JPH11219047A - Device and method for color marking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve image quality by improving transfer performance at a color marking device. SOLUTION: A pre-transfer part 35 including a pre-transfer electrifying device 40 arranged on the first side of a photoreceptor 10 and a pre-transfer erasing lamp 39 arranged on the second side of the photoreceptor 10 opposed to the first side is arranged at the color marking device 8, and the pre-transfer electrifying device 40 applies ion on an image area formed on the photoreceptor 10 and the pre-transfer erasing lamp 35 simultaneously irradiates the image area formed on the photoreceptor 10, so that the transfer performance at the color marking device 8 is improved and the image quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color marking apparatus and method for an electrophotographic color printer, a copying machine and the like.

[0002]

2. Description of the Related Art The electrophotographic marking method is a widely used and well-known document printing and copying method. Electrophotographic marking is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. The photoreceptor discharges in response to the light image, creating an electrostatic latent image of the desired document on the photoreceptor. Thereafter, a toner image is formed by attaching toner particles to the latent image. The toner image is then transferred from the photoreceptor to a substrate such as paper. The transferred toner image is then fixed to the substrate, typically using heat and / or pressure, to produce a copy of the desired image. Thereafter, the surface of the photoreceptor is cleaned and recharged in preparation for generating the next image.

The above description has been a general description of a black-and-white electrophotographic printing apparatus. The electrophotographic marking method repeats the above process for each color toner used to form a composite color image,
You can also create color images. That is, a permanent image can be obtained by adjusting the transfer positions of the respective color toners, stacking them, transferring them to the substrate, and fixing them so that a desired composite color image is obtained.

[0004] Color electrophotographic printing and copying can be implemented in a variety of forms. For example, in this application REaD IOI
In a process referred to as a (Recharge, Expose, and Develop, Image On Image) process, a charged light receiving surface is first exposed to a light image representing a first color, for example, black. next,
The resulting electrostatic latent image is developed with black toner particles to produce a black toner image. Then
The same image area with the black toner layer is recharged, exposed and developed to form a second color, eg, a yellow toner layer, followed by a third color, eg, magenta, and finally a fourth color. For example, a cyan toner layer is formed.
These various color toner layers are transferred to a substrate and fixed.

[0005] The REaD IOI process itself can be implemented in various ways. For example, in a single-pass printer, the final image is generated in one pass (of the photoreceptor). In another mode using a four-pass printer, a toner image of each color (one color) is formed in each pass, and the combined color image is transferred and fixed in a fourth pass. RE
aD IOI can also be implemented on a 5-cycle printer,
In this case, the point that only the toner image of each color (one color) is formed in each pass is the same as in the case of the four-pass printer, but the composite color image is transferred in the fifth pass.
Be established.

The printing speed of single-pass printing is high, but it is expensive because it requires four charging units and four exposing units. In the 4-pass print, the pass of the light receiving surface is 4
Printing is slower than in the case of single-pass printing, but the charging unit and the exposure unit are each one.
It is cheaper because only one is needed. Five-cycle printing requires a further five passes of the light receiving surface, so the printing speed is even lower. However, there is an advantage that multiple use of various process units (for example, a charging unit is used for transfer) can be performed.

As described above, in the REaD IOI process,
The photoreceptor is first charged for the first exposure and then recharged before each subsequent exposure. Recharging is relatively difficult in image areas having 0 to 3 toner layers. It is not easy to recharge an unknown amount of toner to a predetermined level and at the same time recharge a bare photoreceptor. However, efforts to recharge photoreceptors in the REaD IOI process have led to the development of several recharging schemes. Among them, one particularly useful method is a split recharging method. In the split recharging method, an image area and its toner layer are overcharged by a first charging section to a potential higher than that required at the time of subsequent exposure, while the overcharging is brought to an appropriate level by a second charging section. Neutralize.

[0008]

Disadvantageously, in a split recharging scheme, both positive and negative ions are applied to the photoreceptor. As a result, the photoreceptor has "wrong sign" toner particles (ie,
(A positively charged toner in the case of a negatively charged photoreceptor). It is difficult to transfer the wrong sign toner to the substrate. In order to improve this transfer effect, a pre-transfer charging unit (pr
etransfer charging station) is often used.
In the pre-transfer charging section, the wrong sign toner is positive sign (correct
sign) A "positive sign" ion is applied to the toner layer such that it is converted to toner (if a negatively charged photoreceptor is used, the positively charged toner particles are converted to negatively charged toner particles). Unfortunately, however, the application of this positive sign ion acts to overcharge some of the toner particles that already have a positive sign. It is difficult to transfer overcharged toner particles. This overcharging is most likely to occur with the toner particles closest to the photoreceptor.

