JPS6131351A - Post treatment for humidity 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 Field of the Invention The present invention relates to moisture sensitive elements, particularly Zr0
1 thread, ZrO2+y, o, thread and Y, O, thread In order to lower the resistance of ceramic moisture-sensitive elements using the moisture-sensitive material and prevent changes in the moisture-sensing properties over time, immersion in a lithium salt-containing solution followed by The present invention relates to a post-treatment method comprising a firing treatment. 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, moisture sensitive elements have come to be used in many fields. In household products, it is often used for food cooking control in microwave ovens, dryness detection in clothes dryers, humidity control in room air conditioners, and WI exposure in VTR cylinders. 'l Widely used for humidity control during the manufacture of electronic parts. In addition, attempts are being made to use it for air conditioning in agricultural greenhouses and for preventing rear windows from being damaged in automobiles. In each apple automation system such as food cooking, air conditioning, drying, etc.
In addition to temperature control, humidity control is also lacking, and there is a demand for the development of an M-sensitive element that operates 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, and the moisture-sensitive materials used include electrolyte materials such as lithium chloride, organic polymer material threads, ceramic materials, etc. something is proposed. An electrical resistance type moisture sensing element is basically required to have a low electrical resistance 1ifl, good linearity of resistance-humidity characteristics, an appropriate operating range, and not to deteriorate in the usage environment. Ceramic moisture-sensitive materials have recently been in the spotlight as materials that comprehensively satisfy 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. (iii) good responsiveness is required. The present inventors have developed (1) YtO as a ceramic moisture-sensitive material that basically satisfies these characteristics.
s, (2) Ylo, +Zr0t (α01~99.
00%), (3) Y10g+(CaO, MgO,,
BaO1T i O! , Tl1t Ox, Nb, O,
and VtOs) (α01~9900
%) (4) ZrO, + (CaO, MgO1B * OX
T10! , T J On, Nb, O, and Vt
Y of at least one type of Cα01-99.00%), 0. system, L On + Z r O2 system and Z
We have obtained a tie that the r01 series ceramic is good. In particular, Y,01+Zr01 ceramic exhibits stable and good properties.

+N M 'A-shaped layer may be a bulk type in which a pair of electrodes are provided on opposing surfaces of the ceramic sintered body, but the preferred form is on at least one surface of the ceramic substrate. It is a thin film type in which a ft electrode is formed, a mixture of the above ceramic and a binder is applied on one electrode shell, and a moisture sensitive layer is formed after drying. Preferably, the fishermen are formed by screen printing. More importantly, the kanpoku pattern in the nipolar layer should be formed so that the spacing between the kanpolar layers is as small as possible, 0.20 m or less. For example, good results can be obtained by interlocking a pair of comb-shaped electrodes with alternating comb teeth and setting the comb tooth spacing to α20 mm. However, these Y, O1 series, Y, O8+Z
There is still much room for improvement in the performance of the r01 yarn and Zr01 yarn ceramic moisture sensing elements, and trials are currently being carried out. One of the points to be improved is the prevention of # change over time, and it is also desired to further reduce the low resistance value.

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 intended ceramic ivy moisture-sensitive material. For example, Japanese Patent Application Laid-Open No. 59-47705 discloses Na5PO,.1
It is disclosed that scales can be reduced in resistance by applying a dip coating treatment using an aqueous solution of 2MoOs. Although it is stated that changes over time are reduced, no specific data is presented. In addition, Japanese Patent Application Laid-Open No. 59-75601 discloses a Tie having a specific pore size distribution and porosity,
- After impregnating the open pore surface of the SnO, based ceramic porous body with at least one alkali (phosphorus or sulfur), heat treatment is performed at 900 to 1200°C, and at least one pair of electrodes is attached to the surface of the resulting porous body. Disclosed is a method for manufacturing a porous moisture resistor formed by forming a porous moisture resistor.

The surface treatment agent must be compatible with the specific ceramic moisture-sensitive material, and a surface treatment agent suitable for one type of moisture-sensitive material may be suitable for another type of moisture-sensitive material. There are no guarantees.

By the way, JP-A-59-41802 discloses Zr01 and M
Dip coating of a thick film moisture sensitive layer based on a mixture of gQ with an aqueous LiCl solution is disclosed.

