JPH05133921A - Humidity sensor and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] (Modified) [Constitution] In a humidity sensor using a humidity sensitive body 3 comprising a heat treatment product of oxide particles and an inorganic salt as a main component, a solvent-soluble fluorine-containing polymer is formed on the surface of the moisture sensitive body. A humidity sensor characterized in that a fluorine-containing polymer layer 4 is formed on a moisture sensitive body by applying a solution, and an aqueous solution or a general organic solvent is eliminated while maintaining the moisture sensitive property. [Effect] The characteristics did not change even when the electrolyte was contacted, and a highly accurate and highly reliable humidity sensor could be achieved. Moreover, since it can be manufactured by an easy process, it can be widely applied as a low-cost, highly accurate and highly reliable humidity sensor to fields requiring humidity measurement and humidity control. It can also be used for portable purposes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor for detecting humidity by changing electric characteristics of an element in response to humidity.

[0002]

2. Description of the Related Art In recent years, the number of fields requiring humidity measurement and humidity control has increased, and the importance of humidity sensors has come to be recognized.

Humidity sensors that detect humidity by varying the electrical characteristics of the element in response to humidity include electrolyte-based, metal-based, polymer-based, and ceramic-based humidity sensors, and various systems have been studied. However, what is currently put into practical use is a polymer-based and ceramic-based humidity sensor. Both of them utilize the property that the resistance value or the capacitance of the element changes due to the adsorption and desorption of water with respect to the element.

[0004]

However, in the conventional humidity sensor, when the humidity sensitive body comes into contact with the electrolytic solution, the humidity sensor is remarkably deteriorated and the electrolyte cannot be regenerated due to the adhesion of the electrolyte. Therefore, it could not be used under conditions involving seawater, sweat, drinking water and the like.

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a highly accurate and highly reliable humidity sensor whose characteristics do not change even when the electrolytic solution comes into contact therewith. It is in.

[0006]

The humidity sensor of the present invention comprises:
It is characterized in that a fluorine-containing polymer layer is formed on a moisture-sensitive material mainly composed of a heat-treated product of oxide particles and an inorganic salt.

The method of manufacturing the humidity sensor of the present invention is
In a humidity sensor using a moisture-sensitive material whose main component is a heat-treated product of oxide particles and an inorganic salt, a solvent-soluble fluorine-containing polymer solution is applied to the surface of the moisture-sensitive material so that the moisture-containing material has a fluorine-containing content. It is characterized by forming a polymer layer.

[0008]

In the water repellent treatment of the moisture sensitive body, since the liquid must be completely removed, the contact angle with water must be at least 90 degrees or more, preferably 100 degrees or more. Therefore, since the polarizability is small, it is indispensable to introduce fluorine having a remarkably small intermolecular cohesive force.

Further, in order to detect humidity, it is necessary to form a very thin and dense film so that water vapor can move in a short time.

Fluorine-containing polymers represented by polytetrafluoroethylene have excellent characteristics such as heat resistance, chemical resistance, and weather resistance, but they are insoluble in solvents and can only be coated as powder. Further, even if the vapor deposition method is used, only a grainy film can be formed, which does not satisfy the conditions. Also, the adhesion strength was weak, which was a problem. Recently, a copolymer of a solvent-soluble polymer and a fluorine-containing polymer and a synthetic polymer having a special fluorine-containing side chain have been obtained. Maintains the characteristics of conventional fluoropolymers and is soluble in solvents,
By coating, a smooth surface without pinholes can be easily obtained. Depending on the material, a sufficient water repellency effect can be obtained with a film thickness of about 100Å.

[0011]

【Example】

(Example 1) To 75 ml of colloidal silica containing 30 g of silica particles having a particle size of 0.3 μm in 100 g, 150 ml of ethanol, 1 ml of hydrochloric acid and 25 ml of ethyl silicate were added, and after stirring for 1 hour, 27 g of lithium chloride was added,
Stir for a further 30 minutes. This solution was dip-coated on an alumina substrate on which comb-shaped electrodes made of Au paste were formed by screen printing, and heat-treated at 500 ° C. for 1 hour. Next, this substrate was treated with a manganese nitrate aqueous solution (7
(0% by weight) and then heat-treated at 200 ° C. for 1 hour to obtain a moisture-sensitive film.

