JP2001267041A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater excellent in mechanical characteristics such as flexural strength, to say nothing of excellence in functional characteristics such as reaching desired temperature in short time, or excellence in durability. SOLUTION: With a ceramic heater constituted with a resistance heating element, buried in a base material mainly of alumina, with at least one of a group of W, Re, and Mo as a main ingredient and ceramics for the rest, the density of the above base material is 95% or more, and the particles constituting the above base material has 5 to 40 weight % of an average particle diameter of 5 to 45 μm and 60 to 95% of an average particle diameter of 0.5 to 5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater having alumina as a main component and a resistance heating element embedded in a base material comprising a core and an insulating layer.

[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 covering the core material is used as a heat source in an oxygen sensor for automobiles, a glow system, and the like. Further, it is widely used as a heat source for oil vaporizers such as semiconductor heaters and oil fan heaters.

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 with an adhesive layer 37 interposed therebetween. An external terminal 34 provided outside the insulating layer 32 is connected, and a lead wire 36 is fixed to the external terminal 34.

As shown in FIG. 7B, the terminal portion of the resistance heating element 33 and the external terminal 34 are connected via a through hole 35 provided below the external terminal 34 of the insulating layer 32. I have. Then, when a current flows to the external terminal 34 via the lead wire 36, the resistance heating element 33 generates heat, so that the mechanism functions as a heater.

[0005] Core material 3 constituting the above ceramic heater
1 and the insulating layer 32 are usually made of alumina containing SiO ₂ or the like as a sintering aid.
Is composed mainly of a high melting point metal such as W or Mo, and added with a ceramic component such as alumina, silicon nitride or mullite.

[0006] The ceramic heater having such a configuration is as follows.
A green sheet having a conductor paste layer containing a high melting point metal formed on the surface thereof was wound around a cylindrical shaped body containing alumina powder to be the core material 31 with the side on which the conductor paste layer was formed being inside. Thereafter, it is manufactured by degreasing and firing.

The ceramic heater is required to have excellent functional characteristics such as reaching a target temperature in a short time and excellent durability. From the viewpoint of preventing breakage or the like due to vibration or the like during handling, a material having excellent mechanical properties such as bending strength is required.

However, conventionally, thermal characteristics have been emphasized, and mechanical characteristics such as bending strength have not been emphasized so much. Therefore, ceramic heaters having sufficient bending strength and the like have not been manufactured. There was a strong demand for improvements in the characteristics of.

[0009]

In view of the above problems, the present inventors have conducted intensive studies with the aim of improving the mechanical characteristics of a ceramic heater having such a structure.
In the past, it was generally said that ceramics composed of particles having a uniform particle size were excellent in mechanical properties such as bending strength. Have been found to be excellent in mechanical strength when different particles are present, and have completed the present invention.

[0010]

That is, the present invention relates to a resistance heating system comprising, as a main component, at least one selected from the group consisting of W, Re, and Mo in a base material mainly composed of alumina, and the remainder composed of a ceramic component. A ceramic heater having a body embedded therein, wherein the density ratio of the alumina base material is 95% or more, and the particles constituting the base material have particles having an average particle size of 5 to 45 μm. weight%
And 60 to 95% by weight of particles having an average particle size of 0.5 to 5 μm.
It is a ceramic heater characterized by comprising. Hereinafter, the present invention will be described in detail.

[0011]

FIG. 1A is a perspective view schematically showing one example of a ceramic heater manufactured by the manufacturing method of the present invention, and FIG.
FIG. 3 is a sectional view taken along line A.

As shown in FIG. 1, in a 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 mainly composed of alumina. An insulating layer 12 containing alumina as a main component is formed so as to cover almost all of the terminals 13 and the terminals 14.

That is, the resistance heating element 13 is embedded in a base material composed of the core material 11 and the insulating layer 12, and a part of the terminal 14 is exposed outside at the cutout 15 of the insulating layer 12. . The lead wire 16 is connected and fixed to the exposed terminal 14 via a brazing material.

