JP7356935B2 - moisture sensor - Google Patents

Description

The present invention relates to a moisture sensor.

Conventionally, as a moisture sensor, a sensor having a moisture detection portion in which conductive powder is dispersed in polyvinylpyrrolidone is known (see, for example, Patent Documents 1 and 2).

Here, when moisture adheres to the moisture detection section, the polyvinylpyrrolidone swells and the distance between the conductive powders increases, thereby increasing the resistance of the moisture detection section.

JP2008-261691A JP 2017-133833 Publication

On the other hand, as automobiles become equipped with advanced driver assistance systems (ADAS) and become autonomous, sophisticated accident avoidance systems will become necessary. Steering is also automated here, but if the rack and pinion gears of the electric power steering (EPS) system, which converts steering wheel movement into tire movement, get flooded with water, the gears can rust and cause steering failure. There is sex. Therefore, by installing a water intrusion sensor that detects water intrusion into the rack and pinion gear and issuing an alarm, it is possible to avoid the occurrence of steering failure.

However, since the water immersion sensor is an in-vehicle component and is used in a high-temperature environment, it is necessary to improve the heat resistance of the conventional moisture sensor.

If a conventional moisture sensor is used in a high-temperature environment, the polyvinylpyrrolidone contained in the moisture detection part will change in quality, making it difficult for the polyvinylpyrrolidone to swell even if moisture adheres to the moisture detection part. , it is thought that the moisture detection performance of the moisture sensor will deteriorate. Specifically, first, the pyrrolidone ring of polyvinylpyrrolidone is ring-opened or the main chain is cut to generate an organic radical (R.). Next, the organic radical (R.) is oxidized to generate an organic peroxide radical (ROO.), and the organic peroxide radicals undergo a chain reaction.

An object of the present invention is to provide a moisture sensor with excellent heat resistance.

One aspect of the present invention provides a moisture sensor, which includes a moisture detection section including a conductive powder, a homopolymer or copolymer of N-vinyl-2-pyrrolidone, and a phenolic antioxidant; and a pair of electrodes electrically connected to each other.

According to the present invention, a moisture sensor with excellent heat resistance can be provided.

It is a top view showing an example of the moisture sensor of this embodiment.

Next, a mode for carrying out the present invention will be described.

Modes for carrying out the present invention will be described below, but the present invention is not limited to the following embodiments, and may be modified and applied as appropriate without changing the gist of the present invention. Can be done.

<Moisture sensor>
FIG. 1 shows an example of the moisture sensor of this embodiment.

The moisture sensor 10 includes, on a substrate 11, a moisture detection section 12 and a pair of wiring electrodes 13 and 14 electrically connected to the moisture detection section 12. The moisture detection section 12 includes conductive powder, a homopolymer or copolymer of N-vinyl-2-pyrrolidone, and a phenolic antioxidant.

Therefore, even if the moisture sensor 10 is used in a high-temperature environment, deterioration of the N-vinyl-2-pyrrolidone homopolymer or copolymer contained in the moisture detection part 12 can be suppressed, and as a result, Deterioration of the moisture detection performance of the moisture sensor 10 can be suppressed. Specifically, organic radicals (R・) generated from homopolymers or copolymers of N-vinyl-2-pyrrolidone, and organic peroxide radicals (ROO・) generated by oxidation of organic radicals (R・). ) is scavenged by phenolic antioxidants.

Here, an electrode may be used instead of the wiring electrode, and the electrode and the moisture detection section 12 may be electrically connected via the wiring.

Note that the moisture sensor 10 can be applied to a water immersion sensor, a dew condensation sensor, and the like.

[Moisture detection part]
Examples of the conductive powder include inorganic powders such as carbon black, graphite powder, and carbon fiber.

Examples of carbon black include furnace black, channel black, acetylene black, and thermal black.

The content of the conductive powder in the moisture detection part 12 is preferably greater than 22% by mass and 35% by mass or less, and more preferably greater than 22% by mass and not more than 28% by mass. When the content of the conductive powder in the moisture detection part 12 is more than 22% by mass, the water immersion detection performance of the moisture sensor 10 improves, and when it is 35 mass% or less, the water immersion detection performance and heat resistance of the moisture sensor 10 improve. will improve.

