JPS6250777B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a humidity sensing element, and more particularly to a humidity sensing element in which a pair of electrodes is coated with a film of a copolymer of a monomer having ion exchange ability and a hydrophobic monomer. In order to impart an anti-fog effect to architectural window glass, aircraft, or automobile window glass, current is passed through a heating heater to raise the temperature of the glass and evaporate moisture that aggregates or condenses on the glass surface. is being carried out. Particularly in the case of automobile rear windows, the presence or absence of water droplets or moisture on the glass surface is detected and the circuit is automatically turned on and off.
Automatic water drop removal devices have recently become available that incorporate moisture-sensitive elements to turn them off. Regarding such moisture-sensitive elements, a method has been used in which sodium ions near the glass surface between a pair of electrodes are used as a conductor. However, with this method, when cleaning the glass surface by wiping it with a wet cloth, if you accidentally wipe the electrode part, the sodium ions on the glass surface will be wiped off at the same time. It has the disadvantage that it temporarily loses its moisture-sensing function until it diffuses and elutes to the surface, and when using a DC power source, the sodium ions are localized at the negative electrode, so it is necessary to use an AC power source. It had drawbacks. In order to improve these drawbacks, between the electrodes,
A method of coating a hygroscopic resin with a film containing conductive particles (Japanese Patent Laid-Open No. 50-38236), and a method of coating with a hygroscopic resin having an electrolytic functional group (Japanese Patent Laid-Open No. 50-38236)
75479) etc. have been considered. However, in moisture-sensitive elements coated with these hygroscopic resins, the coating resin layer always contains atmospheric moisture, so the conductive particles or electrolytic functional groups in the hygroscopic resin dissociate, causing The interelectrode resistance value becomes smaller.
As a result, the difference between the interelectrode resistance value during cloudy weather becomes smaller, making it extremely difficult to automatically turn on and off the heating heater accurately, and the difference between cloudy weather and clear weather. Due to the slow desorption of water during operation, the response when turned off is slow, the conduction time of the heating heater becomes longer than necessary, shortening the life of the battery or electrode, and accelerating the deterioration of the coating material over time. Since it is a hygroscopic resin, it is easily contaminated by cigarette smoke generated inside automobiles and plasticizers volatilized from plastic interior materials, and has several drawbacks such as lack of durability. It became clear. As a result of intensive research to overcome these drawbacks, the present inventors discovered that a resin having ion exchange ability and moderate hydrophobicity is extremely excellent as a moisture-sensitive element coating, and the present invention has been made based on this finding. It has been reached. That is, in the present invention, a copolymer of a monomer having ion exchange ability and a hydrophobic monomer is formed between a pair of electrodes provided on a base material, and the molar ratio of the monomer having ion exchange ability is This is a moisture-sensitive element characterized by being coated with a film having a moisture content of 1 to 20 mol%. The particular advantages of the humidity sensing element of the present invention compared to conventional ones are: (1) Extremely excellent resistance characteristics as a humidity sensing element (2) Extremely high response speed (3) Pollution resistance This includes being superior in sex. To explain in more detail the excellent resistance characteristics or extremely high response speed mentioned here, for example, 89.3 mol% of vinyl chloride is used as a hydrophobic monomer, and acrylic is used as a monomer with ion exchange ability. Using a copolymer containing 10.7 mol% acid, the interelectrode resistance was measured in a non-condensing state (hereinafter referred to as A state) and in a state where dew condensation had begun (hereinafter referred to as B state), and found that it was infinite. 0.05 MΩ, for example, a similar test in state A and state B using a hygroscopic resin film made by adding a crosslinking agent such as pyromellitic acid to a hygroscopic resin mainly composed of polyhydroxyethyl methacrylate and curing it. 0.05M each
Ω and 0.03MΩ are shown. Therefore, the copolymer composed of a hydrophobic monomer and a monomer having an ion exchange group in the present invention has a higher interelectrode resistance in state A where no dew condensation occurs and in state B where dew condensation has started. It can be seen that it has extremely excellent resistance characteristics as a moisture-sensitive element, with a large difference in resistance between the two, and that it facilitates the on/off setting of the heating heater. Furthermore, when returning from state B to state A, it was observed that while hygroscopic resins have a slow response in interelectrode resistance due to slow desorption of moisture, the hydrophobic resin of the present invention immediately shows infinite resistance. Ta. This shows that the hydrophobic resin film of the present invention has a particularly high response speed when the heater is turned off. The coating resin for achieving the above-mentioned remarkable effects is a copolymer containing a hydrophobic monomer and a monomer having ion exchange ability in an appropriate ratio, and the hydrophobic monomer is vinyl chloride, Styrene, vinyl acetate, ethylene, propylene, acrylonitrile, methacrylate, vinyl ether, vinylidene halide, etc., and monomers having ion exchange ability such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, etc. can be used. These binary or multicomponent copolymers are effective as coating materials, but
It is desirable to limit the amount to an extent that maintains the hydrophobicity of the copolymer. This is because resins having ion-exchange groups cannot be said to be hydrophobic per se, and therefore, as the number of ion-exchange groups increases, the same drawbacks as those of hydrophilic resins will inevitably appear. Furthermore, since polymers having ion exchange groups become spongy, they contain a large amount of water and solvent in the polymer mass, making handling extremely difficult during dehydration, washing, and drying after completion of polymerization. A solution of these copolymers dissolved in a solvent was applied to the electrodes on a glass plate for sensor function testing as shown in the drawing, and the electrodes were placed in a room with a room temperature of 22 ± 3°C and a humidity of 70 ± 10% on the glass without baking the electrodes. Cold water at 8±1° C. was poured over the surface, and the interelectrode resistance in state A and state B was examined (hereinafter, such a test will be referred to as a shower test). Note that 1 in the figure is a resistance measuring device, and a
was 0.5 mm, and b was 30 cm. As a result, a copolymerization of 80 to 99 mol%, preferably 80 to 95 mol% of a hydrophobic monomer and 1 to 20 mol%, preferably 5 to 20 mol% of a monomer having an ion exchange group is obtained. The combination is effective as a moisture-sensitive element, and if the content of the monomer having an ion exchange group is 1 mol% or less, the interelectrode resistance in the B state increases; It has been found that when the amount is 20 mol % or more, the resistance between the electrodes in state A becomes small, making it difficult to turn on and off the heater switch in any case. When coating the electrode part, the solvent used to dissolve the resin may be any solvent as long as it can dissolve the copolymer, such as cyclohexanone, methyl cellosolve, tetrahydrofuran, acetone, and nitrobenzene. When coating the electrode with such a resin solution, if the thickness of the resin film is too large, the response will be slow and the resistance between the electrodes will increase in condensation, which is not preferable, so the film thickness should be 3μ or less. preferable.
Moreover, in the case where the electrode surface is not coated with resin and a resin film is formed only between the electrodes, the present invention is not limited to this. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. Example 1 In a 500 ml or 1000 ml stainless steel reactor or glass reactor, the combinations of hydrophobic monomers and monomers with ion exchange groups include vinyl chloride, acrylic acid, acrylonitrile, methacrylic acid, styrene and itacon. Acid or styrene and methacrylic acid were subjected to suspension copolymerization or solution copolymerization in the presence of a radical initiator, and after drying, a resin having the composition shown in Table 1 was obtained. The resin was dissolved in each good solvent (cyclohexanone, tetrahydrofuran, acetone, etc.) and a 1-5% solution was used as a sample solution. Table 1 shows the results of a shower test performed on the moisture sensitive elements (Samples 1 to 4) coated with the obtained sample liquid to a film thickness of 1 to 2 μm. Comparative Example A solution of polyhydroxyethyl methacrylate, a hygroscopic resin, dissolved in methyl cellosolve, and 15 parts of crosslinking agent pyromellitic acid added to 100 parts of polyhydroxyethyl methacrylate, was applied to the electrodes on a glass plate for sensor function testing. , 30 at 80℃
A comparative sample was prepared by heat treatment. A shower test was conducted on this comparative sample, and the results are also listed in Table 1.

