JP3418561B2 - Conductive particle-polymer strain sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a system in which conductive particles are dispersed in a polymer such as plastic or rubber, a particle chain is formed by contact of particles, and a conductive circuit is formed in the system. The present invention relates to a sensor for measuring extensional strain by measuring the amount of increase in the electric resistance of the system as a result of increase in the electric resistance of the system when it is expanded by external force.

The main field of application of this technology is the safety monitoring of steel frame structures and reinforced concrete structures. Buildings, bridges, elevated roads, tunnels, dams, and other structures in modern society are almost entirely composed of structures made of steel frames and reinforced concrete. It goes without saying that the safety confirmation of these steel frames and reinforced concrete is the main theme of Japan, which is an earthquake-prone country. Moreover, if a computer-based information system is installed, real-time online monitoring is possible anywhere in Japan.

In addition to the above-mentioned structures, it is possible to monitor unequal settlement of tanks of the heavy chemical industry by an online system. In addition, it is stipulated by the Hazardous Materials Handling Law,
It is also possible to inspect dangerous goods storage, such as an underground tank, at any time during normal work, without taking out the contents and inspecting them on the inspection day.

In addition to the above, it can also be installed in ships, megafloats, aircraft, large vehicles, etc. to contribute to safety management.
In particular, megafloats are currently towing and inspecting docks after a certain period of time, so enormous costs are required. If the number of times the dock is used can be reduced by installing the sensor as in the present invention, it will lead to a large cost saving.

[0005]

2. Description of the Related Art Conventionally, for steel structures and reinforced concrete structures, it is necessary to check the safety of the main structure, that is, breakage, cracks, etc., of the main structure unless the fire-resistant coating material or concrete of the external structure is peeled off. I couldn't. In recent years, there has been a demand for a technique for confirming the safety of steel frames, reinforcing bars, etc., without destroying any part by using a strain sensor for these structures.

These techniques include strain gauges using a meandering resistance wire, plastic film on which a meandering pattern is printed with conductive ink based on metal powder, ceramic deformation, and strain measurement by cutting carbon fibers. The vessel is known.

[0007]

Of these, the one obtained by printing a conductive ink on a film is similar to the present invention at first glance, but there are major differences as described below. In the case of a sensor printed with conductive ink, the strain of the sensor is measured from the change in resistance value. In this case, the resistance value is proportional to the strain. That is, the resistance value is a linear function of strain (linear relationship). Therefore, in order to install such a sensor in a building or the like and detect the damage caused by an earthquake, it is necessary to thoroughly calibrate the sensor. Even if strict calibration is performed, it is required that the change in sensor characteristics with time is minute. That is, it is inconvenient if there is a change in the resistance value of the sensor and it is not known whether it is due to strain or the change over time. Generally speaking,
The calibration is done at intervals of several years, but it is unknown whether the earthquake that will destroy the building is 10 years or 100 years ahead. It is required that such long-term characteristics be stable. It is questionable whether printed conductive inks have such long-term stability.

Another problem with sensors printed with conductive ink is related to the calibration of the sensor described above, but in order to maintain a constant relationship between strain and resistance, the sensor must be The printed film must exhibit certain properties. When manufacturing a large sensor, a printed film having a constant resistance value per unit length must be formed in any part of the printed part of the sensor.
Generally, although it is possible to suppress a small area to a certain characteristic, it is difficult to keep a large area to a certain characteristic. For this reason, sensors printed with conductive ink are extremely small.

Since the printed film of the conductive ink is formed by depositing metal particles, the volume resistance of the printed film is naturally limited to a certain range, and the volume resistance cannot be freely adjusted. . This is also one of the reasons why this sensor cannot be made large.

In addition to the problems mentioned above, the first drawback of conventional sensors is their small size. Taking a building as an example, the amount of steel used is enormous, and the number of places to monitor is considerable. If the sensor is small,
Innumerable sensors are required to manage buildings safely, and the increased cost is a burden. This problem becomes even more serious when it comes to elevated roads. Furthermore, these conventional sensors are expensive, so
It is virtually impossible to use it for bridges.

The second drawback of the conventional sensor is that the output from the sensor is linear as described above. Without thorough calibration of sensors and maintenance of their characteristics for decades, designing a monitoring system becomes difficult. In other words, it must be possible to clearly indicate which value is the dangerous state of the structure.

[0012]

The conductive particle-polymer strain sensor of the present invention disperses conductive particles in a polymer to form a sheet-shaped or other predetermined shape molded article, and a tension is applied to the molded article. It is a sensor that reads the elongation strain imposed on the system from the change in electrical resistance caused by the elongation of the system.

