JP2008170596A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device consisting of a fixing belt, pressure member and pressure roller and is free from slip between the fixing belt and pressure roller, and to provide an image forming apparatus that has the fixing device. <P>SOLUTION: The fixing device consisting of the fixing belt, pressing member and pressure roller, is constituted so that the fixing belt is heated by a heating member to a temperature required to melt toner, the pressing member is disposed inside the fixing belt, when a nip is formed by pressing the pressing member and pressure roller against each other via the fixing belt, the ends of the pressing member at the entrance and exit of the nip are located closer to the center of the pressure roller than to the surface of the pressure roller in the unpressed state, and the curvature radius of the nip forming portion of the pressing member is smaller than the curvature radius of the pressure roller in the unpressed state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a belt-type fixing device and an image forming apparatus using the same.

A fixing device including a fixing belt, a pressing member, and a pressure roller. The pressing member is disposed inside the fixing belt, and the pressing member and the pressure roller are pressed through the fixing belt to form a nip portion. A fixing device in which the pressing member and the inner surface of the fixing belt are in contact with each other over the entire nip portion has been studied (see, for example, Patent Document 1 and Patent Document 2). The radius of curvature of the nip portion forming portion of the pressing member is formed to be larger than the radius of curvature of the pressure roll in the non-pressed state. The fixing device has a problem of causing slippage between the fixing belt and the pressure roller.
JP 2005-326702 A JP 2003-287969 A

  A problem to be solved by the present invention is to provide a fixing device that includes a fixing belt, a pressing member, and a pressure roller, and that does not cause slippage between the fixing belt and the pressure roller, and an image forming apparatus including the fixing device. is there.

The present invention is a fixing device including a fixing belt, a pressing member, and a pressure roller. The fixing belt is heated to a temperature necessary for melting the toner by a heating member, and the pressing member is disposed inside the fixing belt. When the pressing member and the pressure roller are pressed via the fixing belt to form the nip portion, the tip of the pressing member at the entrance and exit of the nip portion is more applied than the surface of the pressure roller in the non-pressed state. The fixing device is located on the pressure roller center side and has a radius of curvature of a nip portion forming portion of the pressing member that is smaller than a radius of curvature of the pressure roll in a non-pressed state.
The pressure at the inlet and outlet of the nip portion formed by pressing the pressing member and the pressure roller of the fixing device of the present invention is higher than the pressure at the intermediate portion of the nip portion, and the pressing members at the inlet and outlet of the nip portion Since the leading edge of the belt bites into the pressure roller, the friction followability of the fixing belt to the pressure roller is large. Further, the biting of the front end of the pressing member into the pressure roller at the exit of the nip portion makes it easy to peel the recording member carrying the toner image from the fixing belt.

  In a preferred embodiment of the present invention, in the fixing device, the pressing member and the pressure roller are pressed through the fixing belt so that the pressure at the nip portion outlet becomes larger than the pressure at the nip portion inlet. The above configuration makes it easy to peel the recording member from the fixing belt.

  In another preferred embodiment of the present invention, in the fixing device, the front guide of the nip portion is provided at a position where the recording member is conveyed to the nip portion after the leading end of the recording member is brought into contact with the fixing belt. The above configuration stabilizes the conveyance of the recording member to the nip portion entrance where the tip of the pressing member bites into the pressure roller. When the leading end of the recording member is brought into contact with the pressure roller and then conveyed to the entrance of the nip portion, the leading end of the recording member is brought into contact with the pressing member at an angle close to a right angle, resulting in a defective conveyance of the recording member.

