JP4731218B2 - Development device - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus using an electrophotographic process such as a copying machine, a printer, or a facsimile machine, and more particularly to a developing device using a one-component developer.

  In general, in a developing device using a one-component developer (toner), the toner supplied to a developer carrier (for example, a developing roller) is regulated by a regulating member (layer thickness regulating member: regulating blade) and the toner is regulated. Is charged to form a toner thin layer on the developing roller, and the toner thin layer is brought close to an image carrier such as a photosensitive drum to develop the electrostatic latent image on the photosensitive drum. The developer carrying member has a developing sleeve that includes a fixed magnet roller having a plurality of magnetic poles, and uses a magnetic binding force formed on the developing sleeve by the fixed magnet roller to supply toner onto the developing sleeve. While being held, the layer thickness is regulated by a regulating blade to form a thin toner layer on the developing sleeve.

  In such a developing device, a so-called jumping development system is used, and an alternating electric field is applied between the photosensitive drum and the developing roller to act on the toner on the developing sleeve toward the photosensitive drum. Thus, the toner is caused to fly to the photosensitive drum, and the electrostatic latent image on the photosensitive drum is developed.

  The flying force that causes the toner to fly is proportional to the product of the magnitude of the electric field acting on the toner and the charge amount of the toner, but the toner itself has a higher resistance, and the smaller its particle size, the more electrostatic Capacity increases. For this reason, in the above developing device, the toner having a smaller particle size is consumed earlier, and the toner having a larger particle size tends to stay in the developing device. When the ratio of toner having a large particle diameter increases in the developing device, so-called selective development occurs and image quality deteriorates. That is, a toner having a large particle size has a small specific charge amount and is difficult to be used for development. As a result, an image defect such as a decrease in image density and image fogging occurs.

  In addition, when the toner stays in the developing device, the collision between the toners increases, and not only the charge balance of the toner is lost, but also due to embedding or peeling of the external additive added to the toner, The specific charge amount decreases, and this also causes image density reduction and image defects such as image fogging.

  In particular, there is a problem that toner is attracted to the vicinity of the regulation blade at the rear side of the regulation blade, that is, the upstream portion in the rotation direction of the developing sleeve, and toner retention occurs (particularly, when the regulation blade is a magnetic body, Magnetic toner is easily attracted to the regulating blade).

  On the other hand, in order to prevent image density unevenness and image fogging, a magnet is disposed with a gap from the circumferential surface of the developing sleeve, and the amount of toner passing on the circumferential surface of the developing sleeve is regulated by the magnet, and this magnet Provide a non-magnetic blade on the surface of the photosensitive drum without gaps, and make the gap between the magnet and the peripheral surface of the developing sleeve wider than the gap between the non-magnetic blade and the peripheral surface of the developing sleeve. There is one in which a toner thin layer having a layer thickness is stably formed over a long period of time (see Patent Document 1).

  Further, in order to obtain a good image free from image fog and image unevenness, a magnetic blade that regulates the amount of toner conveyed on the developing sleeve and a supply roller 6 that contacts the developing sleeve and supplies and peels off the toner are provided. In some cases, the supply roller is disposed in contact with a position near the position where the magnetic restraint force generated by the magnet is minimized on the developing sleeve (see Patent Document 2).

JP 2001-117360 A JP 7-44024 A

  By the way, in the developing device described in Patent Document 1, a nonmagnetic blade (regulating blade) is provided to face the developing sleeve, and a magnet is arranged with a gap from the peripheral surface of the developing sleeve, and development is performed by the magnet. Although it has been shown that a toner thin layer having a constant layer thickness is stably formed on the developing sleeve by regulating the passing amount of the toner adhering to the sleeve peripheral surface, it is described in Patent Document 1. In the developing device, a thin toner layer having a constant layer thickness is simply formed, and it is difficult to prevent a problem that toner stays behind the regulating blade.

