JPS5940652A - Two color electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain a two color electrophotographic method which is simple and is highly reliable by writing an image on a photosensitive drum by two light signals which differ in the incident positions of light in the stage of exposing simultaneously with secondary electrostatic charging. CONSTITUTION:A primary electrostatic charger 2, a secondary electrostatic charger 3, a full surface exposing lamp 8, an A color developing device 13 using a toner colored to an A color, a B color developing device 14 using a toner colored to a B color, etc. are disposed around a photosensitive drum 1 successively in the rotating direction. An image is written on the drum by two light beams of a small diameter such as lasers differing in the incident positions of light in the stage of exposing simultaneously with secondary electrostatic charging to form three latent image levels differing in potentials and to stick toners of respectively different colors at the level of the highest potential and the level of the lowest potential, whereby a hard copy of two colors is obtd. The two color electrophotographic method which is simple and highly reliable is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-color electrophotographic method in which a photoreceptor is used and an image is written by a laser beam or the like.

In recent years, laser printers that combine electrophotographic technology and laser technology have been put into practical use. A laser printer uses a laser beam to write an image onto a charged photosensitive drum to form a latent image, which is then developed with toner and transferred onto transfer paper to obtain a hard copy. Since it is a non-impact printer, it has the advantages of low noise, easy speedup, high print quality compared to other non-impact printers, and the ability to use plain paper.

Laser printers are used for a wide range of purposes, including creating forms and documents, and for these purposes, it would be extremely convenient if they could print in two colors. For example, if you print numbers on a form or particularly important parts of a document in red, you will be less likely to overlook them and the print will be easier to read. In general, the number of colors required for creating forms and documents is
It is partially divided into three colors, and there are extremely few cases where three or more colors or full color is necessary.

For this reason, several two-color electrophotographic methods for producing two-color hard copies have been proposed, but many of these require special photoreceptors or complex latent image formation processes, making them impractical. However, even if it is made into a device,
There was a risk that the process would become complicated and unreliable.

In view of the above-mentioned circumstances, the present invention uses a conventional photoreceptor to
The object of the present invention is to provide an electrophotographic method that allows two-color printing. That is, in an electrophotographic method of an electrophotographic apparatus that forms an image using a photosensitive drum having a three-layer structure, an image is written with two narrow light beams such as lasers having different light incident positions during tertiary charging and simultaneous exposure. By forming all three latent image levels with different potentials and attaching toners of different colors to the highest and lowest potential levels, three-color hard copies are obtained2.
The object of the present invention is to provide a color electrophotographic method.

Embodiment 2 of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic front view of a three-color electrophotographic apparatus for explaining the three-color electrophotographic method according to the present invention. / is a photosensitive drum as an example of a photosensitive member, and I
It has a three-layer structure including a photoconductive layer such as a CCDS (N-type semiconductor) photoreceptor and an insulating layer on top of the photoconductive layer 9, and is rotatably supported in the direction of the arrow in the figure. A seventh-order charger (positive if the photoconductive layer is an N-type semiconductor, negative if the photoconductive layer is a P-type semiconductor) is placed around the photosensitive drum according to its rotation direction.
Corona discharger) 2. Secondary charger (DC1 or taAc:yoskNn with opposite polarity to the 7th charger) 3, full-surface exposure lamp, and A color developer using toner colored A color/3
, B color developer/g using toner colored B color, charger/j for aligning the polarities of the A color and 8 color toners of the developed toner image, timing roller so, toner A transfer charger/O (a charger with a polarity opposite to that of charger/J) and a cleaning device/7 are provided for transferring the image onto the transfer material 7.2. In addition, here A color developer/
The polarity of the toner used in 3 and the polarity of the toner used in B color developer/g are opposite to each other.For example, here, the polarity of the toner used in A color developer/3 is all negative, and the polarity of the toner used in 8 color developer/4t is set to be negative. The polarity of the toner used is all positive. 7 is a semiconductor laser which oscillates a laser beam modulated by an image signal to be recorded in B color, and the laser beam Lb from this is sent to the secondary charger 3 via a beam scanning device Sf consisting of a rotating polygon mirror, etc. The photosensitive drum is scanned and exposed at a position within the charged area. At this time, the incident position of the laser beam from the semiconductor laser 7 within the effective charging area of the secondary charger 3 is determined by the contrast of the surface potential of the photosensitive drum when the entire surface is exposed later with the entire surface exposure source (not exposed at all). It is preferable that the distance between the exposed part and the part exposed by the beam Lb is at a maximum. B is also a semiconductor laser that oscillates a laser beam modulated by the image signal to be recorded in color A, and these laser beams
'The beam Lb is incident on the photosensitive drum within the effective charging area of the secondary charger 3 through a beam scanning device S consisting of a rotating polygon mirror and a mirror for changing the optical path. The light enters a position in front of the photoreceptor at a distance of several mm to /θmmM, and exposes the entire photoreceptor. In addition, the semiconductor laser 7 is used for the part to be imaged (the part to which toner is to be attached).
Then, the electricity is turned on, and the parts that you do not want to make into an image (areas on which toner is not attached) are turned off, and the photosensitive drum/
It is assumed that the photosensitive drum is exposed to negative light, and the conductor is de-energized in the area where the image is to be formed, and is energized in the area where the image is to be formed, and the photosensitive drum is exposed to positive light.

