阅读说明：本技术 气体检测器 (Gas detector ) 是由 竹内雅人 古野纯平 福井健太 井泽邦之 佐井正和 三桥弘和 谷口卓史 于 2019-07-25 设计创作，主要内容包括：在本发明的气体传感器中,在壳体内收纳有气体检测部,经由安装于壳体的过滤器将壳体外的气氛气导入气体检测部。过滤器为具有酸性基团或碱性基团且透气性的有机高分子膜。(In the gas sensor of the present invention, the gas detection unit is housed in the case, and the atmosphere outside the case is introduced into the gas detection unit through the filter attached to the case. The filter is an organic polymer membrane having acidic groups or basic groups and having gas permeability.)

1. A gas detector for introducing an atmospheric gas into a gas detection unit through a filter, wherein the filter is an air-permeable organic polymer film having an acidic group or a basic group.

2. The gas detector according to claim 1, wherein the gas detector is a gas sensor having a housing that houses the gas detection unit and has the filter attached thereto, in addition to the gas detection unit and the filter.

3. The gas detector according to claim 1 or 2, wherein the organic polymer film has a carboxyl group as an acidic group or an amino group as a basic group.

4. The gas detector according to claim 1 or 2, wherein the organic polymer film is a film of a polysaccharide.

5. The gas detector according to claim 1 or 2, wherein the organic polymer film is a film of carboxymethyl cellulose having a carboxyl group or a film of chitosan having an amino group.

Technical Field

The present invention relates to a gas detector such as a gas sensor, and more particularly to a filter thereof.

Background

An organic polymer gas-permeable membrane such as PTFE (polytetrafluoroethylene) is known as a filter of a gas sensor (for example, patent document 1: japanese patent application laid-open No. 2008-128687A). Such an organic polymer gas permeable membrane allows small molecules such as hydrogen to permeate rapidly, but allows gases having a large molecular weight to permeate only slowly. Therefore, the organic polymer gas permeable membrane is promising as a filter for siloxane gas.

Patent document 2 (japanese patent application laid-open publication No. 2011-. Ion exchange resins are believed to effectively absorb or adsorb siloxane gases. Further, it is considered that the ion exchange resin is, for example, in the form of beads, and Nafion is supported on a silica carrier. Patent document 3(WO2017-138190a) discloses that if mesoporous silica contains a sulfonic group, siloxane molecules can be polymerized in the mesoporous silica.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2008-128687A

Patent document 2: japanese patent laid-open publication No. 2011-

Patent document 3: WO2017-138190A

Disclosure of Invention

Problems to be solved by the invention

It is believed that: if an organic polymer gas-permeable membrane is exposed to siloxane gas for a long period of time, siloxane molecules accumulate in the membrane and eventually permeate through the membrane, poisoning the gas detection unit.

The present invention addresses the problem of preventing the permeation of siloxane molecules by fixing the siloxane molecules to an organic polymer breathable film.

Means for solving the problems

The present invention is characterized in that, in a gas detector for introducing an atmospheric gas into a gas detection unit through a filter, the filter is an organic polymer film having an acidic group or a basic group and having gas permeability. Preferably, the gas detector is a gas sensor, and includes a housing that accommodates the gas detector and has a filter attached thereto, in addition to the gas detector and the filter. In addition, the filter may be provided outside the housing of the gas sensor. For example, a gas sensor without a filter may be accommodated at the base end of the suction pipe or the like, and the filter of the present invention may be provided on the upstream side of the gas flow path to the gas sensor, such as the tip end of the pipe. So configured, the filter functions the same.

The gas-permeable organic polymer film preferably has a carboxyl group as an acidic group or an amino group as a basic group. In addition, a sulfo group, a phosphoric acid group, or the like may be used. The siloxane molecules diffused into the film are fixed to the acidic group or the basic group through the moiety of- (O-Si-O) -, and are prevented from being detached from the film. And if the siloxane concentration in the film increases, the siloxane molecules that are partially hydrolyzed at- (O-Si-O) -polymerize and the siloxane becomes completely fixed to the film. As described above, by introducing an acidic group or a basic group, the siloxane becomes difficult to permeate through the film. Further, the breathable organic polymer film may be referred to as a film as described above, or a polymer film, a breathable film, or the like.

The air-permeable organic polymer film is preferably a polysaccharide film. The polysaccharide membrane is cellulose membrane, chitosan membrane, fucoidan membrane, other acidic polysaccharide membrane, etc. These polysaccharide films may originally have an acidic group such as a carboxyl group or a basic group such as an amino group, or may have an acidic group or a basic group such as a sulfo group introduced thereto. In addition to the polysaccharide membrane, an acidic group or a basic group may be introduced into a gas selective permeation membrane made of a synthetic polymer. For example, a proton conductive polymer such as Nafion or a hydroxide ion conductive polymer may be introduced. As described in patent document 1, the PTFE membrane has a gas permeability to such an extent that the response of the gas sensor is not impaired, and the cellulose membrane, the gas selective permeation membrane, and the like also have a high gas permeability, so that the decrease in the response of the gas sensor by the membrane is small.

