JP3163950B2 - Image forming device - Google Patents

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 applied to a copying machine, a printer, and the like capable of forming a double-sided image on the front and back surfaces of transfer paper by performing fixing while applying a release agent. is there.

[0002]

2. Description of the Related Art Among various image forming apparatuses using an electrophotographic method or the like, a release agent is applied to a heating roll, a pressure roll, or the like in order to prevent toner offset at the time of fixing a toner image transferred onto transfer paper. In the case of a device equipped with a fixing device of a type that performs fixing while applying, particularly in the case of performing double-sided image formation, the release agent at the time of fixing is transferred to the surface of the photosensitive drum via transfer paper or transfer paper conveying means. There are problems such as adhesion and streaking of oil stains on images. Conventionally, the following solutions have been proposed to solve such problems.

[0003] That is, Japanese Patent Application Laid-Open No. 4-195173 discloses an image in which a blade and a magnetic brush cleaner disposed downstream thereof and using a cleaning agent are used to remove a release agent adhering to a photoreceptor or an intermediate transfer member. A forming device is shown. Japanese Patent Application Laid-Open No. Hei 7-92877 discloses that a developing operation is also performed on an area of a transfer paper carrying sheet that does not carry a transfer paper to prevent transfer of a release agent from the transfer paper carrying sheet to a photoreceptor. An image forming apparatus is shown.

[0004]

However, in the former image forming apparatus, the release agent on the photoreceptor is removed by a magnetic brush cleaner before the next development cycle, so that the release agent is released to the developer. Although it is designed to prevent the deterioration of the image quality due to the mixing of the agent, a magnetic brush cleaner must be newly added, and the installation of the cleaner increases the size or complexity of the device or increases the cost. There is a problem of inviting. In addition, the cleaner must use a cleaning agent such as flat iron powder or fluoropolymer beads, and this also causes a problem that unnecessary cost increase is caused.

On the other hand, in the latter image forming apparatus, a toner layer is formed also on the area of the photoreceptor which does not support the transfer paper on the transfer paper supporting sheet by the developing operation as described above, and the toner layer functions as spacer particles. This prevents the release agent adhering on the transfer paper carrying sheet from being transferred to the photoreceptor side.However, if the toner in the developing device is not used excessively for the developing operation. There is a problem that it does not. Furthermore, since the release agent on the transfer paper carrying sheet is not sufficiently removed by the ordinary transfer sheet cleaner and gradually accumulates on the sheet, a special transfer sheet cleaner has been installed to actually remove the oil. There is also the problem of having to do it.

Accordingly, an object of the present invention is to solve the above-mentioned various problems of the prior art, and to easily and efficiently remove a release agent at the time of fixing from an image carrier such as a photoreceptor. It is an object of the present invention to provide an image forming apparatus capable of preventing poor image quality due to oil contamination of a carrier.

[0007]

An image forming apparatus according to the present invention comprises an image carrier on which an electrostatic latent image is formed, and a toner image formed by developing the electrostatic latent image on the image carrier with a two-component developer. A developing device for forming a toner image, a moving body that moves so as to contact the transfer position of the image carrier and holds and conveys a toner image on the image carrier or a transfer sheet onto which the toner image is transferred, And a fixing unit for fixing the toner transferred to the transfer paper. The image forming apparatus is capable of forming a double-sided image. It has a control means for setting a special developing device operation time for removing a release agent transferred and attached via a body or transfer paper by a magnetic brush.

The setting of the special developing device operating time by the control means is most effective when the double-sided image forming mode is set. However, it is necessary to set the special developing device operating time as needed even when the single-sided image forming mode is set. Is desirable. The time other than the developing step when the special developing device operation time is set is either before or after the start of the developing step for forming a normal toner image, but is preferably after the end of the developing step. Further, when a continuous image forming operation is performed other than the developing process, it may be performed after the continuous image forming operation is completed.

When a special developing device operation time is set when the single-sided image forming mode is set, the cumulative number of transfer sheets on which double-sided image formation is performed is detected and performed based on the detection information. Of a plurality of divided sheets for forming a double-sided image to be supplied and arranged to the same divided area among a plurality of divided areas for arranging a toner image or a transfer sheet to be distributed and set based on the detection information. Alternatively, the control unit may be configured to supply and arrange a double-sided image-formed transfer sheet and a single-sided image to be supplied and arranged to the same divided area among a plurality of divided areas for arranging the transfer paper distributed and set to the moving body. The detection is performed based on the detection information by detecting the ratio of the number of sheets formed to the transfer paper.

When a special developing device operation time setting is performed when the double-sided image forming mode is set, the image density is detected and performed based on the detection information, or the first surface (two-sided image forming) is formed. The total value of the image densities of the front surface) and the second surface (back surface) is detected, and the detection is performed based on the detected information. In the case of performing color double-sided image formation, the special operation time of the developing device is set for the first color.
The total value of the image densities of the surface and the second surface is determined based on the detected information, and a threshold different from that of the other colors is applied only to black for the image density serving as a criterion at the time of setting. Further, in the case where continuous double-sided image formation is performed in a pattern in which printing is performed continuously on the first side only first, and then continuous printing is performed on the second side, the image to be detected is determined based on the capacity of the image memory and the like. The density may be configured to use only the first surface.

