JPH10123896A - Image forming method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely prevent the sticking of a foreign matter or a transfer roller and clean the roller for removing a residual electric charge. SOLUTION: In this method, after an electrostatic transfer is completed, an image carrier 1 is driven to rotate, the transfer roller 6 is rotated in press- contact with the image carrier 1 and a bias charge is applied to the transfer roller 6, to electrify it, so that a foreign matter stuck to the surface of the transfer roller 6 is stuck to the surface of the image carrier 1 and carried, and after that, the foreign matter is removed from the surface of the image carrier 1 by a cleaning means 8. Further, an electric charge on the surface of the transfer roller 6 is transferred to the surface of the image carrier 1 and then, the charge on the surface of the image carrier 1 is removed by one of an electrifier 2, an image exposure means 3, a separating means 7 and a preelectrifying exposure means 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus applied to an electrophotographic copying machine, a printer, a facsimile, and the like, and more particularly, to an image forming method for removing foreign matters and electric charges adhered to a transfer roller. And an image forming apparatus.

[0002]

2. Description of the Related Art In an electrostatic copying machine or an electrostatic printer using an electrophotographic technique, a corona discharger has been widely used as a charging / transferring / separating device. However, the corona discharger requires application of a high voltage of 5 to 10 kV, and has problems such as generation of ozone due to discharge. Therefore, in recent years, a contact charging method, a transfer roller method, a non-corona transfer method, and the like, which are aimed at lowering the voltage and reducing ozone, have attracted attention as alternative technologies.

[0003] The non-corona transfer method of the transfer roller method has the advantages that the amount of generated ozone is smaller, there is no transfer unevenness caused by discharge wire contamination, and the cost is lower than in conventional transfer by corona discharge. For this reason, it has recently come into practical use.

In the transfer means of the transfer roller type, a transfer roller to which a high voltage is applied sandwiches the transfer material and presses against the image carrier with a predetermined pressing force, and rotates following the drive rotation of the image carrier. When the transfer roller is used repeatedly for a long period of time, the surface layer is peeled, dropped off, torn, or deformed when the transfer roller is used repeatedly for a long period of time. When such deterioration and deformation progress on the transfer roller, image defects such as image repelling, black spots, white spots, and streaks occur during transfer,
The image quality on the transfer material is reduced.

As the transfer material, transfer paper such as plain paper, OHP sheet or the like having a different paper quality, or a transfer material having a different size is used in an image forming apparatus. Further, the occurrence of a defect in the toner image in the transfer portion may be caused by forming a color toner image by superimposing at least two or more single-color toner images on the image carrier or the intermediate transfer member, and collectively forming the toner image on the transfer material. This is particularly noticeable in a color image forming apparatus for transferring. In a color image forming apparatus in which toner images of respective colors are superimposed on a photosensitive drum, a toner image for one image must be formed on an image carrier, and the circumference of the image carrier is set to be equal to one circumference. Must be longer than the image length. For this reason, the diameter of the photosensitive drum necessarily increases. In such a color image forming apparatus,
Unless the multi-color toner image superimposed on the large-diameter image carrier is transferred reliably, the color tone and color density of the multi-color toner image on the transfer material will change, and the multi-color toner image will be superimposed and transferred. Even in a color image forming apparatus of a type in which the transfer is collectively transferred onto a transfer material by a roller, the deterioration and deformation of the transfer roller greatly affect the image quality of the transferred image.

The most common contact method is the roller transfer method. However, the brush transfer method, which generates ozone equivalently to the roller transfer method and has a lower manufacturing cost, has recently attracted attention. However, in the brush transfer method, it is difficult to transport the transfer material, so that it is necessary to separately provide a transfer material transport unit.

[0007]

However, in such a conventional image forming apparatus, when a transfer roller is used as a transfer means, there is a problem in cleaning dust, paper dust and toner attached to the transfer roller.

For this reason, Japanese Unexamined Patent Publication No. 1-185572 has been proposed, but has a disadvantage that it is still insufficient.

As a result of various experiments and studies, the present inventor has found a method for removing foreign matter adhering to a transfer roller in Japanese Patent Application No. 7-666.
No. 57 proposed a transfer roller cleaning method. In this method, at the time of standby other than the time of image formation, the transfer roller is pressed against the photosensitive drum, and a reverse bias charge is applied to the transfer roller, or a positive and negative bias charge is alternately applied. In this method, foreign matters such as toner and paper powder adhering to the transfer roller are transferred to the photosensitive drum, and are removed by the cleaning means on the downstream side of the photosensitive drum conveyance.

However, when the transfer roller is cleaned by this method, charging unevenness remains on the surface of the photosensitive drum,
A transfer roller cleaning memory is generated on the photosensitive drum after cleaning.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and solves the above-mentioned problems, achieves the following objects, and has a stable and satisfactory transfer without image defects. An object of the present invention is to provide a high-quality image forming apparatus capable of obtaining high performance.

(1) Using a transfer roller having a transfer material conveying force, a transfer roller cleaning memory on the photosensitive drum generated after cleaning is removed.

(2) In the color image forming apparatus, a high-quality color transfer image without transfer failure is obtained when the image transfer member or the intermediate transfer member is collectively transferred to a transfer material.

(3) Ozone generation based on high-pressure discharge,
To provide a process that does not generate nitrides and causes less deterioration of the photoreceptor and lowering of image quality.

(4) Ensuring transfer stability and ensuring good transferability of both a single color and a superimposed color.

(5) Transfer stability is always ensured for various transfer materials having different paper qualities, for example, plain paper and OHP sheet, and a high-quality transfer image is obtained.

[0017]

According to a first aspect of the present invention, there is provided an image forming method according to the present invention, wherein the surface of an image carrier is charged by a charger, and an electrostatic latent image is formed by an image exposing means. Then, the toner image is formed by developing with the charged toner of the developing unit, and the toner image is electrostatically transferred to a transfer material that is fed from a paper feeding unit and passes between the image carrier and the transfer roller,
Further, in the image forming method, the transfer material is separated from the image carrier by a separation unit on a downstream side of the conveyance, and toner remaining on the image carrier after the electrostatic transfer is removed by a cleaning unit. Thereafter, the transfer roller is pressed against the image carrier that is driven and rotated, and rotated.
Further, after applying a bias charge to the transfer roller, the foreign matter adhered to the surface of the transfer roller is adhered to the surface of the image carrier and conveyed, and then the cleaning means removes the foreign matter from the surface of the image carrier. And then
In order to remove potential unevenness on the surface of the image carrier caused by applying the bias charge to the transfer roller and adhering the foreign matter to the image carrier, the surface of the image carrier is uniformly charged by the charger. By doing so, the charge on the surface of the image carrier is removed.

