JPS6236549A - Moisture-sensitive element - Google Patents

Abstract

PURPOSE:To obtain a moisture-sensing element excellent in the durability with limited deterioration in the sensitivity caused by a thermal moisture or the like by employing as moisture-sensing film a copolymer made of specified amide acrylate derivative and a specified acrylic acid derivative as main monomer components. CONSTITUTION:A copolymer made of an amide acrylate derivative as given by the formula I and an acrylic acid derivative as given by the formula II is dissolved into an organic solvent such as methonol, ethanol and acetone, an alumina substrate 2 with a gold foil electrode 1 is immersed into the solution to form a moisture-sensing film, from which a moisture-sensing element 3 is obtained. Normally, these polymers are preferably controlled to 100-100,000 in the average degree of polymerization an also, preferably shall be 1:4-4:1 in the mol. ratio of the units of the formula I and the formula II viewed from the moisture sensing effect and the moisture stability. As the moisture sensing film thus obtained becomes higher in the moisture, the moisture absorption into the film increases. This enhances the rate of ionization in the electrolytic portion, thereby decreasing the resistance within the film accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a moisture sensitive element. More specifically, the present invention relates to a humidity sensing element that detects humidity in various atmospheres.

(b) Conventional technology Some devices using organic polymers have been put into practical use as humidity-sensitive devices for detecting humidity.

The organic polymer used here is a polymer electrolyte because it is composed of a monomer having a part that ionizes in a part of its structure (hereinafter referred to as a conductive monomer). Moisture sensitive elements are widely used in which a resin film containing this polymer electrolyte is used as a moisture sensitive film and is coated between a pair of electrodes on an insulating substrate. In this case, the principle of detecting the atmospheric humidity of the polymer electrolyte is based on the fact that the polymer electrolyte absorbs moisture in the atmosphere, causes ionization, and decreases the surface resistance value. The relationship between relative humidity and surface resistance of various polymer electrolytes is well known (Chel, Technol, May 1971, No. 304-309).

For example, the characteristics required for such a moisture-sensitive element include (+)
When the relative humidity is changed, the resistance value changes log-linearly, and it has reproducibility even when left in a normal indoor atmosphere.

(H) When changing from a high-humidity atmosphere to a low-humidity atmosphere, there should be little error in returning to the straight line in (I) (that is, small hysteresis).

etc. These conditions are considered to be influenced by the properties of the selected conductive top.

On the other hand, it has also been proposed to make a moisture-sensitive membrane by impregnating a water-absorbing polymer with a conductive compound without using a polymer electrolyte.
A moisture-sensitive element in which an organic polymer is impregnated and supported on an alkali metal salt of -acrylamide-2-methylpropanesulfonic acid (Japanese Patent Application Laid-open No. 36796/1983) has also been proposed.

(c) Problems to be Solved by the Invention However, in addition to the conditions (i) and (red) above, the following conditions are also required for such a moisture-sensitive element. That is, (
g) Since the moisture-sensitive film must contain a water-soluble (ionizable) portion, when left in a high-humidity atmosphere, the moisture-sensitive film often dissolves and desorbs, resulting in an increase in resistance characteristics. , it has sufficient durability even under such high humidity. The moisture-sensitive element disclosed in JP-A-54-36796 also uses a conductive upper knob (2) which is originally highly water-soluble.
-Acrylamide-2-methylpropanesulfonic acid alkali metal salt) is simply impregnated and supported in its original form, and there are concerns about durability, especially changes in properties under high humidity conditions (including dew condensation). . Regarding this point, the present inventors have considered using a polymer electrolyte obtained by directly polymerizing the above-mentioned conductive upper layer as a moisture-sensitive membrane, but this is insufficient in the above-mentioned point (b).

In view of this point, the inventors conducted intensive research and found that
It was discovered that a polymer copolymer obtained by copolymerizing a specific acrylic M derivative with the conductive monomer satisfies the conditions (I) to (g) above, and the moisture-sensitive element of the present invention was completed. .

(d) Means for Solving the Problems According to the present invention, a moisture-sensitive film is formed between a pair of electrodes on an insulating substrate using a monolayer mainly composed of a specific acrylic acid amide derivative and a specific acrylic acid derivative. Provided is a moisture-sensitive element using a copolymer as a body component.

As a specific acrylamide derivative, the following formula (in the formula,
R is a hydrogen atom or a methyl group, X is an alkali metal), i.e., 2-acrylamide-2
-Methylpropanesulfonic acid alkali metal salt or 2-
Methacrylamide-2-methylpropanesulfonic acid alkali metal salt is used. In the above compound, R is preferably a hydrogen atom, and X is preferably a sodium atom. 2-acrylamido-2-methylpropanesulfonic acid (hereinafter abbreviated as AMPS), which is a raw material for such a compound, is available as a product of Nitto Kagaku ■.

