JP2000147845A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent soiling of edge surface and obtain a transfer image without any soiling in an image forming device provided with a contact type transfer device. SOLUTION: In this image forming device utilizing a negative-positive developing process utilizing a photosensitive body with potential by electrification of -800 V, developing bias: B against a photosensitive body part in an non image range corresponding to the space between piece of paper and the range from the leading edge of transfer paper to 15 mm is set to be -450 V which is lowered than the developing bias A: -550 V against normal image range. Thus, the absolute value of developing surface potential is made greater in the range in the non image range and the transfer paper leading edge 15 mm (output timing (2)) than at normal times (output timing (1)). Therefore, the soiling of the edge part of the transfer paper is prevented by preventing the sticking of surface soiling toner in that part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly, to an image forming apparatus having a contact transfer device.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, a contact device is used as a transfer device for transferring a visible image (toner image) held on an image carrier onto a recording medium (transfer paper or the like). The one provided with the type transfer device is well known.

A contact type transfer device, for example, a transfer belt device,
The transfer roller device is not only a transfer unit but also a transfer unit that transfers a recording medium. In these transfer / conveyance means, toner (so-called background toner) attached to a non-image area on the image carrier is transferred to the transfer / conveyance means, thereby causing back contamination of the recording medium.

As a measure for preventing such back contamination, in a transfer roller device, a voltage having the same polarity as that of the toner is applied to the transfer roller in order to clean the toner adhered to the transfer roller, and the transfer roller transfers the toner to the image carrier. Retransfer of toner has been performed.

Further, in a transfer belt device, a transfer belt is cleaned by providing a rubber blade or a bias roller (cleaning roller) facing the surface of the transfer belt.

[0006]

However, the above-described conventional back-stain prevention method can prevent back-stain which can be easily confirmed by eyes, but remains on the transfer belt or transfer roller without being completely cleaned. The toner adheres to the back surface of the paper (recording medium), rubs the conveyance guide member provided in front of the fixing device as the paper is conveyed, and the toner remains in a form swept to the end of the guide member. Then, the toner is attached to the end face of the sheet so that the leading edge of the sheet to be conveyed scoops. Such toner stains appear on the end face (edge face) when the copied and printed sheets are bundled, and are called edge face stains.

[0007] Edge contamination is also generated by picking up the background toner when the leading edge of the sheet entering the transfer section abuts against the image carrier when there is a large amount of background toner on the image carrier. Therefore, in an image forming apparatus provided with a contact transfer device, there are at least two types of edge surface stains.

The present invention solves the problem of edge contamination on an image forming apparatus having a conventional contact transfer device.
It is an object of the present invention to provide an image forming apparatus capable of obtaining a clean transfer image.

[0009]

According to the present invention, there is provided an image forming apparatus having a contact-type transfer device.
The relationship between the developed ground potential of the image area: α and the developed ground potential of the non-image area corresponding to the sheet interval and the area within a predetermined range from the end of the image area: β is controlled so that α <β in absolute value. Is solved by

In order to solve the above-mentioned problems, the present invention proposes that the control for satisfying the condition α <β is performed by a variable control of the developing bias. Further, the present invention proposes, in order to solve the above-mentioned problem, that the control for satisfying α <β is performed by a variable control of a charging output.

In order to solve the above-mentioned problems, the present invention proposes adjusting the exposure amount in accordance with the variable control of the charging output.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus according to an embodiment of the present invention.
In FIG. 1, a charging charger (scorotron charger) 2, a developing device 3, a cleaning unit 4, a belt transfer device 10, and the like are arranged around a photosensitive drum 1, which is an image carrier. A writing position where the exposure light L is irradiated is provided between the charger 2 and the developing device 3.

The electrostatic latent image formed on the photosensitive drum 1 is visualized by toner in a developing device 3 and the toner image is transferred onto a transfer paper sent from a registration roller 5 (FIG. 2). The image is transferred by the transfer device 10. Since the image forming operation in the electrophotographic apparatus is well known, a detailed description is omitted.

FIG. 2 is a sectional view schematically showing a belt transfer device. As shown in this figure, the belt transfer device 1
Numeral 0 indicates that the transfer belt 11 formed in an endless loop shape is stretched over two rollers 12 and 13. The roller 12 is a driving roller for driving the transfer belt 11, and the roller 13 is a driven roller. A bias roller 14 is provided in the loop of the transfer belt 11 near the contact portion between the photoconductor 1 and the belt 11. A higher voltage is applied to a bias roller 14 as a contact electrode from a transfer power supply (power pack: PP) 15.

A cleaning blade 16 is provided below the driving roller 12 and is pressed against the transfer belt 11. The cleaning blade 16 removes toner attached to the transfer belt 11. An exit guide plate 17 for guiding a sheet conveyed leftward in the figure by the transfer belt 11 is provided on the side of the drive roller 12.

