JPH0676982B2 - Moisture sensitive element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a humidity sensitive element using an organic polymer as a moisture sensitive material.

[Conventional technology]

Conventionally, as a moisture sensitive element of this type, an organic polymer such as cellulose acetate butyrate, cellulose acetate propionate, polyimide or polyimide amide is used as a moisture sensitive material, and a moisture sensitive film formed by this moisture sensitive material is used. A humidity sensitive capacitive element that utilizes a change in electric capacitance value for humidity detection has been proposed (Japanese Patent Laid-Open No. 62-88951).

[Problems to be Solved by the Invention]

However, the moisture-sensitive element having such a structure has high hydrophilicity (property of attracting water) and high sorbed water content (water absorption rate). Will probably remain. So, for example, the temperature
If used for a long period of time in a high temperature and high humidity environment of 40 ° C and humidity of 90%, the output value will drift. Also,
There is a problem that the difference in hygroscopic characteristics between the moisture absorption process and the dehumidification process (hysteresis) is small on the low temperature side and is large on the high temperature side, and the sensor response is delayed. Furthermore, there were problems such as the output value drifting due to the occurrence of dew condensation and the immersion in water.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is from low temperature to high temperature,
Another object of the present invention is to provide a humidity sensitive element that has a small hysteresis in a use range from low humidity to high humidity and has a fast sensor response.

Another object of the present invention is to provide a humidity sensitive element which can obtain a stable output value even when exposed to a condition such as high humidity, high temperature and high humidity, humidity cycle, dew condensation or water immersion for a long period of time. is there.

[Means for Solving the Problems]

The moisture-sensitive element according to the present invention constitutes a moisture-sensitive film using a polymer obtained by polymerizing an alkyl methacrylate monomer having no hydroxyl group.

In another moisture-sensitive element according to the present invention, a moisture-sensitive film is formed by using a polymer obtained by copolymerizing an alkyl methacrylate monomer having no hydroxyl group and a crosslinking agent having a plurality of vinyl groups.

[Work]

In the humidity-sensitive element according to the present invention, by using a polymer obtained by polymerizing an alkyl methacrylate monomer having no hydroxyl group, the amount of sorbed water becomes low and the hysteresis becomes small.

In another moisture-sensitive element according to the present invention, by introducing a cross-linking agent having a plurality of vinyl groups, the amount of water sorbed by the polymer is delicately controlled, the water absorption rate can be reduced, and the moisture-sensitive film Without sacrificing output sensitivity
Hysteresis can be reduced. Further, the crosslinking reaction improves the environment resistance and heat resistance.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the moisture sensitive element according to the present invention, and FIG. 2 is a plan view thereof. In these figures,
Reference numeral 1 is an insulating substrate made of, for example, an alumina substrate, glass substrate, or thermal oxide silicon substrate, 2 is a lower electrode made of, for example, platinum formed on the upper surface of the insulating substrate 1,
Reference numeral 3 denotes a moisture-sensitive film laminated and applied so as to cross the lower electrode 2, and reference numeral 4 denotes an upper electrode made of, for example, gold formed on the moisture-sensitive film 3. That is, the moisture sensitive film 3 is sandwiched between the lower electrode 2 and the upper electrode 4 in a sun-de-latent shape, and in order to detect the change in the capacitance value of the moisture sensitive film 3 with respect to relative humidity, the lower electrode 2 and the upper electrode 4 are respectively detected. Lead wire 2a
And 4a are connected.

In the moisture sensitive element having such a structure, the moisture sensitive film 3
Is formed of a moisture-sensitive material obtained by polymerizing methyl methacrylate or a moisture-sensitive material obtained by copolymerizing methyl methacrylate and divinylbenzene.

Next, a specific method for manufacturing the humidity sensitive element will be described.

