JP3484260B2 - Electrostatic image forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electrostatic imaging methods.

[0002]

2. Description of the Related Art A corona discharger is arranged so as to face an image carrier, and a recording medium is fed between the corona discharger and the image carrier while guiding the recording medium by an entrance guide of the corona discharger during transfer. By forming corona discharge from the back surface of the recording medium with the corona discharger, the recording medium is charged on the image carrier with a polarity opposite to that of the toner image formed on the image carrier. There is an electrostatic image forming apparatus that transfers the toner image to the recording medium.

This electrostatic image forming apparatus includes two cases, one in which the image carrier is a drum-shaped photosensitive member and the other in which the image carrier is an intermediate transfer belt.

In the electrostatic image forming apparatus of the type (1), a process of electrostatic photography is applied to a drum-shaped photosensitive member as an image carrier, and a toner image is formed through processes of charging, exposing and developing. This toner image is transferred onto a recording paper as a recording medium by a corona discharger.

In the electrostatic image forming apparatus of the type (1), a charging means, an exposing means, a developing means, a primary transfer means are provided around a drum-shaped photosensitive body, and the photosensitive body and the primary transfer means are provided. A medium resistance intermediate transfer belt as an image carrier is provided on the intermediate transfer belt, and a corona discharger as a secondary transfer means is arranged around the intermediate transfer belt to record between the secondary transfer means and the intermediate transfer belt. The medium is allowed to pass through. In this type of image forming apparatus, when forming an image, a charging step of charging the photoconductor by the charging means, an exposure step of exposing the charged photoconductor according to image information by the exposing means, and a developing step of developing the exposed portion Developing step for making a toner image visible by means, primary transfer step for applying a voltage having a polarity opposite to that of the toner image to the primary transfer means to transfer the toner image onto the intermediate transfer medium, the intermediate transfer A secondary transfer step of applying a voltage having a polarity opposite to that of the toner image on the medium to a corona discharger as the secondary transfer means to transfer the toner image on the intermediate transfer belt as an image carrier to a recording sheet.

Among these electrostatic image forming apparatuses, in the type of electrostatic image forming apparatus, in the case of forming a full color image, a color superimposed transfer image is formed on the image carrier,
The superposed transfer images are collectively transferred to the recording paper. Also,
In the electrostatic image forming apparatus of, when forming a full-color image, the primary transfer is repeated to form a full-color toner image by the superimposed toner image on the intermediate transfer belt.
The full-color toner image is secondarily transferred onto the recording paper all at once.

The intermediate transfer belt has a volume resistivity of 1 ×
10 ⁸ to 10 ¹² Ω · cm, surface resistivity 1 × 10 ⁸ to 10 ¹¹
A medium resistance belt of Ω (JISK6911) is used.
In this way, the medium resistance element is used.If the high resistance element is used, the primary transfer is repeated when creating a full-color image, so that the charging potential gradually increases due to the bias applied at the primary transfer. This is because there is a problem in the primary transfer and the secondary transfer. If an intermediate transfer belt made of a medium resistance body is used as an image carrier and discharge is performed from the intermediate transfer belt through a supporting member, even if primary transfer is repeated in the process of forming a full-color toner image, the intermediate transfer is performed. The charge amount of the belt can be maintained substantially constant.

On the other hand, as the transfer means, there are a method of using a bias roller and a method of using a corona discharger. When the latter transfer bias roller is used, the bias is generated in the process of forming a full-color toner image. When the roller contacts the primary transfer image, the image is disturbed.To avoid this, keep the transfer bias roller away from the intermediate transfer medium as an image carrier until the primary transfer image passes the bias roller. Since it is necessary to keep it in place and a contacting / separating mechanism for that is required, the mechanism is complicated and large in size, and much cost is required.

For this reason, there has been proposed an electrostatic image forming apparatus employing a corona transfer device which can maintain a non-contact state with a toner image without using a bias roller as a transfer means. However, in such an electrostatic image forming apparatus, since the toner image carried on the intermediate resistance intermediate transfer belt has its charge discharged through the supporting member of the intermediate transfer belt, It has a characteristic that toner adhesion is weak.

