JP2903197B2 - Low molecular weight organic liquid detection sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low molecular weight organic liquid detection sensor suitable for detecting the presence of a low molecular weight organic liquid such as gasoline or light oil.

[0002]

BACKGROUND OF THE INVENTION Gasoline is mainly used as fuel for internal combustion engines, especially for automobile engines.
Gasoline is usually refueled at gas stations. As is well known, gasoline is highly volatile and very flammable, so it is necessary to pay close attention to its handling, and gas stations are strictly prohibited from fire. By the way, at a gas station, gasoline is mainly stored in a tank provided underground, and the gasoline is guided to a fuel tank of an automobile by a refueling machine. Careful refueling from the refueling machine is important, otherwise gasoline leaks from the refueling machine could lead to major accidents. The same applies to low-molecular-weight organic liquids other than gasoline.

[0003] Therefore, a sensor for detecting leakage of a low molecular weight organic liquid such as gasoline is known. As one of the sensors, a conductive sheet in which conductive carbon is dispersed in a liquid-absorbing swellable rubber or the like is always energized, and gasoline or the like expands between carbon particles due to swelling when attached to the conductive sheet. There is a method utilizing a phenomenon in which the electric resistance increases due to the above. For example, the present applicant has previously proposed a high-sensitivity sheet-like liquid detection sensor that is superior in swelling property when it comes into contact with a liquid to be sensed or its vapor as compared with conventional products (Japanese Patent Laid-Open No. 3-96846). reference).

This sheet-like liquid detection sensor is obtained by forming a conductive layer, whose electrical resistance changes when it comes into contact with a low molecular weight organic liquid, from a composition mainly composed of a thermoplastic elastomer and conductive carbon into a sheet shape. is there.

[0005]

This sheet-like liquid detection sensor is excellent in swelling property with respect to a low molecular weight organic liquid such as gasoline, has excellent detection sensitivity, and has a sufficient function in practical use. The market is eager for higher performance features.

An object of the present invention is to provide a low-molecular-weight organic liquid detection sensor that satisfies the needs of the market and exhibits an excellent sensor function.

[0007]

A low molecular weight organic liquid detection sensor according to the present invention is a sensor for detecting the presence of a low molecular weight organic liquid by a change in electric resistance due to swelling of a conductive layer. It is formed of a composition mainly composed of a plastic elastomer, conductive carbon and an oil absorbing agent, and has a Shore A hardness of 70 or less and is not crosslinked.

[0008]

In the sensor of the present invention, since the oil absorbing polymer is blended in the conductive layer of the sensor portion, the degree of swelling of the conductive layer can be increased when the conductive layer comes into contact with a low molecular weight organic liquid. Therefore, even in the presence of a trace amount of a low-molecular-weight organic liquid or vapor, the change in electric resistance can be increased and a highly sensitive sensor can be obtained.

Hereinafter, the present invention will be described in more detail. In the low molecular weight organic liquid detection sensor of the present invention, a sensor portion is manufactured using a conductive layer formed of a composition mainly composed of a thermoplastic elastomer, conductive carbon, and an oil absorbing agent as a sensor portion.

The thermoplastic elastomer, the conductive carbon and the oil-absorbing polymer are not particularly limited. Examples of the thermoplastic elastomer include styrene / ethylene / butadiene / styrene copolymer (SEBS) and styrene / butadiene / styrene copolymer. Examples include coalesced (SBS), polybutadiene-based elastomer, and olefin-based elastomer.

In the present invention, the thermoplastic elastomer is characterized in that it is not crosslinked. The term “uncrosslinked” as used herein is a concept including a material which has been partially crosslinked to make it thermoplastic. That is, in the present invention, the uncrosslinked thermoplastic elastomer includes not only a polymer which is not subjected to crosslinking after forming the conductive layer but also a completely uncrosslinked polymer, but also a polymer which is partially crosslinked before processing. Things. It is desirable that such a composition be uncrosslinked and have a Shore A hardness (hardness of rubber) of 70 or less, preferably 65 or less, and particularly about 50.

Here, as the conductive carbon, in particular,
DBP oil absorption 250ml / 100g or more, surface area 500m
Conductive carbon black of ² / g or more (for example, Ketjen Black of Lion), furnace black (for example, vulcan XC-72 of cabot, USA), acetylene black (for example, electrified acetylene black of Denki Kagaku Kogyo) and the like are preferable.

Examples of the oil absorbing agent include natural plant oil absorbing agents such as rice husk, straw, pulp, peat, and cotton; inorganic oil absorbing agents obtained by subjecting inorganic porous powders such as coal, silica, and pearlite to water repellency; and polypropylene. Known are synthetic fiber oil absorbers such as fibers, polystyrene fibers, and polyethylene fibers, foamed resin oil absorbers such as foamed polyurethane foam, and synthetic resin oil absorbers of a type that absorbs and swells oil in certain polymers. . Among these, a synthetic resin-based oil absorbing agent can be preferably used, but the degree of swelling of the conductive layer can be increased,
In particular, a swellable oil-absorbing polymer comprising a crosslinked polymer of a specific (meth) acrylate monomer (JP-A-3-221592)
Is preferred.

