JPS6139503A - Moisture sensitive element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film-type humidity sensing element for a humidity sensor or a dew sensor, and particularly to an electrode conductive material used in the humidity sensing element, which has a smaller ionization tendency than hydrogen or hydrogen. The present invention relates to a method of preventing a moisture sensitive element from deteriorating over time by using a metal and/or a metal compound as a neutral electrode or in combination with the metal and/or metal compound to disperse the metal and/or metal compound in a moisture sensitive material. According to the present invention, a moisture sensing element that stably exhibits good moisture sensing characteristics over a long period of time can be obtained.

BACKGROUND OF THE INVENTION In recent years, humidity sensors have been used in many fields for the purpose of controlling atmospheric humidity. For example, humidity sensors are used to control food cooking in microwave ovens, to detect dryness in clothes dryers, to detect indoor humidity in room air conditioners, and to control humidity in the manufacture of various electronic components. Further, condensation sensors are in demand for detecting condensation in household VTR's, rear window defoggers in automobiles, refrigerated showcases, and the like. In addition to temperature control, humidity or dew condensation control is essential in various automated systems for food cooking, air conditioning, drying, etc., and humidity or condensation sensors that operate with high reliability are required for these humidity or dew sensors. In order to meet these demands, an electrical resistance type moisture sensing element has been put into practical use that utilizes changes in the electrical resistance of the humidity sensing portion of the element depending on atmospheric humidity. In the humidity sensor, a moisture-sensitive material is selected that exhibits good linearity 2 between humidity and electrical resistance, and in the condensation sensor, i! Moisture sensitive materials are selected that have switching properties that change electrical resistance rapidly. As moisture-sensitive materials, electrolyte material-based, organic polymer material-based, and ceramic material-based equal-length types have been proposed.Among them, ceramic material-based moisture-sensitive materials have a wide operating temperature range and are difficult to use in the environment. It is considered very promising because it is physically and chemically stable and does not deteriorate.

As a ceramic moisture sensitive material, Zr02-MgO
1Ti01-8n02.8102-metal oxide, Tl0
I-■20i %MgO-Cr2O4-Tl0t, Y
There are many proposals such as zOs system, YzOs + Zr01 system, ZrO2S and many others. Among these, (1) YzOs・ (2) YzOs +z r (h (no 1~?
9. O0%), (d) Yz 03 + (Ca
0-Mg ON Ba OlT 1 o,, Tlt
O,, Nb, 0. and v, o,) (0,
01-99. O0%) (4) ZrO, + (Cao, MgO1BaO1T
l o,,T,,0. , Nb1O1 and V,O,). Among others, Yz Os +
Z r O@ ceramic exhibits stable and favorable properties.

As for the form of the moisture sensing element, there is also a bulk type in which the above-mentioned ceramic is pressed and sintered under high pressure to create a bulk sintered body, and a pair of electrodes are provided on the opposing surfaces of the bulk sintered body.
A preferred form is to form an electrode layer on at least one surface of the ceramic substrate, and to conduct the electrical t! It is a coating type in which a mixture of the above-mentioned ceramic and a binder is applied onto EiiN, dried and sintered to form a moisture sensitive layer.

The film-type moisture sensitive element is preferably formed by screen printing the electrode layer and the moisture sensitive layer to produce a highly precise and stable moisture sensitive element. More importantly, the electrode pattern in the electrode layer should be formed so that the spacing between the electrodes is as small as possible, such as 0.20 mm or less. For example, good results can be obtained by interlocking a pair of comb-shaped electrodes so that the comb teeth are interlocked and the interval between the comb teeth is 0.20 mm or less.

There is still a lot of room for performance improvement in such ceramic vermillion-coated moisture-sensitive elements, and trials are currently being carried out. Important characteristics are (a) low electrical resistance (the larger the current, better sensitivity) (b) good linearity of resistance-humidity characteristics for humidity sensors, and near dew point for dew point sensors. It is required that the resistance value changes rapidly, (c) has good responsiveness, and (d) has little change over time. Studies have been made to improve the properties of each material, such as adding additives and devising heat treatments, but preventing changes over time is particularly difficult. In order for a humidity sensing element to operate stably over a long period of time, it is absolutely necessary to prevent changes over time.

