JPH0228096B2 - KANSHITSUSEITEIKOTAIOYOBISONOSEIZOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moisture-sensitive resistor, and more particularly to a moisture-sensitive resistor whose electrical resistance changes with changes in relative humidity in the air, and a method for manufacturing the same.

Conventionally, moisture-sensitive resistor materials include, for example,
(i) Various porous bodies impregnated with lithium chloride; (ii) Carbon powder formed into a membrane using a hydrophilic binder, such as cellulose ester; (iii) Selenium membrane; (iv) A large number of materials have been proposed, including porous alumina; (v) magnetite colloid; (vi) nickel ferrite; and (vii) metal oxides such as tin oxide and titanium oxide. However, the material (i) above can only sense a narrow humidity range, and several types of humidity-sensitive resistors are required to measure humidity over a wide range, and lithium chloride deliquesces at high humidity. There are drawbacks such as dripping from a porous body, and when the material (ii) is used for a long period of time, the resistance value changes due to dimensional changes and the occurrence of cracks, resulting in a lack of reliability. The materials iii) to (vii) have shortcomings in terms of reproducibility, product yield, reliability, etc., and also have the disadvantage of being susceptible to surface stains due to dust, etc., making them problematic for industrial use. be.

The inventor of the present invention has made extensive efforts to develop a highly reliable moisture-sensitive resistor material that does not have such drawbacks, is highly durable, resistant to stains, and has developed the following specific polymer: (A) side chain (B) a film-forming thermoplastic polymer having a sulfonic acid group and/or a salt group thereof and an epoxy group, and (B) a polymer having a glass transition temperature (Tg) of 0°C or less and having an isocyanate group at the terminal The present inventors have discovered that the reaction product is very suitable as a moisture-sensitive resistor material, and have completed the present invention.

According to the present invention, there is provided a moisture-sensitive resistor comprising a reaction product of the above polymer (A) and polymer (B).

The moisture-sensitive resistor of the present invention has a high degree of hydrophilicity due to the presence of a sulfonic acid group and/or a salt group thereof in the side chain, and absorbs or dehumidifies moisture in response to changes in relative humidity in the air. , the electrical resistance changes. Also,
The moisture-sensitive resistor of the present invention is a crosslinking reaction product between the epoxy group in the polymer (A) and the isocyanate group in the low Tg polymer (B), and has excellent flexibility. It exhibits excellent dimensional stability, excellent adhesion to electrodes, and is highly reliable and durable (long life).

The film-forming polymer having a sulfonic acid group and/or a salt group thereof and an epoxy group in the side chain, that is, the polymer (A) constituting the moisture-sensitive resistor of the present invention, is A copolymer obtained by copolymerizing a monomer having a group or a salt group thereof and a monomer having an epoxy group in the side chain with other monomers as necessary; an appropriate film-forming polymer A polymer containing a sulfonic acid group and/or a salt thereof and an epoxy group; A polymer containing a sulfonic acid group and/or a salt thereof; an epoxy group introduced into a polymer containing an epoxy group; It includes those into which a group and/or a salt group thereof has been introduced.

Here, the group of the sulfonic acid salt is a group represented by the following formula (-SO _s ) _o M, where M is an n-valent metal ion, and n is an integer from 1 to 3. The ions include alkali metal ions (e.g. K ⁺ , Na ⁺ , Li ^{+ ,} etc.), alkaline earth metal ions (e.g. Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , etc.).
Mg ²⁺ ), other polyvalent metal ions (e.g. Sn ²⁺ ,
Zn ²⁺ , Al ³⁺ , Fe ³⁺ , etc.).

