JPH08328402A - Control method for image forming device - Google Patents

Abstract

PURPOSE: To reduce the amount of developer sticking to a transfer means as small as possible, to prevent the occurrence of staining on the rear side of a transfer material due to the dirt of the transfer means, to easily separate the transfer material from an image carrier and to stably carry the transfer material, as for a transfer system image forming device. CONSTITUTION: This device is provided with an image carrier 21, an image forming means for forming an image on the image carrier 21 and a transfer means 24 which is abutted opposite to the image carrier 21, the transfer material P is introduced into a transfer position T which is an abutting nip part between the image carrier 21 and the transfer means 24, a voltage is impressed on the transfer means 24 so as to transfer the image formed on the image carrier 21 to the transfer material P, and as for a voltage to be impressed on the transfer means 24, the voltage is impressed while switching a transfer voltage VHI for transferring the image formed on the image carrier 21 to the transfer material P and a voltage VNEG having a polarity opposite to that of the transfer voltage when the transfer material P passes through the transfer position T, and the voltage VNEG having the polarity opposite to that of the transfer voltage VHI, is impressed only when the transfer material P exists at the transfer position T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a transfer type image forming apparatus.

More specifically, a transferable image corresponding to desired image information is formed on an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric by an appropriate image forming means such as an electrophotographic process or an electrostatic recording process. Image is formed, and the formed image is introduced into a transfer portion, which is a contact nip portion between the image carrier and the transfer means, and a voltage is applied to the transfer means to transfer the transfer material to the transfer material. , Copy), and a control method of an image forming apparatus such as a transfer type printer / copier.

[0003]

2. Description of the Related Art In a general configuration of an image forming apparatus of this type, an image carrier is constructed as a rotary drum type, and a transfer means is a semiconductive elastic roller to form an image on the image carrier. The image forming unit has a unit for forming an electrostatic latent image on the image carrier and a unit for developing the electrostatic latent image, and is a developer image (toner) as a transferable image formed on the rotating image carrier. image)
When the transfer material reaches the transfer portion which is the contact nip portion between the image carrier and the transfer means as the image bearing member rotates, the transfer material is transferred at a timing so that the tip of the transfer material also reaches the transfer portion. It is introduced to the transfer site and nipped and conveyed.

At this time, a transfer voltage (transfer bias) is applied to the transfer means to apply a charge having a polarity opposite to that of the developer to the back surface of the transfer material to transfer the developer image on the image carrier to the transfer material (transfer). Let

The transfer material having undergone the image transfer at the transfer portion is separated from the image carrier and introduced into the fixing means to undergo the fixing processing of the transferred image.

After the image is transferred onto the transfer material, the surface of the image bearing member is cleaned by the cleaning means to remove residual adhered contaminants such as untransferred developer, and is repeatedly used for image formation.

In such an image forming apparatus, when the transfer voltage for transferring the image on the image carrier is applied to the transfer means even when the rear end of the transfer material passes through the transfer portion, the image carrier of the transfer material is formed. Separation from is not good. Therefore, an image forming apparatus has been proposed in which a transfer voltage for transferring an image on an image carrier and a voltage having a polarity opposite to that of the transfer voltage are applied by being switched when the rear end of the transfer material passes through a transfer portion. .

FIG. 6 shows a typical example of the transfer voltage control of such an image forming apparatus.

The image forming apparatus of this example is a reversal developing system in which the developing means uses a developer having a negative charging polarity, and the image carrier is negatively charged.

The control of the transfer voltage applied to the transfer means is as follows.

[0011]. During the non-sheet passing period until the front end a of the transfer material P reaches the transfer portion, the inter-sheet bias voltage V _LO that minimizes the transfer means to attract the fog developer on the image carrier to the transfer means. Is applied.

[0012]. When the front end a of the transfer material P reaches the transfer portion, application of a predetermined positive transfer positive voltage V _HI to the transfer means is started.

