JPH0453313B2 - - 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 for the purpose of obtaining multicolor images using electrophotography. After developing with the first color toner, it is transferred to a transfer material such as paper, and the same process is repeated for the second and third colors according to the required number of color separations to sequentially create multiple color toner images on the same transfer material. The most common method is to transfer the images one on top of the other to obtain a multicolor 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. Complex electrostatic forces act on the transfer material, such as having 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, a complicated mechanism is required to automatically lock, release, and separate the transfer material, and the speed of the copying operation is reduced due to the need to have different locking positions. There are many problems such as restrictions on the sequence, dirt on the locking part, blanks 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. Problems have arisen, and it has been desired to develop a simpler and more reliable transfer material fixing means. [Object of the Invention] An object of the present invention is to provide an image transfer device for a multicolor electrostatic recording device with a simple structure that can reliably transfer multiple toner images onto a transfer material without causing color misregistration. It's about doing. [Structure of the Invention] The above object is to obtain a color toner image by sequentially overlapping and electrostatically transferring charged toner images formed on an image carrier onto a transfer material held by a transfer material holding means. In the color image transfer device, a charging means charges the surface of the transfer material holding means to a polarity opposite to that of the toner at a position where the transfer material faces the transfer material holding means, and the transfer material holding means is at least grounded. An image transfer device comprising a conductive substrate and an insulating surface layer, and a charging means for charging the transfer material to the same polarity as the charge of the toner at a position in front of the transfer material in contact with the insulating surface layer. was achieved. That is, the transfer material is placed on a transfer drum (hereinafter referred to as a transfer drum) which is a transfer material holding means for adsorbing and holding the transfer material by applying a charge of opposite polarity to that of the toner in advance, and then the toner is drawn from the surface of the transfer drum. After the transfer material is attracted and held by the transfer drum by electrostatic force by applying an electric charge of the same polarity as,
This device transfers a toner image, and this device does not require any gripping means such as a gripper to fix the transfer material on the transfer drum, which causes various problems as described above. Multiple transfers of toner can be performed without color misregistration. At this time, since the transfer material is charged with the same polarity as the toner, a repulsive force is generated between the toner and the transfer material, but the transfer drum has a high static charge with the opposite polarity to the toner. Since a charge is applied, if the amount of transfer applied to the transfer material is set to a low value, the electrostatic field generated by the charge on the transfer drum will overcome the charge on the transfer material and attract the toner together with the transfer material toward the transfer drum. Toner transfer and retention are performed well. Furthermore, since the electric charges of the toner and the transfer material are both opposite in polarity to the electric charge of the transfer drum, the adsorption of the transfer material to the transfer drum becomes extremely strong. The transfer material charge applying means and the transfer drum charge applying means used in the present invention are not particularly limited as long as they can apply charges to the transfer material or the transfer drum, respectively, but a corona discharger is particularly preferably used. The polarity of the charge applied to the transfer material is determined so that it has the same polarity as the charge of the toner to be transferred (determined according to the polarity of the electrostatic image formed on the image carrier). Set. When a corona discharger is used, the applied voltage varies depending on the properties of the image carrier and the toner, but is usually in the range of 4 to 7 KV, which has the same polarity as the toner. Further, it is preferable that the charge applied to the transfer drum is set to a surface potential of 0.5 to 1.5 KV, which has a polarity opposite to that of the toner.
It is appropriate to set the voltage to between 8KV and 8KV. The transfer drum has an insulating layer on the surface of the conductive substrate.
