JP2002072715A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming apparatus where an image defect is not caused by stabilizing secondary transfer properties simultaneously with preventing a secondary transfer separation defect by applying bias to a destaticizing member. SOLUTION: At the time of secondary transfer, secondary transfer bias is applied to a secondary transfer roller abutting on an intermediate transfer belt, constant-current control is started, and simultaneously voltage generated at the time of control is detected. When the constant-current control is finished, constant-voltage control is performed at the average voltage V1 of the generated voltage. After shifting to the constant-voltage control, bias J1 having a reverse polarity to the secondary transfer bias is applied to a destaticizing needle at constant-voltage. When transfer material (paper) reaches the secondary transfer part, a constant-voltage value is switched from V1 to V2 (=V1+V3 (loss component by paper resistance)). At the point in time when the leading edge of the paper is completely separated, destaticizing needle bias is switched to J2 (<<J1) in the midst of paper passing, and simultaneously the transfer bias is changed to the constant-current control at a current value I1 again. At trailing edge of the paper, the destaticizing needle bias is switched to J3 (=J1) and the transfer bias is switched to the constant-voltage control again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for directly transferring a toner image of one or more colors formed on an image carrier onto a transfer material, or via an intermediate transfer member as a second image carrier. The present invention relates to an image forming apparatus for transferring images to an image forming apparatus.

[0002]

2. Description of the Related Art Heretofore, there has been known an electrophotographic color image forming apparatus having an intermediate transfer member in addition to a photosensitive drum as an image carrier. This apparatus repeats a primary transfer step of temporarily transferring a toner image formed on a photosensitive drum serving as a first image carrier onto an intermediate transfer body serving as a second image carrier. After the color toner images are superimposed, the multicolor toner images are secondarily transferred collectively onto a transfer material such as paper.

FIG. 10 shows an example of a conventional color image forming apparatus using an intermediate transfer member.

This color image forming apparatus includes a photosensitive drum 101 rotatably supported in the direction of arrow R1, and black (K), magenta (M), cyan (C), and yellow are provided around the photosensitive drum 101. The four developing devices 105 and 10 containing the developer (toner) of (Y), respectively.
6, 107 and 108 are arranged. These developing devices 105 to 108 are brought into contact with the photosensitive drum 101 by contacting / separating means (not shown), and are used for developing an electrostatic latent image on the photosensitive drum 101.

The surface of the photosensitive drum 101 is uniformly charged by a charger 102, and is exposed and scanned by a laser beam 104 from a laser exposure system 103 or the like.
An electrostatic latent image is formed on the surface of the image forming device 1. This electrostatic latent image is selectively developed by the developing device 105 or the like, and is visualized as a toner image. The toner image obtained on the photosensitive drum 101 is sequentially transferred onto the intermediate transfer drum 109 by the primary transfer roller 110 at a primary transfer section where the photosensitive drum 101 and the intermediate transfer belt 109 are in contact.

The above-described formation, development, and primary transfer of the electrostatic latent image are performed for four colors of yellow, magenta, cyan, and black, and a color image in which four toner images are superimposed on the intermediate transfer belt 109 is formed. . Next, the color image is transferred onto the transfer material P which is nipped and conveyed by the secondary transfer roller 111 and the intermediate transfer belt 109.
Are transferred collectively.

Hereinafter, the primary transfer and the secondary transfer will be further described.

When the photosensitive drum 101 is, for example, an OPC (organic optical semiconductor) photosensitive member having a negative chargeability, the developing units 105 to 108 use a negative polarity for developing the latent image formed on the photosensitive drum 101. Use toner. The toner image on the photosensitive drum 101 is transferred to the primary transfer roller 110 by applying a positive transfer bias from the primary transfer bias power supply 120 to the intermediate transfer belt 109 at the primary transfer section.

The intermediate transfer belt 109 has a volume resistance of 10
^{About 9} to 10 ¹⁶ Ωcm, 100 to 200 μm thick P
VdF (polyvinylidene fluoride), nylon, PET
(Polyethylene terephthalate), polycarbonate,
An endless resin film made of polyimide or the like is used, and the resin film is placed over the secondary transfer facing 112, the driving roller 115, and the tension roller 116.

The toner image transferred onto the intermediate transfer belt 109 is carried to a secondary transfer unit as the intermediate transfer belt 109 rotates. The secondary transfer means is a secondary transfer roller 1
11, secondary transfer facing roller 112 and bias power supply 1
21. In the secondary transfer section, the intermediate transfer belt 1 is formed by a secondary transfer facing roller 112 and a secondary transfer roller 111.
09, a secondary transfer nip N2 is formed. In the secondary transfer nip N2, the toner image is transferred onto the transfer material P by applying a positive secondary transfer bias from the bias power supply 121 to the secondary transfer roller 111 at the same time as the transfer material P is sent. You.

At this time, constant current control is performed for the secondary transfer bias. The reason why the constant current control is performed is to prevent the secondary transferability from fluctuating due to the resistance unevenness of the intermediate transfer belt 109 and the secondary transfer roller 111 in the rotating circumferential direction, thereby preventing the density and color from fluctuating. In particular, in a color image forming apparatus, an image close to a solid image such as a photographic image or graphics is often output, so that prevention of such fluctuation in density and color is more important.

The secondary transfer bias power supply 121 is connected to the CPU 1
A transfer voltage corresponding to the pulse width can be output by a PWM signal having a pulse width corresponding to a desired transfer output voltage output from the power supply circuit 22, and the power supply circuit has a circuit capable of detecting the output current. When performing constant current control using this bias power supply, the pulse width of the PWM signal from the CPU 122 is gradually increased, and the pulse signal is continued until the detected signal reaches a desired current value. (Pulse width) is followed to perform constant current control. The use of this circuit makes it possible to control both the constant current and the voltage.