.. The above-mentioned transfer positive voltage V to the transfer means
The application of _HI is such that, after the front end a of the transfer material P reaches the transfer portion, the transfer material is conveyed through the transfer portion, and the transfer material P is within a predetermined distance α mm from the rear end d of the transfer material P. This is performed until the point i reaches the transcription site. During this time a
At i, a transfer positive voltage V _HI is applied to the transfer means to give a positive charge having a polarity opposite to that of the developer to the back surface of the transfer material, whereby the developer image on the image carrier side is transferred to the transfer material P side. .

.. Point i inside the rear end αmm of the transfer material P
From the time point when the toner reaches the transfer portion, the applied voltage to the transfer means is switched from the transfer positive voltage V _HI to the transfer reverse voltage V _NEG, and the application of the transfer reverse voltage V _{NEG to} the transfer means transfers the transfer material rear end d. This is done until time j after passing the part.

[0015] After that, during the paper interval in which the transfer material is not present at the transfer site, the voltage applied to the transfer means changes from the transfer reverse voltage V _NEG to the paper interval bias voltage V _LO.
Is switched to.

[0016]

However, in the above-mentioned conventional example, the trailing edge d of the transfer material passes through the transfer portion between the transfer means and the image carrier, and the transfer means comes into direct contact with the image carrier. In this state, there is a period β (d to j) in which the transfer reverse voltage V _NEG is applied to the transfer means. Therefore, during this period, the reversely fogged developer on the image carrier (the developer charged to the opposite polarity to the normal charging polarity) adheres to the transfer means, and the transfer means is soiled. The back surface of the transfer material introduced in the above was sometimes soiled.

Therefore, it is an object of the present invention to prevent the back surface of the transfer material from being soiled due to soiling of the transfer means by minimizing the amount of the developer adhering to the transfer means in the transfer type image forming apparatus. Another object of the present invention is to facilitate the separation of the transfer material and the image carrier and stabilize the transfer material transfer.

[0018]

The present invention is a control method for an image forming apparatus, which is characterized by the following configuration.

(1) An image bearing member, an image forming unit for forming an image on the image bearing member, and a transfer unit facing and abutting against the image bearing member, and a contact nip between the image bearing member and the transfer unit. The transfer material is introduced into the transfer portion, which is a part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material, and when the transfer material passes through the transfer portion, A transfer voltage for transferring the image on the image carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied, and the voltage having a polarity opposite to the transfer voltage is applied when the transfer material is present at the transfer site. A method for controlling an image forming apparatus, wherein the voltage is applied only to the image forming apparatus.

(2) An image bearing member, an image forming unit for forming an image on the image bearing member, and a transfer unit facing and abutting against the image bearing member, and a contact nip between the image bearing member and the transfer unit. The transfer material is introduced into the transfer portion, which is a part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer portion with respect to the transfer means, A transfer voltage for transferring the image on the image carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied in the vicinity of the rear end of the transfer material. A method for controlling an image forming apparatus, characterized in that the application is terminated before the edge passes through the transfer portion.

(3) An image carrier, image forming means for forming an image on the image carrier, and transfer means opposed to and abutting the image carrier, and a contact nip between the image carrier and the transfer means. The transfer material is introduced into the transfer portion, which is a part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer portion with respect to the transfer means, A transfer voltage for transferring the image on the image carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied near the tip of the transfer material. A method for controlling an image forming apparatus, characterized in that application is started after entering a transfer site.

(4) An image carrier, image forming means for forming an image on the image carrier, and transfer means opposed to and abutting the image carrier, and a contact nip between the image carrier and the transfer means. The transfer material is introduced into the transfer portion, which is a part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer portion with respect to the transfer means, A transfer voltage for transferring the image on the image carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied between the vicinity of the front end of the transfer material and the vicinity of the rear end of the transfer material to have a polarity opposite to the transfer voltage. The voltage of is to be applied near the front end of the transfer material after the front end of the transfer material has rushed into the transfer site, and is terminated near the rear end of the transfer material before the rear end of the transfer material passes through the transfer site. A control method of a characteristic image forming apparatus.

