JP2009104019A - Image fixing unit and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image fixing unit which can mitigate increase in the mechanical stress of the fixing belt and secure the separation of the recording paper. <P>SOLUTION: This image fixing unit has a pressure roll 62 turning for driving, an image fixing belt 61 which turns facing the pressure roll 62 and forming a nip section N to pass the recording material through, a pressure pad 64 to press the fixing belt 61 toward the pressure roll 62, a belt guide 63 supported behind the pressure pad 64, and eccentric rolls 69, 69b working as a belt deforming mechanism to change the shape of the fixing belt 61 according to the thickness of the recording material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device or the like, and more particularly to a fixing device or the like in a copying machine or a printer using an electrophotographic system.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or printer, a toner image formed on a recording medium such as paper is fixed on the recording medium, and in a fixing process for making a permanent image, a thermal pressure fixing method is used. Is common. In such a heat-pressure fixing method, a non-fixed toner image is fixed on a recording material by heating and pressing at a nip formed by a fixing roll and a pressure roll with a built-in heater (so-called roll nip method). And a method (so-called belt nip method) in which a recording material is pressed against a fixing roll by a pressure pad from the inside of an endless belt used in place of a pressure roll to form a nip portion. Among them, the belt nip method is widely used as a thermal pressure fixing method with the progress of colorization, high speed, and miniaturization of image forming apparatuses.

  With regard to such a belt nip system, Patent Document 1 discloses that an endless belt is brought into contact with a rotating heat fixing roll whose surface is elastically deformed, and the endless belt is pressed against the heat fixing roll with a non-rotating pressure pad. A belt nip through which the sheet passes is provided between the sheet and the heat fixing roll, and the surface of the heat fixing roll is elastically deformed to reduce heat loss at the belt nip and to reduce the speed difference between the sheet and the heat fixing roll. An image fixing device that prevents the disturbance of the toner image due to air or water vapor in the belt nip is described.

  In Patent Document 2, a material to be heated is introduced into a nip portion N formed by press-contacting an endless belt stretched between a plurality of support members to a heating rotator, and is nipped and conveyed. In a heating apparatus that heats a material to be heated by the heat of a rotating body for heating, at least one of a plurality of support members is a rotating body made of a hollow pipe having an outer diameter that increases from both ends toward the center, and is endless. A heating device that saves energy by being in contact with a heating rotating body via a belt is described.

  Further, in Patent Document 3, a nip portion N is provided between a fixing belt module in which a fixing belt is stretched by a fixing roll and a tension roll, and a fixing belt module arranged so as to be pressed against the fixing belt module. A pressure belt module to be formed, and the fixing belt module is disposed so as to support the fixing belt from the inside on the downstream side in the recording material conveyance direction away from the nip portion N, and peels off the direction in which the fixing belt travels An image forming apparatus is described that has a pad to suppress the occurrence of a temperature droop phenomenon and stably peels the recording paper from the fixing roll side.

JP 08-262903 A JP-A-2005-005018 JP 2006-243471 A

By the way, in the belt nip system, in order to maintain the recording paper peeling performance, a pressure pad for locally elastically deforming the exit side of the recording paper on the surface of the fixing roll is provided inside the fixing belt. Such a pressure pad is usually used so that the paper that is the most difficult to peel among the recording papers passing through the nip portion N can be peeled off in order to ensure the recording paper peeling performance. Assuming that the toner on the paper is sufficiently loaded (the coverage is high), for example, the paper is molded in a shape with a sharpened recording paper discharge side.
When the fixing belt is pressed against the fixing roll with such a pressure pad, the fixing belt on the recording paper discharge side of the nip portion N is greatly deformed, and the mechanical stress (distortion) of the fixing belt increases.
In particular, a fixing device (induction heating fixing device) using an electromagnetic induction heating method uses a hard fixing belt having a metal layer laminated on the outer peripheral surface of a base material containing a heat-resistant resin. If the mechanical stress increases, it will be one of the causes of significantly shortening the belt life.

  The present invention has been made to solve such problems. That is, an object of the present invention is to provide a fixing device that reduces the increase in mechanical stress of the fixing belt and secures the recording paper peeling performance.

