JP2012194493A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent density unevenness in an image in an image forming apparatus in which a transfer member such as a secondary transfer roller continuously press-contacts with an image carrier such as an intermediate transfer belt, and a fog toner image is supplied to a cleaning blade to suppress curling-up or chatter of the cleaning blade.SOLUTION: A shape of a fog toner image 7 supplied to a cleaning blade 92 is to be rectangular, the length W in the orthogonal direction to the conveyance direction is to be about the same as the length Wb of the cleaning blade 92 in the longitudinal direction, and the length L in the conveyance direction is to be the integral multiple of the outer periphery of a secondary transfer roller 34. Further provided is constant current generation means for flowing a constant current between the secondary transfer roller 34 and an intermediate transfer belt 33, and detection means for detecting a voltage when the constant value is flowed. When a toner image formed on the intermediate transfer belt 33 is transferred to paper P, it is preferable that the voltage applied to the secondary transfer roller 34 by voltage application means be determined based on the voltage detected by the detection means.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, and more particularly to an image forming apparatus that removes untransferred toner on the surface of an electrostatic latent image carrier with a cleaning blade.

  In an image forming apparatus in which a toner image is formed on an image carrier such as a photosensitive drum or an intermediate transfer belt and then transferred to a sheet or the like, untransferred toner remains on the image carrier even after the toner image is transferred to a sheet or the like. Remains. For this reason, a cleaning unit is provided downstream of the transfer region in the rotation direction of the image carrier, and untransferred toner is removed and collected from the image carrier.

  As a cleaning method, a method of scraping off toner by pressing a cleaning blade made of an elastic material such as urethane rubber against an image carrier is widely used.

  However, in the cleaning method using the cleaning blade, when the frictional resistance between the cleaning blade and the image carrier increases to a predetermined level or more, problems such as the cleaning blade becoming wrinkled and chattering occur.

  Therefore, for example, in Patent Document 1, the mirror surface degree of the surface of the photoconductor as the image carrier is detected, a fog toner image having a predetermined density is formed according to the detected mirror degree, and the fog toner image is cleaned as a lubricant. A technique has been proposed in which the frictional resistance between the cleaning blade and the photosensitive member is reduced by supplying to the blade, thereby suppressing the cleaning blade from being twisted or chattered.

Japanese Unexamined Patent Publication No. 6-318019

  The secondary transfer roller for transferring the color toner image superimposed on the intermediate transfer belt to the paper has been provided so as to be detachable from the intermediate transfer belt. However, in order to reduce the size and weight of the apparatus. In addition, a configuration in which a complicated separation / contact mechanism is eliminated and the intermediate transfer belt is always in pressure contact is being adopted.

  Further, a constant current is passed between the secondary transfer roller and a roller that is in pressure contact with the secondary transfer roller via the intermediate transfer belt to detect a voltage at a predetermined time, and a toner image formed on the intermediate transfer belt is detected. There is a device that adjusts the voltage applied to the secondary transfer roller when transferring to a sheet or the like based on the detection voltage.

  However, in the configuration in which the secondary transfer roller is always in pressure contact with the intermediate transfer belt, the secondary transfer roller may be contaminated with toner when a fog toner image as a lubricant is supplied to the cleaning blade. When toner adheres to the secondary transfer roller, the resistance of that portion increases, so when transferring a toner image by applying a predetermined transfer voltage to the secondary transfer roller, it is necessary to transfer the portion where the toner is attached Insufficient voltage causes insufficient toner transfer (movement), resulting in uneven density.

  The present invention has been made in view of such a conventional problem, and an object thereof is an image forming apparatus in which a transfer member such as a secondary transfer roller is constantly pressed against an image carrier such as an intermediate transfer belt, In an image forming apparatus that suppresses wobbling and chatter of a cleaning blade by supplying a fog toner image to the cleaning blade, density unevenness does not occur in the obtained image.

