JPH0562742B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image transfer device for transferring a toner image formed by electrophotography or the like onto a transfer material such as paper. The present invention relates to an image transfer device suitable for obtaining a multicolor image by performing multiple transfers onto a transfer material.

[Prior art]

Various methods and apparatuses have been proposed in the past for the purpose of obtaining multicolor images using electrophotography. After developing, the toner image is transferred to a transfer material such as paper, and the same process is repeated according to the number of required color separations to sequentially transfer multiple color toner images onto the same transfer material. , most commonly to obtain a polychromatic image. In the method of sequentially overlapping color images on a transfer material, alignment of the transfer material with respect to the image carrier is extremely important, and if this is inaccurate, color misregistration may occur, making the image unusable. I become confused.

As a means for accurately regulating the position of the transfer material relative to the image carrier, a transfer drum is provided in contact with the image carrier, and the transfer material is fixed on the drum and rotated in synchronization with the image carrier, so that the transfer material is aligned with the image carrier. A transfer device that always maintains a constant relative position is often used. Usually, a mechanical locking means (gripper) is provided on the transfer drum to automatically lock the leading end of the transfer material fed by a feed roller or the like and fix it on the drum.

When transferring the toner image on the image carrier to a transfer material, an electrostatic process such as applying a charge to the transfer material is required to move the toner onto the transfer material, and the image carrier is also charged. Because multiple electrostatic forces act on the transfer material, such as having a The current situation is that

For example, US Pat. No. 3,729,311 discloses a color copying machine having a transfer material holding drum in contact with an image bearing drum, and the transfer material holding drum is provided with a gripper for fixing the transfer material. Also Tokukai Akira
Japanese Patent No. 55-18653 discloses a color copying machine having a transfer material support made of a mesh screen having an insulating surface in contact with an image bearing drum. Here, since the transfer material is electrostatically attracted to the transfer material support, it is said that mechanical means for locking the transfer material is not necessarily necessary, but the screen-shaped transfer material support is In order to securely hold and fix the transfer material since the contact area is small, it is necessary to lock it to the support body.

However, when a locking section is provided on the transfer drum, it requires a complicated mechanism for automatically locking, unlocking, and separating the transfer material. There are many problems such as contamination of the locking part, blank space at the leading edge of the transfer material that is locked in the locking part, and the need for a mechanism to avoid the gripper part in the cleaning device for the transfer material holding drum. Therefore, it has been desired to develop a simpler and more reliable transfer material fixing means.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image train device for a multicolor positive electric recording device with a simple structure that can reliably transfer multiple toner images onto a transfer material without causing color misregistration.

[Structure of the invention]

The purpose is to insulate the surface and the thickness is 10~100μm
A transfer drum has a conductive support layer thereunder, and a transfer bias voltage of opposite polarity to the charge of the toner constituting the toner image formed on the image bearing member is applied to the conductive support layer below the transfer drum. The transfer material is provided opposite to the drum on the upstream side of the position where it rolls into contact with the carrier, and charges the surface of the transfer material passing between the drums with the same polarity as the charge of the toner, thereby transferring the transfer material. This was achieved by an image transfer device having a means for applying a charge to the surface of the drum.

That is, the transfer material has a charge of opposite polarity to the transfer bias voltage applied to the conductive support layer below the insulating surface thin layer of the transfer drum, and therefore has the same polarity as the charge of the toner image on the image carrier. By applying this, the transfer material is attracted and fixed to the transfer drum surface by electrostatic force, and there is no need for any locking means such as grippers on the transfer drum to fix the transfer material. Multiple transfer of toner without color shift can be performed without causing the various problems described above.

At this time, the transfer material is charged with the same polarity as the toner, so a repulsive force is generated between the toner and the transfer material, but a high bias voltage with the opposite polarity to the toner is applied to the transfer drum. Since the thickness of the insulating layer on the surface of the transfer drum is as thin as 10 to 100 μm, if the amount of charge applied to the transfer material is set to a low value,
The electrostatic field generated by the bias voltage applied to the transfer drum overcomes the charge on the transfer material and attracts the toner toward the transfer drum, that is, toward the transfer material, so that the toner can be transferred favorably.

The charge applying means used in the present invention is not particularly limited as long as it can apply a charge to the surface of the transfer material, but a corona discharger is particularly preferably used. The polarity of the applied charge is set in accordance with the charge of the toner to be transferred (determined according to the polarity of the electrostatic image formed on the image carrier) so that it has the same polarity as the charge of the toner. The voltage applied to the corona discharger varies depending on the properties of the image carrier, toner, etc., but is usually in the range of 4 to 7 KV (absolute value).

