JPS59182463A - Two color electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain two kinds of electrostatic images having different potentials in a dark part and to enable development with two color toners by subjecting a photoconductor having the nature that the electrostatic charging voltage is increased by the previous exposure to two times of image exposure. CONSTITUTION:A photoconductive consisting of amorphous silicon, etc. doped with oxygen is uniformly electrostatically charged to maintain the surface potential at Vd. If the photoconductor is subjected to the 1st time of image exposure, the potential in the bright part where the light is irradiated decreases (1), but when the photoconductor is electrostatically charged again, the characteristic of the photoconductor changes as the light is applied once thereto and therefore the potential is higher potential Vl1 than the potential before the exposure. The potential in the dark part remains at Vd. When the photoconductor is subjected to the 2nd time of image exposure, the potential in the dard part region where the light is irradiated decreases to Vl2. A two color image is obtd. by using the potential Vd in the dark part where no light is applied in two times of the exposure as a developing bias and developing the image with two kinds of toners having different colors (for example, red and black) and having reversed polarities.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a two-color electrophotographic method for writing an image using two laser beams.

In recent years, laser printers that combine electrophotographic technology and laser technology have been put into practical use. A laser printer writes an image on a charged photosensitive drum with a laser beam to form a latent image, develops the latent image with toner to make it visible, and then transfers this visible image onto transfer paper. Transcribe it.
-It is for obtaining tokobee. 9. Laser gritters are non-impact printers, so they have the advantage of being low noise, easy to operate at high speeds, have higher print quality than other non-impact printers, and can use plain paper.

Laser printers are used for a wide range of purposes, including bookkeeping, document creation, etc.

It would be very convenient to be able to print in two colors. for example,
Printing especially important parts of book numbers and documents in red reduces oversights and makes the prints easier to read. Furthermore, in general, two colors are sufficient for creating ledgers and documents, and there are very few cases where six or more colors or full colors are required. For this reason, several two-color electrophotographic methods for obtaining two-color hard copies have been proposed, but many of these require special photoreceptors or complicated latent image formation processes.

It is difficult to put it into practical use, and even if it were made into a device, there was a risk that it would be expensive and unreliable.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, it is an object of the present invention to provide a two-color electrophotographic method capable of two-color printing with a simple configuration.

The present invention will be explained below using two drawings.

FIG. 1 is a schematic diagram of a conventional laser printer, in which a charger 2. Developing device 4. Transfer charger 5° Transfer paper 6. Cleaning blade 7, pre-exposure lamp 8 crab jj (J order t
It's ti-g. Photosensitive drum 1il-j:, substrate 1a
A photoreceptor 1b as an image carrier is provided on the surface of the
After being uniformly charged by the charger 2, the laser beam 6 performs image registration, forming a latent image. These 7 sheets are developed by the developing device 4 to form a toner image (one ball of oIT). Next, this toner image is transferred by the transfer unit 5.
The image is transferred onto the transfer paper 6 and becomes an output print. On the other hand, after the transfer residual toner remaining on the peripheral surface of the photosensitive drum 1Q is cleaned by the cleaning blade 7, pre-exposure is applied by the front needle and the light lamp 8, and after erasing the charge, the ninth cycle begins.

Thus, pre-exposure erases the charge on the photoreceptor.

Although it is used to eliminate the previous history, in certain Φ cases involving the applicant, the surface potential of the part that was charged after being irradiated with the previous i-light is the same as that of the part that was charged without being irradiated with the previous light. I found that it was higher than that.

The present invention applies this fact to provide a new two-color electrophotographic method.

The phenomenon in which the surface potential increases due to pre-exposure without separation will be explained.

As an example, a case where amorphous silicon doped with oxygen is used as a photoreceptor will be described. When this photoreceptor is repeatedly charged without pre-exposure, the surface potential of 9 becomes second.
It falls like curve a in the figure.

After several rotations, it becomes about A[v] and becomes saturated. here.

When a short-wavelength front light is applied before charging, the falling edge decreases and saturates at about B [V] as shown by the curve in Figure 2.

This phenomenon can be interpreted as follows.

The photosensitive drum 1 is positively charged as shown in FIG. 3(1).

Negative charges corresponding to the surface charges are induced on the substrate, and when charging is repeated, these negative charges are injected from the substrate 1a to the photoreceptor 1b as shown in FIG. 2(2). Therefore, even if the amount of charge on the two surfaces remains unchanged, the apparent potential on the upper surface decreases,
Falling down causes shi. Furthermore, if charging is repeated, the same figure r
As shown in 3) and (4), the injection of negative charges progresses and the amount of fall increases, but the injected negative charges are trapped in the photoreceptor and become space charges, and no further injection is performed on the 9 surface. The potential saturates.

