JPH0212988B2 - - 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 stability over time of conductivity at high temperatures. (Prior Art) In recent years, in order to protect electronic devices from electromagnetic waves generated externally or to prevent leakage of electromagnetic waves from the electronic devices to the outside, the housings of electronic devices have been made of electromagnetic shielding materials. It is requested. The molding material for this shield is required to have higher conductivity than conventional carbon fiber-filled materials, and at the same time requires excellent mechanical strength as a housing, so metal-based conductive filling is required. The material is filled with resin as long fibers. However, although the above-mentioned conventional method using long metal fibers provides excellent electrical conductivity and mechanical strength, it has the drawback of being restricted by the usage environment. In other words, if a highly active metal is used as a conductive filler, it will accelerate the deterioration of the synthetic resin, resulting in the disadvantage that the casing cannot be used in high-temperature locations or in locations exposed to direct external light. Since the bond with the conductive filler is a mere contact, the contact changes with changes in the environmental temperature, resulting in a problem in that the conductivity of the casing gradually decreases. For these reasons, the conventional method using long metal fibers has the disadvantage of significantly impairing reliability, which has been a major obstacle to practical application. Next, it has been known for a long time to mix a low melting point metal and a resin to make a conductive resin composition, but the low melting point metal has poor adhesion to the resin, and when changing the material color in a molding machine, Dry punching was extremely dangerous for the molding process, as the resin and low melting point metal would separate and only the low melting point metal would fly away. Further, in the conventional method using metal fibers, an oxide film is formed on the surface of the metal fibers when the metal fibers are dried before being formed, resulting in a problem such as deterioration of conductivity. (Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the amount of conductive fibers filled, and also to be able to withstand temperature changes in various environments. The object of the present invention is to provide a highly reliable conductive resin composition that exhibits little decrease in conductivity or change over time, retains the original characteristics of the resin, has good moldability, and molded products thereof. [Structure of the Invention] (Means for Solving the Problems) As a result of extensive research in an attempt to achieve the above object, the inventor of the present invention has discovered the use of a combination of conductive fibers and a low melting point metal as a conductive filler. By adding flux and phosphorous antioxidant to it, the conductivity does not decrease even at high temperatures and has excellent electrical conductivity stability over time. Even during molding, the resin and low melting point metal can be separated and scattered. The present invention has been completed based on the discovery that a highly reliable conductive resin composition with improved molding workability and free from such problems can be obtained. That is, the present invention provides a conductive filler made of (A) conductive fibers, (B) a low melting point metal, and (C) a flux, on the surface of which is a conductive filler containing (D) a phosphorous antioxidant and (E) a thermoplastic resin. This is a conductive resin composition characterized in that it is formed by integrally forming layers and cutting them into pellets. The conductive fibers are long metal fibers, or inorganic or organic fibers having a metal layer on the surface. The low melting point metal is a general solder, low temperature solder, high temperature solder, etc., the flux is an organic acid type or rosin type, and the phosphorus antioxidant is a conductive resin composition containing an agent having the structural formula described below. be. The conductive fibers (A) used in the present invention are preferably long fibers, such as metal fibers such as copper fibers, copper alloy fibers, stainless steel fibers, aluminum fibers, and nickel fibers, and metal fibers with copper, aluminum, nickel, etc. on the surface. organic or inorganic fibers with a metal layer;
etc. The conductive fiber has a diameter of 8~
It is best to use one with a diameter of about 100 μm, and one with 100 to 10,000 converged lines. The amount of conductive fibers to be blended is preferably 5 to 80% by weight based on the entire conductive resin composition. This is because if it is less than 5% by weight, the conductivity will be low, and if it exceeds 80% 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 is a general solder alloy containing Sn or Sn-Pb as a main component, Sn
Examples include high-temperature solder alloys whose main components are -Pb-Ag and low-temperature solder alloys whose main components are Sn-Pb-Bi. These low melting point metals may be fibrous, granular, rod-like, or linear, and are not particularly limited in shape. In addition, low melting point metals can be used by converging fibrous low melting point metals together with conductive fibers, converging conductive fibers whose surfaces are coated with low melting point metals, and converging bundles of converged conductive fibers with low melting point metals. Examples include coating with metal. In addition, there is a method in which the surface of the conductive fibers is sprinkled with granular low-melting point metal, and it is sufficient if the conductive fibers are bundled together with the low-melting point metal. The low melting point metal is desirably selected depending on the molding temperature of the thermoplastic resin covering the conductive filler. The low melting point metal is desirably contained in an amount sufficient to bond and coat the conductive fibers, that is, in a proportion of 5 to 30% by weight based on the conductive fibers. If the content is less than 5% by weight, binding and coating of the conductive fibers will be insufficient, and
This is because 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. The flux (C) used in the present invention is preferably an organic acid-based or resin-based flux, and specifically includes organic acid-based stearic acid, lactic acid, oleic acid, glutamic acid, etc., resin-based rosin, activated rosin, etc. These can be used alone or in combination of two or more. It is not preferable to use halogen-based or amine-based fluxes because they corrode conductive fibers, molds, etc. The blending ratio of flux is preferably 0.1 to 5% by weight based on the low melting point metal. If the content is less than 0.1% by weight, it will have no effect on the solderability of the conductive fibers, and if it exceeds 5% by weight, the physical properties of the resin will deteriorate and the mold will corrode.
This is undesirable as it causes dirt. The flux is
