JPH06167896A - Image forming device - Google Patents

Abstract

PURPOSE:To perform satisfactory transfer, to prevent deterioration of an image and to make the separability of a transfer body satisfactory in any environment. CONSTITUTION:The image forming device is provided with a photosensitive body 1 on which a toner image is formed, the transfer body which moves in contact with the photosensitive body 1 with the prescribed nip width between them and is subjected to the transfer of the toner image formed on the photosensitive body 1, a transfer bias impression means 8 which impresses a prescribed transfer bias to the transfer body, and a potential gradation producing means 8 which produces a potential gradation in the transfer bias so that an amount that the toner image is transferred from the photosensitive body 1 to the transfer body is increased in an area from the place which is further upstream than a transfer area in relation to the photosensitive body 1 to the point where the contact of the photosensitive body 1 and the transfer body starts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile, in which a toner image formed on a photoconductor is transferred onto a transfer medium.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a transfer separation device for transferring a toner image on a photoconductor onto a transfer paper and separating the transfer paper from the photoconductor is generally a corona discharge device for transfer. By corona discharge on the back side of transfer paper etc. with an electric device to transfer the toner image on the photoconductor to the front side of transfer paper etc. By corona discharge for separation on the back side of transfer paper etc. A corona transfer separation system is used in which transfer paper or the like is separated from the photoconductor and is conveyed by a conveying device.

Further, while rotating the transfer belt, a bias potential is applied to the transfer belt from a power source to transfer the toner image on the photoconductor onto the transfer paper or the like on the transfer belt. A contact-type transfer separation method has been proposed in which it is electrically adsorbed and separated from a photoreceptor and conveyed. In this contact-type transfer separation method, there is a method in which a transfer roller is used instead of the transfer belt. This contact-type transfer separation method is disclosed in JP-A-2-123385, JP-A-2-123386, and JP-A-2-287380. Japanese Patent Laid-Open No. 2-287
It is known from Japanese Patent No. 381, Japanese Patent Laid-Open No. 3-68976, and the like.

Some electrophotographic image forming apparatuses, such as copying machines, have a carrier on which a toner image is transferred in a transfer area and which carries the toner image by rotation. In this image forming apparatus, a toner image is formed on a photoconductor, and this toner image is transferred onto the belt in the first transfer area. Then, the toner image on the belt is conveyed to the second transfer area by the rotation of the belt and transferred to the transfer paper. Here, a transfer potential is applied to the belt on the upstream side of the first transfer region, and the toner image is transferred from the photoconductor to the belt by this transfer potential.

[0005]

The contact type transfer separation method has advantages such as less ozone generation and less power source voltage than the corona transfer separation method. However, when a transfer belt is used, the proper bias voltage applied to the transfer belt of the power source changes depending on the resistance unevenness of the transfer belt, environmental changes, the type of transfer paper, the area of the toner image, etc. You will not be able to transfer. The reason for this is that the amount of charge due to the bias potential application of the power supply on the transfer belt causes unevenness in the resistance value at the time of manufacturing the transfer belt, the change in the resistance value due to the environmental change, the difference in the material of the transfer paper and the difference in the thickness, and the like This is because the value will change from the value required for image transfer.
That is, when the charge amount due to the applied bias potential of the power source on the transfer belt is a value required for good toner image transfer, as shown in FIG. 17, the transfer area of the nip portion where the photoconductor 37 and the transfer belt contact each other No discharge is generated in the upstream pre-transfer area, and, for example, the positively charged toner 39 on the photoconductor 37 is transferred to the transfer paper 38 on the transfer belt in the transfer area.
Transferred to. In this case, a bias potential is applied to the transfer belt 38 by the power source. In addition, the amount of charge due to the bias potential of the power supply applied to the transfer belt makes it possible to obtain a good toner image transfer due to variations in resistance value during manufacturing of the transfer belt, changes in resistance value due to environmental changes, differences in materials such as transfer paper, and differences in thickness. If the value is different from the value required for, a strong electric field is applied in the pre-transfer area to cause discharge as shown in FIG. As a result, the toner is negatively charged, and positive and negative charges are generated on the front and back surfaces of the transfer paper 38 on the transfer belt.
Even if an appropriate bias potential is applied to the transfer belt from the power source, the toner 39 on the photoconductor 37 does not transfer to the transfer paper 38 on the transfer belt, and white spots in the transfer image on the transfer paper occur.

Further, the transfer belt not only transfers the toner image on the photoconductor to the transfer paper or the like on the transfer belt, but also electrostatically adsorbs the transfer paper or the like on the transfer belt to separate it from the photoconductor. Separability of transfer paper and the like changes depending on environmental conditions. Particularly, when the moisture content of transfer paper etc. increases under high temperature and high humidity conditions, the transfer paper etc. will not be adsorbed on the transfer belt and the transfer paper etc. will be adsorbed by the photoconductor and cannot be separated from the photoconductor. Will end up. Therefore, if the separation paper is used to separate the transfer paper or the like from the photoconductor, the transfer paper or the like will have marks or wrinkles due to the separation nail, and the image quality will be degraded.

In the above electrophotographic image forming apparatus, a transfer potential is applied to the belt on the upstream side of the first transfer area, and the toner image is transferred from the photoconductor to the belt by this transfer potential. Occurs on the upstream side of the first transfer region, causing line thickening, blurring of characters and the like, and image deterioration called sharpness deterioration. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which can improve the above-mentioned drawbacks, can perform good transfer, prevent image deterioration, and have good separability of a transfer target under any environment. .

[0008]

In order to achieve the above object, the invention according to claim 1 is to move a photosensitive member on which a toner image is formed and a photosensitive member on which the toner image is formed with a predetermined nip width. A transfer target to which the toner image formed on the photoconductor is transferred, a transfer bias applying unit that applies a predetermined transfer bias to the transfer target, and a transfer region upstream of the transfer region with respect to the photoconductor. In the region up to the contact start point between the photoconductor and the transfer target, the transfer is performed on the transfer target as the transfer amount of the toner image from the photoconductor to the transfer target increases. And a potential gradient generating means for giving a bias a potential gradient.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer bias applying means is in contact with the transfer target on the downstream side of the nip portion in the moving direction of the transfer target. The potential gradient generating means is an electrode that comes into contact with the transferred body on the upstream side in the moving direction of the transferred body with respect to the nip portion.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, a bias is applied to the potential gradient generating means, and the bias applied to the potential gradient generating means is the transfer bias. The potential is such that the toner image is not transferred from the photoconductor to the transfer target, as compared with the case where the voltage is applied to the applying unit.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the potential gradient generating means is grounded.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the potential gradient generating means is grounded via a constant voltage element.

According to a sixth aspect of the invention, in the image forming apparatus according to the second aspect, the potential gradient generating means is electrically floating.

According to a seventh aspect of the present invention, in the image forming apparatus according to the third aspect, a potential having the same polarity as that of the toner image is applied to the potential gradient generating means, and a potential opposite to that of the toner is applied to the transfer bias applying means. A polar potential is applied.

According to an eighth aspect of the invention, in the image forming apparatus according to the third or seventh aspect, the bias potential applied to the potential gradient generating means and / or the transfer bias applying means is variable.

According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the image forming apparatus further comprises a photoconductor state detecting unit for detecting the state of the photoconductor, and the photoconductor state detecting unit detects the state of the photoconductor. The bias voltage applied to the potential gradient generating means is varied.

The invention according to claim 10 is the invention according to claim 1 or 2.
In the image forming apparatus described above, the transfer-receiving member is a transfer paper carried and conveyed by a transfer belt that is in contact with the photosensitive member with a predetermined nip width.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, the application timing of the bias potential applied to the potential gradient generating means is after the transfer paper comes into contact with the photoconductor. It is a thing.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the tenth aspect, a bias is applied to the potential gradient generating means to contact the transfer belt on the upstream side of the nip portion, and the transfer paper is Before contacting the photoconductor, a bias lower than the transfer bias is applied to the potential gradient generation unit, and after the transfer paper contacts the photoconductor, the potential gradient generation unit is applied with a bias almost the same as the transfer bias. It is applied.

According to a thirteenth aspect of the present invention, the photoconductor on which a toner image is formed and the photoconductor is moved in contact with the photoconductor with a predetermined nip width to carry and convey the transfer paper to transfer the transfer paper. A transfer belt to which the toner image formed on the photoconductor is transferred, a transfer bias applying unit for applying a predetermined transfer bias to the transfer belt, and a transfer belt upstream of the nip portion with respect to the photoconductor. In the area up to the contact start point between the photoconductor and the transfer belt, a potential gradient is applied to the transfer bias with respect to the transfer belt as the transfer amount of the toner image from the photoconductor to the transfer paper increases. And a bias applying means for applying a bias to the potential gradient generating means after the transfer paper passes through the nip portion for a predetermined distance.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, a bias is applied to the potential gradient generating means to contact the transfer belt on the upstream side of the nip portion, and the transfer bias is applied. A distance between the means and the photoconductor is shorter than a distance between the potential gradient forming means and the photoconductor, and the potential gradient forming means has a distance that the transfer paper is conveyed by the transfer belt. The bias is applied after the distance between the transfer bias applying means and the photoconductor is exceeded.

The invention according to claim 15 is the invention according to claims 11 and 1.
In the image forming apparatus described in item 2, 13 or 14, the timing of bias application to the potential gradient generating means can be adjusted.

The invention according to claim 16 is the invention of claims 11 and 1.
In the image forming apparatus described in 2, 13, or 14, a humidity detecting means for detecting humidity, and a bias signal is applied to the potential gradient generating means when the humidity exceeds a predetermined value by a detection signal of the humidity detecting means. The control means does not adjust the bias application timing to the potential gradient generating means when the timing is adjusted and the humidity becomes equal to or lower than a predetermined value.

According to a seventeenth aspect of the present invention, a photosensitive member on which a toner image is formed and a photosensitive member on which the toner image is formed are brought into contact with each other with a predetermined nip width to move and carry and transfer the transfer paper. A transfer belt to which the toner image formed on the photosensitive member is transferred, and a transfer bias applying unit that contacts the transfer belt on the downstream side of the photosensitive member and applies a predetermined transfer bias to the transfer belt; A dielectric layer is provided on the surface and contacts the transfer belt on the upstream side of the photoreceptor,
Upstream of the nip portion with respect to the photoconductor,
In the area up to the contact start point between the photoconductor and the transfer belt, the transfer bias has a potential gradient with respect to the transfer belt as the transfer amount of the toner image from the photoconductor to the transfer paper increases. And a potential gradient generating means for controlling the potential gradient.

