JP5289462B2 - Ceramic heater - Google Patents

Description

  The present invention is, for example, for a heater for ignition or flame detection in a combustion-type in-vehicle heating device, a heater for ignition of various combustion devices such as an oil fan heater, a heater for a glow plug of an automobile engine, and various sensors such as an oxygen sensor. The present invention relates to a ceramic heater used as a heater, a heater for heating a measuring instrument, and the like.

As a ceramic heater used for a glow plug or the like of an automobile engine, for example, a ceramic base and a ceramic heating element that generates resistance by being energized through electrode portions embedded in the ceramic base and connected to both ends thereof, A direction changing portion having a U-shape or the like extending from one base end portion and changing the direction at the tip portion to the other base end portion, and two extending in the same direction from each base end portion of the direction changing portion The thing of the structure provided with the linear part is known (for example, refer patent document 1, 2).
Japanese Patent No. 3346447 Japanese Patent No. 3737845

  Such a ceramic heater has a problem that durability is poor when it is intermittently operated because unevenness in the temperature distribution in the circumferential direction on the surface of a ceramic such as ceramics is likely to occur. This is because the distance from the surface of the heating element to the surface of the porcelain is non-uniform, resulting in a temperature difference depending on the part on the surface of the porcelain.

  Therefore, Patent Document 1 discloses that the temperature distribution on the surface of the porcelain is uneven by correcting the non-uniformity of the distance from the surface of the heating element to the surface of the porcelain by adjusting the cross-sectional shape and position of the heating element. It is described that it is difficult to improve the durability and reduce the temperature difference between the inside and outside of the porcelain.

  Patent Document 2 discloses that the cross section of the U-shaped curved portion at the tip of the ceramic heating element is larger than the cross section of the straight portion, and the transition point from the straight portion to the curved portion in the U-shaped inner outline is U The ceramic heating element, the ceramic base, and the ceramic heating element are located near the tip of the U-shaped curved portion of the ceramic heating element by being located on the U-shaped opening side of the ceramic heating element with respect to the transition point in the outer shape line of the letter shape. It is described that it is possible to suppress a decrease in durability due to stress concentration based on the difference in linear expansion coefficient.

  However, ceramic heaters used for automotive engine glow plugs and the like have recently been required to be further rapidly heated, so that a large current flows through the heating element. As a result, there is a problem that micro cracks or the like occur in the U-shaped direction changing portion at the tip of the heating element, the resistance of the heating element changes, and reliability and durability are lowered. Such a problem is insufficient to be solved depending on the configuration in which the cross section of the U-shaped curved portion at the tip of the heating element is made larger than the cross section of the straight portion as described in Patent Document 2. It was.

  Accordingly, the present invention has been devised in view of the above-described conventional problems, and its purpose is to form a U-shape at the tip of the heating element even when a large current flows through the heating element during rapid temperature rise or the like. An object of the present invention is to provide a ceramic heater having high reliability and durability by suppressing the occurrence of microcracks or the like in the direction changing portion.

The ceramic heater of the present invention has a folded portion located at the tip of the ceramic substrate inside the rod-shaped ceramic substrate, and two heating resistors having two parallel portions extending linearly in parallel from the folded portion. A body is embedded, and the folded portion has a curved portion from an end of the parallel portion and a straight portion between the curved portions, and the heating resistor has the curved portion when viewed in plan. The width of the curved portion is larger than the width of the straight portion, and the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion. It is characterized by this.

  Moreover, the ceramic heater of the present invention is characterized in that, in the above-mentioned configuration, the length of the straight portion on the tip side of the ceramic base is longer than the distance from the tip of the ceramic base to the straight portion. It is.

Moreover, the ceramic heater of the present invention is characterized in that, in the above-described configuration, the heating resistor has a thickness of the straight portion larger than a thickness of the parallel portion.

  Moreover, the ceramic heater of the present invention is characterized in that, in the above configuration, the heating resistor has an elliptical or octagonal cross-sectional shape.

