JP2000021555A - Ceramic heater and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Problem] To manufacture a ceramic heater 1 excellent in durability and temperature rising performance at a low cost even when a drawer portion 5 is formed by a printing method. A drawer (5) in a ceramic heater (1).
Has a thickness of 50 μm or more, and has a two-layer structure of a dense layer and a porous layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel vaporization and ignition heater for glow plugs and oil fan heaters for internal combustion engines,
The present invention relates to a high-temperature ceramic heater suitable for a heater for various sensors or a heater for household use, electronic parts, industrial equipment, and the like.

[0002]

2. Description of the Related Art Conventionally, as a heater for various kinds of ignition and various kinds of heating, such as a glow plug, used for accelerating the start of a diesel engine, a heating resistor made of a high melting point metal wire or the like in a heat-resistant metal sheath. Various sheathed heaters with buried bodies and various ignition devices using spark discharge have been frequently used.However, rapid heating is difficult and wear resistance and durability are inferior. However, there are drawbacks such as lack of reliability in terms of reliable ignition, such as easy occurrence of radio interference.

[0003] Therefore, as a highly reliable ceramic heater having excellent heat transfer efficiency, rapid temperature rise, no radio wave interference, reliable ignition, high safety and excellent wear resistance, ceramic firing High melting point metal and its compound,
And a ceramic heater in which a heating resistor made of various inorganic conductive materials containing them as a main component is joined or embedded.
It has been widely used as a heater for various kinds of heating including glow plugs of internal combustion engines.

In general, as a ceramic heating element, a ceramic heater having a high-melting-point metal heating element on the surface or inside of an alumina ceramic is known. Alumina used as an electrical insulating material has impact resistance and high-temperature strength. As a result, non-oxide ceramics, especially silicon nitride ceramics, which have excellent heat resistance, high temperature strength, small heat capacity, and good electrical insulation, have been studied, and high melting point metals such as tungsten and molybdenum have been studied. Alternatively, a combination with a heating resistor mainly containing a compound of a high melting point metal such as tungsten carbide, molybdenum silicide, titanium nitride or the like is widely used as a ceramic heating element for high temperature.

[0005]

In order to use a ceramic heating element for high temperature, it is necessary to reduce the resistance of the heating section in order to increase the amount of heat generated. Accordingly,
The drawer section for supplying electricity to the heat generating section also needs to be 1 ohm or less to prevent the heat generation. Therefore, at present, a tungsten wire or the like is generally used for the structure of the lead portion. However, this method has problems that the firing method is limited to hot pressing and that the production cost is high.

Therefore, it is conceivable to form the drawer portion by a printing method. However, in order to form the drawer portion by the printing method, the thickness of the drawer portion is preferably 50 μm to reduce the resistance.
There is a problem that cracks occur during firing at such a film thickness.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to improve reliability by forming at least two layers in the drawer section by the same printing method as that of the heating section, and to shorten the manufacturing process to reduce the cost. It is an object of the present invention to provide a highly reliable heater that can be fired in an atmosphere that can be mass-produced.

[0008]

[Means for Solving the Problems]
Is used to join various types of heating elements made of high-melting point metals, carbides and nitrides, which generate heat when energized, and inorganic conductive materials containing them as a main component, to silicon nitride sintered bodies as insulating members. In the ceramic heater in which the heating resistor and the drawer are integrated by being buried, the thickness of the drawer is set to 50 μm or more, and the cross-sectional structure is formed of a dense layer and a porous layer. It is characterized by the following.

In order to aim for a predetermined resistance value, the thickness of the lead portion formed by the printing method needs to be 50 μm or more. In particular, for low-resistance elements such as glow plugs, 2
A thickness of at least 00 μm is required. However, it has been difficult to make the film thickness 50 μm or more by the conventional printing method.

On the other hand, the present invention manages the ratio and viscosity of the paste raw material and the organic component, controls the resist thickness at the time of printing, and controls the pressure and temperature pattern at the time of firing, thereby extracting the paste. Cross section of 2
It has a layer structure so that the thickness can be set within the above range.

[0011]

The ceramic heater of the present invention has a draw-out portion structure formed by a printing method, so that the shrinkage during sintering is close to that of the base material silicon nitride, and it has a dense and porous two-layer structure. Since the difference in thermal stress is reduced, a predetermined low resistance can be aimed at without generating a crack, and the rising speed and durability required as a heater can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic heater according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the ceramic heater of the present invention, and FIG. 2 is a longitudinal sectional view of a main part of the ceramic heater shown in FIG.

1 and 2, reference numeral 1 denotes a heating element 2 made of an inorganic conductive material, a lead section 5, and an electrode take-out section 6.
And a ceramic heater comprising a silicon nitride sintered body 3 as an insulating member.

