JP2002090325A - Filter for sensor, sensor cover, sensor and filter film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter for sensor, a sensor cover, a sensor having them, and a filter film for functioning stably with high accuracy over a long time without disturbing the responsiveness of a sensor element. SOLUTION: This filter for sensor is formed in alternately laminated structure of films containing a water-soluble cation type polymer and a water-soluble anion type polymer in a humidity sensor cover for protecting the sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for a gas sensor, and more particularly, to a protective cover for stably operating a gas sensor for detecting and quantifying a gas concentration in an atmosphere in various atmospheres. About.

[0002]

2. Description of the Related Art In recent years, humidity sensors, carbon dioxide sensors,
Various gas sensors, such as an oxygen sensor, a harmful gas sensor, and a flammable gas sensor, have been put to practical use and used in many fields. For consumer use, there are those for environmental measurement control and disaster prevention, for home electronics and car electronics, and for industrial use there are for process control and disaster prevention.

[0003] A combustible gas sensor of the contact combustion type is disclosed in 1920.
In the 1980s, it was first put into practical use as an alarm for explosion accidents in coal mines, etc., and subsequently harmful and flammable gases were detected as semiconductor-type flammable gas sensors.

On the other hand, other gases have been put into practical use by a method of measuring a change in electric characteristics such as an electric resistance value, an electrochemical type such as a current measurement, and a method of measuring a change in surface potential.

For example, as a humidity sensor, a sensor that detects humidity by a change in electric characteristics such as electric resistance has been put to practical use. Conventionally, as materials for humidity sensors (moisture sensitive materials), those using an electrolyte such as lithium chloride, those using a metal oxide, and those using an organic polymer compound are known. A polymer electrolyte having a base is widely used and widely evaluated for consumer and industrial use.

[0006] With the expansion of applications of gas sensors, gas sensors that exhibit high reliability in various environments such as corrosive gas and oily smoke contained in the use atmosphere are required. However, when these contaminants adhere to the sensor, the sensor element deteriorates, and measurement becomes impossible. Also,
Even if liquid water adheres, the gas sensor deteriorates.
Non-heated sensors are particularly susceptible because they do not actively eliminate corrosive gases, oily smoke, and the like.

As corrosive gases, there are sulfur dioxide, hydrogen chloride, nitrogen monoxide, nitrogen dioxide, hydrogen sulfide, ozone, ammonia, chlorine and the like. Above all, sulfur dioxide and nitrogen dioxide cause a chemical reaction with moisture in moisture to generate sulfurous acid and nitric acid, respectively, so that the gas sensor is severely deteriorated particularly under high humidity.

Further, the sensor is severely deteriorated by hydrogen chloride and chlorine. In such a mixed gas, it is considered that the sensor material is oxidized or deteriorated by SO ₂ ⁻ , NO ₃ ⁻ , and Cl ⁻ .

Oil smoke includes cigarette smoke, oil smoke in cooking exhaust, and the like. Among them, tobacco smoke is composed of a particulate phase that can be collected by a filter and a gas phase that passes therethrough.
It is a complex one consisting of ~ 20,000 types of chemical components.
Furthermore, due to indoor smoking, the concentration is high, and sensors that measure the indoor environment are particularly susceptible.

Therefore, it has been proposed to provide a sensor cover in order to operate the sensor stably under various atmospheres.

Japanese Patent Application Laid-Open Nos. 61-209348 and 2-107958 have proposed providing a protective cover for a porous film. Such a porous protective cover prevents water, dust and the like from entering the moisture-sensitive portion without causing a practical problem in the response of the sensor. However, since this protective cover cannot remove corrosive gas such as acid gas, the element deteriorates.For example, in the case of a resistance change type sensor using a polymer electrolyte as a moisture-sensitive material,
The device is degraded due to ion exchange of counter ions or breakage of the polymer chain, and the resistance value is disturbed.

Further, Japanese Patent Application Laid-Open No. 2-107958 proposes that a layer of a carbonate, activated carbon or carbon fiber which blocks or decomposes and adsorbs an interfering gas is provided on a porous film. . However, these substances alone have low adsorption ability and are insufficient as a sensor cover.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a sensor filter, a sensor cover, and a sensor cover that can be operated stably and with high accuracy for a long period of time without disturbing the response of the sensor element. It is to provide a sensor and a filter membrane having.

[0014]

This and other objects are achieved by the present invention described below. (1) A sensor filter for protecting a gas sensor element, wherein the filter containing a water-soluble cation-type polymer and a water-soluble anion-type polymer has an alternately laminated structure. (2) A sensor filter for protecting a gas sensor element, the sensor filter having a laminated structure in which films containing a water-soluble cationic polymer, a water-soluble anionic polymer, and a water-soluble nonionic polymer are alternately laminated. (3) The sensor filter according to (2), wherein the nonionic polymer layer contains a poorly soluble basic metal salt. (4) The sensor filter according to (2) or (3), wherein the water-soluble nonionic polymer has at least one of a hydroxy group, an acetamido group, a carbonylimide bond, and an ether bond. (5) The sensor filter according to any one of (1) to (4), wherein the sensor filter is arranged to face at least two or more surfaces of the gas sensor element. (6) The sensor cover according to any one of (1) to (5), wherein the sensor filter is disposed in a window of the sensor cover. (7) The above (1) to (1), wherein the sensor filter is provided as an adsorption layer inside the sensor cover.
The sensor cover according to any one of (5). (8) A gas sensor element having the sensor filter according to any one of (1) to (5). (9) A membrane containing a water-soluble cationic polymer, a water-soluble anion polymer and a water-soluble nonionic polymer has a laminated structure alternately, and a poorly soluble basic metal salt is added to the nonionic polymer layer. Filter membrane containing.