Here, in the molded product, conductive particles are mixed and dispersed in a polymer solvent solution to remove the solvent to form a sheet, or conductive particles are mixed and dispersed in a polymer solvent solution for printing. As an ink, apply the printing ink to the base film
Printing, melting and kneading conductive particles and thermoplastic polymer to disperse the conductive particles in the polymer, molding into a sheet or other predetermined shape, conductive particles and curable resin and its curing agent After mixing and dispersing, it is obtained by molding and curing.

Therefore, the conductive particles usable in the present invention include carbon black, graphite, activated carbon, carbon fiber,
Carbon whiskers, fullerenes, carbon nanotubes, metal powders, metal foils, metal fibers, insulator beads or microbeads with carbon added to the surface, mica, potassium titanate, etc.
The one to which conductivity is imparted by the treatment of D or PVD can be selected according to the application.

The polymer usable in the present invention may be any polymer as long as it has the above-mentioned conductive particles dispersed therein and has an appropriate strength and elongation at room temperature, but preferable polymers are as follows. Polyethylene, polypropylene, acrylic resin, polyester, nylon, polyvinyl chloride, polyvinylidene chloride, fluororesin, polyvinyl acetate, polystyrene, polymethylmethacrylate, polyethylmethacrylate, polyhydroxymethacrylate, polyvinylalcohol, polyacrylonitrile, Polyimide, polysulfone, polycarbonate, polyacetal, polyurethane, polyphenylene oxide, polyxylene, polyformal, polybutyral, polyoxyethylene, polyoxymethylene (amorphous), copolymers of two or more of the above polymers, rubbers, silyl Over down resins, phenol resins, modified alkyd resins, cellulose. Among them, as the copolymer of two or more polymers, a vinyl acetate-polyethylene copolymer is suitable for being mounted in various structures in a wide temperature range.

As described above, in place of the conventional expensive sensor using a printed film of carbon fiber, meandering resistance wire, and conductive ink of metal powder, conductive particles are dispersed in a polymer such as plastic or rubber. The invention of a sensor for measuring elongation strain by using a system and increasing the electric resistance of the system at the time of extension has been reached. Moreover, a unique feature of this system is that the sensor output is an exponential function with respect to distortion.
That is, when the distortion reaches a certain value, the output sharply increases, which is extremely advantageous in detecting the dangerous zone.

The sensor of the present invention is remarkably low in cost as compared with the resistance wire and the carbon fiber. As conductive particles, this is an inexpensive carbon black with good performance,
Lower cost graphite can be used, and as polymers, mass-produced rubber and plastics are available at low cost. Moreover, in the production of the sensor, the production cost is not so high because the particles are simply added and dispersed in the polymer dissolved in the solvent or melted by heating.

Electrodes were added to these systems to fabricate a sensor, and the sensor was placed around the structure where a strain can be predicted in advance, and the change in resistance was measured to receive the structure. The distortion value can be obtained. Locations with high strain rates can be estimated from the accumulation of conventional civil engineering and construction technologies, and multiple sensors can be installed in cases where it is difficult to predict.

As a measuring method, there is a method in which a lead wire is pulled out from a sensor and a terminal is provided at an appropriate position to measure periodically or after an earthquake. Alternatively, it is possible to perform on-line measurement by a computer, and when a distortion occurs, display the magnitude and position of the distortion on a screen to give a warning alert or promptly issue a repair instruction.

The method described above can also be used to monitor unequal settlement of heavy chemical plants. From the point where no subsidence occurs or the amount of subsidence is small, the sensor is fixed to this and the tank etc., the elongation due to subsidence is monitored, the subsidence at each position is constantly measured, and if there is unequal subsidence, this I can know. In addition, it is possible to know how much unequal subsidence will occur in the future, even if it cannot be called unequal subsidence at present.

Similarly, if it is installed on a ship, a megafloat, etc., it will lead to a reduction in expensive dock usage charges for inspection, and a great economic effect can be expected.

A sheet heating element in which conductive particles such as carbon are dispersed in a polymer to impart conductivity to the polymer is well known and is currently used in various fields. Some of these sheet heating elements maintain a constant temperature by themselves due to their switching characteristics. Here, the switching characteristic means the following phenomenon. That is, it shows a low electric resistance value at a low temperature, and when the temperature rises, the resistance value sharply increases from a certain temperature. When power is applied to this, a low resistance value at low temperature causes a current to flow (equivalent to switch on) and the system temperature rises, and when the temperature reaches a certain value, the current is limited due to a sharp increase in resistance (equivalent to switch off). ). It is said that the mechanism of this switching characteristic, in other words, the self-temperature control characteristic, depends on the thermal expansion of the polymer constituting the system. Therefore, in such a heating element, rapid volume expansion at the switching temperature is indispensable, so that the polymer used inevitably has a high degree of crystallinity.

