JPH0153484B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a moisture-sensitive switching element comprising a porous body and a moisture-swelling resin membrane electrode. In recent years, with increasing interest in temperature and humidity control, many humidity sensing elements and humidity sensors that convert humidity into electrical characteristics have been developed. Hitherto, moisture-swelling resins, electrolytes, metal oxides, ceramics, semiconductors, and the like have been used as moisture-sensitive element materials, and electrical resistance, capacitance, and impedance have been used as electrical properties. Moisture-sensitive element materials such as ceramics or metal oxides utilize resistance changes of dissociated ions of water adsorbed and condensed on their surfaces and in their pores, so their resistance value decreases as relative humidity increases. These materials are generally called proton conductive moisture sensitive elements. However, attempts have been made to add various trace elements to the humidity sensing elements made of these materials in order to improve their reliability, improve responsiveness, and further improve the precision of humidity sensitivity. There are problems such as the need to strictly control the amount of addition and the need for expensive elements. On the other hand, a moisture-sensitive film in which conductive powder is dispersed in a moisture-absorbing and swelling resin is also known. This type of dispersed resin moisture-sensitive membrane is hygroscopic, so when the humidity of the environment increases, the amount of moisture absorbed increases and the volume expands, thus breaking the contact between the conductive powders in the resin. Such an element has a so-called switching function in which the resistance value increases rapidly at high humidity. However, although such a humidity sensing element has excellent weather resistance, its humidity sensing accuracy is low, and it does not exhibit a switching function unless the humidity is considerably high, for example, relative humidity (RH) of about 90% or more. Therefore, it has excellent humidity sensitivity accuracy, and can be used in an appropriate humidity range (approximately 60 to 90%), such as when growing plants.
There is a need for a moisture-sensitive element that can control humidity based on RH) and has good weather resistance. As a result of intensive research into a humidity sensing element that can control humidity within an appropriate humidity range, the present inventors have found that a porous material having pores with a substantially uniform pore size is used as the material for the humidity sensing element, and the resistance is A moisture sensing element with excellent humidity sensitivity accuracy can be obtained when a film of a moisture sensitive material of increasing value type is used as at least one electrode, and by changing the pore size, the switching function can be adjusted to a desired humidity level. The present invention has been completed based on the discovery that this can be achieved. An object of the present invention is to provide a moisture-sensitive switching element that exhibits a unique and excellent switching function at a desired humidity range of about 60% RH or higher. Another object of the present invention is to provide a humidity-sensitive switching element that has excellent weather resistance, is small in size, and has good compatibility. The moisture-sensitive switching element of the present invention essentially consists of a porous body having capillary-like pores with substantially uniform pore diameters and an electrode, wherein at least one electrode has conductive particles dispersed in a substantially uniform manner. It consists of a moisture-absorbing and swelling resin film. Regarding the relationship between gas adsorption and condensation and pores, the humidity sensing element of the present invention has the following equation: r _k =2γMcosΘ/ρRTl _o P /Ps (where, r _k : Kelvin radius, γ : surface tension of condensate, M : molecular weight of condensate, Θ : contact angle, ρ : density of condensate, R : gas constant, T : absolute temperature, P /
Ps: adsorption equilibrium pressure/saturated vapor pressure. ). That is, capillary condensation of gas occurs when the pore diameter is r _k . When the gas is water vapor, the relationship between relative humidity RH and Kelvin radius r _k is as shown in the table below.

[Table] The capillary pores of the porous body used in the present invention have a substantially uniform diameter, that is, a substantially constant pore diameter, and the pore size distribution of the entire porous body is narrow. in range. The narrower the pore size distribution range, the more
Humidity sensitivity is good. The porous body used in the present invention has a narrow pore size distribution as shown in FIG. 1, for example, compared to the conventional proton conductive moisture sensing element that utilizes resistance changes due to adsorption and condensed water within the pores. Characterized by substantially uniform pores. The material of the porous body is not particularly limited as long as a porous body having capillary-like pores with substantially uniform pore diameter can be obtained, and known proton-conducting materials such as
Al ₂ O ₃ , SiO ₂ , borosilicate glass, TiO ₂ , V ₂ O ₅ ,
Various ceramic materials such as Cr ₂ O ₃ , Fe ₂ O ₃ or metal oxides can be used. As an example of a porous body that can be used in the present invention,
Examples include borosilicate glass made porous by a known phase separation process (Japanese Patent Publication No. 44580/1983).
A particularly preferred porous body is
According to the method described in No. 57-154823, by heat treatment, a composition that separates into a soft phase that dissolves in a high-temperature acid solution and a hard phase that does not dissolve (usually SiO ₂ : 60
~80 wt% _{, B2O3} : 15-35 wt% and _Na2O :
3.5~12% by weight) sodium borosilicate glass,
Usually, after heat treatment at 480-600°C for 0.25-300 hours to cause phase separation, plasma etching treatment is performed in an atmosphere containing fluorine-containing compound (e.g. CF ₄ ) gas before or after soft phase elution treatment. This is a porous body obtained by According to this method, by adjusting the heat treatment temperature, heat treatment time, and/or glass composition, the pore diameter is set to a desired value in the range of several tens of angstroms to several thousand angstroms, and is substantially uniform from the inside to the surface. Porous bodies with various pore sizes can be obtained. Generally, the higher the heat treatment temperature and the longer the heat treatment time, and the more components B ₂ O ₃ and Na ₂ O in the glass composition, the larger the pore diameter becomes. For example, when adjusting the pore diameter to several tens of angstroms, for example, SiO ₂ :65% by weight,
A glass having a composition of 30% by weight of B ₂ O ₃ and 5% by weight of Na ₂ O is heat-treated at 500° C. for 24 hours.
On the other hand, in order to make the pore size approximately several thousand angstroms, for example, using a glass having a composition of 62.5% by weight of SiO ₂ , 32.7% by weight of B ₂ O ₃ and 4.8% by weight of Na ₂ O, it is Heat treated for an hour. In the present invention, the radius of the pores of the porous body is preferably in the range of 10A° to 500A°, and by controlling the pore diameter to a certain value within this range,
A moisture-sensitive element is obtained that exhibits a switching function at a desired humidity of RH 60% to 100%. As the pore size becomes smaller, the switching function is exhibited at lower humidity. The shape of the porous body is not particularly limited, and may be, for example, plate-like, square or round rod-like, or thread-like. However, in order to increase humidity sensitivity, it is preferable to use a shape with a large surface area, such as a hollow fiber shape or a hollow rod shape. When only one electrode is made of a hygroscopic swelling resin film, the other electrode is not particularly limited, and any known electrode may be used. However, from the viewpoint of humidity sensitivity, it is preferable to use a thin film that does not block the pores of the porous body. Such thin film electrodes include, for example, Au, Ag, Pt,
It can be produced by coating a porous body with one or more metals such as Pd using a reverse sputtering method or a vacuum evaporation method. The above thin film usually has a thickness of 10~
It is 300A°. Moisture-sensing elements that essentially consist of porous TC electrodes normally measure the dissociated ions of water adsorbed and condensed within the pores as changes in electrical resistance; therefore, as humidity increases, the resistance decreases. It belongs to the decreasing resistance type where the value decreases. However, in the case of the humidity sensing element of the present invention in which a resistance increasing type moisture sensitive material is used for at least one of the electrodes, the moisture sensing element exhibits a unique switching characteristic of converting from a resistance value decreasing type to a resistance value increasing type at a certain humidity. A wet element can be obtained.
The moisture-absorbing and swelling resin film in which conductive particles are substantially uniformly dispersed as the resistance value-increasing moisture-sensitive material is
As long as the object of the present invention can be achieved, conductive particles can be substantially uniformly supported (adsorbed, attached, absorbed, It may also contain hygroscopic fibers (e.g., moisture-absorbing fibers) and other known resistance-increasing moisture-sensitive materials. The conductive particles dispersed in the resin of the resin film or supported on the hygroscopic fibers are, for example, carbon particles such as graphite and carbon black, and metal particles such as copper and silver. These particles can be used alone or as a mixture of two or more. These particles may also contain other impurities in amounts that do not significantly affect conductivity. The particles usually have a particle size in the range of 30 to 5000 A°, preferably 100 to 5000 A°.
A range of 1000A° is used. In addition, the amount of particles used is usually about 10 to 90% of the resin weight, preferably 50 to 90% when dispersed in a moisture-absorbing swelling resin.
%, typically 10 ^-5 when loaded on hygroscopic fiber surfaces
~10 ^-2 mg/mm ² , but it varies depending on the type of resin or fiber used and the humidity at which desired switching characteristics appear. Hygroscopic swelling resins include, for example, gelatin (glue),
Mention may be made of cellulose, polyamide, polyvinyl alcohol, preferably gelatin and polyamide. The resin film is usually 10 to 100m long.
It is in the μ range. The hygroscopic fibers may be natural, semi-synthetic or synthetic fibers, but those having a moisture absorption of at least 1%, preferably 5% or more at 20° C. and 95% relative humidity are used. Examples of these include almost all natural cellulose fibers such as cotton, linen, silk, wool, and rayon; semi-synthetic cellulose fibers such as cellulose nitrate, cellulose acetate, and triacetate; polyamide (nylon) acrylic, polyvinyl alcohol (vinylon), etc. Synthetic fibers include: In particular, nylon is preferred because the length and thickness of the fibers can be freely changed, and it is resistant to insects and mold and is durable. The conductive particles can be placed directly on the hygroscopic fibers or with an adsorbent,
It can be supported using an adhesive or the like. As adsorbent or adhesive, customary adhesives can be used. In the present invention, the resistance-increasing moisture-sensitive material for obtaining an element exhibiting the above-mentioned unique switching characteristics is a hygroscopic swelling resin film in which conductive particles are dispersed, and in particular, a film made of glue (gelatin) in which carbon particles are dispersed is used. preferable. A carbon particle-dispersed gelatin film can be easily formed by applying India ink to a porous body. Furthermore, when a conductive particle-dispersed resin film is used as an electrode, the resin prevents the dispersed particles from penetrating into the pores of the porous body, so the conductivity that is observed when using some types of metal electrodes is reduced. Another advantage is that there is no short circuit between the electrodes due to the intrusion of particle ions. FIG. 2A is a perspective view showing a preferred embodiment of the moisture-sensitive switching element of the present invention, which includes a hollow fiber-like porous body 1 having capillary-like through holes 4, and a hollow fiber-like porous body 1 provided on the outer surface of the hollow fiber-like body. It consists of a metal thin film electrode 2 and a conductive particle dispersed resin film electrode 3 provided on the inner surface of the hollow fiber body. FIG. 2B is a side view of the moisture sensitive element. Next, the present invention will be explained using Examples and Reference Examples. Reference example Glass hollow fiber (SiO ₂ :B ₂ O ₃ :Na ₂ O=65:30:
5% by weight, outer diameter 200μm, length 3cm, thickness 10μm)
heating to 500℃ for 4 or 8 hours to separate the phases,
Next, after applying a high frequency voltage of 13.56 MHz for 3 minutes in a CF ₄ gas stream and performing plasma etching treatment,
The soft phase was eluted by acid treatment using 1N HCl to obtain a porous body. The porous body was observed using a scanning electron microscope and was confirmed to have capillary pores with a substantially uniform pore diameter. When the pore distribution was investigated, the graph shown in FIG. 1 was obtained. Au-Pd is applied to the outer surface of this hollow porous body.
(Au: 70%, Pd: 30%) was coated using a reverse sputtering method to the extent that the pores were not blocked, and silver particles were substantially uniformly dispersed in the acrylic resin on the inner surface.
1.0 mg of Ag paste (trade name: Dotite) was injected to form metal thin film and resin film electrodes, and lead wires were connected to each electrode. Next, the obtained moisture-sensitive switching element Au-4
The moisture sensitivity characteristics of -Ag and Au-8-Ag (devices whose glass hollow fibers were heat-treated for 4 hours and 8 hours, respectively) were measured. The results are shown in FIG.
The resistance value of Au-8-Ag decreases rapidly between RH70 and 80%, and exhibits switching characteristics in this humidity range. On the other hand, the resistance value of Au-4-Ag rapidly decreases between RH60 and 70%. Example Same as Example 1 except that black ink was injected into the inside of the same hollow fiber porous material used in the reference example and solidified to form a glue (gelatin) film (thickness 100 μm) on the carbon particle dispersion. Thus, a moisture-sensitive switching element Au-4-C (glass hollow fiber heat treatment time: 4 hours) was obtained. Its moisture sensitivity characteristics are shown in FIG. This moisture-sensitive element exhibited a unique switching function in which the resistance gradient reversed at around 90% relative humidity.

[Brief explanation of drawings]

Figure 1 is a graph showing the pore size distribution of the porous bodies used in Reference Examples and Examples, Figure 2A
is a perspective view of a preferred moisture-sensitive switching device of the present invention, FIG. 2B is a side view of the device, and FIG.
FIG. 4 is a graph showing the relationship between relative humidity and electrical resistance of the humidity-sensitive switching element obtained in the reference example, and FIG. 4 shows the relation between relative humidity and electrical resistance of the humidity-sensitive switching element obtained in the example. This is a graph showing. DESCRIPTION OF SYMBOLS 1... Hollow fiber porous body, 2... Metal thin film electrode, 3... Conductive particle dispersed resin membrane electrode, 4... Through hole (capillary tube), 5... Lead wire.

Claims (1)

[Scope of Claims] 1. Essentially composed of a porous body having capillary-like pores with a substantially uniform pore size and an electrode, at least one electrode having conductive particles substantially uniformly dispersed therein. A moisture-sensitive switching element made of a moisture-absorbing and swelling resin film. 2. The device according to claim 1, wherein the pore radius has a substantially constant size within the range of 10A° to 500A°. 3. Claim 1 or 2, wherein the porous body is made porous by subjecting borosilicate glass to phase separation treatment.
Elements described in Section. 4. Claims that the porous body is a porous body obtained by subjecting sodium borosilicate glass to phase separation treatment and then subjecting it to plasma etching treatment in a fluorine-containing compound gas atmosphere before or after acid elution of the soft phase. The device according to any one of items 1 to 3. 5. The device according to any one of claims 1 to 4, wherein the porous body has a hollow fiber shape. 6. Claims 1 to 6, in which one electrode is made of a hygroscopic swelling resin film in which conductive particles are substantially uniformly dispersed, and the other electrode is made of a thin metal film that does not block the pores of the porous body. The device according to any one of Item 5. 7. The device according to any one of claims 1 to 6, wherein the resin film is a glue film in which carbon particles are dispersed.