[0015]

The filter used for the sensor filter and sensor cover of the present invention is formed by alternately laminating membranes containing a water-soluble cationic polymer and a water-soluble anionic polymer, and adsorbs and fixes particles and gas. Have the ability to

The water-soluble cationic polymer and the water-soluble anionic polymer improve the adsorption and retention efficiency of water containing corrosive gas in humid air, and at the same time, efficiently capture charged fine particles having a certain particle size or less. It is possible to gather.
The gas once adsorbed with moisture permeates into the inside and is retained in the cationic polymer layer or the anionic polymer layer depending on the properties of the gas.

The gases that are easily retained in the cationic polymer layer include ammonia and amines, and the gases that are easily retained in the anionic polymer layer include ketones such as acetaldehyde.

Even if a water-soluble anionic polymer film or cationic polymer is applied to the filter, the collection efficiency of the charged fine particles is increased, but since the film is water-soluble, the film becomes brittle with moisture in the air and easily collapses. In the present invention, it is possible to increase the strength of the film by adopting an alternately laminated structure.

In addition, by adopting an alternately laminated structure, a cation layer and an anion layer coexist in the same film, and it becomes possible to adsorb and hold many kinds of gases.

Further, by changing the ratio of laminating the anion-type polymer layer and the cationic-type polymer layer, it is possible to impart selectivity to the gas or fine particles to be adsorbed. For example, in the case of cigarette smoke, which is a typical oily smoke, the adsorption power is maximized by laminating twice the amount of the cationic polymer layer with respect to the anionic polymer layer.

In the present invention, the filter membrane is formed by alternately laminating a membrane containing a water-soluble cationic polymer, a water-soluble anion polymer, and a water-soluble nonionic polymer containing a poorly soluble basic metal salt, and adsorbing the adsorbed gas. By decomposing the corrosive gas, the durability can be further improved.
Basic metal salts decompose corrosive gases. Basic metal salts neutralize acidic corrosive gases. Since the basic metal salt used is poorly soluble, the metal salt does not elute for a long period of time. For this reason, the durability of the sensor particularly in a corrosive gas atmosphere becomes extremely high.

As described above, the corrosive gas includes sulfur dioxide, hydrogen chloride, nitrogen monoxide, nitrogen dioxide, hydrogen sulfide,
There are ozone, ammonia, chlorine, and the like, and among them, sulfur dioxide, hydrogen chloride, nitrogen dioxide, and chlorine significantly deteriorate the sensor. The conventional protective cover cannot sufficiently prevent particularly sulfur dioxide, nitrogen dioxide and the like. The sensor cover of the present invention can sufficiently prevent the deterioration due to the corrosive acidic gas by using the basic metal salt and the water-soluble nonionic polymer in combination.

The prevention of deterioration of corrosive gas is particularly effective for a humidity sensor. Since the humidity sensor itself takes in moisture inside, the corrosive acidic gas component dissolved in the moisture easily penetrates into the inside and is easily attacked. Therefore, by using the filter membrane of the present invention, the life and reliability of the humidity sensor can be significantly improved.

When these filters have a pressure loss,
Although the response of the sensor element is affected, the filter membrane of the present invention is sufficiently effective as long as it does not disturb the response of the sensor, and there is no problem in the response of the element. In addition, since the film is formed by a solution, manufacture is easy.

The use of alternate adsorption films for filters has been proposed by Shiratori et al. (“Construction of a high-performance filter using a mass control type alternate adsorption film” IEICE Technical Report 7, (11), 1).
999). Shiratori and colleagues used a mass-controlled alternating adsorption method to accumulate electrolyte polymer alternating adsorption films on glass fibers to physically adsorb colloidal particles such as smoke by electrostatic attraction and to reduce formaldehyde gas molecules. It is proposed to give the effect of chemisorption. Since these are intended to actively collect particles and odors in the air as in an air purifier, there is no description applied to a cover or a filter for protecting the sensor element. In addition, no specific study as a filter of the sensor element has been made,
No consideration has been given to what type of device is effective. Furthermore, it is limited to charged particles and odor molecules, there is no description about corrosive gases, and further, a water-soluble nonionic polymer containing a poorly soluble basic metal salt that brings about a neutralizing action of these gases is also described. It has not been.

The following methods have been proposed as a method for removing corrosive gas. JP-A-60-20195
In Japanese Patent Application Publication No. 5 (1999) -1995, there is disclosed an air purifier used for an ink jet recording apparatus, which is provided with a corrosive gas adsorbent and an air filter disposed outside the corrosive gas adsorbent. It removes corrosive gases such as sulfur dioxide, nitric oxide, hydrogen chloride, chlorine, and hydrogen sulfide with an adsorbent, and removes dust and solids floating in the air with an air filter. Examples of corrosive gas adsorbents include granular alkaline earth metals and oxides, hydroxides, carbonates or mixtures thereof of alkaline metals, and granular activated carbon.

