WO2001069225A1

WO2001069225A1 - Capacitance type humidity sensor

Info

Publication number: WO2001069225A1
Application number: PCT/JP2001/002101
Authority: WO
Inventors: Tomoko Yoshida; Wataru Yamashita; Yuichi Okawa; Kiyotaka Shindo
Original assignee: Mitsui Chemicals, Inc.
Priority date: 2000-03-16
Filing date: 2001-03-16
Publication date: 2001-09-20

Abstract

A capacitance type humidity sensor having at least two metal electrodes which is excellent in stability to humidity, temperature dependence, response speed, etc. and capable of considerably changing in capacitance. A preferred embodiment of the sensor has, interposed between the electrodes, a moisture-sensitive layer comprising a polyimide resin. The polyimide preferably has a group represented by the formula (1) or (2). (1) (R?1 and R2¿ each is a single bond or an optionally substituted C¿1-20? hydrocarbon group.) (2) (R?3, R4, R6, and R7¿ each is alkyl or halogeno; R5 is a single bond, -SO¿2?-, -CO-, -O-, -S-, alkylene, or arylene; m and n each is an integer of 0 to 4; and p and q each is an integer of 0 to 4.)

Description

Description Capacitive humidity sensor Technical field

The present invention relates to a capacitance type humidity sensor. More specifically, the present invention relates to a capacitance type humidity detection sensor for detecting relative humidity of an atmosphere. Background art

The capacitance type humidity sensor has a structure in which a moisture-sensitive layer is arranged between two electrodes, and utilizes the fact that the dielectric constant changes according to the amount of moisture adsorbed in the moisture-sensitive layer, and the capacitance value changes. Things are known. This type of humidity sensor is used in a wide range of fields from general air conditioning, industrial use, and measurement to high response speed to changes in humidity, and particularly high measurement accuracy at low humidity.

As a material used for the moisture-sensitive layer of the humidity sensor, an organic polymer film, a metal oxide film, and the like are known. Of these, metal oxide films often have a low water absorption rate and a small change in capacitance value with respect to humidity, which has the disadvantage that the circuit for detection is complicated.

On the other hand, if a resin having a large water absorption is selected, the organic polymer film has an advantage that the capacitance value change with respect to humidity can be increased and the film can be easily formed as compared with the metal oxide film.

Among organic polymers, polyimide resin is excellent not only in heat resistance, solvent resistance, and cold resistance, but also in electrical properties, and has an appropriate water absorption of 1 to 3%. It is said to be suitable. A capacitance type humidity sensor using a polyimide resin as a moisture-sensitive material is described in Japanese Patent Application Laid-Open Nos. Sho 55-66749 and Hei 2-14053.

However, polyimide resin was exposed to high temperature and high humidity for a long time. Later, there was the drawback that the capacitance value was largely changed, especially in the high humidity range of 90% or more, and the capacitance value was not reproduced.

Since the reproducibility of measurement results and the lack of other physical or chemical influences are important for humidity measurement, attempts have been made to improve the humidity sensor using conventional polyimide as a moisture-sensitive material. (For example, Patent Publication No. 252291336, Patent—Japanese Patent Publication No. 252191337).

However, with conventional polyimide resins, the change in capacitance value with respect to humidity is still inadequate, or after long-term exposure to a high-temperature, high-humidity atmosphere, the change in capacitance value is large. However, there were drawbacks such as large drift in the region and the capacitance value not being reproduced. Although some improvements have been made by the above proposal, they are not always satisfactory in practical use, and further improvements are desired. On the other hand, there has been proposed a humidity detection sensor that has little change over time when left in the high-temperature and high-humidity atmosphere, but a conventionally known sensor has a small capacitance value change with respect to relative humidity, and thus has a small capacitance value. The disadvantage is that the detection circuit is complicated.

The present invention has arrived at the present invention as a result of diligent efforts to develop a humidity sensor that solves the conventional problems.

Disclosure of the invention

An object of the present invention is to provide a humidity sensor having a small change in capacity after being left in a high-temperature and high-humidity atmosphere for a long time (high stability in high-temperature and high-humidity).

An object of the present invention is to provide a humidity sensor having excellent durability. An object of the present invention is to provide a humidity sensor having a high response speed to humidity.

It is also an object of the present invention to provide a humidity sensor having a large capacitance change (capacitance change rate) with respect to relative humidity. The humidity sensor of the present invention is characterized in that the change in capacitance with respect to relative humidity is linear.

