JP2008275724A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing, with a simple configuration, the bristles of application brushes from inclining and foreign matter from adhering to the application brushes and also capable of ensuring stable application of a lubricant for a long period of time. <P>SOLUTION: The image forming apparatus 1 includes: photoreceptors 21; primary transfer rollers 26, each of which transfers a toner image on the corresponding photoreceptor 21 to the intermediate transfer belt 11; and the application brushes 32, each of which is composed of conductive fiber and used for applying the lubricant to an area of the corresponding photoreceptor 21, whose area is behind a transfer position and in front of a toner image formation position. The image forming apparatus 1 has second charging devices 41, each of which adjusts the charged state of transfer toner remaining on the corresponding photoreceptor 21 in the area of the photoreceptor behind the transfer position and in front of the application position; power sources 42, each of which applies a voltage to the second charging device 41 in the direction in which the transfer toner remaining on the photoreceptor 21 is charged to its original charging polarity; and power sources 22, each of which applies a voltage to the corresponding application brush 32 in the direction in which the transfer toner remaining on the photoreceptor 21 is not attracted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus that forms an image using an image carrier. More specifically, the present invention relates to an image forming apparatus that forms an image while applying a lubricant to an image carrier using an application brush.

  Conventionally, a lubricant is appropriately applied to an image carrier that carries a toner image. This is mainly for the purpose of improving the releasability of the toner during transfer and for reducing the wear at the rubbing spot due to the cleaning blade or the like. As such a lubricant application device, there is known a device in which a rotating brush is disposed so as to contact both a solid lubricant and an image carrier. In such a case, the solid lubricant is pressed against the brush by a spring force or its own weight. Then, the solid lubricant is scraped off with a brush, and the scraped lubricant is applied to the image carrier.

  In some of such apparatuses, a lubricant is applied to the image carrier with an application brush, and foreign matter such as toner remaining on the image carrier is scraped off. For example, Patent Document 1 discloses a lubricant application device that adjusts the charge of the residual toner and actively collects it with a brush. However, if a large amount of toner adheres to the brush, the scraping property of the solid lubricant deteriorates. Therefore, flicker is brought into contact with the brush to repel the adhered toner.

On the other hand, there are some that prevent foreign matter from adhering to the application brush. For example, Patent Document 2 discloses an image forming apparatus in which a cleaning blade is disposed on the upstream side of the coating brush with respect to the rotation direction of the image carrier. According to this, the residual toner on the image carrier is scraped off with a cleaning blade, and after being brought into a clean state, the lubricant is applied.
JP 2003-57996 A JP 2006-251751 A

  However, the apparatus described in Patent Document 1 has a problem in that since flicker is always brought into contact with the brush, the stress on the brush fiber is large, causing hair fall. In the image forming apparatus described in Patent Document 2, a leveling blade is further provided on the downstream side of the application brush in order to level the lubricant applied by the application brush. For this reason, the two blades are in contact with the photosensitive member, which causes a problem of increasing the torque of the image carrier and increasing the size of the apparatus.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus capable of applying a lubricant stably over a long period of time with a simple configuration, preventing both the falling of the application brush and the adhesion of foreign matter to the application brush. There is.

  In order to solve this problem, the image forming apparatus of the present invention includes an image carrier, a toner image forming unit that forms a toner image on the image carrier, and a toner image on the image carrier as a transfer target. An image forming apparatus comprising a transfer portion to be transferred and a coating brush that is made of conductive fibers and applies a lubricant to a position after transfer of the image carrier and before toner image formation, after the transfer of the image carrier In addition, in the position before application, a charge adjustment unit that adjusts the charging state of the transfer residual toner on the image carrier, and a direction in which the charge adjustment unit charges the transfer residual toner on the image carrier to its original charge polarity. And a brush voltage application unit for applying a voltage in a direction not attracting the transfer residual toner on the image carrier to the coating brush.