  An image forming apparatus according to the present invention that achieves the above object includes a rotatable image carrier and a developing unit that includes a developer containing toner and forms a toner image directly or indirectly on the image carrier. A rotatable transfer means for transferring the toner image formed on the image carrier onto a transfer member by constantly pressing the image carrier and applying a voltage having a polarity opposite to the charging polarity of the toner; A voltage applying means for applying a predetermined voltage to the transfer means; and a toner image formed on the image carrier that is in contact with the image carrier and transferred to a member to be transferred. A cleaning blade that removes and collects residual toner remaining on the body surface, and supplies a fog toner image to the cleaning blade during non-image formation, wherein the fog toner image has four shapes. In shape, substantially equal to the longitudinal length of the cleaning blade length in the direction perpendicular to the conveying direction, wherein the length of the conveying direction is an integral multiple of the circumference of the transfer unit. Note that “substantially equivalent” includes a length in a range of ± 10% with respect to the length in the longitudinal direction of the cleaning blade.

  Here, from the viewpoint of obtaining a high-quality image without reducing the image density, a constant current generating means for supplying a constant current between the image carrier and the transfer means, and a voltage when the constant current is supplied are set. Detecting means for detecting the voltage applied by the voltage applying means to the transfer means when the toner image formed on the image carrier is transferred to the transfer member. It is preferable to determine based on the voltage.

  Further, when images having a low printing rate are continuously formed, it is preferable to supply a fog toner image to the cleaning blade during non-image formation.

  In the image forming apparatus of the present invention, since the fog toner image is supplied to the cleaning blade at the time of non-image formation, the cleaning blade is prevented from curling and chattering. In addition, the length of the fogging toner image to be supplied in the rotation direction of the image carrier is an integral multiple of the outer circumference of the transfer means, so that when the fogged toner image comes into contact with the transfer means, the toner on the outer circumference of the transfer means Adheres uniformly. As a result, the resistance of the transfer means becomes uniform, and density unevenness does not occur in the image.

  Further, a constant current generating means for supplying a constant current between the image carrier and the transfer means, and a detecting means for detecting a voltage when the constant current is supplied are further provided, and a toner image formed on the image carrier is obtained. When the voltage applied to the transfer member is determined by the voltage applying means based on the voltage detected by the detecting means, the toner uniformly adheres to the outer periphery of the transfer means and the transfer means. Even when the resistance is increased as a whole, a high-quality image can be obtained without reducing the image density.

1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. It is a section lineblock diagram of a belt cleaning device. It is a perspective view of a secondary transfer roller. FIG. 4 is an explanatory diagram in which a constant current is supplied from a constant current power source between an intermediate transfer belt and a secondary transfer roller, and a voltage at that time is detected by a voltage detector. FIG. 6 is a state diagram when a fog toner image having a predetermined density is supplied to a cleaning blade. FIG. 6 is an explanatory diagram in which a part of a fog toner image adheres to a secondary transfer roller. It is a figure which shows the change of the detection voltage by a voltage detector when a toner adheres to a part of secondary transfer roller. FIG. 4 is a diagram illustrating a shape of a fog toner image formed on an intermediate transfer belt. FIG. 6 is a diagram illustrating a change in detection voltage by a voltage detector when toner adheres to the entire outer periphery of a secondary transfer roller.

  The image forming apparatus according to the present invention will be described below with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. The image forming apparatus D in FIG. 1 is a so-called tandem color printer. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method of creating an image or a monochrome method of creating a monochrome image with one developing device may be used.

  The image forming apparatus D includes an endless intermediate transfer belt (intermediate transfer member) 33 having conductivity. The intermediate transfer belt 33 is hung on a pair of rollers 31 and 32 disposed on both the left and right sides in the drawing. The roller 32 is connected to a motor (not shown), and the roller 32 rotates counterclockwise by driving the motor, whereby the intermediate transfer belt 33 and the roller 31 in contact therewith are driven to rotate. A secondary transfer roller 34 is always in pressure contact with the outer side of the belt portion supported by the roller 32 by a biasing means (not shown). A voltage applying device (voltage applying means) 35 is connected to the secondary transfer roller 34. The toner image formed on the intermediate transfer belt 33 at the nip portion (secondary transfer region) between the secondary transfer roller 34 and the intermediate transfer belt 33 is transferred onto the conveyed paper P.

  A belt cleaning device 9 for cleaning the surface of the intermediate transfer belt 33 is provided outside the belt portion supported by the roller 31. The belt cleaning device 9 includes a cleaning blade 92 that presses against the roller 31 via the intermediate transfer belt 33, and removes and collects untransferred residual toner at the contact portion of the cleaning blade 92 with the intermediate transfer belt 33.

