JP2019012634A - Heater and fixing device - Google Patents

Abstract

To provide a heater that can change a region where a resistance heating layer produces heat depending on a width size of recording member and prevent temperature of both end parts of a fixing belt from decreasing by increasing heating values of a longitudinal end region.SOLUTION: The heater comprises: a connector connected to one terminal and the other terminal of a power source; a substrate extending along a longitudinal direction, which is mounted with the connector to sandwich the two sides of the substrate; a plurality of electrodes 641, 651 and 661 which are provided on the substrate with which the connector contacts; conductor paths 660a and 660b provided from the electrodes toward the longitudinal direction of the substrate; a plurality of branched paths connecting the conductor paths to a heating element 620; and a plurality of heating elements provided to electrically connect the plurality of adjacent branched paths, in which a resistance value of a center part of the heating element of the heating element group connected to the conductor path at a power supply side and resistance values of both end parts of the heating element of the heating element group are appropriately set to Rc and Rf respectively.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a heater used for heating a toner image on a recording material, and a fixing device including the heater. The heater and the fixing device of the present invention are used in an image forming apparatus such as a copying machine, a printer, a fax machine, and a multifunction machine having a plurality of these functions.

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

  Further, Patent Document 1 discloses a configuration in which a region where the heater generates heat is changed according to the width size of the recording material. FIG. 12 is a circuit diagram of the fixing device described in Patent Document 1. In this fixing device, electrodes 1027 (1027a to 1027f) are arranged side by side in the longitudinal direction of the substrate 1021, and the resistance heating layer 1025 is heated by energizing the resistance heating layer 1025 (1025a to 1025e) from each electrode.

  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 electrode 1027b and the electrode 1027d extends to one end in the longitudinal direction of the substrate. The wiring layer 1029a connected to the electrode 1027c and the electrode 1027e extends to the other end in the longitudinal direction of the substrate. Furthermore, the electrode 1027a and the wiring layer 1029b can be connected to the 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. An insulating layer for protecting each wiring is not provided at both ends in the longitudinal direction of the substrate, and the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f are exposed.

  Therefore, the resistance heating layer 1025 is connected to the power supply circuit by the wiring member coming into contact with the exposed portions of the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f. The power supply circuit includes an AC power supply and switches 1033 (1033a, 1033b, 1033c, 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 side or the power supply terminal 1031b side according to the connection pattern in the power supply circuit, and the heat generation area of the resistance heat generation layer 1025 is changed according to the sheet width size. ing.

JP 2012-37613 A

  By the way, in patent document 1, although the characteristic of a material used for a wiring layer and an electrode, resistance value, etc. are not indicated, silver which is a material with low resistivity as a wiring layer generally used with a heater of the same composition, Alternatively, a mixture of silver and palladium is used. Since the heater used in the fixing device is required to reduce the size of the fixing device due to the demand for downsizing the fixing device, it is required to reduce the width of the wiring layer.

Further, in a heater used in a general fixing device, the length of the heating resistor in the longitudinal direction is about 330 mm, which is shorter than the longitudinal length of the fixing belt of 340 mm.
Therefore, the amount of heat generated at both ends of the heater is also lost to both ends of the fixing belt where the heater heat generating area does not face, and the temperature at both ends of the fixing belt is lowered (hereinafter referred to as temperature sag). As a result, unevenness occurs in the temperature in the longitudinal direction of the belt heated by the heater, so that the gloss of the image on the recording material after the fixing process becomes non-uniform.

  Therefore, according to the present invention, it is possible to change the region where the resistance heating layer generates heat according to the width size of the recording material, and to increase the heat generation amount in the longitudinal end region, the temperature at both ends of the fixing belt decreases. There is no heater.

