JPH11149194A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the rising of the resistance values of electrically conductive magnetic grains and to suppress the shaving of an image carrier, in an image forming device provided with a magnetic brush electrifier. SOLUTION: The pressure against a regulating blade 36 of the magnetic grains 33 carried by the rotation of the sleeve 32 of the magnetic brush electrifier 30 is detected by a pressure sensor 39 and the pressure information is outputted to a controller 40. The controller 40 controls the operation of a magnetic grain replenishing device 38, based on the inputted pressure information, to optimally adjust the replenishment of the magnetic grains 33 onto the sleeve 32, so that the rising of the resistance values of the magnetic grains 33 can be prevented and the shaving of the drum 1 can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image by an electrophotographic method. The present invention relates to an image forming apparatus provided with a magnetic brush charging device for charging an image.

[0002]

2. Description of the Related Art FIG. 14 is a schematic diagram showing an example of a conventional image forming apparatus.

In this figure, A is an apparatus main body, and B is an image reading section (image scanner) mounted on the apparatus main body A.

In the image reading section B, reference numeral 20 denotes a fixed original platen glass. The original G is placed on the upper surface of the original platen glass 20 with the surface to be copied facing downward, and an original (not shown) is placed thereon. Set it over the board. An image reading unit 21 includes a document irradiation lamp 21a, a short focus lens array 21b, a CCD sensor 21c, and the like. When a copy button (not shown) is pressed, the image reading unit 21 moves forward from the home position on the left side of the original table glass 20 to the right side along the lower surface of the original table glass 20 when the copy button (not shown) is pressed. When it is driven and reaches a predetermined end point of reciprocation, it is driven backward and returned to the initial home position.

In the forward driving process of the image reading unit 21, the downward image surface of the placed and set original G on the original platen glass 20 is sequentially illuminated and scanned from the left side to the right side by the original irradiating lamp 21a. The light reflected on the document surface is converted into a CCD by the short focus lens array 21b.
An image is incident on the sensor 21c.

The CCD sensor 21c comprises a light receiving section, a transfer section, and an output section (not shown). In the light receiving section, an optical signal is converted into a charge signal, and the transfer section sequentially outputs an output signal in synchronization with a clock pulse. The charge signal is converted to a voltage signal at the output unit, amplified, reduced in impedance, and output. The analog signal obtained in this manner is converted into a digital signal by well-known image processing and output to the exposure device 3 on the apparatus main body A side.

On the other hand, in the apparatus main assembly A, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 has a predetermined peripheral speed (process speed) around a center support shaft and an arrow a.
The charging device 2 is rotated in the rotation direction.
Receives a uniform charging process.

Then, the LED ON / OFF modulated on the uniformly charged surface of the photosensitive drum 1 in accordance with the image signal output from the exposure unit 3 to the apparatus main body A side from the image reading unit B, By performing the scanning exposure L by the OFF light emission, an electrostatic latent image corresponding to the image information of the document G photoelectrically read by the image reading unit B is sequentially formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is reversely developed as a toner image by the developing device 4 sequentially. The developing method by the developing device 4 is preferably a two-component contact developing method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by a magnetic force to develop the photosensitive drum 1 in a contact state. Used for

On the other hand, the transfer material P such as paper stored in the paper feed cassette 5 is fed one by one by the paper feed roller 6,
The paper is fed to the transfer nip 9 between the photosensitive drum 1 and the transfer device 8 at a predetermined timing by the registration roller 7, and is transferred onto the transfer material P by the transfer blade 9 of the transfer device 8.
The upper toner image is transferred. The transfer material P to which the toner image has been transferred is conveyed to the fixing device 12 by the transfer belt 11 also serving as a conveyance belt, is fixed as a permanent fixed image, and is discharged outside.

Further, contaminants such as untransferred toner adhering to the photosensitive drum 1 after the transfer of the toner image are removed by the cleaning blade 14 of the cleaner device 13, and the image is repeatedly formed.

In recent years, since the photosensitive drum has advantages such as low ozone and low power, a contact charging device, that is, a charging member to which a voltage is applied is brought into contact with the photosensitive drum as a charging means for the photosensitive drum. An apparatus of a system for performing charging has been put to practical use.

As a charging member of this type, a conductive roller, a fur brush roller, or the like is generally used. However, from the viewpoint of lightening the pressure and improving the contact property, a magnetic brush using magnetic particles is used. Attention has been focused on a contact charging device of the type (hereinafter referred to as a magnetic brush charging device).

In a magnetic brush charging device, conductive magnetic particles are magnetically constrained directly on a magnet or on a sleeve containing the magnet, and are brought into contact with the photosensitive drum while stopping or rotating to apply a voltage to the magnetic particles. The application starts charging.

FIG. 15 is a schematic view showing an example of a conventional magnetic brush charging device.

This magnetic brush charging device comprises a rotatable non-magnetic sleeve 3 having a fixed magnet 31 provided therein.
The conductive magnetic particles 33, the amount of which is supported on the sleeve 32 by the regulating plate 34, are formed in a brush shape by the magnetic field, and the magnetic particles 33 are conveyed in the direction of the arrow b as the sleeve 32 rotates. Is done.

The sleeve 32 rotates counterclockwise with respect to the photosensitive drum 1 rotating in the direction of the arrow a. For example, when the rotation speed of the photosensitive drum 1 is 100 mm / sec, the sleeve 32 of the magnetic brush charging device is 150 mm / sec. It is spinning. Then, by applying a charging bias to the sleeve 32, a charge is given from the magnetic particles 33 onto the photosensitive drum 1, and charged to a value close to a potential corresponding to the charging bias. It is desirable that the contact nip width of the magnetic particles 33 formed on the photosensitive drum 1 be adjusted to 1 to 10 mm.

