JPH0379707B2 - - 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 performing multiple transfers onto a transfer material to superimpose toner images to obtain a multicolor image. [Prior Art] Various methods and apparatuses 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 with the second and third color toners according to the number of required 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. Further, Japanese Patent Application Laid-open No. 18653/1983 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 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 for fully charging the transfer material to a polarity opposite to that of the toner at a position near the contact of the transfer material with the image carrier, and the transfer material holding means are insulated from at least a grounded conductive substrate. The present invention has been achieved by an image transfer device comprising a charging means for charging the insulating surface layer to the same polarity as the toner before the transfer material comes into contact with the insulating surface layer. In other words, a charge with the opposite polarity to that of the toner is given to the transfer material to promote transfer, and a charge of the same polarity as the toner, that is, the opposite polarity to the transfer material is given to the surface of the transfer drum, so that the transfer material is attracted by electrostatic attraction. This device attempts to attract and fix the transfer material to the surface of the transfer drum. According to this device, there is no need for any locking means such as a gripper to fix the transfer material on the transfer drum, and the various problems mentioned above are avoided. Multiple toner transfers can be performed without color misregistration. The two charge applying means used in the present invention are not particularly limited as long as they can apply a charge to the surface of the transfer material or 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). has the same polarity as the toner.
When using a corona discharger as a charge imparting means,
The voltage applied to the discharge device varies depending on the image carrier, the properties of the toner, etc., but it is usually preferable to set it to 5 to 8 KV (the polarity is opposite to that of the toner) for a corona discharge device that charges the transfer material. . 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 the transfer drum needs to press the transfer material onto the surface of the image carrier to transfer the toner, 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, polyvinyl acetate, methacrylic resin, acrylic resin, polystyrene, silicone resin, fluororesin, 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 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 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 consisting of an insulating layer 5. 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. 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 image bearing 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 fed from the back side by a corona discharger 7. The toner is given a positive charge of opposite polarity to the toner before the transfer section A, and enters the transfer section A 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 back side of the transfer material and migrate to the transfer material side, 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 more strongly attracted to the surface of the transfer drum 3 and is wrapped around and fixed to the surface of the transfer drum 3. Since the transfer material is in full contact with the transfer drum and strongly adsorbed, it will not shift during subsequent processes. As the 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 is switched on at the point where the transfer drum has made one revolution to prevent discharge from occurring on the transfer material.
and stop the operation. 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 number, the transfer material 10 is separated from the drum 3 and advances in the direction of arrow E. When monochrome copying is to be performed, this mode is set from the beginning, and 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 device of the present invention, which has no transfer material locking portion on the transfer drum 3 and can use the drum at any position.
In a device having a locking portion, even in the case of monochrome copying, drum positioning, locking, and locking release 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.
Further, the photoreceptor may be not only drum-shaped but also belt-shaped and various other forms. 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. Next, referring to FIG. 2, conditions under which the transfer can be performed well and the transfer paper is sufficiently retained on the transfer drum will be explained. FIG. 2 is a schematic cross-sectional view of the main part of the pressure bonding part (part A in FIG. 1 ) of the transfer _part in FIG. , the width of the gap 32 is da, the thickness of the transfer paper is dp, the dielectric constant is ε _p , the electric charge is σ _p , the width of the gap 33 is db, the dielectric constant of the insulating layer 5 of the transfer drum 3 is ε _d , When the thickness is da and the voltage is −σ _d , the transfer electric field E _T (vector direction is shown) is E _T =−(d _b +d _d /ε _d )σ _p +d _d /ε _d σ _d /ε ₀ (d _n
/ε _n +d _a +d _p /ε _p +d _b +d _d /ε _d ), and when the value of E _T is negative, negatively charged toner can be transferred. Furthermore, the electric field E ₁ drawn toward the photoreceptor side of the transfer paper is E ₁ =−(d _b +d _d /ε _d )σ _p +d _d /ε _d σ _d /ε ₀ ε _p (
d _n /ε _n +d _a +d _p /ε _p +d _b +d _d /ε _d ). When this value is negative, the transfer paper is pulled toward the photoreceptor, and the force F ₁ is F ₁ = (−(d _b +d _d /ε _d )σ _p +d _d /ε _d σ _d ) ² /2ε
₀ ε _p (d _n /ε _n +d _a +d _p /ε _p +d _b +d _d /ε _d ) ² . On the other hand, the electric field E ₂ that pulls the transfer paper toward the transfer drum is E ₂ = (d _n /ε _n +d _a +d _p /ε _p )σ _p +d _d /ε _d σ _d /
It is expressed as ε ₀ (d _n /ε _n +d _a +d _p /ε _p +d _p +d _d /ε _d ). When this value is positive, the transfer paper is pulled toward the photoreceptor, and the force F ₂ is F ₂ = ((d _n /ε _n +d _a +d _p /ε _p )σ _p +d _d /ε _d σ _d
) ² /2ε ₀ (d _n /ε _n +d _a +d _p /ε _p +d _b +d _d /ε _d ) ² . For good transfer, |E _T |
It must be 100KV/cm or more,
It is preferable that it is 350KV/cm or more. In addition, in order for the transfer paper to wrap around the transfer drum, the relationship |F ₁ |<|F ₂ |...(1) must be established. By substituting F ₁ and F ₂ into the above equation (1), the conditions for each parameter can be found, and by determining some of the parameters, other desirable parameters can be obtained. As will be described later, it was confirmed that the above-mentioned requirements for holding the transfer material by the transfer drum were satisfied in the apparatus in which good transfer was actually performed. [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. 3 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. Development was carried out using a two-component developer. Reference numeral 1 denotes a photosensitive drum configured similarly to the image bearing drum shown in FIG. 1, with relative dielectric constant ε _n =6, film thickness =
A 60 μm Se-Te photoreceptor is used. The drum rotates in the direction of the arrow, and after being given a positive charge to the entire surface 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 4× on its back by corona discharger 7.
