JP3920133B2 - Fixing device, image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device that is used in electrophotographic copying machines, printers, plotters, facsimiles, and the like and fixes a toner image on a recording medium.
[0002]
[Prior art]
Conventionally, a fixing device in an image forming apparatus using an electrophotographic method is transferred between a rotatable heating roller having a heating element therein and a pressure roller rotatably opposed to the heating roller. The recording medium carrying the toner image is sandwiched and conveyed, and the toner is melted by a heating roll heated by the heating element, and at the same time, fixed to the recording medium by the pressing force of the pressure roller.
[0003]
In this fixing device, the pressure roller is in pressure contact with the heating roller when the toner does not fix to the recording medium and adheres to the surface of the heating roller, or when the toner already adhered to the heating roller does not pinch and convey the recording medium In general, the outermost peripheral surfaces of the heating roller and the pressure roller are coated with a fluororesin having a good releasability from the toner.
[0004]
[Problems to be solved by the invention]
However, the fluororesin is a non-conductor having a surface resistivity of 10 ¹² Ω or more. Therefore, the heating roller and the pressure roller rotate while being pressed against each other, and the recording medium is sandwiched and conveyed, so that the outermost peripheral surfaces of the heating roller and the pressure roller are frictionally charged. The charging polarity due to the frictional charging on the outermost peripheral surfaces of the heating roller and the pressure roller is unstable and varies depending on the part.
[0005]
On the other hand, the transferred toner image is carried on a recording medium with a weak electrostatic force, and this carried recording medium is nipped and conveyed by the heating roller and the pressure roller. Here, when the outermost peripheral portion of the heating roller is frictionally charged with the opposite polarity to the toner electrostatically carried on the recording medium, the toner image carried on the recording medium approaches by nipping and conveying the recording medium. The toner image is electrostatically attracted from the recording medium in the direction of the heating roller, and as a result, the adhesion force to the recording medium is reduced.
[0006]
The recording medium absorbs moisture in the atmosphere, and the moisture in the recording medium is heated by the heating roller in the nipping and conveying process, and at the same time receives pressure from the pressure roller, so that it is ejected to the rear of the conveyance. As a result of the ejection, the toner with weakened contact force flies backward and is fixed, resulting in an image defect that results in a partially tailed image.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the fixing device according to the present invention includes a rotatable heating roller having a heating element therein and an opposing pressure contact with the heating roller. In the fixing device, the toner image on the recording medium is nipped and conveyed by the heated pressure roller, and the toner image on the recording medium is melted by the heating roller heated by the heating element. The surface resistivity of the outermost peripheral surface of the roller is set to 10 ⁶ Ω or less, and the surface resistivity of the outermost peripheral surface of the pressure roller is set to 10 ⁶ Ω or less, and the surface of the pressure roller or the heating roller is grounded. It is what.
[0008]
According to the present invention, when the heating roller and the pressure roller are nipping and transporting the recording medium, the recording medium is non-conductive, and therefore the heating roller or the pressure roller is frictionally charged if it is not grounded. Since it is limited to the conveying time and the outermost surface resistivity of the heating roller and the pressure roller is as low as 10 ⁶ Ω, the amount of charge is small, and as a result, the charging potential is lowered.
[0009]
Until the next recording medium is nipped and conveyed until the next recording medium is nipped and conveyed, the recording medium rotates while being in direct contact with nothing between the heating roller and the pressure roller. In addition, since either the heating roller or the pressure roller is grounded, the electric charge due to frictional charging during nipping and conveyance escapes to the ground, and the outermost surface potentials of the heating roller and the pressure roller become zero.
[0010]
That is, while the heating roller and the pressure roller are nipping and conveying the recording medium, the heating roller or pressure roller on the side that is not grounded is frictionally charged, but the charge amount is very small, and the nipping and conveying operation is finished. Then, the process that the frictional charging becomes zero due to the grounding is repeated, so that the outermost peripheral surfaces of the heating roller and the pressure roller can be cumulatively prevented from increasing the potential due to the frictional charging.
[0011]
Therefore, since there is no electrical influence enough to attract the toner image that is electrostatically adhered to the recording medium after transfer with a weak force, it is possible to prevent the image defect due to the back scattering of the toner.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a schematic diagram showing a configuration of a fixing device according to the present invention. In FIG. 1, a recording medium 1 is conveyed in a conveying direction 1a by a conveying mechanism of an image forming apparatus (not shown), transferred by an electrophotographic process of an image forming apparatus (not shown), and a toner 2 is carried on the recording medium 1 by electrostatic force. is doing.
[0014]
Reference numeral 3 denotes a fixing device according to the present invention, which includes a heating roller 4 and a pressure roller 5. The heating roller 4 is urged and installed on the heating roller 4 by a pressure contact means (not shown). Further, a metal roller 6 urged by means not shown is also provided on the outermost peripheral surface of the pressure roller 5. Are connected to each other, and the surface thereof is grounded.