  According to the ceramic heater of the present invention, the rod-shaped ceramic substrate has a folded portion located at the tip of the ceramic substrate, and two parallel portions extending linearly in parallel from the folded portion. The heating resistor is embedded, and the folded portion has a curved portion from the end of the parallel portion and a straight portion between these curved portions, and the cross-sectional area of the curved portion is the cross-sectional area of the straight portion and the parallel portion Therefore, the tip portion of the ceramic base can be efficiently heated by the presence of a straight portion having a smaller cross-sectional area than the curved portion, as compared with the case where the cross-sectional area of the entire folded portion is increased. it can. As a result, the temperature drop at the tip of the ceramic substrate due to heat radiation to the tip of the ceramic substrate can be reduced, so that the maximum temperature range is widened in the axial direction of the rod-shaped ceramic substrate. This makes it difficult for a rapid temperature difference (temperature gradient) to occur on the surface of the ceramic substrate, improving the reliability and durability of the ceramic heater.

  The folded portion has a shape in which current does not easily flow, but the cross-sectional area is larger than the cross-sectional area of the linear portion and the cross-sectional area of the parallel portion, and the cross-sectional area is smaller than that of the curved portion, but current easily flows. Since it has the linear part which is a shape, a large electric current can be efficiently sent through a folding | turning part. As a result, useless resistance is not applied to the folded portion of the heating resistor, and microcracks and the like are prevented from occurring in the folded portion, and can withstand long-term use. Therefore, the reliability and durability of the ceramic heater are improved.

  In the ceramic heater of the present invention, in the above configuration, when the length of the straight portion on the tip side of the ceramic substrate is longer than the distance from the tip of the ceramic substrate to the straight portion, the heat dissipation to the tip side of the ceramic substrate is performed. Therefore, the temperature drop at the tip of the ceramic substrate can be reduced, so that the maximum temperature region becomes wider in the axial direction of the rod-shaped ceramic substrate. As a result, a rapid temperature difference (temperature gradient) is less likely to occur on the surface of the ceramic substrate, and the reliability and durability of the ceramic heater are further improved.

Further, the ceramic heater of the present invention, in the above configuration, the heat generating resistor, rather the width of the curved portion is large for Ri by the width of the straight portion in a plan view, the thickness of the curved portion than the thickness of the straight portions from the fact not large, the resistance of the curved portion is less likely to form a current flow is smaller, it can flow more efficiently a large current to the folded portion. As a result, useless resistance is not applied to the folded portion of the heating resistor, and microcracks and the like are prevented from occurring in the folded portion, and can be used for a longer period of time. Therefore, the reliability and durability of the ceramic heater are further improved.

  In the ceramic heater of the present invention, in the above configuration, when the heating resistor has an elliptical shape or an octagonal shape, the temperature difference between the ceramic substrate and the ceramic substrate depends on the position of the heating resistor and the outer shape of the ceramic substrate. This increases the degree of freedom in constructing such that it is difficult to occur. Therefore, the reliability and durability of the ceramic heater can be further improved.

It is sectional drawing which shows an example of embodiment of the ceramic heater of this invention. It is the expanded sectional view which expanded the front-end | tip part vicinity in the ceramic heater shown in FIG. (A) is a longitudinal sectional view taken along the line AA of FIG. 2, showing a case where the longitudinal sectional shape of the heating resistor is an elliptical shape compressed along a direction orthogonal to the stacking direction, (b) It is a longitudinal cross-sectional view in the AA line of FIG. 2 which shows the case where the longitudinal cross-sectional shape of a heating resistor is an octagon shape compressed along the direction orthogonal to a lamination direction.

  Hereinafter, the example of embodiment about the ceramic heater of this invention is demonstrated in detail with reference to drawings.

  FIG. 1 is a cross-sectional view showing the portions of the heating resistor 3 and the leads 8 of the ceramic heater 1 of the present embodiment, and FIG. 2 is an enlarged cross-sectional view in which the tip 2 of the ceramic substrate 9 in FIG. 1 is enlarged.

  The ceramic heater 1 according to the present embodiment has a folded portion 4 located at the tip 2 of the ceramic base 9 inside the rod-shaped ceramic base 9, and the two from the folded portion 4 are linearly parallel to each other. A heating resistor 3 having an extended parallel portion 5 is embedded, and the folded portion 4 has a curved portion 4b from the end of the parallel portion 5 and a straight portion 4a between the curved portions 4b. The cross-sectional area of the part 4 b is larger than the cross-sectional area of the straight part 4 a and the cross-sectional area of the parallel part 5.

