JP2002156836A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which prevents a transfer material from being stained by toner to form a satisfactory transfer image on the transfer material. SOLUTION: In the image forming device having a transfer belt device, a paper electrifying means which gives electric charge in the contact state with the transfer material to attract the transfer material to a transfer belt is constituted so that a paper electrifying bias voltage is turned on/off so as to satisfy (d1+|P/E|)/v/t/α/v, where d1 is the contact length of the paper electrifying means and P is the paper electrifying bias voltage and E is the upper limit value of the electric field by which transferred toner is not retransferred to the paper electrifying means and αis the upper limit value of the distance by which collected toner does not dirty the transfer material and t is the time of turning-on of the paper electrifying bias voltage, and thus the voltage is applied to the transfer material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer having a transfer belt device for transferring a toner image formed on an image carrier onto a transfer material.

[0002]

2. Description of the Related Art Conventionally, in a color image forming apparatus having a single image bearing member such as a photosensitive drum (hereinafter referred to as a photosensitive drum), a plurality of developing devices for superposing a toner image on the photosensitive drum are used. Is provided on the peripheral portion of the photosensitive drum, so that the drum diameter is often increased. The toner image on the photosensitive drum formed by the developing device is transferred onto a transfer material by applying a transfer voltage, and then the transfer material is separated from the photosensitive drum by applying a separation voltage from the back surface by a separator. You. However, when the drum diameter of the photosensitive drum is large, it is difficult to reliably maintain the separability, and there is a drawback in that a paper jam or the like, in which the transfer material is wound around the photosensitive drum, is likely to occur. A transfer belt device has been proposed as a technique for improving this disadvantage.

The transfer belt device rotates the transfer belt stretched by a plurality of holding rollers at the same speed as the photosensitive drum. The transfer belt device is provided with paper charging means for applying a charge to the transfer material and adsorbing the transfer material to the transfer belt by electrostatic force. The transfer material contacts the photoreceptor drum at the transfer section while being attracted to the transfer belt, and a high voltage having a polarity opposite to that of the toner is applied from a corona discharger (for transfer) disposed on the back of the transfer belt. The toner image is transferred.

The transfer belt device is used as a particularly preferable device in a color image forming apparatus in which a toner image is superimposed on a photosensitive drum and transferred to a transfer material at a time. In such a color image forming apparatus, since the drum diameter is large, sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method, and the transfer belt apparatus is superior in that more reliable separation performance is required. is there.

The paper charging means is a charge applying means (hereinafter referred to as a brush for convenience of description) comprising a grounded conductive brush or roller, and is provided on the upstream side (as viewed from the transfer section) for holding the transfer belt. At a position facing the holding roller, the transfer material is brought into contact with the rotating transfer belt by contacting the transfer material fed to the transfer belt and applying a voltage to apply a charge to the transfer material. And transport it to the transfer section.

However, if the brush is used for a long time, toner remaining on the transfer belt, toner scattered or floating in the image forming apparatus, paper dust, or the like adheres to the brush, and the transfer material is brushed. When the toner passes through the transfer member, the toner or the like attached to the brush moves to the transfer material, and there is a problem that the transfer material is stained.

In order to solve this problem, the present inventors apply a voltage to the brush before the leading end of the transfer material reaches the brush position to transfer the toner adhered to the brush onto the transfer belt and transfer the toner onto the transfer belt. An image forming apparatus for performing cleaning is disclosed in Japanese Patent Application Laid-Open No. Hei 5-249841. In this publication, the inventors of the present application turn on the voltage applied to the brush before the leading end of the transfer material reaches the position of the brush.
It has been suggested that the brush cleaning effect is enhanced by repeating / OFF.

However, if the voltage ON time is too short in order to increase the number of times of ON / OFF, there is a problem that the contaminated toner once transferred to the transfer belt is transferred again to the brush when the voltage is turned off. If the voltage ON time is too long, there is a problem that the brush collects the residual toner on the transfer belt after cleaning and becomes dirty. There is a high risk that the stain on the brush is transferred to the transfer material due to an impact when the transfer material enters.

