JP2018146822A - Heat generating device, image heating device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat generating device that can ensure a temperature distribution bilaterally symmetric in the longitudinal direction and obtain a targeted caloric value.SOLUTION: A heat generating device comprises: a resistance heating element; a power supply part that supplies power to the resistance heating element; and conductive parts that are provided along the resistance heating element and electrically connect the resistance heating element and the power supply part. The temperature distribution of the resistance heating element becomes higher in an area along which the conductive parts are not provided than an area along which the conductive parts are provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heating device having a resistance heating element, an image heating device having the heating device, and an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer provided with the image heating device having the heating device. is there.

  As an image heating device (fixing device) mounted on an electrophotographic copying machine or printer, a heater as a heating body having a resistance heating element on a ceramic substrate, and a flexible member that moves while contacting the heater And a pressure roller that forms a nip portion with a heater via a flexible member. The recording medium carrying the unfixed image is heated while being nipped and conveyed by the nip portion of the fixing device, whereby the image on the recording medium is heated and fixed to the recording medium. This fixing device has an advantage that it takes a short time to raise the temperature to a fixing possible temperature after energizing the heater. In addition, this type of fixing device has an advantage that power consumption during standby waiting for a print command is small.

  When a small-size recording medium is continuously passed through the fixing device having the above-described configuration, the temperature of the small-size recording area is reduced because the recording medium is deprived of heat. The temperature rises because heat is not deprived (non-sheet passing portion temperature rise). When such a phenomenon occurs, image defects such as damage to parts such as a pressure roller and high temperature offset occur.

  Therefore, as a countermeasure, the temperature rise of the non-sheet passing portion is suppressed by performing control to widen the print interval when performing small size continuous sheet passing. However, when such control is performed, the productivity of a small size is significantly reduced as compared with the productivity at the time of continuous large-size paper feeding.

  Recently, in order to solve these problems, a heater 23 has been proposed that suppresses the temperature rise of non-sheet passing as disclosed in Patent Documents 1, 2, and 3. An example of the configuration of the heater 23 is shown in FIG.

  As shown in FIG. 2, the heater 23 includes an elongated substrate 27, and electrodes 29 c provided along the longitudinal direction of the substrate on one end side and the other end side in the short direction perpendicular to the longitudinal direction of the substrate 27. , 30c and the electrodes 29c, 30c are provided with power feeding portions 29a, 30a at one end in the longitudinal direction of the substrate 27, and the resistance heating element 26 electrically connected between the electrodes 29c, 30c is provided. Have. The resistance heating element 26 has a positive resistance temperature characteristic in which the resistance value increases as the temperature rises. Note that the resistance heating element 26 generates heat by energizing the resistance heating element 26 through the electrodes 29c and 30c from the power feeding portions 29a and 30a.

  When the small-size recording medium is continuously passed through the heater 23, the small-size recording medium passing area is deprived of heat by the recording medium. The temperature rises in order not to lose heat. At this time, since the resistance heating element 26 of the heater 23 has a characteristic that the resistance value increases as the temperature rises, the heat generation is suppressed and the temperature rise of the non-sheet passing portion can be suppressed.

  However, since the heater 23 has a slight resistance value in the electrodes along the longitudinal direction, when the energization is performed from the power feeding unit side in the longitudinal direction, the power feeding unit in the longitudinal direction from the power feeding unit side is the other end. A voltage drop occurs toward the side. As a result, the voltage applied to the resistance heating element 26 in the longitudinal direction decreases along the other end side from the power supply portions 29a and 30a, and a non-uniform temperature gradient occurs in the longitudinal direction. At present, the temperature distribution in the longitudinal direction of the heater 23 is a temperature distribution as shown in FIG. 3, and the temperature on the other end side is 40 ° C. lower than the temperature on the power feeding unit side (one end side in the longitudinal direction). A temperature difference of 40 ° C is born in the direction. That is, when the recording medium is passed in this state, a fixing failure may occur on the other end side with respect to the power feeding unit in the longitudinal direction.

  As a means for solving the above problem, as shown in FIG. 4, a symmetrical temperature distribution can be secured by providing an input contact portion to the electrode at the center position in the longitudinal direction and making the voltage drop across the electrode uniform left and right. Further, there is a technique disclosed in Patent Document 2. By making the resistance values of the electrodes 29c, 30c 1/30 or less as compared with the resistance heating element 26, the voltage drop is made minute and the occurrence of temperature gradient in the longitudinal direction is prevented.

