JP6666029B2 - Heater and fixing device - Google Patents

Description

  The present invention relates to a heater used to heat a toner image on a recording material, and a fixing device including the heater. The heater and the fixing device of the present invention can be used in an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction peripheral having a plurality of these functions.

  Conventionally, in an image forming apparatus, a method of fixing a toner image on a recording material by applying heat and pressure by a fixing device after forming a toner image on the recording material has been generally used. On the other hand, in response to recent demands for energy saving and quick start, a fixing device of a type in which a heater is brought into contact with an inner surface of a thin belt to heat the belt has been proposed (Patent Document 1).

  Patent Document 1 discloses a configuration in which an area in which a heater generates heat is changed according to a width size of a recording material. FIG. 12 is a circuit diagram of a heater in the fixing device described in Patent Document 1.

  In this fixing device, the electrodes 1027 (1027a to 1027f) are arranged side by side in the longitudinal direction of the substrate 1021, and electricity is supplied from each electrode to the resistance heating layer 1025 (1025a to 1025e) to generate heat in the resistance heating layer 1025. In this fixing device, each electrode is connected to a wiring layer 1029 (1029a, 1029b) formed on the substrate. Specifically, the wiring layer 1029b connected to the electrodes 1027b and 1027d extends to one longitudinal end of the substrate. The wiring layer 1029a connected to the electrodes 1027c and 1027e extends to the other longitudinal end of the substrate.

  Further, the electrode 1027a and the wiring layer 1029b can be connected to a wiring member at one end in the longitudinal direction of the substrate, and the electrode 1027f and the wiring layer 1029a can be connected to the wiring member at the other end in the longitudinal direction of the substrate. It has become. At both ends in the longitudinal direction of the substrate, an insulating layer for protecting each wiring is not provided, and the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f are exposed. Therefore, when the wiring member comes into contact with the exposed portions of the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f, the resistance heating layer 1025 is connected to the power supply circuit.

  The power supply circuit includes an AC power supply and switches 1033 (1033a, 1033b, 1033c, and 1033d), and the connection pattern of each wiring can be changed by turning on and off the switch 1033. That is, the wiring layers 1029a and 1029b are connected to either the power supply terminal 1031a or the power supply terminal 1031b according to the connection pattern in the power supply circuit, and the heat generation area of the resistance heat generation layer 1025 according to the width size of the recording material. Changing.

  For example, as shown in FIG. 12A, in a connection pattern in which the switches 1033a and 1033b are on and the switches 1033c and 1033d are off, all of the resistance heating layers 1025a to 1025e generate heat. In the case of the connection pattern in which the switches 1033a and 1033b are off and the switches 1033c and 1033d are on as in (b), only the resistance heating layer 1025c generates heat.

JP 2012-37613 A

  By the way, Patent Document 1 does not describe the characteristics, resistance value, and the like of the material used for the wiring layer and the electrode. However, silver, which is a material having a low resistivity, is generally used as a wiring layer used in a heater having a similar configuration. Alternatively, a mixture of silver and palladium is used. Since the heater used in the fixing device is required to be downsized due to a demand for downsizing of the fixing device, it is required to reduce the width of the wiring layer.

  In a heater used in a general fixing device, the length of the wiring layer in the longitudinal direction is about 350 mm. Therefore, even when a material having a low resistivity as described above is used for the wiring layer, for example, the voltage applied to the electrode 1027c is applied to the electrode 1027e due to the resistance of the wiring layer 1029a between the electrodes 1027c and 1027e. Lower than the required voltage. Further, the voltage applied to the electrode 1027e is lower than the voltage applied to the electrode 1027f due to the resistance of the wiring layer 1029a between the right end of the base 1021 and the electrode 1027e.

  This phenomenon similarly occurs in the wiring layer 1029b, and the voltage applied to the electrode 1027b is lower than the voltage applied to the electrode 1027b, and the voltage applied to the electrode 1027b is lower than the voltage applied to the electrode 1027a.

  Therefore, for example, the heat generation amount per unit length in the longitudinal direction of the resistance heating element 1025c between the electrode 1027c and the electrode 1027d is smaller than the heat generation amount of the resistance heating element 1025e between the electrode 1027e and the electrode 1027f. As a result, unevenness occurs in the temperature in the longitudinal direction (width direction) of the belt heated by the heater, so that the gloss of the image on the recording material after the fixing process may be uneven.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a heater capable of changing a region where a resistance heating layer generates heat in accordance with a width size of a recording material and having a uniform heat generation amount in a longitudinal direction.

A typical configuration of the heater according to the present invention for achieving the above object includes an elongated substrate, a resistance heating element extending along the length of the substrate, and one end side of the substrate in the longitudinal direction. And a plurality of electrodes provided on the other end side, a plurality of conductor paths extending along the length of the resistance heating element from each of the plurality of electrodes, and a plurality of conductor paths, respectively. A plurality of branch paths branching at intervals along the length from the branch, electrically connecting to the resistance heating element across the resistance heating element and extending the resistance heating element longitudinally between the branch paths. A plurality of small section heating elements along the branch path, and is located in an area corresponding to the width size of the recording material used in the plurality of small section heating elements according to the width size. Select the plurality of electrodes so that the small section heating element selectively generates heat. A heater for heating a toner image on a recording material to which a voltage is applied, wherein a resistance value between the branch paths of the small-section heating element is at both ends of the plurality of small-section heating elements. each and small sections the heating element, the resistance of each of the small sections the heating element in a position adjacent to the small section heating element of the both ends in the central portion than the small sections the heating element of the both ends of the when RA values respectively, the resistance value of the small section the heating element of the central portion was RB, characterized in that it is a RA> RB.

