JP2019174767A - Heater and fixing device - Google Patents

Abstract

To provide a heater and fixing device, capable of preventing image troubles such as poor fixing and glossy streaks.SOLUTION: A connection between a temperature sensing element and a conductor line includes an overlapping section where they overlap with each other. In a cross-section of a heater passing the temperature sensing element in a direction parallel to a longitudinal direction thereof, a slope easing section is provided next to the overlapping section, the slope easing section having a step smaller than a step from a substrate surface to a surface of the overlapping section.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fixing device mounted on an image forming apparatus such as an electrophotographic recording type copying machine or printer, and a heater mounted on the fixing device.

  As a fixing device mounted on an electrophotographic recording type image forming apparatus, an apparatus using a film is known. The fixing device includes a cylindrical film and a heater that contacts the inner surface of the film. Since the fixing device using a film has a low heat capacity, it has advantages such as a short warm-up time of the device and low power consumption.

  The heater includes a substrate made of a material such as ceramic and a heating resistor (a heating element) provided on the substrate. The temperature of the heater is detected by a temperature detection element such as a thermistor, and the control unit controls the power supply to the heating resistor according to the output of the temperature detection element.

  As a configuration of the temperature detection element, there is a configuration in which a temperature detection element provided independently of the heater is pressed against the heater via an insulating sheet. In addition, there is a heater-integrated configuration in which a temperature detection element and a conductive line electrically connected to the temperature detection element are provided on a heater substrate by a coating method such as screen printing. In the heater integrated type, the temperature detection element, the conductive line, and the heating element are protected by a glass film for insulation. The heater integrated type is advantageous in that the temperature detection element is printed on the substrate, so that there is little variation in responsiveness and the temperature detection accuracy is high.

  Furthermore, there is a proposal that a temperature detection element is provided on the sliding surface side of the heater film in order to accurately detect the temperature of the fixing nip (Patent Document 1). Moreover, the thing of patent document 1 has provided the heating resistor in the surface on the opposite side to the surface which provided the temperature detection element of the board | substrate for size reduction of a heater.

JP 2017-54071 A

  However, in the heater configuration described above, the thickness of the portion provided with the temperature detection element and the conductive line from the surface of the substrate becomes thicker than the other portions, and the heater surface may be uneven. According to the study by the present inventors, it has been found that when the conductive line on the heater substrate is formed in parallel with the conveyance direction of the recording material, fixing failure and gloss streaks can occur. This is because the heat and pressure applied to the toner image become non-uniform due to the stepped portion of the heater surface generated by the conductive line.

  Further, as a result of detailed examination, it has been found that unevenness tends to be larger at the connecting portion where the temperature detection element and the conductive line overlap, and fixing defects and gloss streaks are more likely to occur.

  An object of the present invention is to provide a heater and a fixing device capable of suppressing the occurrence of image defects such as fixing defects and gloss streaks.

  The present invention for solving the above-described problems includes a substrate, a heating element provided on the substrate, a temperature detection element provided on the substrate, and a conductive line connected to the temperature detection element. And a protective layer that covers the temperature detection element and the conductive line, and is used in a fixing device that fixes a toner image formed on the recording material to the recording material. The connecting portion is provided with an overlapping portion where both overlap each other, and in the cross section when the heater is cut in a plane parallel to the longitudinal direction and passing through the temperature detecting element, next to the overlapping portion. Is characterized in that a gradient moderating portion having a smaller step than the step from the surface of the substrate to the surface of the overlapping portion is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the heater and fixing apparatus which can suppress generation | occurrence | production of image defects, such as a fixing defect and a glossy line, can be provided.

