JPS6360384B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multicolor electrophotographic copying method for copying a multicolor original. Conventionally, the following method has been used to obtain multicolor copies, for example, red and black copies. First, the photoreceptor is uniformly charged, and then the original is exposed through a cyan filter to form an electrostatic latent image of the red and black parts of the original, which is visualized with red toner and then transferred to transfer paper. did. Next, the photoreceptor is neutralized and cleaned, and then uniformly charged again. This time, the document is exposed through a red filter to form an electrostatic latent image of only the black portion of the document, which is then visualized with black toner. After forming an image, align it with the transfer paper on which the red image was previously formed and transfer the black toner image to create the red/black 2 image.
Got a color copy. In this conventional method, since a cyan filter is used for visualization using red toner, it is not possible to separate the red and black parts of the document, and red is also visualized in the red and black areas. For this reason, in a two-color copy, red toner and black toner overlap in the black area, resulting in a reddish black image. In order to solve this problem, it is necessary to develop a two-color copy using only red toner and black toner, respectively, corresponding to the red and black colors of the original. To this end, as disclosed in JP-A-54-10737, uniform charging is applied to the photoreceptor from above the toner image remaining after the previous color has been transferred, and a negative mask is applied to the next color. An electrostatic latent image pattern having the function of 1 is created, thereby forming an electrostatic latent image for a specific chromatic color, and visualization may be performed. In this case, since there is a small amount of toner remaining after transfer, the effect of suppressing recharging by the toner layer is small, and the only way to remove static electricity before recharging is by light irradiation, and the difference between toner-adhered areas and toner-free areas on the photoreceptor is small. It was not possible to increase the potential difference. Japanese Patent Application No. 54-1569 was proposed by the applicant as a further improvement on this. In this case, in order to create an electrostatic latent image pattern that functions as a negative mask, an operation is performed to micronize a toner image of a color that has a negative relationship with a specific chromatic color. Then, light irradiation and AC+DC are used to remove static electricity before recharging.
This was done by adding a corona discharge, and the potential of the photoreceptor after static elimination was kept near zero regardless of whether or not toner was attached. Under these conditions, when the subsequent same-polarity recharging potential was measured after cleaning, it was 650 [V] in the toner-free area and 250 [V] in the toner-attached area. Essentially, it is desirable that the toner-containing area, that is, the area to which toner of a color having a negative relationship with the specific chromatic color is attached, be kept at a low potential so as to prevent toner of the specific chromatic color from adhering as much as possible. For this reason, it has been desired to maintain the potential of the toner-attached portion at an even lower potential. Furthermore, if the specific chromatic color is red and the color that has a negative relationship with black is black, if the black area of the document is in the middle to low density area, the negative electrostatic potential of the area corresponding to the black area on the photoconductor will increase. When the image is visualized, this black area cannot be completely covered with black toner, and when recharging, the black area receives some electric charge of the same polarity as the red area, and the resulting copy is The red toner overlaps the black areas of the image, causing the inconvenience that the black areas appear red. In the earlier patent application No. 54-1569, prior to forming an electrostatic latent image for a negative mask, the negative electrostatic latent image is visualized with either black toner or red toner for use in forming this image. is configured to do so. In order to clearly copy the intermediate density area mentioned above using this process, it is necessary to develop the negative electrostatic latent image by increasing the amount of toner attached to it, which corresponds to the intermediate density area to the low density area of the black part of the original image. be. However, when doing so, when a red or black image is created on the entire document using black or red toner, the amount of each toner attached becomes extremely large, resulting in decreased resolution, poor fixing, and even harsh copies. This causes the inconvenience of In order to solve each of the above-mentioned disadvantages, the present invention has the following configuration. First, prior to secondary charging of the photoreceptor over the entire surface in order to visualize a specific chromatic color, static electricity is removed from the entire surface by corona discharge with the same polarity as the primary charging, and each image corresponding area after static electricity is removed. By maintaining a large potential difference between them, the secondary charging potential of the photoreceptor corresponding area of a specific chromatic color is compared to the two of the photoreceptor corresponding area of a color that has a negative relationship with the specific chromatic color.