On the other hand, when pre-exposure is applied, some charge is injected from the substrate 1a side as shown in FIG.

The injected charges are canceled by electron-hole pairs generated by the pre-exposure. In Figure 4 (2), the hole ■ of the electron 〇-hole ■ pair generated by the pre-His light is recombined with the injected electron, and the ○ is surface charge 1 and town bond -4-.

As a result, as shown in FIG. 4(b), the injection If, the charge is canceled, and then it is charged again.

As shown in FIG. 4 (4), a surface potential approximately equal to the initial potential is obtained. In other words, a higher surface potential can be obtained than in the case where there is no pre-exposure (FIG. 6 (4)). However, at this time, when the electron 0-hole 2 pairs are generated in a deep part of the photoreceptor 1b, that is, in a part close to the substrate 1a, the above effect becomes smaller. This is because in amorphous silicon doped with oxygen, electrons O are more likely to be trapped than holes. This is because they tend to be trapped before reaching the surface and remain as new space charges. Therefore, in order to obtain the effect of increasing the surface potential by pre-exposure, it is necessary to select the wavelength of the pre-exposure to generate electron-hole pairs near the surface of the photoreceptor 1b.

The applicant has proposed that when amorphous silicon doped with oxygen is used as the photoreceptor 1b, the pre-exposure is 70%
If light with a wavelength of 0 nm or less is used.

It has been found that the above-mentioned effects can be obtained.

The two-color electrophotographic method of the present invention that utilizes this effect will be described in detail below. First, the photoreceptor 1b is uniformly charged as shown in FIG. 5(1). When this uniform charging is repeated several times, negative charges are injected into the substrate 1a, and the fifth
The result will be as shown in Figure (2). Next, as shown in Figure 5 (6) (
When the portion a) is imagewise exposed with light having a wavelength that produces the effect of raising the surface potential as described above, the injected charges are canceled as shown in FIG. 5(4). Next, when uniform charging is performed again, the surface potential of the part (a) becomes higher than that of the other parts (b) and (C), as shown in FIG. 5 (5). Subsequently, when image exposure is performed on the portion (C) as shown in FIG. 5(6), the surface charge is canceled and the potential of the portion C decreases as shown in FIG. 5(7).

If the above process is illustrated by focusing on the surface potential, the 6th
It will look like the figure. The photoreceptor 1b is in a state where the surface potential has fallen due to repeated charging.

When the first image exposure is performed at time (1), the surface potential of the exposed area decreases, but when uniform charging is subsequently performed at period (2), the injected charge is applied to the light irradiated area of the first image area. is canceled, the surface potential rises higher than that of other parts and reaches the level of Vzl. Following this, (
If you try to perform the second image exposure at point 3), the second
The potential of the image exposure irradiation part decreases to the level of Vt2. Further, the potential Vd of unloaded A is between Vt1 and Vt2.

Here 9. - Negatively charged toner colored in one color A is deposited at a latent image potential level of Vt1 from a developing device to which a developing bias approximately equal to the potential Vd is applied.

If a positively charged toner colored in color B is deposited at the level of the latent image box of Vt2, an image of two colors A and B can be obtained. At this time, the toners of one color A and one color B are.

They may even be in the same developer. They may be developed using separate developing devices.

Next, the configuration of a laser printer to which the two-color electrophotographic method according to the present invention is applied will be explained with reference to FIG. In FIG. 7, a charger 12. Developing device 14 containing toner of color A. Developing device 15° containing the B color toner; Charger 16° for equalizing the charge polarity of the toner on the drum; Transfer charger 17. Cleaning blades 19 are sequentially arranged.

The photosensitive drum 1 is rotated in the direction of the arrow 17. After being charged several times by the charger 12, the image is exposed by the laser beam 11 for writing the first image. In this image exposure, the laser is turned on in the areas that you want to print, and the laser is turned off in the areas that you do not want to print. This is called negative exposure. Therefore.

A latent image is formed on the photosensitive drum by using laser scanning as main scanning and rotation of the photosensitive drum as secondary scanning.

Further, the wavelength of this laser beam is set to a wavelength that is effective in preventing the dark area potential from falling as described above. For example, when the photosensitive drum 1 is made of amorphous silicon doped with oxygen, an Ar laser or the like can be used.

Following the first image exposure, after being uniformly charged by a charger 12, the photosensitive drum 1 is subjected to image exposure by a laser beam 13 for eliminating the image of the cover 2. This image exposure is also negative exposure in which the laser is turned on in the areas where printing is desired and the laser is turned off in areas where printing is not desired.

at this point.

