WO2025089052A1 - Heater - Google Patents

Abstract

A heater according to the present disclosure comprises a plurality of units and a terminal part. The unit includes a heating resistor and two electrodes. The heating resistor includes at least two extension parts, and a folding part that connects one end of the two extension parts to each other. The two electrodes are electrically connected to the two extension parts, respectively. The plurality of units are arranged in a direction orthogonal to the extension direction of the extension parts. The terminal part is electrically connected to the electrodes of the plurality of units.

Description

heater

This disclosure relates to a heater.

　Conventionally, heaters that have a heating resistor inside a plate-shaped ceramic base are known (see Patent Document 1).

JP 2015-52587 A

A heater according to one aspect of the present disclosure includes multiple units and a terminal portion. The units include a heating resistor and two electrodes. The heating resistor includes at least two extension portions and a folded portion that connects one end of the two extension portions. The two electrodes are electrically connected to the two extension portions, respectively. The multiple units are arranged in a direction perpendicular to the extension direction of the extension portions. The terminal portion is electrically connected to the electrodes of the multiple units.

FIG. 1 is a perspective view illustrating an example of a heater according to a first embodiment. FIG. 2 is a perspective view illustrating an example of the heater according to the first embodiment. FIG. 3 is an enlarged plan view perspective view showing an example of the heater according to the first embodiment. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is an enlarged plan view perspective view showing an example of a heater according to the second embodiment. FIG. 7 is a perspective view illustrating an example of a heater according to the third embodiment. FIG. 8 is a perspective view illustrating an example of a heater according to the third embodiment. FIG. 9 is an enlarged plan view perspective view showing an example of a heater according to the third embodiment. FIG. 10 is a cross-sectional view taken along line XX of FIG.

Below, a detailed description will be given of a form for implementing the heater according to the present disclosure (hereinafter, referred to as an "embodiment") with reference to the drawings. Note that the present disclosure is not limited to this embodiment. Furthermore, each embodiment can be appropriately combined as long as the processing content is not contradictory. Furthermore, the same parts in each of the following embodiments are given the same reference numerals, and duplicated descriptions will be omitted.

In addition, in the embodiments described below, expressions such as "constant," "orthogonal," "vertical," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "vertical," or "parallel" in the strict sense. In other words, each of the above expressions allows for deviations due to, for example, manufacturing precision or installation precision.

In addition, in order to make the explanation easier to understand, the drawings referred to below may show an orthogonal coordinate system in which the X-axis, Y-axis, and Z-axis directions are defined as being perpendicular to each other, and the positive direction of the Z-axis is the vertically upward direction. Also, the direction of rotation about the vertical axis may be referred to as the θ direction.

　Conventionally, heaters having a heating resistor inside a plate-shaped ceramic base are known. Patent Document 1 discloses a ceramic heater having a heating resistor with a pair of lead portions and a heating portion whose both ends are connected to the pair of lead portions. Each of the pair of lead portions is connected to an electrode pad, and the heating portion generates heat when a voltage is applied from the electrode pads via the lead portions.

However, if the heater described in Patent Document 1 is damaged in either the pair of leads or the heat generating portion, there is a risk that it will no longer be able to function as a heater.

Therefore, there is a need for technology that can improve the durability of heaters.

First Embodiment
First, the heater according to the first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 and Fig. 2 are perspective views showing an example of a heater 1 according to the first embodiment. For ease of understanding, in Fig. 2, a heating resistor 21 and conductive parts 221, 222 located inside the heater 1 are indicated by dashed lines.

The heater 1 according to the first embodiment includes a plate-shaped base 10, a plurality of units 20, and a plurality of terminal portions 30.

The base 10 has a main surface 101 on which an object to be heated (not shown) is placed. The shape and various dimensions of the main surface 101 of the base 10 may be set appropriately taking into consideration the shape and dimensions of the object to be heated. For example, in the first embodiment, an example is described in which the main surface 101 of the base 10 has a rectangular shape, but the shape of the main surface 101 may be a polygon other than a rectangular shape or a circle.

