JPS58129240A - Manufacture of humidity sensor - Google Patents

Abstract

PURPOSE:To obtain a humidity sensor high in sensitivity of humidity detection and wide in measurable humidity range, by hydrolyzing a mixture of a solvent and org. silicate in the presence of acid in the range of proper hydrolysis rate, coating an insulating base with this polymer obtained thus, drying and heat treating it in a specified temp. range. CONSTITUTION:Organic silicate, such as ethyl silicate, soln. in isopropyl alcohol is hydrolyzed by adding HCl and water so as to give 65-90% hydrolysis rate expressed in the following formula: mol of water added and participating in hydrolysis X2X100/mol of ethyl silicate. The produced silicate polymer is cast on a heat resistant glass plate 1 to give 10-150mum dried film thickness after drying at normal temp. and heat treated at 200-600 deg.C to form a humidity sensitive mateiral 3. A humidity sensor is obtained by attaching comb-shaped electrodes 2 and conductors 4 to it. This sensor is high in change of electrical resistivity all over the whole region of 0-100% relative humidity, high in response speed and stability, strong in adhesion of the film 3 to the base 1, and long in service life.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a silicate ester moisture-sensitive takako that utilizes changes in the electrical resistance value of a moisture-sensitive portion depending on the humidity of the atmosphere.

Conventionally, the moisture-sensing part of a moisture-sensing element having such a function has been made using electrolytes such as lithium chloride or calcium chloride, semiconductor vapor deposited films such as selenium or germanium, and aluminum oxide, titanium oxide, iron oxide, etc. Metal oxides or metal oxide-based ceramics have been used.

Among these, the electrolyte exhibits significant hygroscopicity in a high humidity region and becomes fluid, resulting in low element strength.

The measured humidity range was on the low humidity side and the lifespan was short. Those using semiconductor vapor deposition films require nitrous vapor deposition or a similar method.

The manufacturing method was not easy, and the measured values were greatly affected by temperature. on the other hand.

All-region oxides are physically and chemically stable;
Although the element strength is high, the measurement humidity range is 50 to 100% RH.
and a relatively narrow space, and high temperatures (800 to 1200
Since most of the products require sintering at temperatures (℃), the manufacturing method has become easier. As described above, each of the conventional products had the above-mentioned defects, and could not be said to be sufficient.

The present invention provides a method for manufacturing a silicate ester moisture-sensitive element that has excellent humidity detection sensitivity and a wide measurable humidity range.

Hereinafter, details of the present invention will be explained according to Examples.

[Example 1. ] A solution of ethyl silicate in inpropyl alcohol was used as a starting material, and water was added to it under acidic conditions with hydrochloric acid for hydrolysis. The reaction is thought to proceed as follows.

That is, the hydrolysis product of ethyl silicate is toethyl alcohol, a three-dimensional network polymer (silicate polymer) having siloxane bonds (-〇-151-0-81-). However, the produced silicate polymer does not have to form a completely three-dimensional network structure as shown in the above formula, and may be a linear polymer or may be curved. These conditions change depending on the rate of hydrolysis depending on the amount of water added during hydrolysis.

The film-forming properties of the silicate polymers produced are markedly different.

However, as a result of examining the amount of ethyl silicate as a raw material and the amount of water to be added at various blending ratios, the inventors of 9 discovered a method for producing a silicate polymer film that has good film-forming properties and excellent moisture-sensing properties. Particularly based on this, the present invention is proposed.

Add 100 f of mass, ethyl silicate) and 50 v of inpropyl alcohol into a flask and stir to mix them uniformly. Next, 12.500 g of 0.1 N hydrochloric acid was weighed into the dropping funnel and added to the above mixed solution of ethyl alcohol and isopropyl alcohol while stirring at room temperature.
It was gradually added dropwise over 0 to 40 minutes to hydrolyze the ethyl silicate. At this time, the hydrolysis rate of ethyl silicate is T
'A%. The hydrolysis rate referred to here is [(number of moles of water added)/(number of moles of ethyl silicate) x 2)
Defined by xlOO.

