Patent Grant
9983522
The present invention relates to a fixing device for use with an image forming apparatus, such as a copying machine or a printer, of an electrophotographic type.
In recent years, as a type of the fixing device provided in the image forming apparatus of the electrophotographic type, a film fixing type has been used. The fixing device of the film fixing type generally has a constitution including a cylindrical film, a heater contacting an inner surface of the film, a supporting member for supporting the heater at an opposing surface to a surface where the heater contacts the inner surface of the film, and a pressing member for forming a nip, together with the heater, between the pressing member and the film. Further, the fixing device heats a recording material on which a toner image is carried while feeding the recording material through the nip, thus fixing the toner image on the recording material.
As the heater, a heater prepared by forming a heat generating resistor on a substrate of a ceramic material such as alumina or aluminum nitride is used in general. With respect to the heater, one surface contacts the inner surface of the heater, and an opposing surface (the other surface) to the one surface contacting the film contacts the supporting member. A thermosensitive device, such as a thermistor or a fuse, contacts the opposing surface where the heater contacts the supporting member while being supported by the supporting member. The heater controls the amount of electric power supplied thereto by using wave-number control or phase control so that the detection temperature of the thermistor reaches a target temperature. When the heater causes an abnormal temperature rise, the electric power supply to the heater is blocked by the fuse or a thermostat.
Here, as one of problems in the above-described fixing device, there is heater breaking (cracking) due to thermal runaway. The heater breaking due to thermal runaway refers to a phenomenon such that a triac or the like used for controlling the heater is out of order to disable the control of the heater, and thus the electric power is continuously supplied to the heater to break the heater. The cause of this heater breaking includes thermal stress resulting from generation of a difference in temperature of the heater and the generation of mechanical stress, exerted on the heater, by partial melting of the supporting member.
Particularly, heater breaking due to the thermal stress is generated in some cases from a contact with a thermistor or the like, as a starting point, where the temperature difference becomes large between the contact portion and a non-contact portion with the thermistor or the like to generate large thermal stress.
As a countermeasure against heater breaking, interruption of the electric power supply to the heater is performed, before the substrate is broken due to the thermal stress by overheating of the heater, by using a safety device such as the above-described fuse or the like.
However, in recent years, the demand for shortening of FPOT (first page out time) and improvement in productivity has intensified, and in the future, it has been considered that there will be a need to supply large electric power to the heater, and therefore heater breaking can occur in an early stage.
Therefore, Japanese Laid-Open Patent Application (JP-A) Hei 11-84919 discloses a heating device, as shown in
Accordingly, assuming that the safety device is provided on the metal plate 14a at an opposing surface to a contact surface with the heater 12, it would be considered that the temperature difference between the contact portion with the safety device and a non-contact portion with the safety device becomes small to decrease the thermal stress and thus heater breaking is not readily generated.
However, in the constitution disclosed in JP-A Hei 11-84919, although the metal plate 14a is fixed to the heat-insulating supporting member 11 by an adhesive, the heater 12 and the metal plate 14a are merely contacted to each other by a press-contact force in the nip of the heating device.
Accordingly, in the heating device including a pressure-releasing (eliminating) mechanism for eliminating a press-contact state or alleviating the press-contact force during a non-operating period of the heating device, when the press-contact state in the nip is eliminated or when the press-contact force in the nip is alleviated, there is a possibility that a status in which the heater 12 and the metal plate 14a are not sufficiently contacted to each other is created. That is, in the case where the press-contact force in the nip is sufficient, the plate 14a and the heater 12 are sufficiently contacted to each other by the press-contact force in the nip. However, in the case where the press-contact state in the nip is eliminated or in the case where the press-contact force in the nip is alleviated, by the influence of thickness tolerance, warpage and the like, of the metal plate 14a, a status in which the heater 12 and the metal plate 14a are not sufficiently contacted to each other can occur.
In the case where thermal runaway causing a disabling of the control of the heater is generated in the status in which the heater 12 and the metal plate 14a are not sufficiently contacted, an effect of uniformizing the temperature distribution of the heater 12 by the metal plate 14a is not sufficiently achieved, and thus there is a possibility of the generation of heater breaking.
A principal object of the present invention is to provide a fixing device capable of stably bringing a heater and a metal plate into contact with each other even in the case where in a nip of the fixing device, a press-contact state is eliminated or a press-contact force is alleviated.
