JP2001102161A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater for uniformly heating the matter around it with a sufficient amount of heat. SOLUTION: A ceramic heater comprises a core, insulating sheet coated on the core, and resistance heating body interposed between the core and insulating layer. The heating part of the resistance heating body consists of an axial component arranged in parallel with the axial direction, and radial component arranged perpendicularly to the axial direction, which are sequentially arranged in the peripheral direction so as to form a repeated pattern. The length of the axial component is equal to or longer than the radial component. The axial component is arranged in the peripheral direction with an almost same interval.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic heater having a resistance heating element embedded in ceramic.

[0002]

2. Description of the Related Art A ceramic heater in which a resistance heating element made of a high melting point metal is embedded between a core material and an insulating layer surrounding the core material is used as a heat source in an oxygen sensor for automobiles, a glow system, and the like. As a heat source for oil vaporizers such as semiconductor heaters and oil fan heaters, it is widely used.

FIG. 7A is a perspective view schematically showing an example of this type of ceramic heater, and FIG.
(A) It is AA sectional drawing in a figure. In this ceramic heater, a resistance heating element 33 is embedded between a cylindrical core material 31 and an insulating layer 32 wound around the core material 31 via an adhesive layer 37, and the end of the resistance heating element 33 is An external terminal 34 provided outside the insulating layer 32 is connected, and a lead wire 36 is fixed to the external terminal 34.

An end of the resistance heating element 33 and an external terminal 34
Are connected via a through hole (not shown) provided below the external terminal 34 of the insulating layer 32. And
When a current is supplied to the external terminal 34 via the lead wire 36, the resistance heating element 33 generates heat, so that the resistance heating element 33 functions as a heater. In addition, the left side portion in FIG. 7A that functions as the resistance heating element 33 is sequentially coupled in a U-shape and an inverted U-shape in a left and right direction, and a repetitive pattern is formed in the circumferential direction.

[0005]

However, the components parallel to the axial direction of the resistance heating element 33 are not arranged at equal intervals in the circumferential direction as shown in FIG.
Axial component 33 of the resistance heating element 33 at the portion where
Since the distance between a and the axial component 33b is long, when a voltage is applied to the ceramic heater, the temperature of the heater does not become uniform in the circumferential direction. That is, in this ceramic heater, there is a problem that the temperature of the portion where the insulating layer 32 is interrupted becomes low, so that it is difficult to heat the surrounding heating target to a uniform temperature.

The ceramic heater having such a structure is such that when a voltage is applied to the ceramic heater, the potential difference (voltage) between the axial component 33a and the axial component 33b becomes largest, and When either is used as a cathode, the distance between them is shortened and the temperature is increased, and polyvalent cations such as Mg ²⁺ and Ca ²⁺ contained in the insulating layer are attracted to the cathode and move. This is because so-called migration occurs, and the resistance heating element 33 is easily oxidized due to the migration.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a ceramic heater which has a sufficient heat generation amount, forms a uniform temperature zone in the circumferential direction, and can heat a surrounding object to be heated to a uniform temperature. The purpose is to provide.

[0008]

According to the present invention, there is provided a ceramic heater having a resistance heating element embedded between a core material made of ceramic and an insulating layer made of ceramic surrounding the core material. The high-temperature heat-generating portion of the body has a structure in which an axial component parallel to the axial direction and a circumferential component perpendicular to the axial direction are sequentially joined at an end to form a pattern that is repeated in the circumferential direction, and the length of the axial component The ceramic heater is characterized in that the length is equal to or longer than the length of the circumferential component, and the axial components are arranged at substantially equal intervals in the circumferential direction. Hereinafter, the present invention will be described in detail.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a perspective view schematically showing a ceramic heater of the present invention, and FIG.
(A) It is AA sectional drawing in a figure. FIG.
FIG. 4 is a development view showing a resistance heating element and terminals formed on a core material, which are developed on a plane.

As shown in FIG. 1, a ceramic heater 10 according to the present invention is provided with a resistance heating element 13 and a terminal 14 on the surface of a columnar core material 11, and an insulating layer 12 wrapping the core material 11. , Are formed so as to cover the whole of the resistance heating element 13 and the terminal 14.

