JPS6296978A - Developer thin layer forming device - Google Patents

Abstract

PURPOSE:To obtain good images without ground fog by moving a developer holding member endlessly to form a developer thin layer on the developer holding member at the downstream side of a Blade in the moving direction of the holding member. CONSTITUTION:Magnetic particles 7 carried by rotation of a sleeve 3 are raised by the front end part of an elastic body blade 6 and are dropped by the gravity and a magnetic force and are circulated in the direction of an arrow (c) repeatedly, and magnetic particles 7 are oscillated considerably near the front end of the elastic body blade 6 by the change with time of a magnetic field. By these circulating and oscillating actions of magnetic particles 7, a developer 8 is charged frictionally and is supplied stably from the upper part of a vessel 2 to the surface of the sleeve 3. The frictionally charged developer 8 passes a contacting part and is formed as a developer thin layer on the sleeve 3 and is carried to a developing part facing a photosensitive body 1 on the sleeve 3. Thus, good images are obtained stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developer thin layer forming device that can be used in a developing device that develops an electrostatic latent image using a non-magnetic developer.

Various types of dry-component developing devices have been proposed and put into practical use. However, in any of the development methods, it is extremely difficult to form a layer of dry component developer, and for this reason, a developing device has been constructed by forming a relatively thick layer. However, as improvements in the clarity, resolution, etc. of developed images are currently being sought, it is essential to develop a method for forming a thin layer of a dry component developer and an apparatus therefor.

As a method of forming a thin layer of a conventionally known dry component developer, Japanese Patent Application Laid-Open No. 54-43037 has been proposed and has been put into practical use. However, this was related to the formation of a PM layer in a magnetic developer. Magnetic developers must have a magnetic substance added to them to have magnetism, and this is due to poor fixing properties when thermally fixing the developed image transferred to transfer paper, and because the developer itself contains magnetic substances (magnetic substances do not contain magnetic substances). Since the color (usually black) is added internally, there are problems such as poor color reproduction during color reproduction.

For this reason, as a method for forming a thin layer of non-magnetic developer, there are two methods: using a cylindrical brush made of soft bristles like beaver's hair, and applying the developer to the brush. A method of coating the developing roller with a doctor blade or the like has been proposed. However, when an elastic blade is used as a doctor blade for the above-mentioned fiber brush, it is possible to regulate the amount of developer, but uniform application is not achieved, and the fibers of the brush are simply rubbed by the fiber brush on the developing roller. Since no triboelectric charge is imparted to the developer present in between, there is a problem in that fogging and the like are likely to occur.

In addition, in this type of development method, since the developer comes into contact with the surface of the image carrier regardless of the presence or absence of an electrostatic image, developer adhesion occurs even in non-image areas, that is, areas with no electrostatic charge. Insufficient amount of developer tends to adhere to non-image areas, resulting in fogging and resulting in poor images.

The present applicant has developed a developing device 9 that is completely different from the conventional method described above, in which a non-magnetic developer and magnetic particles are used, a magnetic particle restraining member is provided opposite to a developer holding member, and the surface of the holding member is Regarding the moving direction, a magnetic brush of magnetic particles is formed upstream of the magnetic particle restraining member by the magnetic force of the magnetic field generating means, the magnetic brush is restrained by the magnetic particle restraining member, and a thin layer of non-magnetic developer is transferred to the developer holding member. We have already proposed an apparatus for forming a thin layer of developer.

The present invention further improves this developer thin layer forming device, ensures good binding properties and stability of magnetic particles with a simple configuration, and stably forms a thin developer layer on the surface of a developer holding member over a long period of time. An object of the present invention is to provide a developer thin layer forming device that can form a good copy image.

A further object of the present invention is to provide a developer thin layer forming apparatus that has a simple configuration and is capable of producing good copy images without blurring.

According to the present invention, there is provided a developer supply container having an opening and containing a developer and a small amount of magnetic particles, and a non-magnetic container provided in the opening and capable of being endlessly movable inside and outside the container. A developer holding member, a magnetic field generating means provided inside the developer holding member and generating a temporally varying magnetic field, and an end portion urged to come into contact with the developer holding member. a blade that is inclined from the end toward the downstream side in the rotational direction and elastically contacts the developer holding member; A developer thin layer forming device is provided, which forms a thin layer of developer on a developer holding member downstream of the blade in the direction of the blade, thereby ensuring good magnetic particle restraint with a simple configuration. At the same time, since the developer can be sufficiently charged, it is possible to provide a good image without background fog.

