JP2003316187A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable image by preventing the occurrence of leakage between a fixing member and a pressure member to prevent image defects which are caused by backward scattering of unfixed toner particles due to unstable electric field between the fixing member and the pressure member, and preventing unfixed toner particles held by a weak electrostatic force from being unstably stuck to a recording medium with respect to an image forming device adopting a system of applying a bias between the fixing member an the pressure member to fix an unfixed toner image on the recording medium. <P>SOLUTION: In the image forming device which heats the unfixed toner image electrostatically held on the surface of a recording medium 1 in a fixing nip part formed by bringing a fixing member 2 and a pressure member 3 into pressure welding with each other, to fix the unfixed toner image on the surface of the recording medium while holding and carrying the unfixed toner image, a conductive layer having ≤10<SP>6</SP>Ω/square surface resistivity is provided on the outer peripheral surface of the pressure member and is grounded, and an insulating layer having ≥10<SP>12</SP>Ω/square is provided on the outermost peripheral surface of the pressure 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 electrophotographic image forming apparatus such as a copying machine, a printer, a plotter, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, unfixed toner electrostatically transferred from a photoconductor to a recording material is held by electrostatic force and conveyed to a fixing device to be permanently fixed on a recording medium. . At this time, in the fixing nip portion, since the recording material is momentarily heated to a high temperature, water vapor may be ejected from the recording material to blow the unfixed toner backward. This phenomenon remarkably appears at high humidity. It also appears noticeably when the printing speed is increased.

It is known that the backward scattering of the unfixed toner can be prevented by forming an electric field in the nip portion composed of the fixing member and the pressing member. When a bias is applied to the fixing member, the electric field is formed so as to have the same polarity as the toner.

[0004]

However, in the conventional fixing device, the surface resistivity of the outermost peripheral surface of the pressure member is 10 in order to apply the bias of the fixing member and form the electric field.
Leakage occurs between the fixing member and the pressing member because the conductive material or the surface treatment layer having a resistance of ⁶ Ω / □ or less is provided. This becomes remarkable when a difference occurs between the conductive layers of the fixing member and the pressing member in the width direction perpendicular to the recording medium conveyance direction depending on the size of the recording medium passing through the fixing device, and the fixing member not interposing the recording medium A severe leak occurs between the pressure members. As a result, the electric field between the fixing member and the pressing member becomes unstable, and an image defect occurs due to the backward scattering of the unfixed toner.

[0005]

[Means for Solving the Problems] A material having conductivity or a surface treatment layer having a surface resistivity of 10 ⁶ Ω / □ or less is provided on the outer peripheral surface of the pressure member of a fixing device, and at the same time, a material having conductivity. Alternatively, the surface treatment layer is grounded, and an insulating layer having a surface resistivity of 10 ¹² Ω / □ or more is further provided on the outermost peripheral surface of the pressing member to prevent the occurrence of the image defect.

According to the present invention, the insulating layer having a surface resistivity of 10 ¹² Ω / □ or more is provided on the outermost peripheral surface of the pressing member, so that the fixing member and the pressing member are conveyed between the recording medium and the conveying member. Leakage can be prevented, and an electric field between the fixing member and the pressure member becomes unstable, and an image defect due to backward scattering of the unfixed toner can be prevented.

Further, a conductive material or surface treatment layer having a surface resistivity of 10 ⁶ Ω / □ or less is provided on the outer peripheral surface of the pressing member, and at the same time, the conductive material or surface treatment layer is grounded. Of the unfixed toner held by the weak electrostatic force due to frictional charging of the surface of the pressure member caused by the insulating layer having a surface resistivity of 10 ¹² Ω / □ or more on the outermost peripheral surface of the pressure member. It is possible to prevent unstable fixation on the recording medium.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the structure of the image forming apparatus of the present invention. In the figure, reference numeral 1 is a recording medium carrying unfixed toner, reference numeral 2 is a fixing member that comes into contact with the surface of the recording medium, and reference numeral 3 is a pressure member that is arranged to face the fixing member. The pressing member is configured to abut under a predetermined pressure to nip the inserted recording medium. Reference numeral 4 is a photosensitive member that carries an unfixed toner image until it is transferred to a recording medium, and reference numeral 5 is a charging device for charging the photosensitive member to a constant voltage.

