JPH05249794A - Color image forming method - Google Patents

Abstract

PURPOSE:To prevent the variance of potential contrast caused by the charge of toner sticking to a photosensitive body in development preceding to the formation of a toner image after the first color, in a color image forming method in which the toner images are superimposed on the photosensitive body to form a color toner image, and then, transferred altogether, to a transfer paper. CONSTITUTION:A transparent insulting layer 13 is primarily and electrostatically charged to +800V by a positive corona electrifier while the photosensitive body 1 provided with the layer 13 on a photosensitive layer having the positive and negative sensitivity is irradiated with yellow color light (a), external charges on the surface are all neutralized in the dark by a negative corona electrifier, and simultaneously, only the photosensitive layer is electrostatically charged to -800V by internal charges (b). Then, the image of the first color is exposed with laser light by N/P (c), and has reversal development with negatively charged yellow toner (d). After that, the photosensitive body on which the toner image is formed, similarly has the repetition of primary and secondary electrostatic charges, an image exposure, and the development. At this time, the charge of the toner stuck to the photosensitive body in the primary and secondary electrostatic charges, is neutralized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming method applicable to an image forming apparatus such as a copying machine, a facsimile and a printer, and more specifically, a plurality of toner images having different colors are superposed on a photoconductor. The present invention relates to a color image forming method.

[0002]

2. Description of the Related Art Conventionally, a plurality of toner images of different colors are previously formed on a photoconductor by repeating charging, exposure and development a plurality of times, and then the toner images are formed on a final transfer body such as paper or an intermediate transfer belt. Various color image forming methods of collectively transferring to an intermediate transfer member have been proposed. In this type of color image forming method, since the charging and the image exposure are performed in the state where the toner image is already formed on the photoconductor in the toner image formation for the second and subsequent colors, the light irradiation portion during the image exposure is performed. In addition, the potential after light irradiation differs depending on whether or not the toner has already adhered to the toner, which causes a partial variation in the potential contrast of the latent image. For example, the light irradiation lowers the potential from -800 V to about -100 V in the portion where the toner is not adhered and obtains a potential contrast of approximately 700 V, whereas the portion where the toner is adhered is changed from -800 V to --100 V. The potential drops only up to 400V, and only a potential contrast of about 400V can be obtained. As a result, the development density of the next toner image greatly differs depending on the presence or absence of toner in the light irradiation portion. This leads to a decrease in color reproducibility, and particularly in the formation of a multi-valued one-dot color image, a remarkable decrease in color reproducibility occurs. The cause of this phenomenon is the light shielding effect of the toner and the charging of the toner. Among them, as a measure for avoiding the influence of the toner shielding effect, it has been proposed to perform image exposure from the back side of the photoconductor (for example, JP-A-64-102581 and JP-A-64-102583). Japanese Patent Laid-Open No. 2-219074
Japanese Patent Laid-Open No. 2-198466, etc.). As a measure for avoiding the influence of toner charging, use a photosensitive member having a transparent insulating layer on the photosensitive layer, and perform static erasing so that the potential of the photosensitive member becomes approximately 0V at the same time as image exposure after charging. It has been proposed that the latent image is visualized by irradiating the entire surface with light before developing after erasing the electric charges of the toner layer adhering in the preceding development (for example, JP-A-3-156470). Further, a photosensitive member having a transparent insulating layer on the photosensitive layer is used, and the photosensitive member is subjected to primary charging while being uniformly irradiated with light having sensitivity, and the potential on the photosensitive member in the dark is almost 0 volt. To eliminate the external electric charge accumulated on the transparent insulating layer by the primary charging, the latent image is formed by image exposure, and the latent image is developed with toner of a predetermined color. There is also known a color image forming method for superimposing a plurality of toner images having different colors on the photoconductor, wherein the primary charging is performed using a scorotron corona discharger or a corotron corona discharger. (For example, Japanese Patent Publication No. 3-7946
Publication).

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to:
It is an object of the present invention to provide a novel color image forming method capable of preventing the variation in the potential contrast due to the toner attached to the photoconductor in the preceding development in the toner image formation of the second and subsequent colors.

[0004]

In order to achieve the above object, a color image forming method according to a first aspect of the present invention uses a photosensitive member having a transparent insulating layer on a photosensitive layer having photosensitivity in both positive and negative polarities. , Primary charging of the photoreceptor while uniformly irradiating the photosensitive layer with light having sensitivity, elimination of almost all external charges accumulated on the transparent insulating layer in the dark, latent image exposure A cycle including image formation and development of the latent image with toner of a predetermined color is repeated a plurality of times to superimpose a plurality of toner images of different colors on the photoconductor. Here, having photosensitivity in both positive and negative polarities means being capable of being charged in both positive and negative polarities and capable of attenuating light in both polarities.

The color image forming method of claim 2 is
Using a photosensitive member having a transparent insulating layer on a photosensitive layer having both positive and negative polarities, primary charging of the photosensitive member while uniformly irradiating the photosensitive layer with light having sensitivity, the photosensitive member in the dark The removal of external charges accumulated on the transparent insulating layer by the primary charging so that the upper potential becomes approximately 0 V, the latent image is formed by image exposure, and the latent image is developed with toner of a predetermined color. In a color image forming method in which a plurality of toner images having mutually different colors are superposed on the photoconductor by repeating the cycle including the plurality of times, the primary charging is performed so as to satisfy the following expression. is there. Formula Vs
= K · (1 + a / b) where Vs is the charging potential (volt) of the photoconductor by the primary charging, K is the target potential (volt) of the photoconductor portion irradiated with light by the image exposure, and a is the Capacitance of photosensitive layer (μ
F / m ² ), b is the combined electrostatic capacity (μF / m) of the transparent insulating layer and the toner layer present on the photoconductor layer during the primary charging.
² )

A full-color image forming method according to a third aspect is the full-color image forming method according to the first or second aspect, wherein transparent insulation is provided on a photosensitive layer having a rectifying property with a conductive substrate in place of the photoreceptor. It is characterized in that a photoreceptor having a layer is used, and instead of the above-mentioned primary charging, the photoreceptor is charged with a predetermined polarity.