The structure may be such that the conductive portion can be grounded, but since it is necessary for the transfer drum to transfer the toner by pressing the transfer material onto the surface of the image carrier, it is preferable that the surface has a suitable degree of elasticity. Therefore, it is preferable to have a structure in which a conductive elastic layer is provided on a conductive substrate, and an insulating layer is further provided on the surface of the conductive elastic layer. As the conductive substrate, it is preferable to use metal such as aluminum, for example. Preferred examples of the conductive elastomer include conductive rubber, such as silicon type or chloroprene type 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-butidiene copolymer, and various other insulators. It can be constructed using a polymer or 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 preferably 10 to 100 μm. 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 which is made up of a conductive substrate 1 and a photoconductive photosensitive layer 2, 3 is a conductive substrate 3a, and a conductive elastic layer 4. , a transfer drum consisting of an insulating layer 5. The figure shows a case where a photosensitive layer that forms a positively charged electrostatic image, such as selenium-based or amorphous silicon, is used. The transfer drum 3 is grounded, and its surface is directly given a positive charge by a transfer drum charging corona discharger 6. Reference numeral 7 denotes a corona discharger for applying a charge to the transfer material, which is provided opposite to the transfer drum, and a negative voltage is applied thereto. 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 coated with toner by a corona discharger 7 on its surface. It is charged with a negative polarity and enters the transfer section 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 charge on the surface of the transfer drum and move toward the transfer material, completing the transfer of the first toner image. When the transfer material leaves the pressure contact portion of both drums, electrostatic attraction from both drums is applied to the transfer material, but the negatively charged transfer material 10
is more strongly attracted to the surface of the transfer drum 3 , which has been positively charged in advance by the transfer drum charging corona discharger 6, and is wound and fixed on the surface.
The transfer material is in full contact with the transfer drum and is strongly adsorbed, so it will not shift during subsequent processes. As the transfer drum 3 rotates, the transfer material 10 wrapped around the transfer drum 3 advances again to the transfer section A, where the second toner image is transferred. The corona discharger 6 operates a switch SW to stop its operation at the point where the transfer drum has completed one revolution so that no discharge is applied to the transfer material.
Thereafter, the same transfer process is repeated as many times as necessary, and a multicolor image is completed on the transfer material 10. During this time, the positive charge applied to the surface of the transfer drum is maintained without attenuation because the surface of the transfer drum is insulative, and the toner is transferred smoothly. After the transfer is completed, the transfer material may be separated from the transfer material holding drum using a separation means such as a separation claw and sent to the fixing process. In the figure, reference numeral 11 denotes a separation claw, and by rotating this to the position indicated by the dotted line, the transfer material 10 is separated from the transfer drum 3 and advances 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 3 and can use the drum at any position. It is difficult to increase the speed because positioning, locking, and locking operations of the drum are required. 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.
Further, although the transfer drum 3 is shown as being grounded in FIG. 1, sufficient transfer, winding and separation performance can be obtained by applying an appropriate bias voltage. In addition to the transfer material separation means, the image transfer device of the present invention may be provided with additional devices such as a transfer material static eliminator, a transfer material holding drum static eliminator, a transfer material holding drum cleaner, and a positioning sensor, as necessary. be able to. 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] Hereinafter, an example will be shown in which the image transfer device according to the present invention is used in a color copying machine using a three-color separation method. 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. In the figure, an arrow L indicates an optical path for image exposure by scanning an original image sent from an optical system not shown in the figure. The scanning is repeated three times, and each time the filters F _R (red) and F _G
(green) and F _B (blue) are alternately inserted into the optical path L to perform color separation exposure. The figure shows a state in which a blue filter F _B is placed in the optical path. 1 uses a selenium-based photoreceptor configured in the same manner as the image bearing drum shown in FIG. It is a drum and 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 photosensitive drum 1 , which is then developed by a developing device 21Y loaded with a negatively charged yellow developer to form a yellow toner image. The photosensitive drum carrying the yellow toner image is neutralized by the pre-transfer static eliminating lamp 22 and advances to the transfer position A. On the other hand, the transfer paper 1 is fed through the paper feed roller 23
0 is attracted by electrostatic force to the transfer drum 3 , which has been given a positive charge in advance by the transfer drum charge imparting corona discharger 6 so that its surface potential is +800V to +1000V, and furthermore, the transfer material is charged on its surface. Negative charge is generated by the corona discharger 7 by -1×10 ^-8
It is given to be C/cm ² . As a result, the transfer material 10 is strongly attracted and held by the transfer drum 3 , moves to the transfer position A, and moves to the photosensitive drum 1 and the transfer drum 3.