Thereafter, the transfer material P that has passed through the secondary transfer nip N2 is separated from the intermediate transfer belt 109 and is conveyed to a fixing device (not shown). The transfer material P that has reached the fixing device is discharged out of the image forming apparatus after the toner image transferred to the surface is melted and fixed by the action of heat and pressure of the fixing device.

On the other hand, the photosensitive drum 10 after the primary transfer is completed
Reference numeral 1 denotes a cleaner 11 for remaining primary transfer toner remaining on the surface.
9 removes and collects, and is used for the next image formation.
The intermediate transfer belt 109 after the completion of the secondary transfer process is
After the secondary transfer residual toner remaining on the surface is removed by the intermediate transfer belt cleaner 113, the charge is removed by the charge removal charger 114, and the charge is subsequently supplied to the next primary transfer process.

The image forming speed (process speed) is 10
In a high-speed machine of 0 mm / sec or more, a separation neutralizer (usually a static elimination needle (not shown)) is arranged at a secondary transfer separation position in order to separate a transfer material from the intermediate transfer belt 109, and a secondary transfer bias is applied. And a reverse polarity bias is applied. A4 ・
The same applies to A3-compatible machines that pass letter-size paper by horizontal feed. However, since the paper stitch is transverse (crossing direction) to the paper transport direction, the paper This is because the stiffness is weakened and the paper after fixing is apt to curl, thereby deteriorating the separability.

[0016]

However, the conventional image forming apparatus has the following problems.

When a transfer material after the secondary transfer is separated from the intermediate transfer belt, if a bias is applied to the charge removing needle which is a separation charge removing device, the secondary transfer bias leaks to the charge removing needle.
A phenomenon occurred in which the constant current control of the secondary transfer could not operate normally. If the secondary transfer current control is not performed normally, image defects such as white spots and scattering of the image, density unevenness and color unevenness will occur.

The phenomenon in which the secondary transfer current control is erroneously controlled by the application of the bias to the charge eliminating needle will be described below with reference to FIG. FIG. 11 shows changes in the current and voltage of the secondary transfer bias and the application timing of the static elimination needle bias (static elimination bias) at the leading end of the transfer material during full-color printing on plain paper.

First, before the transfer material reaches the secondary transfer section, the secondary transfer bias is raised to start constant current control (portion "a" in the figure). After the constant current control is performed, a bias J1 is applied to the discharging needle as the secondary transfer separation charger (b in the figure). When a bias is applied to the static elimination needle, the secondary transfer bias leaks to the static elimination needle and the secondary transfer current increases (c in FIG. 4).

When the secondary transfer current increases, the CPU determines that the secondary transfer current is flowing more than the target current amount, and adjusts the PWM pulse width in a direction to limit the current amount. The transfer output voltage is gradually reduced (d in the figure).

Thereafter, when the transfer material reaches the secondary transfer portion, the secondary transfer current decreases at a stretch due to the resistance component of the transfer material (FIG. 3E).

Then, the CPU adjusts the pulse width again until the reduced secondary transfer current reaches the target current value (f in the figure). After the secondary transfer current reaches the target current value, this time, the static elimination needle bias is switched to the bias value J2 during the paper passing (g in the figure), and thereafter, the static elimination needle bias is set to J3 at the rear end of the paper.
Continue to control until switching to. Here, the reason why the static elimination needle bias is switched to J2 is that if the static elimination needle bias for separating the leading end of the transfer material is continuously applied even during the paper passing,
This is because the bias value is too high, causing problems such as omission of secondary transfer and image scattering.

When the static elimination needle bias is switched to the bias value during paper feeding (switch to a lower bias), the secondary transfer bias that has flowed into the static elimination needle up to that point is eliminated. For this reason, the CPU determines that the current secondary transfer current has decreased (h in the figure).

Accordingly, the CPU further adjusts the PWM pulse width so as to follow this current change, and performs control so as to reach the target current value (i in the figure).

When the above control is finally performed, the CP
Depending on the delay of the feedback system between the PWM output unit and the current detection unit in U, oscillation of the secondary transfer bias may occur. Therefore, the output image is an image having density unevenness and color unevenness.

In the present apparatus, the following points can be cited as factors that greatly affect the secondary transfer bias due to the static elimination needle bias applied to the leading end of the transfer material.

In this apparatus, since the intermediate transfer belt is used as the second image carrier, the toner image is directly transferred from the photoreceptor surface to the transfer material, and the transfer material is separated as compared with the case where the transfer material is separated. Separability has deteriorated.

The cause of the deterioration of the separability of the transfer material is that there is a primary transfer step of transferring the toner image from the photosensitive member to the intermediate transfer member. This is because it is less than in comparison. The background fog of the toner greatly affects the degree of adhesion between the surface of the intermediate transfer body and the transfer material. If the amount of background fog is small, the degree of adhesion between the intermediate transfer body and the transfer material is increased, and the adhesion is increased. It will be easier.

FIG. 12 shows the results of experiments conducted by the present inventors on the difference in the fog amount on the photosensitive member and the intermediate transfer member.
FIG. 3 shows the relationship between fog amount and separability. In FIG.
The shaded area in the figure is the separable area. Here, the static elimination needle bias value is used as an index indicating the separability, and the greater the static elimination needle bias value at which separation is possible, the worse the separability. In addition, the fog amount is a value of Densitometer Tex made by Tokyo Denshoku Co., Ltd.
The measurement was performed using C-6DS.

First, FIG. 12 shows that the fog amount on the intermediate transfer member is clearly smaller than the fog amount on the photosensitive member. Next, FIG. 13 shows that the smaller the fog amount, the lower the separability (separation does not occur unless a high bias is applied to the static elimination needle).

