JPS60186748A - Moisture-sensitive element - Google Patents

Abstract

PURPOSE:To obtain excellent responsiveness by using the residue product obtd. after calcination of the compsn. contg. a polymer of org. silicon compd. and conductive carbon powder thereby eliminating the change in the characteristic even in a high moisture atmosphere and decreasing the hysteresis of the moisture-sensitive characteristic. CONSTITUTION:A compsn. contg. a polymer of org. silicon compd. and conductive carbon powder, for example, graphite, is coated on an Al2O3 insulating substrate 1 on which comb-shaped electrodes 2 of Pt-Pd are preliminarily provided and lead wires 4 are attached. The compsn. is calcined and a moisture-sensitive film 3 consisting of the residue product obtd. after such calcination is formed. The sensor using such moisture sensitive material has the resistance value slightly higher than said value in the initial period and maintains the initial sensitivity without deterioration after resting for a long period of time. The sensor has the small hysteresis of the moisture sensitive characteristic and a high response speed. The reason for the difficulty of such moisture sensitive material in having a change in the characteristic with time lies in that electron conductivity is provided thereto by the conductive carbon powder and therefore even if OH is stably formed by chemical adsorption of water, the conductivity is not affected by the OH and that the ions eluting into the adsorbed water are not contained in the material.

Description

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

[Prior art]

As moisture-sensitive materials these days, metal oxide-based sintered bodies (ceramics), which are physically and chemically stable in the atmosphere and have high strength, are most often used. However, when most conventional ceramic moisture-sensitive materials repeatedly adsorb and desorb water (humidity) due to being left in the air or in the air, this becomes chemically adsorbed as hydroxyl groups (OH) on the surface and becomes stable. As a result, it was inevitable that the resistance value of the sensor, which was made entirely of ceramics, would change significantly (increase in resistance) over time.This phenomenon is caused by contamination such as oil mist on the surface of the moisture-sensitive material. Since substances can be generated even if no substances are attached, it has been necessary to take similar measures even when used in a relatively depleted atmosphere.Therefore, in recent years,
Utsukai Showa 55-161248゜+61249. Japanese Patent Publication No. 52-61788.54-70895゜101399
．． 55-87941.56-2542. Same +0904
4. As seen in Japanese Patent Publication No. 160649, etc., the area around the moisture-sensitive material, the cover, and the inside of the substrate.

A heater is installed on the electrode, etc., and the moisture-sensitive material is heated to 500-600℃.
The changed characteristics are restored to their initial characteristics by heating with electricity. However, this method cannot be said to be preferable from an economical, energy saving and safety standpoint. What I did there was
This is an improvement on the surface of the moisture-sensitive material, and as a result, we were able to manufacture a product that has a small change in resistance (humidity-sensitive characteristics) over time without heating the heater. Examples of these include fd,! Showa 56-1201OL
83457, etc., in which alkali salts are added to ceramics and glass, and JP-A-56-4
201. 4202. 4203. 60281゜57
-80703. 90901, 90903. Same 13th
3601, 4139901. 145301. Same 14th
5302, 184203. 180204.58-3
As in Publication No. 7901, etc., alkali metal oxides and alkali metal composite oxides are added to ceramic raw materials and sintered, and all of them are L 1 + and K0.

It appears to be a product with added alkali ions such as Na+ (alkali added type). These items do not show the resistance change over time that is seen in the ceramic types mentioned above, but because the resistance decreases (stabilizes) in a high humidity atmosphere ((Age 7) It is necessary.Characteristics change in an atmosphere where condensation occurs.Moisture sensitive (relative humidity -
The hysteresis of the resistance value (resistance value) characteristics was large, and new drawbacks such as slow response speed were likely to occur.

[Summary of the invention]

The present invention was made to eliminate the drawbacks of the above-mentioned conventional methods, and by using a composition consisting of a firing residue of a composition containing an organic silicon compound and a conductive carbon powder, It does not necessarily require a heating device (heater) to prevent deterioration, but the characteristics change even in a high humidity atmosphere, and even in a high humidity atmosphere, and the moisture sensitive characteristics have a small hysteresis and a fast response speed. The entire purpose is to provide.

