JPH02229498A - Conductive resin composition and molding thereof - Google Patents

Abstract

PURPOSE:To acquire a highly reliable molding by forming a conductive filler by assembling a composite fiber which is made by applying copper to a surface of a stainless alloy fiber and a low melting point metal, by incorporating a flux into the side of thermoplastic resin which forms a coat of the conductive filler, and by mixing a natural pellet thereto. CONSTITUTION:When a conductive resin composition is kneaded inside a heating cylinder of an injection molding device, a composite fiber is dispersed and kneaded. Since the composite fiber is thereby brought into full contact with a flux which is contained in a thermoplastic resin and leakage is provided, a section where the composite fibers are in contact with each other is entirely covered with a low melting point metal. During the kneading, the composite fiber is not cut off or does not bend since it has rigidity and strength. If the composite fiber which is thus dispersed and kneaded is poured into a die, and cooled and hardened, the low melting point metal fuses an interface of mutual composite fibers in a mesh, thus resulting in cooling and hardening. Since firm fusion and bonding by low melting point metal is realized without separation of the interface with the composite fiber in this way, conductivity does not deteriorate even under a high temperature environment.

Description

Detailed Description of the Invention [Objective of the Invention] (Field of Industrial Application) The present invention provides an F8 condyle that has excellent electrical conductivity and does not deteriorate in electrical conductivity even in various environments. Concerning highly conductive resin compositions and molded products thereof. (Prior Art) Conventionally, conductive resin compositions have been made by blending conductive fibers with thermoplastic resins, and the compositions have been used as conductive resin molded products in electronic devices, measuring instruments, etc. These materials have mainly been blended with carbon-based conductive fibers, but their main purpose is to prevent static electricity, and their conductivity is low and they are not very effective against 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 simply referred to as metal fibers) are added, the specific gravity increases and the original properties of the resin are significantly impaired, so it is necessary to minimize the amount of the metal-based conductive fibers. ing. However, when the amount of these metal fibers is reduced, the conductivity decreases and there are also significant restrictions on the usage environment. In other words, due to the difference in thermal expansion between the resin used and the metal fiber, there is a problem that the conductivity deteriorates at high temperatures. There was also the problem that the metal fibers could be cut or bent due to cross-wires caused by the screw during molding. Therefore, at present, metal 8
l! It has been put into practical use by increasing the amount of fiber blended to prevent decreases and deterioration of conductivity, and by limiting the environment in which it can be used. As described above, conventional conductive resin compositions of metal fibers and molded products thereof are limited in their applications, and have problems such as unstable properties and low reliability. On the other hand, there is a method of blending a low-melting point metal into a thermoplastic resin, but the low-melting point metal has poor adhesion to the resin, and the resin and low-melting point metal do not adhere well when changing the color of the material, etc. There was a problem that the metal separated and the metal was scattered, which was extremely dangerous during the forming process. (Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems. It increases the rigidity and strength of conductive fibers, prevents the fibers from being cut or bent when cross-wired, and provides conductive fibers. A highly reliable conductive resin in which the fibers and low-melting point metal are strongly bonded, and the conductivity does not deteriorate even at high temperatures and has excellent stability over time. It is also stable during molding and processing, and does not reduce the mechanical strength of the resin. The purpose is to provide compositions and molded products thereof. [Details of the Invention] (Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventors have improved the strength of conductive fibers and improved their wettability with low melting point metals. The present invention was completed based on the discovery that the above object could be achieved by using composite fibers made of stainless steel alloy fibers whose surfaces were coated with copper. That is, the present invention includes (A) a composite fiber in which the surface of a stainless steel alloy fiber is coated with copper; (B) a conductive filler made of a low melting point metal; and (C) a thermoplastic resin containing flux on the surface of the conductive filler. This is a conductive resin composition characterized by blending master pellets obtained by integrally forming a coating and cutting into pellets, and (E) thermoplastic resin pellets. This is a conductive resin molded product that is characterized by being molded at a temperature above the melting point of the melting point metal. As the composite fiber used in the present invention (A>), long fiber-like fibers made by coating the surface of stainless steel alloy fibers with copper are used. The diameter of the composite fiber is 5 to 10.
A conductive filler is desirably about 0μ1, and is aggregated with a low melting point metal to be described later to form a conductive filler, and a thermoplastic resin containing flux is coated and integrated on the surface, and then a length of 5 to 6
Cut into mn pellets to make master pellets. The compounding ratio of composite fiber is 0.5 to the whole composition.
