JP2003280420A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus provided with a fixing device by which the occurrences of damages, electrostatic offsetting, toner repelling or the like due to a destaticizing means on the surface of a heating roller are prevented. <P>SOLUTION: The image forming apparatus possessing the fixing device by which a toner image is melted and fixed by a heating member and a pressure member coming into press-contact with the heating member possesses a means to detect the surface potential of the heating member and the destaticizing means attachable/detachable to/from the heating member, and when the detected surface potential A of the heating member is -400 V<A<+100 V, the destaticizing means is separated, from the heating member, and when it is A≤-400 V or A≥+100 V, the destaticizing means is brought into contact with the heating member. <P>COPYRIGHT: (C)2004,JPO

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 fixing device for fixing a toner image on a transfer material by a heat roller method.

[0002]

2. Description of the Related Art Conventionally, in image forming apparatuses such as copiers, printers, and facsimiles, a heat roller system is often used as a fixing device for heating and fixing a transfer material carrying a toner made of a heat-meltable resin or the like. Has been done.

The heat roller type fixing device is composed of a heating roller which is a heating member having a heat source such as a halogen heater therein, and a pressure roller which is a pressure member which is in pressure contact with the heating roller. The toner image carried on the transfer material is melted and fixed by passing the transfer material, which is the recording material, through the fixing nip portion, which is the pressure contact portion of the roller. The transfer material is a heating roller and a pressure roller. The electric charge remaining in the toner image during the process of being nipped and conveyed between them is transferred to and accumulated in the heating roller, so that fixing jam, electrostatic offset, toner repelling and the like due to winding of the transfer material occur. In order to avoid this, the static elimination roller or static elimination brush which is the static elimination means is always brought into contact with the heating roller.

However, if the static elimination roller or the static elimination brush is kept in contact, the surface of the heating roller is scratched, which causes problems such as vertical stripes appearing on the transferred image.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus equipped with a fixing device capable of preventing the surface of a heating roller from being scratched by static eliminator, electrostatic offset, and toner repelling. To do.

[0006]

The objects of the present invention can be achieved by the following constitutions.

(1) In an image forming apparatus having a fixing device that melts and fixes a toner image by a heating member and a pressing member that is in pressure contact with the heating member, means for detecting the surface potential of the heating member, and And a static eliminator capable of separating from and contacting the heating member, and the detected surface potential A of the heating member is −4.
When 00V <A <+ 100V, the static elimination means is separated from the heating member, and A ≦ −400V or A ≧ + 10.
The image forming apparatus (first invention) is characterized in that when the voltage is 0 V, the charge eliminating means is controlled so as to come into contact with the heating member.

(2) In an image forming apparatus provided with a heating member having an elastic body and a release layer, and a fixing device having an elastic body in pressure contact with the heating member and a pressing member having a release layer, At least one of the heating member and the pressing member is electrically conductive (second invention).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, an image forming apparatus of the present invention will be described.

In the description of the embodiments of the present invention, the technical scope of the present invention is not limited by the terms used in this specification.

FIG. 1 is a schematic diagram showing an example of the overall configuration of the image forming apparatus. In the figure, 10 is a photoconductor, 11 is a scorotron charger which is a charging unit, 12 is a writing device which is an image writing unit, 13 is a developing unit which is a developing unit, and 14 is cleaning for cleaning the surface of the photoconductor 10. An apparatus, 15 is a cleaning blade, 16 is a developing sleeve, and 20 is an intermediate transfer belt which is an image carrier.
The image forming means 1 includes a photoconductor 10 and a scorotron charger 1.
1, the developing device 13, the cleaning device 14, and the like, and the image forming unit 1 for each color has the same mechanical structure. Therefore, in the drawing, reference numerals are given only to the structure of the Y (yellow) series. Therefore, reference numerals are omitted for the components of M (magenta), C (cyan), and K (black).

The arrangement of the image forming means 1 for each color is in the order of Y, M, C, and K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 is a stretched surface of the intermediate transfer belt 20. And is rotated at the contact point in the same direction as the running direction of the intermediate transfer belt 20 and at the same linear velocity.

The intermediate transfer belt 20 includes a driving roller 21, a ground roller 22, a tension roller 23, and a charge eliminating roller 2.
7. The belt unit 3 is stretched around the driven roller 24, and these rollers, the intermediate transfer belt 20, the transfer device 25, the cleaning device 28 and the like constitute the belt unit 3.

The traveling of the intermediate transfer belt 20 is performed by the rotation of the drive roller 21 by a drive motor (not shown).

