CN110121222B

CN110121222B - Ceramic heater

Info

Publication number: CN110121222B
Application number: CN201910106737.4A
Authority: CN
Inventors: 牧野友亮; 中西直也; 杉山敦俊
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2018-02-05
Filing date: 2019-02-02
Publication date: 2022-09-30
Anticipated expiration: 2039-02-02
Also published as: ES2920133T3; EP3522681B1; CN110121222A; EP3522681A1

Abstract

The invention provides a ceramic heater which restrains the generation of arc in the ceramic heater with a plurality of heater wiring circuits. A ceramic heater (11) includes a heating resistor (40), wherein a plurality of heater wiring circuits (40a, 40b) having connection terminals (41, 42a, 42b) respectively connected to an external power supply are provided on the same surface of the heating resistor so that the heater wiring circuits overlap in the direction in which the connection terminals are arranged, and the heater wiring circuits are made of a material having a temperature coefficient of 3500 ppm/DEG C or more.

Description

Ceramic heater

Technical Field

The present invention relates to a ceramic heater used for, for example, a warm water washing toilet, a warm air blower, an electric water heater, a 24-hour bathtub, a soldering iron, a hair iron, and the like.

Background

Conventionally, a heat exchange unit having a resin container (heat exchanger) is used in, for example, a hot water toilet, and a vertically long tubular ceramic heater is disposed in the heat exchange unit in order to heat washing water stored in the heat exchanger.

As shown in fig. 7, a ceramic heater is used which is configured by winding a ceramic sheet 190 on which a heater wiring circuit 400 is printed around a cylindrical ceramic insulating tube 130 and integrally firing the ceramic sheet (see patent document 1).

The ceramic heater heats water flowing through a gap between an inner wall of the heat exchanger and an outer periphery of the ceramic heater.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3038039

Disclosure of Invention

Problems to be solved by the invention

In addition, when the ceramic heater is miniaturized or the heater wiring circuit 400 is provided in plural, the number of wirings that can be arranged on the ceramic sheet 190 is limited. Further, the resistance value of each circuit of the heater wiring circuit 400 is determined by the wiring length, but when the wiring length is increased in order to keep the resistance value of the heater constant in a narrow area, the number of turns increases accordingly, and the wiring density becomes high.

In this case, the line interval of the heater wiring circuit 400 needs to be made narrow, but considering bleeding of the ink paste when screen printing the wiring, there is a limit to the reduction of the line interval (for example, about 0.3 mm).

Therefore, the number of turns of the heater wiring circuit 400 is increased while maintaining the line interval at a constant value or more. In this case, 1 pair of

external terminals

430 and 430 for supplying current to the heater wiring circuit 400 are formed on the outer surface of the ceramic sheet 190 with the winding end space 191 of the ceramic sheet 190 interposed therebetween. The

external terminals

430 and 430 are connected to the

end wirings

401 and 402 of the heater wiring circuit 400 that are close to each other with the winding end space 191 therebetween.

However, when the number of turns of the heater wiring circuit 400 is increased as described above, the interval T between the

end wirings

401 and 402 becomes narrow. In this state, when the ceramic heater is energized (heated in air) in a dry state such as water cut-off, the arc Ar is likely to be generated in the winding end space 191 between the

terminal wirings

401 and 402 to which power is supplied from the

external terminals

430 and 430 having different polarities, and the ceramic heater may be damaged.

Accordingly, an object of the present invention is to provide a ceramic heater in which generation of an arc is suppressed in a ceramic heater having a plurality of heater wiring circuits.

Means for solving the problems

In order to solve the above problems, the present invention provides a ceramic heater including a heating resistor, wherein a plurality of heater wiring circuits each having a connection terminal connected to an external power supply are provided on the same surface of the heating resistor so as to be overlapped with each other in a direction in which the connection terminals are arranged,

the heater wiring circuit includes a material having a temperature coefficient of 3500 ppm/DEG C or more.

Since the ceramic heater includes the material having the temperature coefficient of 3500 ppm/DEG C or more, the circuit length of the heater wiring circuit can be made shorter when the line width of the heater wiring circuit is constant as compared with the case where the material having the temperature coefficient of 3500 ppm/DEG C or more is not included, and the number of times of folding back the heater wiring circuit can be reduced as compared with the conventional one. Further, the distance between the connection terminals can be increased, and thus, the occurrence of arcing due to a decrease in distance can be suppressed.

The phrase "on the same surface as the heating resistor" means a surface defined by the heating resistor in an expanded state, and in the case of a ceramic heater including the heating resistor in a wound state, means a cylindrical surface having a constant diameter defined by the wound heating resistor.