In another preferred embodiment of the present invention, in the fixing device, in a region where the recording member does not pass, the pressing member and the pressure roller are pressed through the fixing belt at the entrance and exit of the nip portion, and the pressing member is interposed between the nip portions. And the inner surface of the fixing belt do not contact. The above configuration prevents the pressure member tip from biting into the pressure roller at the inlet and outlet of the nip in the area where the recording member is not conveyed, and the pressure member tip at the nip inlet and outlet in the area where the recording member is conveyed. It is larger than the biting into the pressure roller, and the friction followability of the fixing belt to the pressure roller is improved.
The present invention is an image forming apparatus including the fixing device.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  The image forming unit irradiates the photosensitive member 1 that is an image carrier, the charging roller 2 that uniformly charges the photosensitive member, and the uniformly charged photosensitive member 1 with a laser beam modulated by an image signal. It comprises an exposure device 3 for forming an electrostatic latent image. The developing unit is composed of yellow, magenta, cyan, and black color developing machines 5 arranged in the developing rotary 4, and each color developing machine sequentially contacts the photoconductor 1 by the rotation of the rotary, and electrostatic on the photoconductor 1 is developed. Develop the latent image.

  The toner image on the photoconductor is transferred to the intermediate transfer belt 6 that contacts the photoconductor 1 at the primary transfer position. The intermediate transfer belt 6 is stretched between the driving roller 7 and the driven roller 8. The toner image on the intermediate transfer belt 6 transferred at the primary transfer position is secondarily transferred onto the recording member in the secondary transfer portion 10 where the secondary transfer roller 9 is disposed opposite to the driving roller 7. . The recording member is supplied from the paper feed cassette 11, is transported to the secondary transfer unit 10 through the transport path 12, is transported to the fixing unit 13 after the secondary transfer, and the toner image is fixed. In the case of double-sided printing, the recording member is reversed after fixing and conveyed again to the secondary transfer unit 10 via the conveyance path 14 during double-sided printing, and recording on the back surface is performed.

Next, details of the fixing unit in FIG. 1 will be described with reference to FIG.
FIG. 2 is a front sectional view of the fixing unit.
The fixing belt 20 is stretched in a state where a tension force is applied between the heating element 30 as a heating member and the pressing member 40, and is heated to a temperature necessary for melting the toner by the heating element. The amount of heat generated by the heating element 30 is controlled by an external control device (not shown) so that the surface temperature of the fixing belt 20 is kept constant in the range of 150 to 180 ° C. The diameter Φ of the fixing belt 20 is 30 to 50 mm (circumferential length 95 to 160 mm). The fixing belt 20 has (1) a heat-resistant resin film such as PI (polyimide) having a thickness of 30 to 50 μm, or (2) a surface layer of a metal base material such as SUS, Ni, or Fe having a thickness of 20 to 40 μm. It consists of a laminate provided with a layer of fluororesin such as (perfluoroalkoxyalkane) or PTFE (polytetrafluoroethylene). Further, a silicone rubber elastic layer having a thickness of about 150 to 300 μm can be provided between the heat resistant resin film or metal substrate and the fluororesin layer.

  The pressing member 40 is disposed on the inner side of the fixing belt 20 and has curved wing portions 40a and 40b projecting the fixing belt 20 in the lateral direction, an arc-shaped intermediate portion 40c toward the pressure roller 50, and a predetermined longitudinal direction. It consists of a plate-like member 40d provided at every interval. The pressing member 40 is made of a heat resistant resin such as PPS (polyphenylsulfide), PAI (polyamideimide), and PI. A fluororesin layer such as PTFE or PFA can be provided on the surface of the pressing member 40 in order to reduce the frictional force with the inner surface of the fixing belt 6.

  The pressing member 40 is fixed to a metal deflection preventing shaft 60 having a diameter of about 10 to 20 mm, which is a deflection preventing member extending in the longitudinal direction, and presses the pressure roller 50 with a load of about 15 to 40 kgf via the fixing belt 20. A fixing nip is formed. The shape of the pressing member 40 sets the nip width. The nip width is about 8 to 12 mm. The plate-like member 40d provided at every predetermined interval in the longitudinal direction is formed with a depression at the center, and the protrusion 61 of the deflection preventing shaft 60 is fitted into this depression, and the pressing member 40 is caused to bend by this fitting. 60 is fixed. This structure prevents the pressing member 40 from rotating around the shaft due to friction with the inner surface of the fixing belt 20.

