JPH041905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for reliably erasing a black image area from a document having a black image area and a chromatic color image area such as red or blue using a charged particle flow control screen. The present invention relates to an image forming method for reproducing color image areas.

Conventionally, in order to reproduce originals in which black and multiple chromatic colors coexist using electrophotography or electrostatic printing, it is necessary to form an electrostatic charge image that corresponds only to the image area of a certain color and then develop the image in that color. This process was performed for each color. Although images of originals consisting of various color combinations can be reproduced by such a method, in order to simplify the explanation below, we will discuss image reproduction of a two-color original with a black image area and a red image area on a white background. explain.

1 to 7 show the processing steps of a conventionally proposed image forming method. As shown in FIG. (hereinafter simply referred to as photosensitive layer)
With the support 1 of an electrostatic image support 3 (hereinafter simply referred to as a photoreceptor) provided with a photosensitive layer 2 being grounded, the photosensitive layer 2 is uniformly and positively charged by a corona charger 4, and then the photosensitive layer 2 is uniformly and positively charged. As shown in FIG. B, an optical image of the document 5 having a black image area B and a red image area R is irradiated onto the photosensitive layer 2 through a cyan filter 6 which is a complementary color to red. The cyan filter used here is an optical means that transmits only cyan light. As a result, the photosensitive layer 2 is irradiated with light to areas other than the areas corresponding to the black image area B and the red image area R, and the static charge disappears, and the first static charge having a positive static charge only in the area. An image is formed. Arrows indicate light irradiation.

On the other hand, as shown in the cross section of FIG. 2, a photoconductive layer 72 made of, for example, selenium-tellurium is formed on one side of the conductive mesh 71, and an insulating layer 73 is formed on the other side, and a conductive bias layer is formed on the outside thereof. As shown in FIG. 3A, the photoconductive layer 72 of the charged particle flow control screen 7 (hereinafter simply referred to as a photosensitive screen) 7 formed with a conductive mesh 74 is charged by a corona charger 8 with the conductive mesh 71 grounded. The original 5 is uniformly and positively charged, and then the original 5 is charged as shown in FIG. 3B.
The light image is irradiated onto the photoconductive layer 72 of the photosensitive screen 7 through the red filter 9. As a result, the photoconductive layer 72 of the photosensitive screen 7 has a black image area B.
A second electrostatic charge image is formed having positive electrostatic charges only in the region corresponding to . Note that the optical image of the original 5 irradiated onto the photosensitive screen 7 and the optical image onto the photosensitive layer 2 of the photoreceptor 3 are in a mirror image relationship. In FIG. 4, the photosensitive screen 7 is arranged so that the photoconductive layer 72 having the second electrostatic charge image faces the photosensitive layer 2 of the photoreceptor 3 having the first electrostatic charge image. With a bias voltage of an appropriate magnitude having the same polarity as the electrostatic charge image on the photoconductive layer 72 applied to the conductive bias layer 74 of the photoconductive screen 7 , the charged particle source 1 is applied through the photoconductive screen 7 .
A flow of negatively charged particles from zero to the photosensitive layer 2 of the photoreceptor 3,
An electric field is formed between the photoreceptor 3 and the charged particle source 10 for projection. As a result, the negatively charged particle stream from the charged particle source 10 passes through the photosensitive screen 7 in areas where there is a positive electrostatic charge on the photoconductive layer 72 of the photosensitive screen 7 (indicated by arrows), but in other areas. The first region shown in FIG.
Of the electrostatic charge image, as shown in FIG. 4, the positive electrostatic charge only in the area corresponding to the black image portion B disappears.
As a result, an electrostatic charge image is formed in which the black image area is erased and has positive electrostatic charges only in the area corresponding to the red image area R of the photosensitive layer 2. By developing this electrostatic charge image with red toner, a red reproduction portion RT is formed on the photoreceptor 3 as shown in FIG.

Next, in order to reproduce the black image portion B of the original 5, a separate step of forming the black image portion may be performed. That is, as shown in FIG. 6A, the photosensitive layer 2 of the photosensitive member 3 is uniformly positively charged by the corona charger 4, and then
As shown in FIG. B, the light image of the original 5 is irradiated onto the photosensitive layer 2 through the red filter 9, and only the area corresponding to the black image area B of the original 5 has a positive electrostatic charge, resulting in a black image area. An electrostatic charge image is formed and developed with black toner (see Figure 6C).