Support 11 FIG. 1 is a partial sectional view of a developer thin layer forming apparatus according to an embodiment of the present invention.

In this embodiment, the developer thin layer forming device develops an electrostatic latent image on a photoreceptor 1 as a latent image carrier rotating in the direction of arrow a. As the photoreceptor 1, for example, a so-called xerographic photoreceptor on which an electrostatic latent image is formed by the Carlson process, N described in Japanese Patent Publication No. 42-23910,
A photoreceptor having an insulating layer on the surface with an electrostatic latent image formed by the P process, an insulator having a latent image formed by the electrostatic recording method,
It is an insulator to which an electrostatic latent image is transferred by a transfer method, or a member to which an electrostatic latent image (or potential latent image) or magnetic latent image is formed and retained by any other appropriate method.

The developer thin layer forming device includes a developer supply container 2, a sleeve 3 as a developer holding member. It has a magnet 4 and an elastic blade 6 as magnetic field generating means.

The container 2 has an opening extending in the longitudinal direction (perpendicular to the plane of the paper) of the developer thin layer forming device, and a developer sleeve 3 as a developer holding member is provided in the opening. For example, it is made of a non-magnetic material such as aluminum. sleeve 3
In the figure, it is installed horizontally in the opening with its right half-circumferential surface extending into the container 2 and its left half-circumferential surface exposed outside the container so that it can freely rotate on a bearing, and is driven to rotate in the direction of the arrow. . The developer holding member 3 is not limited to the above-mentioned cylindrical body (sleeve), but may be a rotationally driven endless belt type Fi1 or the like, or a conductive rubber roller may be used.
The exposed surface outside the container faces or contacts the surface of the photoreceptor 1 with a small gap therebetween.

The magnet 4 is rotatably provided within the developing sleeve 3, and in this embodiment is a permanent magnet having a plurality of magnetic poles 5, and is rotatable in the direction of the arrow e as the sleeve 3 rotates. The magnetic field generated changes over time at a fixed position. In the present invention, the magnet 4 is assumed to rotate in the opposite direction to the rotation of the sleeve 2, but the present invention is not limited to this.

The elastic blade 6 is provided in contact with the outer surface of the sleeve 3, and is provided so as to be inclined downstream in the direction of rotation of the sleeve 3 (that is, opposite to the direction of rotation of the sleeve).

Further, a small amount of magnetic particles 7 and developer 8 are placed inside the container 2, and the magnetic particles 7 are restrained on the surface of the container 2 by the action of the magnetic field from the magnet 4. Here, the term "very small amount" refers to a very small amount that exists only in the vicinity of the regulating blade with respect to the surface of the developer carrier at the opening of the developer supply container, and more specifically, a minute amount that exists in the vicinity of the blade and does not cause any development in the vicinity. The amount is such that the surface of the agent carrier is hardly covered with magnetic particles and is exposed to the developer. More specifically, this release is 90% due to the distance between the magnetic particles near the blade part.
According to the embodiment of the present invention, the amount of developer in the developer container near the tip of the blade that is brought into elastic contact with the surface of the developer carrier is such that the surface of the developer carrier is freed from magnetic particles. The blade has a small amount of magnetic particles, which forms a circulation of the small amount of magnetic particles near the tip of the blade, which causes agitation of the developer adhering to the surface of the developer carrier and also causes the magnetic particles to circulate on the surface of the developer carrier leading to the developing section. A thin layer of developer is formed on the surface.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

When the sleeve 3 rotates in the direction of arrow A and the magnet 4 rotates in the direction of arrow e, the magnetic particles 7 are conveyed in the direction of rotation of the sleeve 3 while being restrained by the magnetic field formed by the magnet 4. However, the magnetic particles 7 are prevented from being conveyed by the ends of the elastic blades 6 and released outside the container 2, and fall toward the vicinity of the magnetic poles 5 due to gravity and magnetic force. At this time, the magnetic particles 7 circulate near the sleeve surface inside the container 2.

