JP2002365900A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a surface staining due to adhesion of toner to the surface part of an image carrier at the time of the developing operation of a developing device in an image forming device with which an electrostatic latent image formed on the image carrier is visualized as a toner image by the developing device and also the developing device is supplied with toner by a toner supply device. SOLUTION: The toner is previously electrified so as to have a specified polarity by the contact of a stator 7 and a rotor 10 constituting the toner feeding pump 36 of the toner supply device 18 to supply the toner to the developing device 22, with the toner T, and the electrified toner is supplied to the developing device 22, and is further electrified by the developing device 22 and is served for development.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a developing device for visualizing an electrostatic latent image as a toner image and a toner supply device for supplying toner to the developing device.

[0002]

2. Description of the Related Art Electronic copiers, printers, facsimile machines,
Alternatively, an image forming apparatus of the above-described type configured as a multifunction peripheral having at least these two functions has been conventionally known. In this type of conventional image forming apparatus, a toner used for visualizing an electrostatic latent image is charged to a predetermined negative or positive polarity in a developing device, and the charged toner is electrostatically charged on the electrostatic latent image. And the electrostatic latent image is visualized.

However, in the conventional image forming apparatus, there is a possibility that toner adheres to a portion of the image carrier that should not be developed, that is, a background portion, thereby causing background contamination. This is because the toner supplied to the developing device is
Either the toner is not sufficiently charged, or some of the toner is charged to a polarity opposite to the original charge polarity, and the abnormally charged toner is directly used for development, and the toner is applied to a background portion on the image carrier. This is because they will adhere.

Therefore, the toner supplied to the developing device is
If this is sufficiently triboelectrically charged to a predetermined polarity before it is subjected to development to prevent generation of the abnormally charged toner, it is possible to prevent background contamination.

However, particularly in recent image forming apparatuses, the size of the main body of the image forming apparatus is required to be reduced, and the developing device in the main body of the image forming apparatus is also downsized. For this reason, the amount of the developer contained in the developing device is reduced, and the toner cannot be sufficiently charged in the developing device, and the toner with an insufficient charge amount or the toner charged to the opposite polarity is used for development. However, this has inevitably caused the risk of the occurrence of soiling.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forming a high-quality image by suppressing the occurrence of background contamination.

[0007]

According to the present invention, in order to achieve the above-mentioned object, a negatively charged toner is electrostatically transferred to an electrostatic latent image formed on an image carrier and the electrostatic latent image is transferred to the electrostatic latent image. In an image forming apparatus having a developing device for visualizing an image as a toner image and a toner supply device for supplying toner to the developing device, a work function of at least a part of a portion of the toner supply device which is in contact with toner Is set to be 4.2 eV or less (claim 1).

In this case, the toner supply device includes a toner transfer pump having a rotor and a stator, and at least one of the rotor and the stator that comes into contact with the transferred toner has a work function value of 4.2 eV or less. It is advantageous if it is set (claim 2).

According to the present invention, in order to achieve the above object, a positively charged toner is electrostatically transferred to an electrostatic latent image formed on an image carrier, and the electrostatic latent image is transferred to a toner image. In an image forming apparatus having a developing device for visualizing a toner image and a toner supply device for supplying toner to the developing device, a work function value of at least a part of a portion of the toner supply device which is in contact with the toner is 4 The present invention proposes an image forming apparatus characterized by being set to 0.6 eV or more.

In this case, the toner supply device includes a toner transfer pump having a rotor and a stator, and at least one of the rotor and the stator that comes into contact with the transferred toner has a work function value of 4.6 eV or more. It is advantageous if it is set (claim 4).

[0011] In the image forming apparatus according to the second or fourth aspect, it is advantageous that the toner transfer pump comprises a mono pump.

Further, in the image forming apparatus according to any one of the first to fifth aspects, it is possible to configure the image forming apparatus such that a portion that contacts the toner is made of a metal or a metal compound.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of an electrophotographic image forming apparatus. This image forming apparatus has an image carrier 2, and the image carrier 2 shown here is composed of a photosensitive member formed in a drum shape. A belt-shaped image carrier that is wound around a plurality of belts and driven to run can also be used.

During the image forming operation, the image carrier 2 is driven to rotate in the direction of arrow B. At this time, the surface of the image carrier is uniformly charged to a predetermined polarity, in this example, a negative polarity by a charging roller 20 which is an example of a charging device. Is done. On this charged surface,
A light-modulated laser beam L emitted from a laser writing unit (not shown), which is an example of an exposure device, is irradiated to form an electrostatic latent image on the surface of the image carrier. In the example shown in FIG. 1, the portion where the absolute value of the surface potential of the image carrier 2 is reduced by irradiation with the laser beam L becomes an electrostatic latent image, and the surface portion of the image carrier 2 not exposed to the laser beam is It becomes the ground part.

