JPH0540104A - Manufacture of moisture-sensitive or dew formation sensor - Google Patents

Abstract

PURPOSE:To manufacture a moisture-sensitive or dew formation sensor having excellent sensitivity and a high response speed, with excellent reproducibility, uniformly and in an increased yield. CONSTITUTION:A moisture-sensitive resistor forming substance (e.g. a moisture- absorptive macromolecular substance and conductive particles) is dissolved or dispersed in a liquid such as water or alcohol, a liquid-form body prepared by mixing fibrous fillers 1 in this solution is cast and dried and thereby a sheet- shaped material is prepared. A moisture-sensitive or dew formation sensor is manufactured by cutting this material in arbitrary dimensions and sticking it on a base and by fitting electrodes thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a humidity-sensitive or dew condensation sensor capable of detecting humidity in the atmosphere or dew condensation on the surface of a subject.

[0002]

2. Description of the Related Art Condensation becomes a problem in various fields such as various precision electric equipment, automobiles, air conditioning control, storage, housing equipment, etc., and it is desired to accurately detect a high humidity condition or a condensation condition. Demand is growing. As an example, in home video tape recorders, digital audio tape decks, etc., if dew condensation occurs on the cylinder of the rotary head that records / reproduces data on / from magnetic tape, tape winding / cutting / device damage may occur. , A dew sensor is provided.

As the condensation sensor used conventionally,
A moisture-sensitive resistor in which conductive powder is dispersed in a hygroscopic polymer having a property of expanding in volume by absorbing moisture is used to cover a comb-shaped counter electrode formed on an insulating substrate such as a ceramic substrate with 5 to 5 The coating film is formed to have a thickness of several tens of μm (for example, JP-A-57-2110511).

As its characteristic, a material having a large change in resistance value in a high humidity region is used so that a high humidity condition and a condition near dew condensation (relative humidity near 100%) can be distinguished and detected. However, the condensation sensor of the above method has a structure in which a comb-shaped counter electrode is installed directly under the thin film in order to bring the sensor sensitivity to a practical level. The amount of water absorbed by the body coating is easily saturated, and the excess water that cannot be absorbed partially adheres to the surface of the coating as water droplets. When dew condensation is removed, there is a difference in the evaporation rate of water inside the film between the part not covered with water droplets and the part covered with water drops, and the water inside the film is removed first in the part not covered with water drops. It escapes and the resistance value decreases. As a result, there is a deviation in the detection of the sensor when the dew condensation is eliminated. Moreover, the response speed to a slight amount of dew is low. Furthermore, this dew sensor requires a certain thickness in order to obtain a uniform film thickness. for that reason,
It took some time for the water condensed on the surface of the coating film to be absorbed inside and evaporate from the inside, so the response speed at the time of detection and release was unavoidable.

Further, Japanese Patent Laid-Open No. 59-43345 discloses a dew condensation sensor having a sensor in which conductive particles are uniformly carried on the surface of a hygroscopic fiber. In this dew condensation sensor, the hygroscopic fiber shrinks or expands together with the hygroscopic adhesive or adsorbent due to changes in humidity. Therefore, when the amount of dew condensation is large, moisture enters the inside of the fiber more and more, and thus there is a drawback that the dew state is maintained even if the dew state of the atmosphere is released. In particular, when a cellulose fiber is used, there is a problem that the water molecule has a strong holding force by hydrogen bonding, does not dry in the meantime, and cannot accurately detect dew condensation.

On the other hand, by the same applicant as the present invention, a moisture-sensitive or dew-condensing sensor in which a moisture-sensitive resistor is fixed to a cloth in a continuous and dispersed state to form a large number of fine voids in the sensor. Has been proposed (JP-A-2-49).
149). This humidity-sensitive or dew sensor has a fast response speed to changes in humidity and slight condensation, changes in resistance to changes in humidity are large, and has excellent detection performance when there is no dew condensation or dew condensation on the subject. With. That is, this sensor has a fine porous structure, and the condensed water droplets are rapidly dispersed by the capillary phenomenon generated in the void portion, so that the response speed is fast. Further, since the presence of the voids and the large surface area of the moisture-sensitive resistor when the dew condensation is eliminated, the water retained and absorbed is rapidly evaporated, so that the response speed at the time of restoration is also high.

