JP5247126B2 - Cleaning device - Google Patents

Description

  The present invention relates to a cleaning device that contacts a surface of an image carrier after image transfer and removes toner remaining on the surface of the image carrier.

  In recent years, for example, in an image forming apparatus that forms an image by an electrophotographic method, an intermediate as an image carrier for transferring a multicolor image onto a transfer paper due to the need for high-quality image formation on a wide variety of transfer papers. Image forming apparatuses using a transfer body are widely used.

  That is, a toner image (multicolor image) formed on the surface of a photosensitive drum or the like as a primary transfer member (image carrier) based on image data is an intermediate transfer member as a secondary transfer member (image carrier). Then, the toner image is transferred onto the transfer paper (secondary transfer) from the intermediate transfer member.

  In addition, an intermediate transfer belt is widely used as an intermediate transfer member. As this intermediate transfer belt, a resin belt represented by polyimide or the like generally has characteristics such as high image quality and long life. This is why it is widely adopted.

  On the other hand, since residual toner or the like adheres to the intermediate transfer belt after the multicolor image is transferred to the transfer paper, the next image forming process is performed after the residual toner or the like is removed by the cleaning device. .

  As this cleaning device, when a resin belt is used as the intermediate transfer belt, a blade method is widely used in order to maintain a high cleaning ability in consideration of the surface property and the like.

  However, recently, higher image quality and higher speed have been demanded, and the cleaning ability of the blade system has been stabilized, so that the developer (toner) has a smaller particle size and a non-spherical shape. It is changing.

  As a result, in the resin belt as the intermediate transfer belt, a hollowing out phenomenon that occurs at the time of transfer accompanying a change in toner has become a problem.

  This drop-out phenomenon is that when a toner image is transferred to a transfer paper, a large pressure is applied to the toner image, the toner image is stress-deformed and the cohesive force between toner particles increases, and a part of the toner image is transferred. A phenomenon in which the toner image cannot be transferred onto the paper and remains on the surface of the intermediate transfer belt, and particularly appears in a character or a line image as a toner image.

  Therefore, in order to eliminate this hollow-out phenomenon, an elastic intermediate transfer belt using at least one elastic layer in the layer configuration is generally employed instead of the resin belt as the intermediate transfer belt.

  This elastic intermediate transfer belt has flexibility because it has at least one elastic layer in its layer structure, and can reduce the pressure acting on the toner image when transferring to the transfer paper, resulting in the occurrence of a void phenomenon It is known to have a suppressive effect. In addition, since it has good adhesion to transfer paper during secondary transfer, it can not only improve transfer efficiency for general plain paper, but also transfer performance for thick paper and transfer to uneven paper. It can also be effective for sex.

  However, when cleaning the elastic intermediate transfer belt, if the blade method is used, the surface layer has elasticity, so that the contact load of the cleaning blade on the elastic intermediate transfer belt increases.

  For this reason, the edge tip of the cleaning blade bites into the surface layer of the belt, and the behavior of the edge tip of the cleaning blade becomes unstable, which causes a cleaning defect.

  Also, as the frictional force between the elastic intermediate transfer belt and the cleaning blade increases, problems such as turning, chattering, and squealing are likely to occur on the cleaning blade, and the surface layer of the elastic intermediate transfer belt may be damaged. There is a risk that the image quality may be disturbed due to adverse effects such as toner fusion.

  Therefore, in order to avoid the above-described adverse effects, in recent years, a brush system that employs an electrostatic fur brush with a small contact load with the elastic intermediate transfer belt has become common instead of the cleaning blade.

  The configuration of this brush type cleaning device includes a cylindrical electrostatic fur brush in which a large number of brush fibers are wound around a core metal so as to be in contact with the surface of the intermediate transfer belt, and a predetermined amount of biting into the electrostatic fur brush. A recovery roller for recovering the residual toner scraped off by the electrostatic fur brush and a cleaning blade for contacting the surface of the recovery roller with the counter and scraping off the residual toner recovered by the recovery roller are provided.

  At this time, a cleaning bias having a polarity opposite to the polarity of the toner is applied to the collecting roller from the power source, and the voltage is sequentially decreased from the collecting roller by a current circuit formed by the electrostatic fur brush and the intermediate transfer belt. Forming a cleaning electric field.

  Due to the effect of this electric field, the toner or the like remaining on the surface of the intermediate transfer belt is adsorbed by the electrostatic fur brush, then transferred to the collection roller, and scraped off from the collection roller by the cleaning blade.

  However, residual toner on the surface of the intermediate transfer belt after the secondary transfer may have the same polarity as that during development, or may have a reverse polarity due to the influence of discharge during the secondary transfer.

  For this reason, there arises a problem that not all of the remaining toner can be collected only by applying a unipolar cleaning bias using one electrostatic fur brush.