  The invention according to claim 1 is a rotating member that is rotationally driven, an endless belt that rotates opposite to the rotating member and forms a nip portion through which the recording material passes, and the endless A fixing device comprising: a pressure member that presses the endless belt against the rotating member from the inside of the belt; and a belt deformation mechanism that deforms the shape of the endless belt according to the type of the recording material. It is.

  According to a second aspect of the present invention, the belt deformation mechanism increases the curvature of the endless belt on the downstream side of the nip portion and deforms the endless belt into a shape projecting upstream of the nip portion. The fixing device according to claim 1.

  According to a third aspect of the present invention, the belt deforming mechanism presses the endless belt from the inside by rotating an eccentric roller disposed inside the endless belt, and the endless belt is moved upstream of the nip portion. The fixing device according to claim 1, wherein the fixing device is deformed into an overhanging shape.

  According to a fourth aspect of the present invention, the belt deformation mechanism presses the endless belt from the outside by rotating an eccentric roller disposed outside the endless belt, and the endless belt has a downstream side of the nip portion. The fixing device according to claim 1, wherein the curvature is increased.

  The invention according to claim 5 further includes a belt guide member that is supported behind the pressure member and restricts the rotation of the endless belt, and the belt deformation mechanism moves an attachment position of the belt guide member. 2. The fixing device according to claim 1, wherein the endless belt is pressed from inside to deform the endless belt into a shape projecting upstream of the nip portion.

  According to a sixth aspect of the present invention, the endless belt has a metal layer having a thickness of 10 μm to 100 μm on the inner peripheral side and an elastic layer on the outer peripheral side, and a burr formed on both sides of the metal layer in the belt axial direction. The fixing device according to claim 1, wherein the size is 150 μm or less.

  According to a seventh aspect of the present invention, a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image onto a recording material, and a toner image transferred onto the recording material are fixed on the recording material. A fixing member, and a fixing member formed on a heat-resistant resin base material by forming a rotating member that rotates and a nip portion through which the recording material passes between the rotating member and the rotating member. An endless belt having a layer and an elastic layer, an electromagnetic induction heating member that generates heat from the endless belt, a pressure member that presses the endless belt against the rotating member, and the endless belt at a downstream side of the nip portion. An image forming apparatus comprising: a belt deformation mechanism that increases a curvature of the endless belt and deforms the endless belt into a shape projecting upstream of the nip portion.

  According to the first aspect of the present invention, the sheet peeling performance is maintained according to the thickness of the recording material as compared with the case where the belt deformation mechanism is not provided.

  According to the second aspect of the present invention, the paper peeling performance is improved without increasing the mechanical load of the endless belt as compared with the case where no belt deformation mechanism is provided.

  According to the third aspect of the present invention, the endless belt is easily bulged and deformed upstream of the nip portion as compared with the case where no belt deformation mechanism is provided.

  According to the invention which concerns on Claim 4, compared with the case where it does not have a belt deformation | transformation mechanism, the curvature of the downstream of the nip part of an endless belt is enlarged easily.

  According to the invention which concerns on Claim 5, compared with the case where an eccentric roller is used, a fixing device can be made compact.

  According to the invention which concerns on Claim 6, compared with the case where the burr | flash (dent) exceeding 150 micrometers exists in a belt edge part, generation | occurrence | production of the crack of the belt member in long-term use reduces.

  According to the seventh aspect of the invention, the paper peeling performance is maintained while reducing the mechanical load on the hard belt having the metal layer.

  Hereinafter, the best mode (embodiment) for carrying out the present invention will be described. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. Also, the drawings used are used to describe the present embodiment and do not represent the actual size.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus to which the exemplary embodiment is applied. Here, an intermediate transfer type image forming apparatus generally called a tandem type will be described as an example. The image forming apparatus shown in FIG. 1 includes a plurality of image forming units 1Y, 1M, 1C, and 1K that form toner images of respective color components by electrophotography as a toner image forming unit. Next, as the transfer unit, the primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the intermediate transfer belt 15. A secondary transfer unit 20 that collectively transfers (secondary transfer) the transferred superimposed toner image onto a sheet P that is a recording material (recording sheet). Further, the image forming apparatus includes a fixing device 60 that fixes the secondary transferred image on the paper P as a fixing unit. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  As shown in FIG. 1, each of the image forming units 1Y, 1M, 1C, and 1K includes a photosensitive drum 11 that rotates in the direction of arrow A, a charger 12 that charges the photosensitive drum 11, and a photosensitive drum 11. A laser exposure device 13 for writing an electrostatic latent image (in FIG. 1, an exposure beam is indicated by a symbol Bm) and each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. And a developing unit 14. Further, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, a drum cleaner 17 that removes residual toner on the photosensitive drum 11, and Have In the present embodiment, these image forming units 1Y, 1M, 1C, and 1K are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15. Arrange substantially linearly.

