JPH0462581B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a multicolor image forming method using electrophotography. [Prior Art] Conventionally, the following two methods are known as multicolor image forming methods using electrophotography. The first method uses a common photoreceptor for each color, and repeats the formation of an electrostatic latent image by color-specific image exposure and color-specific development, and superimposes color-specific toner images on the photoreceptor. Alternatively, each color toner image is transferred to a transfer material each time a color development is performed, and the color toner images are superimposed on the transfer material. The second method uses multiple photoreceptors for each color, and forms and develops electrostatic latent images for each color separately, and sequentially transfers the color-specific toner images formed on each photoreceptor. This is a method in which toner images of different colors are transferred onto a transfer material and superimposed on the transfer material. This first method has the disadvantage that it takes time to form a multicolor image, and it is difficult to increase the speed, since the formation of electrostatic latent images for each color and the development for each color must be repeated. The second method is advantageous in terms of speedup because multiple photoreceptors can be used in parallel, but it requires multiple photoreceptors and their respective optical systems, developing means, etc., making the device complicated and It has the drawbacks of being large, expensive, and lacking in practicality.
In addition, both of the above methods have a major drawback in that it is very difficult to superimpose color-based toner images without positional deviation, and it is impossible to completely prevent color deviation in multicolor images. In order to fundamentally solve these problems, the present inventors have previously invented a method capable of forming a multicolor image by performing image exposure once on a photoreceptor. In this method, a photoreceptor having an insulating surface layer, a photoconductive layer, and a conductive layer forming a distribution layer of a plurality of filter portions having different spectral transmittance characteristics is charged and imagewise exposed. This is a method of forming a multicolor image on a photoreceptor by exposing the entire surface to light having a different spectral distribution at least each time and developing the electrostatic latent image formed thereby with different colored toners multiple times. According to this method, since the formation of an electrostatic latent image each time is performed using the previously performed charging and image exposure, there is no risk of color shift occurring in the multicolor image. Further, since charging and image exposure, followed by full-surface exposure and development can be repeated during one cycle of the photoreceptor, an excellent effect can be obtained in that multicolor image formation can be achieved at high speed.
However, it has been found that this method has a problem in that the multicolor images formed are seen as lacking in density. [Object of the Invention] The present invention has been made in order to solve the problem that the multicolor images formed in the above-mentioned invention seem to have insufficient density, and to form multicolor images at high speed without color shift. To provide a method for forming a multicolor image, in which the multicolor image is not seen as lacking in density. [Structure of the Invention] The present invention provides a method for charging and imagewise exposing a photoreceptor having a layer including a plurality of filters having different spectral transmittance characteristics, a photoconductive layer, and a conductive layer at least every time. In a method of forming a multicolor image on a photoconductor by performing full-surface exposure with light having different spectral distributions and developing an electrostatic latent image formed thereby with different color toners a plurality of times, the plurality of times of development The present invention is a multicolor image forming method characterized in that one development step is performed using black toner, and this configuration achieves the above object. That is, the multicolor image formed by the method of the above invention appears to have insufficient density because the reproduction of black in the multicolor image is also based on the additive coloring method using color toners of the three primary colors. In this additive coloring method, toners of three primary colors are densely arranged on a recording medium so that they do not overlap each other, and black is expressed by combining the reflected light of these toner colors. It has been determined that the cause of this is that when color toner reflects a large amount of light, it appears gray even if the colors are well balanced. Therefore, the present invention solves the problems of the previous method by using black toner to reproduce black in a multicolor image. [Example] The present invention will be described below with reference to illustrated examples. 1 to 3 are partial plan views showing an example of the distribution of filter portions in the insulating surface layer of the photoreceptor used in the present invention, and FIG. 4 is a graph showing an example of the spectral transmittance characteristics of each filter portion, and FIG. Figure 5 is a graph showing an example of the spectral transmittance characteristics of a filter portion that also transmits ultraviolet light, Figures 6 to 9 are partial cross-sectional views schematically showing examples of the layer structure of the photoreceptor, and Figure 1