The transfer paper fed from a paper feed unit (not shown) is sent out by the registration rollers 5 and enters the transfer area. At this time, the leading end of the sheet once strikes the photosensitive drum 1. Then, the transfer paper on which the toner image has been transferred is electrostatically attracted to the transfer belt 11 and conveyed, and is sent to a fixing device (not shown) while the back surface of the paper rubs the exit guide plate 17.

In the image forming apparatus of the present embodiment, the OPC photosensitive member 1 is charged by the charging output current of the scorotron charger 2 and the grid bias so that the potential of the OPC photosensitive member 1 becomes -800 V at a portion corresponding to a normal image area. Is done. Then, a writing device (not shown) irradiates the photosensitive member 1 with writing light modulated and controlled in accordance with an image signal, and the photosensitive member potential is about -150 at a portion where the amount of light is strongest.
Decay to V. In the developing device 3, a developing bias of -550 V is applied to the developing roller (developing sleeve). As a result, the electrostatic latent image formed on the photosensitive drum 1 is negative-positive (N / P) by the potential (potential difference) between the developing bias and the photosensitive latent image potential due to the negatively charged toner in the developing device 3. ) Developed and visualized.

Here, the difference between the charging potential of the photosensitive member -800 V and the developing bias -550 V (250 V in absolute value) is a developing background potential, so that toner is less likely to electrostatically adhere to the photosensitive member. However, in general, the charging of the toner by the developing device varies, so that a small amount of low-charged toner adheres to the photoconductor as background toner. This background stain is likely to occur in a state where the charging of the toner is generally low and the developing ability is high. At this time, by increasing the developing background potential in absolute value, it is possible to relatively reduce the amount of background toner adhering to the photoconductor 1. Therefore, in the present invention, the developing background potential in a specific area on the photoconductor is increased in absolute value, so that the background toner adhering to the photoconductor is relatively reduced, and the edge of the transfer paper is smeared. I try to prevent it.

FIG. 3 shows a specific method (control) for preventing the edge of transfer paper from being stained in the present embodiment.
This will be described with reference to FIG. In the timing chart of FIG. 3, the charging output for charging the photosensitive drum 1 is turned on by the main motor ON, and the developing for applying the developing bias in the developing unit 3 is performed before the first transfer sheet is passed. The output is turned on, and the transfer output of the transfer device 10 and the write output of a writing device (not shown) become O.
N. Here, in the present embodiment, the developing bias is set to B: -450 with respect to the non-image area between the sheets and the photosensitive member corresponding portion corresponding to the range from the leading end of the transfer sheet to the image area of 15 mm.
V is variably controlled. The output timing of the developing bias B is shown in FIG. Normal output A:-
By changing to the output B for the developing bias of 550 V, the developing background potential can be increased to 350 V in absolute value, and the background smear toner is reduced in that portion. The application timing at the normal output A is shown in FIG.

As a result, the amount of the background toner on the transfer belt 11 in the non-image area between the papers is also reduced, and the toner remaining on the transfer belt 11 without being completely cleaned adheres to the rear surface of the transfer paper and is conveyed. This makes it possible to reduce rubbing and accumulation when coming into contact with the exit guide plate 17 and contaminate the edge surface of the next transfer paper tip.

At the same time, it is possible to reduce the background dirt in the portion corresponding to the photoreceptor from the leading end of the transfer paper to the image area of 15 mm. Is small, so that the edge of the edge of the transfer sheet abutting on the photoreceptor 1 can be reduced.

The variable control of the developing bias has a good control response (compared to the variable control of the charged potential), so that the control is easy. In FIG. 3, when the development output A corresponding to the trailing edge of the first transfer sheet is completed, the gap between the first and second sheets and the image area of 15 mm from the leading end of the second transfer sheet is reached. The development output is again variably controlled to B: -450 V, and the normal output A is maintained until the rear end of the second sheet. In the present embodiment, the development output is set to -450 V during a period corresponding to a predetermined range from the rear end of the final transfer paper (shown in FIG. 3) to reduce the adhesion of the background toner to the transfer belt 11. Like that. Although FIG. 3 illustrates a case where two images are obtained, the same applies to a case where one image or three or more images are formed.

Next, another embodiment of the present invention will be described. In the image forming apparatus of the present embodiment, the developing bias is fixed (−550 V) instead of the variable control of the developing bias.
The charging potential is variably controlled as it is. Note that only different parts from the above embodiment will be described, and overlapping description will be omitted.

As shown in the timing chart of FIG.
In the present embodiment, one non-image area between the paper and the leading end of the transfer paper is used.
The charging potential is changed from a normal output A _{1 of} −800 V to a normal output B _{1 of} −900 V for a portion corresponding to the photoconductor corresponding to a range up to an image area of 5 mm. The control in this case is
This is performed with the grid bias of the charger 2.

