JPS6412305B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a conductive composition used for conductive films, heat absorbers, electrode materials, etc. Structures of conventional examples and their problems Recently, attempts have been made to impart conductivity to organic materials, which were originally known as insulators, and to create unique properties that could not be achieved with inorganic metals, semiconductors, or oxides. It is actively carried out. There are a number of such attempts, and charge transfer type complex compounds are a particularly representative example. Examples of low-resistance organic materials created using this idea include tetracyanoquinodimethane, polyacetylene, polyparaphenylene, and polypyrrole. Also,
Graphite and graphite fibers can also be made to have lower resistance using the same concept. However, a common drawback of these charge transfer type complex compounds is that the charge transfer interaction is inherently very weak, making it difficult to obtain highly stable compounds. A second important alternative method involves the formation of pyrolytic polymers. This is an attempt to obtain a highly conjugated compound that is polycondensed by thermal decomposition starting from a certain special material.The product is mainly carbonaceous, but the starting material The feature is that the conductivity is controlled.
Pyrolytic polymers have a long history and are a material that attracted attention in the early 1960s. For example, in the thermal decomposition of polyacrylonitrile by the Russian school, an electrical conductivity of 2 Scm ^-1 was obtained (AVAirapetjanc et al., DoKl
(Akad.Nauk SSSR, Vol. 148, p. 605, 1963) Furthermore, in 1964, Mr. SDBruck of IBM created a conductor of 20 Scm ^-1 by thermally decomposing polyimide (Kapton H film of DuPont) at 800°C. It has been discovered that it is possible to obtain The types of polymer materials that can become highly conductive through such thermal decomposition are limited, but as a result of our research, we have developed heat-resistant polymers that have been obtained through recent advances in condensation polymer chemistry. Several have been proposed as having this possibility. Examples of the polymer compound include aromatic polyamide, polyamideimide, polyoxathiazole, polythiadiazole, polybenzimidazole, polybenzoxazole, polybenzthiazole, and the like. These materials are pyrolyzed at temperatures between 400 and 1100°C in vacuum or in an inert gas stream.
Gives conductivity of 100Scm ^-1 or more, maximum 500Scm ^-1 .
Based on these discoveries, the present inventors have developed a new method for producing conductive materials, a method for producing thin films by chemical or physical methods, and a method for producing new conductive materials in binders by mixing them with metals such as gold, nickel, copper, and silver. proposed a conductive composition dispersed in The pyrolytic polymer thus obtained is characterized by high electrical conductivity and chemical and thermal stability, and the powder obtained from it is well compatible with many polymeric binders and organic solvents. These characteristics are clearly exhibited in conductive compositions in which pyrolytic polymers are dispersed as powders in polymeric binders, making it possible to form conductive films that cannot be obtained with conventional carbon black or graphite. Make it. However, when producing conductive compositions using the pyrolytic polymers developed to date either alone or by mixing them with metal powders such as silver, there are several unsatisfactory points. These are: (1) The electrical conductivity of the pyrolytic polymer is 500 Scm ^-1 or less. In particular, it is difficult to obtain an electrical conductivity of 100 Scm ^-1 or higher with relatively low-cost polyamideimide and polyesterimide; (2) there is a limit to their thermal stability in air;
(3) Since pyrolytic polymers are carbonaceous materials, conductive compositions containing a large amount of them have poor solderability. (4) As raw materials for pyrolytic polymers. The condensation polymers mentioned are often high-cost in the amounts currently used. OBJECTIVE OF THE INVENTION The purpose of the present invention is to propose a new pyrolytic polymer that improves these drawbacks, especially its electrical conductivity and cost. The purpose of this invention is to propose a conductive composition. That is, in the present invention, a raw material for a pyrolytic polymer that can be obtained as a solution of polyamic acid, etc. is selected, graphite is dispersed in the solution, and after a curing treatment, it is pyrolyzed to improve the above-mentioned drawbacks. The present invention aims to produce an electrically conductive pyrolytic composition. Structure of the Invention Next, the polymer materials and additives which are the constituent elements of the present invention will be specifically explained. As polymer materials, condensed polymers having a heterocycle containing any of nitrogen, oxygen, or sulfur, or condensed polymers without heterocycles such as aromatic polyamides may be used alone or in copolymers. used in the form The first step in preparing the composition of the present invention begins with uniformly dispersing the additives in the solution of the condensation polymer. Therefore, as the polymer material, one obtained in the form of a solution is used, and it is preferable to use it in the form of an intermediate solution of the condensed polymer as described above. For example, polyimide resin is obtained by the reaction of dicarboxylic acid anhydride and diamine, but it is used as an intermediate, for example, A polyamic acid represented by the formula is obtained,
It can be handled relatively stably as a solution dissolved in an amide solvent. Furthermore, polyamideimide can be obtained by, for example, reacting isophthaloyl chloride and m-phenylenediamine with pyromellift acid anhydride, but in the same way as in the case of polyimide. A polyamic acid intermediate with the structure is obtained,
Obtained as a solution in acetamide, xylene, cresol, etc. Similarly, in the case of polyesterimide, it is possible to handle it as a polyamic acid intermediate solution. Also,