(5) Image forming means for forming an image on the image carrier has means for forming an electrostatic latent image on the image carrier and means for developing the electrostatic latent image, and the developing means is a negative device. The method for controlling an image forming apparatus according to any one of (1) to (4), which is a reversal development system using a developer having a charging polarity of.

(6) The control method of the image forming apparatus according to any one of claims 1 to 5, wherein the transfer means is a transfer roller.

[0025]

The transfer reverse voltage, which has a polarity opposite to that of the transfer voltage, is applied to the transfer means only when the transfer material is present at the transfer site, that is, more specifically, the transfer voltage and the reverse transfer voltage. When the polarity voltage is switched and applied near the rear end of the transfer material, the application is terminated before the rear end of the transfer material passes through the transfer site. In the case of switching and applying near the leading edge, the application is started after the leading edge of the transfer material has rushed into the transfer site.-The transfer voltage and the voltage of the opposite polarity to the transfer voltage are applied near the front edge of the transfer material and near the rear edge of the transfer material. In the case of switching and applying in and, application is started near the front end of the transfer material after the front end of the transfer material enters the transfer site, and near the rear end of the transfer material before the rear end of the transfer material passes through the transfer site. By ending the application, the state in which the transfer reverse voltage is applied to the transfer means does not occur in the state where the transfer means is in direct contact with the image carrier, and therefore the reverse fog developer on the image carrier is transferred. It doesn't attract to the means. Therefore, the developer adhering to the transfer means can be minimized, and the back surface of the transfer material due to the dirt of the transfer means can be prevented from being soiled.

Further, the back surface of the transfer material at the rear end portion or the front end portion or both portions corresponding to the application period of the reverse transfer voltage to the transfer means is charged to the polarity repulsive to the image carrier. The separation of the rear end portion, the front end portion, or both portions of the transfer material introduced into the transfer portion from the image carrier becomes easy, and the transfer material can be stably transported.

[0027]

【Example】

<Embodiment 1> (FIGS. 1 and 2) (1) Example of image forming apparatus FIG. 1 is a schematic view of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer (LBP) using a transfer type electrophotographic process.

Reference numeral 21 is a rotary drum type electrophotographic photosensitive member as an image bearing member. The photoconductor 21 of this example is an OPC photoconductor having a diameter of 30 mm, and is rotationally driven in the clockwise direction X indicated by an arrow at a rotational speed (process speed) of 75 mm / sec.

Reference numeral 22 is a charging means. The charging means of this example is a contact charging roller that is brought into contact with the photoconductor 21 with a predetermined pressing force, and a predetermined charging voltage is applied from the power source 22A, and the surface of the rotating photoconductor 21 is protected by the charging roller 22. Is negatively charged.

Scanning exposure L by the image-modulated laser beam output from the laser scanner 27 as the image information writing means is performed on the charged surface of the rotating photoconductor 21 to attenuate the potential of the exposed part of the photoconductor. An electrostatic latent image of image information is formed on the surface of the photoconductor. 27a is a deflecting mirror for laser light.

The potential decay portion of the electrostatic latent image is the developing device 2.
It is developed (reverse development) with the negative polarity developer (toner) of 3. 23A is a power source for applying a developing bias voltage to the developing roller of the developing device 23.

On the other hand, in the pressure contact nip portion between the photoconductive member and the semiconductive transfer roller 24 as the transfer means which is brought into contact with the photoconductive member 21 with a predetermined pressing force on the downstream side of the developing device 23 in the photoconductive member rotation direction. A transfer material (transfer paper) P as a recording material is fed and conveyed to a certain transfer site T from a paper feed mechanism section (not shown).

