JPH1123507A - Moisture-sensitive element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a stable operation for a long period by forming a membrane made of a polymer material into a porous structure capable of holding electrolyte salt after it absorbs moisture and becomes an aqueous solution, and suppressing the electrolyte salt from flowing out of the functional membrane. SOLUTION: A hydrophilic polymer material, e.g. polyvinyl alcohol, is formed into a porous membrane 301. A membrane (holding membrane) 303 of a hydrophobic polymer material, e.g. polyvinyl acetate, is formed on the inner walls of multiple holes 302 formed in the membrane 301. The membrane 303 can be considered as a mixed body of the hydrophilic polymer material and the hydrophobic polymer material. The strength of the membrane 301 is increased by the existance of the membrane 303. When the membrane 301 is impregnated with a lithium chloride aqueous solution, lithium chloride 304 is held in the holes 302. The lithium chloride aqueous solution is held in the porous holes of the functional membrane impregnated with the lithium chloride aqueous solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture-sensitive element for measuring humidity, dew point, and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, moisture in an atmosphere has been regarded as a major factor influencing quality. Indoor humidity control, moisture management during heat treatment such as carburizing and tempering,
There is a demand for measuring and controlling the absolute water content in various fields, such as humidity control of blast furnace air, humidity measurement and control of closed containers in warehouses, storage rooms, and laboratories. In recent years, humidity control in semiconductor manufacturing plants has become indispensable, and there has been an increasing demand for use in managing the growth of agricultural products. On the other hand, the necessity of measuring the dew point in the weather is increasing not only for the weather forecast but also for the laundry forecast, etc., and the demands which are more closely related to daily life are increasing. In response to these demands, some measurements of absolute water content have become widespread.

[0003] A lithium chloride dew point meter that utilizes the deliquescent of lithium chloride (LiCl), which is one of the methods for measuring the absolute moisture content, uses a change in the electrical conductivity of lithium chloride due to moisture absorption and a change in temperature due to a temperature change. A dew point temperature is measured from the change in vapor pressure of a lithium aqueous solution. A glass fiber tape is impregnated with an aqueous solution of lithium chloride, and two thin metal wires are spirally wound in parallel as electrodes on the glass fiber tape. And When an AC voltage is applied to the two electrode wires, a current is generated between the electrodes, the liquid temperature rises, and the water in the aqueous solution evaporates to a saturated state, and lithium chloride crystals begin to precipitate. As the crystals begin to precipitate, the electrical resistance of the aqueous solution increases rapidly, the current decreases and the temperature rise is suppressed, maintaining a temperature corresponding to the surrounding water vapor pressure. When the surrounding water vapor pressure drops, the temperature of the aqueous solution evaporates and precipitates crystals, so the temperature drops further.On the other hand, when the surrounding water vapor pressure rises, the water absorbs the water, the saturated state is broken, and the current increases. , The temperature will rise. In this way, the temperature of the saturated aqueous solution of lithium chloride is maintained so as to equilibrate with the surrounding water vapor pressure. If the equilibrium temperature at this time is known, the dew point temperature can be obtained.

[0004]

However, in such a lithium chloride dew point meter, when a moisture-sensitive element is left for a long time in a high-temperature and high-humidity atmosphere, lithium chloride is eluted sharply.
The properties are significantly reduced. Therefore, it was necessary to perform maintenance while replenishing lithium chloride periodically. As described above, in the conventional lithium chloride dew point meter, if the element is left in a high-temperature, high-humidity atmosphere for a long time, the state will be as follows. That is, since lithium chloride has a strong deliquescence, it absorbs water vapor in the atmosphere and dissolves therein to form an aqueous solution. Normally, an electric current is applied to them to raise the liquid temperature,
Although water is evaporated, in a very hot and humid atmosphere, the evaporation of the water cannot catch up, and the concentration of the aqueous lithium chloride solution decreases. As a result, the fluidity of the aqueous solution of lithium chloride becomes too good, and the aqueous solution flows out from the glass fiber tape holding the aqueous solution. As described above, when the aqueous lithium chloride solution flows out, the amount of lithium chloride used in the dry / wet element decreases, and the resistance increases even with the same water content, so that accurate humidity measurement cannot be performed.

