JP2013037065A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device switching a serial connection and a parallel connection of a first heat generating resistor and a second heat generating resistor of a heating body according to a different voltage of a commercial power source, which is capable of obtaining a same excellent image quality in both the serial connection and the parallel connection.SOLUTION: An image heating device switches a serial connection and a parallel connection of a first heat generating resistor H1 and a second heat generating resistor H2 provided on a substrate 105 of a heating body 300 according to a different voltage of a commercial power source 20. The image heating device is characterized in that a resistance value of the second heat generating resistor on the substrate in the recording material conveyance direction downstream side is smaller than a resistance value of the first heat generating resistor on the substrate in the recording material conveyance direction upstream side.

Description

  The present invention relates to an image heating apparatus suitably used as a fixing device (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  As a fixing device (fixing device) mounted on an electrophotographic copying machine or printer, a film heating type fixing device is known. This film heating type fixing device includes a heater having a resistance heating element that generates heat upon energization on a ceramic substrate, a cylindrical fixing film that moves while being in contact with the heater, and a heater and a nip portion via the fixing film. A pressure roller. The recording material carrying the unfixed toner image is heated while being nipped and conveyed at the nip portion, whereby the image on the recording material is heated and fixed to the recording material.

  This fixing device has an advantage that the time required for starting energization of the heater and raising the temperature to a fixable temperature is short. Therefore, a printer equipped with this fixing device can shorten the time (FPOT: First Print Out Time) until the first image is output after a print command is input. This type of fixing device also has an advantage that power consumption during standby for waiting for a print command is small.

  In the film heating type fixing device, heaters having the same resistance value may be used in regions where the voltage of the commercial power supply is 100V and 200V. In this case, since the power supplied to the heater is proportional to the square of the voltage, the maximum power that can be supplied to the heater is four times that of the 100V system in the 200V system area. When the maximum power that can be supplied to the heater is increased, harmonic current and flicker generated by the heater power control are reduced. Therefore, a fixing device having heaters having different resistance values depending on the commercial power supply voltage of the 100V system and the 200V system. Often used.

  As a means for realizing a fixing device that can be shared in 100V system and 200V system areas, a method of switching the resistance value of the heater using a switching means such as a relay has been proposed. In the fixing device described in Patent Document 1, the heater is provided along the longitudinal direction on the downstream side in the recording material conveyance direction, and the first resistance heating element provided in the longitudinal direction on the upstream side in the recording material conveyance direction. And a second resistance heating element. The first operating state in which the first resistance heating element and the second resistance heating element are connected in series and energized, and the first resistance heating element and the second resistance heating element are connected in parallel and energized. A method of switching the resistance value of the heater in the second operating state has been proposed.

JP 09-329982 A

  In a fixing device that switches resistance values by connecting resistance heating elements in series or in parallel according to the commercial power supply voltage, the resistance heating element upstream of the recording material conveyance direction of the heater and the recording material conveyance depending on the connection method There may be a difference in the heat generation distribution of the resistance heating element on the downstream side in the direction.

That is, in the film heating type fixing device, heat is transferred to the downstream side in the recording material conveyance direction by the rotation of the fixing film. Therefore, the temperature downstream of the recording material conveyance direction of the heater during the rotation operation of the fixing film is the recording material conveyance direction. It tends to be higher than the upstream side.
Although there is a difference depending on the configuration of the fixing device and the rotation speed of the fixing film, the temperature difference between the resistance heating element arranged on the upstream side in the recording material conveyance direction of the heater and the resistance heating element arranged on the downstream side in the recording material conveyance direction is 100 ° C. It also becomes a degree. For this reason, since the resistance value varies depending on the temperature due to the influence of the TCR (temperature resistance coefficient) of the heating resistor, the resistance heating element arranged on the upstream side in the recording material conveyance direction of the heater and the recording by the connection method of series connection and parallel connection. The heat generation distribution of the resistance heating element arranged on the downstream side in the material conveyance direction is also different. Hereinafter, for convenience of explanation, the resistance heating element arranged on the upstream side in the recording material conveyance direction is referred to as an upstream resistance heating element, and the resistance heating element arranged on the downstream side in the recording material conveyance direction is referred to as a downstream resistance heating element.

  The reason is considered as follows. In the case of series connection, the current flowing through the upstream resistance heating element and the downstream resistance heating element is the same. For this reason, the downstream heating resistor having a high temperature and a high resistance value has a larger amount of heat generation than the upstream heating resistor, and the temperature difference between the upstream resistance heating element and the downstream resistance heating element of the heater is large. On the other hand, in the case of parallel connection, the voltage applied to the upstream resistance heating element and the downstream resistance heating element of the heater is the same. For this reason, the upstream resistance heating element having a low temperature and a low resistance value has a larger current flow, and the heat generation amount is larger than that of the downstream resistance heating element. As a result, the temperature difference between the upstream resistance heating element and the downstream resistance heating element of the heater is eliminated.

  In this way, when the temperature distribution of the upstream resistance heating element and the downstream resistance heating element of the heater is different depending on the connection method in series or in parallel, even if the input power to the heater is the same, the paper is passed through the nip portion. The amount of heat given to the recording material is also different. This is because the amount of heat transferred to the recording material increases as the temperature difference between the heating resistor and the recording material increases. As a result, the temperature difference between the heating resistor and the recording material is kept larger in the serial connection in which the temperature difference between the upstream resistance heating element and the downstream resistance heating element of the heater is larger while the recording material passes through the nip portion. it is conceivable that.

  For this reason, the image quality such as fixing property and offset may be affected by the connection method of series connection or parallel connection. That is, the difference in the heat generation distribution between the upstream resistance heating element and the downstream resistance heating element of the heater is caused by the difference in series or parallel connection method, and the fixed image quality on the recording material may be different.

  Further, a temperature increase exceeding a predetermined fixing temperature of the heater is not preferable from the viewpoint of thermal deterioration of a member that contacts the heater or a member that supports the heater. In particular, when a heating resistor having a large TCR (temperature resistance coefficient) is used, the resistance value difference due to the temperature difference between the upstream resistance heating element and the downstream resistance heating element of the heater increases, and the heating value difference also increases. The above temperature difference is significant.

  It is an object of the present invention to provide an image heating apparatus that switches a first heating resistor and a second heating resistor of a heating body to a series connection or a parallel connection according to different voltages of a commercial power source. It is an object of the present invention to provide an image heating apparatus capable of obtaining excellent image quality.