Although many researchers now recognize that the principle of switching in the above-described self-temperature control heating element is thermal expansion, some do not. As a basis for the anti-heat expansion theory, it is claimed that the resistance value did not increase even if these heating elements were pulled by an external force. In addition, there is also a report that in the carbon black-polymer system, no increase in resistance value due to stretching was actually observed.

Despite some of the negative conjectures mentioned above,
We considered that the exponential increase of the resistance value can be expected when the conductive particle-polymer system is extended by an external force when the interaction between the conductive particles and the polymer is sufficiently taken into consideration. In the case of thermal expansion, it is considered that the high crystallinity, which was indispensable as a property of polymer, is not necessary in the case of stretching by external force. The difference between the amorphous polymer and the crystalline polymer is significant also in the present invention, and this point will be described later.

The present invention has been realized from the principle of a self-temperature controlling planar heating element. In the case of a self-temperature controlling planar heating element, one disclosed by a part of the present inventor (Japanese Patent Application No. 9-133
Except for No. 746), all must be crystalline polymers.
However, in the present invention, as long as it is a polymer that is stretched by receiving an external force, superiority or inferiority as a sensor appears depending on the type of the polymer that functions as a sensor regardless of the type of polymer used. It is necessary to choose the right one.

In principle, any kind of conductive particles can function as a sensor. It goes without saying that in reality it is important to select the appropriate one in consideration of usage conditions and manufacturing technology.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, EVA, which is a copolymer of polyethylene and polyvinyl acetate, is dissolved in a solvent, a predetermined amount of graphite is added and mixed, and the solvent is evaporated, followed by molding by hot pressing. Then, a sample was prepared. An external force was applied to this to make it expand, and the elongation strain and electrical resistance were measured simultaneously. As a result, the relationship between elongation strain and electrical resistance of the sample is
The results show that the electrical resistance increases exponentially with the increase of elongation strain.

There are roughly two methods for dispersing conductive particles in a polymer. One is a method in which a polymer is melted at a high temperature and conductive particles are mixed and kneaded therein. However, since the polymer has a high viscosity, it is usually kneaded by a kneader or the like to form a desired shape. An electrode may be provided on this. The method for providing the electrode is to mold the base to which the electrode is applied during the above-mentioned molding and the composition of the molten conductive particles-polymer, or to bond the electrode to the molded composition by ultrasonic waves or the like later. There is a way to do it.

The other is a so-called printing method. The polymer is dissolved in a solvent, and the conductive particles are added thereto and mixed. Basically, any solvent can be used as long as the polymer dissolves, but in view of the next printing process, one with a low boiling point is not preferred. Therefore, xylene, decalin, tetralin, etc. are usually used. In addition, a small amount of additives such as terpene oil and ethylene glycol may be added for improving the spread of the ink (conductive particle-polymer solution) and the adhesion to the printing material.

The resistance value of the sensor obtained by the above method in a strain-free state (a state where it is not stretched) can be determined by changing the size of the printed portion of the composition, the electrode interval, the concentration of conductive particles, etc. Various resistance values can be manufactured. Similarly, by selecting the concentration of the conductive particles and the electrode interval, it is possible to manufacture sensors of various sizes from several millimeters to several meters. Such selectivity has not been possible with conventional strain sensors.

According to the present invention, when the strain of the base material to be installed reaches a certain value (a value that requires caution in use or a value that leads to damage), the resistance value increases exponentially. Is possible. This is the concentration of conductive particles, the size of the sensor,
It can be realized by selecting the electrode interval. Such wide selectivity is also impossible with conventional strain sensors.

The sensor obtained in the present invention is used by closely fixing it to a steel frame / rebar. Steel frame due to earthquake or other external force
When the reinforcing bar is stretched and strained, the sensor that is in close contact with it is also strained equivalent to the steel frame and reinforcing bar. As a result, the electrical resistance of the sensor increases exponentially. Thereby, it is determined whether or not the strain received by the steel frame / rebar is within the allowable range. Since the allowable strain values for steel structures and reinforced concrete structures are currently well known, it is sufficient to design the size of the sensor etc. so that the change in electrical resistance greatly increases per the allowable value. .

As described above, the upper limit value of elongation at which the sensor has a certain relationship between strain and resistance value and the change in resistance per unit elongation strain are the concentration of particles dispersed in the system. Depends on. Therefore, the steel frame to be monitored
It is possible to design the sensor most suitable for this by fully considering the properties of the reinforcing bar and the dimensions of the part where distortion is expected to occur. In this case, the design of the sensor includes not only the shape and size of the sensor but also the particle concentration of the particle-polymer system constituting the sensor, the conductive particles to be used, and an appropriate selection of the polymer.