According to a second aspect of the present invention, there is provided an image forming method according to the second aspect of the present invention, wherein after the completion of the electrostatic transfer, the transfer roller is rotated by pressing the transfer roller against the driven image carrier. And applying a bias charge to the transfer roller to cause the foreign matter attached to the transfer roller surface to adhere to the image carrier surface and to convey the foreign matter, and then remove the foreign matter from the image carrier surface by the cleaning unit. The image exposure unit further removes the image bearing member by applying a bias charge to the transfer roller to remove potential irregularities on the surface of the image carrier caused by causing the foreign matter to adhere to the image carrier. By uniformly exposing the body surface, the charge on the surface of the image carrier is removed.

Further, in the image forming method according to the third aspect of the present invention, which achieves the above object, after the completion of the electrostatic transfer, the transfer roller is rotated by pressing the transfer roller against the rotating image carrier. And applying a bias charge to the transfer roller to cause the foreign matter attached to the transfer roller surface to adhere to the image carrier surface and to convey the foreign matter, and then remove the foreign matter from the image carrier surface by the cleaning unit. The image carrier is separated by the separating unit in order to remove potential unevenness on the surface of the image carrier caused by applying a bias charge to the transfer roller and adhering the foreign matter to the image carrier. By uniformly charging
The charge on the surface of the image carrier is removed.

Further, in the image forming method according to a fourth aspect of the present invention which achieves the above object, after the completion of the electrostatic transfer, the transfer roller is rotated by pressing the transfer roller against the image carrier which is driven and rotated. And applying a bias charge to the transfer roller to cause the foreign matter attached to the transfer roller surface to adhere to the image carrier surface and to convey the foreign matter, and then remove the foreign matter from the image carrier surface by the cleaning unit. In addition, in order to remove potential unevenness on the surface of the image carrier caused by applying a bias charge to the transfer roller and adhering the foreign matter to the image carrier, the image carrier is exposed by a pre-charge exposure unit. It is characterized in that the charge on the surface of the image carrier is removed by uniformly charging the body.

According to a fifth aspect of the present invention, there is provided an image forming apparatus, comprising: a charger for charging a surface of an image carrier which is driven to rotate; and a static charger on the charged image carrier. Image exposure means for forming an electrostatic latent image, developing means for developing the electrostatic latent image formed on the image carrier with charged toner to form a toner image, and feeding the toner image from a paper supply unit Image forming apparatus, comprising: a transfer roller that electrostatically transfers to a transferred transfer material; a transfer material separating unit downstream of the transfer roller; and a cleaning unit that removes toner remaining on the image carrier after the electrostatic transfer. In the apparatus, control means for controlling the image carrier, the charging device, the transfer roller, and the cleaning means is provided, and the control means presses the transfer roller against the driven and rotated image carrier after the end of the electrostatic transfer. Let it rotate, and Applying a bias charge to the transfer roller, transferring foreign matter adhered to the surface of the transfer roller to the image carrier surface, transferring and removing the foreign matter by the cleaning unit, and further applying a bias charge to the transfer roller. In order to remove potential unevenness on the surface of the image carrier caused by attaching the foreign matter to the image carrier, the charge on the surface of the image carrier is removed by uniform charging by the charger. Things.

Further, according to a sixth aspect of the present invention, which achieves the above object, the image forming apparatus comprises:
A transfer roller, a cleaning unit, and a control unit for controlling an image exposure unit are provided, and the control unit rotates the transfer roller by pressing the transfer roller against the image carrier that is driven and rotated after the end of the electrostatic transfer, and A bias charge is applied to the transfer roller to transfer foreign matter adhering to the surface of the transfer roller onto the surface of the image carrier, transported and removed by the cleaning unit, and further apply a bias charge to the transfer roller. Then, in order to remove potential unevenness on the surface of the image carrier caused by causing the foreign matter to adhere to the image carrier, it is necessary to remove charges on the surface of the image carrier by uniform exposure by the image exposure unit. It is a feature.

Further, in the image forming apparatus according to the present invention, which achieves the above object, the image carrier, the charger,
A transfer roller, a cleaning unit, and a control unit for controlling an image exposure unit are provided, and the control unit rotates the transfer roller by pressing the transfer roller against the image carrier that is driven and rotated after the end of the electrostatic transfer, and A bias charge is applied to the transfer roller to transfer foreign matter adhering to the surface of the transfer roller onto the surface of the image carrier, transported and removed by the cleaning unit, and further apply a bias charge to the transfer roller. The charge on the surface of the image carrier is removed by uniform charging by the separation means in order to remove potential unevenness on the surface of the image carrier caused by attaching the foreign matter to the image carrier. It is assumed that.

Further, in order to achieve the above object, the image forming apparatus according to claim 8 of the present invention provides the image forming apparatus,
A transfer roller, a cleaning unit, a control unit for controlling a pre-charging exposure unit, and the control unit presses and rotates the transfer roller against the driving and rotating image carrier after the end of the electrostatic transfer; and Applying a bias charge to the transfer roller to remove foreign matter adhering to the transfer roller surface,
An image carrier that is caused by being transferred and adhered to the surface of the image carrier, removed by the cleaning unit, and further applied with a bias charge to the transfer roller to adhere the foreign matter to the image carrier. In order to remove potential unevenness on the surface, the charge on the surface of the image carrier is removed by uniform exposure by the pre-charging exposure means.

The image carrier is a photosensitive drum or a photosensitive belt. S as the photosensitive drum here
Materials such as e, As ₂ Se ₃ , a-Si, and OPC are used. The OPC used in this case is disclosed in
-17066, JP-A-2-183258,
JP-A-2-183265, JP-A-3-12897
No. 3 using a Y-type titanyl phthalocyanine or a polycrystalline type titanyl phthalocyanine described in JP-A No. 3 is preferred.

During the cleaning of the transfer roller, the pressing force with which the transfer roller presses the image carrier is 25 to 25.
1000 g / cm ² .

The transfer roller is pressed against and separated from the surface of the image carrier.

The image forming apparatus forms a superimposed toner image of a plurality of colors on an image carrier by a plurality of developing means, and transfers the superimposed toner image onto a transfer material by the transfer roller.

The average bubble diameter of the transfer roller is 1 μm or more and 300 μm or less.

