above the solid black area in the direction of movement and dark areas below. especially,
In a system in which the sleeve rotates in the opposite direction, the difference in relative speed between the sleeve and the electrostatic image holding member becomes large, and uneven development tends to occur. Furthermore, even when the sleeve rotates in the forward direction with respect to the electrostatic image holding member, uneven development is likely to occur, although it is not as large as when rotating in the opposite direction. This will reduce the sharpness.

The present invention aims to eliminate such conventional drawbacks, and is characterized by providing the following developing device.

(1) A region through which a moving electrostatic image holding member passes, with a first developing section provided on the upstream side and a second developing section provided on the downstream side relative to the direction in which the electrostatic image moves. A developing device having a developing section and supplying developer to the electrostatic image in a first developing section and a second developing section, wherein the developing device is provided in the first developing section, and the electrostatic image is held in the first developing section. a non-magnetic first developer carrier that moves faster than the moving speed of the member and in the same direction as the moving direction to supply the developer; and a side opposite to the developer carrying surface of the first developer carrier. a first fixed magnetic means that is fixedly provided and forms a magnetic field in the first developing section; and a first fixed magnetic means that is provided in the second developing section and moves at a speed slower than the moving speed of the electrostatic image holding member in the first developing section; a non-magnetic second developer carrier that moves in the same direction as the moving direction and supplies the developer; A developing device comprising: second fixed magnetic means for forming a magnetic field in a developing section.

Specific embodiments of the invention will be understood from the following description.

Next, the technical effects of the developing device according to the present invention will be considered first. When the developer carrier moves in the same direction (forward direction) as the electrostatic image holding member, and the moving speed of the developer carrier is faster than the moving speed of the electrostatic image holding member, as shown in FIG. 1A, As mentioned above, uneven development, which is called "normal sweep development", is likely to occur. On the other hand, when the moving speed of the developer carrying member is slower than that of the electrostatic image holding member, this sweeping tendency is reversed, resulting in uneven development as shown in FIG. 1B. Therefore, in a developing device in which a plurality of developer carriers are installed together, at least one of the developer carriers that provides developer faster than the others moves faster than the moving speed of the electrostatic image holding member, and the rest By making at least one of the developer carriers slower than the electrostatic image holding member, it is possible to substantially eliminate the uneven development caused by the developer sweeping up the developing surface in the conventional apparatus described above. . Furthermore, even in this case, it is preferable that the relative speed of the developer carrier constituting the latter stage with respect to the electrostatic image holding member be as slow as possible.

The relative velocity difference between the developer carrier and the electrostatic image holding member is as follows for both the front and rear developer carriers:
It has been experimentally shown that keeping the moving speed of the electrostatic image holding member within 20%, preferably within 10%, of preventing the above-mentioned sweeping development and preventing the inconvenient stripping phenomenon caused by the developer carrier in the latter stage. It is appropriate from

Examples of the developing device according to the present invention are shown in FIGS.
This will be explained in detail with reference to FIG.

In the embodiment shown in FIG. 2, two non-magnetic hollow cylinders (hereinafter referred to as sleeves) are arranged to face a drum-shaped electrostatic latent image carrier and within the downward rotation range of the carrier. 1 shows an apparatus for developing an electrostatic image on a carrier.

In the figure, the electrostatic image carrier 1 is rotating in the direction of the arrow, and in the developing section, two non-magnetic rotating sleeves 22A,
22B are arranged at a short distance from each other. The sleeve is driven at a rotational speed different from the peripheral speed of the electrostatic image carrier 1 by a known driving means.

As an example, the peripheral speed of the electrostatic image carrier is 500mm/
sec, the peripheral speed of the front sleeve was set to 550 mm/sec, the peripheral speed of the rear sleeve was set to 450 mm/sec, and the sleeve diameter was set to 63 mm. Both sleeves have fixed magnetic means 23A, 23B inside them,
The magnetization poles of each magnetic means are different.

First, the magnetic pole arrangement of the first magnetic means 23A will be explained. The illustrated magnetic means 23A is formed as a magnetic roller, and has magnetized poles N ₂ , S ₂ , and _{N 3 spaced} apart from each other at equal angles near its surface. are placed next to each other.