The photoconductor 10 is formed by forming a conductive layer, an a-Si layer, or a photosensitive layer such as an organic photoconductor (OPC) on the outer periphery of a cylindrical metal substrate formed of, for example, an aluminum material. Rotate in the counterclockwise direction indicated by the arrow in the figure with the grounded.

An electric signal corresponding to the image data from the reading device 80 is converted into an optical signal by the image forming laser, and the writing device 12 projects the light signal onto the photoconductor 10.

The developing device 13 is made of a cylindrical non-magnetic stainless steel or aluminum material which keeps a predetermined distance from the peripheral surface of the photoconductor 10 and rotates in the same direction at the position closest to the rotation direction of the photoconductor 10. The developing sleeve 16 is provided.

The intermediate transfer belt 20 has a volume resistivity of 10 ⁶
It is an endless belt of -10 ¹² Ω · cm, and has a conductive material dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy, and has a thickness of 0.1. A seamless belt having a two-layer structure in which a semi-conductive film substrate having a thickness of ˜1.0 mm is coated with fluorine to a thickness of 5 to 50 μm, preferably as a toner filming prevention layer, is provided. In addition to this, a semi-conductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can be used as the base of the belt.

A transfer device 25 has a function of transferring a toner image formed on the photoconductor 10 onto the intermediate transfer belt 20 by applying a direct current having a polarity opposite to that of the toner. Transfer device 2
As 5, a transfer roller can be used in addition to the corona discharger.

Reference numeral 26 denotes a transfer roller which can be released from contact with the earth roller 22 and retransfers the toner image formed on the intermediate transfer belt 20 onto the transfer material P.

A cleaning device 28 is provided so as to face the driven roller 24 with the intermediate transfer belt 20 interposed therebetween. After transferring the toner image to the transfer material P, the intermediate transfer belt 20
The charge of the residual toner is weakened by the static elimination roller 27 to which an AC voltage having a DC voltage of the same polarity or the opposite polarity of the toner is applied, and the cleaning blade 29 cleans the toner remaining on the peripheral surface.

A fixing device 4 has a heating roller 41 as a heating member and a pressure roller 42 as a pressure member.

Reference numeral 70 is a paper feeding roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a conveying roller.

The fixing device according to the present invention will be described below. FIG. 2 is a schematic view showing a cross section of a heat roller type fixing device.

FIG. 3 is a schematic view of a pressure bonding mechanism of the pressure roller 42. FIG. 3A shows a pressurized state, and FIG. 3B shows a released state.

2 and 3, the front side of the paper is the front side and the back side is the rear side.

FIG. 4 is a cross-sectional view of the heating and pressure roller portion (see FIG. 2, AA arrow). FIG. 5 is a diagram for explaining a method of removing static electricity on the surface of the heating roller.

In FIG. 2, a heating roller 41 includes a cylindrical core metal (hereinafter, simply referred to as core metal) 413 formed of an aluminum tube, and a silicone-based heat-resistant rubber 41 which is an elastic body.
2 is baked, and the outer periphery of the heat resistant rubber 412 is coated with a release layer 411. The heating roller 41 is supported by the front side plates 451 and 452 via heat insulating sleeves 417 shown in FIG. 4 which are inserted into both ends of the core tube 413. Reference numeral 415 denotes a heater, which is disposed in the hollow portion of the heating roller 41, and has both ends with the front side plate 45.
1 and the rear side plate 452 is supported by the support plate 416 shown in FIGS. 3 and 4, and connectors (not shown) are attached to both terminals.

The pressure roller 42 includes a core metal 423 molded from an aluminum tube and a silicone-based heat-resistant rubber 4 which is an elastic body.
22 is baked, and the outer periphery of the heat resistant rubber 422 is coated with a release layer 421. The pressure roller is supported via a heat insulating sleeve 438 fitted in support levers 427 and 428 shown in FIGS. Reference numeral 425 denotes a heater, which is disposed in the hollow portion of the pressure roller 42 and has both end portions having support levers 427 (428).
It is supported by a support plate 426 shown in FIGS. 3 and 4 attached to the connector, and connectors (not shown) are inserted into both terminals.

Reference numerals 433 and 434 denote temperature sensors for the heating roller 41 and the pressure roller 42, which are temperature sensors 433 and 43.
The detection signal No. 4 is transmitted to the control unit B1 (see FIG. 1), and a thermostat (not shown) adjusts each roller to a specified temperature.

In FIG. 3, reference numerals 451 and 452 denote front and rear plates of a frame body which constitutes the skeleton of the fixing device 4, and the heating roller 41 and the support lever shaft via the heat insulating sleeves 417, 437 and 436 shown in FIG. 430 and the cam rotation shaft 431 are supported. The support levers 427 and (428) are reinforced by a stay 432 so as to be integrated.