The terminal 14 is exposed to the outside at the notch 15 of the insulating layer 12 and the exposed terminal 1
The lead wire 16 is connected and fixed to 4 via a brazing material. As shown in FIG. 2, the resistance heating element 13 includes a non-heating section 13b and a high-temperature heating section 13a. The non-heating section 13b has a low resistance to prevent heat generation.
It is composed of a plurality of lines formed in parallel.

The high-temperature heating portion 13a is formed by repeating an axial component 130 parallel to the axial direction of the ceramic heater 10 and a circumferential component 131 perpendicular to the axial direction at the ends in order, so that the pattern repeats in the circumferential direction. , And the length a of the axial component 130 is set to be longer than the length b of the circumferential component 131.

Note that the length a of the axial component 130 may be set to be the same as the length b of the circumferential component 131. However, when the length a of the axial direction component 130 is shorter than the length b of the circumferential direction component 131, the width (area) of the heat generating region is reduced, and the portion where the circumferential direction component 131 exists is mainly Since the heating is performed and the entire length is also reduced, the calorific value is reduced, and it becomes difficult to sufficiently heat the object to be heated.

FIG. 1 (b) shows a cross section of the axial component 130 of the resistance heating element 13 formed on the core material 11, as shown in FIG. The components 130 are arranged on the outer peripheral portion of the core material 11 at substantially equal intervals.

As described above, the axial component 130 is combined with the core material 11.
By arranging them at equal intervals on the outer periphery of the heater, the heating object around the ceramic heater 10 can be heated to a uniform temperature.

Further, the length b of the circumferential component 131 is shortened so that the axial component 13 formed on the outer peripheral portion of the core material 11 is reduced.
By increasing the density of 0, the width of heating is increased and the calorific value is also increased, making it possible to heat to a high temperature.

However, the axial component 130 is
1 by arranging them at equal intervals on the outer periphery of FIG.
As shown in (b), the distance 1 between the axial components 130 at the ends is shorter than in the conventional case, but the insulating layer 12 has a high-purity composition in which migration is less likely to occur. Can be prevented from occurring.

The core 11 and the insulating layer 12 in the ceramic heater 10 are made of ceramic. The ceramic constituting the core material 11 and the insulating layer 12 is not particularly limited. For example, alumina, zirconia,
Examples thereof include oxide ceramics such as mullite, nitride ceramics such as silicon nitride and aluminum nitride, and carbides such as silicon carbide.

Among these, Al_Two O_Three , Murai
And silicon nitride are preferred, and in particular, Al _Two O_Three The main component
And SiO 2 as a sintering aid_Two Less than 4% by weight of Mg
Contains 0.5% by weight or less of O and 1.2% by weight or less of CaO
Alumina ceramic with a density ratio of 96% or more is preferred.
No.

The density ratio of the core material 11 and the insulating layer 12 is 96%
If the amount is less than the above range or if the amount of the sintering aid is larger than the above range, there is a high possibility that pores are present, and the grain boundaries of the alumina ceramic constituting these deteriorate due to migration or the like and become empty. Because holes are easily formed,
When used for a long time, the resistance heating element 13 is easily oxidized. The density ratio is a percentage of the ratio of the density of the actual sintered body to the theoretical density of the ceramic.

In order to prevent migration, the content of impurities such as Ca ²⁺ , Mg ^2+, etc., which is polyvalent ions and has a thickness of about 10 to 15 μm is provided around the resistance heating element 13. A few high-purity layers may be provided. This layer may be provided between the resistance heating element 13 and the insulating layer 12, or may be provided between the resistance heating element 13 and the core material 11,
It may be provided on both sides of the resistance heating element 13 so as to sandwich it. This intermediate layer may be provided at least in a region where the high-temperature heat-generating portion 13a exists.
May also be provided in the area where the.

The resistance heating element 13 and the terminal 14 are W, T
It is desirable to be made of a high melting point metal such as a, Nb, Ti, Mo, Re and the like. These refractory metals may be used alone or in combination of two or more. Further, the resistance heating element 13 and the terminal 14 may be formed by adding a ceramic such as alumina to them.

Next, a method of manufacturing the above ceramic heater will be described. 3 to 5 are cross-sectional views schematically showing a part of a process of manufacturing the ceramic heater 10, in which (a) is a cross-sectional view and (b) is a front view.

