JPS6133372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact, highly accurate, and highly responsive humidity sensing element.

Among the various basic variables in the natural world, such as temperature and pressure/humidity, humidity is the most difficult to measure with high precision. Recently, various industries such as chemicals, medicine, paper/pulp, textiles, wood, tobacco, printing, etc., agriculture, forestry and livestock related such as greenhouses, soil, hatching, poultry farming, pig farming, etc.
Accurate and easy humidity measurement and adjustment are strongly desired in many fields such as home appliances such as cookers, air conditioners, dryers, vegetable preservers, and medical equipment.
The present invention relates to a humidity detection element that satisfies the needs in this field.

Currently, methods that use the change in ionic conduction of deliquescent salts such as lithium chloride to detect humidity as an electrical signal, and methods that use resistance changes due to moisture adsorption and desorption of magnetite and silicon semiconductors are widely used. ing.

However, all of these systems utilize ionic conduction, and have the disadvantage that changes over time due to polarization are large, and indicated values change due to adsorbed gases other than humidity. Also,
The response is poor, the hysteresis is large, and the measurement humidity range is very limited.

There are also devices that combine the deformation of synthetic fibers such as hair, nylon, and styrene with stress elements as they absorb and desorb moisture, but these devices have poor responsiveness, hysteresis, and accuracy.

There are elements that utilize the swelling properties of synthetic resins containing conductive fine particles such as carbon and metal powder, but these have problems with response and hysteresis, and also suffer from significant humidity deterioration.

Furthermore, there is a method that detects water adsorption and desorption in the pores of aluminum oxide as a change in capacitance, but this method has the drawback of large changes over time.

Further, a hygrometer that uses α-ray absorption and transmission has very high accuracy, but the device is large-scale and very expensive, so it cannot be used for general purpose.

In this way, currently developed or commercially available humidity detection elements and their devices are characterized by accuracy, sensitivity, responsiveness, hysteresis, measurement humidity range, heat resistance, influence of environmental gases, changes over time, ease of handling, All of them have advantages and disadvantages in terms of price, etc., and there was no one that was satisfactory in all aspects.

The present invention aims to eliminate these drawbacks of conventional humidity detection elements, and provides a capacitance variable humidity detection element that is small, easy to handle, stable in characteristics, and inexpensive. .

Below, we will discuss the basic structure, humidity detection mechanism and manufacturing method of the capacitance variable humidity sensing element of the present invention, as well as the problems of the humidity sensing element obtained by the manufacturing method and technical means for solving them. This will be explained sequentially with reference to the drawings.

First, the basic configuration of the humidity detection element of the present invention will be described with reference to FIG. In FIG. 1, 1 is a valve metal such as tantalum, titanium, or aluminum or a metal substrate of these metals;
A dielectric anodic oxide film 2 is formed on the surface of the metal base 1 by anodizing or the like. A semiconductor metal oxide film 3 such as manganese dioxide is formed on the dielectric anodic oxide film 2 .
However, the dielectric anodic oxide film 2 has a non-contact space 4 and a contact portion 5 with the semiconductor metal oxide film 3. A carbon layer 6 and a cathode current collecting layer 7 are provided on this semiconductor metal oxide film 3. 8 is a cathode extraction part.

Next, we will discuss the humidity detection mechanism.

Now, when the humidity sensing element of the present invention is placed in an atmosphere with a relative humidity of 0% and the capacitance is measured, since the moisture absorption by the semiconductor metal oxide film 3 is 0, the contact portion shown in FIG. Only the capacitance (hereinafter, this capacitance will be referred to as "solid capacitance" and abbreviated as C _S ) due to the dielectric anodic oxide film of No. 5 is detected. At this time, the semiconducting metal oxide film 3 is made of manganese dioxide, for example, and has semiconducting properties, so it functions as an electrode for extracting capacitance.

Next, when the humidity detection element of the present invention is placed in humidity, since the semiconducting metal oxide film 3 has hygroscopicity, the absorbed moisture will be transferred to the dielectric anodic oxide film 2 and the semiconducting metal oxide film 3. It reaches the surface of the non-contact space 4. Since the amount of moisture absorbed by this semiconducting metal oxide film 3 is proportional to the relative humidity in the air,
The moisture coverage in the dielectric anodic oxide film 2 is proportional to the relative humidity. In this way,
The moisture that has reached the dielectric anodic oxide film 2 contains carbon dioxide gas in the air, metal ions in the semiconductor metal oxide film 3, and other ions, and itself functions as an electrolyte. ing. The capacitance generated by the moisture coating in the non-contact space 4 is called the non-solidified capacitance and abbreviated as C _W (W=0 to 100). When the humidity sensing element of the present invention is placed in a certain humidity atmosphere and the capacitance is measured, the solidified capacitance C _S attributable to the contact portion 5 of the dielectric anodic oxide film 2 and the non-contact space Combined _capacitance ( _C
Abbreviated as 0 to 100. ) will be measured.