Here, since the magnet 4 is rotating inside the sleeve 2, the state of the magnetic field inside the container 2 changes over time, and as a result, the magnetic particles vibrate violently near the surface of the sleeve 3. Here, the rotation speed of the magnet is 10 to 11000r
P is particularly preferably 50 to 500 rpm.

On the other hand, the developer 8 mixed between the magnetic particles 7 enters the contact area between the elastic blade 6 and the sleeve 3 and enters the sleeve 3.
Conveyed out of the container on the surface.

With the circulation of the magnetic particles 7 and the above-mentioned vibration, the developer 8 is stirred inside the container 2 and at the same time rubs against the magnetic particles 7, thereby being triboelectrically charged. Furthermore, when the developer 8 passes through the contact portion between the elastic blade 6 and the sleeve 3, it is rubbed against the surface of the sleeve 3 by the elastic blade 6, and is further subjected to frictional electrification. In this way, the developer 8 can receive sufficient triboelectric charging. As a result,
Image density can be ensured in the developed image and background fog can be further reduced.

The developer 8 that has been sufficiently triboelectrically charged in this manner passes through the contact portion, is formed as a thin layer of developer on the sleeve 3, and is conveyed on the sleeve 3 to a developing section facing the photoreceptor 1. In the developing section, some of the developer is consumed by the developing operation, and other developer is recovered from the lower part of the sleeve 3 as the sleeve 3 rotates. A sealing member 9 is provided in this recovery portion to allow the developer that has not been consumed during development to pass into the container 2, and to prevent the magnetic particles 7 and developer 8 in the container 2 from leaking out from the bottom of the container 2. 0 The collected developer on the sleeve 3 is magnetic particles 7.
The developer is once scraped off by the circulation and intense vibration, and then stirred and mixed by the magnetic particles 7 and applied again to the surface of the sleeve 3 as a thin layer of developer. In this way, the developer not consumed during development is once scraped off from the surface of the sleeve 3, so regardless of the variation in the amount of developer remaining on the surface of the sleeve 3 after development, the surface after passing through the contact area A thin layer of developer of uniform thickness is formed thereon. Further, since the developer is once scraped off in this manner, the developer on the sleeve 3 is replaced, thereby preventing excessive charging of the developer, that is, charge-up.

The developing method is, for example, the method described in Japanese Patent Publication No. 58-32375, in which a minute gap is provided between the photoreceptor 1 and the developing sleeve 3, and an alternating current with a superimposed direct current is applied between them. A method in which a thin layer of the developer described above is imagewise transferred to an electrostatic latent image on a photoreceptor can be used, but a contact development method can also be used.

Next, the elastic brake roller will be explained in detail.

FIG. 2 is a sectional view of the vicinity of one elastic blade of the developer thin layer forming device when the present invention is not used.

In this figure, the elastic blade 6 is tilted upstream with respect to the rotation direction of the sleeve 3 (forward direction with respect to the sleeve rotation direction). In this configuration, when the sleeve 3 rotates, the magnetic particles 7 are The developer 8 in the upper part of the container 2 is clogged near the tip of the container 2, and the magnetic particles 7 are not circulated and vibrated. Therefore, sufficient triboelectric charging is not achieved. It has been found that because the developer cannot be taken in, unevenness tends to occur in the thin developer layer. In addition, the magnetic particles 7 enter the contact portion between the elastic blade 6 and the sleeve 3, and as a result, the contact pressure between them becomes non-uniform, and streak-like unevenness occurs in the formed developer thin layer. Furthermore, in this case, the magnetic particles 7 are partially pressed against the sleeve 3, causing damage to the surface of the sleeve 3.

FIG. 3 is a sectional view of the vicinity of the elastic blade of the developer thin layer forming device when the present invention is used. In the configuration shown in this figure, the elastic blade 6 is tilted downstream in the direction of movement of the sleeve 3 (opposed to the direction of rotation of the sleeve). In this configuration, the magnetic particles 7 transported by the rotation of the sleeve 3 are The elastic blade 6 is lifted upward by the tip, falls down by gravity and magnetic force, and can repeat the circulation in the direction of arrow C. Further, near the tip of the elastic blade 6, the magnetic particles 7 cause the above-mentioned temporal change in the magnetic field. It was confirmed that there was significant vibration.