Examples of monomers having a sulfonic acid group and/or a salt group thereof in the side chain include vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, α
-methylstyrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, etc., or metal salts thereof; monomers having an epoxy group in the side chain include, for example, glycidyl acrylate, glycidyl methacrylate, allyl Examples include glycidyl ether. On the other hand, other monomers that can be polymerized with these monomers include, for example, olefins such as ethylene, propylene, and butylene; styrene, α-methylstyrene,
Examples include vinyl monomers such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, acrylic acid alkyl ester, methacrylic acid alkyl ester, vinyl acetate, vinyl chloride, and vinylidene chloride. Copolymerization of these monomers can be carried out by per se known copolymerization methods, such as solution polymerization, emulsion polymerization, and bulk polymerization.

In addition, base polymers into which sulfonic acid groups and/or salt groups thereof and epoxy groups can be introduced include:
A film-forming thermoplastic polymer having an aromatic ring such as a benzene ring in the side chain or main chain is used, and specific examples of such polymers include polystyrene, styrene copolymer (e.g. styrene-acrylonitrile copolymer) polymers, styrene-butadiene copolymers, etc.),
Included are polyvinylphenol, polysulfone, polyphenylene sulfide, polyphenylene oxide, and the like. Sulfonic acid groups and/or salt groups thereof can be introduced into these base polymers by sulfonation methods known per se, such as treatment with fuming sulfuric acid or treatment with concentrated sulfuric acid using a silver salt as a catalyst. can be done and also
Introduction of an epoxy group can be carried out, for example, by reacting a functional compound having an epoxy group, such as epichlorohydrin, or by graft polymerizing a monomer having an epoxy group, such as glycidyl methacrylate or glycidyl methacrylate.

Furthermore, as the polymer (A), a copolymer of a monomer having a sulfonic acid group and/or a salt group thereof in the side chain and other monomers as described above is added to the epoxy group as described above. and those in which a sulfonic acid group and/or a salt group thereof is introduced into a copolymer of a monomer having an epoxy group in the side chain and other monomers as described above. can also be used.

The polymer (A) mentioned above is a film-forming polymer, and generally has a number average molecular weight of about 500 to about
50,000, preferably from about 1,000 to about 20,000, and the total content of sulfonic acid groups and/or salt groups thereof generally ranges from about 0.04 to about 3.0 meq/g dry polymer, preferably from about 0.06 to about 20,000. about 2.5 meq/g dry polymer, and the epoxy equivalent weight can generally be in the range of 200-4000, preferably 500-3000.

Further, according to the present invention, the polymer (B) to be crosslinked with the above polymer (A) has a Tg of 0°C or less, preferably -10°C to -100°C, and has an isocyanate group at the terminal. For example, a substantially linear polymer having a hydroxyl group at the end is added with a fat such as diphenylmethane diisocyanate, naphthylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, or tetramethylene diisocyanate. Includes those to which a polyhydric isocyanate, alicyclic or aromatic isocyanate is added. As the above-mentioned substantially linear polymer having a hydroxyl group at the terminal, for example, the following formula Polyester glycol represented by the following formula Polyether glycol represented by and the following formula These polymers generally have a molecular weight of 300 to 4000, preferably 500 to
Suitably it has a number average molecular weight within the range of 3000. In each of the above formulas, R ₁ and R ₂ each represent a divalent hydrocarbon group, preferably an alkylene group having 1 to 10 carbon atoms. Examples of such polyester glycols include polyethylene adipate, polypropylene adipate, polybutylene adipate, polyneopentyl adipate, etc.
Examples of polyether glycols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, polypentamethylene glycol, and the like.

The addition reaction between such a hydroxyl group-terminated linear polymer and the above-mentioned polyvalent isocyanate can be carried out using an excess amount of isocyanate relative to the OH in the linear polymer according to a method known per se. , thereby obtaining a reactive polymer (B) having unreacted isocyanate groups at the ends.