Reference numeral 7.2 denotes a transfer material stored in a cassette, and the transfer material /, 2 is supplied to the cassette ram / by a pick-up roller //. In addition, this figure shows the pre-static elimination exposure device and the transfer material/
, 2, a third means for separating the transfer material 7.2 from the photosensitive drum and the transfer material 7.2.
The conveyor belt that conveys the image and the fixing device that fixes the transferred image of the transfer material conveyed by the conveyor belt are omitted for simplicity.

Figure 2 shows the potential contrast due to the surface potential difference between the exposed area and the non-exposed area of the photosensitive drum when the entire surface is exposed by the laser beam, and the potential contrast within the effective charging area of the secondary charger. The relationship with the beam exposure position is shown in a graph. Here, the laser beam Lb of the semiconductor laser 7 in FIG. 1 is made incident on the image exposure position where the potential contrast is maximum, that is, the 0 position in FIG. That is, it is preferable to make the laser beam La of the semiconductor laser B in FIG. 1 enter an appropriate image exposure position shifted by one to -10 degrees. In this way, the present invention provides a ρ-forming charger 3 for the laser beam.
When the exposure position of the photosensitive drum changes within the effective charging area of the photosensitive drum, the balance between the charged state before image exposure and the banded state after image exposure of the photosensitive drum changes, so the potential contrast also changes depending on the image exposure position. This method takes advantage of the special properties of simultaneous exposure with subsequent charging. Furthermore, to be more specific,
The maximum potential contrast at the first exposure position is aV,
The second exposure position is shifted along the drum path from the first exposure position.
Let by be the potential contrast when image exposure is performed at the exposure position. The surface potentials of the exposed and non-exposed parts of the photosensitive drum at the seventh exposure position are V'L and v'D, respectively, and the surface potential of the exposed part of the photosensitive drum at the ρth exposure position is V'L and v'D, respectively. 'L
If D and v'D, a:=v'DV'L+ b=:v'n V'LD l
a>b-(a-b)-■'L-v'LD<0.
b-v'D-V'■,D>0♂, set the developing bias to V
'LD or approximately equal to it, the surface potential of the portion of the photosensitive drum exposed to the laser beam at the first exposure position is:
It becomes a negative potential based on the above development bias,
The surface potential of the non-exposed area of the photosensitive drum was a positive potential, and by utilizing the fact that these surface potentials were of opposite polarity, three-color copying was possible.

FIG. 3 is a schematic diagram showing the charging state of each photosensitive drum in each step of the three-color electrophotographic apparatus shown in FIG.

/a is a conductive substrate, /b is a photoconductive layer, and here, for example, n-type CdS is used.

/C is an insulating layer, and - indicates a state where it is charged with positive and negative charges. This photosensitive drum / is 3
The area is divided into two areas, and the area indicates the area where the photosensitive drum/is exposed by the semiconductor laser 7 of FIG.
Area LD indicates an area where the photosensitive drum is exposed by the semiconductor laser B shown in FIG. 1, and area LD indicates an area where the photosensitive drum is not exposed.