Further, at the time of double-sided printing, an increase in the volume resistance due to the curl of the transfer material and a decrease in the water content also increases the electrostatic attraction force to the intermediate transfer member, making it difficult to separate the transfer material.

When a transfer material is separated from the photoreceptor, a high bias is applied to the static elimination needle as in the case of using the intermediate transfer member. Since a direct discharge occurs to the photoconductor,
This causes a positive memory in the photoconductor. For this reason,
Immediately after printing, charging failure occurs in a portion that was a non-sheet passing area at the time of previous printing, causing a problem that an image failure occurs.

Therefore, when the transfer material is separated from the photoreceptor, it is difficult to apply a static elimination needle bias that can surely separate the transfer material.

In the case of the present apparatus, when such a transfer material separation failure occurs, the transfer material rushes into a cleaner or the like of the intermediate transfer belt, and not only damages the intermediate transfer belt cleaner and the intermediate transfer belt but also damages the photosensitive member. There is also a possibility that other systems such as the paper feeding and feeding system may be damaged, and in the worst case, the apparatus body may fall into an irrecoverable state.

From the above situation, it becomes difficult to separate the transfer material from the intermediate transfer member unless a higher bias of the discharging needle is applied than in the case of separating the transfer material from the photosensitive drum. However, when a high static electricity removing needle bias is applied, the above-described influence on the secondary transfer bias occurs.

For this reason, a method of controlling the secondary transfer and separation which prevents the secondary transfer separation failure by applying a bias to the charge eliminating member, stabilizes the secondary transfer property, and does not cause the image failure is desired. Was.

A similar problem occurs when a black toner image on a photosensitive drum is transferred to a transfer material nipped and conveyed by a photosensitive drum as an image carrier and a transfer roller as a transfer rotating body. Yes, similarly, by applying a bias to the charge removing member, preventing transfer separation failure,
A transfer and separation control method that stabilizes transferability and does not cause image defects has been awaited.

Accordingly, an object of the present invention is to prevent a secondary transfer separation defect by applying a bias to a charge removing member, and at the same time, to stabilize a secondary transfer property and to prevent a single color or a plurality of colors from causing an image defect. To provide an image forming apparatus.

Another object of the present invention is to provide a monochromatic image forming apparatus which prevents transfer separation failure by applying a bias to a charge eliminating member, stabilizes transferability, and does not cause image failure. That is.

[0040]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which a toner image is formed, an intermediate transfer body, and a transfer for transferring the toner image on the intermediate transfer body to a transfer material after the toner image on the image carrier is transferred to the intermediate transfer body When the member and the transfer material are separated from the intermediate transfer member, in an image forming apparatus including a static elimination member that neutralizes the transfer material, when applying a static elimination bias to the static elimination member,
An image forming apparatus is characterized in that a method of controlling a transfer bias applied to the transfer member is changed.

According to the present invention, the transfer bias is initially controlled with a constant current, and the transfer bias is changed from the constant current control to the constant voltage control in conjunction with the timing of applying the charge eliminating bias to the charge eliminating member. . A voltage setting value of the transfer bias at the time of the constant voltage control is changed depending on the presence or absence of the transfer material in a transfer unit that transfers a toner image from the intermediate transfer body to a transfer material. Alternatively, the transfer bias is first controlled at a constant current with a first target current value, and the transfer bias is changed from the first target current value to a second value from the first target current value in conjunction with the timing of application of the charge eliminating bias to the charge eliminating member. To the target current value. A detecting unit configured to detect an amount of current flowing through the static elimination member; and controlling the second target current value based on the amount of current detected by the detecting unit. The second
Is controlled to a value obtained by adding the first target current value to the current amount detected by the detection means. A plurality of color toner images sequentially transferred from the image carrier to the intermediate transfer member are transferred to a transfer material by the transfer material member. A plurality of the image carriers are provided, and a plurality of color toner images sequentially transferred from the plurality of image carriers onto the intermediate transfer member are transferred to a transfer material by the transfer member.

Further, according to the present invention, there is provided an image carrier on which a toner image is formed, a transfer member for transferring the toner image on the image carrier to a transfer material, and when the transfer material is separated from the image carrier. An image forming apparatus comprising: a charge removing member for removing charge from a transfer material, wherein when applying a charge removing bias to the charge removing member, a method of controlling a transfer bias applied to the transfer member is changed. It is.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic cross-sectional view of an electrophotographic color image forming apparatus as an embodiment of the image forming apparatus of the present invention, and details thereof will be described below in order according to an image forming process.

This image forming apparatus is a full-color image forming apparatus for four colors, and includes a photosensitive drum 1 as a first image carrier, a charging means 2, an exposing means 3, a developing means 4, an intermediate transfer body unit 5, Transfer means 6 and a second transfer means 7.

In the main process of image formation, a toner image is formed on the photosensitive drum 1 by the charging means 2, exposure means 3 and developing means 4 of the image forming means, and this toner image is intermediately transferred by the first transfer means 6. This is to transfer the toner image on the intermediate transfer belt 51 of the body unit 5 and then transfer the toner image on the intermediate transfer belt 51 onto the transfer material P such as paper by the second transfer means 7. The details will be described below.

The photosensitive drum 1 as the first image carrier is
It is made up of an aluminum cylindrical base and an OPC (organic optical semiconductor) photoreceptor covering the surface thereof, and is driven to rotate in the direction of arrow R by driving means (not shown).

The charging means 2 comprises a charging roller 21 arranged in contact with the photosensitive drum 1 and a power source (not shown) for applying a charging bias thereto. In the present embodiment, the surface of the photosensitive drum 1 is uniformly charged to a negative polarity potential of -550 V by applying a bias from a charging power source to the charging roller 21.