According to the eighteenth aspect of the present invention, the photoconductor on which a toner image is formed and the photoconductor is brought into contact with the photoconductor with a predetermined nip width to move and carry and convey the transfer paper. A transfer belt to which the toner image formed on the photosensitive member is transferred, and a transfer bias applying unit that contacts the transfer belt on the downstream side of the photosensitive member and applies a predetermined transfer bias to the transfer belt; An elastic dielectric layer is provided on the surface and contacts the back side of the transfer belt on the upstream side of the photoconductor, and on the upstream side of the nip portion with respect to the transfer belt, the photoconductor and the transfer belt. In a region up to the contact start point with the transfer belt, a potential gradient generation unit for imparting a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer paper increases with respect to the transfer belt. Equipment Those were.

According to a nineteenth aspect of the present invention, the photosensitive member on which a toner image is formed is moved in contact with the photosensitive member with a predetermined nip width in the transfer area to move the toner image on the photosensitive member. And a transfer target that is subjected to a plurality of transfer steps,
The first contacting member to be transferred on the downstream side of the transfer area
An electrode, a second electrode in contact with the transfer target on the upstream side of the transfer region, both the first electrode and the second electrode, or a transfer bias is applied to the first electrode, When the transfer target has no toner, a bias having the same polarity as the toner is applied to the second electrode, and when the transfer target has toner, a bias having a reverse polarity to the toner is applied to the second electrode, In the area upstream of the transfer area with respect to the photoconductor and up to the contact start point between the photoconductor and the transfer target, the toner image is transferred from the photoconductor to the transfer target with respect to the transfer target. And a means for giving a potential gradient to the transfer bias as the transfer amount to the transfer body increases.

According to a twentieth aspect of the present invention, in the image forming apparatus according to the nineteenth aspect, the transfer-receiving member is an intermediate transfer belt that directly carries the toner, and has a different color for each of a plurality of transfer steps. It carries toner.

[0028]

According to the first aspect of the invention, the transfer-receiving member comes into contact with the photosensitive member with a predetermined nip width and moves, and the toner image formed on the photosensitive member is transferred. A predetermined transfer bias is applied to the transferred material by the transfer bias applying means, and the potential gradient generation means is an area upstream of the transfer area with respect to the photosensitive member and up to a contact start point between the photosensitive member and the transferred material. Then, the transfer bias is given a potential gradient with respect to the transfer target as the transfer amount of the toner image from the photosensitive member to the transfer target increases. Therefore, good transfer can be performed, image deterioration can be prevented, and the transfer target can be easily separated.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer bias applying means formed of an electrode is in contact with the transfer target on the downstream side in the moving direction of the transfer target with respect to the nip portion. Then, the potential gradient generating means composed of the electrodes comes into contact with the transfer target on the upstream side in the moving direction of the transfer target with respect to the nip portion.

According to a third aspect of the invention, in the image forming apparatus according to the second aspect, a bias is applied to the potential gradient generating means, and the bias applied to the potential gradient generating means is applied to the transfer bias applying means. Therefore, the potential is such that the transfer of the toner image from the photoconductor to the transfer target does not occur.

According to a fourth aspect of the invention, in the image forming apparatus according to the second aspect, the potential gradient generating means is grounded.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the potential gradient generating means is grounded via the constant voltage element.

According to a sixth aspect of the invention, in the image forming apparatus according to the second aspect, the potential gradient generating means is electrically floating.

According to a seventh aspect of the present invention, in the image forming apparatus according to the third aspect, a potential having the same polarity as that of the toner image is applied to the potential gradient generating means, and a potential having the opposite polarity to the toner is applied to the transfer bias applying means. An electric potential is applied.

According to the invention of claim 8, claim 3 or 7
In the image forming apparatus described above, a potential gradient generating unit and / or
Alternatively, the bias potential applied to the transfer bias applying means is variable.

According to a ninth aspect of the invention, in the image forming apparatus according to the eighth aspect, the state of the photoconductor is detected by the photoconductor state detecting means, and the potential gradient is detected according to the detection result of the photoconductor state detecting means. The bias voltage applied to the generating means is changed.

According to a tenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the transfer belt is brought into contact with the photoconductor with a predetermined nip width to carry and convey the transfer paper.

According to the invention of claim 11, in the image forming apparatus of claim 10, the bias potential applied to the potential gradient generating means is applied after the transfer paper comes into contact with the photoconductor.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the potential gradient generating means is biased to come into contact with the transfer belt on the upstream side of the nip portion, and the transfer paper contacts the photoconductor. Before the contact, the bias lower than the transfer bias is applied to the potential gradient generating means, and after the transfer paper contacts the photoconductor, the bias almost the same as the transfer bias is applied to the potential gradient generating means.

According to the thirteenth aspect of the present invention, the transfer belt is brought into contact with the photosensitive member with a predetermined nip width to move, and carries and conveys the transfer paper. The toner image formed on the photoconductor is transferred to this transfer paper, and a predetermined transfer bias is applied to the transfer belt by the transfer bias applying means. The potential gradient generating means is located on the upstream side of the nip portion with respect to the photoconductor and in a region up to the contact start point between the photoconductor and the transfer belt, the toner image is transferred from the photoconductor to the transfer paper on the transfer belt. The transfer bias has a potential gradient as the amount increases. The bias applying means applies a bias to the potential gradient generating means after the transfer paper passes through the nip portion for a predetermined distance.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, a bias is applied to the potential gradient generating means to contact the transfer belt on the upstream side of the nip portion, and the transfer bias applying means and the photosensitive member are exposed. The distance to the body is shorter than the distance between the potential gradient forming means and the photoconductor. The bias is applied to the potential gradient forming means after the distance by which the transfer paper is conveyed by the transfer belt exceeds the distance between the transfer bias applying means and the photoconductor.

According to the invention of claim 15,
In the image forming apparatus described in 12, 13, or 14, the bias application timing to the potential gradient generating means can be adjusted.

According to the invention of claim 16,
In the image forming apparatus described in 12, 13, or 14, the humidity is detected by the humidity detecting means. The control means adjusts the bias application timing to the potential gradient generating means when the humidity becomes higher than a predetermined value by the detection signal of the humidity detecting means, and the potential when the humidity becomes lower than the predetermined value. The bias application timing to the gradient generating means is not adjusted.

According to the seventeenth aspect of the present invention, the transfer belt is brought into contact with the photosensitive member with a predetermined nip width and moved to carry and convey the transfer paper. The toner image formed on the photoconductor is transferred onto this transfer paper. The transfer bias applying unit makes contact with the transfer belt on the downstream side of the photoconductor and applies a predetermined transfer bias to the transfer belt. The potential gradient generating means is provided with a dielectric layer on the surface and contacts the transfer belt on the upstream side of the photoconductor, and on the upstream side of the nip portion with respect to the photoconductor, the contact start point between the photoconductor and the transfer belt. In the region up to, the transfer bias is given a potential gradient with respect to the transfer belt as the transfer amount of the toner image from the photoconductor to the transfer paper increases.

According to the eighteenth aspect of the present invention, the transfer belt is brought into contact with the photosensitive member with a predetermined nip width to move, and carries and conveys the transfer paper. The toner image formed on the photoconductor is transferred onto this transfer paper. The transfer bias applying unit makes contact with the transfer belt on the downstream side of the photoconductor and applies a predetermined transfer bias to the transfer belt. An elastic dielectric layer is provided on the surface of the potential gradient generating means, contacts the back side of the transfer belt on the upstream side of the photoconductor, and is on the upstream side of the nip portion with respect to the transfer belt, and the photoconductor and the transfer belt. In the region up to the contact start point with the transfer belt, the transfer bias is given a potential gradient on the transfer belt as the transfer amount of the toner image from the photoconductor to the transfer paper increases.

According to the nineteenth aspect of the present invention, the transfer object is moved in contact with the photoconductor with a predetermined nip width in the transfer area, and the transfer step is performed to transfer the toner image on the photoconductor to the transfer object. It is done multiple times. The first electrode is in contact with the transferred material on the downstream side of the transfer area, and the second electrode is in contact with the transferred material on the upstream side of the transfer area. The means applies a transfer bias to both the first electrode and the second electrode, or to the first electrode, and applies a bias having the same polarity as the toner to the second electrode when the transfer target has no toner. When toner is present on the transfer target, a bias having a polarity opposite to that of the toner is applied to the second electrode, and the bias is applied to the photoconductor on the upstream side of the transfer area up to the contact start point between the photoconductor and the transfer target. In the region, the transfer bias is given a potential gradient with respect to the transfer target as the transfer amount of the toner image from the photosensitive member to the transfer target increases.

According to a twentieth aspect of the present invention, in the image forming apparatus according to the nineteenth aspect, the transfer medium composed of the intermediate transfer belt directly carries the toner, and the toner of a different color is used for each of a plurality of transfer steps. Carry.

[0048]

FIG. 2 shows a part of a first embodiment of the present invention. The first embodiment is an image forming apparatus including an electrophotographic copying machine. Although not shown, the image carrier 1 composed of a photosensitive drum is rotationally driven by a driving mechanism and uniformly charged by a charger, and then image information is written by a writing device to form an electrostatic latent image. The latent image is developed by the developing device and becomes a toner image. Further, a recording medium composed of transfer paper is fed from the paper feeding device to the registration roller 2 and stands by, and the registration roller 2 is in timing with the toner image on the photoconductor drum 1 and at least the front side of the transfer paper is a dielectric material. To the transfer belt 3.

The transfer belt 3 is stretched around a driving roller 4 and other driven rollers 5 to 7, and the rollers 6 and 7 are grounded. The roller 5 is a transfer bias roller that constitutes an electrode, and the roller 4 is configured in an electrically floating state.
At the same time that the leading edge of the transfer paper comes close to the portion where the photosensitive drum 1 and the transfer belt 3 contact, the solenoid 9 is turned on to drive the push-up lever 10 to drive the push-up lever 10.
Pushes up one side of the belt device including the transfer belt 3 and the rollers 4 to 7, so that the transfer belt 3 comes into contact with the photosensitive drum 1.