[0010]

The recording paper is guided between the corona discharger and the image carrier while being guided by the entrance guide of the corona discharger from the leading end of the recording paper so that the leading end of the recording paper comes into contact with the image carrier. By being sent out, the paper is bent by the electrostatic force generated by the transfer current applied to the corona discharger, and the portion on the rear side from the front end of the recording paper comes into close contact with the image carrier, but Since there is a gap between the leading end of the guide and the image carrier, the recording paper is very unstable until the leading edge of the recording paper comes out of the entrance guide and contacts the image carrier. However, there is a problem in that a contact failure occurs at the tip portion and a transfer failure such as a so-called white spot resulting from this occurs.

On the other hand, when the trailing edge of the recording paper passes through the entrance guide of the corona discharger, the restriction by the entrance guide is released, so that the lower part of the paper is lowered by the waist and the action of gravity. It hangs down to form a minute gap between the image carrier and the paper. Then, since the transfer electric field extends to this minute gap portion, discharge occurs in this minute gap portion, and due to this discharge phenomenon,
There are problems that the toner image on the image carrier is disturbed or white spots occur.

As described above, conventionally, there has been a problem that a transfer failure occurs at the leading end and the trailing end of the recording paper.

An object of the present invention is to provide an electrostatic image forming method capable of obtaining good transfer performance.

[0014]

In order to achieve the above object, the present invention (1) arranges a corona discharger so as to face an image carrier, and at the time of transfer, a recording medium is guided by an entrance guide of the corona discharger. A recording medium is sent between the corona discharger and the image carrier while being guided, and the recording medium is formed on the image carrier by performing corona discharge from the back surface of the recording medium with the corona discharger. In an electrostatic image forming method of transferring a toner image formed on the image carrier to the recording medium by charging the image with a polarity opposite to that of the image, the image carrier is an intermediate transfer belt of medium resistance.
Come from the time the leading end of at least the recording medium enters the transfer electric field area, the time up to the point where the tip comes into contact with the image bearing member, a transfer when transferring the central portion of the recording medium with respect to the corona discharger A transfer current larger than the current is applied (claim 1).

[0015]

( 2 ) A corona discharger is disposed so as to face the image carrier, and the recording medium is guided between the corona discharger and the image carrier while guiding the recording medium by the entrance guide of the corona discharger during transfer. The recording medium is fed and corona discharge is performed from the back surface of the recording medium by the corona discharger so that the recording medium is charged to a polarity opposite to the charging polarity of the toner image formed on the image carrier, and thus the image carrier is charged. In the electrostatic image forming method of transferring the formed toner image onto the recording medium, when the image carrier is an intermediate transfer intermediate transfer belt, the position immediately before the rear end of the recording medium passes through the entrance guide. Alternatively, a transfer current, which is smaller than a transfer current when transferring the central portion of the recording medium, is applied to the corona discharger at the timing when the position reaches the passing position (claim 2 ).

( 3 ) A corona discharger is arranged so as to face the image carrier, and the recording medium is fed between the corona discharger and the image carrier while guiding the recording medium by the entrance guide of the corona discharger during transfer. By forming a corona discharge from the back surface of the recording medium by the corona discharger, the recording medium is charged on the image carrier with a polarity opposite to that of the toner image formed on the image carrier. In the electrostatic image forming method of transferring the formed toner image to the recording medium, when the image carrier is an intermediate transfer intermediate transfer belt, at least from the time when the leading end of the recording medium enters the transfer electric field region, the leading end of the recording medium is transferred. A transfer current larger than a transfer current for transferring the central portion of the recording medium is applied to the corona discharger until the time when the recording medium contacts the image carrier, and Applying a transfer current smaller than the transfer current when transferring the central portion of the recording medium to the corona discharger at the timing when the trailing edge reaches a position immediately before passing the entrance guide or a position where the trailing end passes. (Claim 3 ).

[0018] (4) (1) or (3) Symbol in electrostatic imaging method of mounting, a large transfer current of the transfer current when transferring the central portion of the recording medium to be applied to the corona discharger The magnitude of the transfer current when applied is 50% to 200% of the transfer current when transferring the central portion of the recording medium.
The size of the increase is (claim 4 ).

In the electrostatic image forming method described in ( 5 ), ( 2 ) or ( 3 ), a transfer current smaller than the transfer current applied when transferring the central portion of the recording medium applied to the corona discharger is applied. The magnitude of the transfer current at that time was 20% to 75% less than the transfer current at the time of transferring the central portion of the recording medium (Claim 5 ).

