1. Field of the Invention
The present invention relates to an image heating device to be preferably used as a fixing device provided in an image forming apparatus such as an electrophotographic copying machine and electrophotographic printer.
2. Description of the Related Art
In an image forming apparatus having an image heating device, when print processing is sequentially performed on a small-size recording material of a width narrower than a width of a recording material of a maximum width usable in the apparatuses, a phenomenon in which a temperature of the non-sheet passing part of a fixing unit rises (i.e., non-sheet-passing part temperature rise), occurs. In the technical field of film-heating fixing devices using a fixing film and a ceramic heater contacting the fixing film, as a method for reducing the non-sheet-passing part temperature rise, a method discussed in Japanese Patent Application Laid-Open No. 2003-317898 is proposed. In this method, a high thermal conductive member is held between a holding member for holding a heater and the heater to reduce unevenness in the temperature distribution of the heater.
Meanwhile, in assembling the apparatus, if a position of the high thermal conductive member is misaligned to the heater, temperatures at end portions in a longitudinal direction of the heater may decrease and this may deteriorate the fixation properties, and/or the effects of reducing the temperature rise in the non-sheet-passing part by the high thermal conductive member may decrease. Especially, when a thin sheet is used as the high thermal conductive member, the handling of the sheet is difficult, and consequently, at the time of assembly, it is difficult to determine the position of the sheet to the heater.
The present invention is directed to an image heating device in which a high thermal conductive member can be easily positioned.
According to an aspect of the present invention, an image heating device includes, a moving member configured to move while contacting a recording material at one surface of the moving member, a backup member configured to contact another surface of the moving member, a holding member configured to hold the backup member, a nip portion forming member contacting the one surface of the moving member, and configured to form a nip portion in corporation with the backup member via the moving member, and a high thermal conductive member held between the holding member and the backup member, wherein the recording material on which an image has been formed is heated by heat received from the moving member while being nipped and conveyed at the nip portion, and wherein the holding member includes a holding surface configured to hold the backup member via the high thermal conductive member, and a recessed portion provided adjacent to the holding surface in a direction orthogonal to a recording material conveyance direction, and configured not to apply pressure to the high thermal conductive member, or to reduce the pressure to be applied to the high thermal conductive member as compared to the holding surface.
According to another aspect of the present invention, an image heating device includes, a cylindrical film, a heater contacting the inner surface of the film, a holding member configured to hold the heater, a nip portion forming member configured to form a nip portion in cooperation with the heater via the film, and a graphite sheet held between the holding member and the heater, wherein a recording material on which an image has been formed is heated by heat received from the film while being nipped and conveyed at the nip portion, and wherein the holding member includes a holding surface configured to hold the heater via the graphite sheet, and a recessed portion provided adjacent to the holding surface in a direction orthogonal to a recording material conveyance direction, and configured not to apply pressure to the graphite sheet, or to reduce the pressure to be applied to the graphite sheet as compared to the holding surface.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
The laser printer 100 according to the present exemplary embodiment can handle a plurality of sizes. More specifically, the laser printer 100 can perform printing on paper of a plurality of sizes including a letter-size paper (approximately 216 mm×279 mm), an A4-size paper (210 mm×297 mm), or an A5-size paper (148 mm×210 mm) set in the sheet cassette 11. The laser printer 100 basically performs longitudinal paper feed (conveys paper such that the long sides of the paper are parallel to the conveyance direction), and the largest (widest) size in the usable standard recording material sizes (the usable paper sizes in a catalog) is a width of approximately 216 mm of the letter size paper. Papers (e.g., the A4-size paper and the A5-size paper) of narrower widths than the maximum size usable by the laser printer 100 is defined as small size paper.
