JPH0664405B2 - 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, applies a transfer electric field to the transfer material on the transfer material carrying sheet, and And a device for transferring a toner image on an image bearing member such as an insulating drum onto a transfer material. Examples of the application of such a transfer device include a conventional electrophotographic copying machine, a color copying machine and a recording device in which a toner image of a simple color is repeatedly transferred onto a transfer material.

[Conventional technology]

Conventionally, in this type of transfer device, an air discharge is generated when the transfer material is separated from the transfer material carrying sheet after the transfer is completed, and due to this effect, the toner image on the transfer material is scattered from the surface of the transfer material. As a result, the phenomenon that the image is disturbed is likely to occur.

Conventionally, in order to deal with the above-mentioned problems, at the time of separating the transfer material, the transfer material or the toner is neutralized by applying AC corona charging from the transfer material side or the transfer material carrying sheet side or both the transfer material side and the carrying sheet side. It is known that the scattering of the toner image is prevented by reducing the air discharge at the time of separating the transfer material.

A color electrophotographic copying machine to which such a conventional transfer device is applied will be described with reference to FIG.

In the figure, reference numeral 1 denotes a photosensitive drum having a three-layer structure including a surface insulating layer, a photoconductive layer and a conductive substrate, which is supported by a shaft 2 and rotates in the direction of an arrow 3. When the photosensitive drum 1 rotates, the original O placed on the original table glass 4 is illuminated by the lamp 5. The reflected light is reflected by the first scanning mirror 6 and the second scanning mirror 7, passes through the lens 8 and the third mirror 9, is color-separated by the blue filter 101 of the color separation filter 10, and is further exposed by the fourth mirror 11. An image is formed on the drum 1.

The photosensitive drum 1 is uniformly discharged by the AC discharger 13 and the pre-exposure lamp 14, then charged positively by the primary charging discharger 15, and then blue by the secondary discharger 16 having a polarity opposite to that of the primary. The color separation image exposure 12 is applied and the discharge is performed at the same time. Further, by performing the whole surface exposure by the whole surface exposure lamp 17, a blue color separation latent image is formed on the drum 1.

The electrostatic latent image on the photosensitive drum 1 is next developed by the developing device 18.
It is visualized with toner. The developing device 18 is yellow 18a,
The developing device is composed of four developing devices of magenta 18b, cyan 18c, and black 18d, 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 20 in the cassette 19 is fed into the machine by the paper feed roller 21, and the tip of the transfer material is gripped by the gripper 231 of the transfer drum 23. It should be noted that the mesh screen 23, which is a transfer material carrying sheet described later, provided on the transfer drum 23.
In the case of 2, the charges on the front and back of the screen are removed by the AC dischargers 234 and 235 for separation in advance.

The transfer material gripped by the gripper 231 of the transfer drum 23 is
The yellow toner image on the photosensitive drum is transferred onto the transfer material while being transferred around the screen 232 as the transfer drum 23 rotates and passing between the transfer discharger 233 and the photosensitive drum 1. To be done. Along with this transfer, the transfer material is held on the screen surface by electrostatic attraction.

At the time of the transfer, the transfer drum 23 grips the tip of the transfer material 20 with the gripper 231 and rotates a predetermined number of times while being electrostatically attracted to the mesh screen 232, and the toner image of the required number of colors is transferred onto the transfer material. To be done. That is, in the case of full-color copying, the transfer of the yellow toner image is followed by the transfer of the magenta toner image by the color separation exposure of green and the transfer of the cyan toner image by the color separation exposure of red.

After the transfer has been performed a predetermined number of times, the gripper 231 is released when the tip of the transfer material approaches the separation position, the transfer material and the screen are both discharged by the AC corona discharge from the separation dischargers 234 and 235, and the separation claw 236. The transfer material is forcibly separated by the approach of the screen. After the transfer material is separated, it is guided to the heat roller fixing device 28 by the conveyor belt 27, heated and fixed, and then discharged to the tray 30.

The surface of the photosensitive drum 1 after the transfer is cleaned by a cleaning device 31 composed of an elastic blade, and the surface thereof is cleaned to proceed to the next image forming cycle.