[0020] (6) (1) or (3) in an electrostatic image forming method according greater than the transfer current applied to the corona discharger when transferring the central portion of the recording medium transfer An area on the recording medium to which an electric current is applied is set to an area which is in a transfer electric field area when the leading end of the recording medium comes into contact with the image carrier (claim 6 ). ( 7 ) In the electrostatic image forming method according to any one of (1) to ( 6 ), the intermediate transfer belt having the medium resistance has a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω · cm and a surface resistivity of 1. ×
It has a resistance of 10 ⁸ to 10 ¹¹ Ω · cm (claim 7 ).

[0021]

[Advantages] Adhesion to the image carrier is improved on the leading end side of the recording medium, and discharge does not occur with the corona discharger on the trailing end side of the recording medium even if there is a small gap between the image carrier and the recording medium. .

[0022]

【Example】

(1) Examples of electrostatic image forming apparatus suitable for implementing the present invention A. Type Using Intermediate Transfer Belt FIG. 4 shows the overall structure of a color electrostatic image forming apparatus using an intermediate transfer belt as an image carrier, and FIG. In these drawings, a writing optical unit 400 as an exposure unit converts a color image data from a color scanner 200 for color-separating and reading an original image and converting the color image data as an electrical signal into an optical signal. The optical writing corresponding to the original image is performed to form an electrostatic latent image on the photoconductor 402 which is an image carrier.

The writing optical unit 400 includes a laser light emitting means (laser diode) 404 and its light emission drive control section (not shown), a polygon mirror 406 and its rotation motor 408, an f / θ lens 410 and a reflection mirror 41.
It is composed of 2 etc.

The photoconductor 402 rotates counterclockwise as indicated by the arrow. Around the periphery thereof, the photoconductor cleaning unit 414, the charge eliminating lamp 416, the potential sensor 420,
Of the rotary developing device 422 as the developing means, a selected developing device (developing device 438 in the example of FIG. 4), a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer medium, and the like are arranged. . As the intermediate transfer belt, a volume resistivity of 1 × 10 ⁸ to 10 ¹² Ω · cm, a surface resistivity of 1 × 10 ⁸ to 10 ¹¹ Ω (JISK6911), a medium resistance belt, ethylene tetrafluoroethylene (ETFE),
Epichlorohydrin rubber is used. Alternatively,
It is used not as a belt but as a drum.

The rotary developing device 422 includes a black developing device 428, a cyan developing device 430, and a magenta developing device 4.
32, a yellow developing device 434, and a rotation driving unit (not shown) for rotating each developing device. Each developing device has a developing sleeve that rotates by bringing the brush of the developer into contact with the surface of the photoconductor 402 in order to visualize the electrostatic latent image,
It is composed of a developing paddle or the like that rotates to pump up and stir the developer.

In the standby state, the rotary developing device 422 is
When the copying operation is started at the black developing position, the color scanner 200 starts reading black image data at a predetermined timing,
Based on this image data, optical writing by laser light
Formation of a latent image starts (hereinafter, an electrostatic latent image based on black image data is referred to as a black latent image. The same applies to cyan, magenta, and yellow).

In order to develop from the tip of the black latent image, the developing sleeve is started to rotate to develop the black latent image with black toner before the tip of the latent image reaches the developing position of the black developing device. .

Thereafter, the developing operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black developing position, the developing position for black is immediately rotated to the next color developing position. The developing device rotates. The operation is completed at least before the leading edge of the latent image formed by the next image data arrives.

When the image forming cycle is started, first, the photosensitive member 402 is rotated in the counterclockwise direction as indicated by the arrow, and the intermediate transfer belt 426 is rotated in the clockwise direction by a drive motor (not shown). . With the rotation of the intermediate transfer belt 426, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), and magenta (M). , And yellow (Y) in this order, the toner images are formed on the intermediate transfer belt 426.

Here, in forming the superimposed toner image as described above, the supporting roller of the intermediate transfer belt is moved in order to shorten the time required for aligning the image leading end position, so that the broken line in FIG. The intermediate transfer belt 426 is separated from the photoconductor 402 as indicated by, and the intermediate transfer belt 426 is fast-forwarded under the separated state.

First, black image formation is performed as follows. The charger 418 as a charging unit uniformly charges the photoconductor 402 with a negative charge to about −700 V by corona discharge (charging step). Then, the laser diode 404 performs raster exposure based on the black signal (exposure step). In this way, when raster exposure is performed, the exposed portion of the photoconductor 402 that is initially uniformly charged loses the charge proportional to the amount of exposure light, and an electrostatic latent image is formed.