The organic polymer film is particularly preferably a film of carboxymethyl cellulose having a carboxyl group or a film of chitosan having an amino group.

The organic polymer film is formed by casting, spin coating, spray coating, roll coating, or the like, and may be a single film or a film formed on a support film. The membrane is attached to the case, and the atmosphere outside the case passes through the membrane to reach the gas detection unit inside the case.

The mechanism of the gas permeability of the membrane is arbitrary, and for example, there may be continuous micropores having a pore diameter of the order of nm, and the mechanism of gas molecules diffusing in the micropores. Further, a large free volume (space not occupied by a polymer) may be present in the film, and gas molecules dissolved in the film may diffuse while making a transition between the free volumes.

In the present invention, the gas permeates the membrane and reaches the gas detection unit. And the function of the acidic groups and the basic groups is to fix the siloxane molecules in the film. In this case, since the molecular movement of the siloxane molecule is restricted in the film and the posture is easily fixed, the siloxane molecule is easily stably fixed to an acidic group or a basic group and reacts. In contrast, in patent document 2, a Nafion membrane is supported on a carrier such as silica, and is not a membrane that allows gas to pass through the membrane. The mechanism of removal of siloxane gas is thought to be polymerization by hydrolysis of siloxane molecules adsorbed on the film surface. Further, siloxane molecules tend to move at the interface between the nafion membrane and the gas phase, and thus it is considered that a strong functional group such as a sulfo group is required for polymerization.

Drawings

Fig. 1 is a sectional view showing a gas sensor of an embodiment.

Fig. 2 is a sectional view of a laminated film in an example.

Fig. 3 is a top view of a chip in an embodiment.

Fig. 4 is a diagram showing a driving mode of the gas sensor in the embodiment.

FIG. 5 is a graph showing the durability of siloxane (D5X 100ppm) in examples and comparative examples.

Detailed Description

The following represents the preferred embodiments for carrying out the invention.

Examples

Fig. 1 to 4 show a gas sensor 2 of an example, and fig. 5 shows test results. The gas sensor 2 includes, for example, a Si chip 4, and the Si chip 4 is an example of a gas detection unit. The Si chip 4 is housed in a case 5 made of ceramic or the like, and is fixed in the case 5 by die bonding or the like. The ceramic cover 6 covers the opening of the case 5, and supplies the atmosphere outside the case to the filter 8 through the plurality of openings 7. A film-like filter 8 is attached to the inner surface (surface on the Si chip 4 side) of the cover 6. The type of the gas detection unit and the structure of the housing are arbitrary.

The filter 8 is, for example, a porous support film 10 on which a gas-permeable organic polymer film 12 is laminated. The gas-permeable organic polymer film 12 may be simply referred to as a film 12, and the thickness of the film 12 is, for example, about 0.1 μm to 5 μm. The support membrane 10 is a synthetic resin or polysaccharide membrane having continuous pores, and has a thickness of, for example, about 1 to 100 μm. In the examples, the operation of the gas-permeable organic polymer film 12 is facilitated by the support film 10, but the support film 10 may be omitted.

The air-permeable organic polymer film 12 is formed of a polysaccharide such as carboxymethyl cellulose, sulfated cellulose, fucoidan, and chitosan, and has an acidic group or a basic group such as a carboxyl group (carboxymethyl cellulose), a sulfo group (sulfated cellulose and fucoidan), and an amino group (chitosan). In addition to these functional groups, the polymer may have a phosphate group, a basic hydroxyl group, or the like. Hereinafter, the acidic group and the basic group are simply referred to as functional groups.

In a polysaccharide film, long chain molecules are easily arranged regularly, and therefore continuous micropores are easily formed. The micropores are considered to be gas diffusion paths. Further, it is considered that hydrogen bonds between functional groups such as carboxyl groups and amino groups are responsible for the generation of regular micropores, and the functional groups are present in the vicinity of micropores. It is considered that the functional group is hydrogen-bonded to the- (O — SiO) -portion of the siloxane molecule, and reacts with the portion of the siloxane molecule by hydrolysis or the like to fix the siloxane molecule. It is also believed that if siloxane molecules accumulate within the membrane, the immobilized siloxane molecules polymerize with each other. The inventors have confirmed that: when a sulfonic group is introduced into mesoporous silica, the adsorbed siloxane molecule can be polymerized (patent document 3). The same mechanism should work within the membrane, with siloxane molecules diffusing into the membrane polymerizing by hydrolysis.