FIG. 3 shows a perspective view of the transfer drum 23. The transfer drum 23 has a screen 232 for carrying the transfer material, a cylinder 237 having a notch for supporting the screen at its edge, and a gripper 231 for gripping the leading edge of the transfer material.

As the material of the screen, a material obtained by knitting fibers of polyester, nylon, silk, polypropylene or the like, or a material obtained by punching and pressing a sheet of polyester, polypropylene or the like is used. In each case, a mesh screen of about 50 to 100 mesh is used.

[Problems to be solved by the invention]

In the above-mentioned transfer device, when the transfer material is separated from the screen of the transfer drum, in order to prevent or reduce the air discharge generated between the transfer material and the screen, the AC as described above is used.
Corona discharge is applied from both sides to remove charges on the front and back of the transfer material and the front and back of the screen, thereby preventing image disturbance due to toner scattering. However, even in the above method, it is difficult to sufficiently prevent the image disturbance due to the toner scattering after the transfer material is separated, and sometimes the toner scattering occurs.

FIGS. 4A to 4C are schematic diagrams for explaining the screen 232 which is the transfer material carrying sheet and the state of charge removal of the transfer material or toner by the conventional charge removing method.

FIG. 4A shows a state immediately after the toner image T is transferred onto the transfer material 20. In the following description, for the sake of convenience, the polarity of the toner T is negative (-).

Due to the transfer discharge 233, a positive (+) is generated between the back surface of the screen 232 and the back surface of the transfer material 20 corresponding to the aperture area of the screen.
Is attached. On the other hand, a toner image T having a negative (-) polarity is transferred to the surface of the transfer material 20 by the action of these charges, but after transfer, it is negative (-) due to air discharge when the photosensitive drum and the transfer material are separated from each other. Some polar charges are also attached.

FIG. 4B is a discharger 234 and 23 for static elimination when the transfer material 20 is separated from the screen 232 by the separation claw 236 (FIG. 2).
This is the state of charge when the charge is removed by 5. A in the figure
₁ and A ₂ are A applied to the discharging static dischargers 234 and 235.
C power source. In this state, the negative (−) charge disappears or is reduced by a considerable amount on the surface of the transfer material 20 where the toner T is not present, and the positive (+) charge is attached on the part where the toner T is present and the toner is negative. Neutralize the charge of (-). In addition, the positive (+) charges on the back surface of the transfer material 20 and the back surface of the screen 232 also disappear or are considerably reduced.

FIG. 4C shows the charge state of the transfer material 20 after the transfer material 20 is separated from the screen 232. The toner has no charge or has a slight negative (−) charge, while the transfer material 20 has a front surface and a back surface. The electric charge of disappears or becomes considerably reduced. At this time, the adhesive force of the toner to the transfer material is dominated by the physical adhesive force due to the surface energy and the like, and the adhesive force of the electrostatic force is small. Therefore, the adhesive force of the toner to the transfer material is small as a whole.

In this state, when the heat roller pair of the fixing device 28 to which the heat roller pair is applied enters the heat roller pair, the repulsive force due to the triboelectric charge on the fixing roller or the pressure contact roller or when the transfer material is squeezed by the heat roller pair is generated. Due to the pushing force of the anti-offset liquid or air, the toner image on the transfer material is scattered or ejected in the form of being pushed or pushed to the side opposite to the traveling direction. This phenomenon is particularly likely to occur in a high humidity environment in which the triboelectric charge of the toner itself becomes small.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned problems, and prevents the disturbance of the toner image that occurs when the transfer material is separated from the transfer material carrying sheet, and
Provided is a transfer device capable of preventing a toner image from being disturbed during fixing by a heat roller fixing device.

[Means for solving problems]

The present invention relates to a transfer device for transferring a toner image on an image carrier to a transfer material carried on a transfer material carrier, and when the transfer material is separated from the transfer material carrier, the transfer material carrier and the transfer material are separated from each other. A first discharging unit which is provided on the first side for carrying the transfer material with respect to the transfer material carrier to remove the charge, and which produces positive and negative alternating discharges biased to the same polarity as the toner image;
Second discharge means provided on the opposite side to the first side to generate positive and negative alternating discharges, and the first and second discharge means have a toner image.