The subsequent charging potential is kept low to prevent specific chromatic toner from adhering to areas other than the chromatic image area of the resulting copy. Furthermore, prior to the secondary charging of the entire photoreceptor to visualize a specific chromatic color, a primary charging potential for forming a negative electrostatic latent image or a light image having a specific chromatic color is applied. Of each setting value of exposure amount or development bias voltage when developing a negative electrostatic latent image,
At least one of the values during charging, exposure, and development for a specific chromatic color is changed to increase the amount of toner adhering to the negative electrostatic latent image, thereby increasing the area corresponding to the photoreceptor for the specific chromatic color. On the other hand, the secondary charging potential of the photoreceptor corresponding area of a color having a negative relationship with this is suppressed to a low level, so that the specific chromatic color is attached only to the area corresponding to the specific chromatic color of the obtained copy. According to this invention, it is possible to form an electrostatic latent image pattern that acts as an effective negative mask by utilizing the charging property of toner in the area corresponding to a specific chromatic color on the photoconductor and a color that has a negative relationship with the photoconductor. It is possible to prevent parts other than the specific chromatic color corresponding area of the image surface of the copy from being overlaid with the chromatic color. SUMMARY OF THE INVENTION An object of the present invention is to provide a multicolor electrophotographic method that can create a copy image corresponding to an original using toner of a predetermined color without color cast. The present invention will be described below with reference to the accompanying drawings. 1st
The figure shows a step explanatory diagram of a multicolor electrophotographic copying method as an embodiment of the present invention for copying an original 1 made of three colors, white, red, and black. The photoreceptor 2 used here is polymerized on a conductive substrate (not shown), and when the surface of the photoreceptor is irradiated with light, the photoreceptor becomes conductive, and there is a connection between the photoreceptor and the conductive substrate. Charge is supplied and discharged. First, the photoreceptor 2 is uniformly charged to a positive polarity by the primary charger 3, as shown in FIG. 1A.
Subsequently, the photoreceptor 2 is irradiated with a light image from the original 1 via the red filter 4 to perform exposure. This manuscript 1 has a red part 11 as a specific chromatic color.
It has a black part 12 as a color that has a negative relationship with , and a white part 13 as a background. The photoreceptor 2 is exposed to the optical image of the original 1 through the red filter 4, and the photoreceptor regions 213 and 211 corresponding to the white portion 13 and the red portion 11 are made conductive and emit positive charges on the surface. , the photoreceptor region 212 corresponding to the black portion 12 is not irradiated with light and therefore maintains a positive charge. Therefore, as shown in FIG. 1B, a negative electrostatic latent image a is formed on the photoreceptor, which has a negative relationship with respect to red. This negative electrostatic latent image a is a black toner 5 (red toner 6 may also be used) that holds a negative charge.
is supplied to the photoreceptor 2 as shown in FIG.
The black part corresponding area 212 is visualized with black toner 5. This completes the negative electrostatic latent image developing step A. Next, as shown in FIG. 1D, the entire surface of the photoreceptor 2 is subjected to an operation of eliminating electricity. In this case, the static elimination lamp 7 and the static elimination charger 8 that applies a positive corona discharge having the same polarity as the primary charge are operated, and the toner-free area is removed.
In other words, the surface potential Vs of the white and red corresponding areas 213 and 211 is brought close to a level close to zero, and the surface potential Vs of the white and red corresponding areas 213 and 211 is brought close to zero, and the black toner adhesion area, that is, the black corresponding area 21 is
The potential (hereinafter referred to as total surface potential) Vt of the total surface S of the toner layer/photoreceptor layer No. 2 is maintained at a potential greater than the surface potential Vs of the white and red regions. Furthermore, with respect to this total surface potential Vt, the photoconductor potential (hereinafter referred to as toner back surface potential) Vs ₁ at a position f corresponding to the lower side of the total surface S, that is, the back surface of the black toner 5, is held at a negative potential that is the opposite polarity. This is desirable. The static elimination charger 8 may be configured to apply a corona discharge in which a light current voltage is superimposed on a positive DC voltage. Next, as shown in FIG. 1E, the entire surface of the photoreceptor 2 is uniformly charged with a secondary charging charger 9 to which a positive voltage having the same polarity as the primary charging is applied. In this case, white and red corresponding areas 213, 21
1, that is, the toner-free area is charged to a predetermined surface potential, while the black area corresponding area 212, that is, the toner back surface potential Vs ₁ of the toner-adhered area is subject to the charging suppressing effect of the toner due to the charging property of the toner. Therefore, the amount of charge is regulated as described later. Next, as shown in FIG.
