JPS61277979A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent much toner from sticking in no-image area during positive image formation by setting the DC component of the developing bias of no-image areas larger in absolute value than a development start voltage during positive image formation and lower in absolute value during negative image formation. CONSTITUTION:When a positive image is formed, no-image areas (h) and (k) are areas where pirmary electrostatic charging is not performed and at about 0V and no-image areas (i) and (j) ar applied with a DC voltage of -950V as a developing bias although the photosensitive potential is still at -800V. Therefore, the potential contrast between no-image areas of a photosensitive body and the developing bias is -150V and neither a normal phenomenon nor a reverse fogging phenomenon occurs. When a negative image is formed, a DC voltage of -650V is applied in the no-image areas (i) and (j) as the developing bais and the potential contrast between the photosensitive body potential in the no-image area and the developing bias is +150V, so that no toner sticks. Thus, the absolute value is set larger than the development start voltage during the positive image formation and smaller than the development start voltage during the negative image formation. Consequently, excellent images are obtained without consuming unnecessary toner nor causing contamination, etc., in the device.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image forming apparatus, particularly a microreader printer that selectively uses two types of toner with different charging polarities to form a negative image or a positive image; It relates to image forming devices such as laser beam printers and copying machines.

(Prior Art) Conventionally, in microreader printers, laser beam printers, etc. that obtain negative images using toner with the same polarity as the charged polarity of the photoreceptor, exposure means is used to irradiate non-image areas with exposure light for charge erasing. There are photoreceptor potentials (high potential) in non-image areas that exist before and after one image area.
is retained as is. As the developing bias, a DC component whose absolute value is substantially smaller than the potential of the non-image area is applied, so that the non-image area is not developed.

(Problem to be Solved by the Invention) However, in the case of such conventional technology, the non-image area of the photoreceptor is held at a high potential, and the DC component whose absolute value is approximately smaller than the potential of the non-image area. A developing bias of is applied. Therefore, when regular development is performed using toner with a polarity opposite to that of the photoconductor to obtain a positive image, the non-image area is developed because it has a higher potential than the development bias, and a large amount of toner is used. There was a problem in that it adhered to the surface of the photoreceptor.

Therefore, a large amount of unnecessary toner adheres to the photoconductor, which not only increases toner consumption, but also causes the toner adhered to the photoconductor to scatter into the device, accumulate on the transfer guide, etc., or be deposited on the transfer material. This has caused a problem in that it adheres and causes stains on the image. Furthermore, there is a problem in that the transfer charger is contaminated, causing charging unevenness, which appears as image unevenness.

The present invention has been made to solve the problems of the prior art described above, and its purpose is to prevent a large amount of toner from adhering to non-image areas during positive image formation, and to remove unnecessary toner. It is an object of the present invention to provide an image forming apparatus that can obtain good images by preventing consumption and staining of the inside of the apparatus.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses two types of materials with different charge polarities to form a positive image or a negative image. An image forming apparatus that selectively performs image forming, which has a developing bias applying means for applying a developing bias, and does not have a charge erasing exposure means that irradiates charge erasing exposure to a non-image area of a photoreceptor. In.

The device is configured to include means for setting the DC component of the developing bias in the non-image area to a larger absolute value than the developing start voltage when forming a positive image, and to a smaller absolute value than the developing starting voltage when forming a negative image. has been done.

(Example) The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a schematic diagram of a microreader printer to which the present invention is applied. 1 is a microfilm, this microfilm 1 is illuminated by a film illumination light source 2, and image light is transmitted through a projection lens 3.l. plane mirrors 4 and 5;
The photoreceptor drum 7 is exposed through the slit 6. The plane mirrors 4.5 are arranged to face each other at right angles so as to move rightward in the figure at a speed equal to the circumferential speed of the photoreceptor drum 7.

8 is a cartridge of an image forming means;
The photoreceptor drum 7, which is negatively charged, the negative charger 9, the developer 10, and the cleaner 11 are integrally attached to the apparatus, and are removably incorporated into the main body of the apparatus.

In the developing device 10, the toner 12 is transferred to the doctor blade 1.
3, the developing sleeve 14 is thinly coated,
The developing sleeve 14 faces the photosensitive drum 7 with a small gap therebetween. Note that the negative image forming cartridge 8
The developing device 10 of the positive image forming cartridge 8 is filled with toner 12 that is charged to a negative polarity, and the developing device 10 of the positive image forming cartridge 8 is filled with another toner 12 that is charged to a positive polarity.

Further, a pre-exposure lamp 15 is provided above the cartridge 8.
A transfer charger 16 is also arranged below the cartridge 8 . Note that a charge erasing light source for illuminating the non-image area of the photoreceptor is not provided.