  The heating element 30 includes (1) a heating roller including a halogen heater or (2) a heating member in which a resistance heating element is formed on a ceramic or metal base material. The heating element 30 is provided on the inner side of the fixing belt 6 so as to face the pressing member 40 and on the side opposite to the pressure roller 50. A load of 1 to 3 kgf is applied as a tension force between the heating element 30 and the pressing member 40. Due to this tension force, the heating element 30 is sufficiently pressed against the fixing belt 20, the heat of the heating element 30 is efficiently transmitted to the fixing belt 20, and further, the deflection of the fixing belt 20 at the nip portion is prevented.

  The pressure roller 50 has a structure in which an elastic layer of about 1 to 5 mm is provided on the surface layer of a metal pipe, and a fluororesin layer such as PFA or PTFE is provided on the surface layer of the elastic layer. A driving force is applied to the pressure roller 50, the fixing belt 20 is rotated by a frictional force with the pressure roller 50, and the surface of the pressure roller 50 and the surface of the fixing belt 20 rotate at a constant speed. The outer diameter Φ of the pressure roller 50 is about 30 to 40 mm.

  Next, printing with the fixing device will be described. The recording member on which the image is formed with the toner is conveyed to the fixing device through the pre-fixing guide 15 with the fixing belt side as the printing surface, and between the pressure roller 50 and the fixing belt 20 driven by an external driving device. Passes through the nip part. At this time, the surface of the pressure roller 50, the recording member, and the surface of the fixing belt 20 all move at the same speed, and their moving speeds depend on the printing speed of the image forming apparatus.

The shape of the pressing member 40 on the fixing belt 20 side is an arcuate curve, and the nip portion is formed by pressing the pressing member 40 and the pressure roller 50 via the fixing belt 20. The shape of the nip portion forming portion of the pressing member 40 was examined in more detail.
The outer diameter Φ of the pressure roller 50 in the non-pressing state is set to 30 mm (curvature radius = 15 mm), and the curvature radius of the nip portion forming portion of the pressing member 40 is changed to 5, 8, 12, 15, 18 mm to perform recording. The slip of the fixing belt 20 and the pressure roller 50 was evaluated using cardboard as a member. FIG. 3 is a diagram showing the state of the nip portion and the pressure distribution when the radius of curvature of the nip portion forming portion of the pressing member 40 is 8. As shown in FIG. The tip of the pressing member 40 at the inlet and outlet of the nip is more applied than the surface of the pressing roller 50 (virtual surface 51) when the pressing member 40 and the pressing roller 50 are not pressed (non-pressing state). It is located on the pressure roller 50 center side. The pressure on the surface of the pressure roller 50 is high in the vicinity of the inlet and the outlet, and increases again after decreasing from the inlet and the outlet toward the center of the nip portion. FIG. 4 is a diagram showing the state of the nip portion and the pressure distribution when the radius of curvature of the nip portion forming portion of the pressing member 40 is 15. As shown in FIG. The tip of the pressing member 40 at the entrance and exit of the nip portion is closer to the center of the pressing roller 50 than the surface of the pressing roller 50 (virtual surface 51) when the pressing member 40 and the pressing roller 50 are not pressed. Not located. The pressure on the surface of the pressure roller 50 increases from the inlet and outlet toward the center of the nip portion. When the radius of curvature of the nip portion forming portion of the pressing member 40 is 5, 8, or 12, slip between the fixing belt 20 and the pressure roller 50 does not occur, and the radius of curvature of the nip portion forming portion of the pressing member 40 is 15 or 18. At that time, slipping occurred. When the radius of curvature of the nip portion forming portion of the pressing member 40 is 18, image roughness occurred. Therefore, if (the radius of curvature R2 of the nip portion forming portion of the pressing member) / (the radius of curvature R1 of the pressure roller in the non-pressed state) is small, the effect of preventing slippage between the fixing belt and the pressure roller is high. It can be confirmed that image roughness occurs when R1 is large. A suitable range of R2 / R1 of the fixing device of the present invention is 50 to 90%.

