JP2008064923A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the outflow of heat from a fixing belt; to prevent the slip of the fixing belt; and to reduce the deflection of the fixing belt. <P>SOLUTION: The fixing device includes: the fixing belt (20) heated to a temperature necessary to melt toner by a heating member (30); and a pressing member (40) arranged inside the fixing belt and pressing the fixing belt on a pressure roller (50) to form a fixing nip. The pressing member abuts on the pressure roller through the fixing belt at the entrance part of the nip and the exit part (S1 and S2) of the nip, and its projecting part (40e) comes into contact with the fixing belt at a middle part between the entrance part of the nip and the exit part of the nip. <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 is known in which tension is applied between a heating panel and a pressure pad, a fixing belt is stretched, and the pressure pad and the pressure roller are opposed to each other with the fixing belt interposed therebetween to apply pressure between them. (Patent Document 1). In this fixing device, the sheet is guided to the nip portion where the fixing belt and the pressure roller are in contact with each other, and the toner is fixed.
JP 2003-287969 A

  In the fixing device of Patent Document 1, a pressure pad as a pressing member and a fixing belt are in contact with each other over the entire nip portion. For this reason, the amount of heat held by the fixing belt flows out to the pressure pad side at the nip portion, the warm-up time increases, and it takes time to start up. In addition, there is a problem in that the friction between the pressure roller and the fixing belt cannot be sufficiently ensured and the fixing belt slips.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and it is an object of the present invention to reduce the heat flow from the fixing belt to shorten the rise time, prevent the fixing belt from slipping, and reduce the fixing belt deflection. And
The present invention includes a fixing belt that is heated to a temperature required for toner melting by a heating member, and a pressing member that is disposed inside the fixing belt and that presses the fixing belt against a pressure roller to form a fixing nip. The pressing member is in contact with the pressure roller via a fixing belt at a nip entrance and an exit, and a convex portion is in contact with the fixing belt at an intermediate portion between the nip entrance and the exit.
With this configuration, since the contact area between the pressing member and the fixing belt is small, heat flow from the fixing belt to the pressing member is reduced, the rise time is shortened, and the fixing belt is bent by the convex portion at the nip intermediate portion. Can be reduced.
Further, the present invention is characterized in that the convex portion of the pressing member is in contact with the pressure roller via the fixing belt at the nip inlet portion and the outlet portion.
By having such a configuration, since the tip of the convex portion of the pressing member has a shape that bites into the pressure roller via the fixing belt, the frictional force between the pressure roller and the fixing belt increases, and slipping of the fixing belt is prevented. Can do.
Further, the present invention is characterized in that the pressing member is fixed to a deflection preventing member extending in the axial direction.
With this configuration, it is possible to prevent the pressing member from bending in the axial direction and the nip portion from becoming non-uniform in the axial direction, and the pressing member rotates around the deflection preventing member due to friction with the inner surface of the belt. Can be prevented.
In the present invention, the pressing member is characterized in that a plate-like member perpendicular to the shaft provided at every predetermined interval in the axial direction is fitted to the deflection preventing member.
With this configuration, the contact area between the pressing member and the deflection preventing member is reduced, and heat outflow from the pressing member to the deflection preventing member can be reduced.
In addition, the present invention is an image forming apparatus including the fixing device described above.
By providing the fixing device described above, it is possible to shorten the rise time of the image forming apparatus, and it is possible to obtain high image quality by reducing the deflection of the fixing belt.

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

  The toner image on the photoconductor is transferred to the intermediate transfer belt 6 that contacts the photoconductor 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 recorded on the paper (secondary transfer) in the secondary transfer portion 10 where the secondary transfer roller 9 is disposed opposite to the driving roller 7. Is done. The sheet passes through the paper feed cassette 11 and the transport path 12 and is transported to the secondary transfer unit. After the secondary transfer, the sheet is transported to the fixing unit 13 to fix the fixed toner image. In the case of double-sided printing, the sheet is reversed after fixing and conveyed again to the secondary transfer unit 10 via the conveyance path 14 for double-sided printing, and recording on the back side is performed.

Next, details of the fixing unit in FIG. 1 will be described with reference to FIGS.
FIG. 2 is a front cross-sectional view of the fixing unit, and FIG. 3 is a main cross-sectional view along the center line of FIG.
The fixing belt 20 is stretched between a heating element 30 as a heating member and a pressing member 40 in a state where a tension force is applied by a tension spring 70. The fixing belt 20 is heated to a temperature required for melting the toner by a heating element, and the amount of heat generated by the heating element is controlled by an external control device (not shown) so that the belt surface temperature is kept constant. At this time, the surface temperature of the fixing belt is controlled to about 150 to 180 ° C. The fixing belt 20 has a diameter of 30 to 50 mm (perimeter of 95 to 160 mm) and a heat-resistant resin film such as PI (polyimide) having a thickness of 30 to 50 μm, or a metal such as SUS, Ni, or Fe having a thickness of 20 to 40 μm. A fluororesin such as PFA (perfluoroalkoxyalkane) or PTFE (polytetrafluoroethylene) is provided on the surface layer of the substrate. Further, a silicon rubber layer having a thickness of about 150 to 300 μm may be provided as an elastic layer between the base material and the fluororesin layer.

  The pressing member 40 is disposed on the inner side of the fixing belt 20, and is provided with curved blade portions 40a and 40b projecting the fixing belt in the lateral direction, an intermediate portion 40c having a convex portion 40e in the middle, and at predetermined intervals in the axial direction. It consists of a plate-like member 40d. The pressing member 40 is made of a heat-resistant resin such as PPS (polyphenylsulfide), PAI (polyamideimide), PI, etc., and the surface has PTFE or PFA to reduce the frictional force with the inner surface of the fixing belt. It may have a fluororesin layer.