The first image-exposed area forms a first latent image level with a higher potential than the unexposed area, and the second image-exposed area forms a second latent image level with a lower potential than the unexposed area. Form the image level. Subsequently, development is performed by the developing device 14 containing toner of color A and developing by developing device 15 containing toner of B color, and the first and second latent images are visualized.

The A color toner and the B color toner are charged with opposite polarities, and if the A color toner is negatively charged and the B color toner is positively charged, the first latent image is the A color toner. The second latent image is developed with eight color toners. However, at this time, it is assumed that the charged polarity of the photoreceptor 1b is positive. Further, a bias potential approximately equal to the potential Vd of the unexposed portion is applied to the developing devices 14 and 15.

The two-color image visualized in this way is charged either positively or negatively by the charger 16, and after the toner charge polarity is made uniform, it is transferred onto the transfer paper 18 by the transfer charger 17. Toner remaining on the photosensitive drum 1 without being transferred is cleaned by a cleaning blade 19.

The photoreceptor is not limited to the oxygen-doped amorphous silicon shown in the above embodiment.

Any material that shows a decrease in surface potential due to charge injection from the substrate 1a side during repeated charging may be used.

Further, the laser beam for performing the first image exposure is not limited to an Ar laser, but may be any laser beam that generates electron-hole pairs near the surface of the photoreceptor 1b. For example, when amorphous silicon doped with oxygen is used for the photoreceptor 1b, a He-Cd laser may be used.

The wavelength of the laser beam for performing the second image exposure does not matter as long as the photoreceptor used has practical sensitivity.

The light source for performing the first image exposure and the second image exposure is not limited to a laser, and can be used as long as it satisfies the above conditions. For example, it may be a light emitting diode LED, or it may be one that guides incoherent light onto the photosensitive drum using an optical fiber.

Both or either of the first image exposure and the second image exposure may be document exposure such as in a normal copying machine,
In that case, the document illumination light for the first image exposure and the second image exposure must each have a wavelength that satisfies the above-mentioned conditions.

The A-color toner and the B-color toner do not necessarily have to be different colors, and normal image composition can be performed by using toners of the same color.

As explained above, according to the present invention, a two-color hard copy can be obtained by a simple process of attaching toners of different colors to the pre-charging image opening section and the post-charging image exposing section, respectively. Therefore, as long as the type of photoreceptor is selected, the structure of the photoreceptor can be of the conventional type, and the electrophotographic device can be of the conventional type and only needs to have a process of image exposure before charging. However, a low-cost, highly reliable two-color electrophotographic method was obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the area around the photosensitive drum of a typical electrophotographic device, Figure 2 is a surface potential diagram of the photosensitive member when it is repeatedly charged, and Figures 6 (1) to (4) are Schematic diagram showing the mechanism of body surface potential decrease, Figures 4 (1) to (4)
Figure 5 (1) is a schematic diagram showing the mechanism of the effect of prequel light.
) to (7) are schematic diagrams showing the latent image process according to the present invention, Figure 6 is a diagram of changes in surface potential in the process according to the present invention, and Figure 7 is a photosensitive drum of an electrophotographic apparatus to which the process of the present invention is applied. It is a schematic diagram of the surroundings, 1... Photosensitive drum, 2. 12... Charger. 4.14.15...Developer, 11...Laser beam that emits the first image 14 light, 1ro...2nd
A laser beam that performs single-mount J image exposure. Patent applicant Gyanon Co., Ltd. - Agent
Fuku 1) Encouragement 1. , :Attack Figure 1
Figure 7 (f) (j) Hatake Hatake Hatake (2)
(3) (4-)Figure 4 (?n t3)
(4) $5 figure'(2)"(3)"(5)"(6)"(7)

Claims (1)

[Scope of Claims] (1) A photosensitive member exhibiting a characteristic that the surface potential decreases when repeatedly charged is repeatedly charged. The photoreceptor is subjected to a first image exposure with light of a wavelength that generates many electron-hole pairs near the surface of the photoreceptor.9Then, after uniformly charging the photoreceptor, Second
Image exposure is performed to form areas with a higher potential and areas with a lower potential than the potential of the unexposed area, and then development is performed with toners of different colors and charged with opposite polarities to form a two-color visible image. A two-color electrophotographic method characterized by obtaining. (2) The two-color electrophotographic method according to claim (1), wherein the photoreceptor is amorphous silicon doped with oxygen. (6) Claim (1) or (2) characterized in that the wavelength of the light that generates many electron-hole pairs near the surface when irradiated onto the photoreceptor is 700 nm or less A two-color electrophotographic method.