[0034]

EXAMPLES Example 1 A general example is shown here. As the polymer, EVA (polyethylene 20 wt%) of ethylene and vinyl acetate copolymer was used. Dissolve a predetermined amount of EVA in toluene, add a calculated amount of flake graphite (average particle size 1 μm) and mix, evaporate the solvent, thoroughly remove the solvent with a vacuum dryer, and hot press to 200 × It was molded into a sheet with a thickness of 200 mm and a thickness of 2 mm.
Cut this sheet into a dumbbell shape as shown in Figure 1,
Except for the central portion (25 mm in length), silver paste was applied to the front surface, the back surface, and the side surfaces, and this was used as an electrode.

Both ends of this sample were sandwiched and fixed by an insulating material (polyethylene film), and the electrical resistance was simultaneously measured while applying tensile strain with a tester. The mechanism of the testing machine is a computer controlled step motor that pulls the sample through several gears, the pulling length is a digital display (Sony LY41), and the electrical resistance is a digital multimeter (Advantest R6452A). It was measured and loaded into a computer. Control of the entire device and processing of measurement data were performed by a personal computer (NEC, PC9821 V16).
The tensile length was designed to be measured in μm.

The relationship between the resistance value before applying tension to the sample and the concentration of the added graphite is shown in FIG. In the device this time, due to the relationship between the digital multimeter and the interface, there is a restriction that if the resistance value exceeds 100 MΩ, it cannot be taken into the computer. Therefore, the tensile test was not conducted when the graphite concentration was less than 27.5%.
As can be seen from Fig. 2, the resistance value before applying tension is 1.15 MΩ.
To 133Ω. However, the upper limit of reading is 100 MΩ at any concentration.

The relationships between the elongation strain and the resistance value of the samples having various graphite concentrations are shown in FIGS. Here, the elongation strain is the length (2
5 mm) is expressed as a percentage (%). It should be noted that in this figure the vertical axis is linear and the scale is different in each case. When the graphite concentration is low, the resistance value before pulling is already high and there is an upper limit value for reading, so the increase in resistance appears low. In the case of 30 wt%, an exponential resistance increase is seen, and the most drastic resistance increase is seen in 32.5 wt%. In the case of 35 wt%, this violence weakens a little, and at the end of the period, the disturbance of the signal, which is considered to be due to the destruction (cracking) of the sample, appears. This is a change in mechanical properties with increasing carbon addition concentration. The system becomes hard and brittle as the carbon concentration increases. When it is 37.5 wt%, the resistance increase rate becomes low and the sample is destroyed. At 40 wt%, this tendency becomes more remarkable.

In FIGS. 3 to 8, the resistance value with respect to elongation strain is shown on the vertical axis on a linear scale. Now, the resistance value with respect to elongation strain is shown on a logarithmic scale and shown in FIGS. 9 to 14. What should be noted is that the logarithm of the resistance value and the elongation strain have a substantially linear relationship at any graphite concentration. That is,
The relationship of the equation (1) is recognized between the resistance (R) and the elongation strain (ε).

[0039]

[Equation 1]

Here, a and b mean certain constants. Number 1
It is understood that when is transformed, that is, it becomes the form of Equation 2, and the resistance increases exponentially with respect to the strain.

[0041]

[Equation 2]

Such a linear relationship between the logarithm of the resistance value and the strain has not been reported so far in any literature. Here, the tunnel current is used for explanation. It can be easily expected that pulling the sample creates a gap between the particles that were in contact with each other before the pulling, or that the gap that was present before the pulling also pulls the gap further. If the distance of this gap is sufficiently long, there is no longer electrical conduction through such a gap. However, if the gap distance is short, electric conduction through the potential due to this gap becomes possible. This kind of thing is possible in the quantum world. For example, a tennis ball cannot pass through a wall and reach the other side, but electrons can pass through a potential barrier and reach the other side. Such a phenomenon is called the tunnel effect. The tunnel current flowing through the potential due to this tunnel effect will be described below.

Probability P (E) that an electron having Ex kinetic energy in the X-axis direction moves from the left to the right in the X-axis direction across the potential barrier as shown in FIG.
When x) is obtained, it can be expressed as in Equation 3.

[0044]

[Equation 3]

Here, m, h, s, and f (x) represent mass of electron, Planck's constant, width of potential, and height of potential, respectively. Using this probability P (Ex), the tunnel current can be expressed by equation 4.

[0046]

[Equation 4]

Here, Ex represents the kinetic energy of electrons in the radial direction, and f (E) represents the Fermi-Dirac distribution. The problem is that the integration of equation 4 cannot be done mathematically. Therefore it is necessary to use some approximation. Here, the method by Simmons is used to explain the result of FIG. 4 (JG Simmons,
J. Appl. Phys. 34, 1793 (1963).). Although details regarding this are omitted, the tunnel current can be approximated by Equation 5 when the voltage applied to the potential barrier is low.

