JP2002267627A - Humidity-sensitive element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity-sensitive element enabling measurement with DC, capable of detecting a humidity of <60% RH, having good sensitivity and response, and high in the characteristics stability against repeated operation, and to provide a method of manufacturing the same. SOLUTION: In the humidity-sensitive element, a humidity-sensitive film containing a hygroscopic polymer and conductive particles dispersed in the hygroscopic polymer is provided between a pair of electrodes, the hygroscopic polymer contains a polyethyleneimine type polymer modified with a reactive organic compound having a functional group reactive with a polyethyleneimine type polymer such as polyethyleneimine or the like, or a polyethyleneimine type polymer grafted with a reactive organic compound having a functional group reactive with a polyethyleneimine type polymer and the polyethyleneimine type polymer is crosslinked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a moisture-sensitive element having a moisture-sensitive film containing a hygroscopic polymer and conductive particles, and a method for producing the same. More specifically, the present invention relates to a moisture-sensitive element having a moisture-sensitive film having a composition excellent in physical performance and high reliability, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, as a moisture-sensitive element for detecting humidity and dew condensation, there is known a device provided with a moisture-sensitive film in which conductive particles are dispersed in a hygroscopic polymer (Japanese Patent Laid-Open No. 58-99740). , JP
No. 59-170755, JP-A-60-25041, JP-A-62-21052,
JP-A-6-249813). In low humidity, the conductive particles are in contact with each other at low humidity to form a conductive path and exhibit low resistance. However, at high humidity, the conductive path is cut off due to the moisture-absorbing polymer absorbing moisture and swelling, resulting in high resistance. It becomes a state.

[0003] Other examples of the moisture-sensitive element using a hygroscopic polymer include a humidity sensor using a polymer electrolyte having a quaternary ammonium base and utilizing a change in ionic conductivity corresponding to a humidity atmosphere ( JP-A-7-318526, etc.). This humidity sensor uses a phenomenon in which the degree of dissociation of a counter ion of a quaternary ammonium base changes according to the amount of moisture in the measurement atmosphere, and the phenomenon in which a flowing ion current changes when a voltage is applied is used. Is to be detected.
However, a humidity sensor using a change in ionic conductivity causes polarization to occur when used with a direct current, and thus does not function. Therefore, it is necessary to measure with an alternating current, and the circuit becomes complicated. Also, under high humidity of 90% RH or more, especially in a dew condensation atmosphere, the polymer electrolyte has poor water resistance such as partial elution, and a hysteresis phenomenon in which the output value differs when the humidity increases and decreases even at the same humidity. And the characteristics become unstable.

On the other hand, a moisture-sensitive element in which conductive particles are dispersed in a hygroscopic polymer has the advantage that a direct current can be measured and the measurement circuit can be simplified.

However, a moisture-sensitive element in which conductive particles are dispersed in a hygroscopic polymer can detect only a high humidity region within a range of 60 to 100% RH. Conventionally, polyether polyamines, hydroxymethacrylates, polyvinyl alcohols, etc. have been used as hygroscopic polymers. However, since the amount of water absorption increases rapidly above 60% RH, detection of humidity below 60% RH is difficult. , A sufficient resistance value cannot be obtained, and the sensitivity is low.

On the other hand, when a highly hygroscopic resin such as polyethyleneimine is used as the hygroscopic polymer, it is known that moisture absorption starts from a low humidity region. JP 10-926
No. 03 discloses a sensor using a resistive composition in which crystalline polyethyleneimine is grafted onto conductive particles having a carboxyl group on the surface, such as carbon black, and the resistance value changes in response to a specific substance. Have been. And
Water is also mentioned as a specific substance, and it is shown that it is used as a moisture-sensitive element. However, JP 10
The moisture-sensitive element disclosed in -92603 has a low sensitivity of about 10Ω in a dry state, but a few kΩ in a 100% RH atmosphere and a change in resistance of about 2.5 digits. ,
Also, it takes more than 15 minutes for the resistance to stabilize,
Responsiveness is poor, and it does not have sufficient characteristics as a moisture sensitive element. Here, as the crystalline polyethyleneimine, a product obtained by ring-opening polymerization of 2-methyl-2-oxazoline is used in the above publication. Further, in the above publication, as a comparative example, a sensor using carbon black grafted with non-crystalline polyethyleneimine obtained by ring-opening polymerization of aziridine is disclosed. In addition, the sensor characteristics are inferior.

In general, polyethyleneimine has a large water absorption particularly in a high-humidity region. When the polyethyleneimine is used in a moisture-sensitive element, the moisture-sensitive portion swells significantly when exposed to a high-humidity atmosphere. However, the deformation of the film does not return, the resistance value does not easily return, and the response characteristics become unstable.

Further, a moisture-sensitive element using polyethyleneimine does not have water resistance unless cross-linking is sufficient, and the resin portion flows out in a high-humidity atmosphere, and the change in resistance becomes extremely small. Response characteristics become unstable. On the other hand, if the degree of crosslinking is too high, steric hindrance makes it difficult for water to be adsorbed to the adsorption site of the hygroscopic resin, so that a response in a low humidity region does not occur. Furthermore, if appropriate crosslinking is performed to provide sufficient water resistance and low humidity response, the crosslinking loses the flexibility of the moisture-sensitive film and causes swelling deformation when exposed to a high-humidity atmosphere. However, there is a drawback that characteristic resistance is not obtained and characteristics are not stable.

In general, a moisture-sensitive element based on a composite material of a hygroscopic polymer and conductive particles swells and shrinks when repeatedly exposed to high and low humidity atmospheres. When the amount of adsorption is large, peeling of the moisture-sensitive film from the electrode substrate is likely to occur, which also hinders obtaining a low-humidity detecting element having stable characteristics.

