JPH0212987B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a highly reliable conductive resin composition that has excellent conductivity, particularly its stability over time at high temperatures, and molded articles thereof. (Prior Art) Conventionally, conductive resin compositions have been prepared by blending conductive fibers with thermoplastic resins, and these compositions have been used in conductive resin molded articles. Carbon-based conductive fibers have often been blended into these materials, but their main use is to prevent static electricity, and their conductivity is low and they are not very effective in electromagnetic shielding, which has become a problem in recent years. Therefore, attempts have been made to improve conductivity by using metal-based conductive fibers for electromagnetic shielding. However, when metal-based conductive fibers (hereinafter referred to as metal fibers) are added, the specific gravity increases, which significantly impairs the original properties of the resin.
It is required to minimize the amount incorporated. However, when the amount of metal fiber blended is reduced,
The conductivity decreases, and furthermore, the usage environment is severely restricted. That is, since there is a difference in thermal expansion between the resin and the metal fibers used, a problem arises in that conductivity deteriorates at high temperatures. Therefore, at present, it is put into practical use by increasing the blending amount of metal fibers to prevent the decrease and deterioration of conductivity, and by limiting the usage environment. As described above, conventional conductive resin compositions of metal fibers and molded products thereof have problems in that they have limitations in their applications and usage environments, and have unstable characteristics and low reliability. Also, it is known that conductivity can be obtained by mixing and molding a low melting point metal and a resin, but the low melting point metal has poor adhesion with the resin and separates, reducing the physical properties of the resin. Furthermore, when changing the color of the material in the molding machine, there was a problem that only the metal would fly away, which was extremely dangerous during the molding process. Furthermore, when metal fibers are used in combination with low-melting point metals and mixed into resin, an oxide film is formed on the surface of the metal fibers due to drying before molding, resulting in poor solderability and separation of the low-melting point metals. There was a problem in that the metal fibers were corroded, and as a result, the conductivity deteriorated significantly. (Problems to be Solved by the Invention) The present invention was made to solve the above problems, and the conductive fibers have good wettability and the low melting point metal is firmly bonded to the conductive fibers. , the conductivity of the molded product does not deteriorate even at high temperatures and has excellent stability over time, and there is no separation or scattering of the resin and low-melting point metal during molding, resulting in good moldability and highly reliable conductivity. The present invention aims to provide a resin composition and a molded article thereof. [Structure of the Invention] (Means for Solving the Problems) As a result of intensive research aimed at achieving the above object, the present inventors have developed a method using conductive fibers, low melting point metals, and phosphorous antioxidants. By using a composition made of blended thermoplastic resin, the conductivity of the molded product does not deteriorate even at high temperatures and has excellent stability over time, and the resin and low melting point metal can be separated and scattered during the molding process. The present invention was completed based on the discovery that it is possible to obtain a highly reliable conductive resin composition and a molded article thereof, which has no defects and improved moldability. That is, the present invention provides a method of coating (A) a conductive fiber with (B) a low melting point metal and (C) a phosphorus antioxidant containing (D) a thermoplastic resin that is integrally formed on the surface of the conductive fiber and cut into pellets. This is a conductive resin composition characterized by: Further, the present invention is a conductive resin molded article characterized by being formed by injection molding this conductive resin composition at a temperature equal to or higher than the melting point of a low-melting point metal. The conductive fibers (A) used in the present invention include metal fibers such as long fiber copper fibers, stainless steel fibers, brass fibers, aluminum fibers, and nickel fibers, and metal fibers having a metal layer of copper, aluminum, nickel, etc. on the surface. Examples include organic fibers and inorganic fibers, which may be used alone or in combination of two or more. The conductive fiber preferably has a diameter of about 5 to 100 μm. This conductive fiber is coated with a thermoplastic resin containing a low melting point metal and a phosphorous antioxidant on its surface, and then cut into a length of 5 to 8 mm to obtain a resin composition. The amount of conductive fibers to be blended is preferably 0.5 to 30% by weight based on the entire conductive resin composition. If it is less than 0.5% by weight, the conductivity will be low, and if it exceeds 30% by weight, the fluidity and other properties of the conductive resin composition will deteriorate, which is not preferable. The low melting point metal (B) used in the present invention includes a general solder alloy containing Sn or Sn-Pb as a main component;
Examples include high-temperature solder alloys mainly composed of Sn-Pb-Ag, and low-temperature solder alloys mainly composed of Sn-Pb-Bi. These low melting point metals may be in the form of fibers, granules, lines, or flakes;
It is not particularly limited to the composition. Further, the low melting point metal is preferably selected depending on the molding temperature of the thermoplastic resin to be mixed. The blending ratio of the low melting point metal is preferably an amount sufficient to bond and coat the conductive fibers, and is preferably blended at a ratio of 5 to 30% by weight based on the conductive fibers.