  According to the present invention, it is possible to provide a heater capable of changing a region where the resistance heating layer generates heat in accordance with the width size of the recording material and having a uniform heat generation amount in the longitudinal direction.

Configuration schematic diagram of a heater in an embodiment 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. (A) is a schematic cross-sectional view of a main part of the fixing device in the embodiment, and (b) is a schematic diagram of a layer configuration of the fixing belt. Schematic vertical cross-sectional view of the main part of the fixing device with the middle part omitted. Power supply system diagram for heater Schematic diagram for explaining the heating method and switching method of the heater FIG. 3 illustrates a configuration of a heater according to a comparative example. The figure explaining the equivalent electric circuit of the heater of FIG. The figure explaining the resistance value distribution along the length of the resistance heating element of an Example and a comparative example FIG. 6 is a view for explaining a heating value distribution along the length of the resistance heating element of the example and the comparative example. FIG. 4 is a view for explaining the surface temperature distribution along the longitudinal direction (width direction) of the fixing belts of the example and the comparative example. Conventional heater circuit diagram

  Hereinafter, embodiments of the present invention will be described. In the following embodiments, a laser beam printer using an electrophotographic process will be described as an example of an image forming apparatus.

"Example"
[Image forming apparatus]
FIG. 2 is a schematic sectional view of the printer 1 in the present embodiment. This printer 1 is a tandem-intermediate transfer type full-color printer, and forms four image forming toner images of yellow (Y), magenta (M), cyan (C), and black (Bk). It has sections UY, UM, UC, and UBk.

  Each image forming unit includes a photosensitive drum 2, a charger 3, a laser scanner 4, a developing unit 5, a primary transfer charger 6, and a drum cleaner 7, respectively. In order to avoid complication in the figure, the reference numerals for these devices in the image forming units UM, UC, and UBk other than the image forming unit UY are omitted. Further, since the electrophotographic process and the image forming operation of these image forming units are known, the description thereof is omitted.

  The toner images of the respective colors are primary-transferred to the intermediate transfer belt 8 rotating from the drums 2 of the respective image forming portions in a predetermined superimposed manner. As a result, a toner image of four colors is formed on the belt 8. On the other hand, a recording material (sheet) P is fed one by one from the cassette 9 or 10 or the manual feed tray 11 and passes through the transport path 12 at a predetermined control timing at a pressure contact portion between the belt 8 and the secondary transfer roller 13. It is introduced into a certain secondary transfer nip. As a result, the toner images of the four colors superimposed on the belt 8 are collectively and secondarily transferred onto the recording material P. The recording material P is introduced into the fixing device 40 and undergoes a toner image fixing process.

  In the single-sided image forming mode, the recording material P that has exited the fixing device 40 is guided toward the transport path 15 by the control of the flapper 14 and discharged face-down onto the discharge tray 16. Alternatively, the sheet is guided toward the transport path 17 and discharged face-up onto the discharge tray 18.

  In the case of the double-sided image forming mode, the recording material P that has exited from the fixing device 40 is once guided to the side of the transport path 15 by the control of the flapper 14, and is then switched back and transported to the side of the double-sided transport path 19. Then, the toner image is again introduced into the secondary transfer nip through the transport path 12 in a state where the toner image is reversed, and a toner image is formed on the other surface. Thereafter, it is introduced into the fixing device 40 as in the case of single-sided image formation, and is discharged to the discharge tray 16 or 18 as a double-sided image formed product.

  In the printer 1 of the present embodiment, the conveyance of the recording materials P of various sizes, large and small, is performed on a so-called center basis of the center of the recording material width. Hereinafter, the maximum width recording material usable in the apparatus is referred to as a large-size recording material, and the recording material narrower than that is referred to as a small-size recording material.

[Fixing device]
Next, the fixing device 40 in this embodiment will be described. FIG. 3A is a schematic cross-sectional view of a main part of the fixing device 40, and FIG. 3B is a schematic diagram of a layer configuration of the fixing belt. FIG. 4 is a schematic longitudinal sectional front view of the fixing device 40 in which a middle part of the main part is omitted. The front of the fixing device 40 is a surface viewed from the recording material introduction side. FIG. 5 is a power supply system diagram for the heater.

  The fixing device 40 is a belt heating type image heating device, and is roughly divided into a belt unit 60 for heating an image on the recording material P, an elastic pressure roller 70 as an opposing member (nip forming member), and a housing for accommodating them. And a device housing 41.