[0010] As described above, no moisture-sensitive element provided with a moisture-sensitive film in which conductive particles are dispersed in a hygroscopic polymer and capable of stably detecting a humidity of less than 60% RH has not been obtained. . If the humidity sensing element is used in a wide range of applications such as air conditioners and humidifiers,
Low humidity, not only in the middle and high humidity areas above% RH
There is a need for a moisture sensitive element that can detect a humidity of less than 60% RH.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to be able to measure direct current, to detect a humidity of less than 60% RH, to have good sensitivity and responsiveness, and to have a high characteristic stability for repeated operation. An object of the present invention is to provide a wet element and a manufacturing method thereof.

[0012]

As described above, a sensor using ionic conductivity requires a complicated circuit, is expensive, has low water resistance, and has a large hysteresis. In addition, a moisture-sensitive element consisting of a composite of a hygroscopic polymer and conductive particles, which has a sufficient resistance change at a detection humidity of less than 60% RH, and has a responsive and stable characteristic Not obtained. Based on this background, the present invention provides a moisture-sensitive element using a hygroscopic polymer and conductive particles, and has a flexible and moderate moisture-sensitive film using a polyethyleneimine-based polymer as the hygroscopic polymer. It has been found that the provision of water resistance is important for the function of the moisture-sensitive film. That is, the present invention is as follows.

(1) A moisture-sensitive element having a moisture-sensitive film containing a hygroscopic polymer and conductive particles dispersed in the hygroscopic polymer between a pair of electrodes, wherein the hygroscopic polymer is A polyethyleneimine polymer modified with a reactive organic compound having a functional group reactive with a polyethyleneimine polymer, or a reactive organic compound having a functional group reactive with a polyethyleneimine polymer is grafted A moisture-sensitive element containing a modified polyethyleneimine-based polymer and crosslinked with the polyethyleneimine-based polymer. (2) The reactive organic compound having a functional group reactive with the polyethyleneimine polymer is an aldehyde compound, a ketone compound, an alkyl halide compound, an isocyanate compound, a thioisocyanate compound, a compound having an active double bond, an epoxy compound , A cyanamide compound, a guanidine compound, a urea compound, an acid, an acid anhydride, or an acyl halide compound, wherein the moisture-sensitive film is plasticized by modification or grafting with these reactive organic compounds. Moisture sensitive element. (3) The hardness of the moisture sensitive film is JIS at 25 ° C and 0% RH.
The moisture-sensitive element according to the above (1) or (2), which is a film 3H or a film softer than 3H expressed in pencil hardness according to K5400. (4) The molecular weight of the polyethyleneimine-based polymer skeleton subjected to modification or grafting is 30 in number average molecular weight.
The moisture-sensitive element according to any one of the above (1) to (3), which has a molecular weight of 0 to 70000. (5) an alkylene group bonded to N in the polyethyleneimine-based polymer skeleton subjected to modification or grafting,
Any one of the above (1) to (4), which is at least one kind selected from a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group which may have a substituent, and includes an unsubstituted ethylene group; Such a moisture sensitive element. (6) Among the alkylene groups bonded to N, the ratio of unsubstituted ethylene groups is 20 to 100 mol%, and the substituted ethylene groups, and the methylene groups each having a substituent, The moisture-sensitive element according to the above (5), wherein at least one selected from trimethylene groups and tetramethylene groups is 0 to 80 mol%. (7) The moisture-sensitive element according to any one of (1) to (6), wherein the conductive particles are carbon black. (8) In the method for manufacturing a moisture-sensitive element having a moisture-sensitive film containing a moisture-absorbing polymer and conductive particles dispersed in the moisture-absorbing polymer between a pair of electrodes, Method for producing moisture-sensitive element obtained by curing coating film of polyethyleneimine-based polymer, reactive organic compound having functional group reactive with polyethyleneimine-based polymer, crosslinking agent and conductive particles .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The moisture-sensitive element of the present invention has a moisture-sensitive film between a pair of electrodes, and the moisture-sensitive film contains a hygroscopic polymer and conductive particles dispersed therein. The hygroscopic polymer is a polyethyleneimine polymer modified with an organic compound having a functional group reactive with the polyethyleneimine polymer, or an organic compound having a functional group reactive with the polyethyleneimine polymer. It contains a grafted polyethyleneimine-based polymer, and these polyethyleneimine-based polymers are crosslinked.

The present invention focuses on using a polyethyleneimine-based polymer, which is a highly water-absorbing polymer having a very high hydrophilicity, in a moisture-sensitive film in order to enable detection of humidity in a low humidity region. The polyethyleneimine-based polymer starts absorbing moisture from a low humidity region. On the other hand, when exposed to a high-humidity atmosphere, swelling due to moisture absorption becomes remarkable, and it becomes difficult to recover the resistance value even after drying, and the response characteristics become unstable.

Therefore, in the present invention, the polyethyleneimine-based polymer is appropriately crosslinked to have water resistance so as to enable a response in a low humidity range, and the film cured by the crosslinking has high humidity and high humidity. Repeated low-humidity (dry drying) cycles cause cracks and peeling of the film, change the film characteristics, and make it impossible to obtain stable device characteristics. The problem is solved by using a grafted polyethyleneimine polymer.

That is, by appropriately cross-linking the modified or grafted polyethyleneimine-based polymer as described above, it is possible to plasticize or soften the membrane and obtain appropriate water resistance. it can. Therefore, by using such a water-absorbing polymer, 90% R
Since moisture absorption starts from a humidity region of less than H, particularly 10 to 90% RH, it is possible to detect not only a high humidity region of 60% RH or more but also a low humidity region of less than 60% RH. That is, the humidity-sensitive element of the present invention has a 10 to 100% RH,
H, in particular, humidity in the range of 40 to 100% RH can be detected. In addition, since the amount of moisture absorption is as large as 10 to 50% (mass percentage), a large amount of conductive particles can be taken, and stable resistance / humidity characteristics can be obtained. The resistance value of the moisture-sensitive element of the present invention at the time of drying is about 400 to 2 kΩ, and the change of the resistance value is about 3 to 5 digits.
Further, the resistance value changes quickly, and the response is good. Moreover, the humidity-sensitive element of the present invention has extremely stable resistance humidity characteristics even when repeatedly exposed to a dry atmosphere and a high-humidity atmosphere, and its change is extremely small even after 500 or more (500 to 600) cycles.