  On the other hand, in the developing device described in Patent Document 2, a magnetic blade (regulating blade) is provided, and the supply roller is disposed in contact with a position near the position where the magnetic restraining force generated by the magnet is minimized on the developing sleeve. Although trying to prevent image defects, the developing device described in Patent Document 2 has a problem that toner stays unavoidably behind the magnetic blade.

  In any case, both Patent Documents 1 and 2 have a problem that it is difficult to prevent toner retention occurring behind the regulating blade, and it is difficult to prevent image defects due to toner retention.

  In order to solve the above problems, an object of the present invention is to provide a developing device that effectively prevents toner retention and does not cause image defects.

In order to solve the above-described problems, the present invention includes a developing sleeve including a fixed magnet roller in which a plurality of magnetic poles are formed, and a layer thickness regulating member that regulates the thickness of the developer layer formed on the developing sleeve. A developing device that rotates the developing sleeve to form a thin developer layer on the developing sleeve and then develops the electrostatic latent image on the image bearing member at the developing position, as viewed from the developing position. A repulsive magnetic field forming means for forming a repulsive magnetic field for stirring the developer is disposed upstream of the layer thickness restricting member in the rotation direction of the developing sleeve, and the fixed magnet is opposed to the layer thickness restricting member. One magnetic pole of the roller corresponds, and the repulsive magnetic field forming means includes a plurality of magnets, and the plurality of magnets extend in a radial direction of the developing sleeve with the magnetic poles facing each other, and the plurality of magnets Out of Serial disposed on the developing sleeve side magnet is an magnetic pole and the pole of the magnetic pole facing the developing sleeve the fixed magnet roller, the magnetic poles opposed to each other in the plurality of magnets and wherein homopolar der Rukoto To do.

  In the present invention, it is preferable that the magnetic poles facing each other in the plurality of magnets are in contact with each other, and further, the plurality of magnets are located on the upstream side in the rotation direction of the developing sleeve of the layer thickness regulating member. It is preferable to adhere to.

  As described above, in the developing device of the present invention, the repulsive magnetic field forming means for forming the repulsive magnetic field for stirring the developer is disposed on the upstream side in the rotation direction of the developing sleeve with respect to the layer thickness regulating member as viewed from the developing position. Therefore, toner retention does not occur on the upstream side of the layer thickness regulating member, and as a result, there is an effect that image defects can be prevented.

  In the present invention, one magnetic pole of the fixed magnet roller corresponds to the layer thickness regulating member, the repulsive magnetic field forming means includes a plurality of magnets, and the plurality of magnets are arranged in the radial direction of the developing sleeve with the magnetic poles facing each other. The magnetic poles that extend and are arranged on the developing sleeve side of the plurality of magnets have the same magnetic pole as the one magnetic pole of the fixed magnet roller, and the magnetic poles facing each other in the plural magnets have the same polarity. As a result, the repulsive magnetic field can be effectively formed with a simple configuration, and as a result, toner retention can be effectively prevented.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a diagram schematically showing an example of an image forming apparatus provided with a developing device according to a first embodiment of the present invention. The illustrated image forming apparatus 10 includes an image carrier (photosensitive drum) 11 and a laser scanning unit. 12, a charger 13, a developing device 14, and a cleaning unit 15, and the charger 13, the developing device 14, and the cleaning unit 15 are disposed around the photosensitive drum 11. The surface of the photosensitive drum 11 is charged by the charger 13, and the surface of the photosensitive drum 11 is exposed according to the print data by the laser scanning unit 12, and an electrostatic latent image is formed on the photosensitive drum 11.

  The electrostatic latent image on the photoconductor drum 11 is developed by the developing device 14 to become a toner image. The recording paper is conveyed from the paper feeding device 16 to the nip portion between the transfer roller 18 and the photosensitive drum 11 by the conveying roller 17, the toner image on the photosensitive drum 11 is transferred to the recording paper, and the recording paper is fixed. It is conveyed to the device 19. Then, after the toner image on the recording paper is fixed by the fixing device 19, the toner image is discharged onto the paper discharge tray 20. After the transfer, residual toner remaining on the photosensitive drum 11 is cleaned by the cleaning unit 15.