Fig. 0 is a process diagram explaining an example of the present invention, Fig. 11 is a schematic sectional view showing an example of a recording device that implements the method of the present invention, and Fig. 12 is a diagram of a developing device used in the recording device of Fig. 11. It is a schematic sectional view showing an example. In FIGS. 1 to 3, T, B, G, and R are filter portions having spectral transmittance characteristics as shown in FIG. 4, respectively. Note that the spectral transmittance characteristics of the T filter portion may be such that the transmittance in the visible light region and the ultraviolet light region is changed as shown in FIG. The T-filter portion with low transmittance in the visible light range provides a different effect from the T-filter portion with spectral transmittance characteristics shown in FIG. 4, as will be described later. However, unless otherwise specified below, it is assumed that the T filter portion has sufficient transmittance even in the visible light range as shown in FIG. The insulating surface layer shown in FIG. 1 consists of a distribution in which ribbon-shaped filter parts B, G, and R are arranged in a stripe shape with a narrow ribbon-shaped filter part T sandwiched between them, and the length direction of the stripe shape is, for example, When the photoreceptor is a drum-shaped rotating member, the direction may be in the circumferential direction, in a direction perpendicular to the circumferential direction, or in any arbitrary direction. Such a striped pattern is preferable because it can be formed relatively easily. The insulating surface layer shown in Figures 2 and 3 consists of a mosaic distribution in which circular or square filter parts B, G, and R are arranged at intervals, and the empty ground part is the T filter part. , such a mosaic distribution is preferable because it allows relatively delicate multicolor image reproduction. Note that each filter part in the insulating surface layer is not limited to the combination example of T, B, G, and R as described above, but may include at least a plurality of types of filter parts related to the combination of colors for synthesizing white light. Any material may be used as long as it forms a combination with a filter portion that transmits light that does not pass through any of the filter portions. If the number of colors and types of filter parts related to the combination of colors that synthesize white light changes, the colors and number of types of color toner used for development will change accordingly, and therefore the number of developing devices will change accordingly. will also change depending on the number of color toners.
Furthermore, the distribution pattern of each filter portion is not limited to the examples shown in FIGS. 1 to 3. However, if the individual sizes of the filter portions T, B, G, R, etc. become too large, the resolution and color mixing of the image will decrease, resulting in deterioration of the image quality. If it is about the same level or less, the adhesion of toner becomes more susceptible to the influence of adjacent filter parts, and it becomes difficult to form a distribution pattern. Therefore, the length of l shown in FIGS. 1 to 3 is preferably in the range of 10 to 200 μm, and the upper limit of the length of l' is preferably narrower than 200 μm. The insulating surface layer as described above is formed on the photoreceptor as shown in FIGS. 6 to 9. In FIGS. 6 to 9, 1 is made of metal such as aluminum, iron, nickel, copper, or an alloy thereof, and is formed into an appropriate shape and structure as necessary, such as a cylindrical shape or a non-stick belt shape. The conductive layer 2 is a photoconductor such as sulfur, selenium, amorphous silicon or an alloy containing sulfur, selenium, tellurium, arsenic, antimony, etc., or oxidation of metals such as zinc, aluminum, antimony, bismuth, cadmium, molybdenum, etc. Inorganic photoconductors such as compounds, iodides, sulfides, and selenides, or organic photoconductors such as vinylcarbazole, anthracenephthalocyanine, trinitrofluorenone, polyvinylcarbazole, polyvinylanthracene, and polyvinylpyrene, as well as polyethylene, polyester, and polypropylene. , polystyrene, polyvinyl chloride,
A photoconductive layer consisting of an organic photoconductor dispersed in an insulating binder resin such as polyvinyl acetate, polycarbonate, acrylic resin, silicone resin, fluororesin, epoxy resin, etc. 3 is a coloring material such as various polymers, resins, etc. and dyes, etc. An insulating surface layer consisting of a distribution of color separation filter parts such as R (red), B (blue), and G (green) as described above and a T filter part that transmits light from the ultraviolet region to visible light. It is. The insulating surface layer 3 in FIG. 6 is formed by printing on the photoconductive layer 2 an insulating material such as a resin coated with a coloring agent and a transparent resin without a coloring agent, respectively, to form the color separation filter portion. The insulating surface layer 3 shown in FIG.
First, a transparent insulating layer is formed on the photoconductive layer 2 by conventionally known means, and a coloring agent, colored resin, etc. is applied to the surface in a predetermined pattern by means such as printing or vapor deposition. The insulating surface layer 3 shown in FIG. 8 is formed using a transparent insulating layer 3 formed by conventionally known means on the insulating surface layer 3 shown in FIG.
