JPS6142949B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive composition obtained by dispersing a novel conductive powder in a binder, which is achieved by partially replacing silver in a conventional silver-based conductive film with a novel conductive material. It provides a high performance conductive film. Furthermore, the present invention uses a highly conductive material (hereinafter abbreviated as pyrolytic polymer) obtained by thermally decomposing a heat-resistant polymer as a new conductive material.
The present invention relates to a novel conductive composition characterized by using PYPO). Films obtained by dispersing silver or carbon powder in polymers are widely used, particularly in the electronics field, as conductors for printed circuit boards, resistors, or heaters. A silver-based conductive film generally has a specific resistance of 10 ^-3 Ωcm or less, and a low sheet resistance of 1 Ω/□ or less. on the other hand,
Carbon-based films have a specific resistance of 10 ^-2 Ωcm or more, and it is difficult to obtain a sheet resistance of 10 Ω/□ or less. The cost of silver-based coatings is thought to be 10 to 50 times that of carbon coatings due to fluctuations in the price of silver, and this is a new conductive film that fills the gap between silver and carbon in terms of price and performance (resistance value). The appearance of a film has long been desired. One possibility for such a purpose is to mix silver and carbon, but carbon and silver are poorly compatible and it is difficult to disperse each in a common binder. For this reason, when these are mixed, carbon agglomeration occurs, making it impossible to form a low-resistance film. Other methods include conductive films using copper or nickel, but these also have many problems with dispersibility, oxidation resistance, etc., and reliable products have not been obtained. There is also a coating using powder that coats the surface of copper with silver, but there is almost no cost advantage. In addition, as an approach from carbon, there is the addition of graphite (graphite) or the production of a graphite film, but graphite, like silver, is not compatible with carbon and is often used. Cannot be mixed. Carbon-
The general characteristics of graphite-based films include:
In many cases, the particles are aggregated and dispersed in the binder, resulting in poor adhesion as a film, making it almost impossible to use it as a conductive adhesive. In addition, a recent technique that has been attracting attention is a proposal to use scale-like graphite or carbon. The high conductivity of the silver-based conductive film
Considering that this method is derived from the fact that the effective contact path between the powders is increased by using scaly silver powder, this method is considered to be highly possible, but at this stage there is no There is no scaly carbon or graphite that can be stably supplied at low cost. Therefore, the present invention aims to reduce the cost of an expensive silver-based conductive film and to obtain a conductive film having a resistance value lower than that of a carbon-based film.
In particular, the present invention uses a pyrolytic polymer (PYPO), which is a novel conductor powder and has very high compatibility with silver and a binder, mixed with silver to reduce the amount of silver used and to reduce the area resistance. This method produces a conductive film with a resistance of 1Ω/□ or less. The novel conductor PYPO disclosed in the present invention is obtained by thermally decomposing nitrogen-containing heteropolymers, which are generally called heat-resistant polymers such as polyimide, polyamide-imide, polyoxadiazole, and polybenzothiazole, in a vacuum. The resulting organic conductor is classified as a low-dimensional conductor. Low-dimensional conductors are “chemistry and industry”
As described on pages 221 to 240 of the April 1974 issue, unlike conventional three-dimensional conductors,
It is a general term for materials that have high conductivity only in the two-dimensional direction or in the planar direction (two-dimensional). PYPO is a polymer condensed through thermal decomposition, and is expected to have a planar structure similar to that of graphite, making it a two-dimensional conductor. Dupont's Kapton H film (polyimide) undergoes thermal decomposition in vacuum and becomes 5x
The change to a conductor of 10 ^-2 Ω・cm was reported by IBM's S.
This was reported by D.Bruck in 1964.
(Polymer, Vol. 5, p. 435, 1964). Furthermore, the Russian School reported in 1963 that polyacrylonitrile changes to 1.5×10 ^-1 Ωcm by thermal decomposition. (AVAirapetjanc et al., Dok1.Akad.
Nauk SSSR Vol. 148, p. 605, 1963). like this
Although PYPO has the advantage of high heat resistance, it is expected to be inferior to carbon and graphite as a low-resistance material, and it has been pointed out that its mechanical properties are significantly inferior to ordinary polymers, such as filmability and flexibility. However, research and development has not progressed since then. However, as a result of recent remarkable research into low-dimensional conductors, many organic low-molecular compounds and polymer compounds that exhibit metallic conductivity have been synthesized, and some exhibit higher conductivity than silver and others exhibit superconductivity. etc. have been discovered. In addition, remarkable progress has been made in molecular-level design and synthesis technology aimed at achieving high conductivity. (Refer to Yoshimura, "Chemistry and Industry" Vol. 32, No. 4, p. 225, April 1974 issue) Therefore, the present invention focuses on such viewpoints and the fact that it has outstanding heat resistance,
A novel conductive composition using PYPO is provided. The first feature of the present invention is that PYPO powder is dispersed in a polymeric binder to form a conductive composition, and the advantages of PYPO for this application are listed below. is based on factual findings. That is, 1 PYPO is a very brittle solid, so it can be easily processed into a powder of 1 μm or less by mechanical methods. 2. Since the shape of the polymer before thermal decomposition can be freely selected, fine particles of PYPO can be easily obtained by producing PYPO using, for example, an ultra-thin film by the casting method or ultra-fine particles by the spray-drying method as a starting material. Furthermore, the PYPO obtained from the ultra-thin film becomes a scaly powder. 3 Unlike graphite, PYPO is an organic material containing many hydrogen atoms, so it is compatible with most polymeric binders and solvents, and shows almost no formation of secondary particles due to aggregation. Among these, 1 and 3 mean that they meet the basic requirements when manufacturing filler matrix composite materials. Further, the starting material of PYPO used in the present invention is characterized in that it is polyimide, polyamide-imide, polyoxadiazole, and polybenzothiazole, or a mixture thereof, all of which have a resistance of 2×10 ^-2 Ω.
It is a material that exhibits a specific resistance of less than cm. For example, polyimide was previously reported to have a PYPO of 5 x 10 ^-2 Ωcm, but by using highly pure raw materials and treating it at 850°C for 4 hours, PYPO of 1.4 x 10 ^-2 Ωcm was obtained. The specific gravity of polyimide PYPO was 1.8 (polyimide was 1.4) and the heat resistance temperature was 900°C. Polyamide-imide PYPO is produced under similar conditions,
It showed a specific resistance of 2×10 ^-2 Ωcm. Polyoxadiazole had a specific resistance of 2×10 ^-2 and 1×10 ^-2 Ωcm as a result of treatment at 700°C and 800°C, respectively. Further, polybenzothiazole had a specific resistance of 1×10 ^-2 Ωcm or less when treated at 850°C. Note that the starting materials for PYPO used in the present invention are not limited to the above materials, and include polyimide copolymers such as polyester-imide, polybenzimidazole, polybenzoxazole, polythiadiazole, polyoxadiazolyl, triazole, Heat-resistant polymers consisting of nitrogen-containing heterocycles such as polyquinoxaline and polyimidazopyrrolone are also used. Further, another feature of PYPO that makes the present invention effective is that even when mixed with silver, PYPO does not undergo any chemical reaction with silver, and does not cause any aggregation of silver particles and PYPO particles. As described above, PYPO has properties that are very advantageous for forming conductive compositions when dispersed in a polymeric binder, and is also highly compatible with silver, making it possible to use silver-PYPO as a filler. The resulting film has become a high-performance conductive film. As mentioned earlier, the gap in area resistance between the silver-based conductive film and the carbon-based film is 1 to 10 Ω/□, but even when obtaining a resistance of 1 Ω/□ or less, at least 50 %PYPO
It became possible to replace it by This is approximately 80% when converted to volume %, and it can be seen that the effect of reducing the amount of silver used is remarkable. The sheet resistance of PYPO alone was 5Ω/□ or more for the film without binder and 1KΩ/□ for the film containing binder, so
The low resistance value of the silver-PYPO composite film was mentioned above.
This should be seen as a result of taking advantage of PYPO's features. Examples are shown below to explain specific effects of the present invention. Example 1 A polyimide film is commercially available, for example, as Kapton H film from DuPont. In addition, varnishes such as Dupont's Pyre-ML or Monsanto's Solution7W are also available. Here, an example is shown in which both a 12.5μ Kapton H film and a 1μ film obtained by casting Pyre-ML on glass are used as starting materials. Put the above polyimide film into a quartz tube.
It was pyrolyzed at a temperature of 850°C in a vacuum of 10 ^-3 Torr. Thermal decomposition starts before the sample reaches 850°C and gases such as NOx and COx are released, but the treatment time was set at 4 hours to allow the resistance value to stabilize. The specific resistance of PYPO obtained by thermal decomposition was 1.4×10 ^-2 Ωcm or less. Next, the obtained PYPO was pulverized in a centrifugal ball mill for about 1 hour, and further pulverized in an attritor for 2 hours. The particle size of the powder obtained from Kapton H was 5μ or less, and that of PYPO from Pyre-ML was 1μ or less. A paste was prototyped using commercially available silver paste powder as the silver powder, polyester resin as the binder, and isophorone solvent. The film was printed on a polyester or ceramic substrate using a 200 mesh screen. After printing, it was set at 150°C for 1 hour and the resistance was measured. Figure 1 shows the dependence of the sheet resistance on the PYPO/silver ratio when PYPO obtained from Kapton H film is used. As you can see from the figure, 1Ω/
□Approximately 60% by weight of silver to obtain the following sheet resistance
It is possible to replace PYPO with PYPO. This is 90% when converted to volume %, indicating that PYPO exerted a significant volume increase effect. Comparing this with carbon, when carbon powder is added to silver paste using the same method,
The highest mixing ratio was 10% carbon, and if it was higher than that, the paste would agglomerate, making it impossible to form a film by printing. The sheet resistance of the silver paste containing 10% carbon was about twice that of 0.2Ω/□PYPO. Next, ultrafine particles of PYPO obtained from Pyre-ML
Table 1 shows the results when using .