The fixing unit 200 includes a cylindrical film (moving member) 202, a heater (backup member) 300 that contacts the inner surface of the film 202, and a pressure roller (nip portion forming member) 208 that forms a fixing nip portion N with the heater 300 via the film 202. The base layer of the film 202 is formed of a heat-resistant resin such as polyimide or metal such as stainless steel. The pressure roller 208 includes a core bar (shaft) 209 formed of, for example, iron or aluminum, and an elastic layer 210 formed of, for example, a silicone rubber. The heater 300 is held by a heater holding member 201 formed of a heat-resistant resin. The heater holding member 201 has a guide function of guiding the rotation of the film 202. The heater holding member 201 is an elongated member for holding the heater in the longitudinal direction of the heater. The pressure roller 208 receives power from the motor 30 through a gear GY provided at an end portion of the shaft 209 and rotates in the direction indicated by the arrow. The rotation of the pressure roller 208 causes the film 202 to follow the rotation of the pressure roller 208 to rotate. A metallic stay 204 is used to apply pressure of a spring 7 to the heater holding member 201. The stay 204 also has a function to reinforce the heater holding member 201. The stay 204 is an elongated member provided in parallel with the heater holding member 201. At both ends of the stay 204, regulating members 112 for regulating the deviation movement of the film 202 to the generating line direction are provided. The force of the spring 7 is applied to the regulating members 112, the stay 204, the heater holding member 201, the heater 300, the film 202, and the pressure roller 208 in this order. A bearing 102 is provided to a frame 101 of the fixing unit 200. The bearing 102 rotatably holds the shaft 209 of the pressure roller 208. Consequently, between the pressure roller 208 and the heater holding member 201, through the stay 204, pressure for forming the fixing nip portion N is being applied. A connector 62 is used to supply electric power to the heater 300.
The heater 300 includes a ceramic heater substrate 303, and resistance heating elements (heating elements) 301-1 and 301-2 provided on the heater substrate 303 along the substrate longitudinal direction. The heater 300 further includes an insulating surface protective layer 304 (in the present exemplary embodiment, the insulating surface protective layer 304 is formed of glass) that covers the resistance heating elements 301-1 and 301-2.
Between the heater holding member 201 and the heater 300, a high thermal conductive member 220 is provided. The high thermal conductive member 220 has a higher thermal conductivity in the parallel direction to the plane of the high thermal conductive member 220 than the thermal conductivity of the heater substrate 303. For example, the high thermal conductive member 220 is a flexible sheet member using graphite. The opposite surface (rear surface) of the surface of the heater 300 facing the nip portion N contacts a thermistor (temperature detection element) 211 via the high thermal conductive member 220. The rear surface of the heater 300 also contacts, via the high thermal conductive member 220, a protective element 212 such as a thermoswitch and a temperature fuse that operates when temperature of the heater 300 abnormally rises to shut off the power supply to the heating elements 301-1 and 301-2. The thermistor 211 and the protective element 212 are pressed to the high thermal conductive member 220, for example, by a leaf spring (not illustrated). The recording paper P bearing an unfixed toner image is nipped and conveyed while being heated at the fixing nip portion N, and thereby the unfixed toner image is fixed. In the present exemplary embodiment, as the high thermal conductive member 220, a flexible sheet (tape) is used. More specifically, the Pyrolytic Graphite Sheet (PGS) (registered trademark) manufactured by Panasonic Corporation is used. The PGS has a thermal conductivity of 1000 W/mK in the direction parallel to the surface of the sheet, a thermal conductivity of 15 W/mK in the thickness direction, a thickness of 70 μm, and a density of 1.2 g/cm3.
As described above, the fixing device according to the present exemplary embodiment includes the film (moving member) 202 that moves while contacting the recording material at one surface, the heater (backup member) 300 that contacts the other surface of the moving member, and the holding member 201 for holding the backup member. The fixing device further includes the pressure roller (nip portion forming member) 208 that contacts one surface of the moving member and forms the nip portion with the backup member through the moving member, and the high thermal conductive member 220 that is held by the backup member and the holding member. Pressure is applied between the holding member 201 and the nip portion forming member 208, so that an image on the recording material is heated by the heat generated by the moving member while the recording material is nipped and conveyed with the nip portion N.
With reference to
To the heater holding member 201, a heater attachment groove recessed in the z direction is provided. The bottom surface of the heater attachment groove includes an attachment surface (holding surface) 201a and an attachment surface (second holding surface) 201b. On the attachment surface 201a, the heater 300 is provided via the sheet 220. On the attachment surface 201b, the heater 300 is directly provided. To the x direction end portion of the heater holding member 201, an arc shape butting portion 201c against which the end portion of the heater 300 butts is provided. The butting portion 201c regulates a position in the longitudinal direction (x direction) of the heater 300 in the attachment groove of the heater holding member 201. To the heater holding member 201, a back clearance portion (recessed portion) 201d that is further recessed in the z direction than the heater attachment surface 201a is provided. More specifically, at a part of the surface of the holding member 201 contacting the high thermal conductive member 220, the recessed portion is provided to prevent application of pressure to the high thermal conductive member 220, or to reduce the pressure applied to the high thermal conductive member 220 as compared to the attachment surface 201a. The recessed portion is provided, with respect to the direction (x direction) orthogonal to the conveyance direction (y direction) of the recording material, adjacent to an area (an area H described below) where the pressure is applied to the high thermal conductive member 220. The recessed portion is provided, with respect to the direction (x direction) orthogonal to the conveyance direction, outside of the area (section DE) where the heating elements are positioned.
