JP2018049093A - Heat generating unit, fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat generating unit that, when cracks are generated in the heat generating unit, effectively shuts off energization to a heat generating part.SOLUTION: A heat generating unit comprises: a substrate 27; a heat generating part 26 that is provided on the substrate 27; power feeding parts 29a and 30a that are provided on the substrate 27 and feed power to the heat generating part 26; and conductive parts 29b and 30b that are provided on the substrate 27 and supply the power fed by the power feeding parts 29a and 30a to the power generating part 26 through a conductive path (conductive parts 29b4 and 30b4) over a short direction of the heat generating part 26 on the extension in the longitudinal direction of the heat generating part 26.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a heat generating unit for heating a recording material and an image forming apparatus including a fixing device using the heat generating unit.

  A fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or a printer has, for example, the following configuration. A heater as a heating member having a heating resistor on a ceramic substrate, a flexible member that moves while contacting the heater, and a pressure roller that forms a nip portion with the heater via the flexible member, There are some that have

  The recording material carrying the unfixed image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the image on the recording material is heated and fixed on the recording material. This fixing device has an advantage that it takes a short time to raise the temperature to a fixing possible temperature after energizing the heater. In addition, this type of fixing device has an advantage that power consumption during standby waiting for a print command is small.

  However, the heater may crack due to thermal stress or mechanical stress at the time of abnormal temperature rise. Even in this case, if the energization path is secured, the heater is energized and generates heat.

  In order to solve such a problem, in Patent Document 1, a temperature detection type safety element is installed at an end portion in the electrode side direction in the longitudinal direction of the heating resistor. As a result, the temperature detection type safety element operates regardless of where the heater breaks in the longitudinal direction. Thereby, electricity supply to a heater can be interrupted | blocked.

JP 2008-192398 A

  However, in Patent Document 1, a temperature detection type safety element (thermistor, temperature fuse, thermo switch, thermostat, or the like) may not operate depending on a cracked state, a cracked position, or a cracking method of the heater. In this case, it is not always possible to completely cut off the power supply to the heater. Further, the broken heater is heated to a temperature at which the temperature detection type safety element operates. This cuts off the energization. For this reason, the state in which the cracked heater is generating heat continues for several seconds, and there is a risk of smoking or ignition, so safety was insufficient.

  The present invention solves the above-mentioned problems, and an object of the present invention is to provide a heat generating unit that can effectively cut off the power supply to the heat generating portion when a crack occurs in the heat generating unit. .

  A typical configuration of the heat generating unit according to the present invention for achieving the above object includes a substrate, a heat generating portion provided on the substrate, a power supplying portion provided on the substrate and supplying power to the heat generating portion, A conductive portion that is provided on the substrate and that supplies power from the power feeding portion to the heat generating portion by a conductive path extending in a longitudinal direction of the heat generating portion and extending in a short direction of the heat generating portion. Features.

  According to the present invention, when a crack occurs in the heat generating unit, it is possible to effectively cut off the power supply to the heat generating portion.

1 is an explanatory cross-sectional view illustrating a configuration of an image forming apparatus including a heat generating unit according to the present invention in a fixing device. FIG. 3 is an explanatory cross-sectional view illustrating a configuration of a fixing device including a heat generating unit according to the present invention. (A) is a plane explanatory view showing the composition of a 1st embodiment of the exothermic unit concerning the present invention. (B) is a back surface explanatory view showing the composition of the exothermic unit of a 1st embodiment. (C) is a block diagram which shows the GG cross section of (a), and the structure of a control system. (D) is HH sectional drawing of (a). It is the elements on larger scale near the left end part of Drawing 3 (a). It is plane explanatory drawing which shows a mode that the crack shown with the fracture | rupture line D generate | occur | produced in the heat generating unit of 1st Embodiment. (A) is a plane explanatory view showing the composition of a 2nd embodiment of the exothermic unit concerning the present invention. (B) is back explanatory drawing which shows the structure of the heat-emitting unit of 2nd Embodiment. (C) is a block diagram which shows the II cross section of (a), and the structure of a control system. (D) is JJ sectional drawing of (a). (A) is the elements on larger scale near the left end part of Drawing 6 (a). (B) is the elements on larger scale of the right end part vicinity of Fig.6 (a). (A) is the elements on larger scale which show a mode that the crack shown by the fracture | rupture line E1 generate | occur | produced in the left end part vicinity of Fig.6 (a). (B) is the elements on larger scale which show a mode that the crack shown by the fracture | rupture line E2 generate | occur | produced in the right side edge part vicinity of Fig.6 (a).

  An embodiment of an image forming apparatus provided with a heat generating unit according to the present invention in a fixing device will be specifically described with reference to the drawings.

  First, the configuration of a first embodiment of an image forming apparatus provided with a heat generating unit according to the present invention in a fixing device will be described with reference to FIGS.

<Image forming apparatus>
A configuration of an image forming apparatus provided with a heat generating unit according to the present invention in a fixing device will be described with reference to FIG. FIG. 1 is an explanatory cross-sectional view showing a configuration of an image forming apparatus provided with a heat generating unit according to the present invention in a fixing device. An image forming apparatus 12 shown in FIG. 1 is a laser printer using a transfer type electrophotographic process. In FIG. 1, reference numeral 1 denotes a photosensitive drum 1 made of a rotating drum type electrophotographic photosensitive member as an image carrier. The photosensitive drum 1 rotates at a predetermined peripheral speed in the clockwise direction of FIG. The photosensitive drum 1 is configured by forming a photosensitive material such as an OPC (Organic Photo Conductor) or an amorphous silicon (a-Si) drum on a cylindrical substrate such as aluminum or nickel.

  The surface of the photosensitive drum 1 rotating in the clockwise direction in FIG. 1 is uniformly charged on the surface of the photosensitive drum 1 by rotating in contact with a charging roller 2 serving as a charging unit. Scanning exposure is performed by irradiating the surface of the photosensitive drum 1 uniformly charged by the charging roller 2 with laser light L modulated in accordance with the image information output from the laser scanner 3 as image exposure means. The As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. Toner (developer) is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 1 by a developing roller 4a serving as a developer carrying member provided in the developing device 4 serving as a developing unit to form a toner image. Developed.

  On the other hand, the recording material P accommodated in the feeding cassette 5 is fed out by the feeding roller 6 and separated and fed one by one in cooperation with a separating unit (not shown). The leading end portion of the recording material P fed by the feeding roller 6 is applied to the nip portion of the registration roller 7 that has been stopped, and is handled by the strength of the waist of the recording material P to correct skewing. Is done.

  A toner image formed on the surface of the photosensitive drum 1 rotating in the clockwise direction in FIG. 1 rotates and moves to a transfer nip portion N1 with a transfer roller 9 serving as a transfer unit provided facing the surface of the photosensitive drum 1. To do. In synchronization with this timing, the recording material P is conveyed to the transfer nip portion N1 by the registration roller 7 via the conveyance path 8a. The registration roller 7 has a control unit 41 shown in FIG. 6 so that the leading edge position of the toner image formed on the surface of the photosensitive drum 1 and the leading edge position of the recording material P enter the transfer nip portion N1 at the same timing. The drive is controlled by.

  The recording material P introduced into the transfer nip portion N1 is nipped and conveyed by the photosensitive drum 1 and the transfer roller 9 at the transfer nip portion N1. In this process, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 9 from a transfer bias power source (not shown). As a result, the toner image carried on the surface of the photosensitive drum 1 is electrostatically transferred onto the recording material P.

  The recording material P onto which the toner image has been transferred at the transfer nip N1 is separated from the surface of the photosensitive drum 1 and conveyed to the fixing device 11 serving as a fixing unit through the conveyance path 8b. In the process in which the recording material P to which the toner image has been transferred passes through the fixing nip portion N2 between the fixing film 22 provided in the fixing device 11 and the pressure roller 24, the toner image is heated and pressed and melted. The recording material P is heat-fixed. The recording material P exiting the fixing device 11 is nipped and conveyed by the conveyance roller 15, passes through the conveyance path 8 c, and is further discharged from the discharge port 13 onto the discharge tray 14 by the discharge roller 16.