It has been reported that this can measure the decrease in resistance value. For example, when immersion treatment is performed using a 10% by weight LiCl aqueous solution, the resistance value is greatly reduced. However, the slope of the curve tends to become smaller after paulownia immersion treatment, which increases the
Since it is not possible to achieve a very high Cl4 degree, it is recommended to use an aqueous solution of α5% LIC1. There is no mention of ashing characteristics over time due to Llcxy soaking.

SUMMARY OF THE INVENTION The present inventor has developed the Zr01 series, the ZrOH+Y@03 series, and the Y! We investigated surface treatment agents to prevent aging of 08-series moisture-sensitive elements and reduce resistance, and found that immersion treatment with a lithium salt-containing solution was effective. In this case, the important thing is that preferably 750 to 8
The firing process is carried out at a temperature of 70"C.

The firing process creates a +1) slope in the resistance-humidity curve.

(11) Can prevent changes over time〇 (iii) Prevents the surface treatment agent from flowing out during dew condensation.

This effect occurs for the first time. Said Japanese Unexamined Patent Publication No. 59-4180
Simply immersion coating with a LiCl aqueous solution as in No. 2 is insufficient, and the original meaning of the surface treatment is not realized.

In summary, the present invention provides a Z r OH system, ZrQ, -1
-Y, O, yarn and YtO1 yarn IeL, moisture sensing element using moisture material! Provided is a post-processing method for a humidity-sensitive element for preventing time-dependent changes in IIA humidity characteristics, the method comprising immersing the humidity-sensitive element in a liquid containing a lithium bottle and then performing a baking process. do. Lithium salts include lithium hydroxide, lithium carbonate, and lithium chloride. The preferred firing temperature is 750-870°C. Further, in a preferable Y-type of the moisture-sensitive element based on the premise of the present invention, a comb-shaped electrode layer is formed on at least one surface of a ceramic substrate, and zrO! is formed on the electrode layer. A moisture-sensitive layer of yarn, Zr01 + Y2O3-based and Y,03-based moisture-sensitive materials mixed with a binder is formed by screen printing, and after drying, it is fired at a temperature of 750-870 °C, followed by aging treatment if necessary. 750～
It was produced by heat treatment at a temperature of 870°C.

Specific Description Although the moisture-sensitive element used in the present invention can be realized in a so-called bulk type in which a pair of electrodes are formed on opposing surfaces of a ceramic sintered body, it is preferable to form a moisture-sensitive element on a substrate. It is manufactured as a thin film type. FIG. 1 is a perspective view of a preferred example of a thin film type moisture sensitive element used in the method of the present invention.

An electrode layer 3 is formed on one or both surfaces of the substrate 1, and a moisture sensitive layer 5 is formed thereon (the moisture sensitive layer is partially omitted).

As the substrate, ceramics such as AI, O, 810, Zr01, etc. are used. The formation of the electrode layer on the substrate is
For example, it is possible to evaporate nickel as an under electrode, then evaporate gold, platinum, etc. as an upper electrode for rust prevention, and form a desired electrode pattern using photo-etching technology, or ruthenium paste. Ruthenium electrodes can also be formed by a screen printing method. 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, sputtering is also a useful method. The first electrode pattern is
As shown in the figure, it is preferable to have a pair of comb-shaped electrodes with interlocking teeth. 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 have been obtained using comb spacings of 0.05 to α20 dew.

After forming the electrode layer in this way, the Zr
O2 thread, Y, 0. A moisture sensitive layer consisting of yarn, Y*Os + Z ro, a mixture of yarn moisture sensitive material and binder is formed thereon.

As mentioned above, moisture-sensitive materials include (1) Yx Os alone.

(21Yt Os +Zr0t (α01~99.00
%)0(3) YtOs+(Ca01Mg0
1BaQST102, TatOaNb, O, and Vt
Os ) at least one type (0.01-9900%).

(4) Zr0t + (Cao, , MgO1Bad,
Ti01, TILt 0sNb! 0. and MgO
8) No less <Tomo-Im ((LO1~9900%).

etc. can be suitably used.

Binders are used to provide good sintering at low temperatures. As the binder, substances known as sintering aids can be used, but lead-free borosilicate glass is particularly suitable. The binder is used in an amount of 5 to 15%, preferably 7 to 12% of the total moisture sensitive material.