[0048]

[Equation 5]

Here, if the electric field applied to the tunnel barrier is F, then F = V / s, and this is used to divide both sides of Formula 5 by F and take the logarithm to obtain Formula 6.

[0050]

[Equation 6]

Here, s is the conductivity, that is, the reciprocal of the volume resistance. Therefore, the volume resistance r is expressed by Equation 7.

[0052]

[Equation 7]

That is, when a resistance is obtained by applying a voltage to the tunnel barrier having the width s and the relation between the resistance and the width of the barrier is obtained, it can be understood that the logarithm of the resistance and the width have a linear relationship as shown in Equation 7.

The above-mentioned relation of the equation 7 is unconditionally shown in FIGS.
It cannot be linked to the 14 results. It can be considered that there are innumerable particles in an actual sample and the gap between these particles serves as a tunnel barrier. Strictly speaking, all these tunnel barriers should be considered. For this purpose, consider the Boltzmann distribution for the width of the barrier,
Simulation was performed using an equivalent circuit. As a result, it was theoretically clarified that there is a linear relationship between the logarithm of the electrical resistance and the elongation strain in a system with many tunnel barriers (T. Kimura, N. Yoshimura, T. O.
giso, K. Maruyama and M. Ikeda, Polym. Commun., in
press.). Therefore, the results of FIGS. 9-14 can be explained by the tunnel effect.

The linear relationship between the logarithm of the resistance value and the elongation strain has been clarified. Now, the effect of carbon concentration on this relationship will be described. From the results of FIGS. 9 to 14, it was determined how many times the resistance value increased per unit elongation strain when the sample was pulled. That is, the resistance value when the strain amount has a certain value is R ₀ . From this, the unit strain amount (ε) is defined as R, which is the resistance value when the sample is stretched, and the ratio of resistance values, (R / R ₀ ) / ε is obtained from FIGS. 9 to 14, and this is plotted as a function of carbon concentration. , Shown in FIG. As you can see from Figure 16, [(R /
The value of R ₀ ) / ε] has a maximum value around 30 wt%. Therefore, if the concentration around this is selected, a strain sensor most sensitive to elongation strain becomes possible. This carbon concentration and [(R
It is considered that the relationship of / R ₀ ) / ε] can be explained as follows. That is, when the carbon concentration is low, the gap between particles is wide, and therefore the potential barrier is high in many cases, and therefore the tunnel current is extremely low and virtually no current is observed. Therefore, even if such a sample is stretched, the increase in resistance cannot be expected so much. On the contrary, when the carbon concentration is high, the particles are in direct contact with each other and the contribution of the tunnel effect is small. Therefore, it can be sufficiently predicted that the maximum value appears at a certain carbon concentration as shown in FIG.

Example 2 In Example 1, the effect of the graphite concentration was described in detail for the system of EVA and graphite.
An example in which various kinds of conductive particles are used will be shown. 94 parts by weight of EVA (vinyl acetate 25% by weight, ethylene 75% by weight) was dissolved in toluene, and this toluene solution was dissolved in Ketjen Black EC.
Was crushed in advance and the granulated particles were crushed and mixed in an amount of 6 parts by weight. This was cast on a Teflon bat to evaporate the solvent, and the composition was hot pressed into a dumbbell shape shown in FIG. 1 and silver paste was applied.

The relationship between elongation strain and electric resistance of this system was measured by the method described in Example 1. The result is shown in FIG.
It can be seen that the increase in resistance to elongation is small as compared with Example 1. However, the smaller the added amount, the larger the change in resistance value. As can be seen from the later examples, the case of Ketjen Black has the smallest resistance change. The cause of this is currently under study, but it is thought to be due to strong interaction between carbon particles.

Example 3 80 parts by weight of EVA (25 wt% vinyl acetate, 75 wt% ethylene) was dissolved in toluene, and 20 parts by weight of acetylene black was dispersed in this toluene solution in the same manner as in Example 2 and cast. After hot pressing, a dumbbell-shaped sample similar to that of Example 1 was prepared. The relationship between elongation strain and electric resistance is shown in FIG. Also in this case, the resistance value changes little with elongation strain, as in the case of Ketjen Black. Also in the case of the present embodiment and the second embodiment, when the amount of carbon added is reduced to bring it to near the percolation threshold value, the change in resistance becomes large.