Further, the humidity sensor of the present invention has a feature that the temperature dependency is small. Further, the humidity sensor of the present invention is characterized in that the difference (hysteresis) in the moisture sensitivity between the moisture absorption process and the dehumidification process is small.

Still another object of the present invention is to provide a high-temperature, high-humidity solution having a high-temperature and high-humidity stability of ± 2% RH or less when left at RH of 60 ° and 95% (hereinafter, relative humidity is expressed as% RH) for 2000 hours. An object of the present invention is to provide a highly stable humidity sensor.

According to the present invention, it has at least two metal electrodes capable of realizing a high temperature and humidity stability of 3% RH or less when left at 60 C and 95% RH for 4500 hours. A high humidity sensor can be provided.

According to the present invention, there is provided a humidity sensor having at least two metal electrodes and capable of realizing a capacitance change rate of 10% RH and 90% RH of 1.3 or more and having a large capacitance change with respect to relative humidity. It is possible to

The present invention provides a capacitance-type humidity sensor having at least two metal electrodes and having a moisture-sensitive layer containing a polyimide resin between the electrodes.

The present invention provides a capacitance-type humidity sensor having at least two metal electrodes and having a moisture-sensitive layer containing a specific polyimide resin described later between the electrodes.

A capacitance type humidity sensor in which at least one of the metal electrodes is water vapor permeable is a preferred embodiment of the present invention.

The present invention has at least two metal electrodes, and a moisture-sensitive layer containing polyimide resin is provided between the electrodes. When left at 60 ° C. and 95% RH for 2,000 hours, the temperature is high. Provided is a capacitance-type humidity sensor having a humidity stability of 2% RH or less.

According to the present invention, at least two metal electrodes are provided, and a moisture-sensitive layer containing a polyimide resin is provided between the electrodes, and when left for 4500 hours at 60 ° C. and 95% RH, high temperature and high humidity High-temperature, high-humidity stability that can achieve a stability of ± 3% RH or less A high humidity sensor can be provided.

According to the present invention, at least two metal electrodes are provided, and a moisture-sensitive layer containing a polyimide resin is provided between the electrodes, and is stable at high temperature and humidity when left at 60 ° C and 95% RH for 2000 hours. High temperature and humidity stability of ± 2% RH or less, and high temperature and humidity stability of ± 3% RH or less when left at 60 ° C and 95% RH for 4500 hours A humidity sensor may be provided.

According to the present invention, at least two metal electrodes are provided, a moisture-sensitive layer containing a polyimide resin is provided between the electrodes, and the capacitance change rate can show 1.3 or more. It is possible to provide a sensor. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of a capacitance type humidity sensor according to an embodiment of the present invention, and FIG. 2 is a sectional view of the sensor according to the embodiment 1 after being left in a high-temperature and high-humidity atmosphere. It is a figure which shows the drift state of the output in each relative humidity of 10% RH, 30% RH, 50% RH, 70% RH, and 90% RH in C.

FIG. 3 is a diagram showing the relationship between the relative humidity and the capacitance at 40 ° C., 25 ° C., and 5 ° C. of the sensor according to the second embodiment. FIG. 4 shows the output of the sensor according to Example 2 at each relative humidity of 10% RH, 30% RHs 50 RH, 70% RH, and 90% RH at 25 ° C. after being left in a high temperature and high humidity atmosphere. FIG. 4 is a diagram showing a drift state. FIGS. 5 and 6 show 10% RH, 30% RH, 50% RH, 70% RH at 25 ° C. of the sensors according to Comparative Examples 1 and 2, respectively, after being left in a high-temperature, high-humidity atmosphere. It is a figure which shows the drift state of the output in each relative humidity of 90% RH. Specific modes for carrying out the invention

A preferred structure of the humidity sensor according to the present invention includes a capacitor having at least two metal electrodes, and a moisture-sensitive layer containing a polyimide resin is provided between the electrodes. Things.

Specific examples of preferred polyimide resins of the present invention are polyimide resins containing at least one group selected from a group having a norbornane skeleton or a group represented by the following formula (2). Examples of the group having a norbornane skeleton include a polyimide resin containing a group represented by the following (1).

In the formula, R ¹ and R ² represent a single bond or an optionally substituted hydrocarbon group having 1 to 20 carbon atoms, which may be the same or different. More preferred specific examples of the preferred polyimide resin of the present invention include a polyimide resin containing at least one group selected from a group having a norbornane skeleton represented by the above formula (1) or a group represented by the following formula (2): It is.

