JPH065408B2 - Transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application range] The present invention supports a transfer material on a rotating transfer material carrying sheet,
A device for applying a transfer electric field to a transfer material on a transfer material carrying sheet and sequentially superposing a plurality of toner images sequentially formed on an image carrying body such as a photosensitive drum or an insulating drum on the transfer material, for example, color copying. The present invention relates to a transfer device applicable to a machine, a color printer, or the like.

[Prior art]

FIG. 4 is a schematic view of a conventional alert image forming apparatus,
After the photosensitive drum 1 as an image carrier is charged to a predetermined polarity by the corona discharger 2, information exposure I is applied to form an electrostatic latent image, and the latent image is formed in a predetermined color among the developing devices 3a, 3b, 3c. It is developed by a developing device having the above toner. On the other hand, the transfer drum 4 is a cylinder in which a transfer material carrying sheet is stretched around the peripheral opening area, and after the fed transfer material is wound around the carrying sheet, the transfer corona discharger 5 is used to transfer the transfer material on the photosensitive drum 1. The toner image is transferred onto the transfer material and the transfer material is electrostatically adsorbed onto the transfer material carrying sheet. Next, a latent image based on different information exposure is formed on the photosensitive drum 1 and is developed by a developing device of a predetermined color, and the obtained toner image is aligned on the transfer material with the previously transferred toner image. Transcribe. When the transfer of the toner images of the three colors is completed in this way, the separating claw 10 moves to the transfer drum 4
And the transfer material on the transfer material carrying sheet comes close to the transfer drum 4.
Then, the transfer material is separated by a conveyor belt 11 and conveyed to a fixing device to be heated and fixed to obtain a color image. However, conventionally, when the toner images of a plurality of colors that are sequentially formed on the image carrier that is the photosensitive drum 1 by this type of color transfer device are sequentially superimposed and transferred to the transfer material on the transfer material carrying sheet, the first color The second color compared to the toner transfer rate of
A phenomenon may occur in which the transfer rate decreases as the transfer is repeated with the third color. This phenomenon is likely to occur especially in a low humidity environment.

The main reason for this is that when the transfer material and the transfer material carrying sheet are separated from the image carrier after transfer, a high electric field causes discharge due to dielectric breakdown of air, which causes the transfer material surface or the transfer material carrying sheet surface. This is considered to be due to the accumulation of charges having the opposite polarity to the transfer charge.

In order to deal with this problem in the related art, as shown in FIG. 4, after transfer, corona dischargers 6 and 7 are provided on the transfer material side or on both the transfer material side and the transfer material carrying sheet side to prevent the charge on the transfer material surface from changing. A transfer device has been proposed which removes charges on the back surface of the transfer material carrying sheet (including the back surface of the transfer material when the transfer material carrying sheet has a large number of openings).

However, when static electricity is removed by the corona dischargers 6 and 7, the attracting force of the transfer material to the carrier sheet is reduced, and color shift may occur between the toner images of the respective colors.

Furthermore, in the conventional transfer device, when the transfer material is separated from the carrying sheet after the transfer has been performed a predetermined number of times, electric discharge also occurs due to the dielectric breakdown of air, and due to this effect, the toner image on the transfer material is scattered. As a result, the phenomenon that the image is disturbed is likely to occur.

In order to deal with this problem in the related art, as shown in FIG. 4, corona dischargers 8 and 9 are provided near the position where the transfer material is separated from the carrier sheet, on the transfer material side or the transfer material carrying sheet side, or both. Proposal of a transfer device that removes charges on the surface of the transfer material or removes charges on the back surface of the transfer material carrying sheet (including the back surface of the transfer material when the carrying sheet has a large number of holes, etc.). Has been done.

