JPS632464B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a silicate ester humidity sensing element that utilizes changes in the electrical resistance of a humidity sensing 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 ceramics have been used. Among these, the electrolyte exhibits significant hygroscopicity and fluidity in the high humidity region, resulting in low element strength, measurement humidity in the low humidity region, and short life. Those using a semiconductor vapor deposited film require vacuum vapor deposition or a similar method, and are therefore not easy to manufacture, and the measured values are greatly affected by temperature. On the other hand, metal oxide-based materials are physically and chemically stable and have high element strength, but they have a relatively narrow measurement humidity range of 50 to 100% RH and high temperatures (800 to 1200℃). )
Many of the materials had to be sintered, so the manufacturing method was not easy. As described above, each of the conventional methods has the above-mentioned drawbacks and cannot be said to be satisfactory. 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, the details of the present invention will be explained according to Examples. Example 1 A solution of ethyl silicate in isopropyl alcohol was used as a starting material, and water was added to it under acidic conditions with hydrochloric acid to perform hydrolysis. The reaction is thought to proceed as follows. That is, the hydrolysis product of ethyl silicate is a three-dimensional network polymer (silicate polymer) having siloxane bonds (-O-Si-O-Si-) and ethyl alcohol. However, the produced silicate polymer does not necessarily form a completely three-dimensional network structure as shown in the above formula,
It is a linear polymer, and its structure contains silanol, which is a reaction intermediate.

It is also possible that it contains [Formula]. These conditions change depending on the rate of hydrolysis depending on the amount of water added during hydrolysis, and the film-forming properties of the produced silicate polymer differ significantly. However, the inventors investigated the amount of ethylene silicate as a raw material and the amount of water added at various mixing ratios, and as a result, they discovered a method for producing a silicate polymer film that has good film-forming properties and has a moisture-sensitive function. Based on this, the present invention is proposed. First, 100 g of ethyl silicate and 50 g of isopropyl alcohol are placed in a three-necked flask and stirred to mix them uniformly. Next, 0.1N hydrochloric acid
12.5 cc was weighed into a dropping funnel and gradually added dropwise to the above mixed solution of ethyl alcohol and isopropyl alcohol over 30 to 40 minutes at room temperature with stirring to hydrolyze the ethyl silicate. At this time, the hydrolysis rate of ethyl silicate was 73%. The hydrolysis rate referred to here is [(number of moles of water added)/(number of moles of ethyl silicate) x 2] x 100
Defined by The silicate polymer prepared in this way was applied to a thickness of about 30 μm on a ceramic substrate.
A moisture-sensitive element as shown in the figure was fabricated. In Fig. 1, 1 is an alumina insulating substrate, 2 is a comb-shaped silver electrode, 3 is a moisture sensitive part made of silicate polymer, and 4 is a comb-shaped silver electrode.
is a conductor. Then, after drying this thing at room temperature for 30-60 minutes
The final moisture-sensitive element was prepared by firing in an electric furnace at 400°C for 1 hour. A humidity sensing element as shown in FIG. 1 produced through the process according to the present invention was exposed to air whose relative humidity was varied from 0 to 100%, and the change in electrical resistance of the humidity sensing portion at that time was measured. The results are shown in FIG.
As is clear from the figure, the humidity sensing element of the present invention shows a large change in electrical resistance due to changes in humidity over the entire range of relative humidity from 0 to 100%, indicating that it has good characteristics. Recognize. In addition, as a result of repeated humidity measurements using this element, the amount of change is within 2 to 3% at any relative humidity, and it is an extremely stable element. It took several seconds for the change from 100% to 100%, which was found 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, 100 g of ethyl silicate, 20 g of isopropyl alcohol
g was uniformly stirred in a flask, and 12 c.c. of water was slowly added dropwise thereto over 30 minutes using a dropping funnel under acidic conditions with hydrochloric acid to hydrolyze the ethyl silicate. In this case, the hydrolysis rate of ethyl silicate is 69%. Next, the produced ethylsilicate polymer was poured onto a heat-resistant glass plate in the same manner as in Example 1 to form a film with a thickness of about 15 μm, and a moisture-sensitive element as shown in Fig. 1 was prepared. After drying for 40 minutes,
The final moisture-sensitive element was obtained by baking at 300°C for 2 hours.
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 exhibited good moisture sensing characteristics over the entire relative humidity range, and was found to have excellent adhesion to the glass substrate. Example 3 Using silicon tetrachloride as a starting material, convert it into methyl silicate using a Grignard reagent, and add 100 g of this methyl silicate and isopropyl alcohol.
40 g were mixed uniformly, and 12 c.c. of water was gradually added dropwise under acidic sulfuric acid to hydrolyze the methyl silicate to obtain a silicate polymer with a hydrolysis rate of 69%. The produced silicate polymer was coated on an insulating substrate to a thickness of 40 μm in the same manner as in Examples 1 and 2, and was heated to a thickness of 40 μm at room temperature.
After drying for several minutes, it was fired at 500° C. for 1 hour to produce the moisture-sensitive element shown in FIG. As a result of measuring the moisture sensitivity characteristics of the device, it was revealed that the device had characteristics similar to those shown in FIG. Furthermore, 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 also had very good moisture-sensitive coating strength. 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 Examples 1 and 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 that silanol remains or is formed on the surface of the moisture sensitive part due to chemical adsorption.