  The belt unit 60 has a configuration in which a thin fixing belt (heat transfer member) 603 having flexibility is heated by a heater 600 that contacts the inner surface of the belt. Therefore, the fixing belt 603 can be efficiently heated, and the startup performance is excellent. A nip portion (fixing nip portion) N is formed on the fixing belt 603 by pressurization of the heater 600 and the pressure roller 70, and the recording material P fed to the nip portion N is nipped and conveyed. At this time, the heat generated by the heater 600 is applied to the recording material P via the fixing belt 603, and the toner image T on the recording material P is fixed on the recording material P.

  The belt unit 60 is a unit for heating and pressing an image on the recording material P, is provided so as to be substantially parallel to the pressing roller 70, and includes a heater 600, a heater holder 601, a support stay 602, and a fixing belt 603. .

  The heater 600 presses the fixing belt 603 in the direction of the pressure roller 70 so that the nip portion N has a desired width in the recording material conveyance direction a. The heater 600 includes a substrate 610 and a resistance heating element 620 (resistance heating layer: hereinafter referred to as a heating element) on the substrate 610, and is fixed to a concave portion 601 a on the lower surface of the heater holder 601. In this embodiment, a heating element 620 is provided on the back side of the substrate 610 (the side not in contact with the fixing belt 603). However, the present invention is not limited to this, and it may be provided on the front side (the side in contact with the fixing belt 603).

  A polyimide layer having a thickness of about 10 μm is provided as a sliding layer on the surface side of the substrate 610 which is in contact with the fixing belt 603, and the sliding resistance between the fixing belt 603 and the heater 600 is reduced, thereby fixing the image. This can be achieved by suppressing wear of the inner surface of the belt 603. Further, a lubricant such as grease may be applied to the inner surface of the fixing belt 603 to reduce the rubbing resistance.

  The fixing belt 603 is a cylindrical belt (endless belt) for heating and pressing the toner image T on the recording material P at the nip portion N. In this embodiment, as shown in FIG. 3B, a layered structure in which an elastic layer 603b and a release layer 603c are provided on a base material 603a is used. Specifically, a cylindrical member made of a nickel alloy having an outer diameter of 30 mm, a length (width) of 340 mm, and a thickness of 30 μm is used as the base material 603a. Further, a silicone rubber layer having a thickness of 400 μm is formed as an elastic layer 603b on the base material 603a, and a fluororesin tube having a thickness of about 20 μm is coated as a release layer 603c on the elastic layer 603b.

  The heater holder 601 (hereinafter, referred to as a holder 601) is a member that holds the heater 600 in a state of being pressed toward the fixing belt 603. The holder 601 has a substantially semi-circular cross-sectional shape, and has a function of regulating the rotation trajectory of the fixing belt 603. For the holder 601, a resin or the like having high heat resistance is used. In this embodiment, Zenite 7755 (trade name) manufactured by DuPont is used.

  The support stay 602 is a member that supports the heater 600 via the holder 601. It is desirable that the support stay 602 be made of a material that does not easily bend even when a large load is applied. In this embodiment, SUS304 (stainless steel) is used.

  As shown in FIG. 4, the support stay 602 is supported by flanges 411a and 411b at both ends in the longitudinal direction. The flanges 411a and 411b are collectively called a flange 411. The flange 411 regulates the longitudinal movement and the circumferential shape of the fixing belt 603. A heat-resistant resin or the like is used for the flange 411, and in this embodiment, PPS (polyphenylene sulfide) is used. A pressure spring 415 (415a, 415b) is provided in a contracted state between the flange 411 and the pressure arm 414 (414a, 414b).

  With the above configuration, the elastic force of the pressure spring 415 is transmitted to the heater 600 via the flange 411, the support stay 602, and the holder 601. Then, the fixing belt 603 is pressed against the pressing roller 70 with a predetermined pressing force, and a nip portion N having a predetermined width is formed in the recording material conveying direction a. The applied pressure in this embodiment is about 156.8 N on one end and the other end, respectively, and the total applied pressure is about 313.6 N (32 kgf).

  The connectors 700 a and 700 b are power supply members that are electrically connected to the heater 600 to apply a voltage to the heater 600, and are detachably attached to both ends of the heater 600 in the longitudinal direction.

  The pressure roller 70 is a driving rotator that forms a nip N for heating the toner image T on the recording material (on the sheet) in cooperation with the fixing belt 603 and that rotates the fixing belt 603. The pressure roller 70 has a multilayer structure in which an elastic layer 72 is provided on a metal core 71 and a release layer 73 is provided on the elastic layer 72. As the metal core 71, stainless steel, SUM (sulfur and sulfur composite free-cutting steel), or aluminum can be used. As the elastic layer 72, a silicone rubber, a sponge rubber layer, or an elastic foam rubber can be used. As the release layer 73, a fluorine resin material can be used.

  The pressure roller 70 of this embodiment includes a metal core 71 made of stainless steel, an elastic layer 72 of foamed silicone rubber, and a release layer 73 of a fluororesin tube. The outer diameter is about 25 mm, and the longitudinal length of the elastic layer is 330 mm.

