JPS6032193B2 - developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing machine for developing an electrostatic image.In other words, the present invention relates to a developing machine 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 a powder cloud method, a force cascade method, an Isoko Uko method, etc. Each of these has different characteristics,
They are used in practical applications in various fields depending on their characteristics.

In the case of the powder cloud method and the cascade method, the developing toner is concentrated at the area where the electric field intensity of the static latent image on the latent image bearing surface of the photoconductor is large, that is, at the discontinuous part of the original image density. A reproduced image of this portion is obtained with emphasis.

Because of the occurrence of the so-called peripheral effect, line copying has an advantage in terms of reproducibility in copying office documents. However, this appears to be a disadvantage when it comes to reproducing general tone images (images containing halftone density), that is, reproducing parts of an original image where the density changes continuously. or,
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 developing device itself has the disadvantage of being large in volume. On the other hand, in the case of magnetic brush method, iron powder carrier,
A developer composed of a mixture of developing toners is attracted to a magnet, the developer is formed into a brush shape at the magnetic pole part, and the static latent image on the latent image carrier is developed by sliding and the image is reproduced. .

At this time, since the iron powder itself is softened and acts as a developing electrode, it is possible to attach the developing toner in proportion to the charge density of the electrostatic latent image.In other words, it is suitable for reproducing tone images. be. Further, the developing device itself has the feature that it can be constructed in a small size.

A further improved version of this magnetic brush imager includes a carrier made of magnetic powder, such as iron powder, in order to achieve the purpose of developing an electrostatic image-bearing member at high speed and efficiency.
A two-component developer consisting of a toner with carbon dispersed in a resin is mixed with Takazusa, and the toner is charged by frictional electrification caused by friction between the two components. The developer is held on a hollow cylindrical sleeve made of a magnetic material and transported from the developer reservoir to a position facing the electrostatic image holding member, and at the position facing the electrostatic image holding member, the developer is subjected to the action of the magnetic field. A so-called sleeve developing method is used in which an electrostatic image holding member is developed by allowing developer to stand up and burn the surface of the electrostatic image holding member.

When the speed of the electrostatic image holding member is relatively slow, a short development time is sufficient and a good developed image can be obtained, so one sleeve was sufficient. However, when the speed of the electrostatic image holding member is high or the potential of the electrostatic image on the electrostatic image holding member is low, development is not necessarily sufficient with one sleeve. Therefore, it is necessary to use two or more sleeves so that the developer is continuously conveyed through them to extend the development time. In addition, in order to widen the width of the bristles of the brush in the developing section for more efficient development, two magnetic poles of the same polarity are placed facing the developing section to create a repulsive magnetic field. A method has been proposed (Patent Application No. 99, Paper No. 11 of 1983). Furthermore, when the developer is developed with spikes of developer utilizing this repulsive magnetic field, an image with a relatively strong edge effect can be obtained, and therefore an extremely sharp image can be obtained. Therefore, the magnetic pole arrangement in the sleeve that holds the developer for developing the electrostatic image holding member and makes it stand up at the magnetic pole part, especially the developer on the sleeve facing the electrostatic image holding member is made to stand up for development. As for the arrangement of the developing magnetic poles, providing a sleeve developing device having magnetic poles that form a repulsive magnetic field is very effective in terms of both developing efficiency and image quality. However, if repulsive magnetic poles are used in the developing magnetic field of all sleeve developing devices, the edge effect tends to be overemphasized, and the reproducibility of solid black areas and image density tend to be insufficient, which is not necessarily appropriate. Therefore, when a plurality of sleeves are used, a method has been proposed in which the structure of the developing magnetic pole in each sleeve is given a special aspect to solve this problem (Tokuken Sho 52-Mura No. 5, Tokiso Sho 52). -143573). In this method, as developing magnetic poles involved in development, a sleeve having a magnetic field that forms a repulsive magnetic field due to the same poles and a sleeve having a magnetic field created by a single magnetic pole are used in appropriate combination. An object of the present invention is to provide a high-speed developing device which improves the conventionally proposed developing device and eliminates unstable factors such as fog, developed density, and density unevenness in developed images. The following points apply.