A ceramic heater 1 has a heating resistor 2 made of a layered inorganic conductive material having a U-shaped cross section when viewed in a plan view, and one end of a silicon nitride sintered body 3 as an insulating member. A layer-shaped second lead portion 4 at least partially overlapped with each end of the heating resistor 2 and a lead portion 5 connected to the second lead portion 4 are further connected.
An electrode extraction portion 6 is provided so as to be exposed on the other end side of the silicon nitride sintered body 3 so as to be exposed on the outer peripheral surface of the other end of the silicon nitride sintered body 3. It is arranged in the unit 3. In addition, the tip of the insulating portion on the side of the heating resistor 2 has a substantially spherical shape, and at least a portion corresponding to the highest heat generating portion has a circular cross section in a rod shape.

In the ceramic heater 1 of the present invention, the silicon nitride sintered body 3, which is a material of the insulating portion, is formed by adding silicon nitride powder to silicon nitride powder.
As a sintering aid, an oxide of an element of Group 3a of the periodic table, such as yttrium, is added. From the viewpoint of suppressing ion transfer at a high temperature, Er ₂ O ₃ ,
Yb ₂ O ₃ and Lu ₂ O ₃ are most desirable. In addition, by adding one or more silicides, carbides, and nitrides such as molybdenum and tungsten having a larger thermal expansion coefficient to the silicon nitride-based sintered body, the difference in the coefficient of thermal expansion from the heating element can be reduced. Is also effective.

The heating resistor 2 includes a high melting point metal such as tungsten, molybdenum and rhenium and alloys thereof, and a Group 4a group represented by tungsten carbide, molybdenum silicide, titanium nitride, zirconium boride and the like. , Group 5a, and Group 6a elemental metals or a resistor made of an inorganic conductive material containing carbides, silicides, nitrides, and borides as main components. In view of the high-temperature durability of the heating resistor 2, The most suitable is tungsten carbide and tungsten.

The thickness of the layered heating resistor 2 is as follows:
From the viewpoint of preventing the generation of cracks or the like in the heating resistor layer, when various resistance values are set for a DC power supply of up to about 50 V, at least the highest heating portion desirably has a range of 5 to 150 microns, and particularly preferably 10 to 150 μm. The range of ５０50 microns is optimal.

On the other hand, the lead portion 5 and the second lead portion 4 are made of the same high melting point metal as the heating resistor 2, an alloy thereof, a Group 4a, 5a, 6a metal or a carbide thereof. Inorganic conductive materials containing silicide, nitride, and boride as main components are exemplified. Its conduction resistance must be lower than that of the heating element resistor 2. In particular, 85 to 98% by weight of tungsten is added with 2 to 15% by weight of silicon nitride containing a sintering aid as a base material. It is preferable to use those prepared by

The drawer 5 and the second drawer 4 are formed so as to overlap at least a part of the end of the heating resistor 2. Since these heater circuits are printed on the green sheet and then wound around a rod of the same material as the green sheet to form a product, the heater circuit has a structure in which the distance from the surface of the insulating portion is substantially on the same circumference. It has a structure that can reduce thermal stress.

It is a necessary condition that the thickness of the layered lead portion 5 is 50 μm or more in order to achieve a desired low resistance.

Further, the durability of the drawer 5 is improved,
In order to reduce the resistance, the cross-sectional structure is a two-layer structure. In other words, from the viewpoint of durability, by making the outer surface of the cross section have a porous structure, thermal stress is relaxed during high-temperature durability, which leads to prevention of cracks in the heating element. On the other hand, in order to aim for a low resistance, it is effective to make it denser.

Therefore, in order to satisfy both characteristics, as shown in FIG. 3, it is necessary to form the lead portion 5 into a two-layer structure, that is, to form the outer surface with the porous layer 8 and the inner surface with the dense layer 9. The present inventors have found that it is effective. As for the optimum thickness of each layer, it is desirable that the thickness of the porous layer 8 occupies 50% or more of the entire thickness of the lead portion 5.

The porous layer 8 has a structure formed when the metal powder and the sintering aid are sintered, and the dense layer 9 is completely metallized after sintering and has almost no pores. It means close to the state. These structures can be confirmed by observing the cross section with an electron microscope or the like.

Such a two-layer structure can be formed by controlling the firing conditions as described above. That is, after a heating resistor made of an inorganic conductive material and a lead portion are formed on a ceramic molded body containing silicon nitride as a main component by a printing method, the heating resistor is heated at 1600 to 1850 ° C. in a nitrogen atmosphere.
By firing in a gas pressure of up to 80 atm, it is possible to obtain the ceramic heater 1 having the above-described two-layered lead portion 5.

The electrode lead-out portion 6 may be made of the same material as the lead-out portion 5 and can be suitably used without any problem as long as its conduction resistance is the same as that of the lead-out portion 5. It is desirable that the electrode take-out portion 6 is formed in one or more layers.
The number of the heating resistor layers may be smaller than that of the heating resistor layers by being electrically connected through through holes or the like provided in the silicon nitride sintered body 3. The shape of the electrode take-out portion 6 may be not only rectangular but also comb-like, and the shape is not limited at all.

