JPH06110349A - Roller for fixing and fixing device - Google Patents

Abstract

PURPOSE:To prevent offset developing due to peeling charging by electrically making a conductive tube on a top layer on a floating condition. CONSTITUTION:An electrostatically charging preventing layer 24 is obtained by covering an insulating PFA tube 23 with a conductive PFA tube in which carbon is dispersed. The width of the conductive PFA tube 24 is respectively set shorter than that of the insulating PFA tube 23 on both ends, so that the tube 24 is electrically insulated from a conductive elastic layer 22. The conductive PFA tube 24 is brought into contact with the rear surface of a sheet paper 5, and the trailing edge part of the sheet paper 5 is brought into contact with the surface of a fixing roller 1 in the case of ejecting the trailing edge of the sheet paper 5 from a fixing nipple N so that the peeling charging is relieved; therefore, local and strong peeling charging can be prevented and peeling offset does not occur even though a releasing layer 12 is on a new condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing roller and a fixing device in an image forming apparatus such as a copying machine or a printer to which an electrophotographic method is applied.

[0002]

2. Description of the Related Art FIG. 6 is a vertical sectional view of a conventional fixing device. The fixing roller 1 includes a cored bar 11 and a release layer 12 made of a fluororesin such as PFA or PTFE provided on the cored bar 11. The fixing roller 1 rotates in the arrow direction. The pressure roller 2 comprises an elastic layer 22 made of silicone rubber or the like and a release layer 23 made of fluorocarbon resin such as PFA or PTFE provided on a cored bar 21, and is rotated in the direction of the arrow following the fixing roller 1. . A heater 3 is provided in the core metal 11 of the fixing roller 1 and heats the fixing roller 1 from the inside. The surface temperature of the fixing roller 1 is the temperature sensor 4
Is input to a temperature control circuit (not shown). The heater 3 is turned on / off by a temperature adjusting circuit, and the surface temperature of the fixing roller 1 is controlled to a constant value. The pressure roller 2 is pressed against the fixing roller 1 by urging means (not shown), and a fixing nip N is formed. The unfixed toner 6 electrostatically transferred onto the paper sheet 5 by a well-known electrophotographic process is inserted into the fixing nip N through a guide means (not shown), heated and pressed to be permanently attached to the paper sheet 5. Fixed.

A bias power supply 7 is connected to the core metal 11, a voltage having the same polarity as the intrinsic charge of the toner 6 is applied to the core metal 11, and the toner 6 is electrostatically repelled from the surface of the fixing roller 1. In this way, the offset phenomenon that the toner 6 is transferred to the surface of the fixing roller 1 and stains the subsequent image is prevented. In order to increase the repulsive electric field in the fixing nip N, the elastic layer 22 is preferably conductive, and as an example, the elastic layer 22 made of silicone rubber in which carbon is dispersed can be used. The release layer 12 and the release layer 23 are made of PFA.
It is made of a tube, is electrically insulating, and has a resistivity of 10 ¹² Ω · cm or more to prevent current leakage of the bias power supply 7. For the purpose of not causing electrical breakdown of the release layer 12 and the release layer 23, the method of covering the tube is more suitable than the method of firing the PFA powder because local leakage can be reduced. .

[0004]

However, according to the above-mentioned conventional example, when the paper sheet 5 is discharged from the fixing nip N, the paper sheet 5 is separated from the release layer 12 or the release layer 23. The fixing nip N that is charged and is generated by the power supply 7
It was found to act to weaken the repulsive electric field inside.
As a result, the offset prevention effect is extinguished, and offset may occur especially in a low humidity environment in which the paper sheet 5 has a high resistance. The peeling charge occurs particularly strongly when the rear end of the paper sheet 5 leaves the fixing nip N, and the release layer 12 and the release layer 2
When 3 is in a new state, particularly strong peeling electrification of the rear end is observed, and the surface potential of the rear end corresponding portion locally has a polarity opposite to that of the bias power source 7, that is, a polarity opposite to that of the toner 6, and contacts the portion. The unfixed toner image formed may be peeled off and offset on a subsequent image.