The bias applied at the time of cleaning the transfer roller has a polarity opposite to the bias applied at the time of transfer to the transfer roller.

As the bias applied at the time of cleaning the transfer roller, positive and negative biases are alternately applied.

The developing means is an image carrier for carrying an electrostatic latent image, and a two-component developing means for superimposing a DC component and an AC component on a developing region for carrying a two-component developer.

The developing means is a non-contact developing means.

The developing means is a reversal developing means.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to a cross-sectional view of FIG. 1 showing the structure of a color printer as an example of an image forming apparatus and its operation.

In this color printer, after each color toner image sequentially formed on the image forming body is superimposed, the color image is formed on the recording paper by a transfer unit once to form a color image. This is a color image forming apparatus of a method of peeling off from a surface of a carrier.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image bearing member, which is formed by applying an OPC photosensitive member (organic photosensitive member) on a drum base, and is grounded and driven to rotate clockwise in the drawing. . Reference numeral 2 denotes a scorotron charger, and an image carrier 1
Grid potential V _G uniform charging of the high voltage V _H to the peripheral surface of the
Is provided by a corona discharge by a grid and a corona discharge wire which is held at a potential. Prior to charging by the scorotron charger 2, in order to eliminate the history of the photoconductor up to the previous printing, exposure is performed by a pre-charging exposure unit (PCL) 9 using a light emitting diode or the like to remove the charge on the peripheral surface of the photoconductor. deep.

After the image carrier 1 is uniformly charged, the image exposure means 3 performs image exposure based on the image signal. The image exposing means 3 is a main scanning performed by bending a light path by a reflecting mirror 34 through a polygon mirror 31, an fθ lens 32, and a cylindrical lens 33 which rotate by using a laser diode (not shown) as a light emitting light source. A latent image is formed by (sub-scan). In the present embodiment, a character portion is exposed to form a reversal latent image such that the character portion has a lower potential VL.

On the periphery of the image carrier 1, yellow (Y),
There is provided a developing device 4 including developing units 4Y, 4M, 4C, and 4K each containing a two-component developer including a toner such as magenta (M), cyan (C), and black (K) and a carrier. First, development of yellow of the first color is performed by a developer carrier (developing sleeve) 41 which includes a magnet and rotates while holding the developer. The developer consists of a carrier with ferrite as the core and an insulating resin coated around it, and a toner with polyester as the main material and a pigment according to the color, a charge control agent, silica, titanium oxide, etc. The developer is regulated to a layer thickness (developer) of 100 to 600 μm on the developing sleeve 41 by the layer forming means, and is conveyed to the developing area.

The gap between the developing sleeve 41 and the image carrier 1 in the developing area is 0.2 to 1.0, which is larger than the thickness of the developer layer.
as mm, DC of AC bias and V _DC of V _AC during this time
A bias is superimposed and applied. V _DC and V _H, for charging the toner are the same polarity, the toner given the opportunity to leave from the carrier by V _AC is not adhere to a portion of the high V _H of potential than V _DC, potential than V _DC Adhered to the low V _L portion, and visualization (reversal development) is performed.

After the visualization of the first color is completed, the image forming process for the magenta of the second color is started, and the scorotron charger 2
, And a latent image based on the image data of the second color is formed by the image exposure unit 3. At this time, the charge elimination by the PCL 9 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to a sudden drop in the surrounding potential.

Again, V _H is applied over the entire peripheral surface of the image carrier 1.
A latent image similar to that of the first color is formed and developed in a portion of the image carrier having the potential of not having the image of the first color, but development is performed again in a portion where the image of the first color is present. the part for a latent image of V _M 'is formed by the charge possessed by the shading of the toner itself by the toner adhering the first color, V _DC
And development according to the potential difference between V _M ′ and V _M ′. In the overlapping portion of the first color image and the second color image, the development of the first color is performed by V _L
When the latent image of the first color is formed, the balance between the first color and the second color is lost, so that the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

For the third color cyan and the fourth color black, an image forming process similar to that for the second color magenta is performed, and a visible image of four colors is formed on the peripheral surface of the image carrier 1.

The toner supply device for controlling and replenishing each of the developing units 4Y, 4M, 4C, and 4K with new color toners is as follows.
A plurality of removable toner cartridges 5 (Y, M, C,
K), toner storage means 51 (Y, M, C, K) and toner transport means 52 (Y, M, C, K).

On the other hand, the half-moon roller 1
The one transfer material (transfer paper or the like) P carried out via the printer 1 temporarily stops, and is fed to the transfer area by the rotation of the registration roller pair 12 of the paper feed unit when the transfer timing is adjusted. You. The transfer material P sent from the registration roller pair 12 is conveyed to a transfer area where the transfer roller (transfer means) 6 and the image carrier 1 are pressed against each other.

In the transfer area, the transfer roller 6 is pressed against the peripheral surface of the image carrier 1 in synchronization with the transfer timing, and the supplied transfer material P is applied by applying a high voltage from the bias power supply E1. The multicolor image is transferred collectively by sandwiching.

Next, the transfer material P is discharged from the peripheral surface of the image carrier 1 by the separating means 7 after being discharged by the applied voltage of the power supply E2, conveyed to the downstream side of the separating means 7, and conveyed to the fixing device 13. Then, the toner is fused by heating and pressurizing the heat roller (upper roller) 131 and the pressure roller (lower roller) 132, and then the apparatus is discharged via a paper discharging means including a pair of paper discharging rollers 141 and 142 and a paper discharging guide 143. The paper is discharged onto an external paper discharge tray 15. After the transfer material P has passed through the transfer material P, the transfer roller 6 is retracted and separated from the peripheral surface of the image carrier 1 to prepare for the formation of the next toner image.

On the other hand, the image carrier 1 from which the transfer material P has been separated
The residual toner is removed and cleaned by pressing the cleaning blade 81 of the cleaning means 8, and the PCL 9 is removed again.
And the next image forming process starts. The cleaning blade 81 moves immediately after cleaning the surface of the photosensitive member and retracts from the peripheral surface of the image carrier 1. The waste toner scraped into the cleaning device 8 by the cleaning blade 81 is discharged by a screw 82 and then stored in a waste toner collecting container (not shown).

In the present invention, the transfer means, for example, the transfer roller 6 has an average bubble diameter of 1 μm or more and 300 μm or less.

Here, the definition of the average bubble diameter of the transfer roller is as follows.