  The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction of arrow B shown in FIG. 1 by various rolls. As various rolls, a drive roll 31 that rotates the intermediate transfer belt 15, a support roll 32 that supports the intermediate transfer belt 15, a tension roll 33 that applies a certain tension to the intermediate transfer belt 15 to prevent meandering, and a secondary roll A backup roll 25 provided in the transfer unit 20 and a cleaning backup roll 34 provided in a cleaning unit that scrapes residual toner on the intermediate transfer belt 15 are provided.

  The primary transfer unit 10 includes a primary transfer roll 16 that faces the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. A voltage (primary transfer bias) having a polarity opposite to the charging polarity (minus polarity) of the toner is applied to the primary transfer roll 16, and the toner images on the photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, A superimposed toner image is formed on the transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roll 25. A backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to serve as a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact.
The secondary transfer roll 22 is placed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween, and further, the secondary transfer roll 22 is grounded to form a secondary transfer bias between the secondary transfer roll 22 and the secondary transfer section. The toner image is secondarily transferred onto the paper P transported to the paper 20.

  An intermediate transfer belt cleaner 35 for removing residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer is provided on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15 so as to be able to contact and separate. A reference sensor (home position sensor) 42 that generates a reference signal for taking an image forming timing in each of the image forming units 1Y, 1M, 1C, and 1K is disposed upstream of the yellow image forming unit 1Y. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. In response to an instruction from the control unit 40 based on the recognition of the reference signal, each image forming unit 1Y, 1M, 1C and 1K start image formation.

  In the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that takes out and transports the paper P in the paper tray 50, a transport roll 52 that transports the paper P, and a paper P A transport chute 53 that transports the paper P to the secondary transfer unit 20, a transport belt 55 that transports the paper P secondarily transferred by the secondary transfer roll 22 to the fixing device 60, and a fixing inlet that guides the paper P to the fixing device 60. And a guide 56.

Next, a basic image forming process of the image forming apparatus will be described.
In the image forming apparatus shown in FIG. 1, an image processing apparatus (IPS) (FIG. 1) is added to image data output from an image reading apparatus (IIT) (not shown), a personal computer (PC) (not shown), or the like. The image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In the IPS, input image data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. The image data subjected to the image processing is converted into color material gradation data of four colors Y, M, C, and K, and is output to the laser exposure unit 13.

  The laser exposure unit 13 irradiates, for example, an exposure beam Bm emitted from a semiconductor laser to the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K according to the input color material gradation data. After the surfaces of the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K are charged by the charger 12, the surfaces are scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of Y, M, C, and K by each of the image forming units 1Y, 1M, 1C, and 1K.

  Next, the toner image formed on the photosensitive drum 11 is transferred onto the intermediate transfer belt 15 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Specifically, in the primary transfer unit 10, a voltage (primary transfer bias) having a polarity opposite to the charging polarity (minus polarity) of toner is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, The image is sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  After the toner image is sequentially primary-transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves to convey the toner image to the secondary transfer unit 20. The paper transport system rotates the pickup roll 51 in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and supplies paper P of a predetermined size from the paper tray 50. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) is rotated in accordance with the movement timing of the intermediate transfer belt 15 holding the toner image. Alignment with the position of the toner image is performed.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the paper P is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (minus polarity) is applied from the power supply roll 26, and a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Then, the unfixed toner image held on the intermediate transfer belt 15 is pressed at the secondary transfer unit 20 by the secondary transfer roll 22 and the backup roll 25, and electrostatically transferred onto the paper P at once.