Further, since a moisture-sensitive film in which conductive particles are dispersed in a hygroscopic polymer is used, direct current measurement is possible.
The measurement circuit can be simplified and the cost is low.

In the present invention, the polyethyleneimine-based polymer skeleton constituting the modified polyalkyleneimine or grafted polyethyleneimine-based polymer used in the moisture-sensitive film is obtained, for example, by ring-opening polymerization of ethyleneimine (aziridine). Such as polyethyleneimine obtained, having a constitutional repeating unit obtained by ring-opening ethyleneimine, and having a structure represented by the following formula (1);
In the above structure, a part of the ethylene group bonded to N may be substituted or the number of methylene groups may be increased or decreased as described later. The modified polyethyleneimine-based polymer or the grafted polyethyleneimine-based polymer of the present invention can be obtained by modifying such a polyethyleneimine-based polymer or grafting onto such a polyethyleneimine-based polymer. Can be

[0020]

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In the structure of the formula (1), the ethylene group bonded to N may be partly a methylene group, a trimethylene group, or a tetramethylene group. You may have. Examples of the substituent include an alkyl group, an alkoxy group, a hydroxy group, and the like. The alkyl group preferably has 1 to 3 carbon atoms in total, and may have a substituent (such as a hydroxy group).
For example, a methyl group is preferred. The alkoxy group preferably has the same alkyl moiety as the above-mentioned alkyl group, and includes, for example, a methoxy group. When it has a substituent, one alkylene group is preferably one. Also,
The substituents of each alkylene group may be the same or different.

The polyethyleneimine polymer of the present invention comprises
The alkylene group bonded to N may be an unsubstituted ethylene group, and may be an unsubstituted ethylene group and an ethylene group having a substituent and / or an alkylene group optionally having a substituent ( However, the alkylene group may be composed of a methylene group, a trimethylene group, a tetramethylene group). The ratio is such that the unsubstituted ethylene group is 20 to 100 mol%, the substituted ethylene group and / or the optionally substituted alkylene group (provided that the alkylene group is a methylene group, a trimethylene group or a tetramethylene group). (Methylene group) is preferably 0 to 80 mol%.

That is, such a polyethyleneimine-based polymer may be a homopolymer of a constitutional repeating unit in which the alkylene group bonded to N is an unsubstituted ethylene group. The above-mentioned copolymer (copolymer) may be used, and is usually constituted by such a constitutional repeating unit of an alkylene group bonded to N, but may contain other monomer units in some cases. .

Such a polyethyleneimine-based polymer is a superabsorbent polymer having a high density of amino groups and imino groups, which are hydrophilic groups, and a very high hydrophilicity. Its water absorption is about 40 to 45% (mass percentage) at 25 ° C and 50% RH.

The molecular weight is a number average molecular weight Mn of 300 to
It is 70,000, and there is almost no difference in moisture absorption characteristics even if the molecular weights are different, so that any molecular weight can be used. However, if the molecular weight is too small, it is difficult to form a network structure at the time of crosslinking, and sufficient water resistance cannot be obtained. On the other hand, if the molecular weight is too large, the composition has a high viscosity, so that the curing is fast and the workability when forming a moisture-sensitive film on the electrode substrate is poor. Therefore, the molecular weight of the polyethyleneimine-based polymer is preferably from 1,000 to 10,000.

As such a polyethyleneimine-based polymer, a commercially available product (for example, SP200 manufactured by Nippon Shokubai Co., Ltd. as a polyethyleneimine having an unsubstituted ethylene group in which an alkylene group bonded to N is used) can be used. Further, it can be synthesized according to a conventional method such as ring-opening polymerization of an alkylene imine such as ethyleneimine (aziridine) with a cation catalyst [for example, The Chemical Society of Japan, 4th edition Experimental Chemistry Course, Maruzen, 28, 244 (1992), Etc.].

On the other hand, the modified polyethyleneimine-based polymer or the grafted polyethyleneimine-based polymer is modified with the above-mentioned reactive organic compound having a functional group reactive with the polyethyleneimine-based polymer, It is obtained by grafting an organic compound. In the modification or grafting in this case, the reactive organic compound is reacted with a polyethyleneimine-based polymer, and the amino group of the polyethyleneimine-based polymer and / or
Alternatively, it means that the active proton of the imino group is substituted, and the grafting in this means the case where the reactive organic compound further undergoes graft polymerization.

As the reactive organic compound having a functional group reactive with the polyethyleneimine polymer, any organic compound which reacts with the amino group or imino group of the polyethyleneimine polymer may be used. The number of such reactive functional groups may be at least one, and usually one. As such compounds, specifically, aldehyde compounds, ketone compounds, alkyl halide compounds, isocyanate compounds, thioisocyanate compounds, compounds having an active double bond, epoxy compounds, cyanamide compounds, guanidine compounds, urea compounds, acids, acids Anhydrides (organic anhydrides), acyl halide compounds and the like can be mentioned.
Although the molecular weight is not particularly limited, it is generally 50 to 500.
0 is preferred.

The following are specific examples of these compounds. (1) Epoxy compound Specific examples include the following.

[0030]

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(2) Organic acids Specific examples include the following.

[0032]

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(3) Aldehyde compounds Specific examples include butyraldehyde, isobutyraldehyde, laurinaldehyde, benzaldehyde and the like.

(4) Ketone compounds Specific examples include ethyl methyl ketone, isobutyl methyl ketone, diisopropyl ketone, cyclohexanone, acetophenone, valerophenone and the like.

(5) Alkyl halide compounds Specific examples include hexane chloride and octane bromide.

(6) Isocyanate compound Specific examples include ethyl isocyanate, isopropyl isocyanate, phenyl isocyanate, and octadecyl isocyanate.

(7) Thioisocyanate compound Specific examples include ethylthioisocyanate, isopropylthioisocyanate, and octadecylthioisocyanate.