JP-A-5-182443 discloses a magnetic disk drive equipped with a corrosive gas adsorbent and a dehumidifier. As an adsorbent for chemically adsorbing acidic gases such as nitrogen dioxide and sulfur dioxide, carbonates, specifically, calcium carbonate are mentioned. As an adsorbent for an alkaline gas such as ammonia, calcium chloride is mentioned. In addition, silica gel is mentioned as a dehumidifier.

Japanese Patent Publication No. 7-110333 discloses a filter agent for removing particulate contaminants, and an activated carbon fiber impregnated with a chemical which cooperates with carbon to trap gas or vapor contaminants. A chemical filter assembly comprising a single filter of a structure is disclosed. Chemicals include water-soluble metal carbonates, water-soluble metal bicarbonates, soluble organic acid monomer or polymer metal salts, soluble inorganic acid metal salts, and further, sulfur dioxide, Examples include sodium carbonate for trapping hydrochloric acid or nitric oxide, and lead salts for trapping sulfides. Also, a high molecular weight water-soluble polymer can be used, and a high molecular weight amine such as polyethyleneimine for trapping an acidic gas, a high molecular weight acid such as polyacrylic acid or polysulfonic acid for trapping a basic gas, and an acidic gas can be used. Partially or completely neutralized sodium polyacrylate for trapping is also mentioned. However, none of these documents describes the effect of using a water-soluble polymer film and a basic metal salt in combination.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION A filter membrane for a sensor according to the present invention is a membrane containing at least a water-soluble cationic polymer and a water-soluble anionic polymer or, preferably, as a third layer, a poorly soluble basic metal salt and a water-soluble basic metal salt. It contains a nonionic polymer.

It is preferable that the filter membrane is disposed so as to face at least two or more surfaces of the sensor element. That is, it is located on or inside the sensor cover, usually at the cover opening or inside to protect the sensor. Also, the entire case is made of a porous film or the like,
When the water-soluble cationic polymer and the water-soluble anionic polymer or the substance capable of supporting the poorly soluble basic metal salt and the water-soluble nonionic polymer as the third layer can be directly supported on the entire case. Good. Usually, a window is provided in the case, and the window is disposed here as a filter film.

As the water-soluble cationic polymer, it is desirable to use a polyamine or an ionene polymer. Particularly, polyethyleneimine, polyallylamine, polyvinylamine and poly (amidoamine) are preferred.

As the water-soluble anionic polymer, polyacrylic acid, polymethacrylic acid, polystyrenesulfonic acid + polyethylenesulfonic acid, polyvinylsulfuric acid, polyphosphoric acid, and the above-mentioned metal salts are preferable.

Examples of the water-soluble nonionic polymer include polyvinyl alcohol, poly-2-hydroxyethyl methacrylate, poly-2-hydroxyethyl acrylate, polyethylene glycol, polyvinyl methyl ether, polyvinyl pyrrolidone, polyacrylamide, polydimethylacrylamide, and poly-N -Vinylacetamide, etc.
Alternatively, these copolymers may be mentioned. Among them, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide and the like are preferable.

Here, the water-soluble group of the water-soluble nonionic polymer is preferably a hydroxy group, an acetamido group, a carbonylimide bond, an ether bond, or the like. Further, it is preferable that these water-soluble groups have about 2 to 23 meq / g, particularly about 5 to 20 meq / g per unit mass. By using such a water-soluble polymer, the contact efficiency between the moisture of moisture containing corrosive acidic gas and the basic metal salt is increased, and the thickness of the filter film is reduced so as not to disturb the response of the sensor element. realizable.

The above three types of water-soluble polymers have a weight average molecular weight of 10,000 to 1,000,000, preferably 10,000 to 500,000. If the weight average molecular weight is larger than this, the solubility in water is reduced, and it is difficult to form a laminated film. Further, since the basic metal is difficult to disperse, the ability to decompose corrosive gas is reduced. If the weight average molecular weight is smaller than this, it will easily flow out under high humidity used as a sensor cover.

The water-soluble polymer used may be a copolymer, in which case any of random copolymerization, alternating copolymerization, and block copolymerization may be used. The monomer component of the water-soluble polymer as described above is preferably contained in the water-soluble polymer in a molar ratio of 50 to 100%. If it is less than this, sufficient moisture adsorption efficiency cannot be obtained.

Other monomer components that may be contained include methyl methacrylate, ethyl methacrylate,
Examples thereof include butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and styrene.

Further, the water-soluble polymer may have a three-dimensional cross-linked structure. Crosslinking may be by a covalent bond or by an intermolecular bond. However, since a crosslink by an intermolecular bond is reversible and unstable, a covalent bond is preferable.