The silicate polymer thus prepared was coated on a ceramic substrate to a thickness of about 10 μm to produce a moisture-sensitive element as shown in FIG. In FIG. 1, (an insulating substrate manufactured by Ilti Arunna), (2) a comb-shaped silver electrode, (3) a moisture sensitive part made of a silicate polymer, and (4) a conductive wire.

Next, after drying this product at room temperature for 30 to 60 minutes,
The final moisture-sensitive element was obtained by firing for 1 hour in an electric furnace at .degree.

A humidity sensing element as shown in Fig. 1 produced through the process according to the present invention was exposed to nitrogen gas with relative humidity varied from 0 to 100 degrees, and changes in electrical resistance of the sensitive and humid parts at that time were measured. . The results are shown in FIG. As is clear from the figure, 0
The humidity sensing element of the present invention has relative humidity [over the entire range of 0 to 100%].

The electrical resistance value changes significantly due to changes in humidity.

It can be seen that it has good characteristics. Also.

As a result of repeated humidity measurements using this element,
The amount of change is within 2 to 3% at any relative humidity, making it an extremely stable collector, and the response speed is several seconds for a change in relative humidity from 0% to 1001%.

It turned out to be fast enough for practical use.

It was also found that the ethylsilicate polymer had good adhesion to the ceramic substrate and had excellent film forming performance.

[Example 2. ] Using ethyl silicate as a starting material, ethyl silicate) 10 (1, 20 f of isopropyl alcohol was stirred uniformly in a flask, and 1200 g of water was slowly added dropwise to this under hydrochloric acid acidity using a dropping funnel over 30 minutes. Ethyl silicate was hydrolyzed. In this case, the hydrolysis rate of ethyl silicate was 68%. The produced ethyl silicate polymer was flow-coated onto a heat-resistant glass plate in the same manner as in Example 1 to a thickness of about 15 μm. Arranging the words on the membrane, the first
A moisture-sensitive element as shown in the figure was prepared, dried at room temperature for 40 minutes, and then fired at 300°C for 2 hours to obtain the final moisture-sensitive screen.

The humidity-sensitive characteristics of the moisture-sensitive element were measured in the same manner as in Example 1, and the results are shown in FIG. As is clear from FIG. 3, the humidity sensing element of the present invention exhibits good humidity sensing characteristics over the entire relative humidity range.

It was also found that it has excellent adhesion to glass substrates.

[Example device]

Using silicon tetrachloride as a starting material, it is made into methyl silicate using Grignard reagent, and this methyl silicate)
10(l) and isopropyl alcohol 40F were uniformly mixed, and water 12c, c was gradually added dropwise under acidic sulfuric acid to hydrolyze the methyl silicate to obtain a silicate polymer with a hydrolysis rate of 6s. was spread on an insulating substrate in the same manner as in Examples 1 and 2. After drying at room temperature for 40 minutes, it was heated to 500°C.
The moisture sensitive element shown in FIG. 1 was produced by baking for 1 hour. As a result of measuring the a% sensitivity of this US child, it was ranked 3rd. Spread. It was found that the ethyl silicate polymer also had good adhesion to the insulating substrate, as in the case of the above-mentioned examples, and the strength of the moisture-sensitive coating film was also very good.

By the way, the inventors have developed a moisture-sensing element whose moisture-sensing portion is a polymer (silicate polymer) produced through the same steps as in Example 1.2 using various silicate esters other than those used in the examples. When the moisture characteristics were measured, both exhibited good characteristics as shown in FIGS. 2 and 3. The reason for this is presumed to be that the change in electrical resistance is large when water is adsorbed to the moisture sensitive part due to residual or chemical adsorption. Therefore, in the present invention, any silicate ester may be used as a starting material. However, studies conducted by the inventors have revealed that the film-forming properties of the silicate polymer produced differ significantly depending on the amount of water added. That is, the hydrolysis rate is 65-5Ocs
A good film will be obtained within this range, but if it is outside this range, the film may not be formed, or even if it is formed, it will be a very brittle film, and its adhesion to the insulating substrate will be poor, making it unsuitable for practical use. I found a fact that stands out. That is, when a silicate polymer made from a silicate ester is used as a moisture-sensitive element, as described in detail in Examples.