Using such a contact charging device (magnetic brush charging device), a photosensitive drum having a surface layer in which conductive fine particles are dispersed on an ordinary organic photosensitive member, or an amorphous silicon photosensitive member is used. It is possible to obtain a charging potential on the surface of the photosensitive drum substantially equal to the DC component of the bias applied to the contact charging device.
Such a charging method is called injection charging. With the use of the injection charging, the ozone-free and low-power-consumption type charging can be achieved since the photosensitive drum is not charged using a discharge phenomenon that is performed using a corona charger. By the way, in the cleaner-less system for simultaneous recovery of development by the above-described magnetic brush charging device as a charging device, the transfer residual toner remaining on the photosensitive drum at the time of the transfer process has a polarity opposite to the normal charging polarity due to peeling discharge or the like. Since the amount of charged toner is large and the charging potential is generally lower than the voltage applied to the magnetic brush charging device, the transfer residual toner is collected by the magnetic brush charging device. The collected toner is charged to a normal charging polarity by frictional charging with magnetic particles of the magnetic brush charging device, and is discharged onto the photosensitive drum. The toner discharged in this manner is collected by the developing device due to a fog removal potential difference during development (a DC voltage applied to the developing device and a potential difference between the surfaces of the photosensitive drums) and is reused.

According to this method, the transfer residual toner is collected and used in the subsequent steps, so that waste toner can be eliminated. In addition, since the toner is uniformly discharged after being collected by the magnetic brush charging device, the transfer residual toner is non-patterned, so that the effect on image exposure is small and high image quality can be maintained. Further, since the cleaner device can be omitted, the advantage in terms of space is great, and the size can be significantly reduced.

[0019]

By the way, in an image forming apparatus using the above-described magnetic brush charging device, when image formation is repeated, toner particles as a developing material often mix into the magnetic particles. .

Normally, the electric resistance of the toner particles is relatively high, so that if the toner particles are mixed into the magnetic particles, the resistance of the magnetic particles increases. This phenomenon is particularly likely to occur in the image forming apparatus of the cleanerless system described above, and the charging property is deteriorated due to the increase in the resistance of the magnetic particles, which causes the life of the magnetic brush charging apparatus to be shortened.

Further, the magnetic brush charging device applies electric charges while contacting and rubbing the magnetic particles with the photosensitive drum, so that the shaving amount of the photosensitive drum varies depending on the constituent factors of the magnetic brush charging device. In the image forming apparatus of the cleanerless system described above, the shaving amount is considerably smaller than the shaving amount in the case where the cleaning step of the photosensitive drum surface is performed by the cleaning device, but a slight shaving of the photosensitive drum surface occurs. The life of the photosensitive drum is determined.

As a result of a study by the inventor of the present invention, one of the factors of the shaving of the photosensitive drum surface in the image forming apparatus of the cleanerless system is that the amount of the magnetic particles carried on the sleeve is regulated. It was found to be due to the pressure on the magnetic particles at the plate.

When charging is performed by using magnetic particles for the charging member, a phenomenon occurs in which a small amount of magnetic particles is carried to the photosensitive drum.
The magnetic particles decrease at the ratio of g. As shown in FIG. 15 described above, in order to prevent the charging property from being impaired even when the number of magnetic particles is reduced, as shown in FIG.
A method of providing a pool of magnetic particles 33 on the downstream side in the rotation direction of the sleeve 32 and regulating the flow rate of the magnetic particles 33 by a regulating plate 34 is adopted.

However, when the regulating plate 34 for regulating the flow rate of the magnetic particles 33 is provided, the sleeve 32 of the regulating plate 34 is provided.
It has been found that the state of contamination of the magnetic particles 33 and the state of scraping of the photosensitive drum 1 change depending on the pressure applied to the magnetic particles 33 accumulated on the downstream side in the rotation direction of the magnetic particles 33.

FIG. 16 shows a conventional image forming apparatus of a cleanerless system using the magnetic brush charging device shown in FIG. 15, in which the amount of magnetic particles 33 carried on the sleeve 32 is 25 g, 40 g, 60 g, and 90 g. Change (load 2
5 g, the accumulation of the magnetic particles 33 on the downstream side in the rotation direction of the sleeve 32 of the regulating plate 34 becomes about 2 to 5 g).
FIG. 17 is a diagram illustrating a change in the charging property when 0000 sheets have been subjected to durability, and FIG. 17 is a diagram illustrating a change in the shaving amount of the photosensitive drum 1 at that time.

The chargeability is represented by the difference between the applied voltage and the charge potential, and the smaller the value of the potential difference, the better the chargeability. The amount of scraping of the photosensitive drum 1 is indicated by a difference between an initial layer thickness and a layer thickness after durability. As is clear from both figures, when the carrying amount of the magnetic particles 33 on the sleeve 32 is increased, the chargeability is reduced and the scraping amount of the photosensitive drum 1 is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus using a magnetic brush charging device, which can prevent the increase in the resistance value of magnetic particles and reduce the shaving amount of the photosensitive drum. .

[0028]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an image bearing member for carrying an image and conductive magnetic particles carried on a rotatable magnetic particle carrier. Contact charging means for contacting the image carrier to charge the image carrier; exposure means for forming an electrostatic latent image on the image carrier; and developing the electrostatic latent image to form a toner image An image forming apparatus including a developing unit and a transfer unit configured to transfer the toner image to a transfer material, wherein the conductive magnetic particles are in contact with the conductive magnetic particles carried and conveyed on the magnetic particle carrier. Magnetic particle regulating means for regulating the flow rate of the magnetic particles, magnetic particle accommodating means for accommodating the conductive magnetic particles to be supplied on the magnetic particle carrier, and the conductive material carried and conveyed on the magnetic particle carrier. Magnetic particles for the magnetic particle regulating means Depending on the force is characterized by comprising a magnetic particle replenishing means for replenishing the conductive magnetic particles on the magnetic particle carrier from said magnetic particle storage means.