The drive roller 4 is driven by a motor to rotate, and the transfer belt 3 is rotationally driven by the drive roller 4. The transfer belt 3 comes into contact with the drive roller 4 at the upstream side of the contact portion with the photosensitive drum 1, and comes into contact with the transfer bias roller 5 at the downstream side of the contact portion with the photosensitive drum 1, and contacts with the photosensitive drum 1. Contact with a predetermined nip width. Transfer belt 3
When the toner contacts the photosensitive drum 1, a predetermined bias voltage having a polarity opposite to the charging polarity of the toner on the photosensitive drum 1 is applied from the power source 8 to the transfer bias roller 5 as shown in FIGS. Granted. The transfer belt 3 having a volume resistivity of medium resistance (10 ⁶ to 10 ¹² Ωcm) is used. When a bias voltage is applied from the transfer bias roller 5, a current flows to the rollers 6 and 7 and the voltage drops. go.

When the transfer sheet passes between the transfer belt 3 and the photosensitive drum 1, a predetermined bias voltage having a polarity opposite to the charging polarity of the toner on the photosensitive drum 1 is applied to the transfer belt 3 from the power source 8. As a result, the toner image on the photosensitive drum 1 is transferred. Then, the transfer paper is polarized by the electric charge applied to the transfer belt 3 from the power source 8, and an electrostatic force is generated by the polarization charge of the transfer paper and the true charge of the transfer belt 3, and the transfer paper is transferred by the electrostatic power. The transfer belt 3 is attracted to the belt 3 and conveyed as the transfer belt 3 rotates.

While the transfer paper is being conveyed by the transfer belt 3, the charge is released to the ground through the transfer belt 3 having medium resistance and the rollers 6 and 7, and the charge amount is eased. The speed at which the charge amount of the transfer paper is relaxed is greatly influenced by the resistance value R and the electrostatic capacitance C of the transfer paper, and is represented by a time constant τ = RC. Then, the transfer sheet is conveyed by the transfer belt 3 and sent to the fixing section. However, in the vicinity of the inlet of the fixing section, the electrostatic charge between the transfer sheet and the transfer belt 3 is weakened, and the roller having a small diameter is grounded. 7 is separated from the transfer belt 3 by the curvature separation of the transfer paper 7 and the waist of the transfer paper, and the toner image is fixed at the fixing portion. In this case, the diameter of the roller 7 is φ14.
~ Φ16 is suitable.

At the same time that the trailing edge of the transfer paper leaves the nip between the photoconductor drum 1 and the transfer belt 3, the solenoid 9 is turned off and the push-up lever 10 is released to release the transfer belt 3 and the roller 4. One side of the belt device including .about.7 returns to the original position, and the transfer belt 3 separates from the photosensitive drum 1. This is done to prevent the deterioration of the photoconductor drum 1 due to the contact friction between the transfer belt 3 and the photoconductor drum 1 when the toner image is not transferred. Further, toner that is not transferred from the photosensitive drum 1 to the transfer paper and is scattered on the rotating transfer belt 3 directly adheres to the transfer belt 3 to become residual toner, and this residual toner is grounded. The amount of charge is reduced by the rollers 6 and 7 that are being removed, and the toner is scraped off by the cleaning blade 11 and recovered in the recovery bottle 12.

In this first embodiment, the transfer bias roller 5 is the only roller that applies electric charge to the transfer belt 3,
When a bias voltage is applied from the power source to not only the transfer bias roller 5 but also the driving roller 4, the potential distribution of the transfer belt 3 is linear between the contact portions T of the rollers 4 as shown in FIG. A varying potential gradient is created. According to the experiment, when the moisture content of the transfer paper is increased to 8% to 11% under a high temperature and high humidity environment, the transfer paper is not electrostatically adsorbed on the transfer belt 3. However, in the first embodiment, when the bias voltage is applied only to the transfer bias roller 5 as shown in FIG. 9, the separation failure of the transfer paper from the photosensitive drum 1 does not occur as shown in FIG. This is because when the drive roller 4, which is in contact with the transfer belt 3 on the upstream side of the photosensitive drum 1, gives electric charges, the water content of the transfer paper increases, so that the electric charges get into the leading end of the transfer paper and are transferred. It is considered that this is because the paper is no longer electrostatically attracted to the transfer belt 3. If electric charges are not applied to the transfer belt 3 by the drive roller 4 as in the first embodiment, the electric charges will not enter the leading end portion of the transfer paper during the conveyance of the transfer paper, so that the transfer paper and the transfer belt 3 are not charged. Since the repulsive force is not generated, the separation failure of the transfer paper from the photosensitive drum 1 does not occur.

FIG. 4 shows a part of the second embodiment of the present invention.
In the second embodiment, the drive roller 4 also functions as a transfer bias roller that constitutes an electrode in the first embodiment, and this is also used as a constant voltage element 13 such as a varistor or a Zener diode.
It is designed to be grounded via. The set value of the bias voltage applied to the transfer bias roller 4 is not particularly specified, but it is desirable that the set value be close to the applied bias voltage of the transfer bias roller 5 on the downstream side.

In the second embodiment, a bias voltage is applied from the power source 8 to the transfer bias roller 5 on the downstream side, and the transfer bias roller 5 on the downstream side and the transfer bias roller 4 on the upstream side have substantially the same potential. Therefore, the potential of the transfer portion where the photoconductor drum 1 and the transfer belt 3 are in contact with each other is stably maintained, and good toner image transfer is performed regardless of fluctuations in the resistance value of the transfer belt 3 and other fluctuations. Further, the charge injection into the transfer paper at high humidity is reduced, and the separation of the transfer paper from the photoconductor drum 1 at high humidity becomes good. In particular, compared to the first embodiment, the toner image can be transferred more stably, and the bias voltage applied from the power source 8 to the transfer bias roller 5 on the downstream side has a unique effect.

FIG. 5 shows a part of the third embodiment of the present invention.
In the third embodiment, the drive roller 4 also serves as the transfer bias roller which constitutes an electrode in the first embodiment, and the transfer paper is supplied from the power supply 14 to the photosensitive drum 1 and the transfer belt 3 as shown in FIG. The voltage is applied to apply the electric charge from the time when the photosensitive drum 1 comes into contact with the photosensitive drum 1 and enters the nip with the electric potential distribution of the transfer belt 3 shown in FIG.
As shown in FIG. 5, a linearly changing potential gradient is generated between the portions T where the rollers 4 and 5 contact.

In the third embodiment, similar to the first embodiment, the separability of the transfer paper from the photosensitive drum 1 is improved, and stable toner image transfer is performed regardless of the resistance value variation of the transfer belt 3. be able to. Therefore, the transfer belt 3 can be selected with a good yield even when the transfer belt 3 is manufactured and selected.

FIG. 6 shows a part of the fourth embodiment of the present invention.
The fourth embodiment is the same as the third embodiment except that the power source 14
In place of the above, a variable power source 15 capable of varying the power source voltage is used. As shown in FIG. 11, the variable power source 15 applies a bias voltage lower than the applied bias voltage of the transfer bias roller 5 to the transfer bias roller 4 at the same timing as the application of the bias voltage of the transfer bias roller 5, and the leading edge of the transfer paper is transferred. Is the photoconductor drum 1 and the transfer belt 3
The bias voltage applied to the transfer bias roller 4 is set to the same voltage as the bias voltage applied to the transfer bias roller 5 from the time of entering the nip. The potential distribution of the transfer belt 3 has a potential gradient as shown in FIG.

In this fourth embodiment, the variable power source 15 applies a bias voltage lower than the bias voltage applied to the transfer bias roller 5 before the leading edge of the transfer paper enters the nip between the photosensitive drum 1 and the transfer belt 3. Since the voltage is applied to the roller 4, the transfer paper can be easily separated from the photosensitive drum 1.

FIG. 7 shows a part of a fifth embodiment of the present invention.
The fifth embodiment is the same as the first embodiment except that the power source 16
Therefore, the bias voltage is applied to the transfer bias rollers 4 and 5 at the timing shown in FIG. The power supply 16 applies a bias voltage to the transfer bias rollers 4 and 5 from the time when the front end of the transfer paper passes through the nip between the photoconductor drum 1 and the transfer belt 3 by a predetermined distance of 8 mm or less, and the transfer paper is at the front end side. An area for a predetermined distance is a non-transfer area where the toner image is not transferred. For this reason,
The transfer paper has a blank area of several mm on the leading end side, but is reliably separated from the transfer belt 3 near the entrance of the fixing unit and fixed by the fixing unit. The potential distribution of the transfer belt 3 has a potential gradient as shown in FIG.

Further, in the sixth to eighth embodiments of the present invention, in the third to fifth embodiments, as shown in FIG. 8, from the nip between the photosensitive drum 1 and the transfer belt 3 to the transfer bias roller 4, respectively. The distance LA is the distance LB from the nip between the photosensitive drum 1 and the transfer belt 3 to the transfer bias roller 5.
Further, the timing of applying the bias voltage from the power sources 8, 15, 16 to the transfer bias rollers 4, 5 is set to the time when the leading edge of the transfer paper reaches the point A which is separated from the transfer bias roller 4 by LB to the downstream side. , Transfer paper photosensitive drum 1
It was easy to separate. Further, in the above third to eighth embodiments, the result that the toner image transfer failure does not occur at high temperature and high humidity was obtained.

In the ninth embodiment of the present invention, the bias voltage application timing to the transfer bias roller 4 on the upstream side can be varied from the outside in the third embodiment. In the third embodiment described above, the bias voltage is applied to the transfer bias roller 4 by the power supply 14 after the transfer paper comes into contact with the photoconductor drum 1. However, in some cases, the transfer paper transport control may vary from machine to machine. Even with the same machine, a difference may occur over time due to wear of the transfer paper transport system. If the timing of applying the bias voltage to the transfer bias roller 4 on the upstream side is too early, electric charges are applied to the transfer belt 3 before the transfer paper comes into contact with the photoconductor drum 1 and the transfer paper is applied to the photoconductor drum 1 at high humidity. Separation tends to be unstable.

