JPH0337841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ceramic moisture-sensing element using a ZrO _2- based or ZrO ₂ +Y ₂ O ₃ -based moisture-sensitive material, and particularly to a ceramic moisture-sensitive element using the above-mentioned moisture-sensitive material as a moisture-sensing portion. to Li ₂ CO ₃
The present invention relates to a moisture-sensitive element having a low resistance value, excellent stability over time, and good humidity response, which is characterized by adding at least one of the following: and V ₂ O ₅ .

BACKGROUND OF THE INVENTION In recent years, moisture sensitive elements have come to be used in many fields. For household products, it is used to control food cooking in microwave ovens, to detect dryness in clothes dryers,
It is widely used for humidity control in room air conditioners, for detecting condensation on VTR cylinders, and in industrial applications, for humidity control during the manufacture of various electronic components. In addition, attempts are being made to use it for air conditioning in agricultural houses and for preventing dew condensation on automobile rear windows. Humidity control is essential in addition to temperature control in various automated systems for food cooking, air conditioning, drying, etc., and there is a demand for the development of moisture-sensitive elements that operate with high reliability.

In order to meet these demands, electrical resistance type moisture sensing elements have been put into practical use. This detects changes in humidity as changes in electrical resistance.
Various types of moisture-sensitive materials have been proposed, including electrolyte materials such as lithium chloride, organic polymer materials, and ceramic materials. Electrical resistance type moisture sensing elements are basically required to have a low electrical resistance value, good linearity of resistance-humidity characteristics, have an appropriate operating range, and not deteriorate in the usage environment. Recently, ceramic moisture-sensitive materials have been attracting attention as a material that comprehensively satisfies these requirements.

There have been many proposals for ceramic moisture-sensitive materials, but the important properties are (a) low electrical resistance (the higher the current, the better the sensitivity), and (b) resistance-humidity characteristics. (d) Good linearity is required, and (d) good responsiveness is required. The present inventors have concluded that ZrO ₂ and ZrO ₂ +Y ₂ O ₃ type ceramics exhibit particularly stable and favorable characteristics as ceramic moisture-sensitive materials that basically satisfy these characteristics.

The moisture sensing element may be in the form of a bulk type in which a pair of electrodes are provided on opposing surfaces of the ceramic sintered body, but a preferred form is to form an electrode layer on at least one surface of the ceramic substrate, and to It is of a thin film type, in which a mixture of the ceramic and a binder is coated on the layer, and a moisture sensitive layer is formed by drying and sintering. It is preferable to form the coating film by screen printing. More importantly, the electrode pattern in the electrode layer should be formed so that the spacing between the electrodes is as small as possible, 0.20 mm or less. For example, a pair of comb-shaped electrodes are meshed with the comb teeth alternately, and the spacing between the comb teeth is adjusted.
Good results can be obtained by setting it to 0.20 mm or less.

However, these ZrO ₂ and Y ₂ O ₃ +
There is still a lot of room for improvement in the performance of ZrO ₂ ceramic moisture sensing elements, and trials are currently underway. One of the points to be improved is the prevention of changes over time, and it is also desired to further reduce the resistance value. It is desirable to further shorten the humidity response time.

ZrO ₂ and Y ₂ O ₃ with excellent comprehensive properties
In order to obtain a +ZrO ₂ ceramic humidity sensing element, many studies have been made so far, including the addition of additives to the humidity sensing part, the firing method, the surface post-treatment method, etc. There is no guarantee that additives, firing methods, and surface post-treatment methods suitable for one type of moisture-sensitive material will be compatible with another type of moisture-sensitive material, and selection thereof can be difficult.

Summary of the Invention The present inventor has developed ZrO ₂ -based and ZrO ₂ +Y ₂ O ₃ -based ceramic humidity sensing elements by adding Li ₂ CO ₃ and
It has been found that low resistance, stability over time, and humidity responsiveness can be significantly improved by including at least one type of V ₂ O ₅ . These additives enable low temperature firing and form a very stable moisture sensitive part. Furthermore, KOH or
It was also found that performance was further improved when combined with Na ₂ CO ₃ surface treatment.