Next, a second magnetic means 23B is disposed downstream along the electrostatic latent image carrier of the first magnetic means,
As shown in the figure, it is formed of a four-pole magnetized roller, and the _N1 pole and _S1 pole are magnetic poles that have the function of drawing up and transporting the developer. Both magnetic poles S ₃ and S ₄ are developing magnetic poles arranged at a predetermined angle (θ) apart from each other in opposite directions from the point where the magnetic roller is closest to the surface of the electrostatic image carrier. be. These developing magnetic poles S ₃ and S ₄ having the same polarity are selected to be different in polarity from the developing magnetic pole N ₃ of the first magnetic means.

Reference numeral 25 denotes a developer in the developing device housing 5a, which contains a mixture of a magnetic carrier and a developing toner. Also, inside this housing,
Two screws 26A and 26B for stirring the developer 25 in the direction of rotation of the sleeve, and the sleeve 2
A blade 30 that regulates the thickness of the developer pumped onto the surface of the sleeve 3B to a predetermined value, a cleaning blade 31 that removes residual developer from the sleeve surface after development, and a replenishment developer storage chamber 27 and its lower part. It has a replenishment roller 28 provided in the opening. As the roller 28 rotates, the developer that has entered the recess provided on the surface of the roller 28 is transferred to the roller 28.
8 rotates, the housing 5a of the container is dropped into the developing chamber 29 provided with the sleeve, and the developer is replenished.

The sleeve 22A and the magnetic means 23A
constitutes the first developing section of the present invention, and the sleeve 22B and the magnetic means 23A constitute the second developing section.

To explain the developing operation in the above developing device,
In synchronization with the rotation of the electrostatic image carrier 1, the sleeves 22A and 22B start rotating by a known driving means. Due to the rotation of the sleeve, first the magnetic means 2
The developer adheres to the surface of the sleeve 22B by the magnetic force of the _N1 pole of 3B.