[Table] When compared with the case of coarse PYPO shown in Figure 1, a clear decrease in resistance value can be seen. Example 2 A polyamide-imide resin was cast in the form of a varnish using acetoacide, xylene, etc. as a solvent as a starting material onto a clean glass substrate as a film having an average thickness of 5000 Å. After curing at a temperature of 200 to 250°C, the resin film was mechanically separated after immersing the glass substrate in water and subjected to thermal decomposition treatment. Pyrolysis is
The process was carried out at 850℃ for 4 hours, resulting in a black color with a specific gravity of approximately 1.7.
Got PYPO. By crushing this PYPO with an attritor for 2 hours, the thickness is less than 5000Å and the diameter is 1.
A scaly PYPO powder with a size of less than μ was obtained. A PYPO-silver paste was prototyped using phenoxy resin as a binder, and a film was formed using a 300 mesh screen. When PYPO was 50% by weight (83% by volume) or less, the sheet resistance was 0.3Ω/□ or less, and when PYPO was 1Ω/□ or less, it was possible to add up to 75% PYPO. Further, starting from the same polyamide-imide varnish, a spherical polyamide-imide resin of 1 μm or less was manufactured by spray drying in an atmosphere at 350°C. PYPO obtained by pyrolyzing this is
The result was spherical PYPO with a diameter of less than 0.8μ, and it could also be used by mixing it with silver. However, scaly PYPO
The mixing limit is as low as 65% compared to
It had doubled in size. Example 3 Polyoxadiazole and polybenzothiazole, like imide resins, become electrical conductors similar to metals by thermal decomposition. In each case, the treated PYPO was started from a film, and the treated PYPO was kneaded and pulverized with silver powder and epoxy resin using three rolls. Table 2 shows the results of measuring the resistance value of the silver-PYPO film obtained by printing with a 200 mesh screen.