In the ceramic heater of the present invention, the temperature coefficient may be more than 3800 ppm/deg.c and less than 4300 ppm/deg.c.

With this ceramic heater, the distance between the connection terminals can be further increased, and thus the generation of an arc can be further suppressed.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can suppress the occurrence of an arc in a ceramic heater having a plurality of heater wiring circuits.

Drawings

Fig. 1 is a front view of a ceramic heater according to an embodiment of the present invention.

Fig. 2 is a development view showing a ceramic sheet of the ceramic heater.

Fig. 3 is a sectional view taken along line a-a of fig. 1.

Fig. 4 is a schematic development view of the heater wiring circuit included in fig. 2.

Fig. 5 is a development view showing a heater wiring circuit not pertaining to the present invention.

Fig. 6 is a graph showing the relationship between the resistance value and the temperature coefficient of the resistive ink under high and low temperature conditions of the heater wiring circuit.

Fig. 7 is a partial cross-sectional view showing a heater wiring circuit of a conventional ceramic heater.

Description of the reference numerals

11. A ceramic heater; 40. a heating resistor body; 40a, 40b, a heater wiring circuit; 41. 42a, 42b, connection terminals; o, an axis; s, the direction of the arrangement of the connecting terminals.

Detailed Description

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Fig. 1 is a front view showing a ceramic heater 11 according to an embodiment of the present invention, fig. 2 is a developed view showing a ceramic sheet 19 of the ceramic heater 11, fig. 3 is a cross-sectional view taken along line a-a of fig. 1, fig. 4 is a developed view schematically showing

heater wiring circuits

40a and 40b included in fig. 2, and fig. 5 is a developed view showing heater wiring circuits 50a and 50b not belonging to the present invention.

The ceramic heater 11 of the embodiment of the present invention can be used to heat wash water in a heat exchanger of a heat exchange unit of a warm water washing toilet, for example.

As shown in fig. 1, the ceramic heater 11 includes: a cylindrical ceramic base 13 in which a heating resistor 40 is embedded; and an annular ceramic flange 30 joined to the outer periphery of the ceramic body 13 via a joining member 20. Further, the flange 30 may have a slit in the axial direction.

The ceramic base 13 includes a cylindrical ceramic support body 17 and a ceramic sheet 19 wound around the outer periphery of the support body 17, and the support body 17 has a through hole 17h in the axis O direction thereof. In the heat exchanger, the water flowing inside the through hole 17h is heated by the ceramic heater 11, and the water in the gap between the inner wall of the heat exchanger and the outer periphery of the ceramic heater is also heated by the ceramic heater 11.

The support 17 and the ceramic sheet 19 can be formed of, for example, alumina. The ceramic sheet 19 does not completely cover the outer periphery of the support member 17, and a slit 13s extending in the axis O direction of the support member 17 is formed in the winding end space 19a of the ceramic sheet 19.

On the other hand, as shown in fig. 2, a heating resistor 40 is formed on the ceramic sheet 19 by printing or the like, and the heating resistor 40 includes a plurality of

heater wiring circuits

40a and 40b in a curved pattern shape. The

heater wiring circuits

40a and 40b of the heating resistor 40 are configured as follows: the folded portions 40m at both ends of the plurality of wiring portions 40L (see the upper drawing of fig. 4) extending in the axis O direction of the

heater wiring circuits

40a and 40b extend in the width direction and are connected to the end portions of the adjacent wiring portions 40L. The wiring portions at both ends of each of the

heater wiring circuits

40a and 40b are integrally connected to the pad-like 3

connection terminals

41, 42a, and 42b at one end in the axis O direction.

Specifically, as shown in fig. 4, the wiring portions 40L1 and 40L2 at both ends of the heater wiring circuit 40a are connected to the connection terminal 41 and the positive-side connection terminal 42a, which are commonly grounded, respectively. Similarly, the wiring portions 40L3 and 40L4 at both ends of the heater wiring circuit 40b are connected to the connection terminal 41 and the positive electrode side connection terminal 42b, respectively. In this way, by making the connection terminal 41 a common ground terminal, the number of connection terminals and external terminals can be reduced even if the number of heater wiring circuits increases.

The

connection terminals

41, 42a, and 42b are electrically connected to 3 (only two are shown in fig. 1) external terminals 43 formed on the outer peripheral surface (the rear surface in fig. 2) of the ceramic sheet 19 via through hole conductors (not shown) or the like.

