JP2005266446A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with which color mixture is prevented in an operation in a discharge mode. <P>SOLUTION: The image forming apparatus includes: a photoreceptor; a rotary developing roller that forms a toner image by developing a latent image formed on the photoreceptor with developer; and an intermediate transfer body on which a toner image formed by the developing roller is transferred; and a photoreceptor cleaning means for removing toner present on the surface of the photoreceptor after the transfer of the toner image to the intermediate transfer body and holding the toner on it. In the discharge mode under which the toner held on the photoreceptor cleaning means is discharged onto the photoreceptor and transferred to the intermediate transfer body, the image forming apparatus keeps the photoreceptor and a developer layer formed on the surface of the developing roller apart from each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that does not cause toner color mixing in an ejection mode.

  In recent years, various so-called cleanerless systems for cleaning a photosensitive drum simultaneously with development in an electrophotographic apparatus have been proposed.

  In the cleaner system, a cleaning brush formed in a roller shape is generally used as a cleaning member for cleaning the surface of the photosensitive drum.

  The cleaning brush not only removes toner from the photosensitive drum, but also has a function of holding the removed toner. However, if an excessive amount of toner is held, the function of cleaning the photosensitive drum is deteriorated.

Therefore, in an electrophotographic apparatus having a cleaner-less system, sometimes the toner held by the cleaning brush is discharged on the photosensitive drum and transferred to the intermediate transfer belt to remove the toner from the cleaning brush. doing. In the discharge mode operation, each time toner is transferred to the intermediate transfer belt, the transferred toner is removed by cleaning the intermediate transfer belt (Patent Document 1).
JP 2001-228713 A

  However, in color printers and color copiers, four photosensitive drums that form yellow (Y), magenta (M), cyan (C), and black (K) toner images are tandemly formed along the intermediate transfer belt. It is arranged. A developing unit having a developing roller is disposed in the vicinity of each photosensitive drum. Development is performed by attaching a two-component developer containing toner and magnetic carrier particles to the developing roller of the developing unit and bringing it into contact with the photosensitive drum.

  Therefore, during the discharge mode operation, the photosensitive drum picks up the different color toner transferred to the intermediate transfer belt, and the developing roller picks up the toner to cause color mixing in the developing device, thereby causing deterioration in image quality. There was a problem.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus in which color mixing does not occur in a developing device when operating in a discharge mode.

  The invention according to claim 1 is a photosensitive member, a rotatable developing roller that forms a toner image by developing a latent image formed on the photosensitive member with a developer, and a toner image formed by the developing roller. An intermediate transfer member to which toner is transferred, and a photosensitive member cleaning unit that removes and holds toner existing on the surface of the photosensitive member after the toner image is transferred to the intermediate transfer member. In the discharge mode in which the held toner is discharged onto the photoreceptor and transferred to the intermediate transfer body, the developer layered on the surface of the developing roller and the photoreceptor are held in a non-contact state. The present invention relates to a characteristic image forming apparatus.

  In the image forming apparatus, in the development mode, the developer rises on the developing roller, and the developer contacts the photoconductor, so that the toner in the developer adheres to the photoconductor and the photosensitivity. The latent image on the body is developed to form a toner image. The toner image is transferred from the photosensitive member to an intermediate transfer member, and then transferred to a recording medium such as a recording sheet for printing. The transfer residual toner remaining on the photosensitive member when the toner image is transferred to the intermediate transfer member and the re-toner toner picked up by the photosensitive member once transferred to the transfer member are exposed to the photosensitive member cleaning means. It is removed from the body surface and held.

  On the other hand, when operating in the discharge mode, the transfer residual toner and the retraction toner held by the photosensitive member cleaning unit are discharged onto the photosensitive member and transferred onto the intermediate transferring member, and the intermediate transferring member is cleaned. However, since the developer and the photosensitive member held on the surface of the developing roller are held in non-contact with each other, the toner discharged to the photosensitive member is not picked up on the developing roller by the developer. Therefore, the toner discharged from the photosensitive member cleaning means is not collected by the developing roller, and different color toners are mixed in the developing unit to cause color mixing, or different polarity toners charged to the opposite polarity are mixed. It is possible to prevent the toner charging property in the developing unit from being lowered.

