JPS5823050A - Color image forming method - Google Patents

Abstract

PURPOSE:To obtain a bicolor image free of color mixing by increasing the potential of the 1st red electrostatic latent image and decreasing the potential of a succeeding black electrostatic latent image to <=2/3 when forming electrostatic latent image in two red and black colors in an insulating layer on a photoreceptor. CONSTITUTION:On a conductive substrate of Al, etc., a photoconductive layer and an insulating layer are provided to constitute a photosensitive drum 1. The photoreceptor 1 is charged primarily by a primary corona dischager 11 and the control grating is applied with a bias voltage by using a secondary corona discharger 12 to irradiate the insulating layer with reflected light beams 27a and 27b from a two-color original through a cyan filter 13 and a red filter 14 simultaneously with the secondary charging. As a result, potentials of respective red, white and black areas of the photoreceptor 1 are +300, -80 and -100V, respectively. Thus, the contrast of the red latent image is <=2/3 as high as that of the black latent image, so an excellent image free of color mixing is developed through red and black developing devices 15 and 17.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color image forming method, and more particularly, to a color image forming method for easily obtaining a color image without color mixture.

Conventional color copying requires repeated processes for the number of colors (primary colors and black), and therefore requires a large amount of time to produce a single copy. It was difficult to increase the speed. Furthermore, color shift caused by repeated operations is a big problem, and it is extremely difficult to prevent it.

On the other hand, most of the demand for copying machines in the market is for making copies of documents, meeting materials, and the like. Therefore, it is very rare that natural colors (multicolor reproduction) are required for copies, and when copying extracts, documents, etc., two colors such as black and red are sufficient.For example, 1 Double 4 is often used when corrections or annotations are added to a letter written in black using a red pen, but in cases such as this, multiple colors are not necessary, but it is divided into two colors. Depending on the situation, it can be very effective in calling attention to things.

In this respect as well, two-color color reproduction is extremely useful.

Regarding such a so-called two-color reproduction method, the main applicant has already proposed a method disclosed in Japanese Patent Application Laid-Open No. 146832/1983.

However, in the above electrophotographic method, the polarity of each electrostatic latent image corresponding to the original red and black is the same,
It also has a dark potential on the same level as Nezu.

Therefore, the entire surface is exposed after the first red color, and the black second color is exposed.
When you develop it, it turns red! Due to the latent image charge, the red developed area is also developed to black, resulting in a cloudy tone and a bright red image cannot be obtained.

As a solution to this problem, as in JP-A No. 54-95631, after the red color development step, the photoreceptor is charged with AC, and then the entire surface is N''jt.
A method has been proposed in which a black coating process is performed by performing the following steps.

However, with this method, if an attempt is made to eliminate the residual potential in the red developing area to prevent the adhesion of black toner, the residual potential on the insulating layer in the area that should become a black latent image after full exposure will also be eliminated at the same time. Image density is low after black development
It was difficult to obtain a clear image.

The present invention has been made in view of the above points and relates to a color image forming method that is simple and does not cause color mixture.

According to the present invention, at least two types of electrostatic latent images formed on the surface of a photoreceptor having an insulating layer on a photoconductive layer in accordance with optical information can be sequentially developed and are sequentially developed with different color developers to form a color image. The method is characterized in that each electrostatic latent image is formed with the potential of the first electrostatic latent image to be developed first being lower than the potential of the second electrostatic latent image to be developed next.

In addition to the usual insulating material, the insulating layer of the photoreceptor used in the present invention may be a photoconductive material that is insensitive to the wavelength of light used for electrostatic image formation.

Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings.

FIG. 1 shows a manuscript to be copied by Musha. The basic structure is a conductive layer (1) and a conductive layer (2).

The process will be explained step by step along with the transition of the surface potential of the Jl light body shown in diagram wc2.

(1) The surface of the insulating layer of the photoreceptor B is uniformly and primarily charged by the corona discharger 11 (in the illustrated example, it is charged with positive polarity).

This process induces negative charges of opposite polarity to the charged polarity on the back surface of the insulating layer I.