  Next, the peelability of the recording member when the pressure at the nip inlet and the outlet is different was examined. The outer diameter Φ of the pressure roller 50 in a non-pressing state is 40 mm (curvature radius = 20 mm), the radius of curvature of the nip portion forming portion of the pressing member 40 is 10 mm, and the pressure roller is about 0.5 mm from the entrance to the nip portion. The pressing member 40 was tilted so as to be located at the center side of 50, and the peelability of the recording member after fixing from the fixing belt 20 was evaluated. FIG. 5 is a diagram illustrating the state of the nip portion and the pressure distribution when the pressing member 40 is tilted. The pressure on the surface of the pressure roller 50 is higher near the outlet than near the inlet. Further, the peelability of the recording member after fixing from the fixing belt 20 was also evaluated without tilting the pressing member 40. When the pressing member 40 was tilted as shown in FIG. 5, the recording member could be peeled even if the leading edge margin of the recording member was 1 mm. On the other hand, when the pressing member 40 was not tilted, the recording member could be peeled off with the front end margin of the recording member being 3 mm, but the recording member could not be peeled off with the front end margin of the recording member being 2.5 mm. Therefore, it was confirmed that when the pressing member and the pressure roller are pressed via the fixing belt so that the pressure at the nip portion outlet becomes larger than the pressure at the nip portion inlet, the peelability of the recording member is improved.

  Further, using a fixing device in which the outer diameter Φ of the pressure roller 50 in a non-pressing state is 30 mm (curvature radius = 15 mm) and the radii of the nip portion forming portion of the pressing member 40 is 8 mm, the guide before fixing and recording are performed. The transportability of the member to the nip was examined. When the front nip portion guide 15 is provided at a position where the recording member is conveyed to the nip portion after the front end of the recording member is brought into contact with the fixing belt 20 (FIG. 6), the recording member is attached to the fixing belt 20. Along the nip portion, and no jamming (improper conveyance of the recording member to the nip portion) occurred. However, when the front nip portion guide 15 is provided at a position where the recording member is conveyed to the nip portion after the front end of the recording member is brought into contact with the pressure roller 50, the recording member is perpendicular to the fixing belt 20. A rush occurred at an angle close to, and a jam occurred. Accordingly, when the front guide of the nip portion is provided at a position where the recording member is transported to the nip portion after the front end of the recording member is brought into contact with the fixing belt, the transportability of the recording member to the nip portion is improved. Then I was able to confirm.

