JPS60123871A - Formation of two color image - Google Patents

Abstract

PURPOSE:To obtain an excellent dichroic image which has superior transfer efficiency and stability and is free of toner scattering by irradiating a photosensitive body with light prior to transfer after the development of the 2nd latent image, and then charging it electrostatically with a prescribed voltage. CONSTITUTION:The photosensitive drum 1 is exposed to a negative image by a main charger 2 and the 1st image exposure light source 3, and the image is developed by the 1st magnetic brush developing roller 4. Then, the drum 1 is charged by the 1st scorotron charger 6 and a part with an initial surface potential is exposed to the negative image by the 2nd image exposing light source 7 to form the 2nd electrostatic latent image. The 2nd electrostatic latent image is then developed in a reversal state with the 2nd color toner by the 2nd magnetic brush developing roller 8. Uniform exposure by a light irradiating lamp 9 and charging by the 2nd scorotron charger 10 are carried out prior to transfer so as to decreasing the amount of the 1st color toner charge to or nearly to a normal value. In this case, an AC corona charger which deviates by a fixed DC voltage is usable instead of the charger 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a two-color image forming method that is excellent in transfer efficiency and stability and is capable of obtaining good two-color images.

BACKGROUND ART In recent years, in response to the diversification of information processing, copying machines that enable composite image copying have been developed, that is, copying machines that form a first latent image and a second latent image on a photoreceptor using different exposure sources, and then There is a transfer publication in which two-color scratch images are formed on both temperature images using toners of different colors, and the steps for obtaining a two-color image are as shown in FIGS. 1a to 1C1.

As shown in the Thta diagram, the photoreceptor is first charged to a predetermined initial surface potential (VO,) by a corona charger, and then a negative freeze is projected in a first image exposure to form a first latent image. At this time, the potential of the light irradiation section is attenuated to (Vrz). This first latent image is then reversely developed with toner of the first color while applying a bias voltage (Vbx) set somewhat lower than (1)0 to the developing electrode (see FIG. 1b). Subsequently, as shown in FIG. 1C, a second negative image is exposed to the (■0) potential portion to form a second latent image represented by Vrz). However, prior to this step, the photoreceptor on which the first latent image has been developed is charged. This is to prevent color mixture from occurring due to angle development of the first latent image when developing the second latent image. rise to. The second latent image is then developed with a second color toner under a bias voltage (Vb2) as shown in FIG. 16, and then transferred to obtain a two-color image.

However, since the developed latent image is banded as shown in Figure 1C, the charge amount of the toner is large lJ.
The transfer efficiency during transfer was significantly lowered and toner scattering occurred, making it impossible to obtain a good two-color image.

Purpose of the Invention The present invention has been made in view of the above facts, and its object is to be able to obtain good two-color images with excellent transfer efficiency and stability during transfer and without toner scattering. An object of the present invention is to provide a two-color image forming method.

SUMMARY OF THE INVENTION The gist of the present invention is that after a first negative latent image is formed on a photoreceptor and developed, the second negative latent image is charged to increase the potential of the developed latent image. In a two-color image forming method in which a second latent image is formed, developed with toner of a different color, and then transferred to transfer paper, after the second latent image is developed and prior to transfer, the photoreceptor is irradiated with light using a scorotron charger or a constant DC voltage. The reason is that the battery is charged using a biased AC corona charger.

Embodiment FIG. 2 shows a schematic configuration of a copying machine in which the two-color image forming method according to the present invention can be carried out. be done. (3) is ff1a, in which a negative image is projected using a single image exposure source such as a light emitting diode array, liquid crystal array, OF''r, or a laser scanner.However, the negative image is projected sequentially through an optical system. (4) is a first magnetic brush developing roller for developing the l-th electrostatic latent image into a first color, and its developing electrode is supplied with a first bias voltage (Vbi) from a DC bias voltage source (4a). ) is applied.(6)
is the first scorotron charger, which is used to increase the potential of the first electrostatic latent image after development, and its corona electrode is connected to DC high voltage # (6a), while the corona electrode and photosensitive A grid electrode (6c) connected to a DC bias voltage source (6b) is provided between the body drums.

Note that a corona charger may be used in which an alternating current voltage biased by a constant direct current voltage is applied to the corona electrode instead of the first scorotron charge.

(7) is a second image exposure source which has the same configuration as the first image exposure source (3) and projects a negative image to form a second electrostatic latent image. Further, (8) is a second magnetic brush developing roller for developing the second electrostatic latent image into a second color, and its developing electrode is supplied with a second bias voltage (8a) from a DC bias pressure source (8a).
Vb2) is applied.