  Examples of the photoconductor cleaning means include a cleaning brush that rotates while rubbing the surface of the photoconductor. However, the cleaning brush is not limited as long as it has a function of removing and holding the transfer residual toner and the retraction toner on the photoconductor. It is not limited to brushes.

  Examples of the intermediate transfer member include an intermediate transfer belt and an intermediate transfer drum.

  As a method of keeping the developer held on the surface of the developing roller and the photosensitive member in a non-contact state in the discharge mode, as described later, the developing roller is rotated in a direction opposite to that during development. Examples of the method include a method in which a portion having no developer on the surface is opposed to the photoconductor, but there is also a method in which the developing roller is moved away from the photoconductor.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in the discharge mode, the developing roller is rotated in a direction opposite to that during development so that no developer is present on the surface of the developing roller. The present invention relates to an image forming apparatus in which an area is formed and stopped at a position where the area faces the photoreceptor.

  In the image forming apparatus, since the latent image on the photosensitive member is developed with the two-component developer, there is a gap between the developing roller and the photosensitive member, and the developer spiked on the developing roller is exposed to light. Development is performed by contacting the body.

  On the other hand, in the discharge mode, by rotating the developing roller in the direction opposite to that during development, an area without developer is formed on the surface of the developing roller. Since the magnetic brush is not formed in the region by the magnetic carrier particles in the developer, if the region is opposed to the photosensitive member, the developer and the photosensitive member layered on the surface of the developing roller are formed. Therefore, since the developing roller does not pick up the transfer residual toner and the retraction toner discharged on the photosensitive member, color mixing does not occur in the developing unit having the developing roller.

  A third aspect of the present invention relates to the image forming apparatus according to the first or second aspect, wherein in the ejection mode, an electric field in a direction to attract the toner is applied to the photoconductor.

  In the image forming apparatus, in the discharge mode, the toner discharged from the photosensitive member cleaning unit is adsorbed to the photosensitive member by the electric field applied to the photosensitive member, so that the toner on the photosensitive member is collected by the developing roller. Is more reliably prevented.

  As described above, according to the present invention, there is provided an image forming apparatus in which color mixing does not occur in the developing device when operating in the discharge mode.

1. Embodiment 1
(1) Configuration A color printer as an example of an image forming apparatus that can suitably carry out the image forming method and the discharge product removing method of the present invention will be described below.

  As shown in FIG. 1, the color printer 10 includes a print unit 30 that forms a color image with toners of four colors of cyan, magenta, yellow, and black, a paper feed tray 16 that is positioned below the print unit 30, and a print And a stacking tray 17 located above the unit 30.

  As shown in FIGS. 1 and 2, the print unit 30 is developed by developing units 12C, 12M, 12Y, and 12K for cyan, magenta, yellow, and black, and developing units 12C, 12M, 12Y, and 12K, respectively. Photoconductors 13C, 13M, 13Y, and 13K and an intermediate transfer belt 14. The developing units 12C, 12M, 12Y, and 12K and the photosensitive members 13C, 13M, 13Y, and 13K are arranged in parallel so as to face the intermediate transfer belt.

  The color printer 10 is a so-called tandem full-color printer, and the four color toner images developed by the developing units 12C, 12M, 12Y, and 12K are transferred onto the intermediate belt 14 while the intermediate transfer belt 14 makes one round. Superimposed.

  Above the paper feed tray 16, a paper feed roller 18 is arranged so as to abut on the leading end of the paper P set in the paper feed tray 16 in the transport direction. Further, the transport path 19 for transporting the paper P is S-shaped upward from the side of the paper feed tray 16 where the paper feed roller 18 is provided to the stacking tray 17 via a transfer unit 22 and a fixing unit 28 described later. It extends to. Two sets of transport rollers 20 are arranged on the transport path 19. The paper P is fed one by one from the paper feed tray 16 along the transport path 19 along the transport path indicated by the two-dot chain line arrow in FIG. 1 by a paper feed roller 18 and a paper handling means (not shown). It is conveyed upward by the conveyance roller 20 and is conveyed to the stacking tray 17 via the transfer unit 22 and the fixing unit 28.