Therefore, in order to form a two-color copy image corresponding to the original 5 having the black image area B and the red image area R, the red reproduction section described with reference to FIGS.
It is sufficient to combine the step of forming only RT and the step of forming the black reproduction portion BT exemplarily described with reference to FIG. That is, by separately performing the formation process of the red reproduction part RT and the formation process of the black reproduction part BT, and transferring and fixing each toner image onto the same transfer paper in a well-aligned manner,
Alternatively, after forming the black reproduction part BT, form the red reproduction part
By forming the RT, the black reproduction part BT and the red reproduction part RT are formed on the same photoreceptor as shown in FIG. can be obtained.

By the way, in the electrostatic charge image forming method described above, in order to reproduce a red image part, a photoreceptor (see FIG. B) and a photosensitive screen (see FIG. 3B) having electrostatic charge (second electrostatic charge image) in the area corresponding to the black image area are placed facing each other, and charges of opposite polarity are applied via the photosensitive screen. By projecting a particle stream onto the first electrostatic charge image on the photoreceptor, the potential of the area of the first electrostatic charge image corresponding to the black image area (indicated by a broken line) is changed to the background potential as shown in FIG. I am trying to erase the black image area by using However, with this method of erasing the black image area, when developing with red developer after erasing the black image area, if the edge of the area corresponding to the black image area or the black image area is a thin line, Red developer may adhere and remain at the location corresponding to that line. The reason for this is thought to be as follows.

That is, when erasing the electrostatic charge in the area corresponding to the black image part of the first electrostatic charge image with a stream of charged particles of opposite polarity, the area corresponding to the black image part of the first electrostatic charge image formed on the photoconductor 3 is erased by a stream of charged particles of opposite polarity. It is thought that the charge distribution in the region and the resulting lines of electric force are as shown in FIG. When a stream of charged particles of opposite polarity is projected onto this area through the photosensitive screen 7, the stream of charged particles tends to gather at the center of the area as shown in FIG. 10 under the influence of the electric lines of force. As a result, the charge at the center of the area is erased and the potential becomes zero, but as shown in Figure 11, static charges remain at the edges, and when this is developed, developer adheres to the edges. However, there is a problem in that the reproduced image tends to be unsightly.

The present invention has been made in view of the above points, and when erasing the electrostatic charge in the area corresponding to the black image portion of the first electrostatic charge image with charged particles of opposite polarity, it is necessary to project an excessive amount of charged particles. By doing this, you can also erase the electrostatic charge image that remains on the edges and thin lines of the area that reacts to the black image area.
The above problem can be solved.

The image forming method according to the present invention will be explained below based on the drawings.

Similar to the conventional image forming method described above, considering the image reproduction of an original having a black image area and a red image area on a white background, the method according to the present invention includes the step of forming a first electrostatic charge image on a photoreceptor and the step of forming a first electrostatic charge image on a photoreceptor. Since the step of forming the second electrostatic charge image on the wafer is the same as the conventional method, the different steps thereafter will be explained.

A photoreceptor 3 having a first electrostatic charge image made of positive electrostatic charges and a photosensitive screen 7 having a second electrostatic charge image made of positive electrostatic charges are placed facing each other, and a charged particle source is connected through the photosensitive screen 7. 10 to photoreceptor 3
When negatively charged particles are projected onto the top, when the amount of charged particles is small, the result is as shown in Figure 11, as in the conventional case, but when the amount of charged particles is increased, the center of the area corresponding to the black image area becomes The surface potential first becomes negative, but then some of the charged particles flow toward the edge of the region, repelling the projected stream of negatively charged particles. As a result, the positive static charge remaining at the edge of the area corresponding to the black image area is neutralized. In this way, positive static charges are neutralized over the entire area corresponding to the black image area, and excess negatively charged particles adhere to the area, resulting in a surface potential like that of the black image area in FIG. 12. If you then develop with a red developer of negative polarity, only the area corresponding to the red image area will be developed red, and since the red developer will not adhere to the area corresponding to the black image area, especially the edges, only the red reproduced image will be developed. is obtained. In addition, the first
As can be seen from Figure 3, since the potential of the background area is higher than the potential of the area corresponding to the black image area where the charge has been erased, there is a risk of fogging during the developing process, but this can be done by setting an appropriate bias voltage to the developing device. This can be resolved by applying .

Next, an image forming apparatus using the above image forming method will be explained.