The exposing means 3 includes a laser optical system 31, and scans with a laser beam 32 based on image information.
The surface of the photosensitive drum 1 is exposed to remove the charge on the exposed portion, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

The developing means 4 comprises four developing units 4K, 4Y, 4Y containing four color toners of black (K), yellow (Y), magenta (M), and cyan (C), respectively.
M, 4C. These developing devices 4K to 4C are arranged at a developing position facing the photosensitive drum 1 by a driving device (not shown) at the time of development, and reversely develop the electrostatic latent image on the photosensitive drum 1 with negatively charged toner (FIG. 1). In this case, the black developing device 4K is in the developing position and is being used for development).

The intermediate transfer body unit 5 has the above-described intermediate transfer belt 51 as a second image carrier as a main constituent member. The intermediate transfer belt 51 includes an elastic base layer (elastic layer).
An endless belt having an endless belt is provided so as to extend over a driving roller 52, a tension roller 53 as a driven roller, and a secondary transfer opposing roller 72.
The photosensitive drum 1 is sandwiched between the photosensitive drum 1 on the front side and the primary transfer roller 61 disposed on the back side. Between the intermediate transfer belt 51 and the photosensitive drum 1, a primary transfer nip (first transfer portion) N1 is formed in a strip along the generatrix direction of the surface of the photosensitive drum 1 (axial direction of the photosensitive drum). ing.

The first transfer means 6 is a roller-like transfer member, that is, a primary transfer roller 61, which is disposed in contact with the back surface of the intermediate transfer belt 51 at a position facing the photosensitive drum 1, and applies a primary transfer bias thereto. And a primary transfer bias power supply 62 to be applied. The black (black) toner image formed on the photosensitive drum 1 is supplied to the primary transfer roller 61 from the primary transfer bias power supply 62 by +300 to +500.
By applying a DC bias of about V, primary transfer is performed on the intermediate transfer belt 51.

After the primary transfer, the primary transfer residual toner remaining on the surface of the photosensitive drum 1 is removed by a cleaner 8.
It is used for the next yellow image formation.

The above-described series of image forming processes of charging, exposure, development, primary transfer, and cleaning are also performed for three colors of yellow, magenta, and cyan, and a color image in which four color toner images are superimposed on the intermediate transfer belt 51. To form

The primary transfer bias includes black (first color), yellow (second color), magenta (third color),
In the order of cyan (the fourth color), for example, +400 V, +6
The voltage is sequentially increased from the first color to the fourth color, such as 00V, + 700V, and + 800V.

The second transfer means 7 includes an intermediate transfer belt 51
And a secondary transfer roller 71, which is a roller-shaped secondary transfer member disposed on the front side of the printer, and a secondary transfer opposing roller 72 disposed on the rear side. The intermediate transfer belt 51 is nipped by these two rollers 71 and 72,
A band-shaped secondary transfer nip portion (second transfer portion) N2 is formed between the secondary transfer roller 71 and the intermediate transfer belt 51.

The secondary transfer roller 71 is arranged so as to be movable in the direction of the arrow K7. At the time of the secondary transfer, the secondary transfer roller 71 is brought into contact with the intermediate transfer belt 51, and a secondary transfer bias is applied from a secondary transfer bias power supply 73. . Thereby, the toner image is collectively and secondarily transferred onto the transfer material P such as paper. The transfer material that has completed the secondary transfer process is supplied to the separation / conveyance guide unit 8.
5 and reaches a fixing device (not shown).

The separation guide unit 85 includes a static elimination needle 86 disposed immediately downstream of the secondary transfer nip N2 toward the transfer path of the transfer material P, and a separation transfer guide 87 disposed downstream of the discharge needle 86. It comprises a transport roller 88 arranged on the upper surface of the guide 87 and a static elimination needle bias power supply 89 for applying a static elimination bias (static elimination needle bias) to the static elimination needle. The application of the static elimination needle bias and the secondary transfer bias
It is controlled by the CPU 78.

After the secondary transfer, the residual toner remaining on the surface of the intermediate transfer belt 51 after the secondary transfer residual toner on the surface is cleaned by the cleaning means 9 having the fur brush 91 (or a blade or the like) is removed. It is removed by the neutralizer 10.

The transfer material P on which the toner images of the four colors have been secondarily transferred by the second transfer means 7 is heated and pressed by a fixing device (not shown) to fix the toner image on the surface. Is discharged outside the image forming apparatus main body.

In the above image forming process,
The process speed Vp is set to Vp = 100 mm / sec, and the transfer material P is fed in the direction of the arrow Kp by a conveying means (not shown).

Next, the control of the secondary transfer bias and the static elimination needle bias in the present invention will be described in detail with reference to the timing chart shown in FIG.

When a four-color toner image is formed on the intermediate transfer belt 51, the toner image and the transfer material (paper) are conveyed to the secondary transfer nip portion. The roller 71 is driven in the direction of arrow K7,
It is brought into contact with the intermediate transfer belt 51 (part (1) in FIG. 2). When the contact of the secondary transfer roller 71 is completed, the CPU
A signal for outputting a bias is transmitted from 78 to a secondary transfer bias power supply (high voltage power supply) 73. In response to this signal, the bias power supply 73 applies a secondary transfer bias having a polarity opposite to that of the toner to the secondary transfer roller 71 to start constant current control ((2) in FIG. 2).

At the same time as the start of the constant current control, a voltage generated during the control in the circuit of the bias power supply 73 is detected, and the detected value is converted into a signal and transmitted to the CPU 78.

The target current value of the constant current control at this time is determined based on the surrounding environment (temperature, humidity) detected by an environment sensor (not shown). The determination is performed according to a control table (FIG. 3) recorded in the CPU 78 in advance. For example, when printing is performed in an environment of a temperature of 23.5 ° C./humidity of 60% (absolute water content of 10.5 g / m ³ ), the constant is determined from the line I1 in the graph of the control table shown in FIG. The target current value at the time of current control is determined to be I1 = 24 μA.

