JP4654810B2 - Cleaning device, process unit, and image forming apparatus - Google Patents

Description

  The present invention includes a cleaning device, and more particularly, a cleaning device for collecting a residue such as toner on an image carrier such as a photosensitive member or an intermediate transfer member in an electrophotographic copying machine or printer, and the apparatus. The present invention relates to a process unit and an image forming apparatus including the apparatus or the process unit.

  Conventionally, in an electrophotographic image forming apparatus, the surface of a photosensitive drum is charged, image exposed, and developed with toner to transfer a toner image onto a transfer material such as paper, or from the photosensitive drum to an intermediate transfer member. After the toner image is transferred and synthesized, the synthesized toner image is transferred to a transfer material such as paper, and then the toner image is fixed, and then the toner image is formed on the transfer material.

  Incidentally, in the above image forming process, it is necessary to provide a cleaning device for cleaning residual toner from an image carrier such as a photosensitive drum or an intermediate transfer member. Conventionally, a system in which a rubber blade is brought into contact with the surface of an image carrier is generally used. However, with the blade method, it is difficult to remove even various additives (fine particles) separated from the toner and transfer material paper, and the additive causes a filming phenomenon and causes image defects. was there. Also, if the blade contact force or contact angle is set high in order to remove fine particles, the frictional force with the image carrier increases and the blade turns up or the blade edge is damaged, resulting in poor cleaning and image defects. End up.

  Therefore, in Patent Document 1, a blade is provided as a cleaning means and a rotating brush is provided as an auxiliary means, and cleaning that removes deposits such as fine particles, oxides such as ozone and active oxygen, which cannot be removed by the blade, with the rotating brush. An apparatus is disclosed. However, since this cleaning device requires a blade and a rotating brush, it is very disadvantageous in terms of cost.

  Patent Document 2 discloses a cleaning device in which a rotating brush to which a bias current is applied and a conductive brush that adjusts the charging polarity of toner immediately before being conveyed to the rotating brush are disclosed. When a rotating brush to which a bias current is applied is used, it is possible to remove even fine particles without causing problems due to the blade.

However, the rotating brushes as described in Patent Documents 1 and 2 are relatively hard, and the contact force against the image carrier (in other words, the scraping force against the residue) is stronger than necessary, which causes damage to the image carrier. It will be. In particular, when applied to an intermediate transfer belt, the belt has a resin as a main component, so that damage is increased. On the other hand, if the contact force is too weak, the effect of removing the residue is small and an image defect is caused. There are many factors that determine the contact condition of the rotating brush, and such appropriate conditions have not been elucidated.
JP 2002-182536 A JP 2004-310060 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cleaning device, a process unit, and a cleaning device capable of stably cleaning a residue on an image carrier for a long period of time and suppressing damage to the image carrier as much as possible. An object is to provide an image forming apparatus.

In order to achieve the above object, the present invention provides a conductive cleaning brush that is rotationally driven in contact with the surface of an image carrier that moves in one direction, and a bias application that applies a bias current to the cleaning brush. A cleaning device that collects the residue on the image carrier with a cleaning brush, and the scraping force F of the cleaning brush against the residue on the image carrier satisfies the following conditions:
0.8 ≦ F ≦ 8.5
However, F = 2yEID / L ²
y = √ {L ² − (L−Δu) ² }
I = πd ^4/64
y = Brush fiber deflection (m)
E = Brush fiber Young's modulus (N / m ² )
I = Brush fiber cross-section second moment D = Brush fiber density (lines / m ² )
L = Brush fiber length (m)
Δu = amount of brush fiber bite (m)
d = Brush fiber diameter (m)
It is characterized by.

  In the cleaning device according to the present invention, it is possible to effectively clean not only the residual toner but also the particulate residue by applying a bias current to the cleaning brush. In addition, since the scraping force F with respect to the residue by the cleaning brush is set so as to satisfy the conditional expression, damage to the image carrier can be suppressed as much as possible, and stable cleaning ability can be exhibited in the long term. Moreover, it is possible to manufacture at a low cost as well as not to cause a problem with the blade system. The cleaning device according to the present invention can be effectively used for the intermediate transfer belt.

  The process unit according to the present invention includes the cleaning device. The image forming apparatus according to the present invention includes the cleaning device or the process unit.

  Hereinafter, embodiments of a cleaning device, a process unit, and an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus)
An image forming apparatus 1 shown in FIG. 1 is an electrophotographic color printer, and is configured to synthesize four color images in a so-called tandem system.

  The outline of the print head 20 includes a photosensitive drum 21, a developing device 22, a primary transfer roller 23, a charging device (not shown), an image exposure device, and the like. 20M, 20C, 20K) are juxtaposed directly below the intermediate transfer belt 10. The process of forming a toner image on the photosensitive drum 21 in each print head 20 is well known, and the description thereof is omitted.