(1) When the Transfer Roller 6 is a Single Bubble FIG. 14 is an explanatory diagram of a method for measuring the average bubble diameter of the transfer roller. The transfer roller 6 is arbitrarily cut at 10 points in the direction of the rotation axis (X direction) in FIG. (Point × 3 places = 30 data).

[0052] (sum of all bubbles diameter present per 1 cm ³⁾ / (total number of all bubbles present per 1 cm ³⁾ (where gas bubbles refers here, as shown in FIG. 14 (b) (Calculate excluding bubbles of 5% or less of the total number of bubbles).

(2) When the transfer roller is open cells The measurement is performed in the same manner as in (1). In the case of open cells, the bubbles are not a perfect circle but a hole. In this case, the diameter is an average value of the maximum distance and the minimum distance from the center of the bubble.

Also, artificially created scratches and holes are not regarded as bubbles.

In the present invention, when cleaning the toner adhered to the transfer roller 6, the transfer roller 6
It is preferable that positive and negative biases are alternately applied to each other, or a bias having a polarity opposite to that during transfer is applied.

FIGS. 2 to 4 are schematic views showing this cleaning process. As shown in FIG. 2, after the transfer material P passes through the transfer area where the transfer roller 6 and the image carrier 1 are pressed against each other, the polarity of the bias power supply E1 for the transfer roller 6 is switched to transfer the toner T to the surface. When the roller 6 is pressed against the image carrier 1, as shown in FIG.
The attached toner T moves onto the image carrier 1 and the cleaning blade 81 of the cleaning unit 8 as shown in FIG.
Removed by

Table 1 shows the types of the transfer roller 6, the paper powder per 1 cm ³ including the roller surface after copying 5,000 sheets,
This shows the relationship between dust, toner, and other foreign matter.

[0058]

[Table 1]

The transfer rollers A to E in Table 1 are shown below.

Transfer roller A: ion conductive type manufactured by Bridgestone Corp., hardness 33 (Asker C hardness meter), electric resistance 3 × 10 ⁷ Ω, average bubble diameter 200 μm, single bubble transfer roller B: Sumitomo Rubber Industries, Ltd. Ion conductive type, hardness 36 (Asker C hardness tester), electric resistance 7.5 ×
10 ⁷ Omega, average cell diameter 80 [mu] m, Tan'awa transfer roller C: Nitto Kogyo Co., Ltd. Carbon black-containing Rubiseru (polyurethane foam type), hardness 30 (Asker C hardness meter), the electric resistance 2 × 10 ⁸ Ω, Mean Transfer roller D: average cell diameter 350 μm, single cell, electric resistance 3 × 10 ⁷ Ω Transfer roller E: average cell diameter 500 μm, single cell, electric resistance 5 × 10 ⁷ Ω From Table 1 above, transfer It can be seen that when the average bubble diameter of the roller increases, foreign matter such as paper dust, dust, toner, and dust easily enters the bubbles.

FIGS. 5A to 5E are diagrams for explaining the characteristics of the image forming apparatus of the present invention.

For each of the transfer rollers A to E, at the start of copying (indicated by ・) and after copying 5000 sheets (indicated by ○)
5 shows the change in the applied voltage-transfer current characteristic to the transfer roller of FIG. This characteristic change is caused by a transfer roller (different in material or component composition) manufactured by each company having a diameter of 16 mm.
Length 310 mm, wall thickness 4 mm, diameter 30 mm
Pressed with a force of 170 g / cm ² on the aluminum tube of
It is measured in an environment of a temperature of 20 ° C. and a humidity of 50%.

From this figure, it can be seen that when the average bubble diameter of the transfer roller is increased, foreign matter is likely to enter the bubbles, thereby changing the electrical resistance of the transfer roller.

Table 2 shows that a solid image of 1.2 mg / cm ² of the negative toner was formed on the image carrier in an environment of a temperature of 20 ° C. and a humidity of 50%, and was directly transferred from the image carrier to a transfer roller having a diameter of 18 mm. This shows the cleaning achievement ratio when the toner adhered to the transfer roller is returned to the image carrier again by alternately applying positive and negative biases to the transfer roller. In Table 2, the cleaning achievement rate is defined as (weight of toner initially attached to transfer roller−weight of toner remaining on transfer roller surface after cleaning) / (weight of toner initially attached to transfer roller) in%. It is shown by.

[0065]

[Table 2]

FIG. 6 is a timing chart for applying the positive and negative biases.

The applied bias varies depending on the type and diameter of the transfer roller, the polarity of the toner, and the environment.

Table 3 shows the case where a transfer roller having a diameter of 16 mm was used, and a positive bias was applied at the time of transfer at the timing shown in FIG. 7 and a negative bias was applied at the time of cleaning.

[0069]

[Table 3]

The timing of cleaning the transfer roller is (1) when the power is turned on, (2) immediately after the occurrence of a jam, and (3) after printing.

Table 4 shows the average bubble diameter (1 μm to 300 μm).
An example of a preferred transfer roller of m) is shown.

[0072]

[Table 4]

In general, a transfer roller is made to have a suitable elasticity by adding a plasticizer to rubber, and is made conductive by adding a conductive material. Increasing the plasticizer softens the transfer roller, but increases the bubble diameter. Conversely, if the amount of plasticizer is reduced to reduce the cell diameter, the cell becomes hard. When the image is transferred by the transfer roller, the image bearing member must be soft to some extent in order to prevent the image carrier from being scratched and to secure the roller nip in order to transfer the image by pressing the photosensitive drum. If the average bubble diameter is less than 1 μm, the roller cannot have sufficient elasticity.

The electric resistance value of the transfer roller is determined by the transfer roller manufactured by each company (the material or the composition of components is different from each other).
With a diameter of 16 mm, a length of 310 mm, and a thickness of 4 mm.
^When pressed with a force of ² , the electrical resistance between the rotating shaft of the transfer roller and the aluminum tube measured in an environment of a temperature of 20 ° C. and a humidity of 50%.

Next, an embodiment in which the transfer roller 6 is pressed against the image carrier 1 to remove charging unevenness generated in the surface potential of the image carrier 1 when cleaning foreign matter on the transfer roller 6 will be described. This will be described below.

FIG. 8 shows a cleaning means for removing the toner adhered on the peripheral surface of the transfer roller 6 and the following first embodiment.
FIG. 4 is a block diagram illustrating control of a surface potential removing unit of the image carrier 1 in FIGS.

