JPS6161626B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a humidity-sensitive resistor that detects changes in atmospheric humidity as changes in resistance. It has been known that resins in which conductive powder is dispersed exhibit resistance changes based on changes in atmospheric humidity. Attempts have also been made to utilize such characteristics in humidity sensing elements. However, as the conductive particles in the resin move each time the humidity detection history is repeated, there are problems with response, reproducibility, and hysteresis. In order to overcome these difficulties, attempts have been made to crosslink the resin with an organic compound crosslinking agent to eliminate the movement of conductive particles in the resin. By applying such measures, the strength of the resin film is increased and the movement of the conductive particles is suppressed, but there is a problem that the water wettability deteriorates and the humidity detection ability decreases. Therefore, the present invention was made to solve the above-mentioned problems, and its purpose is to provide a humidity-sensitive resistor having excellent sensitivity to humidity, excellent responsiveness, hysteresis, etc. do. That is, in the humidity-sensitive resistor according to the present invention, a humidity-sensitive resistor film is provided on the counter electrode, and the resistance value increases as the relative humidity increases. The moisture-sensitive resistive film contains a conductive polymer and a conductive powder, and is characterized by being treated with a zirconium salt and dehydrated. A moisture-sensitive resistor having such a structure breaks electrical contact between conductive particles due to the swelling of the resin when absorbing moisture, resulting in an increase in electrical resistance. A feature of this invention is that the surface of the moisture-sensitive resistive film containing a hydrophilic polymer and conductive powder is treated with a zirconium salt and is also dehydrated. The surface treatment of the moisture-sensitive resistive film is carried out as follows. In other words, a film is formed using a paste containing a hydrophilic polymer and conductive powder, and the film is immersed in a solution containing a zirconium salt, or a solution containing a zirconium salt is sprayed onto the film and applied. It is processed by
In short, before treatment with the alkaline solution described below,
It can be treated with zirconium salt. The moisture sensitive resistive membrane treated with the zirconium salt is then subjected to a dehydration treatment. This dehydration treatment is performed as follows. That is, the film is immersed in or brought into contact with an alkaline solution, then washed with water and dried. In addition, the film may be brought into contact with the vapor of an alkaline solution. At this time, a dehydration reaction occurs between the hydrophilic group (OH group) of the hydrophilic polymer's glycol bond and the zirconium salt, and the surface of the moisture-sensitive resistance film becomes strong and hydrophobic, and has stable characteristics. This results in a highly reliable moisture-sensitive resistor. In other words, the hydrophilicity of the surface of the moisture-sensitive resistance film decreases,
As a result of its increased hydrophobicity, it does not dissolve even in the presence of water, making it a stable structure in the presence of water. On the other hand, the interior of the moisture-sensitive resistance film is mainly composed of hydrophilic polymers and conductive powder, and in this region, electrical contact between conductive particles is broken due to swelling of the polymer resin, resulting in an increase in electrical resistance. It works like this. Dehydration treatment includes treatment with alkaline solution,
It can also be carried out by heat treatment. The heating temperature for the heat treatment is sufficient as long as the dehydration reaction is caused by heating; for example, if the treatment is performed at a temperature of 100° C. or higher, the reaction will be completed quickly. The conductive particles constituting a part of the moisture-sensitive resistive film, which is a feature of the present invention, include carbon, for example, but other compound conductors, metals, and the like may also be used. The particle size of the conductive particles is preferably 10 μm or less in order to obtain good response performance. Examples of hydrophilic polymers include polyvinyl alcohol, polyvinyl alcohol and cellulose derivative polymers, saponified polyacrylic acid methyl esters, polyacrylic acid ethyl saponified materials, and the like. In the above configuration, the polyvinyl alcohol polymers include the following. Products obtained by completely saponifying or partially saponifying polymers of vinyl acetate, other vinyl esters, and copolymers thereof. A copolymer made by copolymerizing vinyl acetate, other vinyl esters, and various unsaturated monomers, such as α-olefins, vinyl chloride, acrylonitrile, acrylamide, acrylic esters, and methacrylic esters. monster. Polyvinyl alcohol copolymers esterified with cyclic acid anhydrides of such polyvinyl alcohol polymers and carboxyl group-modified polyvinyl alcohol polymers. Examples of zirconium salts that are compatible with hydrophilic polymers include zirconium oxychloride, chloride, acetate, sulfate, and other zirconium compounds, and water-soluble and alcohol-soluble ones are used. The blending ratio of each component of the hydrophilic polymer, the zirconium salt that is compatible with this hydrophilic polymer, and the conductive powder that make up the moisture-sensitive resistive film whose resistance value increases as the relative humidity increases is as follows: The following range is selected. That is, the hydrophilic polymer is 20 to 80% by weight, the zirconium salt is 20% by weight or less, and the conductive powder is 20 to 80% by weight. The reason why the hydrophobic polymer is 20 to 80% by weight and the conductive powder is 20 to 80% by weight is that if the hydrophilic polymer is less than 20% by weight and the conductive powder is more than 80% by weight, it will cause resistance due to moisture absorption. This is because if the change is small, and if the hydrophilic polymer exceeds 80% by weight and the conductive powder exceeds 20% by weight, the resistance value of the moisture-sensitive resistor itself increases and is not suitable for practical use. Furthermore, the reason why the zirconium salt is set at 20% by weight or less is that if it exceeds 20% by weight, the swelling of the moisture-sensitive resistor due to water absorption will be small and the change in resistance value will be small. The present invention will be described in detail below based on examples. Example 1 Polyvinyl alcohol was dissolved in alcohol and ethylene glycol monobutyl ether. Add an equal amount of carbon black powder with an average particle size of 30 mμ to 100 parts by weight of this polyvinyl alcohol,