  In the following description, the toner includes not only a resin toner (toner particles) containing a colorant but also a toner containing an internal additive such as an external additive and a charge inhibitor.

  Referring to FIG. 2, FIG. 2 is a cross-sectional view showing the developing device 14, and the developing device 14 has a developing container 21 in which a one-component developer (for example, magnetic toner) is accommodated. A developing roller 22 that faces the photosensitive drum 11 at the developing position is disposed in 21. Although not shown in FIG. 2, the developing roller 22 has a developing sleeve 22a including a fixed magnet roller having a plurality of magnetic poles, and the developing sleeve 22a is formed of a nonmagnetic material such as aluminum or stainless steel, for example. Then, it is rotationally driven in the direction indicated by the solid line arrow in the figure.

  The developing container 21 is provided with a regulating blade (magnetic blade (manufactured by SUS)) 23 facing the developing sleeve 22. The regulating blade 23 charges the toner and regulates the amount of toner passing. A thin toner layer is formed on the developing sleeve 22a. A magnet body 24 is fixed to the rear surface of the regulating blade 23 (the surface located upstream of the developing sleeve 22a in the rotation direction as viewed from the developing position). Further, as shown in the figure, first and second stirring screws 25 and 26 are arranged in the developing container 11, and the toner in the developing container 21 is stirred while the stirring screws 25 and 26 are rotated. The toner is conveyed in the direction of the developing roller 22.

  3 to 5, FIG. 3 is a view of the developing device 14 as viewed from above and FIG. 4 is a view of the developing device as viewed from the side. FIG. 5 shows the configuration of the developing roller and the positional relationship between the developing roller, the regulating blade, and the magnet body. In FIG. 4, the magnet body 24 is omitted. As shown in FIG. 3, the developing container 21 is formed in a box shape, and the first and second stirring screws 25 and 26 extend along the longitudinal direction of the developing roller 22. A partition wall 27 extending in the longitudinal direction of the developing roller 22 is disposed between the first and second stirring screws 25 and 26 in the developing container 21, and both ends in the longitudinal direction of the partition wall 27 and the developing container. A passage through which the toner passes is defined between the inner surface 21 and the inner surface. The developing sleeve 22a and the first and second stirring screws 25 and 26 are rotationally driven by a main motor (not shown). In the example shown in FIG. 5, the developing roller 22 has a fixed magnet roller 22b having three magnetic poles and a developing sleeve 22a, and the regulating blade 23 and one magnetic pole (S pole) of the fixed magnet roller 22b face each other. There is a relationship, and a magnet body 24 is fixed to the surface of the regulating blade 23 located upstream of the developing sleeve 22a in the rotation direction (this magnet body 24 includes first and second magnets 24a and 24b as will be described later). have.

  The toner replenished to the developing container 21 from the toner replenishing port 28 (see FIG. 4) is conveyed to the second agitating screw 26 side through the passage described above while being agitated by the rotational drive of the first agitating screw 25. Is done. Then, the toner is supplied to the developing roller 22 by the second stirring screw 26. Then, the toner separated from the developing sleeve 22a is collected by the second stirring screw 26 and sent to the first stirring screw 25 side through the passage. That is, as shown by thick arrows in FIGS. 3 and 4, the toner is circulated in the order of the first stirring screw 25, the passage, the second stirring screw 26, and the passage along the partition wall 27. The toner is supplied to the developing sleeve 22a and the toner separated from the developing sleeve 22a is collected.

  As described above, when toner is supplied to the peripheral surface of the developing sleeve 22a, the toner adheres to the peripheral surface of the developing sleeve 22a by the magnetic force of the fixed magnet roller 22b. As the developing sleeve 22a rotates, the toner adhering to the peripheral surface of the developing sleeve 22a is frictionally charged and restricted in passage when passing through the gap between the developing sleeve 22a and the regulating blade 23. A thin toner layer is formed on the peripheral surface.

