JP2003168546A - Manufacturing method of ceramic heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a ceramic heater that is hardly ruptured and has a long life by forming on a ceramic green sheet a heater resistance body having a smaller rate of shrinkage than the ceramic green sheet and closely contacting and firing around the ceramic shaft. <P>SOLUTION: By forming a heater resistance body having a rate of shrinkage smaller than the ceramic green sheet, the crack once brought about on the heater resistance body is eliminated when it is fired simultaneously, thereby, the durability is improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater for heating an oxygen sensor for automobiles, a soldering iron, a carburetor heater for a petroleum fan heater, an industrial equipment such as a hot water heater, general household use, electronic parts, industrial equipment. TECHNICAL FIELD The present invention relates to a method for manufacturing a ceramic heater used as a heater for various types of heaters.

[0002]

2. Description of the Related Art Conventionally, ceramic heaters having various shapes such as a flat plate, a rod shape, and a tubular shape have been used according to each application. Above all, the rod-shaped heater used in the exhaust gas sensor for automobiles tends to increase in use amount in association with the movement of global environmental protection.

1 to 3 show schematic views of a rod-shaped ceramic heater which has been conventionally used. The ceramic heater is composed of a heating resistor 15 and a ceramic body 1 having the heating resistor 15 built-in, and a metal lead 7 for supplying electric power to the heating resistor 15 inside the ceramic body 1.
Is brazed.

Also, as shown in FIG. 2, the ceramic body 1 has a structure in which a ceramic green sheet 2 having a heating resistor 15 screen-printed on a ceramic shaft 3 is tightly wound around. The heat generating resistor 15 includes a heat generating portion 4 that generates heat when energized and a lead portion 5 for electrically connecting the heat generating portion 4 and the electrode portion 6.

On the ceramic green sheet 2, the heating resistor 15 shown in FIG. 1 and the lead 7 made of metal are formed.
An electrode portion 6 for connecting to and is provided. The electrode portion 6 is electrically connected to the ceramic green sheet 2 by providing a through hole 12 filled with a conductor between the electrode portion 6 and the lead portion 5.

The structure of the electrode portion 6 is shown in FIG. Ni is formed on the surface of the metallization 8 formed on the surface of the ceramic body 1.
The lead wire 7 is plated with Au-Cu, and
It is fixed by brazing with a g-based brazing material. In addition, in order to prevent deterioration of the electrode portion 6 due to temperature and humidity depending on the usage environment of the ceramic heater, N
There is also one in which i plating 11 is applied. The tubular ceramic heater has a structure in which the ceramic shaft 3 of the rod-shaped ceramic heater is hollow.

The respective compositions of the ceramic body 1 and the heating resistor 15 will be described below.
96 wt% of Al ₂ O _3, 3~10 wt% of SiO _2,
0.5-2.5 wt% CaO, 0.2-1.2 wt%
Of MgO, 0.5-2.0 wt% ZrO ₂ ,
The heating resistor 15 contains at least one selected from the group consisting of W, Re, and Mo as a main component, and an organic binder and an appropriately added ceramic component.

[0008]

However, it has been found that there is a variation in the life of the ceramic heater, which is required in the thermal cycle during use, as a characteristic required for the ceramic heater. As one of the causes, when the heating resistor is screen-printed on the above-mentioned ceramic green sheet and bent so that the printed side of the heating resistor becomes convex, a slight crack is generated in the heating resistor. Enters,
It was found that the crack remained until after firing. It is speculated that the resistance of the crack portion increased and the crack portion abnormally generated heat, resulting in disconnection at that portion. As described above, it is presumed that the crack is generated by bending stress or tensile stress due to the handling of the heat-generating resistor which is a generator.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a heating resistor having a smaller shrinkage factor during firing than the ceramic green sheet is formed on a ceramic green sheet, and the ceramic green sheet is placed inside the heating resistor. It is characterized in that it is closely adhered to the ceramic shaft around the circumference and fired.

Further, a resistance heating element is formed on the ceramic green sheet, and after the ceramic green sheet is simultaneously fired in a flat plate shape, the curvature amount of the ceramic green sheet is 10 mm or less with the concave side on the ceramic green sheet side. The feature is that the contraction rate of the sheet and the heating resistor is adjusted.

