JP3372090B2 - Moisture sensitive element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensitive element used for detecting humidity in an atmosphere and outputting an electric signal, and more particularly to a humidity sensitive element used as a humidity sensor in an automatic humidity control device such as an air conditioner. .

[0002]

2. Description of the Related Art Hitherto, as a humidity sensor for detecting humidity in an atmosphere and outputting an electric signal, a film made of a moisture sensitive material is provided between a pair of electrodes, and the humidity sensitive film which changes according to the humidity is used. There is one that detects electrical resistance. As the moisture-sensitive film of such a humidity sensor, for example, an electrolyte such as lithium chloride,
Inorganic oxides, polymer electrolytes, metal oxide films, etc. are used.

Among them, as a compact and good responsiveness, a polymer obtained by crosslinking a polymer of a cationic monomer having at least one hydroxyl group with a thermosetting resin such as a melamine resin. A moisture sensitive element using a wet film has been proposed (Japanese Patent Laid-Open No. 59-171844). However, this humidity sensitive element has a drawback that its humidity sensitive property is apt to change under severe conditions such as high temperature and high humidity and causes deterioration.

On the other hand, in order to improve the deterioration resistance of the moisture sensitive element, a cationic polymer having a quaternary ammonium group and a hydroxyl group, which is a polyelectrolyte, is crosslinked with a dicyano compound which reacts with the hydroxyl group, and further, a melamine resin. A moisture-sensitive element having an interpenetrating network structure using a thermosetting resin such as that described in JP-A-2-253148 has been proposed. Further, a cationic polymer such as the above is added to an acrylic resin such as trimethylolpropane trimethacrylate. A moisture-sensitive element (Japanese Patent Laid-Open No. 4-309855) has been proposed in which a moisture-sensitive film is formed by immobilizing a three-dimensional polymer of a type polyfunctional compound.

However, the above-mentioned moisture-sensitive element obtained by immobilizing a moisture-sensitive polyelectrolyte with a cross-linked polymer is
Although the deterioration due to water wetting and the like has been improved to some extent, the problem that the measured value moves due to the change of the humidity-sensitive property with time and the accurate measurement of humidity cannot be solved cannot be completely solved.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention provides a moisture sensitive element using a moisture sensitive membrane of a polymer electrolyte, which is further improved in water deterioration resistance, which has been a drawback in the past, to accurately measure humidity over a long period of time. The object is to provide a moisture-sensitive element that can be measured.

[0007]

A moisture-sensitive element of the present invention for achieving the above object has a pair of electrodes provided on a water-resistant substrate, and a moisture-sensitive film is laminated so as to cover the electrodes and a gap between the electrodes. In the moisture-sensitive element as described above, the moisture-sensitive film comprises a thin film of a cross-linking reaction product of a moisture-sensitive polymer substance having a hydroxyl group, an acrylic polyfunctional compound and a compound having an aldehyde group.

As the water resistant substrate used in the moisture sensitive element of the present invention, for example, alumina ceramics is preferably used, and a pair of film electrodes are formed on this substrate by means of printing or sputtering. It Such electrodes are
For example, as shown in FIG. 1, it is preferable that they are provided in a comb shape so as to be combined face to face. Here, 1 is a substrate and 2 is an electrode.

The electrode 2 and the moisture sensitive film 3 laminated so as to cover the gap between the electrodes 2 and 2 are, for example, 2-hydroxy-
A polymeric substance obtained by polymerizing a monomer having a hydroxyl group such as 3-methacryloxypropyltrimethylammonium chloride; an acrylic polyfunctional compound such as trimethylolpropane trimethacrylate or pentaerythritol tetramethacrylate; and a cinnamic aldehyde. A compound having an aldehyde group such as terephthalaldehyde, for example, benzoyl peroxide,
A polymerization initiator such as dicumyl peroxide is dissolved in a solvent such as methanol or ethanol to form a moisture-sensitive coating material, which is applied on an electrode and dried, followed by heating to cause a crosslinking reaction by polymerization and condensation, It is obtained by insolubilizing the coating film.

The moisture-sensitive film 3 thus formed is insoluble in a solvent, hardly swells even in water, and is hardly deteriorated even in an environment of high humidity. Further, a protective coating 4 can be provided. As the protective film 4, for example, a cellulose resin such as cellulose diacetate or the like can be used. In FIG. 1, 5 is a lead wire.

[0011]

In the moisture-sensitive element of the present invention in which the moisture-sensitive film as described above is provided between a pair of electrodes, the electric conductivity of the moisture-sensitive film changes according to the humidity of the atmosphere. It is possible to detect the resistance change between the electrodes of the humidity sensitive element and measure the humidity by a method such as connecting the reference resistance and the reference resistance in series and passing a current, and measuring the potential change at these connection points. it can.

[0012]

Reference Example 2-Hydroxy-3-methacryloxypropyltrimethylammonium chloride (50 parts by weight) and benzoyl peroxide (0.2 parts by weight) dissolved in 110 parts by weight of methanol were mixed at 50 ° C. in a nitrogen atmosphere. After the reaction was carried out for 6 hours, the polymer formed was poured into acetone to precipitate the polymer, and further washed with acetone to recover a moisture-sensitive polymer.