The present invention includes a connector (700) connected to one terminal of the power source (110) and the other terminal,
A board (610) extending along the longitudinal direction to which the connector (700) is attached so as to sandwich the front and back thereof; and
A plurality of electrodes (641, 651, 661) provided on a substrate (610) with which the connector (700) contacts;
A conductor path (640, 650, 660) provided from the electrode toward the longitudinal direction of the substrate (610);
A plurality of branch paths (642, 652, 662) connecting the conductor paths (640, 650, 660) and the heating elements (620a to 620l);
A plurality of heating elements (620a to 620l) provided to electrically connect a plurality of adjacent branch paths,
Heating element group 1 (620c to 620j) connected to power supply side conductor path 1 (650), and heating element group 2 (620a, 620b, 620k, 620l) connected to power supply side conductor path 2 (660) )
When the resistance value of the central part (620f, 620g) of the heating element of the heating element group 1 is Rc and the resistance value of both ends (620a, 620l) of the heating element of the heating element group 2 is Rf,
A heater characterized in that the relationship of heating element resistance is Rc>Rf>. It is.

  According to the present invention, it is possible to provide a heater in which the region where the resistance heating layer generates heat can be changed according to the width size of the recording material, and the heat generation amount in the longitudinal direction is uniform.

1 is a diagram illustrating an image forming apparatus according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view illustrating the fixing device according to the first exemplary embodiment. FIG. 3 is a front view illustrating the fixing device according to the first exemplary embodiment. FIG. 3 is a heater circuit diagram according to the first embodiment. The figure explaining the heat_generation | fever method and switching method of the heater 600. FIG. FIG. 3 is a diagram illustrating a configuration of a heater according to the first embodiment. The figure explaining the structure of the heater of a comparative example. The figure explaining the equivalent electric circuit of the heater of a comparative example. The figure explaining resistance value distribution of the heat generating body of Example 1 and a comparative example. The figure explaining the emitted-heat amount distribution of the heat generating body of Example 1 and a comparative example. The heater circuit diagram of a prior art example.

  Embodiments according to the present invention will be described below. In the following embodiments, a laser beam printer using an electrophotographic process will be described as an example.

[Example 1]
[Image forming apparatus]
FIG. 1 is a cross-sectional view of a printer 1 which is an image forming apparatus of this embodiment. The printer 1 is an image forming apparatus in which the toner image formed on the photosensitive drum 11 in the image forming unit 10 is transferred to the recording material P and then the image is fixed on the recording material P by the fixing device 40.

  As shown in FIG. 1, the printer 1 includes an image forming unit (image forming station) 10 that forms toner images of each color of Y (yellow), M (magenta), C (cyan), and Bk (black). Yes. The image forming unit 10 includes four photosensitive drums 11 (11Y, 11M, 11C, and 11Bk) corresponding to the colors Y, M, C, and Bk in order from the left side of FIG. Around each photosensitive drum 11, a charger 12, an exposure device 13, a developing device 14, a primary transfer blade 17, and a cleaner 15 are arranged. Hereinafter, a procedure for forming a Bk color toner image will be described, but a procedure for forming other color toner images is also the same. A photosensitive drum 11 as an electrophotographic photosensitive member is rotationally driven in the direction of an arrow by a driving source (not shown). Around the photosensitive drum 11, a charger 12, an exposure device 13, a developing device 14, a primary transfer blade 17, and a cleaner 15 are sequentially arranged along the rotation direction.

  Next, a procedure until a toner image is formed on the recording material P will be described. After the surface of the photosensitive drum 11 is uniformly charged by the charger 12, it is exposed according to the image information by the exposure device 13, thereby forming an electrostatic latent image. Then, the toner is developed in the portion exposed to the laser beam by the developing device 14, and a toner image is formed on the photosensitive drum 11. At this time, the same process is performed for the other colors.

  The toner image on each photosensitive drum 11 is primarily transferred to the intermediate transfer belt 31 by the primary transfer blade 17, and the toner remaining on the photosensitive drum 11 is removed by the cleaner 15. Thus, the photosensitive drum 11 is ready for the next image formation.

  On the other hand, the recording material P placed on the feeding cassette 20 or the multi-feed tray 25 is fed one by one by a feeding mechanism (not shown) and fed to the registration roller pair 23. The registration roller pair 23 temporarily stops the recording material P, and when the recording material P is skewed with respect to the transport direction, the direction is straightened and synchronized with the toner image on the intermediate transfer belt 31. The recording material P is fed between the intermediate transfer belt 31 and the secondary transfer roller 35. The secondary transfer roller 35 transfers the toner image on the intermediate transfer belt 31 to the recording material P.

