JPS58151383A - Heater coating agent composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition of a coating agent applied to insulate or strengthen a heater used to heat various elements such as a gas detection element or a humidity detection element made of a metal oxide semiconductor. relating to things.

Conventionally, one or two metal oxides such as indium, chromium, magnesium, zirconium, iron, tin, palladium, etc.
BACKGROUND ART A metal oxide semiconductor, which is a hybrid of more than one species, is used to detect flammable gas, moisture, smoke, etc. by utilizing the electrical characteristics of the element. For example, magnesium oxide
A metal oxide semiconductor element made of M9Cr204 as a main component by mixing and firing chromium oxide and zirconium oxide has the property that its electrical resistance changes when it comes into contact with alcohol gas under heating at a constant temperature. It is useful as an alcohol gas detection element.

In this case, if a cylindrical element is inserted into a heater consisting of a spirally wound nichrome wire and a hardened coating applied to the nichrome wire, the temperature of the element can be increased. It was confirmed that despite the conditions of the same temperature and the same concentration of alcohol gas, the resistance value varied greatly depending on the presence or absence of alcohol gas, making it impossible to detect with high reliability. As a result of measuring and analyzing from various angles, we were able to find out that the cause of this was the phosphorus component contained in the coating agent composition.

That is, when an element that should not contain phosphorus was brought into contact with alcohol gas and analyzed as a sample, phosphorus was detected in this element, and it was confirmed through experiments that this phosphorus inhibits changes in resistance. The phosphorus contained in this element is the phosphorus component contained in the coating of the heated heater that evaporates and adheres thereto.

However, the present invention provides a coating agent composition for a heater that solves these problems. The present invention provides a coating agent composition for a heater for heating a metal oxide semiconductor element, characterized in that it contains no phosphorus component.

This invention will be explained in detail below.

The heater coating composition according to the present invention is composed of silicon oxide or aluminum oxide, which constitutes the insulating material group, alone or in combination. The silicon oxide and aluminum oxide have the role of blocking the interlayer current flow of the nichrome wire constituting the spiral and ensuring the amount of heat generated, and therefore, appropriate amounts are required in view of the composition of the composition. If it is too small, interlayer current flow will occur and the amount of heat generated by the heater will decrease; if it is too large, the amount of heat generated will increase, but on the other hand, the strength of the adhesion to the nichrome wire will decrease, resulting in a decrease in strength. This adhesive strength is ensured by sodium silicate. Therefore, the appropriate amounts of sodium silicate, which acts as a binder, and silicon oxide or (and) aluminum oxide, which acts as an insulating agent, are 50% to 80% by weight.
% silicon oxide or (and) aluminum oxide is 20%
~50% is appropriate. It must not contain phosphoric acid, which acts as a binder for the inorganic coating agent. In other words, if phosphoric acid is included, as mentioned above, for example, a coating layer that covers a nichrome wire will contain a phosphorus component, and due to the calorific value of the nichrome wire, phosphorus volatilized from this phosphorus component will adhere to the element and exhibit a predetermined change in resistance value. Because it will disappear.

Regarding silicon oxide, the same effect can be obtained even if a part of the silicon oxide is replaced with saponified chromium.

In this case, the total amount of silicon oxide and saponified chromium is suitably 20% to 50% based on the weight of the entire composition and 10% to 30% relative to silicon oxide. The purpose of adding this chromium oxide is to prevent the coating layer from peeling off from the nichrome wire due to expansion and contraction of the coating layer caused by the heat generated by the nichrome wire.

Next, to explain the coating method, 5 to 30 parts by weight of water is added to 100 parts by weight of the above composition to form a slurry-like suspension. The heater body obtained by spirally winding is immersed to apply the above composition. Next, after air-drying, the material is cured under high-temperature heating while gradually increasing the temperature to form a heater used for externally heating the device. In this case, the gradual temperature rise is unfavorable in terms of strength and insulating performance since the film formed will blister when heated to a certain temperature.

In other words, the temperature increase rate is 100℃/hr~200℃/hr
When r is appropriate, the maximum temperature is limited to below the deterioration temperature at which the nichrome wire turns black, and this maximum temperature is suitably 450 to 650°C.

The coating agent composition for a heater according to the present invention can be used for a limited time as a coating agent for a heater that externally heats a detection element used to detect, for example, fuel gas, moisture, alcohol gas, etc. contained in the atmosphere. The objective is achieved and its usefulness is demonstrated.

In order to support the achievement of the object of the present invention, an example will be given below in which an alcohol gas detection element is used as a coating agent for a heater that heats it from the outside.

In order to confirm the performance of the heater produced using the coating composition according to the present invention, a specific alcohol gas detection element was used as the element.

Here, the specific alcohol gas detection element was manufactured under the following procedure conditions.