JP 2008-192398 A JP 2005-234540 A JP 2000-173752 A JP 2009-103881 A

  However, it is difficult with the current technology to make the resistance value of the electrode extremely low compared to the resistance heating element. As one means, the resistance value can be greatly reduced by widening the width of the electrode in the short direction of the substrate. However, if the electrode width is increased so that it is 1/30 or less of the resistance value of the resistance heating element, a width in the short direction that is greater than the width of the heating element is required. The ratio becomes larger than the width of the heating element, and it is difficult to secure a target heat generation amount. As another means, it is possible to lower the resistance value of the electrode by changing the material used for the electrode, but a material having a lower resistivity is used so that the resistance value is 1/30 or less of the resistance heating element. It is difficult to do in consideration of the cost. Further, in the configuration as shown in FIG. 4, the path portions (route electrodes 29b and 30b) of the electrodes 29c and 30c provided on the power feeding side (one end side in the longitudinal direction) generate heat, as shown in FIG. There is a concern that the temperature distribution is asymmetric in the longitudinal direction. When a recording medium is added in such a temperature distribution state, the output image has the possibility of causing image defects such as uneven fixing and uneven gloss on the left and right.

  Therefore, an object of the present invention is to provide a heat generating device that can suppress the occurrence of non-uniform temperature distribution in the longitudinal direction.

  In order to achieve the above object, the present invention provides a resistance heating element, a power supply unit that supplies electric power to the resistance heating element, and the resistance heating element that is provided along the resistance heating element, and electrically connects the resistance heating element and the power supply unit. And a conductive portion that is electrically connected, wherein a temperature distribution of the resistance heating element is higher in a region not along the conductive portion than in a region along the conductive portion.

  According to the present invention, it is possible to suppress the occurrence of uneven temperature distribution in the longitudinal direction of the heat generating device.

BRIEF DESCRIPTION OF THE DRAWINGS It is a structural model figure of the heater which concerns on Example 1, Comprising: (a) is a front view of a heater, (b) is a side view of a heater, (c) is a back view of a heater. Surface view of the heater of Comparative Example 1 The figure showing the temperature distribution of the longitudinal direction of the heater of the comparative example 1 Surface view of the heater of Comparative Example 2 The figure showing the temperature distribution of the longitudinal direction of the heater of the comparative example 2 Cross-sectional model diagram showing an example of a fixing device (A) (b) is a temperature distribution comparison diagram in the longitudinal direction of each heater. It is a temperature comparison table of the center part of the longitudinal direction of each heater, and an edge part, Comprising: (a) is a temperature comparison table figure in the heater which concerns on Example 1, (b) is a temperature comparison in the heater of the comparative example 1. Table, (c) is a temperature comparison table with the heater of Comparative Example 2. (A) (b) is a figure which shows the emitted-heat amount (electric power consumption) of a heater. (A) (b) is explanatory drawing of the heater which has a resistance heating element from which an electrical resistance value differs (A) (b) is explanatory drawing of the heater which has a resistance heating element from which thickness differs (A) (b) is a figure which shows an example of the electricity supply control path | route used for the heater 23. Structural model diagram of an example of an image forming apparatus provided with a fixing device having the heater

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[Example 1]
A heating body (heat generating device) according to the present embodiment will be described with reference to the drawings. In the following description, an image forming apparatus equipped with a fixing device (image heating device) having a heating body (heat generating device) according to this embodiment will be described as an example. First, the image forming apparatus will be described, then the fixing device in the image forming apparatus will be described, and then the heating body in the fixing apparatus will be described.

(1) Image Forming Apparatus FIG. 13 is a schematic cross-sectional view showing an example of an image forming apparatus equipped with a fixing device using a heating body described later. Here, a laser printer using a transfer type electrophotographic process is exemplified as the image forming apparatus.

  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which rotates at a predetermined speed in the circumferential direction. The photosensitive drum 1 is configured by forming a photosensitive material such as an OPC or an amorphous silicon drum on a cylindrical substrate such as aluminum or nickel.

  Around the photosensitive drum 1, a charging roller 2, a laser beam scanner 3, a developing device 4, a transfer roller 9, a cleaning device 10, and the like are arranged, and an image for forming an image on a recording medium by the photosensitive drum 1 and the like. A forming part is configured.

  The surface of the rotating photosensitive drum 1 is uniformly charged on the surface of the photosensitive drum 1 by rotating in contact with the charging roller 2. The photosensitive drum whose surface is uniformly charged is subjected to scanning exposure with a laser beam L modulated in accordance with image information output from a laser beam scanner 3 as an image exposure unit. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum. The electrostatic latent image is developed as a toner image by toner (developer) by the developing device 4.

  On the other hand, the recording medium P is separated and fed one by one from the feeding cassette 5 by the feeding roller 6 and sent to the registration roller 7. The recording medium P is synchronized with the toner image formed on the surface of the photosensitive drum 1 by the registration roller 7 and introduced into the transfer nip T formed by the photosensitive drum 1 and the transfer roller 9 through the sheet path 8a. The registration roller 7 controls the leading edge of the toner image on the photosensitive drum and the leading edge of the recording medium P so that they enter the transfer nip at the same timing.