  As shown in FIG. 4, both ends of the core metal 71 of the pressure roller 70 are rotatably held between one end side and the other end side plates 41a and 41b of the device housing 41 via bearings 42a and 42b, respectively. Have been. A gear G is provided at one end of the metal core 71 to transmit the driving force of the motor M to the metal core 71. The pressure roller 70 driven by the motor M rotates in the direction of arrow R70 in FIG. 3, and transmits the driving force to the fixing belt 603 at the nip N to rotate the fixing belt 603 in the direction of arrow R603. In this embodiment, the motor M is controlled by the control circuit 100 so that the surface speed of the pressure roller 70 becomes 200 mm / sec.

  A thermistor 630 is a temperature sensor provided on the back side of the heater 600 and detecting the temperature of the heater 600. In the printer 1 of the present embodiment, the recording material P is conveyed on the basis of the center. Therefore, the thermistor 630 includes a heater rear surface portion (a recording material of any width, large or small) corresponding to a longitudinal central portion of a resistance heating element 620 of the heater 600 described later. (A heater area portion through which the air also passes). The thermistor 630 is connected to the control circuit 100 via the A / D converter 101, and transmits an output corresponding to the detected temperature to the control circuit 100.

  The control circuit 100 is a circuit provided with a CPU for performing calculations associated with various controls and a nonvolatile storage medium such as a ROM. A program is stored in this ROM, and various controls are executed by reading and executing the program by the CPU. The control circuit 100 is electrically connected to the power supply 110 so as to control the energization of the power supply 110.

  Further, the control circuit 100 reflects the temperature information obtained from the thermistor 630 in the power supply control of the power supply 110. That is, the control circuit 100 controls the power supplied to the heater 600 based on the output of the thermistor 630. In this embodiment, a method of adjusting the heat generation amount of the heater 600 by performing wave number control on the output of the power supply 110 is used. When fixing the toner on the recording material, the heater 600 is maintained at a predetermined temperature. Is done.

[heater]
Next, the configuration of the heater 600 in the present embodiment will be described in detail. FIG. 1 is a schematic diagram of a configuration of a heater 600 used in the present embodiment, and FIG. 6 is a schematic diagram illustrating a heating method of a heater and a switching method of a heating region.

  As shown in FIG. 6A, a branch path 715a, a branch path 715b, and a branch path 715c are connected to the first conductor path 710. On the other hand, a branch path 725d, a branch path 725e, and a branch path 725f are connected to the second conductor path 720.

  The branch paths 715a, 715b, and 715c connected to the first conductor path 710 and the branch paths 725d, 725e, and 725f connected to the second conductor path 720 are arranged alternately in the longitudinal direction. A body 620 is provided for electrical connection. When a voltage V is applied between the first conductor path 710 and the second conductor path 720, a potential difference occurs between adjacent branch paths, and the resistance heating element 620 generates heat due to generation of a current indicated by an arrow in the drawing.

  When a switch SW is provided between the branch path 725e and the branch path 725f and the switch SW is turned off as shown in FIG. 6B, the branch path 715b and the branch path 715c have the same potential. The heating element 620 between the and the branch path 715c does not generate heat.

  That is, by cutting off the electrical connection of a part of the conductor path, only a part of the heating element can generate heat. When a plurality of heating elements arranged in the longitudinal direction are energized to generate heat, it is preferable to arrange the branch paths so that the directions of currents of adjacent heating elements are alternated.

  As another arrangement of the heating element and the second branch path, there is a configuration in which different-polarity branch paths are connected to both ends of the heating element so that the current direction is the same in the longitudinal direction. However, since two branch paths are required between adjacent heating elements, a short circuit may occur between the branch paths. In addition, since the width of the branch path between the heating elements is increased, the non-heating portion is increased, and the heater and the fixing belt are uneven in temperature in the longitudinal direction. Therefore, a configuration in which the heating element and the branch path are arranged so as to double as the branch path between the adjacent heating elements is desirable.

  Next, the heater 600 of this embodiment will be described in detail with reference to FIG. The heater 600 has an elongated plate-shaped substrate 610. Further, the heating elements 620 (a to l) formed on the substrate 610 and the conductor patterns (640, 650, 660 (a, b), 642 (a to g), 652 (ad), and 662 ( a, b)) and electrodes (641, 651, 661). Further, it has an insulating coat layer (not shown) covering the heating element 620 and the conductor pattern.

  The substrate 610 is a member that determines the size and shape of the heater 600, and is made of a ceramic material such as alumina or aluminum nitride which is excellent in heat resistance, heat conductivity, and electrical insulation. In this embodiment, alumina having a length in the longitudinal direction of 400 mm, a length in the transverse direction of 8.0 mm, and a thickness of about 1 mm is used.

  The heating element 620 and the conductor pattern are formed on the substrate 610 by a screen printing method. In this embodiment, a silver paste which is a low resistivity material or an alloy paste in which a small amount of palladium is mixed with silver is used as the conductor pattern. In addition, a paste of a silver-palladium alloy is used for the heating element 620 so as to have a desired resistance value. Further, the heating element 620 and the conductor pattern are covered with an insulating coat layer (not shown) made of heat-resistant glass, and are electrically protected so as not to cause leakage or short circuit.