[Embodiments of the invention]

As the organosilicon compound substrate according to an embodiment of the present invention, commercially available silicone varnish prepared by dissolving an initial polymer of organopolysiloxane in a bath agent such as toluene or xylene is easily used. Furthermore, modified types such as epoxy-modified silicone and acrylic-modified silicone can also be used.

Incidentally, the inventors have focused on a moisture-sensitive material containing the organosilicon compound polymer as a main component as a starting material.

,=f1. Vc Sho Kaisho 56-126756.57-
A number of proposals have been made, including Publication No. 15402.58-55847.

In one embodiment of this development, the conductive carbon powder is 2. For example, so-called carbon black is subjected to post-treatment Flti.
Guide 1. Materials with improved properties or graphite can be used. For general rubber and color (paint).

Carbon black (added to plastics) has low conductivity and is easily oxidized and vaporized at temperatures above 300°C, so it cannot be used. However, in this invention, the resistance value of the moisture-sensitive coating is determined by the state of dispersion of the carbon powder in the fired product of the organosilicon compound and the content M of the carbon powder remaining in the moisture-sensitive coating after firing. The conductivity (resistivity) of the carbon powder itself cannot be clearly defined. However, graphite has stable and extremely high Vc conductivity (about 10Ω cTn).
This is because the amount of oxidation and vaporization is small below 700''C.

It can be said that it is most suitable for use in this invention.

It should be noted that the moisture-sensitive material of one embodiment of the present invention may contain inorganic material powder such as wire mesh oxide shown below for the purpose of forming a film, accelerating drying and hardening, preventing cracks, and improving adhesion to the underlying substrate. Contains it as a caloric agent.

The present invention will be explained in detail below by showing Examples, but the present 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 FIG. 4) is a lead wire.

That is, 10 pairs of comb-shaped electrodes (21
was screen printed, and the Pt lead wire (41) was attached by post-baking. Thinner was added to the composition of Composition Example 1 below, mixed in a stirrer, and the kneaded material was immersed. Apply to a thickness of approximately 40 μm.

After drying at 80°C for 20 minutes, it was baked at 500°C for 2 hours to obtain a moisture-sensitive film (3), and a humidity sensor using the humidity-sensitive material of an embodiment of the present invention as shown in Fig. 1 was manufactured. Buko.

Composition Example 1 Moriki silicon compound polymer: Methyl phenyl silicone initial polymerization 596% by weight Conductive carbon powder Kographi) 14.0# Additive: M
g5 (8140+o) (OH)2 23.3 z Hardening agent (aluminum octylate) 31M porcelain, A1203-Mg 0-ZnO thread ceramics and ceramics with an alkali Na 20k added to the moisture-sensitive film respectively. A conventional type ceramic humidity sensor and an alkali-added type ceramic humidity sensor were manufactured using a sample fired at 1250° C. for 4 hours and in the same manner as shown in FIG. 1 except for the same procedure as shown in FIG. When we compared and measured the moisture sensitivity characteristics (relative humidity) - electrical resistance (intuition and their changes over time) of the above three noodle samples after baking, we obtained the results shown in Figure 2.The applied voltage was The voltage was 1.0 V and 50 Hz, and the characteristics were measured after being left indoors in a general household as it changed over time.In Figure 2, the song M (AI) is a conventional ceramic type.

(B1) is the initial moisture sensitivity characteristic of the conventional alkali-added type and (CI)H using the moisture-sensitive material of an embodiment of this invention, and (A2)t(B2) and (C2) are the respective initial moisture sensitivity characteristics. This is the moisture sensitivity characteristic of the product after being left for 6 months. As is clear from this figure, for sensors using conventional ceramic-type moisture-sensitive materials, after being left unused for 6 months, the resistance value increases by more than an order of magnitude compared to the initial value. ) has also declined due to low sales. (In practice, this is heated with a heater and the initial characteristics are refined.) On the other hand, in the case of the conventional alkali-added type, after being left under reverse VC for 6 months, the resistance value decreased by about one order of magnitude on average compared to the initial value, and a similar overall decrease in sensitivity was observed. On the other hand, a sensor using a moisture-sensitive material according to an embodiment of the present invention,
After being left for 6 months, the resistance value was only slightly higher than the initial value, and no decrease in sensitivity was observed.

