JPH04315167A - Color image forming device - Google Patents

Abstract

PURPOSE:To offer a color image forming device which is simple, small-sized and inexpensive and where the generation quantity of ozone caused by corona discharge is reduced. CONSTITUTION:An attracting roller 2 which electrostatically attracts a transfer material 17 on a dielectric sheet 15 on the surface of a transfer drum 21 is used also as a destaticizing means for destaticizing the sheet 15 after separating the transfer material 17 where the multiple transfer of the image of each color is finished. Since a destaticizing charger for the sheet 15 is not needed, the device is simplified, miniaturized, and becomes inexpensive, and the corona discharge is reduced because the destaticizing charger for the sheet is eliminated, then the generation quantity of ozone caused by the corona discharge is reduced.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an image forming apparatus using electrophotography or the like, and in particular, the present invention relates to an image forming apparatus using electrophotography or the like. The present invention relates to a color image forming apparatus that obtains images.

0002

2. Description of the Related Art Conventionally, electrostatic recording systems based on electrophotography have been widely used in color image forming apparatuses.

As shown in FIG. 5, this color image forming apparatus includes an image carrier 8 on which an electrostatic latent image of each color image is formed by exposure 14 of an image signal emitted from a light source such as a laser beam; A developing device 7 that develops a latent image formed on a carrier 8 with a developer of a corresponding color to form an image of each color, and has a plurality of developing devices 7 that separately accommodate developers of each color.
A and the transfer drum 18 by electrostatic adsorption by the transfer material holding means.
A transfer device 18A, which includes a transfer material holding means, a transfer means, a transfer drum 18, etc., obtains a color image by multiple-transferring each color image on the image carrier by a transfer means onto the transfer material 17 held above. , a cleaner 9 that cleans residual toner on the image carrier 8 after transferring each color image, and a fixing device that transfers each color image and fixes the image on the transfer material 17 separated from the transfer drum 18 It basically consists of a container 12.

The above-mentioned transfer drum 18 has a side surface of the drum main body, which is a hollow frame, with only the transfer area cut out, and polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), and fluorinated ethylene propylene are used in the cutout. It has a structure in which a dielectric sheet 15 typified by a polymer (FEP) or the like is stretched.

The above transfer device 18A includes a transfer drum 18.
The following equipment is basically placed around the That is, at a position on the opposite side of the transfer drum 18 from the image carrier 8, there is an attraction roller 2, which constitutes a transfer material holding means on the outside, and an attraction charger 3, which also constitutes a transfer material holding means, on the inside, opposite thereto. are arranged, the suction roller 2 holds the transfer material 17 on the dielectric sheet 15 by electrostatic adsorption, and the adsorption charger 3 charges the dielectric sheet 15 at this time to bring the transfer material 17 into close contact with the dielectric sheet 15. The image formed on the image carrier 8 is transferred to a transfer material 17 at a position inside the transfer drum 18 facing the image carrier 8.
A transfer charger 4 constituting a transfer means for transferring the image is disposed on the upper inner side and outer side of the transfer drum. A pair of separation chargers 5 are disposed, and a separation and neutralization charger 6 is further disposed at an outer position downstream of the separation charger 5 in the rotational direction of the transfer drum 18 to prevent peeling discharge occurring in the transfer material 17 after separation. A separating claw 10 is arranged nearby to assist in separating the transfer material 17 and guide it to the transfer material conveyance path 16 to the fixing device 12 . A transfer drum cleaner 11 for removing toner adhering to the surface of the dielectric sheet 15 is installed at an outer position of the transfer drum 18 between the separation claw 10 and the suction roller 2, and a dielectric sheet A sheet charger 1 for electrically initializing the charger 15 is disposed.

An image forming process in a color image forming apparatus equipped with the above-described equipment will be described.

First, the electrostatic latent image of the first color image formed on the image carrier 8 by exposure 14 based on the first color image signal is treated with a developer of a corresponding color, for example, yellow. A yellow image is formed by developing with the developing device 7Y. In parallel with this, in the transfer drum 18, the transfer material 17 supplied thereto is sandwiched between the grounded adsorption roller 2 and the dielectric sheet 15 on the surface of the transfer drum 18, and at the same time, the transfer material 17 is placed on the back side of the transfer drum 15 by the adsorption charger 3. By applying a charge from
The transfer material 17 is held on the dielectric sheet 15 by electrostatic attraction. Transfer material 1 held on dielectric sheet 15
7 is conveyed to an image transfer section facing the image carrier 8 as the transfer drum 18 rotates. In the image transfer section, the yellow image formed on the image carrier 18 by the transfer charger 4 is transferred onto the transferred transfer material 17.