Thus, it would be beneficial if techniques were developed to improve transfer in the REaD IOI process.

[0010]

SUMMARY OF THE INVENTION The present invention provides a technique useful for improving toner transfer in a REaD IOI printing process. In accordance with the principles of the present invention, a charge is provided to the photoreceptor by a transfer front for transfer. The transfer front includes a charging section that applies ions to the toner layer on the photoreceptor so that "false sign" toner is substantially converted to "positive sign" toner. The pre-transfer portion further includes a pre-transfer erase lamp that simultaneously exposes the photoreceptor to maintain photoreceptor conductivity during the pre-transfer charging process. The charging current increases due to the increase in the current drain flowing through the photoreceptor, which is kept conductive, and the charge accumulation near the photoreceptor surface (built-in)
dup) can be prevented. In this way, the incorrectly signed toner at the top of the toner layer is more efficiently converted, while the toner at the bottom is not overcharged. The pre-transfer charging is preferably performed using a DC charging device. Preferably, the pre-transfer charging is performed using a DC charging device that generates a charge of about 30 microamps or more.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an electrophotographic printing apparatus 8 according to an embodiment of the present invention includes a transfer front portion. The toner on the image area is charged to convert it to toner particles while simultaneously exposing the image area to prevent excessive charge accumulation of the toner particles, especially on the toner particles closest to the photoreceptor.

The printing device 8 has an active matrix (AMAT) photoreceptor belt 10 that moves in the direction indicated by arrow 12. The movement of the belt is caused by stretching the photoreceptor belt around a driving roller 14 (driven by a motor not shown) and tension rollers 15 and 16.

As the photoreceptor belt moves, each part passes through each process part described later. For convenience of explanation, a part of the photoreceptor belt called an image area will be described. The image area is that portion of the photoreceptor belt that receives the various toner layers that are transferred and fixed to the substrate to produce the final color image. Although the photoreceptor belt can have multiple image areas, each of those image areas is processed in a similar manner, so the operation of the printing apparatus is sufficiently clear to explain the processing of one image area.

The printing device 8 is a four-cycle device.
That is, the printing device 8 generates a final image by causing the image area to pass through four cycles or four passes in the device. However, it is self-evident that the invention is not limited to a four-cycle device. The invention is also useful in other REaD IOI printing devices, including single pass and five cycle devices.

The first cycle begins with the image area passing through a "precharge" erase lamp 18 which illuminates the image area to discharge any residual charge that may be present in the image area. Such erase lamps are commonly used in high quality systems, and their use for initial erase is well known.

As the photoreceptor belt continues to move, the image area becomes a DC scorotron.
0 and an AC scorotron 22. In preparation for exposure to produce a latent image for black toner, a DC scorotron may be used to reduce the image area to, for example, about -500.
It is charged to a substantially uniform potential of volts. During this initial charging, there is no need to use an AC scorotron. However, by using both a DC scorotron and an AC scorotron, better charging uniformity is usually obtained.
Here, the actual charge charged to the photoreceptor for the first (black) toner depends on the desired toner amount and the first charge.
It will be appreciated that it depends on a number of variables, such as the setting of the (black) developer section (see below).

After passing through the charging section, the image area is
Move further until you reach 4. In the exposure section, the charged image area is exposed by a modulated laser beam 26 that raster scans the image area so that an electrostatic latent image representation of a black image is generated. For example, the illuminated portion of the image area is discharged by beam 26 to about -50 volts.
Thus, after exposure, the image area has a voltage profile consisting of a relatively high voltage area of about -500 volts and a relatively low voltage area of about -50 volts. Here, it will be understood that the exposure unit may use a light emitting printbar.

After passing through the exposure section 24, the exposed image area moves to a black developing section 28 where negatively charged black toner particles adhere to the image area. The charged black toner adheres to the illuminated portion of the image area, causing the illuminated portion of the image area to have a voltage of about -200 volts. The unlit portion of the image area is kept at -500 volts. In this example, development called discharge area development is performed. However, the principle of the present invention is that
The same applies to the case where the charged area development is performed.