The reaction between the polymer (A) and the polymer (B) described above is carried out by mixing the molten or liquid polymer (A) and the molten or liquid polymer (B); and polymer (B)
This can be easily carried out by mixing the two in an inert solvent in which both are dissolved. Polymer (A)
The epoxy group in the polymer (B) and the isocyanate group in the polymer (B) are both active, and the crosslinking reaction proceeds even if the polymer (A) and the polymer (B) are mixed at room temperature. It is generally advantageous to accelerate the crosslinking reaction by heating to a temperature of 200°C.

The mixing ratio of polymer (B) to polymer (A) depends on the epoxy equivalent of polymer (A) and cannot be strictly defined, but it is generally a ratio of polymer (A)/polymer ( B)
Weight ratio of 90/10 to 20/80, preferably 30/70
It can be within the range of 70/30, especially when mixed in a ratio such that 1.5 to 3 isocyanate groups in the polymer (B) per 1 epoxy group in the polymer (A). is suitable.

Furthermore, when the polymer (A) and the polymer (B) are mixed, the total content of sulfonic acid groups or its base groups in the reaction product after the crosslinking reaction is 1 g (dry weight) of the reaction product.
It is desirable that the amount is within the range of 0.01 to 2.0 meq, preferably 0.05 to 1.0 meq.

Note that free sulfonic acid groups that may exist in the reaction product can be easily converted into sulfonic acid salt groups by an ion exchange method.

In addition, the moisture-sensitive resistor of the present invention made of a reaction product of polymer (A) and polymer (B) may optionally have electrical insulation properties and be capable of reacting with epoxy groups and/or isocyanate groups. Inorganic or organic fine powders having functional groups can be blended. Examples of such fine powders include colloidal silica, inorganic fine powders such as zeolite fine powders, and polyurethane,
Examples include fine powders of organic polymers containing active hydrogen, such as phenolic resins, cellulose, and products of these powders treated with silanol or titanate compounds. The amount of the fine powder is not critical and can vary widely depending on its type, particle size, etc., but it is generally less than 100% by weight, preferably 5 to 5% by weight, based on the weight of the final moisture-sensitive resistor. 50
% by weight.

The fine powder can be mixed with the polymer according to a method known per se.

The moisture-sensitive resistor provided by the present invention is a highly reliable humidity sensor that is highly durable, has little performance deterioration even in high humidity, and is resistant to surface dirt, and is used for various measuring instruments or industrial applications. It exhibits excellent effects when used in commercial and household humidity control equipment.

In particular, the moisture-sensitive resistor of the present invention, in which at least some of the sulfonic acid groups are in the form of a monovalent metal salt, has a relatively low electrical resistance and can sense humidity over a wide humidity range. On the other hand, the moisture-sensitive resistor of the present invention, in which at least a portion of the sulfonic acid groups are in the form of a polyvalent metal salt, has a slightly higher electrical resistance and a small change in humidity causes a large change in electrical resistance. In addition, it has the characteristics that there is little deterioration in performance under severe conditions such as dew condensation or immersion in water, and it can be advantageously used in dew condensation sensors and moisture-sensitive switching elements that operate at a specific humidity.

When the moisture-sensitive resistor of the present invention is used in the above applications, it can be formed into a self-supporting film or fiber, or it can be supported on a suitable substrate. As the substrate, materials that have good adhesion to the moisture-sensitive resistor and electrical insulation properties, such as porous ceramics, roughened glass, synthetic resins, etc., can be used. Examples of methods for supporting the moisture-sensitive resistor film on these substrates include printing methods such as gravure printing and screen printing;
A coating method using a doctor knife or a roll can be used.

