JPH0731145B2 - Moisture-sensitive composition - Google Patents

Description

The present invention relates to a humidity-sensitive composition, and more particularly to a humidity-sensitive composition having a large variation range of resistance to humidity and having improved water resistance in a high humidity region. Sex composition.

[Problems to be Solved by Prior Art and Invention]

Known organic moisture-sensitive resistance elements include those obtained by kneading conductive particles in a hygroscopic resin and those utilizing a change in ion conductivity due to moisture absorption using a polymer electrolyte.

The former has been applied to a dew condensation sensor by utilizing the fact that the distance between conductive particles increases due to the volume expansion due to moisture absorption, resulting in a resistance change. Further, an inorganic electrolyte (ion) is added for improving the contact performance of the conductive particles (JP-A-59).
-114449, 59-114450, 59-114451, 59-114452)
There is also a deliquescent salt added to increase hygroscopicity (JP-A-61-44340). But these things are 2
Volume expansion due to moisture absorption at low humidity such as 0 to 90% RH is not large, and since the range of change is small such that it extremely increases near dew condensation, there is no linearity between humidity and resistance value (one logarithmic plot), The application to the dew condensation sensor was limited.
Further, the conduction mechanism is electronic, and there is a drawback that the resistance rapidly increases as the humidity and resistance become higher.

On the other hand, the latter utilizes changes in ionic conductivity due to moisture absorption (Japanese Patent Laid-Open No. 60-225053). When an inorganic salt is added to the polymer electrolyte, it exhibits ionic conductivity. This ionic conductivity is proportional to the mobility of the ion pair of the added inorganic salt, and the impedance (AC resistance) decreases with increasing humidity. , Shows a clear linearity, and the change width of resistance is large. However, since the polyelectrolyte has a high affinity with water, it is easily dissolved in water, so that the strength of the element film is weakened in the high humidity region, the water resistance is lacking, and it is difficult to maintain the shape. It had the drawback of doing so.

[Means for solving problems]

Therefore, the present inventors have taken advantage of both of the above, and as a result of intensive studies to eliminate the drawback, when polyethylene oxide is blended with specific metal ions and conductive particles, the range of change in resistance to humidity is large. It has also been found that a moisture-sensitive composition having improved water resistance at high humidity can be obtained.

That is, the present invention provides a moisture-sensitive composition comprising 75 to 95% by weight of a crystalline complex composed of polyethylene oxide and an alkali metal salt or an alkaline earth metal salt and 25 to 5% by weight of conductive particles. To do.

The molecular weight of polyethylene oxide used in the present invention is not particularly limited, and any molecular weight can be used.

Further, the alkali metal salt or alkaline earth metal salt used for forming the crystalline complex may be any one as long as it forms a crystalline complex with polyethylene oxide, and specifically, sodium iodide, potassium iodide, chloride lithium,
Sodium chloride, potassium chloride, sodium zincate,
Examples thereof include alkali metal salts such as lithium chlorate, sodium chlorate, lithium perchlorate and sodium perchlorate, and alkaline earth metal salts such as magnesium chloride, calcium chloride and barium chloride.

A crystalline complex is formed by reacting the above-mentioned polyethylene oxide with an alkali metal salt or an alkaline earth metal salt in a solvent such as water, methanol or acetonitrile. The amount of alkali metal salt or alkaline earth metal salt compounded is such that the molar ratio of metal salt to CH ₂ CH ₂ O unit is former: latter = 20: 1 to 2: 1, preferably 8: 1 to 2: 1. . When the blending amount is outside this range, a crystalline complex is not formed when the amount of alkali metal salt or alkaline earth metal salt is small, and when the amount of these salts is too large, a uniform crystal having a sharp melting peak is formed. The ionic complex cannot be obtained.

Next, as the conductive particles, there are carbon black, graphite, pulverized carbon fiber, metal powder and the like, and carbon black is particularly preferable. Various types of carbon black can be used, and examples thereof include furnace black, thermal black, channel black, and acetylene black. The particle size of the conductive particles used in the present invention is not particularly limited, but generally the average particle size is 10 to 200 μm.
Something is used. The compounding amount of the conductive particles is 75 to 95% by weight of the crystalline complex, preferably 75 to 85% by weight.
It should be 25 to 5% by weight, preferably 25 to 15% by weight. If the content of the conductive particles exceeds 25% by weight,
The increase rate of the resistance value of the obtained composition in the measured humidity region decreases, and conversely, when it is less than 5% by weight, the initial resistance value becomes large, which is not preferable.