Example 4 EVA (20 wt% vinyl acetate, 80 wt% ethylene) 65 parts by weight was dissolved in toluene, and this toluene solution was dissolved in Dentol WK-2.
35 parts by weight of 00B (conducting carbon by chemical vapor deposition on the surface of needle-shaped crystals of potassium titanate to give conductivity) were dispersed in the same manner as in the above-mentioned example, and elongation strain after sample preparation The electrical resistance relationship was measured and shown in FIG. In this case, unlike carbon black having an extremely fine particle size, a large resistance change was observed with a change in elongation strain.

Example 5 70 parts by weight of EVA (vinyl acetate 20% by weight, ethylene 80% by weight) was dissolved in toluene, and 30 parts by weight of mica fine particles chemically plated with nickel were dispersed in this toluene solution and cast. After hot pressing, a dumbbell-shaped sample was prepared, and the relationship between elongation strain and electric resistance was measured in the same manner as in the above examples, and the result is shown in FIG. Also in this case, as in Example 4, a large change in resistance value was observed with respect to elongation strain.

Example 6 An example in which a sensor is manufactured by using various polymers will be shown over several examples. 65 parts by weight of soft polyvinyl chloride was melted by heat, 35 parts by weight of graphite (Nippon Graphite, J-SP) was kneaded, and a dumbbell-shaped sample was prepared by pressing, and an electrode made of silver paste was applied. The relationship between elongation strain and electric resistance was obtained by the same method. The result is shown in FIG.
Also in this case, a large resistance value change was obtained with respect to elongation strain.

Example 7 To 65 parts by weight of an uncured silicone (Toray Silicone, SE9187) was added 30 parts by weight of toluene, and the mixture was stirred to reduce the viscosity.
35 parts by weight of (Nippon Graphite, J-SP) were kneaded, put in a dumbbell-shaped mold and allowed to stand, the solvent was evaporated, and vacuum drying was performed to obtain a sample. The elongation strain-electrical resistance of this sample was measured, and the results are shown in FIG. In this system, there was a problem with the adhesiveness of the silver paste. For practical use, it is necessary to take measures such as putting a metal mesh electrode in advance at the time of molding instead of the silver paste. In addition, since stress is generated in the sample when the silicone is cured, in the initial strain-resistance logarithmic relationship, the initial non-linear portion may be due to residual stress. However, if the elongation strain and the resistance value are linearly plotted, it can be seen that the resistance value sharply increases from a certain strain amount, so that it is useful as a sensor.

Example 8 65 parts by weight of unvulcanized acrylonitrile-butadiene rubber was dissolved in tetrahydrofuran, 35 parts by weight of graphite (Nippon Graphite, J-SP) was added, and cast in a dumbbell-shaped mold. An electrode was provided with silver paste, and the relationship between elongation strain and electric resistance was determined and shown in FIG. Also in this case, a deviation from linearity is initially seen in the plot of logarithm of elongation strain and resistance value, but the usefulness as a sensor can be fully recognized.

Example 9 In this example, a polymer is not dissolved in a solvent but is melted by heat melting and conductive particles are dispersed to prepare a sensor. 65 parts by weight of low-density polyethylene (Petrosene 203 manufactured by Tosoh Corporation) and 35 parts by weight of graphite (Nippon Graphite, J-SP) were kneaded using a kneader. This was hot pressed, cut into a dumbbell shape, and an electrode was formed with silver paint.
The elongation strain-electrical resistance relationship was similarly measured for this sample and shown in FIG. In this case, it has excellent linearity between the elongation strain and the logarithm of electric resistance, but it is understood that there is considerable skill in reproducibility of kneading, and quality control involves some difficulty in practical use. Was foreseen.

Example 10 From this example onward, an example in which a sensor was manufactured by the printing method and the characteristics were evaluated will be shown. EVA (ethylene 20%) 65 parts by weight is dissolved in tetralin, and graphite (Nippon Graphite, CSP) 35 parts by weight is added to form an ink.
It was printed on a T film (electrodes were previously printed with silver paste). The printed film was 90 microns. A sample is shown in Figure 25. The relationship between the elongation strain and the electrical resistance of this sample was determined and shown in FIG. The relationship between the logarithm of resistance and elongation strain deviates slightly from the linearity in the initial stage, but returns to a straight line immediately thereafter. When plotted on a linear scale, it was found that the electrical resistance increased sharply from a certain amount of strain, confirming its usefulness as a sensor.

Example 11 65 parts by weight of EVA (ethylene 20%) was dissolved in tetralin,
Add 35 parts by weight of graphite (Nippon Graphite, CSP) to make ink,
It was printed on a 100 micron thick polycarbonate film. This was made into the same shape as in Example 10, the elongation strain and the electric resistance were measured, and the result is shown in FIG. In this case, a good linear relationship was obtained between the logarithm of the resistance value and the elongation strain, and it was found that it could be used as a sensor.