Therefore, the surface of the photoreceptor drum 7 is exposed to the pre-exposure lamp 15.
After the charge is uniformly removed through the slit 17, it is primarily charged to approximately -800 cm by the single charger 9. Next, an electrostatic latent image of the image area is formed on the photoreceptor drum 7 by the above-described exposure process. Here, the potential of the non-image area of the photoreceptor drum 7 is equal to 80% when forming a positive image and when forming a negative image, since the charge erasing exposure is not irradiated.
It is maintained at 0V.

Developing sleeve 14 and doctor blade 13 of developing device 10
is connected to a developing bias in which a DC voltage (described later) is superimposed on an AC voltage, and the DC component of the developing bias can be switched between the image area and the non-image area, or even when forming a negative image in the non-image area and when forming a positive image. Switching from the time of formation is performed. As a result, only the electrostatic latent image in the image area is developed, and the developed toner image is controlled by a changeover switch (not shown), with a negative polarity voltage when forming a positive image and a positive polarity voltage when forming a negative image. The image is transferred onto the transfer paper 18 by the transfer charger 16 that applies the voltage. This transfer paper 18 is transferred to a fixing device (
(not shown) and then discharged. The toner 12 remaining on the photoreceptor drum 7 is removed by a cleaner 11, and then the residual charge on the photoreceptor drum 7 is evenly removed by the irradiation light from the pre-exposure lamp 15.

Figure 2 shows the relationship between the amount of toner adhering to the photosensitive drum and the potential contrast (the difference between the absolute value of the potential of the photosensitive drum and the absolute value of the DC component of the developing bias). This figure schematically shows the toner (used in image formation) and the positive toner (that is, the toner used in positive image formation), in which the solid line indicates the positive toner and the dotted line indicates the negative toner. In the following description, both the photoreceptor potential and the DC component of the developing bias have negative polarity, and the magnitudes indicate absolute values.

As can be seen from the figure, in the case of positive toner, normal development is performed in region a where the photoreceptor potential is higher than the DC component of the developing bias, and the amount of toner adhesion increases rapidly as the potential contrast increases. Further, in a region C where the photoreceptor potential is approximately -300 V or more lower than the DC component of the developing bias, a reverse fog phenomenon occurs and some toner adhesion occurs.

Here, the reversal fog phenomenon refers to the phenomenon that when forming a positive image using a positive toner with a polarity opposite to that of the photoreceptor, the developing bias is higher than the photoreceptor's potential and development should not occur, but if the potential contrast becomes extremely large, This is a phenomenon in which toners of opposite polarity contained in toner are developed.

A similar phenomenon occurs in negative image formation when the photoreceptor potential becomes much greater than the development bias.

Therefore, an area where toner does not adhere is an area where the DC component of the developing bias is 0 to 300 V higher than the photoreceptor potential, that is, an area where the absolute value is larger than the development start potential and smaller than the reverse fog start potential. . Here, the development start potential is the boundary between area a and area A, that is, the photoconductor potential, and the one-inversion fog start voltage is approximately 300 V higher than the boundary of area C, that is, the photoconductor potential.

Similarly, in the case of negative toner, in the area a' where the photoreceptor potential is lower than the DC component of the developing bias, toner adhesion increases as the potential contrast decreases due to regular development, and the photoreceptor potential is approximately 300 V lower than the DC component of the developing bias. In the higher region C', some toner adhesion occurs due to the reverse fog phenomenon. Therefore, the area b' where toner does not adhere is an area where the DC component of the developing bias is 0 to 300 V lower than the photoconductor potential, that is, an area where the absolute value is smaller than the development start potential and larger than the reverse fog start potential. It is.

Here, the development start potential is the boundary between area a' and area b', that is, the photoreceptor potential, and the 1-inversion fog starting position is area b'.
The potential is approximately 300 V lower than the boundary between the region C' and the photoreceptor potential.

Note that the development start potential and the reverse fog start potential differ depending on the toner formulation, type, development method, etc., and are not limited to the above-mentioned values.

FIG. 3 shows a first embodiment of the developing bias setting means of the apparatus according to the present invention, in which an alternating current voltage 19 and a direct current voltage are superimposed on the developing sleeve 14 and the doctor blade 13 of the developing device 10. In one image area, the switch S1 is switched to contact d, and a DC voltage 20 is applied, which can be adjusted to a desired voltage using a volume control to obtain a proper image.

In the non-image area, the switch S1 is switched to the contact point e, and when a positive image is formed, the switch S2 is switched to the contact point f, and a predetermined developing bias 21 (-950V) is applied. Further, when forming a negative image, the switch S2 is switched to contact g to apply a predetermined developing bias 22 (-650V).