[Table] Example 2 In a 500ml or 1000ml stainless steel reactor, acrylic acid and vinyl chloride (or with the addition of vinyl acetate) were suspension copolymerized in the presence of a radical initiator, dehydrated, and dried. A resin having the composition shown in Table 2 was obtained. Each of the resins was dissolved in cyclohexanone to make a 1-5% solution, and the film thickness was 1.
A shower test was conducted on the moisture sensitive element coated to a thickness of ~2μ. The results are shown in Table 2.

【table】

[Table] Example 3 In order to investigate the resistance of the copolymer composition of Sample 8 to contamination expected inside an automobile, glass for sensor function testing was installed inside the automobile, and various contamination treatments were performed. Table 4 shows the results of examining the resistance change between the electrodes. Further, Table 5 shows the results of a similar stain resistance test performed on a hygroscopic resin as a comparative example.

【table】

【table】

【table】 [Brief explanation of the drawing]

The drawing is an explanatory diagram showing a sensor function test glass used in a shower test, in which 1 indicates a resistance measuring device and 2 indicates the glass.

Claims (1)

[Claims] 1 A copolymer of a monomer having ion exchange ability and a hydrophobic monomer, which has a molar ratio of the monomer having ion exchange ability of 1
A moisture-sensitive element characterized by being coated with a film containing ~20 mol%.