After the completion of the electrostatic transfer, the control means 15 controls the driving rotation of the image carrier 1 and the image carrier 1 of the transfer roller 6.
And the pressing of the cleaning blade 81 of the cleaning means 8 is operated. That is, the image carrier 1 is driven and rotated, the transfer roller 6 is pressed against the image carrier 1 and driven to rotate, and a bias charge is applied to the transfer roller 6. By uniformly charging the surface of the carrier 1, foreign matter adhering to the surface of the transfer roller 6 is transferred to and adhered to the surface of the image carrier 1, and is conveyed. The carrier 1 is removed by being pressed against the peripheral surface thereof.

The control unit 15 drives and rotates the image carrier 1, presses the transfer roller 6 against the image carrier 1, and sets the charger 2, the image exposure unit 3, and the like during the standby time other than the image formation. The operation of one of the separating means 7 and the pre-charging exposure means 9 is controlled.

(Example 1) FIG. 9A is a schematic view of a main portion around the image carrier 1 for cleaning the transfer roller 6 by the charger 2 and FIG. 9B is a transfer roller by the charger 2. 6 is a timing chart showing removal of potential unevenness on the surface of the image carrier that occurs in the cleaning process of No. 6;

After the completion of the electrostatic transfer, the image carrier 1
Is driven to rotate the transfer roller 6 by pressing the transfer roller 6 against the image carrier 1 and applying a bias charge to the transfer roller 6 to charge the transfer roller 6, thereby starting the cleaning of the transfer roller 6. The foreign matter adhering to the surface of the transfer roller 6 due to the start of the cleaning is transferred and adhered to the surface of the image carrier 1, and is conveyed by the cleaning blade 81 of the cleaning unit 8.
The foreign matter is removed from the surface of the substrate. In this cleaning process, the charge on the surface of the transfer roller 6 is transferred to the surface of the rotating image carrier 1.

After the pressing of the transfer roller 6 against the image carrier 1 and the application of the bias charge to the transfer roller 6 are started, the charging of the charger 2 is started. The charging of the charger 2 is started until the leading position of the transfer of the cleaning bias charge of the transfer roller 6 to the image carrier 1 reaches the charging position of the charger 2. The application of the cleaning bias charge of the transfer roller 6 includes:
This operation is performed during one or more rotations of the transfer roller 6. After the pressing of the transfer roller 6 and the application of the bias charge are performed at a predetermined number of rotations of the transfer roller 6, the pressing of the transfer roller 6 and the application of the bias charge are released, and the cleaning is completed. After the cleaning of the transfer roller 6 is completed, after the final charge on the image carrier 1 transferred from the transfer roller 6 passes through the charger 2, the charging of the charger 2 is turned off after a lapse of a predetermined time. I do. From the start of cleaning of the transfer roller 6 to the OFF of charging of the charger 2, the image carrier 1
Is rotated once or more, and the potential unevenness on the surface of the image carrier 1 due to the residual charge on the image carrier 1 transferred from the transfer roller 6 is removed.

The evaluation of the image memory on the image carrier 1 was carried out by using a Macbeth reflection densitometer and applying a cleaning bias charge to the transfer roller 6 (normal portion).
The evaluation was made based on the difference in density from the portion where no voltage was applied (memory portion).

[0083]

[Table 5]

Table 5 shows an evaluation of the image memory on the image carrier 1 after the number of prints is completed, based on the density difference. The comparative example shows the density difference of the related art in which the control by the charger 2 is not performed. The first embodiment shows an example in which a reverse bias is applied to the transfer roller 6 during transfer and an example in which the transfer roller 6 is charged by applying a positive / negative alternating bias.

According to the first embodiment, the number of prints is 12,000.
There was almost no density difference up to the number of sheets, and the image memory was erased. Further, the density difference was small up to 30,000 copies, and an excellent cleaning effect was obtained by charging by the charger 2.

The transfer roller used had a roller outer diameter of 18 m.
m, shaft diameter 6 mm, manufactured by Sumitomo Rubber Co., Ltd., ion conductive type, hardness 36 (Asker C), electric resistance 7.5 × 10 ⁷
Ω, average bubble diameter 80 μm.

The cleaning conditions were as follows: transfer and reverse bias application: -2.5 kV, positive / negative alternating bias application: -2.5
kV, +2.5 kV Environment: 20 ° C., 50% RH As the charger 2, a discharge wire and a grid electrode or a sawtooth electrode (pitch: 2 mm, peak height: 3 mm) were used. Was done.

(Embodiment 2) FIG. 10A is a schematic view of a main portion around the image carrier 1 related to cleaning of the transfer roller 6 by the image exposing means 3, and FIG. 9 is a timing chart illustrating removal of potential unevenness on the surface of an image carrier that occurs during a cleaning process of a roller.

In a standby state other than the image forming operation, the electric charge on the surface of the transfer roller 6 during the above-described cleaning process is
It is transferred to the surface of the rotating image carrier 1.

After the pressing of the transfer roller 6 against the image carrier 1 and the application of the bias charge to the transfer roller 6 are started, the exposure of the image carrier 1 by the image exposure means 3 is started. You. The charging start timing of the image exposure unit 3 is performed until the leading position of the transfer of the cleaning bias charge of the transfer roller 6 to the image carrier 1 reaches the exposure position of the image exposure unit 3. The application of the cleaning bias charge to the transfer roller 6 is performed during one rotation or more of the transfer roller 6. After the pressing of the transfer roller 6 and the application of the bias charge are performed at a predetermined number of rotations of the transfer roller 6,
The pressing of the transfer roller 6 and the application of the bias charge are released,
Cleaning ends. After the cleaning of the transfer roller 6 is completed, after the final charge on the image carrier 1 transferred from the transfer roller 6 passes through the uniform exposure position by the image exposure unit 3, the image is The uniform exposure of the exposure means 3 is turned off. From the start of the transfer roller 6 cleaning until the uniform exposure of the image exposing unit 3 is turned off, the image carrier 1 makes at least one rotation, and the image due to the residual charge on the image carrier 1 transferred from the transfer roller 6. Uneven potential on the surface of the carrier is removed.

The evaluation of the image memory on the image carrier 1 was carried out by using a Macbeth reflection densitometer, by applying a cleaning bias charge to the transfer roller 6 (a normal portion).
The evaluation was made based on the difference in density from the portion where no voltage was applied (memory portion).

[0092]

[Table 6]

Table 6 shows an evaluation of the image memory on the image carrier 1 after the number of prints is completed, based on the density difference. The comparative example shows the density difference of the related art in which the control by the image exposure means 3 is not performed. Embodiment 2 shows an example in which a reverse bias is applied to the transfer roller 6 at the time of transfer and a case in which a positive / negative alternating bias is applied to the transfer roller 6 to perform uniform exposure.