Example 12 65 parts by weight of EVA (ethylene 20%) was dissolved in tetralin,
Add 35 parts by weight of graphite (Nippon Graphite, CSP) to make ink,
Printed on 100 micron thick rigid polyvinyl chloride film. This was made into the same shape as in Example 10, the elongation strain and the electric resistance were measured, and the result is shown in FIG. Also in this case, the same result as in Example 11 was obtained.

Example 13 65 parts by weight of EVA (ethylene 20%) was dissolved in tetralin,
Add 35 parts by weight of graphite (Nippon Graphite, CSP) to make ink,
Printed on a 125 micron thick polyimide (Ube Industries Upilex) film. This was made into the same shape as in Example 10, the elongation strain and the electric resistance were measured, and the result is shown in FIG. As can be seen from the figure, stable and good results were obtained in this case.

[0069]

As described above, when a system in which carbon is dispersed in a polymer is elongated, the electrical resistance of the system exponentially increases with respect to elongation strain. In the above example, it was also found that the resistance value increase was most sensitive to elongation strain in the system having a carbon concentration of 30 wt%. It is possible from the data presented above to design the dimensions of the sensor so that the resistance changes sharply around the strain tolerance. The fact that the sensor output is exponential with respect to strain makes it extremely easy to establish safety management standards. If the sensor output is linear, it takes a lot of effort to determine the critical value to be judged as dangerous, and the reliability of the judgment itself is also a problem. Regarding the change in sensor characteristics with time, if the sensor output increases by a two-digit resistance value with respect to the strain amount to be recognized, it can withstand use even if the sensor characteristics change by several tens of percent after a long period of time. . From this point as well, this sensor has characteristics that have not been available in the past.

In designing the elongation strain sensor from the above examples, the mechanical properties of the sensor itself are useful in addition to the value of [(R / R ₀ ) / ε]. That is, if the carbon concentration is increased, the sensitivity of resistance change to elongation strain is sacrificed, but the system can be made fragile so that the sensor can be cut. The fact that in this case a certain amount of strain has been recorded is due to the fact that the fracture is a sensor break. On the other hand, when the carbon concentration is low, the restoration of the sensor after being strained can be expected to some extent. In the case of a system that constantly monitors strain, such a system having a low carbon concentration is considered to be useful.

The resistance value can be widely selected depending on the concentration of the conductive particles. It is also possible to select the distance between the electrodes to sharply increase the sensor output against the dangerous strain of the installed substrate. With these selections, a large sensor size is possible, and for the first time, a sensor for buildings, ships, megafloats, etc. has become possible.

When observing a change in electric resistance by stretching a carbon-polymer system, the following two points are important. One is the problem of carbon itself. It is conceivable that the results obtained will differ depending on the type of carbon. It is predicted that the use of Ketjen black, in which the interaction between carbon and polymer is strong, causes little change in electric resistance with respect to elongation strain. On the contrary, in the case of graphite, it can be predicted that the electric resistance change is large. In this way, by selecting the type of carbon, it is possible to manufacture a sensor suitable for the purpose.

As for the polymer, it is clear from the above-mentioned examples that, in principle, the sensor can be prepared by using any polymer within the range of elongation of the polymer. With regard to the further development of this sensor, a new development will occur by appropriately using the two elements of the mechanical properties of the polymer, elasticity and viscosity. If the polymer has a dominant viscosity, even if the external force is removed after being subjected to elongation strain, the electrical resistance tends to remain increased, and if the elastic property is dominant, the external force is applied. If removed, the resistance value will easily return to the original state. In this way, it is possible to discriminate between viscoelasticity and use it as a sensor for constant monitoring or as a type in which the sensor is examined only after receiving an external force.

[Brief description of drawings]

FIG. 1 is a plan view showing the shape of a sample sensor, in which a silver paste is applied except for the gray portion (including the front surface, the back surface, and the side surface) in the central portion.

FIG. 2 is a graph showing the relationship between the resistance value at zero tension and the amount of carbon added.

FIG. 3 is a graph showing a relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 27.5 wt%).

FIG. 4 is a graph showing the relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 30 wt%).

FIG. 5 is a graph showing the relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 32.5 wt%).

FIG. 6 is a graph showing the relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 35.0 wt%).

FIG. 7 is a graph showing the relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 37.5 wt%).

FIG. 8 is a graph showing a relationship between electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 40.0 wt%).

FIG. 9 is a graph showing the relationship between the logarithm of the electrical resistance of a carbon-EVA (PE 20 wt%) based sensor and elongation strain (carbon concentration: 27.5 wt%).

FIG. 10 is a graph showing the relationship between the logarithm of electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 30 wt%).

FIG. 11 is a graph showing the relationship between the logarithm of the electrical resistance of a carbon-EVA (PE 20 wt%) based sensor and elongation strain (carbon concentration: 32.5 wt%).