On the contrary, if the bias voltage application timing to the upstream side transfer bias roller 4 is too late, the transfer bias is applied by the power supply 14 after the leading edge of the transfer paper passes through the nip between the photosensitive drum 1 and the transfer belt 3. A bias voltage is applied to the roller 4, and when the transfer belt 3 has a resistance component, the toner image transfer at the leading end of the transfer paper may not be performed well. In the ninth embodiment, the bias voltage application timing to the transfer bias roller 4 on the upstream side is changed from the outside to eliminate the above-mentioned problem.

FIG. 13 shows a part of the circuit configuration of the image forming apparatus according to the ninth embodiment. The main controller 17 is the CPU 1
8, a ROM 19, a RAM 20, an input circuit 21, a load driver 22, and an interface 23, to which a system controller 24, a high-voltage power supply 25, an operation unit 26, etc. are connected. The serviceman or the like sets the operation mode of the image forming apparatus to the serviceman program mode (SP mode) by the operation unit 26, and then inputs the bias voltage application timing adjustment value of the transfer bias roller 4 by the operation unit 26.

The CPU 18 operates according to the program in the ROM 19, sets to the SP mode by the SP mode signal input from the operation unit 26 via the input circuit 21, and is input from the operation unit 26 via the input circuit 21. The bias voltage application timing adjustment value of the transfer bias roller 4 is loaded into the RAM 20. The RAM 20 is backed up by a battery, and the CPU 18 adjusts the bias voltage application timing of the power supply 14 to the transfer bias roller 4 via the load driver 22 according to the bias voltage application timing adjustment value of the transfer bias roller 4 in the RAM 20.

Also in the fourth to eighth embodiments, the bias voltage application timing to the transfer bias roller 4 on the upstream side can be changed from the outside similarly to the ninth embodiment, so that the toner image transfer performance and the transfer can be improved. It is possible to achieve both paper separation performance.

FIG. 14 shows a part of the circuit configuration of the image forming apparatus according to the tenth embodiment of the present invention. The main control unit 26 is a CP
It has a U27, a ROM 28, a RAM 29, an input circuit 30, a load driver 31, and an interface 32, and is connected to a system controller 33, a high voltage power supply 34, a humidity sensor 35 and the like. The humidity sensor 35 is arranged in the vicinity of the paper feeding device and detects the atmospheric humidity of the transfer paper loaded in the paper feeding device. The CPU 27 detects the humidity detected by the humidity sensor 35 at a predetermined value, for example, 70 at a relative humidity by a humidity detection signal input from the humidity sensor 35 through the input circuit 30 during normal operation of the image forming apparatus (for example, during copying operation).
If it is higher than%, the power source 14 is supplied via the load driver 31.
The application timing of the bias voltage to the transfer bias roller 4 is delayed so that the power supply 14 starts applying the bias voltage to the transfer bias roller 4 after the transfer paper comes into contact with the photosensitive drum 1.

When the relative humidity detected by the humidity sensor 35 is lower than 70%, the CPU 27 determines the bias voltage application timing for the transfer bias roller 4 of the power supply 14 via the load driver 31. The same timing as the bias voltage application to As a result, even if the transfer paper has a high humidity and absorbs moisture, no charge is injected from the transfer bias roller 4 on the upstream side into the transfer paper, and the transfer paper is stably separated from the photosensitive drum 1. After the leading end of the transfer paper is separated from the photosensitive drum 1, charges are applied from both transfer bias rollers 4 and 5, and the toner image is stably transferred on the rear side of the leading end of the transfer belt 3.

When the relative humidity is 70% or less, there is no problem in the separability of the transfer paper from the photosensitive drum 1, and the transfer paper is charged by both transfer bias rollers 4 and 5 to transfer the toner image. Therefore, stable toner image transfer is always performed from the tip. The tenth embodiment is
Although the relative humidity sensor is used, the same effect can be obtained by using the absolute humidity sensor, and the bias voltage application timing of the power supply 14 to the transfer bias roller 4 is controlled using a sensor that detects both temperature and humidity. You may do it. Also in the fourth to eighth embodiments, as in the tenth embodiment, the humidity sensor detects the ambient humidity of the transfer paper loaded in the paper feeding device, and the humidity is used to detect the transfer bias roller 4 of the power supply 14. By controlling the bias voltage application timing with respect to, it is possible to perform stable toner image transfer and transfer paper separation over the entire environment.

FIG. 15 shows a part of the eleventh embodiment of the present invention. In the eleventh embodiment, the transfer bias roller 4 in the fifth embodiment is constituted by the roller 4 whose surface layer 4a is made of a dielectric material. The surface layer 4a of the transfer bias roller 4 has, for example, a volume resistivity of 10 ⁶ to 1
Those having a thickness of 0 ¹² Ωcm and a thickness of 0.2 to 3 mm are used. As the rollers 5, 6 and 7 which come into contact with the transfer belt 3 on the downstream side of the photosensitive drum 1, metal rollers are used. When a voltage is applied from the power supply 16 to the transfer bias rollers 4 and 5, electric charges are applied to the transfer belt 3 from both transfer bias rollers 4 and 5, so that the potential of the transfer portion contacting the photosensitive drum 1 becomes stable. The toner image is maintained and good toner image transfer is performed. Charge transfer from the transfer bias rollers 4 and 5 to the transfer belt 3 is more efficient when applied by the transfer bias roller 5. Therefore, when the humidity is high, charge transfer to the transfer paper is performed from the transfer bias roller 4 on the upstream side. Difficult,
Good separation of the transfer paper at high humidity. As shown in FIG. 19, the potential distribution of the transfer belt 3 has a potential gradient that linearly changes between the portions T where the rollers 4 and 5 contact.

FIG. 16 shows a part of the twelfth embodiment of the present invention. The twelfth embodiment is the same as the eleventh embodiment.
The transfer bias roller 4 is configured to be electrically floating,
The transfer bias roller 36 is brought into contact with the back surface side of the transfer portion of the transfer belt 3 which is in contact with the photosensitive drum 1, and a voltage is applied to the transfer bias rollers 36 and 5 from the power supply 16. The surface layer of the transfer bias roller 36 is made of an elastic dielectric layer, and has a volume resistivity of 10 ⁶ for example.
A medium resistance roller having elasticity of -10 ¹² Ωcm, a thickness of 1 mm or more, and a modulus hardness of 50 ° or less is used. As shown in FIG. 19, the potential distribution of the transfer belt 3 has a potential gradient that linearly changes between the portions T where the rollers 4 and 5 contact.

From the power source 16 to the transfer bias rollers 36, 5
When a voltage is applied to the transfer belt 3 and a charge is applied to the transfer belt 3, the transfer bias roller 36,
5, the charge is satisfactorily applied to the transfer belt 3, and the defective transfer of the hollow portion of the image portion, which is likely to occur when the transfer voltage is too high, can be avoided. Further, since the surface layer of the transfer bias roller 36 has a medium resistance, it is possible to prevent the transfer bias roller 36 and the transfer belt 3 from being broken due to charge leakage, or a toner image transfer failure due to the damage. Furthermore, the charge is applied from the transfer bias rollers 36 and 5 to the transfer belt 3 by
Since it is not performed on the upstream side of the transfer section, the transfer paper is satisfactorily separated without charge injection into the transfer paper before the toner image transfer at high humidity.

In each of the above-mentioned examples, by using the transfer roller instead of the transfer belt 3, it is possible to similarly obtain stable transfer paper separating performance regardless of environmental changes.
It is possible to obtain image quality and machine quality without images such as transfer dust, traces of separation nails on transfer paper, wrinkles, and jams.

The thirteenth embodiment of the present invention relates to an image forming apparatus having a carrier which carries the toner transferred in the first transfer step and conveys it to the second transfer step. Here, the carrier is, for example, an intermediate transfer member that carries the toner image transferred from the image carrier, and conveys the toner image by rotation until it is transferred to a transfer target such as transfer paper. Have a common technical idea regarding a carrier for carrying and carrying an object to be carried. Each embodiment of the present invention in which the carrier is an intermediate transfer belt will be described below. Figure 25
Shows an outline of an electrophotographic color copying apparatus according to an embodiment of the present invention, and FIG. 26 is an enlarged view showing a portion around a photosensitive drum and an intermediate transfer belt. A color image reading device (hereinafter referred to as a color scanner) 101 includes a document table 10
The original 103 on 2 is illuminated by the illumination lamp 4, the reflected light image is formed on the color sensor 109 via the mirror groups 105 to 107 and the lens 108, and the color image information of the original is displayed for each of blue, green and red. Color-separated and read, and converted into an electrical image signal. The color sensor 109 is
In this example, blue (hereinafter referred to as B), green (hereinafter referred to as G),
It is composed of red (hereinafter referred to as R) color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three colors.
Then, B, G, obtained by the color scanner 101
The R color-separated image signal is subjected to color conversion processing by an image processing unit (not shown) on the basis of the intensity level thereof, and black (hereinafter referred to as BK
, Cyan (hereinafter C), magenta (M below)
Are referred to as “Y”) and yellow (hereinafter referred to as “Y”) color image data.

A color image recording apparatus (hereinafter referred to as a color printer) 110 forms visible images of BK, C, M and Y by the color image data from its image processing section to make a final color copy. Here, the color scanner 101 for obtaining the BK, C, M, and Y image data receives a scanner start signal in timing with the operation of the color printer 110 from the control unit, and in FIG. When the systems 105 to 107 move in the direction of the left arrow to scan the document on the document table 102,
Image data of one color is obtained each time the document is scanned. By the color scanner 101 repeating such an operation four times in total, the image processing section sequentially obtains image data of four colors of BK, C, M, and Y. Then, every time image data of each color is obtained, the color printer 102 sequentially forms a visible image from the image data and superimposes them to create a four-color full-color image.

Next, the color printer 110 will be described. The writing optical unit 111 converts the color image data from the image processing section into an optical signal and performs optical writing corresponding to the original image on the photosensitive drum 112 to form an electrostatic latent image. This writing optical unit 111
Is composed of a laser 113, a light emission drive control unit (not shown) for controlling the light emission of the laser 113, a polygon mirror 114, a motor 115 for rotating the polygon mirror 114, an f / θ lens 116, a reflection mirror 117, and the like.