  Electrodes 641, 651, and 661 that are electrically connected to the power supply 110 via the connectors 700a and 700b are provided on both ends in the longitudinal direction of the substrate 610. Further, a heating element 620 and branch paths (642 (ag), 652 (ad), 662 (a, b)) are provided on the substrate 610. The branch path is a conductor path that electrically connects the common conductor path 640, the first opposed conductor path 650, the second opposed conductor path 660a, the third opposed conductor path 660b, and the heating element 620.

  In the present embodiment, the heating elements 620 (a to l) are formed on the substrate 610 as one elongated heating element along the length of the substrate. The heating element 620 of this embodiment has a width (length in the lateral direction) of about 1.5 to 2.0 mm (details will be described later), a thickness of about 20 μm, and a length in the longitudinal direction of about 320 mm. . The length of about 320 mm is a length that can heat the entire area of the large-sized recording material P of A4 size (297 mm in width). The total resistance of the heating element 620 is about 10Ω.

  By stacking seven common branch paths 642a to 642g on the heating element 620 at equal intervals in the longitudinal direction, the heating element 620 is divided into six sections by the common branch paths 642a to 642g. The length of each section of the heating element 620 is about 53.3 mm. Further, six opposing branch paths 652 and 662 are stacked at the center of each section of the heating element 620, and the heating element 620 is divided into 12 sections from 620a to 620l. The length of each section is about 26.7 mm.

The above heater configuration is summarized as follows. The heater 600 has an elongated substrate 610 and a resistance heating element 620 extending along the length of the substrate 610. Further, a plurality of electrodes 641, 651, 661 provided on one end side and the other end side in the longitudinal direction of the substrate, and each of the plurality of electrodes extends along the length of the resistance heating element 620. A plurality of conductor paths 640, 650, 660.

  In addition, there are a plurality of branch paths 642, 652, 662 branching from each of the plurality of conductor paths at intervals along the longitudinal direction. These branches are electrically connected to the resistance heating element across the resistance heating element 620 to divide the resistance heating element into a plurality of small section heating elements 620a to 620l along the length between the branch paths. .

  The resistance values of the common branch path 642 and the opposing branch paths 652 and 662 are significantly smaller than the resistance value of the heating element 620. For this reason, when the width (length in the longitudinal direction) of the branch path is increased, the heating element 620 becomes uneven in the amount of heat generated, so that the heater 600 and the fixing belt 603 have uneven temperature in the longitudinal direction. As a result, the gloss of the image on the recording material becomes uneven. This phenomenon is caused by the fact that the temperature of the fixing belt 603 at the portion facing the branch path becomes low, so that the toner on the recording material cannot be sufficiently heated and melted, so that the gloss becomes low.

  The common branch paths 642 (a to g) are provided so as to be orthogonal to the heating element 620, and are further provided at odd-numbered positions from one longitudinal end of the heating element 620. The common branch path 642 is electrically connected to the terminal 110a (FIG. 5) on one side of the power supply 110 via the first conductor path 640 and the like.

  The opposed branch passages 652 and 662 are provided so as to be orthogonal to the heating element 620, and are provided even-numbered from one end in the longitudinal direction of the heating element 620. The opposing branch paths 652, 662 are electrically connected to the terminal 110b (FIG. 5) on the other side of the power supply 110 via opposing conductor paths 650, 660 and the like.

  That is, the common branch path and the opposite branch path are alternately arranged in the longitudinal direction of the heating element 620. The common conductor path 640 is formed along the longitudinal direction of the substrate 610, is connected to each common branch path 642, and one end is connected to the common electrode 641. Similarly, the first opposing conductor path 650, the second opposing conductor path 660a, and the third opposing conductor path 660b are also formed along the longitudinal direction of the substrate 610. The first opposing conductor path 650 is connected to opposing branch paths 652 (ad), and one end is connected to an electrode 651. The second and third opposed conductor paths 660a and 660b are connected to opposed branch paths 662a and 662b, respectively, and one end is connected to an electrode 661.

  The electrode 641 is provided on one end of the substrate 610 in the longitudinal direction, and the electrodes 651 and 661 are arranged side by side on the other end of the substrate 610 in the longitudinal direction. The electrode 641 is not provided with an insulating coat layer for ensuring electrical connection with the connector 700a, and is provided outside the region that is in contact with the fixing belt 603 in an exposed state. Also, the electrodes 651 and 661 are not provided with an insulating coat layer to secure electrical connection with the connector 700b, and are provided outside a region where the electrodes 651 and 661 are in contact with the fixing belt 603 in an exposed state.

  As described above, the heating element 620 of the heater 600 according to the present embodiment is electrically connected to the power supply 110 via the connector, the electrode, the common conductor path, the opposed conductor path, and the branch path.

[Power supply to heater]
The power is supplied to the heater 600 according to the width size of the recording material used in the small-section heating elements 620a to 620l, so that the small-section heating elements located in the area corresponding to the width size selectively generate heat. , 651, 661 are selectively applied with a voltage.

  This power supply method will be described with reference to FIG. Power supply 110 is a power supply source for heater 600. In the present embodiment, a commercial power source having an effective value of single-phase alternating current of about 100 V is used, and includes a power terminal 110a and a power terminal 110b. The power supply 110 may be a DC power supply as long as it has a function of supplying power to the heater 600.