  In order to achieve the above object, an image heating apparatus according to the present invention includes a substrate, a first heating resistor and a second heating resistor that generate heat by power supplied from a commercial power source on the substrate. A heating member having a cylindrical flexible member that moves in contact with the heating member, a backup member that forms a nip portion with the heating member via the flexible member, and a voltage of the commercial power source. And a switching means for switching the first heating resistor and the second heating resistor to a serial connection or a parallel connection according to the first heating resistor and the second heating resistor. In the image heating apparatus to be heated, the resistance of the second heating resistor on the downstream side in the recording material conveyance direction of the substrate from the resistance value of the first heating resistor on the upstream side in the recording material conveyance direction of the substrate. It is characterized by a smaller value That.

  According to the present invention, in an image heating apparatus that switches a first heating resistor and a second heating resistor of a heating body to a series connection or a parallel connection according to different voltages of a commercial power source, the series connection or the parallel connection is equivalent. It is possible to provide an image heating apparatus capable of obtaining excellent image quality.

Fig. 3 is a schematic cross-sectional side view of the fixing device according to the first embodiment. 1 is a schematic diagram of a configuration of a heater of a fixing device according to a first embodiment and an energization control system of the heater. (A) is explanatory drawing showing the serial connection (200V type | system | group) of the 1st heating resistor H1 and the 2nd heating resistor H2 of a heater, (b) is the 1st heating resistor H1 and 2nd of the heater. Explanatory drawing showing parallel connection (100V system) of heating resistor H2 of FIG. 2 Explanatory drawing of heater shown in FIG. 2 and energization control system of heater Schematic diagram showing the heat generation distribution of the heater shown in FIG. The figure which shows a heating element resistance value change from the printing start of the heater shown in FIG. Diagram showing image evaluation results (A) is a schematic structure schematic diagram from the substrate surface side of the heater of Example 2, (b) is a schematic structure schematic diagram from the substrate surface side of the heater of Comparative Example 2. (A) is a schematic structure schematic diagram from the substrate surface side of the heater of Example 3, (b) is a schematic structure schematic diagram from the substrate surface side of the heater of Comparative Example 3. (A) is a schematic structure schematic diagram from the substrate surface side of the heater of Example 4, (b) is a schematic structure schematic diagram from the substrate surface side of the heater of Comparative Example 4. Schematic configuration schematic diagram of an example of an image forming apparatus

[Example 1]
(1) Example of Image Forming Apparatus FIG. 10 is a schematic diagram schematically illustrating an example of an image forming apparatus in which the image heating apparatus according to the present invention is mounted as a fixing device (fixing device). This image forming apparatus is an electrophotographic laser beam printer. The recording material conveyance reference of the image forming apparatus is a central conveyance reference in which the recording material is conveyed with the center in the longitudinal direction of a fixing film (described later) of the fixing device coincided with the center in the width direction of the recording material.

  The image forming apparatus shown in this embodiment includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 has a configuration in which a photosensitive material layer such as OPC, amorphous Se, or amorphous Si is formed on the outer peripheral surface of a cylinder (drum) -like conductive substrate formed of a metal material such as aluminum or nickel.

  The photosensitive drum 1 is rotated at a predetermined peripheral speed (process speed) in the direction of an arrow in response to a print command output from an external device such as a host computer or a terminal on a network. In this rotation process, the outer peripheral surface (surface) of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 as a charging means.

  The uniformly charged surface of the surface of the photosensitive drum 1 is scanned by a laser beam LB that is modulated and controlled (ON / OFF control) according to image information from an external device that is output from a laser beam scanner 3 as a scanning exposure device. Exposure is made. As a result, an electrostatic latent image (electrostatic image) corresponding to the target image information is formed on the surface of the photosensitive drum 1.

  A toner (developer) TO is attached to the latent image on the surface of the photosensitive drum 1 by a developing device 4 as a developing unit, and the latent image on the surface of the photosensitive drum 1 is developed as a toner image (developed image). As a development method, a jumping development method, a two-component development method, a FEED development method, or the like is used, and is often used in combination with image exposure and reversal development.

  On the other hand, the recording materials P loaded and stored in the feeding cassette 9 are fed one by one by the rotation of the feeding roller 8 and conveyed to the registration roller 11 through a sheet path having a guide 10. The registration roller 11 feeds the recording material P to the transfer nip portion between the surface of the photosensitive drum 1 and the outer peripheral surface (front surface) of the transfer roller 5 at a predetermined control timing. The recording material P is nipped and conveyed at the transfer nip portion, and the toner image on the surface of the photosensitive drum 1 is sequentially transferred onto the recording material by a transfer bias applied to the transfer roller 5 in the conveyance process. As a result, the recording material P carries an unfixed toner image.

  The recording material P carrying an unfixed toner image (unfixed image) is sequentially separated from the surface of the photosensitive drum 1 and discharged from the transfer nip portion, and is conveyed to the nip portion N of the fixing device (fixing device) 6 through the conveyance guide 12. be introduced. When the recording material P passes through the nip portion N, the toner image is heated and fixed on the surface of the recording material P. The recording material P exiting the fixing device 6 is printed out on a discharge tray 16 through a sheet path having a conveyance roller 13, a guide 14, and a discharge roller 15.

  The surface of the photosensitive drum 1 after separation of the recording material P is cleaned by a cleaning device 7 as a cleaning unit to remove adhered contaminants such as transfer residual toner, and the photosensitive drum 1 is used for the next image formation. .

(2) Fixing device (image heating device) 6
In the following description, with respect to the fixing device and members constituting the fixing device, the longitudinal direction refers to a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The length is a dimension in the longitudinal direction. The width is a dimension in the short direction. Regarding the recording material, the width direction means a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the width direction.

  FIG. 1 is a schematic cross-sectional side view of the fixing device 6. The fixing device 6 is a film heating type fixing device.

  The fixing device 6 shown in this embodiment includes a fixing film (endless film) 102 as a flexible tubular member having flexibility and heat resistance, a heater 300 as a heating body, and a heater holder 101 as a support member. have. The fixing device 6 includes a rigid stay 104 as a rigid member, a pressure roller 108 as a backup member, and the like. The fixing film 102, the heater 300, the heater holder 101, the rigid stay 104, and the pressure roller 108 are all members that are long in the longitudinal direction.

  The fixing film 102 has a cylindrical base layer (not shown) having a thickness of 30 to 70 μm made of a heat-resistant resin such as polyimide, polyamide, PEEK, or a metal such as stainless steel. A release layer (not shown) having a thickness of 5 to 30 μm made of fluororesin such as PFA or PTFE is provided on the outer peripheral surface of the base layer.

  In this embodiment, as the fixing film 102, a fixing film having a diameter of 24 mm and a length of 220 mm, in which a release layer made of PFA resin having a thickness of 15 μm is provided on the outer peripheral surface of a cylindrical base layer made of polyimide having a thickness of 60 μm, is used. ing.