Further, when the image forming apparatus includes a plurality of image carriers, and an image forming operation is performed by a part of the plurality of image carriers (for example,
In the case of forming a single color image), the developing device when the special developing device operation time setting is performed may be set so as to drive the developing device of the image carrier not performing the image forming operation. . Further, when the image forming apparatus includes a pressing unit that presses the moving body at the transfer position only when necessary and makes contact with the image carrier, the developing when the special developing device operation time setting is performed is performed. The apparatus may be set so as to be driven at least while the moving body is in contact with the image carrier by the pressing operation of the pressing means.

When the above-described special developing device operation time is set, the charging device for the image carrier provided with the developing device driven to remove the release agent and the developing bias of the developing device are used. And means to operate.

[0013]

According to the present invention, when a double-sided image is formed, the release agent adhering to the image carrier via the transfer paper is:
It is scraped off by a (contact) magnetic brush of a two-component developing device driven by a setting at the time of a special developing device operation.

The release agent scraped off by the magnetic brush (strictly, mainly scraped off by the carrier and captured by the toner particles) is once recovered as it is in the developing device. It does not accumulate one after another and does not continue to increase, but is used for development together with toner and naturally discharged out of the apparatus via transfer paper. Therefore, there is no significant deterioration of the developing characteristics due to the release agent taken into the developing device, and no defective image formation occurs. The details will be described later.

[0015]

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

FIG. 1 shows a full-color image forming apparatus according to an embodiment of the present invention. This full-color image forming apparatus includes photosensitive drums 2K, 2Y, 2M, and 2C as image carriers rotatably supported on a rotating shaft, and image forming means is arranged on the outer peripheral portion of each of the photosensitive drums. Have been. The image forming means may be of any configuration. In this embodiment, a charging device 3 for uniformly charging the surface of the photosensitive drum, and a photosensitive drum separated by irradiating a color-separated light image or a light image corresponding thereto. Exposure means 4 such as a laser beam method for forming an electrostatic latent image thereon, and developing devices 5K, 5Y, 5M and 5 for visualizing the electrostatic latent image on each photosensitive drum.
C. A transfer corona discharger 8, a drum cleaner 9, and the like are provided on the outer peripheral portion of each photosensitive drum.

The developing devices 5K, 5Y, 5M, and 5C store two-component developers of four colors of black (K), yellow (Y), magenta (M), and cyan (C), respectively. A so-called contact magnetic brush development is performed in which a magnetic brush formed on the roll 50 is brought into sliding contact with the surface of the photosensitive drum so that toner adheres to the electrostatic latent image portion. The four color toner images are formed on the respective photosensitive drums 2 by the respective developing devices 5.

The photosensitive drums 2K, 2Y,
Below the 2M and 2C, a seamless endless transfer belt 10 includes a driving roll 11 and driven rolls 12 to 14.
A transfer paper belt transport device is provided which is configured to be stretched and move in the direction of arrow A. Transfer belt 10
The transfer baffle 7 moves up and down by a retract mechanism (not shown) so that the transfer baffle 7 comes into contact with the surface of the photosensitive drum at the transfer position of each photosensitive drum. Also,
On the upstream side of the photosensitive drum 2K of the first color, a paper suction roll 16 is installed at a position opposite to the suction corona discharger 15 with the transfer belt 10 interposed therebetween. Is electrostatically adsorbed on the transfer belt 10. Then, the transfer paper belt conveying device holds the transfer paper P and conveys it to a transfer position opposed to each photoconductor drum 2.
The toner images formed thereon are sequentially transferred.

A peeling corona discharger 17 and a peeling claw 1 are provided on the outer peripheral portion of the transfer belt 10 on the downstream side of the photosensitive drum 2C.
The transfer paper P is separated from the transfer belt 10 after the transfer is completed. The peeled transfer paper P is usually guided to the fixing device 30. The fixing device 30 includes a heating roll 31 and a pressure roll 32 which are installed to face each other. At least one of the rolls includes a release agent such as silicone oil for preventing toner offset (hereinafter simply referred to as “oil”). (May be referred to as a release agent).

After the transfer paper P is peeled off, the transfer belt 10 is neutralized by a belt static eliminator 19 that is opposed to the belt so as to sandwich the belt. Transfer belt 1 from which electricity has been removed
0 is such that the belt surface is cleaned by a belt cleaner 20 provided with a cleaning brush and a blade installed on the downstream side of the static eliminator 19, and then enters the next round.

The paper transport system in this image forming apparatus is as follows. That is, the paper feed tray 30
0, etc., the supply-side transport path 210 for guiding the transfer paper P to the transfer belt 10, the double-sided dedicated transport path 220 for transporting the transfer paper P during double-sided image formation (printing), and the transfer paper P passing through the fixing device 30. , And a discharge-side transport path 240 that guides the transfer sheet P, which has been printed on one side and both sides, to a discharge tray.