  The toner thin layer moves in accordance with the rotation of the developing sleeve 22a, and the photosensitive drum 11 and the developing roller 22 are closest to each other by an alternating electric field applied between the photosensitive drum 11 and the developing roller 22. At the developing position, the toner on the developing sleeve 22a flies to the electrostatic latent image on the photosensitive drum 11, and the electrostatic latent image is developed to form a toner image. At the developing position, the toner remaining on the developing sleeve 22a without flying onto the photosensitive drum 11 moves with the rotation of the developing sleeve 22a and is peeled off from the developing sleeve 22a by the rotating action of the second stirring screw 26. It is done. Then, new toner is supplied to the developing sleeve 22 a by the second stirring screw 26. As described above, the toner peeled off from the developing sleeve 22a is mixed with the newly supplied toner while being circulated by the first and second stirring screws 25 and 26.

  By the way, as described above, when the toner layer thickness is regulated by the regulating blade 23, the toner that could not pass through the gap between the developing sleeve 22a and the regulating blade 23 is behind the regulating blade, that is, upstream in the rotation direction of the developing sleeve 22a. It stays along the regulation blade surface located on the side. Since the developing sleeve 22a is continuously rotated, the toner stays one after another on the upstream side of the regulating blade 22a, and the collision between the toners increases on the upstream side of the regulating blade 23. In addition to the loss of the charge balance, the specific charge amount is reduced due to the embedding or peeling of the external additive externally added to the toner. As a result, image defects such as a decrease in image density and image fogging occur.

  In this embodiment, in order to prevent toner retention as described above, the magnet body 24 described above is fixed to the upstream surface of the regulating blade 23 in the rotation direction of the developing sleeve 22a. Referring to FIG. 6, if the south pole of the fixed magnet roller is opposed to the tip of the regulating blade 23, the north pole appears at the tip of the regulating blade 23 if the regulating blade 23 is a magnetic body. The toner is restrained by the magnetic force from the north pole to the south pole.

  On the other hand, the magnet body 24 has first and second magnets 24a and 24b, and the first and second magnets 24a and 24b extend in the radial direction of the developing sleeve 22a. As shown in the figure, an S pole having the same polarity as the S pole of the fixed magnet roller is magnetized on the lower surface of the first magnet 24a (the surface facing the developing sleeve 22a). The N pole of the second magnet is in contact with the N pole of the first magnet 24a (that is, the first and second magnets 24a and 24b are in contact with each other with the same polarity). become). Therefore, the upper surface and the lower surface of the magnet body 24 are both S poles.

  Referring also to FIG. 7 (only the first magnet 24a is shown in FIG. 7 and the second magnet 24b is omitted), as described above, the lower surface of the magnet body 24 has an S pole. Therefore, a repulsive magnetic field that repels the S pole of the fixed magnet roller is formed, and the first and second magnets 24a and 24b are in contact with each other with the N poles (that is, the same poles). A repulsive magnetic field is also formed between the first and second magnets 24a and 24b.

  Therefore, as shown in FIG. 7, in the vicinity of the first magnet 24a and the developing sleeve 22a, a repulsive magnetic field is formed as shown by a solid arrow, and the gap between the regulating blade 23 and the developing sleeve 22a is formed. Even if the toner that could not pass through is going to wrap around the back side of the regulating blade 23, the rebound magnetic field prevents the wraparound. Furthermore, since the contact surfaces of the first and second magnets 24a and 24b are both N poles, toner does not adhere to the magnet body 24 due to the repulsive magnetic field formed here, and as a result, the regulating blade 23 No toner stays behind the toner. That is, the toner is always subjected to the stirring action behind the regulating blade 23, so that the toner does not stay, the collision between the toners can be reduced, and the charge balance of the toner is not lost. There is no possibility of embedding or peeling of the external additive externally added to the toner.

  Furthermore, since the lower surface of the magnet body 24 is the S pole, and the contact surfaces of the first and second magnets 24a and 24b are both N poles, it acts with the N pole formed at the tip of the regulating blade 23, The magnetic field formed between the regulating blade 23 and the south pole of the fixed magnet roller becomes stronger, and the regulation of the toner passing through the gap is strengthened by the magnetic field, so that the toner can be charged satisfactorily. Further, even if the toner on the upstream side in the rotation direction of the developing sleeve 23 with respect to the regulating blade 23 attempts to flow upward, the repulsive magnetic field prevents the toner from flowing upward.