  The recording material P to which the toner image has been transferred is conveyed to the fixing device 40, and a toner image permanently fixed on the recording material P is formed by heating and pressing.

[Fixing device]
Next, the fixing device 40 will be described. 2 is a cross-sectional view of the fixing device 40, and FIG. 3 is a diagram illustrating a front view of the fixing device 40. The belt unit 60 that heats the image on the recording material P is configured to heat a flexible thin fixing belt 603 by a heater 600 that contacts the inner surface.

  As shown in FIG. 2, the fixing belt 603 has a nip portion N formed by the pressure of the heater 600 and the pressure roller 70, and sandwiches and conveys the recording material P fed to the nip portion N. 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 to the recording material P.

  The belt unit 60 is a unit for heating and pressing an image on the recording material P, and is provided in parallel with the pressure roller. The belt unit 60 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 toward the pressure roller 70 so that the nip portion N has a desired width. The heater 600 includes a substrate 610 and a resistance heating element 620 (hereinafter referred to as a heating element 620) on the substrate 610, and is fixed to a recess on the lower surface of the heater holder 601. In this embodiment, the 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 the front side (the side in contact with the fixing belt 603). ) May be provided.

  A polyimide layer having a thickness of about 10 μm is provided as a sliding layer on the surface side of the substrate 610, and by reducing the frictional resistance between the fixing belt 603 and the heater 600, wear on the inner surface of the fixing belt 603 is suppressed. It can be done. Further, a lubricant such as grease may be applied to the inner surface of the fixing belt 603 in order to reduce the rubbing resistance.

  The fixing belt 603 is a cylindrical belt for heating and pressurizing the toner image on the recording material at the nip portion N. In this embodiment, a substrate provided with an elastic layer 603b and a release layer 603c 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 of 340 mm, and a thickness of 30 μm is used as the base material 603a. Furthermore, 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.

  A 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. Further, the holder 601 has a semicircular cross-sectional shape and has a function of regulating the rotation trajectory of the fixing belt 603. The holder 601 is made of highly heat-resistant resin or the like, and 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. The support stay 602 is desirably made of a material that is not easily bent even when a large load is applied. In this embodiment, SUS304 (stainless steel) is used.

  As shown in FIG. 3, the support stay 602 is supported by the flanges 411a and 411b at both ends in the longitudinal direction. The flanges 411a and 411b are collectively referred to as a flange 411. The flange 411 regulates the movement of the fixing belt 603 in the longitudinal direction and the shape in the circumferential direction. A heat-resistant resin or the like is used for the flange 411, and PPS (polyphenylene sulfide) is used in this embodiment. A pressure spring 415 is provided between the flange 411 and the pressure arm 414 in a contracted state. With the above configuration, the elastic force of the pressure spring 415 is transmitted to the heater 600 via the flange 411 and the support stay 602. The fixing belt 603 is pressed against the pressure roller 70 with a predetermined pressing force, and a nip portion N having a predetermined width is formed. In this embodiment, the applied pressure is about 156.8 N on one end side and the total applied pressure is about 313.6 N (32 kgf).

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

As shown in FIG. 2, the pressure roller 70 is a member that forms the nip portion N by being pressed by 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, silicone rubber, sponge rubber layer, or elastic foam rubber can be used. As the release layer 73, a fluororesin material can be used.

  The pressure roller 70 of this embodiment comprises a stainless steel core 71, 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 340 mm.

  As shown in FIG. 3, the cored bar 71 of the pressure roller 70 is rotatably held via the side plate 41 and the bearings 42a and 42b, and a gear G is provided at one end of the cored bar 71, and the motor M driving force is transmitted to the cored bar 71. As shown in FIG. 2, the pressure roller 70 driven by the motor M is driven to rotate in the direction of the arrow, and the driving force is transmitted to the fixing belt 603 at the nip portion N to be driven to rotate. In this embodiment, the motor M is controlled by the control circuit 100 so that the surface speed of the pressure roller 70 is 200 mm / sec.