A film of carboxymethyl cellulose or the like becomes water-soluble by reaction with alkali, and becomes water-insoluble if treated with acid. Therefore, a film is formed in a water-soluble state, and a water-insoluble film can be formed by treatment with an acid. A film which is difficult to handle between a water-soluble state and a water-insoluble state can be dissolved in an appropriate solvent to form a film, and the solvent is removed to form a stable film.

In addition to the polysaccharide film, an acidic group or a basic group may be introduced into a synthetic resin film having high gas permeability known as a gas selective permeable film. Nafion can be introduced into a fluororesin-based gas selective permeable membrane, for example. Both the material of the gas selective permeation membrane (fluororesin-based synthetic resin film) and the material of the Nafion membrane are commercially available as a solution, and if they are mixed into a membrane, sulfo groups can be introduced into the gas selective permeation membrane.

Fig. 3 shows a Si chip 4, the Si chip 4 having a micro-hotplate 20 comprising electrodes and heaters on a chamber 26. The heater plate 20 is supported by a cross member 24, and a film-like metal oxide semiconductor 22 is provided on the heater plate 20. And 28 is a bonding pad.

Returning to fig. 1, the pad of the Si chip 4 is connected to a terminal 17 provided on the case 5 via a wire 16.

Fig. 4 shows the operation mode of the gas sensor 2. The gas sensor 2 operates at a cycle P, is heated to an operating temperature of about 250 to 450 ℃ during a time T1 every 1 cycle, and detects a gas from the resistance value of the metal oxide semiconductor at the time of heating.

The gas detection portion is not limited to the Si chip 4, and the detection material of the gas is not limited to the metal oxide semiconductor. For example, a contact combustion catalyst may be used as the gas detection material, and in this case, a film-shaped contact combustion catalyst may be provided on the heating plate 20, or a heater coil, not shown, may support the contact combustion catalyst. In the case of the metal oxide semiconductor 22, it may be supported by a member other than the heater plate 20. In addition, an electrochemical gas sensor in which a detection electrode and a counter electrode are connected to a liquid or solid electrolyte, or a reference electrode is connected to the electrolyte may be used as the gas detection unit. Siloxane has catalytic toxicity, and poisons Pt catalysts and the like in contact combustion gas sensors, and poisons Pt catalysts and the like in detection electrodes of electrochemical gas sensors. Therefore, poisoning of these gas sensors can be prevented by the filter of the present invention.

FIG. 5 shows the results of a durability test (100ppm of D5 for 10 days) on silicone. The gas sensor used was the gas sensor shown in FIGS. 1 to 3, and a thin film of carboxymethyl cellulose (thickness of about 0.5 μm) was used in the example (solid line) and a thin film of methyl cellulose (thickness of about 0.4 μm) was used in the comparative example (broken line). The change in sensitivity to hydrogen at 10ppm and the change in sensitivity to ethanol at 10ppm associated with the exposure to D5 were measured, and the sensitivities during and after the exposure were expressed by converting the sensitivities into the concentrations of hydrogen and ethanol from the standard curve before the exposure.

In the comparative example, the hydrogen sensitivity increased from the late stage of exposure, which is an indication of poisoning by siloxane. In the examples, no sign of toxicity of the siloxane was observed.

Data are presented for the carboxymethyl cellulose membrane. However, in other films, siloxane molecules can be immobilized in a gas-permeable organic polymer film by introducing an acidic group or a basic group into the film, and siloxane gas can be prevented from permeating by polymerizing the siloxane molecules.

The method of introducing an acidic group or a basic group into the organic polymer film is arbitrary. For example, an emulsion of water and vinyl acetate contains common salt, granulated sugar, fine oil droplets, and the like to form a film. Then, by removing salt, granulated sugar, etc. with water or removing oil droplets with oil, a porous vinyl acetate film can be obtained. When the membrane is impregnated with an aqueous solution of an organic sulfonic acid compound or the like and dried, the organic sulfonic acid compound can be introduced into the pores of the membrane. The porous organic polymer gas permeable membrane may be impregnated with an aqueous solution of an organic acidic compound or an organic basic compound, or the like, and dried, without being limited to vinyl acetate.

The concentration of the organic acidic substance or the organic basic substance with respect to the organic polymer film is arbitrary, and for example, when the pore diameter is small, the concentration is also low. When the pore diameter is large, the concentration can be increased. For example, in the case of vinyl acetate supporting the organic sulfonic acid compound, the weight ratio of the organic sulfonic acid compound to the membrane is preferably 1: 100-30: about 100.

Description of the symbols

2 gas sensor

4 Si chip (gas detector)

5 casing

6 cover

7 opening

8 Filter

10 support membrane

12 air permeable organic polymer film

16 lead wire

17 terminal

20 micro-hot plate

22 metal oxide semiconductor

24 crossbeam

26 chamber

28 pad