According to the second embodiment, the number of prints is 15,000.
There was almost no density difference up to the number of sheets, and the image memory was erased. Further, the density difference was small up to 30,000 copies, and an excellent cleaning effect was obtained by uniform exposure by the image exposure means 3.

The transfer roller used was an ion conductive type manufactured by Bridgestone Corporation, roller outer diameter 18 mm, shaft diameter 6 mm, hardness 33 (Asker C), electric resistance 3 × 10
⁷ Ω, average bubble diameter 200 μm.

The cleaning conditions were as follows: transfer and reverse bias application: -3 kV, positive / negative alternating bias application: -3 kV, +
3 kV environment: 20 ° C., 50% RH (Embodiment 3) FIG. 11A is a schematic view of a main part around the image carrier 1 related to cleaning of the transfer roller 6 by the separating unit 7, and FIG. Transfer roller 6 by means 7
6 is a timing chart showing removal of potential unevenness on the surface of the image carrier generated in the cleaning process of FIG.

During a standby period other than the image formation, the electric charge on the surface of the transfer roller 6 during the above-described cleaning process is
It is transferred to the surface of the rotating image carrier 1.

After the pressing of the transfer roller 6 against the image carrier 1 and the application of the bias charge to the transfer roller 6 are started, the electrostatic separation of the image carrier 1 by the separating means 7 is started. Is done. The start of the discharge to the separation unit 7 is performed until the leading position of the transfer of the cleaning bias charge of the transfer roller 6 to the image carrier 1 reaches the exposure position of the separation unit 7. The application of the cleaning bias charge to the transfer roller 6 is performed during one rotation or more of the transfer roller 6. After the pressing of the transfer roller 6 and the application of the bias charge are performed at a predetermined number of rotations of the transfer roller 6, the pressing of the transfer roller 6 and the application of the bias charge are released, and the cleaning is completed. After the cleaning of the transfer roller 6 is completed, after the final charge on the image carrier 1 transferred from the transfer roller 6 passes through the discharge position by the separation unit 7, after a predetermined time has passed, the separation unit 7 Turn off the discharge. From the start of cleaning of the transfer roller 6 to the turning off of the separation unit 7, the image carrier 1 makes one or more rotations, and the surface of the image carrier due to residual charges transferred from the transfer roller 6 on the image carrier 1. Is removed.

The evaluation of the image memory on the image carrier 1 was carried out by using a Macbeth reflection densitometer and applying a cleaning bias charge to the transfer roller 6 (normal portion).
The evaluation was made based on the difference in density from the portion where no voltage was applied (memory portion).

[0100]

[Table 7]

Table 7 shows an evaluation of the image memory on the image carrier 1 after the number of prints is completed, based on the density difference. The comparative example shows the density difference of the conventional technique in which the control by the separating means 7 is not performed. Example 3 shows an example in which a reverse bias is applied to the transfer roller 6 during transfer and an example in which a positive and negative alternating bias is applied to the transfer roller 6 to perform uniform exposure.

According to the third embodiment, there is almost no density difference up to 9000 prints, and the image memory is erased. Further, the density difference is small up to 30,000 prints. Obtained.

The transfer roller used was an electronic conductive type (Rubicel containing carbon black) manufactured by Toyo Polymer Co., Ltd., the roller outer diameter was 18 mm, the shaft diameter was 6 mm, and the hardness was 30.
(Asker C), electric resistance 2 × 10 ⁷ Ω, average bubble diameter 2
0 μm.

The cleaning conditions were as follows: transfer and reverse bias applied: -3.5 kV, positive / negative alternating bias applied: -3.5
kV, +3 kV Environment: 20 ° C., 50% RH A discharge wire electrode or a sawtooth electrode (pitch: 2 mm, peak height: 3 mm) was used as the separation means 7, and the same effect was obtained.

(Embodiment 4) FIG. 12A is a schematic view of a main part around the image carrier 1 for cleaning of the transfer roller 6 by the pre-charging exposure unit (PCL) 9, and FIG.
9 is a timing chart showing removal of potential unevenness on the surface of an image carrier, which occurs in a process of cleaning a transfer roller 6 by CL9.

After the end of the electrostatic transfer, the electric charge on the surface of the transfer roller 6 is transferred to the surface of the rotating image carrier 1 in the above-described cleaning process.

After the pressing of the transfer roller 6 against the image carrier 1 and the application of the bias charge to the transfer roller 6 are started, the neutralization of the image carrier 1 by the PCL 9 is started. The timing of starting the charge removal to the PCL 9 is performed until the leading position of the transfer of the cleaning bias charge of the transfer roller 6 to the image carrier 1 reaches the potential removal of the PCL 9. The application of the cleaning bias charge to the transfer roller 6 is performed during one rotation or more of the transfer roller 6. After the pressing of the transfer roller 6 and the application of the bias charge are performed at a predetermined number of rotations of the transfer roller 6, the pressing of the transfer roller 6 and the application of the bias charge are released, and the cleaning is completed. After the cleaning of the transfer roller 6, the final charge on the image carrier 1 transferred from the transfer roller 6 passes through the uniform exposure position by the PCL 9, and after a predetermined time elapses, the uniformity of the PCL 9 is changed. Turn off exposure
I do. From the start of the cleaning of the transfer roller 6 to the turning off of the uniform exposure of the PCL 9, the image carrier 1 makes one or more rotations, and the surface of the image carrier due to the residual charge on the image carrier 1 transferred from the transfer roller 6. Is removed.

The evaluation of the image memory on the image carrier 1 was carried out by using a Macbeth reflection densitometer, by applying a cleaning bias charge to the transfer roller 6 (normal portion).
The evaluation was made based on the difference in density from the portion where no voltage was applied (memory portion).

[0109]

[Table 8]

Table 8 shows the evaluation of the image memory on the image carrier 1 after the number of prints is completed, based on the density difference. The comparative example shows the density difference of the conventional technology in which the control by the PCL 9 is not performed. Embodiment 4 shows an example in which a reverse bias is applied to the transfer roller 6 during transfer, and an example in which a positive and negative bias is applied to the transfer roller 6 and uniform exposure is performed by the PCL 9.

According to the fourth embodiment, there is almost no density difference up to 9000 prints, and the image memory is erased. Further, the density difference is small up to 30,000 prints.
An excellent cleaning effect was obtained by the uniform exposure of

The used transfer roller and cleaning conditions are the same as those in the second embodiment.