  The control circuit 100 is electrically connected to the switches (SW) 643, the switches 653, and the switches 663 to control the switches. The switch 643 is a switch (relay) provided between the power supply terminal 110a and the electrode 641, and switches whether to connect the power supply terminal 110a and the electrode 641 (ON or OFF) according to an instruction from the control circuit 100. Do.

  The switch 653 is a switch provided between the power supply terminal 110b and the electrode 651, and switches whether or not to connect the power supply terminal 110b and the electrode 651 according to an instruction from the control circuit 100. Similarly, the switch 663 is a switch provided between the power supply terminal 110b and the electrode 661, and switches whether to connect the power supply terminal 110b and the electrode 661 according to an instruction from the control circuit 100.

  The control circuit 100 acquires the width size information of the recording material P in response to receiving the print job (print job) execution instruction. Then, on / off of the switches 643, 653, 663 are controlled in accordance with the acquired width size information, and control is performed such that the heat generating area of the heat generating element 620 becomes a heat generating area suitable for fixing the recording material P. .

  The control circuit 100 acquires width size information of the recording material P in response to receiving a print job (print job) execution instruction, and controls ON / OFF of the switches 643, 653, 663 according to the width size information. . That is, control is performed on the basis of the center so that the heat generating area in the longitudinal direction of the heat generating element 620 becomes a heat generating area suitable for fixing the recording material P having a width corresponding to the acquired width size information.

  Next, a method of changing the heating area of the heating element 620 according to the size of the recording material P in the width direction will be described. First, when the recording material P has a large size such as A4 horizontal size (size in the width direction of 297 mm), the control circuit 100 controls the heating element 620 so that the heating width B generates heat. In this embodiment, the entire length of the small section heating elements 620a to 620l corresponds to the width of the usable maximum width recording material.

  More specifically, the control circuit 100 turns on all of the switches 643, 653, and 663. In this case, power is supplied to the heater 600 from the electrodes 641, 651, and 661, and the heating element 620 has 12 heating elements. All of the small sections 620a to 620l generate heat. At this time, the heater 600 generates heat in the entire area of the heating element of about 320 mm, and is in a heat generating state suitable for performing the fixing process of the recording material P of A4 landscape size.

  Next, when the recording material P is a small and small size such as the A4 vertical size (the size in the width direction 210 mm), the control circuit 100 controls the heating element 620 so that the heating width A generates heat. Specifically, since the control circuit 100 turns on the switch 643 and the switch 653 and turns off the switch 663, power is supplied to the heater 600 from the electrodes 641 and 651, and the heating element 620 has 12 small elements. Eight of the sections 620c to 620j generate heat.

  At this time, since the heater 600 generates heat in an area of about 213 mm, the heater 600 is in a heat generating state suitable for performing the fixing process of the recording material P of A4 vertical size. Therefore, even when a fixing process is performed on a recording material having a small size in the width direction such as an A4 vertical size, the heater 600 does not generate heat in a portion where the recording material does not pass, so that no wasteful power is used. .

  Next, a description will be given of a configuration of the heater 600 for equalizing the amount of heat generated in the small sections 620a to 620l of the heating element 620, which is a characteristic part of the present embodiment. First, for comparison, a description will be given using a model (comparative example) in which the short width of the heating element is uniform as shown in FIG. FIG. 8 shows an electric circuit diagram of the configuration of FIG.

  Originally, only the heat generated from the heating element 620 is ideal as a portion that contributes to the heat generation of the heater 600, and the amount of heat generated in a place other than the heating element 620 needs to be minimized. If heat is generated in a place other than the heat generating element 620 (mainly, heat is generated in the conductor path), the heat becomes heat that hardly contributes to fixing (the conductor path is wired at the edge of the substrate, and the fixing nip is formed). Because it will generate heat where it doesn't matter.) As a result, power is consumed wastefully.

  As for the actual heat generation, not only the heat generation of the heating element but also the heat generation of the conductor path is present to a considerable extent. This is because the conductor path also has a considerable resistance and generates heat when a current flows through the conductor path.

  In FIG. 8, the resistance value R indicates the resistance of the heating element 620, and the resistance values r1 to r13 indicate the resistance values of the conductor paths. The sheet resistance of the heating element 620 in this embodiment is 8.99 [Ω / □], the interval between the common branch path of the heating element and the opposing branch path, 26.7 [mm], and the width of the heating element is 2.0. [Mm].

  The resistivity of the conductor path and the branch path is 0.00002Ω · mm, the height of the conductor path is 10 μm, the width of the first opposed conductor path and the second opposed conductor path is 1.0 [mm], and the width of the common conductor path is 1.5 [mm], and the total length of the heating element is 320 [mm]. The length between the common electrode 641 and the branch path 642a, the length between the first power supply electrode 651 and the branch path 642g is 24 mm, the length in the longitudinal direction of the electrode is 4.0 mm, and the distance between the electrodes is 3 mm. 0.5 mm.