  The heater holder 101 is formed of a heat-resistant resin material such as LCP (liquid crystal polymer) and has a substantially concave shape in cross section. The heater holder 101 supports the heater 300 by a groove 101b provided along the longitudinal direction at the center of the lower surface of the heater holder 101 so that the surface protective layer 107 described later faces downward. A rigid stay 104 for preventing deformation of the heater holder 101 is disposed at the center of the upper surface of the heater holder 101 in the short direction. The rigid stay 104 is formed of a predetermined metal material in a substantially inverted U shape in cross section.

  A fixing film 102 is loosely fitted on the outer periphery of the heater holder 101 including the heater 300 and the rigid stay 104. Then, both longitudinal end portions of the heater holder 101 and the rigid stay 104 are supported and fixed to support frames (not shown) on both longitudinal sides of the fixing device 6. The heater holder 101 fitted with the fixing film 102 is rotating (moving) by the outer surface of the arc-shaped protrusion 101a provided along the inner peripheral surface (inner surface) of the fixing film 102 on both sides in the short direction of the heater holder 101. The fixing film 102 is guided.

  FIG. 2 shows a schematic configuration diagram of the heater 300 and the energization control system of the heater 300. The heater 300 has a ceramic heater substrate (hereinafter referred to as a substrate) 105 made of alumina or the like formed to have a width of 5 to 12 mm, a thickness of 0.5 to 1 mm, and a length of 240 mm.

  On the substrate surface (on the substrate) on the side where the fixing nip portion (nip portion) N of the substrate 105 is formed, two heating resistors H1 and H2 made of, for example, Ag / Pd (silver palladium) are pattern printed. It is formed by. Of the two heating resistors H1 and H2, the heating resistor H1 is formed along the longitudinal direction of the substrate 105 inside the upstream end of the recording material conveyance direction, and the heating resistor H2 is formed in the recording material conveyance direction of the substrate 105. It is formed along the longitudinal direction of the substrate 105 inside the downstream end.

  In this embodiment, as the heater, the resistance value of the heating resistor H1 is 20.2Ω, the resistance value of the heating resistor H2 is 19.8Ω, and the TCR (temperature resistance coefficient) of each of the heating resistors H1 and H2 is 1000 ppm / The thing of ° C was used. In the heating resistors H1 and H2, the same material was used for the heating resistors. In the short direction of the heater 300, the resistance value was changed by setting the width of the heating resistor H1 to 19.8 mm and the width of the heating resistor H2 to 20.2 mm. In order to distinguish the two heating resistors H1 and H2, the heating resistor H1 is referred to as a first heating resistor H1, and the heating resistor H2 is referred to as a second heating resistor H2.

  The first heating resistor H1 is provided on the same substrate surface of the substrate 105 as a power supply electrode (hereinafter referred to as an electrode) 303a provided inside one end in the longitudinal direction and inside the other end in the longitudinal direction. The power supply common electrode (hereinafter referred to as a common electrode) 303c is electrically connected. The second heating resistor H2 is electrically connected to a power supply electrode (hereinafter referred to as an electrode) 303b and a common electrode 303c provided on the inner surface of one end in the longitudinal direction on the same surface of the substrate 105. ing. The first heating resistor H1 and the second heating resistor H2 are provided with an insulating (glass in this embodiment) surface protection having a thickness of 0.05 to 0.1 mm provided on the same surface of the substrate 105. Covered by layer 107.

  The energization control system is a triac (power control) that controls power supplied to a control unit (control means) 100 including a CPU, a memory such as a RAM and a ROM, and the first heating resistor H1 and the second heating resistor H2. Means) 21. The energization control system also includes a power supply voltage detection unit (power supply voltage detection means) 401 including a voltage detection circuit that detects a voltage applied from the commercial power supply 20. The energization control system includes a switching unit (switching unit) 402 including energization control relays 401a and 401b serving as two energization changeover switches. Further, the energization control system includes a temperature detection element 112 and a thermo switch 113 as an energization interruption unit.

  Of the two energization control relays 402a and 402b of the switching unit 402, the first energization control relay 402a has a movable contact m and a contact a. The second energization control relay 402b has a common contact c and two contacts a1 and a2. In the first energization control relay 402a, the movable contact m is electrically connected to the common electrode 303c of the first resistance heating element H1, and the contact a is electrically connected to the commercial power source 22. In the second energization control relay 402 a, the common contact c is electrically connected to the electrode 303 b of the second resistance heating element H 2, the contact a 1 is electrically connected to the commercial power supply 22, and the contact a 2 is connected together with the triac 21. 1 is electrically connected to the electrode 303a of the resistance heating element H1.

  The temperature detecting element 112 and the thermo switch 113 are respectively provided on the back surface (on the substrate) of the heater 300 opposite to the side where the fixing nip portion N of the substrate 105 is formed.

  The temperature detection element 112 is disposed in the approximate center of a region (sheet passing region) through which the recording material P passes in the longitudinal direction of the heater 300, detects the temperature of the substrate 105 of the heater 300, and sends a temperature detection signal to the control unit 100. Is output.

  The thermo switch 113 is disposed in contact with the first resistance heating element H1 and the second resistance heating element H2 at a predetermined position in the sheet passing area of the recording material P in the longitudinal direction of the heater 300. The thermo switch 113 operates when the temperature of the heater 300 reaches a predetermined set temperature for some reason so as to cut off the energization to the first resistance heating element H1 and the second resistance heating element H2. It is configured. In this embodiment, the set temperature of the thermo switch 113 is set to 250 ° C.

  In this energization control system, the power supply voltage detection unit 401 detects the voltage of the commercial power supply 20, and the control unit 100 controls the first energization control relay 402 a and the second energization control relay 402 b based on the voltage. It has become.

  The pressure roller 108 is a silicone provided on the outer peripheral surface of the cored bar 109 between a round shaft-shaped cored bar 109 made of iron or aluminum and supported parts (not shown) on both sides in the longitudinal direction of the cored bar 109. An elastic layer 110 having a thickness of 2 to 4 mm made of rubber or the like is included.

  The pressure roller 108 is disposed inside the fixing film 102 so as to face the heater 300 supported by the heater holder 101 via the fixing film 102. The supported parts on both sides in the longitudinal direction of the cored bar 109 are rotatably supported by the support frame of the fixing device 6 via bearings (not shown). The bearings on both sides in the longitudinal direction of the metal core 109 are urged toward the fixing film 102 with a total pressure of 98 to 294 N (total pressure of 10 to 30 kgf) by pressurizing means (not shown) such as a pressurizing spring. .

