JPS6019633B2 - Ceramic heater manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ceramic heater in which a resistance circuit is formed on the surface or inner surface of a ceramic.

A resistive coating is provided on a ceramic substrate using a thick film method, etc.
There is a ceramic heater that generates heat by passing electricity through the resistive coating.

In these conventional ceramic heaters, the resistor changes over time due to the influence of moisture and oxygen, and the resistance value increases, so when intended for high temperature applications, there was a problem with reliability, which was an impediment to practical use. For this reason, as a method to avoid these problems, coating with heat-resistant resin and enameling have been attempted, but sufficient results have not been obtained. Furthermore, in order to solve these problems, ceramic heaters are commercially available which are coated with a paste made of the same type of ceramic as the ceramic substrate as a protective coating material and are co-fired with the substrate to improve heat resistance.

This ceramic heater has considerably improved heat resistance compared to ceramic heaters coated with heat-resistant resin or enameled. However, according to the experiments conducted by the present inventors, unlike the expected situation, the resistance value of these ceramic heaters gradually increases when voltage is applied continuously for a long time, and the resistance value decreases after about 300 hours of energization. is 2.5%
An unexpected result was confirmed:

That is, a heating resistor circuit made of tungsten resistor paste having a resistance value of 70 is formed on an uncondensed ceramic substrate with a substrate thickness of 1 bar and an alumina purity of 93% after firing, and a heat generating resistor circuit made of a tungsten resistor paste having a resistance value of 70%. After coating the ceramic heater with alumina insulation paste to a thickness of 100 mounds, a 20V DC power supply was connected to the ceramic heater 01, which was formed in a slightly reducing atmosphere, and a continuous current conduction experiment was conducted. The value is 2.0-2.5% in 200 hours, 300
It was confirmed that the deterioration phenomenon increased by 2.5 to 3.5% at 0 hours. The cause of the deterioration caused by such continuous energization is unknown, but according to the research of the present inventors, the tungsten-aged bodies are coarse and have many voids, so it is possible that localized heat generation due to tungsten result. It is thought that part of the tungsten metal was oxidized, causing an increase in resistance. On the other hand, ceramic heaters are characterized by completely embedding and embedding the heating resistor circuit in ceramic to prevent oxidation of the heating resistor and extend the heater's lifespan semi-permanently. This poses a major practical obstacle.

Furthermore, since the heating resistor circuit is completely enclosed in ceramic, it is said that it is almost impossible to adjust the resistance value. However, as a recent quality issue with electric heating products, it is often required that the resistance value variation of the heating resistor be kept within 10%, so the increase in the resistance Z value due to current deterioration of these ceramic heaters is not practical. This is a phenomenon that must be resolved.

According to research conducted by the present inventors, such current deterioration phenomena of ceramic heaters depend on the sintering state of the heating resistor, and the lower the density of the sintered resistor, the greater the two tendencies become.

The present invention has been made in view of this situation, and an object of the present invention is to provide a high-temperature ceramic heater with excellent life characteristics that does not cause resistance value deterioration due to continuous energization.
2 In other words, as a result of our research into the causes of resistance value deterioration in these ceramic heaters, we found that resistance value deterioration greatly affects the fiber density of the resistor after sintering, and by improving this. We have invented three manufacturing methods for ceramic heaters that hardly cause resistance deterioration.

The present invention involves mixing high melting point metal powder, ceramic raw material powder, binder, and solvent on a ceramic substrate, then making a paste, drying, and powdering, and then adding a solvent to the powder and mixing again. Repeat the steps of base formation, drying, and powderization several times in the same manner as in step 3, and after the high melting point metal powder, ceramic raw material powder, and binder are uniformly dispersed, a solvent with excellent printability is mixed. The present invention relates to a method for producing a ceramic heater, which comprises applying a resistive paste, then printing an insulating paste on the top surface of the resistor paste, or laminating and pressing four unsealed ceramic sheets, and then firing.

In the present invention, the ceramic substrate includes, for example, a metal oxide mainly composed of alumina, beryllia, magnesia silica, etc., a sintering aid such as calcia, magnesia, silica, etc.
A pre-fired ceramic made by mixing a binder, a solvent, a plasticizer, etc. as necessary, forming a mixture into a sheet by extrusion, rolling, casting, pressing, etc., and processing it into a predetermined shape. A substrate or a brazed ceramic obtained by firing and sintering this substrate once can be used, and there are no particular restrictions. Next, in the resistance paste used in the present invention, tungsten, molybdenum, platinum, or a mixture thereof can be used as long as the high melting point metal powder has a firing property and can be bonded to the ceramic substrate after firing. Generally, the main ingredients of the raw material powder are alumina and an alumina cohesive agent, but as long as they have agglomeration properties, berylia, other metal oxides, or mixtures thereof may be used without any particular restrictions. .

Further, in the present invention, the blending ratio of the high melting point metal powder and the ceramic raw material powder is determined depending on the required resistance value and is not particularly limited. Binders include cellulose resins such as ethyl cellulose and nitrocellulose, acrylic resins such as polymethyl methacrylate, alkyd phenol resins, vinyl resins, epoxy resins, etc., which can easily undergo thermal decomposition in the firing atmosphere. There are no particular restrictions.