The same effect can be obtained even if the image carrier is an intermediate transfer member.

FIG. 13 is a block diagram of an image forming apparatus using an intermediate transfer member as an image carrier.

When this intermediate transfer member 1a is used, the electrostatic latent image formed on the image carrier
To form a toner image, transfer the toner image from the image carrier 1 to the intermediate transfer member 1a, and feed the toner image at a transfer portion where the intermediate transfer member 1a and the transfer roller 6 are pressed against each other. After the electrostatic transfer to the transfer material P fed from the unit and energized, the transfer material P is unloaded. The residual toner on the intermediate transfer member 1a is attached to the intermediate transfer member 1a by applying a bias charge to the transfer roller 6 and charging the transfer roller 6 during standby other than during the image formation, and is further removed by the cleaning unit 8. You. Further, the residual charge on the transfer roller 6 is removed by applying a reverse charge to the separating means 7.

[0116]

As described above, according to the image forming method and the image forming apparatus of the present invention, there is no adhesion of foreign matter to the transfer means and no residual charge of the transfer means, and cleaning can be performed extremely easily and reliably. effective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color printer that is an example of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating a process of cleaning a transfer roller according to the present invention.

FIG. 3 is a schematic view illustrating a process of cleaning a transfer roller according to the present invention.

FIG. 4 is a schematic diagram illustrating a process of cleaning a transfer roller according to the present invention.

FIG. 5 is a diagram illustrating characteristics of the image forming apparatus of the present invention.

FIG. 6 is a timing chart of application of positive and negative biases to a transfer roller.

FIG. 7 is a timing chart of application of positive and negative biases to a transfer roller.

FIG. 8 is a block diagram illustrating control of a surface potential removing unit of the image carrier.

FIG. 9 is a schematic diagram of a main part around an image carrier relating to cleaning of a transfer roller by a charger, and a timing chart showing a process of cleaning residual charge of the transfer roller.

FIG. 10 is a schematic diagram of a main portion around an image carrier relating to cleaning of a transfer roller by an image exposure unit, and a timing chart illustrating a process of cleaning a residual charge of the transfer roller.

FIG. 11 is a schematic diagram of a main part around an image carrier relating to cleaning of a transfer roller by a separating unit, and a timing chart showing a process of cleaning residual charge of the transfer roller.

FIG. 12 is a schematic diagram of a main portion around an image carrier relating to cleaning of a transfer roller by a pre-charging exposure device, and a timing chart showing a process of cleaning a residual charge of the transfer roller.

FIG. 13 is a configuration diagram of an image forming apparatus using an intermediate transfer member.

FIG. 14 is an explanatory diagram of a method for measuring an average bubble diameter of a transfer roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 1a Intermediate transfer body 2 Scorotron charger (charger) 3 Image exposure means 4Y, 4M, 4C, 4K Developing device 4 Developing device 6 Transfer roller (transfer means) 7 Separating means 8 Cleaning means 81 Cleaning blade 9 Pre-charging exposure unit (PCL) 15 Control unit E1 Bias power supply E2 Power supply P Transfer material (transfer paper) T Toner

Claims (14)