The ceramic heater according to the present invention is not limited to the one shown in FIG. 1, but a resistance heating element 33 as shown in FIG. May be connected to the internal resistance heating element via the.

The base material (core material 11 and insulating layer 12) of the ceramic heater 10 is made of a ceramic mainly composed of alumina, and the density ratio of the base material made of alumina is 95% or more. The particles constituting the base material are particles having an average particle size of 5 to 45 μm (hereinafter, referred to as particles).
5 to 40% by weight with an average particle size of 0.5
-5 μm particles (hereinafter also referred to as particles B) in an amount of 60 to 95% by weight.

A ceramic (sintered body) such as alumina ceramic is a polycrystalline body in which microcrystalline particles are aggregated.
Specifically, this sintered body is composed of microcrystalline particles, grain boundaries, grain boundary precipitates, grain boundary bubbles, intragranular precipitates, and the like.

There are many factors that determine the mechanical properties of this sintered body, such as the average particle size of the particles, the particle size distribution, the shape of the particles, the crystallinity of the particles, and the The size, sintering density, characteristics of the grain boundary segregation layer, etc. can be cited as the factors, and among them, the average particle size and density of the particles are important factors that determine the mechanical properties of the sintered body. ing.

In the ceramic heater of the present invention, the density ratio of the alumina base material is 95% or more, which is close to the theoretical density, the number of voids is small, and the size of the voids is extremely small. The voids are considered to be one type of defect, so if the voids are large, the mechanical properties deteriorate, but the ceramic heater of the present invention has excellent mechanical properties because the voids are small and small. The above density ratio is preferably 95% or more. Note that the density ratio refers to the percentage of the ratio of the density of the actual sintered body to the theoretical density of the ceramic.

When the density ratio of the base material is less than 95%, the mechanical strength is deteriorated and the possibility of the presence of holes is increased. Oxygen penetrates into the sintered body through the hole, and the resistance heating element 13 buried inside is easily oxidized.

Further, in the ceramic heater of the present invention,
Particles constituting the alumina base material have a particle size of 5
Particle A having a particle size of 0.5 to 5 μm and particle B having a particle size of 0.5 to 5 μm
And its particle size is small overall.

Usually, in order to increase the sintering density, it is necessary to increase the sintering temperature in order to advance the sintering. If the sintering temperature is too high, the alumina powder constituting the compact becomes abnormal. The average particle size of the particles that grow and form the sintered body becomes too large, and the decomposition of the grain boundaries or the confinement of the bubble boundaries occur, resulting in poor mechanical properties.

However, in the ceramic heater of the present invention, it is not necessary to raise the sintering temperature too much for the following reasons. , Its particle size is 5-45
μm, which is smaller than the normal one.

The reason that the sintering temperature did not need to be raised was that two kinds of powders having different particle size distributions were used when selecting the alumina raw material powder. That is, by using powders having different particle sizes having such a predetermined particle size distribution, relatively large particles and relatively small particles are successfully combined to produce a compact that is densely packed. In the sintering process, by using the glass phase as an auxiliary agent, such large particles and small particles are well combined, and furthermore, the sintering force of only small particles allows the structure of high-density packing. As a result, it is considered that a high-density sintered body was obtained even if sintering was not forcibly advanced by increasing the temperature.

The preferred average particle size of the particles A is 5 to 4
5 μm, and the preferred average particle diameter of the particles B is 0.1 μm.
5 to 5 μm. In the present specification, the particle size refers to a value of (major axis + minor axis) / 2 of the particles.

The abundance of the particles A and B is as follows:
5 to 40% by weight, and the particle B is 60 to 95% by weight. When the particles A and the particles B exist in the above range, the sintered body has a high density, and the ceramic heater has excellent mechanical strength. The preferable amount of the particles A is 15 to 35% by weight, and the preferable amount of the particles B is 65 to 85% by weight.

The bending strength of the ceramic heater of the present invention having such a structure is usually one having a diameter of 3.65 mm.
It has excellent bending strength of 180 to 200N on average.

