JP2002156851A - Thermal fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing soil from adhering to a heating roll in an electrostatic image forming device and made excellent in electrostatic offset resistance. SOLUTION: The heating roll 12 is grounded through a diode 20 so as to hold charge having the same polarity as unfixed toner, and a pressure roll 14 is grounded through a diode 22 so as to hold charge having a reverse polarity to the unfixed toner, then the rolls 12 and 14 are electrically connected through a varistor 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat fixing device and an image forming apparatus.

[0002]

2. Description of the Related Art In an electrostatic image forming apparatus, in order to prevent an electrostatic offset, a technique of grounding through a diode (Japanese Patent No. 2592968, Japanese Patent Laid-Open No. 4-9888) or a technique of applying a bias (for example, Japanese Patent No. 2675886).
It is known to control the potentials of a heating roll and a pressure roll.

Generally, a negative charge is applied to unfixed toner during development, and a positive charge is applied to a recording material during transfer. Calcium carbonate (CaCO ₃ ) is often used as a filler for the recording material, and a positive charge is simultaneously given to the calcium carbonate of the filler during transfer.

In particular, when bias or diode grounding is applied to the heating roll and / or the pressure roll to prevent the above-mentioned electrostatic offset, dirt including positively charged calcium carbonate and the like is removed. It is drawn to the side and easily adheres to the heating roll. Adhesion of dirt deteriorates the releasability of the surface of the heating roll, promotes toner contamination on the heating roll, and finally adversely affects an image, resulting in poor image quality.

[0005] JP-A-2000-112272 discloses that
A technique has been disclosed in which the potential difference between a heating roll and a pressure roll is set to 100 V or less to eliminate the attraction of calcium carbonate due to an electric field. However, even if only the absolute value of the potential difference is restricted, electrostatic offset cannot be prevented.

Japanese Patent Application Laid-Open No. 11-161068 discloses that a bias having the same polarity as the toner paper gap is applied to a roll in contact with an unfixed toner when a recording material is present in a nip, and a bias is applied when a recording material is not present. A technique of not applying a voltage or applying a bias of the opposite polarity is disclosed.
There is a problem that an increase in cost due to the bias application circuit is unavoidable, and that when a bias of the opposite polarity is applied, toner contamination is caused.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device which prevents contamination of a heating member of an electrostatic image forming apparatus and which has good anti-static offset property.

[0008]

According to a first aspect of the present invention, a sheet carrying an unfixed toner image is conveyed while being sandwiched between a heating member and a pressing member. In a thermal fixing device that fixes a toner image on a sheet of paper by pressing and heating, a heating member is grounded via a diode so as to retain a charge of the same polarity as that of the unfixed toner, and the pressing member is unfixed. Along with grounding via a diode to hold a charge of the opposite polarity to the toner,
A heat fixing device, wherein a heating member and a heating member are electrically connected via a varistor.

According to a second aspect of the present invention, a sheet carrying an unfixed toner image is conveyed while being sandwiched between a heating member and a pressing member, and the unfixed toner image is formed on the sheet by pressing and heating. In a heat fixing device for fixing, a first diode is connected to a pressing member between a heating member and a pressing member in a direction in which a charge having a polarity opposite to the charging polarity of the toner is held, and the heating member is connected to the charging polarity of the toner. And a varistor connected in parallel with the first diode while grounding via a second diode so as to retain an electric charge of the same polarity as the fixing device.

In the above invention, the varistor voltage value is 1
A heat fixing device using a varistor of 00 V or less is preferable.

According to a third aspect of the present invention, a sheet carrying an unfixed toner image is conveyed while being sandwiched between a heating member and a pressing member, and the unfixed toner image is formed on the sheet by pressing and heating. In a heat fixing device for fixing, a zener diode is connected between a heating member and a pressing member in a direction in which a charge having a polarity opposite to the charging polarity of the toner is held on the pressing member, and the heating member is charged with the charging polarity of the toner. A heat fixing device, which is grounded via a diode so as to hold an electric charge having the same polarity as that of the heat fixing device.

Incidentally, as the heating member and the pressure member constituting the heat fixing device of the present invention, rolls, films and the like can be appropriately combined and used.