As the transfer material carrying sheet, a mesh-shaped screen sheet or a non-perforated film-shaped sheet such as a polyethylene terephthalate film can be used. Further, the discharging means sets weakly the discharge in the direction of the same polarity or the opposite polarity to the polarity of the toner when the humidity is low, and strengthens the discharge in the direction of the same polarity or the opposite polarity to the polarity of the toner when the humidity is high. You can set it and increase its effect.

[Action]

FIG. 1A and FIG. 1B are schematic diagrams for explaining the static elimination state of the present invention. FIG. 1A corresponds to the above-mentioned conventional FIG. 4B, and FIG. 1B corresponds to FIG. 4C.

In the present invention, as shown in FIG. 1A, a bias voltage having a specific polarity is applied to the AC power supplies A1 and A2 applied to the separating dischargers 234 and 235 which are operated when the transfer material 20 is separated from the screen 232 by the separating claw. Superimpose. That is, power supply A
1 is a negative (-) bias voltage from the DC power source D1
A positive (+) bias voltage is applied to the power source A2 by the DC power source D2.

As a result, the electric charge of the toner T is not neutralized at the time of separation, and the electric charge is left on the toner almost as it is, and a slight negative (-) electric charge is left on the toner-free portion of the transfer material. You can Further, on the back surface of the transfer material and the back surface of the screen, an appropriate amount of positive (+) electric charge is left in order to eliminate static electricity to the extent that toner does not scatter during separation. First
FIG. 6B shows the charge state of the transfer material after the transfer material 20 is separated from the screen 232. The charge of the toner T remains unneutralized, and the toner-free portion of the transfer material is slightly negative. (−) Electric charge exists. In addition, positive (+) charges remain on the back surface of the transfer material in a state of being smaller than that at the time of transfer. In the transfer material that maintains the charge state, the positive (+) charge density on the back surface of the transfer material in the area corresponding to the toner image is increased due to the negative (-) charge of the toner. In this state, the toner is firmly held on the transfer material by the electrostatic force and the negative (−) polarity electric charge is present in the toner-free portion of the transfer material. Since a large potential difference is not generated between the two, it is possible to prevent the toner from scattering.

Even if the transfer material is fed to the fixing device using rollers in such a state to perform fixing, good image quality can be obtained without causing toner scattering.

〔Example〕

The voltage applied to the transfer discharger in the present invention is +6.5 KV,
When the applied voltage of the AC power supplies A1 and A2 is 6.0 KV, the DC bias voltage value is 100 V for the power supply D1 or -1.300.
V range, preferably -200V to -600V
Is the range. The power source D2 is + 200V to +1.50
0V range, preferably + 300V to +800
It is in the range of V. Further, the voltages of the power sources D1 and D2 have a correlation, and when the absolute value of the voltage of the power source D1 | VD1 | is high, the absolute value of the voltage of the power source D2 | VD2 | can be lowered, and vice versa. When | is high, absolute value | VD1 | can be lowered.

As an effect of controlling the absolute value, it becomes possible to set the charge state according to the environment in which the apparatus is used and the material of the transfer material.

For example, in a low-humidity environment, controlling absolute values | VD1 | and | VD2 | to be low is effective in preventing toner scattering during transfer material separation, and at the same time there is no problem with toner scattering during fixing. . Also, in a high humidity environment, absolute values | VD1 | and | VD2
It is more effective to control | to be higher than the toner scattering at the time of fixing, and there is no problem with toner scattering at the time of separating the transfer material. As an example of setting the above absolute value, room temperature 15 ° C, 20%
At RH or 40% RH, absolute values | VD1 | and | VD2 | are 200 V and 300 V, respectively, at the same 30 ° C and 60% R
Absolute values at H or 80% RH | VD1 |, | VD2 |
Obtained good effects against the toner scattering in the ranges of 600 V and 800 V, respectively.