According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording material by heating the toner image while feeding, through a nip, the recording material on which the toner image is carried. The fixing device comprises: a cylindrical film; a planar heater contacting an inner surface of the film; a heat conduction member contacting a surface, of the heater, opposite from a surface where the heater contacts the inner surface of the film; a supporting member for supporting the heater via the heat conduction member; a limiting member for limiting end portions of the heater with respect to a generatrix direction of the film so as to prevent the end portions from moving in a thickness direction of the heater relative to the supporting member; and a pressing member for forming the nip, together with the heater, between the pressing member and the film. A state of the fixing device is switchable between a first state in which a press-contact force in the nip is enough to fix the toner image and a second state in which the press-contact force in the nip is smaller than the press-contact force in the first state. A surface where the supporting member opposes the heat conduction member has a shape such that a central portion of the film with respect to the generatrix direction of the film is projected toward the pressing member more than an end portion of the film with respect to the generatrix direction.
According to a second aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording material by heating the toner image while feeding, in a nip, the recording material on which the toner image is carried. The fixing device comprises: a cylindrical film; a planar heater contacting an inner surface of the film; a heat conduction member contacting a surface, of the heater, opposite from a surface where the heater contacts the inner surface of the film; a supporting member for supporting the heater via the heat conduction member; and a back-up member for forming the nip, together with the heater, between the back-up member and the film. The heat conduction member includes a locking portion at an end portion thereof with respect to a feeding direction of the recording material. The heat conduction member is locked to the supporting member by the locking portion with respect to a direction perpendicular to the feeding direction of the recording material.
According to a third aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording material by heating the toner image while feeding, through a nip, the recording material on which the toner image is carried. The fixing device comprises: a cylindrical film; a planar heater contacting an inner surface of the film; a heat conduction member contacting a surface, of the heater, opposite from a surface where the heater contacts the inner surface of the film; a supporting member for supporting the heater via the heat conduction member; and a back-up member for forming the nip, together with the heater, between the back-up member and the film, wherein the heat conduction member includes a first locking portion provided at a central portion with respect to a direction perpendicular to a feeding direction of the recording material, and a second locking portion and a third locking portion which are provided at end portions so as to sandwich the first locking portion with respect to the direction perpendicular to the feeding direction of the recording material. The heat conduction member is locked to the supporting member by the first locking portion with respect to the direction perpendicular to the feeding direction of the recording material and is locked to the supporting member by the second and third locking portions with respect to the feeding direction of the recording material.
According to a fourth aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording material by heating the toner image while feeding, through a nip, the recording material on which the toner image is carried. The fixing device comprises: a cylindrical film; a planar heater contacting an inner surface of the film; a heat conduction member contacting a surface, of the heater, opposite from a surface where the heater contacts the inner surface of the film; a supporting member for supporting the heater via the heat conduction member; and a back-up member for forming the nip, together with the heater, between the back-up member and the film. The heat conduction member includes a bent portion formed by bending a part of the heat conduction member in a direction crossing the direction perpendicular to a feeding direction of the recording material, and wherein the heat conduction member is locked to the supporting member by the bent portion with respect to the direction perpendicular to the recording material.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Parts (a) and (b) of
Part (a) of
Part (a) of
Part (a) of
Part (a) of
Parts (a) of
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Part (a) of
Parts (a) to (d) of
Parts (a) and (b) of
Parts (a) and (b) of
Part (a) of
Embodiments of the present invention will be described below with reference to the drawings. First, a summary of a fixing device in an embodiment will be described and then a (characteristic) feature of the embodiment will be described.
In the following description of a device structure, a direction refers to a direction perpendicular to a recording material feeding direction in a recording material feeding path. A widthwise direction is the same direction as the recording material feeding direction.
The fixing device 18 includes a film unit 31 including a cylindrical film 36 having flexibility and includes a pressing roller 32 as a pressing member. The film unit 31 and the pressing roller 32 are provided in substantially parallel to each other between left and right side plates 34 of a device frame 33.
The pressing roller 32 includes a metal core 32a, an elastic layer 32b formed outside the metal core 32a, and a parting layer 32c formed outside the elastic layer 32b. As a material for the elastic layer 32b, silicone rubber, fluorine-containing rubber or the like is used. As a material for the parting layer, PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), PTFE (polytetrafluoroethylene) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer) or the like is used.