When the black toner 5 (or red toner 6) is removed from the photoconductor surface, the white and red corresponding areas 21
3 and 211 are corrected to a high potential level, and the black portion corresponding area 212 is corrected to a low potential level, thereby forming an electrostatic latent image for a negative mask (hereinafter referred to as a corrected latent image) n. This modified latent image n acts as a negative mask for the black area 212 when the red area 211 is visualized. After the electrostatic latent image forming step N for a negative mask is performed in this manner, the photoreceptor 2 is exposed to a light image in which the light of the red portion 211 of the original is blocked, as shown in FIG. That is, the light image of the original 1 is exposed again, this time through the cyan filter 15 (which may be a blue or green filter) so that it optically coincides with the modified latent image n. As a result, the white part corresponding area 213 becomes conductive and releases charge, and since the black part corresponding area 2 is negatively masked, a high potential electrostatic latent image is formed only in the red part corresponding area 211. Thereafter, as shown in FIG. 1H, red toner 6 is supplied to the red portion corresponding area 211, a developed image corresponding to the red portion 11 of the original is formed on the photoreceptor 2, and the development of the specific chromatic color is completed. In this case, since the black part corresponding area 212 was negatively masked, only a negligible amount of positive charge remained, and this black part corresponding area 212
The red toner 6 having a negative charge does not adhere to the surface. Next, as shown in FIG. will be done. Further, after (or before) obtaining a reproduced image of the specific chromatic color, that is, the red part 11, by the above-mentioned three steps A, N, and P, the black part is reproduced in the same process as that of obtaining the negative electrostatic latent image a. The electrostatic latent image obtained in the corresponding area 212 is visualized with black toner 5. After that, align it with the transfer paper 16 used in FIG.
The developed image formed by the black toner 5 is transferred, and a development transfer step P1 of other colors having a negative relationship with the specific chromatic color is performed. As described above, in the multicolor electrophotographic copying method, which is an embodiment of the present invention shown in FIG. An electric latent image forming step N is performed, and thereafter, development and transfer of the red portion 11 as a specific chromatic color is performed as a specific color development and transfer step P. Subsequently, charging exposure for forming a copy image of the black portion 12 which has a negative relationship with the specific chromatic color is performed using the same means as for forming the negative electrostatic latent image a, and then another color development and transfer step P1 is performed. There is. By using the multicolor electrophotographic copying method with such a configuration, copies in two colors, red and black, can be obtained. Experimental results regarding the secondary charging in the electrostatic latent image forming step N for a negative mask in the above-mentioned multicolor electrophotographic copying method and the static elimination operation performed prior to this will be described below. The photosensitive layer of the photoreceptor 2 used is made of selenium. The toner used for developing the negative electrostatic latent image a in the negative electrostatic latent image developing step A is a negatively charged red toner 6, and its volume resistivity is 8.
×10 ¹⁰ [Ω・cm), and the relative dielectric constant is 3.3. A tungsten bean lamp was used as the static elimination lamp 7, and the amount of light irradiated was approximately 900 [lx·S]. The static elimination charger 8 is a corotron type, and the secondary charging charger is a scorotron type. The latent image potential of the area corresponding to the black part of the negative electrostatic latent image a is +650 [V], the latent image potential of the area corresponding to the white and red parts is +100 [V], and development with red toner is +200 [V] using the magnetic brush method. This was done by applying a developing bias of . Under these conditions, the experimental results shown in Table 1 below were obtained.