In the formula, R ³ , R ⁴ , R ⁶ and R ⁷ each independently represent an alkyl group or a halogen atom, and R ⁵ is a single bond, one S0 ₂ —, one CO—, — 0—, — S —, Represents an alkylene group or an arylene group, m and n are integers from 0 to 4, And q represent an integer of 0 to 4.

The alkyl group of R ³ , R ⁴ , R ⁶ and R ⁷ is preferably an alkyl group having 1 to 8 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group and a butyl group. These alkyl groups may have a substituent such as a halogen atom. Examples of the halogen atom include chlorine, bromine, and fluorine, and fluorine is more preferable.

m and n are preferably 0 or 1, and p and q are also preferably 0 or 1.

Examples of the alkylene group for R ⁵ include an alkylene group having 1 to 8 carbon atoms, preferably an alkylene group having 1 to 4 carbon atoms such as a methylene group, an ethylene group, and a butylene group. This alkylene group may have a substituent such as a halogen atom. Examples of the arylene group for R ⁵ include an arylene group having 6 to 20 carbon atoms, preferably an arylene group having 6 to 12 carbon atoms such as a phenylene group and a naphthylene group. Can be. The arylene group may have a substituent such as a halogen atom. R ³ is preferably a single bond or an alkylene group. Particularly, a single bond is preferable. The most preferred examples of the group having a norbornane skeleton represented by the formula (1) are the following groups,

The most preferred examples of the group represented by the formula (2) are the following groups (

As a specific example of the polyimide resin containing a group having a norbornane skeleton represented by the above formula (1), a polyimide resin containing at least one repeating unit represented by the following formula (3) or (4) Can be mentioned.

In the formula, R ¹ and R ² represent a single bond or an optionally substituted hydrocarbon group having 1 to 20 carbon atoms, which may be the same or different. R ⁸ represents a single bond, one S0 ₂ -, One CO-, One 0-, One S-, a -O-Ph- 0- group (Ph is phenylene group), an alkylene group or § Li one alkylene group Represent. Further, as a specific example of the polyimide resin containing a group represented by the above formula (2), a polyimide resin containing at least one repeating unit represented by the following formula (5) or (6) is given. be able to.

In the formula, R ^{3 to} R ⁸ are the same as described above. Specific examples of the repeating unit represented by the above formula (3) in the polyimide resin of the present invention include the following repeating units.

Further, specific examples of the repeating unit of the above formula (4) include the following repeating units.

Further, specific examples of the repeating unit of the above formula (5) include the following repeating units.

Further, specific examples of the repeating unit of the above formula (6) include the following repeating units.

The polyimide resin of the present invention may contain a plurality of the above-mentioned repeating units. In the present invention, a mixture of polyimides each consisting of (3) to (6) repeating units may be used, or a plurality of repeating units selected from the above formulas (3) to (6) may be appropriately contained in the molecule. May be a polyimide resin containing at a ratio of

For example, a polyimide resin containing a repeating unit of the above formula (3) and a repeating unit of the above formula (4), wherein 0 to 100 mol% of the repeating unit consists of the unit of the above formula (3), and the remaining repeating unit A polyimide resin having a unit represented by the following formula (4) can be given. A polyimide resin containing 50% of the repeating unit of the formula (3) and the repeating unit of the formula (4) is particularly preferable. Similarly, a polyimide resin containing the repeating unit of the formula (5) and the repeating unit of the formula (6), wherein 0 to 100 mol% of the repeating unit is composed of the unit of the above formula (5); The polyimide resin whose unit is a unit represented by the following formula (6) may be used. The repeating unit of the above formula (5) and the repeating unit of the above formula (6) A polyimide resin containing 50% of repeating units can be mentioned as a particularly preferable one.

Further, the polyimide of the present invention may be used alone, or two or more kinds may be used. In addition, the same kind of polyimides having different degrees of polymerization can be mixed and used.

It is desirable that the polyimide resin of the present invention contains the repeating units of the above formulas (3) to (6) in an amount of about 1 to 100, more preferably about 20 to 80.

The polyimide resin of the present invention has, for example, an acid anhydride having the structural formula shown by the following formulas (7) and Z or (8) and a structural formula shown by the following formulas (9) and / or (10) Polyamic acid (polyamic acid) can be produced from diamine and heated, dehydrated, or heated to obtain a polyimide.