  The thermistor 630 shown in FIG. 4 is a temperature sensor that is provided on the back side of the heater 600 and detects the temperature of the heater 600. The thermistor 630 is connected to the control circuit 100 via an A / D converter (not shown), and transmits an output corresponding to the detected temperature to the control circuit 100.

  The control circuit 100 is a circuit that includes a CPU that performs calculations associated with various controls and a nonvolatile medium such as a ROM. A program is stored in the ROM, and various controls are executed by the CPU reading and executing the program. The control circuit 100 is electrically connected to the power source 110 so as to control energization of the power source 110.

  Further, the control circuit 100 reflects the temperature information acquired from the thermistor 630 in the energization 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 will be described in detail. FIG. 5 is a diagram for explaining a heater heating method and a heating region switching method, and FIG. 6 is a configuration diagram of the heater used in this embodiment.

  As shown in FIG. 5A, in the heater 600 of this embodiment, 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, 715c connected to the first conductor path 710 and the branch paths 725d, 725e, 725f connected to the second conductor path 720 are alternately arranged in the longitudinal direction, and resistance heat is generated between the branch paths. A body is provided for electrical connection.

  When the voltage V is applied between the first conductor path 710 and the second conductor path 720, a potential difference is generated between the adjacent branch paths, and the resistance heating element generates heat due to the generation of the current indicated by the arrows in the drawing.

  Further, as shown in FIG. 5B, when the switch SW is provided between the branch path 725e and the branch path 725f and the switch is turned off, the branch path 715b and the branch path 715c have the same potential. The heating element 620 between 715c does not generate heat.

  That is, in the heater of the present embodiment, only a part of the heating element can generate heat by disconnecting a part of the electrical connection of the conductor path.

  In the case where a plurality of heating elements arranged in the longitudinal direction are energized to generate heat, a configuration in which the branch paths are arranged so that the current directions of adjacent heating elements are staggered as in the present invention is preferable.

  As another arrangement of the heat generating element and the second branch path, there is a configuration in which branch paths having different polarities are connected to both ends of the heat generating element so that the direction of current 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 heat generating elements becomes wider, the non-heat generating portion becomes larger, and temperature unevenness occurs in the heater 600 and the fixing belt 603 in the longitudinal direction. Therefore, the structure which arrange | positions a heat generating body and a branch path so that it may serve as the branch path between adjacent heat generating bodies like this invention is desirable.

  Next, the heater 600 of this embodiment will be described in detail with reference to FIG. The heater 600 includes a substrate 610, a heating element 620 formed on the substrate 610, a conductor pattern (640, 650, 660, 642, 652, 662), an electrode (641, 651, 661), a heating element 620, and a conductor. It consists of an insulating coat layer (not shown) that covers the pattern.

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

  A heating element 620 and a conductor pattern are formed on the substrate 610 by screen printing. In the present embodiment, a silver paste that 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. The heating element 620 is made of a silver-palladium alloy paste so as to have a desired resistance value.

  Further, the heating element 620 and the conductor pattern are covered with an insulating coating layer (not shown) made of heat-resistant glass, and are electrically protected so as not to cause a leak or a short circuit.

  Electrodes 641, 651, and 661 that are electrically connected to the power source 110 are provided on the longitudinal ends of the substrate 610. Further, the substrate 610 is provided with a heating element 620 and branch paths (642, 652, 662). The branch path is a conductor path that electrically connects the common conductor path 640, the first counter conductor path 650, the second counter conductor path 660a, the third counter conductor path 660b, and the heating element 620.

  The heating element 620 (620a to 620l) is formed on the substrate 610 as one heating element. The heating element 620 of this example has a width (length in the short direction) of about 1.5 to 2.0 mm, a thickness of about 20 μm, a length in the longitudinal direction of about 320 mm, and an A4 size (width size). 297 mm) has a length that can heat the entire area of the recording material P. The total resistance of the heating element 620 is about 10Ω.

  On the heating element 620, seven common branch paths 642a to 642g are stacked at equal intervals in the longitudinal direction, so that the heating element 620 is divided into six sections by the common branch paths 642a to 642g. Note that the length of each section of the heating element 620 is about 53.3 mm. Furthermore, 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 620a to 620l. The length of each section is about 26.7 mm.