Solvent-soluble fluoropolymer Cytop CT
X (manufactured by Asahi Glass Co., Ltd.) was dissolved in a perfluoro solvent and applied on the surface of the moisture-sensitive film by dipping. The portions that do not require water repellent treatment were masked with taping, resist, etc. in advance, and were removed after applying Cytop CTX. An appropriate value can be selected for the concentration and the film thickness of the solution, but here, a solution with a concentration of 1% by weight is pulled up at a rate of 10 cm / min
It was dried at 180 ° C. to form a fluorine-containing polymer layer having a film thickness of 500Å. It was confirmed by microscopic observation that the thin film formed was extremely dense and homogeneous. The contact angle with water was 110 degrees, and high water repellency was obtained.

A perspective view of the humidity sensor thus manufactured is shown in FIG. In FIG. 1, 1 is a substrate, 2 is an electrode,
3 is a part of the moisture sensitive film. In addition, a schematic sectional view is shown in FIG.
Shown in. In FIG. 2, 4 is a fluorine-containing polymer layer.
FIG. 3 shows the humidity sensitivity characteristics of this humidity sensor. From FIG. 3, the humidity sensor of the present invention has a low resistance value, an appropriate change width of the resistance value, and the characteristics do not change with temperature.
It turns out to be easy to use. In addition, the response to changes in humidity was fast within 10 seconds, and there was no problem in practical use.

This humidity sensor was immersed in saturated saline solution at 60 ° C.
After the immersion for 0 hour, the characteristics were measured and found to be the same as in FIG. 3 within the range of measurement error. Therefore, it can be seen that this humidity sensor has extremely high durability and reliability.

Example 2 To 200 ml of the same colloidal silica as in Example 1, 30 g of lithium acetate was added and stirred for 1 hour. This solution was spin-coated on a glass substrate having a comb-shaped electrode formed by depositing Cr and Au in this order and heat-treated at 400 ° C. for 1 hour to obtain a moisture-sensitive film.

The fluoroethylene-vinyl ether copolymer was dissolved in toluene and applied on the surface of the moisture-sensitive film by spin coating. An appropriate value can be selected for the concentration and the film thickness of the solution, but here, a solution having a concentration of 2% by weight is applied at 3000 rpm for 1 minute and dried at 120 ° C. to form a fluoroethylene-vinyl ether film having a thickness of 0.1 μm. A copolymer polymer layer was formed. Unnecessary parts were wiped off with toluene. It was confirmed by microscopic observation that the thin film formed was very dense and homogeneous. Contact angle with water is 10
Water repellency as high as 5 degrees was obtained.

The characteristics of the humidity sensor thus manufactured are as follows.
The resistance value was low, the change width of the resistance value was appropriate, and the characteristics did not change with temperature. In addition, the response to changes in humidity was quick within 10 seconds, and there was no problem in practical use.

This humidity sensor was immersed in saturated saline solution at 60 ° C.
After the immersion for 0 hour, the characteristics were measured again, and it was the same within the range of the measurement error as compared with the initial value. Therefore, it can be seen that this humidity sensor has extremely high durability and reliability.
If the fluorine-containing polymer layer was not formed, the resistance value decreased by several orders of magnitude by immersion in saturated saline for 1 minute at room temperature, and the characteristics did not return even after washing with water.

Example 3 100 g of a Pt-Pd comb-shaped electrode was formed on a quartz glass substrate formed by screen printing.
Roll-coat a colloid containing 10 g of alumina particles having a particle size of 0.1 μm into 100 ml of ethyl cellosolve.
It heat-processed at 0 degreeC for 1 hour. Next, this substrate was immersed in a lithium chloride aqueous solution (40% by weight), and then at 1
Heat treated for hours. Further, this substrate was immersed in an aqueous solution of nickel nitrate (50% by weight) and then heat-treated at 200 ° C. for 1 hour to obtain a moisture sensitive film.