[0007]

In the method of forming a color image according to claim 1, a photosensitive member having a transparent insulating layer on a photosensitive layer sensitive to both positive and negative polarities is used, and the photosensitive layer is uniformly irradiated with light. The photoconductor is primarily charged to a predetermined polarity, thereby accumulating external charges of a predetermined polarity on the transparent insulating layer, and at the interface between the photosensitive layer and the transparent insulating layer, an internal charge having a polarity opposite to the external charges. Accumulate. Then, almost all the external charges accumulated on the transparent insulating layer by the primary charging are removed in the dark, whereby the internal charges of the interface and the conductivity of the photoconductor corresponding to the internal charges are left. The photosensitive layer is charged by the electric charge induced in the substrate. Then
The internal charge is partially erased by imagewise exposure, whereby an exposed portion forms a latent image having a lower electric potential than the unexposed portion. Then, the latent image formed by the internal charges is developed with toner of a predetermined color. The above-described cycle including primary charging, predetermined static elimination in the dark, image exposure, and development is repeated a plurality of times to superimpose a plurality of toner images of different colors on the photoconductor. Then, in forming the toner images of the second and subsequent colors, by the above-mentioned primary charging and a predetermined charge removal in the dark,
In the preceding development, the external charge on the transparent insulating layer including the charge of the toner adhering to the photoconductor is almost uniformly erased, and the latent image due to the subsequent image exposure is formed by the internal charge of the interface. Therefore, a substantially uniform potential contrast of the latent image can be obtained regardless of the presence or absence of toner in the preceding development.

In the color image forming method of the present invention, a photosensitive member having a transparent insulating layer on a photosensitive layer having photosensitivity in both positive and negative polarities is used, and the photosensitive layer is uniformly irradiated with light having sensitivity. The photoreceptor is primarily charged to a predetermined polarity to accumulate an external charge having a predetermined polarity on the transparent insulating layer, and the internal charge having a polarity opposite to the external charge is accumulated at an interface between the photosensitive layer and the transparent insulating layer. As a result, the transparent insulating layer is charged with both charges. Then, a part of the external charge accumulated on the transparent insulating layer by the primary charging is removed in the dark to induce the internal charge of the remaining interface and the conductive substrate of the photoconductor corresponding to the internal charge. The electric charge causes the photosensitive layer to be charged, whereby the electric potential on the photosensitive body, which appears by combining the charging of the transparent insulating layer and the charging of the photosensitive layer, becomes approximately 0 volt. Then, the internal charge is partially erased by image exposure, and charging by the remaining external charge appears on the photoconductor to form a latent image in which the potential of the exposed portion becomes higher than that of the non-exposed portion. To do. Next, this latent image is developed with toner of a predetermined color. The above-described cycle including primary charging, predetermined static elimination in the dark, image exposure, and development is repeated a plurality of times to superimpose a plurality of toner images of different colors on the photoconductor. Then, when the toner images of the second and subsequent colors are formed, the primary charging is performed so as to satisfy the predetermined relationship, so that the potential of the exposed portion due to the subsequent image exposure adheres to the photoconductor in the preceding development. Since it does not differ depending on the presence or absence of toner that is present, an accurate latent image potential can be obtained according to the exposure amount.

Now, the primary charging will be described in detail. The equivalent circuit of the photoconductor is, as shown in FIGS. 5A to 5C, a constant capacitance capacitor C1 corresponding to the photoconductive layer of the photoconductor.
And a variable capacity capacitor C2 corresponding to the transparent insulating layer and the toner layer of the photoconductor are connected in series. The specific capacitance of the variable capacitance capacitor C2 varies depending on the amount of the toner layer on the transparent insulating layer, and the toner layer does not exist at all in the primary charging for forming the toner image of the first color. Capacity itself. Figure 5 (a)
Is an equivalent circuit showing the primary charging state, and the fact that both ends of the constant capacity capacitor C1 are short-circuited corresponds to the fact that the photosensitive layer is made conductive by uniform irradiation of predetermined light having sensitivity, The fact that the variable capacitor C2 is charged by the power source E corresponds to the fact that the transparent insulating layer is charged by the primary charging. Variable capacitance capacitor C in the state of FIG. 5 (a)
FIG. 5B, in which 2 is connected to the ground, is an equivalent circuit showing a state of removing some external charges on the transparent insulating layer in the dark,
The variable capacitance capacitor C2 is connected to the ground, which corresponds to the fact that the charge removal is performed until the potential on the photoconductor becomes approximately 0 volt. Here, the constant-capacity capacitor C1 is charged because a part of the electric charge charged in the variable-capacitance variable capacitor C2 in the state of FIG. 5A moves. FIG. 5C is an equivalent circuit showing an image exposure state in which both ends of the constant capacitance capacitor C1 in the state of FIG. 5B are short-circuited and both ends of the variable capacitance capacitor C2 are opened. The fact that both ends are short-circuited corresponds to that the photosensitive layer is made conductive by image exposure.