The insulating surface layer 3 shown in the figure is formed by depositing a coloring agent in a predetermined pattern on the photoconductive layer 2 by direct printing, vapor deposition, etc., or on top of the insulating surface layer 3 shown in FIG. 5, as shown in FIG. Similarly to the insulating surface layer 3, a transparent insulating layer is provided. The formation of the insulating surface layer 3 is not limited to the above-mentioned example, but may also be a method in which a separately formed film is attached or adhered onto the photoconductive layer 2 by an appropriate means. Furthermore, as can be inferred from the above-described forming method, the T filter portion may be formed by continuously forming a transparent resin forming a base layer or a protective film. The method of the present invention using the photoreceptor 4 having the layer structure as described above will be explained with reference to FIG. Although FIG. 10 shows an example in which an n-type photosemiconductor such as cadmium sulfide is used in the photoconductive layer 2 of the photoreceptor 4, it is also possible to use a p-type photosemiconductor such as selenium. The basic process is the same, except that the signs of the charges shown in the figure are all reversed. First, as shown in FIG. 10, the surface of the photoreceptor 4 is uniformly charged by positive corona discharge from the charger 5. In this state, a positive charge is generated on the surface of the insulating surface layer 3, and a corresponding negative charge is induced at the interface between the photoconductive layer 2 and the insulating surface layer 3. As a result, the surface of the photoreceptor 4 has a potential E As shown in the graph, it shows a uniform potential. If it is difficult to inject charges into the photoreceptor 4 during this charging, uniform irradiation with light is also used. Note that the conductive layer 2 of the photoreceptor 4 is grounded. Next, for the above-mentioned charged surface, as shown in 2,
An exposure discharger 6 having an exposure slit and generating alternating current or negative corona discharge performs image exposure of a multicolor image through the exposure slit together with the corona discharge. In the figure, to simplify the explanation, the red component during image exposure is
Let's discuss L _R in detail. In each process diagram, P indicates a bright area of image exposure, and D indicates a dark area of image exposure. Furthermore, when performing normal image exposure, it is desirable to cut out light other than visible light. The red component L _R passes through the R and T filter portions of the insulating surface layer 3 and makes the portion of the photoconductive layer 2 below it conductive. The negative charges on the interface disappear, and the positive charges on the surface of the insulating surface layer 3 are also erased by the discharge of the exposure discharger 6, so that no charges exist. Among these, the transmittance of the T filter part may be selected as shown in Figure 5 depending on the purpose of the image to be obtained, and instead of having sufficient transmittance in the visible light range, When a material with a low transmittance is used, the lower the transmittance, the more charge remains depending on the transmittance. On the other hand, since the B and G filter parts do not transmit the red part L _R , the negative charge of the photoconductive layer 2 remains in that part,
Even if discharge is performed by the exposure discharger 6, positive charges are induced on the surface of the insulating layer 3 by the negative charges of the photoconductive layer 2 after passing through that position. However, not only the R and T filter parts where the charge has disappeared, but also the B and G filter parts where the charge remains and the dark area D.
Due to the balance of positive and negative charges in the R, B, G, and T filter portions, the surface potential of the photoreceptor 4 becomes almost 0 as seen in the graph of the potential E. In other words, where the red component L _R of the image exposure is strongly incident to the R and T filter portions so strongly that it disappears, the charge disappears, but where it is not so strongly incident, the R and T filter portions are also affected by the B and G filter portions. Similarly, positive and negative charges remain in balance depending on the amount of exposure. The green component, blue component, or other wavelength component of image exposure, which is not shown in FIG. It is in a state of
This state of the photoreceptor 4 does not function as an electrostatic latent image indicating a surface potential pattern. Hereinafter, this state will be referred to as a primary latent image. This primary latent image forming surface is entirely exposed to light that passes through only one of the T, B, G, and R filter portions. FIG. 10 shows an example in which this first entire surface exposure is performed by a uniform exposure device 7UV using a filter F _UV that transmits only ultraviolet light L _UV . When the entire surface of the primary latent image formation surface is exposed to ultraviolet light L _UV , the ultraviolet light L _UV passes through only the T filter portion, making the photoconductive layer 2 below it conductive.