If the blending amount is less than 5% by weight, the conductive fibers will not be bonded or
Coating becomes insufficient, and if it exceeds 30% by weight, only the low melting point metal will be liberated and the physical properties of the resin will deteriorate, which is not preferable. It is preferable that the low melting point metal is blended into the thermoplastic resin. Examples of the phosphorus antioxidant (C) used in the present invention include those with the following structural formula. The blending ratio of the phosphorus antioxidant is preferably 0.1 to 5% by weight based on the thermoplastic resin. If the amount is less than 0.1% by weight, it will not be sufficient to remove the oxide film from the conductive fibers, and the solder wettability will be poor.
Moreover, if it exceeds 5% by weight, physical properties such as a decrease in the heat distortion temperature of the resin are undesirable. It is desirable that the phosphorus antioxidant be blended into the thermoplastic resin. The thermoplastic resin (D) used in the present invention includes polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile-butadiene-styrene resin, modified polyphenylene oxide resin, polybutylene terephthalate resin, polycarbonate resin, polyamide resin, polyetherimide. Examples include resins, and these may be used alone or in combination of two or more. It is desirable that the above-mentioned low melting point metal and phosphorus antioxidant be blended into this thermoplastic resin, and the conductive fibers are integrally coated with the resin. These may be those in which the third synthetic resin formed at the interface by mixing thermoplastic resins has a reinforcing effect, that is, a blended polymer. For example, when using a modified polyphenylene oxide resin, polycarbonate resin, etc. as the thermoplastic resin, good results can be obtained if a styrene-based thermoplastic resin is used as the other thermoplastic resin. By doing so, the third synthetic resin formed at the interface has a reinforcing effect. By using such a combination, a molded article with excellent properties can be obtained. The conductive resin composition of the present invention and molded articles thereof are usually produced as follows. The long conductive fibers are passed through the die of an extruder, and the surface of the conductive fibers is coated with a thermoplastic resin containing a low melting point metal and a phosphorous antioxidant, and then cut into appropriate sizes. A pellet-shaped conductive resin composition is prepared. This composition usually has a circular cross section, but the cross section is not limited to a particular shape and may be flat or other shapes. Although it is economically advantageous to carry out the manufacturing process of this composition continuously, it does not necessarily have to be continuous and may be manufactured in batches. The type and amount of the thermoplastic resin are appropriately selected depending on the properties required of the conductive resin composition and its molded product. The conductive resin composition thus produced is injection molded at a temperature equal to or higher than the melting point of the low melting point metal to obtain a conductive resin molded article. The molded product can be used as housings or parts for electronic equipment, measuring equipment, communication equipment, etc. that require electromagnetic shielding. (Function) According to the present invention, excellent effects can be obtained by using conductive fibers, low melting point metals, phosphorous antioxidants, and thermoplastic resins. In other words, when the thermoplastic resin and conductive fibers are kneaded in the heating cylinder of an injection molding machine, the conductive resin composition uses phosphorus-based oxidation inhibitors to remove the oxide film of the conductive fibers formed during the manufacturing process and drying. removed by the reducing action of the agent. Next, the surface of the conductive fiber is firmly coated with a low melting point metal melted within the cylinder. In this case, if an oxide film remains on the conductive fibers or the solder wettability is poor, the conductive fibers will corrode or the low melting point metal will be liberated, deteriorating the physical properties of the resin. Then, when the conductive resin composition is injected into the mold and cooled and solidified, the bonding points between the conductive fibers are fused by the low melting point metal to form a network, which is then cooled and solidified.