The attached developer is the above N ₁ pole and the S ₁ above it.
It is attracted to the surface of the sleeve 22B by the magnetic force of the pole,
The adhesion amount is uniformly regulated by the developer regulating plate 30 on the way, and the developer reaches the _S1 pole position. The developer that has further passed through the _S1 pole position is attracted toward the sleeve 22A by the magnetic force of the _N2 pole of the magnetic means 23A. sleeve 2
The developer that has passed through the sleeve 2A moves along with the sleeve 22A from the magnetic pole S ₂ to the position _{N 3 due} to the magnetic force of the next magnetic pole S 2 . And this magnetic pole N ₃
At this position, the magnetic carrier stands up due to the magnetic force of the magnetic pole N ₃ , forms a magnetic brush, and moves the electrostatic image carrier 1
The upper electrostatic image is first developed. That is, the above magnetic pole N ₃
In this position, the carrier 1 is subjected to development using a conventional magnetic brush development method to form a visible image with rich gradation and minimal edge effects. Furthermore, the spikes of the developer that have stood up are gently folded down again as the sleeve 22A rotates, and reach the direction of the sleeve 22B that is arranged downward. The developer on the sleeve 22A that has approached the sleeve 22B has the magnetic pole N ₃
It is released from the magnetic field caused by the magnetic means 23B, is attracted by the magnetic force of the magnetic pole _S3 on the magnetic means 23B side, and crosses the gap between both sleeves in a bridge shape to the sleeve 22B side. Due to the magnetic force of the magnetic pole _S3 , the developer adhered to the sleeve 22B again forms a magnetic brush at the position of the magnetic pole _S3 , and the electrostatic image on the carrier 1 is developed with the brush. Note that since there is a magnetic pole _S4 of the same polarity in the vicinity of the magnetic pole _S3 below, a repulsive magnetic field exists between these magnetic poles _S3 and _S4 . Therefore, the developer moving as the sleeve 22B rotates passes through the repulsion magnetic field after forming a brush with the magnetic pole _S3 .
At this time, the developer on the sleeve 22B is blown toward the latent image carrier by the action of the repulsive magnetic field before the magnetic brush is pushed down by the magnetic pole _S3 . In this way, the developer separated from the surface of the sleeve 22B is in a state similar to powder cloud development or cascade development due to the cooperation of the centrifugal force, gravity, inertial force of the sleeve 22B, and the magnetic field of the lower magnetic pole _S4 . Developing the electrostatic image carrier. Then above magnetic pole S ₄
The developer scattered by the magnetic force of the sleeve 2
A magnetic brush is formed on 2B to develop the latent image on the latent image carrier. That is, at the development position where the magnetic poles of the magnetic means 23B of the same polarity are arranged, in addition to the advantages of the conventional magnetic brush method, the advantage of the cascade powder cloud development method as described above, that is, the development that expresses the edge effect, can be achieved. It also enables development with The developer that has passed the development position is removed from the sleeve 22B by a scraper 31 placed in a position with weak magnetic force.
The developer is removed from the developer, and the developer conveyance and development steps described above are repeated again. In the above development method, since the relative speed between both sleeves and the electrostatic image carrier 1 is small and the speed of the former sleeve is high, it is also possible to rotate the developer carrier. Even if the toner is consumed in one development section, the developer can be appropriately agitated until the next second development section is reached. In this way, when developing is carried out while the developer on the sleeve is transferred between the sleeves arranged in parallel, if there is a large speed difference between the electrostatic latent image carrier and the sleeve, the sleeve may be The developer on the sleeve is biased and falls on a part of the sleeve, causing unevenness, which is undesirable because the subsequent development becomes uneven. However, in the above-described embodiment, the developer is delivered while the speed of the rear sleeve and the speed of the front sleeve are maintained in the above-described predetermined relationship with respect to the electrostatic latent image holder while taking developer consumption into consideration. In addition, the spacing of the sleeves and the arrangement of the magnetic poles allow for good transfer. Regarding the spikes, when a magnetic brush is formed by a single magnetic pole in the first developing section, almost no deviation of the developer is observed, but when a magnetic brush is formed by a plurality of magnetic poles of the same polarity as in the second developing section, When this occurs, the developer is separated from the sleeve in powder form due to the strong repulsive magnetic field, which tends to cause the problematic deviation of the developer. Therefore, when using a second developing section having a strong repulsive magnetic field like the above-mentioned developing device, a second developing section having a single developing magnetic pole as described above with respect to the moving direction of the electrostatic latent image carrier is used. Good results can be obtained by arranging two developing sections. Note that when the repulsive magnetic field of the second developing section is weak, the first and second developing sections may be arranged in the opposite direction, but in the conveying direction of the developer, the repulsive magnetic field section can be passed from top to bottom or sideways. Directing it in the direction allows the developer to flow smoothly.

It should be noted here that the magnetic pole part of the second developing section is located in the direction in which the developer is drawn by gravity and the centrifugal force and inertial force associated with the rotation of the sleeve, or at least in the horizontal direction. By arranging the developer, smooth conveyance of the developer becomes possible. In the present invention, the sleeve is a cylindrical member made of a non-magnetic material such as aluminum alloy or resin. In addition, the magnetic means constituting the magnetic pole is a magnetized magnetic material,
Alternatively, a columnar magnet fixed to a fixed member with the magnetic pole on the outside, or an electric magnetism generating means may be used. Examples of the latent image carrier include a conventional electrophotographic photoreceptor, a cylindrical intermediate medium carrying a latent image onto which an electrostatic latent image is transferred or formed by other methods, and a sheet member.

An example of the surface magnetic flux density of the magnetic pole in the embodiment shown in FIG. 3 will be given.

N ₁ 800 Gauss S ₁ 800 S ₃ 650, 800 S ₄ 650, 800 N ₂ 800 S ₂ 800 N ₃ 800 The gap between the sleeves 22A and 22B is determined by the strength of the surface magnetic flux density of each magnetic pole. Although it changes depending on factors such as the circumferential speed of the sleeve, it is preferably about 1 to 5 mm, more preferably about 2 mm.

As mentioned above, the peripheral speed of the electrostatic image holder is set to 500 mm/
sec, the circumferential speed of both the front and rear sleeves is 550mm/
sec, 450 mm/sec (sleeve diameter 63 mm), the developer could be circulated in a bridge shape without accumulating in the gap between the two sleeves.