_{In other words , C} Since it changes in response to changes in relative humidity, _CX also changes in response to changes in relative humidity.

By the way, such a humidity detection element is generally manufactured by the manufacturing process shown in FIG. That is, a dielectric anodic oxide film is formed on a valve metal base, a semiconducting metal oxide film is formed, and a carbon layer and a cathode current collecting layer are sequentially formed.
A cathode extraction part is formed using solder or the like, and if necessary, an aging treatment is performed to obtain a finished product.

In this manufacturing process, various methods are currently proposed for forming the semiconducting metal oxide film. For example, there is a method of thermally decomposing a metal nitrate such as manganese nitrate or lead nitrate at an appropriate temperature to obtain the corresponding metal oxide, or a method of forming the metal oxide by electrochemical electrodeposition. Furthermore, various methods are known for forming the cathode current collecting layer. For example, a method using a so-called conductive paste in which fine powder of a good electrical conductor such as gold, silver, copper, platinum, or aluminum is dispersed in a synthetic resin, or a method in which a good electrical conductor such as gold, silver, copper, or aluminum is used There are methods such as direct formation by vapor deposition, thermal spraying, etc.

Furthermore, regarding the formation of the cathode lead-out portion, there may be a method of immersing the element in molten solder, or a method of directly forming a metal layer by vapor deposition or the like.

Among these various methods, combinations of methods that are characteristically stable, easy to handle, and inexpensive are the following methods.

That is, the formation of a semiconducting metal oxide film is performed by thermal decomposition of an aqueous solution of manganese nitrate, the formation of a carbon layer is performed by immersing the element in an aqueous colloidal carbon solution, and the formation of a cathode current collecting layer is performed using silver. The conductive paste is applied and the cathode lead-out portion is formed by a solder dip method.

The capacitance variable humidity sensing element manufactured based on the manufacturing method described above has various characteristics commonly required for humidity sensing elements using other conversion methods, such as sensitivity, response, and hysteresis. In addition, it is necessary that the absolute value of the long-term capacity and the rate of change in capacity with respect to changes in humidity (hereinafter simply referred to as the rate of change in capacity) remain unchanged.

However, the humidity detection element manufactured by the above-described manufacturing method has a drawback that the absolute value of the capacitance gradually decreases in a high-temperature, high-humidity atmosphere. That is, using tantalum metal as a base, after forming a dielectric anodic oxide film by an anodizing method, manganese dioxide is formed by thermal decomposition of an aqueous manganese nitrate solution, and then a cathode current collecting layer is formed from a carbon layer and a silver conductive paste. A humidity sensing element made of
℃, 90% RH), the absolute value of the capacitance decreases. If the absolute value of the capacitance becomes small in this way, when such a humidity detection element is used in a device, the reliability of the device will be significantly impaired. For example, if such a humidity detection element is incorporated into a humidity display device, over a long period of use, the device will display a lower humidity than the correct humidity, and if this device is incorporated into a humidity controller, the humidity will be displayed lower than the correct humidity. Otherwise, it may cause malfunction.

FIG. 4 shows changes in characteristics when such a humidity detection element is left in a high temperature and high humidity environment. FIG. 4 is a humidity-capacitance characteristic diagram, and the solid line 9 in the diagram is the initial humidity characteristic of the humidity detection element. This humidity detection element is then used in a high temperature and high humidity environment (e.g. 85℃, 90℃).
%RH) for about 150 hours and measured after drying, the solid line 10 in the figure shows the humidity characteristics.

As is clear from FIG. 4, the capacity reduction is particularly significant on the low humidity side. Considering this phenomenon, for example, the capacity when the relative humidity is 0% is (1)
In the formula, C _W =0, which is equal to C _S , that is, the solidification capacity. In other words, it can be seen that the solidification capacity decreases before and after the high temperature and high humidity treatment. The reason for this decrease in solidification capacity is
When the humidity sensing element is left in high temperature and high humidity, the silver conductive paste swells, and the carbon layer or manganese dioxide layer adhered to it peels off from the dielectric anodic film, causing the solidification capacity to decrease. This is because it decreases.

The present invention aims to improve the phenomenon of gradual capacity reduction, and provides a humidity sensing element that has stable capacitance characteristics over a long period of time even when left in a high temperature and high humidity environment.

The technical approach of the present invention is to add silane coupling agent into the conventional silver conductive paste and apply it to the humidity sensing element.

FIG. 5 shows the capacitance characteristics when using a conventional silver conductive paste and when using a silver conductive paste containing a silane coupling agent according to the present invention.