[Table] Mixing of PYPO to obtain a sheet resistance of less than 1 Ω/□, the limits were 65 and 70% for polyoxadiazole and polybenzothiazole, respectively. As described above, the present invention involves powdering the conductive material PYPO obtained by thermally decomposing a heat-resistant polymer having a nitrogen-containing heterocycle in the molecule, mixing it with silver particles, and dispersing it in a binder. The purpose is to provide a novel conductive composition, and the amount of PYPO added may be controlled so that the sheet resistance of the composition is 1Ω/□ or less, and the value is 60 to 80% in ratio to silver.
% by weight. As shown in the examples, the limit of mixing varies depending on the shape of PYPO (scales, spheres, blocks), etc., so it is not possible to uniformly define the limit value. Note that the above example is an example of adding PYPO to silver paste, but in addition to silver, it can also be added to silver-palladium, gold, platinum-gold, gold-palladium, palladium, and platinum-palladium pastes. too
Needless to say, it is possible to add PYPO. In addition, the conductive composition obtained by the present invention is
In the electronics field, conductors, heaters,
To fill the cost and performance gap between conventional silver and carbon films, such as resistors,
Widely available.

[Brief explanation of the drawing]

The figure shows the relationship between the area resistance and the composition ratio of PYPO of a conductive composition comprising a pyrolytic polymer (PYPO) obtained from polyimide, silver, and a polyester binder.

Claims (1)

[Scope of Claims] 1. An electrically conductive composition comprising a conductor powder obtained by thermally decomposing a polymer having a heterocycle containing a nitrogen atom, silver powder, and a polymer binder. 2. The conductive composition according to claim 1, wherein the polymer having a heterocycle containing a nitrogen atom is polyimide, polyamide-imide, polyoxadiazole, polybenzothiazole, or a mixture thereof.