Cross section of image forming apparatus Cross section of fixing device Diagram of heater according to Example 1 The figure of the connection part of the thermistor and conductive line concerning Example 1 Diagram of heater according to comparative example Diagram of connecting part of thermistor and conductive line according to comparative example The figure which showed the image defect which occurs in the comparative example The figure of the connection part of the thermistor and conductive line concerning the modification of Example 1 Diagram of heater according to Example 2 The figure of the connection part of the thermistor and conductive line concerning Example 2 The figure of the connection part of the thermistor and conductive line concerning the modification of Example 2 The figure which showed other composition of a heater

[Example 1]
FIG. 1 is a cross-sectional view of an electrophotographic recording type image forming apparatus. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and the surface thereof is uniformly charged by the charging roller 2. Next, the charged surface of the photosensitive drum 1 is scanned by the laser scanner 3 with a laser beam L corresponding to image information. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed with toner supplied from the developing device 4. The toner image formed on the photosensitive drum 1 is transferred to the recording material P fed from the paper feed cassette 6 at a transfer nip portion that is a pressure contact portion between the transfer roller 5 and the photosensitive drum 1. The recording material P onto which the toner image has been transferred is conveyed to the fixing device 7 where the toner image is heated and fixed on the recording material. Thereafter, the recording material P is discharged onto a discharge tray. The toner remaining on the photosensitive drum 1 after the transfer is collected by the cleaning device 8.

(Configuration of the fixing device 7)
Next, the fixing device 7 will be described with reference to FIG. FIG. 2 is a cross-sectional view of the fixing device. The fixing device 7 includes a film unit 10 and a pressure roller 20, and a fixing nip portion N that sandwiches and conveys the recording material P is formed between them. The film unit 10 includes a cylindrical film 11 and a heater 12 that contacts the inner surface of the film 11. The fixing device 7 further includes a heater holder 13 that holds the heater 12 and a metal stay 14 that is biased by a pressure spring (not shown) and presses the heater holder 13 against the pressure roller 20.

  The film 11 has a base layer and a release layer formed outside the base layer. The base layer is formed of a heat resistant resin such as polyimide, polyamideimide, PEEK, or a metal such as SUS (stainless steel). The release layer is a mixed or single layer of a heat-resistant resin having a good release property such as a fluororesin such as PTFE, PFA, FEP, or a silicone resin. Moreover, you may provide the intermediate | middle layer formed with heat resistant rubbers, such as a silicone rubber, between a base layer and a mold release layer. The film 11 of this example has a SUS base layer having a thickness of 30 μm, a silicone rubber layer (elastic layer) having a thickness of 200 μm, and a release layer made of PFA having a thickness of 20 μm. The outer diameter of the film 11 was 24 mm, and the length in the longitudinal direction (width direction of the recording material P) was 240 mm.

  The heater holder 13 holds the heater 12 and also has a guide function for guiding the rotation of the film 11. The heater holder 13 is formed of a heat resistant resin such as a liquid crystal polymer.

  The metal stay 14 is a component that reinforces the heater holder 13. In order to withstand the load when the heater holder 13 is pressed against the pressure roller 20, a high-rigidity metal such as SUS is used for the metal stay 14.

  The pressure roller 20 includes a cored bar 21 and an elastic layer 22 formed outside the cored bar. A release layer such as PFA or PTFE may be provided outside the elastic layer 22. When the core 21 receives power from a motor (not shown), the pressure roller 20 rotates in the direction of the arrow. When the pressure roller 20 is rotated, the film 11 is also rotated. The pressure roller 20 of the present embodiment includes an elastic layer 22 made of silicone rubber having a thickness of 3.5 mm and a release layer made of PFA having a thickness of 70 μm. The outer diameter of the pressure roller 20 was 25 mm, and the length in the longitudinal direction was 230 mm.

  The fixing device 7 fixes the image formed on the recording material P onto the recording material with heat from the heater 12 via the rotating film 11.

(Configuration of heater 12)
The heater configuration of this embodiment will be described with reference to FIG. The heater 12 includes a substrate 30 and a heating element 31 provided on the substrate 30. The heater 12 further includes temperature detecting elements 331 to 333 provided on the surface of the substrate 30 opposite to the surface on which the heating element 31 is provided, and the side opposite to the surface of the substrate 30 on which the heating element 31 is provided. And a conductive line 34 that is electrically connected to the temperature detection element 33.