[0005] For this reason, conventionally, it has been necessary to maintain and maintain the lithium chloride concentration at a predetermined concentration by, for example, periodically replenishing lithium chloride, and there has been a problem that the management is troublesome. The present invention has been made to solve the above problems, and has as its object to enable a moisture-sensitive element to operate stably for a long period of time.

[0006]

Means for Solving the Problems The moisture-sensitive element of the present invention comprises:
In a moisture sensitive element including a functional film formed in contact with each of the opposed electrodes disposed on the substrate, and a temperature measuring unit for measuring the temperature of the functional film, the functional film has a hydrophilic property. A holding film made of a polymer material of No. 1 and having a porous structure provided with a plurality of fine pores and having a hydrophobic second polymer material formed on the inner wall of the pores;
And an electrolyte salt held in the pores. Therefore, the electrolyte salt is in a state of being confined in a plurality of fine pores in which the hydrophilic group is present, and on the other hand, entry and exit of water in the presence of the electrolyte salt are not hindered. In addition, the method for manufacturing a moisture-sensitive element according to the present invention includes a functional film formed in contact with each of the opposing electrodes disposed on the substrate, and a temperature measuring unit that measures the temperature of the functional film. In the method for producing a moisture-sensitive element, a functional film was produced as follows. That is, first, a first polymer material having a hydrophilic property is dissolved in a first solvent having a polarity and dissolving the first polymer material to prepare a base material solution. Next, an organic material having hydrophobicity that is not dissolved in the first solvent is dispersed in the base material solution to prepare an emulsion.
Next, the organic material dispersed in the form of droplets in the emulsion is polymerized, and the organic material is polymerized in the matrix solution. Make a liquid. Next, the suspension is applied to a predetermined region on the substrate to form a coating film. Next, part of the moisture in the coating film is removed, and a part of the particles is exposed to the surface of the coating film. Next, the coating film is immersed in a second solvent in which the first polymer material does not dissolve and the second polymer material dissolves, thereby dissolving the second polymer material. Then, a porous film having a porous structure having a large number of pores formed with a film made of the second polymer is formed. Then, the porous membrane was immersed in an aqueous solution of an electrolyte salt, the porous membrane was impregnated with the aqueous solution of the electrolyte salt, and the electrolyte salt was retained in a plurality of pores constituting the porous membrane. That is, a film made of the first polymer material is formed in a porous structure, and the electrolyte salt is held in the plurality of pores.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration of a moisture-sensitive element according to an embodiment of the present invention, and FIG. 2 is a plan view of the moisture-sensitive element. In this moisture-sensitive element, a comb-shaped opposing electrode 102 is formed at the center of the upper surface of a substrate 101 formed of alumina, and substantially covers the opposing electrode.
A functional film 103 is provided. The functional film 103 is impregnated with an aqueous solution of lithium chloride as an electrolyte salt. A heater 104 and a temperature sensor 105 for measuring the temperature of the substrate 101 are provided in the center of the substrate 101.
Is buried. The heater 104 and the temperature sensor 105 are provided below the counter electrode 102.

Further, the counter electrode 1 is placed on the substrate 101.
02 at the ends of the connection terminals 107a and 107b, respectively.
Is provided. Also, terminals 108a and 108b for supplying power to the heater 104 and the temperature sensor 10
5 are provided with terminals 109a and 109b. Then, lead wires 111a, 111
b, 112a, 112b, 113a and 113b are respectively connected by a conductive adhesive or solder. These leads are connected to a power supply (not shown) and a computer. The material of the substrate 101 may be another ceramic.