First, methyl methacrylate monomer (MMA) purified by vacuum distillation is preliminarily polymerized under a catalyst to form a solution having an appropriate viscosity. Next, this solution is applied on the lower electrode 2 formed on the insulating substrate 1 by spin coating, and then 90 ° C.
A heat treatment is performed at about 200 ° C. to complete the polymerization reaction to form a moisture sensitive film 3 having a film thickness of 0.5 μm to 10 μm. The rotation speed of the spinner at this time is 1000 rpm to 5000 rpm. Then, gold is deposited on the insulating substrate 1 on which the moisture sensitive film 3 is laminated and coated by a vapor deposition method or a sputtering method to obtain 50Å to 500.
The upper electrode 4 having a size of about Å is formed. The lower electrode 2 on the insulating substrate 1 is formed of platinum in a thin film with a thickness of 1000Å to 10000Å by a vapor deposition method or a sputtering method. In this case, the moisture-sensitive film 3 is formed from a methyl methacrylate monomer (MMA) as a starting material, a polymethyl methacrylate (PMMA) simple substance polymer, and is formed in a non-crosslinked state.

According to such a configuration, the moisture sensitive film 3 is formed of a polymethyl methacrylate (PMMA) simple substance polymer,
Sorpted water content is low and hysteresis is small.

With respect to the humidity-sensitive element thus configured, the relative humidity-capacitance characteristics were measured, and as a result, the data shown in FIG. 3 was obtained. Use an LCZ meter for this measurement, and
It was performed under the conditions of ℃ and frequency of 100KHz. As is clear from the figure, the hysteresis was about 1% RH or less, which was extremely good.

Next, another embodiment of the moisture sensitive element according to the present invention will be described with reference to FIGS.

First, methyl methacrylate monomer (MMA) purified by vacuum distillation is temporarily polymerized under a catalyst, and then divinylbenzene (about 30 wt% or less with respect to MMA) is added as a hydrophobic cross-linking agent to form a solution. Next, this solution is applied on the lower electrode 2 formed on the insulating substrate 1 by spin coating, and then heat-treated at about 90 ° C to 200 ° C to copolymerize it to a film thickness of 0.5 µm to 10 µm. The moisture sensitive film 3 is formed to complete the moisture sensitive element. In this case, the moisture sensitive film 3 is formed by using methyl methacrylate monomer (MMA) and divinylbenzene as starting materials to form a polymethylmethacrylate (PMMA) -divinylbenzene copolymer, which is crosslinked.

In addition, in the above-described embodiment, a catalyst may be newly added when divinylben is added.

According to this structure, the moisture-sensitive film 3 is formed of a copolymer polymer into which a hydrophobic cross-linking agent has been introduced, so that the moisture absorption rate is further lower than that of a polymethylmethacrylate (PMMA) simple substance polymer. It became possible to control the amount of sorbed water, and to obtain a polymer with the optimum amount of sorbed water to achieve the target properties and to further improve the membrane properties. That is, about 1 part of the moisture-sensitive element having such a structure is dissolved in a solution such as ethyl acetate, acetone, toluene, dioxane, ethanol, carbon tetrachloride, benzene, ethylene dichloride, n-hexane or cyclohexane.
It was not dissolved at all in the solvent immersion test conducted by immersion for a minute, and the solvent resistance could be improved.

FIG. 4 shows the humidity sensitive element manufactured in this example at about 40 ° C. and 90% R
10% RH to 90% RH after being left in a high temperature and high humidity atmosphere of H
3 shows the change in the moisture-sensitive property in the. As is clear from the figure, the humidity sensitive characteristic drift of 90% RH of the moisture sensitive film 3 formed of the copolymer polymer according to this example is saturated after 200 hours of standing, and from the initial value at that time, Drift is equivalent to + 7% RH. Compared with this, the result of a conventional moisture sensitive element using cellulose acetate butyrate as a moisture sensitive material after being left at about 40 ° C and 90% RH shows that the drift amount becomes saturated after 100 hours of leaving as shown in Fig. 5. The drift from the initial value at that time is equivalent to + 13% RH.
Therefore, the moisture sensitive film 3 according to the present embodiment has a drift amount of about half that of the conventional moisture sensitive film, and is stable and good. In addition, the hysteresis is 1/2 to 1/4 that of the conventional moisture-sensitive film, and the reproducibility is good, and even in a high temperature and high humidity atmosphere, even if it is left in the same atmosphere for a long period of time, it is almost The capacity is stable and stable. Also, after leaving in a high temperature and high humidity atmosphere and then returning to an indoor atmosphere, the initial output is reversibly restored.