The inventors of the present application have found that the ON time of the voltage applied to the brush before the leading end of the transfer material reaches the brush will contaminate the brush if it is too long or too short.
It was noted that it is important to grasp the optimal application time of the voltage applied to the brush.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus for forming a good transferred image on a transfer material by minimizing toner contamination of the transfer material.

[0011]

The object of the present invention can be achieved by the following constitutions.

In an image forming apparatus, a toner image obtained by developing a latent image on an image carrier is transferred onto a transfer material by a transfer belt device having a rotating transfer belt, and the transfer material is conveyed. Paper charging means for applying a charge in contact with the transfer material and adsorbing the transfer material to the transfer belt, wherein a contact length between the paper charging means and the transfer belt in a transfer material advancing direction is d1, and before the transfer material enters Is the paper charging bias voltage of P,
The upper limit of the electric field for preventing the toner transferred to the transfer belt from re-transferring to the paper charging means is E, the linear velocity of the transfer belt when the paper charging bias is applied before the transfer material enters is v, and the paper charging means applies a voltage. Even if the transfer is continued, when the upper limit value converted into the distance on the transfer material is α in order to prevent the collected toner from the transfer belt from contaminating the transfer material, the transfer material before the leading end of the transfer material enters the paper charging means. An ON / OFF operation of the paper charging bias voltage is performed so that the paper charging bias voltage ON time t satisfies (d1 + | P / E |) / v <t <α / v. An image forming apparatus configured to apply a voltage.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One example of an embodiment relating to an image forming apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a color image forming apparatus as one embodiment of the image forming apparatus of the present invention.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is obtained by applying an OPC photosensitive member on the drum, is grounded, and is driven to rotate clockwise. Reference numeral 12 denotes a scorotron charger, which applies a uniform charge of Vh to the peripheral surface of the photosensitive drum 10 by corona discharge using a grid and a corona discharge wire, which are maintained at a potential of Vg. Prior to the charging by the scorotron charger 12, in order to eliminate the history of the photoconductor up to the previous printing, exposure is performed by a pre-exposure lamp 11 using a light emitting diode or the like to eliminate the charge on the peripheral surface of the photoconductor.

Image exposure means 13 after uniformly charging the photosensitive member
Performs image exposure based on the image signal. The image exposure means 13 scans the optical path by a reflecting mirror 132 through a rotating polygon mirror 131, an fθ lens, and the like, using a laser diode (not shown) as a light emitting light source. The rotation of the photosensitive drum 10 (sub-scanning) A latent image is formed. In this embodiment, the character portion is exposed to form a reversal latent image such that the character portion has a lower potential Vs.

Around the periphery of the photoreceptor drum 10, there are provided developing units 14 each containing a developer containing a toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier. First, development of the first color is performed by the developing sleeve 141 which rotates while holding the developer with a built-in magnet. The developer consists of a carrier with ferrite as the core and an insulating resin coated around it, and a toner with polyester as the main material and a pigment according to the color, a charge control agent, silica, titanium oxide, etc. The agent is regulated to a layer thickness (developer) of 300 to 600 μm on the developing sleeve 141 by the layer forming rod, and is conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is set to 0.4 to 1.0 mm, which is larger than the layer thickness (developer), during which the AC bias of Va and the DC bias of Vd overlap. Applied. Since the DC bias Vd, the charge Vh on the drum surface, and the charge of the toner are of the same polarity, the toner that has been triggered to separate from the carrier by the AC bias Va has a charge potential Vh on the drum surface higher in potential than the DC bias Vd. Is adhered to the Vs portion having a lower potential than the DC bias Vd, and visualization (reversal development) is performed.

After the visualization of the first color is completed, the image forming process of the second color is started, and the uniform charging is again performed by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposure means 13. Is done. At this time, the charge removal by the pre-exposure lamp 11 performed in the image forming process of the first color is 1
This is not performed because the toner attached to the color image portion is scattered due to a sharp drop in the surrounding potential.