  According to the image forming apparatus of the present invention, among the toner images formed on the image carrier, the transfer residual toner that has not been transferred to the transfer target by the transfer unit is adjusted by the charge adjusting unit. Here, since the voltage for charging the transfer residual toner to its original charge polarity is applied to the charge adjustment unit by the adjustment voltage application unit, the charge state of the transfer residual toner is aligned with the charge polarity of the main body. . Furthermore, since the application voltage is applied to the application brush so that the transfer residual toner on the image carrier is not attracted by the brush voltage application unit, the transfer residual toner with the same charge polarity is attracted to the application brush. There is nothing. Therefore, it is not necessary to provide a flicker that contacts the application brush. As a result, the image forming apparatus can prevent the falling of the application brush and the adhesion of foreign matter to the application brush with a simple configuration and can stably apply the lubricant over a long period of time.

  Furthermore, in the present invention, it is desirable that the absolute value of the DC component of the applied voltage by the adjustment voltage applying unit is larger than the absolute value of the DC component of the applied voltage by the brush voltage applying unit. In this way, the charging polarity of the transfer residual toner is reliably aligned by the adjustment voltage application unit.

  Furthermore, in the present invention, it is desirable that the application brush rotates in the width direction with the image carrier. In such a case, it is not necessary to increase the rotational torque of the image carrier.

  Further, in the present invention, it is desirable that the charge adjusting unit is a non-contact type using corona discharge. If this is the case, there is no resistance against rotation of the image carrier.

  Furthermore, in the present invention, it is desirable that the charge adjusting unit is of a contact type in which a current flows in contact with the image carrier. In such a case, the voltage applied to the charge adjusting unit may be relatively small.

  According to the image forming apparatus of the present invention, it is possible to prevent the falling of the coating brush and the adhesion of foreign matter to the coating brush with a simple configuration, and to apply the lubricant stably over a long period of time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a so-called tandem color image forming apparatus.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes imaging units 12 </ b> Y, 12 </ b> M, 12 </ b> C, and 12 </ b> K for each color arranged along an intermediate transfer belt 11. A secondary transfer roller 13 and an intermediate transfer cleaning unit 14 are also provided around the intermediate transfer belt 11. At the time of image formation, the intermediate transfer belt 11 rotates counterclockwise in the drawing. The imaging units 12Y, 12M, 12C, and 12K have almost the same configuration. Hereinafter, subscripts representing the respective colors are omitted and referred to as an imaging unit 12.

  A schematic configuration of the imaging unit 12 is shown in FIG. The imaging unit 12 has a cleaning unit 22, a charging unit 23, an exposure unit 24, and a developing unit 25 with the photoreceptor 21 as the center. In addition, a primary transfer roller 26 is disposed on the opposite side of the photoreceptor 21 with the intermediate transfer belt 11 therebetween (see FIG. 1). Here, the photoconductor 21, the charging unit 23, the exposure unit 24, the developing unit 25, and the primary transfer roller 26 are all used in a general image forming apparatus.

  In the present embodiment, the toner used in the developing unit 25 is a negatively chargeable toner having a negative original charging polarity. Furthermore, the image forming apparatus 1 of the present embodiment employs a reversal development method. That is, the portion of the photoconductor 21 exposed by the exposure unit 24 is a portion where a toner image is formed.

  Furthermore, in this embodiment, as shown in FIG. 2, a cleaning blade 31, an application brush 32, a solid lubricant 33, a holder 34, a pressing spring 35, and a screw 36 are provided in the housing 30 of the cleaning unit 22. The cleaning blade 31 is in contact with the photosensitive member 21 at the upper side in the drawing. In this embodiment, the flicker that contacts the application brush 32 is not provided.

  The application brush 32 of this embodiment is a conductive brush. For example, a base fabric in which brush hairs of conductive fibers are planted is wound around and bonded to the outer periphery of a metal shaft. The flocked state of the brush hair may be a straight hair shape or a loop shape. At the time of image formation, the photosensitive member 21 and the application brush 32 are rotated as indicated by arrows in FIG. That is, at these contact points, it is a so-called with rotation that moves in the same direction. In addition, the application brush 32 is rotated so that the linear velocity is equal to or slightly lower than that of the photosensitive member 21. Here, the application brush 32 may be simply moved along with the photosensitive member 21 or may be driven individually.