A pressure detecting means for detecting a pressure of the conductive magnetic particles with respect to the magnetic particle regulating means; and the conductive magnetic particles provided by the magnetic particle replenishing means based on pressure information inputted from the pressure detecting means. Control means for performing replenishment control of the magnetic particle storage means, when the control means determines that the pressure of the conductive magnetic particles with respect to the magnetic particle regulating means has become low based on the input pressure information. Controlling the magnetic particle replenishing means so as to replenish the conductive magnetic particles on the magnetic particle carrier, and when it is determined that the pressure of the conductive magnetic particles with respect to the magnetic particle regulating means has increased, the magnetic particle storage means The magnetic particle supply means is controlled so as to stop supplying the conductive magnetic particles to the magnetic particle carrier.

Further, the magnetic particle regulating means is formed integrally with the magnetic particle replenishing means, and the magnetic particle regulating means is movable according to the pressure of the conductive magnetic particles. When the pressure by the conductive magnetic particles is low, the conductive magnetic particles are moved from the magnetic particle storage means to a position where the conductive magnetic particles can be replenished onto the magnetic particle carrier, and the pressure by the conductive magnetic particles is high. Is characterized in that it is movable to a position where supply of the conductive magnetic particles from the magnetic particle storage means to the magnetic particle carrier is stopped.

Further, the developing means also serves as a cleaning means for collecting residual toner remaining on the image carrier after transferring the toner image to the transfer material.

The image carrier has a surface with a resistance of 10%.
It is characterized by having a layer made of a material of ⁹ to 10 ¹⁴ Ω · cm.

Further, the rotating direction of the magnetic particle carrier for carrying the conductive magnetic particles on the surface thereof is opposite to the rotating direction of the image carrier.

(Function) According to the present invention, the magnetic particles can be replenished on the magnetic particle carrier according to the pressure of the magnetic particles on the magnetic particle regulating means. It is possible to optimally adjust the replenishment, prevent an increase in the resistance value of the magnetic particles, and suppress the scraping of the surface of the image carrier.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus of the present embodiment uses a magnetic brush-type contact charging device (magnetic brush charging device) as a charging unit of the image carrier, and is a cleanerless system device. Note that the same members as those of the conventional example shown in FIG. 14 are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, A is an apparatus main body of the image forming apparatus according to the present embodiment, and B is an image reading unit (image scanner) mounted on the apparatus main body A. The configuration of the image reading unit B is the same as that of the conventional example shown in FIG. 14, and a description thereof will be omitted in the present embodiment.

The apparatus main body A includes a photosensitive drum 1 as an image carrier, a magnetic brush charging device 30, which is a contact charging means, an exposure device 3, a developing device 4, a transfer device 8, a fixing device 12, and a cleaner device 13. I have.

As the photosensitive drum 1, a commonly used organic photosensitive member or the like can be used.
When an organic photoreceptor having a surface layer having a material having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm or an amorphous silicon photoreceptor is used, charge injection charging can be realized, and ozone generation can be prevented and consumption can be reduced. It is effective in reducing power.
Further, the chargeability can be improved.

In the present embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member. The following first to fifth five layers (not shown) are formed on an aluminum drum base (not shown) having a diameter of 30 mm. And is driven to rotate in the direction of arrow a at a predetermined process speed.

The first layer at the bottom of this layer is an undercoat layer, and is a conductive layer having a thickness of 20 μm provided to smooth out defects or the like of the drum base. The second layer is a positive charge injection preventing layer, which serves to prevent positive charges injected from the drum substrate from canceling out negative charges charged on the surface of the photosensitive drum 1, and is formed by an amylan resin and methoxymethylated nylon. Thickness 1 resistance adjusted to about 10 ⁶ Ω · cm
It is a medium resistance layer of μm.

The third layer is a charge generating layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs upon exposure to light. The fourth layer is a charge transport layer in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charges charged on the surface of the photosensitive drum 1 cannot move through this layer (third layer), and only the positive charges generated in the third layer (charge generation layer) are transported to the surface of the photosensitive drum 1. be able to.

The fifth layer, which is a surface layer, is a charge injection layer.
This is a coating layer of a material in which O ₂ ultrafine particles are dispersed. Specifically, SnO ₂ ultrafine particles having a particle diameter of about 0.03 μm obtained by doping antimony, which is a light-transmitting conductive filler, to an insulating resin to reduce the resistance (conducting) are dispersed in the resin by 70% by weight. It is a coating layer of the material obtained. The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. to form a charge injection layer.

The magnetic brush charging device 30 includes a magnet roller 31 fixed in a charging container 35 as shown in FIG.
A sleeve 32 made of a nonmagnetic material (for example, stainless steel) rotatably fitted to the magnet roller 31 and having an outer diameter of 16 mm, and a photosensitive drum 1 supported on the outer peripheral surface of the sleeve 32 in a brush shape by the magnetic force of the magnet roller 31. Conductive magnetic particles 33 that contact the surface and inject charges,
A regulating blade 36 made of a non-magnetic material (for example, stainless steel) for coating the surface of the sleeve 32 with the magnetic particles 33 to a uniform thickness is provided. A magnetic particle storage unit 37 containing new magnetic particles 33 not contaminated with toner, and a magnetic particle supply device 38 for supplying the magnetic particles 33 in the magnetic particle storage unit 37 onto the sleeve 32 are provided in the upper portion of the charging container 35.
Is provided. Magnetic particles 3 in magnetic particle storage 37
3 is a regulating blade 36 through a magnetic particle replenishing device 38.
Is supplied to the magnetic particle reservoir (near the lower part of the magnetic particle supply device 38) on the downstream side in the rotation direction (the direction of the arrow b) of the sleeve 32. The magnetic particles 33 are transported in the direction of arrow b as the sleeve 32 rotates.

The regulating blade 36 has a charging container 35 at its base end.
A pressure sensor 39 is installed on the upper side of the inside of the inside, and on the upstream side in the rotation direction (the direction of the arrow b) of the sleeve 32 on the tip side of the regulating blade 36. The regulating blade 36 is fixed to the upper part in the charging container 35 so that the tip side can be displaced by the magnetic particles 33 conveyed to the photosensitive drum 1.
A control device (CPU) 40 is connected to the pressure sensor 39, and the control device (CPU) 40
9, the magnetic particles 3 conveyed to the photosensitive drum 1
The supply of the magnetic particles 33 is adjusted by controlling the operation of the magnetic particle supply device 38 according to the pressure information on the third regulating blade 36 (details will be described later).

