JPS6351362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a humidity sensing element that uses a humidity sensitive substance whose electrical resistance changes depending on humidity. Moisture-sensitive elements using lithium chloride as a moisture-sensitive substance have conventionally been widely used, but in recent years, moisture-sensitive elements using metal oxides have been developed. This metal oxide-based humidity sensing element is superior to the above-mentioned lithium chloride-based humidity sensing element in terms of changes in characteristics over time and the size of the relative humidity range to which it can be applied. A stable metal hydroxide layer is formed on the surface of the layer, resulting in a decrease in sensitivity, so it is necessary to perform periodic heating cleaning. Furthermore, during temperature cycles and humidity cycles, the adhesion between the substrate and the humidity-sensitive resistor layer may deteriorate, or cracks may occur in the humidity-sensitive resistor layer. Therefore, conventional metal oxide-based moisture sensing elements are equipped with indirect heaters as a countermeasure to the above problem, but this complicates the structure, making it difficult to mass-produce and reduce manufacturing costs. That leaves a big problem. The present invention improves the above drawbacks, has high sensitivity and stable moisture sensing performance over a wide range of relative humidity, has good adhesion between the substrate and the humidity sensitive resistor layer, and is suitable for mass production. It is an object of the present invention to provide a moisture-sensitive element that can be both abundant and low-priced. That is, in the humidity sensing element of the present invention, a pair of electrodes facing each other and a humidity sensing resistor layer extending between the two electrodes are formed on an insulating substrate such as ceramic, and this humidity sensing resistor layer is made of metal oxide containing lithium. The present invention relates to a moisture-sensitive element comprising a sintered body of a composition containing a chemical component powder, a glass powder, and a powder containing MnO as a main component and a specific oxide. As the above-mentioned glass component, a fritted glass fine powder is suitable, such as a lead silicate frit, a lead borosilicate frit, a zinc borosilicate frit, and a lead borosilicate frit containing an alkaline earth metal or zinc. Can be mentioned. Such fritted glass fine powders include, for example, B ₂ O ₃ , SiO ₂ , ZnO,
A mixture of oxide powders, which are raw materials such as PbO and CdO, is heated at high temperature to completely melt it, and this is dropped into water to solidify and form a frit.The frit is taken out and processed using a ball mill etc. to a particle size of 1. ~
Obtained by grinding to about 2μ. Metal oxide component powders containing lithium include LiNbO ₃ , Li ₂ WO ₄ , Li ₂ MoO ₄ , LiZrO ₃ ,
Lithium-based composite oxide powders such as Li ₂ TiO ₃ , LiTa ₂ O ₂ , LiVO ₃ , and LiO ₂ with WO ₃ , TiO ₂ ,
Nb ₂ O ₅ , Ta ₂ O ₅ , MoO ₃ , ZrO ₂ , GeO ₂ , TeO ₂ ,
Examples include powders having a composition containing at least one oxide such as V ₂ O ₅ and Sb ₂ O ₃ , and these can also be made into fine powders with a particle size of about 1 to 2 μm in the same manner as the glass component. Recommended. On the other hand, the oxide powder mainly composed of MnO contains 50 mol% or more of MnO and contains TiO ₂ ,
It is an oxide powder containing at least one selected from SnO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , MgO, and Sb ₂ O ₅ , and is preferably a fine powder with a particle size of about 1 μm. The blending ratio of the glass powder, the metal oxide component powder containing lithium, and the above-mentioned oxide powder mainly composed of MnO is such that if the proportion of the glass powder is less than 5% by weight, the moisture-sensitive resistor that will eventually be formed will be affected. The adhesion strength and abrasion resistance of the layer to the substrate will decrease, and if it exceeds 80% by weight, the sensitivity of the moisture-sensitive element in the low humidity region will decrease significantly. It is desirable to choose appropriately. On the other hand, metal oxide components containing lithium
The blending ratio with the oxide whose main component is MnO is such that if the latter exceeds 90 mol%, the sensitivity of the moisture sensing element in the low humidity region will decrease significantly.
It is desirable to select an appropriate amount within the range of 5 to 90 mol % of the oxide whose main component is . To form the moisture-sensitive resistor layer, a mixture of the above three component powders is added with a vehicle such as ethyl cellulose, an acrylic resin, butyl carbitol acetate, and terepionelle, and thoroughly mixed using a roller or ball mill. A paste-like composition having an appropriate viscosity may be used. Next, the specific structure of the moisture sensitive element of the present invention will be explained with reference to the drawings. FIG. 1 shows an example of the moisture sensing element of the present invention, in which 11 is an insulating substrate made of ceramic or the like, 12 and 13 are a pair of electrodes each having a comb shape and facing each other, This electrode 12
and 13 lead-out parts 12b and 13b, respectively.
The moisture sensitive resistor layer 14 made of the sintered body described above is coated over the main parts 12a and 13a except for the main parts 12a and 13a. 15 and 16 are electrodes for connecting the electrodes 12 and 13 to external leads 17 and 18, respectively. FIG. 2 shows a cross section taken along line 2-2' in FIG. Such a moisture sensitive element is manufactured, for example, by the following method. First, using an insulating substrate 11 on which electrodes 15 and 16 have been provided in advance, comb-shaped electrodes 12 and 13 are formed on the surface thereof by screen printing, and the electrodes are fired at about 850 to 950°C in a firing furnace. Next, the main parts 12a of the electrodes 12 and 13 are formed using the paste-like composition described above.
and 13a to form a coating layer with a uniform thickness, and then in order to increase the adhesion between the insulating substrate 11 and the moisture-sensitive resistor layer, a glass layer is formed in a baking furnace. The melting temperature of, e.g.
Fire at a suitable temperature of 600-1000℃. During the cooling process after firing, the moisture-sensitive resistor layer 14 hardens and becomes a film that has good adhesion to the insulating substrate 11 and has an appropriate pore distribution. After this cooling, external leads 17 and 18 are attached, followed by immersion treatment in hot water and load aging under high temperature and high humidity conditions in order to stabilize the characteristics. In addition, in the above-mentioned example of the humidity sensing device having the structure shown in FIG. 1 and FIG. However, the humidity sensing element of the present invention also includes one in which the order of formation of both is reversed and a pair of electrodes are formed on the humidity sensing resistor layer. Examples of this invention will be shown below. Example Fine powder of lithium niobate and fine powder of lead borosilicate fritted glass (B ₂ O ₃ :
SiO ₂ :PbO weight ratio = 10:25:65) and the fine oxide powder mainly composed of MnO shown in Table 1 were mixed in a ball mill, and ethyl cellulose and butyl cellulose were mixed.
A vehicle consisting of carbitol acetate was added, and a paste composition with a uniform viscosity was prepared using a ball mill.