When the negative developer image on the surface of the rotating photoconductor reaches the transfer portion, the front end of the transfer material P arrives at the transfer portion T at the same timing so that the transfer material P is transferred from the conveying path of the paper feed mechanism. Is supplied to the transfer portion T, and at the same time, a positive transfer voltage applied from the power source 25 to the transfer roller 24 transfers the developer image on the surface of the photoconductor to the transfer material P.

The transfer material P that has passed through the transfer portion T is separated from the surface of the photosensitive member 1, introduced into a fixing device (not shown), and subjected to image fixing processing to be printed out.

Photoreceptor 21 after image transfer onto transfer material P
The surface is cleaned by removing residual contaminants such as transfer residual developer by a cleaning blade of the cleaner 28, and repeatedly used for image formation.

(2) Control of Applied Voltage to Transfer Roller A predetermined current / voltage is applied to the charging roller 22 / transfer roller 24 at a predetermined time point by power sources 22A / 25 capable of constant voltage / constant current control. It is assumed that This power supply 22A / 25 is a control circuit (CPU)
It is controlled by 26 control signals.

FIG. 2 shows a control sequence of the voltage applied to the transfer roller 24, which is performed by the control circuit 26 in this embodiment.

.. Before printing, when the pre-rotation of the photoconductor is not performed, that is, when the transfer material P is not present at the transfer portion T, the transfer roller 24 is controlled with a constant current of 3 μA, and a voltage value (detection voltage V ₀₎ generated there is detected. ) Is stored.

.. Based on the detected voltage V ₀ , the transfer positive voltage V _HI is derived by the following equation (1).

V _HI = V ₀ +1000 (V) (1). The sheet-to-sheet bias voltage V _LO (= 1 / 2V ₀ ) is applied to the transfer roller 24 during the non-sheet passing period until the front end a of the transfer material P reaches the transfer portion T. The sheet-to-sheet bias V _LO is set so as to minimize the fog toner on the photoconductor 21, which is an image carrier, from being attracted to the transfer roller 24.

.. The application of the transfer positive voltage V _HI to the transfer roller 24 is started from the time when the front end a of the transfer material P reaches the transfer site T.

[0042] The transfer positive voltage V _HI is applied to the transfer roller 24. After the tip a of the transfer material P reaches the transfer site T, the transfer material is conveyed through the transfer site T.
Transfer material point b within 5 mm from the rear end d of the transfer material P
Is carried out until it reaches the transcription site T.

.. Point b inside 5 mm of the rear end of the transfer material P
1mm from the trailing edge d of the transfer material after reaching the transfer site T
Until the inner transfer material point c reaches the transfer portion T, the voltage applied to the transfer roller 24 is the transfer positive voltage V _HI.
To the transfer reverse voltage V _NEG (= 2000 V).

[0044] Point c inside 1 mm of the rear end of the transfer material P
From the time when the transfer material reaches the transfer portion T, the trailing edge d of the transfer material P passes through the transfer portion T, and the voltage applied to the transfer roller 24 during the paper interval in which the transfer material does not exist at the transfer portion T. Is switched from the transfer reverse voltage V _NEG to the inter-sheet bias voltage V _LO .

That is, in the present embodiment, the tip a of the transfer material P which is introduced into the transfer portion T and is nipped and conveyed by the above control.
While the part of the transfer material from the rear end to 5 mm on the inner side of the rear end is being conveyed through the transfer part T, the transfer positive voltage V _HI is applied to the transfer roller 24 to reverse the negative developer to the back surface of the transfer material. By applying a positive charge of polarity, the photoconductor 2
The developer image on the first side is transferred to the transfer material P side.

After that, a point b inside the trailing edge of the transfer material P is 5 mm.
Until the rear end 1 mm inside point c passes through the transfer site T, the reverse transfer voltage V _NEG is applied to the transfer roller 24, so that the back surface of the transfer material parts b to c is in between.
A negative charge having the same polarity as that of the negatively charged photoreceptor is applied, and the transfer material rear end portions b to c repel the photoreceptor 21. This facilitates the separation of the transfer material and the photoconductor at the rear end of the transfer material, and makes it possible to stabilize the conveyance of the transfer material.