  The recording medium P introduced into the transfer nip portion T is nipped and conveyed at the transfer nip portion, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 9 from the transfer bias application power source (not shown). Thus, the toner image on the photosensitive drum 1 is transferred onto the recording medium P due to electrostatic characteristics.

  The recording medium P that has received the transfer of the toner image at the transfer nip T is separated from the surface of the photosensitive drum 1 and conveyed to the fixing device 11 through the sheet path 8b. Then, the toner image on the recording medium is permanently fixed on the recording medium by being heated and pressed by the fixing device 11. The recording medium P that has left the fixing device 11 is guided to the sheet path 8c side and is discharged from the discharge port 13 onto the discharge tray.

  After the transfer of the toner image, the toner and paper dust on the surface of the photosensitive drum 1 are removed by the cleaning device 10 to clean the surface of the photosensitive drum and repeatedly used for image formation.

(2) Fixing Device FIG. 6 is a cross-sectional view showing an example of a fixing device 11 having a heating body (heat generating device) described later. Here, a fixing device that heats and fixes an image (unfixed toner image) on a recording medium is illustrated as the image heating device.

  In the following description, with respect to the fixing device or the members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording medium conveyance direction, and the short direction is the same direction as the recording medium conveyance direction. is there.

  The fixing device 11 shown in this embodiment includes a heater 23 as a heating body (heat generating device), a film 22 as a flexible member, a stay 21 as a guide member, and a pressure roller 24 as a pressure member. Have. The stay 21, the film 22, the heater 23, and the pressure roller 24 are all elongated members in the longitudinal direction. Here, the stay 21 and the film 22 constitute a heating member having the heater 23, but the configuration of the heating member having a heating body is not limited to this.

  The stay 21 is formed in a vertical cross-sectional shape using a predetermined material having heat resistance and rigidity, and a heater 23 is held on the stay 21. The film 22 has heat resistance and is endless (cylindrical). The film 22 is fitted on the stay 21. The inner peripheral length of the film 22 and the outer peripheral length of the stay 21 are larger in the film 22 by, for example, about 3 mm. Accordingly, the film 22 is externally fitted to the stay 21 with a margin in the circumference. A lubricant (not shown) is interposed between the inner peripheral surface of the film 22 and the outer peripheral surface of the stay 21. Thereby, the sliding resistance when the stay 21 and the inner peripheral surface of the film 22 rotate in contact with each other is reduced.

  Each member in the fixing device will be described in detail.

(3) Fixing Film In the film 22, the film thickness is preferably 100 μm or less in order to reduce the heat capacity and shorten the start-up time. As the material of the film 22, a heat-resistant single layer film such as PTFE, PFA, FEP or the like, or a composite layer obtained by coating PTFE, PFA, FEP or the like on the outer peripheral surface of a film such as polyimide, polyamideimide, PEEK, PES, PPS, etc. A film can be used. In this example, the film 22 was formed by coating PFA and PTFA on the outer peripheral surface of a 75 μm-thick polyimide film. The outer diameter of the film 22 was 24.0 mm.

(4) Stay The stay 21 can be composed of, for example, a high heat resistant resin such as polyimide, polyamideimide, PEEK, PPS, liquid crystal polymer, or a composite material of these resins with ceramic, metal, glass, or the like. In this embodiment, the stay 21 is formed of a liquid crystal polymer in a vertical cross-sectional shape. Both ends of the stay 21 in the longitudinal direction are held by a pair of side plates (not shown) of the fixing device 11. On the surface of the stay 21 on the pressure roller 24 side, a concave groove 21a is provided along the longitudinal direction, and the heater 23 is held in the groove.

(5) Pressure roller The pressure roller 24 has a metal core 24a and an outermost release layer 24c provided around an elastic body layer 24b provided around the metal core 24a. The pressure roller 24 is rotatably held at both ends in the longitudinal direction of the cored bar 24 a by a pair of side plates (not shown) of the fixing device 11. In this embodiment, the core metal 24a is made of aluminum, the elastic layer 24b is made of silicon rubber containing a microballoon, and the release layer 24c is made of a PFA tube. The outer diameter of the pressure roller was 20 mm, and the thickness of the release layer was 30 μm. And the pressure roller 24 arrange | positioned in parallel with the film 22 under the film 22 is pressed by the stay 21 side by pressure means, such as a pressure spring, at both ends of the core metal. As a result, the pressure roller 24 has a nip portion (pressure contact portion) having a predetermined width necessary for heating and fixing an unfixed toner image on the recording medium P with the film 22 sandwiched between the surface of the pressure roller 24 and the heater 23. N is formed.