The homopolymer or copolymer of N-vinyl-2-pyrrolidone is preferably a homopolymer of N-vinyl-2-pyrrolidone, that is, polyvinylpyrrolidone, but it may be used as long as it does not impair the effects of the present invention. For example, it may be a copolymer of N-vinyl-2-pyrrolidone and other monomers. When synthesizing a copolymer of N-vinyl-2-pyrrolidone, the amount of other monomers used in all monomers is preferably 10% by mass or less, more preferably 1% by mass or less, and 0% by mass or less. It is more preferable that the amount is .1% by mass or less.

The K value of the homopolymer or copolymer of N-vinyl-2-pyrrolidone is preferably from 60 to 120, more preferably from 60 to 100, even more preferably from 70 to 100.

Here, the K value of the homopolymer or copolymer of N-vinyl-2-pyrrolidone is a viscosity characteristic value that correlates with the molecular weight of the homopolymer or copolymer of N-vinyl-2-pyrrolidone, and is as follows: It is calculated by applying the Fikentscher equation.

K=(1.5logη _rel -1)/(0.15+0.003c)+(300clogη _rel +(c+1.5logη _rel ) ² ) ^{1/ 2} /(0.15c+0.003c2)
Here, η _rel is the relative viscosity of an aqueous solution of a homopolymer or copolymer of N-vinyl-2-pyrrolidone with respect to water (25°C), as measured by a capillary viscometer, and c is the relative viscosity of an aqueous solution of N-vinyl-2-pyrrolidone It is the concentration [% by mass] of the homopolymer or copolymer of N-vinyl-2-pyrrolidone in the aqueous solution of the homopolymer or copolymer of -2-pyrrolidone.

A homopolymer or copolymer of N-vinyl-2-pyrrolidone can be synthesized by homopolymerizing or copolymerizing N-vinyl-2-pyrrolidone.

The residual amount of N-vinyl-2-pyrrolidone in the homopolymer or copolymer of N-vinyl-2-pyrrolidone is preferably 200 mass ppm or less, more preferably 100 mass ppm or less. , more preferably 10 mass ppm or less. If the residual amount of N-vinyl-2-pyrrolidone in the homopolymer or copolymer of N-vinyl-2-pyrrolidone is 200 mass ppm or less, the homopolymer or copolymer of N-vinyl-2-pyrrolidone The safety of the combination will be even better.

The remaining amount of N-vinylpyrrolidone in the homopolymer or copolymer of N-vinyl-2-pyrrolidone can be determined by liquid chromatography under the following conditions.

Equipment: NANOSPACE SI-2 (manufactured by Shiseido)
Column: CAPCELLPAK C18 UG120 (manufactured by Shiseido)
Measurement temperature: 20℃
Eluent: LC methanol (manufactured by Wako Pure Chemical Industries)/ultra pure water mixed solvent (mass ratio 1/24) with 0.04% by mass of sodium 1-heptanesulfonate added Flow rate: 100 μL/min
Examples of methods for polymerizing N-vinyl-2-pyrrolidone include bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, and precipitation polymerization.

The content of the homopolymer or copolymer of N-vinyl-2-pyrrolidone in the moisture detection part 12 is preferably greater than 50% by mass. When the content of the homopolymer or copolymer of N-vinyl-2-pyrrolidone in the moisture sensing portion 12 is more than 50% by mass, the heat resistance of the moisture sensor 10 is improved.

The upper limit of the content of the N-vinyl-2-pyrrolidone homopolymer or copolymer in the moisture detection part 12 is not particularly limited, but is usually 68% by mass.

Examples of phenolic antioxidants include hydroquinone, catechol, 2,4-dihydroxybenzophenone, 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, and 2,6-di-t-butyl- Monophenols such as 4-ethylphenol; 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4' - Thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 3,9-bis[1,1-dimethyl-2-[β-( 3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4'-(2,3-dimethyl- Bisphenols such as tetramethylene) dipyrrocatechol; stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 3,4,5-trihydroxybenzoic acid propyl ester, 1,1 ,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4- hydroxybenzyl)benzene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, bis[3,3'-bis-(4'-hydroxy- 3'-t-butylphenyl)butyric acid] glycol ester, 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-s-triazine-2,4, 6-(1H,3H,5H)trione, tocopherol and tocopherol derivatives, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl Examples include polyphenols such as acrylate. Among these, 2,6-di-t-butyl-p-cresol, hydroquinone, tocopherol, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6- Di-tert-pentylphenyl acrylate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene is preferred.