[Table] This composition was coated on an alumina insulating substrate in the configuration shown in FIGS. 1 and 2, in which electrodes 12 and 13 were ruthenium oxide electrodes and electrodes 15 and 16 were Ag-Pd electrodes, to a film thickness of 30 to 30 mm. Screen printed to a thickness of 100μm, heated in air at approximately 350℃ to volatilize and remove vehicle components, and then heated to 850℃.
After cooling and immersing in boiling water,
Aging was performed under electric current at ℃ and 90%RH.
A moisture-sensitive element was prepared according to a conventional method. Regarding the humidity sensing element obtained in the above example, the electrical resistance between the electrodes was measured at 24° C. while changing the relative humidity of the measurement atmosphere. The results are shown in Table 2.

【table】

[Table] From the results in Table 2, it can be seen that each of the elements of the above examples has high sensitivity and excellent linearity over a wide range of relative humidity. In addition, as metal oxide component powder and glass powder containing lithium,
Almost similar results were obtained even when the other components mentioned above were used. Furthermore, it has been confirmed that the moisture-sensitive element of the present invention is very stable when left in a high-humidity atmosphere, and can be washed with water if the element becomes contaminated. In addition, this element can be produced using thick film technology, and does not require the installation of an indirect heater unlike the conventional metal oxide moisture-sensitive elements mentioned above, making the element configuration simple and easy to mass-produce. It has the advantage of being suitable for commercialization and has high industrial utility value.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of the moisture sensitive element of the present invention, and FIG. 2 is a sectional view taken along line 2-2' in FIG. 11... Insulating substrate, 12, 13... A pair of opposing electrodes, 14... Moisture sensitive resistor layer.

Claims (1)

[Claims] 1. A moisture-sensitive element in which a pair of electrodes facing each other and a moisture-sensitive resistor layer extending between the two electrodes are formed on an insulating substrate such as ceramic, in which the moisture-sensitive resistor layer is made of a metal oxide-based component containing lithium. powder, glass powder, MnO as the main component and TiO ₂ ,
A moisture-sensitive element comprising a sintered body of a composition containing an oxide powder containing at least one selected from SnO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , MgO, and Sb ₂ O ₅ .