It is desirable to blend the amount of 30% to 30%. If the blending ratio is less than 0.5% by weight, the conductivity will be low;
This is because if it exceeds this, the fluidity and other physical properties of the conductive resin composition will deteriorate, which is undesirable. (B) used in the present invention
The low melting point metal should be selected depending on the molding temperature of the thermoplastic resin used, and preferably has a melting point slightly higher than the thermoplastic resin. More preferably, a metal with a low melting point that melts at the lowest temperature part of the heating cylinder of the injection-molded Tachibana can be selected. As a low melting point metal,
Sn or Sn-Pb-based general solder, Sn-Pb-A
Examples include g-based high-temperature solder and Sn-Pb-Bi-based low-temperature solder, and these can be used alone or as a mixture of two or more types. The shape of the low melting point metal is not particularly limited and may be fibrous, granular, or linear. The blending ratio of the low melting point metal is sufficient to bind and cover the composite fibers, and it is desirable to blend the metal in an amount of 5 to 30% by weight based on the composite fibers. If the blending ratio is less than 5% by weight, the binding and coating of the composite fibers will be insufficient and the conductivity will be low, and if it exceeds 30% by weight, the low melting point metal will be liberated and the physical properties of the resin will deteriorate, which is undesirable. ．． The low melting point metal may be condensed into long conjugate fibers, each conjugate fiber may be coated with a molten low melting point metal, or the entire conjugate fiber may be coated. In short, it is important to make sure that the composite fiber and low melting point metal are integrated. The material made in this way is used as a conductive filler. The flux (C) used in the present invention includes organic acids used in the shell such as stearic acid, lactic acid, oleic acid,
Examples include glutamic acid, resin-based rosin, and activated rosin. Halogen-based fluxes are undesirable because they tend to corrode composite fibers or molds. In addition, even compounds that are not generally used as fluxes exhibit good wettability and do not harm the resin or mold, such as HHCA (manufactured by Sanko Kagaku Co., Ltd., trade name), which has the following chemical formula. Since it exhibits good wettability, it can be used as a flux in the present invention. The mixing ratio of flux is preferably in the range of 0.1 to 5% by weight based on the low melting point metal. If the amount is less than 0.1% by weight, it will not be effective in improving the wettability of the composite fiber, and if it exceeds 531% by weight, it will cause deterioration of the physical properties of the molded product, corrosion and staining of the mold, etc., which is undesirable. Examples of the thermoplastic resin (D) used in the present invention include polyvinyl resin, polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile-butadiene-styrene resin, modified polyphenylene oxide resin, polybutadiene terephthalate resin, polycarbonate resin, etc. can be used alone or as a mixture of two or more types. These thermoplastic resins are used to coat the surface of a conductive filler made of composite fibers and low-melting metals, and then cut into master pellets. In this case, it is important to include flux in the thermoplastic resin. (E) Thermoplastic resin pellets (also referred to as natural pellets) used in the present invention may be any thermoplastic resin pelletized, such as polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile-ptadiene-styrene copolymer. resin, modified polyphenylene oxide resin, polybutylene terephthalate resin,
Examples include polycarbonate resins, and these may be used alone or as a mixture of two or more. It may be the same kind or the same as the thermoplastic resin (D) mentioned above, or it may be different. Alternatively, the third synthetic resin formed at the interface by mixing with the thermoplastic resin of the master pellet may have a reinforcing effect, that is, it may be a blend polymer. For example, when using modified PPO resin, polycarbonate resin, etc. as the thermoplastic resin of the master pellet, good results can be obtained by using a styrene-based thermoplastic resin as the natural pellet. By doing this, the third synthetic resin formed at the interface has a reinforcing effect. By using such a combination, it is possible to obtain molded products with even better properties. The conductive resin composition of the present invention and molded articles thereof are usually manufactured as follows. A conductive filler is made by assembling long composite fibers and a low-melting metal, and extruded through a die of an extruder together with a thermoplastic resin containing flux to form a covering of the thermoplastic resin on the surface of the conductive filler. Then, cut into appropriate sizes to make master pellets. This master pellet usually has a circular cross section, but it may be flat or curved, and is not particularly limited to the shape. Although it is economically advantageous to carry out the process continuously in the production of master pellets, it is also possible to produce them in a batch manner. A conductive resin composition is produced by blending natural pellets with the master pellets obtained in this way. As with the shape of the master pellet described above, the shape of the natural pellet is not particularly limited. The natural pellets to be mixed are
The type and amount of thermoplastic resin is appropriately selected depending on the characteristics required for the conductive resin composition and its molded product.