The black developing unit 28 may use a magnetic brush developing device, but is not a scavengeless one.
Somewhat better results are obtained with the die development device. An advantage of scavengeless development is that previously deposited toner layers are not disturbed. During the first cycle, the use of scavengeless development is not always necessary as long as the image area has no toner layer from the previous development and this development part (device) is physically separated from other cycles. That is not to say. However, since the other developing sections (described below) use scavengeless development, it is desirable to use a scavengeless development method for each developing section.

After passing through the black development station, the image area passes through several other processing stations (the purpose of which will be described later) and returns to the unlit pre-charge erase lamp 18. Then, the second cycle starts.

After passing through the pre-charging erase lamp 18, the image area advances to the charging section. Then, the DC scorotron 20 and the AC scorotron 22 recharge the image area and its black toner layer by using a divided recharging method. Briefly, the DC scorotron 20 overcharges the image area to a voltage level higher than desired when the image area is recharged, while the AC scorotron applies positive ions to the image area. To lower the voltage level to a desired level. The split recharging almost eliminates the voltage difference between the toner-adhered portion and the toner-non-adhered portion. This is beneficial for subsequent development with different toners.

However, split recharging results in a large amount of "false signature" toner particles, ie, toner particles having incorrect charge polarity. In the printing device 8, the "false sign" toner particles are positively charged because the image area is negative. As a result, the photoreceptor and its black toner layer are charged to the correct potential by divisional recharging, but the charges on the individual toner particles differ greatly. Especially,
False sign toners are most likely to occur above the toner layer.

The image area recharged with the black toner layer then proceeds to the exposure station 24. The exposure unit beam-images the image area to produce an electrostatic latent image representation of the yellow image.
Exposure. For example, the non-illuminated portion of the image area is about -45
The illuminated part can be about -5, while it can have a potential of 0 volts.
Discharged to 0 volts.

After passing through the exposure section 24, the image area that has been exposed this time moves to a yellow developing section 30 where yellow toner is attached to the image area. In the image area, there is already a black toner layer, and it is desirable to use a scavengeless image device for the yellow developing section.

After passing through the yellow developing section, the image area and its two toner layers advance to the charging section through an unlit pre-charging exposure lamp 18. Then, the third cycle starts.

Here, again, the DC scorotron 20 and the AC scorotron 22 recharge the image area and its (two) toner layers. Next, the image area is again exposed to the exposure unit 24.
Proceed to. The exposure unit again exposes the image area with the beam 26, using an optical image representation that discharges a portion of the image area to produce an electrostatic latent image representation of the magenta image.
The image area then proceeds to the magenta developing section 32. The magenta developing unit, which is preferably a scavengeless type developing device, attaches magenta toner to an image area. As a result, a third toner layer is formed on the image area.

Next, the image area together with the three toner layers passes through the pre-charging erase lamp to the charging section, and the fourth cycle starts. In the charging section, the DC scorotron 20 and the AC scorotron 22 again charge the image area (having three toner layers in this case) by split recharging, and generate a desired charge on the photoreceptor. Next, the image area charged substantially uniformly with the three toner layers advances to the exposure unit 24 again. The exposure unit re-exposes the image area, but this time uses a light image representation that discharges a portion of the image area to generate an electrostatic latent image representation of the cyan image. After passing through the exposure section, the image area proceeds to the cyan developing section 34. The cyan developing unit is a scavengeless developing device, and applies cyan toner to an image area.

After passing through the cyan developing section, the image area becomes 4
It has two toner layers, which together form a composite color toner image. The composite color toner image is composed of individual toner particles having greatly different charging potentials. As described above, some of the toner particles have a wrong sign (positive polarity). Transferring such a synthetic toner image to a substrate may degrade the quality of the final image.

In order to adjust the transfer of the composite color toner image, the printing device 8 is provided with a transfer front portion 35. The pre-transfer portion includes a pre-transfer erase lamp 39 inside the photoreceptor belt 10 and a charging device 40 outside the belt. As shown, the charging device and the pre-transfer erase lamp are arranged close to each other. The operation of the pre-transfer portion will be described. As the synthetic toner image advances in the pre-transfer portion 35, the pre-transfer erasing lamp irradiates the image area (and the toner layer) from the back side, and at the same time, the charging device 40 has the positive sign. Apply (negative) ions to the front. As a result, the current drain flowing through the conductive photoreceptor increases, and the charging current increases. This is done in the vicinity of the photoreceptor belt so as to invert almost all of the "false sign" toner particles to positive sign toner particles, while preventing the toner particles closest to the photoreceptor from receiving a charge high enough to make transfer difficult. This has the effect of preventing charge accumulation.