In addition, (9) is for removing (lowering the potential) the first latent image portion by irradiating the photoreceptor with light after the second electrostatic latent image is visualized using a light irradiation lamp.(10) is for reducing the potential. In the second scorotron charger, its corona electrode is connected to an AC or DC high voltage wire (10a), while the grid electrode (
100) is connected to a DC bias voltage source (10b). This scorotron charger is for reducing the amount of charge of the first color toner attached by developing the first latent image. Incidentally, instead of the scorotron charger, a corona charger may be used in which an AC voltage biased by a constant DC voltage is applied to the corona electrode. And (xx
) transfers the two-color image on the photoreceptor drum (1) to the transfer paper (12)
A transfer charger for transferring toner, a toner blade cleaner (13) that remains on the photoreceptor drum after transfer,
Residual toner is removed by an eraser lamp (14).

A two-color image is formed by the copying machine having the above configuration as follows. A rotating photoreceptor drum (1) is first uniformly charged to a predetermined initial surface potential (vO) by a main corona charger (2), for example to a positive polarity. A negative image is then exposed to this charged surface with a first image exposure source (3). As a result, as shown in FIG. 3a, the potential of the light irradiation part (image part) is attenuated to (Vrl) while 5. The first electrostatic latent image is formed in the non-light irradiated area (non-image area) while remaining approximately (■0).

This first electrostatic latent image is then transferred to a first magnetic brush developing roller (4).
), but any two-component developer or component (2) can be used as the developer.

- For example, the developer disclosed in Japanese Unexamined Patent Publication No. 55-32073 is effective. This developer consists of a non-magnetic toner, a frictionally charged toner, a high resistance value of 10 Ω·m or more, a particle size of about 5 to 60 microns, and magnetic fine powder in an insulating resin. It consists of at least two components: a highly antimagnetic carrier which is dispersed and which occupies 50 to 75% by weight of the entire particle of the magnetic fine powder. Specifically, the high-resistance magnetic carrier is manufactured by, for example, melting and mixing an insulating resin and a magnetic fine powder, cooling and pulverizing the mixture, and selecting the particle size to about 5 to 60 microns. Here, the above-mentioned insulating resins include polyethylene, polyacrylic acid ester, polymethyl methacrylate, polystyrene,
Styrene acrylic polymers, epoxy resins, coumaron resins, mylene acid resins, carbolic acid resins, fluorine-resistant resins, etc. can be used. In addition, as the magnetic fine powder, Fe'tOs,
Fe5D4, ferrite, magnetite, etc. may be selected as appropriate.

On the other hand, as the non-magnetic insulating toner, conventionally known ones can be used, and the average particle size thereof is about 5 to 50 microns and the volume resistivity is about 10 Ω·m or more.

Then, the high-resistance magnetic carrier and the non-magnetic insulating toner are stirred and frictionally charged to opposite polarities, and a magnetic brush is formed by a magnetic brush development method, and the non-magnetic insulating toner is deposited in accordance with the first latent image pattern. It is to be developed.

Development by the first magnetic brush developing roller (4) is performed by applying a bias voltage (
Vbx), but this bias voltage (
Vbl) is the non-image area potential (■0) as shown in Figure 3b.
The toner is set somewhat lower than (V
rz) and (Vbz), specifically (Vr
x) and (Vbl), the first electrostatic latent image is deposited by reversal development between the potentials having a constant threshold value, and the first electrostatic latent image is developed into the first color. By this development, the potential (Vrz) is 60 to 70 V for those with a layer, and 120 to 150 V for those that have an AS2Se3 photoconductive layer.

Next, the photoreceptor drum (1) is charged by the first scorotron charger (6), which is charged by a second bias which determines the surface potential of the toner layer after development by the first magnetic brush developing roller (4). This is to raise the potential to the color mixing prevention potential (X/C) near the initial surface potential (Vo) which is higher than the voltage (Vbz) (see figure 'I4' 30).
. Charging is performed by setting the voltage applied from the DC bias voltage source (6b) to the grid electrode (6C) of the first scorotron charger (6) to a value approximately equal to the color mixing prevention potential (Vc), The toner layer surface potential is (Vc
). Note that charging may be performed using a corona charger that applies an AC voltage biased by a constant DC voltage to the corona electrode. Here, the surface potential of the toner layer is increased to (Vc), but the potential of the photoreceptor itself is not significantly affected.

Next, the photoreceptor drum (1) is exposed by a second image exposure source (7) to a negative image on a portion of the initial surface potential (■0).The second electrostatic latent image is then transferred to a second magnetic brush developing roller. (8)
is reversely developed with the second color toner, but at this time, the developing electrode is set to be somewhat lower than the initial surface potential (VO) (and lower than (, Vc') by the DC bias voltage source (8a). A second bias voltage is applied (Vbg) to develop under the egg (Fig. 3e).As a result, the second color toner adheres between (Vr 2 ) and (Vbg, ) to form a two-color image. At this time, the toner of the first electrostatic latent image that has already been developed with the toner of the first color is added to the second layer.
No colored toner will stick to it.