The oil absorbing agent has a large degree of swelling upon contact with the liquid to be detected, and physically blocks the conductivity of the conductive layer. Therefore, the change in electrical resistance is caused even by the presence of a small amount of liquid or vapor. It becomes larger and the sensitivity of the sensor can be increased. Therefore, the oil absorbing agent is an important component for causing the sensor to exhibit a target sensor function.

The mixing ratio of the thermoplastic elastomer and the conductive carbon is 10 to 100% by weight, preferably 12 to 90% by weight, particularly preferably 15 to 80% by weight, based on 100% by weight of the elastomer. . If the amount of the conductive carbon is less than 10% by weight, the conductivity is low, and the detection sensitivity of the sensor is poor. If the amount is more than 100% by weight, the amount of the added compound is too large and the viscosity of the compound becomes unfavorable. .

The mixing ratio of the thermoplastic elastomer to the oil absorbing agent is 2 to 40% by weight, preferably 5 to 30% by weight, particularly preferably 15 to 25% by weight based on 100 parts by weight of the thermoplastic elastomer. %. If the content of the oil-absorbing agent is less than 2% by weight, the effect of improving swellability is not recognized. If it exceeds 40% by weight, the oil-absorbing agent is not uniformly dispersed in the thermoplastic elastomer, which is not preferable.

The above-mentioned composition is usually prepared by kneading a thermoplastic elastomer and conductive carbon into a blend, then blending the blend with an oil-absorbing polymer and kneading the blend.

The composition may be formed by extrusion molding, press molding,
A conductive layer is formed on a sheet or core material by a method such as coating to form a low molecular weight organic liquid sensor.
At this time, the conductive layer is uncrosslinked and has a Shore A
Hardness (hardness of rubber) is 70 or less, preferably 65 or less,
It is particularly preferably about 50 from the viewpoint of the liquid absorption swelling property and workability.

FIG. 1 is a side view showing the basic structure of a low molecular weight organic liquid detection sensor according to the present invention. In the drawing, 1 is a core material, 2 is mainly composed of a thermoplastic elastomer, conductive carbon and an oil-absorbing polymer, and has a Shore A hardness of 7
A conductive layer made of an uncrosslinked material having a value of 0 or less is shown. And a measuring instrument R having an energizing function and an electric resistance measuring function.
A pair of terminals 3a and 3b extended from the conductive layer 2
When a liquid such as gasoline or its vapor adheres to the conductive layer 2, the presence or absence of the liquid is detected from a change in the electric resistance of the conductive layer 2.

The low molecular weight organic liquid to be detected by the low molecular weight organic liquid detection sensor of the present invention is preferably an organic liquid having a molecular weight of 300 or less, particularly 150 or less, such as alcohols, lubricating oils, ketones, and light oils. , Kerosene, gasoline, naphtha, ligroin, benzene, toluene, xylene and the like.

According to the sensor having the above structure, when a low molecular weight organic liquid such as gasoline or its vapor comes into contact with the conductive layer 2, the conductive layer 2 swells and the electric resistance changes quickly.
The change in the electric resistance is detected by the measuring instrument R, and the presence of the low molecular weight organic liquid can be detected.

As described above, the low molecular weight organic liquid detecting sensor of the present invention, particularly the linear sensor, is useful as an area type sensor. For example, gasoline from underground storage tanks such as gas stations or transport pipes such as oil pipelines, etc. It is suitable for detecting leakage of light oil or the like.

The sensor of the present invention detects the presence (leakage) of a low-molecular-weight organic liquid such as gasoline. A galvanometer for detecting a change in current and, if necessary, a sound generator or a light-emitting means to easily notify that a current abnormality has been detected by the galvanometer, making it easier to perceive leakage of gasoline or the like. It is important to do so.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a low molecular weight organic liquid detection sensor of the present invention will be specifically described based on embodiments. FIG. 1 shows an embodiment, in which S is a low molecular weight organic liquid detection sensor, in which a conductive layer 2 which is a low molecular weight organic liquid detection portion is formed around a core material 1. The conductive layer 2 is formed from a composition mainly composed of a thermoplastic elastomer, conductive carbon and an oil-absorbing polymer, and is not crosslinked and has a Shore A hardness of 7
0 or less. A pair of lead wires 3a and 3b extending from the tester R are connected to both ends of the conductive layer 2.

The sensor S is installed in a refueling machine at a gas station, particularly in an internal piping system in which gasoline or the like is likely to leak, and a current is always supplied to the conductive layer 2. At this time, low-molecular-weight organic liquids such as gasoline leak from the piping system,
Alternatively, a vapor of a low molecular weight organic liquid is generated to form the conductive layer 2.
When a low molecular weight organic liquid or its vapor adheres to the surface, the adhering portion immediately starts to swell, and accordingly the electric resistance of the swollen portion increases. As the time elapses, the current flow is suppressed, and this change in current is measured in series with a measuring instrument R
To detect. If a sound or light is connected to the measuring device R to generate sound or light when a current change occurs, it is possible to easily perceive leakage of the low molecular weight organic liquid.