  The resistance value of the common branch path 642 and the opposing branch paths 652 and 662 is significantly smaller than the resistance value of the heating element. Therefore, when the width of the branch path (length in the longitudinal direction) is increased, unevenness in the amount of heat generated in the heating element 620 causes unevenness in temperature in the longitudinal direction of the heater 600 and the fixing belt 603. As a result, the gloss of the image on the recording material becomes non-uniform. This phenomenon is attributed to the fact that the toner on the recording material cannot be heated and melted sufficiently because the temperature of the fixing belt 603 at the portion facing the branch path is low, resulting in low gloss.

  The common branch path 642 (642a to 642g) is provided so as to be orthogonal to the heating element 620, and is further provided at an odd number from one end in the longitudinal direction of the heating element 620. The common branch path 642 is electrically connected to the terminal 110a on one side of the power source 110 via the first conductor path 640 and the like.

  The opposing branch paths 652 and 662 are provided so as to be orthogonal to the heating element 620, and are provided evenly from one end in the longitudinal direction of the heating element 620. The opposing branch paths 652 and 662 are electrically connected to the terminal 110b on the other side of the power supply 110 via the opposing conductor paths 650 and 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 and is connected to each common branch path 642, and one end is connected to the common electrode 641.

  Similarly, the first counter conductor path 650, the second counter conductor path 660a, and the third counter conductor path 660b are also formed along the longitudinal direction of the substrate 610. The first opposing conductor path 650 is connected to the opposing branch path 652 (652a to 652d), and one end is connected to the electrode 651. The second and third opposing conductor paths 660a and 660b are connected to the opposing branch paths 662a and 662b, respectively, and one end is connected to the electrode 661.

  The electrode 641 is juxtaposed on one end side in the longitudinal direction of the substrate, while the electrodes 651 and 661 are juxtaposed on the other end side in the longitudinal direction of the substrate, and an insulating coating layer is provided to ensure electrical connection with the connector 700. Is not provided, and is provided outside the region in contact with the fixing belt 603 in an exposed state.

  As described above, in the heater 600 of this embodiment, the power source 110 and the heating element 620 are electrically connected via the connector, the electrode, the common conductor path, the opposing conductor path, and the branch path.

[Power supply to the heater]
Next, a method for supplying power to the heater 600 will be described with reference to FIG. First, the power source 110 is a circuit that supplies power to the heater 600. In this embodiment, a commercial power supply having an effective value of single-phase alternating current of about 100 V is used, and a power supply terminal 110a and a power supply terminal 110b are provided. Note that the power source 110 may be a DC power source as long as it has a function of supplying power to the heater 600.

  The control circuit 100 is electrically connected to each of the switches 643, 653, and 663 in order to control them. The switch 643 is a switch (relay) provided between the power supply terminal 110 a and the electrode 641, and switches whether the power supply terminal 110 a and the electrode 641 are connected (ON, OFF) according to an instruction from the control circuit 100. Do. The switch 653 is a switch provided between the power supply terminal 110 b and the electrode 651, and switches whether to connect the power supply terminal 110 b and the electrode 651 in accordance with 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 in accordance with an instruction from the control circuit 100.

  As the job execution instruction is received, the control circuit 100 acquires the width size information of the recording material P, controls the on / off of the switches 643, 653, and 663 in accordance with the width size information, and generates heat from the heating element 620. Control is performed so that the region becomes a heat generation region suitable for fixing the recording material P.

  Next, a method for changing the heat generation area of the heat generating element 620 according to the size of the recording material P in the width direction will be described.

  First, when the recording material P is a large size such as A4 horizontal size (size in the width direction 297 mm), the control circuit 100 controls the heat generating body 620 so that the heat generating width B generates heat. Specifically, the control circuit 100 turns on all of the switch 643, the switch 653, and the switch 663. In this case, the heater 600 is supplied with power from the electrodes 641, 651, and 661, and the heating element 620 includes twelve heating elements 620. All of the small sections 620a to 620l generate heat. At this time, the heater 600 generates heat in all regions of the heating element of about 320 mm, so that the heater 600 is in a heat generation state suitable for fixing the recording material P of A4 horizontal size.

