JPH0443375A - Method and device for forming image - Google Patents

Abstract

PURPOSE:To eliminate the scattering of toner and the irregularity in an image by accurately making the potential distribution of the transfer surface of a transfer material where a front toner image is transferred nearly uniform with the maximum value of the potential of the front toner image before multiply transferring a rear toner image on the front toner image. CONSTITUTION:When the toner image is transferred to the transfer surface 8a, the potential distribution of the surface 8a becomes nonuniform by the charge of the toner image 9. Thereafter, the voltage 7e applied from the wire 7a of a scorotron 7 is uniformly applied to the surface 8a by an electric field which is made uniform by the charge 5e added to a non-transfer surface 8b side by a transfer corotron 5 and the voltage impressed on a grid 7c, and the potential distribution of the surface 8a becomes nearly uniform. Thus, even the toner image of second and succeeding colors is accurately transferred to the transfer material 8, and a stable color image in which the scattering of the toner and the irregularity in the image are not caused is formed without depending on the density of the toner image or dot surface contacting rate.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an image forming method in which toner images of a plurality of colors are transferred multiple times to the same transfer material to form a halftone color image using halftone dots, and an image forming method thereof. In particular, an image forming method for forming a halftone color image by halftone dots by accurately transferring multiple transferred toner images by equalizing the potential distribution on the transfer surface of a transfer material during multiple transfer, and Regarding the device.

[Prior Art] Conventionally, as an image forming method for an image forming apparatus such as a copying machine, the method described in, for example, Japanese Patent Application Laid-Open No. 63-43188 is known.

This is a method in which a color image is formed by repeatedly transferring at least two times to the same transfer paper, in which a step is provided to neutralize the transfer surface of the transfer paper after the previous toner image transfer step. This process makes the potential distribution of the transfer surface of the transfer paper on which the preceding toner image is transferred uniform, and by forming this uniform potential distribution, the succeeding toner image is accurately electrostatically attracted. This allows the rear toner image to be accurately transferred onto the front toner image.

For example, as shown in FIG. 4, an apparatus for realizing this image forming method includes a photosensitive drum 1, an exposure device 2, a developing device 3, a transfer paper conveying belt 4, a transfer device 5, and a remover disposed around the photosensitive drum 1. Consists of 6 electrical appliances.

In this apparatus, the toner image 9 is transferred onto the transfer paper 8 as shown in FIG.

That is, when a high voltage having a polarity opposite to the potential charged on the toner image 9 is applied to the wire 5a of the transfer corotron 5, which is a transfer device disposed in the transfer area of the photosensitive drum 1, the transfer paper 8 is A charge 5e having a polarity opposite to the potential charged on the toner image 9 is applied to the non-transfer surface 8b. This charge 5
The charged toner image 9 is electrostatically attracted by the electric field formed by the toner image 9 and transferred to the transfer surface 8a of the transfer paper 8. Further, although not shown, the electric potential of the toner image 9 on the transfer surface 8a is eliminated by the static eliminator 6, and the so-called front toner image 9 and the rear toner image 9 transferred in multiple layers thereon. ′ is eliminated.

However, in the above conventional image forming apparatus, when the preceding toner image 9 is neutralized, not only does the preceding toner image 9 itself lose its electrostatic force, but also this toner image 9 imparts an electric charge of opposite polarity. may be done.

In such a case, there is a problem that the preceding toner image 9 is reversely transferred onto the photosensitive drum 1 in the transfer area where the subsequent toner image 9' is transferred.

Therefore, in order to avoid this problem, in the above-mentioned Japanese Patent Application Laid-Open No. 63-43188, the above-mentioned charge removal is performed every other time, and the potential of the previous toner image 9 is left to some extent, thereby solving the above-mentioned problem. I am proposing that.

However, if this static elimination is performed every other time, the potential of the front toner image 9 remains on the transfer surface 8a of the transfer paper 8, and anisotropic electrical repulsion is applied to the rear toner image 9'. The previous problem of giving .