Thus, the present invention provides ZrO ₂ system and ZrO ₂ +Y ₂ O ₃
Li ₂ CO ₃ and
Provided is a moisture sensing element characterized in that at least one of V ₂ O ₅ is added. Furthermore, the present invention adds at least one of Li ₂ CO ₃ and V ₂ O ₅ to the moisture sensitive part mainly composed of ZrO ₂ type and ZrO ₂ + Y ₂ O ₃ type moisture sensitive materials, and adds KOH or also provides a method for manufacturing a moisture-sensitive element, which is characterized by subjecting the element to surface treatment by immersing it in an aqueous solution of Na ₂ CO ₃ .

Specific Description The moisture-sensitive element used in the present invention can be realized in a so-called "pulk" type in which a pair of electrodes are formed on the facing surfaces of a ceramic sintered body, but it is preferable to form a moisture-sensitive film on a substrate. It is manufactured as a thin film type. FIG. 1 shows an example of a thin film type moisture sensitive element.
An electrode layer 3 is formed on one or both sides of the substrate 1,
Then, a moisture sensitive layer 5 is formed thereon (the moisture sensitive layer is partially omitted). As a substrate, Al ₂ O ₃ , SiO ₂ , ZrO ₂
Ceramics such as are used. To form an electrode layer on a substrate, for example, nickel or the like is deposited as an under electrode, then gold, platinum, etc. is deposited on top of it as an upper electrode for rust prevention, and a desired electrode pattern is formed using photoetching technology. The ruthenium electrode can also be formed by a screen printing method using ruthenium paste. Recently, many microfabrication techniques for manufacturing printed circuit boards for electronic circuits have been put into practical use, and by applying them, it is possible to form fine electrode patterns. For example, the sputtering method 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, so the sensitivity of the moisture sensing element can be increased. Good results were obtained using a comb tooth spacing of 0.05-0.20 mm.

Furthermore, an electrode layer using a neutral electrode has recently been proposed by the applicant. As shown in FIG. 2, a neutral electrode 4 is arranged between each pair of comb-like electrodes. The neutral electrode is formed from a metal and/or a metal compound that is the same as the conductive material constituting the electrode or has a smaller tendency to ionize than hydrogen.
Although the neutral electrode is called an electrode, it does not perform a current-carrying function, but serves to suppress the tendency of ions, which lead to advantageous moisture-sensitive characteristics, to segregate and move toward the original electrode. That is, the moisture-sensitive layer initially has a homogeneous distribution of ions that favor the moisture-sensitive properties by adsorption of water into its matrix. However, due to the difference in ionization tendency between metals, ions that advantageously lead to moisture-sensitive properties migrate toward each electrode side of the electrode layer over time.
Ions that lead to advantageous moisture-sensitive properties are those introduced into the sintered body matrix from the ceramic material used, the binder, and the treatment agent or pre-additive when surface treatment such as dipping treatment or pre-additive treatment has been performed. Ta
These are ions such as Li, Na, Ca, K, etc. These ions in the moisture sensitive layer migrate towards the comb electrodes, for example in the case of comb electrodes, and the uniform distribution of these ions between the comb teeth is impaired. Due to the presence of the neutral electrode, the above-mentioned ions also move around the neutral electrode, so even if ion movement occurs, the initial uniform dispersion of ions is not impaired to a large extent as a whole. In this manner, the neutral electrode is useful in preventing the segregation of ions toward the electrode as described above, thereby suppressing changes in the properties of the moisture sensitive element over time. The neutral electrode is not limited to a straight one as shown in the figure.
It can be formed into a dot array or any other arbitrary shape. By screen printing the electrode layer, the neutral electrode can be easily formed at the same time.

After forming the electrode layer in this manner, a moisture-sensitive layer made of a mixture of a ZrO _2- based and Y ₂ O ₃ +ZrO ₂ -based moisture-sensitive material and a binder, which is the object of the present invention, is formed thereon.