A good moisture-sensitive membrane can be obtained by adjusting the amount of water added so that the hydrolysis rate is 65 to sO. By the way, when the moisture sensitive part of this silicate polymer is coated and formed into a film on an insulating substrate as used in the example, if the film is too thick, cracks are likely to occur, and conversely, if it is too thin, the film will There are many quality problems because it is difficult to apply it uniformly and there are concerns that pinholes may occur. As a result of various studies on the film thickness of the temperature sensitive part, the inventors found that
It has also been found that the most stable moisture-sensitive film can be obtained when the film thickness is in the range of 10 to 150 μm. The application method is spray,
It can be easily done by any method such as dipping or brush printing.

A moisture-sensitive element with a film thickness adjusted to 10 to 150 μm exhibits good moisture-sensing properties in the short term even when dried at room temperature, but by further baking at 200 to 600°C after drying at room temperature, It was found that long-term reliability was significantly improved.

At this time, no moisture sensing element was obtained which had good film strength even when the firing temperature was 200° C. or lower or 600° C. or higher and had excellent long-term moisture sensitive characteristics. From the facts revealed above.

It has been found that the manufacturing process is important in creating a highly sensitive and durable silicate ester moisture sensing element.

As explained above, in a moisture sensing element whose moisture sensing portion is mainly composed of a polymer (silicate polymer) produced by hydrolysis of a silicate ester, a silicate polymer having a hydrolysis rate of silicate ester of 65 to 90 degrees is used. The film thickness of the temperature sensitive part is 10 to 150 μm, and the film thickness is 200 to 60 μm after drying at room temperature.
The humidity sensing element manufactured by the manufacturing method of the present invention, which includes a series of steps of firing at 0°C, has excellent humidity detection sensitivity and a wide range of humidity that can be determined.
It is possible to provide humidity sensing elements such as humidity sensors and dew condensation sensors that require lower firing temperatures than conventional ceramic humidity sensors, are easier to manufacture, and have excellent durability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the structure of a moisture-sensitive element. FIGS. 2 and 3 are graphs showing examples of humidity-sensitive characteristics of humidity-sensitive elements manufactured by the method according to the present invention. The same reference numerals in the figures indicate the same or equivalent parts. (11 insulated substrates, (2) electrodes, (3) moisture sensing section, (
4) is a conductor. Agent Haku Tameno - Figure 1 Figure 2 Comparative 11-1 (U≦,) Figure 3 Relative JLL (%) Procedural amendment (self-exemption) Dear Commissioner of the Japan Patent Office], $ display Special Gansho 57-11 Proverbs 8a No. 2
, Name of the invention: Temperature sensing device O- Manufacturing method 3, Person making the amendment Representative Kata Yuhito Department 4, Agent 5, Detailed description of the invention in the specification to be amended. 6. Contents of amendment (1) Light 1m11 middle page 2nd line from the bottom K “Tatauni,”
I corrected it to ``For good measure.'' (2) On page 4, line 17 of the same text, "isopropyl alcohol" is corrected to "isopropyl alcohol."that's all

Claims (1)

[Claims] A step of hydrolyzing a mixture of a solvent and a silicate ester in the presence of an acid at a hydrolysis rate of 65 to 90% to obtain a compound, and forming a N compound on an insulating substrate with a dry film thickness of 10 to 150 μm.
A step of applying the coating within a temperature range of m and a temperature range of 2.
A method for manufacturing a moisture-sensitive element, comprising a step of firing at a temperature of 00 to 600°C.