In the above equivalent circuit, if the voltage of the variable capacitor C1 in the state of FIG. 5A, that is, the charging voltage of the transparent insulating layer and the toner layer by the primary charging is given, the state of FIG. 5C is obtained. Variable capacitor C2
Voltage, that is, the charging voltage of the transparent insulating layer and the toner layer of the image exposure portion is determined. In the states of FIGS. 5A and 5C, since both ends of the constant capacity capacitor C1 corresponding to the photosensitive layer are short-circuited, the voltage of the variable capacity capacitor C2 becomes the potential of the photoconductor. Therefore, if the potential of the photoconductor due to the primary charging is given, the potential of the photoconductor in the image exposure section is determined. Specifically, the capacity of the constant capacity capacitor C1 corresponding to the photosensitive layer is a (μF / m ² ), and the capacity of the capacity variable capacitor C2 corresponding to the transparent insulating layer and the toner layer is b (μF / m ² ), the primary The voltage of the variable capacitor C2 in the state of FIG. 5A corresponding to the potential of the photoconductor due to charging is Vs (volts), and the voltage of the image exposure unit in the state of FIG. 5C corresponding to the potential of the photoconductor. Variable capacitor C2
If the voltage of V1 is V1 (volt), the following equation (1) is established. Vl = [b / (b + a)] Vs (1) Generally, as is apparent from this equation, the specific potential of the photoconductor of the image exposure portion is attached on the photoconductor in the preceding development. The amount of toner depends on the capacity b of the transparent insulating layer and the toner layer, which have different values. Therefore, in the color image forming method of the present invention, the primary charging is performed so as to satisfy the following expression (2) so that the potential of the photoconductor of the image exposure unit is not affected by the amount of toner adhered on the photoconductor. To do. Vs = K · (1 + a / b) (2) (In the formula (2), K is the target potential (volt) of the photoconductor in the image-exposed portion). Thus, as shown in the following formula (3), It is possible to set the potential Vl of the photoconductor in the image exposure unit to the target potential K without being influenced by the amount of adhered toner. Vl = [b / (b + a)] · K · (1 + a / b) = K

In the full-color image forming method of claim 3, in the color image forming method of claim 1 or 2,
Instead of the above-mentioned photoreceptor, a photoreceptor having a transparent insulating layer on a photosensitive layer having a rectifying property with a conductive substrate is used. Then, instead of the above primary charging, the primary charging of the photoconductor is performed with a polarity in which a charge having a polarity opposite to the polarity of the charge is easily injected from the conductive substrate into the photosensitive layer. Otherwise, a color image is formed in the same manner as the image forming method according to claim 1 or 2.

[0012]

EXAMPLES Examples of the present invention will be described below. FIG. 3A shows an example of the configuration of the photoconductor used in this embodiment. The photoconductor 1 of this example has a sensitivity on both positive and negative polarities, so that the OPC 11 having photosensitivity in the infrared region has
The first charge generation layer 12 having a thickness of 0.4 μm, which is similar to the charge generation layer used for OPC having photosensitivity mainly in the visible region, is formed by a spray method. Further, on the surface of the charge generation layer 12, a transparent insulating layer having a thickness of 15.0 μm is formed.
The polycarbonate resin layer 13 is formed. The OPC 11 has a thickness of 0.4 μm for preventing regular reflection of a laser beam used for forming a latent image on the surface of the aluminum electrode 14 which is a conductive substrate.
a, a second charge generation layer 11b having a thickness of 0.3 μm, and a charge transport layer 11c having a thickness of 15.0 μm.

FIG. 3B shows the spectral sensitivity a when the photoreceptor 1 of this example is negatively charged (charge generation in the second charge generation layer 14b) and positively charged (charges in the first charge generation layer 12). 2 shows the spectral sensitivity b of (generation) and the spectral transmittance c of the first charge generation layer 12. As can be seen from the spectral transmittance c in the figure, it is 78 which is the wavelength of the laser for image exposure described later.
For 0 nm light, the first charge generation layer 12 has a light transmittance of 98% or more. On the other hand, although not shown, the spectral transmittances of the polycarbonate resin layer 13 and the charge transport layer 14c are shown in FIG.
It is 100% in the wavelength range handled in (b). Therefore, the 780 for image exposure applied to the photoconductor 1
98% or more of the laser light of nm passes through the polycarbonate resin layer 13, the first charge generation layer 12 and the charge transport layer 14c and reaches the second charge generation layer 14b. Further, as can be seen from the spectral sensitivity b in the case of positive charging in the figure, the case of positive charging has a strong sensitivity to yellow light and little sensitivity to light of 780 nm.

The color image forming method of this embodiment using the photoconductor 1 shown in FIG. 3 will be described below. Figure 1 (a)
2 (f) and 2 (g) to 2 (m) show the main steps of the color image forming method of this embodiment. The horizontally long strips shown at the top in FIGS. 1 and 2 indicate the document color to be reproduced on each portion of the photoconductor 1 in each of the drawings below. In this example, the black part of the original is replaced by black 1 and black 2.
The former is reproduced by superposing four kinds of toners of yellow, magenta, cyan, and black, and the latter is reproduced only by black toner. First, as the first step, while irradiating the photoconductor 1 with yellow light from, for example, an LED,
For example, the photoreceptor 1 is primarily charged to +800 V by a corona charger to which a voltage of +6 KV is applied (FIG. 1A). As a result, only the polycarbonate resin layer 13 is selectively +8.
It is charged to 00V. Next, as a second step, the photoreceptor 1 is secondarily charged to -800 V by a corona charger to which a voltage of -5.2 KV is applied in the dark (see FIG. 1).
(B)). As a result, all the external charges accumulated on the surface of the polycarbonate resin layer 13 due to the primary charging are neutralized, and only the photosensitive layer is selectively charged to −800 V by the internal charges and the charges induced thereby. Then the third
As a step, the yellow image information is placed on the N / P on the laser beam of 780 nm to perform image exposure (FIG. 1C). As a result, the image exposure part, which is the part irradiated with the laser beam,
It becomes 50V. Then, as a fourth step, for example, -7
Reversal development is performed in a non-contact manner using a negatively charged non-magnetic one-component yellow toner while applying a development bias of 00V (FIG. 1 (d)). As a result, the yellow toner adheres to the image exposure portion and a yellow toner image is formed.

