JPH116809A - Humidity sensor and electronic apparatus using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a humidify sensor which can expand a region to be measured by a method wherein a humidity sensing membrane formed in such a way that a conductive powder is dispersed to a mixture composed of a hygroscopic resin which copolymerizes a monomer containing a hydrophilic group, fluorine and a glycidyl group and of a hardening agent is formed on an insulating substrate. SOLUTION: A comb-shaped electrodes 2 and 3 which are composed of carbon and which are faced with each other are installed on an insulating substrate 1 composed of a ceramic or the like, and a humidity sensing membrane 4 is formed on them. The humidify sensing membrane 4 is formed in such a way that a hardening agent is added to a hygroscopic resin which contains an epoxy group and fluorine inside molecules and that a conductive powder is dispersed to their mixture. For example, the hygroscopic resin which is formed in such a way that a vinyl monomer comprising an epoxy group is copolymerized with a vinyl monomer comprising a hydrophilic group, or that a vinyl monomer comprising a hydrophobic group containing hydrogen is added so as to be copolymerized, is used. A hardening agent for an epoxy resin is added, and a life-resistant property is enhanced. The hydroscopic resin and the hardening agent are dissolved in a solvent, a conductive powder such as carbon, a metal or the like is added so as to be dispersed, and it is laminated on the comb-shaped electrodes 2, 3 installed on the insulating substrate 1 so as to be heated and hardened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor capable of detecting a change in humidity and a dew condensation state, and an electronic device using the same.

[0002]

2. Description of the Related Art Conventionally, dew condensation sensors and humidity sensors have been widely used in video tape recorders, video cameras, etc., and air conditioning electronic devices. The purpose of the former is to protect the video tape by stopping the rotation of the cylinder in the dew condensation state, and the latter is to detect the humidity for maintaining the comfortable humidity, and dew sensors and humidity sensors suitable for each are proposed. Therefore, there has long been a demand for a highly reliable humidity sensor that can detect the dew condensation state with a single sensor and that can detect from low humidity to high humidity.

[0003]

Since a suitable sensor greatly differs depending on a measurement target area, a use environment condition, responsiveness, etc., an almighty sensor has not been developed so far.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention aims to provide a humidity sensor in which a measurement target area is expanded from 30% RH to a dew condensation state and which has excellent reliability and an electronic device using the humidity sensor. It is.

[0005]

SUMMARY OF THE INVENTION A binder system for a humidity sensor according to the present invention is a hygroscopic resin obtained by copolymerizing a monomer having a hydrophilic group, a monomer containing fluorine and a monomer having a glycidyl group, and a curing agent for an epoxy resin. It consists of Only by limiting this fluorine content is the balance between hydrophilicity and hydrophobicity precisely maintained,
It is possible to detect from low humidity to dew condensation with good reproducibility.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings.

(Embodiment) FIG. 1 is a top view showing an embodiment of the humidity sensor of the present invention, and FIG. 2 is a sectional view of the same.

1 and 2, reference numeral 1 denotes an insulating substrate made of ceramic or the like, reference numerals 2 and 3 denote comb-shaped electrodes made of carbon provided on the insulating substrate 1 so as to face each other, and reference numerals 4 and 4 denote electrodes 2 and 3. This is a moisture-sensitive film formed on the insulating substrate 1 on which a curing agent is added to a moisture-absorbing resin having an epoxy group and fluorine in a molecule, and a conductive powder is dispersed therein. It has a configuration. Reference numerals 5 and 6 are leads connected to the electrodes 2 and 3, respectively.

As described above, by using the moisture-sensitive film 4 in which the conductive powder is dispersed in the hygroscopic resin, the swelling and shrinkage of the hygroscopic resin due to the change in humidity are reduced by the contact resistance between the dispersed conductive powders, This is detected as a change in electric resistance.