  In this case, when each resistance value is derived, R = 120Ω, r1 = 0.032Ω, r2 = r3 = r4 = r5 = r6 = r7 = 0.071Ω, r8 = 0.126Ω, r9 = 0.208Ω, r10 = R11 = r12 = 0.107Ω and r13 = 0.650Ω. The applied voltage is 100 [v].

  The currents i1 to i7 flowing in the common conductor path 640 and the currents i8 to i13 flowing in the opposing conductor paths 650 and 660 are obtained using Kirchhoff's law, and the current flowing in the heating element is calculated as shown in Table 1. Further, since the power consumed by the heating element is P = i ＾ 2 × R, the power consumed by the heating element is also shown in Table 1. The power consumed by the heating element is the temperature distribution of the heating element.

  As shown in Table 1, the current / heat generation amount at the central portion of the region (620c to 620j) where a plurality of heating elements are connected in parallel to one conductor path decreases, and as a result, the temperature of that portion decreases. You can see that. Therefore, it is necessary to reduce the resistance value in the central portion of the region where a plurality of heating elements are connected in parallel to one conductor path, and increase the current flowing therethrough.

  Therefore, in this embodiment, in order to reduce the resistance value in the central portion of the region where a plurality of heating elements are connected in parallel to one conductor path, a plurality of heating elements are connected to one conductor path as shown in FIG. Are connected in parallel, the width of the short side of the central part of the region is widened.

  That is, regarding the resistance value Rh between the branch paths of the small section heating elements, the resistance value Rh between the plurality of small section heating elements 620a to 620l is changed by adjusting the short width of the small section heating elements. In other words, regarding the resistance value Rh between the branch paths of the small section heating elements, the resistance value Rh of the small section heating elements at both ends of the plurality of small section heating elements 620a to 620l is RA, and the small section heating element at the central portion is RA. If the resistance value Rh) is RB, then RA> RB. If the resistance value Rh of the small section heating element adjacent to the small section heating element at the center is RC, then RA> RC. In this case, it is possible to set RA = RC. That is, RA ≧ RC.

  FIG. 9 shows longitudinal resistance value distributions of the embodiment of FIG. 1 and the comparative example of FIG. As shown in FIG. 9, in the present embodiment, the resistance value of the central heating element is lower than in the comparative example. The resistance value can be lowered by changing the material (specific resistance), length, width, and thickness. In the present embodiment, the resistance value was lowered by adjusting the width of the heating element.

  Specifically, the width of the heating elements 620a, 620b, 620k, and 620l was a uniform shape of 2.0 [mm]. Further, the width of the heating element of the branch path 642b is 2.0 [mm], the width of the heating element of the branch path 642d is 2.08 [mm], and the width of the heating element of the branch path 642f is 2.0 [mm]. did. Further, the width of the heating element between the branch path 642b and the branch path 642d and the width of the heating element between the branch path 642d and the branch path 642f are linearly changed. Table 2 shows the relationship between the current value and the power (heating value) of each heating element of the present embodiment.

  FIG. 10 shows a heat generation distribution of the comparative example and the present example. As shown in FIG. 10, the configuration of this example was able to increase the calorific value of the central portion as compared with the comparative example. FIG. 11 shows the temperature distribution in the longitudinal direction of the fixing belt 603 in this embodiment. FIG. 11 is a diagram showing the temperature distribution of the fixing belt when the present embodiment in FIG. 6 and the comparative example in FIG. 7 are used.

  The temperature distribution when the heater 600 of the present embodiment is used is indicated by a solid line, and the temperature distribution when the heater of the comparative example is used is indicated by a broken line. The horizontal axis in FIG. 11 indicates the position when the center of the heater is set as the origin. FIG. 11 shows a temperature distribution when the temperature at the center is maintained at 200 ° C. by the thermistor 630.

  In the case of the heater of the comparative example, the temperature at the end is higher than that at the center. Therefore, temperature unevenness occurs in the longitudinal direction, and gloss unevenness occurs in the longitudinal direction in the image after the fixing process.

  In the case of the heater 600 according to the present embodiment, since the amount of heat generated by the heating elements 620c to 620j is changed, the temperature in the longitudinal direction of the fixing belt 603 becomes uniform at about 200 ° C. At this time, the gloss unevenness of the image does not occur as described above. The heater has a thermal conductivity of 90 [W / m * K].

  In order to suppress the power reduction in the conductor path, the width of the conductor path should be designed as wide as possible. However, in this case, there is a disadvantage that the width of the substrate becomes large. Increasing the width of the substrate increases the cost of the heater. It is also effective to make the thickness of the conductor path as thick as possible, but since it is made by screen printing, the thickness that can be printed at one time is determined, and in order to increase the thickness, the number of times of printing must be increased. Increasing the number of printings reduces the manufacturing efficiency of the heater.

  Although the heater of the present embodiment has a configuration having only two regions (FIG. 5) of the heating region A and the heating region B, the present invention is not limited to this configuration. Needless to say, this is also applicable.

  As described above, with the heater of this embodiment, it is possible to change the heating area of the resistance heating layer in accordance with the width size of the recording material introduced and used in the apparatus, and the heat generation amount in the longitudinal direction is uniform. It is possible to provide a simple heater.