Then, in a fifth step, the photosensitive member 1 on which the yellow toner image is still formed is again primary charged in the same manner as in the first step (not shown). As a result, the toner forming the polycarbonate resin layer 13 and the yellow toner image is charged to about + 800V. Then, as a sixth step, secondary charging is performed as in the second step (not shown). As a result, all the external charges accumulated on the surface of the polycarbonate resin layer 13 are neutralized by the primary charging in the fifth step, and only the photosensitive layer is selectively charged to about -800 V by the internal charges and the charges induced thereby. To be done. Here, the charge of the yellow toner, which has been positively charged by the primary charging in the fifth step, is also neutralized. Then, as a seventh step, image exposure is performed by placing magenta image information on the N / P with a laser beam of 780 nm (see FIG. 1).
(E)). As a result, the image exposed portion has a voltage of −50 V at a portion where the yellow toner does not adhere, and −60 V at a portion where the yellow toner adheres. The evaluation of the potential difference (10 V in this case) of the image exposure portion depending on the presence or absence of the yellow toner adhesion will be described in the description of the comparative example described later. Then, as an eighth step, in the same manner as the above-mentioned fourth step for the yellow image, reverse development is carried out in a non-contact manner by using a negatively charged non-magnetic one-component magenta toner while applying a developing bias of, for example, -700V (FIG. 1).
(F)). As a result, the magenta toner adheres to the image exposure portion to form a magenta toner image.

Next, as a ninth step, the photoreceptor 1 on which the yellow toner image and the magenta toner image are still formed.
Is again charged in the same manner as in the first step (FIG. 2 (g)). As a result, the toner forming the polycarbonate resin layer 13 and the yellow toner image and the magenta toner image is charged to about + 800V. Then, as a tenth step, secondary charging is performed as in the second step (FIG. 2 (h)). As a result, all the external charges accumulated on the surface of the polycarbonate resin layer 13 are neutralized by the primary charging in the eighth step, and only the photosensitive layer is selectively charged to about -800 V by the internal charges and the charges induced thereby. To be done. Here, the charges of the yellow toner and the magenta toner that have been positively charged by the primary charging in the eighth step are also neutralized. Then, as the 11th step, 780 nm
The cyan image information is placed on the N / P of the laser light of (1) and image exposure is performed (FIG. 2 (i)). As a result, the image exposure area is -50V at the place where the yellow toner is not attached, and the maximum is -75V at the place where the yellow toner and magenta toner are attached.
become. Then, as a twelfth step, for example, −700V, similarly to the above-mentioned fourth step for the yellow image.
While applying the developing bias of (1), non-contact reversal development is performed using negatively charged non-magnetic one-component cyan toner (FIG. 2 (j)). As a result, the cyan toner adheres to the image exposure portion and a cyan toner image is formed.

Next, in a thirteenth step, the photosensitive member 1 on which the yellow toner image, the magenta toner image and the cyan toner image are still formed is again primary charged in the same manner as in the first step (not shown). As a result, the toner forming the polycarbonate resin layer 13 and the yellow toner image, the magenta toner image, and the cyan toner image is charged to about + 800V. Then, as a fourteenth step, the above second
Secondary charging is performed as in the step (not shown). As a result, all the external charges accumulated on the surface of the polycarbonate resin layer 13 are neutralized by the primary charging in the 13th step, and only the photosensitive layer is selectively charged to about -800 V by the internal charges and the charges induced thereby. To be done. Where the first
The charges of the yellow toner, the magenta toner, and the cyan toner that have been positively charged by the three-step primary charging are also neutralized. Then, as a fifteenth step, image information is exposed by placing black 2 image information on the N / P on 780 nm laser light (FIG. 2 (k)). As a result, the image-exposed portion has a voltage of −50 V at a portion where no toner is attached, and a maximum of −80 V at a portion where yellow toner, magenta toner, and cyan toner are attached. Next, as a 16th step, in the same manner as the 4th step for the yellow image, while applying a developing bias of, for example, -700V, the reversal development is performed in a non-contact manner using the negatively charged non-magnetic one-component black toner (FIG.
(L)). As a result, the black toner adheres to the image exposure portion and a black two toner image is formed. Next, as a 17th step, the four-color toner images on the photoconductor 1 are collectively electrostatically transferred onto a transfer paper. Then, a four-color toner image is fixed on the transfer paper by a normal method (not shown) to form a full-color copy, the residual toner on the photoconductor 1 is cleaned, and the residual charge is removed to prepare for the next image formation. ..

The above-described full-color image forming method was carried out in the full-color image forming apparatus shown in FIG. 4 by performing image exposure with 8-value pulse width modulation for one pixel. It was possible to obtain a full-color image excellent in 1-dot reproducibility. In FIG. 4, the photoconductor 1 is formed in a drum shape, and an image is formed while being rotationally driven in the counterclockwise direction of the arrow. Around this photoreceptor 1, a corona charger 2 with a yellow light emitting LED for primary charging, a corona charger 3 for secondary charging, a yellow developing device 4a using a non-magnetic one-component yellow toner, a non-magnetic one. Cyan developing device 4b using component cyan toner, magenta developing device 4c using non-magnetic one-component magenta toner, black developing device 4d using black toner, transfer charger 5 for batch transfer, and photoreceptor after batch transfer A corona charger 6 for removing residual charge and a cleaning device 7 for removing residual toner on the photosensitive member after batch transfer are provided. The image exposure position of the image exposure device including the laser light source 8a, the polygon mirror 8b, and the reflection mirror 8c is set between the corona charger 3 and the developing device 4a.