Thereafter, the sheet P on which the toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22 and conveyed as it is, and is conveyed to a conveyance belt 55 provided on the downstream side of the secondary transfer roll 22 in the sheet conveyance direction. To do. The conveyance belt 55 conveys the paper P to the fixing device 60. The fixing device 60 processes the unfixed toner image on the paper P with heat and pressure and fixes it on the paper P. The paper P on which the fixed image is formed is conveyed to a paper discharge placement unit provided in the discharge unit of the image forming apparatus.
On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. To remove from the intermediate transfer belt 15.

(Fixing device 60)
Next, as an example of the fixing device 60 to which the exemplary embodiment is applied, a fixing device using an electromagnetic induction heating method (induction heating fixing device) will be described as an example.
FIG. 2 is a diagram illustrating a configuration of the fixing device 60 to which the exemplary embodiment is applied. As shown in FIG. 2, the fixing device 60 faces a fixing belt 61 as an example of an endless belt, a magnetic field generation unit 85 as an example of an electromagnetic induction heating member that generates an AC magnetic field in the fixing belt 61, and the fixing belt 61. A pressure roll 62 as an example of a rotating member disposed in this manner, and a pressure pad 64 as an example of a pressure member that presses the fixing belt 61 against the pressure roll 62 from the inside of the fixing belt 61 are provided.
Further, a belt guide member 63 that is supported behind the pressure pad 64 and restricts the rotation of the fixing belt 61, and a belt deformation mechanism that deforms the shape of the fixing belt 61 according to the type (thickness) of the paper P is exemplified. A core roller 69 is provided. The eccentric roller 69 will be described later.

(Fixing belt 61)
The fixing belt 61 has a cylindrical shape, and is an endless belt having a diameter of about 30 mm, for example. The fixing belt 61 is usually a base material containing a heat-resistant resin such as polyimide resin, polyamide resin, or polyamide-imide resin, a metal layer laminated on the outer peripheral surface of the base material, and a mold release containing a fluororesin that forms the surface. And an elastic layer containing a known heat-resistant rubber such as silicone rubber or fluororubber between the metal layer and the release layer.
Here, for example, even when both ends of the fixing belt 61 abut against an edge guide member (not shown), the base material is required to have a rigidity that does not cause buckling or the like. 5 GPa or more. The metal layer includes a single alloy or two or more kinds of alloys such as copper, nickel, iron, gold, silver, aluminum, chromium, tin, and zinc, and generates heat due to an eddy current generated by the magnetic field of the exciting coil 851.
The fixing belt 61 is rotatably supported by a pressure pad 64, a belt guide member 63, and edge guide members (not shown) disposed at both ends of the fixing belt 61. Then, it is brought into pressure contact with the pressure roll 62 at the nip portion N and is rotated in the direction of arrow C following the pressure roll 62.

(Magnetic field generation unit 85)
The magnetic field generating unit 85, which is an example of an electromagnetic induction heating member, has a round shape with a cross section that follows the shape of the fixing belt 61, and is installed with a clearance of about 0.5 mm to 2 mm from the outer peripheral surface of the fixing belt 61. The magnetic field generation unit 85 includes an excitation coil 851 that generates a magnetic field, a coil support member 852 that holds the excitation coil 851, and an excitation circuit 853 that supplies current to the excitation coil 851.

  The exciting coil 851 is formed, for example, by winding litz wires made by bundling about 16 to 20 copper wires having a diameter of 0.5 mm that are insulated from each other in a closed loop shape such as an oval shape, an elliptical shape, or a rectangular shape. Use things. By applying an alternating current of a predetermined frequency to the exciting coil 851 by the exciting circuit 853, an alternating magnetic field H is generated around the exciting coil 851. When the AC magnetic field H crosses a metal layer of the fixing belt 61 described later, an eddy current I is generated so as to generate a magnetic field that hinders the change of the AC magnetic field H by electromagnetic induction. The frequency of the alternating current applied to the exciting coil 851 is set to 10 kHz to 50 kHz, for example. As the eddy current I flows through the metal layer 611 (see FIG. 4B) of the fixing belt 61, electric power W (W = I2R) proportional to the resistance value R of the metal layer 611 (see FIG. 4B) is obtained. Joule heat is generated to heat the fixing belt 61.