Further, the present invention provides an image forming apparatus equipped with the above-mentioned heat fixing device.

[0014]

Embodiments of the present invention will be described below.

FIG. 8 shows an image forming apparatus 1 to which the present invention is applied.
It is an explanatory view showing the whole of 00. Image forming apparatus 100
The electrostatic roller 104 applies static electricity to the photosensitive drum 102 to charge the photosensitive drum 102, and irradiates light such as a laser from an exposure device 106 to form a latent image on the photosensitive drum 102. At 110, the powder is supplied to cause an image to appear on the photosensitive drum 102. The paper supplied through the paper supply path 128 is transferred to the photosensitive drum 102 and the transfer roll 1.
12, the image is transferred to the paper, and the fixing roll 114 fixes the image to the paper. In the paper supply path, the paper is drawn from the paper supply cassette 120, advanced by feed rolls 122 and 124, positioned by the registration roll 126, and transferred between the photoconductor roll 102 and the transfer roll 112 via the paper supply path 128 at the paper feeding timing. To supply. The paper on which the image has been transferred is fixed by a fixing roll 114 and discharged by a discharge roll 140. 130, 13
Reference numeral 2 denotes a paper feed lever. The present invention provides an invention characterized in the heat fixing device 150 of the image forming apparatus 100.

FIGS. 4 and 5 are explanatory diagrams of the prior art. Paper 10 sent from photoreceptor drum 16 and transfer roll 18
Is heated by the heating roll 12 and the pressure roll 14,
The image is fixed on the sheet 10. The heating roll 12 incorporates a heating source and heats the toner having a negative charge to transfer the toner onto the paper. In order to prevent the electrostatic offset by maintaining the heating roll 12 at a positive voltage and the pressing roll 14 at a negative voltage, the heating roll and the pressure roll are grounded via diodes 20 and 22, respectively, as shown in FIG. .
For the same purpose, as shown in FIG. 5, the heating roll 12 is grounded via a diode 20, and a diode 26 is interposed between the heating roll and the pressing roll so as to maintain a potential difference between the heating roll and the pressing roll. .

The present invention provides the technique shown in FIGS. 1 to 3 which is an improvement on the prior art shown in FIGS. 4 and 5 in order to prevent an electrostatic offset caused by CaCO ₃ or the like contained in paper. . In the embodiment shown in FIG. 1, a varistor 24 is added to the conventional technique shown in FIG. 4, and a heating roll and a pressure roll are electrically connected via the varistor 24. The varistor 24 is a resistor whose voltage and resistance have non-linear characteristics, and a current flows when the voltage rises. By connecting a varistor between the diodes, the upper limit of the potential difference between the diodes is determined. As the varistor, a varistor having a varistor voltage of 300 V or less may be used, and a varistor having a varistor voltage of 100 V or less is more preferably used.
The reason why the varistor voltage is set to 100 V or less is that an appropriate numerical value is selected from both the electric resistance and the responsiveness.

The embodiment shown in FIG. 2 is an improvement of the prior art shown in FIG. 5, in which a varistor 28 is connected in parallel to a diode 26 provided on a heating roll in a direction opposite to the polarity of the charged toner. It was done. The varistor 28 also has a varistor voltage value of 100 V, as in the embodiment shown in FIG.
The following may be used.

FIG. 3 shows an example in which a zener diode 30 is interposed in place of the diode interposed between the heating roll and the pressure roll of the conventional example shown in FIG. Zener diode 3
Reference numeral 0 denotes a constant voltage diode, which has the characteristics of a diode and a varistor, and maintains a constant voltage by using the Zener effect. Preferably, the characteristics are selected so as to perform the same operation as in the embodiment of FIG.

FIG. 6 is a graph showing the measurement results of the surface potentials of the heating roll and the pressure roll when the conventional technique shown in FIG. 4 is used. The horizontal axis indicates the time elapsed, and the curve 50
Represents the surface potential of the pressure roll, and curve 52 represents the surface potential of the heating roll. The surface potential difference between the heating roll and the pressure roll became 0 to 5 kV, and adhesion of dirt to the heating roll was observed under a low humidity environment.