  The intermediate transfer belt 10 is rotationally driven in the direction of arrow A by the drive roller 11 and the support rollers 12 and 13, and the transfer roller is disposed on a portion (secondary transfer portion 14) facing the drive roller 11 through the intermediate transfer belt 10. 15 is arranged.

  In the lower part of the image forming apparatus 1, an automatic paper feeding unit (not shown) that feeds stacked sheets one by one is installed. A toner fixing device (not shown) is installed immediately above the secondary transfer unit 14.

  The color-specific toner images formed on the respective photosensitive drums 21 are sequentially primary-transferred onto the intermediate transfer belt 10 that is rotationally driven in the direction of arrow A, and four-color images are synthesized. On the other hand, the sheets are fed one by one from the direction of arrow B, and are sandwiched between the intermediate transfer belt 10 and the transfer roller 15 by the secondary transfer unit 14, and the composite image is secondarily transferred. Thereafter, the sheet is heated and fixed with toner by a fixing device, and is discharged onto a tray (not shown).

  Here, the toner accommodated in each developing device 22 is charged to a negative polarity, for example, transferred to the intermediate transfer belt 10 by applying a positive electric field from the primary transfer roller 23, and further subjected to a secondary transfer. The image is transferred to the sheet by applying a positive electric field from the roller 15. Residual toner and residual fine particles on the intermediate transfer belt 10 are cleaned by a cleaning device 30 described below.

  Each of the devices constituting the image forming apparatus 1 is preferably configured as a process unit that can be attached to and detached from the main body of the image forming apparatus 1 in order to facilitate replacement and adjustment. In particular, the cleaning device according to the present invention is preferably a process unit configured integrally with the intermediate transfer belt 10. In addition, the cleaning device may be configured as a unit including the photosensitive drum 21 and the developing device 22 in order to clean the photosensitive drum 21.

(Cleaning device)
As shown in FIGS. 1 and 2, the cleaning device 30 includes a conductive cleaning brush 31 that is driven to rotate in the direction of arrow C while being in contact with the surface of the intermediate transfer belt 10 at a portion facing the support roller 13. The conductive brush 35 having conductivity that contacts the surface of the intermediate transfer belt 10 between the support rollers 12 and 13 and the conductivity that is rotationally driven in the same direction (arrow C) in contact with the cleaning brush 31. The recovery roller 32 and a scraping plate 33 that contacts the recovery roller 32 are configured.

  The cleaning brush 31 is connected to a constant current DC power source 36, and the conductive brush 35 is grounded. A positive charge is injected from the DC power source 36 to the cleaning brush 31, and this charge further flows to the conductive brush 35 via the intermediate transfer belt 10 and is dropped to the ground.

  Most of the residual toner on the intermediate transfer belt 10 is charged to a negative polarity having a normal polarity, but many of the toners having an insufficient charge amount or a reverse polarity remain. Further, on the intermediate transfer belt 10, fine particles such as an additive and paper powder separated from the toner adhere. Residues such as toner and fine particles are first collected by the cleaning brush 31 in which the charge polarity is adjusted to negative polarity by passing through the conductive brush 35 and positive charge is injected.

  Residue such as toner collected by the cleaning brush 31 adheres to the outer peripheral surface of the collecting roller 32 into which the positive charge is injected, and is further scraped from the outer peripheral surface of the collecting roller 32 by the scraping plate 33. It is taken and falls to the collection part 37. The residue dropped on the collection unit 37 is collected in a waste bottle (not shown) as the conveyance screw 38 rotates.

  Next, the configuration of the cleaning device 30 and the scraping force F of the cleaning brush 31 will be described.

  The cleaning brush 31 is obtained by winding a pipe-shaped (or solid-shaped) core bar in which conductive fibers are woven into a conductive base fabric and bonding them, and has an axial length equal to the width dimension of the intermediate transfer belt 10. Have. The cored bar is made of a metal material, and the bias current may be applied to the brush fiber via the cored bar. The rotation direction C of the brush 31 is the direction opposite to the movement of the intermediate transfer belt 10, and the peripheral speed ratio with the belt 10 is normally set to 1 or more. If the peripheral speed ratio is too large, the brush fibers are liable to collapse, which is not preferable. Further, the contact biting amount of the brush 31 is set to 0.5 mm or more. However, if the biting amount is too large, the brush fiber falls due to rotation and stoppage.

The conductive brush fiber is obtained by dispersing conductive particles such as carbon in a resin such as polyamide, polyester, acrylic, or rayon. As the brush fibers, those having a yarn diameter of 1 to 10D, a yarn density of 50 to 450 kF / inch ² , and a yarn resistance of 1 × 10 ³ Ω or more can be suitably used.