A paste was made by kneading. On the other hand, an insulating substrate having comb-shaped carbon electrodes with an electrode spacing of 0.3 mm and a total electrode facing length of 6.5 mm is prepared on its surface, and a paste is applied onto this insulating substrate using a coating means so that the carbon electrodes are hidden. Next, this insulating substrate was immersed in a 0.5% alcohol aqueous solution containing 0.2% zirconium oxychloride hydrate, pulled up, and dried to make the coating film contain zirconium salt. Furthermore, the insulating substrate was immersed in an alkaline solution to cause a dehydration reaction between polyvinyl alcohol and zirconium salt. Afterwards, it was washed with water and dried. Next, heat treatment was performed. Heat treatments were performed at temperatures of 100°C, 150°C, and 180°C, respectively, to obtain samples. When the resistance value of the obtained humidity-sensitive resistor was measured for changes in relative humidity, the results shown in FIG. 1 were obtained. In the figure, number 1 is heat treated at 100°C, number 2 is heat treated at 150°C, and number 3 is heat treated at 180°C. In addition, numbers 4 and 5 are outside the scope of this invention as they do not contain zirconium salt, and number 4 is 100°C.
No. 5 was heat-treated at 180°C. It can be seen from FIG. 1 that the device according to the present invention has a characteristic of a large rate of change in resistance in a high humidity region, and has a small hysteresis. On the other hand, when no zirconium salt is contained as in numbers 4 and 5, the maximum value is seen in the resistance-relative humidity characteristic curve near 90% relative humidity, the hysteresis is large, and the initial resistance value (at relative humidity 0%) is The problem is that the resistance value is high. Example 2 A paste film containing zirconium salt was provided on an insulating substrate in the same manner as in Example 1, and heat treated at 150°C without immersing it in an alkaline solution.
A moisture-sensitive resistor was obtained by reacting polyvinyl alcohol with a zirconium salt. When the resistance-relative humidity characteristics of this humidity-sensitive resistor were measured, the results shown by number 6 in FIG. 2 were obtained, and a humidity-sensitive resistor was obtained that showed a large change in resistance in a high humidity region. Example 3 In Example 1, using a sample that was treated with an alkaline solution and then heat-treated at 150°C, the process of repeating drying and dew condensation was one step, and this was repeated 500 times. The initial resistance value in the dry state was 2KΩ, and the initial resistance value in the condensed state was 7.1MΩ, but after 500 cycles, the resistance value in the dry state was 2.2KΩ, and the resistance value in the condensation state was 8MΩ. A moisture-sensitive resistor was obtained which had almost no problems in actual use and had stable characteristics. Example 4 In the treatment step in Example 1, treatment with a zirconium salt was performed with a 0.5% alcohol aqueous solution containing 2% zirconium oxychloride hydrate, and then treated in the same manner as in Example 1 to obtain a moisture-sensitive resistor. . After washing with water, the heat treatment temperature was 150°C. When the resistance-relative humidity characteristics of this humidity-sensitive resistor were measured, a humidity-sensitive resistor with a large resistance change in a high humidity region was obtained, as shown by number 7 in FIG. Example 5 Polyvinyl alcohol was dissolved in alcohol and ethylene glycol monobutyl ether. Additionally, ethyl cellulose was dissolved in ethylene glycol monobutyl ether. To 70 parts by weight of polyvinyl alcohol and 30 parts by weight of ethyl cellulose, 100 parts by weight of carbon black powder having an average particle size of 30 mμ was added and kneaded to prepare a paste. This paste was applied onto the insulating substrate prepared in Example 1 using a coating means. Next, this insulating substrate was immersed in a 0.5% alcohol aqueous solution containing 0.2% zirconium oxychloride hydrate, pulled up, and dried to make the coating film contain zirconium salt. Further, the insulating substrate was immersed in an alkaline solution to react, and then washed with water and dried. Subsequently, heat treatment was performed at a temperature of 100°C to obtain a sample. When the resistance value of the obtained humidity-sensitive resistor was measured for changes in relative humidity, the results shown by number 8 in FIG. 4 were obtained. As is clear from FIG. 4, the humidity sensitive resistor according to this example has a large resistance change rate in a high humidity region. Example 6 As in Example 1, a paste was applied onto an insulating substrate using a coating means. After drying, it was immersed in a zirconium acetate solution. The concentrations of the zirconium acetate solutions were 0.5% and 5%, respectively. moreover,
After drying and heat treatment at 150°C, samples were obtained. When we measured the change in resistance value at each relative humidity for each sample, we found that both
~3KΩ, 5-8KΩ at 80% relative humidity, relative humidity
A resistance change of 150 to 300 KΩ was observed at 100%, and a humidity-sensitive resistor with a large resistance change at high relative humidity was obtained. Example 7 Polyvinyl alcohol was dissolved in alcohol and water. In addition, an alcohol aqueous solution containing 10% zirconium oxychloride hydrate was prepared. Next, 100 parts by weight of polyvinyl alcohol, 5 parts by weight of an alcohol aqueous solution containing zirconium oxychloride hydrate, and 100 parts by weight of carbon black powder having an average particle size of 30 mμ were mixed and kneaded to prepare a paste. This paste was applied onto the insulating substrate prepared in Example 1 using a coating means, and the insulating substrate was further immersed in an alkaline solution to react with polyvinyl alcohol and zirconium salt. Afterwards, it was washed with water and dried. Heat treatments were performed at temperatures of 100°C, 150°C, and 180°C to obtain samples. In addition, samples were also prepared that were heat-treated at 150° C. without being immersed in the alkaline solution. When the resistance value of the obtained humidity-sensitive resistor was measured for changes in relative humidity, the results shown in FIG. 5 were obtained. In the figure, number 9 is heat treated at 100℃, number 10 is heat treated at 150℃, number 11 is heat treated at 180℃, and number 12 is heat treated at 150℃ without alkaline solution treatment. It is. As a reference material, the change in resistance value with respect to relative humidity was similarly measured for a sample heat-treated at 180° C. without containing a zirconium salt, and the results are also shown in FIG. In the figure, number 13 is the measurement result. As is clear from FIG. 5, when no zirconium salt is contained, a large change in resistance due to hysteresis is shown. Furthermore, the resistance value of each sample in a dew condensed state was measured, and the results are shown in Table 1 in comparison with the resistance value at 50% relative humidity.

