JPH051420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a moisture-sensitive material for a humidity sensor that detects the relative humidity of an atmosphere based on a change in electrical resistance.

[Conventional technology]

Recently, metal oxide ceramics, which are physically and chemically stable in the atmosphere and have high strength, have been most commonly used as moisture-sensitive materials having the above-mentioned functions. The moisture sensing mechanism of conventional ceramics is that the concentration of hydrogen ions (H ⁺ ) generated when water vapor dissociates on the porous ceramic surface varies depending on the surrounding relative humidity. This method takes advantage of the fact that the electrical resistance value of And this H ⁺ is
As shown in the following publication, when the relative humidity is low, conduction occurs by hopping on the hydroxyl groups generated on the surface, and when the relative humidity is high, hydrated H ⁺ is transferred to water as in an aqueous solution. It is said to conduct membranes (publications, i.e. JHAnderson and G.
A.Parks: Magazine name: J.Phys.Chem. Volume 72, No. 3662
Page published in 1968). On the other hand, when a humidity sensor is used for applications such as automatic humidity control in an air conditioner, a humidity sensor having a lower electrical resistance value is desired in terms of ease of use in driving and detection circuits. However, as long as the sensor uses electrical conduction by ^H
(about 20KΩ at 90%), and it is currently difficult to obtain sensors with lower electrical resistance values that are easier to use.

In addition, in most conventional ceramic moisture-sensitive materials that utilize electrical conduction through ^H It is unavoidable that the resistance value of the sensor changes greatly over time due to chemical adsorption, so in order to restore this to its initial characteristics,
161248, 55-161249, JP-A-52-61788, 54-
70895, 54−101399, 55−87941, 56−2542, 56−
As seen in Publications No. 109044 and 56-160649, heaters are installed around the moisture-sensitive material, in the cover, inside the substrate, on the electrodes, etc., and the moisture-sensitive material is heated to 500 to 600°C. Efforts are being made to restore the characteristics to their initial characteristics. However, this method cannot be said to be preferable from an economical, energy saving and safety standpoint.

In order to solve the above drawbacks, there is a moisture-sensitive material made of a sintered mixture of an organosilicon compound polymer and a metal oxide, as shown in Japanese Patent Application Laid-Open No. 15402/1983. , a further reduction in electrical resistance has been desired.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the above-mentioned conventional products, and includes at least one of alkali metal oxides, composite oxides, hydroxides, and oxyacid salts, an organosilicon compound polymer, and By firing a zeolite-containing composition to obtain a firing residue and using this as a moisture-sensitive material, the moisture-sensitive properties can be stabilized for a long period of time without necessarily requiring a heating device (heater) to prevent deterioration over time. The object of the present invention is to obtain a method for producing a moisture-sensitive material with lower electrical resistance.

[Embodiments of the invention]

As the organosilicon compound polymer according to an embodiment of the present invention, for example, an initial polymer of organopolysiloxane such as methyl phenyl silicone, methyl silicone, and epoxy resin-modified methyl silicone is dissolved in a solvent such as toluene and scylene. Commercially available silicone varnishes are used, which are fired to become porous and act as a binder to bind the alkali metal and zeolite.

As the alkali metal compound according to an embodiment of the present invention, it is necessary to use at least one of alkali metal oxides, composite oxides, hydroxides, and oxyacid salts. This is because when the inventor conducted experiments similar to those in the example with other compounds of alkali metals (chlorides, etc.), the inventors found that they had poor water resistance and tended to change over time, making it impossible to expect the combined effect of zeolite. This is because it has been confirmed.

Natural and synthetic aluminosilicates can be used as the zeolite according to one embodiment of the present invention. Na salts are common, and synthetic zeolites are commercially available, making them easy to obtain.

It should be noted that the moisture-sensitive material according to an embodiment of the present invention has the following inorganic material powders such as metal oxides added for the purpose of forming a film, accelerating drying and hardening, preventing cracks, and improving adhesion to the underlying substrate. It may be contained as an agent.

EXAMPLES This invention will be explained in detail by showing examples below, but the invention is not limited thereto.

Embodiment 1 FIG. 1 is a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention. In the figure, 1 is an insulating substrate, 2 is an electrode, 3 is a moisture-sensitive film, and 4
is the lead wire.

That is, ten pairs of comb-shaped electrodes 2 were screen printed on an alumina insulating substrate 1 using a Pt--Pd alloy paste at intervals of 0.2 mm, and after attaching Pt lead wires 4, baking was performed. After adding thinner to the composition of Composition Example 1 below and kneading with a stirrer, the mixture was applied to a thickness of about 50 μm by dipping treatment, and after pre-baking at 80°C for 10 minutes, it was heated at 600°C. 30
A moisture sensitive film 3 was obtained by baking for a minute, and a humidity sensor using the moisture sensitive material according to an embodiment of the present invention as shown in FIG. 1 was manufactured.

Composition example 1 Organosilicon compound polymer: methylphenyl silicone initial polymer 41.2% by weight Zeolite: NaAlSi ₂ O ₆ H ₂ O (borausite)
23.5 〃 Alkali metal oxide: Li ₂ O 13.5 〃 Additive: Al ₂ O ₃ 9.4 〃 Mica 7.4 〃 Hardening agent (amine) 5.0 〃 Using the moisture-sensitive material according to an embodiment of the present invention manufactured in this way A conventional type ceramic humidity sensor obtained using Al ₂ O ₃ -MgO-ZnO ceramics sintered at 1250℃ for 4 hours for the humidity sensor and the humidity sensitive film, and in the same manner as in Fig. 1, and As shown in the above-mentioned Japanese Patent Application Laid-open No. 57-15402, a silicone varnish obtained by dissolving methylphenyl silicone in xylene and powdered TiO ₂ of twice the weight of this silicone varnish were used in an example. 1
Using a sample with a humidity sensor using a moisture-sensitive material obtained in the same manner as above, the humidity-sensing characteristics (relative humidity (%)
- Electrical resistance (Ω)) and its change over time were compared and the results shown in Figure 2 were obtained. Note that the applied voltage was 1 V AC and 50 Hz. In Figure 2,
Curves A ₁ and A ₂ show the initial moisture sensitivity characteristics of the conventional ceramic type and after being left indoors for 6 months, and AA ₁ shows the initial moisture sensitivity characteristics of the conventional organosilicon compound sintered type. , curve B ₁
and B ₂ are the moisture sensitivity characteristics of a material using a moisture sensitive material according to an embodiment of the present invention, both initially and after being left indoors for 6 months. As is clear from this figure, the resistance value of a humidity sensor using conventional H ⁺ conductive type ceramics as the moisture-sensitive material increases by two orders of magnitude compared to the initial value after being left unused for 6 months, indicating that the humidity sensor has no moisture-sensing function. On the other hand, the humidity sensor using the moisture-sensitive material according to an embodiment of the present invention only showed a slight decrease in resistance value after being left for 6 months, and the resistance value decreased considerably. No decrease was observed. In addition, the initial moisture sensitivity characteristic curves A ₁ , AA ₁ and
As can be seen by comparing B ₁ , the resistance value of the material using the moisture-sensitive material according to an embodiment of the present invention is more than an order of magnitude lower than that of the conventional material, for example, 50KΩ at 50% relative humidity and 1KΩ at 90% relative humidity. Therefore,
It is easy to use on the circuit. The reason why the resistance value of the moisture-sensitive material according to the present invention is low is that the conduction type is not H ⁺ conduction, but conduction by alkali metal ions (in this case Li ⁺ ) due to hydration of adsorbed water.
This is thought to be due to the fact that these ions can move through the water adsorbed on the surface of the moisture-sensitive material at each relative humidity. Furthermore, the added zeolite has a fine three-dimensional cage-like structure, and the alkali metal ions that contribute to conduction exist in this cage-like structure when there is little humidity; It is thought that this is because the alkali metal ions are called out by H ₂ O and eluted into the adsorbed water, thereby allowing the alkali metal ions to exist stably and allowing them to move in and out smoothly.

Example 2 After adding thinner to the composition of Composition Example 2 below and kneading it with a stirrer, the kneaded product was brushed onto an alumina substrate on which electrodes and lead wires were formed in the same manner as in Example 1 to a thickness of about 40 μm. I applied it. Then, 80℃
After drying for 30 minutes, it was baked at 850°C for 1.5 hours to obtain a moisture-sensitive film, and a humidity sensor similar to that shown in Figure 1 was manufactured.

Composition example 2 Organosilicon compound polymer: Methyl silicone initial polymer 38.0% by weight Zeolite: Na ₈ Al ₈ Si ₄₀ O ₉₆・24H ₂ O (mordenite) 28.6 〃 Alkali metal oxyacid: Na ₂ CO ₃ 21.4 〃 Addition Agent: TiO ₂ 5.2 〃 Mg ₃ (Si ₄ O ₁₀ ) (OH) ₂ 4.3 〃 Hardening accelerator (aluminum octylate)
2.5 〃 A humidity sensor using a moisture-sensitive material according to another embodiment of the present invention manufactured in this way, and using Cr ₂ O ₃ -CaO ceramics sintered at 1450°C for 5 hours as the moisture-sensitive material, and others. As in Example 1, we measured the humidity sensitivity characteristics (relative humidity (%) - electrical resistance (Ω)) and their changes over time using both samples and a conventional ceramic humidity sensor similar to that shown in Figure 1. It was measured. In this case, in order to accelerate deterioration over time, both sensors were left in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 300 hours, and then the moisture sensitivity characteristics were measured and compared with the initial characteristics. The results are shown in FIG. In FIG. 3, curves C ₁ and C ₂ show the initial and after accelerated aging test properties of the conventional type, and curves D ₁ and D ₂ show the properties of the conventional type using a moisture-sensitive material according to another embodiment of the invention. These are the initial characteristics of the product and after the accelerated deterioration test. From FIG. 3, it can be seen that the resistance value of the moisture-sensitive material according to another embodiment of the present invention is about one order of magnitude lower in initial characteristics than that of the conventional type.
After the accelerated deterioration test, the resistance value increased by about two orders of magnitude, whereas in the case of the moisture-sensitive materials according to other embodiments of the present invention, the resistance value only decreased slightly after the test. It is clear that In addition, the reason why the initial characteristics of the conventional type changed significantly in the accelerated deterioration test was due to the strong chemisorption of OH groups and the volume expansion of particles in the ceramic microstructure due to capillary condensation of adsorbed water. It is assumed that closure is the main cause. Furthermore, in the case of using a moisture-sensitive material according to another embodiment of the present invention, it is thought that conduction formation occurs in which hydrated Na ⁺ stably present in the zeolite moves through the moisture-sensitive film. .

Example 3 Using the compositions of Composition Examples 3 to 5 below, humidity sensors using moisture-sensitive materials according to other examples of the present invention as shown in FIG. 1 were manufactured in the same manner as Examples 1 and 2. and moisture sensitivity characteristics (relative humidity (%) -
The electrical resistance (Ω) and its change over time were investigated. As a result, as in Examples 1 and 2, the humidity sensors using moisture-sensitive materials according to other Examples of the present invention show almost no change in moisture-sensing characteristics over time due to the fixation of OH groups. It turns out that there is something.

Composition Example 3 Organosilicon compound polymer: methylphenyl silicone initial polymer 63.5% by weight Zeolite: Synthetic zeolite (trade name A-3 manufactured by Toyo Soda KK) 17.2 Alkali metal composite oxide: K ₂ Cr ₂ O ₄ 6.3 〃 Additive: Mica 6.1% by weight Fe ₂ O ₃ 6.9 〃 Composition example 4 Organosilicon compound polymer: Epoxy resin modified methyl silicone initial polymer 62.1% by weight Zeolite: NaCa ₂ (Al ₅ Si ₅ O ₂₀ )・6H ₂ O (Thomsonite) 13.1 〃 Alkali metal hydroxide: KOH 9.3 〃 Additive: Cr ₂ O ₃ 5.0 〃 Al ₂ O ₃ 6.1 〃 Pentonite 4.4 〃 Composition example 5 Organosilicon compound polymer: Methylphenyl silicone initial stage Varnish with polymer dissolved in xylene
71.5% by weight Zeolite: Synthetic zeolite (trade name F-9 manufactured by Toyo Soda KK) 13.2 〃 Alkali metal oxylate: Li ₂ SO ₄ 8.6 〃 Additive: MgO 3.7 〃 CaO 3.0 〃 Example 4 Composition of composition example 1 A humidity sensor was manufactured in the same manner as in Example 1 by using the following method and the firing temperature was varied, and its moisture sensitivity characteristics (relative humidity (%) - electrical resistance (Ω)) were investigated. As a representative example, Fig. 4 shows the initial moisture sensitivity characteristics when fired at 450°C and 550°C and their changes after 6 months of being left indoors. In FIG. 4, the curve E ₁ is the initial humidity sensitivity characteristic of the product fired at 450°C, the curve F ₁ is the initial moisture sensitivity characteristic of the product fired at 550°C, and the curve E ₂ and F ₂ are the humidity sensitivity characteristics of each product after being left indoors for 6 months. As you can see from E ₁ and E ₂ in this figure, the firing temperature is 500
If the temperature is below .degree. C., thermal decomposition of the organosilicon compound polymer is insufficient, resulting in low sensitivity and a tendency to lower resistance over time. On the other hand, when firing at 500℃ or higher, F ₁ , F ₂ and B ₁ in Figure 2,
As can be seen from B ₂ , the decomposition of organic components progressed considerably, so it was found that the sensitivity was good and the moisture sensitivity characteristics were less likely to change over time. Further, when similar investigations were conducted on other composition examples, the same results as above were obtained. Therefore, the moisture sensitive material according to the embodiment of the present invention has a temperature of 500°C.
It is preferable to obtain the above-mentioned calcination. Also, 1200℃
The above is not preferable because the fired product does not become porous due to sintering and sensitivity cannot be obtained.

〔Effect of the invention〕

As explained above, the present invention involves firing a composition containing at least one of an alkali metal oxide, a composite oxide, a hydroxide, and an oxyacid, an organosilicon compound polymer, and a zeolite. By obtaining the firing residue and using it as a moisture-sensitive material, we can create a heating device (heater) to prevent deterioration over time.
It is possible to obtain a method for producing a moisture-sensitive material with stable moisture-sensitive characteristics over a long period of time and a lower electrical resistance without necessarily requiring the above, and is useful for, for example, a humidity sensor.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention, and FIGS. 2 and 3 are a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention and a conventional humidity sensor, respectively. FIG. 4 is a diagram showing humidity sensitivity characteristics at various firing temperatures of a humidity sensor using a humidity sensitive material according to an embodiment of the present invention. In the figure, 1 is an insulating substrate, 2 is an electrode, 3 is a moisture sensitive film, 4 is a lead wire, A ₁ , A ₂ , AA ₁ , C ₁ , C ₂
are the moisture sensitivity characteristics of the comparative conventional example, B ₁ , B ₂ , D ₁ , D ₂ ,
E ₁ , E ₂ , F ₁ , and F ₂ are the humidity-sensitive characteristics of the humidity sensor using the moisture-sensitive material according to the embodiment of the present invention.

Claims (1)

[Claims] 1. Calcining a composition containing at least one of an alkali metal oxide, composite oxide, hydroxide, and oxyacid, an organosilicon compound polymer, and a zeolite to obtain a firing residue; A method for producing a moisture-sensitive material using as a moisture-sensitive material.