JP2007256426A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of automatically eliminating color mixture in a short time even when the color mixture is caused, and an image forming apparatus. <P>SOLUTION: The developing device 103 includes a developing unit 111K developing a latent image on an image carrier with magnetic toner, and a one-component developing type developing unit 111Y (111C and 111M) developing the latent image on the image carrier with non-magnetic toner whose color is different from that of the magnetic toner. The developing unit 111Y includes a magnetic toner restricting means composed of magnetic substance inside its housing. When toner scattered from the developing unit 111K touches the developing roller of the developing unit 111Y, it is restricted by the magnetic toner restricting means of the developing unit 111Y and prevented from being transferred to the image carrier. Therefore, the color mixture is eliminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device and an image forming apparatus, and more particularly to a developing device that forms an image of a plurality of colors and an image forming apparatus including the developing device.

  Some image forming apparatuses such as printers, copiers, and multifunction machines are equipped with a developing device including a plurality of developing units in order to form a color image. For example, a developing device of a general color image forming apparatus includes yellow, cyan, magenta, and black developing units around an image carrier on which a latent image is formed. As a developing device of this type, by rotating a rotary equipped with a developing unit corresponding to each color, or in a form in which developing units corresponding to a plurality of colors or all colors are mounted, the developing unit corresponding to each color is sequentially arranged along the moving direction of the image carrier. A configuration in which each developing unit is selectively opposed to the image carrier is well known (see, for example, Patent Documents 1 to 3).

Further, in the rotary type developing device, the toner capacity of each developing unit becomes small, and therefore, when the remaining amount of toner stored in the developing unit decreases, an image forming apparatus provided with a replenishment mechanism that supplies toner to the developing unit from the outside. Has also been developed.
JP 2003-107829 A Japanese Patent No. 3347646 Japanese Patent Laid-Open No. 9-15925

  In a developing device including a plurality of developing units, each developing unit is sealed so that toner contained in each developing unit does not scatter to other developing units and color mixing occurs. However, it is not easy to completely prevent fine toner from scattering.

  For example, in the developing unit, at both ends of the developing roller, members that define a region (attachment width) where toner is attached to the developing roller are provided. When the toner thin film is formed on the outer peripheral surface of the developing roller, excess toner adhering to the outer peripheral surface of the developing roller is pushed out toward the member. That is, toner is always sent to the member side during the developing operation. For this reason, toner leaks easily from the boundary between the member and the developing roller to the outside of the developing unit. When toner leakage occurs, toner is gradually accumulated on the spot by repeating the image forming process, and the accumulated toner finally falls on or below the image carrier.

  When the dropped toner comes into contact with the developing roller of another developing unit via the image carrier or directly, color mixing occurs in the developing unit. In a portion where color mixture occurs, development is performed with a development color different from the original development color of the development unit, so that normal image formation cannot be performed. In particular, when black toner comes into contact with the yellow developing unit, the influence on the formed image is great.

  Further, in the image forming apparatus provided with the above-described toner replenishing mechanism, toner may be scattered when toner is replenished. When the scattered toner contacts the developing roller of another developing unit, similar color mixing occurs. Such color mixing is not eliminated until the toner of the other developing units in contact with the developing roller is completely consumed.

  The present invention has been made in view of such a problem in the prior art, and provides a developing device and an image forming apparatus capable of automatically eliminating color mixing in a short time even when color mixing occurs. It is an object.

  In order to achieve the above object, the present invention employs the following means. First, the present invention is premised on a developing device including a plurality of developing units that develop a latent image formed on an image carrier. In the developing device according to the present invention, the latent image on the image carrier is developed with a first developing unit that develops the latent image on the image carrier with magnetic toner, and the non-magnetic toner having a different color from the magnetic toner. And a second developing unit of the one-component developing method. The second developing unit includes magnetic toner restraining means made of a magnetic material inside the housing. The magnetic toner restraining means is disposed at a position where the magnetic toner can be restrained, such as a position close to a part of the outer peripheral surface of the developing roller.