That is, in a device that holds the developer on a hollow cylindrical sleeve having a magnetic pole inside and conveys the developer from a developer reservoir to a development position for development, a spike of development is formed at the developer position. A first sleeve has a single magnetic pole as a developing magnetic pole, and a second sleeve is attached to the first sleeve and has two magnetic poles of the same polarity juxtaposed as a developing magnetic pole, and the first sleeve and static Assuming that the distance between the second sleeve and the electrostatic image holding member is B, the relationship between the two is Q>8, more preferably 3/4Q≦
The developing device is characterized in that 8<Q.

The present invention provides a developing device in which the above-mentioned monopole and repulsive magnetic pole are combined together. It has been found that it is necessary to bring the agent-bearing sleeve closer to the electrostatic image-bearing surface.

When multiple sleeves are installed and the required developer is continuously supplied from one sleeve to the other, a sleeve containing a single magnetic pole (first sleeve) is used. The distance between and the surface of the electrostatic image holding member is Q.
It has been found that it is necessary to have a relationship of at least 8<Q, where B is the distance between the sleeve (second sleeve) containing the repulsion magnetic pole and the surface of the electrostatic image holding member. Ta. This is because, as will be described later, in the case of a sleeve containing a magnet with repulsive magnetic poles in which two poles of the same polarity are arranged, the area where the developer is involved in development is wide, and therefore, it is assumed that there are spikes of developer on the entire surface during this time. The rope is shorter than that on the sleeve containing the fist pole described above. Therefore, in order to perform development with a developer having such a relatively low profile, the sleeve that supports such ears must be brought close to the surface to be developed. Otherwise, development will be performed only at the tips of the rough and long seeds, resulting in insufficient density, rough solid black areas, and poor images, or the magnetic field on the electrostatic image holding surface may not be sufficient. As a result, carrier adhesion,
It becomes easy to cause fogging, etc. On the other hand, if the repulsion pole is too close to the electrostatic image holding surface, fogging and developer accumulation will occur in front of the repulsion pole. Embodiments and examples of the developing device according to the present invention will be described in detail below with reference to FIGS. 1 to 4.

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, the electrostatic image carrier 1 is rotated in the same direction as the rotation direction.
The non-magnetic rotating sleeves 22A, 22B of books are arranged at a short distance from each other.

The rotational speed of this sleeve is substantially the same as the peripheral speed of the electrostatic image carrier 1, or is driven at a slightly higher peripheral speed (10 to 20%) by a known driving means. As an example, the peripheral speed of the electrostatic image carrier was set to 400 to 500 feet/sec.

Both sleeves have fixed magnetic means 23A, 23B inside them, and the magnetization poles of the respective magnetic means are different.
First, the magnetic arrangement of the first magnetic means 23A will be explained.

The illustrated magnetic means 23A is formed as a magnet loaf, and magnetized poles N2 and S2 are spaced apart at equal angles near the surface thereof.
, N3, and the N3 pole is arranged near the surface of the electrostatic image carrier 1. Sleeve 2 in the recent Dan&Dan
Let Q be the distance between 2A and the electrostatic image support member 1. Next, the second magnetic means 23B is disposed downstream of the first magnetic means along the electrostatic image carrier, and is formed of a four-pole magnetized roller as shown in the figure. The N, pole and S, pole are magnetic poles that have the function of drawing up and transporting the developer.

Both magnetic poles S3 and S4 are set at a predetermined angle of 0 in opposite directions from the point where this magnetic roller is closest to the surface of the electrostatic image support member.
development magnetic poles of the same polarity and spaced apart from each other by the same polarity. These developing magnetic poles S3 and S4 having the same polarity are selected to be different in polarity from the developing magnetic pole N3 of the first magnetic means. The distance between the sleeve 228 and the electrostatic image support member 1 at the closest point is 3. Reference numeral 25 denotes a developer in the housing 5a of the developing device, which contains a mixture of magnetic carrier and developing toner.

