JPS61147141A - Moisture sensitive material and its production - Google Patents

Abstract

PURPOSE:To obtain a moisture sensitive material having a stable long-period characteristic even without the provision of a heater for preventing the deteriora tion with lapse of time by applying alkali ion to a calcined mixture composed essen-tially of an org. silicon compd. polymer and metallic oxide. CONSTITUTION:Comb-shaped electrodes 2 are formed of Pt-Pd alloy paste by screen printing on an insulating base plate 1 consisting of alumina and are calcined after Pt lead wires 4 are attached thereto. The mixture prepd. by adding a thinner to a compsn. consisting of, for example, about 55.6wt% org. silicon compd. polymer: methyl phenyl silicone, 20.3wt% metallic oxide: TiO2, 18.4wt% Cr2O3 and 5.7wt% additive: SiO2 and kneading the same with an agitator is coated thereon to about 50mum thickness by a dipping treatment and is calcined for about 1.5hr at about 350 deg.C. Such base plate 1 is thereafter dipped for about 30sec in an aq. sonl. of about 5% K2SO4 to obtain a moisture sensitive film 3. The moisture sensor consisting of such moisture sensitive material is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a moisture-sensitive material for a humidity sensor that detects the relative humidity of an atmosphere by a change in electrical resistance, and a method for manufacturing the same.

[Conventional technology]

Recently, metal oxide ceramics, which are physically and chemically stable in the atmosphere and have a high strength of 65%, have been most often used as moisture-sensitive materials having the above-mentioned functions. The humidity sensing mechanism of such conventional ceramics is that the concentration of hydrogen ions (H+) generated when water vapor dissociates on the porous ceramic surface varies depending on the relative humidity of the surroundings, so the electrical resistance of the humidity sensing part changes. This takes advantage of the fact that the value changes. Then, as shown in the following publication, 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 said to conduct through a water film in the same way as in an aqueous solution (publications, i.e. *J,
H, Anderson and G.

A, Parks: Magazine base: J, Phys, C
hem, volume 72.

No. 3662, published in 1968).

[Problems that the invention helps solve]

Those made of conventional ceramics as mentioned above.

In order to have a certain degree of good sensitivity, the electrical resistance value must have a lower limit (approximately 500Ω at a relative humidity of 50°, 90
When using a humidity sensor using the above ceramic for applications such as automatic humidity control with an air conditioner.

In terms of ease of use in the drive and detection circuits, there was a problem in that the electric resistance value was high and it was difficult to obtain a sensor that was easy to use.

In addition, in most conventional ceramic moisture-sensitive materials that utilize electrical conduction through H+, when the adsorption and desorption of water (moisture) is reversed when used in the air or left unattended, OH groups stabilize and chemically adsorb onto the surface. As a result, it is unavoidable that the resistance value of the sensor changes greatly over time.In order to restore this to its initial characteristics, the following method is proposed. Unexamined Japanese Patent Publication 1972
-61788°54-40895.54-01131!
l, 55-87941゜56-2542.56-109
As seen in Publication No. 044.56-160649, heaters are provided around the moisture-sensitive material, in the cover, inside the substrate, on the electrodes, etc., and the temperature is changed by heating the moisture-sensitive material with electricity at t-500 to 600 t:'. There was a problem in that it was necessary to restore the characteristics to the initial characteristics.

The present invention was made in order to solve such problems, and the purpose is to obtain a moisture-sensitive material that has stable moisture-sensitive characteristics for a long period of time without necessarily requiring a heating device (heater) to prevent deterioration over time. do.

Another invention of the present invention has even better water resistance).

The object of the present invention is to obtain a method for producing a moisture-sensitive material that is less likely to reduce its resistance over time.

[Means for solving problems]

The moisture-sensitive material of the present invention is obtained by adding alkali ions to a fired mixed product containing an organosilicon compound polymer and a metal oxide as main components.