[0007] However, since the method for adhering the moisture sensitive resistor to a cloth such as a non-woven fabric is adopted in the production thereof, if the non-woven fabric has spots, the distribution of the moisture sensitive resistor and the fibers becomes non-uniform. The present invention provides a humidity-sensitive or dew-condensation sensor that has a fast response speed to a change in humidity and a slight amount of dew condensation, a large change in resistance value to a change in humidity, and has no deviation in detection when dew-condensation or when dew-condensation is eliminated. The objective is to produce with good reproducibility, uniformity and higher yield.

[0008]

The present invention provides the following a, b,
A liquid material comprising a moisture-sensitive resistor forming substance consisting of at least one selected from c and d and a fiber filler is cast, dried to form a sheet, and cut into an arbitrary size, A method of manufacturing a humidity sensor or a condensation sensor, characterized in that electrodes are attached to both ends thereof.

A) hygroscopic polymer substance and conductive particles, b) hygroscopic polymer substance and electrolyte substance, c) hygroscopic electrolyte polymer substance d) hygroscopic electrolyte polymer substance and conductive particles. FIG. 1 is a diagram showing an example of a humidity sensor or a condensation sensor according to the method of the present invention.

A moisture sensitive resistor 2, a fiber filler 1 and a fine void portion are provided between a pair of electrodes 4, 4'having lead wires 6, 6'connected to both ends thereof with a conductive resin 5, 5 'interposed therebetween. A detection unit 3 composed of 3 is provided. In the present invention, a liquid material comprising the moisture-sensitive resistor forming substance and the fiber filler 1 is cast and dried to form a sheet. Therefore, in the conventional method of dispersing and fixing the moisture-sensitive resistor forming substance on the non-woven fabric, the distribution of the fiber and the moisture-sensitive resistor is non-uniform due to the influence of non-woven fabric properties (thickness unevenness, void ratio unevenness, etc.). On the other hand, according to the present invention, the distribution of the fibers and the moisture-sensitive resistor can be made uniform, a uniform sensor with less variation can be manufactured, and the yield is improved.

When a mixture of a liquid substance in which a moisture-sensitive resistor forming substance is dissolved or dispersed and a fiber filler is cast and dried, the solvent is vaporized and the moisture-sensitive resistor forming substance is fixed on the fiber filler. However, the moisture-sensitive resistor is formed and a large number of minute voids are uniformly generated in the sensor. Due to this void, the sensor responds quickly to changes in humidity and slight condensation, changes in resistance to changes in humidity are large, and there is no deviation in detection when condensation or removal of condensation occurs on the subject. .. In order to control the amount of the voids, the mixing ratio of the moisture-sensitive resistor forming substance and the fiber filler may be adjusted, or the amount of the fluid may be reduced by squeezing the cast sheet under pressure. ..

When the moisture-sensitive resistor is composed of a hygroscopic polymer and conductive particles, the electrical contact between the particles of the conductive particles deteriorates due to the swelling of the polymer during water absorption, which causes an increase in electrical resistance. Acts like. The hygroscopic polymer constitutes a molded body that is substantially continuous on the fiber, and may be any one that swells and retains its shape when it absorbs moisture.

The swelling degree of the hygroscopic polymer is preferably 20% or more, more preferably 100% or more. Here, the degree of swelling is 25
The percentage (%) of the increase in weight when a 1 cm square humidity-sensitive resistor having a thickness of 100 μ and an immersion in distilled water for 24 h _NS in an atmosphere of ℃ and relative humidity of 65% is shown. When the degree of swelling is less than 20%, the resistance change of the moisture-sensitive resistor when absorbing water is small, and it is not preferable because it is easily affected by noise when it is detected as an electric signal.