For comparison, unlike the photoconductor 1 described above,
A normal OPC photosensitive member not having the polycarbonate resin layer 13 which is a transparent insulating layer was used, and instead of the above-mentioned primary charging and secondary charging, charging was performed at -800 V in the dark. When a full-color image is formed by using the above-mentioned method, the potential of the portion of the image-exposed portion of the magenta image which is the second color, to which the first-color yellow toner is not adhered, is −50 V, as in the above embodiment. On the other hand, the potential of the part to which the yellow toner adheres is -1.
It reached 50V, which was significantly higher than the potential of the yellow toner adhesion portion of the above-mentioned example being −60V. For this reason, in the image-exposed portion, the yellow toner-attached portion lacks the magenta one-dot image, or has a lower density than the portion to which the yellow toner is not attached. Similarly, with respect to the image exposed portions of the third color cyan image and the black two images, the one-dot reproducibility is poor in the toner-attached portion due to the preceding development, and as a result, only the full-color image in which the color reproducibility of the highlight portion is poor is obtained. I couldn't do it.

In the above-mentioned embodiment, the photoconductor 1 having the photosensitive layer sensitive to both positive and negative polarities is used, but instead of this, the photosensitive layer having the rectifying property with the conductive substrate is provided. It is also possible to use a photosensitive member. For example, a Se—Te alloy (Te 15 wt%) is vacuum-deposited on an aluminum electrode at a base temperature of 80 ° C. to a thickness of 60 μm to form a photosensitive layer having a rectifying property with a conductive substrate (aluminum electrode). A photoreceptor having a transparent insulating layer formed thereon by spray coating a polycarbonate resin with a thickness of 15 μm can be used. Using such a photoconductor as a photoconductor, primary charging is performed in the dark at −6.0 KV, secondary charging is performed at +5.2 KV, and image exposure is performed with a laser beam of 680 nm. When a full-color image was formed in the same manner as in the above example, a good full-color image was similarly obtained.

Next, another embodiment of the present invention will be described. As the photoconductor of this embodiment, a photoconductor 1 having a sensitivity in both positive and negative polarities is formed by the same basic structure as in the above-mentioned embodiment.
Can be used. Here, a photoconductor having the same basic structure as the photoconductor 1 of the above-mentioned embodiment but different in the thickness of each layer was used. Specifically, the above polycarbonate resin layer 1
3 has a thickness of 12.0 μm, the first charge generation layer 12 has a thickness of 0.2 μm, and the charge transport layer 14c has a thickness of 24.0 μm.
A photosensitive member was used in which the thickness of the second charge generation layer 14b was 0.3 μm and the thickness of the regular reflection preventing layer 14a was 0.4 μm.

Similar to the photoconductor of the above embodiment, this photoconductor 1 has a spectral sensitivity a when positively charged (charge is generated in the second charge generation layer 14b) and a positive charge as shown in FIG. 3B. In case of (the charge is generated in the first charge generation layer 12), the spectral sensitivity b,
And the spectral transmittance c of the first charge generation layer 12. Similarly, the spectral transmittances of the polycarbonate resin layer 13 and the charge transport layer 14c are 100% in the wavelength range handled in FIG. 3 (b).

The color image forming method of this embodiment using the photoconductor 1 will be described below. Also in the color image forming method of the present embodiment, similar to the color image forming method of the above embodiment, the photosensitive body is uniformly charged with light having sensitivity, and the photoreceptor is subjected to primary charging, and the primary charging in the dark is transparent. A cycle including secondary charging for removing external charges on the insulating layer (polycarbonate resin layer 13), formation of a latent image by image exposure, and development of the latent image with toner of a predetermined color is repeated a plurality of times to perform the exposure to light. After a plurality of toner images of different colors are superposed on the body, they are collectively transferred to a transfer paper. The point that the full-color image forming method of this embodiment is different from the full-color image forming method of the above-described embodiment is that in this embodiment, the above-mentioned primary charging satisfies the formula (2) described in the above-mentioned "Function". And the secondary charge is neutralized by partially neutralizing the external charge so that the potential of the photoreceptor is almost zero.
This is a point to be set to V.

Here, the primary charging which satisfies the above formula (2) when the above-mentioned photoreceptor is used will be described in detail. The measured relative permittivity of the photosensitive layer of the above-mentioned photosensitive member was 2.69. Since this thickness is about 24 μm as described above, its dielectric constant a is about 1.0 (μF / m ² ). Therefore, assuming that the target voltage of the image exposure unit is, for example, +800 V, the above equation (2) is expressed as Vs = 800 (1 + 1 / b). Line i in FIG. 6 (a) indicates a primary charging transparent insulating layer (polycarbonate resin layer 1) that satisfies this equation.
3) shows the surface potential characteristic of the photoconductor with respect to the combined capacity of 3) and the toner layer. Line j and line k in FIG.
For comparison, the same potential characteristics when performing primary charging with an ideal scorotron that can charge the surface of the photoconductor to a constant potential irrespective of the partial change of electrostatic capacity, The same potential characteristics in the case of an ideal corotron that can be charged to a constant charge density without depending on a partial change in the capacitance are shown. Also, FIG. 6 (b)
Unlike FIG. 6A, the horizontal axis represents the dielectric thickness d (μm) instead of the composite capacitance b. Here, in the above photoconductor, the polycarbonate resin layer and the photoconductive layer have substantially the same relative dielectric constant, and in this embodiment, a non-magnetic toner is used,
The relative dielectric constant of the toner layer is almost equal to that of the photosensitive layer. Therefore,
FIG. 6B shows the surface potential characteristics of the photosensitive member with respect to the total thickness of the transparent insulating layer (polycarbonate resin layer 13) and the toner layer which are primary charged. As can be seen from FIG. 6 (a) or (b), the primary charging satisfying the above formula is slightly closer to the scorotron than the ideal intermediate between the scorotron and the corotron. Since the thickness of the transparent insulating layer (polycarbonate resin layer 13) in this example is 12 μm and the maximum thickness of the toner layer is about 20 μm, for example, the abscissa of FIG. 1 in total thickness
If the above equation is satisfied in the range of 2 μm to 36 μm,
It is sufficient for practical use.

