JPH0594100A - Intermediate transfer type image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus of an intermediate transfer system in which a separation failure of a transfer material after secondary transfer is prevented. A secondary transfer roller 37 is controlled by a second direct current power source 39 at a constant current, and in a front end region of the transfer material 311 where an image is not formed, a subsequent image forming region is defined. Set to a value smaller than the secondary transfer current. For example, process speed 180 / sec,
When the intermediate transfer body 32 having a volume resistivity of 10 ⁹ Ω · cm is used, a current of 10 μA, which is considerably smaller than the specified value, is supplied to the secondary transfer roller 37 before the transfer material 311 reaches the secondary transfer portion. The current supplied to the secondary transfer roller 37 is maintained at 10 μA for 20 msec after the transfer material 311 reaches the secondary transfer roller 37. After 20 msec has passed, the current supplied to the secondary transfer roller 37 is set to a prescribed 100 μA suitable for secondary transfer.

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 of an electrophotographic system or an electrostatic recording system,
In particular, the present invention relates to an intermediate transfer type image forming apparatus for transferring a plurality of visible color developed images (color toner images) on an intermediate transfer body in such a manner that the images are sequentially superposed and transferred onto the transfer material. ..

[0002]

2. Description of the Related Art Conventionally, a visible developed image (toner image) formed on an image carrier is primarily transferred onto an endlessly traveling intermediate transfer member, and the primary transfer toner image on the intermediate transfer member is transferred to a sheet. In an image forming apparatus such as a copying machine or a printer that uses an intermediate transfer method in which secondary transfer is performed on a sheet-shaped transfer material, the transfer charging device is operated before the transfer material reaches the secondary transfer portion. A method of controlling the operation of the transfer charging device that applies uniform charges to the whole is adopted. By the way, when the volume resistivity of the intermediate transfer member is 10 ⁹ Ω · cm, the charge decay time is about 0.1 seconds. Therefore, for example, if the peripheral speed of the intermediate transfer member is 180 mm / sec, the leading end portion of the transfer material is About 18 mm may remain adsorbed on the intermediate transfer member even after passing through the secondary transfer portion.

[0003]

As described above, the transfer charging device is operated before the transfer material reaches the secondary transfer portion so as to apply a uniform charge to the entire transfer material. However, due to the volume resistivity and peripheral velocity of the intermediate transfer member, the charge at the front end of the transfer material is not completely attenuated even after passing through the secondary transfer portion. Therefore, there is a disadvantage that the transfer material is poorly separated.

Therefore, an object of the present invention is to provide an intermediate transfer type image forming apparatus in which the separation performance of a transfer material after transfer is improved.

[0005]

The above object can be achieved by an image forming apparatus of an intermediate transfer system according to the present invention. In summary, according to the present invention, a plurality of visible color developed images sequentially formed on an image bearing member are sequentially superposed and transferred onto an intermediate transfer member, and are collectively transferred from the intermediate transfer member to a transfer material. In an image forming apparatus of an intermediate transfer system, a contact type secondary transfer electric field forming means provided in a secondary transfer portion for collectively transferring from the intermediate transfer body to a transfer material, and a constant current control of the secondary transfer electric field forming means. And a constant current control means for controlling the secondary transfer current supplied from the constant current control means to the secondary transfer electric field forming means after a lapse of a predetermined time after the tip of the transfer material reaches the secondary transfer portion. And a control means for setting a specified current value suitable for transfer, and a current smaller than the specified current value until a predetermined time elapses after the leading edge of the transfer material reaches the secondary transfer portion. It is characterized in that it is supplied to the secondary transfer electric field forming means. The image forming apparatus of an intermediate transfer system which.

In one embodiment of the present invention, voltage detection means for detecting the voltage at the time of secondary transfer supplied from the constant current control means to the secondary transfer electric field forming means is provided.
It is detected that the tip of the transfer material reaches the secondary transfer portion by the change in the voltage detected by the voltage detection means, and after a predetermined time has elapsed after the detection of the voltage change, the secondary transfer current is changed to the specified current. Set to the value.

[0007]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are cases where the present invention is applied to an electrophotographic color laser beam printer, but the present invention is applicable to other electrophotographic printers, color image forming apparatuses such as copying machines, or It is also applicable to image forming apparatuses other than the electrophotographic system.

