JPS6114604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an electrical conductor made of an organic substance, and in particular, to obtain an electrical conductor by heat-treating aromatic polyamide in vacuum or in an inert gas.

Recently, there has been an increase in attempts to impart electrical conductivity to organic materials, which have traditionally been known as insulators, and to develop sensors and heaters with unique performance unimaginable with metal conductors. ing. In 1964, IBM's SDBruck introduced polyimide film (Kapton H film manufactured by Dupont).
By thermal decomposition at a high temperature of 800℃ or higher, 5×
It was discovered that a conductor with a specific resistance value of 10 ^-2 Ωcm can be obtained. The specific resistance value of polyimide film is 10 ¹⁸ Ωcm at room temperature, and the resistance value changes as much as 10 ²⁰ Ωcm by thermal decomposition, so this method is a method for imparting electrical conductivity to polymers. This is an excellent method. However, such a method is not necessarily applicable to all polymer films, and in fact, high conductors cannot be obtained with most polymer materials even if such a thermal decomposition method is used.
Furthermore, conductors obtained by pyrolysis are brittle;
The flexibility, which is a characteristic of polymer films, will be lost, and the maximum value of electrical conductivity will be 20 cm ^-1.
However, since the value was insufficient for an electrical conductor, subsequent research has not progressed to this day.

The basic conditions that must be met for a polymer material that can be made into a high conductor by pyrolysis are that the pyrolysis should stop at a certain stage, that the recombination reaction should proceed as the decomposition progresses, This is thought to be due to the presence of a sufficient amount of unsaturated valence states in the recombination product. However, at present, it is not clear at all what kind of molecular structure polymer materials have that satisfy such conditions. One criterion is that the melting point of the polymer material be higher than its decomposition point. This is because if the material has a melting point lower than the decomposition point, the sample will melt and evaporate before the decomposition reaction occurs. Therefore, due to these conditions, commonly known general-purpose polymer materials such as polyester, polystyrene, vinyl chloride, polyethylene, and polypropylene are excluded. Polymer materials to which the thermal decomposition method may be applied include polyimide, polybenzimidazole, and polybenzimidazole, which are generally known as heat-resistant polymers.
Possible materials include polydiphenyl ether and polyparaphenylene. However, although the condition that the melting point is higher than the decomposition point is a necessary condition, it is not a sufficient condition; for example, with polyparaphenylene, the decomposition reaction does not stop at a certain stage, so it decomposes during heat treatment. It is not possible to obtain a conductor.

Polyamide polymers are generally obtained by the reaction of aliphatic dibasic acids and diamines, and famous polymers such as nylon 6, nylon 66, and nylon 610 belong to this family. When these polyamide resins undergo the above thermal decomposition reaction, the sample melts and
Evaporation occurs and no conductor is produced. However, we have found that among polyamide resins, aromatic polyamide resins containing aromatic rings in the main chain can be made into excellent electrical conductors by thermal decomposition.

These conductors have the advantage of requiring much lower temperature heat treatment than conventional polyimide thermal decomposition methods. The present invention will be specifically explained below. Figure 1 shows that an aromatic polyamide (abbreviated as APA) having the following structure obtained from m-phenylene diamine and isophthaloyl chloride is heated in vacuum to 4
time The relationship between the specific resistance value of a conductor obtained by heat treatment and the treatment temperature is shown. The specific resistance value decreases as the processing temperature increases, reaching 5×10 ^-2 at 600℃.
reaching Ωcm. Specific resistance value is 10 ^-2 Ω at 650℃
cm, and remains almost constant even when heat treatment is performed at temperatures higher than that. i.e. heat treated APA (PAPA
It can be seen that the minimum specific resistance value of a conductor is 10 ^-2 Ωcm. This value is smaller than the resistance value of a conductor obtained by thermally decomposing a polyimide film, and it can be seen that a low heat treatment temperature is sufficient. Although the above is the case in vacuum, the same result can be obtained even in inert gas if the heat treatment time is increased.