The photoconductor drum 112 rotates counterclockwise as indicated by the arrow, around which the photoconductor cleaning device (including the pre-cleaning static eliminator 118) 119, the static elimination lamp 120, the charger 121, the potential sensor 122, BK
A developing device 123, a C developing device 124, an M developing device 125, a Y developing device 126, a developing density pattern detector 127, an intermediate transfer belt 128 and the like are arranged. Each developing device 123-
Reference numeral 126 denotes developing sleeves 123a, 124a, 125 which rotate by bringing the brush of the developer into contact with the surface of the photoconductor drum 112 to develop the electrostatic latent image on the photoconductor drum 112.
a, 126a and developing paddles 123b, 124b, 125 that rotate to scoop up and stir the developer inside
b, 126b and toner concentration detection sensors 123c, 124c, 125c, 1 for detecting the toner concentration of the developer.
26c and the like. In the standby state, all of the four developing devices 123 to 126 have the developing sleeves 123a and 123a.
Although the developer on 4a, 125a, 126a is in the state of cutting off (development inoperative), the order of each developing operation of the developing devices 123 to 126 (the order of forming each image of BK, C, M, Y). Is the order of developing the electrostatic latent image in the order of BK, C, M and Y. However, the order of image formation of each color is not limited to this, and may be any order.

At the start of the copying operation, the photosensitive drum 11
2 rotates and is uniformly charged by the charger 121. Then, the color scanner 1 starts the reading for obtaining the BK image data at a predetermined timing, the image processing unit obtains the BK image data from the image data from the color scanner 101, and the writing optical is performed based on the BK image data. The unit 111 performs optical writing with a laser beam on the photoconductor drum 112 to form a latent image. Hereinafter, the electrostatic latent image based on this BK image data is referred to as a BK latent image. C,
Similarly, the electrostatic latent image based on the M and Y image data is the C latent image,
These are called M latent image and Y latent image. In order to make this BK latent image developable from its tip, the developing sleeve 123a starts rotating before the tip of the latent image reaches the developing position of the BK developing device 123, and the developer is spiked. Develop the latent image with BK toner. After that, the developing operation of the BK latent image area on the photoconductor drum 112 is continued, but when the trailing edge of the latent image passes the BK developing position, the developer ears are quickly cut off on the developing sleeve 123a of the BK developing device 123. To make the development inoperative. This is completed at least before the leading edge of the C latent image by the next C image data arrives. The developer is cut off by switching the rotation direction of the developing sleeve 123a to the opposite direction to that during the developing operation. At this time, the other developing devices 124 to 126 remain in the non-developing state.

The BK toner image on the photosensitive drum 112 is
The image is transferred onto the surface of the intermediate transfer belt 128 that is driven at the same speed as the photosensitive drum 112 (hereinafter, referred to as the photosensitive drum 1).
The toner image transfer from 12 to the intermediate transfer belt 128 is referred to as belt transfer). The belt transfer is performed by applying a predetermined bias voltage to the transfer bias rollers 129 and 130 forming the electrodes while the photoconductor drum 112 and the intermediate transfer belt 128 are in contact with each other. Photoconductor drum 1
12 is a static eliminator 1 before cleaning after transferring the BK toner image
The photoconductor cleaning device 119 including 18 performs static elimination and cleaning, and is again uniformly charged by the charger 121. It should be noted that the intermediate transfer belt 128 transfers the BK, C, M, and Y toner images sequentially formed on the photoconductor drum 112 by sequentially aligning and transferring the toner images on the same surface to transfer the four-color belt. An image is formed, and then, the belt transfer image is collectively transferred to a transfer paper. The structure and operation of the intermediate transfer belt unit will be described later.

By the way, on the photosensitive drum 112 side, BK
The image forming process is followed by the C image forming process. In this C image forming process, the color scanner 101 starts reading for obtaining C image data at a predetermined timing, and the color scanner 10
The image processing unit obtains C image data from the image data from 1, and the writing optical unit 111 performs optical writing with laser light on the photosensitive drum 112 based on the C image data to form a C latent image.

The C developing device 124 is
After the trailing edge of the BK latent image has passed and before the leading edge of the C latent image has arrived, the developing sleeve 124a starts to rotate to spike the developer and develop the C latent image with C toner. . After that, the C developing device 124 continues to develop the C latent image area on the photoconductor drum 112, but at the time when the rear end portion of the C latent image passes, as in the case of the BK developing device 123, the C developing sleeve. The ear of the developer on 124a is cut off. This is also completed before the leading edge of the next M latent image arrives. The C toner image on the photoconductor drum 112 is transferred onto the surface of the intermediate transfer belt 128 which is driven at the same speed as the photoconductor drum 112. The photoconductor drum 112 includes a precleaning static eliminator 118 after the transfer of the C toner image.
Charge removal and cleaning by 19 and charging device 1 again
21 is uniformly charged.

On the photosensitive drum 112 side, the C image forming process is followed by the M image forming process. In this M image forming process, the color scanner 1 starts reading for obtaining M image data at a predetermined timing, and The image processing unit obtains M image data from the image data from the scanner 101, and based on the M image data, the writing optical unit 111 performs optical writing on the photosensitive drum 112 with laser light to form an M latent image.

The M developing device 125 is
After the trailing edge of the C latent image has passed and before the leading edge of the M latent image has arrived, the developing sleeve 125a starts to rotate to spike the developer and develop the M latent image with M toner. . After that, the M developing device 125 continues to develop the M latent image area on the photoconductor drum 112, but when the rear end of the M latent image passes, the M developing sleeve is the same as in the case of the C developing device 124. The ear of the developer on 125a is cut off. This is also completed before the leading edge of the next Y latent image arrives. Photoconductor drum 1
The M toner image on 12 is transferred onto the surface of the intermediate transfer belt 128 which is driven at the same speed as the photosensitive drum 112. The photoconductor drum 112 includes a precleaning static eliminator 118 after the transfer of the M toner image.
Charge removal and cleaning by 19 and charging device 1 again
21 is uniformly charged.

On the side of the photosensitive drum 112, the M image forming process is followed by the Y image forming process. In this Y image forming process, the color scanner 101 starts reading for obtaining Y image data at a predetermined timing, and The image processing unit obtains Y image data from the image data from the scanner 101, and based on the Y image data, the writing optical unit 111 performs optical writing on the photosensitive drum 112 with laser light to form a Y latent image.

The Y developing device 126 is
After the trailing end of the previous M latent image has passed and before the leading end of the Y latent image has arrived, the developing sleeve 126a starts to rotate so that the developer spikes and the Y latent image is developed with the Y toner. . After that, the Y developing device 126 continues to develop the Y latent image area on the photoconductor drum 112, but when the trailing end of the Y latent image passes, the Y developing sleeve is similar to the case of the M developing device 125. The ear of the developer on 126a is cut off. This is also completed after the trailing edge of the Y latent image has arrived. Y on the photoconductor drum 112
The toner image is transferred onto the surface of the intermediate transfer belt 128 which is driven at the same speed as the photosensitive drum 112.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 128 includes a driving roller 131,
The belt transfer bias rollers 129 and 130 and the driven roller groups 132 to 134 are stretched, and the drive roller 131 is driven by a drive motor (not shown) to rotate the intermediate transfer belt 128.

The belt cleaning device 135 is composed of a brush roller 135a, a rubber blade 135b, a contact / separation mechanism 135c for the intermediate transfer belt 128, and the like.
While the image and Y image are being transferred to the belt transfer bias roller 129, the brush roller 135a and the rubber blade 135b are separated from the belt transfer bias roller 129 by the contact / separation mechanism 135c.

The paper transfer unit 136 includes a paper transfer bias roller 136a and a roller cleaning blade 136.
b, a contact / separation mechanism 136c for the intermediate transfer belt 128 and the like. The paper transfer bias roller 136a is normally separated from the intermediate transfer belt 128. However, when the four-color superposed images formed on the intermediate transfer belt 128 are collectively transferred to the transfer paper, they are brought into contact with and separated from each other at a timing. It is pressed by the mechanism 136c and comes into contact with the intermediate transfer belt 128,
A predetermined bias voltage is applied to the paper transfer bias roller 136a from a bias power source, and the paper transfer bias roller 1
The four-color superimposed image on the intermediate transfer belt 128 is transferred onto a transfer sheet passing between 36a and the intermediate transfer belt 128.

In this case, the transfer paper is the transfer paper cassette 137.
~ 140 selected from the paper feed roller 141 ~
The sheet is fed to the registration roller 145 by any of 144, or is fed from the manual feed tray 146 to the sheet feeding roller 141.
Is fed to the registration roller 145, and the registration roller 145 feeds the transfer paper at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt 128 reaches the paper transfer position. By the way, the movement of the intermediate transfer belt 128 is as follows as the operation method after the belt transfer of the BK toner image of the first color is completed up to the rear end portion: the constant speed forward movement method, the skip forward movement method, and the reciprocating movement (quick movement). The return method is conceivable, but one of these methods or a method in which these are efficiently combined (in terms of copy speed or the like) according to the copy size is used.

1) -Constant speed forward movement method Even after the intermediate transfer belt 128 has transferred the BK toner image, it continues to move forward at a constant speed. The side of the photoconductor drum 112 is B on the intermediate transfer belt 128.
When the K image front end position reaches the belt transfer position of the contact portion with the photosensitive drum 112 again, an image is formed with a timing so that the front end part of the next C toner image is exactly at the belt transfer position. . As a result, the C image is accurately aligned with the BK image and is transferred onto the intermediate transfer belt 128 in an overlapping manner. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 128. Following the step in which the intermediate transfer belt 128 performs the belt transfer of the Y toner image of the fourth color, the four-color superimposed toner image is collectively transferred to the transfer paper as described above while moving forward.