  Toner, paper dust and the like remaining on the surface of the photosensitive drum 1 after the transfer of the toner image are scraped off and removed by a cleaning blade 10a provided in a cleaning device 10 serving as a cleaning unit. Thus, after the surface of the photosensitive drum 1 is cleaned, it is repeatedly used for image formation.

<Fixing device>
Next, the configuration of the fixing device including the heat generating unit according to the present invention will be described with reference to FIG. FIG. 2 is an explanatory cross-sectional view illustrating the configuration of the fixing device 11 including the heat generating unit according to the present invention. In the following description, each direction regarding the fixing device 11 or each member constituting the fixing device 11 is as follows. The longitudinal direction is a direction (width direction) orthogonal to the conveying direction of the recording material P indicated by the arrow K in FIG. 2, and the short direction is the direction of the recording material P indicated by the arrow K in FIG. The same direction as the transport direction.

  The fixing device 11 shown in FIG. 2 has an endless structure in which a ceramic heater 23 as a heat generating unit, an overcoat layer 28 (heat generating surface) and an inner peripheral surface of the heater 23 (heat generating unit) are slidably provided. And a fixing film 22 as a flexible member. Furthermore, a stay 21 as a guide member and a pressure roller 24 as a pressure member that forms a fixing nip portion N2 between the outer peripheral surface of the fixing film 22 (flexible member) are provided. The stay 21, the fixing film 22, the heater 23, and the pressure roller 24 are all constituted by members that are elongated in the longitudinal direction from the front side to the back side in FIG.

  The stay 21 is formed in a saddle-shaped cross section using a material having heat resistance and rigidity. A heater 23 is supported in a concave groove 21 a having a U-shaped cross section provided at a position facing the pressure roller 24 of the stay 21. The fixing film 22 is formed in an endless (cylindrical) shape using a heat-resistant flexible material. The fixing film 22 is externally fitted so as to be rotatable along the outer peripheral surface of the stay 21. The inner peripheral length of the fixing film 22 is set to be, for example, about 3 mm longer than the outer peripheral length of the stay 21. As a result, the fixing film 22 is externally fitted so as to be rotatable along the outer peripheral surface of the stay 21 with a margin in the inner peripheral length.

  The heater 23 is fixed in a concave groove 21a of the stay 21 by placing a ceramic substrate 27 having electrical insulation with the surface thereof facing the fixing nip portion N2 facing the pressure roller 24. As a result, the heat-resistant overcoat layer 28 of the heater 23 is slid in contact with the inner peripheral surface of the fixing film 22. A lubricant (not shown) is interposed between the inner peripheral surface of the fixing film 22 and the outer peripheral surface of the stay 21. As a result, the sliding resistance when the outer peripheral surface of the stay 21 and the inner peripheral surface of the fixing film 22 come into contact with each other to slide and rotate is reduced.

  Next, the configuration of each member provided in the fixing device 11 will be described in more detail.

<Fixing film>
The fixing film 22 needs to reduce the heat capacity and advance the time to rise to the target fixing temperature. Therefore, the film thickness of the fixing film 22 is preferably 90 μm or less. As a material for the fixing film 22, a single layer film of PTFE (Polytetrafluoroethylene) having heat resistance can be applied. Furthermore, a single layer film of PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) can be applied. Furthermore, a single layer film such as FEP (tetrafluoroethylene hexafluoropropylene copolymer) can be applied.

  Furthermore, as a material for the fixing film 22, a film such as polyimide, polyamideimide, polyether ether ketone (PEEK), or the like can be used as a base material. Furthermore, films such as polyethersulfone (PES) and polyphenylene sulfide (PPS) can be used as a base material.

  And the composite layer film which coat | covered polytetrafluoroethylene (PTFE; Polytetrafluoroethylene) on the outer peripheral surface of those base materials can be used. Furthermore, the composite layer film which coat | covered PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) on the outer peripheral surface of those base materials can be used. Furthermore, the composite layer film which coat | covered FEP (tetrafluoroethylene hexafluoropropylene copolymer) etc. on the outer peripheral surface of those base materials can be used.

  In this embodiment, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) was coated on the outer peripheral surface of a polyimide film having a thickness of 75 μm. Furthermore, polytetrafluoroethylene (PTFE; Polytetrafluoroethylene) was coated. This was used as the fixing film 22. The outer diameter of the fixing film 22 was 24.0 mm.

<Stay>
For the stay 21, for example, a high heat-resistant resin such as polyimide, polyamideimide, or polyether ether ketone (PEEK) can be applied. Furthermore, high heat-resistant resins such as polyphenylene sulfide (PPS) and liquid crystal polymer can be applied. Further, it can be composed of a composite material of these resins and ceramic, metal, glass or the like.

  The stay 21 of this embodiment was formed in a saddle shape in cross section with a liquid crystal polymer. The stay 21 is supported by a pair of side plates provided at the fixing device 11 at both ends in the longitudinal direction. On the surface of the stay 21 facing the pressure roller 24, a concave groove 21a having a U-shaped cross section is provided along the longitudinal direction. A heater 23 is supported in the concave groove 21a.

<Pressure roller>
The pressure roller 24 includes a cored bar 24a, an elastic layer 24b provided around the cored bar 24a, and an outermost release layer 24c provided around the elastic layer 24b. Configured. The pressure roller 24 is rotatably supported by a pair of side plates provided at the fixing device 11 at both ends in the longitudinal direction of the cored bar 24a.

  Aluminum was used for the cored bar 24a of this embodiment. The elastic layer 24b is made of silicon rubber blended with microballoons. The release layer 24c was a PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) tube.

  The outer diameter of the pressure roller 24 was 20 mm. The thickness of the release layer 24c was 30 μm. In the pressure roller 24 arranged in parallel with the fixing film 22 below the fixing film 22 shown in FIG. 2, both ends of the cored bar 24a are pressed toward the stay 21 by a pressing means such as a pressure spring. Yes. As a result, the pressure roller 24 has a fixing nip portion N2 having a predetermined width necessary for heating and fixing the unfixed toner image on the recording material P with the fixing film 22 sandwiched between the surface of the pressure roller 24 and the heater 23. Is forming.

<Heat generation unit>
Next, the structure of the heat generating unit of this embodiment will be described with reference to FIG. FIG. 3A is an explanatory plan view showing the configuration of the heat generating unit of the present embodiment. FIG. 3B is a rear view illustrating the configuration of the heat generating unit of the present embodiment. FIG.3 (c) is a block diagram which shows the structure of the GG cross section and control system of Fig.3 (a). FIG.3 (c) is HH sectional drawing of Fig.3 (a).

  As shown in FIG. 3C, the heater 23 as the heat generating unit shown in FIG. 3 includes an electrically insulating substrate 27 and a longitudinal direction of the substrate 27 on the substrate 27 (on the substrate) (FIG. 3). And a heat generating portion 26 provided along the horizontal direction of (a). Furthermore, a first electrode 29c and a second electrode 30c having electrical conductivity are provided on the substrate 27 along the longitudinal direction of the heat generating portion 26 (the left-right direction in FIG. 3A). The first and second electrodes 29c and 30c have one end side (upper end side in FIG. 3A) and the other end portion in the short side direction (up and down direction in FIG. 3A) of the heat generating portion 26. Each is electrically connected to the lower end side of FIG.

  Furthermore, it has the 1st electroconductive part 29b and the 2nd electroconductive part 30b which are provided on this board | substrate 27, and were electrically connected to the 1st and 2nd electrodes 29c and 30c, respectively. . Furthermore, a first power supply unit 29a and a second power supply unit 30a, which are provided on the substrate 27 and are electrically connected to the first and second conductive units 29b and 30b, respectively, are provided. Have.

  Further, the heater 23 includes a heat generating portion 26 provided on the substrate 27, first and second electrodes 29c and 30c, first and second conductive portions 29b and 30b, and first and second electrodes. An overcoat layer 28 having electrical insulation covering the power feeding portions 29a and 30a is provided. In the present embodiment, a heat-resistant glass layer having a thickness of 60 μm having electrical insulation is used as the overcoat layer 28.