Next, the residual toner on the image carrier 8 after the transfer of the yellow image is completed is removed by a cleaner 9, and the toner of the second color is applied onto the image carrier 8 by exposure 14 based on the image signal of the second color. A developing device 7M that forms an electrostatic latent image of an image and has a developer of a color corresponding to the electrostatic latent image, for example, magenta.
Developed to form a magenta image. This second color magenta image is transferred by the transfer charger 4 in the image transfer section in a superimposed manner onto the transfer material 17 onto which the first color yellow image has been transferred, as described above.

Thereafter, in the same manner, an electrostatic latent image of the third color image is formed on the image carrier 8, development is performed by the developing device 3Y having a developer of a corresponding color, for example, cyan, and the transfer charger 4 is
transfer of the cyan image onto the transfer material 17 by using the transfer material 17, formation of a fourth color electrostatic latent image, for example, development by the developer 3B having a black developer, and transfer of the black image onto the transfer material 17 by the transfer charger 4. Transfer is performed, and a color image in which a yellow image, a magenta image, a cyan image, and a black image are multi-transferred onto the transfer material 17 is obtained.

The transfer material 17 on which the color image has been formed as described above is conveyed to the separation charger 5 on the inside and outside of the transfer drum 18 by the rotation of the transfer drum 18. The electrostatic adhesion between the sheet and the dielectric sheet 15 is removed, and the electric charge is removed by the separation charger 6 and the transfer drum 18 is separated from the transfer drum 18 via the separation claw 10 . The separated transfer material 17 is conveyed to the fixing device 12 by the transfer material conveyance path 16, where the transferred multi-color image on the transfer material 17 is fixed and mixed to form a permanent color image. , and is discharged outside the image forming apparatus. After the transfer material 17 has been separated from the transfer drum 18, toner adhering to the dielectric sheet 15 on the surface of the transfer drum 18 is removed by the transfer drum cleaner 11, and then electricity is removed by the sheet charger 1 and initialized.

[0011]

[Problems to be Solved by the Invention] In the above, a typical example of a conventional color image forming apparatus is provided with a transfer drum 18 having a cutout structure. The image forming process in which a color image is obtained on the transfer material 17 by multiple-transferring the images of the above onto the transfer material 17 has been described.

In this conventional color image forming apparatus, as described above, a large number of devices such as the transfer charger 4 are arranged around the transfer drum 18, making the apparatus complicated, large and expensive. Moreover, since a large number of corona chargers such as the transfer charger 4 are used, a large amount of ozone is generated when the apparatus is operated.

In addition to the above, as a transfer drum used for multiple transfer in a color image forming apparatus, as shown in FIG. By using the transfer drum 21 of the solid drum type and applying a bias to it, multiple transfers similar to the notch structure transfer drum 18 can be performed. According to this method, the dielectric sheet 1
5 is supported from the inside by the entire drum body 20,
This has the advantage of reducing the deformation and damage of the dielectric sheet 15, which is a problem with the transfer drum 18 having a cutout structure, and the interior can be simpler than the above-mentioned transfer drum 18 having a cutout structure. There is no change in the fact that a large number of devices such as the transfer charger 4 must be arranged in a concentrated manner around the transfer charger 4, and therefore the cost reduction is not so great. There is also the problem that a large amount of ozone is generated during operation of the equipment due to the use of a large number of them.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color image forming apparatus which can be made simple, compact and inexpensive, and which can also reduce the amount of ozone generated during operation of the apparatus.

[0015]

Means for Solving the Problems The above objects are achieved by a color image forming apparatus according to the present invention. In summary, the present invention includes an image carrier that forms a latent image of each color, a developing device that develops the latent image with a developer of a corresponding color to form an image of each color, and a transfer drum that uses a suction roller to form an image of each color. and a transfer means for obtaining a color image on the transfer material by multiple-transferring the formed images of each color onto a transfer material held on a dielectric sheet, wherein the suction roller This is a color image forming apparatus characterized in that the color image forming apparatus also serves as a charge eliminating means for eliminating charge from the dielectric sheet after the multi-transferred transfer material is separated from the dielectric sheet of the transfer drum.