Reference numeral 435 is a coil spring that abuts the pressure roller 42 against the heating roller 41 at a predetermined pressure via the support levers 427 and (428). The coil spring 435 has one end hooked on each of the support levers 427 and (428) and the other end locked by a spring hook 429 provided on the front side plate 451 and the rear side plate 452.

The pressure roller 42 is controlled by the controller B1 so that the transfer material contacts the heating roller 41 at least while passing through the nip portion T.

Reference numeral 424 denotes a cam for releasing the abutment of the pressure roller 42 from the heating roller 41 against the coil spring 435. One cam is in phase with the cam surface abutting the support levers 427 and (428). Each of them is attached to the cam rotation shaft 431, and a rotational force is obtained from a power transmission unit (not shown) for rotation.

The support levers 427 and (428) are rotatable about a support shaft 430 as a fulcrum, and are counterclockwise rotated by the coil spring 435, so that the cam 4 is rotated.
The pressure roller 42 is swung up and down in a 180-degree phase by 24, and the pressure roller 42 is brought into contact with the heating roller 41 at a predetermined pressure.

In FIG. 4, the heating roller 41 has a rotational force transmitted from a power source (not shown) to a gear 418 fixed to one side of the core tube 413 via a gear group.

On the other hand, the pressure roller 42 comes into contact with the heating roller 41 and rotates along with the heating roller 41 when pressure is applied. When releasing the pressure, the cam 424 pushes down the support levers 427 and (428) against the coil spring 435 to release the contact between the pressure roller 42 and the heating roller 41.

The structure and mechanism of the heating / pressurizing roller have been described above. Next, static electricity removal on the surface of the heating roller according to the present invention will be described.

When both the pressure roller and the heating roller are non-conductive, the toner on the transfer material carrying the toner image is melted and fixed on the heating roller 41. As described above, the toner is fixed on the heating roller 41. Since the static electricity from the image is accumulated, a fixing jam in which the transfer material is wrapped around the roller, an electrostatic offset, a toner repelling, and the like occur. To avoid that,
Usually, a method of removing static electricity by constantly contacting a removing means such as a discharging roller or a discharging brush is adopted. However, when the heating roller is always in contact with the surface, a trace such as a scratch is generated, which causes vertical stripes in the transferred image.

The present invention minimizes damage to the roller surface by minimizing the time during which the static elimination roller or the static elimination brush contacts the roller, or the static elimination means is not attached and the roller is made conductive. The material is characterized by being able to secure stable separability and images by preventing electrification.

The fixing charge removal will be described below with reference to the drawings. Returning to FIG. 2, reference numeral 46 denotes a fixing static eliminator, which is a conductive static eliminator 461 (grounded) that removes static electricity on the surface of the non-conductive heating roller 41, a static eliminator roller support frame 462, and a cam 463. , Cam shaft 464, pressure spring 46
5, a static elimination roller shaft 466, a frame support shaft 467, and the like. Reference numeral 468 is an electrometer for detecting the surface potential of the heating roller 41, which is arranged near the center of the heating roller 41 in the width direction. The signal is determined by the control unit B1 (see FIG. 1), and the contact and release of the static elimination roller 461 with respect to the heating roller 41 are controlled.

In the first invention of the present embodiment, when the surface potential A is -400V <A <+ 100V,
The cam 463 resists the compression spring 465, and uses the static elimination roller support frame 462 as a fulcrum on the frame support shaft 467 as a fulcrum.
1 is separated from the heating roller 41, the surface potential A
, When A ≦ −400V or A ≧ + 100V,
The cam 463 rotates 180 °, and the static elimination roller 461 is brought into contact with the heating roller 41 by the pressure contact spring 465 to remove static electricity.

Therefore, since the static elimination roller 461 is in the non-contact state except when the surface potential A is -400V <A <+ 100V, the frequency of scratching the surface of the heating roller 41 is reduced, and the vertical stripes in the transferred image are generated. Is suppressed. Also, electrostatic offset and toner repelling can be avoided by controlling the surface potential within a specified range.

Further, in the second aspect of the invention, the heating roller 41 or the pressure roller 42 does not need a charge eliminating means,
It is possible to remove the surface potential of the roller without changing the structure of the fixing device by using a conductive member in which carbon is mixed in the material of the elastic body and the release layer of at least one of the rollers. is there.

Next, the image forming process will be described with reference to FIG. Simultaneously with the start of image recording, the photoconductor 10 of the color signal Y is rotated in the counterclockwise direction by the start of a photoconductor drive motor (not shown), and at the same time, a potential is applied to the photoconductor 10 by the charging action of the scorotron charger 11. Is started.

