JP7234790B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to a fixing device and an image forming apparatus, and more particularly to technology for preventing current leakage in a pad fixing type fixing device.

Conventionally, among fixing devices provided in an electrophotographic image forming apparatus, a pad fixing type fixing device forms a fixing nip by urging a pressure roller toward a fixing pad with a fixing belt interposed therebetween. By passing the recording sheet through the fixing nip, the toner image is thermally fixed (see, for example, Japanese Unexamined Patent Application Publication No. 2002-100003). A fluorine resin material is generally used for the fixing pad for the purpose of suppressing friction with the fixing belt.

However, since fluororesin is the most negatively charged material in the triboelectrification series, as shown in FIG. 401 is positively charged. If the toner T carried on the surface of the recording sheet S is negatively charged, the toner T will be electrostatically attracted to the fixing belt 401 just before entering the fixing nip, and the toner T will be used for subsequent recording. An electrostatic offset transferred to the sheet S occurs.

In order to solve such a problem, for example, a configuration is known in which a static elimination mechanism is provided by applying a conductive material to the surface layer on the inner peripheral surface side of the fixing belt. More specifically, in a pad-fixing type fixing device, as shown in FIG. 4B, a fixing belt 401 is stretched over a heating roller 403 together with a fixing pad 402 to heat the fixing belt 401 . The heating roller 403 is made of metal and has electrical conductivity in order to obtain high thermal conductivity.

If the inner peripheral surface of fixing belt 401 is made conductive and the rotating shaft of heating roller 403 is electrically grounded through grounding circuit 405, the inner peripheral surface of fixing belt 401 is in close contact with heating roller 403. , the fixing belt 401 can be neutralized to prevent electrostatic offset.

JP 2008-055771 A

The fixing belt has an elastic layer to improve fixability. In order to improve the energy saving performance of the fixing device, there is a demand for a configuration in which the elastic layer contains a large amount of high thermal conductivity filler. Since many of the high thermal conductivity fillers are electrically conductive, the more the high thermal conductivity fillers, the easier it is for the elastic layer as a whole to conduct.

In such a configuration, if the surface layer is made thin in order to reduce the hardness of the surface of the fixing belt and improve the fixing image quality, electrical continuity between the elastic layer and the recording sheet is facilitated. Further, even if the surface layer is thick, if the surface insulating layer is worn out at the end of the fixing belt durability, or if the surface layer is damaged due to jam processing or contamination with foreign matter, the elastic layer and the recording sheet are likely to be electrically connected. turn into. When the elastic layer and the recording sheet are electrically connected with the inner peripheral surface of the fixing belt grounded, the recording sheet S is grounded via the fixing belt 401 and the heating roller 403 as shown in FIG. , a current leak occurs in which the surface charge of the recording sheet S is lost.

The distance from the transfer nip 411 that transfers the toner image onto the recording sheet S to the fixing nip 412 is generally shorter than the FD (Feeding Direction) length of the recording sheet. It is not uncommon to have both 411 and fuser nip 412 caught. Therefore, when a current leak occurs, no transfer bias is generated at the transfer nip 411, and the toner image cannot be transferred onto the recording sheet S, resulting in image noise.

The present invention has been made in view of the above problems, and has an energy-saving configuration that has a static elimination mechanism for preventing electrostatic offset and has a large amount of high thermal conductivity filler added to the elastic layer. An object of the present invention is to provide a fixing device and an image forming apparatus capable of preventing image noise from occurring due to current leakage.

To achieve the above object, a fixing device according to one aspect of the present invention includes an endless ring-shaped fixing belt, a fixing pad disposed on the inner circumference side of the fixing belt, and a fixing belt sandwiching the fixing belt together with the fixing pad. and a pressure member forming a fixing nip, wherein the fixing belt passes a recording sheet through the fixing nip to fix a toner image, wherein the fixing belt includes a release layer, a conductive an elastic elastic layer, an insulating intermediate layer and a conductive inner layer, the inner layer being electrically grounded, and the intermediate layer having a surface resistivity of 10 ¹¹ [Ω/□] or more. Characterized by

Further, it is preferable that the surface of the fixing pad that contacts the inner circumferential surface of the fixing belt is made of fluororesin.

Moreover, it is desirable that the thermal conductivity of the elastic layer is 2 [W/m·K] or more.

Also, the release layer may be insulating.

Further, an image forming apparatus according to an aspect of the present invention comprises forming means for forming a toner image, transfer means for transferring the toner image onto a recording sheet, and the fixing device according to any one of claims 1 to 5. and wherein the length of the recording sheet in the conveying direction is longer than the length of the conveying path of the recording sheet from the transfer position of the transfer means to the fixing position of the fixing device. .