According to a preferred embodiment of the present invention, the suction roller is formed of a conductive elastic material having a volume resistivity of 109 Ωcm or less, and according to another preferred embodiment, the suction roller has a crown shape. be done.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an enlarged sectional view showing the vicinity of a transfer material holding section of a transfer device 18A in an embodiment of a color image forming apparatus of the present invention.

In the color image forming apparatus of this embodiment, in the color image forming apparatus shown in FIG. 5, the transfer device 18A is provided with a conductive drum as shown in FIG. A solid drum type transfer drum 21 having the same structure as shown in FIG. 6 is provided, the surface of the main body 20 being covered with a dielectric sheet 15. Transfer drum 2
Similar to the color image forming apparatus shown in FIG.
When the transfer material 17 is held on the dielectric sheet 15 by the bias applied to the drum body 20 from the back side of the dielectric sheet 15 by the adsorption power source 24 connected to the conductive drum body 20, the transfer material 17 is connected to the roller core bar 22. The bias power supply 25 injects charges corresponding to the bias into the transfer material 17 to bring the transfer material 17 into close contact with the dielectric sheet 15.

In the present invention, instead of providing the sheet neutralization charger 1 as a static eliminating means for neutralizing the dielectric sheet 15 after the multiple-transferred transfer material 17 is separated from the dielectric sheet 15 of the transfer drum 21, The feature is that this suction roller 2 also serves as a static eliminating means. Therefore, the following description of the image forming process will be made with reference to the color image forming apparatus shown in FIG.

The image forming process in the color image forming apparatus of the present invention will be explained below.

First, the transfer material 17 conveyed to the transfer drum 21 of the transfer device 18A is pressed against the dielectric sheet 15 by the suction roller 2 which can be moved into and out of contact with the dielectric sheet 15 on the surface of the transfer drum 21, and at the same time, the transfer material 17 is pressed against the dielectric sheet 15 on the surface of the transfer drum 21. The dielectric sheet 15 is attracted by the electrostatic adsorption force caused by the bias applied to the drum body 20 made of metal such as
held on the surface. The transfer material 17 is wound around the transfer drum 21 from its leading end, and is conveyed by the rotation of the transfer drum 21 to an image transfer portion where the image carrier 8 and the transfer drum 21 are in contact with each other. At this time, the suction roller 2 is held at a potential opposite to the bias applied to the drum body 20 by grounding or the power source 25 until the rear end of the transfer material 17 passes through the suction point where the suction roller 2 and the dielectric sheet 15 contact. be done. Thereafter, after the rear end of the transfer material 17 passes the above-mentioned suction point, the suction roller 2 is separated from the dielectric sheet 15.

In parallel with the above suction step, in the image transfer section, the image of the first color on the image carrier 8 is electrostatically transferred onto the conveyed transfer material 17 by the transfer charger 4. Subsequently, the transfer material 17 is transferred with second, third, and fourth color images a plurality of times in the same manner, and then separated from the transfer drum 21 by the separation charger 5 and the separation claw 10, and transferred to the fixing device. 12. According to the invention, this transfer material 17
At the time of rotation when the transfer material 17 is separated from the transfer drum 21, the suction roller 2, which had been separated during the image transfer, is brought into contact with the transfer drum 21 again when the rear end of the transfer material 17 passes the aforementioned suction point, The dielectric sheet 15 on the surface of the transfer drum 21 is neutralized. At this time, the dielectric sheet 15
If it is grounded so that the charge can escape, the static electricity will be eliminated, but
In order to efficiently eliminate static electricity from the dielectric sheet 15 after the transfer material 17 has been separated through the image forming process, it is effective to apply a bias that cancels out the surface potential of the dielectric sheet 15 using the suction roller 2.