9 A method for producing a moisture-sensitive material according to another aspect of the present invention is a method in which alkali ions are added to a mixed fired product containing an organosilicon compound polymer and a metal oxide as main components, and the mixture is fired again. be.

[Effect]

The metal oxide in the present invention increases the film strength of the moisture-sensitive material, and also increases water absorption, resulting in high sensitivity and low resistance.

In addition, the alkali ions provided in the present invention are called out by the adsorbed water on the surface of the moisture-sensitive portion and participate in surface electrical conduction, thereby lowering the resistance value of the moisture-sensitive material.

〔Example〕

Examples of the organosilicon compound polymers used in the present invention include those that become porous upon firing, such as methyl silicone, methyl phenyl silicone, and ethyl silicate polymers. Become. Furthermore, due to the porous nature of the material, the above-mentioned effects of the metal oxide in the moisture-sensitive material of the embodiment of the present invention are clearly manifested.

Since the amount of adsorbed water is increased, a moisture-sensitive material with a lower resistance value can be obtained.

The alkali ions according to the present invention include, for example, at least one of potassium ions, sodium ions, and lithium ions, and is used as one of the respective nitrates, sulfates, carbonates, and halides.

The metal oxide according to the invention is 1, for example + Accu*N
At least one of oxides such as i, Cr, and Ti is used.

In addition, if the mixed fired product containing the organosilicon compound polymer and metal oxide as the main components is added with the alkali ions and then fired again, the water resistance will be better, and the result will be better over time. It becomes even more difficult to lower the resistance.

Note that the moisture-sensitive material of the embodiments of the present invention may contain inorganic material powder as an additive for the purpose of forming a film, accelerating drying and curing, preventing cracking, and improving adhesion to the underlying substrate.

The present invention will be explained in detail below by showing Examples, but the present invention is not limited thereto.

Embodiment 1 Figure 1 is a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention.In Figure 9, (1) is an insulating substrate, (2) is an electrode, and (3) is a Moisture sensitive film, (4) beam single wire.

That is, on an alumina insulating substrate (11), 10 pairs of comb-shaped electrodes (2) were screen printed with Pt-Pd alloy paste at intervals of 012s+, and Pt lead wires (4) were attached. Post-baking was performed.On top of this, thinner was added to the composition of the following composition example, and after mixing with a stirrer,
Apply the mixture to a thickness of about 50 μm by dipping,
530C1. After baking for 5 hours, the above substrate was immersed in a 5% 2SO4 aqueous solution for 30 seconds to obtain a moisture-sensitive skin M(3;
A humidity sensor using a moisture-sensitive material according to an embodiment of the present invention as shown in FIG. 1 was manufactured.

Composition example Organosilicon compound polymer: Methylphenyl silicone 55.6% by weight Metal oxide @ T + 02 20s 3% by weight Cr2
O51a, 4 additive by weight: 5i02 5.1% by weight Example 2 Using the same composition as in Example 1, in the same manner as in Example 1, the above composition was applied, baked, and immersed in a 2S04 aqueous solution. Further, it was baked at 400C for 30 minutes to obtain 1 of the present invention.
A humidity sensor using a moisture-sensitive material according to another embodiment of the invention was manufactured.

A humidity sensor using a moisture-sensitive material according to an embodiment of the present invention manufactured as described above, a humidity sensor using a moisture-sensitive material according to another embodiment of the present invention, and a humidity sensor using a moisture-sensitive film according to another embodiment of the present invention.
2SOt:' Al2O5MgOZ sintered for 4 hours
For a sample of a conventional ceramic humidity sensor obtained using nO-based ceramics but in the same manner as shown in Figure 1, the humidity sensitivity characteristics (relative humidity (q6) - electrical resistance (g)
)) and its change over time were compared and measured, and the results shown in Figure 2 were obtained.