  In FIG. 3A, the overcoat layer 28 is omitted so that the relationship between the electrodes 29c and 30c and the heat generating portion 26 can be easily understood. The main purpose of the overcoat layer 28 is to ensure electrical insulation between the heat generating portion 26 and the surface of the heater 23 and sliding properties between the surface of the heater 23 and the inner peripheral surface of the fixing film 22. . As shown in FIG. 3A, the power feeding portions 29a and 30a, the conductive portions 29b and 30b, and the electrodes 29c and 30c having conductivity have a silver / palladium (Ag · Pd) screen pattern on the surface of the substrate 27. It is formed using. Thus, the power feeding portions 29a and 30a, the conductive portions 29b and 30b, and the electrodes 29c and 30c are electrically connected.

  On the surface of the substrate 27, a long heat generating portion 26 is provided in an electrically connected manner between the electrodes 29c and 30c. The AC power supply 43 shown in FIG. 3C causes an AC current to flow between the power supply units 29a and 30a, thereby supplying the power supply unit 29a, the conductive unit 29b, the electrode 29c, the heat generating unit 26, the electrode 30c, the conductive unit 30b, and the power supply unit 30a. An alternating current flows between them, and Joule heat is generated in the heat generating portion 26. As a result, the heater 23 generates heat and the fixing device 11 is heated to a predetermined fixing temperature. The power feeding units 29a and 30a provided on the surface of the substrate 27 (on the substrate) supply power to the heat generating unit 26 provided on the surface of the substrate 27 (on the substrate).

  The total resistance value of the heater 23 of this embodiment is 20Ω. The heater 23 is elongated in the longitudinal direction, and a heat generating portion 26 is provided on one surface (surface on the fixing nip portion N2 side) of the substrate 27 having heat resistance, electrical insulation, and good thermal conductivity. Further, on one surface of the substrate 27, power supply portions 29a and 30a, conductive portions 29b and 30b, and electrodes 29c and 30c are provided.

  The electrode 29c is in electrical contact with one end portion (the upper end portion in FIG. 3A) along the longitudinal direction of the heat generating portion 26. The electrode 29c and the power feeding part 29a are electrically connected by a conductive part 29b. The electrode 30c is in electrical contact with the other end (the lower end in FIG. 3A) along the longitudinal direction of the heat generating portion 26. The electrode 30c and the power feeding part 30a are electrically connected by the conductive part 30b. The overcoat layer 28 having heat resistance and electrical insulation covers the power supply portions 29a and 30a, the conductive portions 29b and 30b, the electrodes 29c and 30c, and the heat generating portion 26 provided on the substrate 27 throughout. .

  On the surface of the substrate 27 (surface on the fixing nip portion N2 side), long electrodes 29c and 30c are provided on one end side and the other end side in the short direction (vertical direction in FIG. 3A), respectively. ing. The electrodes 29c and 30c are provided in parallel with each other at a predetermined interval along the longitudinal direction of the substrate 27 (the left-right direction in FIG. 3A). Between each electrode 29c, 30c, the heat generating part 26 having a positive resistance temperature characteristic in which the resistance value increases as the temperature rises is electrically connected.

  One end portions 29b1 and 30b1 of the conductive portions 29b and 30b are electrically connected to the substantially central portions of the electrodes 29c and 30c in the longitudinal direction (left and right direction in FIG. 3A), respectively. One end portions 29b1 and 30b1 of the conductive portions 29b and 30b are located in an area through which the recording material P of the minimum size used in the image forming apparatus 12 always passes. In the image forming apparatus 12 of the present embodiment, the recording material P is conveyed through the fixing nip portion N2 with the central reference.

  On the other hand, at both ends in the longitudinal direction of the substrate 27 (the left-right direction in FIG. 3A), the other end portions of the conductive portions 29b and 30b in which one end portions 29b1 and 30b1 are electrically connected to the electrodes 29c and 30c, respectively. Are respectively provided with power feeding portions 29a and 30a. In this embodiment, the power feeding unit 29a is provided on the upper right side of FIG. 3A on the substrate 27, and the power feeding unit 30a is provided on the lower left side of FIG. Therefore, the conductive portions 29b and 30b are each formed in a crank shape.

<Conductive part>
Next, the configuration of the conductive portions 29b and 30b constituting the energization path from the power feeding portions 29a and 30a to the electrodes 29c and 30c will be described. As shown in FIG. 3A, the power feeding portions 29a and 30a are respectively arranged on the upper and lower sides at the left and right end portions in the longitudinal direction of the substrate 27 (left and right direction in FIG. 3A). In this case, the conductive portions 29b and 30b that are output from the power feeding portions 29a and 30a are configured as follows. Folded portions folded back from the power feeding portions 29a, 30a side of the substrate 27 on the other end side opposite to the power feeding portions 29a, 30a side in the short direction of the substrate 27 (vertical direction in FIG. 3A). 29b2 and 30b2 are provided.

  The conductive portions 29b4 and 30b4 extend from the folded portions 29b2 and 30b2 toward the opposite side of the short side direction (vertical direction in FIG. 3A) of the substrate 27 to the positions on the power feeding portions 29a and 30a side. Return. Then, it extends along the longitudinal direction of the substrate 27 (left and right direction in FIG. 3A) to one end portions 29b1 and 30b1 provided at substantially the central portion in the longitudinal direction of the heat generating portion 26, and at the one end portions 29b1 and 30b1. The electrodes 29c, 30c are electrically connected.

  That is, the conductive portions 29b and 30b are provided on the surface of the substrate 27 (on the substrate) and extend in the short direction of the heat generating portion 26 (vertical direction in FIG. 3A) on the longitudinal extension of the heat generating portion 26. Power is supplied from the power feeding portions 29a and 30a to the heat generating portion 26 by the conductive portions 29b4 and 30b4 that are the conductive paths straddling.

  Consider the folded portion 29b2 on the power supply portion 29a side of the conductive portion 29b connected to the electrode 29c shown in FIG. Furthermore, a position 29b3 in which the conductive portion 29b4 extends from the folded portion 29b2 along the short direction of the substrate 27 (upward in FIG. 3A) and returns to the power feeding portion 29a side is considered. Further, an end 29c1 on the power feeding portion 29a side of the electrode 29c and an end 29c2 on the power feeding portion 30a side of the electrode 29c are considered.

  Further, consider the folded portion 30b2 on the power feeding portion 30a side of the conductive portion 30b connected to the electrode 30c shown in FIG. Further, consider a position 30b3 in which the conductive portion 30b4 extends from the folded portion 30b2 along the short direction of the substrate 27 (downward in FIG. 3A) and returns to the power feeding portion 30a side. Further, an end 30c2 on the power feeding unit 30a side of the electrode 30c and an end 30c1 on the power feeding unit 29a side of the electrode 30c are considered.

  The folded portion 29b2 of the conductive portion 29b and the position 29b3 returned from the folded portion 29b2 to the feeding portion 29a side are shorter than the end portions 29c1 and 30c1 on the feeding portion 29a side of the electrodes 29c and 30c. It is located outside (in the vertical direction in FIG. 3A).

  Further, the folded portion 30b2 of the conductive portion 30b and the position 30b3 returned from the folded portion 30b2 to the power feeding portion 30a side are configured as follows. The electrodes 29c and 30c are positioned outside the end portions 29c2 and 30c2 on the power feeding portion 30a side in the short direction of the substrate 27 (vertical direction in FIG. 3A).

  In other words, in the present embodiment, the conductive portions 29b4 and 30b4 which are at least a part of the first and second conductive portions 29b and 30b are supplied with power in the longitudinal direction of the substrate 27 (left and right direction in FIG. 3A). It arrange | positions between the part 29a, 30a and the heat generating part 26. FIG. Further, the conductive portions 29b4 and 30b4 which are at least a part of the first and second conductive portions 29b and 30b are formed in the first and second directions in the short direction of the substrate 27 (vertical direction in FIG. 3A). The electrodes 29c and 30c are straddled.