The content of the phenolic antioxidant in the moisture detection part 12 is preferably greater than 2% by mass, and more preferably greater than 10% by mass. When the content of the phenolic antioxidant in the moisture detection section 12 is more than 2% by mass, the heat resistance of the moisture sensor 10 is improved.

The upper limit of the content of the phenolic antioxidant in the moisture detection section 12 is not particularly limited, but is usually 20% by mass.

The moisture detection section 12 may further contain an antifoaming agent or the like, if necessary.

The moisture detection part 12 is formed by applying an ink containing conductive powder, a homopolymer or copolymer of N-vinyl-2-pyrrolidone, a phenolic antioxidant, and a solvent, and then drying the ink. can do.

Examples of the solvent include ethyl carbitol, butyl carbitol, methyl triglyme, and terpineol.

Examples of the ink application method include a screen printing method, a bar coating method, a spin coating method, and the like.

〔substrate〕
Examples of the substrate 11 include a glass epoxy substrate, a paper phenol substrate, a PET film, and a polyimide film.

Although the shape of the substrate 11 is planar, it may be curved.

[Wiring electrode]
Examples of the wiring electrodes 13 and 14 include gold-plated copper foil.

Note that the wiring electrodes 13 and 14 may be formed by screen printing ink for wiring electrodes such as carbon paste or metal paste.

Examples of the metal paste include silver paste and gold paste.

Further, the wiring portions of the wiring electrodes 13 and 14 may be covered with an overcoat layer. This can prevent short circuits caused by water adhesion.

Examples of the material constituting the overcoat layer include carbon.

Examples of the present invention will be described below, but the present invention is not limited to the examples. In addition, unless otherwise specified, parts mean parts by mass, and % means mass %.

<Manufacture of polyvinylpyrrolidone>
400 kg of N-vinyl-2-pyrrolidone (hereinafter referred to as VP) and 1,600 kg of water were placed in a jacketed pot with a capacity of approximately 2.5 m ³ . While purging with nitrogen, heat to 70°C and add 0.10% by mass (400 g) of V-59 (2,2'-azobis(2-methylbutyronitrile) (manufactured by Wako Pure Chemical Industries) based on VP). was added as a 10% isopropyl alcohol solution to start polymerization. After 1 hour, the temperature of the reaction solution reached 90°C due to the heat of reaction. After that, the reaction solution was placed in a jacket so that the temperature remained at 90 to 99°C until the polymerization was completed. Warm water was flowed. Two hours after the start of the reaction, 0.1% by mass (400 g) of V-59 based on VP was added as a 10% isopropyl alcohol solution, and the polymerization rate was 99.90%. Next, 1000 mass ppm (400 g) of malonic acid was added to VP, the pH of the reaction solution was adjusted to 3.6, and the temperature was maintained for 2 hours. Thereafter, 1000 mass ppm (400 g) of guanidine carbonate was added ), and 1500 mass ppm (600 g) of triethanolamine were added.As a result, polyvinylpyrrolidone with a residual amount of VP of 4 mass ppm and a K value of 92 was obtained.The obtained polyvinylpyrrolidone was heated in a drum dryer. After drying using a pulverizer, it was powdered using a pulverizer.The K value of the powdered polyvinylpyrrolidone was 94.

<Examples 1 to 4, Comparative Example 1>
[Manufacture of ink for moisture detection unit]
After blending 100% pressed Denka Black (manufactured by Denki Kagaku Kogyo), polyvinylpyrrolidone, and hydroquinone (manufactured by Wako Pure Chemical Industries) as acetylene black at the blending ratio [%] shown in Table 1, ethyl carbitol was further added. The mixture was mixed and kneaded in an automatic mortar for 20 hours to obtain an ink for a moisture detection section.