The transfer drum has an insulating layer on the surface of the conductive substrate.
The structure may be such that a transfer bias voltage can be applied to the conductive substrate, but since the transfer drum needs to transfer the toner by pressing the transfer material onto the image bearing surface,
It is preferable that the surface has appropriate elasticity,
For this purpose, a conductive elastic layer is provided on the conductive substrate,
It is preferable to have a structure in which an insulating layer is further provided on the surface.

As the conductive substrate, it is preferable to use metal such as aluminum, for example. Preferred examples of the conductive elastic body include conductive rubber such as silicone-based or chloroprene-based conductive rubber. These conductive elastic bodies preferably have a rubber hardness of 40° to 70° and a volume resistivity of 10 ⁸ Ω·cm or less, and the layer thickness on the conductive substrate is approximately 1 to 10 mm. It is preferable to do so.

The insulating layer is made of various insulators such as polyester, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, methacrylic resin, acrylic resin, polystyrene, silicone resin, fluorine resin, styrene-butadiene copolymer, and various other polymers. It can be constructed using a polymer such as a polymer or a copolymer, rubber, or the like. These insulators may be applied to the surface of a conductive elastic body or directly to the surface of a conductive substrate, or an insulating layer may be formed by covering the tube as a heat-shrinkable tube and heat-shrinking it. The thickness of the insulating layer is 10 to 100 μm. If the thickness of the insulating layer is smaller than this, it will be difficult to manufacture and the mechanical strength will be low, causing practical difficulties, and if the thickness is too large, it will be unfavorable in terms of bias effects and the like. As mentioned above, a transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer drum.The applied voltage and its polarity vary depending on the image carrier, the electrostatic properties of the toner, etc., but the absolute value is 0.5 to 1.5. A range of KV is preferred.

The functions of the image transfer device of the present invention will be explained below. FIG. 1 is a schematic diagram of an image transfer apparatus of the present invention, in which 1 is an image bearing drum consisting of a conductive substrate 1 and a photoconductive photosensitive layer 2, 3 is a conductive substrate 3, and a conductive elastic layer 4. , a transfer drum comprising an insulating layer 5 with a thickness of 10 to 100 μm. The figure shows a case in which a photosensitive layer that forms a positively charged electrostatic image, such as selenium-based or amorphous silicon, is used.

A positive DC bias is applied to the transfer drum 3 from a bias power supply 6. Reference numeral 7 denotes a corona discharger for imparting charge to the transfer material, which is provided opposite to the transfer drum 3 , and is applied with a negative voltage from a power source 8.

The image bearing drum 1 and the transfer drum 3 are pressed against each other in the transfer section A, and rotate in the directions of arrows B and C, respectively, during operation. pictured).

The electrostatic image formed on the image carrier drum 1 is developed by a developing device (not shown) loaded with negatively charged toner to form a toner image. 9 is a toner forming a toner image.

The transfer material 10 (its length is shorter than the circumference of the transfer drum 3 ), which advances in the direction of arrow D by a feeding means not shown in the figure, is charged with toner on its surface by a corona discharger 7. It is given a negative charge of the same polarity as , and enters the transfer section A where the image bearing drum 1 and the transfer drum 3 are in contact with each other. The negatively charged toner particles are attracted by the positive bias voltage applied to the transfer drum and migrate toward the transfer material, completing the transfer of the first toner image. When the transfer material leaves the pressure contact area of both drums, electrostatic attraction from both drums is applied to the transfer material.
The negatively charged transfer material 10 is strongly attracted by the transfer drum 3 to which a positive bias voltage is applied, and is wound and fixed on its surface. The transfer material is in full contact with the transfer drum and is strongly adsorbed, so it will not shift during subsequent processes. The transfer material 10 wrapped around the transfer drum 3 advances to the transfer section A again as the drum 3 rotates, and the second toner image is transferred thereto. Thereafter, the same transfer process is repeated as many times as necessary, and a multicolor image is completed on the transfer material 10. When the transfer material 10 passes through the transfer material 10 for the second time and thereafter, the charge application by the corona discharger 7 may be stopped. Even if the charge application is stopped, the negative charge applied to the transfer material surface is maintained without attenuation because the transfer drum surface is insulating, and the toner transfer is performed well, and the transfer material is not attracted to the transfer drum. Maintained stably.