(6) Arrangement pattern of temperature detection element / safety device The heater 23 has a temperature detection element 25 on the back surface (surface opposite to the nip portion N) of the substrate 27. The temperature detection element 25 is provided to detect the temperature of the heater 23. In this embodiment, a thermistor in contact with and abutting on the back side of the heater 23 is used as the temperature detection element. For example, the thermistor 25 is provided with a heat insulating layer on a support (not shown), an element of the chip thermistor is fixed on the heat insulating layer, and the element is supported on the back surface of the substrate 27 by applying a predetermined pressure. The body is brought into contact with the back surface of the substrate 27.

  In this embodiment, the thermistor is temperature determination means for determining the temperature of the resistance heating element. Two thermistors are provided in the longitudinal direction of the resistance heating element, and one of the thermistors 25a is provided in the minimum size sheet passing area through which the recording medium P in the longitudinal direction of the resistance heating element always passes. The other thermistor 25b is installed in the portion corresponding to the non-sheet passing area when the B5 size recording medium in the longitudinal direction of the resistance heating element is passed in the direction of the arrow R. With this arrangement format, the temperature of the paper passing area is controlled by the thermistor 25a, and the temperature of the non-paper passing area at the time of small-size paper passing is controlled by the thermistor 25b. That is, the temperature control of the sheet passing area is performed by the thermistor 25a, and the thermistor 25b performs the throughput control so that the abnormal temperature rise in the non-sheet passing area at the time of small size continuous sheet passing does not occur. The heater 23 in the present embodiment is configured to suppress the temperature rise in the non-sheet passing area. Therefore, the possibility of entering the throughput control is very low, but the edge temperature rise may occur in extremely small sized continuous paper such as postcards. Yes.

  The heater 23 has a safety device on the back surface (the surface opposite to the nip portion N) of the substrate 27, and is provided to cut off the energization when the heater 23 is abnormally heated. In this embodiment, a thermo switch 31 is used as a safety device. As a configuration, a bimetal is provided inside, and the bimetal is covered with an aluminum cap member. When the cap member contacts the back surface of the heater 23 substrate, the temperature of the heater 23 is transmitted to the bimetal through the cap member. With this configuration, when the heater 23 is abnormally heated, the temperature of the heater 23 is transmitted to the bimetal, and when the critical temperature is reached, the bimetal is deformed and the energization to the heater 23 is cut off.

  In this embodiment, a thermo switch is used as a safety device, but a safety device such as a thermal fuse may be used. The thermo switch is disposed at a position symmetrical about the center in the longitudinal direction of the resistance heating element 26 of the thermistor 25a and the heater 23. Thereby, even if the voltage drop in the longitudinal direction of the heater 23 is taken into consideration, the temperature detected by the thermo switch 31 becomes the same value as the temperature controlled by the thermistor 25. Therefore, it is possible to accurately detect the temperature of the heater 23, and it is possible to more accurately detect the abnormal temperature rise of the heater 23. As the best configuration, as shown in FIG. 12, the thermistor 25a and the thermo switch 31 are placed as close as possible to the central part from both ends in the longitudinal direction of the resistance heating element 26, and are brought into contact with a symmetrical position about the center. It is the composition which is. With the above configuration, the temperature detected by the thermistor 25a is in the vicinity of the maximum temperature location in the longitudinal direction of the heater 23, and it is possible to easily suppress overheating. Further, since the temperature detected by the thermo switch 31 is in the vicinity of the maximum temperature location in the longitudinal direction of the heater 23, an abnormal temperature rise can be detected quickly, and safety can be improved. Further, as shown in FIG. 1, the thermo switch 31 may be installed so that the center position of the thermo switch 31 comes to the center of the resistance heating element 26 in the longitudinal direction. With this configuration, the thermo switch can be brought into contact with a position equivalent to the maximum temperature location in the longitudinal direction of the heater 23. That is, in terms of safety, it can be said that the configuration centered on the thermoswitch as shown in FIG. 12 is the optimal configuration.

(7) Heat-fixing operation of the fixing device A pressure is applied by driving a driving gear (not shown) provided at the end of the cored bar 24a of the pressure roller 24 in the direction of the arrow by a fixing motor (not shown). The roller 24 rotates in the direction of the arrow. Due to the rotation of the pressure roller 24, a rotational force acts on the film 22 by the frictional force between the surface of the pressure roller 24 and the surface of the film 22 at the nip portion (pressure contact portion) N, and the film 22 is driven to rotate. At this time, the film 22 is driven to rotate in the direction of the arrow at the same speed as the rotation speed of the pressure roller 24 while sliding in close contact with the surface of the heater 23 inside. As a result, the fixing device transfers the heat of the heater 23 to the recording medium P in the nip portion N via the film 22.

