JP2001102156A - Method for fabricating a ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater of high durability that does not produce cracks on degreasing or long time use, or the resistance heating body is not oxidized. SOLUTION: A ceramic heater consists of a ceramic core, ceramic insulating layer covering the core, and resistance heating body embedded between them. The shrinkage rate of the green sheet used for the insulating layer is equal to or less than that of the core, and their difference is 3% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a ceramic heater in which a resistance heating element is 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. 6A 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
6B is connected through a through hole 35 provided below the external terminal 34 of the insulating layer 32, as shown in FIG. 6B. When a current flows through the external terminal 34 through the lead wire 36, the resistance heating element 33 generates heat.
It has a mechanism that functions as a heater.

[0005] Core material 3 constituting the above ceramic heater
1 and the insulating layer 32 are usually made of SiO ₂ , MgO, CaO
Etc. are formed of Al ₂ O ₃ or the like including as a sintering agent, when manufacturing such a ceramic heater, a raw formed body of a cylindrical shape including a ceramic powder and a binder comprising a core material 31, heating Ceramic green sheet (insulating layer 3) on which a metal paste layer to be the body 33 is printed
2) with the side on which the metal paste layer is formed being wound inside, and then firing.

However, since the production method of the cylindrical green body and the ceramic green sheet are usually different from each other, their densities are different, and accordingly, their shrinkage rates during sintering are also different. Therefore, when degreasing or sintering,
In some cases, cracks may be generated, or the adhesion between the core material and the insulating layer may not be sufficient, and a gap may be formed between the two. When such a gap is formed between the core material and the insulating layer, the heating element is oxidized by the influence of the outside air when used as a heater, and a crack is formed in the heating element, resulting in disconnection. There was a problem.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention does not cause cracks during degreasing, and also causes cracks and oxidizes the resistance heating element even when used for a long period of time. It is an object of the present invention to provide a method for manufacturing a ceramic heater which has no durability and is excellent in durability.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing 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. The shrinkage of the green sheet used for the insulating layer is equal to or greater than the shrinkage of the green body used for the core, and the shrinkage of the green sheet used for the insulating layer and the shrinkage used for the core are used. A method for manufacturing a ceramic heater, wherein a difference from a shrinkage ratio of a shape is within 3%. 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. As shown in FIG. 1, in the ceramic heater 10 of the present invention, a resistance heating element 13 and a terminal 14 are provided on a surface of a cylindrical core material 11, the core material 11 is wrapped, and the resistance heating element 13 and the terminal 1
An insulating layer 12 is formed so as to cover the entirety of No.4.

The terminal 14 is exposed to the outside at the cutout 15 of the insulating layer 12, and a lead wire 16 is connected and fixed to the exposed terminal 14 via a brazing material.

In FIG. 1, a notch 15 is formed at the lower end of the heater, and a reed wire 16 is connected and fixed to a terminal 14 exposed at the notch 15, but the ceramic heater of the present invention is used. As shown in FIG. 6, there may be a configuration in which there is no cutout and the lead terminal 36 is connected to the internal resistance heating element 33 via the through hole 35 and the external terminal 34.

The core 11 and the insulating layer 12 are made of ceramic. The ceramic constituting the core material 11 and the insulating layer 12 is not particularly limited, and examples thereof include oxide ceramics such as alumina, zirconia, and mullite; nitride ceramics such as silicon nitride and aluminum nitride; and carbides such as silicon carbide. Can be

Of 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 , MgO, CaO, etc.
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 it is less than 1, the possibility of the presence of pores increases, and the grain boundaries of alumina ceramics constituting these deteriorate due to migration or the like, and pores are likely to be formed. 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.

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

The ceramic heater having such a configuration is as follows.
For example, it is manufactured by the following method. FIG.
5 to 5 are explanatory views schematically showing a part of a process of manufacturing the ceramic heater 10, wherein (a) is a cross-sectional view and (b) is a front view.

As shown in FIG. 2, 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. 3, 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. 4, the laminate 20 shown in FIG. 3 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, as shown in FIG.
A raw material molded body for firing is produced by placing a formed body 25 that will be the columnar core material 11 on top of the above, and winding the laminated body 20 around the generated formed body 25, and then degreasing at a predetermined temperature. Then, by firing, the ceramic heater 10 (see FIG. 1) is manufactured. In addition, by making the formed body 25 hollow, in the degreasing step and the sintering step, the generated gas escapes well, and the degreasing is efficiently performed.
Baking can be performed.