  The coil support member 852 is made of a nonmagnetic material having heat resistance. Examples of such non-magnetic materials include heat-resistant resins such as heat-resistant glass, polycarbonate, polyether sulfone, and PPS (polyphenylene sulfide), or heat-resistant resins obtained by mixing glass fibers with these.

(Pressure roll 62)
The pressure roll 62 includes, for example, a solid iron core (columnar core) 621 having a diameter of 16 mm, and a heat-resistant elastic body layer 622 such as a silicone sponge having a thickness of 12 mm, which covers the outer peripheral surface of the core 621. For example, it has a release layer 623 with a heat-resistant resin coating such as PFA having a thickness of 30 μm or a heat-resistant rubber coating. In addition, as a manufacturing method of the pressure roll 62, for example, a fluororesin tube having a bonding primer applied to the inner peripheral surface of a PFA tube and a solid shaft are set in a molding die, and the fluororesin tube and the solid An example is a method in which after the liquid foamed silicone rubber is injected between the shaft and the silicone rubber is vulcanized and foamed by heat treatment (150 ° C. × 2 hrs) to form an elastic layer.
The pressure roll 62 is disposed so as to face the fixing belt 61, rotates in the direction of arrow D at a process speed of, for example, 140 mm / s, and drives the fixing belt 61. Further, the fixing belt 61 is held between the pressure roll 62 and the pressure pad 64 to form a nip portion N, and a sheet P holding an unfixed toner image is passed through the nip portion N to pass heat and Pressure is applied to fix the unfixed toner image on the paper P.

(Pressure pad 64)
The pressure pad 64 forms a nip portion N by pressing the fixing belt 61 against the pressure roll 62. The pressure pad 64 supports the pressure roll 62 by a holder 65 so as to press the pressure roll 62 with a load of, for example, 35 kgf by a spring or an elastic body. The pressure pad 64 is made of an elastic body such as silicone rubber or fluorine rubber, and the pressure roll 62 side is formed in a flat shape, and a substantially uniform nip pressure is formed in the nip portion N. In the present embodiment, a silicone rubber having a rubber hardness of 20 ° (JIS-A) is used as the pressure pad 64, and the width is set to 8.5 mm and the rubber thickness is set to 5 mm.
Since the fixing belt 61 undergoes a sudden change in curvature when leaving the surface of the pressure pad 64 on the pressure roll 62 side, the sheet P after fixing is peeled off from the fixing belt 61.

(Belt guide member 63)
The belt guide member 63 is attached to a holder 65 disposed inside the fixing belt 61 so as to be behind the pressure pad 64 as necessary. A plurality of ribs (not shown) directed in the rotation direction of the fixing belt 61 are formed to reduce the contact area with the inner peripheral surface of the fixing belt 61.
The belt guide member 63 is formed of a heat-resistant resin such as PFA or PPS having a low friction coefficient and a low thermal conductivity, reduces sliding resistance with the inner peripheral surface of the fixing belt 61, and reduces heat dissipation. Configure as follows. Further, as will be described later, the belt guide member 63 also functions as a belt deformation mechanism.

  As illustrated in FIG. 2, when a belt guide member 63 and a belt deformation mechanism (for example, an eccentric roller 69) are provided, they are arranged so as not to interfere with each other. For example, the belt guide member 63 is divided into a plurality of parts, and a plurality of belt deformation mechanisms (e.g., eccentric rollers 69) are arranged in the divided gaps, or the belt guide member 63 is moved when the belt deformation mechanism is operated. Move to a position where there is no interference.

(Peeling auxiliary member 70)
Further, in the fixing device 60 to which this exemplary embodiment is applied, the peeling auxiliary member 70 disposed in the vicinity of the downstream side of the nip portion N is a direction in which the peeling baffle 71 faces the rotation direction of the fixing belt 61 (counter direction). And is held by the baffle holder 72. Further, a low friction sheet 68 is disposed between the pressure pad 64 and the fixing belt 61 to reduce the sliding resistance between the inner peripheral surface of the fixing belt 61 and the pressure pad 64. In the present embodiment, the low friction sheet 68 is configured separately from the pressure pad 64, and both ends are fixed to the holder 65.