A yellow toner image is transferred by sandwiching pressure between them. Although the surface of the transfer material is negatively charged, the transfer drum's strong positive electrostatic field allows the negatively charged toner to be transferred smoothly. The transfer drum 3 has the same structure as that in FIG. 1, but is omitted in FIG. 2. The conductive rubber layer of the transfer drum 3 in this embodiment has a thickness of 2
It was made of polyester with a dielectric constant of 3 and a hardness of 50° and a volume resistivity of 10 ⁵ Ωcm and a thickness of the insulating layer of 12.5 μm. The transferred transfer material 10 is wound and held by the electrostatic force of the positively charged transfer drum 3 and moves. After the photosensitive drum has been transferred, the toner remaining on the surface of the drum is removed by a cleaning device 24, and the residual charge is removed by a charge removal lamp 25, and then the photosensitive drum is reused. The transfer paper 10 held on the transfer drum 3 advances as the transfer drum 3 rotates, and its position is read by the sensor 26, and the second exposure operation is started in synchronization with this position. . Furthermore, when the sensor 26 detects the leading edge of the transfer material, the voltage application to the transfer material charging corona discharger is stopped to prevent damage to the negatively charged toner image transferred to the surface of the transfer material due to negative discharge. To prevent. The second exposure uses a green filter _FG , and development is performed using a developing device 21M loaded with a negatively charged magenta developer. The obtained magenta toner image is transferred overlappingly onto the yellow image on the transfer paper 10 held on the transfer drum and entering point A. The yellow toner is attracted by the positive charge of the transfer drum, so that the image is not disturbed or retransferred to the photosensitive 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. The transfer paper 10, on which the cyan toner image has been transferred, is subjected to AC corona discharge from the transfer machine static elimination corona discharger 27 to eliminate static electricity, and the separating claw 11 is lowered to the transfer drum 3 side to separate it from the surface of 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 paper 10 are fixed and melted and mixed to reproduce a color image by the subtractive color method. The transfer drum 3 from which the transfer paper 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. 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. [Effects of the Invention] The image transfer device of the present invention, which does not require a transfer material locking means on the transfer drum, allows the transfer drum and image carrier to be used in any desired position because there is no locking means. It has many advantages, such as being able to maintain pressure contact at all times, eliminating the need for mechanisms such as release of pressure contact or alignment to prevent the locking means from hitting the image carrier, and easy cleaning of the transfer drum. In addition, in the present invention, since the transfer drum surface is directly charged with a charge using a corona discharger, the transfer material is strongly attracted to the transfer drum surface, so that image transfer is reliable and color misregistration is prevented. It is possible to obtain a multicolor electrostatic recording device that does not require the above-mentioned method 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, and FIG. 2 is a schematic diagram of a color copying machine using the image transfer device of the present invention. 1 ...image bearing drum, 3 ...transfer drum, 3...
... conductive substrate, 4 ... conductive elastic layer, 5 ... insulating layer, 6 ... transfer drum charge imparting corona discharger,
7...Corona discharger for imparting charge to the transfer material.

Claims (1)

[Scope of Claims] 1. A color image in which charged toner images formed on an image carrier are sequentially stacked and electrostatically transferred onto a transfer material held by a transfer material holding means to obtain a color toner image. In the transfer device, the transfer material holding means includes: a charging means for charging the surface of the transfer material holding means to a polarity opposite to that of the toner at a position where the transfer material faces the transfer material holding means; and a conductive member on which the transfer material holding means is at least grounded. a color image comprising a charging means for charging the transfer material to the same polarity as the charge of the toner at a position in front of the transfer material in contact with the insulating surface layer; Transfer device.