The sleeve 32 rotates in the counter direction with respect to the photosensitive drum 1. In the present embodiment, the process speed (peripheral speed) of the photosensitive drum 1 is 100 mm / sec.
On the other hand, the sleeve 32 is rotating at 150 mm / sec. A charging bias (a charging bias in which an AC voltage is superimposed on a DC voltage) is applied to the sleeve 32 from a charging bias power supply (not shown). By applying a charging bias to the sleeve 32, electric charges are given from the magnetic particles 33 onto the photosensitive drum 1, and charged to a value close to the potential corresponding to the charging voltage.

The contact nip width of the magnetic particles 33 formed on the photosensitive drum 1 was adjusted to about 6 mm, and a DC bias of -650 V was applied to the sleeve 32 as a charging condition.

The magnetic particles 33 oxidize the ferrite surface,
On the other hand, after the reduction treatment and the resistance adjustment, a silicone-based resin in which carbon black was dispersed and coated with a coating agent whose resistance was adjusted by 1.0% by weight was used. The core of the magnetic particles 33 has an average particle diameter of 1
0-100 μm, saturation magnetization 20-250 emu / cm
^{3. A} resistor having a resistance of 10 ² to 10 ¹⁰ Ω · cm is used. Further, in consideration of the existence of insulation defects such as pinholes in the photosensitive drum 1, it is preferable to use one having a resistivity of 10 ⁶ Ω · cm or more.

In order to improve the charging performance, it is better to use one having a resistance as small as possible. In order to perform uniform charging, it is preferable to use one having a resistance of 10 ⁹ Ω · cm or less. Therefore, in the present embodiment, the average particle diameter is 25 μm, the saturation magnetization is 200 emu / cm ³ , and the resistance is 5 × 1.
0 using the magnetic particles 33 of ^{6 Ω} · cm.

The resistance value of the magnetic particles 33 was measured by placing 2 g of the magnetic particles 33 in a metal cell having a bottom area of 228 mm ² , applying a load of 6.6 kg / cm ² , and applying a voltage of 100 V to both ends of the metal cell. Was applied.

As shown in FIG. 3, the developing device 4 is a two-component contact developing device (two-component magnetic brush developing device) in the present embodiment. In this figure, reference numeral 51 denotes a developing sleeve which is driven to rotate in the direction of the arrow d, 52 denotes a magnet roller fixedly arranged in the developing sleeve 41, 53 and 54 denote stirring screws, and 55 denotes a developer T on the surface of the developing sleeve 41. A regulating blade 56 for forming a thin layer is a developing container, and 57 is a toner hopper for replenishment.

The developing sleeve 51 has a region closest to the photosensitive drum 1 at least at the time of development at about 500 μm.
Are set so that the developer T can be developed in a state of being in contact with the photosensitive drum 1. The toner t, which is the developer T used in the present embodiment,
A negatively charged toner having an average particle diameter of 6 μm manufactured by a pulverization method and a titanium oxide having an average particle diameter of 20 nm externally added by 1.5% by weight is used. The carrier c has a saturation magnetization of 205 emu / cm ³ . A magnetic carrier having an average particle size of 35 μm was used. A mixture of the toner t and the carrier c at a weight ratio of 8:92 was used as the developer T. Toner in the developer T in this case, the frictional charge amount of about -25 × 10 ^- was ³ c / kg.

Next, an electrostatic latent image formed on the surface of the photosensitive drum 1 by exposure of the exposure device 3 is
Step of Visualizing by Component Brush and Method of Developing Agent T
Will be described.

First, the developing sleeve 51 is
The developer T, which rotates in the counter direction with respect to the rotation direction of the developing sleeve 51, is regulated by a regulating blade 55 arranged perpendicularly to the developing sleeve 51 in the process of being conveyed. A thin layer is formed. Here, when the developer T formed in a thin layer is conveyed to the main development pole (N pole), a spike is formed by its magnetic force. The electrostatic latent image on the photosensitive drum 1 is developed with the developer T formed in a spike shape, and then the N pole and the N pole are used.
The developer T on the developing sleeve 51 by the repulsive magnetic field of the pole
Is returned into the developing container 56.

A developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve 51 from a developing bias power supply (not shown). In the present embodiment, a DC voltage of -480 V, a peak-to-peak voltage Vpp = 1500 V, and a frequency f =
An AC voltage of 3000 Hz was applied.

In general, when an AC voltage is applied in the two-component developing method, the developing efficiency increases, and the image becomes high quality.
Conversely, there is a danger that fogging is likely to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1. The potential difference for preventing fogging is called a fogging removal potential. This potential difference prevents toner from adhering to a non-image area during development,
In the cleaner-less device of the present invention, transfer residual toner is also collected.

The transfer device 8 is a belt transfer device in the present embodiment, and transfers the endless transfer belt 1 to the driving roller 15.
, And is driven to rotate in the direction of arrow e at a peripheral speed substantially equal to the peripheral speed of the photosensitive drum 1. The transfer belt 11 is brought into contact with the surface of the photosensitive drum 1 by a transfer charging blade 10 provided inside the transfer belt 11. Transfer material P
Is transported to the transfer nip 9 on the upper surface of the ascending side belt portion of the transfer belt 11. When the leading end of the transfer material P enters the transfer nip 9, the transfer charging blade 1
0, a predetermined transfer bias is applied from a transfer bias power supply (not shown) to charge the toner P from the back surface of the transfer material P with a polarity opposite to that of the toner t. It is transferred to the upper surface.

