JP2006350063A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus using a brush member as a toner temporarily recovering member, in which the amount of frictional electrification of a brush and a photoreceptor is suppressed. <P>SOLUTION: A color printer 1 is provided with a photoreceptor drum 20, an exposure device 40, a developing device 50, and a transfer device 60. The color printer 1 is provided with a rotating brush member 70 which comes into contact with the position after transfer and before latent image formation of the photoreceptor drum 20, temporarily takes in transfer residual toner from the photoreceptor drum 20, and discharges the transfer residual toner onto the photoreceptor drum 20. The rotating brush member 70 satisfies N×T<SP>4</SP>/L<SP>3</SP>≤0.236, where L(mm) is the length of brush fibers, T(tex) is the thickness of the brush fibers, and N(number of pieces/mm<SP>2</SP>) is the planted fiber density of the brush fibers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a so-called cleanerless type image forming apparatus that returns untransferred toner to a developing unit without discarding. More specifically, the present invention relates to an image forming apparatus using a brush member as a temporary toner collecting member.

  Conventionally, in an electrophotographic image forming apparatus, a toner image is generally formed on an image carrier such as a photosensitive drum, and the toner image is transferred onto a sheet or the like to obtain an image. There is also an image forming apparatus called cleanerless in which residual toner remaining on the photoconductor after transfer is recovered by a developing device and reused instead of being removed and discarded by a cleaning device such as a blade.

  As a conventional cleanerless image forming apparatus, for example, Patent Document 1 has a rotating brush that contacts a photosensitive member between a transfer device and a charging device, and an AC bias voltage is applied to the brush. An image forming apparatus is disclosed. In the image forming apparatus described in this document, the toner is prevented from sticking to the charging brush by causing the rotating brush to disturb the toner and temporarily collect the toner that is easily released.

Patent Document 2 discloses an image forming apparatus in which a rotating brush is used as a cleaning device. According to this document, the bristles of the rotating brush are constituted by at least two types of brushes, whereby a rotating brush having a predetermined resistance value can be obtained while maintaining a predetermined rigidity.
JP 2001-272860 A Japanese Patent Laid-Open No. 11-52807

  However, when the brush member is used as a toner temporary recovery member, the charge amount of the toner changes due to frictional charging between the brush and the photosensitive member in the toner recovery / discharge process. In general, the triboelectric charge increases the charge amount of the toner and increases the force attracted to the photoreceptor. If the increase in the charge amount is large, the adhesion force of the toner to the photoreceptor exceeds the peeling force by the developing device, and there is a possibility that the toner cannot be collected by the developing device. In that case, there is a risk that the image quality may be deteriorated by the toner that cannot be collected.

  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 suppressing the frictional charge amount between the brush and the photosensitive member in the case where the brush member is used as the toner temporary collection member.

An image forming apparatus of the present invention, which has been made for the purpose of solving this problem, includes an image carrier, a latent image forming unit for forming a latent image on the image carrier, and a developer for developing the latent image on the image carrier with toner. And a transfer unit that transfers the toner image on the image carrier to the transfer target, the image forming apparatus being in contact with a position on the image carrier before the formation of the latent image after transfer, and the transfer residual from the image carrier. It has a brush member that takes in toner once and discharges it onto the image carrier. The brush member has a brush fiber length L (mm), a brush fiber thickness T (tex), and a brush fiber flocking density N (Book / mm ² ), N · T ⁴ / L ³ ≦ 0.236 is satisfied.

According to the image forming apparatus of the present invention, a latent image is formed on the image carrier by the latent image forming unit, and the latent image is developed with toner by the developing device. Further, the toner image is transferred to the transfer target by the transfer unit. Here, since the brush member that contacts the position before the latent image after transfer satisfies N · T ⁴ / L ³ ≦ 0.236, the frictional charge amount of the toner by the brush member is in an appropriate range. Is suppressed by. Hereinafter, R = N · T ⁴ / L ^{3 is referred} to as a brush stiffness index.

  According to the present invention, in the case where a brush member is used as the toner temporary collection member, the frictional charge amount between the brush and the photosensitive member can be suppressed.

  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 an electrophotographic color printer.

  The color printer 1 of this embodiment has image forming units 10Y, 10M, 10C, and 10Bk for each color, an intermediate transfer belt 11, a secondary transfer device 12, and a belt cleaner 13, as schematically shown in FIG. Yes. The image forming units 10Y, 10M, 10C, and 10Bk for each color are arranged along the intermediate transfer belt 11 and form the toner images of the respective colors on the intermediate transfer belt 11. The superimposed toner images are transferred to the recording paper 14 by the secondary transfer device 12. Further, the toner remaining on the intermediate transfer belt 11 is scraped off by the belt cleaner 13. In this embodiment, the color printer 1 uses negatively charged toner. In the following description, the subscript YMCBk for each color is omitted when there is no need for distinction.