In practice, it is somewhat preferable to use a DC charger as the charging device 40 rather than an AC charger. This is because the DC charger tends to generate less ozone than the AC charger, and the AC charger tends to overcharge the lowermost toner as compared to the DC charger. However, experiments have shown that if the DC charging current is less than about 30 microamps, there may be a problem of charge non-uniformity between the toned and untoned areas of the image area. I have. Therefore, it may be necessary to experimentally determine an appropriate charging current for a given application or a given pre-transfer exposure lamp.

As shown in FIG. 1, arranging the pre-transfer erasing lamp and the charging device 40 so as to face each other is more valuable than the pre-transfer portion using other erasing / charging combinations. This is advantageous in that space is saved.

After passing through the pre-transfer section 35, the image area continues to advance in the direction of arrow 12 through the rollers 14. Next, the base material 41 is set above the image area using a sheet feeder (not shown). The image area and the substrate continue to move and pass through a transfer corotron 42. This corotron applies positive ions to the back side of the substrate 41.
These ions attract negatively charged toner particles to the substrate.

As the substrate continues to move, it passes through the detack corotron 43. This corotron neutralizes a part of the electric charge on the substrate, and the photoreceptor 1
Facilitates separation of the substrate from zero. As the leading edge of the substrate moves near the tension roller 16, the leading edge is separated from the photoreceptor. The base material is the fixing roller 46.
And a pressure roller 48 toward a fixing portion where a nip passing through the base material 41 is formed. The combination of pressure and heat at the nip fixes the composite color toner image to the substrate. After fixing, the substrate is a chute (not shown)
Is guided to a catch tray (not shown), and is taken out by an operator.

After the substrate has been separated from photoreceptor belt 10, the image area continues to move and passes through pre-clean erase lamp 50. The erase lamp neutralizes most of the charge remaining on the photoreceptor belt. After passing through the preclean erasing lamp, residual toner and / or other residue on the photoreceptor is removed by the cleaning unit 5.
2 to be removed. In the cleaning section, a cleaning blade sweeps residual toner particles from the image area. This completes the fourth cycle. afterwards,
The image area again proceeds to the pre-charge erase lamp and moves to the start of the next four cycles.

The various device functions described above are generally managed and controlled by a controller that supplies electrical command signals for controlling the above operations, using known techniques.

[0036]

According to the present invention, the transfer performance in a color electrophotographic printer or a copying machine is improved, and the image quality of a print or copy is improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an electrophotographic printing apparatus implementing the principle of the present invention.

 ──────────────────────────────────────────────────続 き Continued from the front page (72) James R. Inventor. Beechner United States 14580 New York Webster Independence Drive 864

Claims (3)

[Claims] 1. A photoreceptor having a charged image area including a synthetic toner layer, the synthetic toner layer including toner particles having oppositely charged charges, and a photoreceptor transferred to a first side of the photoreceptor. A pre-transfer unit having a pre-charging device and a pre-transfer erasing lamp disposed on the second side of the photoreceptor opposite to the pre-transfer charging device, wherein the pre-transfer charging device is configured to charge the toner particles. A pre-transfer unit, wherein ions are applied to the synthetic toner layer so as to have the same polarity, and at the same time, the pre-transfer erase lamp illuminates the image area to lower the potential on the photoreceptor. . 2. A charging device comprising: a moving photoreceptor having an image area including a first toner layer; and a DC charging device for charging the image area and the first toner layer to a potential higher than a predetermined potential. A charging unit further comprising an AC charging device for lowering a potential between the image area and the first toner layer to the predetermined potential, and an exposure unit for exposing the image area to generate a latent image A developing unit for adhering a second charged toner layer on the latent image; and a pre-transfer charging device on a first side of the photoreceptor;
A pre-transfer portion having a pre-transfer erase lamp disposed on the second side of the photoreceptor in opposition to the pre-transfer charging device;
The pre-transfer charger applies ions to the toner layer so that the charge on the toner layer is of the same polarity, while the pre-transfer erase lamp illuminates the image area to lower the potential on the photoreceptor. A color marking device comprising: a transfer front part; 3. An adjustment method for transferring a composite toner image containing erroneous sign toner particles to a substrate, wherein the ion having a polarity such that the composite toner image is converted from erroneous sign toner particles to positive sign toner particles. And simultaneously irradiating the photoreceptor to reduce charge build-up near the bottom of the composite toner image.