The conductive resin composition thus obtained can be injection molded at a temperature higher than the melting point of the low-melting point metal and used as molded products for housings and parts of electronic equipment, measuring instruments, communication equipment, etc. that require electromagnetic shielding. can. Although the method of injection molding for obtaining a molded article has been explained, the method is not limited to these, and molding may be performed by extrusion molding, transfer molding, compression molding, etc. (Function) According to the present invention, excellent effects can be achieved by forming composite fibers and low-melting point metals into master pellets and thermoplastic resin pellets by coating them with a thermoplastic resin containing flux and cutting the composite fibers and low-melting-point metal into a beveled shape. This is what you get. In other words, when the conductive resin composition is kneaded in the heating cylinder of the injection molding machine, the composite fibers contained in the master pellets are dispersed and kneaded, and the composite fibers make sufficient contact with the flags contained in the thermoplastic resin. However, since it has wettability, the low melting point metal evenly covers the parts of the composite fibers that are in contact with each other. Also, during this kneading process, the composite fibers are rigid and strong, so they will not be cut or bent. When the thus dispersed and kneaded mixture is injected into a mold and cooled and solidified, the low melting point metal fuses to the bonding points of the composite fibers, forming a network that solidifies upon cooling.
In this way, the bonding points between the composite fibers do not separate and are firmly fused and bonded by the low-melting point metal, so the conductivity does not deteriorate even if placed in a high-temperature environment. This can be confirmed by dissolving and removing the resin content of a conductive resin molded product using a solvent, and it is possible to clearly see the network state in which composite fibers are firmly fused together. 《Example》 Next, the present invention will be specifically explained by referring to an example. Example 500 long composite fibers (stainless steel alloy surface coated with 25 μl thick copper) with a diameter of 50 μl were converged, and a low melting point metal (Sn60
Diamonds containing 2 parts by weight of rosin and 3 parts by weight of HCA (manufactured by Sanko Kagaku Co., Ltd., trade name) per 100 parts by weight of polystyrene resin are applied as flags to the surface of a conductive filler made of aggregated fibers of 40% Pb. Rex HT-91 (boristyrene resin manufactured by Mitsubishi Monsite, trade name) was passed through a die of an extruder to form a coating. After cooling, this was cut into lengths of 6III1 in the fiber direction using a pelletizer to form master pellets. Next, 800 parts by weight of polystyrene resin was blended into this master pellet to produce a conductive resin composition. In this case, the filling rate of the composite fibers was 2.
It was 0% by weight. A molded article was manufactured by injection molding using this conductive resin composition. The obtained molded product was tested for volume resistivity, electromagnetic shielding effect, etc., and the results are shown in Table 1. The present invention has an excellent shielding effect, especially after being treated at 80°C for 3000 hours. However, almost no deterioration of the shielding effect was observed, confirming the extremely significant effect of the present invention. Comparative Example 200 long copper fibers with a diameter of 100 μm were converged,
This is a low melting point metal with a diameter of 100μ [≦n 60%, P
Fibers of 40%) were aggregated to form a conductive filler, and 2 parts of rosin and 3 parts of HCA (as mentioned above) were added to 100 parts by weight of polystyrene resin, and the mixture was kneaded in an extruder and passed through a die. After extrusion and forming a coating on the surface of the conductive filler, the conductive resin composition was cut into pellets, and a molded article thereof was produced. Tests similar to those in Examples were conducted on these and the results are shown in Table 1. Table 1 Table (″)-j) (Unit) (Unit) [Effect of the invention] As is clear from the above explanation and Table 1, the conductive resin composition of the present invention and its molded product can be applied to stainless steel. Composite fibers coated with copper and low melting point metal are aggregated on the surface of alloy fibers to form a conductive filler, and flux is included in the thermoplastic resin side that covers Manako's conductive filler, and natural pellets and By blending the composite fibers, the excellent rigidity and strength of the composite fibers prevents the fibers from cutting or bending, and the fibers have good wettability.They also firmly fuse with low-melting metals, making them conductive even at high temperatures. It has excellent stability over time with no deterioration, is safe to mold, and can produce highly reliable molded products with no decrease in mechanical strength.

Claims (1)

[Scope of Claims] 1 (A) a composite fiber in which the surface of a stainless steel alloy fiber is coated with copper; (B) a conductive filler made of a low-melting point metal; (C) a flux containing (D) a thermoplastic An electrically conductive resin composition comprising a master pellet formed by coating and integrating a resin and cutting into pellets, and (E) a thermoplastic resin pellet. 2. (A) A composite fiber whose surface is coated with copper on the surface of a stainless steel alloy fiber, and (B) a conductive filler made of a low melting point metal, on which (C) a thermoplastic resin containing a flux (D) is integrally coated and integrated. A conductive resin molded article, characterized in that a conductive resin composition containing master pellets cut into pellets and (E) thermoplastic resin pellets is molded at a temperature equal to or higher than the melting point of a low melting point metal.