First, the overall construction of an electrophotographic color laser beam printer to which the present invention is applied will be described with reference to FIG. This color laser beam printer uses an OPC (organic semiconductor) photosensitive drum 21 as an image carrier.
Around the photosensitive drum 21, a pre-exposure unit 22, a primary charger 23, a laser scanner 24 for irradiating a laser beam according to a signal of each color, black, yellow,
A developing unit 25 including four developing devices BK, Y, C, and M containing cyan and magenta toners, respectively, is sequentially arranged. Although not shown, each developing device is composed of a developing cylinder and a non-magnetic blade. The developer is composed of toner and carrier, and is mixed at a constant ratio. The toner and the carrier are triboelectrically charged, so that the toner is negatively charged and the carrier is positively charged. The developer is brushed on the surface of the developing cylinder by the magnetic field of the fixed magnet, and is formed into a developer layer having a uniform thickness by the blade. A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. The toner is attracted to the bright portion of the surface of the photoconductor drum 21 by the surface potential of the photoconductor drum 21 and the negative component of the developing bias, so that the electrostatic latent image becomes a visible image. In this case, when the latent image for the yellow image is formed, only the yellow color is developed. Then, the yellow toner image formed on the photoconductor drum 21 is applied with a positive voltage from the first DC power source 38 to the primary transfer roller 33 which is an opposite electrode of the photoconductor drum 21,
A belt-shaped intermediate transfer member 32 that runs endlessly in the direction of the arrow in the figure.
Electrostatically transferred to the top. Paper feed box 6 for this primary transfer
Paper feed roller 61 above 0 is not activated. Further, at this time, since the secondary transfer roller 37 is released and separated from the intermediate transfer body 32, the yellow toner image is not transferred to the transfer material 311 and is held on the intermediate transfer body 32. As the intermediate transfer body 32 moves, the intermediate transfer body 32 is again conveyed to the primary transfer section. In this embodiment, the intermediate transfer member 32 is made of a material having a volume resistivity of 10 ⁸ to 10 ¹² Ω · cm, and the primary transfer roller 33 and the tension roller 3 are used.
It is stretched between 4 and 36 and the pressing roller 35, and travels in the direction of the arrow shown.

In this way, after the yellow toner image is transferred onto the intermediate transfer member 32, the residual toner on the photosensitive drum 21 is completely cleaned by the drum cleaner 26. Before the latent image of the next color is formed, the surface of the photosensitive drum 21 is irradiated with light from the pre-exposure means (lamp) 22 to erase the residual charge on the surface of the drum. The above-described series of processes of pre-exposure, primary charging, laser exposure, development, primary transfer, and drum cleaning are similarly repeated for cyan toner, magenta toner, and black toner. Image, magenta toner image, and black toner image of three colors are sequentially transferred in an overlapping state, and thus, the primary transfer of all four color toner images is carried in an overlapping state. ing.

When the four color toner images are transferred onto the intermediate transfer member 32, the paper feed roller 61 is operated to transfer the transfer material (paper).
311 passes through the pair of registration rollers 62 and is sent to the secondary transfer portion in synchronization with the position of the four-color image. When the transfer material 311 approaches the secondary transfer portion, the secondary transfer roller 37, which is the secondary transfer electric field forming means, is urged by an appropriate biasing means such as a spring to come into contact with the intermediate transfer body 32 and face it. Pressing roller 35 and this secondary transfer roller 37
In between, the intermediate transfer body 32 and the transfer material 311 are sandwiched together. At this time, a positive voltage is applied to the secondary transfer roller 37 from the second DC power source (constant current source) 39,
The binding force between the transfer material 311 and the toner becomes stronger than the binding force between the intermediate transfer body 32 and the toner, and the toner on the intermediate transfer body 32 adheres to the transfer material 311. The transfer material 311 is further moved to a fixing unit including a pair of fixing rollers 63.
Since each fixing roller 63 has a built-in heater lamp, when the transfer material 311 passes between the fixing rollers 63, four color toner images are simultaneously fixed by heat and pressure. The toner remaining on the intermediate transfer body 32 after the secondary transfer is removed by the intermediate transfer body cleaner 31.

The overall construction and operation of the electrophotographic color laser beam printer adopting the intermediate transfer system have been described above. Next, one embodiment of the present invention applied to this color laser beam printer will be described. Figure 2 for an example
Will be described in detail with reference to. Note that FIG. 2 mainly shows a transfer device portion of the printer, and parts and members corresponding to those in FIG. 3 are denoted by the same reference numerals and the description thereof will be omitted unless necessary.

