JPS5975259A - Copying method - Google Patents

Abstract

PURPOSE:To obtain always a sharp copied image free from fog and excellent in discrimination effect, by forming a primary latent image on a charged photoreceptor, then stabilizing the potential of a photoreceptor, and forming a secondary latent image. CONSTITUTION:A photosensitive drum 1 is uniformly charged to a potential Vs with the first scorotron charger 2. Then, the drum 1 is exposed to a negative light image by the first means 3 for forming an electrostatic latent image to form a latent image desired to be formed in low density, but image part potential VL1 is not stable due to fluctuation of sensitivity among positions of the photoreceptor, change of sensitivity fluctuation of exposure, etc. The drum 1 is correctly charged to stable potential VL2 with the second scorotron charger 4. The second latent image is formed with the potential VL3 in addition to the first latent image to form a synthetic electrostatic latent image consisting of a nonimage part at the potential Vs and the first and the second latent images having potentials VL2 and VL3, respectively. Then, reversal development is executed by setting a development bias voltage Vb to somewhat lower than the nonimage part potential Vs. In this case, since the potential VL2 of the first latent image desired to be formed in low density is higher than the potential VL3 of the second latent image desired to be formed in high density, the amt. of toner attached to the first latent image is smaller than that attached to the second latent image in the result.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a copying method capable of obtaining a copy image containing a mixture of images of different densities.

BACKGROUND OF THE INVENTION In recent years, many copying methods have been proposed in which a photoreceptor is exposed twice to obtain a composite image. For example, JP-A-57
In method 7J shown in Publication No. 8553, a normal positive original is used as the primary exposure Iiζ)? .

Then, secondary exposure of the negative image by laser or OFT)1']
A composite electrostatic latent image is formed by performing this process, and the positive latent image portion is subjected to 1F development and the negative latent image portion is reversely developed to obtain a composite image.

In this case, it is conceivable to develop each latent image portion with toner of a different color for identification purposes, but this usually requires two developing devices and has the drawback of being large in size.

By the way, if the primary and secondary exposures for obtaining a composite image are both positive or negative images, the development of the husband's latent image area will either be regular development or reversal development, and two-color development will be extremely difficult. Become. However, in order to provide the effect of color discrimination between the latent images formed by the primary and secondary exposures, the latent images may be developed to different densities.

For example, when primary and secondary exposures are performed using a laser, the intensity of the laser light is switched between two levels, so that each latent image is formed with a potential difference from each other. The latent image is developed to a low density and has an identification effect.

At this time, in order to obtain a clear image, it is important that the potentials forming each latent image are stable.

However, in particular, the low potential latent image portion is often unstable due to variations in sensitivity between photoreceptors, temperature dependence, fluctuations in light amount during exposure, etc., and it is difficult to obtain a clear image.

Purpose of the Invention The present invention has been made in view of the above-mentioned facts, and its purpose is to provide an excellent discrimination effect by providing a difference in image density, and to eliminate variations in sensitivity between photoreceptors and temperature dependence. It is an object of the present invention to provide a copying method that can always obtain a clear copy image without fogging even if there is a change in sensitivity or a variation in exposure amount.

Embodiment FIG. 1 shows a schematic configuration of a printer for carrying out the copying method according to the present invention, in which a photosensitive drum (1) rotating counterclockwise is first connected to a 941 Scorotron charger (2).
A first latent image is formed by the first electrostatic latent image forming means (3) which is charged to a predetermined polarity and then sequentially exposes a positive image or a negative image. -1- The scorotron charger (2) has its corona electrode (2a) connected to a DC high voltage source (
2b) is connected to the photoreceptor drum (1), and a grid electrode (2d) connected to a DC bias voltage source (2C) is provided between the corona electrode (2a) and the photoreceptor drum (1). ) is charged to a potential approximately equal to the potential applied to the grid electrode (2d) from the DC bias voltage source (2C). Note that charging for forming the first latent image is not limited to the above-mentioned Suflotron charger, but a normal corotron type charger may be used. The first electrostatic latent image forming means (3) is composed of a laser scanner, OFT, a light emitting diode array, a liquid crystal array, etc., and exposes a positive image or a negative image to form a first latent image. In addition to this, a positive or negative original may be projected through a normal optical system.

