JPS6156945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity sensing element that utilizes changes in the electrical resistance of a humidity sensing portion depending on the humidity of the atmosphere.

Conventionally, as a humidity sensing part of a humidity sensing element having the above-mentioned functions, electrolytes such as lithium chloride and calcium chloride, semiconductor vapor deposited films such as selenium and germanium, and aluminum oxide, titanium oxide,
Metal oxides or metal oxide ceramics using iron oxide or the like have been used.

Among these, the electrolyte has remarkable hygroscopicity in a high humidity region, so it becomes fluid, and therefore has low strength, and the measured humidity region is about 0 to 60% relative humidity. Further, since semiconductor vapor deposition films require vacuum vapor deposition, they are not easy to manufacture, and measured values are affected by temperature. Further, metal oxide-based materials are physically and chemically stable and have high element strength, but generally require firing temperatures of 1000° C. or higher, which tends to reduce the moisture-sensitive surface area. Therefore, each of the conventional moisture sensitive parts has its own drawbacks and is not satisfactory.

This invention was made in view of the above-mentioned circumstances, and has excellent humidity detection sensitivity, a wide measurable humidity range, the use of inexpensive and easily available raw materials, an easy manufacturing method, and a strong element. It is an object of the present invention to provide a moisture sensing element having a large moisture sensing portion.

This invention will be explained in detail below.

In this invention, as a material for the moisture sensitive part, a decomposition residue obtained by thermally decomposing a composition whose main component is an organosilicon compound polymer (silicone) such as silicone resin, silicone grease, or silicone oil is used as a bonding component. It has a moisture-sensing ability,
Physically and chemically stable metal oxide powder particles are uniformly contained and dispersed throughout. First, a silicon resin will be explained as an example of the binder. Silicone resin has a structure in which a hydrocarbon group is bonded to the side chain of a siloxane bond --Si--O--Si--O. When this is heated, the hydrocarbon groups in the side chains gradually decompose, leaving behind a hard solid consisting of the siloxane bonds and decomposed products of the hydrocarbon groups. When the firing temperature is increased, decomposition of hydrocarbon groups is promoted, and the surface of the residual solid becomes porous. Therefore, the substance contained inside is exposed to the surface.
That is, in this invention, a microscopic powder or particulate moisture-sensitive electric resistance material is deposited as a moisture-sensitive member, and this is bonded to a strong film by the thermal decomposition residue of a polymer of an organosilicon compound. What will become
This was done based on the discovery that the rate of change in electrical resistance value due to changes in ambient humidity (relative humidity 0 to 100%) is large. Furthermore, the material of the moisture sensing part according to the present invention can be a powder particle material with a large effective moisture sensing surface area, and can be fired at a lower temperature than ordinary metal oxide type (ceramic) materials. Its strength is also relatively high.

Next, embodiments of the invention will be described.

[Example 1] A silicone varnish prepared by dissolving silicone resin (methyl phenyl silicone) in xylene was used as a starting material for the binder, and powdered TiO ₂ twice the weight of the silicone varnish was added as a moisture-sensitive electrical resistance material. The mixed and stirred kneaded material is placed on an alumina insulating substrate to a thickness of approx.
A large number of 200μ, 5mm square films were manufactured, and the firing temperature was varied from 200℃ to 700℃ to 100℃.
We prepared different types of baked goods. A pair of electrodes 1 made of gold (Au) were deposited on this material by vapor deposition, as an example of the structure shown in FIG. 1, and a conductive wire 2 was attached to the electrodes 1. In FIG. 1, numeral 3 represents a substrate, and numeral 4 represents a moisture sensing portion made of the above-mentioned fired product. The humidity sensing part 4 was exposed to air with a relative humidity ranging from 0 to 100%, and the electrical resistance value of the humidity sensing part 4 at that time was measured. 0 to Figure 2
Changes in electrical resistance of the humidity sensitive part at 100% RH are shown at different firing temperatures. As is clear from FIG. 2, as the firing temperature increases, the change in resistance value from 0 to 100% RH increases, and the material exhibits desirable characteristics as a moisture sensing portion of a moisture sensing element. Also,
Figure 3 shows the relationship between relative humidity and logarithm of resistance at firing temperatures of 200°C, 400°C, and 600°C. In Figure 3, curves A, B, and C are each at a firing temperature of 200
It shows the moisture sensitivity characteristics of the humidity sensitive part at ℃, 400℃, and 600℃. It is clear from FIG. 3 that the higher the firing temperature, the better the moisture sensing function. However, as you can see from Figure 2, the firing temperature is 600
When the temperature exceeds ℃, it tends to become saturated. Furthermore, curve D
This shows the humidity sensitivity characteristics of a conventional ceramic (TiO ₂ sintered body) humidity sensor measured under the same conditions.

The above-mentioned characteristics are understandable because it is estimated that the change in the firing components due to the heating temperature of the silicone resin used as the binder is approximately as follows.