[Table] According to Table 1, when the photoreceptor potential after cleaning is constant at +650 [V] in the white and red areas, the potential level in the black area is in the order of >>>, and under the static elimination conditions. Kurobe corresponding area 212
It can be seen that the potential level of is the lowest (+100V here), which is a favorable result. This is because the total surface potential Vt after static elimination is <<<, and the toner back surface potential Vs ₁ is >>>. In this case, when secondary charging of the same polarity is performed, the secondary charging charge 9 moves to the f position (shown in FIG. 1D) in the black area 212.
The amount of charge supplied from the This increases the white and red corresponding areas 213 and 211 by a certain amount (here
650V) and the amount of charge supplied to the f position, the higher the total surface potential Vt of the black part corresponding area 212 is, the more This is because the potential difference between the corona wire and the corona wire becomes lower. Furthermore, the lower the toner back surface potential Vs ₁ in the black portion corresponding area 212 is, the lower the potential level can be suppressed even if the potential increases due to the supplied charges of secondary charging. Note that the reason why the back surface potential Vs ₁ of the toner after the static elimination operation decreases as the total surface potential Vt increases is due to the chargeability of the toner, that is, the resistance and capacitance that the toner has. FIG. 2 shows the charged potentials at the toner-adhered portion and the toner-free portion on the photoreceptor, respectively, as equivalent circuits.
Figure 2a shows the equivalent circuit of the toner-free area, and Figure 2b shows the equivalent circuit of the toner-adhered area, where Cp is the photoconductor capacitance, Ct is the toner layer capacitance, and Rp is the photoconductor capacitance. Dark resistance, Rt is the resistance of the toner layer, Vs is the surface potential of the photoreceptor in the toner-free area, Vs ₁ is the surface potential of the toner-attached area, that is, the toner back surface potential, Vt ₁ is the potential of the toner layer, Vt indicates the total surface potential of Vs ₁ and Vt ₁ , respectively. In this equivalent circuit, the corona current is flowing through the photoreceptor is =
It is represented by As (V-Vs) (V-Vs-Vo). Here, As is a constant, V is the potential difference between the charger wire and the case, and Vo is the discharge starting voltage. From this, if the conditions such as charger shape and corona applied voltage are the same, the corona current is
It will depend only on Vs. Then, at the toner adhering portion on the photoreceptor, the value of the corona current is is determined by setting the photoreceptor surface potential to Vt instead of Vs. Therefore, if the toner used has high chargeability and the total surface potential Vt becomes high, even if the toner back surface potential Vs ₁ is low, the corona current is is suppressed and reduced. In Table 1, when the static electricity removal operation is performed using only light irradiation (), the negative charge of the toner is not completely discharged, so the total surface potential Vt shows the opposite polarity to the primary charging voltage, and the toner back surface potential Vs ₁ has the same polarity. It remains as it is. However, when the static elimination condition is set to , the toner polarity is reversed, and furthermore, when , a sufficient positive charge of the same polarity is applied, so that the total surface potential Vt becomes high. Moreover, the toner back surface potential Vs ₁ holds an induced charge corresponding to the toner capacitance Ct, lowering the positive potential,
As it progresses further, a higher potential appears on the opposite polarity side. As is clear from the above experimental results, in order to obtain a modified latent image n that acts as a negative mask for toners of other colors when visualizing a specific chromatic color,
It is effective to use a component of the same polarity as the primary charging of the corona applied together with light irradiation in the static elimination operation before the secondary charging to increase the total surface potential Vt as much as possible. In order to obtain the same effect, the components applied to the static elimination charger include not only the primary charge and the same polar DC component, but also the same polar DC component (to keep the DC component at a stronger level) to the light current. Furthermore, if the primary charging is of negative polarity, it is possible to use only an AC component depending on the conditions. Furthermore, by adding the present invention to the invention of JP-A-54-10737, a more excellent electrostatic charge pattern can be formed. In the multicolor electrophotographic copying method described above, the relationship between the amount of toner (mask toner) that visualizes the negative electrostatic latent image a attached to the photoreceptor and the surface potential Vs of the photoreceptor will be explained. A color that has a negative relationship with a specific chromatic color of the original 1, for example, a black portion 12 in the embodiment shown in FIG.