The toner in the developing device 422 is negatively charged by stirring with the ferrite carrier, and the black developing sleeve of the present developing device is negatively charged with respect to the metal base layer of the photoconductor 402 by a power source means (not shown). A bias of a potential in which the direct current potential and the alternating current is superimposed is applied.

As a result, the toner does not adhere to the portion of the photoconductor 402 where the electric charge remains, and the black toner is adsorbed to the portion having no electric charge, that is, the exposed portion, and a black image similar to the latent image is formed. A visual image is formed (developing step).

The intermediate transfer belt 426 is driven by the drive roller 44.
4, the transfer counter rollers 446a and 446b, the cleaning counter roller 448, and the driven roller group.
The drive is controlled by a drive motor (not shown).

The black toner image formed on the photoconductor 402 is transferred onto the surface of the intermediate transfer belt 426 which is driven at a constant speed in contact with the photoconductor by a belt corona discharger 450 as a primary transfer means ( Primary transfer process).
Hereinafter, the transfer of the toner image from the photoconductor to the intermediate transfer belt is referred to as primary transfer. The discharge efficiency (distribution ratio) of the belt corona discharger 450 is about 20 to 40%.

A small amount of untransferred residual toner existing on the photoconductor 402 is cleaned by the photoconductor cleaning unit 414 in preparation for reuse of the next color of the photoconductor 402. The toner collected here is stored in a waste toner tank (not shown) via a collection pipe.

On the intermediate transfer belt 426, the black, cyan, magenta, and yellow toner images sequentially formed on the photoconductor 402 are accurately aligned in sequence,
As a result, a belt transfer image of four colors is formed, and then
A transfer corona discharger 454 as a secondary transfer means is used to collectively transfer to a recording paper as a recording medium (secondary transfer step).

On the side of the photoconductor 402, the black process is followed by the cyan process. At a predetermined timing, the reading of the cyan image data by the color scanner starts, and the cyan latent image is written by the laser light writing by the image data. It is formed.

The cyan developing device 430 is located after the trailing edge of the black developing portion has passed the developing position, and
The rotary developing device 422 before the leading edge of the cyan latent image arrives.
And the cyan latent image is visualized with cyan toner.

Thereafter, the development of the cyan developing area is continued,
When the trailing edge of the latent image passes, the cyan developing unit is rotated like the black developing unit. This is also completed before the leading edge of the magenta latent image reaches.

The image data reading, latent image forming, and developing operations of the magenta and yellow processes are the same as those of the black and cyan processes described above, and a description thereof will be omitted.

Corona discharger 454 as secondary transfer means
Applies a DC or AC + DC component by the corona discharge method to transfer the overlapping toner image on the intermediate transfer belt onto the recording medium. The distribution ratio is about 20 to 40%, which is similar to the belt transfer corona discharger.

Each recording paper cassette 4 in the paper supply bank 456
58, 460 and 462 are cassettes 464 in the main body of the apparatus.
Various sizes of recording paper different from the size of the recording paper accommodated in are accommodated in the storage cassette of the designated (selected) size paper, and the paper is fed in the direction of the registration roller by the paper feed roller 466. -Transported. Reference numeral 468 in the figure denotes a manual paper feed tray for OHP paper, thick paper, and the like.

At the time when image formation is started, the recording paper is fed from the paper feed port of any one of the above cassettes and stands by at the nip portion of the registration roller pair 470. Then, when the front end of the toner image on the intermediate transfer belt 426 reaches the corona discharger 454, the registration roller pair 470 is driven so that the front end of the recording paper coincides with the front end of the image. Done.

In this way, the recording paper is superposed on the intermediate transfer belt, and the corona discharger 454 is connected to the positive potential.
Pass over. At this time, the recording paper is positively charged by the corona discharge current, and a substantial part of the toner image is transferred onto the recording paper. Subsequently, when passing through a part of the static elimination brush (not shown) arranged on the left side of the corona discharger 454 in the figure, the recording sheet is destaticized, separated from the intermediate transfer belt 426, and transferred to the paper conveyance belt 472.

The recording paper to which the four-color superposed toner images are collectively transferred from the intermediate transfer belt 426 is conveyed to the fixing device 474 by the paper conveying belt 472, and the fixing roller 476 and the pressure roller 478 which are controlled at a predetermined temperature. The toner image is melted and fixed at the nip portion, sent out of the machine by a pair of discharge rollers 480, and is stacked face up on a copy tray (not shown) to obtain a full-color copy.