To the x direction end portion of the sheet 220, a portion 220a with a narrow width in the y direction is provided. The back clearance portion 201d has a hole 201e for passing the end portion 220a of the sheet 220 therethrough. The sheet 220 is provided such that the end portion 220a of the sheet 220 is passed through the hole 201e, thereby regulating the position of the sheet in the widthwise direction (y direction). Although a position of the sheet 220 in the x direction is regulated by the end portion 220b that is a border with the end portion 220a, the sheet 220 has a flexibility in the x direction since the hole 201e is wide in the x direction.
In a step prior to the attachment of the heater 300 to the heater holding member 201, as described above, the sheet 220 is regulated with respect to the heater holding member 201, while the sheet 220 has a flexibility in the longitudinal direction (the state illustrated in
Next, a positional relationship between the sheet 220 and the heating area (the section DE in
The sheet 220 has the function to reduce overheating of the non-sheet passing area in the process of fixing small size paper. If the close contact area of the sheet 220 with respect to the heater in the x direction is too wide, temperatures at the end portions of the heater can be excessively decreased. Consequently, in the present exemplary embodiment, the pressure area H and the heating area DE are set to have the same area. However, it is not always necessary to set the pressure area H and the heating area DE to have the same area, and the positional relationship between the areas may be appropriately set. According to the present exemplary embodiment, the pressure area H can be easily changed only by changing the shape of the heater holding member 201.
White circles (o) in
White circles (∘) in
In the present exemplary embodiment, the heating area DE of the heater 300 and the pressure area H of the sheet 220 are approximately the same, and consequently, both of the fixation properties at the recording paper end portion and the reduction in the non-sheet-passing part temperature rise by the sheet can be achieved. Further, in the present exemplary embodiment, the positional accuracy of the pressure area H is high, and consequently, the setting accuracy of the excess amount is also high.
Hereinafter, a second exemplary embodiment of the present invention will be described with reference to
With reference to
To the heater holding member 201 according to the present exemplary embodiment, the back clearance portion (recessed portion) 201d that is recessed from the heater attachment surface 201a is provided. The back clearance portion 201d has a hole 201k for the installation of the sheet 220. An end portion of the sheet 220 has a long hole 220e. A stopper 500 is passed through the long hole 220e and the hole 201k to attach the sheet 220 to the heater holding member 201. The stopper 500 has a hook portion 500a, and after attaching to the heater holding member 201, the hook portion 500a is rotated by 180 degrees. This causes the stopper 500 to hook to the heater holding member 201, and the stopper 500 is prevented from coming out of the holding member 201. The sheet 220 is regulated by the long hole 220e in the widthwise direction (y direction). The longitudinal direction position of the sheet 220 has a certain degree of freedom since the stopper 500 holds the sheet 220 with a clearance. Since the stopper 500 does not come out of the holding member 201 with the hook portion 500a, in the assembly of the apparatus, the sheet 220 does not come out of the holding member 201.
Hereinafter, a third exemplary embodiment of the present invention will be described with reference to
In the above-described first to third exemplary embodiments, as the backup member, the heater 300 is used. The backup member may be a substrate (for example, a ceramic substrate) 600 without a heating element. To a structure in which the high thermal conductive member 220 is provided between the backup member 600 and the holding member 201, the holding structure for the sheet 220 according to one of the first to third exemplary embodiments may be applied.
In the first to third exemplary embodiments, as the moving member, the cylindrical film is used as an example. The exemplary embodiments of the present invention can be applied to an apparatus having a take-up film as the moving member, as an alternative to the cylindrical firm.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-248454 filed Nov. 29, 2013, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2013-248454 | Nov 2013 | JP | national |