2) Skip Forward Method The intermediate transfer belt 128 is separated from the photoconductive drum 112 after the belt transfer of the BK toner image is completed, and is skipped at a high speed in the forward direction to move a predetermined amount. Return to speed. Then, the intermediate transfer belt 128 is brought into contact with the photosensitive drum 112 again. The side of the photoconductor drum 112 is B on the intermediate transfer belt 128.
When the K image tip position reaches the belt transfer position again,
An image is formed with a timing so that the front end of the next C toner image will be exactly at the belt transfer position. As a result, the C image is accurately aligned with the BK image and transferred onto the belt in a superimposed manner. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 128. The intermediate transfer belt 128 is moved at a forward speed of 4 times as it is after the step of transferring the Y toner image of the fourth color.
The color-superimposed toner image is collectively transferred onto the transfer paper.

3) Reciprocating (quick return) method When the intermediate transfer belt 128 finishes the belt transfer of the BK toner image, it is separated from the photoconductor drum 112, stops the forward movement, and at the same time, returns in the reverse direction at a high speed. In this return, the front end position of the BK image on the intermediate transfer belt 128 passes through the position corresponding to the belt transfer in the reverse direction, and after moving for a preset distance, it is stopped and becomes a standby state. Next, on the side of the photoconductor drum 12, when the front end of the C toner image reaches a predetermined position before the belt transfer position, the intermediate transfer belt 128 is restarted in the forward direction and comes into contact with the photoconductor drum 112 again. . Also in this case, the condition is controlled such that the C image accurately overlaps the BK image on the intermediate transfer belt 128. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 128. Following the belt transfer process for the Y toner image of the fourth color, the intermediate transfer belt 128 moves forward at the same speed without returning, and transfers the four-color superimposed toner image to the transfer paper in a batch.

The transfer paper on which the four-color superposed toner images are collectively transferred from the intermediate transfer belt 128 is conveyed by the paper conveying unit 147 to the fixing device 148, and the fixing device 148.
Fixing roller 148 controlled to a predetermined temperature of
The toner image is fused and fixed by a and the pressure roller 148b and is carried out to the copy tray 149 as a full-color copy. Further, the photoconductor belt 112 after the belt transfer is removed by the photoconductor cleaning device 119 before the cleaning.
The charge is uniformly removed by 18, and the surface is cleaned by the brush roller 119a and the rubber blade 119b. The surface of the intermediate transfer belt 128 after the toner image is transferred to the transfer paper is cleaned by the cleaning unit 136, and at this time, the cleaning unit 13 is used.
6 is pressed by the contact / separation mechanism 136c.

At the time of repeat copying for continuous copying, the operation of the color scanner 101 and the photosensitive drum 1
Image formation on No. 12 is started following the Y (fourth color) image forming process for the first sheet, and BK for the second sheet is formed at a predetermined timing.
(First color) Proceed to the image forming process. In addition, the intermediate transfer belt 12
In step 8, the surface is cleaned by the cleaning device 135 and the second BK toner image is belt-transferred to the surface following the step of collectively transferring the four-color superimposed image onto the first transfer paper. After that, the same operation as that for the first sheet is performed, and thereafter, the same operation is performed for each sheet.

The transfer sheet cassettes 137 to 140 store transfer sheets of various sizes, and the paper feed roller 141
˜144, the transfer paper is fed to the registration roller 145 at a timing from the transfer paper cassette in which the transfer paper of the size specified by the operation panel (not shown) is stored. The manual feed tray 146 is used when feeding OHP paper or thick paper in the manual feed mode.

The above-mentioned operation is the operation in the copy mode for obtaining a full-color copy in four colors.
When obtaining a copy in the color copy mode, the same operation as described above is performed for the number of colors and the number of times designated by the operation unit. Also, in the case of the monochromatic copy mode for obtaining a monochromatic copy, only the monochromatic developing device is in the development operation (development of developer) state until the copying of a predetermined number of sheets is completed,
The intermediate transfer belt 128 is driven in the forward direction at a constant speed while being in contact with the photosensitive drum 112, and the belt cleaning unit 135 is also kept in contact with the intermediate transfer belt 128 to perform a copying operation.

In this embodiment, as shown in FIG. 22, the intermediate transfer belt 128 is brought into contact with the photosensitive drum 112 to transfer the toner image on the photosensitive drum 112 to the intermediate transfer belt 12.
Transfer to 8. At this time, the belt transfer bias roller 1
29 is arranged on the upstream side of the contact point A between the intermediate transfer belt 128 and the photosensitive drum 112, and the belt transfer bias roller 130 is arranged between the intermediate transfer belt 128 and the photosensitive drum 112.
It is arranged on the downstream side of the contact point B with. Therefore, a transfer potential is applied to a member including the belt transfer bias roller 130 provided on the outlet (downstream) side of the contact point B between the intermediate transfer belt 128 and the photosensitive drum 112, and the intermediate transfer belt 128 and the photosensitive drum 112. Belt transfer bias roller 1 provided at the entrance (upstream) side of contact point A with 112
A potential lower than the transfer potential is applied to the member composed of 30.

For example, the belt transfer bias roller 130
700V is applied to the belt transfer bias roller 12
When 0V is applied to 9, the potential gradient is generated in the contact area between the photoconductor drum 112 and the intermediate transfer belt 128 as shown in FIG. For this reason, good transfer can be performed without discharge in the pre-transfer area, and the separability of the transfer paper is improved under any environment. FIG. 24 shows a contact point A between the belt transfer bias roller 129 and the intermediate transfer belt 128.
FIG. 3 is a characteristic diagram showing the relationship between the potential of the belt transfer bias roller 129 and the contact point A of the intermediate transfer belt 128 at 300V.
When the potentials are set to the following, pre-transfer in which toner flies before the contact between the intermediate transfer belt 128 and the photoconductor drum 112 when transferring the toner image on the photoconductor drum 112 is improved, and line thickening, characters, and the like occur. Image deterioration such as blurring and deterioration of sharpness does not occur.

According to FIG. 24, by setting the potential between the belt transfer bias roller 129 and the contact point A of the intermediate transfer belt 128 to 300 V or less, the sharpness rank of the image is improved. It is also possible to set the potentials of the belt transfer bias rollers 129 and 130 to arbitrary reference potentials so that the potential between the belt transfer bias roller 129 and the contact point A of the intermediate transfer belt 128 becomes 300 V or less.

In FIG. 27, in the above embodiment, the potential of the belt transfer bias roller 129 and the rollers 131 to 134 constituting the other electrodes are grounded, and the belt transfer bias roller 129 receives a transfer potential higher than the ground potential from the transfer power source 150. A part of the embodiment in which the voltage is applied is shown. As the transfer power supply 150, a variable transfer power supply that can change the transfer potential is used. In this embodiment, the pre-transfer is improved as in the thirteenth embodiment, and the structure and the number of parts can be reduced by grounding the belt transfer bias roller 129.

FIG. 28 shows a part of another embodiment of the present invention. In this embodiment, in the embodiment shown in FIG. 27, the belt transfer bias roller 129 is electrically floated, and the belt transfer bias roller 129 is moved relative to the intermediate transfer belt 128.
The roller 151 on the upstream side of the
It is designed to be grounded. In this embodiment, the contact point A between the photosensitive drum 112 and the intermediate transfer belt 128 is greater than that when the belt transfer bias roller 129 is grounded.
Potential of the belt transfer bias roller 130 increases.
The transfer voltage applied to the can be set low.

FIG. 29 shows a part of another embodiment of the present invention. In this embodiment, in the embodiment shown in FIG. 28, a voltage lower than the voltage of the variable transfer power supply 150 is applied from the transfer power supply 152 to the belt transfer bias roller 129, which is the same as the polarity of the toner. It is the one. According to this embodiment, by applying the same voltage as the toner polarity from the transfer power supply 152 to the belt transfer bias roller 129, an electric field having a polarity opposite to that of the toner on the photosensitive drum 112 is generated. The toner on the photosensitive drum 112 is prevented from flying from the side of the intermediate transfer belt by its reverse electric field, and a good transferred image can be obtained.

FIG. 30 shows a part of another embodiment of the present invention. In this embodiment, a variable transfer power supply 153 is used instead of the transfer power supply 152 in the embodiment of FIG. According to this embodiment, as in the embodiment of FIG. 29, the same voltage as the toner polarity is applied from the variable transfer power source 153 to the belt transfer bias roller 129 so that the toner on the photosensitive drum 112 has the opposite polarity. An electric field is generated. The toner on the photosensitive drum 112 is prevented from flying from the side of the intermediate transfer belt 128 by its reverse electric field, and a good transferred image can be obtained. However, as the intermediate transfer belt 128 is used, a toner film (referred to as toner filming) 154 is formed on the surface over time, so that the effective potential of the applied voltage is lowered. Variable transfer power supply 15
By changing the output voltage of No. 3 so as to increase, it is possible to prevent the toner from flying.

FIG. 31 shows a part of another embodiment of the present invention. In this embodiment, the potential sensor 155 and the power supply controller 156 are provided and the roller 151 is omitted from the embodiment of FIG. According to this embodiment, as in the embodiment of FIG. 29, the same voltage as the toner polarity is applied from the variable transfer power source 153 to the belt transfer bias roller 129 so that the toner on the photosensitive drum 112 has the opposite polarity. An electric field is generated. The toner on the photosensitive drum 112 is prevented from flying from the side of the intermediate transfer belt by its reverse electric field, and a good transferred image can be obtained.

As the photosensitive drum 112 is used, a phenomenon occurs in which the residual potential rises due to a change with time.
Although the effective potential of the reverse electric field for preventing the toner from flying decreases due to the increase in the residual potential, the photosensitive drum 112
The power supply controller 15 detects the potential of the
By controlling the output voltage of the variable transfer power source 153 according to the detection potential of the potential sensor 155 by 6, the proper potential as the potential of the intermediate transfer belt 128 can be obtained.