First, magnesium oxide 44.4 mol%, chlorine oxide A44
．． 4 mol% and 11.1 mol% of ruconium oxide were mixed for 30 minutes. This mixture was filled into a mold, and a platinum wire with a diameter of 2-φ and a length of 15-mm was embedded and pressurized to obtain a cylindrical solidified body with a diameter of 2-φ and a height of 2-mm.

This solidified body was placed in heat-resistant porcelain and fired at 1300° C. for 3 hours in an electric furnace to obtain an alcohol gas detection element containing h#Cr 204 as a main component. This element was mounted on a terminal block, the platinum wire electrode of the alcohol gas detection element was spot welded to the lead wire of the terminal block, and a stainless steel explosion-proof net was attached to the alcohol gas detection element. A detector was constructed by surrounding an alcohol gas detection element from the outside with a heater, and was used for performance measurement.

As a condition for the performance test, the concentration of ethyl alcohol in the atmosphere was set to 0.1% volume concentration.

Examples related to the production of heaters will be given below, and their performances will be described.

Example 1゜Silicon oxide (5i02) 30% by weight (hereinafter simply referred to as %)
), 100 parts by weight (hereinafter simply referred to as parts) of a coating composition consisting of 5% chromium oxide (Cr2O3) and 65% sodium silicate (Nm2Si03) and 1 part water.
0 part was added and mixed, the heater body made of spirally swirled nichrome wire was immersed in the mixture, and after air-drying, the temperature was increased at a rate of 150°C/
The mixture was gradually heated to 500° C. for 1 hour, and further heated at 500° C. for 1 hour to form a heater.

No blisters were observed on the coating of this heater.

A sample having the above configuration was prepared using this heater, and the element resistance value and alcohol sensitivity were measured under the above performance test conditions, and the results were as shown in the table.

The performance evaluation of other examples that follow is based on Example 1.
I went with the same.

Example 2 20 parts of water was added and mixed to 100 parts of a coating composition consisting of 20% silicon oxide, 15% aluminum oxide and 65% sodium silicate, and the same heater body as in Example 1 was mixed. After soaking the same heater body and air drying it,
The sample was gradually heated once to 650°C at a heating rate of °C/hr, and further heated at 650°C for 30 minutes to form a heater. There was no blistering in the coating of this heater.

Example 3 10 parts of water was added and mixed to 100 parts of a coating composition consisting of 40% silicon oxide and 60% sodium silicate, and a heater body identical to the heater body in Example 1 was added to the mixture. After soaking and air drying, it was gradually heated to 300°C at a temperature increase rate of 150'C/hr, and further heated at 300°C for 1 hour to use as a heater. No blisters were observed in this film.

Example 4 5 parts of water was added and mixed to 100 parts of a coating composition consisting of 15% silicon oxide, 15% aluminum oxide, and 70% sodium silicate, and the heater body in Example 1 and the mixture were mixed. After soaking the same toyota body and air drying it for 150 min.
It was gradually heated up to 500°C at a temperature increase rate of °C/hr, and further heated at 500°C for 30 minutes to form a heater. There was no blistering in the coating of this heater.

Example 5 25 parts of water was added and mixed to 100 parts of a coating composition consisting of 35% silicon oxide and 65% sodium silicate, and the heater body in Example 1 was immersed in the mixture and air-dried for 120 minutes. A heater without blistering was produced by heating at ℃ for 2 hours.

Comparative Example 1 20 parts of water was added and mixed to 100 parts of a coating composition consisting of 70% aluminum oxide and 30% phosphoric acid, and a heater body identical to the heater body in Example II was added to the mixture. After soaking and air drying, the material was gradually heated to 500° C. at a heating rate of 150″c/hr, and further heated at 500° C. for 30 minutes to produce a heater.

This heater did not have any blisters.

Comparative Example 2: 100 parts of a coating composition consisting of 90% silicon oxide and 10% phosphoric acid was mixed with 30 parts of water, and the same heater body as in Example 1 was immersed in the mixture and air-dried. 1
The film was gradually heated to 500° C. at a heating rate of 50”7 hours, and further heated at 500° C. for 30 minutes to produce a heater with no blisters on the film.

The performance of the alcohol gas detection element specified using the above heater was measured and the results were as per the method.

To specifically explain the performance measurement method, the electrical resistance value was measured as follows. That is, as shown in the figure, a fixed resistor 2 having a resistance value ILc for resistance measurement is connected in series to an alcohol gas detection cord 1, and a constant voltage of 5μ is applied across both ends of the resistor 2, and the electric ratio between both ends of the fixed resistor 2 is By measuring Vc, the resistance value Rs of the alcohol gas detection element l
is calculated based on the following formula.

Note that i in the figure is the current flowing through the circuit.

Rs = Rc, (-y; 1) Next, the air in the tank into which ethyl alcohol vapor was sent was controlled to contain 0.1% by volume of ethyl alcohol, and the resistance value ILG in this atmosphere was measured to determine whether ethyl alcohol was included. The resistance value Ra1r in the air without air is measured and is defined as the alcohol sensitivity based on the following formula.