Conductive paste layer 2 used in the above process
3a is a viscous substance containing the powder of the high melting point metal and a binder, and the green sheet 24 serving as the insulating layer 12 and the formed body serving as the core material 11 are a viscous substance containing the powder of the ceramic and the binder. By passing these through a drying step, a degreasing step, and a baking step, the organic substances and the binder are volatilized, decomposed, and disappear, and become the resistance heating element 13, the terminal 14, the core material 11 made of ceramic, and the insulating layer 12. In such a step, sintering further proceeds, and these green sheets and the like shrink.

In the present invention, the shrinkage rate of the green sheet 24 in the degreasing step and the baking step is equal to or greater than the shrinkage rate of the green body 25, and the shrinkage rate of the green sheet 24 and the shrinkage of the green body 24 are reduced. It is characterized in that the difference from the rate is within 3%. Note that the shrinkage in this case refers to the shrinkage of the dried green sheet 24 and the like until the green sheet 24 becomes ceramic.

The contraction rate is represented by the following equation (1). Shrinkage (%) = [(volume of molded body before firing−volume of ceramic after firing) / volume of molded body before firing] × 100 (1) In the above formula (1), Is green sheet 2
The ceramic means the core material 11 and the insulating layer 12 after sintering.

The reason why the contraction rate of the green sheet 24 is equal to or larger than the contraction rate of the green body 25 is that the contraction rate of the green sheet 24 is equal to or larger than the green body 24.
When the shrinkage ratio is smaller than the shrinkage ratio, the formed body 25 shrinks more, so that the core material 11 and the insulating layer 12 do not tightly adhere to each other, and a void is formed between the core material 11 and the insulating layer 12. This is because the resistance heating element 13 is easily oxidized when used as a heater.

The reason why the difference between the shrinkage rate of the green sheet 24 and the shrinkage rate of the green body 25 is within 3% is that
If the difference in the shrinkage ratio exceeds 3%, the degree of shrinkage of the insulating layer 12 (green sheet 24) surrounding the core material 11 is too large, so that cracks occur in the degreasing step,
This is because a large stress is generated in the core material 11 due to the contraction of the insulating layer 12 after firing, and cracks and the like are easily generated by a heat cycle or the like.

The shrinkage ratio between the green sheet 24 and the green body 25 can be determined by changing the content of the resin component or the solvent in the binder constituting the green sheet 24 or the green body 25 or by changing the particle size of the ceramic powder. Can be adjusted. In general, the shrinkage can be increased by increasing the content of the resin component or the solvent or reducing the particle size of the ceramic powder. In general, it is preferable that the shrinkage ratio is as small as possible. Therefore, the shrinkage ratio of the green body 24 is set to be as small as possible, and the shrinkage ratio of the green sheet 24 is set to be equal to or slightly larger than that.

In the ceramic heater 10 manufactured by the method of the present invention, the insulating layer 12 wrapping the core material 11 is tightly adhered to the core material 11, and the resistance heating element 13 embedded between them is And the resistance heating element 13 does not deteriorate due to oxidation or the like.
Since the contraction rate of the insulating layer 12 is too large, cracks do not occur in the core material 11 and a ceramic heater having excellent durability can be obtained.

[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, a ceramic heater 10 made of alumina having the structure shown in FIG. 1 was manufactured. At this time, Al ₂ O ₃ and a sintering aid were contained in the proportions shown in Table 1, and in addition, as an organic binder,
A green sheet 24 containing 12 parts by weight of an acrylic resin and 23 parts by weight of a solvent or the like was used. Further, a material containing Al ₂ O ₃ and a sintering aid in the proportions shown in Table 1 and containing 10 parts by weight of an acrylic resin and 20 parts by weight of a solvent or the like as an organic binder was used as a formed form 25. used.

The degreasing step is performed in the air for about 60 hours.
It is performed at 0 ° C., and the firing step is performed in an inert gas at 160 ° C.
Performed at 0 ° C. The insulating layer 12 of the manufactured ceramic heater 10 has a thickness of 200 μm and a density of 3.
The core material 11 had a diameter of 3.15 mm and a density of 3.64 g / cm ³ . In the obtained ceramic heater 10, no crack was generated in the degreasing step, and no crack was generated in the obtained ceramic heater.