Example 1 Next, the detection function for a low molecular weight organic liquid was measured using a sensor having the configuration shown in FIG. (Preparation of composition for sensor) Thermoplastic elastomer 100
And 30 parts of Ketjen Black are sufficiently kneaded with a hot roll, and then swellable oil absorbing agent (manufactured by Nippon Shokubai Chemical Industry Co., Ltd.) 20
Was added and kneaded for another 20 minutes to prepare a sensor composition. This composition had a Shore A hardness of 70.
The following are uncrosslinked products.

(Preparation of Area Type Sensor) As shown in FIG. 2, a core material 10 having an outer diameter of 0.6 mm obtained by coating a soft copper wire 11 with a polyethylene coating 12 was coated with the above-mentioned composition for sensor with a thickness of 1 mm.
The linear sensor S having a length of 2 m was manufactured by coating the conductive layer 2 having a length of 50 m by extrusion. Ring-shaped electrodes 5a and 5b are attached to both ends of the conductive layer 2, the soft copper wire 11 and the electrode 5a are connected at one end of the sensor S by a lead wire 33, and the electrode 5b and the soft copper wire 11 are extended from the tester R at the other end. It was connected to a pair of lead wires 34 and 35 respectively. The initial electric resistance of the linear sensor S was 120 kΩ.

(Measurement of Sensor Function) In order to confirm the operation of the linear sensor S prepared above, a light oil layer having a thickness of about 1 mm was formed in a beaker containing water, and the U-shaped sensor was placed therein. The test piece R was used to measure the change in the electrical resistance with the lapse of the immersion time. As a result, Table 1
As shown in the figure, the electric resistance starts to increase after one minute from the immersion of the sensor, the electric resistance increases to 200 kΩ after 5 minutes, to 360 kΩ after 10 minutes, and to 1200 kΩ after 20 minutes. It was confirmed that it had excellent light oil detection ability.

Comparative Examples 1 and 2 A sensor composition having the composition shown in Table 1 was prepared in the same manner as in Example 1 except that the oil absorbing polymer was not blended. Then, using this composition in Example 1
A sensor S was prepared in the same manner as described above, and its sensor function was measured. The results are shown in Table 1.

[0030]

[Table 1]

From the above results, the sensor manufactured in the example had an excellent detection function for light oil as compared with the sensor of the comparative example.

Examples 2 to 5 In the same manner as in Example 1, a composition comprising a thermoplastic elastomer, conductive carbon and an oil-absorbing polymer was prepared as shown in Table 1.
Was prepared in the mixing ratio shown in Table 1. Then, a sensor S was prepared from the obtained uncrosslinked product having the indicated Shore A hardness. Except for using each of the sensors manufactured in the above-described example and gasoline instead of light oil, the same method as in Example 1 was performed.
The electric resistance value over time was measured with a tester R.
The results were as shown in Table 2.

[0033]

[Table 2]

As is clear from Table 2, each of the sensors has an excellent detection function for gasoline.

[0035]

As described above, the low-molecular-weight organic liquid detection sensor of the present invention has a low molecular weight such as gasoline or light oil in comparison with a comparative example in which a conductive layer is formed from a composition containing no oil absorbing agent. It has a conductive layer that quickly reacts and swells with molecular weight organic liquids. Therefore, the low-molecular-weight organic liquid detection sensor of the present invention can increase the change in electric resistance even when a very small amount of low-molecular-weight organic liquid or its vapor is present, and exhibits an ultra-sensitive sensor function.

[Brief description of the drawings]

FIG. 1 is a side view showing a configuration of a low molecular weight organic liquid detection sensor of the present invention.

FIG. 2 is a side view showing one embodiment of the low molecular weight organic liquid detection sensor of the present invention.

[Explanation of symbols]

 Reference Signs List 1 core material 2 conductive layer 3a, 3b terminal R measuring device S low molecular weight organic liquid detection sensor

Claims (3)

(57) [Claims] 1. A sensor for detecting the presence of a low molecular weight organic liquid by a change in electric resistance due to swelling of a conductive layer, wherein the conductive layer is mainly composed of a thermoplastic elastomer, conductive carbon and an oil absorbing agent. A low-molecular-weight organic liquid detection sensor, which is formed from an object and is not crosslinked with a Shore A hardness of 70 or less. 2. The low molecular weight organic liquid detection sensor according to claim 1, wherein the oil absorbing agent is a swellable oil absorbing polymer. 3. The composition according to claim 1, wherein 10 to 100 parts by weight of conductive carbon and 2 to 40 parts by weight of an oil absorbing agent are mixed with 100 parts by weight of the thermoplastic elastomer.
The low-molecular-weight organic liquid detection sensor according to the above.