  According to this configuration, when the magnetic toner scattered from the first developing unit comes into contact with the developing roller of the second developing unit, the magnetic toner enters the housing of the second developing unit as the developing roller rotates. enter in. The magnetic toner that has entered the housing is restrained by the magnetic body provided in the housing and is not transferred to the image carrier. For this reason, even when color mixing occurs, the color mixing is automatically eliminated in a short time.

  The magnetic toner restraining means can be incorporated in the developing roller of the second developing unit, for example. In this case, the magnetic toner of the first developing unit attached to the developing roller of the second developing unit is restrained by the developing roller and does not adhere to the image carrier.

  The first developing unit has a developing position where the developing roller faces the image carrier and develops the latent image, and a non-developing position where the developing roller does not face the image carrier. It can be provided so as to be movable. In this case, it is preferable that the first developing unit includes a cover that covers its own developing roller when in the non-developing position. Thereby, it is possible to prevent the toner of the second developing unit from being mixed into the first developing unit. In this respect, a configuration in which the first developing unit is disposed above the second developing unit can be employed. Further, in order to suppress scattering of toner from the second developing unit, it is preferable that the developer accommodating portion of the second developing unit does not have a mechanism for replenishing toner from the outside.

  For example, the magnetic toner can be black. A plurality of the second developing units corresponding to cyan, magenta, and yellow colors may be provided.

  In another aspect, the present invention can provide an image forming apparatus including the above-described developing device. By developing the latent image on the image carrier using the developing device, high-quality image formation without color mixing can be performed.

  According to the present invention, even if the toner of another developing unit adheres to the developing roller, it is possible to suppress the occurrence of color mixing. In particular, by using black toner as the magnetic toner and other color toners as the non-magnetic toner, it is possible to reliably suppress the color mixture of the black toner that has an extremely large influence on the formed image. Therefore, according to the present invention, high-quality image formation without color mixing can be performed.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the present embodiment, the present invention is embodied as a color printer.

  FIG. 1 is a schematic configuration diagram showing the overall configuration of a color printer in the present embodiment. First, image forming processing in the printer 101 will be described. When the printer 101 is turned on, various parameters are initialized, and the temperature of the heating roller 108a in the fixing device 108 is sensed. When various initializations are completed and the temperature of the heating roller 108a rises to a predetermined value or more, image forming processing in the printer 101 becomes possible.

  In this state, when image data is input from a computer (not shown) or the like, first, the photosensitive drum (image carrier) 102 is charged by the charging roller 109. When the photosensitive drum 102 is charged, the laser unit 104 forms a latent image on the photosensitive drum 102 based on the image data. The laser unit 104 includes a laser light source, a polygon mirror, a polygon mirror drive motor, and the like. The laser emitted from the laser light source is reflected by a polygon mirror that is driven to rotate, thereby causing the photosensitive drum 102 to move in the axial direction. Scan in a direction perpendicular to the paper surface of FIG. The laser is bent by the reflecting mirror 110 according to the position of the laser unit 104.

  When a latent image is formed on the photosensitive drum 102 by the laser unit 104, a rotating drum type developing device 103 (hereinafter referred to as a rotary developing device 103) rotates in a direction perpendicular to FIG. A developing unit 111 that rotates in the circumferential direction 103 b around the shaft 103 a and stores toner of a color corresponding to the latent image on the photosensitive drum 102 is disposed at a position facing the photosensitive drum 102. In this state, the latent image on the photosensitive drum 102 is developed with toner stored in the developing unit and transferred to the intermediate transfer belt 107. The rotary developing device 103 includes four developing units 111 (111Y, 111C, 111M, and 111K) that store yellow, cyan, magenta, and black toners, respectively. The four developing units 111 form a full-color image on the intermediate transfer belt 107 by repeating the transfer to the intermediate transfer belt 107 for each color.

  On the other hand, the sheet taken out from the sheet feeding cassette 113 via the sheet feeding unit 114 is conveyed to the registration roller pair 116 through the conveyance path 115. Thereafter, the sheet is conveyed from the registration roller pair 116 to the intermediate transfer belt 107 in time with the developed image on the intermediate transfer belt 107 and guided to the secondary transfer roller 117. The secondary transfer roller 117 is configured in contact with the intermediate transfer belt 107, and the developed image formed on the intermediate transfer belt 107 is transferred to a sheet by a transfer bias applied to the secondary transfer roller 117. . The sheet on which the developed image is transferred is guided to the fixing device 108 via the conveyance path 118, and the developed image is fixed on the sheet by the heating roller 108a and the pressure roller 108b. Thereafter, the sheet is discharged to the discharge unit 119.