  FIG. 3A is a view showing the back surface side of the heater 12, that is, the surface opposite to the sliding surface of the heater 12 with the film 11. FIG. A heating resistor (heating element) 31 and an electrode 32 are formed on an alumina substrate 30 by screen printing, and the heating resistor 31 is covered with a first protective layer 35 (made of glass). A connector (not shown) is connected to the electrode 32, and the heating resistor 31 generates heat by the power supplied from the power source. The material of the substrate 30 may be a ceramic material such as aluminum nitride or a metal whose surface is covered with an insulating layer.

  FIG. 3B is a diagram illustrating the sliding surface side of the heater 12. Thermistors 331 to 333 as temperature detection elements and conductive lines 34 are formed on the sliding surface side of the heater 12 by screen printing. Since the conductive line 34 is connected to the control circuit 9 in the image forming apparatus via a connector (not shown), the temperature detected by the thermistors 331 to 333 can be known. The conductive line 34 has a region 34a inclined with respect to both the longitudinal direction (longitudinal direction of the heater 12) D1 of the substrate 30 and the short side direction (short direction of the heater 12) D2. By forming the conductive lines 34 in an oblique direction, the occurrence of image defects can be suppressed. The line X indicates the center of the heater 12 in the short direction D2. The angle A is an inclination angle of the region 34a with respect to the direction D1. In the fixing device, the direction D2 is the recording material conveyance direction.

  In the middle of the region 34a of the conductive line 34 arranged in an oblique direction, the thermistors 331, 332, 333 are respectively parallel to the direction D1 (so that the long side of the thermistor is parallel to the direction D1). Has been placed. The reason for this arrangement is to prevent the occurrence of image defects due to the steps generated at the connecting portions of the thermistors 331, 332 and 333 and the conductive line 34. Details will be described later. As shown in FIG. 4A, when the heater 12 is viewed from a direction perpendicular to the sliding surface, the thermistors 331 to 333 have a shape having a long side and a short side.

  The thermistors 331 to 333 and the conductive line 34 are also covered with a second protective layer 36 made of glass. The second protective layer 36 also plays a role of protecting the thermistors 331 to 333 and the conductive lines 34 from abrasion caused by rubbing with the film 11. For this reason, a glass material having higher wear resistance than the first protective layer 35 is used. The material of the resistance heating element 31 is Ag / Pd, and the material of the electrode 32 and the conductive line 34 is Ag.

  A connection portion between the thermistor 332 and the conductive line 34 will be described with reference to FIGS. 4 (a) to 4 (c). FIG. 4A is an enlarged view in the vicinity of the thermistor 332, and the line widths of the thermistor 332 and the conductive line 34 are both W1. W1 is 0.5 mm. However, the line width of the conductive line 34 at the connection portion with the thermistor 332 is W2 wider than W1. This is also for preventing the occurrence of image defects due to the step generated at the connection portion between the thermistor 332 and the conductive line 34, and will be described in detail below. W2 is 0.7 mm. In this embodiment, both are connected so that the thermistor 332 overlaps from above the conductive line 34. Both overlapping portions OLP are indicated by hatched portions in FIG.

  FIG. 4B is a cross-sectional view taken along line L1 shown in FIG. h0 is the height of the substrate 30, h1 is the height of the overlapping portion OLP of the conductive line 34 and the thermistor 332 as the first height, and h2 is the height of the conductive line 34 as the second height. ing.

  Furthermore, g0 is the height of the second protective layer 36 in the blank portion on the substrate 30, g1 is the height of the second protective layer 36 above the overlapped OLP portion, and g2 is above the conductive line 34 portion. The height of the second protective layer 36 is shown. The thermistor 332 and the conductive line 34 are set to the same thickness, and the thickness is 7 μm. Therefore, h1-h0 = 14 μm and h2-h0 = 7 μm. Further, the difference in height g0 to g2 (step size) of the second protective layer 36 is substantially the same as the difference in height h0 to h2 (step size).