The heating resistor 40 and the

connection terminals

41, 42a, and 42b can be formed using tungsten, for example, as a main component.

Here, as shown in fig. 3, in the present embodiment, the connection terminal 41 and the connection terminal 42b face each other in the winding end space 19a of the ceramic sheet 19, and the wiring portions 40L3, 40L4 at both ends of the heater wiring circuit 40b connected to the

connection terminals

41, 42b are adjacent to each other across the winding end space 19 a.

Therefore, it is necessary to suppress arcing between the wiring portions 40L3, 40L4 at the winding end space 19 a.

Next, the

heater wiring circuits

40a and 40b will be described with reference to fig. 4 to 5.

As shown in fig. 4, the

heater wiring circuits

40a and 40b are provided on the same surface of the heating resistor 40 so as to overlap in a direction S (a direction intersecting the axis O direction) in which the

connection terminals

41, 42a, and 42b are arranged.

On the other hand, as shown in fig. 5, the

heater wiring circuits

140a and 140b of the heating resistor 140 do not overlap in the direction S in which the

connection terminals

51, 52a, and 52b are arranged, and do not belong to the present invention.

This is because, in the example of fig. 5, since the

heater wiring circuits

140a and 140b are independently arranged in the direction S (that is, the winding direction of the ceramic sheet 19 and the direction in which the width of the ceramic sheet 19 is narrow), even if a plurality of heater wiring circuits are provided, the wiring density D in the narrow direction S does not become high, and problems such as arcing in the winding end space 19a are not likely to occur.

In contrast, since the

heater wiring circuits

40a and 40b shown in fig. 4 overlap in the direction S, the wiring density D in the direction S becomes high, and arcing is likely to occur in the winding end space 19 a.

Further, "the plurality of heater wiring circuits overlap in the direction S in which the connection terminals are arranged" means that at least the folded portions 40m of the respective

heater wiring circuits

40a, 40b overlap in the direction S, and does not include the case where only the wiring portions 50L1, 50L2 connected to the

connection terminals

51, 52a, 52b at the distal end portions of the respective

heater wiring circuits

140a, 140b overlap in the direction S as shown in fig. 5.

Further, in the present invention, since the

heater wiring circuits

40a and 40b are made of a material having a temperature coefficient of 3500ppm/° c or more, even if the

heater wiring circuits

40a and 40b are overlapped in the direction S to increase the wiring density, the generation of arc in the winding end space 19a can be suppressed.

This reason will be described with reference to fig. 6.

In addition, as a method of "the

heater wiring circuits

40a and 40b include a material having a temperature coefficient of 3500ppm/° c or higher", a method of defining a temperature coefficient of a resistance ink for forming the

heater wiring circuits

40a and 40b by printing or the like to 3500ppm/° c or higher is generally cited. Therefore, the following description focuses on the temperature coefficient of the resistive ink.

As shown in fig. 6, the resistance value RH of the heater wiring circuit under the heating temperature (use temperature) H condition needs to be constant regardless of the temperature coefficient k of the resistive ink from the viewpoint of the heating capability of the heater. On the other hand, if the temperature coefficient k of the resistance ink of the heater wiring circuit is made large, the resistance value R1 of the heater wiring circuit can be made smaller than the resistance value R2 in the case where the temperature coefficient is small under the condition of a low temperature L (for example, room temperature) lower than the heating temperature H.

Here, the compound can be represented by the following formula (1),

RH＝RL×{1+k×(H－L)} (1)

where RL is the resistance value (R1, R2) of the heater wiring circuit under the temperature L condition.

Similarly, the surface resistivity (sheet resistance) Rs of the heater wiring circuit can be expressed by the following formula (2),

RsH＝RsL×{1+k×(H－L)} (2)

here, RsH and RsL are surface resistivities of the heater wiring circuit at a temperature of H, L, and RsL is regarded as constant.

Now, when the circuit length of the heater wiring circuit is represented by CL and the line width of the wiring portion of the heater wiring circuit is represented by W, it can be represented by the following formula (3),

CL＝(RH/RsH)×W (3)

wherein RH and W are constant, and therefore

CL∝(1/RsH) (4)

Here, since the value of RsH increases as the temperature coefficient k increases according to equation (2), CL decreases as the temperature coefficient k increases according to equation (4).

That is, by setting the temperature coefficient k of the resistive ink (that is, the temperature coefficient k of the

heater wiring circuits

40a and 40b) higher than the conventional one, the circuit length CL that can be used to achieve the target resistance value RH under the heating temperature (use temperature) H condition is short, and accordingly, the number of times of folding the heater wiring circuit can be reduced as compared with the conventional one. Further, since the distance T between the connection terminals in the winding end space 19a can be increased, the occurrence of arcing due to the narrowing of the distance T can be suppressed.