  FIG. 12 shows an energization control path of the heater 23. Upon receipt of a printing operation signal, energization of the heater 23 is started, and the control unit 41 as the control unit turns on the temperature control unit 42 as the energization control unit. As a result, the AC power supply 43 is energized to the electrode power feeding portions 29 a and 30 a of the heater 23 via the thermo switch (temperature detection type safety device) 31. When the heater 23 is energized to the electrodes 29c and 30c via the path electrodes 29b and 30b through the power feeding parts 29a and 30a, the entire resistance heating element 26 generates heat and the temperature is raised. The thermistor 25 detects the temperature of the substrate 27 that is heated in accordance with the temperature rise and continues energization until the temperature of the substrate 27 reaches the target temperature, during which the control unit 41 outputs the output (detected temperature) of the thermistor 25. A / D convert and capture. When the target temperature is reached, based on the output signal from the thermistor 25, the electric power supplied to the heater 23 by the temperature control means 42 is controlled by phase control or wave number control to control the temperature of the heater 23. That is, the control unit 41 controls the temperature control means 42 so as to increase the temperature of the heater 23 when the temperature detected by the thermistor 25 is lower than a predetermined set temperature and to decrease the temperature of the heater 23 when higher than the set temperature. As a result, the heater 23 is kept at the set temperature.

  The recording medium P is introduced into the nip portion (pressure contact portion) N in a state where the temperature of the heater 23 rises to the set temperature and the rotational peripheral speed of the film 22 is stabilized by the rotation of the pressure roller 24. The recording medium P is nipped and conveyed together with the film 22 in the short direction perpendicular to the longitudinal direction of the substrate 27 of the heater 23 at the nip portion N. As a result, the heat of the heater 23 is applied to the recording medium P through the film 22, and the unfixed toner image t on the recording medium P is heated and fixed to the recording medium P. The recording medium P that has exited the nip N is separated from the surface of the film 22 and conveyed. When these printing operations are finished, the temperature control means 42 is turned off and the energization of the heater 23 is finished.

(8) Heater FIG. 1 shows an example of the heater 23 as a heating body according to the present embodiment. FIG. 1A is a front view of the heater 23, FIG. 1B is a side view of the heater 23, and FIG.

  The heater 23 according to the present embodiment includes a substrate 27, a resistance heating element 26, power feeding portions 29a and 30a, path electrodes 29b and 30b, electrodes 29c and 30c, and a heat-resistant overcoat layer 28. doing. The substrate 27 is a heat-resistant / insulating / good heat conductive substrate elongated in the longitudinal direction. The electrodes 29 c and 30 c are provided along the longitudinal direction of the substrate 27 on one end side and the other end side in the lateral direction orthogonal to the longitudinal direction of the substrate 27, respectively. The electrode 29 c is provided on one end side in the short direction of the substrate 27 and is a first electrode in contact with one end side in the short direction of the resistance heating element 26. The electrode 30 c is a second electrode that is provided on the other end side in the short direction of the substrate 27 and is in contact with the other end side in the short direction of the resistance heating element 26.

  The power feeding portions 29 a and 30 a are provided on one end side in the longitudinal direction of the substrate 27. The route electrodes (conductive portions) 29b and 30b are provided along the resistance heating element 26, and electrically connect the power supply portions 29a and 30a to the electrodes 29c and 30c. The power feeding unit 29a is electrically connected to an electrode 29c that is in contact with the resistance heating element 26 via a path electrode 29b. The path electrode 29b is connected to the central portion (input contact) in the longitudinal direction of the electrode 29c. The power feeding unit 30a is electrically connected to an electrode 30c that is in contact with the resistance heating element 26 via a path electrode 30b. The path electrode 30b is connected to the central portion (input contact) in the longitudinal direction of the electrode 30c. That is, a contact portion (input contact) from the path electrodes 29b and 30b to the electrodes 29c and 30c is provided at a central portion in the longitudinal direction of the resistance heating element 26, and a recording medium P having a predetermined size always passes through the central portion. It is located within the minimum size paper passing area. The power feeding units 29a and 30a supply power to the resistance heating element 26 through the electrically connected path electrodes 29b and 30b and the electrodes 29c and 30c. The resistance heating element 26 is disposed between the electrodes 29c and 30c in the short direction of the substrate 27 and is electrically connected. The resistance heating element 26 is provided on one surface (surface on the nip portion N side, surface, surface on the same side) of the substrate 27 together with the power feeding portions 29a, 30a, the path electrodes 29b, 30b, and the electrodes 29c, 30c. Yes.

  The material of the path electrodes 29b and 30b is formed of a mixture of silver and palladium (hereinafter referred to as silver palladium), and the material mixing ratio is adjusted so that the total electric resistance value thereof is 1.0Ω.

