JPS60247650A - Electrophotographic process - Google Patents

Abstract

PURPOSE:To enable good images to be obtained from different latent images by applying uniform electrostatic charging to the whole surface of a photosensitive drum after developing the first latent image, maintaining the potential difference between the exposed parts of the second latent image and the first developed part and lowering the DC current component of the second developing bias than the surface potential of the first developed part. CONSTITUTION:In the step ( I ), a photosensitive body A prepared by forming an Se photoconductive layer a1 on an electrically conductive layer a2 is electrostatically charged with a corona discharger C1; in the step (II), the first exposure L1 to optical image information in the form of format or the like is executed to form the first electrostatic latent image, and, at that time, the surface potential is decayed; in the step (III), bias voltage is impressed to the magnetic sleeve of the first developing device having a binary developer composed of, e.g., a positive red toner T(R) and an iron powder to reversely developing the exposed part; in the step (IV), the surface of the photosensitive body A is corona discharged opposite in polarity to the primary charging with a charger C2; in the step (V), the second scanning exposure L2 is executed to form the second latent image; and in the step (VI), e.g., a black magnetic positive insulating TB is spread on the developing sleeve to carry out jumping development and reversely develop the second latent image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming method, and more particularly to an image forming method for obtaining images based on different latent images.

Conventionally, two different types of latent images (
For example, various methods have been proposed in which an image is obtained by forming a combination of a format frame, text information, black text information, red mark, seal impression, etc.) and developing these with developers of the same or different colors. There is.

However, there are disadvantages in that color mixing occurs between different images, and furthermore, the previously formed developed image is disturbed by subsequent development.

FIG. 1 explains an example of a conventional image forming process. (I) to (V) indicate each step, and in each step, the charge state of the photoreceptor is shown on the upper side, and the photoreceptor at that time is shown on the lower side. Each surface potential is schematically shown.

In step (I) in FIG. 1, a photoconductive layer a of Se etc.
A photoreceptor A having a conductive layer A2 provided with a conductive layer A2 is charged with a corona charger C to, for example, ÷800V, and then in a step (■), a first exposure Ll is performed using optical information such as a format, and the surface of the exposed area is The potential is attenuated to, for example, +50V to form an image-shaped first electrostatic latent image on the surface of the photoreceptor.

Next, in step (III), a bias voltage (for example, +400 V: shown by a broken line) is applied to the magnetic sleeve of the first developing device, which has a two-component developer consisting of, for example, positive polarity red toner T (R) and iron powder carrier. is applied to reversely develop the exposed area.

After the first development, in the (■) step, the photoreceptor A is exposed to a second light of image information such as characters (2), and the potential of the exposed area is attenuated to, for example, +50V to form a second electrostatic latent image. . Next, in step (V), for example, black toner T (B) of positive polarity is used.
) and an iron powder carrier, a bias voltage (e.g. +
400V (indicated by a broken line) is applied to reversely develop the second exposed area.

In the above process, red toner T (
Color mixing of black toner particles (, B) was likely to occur in the areas developed with R).

For example, the unexposed area is ÷eoov! Light part +50
When V, after the first development, the potential of the exposed area increases due to the toner charge and becomes around +150V. Next, after the formation of the second latent image, when a developing bias of +400V is applied to perform second development, the second exposed area is sufficiently developed, but at the same time, the first
This is because a considerable amount of black toner is also developed in the N light area.

During this second development, if the developing bias voltage is set low enough (for example, +150V) so that the first exposed area is not developed, the development of the second exposed area becomes insufficient and carrier adhesion occurs in the unexposed area.

Furthermore, the problem with the process shown in FIG.
This is the point where it is scraped off. This is because in the second development,
The main cause is that the magnetic brush formed by the two-component developer mechanically rubs the red toner developing area, but it is also caused by the electrostatic action of the positively polarized red toner on the negatively charged carrier in the developer. Being adsorbed also has an effect.

As a countermeasure to this problem, it has been proposed to make the developing bias voltage higher during the f@2 development than during the first development, but this is inappropriate because it causes the above-mentioned disadvantages.