In the present embodiment, the transfer belt 11
A film made of a polyimide resin having a film thickness of 75 μm was used. The material of the transfer belt 11 is not limited to a polyimide resin, but may be any other material such as a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, or a polyether. Plastics such as sulfone resins and polyurethane resins, and fluorine-based and silicon-based rubbers can be suitably used. Also, the thickness is not limited to 75 μm, but is 25 to 2000 μm, preferably 50 μm.
Those having a thickness of up to 150 μm are preferably used.

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate in the direction of arrow a by driving means (not shown), and the surface is uniformly charged by the magnetic brush charging device 30. At this time, a DC voltage of -650 V is applied to the magnetic brush charging device 30 from a charging bias power supply (not shown) in the present embodiment. Then, an image exposure L is given to the charged photosensitive drum 1 by the exposure device 3 to form an electrostatic latent image corresponding to the image information input from the image reading unit 21 of the image reading section B. The electrostatic latent image is developed by the developing device 4 as a toner image. At this time, the developing sleeve 51 of the developing device 4 has -4
An DC voltage of 80 V and an AC voltage of 3000 V at a frequency of 3000 Hz are applied. Then, the toner image on the photosensitive drum 1 is transferred to the photosensitive drum 1 and the transfer belt 11.
When the transfer nip 9 is reached, the transfer material P such as paper in the paper feed cassette 5 is fed by the feed roller 6 and conveyed by the registration roller 7 in accordance with this timing, and the transfer bias is applied. A charge having a polarity opposite to that of the toner t is applied to the back side of the transfer material P by the transfer charging blade 10, and the toner image on the photosensitive drum 1 is transferred to the front side. The transfer material P to which the toner image has been transferred is conveyed to the fixing device 12 by the transfer belt 11, and the toner image is fixed as a permanently fixed image on the surface of the transfer material P by heating and pressing by the fixing device 12, and is discharged. .

On the other hand, the transfer residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image. In this embodiment, since the cleaning device 13 is provided, the transfer residual toner is scraped and collected by the cleaning blade 14 of the cleaning unit 13. in this way,
In the present embodiment, since the cleaning device 13 is provided, the amount of toner mixed into the magnetic particles 33 of the magnetic brush charging device 30 can be reduced.

However, even when the transfer residual toner is collected by the cleaning device 13, a small amount of toner and external additives are rubbed off, so that the conventional image forming apparatus shown in FIG. When a large amount of the magnetic particles 33 are carried on the sleeve 32, the resistance of the magnetic particles 33 increases.

For this reason, in this embodiment, the sleeve 3
The pressure sensor 39 detects the pressure of the magnetic particles 33 conveyed by the rotation of the magnetic particles 33 against the regulating blade 36 and outputs the pressure information to the control device 40. The control device 40 supplies magnetic particles based on the input pressure information. The device 38 was controlled to adjust the supply of the magnetic particles 33 onto the sleeve 32.

That is, when the control device 40 determines that the pressure applied to the regulating blade 36 is higher than a predetermined value (there are many magnetic particles 33 carried on the sleeve 32), the supply of the magnetic particles 33 from the magnetic particle supply device 38 is performed. Is stopped, and the pressure applied to the regulating blade 36 is lower than a predetermined value (the number of the magnetic particles 33 carried on the sleeve 32 is small).
, The magnetic particles 3 from the magnetic particle supply device 38
3 is controlled to be supplied. Specifically, the sleeve 3
2 so that the carrying amount of the magnetic particles 33 on the magnetic particle 33 is controlled to 22 to 28 g, and the magnetic particles 3 in the magnetic particle reservoir on the downstream side in the rotation direction (direction of the arrow b) of the sleeve 32 of the regulating blade 36 are controlled.
The accumulation amount of No. 3 is set to be about 0 to 10 g.

Therefore, when the magnetic particles 33 were replenished little by little from the magnetic particle replenishing device 38 under the control of the control device 40, the resistance of the magnetic particles 33 hardly increased.

FIG. 4 shows this embodiment and a comparative example (the above-described magnetic particle replenishing device 38, pressure sensor 39, control device 4
The relationship between the number of durable sheets and the chargeability (difference between the applied voltage and the charged potential) when 10,000 sheets were durable in an image forming apparatus having the same configuration as that of the present embodiment except that 0 was not provided. FIG. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.

As is clear from the results shown in this figure, in the present embodiment, the difference between the applied voltage and the charging potential changes to a low value of 20 V or less even in the case of the durability of 10,000 sheets.
The increase in the resistance value of No. 3 was kept low, and the chargeability was good. On the other hand, in the comparative example, the difference between the applied voltage and the charging potential was about 50 V after the durability of 10,000 sheets, and the resistance of the magnetic particles 33 increased and the charging property was poor as compared with the present embodiment.

FIG. 5 shows this embodiment and a comparative example (the above-described magnetic particle supply device 38, pressure sensor 39, control device 4).
FIG. 10 is a diagram illustrating the relationship between the number of endurable sheets and the amount of photosensitive drum scraping when the endurance of 10,000 sheets is performed in an image forming apparatus having the same configuration as that of the present embodiment except that 0 is not provided. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.

As is apparent from the results shown in this figure, in the present embodiment, the amount of scraping of the photosensitive drum 1 was as small as about 1.4 μm with the durability of 10,000 sheets. Further, in the comparative example, the shaving amount of the photosensitive drum 1 was 2.000 with a durability of 10,000 sheets.
It was about 1 μm.

As described above, the pressure sensor 39 detects the pressure of the magnetic particles 33 conveyed by the rotation of the sleeve 32 with respect to the regulating blade 36, and outputs the pressure information to the control device 40. The magnetic particle supply device 38 is controlled based on the pressure information to
By optimally adjusting the replenishment of the magnetic particles 33 on the upper surface 2, it is possible to prevent an increase in the resistance value of the magnetic particles 33 and suppress the scraping of the photosensitive drum 1.

(Embodiment 2) In the embodiment 1, the cleaning device 13 for removing the transfer residual toner on the photosensitive drum 1 is provided. In the present embodiment, as shown in FIG. This is an image forming apparatus of a cleanerless system that does not include the image forming apparatus. Other configurations and image forming operations are the same as in the first embodiment.