However, even when the above charge removal is performed, there is a problem that charge removal on the surface of the transfer material or the back surface of the transfer material carrying sheet, or charge removal on both charges is insufficient or excessive. When the charge removal is insufficient, it is difficult to prevent the toner image from scattering when the transfer material is separated. If the charge is excessively removed, the electrostatic attraction of the toner to the transfer material is reduced, and the toner on the transfer material may be scattered when entering the heat roller pair of the heat roller fixing device including the fixing roller and the pressure contact roller. there were. This is because the toner receives electrostatic repulsion due to the triboelectric charge on the surface of the fixing roller or the pressure contact roller, and when the transfer material is squeezed by the heat roller pair, the offset prevention liquid or air is pushed out. The toner image is scattered on the transfer material due to the fact that the toner receives the mechanical force.

Further, providing a corona discharger for preventing toner scattering in addition to the corona discharger for preventing the transfer rate reduction as described above requires a large number of corona dischargers and a high-voltage power supply accompanying them, and There was a problem in terms of complexity and spatial restrictions on placement.

[Object of the Invention]

The present invention is to eliminate the above problems,
Prevents lowering of transfer rate or color misregistration at each transfer when sequentially transferring toner images of multiple colors, and further, toner image scattering and heat roller fixing when separating the transfer material from the transfer material carrying sheet An object of the present invention is to provide a transfer device capable of preventing the toner image from scattering during fixing by a container.

[Means for solving problems]

That is, the present invention comprises a transfer material carrying member carrying a transfer material, and a transfer charging means for carrying out multiple transfer of toner images of a plurality of colors sequentially formed on the image carrying member onto the transfer material carried on the transfer material carrying body. A first for carrying a transfer material on the transfer material carrier
And a second charge removing unit provided on the opposite side of the transfer material carrier for removing charge from the transfer material and a second charge removing unit provided on the opposite side of the transfer material carrier from the first side. In the transfer device having: and, the first and second charge eliminating means perform charge eliminating operation between the transfer during the multiple transfer and the next transfer, and transfer when separating the transfer material from the transfer material carrier. To provide a transfer device characterized in that the material and the toner on the transfer material are charged to the same polarity as the transfer charging means and the back surface of the transfer material carrier is charged to the opposite polarity to the transfer charging means. Is.

Example of Invention

The present invention will be described in detail below with reference to an embodiment of the color copying machine shown in FIGS.

Reference numeral 21 denotes an image carrier (photosensitive drum). The image carrier 21 is composed of a surface insulating layer, a photoconductive layer and a conductive substrate.
The image carrier 21 has a layered structure and is supported by a support shaft 22 and rotates in the direction of arrow (A). When the image carrier 21 rotates, a document 24 placed on the document table glass 23 is rotated.
Is illuminated by the lamp 25, the reflected light is reflected by the first scanning mirror 26 and the second scanning mirror 27, and the lens 2
8. After passing through the third mirror 29, color separation is performed by the blue filter 301 of the color separation filter 30 and further an image is formed on the image carrier 21 by the fourth mirror 31. Image carrier 2
1 is uniformly discharged by the AC corona discharger 32 and the pre-exposure lamp 33, and then charged by the primary charging corona discharger 34 to, for example, a positive (plus) polarity, and then a negative (minus) polarity. The secondary charging corona discharger 35 removes electricity. At the same time, a blue color separation image exposure 36 is provided. Further, by performing the whole surface exposure by the whole surface exposure lamp 37, a blue color separation latent image is formed on the image carrier 21. The electrostatic latent image on the image carrier 21 thus obtained is visualized by the developing device 38 with the toner of negative polarity. The developing device 38 is yellow 38a,
It is composed of four developing devices of magenta 38b, cyan 38c and black 38d, and the developing device designated corresponding to the color separation filter used for exposure works to obtain a toner image of a required color. .

On the other hand, the transfer material 40 in the cassette 39 is fed into the machine by the feeding roller 41, and the leading end of the transfer material 40 is transferred to the transfer drum 42.
Is gripped by the gripper 421. This transfer drum 4
Reference numeral 2 denotes a cylinder frame 420, a gripper 421 that holds the tip of the transfer material 40, and a screen-shaped transfer material carrying sheet 422 stretched over the cylinder frame. By the corona discharger 423 on the transfer material side and the corona discharger 424 on the transfer material carrying sheet side which are arranged in the vicinity of the separating position, the charges on the front and back sides of the transfer material carrying sheet 422 are removed in advance.