7A and 7B, the preceding paper sheet 5 is shown.
It is shown that the peeling offset occurs on the succeeding paper sheet 52 due to the strong peeling charge generated at the rear end portion of No. 1. FIG. 8 shows an offset image on the paper sheet 52, and shows that the toner 6 peeled off at the X portion is offset on the image after the peripheral length L of the fixing roller 1. The stripping offset occurs most clearly in the halftone image as in (1), and in the case of the character image as in (2), the character loss due to stripping does not occur, but the offset in the subsequent portion occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing roller and a fixing device which can solve the above problems and prevent the offset phenomenon due to peeling charging.

[0007]

According to the present invention, the above objects are
First, regarding the fixing roller, in the fixing roller having a surface layer on the core metal and sandwiching and conveying the support supporting the image to be fixed, the surface layer is the uppermost layer of the conductive tube, This is achieved by forming at least one layer from the lower layer of the insulating tube, and the conductive tube of the uppermost layer being electrically floated. Next, the fixing device is achieved by providing the fixing device with the fixing roller.

[0008]

According to the present invention, since the uppermost layer of the fixing roller is formed of the conductive tube, if the fixing device is constructed by using the roller and the fixing rotator, the rear end of the paper sheet as the support is formed. When the portion is discharged from the fixing nip portion, the rear end portion and the surface of the fixing rotator come into contact with the uppermost layer to alleviate peeling charge. Further, since the lower layer has an insulating tube and the uppermost layer is electrically floated, the repulsive electric field for offset prevention formed in the nip is maintained, and a large number of paper sheets are provided. While the paper is passing, the release layer of the fixing rotator is worn by the abutting part of the sensor, etc., and finally the cored bar is exposed, and even when it comes into direct contact with the fixing roller, the leakage current Prevent occurrence.

[0009]

Embodiments of the present invention will be described with reference to the drawings.

<Embodiment 1> First, Embodiment 1 of the present invention will be described with reference to FIGS. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

The antistatic layer 24 shown in FIG.
Insulating PFA tube with dispersed conductive PFA tube
Thickness of PFA tube 23
Is 20 to 100 μm, and the resistivity is 10¹²-10¹⁸In Ω · cm
Yes, the thickness of the conductive PFA tube is 10-30 μm,
Resistivity 10³-10⁶Ω · cm. Conductive PFA Chu
Width L of tube 24₁Is the width L of the insulating PFA tube 23₂
Both ends are set to be shorter by ΔL.
It is electrically insulated from the electrically conductive elastic layer 22.
Width L Is larger than the width of the paper sheet 5 used,
It may be 2 to 10 mm.

A conductive PF is formed on the insulating PFA tube 23.
As a method of forming the A tube 24, there is a method in which the insulating PFA tube 23 is once adhered and fired on the elastic layer 22, and then the conductive PFA tube 24 is adhered and fired. In addition, the tube itself is an insulating PFA tube 23.
A desired pressure roller can also be obtained by using a method in which a conductive PFA tube 24 is molded in two layers on the elastic layer 22, and the conductive PFA tube 24 is adhered and baked on the elastic layer 22 and then the end portion ΔL of the conductive PFA tube 24 is peeled off. 2 can be obtained.

As shown in FIG. 2, the conductive PFA tube 24 comes into contact with the back surface of the sheet body 5, and when the rear end portion of the sheet body 5 is discharged from the fixing nip N, the rear end portion and the fixing roller. Since the peeling electrification is relieved by making contact with the surface of No. 1, local strong peeling electrification can be prevented, and peeling offset does not occur even if the release layer 12 is in a new state. Here, the role of the insulating PFA tube 23 of the pressure roller 2 is to maintain the repulsive electric field for offset prevention formed in the fixing nip N by the power supply 7 and the diode 8, and pay attention only to the stripping offset. Insulating PFA
Although the tube 23 is unnecessary, the release layer 12 of the fixing roller 1 is abraded by the abutting portions of the sensor 4 and the like while a large number of sheets 5 are being passed, and finally the core bar 11 is exposed. In order to prevent the leakage current from being generated even when it comes into direct contact with the pressure roller 2, the insulating PFA tube 23
Is mandatory.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 3 is a vertical sectional view of the fixing device of the second embodiment. The pressure roller 2 of this embodiment has the same structure as that of the first embodiment.