A latent image similar to that of the first color is formed on a portion of the photoconductor which has the charging potential Vh over the entire peripheral surface of the photoconductor drum 10 and has no image of the first color. Although the development is performed, in the portion where the development of the image of the first color is performed again, the latent image of Vm is formed by the toner adhered to the first color and the charge of the toner itself, and the DC bias Vd and 1 Development according to the potential difference of the latent image potential Vm of the color is performed. In the overlapping portion of the images of the first color and the second color, if the development of the first color is performed by forming a latent image having a low potential Vs, the balance between the first color and the second color is lost, so that the exposure amount of the first color is reduced. The intermediate potential may be such that the charging potential Vh on the drum> the latent image potential Vm of the first color> the low potential Vs on the drum.

For the third color and the fourth color, the same image forming process as that for the second color is performed.
A visible color image is formed.

On the other hand, a sheet feeding mechanism 22 is
The transfer material P fed by the transfer belt 30 is fed to a transfer area by a transfer belt device 30 on which a transfer belt 31 is stretched.
The multicolor image on the peripheral surface of the photosensitive drum 10 is transferred onto the transfer material P in a lump.

The transfer belt 31 is an endless rubber belt having a resistivity of 10 ⁶ to 10 ¹⁴ Ω · cm and a thickness of 0.4 to 1.0 mm, in which an FLC layer is formed on the outside of a urethane rubber substrate.

If a static elimination mechanism or the like is provided, a high resistance belt such as a film such as PET or a film coated with PET or the like may be used.

A voltage Vp is applied to a shaft 321 (no reference numeral) of the holding roller 32 on the upstream side of the holding rollers 32, 33 which stretches the transfer belt 31, and the shaft 321 (no reference numeral) is applied. 2), a conductive brush 34, which will be described in detail later, is provided as a means for charging the transfer material P with paper at a position facing the transfer belt 31. The transferred transfer material P enters between the brush 34 and the transfer belt 31 (also referred to as a paper charging unit), charges are injected into the transfer material P from the brush 34, and the transfer material P and the transfer belt 31 are transferred. And an adsorption force is generated. Thereafter, the transfer material P is transferred to the photosensitive drum 1
Nip (transfer area) formed by transfer belt 31 and transfer belt 31
35, and the corona discharger 3
6 or, alternatively, a transfer electric field is applied by a bias roller to transfer a multicolor image onto the transfer material P.

Transfer material P separated from photosensitive drum 10
Is a downstream holding roller 33 that stretches the transfer belt 31.
The shaft 331 (without reference numeral) is separated from the transfer belt 31 after being subjected to AC corona discharge by using the shaft 331 as a counter electrode or while receiving AC corona discharge. Reference numeral 37 denotes a cleaning blade for removing toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photoreceptor drum 10 about a shaft 331 (no reference numeral) of the holding roller 33 on the downstream side during the formation of the multicolor image.

The transfer material P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure rollers having a heater at least inside one roller or in the vicinity of the roller. When heat and pressure are applied between the rollers, the adhered toner melts and the transfer material P
After being fixed on the top, it is discharged out of the device.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then reaches a cleaning device 16 from a rubber material in contact with the photosensitive member. The cleaning blade 16 is scraped into the cleaning device 16 by a cleaning blade (not shown), and is discharged or stored by a screw or the like.
In addition, depending on the arrangement, the above-described static eliminator 15 can also serve as static elimination of the transfer material as shown in FIG.

The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed to the light by the pre-exposure lamp 11, and then uniformly charged by the scorotron charger 12, and enters the next image forming cycle. During the formation of the multicolor image, the cleaning blade (without reference numeral) is separated from the photoreceptor surface, and the AC neutralization by the neutralizer 15 is performed by OF.
It is kept in the F state.