In this embodiment, the pressing roller 32 prepared by forming an about 3.5 mm-thick silicone rubber layer 32b on a stainless steel-made more metal 32a of 11 mm in outer diameter by injection molding and then by coating an outside of the layer 32b with an about 40 μm-thick PFA resin tube 32c was used. An outer diameter of the pressing roller 32 is 18 mm. A hardness of the pressing roller 32 may desirably be, from the viewpoints of ensuring of a nip N and durability, in a range of 40-70 degrees as measured by an Asker-C hardness meter under a load of 9.8 N. In this embodiment, the hardness is 54 degrees. A length of the elastic layer 32b of the pressing roller 32 with respect to a longitudinal direction is 226 mm. The pressing roller 32 is, as shown in
The film unit 31 shown in
The film 36 includes a base layer, an elastic layer formed outside the base layer and a parting layer formed outside the elastic layer, and is a cylindrical flexible member. The film 36 in this embodiment is 18 mm in outer diameter. As the base layer, a 60 μm-thick polyimide base material is used. As the elastic layer, an about 150 μm-thick silicone rubber layer is used. As the parting layer, a 15 mm-thick PFA resin tube is used. The supporting member 38 has, as shown in
The heater 37 is, as shown in
The thermistor 42 is prepared by providing a thermistor element in a casing via ceramic paper or the like for stabilizing a contact state with the heater 37 and then by coating the thermistor element with an insulating material such as a polyimide tape. The temperature fuse 43 is a part for detecting abnormal heat generation to block electric power supply to the heater 37 when the heater 37 causes abnormal temperature rise. The temperature fuse 43 is prepared by mounting a fuse element, which fuses at a predetermined temperature, in a cylindrical metal casing, and blocks a circuit for supplying electric power to the heater 37 when the fuse element is fused due to the abnormal temperature rise of the heater 37. A size of the temperature fuse 43 in this embodiment is about 10 mm in length of a metal casing portion contacting the heater 37 and is about 4 mm in width of the metal casing. The temperature fuse 43 is provided on the metal plate 39 via a heat conductive grease to float over the heater 37, thus preventing improper operation.
A controller for controlling the amount of electric power supply to the heater 37 will be described with reference to
Next, the pressing stay 40 shown in
Next, assembling of the film unit 31 will be described. The pressing stay 40 is, as shown in (a) of
As shown in
Then, as shown in (a) of
In this embodiment, pressure of the pressing spring 45 is set so that a press-contact force between the film 36 and the pressing roller 32 is 160 N as a total pressure.
Then, to the driving gear G of the pressing roller 32, a rotational force is transmitted from an unshown driving source, so that the pressing roller 32 is rotationally driven in the clockwise direction in
The film 36 is rotated and the electric power is supplied to the heater 37, and in a state in which the temperature of the heater 37 detected by the thermistor 42 reaches the target temperature, the recording material P is introduced. As entrance guide 30 performs the function of guiding the recording material P, on which a toner image t in an unfixed state is placed, so as to be directed toward the nip N.
Into the nip N, the recording material P carrying thereon the unfixed toner image t is introduced, and then a toner image-carrying surface of the recording material P is in close contact with the film 36 in the nip N and the recording material P is fed through the nip N. In this feeding process, the unfixed toner image t on the recording material P is heated and pressed by heat of the film 36 heated by the heater 37 to be fixed on the recording material P. The recording material P passing through the nip N is curvature-separated from the surface of the film 36 and then is discharged to an outside of the fixing device by an unshown discharging roller pair.
Further, a pressure releasing (eliminating) mechanism for spacing the film unit 31 from the pressing roller 32 as shown from (a) of
That is, the fixing device 18 in this embodiment is switchable between a first state in which the press-contact force in the nip is set at a fixable press-contact force and a second state in which a press-contact state in the nip is eliminated or in which the press-contact force in the nip is set at a press-contact force smaller than the press-contact force in the first state.
In this embodiment, although the press-contact state in the nip is automatically eliminated by an unshown pressure releasing motor, a constitution in which the press-contact state in the nip is eliminated by manually rotating the pressure releasing cam may also be employed.
A constitution, as a (characteristic) feature of this embodiment, of the fixing device 18 including the metal plate 39 as the heat conduction member will be described. Part (a) of
In this embodiment, as the metal plate 39, an aluminum plate having a thickness of 0.3 mm constant with respect to the generatrix direction of the film 36 is used. A contact portion contacting the heater 37 has a straight shape of 226 mm in length with respect to the generatrix direction of the film 36 and 5 nm in width with respect to a direction perpendicular to the generatrix direction of the film 36. The metal plate 39 includes a bent portion 39a of 1.5 mm at each of end portions with respect to the generatrix direction of the film 36, and the bent portion 36a is inserted into a hole 38a of the supporting member 38. Incidentally, the hole 38a is provided in a somewhat large depth relative to the metal plate 39 in order to absorb and difference in linear expansion coefficient between the metal plate 39 and the supporting member 38, and therefore it is difficult to completely fix the metal plate 39 to the supporting member 38. Incidentally, as the material for the heat conduction member, aluminum is used in this embodiment, but it is possible to use a member, having a higher thermal conductivity than the substrate of the heater 37, such as a metal plate of copper or the like or a graphite sheet.