After the image is transferred onto the intermediate transfer belt 426, the surface of the photoconductor 402 is cleaned by the photoconductor cleaning unit 414 including a brush roller and a rubber blade, and the charge is uniformly discharged by the charge removing lamp 416.

The surface of the intermediate transfer belt 426 after transferring the toner image on the recording paper is cleaned by pressing the blade again with the blade contacting / separating mechanism in the cleaning device 452.

In the case of repeat copying, the operation of the color scanner and the image formation on the photoconductor are carried out subsequent to the fourth color image process of the first sheet, and the first sheet of the second sheet is formed at a predetermined timing.
The process proceeds to the color image process. Further, in the intermediate transfer belt, the second black toner image is primarily transferred to the surface area cleaned by the cleaning device 452 following the batch transfer process of the first four-color superimposed image onto the transfer paper. It After that, the same operation as the first sheet is performed as described above.

The above is the description of the copy mode for obtaining four full colors of A4 size horizontal feed. In the case of the three-color copy mode or the two-color copy mode, the designated color and the number of times are the same as above. Will be performed.

In the single color copy mode, until the predetermined number of sheets are finished, only the developing device of the predetermined color of the rotary developing device 422 is in the developing operation state, that is, the developing position state of the predetermined color, The copying operation is continuously performed while the blade of the cleaning device 452 is pressed against the belt.

Next, A3, which is the longest size for this device
A case where full-color copying is performed in size will be described.

It is efficient for a color copy of that size to form one color each time the intermediate transfer belt 426 makes one revolution and complete four-color image formation after four rotations. If the circumference of is shortened to the maximum size as much as possible, in the copy operation of the maximum size,
There are problems such as running out of scanner return time.

On the other hand, when the intermediate transfer belt is dimensioned assuming a copy operation in a maximum size which is less frequently used such as A3 size, when the size of the intermediate transfer belt is smaller than that size and frequently used, A4 or B5 size is used. However, there is a problem that dead time that does not contribute to image formation increases. Therefore, in the case of copying A3 size, one image is formed while the intermediate transfer belt is rotated twice. That is, after the black toner image is transferred to the belt, the next one cycle of development,
It rotates without being transferred, and development and primary transfer are performed in the next one rotation.

As described above, the so-called "idle rotation" is a method for suppressing the peripheral length of the intermediate transfer belt so as to ensure a predetermined copy speed even in the case of a small-sized copy and not to reduce the maximum printable size. It is proposed that a scanner return or other operation be performed during "idle rotation" in which no transfer is performed on the intermediate transfer belt during primary transfer of each color when copying a size close to the circumference of the intermediate transfer belt. Are going to do.

However, in this case, when forming a full-color image, the toner image on the intermediate transfer belt 426 passes through the corona discharger 454 portion six times, and the frequency at which the loose toner adheres to the discharge wire. Will increase.

In any case, in the case of the electrostatic image forming apparatus of the type using the intermediate transfer medium, in the case of color copying, the toner images formed on the surface of the intermediate transfer medium are superposed and transferred, While being carried on the intermediate transfer medium,
If the present invention is not applied, the free toner will pass through the corona discharger 454.
The situation is such that it easily attaches to the discharge wire.

B. Type without intermediate transfer belt In the examples shown in FIGS. 4 and 5, the type using an intermediate transfer belt is used. However, in this example, a photosensitive drum-shaped photosensitive member without an intermediate transfer belt is used. A toner image is formed on the body by the well-known electrostatic photography method, and the toner image is charged from the back side of the recording paper by a corona discharger using a corona discharger. It is charged with a polarity opposite to that of the polarity and transferred, and the recording paper after the transfer is sent toward a fixing device, and a copy is obtained through a fixing process.

As described above, even in the electrostatic image forming apparatus of the type which does not use the intermediate transfer medium belt, the photosensitive member cleaning unit is separated from the photosensitive member each time the toner image passes when forming a full-color image. It is possible to successively superpose color images on the photoconductor to form a superposed transfer image. Then, after the full-color toner image is collectively transferred to the recording paper, the photoconductor cleaning unit is brought into contact with the photoconductor to clean the photoconductor.