This is presumed to be due to the large change in electrical resistance when water is adsorbed to [Formula]. Therefore, in the present invention, any silicate ester may be used as a starting material. However, according to the inventors' study,
It has become clear that the film-forming properties of the silicate polymer produced differ significantly depending on the amount of water added.
That is, when the hydrolysis rate is in the range of 65 to 90%, a good film will be obtained, 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.
It was discovered that the adhesion to the insulating substrate also deteriorated, making it impossible to put it into practical use. That is, when using a silicate polymer made from a silicate ester as a moisture-sensitive element, as detailed in the examples, the amount of water to be added is adjusted so that the hydrolysis rate is 65~65.
A good moisture-sensitive film can be obtained by setting the ratio to 90%. By the way, when forming a moisture-sensitive part of this silicate polymer in the form of a film on an insulating substrate as used in the example, if the film is too thick, cracks are likely to occur, and on the other hand, if it is too thin, the film may not be uniform. There are many quality problems, as it is difficult to apply and there are concerns that pinholes may occur. As a result of various studies regarding the thickness of the moisture sensitive portion, the inventors have also found that the most stable moisture sensitive film can be obtained when the thickness is in the range of 10 to 150 μm. Incidentally, the coating method can be easily carried out by any method such as spraying, dipping, brushing, etc. A moisture-sensitive element with a film thickness adjusted to 10 to 150 μm exhibits good moisture-sensing characteristics in the short term even when dried at room temperature, but after drying at room temperature,
It has become clear that long-term reliability is significantly improved by firing at ℃. At this time, it was not possible to obtain a moisture-sensitive element that had good film strength even when the firing temperature was below 200°C or above 600°C and had excellent long-term moisture-sensitive characteristics. From the facts that have become clear as described above, it has become clear that the manufacturing process is important in producing a highly sensitive and durable silicate ester moisture sensitive 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, the hydrolysis rate of the silicate ester is 65 to 90%. Using silicate polymer, the thickness of the moisture sensitive part is 10 to 150 μm,
The humidity sensing element manufactured by the manufacturing method of the present invention, which includes a series of steps of drying at room temperature and then firing at 200 to 600°C, has excellent humidity detection sensitivity and a wide measurable humidity range, and is superior to conventional methods. The firing temperature is lower than that of ceramic humidity sensors, making it easier to manufacture.
Furthermore, it is possible to provide a humidity sensing element such as a humidity sensor or a dew condensation sensor that has good durability.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the structure of a humidity-sensitive element, and FIGS. 2 and 3 are graphs showing examples of humidity-sensitive characteristics of a humidity-sensitive element manufactured by the method according to the present invention. The same symbols in the figures indicate the same or equivalent parts,
1 is an insulating substrate, 2 is an electrode, 3 is a moisture sensing portion, and 4 is a conducting wire.

Claims (1)

[Claims] 1 A step of obtaining a polymer by hydrolyzing a mixture of a solvent and a silicate ester in the presence of an acid within a hydrolysis rate of 65 to 90%, and depositing the polymer on an insulating substrate with a dry film thickness of 10 to 150 μm. 1. A method for manufacturing a moisture-sensitive element, comprising the steps of: coating within a temperature range of 200 to 600°C; and baking the coated material within a temperature range of 200 to 600°C.