From the time when the point c 1 mm inside the rear end of the transfer material P reaches the transfer site T, the transfer site T is transferred to the transfer site P.
During the sheet interval in which the trailing edge d passes and there is no transfer material, the voltage applied to the transfer roller 24 is switched from the reverse transfer voltage V _NEG to the sheet interval bias voltage V _LO .

That is, the reverse transfer voltage V _NEG having a reverse polarity to the positive transfer voltage V _HI is applied only when the transfer material P is present at the transfer site T. In the present embodiment, the transfer material rear end d is transferred to the transfer site T. Since the application is terminated at time c before passing through the transfer roller 24, the state in which the transfer reverse voltage V _NEG is applied to the transfer roller 24 does not occur when the transfer roller 24 is in direct contact with the photoconductor 21. Therefore, the reversely fogged developer on the photoconductor 21 is not attracted to the transfer roller 24. Therefore, the developer adhering to the transfer roller 24 can be minimized, and the back surface of the transfer material can be prevented from being contaminated by the transfer roller.

<Embodiment 2> (FIG. 3) In this embodiment, the structure of the image forming apparatus is the same as that of Embodiment 1, and therefore the repetitive description will be omitted.

FIG. 3 shows a control sequence of the voltage applied to the transfer roller 24, which is performed by the control circuit 26 in this embodiment.

.. Before printing, when the front rotation of the photoconductor is not performed, that is, when the transfer material P does not exist at the transfer site T, the transfer roller 24 is controlled with a constant current of 3 μA, and a voltage value (detection voltage V ₀ ) generated there is detected. Is memorized.

.. Based on the detected voltage V ₀ , the transfer positive voltage V _HI is derived from the equation (1).

.. Then, the tip a of the transfer material P is transferred to the transfer site T.
While the paper is not passing until
The inter-sheet bias voltage V _LO (= 1 / 2V) that minimizes the fog toner on the photoconductor 21 from attracting to the transfer roller 24.
₀ ) is applied.

[0054] The application of the inter-sheet bias voltage V _{LO to} the transfer roller 24 _causes the transfer material T to be transferred to the transfer portion T at the front end a of the transfer material P.
Is reached until the transfer material point e 1 mm inside from the tip a reaches the transfer site T.

.. Point e 1 mm inside the tip of the transfer material P
To the transfer material point f, which is 5 mm inside from the tip a of the transfer material P.
Until the transfer material portions e to f pass through the transfer portion, the applied voltage to the transfer roller 24 is the transfer reverse voltage V.
_{Switched to NEG} (= 2000V).

.. After the point 5 mm inside the front end of the transfer material P reaches the transfer site T, the voltage applied to the transfer roller 24 is switched from the transfer reverse voltage V _NEG to the transfer positive voltage V _HI , and the transfer roller 24 is transferred. When the positive voltage V _HI is applied, the transfer material P is transported through the transfer site T,
The process is continued until the trailing edge d of the transfer material P reaches the transfer site T.

.. From the time when the trailing edge d of the transfer material P reaches the transfer portion T, the applied voltage to the transfer roller 24 is from the above-described transfer positive voltage V _HI during the paper interval in which the transfer material is not present at the transfer portion T. The sheet-to-sheet bias voltage V _LO is switched to.

That is, in the present embodiment, the leading edge 1 of the transfer material P introduced into the transfer site T and nipped and conveyed by the above control.
The part between the point e inside 5 mm and the tip 5 mm is the transfer site T.
While the sheet is being conveyed, a reverse transfer voltage V _NEG is applied to the transfer roller 24, so that the back surface of the transfer material portions e to f in the meantime has a negative polarity of the same polarity as the negatively charged photoreceptor. Of the transfer material and the transfer material tip portions e to f are transferred to the photoconductor 2
Repulsive with 1. This facilitates the separation of the transfer material and the photoconductor at the tip of the transfer material and stabilizes the transfer material conveyance.