FIG. 7 shows changes in surface potential of the photosensitive drum shown in FIG. 3 in each charging state. Here, VL is the third
The surface potential of the photosensitive drum / in the figure is shown, and VLD and VD respectively show the surface potential of the region LD and the surface potential of the region LD, respectively.

Further, (a) to (e) in the figure correspond to the charged states of the photosensitive drum shown in (a) to (e) of FIG. 3, respectively.

Next, the steps of the three-color electrophotographic method according to the present invention will be explained with reference to FIGS. The photosensitive drum / rotates in the direction of the arrow in the figure, and at the same time, a pre-static discharge exposure device (not shown) eliminates static electricity with a negative corona, and at the same time performs pre-exposure to erase residual charges on the surface of the photosensitive drum / and photoconductive. The internal resistance of the layer /b is lowered, and in the next seventh charging, the negative charge injection action from the conductive substrate /a is performed smoothly. Next, a positive corona discharge is performed by the seventh charger 2 to uniformly charge the surface of the photosensitive drum to a positive value, thereby securing the next potential. The charged state of this photosensitive drum is as shown in FIG. 3(a), as shown in FIG.
A positive charge is uniformly charged on the surface of the substrate, and a negative charge injected from the conductive substrate /a to the boundary between the insulating layer /C and the photoconductive layer /b corresponds to the positive charge. After being seventh-order charged, the photosensitive drum / is subjected to negative corona discharge by the secondary charger 3, and at the same time, it is simultaneously charged and exposed by the laser beam La from the semiconductor laser B via the beam scanning device q and the mirror /. box office. Furthermore, the photosensitive drum/
is simultaneously charged and exposed by a laser beam Lb from a semiconductor laser 7 via a beam scanning device j. After the photosensitive drum is subjected to imagewise exposure by these laser beams, it is further subjected to negative corona discharge by the secondary charger 3. At this time, the semiconductor lasers 7 are each modulated according to the image signal, and as mentioned above, the semiconductor laser 7 exposes the photosensitive drum / to positive light, and the semiconductor laser 7 exposes the photosensitive drum / to negative light. The beam scanning devices G and J scan the laser beam in the generatrix direction of the photosensitive drum, that is, in a direction parallel to the rotation axis of the photosensitive drum.

The charging state of the photosensitive drum during this secondary charging and simultaneous exposure is shown in FIGS. 3(b), 3(c), and 3(d). FIG. 3(b) shows the charged state of the photosensitive drum immediately before it is imagewise exposed by the semiconductor laser 7. Therefore, in this figure, although the region and LDTh are drawn side by side, the region is later than the LD in terms of time. In the area,
There is sufficient time from the start of secondary charging to the incidence of the laser beam, and the secondary charger 3 generates a sufficient negative corona discharge, so that most of the positive charges on the insulating layer /C are neutralized and erased. However, the remaining positive charges remain on the insulating layer /C. Furthermore, the negative charges at the boundary between the insulating layer /C and the photoconductive layer /b are retained as they are because the photoconductive layer /b has not yet been irradiated with light and the photoconductive layer /b is in an insulating state. A positive charge is induced from the conductive substrate /a in response to the charge needle of the negative charge other than the negative charge and the positive charge on the insulating layer /C, and this positive charge is It is held at the boundary between /a and photoconductive layer /b. The region LD is also subjected to negative corona discharge by the secondary charger 3, and a portion of the positive charge on the insulating layer/C is neutralized and erased. The amount of neutralization is smaller than that of the area because it is shorter than the time. Therefore, in the region LD, more positive charges remain on the insulating layer /C than in the region, and negative charges are retained at the boundary between the photoconductive layer /b and the insulating layer /C, and the conductive substrate /a and the photoconductive A positive charge is held at the boundary with layer /b. Area D
K will be explained later 〇 Figure 3 (c) shows the photosensitive drum when subjected to charging and simultaneous exposure.
It shows the charging state of . This figure also shows the area.