The composition of lead-free borosilicate glass that is preferred for use is a sodium oxide content of 10 to 15 weight percent, a potassium oxide content of 2 to 5 weight percent, and a calcium oxide content of 5 to 5 weight percent.
10% by weight, magnesium oxide content α5~3x
1%, the content of aluminum oxide is 5-10% by weight, the content of silicon dioxide is 50-45% by weight, and the content of boron oxide is 20-50% by weight. This binder has a higher content of alkali metal and alkaline earth metal oxides than general lead-free borosilicate glass.
, is preferred because of its low melting point.

After pulverizing and kneading the mixture of the above ceramic and binder, the viscosity is adjusted with a resin paint, and then the thickness of the moisture-sensitive layer is 5 to 5.
A moisture sensitive layer is coated and formed by screen printing to a thickness of 200 μm, preferably around 40 to 120 μm. The thicker the film, the lower the electrical resistance of the final product.

Thereafter, after preliminary drying for α2 to 2 hours at a temperature of 130 to 190°C, a firing process is performed at a temperature lower than conventional. The firing process sinteres the ceramic powder particles to form the skeleton structure of the moisture-sensitive membrane and to impart W structural strength.

Previously, it was thought that a minimum firing temperature of 900°C was necessary to obtain the required structural strength, but it has been found that such high-temperature firing actually deteriorates the performance of the fabricated moisture-sensitive element, especially the electrical resistance. . Therefore, the firing process is 750 to 87
It is carried out at a temperature of 0°C. It is believed that when high-temperature firing is performed as in the past, the ceramic powder particles or binder are melted (slag-formed) and the porosity of the moisture-sensitive element is reduced, thereby increasing the electrical resistance. Furthermore, it is also believed that the ceramic that is the object of the present invention tends to undergo transformation into an unstable crystalline form, resulting in insufficient stability. 87
This situation can be avoided by setting the upper limit of the firing temperature to 0°C. If the firing temperature is 750° C. or higher, the required structural strength of the moisture-sensitive element, which is the object of the present invention, is guaranteed.

The firing holding time may be 5 minutes to 1 hour, typically several tens of minutes.

A humidity sensing element with a certain level of performance can be produced by firing alone, but in order to make the humidity sensing element even more stable, it is necessary to perform an aging treatment on the humidity sensing element after firing, followed by heat treatment. There are various proposals regarding the method of aging treatment, but as a result of many studies, the present inventors have found that the aging process can be changed from a low humidity of, for example, 10% RH to a high humidity of, for example, 90% RH, and vice versa. The humidity increase/decrease cycle is carried out alternately for 20 to 50 minutes, preferably 30 minutes at 30 to 9D''C1, preferably at 60°C, for a total of 1 to 3 weeks, preferably around 2 hours. As a result of this aging treatment, a moisture-sensitive membrane is produced that can withstand long-term stable use without deterioration even under harsh conditions during use.

Furthermore, it is noteworthy that this aging process creates very fine racks in the moisture sensitive layer. It is not clear whether this is due to repeated cycles of humidity increase/decrease or something unique to this material system, but it is thought to be the cause of a highly stable element.

After this, the device is subjected to a heat treatment at a temperature of 750-870"C. This heat treatment is intended to provide complete dehydration and to immobilize the moisture-sensitive membrane, increasing electrical resistance and preventing transformation. (If the temperature exceeds 870°C, melting of the glass or transformation of the crystal structure may occur, increasing the electrical resistance of the element beyond the allowable range.) This is because it cannot be immobilized.Thus, a he wet element with low resistance, high sensitivity and stability is produced.

The immersion treatment in the lithium salt-containing liquid is carried out by immersing the generated moisture-sensitive element in the liquid for an appropriate period of time, such as 1 to 120 minutes. As lithium salts, lithium hydroxide, lithium carbonate and lithium chloride are used. Since lithium chloride has t'S lfi properties, it is likely to be eluted if dew condensation occurs during use, and therefore lithium hydroxide and lithium carbonate are preferably used. Lithium salt concentration is 1% by weight
It is preferable to set the resolution to ffj or more. The solubility of lithium hydroxide is 12.7% (0°C water), and the solubility of lithium carbonate is 1.54% (0°C water).

After the dipping treatment, the device is fired at a temperature of 750-870°C. Firing prevents the surface treatment agent from leaching out during condensation,
It plays a very important role in increasing the slope of the resistance-humidity curve, making humidity measurement easier, and preventing changes over time. Firing once at 759 to 870°C is necessary to sufficiently stabilize the surface treatment agent while preventing melting of the ceramic and binder.

Moisture-sensitive element products that have been post-treated in this way exhibit stable performance over a long period of time because they exhibit little change over time and have low resistance.