The cleanerless system used in this embodiment will be briefly described.

The transfer residual toner remaining on the photosensitive drum 1 without being transferred to the transfer material at the time of transfer includes those whose charge polarity is inverted due to peeling discharge or the like at the time of transfer and those which are not inverted. . The transfer residual toner in which the both polarities are mixed is collected by the magnetic brush charging device 30, is charged to the negative polarity by the influence of the frictional charging with the magnetic particles 33 constituting the magnetic brush and the influence of the applied bias, and is discharged onto the photosensitive drum 1. It is. The discharged negative polarity toner is developed and collected simultaneously by the developing device 4 and reused. This simultaneous recovery of development utilizes the fog removal potential during development. In the normal developing step, fog is prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1. The potential difference for preventing fogging is called a fogging potential. This potential difference prevents toner from adhering to a non-image area during development, and the cleaner-less apparatus according to the present embodiment also collects untransferred toner. Is going.

This cleaner-less system is not necessarily limited to the magnetic brush charging device. For example, in the case of a charging device using a conductive roller, the non-surface area is small. Poor charging may occur. In addition, when a corona charger is used, charging can be performed even when toner is present, but the remaining toner remains in a pattern of untransferred toner, such as when a discharge substance or the like easily adheres or when transfer efficiency is reduced. Exposure is interrupted, or collection failure occurs in the developing unit.

On the other hand, when the magnetic brush charging device 30 is used as in the present embodiment, the non-surface area is large, so that even if a small amount of toner is mixed, the charging property is not greatly reduced. Since the transfer residual toner is once collected and discharged, the remaining transfer residual toner is non-patterned, so that even if the transfer efficiency is reduced, light collection during image exposure and collection failure in development are less likely to occur.

The effect of the present invention is particularly great in the image forming apparatus of this embodiment using such a cleanerless system. The increase in the resistance value of the magnetic particles 33 is more remarkable when there is no cleaning device, and the effect of reducing the amount of scraping of the photosensitive drum 1 is greater when the cleaning device is not provided.

Also in this embodiment, similarly to the first embodiment, the pressure sensor 39 detects the pressure of the magnetic particles 33 conveyed by the rotation of the sleeve 32 against the regulating blade 36, and the pressure information is used as a control device. The controller 40 controls the magnetic particle supply device 38 based on the input pressure information to adjust the supply of the magnetic particles 33 onto the sleeve 32.

FIG. 7 shows this embodiment and a comparative example (the above-described magnetic particle replenishing device 38, pressure sensor 39, control device 4
The relationship between the number of durable sheets and the chargeability (difference between the applied voltage and the charged potential) when 10,000 sheets were durable in an image forming apparatus having the same configuration as that of the present embodiment except that 0 was not provided. FIG. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.

As is apparent from the results shown in this figure, in the present embodiment, the difference between the applied voltage and the charging potential changes to a low value of 40 V or less even in the case of the durability of 10,000 sheets.
The increase in the resistance value of No. 3 was kept low, and the chargeability was good. On the other hand, in the comparative example, the difference between the applied voltage and the charging potential was about 95 V after the durability of 10,000 sheets, and the resistance of the magnetic particles 33 increased and the charging property was poor as compared with the present embodiment.

FIG. 8 shows this embodiment and a comparative example (the above-described magnetic particle supply device 38, pressure sensor 39, control device 4
FIG. 10 is a diagram illustrating the relationship between the number of endurable sheets and the amount of photosensitive drum scraping when the endurance of 10,000 sheets is performed in an image forming apparatus having the same configuration as that of the present embodiment except that 0 is not provided. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.

As is clear from the results shown in this figure, in the present embodiment, since the shaving by the cleaning device is eliminated as in the first embodiment, the shaving amount of the photosensitive drum 1 is 0.3 μm with the durability of 10,000 sheets. The degree was small.
In the comparative example, the shaving amount of the photosensitive drum 1 was about 1.0 μm after the durability of 10,000 sheets.

As described above, in the image forming apparatus of the cleanerless system according to the present embodiment, similarly to the first embodiment, an increase in the resistance value of the magnetic particles 33 is prevented and the scraping of the photosensitive drum 1 is suppressed. be able to.

(Third Embodiment) In the first and second embodiments, the pressure sensor 3 controls the pressure of the magnetic particles 33 conveyed by the rotation of the sleeve 32 against the regulating blade 36.
9, the control unit 40 controls the magnetic particle replenishing device 38 based on the pressure information to adjust the supply of the magnetic particles 33 optimally. However, in this embodiment, FIG. As shown in FIG. 1, there is provided an image forming apparatus of a cleanerless system in which the supply of magnetic particles 33 is mechanically adjusted by a magnetic particle regulating member 42 which also serves as a rotatable magnetic particle supply means having a cutout portion 42a. Other configurations and image forming operations are the same as those in the second embodiment.

In this embodiment, the magnetic brush charging device 3
A magnetic particle regulating member 42 is provided in an opening below the magnetic particle storage part 41 of Oa.

As shown in FIG. 10, the magnetic particle regulating member 42 is rotatably supported on the rotating shaft 43 along the longitudinal direction of the sleeve 32, and has a cylindrical portion having a notch 42a cut out at approximately 90 °. Shaped member. The distal ends of the wall surfaces 41 a and 41 b on both surfaces of the magnetic particle storage 41 are formed so as to substantially contact the outer peripheral surface of the magnetic particle regulating member 42.

Next, the supply control of the magnetic particles 33 onto the sleeve 32 by the magnetic particle regulating member 42 in the present embodiment will be described with reference to FIGS. 11 (a), 11 (b) and 11 (c).