Moisture-sensitive materials include (1) Y ₂ O ₃ + ZrO ₂ (0.01-99.00%) (2) ZrO ₂ + (CaO, MgO, BaO, TiO ₂ , Ta ₂ O ₅
and Nb ₂ O ₃ ) (0.01 to 99.00
%) etc. can be particularly preferably used.

According to the invention, the binder comprises Li ₂ CO ₃ and
It is constituted as a common species among V ₂ O ₅ . A combination of both is preferred. Li ₂ CO ₃ is used in an amount of 1 to 10 mol %, and V ₂ O ₅ is used in an amount of 10 mol % or less, and the total amount of both is preferably in a range of 1 to 10 mol %.

Alternatively, traditionally used binders, particularly lead-free borosilicate glass with Li ₂ CO ₃ and
V ₂ O ₅ may be added and mixed. A preferred composition for use as lead-free borosilicate has a sodium oxide content of 10 to 15% by weight, a potassium oxide content of 2 to 5% by weight, and a calcium oxide content of 5% by weight.
~10% by weight, magnesium oxide content ~0.5
3% by weight, the content of aluminum oxide is 5-10% by weight, the content of silicon dioxide is 30-45% by weight, and the content of boron oxide is 20-30% by weight.
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.

Generally, a moisture-sensitive paste is prepared by pulverizing and kneading a mixture of the above ceramic and binder, and then adjusting the viscosity with a resin paint. However, when only Li ₂ CO ₃ + V ₂ O ₅ is used as a binder, the following method is used: It has been found that preparing the moisture-sensitive paste in a manner that leads to good results.

() Ceramic (ZrO ₂ , Y ₂ O ₃ ) and Li ₂ CO ₃ are stirred with the addition of an organic binder.

() After the organic binder is evaporated and removed, primary firing is performed at a temperature of around 800℃.

() The fired product is crushed with the addition of an organic binder.

() After the organic binder is evaporated and removed, V ₂ O ₅ and resin paint are added.

() Knead and adjust viscosity to form a moisture-sensitive paste.

After the moisture-sensitive paste has been prepared in this manner, the moisture-sensitive layer is coated by screen printing so that the thickness of the moisture-sensitive layer is about 5 to 200 μm, preferably about 40 to 120 μm. The thicker the film, the lower the electrical resistance of the final product.

Thereafter, after preliminary drying at a temperature of 130 to 190° C. for 0.2 to 2 hours, a firing treatment is performed at a temperature lower than conventional. Since Li ₂ CO ₃ and V ₂ O ₅ have low melting points, their use as binders or their presence in binders allows low temperature firing. The firing process sinters the ceramic particles to form the skeleton structure of the moisture-sensitive membrane.
It provides structural strength. Previously, it was thought that a firing temperature of at least 900°C was necessary to obtain a certain level of structural strength, but it has been found that such high-temperature firing actually deteriorates the properties of the fabricated moisture-sensitive element, especially the resistance properties. In the present invention, 500 to 870℃
The calcination is carried out at a temperature of 550-700°C, preferably 550-700°C. The firing holding time may be 5 minutes to 1 hour, typically several tens of minutes.

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

In this way, a moisture-sensitive element with low resistance and high sensitivity and stability is produced, preferably by carrying out a subsequent surface treatment to further improve the stabilization and low resistance. Can be done. Although various surface treatment methods have been proposed, the preferred method in the present invention is immersion treatment in a solution containing KOH or Na ₂ CO ₃ .

The immersion treatment in the KOH-containing liquid is carried out by immersing the produced moisture-sensitive element in the liquid for an appropriate period of time, such as 1 to 120 minutes. KOH concentration is 10~
30% by weight is suitable. If it is less than 10%, it will take a long time for impregnation, and if it exceeds 30%, the degree of surface modification will increase, causing harmful effects such as increased hysteresis.

After the dipping treatment, the device is preferably fired at a temperature of 600-870°C. Firing is necessary to prevent the KOH surface treatment agent from dripping during condensation and to produce a stable modified surface. Firing temperature range: 600~
The reason why the temperature is preferably 870°C is to prevent an increase in electrical resistance, as described above.