Further, the shrinkage rate of each of the ceramic green sheet and the heating resistor is adjusted by adjusting the binder amount or particle size of the heating resistor.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic view of a conventionally used rod-shaped ceramic heater. The ceramic heater comprises a heating resistor 15 and a ceramic body 1 having the heating resistor 15 built-in, and a metal lead 7 for supplying electric power to the heating resistor 15 inside the ceramic body 1. It is attached.

Further, as shown in FIG. 2, in the ceramic body 1, the heating resistor 15 is cut after cutting the ceramic green sheet 2 in which the heating resistor 15 is screen-printed on the core material of the ceramic shaft 3 into an appropriate size. The structure is such that the inner side is closely contacted with the circumference, and is co-fired at a temperature of 1500 to 1600 ° C. in a reducing atmosphere to form a rod-shaped ceramic heater. The heat-generating resistor 15 is composed of a heat-generating part 4 that generates heat when energized and a lead-out part 5 for establishing electrical connection between the heat-generating part 4 and the electrode part 6.

On the ceramic green sheet 2, the heating resistor 15 shown in FIG. 1 and the lead 7 made of metal are formed.
An electrode portion 6 for connecting to and is provided. The electrode portion 6 is electrically connected to the ceramic green sheet 2 by providing a through hole 12 filled with a conductor between the electrode portion 6 and the lead portion 5.

The structure of the electrode portion 6 is shown in FIG. A Ni plating 9 having a thickness of 2 to 6 μm is formed on the W metallization 8 formed on the surface of the ceramic body 1, and then Ag, Au, C
The Ni wire lead 7 is brazed using a brazing material made of at least one of u, Ni, and Pd. Then, in order to prevent the deterioration of the electrode portion 6 due to temperature and humidity, etc., Ni plating 11 is further applied onto the brazing material 10, and 600 to 1
Heat treatment is performed in a reducing atmosphere at 000 ° C. to obtain a ceramic heater. The tubular ceramic heater has a structure in which the ceramic shaft 3 of the rod-shaped ceramic heater is hollow.

The present invention is characterized in that the heating resistor 15 having a smaller shrinkage factor during firing is formed on the ceramic green sheet 2.

When the ceramic green sheet 2 on which the heating resistor 15 is formed is handled, if the heating resistor 15 is subjected to bending stress or tensile stress, cracks may occur in the heating resistor 15 because these are molded bodies. . At this time,
When the shrinkage rate of the ceramic green sheet 2 is smaller than the shrinkage rate of the heating resistor 15, the crack grows and the effective width of the heating resistor 15 becomes narrow, and the cracked portion is abnormal when the ceramic heater is heated to a high temperature. It turns out that it will generate heat and break.

On the other hand, by forming the heat generating resistor 15 having a shrinkage rate smaller than that of the ceramic green sheet 2 as in the present invention, a compressive stress acts on the crack portion at the time of shrinkage by firing, whereby Sintering progresses so that the cracks disappear when the heating resistor 15 contracts, and the durability of the ceramic heater improves.

Regarding the difference in shrinkage between the heat generating resistor 15 and the ceramic green sheet 2, the heat generating element 1 should originally be used.
5 and the ceramic green sheet 2 alone should be measured and compared with each other.
Since sintering is promoted by diffusion of grain boundary components from the side,
It is difficult to measure the shrinkage rate by itself. Therefore, in the present invention, the heating resistor 15 is screen-printed on the ceramic green sheet 2 and the amount of bending to the side of the ceramic green sheet 2 after simultaneous firing in the flat plate shape is measured. Here, the amount of bending is preferably 10 mm or less with the ceramic green sheet side being concave. This bending amount is 10
If it exceeds mm, the contact portion is peeled off due to the difference in contraction between the two, and the heating resistor 15 abnormally generates heat during the temperature rise, or the heating resistor 15 is oxidized, which is not preferable.

As a means for forming the heating resistor 15 having a shrinkage rate smaller than that of the ceramic green sheet 2, there is a method of increasing the shrinkage rate of the ceramic green sheet 2. Specifically, the ceramic green sheet 2
There are means such as reducing the particle size of the raw material for forming, or increasing the type and molecular weight of the organic binder, increasing the amount of the organic binder, and the like.

