JPS61180401A - 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 <Industrial Application Field> The present invention relates to a humidity sensing element made of an oxide semiconductor that detects humidity as a change in electrical resistance.

Such a humidity sensing element can be used, for example, as a means for controlling humidity in air conditioning equipment, humidifiers, and the like.

<Prior art> Conventionally, it has been known that fine powders of various metal oxides (Sn02, AI203, Cr2o3, etc.) having hygroscopic properties are fired as humidity sensing elements, and this fired body is Changes in humidity can be detected by attaching a pair of opposing electrodes and measuring changes in electrical resistance between the electrodes.

In addition, titanium dioxide (Ti02
) is also being considered for use as a moisture-sensitive element material.

However, moisture-sensitive elements using fired bodies of the above-mentioned metal oxide fine powders, including TiO2, generally have a high specific resistance, and even if there is a change in electrical resistance due to a change in humidity,
It was difficult to measure accurately, and responsiveness and reproducibility were insufficient.

Therefore, in order to lower the resistivity, alkali metal oxides (L!02.20, etc.) and alkali metal salts (L i
Attempts have also been made to add C1, etc.).

Also, cobalt oxide (Coo) or nickel oxide (N
ip), an oxide with a pseudo-spinel structure (L
+MeVO4, where Me is Go or Ni> is also known as a low-resistivity moisture-sensing element (Japanese Patent Publication No. 5
7-40641).

<Problems to be Solved by the Invention> Among the above-mentioned conventional techniques, attempts to reduce the specific resistance by adding an alkali metal oxide or alkali metal salt to a metal oxide have Although it is lower,
It was observed that the humidity-electrical resistance value linearity tended to shift depending on the humidity cycle, and the durability was insufficient.

SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a moisture sensing element that has low specific resistance, excellent moisture sensitivity characteristics and responsiveness to changes in humidity, and sufficient durability.

<Means for solving the problem> The present inventors have discovered that the electrical resistance is 10-1 to 101 Ω・cm.
Titanium oxide with low resistance semiconductor properties such as (10kMcI2 green compact)
Focusing on 1.5), we added lead oxide (PbO) to this titanium oxide.
The present invention was completed based on the discovery that a moisture-sensitive element obtained by firing a powder mixture containing an effective amount of System Frit 1 is a moisture-sensitive element suitable for the above-mentioned purpose.

Titanium monoxide, which is generally represented by the molecular formula of TiO, is an unstable substance that is easily oxidized and is usually difficult to exist, but it is used in this invention.
-1 is not easily oxidized like -titanium oxide, even though the atomic ratio of oxygen/titanium in the molecule is close to 1.
It is a stable substance.

This T1□02n-1 is white titanium dioxide (TiO
2) in a reducing atmosphere containing nitrogen at a temperature in the range of about 750-850'C. The reason why nitrogen is included in the reducing atmosphere is to stabilize the titanium oxide product. The product has a black color and n in the molecular formula has a range of 1≦n<1.5, and is different from white TiO2, which is generally said to have a range of 1.9<n≦2.0. can be distinguished.

Such Ti0 (1≦n<1.5>n 2n-1 ) is also available as a commercial product such as Titanium Black 20MJ (trade name, manufactured by Mitsubishi Metal Industries, Ltd.).

In this invention, 30% by weight of lead oxide (PbO)-based frit is added to 70% by weight or more of titanium oxide having the above molecular formula.
A moisture-sensitive element can be obtained by firing a powder mixture containing an effective amount of less than % by weight. By blending PbO-based frit, sintering at a low temperature becomes possible, and a fired body can also be produced using a screen printing method. In addition, the amount of PbO-based frit added is determined by the addition effect so that the obtained fired body has sufficient adhesion strength and adhesion strength, and becomes a durable moisture-sensitive element with excellent humidity-electrical resistance linearity. It may be added in an effective amount to achieve the desired effect, but it is generally added in an amount of about 1 to 30% by weight based on the weight of the mixture.

If more than 30% by weight of PBO frit is added, the moisture sensitivity characteristics will deteriorate and at the same time the electrical resistance will increase, which is not preferable. Moreover, if it is less than 1% by weight, the effect of blending the PbO-based frit will not be sufficiently expressed, and the adhesion to the substrate will be reduced, causing a problem in durability.