The formation of a covalent bond can be obtained by crosslinking a polymer for forming a laminated film. A functional group may be introduced into the water-soluble polymer in advance, and may be formed by heat, light, radiation, plasma, or the like. As the crosslink density increases, the water absorbing power of the resin decreases. When performing crosslinking, the degree of crosslinking is preferably 20% or less, particularly preferably 5 to 15%.

As the basic metal salt, a poorly soluble basic metal salt is used. When a basic metal salt having low water solubility is used,
Metal salts are less eluted over a long period of time, and the performance of the filter and the protective cover is kept high. In the case of a basic metal salt having good solubility, a problem occurs in the long-term stability of the sensor. The solubility product of the basic metal salt used in an aqueous solution at 25 ° C. is preferably 10 ⁻⁴ or less, particularly preferably 10 ⁻⁵ to 10 ⁻¹² . The smaller the solubility product, the less the metal salt elutes and the higher the durability. However, if it is too small, the reaction efficiency with a corrosive gas such as a strongly acidic gas decreases.

As the basic metal salt, carbonates and hydroxides are preferable. For example, lithium carbonate (Li ₂ CO ₃ ),
Magnesium carbonate (MgCO ₃ ), magnesium hydroxide (Mg (OH) ₂ ), calcium carbonate (CaCO ₃ ),
Calcium hydroxide (Ca (OH) ₂ ), strontium carbonate (SrCO ₃ ), strontium hydroxide (Sr (O
H) ₂ ), barium carbonate (BaCO ₃ ), barium hydroxide (Ba (OH) ₂ ) and the like. Among them, magnesium carbonate, magnesium hydroxide and barium carbonate are preferred.

In addition, aluminum hydroxide (Al (OH)
₃ ), scandium hydroxide (Sc (OH) ₃ ), yttrium carbonate (Y ₂ (CO ₃ ) ₃ ), yttrium hydroxide (Y (OH) ₃ ), titanium hydroxide (Ti (OH) ₄ ),
Zirconium hydroxide (Zr (OH) ₄ ), vanadium hydroxide (V (OH) ₄ ), chromium hydroxide (Cr (O
H) ₂ , Cr (OH) ₃ ), manganese carbonate (MnCO
₃ ), manganese hydroxide (Mn (OH) ₂ ), ferrous carbonate (FeCO ₃ ), ferrous hydroxide (Fe (OH) ₂ ), ferric hydroxide (Fe (OH) ₃ ), water Ruthenium oxide (R
u (OH) ₃ , Ru (OH) ₄ ), cobalt hydroxide (C
o (OH) ₂ , Co (OH) ₃ ), nickel carbonate (Ni
CO ₃ ), nickel hydroxide (Ni (OH) ₂ ), palladium hydroxide (Pd (OH) ₂ ), platinum hydroxide (Pt (O
H) ₂ ), copper carbonate (CuCO ₃ ), cupric hydroxide (Cu
(OH) ₂ ), silver carbonate (Ag ₂ CO ₃ ), silver hydroxide (A
gOH), zinc carbonate (ZnCO ₃ ), zinc hydroxide (Zn
(OH) _2), cadmium carbonate (CdCO _3), lead carbonate (PbCO _3), gallium hydroxide (Ga (OH) _3),
Thallium carbonate (Tl ₂ CO ₃ ), tin hydroxide (Sn (O
H) ₂ ), lead hydroxide (Pb (OH) ₂ , Pb (OH)
₄ ) can also be used. Further, lanthanum, a carbonate of a lanthanide element and the like can be used. Note that the above basic metal salt may slightly deviate from the stoichiometric composition.

These basic metal salts may be used alone or in combination of two or more. The average particle size of the basic metal salt used is preferably 0.1 to 5 μm. If the average particle size is larger than this, the reaction efficiency with the corrosive gas decreases. If the average particle size is smaller than this, the permeability of the membrane is impaired.

The basic metal salt is used in an amount of 20 to 500% by mass, more preferably 40 to 300% by mass, based on the water-soluble nonionic polymer.
It is preferable to use mass%. If the amount of the basic metal salt is larger than this, it becomes difficult to retain the basic metal salt. When the amount of the basic metal salt is smaller than this, the reaction efficiency with the corrosive gas is reduced.

In addition, aerosil, talc,
Clay or the like may be contained in an amount of 10% by mass or less.

The method of forming the film is not particularly limited as long as the water-soluble cationic polymer and the water-soluble anionic polymer can be alternately laminated, but the following method is preferable.

An aqueous solution of a water-soluble nonionic polymer containing a water-soluble cationic polymer, a water-soluble anion polymer and a basic metal salt is prepared. At this time, the concentration is 0.1 to 10% by mass, and after sufficiently dissolving, the pH of the solution is adjusted. Desirably, the pH is adjusted to about 5.0.

Next, an initial charge is applied to the substrate on which the film is formed by a chemical treatment. For this chemical treatment, washing with an alkaline aqueous solution or the like is sufficient. A base material for forming a film is immersed in an electrolyte polymer solution having the opposite charge to the charge, and a polymer film is formed by spontaneous adsorption. At this time, when the substrate is washed with pure water, the outermost surface layer of the polymer is detached, and only the polymer firmly adsorbed on the substrate base by Coulomb force remains. Subsequently, when the substrate is immersed in an aqueous solution of the oppositely charged electrolyte polymer, the second polymer layer is laminated on the polymer layer that has already been adsorbed. When the washing is performed similarly, only the polymer firmly adsorbed on the surface of the first layer is left as the second layer. By repeating this, a laminated structure is formed. The number of laminations is not particularly limited, but is practically 2 to 200.
Times are appropriate. The nonionic polymer is usually neutral, but when the pH is adjusted to 5, it slightly dissociates and becomes anionic, so that the nonionic polymer can be laminated on the cationic polymer.