  FIG. 2 is a partial cross-sectional view for explaining a schematic configuration of the rotary developing device 103. In the rotary developing device 103 in this embodiment, the black developing unit 111K uses magnetic toner (first developing unit), and the yellow developing unit 111Y, the cyan developing unit 111C, and the magenta developing unit 111M use non-magnetic toner. (Second developing unit).

  The black developing unit 111K develops the latent image formed on the photosensitive drum 102 by a one-component developing method. As shown in FIG. 2, the black developing unit 111 </ b> K includes a developing roller 201, a layer thickness regulating blade 202, and a toner container 205 in a housing 200. The developing roller 201 is supported in the vicinity of the outer peripheral surface of the rotary developing device 103 so as to be rotatable around an axis parallel to the rotation shaft 103a.

  The toner container 205 is divided into a primary chamber 206 and a secondary chamber 207 by a partition plate 208. The primary chamber 206 and the secondary chamber 207 are communicated at both ends in the direction of the rotating shaft 103a. The chambers 206 and 207 are respectively provided with stirrers 203 and 204 made of paddles, spirals, and the like that are rotatably supported around an axis parallel to the rotation shaft 103a. As the stirrers 203 and 204 rotate, the magnetic toner is stirred while circulating through the primary chamber 206 and the secondary chamber 207, thereby homogenizing the magnetic toner. The magnetic toner is restrained by a fixed magnetic field formed by a magnetic pole built in the developing roller on the outer peripheral surface of the developing roller 201 rotating at a predetermined peripheral speed, and is conveyed along with the rotation of the developing roller 201.

  The layer thickness regulating blade 202 is supported by the housing 200 in a state where the tip thereof is at a predetermined distance from the outer peripheral surface of the developing roller 201. The magnetic toner constrained by the developing roller 201 passes between the developing roller 201 and the layer thickness regulating blade 202, whereby a frictionally charged thin toner layer 209 is formed on the outer peripheral surface of the developing roller 201. When the toner thin layer 209 reaches a position facing the photosensitive drum 102, the toner is transferred by electrostatic adsorption, and the latent image on the photosensitive drum 102 is developed.

  On the other hand, the yellow developing unit 111Y, the cyan developing unit 111C, and the magenta developing unit 111M develop the latent image formed on the photosensitive drum 102 by a one-component developing method. FIG. 3 is a cross-sectional view showing a schematic structure of the yellow developing unit 111Y (the same applies to 111C and 111M). The yellow developing unit 111Y includes a developing roller 301, a supply roller 303, and a toner container 305 in a housing 300. Similar to the black developing unit 111K, the developing roller 301 is supported in the vicinity of the outer peripheral surface of the rotary developing device 103 so as to be rotatable about an axis parallel to the rotating shaft 103a.

  The toner storage unit 305 is divided into a primary chamber 306 and a secondary chamber 307 by a partition plate 308. The primary chamber 306 and the secondary chamber 307 communicate with each other in the vertical direction of the partition plate 308. The primary chamber 306 is provided with a stirrer 304 made of a paddle or the like that is rotatably supported around an axis parallel to the rotation shaft 103a. As the stirrer 304 rotates, the toner is stirred and homogenized while circulating through the primary chamber 306.

  The supply roller 303 is configured by a roller having elasticity such as a sponge roller or a rubber roller. The supply roller 303 is disposed so as to be in pressure contact with the developing roller 301 by an elastic force. In the present embodiment, the rotation direction of the supply roller 303 is a direction from the top to the bottom at the contact portion with the developing roller 301 (indicated by an arrow in FIG. 3). The non-magnetic toner is conveyed to the developing roller 301 along with the rotation of the supply roller 303, and adheres to the developing roller 301 as both rollers rub against each other at the contact portion.