  Further, the lengths S and X in the short direction (vertical direction in FIG. 3A) of the conductive portions 29b4 and 30b4 which are at least a part of the first and second conductive portions 29b and 30b. Is set as follows. It is larger than the distances T and Y from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 3A).

  FIG. 4 is a partially enlarged view of the vicinity of the left end portion of FIG. The substrate 27 of the heater 23 shown in FIGS. 3 and 4 is made of, for example, a ceramic material such as alumina or aluminum nitride. The length of the substrate 27 of the present embodiment in the longitudinal direction (left-right direction in FIG. 3A) is 270 mm. The length (width) of the substrate 27 in the short direction (vertical direction in FIG. 4) is 8 mm. Further, the thickness of the substrate 27 in the vertical direction in FIG. 3C is 1 mm.

  Further, the widths of the electrodes 29c and 30c in the vertical direction in FIG. 4 are each 0.7 mm. The length of the heat generating portion 26 in the longitudinal direction (left and right direction in FIG. 3A) is 221 mm. The length (width) of the heat generating portion 26 in the short direction (vertical direction in FIG. 4) is 3.2 mm. Further, the thickness of the heat generating portion 26 in the vertical direction in FIG. 3C is 10 μm.

The heat generating portion 26 is a paste formed by kneading ruthenium oxide (RuO ₂ ), glass powder (inorganic binder), and organic binder, and formed on the substrate 27 in a line band shape by screen printing. is there. As a material of the heat generating portion 26, an electric resistance material such as silver / palladium (Ag / Pd), tantalum nitride (Ta2N) may be used in addition to ruthenium oxide.

  Next, a configuration in the vicinity of the power feeding unit 30a provided on the lower left side of FIG. Consider the folded portion 30b2 that once extends upward from FIG. 4 from the power feeding portion 30a of the conductive portion 30b that connects the power feeding portion 30a and the electrode 30c. Further, a position 30b3 returned from the folded portion 30b2 to the power feeding portion 30a side is considered. Then, the distance along the short direction (vertical direction in FIG. 4) of the substrate 27 between the outermost edge of the folded portion 30b2 and the position 30b3 returned from the folded portion 30b2 to the power feeding portion 30a side is defined as X. And The distance X is the length of the conductive portion 30b4 in the short direction (vertical direction in FIG. 4) of the substrate 27.

  Further, the distance along the short side direction (vertical direction in FIG. 4) of the substrate 27 between the outermost edges of the electrodes 29c and 30c is Y. The distance Y is a distance from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 4). The folded portion 30b2 and the position 30b3 returned from the folded portion 30b2 through the conductive portion 30b4 to the power feeding portion 30a side are the power feeding portion 30a, the heat generating portion 26, and the longitudinal direction of the substrate 27 (left and right direction in FIG. 4). Located between.

  Further, the conductive portion 30b4 between the folded portion 30b2 and the position 30b3 returned from the folded portion 30b2 to the power feeding portion 30a side is configured as follows. In the short direction of the substrate 27 (up and down direction in FIG. 4), the width of the heat generating portion 26 provided between the electrodes 29c and 30c extends in the short direction (up and down direction in FIG. 4).

  Further, along the short direction (vertical direction in FIG. 4) of the substrate 27 between the outermost edge of the folded portion 30b2 and the position 30b3 returned from the folded portion 30b2 to the power feeding portion 30a side through the conductive portion 30b4. The distance X is 6.5 mm. That is, the length X of the conductive portion 30b4 in the short direction (vertical direction in FIG. 4) of the substrate 27 is 6.5 mm.

  On the other hand, the distance Y along the short direction (vertical direction in FIG. 4) of the substrate 27 between the outermost edges of the electrodes 29c and 30c is 4.6 mm. That is, the distance Y from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 4) is 4.6 mm.

  Here, the length (width) of the electrodes 29c and 30c shown in FIG. 4 along the short direction (vertical direction in FIG. 4) of the substrate 27 is 0.7 mm. Further, the length (width) along the short direction (vertical direction in FIG. 4) of the substrate 27 of the heat generating portion 26 shown in FIG. 4 is set to 3.2 mm. Considering the distance X and the distance Y using these, even if the distance X is the shortest length and the distance Y is considered the longest length, the relationship expressed by the following formula 1 is satisfied.

[Equation 1]
X (6.5 mm)> Y (4.6 mm)

  4 shows the configuration in the vicinity of the power feeding unit 30a, the configuration in the vicinity of the power feeding unit 29a shown in FIG. The short direction of the substrate 27 between the outermost edge of the folded portion 29b2 shown in FIG. 3A and the position 29b3 returned from the folded portion 29b2 to the power feeding portion 29a side through the conductive portion 29b4 (FIG. 3 ( Let S be the distance along the vertical direction of a).

  That is, the distance S is the length of the conductive portion 29b4 in the short direction of the substrate 27 (vertical direction in FIG. 3A). Further, T is a distance along the short side direction (vertical direction in FIG. 3A) of the substrate 27 between the outermost edges of the electrodes 29c and 30c. That is, the distance T is a distance from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 3A). Even if the distance S is the shortest length and the distance T is the longest length, the relationship expressed by the following formula 2 is established.

[Equation 2]
S (6.5 mm)> T (4.6 mm)

  In the heater 23 of this embodiment shown in FIG. 3A, each one end part electrically connected to each electrode 29c, 30c of each conductive part 29b, 30b electrically connected to each power feeding part 29a, 30a. 29b1 and 30b1 are configured as follows. The electrodes 29c and 30c are located at the center in the longitudinal direction (left and right direction in FIG. 3A). Each of the one end portions 29b1 and 30b1 located in the central portion is located in an area through which the recording material P having the minimum size that can be used in the image forming apparatus 12 passes.

  Thereby, the voltage drop by each electrode 29c, 30c can be made symmetrical in the longitudinal direction (left-right direction of Fig.3 (a)) of each electrode 29c, 30c. Further, the heat generated by Joule heat generated by energizing each electrode 29c, 30c becomes the same amount of heat generated in the longitudinal direction of each electrode 29c, 30c (left-right direction in FIG. 3A). As a result, the temperature difference in the longitudinal direction of each of the electrodes 29c, 30c (the left-right direction in FIG. 3A) can be reduced.

  Furthermore, a uniform temperature distribution on the left and right can be realized in the longitudinal direction of each of the electrodes 29c and 30c (the left and right direction in FIG. 3A). As a result, the temperature control is facilitated, and the fixability at the end in the longitudinal direction of the fixing nip N2 can be ensured to be equal to the center in the longitudinal direction of the fixing nip N2. If the temperature difference between the longitudinal center portion of the fixing nip portion N2 and the longitudinal end portion of the fixing nip portion N2 exceeds 15 ° C., the fixing property at the longitudinal end portion of the fixing nip portion N2 is ensured. It becomes difficult. Therefore, in practice, the temperature difference in the longitudinal direction of the heater 23 is desirably 15 ° C. or less.

  In the heater 23 of this embodiment shown in FIG. 3A, an input voltage of 100 V, which is an input voltage generally used for the AC power supply 43, is applied based on the actual usage situation in the image forming apparatus 12. At that time, voltage values applied to the heat generating portion 26 were measured in three sections between H-H, M-M, and Q-Q in the longitudinal direction of the heat generating portion 26 (left-right direction in FIG. 3A). The voltage between H and H was 100 V, and the voltage between M and M and Q and Q was 85 V.

  Of the three sections shown in FIG. 3A, the section between H and H is located at the midpoint in the longitudinal direction of each electrode 29c, 30c (left-right direction in FIG. 3A). Between M and M, the electrodes 29c and 30c are positioned on the power feeding unit 30a side in the longitudinal direction (the left-right direction in FIG. 3A). Between Q-Q, it is located in the electric power feeding part 29a side in the longitudinal direction (left-right direction of Fig.3 (a)) of each electrode 29c, 30c.