Wherein R ⁸ has the same meaning as described above.

(8)

(In the formula, R ^{1 to} R ⁸ , m and n, and p and q have the same meanings as described above.)

For example, a polyamic acid (polyamic acid) having a repeating unit represented by the following formula (11) and / or (12) as a polyimide precursor on a stainless steel foil serving as an electrode, 、, Ν-dimethylacetamide, A solution obtained by dissolving in a solvent such as Ν-methyl-1-pyrrolidone is spin-coated, heat-treated, and subjected to a cyclization reaction to give a polyimide having a repeating unit of the above formula (3) and / or (4). It can be a film containing.

The heat treatment temperature is usually 100-400. C; preferably at 200-350 ° C, more preferably at 240-300 ° C.

(11)

Similarly, a polyamide acid (polyamic acid) having a repeating unit represented by the following formula (13) and / or (14) as a polyimide precursor is heat-treated and polymerized to repeat the above formula (5) and / or (6). It can be a polyimide having units.

The humidity sensor of the present invention is provided with at least two metal electrodes and a moisture-sensitive layer made of a resin containing polyimide between the electrodes. That is, the humidity sensor of the present invention is constituted by a capacitor having at least two metal electrodes, and a moisture-sensitive layer made of the resin containing the polyimide of the present invention is provided between the electrodes.

A humidity sensor in which at least one of the metal electrodes is water vapor permeable is a preferred embodiment of the present invention. As the structure of the humidity sensor of the present invention, known structures can be used without any limitation.

A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing one embodiment of a humidity sensor according to the present invention. 1 in FIG. 1 is a metal electrode, and 3 is a metal electrode. A moisture-sensitive layer 2 is provided between the electrodes 1 and 3. Leads are connected to electrodes 1 and 3, respectively, in order to detect a change in the capacitance value with respect to a change in the relative humidity of the moisture-sensitive layer. As a material of the electrode, a metal such as gold, platinum, silver, palladium, chromium, iron, and stainless steel, or an alloy containing these can be used.

At least one of the at least two metal electrodes in the present invention is preferably a water vapor permeable electrode. The water vapor permeable electrode of the present invention is preferably in the form of a thin film of the above metal and has a thickness of 0.05 to lzm. This electrode can be formed by a vapor deposition method, a sputtering method, an ion plating method, a plating method, a screen printing method, or the like. In particular, a thin film of gold or platinum is preferable.

In order to make the electrode permeable to water vapor, for example, a method of forming the metal thin film into a mesh or porous shape through which water vapor can pass can be adopted. In addition, an electrode film that is permeable to water vapor can be obtained by setting the thickness of the metal thin film to an extremely thin thickness of about 0.05 to 0.0 l〃m.

The other electrode may be a water vapor permeable electrode or a water vapor impervious metal foil / metal plate. Further, it may be a metal film formed on a supporting substrate.

In forming the humidity sensor of the present invention, for example, a solution obtained by dissolving the polyimide precursor of the present invention in a suitable solvent is spin-coated, dip-coated, vapor-deposited, or screen-printed on a metal electrode foil. It is applied by a conventionally known method such as a roll coating method, a flow coating method, a dough coating method, a bar coating method, a casting method, etc., and is heated and polymerized to form a polyimide layer having a desired thickness as a moisture-sensitive layer. Then, a method of forming a metal thin film such as gold or platinum on the moisture-sensitive layer by a vapor deposition method or a sputtering method can be adopted.

As a method for forming the humidity sensor of the present invention, a conventionally known method can be used without any limitation. The humidity sensor of the present invention has at least two metal electrodes, and has a high-temperature high-humidity stability, high durability, and high static resistance by providing a moisture-sensitive layer made of the above-mentioned polyimide-containing resin between the electrodes. Demonstrate excellent performance such as capacitance change rate Can be. The high temperature and high humidity stability in the present invention was measured as follows.

After leaving for a certain period of time in a high-temperature and high-humidity atmosphere, that is, a constant-temperature and constant-humidity bath at 60 ° C and 95% RH, the humidity sensor was taken out, and the capacitance at each humidity was measured at 25 ° C. The measurement was performed in about 2 hours. After the measurement, this humidity sensor was returned to the constant temperature and humidity chamber of 60 ° C and 95% RH. This measurement was repeated. The measured value was expressed as a value obtained by subtracting the capacitance value before leaving from the capacitance value at each humidity after leaving it in a high-temperature, high-humidity atmosphere, and converting it to relative humidity.