In the above structure, as a hygroscopic resin of the moisture-sensitive film 4, a vinyl monomer having a hydrophilic group is copolymerized with a vinyl monomer having an epoxy group as described in JP-B-62-22097. It is known that a hygroscopic resin obtained by adding and copolymerizing a vinyl monomer having a hydrophobic group is excellent in reproducibility and life resistance. Further, a curing agent for epoxy resin is used to improve the life resistance.

The present inventors have studied diligently to protect a small and light electronic device product in a dew condensation state, control humidity in an amenity space, and develop a humidity sensor capable of detecting from a dew condensation state to a low humidity of 30% RH with one element. As a result,
This has led to the present invention.

The feature lies in the binder design which makes it possible to detect the moisture absorption characteristic from the required characteristic of low humidity to dew condensation. This is due to the fact that fluorine-containing monomers were selected as hydrophobic monomers and their number per mole was limited. Although the details of the effect mechanism are not yet clear, the interaction with water molecules is possible from low to high humidity depending on factors such as the number of fluorine in the polymer and the steric conformation centered on fluorine, and as a result, It is considered that the swelling and shrinkage could be controlled.

As the monomer having a hydrophilic group used in the present invention, there are hygroscopic (meth) acrylates, hygroscopic (meth) acrylamides and vinylpyrrolidones. Here, (meth) acrylate is a generic term for acrylate and methacrylate, and (meth) acrylamide is a generic term for acrylamide and methacrylamide. The same applies to the following specific compounds.

Examples of the hygroscopic (meth) acrylate include hydroxy lower alkyl (meth) acrylate and hydroxy lower alkoxy (meth) acrylate.

Among the above compounds, preferred vinyl monomers include 2-hydroxyethyl (meth) acrylate, diethylene glycol mono (meth) acrylate,
Examples include 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, triethylene glycol mono (meth) acrylate, and dipropylene glycol mono (meth) acrylate. Examples of vinylpyrrolidones include N-vinylpyrrolidone and 2-methyl-N-vinylpyrrolidone.

Examples of the vinyl monomer containing an epoxy group include glycidyl (meth) acrylate and P-vinyl glycidyl benzoate.

As the fluorine-containing (meth) acrylate, a compound containing 2 to 5 fluorines per molecule, preferably a compound having 3 to 4 fluorines, is selected. 2
If it is less than 10, the effect of adding fluorine is not seen. Opposite 6
Above this, the responsiveness in the dew state is significantly reduced due to the influence of fluorine. Specific examples of the fluorine-containing compound include trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, and pentafluoropropyl (meth) acrylate.

To provide flexibility, other monomers, such as tetrahydrofurfuryl (meth) acrylate,
It is also possible to add an aliphatic (meth) acrylate such as 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and tridecyl (meth) acrylate.

As the curing agent, basically any curing agent for epoxy resins can be used. Preferably, aromatic diamines such as 4,4'-diaminodiphenylmethane and aliphatic diamines such as 1,12-diaminododecane are used. Further, an aromatic diamine and an aliphatic diamine may be used in combination. As the conductive powder, acetylene black, carbon black, graphite, metal powder such as gold powder and silver powder, and a mixture thereof can be used.

The addition amount is desirably 15 to 40 parts by weight based on the hygroscopic resin. More preferably, 20 to 30 parts by weight is selected. If the amount is less than 15 parts by weight, the resistance value increases, and it is difficult to obtain sufficient reproducibility. Conversely, if it exceeds 41 parts by weight, the resistance value decreases, and the responsiveness of the resistance value change to the humidity change decreases.

In the humidity sensor of the present invention, the hygroscopic resin having the above composition and the curing agent are dissolved in a solvent, and a conductive powder such as carbon or metal is added to the solution and dispersed well. It is manufactured by laminating on the provided comb-shaped electrodes 2 and 3 and curing by heating. As the electrodes 2 and 3 of the humidity sensor thus obtained, conductive paint and ordinary electrode materials can be used.

Hereinafter, the present invention will be described with reference to more specific examples.