The feature of the present embodiment is that the rotating body contacting the toner 6 is the thin fixing belt 1 ', and the plate heater 3'having a small heat capacity is turned on / off based on the output of the temperature sensor 4. This is an energy-saving type fixing device that can instantly realize a fixing possible state. The fixing belt 1'is based on a resin film 11 'such as polyimide having a thickness of 30 to 100 .mu.m and a thickness of 5 to 10 .mu.m.
Conductive layer 12 ′ which is also an adhesive layer of m and has a thickness of 5 to 30 μm
It has a release layer 13 made of fluororesin such as PTFE or PFA, and is rotated by drive rollers 9 and 9 '. The conductive layer 12 ′ is grounded via a diode 8 ′, and cooperates with the diode 8 connected to the cored bar 21 of the pressure roller 2 to electrostatically release the toner 6 in the fixing nip N. An electric field repulsive from 13 is formed to prevent offset. Also in this configuration, when the rear end of the paper sheet 5 is discharged from the fixing nip N, the conductive tube 24 comes into contact with the release layer 13 to prevent peeling electrification of the rear end portion, and peeling off. No offset occurs.

In the case of an apparatus for energy saving such as the apparatus of this structure, the elastic layer 2 of the pressure roller 2 is used.
It is preferable that 2 is a conductive sponge to reduce heat escape.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

4 and 5 are a perspective view of a main part of a fixing roller 1 and a vertical sectional view of a fixing device according to a third embodiment of the present invention.

The fixing roller 1 is formed by firing the conductive tube 13 'on the insulating tube 12 on the core metal 11 in the same manner as described for the pressure roller 2 in the first embodiment. The insulating tube 12 was exposed at the end of the conductive tube 13 ′ for a length of ΔL so that the conductive tube 13 ′ was electrically floated without being electrically connected to the cored bar 11. It is designed to be done.

In the case of this embodiment, since the surface of the fixing roller 1 has a conductive layer, the surface potentials do not have locally different values, and even when the sheet 5 is discharged from the fixing nip N, Since strong peeling charge does not occur at the end corresponding portion, peeling offset does not occur. Further, in the fixing nip N, the conductive tube 13 'acts as a float electrode, and an electric potential in the middle between the toner 6 adhering portion and the non-image portion is induced therein. There is also an effect that electrostatic offset can be prevented.

Although the above-mentioned peeling charging of the rear end of the paper sheet 5 is remarkably generated in the fixing roller 1 or particularly in a new state, the bias power source 7 and the diodes 8 and 8'are not used, and each roller is used. It is clear that the effects of the present invention can be exhibited even when grounded.

[0023]

As described above, a fixed image is obtained by disposing a conductive tube electrically kept in a floating state on an insulating tube as a surface release layer of a fixing roller or a pressure roller. The electrostatic offset image generated above can be prevented.

[Brief description of drawings]

FIG. 1 is a perspective view of a pressure roller according to a first embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view of a fixing device according to a second exemplary embodiment of the present invention.

FIG. 4 is a perspective view of a main part of a fixing roller according to a third exemplary embodiment of the present invention.

FIG. 5 is a vertical cross-sectional view of a fixing device according to a third exemplary embodiment of the present invention.

FIG. 6 is a vertical sectional view of a conventional fixing device.

FIG. 7 is a schematic explanatory diagram showing the occurrence of peeling charge and peeling offset at the rear end of the paper sheet.

FIG. 8 is a diagram showing an offset image caused by peeling charging.

[Explanation of symbols]

 1 fixing roller 2 pressure roller 23 insulating tube 24 conductive tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroaki Sakai, 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hideo Nanataki, 3-30-2 Shimomaruko, Ota-ku, Tokyo Within the corporation

Claims (3)

[Claims] 1. A fixing roller, which has a surface layer on a core metal and holds and fixes a support supporting an image to be fixed, wherein the surface layer is at least an uppermost layer of a conductive tube. And a lower layer of an insulating tube, and the conductive tube of the uppermost layer is electrically floated. 2. A fixing device comprising the fixing roller according to claim 1. 3. The fixing device according to claim 2, wherein a bias voltage is generated between the fixing rollers forming the fixing device.