<2) After the above process has been completed, the photoreceptor is subjected to primary charging and secondary corona discharge of opposite polarity or alternating current using the corona discharger 12, while passing through a cyan filter (C, F) that continuously cuts only red light. Irradiates a two-color original image.

During this cyan filter exposure, part of the reflected light from the red image (b) of the original is transmitted through, and by exposing the photoreceptor to BK'in degree, that is, the part of the original where the light is reduced to By lowering the exposure contrast, the potential of the electrostatic latent image corresponding to red IIk to be developed first can be made lower than the potential of the electrostatic latent image to be developed later.

Through this process, in the realm (Feng), party 4 comes from the manuscript person.
Of these, colors other than white and red are filters (C0'F
) and acts on the photoconductive layer I, so the summer resistance of the original conductive layer decreases, and the negative charges induced on the back surface of the insulating layer I escape, increasing the positive primary charge on the surface of the insulating layer. Disappears due to reverse polarity or AC charging.゛On the other hand, in region (b), most of the red light coming from the statue opening is blocked by the filters (C, F), but some of it passes through, and the resistance of the photoconductive layer 1 decreases slightly. . As a result, a portion of the induced negative charge on the back surface of the insulating layer l becomes close to zero.

On the other hand, in region 1 (C), since no light comes from the image C, the resistance of the photoconductive layer I is maintained without decreasing, but the potential on the surface of the insulating layer is near zero.

(6) Next, when the entire surface of the photoreceptor is exposed to the original image through the red filter (R, F), the photoreceptor area (b) corresponding to the red image aperture becomes conductive, and the insulating layer and photoconductive layer are The induced negative charges near the interface escape to the conductive layer (2), except those that are restrained by the positive charges on the surface of the insulating layer. On the other hand, the black image corresponding area (
In C), the induced negative charge is retained near the interface between the insulating layer and the photoconductive layer.

As a result, the surface of the insulating layer rises to a positive potential in the region (b) corresponding to the red image cIK, while in the region C corresponding to the black image
The potential remains near zero.

(4) The latent image generated by the above process is developed with red toner.

In this red development process, development with higher contrast is performed than in the subsequent black development process.

Development with high contrast cannot be obtained by known methods, i.e.
In the developer, by controlling the particle size, particle size distribution, triboelectric charge characteristics, etc. of the toner, the toner concentration in the TI two-component developer, and the resistance value of the carrier iron powder, In the developing method, the resistance value and the like can be controlled by the frequency of an alternating voltage applied as a developing bias in the so-called jumping development method of one-component toner.

6) Next, when the surface of the photoreceptor developed with the red toner is uniformly irradiated with white light, the photoreceptor area c corresponding to the black part
11 The induced negative charge near the interface layer escapes toward the conductive layer (1) when it becomes conductive, and as a result, a positive potential appears on the surface of the photosensitive plate in the black image area.

(6) The photosensitive plate is developed using negatively charged black toner. This black developed image has a sufficiently high latent image contrast even without special high-contrast development as in the case of red development described in (4) above, so that a clear black image can be obtained by a normal developing method.

In this way, two color images of red and black are formed on the photoreceptor, and this is transferred onto a transfer material such as paper to provide a two-color copy.

Here, the red latent flaw contrast is preferably approximately two-sixths or less of the black latent image contrast.

This means that the residual potential in the image area after red development can be used to control red latent flaws! This is because the contrast of the red latent image must be kept low in order to make the residual potential as small as possible and to maintain a voltage that prevents black toner from adhering to the red image area during subsequent black development.

Residual potential after tax The force varies depending on the triboelectric properties of the toner, the development time, the resistance value of the carrier iron powder, etc.
The potential ranges from 60th rumor to 801st place.

In addition, the latent flaw contrast of black is larger than that of red, and when developing black, it is necessary to increase the contrast in the black image area #'i (and at the same time, suppress the development of the red image area. For example, if the red latent image contrast is set to about two-thirds or less of the black latent image contrast, a good color image without color mixture can be obtained.