It is usually preferable to fill it with a low melting point metal. Examples of the phosphorus antioxidant (D) used in the present invention include those with the following structural formula. The content 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 be insufficient to remove the oxide film from the conductive fibers and the solder wettability will be poor, and if it exceeds 5% by weight, the physical properties will deteriorate, such as the heat deformation temperature of the resin will drop, which is not preferable. It is desirable that the phosphorus antioxidant be blended into the resin of the thermoplastic resin layer, which will be described later. The resin of the thermoplastic resin layer (E) 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, Examples include polyetherimide resins, which can be used in combination of one or two types.
Use by mixing more than one species. The conductive resin composition of the present invention is usually produced as follows. This will be explained below using the drawings. Figures 1a to 1d are sketches of a conductive filler in which conductive fibers and low-melting metals are aggregated. That is, as shown in FIG. 1a, a certain number of fibrous low melting point metals 3 containing flux are added to and aggregated into a bundle of conductive fibers 2 to form a conductive filler 1. In addition, conductive fibers and low melting point metals can be assembled by assembling conductive fibers 2 coated with low melting point metal 3 on the surface as shown in FIG.
The entire assembled conductive fibers 2 may be coated with a low melting point metal 3 as shown in Fig. Then, a conductive filler 1 is prepared. A thermoplastic resin layer 4 containing a phosphorous antioxidant is integrally coated on the surface of the conductive filler 1 and cut into pellets of the conductive resin composition. 1e-h showing cross-sectional views of the pellet 10 correspond to FIGS. 1a-d showing the conductive filler 1, respectively. That is, a thermoplastic resin 4 containing a phosphorous antioxidant is integrally coated on the surface of a conductive filler 1 made of conductive fibers and a low-melting metal. The pellets 10 usually have a circular cross section, but may be flat or other shapes, and are not particularly limited in shape. As shown in FIG. 2, the pellets are composed of conductive fillers 1 assembled in FIGS. 1a to d.
1 is passed through a die 13 of an extruder 12 to integrally coat the surface of the conductive filler 11 with a thermoplastic resin 14, and then cut 15 to form pellets 16. Although it is economically advantageous to carry out the pellet production process continuously, it is not necessarily necessary to carry out the pellet production process continuously, but it is also possible to produce the pellets in batches. The conductive resin composition thus obtained can be injection molded at a temperature higher than the melting point of the low-melting point metal to form molded products for housings and parts of electronic devices, measuring instruments, communication devices, etc. that require electromagnetic shielding. can. (Function) According to the present invention, the conductive fiber, the low melting point metal, the flux, the phosphorous antioxidant, and the thermoplastic resin function as follows, and excellent conductivity can be obtained. In other words, the conductive resin composition is produced in the heating cylinder of an injection molding machine, in which the conductive fibers are dispersed in the thermoplastic resin, and in the process of being injected into the mold and cooling and solidifying, the low melting point metal melts in the same way as the thermoplastic resin. Then, the conductive fibers are fused and bonded to the conductive fibers, and the conductive fibers are coated and fused with the low melting point metal to form a network, which is then cooled and solidified. When the conductive fibers and the low-melting point metal are fused together, the oxide film formed on the conductive fibers during the manufacturing process or during drying is removed by the reducing action of the phosphorus antioxidant, resulting in improved flux wettability. Because of this, the conductive fibers and the low melting point metal form a strong network. If an oxide film remains on the conductive fibers or the wettability of the conductive fibers is poor, corrosion of the conductive fibers and release of low melting point metals will occur, reducing the physical properties of the resin.
Furthermore, the conductivity also deteriorates. Since the conductive fibers and the conductive fibers are firmly bonded to the low melting point metal to form a network, the conductivity is significantly improved and the physical properties of the resin are not impaired. This can be confirmed by dissolving the resin component of the molded product with a solvent and confirming the network state in which the conductive fibers are combined. This improvement in conductivity allows the amount of conductive fibers to be reduced, and also eliminates separation and scattering of low-melting point metals, resulting in operational safety. (Example) Next, the present invention will be explained by referring to an example. Example 300 long copper fibers with a diameter of 50 μm and one long low-melting point metal (Sn60%, Pb40%) with a diameter of about 300 μm containing 2% by weight of flux were assembled and converged to make them conductive. It was a filling material. on the surface of conductive filler
Toughflex 410 (ABS resin manufactured by Mitsubishi Monsanto Chemical Co., Ltd.) containing 2% by weight of MARK PEP24 (manufactured by Adeka Argus Chemical Co., Ltd., a phosphorus antioxidant trade name)
(trade name) was passed through a die of an extruder to form a coating, and after cooling, it was cut to produce a conductive resin composition having a diameter of 3 mm and a length of 6 mm. A molded article was obtained by injection molding using this composition, and the volume resistivity, electromagnetic shielding effect, and mechanical strength of this molded article were tested. The results are shown in Table 1. Also,
Wash the molded product with methylene chloride to dissolve the resin,
The network state of the remaining conductive fibers was photographed using an electron microscope, and is shown in FIG. In the figure, it can be seen that the conductive fibers 20 and 21 are tightly fused and bonded by the low melting point metal 22. Even after 3,000 hours of environmental testing at 80°C, the molded product's shielding effectiveness did not deteriorate at all.
Furthermore, the mechanical strength was maintained at 80% or more of the initial value, confirming the extremely significant effect of the present invention. Comparative Example A conductive resin composition having a diameter of 3 mm and a length of 6 mm was produced in the same manner as in the example except that the low melting point metal, flux and phosphorous antioxidant were removed. Molded articles were obtained using this conductive resin composition in the same manner as in the examples, and the same characteristic tests were conducted. The results are shown in Table 1.