R-1r-RG Alcohol Sensitivity ""Ra1r'"00 During the measurement, the voltage applied to the heater was adjusted and the temperature of the element was set at 450°C.

As is clear from the above Examples and Comparative Examples, when heated with a heater made using a coating composition containing phosphoric acid, not only does the resistance value increase even though the element is the same, but also The sensitivity is also low, and the ability to detect alcohol gas is greatly reduced, whereas it was confirmed that the ability to detect alcohol gas was maintained when heated with a heater made using the coating composition according to the present invention. Ta.

Of the general examples of the present invention, an example of a metal oxide semiconductor element will be added. It is also effective for improving the reliability of devices made of sintered bodies of indium oxide, tin oxide, and saponified palladium as devices for detecting gases contained in fuel gas such as methane gas, butane gas, and hydrogen gas. An example in which this element is applied to a heater will be described.

Example 6゜Silicium oxide 1A 30%, chromium oxide 5% and sodium silicate 6
1 part of water to 100 parts of a coating composition consisting of 5%
0 part was added and mixed, a heater body made of spirally wound nichrome wire was immersed in the mixture, and after air drying, the temperature was increased at a rate of 150°C/h.
Gradually heat to 500℃ with r, and further heat at 500℃ for 1
It was heated for a while and used as a heater. Note that this heater was obtained under exactly the same conditions as in Example 1.

Comparative example 3゜ A heater was obtained under the same conditions as Comparative Example 1.

The heaters according to Example 6 and Comparative Example 3 were used to externally heat a fuel gas detection element made of a sintered body of indium oxide, tin oxide, and palladium oxide, and their performance was measured.

The sample used for performance measurement had the same configuration as the alcohol gas detection element described above.

Here, the fuel gas detection element was manufactured as follows.

First, 39.2% by weight of indium oxide (hereinafter simply referred to as %), 58.8% of tin oxide, and 2% of palladium oxide were mixed, and 2 cc of water was poured over this mixed powder IP. were mixed for 30 minutes.

15 ml of this mixed powder was sampled, filled into a mold, embedded with a platinum wire, and compression molded at a molding pressure of 1 to 2 to obtain a cylindrical assimilated body with a diameter of 2 mφ and a height of 2 mm. This solidified body was fired at a firing temperature of 600° C. for 3 hours to obtain a fuel gas detection element. When the mixed state of this element was observed by X-ray diffraction, it was confirmed that it was uniform.Furthermore, when the dispersion state of each component was analyzed using an X-ray microanalyzer, it was also confirmed that it was highly uniform. Further analysis using photoelectron spectroscopy confirmed that some of the palladium oxide was reduced and converted to metallic palladium.

Using this detection element, the same birch paste detector was prepared and its performance was measured.

The results are shown in the table below.

In the above table, the margin value 2 is an index for determining whether the fuel gas is equally affected by hydrogen, methane, and butane contained in the gas, and was determined by the following formula.

In the above equation, iLl is 0.04% hydrogen, 0.05% methane, and 0.05% butane, which is 1/100 of the lower explosive limit.
R2 is the minimum value of each element resistance that can be determined at 0.02%, and R2 is 1.0% hydrogen and 1.0% methane, which is one quarter of the lower explosive limit.
．． The maximum value of the element resistance value at 0.45% butane and 0.45% butane was calculated, and the detection capability for fuel gases with different constituent gas compositions was determined. A large value means that the detection ability is high and there is room for wide application.

The concentration dependence α is evaluated by varying the concentrations of methane, butane, and hydrogen contained in the atmosphere, determining the resistance value at each concentration, and using the ratio of these resistance values.

The element temperature at this time was set at 450°C. If the specific significance is high, it means that the concentration dependence is high and the detection ability is excellent.

Furthermore, the gas sensitivity for each of methane, butane, and hydrogen is the same as the alcohol sensitivity described above, and the resistance value R6 when each gas is 0.1% by volume and the above performance evaluation in air that does not contain each gas are based on the present invention. In the heater manufactured using the coating agent according to the above, the index E, which is equally impressive for hydrogen, methane, and butane, is greater than that of the heater manufactured using the coating agent containing the phosphorus component listed as a comparative example. It has been clarified that the detection ability is excellent, and it is also clear that both concentration dependence and gas sensitivity are excellent.

[Brief explanation of drawings]

The figure is a resistance measurement circuit diagram of an element related to the present invention. patent applicant Matsushita Electric Works Co., Ltd. Representative Patent Attorney Toshimaru Takemoto (2 idiots)

Claims (1)

[Scope of Claims] (A metal oxide semiconductor device characterized by containing one or two selected from the group of insulating materials of silicon 11II oxide or aluminum oxide and sodium silicate and containing no phosphorus component) Coating agent composition for a heater that heats. (2) The metal oxide semiconductor element is made of magnesium oxide (31
Claim 1, wherein the metal oxide semiconductor element is a fired body made of indium oxide, tin oxide, and palladium oxide.
A coating agent composition for a heater as described in 1.