The kneading of the above crystalline complex and carbon black may be carried out at a kneading temperature of 180 to 200 ° C. for 5 to 20 minutes using an ordinary kneading machine such as a Banbury mixer or a kneading roll.
An organic peroxide may be added as a crosslinking agent during or after kneading. In that case, a known one can be arbitrarily used. In the present invention, it is preferable to add a known antioxidant such as a phenol-based compound, an amine-based compound, or a sulfur-containing compound in an amount of 0.5 to 1.0 part by weight per 100 parts by weight of the complex in order to prevent oxidation during kneading. Instead of adding a crosslinking agent, it is also possible to carry out crosslinking by electron beam irradiation after molding the composition of the present invention.

The composition of the present invention thus obtained comprises alumina,
A moisture-sensitive resistor element can be obtained by forming a sheet on a substrate such as glass or bakelite by a known method such as a pressing method or a casting method and forming an electrode by applying a silver paste or screen printing. At this time, a silicone resin, an epoxy resin, a porous olefin film, a porous fluorine resin film, or the like may be used as the protective film. Also,
Various methods such as conductive adhesive and rivets can be used to take out the lead wires.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 Polyethylene oxide (manufactured by Meisei Chemical Co., Ltd .: E-30, molecular weight 30)
120-g) was placed in a 5-necked three-necked flask, and 2500 ml of methanol was added and dissolved by heating. Next, 102 g of sodium iodide (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 500 ml of methanol in advance and then added to the flask. The mixture was stirred and mixed under reflux for about 10 hours. Then, the methanol was distilled off.
This was vacuum dried for one day to obtain a polyethylene oxide-sodium iodide complex.

80 g of the obtained polyethylene oxide-sodium iodide complex was put into Labo Plastomill (200 ° C.), 0.4 g of an antioxidant (A-60, manufactured by ADEKA ARGUS CORPORATION) was further added, and after melting, carbon black (Mitsubishi Kasei Co., Ltd.
Manufacturing: 20 g of Diablack E) was added and kneaded for 20 minutes to obtain a moisture-sensitive composition.

The composition thus obtained was press-molded into a sheet (15 × 20 mm, t = 0.2 mm), which was then bonded on an alumina substrate and silver paste was used to form electrodes on both ends to reduce moisture sensitivity. An antibody device was obtained. The electric resistance value of this element was adjusted to 40 to 90% RH (30% in a constant humidity and constant temperature chamber (PL-IG manufactured by Tabai Espec).
When measured in ° C), the resistance change width is 10 ^6.0 Ω (40% RH)
It was ~ 10 ^2.8 Ω (90% RH). The results are shown in FIG. Moreover, the shape of this element was stably maintained even in a high humidity region.

Comparative Example 1 The same operation as in Example 1 was performed except that the amount of polyethylene oxide-sodium iodide complex was 60 g and the amount of carbon black was 40 g. The relationship between humidity and resistance value of the obtained device was not linear, and the resistance change width was also small. The results are shown in Fig. 1.

Comparative Example 2 The same operation as in Example 1 was performed except that the polyethylene oxide-sodium iodide complex obtained in Example 1 was directly press-molded to form a sheet. The resistance change width of the obtained device is 10 ^5.4 Ω (40% RH) to 10 ^3.6 Ω (90% RH)
Met. The results are shown in FIG. In addition, this element was found to dissolve in the high humidity range.

〔The invention's effect〕

The composition of the present invention is a moisture-sensitive composition that has a large range of change in resistance to humidity and has improved water resistance in a high humidity range. Therefore, the composition of the present invention can be effectively used as a material for a humidity sensor or a condensation sensor.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the humidity and the resistance value of the elements obtained in Example 1, Comparative Examples 1 and 2.

Claims (2)

[Claims] 1. A crystalline complex comprising polyethylene oxide and an alkali metal salt or an alkaline earth metal salt.
A moisture-sensitive composition comprising 95% by weight of 25 to 5% by weight of conductive particles. 2. The composition according to claim 1, wherein the conductive particles are carbon black.