+4+1lj42 scorotron charger with substantially the same configuration as the first scorotron charger (2), the corona electrode (4a) is connected to a direct current high voltage source (4b), and the grid electrode (4d) is connected to a direct current Bias voltage source (
4C) are connected. In addition, instead of the DC bias voltage source (4C), a constant voltage diode, a discharge tube, and a Z
A constant voltage passive element such as nR may also be used. As will be described later, this second scorotron charger (4) changes the potential of the background portion of the first electrostatic latent image to a potential approximately equal to the potential applied to the grid electrode (4d) from the DC bias voltage source (4C). It is set to .

(5) is a second latent image forming means such as a laser scanner, an OFT'', a light emitting diode array, or a liquid crystal array; Similarly, a positive image is exposed, or when a negative image is exposed, a negative image is exposed to form a second latent image. still,
As will be described later, when a positive image is exposed, it is exposed so that the positive image exposed by the first electrostatic latent image forming means (3) is also included. Further, (6) is a magnetic brush developing roller for developing the first and second electrostatic latent images, and a predetermined bias voltage (Vr3) is applied to it from a DC voltage source (6a). As will be described later, development is performed by attaching toner to the first and second electrostatic latent images. (8) is the rotating corona charger for transferring the developed image onto the transfer paper, and (8) is the separating force for separating the transfer paper from the drum surface. [1] (9) is a blade cleaner for removing residual developer, and (10) is an eraser lamp for eliminating residual charges.

The copying method according to the present invention is performed using the printer configured as described above as follows.

(5) First, the case where a positive image is exposed by the first and second electrostatic latent image forming means +3+16-)- will be explained.
The process is to charge the photoreceptor drum (1) to, for example, positive polarity with the first scorotron charger (2), and apply a voltage to the grid electrode (2 (1) from the DC bias voltage source (2C)). (See FIG. 2(a)). As described above, charging in the first step is not limited to the scorotron charger, but a normal corotron charger may be used.

In the second step, the first electrostatic latent image forming hand (
In the step of exposing a positive image that is to be developed to a high density by 3), the potential of the image area is approximately (Vs
), but the non-image area attenuates to a potential of (VLI). That is, for example, when you want to obtain as a final image an image consisting of the character A, which you want to form as a high-density image, and the character B, which you want to form as a low-density image, this second
In the process, the letter A, which is desired to be formed in high density, is exposed to light.

At this time, as will be described later, a certain area including A may be captured as an image and exposed. As a result, the potential of the non-image area excluding the image area of A becomes (VLl) as shown in "-. However, this potential (VLl, ) is due to variations in sensitivity between photoreceptors, changes in sensitivity due to temperature dependence, and even during exposure. It is not always constant and unstable due to changes in the amount of light, etc. This instability of the potential (VL1) makes it difficult to set the bias voltage during development, which will be described later, and the occurrence of fog is unavoidable.

From this point of view, in the third step of the present invention,
The unstable potential (VLl) is always set to a constant stable potential (VL2). This is achieved by charging with the second scorotron charger (4), and the grid electrode (4d
) by setting the voltage (Vg) applied to the above (Vr, 1) to a value higher than the above (Vr, 1) but lower to some extent than the initial surface potential (Vs), the unstable potential ( VLt) is correctively charged to a stable constant potential (VL2) approximately equal to (Vg). Note that the charging at this time has the same polarity as the charging in the first step.