By the way, as is clear from FIG. 3C, the first color toner is transferred to the first scorotron charger (6) to prevent color mixing.
), the amount of charge becomes quite high.

The charge amount of normal toner is about 10 to 20μc/y, but the first scorotron charger (6) has a charge of about 400V.
When charged to (Vc), the amount of charge is 80 to 100 μc/y. However, the first and second /i! ! In the state shown in Fig. 3E, in which both the image I and the image are developed, the amount of charge of the first color toner is very high, and the amount of charge of the second color toner is normal and low. The first color toner is not easily transferred to the transfer paper, which only reduces the transfer efficiency.
Color images cannot be obtained.

Therefore, in the present invention, in order to reduce the charge amount of the first color toner to a normal value or a value close to it, uniform exposure is performed using a light irradiation lamp (9) and charging is performed using a second scorotron charger (IO) prior to transfer. .

That is, as shown in FIG. 3f, when uniform exposure is performed using the light irradiation lamp (9), the initial surface potential (Vo) attenuates to a potential (Vi) close to zero, while the color mixture prevention potential (Vc) decreases when the first color toner is exposed. Since it is attached, it is virtually unaffected. Next, the second scorotron charger (10) charges the first color toner to a low charge amount (preferably approximately equal to the charge amount of the second color toner). The color mixture prevention potential (Vc) of the surface potential is lowered to (Vi) as shown in Fig. 32.In other words, the polarity opposite to that of the first color toner is lowered from the grid electrode (10G) of the second scorotron charger (10). ion is induced to reduce the charge amount of the first color toner.Specifically, the high voltage source (10a)
may be alternating current or direct current, but in the latter case, a voltage with a polarity opposite to that of the latent image is applied to the corona electrode, while a voltage lower than (Vc) from the DC bias voltage source (10b) is preferably applied to the grid electrode (IOC) (■1 ).Apply a voltage equal to or close to ). Also, instead of the scorotron charger, an AC corona charger biased by a constant DC voltage may be used; in this case as well, the corona charger side is (Vc
) is set to a sufficiently smaller potential. Incidentally, regardless of whether a scorotron charger or an AC corona charger is used, as shown in Figure 3-f, most of the potential is attenuated to (Vi) by the light irradiation lamp (9), so each It has the advantage that the output can be small.

Furthermore, the light irradiation lamp (9) and the second Suflotron charger (10) or AC corona charger may be integrally configured to charge while irradiating the light.

The composite image, which has been developed in two colors as described above and whose charge amounts of the first and second color toners are suitable for transfer, is then transferred onto transfer paper (12) by a transfer charger (11). On the other hand, residual toner on the photoreceptor drum (13) is removed by a blade cleaner (13), and residual charge is removed by an eraser lamp (13).
J4) in preparation for the next copy.

Effects As is clear from the following explanation, according to the two-color image forming method according to the present invention, a good two-color image can be obtained with excellent transfer efficiency and no toner scattering. Moreover, it is simple in terms of control and construction, does not cause color mixture, and has excellent transfer stability.

[Brief explanation of drawings]

1a to 1d are diagrams showing the image forming process of a conventional two-color image forming method, FIG. 3-a to 3-f are diagrams showing the image forming process of the two-color image forming method according to the present invention. (1)...Photosensitive drum, (4)...
First magnetic brush developing roller, (6)...First scorotron charger, (8)...Second magnetic brush developing roller, (9)...Light irradiation lamp,(
10)...Second scorotron charger. Applicant: Minolta Camera Co., Ltd. Figure 3α Figure 3b Figure 3d Figure 30 Figure 3c Figure 38 vL 1L

Claims (1)

[Claims] (1) A first step of uniformly charging the photoreceptor to a predetermined initial surface potential; a second step of exposing the uniformly charged photoreceptor to a negative image to form a first electrostatic latent image; The first electrostatic latent image is
A third step of reversal development with color toner, and a fourth step of increasing the toner layer surface potential of the developed first electrostatic latent image to a color mixing prevention potential near the initial surface potential by charging.
a fifth step of exposing the negative image to form a second electrostatic latent image; and a fifth step of exposing the negative image to light to form a second electrostatic latent image; and a fifth step of exposing the negative image to light to form a second electrostatic latent image. A sixth step in which the electrostatic latent image of No. 2 is reversely developed with a second color toner, and a seventh step in which the potential of the portion excluding the color mixture prevention potential is attenuated by uniform exposure by a light irradiation means. A second color image forming method, comprising: an eighth step of lowering the electric potential and the charge l of the first color toner.