Although the LDs are shown side by side, the exposure of the area LD is earlier than the exposure of the other area in terms of time. Here, the area LD
, L are semiconductor lasers B in Fig. 1, respectively.

At the same time as being exposed to light by 7, it is also subjected to negative corona discharge from the secondary charger 3. At this time, the insulating layer /C and the photoconductive layer /b
Among the negative charges on the boundary between the semiconductor laser and the semiconductor laser,
When the resistivity of the photoconductive layer /b is reduced by exposure to the laser beam in step 7, it is attracted to the positive charges at the boundary between the conductive substrate /a and the photoconductive layer /b, and is neutralized and erased. The area will be described later.

FIG. 3(d) shows the charged state of the photosensitive drum after being further subjected to negative corona discharge by the tertiary charger 3 after exposure. The area is further subjected to negative corona discharge by the secondary charger 3, and negative charges are charged on the insulating layer 1C from which all positive charges have been erased. Area LD also has 2 more
In response to the negative corona discharge sound from the next charger 3VC, most of the positive charges on the insulating layer /C are neutralized and erased. A slight positive charge is charged on the insulating layer 1C, and light is emitted in response to the amount of negative charge other than the negative charge at the boundary between the insulating layer /C and the photoconductive layer /b, which is in balance with this charge. A positive charge is induced from the conductive substrate /a at the boundary between the conductive layer /b and the conductive substrate /a. As shown in FIG. 3(b), (c), and (d) in area DH, the secondary charger 3 generates a negative corona discharge on the photosensitive drum/, and the photosensitive drum/ is 7th charged on the insulating layer/C. The positive charges that were charged are neutralized and erased one after another over time. However, even after the static electricity removal by the secondary charger 3 is completed, a considerable amount of positive charge remains on the insulating layer /C. On the other hand, the negative charges at the boundary between the insulating layer /C and the photoconductive layer /b are not exposed and are therefore held as they are. Positive charges are induced from the conductive substrate /a in response to the amount of negative charges other than the negative charges that are in balance with the positive charges charged on the insulating layer 1C, and the conductive substrate /a It exists at the boundary with the photoconductive layer /b.

Therefore, the charged state of the surface of the photosensitive drum after the secondary charging is as shown in FIG. 3(d).

Next, the entire surface of the photosensitive drum is exposed to light by a full-surface exposure source to form an electrostatic latent image on the photosensitive drum. The charged state of the photosensitive drum at this time is shown in FIG. 3(e). Even if the entire area is exposed and the resistance of the photoconductive layer /b is reduced, the negative charge on the insulating layer /C remains unchanged. Insulating layer in regions LD and D/Insulating layer that is in electrical balance with the positive charge charged on C/
Excess negative charges other than the negative charges at the boundary between C and the photoconductive layer/b are exposed to light on the entire surface and the resistivity of the photoconductive layer/b is lowered. It is attracted to the positive charge at the boundary and is neutralized and erased. Therefore, after the entire surface is exposed, a negative charge in the area LKId is charged on the surface of the insulating layer/C, resulting in a negative surface potential as shown in FIG. In addition, a positive charge remains on the insulating layer/C in the area, and in balance, a negative charge is retained at the boundary between the insulating layer/C and the photoconductive layer/b. However, the influence of the potential of the positive charges on the insulating layer/C is strong, resulting in a positive surface potential ♂.

Electrostatic latent image FiA formed on the photosensitive drum after full exposure
It is developed using the negatively charged A color toner by the color developer /3, and the area of the photosensitive drum / is developed as an A color toner image, and then it is further developed into a positive color by the KB color developer /3. It is developed using charged B color toner, and the area around the photosensitive drum is visualized as a B color toner image.