With such a paper transport system, the transfer paper P
Is supplied from the paper feed trays 300 and 305 of various sizes by the feed roll 301, the transport roll 302, etc.
It is sent to 10. The transfer paper P that travels along the supply-side transport path 210 by the transport rolls 221 is once positioned by the registration gate 225, and then is transferred to the transfer belt 10 at a predetermined timing.
Supplied to Then, the transfer paper P is electrostatically attracted to the transfer belt 10 and moves with the progress of the transfer belt 10. After the respective toner images are sequentially transferred to the surface of the transfer paper P, the transfer paper P is separated from the transfer belt 10. As a result, the toner image is heated and fixed. At the time of this fixing, a large amount of release agent is applied to the surface of the transfer paper P.

In the case of single-sided printing, the discharge side conveyance path 2
A switching gate 235 provided at the intersection of the sheet reversing conveyance path 230 and the paper reversing conveyance path 230 and selecting one of the conveyance paths is switched to the discharge side conveyance path 240, whereby printing is performed on the front surface (first surface). The transfer paper P is discharged by the transfer roll 241 via the discharge-side transfer path 240.

On the other hand, in the case of double-sided printing, the switching gate 235 is switched to the sheet reversing conveyance path 230, whereby the transfer paper P printed on the first side is sent to the sheet reversing conveyance path 230 and is conveyed. The paper is turned upside down on the way through the road, and sent to the double-sided exclusive conveyance path 220. Then, the transfer paper P advances to the upstream side of the belt conveyance device by the conveyance roll 211, and again the transfer belt 10
, The toner image is transferred to the back surface (second surface).

This full-color image forming apparatus is provided with an image memory for a maximum of two sheet sizes. When performing double-sided printing, for example, an image reading device first stores an image of the first side of a document, and Subsequently, after storing the second side of the original, image formation (double-sided printing) is started.

Further, in the case of this embodiment, the transfer paper P is continuously supplied in the belt traveling direction on the transfer belt 10 in the single-sided print mode.
In the double-sided print mode, after the first transfer sheet is supplied, the second transfer sheet is supplied at an interval of one sheet (size). Then, after the supply of the transfer paper P on the first surface is intermittently continued for one rotation of the transfer belt 10, the transfer paper on the first surface is supplied intermittently in the second rotation, and the interval portion provided therewith is provided. Then, the transfer paper that has been printed on the first side and circulated in the apparatus is supplied, and the second side is printed. With this configuration, automatic double-sided printing can be continuously performed without having a dedicated double-sided stack tray. Hereinafter, such an automatic duplex printing mechanism is referred to as a “trayless device”.

When double-sided printing is performed, generally, the transfer paper P after the completion of printing on the first side (front side) after fixing is transferred to the sheet reversing conveyance path 230 and the double-sided exclusive conveyance path 22.
After the toner image is transferred onto the transfer belt 10 with the front side down after transferring the toner image on the second surface, the toner image is peeled off from the belt. The released release agent oozes on the back side of the transfer paper P or adheres to the transfer belt 10. Then, the release agent adhered on the transfer belt 10 and the release agent on the back surface of the transfer paper are transferred to the surface of the photosensitive drum at a transfer position where the release agent comes into contact with the photosensitive drum 2, thereby causing the surface of the photosensitive drum to move. Streak-like oil stains occurred, which had an adverse effect on image formation.

In order to solve such a problem caused by oil adhesion to the photosensitive drum 2, in this embodiment, the operation time setting of the developing device 5 is appropriately changed, and the magnetic brush of the developing device is used to change the operating time on the photosensitive member. Control for removing the adhering oil is performed.

That is, as shown in FIG. 2, the operation time of the developing device 5 is selectively set to one of a mode and a mode. The mode is a very general operation time setting for stopping after the development process is completed, and is a predetermined time T when the stop signal is transmitted.
_This is set so that the driving of the developing device 5 (the driving motor for the developing roll, etc.) is stopped after one. On the other hand, the mode is a special operation time setting for removing the oil adhering to the photosensitive drum by driving the developing device 5 longer than usual (mode) after the development process is completed. The driving of the developing device 5 is set to be stopped after the time T ₂ (> T ₁ ). Extended operation time T ₂ of the developing device in the mode, at least, be more than a time corresponding to the distance to reach the developing position from the transfer position of the photosensitive drum and f the drum rotation direction downstream side (circumference), Moreover, this is the time during which the transfer belt 10 is in contact with the surface of the photosensitive drum due to the ON operation of the transfer baffle 7. In this embodiment, for example, T ₁ = 200 ms
ec, T ₂ = 3000 msec.