  The transfer unit 22 is provided with a belt conveyance roller 24A around which the intermediate transfer belt 14 is wound, and a transfer roller 26 pressed against the belt conveyance roller 24A. The intermediate transfer belt 14 is sandwiched between the nip portion of the belt conveyance roller 24A and the transfer roller 26, and the toner image is transferred from the intermediate transfer belt 14 when the paper P passes through the nip portion.

  A fixing unit 28 is disposed above the transfer unit 22. The fixing unit 28 includes a heat roller 28A and a backup roller 28B pressed against the heat roller 28A. When the paper P passes through the nip portion between the heat roller 28A and the backup roller 28B, the toner melts and solidifies. The image is fixed. The paper P on which the toner image has been fixed by the fixing unit 28 is discharged onto the stacking tray 17 by a paper discharge roller 29 disposed on the downstream side of the fixing unit 28 in the transport direction.

  Hereinafter, the print unit 30 will be described in more detail.

  As shown in FIGS. 1 and 2, the intermediate transfer belt 14 includes a belt conveyance roller 24A, a belt conveyance roller 24B disposed below the belt conveyance roller 24A, and an obliquely upper side of the belt conveyance roller 24B. It is wound around and supported by a belt conveyance roller 24C disposed on the opposite side of the conveyance path.

  The outer surface of the intermediate transfer belt 14 is a transfer surface 14A to which a toner image is transferred. The development units 12C, 12M, 12Y, and 12K, and the photoreceptors 13C, 13M, 13Y, and 13K face the transfer surface 14A. Are arranged in parallel, and the photosensitive members 13C, 13M, 13Y, and 13K are in contact with the transfer surface 14A. On the other hand, transfer rollers 32C, 32M, 32Y, and 32K are disposed on the opposite side of the photoreceptors 13C, 13M, 13Y, and 13K across the intermediate transfer belt 14, and the intermediate transfer belt 14 includes the transfer rollers 32C, 32M, and 32Y. , 32K are pressed against the photoreceptors 13C, 13M, 13Y, 13K.

  The photoreceptors 13C, 13M, 13Y, and 13K rotate in the counterclockwise direction as indicated by an arrow b in FIG.

  In FIG. 2, a toner concentration detection sensor 15 is disposed adjacent to the downstream side of the photoreceptor 13K with respect to the rotation direction of the intermediate transfer belt 14 indicated by an arrow a and facing the transfer surface 14A. The toner concentration detection sensor 15 has a function of detecting the concentration of toner transferred to the transfer surface 14A.

  Hereinafter, the developing units 12C, 12M, 12Y, and 12K and the photoreceptors 13C, 13M, 13Y, and 13K will be described. Hereinafter, the developing units 12C, 12M, 12Y, and 12K may be collectively referred to as “developing unit 12”, and the photosensitive members 13C, 13M, 13Y, and 13K may be collectively referred to as “photosensitive member 13”.

  As shown in FIGS. 2 and 3, an intermediate transfer belt 14, a brush roller 34, a charging roller 36, and a developing unit 12 are provided around the photoconductor 13 in order along the rotation direction b. The intermediate transfer belt 14, the brush roller 34, and the charging roller 36 are all in contact with the photosensitive surface 13 </ b> A of the photoreceptor 13. Further, between the charging roller 36 and the developing unit 12, an LED array head 40 that performs line exposure of the photosensitive surface 13A is disposed. The intermediate transfer belt 14 and the brush roller 34 correspond to the intermediate transfer member and the photosensitive member cleaning unit in the present invention, respectively.