(Lubricant application member 67)
A lubricant application member 67 is disposed in the holder 65 over the longitudinal direction of the fixing device 60. The lubricant applying member 67 contacts the inner peripheral surface of the fixing belt 61 and supplies the lubricant to the sliding portion between the fixing belt 61 and the low friction sheet 68. Examples of the lubricant include liquid oils such as silicone oil and fluorine oil; greases obtained by mixing solid substances and liquids, and combinations thereof.

(Belt deformation mechanism)
The fixing device 60 to which this exemplary embodiment is applied includes an eccentric roller 69 as an example of a belt deformation mechanism that deforms the shape of the fixing belt 61 according to the type (thickness) of the paper P.
As shown in FIG. 2, the eccentric roller 69 has an elliptical cross section. Normally, without changing the shape of the fixing belt 61, a long axis direction of the elliptical shape and a circle formed by the cross section of the fixing belt 61 are formed. Is arranged in parallel to the tangential direction of the fixing belt 61 so as to be inscribed in the inner surface of the fixing belt 61. The method of attaching the eccentric roller 69 is not particularly limited. For example, the eccentric roller 69 is rotatably attached to an edge guide member (not shown) that disposes the shaft at both ends of the fixing belt 61.
In the eccentric roller 69, for example, when the thickness of the paper P is small and it is difficult to peel off at the exit side of the nip portion N, the major axis direction of the ellipse and the tangential direction of the circle formed by the cross section of the fixing belt 61 are predetermined. The fixing belt 61 is pressed from the inside by being rotated so that the angle becomes the angle, and the shape of the fixing belt 61 is deformed.
Although not shown, the eccentric roller 69 can be disposed outside the fixing belt 61 and the shape of the fixing belt 61 can be changed by pressing the fixing belt 61 from the outside.
Further, the attachment position of the belt guide member 63 arranged behind the pressure pad 64 can be moved, the fixing belt 61 can be pressed from the inside, and the fixing belt 61 can be deformed into a shape protruding to the upstream side of the nip portion N. .

FIG. 3 is a view for explaining deformation of the fixing belt 61 by the belt deformation mechanism.
FIG. 3A shows that the fixing belt 61 is deformed by rotating the eccentric roller 69 disposed inside the fixing belt 61. As shown in FIG. 3A, when a thin sheet P or a sheet P that is difficult to peel off is sent to the fixing device 60, an elliptical eccentric roller 69 is controlled by the control unit 40 (see FIG. 1). Rotates in the direction of arrow E so that the major axis direction of the elliptical shape and the tangential direction of the circle formed by the cross section of the fixing belt 61 form a predetermined angle. At this time, the eccentric roller 69 is inscribed in the fixing belt 61 and pressed from the inside. For this reason, the shape of the fixing belt 61 protrudes to the upstream side of the nip portion N, and deforms so that the curvature of the fixing belt 61 increases on the downstream side of the nip portion N. As a result, the peel angle of the paper P discharged on the downstream side of the nip portion N increases, and the paper P is prevented from being wound around the fixing belt 61.

  FIG. 3B shows that, as another embodiment, the fixing belt 61 is deformed by rotating an eccentric roller 69 b disposed outside the fixing belt 61. As shown in FIG. 3B, the elliptical eccentric roller 69b arranged outside the fixing belt 61 is controlled by the control unit 40 (see FIG. 1), and the elliptical long axis direction and the fixing belt 61. Rotate in the direction of arrow F so that the tangential direction of the circle formed by the cross section of the cross section becomes a predetermined angle. At this time, the eccentric roller 69b circumscribes the fixing belt 61 and presses the fixing belt 61 from the outside. For this reason, the shape of the fixing belt 61 is deformed so that the curvature of the fixing belt 61 is increased on the downstream side of the nip portion N, and is projected to the upstream side of the nip portion N. As a result, similarly to FIG. 3A, the peeling angle of the paper P discharged downstream of the nip portion N is increased, and the paper P is prevented from being wound around the fixing belt 61.