The substrate of the heater 37 in this embodiment has a rectangular parallelopiped shape which is 260 mm in length with respect to the generatrix direction of the film 36, 5.8 mm in width with respect to the direction perpendicular to the generatrix direction of the film 36, and 1.0 mm in thickness. Further, a material for the substrate in this embodiment is aluminum.
In this embodiment, the metal plate 39 is constituted so as to be bent, with respect to a load toner the recording material feeding path surface, easier than the supporting member 38 and the heater 37. That is, when Young' modulus is E (GPa) and geometrical moment of inertia is I (m4), flexural rigidity EI (N·m2) is smaller than those of the heater 37 and the supporting member 38. Further, the flexural rigidity of the heater 37 is smaller than the flexural rigidity of the supporting member 38.
The metal plate 39 in this embodiment is constituted by aluminum, and has the Young's modulus of about 70 (GPa) and the geometrical moment of inertia of about 0.011 (mm4), so that the flexural rigidity EI is about 7.9×102 (N·mm2). On the other hand, the heater 37 has the Young's modulus of about 350 (GPa) and the geometrical moment of inertia of about 0.483 (mm4), so that the flexural rigidity EI is 1.7×105 (N·mm2). The liquid polymer used as the material for the supporting member 38 has the Young's modulus of about 13 (GPa) and the geometrical moment of inertia of about 29.4 (mm4), so that the flexural rigidity EI is 3.8×105 (N·mm2). Incidentally, the cross-sectional shape of the supporting member 38 partly includes ribs which stand in actuality and is not uniform with respect to the generatrix direction of the film 36, and therefore the above values were shown as average values.
Here, the functions of the metal plate 39 will be described. The function of the metal plate 39 is such that the heater breaking (cracking) is suppressed by uniformizing the heat of the heater 37 during thermal runaway of the heater 37. When the thermistor 42, the fuse 43 and the like are directly contacted to the substrate of the heater 37, the heater 37 is broken (cracked) in some cases by thermal stress due to a temperature difference between a contact portion and a non-contact portion of these members during the thermal runaway of the heater 37. Therefore, as in this embodiment, by providing the thermistor 42 and the fuse 43 on the metal plate 39 contacting the heater 37, the heater breaking generated due to the thermal stress is not readily generated as a result of heat uniformization of the substrate of the heater 37 during the thermal runaway of the heater 37.
The heat uniformization of the heater 37 will be described with reference to
Next, a shape of a supporting surface of the supporting member 38 which supports the heater 37 via the metal plate 39 will be described. As shown in (a) of
Next, a constitution of, as a limiting member, an electric power supplying connector 46 and a clip 47 will be described with reference to
The electric power supplying connector 46 includes a housing portion 46a formed of a recording material in a U-shape and includes a contact terminal 46b ((a) of
The clip 47 is U-shaped metal plate, and elastically sandwiches the heater 37 and the supporting member 38 from outsides thereof, thus limiting movement of the end portions of the heater 37, with respect to the generatrix direction of the film 36, in the thickness direction of the heater 37 relative to the supporting member 38 ((b) of
Further, the electric power supplying connector 46 and the clip 47 limit the movement of the end portions of the heater 37, with respect to the generatrix direction of the film 36, in the thickness direction of the heater 37 relative to the supporting member 38, and are constituted so as to be movable in a direction parallel to the surface of the heater 37. Accordingly, application of unnecessary stress to the heater 37 is prevented during an occurrence of the thermal expansion of the heater 37 and an occurrence of flexure during pressure application and spacing.
The action of this embodiment is such that even in a state in which the press-contact state in the nip is eliminated or in which the press-contact force in the nip is alleviated, the heater 37 and the metal plate 39 are stably contacted to each other.
A mechanism of this action will be described with reference to
The movement of the heater 37 in the thickness direction relative to the supporting member 38 at the end portions of the heater 37 with respect to the generatrix direction of the film 36 in this embodiment is limited by the electric power supplying connector 46 or the like. Accordingly, a position of the heater 37 relative to the supporting member 38 with respect to the thickness direction at the end portions of the heater 37 is not changed even in a state in which the press-contact force in the nip is set at a fixable press-contact force and even in a state in which the press-contact state in the nip is eliminated or in which the press-contact force in the nip is alleviated.