Also, within this housing are two screws 26A and 26 for feeding the developer 25 in the direction of rotation of the sleeve.
B, a blade 30 that regulates the thickness of the developer pumped onto the surface of the sleeve 23B to a predetermined value; a cleaning blade 3 that removes residual developer from the sleeve surface after development;
1, further includes a replenishment developer storage chamber 27 and a replenishment roller 28 provided at a lower closed portion thereof. As the roller 28 rotates, the developer that has entered the recess provided on its surface falls into the developing chamber 29 where the sleeve of the housing 5a of the container is provided, thereby replenishing the developer. . And the sleeve 22A
The sleeve 22B and the magnetic means 23A constitute 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-mentioned developing device, the sleeves 22A and 228 start rotating in synchronization with the rotation of the electrostatic image carrier 1 by a known driving means.

Due to the rotation of the sleeve, first the N of the magnetic means 23B,
The developer adheres to the surface of the sleeve 22B as much as possible.
The adhered developer is attracted to the surface of the sleeve 22B by the magnetic force of the N pole and the S pole above it, and the amount of adhered developer is uniformly regulated by the developer regulating plate 30 in the middle, and reaches the S pole position.

The developer that has further passed through the S, pole position is attracted toward the sleeve 22A by the magnetic force of the N2 pole of the magnetic means 23A. The developer that has passed over the sleeve 22A moves along with the sleeve 22A from the magnetic poles S2 to N3 due to the magnetic force of the next magnetic pole S2. At the magnetic pole N3 position, the magnetic carrier is erected by the magnetic force of the magnetic pole N3.
First, the electrostatic image on the electrostatic image carrier 1 is developed by forming a magnetic brush. That is, at the magnetic pole N3 position, the carrier 1 is subjected to development by the conventional magnetic brush development method,
A visible image with very little edge effect and rich gradation is formed. 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 approaches the sleeve 22B is released from the magnetic field by the magnetic pole N3, 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. cross And due to the magnetic force of the magnetic pole S3,
The developer deposited on the sleeve 228 forms a magnetic brush again at the magnetic pole S3 position, and the electrostatic image on the carrier 1 is brush-developed. Note that since there is a magnetic pole S4 of the same polarity in the vicinity of the magnetic pole S3 below, these magnetic poles S3 and S4 form a repulsive magnetic field. Therefore, the developer moving as the sleeve 22B rotates forms a brush with the magnetic pole S3, and then passes through the repelling magnetic field. At this time, the developer on the sleeve 22B is blown toward the electrostatic 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, and inertial force of the sleeve 22B and the magnetic field of the lower magnetic pole S4.
Developing the electrostatic image carrier. Thereafter, the developer scattered by the magnetic force of the magnetic pole S4 forms a magnetic brush on the sleeve 22B again to develop the latent image on the latent image carrier. That is,
In addition to the advantages of the conventional magnetic brush method, the development position where magnetic poles of the same polarity of the magnetic means 23B are arranged has the advantages of the above-mentioned cascade powder cloud development method, in which the edge effect is expressed at the highest point. enables development with The developer that has passed the development position is removed from the sleeve 22B by a scraper 31 placed at a position where magnetic force is weak.
The developer conveyance and development process described above is repeated again. Note that the distances Q and 8 between the first and second sleeves 22A and 22B and the electrostatic image carrier 1 have a relationship of 8<Q, and as the lower limit of B, However, the condition of 3/4Q≦8 is set.

In particular, B is preferably set to a value 15 to 25% smaller than Q. This value of 8 is experimentally selected to be a suitable value within the above range depending on the amount of developer (which affects the height of the spike), the speed of the sleeve, etc., but it is experimentally determined to be a practically suitable value. When calculated, it was in the range of 5.5 to 2 fences. As a result, a phenomenon in which a wide range of spikes appears even on the sleeve which performs the development action by the repelling magnetic field, and these spikes can be fully utilized for development. In this way, when the developer carried on the sleeve is transferred between the sleeves arranged in parallel and continuously conveyed for development, the distance between the electrostatic latent image carrier and the first and second sleeves is adjusted as described above. By establishing such a positional relationship, it is possible to perform beautiful development with little density deficiency, unevenness, or fog.