The moisture-sensitive resistor of the present invention formed into a film, a fiber, or a membrane supported on a substrate can be heated to a temperature of about 50°C or higher, preferably 80 to 150°C, if necessary. The crosslinking reaction between the epoxy groups in the aggregate (A) and the isocyanate groups in the polymer (B) can be completed. As a result, the moisture-sensitive resistor of the present invention becomes even stronger, and changes in performance over time due to dimensional changes and other causes can be reduced, and reliability and reproducibility can be further improved.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Polystyrene with an average degree of polymerization of 3000 was sulfonated, 0.8 meq/g of sulfonic acid was introduced, and then 3000 epoxy equivalents of glycidyl methacrylate were introduced by graft polymerization. 150 parts by weight of this modified polystyrene and 100 parts by weight of a polymer obtained by adding hexamethylene diisocyanate to the ends of polyethylene adipate with an average molecular weight of 1900 were dissolved in 600 parts by weight of dimethylformamide, mixed for 10 minutes, and the surface was smooth. By casting on a polytetrafluoroethylene plate and drying at 80℃,
A moisture-sensitive resistor film with a thickness of 20 μm was obtained.

20mm long at 0.2mm intervals on this resistor film.
A humidity sensor was fabricated by attaching an electrode with a width of 1 mm. The characteristics of this humidity sensor are shown in curve A of the attached FIG.

Example 2 Sodium styrene sulfonate, glycidyl methacrylate and acrylonitrile were copolymerized in an aqueous medium using a redox initiator consisting of potassium persulfate and sodium metabisulfite, with a sulfonic acid group content of 0.6 meq/g, an epoxy equivalent of 2300, A polymer with a number average molecular weight of 2000 was obtained. This polymer 100
75 parts of a polymer obtained by adding diphenylmethane diisocyanate to the ends of polytetramethylene glycol having a number average molecular weight of 2,200 and a number average molecular weight of 2,200 are dissolved in 500 parts by weight of dimethylformamide, mixed for 15 minutes, and the resulting mixture is mixed at an electrode spacing of 0.15. mm, width 2mm, length 20
A film with a thickness of 20 μm was formed by coating a printed alumina substrate with platinum electrodes of 1 mm thick, and dried at 80°C. Curve B in FIG. 1 shows the moisture sensitivity characteristics of the humidity sensor thus obtained.

Example 3 Modified polystyrene with an epoxy equivalent of 2500 was obtained by treating polystyrene with an average degree of polymerization of 1500 with concentrated sulfuric acid, introducing 0.3 meq/g of sulfonic acid groups, and then graft polymerizing glycidyl methacrylate thereto.
Hexamethylene isocyanate was added to the end of polyethylene adipate having 120 parts by weight and a number average molecular weight of 1800, and 70 parts by weight of the polymer was dissolved in 700 parts by weight of dimethyl sulfoxide and mixed for 20 minutes.
The solution was applied onto a glass plate and dried to produce a moisture-sensitive resistor film with a thickness of 50μ, and on this
Electrodes with a length of 20 mm and a width of 2 mm were formed at mm intervals by ion coating. This was then immersed in a 5% calcium chloride solution for 1 hour at room temperature, and then
Washed with water and dried. The moisture sensitivity characteristics of the sensor thus obtained are as shown in curve C of the attached FIG. 2.

Example 4 Magnesium styrene sulfonate, glycidyl methacrylate and acrylonitrile were copolymerized in dimethyl sulfoxide using benzoyl peroxide as an initiator, and the polymer concentration was 20.
A polymer solution (number average molecular weight 1500) with a weight% sulfonic acid group content of 0.45 meq/g and an epoxy equivalent of 1500 was prepared, and a polymer obtained by adding isophorone diisocyanate to the terminals of polycaprolactone with a number average molecular weight of 3000 was added to this. An equal amount of the above polymer was added, mixed thoroughly, and prepared as a film forming stock solution. This film-forming stock solution was applied onto an alumina substrate printed with platinum electrodes with an electrode spacing of 0.15 mm, a width of 2 mm, and a length of 40 mm, dried, and the thickness
A moisture sensitive film of 20μ was formed. The moisture sensitivity characteristics of the sensor thus obtained are shown by curve D in FIG.