Further, when the metal plate 39 is mounted on the supporting surface, having the crown shape, of the supporting member 38, a surface of the metal plate 39 to which the heater 37 is contacted at the central portion with respect to the generatrix direction of the film 36 is projected more than the end portion supporting surfaces 90 to which the heater 37 is contacted at the end portions with respect to the generatrix direction of the film 36. That is, the heater 37 is in a state in which the movement in the thickness direction thereof at the end portions with respect to the generatrix direction of the film 36 is limited, and is in a state in which the heater 37 is pressed and deformed in a direction, in which the heater 37 approaches the pressing roller, at the central portion with respect to the generatrix direction of the film 36. Accordingly, a restoring force F for restoring a shape of the heater 37 to the original straight shape is generated with respect to the heater 37 itself. The flexural rigidity in this embodiment satisfy: (flexural rigidity of metal plate 38)<(flexural rigidity of heater 37)<(flexural rigidity of supporting member 38), and therefore by the restoring force F of the heater 37, the metal plate 39 is stably contacted to the supporting member 38 while contacting the heater 37 and following the crown shape of the supporting member 38. This stable contact state between the metal plate 39 with the supporting member 38 and the heater 37 is generated by the restoring force of the heater itself, and therefore is not changed even in a state in which the press-contact state in the nip is eliminated or in which the press-contact force in the nip is alleviated.
Here, a magnitude of the restoring force F in this embodiment was measured. When a load required for flexing the heater 37 from the straight shape at the central portion of the supporting member 38 with respect to the generatrix direction of the film 36 by 0.6 mm was measured, as a simple center load, 0.42 N was obtained. In this embodiment, the crown shape of the supporting member 38 is a moderately curved shape, and therefore the heater 37 is, in actuality, in a state close to a uniform load state, so that the restoring force F of 0.42 N or more is generated over the entire heater 37 with respect to the generatrix direction of the film 36. Accordingly, even in a pressure-released state in which the press-contact force in the nip of the fixing device 18 is eliminated or alleviated, the heater 37 is stably contacted to the metal plate 39 by the restoring force F of the heater 37 itself.
Incidentally, the supporting member 38 is backed up by the pressing stay 40 having the high flexural rigidity, and therefore flexure of the supporting member 38 due to the restoring force F of the heater 37 is not generated. Even in the case where the supporting member 38 is not backed up by the pressing stay 40, when the flexural rigidity of the supporting member 38 is sufficiently larger than the flexural rigidity of the heater 37, the heater 37 is flexed to generate the restoring force F. Further, in the case where the flexural rigidity of the supporting member 38 is smaller than the flexural rigidity of the heater 37, as shown in
As described above, according to this embodiment, even in the state in which the press-contact state in the nip is eliminated or in which the press-contact force in the nip is alleviated, the heater 37 and the metal plate 39 are contacted to each other stably.
For that reason, an effect of uniformizing the temperature distribution of the heater 37 by the metal plate 39 can be sufficiently achieved, so that the heater breaking can be suppressed.
Incidentally, in this embodiment, the supporting surface of the supporting member 38 has the crown shape in the region C, but the supporting member 38 may only be required to have a projected shape such that in the region C, the central portion is projected more than the end portions with respect to the generatrix direction of the film 36. A modified embodiment of Embodiment 1 is shown in
However, in the constitution of Embodiment 1, the heater 37 to which the press-contact force is applied in the state in which the press-contact force in the nip Ni is set at the fixable press-contact force is backed up by the supporting member 38 via the metal plate 39 over the longitudinal direction, and therefore the constitution of Embodiment 1 has an advantage such that the pressure in the nip N is stabilized.
In this embodiment, different from Embodiment 1 in which the crown shape is provided at the supporting surface of the supporting member 38, a constitution in which the crown shape is provided at an opposing surface, of the metal plate 39, to the heater 37 is employed. The metal plate 39 is, similarly as in Embodiment 1, constituted by aluminum. A difference between this embodiment and Embodiment 1 is only the supporting member 38 and the metal plate 39, and other constitutions are substantially the same as those in Embodiment 1 and therefore will be omitted.
A feature of this embodiment will be described. The metal plate 39 has, as shown in
As a result, also in Embodiment 2, the heater 37 and the metal plate 39 are stably contacted to each other even in the state in which the press-contact force is set at the fixable press-contact force or even in the state in which the press-contact state in the nip is eliminated or in which the press-contact force in the nip is alleviated.
An effect in this embodiment different from the effect in Embodiment 1 will be described. The plate 39 is subjected to bending in L-shape at each of the end portions thereof with respect to the generatrix direction of the film 36, and therefore heat of the heater 37 is liable to be dissipated from the end portions during fixing, so that a temperature decrease at the end portions of the film 36 with respect to the generatrix direction of the film 36 is generated in some cases. Therefore, with respect to the generatrix direction of the film 36, the thickness of the metal plate 39 is made thinner at the end portions than at the central portion, such an effect that the heat at the end portions is not readily dissipated is achieved.
In this embodiment, the thickness of the p 39 is changed with respect to the generatrix direction of the film 36, whereby the crown shape is formed, and thus it is possible to achieve a heat-uniformizing effect of the heater 37 while suppressing the end portion temperature lowering of the heater 37 with respect to the generatrix direction of the film 36.