  The material of the resistance heating element 26 was formed of silver palladium, and the total electric resistance value was 18 [Ω]. The resistance heating element 26 has different electrical resistance values in the longitudinal direction, particularly at a line (between FIGS. 1A and 1A) connecting the contact portion on the electrode 29c side and the contact portion on the electrode 30c side. Here, in the resistance heating element 26, the electrical resistance value of the resistance heating element 26 a on the non-feeding part side is made smaller than the electrical resistance value of the resistance heating element 26 b on the feeding part side, with the contact portion as a boundary. Specifically, the material of silver and palladium so that the electric resistance value of the resistance heating element 26a on the non-feeding portion side is 32 [Ω] and the electric resistance value of the resistance heating element 26b on the feeding portion side is 41 [Ω]. The ratio is adjusted (see FIG. 10). That is, the temperature distribution of the resistance heating element 26 is set so that the resistance heating element 26a on the non-feeding part side is higher than the resistance heating element 26b on the feeding part side. Here, the power supply unit side (power supply side) is the side where the power supply units 29 a and 30 a are provided in the longitudinal direction of the resistance heating element 26. On the other hand, the non-power feeding part side (non-power feeding side) is a side where the power feeding parts 29 a and 30 a are not provided on the opposite side to the power feeding part side in the longitudinal direction of the resistance heating element 26. Further, the resistance heating element 26b on the power feeding unit side is a region along the path electrodes 29b and 30b, and the resistance heating element 26a on the non-power feeding unit side is a region not along the path electrodes 29b and 30b.

  The adjustment of the electric resistance value of the resistance heating element 26a on the non-feeding portion side and the electric resistance value of the resistance heating element 26b on the feeding portion side is not a method of adjusting the material ratio of the silver palladium, but different materials (for example, It may be adjusted to a predetermined electric resistance value with silver palladium and uteum oxide). Furthermore, the adjustment of the electrical resistance value of the resistance heating element 26a on the non-feeding portion side and the resistance value of the resistance heating element 26b on the feeding portion side uses the same material (for example, silver palladium), and the thickness of the resistance heating element. The electrical resistance value of the resistance heating element 26a on the non-feeding part side and the electrical resistance value of the resistance heating element 26b on the feeding part side may be adjusted by changing (the height direction with respect to the substrate surface). Specifically, as shown in FIG. 11, in the resistance heating element 26, the thickness of the resistance heating element 26a on the non-feeding part side is made larger than the thickness of the resistance heating element 26b on the feeding part side, with the contact portion as a boundary. The resistance value may be adjusted by increasing the thickness.

  The effect of the present embodiment will be described together with a comparative example described below.

  As a comparative example, the input contact position to the electrode as shown in FIG. 2 is a heater 23 (Comparative Example 1) provided at the power supply side end in the longitudinal direction, and the input contact position to the electrode as shown in FIG. Is a heater 23 (Comparative Example 2) provided at the center in the longitudinal direction. Considering the situation in which an electrophotographic printer is actually used as a comparative experiment, a general electric power of 500 W actually inputted during sheet feeding is input to both heaters 23 so that the temperature of the heaters 23 becomes 210 ° C. The temperature of the electrode part, the temperature of the heating element part, and the actual temperature as the heater 23 are compared with each other when the temperature is adjusted. At this time, the temperature control thermistor (temperature detection element) 25 is brought into contact with the substrate side at the center position in the longitudinal direction of the heater 23, and the temperature distribution in the longitudinal direction on the heating element surface side of the heater 23 and the longitudinal direction are detected by the infrared thermography camera. The central part and the end part (here, the boundary part between the heating element and the substrate) were measured. The comparison results are shown in FIGS.

  In the case of a heater configuration in which an input contact position to an electrode having a region in contact with a heating element, such as the heater 23 of the configuration of the comparative example 1, is provided at the power supply side end in the longitudinal direction, the electrical resistance value of the electrode As shown in Comparative Example 1 of FIG. 8B, a temperature distribution is shown in which the temperature of the resistance heating element decreases from the power supply side to the non-power supply side. Specifically, the heating element temperature is 225 ° C. at the power supply end, 205 ° C. at the center, and 185 ° C. at the non-power supply end. Therefore, the temperature distribution of the entire heater including heat generation at the electrodes is 230 ° C. at the power supply end, 210 ° C. at the center, and 190 ° C. at the non-power supply end.

  In the case of the heater configuration in which the input contact position to the electrode having the region in contact with the resistance heating element is provided in the central portion in the longitudinal direction like the heater 23 of the configuration of the comparative example 2, as in the comparative example 1 The voltage drop due to the electrode in contact with the resistance heating element is equal between the power supply side and the non-power supply side. However, there is a left-right difference (difference between the power feeding side and the non-power feeding side) in the heater temperature distribution as shown in Comparative Example 2 in FIG. The reason is that there is a path electrode from the power supply section to the resistance heating element on the power supply section side of the heater, and this path electrode itself generates heat. Specifically, since the heating element temperature is 185 ° C. at both ends and 200 ° C. at the center, a symmetrical temperature distribution can be secured. On the other hand, the heating temperature of the path electrode is 70 ° C. Therefore, the temperature distribution of the entire heater including the heating element and the path electrode is 205 ° C. at the power supply end, 210 ° C. at the center, and 190 ° C. at the non-power supply end.