The material of the base 10 is, for example, ceramic having insulating properties. This makes it possible to provide a heater 1 that is highly reliable during rapid heating. The material of the base 10 may be, for example, oxide ceramics, nitride ceramics, or carbide ceramics. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, or silicon carbide ceramics may be used as the material of the base 10. In particular, when silicon nitride ceramics are used, the main component, silicon nitride, is superior in terms of strength, toughness, insulation, and heat resistance.

The base 10 made of silicon nitride ceramics can be obtained by mixing, for example, silicon nitride as the main component, 3 to 12 mass% of rare earth oxide such as Y ₂ O ₃ , Yb ₂ O ₃ or Er ₂ O ₃ as a sintering aid, 0.5 to 3 mass% of Al ₂ O ₃ , and SiO ₂ so that the amount of SiO ₂ contained in the sintered body is 1.5 to 5 mass%, forming each unit 20 into a predetermined shape, incorporating a heating resistor 21, arranging each unit 20 without any gaps, and hot-pressing and firing at 1650 to 1780° C. to obtain a sintered body in which each unit 20 is integrated. Note that each individual unit 20 may be pre-fired at 1200 to 1650° C., and then arranging each unit 20 without any gaps, and hot-pressing and firing at 1650 to 1780° C. to obtain a sintered body in which each unit 20 is integrated. Alternatively, the sintered body may be obtained by using other methods. By subjecting this sintered body to processing such as polishing, it is possible to obtain a base body 10 having a flat surface.

When silicon nitride ceramics is used as the base 10, _MoSiO2 or _WSi2 may be mixed and dispersed therein. In this case, the thermal expansion coefficient of the silicon nitride ceramics, which is the base material, can be made close to that of the heating resistor 21, and the durability of the heater 1 can be improved.

The multiple units 20 have a longitudinal direction that is the extension direction (here, the Y-axis direction) of the extension parts 2111, 2112 described below. These multiple units 20 are arranged at intervals from each other along a direction (here, the X-axis direction) perpendicular to the extension direction of the extension parts 2111, 2112. Note that while FIG. 2 shows an example in which the heater 1 includes 12 units 20, the number of units 20 included in the heater 1 is not limited to this.

Each unit 20 includes a heating resistor 21, two conductive parts 221, 222, and two electrodes 231, 232. The heating resistor 21 is embedded in the base 10 and connected to the two conductive parts 221, 222. The cross-sectional area of the heating resistor 21 can be about 0.1 to 0.8 ^mm2 .

The heating resistor 21 is a member that generates heat when a current flows through it. The heating resistor 21 is embedded in the base 10 and connected to two conductive parts 221, 222. Specifically, the heating resistor 21 includes two extending parts 2111, 2112 and a folded part 212 that connects one end of the two extending parts 2111, 2112 to each other. The extending part 2111 connects the conductive part 221 to one end of the folded part 212, and the extending part 2112 connects the conductive part 222 to the other end of the folded part 212. The cross-sectional area of the heating resistor 21 can be about 0.1 to 0.8 ^mm2 . The two extending parts 2111, 2112 may extend in parallel as shown in FIG. 2.

The heating resistor 21 may include a high resistance conductor containing, for example, tungsten or molybdenum. When the base 10 is made of silicon nitride ceramics, tungsten carbide is an excellent material for the heating resistor 21 because it has a small difference in thermal expansion coefficient with the base 10 and has high heat resistance.

When the base 10 is made of silicon nitride ceramics, the heating resistor 21 may be mainly composed of tungsten carbide, an inorganic conductor, with the content of silicon nitride added to it being 20% by mass or more. For example, in the base 10 made of silicon nitride ceramics, the conductor component that becomes the heating resistor 21 has a larger thermal expansion coefficient than silicon nitride, and is therefore normally under tensile stress. In contrast, by adding silicon nitride to the heating resistor 21, the thermal expansion coefficient can be brought closer to that of the base 10, and the stress caused by the difference in thermal expansion coefficient when the heater 1 is heated and cooled can be alleviated.

Furthermore, when the content of silicon nitride contained in the heating resistor 21 is 40 mass% or less, the variation in the resistance value of the heating resistor 21 can be reduced. Therefore, the content of silicon nitride contained in the heating resistor 21 may be 20 to 40 mass%. Furthermore, as a similar additive to the heating resistor 21, 4 to 12 mass% of boron nitride can be added instead of silicon nitride.

