JPS61277978A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent much toner from sticking in no-image areas by setting the DC component of the developing bias in no-image areas so that the DC components has the same polarity with the potential of a photosensitive body and is smaller in absolute value than a development start voltage during negative-positive image formation and also has the same potential with the photosensitive body potential and is larger in absolute value than the development start voltage during positive-positive image formation. CONSTITUTION:When positive toner is used, normal development is performed in an area (a) where the absolute value of the photosensitive body potential is larger than that of the DC component of the developing bias, and reverse fogging occurs in an area (c) where the photosensitive body potential is about >=-300V lower than the DC component of the developing bias to cause a little toner to stick. The development start potential is as high as the boundary between the areas (a) and (b), i.e. the photosensitive body potential and a reverse fogging start potential is as high as the boundary between the areas (b) and (c), i.e. about 300V higher than the photosensitive body potential. Similarly, when negative toner is used, the development start potential is as high as the boundary between areas a' and a', i.e. the photosensitive body potential and the reverse fogging start potential is as high as the boundary between areas b' and c', i.e. about 300V lower than the photosensitive body potential. 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, and particularly to a method for forming a positive image from a negative original image (hereinafter referred to as negative-positive image formation) or from a positive original image to a positive image. The present invention relates to an image forming apparatus such as a microreader printer that selectively performs image formation in the form of J& (hereinafter referred to as positive-positive image formation).

(Prior art) Conventionally, in the above-mentioned microreader printers, etc.
The relationship between the potential of the photoreceptor and the developing bias in the non-image area is as shown below. That is, when forming a positive image, as shown in FIG.
Since charge erasing exposure is applied to 1 and m, the photoreceptor potential (real & i) of these non-image areas 1 and 'rn is a low potential (
For example, -50V), and the developing bias (
(dashed line) is applied only to the image area, and is applied only to the non-image area 1. m
In this case, the developing bias is turned off.

On the other hand, during negative-positive image formation, as shown in FIG. 9, since the non-image area 9 m is not irradiated with the charge erasing exposure light, the non-image area 1. The photoreceptor potential (solid line) of m is a high potential (for example -aoov), and the developing bias (
(dashed line) is applied only to the image area, and is applied only to the non-image area 1. m
In this case, the developing bias is turned off. In Figure 8, VD
In FIG. 9, ``■'' represents the image area potential, VD represents the background area potential, and VL represents the image area potential.

(Problem to be Solved by the Invention) However, in the case of such prior art, when forming a positive image in which a positive toner with a polarity opposite to that of the photoconductor is used for development, the non-image area of the photoconductor has a low potential. However, despite being negatively charged, since no developing bias is applied, there is a problem in that the torch is attracted to the non-image area of the photoreceptor and adheres in large quantities. Furthermore, when forming a negative-positive image in which a negative toner with the same polarity as the charged polarity of the photoconductor is used for development, the non-image area of the photoconductor is at a high potential, but since no developing bias is applied, the non-image area The difference between the potential of the area and the potential of the developing bias becomes very large, causing a so-called reverse fog phenomenon in which toner of the opposite polarity (in this case, positive) contained in the toner adheres to the non-image area, albeit in a small amount. There was a problem.

Therefore, when forming a positive image, a large amount of unnecessary toner adheres to the photoreceptor, which not only increases toner consumption, but also causes the toner adhered to the photoreceptor to scatter into the device and accumulate on the transfer guide, etc. This has caused a problem in that it adheres to the transfer material 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. Further, there is a problem in that toner adheres to the photoreceptor even when forming a negative-positive image, albeit in a small amount.

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-positive image formation. Furthermore, in a preferred embodiment, by making it possible to prevent toner adhesion due to reversal gobble during negative-positive image formation, unnecessary consumption of toner and staining of the inside of the device can be prevented, and good images can be obtained. An object of the present invention is to provide an image forming apparatus that has the following features.