A rotation force in the direction of arrow f is always applied to the magnetic particle regulating member 42 with a constant force. However, the magnetic particle regulating member 42 is also rotatable in the direction opposite to the arrow f direction, and the rotational movable range of the magnetic particle regulating member 42 is as shown in FIG.
From the position where the peripheral surface of the magnetic particle regulating member 42 of FIG. 1A blocks the opening at the lower part of the magnetic particle storage part 41, the cutout part 42a of FIG. 11C is located at the opening at the lower part of the magnetic particle storage part 41. It is rotatable and movable within the range.

First, as shown in FIG. 11A, the magnetic particles 3 supported on the sleeve 32 and moving in the direction of arrow b
When the number 3 is equal to or larger than a predetermined amount (there are many magnetic particles 33 carried on the sleeve 32), the conveying force of the magnetic particles 33 on the surface acts in the direction of arrow g. At this time, the magnetic particles 3
When the conveying force in the direction indicated by the arrow g in FIG. 3 is larger than the rotational force of the magnetic particle regulating member 42 in the direction indicated by the arrow f, that is, when the pressure exerted on the magnetic particle regulating member 42 by the magnetic particles 33 increases, the magnetic particle regulating member 42 By rotating in the direction opposite to the direction f, the magnetic particle storage 41
The lower opening is closed, and the magnetic particles 33 on the surface of the sleeve 32 enter the notch 42a of the magnetic particle regulating member 42.

In such a state, the magnetic particle storage 41
When the magnetic particles 33 on the sleeve 32 are reduced due to durability, that is, when the pressure applied to the magnetic particle regulating member 42 by the magnetic particles 33 decreases, the magnetic particles 33 in FIG. Arrow g
The conveyance force in the direction disappears (FIG. 11B).

Then, from this state, the magnetic particle regulating member 4
When the notch 42a of the magnetic particle restricting member 42 comes to the opening below the magnetic particle storing portion 41 by rotating the magnetic particle controlling member 42 by a predetermined amount in the direction of the arrow f, the magnetic particle restricting member 42 The magnetic particles 33 are supplied onto the sleeve 32 through the notch 42a (FIG. 11).
(C)). Then, when the conveying force of the magnetic particles 33 in the direction of the arrow g becomes larger than the rotational force of the magnetic particle regulating member 42 in the direction of the arrow f, the state returns to the state of FIG.

FIG. 12 is a view showing a 1000-degree image of the present embodiment and a comparative example (an image forming apparatus having the same configuration as that of the present embodiment except that the above-described magnetic particle regulating member 42 is not provided).
FIG. 6 is a diagram illustrating a relationship between the number of endurable sheets and the chargeability (difference between an applied voltage and a charged potential) when 0 sheets are endured. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.
And

As is clear from the results shown in this figure, in the present embodiment, the difference between the applied voltage and the charging potential changes at a value of 50 V or less even in the case of 10,000 sheets, and the resistance value of the magnetic particles 33 increases. The chargeability was good by keeping it low. On the other hand, in the comparative example, the difference between the applied voltage and the charging potential was about 95 V after the durability of 10,000 sheets, and the resistance of the magnetic particles 33 increased and the charging property was poor as compared with the present embodiment.

FIG. 13 shows the image forming apparatus of the present embodiment and a comparative example (an image forming apparatus having the same configuration as that of the present embodiment except that the above-described magnetic particle regulating member 42 is not provided).
FIG. 7 is a diagram illustrating a relationship between the number of endurable sheets and the amount of scraping of the photosensitive drum when zero endurance is performed. In the drawing, (a) is the present embodiment, and (b) is a comparative example, in which the amount of magnetic particles 33 carried on the sleeve 32 is 60 g.

As is clear from the results shown in this figure, in the present embodiment, since the shaving by the cleaning device is eliminated as in the first embodiment, the shaving amount of the photosensitive drum 1 is 0.4 μm with the durability of 10,000 sheets. The degree was small. On the other hand, in the comparative example, the abrasion amount of the photosensitive drum 1 was about 1.0 μm after the durability of 10,000 sheets.

As described above, in the present embodiment, the magnetic particles 3
When the pressure of the magnetic particles 33 on the magnetic particle restricting member 42 is increased by rotating the magnetic particle restricting member 42 having the notch 42a by the conveying force in the direction of the arrow g in FIG. The opening of the lower part of the magnetic particle storage part 41 is closed by the peripheral surface of the magnetic particle restriction member 42 by rotating in the direction opposite to the direction, and the supply of the magnetic particles 33 from the magnetic particle storage part 41 is stopped. When the pressure exerted on the magnetic particles 33 by the magnetic particles 33 decreases, the magnetic particle regulating member 42 rotates in the direction indicated by the arrow f and replenishes the magnetic particles 33 from the opening at the lower portion of the magnetic particle storage 41 through the notch 42 a of the magnetic particle regulating member 42. By doing so, it is possible to prevent an increase in the resistance value of the magnetic particles 33 and suppress the scraping of the photosensitive drum 1.

[0096] Further, the configuration in which the magnetic particles 33 can be supplied according to the pressure applied to the magnetic particle regulating member 42 is as follows.
The present invention is not limited to the configuration in which the column is cut out as in the present embodiment, but can be applied to all configurations in which magnetic particles can be replenished mechanically according to pressure.

According to the present invention, in the image forming apparatus in which the developing unit also serves as a unit for collecting the transfer residual toner, the charging unit is a contact charging unit using magnetic particles, and the passing amount of the magnetic particles is regulated by the regulating unit. Further, the present invention includes all configurations in which magnetic particles are supplied in response to a decrease in pressure by the magnetic particles on the restricting means.

The photosensitive drum 1 has a surface resistance of 10 ⁹
It is desirable to have a low resistance layer of 10 ¹⁴ Ω · cm from the viewpoint of realizing charge injection and preventing generation of ozone. However, even with an organic photoreceptor other than the above, a sufficient effect can be obtained for improving durability. can get.

Further, as the developing method, only the two-component developing method has been described in the above embodiment, but other developing methods are also effective.

In the present embodiment, the bias applied to the magnetic brush charging device has been described only in the case where a DC bias is applied. However, from the viewpoint of charging uniformity and recovery of untransferred toner, alternating bias is applied. More preferably, the bias is superimposed.