The substrate 101 is, for example, 6 mm × 50 m
An alumina substrate having a thickness of 2 m and a thickness of 2 mm may be used. However, in FIG. 2, the narrower one is enlarged for easy viewing. The counter electrode 102 is formed by a known printed wiring technique, has a width of 0.15 mm, and the interval d between the comb teeth is about 0.10 mm. Also, the temperature sensor 105
25Ω ± 20% (at 23 ° C.); C. R. 4440
ppm / ° C (23 to 800 ° C), and the heater specification is D
C12V, 500 ± 50 ° C. is used.

Next, the functional film 103 will be described in more detail. The functional film 103 in this embodiment (FIG. 1, FIG.
As shown in FIG. 3, 2) is obtained by forming a hydrophilic polymer material such as polyvinyl alcohol on the porous film 301. In addition, a film (holding film) 303 of a hydrophobic polymer material such as polyvinyl acetate is formed on the inner wall of a large number of holes 302 formed in the film 301. This film 303
It is also considered as a mixture of a hydrophilic polymer material and a hydrophobic polymer material. The presence of the film 303 allows the strength of the film 301 to be increased. Then, the porous membrane 301 made of a hydrophilic polymer material is impregnated with an aqueous solution of lithium chloride having a predetermined concentration, whereby the pores 30 are formed.
2 becomes the functional film 103 in which lithium chloride 304 is held.

As described above, since the functional film 103 has a plurality of porous fine pores in the film made of the hydrophilic polymer material, the porous fine pores are not allowed to flow out. Can hold an aqueous solution. And
Since a film of a hydrophobic polymer material is formed on the inner wall of the hole, elution of the hydrophilic polymer material can be suppressed even when an aqueous solution is held in the hole. Therefore, the functional film 1 impregnated with the lithium chloride aqueous solution
In the porous pore No. 03, an aqueous solution of lithium chloride is held without flowing out.

By the way, in actual use, the aqueous solution of lithium chloride held in the porous pores of the functional film 103 is used in such a state that the water content is small enough to precipitate lithium chloride. Here, when the functional film 103 is left for a long time in a high-temperature and high-humidity state, lithium chloride absorbs moisture in the porous pores of the functional film 103, the concentration of the retained aqueous solution decreases, and the viscosity increases. Decreases. As described above, even if the retained lithium chloride aqueous solution has a low concentration, the functional film 103 has a base material made of a hydrophilic polymer material and has a hydrophilic group , It is possible to hold the aqueous solution of lithium chloride.

The diameter of the pores constituting the functional film 103 may be about 0.01 μm to 1 μm.
If it is smaller than this, it will be in a substantially non-porous bulk state, and it will not be possible to impregnate the film made of the hydrophilic polymer material with the aqueous solution. On the other hand, if the pore size is too large, a film made of a hydrophilic polymer material cannot be formed. If the thickness of the functional film 103 is too small, it is impossible to obtain a stable film while maintaining the porosity. On the other hand, if it is too thick, water vapor or moisture in the atmosphere will not easily permeate the entire film, and the response speed of the moisture-sensitive element will be slow, resulting in hysteresis.
From these, the thickness of the functional film 103 is 0.1 μm to 20 μm.
m can be said to be the optimal condition.

Next, a method for forming the functional film 103 will be described. Hereinafter, a description will be given by taking polyvinyl alcohol as an example of the hydrophilic polymer material and polyvinyl acetate as the hydrophobic polymer material. As shown in the flowchart of FIG. 4, first, in step 400, vinyl acetate is mixed with an aqueous solution of polyvinyl alcohol to form an emulsion. Next, in step 401, the vinyl acetate is polymerized while stirring the mixture. At this time, an inhibitor for preventing copolymerization may be added so that polyvinyl alcohol and vinyl acetate do not copolymerize. Next, in step 402, a polyvinyl alcohol aqueous solution (suspension) in which vinyl acetate is polymerized to form polyvinyl acetate is applied to a predetermined area on a predetermined substrate, and the coated film is heated at about 50 ° C. Allow to dry to some extent. As shown in FIG. 2, a predetermined electrode wiring is formed on this substrate.