In the case of Na ₂ CO ₃ treatment, it can be carried out in substantially the same manner as above.

Example 1 A comb-shaped ruthenium electrode as shown in FIG. 1 was formed by screen printing on an Al ₂ O ₃ substrate having a length of 18 mm and a width of 9 mm. The spacing between each electrode comb tooth was 0.20 mm, and printing was performed over a length of 12 mm.

1.5 mol % of Li ₂ CO ₃ was added to the mixed ceramic with ZrO ₂ :Y ₂ O ₃ =50:50 weight ratio and stirred under addition of ethyl acetate. After evaporating the ethyl acetate
Primary firing was performed at 800°C for 1 hour. Crushing was carried out with the addition of ethyl acetate to evaporate the ethyl acetate, then 0.5 mol of V ₂ O ₅ , butyl carbitol and epoxy resin paint were added, and after mixing, the viscosity was adjusted to prepare a moisture sensitive paste.

Apply the moisture sensitive paste on the electrode so that the thickness of the moisture sensitive layer is
Apply by screen printing to a thickness of 40μm,
It was dried at a temperature of 170°C for 1 hour. Thereafter, it was low-temperature baked at 600°C for 15 minutes.

Subsequently, post-treatment was carried out by immersing it in a 20% KOH aqueous solution for 5 minutes and then baking it at 800°C for 20 minutes.

Humidity-resistance characteristics of the humidity-sensitive element thus obtained,
Humidity response (90% response, 33%RH → 55%RH and
85%RH → 55%RH) and stability over time (standing at 80°C and various humidity conditions) were investigated. The results are shown in Figures 3, 4 and 5, respectively. From the graph in FIG. 3, it can be seen that the resistance value is very low and the linearity is maintained as before. From Figure 4, it can be seen that the response characteristics are extremely good (10 seconds). FIG. 5 shows that the stability over time is also good. It can be seen that the present invention provides a moisture-sensitive element that is overall excellent.

Example 2 A moisture sensitive layer was coated on an electrode layer having a neutral electrode as shown in FIG. 2 in the same manner as in Example 1 to form a moisture sensitive element. As shown in FIG. 3, the resistance value is only somewhat low, and the response is good as shown in FIG. 4. The stability over time was measured in the same manner as in FIG. The results are shown in Figure 6. Very good stability over time has been obtained.

In addition, in the above test example, the resistance value corresponds to the measurement frequency.
Measured at 1000Hz and measurement voltage 1V.

Effects of the Invention The present invention provides a moisture sensing element with extremely low resistance, excellent stability over time, and extremely good response characteristics, compared to various moisture sensing elements currently on the market or proposed. Overall, it is excellent.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an example of a coating film type moisture-sensitive element, Figure 2
The figure is a plan view of the electrode pattern using a neutral electrode, the third
The figure is a graph showing the humidity-resistance characteristics of the humidity sensing elements of Example 1 and Example 2, Figure 4 is a graph showing the humidity responsiveness, and Figure 5 is a graph showing the temporal stability of the humidity sensing element of Example 1. The graph shown, and FIG. 6 is Example 2.
3 is a graph showing the stability over time of the humidity-sensitive element of FIG. 1: Substrate, 3: Electrode, 4: Neutral electrode, 5: Moisture sensitive layer.

Claims (1)

[Scope of Claims] 1. Adding at least one of Li ₂ CO ₃ and V ₂ O ₅ as a binder to a moisture sensitive part mainly composed of ZrO ₂ type and ZrO ₂ +Y ₂ O ₃ type moisture sensitive materials. A moisture-sensitive element characterized by: 2 At least one of Li ₂ CO ₃ and V ₂ O ₅ is added as a binder to the moisture sensitive part mainly composed of ZrO ₂ type and ZrO ₂ +Y ₂ O ₃ type moisture sensitive materials, and KOH or Na ₂ CO _3. A method for producing a moisture-sensitive element, which comprises immersing it in an aqueous solvent and subjecting it to surface treatment.