  Further, contact blades 302 (upper-end contact blade 302a and lower-end contact blade 302b) are provided near the upper end and the lower end of the development roller 301 in a state where the developing roller 301 faces the photosensitive drum 102, respectively. The contact blade 302 is fixed to the housing 300 so that its tip is in pressure contact with the developing roller 301 by its own elastic force. As the developing roller 301 rotates, the non-magnetic toner that has reached the upper contact blade 302a passes between the developing roller 301 and the upper contact blade 302a, so that the frictionally charged toner thin layer 309 is developed into the developing roller. It is formed on the outer peripheral surface of 301. When the toner thin layer 309 reaches a position facing the photosensitive drum 102, the toner is transferred by electrostatic adsorption, and the latent image on the photosensitive drum 102 is developed. A magnetic body 310 is disposed on the surface of the upper end side contact blade 302a that is not in contact with the developing roller 301.

  In the printer having the above-described configuration, it is assumed that, for example, toner leakage occurs from the black developing unit 111K and black toner 311 adheres to the surface of the developing roller 301 of the yellow developing unit 111Y in the process of repeatedly performing image formation (see FIG. 3).

  The black toner 311 enters the housing 300 of the yellow developing unit 111Y as the developing roller 301 rotates. When the adhesion position of the black toner 311 reaches the contact portion with the supply roller 303 as shown in FIG. 4, a part of the black toner 311 is rubbed against the supply roller 303 from the outer peripheral surface of the developing roller 301. break away. The black toner 311 that has passed through the contact portion without being detached from the developing roller 301 reaches the upper end side contact blade 302a.

  At this time, the black toner 311 that is a magnetic toner is separated from the developing roller 301 by the magnetic field formed by the magnetic body 310 and is restrained by the surface of the magnetic body 310. That is, the black toner 311 attached to the developing roller 301 is removed from the developing roller 301 in the housing 300 and is restrained in the housing 300. Since the black toner 311 restrained by the magnetic body 310 cannot be detached from the magnetic body 310, it does not reattach to the developing roller 310. Note that the black toner 311 detached from the developing roller 301 at the contact portion between the developing roller 301 and the supply roller 303 may be attached to the developing roller 301 again. However, the black toner 311 reattached to the developing roller 301 is also restrained by the magnetic body 310 when it reaches the upper end side contact blade 302a, and therefore is not transferred onto the photosensitive drum 102. Therefore, no color mixing occurs in subsequent image formation.

  Even when the black toner 311 adheres to the developing roller 301 via the photosensitive drum 102, the black toner 311 is attracted to the magnetic field generated by the supply roller 303 and is restrained in the housing 300. In this case, the black toner attached on the photosensitive drum 102 is removed by the cleaning device 112 together with other toners on the photosensitive drum 102.

  As described above, in the developing device according to this embodiment, the magnetic toner attached to the developing roller of the developing unit in which the nonmagnetic toner is accommodated is restrained inside the developing unit. For this reason, the magnetic toner is automatically and promptly removed from the developing roller. Therefore, continuous generation of color mixture can be prevented and high-quality image formation can be performed.

  It is also conceivable that the non-magnetic toner of the yellow developing unit 111Y, the cyan developing unit 111C, or the magenta developing unit 111M is scattered and adheres to the developing roller of the black developing unit 111K. However, even if yellow, cyan, and magenta toners are mixed in the black toner, it is difficult to confirm other colors mixed in the low-lightness black on the formed image. Therefore, the quality of the formed image is not greatly reduced.

  In the above description, the magnetic body 310 is disposed on the upper contact blade 302a. However, the present invention is not limited to this. A similar effect can be obtained if the magnetic material 310 is disposed at a position where the magnetic toner can be restrained. FIG. 5 is a cross-sectional view showing a schematic structure of a yellow developing unit 111Y of the one-component developing system in which the magnetic body 310 is disposed at another position. In this configuration, the magnetic body 310 is disposed in the vicinity of the downstream side of the lower end side contact blade 302b. In this example, the black toner 311 attached to the developing roller 310 is released from the developing roller 310 immediately after entering the housing 300 as the developing roller 301 rotates, and is restrained by the magnetic body 310. Therefore, as in the case of the developing unit described above, the occurrence of color mixing is prevented.