The shape of the heating resistor 21 is not limited to that shown in the figure, and can be changed as appropriate depending on the heating characteristics required for the heater 1, for example.

The two conductive parts 221, 222 electrically connect the heating resistor 21 to the two electrodes 231, 232. Specifically, the conductive part 221 electrically connects the extension part 2111 of the heating resistor 21 to the electrode 231, and the conductive part 222 electrically connects the extension part 2112 of the heating resistor 21 to the electrode 232.

The conductive parts 221, 222 are formed, for example, using the same material as the heating resistor 21. The conductive parts 221, 222 have a lower resistance per unit length by making the cross-sectional area larger than that of the heating resistor 21, or by making the content of the material forming the base 10 less than that of the heating resistor 21. The conductive parts 221, 222 may be tungsten wires, or may be made mainly of tungsten carbide, an inorganic conductor, to which silicon nitride is added so that the content is 15% by mass or more. As the content of silicon nitride increases, the thermal expansion coefficient of the conductive parts 221, 222 can be made closer to the thermal expansion coefficient of silicon nitride constituting the base 10. When the content of silicon nitride is 40% by mass or less, the resistance value of the conductive parts 221, 222 becomes lower and stable. Therefore, the content of silicon nitride may be 15 to 40% by mass.

The two electrodes 231, 232 are electrically connected to the two extensions 2111, 2112 of the heating resistor 21. Specifically, the electrode 231 is electrically connected to the extension 2111 via the conductive portion 221, and the electrode 232 is electrically connected to the extension 2112 via the conductive portion 222. The two electrodes 231, 232 are positioned side by side on one side of the base 10. The electrodes 231, 232 are connected to the terminal portion 30, so that the unit 20 is electrically connected to an external power source. The electrodes 231, 232 are made of, for example, molybdenum or tungsten. The electrodes 231, 232 may also be made of molybdenum or tungsten plated with nickel. The positions of the electrodes 231, 232 are not limited to those shown in FIG. 1 and FIG. 2. Other specific examples of the positions of the electrodes 231, 232 will be described later.

The terminal portion 30 electrically connects the heating resistor 21 to an external power source. Two terminal portions 30 are connected to one heating resistor 21. One of the two terminal portions 30 is connected to the heating resistor 21 via an electrode 231 and a conductive portion 221, and the other is connected to the heating resistor 21 via an electrode 232 and a conductive portion 222. One of the two terminal portions 30 is connected to an external power source, and the other is connected to ground. Among the multiple terminal portions 30, the terminal portions 30 connected to the external power source are connected to each other in series. Furthermore, the multiple terminal portions 30 connected to ground are individually connected to ground.

The terminal portion 30 is a wire material containing a metal material such as nickel, iron, or a nickel-based heat-resistant alloy. The cross section of the terminal portion 30 may be, for example, circular, elliptical, or rectangular. The outer diameter of the terminal portion 30 may be, for example, 0.5 to 2.0 mm. The pull-out direction of the terminal portion 30 is not limited to the shape shown in the figure and can be changed as appropriate.

In the heater 1 according to the first embodiment configured as described above, the multiple units 20 are arranged in a direction perpendicular to the extension direction of the extension parts 2111, 2112, and the extension parts 2111, 2112 of the multiple units 20 extend from the folded part 212 toward one side surface of the base 10. Therefore, the electrodes 231, 232 of the multiple units 20 are positioned side by side on one side surface of the base 10.

The heater 1 according to the first embodiment is configured such that the electrodes 231, 232 and the terminal portion 30 connected to the electrodes 231, 232 are shared by a plurality of units 20. Specifically, one of the two electrodes 231, 232 of one unit 20 is formed integrally with one of the two electrodes 231, 232 of the unit 20 adjacent to the unit 20. In other words, one of the two electrodes 231, 232 is shared by two adjacent units 20. Since the terminal portion 30 is connected to this shared electrode, the terminal portion 30 is also shared by two adjacent units 20. In other words, the terminal portion 30 is electrically connected to the electrodes 231, 232 of the plurality of units 20.