When the constant current control is completed, the generated voltages detected during this period are averaged, and the constant voltage control is performed with the calculated voltage V1 ((3) in FIG. 2).

After the control of the secondary transfer bias is shifted to the constant voltage control, a bias having a polarity opposite to that of the secondary transfer bias is applied to the static elimination needle at a constant voltage.

Here, the static elimination needle bias will be described.
The static elimination needle bias is divided into three parts, a transfer material front end J1, a transfer material center J2, and a transfer material rear end J3, according to the purpose, and an optimum bias is applied at each timing.

The transfer material tip discharging needle bias J1 is applied to separate the transfer material tip from the intermediate transfer belt. The transfer material center bias J2 is intended to prevent occurrence of image defects (polka dot-shaped image scattering and scattering due to static elimination needles) and to stabilize the transfer of the transfer material. Transfer material rear end bias J3
This prevents the rear end of the transfer material from being attracted to the intermediate transfer body and the rear end of the transfer material from jumping with the rotation. The bouncing of the rear end of the transfer material induces rubbing of the image at the rear end and generation of fixing wrinkles. The static elimination needle biases J1 to J3 are all applied at a constant voltage.

The ON / OFF timing and the switching timing of each of the static elimination needle biases J1, J2 and J3 in the apparatus in which the present invention was studied were set as shown below so as to achieve the effect of each bias.

ON of the transfer material tip static elimination needle bias J1:
100 msec before the leading end of the transfer material reaches the secondary transfer unit. Switching to the transfer material center charge eliminating needle bias J2: 100 msec after the transfer material leading end passes through the charge eliminating needle tip position. To the transfer material trailing end charge eliminating needle bias J3. Switching: 100 msec before the rear end of the transfer material reaches the secondary transfer section.-Static electricity removal needle bias OFF: 100 msec after the rear end of the transfer material passes the tip position of the static electricity removal needle.

The bias applied to the static elimination needle at the above timing is the same as when the secondary transfer bias is set.
Each is determined based on the control graph shown in FIG.
As can be seen from the graph, the biases J1, J2, and J3 of the static elimination needles in FIG. 4 are higher (the absolute values are larger) than the biases J1 and J3 at the leading and trailing ends.

For example, in FIG.
In an environment of 0% (absolute water content 10.5g / m3),
J1, J3 = −400 V, J2 = 0 V on the first side, and J1, J3 = −2400 V, J2 = −250 V on the second side, respectively. For this reason, at the front and rear end portions of the transfer material, the influence of the static elimination needle bias on the secondary transfer bias control increases.

When the neutralization needle bias J1 described above is applied, the bias leaks from the secondary transfer roller to the neutralization needle, so that the secondary transfer current increases. At this time, the amount of current flowing to the secondary transfer roller increases because the constant voltage control is performed for the secondary transfer bias, but the change in the amount of charge flowing to the secondary transfer opposing roller, the intermediate transfer belt, and the transfer material is changed. It is thought that there is no.

When the transfer material arrives at the secondary transfer portion, the constant voltage value of the secondary transfer bias is changed to V in accordance with the timing.
Switch to 2. The constant voltage value V2 at this time is a value obtained by adding a bias V3 that is lost due to the resistance of the transfer material (paper) to the previously applied voltage value V1, that is, V2 = V1 + V3. In the present invention, the bias value V3 lost by the resistance of the transfer material is +500 V on the first side and +1000 V on the second side.
And

The reason why V3 was set to these voltage values was that the voltage value generated as a result of performing the constant current control under the conditions of paper presence and absence, respectively, was examined by using an apparatus to which the present invention was applied. This is due to the occurrence of a voltage difference. Also the first side and 2
The reason why the voltage value of the second side is different is that the volume resistance value of the second side paper increases because the water content of the paper decreases after the fixing step.

Next, at a point in time when it is estimated that the leading end of the transfer material is sufficiently separated (after 100 msec (msec) after passing the leading end position of the discharging needle), the discharging needle bias is set to the paper center discharging needle bias J2. Switching ((4) in FIG. 2).
Since the central paper discharging needle bias J2 is much lower than the discharging needle bias J1 at the leading end of the transfer material, it hardly affects the secondary transfer bias. At this timing, the secondary transfer bias is changed to the constant current control of the current value I1 again, and the control is continued until the discharging needle bias is switched to J3 at the rear end of the paper.

On the other hand, at the rear end of the transfer material, the neutralization needle bias is switched to J3 ((5) in FIG. 2), so the secondary transfer bias is switched to constant voltage control again. As the voltage value V4 to be applied at this time, a voltage generated when constant current control is performed at the time of paper passing is detected, and a value calculated from the average value is applied. This prevents the rear end of the transfer material from jumping and causing image defects.

Thereafter, after the transfer material has passed through the secondary transfer portion,
The secondary transfer bias is turned off, the charge removing needle bias is turned off, and the secondary transfer roller is separated, and the secondary transfer process is completed.

In the present embodiment, by controlling as described above, even if the static elimination needle bias J1 is applied at the leading end of the transfer material, no problem such as uneven image density occurs.

Accordingly, the leading edge of the transfer material can be surely separated from the intermediate transfer member by the charge eliminating needle bias, and the secondary transfer bias can be stably controlled. Therefore, a good image can always be output stably.

Embodiment 2 The configuration of the apparatus of this embodiment is almost the same as that of Embodiment 1, and the description of the same parts will be omitted.

The feature of this embodiment is that the constant current control value, which has been controlled up to that point, is switched to the second control current value set in advance according to environmental conditions at the same time as the timing of applying the bias of the charge eliminating needle at the leading end of the transfer material. It is to perform current control.