Developing device/3. Since the developing bias of /g is set to 0, which is almost the same as the surface potential of the area LD, no toner is deposited on the area LD. The state of this developed photosensitive drum is shown in Figure 3 (
f) and (g). Furthermore, these A colors and 8
Color developer/3. The toner of the toner image on the photosensitive drum / developed and formed by /l is made to have the same polarity by a charger /j. Furthermore, the A and B color toners on the photosensitive drum are transferred from the cassette to the transfer material /2 which is sent out from the cassette by the pickup roller // and sent to the photosensitive drum through the roller 10 and the timing roller 9. The image is transferred. Transfer material 7 having this transferred image.
2 is separated from the photosensitive drum by an unillustrated separating means, conveyed by an unillustrated conveyor belt, and then fixed by an unillustrated fixing device to a transfer material 7.2 in which one color of A and B is transferred. A print image is formed. On the other hand, the photosensitive drum / which has completed the transfer process is cleaned by a cleaning device / 7 and moves on to the next operation. These operations enable two-color printing.

FIG. 9 shows the surface potentials of the regions LD, D, and VLI, VLDI, and VD rise to the positive side due to seventh-order charging. When the secondary charging and simultaneous exposure ends, v'L+
VLDI VD falls to the negative side. The charged state of the photosensitive drum, which has reached the most negative surface potential, is shown in FIG. 3(d). Here, the regions LD and D are the positive charges charged on the insulating layer/C.
The amount of negative charges held at the boundary between the photoconductive layer and the photoconductive layer/b is much larger, and this influence appears on the surface potential, so that the surface potential becomes negative. Furthermore, after full exposure, V
t does not change on the negative side, VLD is around 0 [v], and VD is reversed to the positive side. This is as described above, and preferably l, < tri VLD=C
VL+Vn)/,,? It is desirable that the developing bias be set approximately equal to VL, D, or VLD.

In the above embodiments, an apparatus using a conductor laser as the image exposure light source has been described, but the present invention is not limited to this, and the image exposure light source may be a gas laser or a light emitting diode. However, incoherent light may be guided onto the photosensitive drum using an optical fiber or the like. Furthermore, an AC static eliminator may be used as the secondary charger.

As described above, in accordance with the steps of the two-color electrophotographic method of the present invention, secondary During charging and simultaneous exposure, a two-color print image is obtained through a simple process of writing the photosensitive drum ζ image using two optical signals with different light incident positions, and the structure of the photosensitive body such as the photosensitive drum is also conventional. It is sufficient to improve only the light signal incidence position in the conventional electrophotographic equipment, which has the effect of providing a simple and highly reliable three-color electrophotographic method. It is.

[Brief explanation of drawings]

Fig. 1 is a schematic front view of a ρ-color electrophotographic apparatus for explaining the two-color electrophotographic method according to the present invention, and Fig. β shows the relationship between image exposure position and potential contrast during secondary charging simultaneous exposure. Explanatory diagram, Figure 3! FIG. 7 is a schematic diagram showing the charged state on the photosensitive drum during each step of the two-color electrophotographic method, and FIG. 7 is an explanatory diagram similarly showing changes in the surface potential on the photosensitive drum. /: Photosensitive drum, 2: / Wide charger 3:, Secondary charger G9.5: Beam scanning device B, 7: Semiconductor laser Z: Full-surface exposure source 2: Timing roller 7.2:
Transfer material/328 color developer/Dani B color developer/j
: Charger / B: Transfer charger / a a Conductive substrate / b Double photoconductive layer / c: Insulating layer L: (Exposed by the laser beam of the semiconductor laser 7) Area LD: (Laser beam of the semiconductor laser B) (exposed) area D: (unexposed) area Patent applicant Canon Corporation

Claims (1)

[Claims] A photoreceptor in which a photoconductive layer and an insulating layer are laminated in this order on a conductive substrate is seventh-order charged to a predetermined polarity, and then secondarily charged with alternating current or with a polarity opposite to the seventh-order charging,
At a first position within the effective charging area of the secondary charging, negative exposure is performed to irradiate light only to the portion to be imaged in the first color, and further within the effective charging area, the light is irradiated from the first position. At the second position, positive exposure is performed to irradiate light only to the areas that are not to be imaged in the second color, and then full-area exposure is performed to expose the electrostatic potential corresponding to the image to be imaged in the first color. and a second color to form electrostatic latent images corresponding to the image to be imaged, and then these electrostatic latent images are injected into toner of the first color and toner of the second color, each of which is charged with opposite polarity to each other. A two-color electrophotographic method characterized by visualization using colored toners.