Example 5 Using sodium styrene sulfonate instead of magnesium styrene sulfonate used in Example 4, a polymer having a sulfonic acid group content of 0.43 meq/g and an epoxy equivalent of 1900 was prepared, and the polymer was treated in the same manner as in Example 2. A humidity sensor was created. The moisture sensitivity characteristics are shown in curve E in FIG.

Example 6 The humidity sensor produced in Example 1 was used to measure relative humidity.
It was left in an atmosphere of 100% and 40℃ for one month, but there was very little change in electrical resistance during that time, and relative humidity
In the range of 30 to 100%, equivalent to 2% relative humidity
It was within

Example 7 The humidity sensor prepared in Example 4 was immersed in water for 12 hours and then dried at 60°C for 12 hours for 30 minutes.
After repeated repetitions, the change in relative humidity reading was within 2% in the relative humidity range of 70 to 100%.

Comparative Example 1 Porous polypropylene filter [Polyblastics Co., Ltd.; "Jyura Guard" 3401, porosity 38
%; Maximum hole diameter 0.05×0.125μ; Total surface area 50m ² /g;
25μ thick] was impregnated with a 10% lithium chloride aqueous solution until the weight increase rate was 50%, dried, and then fixed on a glass plate with double-sided adhesive tape to form a 10mm
Two rods of gold were vacuum-deposited at intervals to form electrodes.

[Dry/wet cycle test method]

1 hour in a saturated steam atmosphere at 50℃, then 50℃
A dry-wet cycle test is conducted in which one cycle is to leave the product under no load for one hour in a dry atmosphere with a relative humidity of 20% or less at ℃.

After a given cycle, the humidity sensor is connected to a circuit that changes the voltage output according to the relative humidity (0 to 100% relative humidity is output as 0 to 1V), and when the relative humidity is 40% and 80%, Read the output voltage of the humidity sensor in the atmosphere.

The results are shown in FIG. a in the graph of Figure 3
b is the output change at 40% relative humidity, and b is the output change at 80% relative humidity. From FIG. 3, it can be seen that the conventional humidity sensor (comparative example) has a much shorter lifespan due to repeated drying and wetting than the humidity sensor of the present invention (example 1).

[Brief explanation of drawings]

Figures 1 and 2 are graphs (resistance-relative humidity curve) showing the characteristics of the humidity sensor manufactured in the example.
It is. FIG. 3 is a graph showing changes in output of the humidity sensors produced in Example 1 and Comparative Example 1 due to dry/wet cycles.

Claims (1)

[Claims] 1 (A) A compound having a sulfonic acid group and/or a salt group thereof and an epoxy group in the side chain, and a number average molecular weight of 500
~50,000, and the total content of the sulfonic acid groups and/or their salt groups is from 0.04 to
3.0 meq/g dry polymer and an epoxy equivalent within the range of 200 to 4000, and (B) a glass transition temperature of 0°C or less and a number average molecular weight of 300 to 4000. Polymer (B)/polymer (B) weight ratio of 90/10 to 20/80 is within the range of 4000 and has an isocyanate group at the end.
The total content of sulfonic acid groups and/or its salt groups obtained by mixing and reacting in a ratio of 0.01 to
A moisture-sensitive resistor comprising a reaction product within a range of 2.0meq/g (dry weight). 2 (A) Has a sulfonic acid group and/or its salt group and an epoxy group in the side chain, and has a number average molecular weight of 500
~50,000, and the total content of the sulfonic acid groups and/or their salt groups is from 0.04 to
3.0 meq/g dry polymer and an epoxy equivalent within the range of 200 to 4000, and (B) a glass transition temperature of 0°C or less and a number average molecular weight of 300 to 4000. Polymer (B)/polymer (B) weight ratio of 90/10 to 20/80 is within the range of 4000 and has an isocyanate group at the end.
A sulfonic acid group and/or a sulfonic acid group characterized by mixing in a ratio of The total content of the salt groups is
A method for producing a moisture-sensitive resistor within the range of 0.01 to 2.0 meq/g (dry weight).