Therefore, even if the molded product is placed in a high-temperature environment, the bonding points between the conductive fibers will not separate.
Conductivity also does not deteriorate. This can be confirmed by dissolving the resin component of the molded article with a solvent and confirming the state of the network in which the conductive fibers are bonded. Therefore, it becomes possible to reduce the amount of conductive fiber blended. Furthermore, separation and scattering of low melting point metals are eliminated. (Example) Next, the present invention will be explained by referring to an example. Example Toughflex 410 (manufactured by Mitsubishi Monsanto) containing 300 converged copper fibers with a diameter of 50 μm, low melting point metal beads (Sn40%, Pb60%) and HCA (phosphorus antioxidant manufactured by Sanko Kagaku Co., Ltd., trade name) ABS resin,
(trade name) was passed through the die of an extruder to form a molten coating of ABS resin on the surface of copper fibers. This was cooled and cut into lengths of 6 mm in the fiber direction using a pelletizer to produce a conductive resin composition. The copper fiber filling rate of this composition was 60% by weight. Injection molding was performed using this conductive resin composition to obtain a molded article. The obtained molded product was tested for volume resistivity and shielding effect, and the results are shown in Table 1, and the extremely remarkable effects of the present invention were confirmed. Comparative Example In the example, a conductive resin composition and a molded article were made in the same manner as in the example except for the phosphorus antioxidant, and the molded article was tested in the same manner as in the example. The results are shown in Table 1. In addition, the molded product is washed with methylene chloride,
After dissolving the resin, the network state of the remaining conductive fibers was photographed using an electron microscope, and this is shown in FIG. It can be seen that the conductive fiber 1 and the conductive fiber 2 are tightly fused and bonded by the low melting point metal 3.

【table】

[Table] [Effects of the Invention] As is clear from the above explanation and Table 1, the conductive resin composition of the present invention comprises conductive fibers,
By using a low melting point metal and a phosphorus-based antioxidant, the conductive fibers have good wettability and the bond between the conductive fibers becomes strong.As a result, the conductive fibers have excellent conductivity and It has become possible to reduce the amount of compounding, and molding processability has been improved because there is no separation or scattering of the thermoplastic resin and low melting point metal during molding. A molded article using this conductive resin composition has excellent electromagnetic shielding effect over time without a decrease in conductivity even under environmental changes at high temperatures. If this molded product is used in electronic equipment, communication equipment, etc., extremely high reliability can be provided.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the shape of conductive fibers fused and bonded in a network shape by a low-melting point metal in a molded article of the present invention. 1, 2... Conductive fiber, 3... Low melting point metal.

Claims (1)

[Claims] 1. (A) On the surface of the conductive fiber, (B) A low melting point metal and
1. A conductive resin composition comprising (D) a thermoplastic resin containing (C) a phosphorous antioxidant, which is integrally formed into a coating and cut into pellets. 2. The conductive fiber according to claim 1, wherein the conductive fiber is copper fiber, brass fiber, stainless steel fiber, aluminum fiber, nickel fiber, or organic or inorganic fiber having a layer of copper, aluminum or nickel on the surface. Resin composition. 3. The conductive resin composition according to claim 1 or 2, wherein the low melting point metal is a solder alloy containing Sn or Sn-Pb as a main component. 4 The conductive fiber is 0.5 to 0.5% of the total composition.
The conductive resin composition according to any one of claims 1 to 3, containing 30% by weight. 5. The conductive resin composition according to any one of claims 1 to 4, wherein the low melting point metal is blended in a proportion of 5 to 30% by weight based on the conductive fibers. 6 Adding phosphorus-based antioxidants to thermoplastic resins
The conductive resin composition according to any one of claims 1 to 5, which is blended in a proportion of 0.1 to 5% by weight. 7 (A) On the surface of the conductive fiber, (B) Low melting point metal and
(C) A conductive resin composition containing (D) a phosphorus-based antioxidant is integrally formed into a coating and cut into pellets, and then injection molded at a temperature higher than the melting point of the low melting point metal. Characteristic conductive resin molded product.