  The outer peripheral surface (surface) of the pressure roller 108 comes into contact with the outer peripheral surface (surface) of the fixing film 102 in a pressurized state by the pressure of the pressing means. As a result, the elastic layer 110 of the pressure roller 108 is elastically deformed over the entire longitudinal direction of the heater 300 to form a fixing nip portion (nip portion) N having a width of 5 to 11 mm between the surface of the pressure roller 108 and the surface of the fixing film 102. Forming.

  In this embodiment, as the pressure roller 108, an elastic layer 110 made of silicone rubber is provided on the outer peripheral surface of a cored bar 109 made of aluminum, and a release layer 111 made of PFA is provided on the outer peripheral surface of the elastic layer 110. A pressure roller is used. The metal core 109 is φ18, the elastic layer 110 is 3 mm thick, the release layer 111 is 50 μm thick, the pressure roller is φ24, and the length is 220 mm. The pressure roller 108 was urged toward the fixing film 102 with a total pressure of 147 N (total pressure of 15 kgf) to form a fixing nip portion N having a width of 7 mm.

(3) Heat Fixing Operation of Toner Image t of Fixing Device 6 In the fixing device 6 of this embodiment, the pressure roller 108 is rotated around a predetermined circumference by the rotation of a motor M (see FIG. 1) that is driven to rotate in response to a print command. It is rotated in a direction (see FIG. 1) indicated by an arrow at a speed (process speed). In this embodiment, the pressure roller 108 is rotated so that the conveyance speed of the recording material P is 300 mm / sec. The rotation of the pressure roller 108 is transmitted to the fixing film 102 by the frictional force between the surface of the pressure roller and the surface of the fixing film 102 at the fixing nip portion N. As a result, the fixing film 102 rotates (moves) in the direction indicated by the arrow (see FIG. 1) following the rotation of the pressure roller 108 with the inner surface of the fixing film 102 in contact with the surface protective layer 107 of the heater 300. .

  Here, the operation of the switching unit 402 that switches the first heating resistor H1 and the second heating resistor H2 of the heater 300 to series connection or parallel connection will be described.

  3A is an explanatory diagram showing a series connection (200 V system) of the first heating resistor H1 and the second heating resistor H2 of the heater 300, and FIG. 3B is a first heating resistor of the heater 300. FIG. It is explanatory drawing showing the parallel connection (100V type | system | group) of the body H1 and the 2nd heating resistor H2.

  When the main power switch of the image forming apparatus is turned on, a voltage is applied from the commercial power supply 22 to the power supply voltage detection unit 401. The power supply voltage detection unit 401 determines whether the range of the effective voltage value applied from the commercial power supply 20 is a 100 V system (ex. 100 V to 127 V) or a 200 V system (ex. 200 V to 240 V). When it is determined that the system is 100V, a voltage detection signal that indicates the 100V system is output. When it is determined that the system is 200V, a voltage detection signal that indicates the 200V system is output.

  The control unit 100 takes in a voltage detection signal meaning a 200V system from the power supply voltage detection unit 401. Then, the control part 100 controls the 2nd electricity supply control relay 402b, and makes the common contact c contact the contact a1 (refer Fig.3 (a)).

  Thereby, the commercial power source 20, the triac 21, the thermo switch 113, the electrode 303a, the first heating resistor H1, the common electrode 303c, the second heating resistor H2, the electrode 303b, and the second The energization control relay 402b and the commercial power supply constitute a closed circuit. That is, a first conduction path is formed in which the first heating resistor H1 and the second heating resistor H2 are connected in series.

  Next, the control unit 100 turns on the triac 21 and controls the triac 21 so that the total resistance value of the first heating resistor H1 and the second heating resistor H2 of the heater 300 becomes 40Ω. Like that. When the triac 21 is turned on, electric power is applied from the commercial power supply 20 to the triac 21, and the electric power corresponding to the total resistance value from the triac 21 is supplied to the first heating resistor H1 and the second heating resistor H2 of the heater 300. To be supplied. As a result, the first heating resistor H1 and the second heating resistor H2 are energized, and the first heating resistor H1 and the second heating resistor H2 generate heat.

  The fixing film 102 is heated through the surface protective layer 107 by the heat generated by the first heating resistor H1 and the second heating resistor H2. Then, the control unit 100 takes in a temperature detection signal output from the temperature detection element 112, and based on this temperature detection signal, a predetermined fixing temperature necessary for the temperature detection element to heat and fix the toner image t on the recording material. The TRIAC 21 is controlled to maintain (target temperature). In this embodiment, the fixing temperature (hereinafter also referred to as control target temperature) is set to 185 ° C.

  The control unit 100 takes in a voltage detection signal indicating a 100V system from the power supply voltage detection unit 401. Then, the control unit 100 controls the first energization control relay 402a to bring the movable contact m into contact with the contact a, and controls the second energization control relay 402b to bring the common contact c into contact with the contact a2 (FIG. 3). (See (b)).

  Thereby, the commercial power source 20, the triac 21, the thermo switch 113, the second energization control relay 402b, the electrode 303b, the second resistance heating element H2, the common electrode 303c, and the first energization control relay. 402a and the commercial power source 20 constitute one closed circuit. In addition, the commercial power source 20, the triac 21, the thermo switch 113, the electrode 303a, the first resistance heating element H1, the common electrode 303c, the first energization control relay 402a, and the commercial power source 20 One closed circuit is configured. That is, a second conduction path is formed in which the first resistance heating element H1 and the second resistance heating element H2 are connected in parallel.

  Next, the control unit 100 turns on the triac 21 and controls the triac 21 so that the total resistance value of the first resistance heating element H1 and the second resistance heating element H2 of the heater 300 becomes 10Ω. Like that. When the triac 21 is turned on, electric power is applied from the commercial power supply 20 to the triac 21, and electric power corresponding to the total resistance value is applied from the triac 21 to the first resistance heating element H 1 and the second resistance heating element H 2 of the heater 300. To be supplied. As a result, the first resistance heating element H1 and the second resistance heating element H2 are energized, and the first resistance heating element H1 and the second resistance heating element H2 generate heat.

  The fixing film 102 is heated through the surface protective layer 107 by the heat generated by the first resistance heating element H1 and the second resistance heating element H2. Then, the control unit 100 takes in the temperature detection signal output from the temperature detection element 112, and controls the triac 21 so that the temperature detection element 112 maintains the fixing temperature based on the temperature detection signal.

  The recording material P carrying the toner image t in the state where the pressure roller 108 is rotated and the temperature of the temperature detecting element 112 is maintained at a predetermined fixing temperature is introduced into the fixing nip portion N with the toner image carrying surface facing upward. (Pass through). Then, in the fixing nip portion N, the recording material P is nipped between the surface of the fixing film 102 and the surface of the pressure roller 108 and conveyed to that state (nipping conveyance). In this conveying process, heat and pressure are applied to the toner image, whereby the toner image t is heated and fixed on the recording material. The recording material P that has passed through the fixing nip N is separated from the surface of the fixing film 102 and discharged from the fixing nip N.