(Means for Solving the Problems) In order to achieve the above object, the present invention changes the DC component of the developing bias in the non-image area to
It is provided with a setting means that has the same polarity as the photoreceptor potential and a smaller absolute value than the development start voltage, and when forming a positive image, sets an absolute value that has the same polarity as the photoreceptor potential and is larger than the development start voltage. It is composed of

(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 one image light is transmitted to a projection lens 3. The photoreceptor drum 7 is exposed through the plane mirrors 4 and 5 and the slit 6. The plane mirrors 4.5 are arranged to face each other at a constant interval at right angles so that they move rightward in the figure at a speed equal to the circumferential speed of the photoreceptor drum 7.

Reference numeral 8 denotes an image forming cartridge, and the cartridge 8 includes the photosensitive drum 7, which is negatively charged, and a charger 9.
, a developing device 10 and a cleaner 11 are integrally attached and removably incorporated into the main body of the apparatus. In the developing device 10, the toner 12 is thinly coated on the developing sleeve 14 by the doctor blade 13, and the developing sleeve 14 faces the photosensitive drum 7 with a small gap therebetween. Note that the developing device 10 of the negative-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-positive image forming cartridge 8 is filled with a different toner 12 that is charged to a positive polarity. There is.

Further, above the cartridge 8, a pre-exposure lamp 1 is provided.
5, a slit 16, a first shutter 17, and a second shutter 18 are arranged, and a transfer charger 19 is arranged below the cartridge 8. The second shutter 18 is configured to open and close around a shaft 18a, and the photosensitive drum surface side of the second shutter 18 receives irradiation light (exposure for charge erasing) from the pre-exposure lamp 15. , and serves as a reflective surface for guiding the light onto the photosensitive drum 7 through the pickpocket 7) 16. The opening/closing operation of the second shutter 18 is such that it maintains the closed state 18' in the non-image area (other than the image area) to block image exposure, and maintains the open state 18'' in the image area to prevent image exposure. It irradiates the photosensitive drum 7. Also, the first shutter 1
7 is arranged to be slidable in the vertical direction, and when forming a positive-positive image, the shutter 17 is lowered to irradiate exposure for erasing charges, and when forming a negative-positive image, the shutter 17 is raised to block the exposure for erasing charges. Therefore, the first and second shutters 17 and 18 irradiate the non-image area with charge erasing exposure light when forming a positive image, and block the charge erasing exposure light when forming a negative-positive image.

Thus, one surface of the photoreceptor drum 7 has a pre-exposure lamp 15.
After the static electricity is uniformly removed through the slit 20, the zero-order is primarily charged to approximately -800V by the negative charger 9.
Through the above-described exposure process, the non-image area of the photosensitive drum 7 is exposed and an electrostatic latent image is formed in the image area. Here, the potential of the non-image area of the photoreceptor drum 7 is attenuated to approximately -50V because the above-mentioned charge erasing exposure is applied when forming a positive image, and when forming a negative-positive image, the potential of the non-image area is attenuated to approximately -50V. Since the exposure is blocked, -ao
It remains as ov.

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 an image area and a non-image area, or when forming a negative-positive image in a non-image area. Switching is performed during positive-positive image formation. As a result, only the electrostatic latent image in the image area is developed, and when forming a negative-positive image, a positive polarity voltage is applied to the developed toner image by a changeover switch (not shown).
When forming a positive image, the image is transferred onto the transfer paper 21 by the transfer charger 19 to which a voltage of negative polarity is applied. The toner image transferred to this transfer paper 21 is transferred to a fixing device (not shown).
established by The toner 12 remaining on the photosensitive drum 7 is removed by a cleaner 11, and then the charge is evenly removed by a pre-exposure lamp 15.

FIG. 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) using the negative toner used in the present invention (i.e. This figure schematically shows the toner (used when forming a negative-positive image) and the positive toner (that is, the toner used when forming a positive-positive image), in which the solid line indicates the positive toner and the dotted line indicates the negative toner.