The number of layers of the cationic polymer and the anionic polymer, preferably the nonionic polymer, is 2 as described above.
To 200, particularly preferably 20 to 120. If the number of layers is too small, it is difficult to obtain the effect of gas adsorption, and if it is too large, the film becomes brittle.

The adjustment of the film thickness can be controlled by the solution temperature and the time. However, when the film thickness is more strictly controlled, it is desirable to perform the control by the adsorption mass control. In this method, the thickness of the adsorbed film is measured and controlled using a quartz oscillator or the like at the time of adsorbing the polymer. By changing the ratio of the thicknesses of the polymer layers having different charges, the properties of the entire film can be changed.

The film thickness depends on the type of the polymer and the lamination conditions, but as a stable film, one layer is about 50 to 800 °.

In addition, aerosil, talc,
Clay or the like may be contained in an amount of 10% by mass or less.

The membrane may be a laminated film of a water-soluble cationic polymer, a water-soluble anion polymer and a water-soluble nonionic polymer containing a basic metal salt. In this case, it is usually arranged inside the case.

On the other hand, it is preferable that the membrane component is supported on a nonwoven fabric, a glass filter, or the like by impregnation or the like, and this is disposed as a filter membrane in a window of a case.

In this case, the porosity of the film is preferably 30 to 80%. If the porosity is higher than this, it is difficult to sufficiently remove fine particles and corrosive gas, and the durability of the sensor element tends to decrease. If the porosity is lower than this, the response of the device becomes worse.

The pore diameter of the membrane is preferably 5 to 100 μm. If the pore diameter is larger than this, it becomes impossible to prevent water, dust and the like from entering the moisture-sensitive portion. If the pore diameter is smaller than this, the response of the device becomes worse.

The thickness of the filter membrane of the present invention is 10 to 100.
μm, the thickness of the membrane carried in the filter is 5 to 50
μm, and about 10 to 50 μm for a film. Even with such thinness, the effect of removing corrosive gas can be sufficiently obtained.

FIG. 1 is a sectional view of an example of the sensor cover of the present invention, and FIG. 2 is a front view of the sensor cover. Although the sensor 1 is exemplified as a thin film type having the sensor film 5, its shape and size are not particularly limited, and the sensor cover of the present invention can be applied to any sensor. The sensor 1 is housed in a case 2. This case 2 mechanically protects the sensor 1. Case 2 is made of polypropylene, polybutylene terephthalate (PBT), polyethylene (PE), A
A plastic material such as a BS resin is used.
The shape and size of the case 2 are not particularly limited as long as the case 1 can accommodate the sensor 1. However, the case 2 is usually substantially rectangular parallelepiped, and the lead wire 6 of the sensor 1 extends from the rear end. A window 3 is formed inside the case 2 at least facing the moisture-sensitive portion, and the other portions seal the sensor 1. Then, the filter membrane 4 of the present invention containing a laminate of a water-soluble cationic polymer, a water-soluble anionic polymer, and a water-soluble nonionic polymer containing a basic metal salt is attached along the periphery of the window 3. Have been. In this case, the filter film 4 is arranged along the inner surface from the inner surface facing the case 2. The shape and size of the window 3 are not particularly limited as long as the sensor functions sufficiently. In the illustrated example, since the sensor film 5 is formed on both sides, the configuration is such that the window 3 is provided on the opposite surface of the case 2.

When forming the filter film, in the case as shown in FIG. 1, the filter film is arranged inside or outside the case so as to prevent a window, and attached by adhesion, pressure bonding, heat fusion, or the like.
The size of the window is preferably about 80 to 200% of the effective area of the detection unit of the sensor element.

In the case where the whole case is made of a porous film or the like and is capable of supporting a dried product of the above solution, it can be applied directly to the whole case.

Although sensors having various structures are known according to the operation type, the sensor cover of the present invention is not limited to the structure of the sensor at all, and the sensor cover is exposed to a measurement atmosphere. It can be applied to all sensors as long as the basics are performed. For example, there are a humidity sensor, a carbon monoxide sensor, a carbon dioxide sensor, an oxygen sensor, an LPG sensor, a methane sensor, a hydrogen sensor, an alcohol sensor, and the like.

However, a more effective effect is provided by a passive sensor having no heating means in the element portion, in which a polymer material is used as the sensor film. In particular, moisture is taken into the sensor film. A humidity sensor for measuring a physical / chemical change of a film is preferable.

FIG. 3 is a plan view showing an example of the configuration of such a sensor. The humidity sensor shown here is a resistance value change type humidity sensor using a polymer sensor film.