Incidentally, in this embodiment, a constitution in which the crown shape is formed on both of the supporting member 38 and the metal plate 39 may also be employed.
A fixing device 18 according to this embodiment is the same as the fixing device 18 in Embodiment 1 except for a heat conduction member 39 and a supporting member 38 and therefore will be omitted from description. With reference to
The heat conduction member 39 is formed with an aluminum plate. Part (a) of
In this embodiment, as shown in (a) of
The electric power supplying connector 46 includes, as shown in (a) of
The contact terminal 46b is connected with the AC power source and a triac (not shown) via a bundle wire 48. The heater clip 47 is, as shown in (b) of
With reference to (d) of
In this embodiment, the shape of the supporting surface, of the supporting member 38, where the supporting member 38 supports the heater 37 via the metal plate 39 may be the crown shape similarly as in Embodiment 1 and may also be a shape of a flat surface parallel to the surface of the metal plate 39.
The substrate 37a in this embodiment has a shape of a rectangular parallelopiped of 270 mm in width with respect to the direction perpendicular to the recording material feeding direction, 5.8 mm in width with respect to the recording material feeding direction, and 1.0 mm in this embodiment, and is formed of alumina. Further, the heat generating resistor 37b is 222 mm in length with respect to the direction perpendicular to the recording material feeding direction, and the length is the same as the width of the contact region of the heat conduction member 39 with the heater 37.
A mechanism for uniformizing the heat of the heater 37 with respect to the direction perpendicular to the recording material feeding direction in a status in which a small-sized recording material is continuously subjected to fixing to generate non-sheet-passing portion temperature rise will be described.
In this embodiment, alumina used as the material for the substrate 37a has thermal conductivity of about 26 W/mK, and aluminum used as the material for the heat conduction member 39 has thermal conductivity of about 230 W/mK. In the case where the thermal conductivity of the heat conduction member 39 is larger than the thermal conductivity of the substrate 37a, the heat of the heater 37 becomes easy to be uniformized. As the material for the heat conduction member 39, in addition to aluminum, it is also possible to use copper or graphite sheet. As shown in (a) of
Here, a relationship between a width of the heat generating resistor 37b of the heater 37 and a width of the heat conduction member 39 with respect to the direction perpendicular to the recording material feeding direction will be described. Parts (a) and (b) of
In view of the above-described circumstances, in this embodiment, with respect to the direction perpendicular to the recording material feeding direction, the width of the heat generating resistor 37b and the width of the heat conduction member 39 are made substantially equal to each other. Further, as shown in (b) of
Next, the reason why the bent portion 39a in this embodiment is provided at the end portion of the heat conduction member 39 with respect to the recording material will be described. As Comparison example for this embodiment, as shown in
Here, a deformation amount ΔL (mm) of the heat conduction member 390 due to the thermal expansion with respect to the direction perpendicular to the recording material feeding direction can be calculated by the following equation:
ΔL=L×α×ΔT,
where α represents coefficient of linear expansion, and ΔT represents a difference in temperature.
The heat conduction member 390 is 222 mm in width L, 2.3×10−5/° C. in the coefficient α of linear expansion of aluminum, and about 200° C. in temperature of the substrate 37a during fixing, and therefore assuming that normal temperature is 20° C., ΔT is 180° C. When the calculation is made by substituting these values into the above equation, ΔL is 0.92 mm. Similarly, a deformation amount ΔM (mm) of the heat conduction member 390 due to the thermal expansion with respect to the recording material feeding direction is 0.02 mm. On the other hand, a liquid crystal polymer (“SUMIKA SUPER LCP E5204L”, manufactured by Sumitomo Chemical Company) as a material for the supporting member 380 is 1.3×10−5/° C. in coefficient α of linear expansion, and therefore elongates in the direction perpendicular to the recording material feeding direction by 0.52 mm.