  With such a configuration, the tip portion 2 of the ceramic base 9 is efficiently heated by the presence of the straight portion 4a having a smaller cross-sectional area than the curved portion 4b, compared to the case where the entire cross-sectional area of the folded portion 4 is increased. be able to. In other words, the straight portion 4a, which has a shape in which current easily flows, but has a smaller cross-sectional area than the curved portion 4b, has a slightly larger resistance than the case where the cross-sectional area is larger than that of the curved portion 4b. It will be. As a result, the temperature drop of the tip 2 of the ceramic substrate 9 due to the heat radiation to the tip of the ceramic substrate 9 can be reduced, so that the maximum temperature range is widened in the axial direction of the rod-shaped ceramic substrate 9. Thereby, it becomes difficult to generate a rapid temperature difference (temperature gradient) on the surface of the ceramic substrate 9, and the reliability and durability of the ceramic heater 1 are improved.

  In addition, the folded portion 4 has a shape in which current does not easily flow, but the cross-sectional area is larger than the cross-sectional area of the straight portion 4a and the cross-sectional area of the parallel portion 5, and the cross-sectional area is smaller than the curved portion 4b. Since the linear portion 4a having a shape in which current easily flows is provided, a large current can be efficiently passed through the folded portion 4. As a result, useless resistance is not applied to the folded portion 4 of the heating resistor 3, and the occurrence of microcracks or the like in the folded portion 4 is suppressed, so that it can withstand long-term use. Therefore, the reliability and durability of the ceramic heater 1 are improved.

  The straight portion 4a is a portion having a linear shape formed at least outside the folded portion 4 (at the front end side of the ceramic base 9) between the curved portions 4b and 4b when viewed in plan. is there. Also, a portion having a linear shape facing not only the outside of the folded portion 4 but also the portion having the linear shape outside the folded portion 4 inside the folded portion 4 between the curved portions 4b and 4b. There may be.

The ceramic substrate 9 in the ceramic heater 1 of the present embodiment is made of ceramics having electrical insulation properties such as oxide ceramics, nitride ceramics, carbide ceramics. In particular, the ceramic substrate 9 is preferably made of silicon nitride ceramics. This is because silicon nitride ceramics is excellent in terms of high strength, high toughness, high insulating properties, and heat resistance. This silicon nitride ceramic is, for example, 3 to 12% by mass of a rare earth element oxide such as Y ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O ₃ as a sintering aid with respect to silicon nitride as a main component, 0.5 to 3% by mass of Al ₂ O ₃ , and further SiO ₂ is mixed so that the amount of SiO ₂ contained in the sintered body is 1.5 to 5% by mass, molded into a predetermined shape, and then 1650 to 1780 ° C. It can be obtained by hot press firing.

Further, when a ceramic substrate 9 made of silicon nitride ceramics is used, it is preferable to mix and disperse MoSiO ₂ , WSi ₂ or the like. In this case, the thermal expansion coefficient of the silicon nitride ceramic as the base material can be brought close to the thermal expansion coefficient of the heating resistor 3, and the durability of the ceramic heater 1 can be improved.

  The heating resistor 3 may be composed mainly of carbides such as W, Mo and Ti, nitrides and silicides. Among the above materials, tungsten carbide (WC) has a small difference in thermal expansion coefficient from the ceramic substrate 9, has high heat resistance, and has low specific resistance. It is excellent as a material. Furthermore, it is preferable that the heating resistor 3 is mainly composed of WC of an inorganic conductor, and the content of silicon nitride added thereto is 20% by mass or more. For example, in the ceramic substrate 9 made of silicon nitride ceramics, the conductor component serving as the heating resistor 3 has a higher coefficient of thermal expansion than silicon nitride, and therefore is usually in a state where tensile stress is applied. On the other hand, by adding silicon nitride to the heating resistor 3, the thermal expansion coefficient is brought close to that of the ceramic substrate 9, and the stress due to the difference in thermal expansion coefficient when the ceramic heater 1 is heated and lowered is reduced. Can be relaxed.