  Next, when the recording material P is a small size such as A4 vertical size (size 210 mm in the width direction), the control circuit 100 controls the heat generating width 620 so as to generate heat. Specifically, since the control circuit 100 turns on the switch 643 and the switch 653 and turns off the switch 663, the heater 600 is supplied with power from the electrodes 641 and 651, and the heating element 620 includes twelve small elements. Of the sections, eight sections from 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 generation state suitable for performing the fixing process of the recording material P of A4 vertical size. Accordingly, even when the recording material having a small size in the width direction such as A4 vertical size is subjected to the fixing process, the heater 600 does not generate heat in a portion where the recording material does not pass, so that useless power is not used. .

  Next, the configuration of the heater 600 for equalizing the heat generation amount in the small sections 620a to 620l of the heating element 620, which is a characteristic part of the present embodiment, will be described.

First, for comparison, a description will be given using a model in which the short width of the heating element is uniform as shown in FIG. FIG. 8 is an electric circuit diagram of the configuration of FIG. In FIG. 8, the resistance value R represents the resistance of the heating element 620, and the resistance values r1 to r13 represent the resistance values of the conductor paths.
The sheet resistance of the heating element 620 in this example is 8.99 [Ω / □], the distance between the common branching path of the heating element and the opposite branching path, 26.7 [mm], and the width of the heating element is 2.0 [mm]. is there.

  The resistivity of the conductor path and the branch path is 0.00002 Ω · mm, the height of the conductor path is 10 μm, the width of the first opposing conductor path and the second opposing conductor path is 1.0 [mm], and the width of the common conductor path is 1.5 [ mm], the overall length of the heating element is 320 [mm], the length to the common electrode 641 and the branch path 642a, the length to the first feeding electrode 651 and the branch path 642g is 24 “mm”, the length in the longitudinal direction of the electrode When each resistance value is derived with 4.0 “mm” and electrode spacing of 3.5 “mm”, 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].

  Using the Kirchhoff's law, the currents i1 to i7 flowing through the common conductor path 640 and the currents i8 to i13 flowing through the opposing conductor paths 650 and 660 are obtained, and the current flowing through the heating element is calculated as shown in Table 1. In addition, 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 becomes the temperature distribution of the heating element.

  As shown in Table 1, the current / heat generation amount in the central portion of the region (620c to 620j) where a plurality of heating elements are connected in parallel to one conductor path is lowered, and as a result, the temperature of that portion is lowered. I understand that.

  Thus, it can be seen that the heater heating temperature in the conventional configuration tends to be higher in the heater short region as shown in FIG. However, as shown in FIG. 10, the longitudinal temperature distribution of the fixing belt 603 in the case where the heater having the heat generation distribution is used in the fixing device tends to decrease in temperature at both ends of the fixing belt (hereinafter, temperature sagging). I know. This temperature sagging phenomenon is caused by the fact that the heat generation at the end of the heater is taken away by the heat generation at the end of the fixing belt because the length of the fixing belt is longer than the length of the heater. Therefore, in order to prevent the above-described problems, it is necessary to set a large end region in advance for the longitudinal heat generation amount of the heater.

  Therefore, in the heater configuration in the present embodiment, it is necessary to reduce the resistance value at both ends 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 of both end portions of the region where a plurality of heating elements are connected in parallel to one conductor path, a plurality of heating elements in one conductor path as shown in FIG. In the region where the two are connected in parallel, the width of the short side at both ends of the region is widened.

FIG. 9 shows the longitudinal resistance heating amount of the present case of FIG. 6 and the comparative example of FIG. As shown in FIG. 9, in this embodiment, the resistance values of the heating elements at both ends are lowered compared to the comparative example. The resistance value can be lowered by changing the material (specific resistance), length, width, and thickness. In this example, 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 is 2.15 [mm], the width of the heating element in the branch path 642b is 2.15 [mm], and the width of the heating element in the branch path 642d is. 2.0 [mm], the width of the heating element of the branch path 642f is 2.15 [mm], the width of the heating element between the branch path 642b and the branch path 642d, the width of the heating element between the branch path 642d and the branch path 642f The heating element configuration was changed linearly.
Table 2 shows the relationship between the current value and power (heat generation amount) of each heating element of this example.