Regarding the rope stand, when a magnetic brush is formed by a single magnetic pole in the first developing section, there is almost no uneven bridge of the developer.
When a magnetic brush is formed by a plurality of magnetic poles of the same polarity, as in the second developing section, the developer is separated from the sleeve in powder form due to a strong repulsive magnetic field, which tends to cause the problem of unevenness 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. What should be noted in the embodiment shown in Fig. 1 is that the magnetic pole part of the second developing section is in the direction in which the developer is drawn by gravity and centrifugal force and inertial force due to the rotation of the sleeve, or at least in the direction in which the developer is horizontal. By arranging the developer at a position where it advances in the direction, 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 poles may be a magnetized magnetic material, a columnar magnet fixed to a fixed part so that the magnetic pole is attached to the outside, or an electric magnetism generating means. . Examples of the latent image carrier include a conventional electrophotographic photoreceptor, a cylindrical intermediate medium carrying a latent image onto which a static latent image is transferred or formed by other methods, and a sheet member. An example of the surface magnetic flux density of the developing magnetic pole in the embodiment shown in FIG. 1 will be given.

This value is the same for other embodiments described later. Surface magnetic flux density of developing magnetic pole (unit: Gauss) Single pole Repulsion magnetic pole (N3)
(S3S4)800
800800650
800800800
650650650
650650 The surface magnetic flux densities of these magnetic poles can be intermediate values between 650 and 850 Gauss.

The gap between the sleeves 22A and 22B varies depending on factors such as the strength of the surface magnetic flux density of each magnetic pole and the circumferential speed of the sleeve, but is preferably about 1 to 5 inches wide. FIG. 2 shows another embodiment of the present invention, and elements common to those shown in FIG. 1 are given 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;
3B' is a fixed magnetic means having a corresponding magnetized magnetic pole as shown in FIG.
The sleeve 328 and the magnetic means 33B constitute a second developing section. In the developing device shown in FIG. 2, the developer adsorbed onto the sleeve 32A forms a magnetic brush at the single developing magnetic pole N3 to perform the first development. Thereafter, the developer smoothly passes to the parallel sleeves 32B due to the magnetic force of the magnetic means 33B, and after performing development peculiar to the repulsive magnetic field of the magnetic poles S3-S4 at a closer position, it falls from the sleeve 32B. In this way, by arranging the first and second developing means horizontally in parallel while maintaining a predetermined positional relationship with respect to the electrostatic latent image carrier described above, the desired purpose and effect can be achieved. We were able to. The embodiment shown in FIG. 3 is a modification of the embodiment shown in FIG. This design also aims to extend the life of the developer used during high-speed development.

In the figure, reference numeral 5a denotes a housing for the entire developer device, and the interior thereof is partitioned into a magnetic brush chamber 43 and a storage device chamber 44 by a partition plate 42. 33A', 33B'
, 46 are multi-pole magnet cylinders for forming magnetic brushes arranged in parallel in the magnetic brush chamber 43, and are fixedly arranged.

Also, 32A', 32B', and 45 are the magnets 33A mentioned above.
A non-magnetic cylinder (sleeve) enclosing magnets 1, 338 and 46 is arranged around the magnets in the directions of arrows a, b and c with respect to the electrostatic latent image carrier 1 moving in the direction of the arrows. The sleeves b and c are rotated and driven by a driving means (not shown) installed in the developing device while maintaining the above-mentioned relationship with respect to the arrangement of the sleeves b and c. 51 is a magnetic brush that connects each cylinder 4
5, 32A', 32B', the magnet 46,
The latent image is formed by attracting and collecting by the magnetic force of the magnetic poles 33A' and 338, and is brought into contact with the surface of the electrostatic image carrier 1, thereby visualizing the latent image.