  Below the intermediate transfer belt 33 suspended between the rollers 31 and 32, yellow (Y), magenta (M), cyan (C), black ( K) four image forming units 2Y, 2M, 2C, and 2K (hereinafter, sometimes collectively referred to as “image forming unit 2”) are detachably disposed on the apparatus main body 10. In these image forming units 2, corresponding color toner images are created using the respective color developers.

  The image forming unit 2 has a cylindrical photosensitive member 20 as an electrostatic latent image carrier. A charging device 21, a developing device 23, a primary transfer roller 24, and a photoconductor cleaning device 6 are arranged around the photoconductor 20 in this order along the rotation direction (clockwise direction). The photoconductor cleaning device 6 includes a cleaning blade, and one end of the photoconductor cleaning device 6 is brought into contact with the outer peripheral surface of the photoconductor 20 to remove and collect toner remaining on the surface of the photoconductor 20. The primary transfer roller 24 is in pressure contact with the photoconductor 20 with the intermediate transfer belt 33 interposed therebetween to form a nip portion (primary transfer region). An exposure device 22 is disposed below the image forming unit 2.

  In the embodiment shown in this figure, a roller charging type is used as the charging device 21, but the type of the charging device 21 is not particularly limited, and a corona discharge charging charger, a blade-shaped charging member, Of course, a brush-like charging member or the like may be used. However, the present invention is preferably applied to a contact charging method such as a roller charging device in which a large amount of discharge products adhere to the photoreceptor.

  Above the intermediate transfer belt 33, hoppers 4Y, 4M, 4C, and 4K (hereinafter sometimes collectively referred to as “hopper 4”) containing toner to be supplied to the developing devices 23 of the respective colors are arranged. A paper feed cassette 50 is detachably disposed as a paper feed device below the exposure device 22. The sheets (transferred members) P stacked and accommodated in the sheet feeding cassette 50 are sent out one by one to the conveyance path in order from the uppermost sheet by the rotation of the sheet feeding roller 51 disposed in the vicinity of the sheet feeding cassette 50. The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 2, the outer peripheral surface of the photoreceptor 20 that is rotationally driven at a predetermined peripheral speed is charged by the charging device 21. Next, light corresponding to image information is projected from the exposure device 22 on the surface of the charged photoconductor 20 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by toner as a developer supplied from the developing device 23. When the toner images of the respective colors formed on the surface of the photoconductor 20 reach the primary transfer area by the rotation of the photoconductor 20, the toner image is transferred from the photoconductor 20 to the intermediate transfer belt in the order of yellow, magenta, cyan, and black. 33 is transferred (primary transfer) and superimposed.

  Residual toner remaining on the photoconductor 20 without being transferred to the intermediate transfer belt 33 is scraped off by the photoconductor cleaning device 6 and removed from the outer peripheral surface of the photoconductor 20.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 33. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer area in accordance with the timing. Then, a voltage having a polarity opposite to the charging polarity of the toner is applied from the voltage application device 35 to the secondary transfer roller 34, and the four color toner images are transferred from the intermediate transfer belt 33 to the paper P in the secondary transfer region (secondary). Next transfer). The sheet P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through the nip portion between the fixing roller 11 and the pressure roller 12. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. The paper P on which the toner image is fixed is discharged to the paper discharge tray 54 by the discharge roller pair 53.

  On the other hand, residual toner remaining on the intermediate transfer belt 33 without being transferred onto the paper P is scraped off by the cleaning blade 92 of the belt cleaning device 9 and removed from the outer peripheral surface of the intermediate transfer belt 33. Thereafter, the rotational drive of each photoconductor 20 and the intermediate transfer belt 33 is stopped.

  FIG. 2 shows a cross-sectional configuration diagram of the belt cleaning device 9. The belt cleaning device 9 in this figure conveys the residual toner scraped off by the housing 91, the cleaning blade 92, the blade holder 93 that supports the cleaning blade 92, and the cleaning blade 92 to a waste toner box (not shown). And a screw member 95. More specifically, one end side in the short direction of the long cleaning blade 92 is fixed to the blade holder 93 having an L-shaped cross section with an adhesive or the like, and the blade holder 93 is attached to the housing 91 with a screw 94. Yes. The free end of the cleaning blade 92 is in contact with the counter transfer direction of the intermediate transfer belt 33 that rotates counterclockwise. The contact direction of the cleaning blade 92 with respect to the intermediate transfer belt 33 may be the trail direction, but from the viewpoint of efficiently removing residual toner from the intermediate transfer belt 33, the cleaning blade 92 is contacted in the counter direction. Is preferred.