(8) Compound having an active double bond (ethylenically unsaturated monomer) Specifically, alkyl acrylate, alkyl methacrylate, alkyl crotonate, alkyl itaconate, alkyl maleate Examples thereof include esters, alkyl fumarate (all alkyl groups have 1 to 5 carbon atoms), acrylonitriles, methacrylonitriles, and the like. Examples thereof include propyl acrylate, isobutyl methacrylate, and acrylonitrile.

(9) Cyanamide compound Specific examples include cyanamide (NCNH ₂ ).

(10) Guanidine compound Specifically, guanidine ((NH_Two)_TwoC = NH), ace
Tilguanidine (CH _ThreeN_Two(NHCOCH_Three)), Hyp
Lilguanidine (C₆H_Five-CONHCH_TwoCONH-C
(= NH) NH_Two).

(11) Urea compound Specifically, urea (carbamide; CO (NH ₂ ) ₂ ) or the like is used.

(12) Organic anhydride Specific examples thereof include acetic anhydride and phthalic anhydride.

(13) Acyl halide compound Specific examples include valeric chloride.

Of these, the use of epoxy compounds and carboxylic acids is common.

These reactive organic compounds are usually used alone, but may be used in combination of two or more in some cases.

Such reactive organic compounds include the number of active protons contained in amino groups and imino groups present in polyethyleneimine polymers such as polyethyleneimine, and the number of reactive organic compounds reactive with groups having these active protons. The ratio with the number of functional groups in the compound is 1: 0.01 to 1:
It is preferable to add so that it may become about 0.5, and it is preferable to add so that the weight ratio of a polyethyleneimine polymer and a reactive organic compound may be 1: 0.1 to 1: 2. With such an addition amount, it is possible to plasticize the moisture-sensitive film and to impart flexibility while maintaining the hydrophilicity of the polyethyleneimine-based polymer at an appropriate level, and the characteristics as the moisture-sensitive film are improved. improves. On the other hand, if the amount of the reactive organic compound added is small, the effect of plasticization cannot be obtained, and if the amount of the reactive organic compound added is large, the moisture absorption properties of the polyethyleneimine-based polymer itself are hindered.

Further, the polyethyleneimine-based polymer used in the present invention is crosslinked to impart water resistance, and a crosslinking agent is preferably used.

The crosslinking agent is the same as the reactive organic compound used for the modification or grafting, except that it is a polyfunctional compound having two or more functional groups reactive with the polyethyleneimine polymer. May be a compound,
Usually, an epoxy compound having good reactivity is preferably used. In this case, the epoxy equivalent is preferably from 50 to 700 WPE, particularly from 100 to 700 W to achieve both sensitivity and water resistance.
Preferably it is 250 WPE. Specifically, a commercially available product can be used. For example, as a sorbitol polyglycidyl ether, Nagase Kasei's Denacol EX-6
11, 612, 614, 614B etc., as sorbitan polyglycidyl ether, Nagase Kasei Denacol EX-651, 651A etc., as polyglycerol polyglycidyl ether, Nagase Kasei Denacol EX-512, 521 etc., pentaerythritol poly As glycidyl ether, Nagase Kasei Denacol EX-411 etc., as diglycerol polyglycidyl ether, Nagase Kasei Denacol EX-421 etc., and as triglycidyl tris (2-hydroxyethyl) isocyanurate, Nagase Kasei Denacol EX-411 etc. 301
Etc., as glycerol polyglycidyl ether, Nagase Kasei Denacol EX-313, 314, etc., as trimethylolpropane polyglycidyl ether, Nagase Kasei Denacol EX-321, etc., and as neopentyl glycol diglycidyl ether, Nagase Kasei. Denacol EX-2
11 etc., as ethylene glycol diglycidyl ether, Nagase Kasei Denacol EX-810, 811 etc., as polyethylene glycol diglycidyl ether, Nagase Kasei Denacol EX-850, 851, 821, 830, 832, 841, 8 as polyethylene glycol diglycidyl ether.
61 and the like, and propylene glycol diglycidyl ether includes Denacol EX-911 manufactured by Nagase Kasei, and polypropylene glycol diglycidyl ether includes Denacol EX-941, 920, 921, 931 manufactured by Nagase Kasei.

In addition to epoxy compounds, crosslinking agents include polyfunctional carboxyl compounds, polyfunctional aldehyde compounds, polyfunctional carbonyl compounds, polyfunctional alkyl halide compounds, polyfunctional isocyanate compounds, polyfunctional thioisocyanate compounds, and active double bonds. A compound having two or more,
There are polyfunctional acyl halide compounds and the like. In addition, there are polyfunctional compounds containing two or more combinations of two or more of the above functional groups.

The crosslinking agent is usually used alone, but may be used in combination of two or more in some cases.

The number of active protons contained in amino groups and imino groups present in a polyethyleneimine-based polymer such as polyethyleneimine, and the number of functional groups in the crosslinker reacting with groups having these active protons are as follows. And the ratio
1: 0.05 to about 1: 1, especially 1: 0.1 to 1: 0.
It is preferable to add so as to be about 3. The weight ratio between the polyethyleneimine polymer and the crosslinking agent is 1: 0.1.
１ ： 1: 3.9, particularly preferably 1: 0.2-1: 1.4. With such an addition amount, appropriate water resistance can be imparted, and detection from low humidity to high humidity becomes possible. In contrast, when the amount of the cross-linking agent is reduced, the insolubilization due to cross-linking is not sufficient, the water resistance is reduced, and the composition of the moisture-sensitive film changes due to the outflow of the resin in a high-humidity atmosphere. It is difficult to maintain the characteristics. When the amount of the cross-linking agent is increased, the cross-linking density becomes extremely high, the adsorption of water is hindered by steric hindrance, the detection shifts to high humidity, and the film loses its elasticity. Many cracks occur, making it very difficult to maintain initial properties.