In this way, by configuring the wiring (heating resistor 21 and conductive parts 221, 222) of multiple units 20 to be connected in parallel, even if one wiring is broken, the other units 20 will still function. Therefore, the durability of the heater 1 can be improved compared to a heater configured with only one wiring.

Next, the detailed configuration of the heater 1 according to the first embodiment will be described with reference to Figs. 3 to 5. Fig. 3 is an enlarged plan view perspective view showing an example of the heater 1 according to the first embodiment. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a cross-sectional view taken along line V-V in Fig. 3. For ease of understanding, the imaginary boundary between two adjacent units 20 is shown by a dashed line in Figs. 3 and 4.

As described above, the heater 1 according to the first embodiment is configured such that the electrodes 231 and 232 are shared between adjacent units 20. In the example shown in FIG. 3, the electrode 231a of the unit 20a is also the electrode of the unit 20b adjacent to the unit 20a. Specifically, the conductive part 222a of the unit 20a is connected to the electrode 231a, and the conductive part 221b of the unit 20b is connected to the electrode 231a. As a result, the wiring of the two adjacent units 20a and 20b is configured to be connected in parallel, so that even if the wiring of the unit 20a is broken, the other unit 20 will function. Therefore, the durability of the heater 1 can be improved compared to a heater configured with only one wiring. Also, for example, if the unit 20a is broken, the heat of the adjacent unit 20b is transferred to the unit 20a, and the temperature drop of the broken unit 20a is mitigated. Therefore, it is possible to prevent the heater 1 from being broken due to thermal shock or the like. Therefore, it is possible to improve the durability of the heater 1.

In the thickness direction of the heater 1 (here, the Z-axis direction), the positions of the heating resistors 21 of two adjacent units 20 may be different. In the example shown in FIG. 4, the heating resistor 21a of unit 20a is positioned offset in the positive direction of the Z-axis relative to the heating resistor 21b of unit 20b.

This reduces the concentration of heat between adjacent units 20 compared to when the heating resistors 21 of two adjacent units 20 are located at the same position in the thickness direction of the heater 1. As a result, damage to the heater 1 due to thermal expansion is reduced, improving the durability of the heater 1.

Furthermore, the thicknesses of the heating resistors 21 of two adjacent units 20 in the thickness direction of the heater 1 may be different. In the example shown in FIG. 4, the thickness t1 of the heating resistor 21a of unit 20a is smaller than the thickness t2 of the heating resistor 21b of unit 20b.

This reduces the concentration of heat between adjacent units 20 compared to when the heating resistors 21 of two adjacent units 20 in the thickness direction of the heater 1 are the same thickness. As a result, damage to the heater 1 due to thermal expansion is reduced, improving the durability of the heater 1.

Also, as shown in FIG. 4, in one unit 20a, an imaginary line X connecting the centers of the two extensions 2111a, 2112a of the heating resistor 21a may extend parallel to the main surface 101 of the base 10 of the heater 1. The "center of the extension" here refers to, for example, the center of the heating resistor 21a in the thickness direction of the base 10.

With this configuration, there is no variation in the position of the heating resistor 21a in the thickness direction of the base 10 in one unit 20a, improving the thermal uniformity of the heater 1.

In addition, in a planar perspective view of the heater 1, the folded portions 212 of the heating resistors 21 of two adjacent units 20 may be positioned differently in the extension direction (here, the Y-axis direction) of the extension portions 2111, 2112. In the example shown in FIG. 3, the folded portion 212a of the heating resistor 21a of unit 20a is shifted in the positive Y-axis direction relative to the folded portion 212b of the heating resistor 21b of unit 20b.

As a result, the distance from the electrodes 231, 232 to the folded portion 211 differs for each unit 20, so that stress is less likely to concentrate at the position of the folded portion 211 when the heater 1 is heated, improving the durability of the heater 1.

Furthermore, the conductive parts 221, 222 of two adjacent units 20 may be positioned differently in the thickness direction of the heater 1. In the example shown in FIG. 5, the conductive parts 221a, 222a of unit 20a are positioned offset in the positive direction of the Z axis with respect to the conductive parts 221b, 222b of unit 20b.