When the mode is set,
Since the developing device 5 is continuously driven even after the completion of the developing process, the magnetic brush of the two-component developer on the developing roll 50 rubs the surface of the photosensitive drum 2. At this time, the photosensitive drum on which the developing device 5 to be driven is disposed is charged by the charger 3, and a developing bias is applied to the developing device 5 from the bias power supply under the same conditions as in the developing process. , Thereby, the developer (toner)
Is collected in the developing device without adhering to the photosensitive drum. As a result, the release agent at the time of fixing, which has adhered to the surface of the photosensitive drum, is scraped off by the magnetic brush, and collected together with the developer into the apparatus.

The inventor of the present invention has found that the releasing agent scraped off by the magnetic brush is collected together with the unused two-component developer into the developing device, and the deterioration of the developing characteristics, especially the charging of the developer, is considered. Although it was concerned that the characteristics would fluctuate, it was confirmed that development defects (image formation defects) due to such factors did not actually occur. Further, the charge (distribution) characteristics of each of the two-component developers contained in the developing device after the mode and the mode were set and the image formation was performed, respectively, were examined. As described above, when the mode is performed, the stirring time of the developer per print in the developing device is longer than in the mode, so that the charge amount of the developer starts to decrease slightly faster. It was also confirmed that no large fluctuations occurred in. In particular, it was also found that the charging characteristics of the developer ensured a sufficient amount of charge that had no practical problem until the time for replacement of the developer came.

The mode or the mode selection setting is shown in FIG.
Are performed according to a control flow as shown in FIG. First, in step 1 (ST1), it is determined whether the double-sided print mode is set. When the double-sided print mode is set, the image density for each toner color is set to a predetermined threshold (P,
Q) It is determined whether the image density is equal to or greater than the threshold value. If the image density exceeds the threshold value, the mode is set. On the other hand, if the image density of each color is less than the threshold, the mode is set instead of the mode. As the above image density, the sum of the image density on the front surface of the document and the image density on the back surface thereof calculated using image information stored in the image memory in advance is used. As the threshold value of the image density, “A” is applied only to black, and “B” is applied to other colors, that is, yellow, magenta, and cyan.

Here, the reason why the image density is detected when the double-sided print mode is set and the mode or setting is performed based on the detected information will be described.

When the image density is low, the amount of toner consumed is small and the amount of newly supplied toner is small. If the developing device is driven for a long time in such a state, as shown in FIG. In addition, since the developer is excessively stirred in the developing device and the charging performance gradually decreases, problems such as fogging and increase in density occur. The cover is
When the number of prints exceeds a certain number, the charge exchange between the newly supplied new toner and the old toner in the apparatus is not smooth, and the new toner is charged to the opposite polarity to cause a two-peak distribution. I do. Also, as shown in FIG.
Critical value (threshold) of image density when fogging increases sharply
Indicates black (K) developer and other colors (Y, M,
It differs from the developer of C). On the other hand, as the image density increases (oil is absorbed by the toner), the oil at the time of fixing becomes more adhered to the transfer paper, but when the image density is low, the amount of the oil adhered is relatively small. The transfer of oil to the photosensitive drum is also minimal.

From the above, when the image density is small to some extent, it is desirable not to drive the developing device excessively, and it is less necessary to set the mode because the oil transfer to the photosensitive drum is small. , Mode. Further, since the image density level at which the above-mentioned fog tends to occur is different between black and other colors, the threshold values of the image density are set to different values (A, B) between black and other colors. Although the threshold values A and B of the image density can be set arbitrarily, in this embodiment, the threshold value A of black is set to A = 4.
The threshold value B for the other colors is set to B = 1.0%.

When the single-sided print mode is set in step ST1 instead of the double-sided print mode,
In steps ST6 to ST8, the cumulative number of double-sided prints printed so far (ST6), the cumulative number of double-sided prints on the same divided area allocated and set on the transfer belt (ST7), and the same division The cumulative number ratio (ST8) of double-sided printing and single-sided printing on the area is detected, and it is individually determined whether or not each set threshold value is exceeded. If the detection information does not exceed the threshold value in each step, detection is performed in the order of ST6 to ST8, and finally, if the detection information does not exceed the threshold value in step ST8, the mode is set. On the other hand, when the detection information becomes equal to or larger than the threshold in each step, the mode is set. As the cumulative number of double-sided prints to be detected in step ST6, the number of prints in the case of double-sided printing and the stored cumulative number may be used as it is.

Here, the reason why the accumulated number of double-sided prints and the ratio of the number of double-sided / single-sided prints are performed based on the divided areas of the transfer belt divided and distributed in steps ST7 and ST8 will be described.

First, in this embodiment, a plurality of image areas (divided areas) are formed on the transfer belt 10 by forming a plurality of image areas (divided areas) by the panel dividing method for each size of each transfer paper at equal intervals. Hereafter, one transfer sheet is placed on a panel), and an integral number of transfer sheets are always arranged around one circumference of the transfer belt. The gap is controlled to be constant. This is the transfer belt 10
If you are using a seamless belt as
When a transfer belt having a seam is used, the panel is divided and the transfer paper is sent out so as to avoid the seam.