  FIG. 6 is a cross-sectional view showing a cross-sectional structure of another modified example of the yellow developing unit 111Y of the one-component developing system. In this configuration, the magnetic body 310 is disposed as the rotation axis of the supply roller 303. In this example, the black toner 311 attached to the developing roller 310 is separated from the developing roller 310 by the magnetic field formed by the magnetic body 310 when it reaches a position facing the supply roller 303 as the developing roller 301 rotates. Restrained on the outer peripheral surface of the supply roller 303 or enclosed in a sponge part. Therefore, as in the case of the developing unit described above, the occurrence of color mixing is prevented.

  Further, FIG. 7 is a cross-sectional view showing a cross-sectional structure of the yellow developing unit 111Y in which the magnetic body 310 is disposed inside the developing roller 301. In this example, the developing roller 301 is formed as a sleeve that encloses a magnetic body 310 that is fixedly arranged so as to form a magnetic pole in the vicinity of the upstream side of the upper end side contact blade 302a. When the black toner 311 attached to the developing roller 310 reaches the vicinity of the upper end side contact roller 302 a as the developing roller 301 rotates, the black toner 311 is restrained by the magnetic field formed by the magnetic body 310. Therefore, as in the case of the developing unit described above, the occurrence of color mixing is prevented.

  By the way, although the black developing unit uses magnetic toner in the above, even if the magnetic toner is in another color, it is possible to obtain an effect of automatically and promptly eliminating the color mixture with the non-magnetic toner. For example, the yellow developing unit may use magnetic toner, and the other developing unit may use non-magnetic toner. As a result, color mixing can be prevented when yellow toner adheres to the developing roller of another developing unit. In this case, when the black toner, which is a non-magnetic toner, adheres to the developing roller of the yellow developing unit, the color mixture continuously occurs until the attached black toner is completely consumed.

  As a countermeasure against color mixing in the magnetic developing unit, each developing unit moves between a developing position where the latent image is developed and a non-developing position where the latent image is not developed, like the rotary developing device 103 described above. In the case where it is possible, the developing unit using magnetic toner is preferably provided with a cover that covers its own developing roller when in the non-developing position. Thereby, it is possible to suppress the toner of another developing unit from adhering to the developing roller of the developing unit using magnetic toner. Of course, the above-described cover may be provided even when the magnetic toner is black toner. The developing unit using non-magnetic toner may further include a cover that covers the developing roller when the developing unit is in the non-developing position.

  In such a situation where there is a concern about the nonmagnetic toner adhering to the developing unit using magnetic toner, it is preferable that the printer 101 does not include a toner replenishment mechanism for the developing unit 111 using nonmagnetic toner. . Thereby, scattering of the nonmagnetic toner can be suppressed, and adhesion of the nonmagnetic toner to the developing unit using the magnetic toner can be reduced.

  Conversely, the printer 101 may include a toner replenishment mechanism for a developing unit that uses magnetic toner. The toner replenishing mechanism can be constituted by, for example, a toner hopper 105 and a toner replenishing tube 106 (see FIG. 1). The toner hopper 105 and the toner supply pipe 106 are provided corresponding to the developing unit 111 that uses magnetic toner. The toner supply pipe 106 is configured to be insertable into and removed from a toner supply port (not shown) provided in the toner storage portion 205 of the corresponding developing unit 111 from above the rotary developing device 103. The toner replenishing ports of the developing units 111 that use magnetic toner are formed so as to be at different positions in the direction perpendicular to the paper surface of FIG. When the toner remaining amount detecting means attached to the toner storage unit 205 of each developing unit 111 detects that the amount of toner remaining in the storage unit is below a predetermined value, the corresponding toner hopper 105 passes through the toner supply pipe 106 to a predetermined amount. The new toner is replenished to the developing unit 111. By providing the toner replenishment mechanism as described above, it is possible to compensate for the disadvantage that the toner capacity is structurally reduced in the rotary developing device by using a magnetic toner as a color that uses a larger amount of toner than other colors. it can.