As a result, the electric charges at the upper and lower interfaces of the photoconductive layer 2 in that part are neutralized, and as a result, the potential increases in the dark area D on the surface of the insulating surface layer 3 in the T filter part, and the potential almost decreases in the bright area P. As it is, a potential pattern is generated that provides a black image of the primary latent image, as shown by the solid line in the graph below. Here, since the B, G, and R filter portions do not transmit ultraviolet light L _UV , the charged state of these portions is the same as the primary latent image formation state described in 2. The electrostatic latent image formed by the potential of the T filter portion is developed as shown in FIG. 10 by a developing device 8K containing negatively charged black toner _TK . Black toner T _K has a relatively high potential.
It adheres only to the filter portion, and does not adhere to the B, G, and R filter portions, which have relatively low potentials. In addition,
If the T-filter part is one that sufficiently transmits light in the visible light range, the T-filter part will not show any potential increase in the bright region P as shown by the solid line in the graph of 3 (the charge will not increase in the process of 2). (disappeared), so toner will not stick to it. However, T
If the filter part has low transmittance in the visible light range, a potential increase will appear in the bright region P as shown by the dotted line in the graph of 3, depending on the absorption rate of the T filter part. Toner adheres accordingly. Therefore, by selecting the visible light transmittance of the T-filter portion or by selecting the ultraviolet light transmittance, toner does not adhere during white image exposure, and when colored image exposure Sometimes it can be changed so that toner adheres slightly. Through the above steps, a black toner image is formed on the surface of the photoreceptor 4, giving the black portion of the multicolor image. Then, the potential of the T filter portion decreases as shown in the graph of potential E in 4 due to the adhesion of black toner _TK . However, even if the potential decreases, it still shows a slightly high potential, and therefore, in the next development, toner of another color may adhere to this area, causing color smearing. Therefore, if necessary, a charger 9 that performs a corona discharge similar to the exposure discharger 6 is used to discharge the developed surface as shown in FIG.
The potential of the T filter portion to which black toner _TK is attached is uniformly lowered as shown in the graph of potential E so as to have almost no effect on the G and R filter portions. This step is for preventing color smearing as described above, and may be omitted depending on the case. The exposure discharge device 6 can also be used as a charger used in this step. FIG. 10 4 where a black toner image is formed as described above.
Alternatively, the entire surface of the photoreceptor 5 is exposed to blue light using, for example, a uniform exposure device using a blue filter in the same manner as in FIG. 10. As a result, a potential pattern that gives a complementary color image of blue of the primary latent image appears in the B filter portion (see Japanese Patent Application No. 83096/1983). Developed using a developing device. As a result, a color-separated one-color yellow toner image is formed on the surface of the photoreceptor 4. The potential of the B filter portion to which the yellow toner was attached was lowered uniformly by the charger 9 as required, as shown in the potential E graph in FIG. This time, the entire surface of 4 is exposed to green light, for example. As a result, a potential pattern appears in the G filter portion, and this electrostatic image is developed by a developing device containing magenta toner to form a magenta toner image. The potential of this image forming surface is also lowered as necessary in the same manner as before, and finally the entire surface of the image forming surface is exposed to red light. As a result, a potential pattern appears in the R filter portion, and the electrostatic image is developed by a developing device containing cyan toner to form a cyan toner image in the same manner as in FIG. 10 and 4. However, when the cyan toner adheres, it occurs when the amount of light in the dark area D or the red component L _R is small. As described above, a multicolor image using four color toners is formed on the surface of the photoreceptor 4 without color shift or color turbidity. In this multicolor image, since the black portion is expressed by the color of the black toner, the image does not appear to lack image density and gives a very clear impression. This multicolor image is transferred and fixed onto a transfer material by conventionally known means. In the multicolor image forming method of the present invention, as in the example described above, it is preferable to form a black component image first because it reduces the possibility of black toner adhering to other color toner images. The invention is not limited thereto, and the color component images may be formed in any order. Table 1 shows the changes in each filter portion of the photoreceptor in each step of the present invention described with reference to FIG. 10 in relation to the color of the original image. In the table, symbol "〓"
is the primary latent image, symbol "〇" is the electrostatic latent image, symbol "〓"
indicates a toner image, the symbol "↓" indicates a state in which the state in the upper column is maintained as it is, and a blank column indicates a state in which no image exists. Further, in the attached toner column, - indicates that no toner is attached, and Y, M, C, and K indicate that yellow, magenta, cyan, and black toners are attached, respectively. moreover,
() indicates that toner will adhere if the visible light absorption rate of the T-filter part is higher than a certain level, and that toner will not adhere if the T-filter part's visible light transmittance is sufficiently high. show. In addition, 〓 〓 indicates that toner will adhere if the absorption rate in the visible light range of the T filter part is higher (sufficiently high), and if the transmittance of the visible light range of the T filter part is high to a certain extent, toner will adhere to the T filter part. Indicates no adhesion. In these cases, the T filter portion transmits light other than visible light to the same extent, and the original image is composed of visible light. Of course, the colors of the original image and the reproduced colors in Table 1 indicate the colors of the constituent parts of a multicolor image. Black in the reproduced color is created by an additive coloring method using black toner and three primary color toners, and the density of the reproduced multicolor image is determined by the presence of parts that are represented by this black toner. can be seen to have improved significantly.