  FIG. 9 shows the heat generation distribution of the comparative example and this example. As shown in FIG. 9, by using the configuration of this example, the amount of heat generated at both ends of the heater could be increased as compared with the comparative example.

FIG. 10 shows the temperature distribution in the longitudinal direction of the fixing belt 603 in this embodiment. FIG. 10 is a diagram showing the temperature distribution of the fixing belt when the present embodiment of FIG. 6 and the comparative example of FIG. 7 are used.
The horizontal axis of FIG. 10 is the position when the center of the heater is the origin, or the temperature distribution when the temperature of the center is maintained at 200 [° C.] by the thermistor 630.

  In the case of the heater of the comparative example, temperature sagging 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 of this embodiment, since the heat generation amount of the heating elements 620a, 620b, 620k, and 620l is changed, the temperature in the longitudinal direction of the fixing belt 603 becomes uniform at about 200 ° C. At this time, gloss unevenness of the image as described above does not occur. The heat conductivity of the heater is 90 [W / m * K].

  Note that the heater of the present embodiment has a configuration having only two regions, the heat generation region A and the heat generation region B, but is not limited to this configuration, and can be applied to a configuration having three or more patterns of heat generation regions. Needless to say.

  As described above, the heater of this embodiment can change the heat generation region of the resistance heat generation layer according to the width size of the sheet, and can provide a heater with a uniform heat generation amount in the longitudinal direction.

40 fixing device 60 heater unit 70 pressure roller 100 control circuit 110 power supply 110a, 110b power supply terminal 600 heater 603 fixing belt 610 substrate 620 resistance heating element 640 common conductor path 650, 660 counter conductor path 641, 651, 661 electrode 642 common branch Routes 652, 662 Opposed branch 700 connector

Claims (5)

A connector (700) connected to one terminal of the power source (110) and the other terminal;
A board (610) extending along the longitudinal direction to which the connector (700) is attached so as to sandwich the front and back thereof; and
A plurality of electrodes (641, 651, 661) provided on a substrate (610) with which the connector (700) contacts;
A conductor path (640, 650, 660) provided from the electrode toward the longitudinal direction of the substrate (610);
A plurality of branch paths (642, 652, 662) connecting the conductor paths (640, 650, 660) and the heating elements (620a to 620l);
A plurality of heating elements (620a to 620l) provided to electrically connect a plurality of adjacent branch paths,
Heating element group 1 (620c to 620j) connected to power supply side conductor path 1 (650), and heating element group 2 (620a, 620b, 620k, 620l) connected to power supply side conductor path 2 (660) )
When the resistance value of the central part (620f, 620g) of the heating element of the heating element group 1 is Rc and the resistance value of both ends (620a, 620l) of the heating element of the heating element group 2 is Rf,
A heater characterized in that the relationship of heating element resistance is Rc>Rf>. 2. The heater according to claim 1, wherein the resistance value of the central portion (620f, 620g) of the heating elements of the heating element group 1 is Rc, and the resistance value of both ends (620a, 620l) of the heating elements of the heating element group 2 is Rf. ,
The resistance adjacent to the nth in the direction from the center to both ends of the heating element group 1 is Rn,
The resistance adjacent to n + 1 first in the direction from the center to both ends of the heating element group 1 is Rn + 1,
If
A heater characterized in that the relationship of resistance is Rc> Rn ≧ Rn + 1> Rf.   The heater according to claim 1, wherein the short width x at the center of the heating element group 1 (620 c to 620 j) connected to the conductor path 1 (650) on the power feeding side is wider than the short width y at the end. It is characterized by. At least an endless fixing belt (603) for heating the image on the sheet;
A pressure member that forms a fixing nip portion by closely contacting the fixing belt (603) to the heater (600);
The fixing device (40) according to claim 1 or 2, further comprising a heater (600) for heating the fixing belt. When heating the maximum width sheet that can be used in the apparatus, power is supplied to all the plurality of electrodes (641, 651, 661),
2. When heating a sheet having a width narrower than the maximum width sheet, only a part of the plurality of (641, 651, 661) electrodes is fed. The fixing device (40) according to any one of claims 4 to 4.