In the humidity sensor of the present invention, the high temperature and high humidity stability is 2% RH or less after leaving for 2,000 hours. Further, the high-temperature and high-humidity stability of the present invention is ± 3% RH or less after standing for 4500 hours. The high-temperature and high-humidity stability of the present invention is ± 3% RH or less after standing for 6000 hours. According to the humidity sensor of the present invention, a measurement result with very small instability due to humidity can be obtained.

That is, according to the present invention, a capacitance type having at least two metal electrodes and exhibiting a high temperature and humidity stability of ± 2% RH or less when left at 60 ° C. and 9′5% for 2000 hours. It is possible to provide a humidity sensor.

That is, according to the present invention, at least two metal electrodes are provided, and a moisture-sensitive layer containing a polyimide resin is provided between the electrodes. It is possible to provide a capacitance-type humidity sensor that can show a characteristic of 2% HH or less.

Further, according to the present invention, it has at least two metal electrodes, preferably has at least two metal electrodes, and has provided a moisture-sensitive layer containing a polyimide resin between the electrodes, 60 ° C; 95% RH It is also possible to provide a capacitance type humidity sensor that can exhibit high temperature and high humidity stability of ± 3% RH or less after being left for 4500 hours.

Furthermore, according to the present invention, it has at least two metal electrodes, preferably has at least two metal electrodes, and has provided a moisture-sensitive layer containing a polyimide resin between the electrodes. It is also possible to provide a capacitance-type humidity sensor that can exhibit a capacitance change of ± 3% or less after standing at 60 ° C. and 95% RH for 6000 hours. The humidity sensor of the present invention has a feature that the response speed is fast. A fast response speed means that the time to reach 90% response is short.

With the humidity sensor of the present invention, it is possible to achieve a response speed of 20 seconds or less. The capacitance change rate is the ratio of the capacitance when the relative humidity is 90% RH to the capacitance when the relative humidity is 10% RH at 25 ° C (90% RH capacitance 10% RH static). (Capacitance). The humidity sensor of the present invention can achieve a capacitance change rate of 1.3 or more. This is an excellent effect that conventional capacitance humidity sensors cannot achieve.

In terms of the rate of change in capacitance, the polyimide resin containing a group having a norbornane skeleton represented by the formula (1) is more excellent among the above-mentioned polyimides, so that the rate of change in capacitance is 1.30 or more. In order to obtain the humidity sensor described above, it is more preferable to select the above-mentioned polyimide having a norbornane skeleton represented by the formula (1) as the polyimide of the present invention.

That is, according to the present invention, at least two metal electrodes are provided, and a moisture-sensitive layer containing a polyimide resin is provided between the electrodes, and the capacitance change rate can show a capacitance change rate of 1.3 or more. It is possible to provide a type humidity sensor. The humidity sensor according to the present invention is characterized by low temperature dependency.

The temperature dependency was measured by the following method. In the temperature range of 5 to 40 ° C, the capacitance was measured at 0% RH, 10% RH, 30% RH, 50% RH, 70% RH, and 90% RH, respectively. Convert the value obtained by subtracting the capacitance value at each humidity at 25 ° C from the capacitance value at each humidity at each temperature into the relative humidity at 25 ° C. Calculated and expressed.

According to the present invention, it is possible to provide a humidity sensor having a small temperature dependency within ± 2% RH within a range of 5 to 40 ° C.

The hysteresis of the humidity sensor is a value obtained by subtracting the capacitance value when the humidity sensor is dehumidified from the low humidity side from the capacitance value when the humidity sensor is dehumidified from the high humidity side for a certain humidity atmosphere. Is expressed in terms of relative humidity. For example, from the capacitance value at 50% RH when the atmosphere around the humidity sensor is dehumidified from 70% RH to 50% RH at 25 ° C, the value when the humidity is increased from 30% RH to 50% RH The value obtained by subtracting the capacitance value at% RH is expressed in terms of relative humidity.

The humidity sensor of the present invention can realize a low hysteresis of ± 2% RH or less. .

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The detailed conditions for evaluating each item of the humidity sensor according to the present invention were as follows.