  Further, when the content of silicon nitride contained in the heating resistor 3 is 40% by mass or less, the resistance value of the heating resistor 3 can be made relatively small and stabilized. Therefore, the content of silicon nitride contained in the heating resistor 3 is preferably 20% by mass to 40% by mass. More preferably, the content of silicon nitride is 25% by mass to 35% by mass. Further, as a similar additive to the heating resistor 3, boron nitride can be added in an amount of 4% by mass to 12% by mass instead of silicon nitride.

  The thickness of the heating resistor 3 is preferably about 0.5 mm to 1.5 mm. By setting the thickness within this range, the resistance of the heating resistor 3 is reduced and heat is efficiently generated, and the adhesion at the laminated interface of the ceramic base 9 having a laminated structure can be maintained.

  The width of the heating resistor 3 is preferably about 0.3 mm to 1.3 mm. By setting the width within this range, the resistance of the heating resistor 3 is reduced and heat is efficiently generated, and the adhesion at the laminated interface of the ceramic base 9 having a laminated structure can be maintained.

  The folded portion 4 of the heating resistor 3 has a cross-sectional area of the curved portion 4b larger than that of the straight portion 4a and that of the parallel portion 5, but the cross-sectional area of the curved portion 4b is equal to the cross-sectional area of the straight portion 4a. It is preferable that the cross-sectional area of the parallel part 5 is about 10% to 50% larger (however, the cross-sectional area of the straight part 4a and the cross-sectional area of the parallel part 5 are assumed to be substantially the same). By setting it within this range, the resistance of the curved portion 4b having a shape in which current does not easily flow becomes as small as that of the straight portion 4a and the parallel portion 5, and the curved portion 4b generates heat efficiently.

  In the ceramic heater 1 of the present embodiment, the length L of the straight portion 4a on the tip side of the ceramic base 9 is preferably longer than the distance D from the tip of the ceramic base 9 to the straight portion 4a.

  With this configuration, the temperature drop of the tip 2 of the ceramic substrate 9 due to heat radiation to the tip of the ceramic substrate 9 can be reduced, so that the maximum temperature region becomes wider in the axial direction of the rod-shaped ceramic substrate 9. As a result, an abrupt temperature difference (temperature gradient) is less likely to occur on the surface of the ceramic substrate 9, and the reliability and durability of the ceramic heater 1 are further improved.

  The length L of the straight portion 4a on the tip side of the ceramic base 9 is preferably about 20% to 70% longer than the distance D from the tip of the ceramic base 9 to the straight portion 4a. By setting it within this range, the temperature drop of the tip 2 of the ceramic substrate 9 due to heat radiation to the tip of the ceramic substrate 9 can be reduced, and the local tip of the tip 2 of the ceramic substrate 9 in the axial direction can be reduced. It is possible to prevent the temperature distribution from locally deteriorating and a sudden temperature difference from occurring locally due to a significant temperature drop. Specifically, the length L of the straight portion 4a on the tip side of the ceramic base 9 is about 0.4 mm to 1.4 mm, and the distance D from the tip of the ceramic base 9 to the straight portion 4a is about 0.3 mm to 0.8 mm. However, it is preferable for the above reason.

  The shape of the folded portion 4 shown in FIG. 2 is a shape in which the outer contour line of the bending portion 4b is curved by connecting a plurality of straight portions, and the outer contour line of the bending portion 4b is one straight portion. The straight portion 4a is formed on the outer side of the folded portion 4 (the tip side of the ceramic base 9) (outer straight portion), and the outer straight line formed on the inner side of the folded portion 4. However, the present invention is not limited to such a shape.

  For example, the shape of the folded portion 4 may be such that at least one of the outer contour line and the inner contour line of the curved portion 4b is a curved shape such as an arc shape, and the outer contour line and the inner contour line of the curved portion 4b. Both of the outlines may have a curved shape such as an arc. Further, one of the outer outline and the inner outline of the curved portion 4b may be a curved shape such as an arc, and the other may be composed of at least one straight line portion.

  Further, when both the outer outline and the outer outline of the curved portion 4b are arcuate, their radii of curvature may be different. For example, the curvature radius of the outer contour line of the curved portion 4b can be larger than the curvature radius of the inner contour line. In this case, the outer outline of the curved portion 4b can be formed in a gentle arc shape so that current can easily flow in the vicinity of the outer outline.