In addition, if you use plain paper as the transfer material, or
Comparing the case of using a synthetic resin sheet for (over head, projector), the former is effective in eliminating static electricity when separating the transfer material, while the latter is effective in eliminating static electricity as much as the former. Absent. Therefore, in the case of plain paper, increase the absolute values of superimposing bias with respect to the AC voltage | VD1 | and | VD2 |
Conversely, in the case of OHP sheets, this absolute value | VD1 |, | VD2 |
It is effective to control the toner to a low value to prevent the toner from scattering during both separation and fixing of the transfer material.

The voltage of the AC power source applied to the separating dischargers 28 and 29 is appropriately in the range of 5 to 7 KV, and the frequency at that time is suitably in the range of 50 Hz to 800 Hz.

By the way, as described above, instead of superposing the DC bias voltage on the AC power supply of the separating discharger, only the voltage of the AC power supply is adjusted to obtain the effects of the present invention described with reference to FIGS. 1A and 1B. Is not practical because it requires delicate adjustment and is unstable.

Note that a large number of grid wires may be stretched over the openings of the shield plates of the separating dischargers 234 and 235, and a bias voltage may be applied to the wires to adjust the positive and negative components of the AC corona discharge to control the static elimination potential. However, in this case, the discharger on the transfer material side is provided close to the transfer material transport path. Therefore, it is necessary to pay attention to the arrangement because contact with the transfer material is likely to occur. On the other hand, on the screen side, the cylinder 237 of the transfer drum cylinder or the gripper member needs to be provided with a margin to pass through.

In each of the above methods, the method of applying a bias to the grid is limited in arrangement, and therefore it is considered that the method of superimposing an appropriate amount of DC voltage on the AC power source is easy to implement.

In the above-mentioned embodiment, the transfer drum is used for explanation, but it may be a belt-like one that moves endlessly.
The grippers provided on the transfer material carrying sheet side may be provided as needed. Further, the corona discharger is exemplified as the discharge means for transfer, separation, etc., but it is not limited to the corona discharger, and it is not necessarily limited to the use of the corona discharge phenomenon as long as it can impart or remove charges. Absent.

In addition, the control of the bias voltage by the radio wave of the discharger for the environmental conditions in the present invention or the material of the transfer material is performed by manual adjustment, or by a known combination of a sensor and a control circuit. This is done by automatically controlling.

〔The invention's effect〕

As described above, according to the present invention, the toner is prevented from scattering when the transfer material is separated from the transfer material-carrying sheet or when the transfer material is fixed by a simple structure and simple adjustment, and a transfer image having a good image quality is obtained. In particular, it is effective in preventing toner scattering that tends to occur when a thick toner layer is formed by stacking a plurality of toner layers such as a full-color image.

[Brief description of drawings]

1A and 1B are schematic views for explaining the result of static elimination of the present invention, FIG. 2 is a cross-sectional view of a main part of a color electrophotographic copying machine to which the present invention can be applied, and FIG. 3 is a perspective view of a transfer drum. Fourth A
FIG. 4, FIG. 4B, and FIG. 4C are schematic diagrams showing states of charges on a transfer material and a transfer material-carrying sheet by a conventional separation charge removal. In the figure, 1 is a photosensitive drum, 20 is a transfer material, 23 is a transfer drum, 232 is a screen which is a transfer material carrying sheet, 2
34 and 235 are dischargers for static elimination.

Claims (1)

[Claims] 1. A transfer device for transferring a toner image on an image carrier to a transfer material carried on a transfer material carrier, wherein the transfer material carrier and the transfer material when the transfer material is separated from the transfer material carrier. A first discharging unit that is provided on the first side for carrying the transfer material with respect to the transfer material carrying member and that generates positive and negative alternating discharges that are biased to the same polarity as the toner image, Second discharge means provided on the opposite side to the first side and generating positive and negative alternating discharges biased to the opposite polarity to the polarity of the toner image, and the first and second discharge means are provided. A transfer device which operates over the entire area of a transfer material having a toner image.