A predetermined humidity atmosphere was created using a split-flow type precision humidity generator (MODEL RH-1 manufactured by Shinei). By appropriately mixing 100% RH nitrogen and 0% RH nitrogen, a predetermined humidity atmosphere, that is, 0% RH, 10% RH, 30% RH, 50% RH, 70% RH, 90% RH nitrogen To produce This atmosphere is used for the humidity sensor set in the thermostat. By switching the atmosphere, the humidity sensor can be exposed to each humidity atmosphere. The above-mentioned humidity and nitrogen were switched every 5 minutes in the humidification direction and the dehumidification direction, flowed to the humidity sensor, and the sensor characteristics were evaluated by measuring the capacitance of the humidity sensor at each humidity. What The capacitance was measured at a frequency of 10 KHz using an LCR meter (4275A MULTI-FREQUENCY METER manufactured by HEWLETT PACKAKD).

(Example 1)

A solution prepared by dissolving polyamic acid (polyamic acid) having the following repeating unit as a polyimide precursor in N-methyl-1-pyrrolidone was spin-coated on a stainless steel foil 1 serving as an electrode.

The polyamic acid used in the present invention has a charge ratio of a diamine component to a tetracarboxylic dianhydride component of 1: 0.999, and a weight average molecular weight Mw (in terms of polystyrene) of 8 3 as measured by GPC. The weight average molecular weight / number average molecular weight ratio (Mw / Mn) was 3.57.

This was subjected to a cyclization reaction by a heat treatment at 250 ° C. to obtain a polyimide film 2 having a thickness of the following repeating unit. On this, a platinum thin film 3 having a thickness of 0.01 zm was formed as an electrode by sputtering, and leads and wires were connected to the stainless steel foil 1 and the gold thin film 3.

For this humidity sensor, the capacitance was measured in the range of 10 to 90% relative humidity, and a linear response was obtained. The results are shown in response curve 4 in FIG. The capacitance change rate of this humidity sensor was 1.33.

The high temperature and high humidity stability of this sensor was measured by leaving it in a 60 ° C; 95% RH atmosphere.

Figure 2 shows the drift of capacitance at 10% RH, 30% RH, 50% RH, 70% RH, and 90% RH at 25 ° C after being left in a high-temperature, high-humidity atmosphere. Indicated.

FIG. 2 shows that the sensor of the present invention can provide a stable capacitance without drifting.

The temperature and humidity stability of this humidity sensor at 4475 hours was ± 2% RH.

Table 1 shows the performance of the humidity sensor together with other examples and comparative examples. (Example 2)

A solution prepared by dissolving a polyamic acid (polyamic acid) containing 50 mol% of each of the following two repeating units in N-methyl-12-pyrrolidone as a polyimide precursor on a stainless steel foil 1 serving as an electrode is used as a polyimide precursor. I got it.

In the polyamic acid used in the present invention, the charge ratio of the diamine component to the tetracarboxylic dianhydride component was 1: 0.98, the weight average molecular weight Mw determined by the Carosas equation was 30,000, It showed good agreement with that obtained by the GPC.

This was subjected to a cyclization reaction by heat treatment at 280 ° C. to obtain a polyimide film 2 having a thickness of l〃m and containing 50 mol% of the following two repeating units. On this, a gold thin film 3 having a thickness of 0.0 l / m was formed as an electrode by sputtering, and a lead wire was connected to the stainless steel foil 1 and the gold electrode 3.

For this humidity sensor, the capacitance was measured at 40 ° C; 25 ° C, 5 ° C in the range of 0 to 90% relative humidity, and a linear response was obtained. The results are shown in FIG. As is clear from the figure, the temperature dependency was within ± 2.0% RH at all relative humidities, indicating that the temperature dependency was small and good moisture sensitivity was obtained. The capacitance change rate of this humidity sensor was 1.11.

The same high-temperature, high-humidity stability test as in Example 1 was performed on the sensor manufactured in the same manner. FIG. 4 shows the drift of the capacitance at each humidity as in FIG. FIG. 4 shows that a stable capacitance can be obtained without drifting by the sensor of the present invention.

The high temperature and humidity stability of the sensor at 6026 hours was ± 3.0% RH.

Table 1 shows the performance of the humidity sensor together with other examples and comparative examples. (Comparative Example 1)

A humidity sensor was prepared in the same manner as in Example 1, except that a film of another polyamic acid (trade name: Semicofine) was used instead of the polyamic acid (polyamic acid) of the same example. .