  As shown in FIGS. 3 and 4, the developing unit 12 is positioned below the developing roller 38 and the developing roller 38 disposed so as to face the photosensitive member 13, and the two-component developer is placed on the developing roller 38. Screw feeders 39A and 39B, and a housing 37 for housing the developing roller 38 and the screw feeders 39A and 39B. The two-component developer contains toner and magnetic carrier particles as main components. An opening 37 </ b> A is provided in a portion of the housing 37 that faces the photoreceptor 13.

  As shown in FIG. 3, the developing roller 38 is disposed such that a gap, that is, a developing gap is formed between the developing roller 38 and the photosensitive surface 13A. The developing roller 38 includes a cylindrical magnet roll 38B and a sleeve 38A that covers the magnet roll 38B. The magnet roll 38B has a cylindrical shape, and the sleeve 38A has the same counter-clockwise direction as the rotation direction b of the photoconductor 13 in other words, as shown by an arrow c in FIG. It rotates in a direction facing the photoconductor 13 at a portion facing the body 13, in other words, it is against the rotation. Thereby, the transfer efficiency of the toner from the developing roller 38 to the photosensitive member 13 is enhanced.

  As shown in FIG. 3, magnetic poles are formed on the magnet roll 38A in order of the developing pole S1, the pick-off pole N1, the pickup pole N2, the trimming pole S2, and the transport pole N3 in this order along the rotation direction c. The development pole S1 and the trimming pole S2 are all S poles, and the pickoff pole N1, the pickup pole N2, and the transport pole N3 are all N poles.

  A trimming blade 41 that aligns the height of the magnetic brush in cooperation with the trimming pole S <b> 2 extends toward the developing roller 38 at the opposing portion of the trimming pole S <b> 2. A negative developing bias voltage is applied to the developing roller 38.

  As shown in FIGS. 3 and 4, the magnet roll 38 </ b> B is held at a position where the developing pole S <b> 1 faces the photoreceptor 13.

(2) Operation of Color Printer The operation of the color printer 10 will be described. The color printer 10 is normally operated in a development mode in which an image is formed on the paper P. However, the color printer 10 is operated in a discharge mode for a predetermined time, for example, 3 to 5 minutes every predetermined number of prints, for example, 100 sheets.

  The development mode and the discharge mode will be described below.

(2-1) Development Mode In the development mode, the photoreceptor 13 rotates in the direction of arrow b at a constant speed, and the sleeve 38A rotates in the direction of arrow c.

  Therefore, in the developing unit 12, the two-component developer supplied to the housing 37 by the screw feeders 39A and 39B is picked up on the sleeve 38A by the pickup pole N2, and the toner adheres as shown in FIG. A magnetic brush is formed.

  The magnetic brush has the same height at the trimming pole S2, and is conveyed toward the developing pole S1 by the conveying pole N3. Then, as shown in FIG. 5, the developing electrode S1 contacts the photoconductor 13.

  Here, since the photosensitive surface 13A is negatively charged by the charging roller 36 and exposed by the LED array head 40 to form a latent image, it is attached to the magnetic brush as shown in FIGS. The toner adheres to the latent image portion to form a toner image.

  The toner adhering to the photosensitive surface 13A is electrically drawn toward the intermediate transfer belt 14 by the transfer roller 32 to which a positive transfer voltage having a polarity opposite to that of the toner is applied. As a result, the toner image on the photosensitive surface 13A is transferred from the photosensitive member 13 to the intermediate transfer belt.

  On the other hand, a magnetic brush almost entirely composed of a magnetic carrier remains on the surface of the sleeve 38A. The magnetic brush, which is almost only a magnetic carrier, falls off the surface of the sleeve 38A at the pick-off pole N1 and returns into the housing 37 as the sleeve 38A rotates. Therefore, as shown in FIG. 4, a region without a magnetic brush is formed between the pick-off pole N1 and the pickup pole N2.