The present invention is characterized by solving the above-mentioned problems and providing an electrophotographic method that satisfactorily obtains images based on different latent images.
After developing the latent image, the entire drum surface is uniformly charged, the potential difference between the exposed area of the second latent image and the first developing area (toner image area) is kept large, and the second developing area is It is characterized by a configuration in which an image without fogging or color mixture can be obtained by setting the DC voltage component of the bias lower than the surface potential of the first developing section. Further, it is characterized in that at least the second and subsequent development is performed by a non-contact development method.

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

FIG. 2 explains one embodiment of the process steps based on the present invention, and CI) to (IV) are each step process, and in each process, the upper side shows the charge state of the photoreceptor, and the lower side shows the photoreceptor charge state. FIG. 2 is a schematic diagram showing the surface potential of the body.

In step (I), the photoreceptor A having the Se photoconductive layer a1 provided on the conductive layer a2 is charged to about +6 oov with a corona charger C1.

In step (II), first exposure L1 is performed based on image information such as format and other optical information to form a first electrostatic latent image. At this time, the surface potential is attenuated to about +50V in the bright exposed area, for example.

Next, in step (m), a bias voltage (for example, +40QV: shown by the broken line) is applied to the magnetic sleeve of the first developing device, which has a two-component developer consisting of, for example, positive polarity red toner T (R) and iron powder carrier. is applied to reversely develop the exposed area.

In step (IV), the surface of the photoreceptor is charged with a charger c2.
A large number of grid wires are stretched parallel to the corona discharge wires at intervals of about 1 mm in the opening of the shield of this charger C2, which performs corona discharge with the same polarity as the next charging.

A bias voltage of V is applied. Further, the distance between the grid wire and the surface of the photoreceptor is approximately 1 s+m.

Due to this charging, the surface potential of the portion to which the red toner TR is applied becomes lower than the drum surface potential to which the red toner TR is not applied.

This is because even though the capacitance of the toner applying section has increased, a sufficient amount of charge is not irradiated. In order to almost eliminate the potential difference between the toner-applied area and the toner-free area, a high-performance charger is required, which increases the cost. The difference in potential mentioned above depends on the thickness of the toner layer, the material of the toner, the backing state of the toner, the tripo value, etc., and is also related to the charging time constant related to the performance of the charger, but ultimately it depends on the charging ability. This is because a charger that is highly effective and takes up a lot of space inside the machine is required.

Next, in step (V), a second scanning exposure L2 is performed to form a second latent image, and in step (VI), for example, a black magnetic insulating toner Ts having a positive polarity is coated on the developing sleeve. Then, jumping development is performed, the second latent image is reversely developed, and black toner TB is applied to the scanning exposure L2 portion. During this second development, a DC bias voltage is superimposed on an alternating voltage and applied to the developing sleeve to perform reversal development. Surface potential after the process (
V+) and higher than the surface potential (v2) of the drum exposed in the (VT) step. That is, the relationship is set such that v2×VB<Vl.

When a bias is applied to the developing sleeve within this value range, the potential of the red toner developing section becomes a bias that repels the black toner TB, thereby preventing color mixing of black toner with a portion of the red toner. At this time, the bias value of the DC component of the developing bias is set to a value within the range of v2 and vl.

Regarding the alternating voltage, during the second development, if a high frequency as high as possible is applied and the toner in the developing section is clouded and development is performed, γ increases during the second development and an image with high contrast can be obtained.

In this case, if the potential difference between the sleeve potential and the drum surface potential is small, toner is not attached to the drum surface; conversely, the difference between the sleeve potential and the drum surface potential is If the threshold value is greater than a certain threshold value, then complete toning occurs.

FIG. 3 is an explanatory diagram of a specific example of an image forming apparatus that implements the method of the present invention. In FIG. 3, the surface of the Se photosensitive drum 1 is charged to about +600■ by the primary charger 3 (I
process). Next, the photosensitive drum 1 is subjected to first scanning exposure with a laser beam based on the format information. This scanning exposure L1 is performed by a laser light source, a light modulator, a rotating mirror, and an imaging lens (not shown) in response to an electric signal (step (2)).

The first electrostatic latent image thus obtained is reversely developed by the first developing device 4 containing a red non-magnetic one-component insulating toner T1 having a positive polarity (step (2)). The distance between the developing sleeve 41 of the first developing device 4 and the photosensitive drum l is 30 mm.
G#Lm, and a bias voltage is applied to the sleeve 41 at voltage #i42. This bias voltage is an alternating voltage, with a frequency of 1,500 Hz and 1,50 Hz.
0HzVP=p(53OVr, m, s), +500■ is superimposed as a DC component.