The same high-temperature and high-humidity stability test as in Example 1 was performed on this humidity sensor. Fig. 5 shows that the sensor of this comparative example is unstable because of the drift of the capacitance.

The capacitance change rate of this humidity sensor was 1.21.

Table 1 shows the performance of this sensor together with other examples and comparative examples.

(Comparative Example 2)

The high temperature and high humidity stability was measured in the same manner as in Comparative Example 1 except that fluorinated polyamic acid (OPI-N 1005-8, manufactured by Hitachi Chemical Co., Ltd.) was used as a polyimide precursor. The results are shown in FIG. Table 1 shows the performance of this sensor together with other examples and comparative examples.

Industrial applicability

In the sensor of the present invention, the capacitance value relative to the relative humidity returns to the initial value even after being left in a high-temperature and high-humidity atmosphere for a long time. Further, it is possible to provide a sensor having a large change in the capacitance value with respect to the relative humidity.

Since the sensor of the present invention has low temperature dependency, temperature correction is not required. Therefore, the present invention can realize a humidity sensor that does not require a complicated detection circuit and is stable even when used for a long time.

Claims

The scope of the claims

1. A moisture-sensitive layer containing a polyimide resin having at least two metal electrodes and containing at least one group selected from a group having a norbornane skeleton or a group represented by the following formula (2) between the electrodes. Capacitive humidity sensor equipped with.

^{^{(Wherein, R 3, R 4, R}} 8 and R ⁷ each independently represent an alkyl group or a C androgenic atom, R ⁵ represents a single _{bond, - S0 2 -, -CO-,} - 0-, - S— represents an alkylene group or an arylene group, m and n represent an integer of 0 to 4, and p and q represent an integer of 0 to 4.)

2. The capacitance type humidity sensor according to claim 1, wherein the group having a norbornane skeleton is a group represented by the following formula (1).

(In the formula, R ¹ and R ² represent a single bond or a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and may be the same or different. )

3. The polyimide resin is a repeating unit represented by the following formulas (3) and (4) 3. The capacitance type humidity sensor according to claim 2, wherein the resin is a resin containing at least one selected from the group consisting of:

(In the formula, R ¹ and R ² represent a single bond or a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and may be the same or different. R ⁸ represents a single _{bond, - S0 2 -, -CO-,} - 0-, -S-, a -0-Ph- 0- group (Ph is phenylene group), an alkylene group or § Li one alkylene group Represents.)

4. The capacitance according to claim 1, wherein the polyimide resin is a resin containing at least one selected from repeating units represented by the following formulas (5) and (6). Type humidity sensor.

(Five)

(Wherein, R ^{3 to} R ⁸ are the same as described above.)

5. The capacitance-type humidity sensor according to claim 3, wherein the polyimide resin is a resin containing at least one selected from the following repeating units.

6. The capacitance type humidity sensor according to claim 4, wherein the polyimide resin is a resin containing at least one selected from the following repeating units.

7. The capacitance-type humidity sensor according to claim 1, wherein at least one of the metal electrodes is permeable to water vapor.

8. A capacitive humidity sensor that has at least two metal electrodes and has a high-temperature and high-humidity stability of 2% RH or less when left at 60 ° C and 95% RH for 2000 hours.

9. Capacitive humidity sensor with at least two metal electrodes and high temperature and humidity stability of ± 3% RH or less when left at 60 ° C and 95% RH for 4500 hours.

10. The capacitance type humidity sensor according to claim 8, wherein a moisture-sensitive layer containing a polyimide resin is provided between the electrodes.

11. It has at least two metal electrodes, and a moisture-sensitive layer containing polyimide resin is provided between the electrodes. When left at 60 ° C and 95% RH for 2000 hours, the high temperature and humidity stability is ± Capacitance type humidity sensor whose stability at high temperature and humidity is less than 3% RH when it is left for 4500 hours at 2% RH or less and at 60 ° C; 95% 1111 for 4500 hours.

12. With at least two metal electrodes and 90% relative humidity A capacitance-type humidity sensor whose capacitance change rate, expressed as a ratio to the capacitance at 0% (90% RH capacitance Zl 0% RH capacitance), can show 1.3 or more .

13. The capacitance-type humidity sensor according to claim 12, wherein a moisture-sensitive layer containing a polyimide resin is provided between the electrodes.

14. The capacitance type humidity sensor according to claim 13, wherein the polyimide resin is a polyimide containing a group having a norbornane skeleton represented by the following formula (1).