Finally, using a fixing device in which the outer diameter Φ of the pressure roller 50 in the non-pressing state is 35 mm (curvature radius = 17.5 mm), the nip portion forming portion of the pressing member 40 in the region where the recording member does not pass is used. The shape was examined. FIG. 7 shows a shape in which the nip portion forming portion of the pressing member 40 is pressed so that the pressing member and the pressure roller are pressed through the fixing belt at the inlet and outlet of the nip portion, and the pressing member and the inner surface of the fixing belt are not in contact with each other in the middle of the nip portion. It is front sectional drawing of the fixing | fixed part of the fixing device which was done. In FIG. 8, the shape of the nip portion forming portion of the pressing member 40 in the recording member passage region is an arc shape, and the shape of the nip portion forming portion of the pressing member 40 in the region where the recording member does not pass is formed as shown in FIG. FIG. 6 is a cross-sectional view at the center of the nip portion in the longitudinal direction of the nip portion of the fixing portion in a case where the fixing is performed. When the curvature radius of the nip portion forming portion of the pressing member 40 in the recording member passing region of the fixing device as shown in FIG. 8 is set to 9 mm, 17 mm, and 20 m, the fixing belt 20 and the pressure roller 50 slip. There wasn't.
When the radius of curvature of the nip portion forming portion of the pressing member 40 of the fixing device in which the shape of the nip portion forming portion of the pressing member 40 in the recording member passage region and the recording member non-passing region is an arc shape is set to 9 mm and 17 mm, fixing is performed. The belt 20 and the pressure roller 50 did not slip. However, when the radius of curvature of the nip portion forming portion of the pressing member 40 was set to 20 mm, the fixing belt 20 and the pressure roller 50 slipped.
FIG. 9 shows the nip portion forming portion of the pressing member 40 in the recording member passage region and the recording member non-passage region when the shape of the nip portion is formed as shown in FIG. It is sectional drawing. The fixing device as shown in FIG. 9 caused image roughness.
Therefore, the shape of the nip portion forming portion of the pressing member 40 in the recording member passing region is an arc shape, and the nip portion forming portion of the pressing member 40 in the region where the recording member does not pass is passed through the fixing belt at the nip portion inlet and outlet. It has been confirmed that the fixing device in which the pressing member and the pressure roller are pressed and the pressing member and the inner surface of the fixing belt do not contact each other in the middle of the nip portion prevents the fixing belt and the pressure roller from slipping and improves the image quality. .

The figure explaining the whole structure of an image forming apparatus Front sectional view of fixing section The figure which shows the mode and pressure distribution of a nip part when the curvature radius of the nip part formation part of a press member is smaller than the curvature radius of a pressure roller. The figure which shows the mode and pressure distribution of a nip part when the curvature radius of the nip part formation part of a press member is larger than the curvature radius of a pressure roller. The figure which shows the mode of a nip part when a pressing member is inclined, and pressure distribution Diagram showing the entry position of the recording member into the nip Front sectional view of fixing section Cross-sectional view in the longitudinal direction of the nip part of the fixing part Cross-sectional view in the longitudinal direction of the nip part of the fixing part

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charging roller, 3 ... Exposure machine, 4 ... Development rotary, 5 ... Developer, 6 ... Intermediate transfer belt, 7 ... Drive roller, 8 ... Driving roller, 9 ... Secondary transfer roller, 10 ... Secondary transfer section, 11 ... feed cassette, 12 ... conveyance path, 13 ... fixing section, 14 ... conveyance path for double-sided printing, 15 ... pre-fixing guide, 20 ... fixing belt, 30 ... heating element, 40 ... pressing member, 50 ... Pressure roller, 60 ... Deflection prevention shaft, 61 ... Projection, 70 ... Recording member

Claims (5)

A fixing device including a fixing belt, a pressing member, and a pressure roller,
The fixing belt is heated to a temperature necessary for melting the toner by a heating member,
The pressing member is disposed inside the fixing belt,
When the pressing member and the pressure roller are pressed via the fixing belt to form the nip portion, the tip of the pressing member at the entrance and exit of the nip portion is more applied than the surface of the pressure roller in the non-pressed state. Located on the center side of the pressure roller,
A fixing device in which a radius of curvature of a nip portion forming portion of a pressing member is smaller than a radius of curvature of a pressure roll in a non-pressed state. The fixing device according to claim 1, wherein the pressing member and the pressure roller are pressed via the fixing belt so that the pressure at the nip portion outlet becomes larger than the pressure at the nip portion inlet. The fixing device according to claim 1, wherein a front nip portion guide is provided at a position where the recording member is conveyed to the nip portion after the leading end of the recording member is brought into contact with the fixing belt. The press member and the pressure roller are pressed through the fixing belt at the entrance and exit of the nip portion in the area where the recording member does not pass, and the press member and the inner surface of the fixing belt do not contact each other in the middle of the nip portion. The fixing device according to claim 1. An image forming apparatus comprising the fixing device according to claim 1.

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