When the original is an image in a medium to low density range, when the original is copied, red toner slightly adheres to the image surface corresponding to the black area.
This is the black area corresponding area 21 when developing with red toner.
This is because the potential of the corrected latent image n, which acts as a negative mask for the black area 212, is not kept sufficiently low in the black portion corresponding area 212. That is, the total surface potential Vt shown in FIG. 2b becomes low when the amount of toner adhering to the photoreceptor is small, and as a result, the toner back surface potential Vs ₁ becomes high. For this reason, charges of the same polarity as those of the red area 211 remain in the black area 212, and red toner slightly adheres to the black area 212. To prevent this, it is necessary to increase the amount of mask toner that adheres to the black area 212 or to use a toner material with high resistance. Figure 3 shows two photoreceptors with mask toner attached.
A diagram showing the relationship between the amount of mask toner attached and the surface potential Vs of the photoreceptor when it is subsequently charged and cleaned is shown. In this figure, the area where the amount of toner adhesion is zero, that is, the areas 213 and 211 corresponding to the white and red parts shown in FIG.
640V, and the photoreceptor surface potential Vs becomes smaller in parts where the image density of the document is higher. The volume resistivity of the mask toner used here was 10 ¹⁰ [Ω-cm]. Figure 4 shows the photoreceptor surface potential Vs corresponding to the diagram shown in Figure 3.
The relationship between the image density and the image density of the original is shown in a diagram. The relationship shown in this figure shows the surface potential Vs of each photoconductor with respect to the photoconductor corresponding area at the stage shown in FIG.
is shown by line b, and the black area 212 is shown by line c. Similarly, FIG. 5 shows the surface potential Vs of each photoreceptor obtained by exposing the original through a cyan filter with the exposure position aligned with the surface of the photoreceptor in the state shown in FIG. This shows the surface potential of the photoreceptor at the stage of FIG.
12 is indicated by a broken line (line e). The potential of this black portion corresponding area 212 increases slightly from the intermediate density area to the low density area, and red toner actually adheres to this area. In order to eliminate this problem, it is sufficient to increase the exposure amount when exposing the original 1 to the photoreceptor 2 through the cyan filter, and as shown by the two-dot chain line in FIG. Although red toner is prevented from adhering to the red area 21,
The toner density of No. 1 also decreases, resulting in the disadvantage that pinkish, orange, and low-density red colors cannot be reproduced.
Although the developing bias potential during development with red toner may be increased, the same drawback as shown by the two-dot chain line in FIG. 5 occurs. In order to eliminate this drawback, it is sufficient to increase the amount of mask toner that adheres to the entire black area 212, that is, from the intermediate density area to the low density area. In this case, there is no need to use a special toner with a high resistance value, and it is sufficient to use a commonly used toner. FIG. 6 is a process explanatory diagram of a multicolor electrophotographic copying method as another embodiment of the present invention. The photoreceptor 2 used in this case is a boss charger photoreceptor that can be charged with both positive and negative polarities. First, the photoreceptor 2 is negatively charged by the primary charger 3 as shown in FIG. 6A, and then the light image of the original 1 is exposed through the red filter 4 (see FIG. 6B). . As a result, only the black portion corresponding area 212 is not irradiated with light, so that the negative polarity is maintained. As a result, a negative electrostatic latent image a is formed on the photoreceptor 2.
is formed. This negative electrostatic latent image a is developed into a toner image used for forming a corrected latent image n by black toner 5 holding a positive charge, and the negative electrostatic latent image developing step A is completed (Fig. 6). (see c). Next, as shown in FIG. 6D, secondary charging is performed by a secondary charging charger 9 to which a voltage of opposite polarity to the primary charging, that is, positive polarity, is applied. At this time, the black toner 5 in the black portion corresponding area 212 on the photoreceptor 2 is charged to a high voltage similarly to the toner-free area. Subsequently, as shown in FIG. 1E, the toner on the photoreceptor 2 is cleaned with a cleaner 14. As a result, a modified latent image n is formed, in which the white and red corresponding regions 213 and 211 maintain a high potential level, and the black corresponding region 212 maintains a low potential level. This completes the negative mask electrostatic latent image forming step N. The subsequent operations of F, G, and C in Figure 6 are as follows.