In this way, in order to lower the fixing temperature and improve energy efficiency, even in a fixing device in which a high thermal conductivity filler is added to increase the heat transferability of the fixing belt, the fixing belt has an insulating property. Since the intermediate layer is provided, image noise can be prevented even when the insulating release layer is thin or when the thick release layer is worn out or damaged.

1 is a diagram showing the main configuration of an image forming apparatus according to an embodiment of the invention; FIG. 2 is a diagram showing the main configuration of the fixing device 100; FIG. 2 is a diagram showing a layer structure of a fixing belt 200; FIG. (a) is a diagram for explaining the electrostatic offset generation mechanism, (b) is a diagram for explaining a static elimination mechanism for preventing the electrostatic offset, and (c) is a diagram for explaining the current leakage generation mechanism. is.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a fixing device according to the present invention will be described with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of an image forming apparatus according to the present embodiment will be described.

As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem type color multifunction peripheral (MFP: Multi-Function Peripheral), and includes an image reading section 110, an image forming section 120, and a paper feeding section 130. .

The image reading unit 110 includes an automatic document feeder (ADF) 111 and a scanner device 112 . The automatic document feeder 111 feeds and conveys the documents one by one from the document stack placed on the document tray 113, and causes the scanner device 112 to read and generate image data. After that, the document is discharged onto the discharge tray 114 .

The image forming unit 120 forms an image using image data generated by the image reading unit 110 or image data received from another device. In this embodiment, image forming units 121Y, 121M, 121C and 121K form yellow (Y), magenta (M), cyan (C) and black (K) toner images, respectively.

YMCK toner images formed by the image forming units 121Y, 121M, 121C, and 121K are sequentially electrostatically transferred (primary transfer) so as to overlap each other on the intermediate transfer belt 122, thereby forming a color toner image. The intermediate transfer belt 122 is an endless belt, and conveys the color toner image to the secondary transfer roller pair 123 by rotating.

In parallel with this, the paper feed roller 132 feeds out the recording sheet S from the paper feed cassette 131 containing the recording sheet S of the paper type specified by the user. The skew of the sent-out recording sheet S is corrected by bringing its leading edge into contact with the pair of registration rollers 124 . After that, the registration roller pair 124 is started to rotate in synchronization with the secondary transfer timing, and the recording sheet S is conveyed to the secondary transfer roller pair 123 .

In the secondary transfer roller pair 123 , a secondary transfer nip 125 is formed by pressing two rollers with the intermediate transfer belt 122 interposed therebetween. A secondary transfer bias is applied between the two rollers of the secondary transfer roller pair 123 , and the color toner image carried by the intermediate transfer belt 122 is electrostatically transferred onto the recording sheet S at the secondary transfer nip 125 . Transcribe (secondary transcription). At this time, if the recording sheet S is electrically grounded, the positive charges flow out, making it impossible to electrostatically attract the negatively charged toner.

The recording sheet S on which the color toner image has been secondarily transferred is conveyed to the fixing device 100 , and after the color toner image is thermally fixed, the recording sheet S is discharged onto the paper discharge tray 127 by the paper discharge roller pair 126 .
[2] Configuration of Fixing Device 100 Next, the configuration of the fixing device 100 will be described.

The fixing device 100 is a so-called upper two-axis belt fixing system, and as shown in FIG. , the fixing belt 200 is wound around the fixing pad 201 , the heating roller 203 and the belt supporting member 205 .

The heating roller 203 has a hollow cylindrical shape, is made of a metal material such as aluminum (Al), SUS (Steel Use Stainless), or iron (Fe), and has electrical conductivity. A halogen heater 207 is arranged inside the heating roller 203 . When the halogen heater 207 is turned on, the heating roller 203 is heated, so that the portion of the fixing belt 200 that contacts the heating roller 203 is heated.

When pressure roller 202 is rotationally driven in the direction of arrow C, fixing belt 200 rotates in the direction of arrow B following pressure roller 202 . As the fixing belt 200 rotates, the contact area of the fixing belt 200 with the heating roller 203 changes, so that the entire fixing belt 200 is evenly heated.

The fixing pad 201 is provided with a fluorine layer on the surface with which the fixing belt 200 slides. The fluorine layer reduces frictional resistance when the fixing belt 200 and the fixing pad 201 slide. As the fluorine layer, a fluorine sheet, a sheet obtained by impregnating a glass fiber woven fabric with fluorine, or the like can be used. In consideration of abrasion resistance, it is desirable to use an insulating fluororesin because adding a filler such as carbon to the fluorine layer to make it conductive shortens the life of the layer.

A pressure roller 202 is pressed against the fixing pad 201 with the fixing belt 200 therebetween, thereby forming a fixing nip 206 . Further, the heating roller 203 rotates in the arrow A direction following the rotation of the fixing belt 200 in the arrow B direction.