  The bias current is applied from the collection roller 32 as described above, but may be applied from the scraping plate 33 when the scraping plate 33 is made of a conductive material. Either a constant current or a constant voltage may be used, and an optimum method may be selected for the entire system of the image forming apparatus 1. The application point of the bias current may also be the collection roller 32, the metal core of the cleaning brush 31, the conductive brush 35, the base layer of the intermediate transfer belt 10, or the support rollers 12 and 13, and is optimally applied to the image forming apparatus 1. A point and a bias current value may be selected.

  When cleaning the residue on the image carrier with a cleaning brush to which a bias current is applied, first, the residue adhered to the image carrier by van der Waals force or Coulomb force due to the mechanical scraping force of the brush fiber. Things are torn off. Next, the residue is adsorbed to the brush fiber by the electric adsorption force generated by the bias current applied to the brush fiber. For this reason, by setting the mechanical scraping force of the brush fibers to an appropriate condition, the residue on the image carrier can be removed stably over a long period of time and the damage to the image carrier is minimized. can do.

  Here, the scraping force F of the cleaning brush 31 will be considered with reference to FIGS. In FIG. 3, 41 is a metal core, 42 is a base fabric, and 43 is a brush fiber.

Since the scraping force per filament of the brush fiber 43 is considered to be generated by the moment force of one filament, it can be obtained as the bending moment Mo.
Mo = 2yEI / L ²

If the cross-sectional shape of the brush fiber 43 is circular, the cross-sectional secondary moment I is
I = πd ^4/64

here,
y = Brush fiber deflection (m)
E = Brush fiber Young's modulus (N / m ² )
I = Brush fiber cross-section second moment D = Brush fiber density (lines / m ² )
L = Brush fiber length (m)
Δu = amount of brush fiber bite (m)
d = Brush fiber diameter (m)
And

Since the brush fiber 43 is curved in a quadratic curve when being brought into contact with the intermediate transfer belt 10, the deflection amount y is simplified by a trigonometric function as follows and obtained as an approximate value, avoiding the complexity of calculation. (See FIG. 4).
y = √ {L ² − (L−Δu) ² }

Therefore, the scraping force F of the cleaning brush 31 is considered to be proportional to the bending moment Mo per filament multiplied by the brush fiber density D.
F = Mo × D = 2yEID / L ²

  According to the experiments by the present inventors, when the scraping force F is less than 0.8, the mechanical scraping force is insufficient, and particularly under high humidity, poor toner cleaning occurs, resulting in an image defect. . On the other hand, when the scraping force F exceeds 8.5, the mechanical scraping force becomes too strong, and the intermediate transfer belt 10 is scratched to cause image defects. For this reason, the scraping force F of the cleaning brush 31 is preferably in the range of 0.8 ≦ F ≦ 8.5. More preferable contact conditions are in the range of 1.0 ≦ F ≦ 6.0, more preferably in the range of 2.0 ≦ F ≦ 6.0, in view of durability under various environments.

  Incidentally, the intermediate transfer belt 10 is provided with a surface layer having high toner releasability on the surface of a base material made of a material having high heat resistance, and the surface is finished smooth. For example, as the base material, polyimide, polyamide, polyester or the like to which a conductive material such as carbon black is added can be used. As the surface layer, silicon resin, fluorine resin, or the like can be used. In addition, it is flexible enough to be circulated and moved around the drive roller 11 and the support rollers 12 and 13, and has a hardness that can withstand use while in contact with a cleaning brush. Is preferably 160 to 220. The intermediate transfer belt used in the evaluation experiment described below was made of polyimide and had a universal hardness of 193.

  Tables 1 and 2 below show specific numerical values for the brushes 2 to 9 used in the cleaning device according to the present invention. The brushes 1 and 10 are comparative examples. FIG. 5 shows the evaluation results of the cleaning performance experimentally performed by the present inventors. In Tables 1 and 2, the brush fiber T1 is a fiber in which carbon black is dispersed in a polyamide resin, and the brush fiber T2 is a fiber in which carbon black is dispersed in a polyester resin.

  For the evaluation of the cleaning performance, an image forming apparatus equipped with Bizhub C450 (manufactured by Konica Minolta Business Technologies) equipped with the cleaning device 30 shown in FIG. 2 was used. Specifically, a blue solid image is formed, and the residual toner after the secondary transfer on the intermediate transfer belt is cleaned under the conditions where the cleaning currents are set to 5, 10, and 20 μA, respectively, and the color difference ΔE after cleaning is determined. It was measured. A spectral colorimeter CM-2002 (manufactured by Konica Minolta Sensing) was used for color difference measurement.