After the point 5 mm inside the front end of the transfer material P reaches the transfer site T, the voltage applied to the transfer roller 24 is switched from the transfer reverse voltage V _NEG to the transfer positive voltage V _HI , and the transfer positive voltage V The application of _HI is continued until the rear end d of the transfer material P reaches the transfer site T, and a positive charge having a polarity opposite to that of the negative developer is applied to the back surface of the transfer material. As a result, the developer image on the photoconductor 21 side is transferred to the transfer material P side.

From the time when the trailing edge d of the transfer material P reaches the transfer portion T, the applied voltage to the transfer roller 24 is the transfer positive voltage V _HI during the paper interval in which the transfer material is not present at the transfer portion T. To the sheet-to-sheet bias voltage V _LO .

That is, the transfer reverse voltage V _NEG having a reverse polarity to the transfer positive voltage V _HI is applied only when the transfer material P is present at the transfer site T, and in this embodiment, the transfer reverse voltage V _NEG is transferred. Since the application is started at time e after the material tip a has entered the transfer site T, the transfer reverse voltage V _NEG is applied to the transfer roller 24 in the state where the transfer roller 24 is in direct contact with the photoconductor 21. The photoconductor 2
The reversely fogged developer on No. 1 is not attracted to the transfer roller 24. Therefore, the developer adhering to the transfer roller 24 can be minimized, and the back surface of the transfer material can be prevented from being contaminated by the transfer roller.

<Embodiment 3> (FIG. 4) In this embodiment, the structure of the image forming apparatus is the same as that of Embodiment 1, and therefore the repetitive description will be omitted.

FIG. 4 shows the control sequence of the voltage applied to the transfer roller 24, which is performed by the control circuit 26 in this embodiment.

.. Before printing, when the pre-rotation of the photoconductor is not performed, that is, when the transfer material P is not present at the transfer portion T, the transfer roller 24 is controlled with a constant current of 3 μA, and a voltage value (detection voltage V ₀₎ generated there is detected. ) Is stored.

.. Based on the detected voltage V ₀ , the transfer positive voltage V _HI is derived from the equation (1).

.. Then, the tip a of the transfer material P is transferred to the transfer site T.
During the non-sheet passing period until the sheet reaches the transfer roller 24, the inter-sheet bias voltage V _LO (= 1 / 2V) that minimizes the fog toner on the photoconductor 21 from being attracted to the transfer roller 24.
₀ ) is applied.

.. The application of the transfer positive voltage V _HI to the transfer roller 24 is started from the time when the front end a of the transfer material P reaches the transfer site T.

.. The application of the above-mentioned transfer positive voltage V _{HI to} the transfer roller 24 is such that the transfer material P is conveyed through the transfer area T after the leading edge a of the transfer material P reaches the transfer area T, and the surface of the photoconductor 21 is developed. The transfer A of the agent image is performed, the rear end of the developer image on the surface of the photoreceptor 21 is transferred to the transfer material P, and the transfer material point h 5 mm behind the rear end g of the transfer image A is the transfer portion T. It will be continued until it reaches.

.. Then, after the transfer material point h 5 mm behind the rear end g of the transfer image A reaches the transfer portion T, until the transfer material point c 1 mm inside from the transfer material rear end d reaches the transfer portion T. During the period, the voltage applied to the transfer roller 24 is changed from the transfer positive voltage V _HI to the transfer reverse voltage V _NEG (= 2).
000V).

.. Point c inside 1 mm of the rear end of the transfer material P
From the time when the transfer material reaches the transfer portion T, the trailing edge d of the transfer material P passes through the transfer portion T, and the voltage applied to the transfer roller 24 during the paper interval in which the transfer material does not exist at the transfer portion T. Is switched from the transfer reverse voltage V _NEG to the inter-sheet bias voltage V _LO .