Next, still another embodiment of the moisture sensitive element according to the present invention will be described with reference to FIGS.

First, methyl methacrylate monomer (MMA) purified by vacuum distillation and divinylbenzene (about 30 wt% or less with respect to MMA) are added and prepolymerized while stirring the solution under a catalyst to obtain a viscosity suitable for spin coating. Produce a solution with. After that, the moisture-sensitive film 3 is processed through the same steps as those in the above-described embodiment.
Are formed to complete the moisture sensitive element.

Even in such a configuration, the same effect as that of the above-described embodiment can be obtained.

In the above-described embodiment, the solution was applied onto the lower electrode 2 by the spinner method, and then the heat treatment for crosslinking was performed. However, instead of this heat treatment, light irradiation may be performed to cause copolymerization. good.

Further, in the above-described embodiments, the moisture sensitive element having the Saint-Gerache structure has been described as an example, but the present invention is not limited to this, and a pair of comb-shaped thin films facing each other on the surface of the insulating substrate. It goes without saying that the same effect can be obtained by applying it to a humidity sensitive element having a comb structure obtained by forming an electrode and laminating a moisture sensitive film so as to cover the comb thin film electrode.

Further, in the above-described embodiment, the humidity is detected by focusing on the change of the electric capacitance value with respect to the relative humidity of the humidity sensitive film, but the humidity is detected by focusing on the change of the impedance with respect to the relative humidity. The method may be adopted.

Further, the moisture-sensitive film in the above-described examples is also suitable as a humidity-sensitive film of a humidity sensor having a configuration in which it is formed on a crystal oscillator and humidity is detected from a shift in resonance frequency due to adsorption of the moisture-sensitive film. Yes, also, by forming a moisture sensitive film on the surface acoustic wave element, and by changing the speed of passing through the surface acoustic wave element,
It is also suitable as a moisture-sensitive film of a humidity sensor having a configuration for detecting humidity.

〔The invention's effect〕

As described above, according to the moisture-sensitive element of the present invention, since the moisture-sensitive film is formed by using the polymer obtained by polymerizing the methyl methacrylate monomer having no hydroxyl group, the amount of adsorbed water decreases and the drift It is possible to obtain stable moisture-sensitive characteristics with less hysteresis and good response. Also, by forming a moisture-sensitive film using a polymer obtained by copolymerizing an alkyl methacrylate monomer having no hydroxyl group and a crosslinking agent having a plurality of vinyl groups, the amount of adsorbed water is controlled,
Low hysteresis, good response and heat resistance,
It has an extremely excellent effect of obtaining a moisture-sensitive element having good solvent resistance and environment resistance and obtaining a stable output value.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a moisture sensitive element according to the present invention, FIG. 2 is a plan view of this moisture sensitive element, FIG. 3 is a relative humidity-electric capacitance characteristic diagram of this moisture sensitive element, and FIG. FIG. 5 is a diagram showing a humidity sensitive characteristic of the moisture sensitive element according to the present invention, and FIG. 5 is a diagram showing a moisture sensitive characteristic of a conventional moisture sensitive element. 1 ... Insulating substrate, 2 ... Lower electrode, 3 ... Moisture sensitive film, 4
...... Upper electrode, 2a, 4a ...... Lead wire.

Claims (2)

[Claims] 1. A moisture-sensitive element comprising a polymer obtained by polymerizing an alkyl methacrylate monomer having no hydroxyl group as a moisture-sensitive film. 2. A humidity sensitive element comprising a polymer obtained by copolymerizing an alkyl methacrylate monomer having no hydroxyl group and a crosslinking agent having a plurality of vinyl groups as a moisture sensitive film.