In this apparatus, the control of the secondary transfer bias during the secondary transfer and the control of the static elimination needle bias are described with reference to FIG.
This will be described below based on the timing chart shown in FIG.

First, similarly to Embodiment 1, before the transfer material is conveyed to the secondary transfer nip, the secondary transfer roller is brought into contact with the intermediate transfer belt ((1) in FIG. 5). After the secondary transfer roller is brought into contact with the intermediate transfer belt, a secondary transfer bias is applied to perform constant current control ((2) in FIG. 5).
At this time, the target value of the control current is determined from the condition of the environment (temperature, humidity) data detected by the environment detection sensor using the control table of FIG. Here, the target current value of the constant current control set at this time is defined as a first target constant current value I1.

Next, when the constant current control at I1 is completed, a static elimination needle bias J1 is applied ((3) in FIG. 5).
The bias set at this time is also applied to the static elimination needle bias J1 as in the first embodiment.

When the discharging needle bias J1 is applied, the secondary transfer current increases. The amount of increase in the amount of current corresponds to the amount of current Ij flowing into the static elimination needle, using the diagram of the current flow in the secondary transfer portion in FIG. Therefore, the setting of the target current value of the secondary transfer constant current is determined by I2 (= Ie + I) shown in FIG.
j. Ie is changed to the current flowing through the secondary transfer facing roller and the intermediate transfer belt) to perform control ((4) in FIG. 5).

After changing the target constant current value to the graph of I2 and performing control, the transfer material is made to reach the secondary transfer portion ((5) in FIG. 5). When the transfer material reaches the secondary transfer portion, the secondary transfer current value decreases due to the resistance of the transfer material and the like. At this time, since the secondary transfer bias performs the constant current control, the CPU increases the secondary transfer voltage so as to supplement the reduced amount of current.

Then, after the separation of the leading end of the transfer material is finally completed, the charge eliminating needle bias J1 at the leading end of the transfer material is switched to the paper center removing needle bias J2 (FIG. 5 (6)). J
Since 2 is a very small value compared to J1 (see FIG. 4), the amount of the secondary transfer bias flowing into the static elimination needle is extremely small. Therefore, the current flowing through the secondary transfer roller decreases. Therefore, the target current value of the secondary transfer current is returned to I1 again ((7) in FIG. 5).

The above control will be described below with reference to the graph of FIG. 7 from the viewpoint of the secondary transfer current.

The four graphs Ia, Ib, I shown in FIG.
a ′ and Ib ′ show the relationship between the secondary transfer voltage and the current in the following cases.

Ia flows to the secondary transfer roller when a secondary transfer bias is applied to the secondary transfer roller in contact with the intermediate transfer belt in a state where there is no transfer material in the secondary transfer portion (no paper). Indicates the amount of current (secondary transfer current).

Ib indicates that in the state where there is no transfer material in the secondary transfer portion (no paper), a secondary transfer bias is applied to the secondary transfer roller in contact with the intermediate transfer belt, and a static elimination needle bias is applied to the static elimination needle. (When the graph is -2500 V applied)
Indicates the amount of current flowing through the secondary transfer roller (secondary transfer current + static elimination needle current).

Ia ′ indicates that when a secondary transfer bias is applied to the secondary transfer roller in contact with the intermediate transfer belt in a state where the transfer material is present in the secondary transfer portion (paper is present), Indicates the amount of current flowing (secondary transfer current).

Ib ′ indicates that in the state where the transfer material is present in the secondary transfer portion (paper is present), a secondary transfer bias is applied to the secondary transfer roller in contact with the intermediate transfer belt, and the neutralization needle bias is applied to the neutralization needle. When the voltage is applied (the graph is at the time of applying -2500 V),
Indicates the amount of current flowing through the secondary transfer roller (secondary transfer current + static elimination needle current).

In the graph in FIG. 7, the flow of control according to the conditions of each bias applied at the leading end of the transfer material is as follows.

First, the state where the secondary transfer roller is brought into contact with the intermediate transfer member and constant current control is started at the first target current value I1 is the point (1) on the graph Ia.

Next, when a static elimination needle bias is applied,
The secondary transfer current instantaneously increases, and becomes the state (2) in the graph Ib of FIG.

Then, based on the control table of FIG. 4 in which the amount of current flowing into the static elimination needle at this time is predicted and set in advance,
The target constant current value is switched to the second target current value I2.

Further, when the transfer material reaches the secondary transfer portion, the amount of the secondary transfer current tends to decrease due to the resistance of the transfer material. However, since the secondary transfer bias controls the constant current, The applied bias is controlled by increasing from Vt1 to Vt1 '((3) in the graph Ib' in FIG. 7).

On the other hand, when the transfer material starts to be discharged from the secondary transfer portion, the transfer material is separated from the intermediate transfer belt by the bias applied to the discharging needle. The transfer material separated from the intermediate transfer belt is transported on a transport guide. When the separation of the leading end of the transfer material is completed, the bias of the static elimination needle is switched from J1 to J2, so that the secondary transfer current amount is in the state of (4) in the Ia ′ graph of FIG.

When the state (4) is reached, the target constant current value of the secondary transfer bias is switched to the first target current value I1 at the same timing. As a result, the control voltage becomes Vt2, and control can be performed with the first target current value I1.

By performing control as described above, the same effect as in the first embodiment can be obtained even when the constant voltage control circuit is not used.

Therefore, the leading edge of the transfer material can be surely separated from the intermediate transfer member by the neutralization needle bias, and the secondary transfer bias can be stably controlled. Therefore, it is possible to always output a good image stably.

Embodiment 3 Still another embodiment of the present invention will be described. Since the device configuration of this embodiment is almost the same as those of the first and second embodiments, the description of the same parts will be omitted.