FIG. 32 shows a part of another embodiment of the present invention. This embodiment differs from the embodiment of FIG. 30 in that positive and negative variable transfer power supplies 153 are provided instead of the variable transfer power supply 153, and a power supply controller 157 is provided. In the above embodiment, when a color copy is to be obtained, a toner image of each color is formed, and the toner images of the respective colors are overlapped with each other to perform color reproduction by performing the overlap transfer mode. In this example, two colors, three
In the case of obtaining a color and four-color overlapping copy, the power supply control unit switches the positive and negative variable transfer power supplies 153 by a copy mode signal from the control unit for controlling the whole of this embodiment to transfer the toner image of the first color to the photosensitive drum. In the first transfer step of transferring from 112 to the intermediate transfer belt 128, the variable transfer power source 1 is applied to the belt transfer bias roller 129 as a potential having the same polarity as the toner.
The voltage of 53- () polarity is output to the belt transfer bias roller 129. Next, the power supply controller 157 transfers the toner image of the second color from the photosensitive drum 112 to the intermediate transfer belt 12
When a potential having a polarity opposite to that of the toner is provided from the second transfer step of transferring to the intermediate transfer belt 8, the toner transferred to the intermediate transfer bell 128 in the first transfer step has a negative polarity and the intermediate transfer belt 128 has a negative polarity. Since the upper toner is scattered, the voltage of the (+) polarity of the variable transfer power supply 153a is output, that is, the potential of the intermediate transfer bell 128 is switched to the potential of 0 V or the potential of the (+) polarity, and a good image is obtained. Is obtained.

[0108]

As described above, according to the first aspect of the present invention, the photosensitive member on which a toner image is formed and the photosensitive member are brought into contact with the photosensitive member with a predetermined nip width to move the photosensitive member. A transfer target to which the toner image formed on the transfer target is transferred, transfer bias applying means for applying a predetermined transfer bias to the transfer target, and the transfer member upstream of the transfer region with respect to the transfer member. In the region up to the contact start point between the body and the transfer target, a potential gradient is applied to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer target increases. Since the potential gradient generating means is provided, good transfer can be performed, image deterioration can be prevented, and the separability of the transfer target can be improved.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer bias applying means is provided on the downstream side in the moving direction of the transfer target body with respect to the nip portion. Since the potential gradient generating means is an electrode in contact with the transferred body on the upstream side in the moving direction of the transferred body with respect to the nip portion,
The same effect as the invention according to claim 1 is obtained.

According to the invention of claim 3, in the image forming apparatus of claim 2, a bias is applied to the potential gradient generating means, and the bias applied to the potential gradient generating means is the Since the potential is such that the toner image is not transferred from the photosensitive member to the transferred member, the same effect as the invention according to claim 2 can be obtained, as compared with the case where the transfer bias is applied to the transfer bias applying unit.

According to the invention of claim 4, in the image forming apparatus of claim 2, since the potential gradient generating means is grounded, the same effect as the invention of claim 2 can be obtained.

According to a fifth aspect of the invention, in the image forming apparatus according to the fourth aspect, since the potential gradient generating means is grounded via the constant voltage element, the same as the fourth aspect of the invention. The effect is obtained.

According to the invention of claim 6, in the image forming apparatus of claim 2, since the potential gradient generating means is electrically floating, the same effect as the invention of claim 2 can be obtained. .

According to a seventh aspect of the invention, in the image forming apparatus according to the third aspect, a potential having the same polarity as that of the toner image is applied to the potential gradient generating means, and a toner is applied to the transfer bias applying means. Since the electric potential of the opposite polarity is applied, the same effect as the invention of claim 3 is obtained.

According to the invention described in claim 8, in the image forming apparatus according to claim 3 or 7, since the bias potential applied to the potential gradient generating means and / or the transfer bias applying means is variable, The same effect as the invention according to claim 33 or 7 can be obtained.

According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, there is provided a photoconductor state detection means for detecting the state of the photoconductor, and the detection result of the photoconductor state detection means is used. Accordingly, since the bias voltage applied to the potential gradient generating means is varied, good transfer can be performed, image deterioration can be prevented, and the transfer target can be separated under any environment. .

According to the invention of claim 10, claim 1
Alternatively, in the image forming apparatus described in 2,
Since the transfer paper is carried and carried by the transfer belt that is in contact with the photosensitive member with a predetermined nip width, the same effect as the invention according to claim 1 or 2 can be obtained.

According to the invention of claim 11, claim 1
10. The image forming apparatus according to claim 0, wherein the application timing of the bias potential applied to the potential gradient generating means is after the transfer paper comes into contact with the photoconductor.
The same effect as that of the invention described above can be obtained, and good transfer can be performed regardless of the change in the resistance value of the transfer belt.

According to the invention of claim 12, claim 1
0. In the image forming apparatus according to item 0, a bias is applied to the potential gradient generation means to contact the transfer belt on the upstream side of the nip portion, and the transfer paper is lower than the transfer bias before contacting the photoconductor. 11. A bias is applied to the potential gradient generating means, and after the transfer paper comes into contact with the photoconductor, a bias substantially the same as the transfer bias is applied to the potential gradient generating means. The effect is obtained.

According to the thirteenth aspect of the present invention, the photosensitive member on which the toner image is formed and the photosensitive member are brought into contact with the photosensitive member with a predetermined nip width to move and carry and convey the transfer paper. A transfer belt on which a toner image formed on the photoconductor is transferred onto a transfer paper, a transfer bias applying unit that applies a predetermined transfer bias to the transfer belt, and a transfer belt on the upstream side of the nip portion with respect to the photoconductor. In the area up to the contact start point between the photoconductor and the transfer belt, the potential of the transfer bias is increased with respect to the transfer belt as the transfer amount of the toner image from the photoconductor to the transfer paper increases. Since the potential gradient generating means for providing a gradient and the bias applying means for applying a bias to the potential gradient generating means after the transfer paper has passed the nip portion by a predetermined distance, the transfer paper separability is improved. Well, image deterioration can be prevented to be able to perform good transfer regardless of the resistance value variation of the transfer belt.

According to the invention of claim 14, claim 1
0. In the image forming apparatus according to item 0, a bias is applied to the potential gradient generation unit to contact the transfer belt on the upstream side of the nip portion, and the distance between the transfer bias application unit and the photoconductor is set to the potential. The distance between the transfer bias applying means and the photoconductor is shorter than the distance between the gradient forming means and the photoconductor, and the potential gradient forming means has a distance at which the transfer paper is conveyed by the transfer belt. Since the bias is applied after exceeding the value, the separation property of the transfer paper is good, good transfer can be performed regardless of the resistance value variation of the transfer belt, and image deterioration can be prevented.

According to the invention of claim 15, claim 1
In the image forming apparatus described in 1, 12, 13 or 14,
Since the bias application timing to the potential gradient generating means can be adjusted, the separation property of the transfer paper is good, and the transfer control of the transfer paper is good even if there is a difference between machines or a difference with time in the same machine. It is possible to prevent deterioration of the image.

According to the invention of claim 16, claim 1
In the image forming apparatus described in 1, 12, 13 or 14,
Humidity detecting means for detecting the humidity, and when the humidity becomes higher than a predetermined value by the detection signal of the humidity detecting means, the bias application timing to the potential gradient generating means is adjusted so that the humidity becomes equal to or lower than the predetermined value. In this case, since the control means that does not adjust the bias application timing to the potential gradient generation means is provided, the transfer paper can be favorably separated and transferred regardless of changes in the environment.

According to the seventeenth aspect of the present invention, the photosensitive member on which a toner image is formed and the photosensitive member are brought into contact with the photosensitive member with a predetermined nip width to move and carry and convey the transfer paper. A transfer belt to which a toner image formed on the photoconductor is transferred onto a transfer paper, and a transfer bias applying unit that contacts the transfer belt on the downstream side of the photoconductor and applies a predetermined transfer bias to the transfer belt. And a dielectric layer is provided on the surface to make contact with the transfer belt on the upstream side of the photosensitive member, and on the upstream side of the photosensitive member with respect to the nip portion, the contact between the photosensitive member and the transfer belt. In the region up to the start point, the transfer belt is provided with a potential gradient generation unit that imparts a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer sheet increases. , Turn Good separation of the paper, image deterioration can be prevented to be able to perform good transfer regardless of the resistance value variation of the transfer belt.

According to the eighteenth aspect of the present invention, the photosensitive member on which the toner image is formed and the photosensitive member are brought into contact with the photosensitive member with a predetermined nip width to move and carry and convey the transfer paper. A transfer belt to which a toner image formed on the photoconductor is transferred onto a transfer paper, and a transfer bias applying unit that contacts the transfer belt on the downstream side of the photoconductor and applies a predetermined transfer bias to the transfer belt. And an elastic dielectric layer is provided on the surface of the transfer belt to contact the back side of the transfer belt on the upstream side of the photoconductor, and to the transfer belt on the upstream side of the nip portion to the photoconductor and the photoconductor. In the area up to the contact start point with the transfer belt, with respect to the transfer belt,
Since a potential gradient generating means is provided for imparting a potential gradient to the transfer bias as the transfer amount of the toner image from the photosensitive member to the transfer sheet increases, the transfer sheet has good separability and the resistance of the transfer belt is high. It is possible to perform good transfer regardless of the value change, prevent image deterioration, and prevent damage to the electrodes or the transfer belt due to charge leakage or transfer failure due to the damage.

According to the nineteenth aspect of the present invention, the toner image on the photoconductor is moved by contacting the photoconductor on which the toner image is formed with the photoconductor with a predetermined nip width in the transfer area. A transfer target that is subjected to a plurality of transfer steps to transfer the transfer target, a first electrode that contacts the transfer target on the downstream side of the transfer region, and a first electrode that contacts the transfer target on the upstream side of the transfer region. A second electrode is applied with a transfer bias to both the first electrode and the second electrode, or to the first electrode.
A bias having the same polarity as the toner is applied to the electrode of No. 3, and a bias having the opposite polarity to the toner is applied to the second electrode when there is toner on the transfer target, so that the bias is applied to the photoconductor on the upstream side of the transfer area. In the region up to the contact start point between the photoconductor and the transfer target, the transfer is performed on the transfer target as the transfer amount of the toner image from the photoconductor to the transfer target increases. Since a means for imparting a potential gradient to the bias is provided, good transfer can be performed, image deterioration can be prevented, and the separability of the transferred material can be improved.

According to the invention of claim 20, claim 1
20. The image forming apparatus according to claim 9, wherein the transfer target is an intermediate transfer belt that directly carries toner, and carries different color toners each time a plurality of transfer steps are performed. Similar effects are obtained.

[Brief description of drawings]

FIG. 1 is a front view showing a part of a first embodiment of the present invention.

FIG. 2 is a sectional view showing the first embodiment.