Therefore, in order to collect such residual toners having different polarities, a pair of fur brushes that are independently in contact with each other at two locations on the surface of the intermediate transfer belt are installed, and each of the pair of fur brushes has a different polarity. A technique for applying a cleaning bias is known (see, for example, Patent Document 1).
JP 2002-207403 A

  However, in the cleaning device configured as described above, the residual toner after the secondary transfer is very unstable in polarity, and depending on the print pattern and usage environment, all of the residual transfer toner is not developed. In some cases, the polarity remains the same.

  In such a case, all of the residual toner on the surface of the intermediate transfer belt can be collected by one of the pair of fur brushes.

  Therefore, if the remaining toner is not collected by the other fur brush, the remaining toner is not supplied to the other collecting roller, and the cleaning becomes uneven.

  If printing continues in this state, a new problem arises in that the residual toner that acts as a lubricant decreases between the collection roller and the blade that is in contact with the collection roller, and the blade rolls up. It was happening.

  In view of the above circumstances, an object of the present invention is to provide a cleaning device capable of realizing stable cleaning performance.

  The cleaning device of the present invention is a cleaning device that removes toner remaining on the surface of the image carrier by contacting the surface of the image carrier after image transfer. A pair of rotary cleaning bodies in contact with the surface; a cleaning power source that applies a cleaning bias to the pair of rotary cleaning bodies; and a cleaning bias having the same polarity as the toner charging polarity that contributes to development on one of the pair of rotary cleaning bodies. A bias that is applied and a cleaning bias having a reverse characteristic to the toner charging polarity is applied to the other of the pair of rotary cleaning bodies, and the polarity of the cleaning bias between the pair of rotary cleaning bodies is periodically switched alternately at a predetermined timing. And a polarity control unit.

  At this time, the bias polarity control unit switches the polarity of the cleaning bias between the pair of rotary cleaning bodies in consideration of the moving time of the image carrier relative to the separation distance of the pair of rotary cleaning bodies as a time lag. Is preferred.

  In addition, the bias polarity control unit sets a predetermined timing when any one of the number of image forming processes, the image forming processing time, and the cumulative printing rate reaches a predetermined value set between the pair of rotary cleaning bodies. It is preferable to switch the polarity of the cleaning bias.

  The cleaning device of the present invention can realize a stable cleaning property.

  Next, a cleaning device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram of a printer as an image forming apparatus equipped with a cleaning device according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the cleaning device according to an embodiment of the present invention.

  In FIG. 1, a color printer 1 as an image forming apparatus according to an embodiment of the present invention is turned upside down on a paper feed cassette 3 that can be pulled out from one surface (for example, the front surface) of a printer main body 2 and one surface of the printer main body 2. A manually feed tray 4 that can be provided, a transport path 5 that transports transfer paper (not shown) set in the paper feed cassette 3 or the manual feed tray 4, and an upstream end of the transport path 5 are configured. A sheet feeding unit 6, a secondary transfer roller 7 disposed in the middle of the conveyance path 5, and an endless belt-shaped intermediate for forming a toner transfer image on the surface of the transfer paper in cooperation with the secondary transfer roller 7 A plurality of colors (for example, yellow (Y), magenta (M), cyan (C), and black (K)) toners that are transferred onto the surface of the transfer belt 8 and the intermediate transfer belt 8 as necessary. An image forming unit 9; A fixing unit 10 that is arranged near the end of the feeding path 5 and fixes a toner transfer image formed on the surface of the transfer paper, and a paper discharge tray portion of the printer main body 2 from the downstream end of the transport path 5 for the fixed transfer paper. 11 is provided.

  The intermediate transfer belt 8 has a function as an image carrier, and an elastic intermediate transfer belt using at least one elastic layer is adopted for the layer structure, and includes a driving roller 13, a driven roller (tension roller) 14, an additional roller. Rotating movement between the pressure rollers 15 (see the arrow in the figure).

  The pressure roller 15 is disposed opposite to the secondary transfer roller 7 with the intermediate transfer belt 8 interposed therebetween, and the toner is applied to the surface of the transfer paper conveyed to the conveyance path 5 by applying a transfer bias to the secondary transfer roller 7. The image is transferred to form a toner transfer image.