  Moreover, the linear part 4a should just be a shape which has an outside linear part at least. In this case, the outer outlines of the two curved portions 4b can be connected with the shortest distance, and the resistance of the straight portion 4a can be reduced. The outline of the inside of the straight part 4a is not necessarily a straight part because the distance between the outlines of the inside of the two curved parts 4b is originally small, but the straight part is not necessarily a straight part. 4a is preferable because current easily flows.

Further, the ceramic heater 1 of this embodiment, the heat generating resistor 3, in a plan view, the width of the curved portion 4b is larger Ri by the width of the linear portion 4a. The heating resistor 3 preferably has a width of the curved portion 4b larger than a width of the parallel portion 5 when viewed in plan .

  With this configuration, the resistance of the curved portion 4b, which has a shape in which the current does not easily flow, is further reduced, so that a large current can flow through the folded portion 4 more efficiently. As a result, useless resistance is not applied to the folded portion 4 of the heating resistor 3, and the occurrence of microcracks or the like in the folded portion 4 is suppressed, so that it can withstand long-term use. Therefore, the reliability and durability of the ceramic heater 1 are further improved.

  The width of the curved portion 4b is preferably about 5% to 45% larger than the width of the straight portion 4a and the width of the parallel portion 5 (however, the width of the straight portion 4a and the width of the parallel portion 5 are substantially the same. Included). By setting it within this range, the resistance of the curved portion 4b, which has a shape in which current does not easily flow, becomes smaller, so that a large current can flow more efficiently through the folded portion 4, and the heating resistor 3 and the ceramic substrate It is possible to maintain the insulating property while maintaining the insulating distance between the surface 9 and the surface 9. Specifically, the width of the curved portion 4b is preferably about 0.35 mm to 1.3 mm, and the width of the straight portion 4a and the width of the parallel portion 5 are preferably about 0.3 mm to 1.25 mm.

In addition, when each thickness of the curved part 4b, the linear part 4a, and the parallel part 5 is the same, there exists an advantage that resistance of the folding | returning part 4 can be adjusted only by adjusting those widths as mentioned above.

  In addition, the curved portion 4b may have a curved shape with a round shape such as an arc shape or an elliptical arc shape in plan view, or a shape curved as a whole by connecting a plurality of linear portions. When the plan view shape of the curved portion 4b is an arc shape, the curvature radius of the central portion is preferably about 0.3 mm to 0.8 mm. By setting it within this range, it is possible to suppress an increase in resistance of the curved portion 4b and to easily form the straight portion 4a having a desired length.

  In the ceramic heater 1 of the present embodiment, the heating resistor 3 preferably has an elliptical or octagonal cross-sectional shape.

  With this configuration, the degree of freedom in configuring the ceramic base 9 so that a rapid temperature difference is less likely to occur due to the position of the heating resistor 3 and the outer shape of the ceramic base 9 is increased. Therefore, the reliability and durability of the ceramic heater 1 can be further improved.

  When the ceramic substrate 9 has a laminated structure, as shown in FIG. 3, the heating resistor 3 has an elliptical or octagonal longitudinal sectional shape compressed along a direction orthogonal to the lamination direction S. It is preferable. In this case, the upper and lower layers of the laminated interface 9 a of the ceramic substrate 9 having a laminated structure can be brought into close contact by the anchor effect of the heating resistor 3.

  3A is a longitudinal sectional view taken along line AA in FIG. 2, showing a case where the longitudinal sectional shape of the heating resistor 3 is an elliptical shape compressed along a direction orthogonal to the stacking direction S. FIG. FIG. 3B shows a longitudinal section taken along the line AA of FIG. 2, showing a case where the longitudinal sectional shape of the heating resistor 3 is an octagonal shape compressed along a direction orthogonal to the stacking direction S. FIG. The shape compressed along the direction orthogonal to the stacking direction S has a longitudinal direction or a major axis direction in the direction along the stacking direction S and is short in a direction along the direction orthogonal to the stacking direction S. A shape having a hand direction or a minor axis direction is meant.