FIG. 13 shows an example of an image forming apparatus for forming a two-color copy image using the image forming method according to the present invention. A document 5 placed on a table 11 is illuminated by an illumination lamp 12 . 13 and 14 are mirrors, 15 is a fixed lens,
16 is a movable red filter configured to be able to move in and out of the optical path; 17 reflects red light;
The cyan color, which is auxiliary to the red color, is a dichroic filter that allows the light to pass through, and is configured so that it can be inserted into and removed from the optical path. In FIG. 13, the red filter 16 is shown out of the optical path, and the dichroic filter 17 is placed in the optical path. A photosensitive layer 2 is provided on the surface of a drum-shaped photosensitive member 3, and when the photosensitive member 3 rotates clockwise, the photosensitive layer 2 is uniformly charged by a corona charger 4. The photosensitive layer 2 is made of selenium or an organic semiconductor, and in the case of selenium, for example, it is positively charged by the charger 4. The case where a selenium photoreceptor is used will be explained below.

Around the photoreceptor 3, there are a charger 4 that uniformly charges the photoreceptor layer 2, a black developer 18 containing negatively charged black toner, and a red developer 19 containing negatively charged red toner. , and a cleaning device 20 for removing toner and charges remaining on the photosensitive layer 2. Reference numeral 21 indicates a transfer drum having the same diameter as the photoreceptor 3 and is driven in contact with the photosensitive layer 2 or rotates counterclockwise to which a positive potential has been previously applied. Reference numeral 22 indicates a transfer paper feed plate; and 23 indicates a transfer paper. A paper feed roller feeds the transfer paper received into the paper feed tray 22 one by one, 24 is a first conveyance roller that conveys the transfer paper to the transfer drum 21, and 25 separates the transfer paper from the transfer drum 21 after transfer. 26 is a separation claw that forcibly separates the transfer paper from the transfer drum 21 when the transfer paper is not separated by static electricity removal by the electrostatic separator 25; and 27 is a fixing device.

On the other hand, a cylindrical photosensitive screen drum 28 is placed on the document table 2 at a predetermined position on the opposite side of the photosensitive layer 2 from the transfer drum 21 so that the photoconductive layer is placed on the outside.
1 and photosensitive layer 2 so as to be able to rotate counterclockwise. Around the outside thereof, there is a screen charger 8, a screen charge remover 29 made of an EL (electroluminescence) plate for removing charges remaining on the photosensitive screen drum 28, or an AC corona charge remover, and the photosensitive screen drum 2.
A charged particle source 10 for projecting negatively charged particles is provided at a position facing the photoreceptor 3 inside the photoreceptor 8 .

Next, the operation of the image forming apparatus will be explained.

With the document 5 placed on the document table 11 and the dichroic filter 17 placed in the optical path, the illumination lamp 1 is turned on.
2 is turned on to irradiate the original 5, the original table 11 is moved, and exposure scanning is performed. At this time, the photosensitive layer 2, transfer drum 21, and photosensitive screen drum 28 are placed on the document table 11.
Rotate in sync with. The light from the original 5 passes through mirrors 13, 14 and a fixed lens 15 and reaches the dichroic filter 17, where the cyan light passes through and is projected onto the photosensitive layer 2, and the red light, which is complementary to the cyan light, is reflected and exposed. Screen drum 28
onto the photoconductive layer. Since the photosensitive layer 2 is uniformly charged by the charger 4, as a result, there are areas on the photosensitive layer 2 corresponding to the black developing area B and the red image area R of the original 5 as shown in FIG. 1B. A first electrostatic charge image having only a positive electrostatic charge is formed. On the other hand, since the photosensitive screen drum 28 is uniformly charged by the screen charger 8, there is a positive charge on the photosensitive screen drum 28 only in the area corresponding to the black image area B of the original 5 as shown in FIG. 3B. A second electrostatic charge image having an electrostatic charge is formed. The first electrostatic charge image and the second electrostatic charge image thus formed have a mirror image relationship and are also positioned opposite to each other.

As described above, when an excessive stream of negatively charged particles is projected from the charged particle source 10, a positive electrostatic image is formed on the photosensitive layer 2 in the area corresponding to the red image area R as shown in FIG. , the area corresponding to the black image portion B has a negative potential. When the photosensitive layer 2 further rotates in the direction of the arrow, red toner adheres to the positively charged red image area in the red developing device 19 to which an appropriate bias voltage is applied, forming a red reproduction area RT. This red reproduction portion RT is a transfer drum 2 to which a positive potential is applied in advance to the support 1 of the photoreceptor 3.
The image is transferred to the transfer paper above 1.