After the electric potential is applied to the photoconductor 10, the writing device 12 starts writing the image corresponding to the Y image data, and the Y of the original image is printed on the surface of the photoconductor 10.
An electrostatic latent image corresponding to the image is formed.

The electrostatic latent image is reversely developed by the Y developing device 13 in a non-contact state, and Y is developed according to the rotation of the photoconductor 10.
Toner image is formed on the photoconductor 10.

The Y toner image formed on the photoreceptor 10 is transferred to the intermediate transfer belt 2 by the action of the Y transfer device 25.
0 is transcribed.

After that, the photoconductor 10 is cleaned by the cleaning device 14 and the next image forming cycle is started (the same applies to the M, C and K cleaning processes, so the description thereof is omitted).

Next, the writing device 12 writes an image corresponding to the M (magenta) color signal, that is, the image data of M, and the M of the original image is printed on the surface of the photoconductor 10.
An electrostatic latent image corresponding to the image is formed. The electrostatic latent image becomes an M toner image on the photoconductor 10 by the M developing device 13, and the intermediate transfer belt 20 is transferred to the M transfer device 25.
It is synchronized with the Y toner image above and is superimposed on the Y toner image.

By the same process, the Y and M superimposed toner images are synchronized with each other, and the C (cyan) toner image is transferred onto the Y and M superimposed toner images at the C transfer device 25. The toner images of K (black) are superposed and synchronized with the superposed toner images of Y, M, and C.
In the K transfer device 25, the superimposed toner images of Y, M, and C are superimposed, and the superimposed toner images of Y, M, C, and K are formed on the intermediate transfer belt 20.

The intermediate transfer belt 20 carrying the superposed toner image is sent in the clockwise direction as shown by the arrow, and the transfer material P is sent out from the paper cassette 72 by the paper sending roller 70, and passes through the carrying roller 73, The transfer roller 26 is conveyed to the timing roller 71 and driven by the timing roller 71 so as to be synchronized with the superimposed toner image on the intermediate transfer belt 20 and to which a DC voltage having a polarity opposite to that of the toner is applied (intermediate transfer roller 26). The superposed toner image on the intermediate transfer belt 20 is transferred to the transfer material P by being fed to the transfer area S (which is in contact with the belt 20).

After that, the intermediate transfer belt 20 travels, the charge of the residual toner is weakened by the charge eliminating roller 27, and the cleaning blade 29 abutting on the intermediate transfer belt 20 cleans the intermediate transfer belt 20 to start the next image forming cycle.

Transfer material P on which the superimposed toner images have been transferred
Is further conveyed to the fixing device 4, and is nipped and conveyed while heat and pressure are applied in the nip portion T between the heating roller 41 and the pressure roller 42, and the transfer material P on which the superimposed toner images are fused and fixed The sheet is conveyed to the sheet discharge tray 82 by the sheet discharge roller 81.

[0055]

By removing the static electricity accumulated on the surface of the heating roller, it is possible to prevent the fixing jam, electrostatic offset and toner repelling due to the winding of the roller.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of the overall configuration of an image forming apparatus.

FIG. 2 is a schematic view showing a cross section of a heat roller type fixing device.

FIG. 3 is a schematic view of a pressure roller pressing mechanism. (A) shows a pressurized state, and (b) shows a released state.

FIG. 4 is a cross-sectional view of the heating / pressurizing roller portion (see FIG. 2, AA arrow).

FIG. 5 is a diagram for explaining a method of removing static electricity on the surface of a heating roller.

[Explanation of symbols]

4 fixing device 41 heating roller 42 Pressure roller 46 Fixing static eliminator 433,434 Temperature sensor 461 neutralization roller 462 Discharge roller support frame 463 cam 468 electrometer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H033 AA09 AA16 AA26 BA13 BB06                       BB08 BB29 CA01 CA26

Claims (4)

[Claims] 1. An image forming apparatus having a fixing device for fusing and fixing a toner image between a heating member and a pressing member in pressure contact with the heating member, a means for detecting the surface potential of the heating member, and the heating device. And a static elimination means capable of separating from and contacting the member, and the detected surface potential A of the heating member is -400.
When V <A <+ 100V, the static eliminator is separated from the heating member, and A ≦ −400V or A ≧ + 100V.
In this case, the charge eliminating device is controlled so as to be in contact with the heating member. 2. The image forming apparatus according to claim 1, wherein the discharging unit is a discharging roller. 3. The image forming apparatus according to claim 1, wherein the discharging unit is a discharging brush. 4. An image forming apparatus provided with a heating device having an elastic body and a release layer, and a fixing device having an elastic body in pressure contact with the heating member and a pressure member having a release layer. An image forming apparatus, wherein at least one of a heating member and the pressing member is conductive.