  The interval between the two parallel portions 5 is preferably about 0.3 mm to 0.6 mm. By making it within this range, it is possible to suppress the occurrence of a short circuit between the two parallel portions 5, and migration that causes microcracks in the heating resistor 3 occurs due to a volume change due to ion movement. Can be reduced.

  The lead portion 8 can be formed using the same material as the heating resistor 3. In particular, WC is suitable as a material for the lead portion 8 in that it has a small difference in coefficient of thermal expansion from the ceramic substrate 9, high heat resistance, and low specific resistance. The lead portion 8 is preferably composed mainly of WC, which is an inorganic conductor, and silicon nitride is added to the lead portion 8 so that the content is 15% by mass or more. As the silicon nitride content increases, the thermal expansion coefficient of the lead portion 8 can be made closer to the thermal expansion coefficient of silicon nitride constituting the ceramic substrate 9. Further, when the content of silicon nitride is 40% by mass or less, the resistance value of the lead portion 8 becomes small and stable. Therefore, the content of silicon nitride is preferably 15% by mass to 40% by mass. More preferably, the content of silicon nitride is 20% by mass to 35% by mass.

  Next, the manufacturing method of the ceramic heater 1 of this Embodiment is demonstrated. The ceramic heater 1 can be formed by, for example, the heating resistor 3 having the configuration of the present embodiment by an injection molding method using a mold.

  First, a conductive paste to be the heating resistor 3 and the lead portion 8 including the conductive ceramic powder and the resin binder, and a ceramic paste to be the ceramic base 9 including the insulating ceramic powder and the resin binder are prepared.

  Next, a conductive paste molded body (molded body A) having a predetermined pattern to be the heating resistor 3 is formed by an injection molding method or the like using the conductive paste. With the molded body A held in the mold, the conductive paste is filled into the mold to form a conductive paste molded body (molded body B) having a predetermined pattern to be the lead portion 8. Thereby, the molded object A and the molded object B connected to it will be in the state hold | maintained in the metal mold | die.

  Next, in a state where the molded body A and the molded body B are held in the mold, a part of the mold is replaced with one for molding the ceramic base 9, and then a ceramic paste that becomes the ceramic base 9 is placed in the mold. Fill. Thereby, the molded body (molded body E) of the ceramic heater 1 in which the molded body A and the molded body B are covered with the molded body of the ceramic paste (molded body C) is obtained.

  Next, the obtained molded body E is fired at about 1700 ° C., whereby the ceramic heater 1 can be manufactured. The firing is preferably performed in a non-oxidizing gas atmosphere such as hydrogen gas.

  The ceramic heater of the example of the present invention was produced as follows.

First, a conductive paste containing 50% by mass of tungsten carbide (WC) powder, 35% by mass of silicon nitride (Si ₃ N ₄ ) powder, and 15% by mass of a resin binder is injection-molded into a mold to form a heating resistor. A molded product A was produced.

  Next, with the molded body A held in the mold, the conductive paste serving as the lead portion is filled in the mold, thereby connecting the molded body A to the molded body B serving as the lead portion. Formed. At this time, sample No. As shown in 1 to 13, 13 types of heating resistors were formed using molds having various shapes.

Next, 85% by mass of silicon nitride (Si ₃ N ₄ ) powder and ytterbium (Yb) oxide (Yb ₂ ) as a sintering aid while the molded body A and the molded body B are held in the mold. A ceramic paste containing 10% by mass of O ₃ ) and 5% by mass of WC for bringing the coefficient of thermal expansion close to the heating resistor and the lead part was injection molded into a mold. Thus, a molded body E having a configuration in which the molded body A and the molded body B were embedded in the molded body C serving as a ceramic base was formed.

  Next, the obtained compact E is put into a cylindrical carbon mold, and then hot pressed at a temperature of 1650 ° C. to 1780 ° C. and a pressure of 30 MPa to 50 MPa in a non-oxidizing gas atmosphere made of nitrogen gas. And sintered. A cylindrical metal fitting was brazed to the end portion of the lead portion exposed on the surface of the obtained sintered body to produce a ceramic heater.