According to SDBruck, in the case of pyrolytic polyimide, the elemental analysis values of a film heat-treated in vacuum at 620°C for 1 hour are C: 76.4%, H: 3.4%, O:
14.0%, N: 5.9%, and the elemental analysis value of the film that was similarly heat-treated at 700°C for one hour was C:
88.0%, H: 2.8%, O: 7.2%, N: 4.8%, and it is reported that almost no oxygen component exists in the film after heat treatment at 800°C. (J.
Polymer Science, C, No. 17, 169 (1967)). On the other hand, the elemental analysis values of PMPA heat-treated at 550℃ for 4 hours are C: 77.5%, H: 3.8
%, O: 10.1%, N: 8.8%, and at 650°C, C: 86.5%, H: 3.0%, O: 4.2%,
It was N6.2%. In other words, if we compare the compositions when the resistance reaches its lowest value, PAPA contains far more oxygen and nitrogen than polyimide, indicating that the structures of the two are different. .

FIG. 2 shows the relationship between the treatment temperature of PAPA obtained after 4 hours of treatment and the B constant of the obtained low antibody. The B constant of the resistor obtained at 400℃ is
3000, and the B constant of the resistor obtained at 500°C is 1700.

When processed at a temperature of 650°C or higher, the B constant becomes zero. In this way, in PAPA, its B constant and resistance value can be varied over a wide range by controlling the heat treatment temperature. Therefore, PAPA can be used not only as a simple conductor but also as a temperature sensor or a unique resistor.

In general, when using an electronic circuit to operate a temperature sensor, the optimum impedance of the sensor is
It is 10 ³ to 10 ⁷ Ω. Therefore, even if the shape of the element is modified, the specific resistance value of the resistor is 10 ¹⁰
It is desirable that it be less than Ωcm. Due to such restrictions, the heat treatment temperature for PAPA must be 400°C or higher. Of course, 10 ¹⁰ Ωcm even above 400℃
Although it is possible to set the specific resistance value to the following, it is not practical in this case because the heat treatment requires a long time.
Examples will be described in detail below.

[Example 1] In this example, electrodes are printed directly on a PAPA film and used as a resistor or conductor as is. FIG. 3 shows a configuration diagram of a parallel electrode type resistor used when the resistivity value is 10 ⁵ Ωcm or less. In the figure, reference numeral 1 denotes an insulating substrate made of ceramic, Bakelite, or the like, and a resistor film 2 is adhered onto the surface thereof. The reason why such an insulating substrate 1 is used is to supplement the mechanical strength of the sensor film. The electrode 3 is selected from conductor pastes such as carbon paste, graphite paste, silver paste, silver-palladium paste, etc., and is printed on the sensor film 2.

Figure 4 shows a 25μ thick APA film in vacuum at 650℃.
The resistance-temperature characteristics are shown when the conductor obtained by heat treatment for 4 hours is used as a parallel electrode type element. The electrodes are silver palladium and are hardened at the same time as the heat treatment. The resistance value of the element was 60Ω. The temperature dependence of the resistance temperature characteristics becomes zero over a wide range of 100 to 300°C, indicating that this element has excellent conductive characteristics. Therefore, such an element can be used as a heater by applying a constant current or voltage between the electrodes.

[Example 2] Figures 5a and 5b show the construction of a Sanderch type resistor or conductor, which is generally used when the resistivity value is 10 ⁴ Ωcm or more. Reference numeral 4 indicates an electrode coated or printed on the conductive film 2, and 4 indicates a metal foil for taking out a lead wire.
Furthermore, the entire device is coated with a coating material 5 such as epoxy.

To use such an element as a temperature sensor, for example, it is sufficient to read the resistance change of the element in response to external temperature change. A well-known method such as a Wheatstone bridge may be used to measure this resistance value. It has already been mentioned that in such a case, the internal impedance of the element is preferably in the range of 10 ³ to 10 ⁷ Ω. Basically a third option if necessary.
An element having a structure as shown in the figure or FIG. 4 may be selected. Since such an element can be essentially a thin film, it has a characteristic of faster response speed than conventional thermistors. Therefore, such an element can be used not only as a thermometer but also as a bolometer, anemometer, liquid level sensor, etc.

[Example 3] Here, an example of a composition obtained by dispersing PAPA powder in a polymer binder is shown. Linear APA
Heat treatment is performed at 700℃ for 4 hours, and after thermal decomposition, it is crushed for 2 hours using an attritor, and the powder is separated using a 400 mesh sieve. Using separated powder and polyimide resin as a binder,
The ratio of PAPA to binder was 80:20. The printing paste was thoroughly kneaded using three rolls and printed on ceramic using a 200 mesh screen.