To explain the third step more specifically, FIG. 3 shows the charging principle of the second scorotron charger (4). There is an unstable potential (VL1) mentioned above in the region, and a potential corresponding to (Vs) in the region (Bl).Now, suppose t
Although the potential of the background part of the Al region varies, it is approximately 1
50 volts, the potential of the image area in the area of fBl is 600 volts, and (VLl, ) is the stable background potential (VL2)
9 - shall be correctively charged to 300 volts. in this case,
DC bias voltage source (4C) to grid electrode (4d)
The voltage (Vg) applied to the desired stable potential (VL
2) Set to 300 volts equal to 2). In this state, a high voltage is applied from the DC high voltage source (4b) to the corona electrode (4a) to start corona discharge, and a DC voltage (Vg) of 300 volts is applied to the grid electrode (4d). 4d) and the photoreceptor drum (1) [A
Since the potential of the latter region is lower between the + regions, an electric field is formed that moves the corona ions toward the photoreceptor.
Since the voltage on the grid electrode is lower between the region Bl and the grid electrode, an electric field is formed in the direction of the grid electrode, contrary to the above.Therefore, the potential (VLz) of the +A region of the photoreceptor is lower than the voltage on the grid electrode ( The potential increases to a potential (VL2) of 300 volts, which is approximately equal to the voltage (Vg) applied to the terminal 4d), becomes uniform at that value, and is not charged any more. On the other hand, the fourth area is not affected by the discharge action from the corona electrode, and the potential (Vs) corresponding to the image area is maintained. That is, in the third step, the pattern of the first electrostatic latent image is not affected, and the potential 10- (VL) of the non-image area is corrected to a stable potential (Vl2). Furthermore, ten.

In the following, the voltage (Vg) applied to the grid electrode (4d)
Although it has been explained that the intermediate potential (VL 2 ) and the intermediate potential (VL 2 ) are approximately equal, this relationship depends on various factors such as the relationship between the grid electrode (4d) and the photoreceptor drum (1), the moving speed of the photoreceptor drum (1), etc. It depends on the conditions, so it is not always (Vg
) is not required to be set equal to (Vl2) and the desired (
(Vg) may be set higher than (Vl2) as long as it is charged to Vl2).

The fourth step is the thus formed (Vs) and (Vl2)
For the ηi potential pattern, the second electrostatic latent image forming means (5)
Expose the entire desired final positive image.

That is, in addition to the positive image that is exposed in the second step and that is desired to be formed at a high density, a positive image that is desired to be formed at a low density is exposed. In other words, the entire image 9 including A and B is exposed. At this time, the high-density image portion is the 2-1. It is exposed to light so as to overlap with the image potential part of (Vs) formed in the culm, and the low density image part is exposed to the stabilized potential part of (Vl,z). As a result, an electrostatic latent image as shown in FIG. 2 Fdl is formed. Specifically, the negative potential in the high-density image area remains the same (Vs), and the potential in the low-density IΩ-image area becomes (v
r, 2), and the non-image area is attenuated to (VL 3 ), forming a latent image pattern consisting of three potentials, and the potential (Vs) of the high-density image area of the first latent image is the same as that of the second latent image. It is higher than the potential (Vl2) of the low-density image portion of the latent image.

In the next fifth step, the electrostatic latent image thus formed is developed by a developing roller (6) under application of a predetermined developing bias voltage (Vl) from a DC power source (6a).

That is, as shown in FIG. 2 fe+, the developing bias voltage (
Vl)) is set approximately equal to or somewhat higher than the non-image area potential (VL a ), and development is performed by regular development. At this time, the first latent image has a high potential as shown by (Vs), so it has a high density, and the second latent image has a lower density than (Vs) (Vl2
), it can be developed to a low density and an image with a distinguishing effect can be obtained.

In addition, in the second series of two steps, the image desired to be obtained as a high-density image itself may not be exposed, but a certain area including the image may be exposed as a positive image dark area. That is, Fig. 4 ta
When you want to obtain an image in which the letter A (a) is copied in high density and the letter B (b) is copied in low density as shown in +,
As shown in FIG. 4 (bl), in the second step, the first electrostatic latent image forming means (3) is used to expose a certain area +c+ including the letter A (al) as a positive image dark area.In other words, A
Rather than exposing the letters ``fa'', an area of a size equal to or including at least A is exposed as a dark area, and the remainder is exposed as a bright area. As a result, the potential pattern becomes as shown in FIG. 5 tal, which is substantially the same as FIG. 2 fbl. Next, in the third step, the unstable background potential (VLl)
is corrected to a stable potential (Vl2) by the second scorotron charger (4) (FIG. 5(b)), and subsequently, in the fourth step, the second scorotron charger (4) 4. Expose the image shown in Figure [a]. At this time, the character f2+ of A is exposed so as to overlap the part represented by the potential of (Vs), and the character (b) of B is exposed to the part of (Vl2). In this way, as shown in Figure 5 (tc), an electrostatic latent image consisting of an image corresponding to A expressed by Vs) relative to the non-image area potential (VL3) and an image corresponding to B expressed by (Vl2) is created. In the following fifth step, A is developed to a high density and B is developed to a low density. Therefore, since the second electrostatic latent image forming means (5) performs the actual image exposure, it is not necessary to use a first electrostatic latent image forming means (3) particularly excellent in performance such as resolution.