  Each color image forming unit 10 has the same configuration. As shown in FIG. 1, each image forming unit 10 has a charging device 30, an exposure device 40, a developing device 50, and a transfer device 60 around the photosensitive drum 20. Each device uses a general one. In the color printer 1 of this embodiment, a rotating brush member 70 is provided between the transfer device 60 and the charging device 30. Each rotating brush member 70 is controlled by a controller 80 so that a bias voltage is applied. Since both the rotating brush member 70 and the photosensitive drum 20 are rotated clockwise in the drawing, they are rotated in the counter direction. Further, the rotating brush member 70 is arranged so that the hair tip contacts the surface of the photosensitive drum 20 with a certain amount of pushing.

  During the operation of the color printer 1, the tip of the rotating brush member 70 and the surface of the photosensitive drum 20 are rubbed with each other, so that the charge amount of toner existing between them changes. In the experiments by the inventors, it has been found that this triboelectric charge amount depends on the length of the brush fiber, the thickness of the brush fiber, the flocking density of the brush fiber, etc., even when the same material of the brush fiber is used. In general, the shorter the length of the brush fiber, the thicker the brush fiber, and the higher the flocking density of the brush fiber, the greater the triboelectric charge amount.

  Results of experiments on the nylon rotating brush member 70 are shown in FIGS. In these drawings, the horizontal axis represents the ratio of the rotational speed of the rotating brush member 70 to the rotational speed of the photosensitive drum 20. The DC component of the bias voltage applied to the rotating brush member 70 was −100 V, and the amount of pushing of the rotating brush member 70 into the photosensitive drum 20 was 0.4 mm. In any of the results, as the rotational speed increases, the charging friction increases and the toner charge change amount increases.

  For example, FIG. 2 shows a result of measuring the toner charge change amount by using a fiber having an outer diameter of 13 mm and changing the length to 1.5 mm, 2.5 mm, and 3.5 mm. In the rotating brush member 70 having a short brush fiber, the amount of change in toner charge increased rapidly as the number of rotations was increased. Also, FIG. 3 shows the relationship between the thickness of the brush fibers of the rotating brush member 70 and the triboelectric charge amount. The circle mark indicates 0.222 tex (2 denier), the triangle mark indicates 0.444 tex (4 denier), and the square mark indicates 0.667 tex (6 denier). It is a result using the used brush. That is, the thicker the brush fiber, the larger the toner charge change amount.

FIG. 4 shows the relationship between the flocking density of the brush of the rotating brush member 70 and the triboelectric charge amount. The circle marks indicate 93 lines / mm ² (60 kF), the triangle marks indicate 186 lines / mm ² (120 kF), and the square marks indicate 666.5 lines / mm ² (430 kF). It is the result using the brush using a fiber. That is, the toner charge change amount is larger as the brushing density of the brush is larger. In FIGS. 3 and 4, since the unit system conventionally used is used, the numerical values based on these unit systems are shown in parentheses in addition to the millimeter unit system.

  In the color printer 1 of this embodiment, the charge amount of the toner accommodated in the developing device 50 is about 20 to 40 (−μC). Further, in the transfer device 60, since a positive transfer bias is applied to the toner, the charge amount of the toner that has passed through the transfer device 60 is reduced to about 0 to 20 (−μC). Thereafter, the amount of charge is increased to some extent at the position of the rotating brush member 70 and again faces the developing device 50.

  Here, in order for the toner to be faced to be collected by the developing device 50, it is necessary that the amount of charge is substantially the same as that of the toner in the developing device 50. If this amount of charge is too large, the attracting force between the toner and the photosensitive drum 20 is larger than the toner attracting force due to the electric field between the photosensitive drum 20 and the developing device 50, and This is because recovery becomes difficult. Therefore, the amount of increase in charge at the rotating brush member 70 is suppressed so that the charge amount of the toner when facing the developing device 50 is 40 (−μC) or less. That is, the rotating brush member 70 is employed such that the amount of increase in charge at the rotating brush member 70 is within 20 (−μC).

As described above, the triboelectric charge amount by the rotating brush member 70 depends on the length L (mm) of the brush fibers, the thickness T (tex) of the brush fibers, and the flocking density N (lines / mm ² ) of the brush fibers. Dependent. Here, the inventors have found that an appropriate brush can be easily selected by using the brush stiffness index R = N · T ⁴ / L ³ as an index of the frictional charge amount of the brush. That is, it has been found that if the rotating brush member 70 having R ≦ 0.236 is employed, the amount of increase in charge at the rotating brush member 70 is within 20 (−μC).