In the fixing device in Comparison example, in some cases, the following problem due to a difference in thermal expansion coefficient between the supporting member 380 and the heat conduction member 390 occurs. Parts (a) to (d) of
On the other hand, the heat conduction member 39 in Embodiment 3 includes the bent portion 39a formed by bending the end portion thereof with respect to the recording material central portion in the direction crossing the direction perpendicular to the recording material feeding direction. The heat conduction member 39 is locked to the supporting member 38 with respect to the direction perpendicular to the recording material feeding direction by inserting the bent portion 39a into the hole 38a of the supporting member 38. Further, the bent portion 39a is provided at a substantially central portion with respect to the direction perpendicular to the recording material feeding direction. The bent portion 39a in this embodiment is 8 mm in width a with respect to the direction perpendicular to the recording material feeding direction, and therefore is 0.03 mm in thermal expansion amount with respect to the direction perpendicular to the recording material feeding direction, thus being very small in thermal expansion amount. For that reason, play of the width of the hole 38a relative to the bent portion 39a can be made small, and therefore positional deviation of the heat conduction member 39 relative to the supporting member 38 can be made small. As a result, the position of the heater 37 with respect to the direction perpendicular to the recording material feeding direction is determined by the supporting member 38, and therefore the positional deviation of the heat conduction member 39 relative to the heater 37 can be made small. As described above, in this embodiment, the width of the hole 38a is set at 8.1 mm. Further, the end portions of the heat conduction member 39 with respect to the direction perpendicular to the recording material feeding direction are free, and therefore the bent portion 39a is not deformed by thermal expansion and thermal contraction of the heat conduction member 39 itself. Further, a thermal expansion amount ΔM of the heat conduction member 39 with respect to the recording material feeding direction is 0.02 mm, and therefore also with respect to the recording material feeding direction different from Comparison example, the bent portion 39a is prevented from opening largely. Further, the bent portion 39a is formed by being bent in the direction crossing the direction perpendicular to the recording material feeding direction, and therefore even when the force in the recording material feeding direction is applied to the bent portion 39a, the bent portion 39a does not deform in the open direction.
As described above, in this embodiment, the state in which the heat conduction member 39 is locked to the supporting member 38 is maintained, and therefore such an effect that the position of the heat conduction member 39 is not readily deviated relative to the heater 37 is achieved. As a result, it is possible to suppress the non-sheet-passing portion temperature rise without lowering the fixing property at the end portions with respect to the direction perpendicular to the recording material feeding direction.
Incidentally, the heat conduction member 39 is locked to the supporting member 38 also with respect to the recording material feeding direction by providing the bent portion 39a at an upstream end portion with respect to the recording material feeding direction and then by inserting the bent portion 39a into the hole 38a.
In this embodiment, the bent portion 39a is provided at the end portion of the heat conduction member 39 with respect to the recording material feeding direction, but may also be provided at a central portion of the heat conduction member 39 with respect to the recording material feeding direction. That is, a constitution in which a bent portion formed by bending a part of the heat conduction member itself in the direction crossing the direction perpendicular to the recording material feeding direction is used as a locking portion and the heat conduction member is locked to the supporting member with respect to the direction toner the recording material feeding direction may only be required. However, when the bent portion 39a is formed by bending and erecting the central portion of the heat conduction member 39 with respect to the recording material feeding direction, a hole is formed in the heat conduction member 39 to lower a heat conduction performance for uniformizing the heat of the heater 37, and therefore the locking portion may preferably be formed as a separate member.
In recent years, in order to shorter the FPOT (first print cut time), shortening of a warm-up time of the fixing device has been required. Therefore, in this embodiment, a constitution in the case where thermal capacity of the heat conduction member is made smaller will be described.
A heat conduction member 391 in this embodiment is made small in thermal capacity by decreasing the width thereof with respect to the recording material feeding direction and the thickness thereof compared with those in Embodiment 3. In this embodiment, as the heat conduction member 391, a 0.2 mm-thick aluminum plate of 3 mm in width with respect to the recording material feeding direction is used. The thermal capacity of the heat conduction member 391 is 40% of the heat conduction member 39 in Embodiment 3, so that the warm-up time can be shortened by 0.1 sec. In this embodiment, a constitution is the same as that in Embodiment 3 except for the heat conduction member 391 and a supporting member 381, and therefore will be omitted from description.
A characteristic constitution of the heat conduction member 391 in this embodiment is that a plurality of locking portions are provided with respect to the direction perpendicular to the recording material feeding direction. As in this embodiment, in the case where the heat conduction member 391, which is thin and small in rigidity, as in this embodiment is used, if the locking portion is provided singly at the central portion as in Embodiment 3, the heat conduction member is deformed in a bow-like shape with respect to the recording material feeding direction as shown in
Therefore, in this embodiment, with respect to the direction perpendicular to the recording material feeding direction, the heat conduction member 391 includes a bent portion 391a (first locking portion) at a central portion, a bent portion 391c (second locking portion) at one end portion and a bent portion 391d (third locking portion) at the other end portion. By inserting these bent portions into, as locked portions, holes 381a, 381c and 381d, respectively, so that the heat conduction member 391 is locked to the supporting member 381. The bent portion 391a is constituted so as to perform the function as the position with respect to at least the direction perpendicular to the recording material feeding direction, and the bent portions 391c and 391d are constituted so as to perform the function as the locking portion with respect to at least the recording material feeding direction. Sizes of the bent portion 391a and the hole 381a were set at a=8 mm, b=3 mm, c=8.1 mm and d=0.3 mm. Sizes of the bent portions 391c and 391d and the holes 381c and 381d were set at the same values as those of the bent portion 391a and the hole 381a. Further, in the contact region of the heat conduction member 391 with the heater 37, the heat conduction member 391 is 222 mm in width L with respect to the direction perpendicular to the recording material feeding direction and 3 mm in width M with respect to the recording material feeding direction.