In addition, as shown in FIG. 6, the static eliminator 6 shown in FIG.
It is conceivable to apply charges of the same polarity as the previous toner image 9 to the transfer surface 8a of the transfer paper 8 to remove the above-mentioned anisotropic electrical repulsion. However, such a static eliminator 6 simply applies charge and cannot control the potential of the transfer surface 8a, so the potential distribution is not uniform and the above problem cannot be solved. Furthermore, since the voltage applied to the wire 6a of the static eliminator 6 varies depending on the density of the toner or the halftone dot area ratio, equipment for setting the voltage is required to enable the use of various toners. Shimatsu.

Furthermore, in an apparatus that transfers a toner image many times to form a halftone color image using halftone dots, the static eliminator 6 charges the transfer surface 8a each time after each toner image is transferred. Since the transfer paper 8 is applied in layers, there is a problem that if the transfer paper 8 is charged many times, the potential of the transfer paper 8 becomes dangerously high.

[Problems to be Solved by the Invention] Therefore, as a result of intensive research in order to solve such problems, it has been found that toner images of multiple colors are sequentially and multiple-transferred onto the transfer surface of the same transfer material, and halftone dots are used to create an intermediate image. When forming a toned color image, these problems can be solved by applying a potential of the same polarity as the toner image to the transfer surface having the preceding toner image, thereby making the potential of the transfer surface approximately uniform. They discovered that this problem could be solved and completed the present invention.

Therefore, it is an object of the present invention to provide a method for forming a halftone color image using halftone dots by sequentially multiple-transferring toner images of a plurality of colors onto the same transfer material, even if the toner images of the second and subsequent colors are transferred to the transfer material. It is an object of the present invention to provide a method and an apparatus for forming a stable color image which is not dependent on toner density or halftone dot coverage and does not cause toner scattering or image disturbance.

[Means for Solving the Problems 1] That is, the present invention provides an image forming method in which toner images of a plurality of colors are sequentially and multiple-transferred onto the surface of the same transfer material to form a halftone color image using halftone dots. Before multiple toner images are transferred onto the previous toner image, the potential distribution of the transfer surface of the transfer material to which the previous toner image is transferred is accurately set to the maximum potential of the previous toner image. This is an image forming method characterized by making the image substantially uniform.

Here, in the image forming method of the present invention, the transfer material may be any material as long as it can fix a toner image, and may include, for example, a resin film in addition to ordinary transfer paper. In the present invention, the transfer surface refers to the surface of the transfer material on which the toner image is transferred, the non-transfer surface refers to the surface opposite to the transfer surface, and the preceding toner image refers to the surface of the transfer material on which the toner image is transferred. A toner image that has already been transferred to the transfer material when multiple toner images are multiplex transferred to the same transfer material, and a subsequent toner image refers to a toner image that has already been transferred to the transfer material when multiple toner images are transferred to the same transfer material. A toner image that is transferred on top of the preceding toner image that has already been transferred to a transfer material during multiple transfer.

In addition, transfer refers to applying a charge of opposite polarity to the charge applied to the toner image to the non-transfer surface of the transfer material, and electrostatically attracting the toner image to the transfer surface of the transfer material. Furthermore, multiple single transfer refers to transferring a subsequent toner image in a layered manner on top of the previous toner image that has already been transferred onto the transfer material. Generally, cyan, magenta,
3 colors of yellow or 4 colors with black added to these 3 colors
Transferring color toner images onto the same transfer material.

Further, in the image forming method of the present invention, the potential distribution on the transfer surface of the transfer material to which the previous toner image is transferred is made to have the same polarity as the potential of the previous toner image and to be substantially uniform. This potential distribution refers to the distribution of potential electrostatically generated on the transfer surface of the transfer material, and "substantially uniform" refers to a state in which the potential of the transfer surface of the transfer material is constant at a predetermined value. Here, if the potential of the transfer surface after the transfer of the front toner image and before the multiple transfer of the rear toner image is set to the maximum potential of the front toner image or more, the rear toner image The charges are buried in this potential, and a uniform electric field can be formed that can completely eliminate the electrostatic repulsion exerted on the subsequent toner image.