[Claims] An image carrier is charged by a charger, an electrostatic latent image is formed by an image exposing unit, and a toner image is formed by developing with a charged toner of a developing unit. Is electrostatically transferred to a transfer material fed from the image carrier and passed between the image bearing member and the transfer roller. The transfer material is further separated from the image carrier by a separation unit on the downstream side of the conveyance, and the electrostatic transfer is performed. In the image forming method for removing the toner remaining on the image carrier by a cleaning unit later, after the electrostatic transfer is completed, the transfer roller is pressed against the image carrier that is driven and rotated, and rotated. After applying foreign matter adhering to the transfer roller surface by applying a bias charge to the transfer roller and transporting the foreign matter adhered to the image carrier surface, the cleaning means removes the foreign object from the image carrier surface. Further, in order to remove potential unevenness on the surface of the image carrier caused by applying a bias charge to the transfer roller and adhering the foreign matter to the image carrier, the charger is used to clean the surface of the image carrier. An image forming method comprising: removing an electric charge on the surface of an image bearing member by charging in a similar manner. 2. An image carrier is charged by a charger, an electrostatic latent image is formed by an image exposing unit, and a toner image is formed by developing with a charged toner of a developing unit. Is electrostatically transferred to a transfer material fed from the image carrier and passed between the image bearing member and the transfer roller. The transfer material is further separated from the image carrier by a separation unit on the downstream side of the conveyance, and the electrostatic transfer is performed. In the image forming method for removing the toner remaining on the image carrier by a cleaning unit later, after the electrostatic transfer is completed, the transfer roller is pressed against the image carrier that is driven and rotated, and rotated. After applying foreign matter adhering to the transfer roller surface by applying a bias charge to the transfer roller and transporting the foreign matter adhered to the image carrier surface, the cleaning means removes the foreign object from the image carrier surface. Further, in order to remove potential unevenness on the surface of the image carrier caused by applying a bias charge to the transfer roller and causing the foreign matter to adhere to the image carrier, the surface of the image carrier is removed by the image exposure unit. A charge on the surface of the image carrier by uniformly exposing the image carrier. 3. An image carrier is charged by a charger, an electrostatic latent image is formed by an image exposing unit, and a toner image is formed by developing with a charged toner of a developing unit. Is electrostatically transferred to a transfer material fed from the image carrier and passed between the image bearing member and the transfer roller. The transfer material is further separated from the image carrier by a separation unit on the downstream side of the conveyance, and the electrostatic transfer is performed. In the image forming method for removing the toner remaining on the image carrier by a cleaning unit later, after the electrostatic transfer is completed, the transfer roller is pressed against the image carrier that is driven and rotated, and rotated. After applying foreign matter adhering to the transfer roller surface by applying a bias charge to the transfer roller and transporting the foreign matter adhered to the image carrier surface, the cleaning means removes the foreign object from the image carrier surface. Further, in order to remove potential unevenness on the surface of the image bearing member caused by applying a bias charge to the transfer roller and adhering the foreign matter to the image bearing member, the separating unit is used to remove the image bearing member. An image forming method for removing an electric charge on the surface of the image bearing member by charging in a similar manner. 4. An image carrier surface is charged by a charger, an electrostatic latent image is formed by an image exposure unit, and a toner image is formed by developing with a charged toner of a developing unit. Is electrostatically transferred to a transfer material fed from the image carrier and passed between the image bearing member and the transfer roller. The transfer material is further separated from the image carrier by a separation unit on the downstream side of the conveyance, and the electrostatic transfer is performed. In the image forming method for removing the toner remaining on the image carrier by a cleaning unit later, after the electrostatic transfer is completed, the transfer roller is pressed against the image carrier that is driven and rotated, and rotated. After applying foreign matter adhering to the transfer roller surface by applying a bias charge to the transfer roller and transporting the foreign matter adhered to the image carrier surface, the cleaning means removes the foreign object from the image carrier surface. Further, in order to remove potential unevenness on the surface of the image carrier caused by applying a bias charge to the transfer roller and adhering the foreign matter to the image carrier, the image carrier is exposed by a pre-charging exposure unit. An image forming method, wherein the charge on the surface of the image carrier is removed by uniformly charging. 5. A charging device for charging the surface of an image carrier that is driven and rotated, an image exposure unit that forms an electrostatic latent image on the charged image carrier, and an image exposure unit formed on the image carrier. Developing means for developing the electrostatic latent image with charged toner to form a toner image; a transfer roller for electrostatically transferring the toner image to a transfer material fed from a paper supply unit; In an image forming apparatus having a transfer material separating unit and a cleaning unit for removing toner remaining on the image carrier after the electrostatic transfer, control for controlling the image carrier, a charger, a transfer roller, and a cleaning unit Means for rotating the transfer roller by pressing the transfer roller against the image carrier which is driven and rotated after the end of the electrostatic transfer, and applying a bias charge to the transfer roller; Foreign matter adhering to the surface An object is transferred and adhered to the surface of the image carrier, conveyed and removed by the cleaning unit, and a bias charge is further applied to the transfer roller to cause the foreign matter to adhere to the image carrier. An image forming apparatus, comprising: removing an electric charge on the surface of the image carrier by uniform charging by the charger in order to remove potential unevenness on the surface of the carrier. 6. A charging device for charging a surface of an image carrier which is driven and rotated, an image exposure means for forming an electrostatic latent image on the charged image carrier, and an image exposure means formed on the image carrier. Developing means for developing the electrostatic latent image with charged toner to form a toner image; a transfer roller for electrostatically transferring the toner image to a transfer material fed from a paper feeding unit; In an image forming apparatus having a transfer material separating unit and a cleaning unit for removing toner remaining on the image carrier after the electrostatic transfer, the image carrier, a charger, a transfer roller, a cleaning unit, and an image exposure unit After the electrostatic transfer, the control unit rotates the transfer roller by pressing the transfer roller against the image carrier that is driven and rotated, and applies a bias charge to the transfer roller. And the transfer roller table The foreign matter adhering to the surface is transferred and adhered to the surface of the image carrier, transported and removed by the cleaning unit, and a bias charge is further applied to the transfer roller to cause the foreign matter to adhere to the image carrier. An image forming apparatus for removing electric charges on the surface of the image carrier by uniform exposure by the image exposure means in order to remove potential unevenness on the surface of the image carrier generated in the step (a). 7. A charging device for charging a surface of an image carrier which is driven and rotated, an image exposure means for forming an electrostatic latent image on the charged image carrier, and an image exposure means formed on the image carrier. Developing means for developing the electrostatic latent image with charged toner to form a toner image; a transfer roller for electrostatically transferring the toner image to a transfer material fed from a paper supply unit; In an image forming apparatus having a transfer material separating unit and a cleaning unit for removing toner remaining on the image carrier after the electrostatic transfer, the image carrier, a charger, a transfer roller, a cleaning unit, an image exposure unit After the completion of the electrostatic transfer, the control unit rotates the transfer roller by pressing the transfer roller against the image carrier that is driven to rotate, and applies a bias charge to the transfer roller. And the transfer roller table The foreign matter adhering to the surface is transferred and adhered to the surface of the image bearing member, conveyed and removed by the cleaning means, and a bias charge is further applied to the transfer roller to cause the foreign matter to adhere to the image bearing member. An image forming apparatus for removing electric charges on the surface of the image carrier by uniform charging by the separation means in order to remove potential unevenness on the surface of the image carrier generated in the step (a). 8. A charging device for charging a surface of an image carrier which is driven and rotated, an image exposure means for forming an electrostatic latent image on the charged image carrier, and an image exposure means formed on the image carrier. Developing means for developing the electrostatic latent image with charged toner to form a toner image; a transfer roller for electrostatically transferring the toner image to a transfer material fed from a paper supply unit; An image forming apparatus comprising: a transfer material separating unit; a cleaning unit configured to remove toner remaining on the image carrier after the electrostatic transfer; and a pre-charging exposure unit configured to remove charges on the image carrier. A control unit for controlling a carrier, a charger, a transfer roller, a cleaning unit, and a pre-charging exposure unit is provided, and the control unit presses the transfer roller against the driven and rotated image carrier after the end of the electrostatic transfer. To rotate and transfer Apply a bias charge to the roller,
Foreign matter adhering to the surface of the transfer roller is transferred and adhered to the surface of the image carrier, removed by the cleaning unit, and further applied with a bias charge to the transfer roller to adhere the foreign matter to the image carrier. In order to remove potential unevenness on the surface of the image carrier caused by the
An image forming apparatus, wherein the charge on the surface of the image carrier is removed by uniform exposure by the pre-charging exposure unit. 9. A pressing force for pressing the transfer roller against the image bearing member when cleaning the transfer roller is 25.
6. The composition according to claim 5, wherein the weight is from 1000 g / cm ² to 1000 g / cm ^2.
The image forming apparatus according to any one of claims 1 to 8, wherein 10. The image forming apparatus according to claim 5, wherein the transfer roller is pressed against and separated from the surface of the image carrier.
The image forming apparatus according to claim 1. 11. A multi-color superimposed toner image is formed on the image carrier by a plurality of developing means, and the superimposed toner image is collectively transferred onto a transfer material by the transfer roller. An image forming apparatus according to claim 5. 12. The transfer roller has an average bubble diameter of 1 μm.
The thickness is not less than 300 μm.
The image forming apparatus according to any one of claims 1 to 8, wherein 13. The transfer roller according to claim 5, wherein the bias applied during cleaning of the transfer roller has a polarity opposite to that of the bias applied during transfer to the transfer roller. Image forming apparatus. 14. The image forming apparatus according to claim 5, wherein the bias applied at the time of cleaning the transfer roller alternately applies positive and negative biases.