Next, corona discharge is performed on the surface of the photosensitive drum 1 by the secondary charger 6 (step (2)). The corona discharge wire of the secondary charger 6 has +13. A bias voltage of +600 cm is applied to the OKV and the grid wire at the shield opening of the secondary charger. Due to this secondary charging, both the developed area with the red toner T1 and the unexposed area are charged to about +6 OOV.

Next, the surface of the photosensitive drum 1 is subjected to scanning exposure 2 corresponding to an electric signal using a laser oscillator (not shown) to form a second latent image based on the black print information (Step V).

Next, this second latent image is subjected to jumping development and reversal development using the second developing device 7 containing a monocomponent magnetic toner T2 having a black magnetic positive polarity (step (2)). Second
The distance between the developing sleeve 71 of the developing device 7 and the photosensitive drum 1 is approximately 3004 m, and a bias voltage under the same conditions as the first development is applied to the sleeve 7□ by the power source 72.

Due to the action of the alternating electric field during the second development, the black toner moves back and forth between the sleeve and the drum, and the bright area potential is sufficiently developed in accordance with the scanning exposure L2. On the other hand, unnecessary black toner does not adhere to the red toner image area, and the red toner is not scraped off by the black toner. Scanning exposure 2
Of course, the black toner will not adhere to the areas that were not exposed to the black toner.

Note that when charging is not performed by the secondary charger 6, the surface potential of the photosensitive drum in the unexposed area at the second development position decreases to approximately ÷550 V due to dark decay, and the DC bias voltage for the second development is fogged. To prevent this, it has to be lowered, and as a result, the contrast of the black toner image is slightly lowered. On the other hand, when the secondary charging of the present invention is performed, the drum surface potential during the second development is approximately +580 V and a portion of the red toner is 530 V.
The latent image contrast (potential difference between the exposed area and the unexposed area) due to the scanning exposure L2 is the same as that of the scanning exposure L2 during the first development.
The latent image contrast is the same as that of , and a black image with high contrast can be obtained.

At this time, the DC component applied to the developing sleeve is set to a value of approximately +480 V, which is lower than the area to which the red toner is attached. For this reason, in the second development, the black toner is not developed on a part of the red toner, but is developed on the part exposed by the second scanning exposure 2. At this time, the AC component is 1700H2~2000H2・1500VP-
P (530 Vr, m, s) is applied to improve the contrast.

Next, a secondary charger 8 charges the surface of the photosensitive drum 1 to +8. OK
Perform a corona discharge of V. A bias voltage of +600 cm is applied to the grid wire at the shield opening of the tertiary charger 8. As a result of this secondary charging, the area developed by the black toner T2 is charged to +600V, and the unexposed areas are both charged to approximately 550V.

Next, a third scanning exposure corresponding to the electrical signal is performed on the surface of the photosensitive drum 1 using a laser oscillator (not shown) or the like to form a third latent image based on, for example, blue print information.

Next, this third latent image is reversely developed using a jumping development method using a third developer having a blue non-magnetic insulating component toner T3 having a positive polarity.

The distance between the developing sleeve 9I of the third developing device 9 and the photosensitive drum 1 is approximately 3001 Lm. A bias voltage under the same conditions as for the first development and the second development is applied by the power supply 92.

Through this third development, a blue toner image with high contrast is obtained in the portion corresponding to the scanning exposure L3. On the other hand, unnecessary blue toner does not adhere to the red toner image area and the black toner image area, and the red toner and black toner are not scraped off by the blue toner.
Blue toner does not adhere to areas that were not exposed.

Note that when secondary charging and tertiary charging are not performed, the surface potential of the photosensitive drum in the unexposed area at the third development position decreases to approximately +520 V due to dark decay, and the contrast of the blue toner image obtained by the third development decreases. .

On the other hand, when the secondary charging and tertiary charging of the present invention are performed, the drum surface potential during the third development is approximately +580V, and the drum surface potential during the third development is approximately +580V.
The latent image contrast is the same as that obtained by the scanning exposure L1 and the second scanning exposure L2, and a blue image with high contrast is obtained.

When the third development is completed, the three-color toner image of red, black, and blue on the photosensitive drum l is transferred to the transfer material l by the transfer charger lO.
are simultaneously transferred to the top.