  In the fixing device 6 of the present embodiment, the connection of the first resistance heating element H1 and the second resistance heating element H2 of the heater 300 is switched to a serial connection or a parallel connection based on the determination by the power supply voltage detection unit 401. .

  That is, when the power supply voltage detection unit 401 determines that the system is 200V, the first resistance heating element H1 and the second resistance heating element H2 are connected in series by the second energization control relay 401b, and the total resistance value of the heater 300 is determined. To be 40Ω. On the other hand, when the power supply voltage detector 401 determines that the system is a 100V system, the first resistance heating element H1 and the second resistance heating element H2 are connected in parallel by the first energization control relay 401a and the second energization control relay 402b. Connected so that the total resistance of the heater 300 is 10Ω. Thus, by switching the total resistance value between the 100V system and the 200V system, the maximum power input in the 100V system and the 200V system can be made equal.

  Hereinafter, referring to FIGS. 4 and 5, an image forming apparatus equipped with the fixing device 6 equipped with the heater 300 of this embodiment and an image forming apparatus equipped with the fixing device (not shown) equipped with the heater of Comparative Example 1 are used. The heat generation of each heater when printing is performed using the apparatus will be described.

  In the heater of Comparative Example 1, the resistance values of the heating resistors H1 and H2 are 20Ω each, and the TCR is 1000 ppm. The configuration is the same as that of the heater 300 of the present embodiment, except that a heater at / ° C is used. The fixing device provided with the heater of Comparative Example 1 has the same configuration as that of the fixing device 6 of the present embodiment except that the configuration of the heater is different as described above. In the fixing device provided with the heater of Comparative Example 1, the fixing temperature was set to 185 ° C., which is the same as that of the fixing device of this example.

  FIG. 4 shows that 20 sheets of recording material are passed through the image forming apparatus equipped with the fixing device 6 equipped with the heater 300 of this embodiment and the image forming apparatus equipped with the fixing device equipped with the heater of Comparative Example 1, respectively. It is the figure which showed the temperature distribution of the board | substrate back surface of the short side direction of the heater 300 when paper (introduction) was carried out. The solid line shows the case where the heating resistors H1 and H2 are connected in series, and the dotted line shows the case where the heating resistors H1 and H2 are connected in parallel.

  In the image forming apparatus equipped with the fixing device 6 including the heater 300 of this embodiment, the temperature distribution when the heating resistors H1 and H2 of the heater 300 are connected in series and in parallel is almost the same, and the temperature distribution. The difference was within 3 ° C.

  On the other hand, in the image forming apparatus equipped with the fixing device provided with the heater of Comparative Example 1, when the heating resistors H1 and H2 are connected in series on the downstream side in the recording material conveyance direction where the temperature is particularly high in the heater, It was 288 ° C. when connected in parallel. Therefore, it can be seen that the difference in temperature distribution is as large as 5 ° C. compared to the present embodiment.

  As described above, in the image forming apparatus equipped with the fixing device having the heater of Comparative Example 1, there is a difference in the amount of generated heat and the temperature distribution between the case where the heating resistors H1 and H2 are connected in series and the case where they are connected in parallel. Is considered as follows.

  Immediately after the image forming apparatus is turned on, or when the fixing device 6 is cold, such as when the elapsed time from the end of printing is long, the amount of heat generated in accordance with the resistance values of the heating resistors H1 and H2 is increased. Show. In this embodiment, since the resistance value of the heating resistor H1 is larger than the resistance value of the heating resistor H2, in the case of series connection, the heater 300 is upstream in the short direction, and in the case of parallel connection, the heater 300 is downstream in the short direction. The side heat generation is large. On the other hand, in Comparative Example 1, since the resistance values of the heating resistor H1 and the heating resistor H2 are the same, the amount of heat generated on the upstream side in the short direction and the downstream side in the short direction of the heater 300 is the same in both the series connection and the parallel connection. It will be the same.

  However, when the fixing film 102 rotates with the start of printing, a part of the heat generated by the heating resistor H1 and the heating resistor H2 is carried to the downstream side of the heater 300 in the recording material conveyance direction by the rotation of the fixing film 102. . Then, the temperature of the heater 300 on the downstream side in the recording material conveyance direction becomes higher than that on the upstream side in the recording material conveyance direction. Therefore, the resistance increase is greater in the heating resistor H2 in the downstream portion of the heater 300 in the recording material conveyance direction than in the heating resistor H1 in the upstream portion in the recording material conveyance direction of the heater 300.

  FIG. 5 is a diagram showing changes in the resistance values of the heating element resistance H1 and the heating element resistance H2 with respect to the elapsed time (sec) from the start of printing.

  First, in the case of the series of Comparative Example 1 in FIG. 5A (series connection), the resistance value of the heating resistor H1 and the heating resistor H2 is the same 20Ω immediately after the start of printing. After printing is started, the temperature on the downstream side in the recording material conveyance direction of the heater 300 increases from the upstream side in the recording material conveyance direction as described above. Therefore, the resistance value of the heating resistor H2 on the downstream side in the recording material conveyance direction of the heater 300 increases. It becomes larger than the heating resistor H1 on the upstream side in the recording material conveyance direction. Furthermore, since the currents flowing through the heating resistor H1 and the heating resistor H2 are the same, the heating resistor H2 on the downstream side in the recording material conveyance direction of the heater 300 having a large resistance value due to the temperature rise is upstream in the recording material conveyance direction. The amount of heat generated is larger than that of the side heating resistor H1.

  Therefore, the temperature difference between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction is further widened. As a result, in the steady state, the resistance value of the heating resistor H1 is 24.2Ω, and the resistance value of the heating resistor H2 is 25.4Ω. Here, the steady state refers to a state in which there is almost no temperature change in the heater 300.

  On the other hand, in the case of paralleling (parallel connection) in Comparative Example 1 in FIG. 5B, the temperature on the downstream side in the recording material conveyance direction of the heater 300 rises from the upstream side in the recording material conveyance direction as described above after starting printing. Therefore, the increase in the resistance value of the heating resistor H2 on the downstream side in the recording material conveyance direction of the heater 300 is larger than that on the heating resistor H1 on the upstream side in the recording material conveyance direction. However, since the voltage applied to the heating resistor H1 and the heating resistor H2 is the same, the current flowing through the heating resistor H1 having a small resistance value is larger due to the difference in temperature rise. For this reason, the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 generates more heat than the heating resistor H2 on the downstream side in the recording material conveyance direction.

  This acts to eliminate the temperature difference between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction. As a result, in the steady state, the resistance value of the heating resistor H1 is 24.6Ω, and the resistance value of the heating resistor H2 is 24.9Ω.