Transfer paper is supplied to the transfer belt divided into panels as described above during double-sided printing as follows. FIGS. 4 to 7 show the supply state of the transfer paper, and the transfer belt 10 shown in the drawing is a plate-like shape obtained by developing one endless belt for convenience. In the case of a transfer belt having a seam, the illustrated belt end portions 71 correspond to the seam. FIGS. 4 and 5 show a case where the entire length of the transfer belt 10 is evenly divided into even panels. Here, for example, the panel 1 to the panel 8 are divided into eight equal parts. FIG. 6 shows a case of odd-numbered panel division in which the entire length of the transfer belt 10 is equally divided into odd numbers. Here, for example, panels 1 to 7 are divided into seven equal parts. In any of the panel divisions, a pulse signal (an inverted triangle mark in the figure) is transmitted for each panel to constantly detect and control the position of the belt. Then, the transfer paper P is supplied and placed on the panel of the transfer belt thus divided and arranged. In the figure, the transfer paper printed on the first side (front side) is represented by “S”, and the transfer paper printed on the second side (back side) is represented by “D”.

In the case of the even panel division, FIGS.
Is supplied as shown in FIG. Here, the printing conditions are such that A4 size transfer paper is placed in the horizontal direction and ten sheets of double-sided printing are performed. The transfer paper supply shown in FIG. 4 supplies the transfer papers S1, S2, S3, S4 of the first surface to the positions of the panels 1, 3, 3, 5 and 7 which are the odd panels in the first round, and the even panel. Panel 2, Panel 4, Panel 6, and Panel 8 indicate that the first page of the document is to be printed. The transfer paper supply shown in FIG. 5 is such that the transfer papers S1, S2, S3, S4 on the first side are provided at the positions of panels 2, 4, 6, and 8 which are even-numbered panels in the first rotation.
Is supplied, and the odd-numbered panels 1, 3, 5, and 7 are skipped to print the first side of the document.

The transfer paper supply shown in FIGS. 4 and 5 is the transfer paper printed on the first side in the first lap at the position of the even or odd panel skipped in the first lap in the second lap. S1, S2, S3, S4 are circulated in the apparatus and inverted, and transfer paper D1, D2, D for printing the second side
3 and D4 are supplied from the two-sided exclusive conveyance path, and the toner image on the second side of the document is transferred to the transfer paper. On the other hand, the transfer paper S1, S printed on the first side in the first lap
New transfer papers S5, S6, S7, and S8 are supplied from the paper feed tray to the position of the panel where the sheets 2, S3, and S4 are placed, and the first side of the document is printed.

Transfer paper is supplied in the same pattern in the third and fourth laps (however, in the third lap, two sheets of transfer paper newly supplied are S9 and S10, so two panels are provided). In the skip state, there is no newly supplied transfer paper in the fourth rotation), and the double-sided printing of ten transfer papers is completed after the transfer belt 10 makes four rotations.

When double-sided printing is performed by supplying the transfer paper at the time of dividing the even-numbered panel, the transfer paper that has passed through the fixing unit 30 by printing the first side is turned over after a large amount of release agent is applied. Re-supplied on the transfer belt,
At this time, the release agent adheres to the belt position of the panel on which the transfer paper after printing on the first side is placed. If the transfer belt is divided into an even number of panels and double-sided printing is performed, there are panels on which the release agent adheres and belts on which the release agent does not adhere. That is, in the case of the transfer paper supply operation of FIG. 4, the release agent adheres only to the even-numbered panel, and in the case of the transfer paper supply operation of FIG. 5, the release agent adheres only to the odd-numbered panel.

Incidentally, when the transfer belt is divided into even-numbered panels for double-sided printing, in order to prevent such uneven oil adhesion on the transfer belt, the transfer paper supply operation shown in FIG. Mode of mounting on odd panel)
Control may be performed such that the transfer paper supply operation shown in FIG. 5 (the first transfer paper S1 is placed on the even-numbered panel) is alternately performed.

In the case of odd panel division, transfer paper is supplied as shown in FIG. The printing conditions are the same as in the case of the even panel division. As shown, in this case, the belt portion at the odd panel (1, 3, 5, 7) position is 1
New transfer paper S and transfer paper D printed on the first side every week
Are also disposed, and a new transfer sheet S and a transfer sheet D on which the first side has been printed are also disposed in the belt portion of the even-numbered panel (2, 4, 6) at every turn.

Therefore, in the case of odd-numbered panel division, the paper supply operation is the same as in the case of even-numbered panel division, except that the first and second sides of the transfer paper are alternately placed at all panel positions in a double-sided print job. Is supplied, no matter which panel position the first transfer paper S1 on the first side is supplied to, the releasing agent at the time of fixing always adheres to all panels automatically as the transfer belt 10 rotates. .