The resistance heating element 13 and the terminal 14 are W, Re.
And at least one selected from the group consisting of high melting point metals of Mo and Mo, and the remainder is composed of a ceramic component.
Therefore, the high melting point metal as the main component may be used alone, or two or more kinds may be used in combination. The remaining ceramic components include alumina, silicon nitride, mullite, etc.
Alternatively, a ceramic made of a mixture of these may be used.

Next, an example of a method for manufacturing the ceramic heater of the present invention will be described. 2 to 5 are views schematically showing a part of a process of manufacturing the ceramic heater 10, in which (a) is a sectional view,
(B) is a front view.

First, as shown in FIG. 2, an adhesive layer 22 is formed on a plastic film 21 having releasability.
Then, as a conductor paste printing step, a conductor paste layer 23a serving as the resistance heating element 13 and a conductor paste layer 23b serving as the terminals 14 are formed by printing, and the conductor paste layers 23a and 23b are dried.

The adhesive layer 22 is formed when the heater 1 is manufactured, and the portion of the terminal 1 exposed from the notch 15 is formed.
This is because 4 is firmly adhered 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.

The conductor paste layers 23a and 23b are made of W, R
It contains at least one selected from the group consisting of high melting point metals of e and Mo, a ceramic component such as alumina, a binder resin, and a solvent.

Next, as shown in FIG. 3, in a green sheet printing step, a region including the conductor paste layers 23a and 23b printed in the conductor paste printing step is covered with the conductor paste layers 23a and 23b. Then, a paste for an insulating layer containing alumina powder, a binder resin, and a solvent is overlaid and printed to form a layer of the green sheet 24, and the green sheet 24 is dried. At this time, a portion of the conductive paste layer 23b where the notch is formed after firing is formed.
Are not covered with the green sheet 24 and are exposed.

The alumina particles contained in the green sheet 24 are alumina particles 5 to 4 having an average particle size of 5 to 45 μm.
0% by weight and alumina particles 6 having an average particle size of 0.5 to 5 μm.
Preferably, the sintering aid contains 4% by weight or less of SiO ₂ , 0.5% by weight or less of MgO, and 1.2% by weight or less of CaO. preferable. Further, as the alumina particles, those obtained by pulverizing a commercially available product using a ceramic ball mill are preferable.

Next, 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. Stand 25
The film 25 is fixed to the base 25 by using air suction force or the like through a through hole (not shown) formed in the plastic film 2.
1 is peeled off. (B) shows the laminate 20 after the plastic film 21 has been peeled off.

Subsequently, as a winding step, as shown in FIG. 5, the forming body 26 to be the cylindrical core material 11 is placed on the laminated body 20, and the laminated body 2 is formed around the forming body 26.
By winding 0, a raw material compact for firing is produced. It is desirable that the average particle size of the alumina particles constituting the green compact 26 and the ratio of the sintering aid are the same as those of the green sheet.

Thereafter, in the presence of oxygen, at 400 to 600 ° C.
Degreasing at a temperature of 30 ° C. to form the formed body 26, the conductive paste layer 2
3a, 23b, and the organic material in the green sheet 24 are removed, and subsequently, firing is performed to sinter alumina, a high melting point metal, or the like, thereby forming the ceramic heater 10 (FIG. 1).
See). The firing temperature is 1450-1650 ° C
The firing time is preferably 0.5 to 12 hours.

By making the formed body 25 hollow, the gas generated during the degreasing step and the baking step can be easily removed, and degreasing and baking can be performed efficiently.

The obtained ceramic heater is not only excellent in functional properties such as reaching a target temperature in a short time and excellent in durability, but also has a mixture of particles having different particle diameters. And small particles are well combined and densely packed, so that they have excellent mechanical properties such as bending strength. For high-density packing, a two-component system having a different particle size distribution is preferable because it is not complicated, but a three-component system or a combination having a higher particle size may be used.

[0039]

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.

