JPH0453312B2 - - 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 devices have been proposed in the past 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 create multiple color toner images on the same transfer material. The most common method is to obtain a multicolor image by sequentially overlapping and transferring the images. 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 Tokkai 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. [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 provide a color image transfer device that obtains a color toner image by sequentially overlapping and transferring charged toner images formed on an image carrier onto a transfer material. A conductive elastic layer is formed thereon, an insulating layer is provided on the outermost layer of the insulating layer, and a rotatable transfer drum that supports the transfer material on the insulating layer is paired with the image carrier and the transfer drum. A transfer material charge is provided facing the transfer drum on the upstream side of the transfer material conveyance in a space near the contacting transfer position, and provides a charge of opposite polarity to the charge of the color toner of the transfer material to which the color toner image is transferred. and a transfer drum charge applying means that is provided facing upstream of the transfer position of the transfer drum and applies a charge of the same polarity as the toner to the surface of the transfer drum. Achieved by equipment. In other words, the transfer material is placed on a transfer drum that has been charged with the same polarity as the toner charge, and then a charge of the opposite polarity is applied to the surface of the drum, so that the transfer material is attracted and held onto the transfer drum by electrostatic force. After this, the toner image is transferred. According to this device, there is no need for any locking means such as grippers to fix the transfer material on the transfer drum. Multiple toner transfer without color misregistration can be performed without any problems.
Furthermore, since the transfer material has a charge of opposite polarity to the toner, toner can be transferred with high efficiency. The two 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 surface of the transfer drum, but a corona discharger is particularly preferably used. The polarity of the charge applied depends on the charge polarity of the toner to be transferred (determined according to the polarity of the electrostatic image formed on the image carrier), and for the transfer material, the polarity of the toner is opposite to that of the toner,
The transfer drum has the same polarity as the toner. When a corona discharger is used as a charge imparting means, the voltage applied to the discharger varies depending on the properties of the image carrier, toner, etc., but is usually 5 to 8 KV ( It is preferable that the polarity is opposite to that of the toner. The surface potential of the transfer drum is 100 to 300V (the polarity is the same as the toner)
It is preferable to apply a charge so that
It is preferable to apply a voltage of 6 KV (the polarity is the same as that of the toner). 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 thereof has appropriate elasticity. For this reason, 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 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, polyvinylacetate, methacrylic resin, acrylic resin, polystyrene, silicone resin, fluorine resin, styrene-butadiene copolymer, and various other materials. 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 composed of a conductive substrate 1 and a photosensitive layer 2; 3 is a conductive substrate 3; a conductive elastic layer 4; This is a transfer drum made 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 negatively charged 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 positive 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 material holding drum 3 ), which advances in the direction of arrow D by a feeding means not shown in the figure, is coated with toner on its surface by a corona discharger 7. It is given a positive charge of opposite polarity and enters the transfer section where the image bearing drum 1 and the transfer material holding drum 3 are in contact. The negatively charged toner particles are attracted by the positive charges on the surface of the transfer material and move toward the transfer material, completing the transfer of the first toner image. When the transfer material comes out of the pressure contact portion of both drums, electrostatic attraction from both drums is applied to the transfer material, but the positively charged transfer material 10 is negatively charged in advance by the transfer drum charge-applying corona discharger 6. It is strongly attracted to the surface of the transfer drum 3 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 drum 3 rotates, the transfer material 10 wrapped around the transfer drum 3 advances to the transfer section A again and transfers to the second transfer section A.
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 rotation 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 back surface of the transfer material is maintained without attenuation because the surface of the transfer drum is insulating, 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 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 directly ejected 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 device of the present invention, where there is no transfer material locking portion on the transfer drum 3 and the drum can be used at any position. Also, 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, the photoreceptor can be not only drum-shaped but also belt-shaped and various other shapes. 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. Known two-color image forming means including an erasing process can be used in combination with various multi-color image forming means. 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 the filter F _B is placed in the optical path. 1 is a photosensitive drum configured similarly to the image bearing drum shown in FIG. 1, and has a specific dielectric constant ε=6 and a film thickness.
A 60 μm Se-Te photoreceptor is used. The drum rotates in the direction of the arrow, and after its 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 negatively charged in advance to a surface potential of -200V by the transfer drum charge adding corona discharger 6, and furthermore, the transfer material is charged by corona discharge on its surface. A positive charge of 3×10 ⁻⁴ C/m ² is given by the electric device 7 . 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.
The yellow toner image is transferred between the transfer drum 3 and the transfer drum 3 . Since the surface of the transfer material is positively charged, negatively charged toner transfers extremely well. The transfer drum 3 has the same structure as that shown in FIG. 1, but the details are omitted in the figure. Transfer drum 3
has a diameter of 150 mm, the conductive elastic layer is made of conductive rubber with a thickness of 2 mm, a hardness of 50°, and a volume resistivity of 10 ⁵ Ωcm, and the insulating layer has a thickness d _d = 10 μm and a specific dielectric constant ε _d =
Constructed from No. 3 polyester. The transferred transfer material 10 is wound and held by the electrostatic force of the negatively 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 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 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 transfer paper due to its positive charge, and 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. After the transfer of the cyan toner image, the transfer paper 10 is charged with alternating current corona discharge from the transfer machine charge-eliminating corona discharger 27, and separated from the surface of the drum 3 by lowering the separating claw 11 toward the transfer drum 3 . It is sent to an unheated heat roller fixing device to be fixed. The three color toners transferred onto the transfer paper 10 are fixed and melted and mixed to reproduce a color image using a 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 using this device, use the developing device 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] In 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. It has many advantages, such as making it possible to keep the transfer drum in pressure contact with the image carrier 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. A multicolor electrostatic recording device with reliable image transfer, no color shift, and simple structure can be obtained.

[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. In a color image transfer device that obtains a color toner image by sequentially overlapping and transferring charged toner images formed on an image carrier onto a transfer material, A transfer drum in which a conductive elastic layer is formed, an insulating layer is provided on the outermost layer, a rotatable transfer drum supports the transfer material on the insulating layer, and the image carrier and the transfer drum are in contact with each other. A transfer material charge that is provided facing the transfer drum on the upstream side of the transfer material conveyance in a space near the position, and applies a charge of opposite polarity to the charge of the color toner to the surface of the transfer material to which the color toner image is transferred. and a transfer drum charge applying means that is provided facing upstream of the transfer position of the transfer drum and applies a charge of the same polarity as the toner to the surface of the transfer drum. Device.