An AC power source and a DC power source are connected in series to the discharge wires of the corona dischargers 423 and 424, respectively.
A DC biased AC corona discharge is generated. Each DC power supply voltage is controllable, and the bias level is controlled. At the time of destaticizing the transfer material carrying sheet 422, the corona dischargers 423 and 424 are used.
An AC voltage of 5.5 kV is applied to each of them, and the bias voltage superimposed on these AC voltages is controlled to +0.1 kV.

At this time, the potentials on the front and back of the transfer material carrying sheet are about 0, respectively.
It becomes V. Thus, the surface of the transfer material carrying sheet 422 is
Negative charges that inhibit electrostatic attraction of the transfer material (electrostatic adsorption of the positive charges on the back surface of the transfer material carrying sheet 422 and the negative charges induced or injected on the transfer material surface or inside the transfer material), which will be described later, are removed, As a result, good electrostatic attraction of the transfer material is achieved.

Further, the potential on the back surface of the transfer material carrying sheet 422 is also neutralized to about 0 V, so that the next time the transfer corona discharge is performed, it is uniform and sufficient with respect to the back surface of the transfer material carrying sheet and the back surface of the transfer material passing through the opening area of the transfer material carrying sheet. Corona discharge charge can be applied.

Next, the transfer material 40 gripped by the gripper 421 of the transfer drum 42 is squeezed by the transfer material holding member 425 while being wound around the transfer material carrying sheet 422 as the transfer drum 42 rotates, and conveyed to the transfer portion. Transfer corona discharger 4
+ 6.0k while the transfer material passes between 26 and the image carrier 21
The transfer corona discharge of the applied voltage of V is performed, and the charges attached to the back surface of the transfer material through the openings of the transfer material carrying sheet 422 and the charges attached to the back surface of the transfer material carrying sheet cause the transfer material on the transfer material.
The yellow toner image on the image carrier 21 is transferred. Along with this transfer, the transfer material is held on the surface of the transfer material carrying sheet by electrostatic attraction.

Next, the surface of the transfer material having the yellow toner image is discharged by the corona discharger 423. The applied voltage at this time is an alternating voltage of 5.5 kV, and the bias voltage superimposed on the alternating voltage is -0.6 kV. Further, almost simultaneously, the back surface of the transfer material carrying sheet 422 and the back surface of the transfer material carrying sheet in the opening area of the transfer material carrying sheet are discharged by the corona discharger 424. The applied voltage at this time is 5.5 kV AC voltage and +3.0 kV bias voltage.

After this charge removal, a counter electrode grounded is provided on the back surface side of the transfer material carrying sheet 422, and a surface electrometer probe is provided on the transfer material side. When the surface potential on the transfer material 40 is measured, a white background portion (non-image portion) is obtained. It becomes + 2.4kV. This potential is due to the influence of positively charged charges on the back surface of the transfer material and the back surface of the transfer material carrying sheet 422.

When the static electricity is not removed by the corona dischargers 423 and 424, the surface potential on the transfer material at the same position as described above is as low as +2.0 kV in the white background portion. In this case, since the potentials of the back surface of the transfer material and the back surface of the transfer material carrying sheet 422 are higher than the potentials in the present invention, the surface potential on the transfer material is lowered because the negative charge accumulation on the transfer material surface has an effect. Is.

Next, the transfer drum 42 grips the front end of the transfer material by the gripper 421, rotates while being electrostatically attracted to the transfer material carrying sheet 422, and is magenta toner formed on the image carrier 21 by color separation image exposure of green. The image is transferred, and then the transfer corona dischargers 423 and 424 perform the charge removal on the transfer material front surface and the transfer material carrying sheet back surface and the transfer material back surface. At this time, the AC voltage and the bias voltage applied to the transfer corona dischargers 423 and 424 are the same as the charge removal after the yellow toner image transfer. After this static elimination, the surface potential on the transfer material measured by the same method as the previous time was + 2.4k in the white area.
V is the same as after transfer of the yellow donor image. When the static electricity is not removed by the corona dischargers 423 and 424, the surface potential on the transfer material is +1.6 kV at the white background, which is lower than that after the first transfer.