The sheet resistance value of the printed film made in this way is
It is 30Ω/□, and the resistance change after 5000 hours at 85℃ is 10
It was within %. This excellent thermal stability is due to
It was superior to a carbon printed film obtained by a similar method.

In other words, it can be seen that the printed film using PAPA powder has excellent compatibility with the paste and does not cause instability of the resistance value due to agglomeration. This is thought to be due to the nitrogen, oxygen, hydrogen, etc. contained in PAPA.

As a binder, epoxy, polyurethane,
Phenoxy, polyamideimide, polyester,
Silicone etc. can be used.

[Example 4] Here, it is shown that it is possible to further add metal powder to the composite dispersed in the polymer binder obtained in Example 3. Metals to be added include silver, gold, nickel, copper, zinc, chromium,
Any of tin, indium, cobalt, or iron can be used, but here we will discuss silver, which is particularly commonly used.

400 meshes of PAPA powder heat treated, crushed and sieved by the method of Example 2 were mixed with silver powder in a weight ratio of 40:60. Next, a varnish containing 30% polyamide-imide resin (manufactured by Hitachi Chemical)
HI-400) and the above mixed powder were mixed at a ratio of 10:12, and further kneaded using three rolls while dropping methylpyrrolidone as a solvent to obtain a paste. The paste thus obtained was printed on an alumina substrate using a 200 mesh screen, and after curing at 200°C for about 2 hours, the electrical resistance was measured and found to be 0.3Ω/□. On the other hand, when the mixing ratio of PAPA and silver powder is 50:50, the resistance value is approximately 0.6Ω/
It became □.

The color of the printing paste made according to this example was almost the same as that of silver, and there was no change in the viscosity of the paste or agglomeration of particles, which was observed when carbon black was mixed.

As is clear from the above four examples, PAPA is widely applied as a temperature sensor, an electric conductor, and a heater. It goes without saying that the aromatic polyamide used in the present invention is not limited to aromatic polyamides obtained simply from n-phenylenediamine and isophthaloyl chloride, but can also be applied to other aromatic polyamides obtained from acid chlorides and diamines. stomach.

For example, acid chlorides include phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, terephthaloyl chloride, etc., and diamines include phenylenediamine, benzidine, diaminostilbene, diaminodiphenylmethane, diaminomephthalene, diaminoazobenzene, etc. Aromatic polyamides of the structure below can also be used.

As described above, the present invention allows polyamide containing an aromatic ring in the main chain to be heated at 400°C to 700°C in vacuum or inert gas.
This is a method for producing an electrical conductor characterized by heat treatment at °C, and provides an electrical conductor with far superior electrical conductivity at a lower temperature than conventionally known polyimide thermal decomposition products.

[Brief explanation of the drawing]

Figure 1 shows the relationship between resistivity and heat treatment temperature when the aromatic polyamide resin used in the present invention is heat treated in vacuum for 4 hours, and Figure 2 shows the relationship between the B constant and heat treatment temperature. 3 is a plan view of a resistor constructed using the conductor obtained according to the present invention, FIG. 4 is a resistance-temperature characteristic diagram of the conductor element according to the embodiment of FIG. 3, and FIG. b is a plan view and a cross-sectional side view showing another example of the structure of a resistor using a conductor obtained by the method of the present invention. 1... Insulating substrate, 2... PAPA film, 3...
Electrode, 4...Metal foil for taking out the electrode.

Claims (1)

[Claims] 1. General formula 1. A method for producing an electrical conductor, which comprises heat-treating an aromatic polyamide resin represented by: in vacuum or in an inert gas. 2 General formula 1. A method for producing an electrical conductor, which comprises heat-treating an aromatic polyamide resin represented by the formula in vacuum or in an inert gas, and mixing the obtained electrical conductor powder with a polymer binder. 3 Silver, gold, nickel, copper, zinc, chromium, tin,
3. The method of manufacturing an electrical conductor according to claim 2, further comprising mixing powder of a metal selected from the group consisting of indium, cobalt, and iron.