Next, in step 403, the coating film of a solvent such as acetone is immersed to elute polyvinyl acetate in the coating film to some extent (elution rate: 55 to 75%).
Form a porous polyvinyl alcohol thin film. On the other hand,
In step 404, lithium chloride is dissolved in water to prepare a lithium chloride aqueous solution having a predetermined concentration. Next, in step 405, the coating film subjected to the processing in step 403 is immersed in the aqueous solution of lithium chloride prepared in step 404, and the coating film (porous PVA thin film) having a plurality of porous holes formed therein is coated with chloride. Impregnate with aqueous lithium solution. As a result, a porous polymer film (functional film) in which lithium chloride is held in polyvinyl alcohol having a plurality of porous holes is formed on a substrate, and a moisture-sensitive element using lithium chloride is completed. (Step 40)
6).

Here, the formation of the polyvinyl alcohol film in a porous state will be described in more detail. First, vinyl acetate is added to an aqueous solution of polyvinyl alcohol, and these are sufficiently stirred to disperse vinyl acetate to form an emulsion. At this time, a predetermined emulsifier may be added. In addition, by irradiating ultrasonic waves,
You may make it disperse | distribute vinyl acetate. It is expected that the use of ultrasonic waves can make the vinyl acetate droplets smaller.

In this emulsion state, vinyl acetate is polymerized by adding a polymerization initiator and maintaining the temperature at a predetermined temperature, whereby fine particles of polyvinyl acetate are dispersed in an aqueous solution of polyvinyl alcohol. Suspension. Then, as shown in FIG.
If it is applied on a predetermined substrate 501,
Polyvinyl acetate is present in the polyvinyl alcohol film 502 in the form of fine particles 503 dispersed therein. Here, when the volume of the polyvinyl alcohol film 502 is reduced by drying the applied film to some extent,
As shown in FIG. 5B, a part of a plurality of fine particles 503 of polyvinyl acetate is exposed on the surface of the polyvinyl alcohol film.

When the substrate 501 is immersed in acetone for a predetermined time in this state, only the polyvinyl acetate dissolves in the acetone, so that the particles 503 become hollow. That is, as shown in FIG. 5C, the polyvinyl alcohol film 502 on the substrate 501 is in a porous state (porous structure) in which the holding film 503a made of polyvinyl acetate is formed on the inner wall of the hole 504. A polyvinyl alcohol film 502 is obtained.

Here, the amount of vinyl acetate to be mixed into the aqueous solution of polyvinyl alcohol is about 1:10 to 3:10 by weight ratio of polyvinyl alcohol: vinyl acetate. Here, if the component ratio of vinyl alcohol is too small, the film itself cannot be formed. On the other hand, if the component ratio of vinyl acetate is smaller than the above component ratio, a desired porous structure cannot be obtained. That is, if the component ratio of vinyl acetate is increased, the pore size that can be formed increases, and a film cannot be formed. On the other hand, when the component ratio of vinyl acetate is reduced, the pore size that can be formed decreases, and when the component ratio of vinyl acetate is further reduced, the number of pores formed decreases, and a porous structure cannot be obtained. That is, the mixing ratio of vinyl acetate is expressed by weight ratio of polyvinyl alcohol: vinyl acetate = 1: 10.
By setting it to about 3:10, one pore diameter of the porous structure that can be formed becomes about 0.01 μm to 1 μm.

If the time of immersion in acetone for eluting the polyvinyl acetate is too long, the polyvinyl acetate is completely eluted. That is, if the polyvinyl acetate is eluted too much, the retaining film of the polyvinyl acetate almost disappears on the inner wall of the plurality of holes in the porous polyvinyl alcohol film 502, and the water resistance cannot be imparted. On the other hand, if the amount to be eluted is too small, sufficient pores cannot be formed in the polyvinyl acetate particles, and the particles will not be porous. Therefore, as described above, the amount of polyvinyl acetate to be eluted is preferably about 55 to 75% in terms of elution rate. By the way, as the mixing ratio after the porous shape, polyvinyl alcohol: polyvinyl acetate = 6: 5 to 6:27
Is suitable. However, when the strength such as water resistance of the porous film due to polyvinyl alcohol can be somewhat sacrificed, the amount of polyvinyl acetate to be eluted is 75%.
%.