After the transfer is completed, the transfer material may be separated from the transfer drum using a separation means such as a separation claw and sent to the fixing process. In the figure, reference numeral 11 is a separation claw, and by rotating this to the position indicated by the dotted line, the transfer material 10 is separated from the drum 3.
It separates further and moves in the direction of arrow E. In the case of monochrome copying, if this mode is set from the beginning, the transferred transfer material is immediately discharged in the direction of arrow E, making it possible to perform high-speed and continuous copying. This is an advantage that can only be obtained in the image transfer apparatus of the present invention, which does not have a transfer material locking part on the transfer drum and can use the drum at any position. Positioning, locking, and unlocking operations are required, making it difficult to increase the speed.

All of the above explanations have been made using photosensitive layers that form positively charged electrostatic images such as selenium-based or amorphous silicon, but negatively charged types such as zinc oxide, cadmium sulfide, and various organic photoreceptors are used. Even when a photosensitive layer is used, the functions and effects are the same, except that the polarities of the electrostatic charges are all reversed.

In addition to the transfer material separating means, the image transfer apparatus of the present invention may be provided with additional devices such as a transfer material static eliminator, a transfer drum static eliminator, a transfer drum cleaner, and a positioning sensor, as required.

The image transfer apparatus of the present invention can be used with various known color image forming means using the three-color separation method, or with black image forming means such as those disclosed in Japanese Patent Publication No. 48-34770 and Japanese Unexamined Patent Publication No. 56-5561. It can be used in combination with various multicolor image forming means such as known two color image forming means including an erasing process. Further, various known paper feeding and fixing means can be used as a paper feeding means for supplying a transfer material such as paper to this apparatus, a fixing means for fixing an image transferred by this apparatus, and the like.

〔Example〕

An example in which the image transfer device according to the present invention is used in a color copying machine using a three-color separation method will be described below.

FIG. 2 is a schematic diagram of an image forming section and an image transfer section of a color copying machine using an image transfer device according to the present invention. In this figure, members having the same functions as those in FIG. 1 are designated by the same numbers. A two-component developer was used as the developer. In the figure,
Arrow L indicates an optical path for image exposure by scanning an original image sent from an optical system not shown in the figure. Scan is 3
This is repeated several times, and each time filters F _R (red), F _G (green), and F _B (blue) are alternately inserted into the optical path L to perform color-separated exposure. The figure shows a state in which a blue filter F _B is placed in the optical path.

1 used a selenium-based photoreceptor configured similarly to the image bearing drum shown in FIG. 1 (in this example, a Se/Te photoreceptor with a dielectric constant of 6 and a thickness of 60 μm was used). an image carrier, which rotates in the direction of the arrow;
After the entire surface is positively charged by the corona discharger 20, it is exposed to image by light from the optical path L.
First, a blue filter is placed in the optical path and exposed to light to form an electrostatic image on the image bearing drum 1. After that, it is developed by a developing device 21Y loaded with a negatively charged yellow developer to form a yellow toner image. The image carrier drum carrying the yellow toner image is neutralized by the pre-transfer neutralization lamp 22 and advances to the transfer position A.

On the other hand, the transfer material 1 is fed through the paper feed roller 23
0 is given a negative charge (-1×10 ^-8 C/cm ² ) to its surface by a transfer material charge-imparting corona discharger 7, and a positive bias voltage (+800 to
The yellow toner image is attracted to the transfer drum 3 to which a voltage of 1000 V) is applied, is sent to the transfer position A, is pressed between the image carrier drum 1 and the transfer drum 3 , and is transferred with a yellow toner image. The transfer drum 3 has the same structure as that shown in FIG. 1, but the details are omitted in this figure. The conductive rubber layer of the transfer drum 3 in this embodiment has a thickness of 2 mm, a hardness of 50°, and a volume resistivity of 10 ₅ Ωcm, and the insulating layer has a thickness of 2 mm.
It was made of polyester with a dielectric constant of 3 and a diameter of 12.5 μm.

After the transfer, the transfer material 10 is wrapped around the drum 3 by electrostatic force, held, and moved.

The image bearing drum after transfer is cleaned by a cleaning device 2.
4 to remove residual toner from the surface, and a static elimination lamp 25 to remove any residual charge before being reused.

The transfer material 10 held on the transfer drum 3 advances as the drum 3 rotates, and its position is read by the sensor 26, and the second exposure operation is started in synchronization with this position. The second exposure uses a green filter _FG , and development is performed by a developing device 21M loaded with a negatively charged magenta developer. The obtained magenta toner image is transferred overlappingly with the yellow image on the transfer material 10 held on the transfer drum and entering point A. The yellow toner is attracted by the positive bias voltage of the transfer drum, so that the image is not disturbed or retransferred to the image bearing drum 1 side.