However, in the above formula, R: methyl group, phenyl group C: carbon Furthermore, when the moisture-sensitive part was observed under a microscope at each firing temperature, it was found that at temperatures of 300°C or higher, as the firing temperature rose, silicone It was found that as the surface decomposes and becomes porous, the moisture-sensitive material becomes exposed and the moisture-sensing function increases as the surface becomes more porous. Furthermore, from FIG. 3, it is clear that the humidity sensor of the present invention has better moisture sensitivity characteristics than the conventional one by increasing the firing temperature.

Next, another embodiment of this invention will be described.

[Example 2] The same binder as in Example 1 was used, and powdered ZnO, which was about 1.5 times the weight of the binder, was mixed and stirred as a moisture-sensitive material. Figure 4 shows the relationship between the relative humidity and the logarithm of the resistance value at firing temperatures of 200, 400, and 600°C, which were produced in the same manner as in the case of Figure 3. For comparison, similar characteristics were also measured for a humidity sensor with a conventional ZnO-based ceramic in its humidity sensing section. In FIG. 4, curves E, F, and G show the characteristics of the moisture sensitive part at firing temperatures of 200, 400, and 600°C, respectively, and curve H shows the same characteristics of the conventional one.

[Example 3] A silicone varnish in which methyl silicone was dissolved in a mixed solvent of toluene and xylene was used as a binder, and powdered C _r2 O ₃ about twice the weight of the binder was mixed and stirred as a moisture-sensitive material. Figure 5 shows the relationship between the relative humidity and the logarithm of the resistance value at firing temperatures of 200, 400, and 600°C. be.
In this case as well, for comparison, similar characteristics were measured for a humidity sensor having a conventional C _r2 O ₃ ceramic in its humidity sensing section. In Figure 5, curves I, J, and K correspond to firing temperatures of 200, 400, and 600, respectively.
It shows the characteristics of the humidity sensitive part at .degree. C., and the curve L shows the same characteristics of the conventional one.

As is clear from FIGS. 4 and 5, the higher the firing temperature of the humidity sensor according to the present invention is, the better the humidity sensitivity characteristic is than that of the conventional sensor.

In addition, this invention uses silicon resins other than methylphenyl silicone and methyl silicone used in the above-mentioned examples, modified silicon resins such as epoxy-modified silicone, polymers of organosilicon compounds such as silicone oil, and silicone rubber, In other words, any decomposition residue obtained by thermally decomposing a composition whose main component is silicone can be used as a binder, and this decomposition residue can also be used as a binder. Experiments have shown that it has moisture-sensitive properties.

In addition, the moisture-sensitive materials used in this invention include TiO ₂ , ZnO, and _Cr2 O ₃ used in Examples 1 to 3.
In addition, metal oxide powders such as F _e2 O ₃ , A ₂ O ₃ , CuO, composite metal oxides, metal oxide ceramics, and mixtures of two or more of these can be used. be able to. According to the inventor's experiments, it has been confirmed that these powdered moisture-sensitive materials have a larger effective moisture-sensing surface area than conventional vapor-deposited films or sintered bodies, and therefore have better moisture-sensing properties. It was done.

As a result of repeated humidity measurements using the humidity sensing element of this invention, the amount of change was within 2 to 3%, indicating that it was an extremely stable element, and the response speed also increased from 0% relative humidity to 100% relative humidity. It was confirmed that the change took only a few seconds, which is sufficiently fast for practical use.

In the moisture-sensitive element of the present invention, the higher the firing temperature during production, the more inorganic the skeleton of the binder becomes, and thus the higher the strength and physical and chemical stability become. Further, a firing temperature of about 600° C. at most during production is sufficient. Therefore, conventionally, metal oxide type (ceramic) devices, which are the most practical moisture sensing elements, are manufactured at a minimum temperature of about 800℃, usually
Because it requires a firing temperature of over 1000℃,
The moisture-sensitive element according to the present invention is advantageous because it can be fired at a lower temperature.

As explained above, according to the present invention, the moisture sensitive part is made of metal oxide powder particles whose binding component is the thermal decomposition residue of a composition whose main component is an organosilicon compound polymer (silicone). Therefore, the humidity detection sensitivity is excellent, the measurable humidity range is wide, and inexpensive and easily available raw materials can be used.
It is easy to manufacture and has the effect of having high element strength, so it can be widely used in various applications such as humidity sensors and dew condensation sensors.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a humidity sensing element according to an embodiment of the present invention, FIG. 2 is a firing temperature-resistance characteristic diagram of the humidity sensing element of this invention, and FIGS. 3, 4, and 5 are, respectively. FIG. 4 is a logarithmic characteristic diagram of relative humidity-resistance value of different examples. DESCRIPTION OF SYMBOLS 1...Electrode, 2...Conducting wire, 3...Substrate, 4...Moisture sensing part.

Claims (1)

[Claims] 1. A humidity sensor made of metal oxide powder particles whose binding component is the thermal decomposition residue of an organosilicon compound polymer.