  The solid lubricant 33 is obtained by melt-molding metal soap powder such as zinc stearate. The solid lubricant 33 is attached to a holder 34 and is urged toward the application brush 32 by a pressing spring 35. The solid lubricant 33 is scraped off by the rotation of the application brush 32 and adheres to the application brush 32. Further, it is carried by the rotation of the application brush 32 and adheres to the surface of the photoreceptor 21. It should be noted that the solid lubricant 33 contains powder particles only by being scraped off by the application brush 32 and attached to the photoreceptor 21. When it passes through the cleaning blade 31, it is smoothed to form a film and adheres uniformly to the surface of the photoreceptor 21.

  Further, a second charging device 41 is provided above the cleaning unit 22 in FIG. 2 so as to face the surface of the photoreceptor 21. A power source 42 is connected to the second charging device 41. Then, another power source 43 is connected to the application brush 32. The second charging device 41 is for aligning the charged state of the transfer residual toner remaining on the surface of the photoreceptor 21. For this reason, the second charging device 41 is disposed downstream of the transfer position and upstream of the contact position between the photoconductor 21 and the application brush 32 in the rotation direction of the photoconductor 21. Further, in order to avoid the influence on the collected waste toner, it is desirable that the cleaning unit 22 be disposed outside the housing 30.

  At the time of image formation, the toner image formed on the photoreceptor 21 is transferred to the intermediate transfer belt 11 by the primary transfer roller 26. In this embodiment, since negatively chargeable toner is used, a voltage on the positive side compared to the surface potential of the photoconductor 21 is applied to the primary transfer roller 26 during transfer. As a result, as shown in FIG. 3, the negatively charged toner is attracted to the primary transfer roller 26 and moves from the photoreceptor 21 to the intermediate transfer belt 11. At this time, the toner remaining on the photosensitive member 21 without being transferred becomes the transfer residual toner.

  It is known that the untransferred toner contains not only a normal charged toner but also a toner whose charged state has changed. In this embodiment, as shown in FIG. 4, the untransferred toner includes a weakly charged toner having a reduced charge amount or a reverse charge polarity compared to a normal well-charged toner (development toner). Thus, a lot of positively charged reversely charged toner is contained. For this reason, the charged state is not uniform as a whole. Although it depends on the environment and durability conditions, about 30% of the transfer residual toner is reversely charged toner.

  In the present embodiment, the second charging device 41 is disposed on the downstream side of the transfer position with respect to the rotation direction of the photoconductor 21. Then, the untransferred toner faces the second charging device 41 by the rotation of the photosensitive member 21 and is charged again here. As a result, the charged state of the transfer residual toner is corrected. In this embodiment, a negative voltage is applied to the second charging device 41 by the power source 42 to charge the untransferred toner negatively, which is the original charging polarity.

  Furthermore, in this embodiment, a voltage is also applied to the application brush 32 by the power source 43. At this time, the voltage applied to the application brush 32 is the same direction as that applied to the second charging device 41. In this embodiment, a negative voltage is applied to the second charging device 41 and a negative voltage is also applied to the coating brush 32. The power source 43 may be lower in voltage than the power source 42 that applies a voltage to the second charging device 41. As a result, the transfer residual toner negatively charged by the second charging device 41 receives a repulsive force due to the negative voltage of the application brush 32, and therefore hardly adheres to the application brush 32.

  Therefore, according to the image forming apparatus 1 of the present embodiment, a toner image is formed on the photoreceptor 21 by the charging unit 23, the exposure unit 24, and the developing unit 25. The toner image is transferred to the intermediate transfer belt 11 by the primary transfer roller 26, and at this time, the transfer residual toner remains on the photosensitive member 21. The untransferred toner faces the second charging device 41 as the photoconductor 21 rotates. Then, it is negatively charged by the negative voltage of the second charging device 41.

  On the other hand, the application brush 32 scrapes the solid lubricant 33 and adheres it to the surface of the photoreceptor 21. At this time, the portion facing the photoconductor 21 comes into contact with the untransferred toner. In this embodiment, the transfer residual toner is negatively charged and the application brush 32 is also applied with a negative voltage, so that the transfer residual toner hardly adheres to the application brush 32. Accordingly, the transfer residual toner and the solid lubricant 33 are attached to the surface of the photoreceptor 21. Thereafter, the photosensitive member 21 is further rotated, the transfer residual toner is scraped off by the cleaning blade 31, and the solid lubricant 33 is leveled to form a film.