FIG. 3 shows another embodiment of the present invention,
Elements common to those shown in FIG. 2 are designated by the same reference numerals and their explanations will be omitted. In this embodiment, the first and second developing sections are arranged side by side. In the figure, 32A and 32B are sleeves that rotate in the same direction as the electrostatic image carrier in the direction of the arrow at the aforementioned speed relationship, and 33 and 33B are substantially 23A and 2, respectively.
The sleeve 32A and the magnetic means 33A constitute a first developing section, and the sleeve 32B and the magnetic means 33B constitute a second developing section. There is. In the developing device shown in FIG. 3, the developer adsorbed onto the sleeve 32A forms a magnetic brush at a single developing magnetic pole _N3 to perform the first development. Thereafter, the developer is smoothly transferred to the parallel sleeve 32B which has a slightly slower speed due to the magnetic force of the magnetic means 33B, and at the developing position, the magnetic poles S ₃ - _{S 4}
After performing the development peculiar to the repulsive magnetic field, it falls from the sleeve 32B. In this way, it is also possible to arrange the first and second developing means side by side in parallel while maintaining a predetermined speed relationship with respect to the electrostatic latent image carrier described above.

The embodiment shown in FIG. 4 is a modification of the embodiment shown in FIG. This shows a configuration aimed at extending the life of the developer used during high-speed development. In the figure, reference numeral 5a denotes a housing for the entire developing device, and its interior is partitioned into a magnetic brush chamber 43 and a storage device chamber 44 by a partition plate 42. 33A',3
3B' and 46 are magnets that connect the magnetic brush chamber 43.
It has a cylindrical shape with multiple magnetic poles arranged in parallel to form magnetic brushes, and is fixedly arranged. Also, 32A', 3
2B', 45 are the magnets 33A', 33B',
46, and the cylinder moves around the magnet in the directions of arrows a, b, and c with respect to the electrostatic latent image carrier 1, which moves in the direction of the arrows.
Regarding the rotation of , while maintaining the speed relationship mentioned above,
It is rotated by a driving means (not shown) installed in the developing device.

51 is a magnetic brush that connects each cylinder 45, 32A', 3
The above magnets 46, 33A', 3 are placed around 2B'.
The latent image is formed by attracting and collecting flux by the magnetic force of the magnetic pole 3B', and is visualized by contacting the surface of the electrostatic image carrier 1.

Here, the magnet 33A has a single pole _N4 in the developing area and forms the first developing part together with the sleeve 32A' as described above, and the magnet 33B has a same pole in the developing area with a different polarity from the single pole. As described above, the pair S ₄ and S ₅ form a second developing section together with the sleeve 32B'. The third sleeve 45 and its magnet 46 are
Means for supplying developer to the first developing section from below is formed.

The developing action in the first and second developing sections is similar to that in the third developing section.
Since it is the same as the case in the figure, detailed explanation will be omitted.

Reference numerals 26A' and 26B' denote stirring members such as screws for stirring the developer, and the stirring members are arranged close to the magnet 46 at a position buried in the developer at the bottom of the housing 5a. Then, the developed developer that has left the top of the cylinder 32B' and fallen due to its own weight is mixed and stirred with the developer at the bottom of the housing 5a. 40
is a blade that regulates the developer layer supplied onto the sleeve 45.

The storage device chamber 44 has an opening 44a in a portion close to the cylinder 32B' through which the magnetic brush 51 on the cylinder 32B' can flow, and furthermore, the stirring member 2
An opening 44b is provided in a portion near 6A', through which an amount of developer substantially equal to the inflow amount can flow out from the storage device chamber 44 to the magnetic brush chamber 43.

Furthermore, a feeder shaft 55 is installed in the storage device chamber 44 for rotating a rotary member capable of mixing and stirring the developer in the storage device and conveying it to the magnetic brush chamber 43.

Blades 56 and 57 are fixedly attached to the feeder shaft 55, and by rotating the feeder shaft at a slow speed in the direction of arrow d, the developer in the storage chamber 44 is transferred to the magnetic brush. It is transported into the chamber 43.

Several blades 56 and 57 are installed in the axial direction of the feeder shaft 55 to evenly convey and stir the developer.

Here, the rotation speed of the feeder shaft 55 is determined by the useful life of the developer used and the capacity of the developing device and the storage device.