【table】

〔Effect of the invention〕

According to the method of the present invention, since each color component image is superimposed and formed using one image exposure, there is no risk of color misregistration, and each color component image contains a black toner image. , the black toner image can compensate for the lack of image density due to the additive coloring method and reproduce a clear multicolor image with excellent contrast. The present invention is not limited to color copying machines, but can be widely used in various multicolor image recording devices, color photo printers, and the like. As already mentioned, the color of the separation filter and the combination of the corresponding toner colors can be arbitrarily selected depending on the purpose, and the photoreceptor is not limited to the shape of a drum or belt. Of course.

[Brief explanation of the drawing]

1 to 3 are partial plan views showing an example of the distribution of filter portions in the insulating surface layer of the photoreceptor used in the present invention, and FIG. 4 is a graph showing an example of the spectral transmittance characteristics of each filter portion, and FIG. Figure 5 is a graph showing an example of the spectral transmittance characteristics of a filter portion that also transmits ultraviolet light, Figures 6 to 9 are partial cross-sectional views schematically showing examples of the layer structure of the photoreceptor, and Figure 1
Fig. 0 is a process diagram explaining an example of the present invention, Fig. 11 is a schematic sectional view showing an example of a recording device that implements the method of the present invention, and Fig. 12 is a diagram of a developing device used in the recording device of Fig. 11. FIG. 3 is a schematic cross-sectional view showing an example. T, B, G, R... Filter portion, 1... Conductive layer, 2... Photoconductive layer, 3... Insulating surface layer, 4... Photoreceptor, 5... Charger, 6... Exposure discharger, 7
UV, 7B, 7G, 7R...Uniform exposure device, F _UV
...Ultraviolet filter, F _B ...Blue filter, F _G ...
...Green filter, F _R ...Red filter, L _R ...
Red component, L _UV ...Ultraviolet light, 8K, 8Y, 8M,
8C... Developing device, T _K ... Black toner, 9... Charger, 10... Recording paper supply device, P... Recording paper,
DESCRIPTION OF SYMBOLS 11...Transfer device, 12...Separator, 13...Transporting means, 14...Fixing device, 15...Cleaning device, 80...Bias power supply, 81...Developing sleeve, 82...Magnet, 83... ...Developer reservoir, 8
4... Layer thickness regulating blade, 85... Cleaning blade, 86... Stirring means, 87... Toner hopper, 88... Toner supply roller.

Claims (1)

[Claims] 1. After performing charging and image exposure on a photoreceptor having a layer including a plurality of filters having different spectral transmittance characteristics, a photoconductive layer, and a conductive layer, at least different spectral transmittance characteristics are generated each time. In a method of forming a multicolor image on a photoconductor by performing full-surface exposure with distributed light and development of an electrostatic latent image formed thereby with different color toners a plurality of times, one of the plurality of development steps is performed. A multicolor image forming method characterized in that one development step is performed using black toner. 2. The multicolor image forming method according to claim 1, wherein the development with the black toner is performed before the development with other color toners. 3. The multicolor image forming method according to claim 1, wherein the color toner is a black toner and a chromatic color toner.