In the above embodiment, polyvinyl alcohol is used as the hydrophilic polymer material. However, the present invention is not limited to this. Gelatin, tragacanth, starch, methyl cellulose, CMC (carboxymethylcellulose) may be used. ), Synthetic polymers such as PVA, partially saponified PVA, other vinyl alcohol copolymers, polyacrylates, and the like. Further, the hydrophobic polymer material is not limited to polyvinyl acetate (vinyl acetate). Polystyrene (styrene), polychlorinated ethylene (ethylene dichloride), or polyvinylbenzene (divinylbenzene) may be used.

The electrolyte salt is not limited to lithium chloride, and other salts such as calcium chloride may be used. However, lithium chloride is one of the most hygroscopic among the inorganic compounds, and its aqueous solution has a lower vapor pressure than other salts such as calcium chloride. The freezing point temperature of the aqueous solution is also low. And it has the advantage that handling is very easy.

[0023]

As described above, according to the present invention, the functional film formed in contact with each of the opposing electrodes disposed on the substrate and the temperature measuring means for measuring the temperature of the functional film are provided. In the moisture-sensitive element, the functional film is formed of a first polymer material having hydrophilicity, is formed in a porous structure having a plurality of fine holes, and has a hydrophobic structure formed on an inner wall of the hole. 2 and a holding film made of a polymer material and an electrolyte salt held in the pores. Therefore, the electrolyte salt is in a state of being confined in a plurality of fine pores in which the hydrophilic group is present, and on the other hand, entry and exit of water in the presence of the electrolyte salt are not hindered.
That is, even if the electrolyte salt absorbs moisture and becomes an aqueous solution, it is suppressed from flowing out from the functional film. As a result, the moisture-sensitive element of the present invention can be operated stably for a long period of time.

In the method for manufacturing a moisture-sensitive element according to the present invention,
The functional film was produced as follows. That is, first, a first polymer material having a hydrophilic property is dissolved in a first solvent having a polarity and dissolving the first polymer material to prepare a base material solution. Next, an organic material having hydrophobicity that is not dissolved in the first solvent is dispersed in the base material solution to prepare an emulsion. Next, the organic material dispersed in the form of droplets in the emulsion is polymerized, and the organic material is polymerized in the matrix solution. Make a liquid. Next, the suspension is applied to a predetermined region on the substrate to form a coating film. Next, part of the moisture in the coating film is removed, and a part of the particles is exposed to the surface of the coating film. Next, the coating film is immersed in a second solvent in which the first polymer material does not dissolve and the second polymer material dissolves, thereby dissolving the second polymer material. Then, a porous film having a porous structure having a large number of pores formed with a film made of the second polymer is formed. Then, the porous membrane is immersed in an aqueous solution of an electrolyte salt, and the porous membrane is impregnated with the aqueous solution of an electrolyte salt,
The electrolyte salt was held in a plurality of pores constituting the porous membrane. That is, a film made of the first polymer material is formed in a porous structure, and the electrolyte salt is held in the plurality of pores. Since the first polymer material is hydrophilic, even if the electrolyte salt absorbs moisture and becomes an aqueous solution, the aqueous solution can be retained, and the electrolyte salt is prevented from flowing out of the functional film. As a result, the moisture-sensitive element according to the present invention can be operated stably for a long period of time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a partial configuration of a moisture-sensitive element according to an embodiment of the present invention.

FIG. 2 is a plan view showing a partial configuration of the moisture-sensitive element according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a part of the structure of a functional film.