  For the reason described above, in Comparative Example 1, there is a difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction in the case of series. Will occur.

  In the case of the present embodiment of FIG. 5C, the temperature and the heating resistor H1 and the heating resistor H2 are equal in temperature so that the resistance values of the heating resistor H1 and the heating resistor H2 in the steady state are the same in series (series connection) and parallel (parallel connection). The resistance values of the heating resistor H1 and the heating resistor H2 are set in consideration of the TCR. Here, the steady state means a state in which the temperature change of the heater 300 is small (a state where the recording material is continuously fed).

  Specifically, first, a heater 300 in which the resistance values of the heating resistor H1 and the heating resistor H2 are changed is prototyped so that the current flowing through the heating resistor H1 and the heating resistor H2 can be measured both in series and in parallel. I made it. Then, a combination of heating element resistance values was found so that the currents in series and parallel were the same during printing. In this example, the resistance value of the heating resistor H1 was set to 20.2Ω, and the resistance value of H2 was set to 19.8Ω.

  Thus, in this embodiment, the resistance value of the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 is set to be larger than that of the heating resistor H2 on the downstream side in the recording material conveyance direction. For this reason, the amount of heat generated on the upstream side in the short direction of the heater 300 is large in series, and the temperature difference between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction. It works to eliminate. Eventually, when a steady state is reached in which there is almost no temperature change in the heater 300, the resistance values of the heating resistor H1 and the heating resistor H2 become substantially the same. At the time of parallel printing, immediately after printing is started, the heating resistor H2 on the downstream side in the recording material conveyance direction of the heater 300 has a smaller resistance value than the heating resistor H1 on the upstream side in the recording material conveyance direction. The heat generation amount is larger than that of the heating resistor H1.

However, since the heat is transferred to the downstream side in the recording material conveyance direction of the heater 300 by the rotation of the fixing film 102, the temperature on the downstream side in the recording material conveyance direction of the heater 300 becomes higher than the upstream side in the recording material conveyance direction. As a result, the resistance increase of the heating resistor H2 on the downstream side in the recording material conveyance direction is larger than that on the upstream side of the heater 300 in the recording material conveyance direction. Eventually, when the temperature in the heater 300 is almost constant, the resistance values of the heating resistor H1 and the heating resistor H2 become approximately the same 24.8Ω. For the reasons described above, the resistance values of the heating resistors H1 and H2 are substantially the same in the steady state in series and parallel, and as a result, the heating resistor H1 on the upstream side in the recording material transport direction of the heater 300 and the recording material transport. There is no difference in temperature distribution with the heating resistor H2 on the downstream side in the direction.

FIG. 6 shows the temperature and image of a recording material when an image formation evaluation is performed in a 200 V system / 100 V system (series / parallel) using an actual image forming apparatus in order to confirm the effect of this embodiment. The evaluation (fixability test, offset evaluation) results are shown.

  Here, the fixability means that 20 rough sheets on which halftone images are printed are conveyed continuously to the fixing nip portion from a state where the fixing device is cooled. Then, a rubbing test is performed on the recording material P on which the halftone image is fixed, and an optical density difference before and after the rubbing test is measured under a certain condition. That is, a weight (200 g) of a predetermined weight (200 g) is placed on the image forming surface of the recording material, and the image forming surface is rubbed with the interposed paper while applying the weight, and the image density before and after the rubbing. Find the rate of decline. If the density reduction rate is 20% or more after passing 20 sheets, it is judged as an unacceptable level in the market x. If the density reduction rate is less than 20%, it is judged as an acceptable level in the market It is written.

  In the offset evaluation, from the state where the fixing device is cooled, 50 sheets of halftone images and interlaced character images are continuously conveyed, and smooth paper on which about one turn of the fixing film is printed is conveyed to the fixing nip portion. When the offset is low, a part of the unfixed toner on the recording material receives heat more than the amount fixed and adheres to the surface of the fixing film. The toner on the surface of the fixing film is transferred to the recording material after one round of the fixing film. For this reason, an offset image appears after one round of the fixing film. In the offset evaluation, subjective evaluation was performed focusing on this part, and “◯” was given when it was judged as an acceptable level in the market, and “X” was judged when it was judged as an unacceptable level in the market.

  In this example (Example 1), the control target temperature was set to 185 ° C. In Comparative Example 1, the control target temperatures were set to 195 ° C., 185 ° C., and 175 ° C. in consideration that the detected temperature error of the temperature detecting element 111 is approximately 6 ° C.

  As a result, in this embodiment, the fixing property and the offset are satisfied both in series and in parallel. On the other hand, in Comparative Example 1, it was not possible to satisfy the offset in series and the fixability in parallel at the same control target temperature. This is presumably because in the present embodiment, the paper temperature is the same both in series and in parallel, and the occurrence of image defects due to temperature differences or the like is suppressed, and good image quality is obtained.

  On the other hand, when the control target temperature is 185 ° C. in Comparative Example 1, it is considered that the paper temperature at the time of series becomes higher than that at the time of parallel and the hot offset is lowered. On the other hand, it is considered that the paper temperature at the time of parallel is lower than that at the time of serial, and the fixing property is lowered. When the control target temperature is increased to 195 ° C., the paper temperature increases, so that the fixing property in parallel is improved, but the offset in series is reduced. Further, when the control target temperature is lowered to 175 ° C., the paper temperature is lowered, so that the offset in the series is improved, but the fixing property in the parallel is lowered.

  As described above, when the resistance value of the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater is larger than the resistance value of the heating resistor H2 on the downstream side in the recording material conveyance direction, the connected state in series and parallel Regardless of this, it is possible to achieve both fixability and offset at the same control target temperature.

  As another effect, in this embodiment, the maximum temperature of the back surface of the substrate of the heater 300 can be suppressed both in series and in parallel, and thermal deterioration of the heater holder 101 can be suppressed.

[Example 2]
Another example of the heater 300 used instead of the heater 300 of the first embodiment will be described. FIG. 7A is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of this embodiment, and FIG. 7B is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of Comparative Example 2.

  The heater 300 shown in this embodiment has a resistance value per unit length in the longitudinal direction of the substrate 105 in the first heating resistor H1, and a part of the first heating resistor H1 is the first heating resistor H1. It is characterized by being larger than other parts except for a part of.

  As shown in FIG. 7A, the thermo switch 113 is disposed in contact with the first resistance heating element H1 and the second resistance heating element H2 on the back surface of the substrate of the heater 300. It will take heat from 300. As a result, the amount of heat transmitted to the recording material P is smaller than in other portions, and there is a possibility that image defects such as uneven gloss and a decrease in fixability may occur. Therefore, it is necessary to increase the amount of heat generation so as to compensate for the amount of heat lost.