In the electrostatic image forming apparatus of the type described above, the toner image formed on the intermediate resistance intermediate transfer belt is, as described above, discharged through the supporting member. In the above, since the toner carried on the intermediate transfer belt has a characteristic that the adhesive force is weak, the transfer defects at the leading end and the trailing end of the recording paper, which is a problem of the present invention, are likely to occur. is there.

[0061] (2) according to claim 1,請 Motomeko 4, an enlarged view of a portion of the corona discharger 454 along with the leading end portion of the recording paper which is provided as a secondary transfer unit in illustration 5 corresponding to claim 6 Figure 3 shows In FIG. 3, the intermediate transfer belt 426 faces the corona discharger 454 with a paper-passing gap, and this facing portion is supported by two transfer facing rollers 446a and 446b and is a flat portion. Is formed.

In the figure, the right side of the corona discharger 454 is the entrance side of the recording paper, the left side is the exit side of the recording paper, and the entrance guide is formed by the plate-shaped guide members 1 to 6 on the entrance side. . These guide members are configured to face each other in the vertical direction, and the guide member 5 and the guide member 6 made of a synthetic resin thin plate finally guide the recording paper on the inlet side. Is fixed to the guide member 3 and is located on the upper side, and the guide member 6 is fixed to the guide member 4 which is a part of the casing of the corona discharger 454 and is located on the lower side. The transfer facing roller 44 is in the flat portion of the flat portion because the recording paper feeding direction is arranged so as to gradually narrow the facing distance in the recording paper feeding direction indicated by the broken line 10 in a mutually opposing relationship.
It is specified to the part on the 6a side.

Further, of the guide members 5 and 6, the guide member 6 extends slightly longer than the guide member 5 in the traveling direction of the recording paper, and receives the recording paper hanging downward. There is. On the other hand, on the outlet side, the guide member 8 serves to guide the leading end 11F of the recording paper 11 so as not to enter the roller discharger 454, and the guide member 90 further includes the conveyor belt 472 (see FIG. 4). It is for guiding towards.

The discharge wire 7 of the corona discharger 454 extends in a direction penetrating the paper surface in FIG. 3 corresponding to the width of the intermediate transfer belt 426, and an image formed on the intermediate transfer belt 426 at the time of secondary transfer. A transfer current having a polarity opposite to the charging polarity of the toner forming the toner is applied to cause corona discharge. By this corona discharge, the transfer facing roller 446a,
The flat portion formed by the intermediate transfer belt between 446b is covered, and the drawing sheet surface is shown in a region limited by the end portion of the guide member 6 on the inlet side and the end portion of the guide member 8 on the outlet side. A transfer electric field region 9 having a depth in the penetrating direction is formed.

In FIG. 1, the recording paper 11 traveling in the feeding direction shown by the broken line 10 has its leading end 11F guided by the guide member 6.
The recording sheet 11 is located at the edge of the recording paper 11
Corresponds to the time (t1) when the tip 11F enters the transfer electric field region 9. From this time point, as the time further advances, the recording paper 11 advances along the broken line 10 and contacts the intermediate transfer belt 426 at the position 12 at the time point (t2).

The time from the time point (t1) to the time point (t2) is a preliminary time for electrostatically adhering the recording paper 11 from the front end 11F to the intermediate transfer belt 426, and is usually It has been found by experiments that even a transfer electric field sufficient to perform the transfer is still inadequate from the viewpoint of the adhesion of the tip portion, resulting in poor adhesion.

Therefore, in the process of moving the recording paper 11,
During the time from the time point (t1) to the time point (t2),
A transfer current larger than the transfer current (I ₁ ) for transferring the toner image to the discharge wire 7 of the corona discharger 454 at the central portion (intermediate portion between the front end and the rear end) in the feeding direction of the recording paper. When a current (I ₂ ) was applied, the adhesion of the leading end portion of the recording paper to the intermediate transfer belt 426 was improved, and transfer defects such as white spots and image disturbance could be eliminated. Specifically, when the toner image formed on the intermediate transfer belt 426 has the (−) polarity and I ₁ = + 200 μA,
When a transfer current of I ₂ = + 400 μA was applied, a sufficient effect could be obtained.

More generally, I ₂ is 50% of I ₁
When taking a value of 200% increase, more preferably 50% to 1
Good results were obtained when taking a value of 00% increase.