Thus, the objects of the present invention are achieved, and practical two-color copying becomes possible. Preferably, the contrast is set to about three-fifths, and the contrast of red development is increased.

FIG. 3 shows a specific example of an apparatus for carrying out the process of the present invention. FIG. 4 is a detailed view of the goose means around the photoreceptor of the apparatus shown in FIG. 3.

An original (for example, a two-color image consisting of black and red) placed on the original table glass 2 is irradiated by the illumination lamp 6, and the reflected light is split into light beams 271m and 27b, which are sent to the movable mirror 4.
, 5, lens 7, and mirror 8.9, cyan filters 13 (C, P) and red
Since the document table 2 is scanned in the direction of the arrow X, each point on the document first passes through the path of the light ray 27a, then the light ray 27b. The image is projected onto the photoreceptor drum through this path.

The photoreceptor drum 1 is primarily charged with a negative corona discharger 11, and then is charged with an original charge of +1!1l127! A secondary corona discharger 12 provides a primary charge and an opposite polarity charge or a discharge at the same time as the optical image exposure (color separation mist light by a filter 13) from the path.

As shown in the enlarged view around the filter 16 shown in FIG. 5, the filter 16 has a cyan filter 151 and a red filter.
132 are connected to form an integrated filter, which can be moved up and down within the range of dialysis of the exposure slit. The portion of the red filter that occupies the first exposure slit 141 is thick (as a result, the latent image of the red portion of the original becomes smaller).

In this manner, by appropriately adjusting the position of the filter 13 depending on the original, a clear red image without color mixture can be obtained.

Also, in place of filter 15 in Figure 5, the first
Exposure slit 141. cyan filter 131', red filter 1+2 identified in 2nd jllyt slot) 142
・You may also use In this case cyanophile! -131/
is 1 in order to transmit a part of the reflected light from the red part of the original.
It is necessary to use a cyan filter (■ or X) having the spectral transmittance shown in FIG. In Figure 7, the spectral reflectance of a general red color is indicated by ■ for reference. have Cyan Filter Co., Ltd., whose spectral transmission is selected to provide optimal red latent image contrast.

Of course, the document is scanned in synchronization with the movement of the photoreceptor drum 1, but the photoreceptor drum 1, which has been subjected to secondary charging of opposite polarity, passes through the red filter 14 through the path of the light beam 27b.
The original image that passes through the screen is illuminated. That is, in this way, all light other than red is irradiated with light, and a potential gradient that can be imaged is formed in the red-corresponding portion of the formed electrostatic latent image.

A red color is developed by the developing device 15.

Next, the photoreceptor drum 1 is exposed to the full surface exposure lamp 16.
irradiation, and a high potential image is formed on the sensory body portion corresponding to the black color of the original document. Next, the negatively charged black toner is supplied by the developing device 17 and developed onto the paper 21 and the roller 21' fed by the lip feeding roller 19 and the roller 19': 1a and the transfer device 22. The paper in the transfer device is separated from the drum 1 by the separation roller 23. Powder a#i contact heating fusing scissors device.

The image is fixed on the paper and discharged to the F-sheet 30 by the paper discharge p-ra 25.

After the transfer is completed, the residual toner on the drum surface is removed by the cleaner device 26 and accumulated at -.

FIG. 4 illustrates the booth means around the photoreceptor of the embodiment apparatus.

Magnet-roller or sleeve-loaf-51,5 for supplying developer to each dust imager 15.17 photoreceptor drum 1
6, there is a tube 9 that circulates and conveys the developer within the container: L-
54 and 55 are provided.

A member 621 for preventing developer toner scattering is provided at the opening of each developing device, for example, by 0.5×1 with respect to the photoreceptor 1irK.
Provided with a gap of 1&. On the other hand, Sono-2-5
A scraper 33 is provided around '1.56 to regulate the thickness of the wax and wax that adheres to the wax. Further, a t bias is applied to the am device in the copying apparatus of the present invention.

This is to prevent the latent image potential of colors other than red from increasing due to the bias light inside the first developing device and red toner from adhering to the area, for example, +50 to +100.
v is applied.