  The voltage value (85 V) applied between MM and Q-Q is about 15 V (= 100 V-85 V) smaller than the voltage value (100 V) between H and H. That is, even when a small size recording material P is continuously printed, the amount of heat generated in the non-passing region of the recording material P at the longitudinal end of the fixing nip N2 is determined by the amount of heat generated by the recording material P in the longitudinal center of the fixing nip N2. It can suppress compared with a passage area. As a result, the temperature rise at the end in the longitudinal direction of the fixing nip N2 that is a non-passing area of the recording material P can be suppressed, and the same effect can be obtained even under actual use conditions in the image forming apparatus 12.

  In the present embodiment, the resistance value in the longitudinal direction of each electrode 29c, 30c (left and right direction in FIG. 3A) is changed. As a result, the temperature in the longitudinal direction of the heater 23 (left and right direction in FIG. 3A) was changed to a uniform state on the left and right. In addition, even if the temperature in the longitudinal direction of the heater 23 (left and right direction in FIG. 3A) is not uniform in the left and right directions, the resistance value in the longitudinal direction of the electrodes 29c and 30c (left and right direction in FIG. 3A). To change.

  Thus, the temperature distribution in the longitudinal direction of the heater 23 (left and right direction in FIG. 3A) may be changed to a necessary state that is not uniform left and right. For example, a configuration may be used in which the resistance value of each electrode 29c, 30c is increased at a location where a member such as a thermistor or a thermo switch (SW) that locally lowers the temperature of the heater 23 is in contact.

<Arrangement of temperature detection element and safety device>
As shown in FIGS. 3B to 3D, the heater 23 has thermistors 25a and 25b serving as temperature detection elements on the back surface of the substrate 27 (the surface opposite to the fixing nip portion N2). The thermistors 25 a and 25 b are provided for detecting the temperature of the heater 23. The thermistors 25 a and 25 b of the present embodiment are in contact with the back surface of the substrate 27. For example, the thermistors 25a and 25b are provided with a heat insulating layer on a support (not shown), a chip thermistor element is fixed on the heat insulating layer, and the element is pressed against the back surface of the substrate 27 with a predetermined pressure. Thus, the support is configured to contact the back surface of the substrate 27.

  The thermistors 25a and 25b of this embodiment are installed in two places in the longitudinal direction of the heat generating portion 26 (left and right direction in FIG. 3C). One of the thermistors 25b in the two places is provided in an area through which the recording material P of the minimum size that can be used for the image forming apparatus 12 always passes in the longitudinal direction of the heat generating portion 26 (the left-right direction in FIG. 3C). It has been.

  In the other thermistor 25a, the recording material P of B5 size is in the R direction (the direction in which the longitudinal direction of the recording material P and the conveying direction are parallel) in the longitudinal direction of the heat generating portion 26 (left-right direction in FIG. 3C). It is provided in a non-passing area when passing.

  With these arrangements, the temperature of the passing region of the recording material P is controlled by the detection result of the thermistor 25b, and the temperature of the non-passing region when the small size recording material P passes is controlled by the detection result of the thermistor 25a. That is, the temperature control of the passage region of the recording material P is performed based on the detection result of the thermistor 25b, and the detection result of the thermistor 25a prevents the abnormal temperature rise in the non-passage region when continuously printing the small size recording material P. Throughput control is performed.

  In the heater 23 of the present embodiment, the temperature rise in the non-passing area of the recording material P can be suppressed. For this reason, the possibility of entering the throughput control is extremely low. However, in continuous printing of a small-sized recording material P such as a postcard (postcard), there is a possibility that the temperature rise at the end in the longitudinal direction of the fixing nip portion N2 may occur. For this reason, throughput control is performed.

  Further, as shown in FIGS. 3B and 3C, the heater 23 has a thermo switch 31 serving as a safety device on the back surface of the substrate 27 (surface opposite to the fixing nip portion N2). The thermo switch 31 is provided to cut off the energization when an abnormal temperature rise of the heater 23 occurs.

  In this embodiment, the thermo switch 31 is used as a safety device. The thermoswitch 31 is provided with a bimetal inside, and the bimetal is covered with an aluminum cap member. Bimetal (Bi-metallic strip) is a laminate of two metal plates with different coefficients of thermal expansion. It is used for thermometers, temperature control devices, etc. by utilizing the property that the way of bending changes according to temperature change. When the cap member contacts the back surface of the substrate 27, the temperature of the heater 23 is transmitted to the bimetal through the cap member. With this configuration, when the heater 23 is abnormally heated, the temperature of the heater 23 is transmitted to the bimetal, and when the critical temperature is reached, the bimetal is deformed and the energization to the heater 23 is interrupted.

  In the present embodiment, the thermo switch 31 is used as a safety device, but a safety device such as a thermal fuse may be used. The thermo switch 31 is installed between the thermistor 25b provided at the longitudinal center of the heat generating portion 26 and the thermistor 25a provided at the longitudinal end of the heat generating portion 26. As a result, even if the voltage drop in the longitudinal direction of the heater 23 is taken into consideration, the temperature detected by the thermoswitch 31 is equal to the temperature detected by the thermistors 25a and 25b. For this reason, the temperature of the heater 23 can be accurately detected, and the abnormal temperature rise of the heater 23 can be detected more accurately.

  As the best configuration, as shown in FIGS. 3B and 3C, the thermistor 25b and the thermo switch 31 are placed at the center in the longitudinal direction of the heat generating portion 26 (left and right direction in FIG. 3C) as much as possible. It is a close-up configuration. As a result, the temperature detected by the thermistor 25a is in the vicinity of the maximum temperature location in the longitudinal direction of the heater 23, and the excessive temperature rise can be easily suppressed.

  Further, the temperature detected by the thermo switch 31 is near the maximum temperature location in the longitudinal direction of the heater 23. For this reason, the abnormal temperature rise can be quickly detected by the thermo switch 31, and safety can be improved. Moreover, you may install so that the center position of the thermoswitch 31 may come to the longitudinal direction center part of the heat generating part 26. FIG. As a result, the thermo switch 31 can be brought into contact with a position equivalent to the maximum temperature location in the longitudinal direction of the heater 23. That is, in terms of safety, it can be said that the configuration in which the thermistors 25a and 25b are arranged around the thermoswitch 31 as shown in FIGS. 3B and 3C is the optimum configuration.

<Heat fixing operation of fixing device>
A driving gear (not shown) provided at the longitudinal end of the cored bar 24a of the pressure roller 24 shown in FIG. 2 is rotationally driven by the fixing motor. As a result, the pressure roller 24 rotates counterclockwise in FIG. As the pressure roller 24 rotates, a rotational force acts on the fixing film 22 by a frictional force between the surface of the pressure roller 24 and the surface of the fixing film 22 in the fixing nip portion N2 shown in FIG. As a result, the fixing film 22 rotates following the rotation of the pressure roller 24.

  At this time, the inner peripheral surface of the fixing film 22 is driven to rotate at the same speed as the peripheral speed of the pressure roller 24 in the clockwise direction in FIG. 2 while sliding in close contact with the surface of the heater 23. . As a result, the heat generated by the heater 23 is applied to the recording material P passing through the fixing nip N2 via the fixing film 22.

  FIG. 3C is a block diagram in which the configuration of the control system is added to the GG sectional view of the heater 23 shown in FIG. When the image forming apparatus 12 shown in FIG. 1 receives a printing operation signal, energization to the heater 23 shown in FIG. First, the control part 41 as a control means shown in FIG.3 (c) turns on the triac 42 as an electricity supply control means. The triac 42 is widely used as an AC switch because it is composed of a semiconductor switching element having three terminals and can pass a current in both directions.

  As a result, an AC voltage is applied from the AC power source 43 shown in FIG. 3C to the power feeding units 29a and 30a provided at both ends in the longitudinal direction of the heater 23 via the thermoswitch 31 serving as a temperature detection type safety device. . As a result, the heater 23 is energized from the power supply portions 29a, 30a to the electrodes 29c, 30c through the conductive portions 29b, 30b, so that the entire area of the heat generating portion 26 generates heat, and the heater 23 is heated.