  The measurement of the color difference ΔE was performed on the toner on the tape by collecting the residual toner on the intermediate transfer belt with a transparent tape. Further, the secondary transfer current was adjusted so that the color difference ΔEi of the residual toner after the secondary transfer before cleaning becomes 60.

  The evaluation of the cleaning performance used the color difference after cleaning with respect to the color difference before cleaning, that is, the value of ΔE / ΔEi (see the vertical axis in FIG. 5) in order to see the degree of decrease in the toner amount due to cleaning. In the evaluation of the cleaning performance, if the color difference ΔE after cleaning is 1% or less of the color difference ΔEi before cleaning, that is, ΔE / ΔEi ≦ 0.01, it can be considered that the cleaning is satisfactorily performed. After the evaluation experiment, the intermediate transfer belt was visually confirmed, and a halftone image was formed to perform image evaluation.

  As shown in FIG. 5, the value of ΔE / ΔEi was 0.01 or less in the region where the F value was 0.8 to 8.5 regardless of the current value of the cleaning current. Although not shown in FIG. 5, when no cleaning current is applied, the value of ΔE / ΔEi is larger than 0.01 in all the areas of the measured F value.

  Further, in the visual evaluation after the cleaning performance evaluation experiment, scratches were observed on the intermediate transfer belt 10 only in the case of the brush 10 (see Table 2), and when the halftone image was formed, the image of the scratched part was whitened. .

(Scraping power in the conventional example)
Here, the contact conditions 1 and 2 of the rotating brush described in Patent Document 1 are as follows. The scraping force F under the contact condition 1 is 30.5 and the scraping force under the contact condition 2 is as follows. The taking force F is 9.2.

(Contact condition 1: F = 30.5)
Young's modulus E: 6.5 × 10 ⁹ (N / m ² )
Density D: 1.00 × 10 ⁸ (lines / m ² )
Length L: 4.5 × 10 ⁻³ (m)
Encroachment amount Δu: 1.0 × 10 ⁻³ (m)
Diameter d: 43 × 10 ⁻⁶ (m)

(Contact condition 2: F = 9.2)
Young's modulus E: 6.5 × 10 ⁹ (N / m ² )
Density D: 1.67 × 10 ⁸ (lines / m ² )
Length L: 4.5 × 10 ⁻³ (m)
Encroachment amount Δu: 1.0 × 10 ⁻³ (m)
Diameter d: 28 × 10 ⁻⁶ (m)

  Under the conditions shown in the contact conditions 1 and 2, the scraping force F is set to be quite strong. In the conventional example, the bias current is not applied to the rotating brush, and the cleaning is performed only by the mechanical scraping force of the brush, or the object to be cleaned is a photosensitive drum having a higher hardness than the intermediate transfer belt. it is conceivable that.

(Other examples)
The cleaning device, the process unit, and the image forming apparatus according to the present invention are not limited to the above-described embodiments, and can be variously changed within the scope of the gist.

  For example, the present invention can be applied to various image forming apparatuses such as a monochrome printer, a color / monochrome copying machine, and a facsimile, not limited to the tandem type color printer shown in the above embodiment. The image carrier may be in the form of a belt or a roller, and the present invention may be applied as a cleaning device for the photosensitive drum 21 of the print head 20.

1 is a schematic configuration diagram illustrating an image forming apparatus including a cleaning device according to the present invention. It is a principal part enlarged view of the said cleaning apparatus. It is explanatory drawing for showing the contact conditions of a cleaning brush. It is explanatory drawing for showing the contact conditions of a cleaning brush. It is a graph which shows evaluation of cleaning performance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Intermediate transfer belt 14 ... Secondary transfer part 30 ... Cleaning device 31 ... Cleaning brush 32 ... Collection roller 35 ... Conductive brush 36 ... DC power supply

Claims (4)

A conductive cleaning brush that is rotationally driven in contact with the surface of the image carrier that moves in one direction, and bias applying means for applying a bias current to the cleaning brush;
In the cleaning device for collecting the residue on the image carrier with the cleaning brush,
Scraping force F with respect to the residue on the image carrier of the cleaning brush satisfies the following conditions:
0.8 ≦ F ≦ 8.5
However, F = 2yEID / L ²
y = √ {L ² − (L−Δu) ² }
I = πd ^4/64
y = Brush fiber deflection (m)
E = Brush fiber Young's modulus (N / m ² )
I = Brush fiber cross-section second moment D = Brush fiber density (lines / m ² )
L = Brush fiber length (m)
Δu = amount of brush fiber bite (m)
d = Brush fiber diameter (m)
A cleaning device characterized by.   The cleaning apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt.   A process unit comprising the cleaning device according to claim 1, wherein the process unit is detachable from the image forming apparatus.   An image forming apparatus comprising the cleaning device according to claim 1 or the process unit according to claim 3.

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