Effects of the invention A very simple surface treatment operation can prevent the moisture-sensitive characteristics of the moisture-sensitive element from changing over time, and at the same time lower the resistance value.
A more excellent moisture sensitive element is manufactured.

Example (manufacture of a moisture-sensitive element) A comb-shaped ruthenium electrode as shown in FIG. 1 was formed by screen printing on an Al, O, substrate 18 meters long by 9 meters wide. The interval between each electrode comb tooth was α204, and printing was performed over a length of 12 parrots. Yt Oa' Z on the electrode layer
Mixed ceramic 93 with a ratio of 50:50 Jl
A moisture sensitive layer was formed consisting of a mixture of 10% lead-free borosilicate glass and 7% lead-free borosilicate glass. The moisture-sensitive layer was formed as follows: The above-mentioned mixture was crushed and kneaded in an automatic mortar made of alumina, and then the viscosity was adjusted with butyl calpitol and epoxy-based fat paint, so that the thickness of the moisture-sensitive layer was approximately 20 μm. It was applied by screen printing. Thereafter, it was pre-dried at a temperature of 170'C for 1 hour and fired at a temperature of 800C for 15 minutes.

Next, the samples were aged for two weeks at 60° C. while undergoing a humidity increase/decrease cycle of 10% RF and 90% RH, with cycles repeated every 30 minutes, followed by ripening at 870° C.

Practical row 1 The moisture sensitive element obtained in the reference example was immersed in a 10 volume% LiC1 aqueous solution for 5 minutes and dried in the air (20"C160%R)
I) After-treatment was carried out by firing 20 at 800C. Resistance-humidity characteristics before post-treatment, after immersion, and during firing! I paid ¥. The resistance value is measured at the measurement frequency 10001 (z
Then, the measurement pressure was set at 1 cm. The results are shown in Figure 2. The resistance decreases drastically from the initial value due to impregnation, but
It can be seen that the slope of the curve becomes very small. This makes accurate measurement difficult. However, when it is fired, the slope of the curve becomes larger, and the resistance remains lower than the initial value.

FIG. 3 is a graph showing how the resistance value changes over time under various humidity conditions. It can be seen that the post-treatment of the present invention can prevent deterioration over time.

Comparative Example Q: The same 1flI determination as in the example was carried out using a 5% Li C1 aqueous solution, but the resistance did not decrease much and the aging characteristics were poor.

Example 2 After 1% lithium carbonate immersion, 800°C was fired.
As shown in the figure, the resistance value is low and linear,
The change over time was also favorable, with no fluctuations as in the case of L i C1!10% in the example.

Practical Example 3 A product immersed in a 10% lithium oxide solution and fired at 800°C has a resistance value of 10% at the 10% temperature. It had a low Ω and linearity, and its change over time was the same as in Example 1, showing favorable properties compared to the others.

[Brief explanation of drawings]

Figure 1 is a perspective view of a preferred example of a humidity sensing element, Figure 2 is a graph showing the resistance and humidity characteristics of a temperature sensing element using lithium chloride, and Figure 3 is a graph showing the resistance and humidity characteristics of a temperature sensing element using lithium chloride. FIG. 4 is a graph showing changes over time, and FIG. 4 is a graph showing resistance-humidity characteristics in the case of immersion in lithium carbonate. 1 °ai plate 5 = 1 type pole

Claims (1)

[Claims] 1) ZrO_2 system, ZrO_2+Y_2O_3 system, and Y
A post-treatment method for preventing changes over time in the moisture-sensing characteristics of a moisture-sensing element using a _2O_3-based moisture-sensitive material, characterized by immersing the moisture-sensing element in a lithium salt-containing liquid and then performing a baking treatment. A method for post-processing moisture-sensitive elements. 2) The method according to claim 1, wherein the firing temperature is 750 to 870°C. 3) A method according to claim 1, wherein the lithium salt is selected from lithium hydroxide, lithium carbonate and lithium chloride. 4) In the moisture sensing element, a comb-shaped electrode layer is formed on at least one surface of a ceramic substrate, and ZrO_2-based, ZrO_
A moisture-sensitive layer of 2+Y_2O_3-based and Y_2O_3-based moisture-sensitive materials mixed with a binder is formed by screen printing, and baked at a temperature of 750-870°C after drying, followed by aging treatment if necessary at a temperature of 750-870°C. Claim 1 produced by heat treatment with
The method described in section.