As the nonionic hygroscopic polymer, polyacrylamide, polyvinyl alcohol, polyethylene oxide, or cellulose derivative polymer such as methylcellulose or ethylcellulose, polyamide resin such as nylon, polyvinylpyrrolidone, hygroscopic acrylate, isobutylene and maleic anhydride. A hygroscopic polymer such as an acid condensation polymer or a hygroscopic methacrylate can be used. Further, their modified products and composites may also be used. When the humidity-sensitive resistor is made by mixing conductive particles into the nonionic hygroscopic polymer, electric conduction in the humidity-sensitive resistor is performed by an electron conduction mechanism. Therefore, the humidity-sensitive or dew-condensing sensor using this humidity-sensitive resistor can be operated by direct current, and as a result, a circuit having a simple structure can be used as a circuit for connecting to the sensor.

As the hygroscopic polymer, a hygroscopic polymer electrolyte such as sodium polyacrylate or a mixture of a nonionic hygroscopic polymer and an electrolyte can be used. Since the electrolyte has ionic conductivity, a humidity sensitive resistor can be produced without using conductive particles. Of course, conductive particles may be further added and used. However, in order to prevent the influence of the change in resistance value caused by ion conduction, it is preferable to operate with an alternating current when an electrolyte is included.

In the case of the above-mentioned various polymers, the moisture-sensitive resistor sufficiently adheres to the fibers in the cloth because it has adhesiveness to various fiber materials, but it becomes insoluble when water is absorbed during dew condensation. In order to further improve stability, durability, environmental resistance and adhesion to fibers, the above polymer is partially crosslinked with a hydrophilic crosslinker, crosslinkable polymer, etc. Other bainida resin that has been treated to impart insolubility to it or has a high compatibility with the above-mentioned polymer and a large adhesive force to fibers (for example, acrylic resin, urethane resin, epoxy resin, polyester resin, polyamide resin, etc.) May be mixed.

The conductive particles dispersed in the hygroscopic polymer include, for example, carbon black, but carbon fibers and other compound conductors, and metals such as copper, nickel, silver and alloys may be used. The average particle diameter of the conductive particles is preferably equal to or smaller than the diameter of the fibers constituting the cloth because a thin moisture-sensitive resistor layer can be formed and good response performance can be obtained. Further, in order to disperse the particles uniformly on the fiber surface, it is more preferably 1 μm or less on average.

In an atmosphere of 25 ° C. × 60% RH, the weight ratio of the conductive particles to the hygroscopic polymer is preferably 30 to 2500 parts by weight with respect to 100 parts by weight of the hygroscopic polymer.
When the conductive particles are carbon black, 30 to 400 parts by weight is preferably used with respect to 100 parts by weight of the hygroscopic polymer, and preferably 40 to 300 parts by weight. When the amount of carbon black exceeds 400 parts by weight, the adhesive force of the moisture-sensitive resistor to the fibers becomes small, the mechanical strength becomes weak, and the resistance value change due to water absorption becomes small. If the amount of carbon black is less than 30 parts by weight, the resistance value of the moisture-sensitive resistor itself becomes large, which is not preferable in practice.

Further, when the carbon black is 30 to 200 parts by weight, the characteristics as a dew condensation sensor in which the resistance value increases in a high humidity or dew condensation state can be obtained, and when it is 200 to 400 parts by weight, a wide humidity range can be obtained. A characteristic as a humidity sensor whose resistance value changes gradually can be obtained. The moisture-sensitive resistor-forming substance made of a polymer is dissolved or dispersed in water or alcohol depending on its property, or is melted to be a liquid substance, and conductive particles, an electrolyte substance, or a fiber filler is dissolved or dispersed therein. To produce a liquid.

As the fiber filler, for example, filaments, tows, etc. spun by ordinary melt spinning, wet spinning, dry spinning, liquid crystal spinning, etc. are cut into short pieces, split fiber, synthetic pulp, flash spun fiber, etc. Used.
Fine reticulated fibers such as synthetic pulp are preferred for providing good dispersibility. It is preferable that the material of the fiber filler has a small change with humidity. Specifically, synthetic fibers such as polyester-based, polyacrylic-based, polyamide-based, polypropylene-based, polyethylene-based, aramid-based,
Fibers such as glass fiber, mineral fiber and ceramic fiber can be mentioned.

In order to uniformly disperse the fiber filler, it is preferable to adjust its length and diameter. The length of the fiber filler is preferably 10 mm or less, more preferably 5 mm or less. The diameter of the fiber filler is preferably 30 μm or less, more preferably 15 μm or less, and most preferably 5 μm or less.