Note that the applied voltage was AC IV, 50 Hz. In FIG. 2, 0 curves (A1) and (A2) represent the moisture sensitivity characteristics of the conventional type at the initial stage and after being left indoors for one year, respectively, and 1 curves (D) and (B2) represent the moisture sensitivity characteristics of the conventional type, respectively. Curves (C1) and (C2) of moisture sensitivity characteristic 1 for the initial period and after being left indoors for one year using a moisture sensitive material are the initial and one year period results for a device using a moisture sensitive material according to another embodiment of the present invention, respectively. Moisture sensitivity characteristics after being left indoors.

As is clear from this figure, the resistance value of a humidity sensor using conventional H10 conduction type ceramics as the moisture-sensitive material is two orders of magnitude higher than the initial value after being left unused for one year. However, the humidity sensor using the moisture-sensitive material according to one embodiment of the present invention and the humidity sensor using the moisture-sensitive material according to another embodiment of the present invention have significantly reduced functionality.

After being left for one year, the resistance value only slightly decreased, and no deterioration of the moisture sensing function was observed, especially in the case of another embodiment of the present invention, as shown in (C2). It can be seen that the resistance value decreased only slightly after being left for one year. Furthermore, as can be seen by comparing the initial moisture sensitivity characteristic curves (AI), (B1), and (C1), one using the moisture sensitive material according to one embodiment of the present invention and another using the moisture sensitive material according to another embodiment of the present invention. Those using wet materials have a resistance value that is more than an order of magnitude lower than conventional ones, and are easier to use in one circuit.
In the case of (CI), the moisture sensitivity is also good.

The reason why the resistance value of the humidity sensor using the above moisture-sensitive material is low is that the applied alkali ions (+ in this case) are easily called out by the adsorbed water on the surface of the humidity-sensing part and participate in the surface electrical conduction. In particular, the reason why the humidity sensor using the moisture-sensitive material according to another embodiment of the present invention has good sensitivity and does not easily reduce its resistance over time is due to re-firing). This is because the amount increases.

In addition, in the above example, the case of immersion in a solution containing the above-mentioned ions was shown as a method of applying alkali ions, but the same effect can be obtained by other methods such as ion implantation, vapor deposition, and leaving in the above-mentioned ion vapor. Similar effects can also be obtained by changing the types of organosilicon compound polymer, metal oxide, and alkali ion.

〔Effect of the invention〕

As explained above, the present invention provides a heating device (heater) for preventing deterioration over time by using a mixed fired product containing an organic silicon compound polymer and a metal oxide as main components to which alkaline ions are added. It is possible to obtain a moisture-sensitive material with stable moisture-sensing properties over a long period of time without necessarily requiring 1, which is useful for, for example, a humidity sensor.

Another invention of the present invention is to further improve water resistance by adding alkali ions to a fired mixed product mainly composed of an organosilicon compound polymer and a metal oxide and then firing it again. Nashi.

It is possible to obtain a method for producing a moisture-sensitive material whose resistance is less likely to decrease over time.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a humidity sensor using a moisture-sensitive material according to an embodiment of the present invention, and FIG. 2 is a perspective view of a humidity sensor using a humidity-sensitive material according to an embodiment of the present invention and another embodiment of the present invention. It is a humidity sensitivity characteristic diagram comparing a sensor and a conventional humidity sensor. In the figure, (1) is an insulating substrate, (2) is an electrode, and (3)
is a moisture-sensitive film, (4) is a lead wire, (AI), (A
2) is the moisture sensitivity characteristic of the comparative conventional example e (nl)t (
B2), (CI)# (C2) is the moisture sensitivity characteristic of a humidity sensor using the moisture sensitive material of the present invention and another embodiment of the present invention.

Claims (2)

[Claims] (1) A moisture-sensitive material in which alkali ions are added to a fired mixed product containing an organosilicon compound polymer and a metal oxide as main components. (2) A method for producing a moisture-sensitive material, which comprises adding alkali ions to a fired mixed product containing an organosilicon compound polymer and a metal oxide as main components and firing the mixture again.