Further, the magnetic brush on the cylinder 32B' is
The cylinder 32 of the storage device chamber 44 is always
It is close to the opening 44a in the portion near B', and substantially the same volume of developer as the developer conveyed from the storage device chamber 44 into the magnetic brush chamber 43 flows into the storage device chamber 44. It is structured so that you can get it.

Therefore, a constant volume of developer is always secured in the storage device chamber 44, and the feeder shaft 5
The outflow and inflow of the developer is performed only by the rotation of 5. Therefore, substantially the same volume of developer as that supplied from the storage device to the reservoir section of the developing device is
The developer flows into the storage device, and the amount of developer in the storage device is always constant.

Furthermore, the amount of developer in the reservoir of the developing device is always substantially constant, making it possible to always obtain a stable developing state.

FIG. 5 shows a further modified embodiment of the embodiment shown in FIG. 2, in which the first and second developing sections are placed close to each other, and the relationship between the magnetic poles of both is reversed from that shown in FIG. 2. be.

Sleeve 65A' and magnetic means 64 therein
A' completely corresponds in structure to the sleeve 22B' shown in FIG. 2 and the magnetic means 23B' therein. Also, the sleeve 64B' and the magnetic means 6 therein.
5B' completely corresponds in structure to the sleeve 22A' shown in FIG. 2 and the magnetic means 23A' therein. Among other constituent elements, elements common to those shown in FIG. 2 are given the same reference numerals and their explanations will be omitted.

In this embodiment, the above double sleeve 65
A' and 64B' are arranged so as to face the lower rotating portion of the electrostatic image bearing drum 1, and both sleeves rotate in the same direction as the rotational direction of the drum at the speed relationship described above. That is, the rotational speeds of these two sleeves are a little higher for the sleeve 65A' at the front stage and a little slower for the sleeve 64B' at the rear stage than the peripheral speed of the drum, and preferably the speed difference with respect to the drum peripheral speed is about 20. It is desirable to set the amount to about % from the viewpoint of ensuring a sufficient supply of developer. Further, it is preferable that the gaps between the two sleeves be as close as possible, and for example, the sleeves are arranged with a closest gap of 2 mm.

Next, the degree of adhesion of the developer to the electrostatic image surface when the developing method in each of the embodiments of the present invention described above is applied will be explained.

The electrostatic image plane is first subjected to conventional magnetic brush development using a magnetic means having a single magnetic pole in the developing section and a sleeve surrounding it. This magnetic brush is
It has a structure that stands up on the magnetic pole, and lines of electric force extend perpendicularly between the iron powder carrier on the sleeve surface side and the electrostatic charge of the electrostatic image, and development is performed with a substantial development electrode effect. Toner of different polarity adheres to the electrostatic charge.

It has been experimentally confirmed that this toner layer has a thickness of one to three or four layers.

Next, as shown in FIGS. 2, 3, and 4, the electrostatic image carrier smoothly moves between the sleeve and the magnet that constitute the second developing section due to the speed difference between the two sleeves and the drum. are moved while stirring and face each other, where the second development is performed.

As described above, the development at this time is performed using the developer in a powder cloud state due to the repulsive magnetic field formed by the two magnetic poles of the same polarity.
Therefore, at this time, since the iron powder carrier is repelled from the sleeve surface and suspended in the air, it does not substantially function as a developing electrode, and the edge effect is therefore prominent. Also, this sleeve has a lower speed than the preceding sleeve and is slightly slower than the drum surface, so as a result, the toner smoothly adheres to the surface to be developed by the first developing section, and the toner is transferred to the developing section by the preceding sleeve. Development that emphasizes the edges of the image without disturbing the image.
That is, toner adheres to the edge portions.

Therefore, on the surface to be developed that has passed through the first and second developing sections, the development sag (development where the sharpness of the edges decreases) around the image by the first developing section moves more slowly, and the cloud Due to the nature of the condition, in the second developing section, the peripheral areas are emphasized by the edge effect, so by developing the two in combination, sufficient toner adhesion can be obtained in both the peripheral and central areas of the image. Therefore, on the other hand, the conventional toner sweeping and peeling phenomena caused by speed differences can be completely eliminated, making it suitable for high-quality, high-speed development.