In the case of the so-called solid drum type transfer drum 21 in which the surface of the conductive drum body 20 is covered with the dielectric sheet 15 shown in FIG. 1, when a final color transfer bias is applied to the transfer drum 21, To remove the residual charge on the dielectric sheet 15, apply a DC bias of the same polarity and degree as the transfer bias that converges with the applied transfer bias, and remove the residual charge on the dielectric sheet 15 when the transfer bias is not applied and is grounded. When this happens, the residual charge on the dielectric sheet 15 can be removed using the grounded suction roller 2. At this time, if an AC bias component is applied superimposed on the DC bias component of the static elimination bias for the dielectric sheet 15, the static elimination effect is further improved. In order to more effectively eliminate static electricity from the sheet, after the transfer material 17 is completely separated from the transfer drum 21, the suction roller 2 is applied while applying an AC bias to the conductive drum body 20.
It is recommended that static electricity be removed by At this time, it is effective to shift the periods of both applied AC biases to promote the static elimination effect. In addition, the surface potential of the dielectric sheet 15 after the transfer material 17 is separated varies greatly depending on the environment such as humidity, and also depends on the material that makes up the dielectric sheet 15. It is desirable to vary the sheet static elimination bias value applied depending on the environment and the like.

The sequence of the contact of the suction roller 2 and the application timing of the sheet static elimination bias in the image formation described above is as shown in FIG. This figure shows a sequence in which the entire process of image formation is completed by the transfer drum 21 rotating five times starting from the suction point, so that the sheet electricity has already been removed when the transfer bias is applied. However, if there is time to spare in the image forming process, the charge may be removed after the final color image transfer is completed or after the transfer material 17 is completely separated.

As described above, in the present invention, after the multiple-transferred transfer material 17 is separated from the dielectric sheet 15 of the transfer drum 21, the suction roller 2
5, the sheet static eliminating charger 1 is not provided, and the adsorption roller 2 is made to also function as a sheet static eliminating means, so the number of corona chargers around the transfer drum 21 can be reduced. Therefore, the color image forming apparatus can be made simple, small, and inexpensive, and the generation of ozone due to corona discharge can be reduced by the reduction in the number of sheet chargers 1.

Image formation has been described above using the case where the solid drum type transfer drum 21 is used as the transfer device 18A, but when the transfer drum 18 with the cutout structure shown in FIG. 5 is used as the transfer device 18A, However, similarly, the suction roller 2 may be brought into contact with the dielectric sheet 15 by grounding the suction roller 2 or by applying a bias that cancels out the potential on the surface of the dielectric sheet 15 with the suction roller 2 using the power source 25. . However, unlike in the case of the solid drum type transfer drum 21, charge removal from the sheet in this case is performed by only the AC component because the back surface of the dielectric sheet 15 is electrically insulated. Of course, it goes without saying that the DC component may be applied in a superimposed manner on the AC component.

As described above, these bias conditions vary greatly depending on the physical property values of the dielectric sheet 15, environmental conditions, and static elimination time. Experiments have shown that in PET, sufficient static elimination can be achieved with just the AC component, whereas in PVdF, the internal polarization is strong, so the DC component, which is opposite to the surface potential, can be removed by several orders of magnitude.
A more effective static elimination effect was obtained when 00 to several kV was applied. In addition, when applying a bias, the shield of the attraction charger 3, which serves as a counter electrode to the attraction roller 2, may be grounded, but it may also be held at a potential of opposite polarity to the bias applied to the attraction roller 2. When an AC voltage is applied to the suction roller 2, it is effective to apply an AC voltage with a period different from that period.

The case where the generation of ozone in the static elimination process is suppressed as much as possible has been described above, but if the speed of the image forming process is too fast and sufficient static elimination time cannot be obtained, the adsorption charger 3 may be used to suppress the generation of ozone as much as possible. It is effective to apply a polar corona discharge. Of course, in this case as well, it is more desirable to superimpose the AC component than only the DC component, and it is even more desirable to make the period different from the period of the AC component applied to the suction roller 2.

FIG. 3 is an enlarged sectional view showing the vicinity of the transfer material holding section of the transfer device 18A in another embodiment of the color image forming apparatus of the present invention. This embodiment is characterized in that the surface layer of the suction roller 2 is formed of an elastic body 19 having low to medium resistance. Other aspects of this embodiment are basically the same as the embodiment shown in FIGS. 1 and 2.