  A cooling / heating cycle test was conducted using this ceramic heater. The conditions of the thermal cycle test are as follows: First, the ceramic heater is energized, the applied voltage is set so that the temperature of the heating resistor is 1400 ° C, 1) energized for 5 minutes, 2) non-energized for 2 minutes 1), 2) Was 1 cycle and repeated 10,000 cycles. The change in the resistance value of the ceramic heater before and after the thermal cycle test was measured. If the change in resistance value was less than 10%, there was no problem with durability (indicated by “O” in Table 1), and the change in resistance value was 10 % Or more was determined to have a problem with durability (indicated by “x” in Table 1). The results are shown in Table 1.

  Note that microcracks were generated in the heating resistor in the sample determined to have a problem in durability.

  From Table 1, No. which is within the scope of the present invention. 3, 4, 11 and 12 are such that the cross-sectional area of the curved portion in the folded portion of the heating resistor is larger than the cross-sectional area of the straight portion and the parallel portion in the folded portion, and the length of the straight portion on the tip side of the ceramic base is The length L is longer than the distance D from the tip of the ceramic substrate to the straight portion, the width of the curved portion is larger than the width of the straight portion and the width of the parallel portion, and the cross-sectional shape of the heating resistor is elliptical or octagonal. The resistance change was 1%, which was the smallest among the ceramic heaters of the present invention.

  In addition, No. 3, L / D = 1.6, the thickness of the curved portion was 0.97 mm, the thickness of the straight portion was 0.93 mm, and the thickness of the parallel portion was 0.72 mm. No. No. 4 was L / D = 1.6, the thickness of the curved portion was 0.96 mm, the thickness of the straight portion was 0.84 mm, and the thickness of the parallel portion was 0.64 mm. No. 11, L / D = 1.2, the thickness of the curved portion was 0.90 mm, the thickness of the straight portion was 0.77 mm, and the thickness of the parallel portion was 0.64 mm. No. No. 12 had L / D = 1.6, the thickness of the curved portion was 0.85 mm, the thickness of the straight portion was 0.82 mm, and the thickness of the parallel portion was 0.82 mm.

  In addition, No. which is within the scope of the present invention. 5, the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion, the length L is longer than the distance D, and the width of the curved portion is larger than the width of the straight portion and the parallel portion. This is a large case where the cross-sectional shape of the heating resistor is circular, and the resistance change is 2%.

  In addition, No. 5, L / D = 1.6, the thickness of the curved portion was 0.71 mm, the thickness of the straight portion was 0.62 mm, and the thickness of the parallel portion was 0.62 mm.

  In addition, No. which is within the scope of the present invention. 6, the cross-sectional area of the curved portion is larger than the cross-sectional areas of the straight portion and the parallel portion, the length L is shorter than the distance D, and the width of the curved portion is the same as the width of the straight portion and the parallel portion. This is the case where the cross-sectional shape of the heating resistor is a square shape, and the resistance change is 8%, which is the largest among the ceramic heaters of the present invention.

  In addition, No. 6 was L / D≈0.7, the thickness of the curved portion was 0.73 mm, the thickness of the straight portion was 0.65 mm, and the thickness of the parallel portion was 0.65 mm.

  In addition, No. which is within the scope of the present invention. 7, the cross-sectional area of the curved portion is larger than the cross-sectional areas of the straight portion and the parallel portion, the length L is longer than the distance D, and the width of the curved portion is the same as the width of the straight portion and the parallel portion. This is the case where the cross-sectional shape of the heating resistor is a square shape, and the resistance change is 6%, which is the larger of the ceramic heaters of the present invention.

  In addition, No. 7 was L / D≈1.6, the thickness of the curved portion was 0.73 mm, the thickness of the straight portion was 0.65 mm, and the thickness of the parallel portion was 0.65 mm.

  In addition, No. which is within the scope of the present invention. 8 is that the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion, the length L is longer than the distance D, and the width of the curved portion is larger than the width of the straight portion and the width of the parallel portion. It was a large case where the cross-sectional shape of the heating resistor was hexagonal, and the resistance change was 3%.

  In addition, No. 8 was L / D≈1.6, the thickness of the curved portion was 1.00 mm, the thickness of the straight portion was 0.87 mm, and the thickness of the parallel portion was 0.67 mm.