  In the L1 cross section, the gradient relaxation portion having the height (second height) h2 is provided between the substrate 30 having the height h0 and the overlapping portion OLP having the height (first height) h1. Conductive lines 34 are present. For this reason, the change in height from the surface of the substrate 30 to the surface of the overlapping portion OLP is gentle, and the change in the height of the surface of the second protective layer 36 in the direction D1 is also gentle. The thickness of the second protective layer 36 is set to 20 μm.

  As shown in FIG. 4B, in the cross section along the line L1, there is no region that changes from the height h0 to the height h1 in the vicinity of the thermistor 332 without passing through the region of the height h2. When the height changes from the height h0 to the height h1, there is always a conductive line 34 having a second height h2 as a gradient relaxing portion between them. In the heater 12 of this example, the cross-sectional structure in the line L1 is the same as that of the thermistor 332 in the region in the vicinity of the thermistor 331 and the region in the vicinity of the thermistor 333. Note that the cross-sectional structure in the line L1 in the vicinity of all the thermistors does not necessarily have the above-described structure. The structure in the vicinity of at least one thermistor that needs to suppress the change in the height of the surface of the second protective layer 36 only needs to be the above-described structure. Further, in this embodiment, the length L34 in the direction D1 of the portion of the conductive line 34 that is the gradient relaxation portion (excluding the portion that is the overlapping portion OLP) is 0.5 mm or more.

  FIG. 4C is a cross-sectional view taken along line F1 shown in FIG. As described above, the line width W2 of the connection portion between the conductive line 34 and the thermistor 332 is wider than the width W1. For this reason, in the cross section in the line F1, in the vicinity of the thermistor 332, there is no region that changes from the height h0 to the height h1 without passing through the region of the height h2. When the height changes from the height h0 to the height h1, there is always a conductive line 34 having a second height h2 as a gradient relaxing portion between them. For this reason, the change in the height of the surface of the second protective layer 36 in the direction D2 is also gentle.

  In the heater 12 of this example, the cross-sectional structure in the line F1 is the same as that in the vicinity of the thermistor 332 in the region in the vicinity of the thermistor 331 and the region in the vicinity of the thermistor 333. Note that the cross-sectional structure in the line F1 in the vicinity of all the thermistors does not necessarily have the above-described structure. The structure in the vicinity of at least one thermistor that needs to suppress the change in the height of the surface of the second protective layer 36 only needs to be the above-described structure. Further, in this embodiment, the length F34 in the direction D2 of the portion of the conductive line 34 that is the gradient relaxation portion (excluding the portion that is the overlapping portion OLP) is 0.1 mm or more.

  Although the heater 12 of this example has a total of three thermistors, the second protective layer 36 may be provided if the above-described gradient relaxation portion is provided in a heater having one thermistor, or four or more heaters. The change in the height of the surface can be moderated.

  Next, a heater according to a comparative example will be described with reference to FIG. The heater of Comparative Example 1 shown in FIG. 5 also has three thermistors. The location of the three thermistors is the same as that of the heater 12 of the first embodiment, and the thickness of the thermistor, the conductive line and the thickness are also the same as those of the first embodiment.

  The thermistors 334, 335, and 336 of the heater shown in FIG. 5 are arranged so that the long sides of the thermistor are parallel to the direction D2. Further, the thermistor and the conductive line 34 are connected so that their two connection positions are aligned in a direction parallel to the direction D2.

  Next, the connection part of the thermistor 335 and the conductive line 34 in the comparative example 1 is demonstrated using FIG. 6A is an enlarged view of the vicinity of the thermistor 335 of the heater of Comparative Example 1, FIG. 6B is a cross-sectional view taken along line L2 in FIG. 6A, and FIG. 6C is FIG. 6A. It is sectional drawing in the line F2. The line widths of the thermistor 335 and the conductive line 34 are both W1.