FIG. 4 is a flowchart showing a procedure of a method for manufacturing a functional film.

FIG. 5 is an explanatory diagram for explaining a method for manufacturing a functional film.

[Explanation of symbols]

101: substrate, 102: counter electrode, 103: functional film, 1
04: heater, 105: temperature sensor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sachiko Suzuki 2-12-19 Shibuya, Shibuya-ku, Tokyo Inside Yamatake Ha Newel Co., Ltd. (72) Inventor Noriaki Honda 2-12-19 Shibuya, Shibuya-ku, Tokyo Yamatake Honeywell Co., Ltd.

Claims (12)

[Claims] 1. A moisture-sensitive element comprising: a functional film formed in contact with each of opposing electrodes disposed on a substrate; and a temperature measuring means for measuring a temperature of the functional film, wherein the functional film is A retaining film formed of a first polymer material having a hydrophilic property and having a porous structure provided with a plurality of fine pores, and formed of a second polymer material having a hydrophobic property formed on an inner wall of the pore; And an electrolyte salt held in the pores. 2. The moisture-sensitive element according to claim 1, wherein the plurality of pores constituting the porous structure have an average pore diameter of:
A moisture-sensitive element having a thickness of 0.01 to 3 μm. 3. The moisture-sensitive element according to claim 1, wherein said functional film has a thickness of 0.1 to 20 μm. 4. The moisture-sensitive element according to claim 1, wherein the first polymer material and the second polymer material have a component weight ratio of 6: 5 to 6:27. A moisture-sensitive element, characterized in that: 5. The moisture-sensitive element according to claim 1, wherein the first polymer material is polyvinyl alcohol. 6. The moisture-sensitive element according to claim 1, wherein the second polymer material is polyvinyl acetate. 7. A method for manufacturing a moisture-sensitive element, comprising: a functional film formed in contact with each of opposed electrodes disposed on a substrate; and a temperature measuring unit for measuring a temperature of the functional film. The functional film comprises a first polymer material having a hydrophilic property and a first polymer material having a polarity.
A first step of preparing a base material solution by dissolving the polymer material in a first solvent, and dispersing a hydrophobic organic material insoluble in the first solvent in the base material solution. A second step of preparing an emulsion, and having the hydrophobicity in which the organic material is polymerized in the base material solution by polymerizing the organic material dispersed as droplets in the emulsion. A third step of preparing a suspension in which particles of the second polymer material are dispersed, a fourth step of applying the suspension to a predetermined region on the substrate to form a coating film, and A fifth step of removing a part of the moisture in the film and leaving a part of the particles exposed on the surface of the coating film; and the second polymer without dissolving the first polymer material. The coating film is immersed in a second solvent in which the material is dissolved to dissolve the second polymer material, and the coating film is formed on the inner wall. A sixth step of forming a porous film having a porous structure having a large number of pores in which a film made of the second polymer is formed; and immersing the porous film in an aqueous solution of an electrolyte salt, A seventh step of impregnating the electrolyte membrane with the aqueous solution of the electrolyte salt and retaining the electrolyte salt in a plurality of pores constituting the porous membrane.
A method for producing a moisture-sensitive element, characterized by comprising: 8. The method for manufacturing a moisture-sensitive element according to claim 7, wherein, in the second step, the first step in the emulsion is performed.
Wherein the component ratio of the polymer material to the organic material is 1:10 to 3:
10. A method for producing a moisture-sensitive element, wherein the component weight ratio is 10. 9. The method for manufacturing a moisture-sensitive element according to claim 7, wherein the first solvent is water. 10. The method for manufacturing a moisture-sensitive element according to claim 7, wherein the first polymer material is polyvinyl alcohol. 11. The method for manufacturing a moisture-sensitive element according to claim 7, wherein the organic material is vinyl acetate. 12. The method for manufacturing a moisture-sensitive element according to claim 7, wherein in the third step, an inhibitor that prevents the first polymer material and the organic material from copolymerizing is added. And polymerizing the organic material.