As shown in FIG. 3, the sensor 1 has a pair of comb-shaped electrodes 8 on an insulating substrate 7.
Are arranged on the insulating substrate 7 via a gap 9 at a fixed distance and in such a manner that both electrodes are engaged with each other. The sensor film 5 is provided on the insulating substrate 7 and the comb-shaped electrode 8 as shown in the figure. An electrode terminal 10 is attached to one end of each of the comb-shaped electrodes 8, and a lead wire 6 is connected to each of the electrode terminals 10 using solder 11.

In such a configuration, an AC voltage is preferably applied between both electrodes. The output voltage changes due to the resistance or impedance change according to the humidity of the sensor film, and the humidity is detected. The applied voltage is about 12 V or less.

Referring to FIG. 3, the sensor film 5 is
A cationic polymer having a quaternary ammonium base is preferably used. For example, Japanese Patent Application Laid-Open No. 7-31852 described above.
No. 6 publication. Among, Cl ^- sensor cover of the present invention to those having as a counter ion is most effective. The film thickness is 0.5 to 10 μm
It is preferred that it is about.

The insulating substrate 7 may be made of any material as long as it has good adhesiveness to the sensor film 5 and has electrical insulation. For example, glass, plastic, ceramic, or metal coated with insulation. Are used.

The electrode 8 is not particularly limited as long as it is a commonly used electrode. For example, the electrode 8 contains Au or RuO ₂ , and if necessary, a low-resistance paste containing glass frit or the like is screen-printed. High temperature sintering can be used. The electrode terminals 10 are solder 11
Any material may be used as long as it is compatible with, for example, an Ag-Pd alloy or the like, which may be printed by a normal method and baked at a high temperature.

The gap 9 between a pair of electrodes in this humidity sensor is usually about 100 to 500 μm.

Further, a water-repellent film may be formed on the sensor film in order to prevent the influence of the attached water droplets and quickly and accurately measure the humidity.

The water-repellent coating preferably has a contact angle with water of 90 ° or more, particularly preferably 90 to 130 °. Also,
As the film thickness, it is necessary to ensure sufficient moisture permeation, and for that purpose, the thickness is 5 μm or less, particularly 0.1 to 2 μm.
m is preferred.

As a material constituting such a water-repellent film, a hydrophobic polymer, for example, a fluorine-based polymer such as polytetrafluoroethylene, an olefin-based polymer such as polyethylene or polypropylene, or a silicone-based polymer is preferably used. You.

The method for forming such a water-repellent film is not limited, but the above-mentioned material may be dissolved in a soluble solvent (for example, saturated fluorocarbon or the like) and applied.

[0074]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention together with comparative examples.

<Example 1> As a water-soluble cationic polymer, polyallylamine hydrochloride (PAH;
Weight-average molecular weight 10,000) and polyacrylic acid (PAA; weight-average molecular weight: 10,000) as a water-soluble anionic polymer.

First, a 3% by mass aqueous solution of each of PAH and PAA was prepared, and the pH was adjusted to 5.0 with NaOH. Polyethylene terephthalate (PET;
20 μm thick, 50% porosity, 10 μm pore diameter) Nonwoven fabric was used. It was immersed in a 10% by mass aqueous NaOH solution for 3 hours in advance to give an initial charge to the surface. PAH and PAA were alternately laminated on this filter by a mass control type alternate adsorption film forming apparatus (manufactured by Nippon Laser Electronics Co., Ltd.) to carry a laminated film. The number of laminations was 80, and the film thickness was 5 μm.

The sensor used was a comb-shaped electrode resistance change type humidity sensor using a cationic ionene polymer sensor film (film thickness: 2 μm).

Then, as shown in FIG. 1, the humidity sensor was housed in a case made of polybutylene terephthalate (PBT), and the window was covered with a PET non-woven fabric treated as described above to obtain a humidity sensor. The total area of the window was 1.5 cm ² .

First, each relative humidity (% R) of this humidity sensor
The output value (%) with respect to H) was examined. Then, it was confirmed that the relationship was almost linear.

Then, while flowing nitrogen dioxide gas, hydrogen chloride gas, ammonia gas, and sulfur dioxide gas at a concentration of 5 ppm each, the mixture was allowed to stand at a temperature of 40 ° C. and a humidity of 70 to 80% RH for 100 hours. The output value (%) of the humidity sensor with respect to (% RH) was examined, and a gas resistance test was performed. As a result, for the ammonia gas, no change was observed in the output value of the humidity sensor before and after the test. FIG. 4 shows the results.

To investigate the effect of cigarette smoke, 1 cm ³
After burning five mild sevens in an acrylic box and leaving the humidity sensor in the box for 72 hours, the output value (%) of the humidity sensor for each humidity (% RH) was examined. At the same time, a humidity sensor provided with a polyethylene terephthalate nonwoven fabric to which no alternate adsorption film was provided was also left for evaluation. As a result, the change in the output value of the humidity sensor before and after the gas resistance test was smaller in the element provided with the filter with the alternating adsorption film than in the filter without the alternate adsorption film. FIG. 5 shows the results.

<Example 2> A sensor cover was manufactured in the same manner as in Example 1 except that the PAH was set so as to have a thickness twice as large as that of the PAA to form a laminated film. , A humidity sensor was obtained. Then, the same gas resistance test and cigarette smoke test as in Example 1 were performed on this humidity sensor.

