JPS6239939B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrical resistance humidity sensor,
In particular, it prevents deterioration of moisture-sensitive materials and decreases in moisture-sensitive properties.
This article relates to an electrical resistance humidity sensor with improved stability and reliability. Electrical resistance humidity sensors generally detect humidity by utilizing the phenomenon in which the electrical resistance of a moisture-sensitive material changes when the humidity changes. Until now, moisture-sensitive materials include ceramic materials,
Electrolytes such as LiCl, those in which conductive powder is dispersed in a hygroscopic resin, and those using hydrophilic polymer substances or polymer electrolytes are known. However, these moisture sensitive materials have their own drawbacks. In the case of ceramic materials, some of the moisture adsorption onto the ceramic is irreversible chemical adsorption, and the hysteresis is large. When using LiCl, the humidity range that can be measured with a single sensor is narrow, and if left in a high humidity atmosphere for a long time, LiCl itself deliquesces and dissolves, so it is necessary to correct it from time to time. A product in which conductive powder (eg carbon black) is dispersed in a hygroscopic resin has no moisture sensitivity in a low-humidity atmosphere, and because the degree of dispersion is not uniform, the manufacturing yield is extremely low and reliability is poor. Compared to these moisture-sensitive materials, electrical resistance humidity sensors using polymer electrolytes as moisture-sensitive materials exhibit superior moisture-sensing characteristics. In particular, internal hydrophobic groups,
Due to its unique structure, the moisture-sensitive material obtained by coating and drying latex, which is a dispersion of polymeric copolymer particles having ionic groups on its surface layer, exhibits a low electrical resistance value and is superior to conventional moisture-sensitive materials. It exhibits excellent temperature-sensitive properties not found in other materials. However, when using a dried latex as described above as a moisture-sensitive material, care must be taken to avoid condensation of moisture. The reason for this is that when water condenses (condenses) on the surface of the moisture-sensitive material, the moisture-sensitive material locally swells and its moisture-sensitive characteristics change. or,
It also has the disadvantage that its moisture sensitivity characteristics change when exposed to various chemical atmospheres. The purpose of the present invention is to eliminate the above-mentioned drawbacks.
To provide a highly stable and reliable electrical resistance humidity sensor by preventing deterioration of a moisture sensitive material layer formed using a moisture sensitive material made of a copolymer due to adhesion of dust or condensation and deterioration of moisture sensitive characteristics. That's true. The present invention provides a humidity sensor that detects humidity using a moisture-sensitive material whose electrical resistance value changes in response to changes in humidity in the atmosphere, in which the moisture-sensitive material is composed of a hydrophobic monomer and an ionic or non-ionic hydrophilic material. A moisture-sensitive material layer consisting of an aggregate of latex particles that are a copolymer with a hydrophilic monomer and have a hydrophilic surface, and the surface of the moisture-sensitive material layer is a solvent-free condensation type or addition type thermosetting material. An electrical resistance humidity sensor characterized by having a protective layer made of silicone resin. The moisture sensitive material of the present invention comprises a hydrophobic monomer such as an ester of methacrylic acid or a nonionic vinyl monomer such as styrene, and an ionic monomer such as a cationic compound such as 2-methacryloyloxyethyltrimethylammonium salt or a styrene sulfonate. A copolymer with an anionic compound of
The surface layer consists of an aggregate of hydrophilic latex particles. In the present invention, as the silicone resin forming the protective film, a condensation type (hydroxyl group-containing) silicone resin and an addition type silicone resin that do not contain a solvent can be used alone or a mixture thereof can be used. When forming the protective film of these silicone resins, the curing temperature is 150℃.
The following is desirable. The silicone resin of the present invention includes:

【formula】

[Formula] (where R is hydrogen or indicates an alkyl group),

[Formula] and

Siloxanes having reactive groups such as [formula] are reacted in the presence of a catalyst to increase the molecular weight or crosslinked to form a rubber. For example, condensation type silicone resins include α,ω-dihydroxypolymer. Some have dimethylsiloxane and vinyltrimethoxysilane as their main ingredients. In addition, addition-type silicone resins include commercially available products such as KE109 manufactured by Shin-Etsu Silicone Co., Ltd., and α,ω-
There are those whose main components are divinyldimethylpolysiloxane and hydrosilyldimethylpolysiloxane. These silicone resins are compatible with the moisture-sensitive material layer made of an aggregate of latex particles of the copolymer and have excellent moisture permeability. From the viewpoint of the responsiveness of the humidity sensor, it is desirable that the thickness be 20 μm or less. Next, the present invention will be explained by examples. Example 1 and Control 1 (a) Production of moisture-sensitive material 0.2 mol of methyl methacrylate (MMA) as a hydrophobic monomer, 2-methacryloyloxyethyltrimethylammonium iodide (METAI) as a cationic monomer (also serving as an emulsifier) 0.1 mol and azobisisobutyramidine hydrochloride (AIBA) as polymerization initiator
Emulsion copolymerization of 0.001 mol was carried out in 300 ml of an aqueous medium under a nitrogen atmosphere at 60° C. for 10 hours with high speed stirring. As a result, a stable latex was obtained in which fine particles containing MMA units inside the particles and having trimethylammonium groups, which are cationic groups, were dispersed on the surface. This latex was purified by dialysis using a cellophane dialysis tube for 2 months to remove low molecular weight impurities. (b) Fabrication of humidity sensor This will be explained with reference to the drawings. FIG. 1 is a plan view showing a specific example of a humidity sensor having a comb-shaped gold electrode, and FIG. 2 is a top view of the humidity sensor shown in FIG.
A' cross-sectional view, where 1 is an alumina substrate, 2
3 represents a gold electrode, 3 represents a moisture sensitive material layer, and 4 represents a lead wire connection terminal. The latex obtained in (a) above is
As shown in the figure and Fig. 2, a comb-shaped gold electrode 2
It was coated on an alumina substrate provided with and dried to obtain an electrical resistance humidity sensor (Control 1). The weight of the moisture sensitive material layer formed at this time was 5 mg. (c) Formation of a protective film according to the present invention A liquid addition-type silicone resin (manufactured by Shin-Etsu Silicone Co., Ltd.,
KE109) was applied using a spinner and cured at 100° C. for 2 hours to obtain a humidity sensor (Example 1) provided with a protective film having a thickness of 5 μm. The humidity sensitivity characteristics of the humidity sensors of Example 1 and Control 1 were investigated. That is, Fig. 3 is a graph showing the relationship between relative humidity (%) (horizontal axis) and electrical resistance (Ω) (vertical axis) of the humidity sensor, and A(-●
-) indicates the case of Example 1, and B(-0-) indicates the case of Control 1. As is clear from the graph in FIG. 3, there was almost no difference between the two, confirming that the formation of the protective film had no effect on the moisture sensitivity characteristics. Note that the response time of Example 1 in which a protective layer was formed was approximately 1.3 times greater than that of Control 1. Next, we investigated changes in the characteristics of both humidity sensors due to water condensation. That is, both humidity sensors were left in an atmosphere with a relative humidity of 30%, and 0.005 ml of water droplets were placed on the surfaces of these humidity sensors.
The solution was dropped 5 times every 30 minutes and the change in electrical resistance was measured. The results obtained are shown in FIG. Figure 4 is a graph showing the relationship between time (hours) (horizontal axis) and electrical resistance (Ω) (vertical axis) when water droplets are dropped on the surface of a humidity sensor at regular intervals, and shows the relationship between A(- ●-) is B in the case of Example 1
(-0-) indicates the case of Control 1, and the arrow indicates the time point at which the water droplet was dropped. As is clear from the graph in Figure 4, the initial electrical resistance value R _x and 5
If the difference between the electrical resistance value R after dropping water droplets and drying is R-R _x = ΔR, then Δ of Example 1
Although R was zero, ΔR of Control 1 was quite large, indicating that the electrical resistance value was changing due to condensation of water, and these results clearly demonstrate the effectiveness of the protective film. Comparative Example Using the sensor of Control 1, silicone varnish KR100 manufactured by Shin-Etsu Silicone was applied in the same manner as in Example 1.
(50% xylene solution for surface protection) and leave it at room temperature.
A sensor that had been dried for 24 hours and a sensor that had been coated with straight silicone varnish KR282 (50% xylene solution) also manufactured by Shin-Etsu Silicone and dried at 200°C for 1 hour were created, and the relationship between relative humidity and electrical resistance was compared. The results are shown in Figure 3. The graph shows KR100 dried at room temperature (line C) and KR282 dried at 200° C. (line D). Also, the response time is better with KR100 as a protective layer.
The increase was 2.3 times, and that using KR282 as a protective layer was 2.7 times. Example 2 and Control 2 (a) Production of moisture-sensitive material 0.1 mol of styrene, 0.01 mol of sodium styrene sulfonate (also serves as an emulsifier), and 0.001 mol of potassium persulfate as a catalyst in 500 ml of an aqueous medium under nitrogen atmosphere, 60 while stirring at high speed at °C.