As described above, a polyethyleneimine-based polymer such as polyethyleneimine is appropriately modified or grafted with a reactive organic compound having a functional group reactive therewith, and is appropriately crosslinked. Its water absorption becomes 10 to 20% (mass percentage) at 25 ° C and 50% RH. With such a water absorption rate, it is possible to return to the initial characteristics even when exposed to a high humidity atmosphere, and to obtain a sufficient sensitivity. As the water absorption rate increases, the change in resistance increases. However, when exposed to a high-humidity region, the resistance value may not return to the original state while increasing. If the water absorption rate is low, the polymer will not swell sufficiently during moisture absorption, and the sensitivity will be low.

Such a modified or grafted polyethyleneimine-based polymer is usually used alone.
In some cases, two or more kinds may be used in combination.

The conductive particles used in the present invention include carbon-based particles such as carbon black and graphite, and metal powders such as nickel, gold, silver and copper. Particularly, carbon black and the like are preferably used. Carbon black has a specific surface area of 30 to 300 m ² / g,
It is preferably from 150 to 150 m ² / g, particularly preferably from 30 to 75 m ² / g. The average particle size of the primary particles of carbon black is preferably 20 to 50 nm, and those having a well-developed structure are preferable, and the DBP oil absorption is 100 ml / 100 g or more (usually 15
0 ml / 100 g or less) is preferable. In general, it is preferable that the average particle size of the conductive particles (when the particles are not spherical particles, the diameter when the projected area is converted into a circle) is about 20 nm to 3 μm.

The filling amount of the conductive particles in the moisture-sensitive film of the present invention is preferably 5 to 40% (mass percentage) in the case of carbon black, more preferably 10 to 30%.
(Mass percentage). If the filling amount of conductive particles is small,
The resistance value during drying becomes too high, and the resistance value changes when repeatedly exposed to a dry atmosphere and a high humidity atmosphere. On the other hand, if the amount is too large, the change in the resistance value with respect to the change in the humidity becomes small, and the sensitivity as a moisture-sensitive element decreases. The other conductive particles may have a filling amount according to this.

The moisture-sensitive film in the present invention is a coating film of a dispersion containing a polyethyleneimine-based polymer such as polyethyleneimine, a reactive organic compound having a functional group reactive therewith, a crosslinking agent and conductive particles. And cured. In this case, the amount ratio of the polyethyleneimine-based polymer, the reactive organic compound having a functional group reactive therewith, and the cross-linking agent is regulated as described above, so that after curing, it has appropriate water resistance and Flexibility is provided. In addition, by curing, the reactive organic compound having a functional group reactive with the polyethyleneimine-based polymer is substituted with an amino group or an imino group of the polyethyleneimine-based polymer, but a part thereof is in a free state. Or they may interact with each other in a state that does not lead to bond formation. Similarly, some polyethyleneimine-based polymers that are not modified or grafted may be present.

In the above, modification or grafting with a reactive organic compound is carried out together with curing of the coating film, and this is preferred. However, in preparing the dispersion, modification or grafting with the reactive organic compound is performed in advance. Polyethyleneimine-based polymer may be used.

The dispersion medium or solvent for preparing the above-mentioned dispersion is preferably a solvent having a polarity such as alcohol or water, and particularly preferably ethyl cellosolve (ethylene glycol monoethyl ether).

As a coating method, a screen printing method is usually used.

The coating is preferably cured by heat treatment. After forming the coating, the coating is cured at a temperature of about 120 to 180 ° C. for about 30 minutes to 3 hours. When heat treatment (crosslinking) is performed in the presence of oxygen, oxidation or decomposition of a polyethyleneimine-based polymer such as polyethyleneimine occurs, and the amount of absorbed moisture is reduced. Therefore, the heat treatment (crosslinking) is preferably performed in an inert atmosphere.

The dry thickness of the moisture-sensitive film thus obtained is preferably 15 μm or less, particularly preferably 8 to 12 μm. Thereby, permeation of moisture is sufficiently ensured.

The hardness of the moisture-sensitive film is preferably 3H or a film softer than 3H (usually about 3H to B) expressed in pencil hardness according to JIS K 5400 at 25 ° C. and 0% RH. Pencil hardness of 5H to 9H or 9% when polyethyleneimine-based polymer such as polyethyleneimine is used as it is without being modified or grafted with an organic compound.
Compared with H, the moisture-sensitive film is plasticized or softened, cracks and the like in the moisture-sensitive film are prevented, and the initial characteristics of the element can be maintained. The hardness of the moisture-sensitive film was measured by forming a film having the same composition as the moisture-sensitive film on a glass substrate to a dry thickness of about 10 μm.

The humidity-sensitive element of the present invention is specifically manufactured as follows.

A predetermined amount of a polyethyleneimine polymer such as polyethyleneimine is diluted in a polar solvent, and a predetermined amount of a reactive organic compound having a functional group reactive with the polyethyleneimine polymer is added. In this case, a polyethyleneimine-based polymer modified or grafted with this compound in advance may be used. Further, a predetermined amount of conductive particles is added, stirred, and dispersed. A predetermined amount of a crosslinking agent is added to the dispersion, and the mixture is further stirred and dispersed. The moisture-sensitive material paste thus obtained is applied on a predetermined electrode (for example, a comb-shaped electrode), and is heat-treated under a predetermined condition in an inert atmosphere such as N ₂ gas as described above to obtain a moisture-sensitive paste. Form a film.

The moisture-sensitive element of the present invention is not limited as long as it has a moisture-sensitive film between a pair of electrodes. For example, the configuration shown in FIG. 1 may be used. The moisture-sensitive element 1 has a pair of comb-shaped electrodes 4 on an insulating substrate 2, and the pair of comb-shaped electrodes 4
It is arranged on the insulating substrate 2 via a gap 5 at a fixed distance. Then, on the insulating substrate 2 and the comb-shaped electrode 4,
As shown, a moisture sensitive film 3 is provided. An electrode terminal 6 is attached to one end of each of the comb-shaped electrodes 4. Further, as shown, a resist film 9 may be provided.

With such a configuration, a voltage is applied between both electrodes. The output voltage changes due to a change in resistance according to the humidity of the moisture-sensitive film, and the humidity is detected.