This embodiment is different from the first and second embodiments in that the secondary transfer high-voltage power supply (secondary transfer bias power supply) is used.
In this circuit, the amount of current flowing through the secondary transfer roller and the amount of current flowing through the static elimination needle can be detected.

The feature of this embodiment is that the amount of current of the static elimination needle when the secondary transfer bias is applied is detected, and the subsequent secondary transfer constant current control value is determined based on the detected value. On the point.

The control of the secondary transfer bias and the control of the static elimination needle bias in this apparatus will be described below with reference to the control flowchart shown in FIG.

First, just as in the first and second embodiments, immediately before the color image formed by the four color toners formed on the intermediate transfer belt is conveyed to the secondary transfer nip, the secondary transfer roller is moved to the intermediate transfer member. (Step S1). When the contact of the secondary transfer roller with the intermediate transfer member is completed, a predetermined value predicted in advance from the environment (temperature, humidity) in which the apparatus main body is installed, detected by an environment detection sensor (not shown) inside the apparatus main body. The secondary transfer bias is increased up to the transfer current value I1 (S2).

The target transfer current value under each condition is determined using the control table shown in FIG. When the secondary transfer bias reaches the target current value, the static elimination needle bias J1 is thereafter turned on (S3). However, the static elimination needle bias gradually rises in a slope shape so as to reach a target voltage value during a certain period. At this time, since the secondary transfer bias is affected in the course of the rising of the static elimination needle bias, the voltage of the static elimination needle is gradually increased, and at the same time, the amount of current flowing through the static elimination needle is detected (S4). The secondary transfer bias is controlled so that the value obtained by subtracting the charge removal needle current from the secondary transfer current becomes the target current I1 for secondary transfer current control (S5, 6).

After the secondary transfer current reaches that value, the transfer material is sent to the secondary transfer section (S7). When the transfer material enters the secondary transfer, the secondary transfer current decreases, so the secondary transfer bias is increased. At that time, when the secondary transfer bias rises, the amount of the static elimination needle current also increases, so detection of the static elimination needle current is started (S8), and the static elimination needle current is subtracted from the secondary transfer current as in the previous control. Control is performed so that the value becomes the target current value (S9, 10).

On the other hand, when the transfer material starts to be discharged from the secondary transfer portion, the transfer material starts to be separated from the intermediate transfer body by the bias applied to the static elimination needle. At the timing when the transfer material starts to be separated from the intermediate transfer belt, the static elimination needle bias is switched from J1 to J2 (S11). When the static elimination needle bias is switched to J2, the current flowing through the static elimination needle decreases, and constant current control with the target current I1 is started (S
12).

When the rear end of the transfer material reaches the secondary transfer portion,
The static elimination needle bias is switched to J3 (S13), and the secondary transfer bias is switched to the constant voltage control again in synchronization with the timing (S14). As the voltage value V4 to be applied at this time, a voltage generated when constant current control is performed at the time of paper passing is detected, and a value calculated from the average value is applied.

Thereafter, after the transfer material has passed through the secondary transfer section (S15), the secondary transfer bias is turned off (S16), the static elimination needle bias is turned off (S17), and the secondary transfer roller is separated (S15).
18) are sequentially performed to complete the secondary transfer process (S1).
9).

By controlling as described above, the secondary transfer current is calculated from the amount of current actually flowing through the static elimination needle without using a control table predicted in advance in the CPU.
The accuracy of the constant current control can be improved.

Therefore, the tip of the transfer material can be reliably separated from the intermediate transfer member by the bias of the static elimination needle, and the control of the secondary transfer bias can be stably performed. Therefore, it is possible to always output a good image stably.

Embodiment 4 FIG. 9 is a schematic structural view showing still another embodiment of the image forming apparatus of the present invention. 9, the same reference numerals as those shown in FIG. 1 indicate the same members.

In each of the first to third embodiments, a color image forming apparatus including one photosensitive drum and an intermediate transfer belt has been described. However, the present invention relates to an intermediate transfer belt 51 as shown in FIG. A plurality of photosensitive drums 1 are arranged side by side to form toner images of a plurality of colors on the plurality of photosensitive drums 1, and each toner image is primary-transferred to each photosensitive drum 1 with an intermediate transfer belt 51 interposed therebetween. The present invention can also be applied to an in-line type color image forming apparatus in which primary transfer is performed by superimposing on the intermediate transfer belt 51 by the roller 50, and then secondary transfer is collectively performed on the transfer material P by the secondary transfer roller 71.

Also in this embodiment, when the toner image is secondarily transferred to the transfer material P, and the transfer material P is separated from the intermediate transfer belt 51 while applying a charge erasing needle bias to the charge elimination needle 86,
Similar effects can be obtained by performing the same operations as in the first to third embodiments.

Further, the present invention is applicable not only to a color image forming apparatus but also to a transfer material nipped and conveyed by a photosensitive drum as an image carrier and a transfer roller (to which a transfer voltage is applied) as a transfer rotating body. The present invention is also applicable to a monochrome image forming apparatus such as a black and white image forming apparatus that transfers a black toner image on a photosensitive drum. In this case, the switching control of the bias applied to the transfer roller is linked to the timing of applying the charge-eliminating bias to the charge-eliminating member (static-elimination needle) provided downstream of the transfer roller in the transfer material transport direction.