This process is carried out in the same manner as shown in FIGS. Further, the development and transfer step P1 of the black portion 12 is performed in the same manner as explained in FIG. In this way, you can get two copies of red and black. In the multicolor electrophotographic copying method described in FIG. 6, black toner 5 is used to visualize the negative electrostatic latent image a, and red toner 6, which is charged to the opposite polarity, is not used. On the other hand, in the copying method explained with reference to FIG. 1, since both the black and red toners 5 and 6 had the same polarity, both could be used to visualize the negative electrostatic latent image a. The toner for making this negative electrostatic latent image a visible is used in the electrostatic latent image forming step N for a negative mask,
It acts as a mask toner. As is clear from the description of FIGS. 3, 4, and 5, this mask toner does not function effectively as a mask toner unless it adheres to the photoreceptor in a predetermined amount or more. For this reason, in order to attach sufficient mask toner to the negative electrostatic latent image a, in this invention, when making copies of the red and black corresponding areas 211 and 212, when the negative electrostatic latent image a is visualized, Change the following setting values. That is, when attaching the mask toner to the negative electrostatic latent image a, the potential of the primary charge is increased, or the amount of exposure to the photoreceptor by the red light image is reduced, or the negative electrostatic latent image a is Lower the developing bias voltage during development. Then, at least one of these operations is selected and performed, and when the electrostatic latent image is visualized for the next copy making with black toner 5 or red toner 6, based on the changed setting value. Perform the return operation. The broken line (g) in FIG. 4 shows the result of increasing the potential of the negative electrostatic latent image a by reducing the amount of exposure to the photoconductor from the red light image described above, thereby sufficiently depositing mask toner on the black area corresponding area 212. line), the fifth
In the figure, it is indicated by a broken line (h line). As shown in FIG. 4, in the intermediate density region x of the black part corresponding region 212, the total surface potential Vt
As a result, the corona current is flowing through the photoreceptor during secondary charging is suppressed, and the photoreceptor surface potential Vs
is declining. Furthermore, as shown in FIG. 5, in the intermediate density region x of the black region 212 after exposure through the cyan filter 15, the photoreceptor surface potential Vs is kept sufficiently lower than that of the red region 211 due to the increase in mask toner. Even if this is developed with the red toner 6, the result is that the red toner 6 rarely adheres to the black portion corresponding area 212. Therefore, even if the red portion 11 of the original is pink, orange, or low-density red, it can be copied. An example of a copying apparatus used in the multicolor electrophotographic copying method described above is shown in FIG. 7, and two embodiments using this apparatus to obtain two-color copies, red and black, will be described below. First Embodiment The photosensitive layer of the photoreceptor 2 shown in FIG. 7 is made of selenium. First, the photoreceptor 2 was uniformly charged to +700 [V] by the primary charger 3, and the original optical image 17 was exposed through the red filter 4. As a result, the white and red corresponding regions were set to +100 [V], and the black corresponding region was set to +650 [V], and development was performed while applying a developing bias of +200 [V] in the red developing unit 18. With this, red toner (mask toner) is applied only to the black area.
was attached. Next, under the above-mentioned static elimination conditions, i.e., light irradiation of 900 [lx・S] is performed using the static elimination lamp 7, and corona discharge of DC+6.5 [KV] is applied using the static elimination charger 8 to remove the white and red areas. +50 [V]
, the total surface potential of the black part corresponding area is +300 [V]
The backside potential of the toner was maintained at -90 [V]. Next, the secondary charger 9 charges the white and red areas to +700 [V], the cleaner 14 removes the red toner, and the white and red areas correspond to +650 V.
At [V], a modified latent image was obtained in which the black part corresponding area was kept at +100 [V]. Next, switch to the cyan filter 15, perform optical alignment, and then perform the exposure operation, setting the white and black areas to +100 [V] and the red area to +100 [V].