  As is clear from the above description, the magnet body 24, that is, the first and second magnets 24a and 24b are located upstream of the regulating blade 23 in the rotation direction of the developing sleeve 22a as viewed from the developing position. It functions as a repulsive magnetic field forming means for forming a repelling magnetic field for stirring the toner. In the above example, the first and second magnets 24a and 24b are brought into contact with each other. However, the first and second magnets 24a and 24b may be brought into contact with each other with a gap therebetween. Good (in order to prevent adhesion of toner between the gaps, the gap interval is preferably less than 1 mm). In the above example, the first and second magnets 24a and 24b, that is, the repulsive magnetic field forming means is configured by two magnets. However, the repulsive magnetic field forming means includes three or more magnets. These magnets are extended in the radial direction of the developing sleeve in a state where the magnetic poles are opposed to each other, and one of the magnets arranged on the developing sleeve side of these magnets is opposed to the developing sleeve by one magnetic pole (for example, a fixed magnet roller) , S poles), and the same magnetic poles facing each other between the magnets.

  Since the magnet body (first and second magnets) that forms a repulsive magnetic field that stirs the developer is disposed upstream of the regulating blade in the rotation direction of the developing sleeve as viewed from the development position, the rear of the regulating blade As a result, no toner retention occurs on the side, so that it can be applied to a developing device using a one-component developer.

1 is a diagram schematically showing an example of an image forming apparatus using a developing device according to Embodiment 1 of the present invention. FIG. 2 is a transverse sectional view showing the developing device shown in FIG. 1 together with a photosensitive drum. It is the figure which fractured | ruptured the image development apparatus shown in FIG. 1, and was seen from upper direction. It is the figure which fractured | ruptured the image development apparatus shown in FIG. 1, and was seen from the side. It is a figure which shows the positional relationship of a developing roller, a control blade, and a magnet body while showing the structure of a developing roller. In the developing device shown in FIG. 1, it is a figure which shows the relationship between a developing sleeve, a control blade, and a magnet body. It is a figure which shows roughly the magnetic force line formed with a magnet body in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Photosensitive drum 12 Laser scanning unit 13 Charger 14 Developing device 15 Cleaning unit 16 Paper feeding device 17 Conveying roller 18 Transfer roller 19 Fixing device 20 Paper discharge tray 21 Developing container 22 Developing roller 22a Developing sleeve 23 Control blade 24 Magnet body 24a, 24b Magnet 25, 26 Stir screw

Claims (3)

A developing sleeve including a fixed magnet roller formed with a plurality of magnetic poles; and a layer thickness regulating member for regulating a developer layer thickness formed on the developing sleeve, and rotationally driving the developing sleeve In a developing device for developing an electrostatic latent image on an image carrier at a development position after forming a thin developer layer on the developing sleeve,
Repulsive magnetic field forming means for forming a repulsive magnetic field for stirring the developer is disposed on the upstream side in the rotation direction of the developing sleeve with respect to the layer thickness regulating member as viewed from the developing position .
One magnetic pole of the fixed magnet roller corresponds to the layer thickness regulating member,
The repulsive magnetic field forming means includes a plurality of magnets, and the plurality of magnets extend in a radial direction of the developing sleeve with their magnetic poles facing each other.
Of the plurality of magnets, the magnet disposed on the developing sleeve side has a magnetic pole opposite to the developing sleeve and the same magnetic pole as one magnetic pole of the fixed magnet roller,
Magnetic poles opposed to each other in said plurality of magnets are developing apparatus is characterized homopolar der Rukoto. A developing device according to claim 1, wherein the magnetic poles opposed to each other in said plurality of magnets are in contact. Wherein the plurality of magnets developing apparatus according to claim 1 or 2, characterized in that fixed to the surface located on the upstream side in the rotational direction of the developing sleeve of the layer thickness regulating member.

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