  PH1 and PH2 indicate paths in which the height changes from the height h0 of the substrate 30 to the height h1 of the overlapping portion OLP. In the path PH1, there is a conductive line 34 as a gradient relaxing part having the second height h2, so that the change in height from the substrate height h0 to the height h1 of the overlapping part OLP is gentle. However, the path PH2 does not have a slope mitigation part, and changes directly from the substrate height h0 to the height h1 of the overlapping part OLP, so that the height gradient becomes large. For this reason, the height of the surface of the second protective layer 36 corresponding to the path PH2 also suddenly changes from the height g0 corresponding to the height h0 of the substrate 30 to the height g1 corresponding to the overlapping portion OLP portion. To do. For this reason, fixing defects and gloss streaks due to the unevenness of the surface of the second protective layer 36 are likely to occur.

  The path PH3 and the path PH4 also indicate paths whose height changes from the height h0 of the substrate 30 to the height h1 of the overlapping portion OLP. In both the path PH3 and the path PH4, there is no gradient relaxing portion, and the height changes directly from the substrate height h0 to the height h1 of the overlapping portion OLP, and therefore the gradient is large. Along with the magnitude of the gradient, the surface portion of the second protective layer 36 corresponding to the paths PH3 and PH4 also has a height g1 corresponding to the overlapping portion OLP portion from the height g0 corresponding to the height h0 of the substrate 30. The height changes suddenly. For this reason, fixing defects and gloss streaks due to the unevenness of the surface of the second protective layer 36 are likely to occur.

  As described above, in Comparative Example 1, there is a region that changes from the height h0 to the height h1 without passing through the region of the height h2 in both directions D1 and D2. There is a portion where the gradient relaxation portion does not exist. Further, the heater of the comparative example 1 does not have a gradient relaxation portion in directions other than the directions D1 and D2 (for example, the direction D3 shown in FIG. 6A) in the plane where the thermistor and the conductive line are installed. An area exists. On the other hand, between the area of the height h0 and the area of the height h1 of the heater 12 of the first embodiment, in all directions other than the directions D1 and D2 in the plane where the thermistor and the conductive line are installed. In addition, there is a gradient relaxation portion that is a region of height h2.

  Next, the effect of the heater of this example was verified under the following conditions. The recording material P used is plain paper “HP Laser Jet 90 g” and glossy paper “HP Brochure Paper 200 g”. The image after the toner image formed on the recording material P was heated and fixed on the recording material P was compared between the case where the heater of this embodiment was used and the case where the heater of the comparative example was used. When plain paper was used as the recording material P, the conveyance speed was set to 300 mm / sec, and when glossy paper was used, the conveyance speed was set to 75 mm / sec.

  The results are shown in Table 1. When the heater of Comparative Example 1 was used, image failure occurred on both plain paper and glossy paper. However, when the heater of this example was used, a good image was obtained over the entire area of the recording material P. It was.

  In Comparative Example 1, as shown in FIG. 7, in the regions Y1, Y2, and Y3 corresponding to the installation positions of the thermistors 334, 335, and 336, the fixing of the toner image T becomes insufficient and the gloss becomes low. Glossy streaks occurred.

  As described above, it is possible to suppress the occurrence of image defects by using the heater configuration of this embodiment. The reason will be described below.

  The reason why the image defect occurs in the comparative example is that heat and pressure applied to the toner image locally are insufficient due to a large step of the heater sliding surface in the overlapping portion OLP between the conductive line and the thermistor.

  As described above, in this embodiment, in the direction D1 and the direction D2, the slope alleviating part is always provided so as not to cause a large step around the overlapping part OLP between the conductive line and the thermistor. As described above, the generation of a region where heat and pressure applied locally to the toner image are insufficient is suppressed. As a result, an effect of suppressing the occurrence of image defects can be obtained.

  In the apparatus configuration of the present embodiment, it has been confirmed that the frequency of image defects increases when the height of one step exceeds approximately 10 μm. In Example 1, since the height of one step (h1-h2) is about 7 μm, an effect of suppressing image defects was obtained. Therefore, it is preferable to provide the slope relaxation portion so that the step is 10 μm or less.

  Next, a modification of the present embodiment will be given. FIG. 8 shows two examples in which the connection direction of the thermistor and the conductive line is 90 ° different from that in the first embodiment.