[Manufacture of moisture sensor]
A moisture sensor shown in FIG. 1 was manufactured.

Specifically, after screen printing ink for wiring electrodes on a glass epoxy substrate with a thickness of 0.8 mm, heat treatment was performed at 200 ° C. for 3 minutes to form a pair of gold-plated copper foils (wiring electrodes) with a thickness of 35 μm. . Next, after screen-printing the ink for the moisture detection portion, heat treatment was performed at 200° C. for 3 minutes to form a moisture detection portion with a thickness of 5 μm. Next, after screen printing the ink for the overcoat layer, heat treatment was performed at 220° C. for 10 minutes to cover the wiring portion of the wiring electrode with a carbon film (overcoat layer) to obtain a moisture sensor.

Next, the moisture absorption characteristics and heat resistance of the moisture sensor were evaluated.

<Moisture absorption characteristics>
The moisture sensor was placed in an Erlenmeyer flask whose humidity had been adjusted by dissolving the electrolyte in water in a saturated state, and the resistance value of the moisture detection section at 20° C. was checked to evaluate the moisture absorption characteristics of the moisture sensor. Here, by using sodium chloride or ammonium dihydrogen phosphate as the electrolyte, humidity can be controlled as described below.

Sodium chloride: 75%RH
Ammonium dihydrogen phosphate: 93%RH
Here, 75% RH and 95% RH were used as the humidity in a non-flooded state and the humidity in a submerged state, respectively.

Note that the criteria for determining the moisture absorption characteristics of the moisture sensor are as follows.

○: When the resistance value of the moisture detection part at 75% RH is 20 kΩ or less ×: When the resistance value of the moisture detection part at 75% RH exceeds 20 kΩ <Heat resistance>
After leaving the moisture sensor in a tank at 125° C., the resistance value of the moisture detection portion was checked to evaluate the heat resistance of the moisture sensor. At this time, the moisture sensor was taken out of the tank every 250 hours, and after being left in an environment of normal temperature and normal humidity for 1 hour or more, the resistance value of the moisture detection part was checked. The resistance value of the moisture detection section was confirmed before dropping distilled water onto the moisture detection section and 1 minute after dropping distilled water onto the moisture detection section.

Note that the criteria for determining the heat resistance of the moisture sensor are as follows.

○: The resistance value of the moisture detection part before dropping distilled water on the moisture detection part is 20kΩ or less, and the resistance value of the moisture detection part 1 minute after dropping distilled water on the moisture detection part is 1MΩ or more. In the case of ×: The resistance value of the moisture detection unit before dropping distilled water on the moisture detection unit exceeds 20 kΩ, or the resistance value of the moisture detection unit 1 minute after dropping distilled water on the moisture detection unit When it is less than 1 MΩ Table 1 shows the evaluation results of the moisture absorption characteristics and heat resistance of the moisture sensor.

表１から、実施例１～４の水分センサは、耐熱性及び浸水検知性能に優れることがわかる。

Table 1 shows that the moisture sensors of Examples 1 to 4 have excellent heat resistance and water immersion detection performance.

On the other hand, the moisture sensor of Comparative Example 1 has poor heat resistance because the moisture detection part does not contain a phenolic antioxidant.

10 Moisture sensor 11 Substrate 12 Moisture detection section 13, 14 Wiring electrode

Claims (4)

conductive powder;
A homopolymer or copolymer of N-vinyl-2-pyrrolidone,
a moisture detection section containing a phenolic antioxidant;
a pair of electrodes electrically connected to the moisture detection section ;
A moisture sensor in which the content of the phenolic antioxidant is more than 2% by mass . The moisture sensor according to claim 1, wherein the phenolic antioxidant is hydroquinone. The moisture detection section is
The content of the conductive powder is more than 22% by mass and not more than 28% by mass,
The content of the homopolymer or copolymer of N-vinyl-2-pyrrolidone is more than 50% by mass,
The moisture sensor according to claim 1 or 2, wherein the content of the phenolic antioxidant is more than 10% by mass. The moisture sensor according to any one of claims 1 to 3, which is a water immersion sensor.

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