The results are shown in FIGS. As a result, for the ammonia gas and the sulfur dioxide gas, no change was observed in the output value of the humidity sensor before and after the test. In the element provided with the filter having the alternating adsorption film, no change was observed in the output value of the humidity sensor before and after the tobacco smoke test.

Example 3 As a water-soluble cationic polymer, polyallylamine hydrochloride (PAH;
Weight average molecular weight 10,000), water-soluble anionic polymer, polyacrylic acid (PAA; weight average molecular weight: 10,000), water-soluble nonionic polymer polyvinyl alcohol (PVA; weight average molecular weight: 200)
00) was used as a basic metal salt with barium carbonate (solubility at 25 ° C: 1.8 mg / 100 g).

First, PAH, PAA, PVA each 3% by mass
An aqueous solution was prepared, and twice the amount of barium carbonate as PVA was added to the PVA solution, and the pH was adjusted to 5.0 with NaOH. As a filter substrate, polyethylene terephthalate (PET; thickness: 20 μm, porosity 50%, pore diameter 10
μm) A nonwoven fabric was used. 10% wt NaOH in advance
Immersion in the aqueous solution for 3 hours gave the surface an initial charge. PAH and PAA are alternately laminated on this filter by a mass control type alternate adsorption film forming apparatus (manufactured by Nippon Laser Electronics),
PVA was laminated at a rate of once every six times to carry a laminated film. The number of laminations was 70, and the film thickness was 5.2 μm.

A sensor cover was prepared in the same manner as in Example 1 to obtain a humidity sensor. Then, a gas resistance test and a cigarette resistance test similar to those in Example 1 were performed on this humidity sensor.

The results are shown in FIGS. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

Example 4 As a water-soluble nonionic polymer, polyethylene glycol (weight average molecular weight: 1000)
A humidity sensor cover was prepared in the same manner as in Example 1 except that 0) was used to obtain a humidity sensor. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

FIG. 10 shows the results. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

Example 5 Magnesium carbonate as basic metal salt (solubility at 25 ° C .: 0.152 g / 100 g)
), Except that polyvinylpyrrolidone (weight average molecular weight: 40000) was used as the water-soluble nonionic polymer,
A humidity sensor cover was manufactured in the same manner as in Example 1 to obtain a humidity sensor. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

FIG. 11 shows the results. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

Example 6 Magnesium hydroxide as basic metal salt (solubility at 25 ° C .: 0.9 mg / 100 g)
Was prepared in the same manner as in Example 1 except that polyacrylamide (weight average molecular weight: 100,000) was used as a water-soluble nonionic polymer to obtain a humidity sensor. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

The results are shown in FIG. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

<Embodiment 7> A humidity sensor element HIS-02-04 (Hokuriku Denko Co., Ltd.) is provided on the sensor cover prepared in Embodiment 3.
Manufactured) to obtain a humidity sensor. The output value (%) for each relative humidity (% RH) was examined using a dedicated circuit.
Then, it was confirmed that the relationship was almost linear. A gas resistance test similar to that of Example 1 was performed on this humidity sensor.

FIG. 13 shows the results. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

Next, the same cigarette smoke resistance test as in Example 1 was conducted.

FIG. 14 shows the results. As a result, Example 1
As in the case of the element with the filter with the alternate adsorption film, the degree of change in the output value of the humidity sensor before and after the gas resistance test was smaller than that of the filter without the alternate adsorption film.

Example 8 A humidity sensor was obtained by mounting a humidity sensor element C7-M3 (manufactured by Shinei Co., Ltd.) on the sensor cover prepared in Example 3. The output value (%) for each relative humidity (% RH) was examined using a dedicated circuit. Then, it was confirmed that the relationship was almost linear. A gas resistance test similar to that of Example 1 was performed on this humidity sensor.

FIG. 15 shows the results. As a result, no change was observed in the output value of the humidity sensor before and after the gas resistance test for any of the gases.

Next, the same cigarette smoke test as in Example 1 was conducted.

The results are shown in FIG. As a result, Example 1
As in the case of the element with the filter with the alternate adsorption film, the degree of change in the output value of the humidity sensor before and after the gas resistance test was smaller than that of the filter without the alternate adsorption film.

<Example 9> A carbon dioxide sensor disclosed in JP-A-1998-208543 was mounted on the sensor cover prepared in Example 3 to obtain a carbon dioxide sensor.

In this carbon dioxide sensor, a solid electrolyte obtained by heat-treating a polymer having a quaternary ammonium group in the main chain and having a halogen ion as a counter ion, and a metal halide are referred to as a detection electrode. This sensor is sandwiched between poles and measures the electromotive force generated between both electrodes. Using a dedicated circuit, the output electromotive force (mv) with respect to the carbon dioxide concentration (ppm) in the atmosphere was examined. Then, it was confirmed that the relationship between the logarithm of the carbon dioxide concentration and the electromotive force was linear. This carbon dioxide sensor was subjected to the same gas resistance test as in Example 1.

FIG. 17 shows the results. As a result, there was no change in the output value of the carbon dioxide sensor between before and after the gas resistance test.