Examples 1 and 2 and Comparative Example 1 Using the method described in the above embodiment, a ceramic heater 10 having the structure shown in FIG. 1 was manufactured. In Examples 1 and 2 and Comparative Example 1, the firing temperature was changed, and the obtained ceramic heater was tested for its basic performance as a heater, and the bending strength was measured.

The conductor components in the conductor paste layers 23a, 23b and 23c are composed of 80% by weight of W, 17% by weight of Re, and 3% by weight of alumina, an acrylic resin as a binder resin, and α-terpineol as a solvent. Using.

The composition of the ceramic component in the green form 26,
Table 1 below shows the average particle size of the alumina powder, the density of the dried body, and the firing conditions of the molded body. Note that the generation feature 26
As the binder resin, methylcellulose was used, and as the solvent, ceramisol glycerin was used. The alumina powder used was obtained by pulverizing a commercially available product using a zirconia ball mill.

Table 2 also shows the density ratio of the core material of the ceramic heater 10 obtained by firing, the average particle size of the microcrystalline particles, and the bending strength of the ceramic heater. Further, FIGS. 6A and 6B show scanning electron microscope (SEM) photographs after the core material of the ceramic heater according to Example 1 was cut with a cutter and etched. In FIG. 6, (a) is a 2000-fold SE.
It is an M photograph and (b) is a 3000 times SEM photograph.

[0044]

[Table 1]

[0045]

[Table 2]

As is clear from the results shown in Table 2 above, in the ceramic heaters according to Examples 1 and 2, the density ratio of the substrate made of alumina was 95% or more, and the particles constituting the substrate were: Particles 5 to 40 having an average particle size of 5 to 45 μm
% By weight and 60 to 95% by weight of particles having an average particle size of 0.5 to 5 μm, and a bending strength of 180 to 200 N
On the other hand, in the ceramic heater according to Comparative Example 1, the particle size distribution was out of this range, and the bending strength was as small as 145N. In addition, about the basic performance of the ceramic heater according to the example and the comparative example,
There was no problem.

[0047]

Since the ceramic heater of the present invention is configured as described above, it naturally has excellent functional characteristics such as reaching a target temperature in a short time and having excellent durability. Excellent in mechanical properties such as bending strength.

[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 cross-sectional view taken along line AA.

FIG. 2A is a cross-sectional view schematically showing one step in the method for manufacturing a ceramic heater of the present invention,
(B) is a front view.

FIG. 3A is a cross-sectional view schematically showing one step in a method for manufacturing a ceramic heater according to the present invention;
(B) is a front view.

FIG. 4A is a cross-sectional view schematically showing one step in a method for manufacturing a ceramic heater according to the present invention;
(B) is a front view.

FIG. 5A is a cross-sectional view schematically showing one step in a method for manufacturing a ceramic heater of the present invention,
(B) is a front view.

FIGS. 6A and 6B are SEM photographs of a core material of the ceramic heater according to Example 1. FIG.

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 10 Ceramic heater 11 Core material 12 Insulating layer 13 Resistance heating element 14 Terminal 15 Notch 16 Lead wire

Continued on the front page F term (reference) 3K092 PP15 PP16 QA01 QB02 QB03 QB20 QB33 QB45 QB70 QB74 QB76 QC27 QC38 QC62 RA02 RB02 RB05 RB22 VV16 VV31 VV34

Claims (2)

[Claims] 1. In a substrate mainly composed of alumina,
At least one selected from the group consisting of W, Re and Mo
A ceramic heater in which a resistance heating element comprising a seed as a main component and the remainder comprising a ceramic component is embedded, wherein a density ratio of the alumina base material is 95% or more, and particles forming the base material are provided. Has an average particle size of 5 to 45 μ
5 to 40% by weight of particles having an average particle size of 0.5 to 5 μm
A ceramic heater comprising 60 to 95% by weight of particles of 2. The substrate according to claim 1, wherein the base material includes a core material and an insulating layer surrounding the core material, and a resistance heating element is buried between the core material and the insulating layer. Manufacturing method of ceramic heater.