  In contrast to the comparative example 1 and the comparative example 2, the heater 23 in the present embodiment is provided with an input contact position to an electrode having a region in contact with the heating element at the center in the longitudinal direction, and the electrical resistance of the resistance heating element. The position of the input contact to the electrode having the region in contact with the heating element is changed in the longitudinal direction from the central part in the longitudinal direction to the boundary, and the heating temperature of the heater 23 on the power feeding side including the path electrode and the path electrode are not provided. The heat generation temperature of the non-power supply side heater 23 is made equal. Thereby, the heater 23 temperature distribution in the longitudinal direction can be made symmetrical, and the temperature difference between the central portion and the end portion of the heater 23 can be reduced. In the case of this heater configuration, the temperature distribution in the longitudinal direction of the heater takes a distribution as shown in the embodiment of FIG. Specifically, the heating element temperature is 185 ° C. at the feeding end, 200 ° C. at the center, and 185 ° C. at the non-feeding end. Heat generation temperature by the path electrode is 70 ° C. Therefore, the temperature distribution of the entire heater including the heating element and the path electrode is 195 ° C. at the power supply side end, 210 ° C. at the central portion, and 195 ° C. at the non-power supply side portion. The temperature difference can be made 15 ° C. smaller than the comparative example.

  According to this embodiment, considering the heat generated by the path electrode, the amount of heat generated by the resistance heating element is adjusted on the left and right sides of the central portion in the longitudinal direction, which is the input contact point to the electrode in contact with the resistance heating element. By doing so, it is possible to ensure a uniform temperature distribution in the left and right directions in the longitudinal direction and to obtain a target heat generation amount. For this reason, in the image forming apparatus using the heater, it is possible to improve image defects such as fixing unevenness and gloss unevenness of the output image. In addition, the above-described effects can be exhibited without increasing the width of the substrate in the short direction.

  Next, specific means of the present embodiment will be described below.

  In this embodiment, the total electrical resistance value of the heater 23 is set to 20 [Ω], and the electrical resistance values of the first electrode path electrode 29b and the second electrode path electrode 30b are set to 1.0 [Ω]. The remaining 18 [Ω] is held by the resistance heating element 26. Considering a system in which an AC voltage of 100 V is applied between the first power supply unit 29a and the second power supply unit 30a with this heater configuration, the current flowing through the heater 23 is 5.0 [A] according to Ohm's law. The power consumption of the entire heater is 500 [W]. At this time, the amount of power consumed by the path electrodes 29b and 30b is 25 [W], and there is a power consumption difference (heat generation amount difference) corresponding to 50 [W] between the power feeding side and the non-power feeding side of the heater 23. . This power consumption difference is covered by the difference between the electrical resistance value of the non-power-feeding resistance heating element 26a and the electrical resistance value of the feeding-side resistance heating element 26b. Specifically, as shown in FIGS. 9 and 10, the power consumption of the resistance heating element 26a on the non-power supply side is 250 [W], and the power consumption of the resistance heating element 26b on the power supply side is 200 [W]. Thus, the electrical resistance value of the resistance heating element 26a on the non-feeding side is determined to be 32 [Ω], and the electrical resistance value of the resistance heating element 26b on the feeding side is determined to be 41 [Ω].

  The resistance heating element 26 is obtained by forming a silver palladium (Ag / Pd) paste on the substrate 27 in the form of a line band by screen printing. In this embodiment, the resistance heating element has a length of 220 mm in the longitudinal direction (the length of each of the resistance heating element 26a on the non-feeding side and the resistance heating element 26b on the feeding side is 110 [mm]), and the width in the short direction. A resistance heating element having a thickness of 0 mm and a thickness of 10 μm is used. As a material of the resistance heating element 26, other than ruthenium oxide, an electric resistance material such as ruthenium oxide or Ta2N may be used to adjust a predetermined electric resistance value.

  The substrate 27 is made of a ceramic material such as alumina or aluminum nitride. In this embodiment, a substrate having a width of 7 mm in the lateral direction, a length of 270 mm in the longitudinal direction, and a thickness of 1 mm is used. The electrodes 29 and 30 used a silver screen pattern. The overcoat layer 28 has electrical insulation between the resistance heating element 26 and the surface of the heater 23, electrical insulation between the surface of the heater 23, and slidability between the surface of the heater 23 and the inner peripheral surface of the film 22. , Is the main purpose.

  In the heater 23, the substrate 27 is fixed in the groove of the stay 21 with the substrate surface facing the nip portion N surface. Thereby, the overcoat layer 28 of the heater 23 is brought into contact with the inner peripheral surface of the film 22.