Keep it at 600 [V] and then increase it to +200 [V] with red developer 18 again.
Developed with a developing bias of This was transferred onto a transfer paper 16 fed from a paper feed cassette 19 by a transfer charger 21. As a result, a red copy with red toner was obtained. Next, conveyor belt 2
2, the transfer paper 16 was conveyed and fixed by the fixing device 23, and then fed to the registration rollers 28 by the guide claws 24 and guide plates 25, 26. On the other hand, the photoreceptor 2 is processed by a cleaner 14 and a static elimination charger 20, and is charged again to +700 [V], and the original image is exposed through a red filter 4, and a black developer 27
It was developed in Then, a black toner image was transferred onto the transfer paper 16 that was fed in at the appropriate timing, and this was fixed, and then delivered to the copy tray 29 by a paper delivery roller 31. The obtained copy was a clear red-black two-color copy in which only black toner 5 was used for the black part of the original, and only red toner 6 was used for the red part. Note that the red and black developing devices 18 and 27 are controlled so that when one is in a developing operation, the other is inactive. In this embodiment, the modified latent image is obtained by performing red development once, but even if it is black development, the static elimination conditions may be set so that the state after static elimination is the same. Although only red and black copying has been described in this embodiment, similar effects can be obtained even in the case of other colors by selecting the color separation filters, toners, and static elimination conditions to be combined. Second Example Using the selenium photoreceptor 2 shown in Fig. 7, +800
The photoreceptor 2 was uniformly charged to [V]. After that, when exposing the original through the red filter 4, the slit width adjuster 30 is operated to regulate the amount of exposure by the red light image, so that the white and red corresponding areas are +200 [V],
Exposure was performed so that the area corresponding to the black part became an electrostatic latent image of +700 [V]. Next, this area corresponding to the black part is processed using the black developer 27.
Developing was carried out using a developer while applying a developing bias of +200 [V], and black toner 5 (mask toner) was attached. In this case, a small amount of toner was also attached to the white and red areas. Next, for photoconductor 2
Light irradiation of 900 [lx・s] is performed using the static elimination lamp 7, and corona discharge of DC + 6.5 [KV] is applied using the static elimination charger 8. is approximated to almost zero, and the potential on the mask toner in the area corresponding to the black area is increased to +
It was kept at 100 to +350 [V]. Next, the secondary charger 9 charges the white and red corresponding areas to +700 [V], and then the cleaner 14 removes the mask toner, and the white and red corresponding areas are charged to +650 [V].
A corrected latent image was obtained in which the black part corresponding area was kept at +100 [V]. Next, after aligning with this corrected latent image, the original light image is exposed through the cyan filter 15, and the white and black areas are set to +100 [V], and the red area is set to +600 [V]. Then, development was carried out by applying a developing bias of +200 [V] using the red developing device 18. Transfer paper 16 fed from the paper feed cassette 19
transcribed into. As a result, a red copy with red toner was obtained. Subsequently, the transfer paper 16 was conveyed by the conveyor belt 22 and fixed by the fixing device 23, and the transfer paper 16 was sent to the registration rollers 28 by the guide claws 24 and guide plates 25 and 26. On the other hand, the photoreceptor 2 was treated with a cleaner 14 and a static eliminating charger 20, and was again charged to +700 [V], and the original image was exposed through the red filter 4. In this case, the slit width adjuster 30 was adjusted so that the exposure amount for the red light image was +100 [V] in the white and red regions. As a result, an electrostatic latent image in the area corresponding to the black part was created, and this was visualized by the black developer 27. Then, the above transfer paper 1 was sent in at the right time.
A black toner image was transferred to the copy tray 29, which was fixed and delivered to the copy tray 29 as a clear red and black two-color copy. In this example, the secondary charging potential had the same polarity as the primary charging, but the secondary charging potential may have the opposite polarity. In that case, the photoconductor is a boss charge photoconductor that can perform bipolar charging. (OPC) can be used. In this case, only black toner having opposite polarity charges is used as the mask toner so that it is attracted by the primary charge. Even in this case, clear red and black two-color copies can be obtained.