(Modification 1)
Modification 1 shown in FIG. 8A has a configuration in which the periphery of the connection portion between the thermistor 332 and the conductive line 34 of Example 1 is rotated by 90 °.

  The cross sections in the direction D1 and the direction D2 including the overlapping portion OLP are configured to be replaced with those in the first embodiment, and the effects obtained in the respective cross sections are the same as those in the first embodiment.

(Modification 2)
Modification 2 shown in FIG. 8B has a configuration in which the relationship between the thermistor and the conductive line in the connection portion is different from that in Example 1 and Modification 1.

  In the modified example 2, the line width of the thermistor 332 is set to W3 wider than the line width W1 of the conductive line 34. In this configuration, the conductive line 34 functions as the gradient reducing part in the transport direction as in the first and modification examples 1. However, the first example and the modified example function as the gradient relaxing part in D1. Unlike the case 1, the thermistor 332 is used. Since the thermistor and the conductive line have the same thickness, the same effects as those of the first embodiment and the first modification can be obtained.

  In the above example, a part of the conductive line and the thermistor functioned as the gradient relaxing part. However, for example, an insulator having a second height can be used as the gradient relaxing portion.

  As described above, the heater of this embodiment includes the substrate, the heating element provided on the substrate, the temperature detection element provided on the substrate, the conductive line connected to the temperature detection element, and the temperature detection. A protective layer covering the element and the conductive line. This heater is used in a fixing device that fixes a toner image formed on a recording material to the recording material. And the connection part of a temperature detection element and a conductive line is provided with the overlap part in which both overlapped. In the cross section when the heater is cut in a plane parallel to its longitudinal direction and passing through the temperature detection element, the slope is smaller next to the overlap than the step from the surface of the substrate to the surface of the overlap. Is provided. Further, in the cross section when the heater is cut in a plane parallel to the short side direction and passing through the temperature detection element, a step is adjacent to the overlapping portion, next to the step from the surface of the substrate to the surface of the overlapping portion. A small slope mitigation part is provided.

(Example 2)
Next, Example 2 will be described. A feature of the present embodiment is that a gradient relaxation portion is always provided only in the direction D1. Unlike the first embodiment, the direction D2 has a configuration in which there is a portion in which the gradient relaxing portion does not exist or does not exist in part.

  The basic configurations and operations of the image forming apparatus 100 and the image heating apparatus 7 are the same as those in the first embodiment. Only the shape of the sliding surface side of the heater 12 mounted on the image heating device 7 is different.

(Characteristics of the heater)
The characteristics of the heater used in Example 2 will be described. FIG. 9A shows the back side of the substrate 30 and has the same shape as that of the first embodiment shown in FIG. FIG. 9B shows the sliding surface side, and the configuration is the same as that of the first embodiment shown in FIG. 3B except for the portions described below. Differences from the first embodiment will be described with reference to FIG.

  FIG. 10A is an enlarged view in the vicinity of the thermistor 338, and the line widths of the thermistor 338 and the conductive line 34 are both W1. In the second embodiment, W1 is 0.5 mm. Unlike the first embodiment, the line width of the conductive line 34 at the connection portion with the thermistor 338 is also W1. Others are the same as those in the first embodiment. FIG. 10B is a cross-sectional view taken along line L3 shown in FIG. 10A, and is exactly the same as FIG. 4B described in the first embodiment. FIG. 10C is a cross-sectional view at F3 shown in FIG.

  As described above, in the second embodiment, the line widths of the thermistor 338 and the conductive line 34 at the connection portion are the same W1, and they are exactly overlapped. For this reason, in the cross section in the line F3, unlike the cross section in the line F1 of Example 1 shown in FIG.4 (c), a gradient relaxation part does not exist. Therefore, in the second embodiment, the height change on the surface of the second protective layer 36 is more abrupt than in the first embodiment in the cross section along the line F3.

  When confirmation was performed under the same conditions as those for confirming the effect of Example 1, neither fixing failure nor gloss streaking occurred in Example 2. This result shows that if there is a gradient relaxation part in the direction D1, image defects can be avoided. The reason is as follows.