Referring to FIG. 1, as the insulating substrate 2 used in the present invention, any material may be used as long as it has good adhesion to the moisture sensitive film 3 and has electrical insulation. For example, glass, plastic, ceramic or metal coated with insulation is used.

The electrode 4 is not particularly limited as long as it is a commonly used one. For example, it contains Au, RuO ₂ , carbon particles such as carbon black and graphite, and further contains glass frit as required. A low-resistance paste or the like which is screen-printed and sintered at a high temperature can be used. The electrode substrate on which the electrodes 4 are formed is the moisture sensitive film 3
In order to enhance the affinity with, a surface treatment with a silane coupling agent or the like is preferable. Also, the electrode terminal 6
For example, an Ag-Pd alloy or the like may be used, and these may be printed by a normal method and baked at a high temperature. Further, as shown in FIG. 1, a resist film 9 made of glass or the like may be provided. The thickness and shape of the resist film 9 are not limited.

The moisture-sensitive element of the present invention is not limited to the illustrated example, but may be of various types.

Incidentally, the gap between the pair of electrodes in the present invention is usually about 0.1 to 1.0 mm.

[0071]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention together with comparative examples. The electrode substrates used in the following examples and comparative examples were manufactured as follows.

<Preparation of Electrode Substrate> An electrode obtained by forming a ruthenium oxide electrode on an alumina substrate was replaced with KBM403 (γ-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.).
Was immersed in a 5% (mass percentage) aqueous solution for 1 hour, washed with water, heat-treated at 100 ° C. for 5 minutes, and used as an electrode substrate.

Example 1 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.417 g was dissolved. To this, 0.319 g of reactive organic compound Denacol EX-145 (manufactured by Nagase Kasei Kogyo, phenol ethylene oxide glycidyl ether) reactive with polyethyleneimine and 0.20 g of carbon black (Tokai Carbon # 4500F manufactured by Tokai Carbon) were added. The mixture was dispersed for 9 minutes with a Kurabo Industries planetary stirrer KK-100. Then, crosslinker Denacol EX-512 (manufactured by Nagase Kasei Kogyo Co., Ltd., polyglycerol polyglycidyl ether, epoxy equivalent 168 WPE)
0.265 g was added and further dispersed for 1 minute to obtain a moisture-sensitive paste.

A moisture-sensitive material paste is printed by screen printing on a pair of comb electrodes made of ruthenium oxide on the alumina substrate, and then heat-treated at 165 ° C. for 1 hour in a nitrogen atmosphere to obtain a moisture-sensitive element. (See FIG. 1). The dry thickness of the moisture-sensitive film was 10 μm. Further, the hardness of the moisture-sensitive film obtained under the above conditions was HB in pencil hardness.

Example 2 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.540 g was dissolved. To this, a reactive organic compound denacol EX-192 (manufactured by Nagase Kasei Kogyo Co., Ltd., glycidyl ether alkoxide), which is reactive with polyethyleneimine, is added to 0.1%.
Add 288 g and 0.20 g of carbon black (Tokai Carbon Toka Black # 4500F) and add a Kurabo Industries planetary stirrer
Disperse with KK-100 for 9 minutes. After that, the crosslinking agent Denacol EX-
0.172 g of 512 (manufactured by Nagase Kasei Kogyo Co., Ltd., polyglycerol polyglycidyl ether, epoxy equivalent: 168 WPE) was added, and the mixture was further dispersed for 1 minute to obtain a moisture-sensitive material paste. A moisture-sensitive element was obtained in the same manner as in Example 1. The hardness of the moisture sensitive film is 3H
Met.

Example 3 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP-200 manufactured by Nippon Shokubai, number average molecular weight: 1000).
0) 0.625 g was dissolved. To this, 0.177 g of reactive organic compound 12-hydroxystearic acid reactive with polyethyleneimine and 0.20 g of carbon black (Toka Black # 4500F, manufactured by Tokai Carbon Co., Ltd.) were added, and dispersed with a Kurabo Industries planetary stirrer KK-100 for 9 minutes. did. Thereafter, 0.198 g of a crosslinking agent Denacol EX-512 (manufactured by Nagase Kasei Kogyo Co., Ltd., polyglycerol polyglycidyl ether, epoxy equivalent: 168 WPE) was added, and further dispersed for 1 minute to prepare a moisture-sensitive material paste. A moisture-sensitive element was obtained. The hardness of the moisture-sensitive film was H.

Example 4 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.359 g was dissolved. To this, 0.30 g of reactive organic compound X22-173DX (Shin-Etsu Chemical Co., Ltd., epoxy-modified silicone oil) reactive with polyethyleneimine and carbon black (Tokai Carbon # 45 manufactured by Tokai Carbon Co., Ltd.)
00F) Add 0.20 g, and add Kurabo's planetary agitator KK-100 to 9
Dispersed for minutes. Thereafter, 0.341 g of a cross-linking agent Denacol EX-512 (manufactured by Nagase Kasei Kogyo Co., Ltd., polyglycerol polyglycidyl ether, epoxy equivalent: 168 WPE) was added, and further dispersed for 1 minute to obtain a moisture-sensitive material paste. A wet element was obtained. The hardness of the moisture-sensitive film was 2H.

Comparative Example 1 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.612 g was dissolved. 0.20 g of carbon black (Tokai Carbon # 4500F) is added to the mixture, and the mixture is dispersed with a Kurabo Industries planetary stirrer KK-100 for 9 minutes. The cross-linking agent Denacol EX-512 (Nagase Kasei Kogyo, polyglycerol polyglycidyl ether) , Epoxy equivalent 168WPE) 0.38
8 g was added, and the mixture was further dispersed for 1 minute to obtain a moisture-sensitive paste.

A moisture-sensitive paste was printed by screen printing on a pair of comb-shaped electrodes formed of ruthenium oxide on an alumina substrate, and then heat-treated at 165 ° C. for 1 hour in a nitrogen atmosphere to obtain a moisture-sensitive element. The amount ratio of polyethyleneimine to the crosslinking agent was the same as in Example 1. The moisture-sensitive film had a hardness of 9H or a film harder than 9H.