Further, the tip shape of the ceramic heater 1 in which the heating resistor 2 is present is substantially spherical, and the cross-sectional shape of at least the portion in which the heating resistor 2 is present is circular. The purpose is to effectively and uniformly generate heat at the outer periphery thereof, but the shape is not limited at all if the object is achieved.

[0028]

EXAMPLE Next, in evaluating the ceramic heater of the present invention, a silicon nitride raw material containing a predetermined sintering aid was prepared, and the raw material was used as a base material, and toluene was used as a binder and a solvent for the base material. Was mixed by a ball mill for a predetermined time, and a green sheet was produced by a doctor blade method using the slurry.

The paste for the heat generating resistor was prepared by adding a binder and a solvent to a mixed powder containing 90% by weight of tungsten carbide and 10% by weight of silicon nitride containing a sintering aid. Paste for drawer is Tungsten 90
A mixture prepared by adding a binder and a solvent to a mixed powder body containing 10% by weight of silicon nitride containing 5% by weight and a sintering aid was used.

Using the paste for forming a heating resistor, a substantially U-shaped pattern is formed by screen printing at a position where the entire pattern is within 5 mm from the end of the insulating portion after sintering. The heating resistor 2 of 20 microns is formed.

Then, the above-mentioned pattern is formed in a predetermined shape by a screen printing method using the paste for the drawer so as to partially overlap both ends of the substantially U-shaped pattern. A lead portion 5 of about 200 microns is formed.

On the other hand, a predetermined pattern is formed on the back surface of the green sheet by the same screen printing method as described above, using the paste for forming the electrode take-out portion having the same composition as the paste for forming the lead-out portion, thereby forming the electrode take-out portion 6. did.

The sheet on which the heater circuit is printed is cut into a predetermined shape, and a core material manufactured by extrusion using a material having the same composition as the sheet is formed using a material having the same composition as the sheet. A rod-shaped heater was manufactured by joining with the manufactured contact liquid.

The rod-shaped heater is set in a nitrogen pressurized atmosphere at a pressure of 5 to 30 atm and a second pattern of 50 to 30 atm.
It baked at 1600-1850 degreeC at 80 atm.

After a nickel coating is formed on the exposed surface of the electrode take-out portion 6 of the obtained ceramic heater 1 by a metallizing method, a plating method, or the like, the cathode heater is electrically connected to each of the electrode take-out portions 6. Then, an electrode fitting for an anode was joined with a silver braze to produce a ceramic heater 1 for evaluation.

Next, the heating performance of the heater was confirmed. A DC voltage of 11 V was applied to the heater, and the time required to reach 800 ° C., which is one of the evaluation items of the glow plug of the internal combustion engine, was measured.

In addition, a high-load durability test in which a DC voltage of 10 to 35 V at which the ceramic heater for evaluation saturates at a heating temperature of 1400 ° C. is continuously conducted, and the resistance value between the two electrodes is measured at regular intervals. If the rate of change with respect to the resistance value before the start of the test exceeds 10%, it is determined to be defective, and when the rate of change exceeds 10%, 850 hours, which is one index for evaluating the durability of the glow plug of the internal combustion engine, is used as the durability time. The durability was evaluated as a standard.

The results are shown in Table 1. As is clear from the results, it is understood that the thickness of the porous layer 8 and the dense layer 9 of the lead portion 5 can be adjusted by controlling the pressure at the time of firing. Further, even when the lead portion 5 is formed by a printing method, the embodiment of the present invention in which the porous layer 8 and the dense layer 9 have the two-layer structure has the same or better durability than the conventional tungsten wire. It was confirmed that the properties and the temperature rise characteristics were obtained.

[0039]

[Table 1]

[0040]

As described above, according to the present invention, the thickness of the drawer portion of the ceramic heater is set to 50 μm or more, and the cross-sectional structure of the ceramic heater is a two-layer structure of a dense layer and a porous layer. However, a ceramic heater excellent in durability and temperature raising performance can be manufactured at low cost.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along line XX in FIG.

FIG. 3 is an enlarged sectional view of a drawer portion in the ceramic heater of the present invention.

[Explanation of symbols]

 1: Ceramic heater 2: Heating resistor 3: Silicon nitride sintered body 4: Second lead-out part 5: Lead-out part 6: Electrode take-out part 8: Porous layer 9: Dense layer

Claims (2)

[Claims] 1. A ceramic heater comprising a silicon nitride sintered body, a heating resistor made of an inorganic conductive material that generates heat when energized, and a lead portion, wherein the lead portion has a thickness of 5 mm.
0 μm or more, and the cross-sectional structure of the dense layer and the porous layer
A ceramic heater comprising a layer. 2. A heating resistor made of an inorganic conductive material and a lead portion are formed on a ceramic molded body containing silicon nitride as a main component by a printing method, and then heated to a temperature of 1600 to 1850 ° C. and a nitrogen atmosphere of 3 to 80 atm. A method for manufacturing a ceramic heater, comprising firing in a gas pressure.