Next, changes in the brush stiffness index when the length, thickness, and flocking density of the brush fibers are changed are shown in FIGS. In these graphs, the horizontal axis represents the length L (mm) of the brush fiber, and the vertical axis represents the brush stiffness index as a logarithmic graph. However, in FIG. 5 to FIG. 8, the notation based on the conventionally used unit system is also made. The brush stiffness index G in the figure is expressed as G = M · D ⁴ / D using D representing the thickness of the brush fiber in denier units and M representing the flock density of the brush fibers in kilofilament (kF) units. It is those calculated as L ^3, and has a different numeric from the above brush stiffness index R. In the following, the numerical values based on the unit system conventionally used in addition to the millimeter unit system are shown in parentheses.

These are shown by changing the flocking density for each figure. FIG. 5 shows a flocking density of 93 / mm ² (60 kF), FIG. 6 shows a flocking density of 186 / mm ² (120 kF), and FIG. density 372 present / mm ² (240kF), 8 is the result of the flocking density 744 present / mm ² (480kF). In addition, the thickness of the brush fiber in each graph is shown in denier units with each symbol in the graph.

  If the brush stiffness index R is in the range of R ≦ 0.236, the brush stiffness index G obtained in this conventional unit system is in the range of G ≦ 1000. Therefore, an appropriate brush fiber characteristic may be selected from the range of G ≦ 1000 in the drawing. For example, a range indicated by a dashed square in FIG. 5 is desirable. In practice, however, the length L (mm) of the brush fiber is not preferable due to other factors, whether it is too long or too short. If the rotating brush member 70 is made of fibers that are too long, the bristles may fall asleep due to rotation and may become wrinkled as they are used. In addition, it is difficult to set an appropriate push-in amount with the rotating brush member 70 of a fiber that is too short.

Therefore, a practical and preferable range of the brush fibers is a range surrounded by a solid square in each figure. For example, in the case of a flocking density of 93 / mm ² (60 kF) and a fiber thickness of 0.222 tex (2 denier) indicated by a circle in FIG. 5, the fiber length L is in the range of 2 to 4 mm. Appropriate. It has also been found that the rotating brush member 70 using finer fibers is required as the flocking density increases.

As described above in detail, according to the color printer 1 having the rotating brush member 70 of this embodiment, the length L (mm) of the brush fiber and the thickness T ( Tex) and the brush fiber density N (lines / mm ² ) of the brush fibers are selected, so that the amount of charge increase in the rotating brush member 70 can be suppressed to within 20 (−μC). Therefore, in the case where the rotating brush member 70 is used as the toner temporary collection member, the frictional charge amount between the brush and the photosensitive member can be suppressed.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, a fixed brush may be used as the brush member instead of the rotating brush.

1 is a schematic configuration diagram of a color printer according to an embodiment. It is explanatory drawing which shows the difference in the triboelectric charge amount by the length of a brush fiber. It is explanatory drawing which shows the difference in the triboelectric charge amount by the thickness of a brush fiber. It is explanatory drawing which shows the difference in the triboelectric charge amount by the flock density of a brush fiber. It is explanatory drawing which shows the relationship between the length / thickness of a brush fiber, and a brush rigidity index | exponent in the case of the flocking density of 60 kF. It is explanatory drawing which shows the relationship between the length / thickness of a brush fiber, and a brush rigidity index | exponent in the case of the flocking density of 120 kF. It is explanatory drawing which shows the relationship between the length / thickness of a brush fiber, and a brush rigidity index | exponent in the case of the flocking density of 240 kF. It is explanatory drawing which shows the relationship between the length / thickness of a brush fiber, and a brush rigidity index | exponent in the case of the flocking density of 480 kF.

Explanation of symbols

1 Color printer (image forming device)
20 Photosensitive drum (image carrier)
40 Exposure device (latent image forming section)
50 Developer (Developer)
60 Transfer device (transfer device)
70 Rotating brush member (brush member)

Claims (1)

An image carrier, a latent image forming unit that forms a latent image on the image carrier, a developing unit that develops the latent image on the image carrier with toner, and a toner image on the image carrier on a transfer target In an image forming apparatus having a transfer portion for transferring,
A brush member that contacts a position before formation of a latent image after transfer on the image carrier, takes in transfer residual toner from the image carrier, and discharges the toner onto the image carrier;
When the length of the brush fiber is L (mm), the thickness of the brush fiber is T (tex), and the flocking density of the brush fiber is N (lines / mm ² ),
N · T ⁴ / L ³ ≦ 0.236
An image forming apparatus satisfying the requirements.

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