  The overcoat layer 28 is provided on the surface of the substrate 27 so as to cover the resistance heating element 26 and the electrodes 29 and 30. In this example, a heat-resistant glass layer having a thickness of 60 μm was used as the overcoat layer 28. In FIG. 1, the overcoat layer is omitted so that the relationship between the electrodes 29 and 30 and the resistance heating element 26 can be easily understood.

  As shown in FIG. 1 (a), the input positions from the power supply portions 29a and 30a to the electrodes 29c and 30c in contact with the resistance heating element 26 via the path electrodes 29b and 30b are in the longitudinal direction of the resistance heating element. It is the heater 23 located in the center part from both ends. The central portion is located in the minimum size sheet passing area through which the recording medium P having a predetermined size always passes. With the above configuration, the voltage drop due to the electrodes can be made symmetrical, and the heat generation by the electrode path is the same amount of heat generation in the longitudinal direction, so the temperature difference is shown in Comparative Example 1 shown in FIG. It is possible to reduce more than the heater configuration. Furthermore, since a uniform temperature distribution in the longitudinal direction can be realized on the left and right, temperature control becomes easier than the non-uniform temperature distribution on the left and right in Comparative Example 1, and the fixing property at the end can be ensured to be equal to that in the center. is there. On the other hand, if the temperature exceeds 15 ° C., it becomes difficult to secure the fixability of the end portion in the longitudinal direction. Therefore, in practice, the temperature difference in the longitudinal direction of the heater 23 is desired to be 15 ° C. or less.

  In this embodiment, the resistance value of the electrode is changed to change the temperature in the longitudinal direction of the heater 23 to a uniform state on the left and right. However, the resistance value of the electrode can be changed even if the left and right are not uniform. Thus, a configuration in which the temperature distribution in the longitudinal direction of the heater 23 is changed to a necessary state that is not uniform left and right is also within the scope of the present invention. For example, a configuration in which the resistance value of the path electrode at a location where a member that locally lowers the temperature of the heater 23 such as the thermistor or the thermo SW is in contact is also included in the scope of the present invention.

[Other Examples]
In the above-described embodiment, a printer is exemplified as the image forming apparatus, but the present invention is not limited to this. For example, the image forming apparatus may be another image forming apparatus such as a copying machine or a facsimile machine, or another image forming apparatus such as a multi-function machine combining these functions. The same effect can be obtained by applying the present invention to the heating body of the fixing device used in these image forming apparatuses.

  In the above-described embodiment, the heat fixing device mounted on the image forming apparatus such as a printer or a copying machine is exemplified as the image heating apparatus. However, the present invention is not limited to such a heat fixing apparatus, and can be applied to an image heating apparatus such as a gloss applying apparatus for improving the gloss of an image formed on a recording medium. Further, the present invention can be applied to an image heating apparatus that is not mounted on the image forming apparatus.

N: Nip part P ... Recording medium 11 ... Fixing device 21 ... Stay 22 ... Fixing film 23 ... Heater 24 ... Pressure roller 25, 25a, 25b ... Thermistor (temperature detection element)
26, 26a, 26b ... resistance heating element 27 ... substrate 28 ... overcoat layer 29a, 30a ... power feeding part 29b, 30b ... path electrode 29c, 30c ... electrode 31 ... thermo switch 41 ... control part 42 ... temperature control means 43 ... AC Power supply

Claims (7)

A resistance heating element;
A power feeding section for supplying power to the resistance heating element;
A conductive portion that is provided along the resistance heating element and electrically connects the resistance heating element and the power feeding unit;
With
The heating device according to claim 1, wherein a temperature distribution of the resistance heating element is higher in a region not along the conductive portion than in a region along the conductive portion.   2. The heating device according to claim 1, wherein the resistance heating element has an electric resistance value in a region not along the conductive portion smaller than an electric resistance value in a region along the conductive portion.   The heating device according to claim 2, wherein the resistance heating element has a thickness of a region not along the conductive portion larger than a thickness of a region along the conductive portion.   The heating device according to any one of claims 1 to 3, wherein the resistance heating element, the power feeding unit, and the conductive unit are provided on the same surface. Temperature determining means for determining the temperature of the resistance heating element;
5. The temperature determination unit is provided in a minimum size sheet passing area through which a recording medium passes and a non-sheet passing area when the minimum size recording medium is passed. Heating device.   An image heating apparatus for heating and nipping and conveying a recording medium by a heating means having a heating body and a pressurizing means, wherein the heating body has the heating device according to any one of claims 1 to 5. An image heating apparatus.   An image forming apparatus comprising the image heating apparatus according to claim 6 as fixing means for applying heat and pressure to a toner image formed on a surface of a recording medium to fix the toner image on the recording medium.

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