The recording sheet S entering the fixing device 100 along the transport path 208 is guided to the fixing nip 206 by transport guides 209 and 210 . The distance from the secondary transfer nip 125 to the fixing nip 206 in the conveying path 208 is shorter than the FD (Feeding Direction) length of the recording sheet S. As shown in FIG. Therefore, during the period from when the leading edge of the recording sheet S enters the fixing nip 206 to when the trailing edge of the recording sheet S leaves the secondary transfer nip 125 , the recording sheet S moves between the fixing nip 206 and the secondary transfer nip 125 . and become stuck in both.

A peeling pawl 212 is arranged downstream of the fixing nip 206 in the sheet conveying direction to prevent the recording sheet S passing through the fixing nip 206 from winding around the pressure roller 202 . After passing through the fixing nip 206 , the recording sheet S separated from the fixing device 100 along the transport path 213 is guided to the outside of the fixing device 100 by transport guides 214 and 215 .

In order to prevent electrostatic offset, the inner peripheral surface of fixing belt 200 is conductive, and conductive heating roller 203 that contacts the inner peripheral surface of fixing belt 200 is electrically grounded. . Specifically, both the cylindrical portion and the rotating shaft of heating roller 203 are made of a conductive material and are electrically connected to each other. Since the rotating shaft of heating roller 203 is electrically connected to ground circuit 216 , the inner peripheral surface of fixing belt 200 is grounded via the cylindrical portion of heating roller 203 , the rotating shaft, and ground circuit 216 . It will be.
[3] Configuration of Fixing Belt 200 Next, the configuration of the fixing belt 200 will be described.

As shown in FIG. 3, the fixing belt 200 has a configuration in which a release layer 301, an elastic layer 302, an intermediate layer 303 and an inner layer 304 are sequentially laminated from the outer peripheral side.

The release layer 301 is made of resin such as fluororesin (PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), etc.), silicone resin, polyimide resin, polyamide resin, polyimideamide resin, etc. For example, fluororesin It is better to select insulating properties rather than releasability. The layer thickness of the release layer 301 is desirably in the range of 10 [μm] or more and 50 [μm] or less. Although the release layer 301 according to the present embodiment is insulating, conductivity may be imparted by adding a conductive filler as necessary.

The elastic layer 302 is made of silicone rubber or fluororubber. The elastic layer 302 contains high thermal conductivity fillers to improve thermal conductivity. Carbon nanotube (CNT: Carbon Nano Tube), magnesium oxide (MgO), alumina (Al ₂ O ₃ ), hexagonal boron nitride (BN), aluminum nitride (AIN), silicon carbide (SiC) , diamond (C), silica (SiO ₂ ), and the like. The thermal conductivity of the elastic layer 302 is desirably 2 [W/m·K] or more. Also, the layer thickness of the elastic layer 320 is preferably in the range of 50 [μm] or more and 500 [μm] or less.

The intermediate layer 303 is an insulating layer. In order to reliably prevent current leakage, the intermediate layer 303 preferably has a surface resistivity of 10 ¹¹ [Ω/□] or more. As a material for the intermediate layer 303, for example, an insulating polyimide resin can be used.

The inner layer 304 is conductive to prevent the fixing belt 200 from being charged and causing electrostatic offset.

Both the intermediate layer 303 and the inner layer 304 have a layer thickness of 10 [μm] or more. Considering the shape retention of the fixing belt 200, the total layer thickness of the intermediate layer 303 and the inner layer 304 is preferably 50 [μm] or more. is preferably 150 [μm] or less. That is, it is preferable that the total layer thickness is in the range of 50 [μm] or more and 150 [μm] or less.

As a specific example, when a conductive polyimide resin is used as the material of the inner layer 304, the layer thickness of one of the intermediate layer 303 and the inner layer 304 is set to 30 [μm], and the layer thickness of the other is set to 40 [μm]. may be Further, when a conductive fluorine coat is used as the material of the inner layer 304, the layer thickness of the intermediate layer 303 may be set to 60 [μm] and the layer thickness of the inner layer 304 may be set to 10 [μm]. In either case, the total layer thickness is 70 [μm], which is within the above range.

As the material of the inner layer 304, in addition to the above-described polyimide resin, fluorine resin, silicone resin, polyamide resin, polyimideamide resin, etc. can be used, and conductivity can be imparted by adding a conductive filler.
[4] Modifications Although the present invention has been described above based on the embodiments, the present invention is of course not limited to the above-described embodiments, and the following modifications can be implemented. .
(4-1) In the above embodiment, the halogen heater is used to heat the fixing belt 200. However, it goes without saying that the present invention is not limited to this. can be

For example, in the case of using an electromagnetic induction heating method in which an alternating magnetic field is formed using an electromagnetic induction coil to generate eddy current in the metal heat generating layer of the fixing belt to generate Joule heat, the elastic layer 302 and the intermediate layer are used as the metal heat generating layer. A nickel electroformed sleeve may be provided between the layer 303 and a metal heating layer may be provided between the intermediate layer 303 and the inner layer 304 . In addition to nickel (Ni) mentioned above, materials for the metal heating layer include copper (Cu), iron, aluminum, titanium (Ti), cobalt (Co), tin (Sn), lead (Pb), silver (Ag ), SUS or alloys thereof may be used.