Comparative Example A paint containing gold as a conductive material was printed and baked on an alumina ceramic substrate of 8 mm × 16 mm × 0.64 mm to form an electrode having a thickness of about 7 μm shown in FIG. The distance between the electrode portions is 0.3 mm, and the equivalent length is 6.2 mm. On the other hand, 10 parts by weight of the moisture-sensitive polymer obtained in Reference Example, 5 parts by weight of trimethylolpropane trimethacrylate, and 0.6 part by weight of dicumyl peroxide were dissolved in 100 parts by weight of methanol to prepare a moisture-sensitive paint. . Then, the above-mentioned moisture-sensitive coating material is spin-coated on the above-mentioned electrode portion, dried, and then heat-treated in a nitrogen stream at 120 ° C. for 2 hours to form a moisture-sensitive film having a thickness of about 5 μm. Moisture-sensitive element A according to the technique disclosed in No. 309855 was obtained.

The moisture-sensitive element A thus obtained was placed at 25 ° C. and 100
It was held in a humidity-resistant test chamber with a water fog generator of% RH, and after a lapse of a predetermined number of holding days, it was moved into a humidity generator shown in FIG. In FIG. 2, 6 is an air inlet, 7 and 8 are control valves, 9 and 10 are flowmeters, 11 is a humidifier, 12 is a measurement chamber, and 13 is an exhaust port.

The moisture sensitivity characteristics were examined as follows. That is, the measurement room 1 in which the humidity is adjusted to 30% RH in advance
After the humidity sensitive element A was placed in 2 and the humidity was controlled for 20 minutes, an AC voltage of 1 V and 1 kHz was applied between the electrodes to measure the electric resistance, and then the humidity in the measuring chamber 12 was changed from 30% RH to 50%.
After increasing the humidity to RH and controlling the humidity for 5 minutes, measure the electrical resistance, and then similarly increase the humidity to 70% RH and 90% RH and measure the electrical resistance each time. Recorded the relationship. Table 1 shows the change in the reproducibility of the humidity measurement value in comparison with the relationship between the humidity and the electric resistance value of the humidity sensitive element before the moisture resistance test.

Example 1 10 parts by weight of the moisture-sensitive polymer obtained in Reference Example, 5 parts by weight of trimethylolpropane trimethacrylate and 0.6 part by weight of dicumyl peroxide were further added with 17 parts by weight of cinnamic aldehyde. In the same manner as in Comparative Example, a moisture-sensitive paint was prepared by dissolving these in 100 parts by weight of methanol. Then, the above-mentioned moisture-sensitive agent coating material was coated on the electrode portion and heat-treated in the same manner as in Comparative Example to obtain a moisture-sensitive element B of the present invention.

The humidity-sensitive characteristics of this humidity-sensitive element B were measured by the same method as that used in the comparative example, and the results are shown in Table 1 as the change in reproducibility of the humidity measurement value similar to that of the humidity-sensitive element A of the comparative example. However, it can be seen that the moisture-sensitive element B of the present invention has significantly improved resistance to water deterioration compared to the moisture-sensitive element A.

[0018]

[Table 1]

Example 2 A moisture-sensitive element C of the present invention was prepared using the same moisture-sensitive coating material as in Example 1 except that phthalaldehyde was added in the same amount by weight in place of cinnamic aldehyde, and its moisture-sensitive characteristics Was examined in the same manner as in Example 1, and it was confirmed that the moisture-sensitive element B of the present invention had almost the same resistance to water deterioration.

[0020]

EFFECTS OF THE INVENTION The moisture-sensitive element of the present invention uses a moisture-sensitive film obtained by crosslinking reaction in the coexistence state of a moisture-sensitive polymer substance, an acrylic polyfunctional compound and a compound having an aldehyde group. It has an excellent resistance to water deterioration that could not be obtained by the conventional method of immobilizing a polymeric substance with a three-dimensional cross-linked polymer, and enables highly accurate humidity measurement over a long period of time. It is a thing.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing the structure of a moisture sensitive element of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a humidity generator used to measure humidity characteristics of a humidity sensitive element.

[Explanation of symbols]

1 substrate 2, 2 electrodes 3 moisture sensitive film 4 protective film 5, 5 lead wire 6 Air inlet 7, 8 control valve 9,10 flow meter 11 humidifier 12 Measuring room 13 Exhaust port

Claims (4)

(57) [Claims] 1. A moisture-sensitive element comprising a water-resistant substrate having a pair of electrodes provided side by side, and a moisture-sensitive film laminated to cover the electrodes and the electrode gap, wherein the moisture-sensitive film has a hydroxyl group. A moisture-sensitive element comprising a thin film of a cross-linking reaction product of a molecular substance, an acrylic polyfunctional compound and a compound having an aldehyde group. 2. The polymer substance having a moisture-sensitive polar group is 2
The moisture-sensitive element according to claim 1, which is -hydroxy-3-methacryloxypropyltrimethylammonium chloride. 3. The moisture-sensitive element according to claim 1, wherein the acrylic polyfunctional compound is trimethylolpropane trimethacrylate. 4. The moisture sensitive element according to claim 1, wherein the compound having an aldehyde group is cinnamic aldehyde.