The solvent used for pasting will vary depending on the type of binder, as long as it dissolves the binder.If the binder is ethyl cellulose, it may be an aromatic solvent such as toluene or xylene, or an ester-based solvent such as acetate. The solvent may be a ketone solvent such as methyl ethyl ketone, or a mixed solvent thereof. When using other binders in the same machine, any solvent that is normally used for each binder can be used, and there are no particular limitations. Furthermore, carbitol acetate, terpineol, etc. are usually used as solvents with excellent printability, and there are no particular limitations as long as they have printability.

In addition to the above, a plasticizer, a surfactant, etc. may be added to the resistance paste used in the present invention, if necessary. There are no particular restrictions on the firing atmosphere, such as an oxidizing atmosphere or a weakly reducing atmosphere, so it may be selected depending on the type of high melting point metal powder used as the sintered resistor. The aging of the ceramic resistor is carried out by firing the resistive paste printed on the substrate and the insulating paste or the formed ceramic formed on the upper surface of the resistive paste together with the ceramic substrate in the above atmosphere.

The present invention will be explained below with reference to Examples.

Example 1 Parts by weight of tungsten metal powder with an average particle size of 1 and 5 parts by weight
4 parts by weight of silica, 1 part by weight of calcia, 2 parts by weight of magnesia in 9 parts by weight of alumina powder, of which 0% or more has a particle size of 3 to 5 degrees.
10 parts by weight of ceramic raw material powder mixed with parts by weight were uniformly mixed.

Next, add 5 parts by weight of ethyl cellulose as a binder to the mixed powder-10 and 5 parts by weight of phthalate plasticizer Blood○P.
Mixed solvent 3 containing 2 parts by weight of (dioctyl phthalate) and a 1:1 ratio of ethyl acetate and ethyl alcohol.
The mixture was put into a sugar crusher along with parts by weight of the mixture, and mixed into a paste to form a paste.Furthermore, the mixture was continued to gradually remove the solvent, and the mixture was dried and solidified to form a powder. Next, the same mixed solvent as used above was newly added to the powder, and the same process was performed. The above mixing, pasting, drying, and powdering were repeated 5 times in a tungsten metal powder,
Ceramic raw material powder and ethyl cellulose were uniformly dispersed, and then part by weight of carbitol acetate 3, which has excellent printability, was added to the powder and mixed to obtain resistance paste A. Example 2 Tungsten metal powder 8 same as that used in Example 1
Resistance paste B
I got it.

Comparative Example 1 Tungsten metal powder 9 same as that used in Example 1
1Q parts by weight of ceramic raw material powder were uniformly mixed with parts by weight of ceramic raw material powder, and the binder, plasticizer, and solvent were mixed into a paste in the same mixing ratio as in Example 1, taking care not to dry the binder, plasticizer, and solvent in a distiller ( (The process was stopped before the drying step) to obtain a resistance paste C.

Comparative Example 2 Parts by weight of ceramic raw material powder 2 were uniformly mixed with parts by weight of the same tungsten metal powder 8 used in Example 1, and the same steps as in Comparative Example 1 were carried out to obtain resistance paste D. .

Next, the resistance pastes A, B, C, and D obtained by the above method and each reference example of Examples and Comparative Examples (ceramic raw material powder was not mixed, and the other steps were the same as those of Examples and Comparative Examples were carried out. The resistor paste produced as a sample was screen printed onto an alumina ceramic green sheet substrate containing a mixture of magnesia, calcia and silica so that the alumina purity after firing was 96%, and the electrode terminal portions of the printed substrate were further removed. A ceramic insulating paste made of the same material as the printed circuit board was applied to the entire surface of the printed circuit board and heated at 80°C for 20 minutes.
Dry for a minute.

Next, the printed circuit board was heated to 1,500 oo in a slightly reducing atmosphere, and the alumina ceramic green sheet, resistance paste, and insulation paste were co-fired to manufacture a ceramic heater. The electrode terminal portion of the ceramic heater obtained by the above method is plated with nickel to a thickness of 3 mm by an electroless method, and a Kovar wire is silver-brazed to the terminal portion to be plated, and a Kovar lead wire is attached to the ceramic heater. A continuous current deterioration test was conducted by connecting a 20V DC power supply through the battery. The results are shown in Table 1. Table 1 As can be seen from Table 1, when manufacturing a ceramic heater using a resistance paste mainly composed of high-melting point metal powder, resistance pastes C and D, which are manufactured by a conventionally commonly used method, are used. Ceramic heaters manufactured using ceramic heaters have a coarse sintered resistor with many defects such as voids, so when the sintered resistor generates heat due to electricity, the resistor deteriorates due to oxidation etc. even in a relatively short period of time, resulting in an increase in resistance value. do.

Claims (1)

[Claims] 1. Mix high melting point metal powder, ceramic raw material powder, binder and solvent on a ceramic substrate, then paste it,
Dry, powder, and then add a solvent to the powder and mix again. Repeat the process of pasting, drying, and powder several times in the same way as before to obtain high melting point metal powder, ceramic raw material powder, and bonding. After the agent is uniformly dispersed, a resistive paste made by mixing a solvent with excellent printability is applied, and then an insulating paste is printed on the top surface or an unsintered ceramic sheet is laminated and pressure-bonded, and then fired. A method for manufacturing a ceramic heater characterized by: