JPH0244390B2 - KANSHITSUZAIRYO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moisture-sensitive material for a humidity sensor that detects the relative humidity of an atmosphere based on changes in electrical resistance.

Recently, metal oxide ceramics, which are physically and chemically stable in the atmosphere and have strong strength, have been most often 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 increases.
This method takes advantage of the fact that the electrical resistance value of the humidity sensing section varies depending on the surrounding relative humidity.

According to the publication below, when the relative humidity is low, this H ⁺ is conducted by hopping on the hydroxyl groups generated on the surface, and when the relative humidity is high, the hydrated H ⁺ is transferred to the aqueous solution. It has been announced that the film conducts water in the same way as (Publication, i.e., magazine name:
J.Phys.Chem., Vol. 72, p. 3662, published in 1968).

On the other hand, when a humidity sensor is used for applications such as automatic humidity control by an air conditioner, a humidity sensor having a lower electrical resistance value is desired from the viewpoint of ease of use in driving and detection circuits. but,
As long as the sensor utilizes electrical conduction due to H ⁺ as described above and has a certain degree of sensitivity, its electrical resistance value must have a lower limit (approximately KΩ at 50% relative humidity, 90% (approximately 20KΩ), and it is currently difficult to obtain a sensor with a lower electrical resistance value that is easy to use.

Furthermore, in most conventional ceramic moisture-sensitive materials that utilize electrical conduction through ^H Due to chemical adsorption, the resistance value of the sensor changes greatly over time, so in order to restore it to its initial characteristics, it is necessary to heat it to a temperature of 500 to 600 degrees Celsius or higher using the attached heater. Ta.

This invention was made in order to eliminate the above-mentioned drawbacks of ceramics, which are the mainstream of conventional moisture-sensitive materials. By using this method, we aim to obtain a moisture-sensitive material that has low electrical resistance, does not require a heating device (heater) to prevent deterioration over time, and can be produced by low-temperature firing.

The organosilicon compound polymer of this invention includes:
For example, a commercially available silicone varnish prepared by dissolving an initial polymer of organopolysiloxane such as methylphenyl silicone, methyl silicone, and epoxy resin-modified methyl silicone in a solvent such as toluene and xylene is used.

In addition, as the alkali metal compound, a very wide range of alkali metal salts can be used, but when making the fired product vitrified, alkali metal oxides,
Peroxides, oxysalts such as carbonates, nitrates and sulfates, and hydroxides are used.

By firing the composition of the present invention formed in this way, the alkali metal compound is coated and bonded with X-ray amorphous Sio ₂ , which is the firing residue of the organosilicon compound polymer, The hydration property of the alkali metal compound and the good low surface energy property, ie, water repellency, of the organosilicon compound polymer are matched.

In addition, when the composition of this invention is used as a moisture-sensitive material, the film-forming effect, drying and curing acceleration,
It is desirable to add suitable additives to prevent cracking and improve adhesion to the underlying substrate.

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

Example 1 Ten pairs of comb-shaped electrodes were screen printed on an alumina insulating substrate using a Pt-Pd alloy paste at intervals of 0.2 mm, and baked after attaching Pt lead wires. On top of this, after adding thinner to the composition of Composition Example 1 below and kneading, the kneaded product was applied to a thickness of about 50 μm by dipping treatment, and after pre-baking at 80°C for 10 minutes, it was baked at 500°C for 30 minutes. Then, a humidity sensor using the moisture-sensitive material of the present invention was fabricated.

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

Composition example 1 Organosilicon compound polymer: methylphenyl silicone initial polymer 55.0% by weight Alkali metal compound: LiCl 16.2 〃 Additive: SIO ² 14.4 〃 Mg ₃ (Si ₄ O ₁₀ ) (OH) ₂ 11.3 〃 Hardening agent (Metal soap) 3.1 〃 A humidity sensor using the moisture-sensitive material according to the present invention prepared as described above, and
A conventional ceramic humidity sensor was fabricated using time-sintered Al ₂ O ₃ -MgO-ZnO ceramic and the other constituent materials were the same as those shown in Figure 1. The change in electrical resistance value [Ω] due to the change in relative humidity [%] of both humidity sensors in terms of voltage, that is, the change in humidity sensitivity characteristics over time, was compared and measured, and the results shown in FIG. 2 were obtained.

In the figure, curves A1 and A2 indicate the initial and six-month sensitive room characteristics of a conventional type, respectively, and curves B1 and B2 indicate the initial and six-month sensitivity characteristics of a conventional type, respectively, using a moisture-sensitive material according to an embodiment of the present invention. Moisture sensitivity characteristics after being left indoors for a month.

As is clear from this figure, after being left unused for 6 months, the resistance value of a humidity sensor that uses conventional H ⁺ conduction type ceramic as the moisture-sensitive material increases by two orders of magnitude compared to the initial value, and the humidity sensor is unable to function properly. On the other hand, the humidity sensor using the moisture-sensitive material of one embodiment of the present invention showed only a slight decrease in resistance value after being left for 6 months, indicating that the humidity sensor had no moisture-sensing function. No decrease was observed. Furthermore, as can be seen by comparing the initial moisture sensitivity characteristic curves A1 and B1,
The resistance value of the product of this invention is more than one order of magnitude lower than that of the conventional product, for example, 90K at a relative humidity of 50%.
Ω, 8KΩ at 90%, making it easy to use in terms of circuitry.

The reason why the resistance value of the moisture-sensitive material of one embodiment of this invention is low is that the conductive formation is not H ⁺ conduction, but alkali metal ions due to hydration of adsorbed water (L ⁺ _i in this case).
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.

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 were formed in the same manner as used in Example 1 to a thickness of about 40 μm. It was applied thickly. Then, 80℃, 20
After preliminarily baking for 1 minute, baking was carried out at 820°C for 2 hours, and the moisture sensitive area became a transparent glassy film. A lead wire was attached to this to create a humidity sensor similar to that shown in Figure 1.

Composition Example 2 Organosilicon compound polymer: varnish prepared by dissolving methylphenyl silicone initial polymer in xylene
55.9% by weight Alkali metal compound: Na2CO ₃ 22.0 〃 Additives: SiO ₂ 8.9 〃 TiO ₂ 7.7 〃 Mg ₃ (Si ₄ O ₁₀ ) (OH) ₂ 5.5 〃 According to other embodiments of this invention prepared in this way A humidity sensor using a moisture-sensitive material, and a Cr ₂ O ₃ -CaO ceramic sintered at 1250℃ for 5 hours as the moisture-sensitive material, and the other constituent materials were the same as those shown in Figure 1. A conventional type ceramic humidity sensor was manufactured, and the change in humidity sensitivity characteristics over time was measured in the same manner as in Example 1. In this case, both sensors were heated at 60°C and 95% relative humidity to accelerate aging.
The moisture sensitivity characteristics after being left in a constant temperature and humidity chamber for 300 hours were measured and compared with the initial characteristics. The results are shown in FIG. In Figure 3, curves C1 and C2
shows the characteristics of the conventional type after the initial and accelerated deterioration tests, respectively, and the curves D1 and D2 are
These are the characteristics after the initial and accelerated deterioration tests of moisture-sensitive materials according to other embodiments of the present invention, respectively.

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, and that the conventional type has a resistance value of Later on, the resistance value increased by about two orders of magnitude, but in the case of using a moisture-sensitive material according to another embodiment of the present invention,
It is clear that the resistance value only became slightly smaller after the test. In addition, the reason why the moisture sensitivity characteristics of the conventional type changed significantly in the accelerated deterioration test was due to strong chemical adsorption of OH groups and the expansion of pores due to the volume expansion of particles in the ceramic microstructure due to capillary condensation of adsorbed water. It is assumed that occlusion is the main cause.

In addition, in the moisture-sensitive material according to another embodiment of the present invention, conduction formation is considered to occur in which hydrated N ⁺ _a moves in the glassy film.

Example 3 Using the compositions of Composition Examples 3 to 5 below, a humidity sensor using a moisture-sensitive material according to still another example of the present invention having the configuration as shown in FIG. 1 in the same manner as Examples 1 and 2. were prepared and the changes in moisture sensitivity characteristics over time were investigated. As a result, as in Examples 1 and 2, humidity sensors using moisture-sensitive materials according to still other embodiments of the present invention show almost no change in moisture-sensing characteristics over time due to the fixation of OH groups. It has been found.

Composition Example 3 Organosilicon compound polymer: methyl silicone initial polymer 38.0% by weight Alkali metal compound: Na ₂ NO ₃ 22.5 〃 Additive SiO ₂ 17.0 〃 Al ₂ O ₃ 9.6 〃 Mica 9.4 〃 Hardening agent (metallic soap, amine) ) 3.5 〃 Composition example 4 Organosilicon compound polymer: Epoxy resin modified methyl silicone initial polymer 46.1% by weight Alkali metal compound: K ₂ O 20.6 〃 Additive: Al ₂ O ₃ 16.1 〃 TiO ₂ 9.4 〃 Bentonite 5.3 〃 Curing Agent 2.5 〃 Composition example 5 Organosilicon compound polymer: Varnish made by dissolving methylphenyl silicone initial polymer in a mixture of toluene and xylene 74.3% by weight Alkali metal compound: Li ₂ CO ₃ 10.2 〃 Additive: SiO ₂ 7.1 〃 MgO 6.0 〃 CaO 2.5 〃 The humidity sensors shown in the above examples each have excellent moisture-sensitive characteristics, but a humidity sensor similar to that of Example 1 was prepared and the main composition of the present invention has moisture-sensitive characteristics. An investigation into the optimal composition of the organosilicon compound polymer and the alkali metal compound revealed that the organosilicon compound polymer desirably ranges from 10 to 85% by weight based on the total starting materials. If it is less than 10% by weight, the particles of the alkali metal additive and additive cannot be sufficiently coated and bonded, resulting in poor water resistance.
If the content exceeds 85% by weight, the adhesion to the base substrate during firing will be poor, making it unusable as a moisture-sensitive material.

Furthermore, even when the types of the organosilicon compound polymer, alkali metal, and additives are variously changed, it is desirable that the organosilicon compound polymer be approximately within the above composition range for the same reason.

Next, in the case of alkali metal compound polymers, we investigated the relationship between the electrical resistance value [Ω] and the composition ratio of alkali metal compounds of moisture-sensitive materials with varying alkali metal compound compositions in an atmosphere with a relative humidity of 60%. However,
As can be seen from the characteristics shown in Figure 4, alkali metal compounds account for 3 to 30% of all starting materials.
A range of 50% by weight is desirable. If it is less than 3% by weight, the effect of alkali ion conduction is small, so the resistance value is hardly reduced, and 50
If it exceeds % by weight, the water resistance deteriorates and the moisture sensitivity changes over time so much that it cannot be put to practical use.

Furthermore, regardless of the type of alkali metal compound, organosilicon compound polymer, or additive, it is desirable that the alkali metal compound be within the above composition range for the same reason as above.

Next, in order to investigate the firing temperature when producing a humidity sensor using the humidity sensitive material of this invention and the humidity sensitivity characteristics of the obtained humidity sensor, the humidity sensor obtained in Example 2 and the baking temperature were 400℃, 500℃,
Humidity sensors were produced in the same manner as in Example 2 except that the temperature was 600° C., and changes in humidity sensitivity characteristics were measured after each humidity sensor was left indoors for one year.

Note that the sensitive part of the humidity sensor fired at 400°C to 600°C did not become glassy, but formed a white porous film, and that of the humidity sensor fired at 820°C became vitrified.

FIG. 5 shows the changes in the humidity sensitivity characteristics of the humidity sensor fired at 400° C. to 600° C. In the figure, the curve E1 is the initial humidity sensitivity characteristic, and the curve E2 is the humidity sensitivity characteristic one year later. On the other hand, the vitrified material produced in Example 2 exhibited moisture sensitivity characteristics as shown in FIG.

In FIG. 6, the curve F1 represents the initial moisture sensitivity characteristic;
F2 is the moisture sensitivity characteristic after one year. Comparing FIG. 5 and FIG. 6, it can be seen that the vitrified material shows smaller changes in moisture sensitivity characteristics over time.

Furthermore, the vitrification increases the response speed and makes it difficult for the resistance value to fluctuate even when dew condenses on the surface of the moisture-sensitive material.

However, even for those that do not vitrify in Figure 5, the change after one year is within a 10% error in the relative humidity indicated value, and this change appears to be almost saturated, so it is not practical. It is enough to provide.

Based on the above results, we investigated the conditions under which the moisture-sensitive material of this invention becomes vitrified, and found that other factors such as the composition ratio of the alkali metal compound and the cooling conditions after firing are involved in a complex manner. Although there are some limitations, at least the alkali metal compound used is an oxide (including peroxide), oxyacid (carbonate, nitrate, sulfate, etc.) or hydroxide of the alkali metal. temperature is 700
It was found that the temperature was above ℃. Various types of glassy films were formed under these conditions, and their moisture sensitivity and changes over time were investigated, and it was found that all changes over time were small, as in the case shown in Figure 6. .

The reason why the resistance value is low and the moisture sensing function is good when vitrified is not clear at present, but it is due to the existence of fine classical and mobile alkali metal ions and the segregation of alkali ions. I suspect that it is related. In this case, the fact that SiO ₂ , which is one of the important components in the glassy fired product, is occupied by the firing decomposition residue of the organosilicon compound polymer, which is the starting material, also contributes to the moisture-sensing function. This is thought to have some influence on the expression of

As explained above, the present invention uses the firing residue of a composition containing an organosilicon compound and an alkali metal compound, which has low electrical resistance and does not require a heating device (heater) to prevent deterioration over time. First, it is possible to obtain a moisture-sensitive material that can be produced by low-temperature firing.

[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 show a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention and a conventional humidity sensor. FIG. 4 is a diagram showing the change in electrical resistance value depending on the alkali metal compound composition ratio of a humidity sensor using the humidity-sensitive material of the embodiment of the present invention, and FIGS. FIG. 3 is a diagram of humidity sensitivity characteristics of a humidity sensor using a humidity sensitive material of an example. In the figure, 1 is a substrate, 2 is an electrode, 3 is a humidity sensing part, 4 is a lead wire, A1, A2, C1, C2 are characteristics of a comparison conventional humidity sensor, B1, B2, D1,
D2, E1, E2, F1, and F2 indicate the characteristics of the humidity sensor using the moisture-sensitive material of the embodiment of the present invention.

Claims (1)

[Claims] 1. A moisture-sensitive material comprising a firing residue of a composition containing an organosilicon compound polymer and an alkali metal compound. 2 Claim 1 consisting of a firing residue of a composition containing 10 to 85% by weight of an organosilicon compound polymer and 3 to 50% by weight of an alkali metal compound
Moisture-sensitive materials as described in section. 3. The moisture-sensitive material according to claim 1 or 2, wherein the alkali metal compound is at least one of alkali metal oxides, oxyacid salts, and hydroxides, and is glassy.