That is, in FIG.
Charging output by N B _1: the photosensitive member 1 is charged with -900 V, to the transfer sheet the rear end of the subsequent portion corresponding to 15mm from the leading edge of the transfer sheet is charging the photosensitive member in the normal output A _1. 15 mm from the gap between the first and second sheets and from the leading edge of the second transfer paper
Until a portion corresponding to the charging the photosensitive member 1 again charging the output B _1. From the second sheet of transfer paper tip to the transfer sheet the rear end of the subsequent portion corresponding to 15mm is charging the photosensitive member in the normal output A _1. Timing of charging at high charge output B ₁ than normal is a portion shown in Figure 4 two. The timing for performing the charging with the normal output is the portion shown in FIG. The developing bias is fixed (−550 V) until the end of image formation.

As described above, the charging potential of the non-image area between the sheets and the portion corresponding to the photoreceptor corresponding to the range of the image area of 15 mm from the leading end of the transfer paper is normally output A ₁ : −800 V
From _B 1: by changing the -900 V, developing the background potential absolute value increases and the 350V (usually partial: 250V), it is possible to reduce the edge surface contamination of the transfer sheet.

When the photosensitive member charging potential is increased, the photosensitive member potential cannot be attenuated to a target value (-150 V) at the time of writing if the amount of writing light is the same as usual, so that the image density and the like can be reduced. Will be affected. Therefore, in the present embodiment, the amount of writing light is controlled to be strong in accordance with the variable control of the charging potential. That is, in FIG. 4, at the beginning of writing (1
Output power larger than normal output:
Writes as B _2, usually output to the transfer sheet the rear end of the subsequent: Output A _2. Write output B ₂ higher than normal
The timing at which the writing is performed is shown in FIG. The timing for performing the writing with the normal output is the portion shown in FIG.

As described above, the developing potential can be made the same as that of the normal image area by changing the writing light amount (here, strong) in accordance with the variable control of the charging potential. The image at 15 mm from the tip) does not have a lower density than other parts and the gradation reproduction does not change.

In the present embodiment, the charging output is set to B ₁ : −900 V during the period corresponding to a predetermined range from the rear end of the final image (shown in FIG. 4), and the background toner adheres to the transfer belt 11. (The developing bias at this time is fixed). FIG. 4 illustrates a case where two images are obtained, but the same applies to a case where one or three or more images are formed.

Although the present invention has been described with reference to the two embodiments, the present invention is not limited to the described embodiments. For example, the area in which the variable control of the development background potential is performed is not limited to the value of 15 mm from the leading edge of the transfer paper.
It can be set to any range. The specific values of the developing bias and the charging output are also examples, and can be set to appropriate values. In addition to the variable control of the developing bias or the charging output, the present invention can be achieved by any method capable of changing the developing background potential, or a combination thereof. In addition, the same effect can be obtained when using not only the transfer belt device but also a transfer roller device.

In each of the above embodiments, a negative-positive development (reversal development) type apparatus has been described.
The same effect can be obtained in a positive / positive development (regular development) system used in an analog copying machine or the like. Positive
In the positive development, "development bias-potential after exposure" is a development background potential in the image area.

[0032]

As described above, according to the image forming apparatus of the present invention, the developing background potential from the leading end of the non-sheet passing area and the image forming area corresponding to the paper interval to the predetermined area is developed in the image area. Since the potential is larger than the background potential, the amount of background toner in a predetermined area from the leading end of the non-image area and the image forming area is reduced, and the edge of the transfer paper is prevented from being stained. it can.

According to the second aspect of the present invention, the development background potential is changed by the variable control of the developing bias, so that the control is easy and the output timing control of the developing bias can be easily performed.

According to the third aspect of the present invention, the edge of the transfer sheet can be prevented from being stained even by the variable control of the charging output, and an image free of stain can always be obtained. According to the configuration of the fourth aspect, it is possible to obtain an image which is not different from a normal image without affecting the image density and gradation reproduction at the development ground potential change portion at the leading end of the image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of the belt transfer device shown in FIG.

FIG. 3 is a timing chart of variable control of a development background potential in the embodiment.

FIG. 4 is a timing chart of variable control of a development background potential in another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging device 3 Developing device 4 Cleaning unit 5 Registration roller 10 Belt transfer device 11 Transfer belt 16 Cleaning blade 17 Exit guide plate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/16 9A001 F term (Reference) 2H003 BB11 CC01 DD01 EE03 EE11 2H027 DA39 ED03 ED06 ED09 EE02 EF10 ZA07 2H032 AA05 BA05 BA18 BA21 CA02 2H073 AA05 BA09 BA45 2H076 CA16 DA22 9A001 BB06 HH34 KK42

Claims (4)

[Claims] An image forming apparatus provided with a contact transfer device, wherein: a developing background potential of an image area: α; and a developing background potential of a non-image area corresponding to a space between sheets and a predetermined range from an image area front end: β. An image forming apparatus, wherein the relationship is controlled such that α <β in absolute value. 2. The image forming apparatus according to claim 1, wherein the control for satisfying α <β is performed by a variable control of a developing bias. 3. The image forming apparatus according to claim 1, wherein control for satisfying α <β is performed by variable control of a charging output. 4. The image forming apparatus according to claim 3, wherein an exposure amount is adjusted according to the variable control of the charging output.