BACKGROUND OF THE INVENTION Several proposals have been made so far as methods for preventing deterioration of moisture-sensitive elements over time, including the addition of additives, firing methods, etc., and one of them is a surface treatment method. This is intended to prevent deterioration over time by impregnating the fired body with a surface treatment agent and modifying its surface. The surface treatment agent is
It must be selected specifically depending on the ceramic moisture-sensitive material in question. Although the surface treatment method is a very effective method for preventing deterioration over time, it is difficult to find the optimal surface treatment agent for a particular type of moisture-sensitive element, and its effectiveness is not perfect. (For example, JP-A-59-47703
(See JP-A No. 59-756C11) Therefore, there is a desire in this field to develop a basic method for preventing aging that can be applied to ceramic coating film type moisture-sensitive devices in general.

Summary of the Invention The present inventor has repeatedly considered the phenomenon of changes over time in moisture-sensitive elements. In a film-type moisture-sensitive element, ions that advantageously lead to moisture-sensitive properties by adsorption of water into the matrix are initially uniformly distributed in the moisture-sensitive layer constituting the moisture-sensitive part. However, due to the difference in the ionization tendency of the metals, ions that lead to softening of the moisture-sensitive characteristics migrate toward each electrode side of the electrode layer over time. The ions that lead to advantageous moisture-sensitive characteristics include the ceramic material used, the binder, and if surface treatment such as dipping treatment or pre-additive treatment has been performed, the treatment agent or pre-additive to the sintered body (IJ Lux) Introduced Li
, Na5Ca, etc.

In the case of comb-shaped electrodes, these ions in the moisture-sensitive layer migrate toward the comb-shaped electrodes, and the uniform distribution of these ions between the comb teeth is impaired. Therefore, if the tendency of ions that lead to advantageous moisture-sensitive characteristics to segregate and move toward the electrode can be minimized, it should be possible to suppress the aging of the moisture-sensitive element.

From this point of view, as a measure to prevent ion segregation and movement to the electrode, neutrality is created between the opposing electrode pair of the electrode layer using a metal and/or metal compound that is the same as the conductive material constituting the electrode or has a smaller ionization tendency than hydrogen. We have found that forming electrodes is effective. A metal and/or metal compound that is the same as the conductive material constituting the electrode or has a smaller ionization tendency than hydrogen is simply referred to herein as a "quasi-electrode agent." By forming a neutral electrode with a quasi-electrode agent, the above-mentioned ions also move around the neutral electrode, so even if ion movement occurs, the initial uniform dispersion of ions will not be as large as the left. is not damaged.

Furthermore, by uniformly dispersing the quasi-electrode agent not only in the neutral electrode but also in the moisture-sensitive layer, the state of uniform ion dispersion can be further maintained.

Thus, the present invention provides a ceramic coating film type moisture-sensitive element comprising a substrate, an electrode layer, and a moisture-sensitive layer, in which the electrode layer has a conductive material that is the same as the conductive material constituting the electrode. Alternatively, there is provided a moisture sensing element characterized in that it is provided with a neutral electrode made of a metal and/or a metal compound that has a smaller ionization tendency than hydrogen. Furthermore, the present invention also provides a humidity sensing element characterized in that the neutral electrode is provided and the metal and/or metal compound is dispersed in the humidity sensitive layer.

A neutral electrode can be regarded as a quasi-electrode agent fixed in a specific shape.

DETAILED DESCRIPTION OF THE INVENTION A coating film type moisture sensitive element has a structure as shown in FIG. 1(a), for example. An electrode j953 is formed on one or both surfaces of the substrate 1, and a moisture sensitive layer M5 is formed thereon (the moisture sensitive layer is partially omitted). As the substrate, A1103, S l
oz., ZrO24 ceramic is used. Formation of the electrode layer on the substrate involves, for example, depositing nickel or the like as an under electrode, and then depositing nickel or the like on the substrate.
LCJ 71% 〒1ri, J --(17)
1. A desired electrode pattern can be formed using the 7-etching technique, and a ruthenium electrode can also be formed using a screen printing method using ruthenium paste. You can also do that. Recently, many microfabrication techniques for manufacturing printed circuit boards for electronic circuits have been put into practical use, and by applying them, fine 'N, @ patterns can be formed. For example, sputtering is also a useful method. The electrode pattern is preferably one in which a pair of comb-shaped electrodes are interlocked with comb teeth as shown in FIG. The smaller the interval between the comb teeth, the lower the resistance value, and therefore the sensitivity of the moisture sensing element can be improved.