As shown in FIG. 3, first, an adhesive layer 22 is formed on a plastic film 21 having releasability, and then a conductive paste layer 23 serving as the resistance heating element 13 is formed.
a and a conductive paste layer 23b to be the terminals 14 are formed. The reason why the adhesive layer 22 is formed is that when the heater is manufactured, the portion of the terminal 14 exposed from the cutout portion 15 is firmly bonded to the core material 11. The conductive paste layer 23a and the conductive paste layer 23b are formed in a state where they are in contact with each other so as to be firmly connected.

Next, as shown in FIG. 4, a layer of a green sheet 24 serving as the insulating layer 12 is formed so as to cover the conductive paste layers 23a and 23b. At this time, the portion of the conductive paste layer 23b where the notch is formed after firing is not covered with the green sheet 24,
It is exposed.

Thereafter, as shown in FIG. 5, the laminate 20 shown in FIG. 4 is turned over so that the green sheet 24 is on the lower side, and is placed on a predetermined table 25. The plastic film 21 is peeled off by fixing it to the table 25 by using air suction force or the like through a through hole (not shown) formed in the table 25. Subsequently, the formed shaped body 25 to be the core material 11 is placed on the laminated body 20, and the laminated body 20 is wound around the core material 11, thereby producing a raw material molded body for firing. By firing at the temperature, the ceramic heater 10 is manufactured.

The manufactured ceramic heater 10 has a sufficient calorific value and the axial components 130 of the resistance heating element 13 are uniformly arranged on the outer periphery of the core material 11.
The surrounding heating object can be heated to a uniform temperature.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Using the method described in the above embodiment, the ceramic heater 10 having the structure shown in FIG.
The distance l (see FIG. 1B) between the axial components 130 at the ends was 1 mm. The firing temperature at this time was 1600 ° C. The resistance heating element 13 of the manufactured ceramic heater 10 contains 80% by weight of W,
It contains 17% by weight of Re and ₃ % by weight of Al ₂ O ₃ , and the insulating layer 12 has a thickness of 200 μm, and contains 9% of Al ₂ O ₃ .
2.5 wt%, as a sintering aid, a SiO ₂ 5.8 wt%, the MgO 0.5 wt%, the CaO contained 1.2 wt%, the density was 3.70.

The obtained ceramic heater 10 was set to 12 V
And a current is supplied to the resistance heating element 13 at six locations (p _{1 to} p ₆ , FIG. 1B) around the high-temperature heating portion 13 a.
) Was measured with a thermocouple. As a result, p ₁
Temperature of ~p ₆ was in the range of 700 ± 10 ° C.. Thereafter, current was continuously passed through the ceramic heater 10 and the time required for the resistance change rate to reach 10% was measured.
00 hours.

The resistance change rate is a value represented by the following equation (1). Resistance change rate (%) = (resistance value after test-resistance value before test) x 100 / (resistance value before test) ... (1)

Example 2 After forming an adhesive layer 22 and conductive paste layers 23a and 23b on a plastic film 21, a green sheet as an intermediate layer is formed thereon, and an insulating layer 12 is formed thereon.
Example 1 except that a green sheet 24 was formed.
In the same manner as in the above, a ceramic heater 10 was manufactured. The size of the green sheet serving as the intermediate layer is green sheet 2
Same as 4. The firing temperature was 1600 ° C.

In the middle of the manufactured ceramic heater 10
The layer is 15 μm thick and is made of SiO 2 _Two The 0.1 weight
%, MgO 0.05% by weight, CaO 0.05% by weight
It is made of alumina ceramic with a density of 3.70.
The insulating layer 12 has a thickness of 200 μm_Two O
_Three 92.5% by weight of SiO 2 as a sintering aid_Two To 5.
8% by weight, 0.5% by weight of MgO, 1.2% by weight of CaO
% Alumina ceramic with a density of 3.70
Was.

The obtained ceramic heater 10 was set to 12 V
And a current is passed through the DC power supply, and six places (p _{1 to} p ₆ , FIG. 1B) around the high-temperature heating portion 13 a of the resistance heating element 13.
) Was measured with a thermocouple. As a result, p ₁
Temperature of ~p ₆ was in the range of 700 ± 20 ° C.. Next, current was continuously passed through the ceramic heater, and the time until the resistance change rate became 10% was measured.
000 hours.