In order to perform the primary charging satisfying the above expression (2), a shield corotron as shown in FIG. 7A can be used as a charger for the primary charging. In this shield corotron, the tip 2a of the grounded casing is bent inward by 2 to 3 mm. Depending on the voltage applied to the discharge wire and the relative movement speed of the surface of the photoconductor, the layout of the casing tip portion 2a can create various charge states intermediate between the corotron and the scorotron.

The color image forming method of this embodiment will be specifically described below with reference to FIGS. 7 (a) to 7 (f).
7A to 7C show a part of the basic steps of forming the toner image of the first color, and FIGS. 7D to 7F show the basic steps of forming the toner image of the second color. It shows a part of the process. As described above, the total number of basic steps in the color image forming method of the present embodiment is the same as that in the color image forming method of the above embodiment, and the step numbers in the following description are the same as those in the above embodiment. It corresponds to the one. First, as the first step, while irradiating the photoconductor 1 with yellow light from, for example, an LED,
Photoconductor 1 + with a corona charger to which a voltage of 6 KV is applied
Primary charging is performed at 1200V (FIG. 7A). As a result, only the polycarbonate resin layer 13 is selectively +1200.
It is charged to V. Here, even though the voltage applied to the corona charger is the same value as that in the above-described embodiment, the charging potential of the photoconductor 1 is different because the thickness of each layer constituting the photoconductor is different as described above. This is because the electrostatic capacity is different. Then, as a second step, in the dark, for example, -4.7.
The photoreceptor 1 is secondarily charged to approximately 0 V by the corona charger to which a voltage of KV is applied (FIG. 7B). As a result, a part of the external charges accumulated on the surface of the polycarbonate resin layer 13 due to the primary charging is neutralized, the charging of the polycarbonate resin layer 13 due to the external charges and a part of the internal charges becomes + 800V, and The photosensitive layer is charged to -800 V by the remaining internal charges and the charges induced thereby.
Then, as a third step, the yellow image information is placed on the N / P on the laser beam of 780 nm to perform image exposure (see FIG. 7).
(C)). As a result, the potential of the image exposure part, which is the part irradiated with the laser beam, becomes a little less than + 800V. Next, as a fourth step, while applying a developing bias of, for example, +50 V, non-contact regular developing is performed using a negatively charged non-magnetic one-component yellow toner. As a result, the yellow toner adheres to the image exposure portion to form a yellow toner image.

Then, in the fifth step, the photosensitive member 1 on which the yellow toner image is still formed is again primary charged in the same manner as in the first step (FIG. 7 (d)). As a result, the polycarbonate resin layer 13 and the toner forming the yellow toner image are charged, and the potential of the photoconductor becomes + 1200V to + 1400V depending on the toner adhesion amount. Next, as a sixth step, secondary charging is performed as in the second step (FIG. 7E). As a result, a part of the external charges accumulated on the surface of the polycarbonate resin layer 13 by the fifth step of the primary charging is neutralized, and the charging of the polycarbonate resin layer 13 due to the external charges and a part of the internal charges becomes + 800V. In addition, the photosensitive layer is charged to about -800V by the residual internal charges and the charges induced by the internal charges, and the surface potential of the photosensitive member becomes approximately 0V. Where the fifth
The charge of the yellow toner, which has been positively charged by the primary charging in the step, is also partially neutralized. Then, as a seventh step, the magenta image information is N / Ped to the laser beam of 780 nm.
And imagewise exposed (FIG. 7 (f)). As a result, the image exposure area becomes a little less than + 800V both at a portion where the yellow toner does not adhere and at a portion where the yellow toner adheres. The point that the potentials of the image exposure portions become equal regardless of whether or not the yellow toner adheres will be described in detail later. Then, as an eighth step, the fourth step for the yellow image is performed.
Similar to the step, while applying a developing bias of, for example, +50 V, normal development is performed in a non-contact manner using a negatively charged non-magnetic one-component magenta toner. As a result, the magenta toner adheres to the image exposure portion to form a magenta toner image.

Then, as a ninth step, the photosensitive member 1 on which the yellow toner image and the magenta toner image are still formed.
Is again subjected to primary charging in the same manner as in the first step. As a result, the polycarbonate resin layer 13 and the toner forming the yellow toner image and the magenta toner image are charged,
The potential of the photoconductor is + 1200V to + 1600V depending on the toner adhesion amount. Then, as a tenth step, secondary charging is performed as in the second step. As a result, the polycarbonate resin layer 1 is subjected to the primary charging in the fifth step.
Part of the external charge accumulated on the surface of 3 is neutralized,
The external charge and a part of the internal charge cause the electrostatic charge of the polycarbonate resin layer 13 to become +800 V, and the residual internal charge and the charges induced therein cause the photosensitive layer to move to about −8 V.
The surface potential of the photoconductor becomes almost 0V by being charged to 00V. Here, the charges of the yellow toner and the magenta toner, which have been positively charged in the primary charging in the fifth step, are also partially neutralized. Next, as an 11th step, cyan image information is placed on the N / P with a laser beam of 780 nm to perform image exposure. As a result, the image exposure area becomes a little less than + 800V both in the places where the yellow toner and the like are not attached and in the places where the yellow toner and the like are attached. Next, as a twelfth step, in the same manner as the above-mentioned fourth step for the yellow image, for example, while applying a developing bias of +50 V, non-contact regular development is performed using a negatively charged non-magnetic one-component cyan toner. As a result, the cyan toner adheres to the image exposure portion and a cyan toner image is formed.