As described above, in the present embodiment, the intermediate transfer member 32 is made of a material having a volume resistivity of 10 ⁸ to 10 ¹² Ω · cm, and is provided between the primary transfer roller 33, the tension rollers 34 and 36, and the pressing roller 35. It is stretched over and runs in the direction of the arrow shown. Now, in the primary transfer section, the intermediate transfer member 3
2 and the toner adhering surface of the photosensitive drum 21 are
Angle at the entry side (angle at which the intermediate transfer body 32 approaches)
Is θ1 and the advancing side angle (angle on the side where the intermediate transfer body 32 is separated) is θ2, in the present embodiment, θ1 <
It has the configuration of θ2. The reason for this configuration is to increase the nip width between the surface of the photosensitive drum 21 upstream of the transfer position and the intermediate transfer member 32 in order to avoid the pre-transfer before the substantial transfer area as much as possible. On the other hand, the angle formed by the transfer material 311 and the intermediate transfer body 32 in the secondary transfer portion is θ3, which is the approach side angle (angle on the side where the transfer material 311 approaches),
When the advancing side angle (angle on the side where the transfer material 311 is separated) is θ4, the configuration of θ3 <θ4 is adopted in this embodiment. The reason for this configuration is to reduce the above-mentioned pre-transfer. In order to further enhance the effect of preventing pre-transfer, θ1 and θ3 are approximately the same, and θ4 is θ for separating the transfer material.
A value larger than 2 is preferable.

As described above, the conditions for the entrance side angle and the advance side angle in the primary transfer portion and the secondary transfer portion are θ1 <
In the configuration of θ2, θ3 <θ4, the primary transfer roller 3
The voltage applied to the 3rd color is 3rd from the 2nd color from the 1st color
Gradually increase the color, and so on. Further, after the toner images of all the plurality of colors are sequentially transferred onto the intermediate transfer body 32 in an overlapping manner, they are collectively transferred from the intermediate transfer body 32 to the transfer material 311 at the secondary transfer portion. In the process, the toner image superimposed on the intermediate transfer member 32 is pressed against the transfer material 311 by the pressing roller 35 coupled to the motor 310, and the secondary transfer roller 37 is used.
A second direct current power supply 39 applies a direct current larger than the direct current applied during the transfer of the final color toner image in the primary transfer process.

By the way, when an intermediate transfer member having a large volume resistivity is used, a higher transfer voltage is required to obtain the same image transfer efficiency. If the charge potential of the intermediate transfer member is high,
After the primary transfer and the secondary transfer are completed, discharge is likely to occur. As a result, toner scattering occurs and the image is significantly deteriorated. As a countermeasure against this, there is a method of removing electricity by an AC corona discharger, but there are drawbacks such as insufficient effect, generation of ozone, complicated apparatus configuration, and cost increase.

Further, when an intermediate transfer member having a small volume resistivity is used, charged charges at the time of transfer are likely to escape through the peripheral constituent members or moisture in the air, causing disturbance of the toner image. For the above reasons, the volume resistivity of the intermediate transfer member is preferably within the range of 10 ⁸ Ω · cm to 10 ¹² Ω · cm.

Further, in this embodiment, the secondary transfer roller 37, which is a contact type secondary transfer electric field forming means, is subjected to constant current control by the second DC power source 39, and the tip of the transfer material on which the image is not formed is formed. The partial area is set to a value (including zero current) that is smaller than a prescribed proper secondary transfer current for the area where the subsequent image is formed.

Next, a specific example of the present invention will be described with reference to the timing chart of FIG. Figure 1 shows a process speed of 180 / sec and a sheet volume resistivity of 10 ⁹ Ω.
6 is a timing chart of a secondary transfer current I and a secondary transfer voltage V when a cm intermediate transfer member is used. As shown in FIG. 1, in the present example, before the transfer material 311 reaches the secondary transfer portion, the secondary transfer roller 37 receives a second DC power source 39, which is a constant current source, of 10 μA, which is considerably smaller than the specified value. Supply current. At this time, the secondary transfer voltage detected by the voltmeter 40 was 4 KV. When the transfer material 311 enters the secondary transfer portion, that is, the secondary transfer roller 37, the voltmeter 40
The voltage detected by was increased to 5 KV. For 20 msec after entering the secondary transfer roller 37,
The current supplied to the secondary transfer roller 37 is maintained at 10 μA. After 20 msec has passed, the current supplied to the secondary transfer roller 37 is set to a prescribed 100 μA suitable for secondary transfer. The rising time of the second DC power supply 39 is 0.1 ms
Therefore, when the transfer material has a tip margin of 5 mm, the tip of the image transferred to the transfer material reaches the secondary transfer portion after 28 msec from the tip of the transfer material. The reason why the secondary transfer current is set to the specified value before the leading edge of the image reaches the secondary transfer portion is in consideration of the rising time of the second DC power supply 39. As a result of setting the secondary transfer current in this way, the separation performance of the transfer material 311 is dramatically improved, and there is no defective separation of the transfer material in which the leading end of the transfer material remains adsorbed to the intermediate transfer body 32. .. Moreover, since the secondary transfer current is completely at the specified value when the front end of the image reaches the secondary transfer portion, there is no defect that the front end portion of the image causes transfer defects such as transfer omission.