Comparative Example 1 A ceramic heater having the same structure as in Example 1 except that the composition of the insulating layer was different was manufactured. The firing temperature at this time was 1600 ° C. The material of the resistance heating element 13 of the manufactured ceramic heater 30 is the same as that of the first embodiment, and the thickness of the insulating layer 12 is 200 μm.
94.0% by weight of Al ₂ O ₃ and S as a sintering aid
4.0% by weight of iO ₂ , 0.5% by weight of MgO, CaO
And its density was 3.69.

The obtained ceramic heater 10 was set to 12 V
And a current is passed through the DC power supply, and six places (p _{1 to} p ₆ , FIG. 1B) around the high-temperature heating portion 13 a of the resistance heating element 13.
) Was measured with a thermocouple. As a result, p ₁
Temperature of ~p ₆ was in the range of 700 ± 10 ° C.. Thereafter, a current was continuously applied to the ceramic heater 10 and the time until the rate of change in resistance became 10% was measured.
00 hours.

Thereafter, the ceramic heater was cut at the portion where the resistance heating element was present, and the state of the alumina ceramic around the ceramic heater was observed with a scanning electron microscope (SEM). As a result, many holes were formed. This is considered to be caused by migration of Ca ²⁺ , Mg ^2+, etc. in the alumina ceramic.

Comparative Example 2 Distance l between axial components 130 at the end of resistance heating element 13
A ceramic heater 10 having the configuration shown in FIG. 1 was manufactured in the same manner as in Example 1, except that the resistance heating element was formed so that the length of the resistance heating element was 2 mm (see FIG. 1B).

The obtained ceramic heater 10 was set to 12 V
And a current is passed through the DC power supply, and six places (p _{1 to} p ₆ , FIG. 1B) around the high-temperature heating portion 13 a of the resistance heating element 13.
) Was measured with a thermocouple. As a result, p ₂
~ P _{6 was in} the range of 700 ± 20 ° C.
_{For 1} , the temperature was 670 ° C., which was low.

As is evident from the results of the temperature measurement shown in Examples 1 and 2, the axial components of the resistance heating element are arranged at equal intervals in the circumferential direction of the core material, thereby obtaining The temperature can be made uniform. In addition, by providing a high-purity component of the insulating layer or providing a high-purity intermediate layer, Ca ²⁺ , M
Migration of g ²⁺ or the like can be prevented.

[0041]

According to the ceramic heater of the present invention,
Since the resistance heating element is configured as described above, the heating element has a sufficient heat generation amount, and the temperature in the circumferential direction of the heater becomes uniform, so that a heating object around the heater can be heated to a uniform temperature. .

[Brief description of the drawings]

FIG. 1A is a perspective view showing a structure of a ceramic heater according to the present invention, and FIG. 1B is a sectional view thereof.

FIG. 2 is a developed view in which a resistance heating element and terminals constituting the ceramic heater of the present invention are developed in a plane.

FIG. 3A is a cross-sectional view schematically showing one step in manufacturing the ceramic heater of the present invention, and FIG.
Is a front view.

FIG. 4A is a cross-sectional view schematically showing one step in manufacturing the ceramic heater of the present invention, and FIG.
Is a front view.

FIG. 5A is a cross-sectional view schematically showing one step in manufacturing the ceramic heater of the present invention, and FIG.
Is a front view.

FIG. 6A is a cross-sectional view schematically showing one step in manufacturing the ceramic heater of the present invention, and FIG.
Is a front view.

FIG. 7A is a perspective view showing a structure of a conventional ceramic heater, and FIG. 7B is a sectional view thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Core material 12 Insulating layer 13 Resistance heating element 14 Terminal 13a High temperature heating part 13b Non-heating part 130 Axial component 131 Circumferential component 15 Notch 16 Lead wire

Claims (2)

[Claims] 1. A ceramic heater in which a resistance heating element is buried between a core material made of ceramic and an insulating layer made of ceramic surrounding the core material, wherein the high-temperature heating portion of the resistance heating element has a shaft. The axial component parallel to the direction and the circumferential component perpendicular to the axial direction are sequentially combined at the ends to form a pattern that repeats in the circumferential direction, and the length of the axial component is the length of the circumferential component. Equal to or longer than the length of
The ceramic heater is characterized in that the axial components are arranged at substantially equal intervals in a circumferential direction. 2. An intermediate layer having less impurities than the insulating layer at least between the high-temperature heating section of the resistance heating element and the core material and / or at least between the high-temperature heating section of the resistance heating element and the insulation layer. The ceramic heater according to claim 1, wherein a layer is provided.