Further, as an apparatus for realizing the above-described image forming method, for example, the latent image carrying means includes a latent image carrying means, a latent image forming means, a developing means, a transfer means, and a transfer material conveying means. In an image forming apparatus that forms a halftone color image using halftone dots by passing the same transfer material through a transfer area multiple times to multiplexly transfer toner images of multiple colors, there is a front transfer material near the rear of the transfer area. An image characterized in that charging means is provided to make the potential distribution of the transfer surface of the transfer material on which the toner image is transferred substantially uniform to the maximum value of the same polarity as the potential of the previous toner image. There is a forming device.

In this image forming apparatus, the latent image carrying means is one on which a predetermined latent image is formed by providing a potential difference on its surface, and is generally a photosensitive drum or dielectric drum whose surface carrying the latent image is movable. There are body drums, etc.

Further, the charging means used in the image forming apparatus of the present invention may be of any type as long as it can make the transfer surface of the transfer material substantially uniform at the maximum value of the same polarity as the potential of the previous toner image.
Examples include, but are not limited to, a scorotron.

This scorotron generally consists of a wire to which a high voltage is applied to generate an electric charge, a shield placed around the outer circumference of the wire and open only in the direction in which the transfer paper is conveyed, and a grid to which a predetermined potential is applied. The electric field on the transfer surface of the transfer material can be made substantially uniform due to the relationship between this grid and the charge applied by the transfer means.

In the image forming apparatus of the present invention, the charging means is disposed near the rear of the transfer area, and the vicinity of the rear of the transfer area refers to the transfer area of the front toner image and the rear toner image. There is no particular restriction as long as the potential on the transfer surface side of the transfer material can be charged to a predetermined constant value between the transfer area and the transfer area.
In this case, it is the position near the transfer surface where the transfer material is conveyed after the previous toner image is transferred.

In addition, in the image forming apparatus according to the present invention, other constituent means such as a latent image forming means, a developing means, a transfer means, a transfer material conveying means, and other residual toner removing means and static eliminating means are not shown. Of course, it is possible to use conventionally known ones for this type of image forming apparatus. Note that in the case of a scorotron that charges using electric charge, which is used in the present invention, a charge is applied to a transfer area to electrostatically attract a toner image and transfer it to a transfer material.

In addition, in the above-mentioned device that forms halftone color images using halftone dots, toner images of three colors cyan, magenta, and yellow, or four colors in which black is added to these three colors, are used to form a color image. There is a so-called tandem system in which a transfer area is configured for each color toner image by configuring three or four latent image carrying means for transfer, and a transfer material is sequentially conveyed to this transfer area. Further, a developing device for toner of each color is arranged around the two latent image bearing means, and the transfer material is fixed to the transfer drum and passed through the transfer area of the two latent image bearing means several times to develop the toner for each color. There is a so-called transfer drum method in which a toner image is transferred. In these devices, by configuring the charging means in the vicinity of the rear of the transfer area, the potential distribution on the surface of the transfer material is changed to that of the front toner image before the rear toner image is multiple-transferred onto the front toner image. It can be made to have the same polarity as the potential of the toner image and to be substantially uniform.

[Operation] According to the present invention, when toner images of a plurality of colors are sequentially and multiple-transferred onto the transfer surface of the same transfer material, after the previous toner image is transferred, the subsequent toner image is transferred in multiple layers. Before being transferred, in order to make the potential distribution on the surface of the transfer surface of the transfer material substantially uniform and of the same polarity as the potential of the previous toner image, the toner on the latent image bearing means is transferred from the transfer means to the latent image bearing means even in the case of multiple transfers. A uniform electrostatic attraction force can be applied to the image, thereby making it possible to form a stable color image without toner scattering or image disturbance.

Furthermore, if the potential of the transfer surface of the transfer material after the previous toner image transfer and before the multiple transfer of the subsequent toner image is set to the maximum potential of the previous toner image or more, the charge of the subsequent toner image will increase. Since the toner image is submerged in this potential, the electrostatic repulsion exerted by the toner image at the front end on the toner image at the rear end is completely eliminated, making it possible to form a more stable color image.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the accompanying drawings.