The fixing member 2 is a hollow member made of metal.
The outer peripheral portion of the conductive core 21 has an insulating layer 22 (for example,
PFA), and inside the
A heating source 23 is placed to melt the toner and fix it on the recording material.
The conductive core is connected to the voltage regulator.
It In this embodiment, the constant voltage unit is used as a constant voltage unit of the charging device.
Use wood. The pressure member has a fixed pressure on the fixing member.
From the silicone rubber etc. around the shaft 31
Insulating elastic layer 32 is provided, and the surface resistivity is
10 ⁶Provide a conductive layer 33 of Ω / □ or less, and
Surface resistivity of 10¹²Good peelability with Ω / □ or more
It is covered with an insulating layer 35 (eg P FA). Both sides of the conductive layer 33
The end face is grounded from the surface with the grounding shaft 34.
It The above charging device is a belt connected to a high voltage / constant current source.
Grounded via power wire 51 and Zener diode 52
It consists of a constant voltage member 53 and a shield 54 that surrounds the charging wire.
Is made. The constant voltage member 53 has a thickness of 0.1 m in the present invention.
It is made by punching SUS of m into a mesh shape.
Placing a Zener diode between ground and a constant voltage
Kept under pressure. In this embodiment, the unfixed toner on the recording medium is
The toner 11 is negatively charged, and the constant voltage member 53 and the fixing member 2 are
 A voltage of 400V is applied. Conversely, unfixed toner is positively charged
, The positive voltage is applied to the constant voltage member 53 and the fixing member 2.
Is applied.

With such a structure, an electric field is formed in the nip portion between the fixing member and the pressure member from the back surface to the front surface of the recording medium, and the recording medium on which the unfixed toner is transferred is inserted through the nip portion. Then, the negatively charged toner is attracted to the pressure member side by the electric field. As a result, the unfixed toner enters the nip portion while being positively fixed on the recording paper, and is fixed on the recording medium.

[0012]

As described above, according to the present invention,
Since it is possible to prevent a leak from occurring between the fixing member and the pressure member during the conveyance of the recording medium, the electric field between the fixing member and the pressure member becomes unstable, and the image due to the backward scattering of the unfixed toner is generated. Defects can be prevented, and unstable fixation of unfixed toner held by a weak electrostatic force to a recording medium can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1 recording medium 2 fixing member 21 conductive core 22 Insulation layer 23 heating source 3 Pressure member 31 shaft 32 elastic layer 33 Conductive layer 34 Grounding shaft 35 Insulation layer 4 Photosensitive member 5 Charging device 51 electrified wire 52 Zener diode 53 Constant voltage member 54 shield 55 Limiting resistance 56 resistance 57 Zener diode

Claims (3)

[Claims] 1. A recording medium carrying an electrostatically unfixed toner image is nipped and conveyed by a rotatable fixing member having a heating element therein and a pressure member rotatably opposed to the fixing member. A fixing device for melting the toner image on the recording medium by the fixing member heated by the heating element, and at the same time fixing the toner image on the recording medium by the pressure contact force of the pressure member,
And equipped with a constant voltage device connected to a high voltage and constant current source,
An image forming apparatus for connecting a bias voltage to the fixing member by connecting the fixing member in contact with an unfixed toner image to the constant voltage device, wherein the pressure member of the fixing device is the pressure member of the pressure member. A material or surface treatment layer having conductivity is provided on the outer peripheral surface, and the material or surface treatment layer having conductivity is grounded,
Further, the image forming apparatus is characterized in that an insulating layer is provided on the outermost peripheral surface of the pressing member. 2. The surface resistivity of the conductive material or surface treatment layer provided on the outer peripheral surface of the pressure member is 1
The image forming apparatus according to claim 1, wherein the image forming apparatus has a resistance of 0 ⁶ Ω / □ or less. 3. The image forming apparatus according to claim 1, wherein the insulating layer provided on the outermost peripheral surface of the pressing member has a surface resistivity of 10 ¹² Ω / □ or more.