  The thermistors 25a and 25b detect the temperature of the substrate 27 that is heated by the heat generated by the heat generating portion 26 according to the temperature rise of the heater 23. Then, the heating unit 26 is energized until the temperature of the substrate 27 detected by the thermistors 25a and 25b reaches the target temperature. Meanwhile, the control unit 41 takes in the output signals (detected temperatures) of the thermistors 25a and 25b after A / D (analog / digital) conversion.

  The temperature of the substrate 27 detected by the thermistors 25a and 25b reaches the target temperature. Then, based on the output signals from the thermistors 25a and 25b, the temperature of the heater 23 is controlled by controlling the power supplied to the heater 23 by the triac 42 by phase control or wave number control.

  That is, the control unit 41 controls the triac 42 so as to raise the temperature of the heater 23 when the temperature detected by the thermistors 25a and 25b is lower than a predetermined set temperature. On the other hand, when the detected temperature of the thermistors 25a and 25b is higher than a predetermined set temperature, the triac 42 is controlled so as to lower the temperature of the heater 23. As a result, the heater 23 is kept at the set temperature. The current detector 44 detects an AC current flowing between the triac 42 and the AC power source 43 and transmits the detected AC current to the control unit 41.

  The recording material P is introduced into the fixing nip portion N2 in a state where the temperature of the heater 23 rises to the set temperature and the peripheral speed of the fixing film 22 is stabilized by the rotation of the pressure roller 24. Then, the recording material P is nipped and conveyed by the outer peripheral surface of the fixing film 22 heated by the heater 23 and the pressure roller 24 in the fixing nip portion N2. As a result, the heat of the heater 23 is applied to the recording material P through the fixing film 22, and the unfixed toner image t carried on the recording material P is melted by heat and fixed to the recording material P.

  The recording material P that has passed through the fixing nip N2 is separated from the surface of the fixing film 22 and further conveyed downstream. When these heating and fixing operations are completed, the triac 42 shown in FIG. 3C is turned off, and energization of the heater 23 is completed.

  For example, in Comparative Example 2 shown in FIG. 11, when the heater 23 is cracked as indicated by the breaking line A, the power feeding portions 29a and 30a are configured to be extremely small in order to completely cut off the power supply to the heat generating portion 26. Is also possible. In that case, the power feeding portions 29a and 30a are arranged on one end side and the other end side in the short direction (vertical direction in FIG. 11) perpendicular to the longitudinal direction on the substrate 27 (left and right direction in FIG. 11), and on the heating portion 26. Place outside.

  However, in practice, it is difficult to ensure a stable conduction state by configuring the power feeding units 29a and 30a to be extremely small. Further, the width of the heat generating portion 26 in the vertical direction in FIG. 11 is secured to some extent, and the power feeding portions 29a and 30a are arranged in the short direction (vertical direction in FIG. 11) perpendicular to the longitudinal direction of the substrate 27 (left and right direction in FIG. Are arranged at one end side and the other end side of the heat generating portion 26. As a result, the width of the substrate 27 in the short direction (vertical direction in FIG. 11) is increased.

  Therefore, in the present embodiment, as shown in FIG. 3A, the substrate 27 and the short direction (FIG. 3A) orthogonal to the longitudinal direction of the substrate 27 (left-right direction in FIG. 3A). Electrodes 29c and 30c are provided on one end side and the other end side in the vertical direction, respectively. The electrodes 29c and 30c are provided in parallel with each other at a predetermined interval along the longitudinal direction of the substrate 27. Further, a heat generating portion 26 electrically connected between the electrodes 29c and 30c and power feeding portions 29a and 30a for supplying electric power are provided. Furthermore, conductive portions 29b and 30b are provided for electrically connecting the power feeding portions 29a and 30a and the electrodes 29c and 30c, respectively.

  Then, the conductive portions 29b4 and 30b4 that are part of the respective conductive portions 29b and 30b connected to the respective power supply portions 29a and 30a are respectively connected to the power supply portion 29a in the longitudinal direction of the substrate 27 (the left-right direction in FIG. 3A). 30a and the heat generating portion 26. The conductive portions 29b4 and 30b4 straddle one side and the other side in the short direction (vertical direction in FIG. 3A) of the electrodes 29c and 30c. Then, the lengths S and X of the conductive portions 29b4 and 30b4 that are part of the conductive portions 29b and 30b in the short direction of the substrate 27 (vertical direction in FIG. 3A) are considered. Further, the distances T and Y between the electrodes 29c and 30c electrically connected to the heat generating portion 26 are considered. The lengths S and X and the distances T and Y have a relationship represented by the above formula 1 and formula 2, respectively.

  As a result, as shown by the broken line D in FIG. 5, when the heater 23 is cracked, the conductive portion 29b4, which is a part of the conductive portion 29b connected to the power feeding portion 29a, is completely cut off and the heat generating portion 26 is removed. It is possible to reliably cut off the power supply to the. Although not shown, even when the heater 23 is cracked on the left side of FIG. 3A, the conductive portion 30b4 which is a part of the conductive portion 30b connected to the power supply portion 30a is completely cut off and the heat generating portion 26 is removed. It is possible to reliably cut off the power supply to the.

  As shown in FIG. 3A, the length of the heat generating portion 26 in the short direction (vertical direction in FIG. 3A) is considered. The length in the short direction (vertical direction in FIG. 3A) of the substrate 27 of the conductive portions 29b4 and 30b4 to be a part of the respective conductive portions 29b and 30b connected to the respective power feeding portions 29a and 30a than this length. S and X are long.

  As a result, when the heater 23 is cracked in any direction, the conductive portions 29b and 30b are surely blocked by the conductive portions 29b4 and 30b4. Thereby, it is possible to interrupt | block the electricity supply to the heat generating part 26 instantaneously. As a result, energization of the heat generating portion 26 continues in a state where the heater 23 is broken, and the heater 23 does not generate heat, and safety can be ensured.

  Next, the configuration of a second embodiment of an image forming apparatus provided with a heat generating unit according to the present invention in a fixing device will be described with reference to FIGS. In addition, what was comprised similarly to the said 1st Embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description.

  FIG. 6A is an explanatory plan view showing the configuration of the heat generating unit of the present embodiment. FIG. 6B is a rear view illustrating the configuration of the heat generating unit of the present embodiment. FIG. 6C is a block diagram showing a cross section taken along the line II in FIG. 6A and the configuration of the control system. FIG.6 (c) is JJ sectional drawing of Fig.6 (a).

  As shown in FIG. 6C, the overcoat layer 28 of the heater 23 covers the substrate 27 so as to cover the heat generating portion 26, the electrodes 29c and 30c, the conductive portions 29b and 30b, and the power feeding portions 29a and 30a. Is provided on the surface. In the present embodiment, a heat-resistant glass layer having a thickness of 60 μm is used as the overcoat layer 28.

  In FIG. 6A, the overcoat layer 28 is omitted so that the relationship between the electrodes 29c and 30c and the heat generating portion 26 can be easily understood. The overcoat layer 28 is mainly intended to ensure electrical insulation between the heat generating portion 26 and the surface of the heater 23 and slidability between the surface of the heater 23 and the inner peripheral surface of the fixing film 22. is there. Silver / palladium (Ag · Pd) screen patterns were used for the power feeding portions 29a and 30a, the conductive portions 29b and 30b, and the electrodes 29c and 30c.

  The total resistance value in the heater 23 of this embodiment is 20Ω. The heater 23 has a substrate 27 having heat resistance, electrical insulation, and good thermal conductivity that is elongated in the longitudinal direction (left-right direction in FIG. 6A). Further, it has a heat generating portion 26 provided on one surface of the substrate 27 (surface on the fixing nip portion N2 side). Furthermore, electrodes 29c and 30c electrically connected to the heat generating part 26 are provided on both sides of the heat generating part 26 in the short direction (vertical direction in FIG. 6A).