Explaining the above example from another angle, the area on the recording paper 11 to which a transfer current larger than the transfer current for transferring the central portion of the recording paper to the corona discharger 454 is applied is , The front end 11F of the recording paper 11 is an area that is included in the transfer electric field region 9 when the intermediate transfer belt 426 is first contacted, that is, the front end 1 of the recording paper 11.
This is an area having a length corresponding to at least the distance from 1F between the position where the leading end 11F of the recording paper 11 enters the transfer electric field region 9 and the position 12 where the leading end 11F contacts the intermediate transfer belt 426.

(3) Description of Claims 2 and 5 In FIG. 5, the portion of the corona discharger 454 provided as the secondary transfer means is shown enlarged together with the trailing edge of the recording paper. It is 2. As described above with reference to FIG. 1, by applying a transfer current larger than usual to the corona discharger 454, the leading end of the recording paper 11 can be brought into close contact with the intermediate transfer belt 426. When the leading end of the recording paper 11 comes into close contact with the intermediate transfer belt 26, the corona discharger 45
The transfer current applied to No. 4 is returned to the normal transfer current value, and the transfer current value transfers the central portion of the recording paper 11.

The front end 11F of the recording paper 11 eventually reaches the transfer facing roller 446b, and the intermediate transfer belt 42 is sequentially transferred from the front end 11F by the curvature separation utilizing the curvature of the roller.
Separated from 6. When the trailing edge 11E of the recording paper 11 eventually comes off the guide member 5, as shown in FIG. 2, the trailing end of the recording paper 11 becomes a free end that is not supported anywhere, and becomes a cantilever shape. The waist and the gravity are balanced, for example, as shown in FIG. 2, and a wedge-shaped minute gap is formed between the waist and the intermediate transfer belt 11.

In this wedge-shaped minute gap, discharge occurs in a region overlapping with the transfer electric field region 9. When this discharge occurs, the toner image on the intermediate transfer belt 426 is disturbed,
It becomes impossible to obtain a normal transferred image.

Therefore, at least when the trailing edge of the recording paper 11 reaches the position immediately before passing through the guide member 6 forming the entrance guide, that is, as shown in FIG.
When the rear end 11E of 1 enters the transfer electric field region 9,
When transferring the central portion of the recording paper 11, the corona discharger 454
When the current was changed so as to apply a current (I ₃ ) smaller than the transfer current (I ₁ ) applied to, it was possible to eliminate the above-mentioned discharge phenomenon and thereby improve the transfer performance. Specifically, the transfer current I ₃ is equal to 2 of the transfer current I ₁ .
By selecting a value of 0% to 75% reduction, more preferably 50% reduction, it was possible to avoid the discharge phenomenon and obtain good transfer performance.

(4) Description of Claim 3 In the embodiment described with reference to FIGS. 1 and 2, the recording paper 1 is used.
While the front end of the recording sheet 11 is located at a predetermined position on the entrance side of the corona discharger 454, the transfer current is set higher than the normal transfer current in order to secure the adhesion to the intermediate transfer belt 426. Although the example in which the transfer current is made lower than the normal transfer current after the portion is located at the predetermined position of the position opening of the corona discharger 454 has been described, respectively, these examples may be combined. That is, if the transfer current value is sequentially changed as the recording paper passes through the corona discharger 454 in the order of the front end, the center, and the rear end,
Good transfer performance can be obtained for the entire recording paper.

(5) Others In each of the above-mentioned embodiments, the electrostatic image in "(1) an electrostatic image forming apparatus suitable for carrying out the present invention, A. an electrostatic image forming apparatus of a type using an intermediate transfer belt" is used. In the forming method, the description has been given of the embodiment relating to the transfer current control of the corona discharger as the secondary transfer means from the intermediate transfer belt which is the image carrier, but the present invention is not limited to this, and the description in "B. In a method of forming an electrostatic image in an electrostatic image forming apparatus of a type that does not use ", a transfer current control for a corona discharger as a transfer unit of a toner image from a photoconductor that is an image carrier can be similarly performed.

[0076]

According to the present invention, good transfer performance can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a relationship between a recording paper and a transfer electric field region when a leading end of the recording paper is located at an entrance of a corona discharger.

FIG. 2 is a diagram illustrating a relationship between a recording paper and a transfer electric field region when a trailing end of the recording paper is located at an entrance of a corona discharger.

FIG. 3 is a diagram illustrating a moving path of a recording sheet in a secondary transfer unit.