Next, there is a method of reducing the shrinkage ratio of the heating resistor 15. Specifically, contrary to the above-mentioned ceramic green sheet 2, the particle size of the metal powder that is the raw material for forming the heating resistor 15 is increased, or the type and molecular weight of the organic binder is decreased, and the amount of the organic binder is increased. There are measures such as reducing. By combining these, it becomes possible to form the heating resistor 15 having a smaller shrinkage than the ceramic green sheet 2 of the present invention.

Now, the process of producing the ceramic green sheet 2 will be described. As a raw material, for example, A
l ₂ O ₃ 91% by weight, SiO ₂ 6% by weight, CaO 1.2% by weight, MgO 0.8% by weight, ZrO ₂ 1% by weight were prepared as a ceramic powder, and further an organic binder and an organic solvent were appropriately mixed. To form a slurry, which is formed into a sheet by the doctor blade method.

The ceramic shaft 3 can be manufactured by using a ceramic powder having the same composition as the ceramic green sheet 2 to adjust the binder and water content, and then extruding. Regarding the composition of the ceramic shaft 3, the ceramic green sheet 2
It is not necessary to limit the composition to the same as the ceramic green sheet 2, and the firing shrinkage rate may be set to a value smaller than that of the heating resistor 15 so that the compressive stress acts on the heating resistor 15. .

Next, as the material of the heating resistor 15 built in the ceramic heater, at least one metal powder of W, Mo and Re, an organic binder, and a ceramic powder having the same composition as the green sheet 2 are appropriately used. It is a mixture. At this time, if the material used for the heating resistor 15 is an alloy composition such as W-Re or W-Mo having a small temperature coefficient of resistance, and the material of the lead portion 5 is W having a large temperature coefficient of resistance, the voltage is applied to the ceramic heater. When the inrush current at the time of applying the heat is reduced and the temperature of the heat generating portion 4 is increased, the resistance value of the heated lead portion 5 is increased, and the amount of current supplied to the heat generating portion 4 is decreased to limit the temperature rise. Come to do.

[0026]

EXAMPLES Next, examples of the present invention will be shown.

Example 1 Here, a ceramic green sheet 2 and a heating resistor 1 were used.
Adjusting the shrinkage rate during firing of No. 5, the cracks intentionally generated during raw processing remain after firing under any conditions,
The durability test evaluated under what conditions it disappeared.

As shown in FIGS. 1 to ₃ , 92% by weight of Al ₂ O ₃ and 4.5% by weight of SiO ₂ containing Al ₂ O ₃ as a main component.
₂ , 1.5% by weight CaO, 1.5% by weight MgO,
The ceramic green sheet 2 was prepared by the doctor blade method after adjusting to have a composition of 0.5% by weight of ZrO ₂ and adding an organic solvent such as an organic binder to form a slurry. On this surface, the heat generating part 4 made of W-Re
The lead portion 5 was printed to form the heating resistor 15, and W metallization 8 was screen-printed on the back surface to form the electrode portion 6. Then, a through hole 12 was formed at the end of the lead portion 5 made of W, and the paste was injected into the through hole 12 to establish electrical continuity of the electrode portion 6.

Next, a ceramic shaft 3 was produced by adjusting the same material as that of the ceramic sheet 2 and forming a slurry to which an organic solvent such as a molding binder was added, followed by extrusion molding and press molding. After that, the ceramic sheet 2 is cut into a predetermined size, an adhesive containing an organic solvent as a main component is applied to the cut ceramic sheet 2, and the ceramic shaft 3 is circulated and closely adhered to be integrated to 1500 ° C. to 1650 ° C.
The furnace was placed in a reducing atmosphere furnace at 0 ° C. to obtain a sintered ceramic body 1. In order to braze the metal lead 7 to the electrode portion 6, a tunnel type furnace in an ammonia decomposition gas atmosphere was used, and pure Ag was used as a brazing material.

In order to quantify the difference between the shrinkage rate of the ceramic green sheet 2 and the shrinkage rate of the heating resistor 15, the heating resistor 15 is screen-printed on the ceramic green sheet 2 and simultaneously fired as a flat plate. The amount of bending toward the sheet 2 side was measured. This time, the binder amount for the ceramic green sheet 2 and the ceramic shaft 3 was changed into two levels of 8% by weight and 12% by weight in terms of solid content, and the average particle diameter of W of the paste for the heating resistor 15 was set to 0. 5 μm, 1.2 μm, 2.3 μm, 3.2 μm and 4
Eight types of combinations were prepared by using the ones whose levels were changed.