The developed image is then transferred to transfer paper by a transfer corona charger (7), and the transfer paper is then separated from the photoreceptor drum (1) by a separation corona charger (8) and fixed by a fixing device (not shown). the final copy. On the other hand, residual developer is removed from the photosensitive drum (1) by a blade cleaner (9), and then residual charges are removed by an eraser lamp (10) to perform the next copy.

Next, the case where a negative image is exposed and copied by the first and second electrostatic latent image forming means (3) and (5) will be explained.

The first step is the step of charging the photoreceptor drum (1) by the first scorotron charger (2), as in the case described above, and as shown in FIG. Uniformly charged.

The second step is the photosensitive drum (1) which is uniformly charged to (Vs).
), a negative image is formed by the first electrostatic latent image forming means (3).
4- Expose to form a first latent image. At this time, a negative image to be formed at a low density is exposed, and the potential pattern is as shown in FIG. 6tb). However, the image area potential (VLl
) is unstable due to variations in sensitivity between photoreceptors, changes in sensitivity, fluctuations in exposure, etc. .

In the third step that follows, the second scorotron charger (
4) stabilized (VL2) as shown in Figure 6 (C).
Correctly charged to the potential of . Note that the charging method is the same as in the case of FIG. 2fcl.

The fourth step is a process in which a negative image to be formed with high density by the second electrostatic latent image forming means (5) is exposed to a portion of potential (Vs), which is formed through the second and third steps. In addition to the first latent image, a second latent image represented by the potential (VL a )
A latent image is formed as shown in FIG. 6 td+. In this way, VL 2 with respect to the potential (Vs) of the non-image area on the photoreceptor drum.
) and (VL 3), a composite electrostatic latent image is formed consisting of the first and second latent images. This latent image is transferred to the DC voltage source (6) by the developing roller (6) in the next fifth step.
From a), a color image is formed under application of a predetermined developing bias voltage (Vl). That is, as shown in FIG. 6 (fe), the developing bias voltage (vb) is set approximately equal to or somewhat lower than the non-image area potential (Vs), and development is performed by reversal development.

In this case, the potential of the first latent image (VT-
z) is higher than the potential (VL3) of the second latent image that is desired to be formed with high density, as a result, the amount of toner adhering to the first latent image is less than that of the second latent image, resulting in an image with a discrimination effect. It will be done.

The thus developed image is then transferred and fixed, while the photosensitive drum (1) is cleaned and neutralized to prepare for the next copying.

FIG. 7 shows another embodiment of a printer capable of carrying out the composite image copying method according to the present invention, in which, compared to the printer shown in FIG. It is characterized by uniform charging, by using a single means as the first and second electrostatic latent image forming means, and by rotating the photosensitive drum (1) twice. That is, in the case of a copying machine configured as shown in FIG. 1, the initial surface potential (Vs) and stable potential (Vs)
two sets of first and second scorotron chargers (2), (4) for charging L2) and also two latent image forming means (3) for forming first and second latent images; (5), it is inevitable that it will be extremely large and complicated, and it will also be quite expensive, but the configuration of No. 7171 requires only one set of charging means and latent image forming means, so it can be downsized. It also becomes cheaper.

To explain more specifically, in FIG. 7, (11) is a scorotron charger whose corona electron NU (1] a
) is connected to a DC high voltage source (11b), while the grid electrode (IIC) is connected to a first DC voltage source (13d) that applies a bias voltage (Vgl) and a bias voltage (Vgz) through a switch +51. A second DC voltage source (1
1, 6). (12) is an electrostatic latent image means, which is composed of an OFT, a laser scanner, a liquid crystal shutter, an LED, etc., and exposes a positive or negative image during the first rotation of the photoreceptor drum (1), and exposes a positive or negative image during the second rotation of the photoreceptor drum (1). If the rotation is a positive image, the positive image is exposed, and if it is a negative image, the negative image is exposed. Further, the photosensitive drum (1) is formed so that its circumferential length is somewhat longer than the maximum image length. The rest of the structure is the same as that in FIG. 1, so the same reference numerals are given and the description thereof will be replaced.