  As the cleaning blade 92 used in the present invention, a conventionally known cleaning blade can be used. For example, a cleaning blade made of urethane rubber is preferably used. The thickness of the cleaning blade 92 is generally preferably in the range of 1 mm to 5 mm.

  As the secondary transfer roller 34 used in the present invention, conventionally known ones such as a roller made of metal, a roller having a rubber layer formed on the outer periphery of the core metal, and a roller having a foamed elastic layer formed on the outer periphery of the core metal can be used. However, as shown in FIG. 3, a material in which foamed rubber (foamed elastic layer) 342 is formed on the outer periphery of the cored bar 341 is preferably used.

  The transfer voltage applied from the voltage application device 35 to the secondary transfer roller 34 is preferably variable. For example, with a circuit as shown in FIG. 4, a constant current is supplied from a constant current power source between the roller 32 and the secondary transfer roller 34 before the paper P passes through the nip portion, and the applied voltage at that time is detected as a voltage. The transfer voltage applied to the secondary transfer roller 34 when the toner image is transferred onto the paper P is determined based on the detected voltage. As a result, an appropriate transfer voltage can always be applied to the secondary transfer roller 34, and a high-quality image can be obtained. The transfer voltage applied to the secondary transfer roller 34 may be a constant voltage instead of being variable.

  In the image forming apparatus D having such a configuration, for example, when images with a low printing rate are continuously formed, the amount of residual toner that is not transferred onto the paper P and remains on the intermediate transfer belt 33 is reduced. As a result, the amount of toner acting as a lubricant in the cleaning blade 92 is reduced, the frictional resistance between the cleaning blade 92 and the intermediate transfer belt 33 is increased, and the cleaning blade 92 may be bent or chattered. Therefore, as shown in FIG. 5, a fog toner image 71 having a predetermined density is formed, and the fog toner image 71 is supplied to the cleaning blade 92 to reduce the frictional resistance between the cleaning blade 92 and the intermediate transfer belt 33.

  In the conventional image forming apparatus, when the fog toner image 71 is supplied to the cleaning blade 92, the secondary transfer roller 34 is separated from the intermediate transfer belt 33 so that the toner does not adhere to the secondary transfer roller 34. However, in the image forming apparatus of the present invention, the intermediate transfer belt 33 and the secondary transfer roller 34 are always in pressure contact with each other, as shown in FIG. 6, even if no voltage is applied to the secondary transfer roller 34. Part of the fog toner image 71 on the intermediate transfer belt 33 adheres to the secondary transfer roller 34.

  When toner adheres to a part of the secondary transfer roller 34, the resistance of the toner adhesion portion increases. For this reason, the detected voltage when a constant current is passed between the roller 32 and the secondary transfer roller 34 by the circuit shown in FIG. 4 becomes high at the toner adhesion portion, and the secondary transfer as shown in FIG. The waveform changes periodically with the circumference of the roller 34. For example, when the voltage to be applied to the secondary transfer roller 34 is determined based on the detection voltage of the portion where the toner is not attached, a normal transfer voltage is applied to the portion where the toner is not attached. The transfer voltage is insufficient at the portion where the toner is adhered. As a result, in the image transferred onto the paper P, image unevenness appears in which a portion with a low image density appears in the period of the peripheral length of the secondary transfer roller 34.

  Therefore, as shown in FIG. 8, in the present invention, the fog toner image 7 has a quadrangular shape, and the length W in the direction perpendicular to the transport direction is substantially the same as the length Wb in the longitudinal direction of the cleaning blade 92. The length L in the transport direction is an integral multiple of the outer circumference of the secondary transfer roller 34. By forming the fog toner image 7 in such a shape, when the fog toner image 7 on the intermediate transfer belt 33 comes into contact with the secondary transfer roller 34, the toner uniformly adheres to the entire outer periphery of the secondary transfer roller 34. . As a result, as shown in FIG. 9, the detection voltage when a constant current is passed between the roller 32 and the secondary transfer roller 34 becomes high as a whole regardless of the outer peripheral position of the secondary transfer roller 4. Even if the voltage to be applied to the secondary transfer roller 34 is determined based on the detection voltage of the portion, density unevenness does not occur in the image transferred to the paper P. Further, since the voltage to be applied to the secondary transfer roller 34 is determined based on the detection voltage, the image density of the paper P does not become thin as a whole.