Next, the initial moisture sensitivity characteristics of the conventional alkali-added type and the moisture-sensitive material according to an embodiment of the present invention were investigated. The results are shown in Figure 3.All measurements were carried out in the order of low humidity → high humidity summer → low humidity, with a 10 minute interval between each measurement point.In Figure 3, one curve ( B.6) shows the characteristics when measured from the high humidity side to the low humidity side of the conventional alkali-added type and (C5)U using the moisture sensitive material of an embodiment of this invention. As is clear from Figure 3, the conventional alkali-added type has greater hysteresis, especially on the high humidity side.In addition, when we measured the response speed of water vapor absorption and depletion for the three types of sensors mentioned above, 1
The results shown in Table 1 were obtained.

As can be seen from Table 1, the adsorption growth of the conventional alkali-added type mononoke (50→so%RH) Oh! :U desorption side (
90→50% RH), the response was slow for both cases, whereas the one using the moisture-sensitive material of one embodiment of the present invention showed a response speed equal to or higher than that of the conventional ceramic type.

Table 1 Example 2 After adding thinner to the composition of Composition Example 2 below and kneading it with a stirrer, Example 1! /Is it the same electrode as used in IJ 1? This kneaded mixture was coated onto the formed Al2O5 substrate to a thickness of about 40 μm. Then, after drying at 80°C for 20 minutes, baking at 550°C for 2 hours Composition Example 2 Organosilicon compound polymer: Methyl silicone initial 1 compound 581% by weight Leading wire powder: Carbon black (trade name) (Lucan XC- 72R (Cabot, USA) 23.5% by weight Additives: TlO2'10.6" Mg5 (Si, aolo) (OH)2r, 8z was formed to form a moisture sensitive film, and a lead wire was attached to it as shown in Figure 1. A similar humidity sensor was made.A humidity sensor using the humidity-sensitive material sound of another embodiment of the present invention manufactured in this way, and a Cr203-CaO ceramic fired at 1450°C for 5 hours and this KL12LO5 were used as the humidity-sensitive material. Add 1350
Using alkali-added ceramic skein sintered at ℃ for 4 hours,
Other configurations were obtained in the same way as in Figure 1, and three types of samples were used, including a conventional humidity sensor and an Eve humidity sensor, to measure humidity sensitivity characteristics relative humidity (%) - electrical resistance (intuition and its change over time). .

In this case, to accelerate aging, the sensor is
After opening at 200 o'clock in a constant temperature and humidity chamber at 0°C and relative humidity of 95%, all moisture sensitivity characteristics were measured and compared with the initial characteristics. The results are shown in FIG. In Figure 4, 2 curves (Dl)
is the conventional ceramic type, (El) is the conventional alkali-added type, and (F'1) is the initial moisture sensitivity characteristic of the moisture-sensitive material according to another embodiment of the present invention, respectively.
(D2)l(F2) and (F2) are the moisture sensitivity characteristics of each product after being left in a constant temperature and humidity bath for 200 hours.

As can be seen from this figure, the resistance value of the conventional ceramic type became considerably higher after 200 hours compared to the initial value, as in the case of Fig. 2.

Furthermore, as in the case of the conventional alkali-added type, a decrease in resistance value was observed after 200 hours, and the sensitivity also decreased overall. On the other hand, in the case of using the moisture-sensitive material according to another embodiment of the present invention, almost no change is observed, so it can be said that the case is considerably more stable than the conventional one in a high-humidity atmosphere.

Next, the condensation resistance of the three glaze samples described above was evaluated using a due cycle tester. Test at 30℃1
The dew condensation state for 1 hour and the dry state for 1 hour at 50° C. were repeated for 30 days. Figure 5 shows its humidity-sensitive characteristics (relative humidity (working - electrical resistance)). These are the moisture sensitivity characteristics after 30 days using the moisture sensitive materials of other examples.

As can be seen from this figure, the ceramic type also showed high resistance after testing. however.

Unlike the cases shown in FIGS. 2 and 4, the alkali-added type showed a high resistance after the test. This is because the moisture-sensitive surface is almost completely wet with water in the condensation state in the chew cycle test, so with the alkali-added type, the added alkali ions dissolve in the water and then become water droplets and disappear from the moisture-sensing area. This is thought to be a phenomenon caused by something that has been neglected. On the other hand, the moisture-sensitive material according to another embodiment of the present invention is used.

Even after the test, the properties were almost the same as those at the initial stage, and it was confirmed that the film had excellent dew condensation resistance.