  In the present embodiment, the image forming units 9 are arranged at four locations along the rotational movement direction of the intermediate transfer belt 8, and basically have the same configuration. The image forming unit 9 includes a toner cartridge 16 that stores toner of each color, a supply unit 17 that supplies toner stored in the toner cartridge 16, and aluminum that is supplied with toner from the supply unit 17 on the surface. The drum-shaped (tubular) photosensitive drum 18, the transfer roller 19 disposed opposite to the photosensitive drum 18 across the intermediate transfer belt 8, and residual toner attached to the surface of the photosensitive drum 18 are removed. A cleaning device 20 that removes charges from the photosensitive drum 18, a charging device 22 that charges the surface of the photosensitive drum 18, and a predetermined electrostatic latent image is formed on the surface of the photosensitive drum 18. And an exposure device 23. In the present embodiment, each image forming section 9 is provided with a black image forming section 9 (K) at the left end in the figure, and hereinafter, cyan along the rotational movement direction of the intermediate transfer belt 8. The image forming unit 9 (C) for magenta, the image forming unit 9 (M) for magenta, and the image forming unit 9 (Y) for yellow are arranged in this order.

  On the other hand, the intermediate transfer belt 8 after the toner image is transferred by the secondary transfer roller 7 is a pair of cleaning units 24 arranged downstream of the secondary transfer roller 7 in the rotational movement direction, as shown in FIG. , 25, the toner remaining on the surface is removed.

  The cleaning units 24 and 25 have a cylindrical electrostatic fur brush 27 as a rotary cleaning body in which a large number of conductive brush fibers are wound around a core metal so as to come into contact with the surface of the intermediate transfer belt, and an electrostatic fur brush 27. A recovery roller 28 that collects a predetermined amount of toner and scrapes the residual toner scraped off by the electrostatic fur brush 27; and a cleaning blade 29 that counter-contacts the surface of the recovery roller 28 and scrapes the residual toner recovered by the recovery roller 28; And a spiral 30 that conveys and collects the residual toner scraped off by the cleaning blade 29.

  The cleaning device 26 also includes a power supply circuit 31 that applies a bias to each collection roller 28 and the secondary transfer roller 7, and a cleaning bias and a transfer bias voltage and polarity applied to each collection roller 28 and the secondary transfer roller 7. Bias control circuits 32, 33, and 34 to be controlled, a control circuit 35 to control the entire image forming process including the power supply circuit 31, various control programs related to the entire image forming process, and control related to the cleaning control according to the present invention. The number of image forming processes is counted so that the ROM 36 in which the program is stored and the polarity of the cleaning bias by the control circuit 35 are switched every predetermined number of image processing sheets (for example, 1 sheet, 3 sheets, 5 sheets, etc.). Counter 37 is provided.

  At this time, when switching the polarity of the cleaning bias by the control circuit 35 at a predetermined timing, it is preferable to switch every transfer sheet (completed).

  The control circuit 35 and the ROM 36 constitute a microcomputer that executes cleaning control according to the present invention.

In the above configuration, specifically,
The intermediate transfer belt 8 is
Material: CR rubber (SiAc coat + PTFE coat) + PVDF
Thickness: 618 [μm] (CR rubber: 500 μm, PTFE: 5 μm + Si: 10 μm)
PVDF: 100 μm
Volume resistivity: 11.0 [log (Ω · cm)] (500 V N / N)
Surface resistivity: 12.0 [log (Ω / sqr)] (500 V N / N)
The electrostatic fur brush 27 is
Brush material: BR-1 (polyester) SUM Ni plating Brush density / thickness: 150KF / 330D / 48F
Outer diameter: φ14 (shaft diameter φ6)
Resistance value: Brush hair / main 12.0 log (Ω · cm) 100 (V) N / N
Linear velocity: 123.2 (mm / sec) <Counter direction with respect to belt rotation direction>
The collection roller 28
Material: SUS
Outer diameter: φ13
Linear velocity: 130.6 (mm / sec) <Trading direction relative to brush rotation direction>
The cleaning blade 29
Material: Urethane blade # 1577E
Free end: 6.0mm
Thickness: 1.6mm
FIG. 3 shows the present embodiment and comparative examples using these. FIG. 4 shows an outline of a timing chart of the polarity change of bias application according to the present embodiment (the polarity change is not performed in the comparative example). At this time, the control circuit 35 separates the cleaning unit 24 disposed on the upstream side in the rotational movement direction of the intermediate transfer belt 8 from the cleaning unit 25 disposed on the downstream side in the rotational movement direction of the intermediate transfer belt 8. Therefore, the polarity of the cleaning bias is switched in consideration of the rotational movement time t of the intermediate transfer belt 8 corresponding to the separation distance of the electrostatic fur brush 27 of each of the cleaning units 24 and 25 as a time lag. .

  In order to confirm the effect when the present invention is carried out, an experiment was performed by changing the condition of the secondary transfer current from −20 to −50 μA in order to intentionally change the charged polarity state of the residual toner.

  As a result, the higher the secondary transfer current, the greater the proportion of the charged toner on the opposite side of the regular charge that contributes to development in the polarity of the residual toner due to the influence of the discharge at the secondary transfer portion.

  Under the above conditions, an image forming process of a 25% color print pattern original was performed.