That is, in the present embodiment, the leading edge a of the transfer material P introduced into the transfer site T and nipped and conveyed by the above control.
Transfer material point h 5 mm behind the trailing edge g of transfer image A
During the time period a to h are being transported to the transfer site T, the transfer positive voltage V _HI is applied to the transfer roller 24, and the negative charge of the negative developer and the positive charge of the reverse polarity are applied to the back surface of the transfer material. As a result, the developer image on the photoconductor 21 side is transferred to the transfer material P side.

After that, from the transfer material point h 5 mm behind the transfer image A of the transfer material P to the transfer material rear end 1 mm inside point c passing through the transfer site T, h to c are the transfer roller 24. transcription by reverse voltage V _NEG is applied to the back surface in between the transfer material portion H～c, the transfer material trailing portion negative charge charged photoreceptor same polarity is applied to the negative polarity with respect to h to c repel the photoconductor 21. This facilitates the separation of the transfer material and the photoconductor at the rear end of the transfer material, and makes it possible to stabilize the conveyance of the transfer material.

In the case of this embodiment, the reverse transfer voltage V _NEG is applied to the transfer roller 24 from the transfer material point h, which is 5 mm behind the rear end g of the transfer image A of the transfer material P, to the transfer material rear end 1 m.
Since the inside point c is set to pass the transfer portion T, a sufficient area for repelling the transfer material P from the photoconductor 21 can be secured, and the transfer material and the photoconductor at the rear end of the transfer material can be secured. Can be more easily separated, and the transfer material can be more stably conveyed.

From the time point where the point c 1 mm inside the rear end of the transfer material P reaches the transfer portion T, the transfer portion T is transferred to the transfer material P.
During the sheet interval in which the trailing edge d passes and there is no transfer material, the voltage applied to the transfer roller 24 is switched from the reverse transfer voltage V _NEG to the sheet interval bias voltage V _LO .

That is, the transfer reverse voltage V _NEG having a reverse polarity to the transfer positive voltage V _HI is applied only when the transfer material P is present at the transfer site T, and in this embodiment, the transfer material rear end d is transferred to the transfer site T. Since the application is terminated before passing through the transfer roller 24, the transfer reverse voltage V _NEG is not applied to the transfer roller 24 when the transfer roller 24 is in direct contact with the photoconductor 21. The reversely fogged developer on the body is not attracted to the transfer roller. Therefore, the developer adhering to the transfer roller 24 can be minimized, and the back surface of the transfer material can be prevented from being contaminated by the transfer roller.

<Embodiment 4> (FIG. 5) As compared with Embodiment 1 or Embodiment 3, the transfer roller 2 is provided after the transfer material front end a has entered the transfer portion T as in Embodiment 2.
4 may be combined with a sequence for starting the application of the transfer reverse voltage V _NEG .

FIG. 5 shows a sequence in which the first and second embodiments are combined.

Although each of the above embodiments is an image forming apparatus utilizing an electrophotographic process, the image carrier and the image forming principle and process for the image carrier are appropriate, and an electrostatic element using a dielectric as the image carrier is used. An image forming apparatus of a recording system or a magnetic recording system using a magnetic material as an image carrier may be used. In short, the present invention forms a transferable image corresponding to the target image information on the image carrier by an appropriate image forming means, and the formed image is transferred to a transfer portion which is a contact nip portion between the image carrier and the transfer means. The present invention can be effectively applied to a transfer type image forming apparatus in which a transfer material is introduced and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material to output an image formed product.

The image bearing member is not limited to the drum type, but may have other forms such as a rotating belt type. The transfer means is not limited to the roller type, but may be another type such as a belt type.