In addition to this trayless apparatus, as an image forming apparatus for performing double-sided printing, as shown in FIG. A special intermediate tray 350 is provided, and a transfer roll 35 for feeding the transfer paper from the double-sided stack tray 350 to the double-sided exclusive conveyance path 210.
1 is provided with a so-called stack tray dedicated to both sides (hereinafter, this type of device is referred to as a stack tray equipped device). In the case of this stack tray-equipped device, all the transfer papers after the printing on the first side are once all in the intermediate tray 3.
The transfer paper is continuously fed from the double-sided intermediate tray 350 when the preparation for the second side is completed, and the transfer of the second side is performed. This image forming apparatus has a maximum paper size of 2
There is no need to have as many image memories. Other configurations are the same as those of the trayless device.

FIGS. 8 and 9 show the supply state of transfer paper when the transfer belt is divided into eight panels and five double-sided printings are performed under the above-mentioned printing conditions using the stack tray equipped device. The transfer paper supply operation is performed for five transfer papers S.
1, S2, S3, S4, and S5 are successively supplied to predetermined panels (panels 1, 2, 3, 4, and 5 in FIG. 8, and panels 4, 5, 6, 7, and 8 in FIG. 9) and Is printed on the intermediate tray 350 for exclusive use on both sides.
Then, when the preparation for the second side is completed, the transfer papers D1, D2, D3, D4, and D5 are sent out from the double-sided intermediate tray 350, and a predetermined panel (panels 1, 2, 3, and 3 in FIG.
4, 5 and in FIG. 9, the panels 4, 5, 6, 7, and 8), and the transfer of the second side of the document is performed on the second side of the transfer paper.

As described above, in the stack tray equipped apparatus, it is not necessary to change the panel division of the transfer belt between one-sided printing and two-sided printing. In the transfer paper supply operation illustrated in FIGS. 8 and 9, the first sheet supply panel at the time of printing the first side and the second side is set to the same panel position, but the panel position used for the first side printing and the second side printing are used. It is not necessary to make the positions of the panels used in the same manner.

As described above, in any apparatus equipped with a two-sided printing mechanism, when the transfer belt is divided into a plurality of divided areas (panels) by the panel dividing method to perform the two-sided printing, the first-side printing is performed. The position where the transfer paper (D) is placed again on the transfer belt 10 after the completion differs depending on the transfer paper supply operation pattern. As a result, the ratio (amount) of the release agent attached to the transfer belt 10 differs depending on the panel.

For example, in the supply operation pattern shown in FIG. 4, double-sided printing is performed on the even-numbered panel (paper after the first-side printing is completed).
Are placed on the panels 2 and 4, and more release agents adhere to the panels 2 and 4 in particular because a larger number of double-sided prints are placed on the panels 2 and 4. In the supply operation pattern shown in FIG. 5, since a large number of double-sided prints are placed on the odd-numbered panels, a large amount of release agent also adheres.
Since more double-sided prints are placed on the sheet, more release agent adheres. In the supply operation pattern of FIG. 6, the release agent adheres to both the even-numbered and odd-numbered panels, but more release agent adheres to the even-numbered panel from the placement ratio of double-sided printing. In the supply operation pattern of FIG.
5, in the supply operation pattern of FIG. 9, more release agent adheres to the panels 4 to 8.

Therefore, since the transfer of the release agent to the photosensitive drum varies depending on the ratio of the release agent adhered to the transfer belt 10, the accumulated number of double-sided prints can be detected for each panel. Required. For this reason, the cumulative number of double-sided prints on the same panel to be detected is detected as in step ST6, or the ratio of the cumulative number of double-sided prints to the single-sided print on the same panel is determined in step ST7. Detect. Then, in step ST6, when the accumulated number of double-sided prints on the same panel exceeds the threshold (M), or
When the ratio of the number of single-sided prints exceeds the threshold (X),
Set the mode.

Further, in the above-described example, when the one-sided print mode is selected and the threshold value is exceeded in steps ST6 to ST8, control for immediately setting the mode is performed. If the threshold value is exceeded in ST6 to ST8, as shown in the control flow R3, the image density (one side of the document) is further detected as in the control flow when duplex printing is set, and the mode is set based on the detection information. The control for determining whether or not to set to may be performed.

When the operation time setting of the developing device is set to the mode based on the various detection information described above, the release agent transferred to the photosensitive drum 2 via the transfer belt 10 or the like can be removed. . When the state of oil streaks on the printed image was examined when the mode was set and when the mode was set, measurement results as shown in FIG. 13 were obtained. As is evident from the result, when the mode is set, the generation of oil streaks can be suppressed to a level having no practical problem.

Further, when the increase / decrease of the oil content in the developer in the developing device when the mode was set was examined, measurement results were obtained as shown in FIG. From this result, it can be seen that the amount of oil (release agent) scraped off by the magnetic brush and collected in the apparatus changes at a certain fixed amount without simply increasing. This is presumed to be because the oil collected by the magnetic brush becomes a toner image together with the developer (toner) used for development in the subsequent development step, and is discharged outside the apparatus via transfer paper.