Here, the magnet 33A has a single pole N4 in the developing area and forms the first phenomenon part together with the sleeve 32A' as described above, and the magnet 33B has a pair of same poles in the developing area with a different polarity from the single pole. S4 and S5, and together with the sleeve 32B' form the second developing section as described above. The third sleeve 45 and its magnet 46 form a means for supplying the developer of the first developing section from below. Since the developing action in the first and second developing sections is the same as that shown in FIG. 2, detailed explanation will be omitted.

Further, reference numerals 26A' and 26B' are clear members such as screws for fixing the developer, and the above-mentioned frame members are placed close to the magnet 46 and buried in the developer at the bottom of the housing 5a. The developer which has left the cylinder 328 and has fallen due to its own weight is mixed 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 4 near the cylinder 326 through which the magnetic brush 51 on the cylinder 326 can flow.
4a, and further includes a entrance portion in a portion close to the Toazusabemura 26A' that is capable of flowing out the developer in an amount substantially equal to the inflow amount from the storage device chamber 44 to the magnetic brush chamber 43. 44b.

Furthermore, a feeder shaft 55 is installed in the storage device chamber 44 for rotating a rotating member capable of mixing and feeding 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 certain slow speed in the direction of arrow d, the developer in the storage device chamber 44 is transferred to the magnetic brush chamber. 43.

Several blades 56 and 57 are installed in the direction of the feeder shaft 55 to evenly transport and spread the developer.

Here, the rotational 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 always close to the closed part 44a of the storage chamber 44 near the cylinder 328 during movement, and is moved from the storage chamber 44 into the upper air magnetic brush chamber 43. The structure is such that substantially the same volume of developer as the developer transported in can flow into the storage device chamber 44 .

Therefore, a constant volume of developer is always secured in the storage chamber 44, and the developer is flowed in and out only by the rotation of the feeder shaft 55. Therefore, substantially the same volume of developer as the developer supplied from the storage device to the reservoir of the developing device 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. 4 shows a further modification of the embodiment shown in FIG. 1, in which the first and second developing sections are placed close to each other, and the relationship between the magnetic poles of the two is reversed from that shown in FIG. 1. The other parts are the same as those in FIG.

The sleeve 65A and the magnetic means 64A therein are
The structure corresponds completely to the sleeve 22B shown in the figure and the magnetic means 23B therein.

Moreover, the sleeve 64B and the magnetic means 65B therein are
Sleeve 22A shown in FIG. 1, magnetic means 23 therein
It completely corresponds to A in composition. Among other constituent elements, elements that are compatible with those shown in FIG. 1 are designated by the same reference numerals and their explanations will be omitted. In this embodiment, the two lotus sleeves 65A and 64B are disposed so as to face the lower rotating portion of the electrostatic image bearing drum 1, and the two sleeves are disposed so as to face the lower rotating portion of the electrostatic image bearing drum 1, and the two sleeves are disposed so as to face the lower rotating portion of the electrostatic image bearing drum 1. It rotates in close proximity to the image carrier 1 in the positional relationship described above. Further, it is preferable that the gaps between the two sleeves be as close as possible, and for example, the sleeves are arranged so that the two legs are spaced apart from each other with a saddle gap between them.

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

In the embodiment of FIGS. 1-3, the electrostatic image plane is first subjected to conventional magnetic brush development using a magnetic means having a single magnetic pole developing section and a sleeve containing the magnetic means.

This magnetic brush 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 there is a substantial developing electrode effect. Development is performed in this state, and 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. 1 to 3, the electrostatic image carrier is moved so that the sleeve constituting the second developing section is farther away from the sleeve constituting the first developing section by a predetermined distance. , so that a second development can take place there in succession.