<< Other Examples >>
(1) The numerical values such as dimensions exemplified in the embodiments are merely examples, and the present invention is not limited to these numerical values. Numerical values can be appropriately selected within a range to which the present invention can be applied. Further, the configurations described in the embodiments may be appropriately changed within a range in which the present invention can be applied.

  (2) In the heater 600 of the embodiment, the shape of the heating element 620 is changed by changing the screen pattern. However, the heating layer is divided into a plurality of layers, the thickness of the heating element itself is changed, and each of the small heating elements 620 is changed. The resistance values of the section heating elements 620 (a to l) may be changed.

  (3) The control for changing the width of the heating area of the heater 600 is not limited to the central reference. For example, the control for changing the width of the heat generation area of the heater 600 may be based on the end portion. Therefore, when the heat generation area of the small-size recording material is set to be the heat generation area of the large-size recording material, the heat generation areas at both ends in the width direction of the small-size recording material are not enlarged, but are generated at one end in the width direction of the small-size recording material. A configuration in which the heat generation area on the side is enlarged may be employed.

  (4) The change pattern of the heating area of the heater 600 is not limited to the two patterns of the large-size recording material and the small-size recording material. For example, a change control of three or more heating regions may be provided.

  (5) The method for forming the heating element 620 is not limited to the method described in the embodiment. Specifically, in the embodiment, the common electrode 642 and the counter electrodes 652 and 662 are stacked on the heating element 620 extending along the longitudinal direction of the substrate 610. Electrodes may be arranged side by side in the longitudinal direction of the substrate 610, and the heating elements 620a to 620l may be formed between adjacent electrodes.

  (6) The number of electrical contacts is not limited to three or four. If all the electrical contacts are arranged on one end side 610a of the substrate, five or more electrical contacts may be provided. For example, in the embodiment, an electrical contact different from the electrical contacts 641, 651, 661a, 661b may be provided on one end side 610a of the substrate.

  (7) The electrical contacts connected to the power terminal 110a are not limited to the electrical contacts 641. For example, on one end side 610a of the substrate, an electrical contact that is connected to the power supply terminal 110a side and that is different from the electrical contact 641 may be provided.

  (8) The belt 603 is not limited to the configuration in which the inner surface of the belt 603 is supported by the heater 600 and driven by the roller 70. For example, a belt unit system that is wound over a plurality of rollers and driven by any of the plurality of rollers may be used.

  (9) The nip forming member that forms the nip portion N with the belt 603 is not limited to a roller member such as the roller 70. For example, a pressure belt unit in which a belt is stretched over a plurality of rollers may be used.

  (10) The fixing device is not limited to use as a device that heats and fixes an unfixed toner image formed on a recording material as a fixed image. It is also effective as a device for adjusting the surface properties of an image such as improving the glossiness of the image by heating and pressing the toner image once fixed or temporarily assumed to be applied to the recording material. Device).

  (11) The image forming apparatus is not limited to the image forming apparatus that forms a full-color image as in the embodiment, but may be an image forming apparatus that forms a monochrome image. The image forming apparatus can be implemented in various applications such as a copier, a facsimile, and a multifunction peripheral having a plurality of these functions, in addition to necessary devices, equipment, and a housing structure.

  600 heaters, 620 resistance heating elements, 641, 651, 661 electrodes, 640, 650, 660 conductor paths, 642, 652, 662 branch paths, 620a to 620l small section heating elements

Claims (5)

An elongated substrate,
A resistance heating element extending along the length of the substrate;
A plurality of electrodes provided on one end side and the other end side in the longitudinal direction of the substrate,
A plurality of conductor paths extending from each of the plurality of electrodes along the length of the resistance heating element,
A plurality of branch paths branching from each of the plurality of conductor paths at an interval along the longitudinal direction, wherein the branch paths are electrically connected to the resistance heating elements across the resistance heating elements. A branch that divides the resistance heating element into a plurality of small section heating elements along its length,
Selective for the plurality of electrodes so that the small-section heating element located in the area corresponding to the width size of the recording material used in the plurality of small-section heating elements selectively generates heat. A voltage is applied to the heater for heating the toner image on the recording material,
Regarding the resistance value between the branch passages of the small section heating element, each of the plurality of small section heating elements is located at a position adjacent to each of the small section heating elements on both ends and the small section heating element on both ends. When the resistance value of each of the small section heating elements located on the center side of the small section heating elements on both ends is RA, and the resistance value of the central small section heating element is RB, RA> A heater characterized by being RB. 2. The heater according to claim 1, wherein the resistance value between the plurality of small-section heating elements is changed by adjusting a short width of the small-section heating elements. 3. 3. The heater according to claim 1, wherein a total length of the plurality of small section heating elements corresponds to a width size of a usable maximum width recording material. 4. A heater according to any one of claims 1 to 3, a heat transfer member which moves while sliding in contact with the heater, contact with the nip forming member across said heat transfer member between the heater Wherein the recording material is nipped and conveyed in a nip portion formed between the heat transfer member and the nip forming member and heated. The fixing device according to claim 4 , wherein the heat transfer member is an endless belt.