Due to the circulation and vibration of the magnetic particles 7, the developer is sufficiently triboelectrically charged and is stably supplied onto the surface of the sleeve 30 from the top of the container 2. Further, due to the above-mentioned action, residual developer on the sleeve 3 can be scraped off, so that in combination with the effect of using the elastic blade described above, a thin layer of developer with a uniform thickness can be stably formed.

Next, as the material of the elastic blade 6, for example, JIS
Rubber with a hardness of 40 to 80 degrees, preferably 50 to 70 degrees, is suitable for stable formation of a thin layer of developer.The thickness of the elastic blade 6 is such that the magnetic particles 7 ride on the back surface of the elastic blade 6. In order to prevent this, it is preferable to have a certain degree of thickness, and according to the inventor's experiments and considerations,
It is 1 mm or more, preferably 2.0 mm or more.

FIG. 4 is a cross-sectional view showing the elastic blade mounting configuration.
Since the elastic blade 6 is pressed against and in contact with the surface of the sleeve 3, it is deformed as shown. This urges the end of the blade 6 to come into contact with the sleeve 3. Note that the term "blade end" as used herein refers to the tip of the blade, the vicinity including the tip, or the vicinity of the tip not including the tip. The blade 6 is inclined downstream in the rotational direction of the sleeve from the end. The zero dotted line indicates the state of the elastic blade 6 assuming that the sleeve 3 does not exist. The straight line m is a vertical line passing through the center of the sleeve 3. n is a straight line passing through the contact portion Q between the elastic blade 6 and the sleeve 3 and the center of the sleeve 3. 0 plane T, where the angle formed by straight line m and straight line n is
and the surface of the sleeve 3, the angle θ is the angle between the tangent of the sleeve 3 passing through point P and the surface T, and the distance #d is the length of the surface T entering the inside of the sleeve 3. be. Although the straight line m passes through the point P here, this is not necessarily necessary.

The angle θ is set between 0 and 40", preferably between 2 and 2 degrees, in order to prevent problems such as the elastic blade 6 recurving due to frictional force when the sleeve 3 rotates.
It is in the range of 0#.

Further, the penetration amount d of the elastic blade 6 is preferably 0.5 to 2 mm, and it is preferable that the edge portion of the tip of the elastic blade 6 is in contact with the sleeve 3. This is because it has been found that if the edge of the tip is separated from the surface of the sleeve 3, the magnetic particles 7 will enter this gap, impairing the uniformity of contact pressure and potentially damaging the surface of the sleeve 3. .

Furthermore, it is preferable that the angle X satisfies the condition 0≦x90'.

In the case of X<O, since the direction of one gravitational force at the tip of the elastic blade 6 is directed toward the elastic blade 6, the magnetic particles 7 tend to stay near the tip of the elastic blade 6. The preferred range of angle

In addition, when x>90'', the magnetic particles 7 are not well conveyed on the sleeve 3 to the position of the elastic body blade 16, and the magnetic particles 7 are dispersed within the sleeve 3 due to gravity, and the elastic body blade 6
It has been found that the magnetic particles 7 circulating and vibrating just before are no longer present, which is undesirable.

From the above considerations, more preferable ranges are as follows.

5@<x<30'' In this range, sufficient circulation and vibration of the magnetic particles 7 can be obtained, and therefore stable developer application can be obtained.

The surface of the sleeve 3 is preferably provided with minute irregularities rather than a mirror surface from the viewpoint of circulation and vibration of the magnetic particles 7.

As the magnetic particles 7, iron powder, ferrite powder, etc. can be used. Furthermore, it is more preferable that these are coated with a resin in accordance with the charging polarity of the developer 8.
The magnetic particles 7 may have a particle size of 50 to 200 JLm. Below 501 parts m, the fluidity of the magnetic particles 7 is poor;
It was confirmed that sufficient circulation and vibration were not obtained, the amount of developer 8 taken in was reduced, and a stable thin layer of developer 8 was not formed. In addition, if the particle size is 200 pm or more, although the developer 8 is sufficiently supplied, the frictional charging is not sufficient, which is not preferable. Particularly preferred for obtaining vibrations.

FIG. 5 is a sectional view of a specific example of a developing device using the developer thin layer forming device according to the present invention. In this figure, the same reference numerals as in FIG. 1 are given to corresponding members and means, so detailed explanations thereof will be omitted.