Next, the same cigarette smoke resistance test as in Example 1 was conducted.

FIG. 18 shows the results. As a result, Example 1
In the device provided with the filter having the alternating adsorption film, the degree of change in the output value of the carbon dioxide sensor before and after the gas resistance test was smaller than that of the filter without the alternate adsorption film.

Comparative Example 1 A PET nonwoven fabric filter
A sensor cover was prepared without providing an alternate adsorption film, and a humidity sensor was obtained. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

FIG. 19 shows the result. This sensor is
The output value of the humidity sensor decreased according to the standing time under the gas, and the humidity could not be detected.

<Comparative Example 2> Calcium carbonate (solubility at 25 ° C: 1.5 mg / 100 g) was used as a basic metal salt, and a water-insoluble resin was used instead of a water-soluble nonionic polymer:
Polymethyl methacrylate (weight average molecular weight: 4000
0) and a sensor cover was prepared in the same manner as in Example 1 except that a filter membrane was manufactured using ethyl cellosolve as a solvent to obtain a humidity sensor. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

The results are shown in FIG. This humidity sensor also
As in Comparative Example 1, the output value of the humidity sensor decreased after the gas resistance test, and the humidity could not be detected.

Comparative Example 3 Sodium carbonate (solubility product at 25 ° C .: 7.1 g / 100 g) was used as a basic metal salt.
A sensor cover was prepared in the same manner as in Example 1 except that polyvinyl alcohol (weight average molecular weight: 20,000) was used as the water-soluble nonionic polymer, and a humidity sensor was obtained. Then, a gas resistance test similar to that in Example 1 was performed on this humidity sensor.

FIG. 21 shows the result. This sensor is
The output value of the humidity sensor decreased according to the standing time under the gas, and the humidity could not be detected.

[0113]

As described above, according to the present invention, it is possible to stably operate the sensor element for a long period of time without disturbing the response of the sensor element.
It is possible to provide a sensor filter, a sensor cover, a sensor having the same, and a filter membrane for functioning with high accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a sensor cover of the present invention.

FIG. 2 is a front view of an example of the sensor cover of the present invention.

FIG. 3 is a plan view showing one configuration example of a humidity sensor element.

FIG. 4 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 1.

5 is a graph showing output values before and after a cigarette smoke test of a humidity sensor using the sensor cover of Example 1. FIG.

FIG. 6 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 2.

FIG. 7 is a graph showing output values before and after a cigarette smoke test of a humidity sensor using the sensor cover of Example 2.

FIG. 8 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 3.

FIG. 9 is a graph showing output values before and after a cigarette smoke test of a humidity sensor using the sensor cover of Example 3.

FIG. 10 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 4.

FIG. 11 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 5.

FIG. 12 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 6.

FIG. 13 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 7.

FIG. 14 is a graph showing output values before and after a cigarette smoke test of a humidity sensor using the sensor cover of Example 7.

FIG. 15 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Example 8.

FIG. 16 is a graph showing output values of a humidity sensor using the sensor cover of Example 8 before and after a cigarette smoke test.

FIG. 17 is a graph showing output values before and after a gas resistance test of a carbon dioxide sensor using the sensor cover of Example 9.

FIG. 18 is a graph showing output values before and after a cigarette smoke test of a carbon dioxide sensor using the sensor cover of Example 9.

FIG. 19 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Comparative Example 1.

FIG. 20 is a graph showing output values before and after a gas resistance test of a humidity sensor using the sensor cover of Comparative Example 2.

FIG. 21 is a graph showing output values before and after a gas resistance test of a humidity sensor using a sensor cover of Comparative Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Humidity sensor 2 Case 3 Window 4 Filter film 5 Sensor film 6 Lead wire 7 Insulating substrate 8 Electrode 9 Gap 10 Electrode terminal 11 Solder

Claims (9)

[Claims] 1. A sensor filter for protecting a gas sensor element, wherein the filter containing a water-soluble cation type polymer and a water-soluble anion type polymer has an alternately laminated structure. 2. A filter for a sensor for protecting a gas sensor element, wherein the film containing a water-soluble cationic polymer, a water-soluble anion polymer and a water-soluble nonionic polymer has an alternately laminated structure. filter. 3. The sensor filter according to claim 2, wherein the nonionic polymer layer contains a poorly soluble basic metal salt. 4. The sensor filter according to claim 2, wherein the water-soluble nonionic polymer has at least one of a hydroxy group, an acetamido group, a carbonylimide bond and an ether bond. 5. The sensor filter according to claim 1, wherein the sensor filter is arranged so as to face at least two or more surfaces of the gas sensor element. 6. The sensor cover according to claim 1, wherein the sensor filter is disposed in a window of the sensor cover. 7. The sensor filter according to claim 1, wherein the sensor filter is provided as an adsorption layer inside the sensor cover.
5. The sensor cover of any one of 5. 8. A gas sensor element having the sensor filter according to claim 1. 9. A film containing a water-soluble cationic polymer, a water-soluble anionic polymer and a water-soluble nonionic polymer has an alternately laminated structure, and the nonionic polymer layer contains a poorly soluble basic metal. Filter membrane containing salt.