Then, in a thirteenth step, the photosensitive member 1 on which the yellow toner image, the magenta toner image and the cyan toner image are still formed is primary charged again in the same manner as in the first step. As a result, the polycarbonate resin layer 1
3 and the toner forming the yellow toner image and the like are charged, and the potential of the photoconductor is +1200 V according to the toner adhesion amount.
To + 1800V. Next, as a fourteenth step, secondary charging is performed (not shown) as in the above second step. As a result, almost half of the external charges accumulated on the surface of the polycarbonate resin layer 13 are neutralized by the primary charging in the 13th step, and the charging of the polycarbonate resin layer 13 by the external charges and a part of the internal charges is +80.
The voltage becomes 0 V, and the photosensitive layer is charged to approximately -800 V by the residual internal charges and the charges induced by the internal charges, and the surface potential of the photoconductor becomes approximately 0 V. Here, the charges of the yellow toner, the magenta toner, and the cyan toner, which have been positively charged in the primary charging in the 13th step, are almost half neutralized. Next, as a fifteenth step, black image information is placed on the N / P on the laser beam of 780 nm to perform image exposure. As a result, the image exposure portion, which is the portion irradiated with the laser light, becomes a little less than +800 V both in the portion where the toner is not attached and the portion where the yellow toner is attached. Next, as a 16th step, in the same manner as the above-mentioned 4th step regarding the yellow image, while applying a developing bias of, for example, +50 V, normal development is performed in a non-contact manner using a negatively charged non-magnetic one-component black toner. As a result, black toner adheres to the image exposure portion and a black toner image is formed.

Next, as a 17th step, the four-color toner images on the photoconductor 1 are collectively and electrostatically transferred onto a transfer paper.
Then, a four-color toner image is fixed on the transfer paper by a normal method (not shown) to form a full-color copy, the residual toner on the photoconductor 1 is cleaned, and the residual charge is removed to prepare for the next image formation. ..

According to the above full-color image forming method, the image exposure is carried out in the full-color image forming apparatus shown in FIG. 4 using the shield corotron with the yellow light emitting LED as the corona charger 2 with the yellow light emitting LED for the primary charging.
As a result of performing the power modulation with DPI and 128 gradations, it was possible to obtain a full-color image with 200 gradations of 256 gradations, particularly excellent in reproducibility of the highlight part. Also, for each gradation, there is a very good match between the part where toner is attached due to development, which is preceded by the potential of the image exposure part, and the part where such toner is not attached at all, and the color reproduction is excellent. I was able to get the image.

For comparison, a scorotron was used instead of the shield corotron as the corona charger 2 for the primary charging, and a full-color image was formed in the same manner as in this example except for the second color. In the image-exposed portion by the subsequent image exposure, the potential of the portion to which the toner due to the preceding development is attached is lower than the potential of the portion to which the toner is not attached, and accurate color reproduction cannot be performed. This is because, as shown in (d) in the process charts of FIGS. 8A to 8F corresponding to FIGS. 7A to 7F according to this embodiment, When comparing the toner-attached portion in which the dielectric thickness of the toner layer due to the development of the color is 12 μm, which is the same as the dielectric thickness of the transparent insulating layer (polycarbonate resin layer 13), and the portion in which the toner is not adhered, the scorotron of the second color is compared. Since the photoconductor 1 is uniformly charged to +1200 V by the primary charging by the toner, the charge density of the toner adhering portion is about half that of the portion without toner adhering. This is because the density is greatly reduced. For example, in this case, as shown in FIG. 8F, the charge amount of the photosensitive layer due to the secondary charging is + 800V in the portion where the toner is not attached, whereas it is + 600V in the toner attached portion. And
As shown in FIG. 8 (f), the potential after image exposure is +800 V in the portion where the toner is not attached, whereas it is +600 V in the portion where the toner is attached. As described above, since the potential of the toner adhesion portion after image exposure is low, the toner density is lowered. For example, in the portion where the toner layers of the three colors are overlapped, even if the power of the laser light is maximized, only an exposed portion potential of +500 V or more is obtained, and the developed toner image density is also
It was only about half of the area without toner adhesion due to the preceding development.

For comparison, a corotron was used as the corona charger 2 for primary charging instead of the shield corotron, and a full-color image was formed in the same manner as in this example, except that the corotron was used. The potential of the portion of the image-exposed portion formed by the image exposure of the second and subsequent colors where toner is attached due to the preceding development increases in proportion to the toner attachment amount and reaches up to +3000 V, and the toner is attached. It was higher than the electric potential of the unmarked part, and accurate color reproduction was not possible. This is shown in FIG. 9A corresponding to FIGS. 7A to 7F according to the present embodiment in the comparative example.
As shown in (d) in the process drawings of (f) to (f), the dielectric thickness of the toner layer by the development of the first color is, for example, 12 μm which is the same as the dielectric thickness of the transparent insulating layer (polycarbonate resin layer 13).
When comparing the toner adhering portion which is the same with the toner adhering portion, the electric potential of the toner adhering portion is determined because the photoreceptor 1 is charged to a uniform charge density by the primary charging by the second color corotron. This is because the charge potential of the toner-attached portion due to the primary charging is significantly increased, such as + 2400V, while the potential of the portion to which toner is not attached is + 1200V. For example, in this case, as shown in FIG. 9E, the charge amount of the photosensitive layer due to the secondary charging is + 800V in the portion where the toner is not attached, whereas it is + 1200V in the toner attached portion. Then, FIG. 9 (f)
As shown in FIG. 7, the potential after image exposure is +800 V in the portion where the toner is not attached, whereas it is +1200 V in the toner attached portion. As described above, since the potential of the toner adhesion portion after the image exposure is high, the toner density is increased. For example, the potential at the maximum of about 600 V is higher in the portion where the toner layers of the three colors overlap, compared to the portion where there is no toner adhesion, and the developed toner image density is about 1. It became five times.