The electrostatic latent image is visualized as a toner image by the developing device 22. The developing device 22 shown as an example here includes a developing case 23 and the developing case 2.
3, a developing roller 24 rotatably supported in a counterclockwise direction and rotatably supported in a developing case 23, and a stirring roller 25 rotatably supported in a developing case 23. Dry two-component developer D having
Is housed. A one-component developer having no carrier can also be used.

The developer D is agitated by the agitation roller 25, and the toner and the carrier are frictionally charged to polarities opposite to each other. In this example, the toner is negatively charged, which is the same as the charging polarity of the image carrier, and the carrier is positively charged. The developer D is conveyed below the developing roller 24 to which the negative bias voltage is applied, and is then pumped up by the developing roller 24 and carried on the developing roller 24 to be conveyed. The amount of the developer carried and conveyed by the developing roller 24 is regulated by the regulating blade 26, and further charged here, and then carried to a developing area between the developing roller 24 and the image carrier 2, The toner in the developer electrostatically transfers to the electrostatic latent image formed on the surface of the image carrier, and the electrostatic latent image is visualized as a toner image. As described above, in this example, the electrostatic latent image is developed by the reversal developing method, but a regular developing method may be adopted. The developer that has passed through the developing area is returned to the stirring roller 25 again, and is subjected to a stirring action by the stirring roller 25. When the toner concentration sensor 35 detects a decrease in the toner concentration of the two-component developer D stored in the developing case 23, the toner supply device 1 described later
The toner is supplied into the developing case 23 by 8.

On the other hand, a transfer material composed of, for example, transfer paper or a resin sheet is fed from a paper feeder (not shown). The transfer material P is opposed to the image carrier 2 and an arrow A
It is carried on a transfer belt 8 driven to travel in the direction, and is conveyed to a transfer area between the image carrier 2 and the transfer belt 8. At this time, a transfer voltage having a polarity opposite to the charge polarity of the toner on the surface of the image carrier is applied to a transfer brush 9 which is an example of a transfer device, whereby the toner image on the image carrier is transferred onto the transfer material P. Is done. Instead of the transfer brush, a transfer device such as a transfer roller, a transfer blade, or a corona discharger can be used. The transfer material P on which the toner image has been transferred is continuously conveyed in the direction of arrow A, and after leaving the transfer belt 8, passes through a fixing device (not shown). It is fixed on the transfer material. The transfer material that has passed through the fixing device is discharged out of the image forming apparatus main body.

The transfer residual toner adhering to the surface of the image carrier after transferring the toner image is removed by the cleaning device 27. The cleaning device 27 includes a cleaning case 28, a cleaning brush 29 rotatably supported by the cleaning case 28 and driven to rotate in an arrow direction, and a cleaning blade 30 having a base end fixed to the cleaning case 28. The cleaning brush 29 and the cleaning blade 30 come into contact with the surface of the image carrier 2 to scrape and remove transfer residual toner on the surface.

Although the toner supply device for supplying the toner to the developing case 23 of the developing device 22 can be configured in an appropriate form, the toner supply device 18 shown as an example in FIG.
Is a toner transfer pump 36 disposed above the developing case 23, and a toner container 37 containing powdered toner T.
And a toner transfer pipe 38 through which the toner sent from the toner container 37 to the toner transfer pump 36 passes.

Various types of pumps can be used as the toner transfer pump. In the image forming apparatus of this embodiment, a mono pump shown in FIG. 2 is used.
The toner transfer pump 36 includes a stator 7, a rotor 10 disposed in a through hole 6 formed in the stator 7 and driven to rotate, a stator case 11 in which the stator 7 is housed, and a stator case 11 , And a casing 13 provided adjacent to the casing.

The through-hole 6 of the stator 7 is formed by two grooves extending spirally around the central axis of the through-hole 6. The rotor 10 has an outer peripheral surface of the rotor 10 and the through-hole 6 of the stator 7. And spirally formed so as to form a plurality of sealed voids S for toner transfer between the inner peripheral surface and the inner peripheral surface. The stator 7 wraps around and includes the helical rotor 10 and is in contact with and engaged with the rotor 10.
3 and the case 11 for the stator. The pump having the rotor 10 and the stator 7 is a mono pump.

A connecting shaft 39 is connected to an end of the rotor 10 via a pin joint 40, and the connecting shaft 39 is further connected to the drive shaft 16 via another pin joint 19.
The drive shaft 16 is provided with an opening 15
Are rotatably supported by a casing 13 having the same.
A gear 14 is fixed to a drive shaft portion protruding outside the casing 13, and a mating gear (not shown) is meshed with the gear 14, and the rotation of a drive motor (not shown) is also transmitted through these gears. Drive shaft 16 and connection shaft 39
, Whereby the rotor 10 is driven to rotate.