In addition, the response speeds of the above three types of sensors were measured in the same manner as in Example 1.As shown in Table 1, the sensors using the moisture-sensitive materials of other examples of this invention were different from the conventional ceramic type. VC is faster than the same.

It was also confirmed that the response time was less than half that of the conventional alkali-added type.

Example 3 A composition of composition examples 3 and 4 below? In the same manner as in Example 1, humidity sensors using the moisture-sensitive material of another example of the present invention similar to that shown in FIG. As a result, similar to Examples 1 and 2, the humidity sensor using the moisture-sensitive material of the other embodiments of the present invention showed almost no change in its moisture-sensing characteristics over time, and was able to withstand high humidity. It was also found that the characteristics were stable even in a dew-condensing atmosphere without any change in characteristics.It was also confirmed that the response speed was quite fast as in the case of Table 1.

Composition Example 3 Organosilicon compound polymer: 46.2% by weight of methylphenyl silicone initial polymer Conductive carbon powder dicarbon black (trade name: Black Pearls 2000, manufactured by Cabot, USA) 104-layer additive: A12o634.1 # Mica 9.3N Composition Example 4 Organosilicon compound and combination: Methyl silicone initial polymer 636% conductive carbon powder: Graphite 17.01 Additive 2Mg
O9,ly Bentonite 7.3N Hardening agent (amine) 3.17 By the way, the reason why the moisture-sensitive material according to the embodiment of this invention does not easily change its characteristics over time is considered as follows. . In other words, since the conductive carbon powder imparts t-conductivity, even if OH is generated cheaply due to chemical adsorption of water as in conventional ceramic types, the proprietary properties are not affected by this. Another reason is that it does not contain ions that are released into the adsorbed water, unlike conventional alkali-added types.

Example 4 Using the composition of Composition Example 1, changes in humidity sensitivity characteristics (relative humidity) - electrical resistance (54) depending on firing temperature were investigated. The results are shown in Figure 6. In Figure 6, two curves (GJ is 250℃
, (B) is for firing at 800℃, (F is for firing at 600℃. In this figure, the above three are shown as one representative example, or if the firing temperature is 300℃ or less, the curve (G) As you can see, the resistance was extremely high and the sensitivity was low.

In addition, in the case of 700℃J In one example, the moisture sensitive material has a moisture content of 300 to 700.
Low resistance values can be obtained by firing at temperatures within the range of °C.

It has good sensitivity and is easy to use. This tendency was also the same in other examples.

〔Effect of the invention〕

As explained above, the present invention uses the firing residue of a composition containing an organosilicon compound polymer and conductive carbon powder, thereby achieving moisture-sensitive characteristics without necessarily having to be equipped with a heating mechanism for heating. It is stable, and its moisture-sensitive characteristics hardly change even in high-humidity or dew-condensing atmospheres, and the hysteresis of the moisture-sensing characteristics is small, making it possible to obtain all kinds of moisture-sensitive materials with response speeds equal to or higher than conventional ones. Extremely useful.

[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 to 5 are a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of this invention and a conventional humidity sensor FIG. 6 is a humidity sensitivity characteristic diagram for comparing the sensors.
This is a moisture sensitivity characteristic diagram. In the figure! (11 insulation board, (2) frost pole, (31
Moisture sensitive film, 141Vi lead wire, (AI)l (A2)
l(B1)l(B2)+(B3)l(DI)l(B2
), (B3) + (subtraction) + (''2), (B3) is the moisture sensitivity characteristic of the comparative conventional example, (cl), (c2), (c3), ()'
1). ('F2), (F5)l(()), (1勺, (1) are the moisture sensitivity characteristics of the humidity sensor using the moisture-sensitive material sound of the embodiment of this invention. Note that the same reference numerals in the two figures are The same - or a corresponding part? Show. Agent Masuo Oiwa Figure 1 @ Figure 2 0 50 100 1st sentence 1 Moxibustion /! C=4) @ 3 Figure 81 vs. mixed coal (Fig. ) Fig. 5 Japanese pattern (Japanese pattern)

Claims (1)

[Claims] (1) Moisture sensitive monthly consisting of calcination residue of composition containing organosilicon compound polymer and conductive carbon powder. (21) The moisture-sensitive material according to claim 1, wherein the conductive carbon powder is graphite (and at least one type of carbon black).