The conductive parts 221, 222 close to the electrodes 231, 232 of the unit 20 are easily affected by the rise in temperature of the heater 1. In contrast, by positioning the conductive parts 221, 222 as described above, stress is less likely to concentrate at the positions of the conductive parts 221, 222 when the heater 1 rises in temperature, and the durability of the heater 1 can be improved.

As described above, the heater 1 according to the first embodiment includes multiple units 20, and the multiple units 20 share the electrodes 231, 232 and the terminal portion 30 connected to the electrodes 231, 232. By configuring the wiring of the multiple units 20 to be connected in parallel in this manner, even if one wiring is broken, the other units 20 will still function. Therefore, the durability of the heater 1 can be improved compared to a heater configured with only one wiring.

Second Embodiment
FIG. 6 is an enlarged plan view perspective view showing an example of the heater 1 according to the second embodiment.

As shown in FIG. 6, in a planar perspective view of the heater 1, the extending directions of the extending portions 2111, 2112 of two adjacent units 20 may be different. In the example of FIG. 6, the extending portions 2111c, 2112c of the heating resistor 21c of unit 20c extend in a direction inclined with respect to the extending direction (Y-axis direction) of the extending portions 2111d, 2112d of the heating resistor 21d of unit 20d.

In this configuration, the directions of thermal expansion of adjacent units 20 can be made different. Therefore, compared to when the extension directions of the extension parts 2111, 2112 of adjacent units 20 are the same, stress is less likely to concentrate on the boundary portion between adjacent units 20 when the heater 1 is heated, and the durability of the heater 1 can be improved.

The direction in which the units 20 are arranged is a direction perpendicular to the extension direction of the extension portions 2111, 2112, but in the example of FIG. 6, it can be a direction perpendicular to the extension portion 2111 (2112) of any one of the multiple units 20. Also, the inclination between the extension direction of the extension portions 2111c, 2112c and the extension direction of the extension portions 2111d, 2112d may be, for example, less than 45 degrees.

Third Embodiment
Figures 7 and 8 are perspective views showing an example of a heater 1 according to a third embodiment. For ease of understanding, in Figure 8, the heating resistor 21 and conductive parts 221, 222 located inside the heater 1 are shown by dotted lines. Figure 9 is an enlarged plan view perspective view showing an example of the heater 1 according to the third embodiment. Figure 10 is a cross-sectional view taken along line X-X in Figure 9.

In the first embodiment, an example in which the electrodes 231, 232 and the terminal portion 30 are shared between two adjacent units 20 has been shown, but this is not limited thereto, and the electrodes 231, 232 and the terminal portion 30 may be shared between two or more units 20. For example, as shown in FIG. 7 and FIG. 8, one of the two electrodes 231, 232 provided in all units 20 provided in the heater 1 may be integrally formed on one side surface 102 of the base 10, and the other of the two electrodes 231, 232 provided in all units 20 provided in the heater 1 may be integrally formed on the side surface 103 opposite the side surface 102 of the base 10. The terminal portion 30 is connected to the integrally formed electrodes 231, 232, so that the terminal portion 30 is also shared between a plurality of units 20 in a similar manner.

In this case as well, the wiring of the multiple units 20 is configured to be connected in parallel, so even if one wiring is broken, the other units 20 will still function. Therefore, the durability of the heater 1 can be improved compared to a heater configured with only one wiring.

Also, as in the first embodiment, the positions of the heating resistors 21 of two adjacent units 20 in the thickness direction of the heater 1 (here, the Z-axis direction) may be different. In the example shown in FIG. 10, the heating resistor 21e of unit 20e is positioned offset in the positive direction of the Z-axis relative to the heating resistor 21f of unit 20f. Also, as in the first embodiment, the thicknesses of the heating resistors 21 of two adjacent units 20 in the thickness direction of the heater 1 may be different. In the example shown in FIG. 10, the thickness of the heating resistor 21e of unit 20e is smaller than the thickness of the heating resistor 21f of unit 20f.