[Table] As is clear from Table 1, the products according to the present invention (sample numbers 9, 10, 11, and 12) are moisture sensitive because the moisture sensitive resistive film contains a reaction product of polyvinyl alcohol and zirconium salt. The surface of the resistive film has good water wettability and exhibits a large resistance change rate. In addition, regarding sample number 11, the process of repeating the dry state and dew state is one process, and this is repeated 1000 times.
After repeating the test several times, the resistance of sample number 11 only changed from 8.0 MΩ to 13 MΩ during condensation, but the resistance of sample number 13 returned to its original value after drying after the condensation test. The resistance value did not return to its original value and increased to 75KΩ. As described above, in the humidity-sensitive resistor according to the present invention, the hydrophilic polymer constituting a part of the humidity-sensitive resistive film and the zirconium salt having compatibility with the hydrophilic polymer undergo a reaction or heat treatment by contact with an alkaline solution. It is composed of a moisture-sensitive resistive film that can improve the film strength without reducing its water wettability, has good moisture-sensitive characteristics, and has small hysteresis. be. In addition, the reaction product between a hydrophilic polymer and a zirconium salt introduces zirconium into the polymer by bonding with oxygen, which improves the thermal conductivity of the polymer and enhances its moisture-sensing function. It is possible to construct something with excellent responsiveness. Furthermore, when treated with an alkaline solution, the reaction can be carried out at room temperature, and a moisture-sensitive resistor with excellent properties can be obtained with simple operations.

[Brief explanation of the drawing]

FIGS. 1 to 5 are diagrams showing resistance-relative humidity characteristics.

Claims (1)

[Claims] 1. A moisture-sensitive resistive film is provided on the counter electrode,
In a humidity-sensitive resistor whose resistance value increases with an increase in relative humidity, the humidity-sensitive resistive film contains a hydrophilic polymer and a conductive powder,
A moisture-sensitive resistor, characterized in that the moisture-sensitive resistor film is coated with a zirconium salt and subjected to dehydration treatment. 2. Among the components of the moisture-sensitive resistance film, the proportions of hydrophilic polymer and conductive powder are 20 to 80% by weight, respectively.
Claim 1 comprising a range of 80 to 20% by weight
Moisture-sensitive resistor as described in section. 3. The moisture-sensitive resistor according to claim 1, wherein the dehydration treatment is performed by contacting with an alkaline solution. 4. The moisture-sensitive resistor according to claim 1, wherein the dehydration treatment is performed by heat treatment. 5. The polymer according to claim 1, wherein the hydrophilic polymer is at least one selected from polyvinyl alcohol, polyvinyl alcohol and cellulose derivative polymer, saponified polyacrylic acid methyl ester, and polyacrylic acid ethyl saponified product. Moisture resistor.