By forming the surface layer of the suction roller 2 with an elastic material 19 having low to medium resistance, pinholes in the dielectric sheet 15 caused by rush current generated by applying a bias when removing static electricity from the dielectric sheet 15 can be prevented. In addition, the degree of adhesion to the dielectric sheet 15 is improved compared to when the suction roller 2 is entirely made of a rigid body, so that the transfer material 17 and the dielectric sheet 15 when holding the transfer material 17 on the surface of the dielectric sheet 15 can be prevented. The air layer between the transfer material 17 and the transfer material 17 can be suppressed as much as possible, and the transfer material 17 can be stably electrostatically attracted onto the dielectric sheet 15 with little dielectric loss.

The elastic body 19 on the surface of the suction roller 2 is as follows:
A material having a volume resistivity of about 109 Ωcm or less is preferable. In addition, the hardness of the elastic body 19 is set at 5°, taking into consideration friction with the dielectric sheet 15 due to the hardness of the dielectric sheet 15, etc.
It is preferable to set the hardness to be suitable for the hardness of the dielectric sheet 15 within the range of ~80° (JISA). For example, when the dielectric sheet 15 is made of a PVdV sheet with a thickness of 150 μm, according to experiments, silicone rubber with an angle of 30° to 50°, C
When the elastic body 19 is formed of R rubber, urethane rubber, etc., the transfer material 1 is transferred onto the dielectric sheet 15 by the suction roller 2.
Good results were obtained in terms of adsorption of No. 7 and static elimination of dielectric sheet 15.

In the embodiments described above, the shape of the suction roller 2 is not particularly limited and is cylindrical as usual. However, as shown in FIG. If the suction roller 2 has a so-called crown shape in which the central part in the width direction is thicker than the end parts, the air between the transfer material 17 and the dielectric sheet 15 when the transfer material 17 is suctioned onto the dielectric sheet 15. This is preferable as the shape of the suction roller 2 because it has the effect of pushing out the layer to both ends of the transfer material 17 in the width direction.

[0033]

[Effects of the Invention] As explained above, the color image forming apparatus of the present invention is configured so that a sheet static elimination bias can be applied to the suction roller that brings the transfer material into close contact with the dielectric sheet, so a sheet static elimination charger is not required. Therefore, the device can be made simple, small, and inexpensive. In addition, since the number of corona chargers is reduced by eliminating the need for a sheet charger, the amount of ozone generated due to corona discharge can also be reduced. In addition, if the surface layer of the suction roller is made of an elastic material with low to medium resistance, it is possible to easily prevent the formation of pinholes in the dielectric sheet when static electricity is removed from the dielectric sheet by the suction roller. There is also the advantage that the transfer material can be stably electrostatically attracted onto the dielectric sheet, compared to when it is formed of a rigid body.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view showing the vicinity of a transfer material holding section of a transfer device in an embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a sequence diagram of an image forming process in the color image forming apparatus of FIG. 1;

FIG. 3 is an enlarged sectional view showing the vicinity of a transfer material holding section of a transfer device in another embodiment of the color image forming apparatus of the present invention.

FIG. 4 is a front view showing a preferable shape of the suction roller of the transfer device in still another embodiment of the color image forming apparatus of the present invention.

FIG. 5 is an overall configuration diagram of a conventional color image forming apparatus.

6 is a perspective view showing another example of a transfer drum used in the transfer device of the color image forming apparatus shown in FIG. 5. FIG.

[Explanation of symbols]

1 Static eliminator charger 2
Adsorption roller 3
Adsorption charger 4
Transfer charger 7, 7Y-7B Developing device 15 Dielectric sheet 17
Transfer material 18, 21 Transfer drum 18A Transfer device 19 Elastic body

Claims (3)

[Claims] 1. An image carrier that forms a latent image of an image of each color, a developing device that develops the latent image with a developer of a corresponding color to form an image of each color, and a suction roller that forms a dielectric of a transfer drum. In the color image forming apparatus, the adsorption roller includes a transfer means for multiple-transferring the formed images of each color onto a transfer material held on a body sheet to obtain a color image on the transfer material. After the multi-transferred transfer material is separated from the dielectric sheet of the transfer drum,
A color image forming apparatus characterized in that the device also serves as a static eliminating means for eliminating static electricity from the dielectric sheet. 2. The suction roller has a volume resistivity value of 1
Claim 1: Made of a conductive elastic material having a resistance of 09 Ωcm or less
color image forming device. 3. The color image forming apparatus according to claim 1, wherein the suction roller has a crown shape.