  In Example 2, although there is a steep step in the direction D2, the contact pressure with respect to the inner peripheral surface of the film is lowered, the pressure is lower than the other portions, and heat transfer is deteriorated only for a moment. For this reason, there is little influence on the image, and image defects such as fixing defects and gloss streaks did not occur.

  Thus, it is preferable to provide the conductive line 34 so that the gradient relaxation portion appears at least in the cross-sectional structure of the line L3.

  Next, as a modification of the present embodiment, there is a configuration in which there is a portion where the gradient relaxing portion does not exist partially in the direction D2, but the gradient relaxing portion is always provided in the direction D1. FIG. 11 shows two examples of modification 3 and modification 4 as modifications of the second embodiment.

(Modification 3)
In Modification 3 shown in FIG. 11A, the thermistor 338 is arranged obliquely, and two connection portions with the conductive line 34 are also arranged obliquely. However, as shown in the figure, the thermistor 338 is not a rectangle but a parallelogram. Further, the shape in the vicinity of the connection portion of the conductive line 34 is also a parallelogram shape, and the overlapping portion OLP is also a parallelogram shape. By doing so, a part of the conductive line 34 always exists as a gradient relaxing part in the direction D1.

  On the other hand, in the direction D2, the conductive line 34 or the thermistor 338 is present as a gradient relaxation portion in most parts, but the gradient relaxation portion does not exist at points PA and PB in the figure. However, since it is limited to the above two points, the influence on the image is smaller than that in Example 2, and no image defect occurred in the confirmation under the same conditions as before.

(Modification 4)
Modification 4 shown in FIG. 11B has a configuration in which the relationship between the thermistor 338 and the width of the conductive line 34 in the connecting portion is opposite to that of Modification 3. In the direction D1, a part of the thermistor 338 always exists as a gradient relaxing part.

  On the other hand, in the direction D2, the conductive line 34 or the thermistor 338 is present as a gradient relaxation portion in most parts, but the gradient relaxation portion does not exist at the points PC and PD in the drawing. However, since it is limited to the above two points, the influence on the image is smaller than that in Example 2, and no image defect occurred in the confirmation under the same conditions as before.

  The shape of the resistance heating element 31 is not limited to the shape shown in the present embodiment and the modification. For example, as shown in FIG. 12, a plurality of resistance heating elements 31 may be provided in the heater longitudinal direction, and each resistance heating element 31 can be controlled independently. The resistance heating element 31 shown in FIG. 12 is divided into five regions. And each resistance heating element 31 can be controlled independently by supplying electric power from an external power source through the electrodes 32 provided in the respective regions. A thermistor is provided for each region on the sliding surface side of the heater with the film 11.

12 Heater 31 Resistance Heating Element 331-339 Thermistor 34 Conductive Line

Claims (3)

A substrate,
A heating element provided on the substrate;
A temperature sensing element provided on the substrate;
A conductive line connected to the temperature sensing element;
A protective layer covering the temperature sensing element and the conductive line;
In a heater used in a fixing device for fixing a toner image formed on a recording material to the recording material,
The connecting portion between the temperature detection element and the conductive line is provided with an overlapping portion where both overlap,
In the cross section when the heater is cut in a plane parallel to the longitudinal direction and passing through the temperature detecting element, the step next to the overlapping portion is more than the step from the surface of the substrate to the surface of the overlapping portion. A heater characterized in that a slope alleviation part having a small step is provided.   In the cross section when the heater is further cut in a plane parallel to the lateral direction of the heater and passing through the temperature detecting element, the heater is adjacent to the overlapping portion next to the overlapping portion from the surface of the substrate. A heater characterized in that a slope relaxation portion having a step smaller than the step up to the surface is provided. A tubular film,
A heater in contact with the inner surface of the film;
A fixing device for fixing the toner image formed on the recording material by the heat of the heater through the film to the recording material,
The fixing device according to claim 1, wherein the heater is a heater according to claim 1.

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