  However, as indicated by the black circles in FIG. 6, the toner adhering to the photosensitive member 13 by the developing roller 38 is not completely transferred to the intermediate transfer belt 14, and a part of the toner is transferred onto the photosensitive surface 13A as residual transfer toner. Remains. In addition, as indicated by white circles in the same drawing, a part of the toner that has already been transferred to the intermediate transfer belt 14 is transferred to the photosensitive member 13 as a retro toner. These transfer residual toner and retra toner are scraped and held by the brush roller 34, and the photosensitive surface 13A is cleaned.

(2-2) Discharge Mode In the discharge mode, the sleeve 38A rotates about ½ in the direction opposite to the rotation direction c during development as indicated by an arrow d in FIG. Accordingly, since the developer picked up by the pickup pole N2 is immediately picked off by the pick-off pole N2, as the sleeve 38A rotates along the rotation direction d, the area without the magnetic brush is expanded. Then, when the rotation is about ½, the area without the magnetic brush extends beyond the developing gap where the developing roller 38 faces the photosensitive member 13, and the sleeve 38A is stopped at this position.

  In this state, when a voltage having the same polarity as the transfer residual toner and the retraction toner held by the brush roller 34 is applied to the brush roller 34 and a voltage having the opposite polarity is applied to the photoconductor 13, as shown in FIG. The transfer residual toner and the retraction toner are discharged from the brush roller 34 onto the photosensitive member 13.

  The untransferred toner and the retraction toner discharged on the photoconductor 13 pass through the developing gap when the photoconductor 13 rotates along the rotation direction b. However, since there is no magnetic brush in the development gap as shown in FIG. 7, the transfer residual toner and the retraction toner pass through the development gap without being picked up by the sleeve 38A, and are transferred to the intermediate transfer belt 14 by the transfer roller 32. Is done. The untransferred toner and the re-toner transferred to the intermediate transfer belt 14 are removed from the intermediate transfer belt 14 by an intermediate transfer belt cleaner (not shown).

(3) Features of the Color Printer of Embodiment 1 In the discharge mode, the developing roller 38 does not pick up the transfer residual toner and the retraction toner discharged from the brush roller 34 onto the photosensitive member 13. There is no color mixing due to the retraction toner or the like inside the body 37.

  Accordingly, it is possible to effectively prevent deterioration of the image quality of the printed image due to color mixing.

FIG. 1 is a schematic cross-sectional view illustrating an outline of the configuration of the color printer according to the first embodiment. FIG. 2 is an enlarged view showing a configuration of a printing unit of the laser printer shown in FIG. FIG. 3 is an enlarged cross-sectional view showing the configuration of the developing unit and the vicinity thereof in the print unit shown in FIG. 4 is a schematic diagram showing a state in which a magnetic brush is formed on the surface of the developing roller provided in the developing unit shown in FIG. 3 in the developing mode. FIG. 5 is a schematic diagram showing the behavior of the magnetic brush and toner near the development pole S1 in the development mode. FIG. 6 is an enlarged view showing toner movement in the development mode. FIG. 7 is a schematic view showing a state where the magnetic brush is removed from the surface of the developing roller in the discharge mode. FIG. 8 is an enlarged view showing the movement of the toner in the ejection mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color printer 13 Photoconductor 14 Intermediate transfer belt 34 Brush roller 36 Charging roller 38 Developing roller 40 LED array head

Claims (3)

A photosensitive member, a rotatable developing roller for developing a latent image formed on the photosensitive member with a developer to form a toner image, an intermediate transfer member onto which the toner image formed by the developing roller is transferred, Photoconductor cleaning means for removing and holding the toner present on the surface of the photoconductor after the toner image is transferred to the intermediate transfer body;
In the discharge mode in which the toner held by the photosensitive member cleaning unit is discharged onto the photosensitive member and transferred to the intermediate transfer member, the developer layered on the surface of the developing roller and the photosensitive member are not contacted with each other. An image forming apparatus characterized by being held in a state.   In the discharge mode, the developing roller is rotated in a direction opposite to that during development to form a developer-free area on the surface of the developing roller, and the area stops at a position facing the photoconductor. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein an electric field in a direction to attract the toner is applied to the photoconductor in the discharge mode.

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