In the case of using a resistance heating system in which Joule heat is generated by energizing the resistance heating layer of the fixing belt, the resistance heating layer may be provided between the elastic layer 302 and the intermediate layer 303, or between the intermediate layer 303 and the intermediate layer 303. A metal heat-generating layer may be provided between the inner layer 304 and the inner layer 304 . The resistive heating layer 512 is adjusted to have a predetermined electrical resistivity by dispersing conductive fillers in the base resin material.

As the resin material, heat-resistant resins such as PPS (Polyphenylene Sulfide) and PEEK (Polyether Ether Ketone) can be used in addition to polyimide resin. In addition, as the conductive filler, metals such as silver, copper, aluminum, magnesium (Mg), and nickel, and carbon-based materials such as carbon nanotubes, carbon nanofibers, and carbon microcoils may be used. The above may be mixed and dispersed.

As for the shape of the conductive filler, a fibrous shape is desirable in order to increase the probability that fillers with the same content will come into contact with each other. The thickness of the conductive filler is desirably about 5 to 100 [μm]. Furthermore, it goes without saying that the electrical resistivity of the conductive filler should be determined according to the applied voltage and current, the thickness of the resistance heating layer 512, and the diameter and length of the fixing belt 51. For example, , 1.0 × 10 ^{-6 to} 9.9 × 10 ^-3 [Ωm] ^. is more preferred.
(4-2) If the strength of the fixing belt 200 cannot be sufficiently ensured depending on the layer structure of the above embodiment, a reinforcing layer may be added. The reinforcing layer may be made of a material such as polyimide resin, for example, and can be provided between the elastic layer 302 and the intermediate layer 303 or between the intermediate layer 303 and the inner layer 304 .
(4-3) In the above embodiment, the case where the inner peripheral surface of fixing belt 200 is indirectly grounded by connecting heating roller 203 to the grounding circuit has been described as an example, but the present invention is limited to this. Needless to say, the ground circuit may be directly connected to the inner circumferential surface of the fixing belt 200 instead. For example, the inner peripheral surface of the fixing belt 200 may be grounded by connecting a conductive roller, brush, or pad to the inner peripheral surface of the fixing belt 200 and grounding the roller, brush, or pad.
(4-4) In the above embodiment, the case where the fixing nip 206 is formed using the pressure roller 202 has been described as an example. Even if the fixing nip 206 is formed using a pressure pad instead, the same effect as above can be obtained.
(4-5) In the above embodiments, the case where the image forming apparatus is a tandem type color multifunction machine has been described as an example. It may be a color multifunction machine of a method other than the method, or it may be a monochrome multifunction machine. Further, even if the present invention is applied to a single-function device such as a printer device, a copy device, or a facsimile device, it is possible to obtain the same effect as the above embodiment.

INDUSTRIAL APPLICABILITY A fixing device and an image forming apparatus according to the present invention are useful as a device for preventing current leakage in a pad fixing type fixing device.

REFERENCE SIGNS LIST 1 image forming apparatus 100 fixing device 200 fixing belt 301 release layer 302 elastic layer 303 intermediate layer 304 inner layer

Claims (5)

An endless annular fixing belt, a fixing pad disposed on the inner circumference side of the fixing belt, and a pressing member that sandwiches the fixing belt together with the fixing pad to form a fixing nip, A fixing device for fixing a toner image through a recording sheet,
The fixing belt comprises a release layer, a conductive elastic layer, an insulating intermediate layer and a conductive inner layer in this order from the outer peripheral side,
the inner layer is electrically grounded ;
The intermediate layer has a surface resistivity of 10 ¹¹ [Ω/□] or more.
A fixing device characterized by: 2. The fixing device according to claim 1, wherein the surface of said fixing pad that contacts the inner peripheral surface of said fixing belt is made of fluororesin. 3. The fixing device according to claim 1 , wherein the elastic layer has a thermal conductivity of 2 [W/m·K] or more. 4. The fixing device according to claim 1, wherein the release layer is insulating. forming means for forming a toner image;
a transfer means for transferring the toner image onto a recording sheet;
a fixing device according to any one of claims 1 to 4 ,
An image forming apparatus, wherein the length of the recording sheet in the conveying direction is longer than the length of the conveying path of the recording sheet from the transfer position of the transfer means to the fixing position of the fixing device.

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