In the above embodiment, the photoconductor 1 having the photosensitive layer having sensitivity to both positive and negative polarities was used, but instead, the photosensitive layer having a rectifying property with the conductive substrate is provided. It is also possible to use a photosensitive member. For example, a Se—Te alloy (Te 15 wt%) is vacuum-deposited on an aluminum electrode at a base temperature of 80 ° C. to a thickness of 55 μm to form a photosensitive layer having a rectifying property with a conductive substrate (aluminum electrode), A photoreceptor having a transparent insulating layer formed thereon by spray coating a polycarbonate resin to a thickness of 12 μm can be used. Using such a photoconductor as the photoconductor, the primary charging is performed in the dark at −6.0 KV, the secondary charging is performed at +4.7 KV, and the image exposure is performed with a laser beam of 680 nm. When a full-color image was formed in the same manner as in the above example, a good full-color image was similarly obtained.

Although polycarbonate is used as the material of the transparent insulating layer 12 in each of the above embodiments, polystyrene, phenol resin, polyamide resin, or the like may be used instead.

[0036]

According to the first aspect of the present invention, in forming the toner images of the second and subsequent colors, the toner adhered on the photosensitive member in the preceding development by the primary charging and the predetermined charge removal in the dark. Almost all external charges on the transparent insulating layer including the electric charges are erased uniformly, and the latent image due to the subsequent image exposure is formed by the internal charges on the interface. Therefore, it is possible to obtain a substantially uniform potential contrast of the latent image. Therefore, there is an excellent effect that it is possible to prevent the variation in the potential contrast due to the charge of the toner attached to the photoconductor in the preceding development in the toner image formation for the second and subsequent colors.

According to the color image forming method of claim 2,
When the toner images of the second and subsequent colors are formed, the primary charging is performed so as to satisfy the predetermined relationship, so that the potential of the exposed portion due to the subsequent image exposure causes the toner adhered on the photoconductor in the preceding development. Since it does not differ with or without,
It is possible to obtain an accurate image exposure portion potential according to the exposure amount. On the other hand, by partially eliminating the external charges on the transparent insulating layer in the dark after the primary charging, the potential on the photoconductor, which appears by combining the charging of the transparent insulating layer and the charging of the photosensitive layer, becomes approximately 0 volt. As a result, the potential of the non-image-exposed portion that was not irradiated with light by image-exposure does not differ depending on the presence or absence of toner adhering to the photoconductor in the preceding development.
It is possible to obtain an accurate image exposure portion potential according to the exposure amount. Therefore, there is an excellent effect that a color image excellent in gradation and color reproducibility can be formed.

According to the color image forming method of claim 3,
The same effect as the color image forming method according to claim 1 or 2 can be obtained.

[Brief description of drawings]

1A to 1F are process diagrams showing a part of the process of a color image forming method according to an embodiment.

2 (g) to (m) are process diagrams showing the remaining steps of the same color image forming method.

FIG. 3A is a schematic configuration diagram of a photoconductor according to an embodiment,
(B) is a characteristic view of the same photoconductor.

FIG. 4 is a schematic configuration diagram of an example of an image forming apparatus that performs the same color image forming method.

FIG. 5 is an explanatory diagram for explaining the principle of a color image forming method according to another embodiment of the present invention.

6A and 6B are characteristic diagrams showing the characteristics of primary charging in the same color image forming method.

7A to 7F are process diagrams showing a part of the process of the same color image forming method.

8A to 8F are process diagrams showing a part of the process of a color image forming method according to a comparative example.

9A to 9F are process diagrams showing a part of the process of a color image forming method according to another comparative example.

[Explanation of symbols]

1 photoconductor, 2 corona charger for primary charging 3 corona charger for secondary charging, 4a, b,
c, d developing device 5 transfer charging device, 6 static elimination charging device 7 cleaning device, 11 O
PC 11a Antireflection layer, 11b Second charge generation layer 11c Charge transport layer, 12 First charge generation layer 13 Polycarbonate resin layer

Claims (3)

[Claims] 1. A photosensitive member having a transparent insulating layer on a photosensitive layer having both positive and negative polarities, and the photosensitive layer is uniformly irradiated with light having sensitivity. By repeating a cycle including removing all external charges on the transparent insulating layer by the primary charging, forming a latent image by image exposure, and developing the latent image with a toner of a predetermined color, A method for forming a color image, characterized in that a plurality of toner images of different colors are superposed on a photoconductor. 2. A photosensitive body having a transparent insulating layer on a photosensitive layer having both positive and negative polarities, and the photosensitive layer is uniformly irradiated with light having a sensitivity. Of the external charge accumulated on the transparent insulating layer by the primary charging so that the potential on the photoconductor becomes almost 0 volt, a latent image is formed by image exposure, and the latent image is formed by toner of a predetermined color. In a color image forming method in which a plurality of toner images having different colors are superposed on the photoconductor by repeating a cycle including image development a plurality of times, the primary charging is performed so as to satisfy the following expression. And a color image forming method. Formula Vs = K · (1 + a / b) where Vs is a charging potential (volt) of the photoconductor by the primary charging, K is a target potential (volt) of the photoconductor portion irradiated with light by the image exposure, and a Is the capacitance of the photosensitive layer (μ
F / m ² ), b is the combined electrostatic capacity (μF / m) of the transparent insulating layer and the toner layer present on the photoconductor layer during the primary charging.
² ) 3. A photosensitive member having a transparent insulating layer on a photosensitive layer having a rectifying property with a conductive substrate is used instead of the photosensitive member, and the photosensitive member having a predetermined polarity is used instead of the primary charging. The color image forming method according to claim 1, wherein the primary charging of the body is performed.