It is given a positive charge of 10 ^-4 C/m ² and sent to the transfer position A, and is pressed between the photosensitive drum 1 and the transfer drum 3 to transfer the yellow toner image . Before contacting the transfer drum, a negative charge of -5.3×10 ^-5 C/m ² is applied in advance by a charge-applying corona discharger 7 . 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 of d _d = 100 μm and a relative permittivity ε _d =
Constructed from 3 polyester. Also, the dielectric constant ε _p = 2, thickness dp of the transfer paper used
= 100 μm, and the distance da between the photoreceptor and the transfer paper and the distance db between the transfer drum and the transfer paper were both 1 μm. After the transfer, the transfer material 10 is wound around the negatively charged transfer drum 3 by electrostatic force, held and moved. 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. At this time, the discharge by the corona discharger 6 to the transfer drum surface is stopped. The second exposure uses green filter F _G ,
Development is performed by a developing device 21M loaded with 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 paper, 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. Transfer paper 1 on which the cyan toner image has been transferred
The transfer material 0 is charged by an alternating current corona discharge from the transfer material static elimination corona discharger 27, separated from the surface of the drum 3 by lowering the separating claw 11 toward the transfer drum 3 , and sent to a heat roller fixing device (not shown in the figure). The toner image is 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. The parameters of this example are summarized as follows. Photoreceptor: Se/Te ε _n = 6, dm = 60 μm da, db: 1 μm Paper: ε _p = 2, dp = 100 μm σ _p : 4×10 ^-4 C/m ² σ _d : −5.3×10 ^-5 C/m ² Insulating layer: Polyester ε _d = 3, d _d = 100 μm E _T , E ₁ , calculated using these parameters
The values of E ₂ , F ₁ , F ₂ are as follows, which meet the requirements for the transfer described above. E _T =-1.4×10 ⁷ V/m E ₁ =-7×10 ⁶ V/m E ₂ =3.1×10 ⁷ V/m F ₁ =4.4×10 ² N/m ² F ₂ =4.2×10 ³ N/m ² When making monochrome copies using this device, 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] 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 is possible to keep the transfer drum in pressure contact with the image bearing member at all times, there is no need for a mechanism such as release of pressure contact or positioning to avoid the locking means hitting the image carrier, cleaning of the transfer drum is easy, and many other advantages. A multicolor electrostatic recording device with reliable image transfer, no color shift, and simple structure can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the operation of the image transfer device according to the present invention, FIG. 2 is a schematic diagram of the pressure contact portion of the transfer section, and FIG.
The figure is a schematic diagram of a color copying machine using the image transfer device of the present invention. DESCRIPTION OF SYMBOLS 1 ... Image carrying drum, 3 ... Transfer drum, 3... Conductive base, 4... Conductive elastic layer, 5... Insulating layer, 6...
Transfer drum charge imparting corona discharger, 7... Transfer material charge imparting corona discharger.

Claims (1)

[Scope of Claims] 1. A color image in which a colored toner image is obtained by electrostatically transferring a charged toner image formed on an image carrier onto a transfer member held by a transfer material holding means in order. In the transfer device, a charging device charges the transfer material to a polarity opposite to that of the toner at a position before the transfer material comes into contact with the image carrier, and the transfer material holding device includes at least a grounded conductive substrate and an insulating surface layer. A color image transfer device comprising: a charging means for charging the insulating surface layer to the same polarity as the toner before the transfer material comes into contact with the insulating surface layer. 2. The transfer drum having an insulating surface has a conductive drum base, a conductive elastic layer provided on the base, and an insulating layer provided on the surface of the conductive elastic layer. A color image transfer device according to claim 1.