[Formula] is an intermediate of polyoxadiazole,

A compound having a unit of [formula] is an intermediate of polybenzoxazole,

[Formula] is an intermediate of polybenzthiazole,

[Formula] is an intermediate for polybenzimidazole. Polythiadiazole also has intermediates, all of which are soluble in N-methylpyrrolidone and/or acetamide. To obtain a desired heat-resistant polymer from these intermediate solutions, the solution is applied onto a substrate, the solvent is dried, and the reaction is further carried out at a temperature of 80°C to 320°C. This final stage reaction is, for example, This is a cyclization reaction that accompanies dehydration by heating, and any reaction that causes a ring-closing dehydration reaction by such heating can be used. Next, graphite is used as an additive added to the polymer solution. Graphite improves the electrical conductivity of the pyrolytic polymer and also significantly contributes to reducing the cost of the resulting composition. Furthermore, in order to improve the dispersibility of graphite in a polymer solution, it is effective to add a surfactant such as sodium oleate as a dispersant. Inorganic silica powder, aluminum oxide, zinc oxide, zinc sulfide, etc. can also work effectively as dispersants. Next, a general method for manufacturing the conductive composition of the present invention will be described. First, the above-mentioned additives are mixed into a polymer solution having a polymer content of 30 to 45 weight percent, and thoroughly kneaded using blade stirring or three rollers. Next, this solution is spread on a glass plate or the like and heat-treated at a temperature of 80 to 320°C. In this step, the solvent is scattered, and at the same time a curing reaction proceeds, resulting in a solid film. Next, this film is peeled off from the glass plate, filled into a quartz tube, heated slowly while flowing an inert gas such as nitrogen into the tube, and heat-treated at a temperature of 700 to 1100°C for 30 minutes or more. If the thermal decomposition temperature is lower than 700°C, a large amount of NH component remains and the conductivity does not improve. Therefore, the temperature is preferably 700°C or higher. On the other hand, when the temperature exceeds 1100°C, the C ratio exceeds 98%, so the dispersibility of the metal powder becomes poor and the effect of adding the metal powder is not seen. Therefore, it is preferable to keep the temperature below 1100℃, and from 700℃
A pyrolysis temperature of 1100°C is suitable. All polymers that have been treated become graphite films with metallic luster. When this film is used as a composite material such as a conductive paste, the heat-treated film must be ground for about 3 days using a ball mill and passed through a 400-600 mesh sieve to form a powder. As described above, the present invention aims to easily improve the drawbacks of conventional thermally decomposed polymers by adding an inorganic additive to a condensed polymer solution and then thermally decomposing it. This is an attempt to significantly improve the above-mentioned drawbacks of internal conductivity and cost by dispersing and adding graphite powder. Looking at the structure of the conductive composition of the present invention from another perspective, this can be said to be a novel method for surface modification of graphite.
Graphite is crushed and dispersed in a polymer binder and used as a composite conductive film. Taking advantage of its higher conductivity than carbon black, it can be used as an additive to carbon black-based conductive pastes and silver pastes. It is used. In this case, since graphite does not have active groups on its surface, it has poor dispersibility in polymers, and in order to improve this, various complex surface treatment methods have been proposed and implemented. However, as mentioned above, the pyrolytic polymer powder that is the basis of the present invention is highly dispersed in many polymer binders and organic solvents, so the graphite dispersed in this pyrolytic polymer is can be considered to be surface-modified to improve dispersibility. Examples are given below to show specific examples and effects of the present invention. Description of Examples Example 1 Polyamide-imide resin manufactured by Hitachi Chemical Co., Ltd. (trade name
Natural graphite 625 mesh powder was added to HI-400 (a 30% solution containing acetamide and xylene as solvents). Kneading was carried out using blade stirring for about 2 hours, and after a completely dispersed solution was obtained, the solution was spread on a glass substrate and heat-treated at 180° C. for 2 hours in an oven. The resulting film had a black to green luster. This film was filled into a quartz tube and thermally decomposed in a vacuum of 10 ^-3 Torr.
Although the pyrolysis temperature was 600-1100°C and the holding time was 1 hour, the conductivity of the product was strongly dependent on temperature and only weakly dependent on holding time. The conductivity was measured at room temperature in air using a 4-terminal electrode using silver paste and gold wire after thermal decomposition. Table 1 shows the conductivity data.