[0101]

As described above, according to the present invention, the magnetic particles can be supplied to the magnetic particle regulating means by replenishing the magnetic particles on the magnetic particle carrier in accordance with the pressure applied to the magnetic particle restricting means. When the pressure increases (the number of magnetic particles supported on the magnetic particle support increases), replenishment of the magnetic particles is stopped, and the pressure of the magnetic particles on the magnetic particle restricting means decreases (the magnetic particles are supported on the magnetic particle support). Magnetic particles are reduced due to durability, etc.), it is possible to control to supply magnetic particles, suppress the rise in the resistance value of the magnetic particles, prevent the charging performance from lowering, and scrape the surface of the image carrier. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a magnetic brush charging device of the image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is a sectional view showing a developing device of the image forming apparatus according to Embodiment 1 of the present invention.

FIG. 4 is a diagram showing the relationship between the number of durable sheets and the charging property in the first embodiment of the present invention and a comparative example.

FIG. 5 is a diagram showing the relationship between the number of durable sheets and the amount of photosensitive drum scraping in the first embodiment of the present invention and a comparative example thereof.

FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram showing the relationship between the number of durable sheets and the charging property in the second embodiment of the present invention and a comparative example.

FIG. 8 is a diagram showing the relationship between the number of durable sheets and the amount of photosensitive drum scraping in the second embodiment of the present invention and a comparative example thereof.

FIG. 9 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 3 of the present invention.

FIG. 10 is a perspective view showing a magnetic particle regulating member of the image forming apparatus according to Embodiment 3 of the present invention.

FIGS. 11A, 11B and 11C are diagrams showing control of replenishment of magnetic particles by a magnetic particle regulating member of an image forming apparatus according to Embodiment 3 of the present invention.

FIG. 12 is a diagram illustrating the relationship between the number of durable sheets and the charging property in the third embodiment of the present invention and a comparative example thereof.

FIG. 13 is a diagram illustrating a relationship between the number of durable sheets and the amount of photosensitive drum scraping in the third embodiment of the present invention and a comparative example thereof.

FIG. 14 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

FIG. 15 is a cross-sectional view illustrating a magnetic brush charging device of an image forming apparatus in a conventional example.

FIG. 16 is a diagram showing the relationship between the number of durable sheets and the chargeability in a conventional example.

FIG. 17 is a diagram showing the relationship between the number of durable sheets and the amount of photosensitive drum scraping in a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 3 exposure device (exposure device) 4 developing device (developing device) 8 transfer device (transfer device) 12 fixing device 30, 30a magnetic brush charging device (contact charging device) 32 sleeve (magnetic particle carrier) 33) Magnetic particles (conductive magnetic particles) 36 Restriction blade (magnetic particle restriction means) 37, 41 Magnetic particle storage unit 38 Magnetic particle supply device (magnetic particle supply device) 39 Pressure sensor (pressure detection device) 40 Control device ( Control means) 42 Magnetic particle regulating member (magnetic particle regulating means) 42a Notch

Claims (6)

[Claims] An image carrier for carrying an image; contact charging means for contacting the magnetic carrier with conductive magnetic particles carried on a rotatable magnetic particle carrier to charge the image carrier; An exposure unit for forming an electrostatic latent image on the image carrier, a developing unit for developing the electrostatic latent image to form a toner image, and a transfer unit for transferring the toner image to a transfer material In the image forming apparatus, a magnetic particle regulating unit that contacts the conductive magnetic particles carried and conveyed on the magnetic particle carrier and regulates a passing amount of the conductive magnetic particles; Magnetic particle storage means for storing the conductive magnetic particles to be replenished; and the magnetic particle storage means according to the pressure of the conductive magnetic particles carried and conveyed on the magnetic particle carrier against the magnetic particle regulating means. From the conductive magnetic particles An image forming apparatus comprising: magnetic particle replenishing means for replenishing the magnetic particle carrier. 2. A pressure detecting means for detecting a pressure of said conductive magnetic particles on said magnetic particle regulating means, and said conductive magnetic particles by said magnetic particle replenishing means based on pressure information inputted from said pressure detecting means. Control means for performing replenishment control of the magnetic particle storage means, when the control means determines that the pressure of the conductive magnetic particles with respect to the magnetic particle regulating means has become low based on the input pressure information. Controlling the magnetic particle replenishing means so as to replenish the conductive magnetic particles on the magnetic particle carrier, and when it is determined that the pressure of the conductive magnetic particles with respect to the magnetic particle regulating means has increased, the magnetic particle storage means 2. The image forming apparatus according to claim 1, wherein a magnetic particle replenishing unit is controlled to stop supplying the conductive magnetic particles onto the magnetic particle carrier. . 3. The magnetic particle restricting means is formed integrally with the magnetic particle replenishing means, and the magnetic particle restricting means is movable according to a pressure of the conductive magnetic particles. When the pressure by the conductive magnetic particles is low, the conductive magnetic particles are moved from the magnetic particle storage means to a position where the conductive magnetic particles can be supplied onto the magnetic particle carrier, and the pressure by the conductive magnetic particles is high. In
The image forming apparatus according to claim 1, wherein the image forming apparatus is movable to a position where supply of the conductive magnetic particles from the magnetic particle storage unit to the magnetic particle carrier is stopped. 4. The image forming apparatus according to claim 1, wherein the developing unit also serves as a cleaning unit that collects residual toner remaining on the image carrier after transferring the toner image onto the transfer material. 5. The image carrier has a surface having a resistance of 10 ⁹ to 10 ⁹ .
The image forming apparatus according to claim 1, further comprising a layer made of a material of 10 ¹⁴ Ω · cm. 6. The image forming apparatus according to claim 1, wherein a rotation direction of the magnetic particle carrier that carries the conductive magnetic particles on a surface and moves the magnetic particle carrier is opposite to a rotation direction of the image carrier.