Comparative Example 2 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.759 g was dissolved. 0.20 g of carbon black (Tokai Carbon # 4500F) is added to the mixture, and the mixture is dispersed with a Kurabo Industries planetary stirrer KK-100 for 9 minutes. Then, the crosslinking agent Denacol EX-512 (Nagase Kasei Kogyo, polyglycerol polyglycidyl) Ether, epoxy equivalent 168WPE) 0.24
1 g was added and further dispersed for 1 minute to prepare a moisture-sensitive paste, and a moisture-sensitive element was obtained in the same manner as in Comparative Example 1. The ratio between polyethyleneimine and the crosslinking agent was the same as in Examples 2 and 3. The moisture-sensitive film had a hardness of 5H.

Comparative Example 3 1 g of ethyl cellosolve was mixed with polyethyleneimine (SP200 manufactured by Nippon Shokubai, number average molecular weight 1000
0) 0.512 g was dissolved. 0.20 g of carbon black (Tokai Carbon # 4500F) is added to the mixture, and the mixture is dispersed with a Kurabo Industries planetary stirrer KK-100 for 9 minutes. Then, the crosslinking agent Denacol EX-512 (Nagase Kasei Kogyo, polyglycerol polyglycidyl) Ether, epoxy equivalent 168WPE) 0.48
Add 8 g and disperse for another minute to obtain a moisture-sensitive paste
A moisture-sensitive element was obtained in the same manner as in Comparative Example 1. The amount ratio between polyethyleneimine and the crosslinking agent was the same as in Example 4.
The moisture-sensitive film had a hardness of 9H or a film harder than 9H.

<Evaluation, Results and Discussion> First, the humidity responsiveness of the moisture-sensitive elements of Examples 1 to 3 was measured. Humidity from 0% RH to 100% in a thermostat at a temperature of 25 ° C
After observing the resistance change of the humidity-sensitive element when the temperature was rapidly changed to RH, the change with time when the atmosphere was rapidly returned to the 0% RH atmosphere was also observed. The results are shown in FIG.

From these results, it was found that when the voltage was changed to 100% RH, the resistance value rapidly changed by about 3.5 to 4 digits, and the response almost converged within one minute for all the elements, and thereafter, the resistance value changed for 30 minutes. Little change was observed and very high sensitivity and responsiveness were obtained. Thereafter, when the atmosphere was returned to the 0% RH atmosphere, the change in resistance value converged within 5 to 10 minutes, and the resistance value returned to the dry state before the exposure to 100% RH. From this, it was recognized that the device has extremely sharp response, small hysteresis, and can withstand repetitive operations.

Next, the resistance-humidity characteristics of the humidity sensitive devices of Examples 1 to 3 and Comparative Examples 1 and 2 at the initial stage (Initial) and the humidity sensitive devices of 0% RH
The resistance-humidity characteristics after repeated exposure for more than 500 cycles for 10 minutes each in the atmosphere of 100% RH and the atmosphere of 100% RH were shown.
These results are shown in FIGS. 3 to 5 and FIGS. Example 1
3 and Comparative Example 2 after 563 cycles, and Comparative Example 1 after 606 cycles.

In each of the moisture-sensitive elements of Examples 1 to 3,
Humidity of less than 60% RH (particularly 40 to 50% RH) was detectable, and after the response, the resistance increased by about 3.5 to 4 digits from the resistance at the time of drying.

On the other hand, the humidity-sensitive element of Comparative Example 1 using polyethyleneimine and a crosslinking agent and no reactive organic compound showed 0% RH and 100% RH with respect to the initial resistance and humidity characteristics.
The characteristics after repeated exposure showed a remarkable change, and it was almost close to the insulator even in the low humidity area, and the insulating property was further increased in the high humidity area, making it impossible to measure the resistance.

Similarly, the humidity-sensitive element of Comparative Example 2 in which no reactive organic compound was used was different from the initial resistance-humidity characteristic.
In the characteristics after repeated exposure to 0% RH and 100% RH, the resistance during dry operation increases by more than two orders of magnitude, and the range of change in resistance after response is small. Further, the resistance at the time of the initial dry operation is about 10 kΩ, and sufficient characteristics and reliability as a moisture-sensitive element cannot be obtained.

In Example 1, the amount ratio of polyethyleneimine and the crosslinking agent was the same as that of Comparative Example 1, and the reactive organic compound Denacol EX-145 was used to determine the number of active hydrogens contained in the amino group and imino group of polyethyleneimine. In Examples 2 and 3, Comparative Example 2 was added so that the ratio of the group having an active proton to the functional group reacting with the group having an active proton was 1: 0.1.
The ratios of the reactive organic compounds denacol EX-192 and 12-hydroxystearic acid were the same, and the number of active hydrogens contained in the amino and imino groups of polyethyleneimine, and the number of active protons Are added so that the ratios of the functional group reacting with the group having the formula are 1: 0.1 and 1: 0.05, respectively. By adding the reactive organic compound, 0% RH and 100%
Even after repeated exposure to RH for more than 500 cycles, the change in resistance-humidity characteristics from the initial stage became very small.

For the humidity-sensitive devices of Example 4 and Comparative Example 3, the initial resistance-humidity characteristics and the resistance-humidity characteristics after leaving the devices in a high-temperature and high-humidity state of 60 ° C. and 95% RH for 300 hours or more are shown. Examined. These results are shown in FIGS. Both 3
After leaving for 51 hours.

The humidity-sensitive element using the polyethyleneimine and the cross-linking agent of Comparative Example 3 and no reactive organic compound was characterized in that the initial resistance / humidity characteristics after drying at 60.degree. The resistance at the time increases by about 1.5 digits, and sufficient reliability as a moisture sensitive element cannot be obtained.