FIG. 2 is a schematic diagram for explaining the structure and operation of the transfer belt device according to the present invention.
2A illustrates a state in which the transfer belt is separated from the photosensitive drum, and FIG. 2B illustrates a state in which the transfer belt is in contact with the photosensitive drum.

During image formation on the photosensitive drum 10, the transfer belt device 30 is in the state shown in FIG.
And the voltage of the bias power supply 38 of the paper charging means is not applied since the switch SW is OFF. When the image formation on the photosensitive drum 10 is completed, the transfer belt 31 rotates counterclockwise around the shaft 331 of the downstream holding roller 33 as a rotation center, and the transfer belt 31 contacts the photosensitive drum 10. At the same time, the brush 34 comes into contact with the brush 34, and the state shown in FIG. In the embodiment described here, the brush 34 is fixed. However, it is not always necessary to fix the brush 34. The brush 34 may be moved or rotated by the operation of a solenoid or the like. The brush 34 comes into contact with the transfer belt 31 separately from the contact of the photosensitive drum 10 with the transfer belt 31. The present invention has the same effect even when the brush 34 is fixed to the holding roller 32 and is always in contact with the transfer belt 31.

FIG. 3 shows ON / OFF of the paper charging bias voltage.
FIG. 5 is a timing chart for explaining the operation. As shown, the brush 34 is pressed against the transfer belt 31, and the paper charging switch SW is turned ON / OFF before the transfer material P enters the paper charging unit, and the time T (B) , The brush 34 directly contacts the moving transfer belt 31, and the subsequent time T
In (P), the transfer material P is sandwiched and conveyed between the brush 34 and the transfer belt 31. The present invention provides a time T (B),
During this time, the paper charging switch SW is turned ON / OFF. During the time T (B), the paper charging bias Vp is repeatedly turned ON / OFF, and the brush 3 is turned ON.
Reference numeral 4 is in sliding contact with the transfer belt 31, and the toner attached to the brush 34 moves and adheres to the transfer belt 31 and is carried away. After the brush 34 comes into contact with the transfer belt 31 and before the leading end of the transfer material P enters the paper charging unit, the ON / OFF operation is repeated a plurality of times. Since the toner is transferred from the transfer belt 31 to the transfer belt 31, more effects can be expected. Therefore, when the transfer material P has newly entered, the paper surface is hardly stained, and charges are injected onto the transfer material P and adhere to the transfer belt 31. On the other hand, the toner that has moved and adhered to the transfer belt 31 from the brush 34 is removed by the cleaning blade 37, and the rear surface of the transfer material P is hardly stained.

As described above, ON of the voltage applied to the brush
It is necessary to set an optimum range for the time. However, as a result of the experiment, the present inventors can obtain a good transfer image without toner contamination by setting the voltage ON time t as the following equation. I discovered that.

(D1 + | P / E |) / v <t <α / v The signs in the above equation will be described below.

T is the application time of the paper charging bias before the transfer material enters the transfer portion, and indicates the ON time of the voltage that repeats ON / OFF.

FIGS. 4A and 4B are schematic diagrams for explaining the upper limit value and the lower limit value of the paper charging bias application time t. FIG. 4A illustrates the lower limit value, and FIG. 4B illustrates the upper limit value. FIG. P is the paper charging bias voltage before the transfer material enters, and E is the upper limit of the electric field for preventing the toner having the same polarity as the bias voltage transferred to the transfer belt from being transferred again to the brush after the voltage is turned off. The value obtained in the experiment is E = 10 ⁶ V / m. | P / E |
Indicates that the paper charging bias voltage is ON as shown in FIG.
In order to prevent the toner r1 once transferred to the transfer belt 31 from flying and reattaching to the brush 34 (in the direction indicated by the dotted line) when switching from OFF to OFF, the time during which voltage application should be continued is converted into a distance. The lower limit (absolute value) of the distance from the end of the toner to the end of the brush 34. v represents the linear velocity of the transfer belt when the paper charging bias is applied before the transfer material enters the charging unit.
α is a value obtained by replacing the longest application time of the paper charging bias voltage for preventing toner contamination on the transfer material with the longest transfer distance of the transfer material, and the value obtained in an experiment described later is α =
0.1 m. That is, as shown in FIG. 4B, when the voltage is continuously applied, the brush 34 collects a very small amount of the residual toner r2 on the transfer belt 31 (the polarity of the toner is different from the voltage). In the case of the polarity, the toner r2 is accumulated near the brush 34 and then transferred to the brush 34 by the electrostatic attraction, and in other cases, the toner r2 is accumulated. There is a possibility that discriminable stain may be generated on the transfer material. To prevent this (especially suction of a different polarity toner), the longest application time of the paper charging bias voltage that does not cause the transfer material to cause the stain, that is, the longest transfer distance of the transfer material Is calculated based on an experiment. The larger the value of α, the longer the collection distance, and the larger the amount of collected toner that causes contamination.