  FIG. 3C shows that the fixing belt 61 is deformed by the belt guide member 63. As shown in FIG. 3C, the belt guide member 63 supported behind the pressure pad 64 is on the upstream side (in the direction of arrow G) to which the paper P is supplied under the control of the control unit 40 (see FIG. 1). Move to. At this time, the belt guide member 63 is inscribed in the fixing belt 61 and presses the fixing belt 61 from the inside. For this reason, the shape of the fixing belt 61 protrudes to the upstream side of the nip portion N, and deforms so that the curvature of the fixing belt 61 increases on the downstream side of the nip portion N. As a result, similarly to FIG. 3A, the peeling angle of the paper P discharged downstream of the nip portion N is increased, and the paper P is prevented from being wound around the fixing belt 61.

  As described above, in the fixing device 60 to which the present exemplary embodiment is applied, the shape of the fixing belt 61 is deformed according to the thickness of the paper P. Therefore, the pressure pad 64 is sharpened toward the discharge side of the paper P, for example. The sheet peeling performance can be ensured when the sheet P that is difficult to peel off or the coverage is high, without taking any measures such as forming a different shape. Further, since the mechanical load on the pressure pad 64 is usually small, the fixing belt 61 can be used for a long period of time. In particular, this effect is remarkable in the case of the hard fixing belt 61 having a metal layer used in the fixing device 60 using the electromagnetic induction heating method.

(Manufacturing method of fixing belt 61)
As described above, in the present embodiment, in the fixing device 60 using the electromagnetic induction heating method, the fixing belt 61 having the metal layer and the elastic layer laminated on the outer peripheral surface of the base material containing the heat resistant resin. Is used. The fixing belt 61 having such a metal layer is usually manufactured by the following operation.
First, a heat resistant resin such as a polyimide resin is applied to the surface of a metal pipe having a diameter of about 30 mm and dried by heating to form an endless belt. Next, a nickel plating film having a thickness of about 1 μm is formed on the outer peripheral surface of the endless belt by an electroless nickel plating process. Subsequently, the nickel plating film is used as an electrode, and a copper plating is formed thereon by an electrolytic copper plating process. A film and an electrolytic nickel film are formed, and a metal layer having a thickness of about 10 μm to 100 μm is formed.
Subsequently, for example, liquid silicone rubber or the like is applied to the metal layer, and an elastic layer having a predetermined thickness is bonded and solidified. Next, on the elastic layer, for example, a silane coupling agent-based primer is applied, and subsequently, a fluororesin tube that has been subjected to adhesion activation treatment on the back surface in advance is placed on the surface of the elastic layer, at 200 ° C. to 240 ° C. A release layer is formed by heat bonding.

Next, the endless belt formed in this way is cut at a right angle to the longitudinal direction and aligned to a predetermined width. At this time, the elastic layer and the release layer formed on the outer peripheral side of the endless belt are cut by a cutter blade having a sharp tip, and the metal layer formed on the inner peripheral side of the endless belt is the endless belt. It is preferable to cut from the back surface with a lathe tool having an obtuse tip.
That is, depending on the thickness of the metal layer and the material of the cutter blade to be used, when an endless belt having a metal layer with a thickness of about 20 μm is cut using the cutter blade, it is usually repeatedly cut about 30 times. The cutting edge of the cutter blade spills out during processing. Therefore, a lathe tool with an obtuse tip is more suitable for cutting the metal layer than a cutter blade with an acute tip, and a lathe tool with an obtuse angle (about 60 °) is used to have the metal layer. The endless belt can be repeatedly cut.
However, if the elastic layer that is softer than the metal layer is cut using a lathe tool having an obtuse angle, the elastic layer material scatters at the cut end, causing problems such as adhesion. Therefore, when a hard metal layer and a soft elastic layer are cut with one kind of blade, it is often difficult to obtain a good cut surface.