  At the ends of the wing portions 40a and 40b, the connecting portion with the intermediate portion 40c forms a convex portion, and the tip of the convex portion abuts against the pressure roller 50 via the fixing belt, and the convex portion 40e formed on the intermediate portion 40c. Is in contact with the fixing belt. The tips of the convex portions at the ends of the blade portions 40a and 40b have an R shape with a radius of curvature R0.5 to 2.0 mm, and the belt wear due to sliding of the fixing belt is reduced by the curvature of the tips of the convex portions. The The contact portions S1 and S2 with which the tips of the convex portions at the ends of the wing portions 40a and 40b come into contact form an entrance portion and an exit portion of the fixing nip, and when the fixing belt is rotated clockwise in FIG. The abutting portion S1 is an inlet portion, the abutting portion S2 is an outlet portion, and a space between S1 and S2 is a fixing nip width. Because of such a configuration, the nip width can be set according to the shape of the pressing member 40. In this embodiment, the nip width is set to about 8 to 12 mm.

  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 axial direction, and presses the pressure roller 50 through the fixing belt 20 with a load of about 15 to 40 kgf to fix the fixing nip. Is forming. The plate-like member 40d provided at predetermined intervals in the axial direction has a depression formed at the center, and the protrusion 61 of the deflection preventing shaft 60 is fitted into the depression, and the pressing member 40 is caused to bend by this fitting. 60 is fixed. With this structure, the pressing member can be prevented from rotating around the shaft due to friction with the inner surface of the belt.

  In the present invention, the pressing member 40 comes into contact with the inner surface of the fixing belt only at the inlet and outlet of the fixing nip portion and the convex portion in the middle thereof, and the contact area with the fixing belt is small. Heat outflow is reduced and the rise time is shortened. In addition, since the tips of the protrusions at the ends of the wing portions 40a and 40b of the pressing member bite into the pressure roller via the fixing belt, the frictional force between the pressure roller and the fixing belt increases, and the fixing belt slips. Can be prevented. Further, since the convex portion 40e formed in the intermediate portion 40c is in contact with the fixing belt, the deflection of the fixing belt can be reduced. In the above embodiment, only one protrusion 40e is provided, but a plurality of protrusions 40e may be provided. However, if a large number of them are provided, the contact area with the fixing belt increases and heat outflow increases. In addition, since the pressing member is a plate-like member provided at predetermined intervals in the axial direction and is in contact with the deflection preventing shaft, the contact area between the pressing member and the deflection preventing member is reduced, and heat flows from the pressing member to the shaft. Can be reduced.

  The heating element 30 includes a heating roller including a halogen heater or a heating member in which a resistance heating element is formed on a ceramic or metal base material. The heating element 30 faces the pressing member 40 on the inner side of the fixing belt and is provided on the opposite side of the pressure roller 50. A tension spring 70 provides a tension force of 1 to 3 kgf between the heating element 30 and the pressing member 40. The load is applied. With this tension force, the heating element can be sufficiently pressed against the fixing member, the heat of the heating element can be efficiently transmitted to the fixing belt, and at the same time, the deflection of the belt inside the nip can be prevented.

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

  The axial length of the pressing member 40, the deflection preventing shaft 60, and the pressure roller 50 and the width (longitudinal length) of the belt are substantially the same, about 310 to 340 mm for the A3 machine, and about 220 to 250 mm for the A4 machine. Therefore, the fixing device can be applied to both the A3 machine and the A4 machine.

  The printing with such a fixing device will be described. A sheet on which an image is formed with toner is conveyed to the fixing device with the fixing belt side as a printing surface, and the pressure roller 50 and the fixing belt driven by an external driving device. 20 passes through the fixing nip portion. At this time, the pressure roller surface, the paper, and the fixing belt surface all move at the same speed, and the moving speed depends on the printing speed of an image forming apparatus such as a printer.

  In the experiment, when 700 W was applied to the heating element and the rise time up to 160 ° C was compared, it was 36 seconds when the pressing member was in contact with the pressure roller via the belt throughout the entire area, and the nip inlet and outlet It was 30 seconds when the contact was made with only one part and one convex part therebetween. From this, it was confirmed that reducing the contact area with the pressing member was effective in shortening the rise time.

1 is a diagram illustrating an overall configuration of an image forming apparatus of the present invention. It is a front sectional view of a fixing unit. It is principal part sectional drawing along the centerline of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Fixing belt, 30 ... Heat generating body, 40 ... Pressing member, 50 ... Pressure roller, 60 ... Deflection prevention shaft, 70 ... Tension spring

Claims (5)

A fixing belt that is heated to a temperature required for melting the toner by a heating member, and a pressing member that is disposed inside the fixing belt and presses the fixing belt against a pressure roller to form a fixing nip,
The pressing member is in contact with a pressure roller through a fixing belt at a nip entrance and an exit, and a convex portion is in contact with the fixing belt at an intermediate portion between the nip entrance and the exit. apparatus. The fixing device according to claim 1, wherein the convex portion of the pressing member is in contact with the pressure roller via the fixing belt at the nip inlet portion and the outlet portion. The fixing device according to claim 1, wherein the pressing member is fixed to a deflection preventing member extending in an axial direction. The fixing device according to claim 3, wherein the pressing member includes a plate-shaped member orthogonal to an axis provided at predetermined intervals in the axial direction and fitted in a deflection preventing member. An image forming apparatus comprising the fixing device according to claim 1.

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