The PbO frit used in this invention includes Pbo
(7) Other k [(lJ'7 elements (B203), zinc monoxide (Z
nO), Z silicon oxide (Sin2).

It may contain metal oxides such as calcium oxide (Cab), and alkali metal oxides such as lithium oxide (Li20>, lithium oxide (Nap), and potassium oxide (K20>).

In manufacturing the moisture-sensitive element of the present invention, a powder mixture of titanium oxide having the above molecular formula and PbO-based frit in a predetermined amount is press-molded by a conventional method and then sintered. A method can be adopted in which the powder mixture is made into a paste, printed on the electrode using a screen printing method, and then fired.

<Example> Example 1゜Titanium Black 20MJ (product name manufactured by Mitsubishi Metal Industries ■) as T' n02n-1 (1≦n<1.5)
Pb0 (75@amount%) was used as PbO-based frit 1~
)-B203 (9% by weight)-ZnO (12% by weight) based frit was used to prepare four types of raw powder mixture samples having the formulations shown in Table 1.

Table 1 Δ 95 5 B 90 10 C8515 D 80 20 Each of the above powder mixture samples was mixed with Butylcarbyl 1 to 100
'aQ, 3.5 g of nitrocellulose and 25 mN of α-television to form a paste, and the paste was applied onto a prefabricated substrate as shown in Figure 1 using a 320 mesh screen printing plate. Printed. The substrate shown in Fig. 1 has ruthenium oxide (RuO2) electrodes 2 and silver-palladium (Aq-Pd) electrodes 3a and 3b formed on 95% alumina (A12o3) 1, and further has Ag-
A lead wire 4a is connected to the Pd electrodes 3a and 3b.

4b is soldered together, and 5 in the figure indicates the base 1 to the printing section.

After printing, this substrate was dried at 150'C for 15 minutes and then baked at 450'C for 30 minutes to obtain 1 q of moisture-sensitive elements of the present invention. The graph of FIG. 2 shows the results of examining the relationship between relative humidity and resistance value of the obtained fired body humidity sensing element.

As a result, the relationship between humidity and resistance value of each sample showed no deviation due to humidity cycles, and stable characteristics with good linearity were observed.

Further, when these fired humidity sensing elements were left for 100 hours at a 40'C1 relative humidity of 90% or higher, no change over time was observed in any of the samples.

Example 2 Methyl cellulose was added as a binder to the four types of mixture samples shown in Table 1, and after press molding at a pressure of 100k (II/cvl), the molded product was
It is heated and sintered at a temperature of C for 10 to 600 minutes to a thickness of 1.
A disk-shaped fired body 11 as shown in FIG. 3 with a diameter of 0 mm and a diameter of 10 mm was obtained.

A pair of electrodes 12a and 12b were formed by baking silver paste 1 to the main surface of this fired body 11, and lead wires 14a and 14b were soldered to these electrodes to produce a fired body moisture sensing element of the present invention.

The obtained humidity sensing element, like the humidity sensing element of Example 1, exhibited stable characteristics with no deviation in humidity-resistance linearity during humidity cycles, and had a relative humidity of 40'C1 relative humidity of 9.
No change over time was observed when the device was placed on a sheet for 1000 hours at 0% or more.

<Effects of the Invention> As explained above, the humidity sensing element of the present invention always exhibits stable characteristics without deviation in humidity-resistance linearity due to humidity noise. Further, since the resistance value changes greatly and has good responsiveness to humidity changes, humidity can be measured with high accuracy. Furthermore, since the sintering temperature can be set to a relatively low temperature and the fired body can be produced by screen printing, it is advantageous from the viewpoint of productivity and economy.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the humidity sensing element of the present invention, FIG. 2 is a graph showing an example of the relationship between relative humidity and resistance value of the fired body humidity sensing element of the invention, and FIG. FIG. 7 is an explanatory diagram showing another embodiment of the moisture-sensitive element of the invention. 1... Alumina substrate, 2.3a, 3b, 12a. 12b...electrode, 4a, 4b, 14a, 14t
l/IJ-t line, 5... paste printing section, 11...
fired body.

Claims (1)

[Claims] 1. Molecular formula Ti_nO_2_n_-_1 (1≦n<1.
5) A moisture-sensitive element comprising a fired body of a powder mixture comprising 70% by weight or more of titanium oxide represented by the formula 5) and an effective amount of 30% by weight or less of a lead oxide frit.