As shown in the figure, in the case of positive toner, normal development occurs in region a where the absolute value of the photoconductor potential is greater than the absolute value of the DC component of the developing bias, and the amount of toner adhesion increases rapidly as the potential contrast increases. do. 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 a small amount of toner adheres to the photoreceptor. Therefore, in an area without toner adhesion, the difference between the photoconductor potential and the DC component of the developing bias is 0 to -300V.
was the area of Here, the development start potential is the boundary between area A and area A, that is, the photoreceptor potential, and the inverted capri start potential is approximately 3.3 degrees lower than the boundary of area C, that is, the photoreceptor potential.
00V high potential.

Similarly, in the case of negative toner, in a region a' where the absolute value of the photoconductor potential is smaller than the absolute value of the DC component of the developing bias, toner adhesion increases as the potential contrast decreases due to regular development, and the photoconductor potential decreases due to development. In the region C' which is approximately 300 V or more higher than the DC component of the bias, some toner adhesion occurs due to the reverse fog phenomenon. Therefore, in the area b' where no toner adhered, the difference between the photoreceptor potential and the DC component of the developing bias was 0 to 300V. Here, the development start potential is the boundary between area a' and area b', that is, the photoreceptor potential, and the inversion fog start potential is approximately 300 V lower than the boundary between area b' and area C', that is, the photoreceptor potential.

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 22 and a direct current voltage are applied in a superimposed manner to the developing sleeve 14 and the doctor blade 13 of the developing device 10. Sl is a changeover switch, and in one image area, switch Sl is switched to contact d, and DC voltage 23 is applied. This DC voltage 23 is common to both negative-positive image formation and positive-positive copying, and can be varied to a desired voltage by adjusting the volume so that a proper image can be obtained.

In the non-image area, the switch S1 is switched to contact e, and a predetermined DC voltage (for example, -450 V) 24 is applied both during negative-positive image formation and during positive-positive image formation.

As a result, during negative-positive image formation, the photoreceptor potential is -80
0V, whereas the potential of the DC component of the developing bias is -450V, so the potential contrast is +350V. Further, when forming a positive image, the potential of the photoreceptor is about -50V due to charge erasing exposure, and the DC component of the developing bias is -450V, so the potential contrast is -400V. Therefore, as is clear from FIG. 2, in the non-image area, although some toner adhesion occurs due to the reverse fog phenomenon both during negative-positive image formation and positive-positive image formation, a large amount of toner adhesion due to regular development is prevented. Ru.

FIG. 4 shows a second preferred embodiment of the developing bias setting means of the apparatus according to the present invention.

Developing sleeve 14 and doctor blade 1 of developing device 10
3, the AC voltage 22 and the DC voltage are superimposed, and in one image area, the switch S1 switches to contact d, and the DC voltage 2
3 is applied, and can be adjusted to a desired voltage using a volume in order to obtain a proper image.

In the non-image area, the switch S1 is switched to the contact point e, and when forming a negative-positive image, the switch S2 is switched to the contact point f, and a predetermined developing bias 25 (-600V) is applied. Further, when forming a positive image, the switch S2 is switched to the contact g, and the predetermined developing bias 26 (-250V
) is applied.

FIG. 5 shows the correspondence between the photoconductor potential behavior in one cycle and the DC component of the developing bias during positive image formation in the second 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 shown in order to obtain an appropriate image at the image portion potential and background portion potential, respectively. In addition, in the non-image area and k is approximately O in the area where no primary charge is applied.
v, while in non-image areas i and j, the photoreceptor potential is 150V due to charge erasing exposure.

As for the developing bias, a DC voltage of -250 V is applied to the non-image areas i and j. Therefore, the potential contrast between the non-image area of the photoreceptor and the developing bias was -200 V, and as is clear from FIG. 2, neither normal development nor reverse fogging occurred.

FIG. 6 shows one example of negative/positive image formation in the second embodiment.
This figure shows the correspondence between the photoreceptor potential behavior of the cycle and the DC component of the developing bias, where the solid line shows the photoreceptor potential and the dotted line shows the developing bias.Vo and Vt in the 0 image area are the foreground potential and the image, respectively. A desired developing bias is applied to obtain a proper image at partial potential. In addition, since no primary charge is applied to the non-image area and k, approximately Ov,
Since the non-image areas i and j are not irradiated with the charge erasing exposure light, they are at a high potential of -800 V, whereas the developing bias is a DC voltage of -600 V applied to the non-image area 1+j. Therefore, the potential contrast between the non-image area of the photoreceptor and the developing bias was +200V, and as is clear from FIG. 2, no toner adhesion occurred.