FIG. 3 is a diagram showing a result of an experiment.

FIG. 4 is a front view showing a part of a second embodiment of the present invention.

FIG. 5 is a front view showing a part of a third embodiment of the present invention.

FIG. 6 is a front view showing a part of a fourth embodiment of the present invention.

FIG. 7 is a front view showing a part of a fifth embodiment of the present invention.

FIG. 8 is a front view showing a part of another embodiment of the present invention.

FIG. 9 is a timing chart of the first embodiment.

FIG. 10 is a timing chart of the third embodiment.

FIG. 11 is a timing chart of the fourth embodiment.

FIG. 12 is a timing chart of the fifth embodiment.

FIG. 13 is a block diagram showing a part of a circuit configuration of an image forming apparatus using a ninth embodiment of the present invention.

FIG. 14 is a block diagram showing a part of a circuit configuration of an image forming apparatus using a tenth embodiment of the present invention.

FIG. 15 is a front view showing a part of the eleventh embodiment of the present invention.

FIG. 16 is a front view showing a part of the twelfth embodiment of the present invention.

FIG. 17 is a schematic diagram for explaining a conventional image forming apparatus.

FIG. 18 is a schematic diagram for explaining a conventional image forming apparatus.

FIG. 19 is a characteristic diagram showing a potential distribution of the transfer belt of the first embodiment and the like.

FIG. 20 is a characteristic diagram showing the potential distribution of the transfer belt of the fourth embodiment.

FIG. 21 is a characteristic diagram showing the potential distribution of the transfer belt of the fifth embodiment.

FIG. 22 is a side view showing a part of the thirteenth embodiment of the present invention.

FIG. 23 is a diagram showing a potential gradient of the intermediate transfer belt in the example.

FIG. 24 is a characteristic diagram showing the relationship between the potential between the belt transfer bias roller and the contact point of the intermediate transfer belt and the sharpness rank of the image in the example.

FIG. 25 is a cross-sectional view showing the outline of the same example.

FIG. 26 is an enlarged view of a portion around the photosensitive drum and the intermediate transfer belt of the embodiment.

FIG. 27 is a side view showing a part of another embodiment of the present invention.

FIG. 28 is a side view showing a part of another embodiment of the present invention.

FIG. 29 is a side view showing a part of another embodiment of the present invention.

FIG. 30 is a side view showing a part of another embodiment of the present invention.

FIG. 31 is a side view showing a part of another embodiment of the present invention.

FIG. 32 is a side view showing a part of another embodiment of the present invention.

[Explanation of symbols]

 1 photoconductor 3 transfer belt 4,5 roller 8 power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Yu 1-3-6 Nakamagome, Ota-ku, Tokyo ・ Ricoh Co., Ltd. (72) Yasunori Kawaishi 1-3-3 Nakamagome, Ota-ku, Tokyo -In stock company Ricoh (72) Inventor Hideki Ueyama 1-3-6 Nakamagome, Ota-ku, Tokyo-In stock company Ricoh (72) Inventor Toshiaki Motohashi 1-3-6 Nakamagome-Tokyo Within Ricoh Company (72) Inventor Mitsuru Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Stocks In-house (72) Inventor Takashi Misasai 1-3-3 Nakamagome, Ota-ku, Tokyo Stocks Company Ricoh

Claims (20)

[Claims] 1. A photoconductor on which a toner image is formed, and a transfer body on which the toner image formed on the photoconductor is transferred by abutting and moving to the photoconductor with a predetermined nip width. A transfer bias applying means for applying a predetermined transfer bias to the transfer target, and a region upstream of the transfer region with respect to the photoconductor to a contact start point between the photoconductor and the transfer target. And a potential gradient generating means for imparting a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer target increases with respect to the transfer target. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the transfer bias applying means is an electrode that is in contact with the transfer target on the downstream side in the moving direction of the transfer target with respect to the nip portion, The image forming apparatus, wherein the potential gradient generating means is an electrode that is in contact with the transferred body on the upstream side of the nip portion in the moving direction of the transferred body. 3. The image forming apparatus according to claim 2, wherein a bias is applied to the potential gradient generating means, and the bias applied to the potential gradient generating means is applied to the transfer bias applying means. Further, the image forming apparatus is characterized in that the potential is such that transfer of the toner image from the photoconductor to the transfer target does not occur. 4. The image forming apparatus according to claim 2, wherein the potential gradient generating means is grounded. 5. The image forming apparatus according to claim 4, wherein the potential gradient generating means is grounded via a constant voltage element. 6. The image forming apparatus according to claim 2, wherein the potential gradient generating means is electrically floating. 7. The image forming apparatus according to claim 3, wherein a potential having the same polarity as the toner image is applied to the potential gradient generating means, and a potential having a reverse polarity to the toner is applied to the transfer bias applying means. An image forming apparatus characterized by the above. 8. The image forming apparatus according to claim 3, wherein the bias potential applied to the potential gradient generating means and / or the transfer bias applying means is variable. 9. The image forming apparatus according to claim 8, further comprising a photoconductor state detection means for detecting the state of the photoconductor,
An image forming apparatus, wherein a bias voltage applied to the potential gradient generating means is varied according to a detection result of the photosensitive body state detecting means. 10. The image forming apparatus according to claim 1, wherein the transfer-receiving member is a transfer paper carried and carried by a transfer belt that is in contact with the photosensitive member with a predetermined nip width. A characteristic image forming apparatus. 11. The image forming apparatus according to claim 10, wherein the bias potential applied to the potential gradient generating means is applied after the transfer paper comes into contact with the photoconductor. Forming equipment. 12. The image forming apparatus according to claim 10, wherein the potential gradient generating means is biased to come into contact with the transfer belt at an upstream side of the nip portion, and the transfer paper comes into contact with the photoconductor. Before the transfer bias, a bias lower than the transfer bias is applied to the potential gradient generating means, and after the transfer paper comes into contact with the photoconductor, a bias substantially the same as the transfer bias is applied to the potential gradient generating means. Image forming apparatus. 13. A photoconductor on which a toner image is formed, and abutting and moving the photoconductor with a predetermined nip width, carrying and carrying a transfer paper, and transferring the transfer paper onto the photoconductor. A transfer belt to which the formed toner image is transferred, a transfer bias applying unit that applies a predetermined transfer bias to the transfer belt, and an upstream side of a nip portion with respect to the photoconductor, and the photoconductor and the photoconductor. In the area up to the contact start point with the transfer belt,
With respect to the transfer belt, a potential gradient generating unit that gives a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer sheet increases, and the transfer sheet has a predetermined nip portion. An image forming apparatus comprising: a bias applying unit that applies a bias to the potential gradient generating unit after passing a distance. 14. The image forming apparatus according to claim 10, wherein the potential gradient generating means is applied with a bias and comes into contact with the transfer belt on the upstream side of the nip portion, and the transfer bias applying means and the photoconductor are connected to each other. Between the potential gradient forming means and the photoconductor,
An image forming apparatus, wherein a bias is applied to the potential gradient forming means after a distance by which the transfer paper is conveyed by the transfer belt exceeds a distance between the transfer bias applying means and the photoconductor. . 15. The image forming apparatus according to claim 11, 12, 13 or 14, wherein the bias application timing to the potential gradient generating means can be adjusted. 16. An image forming apparatus according to claim 11, 12, 13 or 14, wherein humidity detecting means for detecting the humidity, and when the humidity exceeds a predetermined value by the detection signal of the humidity detecting means. And a control unit that does not adjust the bias application timing to the potential gradient generation unit when the bias application timing to the potential gradient generation unit is adjusted and the humidity becomes a predetermined value or less. Image forming apparatus. 17. A photoconductor on which a toner image is formed, and abutting and moving the photoconductor with a predetermined nip width, carrying and carrying a transfer paper, and transferring the transfer paper onto the photoconductor. A transfer belt to which the formed toner image is transferred, a transfer bias applying unit that contacts the transfer belt on the downstream side of the photoconductor and applies a predetermined transfer bias to the transfer belt, and a dielectric layer is provided on the surface. Is contacted to the transfer belt on the upstream side of the photoconductor, and on the upstream side of the nip portion with respect to the photoconductor, to a contact start point between the photoconductor and the transfer belt, An image forming apparatus comprising: a transfer belt; and a potential gradient generating unit that imparts a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer sheet increases. 18. A photoconductor on which a toner image is formed, and abutting and moving the photoconductor with a predetermined nip width, carrying and conveying a transfer paper, and transferring the transfer paper onto the photoconductor. A transfer belt to which the formed toner image is transferred, a transfer bias applying unit that contacts the transfer belt on the downstream side of the photoconductor, and applies a predetermined transfer bias to the transfer belt, and a dielectric of an elastic body on the surface. A layer is provided to contact the back side of the transfer belt on the upstream side of the photoconductor, and to the transfer belt on the upstream side of the nip portion to the contact start point of the photoconductor and the transfer belt. In the area, a potential gradient generating means is provided on the transfer belt for imparting a potential gradient to the transfer bias as the transfer amount of the toner image from the photoconductor to the transfer paper increases. Do Image forming apparatus. 19. A photoconductor on which a toner image is formed, and a transfer process of abutting and moving the photoconductor with a predetermined nip width in a transfer region to transfer the toner image on the photoconductor a plurality of times. A transfer target to be transferred, and a first contact member that contacts the transfer target downstream of the transfer area.
Second electrode that contacts the transfer member on the upstream side of the transfer region.
When a transfer bias is applied to both the first electrode and the first electrode and the second electrode, or to the first electrode, and the transfer target has no toner, the second electrode has the same polarity as the toner. A bias is applied, and when the transfer target has toner, a bias having a polarity opposite to that of the toner is applied to the second electrode,
In the area upstream of the transfer area with respect to the photoconductor and up to the contact start point between the photoconductor and the transfer target, the toner image is transferred from the photoconductor to the transfer target with respect to the transfer target. An image forming apparatus comprising: a unit that gives the transfer bias a potential gradient as the transfer amount to the transfer body increases. 20. The image forming apparatus according to claim 19, wherein the transfer-receiving member is an intermediate transfer belt that directly carries toner, and carries different color toners for each of a plurality of transfer steps. A characteristic image forming apparatus.