The toner transfer pump 36 of the present embodiment is configured as described above. The toner transfer pipe 3 is provided at the entrance opening of the stator case 11 on the side opposite to the side where the connecting shaft 39 is located.
8 is connected, and the other end of the toner transfer pipe 38 is connected to
It is connected to the toner outlet of the toner container 37 shown in FIG. The casing 13 has a lower portion provided with the developing device 2.
The inside of the casing 13 and the inside of the developing case 23 communicate with each other through the opening 15.

As described above, when the toner concentration sensor 35 detects a decrease in the toner concentration of the two-component developer D in the developing case 23, the drive shaft 16 and the connection shaft 39 are rotated by the drive motor. , The rotor 10 starts rotating. As a result, suction pressure is generated on the suction side of the toner transfer pump 36, that is, on the side to which the toner transfer pipe 38 is connected, and the toner in the toner transfer pipe 38 is sent into the gap S in the through hole 6. The gap S in which the toner is sealed moves to the left in FIG. 1 and the toner is transferred.

Next, the toner is discharged from the through hole 6 into the casing 13. The toner T thus discharged
Is supplied into the two-component developer in the developing case 23 through the opening 15 in the lower part of the casing 13. The toner supplied to the developing case 23 is the stirring roller 2 shown in FIG.
While being transported by 5, the developer D is agitated. After a lapse of a predetermined time, the rotation of the rotor 10 stops. By supplying the toner from the toner container 37 to the developing device 22 in this manner, the toner concentration of the developer in the developing case 23 is maintained within a predetermined range, and a toner image of a predetermined density is formed on the image carrier. Can be formed.

The aforementioned stator 7 of the toner transfer pump 36
One of the rotor 10 and the rotor 10 can be made of an elastic body, and the other can be made of a rigid body. As a result, the rigid body side is inserted into the elastic body side while elastically deforming the elastic body side, so that the above-mentioned closed space S can be reliably formed.

When the rotor 10 is made of an elastic material, if the rotor 10 is entirely made of an elastic material, the rotor 10 is twisted or cut off by the frictional force received from the stator 7 when the rotor 10 rotates. And stator 7
Since the airtightness of the rotor deteriorates, suction pressure cannot be generated and toner cannot be transferred, the rotor core is made of metal or hard resin, and an elastic body is integrally formed around it. It is preferable to prevent the rotor 10 from being greatly twisted.

As described above, the image forming apparatus of this embodiment electrostatically transfers the negatively charged toner to the electrostatic latent image formed on the image carrier, and converts the electrostatic latent image to a toner image. And a toner supply device for supplying toner to the developing device.

Here, as described above, in the conventional image forming apparatus of the above-mentioned type, the toner supplied to the developing device is insufficiently charged or the toner is charged to a polarity opposite to a predetermined polarity. As a result, a large amount of toner adheres to the background portion on the image carrier, and there is a possibility that background contamination may occur.

Therefore, in the image forming apparatus of this embodiment,
The toner before being supplied to the developing device 22 is charged to a predetermined polarity in advance, a negative polarity in the example shown in the drawing, whereby the toner supplied to the developing device 22 is insufficiently charged or the toner is charged to the opposite polarity. Is adopted to prevent the above. Toner is mainly composed of a polymer compound.The polymer compound is charged by friction with a metal, and is positively charged by friction with a metal having a large work function value, and is charged with a metal having a small work function value. Has the property of being negatively charged by the friction of. In the image forming apparatus of the present embodiment, by utilizing this property, the value of the work function of at least a part of the portion of the toner supply device 18 that comes into contact with the toner is set to 4.2 eV or less, and the toner is supplied to the toner supply device. The toner is configured to be negatively charged when transported by the toner transfer device 18. As a result of the study by the present inventors, the value of the work function of the portion of the toner supply device that comes into contact with the toner to be transferred is 4.
It is clear that the toner can be effectively negatively charged at 2 eV or less. By supplying the charged toner to the developing device 22,
The occurrence of soiling can be effectively suppressed. The toner supply device 18 is configured as a toner charging auxiliary device.

Specifically, at least the inner wall surface of the toner container 37 and the toner transfer pipe 38 of the toner supply device 18, the inner peripheral surface of at least the through hole of the stator 7, and at least the outer peripheral surface of the rotor 10 are made of, for example, Cr or Ti. Of a metal or a metal compound having a work function value of 4.2 eV or less. With this configuration, the toner before being supplied to the developing device 22 is preliminarily charged to a negative polarity, and when the toner is supplied into the developing case 23, the toner is further negatively charged due to friction with the carrier. The charged toner is conveyed to the development area and is used for development, thereby effectively preventing the occurrence of background contamination.