The sleeve 3 is made of an aluminum sleeve with a diameter of 20 mm, whose surface is sandblasted with 7 random abrasive grains, and the magnet 4 has 6 equally divided magnetic poles with a peak magnetic flux density of 700 Gauss. Silicone rubber (
Rubber hardness JIS 60" and thickness 2 mm) was used.

These mounting positions are θ=10'', d=1, -0m
m, x=15''.

The magnetic particles have a particle size of lOO~80 lm (150/20
0 mesh) iron particles (maximum magnetization = 190 emu/g
) coated with acrylic and fluorine resin, and the developer is a toner with an average particle size of 13 pm consisting of 100 parts of a copolymer of styrene/acrylic resin and styrene-butadiene resin and 5 parts of perylene-based pigment. When we used red toner with 1.0% colloidal silica externally added to the powder, the above-mentioned application action caused the sleeve to become approximately 5" thick.
A uniform coating layer of 0.031 m was obtained. When the amount of charge on this layer was measured using the blow-off method, the amount of charge was +12 g.
c/g, which is a sufficient value.

The developing method used here is
A voltage is applied between the electrophotographic photoreceptor and the sleeve 3 by a bias power source.

The bias power source may be alternating current or direct current, but preferably one in which direct current is superimposed on alternating current.The developing method is not limited to this, and development may be performed by bringing a thin layer of developer into contact with the photoreceptor 1.

This developer thin layer forming device was installed on a PC-PC manufactured by Canon Corporation.
20 built into a copying machine, frequency 160 as a bias power supply
0Hz, AC voltage with peak-to-peak voltage of 1300■,
Using a superimposed DC current of -300V, the surface potential of the latent image l on the photoconductor was set to -540V in the dark area and -220V in the bright area, and the distance between the sleeve 3 and the photoconductor 1 (organic photoconductor) was adjusted. When development was performed at a setting of 250 pLm, a good red image with a reflection density of 1.2 could be obtained.

Furthermore, when images were continuously formed on 1000 sheets, good images without sleeve ghosts could be obtained up to the final image formation.

In order to investigate the influence of the particle size of magnetic particles in the developer thin layer forming device of the present invention, magnetic particles of various particle sizes were prepared at a rate of 0.81 g per unit length of the developer holding member (2.1 g in total). Table 1 shows the results of putting the sample into a developing device, adding 50 g of the above-mentioned red toner, and setting the developing area to 210 mm (corresponding to A4 lengthwise).

Table 1 Particle size and image quality of magnetic particles As a result, magnetic particles with a particle size of 50 lm or less result in a very thin developer layer and an image with noticeable uneven development, which is undesirable. Although uneven development was observed, the image was quite good. 80-100
A very good image was obtained with the lens m. In the case of 200 lumens, fogging, which was thought to be due to insufficient triboelectric charging, was observed.

Next, in order to investigate the influence of the amount of magnetic particles, in the same developing device, 0.2 g of magnetic particles with a particle size distribution of 80 to 150 gm (per unit length of the developer holding member (0.01 g/am in the longitudinal direction) was added. ), 1.

0 (0,05), 2.1 (0,1), 10.5 (0
, 5), 21.5 (1,0) Input (space in the container sandwiched between the plane connecting the center line of the sleeve 3 and the tip of the blade 6 and the plane connecting the center line of the sleeve 3 and the center line of the magnetic pole) The total amount of magnetic particles (g) present in the effective length of the sleeve (cm
) and the case where no magnetic particles were added were developed using 50 g of the red toner described above, and the results shown in Table 2 were obtained.

Table 2 Magnetic particle input amount and image quality According to the results, when no magnetic particles are present and a thin layer is formed using only one elastic blade 6, development unevenness is significant and 0. In O1 to 0.5 g/Cm, development unevenness is not noticeable. In addition, in this range, the magnetic particles are completely restrained by the magnetic pole 5, and there are no particles that can freely move inside the developer thin layer forming device, so the development is difficult. Even when an impact was applied to the agent thin layer forming device, the magnetic particles were not biased. In particular, 0,05~0,1 g/cm (7)
It was good within the range. Furthermore, if the weight is 1.0 g or more, uneven development, which is thought to be caused by sleeve ghost, becomes noticeable. However, since the magnetic particles are forcibly vibrated by the rotation of the magnet 5, the amount of frictional electrification of the developer is much greater than in areas without a magnet or in the case where the magnet is fixed, resulting in a better image. .