The bias in the second developing device is an auxiliary means to prevent the black toner from adhering to the red toner adhesion area, and is usually +
50 to +250v is applied.

Although black and red have been described for the original color and reproduction color above, it is of course possible to use an original having any of the six components.
Of course, the original color and the developed color do not have to be the same.

In order to facilitate understanding of the present invention, examples are shown below.

〔Example〕

As shown in FIG. 1(1), a photoreceptor having a photoconductive layer (2) and an insulating layer (2) provided on a conductive substrate (1) was prepared as follows.

A 10:1 dispersion mixture of photoconductive cadmium sulfide powder and vinyl chloride-vinyl acetate copolymer resin is coated on the MuI substrate to a thickness of 65 mm as an original conductive layer. After drying, add 2 more
A photoreceptor was prepared by adhering a polyethylene terephthalate film having a thickness of 5 tones.

% +6. using the above photoreceptor. OK V primary charging, then a bias voltage of 100 V was applied to the control grid.
7. Simultaneously with the secondary charging of OK V, the two-color original was exposed through a connected filter (cyan filter 10 red filter), and then the two-color original image was irradiated through the red filter. As a result, the potential of each red, black and white area on the surface of the photoreceptor was +3 nov.

-5ov, -1oov.

Next, red development was carried out using a two-component developing agent consisting of a red toner with a coarse grain size and a low tripo charge and an iron powder carrier, with the developing device 15 being in a floating state 11 that was not grounded. The surface potential of the red image area at this time was +180V.

After applying uniform white light irradiation to the surface of the photoreceptor, ShimaColleK
The surface potential of the black area increased to +500.

Next, a bias voltage of +200 V was applied to the developer sleeve to perform development with black toner.

The surface potential of the photoreceptor at the time of red 1m image and black image above, (
FIG. 8 shows the relationship (Vs-np characteristics) between the image density (Dp * * after fixing) and Vl).

After black development, a good two-color copy was obtained by transferring and fixing onto transfer paper while applying a corona transfer voltage of +6-2 Y-V.

For comparison, the red latent potential was set to +500V without color separation using a cyan filter as in the present invention.

In addition, the potential of the black latent image was set to +500V, and the high-contrast red development of the present invention was carried out. Even when a bias was applied, color mixing of black toner was observed in the red developing area, and only a dark and muddy red image was obtained. Also, the density of the black painting was low and it was not suitable for practical use.

As described above in detail in the specific examples, the present invention is an excellent product that enables good color image formation without color mixture.

[Brief explanation of drawings]

Fig. 1 (1) to (6) are schematic diagrams illustrating specific example steps of the method of the present invention; Figure 1g4 is a detailed view of the main part around the photoreceptor of the device shown in Figure 3. Figures 5 and 6 are a side view of a specific example device for carrying out the method of the present invention. FIG. 7 is an explanatory diagram of the characteristics of the filter shown in FIG. 6, and FIG. 8 is a characteristic diagram showing the correlation between the surface potential and the a degree of each color image. In the figure, 1: Photoreceptor, 2: Original table glass, 4.5: Movable door, 6: Illumination lamp, 7: Lens, 11: Primary corona discharger, 12: Secondary: Rona discharger, 13: Continuous cyanide Filter, 14: Red filter. Tanfu Canon Co., Ltd. 4pfL5 Finished map Vshi V 7th area 7th) g λ (Komachi Vs <v)

Claims (1)

[Claims] (1) At least two types of electrostatic latent images formed on the surface of a photoreceptor having a high-density layer on a photoconductive layer according to one party information can be sequentially developed in different colors! In a color image forming method in which development is performed sequentially using a liquid additive, the first electrostatic potential to be developed first is made lower than the second electrostatic latent potential to be developed next. A color image forming method characterized by forming calligraphy. (2. In the invention described in claim 1, the first
A method for forming a color image, characterized in that the electrostatic latent potential of the second electrostatic latent potential is less than or equal to j of the second electrostatic potential. (3) A method for forming color III, characterized in that a bias equal to or higher than that set forth in claim 1 or 2 is applied to the developing means.