As the method for mixing the moisture-sensitive resistance-forming substance and the fiber filler, for example, a method of mixing by stirring with a blade type mixer, a method of mixing with a jet mixer, a method of mixing with a homomixer, a method of mixing with a ball mill, and a milk dope There are methods such as mixing while sipping, mixing by putting in a rotating drum, and mixing while crushing with a disc refiner. In the dry state, the fiber filler may be directly mixed with the liquid substance of the moisture sensitive resistance-forming substance, but in order to disperse it more uniformly, the fiber filler should be dispersed in water or alcohol in advance. If necessary, a method of filtering and mixing with the liquid material before completely drying is also effective.

As a method for casting the liquid material thus obtained and drying it to obtain a sheet-like material, for example, the liquid material is cast on a release paper or film with a constant thickness using a roll coater. Then, a method of drying this can be mentioned. Further, at this time, it is desirable that the groove is provided by winding a metal wire on the surface of the roll bar or by directly cutting the groove, because the casting is easy.

When casting is carried out by a coating method, various coating methods such as a kiss roll method, a reverse roll method, a gravure roll method, a knife edge method and the like can be mentioned. Further, it may be cast to a constant thickness by an extrusion method and dried. Alternatively, it may be cast and dried by a papermaking method. Alternatively, it may be poured into a mold and dried.

Next, the present invention will be specifically described with reference to examples.

[0026]

【Example】

[0027]

Example 1 80 parts by weight of conductive carbon black having an average particle diameter of 30 nm, 0.5 parts by weight of formalin, and 300 parts by weight of water were mixed with 100 parts by weight of polyacrylamide, and the mixture was stirred with a blade-type rotary mixer (liquid. object). Acrylic fiber (average diameter 2μm, average fiber length 1mm)
Is dispersed in ion-exchanged water and then filtered to obtain a water content of 1
3000 parts by weight of 000% (weight ratio) was added,
Mixed with a homomixer. The liquid Teflon mold (10 × 20 cm) was poured into the mold to a thickness of 5 mm and dried to obtain a sheet-like product having a fiber / moisture-sensitive resistor weight ratio of 100: 60 and a thickness of 30 μm. 100 sheets of this sheet-like material were punched out to a diameter of 5 mmφ with a Thomson blade die, and were stuck on a ceramic substrate having copper electrodes etched with a conductive resin (containing phenolic resin and carbon black powder) to manufacture 100 sensors. ..

[0028]

Example 2 80 parts by weight of conductive carbon black having an average particle diameter of 30 nm, 0.5 parts by weight of formalin and 3000 parts by weight of water were mixed with 100 parts by weight of polyacrylamide, and the mixture was stirred with a blade-type rotary mixer (liquid. object). Polyester fiber (average diameter 2μm, average fiber length 1m
m) was added in an amount of 300 parts by weight and stirred with a homomixer. The liquid thus obtained was poured into a Teflon mold similar to that of Example 1 to a thickness of 5 mm and dried, and a sheet having a weight ratio of fiber to moisture-sensitive resistor of 100: 60 and a thickness of 37 μm was formed. I got a thing. 100 sheets of this sheet-like material were punched out to a diameter of 5 mmφ with a Thomson blade die, and were attached on a ceramic substrate having copper electrodes etched in the same manner as in Example 1,
100 sensors were manufactured.

[0029]

Example 3 Liquid material and polyester fibers prepared in the same manner as in Example 2 (average diameter 2 μm, average fiber length 1 m)
m) The liquid material mixed with 300 parts by weight was poured into a Teflon mold similar to those in Examples 1 and 2 to a thickness of 2 mm and dried, and the weight ratio of the fiber to the moisture-sensitive resistor was 100: 60 and the thickness was 100: 60. A sheet having a thickness of 15 μm was obtained. This sheet-shaped material was punched out into a diameter of 5 mm and 100 sensors were manufactured in the same manner as in Examples 1 and 2.