From the above experiments and considerations, it is understood that the presence of magnetic particles and their properties are important in the developer thin layer forming apparatus of the present invention.

Next, the time-varying magnetic field generated by the magnet 4 will be explained. In the present invention, magnetic particles circulate and vibrate in the vicinity of the elastic blade as the sleeve 3 rotates. This vibration and circulation is greatly facilitated by changes in the magnetic field near the surface of the sleeve 3. As a result, compared to the case where the magnetic field is fixed, frictional charging, ability to scrape off residual toner, and ability to supply toner are improved, and image quality can be further improved. Therefore, even when the amount of magnetic particles is small, the effect can be performed effectively, and even when the amount is large, sufficient circulation and vibration can be ensured. From this point of view, the tolerance range for the amount of magnetic particles relative to the amount of developer becomes large.

FIG. 6 is a cross-sectional view of a device according to another embodiment of the invention. In this embodiment, the magnet 4 is unipolar and the magnetic poles 5. , which can be swung around the center of the sleeve 3 by a drive means (not shown).

The oscillations create a time-varying magnetic field. The frequency of the oscillation was 100 Hz. Since the other configurations of the device of the present invention are the same as those of the previous embodiment, corresponding parts are given the same reference numerals and detailed explanations will be omitted. The same effects as in the previous embodiment can be obtained, and since only a small amount of magnets are needed, the structure is simple and inexpensive.

FIG. 7 shows yet another embodiment of the present invention. In this embodiment, the magnet 5 is an electromagnet. It is energized by a coil to which an alternating voltage is applied, creating a time-varying magnetic field. The frequency of the alternating voltage was 200 Hz. Since the other configurations of the device of the present invention are the same as those of the previous embodiment, corresponding parts are given the same reference numerals and detailed explanations will be omitted. It is possible to obtain the same effect as in the case of the above-mentioned embodiment, and in particular, in this embodiment, mechanical movement parts such as rotation and rocking are not required.
The configuration can be extremely simplified. The applied voltage is not limited to an alternating voltage, and may be any voltage that can form a magnetic field that changes over time.

Although a non-magnetic developer was used in the above embodiments, a magnetic developer can also be used as long as it has weaker magnetism than magnetic particles and can be triboelectrically charged.

As explained above, according to the present invention, a thin developer layer having a uniform developer layer thickness and a uniform and sufficient amount of triboelectric charge is stably formed, and this thin developer layer By using this in the developing operation, good images can be stably obtained.

Furthermore, since the formed magnetic field changes over time, the magnetic particles actively vibrate, ensuring frictional electrification of the developer, and a stable thin layer can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a developer thin layer forming apparatus according to an embodiment of the present invention. FIG. 2 is a sectional view of the vicinity of the elastic blade of the developer thin layer forming device when the present invention is not used. FIG. 3 is a sectional view of the vicinity of the elastic blade of the developer thin layer forming device when the present invention is used. FIG. 4 is a sectional view showing the mounting structure of the elastic plate. FIG. 5 is a sectional view of a specific example of a developing device using the developer thin layer forming device according to the present invention. FIG. 6 is a sectional view of a developer thin layer forming apparatus according to another embodiment of the present invention. FIG. 7 is a sectional view of a developer thin layer forming apparatus according to still another embodiment of the present invention. 1 to 1” 1: Photoreceptor 2: Container 3 Nisleeve 4: ? a Stone 5: Magnetic pole 6: Elastic blade

Claims (1)

[Scope of Claims] A developer supply container having an opening and containing a developer and a small amount of magnetic particles, and a non-magnetic developer provided in the opening and capable of moving endlessly inside and outside the container. a holding member; a magnetic field generating means provided inside the developer holding member for generating a temporally varying magnetic field; and an end portion biased to come into contact with the developer holding member; provided inclined from the end toward the downstream side in the rotational direction,
a blade elastically abutting a developer retaining member, the developer retaining member being moved endlessly to form a thin layer of developer on the developer retaining member downstream of the blade in the direction of movement of the retaining member; A developer thin layer forming device characterized by forming a developer thin layer.