[0023]

【Example】

(Example 1) 2-hydroxyethyl methacrylate 2
5.4 g, trifluoroethyl methacrylate 2.42
g, 1.85 g of glycidyl methacrylate, and 0.24 g of azobisisobutyronitrile as a polymerization initiator were dissolved in 64.5 g of ethyl cellosolve.
It was heated for 5 hours for copolymerization. After reprecipitation purification with a methanol-ether system, drying under reduced pressure at room temperature gave a white polymer. 2 g of this resin is dissolved in 20 g of ethyl cellosolve, 0.5 g of acetylene black having an average particle size of 40 μm as conductive powder and 7 g of benzyl alcohol are added, and the mixture is sufficiently kneaded with a three-roll mill.

Next, 0.02 g of 4,4'-diaminodiphenylmethane as a curing agent is dissolved in the minimum necessary amount of benzyl alcohol, then added to the above kneaded material, and dispersed to form a paste. The obtained paste is applied on a ceramic insulating substrate having a comb-shaped carbon electrode shown in FIG.
For 30 minutes to prepare a humidity sensor.

FIG. 3 shows the humidity sensing characteristics of the humidity sensor. The horizontal axis represents the relative humidity and the vertical axis represents the inter-terminal resistance. The curve of A is Example 1.

Comparative Example 1 In Example 1, trifluoroethyl methacrylate was replaced with ethyl methacrylate 1.4.
A humidity sensor was produced in the same manner except that the humidity sensor was replaced with 8 g.

The curve B in FIG. 3 shows the humidity sensitivity of Comparative Example 1. (Example 2) A humidity sensor was manufactured in the same manner as in Example 1, except that trifluoroethyl methacrylate was replaced with 2.6 g of tetrafluoropropyl methacrylate.

Comparative Example 2 A humidity sensor was manufactured in the same manner as in Example 2, except that tetrafluoropropyl methacrylate was replaced with 1.66 g of propyl methacrylate.

Next, in order to compare the characteristics of the humidity sensors of the embodiment and the comparative example, the ratio (R70 / R30) of the resistance values at 70% RH and 30% RH is shown in Table 1. It can be said that the larger this value is, the better the humidity sensitivity on the low humidity side is and the more excellent it is as a humidity sensor. Further, the time when the resistance between terminals reaches 100 kΩ by applying steam at 60 ° C. is defined as the response, and the time (seconds) is also shown in Table 1. The smaller this value, the better the condensation sensor.

[0030]

[Table 1]

As is clear from Table 1, the sensors of Examples 1 and 2 of the present invention show little difference in response to the sensors of Comparative Examples 1 and 2, but are almost inferior in terms of humidity sensitivity. It is much better. That is, it can be said that the sensor of the present invention is a humidity sensor having excellent characteristics as a condensation sensor.

[0032]

As described above, the present invention crosslinks and cures a hygroscopic epoxy resin containing a specific amount of fluorine in a molecule and uses it as a humidity sensor, so that a single sensor can be used from the low humidity side to the dew condensation state. It is intended to be detectable.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a humidity sensor of the present invention.

FIG. 2 is a cross-sectional view taken along line X-X ′ of FIG.

FIG. 3 is a characteristic diagram for explaining the humidity sensitivity of the humidity sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2, 3 Electrode 4 Moisture sensitive film 5, 6 Lead

Claims (4)

[Claims] An insulating substrate is provided with an opposing electrode, and a hygroscopic resin obtained by copolymerizing a monomer having a hydrophilic group, a monomer containing fluorine and a monomer having a glycidyl group on the insulating substrate including the electrode is cured. A humidity sensor having a moisture-sensitive film in which conductive powder is dispersed in a mixture of agents. 2. The humidity sensor according to claim 1, wherein the fluorine-containing monomer contains 3 to 4 fluorines per molecule. 3. The humidity sensor according to claim 1, wherein the conductive powder is contained in an amount of 15 to 40 parts by weight based on 100 parts by weight of the hygroscopic resin. 4. An electronic device using the humidity sensor according to claim 1.