One specific acrylic acid derivative has the following formula (where R
is a hydrogen atom or a methyl group, and Y is a lower alkyl group), that is, a lower alkyl acrylate ester or a lower alkyl methacrylate ester is used. In the above compound, R has a thymel group and Y
A methyl group and an ethyl group are preferred.

Such compounds can usually be synthesized from methacrylic Fll-R conductors and corresponding lower alkyl alcohol derivatives, which are also commercially available as reagents.

The polymer used in the present invention is a copolymer mainly composed of units represented by formula (I) and formula (I[), and the average degree of polymerization thereof is usually adjusted to 100 to 10,000. is preferable. The copolymer may also contain copolymerizable vinyl monomers such as styrene, methyl methacrylate, and methyl acrylate as other monomer components. However, C outside the above average degree of polymerization range can also be applied as long as it exhibits moisture sensitivity. Such copolymers can be synthesized by known polymerization methods such as radical polymerization, usually using a radical generator.

Further, the ratio of the units of formula (I> and the units of formula (II>) is not particularly limited, but is usually 1:4 to 4:1 as a molar ratio of formula (I):formula (II). is preferable from the viewpoint of humidity sensitivity effect and humidity stability.

The thus obtained copolymer was mixed with methanol, ethanol,
The moisture-sensitive element of the present invention can be obtained by dissolving it in an organic solvent such as acetone, applying it to the substrate of the moisture-sensitive element, especially between the electrodes, and drying it to form a moisture-sensitive film.

(E) Function In the moisture-sensitive membrane of the present invention obtained in this way, as the humidity increases, the absorption i@1ffl into the membrane increases, and the proportion of ionization of the electrolyte portion increases accordingly. As a result, the resistance value within the wire film shows a corresponding decrease. This makes it possible to detect humidity in various atmospheres.

(F) EXAMPLES The present invention will be explained in detail below with reference to Examples and drawings, but the present invention is not limited thereby.

Amount m*+ri' mouth & Example anhydrous methanol 251! 2.25L of sodium carbonate inside
A M P 38.3<+ was added and the resulting solution was 250
Pour into yrl acetone, dry the precipitate, and AMPS
The sodium salt of (hereinafter abbreviated as AMPS-Na) was obtained.

AMPS-Na9Q, methyl methacrylate) L/-door, ag (molar ratio 1:2) and as a polymerization initiator, 150 mg of benzoyl peroxide was dissolved in methanol and the total amount was
011 and reacted under vacuum at 60° C. for 24 hours to obtain a gel-like reaction product. This was dissolved in methanol and poured into ethyl acetate to obtain a white precipitate. The colander was reprecipitated with methanol-ethyl acetate to obtain a moisture sensitizer used in the present invention.

In the case of the lithium salt of AMPS, a copolymer of the lithium salt of AMPS and methyl methacrylate can be produced by using lithium carbonate and performing the same operation as described above.

Comparative Example For comparison, a moisture sensitizer comprising a copolymer of sodium p-styrene sulfonate and methyl methacrylate was prepared as follows.

Commercially available sodium p-styrene sulfonate 10Q1 methyl methacrylate 9,7(I (molar ratio 1:2) and 150 mg of benzoyl peroxide as a polymerization initiator were added with 151! of methanol and water to make the entire surface 6011.

The reaction was carried out under vacuum at 60° C. for 65 hours to obtain a reaction product with increased viscosity. This was dissolved in methanol and poured into acetone to obtain a white precipitate. Further, reprecipitation was performed with methanol-ethyl acetate to obtain a comparative moisture sensitizer.

Approximately 4% of the above moisture sensitive agent (example) was dissolved in methanol.
A moisture sensitizer solution was prepared. After immersing an alumina insulating substrate (2) with a pair of comb-shaped gold electrodes (I) [1) in this solution as shown in Figure 1, it is fired (dried), and then a gas permeable A moisture-sensitive element (3) was completed by providing a silicone coating with excellent properties. Figure 2 shows the results of measuring the resistance value at each relative humidity for 20 minutes at 25°C by applying an AC power supply of 5V at a frequency of 120Hz to the humidity sensing element (3) obtained in this way. It is.

Next, FIG. 3 is a graph showing an example of a relative humidity-resistance characteristic diagram of the humidity sensing element of the present invention at an initial stage and after a heat resistance test.
The results are shown in which changes in characteristics were investigated in the same manner as above after the humidity sensing element of the present invention was left in a hot air drying oven at 700° C. for 30 days.