[Table] When graphite powder is not added, the electrical conductivity of pyrolyzed polyamideimide is 600, 700, 800, 900, 1000,
and 7×10 ^-4 and 0.1 for 1100℃, respectively.
5, 90, 150, and 220 Scm ^-1 , it can be seen that the addition of graphite brings about a significant improvement in electrical conductivity. Example 2 Using N-methylpyrrolidone of polyamic acid, which is a polyimide intermediate, as the polymer, Example 1
conducted a similar experiment. However, in this example, thermal decomposition was performed in a nitrogen atmosphere. The effects of the amount added and the thermal decomposition temperature on the conductivity were similar to those in Example 1, but the use of this polymer was characterized by the fact that even higher conductivity was obtained overall. Ta. Examples are shown in Table 2.

[Table] Example 3 Polyester-imide containing 60% by weight of graphite
Pyrolyzed at 800℃ for 2 hours, conductivity is approximately 500Scm ^-1
A black film was obtained. This was ground in a ball mill for 5 days and passed through a 625 mesh sieve to obtain a powder. Next, x g of this powder was added to a paste containing 8 g of silver, 3 g of polyvinyl butyral, and 6 ml of isophorone, thoroughly kneaded, and printed on an alumina ceramic substrate using a 200 mesh screen. First, regarding the results regarding the amount of x, it was possible to add only about 1.5 g for graphite and about 2 g for graphite alone, but in the case of the powder of the conductive composition of the present invention, x can easily be added up to 10 g with the above composition. It can be said that the surface has been significantly improved when looking at graphite. Next, Table 3 summarizes the relationship between x and the resistance of the printed film.

【table】

[Table] 0.009Ω/□ for the optimal composition film containing only silver powder
This means that when the conductive composition of the present invention was further added, a resistance value higher than that of silver paste but far lower than that of ordinary carbon paste was obtained. Furthermore, the ability to mix as much as 10 g as in the example leads to a reduction in the cost of silver paste, making it possible to manufacture a composite conductive film that fills the gap between silver paste and carbon paste in terms of both resistance and cost. Effects of the Invention As described above, the present invention involves dispersing graphite powder into a condensation polymer intermediate that is soluble in a solvent, and then
A novel conductive composition is provided by curing the polymer in air or a gas atmosphere at a temperature of 700 to 1100 °C, and then thermally decomposing it in a vacuum or in an inert gas stream at a temperature of 700 to 1100 °C. This significantly improves the electrical conductivity and cost, which are disadvantages of conventional simple pyrolytic polymers. This composition can be obtained in various forms, such as a flexible film, a film obtained by chemical vapor deposition or physical vapor deposition, or a composite film formed into a powder and dispersed in a polymeric binder or glass crystal.
It is widely used in conductive films, heat absorption films for solar collectors, electrode materials, magnetic recording media, sensor materials, etc. The heat-resistant condensation polymers used in the present invention are not limited to those obtained from the polyamic acid intermediate described in the examples, but include polybenzimidazole, polyoxadiazole, polybenzthiazole, polythiadiazole, etc. It is possible to use anything that causes a ring-closing dehydration reaction when heated.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of a conductor constructed using the conductive composition of the present invention, and Figures 2a and b are diagrams of a composite film element in which the powder of the conductive composition of the present invention is dispersed in a polymer binder. FIG. 2 is a plan view and a cross-sectional side view showing the configuration. 11... Conductive composition film, 12... Electrode, 21...
Composite conductive film, 22... Silver electrode, 23... Insulating substrate.

Claims (1)

[Claims] 1. Graphite powder is dispersed and added to an intermediate solution of an aromatic polyamide, a condensed polymer having a heterocycle containing at least one of nitrogen, oxygen, or sulfur, or a copolymer thereof. A method for producing an electrically conductive composition, which is characterized by carrying out a heat treatment at a temperature of 80 to 320°C in air or a gas atmosphere, and further heat treating at a temperature of 700 to 1100°C in a vacuum or an inert gas. 2. Production of the conductive composition according to claim 1, wherein the condensation polymer is any one of polyimide, polyamideimide, polyesterimide, polybenzimidazole, polyoxadiazole, polybenzthiazole, and polythiadiazole. Method.