FIG. 7 is a graph showing the results of measuring the surface potentials of the heating roll and the pressure roll when the embodiment shown in FIG. 1 is used. The varistor voltage is 300V. Curve 5
0 indicates the surface potential of the pressure roll, and curve 52 indicates the surface potential of the heating roll. The surface potential difference between the heating roll and the pressure roll was 0 to 100 V, no contamination was attached to the heating roll even in a low humidity environment, and the electrostatic offset resistance was good.

[0022]

According to the present invention, it is possible to prevent dirt from adhering to the heating member without significantly increasing the cost.
In addition, a thermal fixing device having good antistatic offset resistance was obtained. Therefore, the image processing apparatus equipped with the heat fixing device has an excellent effect that the heating member is less likely to be stained and the electrostatic offset is generated, the maintenance work is reduced, and an excellent image can be obtained.

[Brief description of the drawings]

FIG. 1 is a ground circuit diagram of a heat fixing device according to an embodiment.

FIG. 2 is a ground circuit diagram of the heat fixing device of the embodiment.

FIG. 3 is a ground circuit diagram of the heat fixing device of the embodiment.

FIG. 4 is a ground circuit diagram of a conventional heat fixing device.

FIG. 5 is a ground circuit diagram of a conventional heat fixing device.

FIG. 6 is a graph showing measurement results of surface potentials of a heating roll and a pressure roll of a conventional example.

FIG. 7 is a graph showing the measurement results of the surface potential of the heating roll and the pressure roll of the example.

FIG. 8 is an explanatory diagram illustrating the entire image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Paper 12 Heating roll 14 Pressure roll 16 Photoreceptor drum 18 Transfer roll 20,22 Diode 24 Varistor 26 Diode 28 Varistor 30 Zener diode 50,52,54,56 Curve 100 Image forming apparatus 102 Photoreceptor drum 104 Electrostatic roll 106 Exposure device 108 Developing device 110 Developing roll 112 Transfer roll 114 Fixing roll 120 Feed cassette 122, 124 Feed roll 126 Registration roll 128 Paper supply path 130, 132 Paper delivery lever 140 Discharge roll 150 Thermal fixing device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Keiji Negima, Inventor 3-7-1 Fuchu, Iwatsuki-shi, Saitama Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Yoshiyuki Namba 3-7-1 Fuuchi, Iwatsuki-shi, Saitama No. 1 Fuji Xerox Co., Ltd. Iwatsuki Office F-term (reference) 2H033 AA09 BA13 BB01 BB28

Claims (5)

[Claims] A heat fixing device for conveying a sheet carrying an unfixed toner image by sandwiching the sheet between a heating member and a pressing member, and fixing the unfixed toner image to the sheet by applying pressure and heat. Grounding the member via a diode to retain a charge of the same polarity as the unfixed toner,
A heat-fixing device, wherein the pressure member is grounded via a diode so as to retain a charge having a polarity opposite to that of the unfixed toner, and the heating member is electrically connected to the heating member via a varistor. apparatus. 2. A heat fixing device for conveying a sheet carrying an unfixed toner image by sandwiching the sheet between a heating member and a pressing member, and fixing the unfixed toner image to the sheet by applying pressure and heat. A first diode is connected between the member and the pressing member in a direction in which a charge having a polarity opposite to the charge polarity of the toner is held on the pressure member, and the heating member is charged with a charge having the same polarity as the charge polarity of the toner. A thermal fixing device, wherein a varistor is connected in parallel to the first diode while being grounded via a second diode for holding. 3. The heat fixing device according to claim 1, wherein a varistor voltage value is 100 V or less. 4. A heat fixing device for conveying a sheet carrying an unfixed toner image by sandwiching the sheet between a heating member and a pressing member, and fixing the unfixed toner image to the sheet by applying pressure and heat. A zener diode is connected to the pressing member between the member and the pressing member in a direction in which a charge having a polarity opposite to the charge polarity of the toner is held, and the heating member holds a charge having the same polarity as the charge polarity of the toner. As described above, wherein the heat fixing device is grounded via a diode. 5. An image forming apparatus comprising the heat fixing device according to claim 1.