[Brief explanation of the drawing]

1 and 6 are process explanatory diagrams showing multicolor electrophotographic copying methods which are different embodiments of the present invention, FIG. 2 is an equivalent circuit diagram showing the surface potential on the photoreceptor, and FIG. 4 is a graph showing the surface potential of each part of the negative electrostatic latent image on the photoconductor versus the density of the original image, and FIG. 5 is a graph of the modified latent image on the photoconductor. FIG. 7 is a schematic front view of a copying apparatus used in a multicolor electrophotographic copying method according to an embodiment of the present invention. 1... Original, 2... Photoreceptor, 3... Primary charger, 5... Black toner, 6... Red toner,
7... Static elimination lamp, 8... Static elimination charger, 9
...Secondary charger, 17...Original light image,
30...Light amount adjustment device, a...Negative electrostatic latent image, n
...Corrected latent image, Vs ₁ ...Toner backside potential, Vt...
Total surface potential, A: Negative electrostatic latent image development process, N: Electrostatic latent image forming process for negative mask.

Claims (1)

[Scope of Claims] 1. In a multicolor electrophotographic copying method in which a photoreceptor is sequentially charged, exposed, developed, and transferred for a predetermined number of colors, the photoreceptor is polarized to a positive or negative polarity.
Next, charging is applied, and then exposure is performed using a light image having a specific chromatic color of the original image to form a negative electrostatic latent image that has a negative relationship with the specific chromatic color. A negative electrostatic latent image development process for developing, and a negative mask electrostatic latent image forming process for secondary charging the entire surface of the photoconductor on which the negative electrostatic latent image has been developed, and then cleaning the photoconductor surface. multicolor electrophotographic copying characterized in that, after performing the secondary charging, exposure is performed using a light image that blocks specific chromatic colors, and a static elimination operation consisting of light irradiation and corona discharge to the photoreceptor is performed prior to secondary charging. Method. 2. The multicolor electrophotographic copying method according to claim 1, wherein in the static elimination operation performed prior to the secondary charging, a corona discharge having the same polarity as the primary charging potential is performed. 3. After the static elimination operation performed prior to the secondary charging, the toner back side photoconductor potential of the toner-attached portion on the photoconductor is maintained at a polarity opposite to the total surface potential of the toner layer and photoconductor layer. A multicolor electrophotographic copying method according to claim 1 or 2. 4. In a multicolor electrophotographic copying method in which a photoreceptor is sequentially charged, exposed, developed, and transferred for a predetermined number of colors, the photoreceptor is charged with a positive or negative polarity.
Next, the original image is charged, and then exposed with a light image having a specific chromatic color to form a negative electrostatic latent image that has a negative relationship with the specific chromatic color. a negative electrostatic latent image development step in which the negative electrostatic latent image is developed; and a negative mask electrostatic latent image forming step in which the photoconductor on which the negative electrostatic latent image has been developed is secondarily charged again over the entire surface, and then the surface of the photoconductor is cleaned. After that, exposure is performed using a light image with specific chromatic colors blocked, and the potential of the primary charge, the amount of exposure using a light image having a specific chromatic color, or the developing bias voltage when developing a negative electrostatic latent image is At least one of the setting values is set to a specific chromatic color charge,
A multicolor electrophotographic copying method characterized by increasing the amount of toner attached to a negative electrostatic latent image by changing values during exposure and development. 5. The multicolor electrophotographic copying method according to claim 4, wherein a static elimination operation consisting of light irradiation and corona discharge to the photoreceptor is performed prior to secondary charging. 6. The multicolor electrophotographic copying method according to claim 5, wherein in the static elimination operation performed prior to the secondary charging, a corona discharge having the same polarity as the primary charging potential is performed. 7. After the static elimination operation performed prior to the secondary charging, the toner back side photoconductor potential of the toner-attached portion on the photoconductor is maintained at a polarity opposite to the total potential of the toner layer and photoconductor layer. A multicolor electrophotographic copying method according to claim 5 or 6.