  In the present embodiment, as shown in FIG. 7A, the width of the 8 mm heating resistor H1 is narrowed from 19.8 mm to 18.8 mm in the longitudinal direction at the place where the thermo switch 113 comes into contact. As a result, the resistance value per unit length in the longitudinal direction of the heating resistor H1 is increased by 5% to improve the gloss unevenness generated at the 113 thermoswitches.

  In the heater 300 of this embodiment, the recording material of the heater 300 is increased when the resistance value of a part where the thermo switch 113 is in contact with each of the heating resistors H1 and H2 in the longitudinal direction of the heating resistors H1 and H2 is increased. The resistance value of the heating resistor H1 on the upstream side in the transport direction is increased. As a result, as described above, the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction is reduced, as described above. It is possible to achieve both fixing properties and offset at the same temperature control temperature.

  Furthermore, there are the following effects. As described above, the temperature of the back surface of the substrate of the heater 300 is higher on the downstream side in the recording material conveyance direction than on the upstream side in the recording material conveyance direction. For this reason, like the heater 300 of the comparative example 2 shown in FIG. 7B, the longitudinal direction of the heating switch H2 on the downstream side of the recording material conveyance direction of the heater 300 is the point where the thermo switch 113 contacts. The width of the 8 mm heating resistor H2 is reduced from 20.2 mm to 19.2 mm. When the resistance value per unit length in the longitudinal direction of the heating resistor H2 is increased by 5% in this way, the temperature on the downstream side in the recording material conveyance direction on the back surface of the substrate of the heater 300 at the location where the thermo switch 113 is disposed is further increased. Get higher.

  As described above, in the heater 300 of Comparative Example 2, when the maximum temperature on the back surface of the heater 300 is increased, the thermal switch 113 and the heat-resistant resin heater holder 101 are thermally deteriorated and the heat resistance is improved. This is not preferable because the degree of freedom in design occurs.

  As described above, when the resistance value is increased in a part of the heating resistors H1 and H2 in order to compensate for the amount of heat taken away by the thermo switch 113, the heating resistance is higher than that of the heating resistor H2 at the location where the thermo switch 113 is in contact. The resistance of the body H1 is increased. Here, the other portion where the resistance of the first heat generating resistor H1 is large is a portion in contact with the thermo switch 113 that cuts off the power supply to the first heat generating resistor H1 and the second heat generating resistor H2.

  This reduces the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction, and eliminates the need for special control. It becomes possible. Further, it is possible to suppress the temperature rise of the heater 300 at the downstream side in the recording material conveyance direction in series, and to suppress the thermal deterioration of the thermo switch 113 and the like.

[Example 3]
Another example of the heater 300 used instead of the heater 300 of the first embodiment will be described. FIG. 8A is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of this embodiment, and FIG. 8B is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of Comparative Example 3.

  The heater 300 shown in the present embodiment also has a resistance value per unit length in the longitudinal direction of the substrate 105 in the first heating resistor H1, and a part of the first heating resistor H1 is the first heating resistor H1. It is characterized by being larger than other parts except for a part of.

  The heater 300 of the present embodiment is suitable for use when there is a large amount of heat outflow from both longitudinal ends of the heater 300 and it is desired to increase the amount of heat generated at both longitudinal ends of the heater 300. Specifically, the resistance value per unit length in the longitudinal direction of the heating resistors H1 and H2 of the heater 300 is set to the heating resistor H2 on the upstream side in the recording material conveyance direction from the heating resistor H1 on the downstream side in the recording material conveyance direction. It is characterized by enlarging. That is, in the configuration for suppressing the temperature drop at both ends in the longitudinal direction of the heater 300, the width of both longitudinal ends of the heating resistor H1 on the upstream side in the recording material conveyance direction is narrowed, and the resistance value per unit length in the longitudinal direction. To increase the amount of heat generation at both ends in the longitudinal direction.

  The reason why the temperature at both ends in the longitudinal direction of the heater 300 decreases is that the heat loss transmitted to the fixing film 102, the pressure roller 108, the heater holder 101, etc., and the heat loss due to convection and radiation have a temperature difference. It originates in becoming large at both ends in the longitudinal direction.

  In the heater 300 of the present embodiment, as shown in FIG. 8A, the width of the heating resistor H1 is narrowed from 19.8 mm to 18.8 mm at both ends in the longitudinal direction of the heating resistor H1. As a result, the resistance value per unit length in the longitudinal direction of the heating resistor H1 is increased by 5%, and the fixability at both ends in the longitudinal direction of the heater 300 is improved.

  As described above, when the resistance value at both ends in the longitudinal direction of the heater 300 is increased in the longitudinal direction of the heating resistors H1 and H2, the resistance value of the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 is increased. doing. As a result, as described above, the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction is reduced, as described above. It is possible to achieve both fixing properties and offset at the same temperature control temperature.

  Furthermore, there are the following effects. As described above, the temperature of the back surface of the substrate of the heater 300 is higher on the downstream side in the recording material conveyance direction than on the upstream side in the recording material conveyance direction. For this reason, like the heater 300 of the comparative example 3 shown in FIG. 8B, the heating resistor H2 has a width of 6 mm at both ends in the longitudinal direction, and the width of the heating resistor H2 is 20.2 mm to 19.2 mm. The resistance value per unit length in the longitudinal direction is increased by 5%. As a result, the amount of heat generated on the downstream side of the heater 300 in the recording material conveyance direction is further increased. In addition, since the temperature and the amount of heat generated at the longitudinal end of the heater 300 are increased on the downstream side in the recording material conveyance direction, the temperature on the downstream side of the recording material conveyance direction on the back surface of the substrate of the heater 300 is further increased. Become.

  As described above, in the heater 300 of Comparative Example 3, the maximum temperature of the back surface of the heater 300 is increased, and the heat resistance and the heat resistance of the heater holder 101 made of heat resistant resin are improved. A decrease or the like is not preferable.

  In the heater 300 of this embodiment, the resistance value per unit length in the longitudinal direction of the heating resistors H1 and H2 of the heater 300 is set to the heat generation upstream in the recording material conveyance direction from the heating resistor H1 in the recording material conveyance direction downstream. The resistor H2 is made larger.

  This reduces the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction, and eliminates the need for special control. It becomes possible. Furthermore, the temperature rise on the downstream side of the recording material conveyance direction of the heater 300 in series can be suppressed, and the thermal deterioration of the heater holder 101 can be suppressed.

[Example 4]
Another example of the heater 300 used instead of the heater 300 of the first embodiment will be described. FIG. 9A is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of this embodiment, and FIG. 9B is a schematic configuration schematic diagram from the substrate surface side of the heater 300 of Comparative Example 4.