FIG. 4 is a diagram for explaining cutting of an endless belt having a metal layer and an elastic layer. FIG. 4A shows a state where the endless belt 610 is attached to a predetermined lathe (not shown). FIG. 4B is an enlarged view of the cut portion.
As shown in FIG. 4A, an endless belt 610 attached to a lathe (not shown) and rotating in the direction of arrow H has a metal layer formed on the inner peripheral side of the endless belt 610 as an endless belt. From the back surface of 610, cutting is performed with a lathe tool 81 having an obtuse tip, and the elastic layer and the release layer on the outer peripheral side are cut with a cutter blade 82 having an acute tip.
At this time, a lathe cutting tool 81 and a cutter blade 82 are connected, a cutting jig 83 having a U-shape is attached to the lathe, and the cutting jig 83 is appropriately moved in the direction of arrow I while rotating the endless belt 610. The metal layer and the elastic layer of the endless belt 610 are cut at the same position.
4B, the metal layer 611 formed on the inner peripheral side of the endless belt 610, and the elastic layer 612 and the release layer 613 on the outer peripheral side are lathes with blunt ends. A cutting surface having no step is obtained by cutting at the same position of the endless belt 610 by the cutting tool 81 and the cutter blade 82 having a sharp tip.

Further, the endless belt 610 having the metal layer 611 having a thickness of about 10 to 100 μm is cut by the above-described operation, whereby burrs (dents) existing in the belt axial direction of the belt end section of the metal layer 611 are obtained. The size can be made 150 μm or less.
That is, if burrs (dents) present on the fracture surface of the metal layer 611 are excessively large, the mechanical load applied to the fixing belt 61 causes these burrs (dents) to start and crack in the belt axis direction (cracks). ) Occurs. When a crack occurs at the belt end, the crack develops toward the center of the belt due to continuous use, so that the fixing function cannot be normally exhibited.

1 is a schematic configuration diagram of an image forming apparatus to which the exemplary embodiment is applied. 1 is a diagram illustrating a configuration of a fixing device to which the exemplary embodiment is applied. FIG. 6 is a diagram illustrating deformation of a fixing belt by a belt deformation mechanism. It is a figure explaining the cutting process of the endless belt which has a metal layer and an elastic layer.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developing device, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... secondary transfer section, 60 ... fixing device, 61 ... fixing belt, 62 ... pressure roll, 63 ... belt guide member, 64 ... pressure pad, 65 ... holder, 67 ... lubricant application member, 68 ... low friction Sheet, 69, 69b ... Eccentric roller, 70 ... Peeling auxiliary member, 85 ... Magnetic field generating unit, 851 ... Excitation coil, 852 ... Coil support member

Claims (7)

A rotating member for rotational driving;
An endless belt that rotates opposite the rotating member and forms a nip portion between which the recording material passes;
A pressure member that presses the endless belt against the rotating member from the inside of the endless belt;
And a belt deformation mechanism that deforms the shape of the endless belt according to the type of the recording material.   2. The belt deformation mechanism is characterized in that the endless belt is deformed into a shape that increases the curvature of the endless belt on the downstream side of the nip portion and projects to the upstream side of the nip portion. The fixing device according to 1.   The belt deformation mechanism presses the endless belt from the inside by rotating an eccentric roller arranged inside the endless belt, and deforms the endless belt into a shape protruding to the upstream side of the nip portion. The fixing device according to claim 1.   The belt deformation mechanism presses the endless belt from the outside by rotating an eccentric roller arranged outside the endless belt, and increases the curvature of the endless belt on the downstream side of the nip portion. The fixing device according to claim 1. A belt guide member that is supported behind the pressure member and regulates rotation of the endless belt;
The belt deformation mechanism is configured to press the endless belt from the inside by moving an attachment position of the belt guide member, and to deform the endless belt into a shape protruding to the upstream side of the nip portion. Item 4. The fixing device according to Item 1.   The endless belt has a metal layer having a thickness of 10 μm to 100 μm on the inner peripheral side and an elastic layer on the outer peripheral side, and the size of burrs existing in the belt axial direction on both side surfaces of the metal layer is 150 μm or less. The fixing device according to claim 1. A toner image forming unit for forming a toner image;
A transfer portion for transferring the toner image onto a recording material;
A fixing unit that fixes the toner image transferred onto the recording material onto the recording material,
The fixing unit is
A rotating member for rotational driving;
An endless belt that forms a nip portion through which the recording material passes between the rotating member and has a metal layer and an elastic layer on a base made of heat-resistant resin;
An electromagnetic induction heating member that heats the endless belt;
A pressure member that presses the endless belt against the rotating member;
An image forming system comprising: a belt deformation mechanism that increases the curvature of the endless belt on the downstream side of the nip portion and deforms the endless belt into a shape protruding on the upstream side of the nip portion. apparatus.

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