  The fog toner image 7 is formed and the toner is supplied to the cleaning blade 92 when the amount of residual toner that has not been transferred onto the intermediate transfer belt 33 is reduced. For example, an image with a low printing rate is continuously displayed. And the like. For example, when the rotational distance of the intermediate transfer belt is 200 m, the printing rate during that time is 3% of the normal, and the secondary transfer efficiency is 95%, the residual toner supplied to the cleaning blade is intermediate transfer. It becomes 300 mm in terms of the belt rotation distance. On the other hand, when the actual printing rate is 0.5%, which is lower than usual, the residual toner supplied to the cleaning blade is 50 mm in terms of the rotational distance of the intermediate transfer belt, which is higher than usual. Will be less than 250 mm. Therefore, in this case, the toner for 250 mm in terms of the rotational distance of the intermediate transfer belt is supplied as the fog toner image 7 to the cleaning blade. Of course, at this time, the density or the like of the fog toner image 7 is adjusted so that the length L in the transport direction of the fog toner image 7 is an integral multiple of the outer circumference of the secondary transfer roller 34. Since the fog toner image 7 cannot be formed during the image forming process, it is formed after the series of image forming processes is completed or between sheets.

  Although the case where the image carrier is the intermediate transfer belt 33 has been described above, the same problem as that of the intermediate transfer belt 33 occurs with respect to the photosensitive drum 20 which is another image carrier. By using the same configuration as in the case of 33, the same effect can be obtained.

  In the image forming apparatus of the present invention, since the fog toner image 7 is supplied to the cleaning blade 92, the cleaning blade 92 can be prevented from being bent or chattered. In addition, since the length L in the transport direction of the supplied fog toner image 7 is set to an integral multiple of the outer circumference of the secondary transfer roller 34, when the fog toner image 7 comes into contact with the secondary transfer roller 34, This is useful because the toner uniformly adheres to the outer periphery of the secondary transfer roller 34, the resistance of the secondary transfer roller 34 becomes uniform, and density unevenness does not occur in the image.

7 fogged toner image D image forming apparatus L length of fogged toner image in the conveying direction W length of fogged toner image in the direction perpendicular to the conveying direction 23 developing device (developing means)
33 Intermediate transfer belt (image carrier)
34 Secondary transfer roller (transfer means)
35 Voltage application device (voltage application means)
92 Cleaning blade

Claims (3)

A rotatable image carrier;
A developing unit having a developer containing toner and forming a toner image directly or indirectly on the image carrier;
A rotatable transfer means for transferring a toner image formed on the image carrier onto a transfer member by constantly pressing the image carrier and applying a voltage having a polarity opposite to the charging polarity of the toner;
Voltage application means for applying a predetermined voltage to the transfer means;
A cleaning blade that contacts the image carrier and removes and collects residual toner remaining on the surface of the image carrier without being transferred after the toner image formed on the image carrier is transferred to a transfer member. And
An image forming apparatus for supplying a fog toner image to the cleaning blade during non-image formation,
The fog toner image has a quadrangular shape, the length in the direction perpendicular to the transport direction is substantially the same as the length in the longitudinal direction of the cleaning blade, and the length in the transport direction is an integral multiple of the outer circumference of the transfer means. An image forming apparatus, comprising: A constant current generating means for supplying a constant current between the image carrier and the transfer means; and a detecting means for detecting a voltage when the constant current is supplied,
The voltage applied by the voltage applying unit to the transfer unit when the toner image formed on the image carrier is transferred to a transfer member is determined based on the voltage detected by the detection unit. The image forming apparatus described.   3. The image forming apparatus according to claim 1, wherein when an image having a low printing rate is continuously formed, a fog toner image is supplied to the cleaning blade during non-image formation.

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