It is needless to say that the numerical values in the above specific examples are merely examples, and the above numerical values may be appropriately changed depending on the process speed, the volume resistivity of the intermediate transfer member, the material of the transfer material, and the like. The secondary transfer current is initially set to zero (the second DC power source 39 is turned off), and the secondary transfer current is set to a specified value after 20 msec has elapsed after the transfer material entered the secondary transfer portion. The second DC power supply 39
May be turned on). Further, the detection that the front end of the transfer material has reached the secondary transfer portion is not only based on the above-described change in the detection voltage, but is also counted by, for example, counting the time based on the ON (operation) of the registration roller pair 62, or Can be carried out by a suitable means such as disposing the position detecting sensor at the secondary transfer portion or at a suitable position. Further, although the transfer roller is used as the secondary transfer electric field forming means in the above-mentioned embodiment, other contact type electric field forming means such as a metal sheet or a conductive brush may be used. Of course,
The present invention can be applied to an image forming apparatus such as a color copying machine or a printer having various configurations such as an electrophotographic system and an electrostatic recording system other than the above embodiment.

[0019]

As described above, according to the present invention,
Intermediate transfer that transfers the visible color development image formed on the image carrier to the intermediate transfer body and carries it, and transfers all the color developed images by superimposing on the intermediate transfer body, and then collectively transferring to the transfer material. In the image forming apparatus of the system, a contact type secondary transfer electric field forming means is used, and a constant current is controlled by a DC power source,
In addition, in the front end area where the image of the transfer material is not formed, the value is set to a value (including current zero) smaller than the proper secondary transfer current specified for the area where the image is formed thereafter. The separation performance of the material is dramatically improved, there is no separation failure where the leading edge of the transfer material remains adsorbed on the intermediate transfer body, and the secondary transfer current is completely complete when the leading edge of the image reaches the secondary transfer section. Since it is a specified value, there is a remarkable effect that the leading edge of the image does not become defective.

[Brief description of drawings]

FIG. 1 is a timing chart of a secondary transfer current and a secondary transfer voltage for explaining the features of the present invention.

FIG. 2 is a schematic configuration diagram showing a transfer device portion of an embodiment in which the present invention is applied to an electrophotographic color laser beam printer.

FIG. 3 is a schematic configuration diagram showing an overall configuration of an electrophotographic color laser beam printer to which the present invention is applied.

[Explanation of symbols]

 21 Photoreceptor Drum 32 Intermediate Transfer Body 33 Primary Transfer Roller 34, 36 Tension Roller 35 Pressing Roller 37 Secondary Transfer Roller 38, 39 DC Power Supply 40 Voltmeter 310 Motor 311 Transfer Material

Claims (2)

[Claims] 1. An intermediate transfer system in which a plurality of visible color developed images sequentially formed on an image bearing member are sequentially superposed and transferred onto an intermediate transfer member, and transferred from the intermediate transfer member to a transfer material at once. In the image forming apparatus, the contact type secondary transfer electric field forming means provided in the secondary transfer portion for transferring the intermediate transfer body to the transfer material at a time, and the constant current for controlling the secondary transfer electric field forming means with the constant current. The control means and the secondary transfer current supplied from the constant current control means to the secondary transfer electric field forming means after a lapse of a predetermined time after the leading edge of the transfer material reaches the secondary transfer portion is suitable for the secondary transfer. And a control means for setting the specified current value to a predetermined value, and a current smaller than the specified current value is applied to the secondary transfer until a predetermined time elapses after the leading edge of the transfer material reaches the secondary transfer portion. Intermediate characterized by supplying to electric field forming means Transfer type image forming apparatus. 2. A voltage detecting unit for detecting a voltage at the time of secondary transfer supplied from the constant current control unit to the secondary transfer electric field forming unit, further comprising: a voltage detecting unit for detecting a voltage detected by the voltage detecting unit. Detecting that the tip of the transfer material has reached the secondary transfer portion, and after a lapse of a predetermined time after detection of the voltage change,
The image forming apparatus according to claim 1, wherein the secondary transfer current is set to the specified current value.