On the other hand, in Example 4, the amount ratio of polyethyleneimine and the cross-linking agent was the same as that of Comparative Example 3, and the reactive organic compound X22-173DX was replaced with polyethyleneimine at a weight ratio of 1: Although it was added so as to be about 0.85, the change in the resistance-humidity characteristics from the initial stage became very small even when the compound was left in a high-temperature and high-humidity atmosphere for 3 OO hours or more.

Example 5 A copolymer of ethylene imine and propylene imine (ethylene (-) was added to 1 g of ethyl cellosolve.
CH ₂ -CH _2- ) unit: trimethylene unit (-CH ₂ -CH ₂ -CH _2- ) =
(8: 2 (molar ratio): number average molecular weight 10,000). To this, 0.3 g of reactive organic compound Denacol EX-145 reactive with such a polyethyleneimine-based polymer and 0.2 g of carbon black were added, and the mixture was dispersed for 9 minutes with a Kurabo Industries planetary stirrer KK-100. . afterwards,
0.3 g of a crosslinking agent Denacol EX-512 was added, and the mixture was further dispersed for 1 minute to obtain a moisture-sensitive material paste. A moisture-sensitive element was obtained in the same manner as in Example 1. The hardness of the moisture-sensitive film was 3H.

This moisture-sensitive element was subjected to a 0% RH atmosphere and a 100% RH atmosphere.
The resistance-humidity characteristics after repeated exposure to the RH atmosphere for 10 minutes for 500 cycles or more did not change from the initial characteristics, and the same effects as in Examples 1 to 3 were observed.

Example 6 0.4 g of partially methylated polyethyleneimine was dissolved in 1 g of ethyl cellosolve.
The number average molecular weight of such a polyethyleneimine is 1000, ethylene (-CH ₂ -CH ₂ -) units: propylene (-CH (CH ₃₎
—CH ₂ —) units = 9: 1 (molar ratio). To this, 0.3 g of reactive organic compound Denacol EX-145 reactive with polyethyleneimine and 0.2 g of carbon black
Was added and dispersed with a Kurabo Industries planetary stirrer KK-100 for 9 minutes. Then add 0.3g of crosslinker Denacol EX-512,
After further dispersing for 1 minute, a moisture-sensitive paste was obtained.
A moisture-sensitive element was obtained in the same manner as described above. The moisture-sensitive film has a hardness of 3
H.

This moisture-sensitive element was subjected to a 0% RH atmosphere and a 100%
The resistance-humidity characteristics after repeated exposure to the RH atmosphere for 10 minutes for 500 cycles or more did not change from the initial characteristics, and the same effects as in Examples 1 to 3 were observed.

[0096]

According to the present invention, direct current can be measured and 6
Humidity in a low humidity range of less than 0% RH can be detected, and a moisture-sensitive element having good sensitivity and responsiveness and having high characteristic stability against repeated operation can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing one configuration example of a moisture-sensitive element of the present invention.

FIG. 2 is a graph showing humidity response characteristics of the moisture-sensitive elements of Examples 1 to 3.

FIG. 3 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Example 1.

FIG. 4 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Example 2.

FIG. 5 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Example 3.

FIG. 6 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Example 4.

FIG. 7 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Comparative Example 1.

FIG. 8 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Comparative Example 2.

FIG. 9 is a graph showing resistance-humidity characteristics of the humidity-sensitive element of Comparative Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Moisture sensitive element 2 Insulating substrate 3 Moisture sensitive film 4 Electrode 5 Gap 6 Electrode terminal 9 Resist film

Claims (8)

[Claims] 1. A moisture-sensitive element having a moisture-sensitive film containing a hygroscopic polymer and conductive particles dispersed in the hygroscopic polymer between a pair of electrodes, wherein the hygroscopic polymer is Polyethyleneimine polymer modified with reactive organic compound having functional group reactive with polyethyleneimine polymer, or reactive organic compound having functional group reactive with polyethyleneimine polymer grafted A moisture-sensitive element comprising a modified polyethyleneimine-based polymer and crosslinked with the polyethyleneimine-based polymer. 2. The method according to claim 1, wherein the reactive organic compound having a functional group reactive with the polyethyleneimine polymer is an aldehyde compound, a ketone compound, an alkyl halide compound, an isocyanate compound, a thioisocyanate compound, a compound having an active double bond, An epoxy compound, a cyanamide compound, a guanidine compound, a urea compound, an acid, an acid anhydride, or an acyl halide compound, wherein the moisture-sensitive film is plasticized by modification or grafting with these reactive organic compounds. Moisture sensitive element. 3. The hardness of the moisture-sensitive film is J at 25 ° C. and 0% RH.
3H or 3 in pencil hardness according to IS K5400
3. The moisture-sensitive element according to claim 1, wherein the moisture-sensitive element is a film that is more flexible than H. 4. The moisture-sensitive element according to claim 1, wherein the molecular weight of the polyethyleneimine-based polymer skeleton subjected to the modification or grafting is 300 to 70000 in number average molecular weight. 5. An alkylene group bonded to N in a polyethyleneimine-based polymer skeleton subjected to modification or grafting, wherein each of the alkylene groups may have a substituent.
The moisture-sensitive element according to any one of claims 1 to 4, wherein the element is at least one selected from an ethylene group, a trimethylene group, and a tetramethylene group and contains an unsubstituted ethylene group. 6. Among the alkylene groups bonded to N,
The ratio of unsubstituted ethylene groups is 20 to 100 mol%, and at least one selected from ethylene groups having substituents and methylene groups, trimethylene groups, and tetramethylene groups which may have substituents, respectively. The moisture-sensitive element according to claim 5, wherein the content is 0 to 80 mol%. 7. The moisture-sensitive element according to claim 1, wherein the conductive particles are carbon black. 8. A method for manufacturing a moisture-sensitive element having a moisture-sensitive film containing a hygroscopic polymer and conductive particles dispersed in the hygroscopic polymer between a pair of electrodes, wherein the moisture-sensitive film is Of a moisture-sensitive element obtained by curing a coating film of a dispersion liquid containing a polyethyleneimine polymer, a reactive organic compound having a functional group reactive with the polyethyleneimine polymer, a crosslinking agent, and conductive particles. Production method.