The characteristics of the embodiment shown in FIG. 5 are that in the same lot, everything from anodizing to carbon coating was performed, and after the carbon coating was formed, it was divided into two parts, one part was filled with conventional silver conductive paste, and the other part was filled with silane according to the present invention. Using a silver conductive paste containing a coupling agent, a cathode extraction part was then formed under exactly the same conditions to form a completed product, and the above two types of humidity detection elements were heated at 85°C.
66% after a certain period of time when left in a 90%RH environment
The capacitance was measured in an RH atmosphere (20°C, using the space in the NaNO ₂ supersaturated solution) and is a characteristic diagram showing its change over time. This is a case where a silver conductive paste to which a silane coupling agent according to the present invention was added was used.

As is clear from FIG. 5, the change over time in the capacitance of the humidity sensing element when using the silver conductive paste containing the silane coupling agent according to the present invention is different from that when using the conventional silver conductive paste. It can be seen that it is significantly smaller in comparison.

As described above, when a silver conductive paste containing a silane coupling agent is used, the phenomenon of gradual decrease in capacitance is prevented, and a humidity sensing element having stable humidity characteristics for a long period of time can be obtained.

Next, the stabilization of the long-term capacitance of the humidity sensing element by using a silver conductive paste using a silane coupling agent will be described in more detail.

The silane coupling agent is, for example, an organosilicon compound monomer having two or more different reactive groups in its molecule, with a silicon atom at its center, as shown in formula (2).

R−S _i ≡(R′) ...(2) One of the two reactive groups, R, is a functional group that can chemically bond with organic materials (various synthetic resins), and these include, for example, vinyl groups. , epoxy group, acrylic group, amino group, mercapto group, etc. The other functional group R' can be bonded to inorganic materials (glass, metals, metal oxides, ceramics, etc.), such as methoxy groups, ethoxy groups, β-methoxyethoxy groups, halogens, etc. be. In other words, a silane coupling agent has in a single molecule both a functional group that selectively binds to an organic substance and a functional group that selectively binds to an inorganic substance. It has the property of chemically bonding an organic substance and an inorganic substance through a substance.

In other words, when a silane coupling agent with the above properties is added to a conventional silver conductive paste, the adhesive strength to inorganic substances is significantly improved compared to the conventional silver conductive paste. If a silver conductive paste modified in this way is used, it will chemically bond with manganese dioxide and a dielectric anodic oxide film, and the silver conductive paste is composed of a liquid resin, and the silane coupling agent is also liquid. Therefore, by easily penetrating the colloidal carbon layer and porous manganese dioxide layer and easily adhering to manganese dioxide and the dielectric anodic oxide film, the humidity sensing element of the present invention can be left in high temperature and high humidity. This also prevents the capacitance from decreasing.

As explained above, according to the present invention, it is sufficient to simply add a silane coupling agent to a conventional silver conductive paste, and it can be handled in exactly the same way as a conventional silver conductive paste. This has great industrial value as it is possible to prevent a decrease in capacity and to obtain a humidity sensing element that is stable over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the capacitance variable humidity sensing element of the present invention, and FIG. 2 is an enlarged cross-sectional view showing the contact state between the dielectric anodic oxide film and the semiconducting metal oxide layer of the same element. Figure 3 is a general manufacturing process diagram for manufacturing the same element, and Figure 4 is a diagram of the same element.
Humidity characteristic diagram when conventional silver conductive paste is used. Figure 5 shows the capacitance decrease when a capacitance variable humidity sensing element using the silver conductive paste of the present invention is left at 85℃ and 90%RH. FIG. DESCRIPTION OF SYMBOLS 1...Metal base, 2...Dielectric anodic oxide film, 3...Semiconductor metal oxide film, 4...Non-contact space part, 5...Contact part, 6...Carbon layer, 7
...Cathode current collecting layer.

Claims (1)

[Scope of Claims] 1. A moisture-sensitive film made of a dielectric anodic oxide film is formed on an electrode substrate, and a semiconductor metal oxide layer, a carbon layer, and a cathode current collecting layer are sequentially laminated on this film,
1. A humidity detection element, characterized in that a conductive paste containing a silane coupling agent is used in the cathode current collection layer, and a change in capacitance between the cathode current collection layer and the electrode substrate is detected. 2 The silane coupling agent has a functional group R′ that can be hydrolyzed and a functional group R that can bond with an organic substance.
The humidity detection element according to claim 1, characterized in that the humidity detection element has at least one or more of the following. 3. The humidity sensing element according to claim 2, wherein R' is any one of a methoxy group, an ethoxy group, a β-methoxyethoxy group, and a halogen. 4. The humidity sensing element according to claim 2, wherein R is any one of a vinyl group, an acrylic group, an amino group, and a mercapto group.