[0080]

According to the present invention as described above,
A transferable image corresponding to the desired image information is formed on the image carrier by an appropriate image forming means, and the formed image is introduced into a transfer portion which is a contact nip portion between the image carrier and the transfer means. In a transfer-type image forming apparatus that applies a voltage to the transfer unit to transfer the image on the image carrier to a transfer material and output an image-formed product, transfer is performed by minimizing the developer attached to the transfer unit. It is possible to prevent the back surface of the transfer material from being soiled by the soiling of the means. Further, the transfer material and the photoconductor can be easily separated, and the transfer material can be stably conveyed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an example of an image forming apparatus.

FIG. 2 is a control sequence diagram of applied voltage to the transfer roller in the first embodiment.

FIG. 3 is a control sequence diagram of applied voltage to the transfer roller in the second embodiment.

FIG. 4 is a control sequence diagram of an applied voltage to a transfer roller in the third embodiment.

FIG. 5 is a control sequence diagram of applied voltage to the transfer roller in the fourth embodiment.

FIG. 6 is a control sequence diagram of a voltage applied to a transfer roller in a conventional example.

[Explanation of symbols]

 21 image carrier (rotary drum type electrophotographic photoreceptor) 22 charging means (charging roller) 27 laser scanner L scanning exposure light L (laser beam) 23 developing device 24 transfer means (transfer roller) 22A, 23A, 25 bias voltage Applied power 26 Control circuit (CPU) 28 Cleaner P Transfer material

Claims (6)

[Claims] 1. An abutting nip portion between the image carrier and the transfer means, which has an image carrier, an image forming means for forming an image on the image carrier, and a transfer means opposed to and abutted on the image carrier. The transfer material is introduced into the transfer part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer part, the image is transferred to the transfer means. A transfer voltage for transferring the image on the carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied, and the voltage having a polarity opposite to the transfer voltage is applied only when the transfer material is present at the transfer site. A method for controlling an image forming apparatus, characterized in that the voltage is applied to the image forming apparatus. 2. An abutting nip portion between the image carrier and the transfer means, which has an image carrier, an image forming means for forming an image on the image carrier, and a transfer means opposed to and abutted on the image carrier. The transfer material is introduced into the transfer part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer part, the image is transferred to the transfer means. A transfer voltage for transferring the image on the carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied in the vicinity of the rear end of the transfer material. A method for controlling an image forming apparatus, characterized in that the application is terminated before the toner passes through the transfer site. 3. An image carrier, an image forming unit for forming an image on the image carrier, and a transfer unit facing and abutting the image carrier, and a contact nip portion between the image carrier and the transfer unit. The transfer material is introduced into the transfer part, and a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material. When the transfer material passes through the transfer part, the image is transferred to the transfer means. A transfer voltage for transferring the image on the carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are switched and applied in the vicinity of the tip of the transfer material. A method for controlling an image forming apparatus, characterized in that application is started after entering a site. 4. An abutting nip portion between the image carrier and the transfer means, which has an image carrier, an image forming means for forming an image on the image carrier, and a transfer means facing and abutting against the image carrier. The transfer material is introduced into the transfer part, a voltage is applied to the transfer means to transfer the image on the image carrier to the transfer material, and when the transfer material passes through the transfer part, the image is transferred to the transfer means. A transfer voltage for transferring the image on the carrier to the transfer material and a voltage having a polarity opposite to the transfer voltage are applied by switching between the vicinity of the front end of the transfer material and the vicinity of the rear end of the transfer material. In the vicinity of the transfer material tip, the voltage starts to be applied after the transfer material tip plunges into the transfer site,
A method for controlling an image forming apparatus, characterized in that, near the trailing edge of the transfer material, the application is terminated before the trailing edge of the transfer material passes through the transfer site. 5. An image forming means for forming an image on an image carrier,
A means for forming an electrostatic latent image on an image carrier and a means for developing the electrostatic latent image, and the developing means is a reversal developing system using a developer having a negative charging polarity. The method for controlling an image forming apparatus according to claim 1, wherein 6. The control method for an image forming apparatus according to claim 1, wherein the transfer unit is a transfer roller.