Next, in the case of the embodiment shown in FIG.
In the second development, development with an enhanced edge effect is performed using powder cloud development using a repulsive magnetic field, and the edges are emphasized, while other image areas, including the center, are developed with less toner adhesion. becomes. Then, by undergoing a second development using a single pole without the developer being swept away or peeled off, more toner adheres to the areas where less toner adhered in the first development. Therefore, the results of both developments are clear enough to withstand high-speed development.

As described above, the present invention provides a plurality of developer carriers that move in the same direction as the moving direction of the electrostatic image holding member. are arranged so that the developer is applied to the electrostatic image in this order, the moving speed of the first developer carrier is faster than that of the electrostatic image holding member, and the moving speed of the second developer carrier is faster than that of the electrostatic image holding member. Since it was set to move slower than that, the combination of both developer carriers
As a developing effect, the conventional sweep development and stripping phenomenon can be completely eliminated, and the developer can be transferred smoothly through the gap between both developer carriers while adding necessary agitation.

In addition, a qualitative difference is provided in the development effect between the first developing section equipped with the first developer carrier and the second developing section equipped with the second developer carrier. It is possible to synergistically combine the development effects obtained by eliminating the sweeping and peeling phenomena to produce a good development effect. In this case, the number of sleeves in the first developing section and the second developing section is not limited to one each as in the embodiment apparatus. For example, if the number of sleeves in the first developing section is large, it is possible to On the other hand, if the number of sleeves in the second developing section is large, development that exhibits the characteristics of the cascade powder cloud development method can be performed at high speed.

As a conventional device, for example, there is a developing device described in US Pat. No. 3,543,720. With this device,
Two sleeves are provided side by side, each of which is rotated in a direction opposite to the moving direction of the electrostatic image holding strip, and the first sleeve that initially applies developer to the electrostatic image holding member is moved from the second sleeve. is brought closer to the electrostatic image holding member while rotating slower than the second sleeve so that developer is temporarily stored in the wedge-shaped gap between the first and second sleeves, and then development is performed. Since the second sleeve is disposed a little apart from the electrostatic image holding member, the developer thereon barely makes contact with it. Therefore, this invention is completely different in purpose, structure, and effect from the above-mentioned prevention of developer sweeping and stripping by the first and second developer carriers according to the present invention.

[Brief explanation of the drawing]

FIGS. 1A and 1B are explanatory diagrams illustrating the developer sweeping phenomenon in a conventional developing device, and FIGS. 2 to 5 are sectional views showing each embodiment of the developing device according to the present invention. 22A, 23A; 32A, 33A; 32A',
33A';64B',65B'...first developer carrier, 22B, 23B; 32B, 33B; 32B',
33B';64A',65A'...Second developer carrier.

Claims (1)

[Scope of Claims] 1. A first developing section provided on the upstream side and a first developing section provided on the downstream side with respect to the moving direction of the electrostatic image in a passing area of a moving electrostatic image holding member. and a second developing section configured to supply a developer to the electrostatic image in the first developing section and the second developing section, a non-magnetic first developer carrier that supplies developer by moving faster than the moving speed of the electrostatic image holding member and in the same direction as the moving direction; a developer carrying surface of the first developer carrier; a first fixed magnetic means which is fixedly provided on the opposite side and forms a magnetic field in the first developing section; and a first fixed magnetic means which is provided in the second developing section and moves the electrostatic image holding member in the first developing section. a non-magnetic second developer carrier that moves slower and in the same direction as the above-mentioned moving direction and supplies the developer; and a second developer carrier fixedly provided on the side opposite to the developer carrying surface of the second developer carrier. a second fixed magnetic means for forming a magnetic field in a second developing section; 2. The developing device according to claim 1, wherein the first and second developer carriers are rotatably supported non-magnetic sleeves. 3. One of the first and second magnetic means has a magnet with a single magnetic pole corresponding to the developing section, and the other has a magnet with two repulsive magnetic field forming magnetic poles of the same pole corresponding to the developing section. A developing device according to claim 1 or 2, characterized in that: 4. Claims 1 to 3, wherein the relative speed difference between the electrostatic image holding member and the first and second developer carriers is within 20% of the moving speed of the electrostatic image holding member. The developing device according to any one of the above. 5. The developing device according to claim 4, wherein the relative speed difference is within 10% of the moving speed of the electrostatic image holding member.