FIG. 12 is a graph showing the relationship between the logarithm of the electrical resistance of a carbon-EVA (PE 20 wt%) based sensor and elongation strain (carbon concentration: 35.0 wt%).

FIG. 13 is a graph showing the relationship between the logarithm of electric resistance and elongation strain of a carbon-EVA (PE 20 wt%) sensor (carbon concentration: 37.5 wt%).

FIG. 14 is a graph showing the relationship between the logarithm of the electrical resistance of a carbon-EVA (PE 20 wt%) sensor and the elongation strain (carbon concentration: 40.0 wt%).

FIG. 15 is an explanatory diagram of a tunnel barrier. The electrons pass through the barrier φ (x) of width s and height quantum mechanically.

FIG. 16 is a graph showing a relationship between a resistance increase ratio per unit elongation strain and carbon concentration.

[Fig. 17] 6 wt% Ketjen Black-EVA (ethylene 7
5%) is a graph showing the relationship between elongation strain and electrical resistance.

FIG. 18: 20 wt% acetylene black-EVA (ethylene 7
5%) is a graph showing the relationship between elongation strain and electrical resistance.

FIG. 19: 35 wt% Dentol WK-200B-EVA (Ethylene 8
It is a graph showing the relationship between the elongation strain of 0%) system and the electrical resistance.

FIG. 20 is a graph showing a relationship between elongation strain and electric resistance of a 30 wt% nickel-plated mica-EVA (ethylene 80%) system.

FIG. 21 is a graph showing the relationship between elongation strain and electric resistance of 35 wt% graphite (J-SP) -hard polyvinyl chloride system.

FIG. 22 is a graph showing the relationship between elongation strain and electric resistance of a 35 wt% graphite (J-SP) -soft polyvinyl chloride system.

FIG. 23 is a graph showing the relationship between elongation strain and electric resistance of a 35 wt% graphite (J-SP) -acrylonitrile-butadiene rubber system.

FIG. 24 is a graph showing the relationship between elongation strain and electric resistance of a 35 wt% graphite (J-SP) -low density polyethylene (Petrosene 203 manufactured by Tosoh Corp.) system.

FIG. 25 is a plan view showing the shape of a printed sample in which electrodes on both left and right sides are provided with silver paste.

FIG. 26 is a graph showing the relationship between elongation strain and electric resistance of a 35 wt% graphite (CSP) -EVA PET printed sample.

FIG. 27 is a graph showing the relationship between elongation strain and electrical resistance of a sample obtained by printing a 35 wt% graphite (CSP) -EVA system on a polycarbonate film.

FIG. 28 is a graph showing the relationship between elongation strain and electric resistance of a sample obtained by printing 35 wt% graphite (CSP) -EVA system on a hard polyvinyl chloride film.

FIG. 29 is a graph showing the relationship between elongation strain and electrical resistance of a sample obtained by printing a 35 wt% graphite (CSP) -EVA system on a polyimide film.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyoaki Kimura 75 Yamatogaike, Arako-machi, Nakagawa-ku, Nagoya, Aichi Prefecture (72) Inventor Tadashi Fujisaki 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd. In-company (56) Reference JP-A-7-243805 (JP, A) JP-A-9-100356 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 7/16 G01L 1/00

Claims (4)

(57) [Claims] 1. A composition in which conductive particles are dispersed in a polymer .
In the strain sensor consisting of, the conductive particles are graphite.
The composition in which the polymer is an ethylene-vinyl acetate copolymer
The product is a sheet- shaped molded product, and the molded product is a steel frame structure or iron.
Must be installed in close contact with the surface of a reinforced concrete structure.
Then, from a change in electrical resistance caused by tension acting on the structure and elongation of the system, a sensor for reading elongation strain imposed on the system is a conductive particle-polymer structure steel structure, reinforced concrete structure Strain sensor for objects . 2. The steel structure of conductive particles-polymer system according to claim 1, wherein the molded product is formed by mixing and dispersing conductive particles in a solvent solution of a polymer, removing the solvent, and molding into a sheet.
Strain sensor for objects and reinforced concrete structures . 3. The molded product is obtained by mixing and dispersing conductive particles in a solvent solution of a polymer to form a printing ink, applying the printing ink on a substrate film and printing the molded product to form a sheet. Conductive Particles-Polymer-Based Steel Structures and Reinforcing Bars
Strain sensor for concrete structures . 4. The conductive particle-polymer according to claim 1, wherein the molded product is obtained by melting and kneading conductive particles and a thermoplastic polymer to disperse the conductive particles in the polymer, and molding into a sheet. Strain sensor for steel frame structure and reinforced concrete structure .