  As a result, in this embodiment, since the bias is alternately applied to both the cleaning units 24 and 25 periodically, both the electrostatic fur brushes 27 on the upstream side and the downstream side in the belt rotational movement direction respectively. Since the toner is supplied to the collecting roller 28, the toner is sufficiently interposed between the collecting roller 28 and the cleaning blade 29, so that the cleaning blade 29 is not turned over.

  On the other hand, in the comparative example, when the secondary transfer current is −40 μA or more, toner having a polarity opposite to the normal charging polarity that contributes to toner development is generated, and the cleaning unit 24 arranged on the upstream side in the belt rotational movement direction generates. Since the cleaning performance cannot be ensured and the toner is also collected by the cleaning unit 25 disposed downstream in the belt rotational movement direction, the toner is sufficiently interposed between the collection roller 28 and the cleaning blade 29, and the blade No turning-up phenomenon occurred.

  However, in the comparative example, in the region where the secondary transfer current is low from −20 to −40 μA, most of the toner remains in the normal charging polarity, and therefore the upstream side cleaning to which a bias having a polarity opposite to the polarity of the toner is applied. Since the toner on the belt is collected by the unit 24, the toner is not supplied to the collection roller 28 in the downstream cleaning unit 25, so that the toner serving as a lubricant is insufficient between the collection roller 28 and the cleaning blade 29, A turning phenomenon occurred in the cleaning blade 29.

  As described above, according to the present invention, the electrostatic fur brush having a bias of the same polarity and the opposite polarity with respect to the normal charge of the toner, no matter what charge polarity the residual toner after the secondary transfer has. 27, the toner is electrostatically collected and the toner is collected on both the upstream / downstream collecting rollers 28, so that the cleaning blade 29 can be prevented from being turned over.

  In the above embodiment, the cleaning device 26 according to the present invention is applied to the color printer 1. However, it is needless to say that the cleaning device 26 can be applied to general image forming apparatuses such as a copying machine and a multifunction machine.

  In the above-described embodiment, the polarity of the cleaning bias is switched by the number of image forming processes using the counter 37. However, instead of the counter 37, the image forming processing time by the timer or the printing rate detection is detected. It is also possible to switch according to the cumulative printing rate (including the cumulative toner usage) by (known technology).

1 is an explanatory diagram of a printer as an image forming apparatus equipped with a cleaning device according to an embodiment of the present invention. FIG. It is explanatory drawing of the cleaning apparatus which concerns on one Embodiment of this invention. It is a comparison figure which shows the conditions of the cleaning apparatus which concerns on one Embodiment of this invention, and a comparative example. FIG. 6 is a timing diagram illustrating an example of a cleaning bias application timing in the cleaning device according to the embodiment of the invention.

Explanation of symbols

8 ... Intermediate transfer belt (image carrier)
26 ... Cleaning device 27 ... Electrostatic fur brush (rotary cleaning body)
31 ... Power supply circuit (cleaning power supply)
35 ... Control circuit (bias polarity control unit)

Claims (2)

In the cleaning device for removing the toner remaining on the surface of the image carrier in contact with the surface of the image carrier after the image transfer,
The image carrier is an intermediate transfer belt,
The cleaning device includes a pair of rotating cleaning bodies that are in contact with the surface of the image carrier in a separated state, a pair of collecting rollers that collects toner removed by the pair of rotating cleaning bodies, and a pair of collecting rollers. A cleaning power source that applies a cleaning bias, a cleaning bias having the same polarity as the toner charging polarity that contributes to development is applied to one of the pair of collecting rollers, and a cleaning that is opposite to the toner charging polarity is applied to the other of the pair of collecting rollers. A bias polarity controller that applies a bias and periodically switches the polarity of the cleaning bias between the pair of collecting rollers at a predetermined timing; and
The pair of rotary cleaning bodies are electrostatic fur brushes that face each other with the corresponding individual rollers sandwiching the intermediate transfer belt, and rotate in the counter direction with respect to the moving direction of the image carrier,
Each of the pair of collecting rollers is provided by being bitten into the electrostatic fur brush, rotated in the trading direction with respect to the rotation direction of the pair of rotary cleaning bodies, and scraped off by the electrostatic fur brush. Collect the remaining toner ,
The bias polarity control unit switches the polarity of the cleaning bias between the pair of collecting rollers in consideration of the moving time of the image carrier with respect to the separation distance of the pair of rotary cleaning bodies as a time lag. Cleaning device to do. The bias polarity control unit sets a cleaning bias between the pair of collecting rollers with a predetermined timing when any one of the number of image forming processes, the image forming process time, and the cumulative printing rate reaches a predetermined value set in advance. The cleaning apparatus according to claim 1, wherein the polarity is switched.

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