1 and 2, an image forming apparatus according to a first embodiment to which the image forming method of the present invention is applied is shown.

The image forming apparatus according to this embodiment includes a photosensitive drum 1 as a latent image bearing means, an exposure device 2 for forming a latent image on the photosensitive drum 1, and a toner for applying toner to the latent image on the photosensitive drum 1. a developing device 3 that develops the toner image 9 using the photosensitive drum 1; a conveyor belt 4 that transports the transfer material such as the transfer paper 8 while fixing it at the same time that the toner image 9 developed on the photosensitive drum 1 reaches the transfer area; a transfer corotron 5 that sucks the toner image 9 developed on the photosensitive drum 1 and sucks the toner image 9 onto the transfer surface 8a of the transfer paper 8 at the same time as it comes to the transfer area;
Near the rear of the transfer area of the photosensitive drum 1, there is a scorotron 7 and the like that applies a potential of the same polarity as the potential of the toner image 9 to the transfer surface 8a.

Here, this scorotron 7 has a wire 7a to which a high voltage current is applied with the same polarity as the potential of the toner image 9;
The wire 7a includes a shield 7b which is open only in the direction in which the transfer paper 8 is present, and a grid to which a current having the same polarity as the potential of the toner image 9 is applied.

Although not shown, a cleaning device, a static eliminator, and the like are configured to remove residual toner and residual potential on the surface of the photosensitive drum 1 after the toner image 9 is transferred to the transfer paper 8.

Next, a method for forming a stable color image by substantially uniforming the potential distribution on the transfer surface 8a of the transfer paper 8 in the image forming apparatus of this embodiment will be explained based on FIGS. 1 and 2 as follows. It is.

In FIG. 1, a predetermined latent image is formed on the surface of a photosensitive drum 1 by an exposure device 2, and as the photosensitive drum 1 rotates, this latent image moves to a position where a developing device 3 is disposed. This latent image is developed with toner applied from the developing device 3 to become a toner image. This toner image moves to a transfer area where a transfer corotron 5 is provided as the photosensitive drum 1 rotates. A transfer paper 8 is conveyed to this transfer area by a conveyor belt 4 as the toner image developed on the surface of the photosensitive drum 1 rotates. Further, when this transfer paper 8 is conveyed, a charge having a polarity opposite to that charged on the toner image is applied by the transfer corotron 5 to the non-transfer surface 8b side of the transfer paper 8, and a predetermined electric field is applied to this transfer area. is formed, and the toner image 9 is transferred from the surface of the photosensitive drum 1 to the transfer surface 8 of the transfer paper 8.
transferred to a.

When the toner image is transferred to the transfer surface 8a, the potential distribution on the transfer surface 8a becomes non-uniform due to the charge of the toner image 9. However, as shown in FIG. 2, the electric field made uniform by the charge 5e applied to the non-transfer surface 8b side by the transfer corotron 5 and the voltage applied to the grid 7C causes the wire 7a of the scorotron 7 to
The charges 7e applied from the transfer surface 8a are uniformly applied to the transfer surface 8a, and the potential distribution on the transfer surface 8a becomes substantially uniform.

As described above, the potential distribution on the transfer surface 8a becomes substantially uniform. Further, the potential of the transfer surface 8a is determined by the voltage applied to the grid 7c. Therefore, by adjusting the voltage applied to the grid 7c, the potential of the transfer surface 8a can be easily adjusted. Here, if this potential is adjusted to a value such that the charge of the front toner image 9 does not give an electrical repulsion to the rear toner image 9', the potential distribution on the transfer surface 8a, which is the object of the present invention, can be made uniform. can be achieved. In particular, the potential of the transfer surface 8a is set to the maximum potential of the toner image (
When set to the solid image potential), the transfer surface 8a is always completely
It is possible to make the potential distribution uniform.

Next, this transfer paper 8 with a uniform potential is conveyed by the conveyor belt 4 to the transfer area of the photosensitive drum 1 where the second color toner image 9' is transferred, and the second color toner image 9' is transferred multiple times. Ru.