After forming the electrode layer in this way, a moisture sensitive layer 1c made of a mixture of a ceramic moisture sensitive material and a binder is formed thereon. That is, a moisture sensitive layer is applied and formed by screen printing on the front and back of the ceramic material pie. The thicker the film, the lower the electrical resistance of the final product. After this, sintering is performed after preliminary drying.

According to the present invention, as shown in FIG. 1(a) and more particularly in FIG. 1(b), a neutral electrode 4 is preferably simultaneously formed between each pair of comb-shaped electrodes. The neutral electrode 4 is not limited to a linear shape as shown in the figure, but may be formed in a dot array or any other arbitrary shape. By screen printing the electrode layer, the neutral electrode can be formed on the surface side at the same time.

Furthermore, the above neutral i! It is also useful to use the pseudo z-polar agent in combination with the electrode to uniformly disperse it in the moisture-sensitive film. ``As electrode materials, materials such as gold, silver, and platinum group materials are used, but recently ruthenium oxide paste has become mainstream. A mixed powder of ruthenium oxide and glass is uniformly dispersed in an organic solvent to prepare a paste suitable for screen printing, and the paste is screen printed on a bulk sintered body or a substrate. Since RuO2 hardly dissolves in glass, it is segregated to the grain boundaries of the glass, forming a conductive path network. In any case, the quasi-electrode material is preferably of the same origin as the 'g-electrode material used. However, this does not prevent the use of metals and/or metal compounds that have a smaller ionization tendency than hydrogen.

When a quasi-electrode is mixed into a moisture-sensitive membrane, the amount used shall be such as to establish an appropriate dispersion state so as not to adversely affect the original moisture-sensing properties of the membrane and to avoid short circuits. That's enough. Generally, 0.1 to 15%, preferably 1 to 7%, is mixed. It is necessary to thoroughly mix it with ceramics and other W and materials, and be careful not to cause agglomeration.

- A binder is used to provide good sintering at low temperatures. As the binder, qf/J quality known as sintering aid is used, and lead-free borosilicate glass is particularly suitable. The binder accounts for 5 to 15 of the entire moisture-sensitive material.
%, preferably 7 to 12%.

The composition of lead-free borosilicate glass preferred for use is 10-15% sodium oxide, 2-5% potassium oxide, and 5-5% calcium oxide.
The content of magnesium oxide is 0.5 to 3 ft%, the content of aluminum oxide is 5 to 10%, the content of silicon dioxide is 60 to 45%, and the content of borium oxide is 60 to 45%. The content is 20-30%. This binder is preferable because it has a higher content of alkali metal and alkaline earth metal oxides and a lower melting point than general lead-free borosilicate glass.

In the sintering process, ceramic powder particles are sintered to form a skeletal structure of the coating film and provide structural strength. As for the firing humidity, it is desirable to select a low temperature so that melting (slag formation) of the ceramic powder particles or the binder does not occur.

Selection is made according to the type of ceramic used.

In order to make the humidity sensing element even more stable, it has been proposed to subject the sintered humidity sensing element to an aging treatment, followed by a heat treatment, and this does not preclude its use.

After the sintering treatment or the aging-heat treatment described above, immersion treatment in a surface treatment agent is preferably performed.

Various surface treatment agents have been proposed depending on the type of ceramic used. Na3PO4・12 Mo 0
1 aqueous solution, lithium hydroxide, lithium carbonate and chloride 11
6 hands)'l tPll -$ *Person 44t-Ae
'12-mentioned N*nTJ solution, silane coupling agent solution, Na5ty, solution, etc. are examples of the zero immersion treatment, which is achieved by immersing the moisture sensitive element in the solution for an appropriate time such as 1 to 120 minutes. It will be done.

After the immersion treatment, the element is fired at a temperature that does not cause melting of the ceramic and binder in order to prevent the surface treatment agent from leaching out during dew condensation and to stabilize the surface treatment agent.

Instead of a surface treatment, such as a dipping treatment, it is also possible to preload the membrane with these ions, which lead to advantageous moisture-sensitive properties.

Formation of a neutral electrode using a pseudo-ta polar agent and its dispersion into a coating film can sufficiently prevent deterioration over time, but it is preferable to use the above-mentioned surface treatment or preliminary addition.

By using it in combination with the ON addition method, the effect of preventing changes over time is further improved.