Next, the cyan toner image formed on the image carrier 21 is transferred to the transfer material on the transfer material carrying sheet 422 by the color separation image exposure of red, and then the three color toner images are transferred. When the tip of the transfer material approaches the separation position, the gripper 4
21 is released, and the separation claw 427 provided near the corona dischargers 423 and 424 approaches the transfer material carrying sheet 422, and the transfer material 40 is forcibly separated. At this time, the corona dischargers 423 and 424 simultaneously remove the charge on the surface of the transfer material and remove the charge on the back surface of the transfer material carrying sheet 422 and the back surface of the transfer material. An AC voltage of 5.5 kV is applied to the corona dischargers 423 and 424, and the bias voltage is +2.0 kV for the former,
The latter is -2.0kV. The potential of the surface of the transfer material after separation is +0.6 kV in the white background portion and +0.3 kV in the toner adhering portion (solid portion).

Thus, after the transfer material is separated, it is guided to the heat roller pair 45 of the heat roller fixing device 44 by the conveyor belt 43, heated and fixed, and then discharged to the tray 46.

A cleaning device 47 has an elastic blade and cleans the surface of the image carrier 21. The screen used for the transfer material carrying sheet 422 is a mesh screen knitted using fibers of a derivative such as polyester, nylon or polypropylene, or a dielectric sheet such as polyester, triacetate or polypropylene is pressed to form a large number of holes. A screen provided with is effective. The transfer material carrying sheet 422 has
The dielectric sheet itself may be used instead of the screen. Further, the AC voltage applied to the corona dischargers 423 and 424 is suitable in the range of 4 to 7 kV, and the frequency at that time is suitable in the range of 50 to 800 Hz.

As described above, in this embodiment, the corona discharger 423 is provided near the position where the transfer material is separated from the transfer material carrying sheet.
And 424 are provided so that the charges of the transfer material and the transfer material-carrying sheet are discharged by the corona discharger so that an optimum state can be obtained at each transfer and at the time of separating the transfer material. According to this embodiment, there is an effect that it is possible to obtain a good color image with no color shift and a good color balance, and further it is possible to obtain a clear image without toner scattering and transfer unevenness.

Note that it is important to control the amount of static electricity removed by the corona dischargers 423 and 424 for each transfer in order to maintain the electrostatic charge of the transfer material on the screen surface. Therefore, the DC bias voltage superimposed on the AC voltage applied to the corona dischargers 423 and 424 has a negative polarity of the toner (positive polarity of the transfer corona discharge) as in the above-described embodiment, the corona discharger 423. Negative polarity on the (transfer material side), corona discharger 424 (transfer material carrying sheet 42
A predetermined voltage of positive polarity is applied to (2 side) to control the amount of static elimination.

In this embodiment, corona dischargers 423 and 424 are provided for each transfer.
The DC bias voltage applied to the same was the same after the transfer of the first and second colors, but the absolute value of the bias voltage was lowered so as to perform strong static elimination in stages, and it increased according to the increase in charge accumulation. The charge removal amount for each transfer may be controlled. That is, the bias voltage applied to the corona discharger 423 is -0.6 kV after the transfer of the first color (hereinafter) -0.6 kV and after the transfer of the second color (hereinafter).
-0.4 kV, +2.0 kV at the time of transfer material separation (hereafter), and the bias voltage applied to the corona discharger 424 is +3.0 kV, +2.0 kV, and -2.0 kV. The above image quality was obtained.

The polarity of the DC bias voltage applied to the corona dischargers 423 and 424 when separating the transfer material from the screen surface as in the above-described embodiment is opposite to the polarity of the bias voltage applied after the transfer of the first and second colors. And This is because once the negative charge on the transfer material surface and the positive charge on the screen back surface and the transfer material back surface have been completely neutralized by the charge removal during separation, the transfer material surface is set to the positive polarity and the screen back surface and the transfer material back surface are set to the negative polarity. It is to be charged.
As a result, the toner on the surface of the transfer material is charged to the positive polarity and the back surface of the transfer material is charged to the negative polarity. Therefore, when the toner charge on the transfer material and the toner constrained charge on the back surface of the transfer material are almost eliminated (for example, corona discharger 423 and In comparison with the case where only AC voltage is applied to 424 to remove electricity), toner scattering at the time of separation and toner scattering at the time of fixing by the heat roller fixing device are significantly reduced.