As described above, the development at this time is mainly performed by the developer in a powder cloud state in the middle of 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 therefore, the edge effect is noticeable. Also, since this sleeve is closer to the drum surface than the preceding sleeve, as described above, as a result, the toner is smoothly adhered to the developing surface by the first developing section. As a result, it is possible to develop an image in which the edge portion is emphasized, that is, the toner adheres to the edge portion, without obstructing the developing section by the front sleeve. Therefore, on the developing surface that has passed through the first and second developing sections,
Development sag in the periphery of the image by the first developing section (development in which the edge becomes less sharp) moves more slowly than this, and due to its cloud-like nature, the periphery is emphasized by the edge effect in the second developing section. Therefore, by developing the two in combination, sufficient toner adhesion can be obtained in both the peripheral and central areas of the image.

Therefore, it is suitable for high-quality, high-speed development without unevenness in development, insufficient density, or blurring.

Next, in the case of the embodiment shown in FIG. 4, in the first development, development with an emphasized edge effect is performed by powder cloud-like development using a repulsive magnetic field, and the periphery is emphasized, including the central part. , there is a little toner adhesion on other image areas, resulting in poor development.

Then, by performing a second development using a single pole without sweeping the developer or stripping the developer, more toner adheres to the areas where less toner adhered in the first development. Therefore, the results of both developments are clear images that can withstand high-speed development. As described above, the present invention holds a developer on a hollow cylindrical sleeve having a magnetic pole therein, and in an apparatus for developing with a plurality of such sleeves, a single developing magnetic pole is used as a developing magnetic pole to form a spike at a developing position. It has a first sleeve having a magnetic pole and a second sleeve having two magnetic poles of the same polarity juxtaposed as developing magnetic poles, and the distance between the second sleeve and the electrostatic image holding member at the developing position is set as above. It is characterized in that the distance is smaller than the distance between the first sleeve and the electrostatic image holding member, and is set equal to or larger than 3/4 of the distance between the first sleeve and the electrostatic image holding member.
When developing by continuously applying developer to the electrostatic loss carrier using the first and second sleeves, it is possible to simply increase the development area and make the developer ears as uniform as possible. Because the first and second sleeves are qualitatively different and can complement each other, the edge effect can be avoided. It was possible to create a high-quality head image that was not significantly emphasized, and also substantially removed the ground pretension, and in addition, had almost no unevenness in development density.

As for a conventional device using a plurality of sleeves, for example, U.S. Pat. The moving direction of the image holding strip is rotated in the opposite direction, and a first sleeve that initially applies developer to the electrostatic image holding member is brought closer to the electrostatic image holding member village than a second sleeve. On the other hand, an apparatus has been described in which the second sleeve is rotated more slowly than the second sleeve, and the developer is temporarily stored between the two sleeves.

However, the present invention has improved such a follower device by focusing on the relationship between the arrangement of the magnetic poles and the distance of the sleeve, and has the above-mentioned special effects.

[Brief explanation of the drawing]

1 to 4 are sectional views showing embodiments of a developing device according to the present invention. Figure 2 Figure 1 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A developing device that applies developer to an electrostatic image on a moving electrostatic image holding member to develop the image, comprising a first developer carrying means having a single phenomenon magnetic pole and a reverse image magnetic pole. and maintaining a positional relationship such that α>β, where the distances between the first and second developer carrying means and the electrostatic image holding member are α and β, respectively. A developing device characterized in that it performs development. 2. The developing device according to claim 1, wherein the first and second developer carrying means include a magnet and a sleeve containing the magnet. 3. The developing device according to claim 1, wherein the second developer carrying means is a magnet in which two magnetic poles of the same polarity are placed side by side at the developing position and a sleeve containing the magnet. 4. The developing device according to claim 1, wherein the first and second developer carrying means move in the same direction as the electrostatic image carrying member. 5. In a developing device that applies developer to an electrostatic image on a moving electrostatic image bearing member to develop the image, the first developer carrying means has a single developing magnetic pole, and the second developer has a reverse image magnetic pole. and maintaining a positional relationship such that 3/4α≦β<α, where the distances between the first and second developer carrying means and the electrostatic image carrying member are α and β, respectively. A developing device characterized by developing.