  Further, the electrodes 29c and 30c have conductive portions 29b and 30b in which one end portions 29b1 and 30b1 are electrically connected to the central portion in the longitudinal direction (left and right direction in FIG. 6A), respectively. Furthermore, it has electric power feeding parts 29a and 30a to which the other end parts of the conductive parts 29b and 30b are electrically connected, respectively. Furthermore, the heat generating part 26 on the board | substrate 27, electrode 29c, 30c, the electroconductive part 29b, 30b, and the heat-resistant overcoat layer 28 which covers the electric power feeding part 29a, 30a are comprised.

  On the surface (surface on the fixing nip portion N2 side) of the substrate 27 having electrical insulation, the longitudinal direction of the substrate 27 (on the one end side and the other end side in the short side direction (vertical direction in FIG. 6A)) ( Electrodes 29c and 30c having electrical conductivity are provided along the horizontal direction in FIG. A heat generating portion 26 having a positive resistance temperature characteristic is provided between the electrodes 29c and 30c.

  In addition, one end portions 29b1 and 30b1 of the conductive portions 29b and 30b serving as input contact portions to the electrodes 29c and 30c having regions in contact with the heat generating portion 26 from the conductive portions 29b and 30b having electrical conductivity are as follows. Composed. The electrodes 29c and 30c are provided at the center in the longitudinal direction (left and right direction in FIG. 6A). The one end portions 29b1 and 30b1 are located in an area through which the recording material P having the minimum size usable in the image forming apparatus 12 always passes. At both ends in the longitudinal direction of the substrate 27 (left and right direction in FIG. 6A), the other end portions of the conductive portions 29b and 30b in which the one end portions 29b1 and 30b1 are electrically connected to the electrodes 29c and 30c are electrically connected. Feeding portions 29a and 30a connected to the are provided.

  In the present embodiment, as shown in FIG. 6A, the power feeding portions 29a and 30a are arranged on one end side (the right side of FIG. 6A) in the longitudinal direction of the substrate 27 (left and right direction in FIG. 6A). The provided structure will be described.

<Conductive part>
First, the configuration of the conductive portions 29b and 30b that electrically connect the power feeding portions 29a and 30a to the electrodes 29c and 30c will be described. As shown in FIGS. 6 (a) and 6 (c), the power feeding portions 29a and 30a are arranged at one end side in the longitudinal direction of the substrate 27 (the left-right direction in FIGS. 6 (a) and 6 (c)) (on FIG. 6 (a)). On the right). In this case, the conductive portion 29b that has come out of the power feeding portion 29a shown in FIG. 6A is folded back from the power feeding portion 29a side of the substrate 27 on the other end side in the short direction (vertical direction in FIG. 6A). A portion 29b2 is provided.

  The conductive portion 29b4 further extends from the folded portion 29b2 along the short direction (upward direction in FIG. 6A) and returns to the power feeding portion 29a side. Then, it extends along the longitudinal direction (left-right direction of FIG. 6A) to the other end side in the longitudinal direction of the heat generating portion 26 (left-right direction of FIG. 6A). Further, the other end side in the longitudinal direction (left-right direction in FIG. 6A) also passes through the conductive portion 29b8 extending in the short direction (downward in FIG. 6A) and extends in the short direction (FIG. 6). A folded portion 29b9 is provided on the other end side in the vertical direction (a).

  Furthermore, it further folds and extends in the longitudinal direction (left and right direction in FIG. 6A) of the heat generating portion 26 through the conductive portion 29b6 extending along the short direction (up and down direction in FIG. 6A) from the folded portion 29b9. One end portion 29b1 of the conductive portion 29b is provided. The one end 29b1 is electrically connected at the center in the longitudinal direction of the electrode 29c (the left-right direction in FIG. 6A).

  On the other hand, the conductive portion 30b from the power supply portion 30a shown in FIG. 6A linearly extends from the power supply portion 30a side to the other end side in the short direction of the substrate 27 (vertical direction in FIG. 6A). Extend. Thereafter, the substrate 27 is bent in the longitudinal direction (the left-right direction in FIG. 6A) and extends linearly from the power feeding unit 30a side to the other end side. And the folding | returning part 30b5 is provided in the edge part on the opposite side to the electric power feeding part 30a side in the longitudinal direction (left-right direction of Fig.6 (a)) of the heat generating part 26. FIG. It extends along the longitudinal direction (left and right direction in FIG. 6A) from the folded portion 30b5 to the central portion in the longitudinal direction of the heat generating portion 26 (left and right direction in FIG. 6A). One end portion 30b1 of the conductive portion 30b is electrically connected at the central portion in the longitudinal direction of the electrode 30c (the left-right direction in FIG. 6A).

  In the present embodiment, the conductive portions 29b4, 29b8, 29b6, which are at least part of the first and second conductive portions 29b, 30b, are arranged in the short direction of the substrate 27 (the vertical direction in FIG. 6A). It straddles the first and second electrodes 29c and 30c. Further, the lengths X, Z, and U of the conductive portions 29b4, 29b8, and 29b6 shown in FIGS. 7A and 7B in the short direction of the substrate 27 (vertical direction in FIGS. 7A and 7B). Is set as follows. It is larger than the distance Y from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIGS. 7A and 7B). The conductive portion 29b4 of the present embodiment is disposed between the power feeding portion 29a and the heat generating portion 26 in the longitudinal direction of the substrate 27 (left and right direction in FIG. 7B).

  Consider the folded portion 29b2 that is folded from the power supply portion 29a side of the conductive portion 29b shown in FIG. 6A to the other end portion side in the short direction of the substrate 27 (vertical direction in FIG. 6A). Further, a position 29b3 returned to the power feeding portion 29a side through the conductive portion 29b4 extending from the folded portion 29b2 along the short direction of the substrate 27 (upward direction in FIG. 6A) is considered. Further, an end portion 29c1 on the power feeding portion 29a side of the electrode 29c shown in FIG. Further, an end portion 29c2 on the other end side in the longitudinal direction of the electrode 29c from the end portion 29c1 (left direction in FIG. 6A) is considered.

  Further, it extends along the longitudinal direction of the conductive portion 29b (left direction in FIG. 6A) to the other end side opposite to the power feeding portion 29a, and further in the short direction of the substrate 27 (in FIG. 6A). Consider the conductive part 29b8 extending in the downward direction. Further, a folded portion 29b9 that is folded back in the short direction of the substrate 27 (upward in FIG. 6A) through the conductive portion 29b8 is considered. Further, it is further folded in the longitudinal direction of the substrate 27 (right direction in FIG. 6A) through the conductive portion 29b6 extending from the folded portion 29b9 along the short direction of the substrate 27 (upward direction in FIG. 6A). The position 29b5 heading toward the power feeding unit 29a is taken into consideration.

  Further, in the longitudinal direction of the electrode 30c (the left-right direction in FIG. 6A), the end 30c1 on the power feeding unit 30a side and the end 30c2 on the opposite side to the power feeding unit 30a side are considered. Consider the folded portion 29b2 of the conductive portion 29b shown in FIG. Further, a position 29b3 returned from the folded portion 29b2 to the power feeding portion 29a side through the conductive portion 29b4 is considered. The folded portion 29b2 and the position 29b3 returned from the folded portion 29b2 to the power feeding portion 29a side through the conductive portion 29b4 are configured as follows. Positioned outward in the lateral direction (vertical direction in FIG. 6A) from the end portions 29c1 and 30c1 on the power feeding portions 29a and 30a side in the longitudinal direction (left and right direction in FIG. 6A) of the electrodes 29c and 30c. doing.

  In addition, the folded portion 29b9 on the side opposite to the power feeding portions 29a, 30a side in the longitudinal direction of the conductive portion 29b shown in FIG. 6A (left and right direction in FIG. 6A) is considered. Furthermore, a position 29b5 that further folds through the conductive portion 29b6 extending from the folded portion 29b9 along the short direction of the substrate 27 (upward in FIG. 6A) toward the power feeding portion 29a is considered. The folded portion 29b9 and the position 29b5 from the folded portion 29b9 to the power feeding portion 29a side through the conductive portion 29b6 are configured as follows. The shorter direction (vertical direction in FIG. 6A) than the end portions 29c2 and 30c2 on the opposite side to the power feeding portions 29a and 30a in the longitudinal direction of the electrodes 29c and 30c (left and right direction in FIG. 6A). At the outside.