Polydiperfluoroalkyl fumarate was dissolved in a fluorine-based solvent and applied on the surface of the moisture-sensitive film by spin coating. The concentration and film thickness of the solution can be selected as appropriate, but here, a solution with a concentration of 0.3% by weight is applied at 3000 rpm for 1 minute, dried at 80 ° C, and a polydiperfluoroalkyl film with a film thickness of 300Å is applied. A fumarate layer was formed.
It was confirmed by microscopic observation that the thin film formed was very dense and homogeneous. The contact angle with water was 115 degrees, and high water repellency was obtained.

The characteristics of the humidity sensor thus manufactured are as follows.
The resistance value was low, the change width of the resistance value was appropriate, and the characteristics did not change with temperature. In addition, the response to changes in humidity was quick within 10 seconds, and there was no problem in practical use.

This humidity sensor is immersed in saturated saline solution at 60 ° C.
After the immersion for 0 hour, the characteristics were measured again, and it was the same within the range of the measurement error as compared with the initial value. Therefore, it can be seen that this humidity sensor has extremely high durability and reliability.

Example 4 10 g of silica, 20 g of manganese dioxide and 20 g of potassium nitrate were mixed, press-molded and then heat-treated at 600 ° C. for 1 hour. A cube having a side of 5 mm was cut out from the obtained heat-treated product, and an electrode was attached to the cube to prepare a humidity sensor as shown in FIG. In FIG. 4, 3 is a moisture sensitive material, 2 is an electrode, and 5 is a lead wire.

"Teflon AF" (manufactured by DuPont) was dissolved in a fluorine-based solvent to prepare a solution having a concentration of 0.5% by weight. Completely immerse the above-mentioned humidity sensor there, 10 cm
It is pulled up at a speed of every minute, dried at 180 ° C.
A 0Å fluorine-containing polymer layer was formed. It was confirmed by microscopic observation that the thin film formed was extremely dense and homogeneous. The contact angle with water was 110 degrees, and high water repellency was obtained.

The characteristics of the humidity sensor thus manufactured are as follows.
The resistance value was low, the change width of the resistance value was appropriate, and the characteristics did not change with temperature. In addition, the response to changes in humidity was quick within 10 seconds, and there was no problem in practical use.

This humidity sensor was immersed in saturated saline solution at 60 ° C.
After the immersion for 0 hour, the characteristics were measured again, and it was the same within the range of the measurement error as compared with the initial value. Therefore, it can be seen that this humidity sensor has extremely high durability and reliability.

[0027]

As described above, the humidity sensor of the present invention does not change its characteristics even when the electrolytic solution comes into contact with it, and it is possible to achieve a highly accurate and highly reliable humidity sensor. Moreover, since it can be manufactured by an easy process, it can be widely applied as a low-cost, highly accurate and highly reliable humidity sensor to fields requiring humidity measurement and humidity control. It can also be used for portable purposes.

[Brief description of drawings]

FIG. 1 is a perspective view of a humidity sensor of the present invention with a part of a moisture sensitive film removed.

FIG. 2 is a schematic cross-sectional view of the humidity sensor of the present invention.

FIG. 3 is a humidity sensitive characteristic diagram of the humidity sensor of the present invention.

FIG. 4 is a perspective view of the humidity sensor of the present invention.

[Explanation of symbols]

 1 Substrate 2 Electrode 3 Moisture Sensitive Body or Moisture Sensitive Film 4 Fluorine-Containing Polymer Layer 5 Lead Wire

Claims (2)

[Claims] 1. A humidity sensor characterized in that a fluorine-containing polymer layer is formed on a moisture sensitive body containing, as a main component, a heat-treated product of oxide particles and an inorganic salt. 2. A humidity sensor using a humidity sensitive material containing a heat-treated product of oxide particles and an inorganic salt as main components, wherein a moisture-sensitive fluorine-containing polymer solution is applied to the surface of the moisture sensitive material to obtain moisture sensitivity. A method for manufacturing a humidity sensor, which comprises forming a fluorine-containing polymer layer on a body.