  In the heater 300 shown in this embodiment, the second heating resistor H2 of the heater 300 has a resistance value per unit length in the longitudinal direction of the substrate 105, and a part of the first heating resistor H1 generates the first heat. It is smaller than other parts except for a part of the resistor H1. The other part where the resistance value of the second heating resistor H2 is small is the end of the second heating resistor H2 in the longitudinal direction of the substrate 105.

  The heater 300 of the present embodiment is suitable for use in suppressing the temperature rise at both ends in the longitudinal direction of the heater 300. Specifically, in the configuration for suppressing the temperature rise at the end of the heater 300, the width of both ends in the longitudinal direction of the heating resistor H2 is increased, the resistance value per unit length in the longitudinal direction is decreased, and as a result the heater The amount of heat generated at both ends in the longitudinal direction 300 is reduced.

  The reason for suppressing the temperature rise at both ends in the longitudinal direction of the heater 300 is as follows. Regardless of the width of the recording material, the heat generation amount in the longitudinal direction of the heater 300 does not change. Therefore, when a narrow recording material is passed through the fixing nip portion N, the amount of heat originally lost to the recording material is accumulated in members such as the heater 300, the fixing film 102, the pressure roller 108, and the heater holder 101. . For this reason, the temperature of the longitudinal direction both ends of the heater 300 rises, which is not preferable from the viewpoint of durability and thermal deterioration of each member. Generally, the shape of the longitudinal ends of the heating resistors H1 and H2 is determined so as to be compatible with both the A4 size width of 210 mm and the LTR size width of 216 mm.

  In the present embodiment, as shown in FIG. 9A, the width of the heating resistor H2 is increased from 20.2 mm to 21.2 mm at both ends in the longitudinal direction of the heating resistor H2. Thereby, the resistance value per unit length in the longitudinal direction of the heating resistor H2 is reduced by 5%, and even when the A4 size and the LTR size are passed, the fixing properties at both ends in the width direction of the recording material, The temperature increase suppression at both ends in the longitudinal direction of the heater 300 can be made compatible.

  As described above, when the resistance value of the end portion in the longitudinal direction of the heater 300 in the longitudinal direction of the heating resistors H1 and H2 is reduced, the resistance value of the heating resistor H2 on the downstream side in the recording material conveyance direction of the heater 300 is reduced. Is made smaller. As a result, as described above, the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction is reduced in series and parallel. It is possible to achieve both fixing properties and offset at the same temperature control temperature.

  Furthermore, there are the following effects. As described above, the temperature of the back surface of the substrate of the heater 300 is higher on the downstream side in the recording material conveyance direction than on the upstream side in the recording material conveyance direction. For this reason, like the heater 300 of the comparative example 4 shown in FIG. 9 (b), the width of the heating resistor H1 is changed from 19.8 mm to 20.8 mm at both ends in the longitudinal direction of the heating resistor H1. To increase the resistance value per unit length in the longitudinal direction by 5%. In the heater 300 of this comparative example 4 and the heater 300 of this embodiment, the heater 300 of this embodiment is heated downstream at both ends in the longitudinal direction of the heater 300 and the heater 300 temperature is the highest in the recording material conveyance direction. Heat generation at can be suppressed.

  Therefore, the heater 300 of the present embodiment can suppress the temperature rise at both ends in the longitudinal direction of the heater 300, and the heat deterioration and the heat resistance of the heater holder 101 made of the heat resistant resin are improved. Therefore, it is possible to suppress a decrease in design freedom.

  In the heater 300 of this embodiment, the resistance value per unit length in the longitudinal direction of the heating resistors H1 and H2 of the heater 300 is determined from the downstream side in the recording material transport direction at both ends in the longitudinal direction of the heating resistor. The upstream side is enlarged.

  This reduces the difference in temperature distribution between the heating resistor H1 on the upstream side in the recording material conveyance direction of the heater 300 and the heating resistor H2 on the downstream side in the recording material conveyance direction, and eliminates the need for special control. It becomes possible. Furthermore, the temperature rise on the downstream side of the recording material conveyance direction of the heater 300 in series can be suppressed, and the thermal deterioration of the heater holder 101 can be suppressed.

[Other embodiments]
The fixing devices shown in the first to fourth embodiments are not limited to use as a fixing device that heat-fixes an unfixed toner image on a recording material. For example, it can also be used as an image heating device that heats an unfixed toner image and attaches it to a recording material, or an image heating device that heats a toner image heat-fixed on a recording material to increase the gloss of the toner image surface. it can.

6 ... Image heating device, 20 ... Commercial power supply, 102 ... Fixing film, 105 ... Substrate, 108 ... Pressure roller, 300 ... Heater, 402 ... Switching section, H1 ... First heating resistance H2, second heating resistor, P, recording material, t, unfixed toner image

Claims (5)

A heating body having a substrate, a first heating resistor that generates heat by electric power supplied from a commercial power source, and a second heating resistor on the substrate, and a cylindrical movable body that moves while contacting the heating body A flexible member, a backup member that forms a nip portion together with the heating body via the flexible member, and the first heating resistor and the second heating resistor according to the voltage of the commercial power source. Switching means for switching to serial connection or parallel connection, and an image heating apparatus that heats an image while nipping and conveying a recording material that carries an image at the nip portion,
The resistance value of the second heating resistor on the downstream side in the recording material conveyance direction of the substrate is smaller than the resistance value of the first heating resistor on the upstream side in the recording material conveyance direction of the substrate. An image heating apparatus.   The resistance value per unit length in the longitudinal direction perpendicular to the recording material conveyance direction of the substrate in the first heating resistor is such that a part of the first heating resistor is the same as that of the first heating resistor. The image heating apparatus according to claim 1, wherein the image heating apparatus is larger than other portions except a part.   The other location where the resistance of the first heat generating resistor is large is a location where the first heat generating resistor and the second heat generating resistor are in contact with the power supply interrupting means for cutting off the power supply to the second heat generating resistor. The image heating apparatus according to claim 2.   The other portion where the resistance of the first heating resistor is large is an end portion of the first heating resistor in a longitudinal direction perpendicular to the recording material conveyance direction of the substrate. The image heating apparatus described.   The resistance value per unit length in the longitudinal direction perpendicular to the recording material conveyance direction of the substrate in the second heating resistor is such that a part of the first heating resistor is the same as that of the first heating resistor. Other portions where the resistance value of the second heating resistor is small compared to other portions except for a part are the second heating resistor in the longitudinal direction perpendicular to the recording material transport direction of the substrate. The image heating apparatus according to claim 1, wherein the image heating apparatus is an end portion of the image heating apparatus.