In the apparatus of the embodiment described above, for example, there is no image memory for two sheets of maximum paper size.
When double-sided printing is performed by the stack tray device, the image density needs to be detected only for the image density of the first side of the document. Further, the operation of the developing device for removing the release agent in the mode is not limited to the setting performed each time each developing step is completed.For example, when performing continuous printing, after the continuous printing is completed, It may be performed. Further, in the case of forming an image of only one color such as black instead of forming a full-color image, the mode is a developing device (5Y, 5Y, 5M, 5
C) may be set to drive to remove the release agent.

Further, in the above-described embodiment, the case where the transfer belt for sucking and transferring the transfer paper is used as the moving body is illustrated. However, in the present invention, the cylindrical transfer for sucking and transferring the transfer paper is used as the moving body. It is also possible to use a drum, and in this case, the same operation and effect as described above can be obtained. Further, in the present invention, a belt-like or cylindrical intermediate transfer body that transfers, holds and transfers a toner image formed on an image carrier can be used as a moving body,
In this case, the same operation and effect as described above can be obtained.

[0058]

As described above, in the image forming apparatus of the present invention, the control device drives the developing device extra than during the developing process, so that the developing device is transferred onto the image carrier via the moving body or the like. The release agent can be easily and efficiently removed by the magnetic brush. Further, the removal of the release agent does not require the provision of a new oil removing means or the like, wastes the developer, accumulates the release agent on the moving body, or removes the release agent. Can be performed without storing more than necessary in the device. Accordingly, since such excellent release agent removal is possible, it is possible to reliably prevent image quality defects due to oil contamination of the image carrier.

The control by the control means detects the cumulative number of transfer sheets on which double-sided images are formed, the cumulative number of transfer sheets in the same divided region of the moving body, and the ratio of transfer sheets on both sides / single-sided image formation. When the release is performed based on the information, the release agent on the image carrier can be more accurately removed in accordance with the substantial release agent adhesion state of the moving body. This is particularly effective when the one-sided image forming mode is set.

Further, when the control by the control means is performed based on the information on the detection of the image density, it is possible to prevent fogging caused by long-time driving of the developing device when the image density is low. Further, the release agent on the image carrier can be more accurately removed in accordance with the amount of the release agent (oil) actually transferred to the image carrier.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a full-color image forming apparatus (trayless apparatus-equipped type) according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a setting mode of an operation time of a developing device.

FIG. 3 is a flowchart showing the control contents of setting the operation time of the developing device by the control means.

FIG. 4 is a developed schematic diagram showing a state in which transfer paper is supplied to a transfer belt divided into even panels.

FIG. 5 is a developed schematic diagram showing a state in which transfer paper is supplied to a transfer belt divided into even-numbered panels.

FIG. 6 is a developed schematic diagram showing a state in which transfer paper is supplied to a transfer belt divided into odd-numbered panels.

FIG. 7 is a configuration explanatory view showing an example of a full-color image forming apparatus of a type equipped with a stack tray dedicated to both sides to which the present invention is applied.

8 is a developed schematic diagram showing a state in which transfer paper is supplied to a transfer belt divided into even panels in the apparatus of FIG. 7;

9 is a developed schematic diagram showing a state in which transfer paper is supplied to a transfer belt divided into even panels in the apparatus shown in FIG. 7;

FIG. 10 is a characteristic diagram illustrating a charging characteristic of a developer according to a setting mode of a developing device operation time.

11A is a characteristic diagram showing a charging characteristic of a developer when fogging occurs, and FIG. 11B is a diagram showing a fogging generation level.

FIG. 12 is a diagram illustrating a fog occurrence level for each toner color at each image density.

FIG. 13 is a diagram showing a fogging occurrence level according to a setting mode of a developing device operation time.

FIG. 14 is a diagram illustrating a transition of an oil content in a developer in a developing device operation time setting mode.

[Explanation of symbols]

2 ... image carrier, 5 ... developing device, 10 ... moving body (transfer belt), 30 ... fixing device, P ... transfer paper.

Continued on the front page (72) Inventor Yukio Hayashi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Junichiro Samejima 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Tsuruoka Ryoichi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Masanori Kato 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (56) References JP-A-4-195173 (JP, A) JP-A-4-287706 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08-15/095 G03G 21/00 370 G03G 21/10-21/12 G03G 15 / 00 106

Claims (13)