The method of measuring the bending amount is as shown in FIG. 4 (a): length 25 mm, width 50 mm, thickness 0.30 to 0.35 mm.
On the ceramic green sheet 2 of FIG.
After screen-printing with a thickness of 7 μm, and then simultaneously firing with the flat plate-shaped surface on which the heating resistor 15 is formed, the ceramic green sheet 2 side as shown in FIGS. The portion with the largest amount of bending was measured.

Further, when the heating resistor 15 is curved, the amount is indicated by- (minus). This allows
The difference in shrinkage between the ceramics and the heating resistor 15 was quantified.

Also, a sample was prepared by using the one in which the heating resistor 15 was screen-printed on the ceramic green sheet 2 and then intentionally bent so that the heating resistor 15 side was convex so as to be convex by handling. . In addition, as an evaluation method, a voltage was applied so that the maximum heat-generating portion of each of the eight kinds of samples was 1200 ° C., and then the change of the resistance value between the two electrode portions 6 of the ceramic heater was changed with the passage of time. The number of occurrence of disconnection was measured and compared.

[0034]

[Table 1]

As can be seen from the results shown in Table 1, there is a correlation between the amount of bending and the number of wire breaks, and No. 1 showing a curve in which the heating resistor 15 side is concave. 1, 2 and N without curvature
o. In No. 3, disconnection occurred. In addition, in the case of No. 3 in which the amount of curvature in which the heating resistor 15 side is convex exceeds 10 mm. In No. 8, one wire breakage occurred within 50 hours. On the other hand, the shrinkage factor of the heating resistor 15 is smaller than that of the ceramic green sheet 2, that is, the ceramic green sheet 2 shrinks more and compressive stress is generated in the heating resistor 15 during sintering.
No breakage occurred in Nos. 4 to 7 and good durability was exhibited. No. with a bending amount exceeding 10 mm It was estimated that in No. 8, the adhered portion was peeled off due to the difference in shrinkage between the ceramic green sheet 2 and the heating resistor 15, so that the one with short durability was generated.

[0036]

As described above, according to the ceramic heater of the present invention, a heating resistor having a shrinkage rate smaller than that of the ceramic green sheet is formed on the ceramic green sheet, and the ceramic resistor is closely wound around the ceramic shaft and fired to break the wire. It is possible to obtain a ceramic heater that is difficult to perform and has a good life.

[Brief description of drawings]

FIG. 1 is a perspective view of a ceramic heater of the present invention.

FIG. 2 is a development view of the ceramic heater of the present invention.

FIG. 3 is an enlarged view taken along line ZZ of FIG.

FIG. 4A is a perspective view of a ceramic green sheet on which a heating resistor is formed for measuring the amount of bending, FIG. 4B is a perspective view after firing, and FIG. It is a figure.

[Explanation of symbols]

1: Ceramic body 2: Ceramic green sheet 3: Ceramic shaft 4: Heat generating part 5: Drawer 6: Electrode part 7: Lead wire 8: W metallization 9, 11: Ni plating 10: brazing material 12: Through hole (via hole) 15: Heating resistor

Claims (3)

[Claims] 1. A heating resistor having a shrinkage factor smaller than that of the ceramic green sheet when fired is formed on the ceramic green sheet, and the ceramic green sheet is lapped and closely adhered to a ceramic shaft with the heating resistor inside and is fired. A method of manufacturing a ceramic heater, comprising: 2. A ceramic green sheet is formed so that a resistance heating element is formed on the ceramic green sheet and the flatness of the ceramic green sheet is simultaneously fired so that the amount of curvature of the ceramic green sheet is 10 mm or less with the concave side on the ceramic green sheet side. The method for manufacturing a ceramic heater according to claim 1, wherein the shrinkage rates of the sheet and the heating resistor are adjusted. 3. The method for producing a ceramic heater according to claim 1, wherein the shrinkage ratio of each of the ceramic green sheet and the heating resistor is adjusted by adjusting the binder amount or particle size of the heating resistor.