The obtained ceramic heater 10 was subjected to a heat cycle test in which a cooling cycle of cooling to room temperature was repeated 100 times after the temperature was raised to 500 ° C., and the surface and the inside of the heater were observed, but no crack was found. Further, the current was continued to flow through another ceramic heater 10 obtained in the above example, and the time until the resistance change rate became 10% was measured, and it was 10,000 hours.

The resistance change rate is a value represented by the following equation (2). Resistance change rate (%) = (resistance value after test-resistance value before test) x 100 / (resistance value before test) ... (2)

Table 1 shows the densities of the formed body 25 and the green sheet 24, and the densities and shrinkage ratios of the core material and the insulating layer of the manufactured ceramic heater, and the difference between the two.
Shown in Table 2 below shows the results of the heat cycle test and the time required for the rate of change in resistance to reach 10%.

Examples 2 to 3 The characteristics shown in Table 1 below were changed in the same manner as in Example 1 except that the density of the green body 25 and the density of the green sheet 24 were changed as shown in Table 1. Was manufactured. In the obtained ceramic heater 10, no crack was generated in the degreasing step, and no crack was generated in the obtained ceramic heater.

A heat cycle test was performed on this ceramic heater in the same manner as in Example 1, and the resistance change rate was 1
The time to reach 0% was measured. Table 1 below shows the densities of the formed body 25 and the green sheet 24, and the densities and shrinkage rates of the core material and the insulating layer of the manufactured ceramic heater, and the difference between the two. Table 2 below shows the results of the heat cycle test and the time required for the rate of change in resistance to reach 10%.

Comparative Examples 1-2 The characteristics shown in Table 1 below were changed in the same manner as in Example 1 except that the density of the green body 25 and the density of the green sheet 24 were changed as shown in Table 1. Was manufactured. The obtained ceramic heater is
After firing, some cracks occurred.

A heat cycle test was performed on this ceramic heater in the same manner as in Example 1, and the resistance change rate was 1
The time to reach 0% was measured. Table 1 below shows the densities of the formed body 25 and the green sheet 24, and the densities and shrinkage rates of the core material and the insulating layer of the manufactured ceramic heater, and the difference between the two. Table 2 below shows the results of the heat cycle test and the time required for the rate of change in resistance to reach 10%.

[0038]

[Table 1]

[0039]

[Table 2]

As is clear from the results regarding the resistance change and the like shown in the above Examples 1 to 3 and Comparative Examples 1 and 2,
In the case of the comparative example, cracks occurred in the heater and the resistance heating element was oxidized in a short period of time, whereas in the case of the example, the cracks occurred in the heater even when the heat load was repeatedly applied. It did not occur, and even when the heater was used for a long time, the resistance change of the resistance heating element could be effectively suppressed.

The method for manufacturing a ceramic heater according to the present invention is constructed as described above, so that cracks do not occur at the time of degreasing, and even when used for a long time, cracks occur. A ceramic heater having excellent durability can be manufactured without the resistance heating element being oxidized.

[Brief description of the drawings]

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

FIG. 2A 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. 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 perspective view showing an example of a conventional ceramic heater, and FIG. 6B is a cross-sectional view thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ceramic heater 11 Core material 12 Insulating layer 13 Resistance heating element 14 Terminal 15 Notch 16 Lead wire 22 Adhesive layers 23a, 23b Conductive paste layer 24 Green sheet 25 Forming form

Claims (2)

[Claims] 1. A method for manufacturing a ceramic heater in which a resistance heating element is embedded between a core material made of ceramic and an insulating layer made of ceramic surrounding the core material, wherein a green sheet used for the insulating layer is provided. Is equal to or greater than the shrinkage rate of the formed body used for the core material, and the difference between the shrinkage rate of the green sheet used for the insulating layer and the shrinkage rate of the formed body used for the core material is A method for producing a ceramic heater, which is within 3%. 2. The method for manufacturing a ceramic heater according to claim 1, wherein the ceramic constituting the core material and the insulating layer is at least one selected from the group consisting of Al ₂ O ₃ , mullite, and silicon nitride.