Also, as in the first embodiment, in one unit 20e, an imaginary line Y connecting the centers of the three extension portions 2111e, 2112e, 2113e of the heating resistor 21e may extend parallel to the main surface 101 of the base 10 of the heater 1. Also, as in the first embodiment, in a planar perspective view of the heater 1, the folded portions 212 of the heating resistors 21 of two adjacent units 20 may be positioned differently in the extension direction (here, the Y-axis direction) of the extension portions 2111, 2112, 2113. In the example shown in Figure 9, the folded portion 2121e of the heating resistor 21e of unit 20e is positioned shifted in the positive Y-axis direction with respect to the folded portion 2121f of the heating resistor 21f of unit 20f. The folded portion 2122e of the heating resistor 21e of unit 20e is shifted in the negative direction of the Y axis relative to the folded portion 2122f of the heating resistor 21f of unit 20f.

The heater 1 according to the third embodiment may be used in a heater equipped with multiple such heaters 1.

The present technology can also be configured as follows.
(1)
The heater (for example, heater 1) includes a plurality of units (for example, units 20) and a terminal portion (for example, terminal portion 30). The unit includes a heating resistor (for example, heating resistor 21) and two electrodes (for example, electrodes 231, 232). The heating resistor includes at least two extension portions (for example, extension portions 2111, 2112) and a folded portion (for example, folded portion 212) that connects one ends of the two extension portions. The two electrodes are electrically connected to the two extension portions, respectively. The multiple units are arranged in a direction perpendicular to the extension direction of the extension portions. The terminal portion is electrically connected to the electrodes of the multiple units.
(2)
In the heater described in (1) above, the heating resistors of two adjacent units may be positioned differently in the thickness direction of the heater.
(3)
In the heater according to (1) or (2) above, the heating resistors of two adjacent units may have different thicknesses in the thickness direction of the heater.
(4)
In the heater described in any one of (1) to (3) above, in a cross section perpendicular to a main surface (for example, main surface 101) of the heater and perpendicular to the arrangement direction of the multiple units, a virtual line (for example, virtual line X) connecting the centers of the multiple extension portions may extend parallel to the main surface of the heater.
(5)
In the heater according to any one of (1) to (4) above, in a plan view perspective of the heater, the folded-back portions of the heating resistors of two adjacent units may be located at different positions in the extension direction.
(6)
The heater described in any one of (1) to (5) above further includes a conductive portion (for example, conductive portions 221, 222) that electrically connects the extension portion of the heating resistor and the electrode, and in a cross section perpendicular to the main surface of the heater and perpendicular to the arrangement direction of the multiple units, the conductive portions of two adjacent units may be located at different positions in the thickness direction of the heater.
(7)
In the heater according to any one of (1) to (6) above, the extending directions of the extending portions of two adjacent units may be different from each other in a planar perspective view of the heater.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in a variety of forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims.

REFERENCE SIGNS LIST 1 heater 10 base 20 unit 21 heating resistor 30 terminal portion 212 folded portion 221, 222 conductive portion 231, 232 electrode 2111, 2112 extension portion

Claims (7)

Multiple units and
A terminal portion and
The unit comprises:
a heating resistor including at least two extending portions and a folded portion connecting one ends of the two extending portions to each other;
two electrodes electrically connected to the two extension portions, respectively;
The units are arranged in a direction perpendicular to the extension direction of the extension portion,
The terminal portion is electrically connected to the electrodes of the plurality of units. The heater according to claim 1, wherein the heating resistors of two adjacent units are positioned differently in the thickness direction of the heater. The heater according to claim 1 or 2, wherein the thicknesses of the heating resistors of two adjacent units are different in the thickness direction of the heater. The heater according to any one of claims 1 to 3, wherein in a cross section perpendicular to the main surface of the heater and perpendicular to the arrangement direction of the units, a virtual line connecting the centers of the extensions extends parallel to the main surface of the heater. The heater according to any one of claims 1 to 4, wherein, in a planar perspective view of the heater, the folded-back portions of the heating resistors of two adjacent units are positioned at different positions in the extension direction. a conductive portion electrically connecting the extension portion of the heating resistor and the electrode,
The heater according to any one of claims 1 to 5, wherein in a cross section perpendicular to a main surface of the heater and perpendicular to an arrangement direction of the units, the conductive portions of two adjacent units are positioned at different positions in the thickness direction of the heater. The heater according to any one of claims 1 to 6, wherein, in a planar perspective view of the heater, the extending directions of the extending portions of two adjacent units are different.

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