In the second embodiment, a case has been described in which the developing bias of the non-image area is switched between when forming a negative-positive image and when forming a positive-positive image.
This switching is made because the areas where no toner is attached do not overlap between the time of forming a positive image and the time of forming a positive image.

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 copy mode.

FIG. 7 shows another embodiment of the image forming apparatus according to the present invention, and the same parts as in the embodiment shown in FIG. 1 are given the same reference numerals and will be described. Instead of setting the developing bias of the non-image area to a predetermined value in advance, a detection element 27 for detecting the potential of the non-image area of the photoreceptor drum 7 is arranged between the image exposure section and the developing device IO. , the DC components 25 and 26 of the developing bias are controlled according to the potential of the non-image area, and the potential contrast between the potential of the non-image area and the DC component of the developing bias is always kept constant.

By doing so, it becomes possible to compensate for a potential shift during continuous copying in the non-image area or a potential shift due to environmental changes, etc., and it is possible to prevent toner from adhering to the non-image area in any case.

In addition, in the embodiment shown in Figure 1, a case has been described in which a plurality of power supply voltages are set and the DC component of the developing bias is switched. However, the present invention is not limited to this, and the resistance value The DC component of the developing bias may be switched by switching the .

Further, the developing bias may consist of only a DC component.

(Effects of the Invention) The present invention has the above-described structure and operation, and when forming a negative-positive image, the DC component of the developing bias in the non-image area is set to have the same polarity as the photoreceptor potential and an absolute value lower than the development start voltage. By setting a large value, it is possible to prevent a large amount of toner from adhering to the non-image area of the photoreceptor due to inadvertent regular development, which can prevent unnecessary toner consumption and dirt inside the device. It is possible to obtain good images without causing any problems.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a graph showing the relationship between potential contrast and toner adhesion amount, and FIG. 3 is a first embodiment of the means for setting the developing bias. A schematic diagram showing an embodiment, FIG. 4 is a schematic diagram showing a second embodiment of the developing bias setting means, FIGS. 5 and 6,
are when forming a positive image in the second embodiment and when forming a negative image.
Graphs showing the relationship between photoreceptor potential and developing bias during positive image formation, FIG. 7 is a schematic diagram showing another embodiment of the image forming apparatus according to the present invention, and FIGS. Positive image formation and negative image formation in image forming equipment
3 is a graph showing the relationship between photoreceptor potential and developing bias during positive image formation. Explanation of symbols 10... Developing device 13... Doctor blade 14... Developing sleeve

Claims (3)

[Claims] (1) Using two types of toners with different charging polarities, a positive image is selectively formed from a negative original image or a positive image is formed from a positive original image, and a positive image is formed from a negative original image. When forming an image, the charge erasing exposure to the non-image area of the photoreceptor is blocked, and when forming a positive image from a positive original image, the charge erasing exposure is cut off to the non-image area of the photoreceptor. In an image forming apparatus that performs irradiation, when forming a positive image from a negative original image, the DC component of the developing bias in the non-image area is set to have the same polarity as the photoconductor potential and to be lower than the development start voltage. An image forming method characterized by comprising means for setting a small absolute value and setting the absolute value to be the same polarity as the photoreceptor potential and larger than a development start voltage when forming a positive image from a positive original image. Device. (2) When forming a positive image from a negative original image, the DC component of the developing bias in the non-image area should be set to have the same polarity as the photoreceptor potential and a larger absolute value than the reverse fog start voltage. When a positive image is formed from the original image, the image forming method according to claim 1 is characterized in that the absolute value is set to be the same polarity as the photoreceptor potential and smaller than the reverse fog start voltage. Device. (3) The image forming apparatus according to claim 1 or 2, wherein the DC component of the developing bias in the non-image area is adjustable in accordance with the potential of the photoreceptor in the non-image area. .