On the other hand, when the temperature coefficient of the resistive ink of the

heater wiring circuits

40a, 40b is less than 3500ppm/° c, it is difficult to sufficiently shorten the circuit length CL, and the distance T between the connection terminals of the winding end space 19a becomes narrow, so that arcing is likely to occur.

In particular, the temperature coefficient is preferably more than 3800 ppm/DEG C and less than 4300 ppm/DEG C. When the temperature coefficient is 4300 ppm/DEG C or more, the resistance value at room temperature may become too small and the impact current may become too large. For example, when a power source is shared with other household electrical appliances at home, there is a possibility that the input current of the other household electrical appliances is drastically reduced.

Examples of the resistive ink include metallic inks prepared in a slurry form as follows: the tungsten powder and the molybdenum powder are mixed with a ceramic powder (alumina or the like) as necessary, and a solution in which a resin powder serving as a binder is dissolved by a solvent is added to the mixture to prepare a slurry. By increasing the proportion of the ceramic powder in the metal ink, the resistance value can be increased. In addition, the temperature coefficient can be adjusted by changing the mixing ratio between the tungsten powder and the molybdenum powder.

Specifically, when the weight of tungsten/(the weight of tungsten + the weight of molybdenum) is 70% or more, the temperature coefficient is 3500 ppm/DEG C or more. When the weight of tungsten/(the weight of tungsten + the weight of molybdenum) is set to 85% to 100%, the temperature coefficient is more than 3800 ppm/DEG C and less than 4300 ppm/DEG C.

Therefore, the claimed "material having a temperature coefficient of 3500ppm/° c or more" includes tungsten powder and molybdenum powder remaining after firing the resistive ink.

The ceramic heater 11 can be manufactured as follows, for example.

First, a member to be the support 17 is extrusion-molded from a slurry of ceramic powder such as alumina, and is presintered. Further, green sheets to be the ceramic sheets 19 are formed from the same slurry, and the metal ink to be the heating resistors 40 and the

connection terminals

41, 42a, and 42b as shown in fig. 2 is printed on the surfaces of the green sheets and dried. Then, another green sheet is stacked on the printing surface of the green sheet and pressed, and the heating resistor 40 and the

connection terminals

41, 42a, and 42b are embedded between the two green sheets. Further, a via hole is provided on one surface of the laminate of the two green sheets and filled with a via hole conductor, and a conductive paste to be an external terminal 43 is printed and dried directly above the via hole conductor.

Then, a ceramic paste is applied to the surface of the laminate of the two green sheets opposite to the one surface, and the laminate of the two green sheets is wound around the support 17 and bonded, and the whole is sintered.

Further, a ceramic powder such as alumina is press-molded by a die and sintered to obtain the flange 30.

In the ceramic body 13 and the flange 30 thus manufactured, the bonding material 20 (glass) to be a solid of the bonding member 20 is placed in the gap between the ceramic body 13 and the flange 30, and the flange 30 is bonded to the outer periphery of the ceramic body 13 by heating the bonding material to the melting temperature of the glass or higher.

The present invention is not limited to the above embodiments, and it goes without saying that various modifications and equivalents are included in the spirit and scope of the present invention.

The number and shape of the heater wiring circuits are not limited.

The material of the resistive ink, i.e., the material constituting the heater wiring circuit, is not limited.

Claims

1. A ceramic heater comprising a heating resistor formed on a ceramic sheet wound around the outer periphery of a ceramic support to constitute a ceramic heater,

a slit extending in the axial direction of the support body is formed in the winding end space of the ceramic sheet,

a plurality of heater wiring circuits each having a connection terminal connected to an external power supply and constituting the heating resistor, the heater wiring circuits being provided on the same surface of the heating resistor so as to be overlapped in a direction in which the connection terminals are arranged and in a direction along a circumferential direction of the ceramic sheet,

the heater wiring circuit entirely comprises a material having a temperature coefficient of 3500 ppm/DEG C or more,

the plurality of heater wiring circuits are connected to a common ground terminal among the connection terminals,

the ground terminal of the connection terminals faces a connection terminal other than the ground terminal with the winding end space therebetween, and wiring portions at both ends of the heater wiring circuit connected to the connection terminals are adjacent to each other with the winding end space therebetween.

2. The ceramic heater according to claim 1,

the temperature coefficient is more than 3800 ppm/DEG C and less than 4300 ppm/DEG C.