FIG. 4 shows the correspondence between the photoreceptor potential behavior in one cycle during positive image formation and the DC component of the developing bias in the first embodiment, where the solid line is the photoreceptor potential and the dotted line is the developing bias. A desired developing bias is applied to VD and Vf of the 0 image area shown in order to obtain a proper image at the image part potential and background part potential, respectively. In addition, the non-image area and k are approximately OV in the area where no primary charge is applied,
Since the non-image areas i and j are not irradiated with the charge erasing exposure light, the photoreceptor potential remains at -aoov, while the developing bias is such that a DC voltage of -950V is applied to the non-image areas i and j. Ru. Therefore, the potential contrast between the non-image area of the photoreceptor and the developing bias was -150 V, and as is clear from FIG. 2, neither normal development nor reverse fogging occurred.

FIG. 5 shows the correspondence between the photoconductor potential behavior in one cycle during negative image formation and the DC component of the developing bias in the above embodiment, where the solid line indicates the photoconductor potential and the dotted line indicates the developing bias. A desired developing bias is applied to VD and vL of the 0 image area to obtain a proper image at the background potential and the image potential, respectively. In addition, non-image areas i and k are approximately Ov because no primary charge is applied, and non-image areas i and j are not irradiated with charge erasing exposure light, so the photoreceptor potential remains at 1800V. On the other hand, as the developing bias, a DC voltage of -650V is applied to the non-image areas i and j. Therefore, the potential contrast between the photoreceptor potential and the developing bias in the non-image area is +150V,
As is clear from FIG. 2, no toner adhesion occurred.

In the above embodiment, a case was explained in which the developing bias of the non-image area was switched between when forming a positive image and when forming a negative image. This was done to avoid overlapping areas that do not exist. However, the development start voltage and the reverse fog start voltage differ depending on the toner characteristics or charging settings, and in some cases, areas where toner does not adhere may overlap. At that time, it is not necessarily necessary to switch the developing bias according to the image forming mode.

FIG. 6 shows a second embodiment of the developing bias setting means of the apparatus according to the present invention.In this embodiment, the power supply voltage is not set according to the developing bias, but one power supply voltage 23 is set. By using the resistors R1, R2, and R3 to set the DC component of each developing bias.

In the illustrated embodiment, the present invention is applied to a microreader printer, but of course it can also be applied to a laser beam printer, a copying machine, or the like.

In addition, in the above explanation, the DC component of the developing bias
Although we have explained the case where - is set to a predetermined value in advance, the potential of the photoconductor is detected and the DC component of the developing bias is adjusted according to the potential of the photoconductor.
- may be controlled so that the potential contrast remains constant. In such a case, even if the potential of the photoreceptor varies, it is possible to reliably prevent toner from adhering to the non-image area.

Note that it can also be applied to a case where the developing bias consists of only a DC voltage.

(Effects of the Invention) The present invention has the above configuration and operation, and the DC component of the developing bias in the non-image area is made larger in absolute value than the development start voltage when forming a positive image, and when forming a negative image. ,
Since the absolute value is set smaller than the development start voltage, in an image forming apparatus that does not irradiate charge erasing exposure to the non-image area of the photoreceptor, both when forming a positive image and when forming a negative image, the non-image area of the photoreceptor is It is possible to prevent a large amount of toner from adhering to the area, and it is possible to obtain a good image without unnecessary consumption of toner or staining of the inside of the device.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a microreader printer as an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a graph showing the relationship between potential contrast and toner adhesion amount.
FIG. 3 is a schematic diagram showing a first embodiment of the means for setting the developing bias, and FIGS. 4 and 5 show the relationship between the photoreceptor potential and the developing bias during positive image formation and negative image formation in the same embodiment. Graphs showing the relationships, and FIG. 6 are schematic diagrams showing a second embodiment of the developing bias setting means. Explanation of symbols 10...Developer 13...Doctor blade 14...Developing sleeve 20.21.22...DC voltage of developing bias

Claims (2)

[Claims] (1) An image forming apparatus that selectively forms a positive image or a negative image using two types of toner with different charging polarities, and includes a developing bias applying means for applying a developing bias. In an image forming apparatus that does not have a charge erasing exposure unit that irradiates charge erasing exposure onto the non-image area of the photoreceptor, the DC component of the developing bias in the non-image area is set to the development start voltage when forming a positive image. 1. An image forming apparatus comprising means for setting an absolute value larger than a development start voltage, and setting the absolute value smaller than a development start voltage when forming a negative image. (2) The DC component of the developing bias in the non-image area has a smaller absolute value than the reverse fog start voltage when forming a positive image, and a larger absolute value than the reverse fog start voltage when forming a negative image. The image forming apparatus according to claim 1, characterized in that the image forming apparatus controls the image forming apparatus.