Next, FIG. 4 is a relative humidity-resistance characteristic diagram showing, together with a comparative example, an example of error fluctuation when a durability test was conducted under dew condensation using the humidity sensing element of the present invention. The humidity sensing element of the present invention was left in a desiccator with water at the bottom (that is, in a modern model with condensation) for 30 days, and changes in characteristics were examined in the same manner as above.The solid line (A) shows the results. It shows.

On the other hand, 3 days after leaving the humidity sensing element prepared in the same manner as above using the humidity sensing agent prepared in the comparative example in the desiccator,
Characteristic changes were investigated in the same manner as above. This result is shown by a broken line (b).

It can be seen from FIG. 2 that the moisture sensitive element of the present invention has good return characteristics. From FIG. 3, it can be seen that the humidity sensitive element of the present invention is extremely stable with an error due to thermal deterioration of within 1% RH, and has excellent heat resistance. Furthermore, Figure 4 shows that the humidity sensitive element of the present invention has far superior durability under dew condensation compared to that obtained in the comparative example.

(g) Effects of the Invention The moisture-sensitive element of the present invention has extremely little deterioration in sensitivity due to heat, moisture, etc., and the moisture-sensing agent has good bonding properties to the insulating substrate, so it is resistant to changes in heat, moisture, etc. Under extreme conditions, i.e. high temperatures,
It is a highly durable moisture-sensitive element that can withstand long-term use even under high humidity conditions.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of a humidity-sensitive cord to which the moisture-sensing agent of the present invention is applied, and FIG. 2 is an example of the initial characteristic and return characteristic of the relative humidity-resistance value of the moisture-sensing element of the present invention. The graph shown in FIG. 3 is a graph showing an example of the relative humidity-resistance characteristic diagram of the humidity sensing element of the present invention at the initial stage and after the heat resistance test, and FIG.
(b) is a relative humidity-resistance characteristic diagram showing an example of error fluctuations when a durability test under dew condensation conditions is conducted using the humidity sensing element of the present invention, together with a comparative example. (I)...Comb-shaped gold foil electrode, (2...
・Alumina insulating substrate, (3)...Moisture sensing element,
(4)...Lead wire. Procedure: 1985 (1985)
January 27th 1, Incident Display 1985 Patent Application No. 17656
No. 4 No. 2, Title of the invention Moisture sensing element 3, Relationship to the amended person case Patent applicant (I) Address 2-18 Keihan Hondori, Moriguchi City Name <188) Sanyo Electric Co., Ltd. Representative Iue Kaoru (2 Address: 180 Sakata, Oizumi-cho, Oura-gun, Gunma Prefecture Name: Tokyo Sanyo Electric Co., Ltd. Representative: Kaoru Iue 4, Agent: 530 Address: 1-3 Quarter, 5-chome Nishitenma, Kita-ku, Osaka City
One Bill 5, date of amendment order October 29, 1985
Date (shipment date) 6, Contents of the amendment subject to amendment 1, The statement ``Have reproducibility.'' in the 7th line of page 3 of the Letter of Inquiry shall be amended to ``Have reproducibility.'' 2, page 6 of the same book, lines 9 to 9 [R has a thymel group, and J has been corrected to read ``R has a methyl group.'' 3. On page 11, line 3 of the same book, the statement "the produced moisture-sensitive element" is corrected to "the produced moisture-sensitive element". 4. The description in lines 5 and 6 of page 12 of the same book “Figure 4 (a),
(b) respectively of this invention" is amended to read "Figure 4 is of this invention." Procedural amendment December 68, 1985 2. Title of the invention Moisture sensing element 3. Relationship to the case of the person making the amendment Patent applicant (I) Address 2-18 Keihan Hondori, Moriguchi City Name (I88) Sanyo Denki Co., Ltd. Representative Kaoru Iue +21 Address 18 Sakata, Oizumi-cho, Oura-gun, Gunma Prefecture
Address 0 Name Tokyo Sanyo Electric Co., Ltd. Representative Kaoru Iue 4, Agent 〒530

Claims (2)

[Claims] 1. The following formula (
I); ▲There are mathematical formulas, chemical formulas, tables, etc.▼・・・・・・( I
) (In the formula, R is a hydrogen atom or a methyl group, and X is an alkali metal.) Acrylic acid amide derivatives represented by the following formula (II): ▲Mathematical formulas, chemical formulas, tables, etc. are available▼・・・・・・...
(II) A moisture-sensitive element using a copolymer having an acrylic acid derivative represented by the following formula (wherein R is a hydrogen atom or a methyl group, and Y is a lower alkyl group) as a main monomer component. 2. The molar ratio of copolymerization of (I) and (II) is 1:4 to 4:
1. The moisture sensing element according to claim 1, which is