(57) [Claims] An image carrier on which an electrostatic latent image is formed, a developing device for developing the electrostatic latent image on the image carrier with a two-component developer to form a toner image, and a transfer of the image carrier A moving body for holding and transporting the toner image on the image carrier or the transfer paper on which the toner image is transferred, and a toner having a release agent applying means. An image forming apparatus comprising a fixing unit for fixing and capable of forming a two-sided image, wherein the developing device is driven even in a process other than the developing step, and the transfer device adheres to the image carrier via a moving body or transfer paper. agents have a control means for setting a special developing device operating time for removal by the magnetic brush, and the control means, the cumulative transfer paper was double-sided image formation
Detects the number of sheets and uses a special developing device based on the detected information
An image forming apparatus for setting an operation time . 2. The apparatus according to claim 1, wherein the control means arranges the toner image or the transfer paper distributed and set to the moving body.
To the same sub-region among multiple sub-regions
The cumulative number of double-sided image-formed transfer paper
When a special developing device is activated based on the detected information
An image forming apparatus, wherein a setting is made between the two . 3. The apparatus according to claim 2, wherein the control means is provided for arranging the transfer paper distributed and set to the moving body.
Of the same number of divided areas
Double-sided transfer paper and single-sided transfer paper
And the ratio of the number
An image forming apparatus for setting a developing device operation time . 4. An image bearing member on which an electrostatic latent image is formed, and an image bearing member.
The electrostatic latent image on the carrier is developed with a two-component developer to form a toner.
A developing device for forming an image and a transfer position of the image carrier
Move the toner image on the image carrier or this toner
A moving body that holds and conveys a transfer sheet onto which an image is transferred, and a release agent
A fixing means for fixing the toner transferred to the transfer paper
And an image forming apparatus capable of forming a two-sided image.
In addition, the developing device is driven even in a process other than the developing process to
Release agent that transfers and adheres to the carrier via a moving object or transfer paper
Operation of a special developing device to remove the toner with a magnetic brush
Control means for setting the time, and the control means sets a double-sided image forming mode.
An image forming apparatus for setting a special operation time of the developing device when the image forming apparatus is operated . 5. The apparatus according to any one of claims 1-4, the control unit detects the image density, the detected information
An image forming apparatus characterized in that a special developing device operation time no is set based on the image forming apparatus. 6. The apparatus according to claim 5 , wherein the control means detects the image density of the first surface during double-sided image formation.
Based on the detection information,
An image forming apparatus for performing setting . 7. The apparatus according to claim 5 , wherein the control unit is configured to control an image on the first side and the second side during double-sided image formation.
Detects the total value of the image density and performs special processing based on the detected information.
An image forming apparatus for setting an operating time of a developing device. 8. The apparatus according to claim 7 , wherein the control means, when performing color double-sided image formation , controls the first surface of each color.
And the total value of the image densities on the second side
Criterion for setting special developing device operation time
Black is different from other colors for different image densities
An image forming apparatus characterized by applying a value . 9. An image bearing member on which an electrostatic latent image is formed, and an image bearing member.
The electrostatic latent image on the carrier is developed with a two-component developer to form a toner.
A developing device for forming an image and a transfer position of the image carrier
Move the toner image on the image carrier or this toner
A moving body that holds and conveys a transfer sheet onto which an image is transferred, and a release agent
A fixing means for fixing the toner transferred to the transfer paper
And an image forming apparatus capable of forming a two-sided image.
In addition, the developing device is driven even in a process other than the developing process to
Release agent that transfers and adheres to the carrier via a moving object or transfer paper
Operation of a special developing device to remove the toner with a magnetic brush
Control means for setting the time, and this control means is special when performing continuous image formation.
When the developing device operation time is set, the developing device
An image forming apparatus, wherein the image forming apparatus is extended and driven after completion of a forming operation . 10. The apparatus according to claim 9 , wherein the extension is
The operating time of the developing device driven by
From the transfer position of the carrier to the downstream side in the moving direction of the image carrier.
Over the time equivalent to the distance to reach the development position
An image forming apparatus wherein there. 11. A plurality of image carriers on which an electrostatic latent image is formed.
And developing the electrostatic latent image on the image carrier with a two-component developer.
Developing device for forming a toner image by transfer and the transfer position of the image carrier
The toner image on the image carrier or
Moving body that holds and conveys the transfer paper on which the toner image is transferred
And releasing the toner transferred to the transfer paper
An image capable of forming a two-sided image, comprising:
In the forming apparatus, an image is formed by a part of the plurality of image carriers.
When performing the operation, the image carrier not performing the image forming operation
Of the moving body and transfer paper on the image carrier
Release agent that adheres through the surface is removed by a magnetic brush
Means for setting a special developing device operating time for
An image forming apparatus comprising: 12. A plurality of image carriers on which an electrostatic latent image is formed.
And developing the electrostatic latent image on the image carrier with a two-component developer.
Developing device for forming a toner image by transfer and the transfer position of the image carrier
The toner image on the image carrier or
Moving body that holds and conveys the transfer paper on which the toner image is transferred
And press the moving body at the transfer position only when necessary
A pressing means for contacting the holding body and a releasing agent applying means;
Fixing means for fixing the toner transferred to the paper,
In an image forming apparatus capable of forming a two-sided image, at least the moving body bears an image by a pressing operation of a pressing unit.
While being in contact with the carrier, drive the developing device to
Release agent that transfers to and adheres to the carrier via a moving object or transfer paper
During operation of special developing device to remove by magnetic brush
An image forming apparatus, comprising: a control unit configured to set a time interval . 13. The method according to claim 1, 11 or 12.
In the apparatus as described, the control means includes a special developing device operation.
When setting the time, the image on which the developing device to be driven is
Charging means for the carrier and means for applying a developing bias to the developing device
An image forming apparatus characterized by operating a step .