  Next, an embodiment in which the image forming apparatus 1 according to this embodiment is embodied will be described. The principal part of the first embodiment is shown in FIG. Here, a corotron charger 41 </ b> A is used as the second charging device 41 and is disposed in a non-contact manner with respect to the photoreceptor 21. The corotron charger 41A discharges by applying a high voltage to a tungsten wire. Here, a DC voltage of about −5 kV is applied to the wire, causing a negative discharge. Thereby, the transfer residual toner on the photoreceptor 21 can be negatively charged.

  Although a DC voltage is applied here, a superimposed voltage of DC and AC may be used. Alternatively, a scorotron charger may be used instead of the corotron charger 41A. The scorotron charger is provided with a grid mesh, and the amount of charge is adjusted by the voltage applied thereto.

The application brush 32 had an outer diameter of 12 mm, a shaft diameter of 6 mm, a base fabric thickness of 0.5 m, that is, a fiber length of 2.5 mm. The fiber thickness was 2T (decitex), and conductive nylon having a fiber resistance of 10 ⁸ Ω was planted at a fiber density of 230 k pieces / (25.4 mm) ² . Further, the rotation direction of the application brush 32 is a direction (wiz rotation) with the photoconductor 21 and is rotated at a linear velocity ratio 0.7 with respect to the photoconductor 21. The amount of fiber biting into the photoreceptor 21 was 0.3 mm.

  A DC voltage of −200 V is applied to the application brush 32 by a power supply 43. As a result, the negatively charged transfer residual toner is not attracted electrostatically. Further, since the amount of fiber biting into the photosensitive member 21 is relatively small, the transfer residual toner is hardly collected mechanically. The voltage applied to the application brush 32 is set to a voltage that does not cause a discharge with the photoconductor 21 or less. In this embodiment, the absolute value is preferably 500 V or less. This is because if a discharge occurs, a pinhole is generated on the surface of the photosensitive member 21 due to dielectric breakdown, causing image noise.

  Next, the main part of the second embodiment is shown in FIG. As the second charging device 41, instead of the corotron charger 41A of the first embodiment, a contact conductive brush 41B is used. In the conductive brush 41B, it is sufficient to apply a low voltage compared to the corotron charger 41A. This is represented by the difference in the number of power supply symbols of the power supply 42 in the figure. For example, in this embodiment, a DC voltage of −400 V is applied to the conductive brush 41B, and a current flows from the photosensitive member 21 side to the conductive brush 41B depending on the relationship with the surface potential of the photosensitive member 21 of about −100V. Like that.

  In the above description, the surface potential of the photosensitive member 21 is set to −100 V for the following reason. In the case of the reversal development method, the toner is developed in the photosensitive member 21 where it is exposed and the absolute value of the surface potential becomes small (exposed portion). For this reason, a large amount of untransferred toner is also present at the exposed portion. In this embodiment, the surface potential of the exposed portion is about −100V.

  The reason why the voltage applied to the conductive brush 41B is -400V is as follows. In order to make the charging polarity of the untransferred toner negative with the conductive brush 41B, it is necessary to apply a negative voltage that is larger than the surface potential (about −100 V) of the photoconductor 21 to some extent. On the other hand, as in the case of the application brush 32, it is necessary to set the voltage so as not to cause a discharge with the photosensitive member 21. Therefore, the voltage applied to the conductive brush 41B is a value between −100 to −500 (V), and is set to −400 V here.

In order to make the positively charged toner have a negative polarity, the current amount needs to be about −10 μA or more. Therefore, it is desirable to use a conductive brush 41B having a fiber resistance in the range of 10 ⁶ to 10 ⁸ Ω. Here, a 10 ⁷ Ω conductive nylon brush was used. In this embodiment, the conductive brush 41B is a brush having a fiber length of 3 mm, a fiber thickness of 2 T (decitex), and a fiber density of 430 k fibers / (25.4 mm) ² . The fiber bite amount was arranged to be 0.5 mm.