Incidentally, there is no need to form the bent portions 391a, 391c and 391d in the same size. Further, the bent portions 391c and 391d may also be provided at end portions with respect to the direction perpendicular to the recording material feeding direction as shown in (a) of
As described above, Embodiment 4 has an effect such that the position of the heat conduction member 391 relative to the heater 37 is not readily deviated while decreasing the thermal capacity of the heat conduction member 391.
There is an advantage such that when the press are in the nip is released, engagement (locking) between the heat conduction member and the supporting member is less eliminated with a longer length of the bent portion as the locking portion of the heat conduction member. However, the longer length of the bent portion leads to an increased thermal capacity of the heat conduction member, and in addition, heat is liable to dissipate from the bent portion into the air, and therefore the warm-up time of the fixing device is increased.
Therefore, as the heat conduction member, a member which has a shorter bent portion and which is less disengaged from the supporting member is required.
Therefore, a heat conduction member 392 in this embodiment will be described with reference to
A further specific constitution of the heat conduction member 392 in this embodiment will be described. The heat conduction member 392 is a 0.2 mm thick aluminum plate of 3 mm in width M with respect to the recording material feeding direction. The heat conduction member 392 includes a bent portion 392a at the end portion with respect to the recording material feeding direction similarly as in Embodiment 3 and 4, and the by bent portion 392a, the heat conduction member 392 itself is locked to the supporting member 382 with respect to the direction perpendicular to the recording material feeding direction. In Embodiment 5, the heat conduction member 392 further includes the bent portions 392c and 392d, each having a length b of 2 mm at the end portions with respect to the direction perpendicular to the recording material feeding direction, and each of the bent portions 392c and 392d is provided with a square through hole 392e having a size of 1 mm×1 mm. On the other hand, as shown in (b) of
In the constitution in this embodiment, in the case where the pressure in the nip is eliminated, even when the length b of each of the bent portions 392c and 392d is short, the heat conduction member 392 is not readily disengaged from the supporting member 382 in an arrow direction in (b) of
Incidentally, as described in Embodiment 5, the heat conduction member 392 includes the bent portion 392a, and therefore different from Comparison example for Embodiment 3, the bent portions 392c and 392d are prevented from opening.
As described above, the fixing device in this embodiment has, in addition to an effect that the heat conduction member 392 is not readily deviated relative to the heater 37, an effect that the constitution in this embodiment contributes to shortening of the warm-up time.
Incidentally, in this embodiment, the constitution in which each of the bent portions 392c and 392d is provided with the hole 392e is employed, but the bent portions 392a may be provided with the hole 392e and then may be engaged with the supporting member 382. In that case, each of the bent portions 392c and 392d is not necessarily be required to be provided with the hole 392e to be engaged with the supporting member 382.
Further, in Embodiments 3 to 5, the locking portion is constituted by the bent portion provided at the end portion of the heat conduction member, but a similar effect is obtained by employing a constitution in which a separate member is mounted, as the locking portion, to the heat conduction member in place of the bent portion.
Further, the problem in Embodiments 3 to 5 described above results from the difference in coefficient of linear expansion between the supporting member and the heat conduction member, and occurs unless those members are formed of the same material. Accordingly, in the case where the heat conduction member and the supporting member are formed of different materials, the effect of the present invention is achieved.
Further, the constitutions of Embodiments 3 to 5 are not limited to those for the fixing device but may also be applicable to an image heating apparatus (device) for heating a toner image.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application is a Divisional Application of U.S. patent application Ser. No. 14/955,334, filed on Dec. 1, 2015, which is a Divisional Application of U.S. patent application Ser. No. 14/141,687, filed on Dec. 27, 2013, and issued as U.S. Pat. No. 9,229,388, on Jan. 5, 2016. These U.S. patent applications claim the benefit of priority from Japanese Patent Application Nos. 2012-288234, filed Dec. 28, 2012, and 2013-122215, filed Jun. 10, 2013. Each of these documents is incorporated by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-288234 | Dec 2012 | JP | national |
| 2013-122215 | Jun 2013 | JP | national |
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 14955334 | Dec 2015 | US |
| Child | 15294942 | US | |
| Parent | 14141687 | Dec 2013 | US |
| Child | 14955334 | US |