  Although the rotary type developing device has been described above, the present invention can also be applied to other types of developing devices. For example, as shown in FIG. 8, the developing units 811 (the black developing unit 811K, the yellow developing unit 811Y, the cyan developing unit 811C, and the magenta developing unit 811M) are fixedly arranged along the rotation direction of the photosensitive drum 102. The present invention can be applied to the developing device 803. The developing device 803 develops the latent image formed by the laser unit 104 on the photosensitive drum 102 charged by the charging roller 109 via the reflection mirror 110. Although not particularly limited, in the developing device 803, for example, the black developing unit 811K uses magnetic toner, and the other developing units 811Y, 811C, and 811M use nonmagnetic toner. An effect can be obtained. In this case, the developing unit using magnetic toner is preferably arranged above the developing unit using non-magnetic toner. Thereby, it is possible to suppress the nonmagnetic toner from adhering to the developing roller of the developing unit using magnetic toner.

  Further, the present invention can also be applied to a developing device in which the above-described rotary developing device and a fixed developing device are combined. For example, a developing unit that uses non-magnetic toner is configured as a rotary type, and a developing unit that uses magnetic toner is fixedly arranged above the rotary. In this configuration as well, the above-described color mixing prevention effect can be obtained, and adhesion of nonmagnetic toner to the developing roller of the developing unit using magnetic toner can be suppressed.

  The embodiments described above do not limit the technical scope of the present invention, and various modifications and applications can be made within the scope of the present invention other than those already described. For example, in the above-described embodiment, in a full-color developing device, one developing unit uses magnetic toner and the other three developing units use non-magnetic toner, but at least one developing unit uses magnetic toner. If at least one developing unit uses a non-magnetic toner, the effects of the present invention can be obtained. In this case, the number of developing units using magnetic toner and the combination of colors are arbitrary. Further, the number of developing units provided in the developing device is not limited to four, and may be any number of two or more. Further, any developing system using magnetic toner can be used as the magnetic toner developing unit.

  In addition, the present invention can be applied not only to color printers but also to devices such as printers, copiers, facsimiles, and multi-function peripherals that perform image formation using a plurality of colors.

  According to the developing device and the image forming apparatus of the present invention, even when color mixing occurs, it can be quickly and automatically restored, and is useful for various devices such as printers, copiers, facsimiles, and multi-functional devices thereof. It is.

1 is a schematic configuration diagram showing an overall configuration of a printer to which the present invention is applied. 1 is a partial cross-sectional view of a developing device according to an embodiment of the present invention. Sectional drawing of the image development unit in one Embodiment of this invention. Sectional drawing of the image development unit in one Embodiment of this invention. Sectional drawing which shows the modification of the image development unit in one Embodiment of this invention. Sectional drawing which shows the modification of the image development unit in one Embodiment of this invention. Sectional drawing which shows the modification of the image development unit in one Embodiment of this invention. Sectional drawing which shows the modification of the image development apparatus of this invention

Explanation of symbols

101 Printer 102 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 103 Rotary developing device 111,811 Developing unit 201,301 Developing roller 202 Layer thickness control blade 209,309 Thin toner layer 302 Contact blade 303 Supply roller 310 Magnetic body (magnetic toner restraining means)
803 Development device

Claims (8)

In a developing device including a plurality of developing units for developing a latent image formed on an image carrier,
A first developing unit for developing the latent image of the image carrier with magnetic toner;
A second developing unit of a one-component developing system that develops the latent image of the image carrier with a nonmagnetic toner having a different color from the magnetic toner;
With
The developing device, wherein the second developing unit includes a magnetic toner restraining means made of a magnetic material inside the housing.   The developing device according to claim 1, wherein the magnetic toner restraining means is built in a developing roller of the second developing unit.   The first developing unit moves between a developing position where the developing roller faces the image carrier and develops the latent image, and a non-developing position where the developing roller does not face the image carrier. The developing device according to claim 1, further comprising a cover that covers the developing roller when the developing roller is in the non-developing position.   The developing device according to claim 1, wherein the first developing unit is disposed above the second developing unit.   The developing device according to claim 1, wherein the developer container of the second developing unit does not have a mechanism for replenishing toner from the outside.   The developing device according to claim 1, wherein the magnetic toner is black.   The developing device according to claim 1, further comprising a plurality of the second developing units corresponding to cyan, magenta, and yellow colors. An image forming apparatus comprising the developing device according to claim 1.

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