  In the present embodiment, the folded portion 29b2 of the conductive portion 29b and the position 29b3 from the folded portion 29b2 to the power feeding portion 29a side through the conductive portion 29b4 are configured as follows. The electrodes 29c and 30c are located on the outer side in the lateral direction (vertical direction in FIG. 6A) than the end portions 29c1 and 30c1. Further, the folded portion 29b9 of the conductive portion 29b and the position 29b5 that further folds from the folded portion 29b9 through the conductive portion 29b6 extending along the short direction of the substrate 27 toward the power feeding portion 29a are configured as follows. . The electrodes 29c and 30c are located on the outer side in the lateral direction (vertical direction in FIG. 6A) than the end portions 29c2 and 30c2.

  That is, the conductive portions 29b and 30b provided on the surface of the substrate 27 (on the substrate) extend over the longitudinal direction of the heat generating portion 26 (the left-right direction in FIG. 6A) on the extension of the heat generating portion 26 in the short direction. The power supply from the power supply units 29a and 30a is supplied to the heat generating unit 26 by the conductive path.

  Fig.7 (a) is the elements on larger scale of the left end part vicinity of Fig.6 (a). FIG.7 (b) is the elements on larger scale of the right end part vicinity of Fig.6 (a). The short direction of the substrate 27 between the outermost edge of the folded portion 29b2 of the conductive portion 29b shown in FIG. 7B and the position 29b3 returned from the folded portion 29b2 through the conductive portion 29b4 to the power feeding portion 29a side. Let X be the distance along the vertical direction of FIG. That is, the distance X is the length of the conductive portion 29b4 in the short direction of the substrate 27 (vertical direction in FIG. 7B).

  Further, the distance along the short side direction of the substrate 27 (up and down direction in FIG. 7B) between the outermost edges of the electrodes 29c and 30c is Y. The distance Y is a distance from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 7B).

  Further, consider the folded portion 29b9 of the conductive portion 29b shown in FIG. Further, a position 29b5 that further folds through the conductive portion 29b6 extending from the folded portion 29b9 along the short direction of the substrate 27 (upward direction in FIG. 7A) toward the power feeding portion 29a is considered. Along the short side direction (vertical direction in FIG. 7A) of the substrate 27 between the outermost edge of the folded portion 29b9 and the position 29b5 from the folded portion 29b9 to the power feeding portion 29a side through the conductive portion 29b6. Let Z be the distance. The distance Z is the length of the conductive portion 29b6 in the short direction of the substrate 27 (vertical direction in FIG. 7A). Further, U is the length of the conductive portion 29b8 in the short direction of the substrate 27 (vertical direction in FIG. 7A).

  Consider the folded portion 29b9 of the conductive portion 29b shown in FIG. Further, a position 29b5 extending from the folded portion 29b9 along the short direction of the substrate 27 (upward in FIG. 7A) and then bent toward the power feeding portion 29a is considered. The conductive portion 29b6 provided between the folded portion 29b9 and the position 29b5 from the folded portion 29b9 toward the power feeding portion 29a side is configured as follows. The distance Z between the electrodes 29c and 30c and shown in FIG. 7A is the length of the conductive portion 29b6 of 5.5 mm. Further, the length U of the conductive portion 29b8 in the short direction (vertical direction in FIG. 7A) of the substrate 27 is 6.5 mm.

  The width of the electrodes 29c and 30c shown in FIG. 7A in the short direction (vertical direction in FIG. 7A) is 0.7 mm. Further, the width of the heat generating portion 26 in the short direction (vertical direction in FIG. 7A) is set to 3.2 mm. Then, the distance Y shown in FIG. 7A is 4.6 mm (= 0.7 mm × 2 + 3.2 mm). Even if the distance Z shown in FIG. 7A is considered to be the shortest length and the distance Y is considered to be the longest length, there is a relationship expressed by the following equation (3).

[Equation 3]
Z (5.5 mm)> Y (4.6 mm)

  Thus, in the present embodiment, there is a relationship that the distance Z is longer than the distance Y shown in FIG. 7B, the conductive portion 29b4 connecting the folded portion 29b2 of the conductive portion 29b and the position 29b3 returning from the folded portion 29b2 to the power feeding portion 29a side is configured as follows. Is done. In the longitudinal direction of the substrate 27 (left and right direction in FIG. 7B), it is provided between the power feeding portion 29a and the heat generating portion 26.

  The conductive portion 29b4 straddles between the electrodes 29c and 30c in the short direction of the substrate 27 (vertical direction in FIG. 7B). Further, the short side direction of the substrate 27 (see FIG. 7B) between the outermost edge of the folded portion 29b2 and the position 29b3 returned from the folded portion 29b2 to the power feeding portion 29a side through the conductive portion 29b4. The distance X along the vertical direction is 5.5 mm. That is, the length X of the conductive portion 29b4 is 5.5 mm.

  The width of each electrode 29c, 30c in the short direction (vertical direction in FIG. 7B) is set to 0.7 mm. Further, the width of the heat generating portion 26 in the short direction (vertical direction in FIG. 7B) is set to 3.2 mm. Then, the distance Y along the short side direction (vertical direction in FIG. 7B) between the outermost edges of the electrodes 29c and 30c is 4.6 mm (= 0.7 mm × 2 + 3.2 mm). It is. That is, the distance Y from the first electrode 29c to the second electrode 30c in the short direction of the substrate 27 (vertical direction in FIG. 7B) is 4.6 mm. Even if the distance X shown in FIG. 7 (b) is the shortest length and the distance Y is the longest length, the relationship expressed by the following equation (4) is satisfied.

[Equation 4]
X (5.5 mm)> Y (4.6 mm)

  Thereby, in this embodiment, it has the relationship that the said distance X is longer than the said distance Y shown in FIG.7 (b). FIG. 8A is a partially enlarged view showing a state in which a crack indicated by a break line E1 has occurred in the vicinity of the left end portion of FIG. FIG.8 (b) is the elements on larger scale which show a mode that the crack shown with the fracture | rupture line E2 generate | occur | produced in the right side edge part vicinity of Fig.6 (a).

  On the other hand, in the heater 23 of the present embodiment shown in FIGS. 6A, 8A, and 8B, the power feeding portions 29a and 30a are provided on one side in the longitudinal direction of the substrate 27 (left and right direction in FIG. 8B). Have In such a configuration, the heater 23 can be split across the conductive portions 29b6 and 29b8 on both sides of the folded portion 29b9 shown in FIG. 8A and the conductive portion 29b4 shown in FIG. For this reason, each of the conductive portions 29b4, 29b6, 29b8 is completely cut off, and the power supply to the heat generating portion 26 can be cut off completely. Other configurations are the same as those in the first embodiment, and the same effects can be obtained.

26 ... Heat generating portion 27 ... Substrate 29a ... Power feeding portion 29b ... Conductive portion 29b4 ... Conductive portion (conductive path)
30a ... Power feeding part 30b ... Conducting part 30b4 ... Conducting part (conducting path)

Claims (4)

A substrate,
A heat generating portion provided on the substrate;
A power feeding unit that is provided on the substrate and feeds power to the heat generating unit;
A conductive portion that is provided on the substrate and that supplies power from the power feeding portion to the heat generating portion by a conductive path extending in a short direction of the heat generating portion on the longitudinal extension of the heat generating portion;
A heat generating unit characterized by comprising: A substrate,
A heat generating portion provided on the substrate;
A power feeding unit that is provided on the substrate and feeds power to the heat generating unit;
A conductive portion that is provided on the substrate and that supplies power from the power feeding portion to the heat generating portion through a conductive path extending in the longitudinal direction of the heat generating portion on the short direction extension of the heat generating portion;
A heat generating unit characterized by comprising: The heat generating unit according to claim 1 or 2,
An endless flexible member slidably provided on the heat generating surface and the inner peripheral surface of the heat generating unit;
A pressure member that forms a fixing nip portion with the outer peripheral surface of the flexible member;
A fixing device.   An image forming apparatus comprising the fixing device according to claim 3.

Images