In the copying machine configured as described above, the photosensitive drum (1) rotating in the direction shown in the figure is first connected to the scorotron charger (1).
1), it is uniformly charged so that its surface potential becomes (Vs). This connects the switch (S) to the first DC voltage source (n
d) side, and apply (V) to the grid electrode (1, IC).
This is carried out by applying a voltage of gl), and is charged to a potential of (Vs) as shown in FIG. 2(a) and FIG. 6fat, same as the first step described above. In the subsequent second step, a positive image or a negative image is exposed by the electrostatic latent image forming means (12).
When a negative image is exposed, the first latent image as shown in FIG. 1 is formed, and the latent image shown in FIG. 6 (bl) is formed. As mentioned above, it is unstable.

The photosensitive drum (1) has completed exactly one rotation and when it enters the second rotation, it is charged again by the scorotron charger (11).

At this time, the switch (Sl is the second DC voltage source (11e)
The grid electrode (OC) has (
As mentioned in the connection with Figure 3, the unstable potential (VL 1 )
is correctively charged to a stable potential (VL 2 ), while
It does not affect the initial surface potential (Vs) (Fig. 2 (C)
1, see Figure 5(b) and Figure 6 (tel). Next, the electrostatic latent image forming means (12) exposes the photosensitive drum (1) to a positive image when it is exposed to positive acid in the first rotation, and a negative image when it is a negative image, as shown in FIG. , the electrostatic latent image shown in FIG. 5 (C) or FIG. 6), and an image with an identification effect is developed (see tel in Figure 2 and tel in Figure 6).The developed image is transferred to the transfer paper by the transfer corona charger (9) and transferred to the photoreceptor. It is separated from the drum (1) and fixed by a fixing device (not shown).On the other hand, residual developer is removed from the photoreceptor drum (1) by a blade cleaner (11), and residual charge is removed by an eraser lamp (12). The static electricity is removed and it is ready for the next copy.

Effects As is clear from the above explanation, according to the copying method according to the present invention, 411.1↓light>1. ′
It is possible to form an image having an identification effect by providing the . In addition, even if there are variations in sensitivity between photoreceptors, changes in sensitivity, or variations in exposure amount, it is possible to always obtain clear images without fogging, and it can be implemented with an extremely simple configuration. It has excellent effects such as:

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a printer capable of carrying out the copying method according to the present invention, FIG. Figures 4 (al) and 5 (a) to (C) are diagrams showing the charging principle of the scorotron charger used in to tel are process diagrams showing a copying method using negative image exposure, and FIG. 7 is a diagram showing another embodiment of a printer capable of carrying out the copying method according to the present invention. (1)...Photosensitive drum , +21, +4.1...
・First and second scorotron chargers, f3), (
51...First and second electrostatic latent image forming means, (6)...
developing roller.

Claims (3)

[Claims] (1) A first step of uniformly charging a photoreceptor to a first polarity, and exposing the photoreceptor to a first positive image, an area image including the positive image, or a negative image to form a first electrostatic latent image. a third step of charging the photoreceptor on which the first electrostatic latent image is formed using a scorotron charger to make the potential that was photoattenuated in the second step high and uniform; When a positive image is exposed on the photoreceptor in the second step, the second positive image including the first positive image is exposed by applying a force V' such that the first positive image overlaps the image area of the first electrostatic latent image. , a fourth step of exposing a second negative image when the negative image is exposed to form an electrostatic latent image corresponding to the second positive image or the first and second negative images; A fifth step for developing the electrostatic latent image
and a sixth step of transferring the developed image, forming an image having a distinguishing effect based on the difference in shading. (2) The scorotron charger includes a DC voltage source that applies a voltage to its grid electrode, and the applied voltage is set lower than the charging potential in the first step and higher than the optically attenuated potential in the second step. A copying method according to claim 1, characterized in that: (3) A patent characterized in that charging in the first step is performed by a scorotron charger used in the third step, and a single image exposure source is used in the second and fourth steps. A copying method according to claim 2.