After the transfer, the surface of the photosensitive drum is neutralized by an AC static eliminator 2, and then the untransferred toner is cleaned by a blade cleaner 12. On the other hand, the toner on the transfer material 11 is fixed by a fixing device (not shown).

In the above-mentioned secondary charging and tertiary charging, if a control grid is provided at the opening of the shield of the chargers 6 and 8 and charging is not performed by applying a predetermined bias voltage, accurate control of the drum surface potential may be difficult. However, the stability of each color image cannot be obtained, and the effect of suppressing the charging of the unexposed area and selectively and rapidly charging the developing area cannot be obtained, and color mixing or fogging is likely to occur.

In addition, in the above-mentioned second charging and third charging, if the bias voltage applied to the grid of the charger opening is gradually increased toward the dark area potential side, the latent image contrast due to scanning exposure and L2eL3 is gradually increased. , the effects of the present invention can be further enhanced, and a three-color image with high contrast without color mixture and image blur can be obtained.

For example, by setting the grid bias voltage in the second charging number and the third charging to +640v and +700v, respectively, it is possible to control the surface potential of the developed area and the unexposed area at each charging time to approximately the bias voltage. . Therefore, the latent image contrast in the second developing section and the third N light section is 580V-8OOV, respectively, and the latent image contrast in the first developing section is 580V-8OOV.
30■ can be increased in stages.

Although red, black, and blue are exemplified as the developer color combinations described above, other colors can be selected and combined as desired. Further, in the present invention, as is clear from the above embodiments, it is sufficient that the optical information can remove the potential on the photoreceptor, so as a means for imparting optical information to the photoreceptor, modulated In addition to laser light, LED elements are arranged in an array and each L
An ED that blinks in response to a control signal, a combination of a uniform light source and a liquid crystal shutter, or optical information from a document table, microfilm, etc. are used.

Note that the developing bias described herein may be a DC voltage alone or a DC voltage with an alternating voltage superimposed thereon. Here, the definitions of the DC voltage component and the alternating voltage component will be clarified.

1. DC voltage component of developing bias (potential relative to ground potential) It may be a sine wave, a rectangular wave, or a pulse indicating the average value of peak to peak of two alternating voltages.

2. AC voltage component of the developing bias: This indicates the average amplitude of the alternating voltage, and in particular, in the present invention, during the developing process, the toner on the sleeve and the toner on the drum are transferred and transferred to the opposing surfaces, respectively. It means an AC voltage component that does not undergo reverse transition. That is, it means that, for example, the first developed image is not mixed with the developer used in the second development.

In addition, this AC voltage component enables non-contact development by applying a bias of a high frequency AC voltage component in the DC component in a type of powder cloud development method as described in JP-A No. 58-27158. This also applies to what you do.

Other known powder cloud generation methods may be used, such as generating a powder cloud using long sound waves, and developing by applying the DC voltage value of the present invention to the developing roller.

As described in detail in the specific examples below, the present invention enables images based on different latent images to be formed satisfactorily with simple means.

[Brief explanation of the drawing]

1(I) to 1(V) are explanatory diagrams of each step of the conventional image forming process, and FIG. 2(I) to 2(■) are explanatory diagrams of each step of the image forming process of the present invention. Figure 3 is
FIG. 1 is an explanatory diagram of an image forming apparatus implementing the present invention. 1 is a photosensitive drum, 3 is a primary charger or first scanning exposure, 4 is a first developing device, and 6 is a secondary charger. L2 is a second scanning exposure, 7 is a second developing device, 8 is a tertiary charger, L3 is a third scanning exposure, 9 is a third developing device, IO is a transfer charging device, and 42, 72, and 92 are bias power supplies.

Claims (1)

[Claims] (1) At least one step of forming an electrostatic latent image by exposing the surface of the charged electrophotographic photoreceptor to light information, and reversing and developing the latent image with toner having the same polarity as the charging polarity. In an electrophotographic method that is repeated several times, after uniformly charging the surface of a photoreceptor that has undergone one development step,
Perform the next process of latent image formation and development. The absolute value of the DC voltage component of the developing bias during development is
An electrophotographic method, characterized in that the absolute value of the surface potential of the toner image is set lower than the absolute value of the toner image in the previous step after the charging, and at least the second and subsequent reversal development is performed by a non-contact development method.