Emulsion copolymerization was carried out for 10 hours. As a result, a latex was obtained in which styrene entered the interior and particles containing sodium styrene sulfonate in the surface layer were dispersed. This latex was purified by dialysis using a cellophane dialysis tube for 2 months to remove impurities. (b) Preparation of Humidity Sensor Using the latex obtained in (a) above, an electrical resistance humidity sensor (Control 2) was obtained in the same manner as in Example 1. The weight of the moisture sensitive material layer formed at this time was 5 mg. (c) Formation of protective film according to the present invention α,
A condensed silicone resin blended with 95 parts by weight of ω-dihydroxypolydimethylsiloxane, 6 parts by weight of vinyltrimethoxysilane, and 0.3 parts by weight of dibutyltin dioctanoate was applied with a spinner and reacted for 100 hours at room temperature and 50% relative humidity. After that, it was cured at 100℃ for 2 hours to a thickness of 3μm.
Humidity sensor provided with a protective film (Example 2)
I got it. Hereinafter, as in Example 1, we examined how the characteristics of both humidity sensors change due to condensation of moisture. As a result, the relative humidity is 30
The electrical resistance values of Example 2 and Control 2 in an atmosphere of 9.0×10 ⁵ Ω were almost the same. However, while ΔR of Example 2 was almost zero, ΔR of Control 2 was 1.6×10 ⁵ Ω. Example 3 and Control 3 (a) Preparation of moisture-sensitive material 0.2 mol of acrylonitrile as hydrophobic monomer, 0.02 mol of allyl glycidyl ether and 0.02 mol of aminoethyl methacrylate as crosslinking agent, hydroxyethyl methacrylate as monomer providing grafting points in 500 ml of water. 0.01 mol and 0.001 mol of azobisisobutyramidine hydrochloride as a polymerization initiator, and the liquid temperature was raised to 70°C.
The copolymerization reaction and crosslinking reaction were simultaneously carried out at 10°C under a nitrogen atmosphere with high speed stirring for 10 hours. Next, ceric ammonium nitrate was added to the latex thus obtained as a graft polymerization initiator.
Add 0.01 mol and 0.1 mol of 2-methacryloyloxyethyltrimethylammonium bromide as a cationic monomer to be grafted, set the liquid temperature to 50°C, and under nitrogen atmosphere for 6 hours.
The graft reaction was carried out with high speed stirring. As a result, a latex containing dispersed fine particles whose surface layer was covered with a cationic polymer was obtained. (b) Preparation of humidity sensor Using the latex obtained in (a) above, an electrical resistance type humidity sensor was obtained in the same manner as in Example 1 (Control 3). The weight of the moisture-sensitive latex film formed at this time was 4 mg. (c) Formation of protective film according to the present invention α,
ω-divinyldimethylpolysiloxane (molecular weight
34000), 3 parts by weight of hydrosilyldimethylpolysiloxane (molecular weight 1354), and 0.08 parts by weight of a platinum catalyst was applied using a spinner and reacted at 100°C for 2 hours and then at 150°C for 1 hour. In this way, a humidity sensor provided with a protective film having a thickness of 5 μm was obtained. Hereinafter, in the same manner as in Example 1, it was examined whether or not the characteristics of both humidity sensors would change due to condensation of moisture. As a result, the electrical resistance values of Example 3 and Control 3 in an atmosphere of 30% relative humidity were
The resistance was 1.2×10 ⁵ Ω, which was almost the same. However, the ΔR of Example 3 was almost zero, while the ΔR of Control 3 was 2.5×10 ⁵ Ω. Examples 4 to 7 and Controls 4 to 7 In the same manner as in Examples 1 to 3 and Controls 1 to 3, various moisture sensitive materials were tested to see how the characteristics of humidity sensors change depending on the presence or absence of a protective film. We investigated the components of the protective film and the constituent materials of the protective film. The results obtained are shown in the table below. As is clear from the table, Examples 4 to 7 of the present invention
Compared to controls 4 to 7, the ΔR
remains almost unchanged at zero, and the effect of the silicone resin protective film is remarkable. As explained above, according to the present invention, by providing a protective layer of the specific silicone resin on the surface of the specific moisture-sensitive material made of the latex, deterioration due to dust adhesion or dew condensation to the moisture-sensitive material layer can be prevented. Furthermore, it is possible to provide a stable and reliable electrical resistance humidity sensor with little deterioration in moisture sensitivity characteristics.

【table】

【table】 [Brief explanation of the drawing]

Fig. 1 is a plan view showing an example of a humidity sensor having a comb-shaped gold electrode, and Fig. 2 is a plan view showing an example of a humidity sensor having a comb-shaped gold electrode.
A' cross-sectional view, Figure 3 is a graph showing the relationship between the relative humidity and electrical resistance of the humidity sensor, and Figure 4 is the relationship between time and electrical resistance when water droplets are dropped on the surface of the humidity sensor at regular intervals. This is a graph showing. 1...Alumina substrate, 2...Gold electrode, 3...Moisture sensitive material layer, 4...Lead wire connection terminal.

Claims (1)

[Claims] 1. In a humidity sensor that detects humidity using a moisture sensitive material whose electrical resistance value changes in response to changes in humidity in the atmosphere, the moisture sensitive material is composed of a hydrophobic monomer and an ionic or nonionic hydrophilic monomer. A moisture-sensitive material layer consisting of an aggregate of latex particles having a hydrophilic surface and a copolymer of An electrical resistance humidity sensor characterized by having a protective layer made of a material.