  Also here, the application brush 32 is the same as that of the first embodiment and is used with the same setting. As a result, a negative charge is injected by the current flowing from the photosensitive member 21 to the conductive brush 41B with respect to the transfer residual toner in which the negative polarity and the positive polarity are mixed. The charge amount distribution of the untransferred toner is almost the same as that of the developing toner. Accordingly, since −200 V is applied to the application brush 32 that faces thereafter, the transfer residual toner is prevented from adhering to the application brush 32.

  As described above in detail, according to the image forming apparatus 1 of the present embodiment, the second charging device 41 and the application brush 32 are provided in this order on the downstream side of the transfer position in the rotation direction of the photosensitive member 21, and the application brush 32. Are made conductive. And the voltage of the same polarity is applied to these by the power supplies 42 and 43, respectively. Thereby, the transfer residual toner which is not transferred at the transfer position and remains on the surface of the photosensitive member 21 is charged by the second charging device 41 and the polarity thereof is aligned.

  The untransferred toner then faces the application brush 32. At this time, since the voltage having the same polarity as the polarity of the transfer residual toner is applied to the application brush 32, the transfer residual toner does not adhere to the application brush 32. Further, since the flicker is not in contact with the application brush 32, there is no possibility of the hair falling due to the flicker. The solid lubricant 33 applied to the photoconductor 21 by the application brush 32 is leveled by the cleaning blade 31. Therefore, the image forming apparatus 1 can prevent the falling of the coating brush and the adhesion of foreign matter to the coating brush with a simple configuration and can stably apply the lubricant over a long period of time.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in the above embodiment, a voltage having the same polarity as the original charging polarity of the toner is applied to the second charging device 41, but it may be of a reverse polarity. In that case, the polarity of the voltage applied to the application brush 32 may be reversed. In addition, although conductive nylon is used as the brush bristles of the application brush 32, rayon, acrylic, polyester, metal fiber, or the like can also be used. In addition, although zinc stearate is used as the solid lubricant 33, a fatty acid metal salt such as magnesium stearate or lithium stearate can be used instead.

It is a schematic sectional drawing which shows the image forming apparatus of this form. It is a schematic sectional drawing which shows an imaging unit. It is explanatory drawing which shows the mode of the toner at the time of transfer. It is explanatory drawing which shows the change of the charge distribution of the toner before and behind transfer. It is explanatory drawing which shows the application brush vicinity of a 1st Example. It is explanatory drawing which shows the application brush vicinity of a 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor 25 Development part 26 Primary transfer roller 32 Application brush 41 2nd charging device 41A Corotron charger 41B Conductive brush 42 Power supply 43 Power supply

Claims (5)

An image carrier, a toner image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image on the image carrier to a transfer target, and a conductive fiber. In an image forming apparatus having an application brush for applying a lubricant to a position after transfer of a carrier and before toner image formation,
A charge adjusting unit that adjusts a charging state of a transfer residual toner on the image carrier at a position after the image carrier is transferred and before coating;
An adjustment voltage applying unit that applies a voltage in a direction to charge the transfer residual toner on the image carrier to its original charging polarity to the charge adjusting unit;
An image forming apparatus comprising: a brush voltage applying unit that applies a voltage in a direction not attracting the transfer residual toner on the image carrier to the application brush. The image forming apparatus according to claim 1,
An image forming apparatus, wherein an absolute value of a DC component of an applied voltage by the adjustment voltage applying unit is larger than an absolute value of a DC component of an applied voltage by the brush voltage applying unit. The image forming apparatus according to claim 1, wherein the coating brush is
An image forming apparatus that rotates in the width direction with the image carrier. 4. The image forming apparatus according to claim 1, wherein the charge adjustment unit includes:
An image forming apparatus that is a non-contact type using corona discharge. 4. The image forming apparatus according to claim 1, wherein the charge adjustment unit includes:
An image forming apparatus, wherein the image forming apparatus is of a contact type in which a current flows in contact with the image carrier.

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