Experimental results as shown in Table 1 were obtained when the charging means for the transfer material P was a brush.

[0038]

[Table 1]

Table 2 shows the numerical values used in the experiment of this embodiment.

[0040]

[Table 2]

When the paper charging bias application time t is calculated by inserting the numerical values shown in Table 2 into the above equation, the value of t becomes 0.087.
０．１0.134 seconds, which is consistent with the results in Table 1. Within this range, contamination of the paper charging means and the transfer material can be substantially prevented. Since a small amount of toner may adhere to the leading edge of the transfer material near the boundary value of the appropriate range, it is preferable to use a value of t close to the center of the range to obtain a preferable result.

In the embodiment described above, an example in which the brush 34 is used as the charge applying means has been described. A brush made of a number of conductive resin fibers or a number of metal wires is used for this brush, but a conductive rotating roller is used instead of the brush, and this roller is connected to an upstream holding roller 32 via a belt 31. Of course, it is also possible to cause the toner to adhere to the transfer belt 31 during the time T (B) even if toner adheres to the peripheral surface of the roller according to the present invention. Therefore, the transfer and fixing of the toner image can be performed without soiling the paper surface of the newly transferred transfer material P.

[0043]

According to the present invention, it is possible to provide an image forming apparatus which can form a good transfer image without contamination on the transfer material with a simple structure.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view illustrating a configuration of a color image forming apparatus.

FIG. 2 is a schematic diagram for explaining the configuration and operation of a transfer belt device according to the present invention.

FIG. 3 is a timing chart for explaining ON / OFF operation of a paper charging bias voltage.

FIG. 4 is a schematic diagram for explaining an upper limit value and a lower limit value of an application time t of a paper charging bias, and FIG.
FIG. 4B is a schematic diagram for explaining a lower limit, and FIG. 4B is a schematic diagram for explaining an upper limit.

[Explanation of symbols]

 Reference Signs List 30 transfer belt device 31 transfer belt 34 paper charging brush (brush) 38 bias power supply SW paper charging switch

Claims (1)

[Claims] An image forming apparatus that transfers a toner image obtained by developing a latent image on an image carrier onto a transfer material by a transfer belt device having a rotating transfer belt, and conveys the transfer material. A paper charging means for applying a charge in contact with a transfer material and adsorbing the transfer material to the transfer belt, wherein a contact length between the paper charging means and the transfer belt in a transfer material advancing direction is d1, and the transfer material is d1. The paper charging bias voltage before entry is P, the upper limit of the electric field for preventing the toner transferred to the transfer belt from re-transferring to the paper charging means is E, and the linear velocity of the transfer belt when the paper charging bias is applied before the transfer material enters. And v is the upper limit value in terms of the distance on the transfer material so that the collected toner from the transfer belt does not stain the transfer material even if the paper charging means continues to apply the voltage.
When the paper charging bias voltage ON time t before the leading end of the transfer material enters the paper charging means, the paper charging bias voltage that satisfies (d1 + | P / E |) / v <t <α / v An image forming apparatus configured to perform an ON / OFF operation of the image forming apparatus and apply a paper charging bias voltage to the entering transfer material.