[0015]
On the other hand, a heating element 4a such as a halogen heater is disposed inside the heating roller 4, and is covered with a metal heating roller core 4b for transferring the heat of the heating element 4a. A conductive material such as carbon fiber is added to the outer periphery of the heating roller core 4b, which has good releasability from the toner, for example, to impart conductivity to the fluororesin PTFE, and has a surface resistivity of 10 ⁶ Ω or less. The coating agent 4c prepared in the above is applied in a thickness of 1 μm to 100 μm. The heating roller 4 can be rotated in the rotation direction 4d by a driving means (not shown).
[0016]
The pressure roller 5 is an elastic member for securing a nip length with the heating roller 4 around the pressure roller core 5a, for example, foamed silicon 5b is fixed, and the outer periphery thereof has a thickness of 1 μm to 100 μm. Tube 5c having good releasability from other toner, for example, a conductive material such as carbon fiber for adding conductivity to PFA of a fluororesin tube, and having a surface resistivity of 10 ⁶ Ω or less. It is covered.
[0017]
Note that the pressure roller 5 is rotatably supported by the rotation of the heating roller 4 so as to rotate in the rotational direction 5d. Further, since the metal roller 6 is rotatably supported and is urged by the pressure roller 5, if the pressure roller 5 rotates, the metal roller 6 rotates along the rotation direction 6a.
[0018]
According to the fixing process of a series of electrophotographic processes, the heating roller 4, the pressure roller 5, and the metal roller 6 are rotated by driving means (not shown). At the same time as the rotation, the heating element 4 a In order to set the temperature to a desired temperature at which the toner melts, energization is performed to generate heat. At this time, since the heating roller 4 and the pressure roller 5 are pressed against each other, friction charging is attempted. However, since the surface resistivity of the heating roller 4 and the pressure roller 5 is as low as 10 ⁶ Ω or less, the charged charge is Immediately escapes to the ground through the grounding of the metal roller 6, and as a result is not charged.
[0019]
When the surface temperature of the heating roller 4 reaches a desired temperature, the toner 2 transferred by an electrophotographic process (not shown) is electrostatically carried on the surface of the recording medium 1. At the same time, the recording medium 1 is transported in the transport direction 1 a by a transport mechanism (not shown), and is finally sandwiched and transported between the heating roller 4 and the pressure roller 5.
[0020]
In this embodiment, since the heating roller 4 is not grounded, it is triboelectrically charged while the recording medium 2 that is a non-conductor is nipped and conveyed, but is electrostatically carried because the surface resistivity of the heating roller 4 is low. The potential does not increase so as to attract the toner 2 from the recording medium 1. Therefore, the toner 2 is melted by the heat of the heating roller 4 while being held at a predetermined position of the recording medium 1, and at the same time, the toner 2 is fixed to the recording medium 1 by the pressing force of the pressure roller 5, and a good image is obtained.
[0021]
Since the heating roller 4 is driven until the recording medium 2 is completely discharged out of the image forming apparatus (not shown) even after the nipping and conveyance is completed, the charged charge is grounded through the grounding of the pressure roller 5 and the metal roller 6. The surface potential of the escape roller, the heating roller 4 and the pressure roller 5 becomes 0, and the next fixing process of the recording medium 2 can be started from an electrically reset state.
[0022]
【The invention's effect】
As described above, according to the present invention, even when the toner is intermittently or continuously fixed on one or a plurality of recording media, the toner can be prevented from being scattered at low cost. Image defects can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a fixing device of an image forming apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Recording medium 1a Conveying direction 2 Toner 3 Fixing device 4 Heating roller 4a Heat generating body 4b Heating roller metal core 4c Coating agent 4d Rotation direction 5 Pressure roller 5a Pressure roller metal core 5b Foamed silicon 5c Tube 5d Rotation direction 6 Metal roller 6a Direction of rotation

Claims (2)

A recording medium that electrostatically carries a toner image is sandwiched and conveyed between a rotatable heating roller having a heating element inside and a pressure roller that is rotatably pressed against the heating roller. In a fixing device in which a toner image is melted by a heating roller heated by the heating element and is simultaneously fixed on a recording medium by a pressure contact force of a pressure roller.
A metal roller biased by the pressure roller, grounded, and rotated by the rotation of the pressure roller;
The outermost peripheral surface of the heating roller is coated with a coating agent to which a conductive material is added so as to have a surface resistivity of 10 ⁶ Ω or less ,
The pressure roller is covered with a tube to which a conductive material is added, and has a surface resistivity of 10 ⁶ Ω or less ,
The heating roller is in contact with the pressure roller, and is grounded via the pressure roller and the metal roller,
The heating roller is driven after the recording medium is nipped and conveyed until the recording medium is further discharged from the image forming apparatus, and after the recording medium is nipped and conveyed, the recording medium is moved to the image forming apparatus. The heat roller and the pressure roller are in contact with each other while rotating until they are discharged to the outside, and the charge charged on the heat roller is discharged through the metal roller in contact with the pressure roller while rotating. A fixing device characterized by that. An image forming apparatus comprising the fixing device according to claim 1 .

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