Furthermore, through the same process, a cyan toner image obtained by exposure through a red filter F _R and development by a developing device 21C loaded with cyan developer is transferred overlappingly. After the transfer of the cyan toner image, the transfer material 10 is charged with an alternating current corona discharge from the transfer machine charge-eliminating corona discharger 27, and is separated from the surface of the drum 3 by lowering the separating claw 11 toward the transfer drum 3, as shown in the figure. The image is sent to a heat roller fixing device (not shown) and fixed. The three color toners transferred onto the transfer material 10 are
Upon fixing, the colors are melted and mixed to reproduce a color image using the subtractive color method.

The transfer drum 3 from which the transfer material has been separated is neutralized by a transfer drum static eliminator 28, and the toner adhering to the surface thereof is removed by a transfer drum cleaner 29, in preparation for the next copying operation cycle.

When making monochrome copies with this device, the developer 1
Copies can be made continuously and at high speed by operating only the base, placing the separating claw 11 in a lowered position, and continuously operating the static eliminator 27.

FIG. 3 shows an example in which a double-sided copying function is added to the color copying machine shown in FIG. 2, and the developing device and other omitted parts are the same as in FIG. 2.

The transfer material 10 is supplied in the same manner as in FIG.
The image carrier drum 1 is held on a transfer drum 3 which is negatively charged by a corona discharger and applied with a positive bias voltage, and rotates together with the transfer drum.
Yellow, magenta, and cyan toner images sequentially formed thereon are transferred to the first surface. The transfer material 10, on which the cyan image has been transferred, is discharged along the path indicated by the dashed line by a corona discharger 27 for eliminating static electricity from the transfer material, separated from the transfer drum 3 by the separating claw 11, and sent to the fixing device 31, where the upper surface is Once the color image is completed, it is temporarily discharged onto the paper discharge tray 32. The ejected transfer material is drawn into the copying machine from the rear by a second feeding roller 33, and is fed so that the first surface, on which an image has already been formed, contacts the transfer drum 3 . The transfer material that has reached the transfer drum 3 is cleaned by the corona discharger 34 on its second surface (the back side of the first surface).
Drum 3 is attracted and fixed to the transfer drum which is given a negative charge and a positive bias voltage is applied.
progresses with the rotation of. Thereafter, in the same way as for the first side, yellow, magenta, and cyan toner images are sequentially transferred, then peeled off from the drum surface, passed through the fixing device 31, and are deposited on the paper output tray 32 as a copy having color images on both sides. be discharged.

In addition to applying a positive bias voltage to the transfer drum 3 in this way, a corona discharger is provided opposite the transfer drum 3 to impart a negative positive charge to the transfer material with the same polarity as that of the toner. It's okay.

In the above embodiment, the case of color copying using a normal three-color separation filter and yellow, magenta, and cyan toners was explained, but the color and number of color separation filters and toners, the number of developing devices, etc. Of course, it is not limited.

〔Effect of the invention〕

With the image transfer device of the present invention, which does not require a transfer material locking means on the transfer drum, the transfer material holding drum can be used at any position because there is no locking means, and the transfer drum and image carrier are kept in pressure contact at all times. This has many advantages, such as eliminating the need for mechanisms such as pressure release or positioning to avoid the locking means hitting the image carrier, and easy cleaning of the transfer drum. It is possible to obtain a multicolor electrostatic recording device that is reliable, has no color shift, and has a simple structure.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the operation of an image transfer device according to the present invention, Fig. 2 is a schematic diagram of a color copying machine using the image transfer device of the present invention, and Fig. 3 is a schematic diagram of a color copying machine with a double-sided copying function added. It is. 1 ...Image carrier drum, 3 ...Transfer drum, 3
... Conductive substrate, 4 ... Conductive elastic layer, 5 ...
Insulating layer, 7...corona discharger for imparting charge to the transfer material.

Claims (1)

[Scope of Claims] 1. An image transfer device that transfers a charged toner image formed on a rotating image carrier to a transfer material through a transfer material between the image carrier and the transfer drum during rotational contact between the image carrier and the transfer drum. The transfer drum has a thin insulating surface layer with a layer thickness of 10 to 100 μm and a conductive support layer therebelow, and a transfer bias voltage having a polarity opposite to the charge of the toner is applied to the conductive support layer. , a charge having the same polarity as the charge of the toner for electrostatically adhering the transfer material to the surface of the transfer drum on the outer surface of the transfer material on the side that contacts the image carrier before passing during the rolling contact; An image transfer device characterized in that it is provided with a charge applying means that provides a charge. 2. The image transfer device according to claim 1, wherein the conductive support layer of the transfer drum is an elastic layer provided on a conductive substrate.