As described above, when the toner container 37 and the toner transfer pipe 38 are made of a material having a small work function, the toner contacting them can be charged negatively. , The toner is attracted to the toner container 37 and the inner wall surface of the toner transfer pipe 38 by electrostatic force, and the toner transportability may be reduced.

Attention is paid to the fact that the toner supply device is provided with a toner transfer pump having a rotor and a stator, and the work function value of at least one of the rotor and the stator in contact with the transferred toner is set to 4 .2 eV or less. For example, the whole of the stator 7,
Alternatively, the surface portion is made of a metal or a metal compound having a work function value of 4.2 eV or less, specifically, Cr, Ti, or the like. Further, the entire rotor 10 or its surface portion is made of a similar material. When the entire rotor 10 or its surface portion is made of metal, the stator is made of an elastic material. Conversely, when the entire stator 7 or its surface portion is made of metal, the rotor 10 is made of an elastic material. Can be configured.

As described above, if at least one of the stator 7 and the rotor 10 is made of a material having a small work function, the rotating rotor 10 can be rotated even if the toner transferred by the contact with the material is charged. 7, the toner is electrostatically attached to the rotor 10 and the stator 7, and the transportability of the toner can be reliably prevented.

The technical idea described above can be similarly applied to the case where the toner contained in the developing device is charged to a positive polarity and the electrostatic latent image is visualized by the toner. When the developing device 22 charges the toner to a positive polarity and develops the electrostatic latent image on the image carrier 2 by the reversal development method, the surface of the image carrier is also positively charged by the charging device. A positive bias voltage is also applied to the developing roller 24. In this case, the portion of the toner supply device 18 that comes into contact with the toner is made of a material having a large work function, and its value is set to 4.6 e.
By setting the voltage to V or more, the toner before being supplied to the developing device 22 is charged to a positive polarity, whereby the occurrence of background contamination can be effectively suppressed. As a material having a work function value of 4.6 eV or more, for example, Ni, P
A metal or metal compound such as t can be used. Other configurations when the toner is positively charged are the same as those of the above-described image forming apparatus that performs development using negatively charged toner, except that the work function value is different. In other words, the image forming apparatus electrostatically transfers the positively charged toner to the electrostatic latent image formed on the image carrier, and visualizes the electrostatic latent image as a toner image. And a toner supply device for supplying toner to the developing device, and a work function value of at least a part of a portion of the toner supply device that contacts the toner is set to 4.6 eV or more. When the toner supply device includes a toner transfer pump having a rotor and a stator, the work function value of at least one of the rotor and the stator in contact with the transferred toner is set to 4.6 eV or more. Is preferred.

FIG. 1 shows the developing device 22 using a two-component developer. However, the above-described configurations can be applied to an image forming apparatus having a developing device using a one-component developer. It is.

As described above, the strength and rigidity of the toner supply device in which the portion in contact with the toner is made of a metal or a metal compound can be increased, and the life thereof can be extended.

According to the first to sixth aspects of the present invention,
Since the toner before being supplied to the developing device is charged to a predetermined polarity in advance, and the toner is supplied to the developing device and further charged here, the occurrence of background contamination can be effectively suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus.

FIG. 2 is a vertical sectional view of the toner transfer pump.

[Explanation of symbols]

 2 Image Carrier 7 Stator 10 Rotor 18 Toner Supply Device 22 Developing Device T Toner

Claims (6)

[Claims] A developing device that electrostatically transfers the negatively charged toner to an electrostatic latent image formed on an image carrier and visualizes the electrostatic latent image as a toner image; An image forming apparatus having a toner supply device that supplies toner to a developing device, wherein a work function value of at least a part of a portion of the toner supply device that contacts the toner is set to 4.2 eV or less. Image forming apparatus. 2. The toner supply device according to claim 1, further comprising a toner transfer pump having a rotor and a stator, wherein at least one of the rotor and the stator in contact with the transferred toner has a work function value of 4.2 eV or less. The image forming apparatus according to claim 1, wherein: 3. A developing device for electrostatically transferring the positively charged toner to an electrostatic latent image formed on an image carrier to visualize the electrostatic latent image as a toner image, and An image forming apparatus having a toner supply device that supplies toner to a developing device, wherein a work function value of at least a part of a portion of the toner supply device that contacts the toner is set to be 4.6 eV or more. Image forming apparatus. 4. The toner supply device includes a toner transfer pump having a rotor and a stator, and a work function value of a part of the rotor and the stator that comes into contact with the transferred toner is set to be 4.6 eV or more. The image forming apparatus according to claim 3, wherein: 5. The image forming apparatus according to claim 2, wherein said toner transfer pump comprises a mono pump. 6. The image forming apparatus according to claim 1, wherein a portion in contact with the toner is made of a metal or a metal compound.