Thereafter, residual charges and residual toner on the photosensitive layer 2 are removed by a cleaning device 20, and the photosensitive layer 2 is uniformly charged again by a charger 4 and subjected to the image forming process for the next black image area. That is, when the dichroic filter 17 is removed from the optical path and the red filter 16 is placed in the optical path and the original platen 11 is moved again, a black image area B of the original 5 appears on the photosensitive layer 2 as shown in FIG. 6B. An electrostatic charge image consisting of positive electrostatic charges is formed only in the corresponding region. At this time, no electrostatic charge image is formed on the photosensitive screen drum 28. The electrostatic charge image on the photosensitive layer 2 is developed by a black developing device 18 to become a black reproduction portion BT, which is transferred to a transfer drum 21. A red reproduction portion RT is already held on the transfer drum 21, and by transferring this black reproduction portion BT, an image corresponding to the original image is reproduced without positional deviation. This reproduced image is transferred to the transfer paper conveyed from the transfer paper feed tray 22 , and after the transfer paper is neutralized by the separator 25 , it is separated by the separation claws 26 and conveyed to the fixing device 27 . In the fixing device 27, the toner image on the transfer paper is melted, adhered to the transfer paper, and discharged.

As explained above, in the present invention, in order to form an electrostatic charge image having a black image area and a color image area such as red or blue, with the black image area erased, the black image area is placed on the photoreceptor. A first electrostatic charge image is formed in an area corresponding to the black image area on the photosensitive screen, and a second electrostatic charge image is formed in an area corresponding to the black image area on the photosensitive screen.
The electrostatic charge image and the second electrostatic charge image are made to face each other, and a flow of charged particles having an amount of opposite polarity in excess of the amount of electrostatic charge in the area corresponding to the black image area is applied to the second electrostatic charge image on the photoreceptor through a photosensitive screen. By projecting, the static charge in the area corresponding to the black image area disappears, so that no static charge remains on the edge of that area, and therefore even when developed, the edge of the black image area and thin areas will disappear. Developers of other colors will not adhere to the lines, and the reproduced image will not look unsightly.

[Brief explanation of drawings]

FIGS. 1, 3, and 4 show a first electrostatic charge image forming step and a step in a conventional method for forming an electrostatic charge image by erasing a black image area from a document having a black image area and a red image area. 2. A diagram showing the formation process and final step of an electrostatic charge image. FIG. 2 is a sectional view showing the schematic structure of a photosensitive screen with a four-layer structure. FIG. 6 is an explanatory diagram of the process of reproducing a black image area by a conventional method. FIG. 7 is an explanatory diagram of a two-color copy image reproduced by a conventional electrostatic image forming method. FIG. 8 is a diagram conceptually showing the surface potential of the photoreceptor after charged particles are projected, FIG. 9 is a diagram showing the distribution of electric lines of force in the area corresponding to the black image area on the photoreceptor, and FIG. The figure shows the path of the charged particle flow projected onto the photoreceptor, Figure 11 shows the surface potential of the area corresponding to the black image area after conventional charged particles are projected, and Figure 12 shows the excess potential of the area corresponding to the black image area after the charged particles are projected onto the photoreceptor. FIG. 13 is a schematic diagram of an embodiment of an image forming apparatus according to the image forming method of the present invention. 1... Conductive support, 2... Photoconductive material layer,
3... Electrostatic image support, 4, 8... Corona charger, 5... Original, 6... Cyan filter, 7
...Charged particle flow control screen (photosensitive screen), 71... Conductive mesh, 72... Photoconductive layer, 73... Insulating layer, 74... Conductive bias layer, 9, 16... Red filter, 10... ...Charged particle source, 11... Document table, 12... Illumination lamp,
13, 14...Mirror, 15...Fixed lens, 1
7...Dichroitsch filter that passes cyan light and reflects red light, 18...Black developer,
19...Red developing device, 20...Cleaning device, 21...Transfer drum, 22...Transfer paper feed tray, 23...Paper feed roller, 24...Transport roller,
25... Electrostatic separator, 26... Separation claw, 27...
Fixing device, 28...Photosensitive screen drum, 29
...Screen static eliminator.

Claims (1)

[Claims] 1. In an image forming method for forming an image corresponding to at least a color image portion from a document having a black image portion and a color image portion, an electrostatic charge image support is provided with an area corresponding to the black image portion and the color image portion of the document. forming a first electrostatic charge image having an electrostatic charge, and forming a first electrostatic charge image having the same polarity as the first electrostatic charge image in an area of the electrostatic charge image support layer of the charged particle flow control screen corresponding to the black image area of the document; forming a second electrostatic charge image having an electrostatic charge of projecting a stream of charged particles having a polarity opposite to that of the first electrostatic image onto the electrostatic image support in an amount that exceeds the electrostatic charge in an area corresponding to a black image area on the electrostatic image support. Characteristic image forming method.