It is considered that this also contributes to the fact that the white background portion (portion to which toner is not attached) on the transfer material is also charged to the same polarity (plus) as the toner, and the white background portion acts as a barrier against toner scattering.

Further, a large number of grid wires are stretched over the opening of the shield plate of the corona discharger 423 or 424, and a DC bias voltage is applied to this wire to adjust the positive and negative components of the AC corona discharge, and for each transfer and during transfer material separation. The charge removal amount may be controlled. However, in this case, since the corona discharger on the transfer material side is provided in the vicinity of the transfer material transport path, contact with the transfer material is likely to occur, so care must be taken in the arrangement. On the other hand, in the corona discharger 424 on the screen side, it is necessary to provide the cylinder of the transfer drum or the gripper member with an allowance. In the above embodiment, the transfer drum is used for the description, but it goes without saying that a belt-shaped member may be used. Further, the corona dischargers 423 and 424 do not necessarily have to be provided facing each other, but when not facing each other, the transfer material carrying sheet is provided in order to improve discharge efficiency.
A counter electrode plate that is grounded across 422 may be provided. That is, as shown in FIG. 3, the corona dischargers 423 and 424 are provided with counter electrode plates S2 and S1 facing the corona dischargers 424 and 423, respectively.

〔The invention's effect〕

According to the present invention, it is possible to prevent a decrease in transfer efficiency at each transfer and prevent toner scattering when separating the transfer material from the transfer material carrier.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of a transfer device according to the present invention, FIG. 2 is a perspective view of only the transfer drum, and FIG. 3 shows another embodiment of the transfer drum according to the present invention. FIG. 4 is a side view, and FIG. 4 is a main part explanatory view of a conventional color image forming apparatus. 21 ... Image carrier 22 ... Spindle 23 ... Platen glass 24 ... Document 25 ... Lamp 26 ... First scanning mirror 27 ... Second scanning mirror 28 ... Lens 29 ... Third mirror 30 ... Color separation filter 301 ... Blue filter 31 ... 4th mirror 32 ... AC corona discharger 33 ... Pre-exposure lamp 34 ... Primary charging corona discharger 35 ... Secondary charging corona discharger 36 ... Color separation image exposure 37 ... Full exposure lamp 38 ... Development device 38a ... Yellow developing device 38b ... Magenta developing device 38c ... Cyan developing device 38d ... Black developing device 39 ... Cassette 40 ... Transfer material 41 ... Feed roller 42 ... Transfer drum 420 ... Cylinder frame 421 ... Gripper 422 ... Transfer material carrying sheet 423, 424 ... Corona Discharger 425 ... Transfer material pressing member 426 ... Transfer corona discharger 427 ... Separation claw 43 ... Conveyor belt 44 ... Heat roller fixing device 45 ... Heat roller 46 ... Tray 47 ... Cleaning device

Claims (1)

[Claims] 1. A transfer material carrying member carrying a transfer material, and transfer charging means for carrying out multiple transfer of a plurality of color toner images sequentially formed on the image carrying member onto the transfer material carried on the transfer material carrying member. And a first member for carrying a transfer material on the transfer material carrier.
And a second charge removing unit provided on the opposite side of the transfer material carrier for removing charge from the transfer material and a second charge removing unit provided on the opposite side of the transfer material carrier from the first side. In the transfer device having the following, the first and second charge eliminating means perform charge eliminating operation between the transfer during the multiple transfer and the next transfer, and transfer when separating the transfer material from the transfer material carrier. A transfer device, wherein the material and the toner on the transfer material are charged to the same polarity as the transfer charging means, and the back surface of the transfer material carrier is charged to the opposite polarity to the transfer charging means.