[0121]

As described above, according to the present invention, in an image forming apparatus using an intermediate transfer member as a second image carrier, separation of a transfer material in a secondary transfer portion and secondary transfer are performed. When applying a neutralization bias to a neutralization member such as a static elimination needle at the leading end of the transfer material to balance the prevention of image defects, switch the control of the secondary transfer bias to constant voltage control, or set the target current for constant current control. Since the control to change the secondary transfer bias, such as switching the value, was performed, if the static elimination bias to the leading end of the transfer material is applied, the secondary transfer voltage does not drop even if the transfer current flows into the static elimination member. In addition, the transfer charge necessary for the secondary transfer can be supplied to the transfer material, and the secondary transfer bias control does not become unstable even if the secondary transfer current flows into the charge removing member. Further, since the discharging bias is switched when the leading end of the transfer material passes the position of the discharging member, the non-uniformity of the image density can be minimized by shifting the secondary transfer bias control to the constant current control. Therefore, stable secondary transfer separability and image quality can be secured.

Further, according to the present invention, in an image forming apparatus for directly transferring an image on an image carrier to a transfer material without using a second image carrier, the leading end of the transfer material is transferred to a charge removing member such as a charge removing needle. When applying the static elimination bias, the transfer bias was controlled by changing the transfer bias control to constant voltage control or by switching the target current value during constant current control. And the prevention of defects in the transferred image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a timing chart showing application of a secondary transfer-related bias employed in the embodiment of FIG.

FIG. 3 is an explanatory diagram showing the contents of a correspondence control table of an absolute water content and a secondary transfer control current used in the present invention.

FIG. 4 is a table showing a relationship between a secondary transfer voltage and a static elimination needle current used in the present invention.

FIG. 5 is a timing chart showing the application of a secondary transfer-related bias employed in another embodiment of the present invention.

FIG. 6 is a diagram showing a current flow around a secondary transfer.

FIG. 7 is a graph showing a relationship between a secondary transfer voltage and a secondary transfer current under each condition.

FIG. 8 is a flowchart showing each bias control employed in still another embodiment of the present invention.

FIG. 9 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

FIG. 10 is a schematic configuration diagram showing a conventional color image forming apparatus.

FIG. 11 is a timing chart of a bias showing fluctuation of a secondary transfer current and a voltage of the image forming apparatus of FIG.

FIG. 12 is a graph comparing fog amounts on a photoreceptor and an intermediate transfer member.

FIG. 13 is a graph showing the correlation between the fog amount and the static elimination needle bias (separability).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 51 intermediate transfer belt 71 secondary transfer roller 73 secondary transfer bias power supply 78 CPU 86 static elimination needle 89 static elimination needle bias power supply N2 secondary transfer nip P transfer material

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hisahiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-term (reference) 2H032 AA05 AA15 BA09 BA15 BA23 CA02 CA12 CA13 DA03

Claims (14)

[Claims] An image carrier on which a toner image is formed; an intermediate transfer member; and a toner image on the intermediate transfer member after the toner image on the image carrier is transferred to the intermediate transfer member. An image forming apparatus comprising: a transfer member for transferring to a material; and a static elimination member for neutralizing the transfer material when the transfer material is separated from the intermediate transfer body. An image forming apparatus, wherein a method of controlling a transfer bias applied to a member is changed. 2. The method according to claim 1, wherein the transfer bias is controlled by a constant current at first.
2. The image forming apparatus according to claim 1, wherein the transfer bias is changed from constant current control to constant voltage control in conjunction with the timing of applying the charge eliminating bias to the charge eliminating member. 3. The image according to claim 2, wherein a voltage set value of the transfer bias at the time of the constant voltage control is changed according to the presence or absence of the transfer material in a transfer unit that transfers a toner image from the intermediate transfer body to a transfer material. Forming equipment. 4. A constant current control of the transfer bias initially at a first target current value, and the transfer bias is adjusted to the first target current value in conjunction with the timing of application of the charge eliminating bias to the charge eliminating member. 2. The image forming apparatus according to claim 1, wherein the current value is changed from the second current value to the second target current value. 5. A detecting means for detecting an amount of current flowing through the static elimination member, and controlling the second target current value based on the amount of current detected by the detecting means.
Image forming apparatus. 6. The image forming apparatus according to claim 5, wherein said second target current value is controlled to a value obtained by adding said first target current value to a current amount detected by said detection means. 7. The image forming apparatus according to claim 1, wherein a plurality of color toner images sequentially transferred from the image carrier to the intermediate transfer member are transferred to a transfer material by the transfer material member. Image forming device. 8. A transfer material having a plurality of image carriers, and transferring a plurality of color toner images sequentially transferred from the plurality of image carriers onto the intermediate transfer member onto a transfer material by the transfer member. The image forming apparatus according to any one of Items 1 to 6, 9. An image carrier on which a toner image is formed, a transfer member for transferring the toner image on the image carrier to a transfer material,
When the transfer material is separated from the image bearing member, in an image forming apparatus having a static elimination member for static elimination of the transfer material, when applying a static elimination bias to the static elimination member, the transfer bias applied to the transfer member An image forming apparatus, wherein a control method is changed. 10. The transfer bias according to claim 9, wherein the transfer bias is first controlled with a constant current, and the transfer bias is changed from the constant current control to the constant voltage control in conjunction with the timing of applying the charge removing bias to the charge removing member. Image forming device. 11. The image according to claim 10, wherein a voltage set value of said transfer bias during said constant voltage control is changed according to the presence or absence of said transfer material in a transfer section for transferring a toner image from said intermediate transfer body to a transfer material. Forming equipment. 12. The transfer bias is first controlled at a constant current by a first target current value, and the transfer bias is set to the first target current value in conjunction with the timing of applying the charge removal bias to the charge removal member. The image forming apparatus according to claim 9, wherein the target current value is changed to a second target current value. 13. The image forming apparatus according to claim 12, further comprising detecting means for detecting an amount of current flowing through said static elimination member, and controlling said second target current value based on the amount of current detected by said detecting means. apparatus. 14. The image forming apparatus according to claim 13, wherein said second target current value is controlled to a value obtained by adding said first target current value to a current amount detected by said detecting means.