When transferring the second color toner image 9', even if the toner image 9' has already been transferred to the transfer surface 8a of the transfer paper 8, the potential is the same as that of the toner image 9 that has already been transferred to the transfer surface 8a. Since a polar and substantially uniform potential distribution is formed, the second color toner image 9' is different from the already transferred toner image 9.
does not receive anisotropic electrical repulsion from Therefore, due to the electric attraction force from the transfer corotron 5, the second color toner image 9' is accurately transferred in the same way as the first color toner image 9 is transferred.

Further, the third color toner image is transferred in the same manner after the second color toner image is transferred and after the potential distribution on the transfer surface 8a is made uniform again by the scorotron 7.

Although not shown, even in an apparatus that transfers toner images of a fourth color or more colors to form a halftone color image using halftone dots, a toner image that is newly multi-transferred may be used. Of course, the effects of the present invention can always be obtained by making the potential distribution on the transfer surface 8a uniform again by the scorotron 7 before the transfer.

As shown in FIG. 1, since the transfer paper 8 to which the third (last) color toner image has been transferred does not receive any further toner images, the transfer area of the third (last) color toner image is Scorotron 7 is not configured near the rear.

FIG. 3 shows an image forming apparatus according to a second embodiment of the image forming apparatus that implements the image forming method of the present invention, in which a photosensitive drum is provided for each toner image in the first embodiment. 1, an exposure device 2, a transfer corotron 5, a scorotron 7, and the like. The image forming apparatus according to the second embodiment is different from the image forming apparatus according to the first embodiment in that the transfer paper 8 is conveyed and fixed to the transfer drum 4'b by a conveyor belt 4'a. Transfer drum 4
The rotation of 'b' causes the transfer paper 8 to pass through one transfer area multiple times to form a halftone color image with halftone dots.

According to the image forming apparatus according to the second embodiment, since the photosensitive drum 1, the exposure device 2, the transfer corotron 5, the scorotron 7, etc. are each comprised of one piece, a more compact image forming apparatus can be provided. be able to.

[Effect 1] According to the image forming method and apparatus of the present invention, when forming a halftone color image by halftone dots by sequentially multiple-transferring toner images of a plurality of colors onto the same transfer material, toner images of the second and subsequent colors are A method and an apparatus for accurately transferring an image onto a transfer material and forming a stable color image without toner scattering or image disturbance, regardless of the density of the toner image or halftone dot area ratio. can provide.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the scorotron of FIG. 1, and FIG. 3 is an explanatory diagram showing another embodiment of the present invention. FIG. 4 is an explanatory diagram showing a conventional example, FIG. 5 is an explanatory diagram showing a state during toner image transfer in a conventional example, and FIG. 6 is an explanatory diagram showing a charging state of transfer paper in a conventional example. It is. [Description of symbols] 1: Photosensitive drum 5: Transfer corotron 7: Scorotron

Claims (3)

[Claims] (1) In an image forming method in which toner images of multiple colors are sequentially and multiple-transferred onto the surface of the same transfer material to form a halftone color image using halftone dots, a later toner image is placed on top of the earlier toner image. Before multiple transfer, the potential distribution on the transfer surface of the transfer material to which the previous toner image is transferred is accurately made almost uniform to the maximum value of the same polarity as the potential of the previous toner image. An image forming method. (2) A latent image bearing means such as a photosensitive drum or a dielectric drum, a latent image forming means that forms a latent image on the latent image bearing means, and a toner image by developing the formed latent image with toner. a developing means; a transfer means disposed in a transfer area of the latent image bearing means and configured to transfer the toner image onto a transfer material conveyed to the transfer area at a predetermined timing; and a transfer material conveyance means for conveying the transfer material at the timing of , the same transfer material is passed through the transfer area multiple times to multiplexly transfer toner images of multiple colors to form a halftone color image by halftone dots. In the forming device, the potential distribution on the transfer surface of the transfer material on which the front toner image is transferred near the rear of the transfer area is made substantially uniform to the maximum value of the same polarity as the potential of the front toner image. An image forming apparatus characterized in that it is provided with a charging means. (3) The image forming apparatus according to claim 2, wherein the charging means is a scorotron.