FIG. 4 is a diagram illustrating a configuration of an electrostatic image forming apparatus suitable for implementing the present invention.

FIG. 5 is a diagram illustrating a configuration main part of an electrostatic image forming apparatus suitable for implementing the present invention.

[Explanation of symbols]

1 discharge wire 9 Transfer electric field area 11 Recording paper (as recording medium) 11E (recording paper) tip 11F (recording paper) rear edge 426 Intermediate transfer belt (as image carrier) 454 Corona Discharger

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-134264 (JP, A) JP-A-7-92830 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/16

Claims (7)

(57) [Claims] 1. A corona discharger is disposed so as to face an image carrier, and a recording medium is fed between the corona discharger and the image carrier while guiding the recording medium by an entrance guide of the corona discharger during transfer. By forming a corona discharge from the back surface of the recording medium by the corona discharger, the recording medium is charged on the image carrier with a polarity opposite to that of the toner image formed on the image carrier. In the electrostatic image forming method of transferring the formed toner image to the recording medium, when the image carrier is an intermediate transfer intermediate transfer belt, the leading end of the recording medium enters the transfer electric field region from at least the leading end of the recording medium. Is applied to the corona discharger for a period of time up to the point of contact with the image carrier, and a transfer current larger than a transfer current for transferring the central portion of the recording medium is applied to the corona discharger. Image forming method. 2. A corona discharger is arranged so as to face the image carrier, and the recording medium is fed between the corona discharger and the image carrier while guiding the recording medium by an entrance guide of the corona discharger during transfer. By forming a corona discharge from the back surface of the recording medium by the corona discharger, the recording medium is charged on the image carrier with a polarity opposite to that of the toner image formed on the image carrier. In the electrostatic image forming method of transferring the formed toner image to the recording medium, when the image carrier is an intermediate transfer intermediate transfer belt, the rear end of the recording medium immediately before passing through the entrance guide is used.
At the timing of reaching the position or the passing position, the above-mentioned
The transfer current is smaller than the transfer current when transferring the central part of the recording medium.
An electrostatic image forming method characterized in that an electric current is applied to the corona discharger . 3. A corona discharger is disposed so as to face the image carrier, and a recording medium is fed between the corona discharger and the image carrier while guiding the recording medium by an entrance guide of the corona discharger during transfer. By forming corona discharge from the back surface of the recording medium with the corona discharger, the recording medium is charged on the image carrier with a polarity opposite to that of the toner image formed on the image carrier. An electrostatic image forming method for transferring a toner image onto a recording medium, wherein the image carrier is an intermediate transfer belt having a medium resistance, and at least when the leading end of the recording medium enters a transfer electric field region.
From the point to the time when the tip contacts the image carrier
Time, rotate the center of the recording medium against the corona discharger.
Apply a transfer current that is larger than the transfer current for copying, and
At the timing when the trailing edge of the recording medium reaches the position immediately before passing the entrance guide or the position where the trailing end passes,
Electrostatic imaging method characterized by indicia pressure to less transfer current of the transfer current when transferring the central portion of the recording medium relative to the corona discharger. 4. The electrostatic image forming method according to claim 1 or 3.
In the recording medium applied to the corona discharger
Print a transfer current that is larger than the transfer current when transferring the central area.
The magnitude of the transfer current when applied is the center of the recording medium.
50% to 200% increase in transfer current when transferring a part
Electrostatic image forming method is characterized in that Satoshi. 5. The electrostatic image forming method according to claim 2 or 3, wherein a transfer current smaller than a transfer current applied when transferring the central portion of the recording medium applied to the corona discharger is applied. The magnitude of the transfer current at this time is 20% to 75 % less than the transfer current at the time of transferring the central portion of the recording medium. 6. An electrostatic imaging process according to claim 1 or 3, wherein the roller when transferring the central portion of the recording medium
Transfer greater than the transfer current applied to the discharger
The area on the recording medium to which an electric current is applied is described above.
Transfer electric field when the tip of the recording medium comes into contact with the image carrier
An electrostatic image forming method , which is an area within an area . 7. The electrostatic imaging process according to any one of claims 1 to 6, an intermediate transfer belt in said resistance body
Product resistivity 1 × 10 8 to 10 12 Ω · cm, surface resistivity 1
× electrostatic imaging wherein the Oh <br/> Rukoto belt having a resistance of 108~1011Ω · cm.