In the humidity-sensitive element of the present invention, a neutral electrode is formed between the pair of opposing electrodes in the electrode layer, and furthermore, the quasi-electrode agent is uniformly dispersed in the humidity-sensitive film. Uniformly distributed elements such as Li and K-Ca-Na, which lead to advantageous re and temperature characteristics, do not move only toward the electrode after water adsorption, but also move toward the neutral electrode and even around the M electrochromic agent. Also move to. Therefore, in the absence of a neutral electrode or pseudoelectrode agent, segregation of these ions would have occurred in the moisture sensitive membrane, but even if ion migration occurred due to the presence of a neutral electrode or pseudoelectrode agent, segregation of these ions would have occurred in the moisture sensitive membrane. Even°
These ions remain generally dispersed. This prevents deterioration over time.

The advantage of providing a neutral electrode is that it eliminates the risk of short circuits. Dispersing a large amount of 83 polar agent only in the moisture-sensitive membrane may lead to short circuits, but by screen printing the neutral electrodes, the risk of short circuits can be completely eliminated. Even when a neutral electrode is used in conjunction with the dispersion of a quasi-electrode agent in the moisture-sensitive membrane, the risk of short circuits is virtually eliminated by reducing the dispersion concentration of the latter.

Effects of the Invention This invention proposes a fundamental method for preventing aging that can be applied to ceramics in general, based on consideration of the aging phenomenon of moisture-sensitive elements, and is of great interest. By using surface treatment and ion addition methods such as pre-addition, extremely effective measures to prevent aging can be established. Neutral electrode eliminates the risk of short circuit.

Example 1 A comb-shaped ruthenium electrode with a neutral polarity as shown in FIG. 1(b) was formed by screen printing on an Alx0a substrate having a length of 20 strips and a width of 10 cm. The width of each electrode and the electrode spacing were 0.20 m, and printing was performed over a length of 12W.

[On top of the polar layer was formed a wet layer consisting of a mixture of 96% mixed ceramic and 7% lead-free borosilicate glass with a ratio of 50i501 Y2O2:Zr01. The moisture-sensitive layer was formed as follows: The above mixture was pulverized and kneaded in an automatic alumina mortar, the viscosity was adjusted with butyl calpitol and an epoxy resin paint, and the pj (pj of the moisture-sensitive layer was approximately 20 μm). It was applied by screen printing so that 170
Preliminary drying was carried out at a temperature of "C" for 1 hour, main drying was carried out at a temperature of 300°C for 30 minutes, and then baking was performed at a temperature of 800°C for 20 minutes.

The thus obtained moisture sensitive element was immersed in a 15% by weight KOH aqueous solution for 5 minutes, and then baked at 800° C. for 20 minutes to perform surface treatment.

Immediately after this, the resistance-humidity characteristics were measured. The resistance value was measured at a measurement frequency fi of 1000 Hz and a measurement voltage of 1 V. The results are shown in Figure 2.

The curves marked ■, ■, and ■ in FIG. f! 5 minutes in a wet bottle) ■: After ■, treated in 80℃, 93% RH for 100 hours (each ml! left in a wet bottle for 5 minutes) From Figure 2, extremely excellent aging prevention effect. 0 Example 2 In Example 1, not only the neutral electrode but also the moisture sensitive layer m! RuQ and paste were added as polar agents. That is, FIG. 3 shows the results of a test over time similar to that shown in FIG. 2, using a wet layer material having a composition of 42.53 Ii% of Zr01 and 10% by weight of Y, O, and Nilas frit.

As shown in FIG. 6, an effect of preventing changes over time superior to that of Example 1 was obtained.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of an example of an mi-type moisture-sensitive element,
1(b)(2) is a top view showing the electrode pattern in the electrode layer; The figure is a graph of the same characteristics showing changes over time in Example 2. 18 Substrate 3: [Polar layer 4: Neutral electrode

Claims (1)

[Scope of Claims] 1) In a ceramic coating film type moisture-sensitive element comprising a substrate, an electrode layer, and a moisture-sensitive layer, a conductive material that is the same as the conductive material forming the electrode between the electrode pairs of the electrode layer, or 1. A moisture-sensitive element comprising a neutral electrode made of a metal and/or a metal compound that has a smaller ionization tendency than hydrogen. 2) In a ceramic coating type moisture-sensitive element comprising a substrate, an electrode layer, and a moisture-sensitive layer, a conductive material that is the same as the conductive material forming the electrode between the electrode pairs of the electrode layer or has a smaller ionization tendency than hydrogen. 1. A moisture-sensitive element, characterized in that a neutral electrode made of a metal and/or a metal compound is provided, and the metal and/or metal compound is dispersed in the moisture-sensitive layer.