  In addition, No. which is within the scope of the present invention. 9 is that the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion, the length L is the same as the distance D, and the width of the curved portion is larger than the width of the straight portion and the width of the parallel portion. This is the case where the cross-sectional shape of the heating resistor is elliptical, and the resistance change was 4%.

  In addition, No. 9 was L / D≈1, the thickness of the curved portion was 0.85 mm, the thickness of the straight portion was 0.82 mm, and the thickness of the parallel portion was 0.82 mm.

  In addition, No. which is within the scope of the present invention. 10, the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion, the length L is shorter than the distance D, and the width of the curved portion is larger than the width of the straight portion and the parallel portion. This is a case where the cross-sectional shape of the heating resistor is elliptical, and the resistance change is 5%, which is larger in the ceramic heater of the present invention.

  In addition, No. 10 was L / D≈0.7, the thickness of the curved portion was 0.85 mm, the thickness of the straight portion was 0.82 mm, and the thickness of the parallel portion was 0.82 mm.

  In addition, No. which is within the scope of the present invention. 13 is such that the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the parallel portion, the length L is longer than the distance D, and the width of the curved portion is the same as the width of the straight portion and the parallel portion. This is the case where the cross-sectional shape of the heating resistor is elliptical, and the resistance change was 3%.

  In addition, No. No. 13 had L / D = 1.6, the thickness of the curved portion was 0.92 mm, the thickness of the straight portion was 0.82 mm, and the thickness of the parallel portion was 0.82 mm.

  As described above, the configuration (Configuration 1) in which the cross-sectional area of the curved portion of the folded portion of the heating resistor is larger than the cross-sectional area of the straight portion and the parallel portion of the folded portion is satisfied. Satisfies the configuration (configuration 2) in which the length L is longer than the distance D from the tip of the ceramic substrate to the straight portion, and the configuration in which the width of the curved portion is larger than the width of the straight portion and the width of the parallel portion (configuration 3). ) And the configuration (configuration 4) in which the cross-sectional shape of the heating resistor is an elliptical shape or an octagonal shape is satisfied. 3, 4, 11, 12 were found to have the smallest resistance change.

  No. 3, 4, 11, 12 and No. 5 and No. 5 in which the cross-sectional shape of the heating resistor is circular. The resistance change of 5 was slightly increased.

  No. 3 and 4 and no. 13, No. 13 satisfying the configuration 3 in which the width of the curved portion is larger than the width of the straight portion and the width of the parallel portion. No. 3 and 4 do not satisfy the configuration 3. The resistance change was smaller than 13.

  No. 6 and no. 7 and No. 7 satisfying the configuration 3 in which the length L is greater than the distance D. 7 (L / D = 1.6) is No. The resistance change was smaller than 6 (L / D≈0.7).

  No. which is outside the scope of the present invention. For 1 and 2, the resistance change was 55% and 40%, both of which were very large.

1: Ceramic heater 2: Tip part 3: Heating resistor 4: Folded part 4a: Straight line part 4b: Curved part 5: Parallel part 9: Ceramic base L: Length D of the straight part 4a on the tip side of the ceramic base 9: Distance from the tip of the ceramic substrate 9 to the straight portion 4a

Claims (4)

A heating resistor having a folded portion located at the tip of the ceramic substrate, and two parallel portions extending linearly in parallel from the folded portion is embedded in the rod-shaped ceramic substrate, The folded portion has a curved portion from the end of the parallel portion and a straight portion between the curved portions, and the heating resistor has a width of the curved portion of the straight portion when viewed in plan. A ceramic heater characterized in that it is larger than the width, the thickness of the curved portion is larger than the thickness of the straight portion, and the cross-sectional area of the curved portion is larger than the cross-sectional area of the straight portion and the cross-sectional area of the parallel portion. .   2. The ceramic heater according to claim 1, wherein a length of the straight portion on a tip side of the ceramic base is longer than a distance from a tip of the ceramic base to the straight portion. 2. The ceramic heater according to claim 1, wherein the heating resistor has a thickness of the straight portion larger than a thickness of the parallel portion.   The ceramic heater according to claim 1, wherein the heating resistor has an elliptical shape or an octagonal cross-sectional shape.

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