[0030]

COMPARATIVE EXAMPLE 1 700 parts by weight of water was added to a liquid material prepared in the same manner as in Example 1 and stirred. Acrylic fiber nonwoven fabric (average diameter 2 μm, average fiber length 1 mm, basis weight 2
Gravure coating (60 mesh / 5g / m ² )
Inch) and dried to obtain a sheet-like material having a weight ratio of fiber to moisture-sensitive resistor of 100: 60 and a thickness of 60 μm. This was punched out in the same manner as in Examples 1 to 3 and stuck on a ceramic substrate to manufacture 100 sensors.

[0031]

Comparative Example 2 700 parts by weight of water was added to a liquid prepared in the same manner as in Example 1 and stirred. This is a polyester non-woven fabric (average diameter 2μ
m, basis weight 15 g / m ² ) gravure coating (60
(Mesh / inch) and then dried to obtain a sheet-like material having a weight ratio of fiber to moisture-sensitive resistor of 100: 60 and a thickness of 51 μm. This was punched out in the same manner as in Examples 1 to 3 and stuck on a ceramic substrate to manufacture 100 sensors.

100 sensors each of the above Examples 1 to 3 and Comparative Examples 1 and 2 were inspected by the following method to examine the yield.
First, in an environment of 25 ° C. × 60% RH, multimeter (manufactured by Advantest, TR6845, measuring current 0.1
The electrical resistance value was measured using μA), and those having a resistance of 0.6 to 3.0 kΩ were accepted, and the others were rejected. Next, with an atomizer, water was sprayed for 2 seconds, and after 10 seconds, those having an electric resistance value of 1 megohm or more were passed, and those having an electric resistance value of less than 1 megohm were rejected. The above results are shown in Table 1. The overall yields of Examples 1-3 are 80, 85, 8 respectively.
0% and 45% and 39% of Comparative Examples 1 and 2, respectively, were higher.

Next, each of the 5 acceptable sensors of Examples 1 to 3 and Comparative Examples 1 and 2 is randomly selected at a temperature of 25 ° C.
The electric resistance value under 60, 70, 80, 90, 95% RH and the electric resistance value when atomizer spraying was performed for 1 second were measured. The results are shown in Figure 2. In the figure, I to III
Curves correspond to Examples 1 to 3, and curves IV and V correspond to Comparative Examples 1 and 2.

Next, for confirmation, Examples 1 to 3 and Comparative Example 1
The response speed was measured for each of the five sensors selected from the acceptable products of ~ 2. The method is to put the sensor in an atmosphere of 30 ° C. × 80% RH from an atmosphere of 25 ° C. × 50% RH,
The time until the electric resistance value increased to 1 MΩ was measured.
The results are shown in Table 2. The response speed was good in both Examples and Comparative Examples, and there was no difference.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

As described above, according to the present invention, the response speed at the time of dew condensation detection or at the time of dew condensation elimination is fast, the change of the resistance value with respect to the change of humidity is large, and the detection at the time of dew condensation or elimination of dew condensation of the subject is performed. It is possible to manufacture a moisture-sensitive or dew-condensation sensor having no deviation with good reproducibility, uniformity, and higher yield.

[Brief description of drawings]

FIG. 1 is a plan view of a humidity sensor or a condensation sensor manufactured by a manufacturing method of the present invention.

FIG. 2 is a change curve of an electric resistance value with respect to humidity in Examples 1 to 3 and Comparative Examples 1 and 2 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fiber filler 2 Moisture-sensitive resistor 3 Fine void part 4, 4'electrode 5, 5'conductive resin (conductive contact part) 6, 6'lead wire 7 detection part I Electric resistance value to relative humidity of Example 1 Change curve II Example 2 〃 〃 〃 〃 III Example 3 〃 〃 〃
〃 IV Comparative Example 1 〃 〃 〃 〃 V Comparative Example 2 〃 〃 〃 〃

Claims (1)

[Claims] 1. A sheet material is prepared by casting a liquid material comprising a moisture-sensitive resistor forming substance consisting of at least one selected from the following a, b, c and d and a fiber filler, and drying it. A method for manufacturing a moisture-sensitive or dew-condensing sensor, which comprises cutting this into an arbitrary size and attaching electrodes to both ends thereof. a) Hygroscopic polymer substance and conductive particles b) Hygroscopic polymer substance and electrolyte substance c) Hygroscopic electrolyte polymer substance d) Hygroscopic electrolyte polymer substance and conductive particle