【table】

[Table] [Effects of the Invention] As is clear from the above explanation and Table 1, the conductive resin composition of the present invention uses a conductive fiber and a low melting point metal together as a conductive filler, and a flux By blending with phosphorus-based antioxidant, the conductive fibers have good wettability, and the conductive fibers are firmly bonded to each other by the low-melting point metal.
The conductivity does not decrease even under environmental changes at high temperatures, and the shielding effect has excellent stability over time.
Furthermore, since the resin has excellent electrical conductivity, it is possible to reduce the amount of the electrically conductive filler to be filled, and furthermore, the inherent physical properties of the resin can be maintained. By firmly bonding the low melting point metal with the conductive fiber,
There is no separation or scattering of low melting point metals, making it safer and improving moldability. If the molded article of the present invention using this conductive resin composition is used in electronic equipment, measuring equipment, communication equipment, etc., extremely high reliability can be imparted.

[Brief explanation of drawings]

Figures 1a to d are perspective views showing the conductive filler in the present invention, Figures 1e to h are sectional views of the pellets in the present invention, and Figure 2 is a diagram for explaining the pellet manufacturing process in the present invention. The conceptual diagram and FIG. 3 are electron micrographs showing the shape of conductive fibers fused and bonded in a network with a low melting point metal in a molded article made of the conductive resin composition of the present invention. 1, 11... Conductive filler, 2, 20, 21... Conductive fiber, 3, 22... Low melting point metal, 4, 14... Thermoplastic resin layer, 10, 16... Pellet.

Claims (1)

[Scope of Claims] 1 (A) conductive fibers (B) a low melting point metal and (C) a conductive filler made of flux, on the surface of which (D) a phosphorous antioxidant is contained (E) a thermoplastic resin 1. A conductive resin composition characterized in that it is formed by integrally forming a coating layer and cutting this into pellets. 2. The conductive fiber according to claim 1, wherein the conductive fiber is a long fiber copper fiber, brass fiber, stainless steel fiber, aluminum fiber, nickel fiber, or an organic or inorganic fiber having a metal layer 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 resin composition according to any one of claims 1 to 3, wherein the flux is stearic acid, lactic acid, oleic acid, glutamic acid, rosin or activated rosin. 5 The conductive fiber is 5% of the conductive resin composition.
Claim 1 containing in a proportion of ~80% by weight
5. The conductive resin composition according to any one of items 1 to 4. 6. The conductive resin composition according to any one of claims 1 to 5, wherein the low melting point metal is contained in a proportion of 5 to 30% by weight based on the conductive fibers. 7 The flux is 0.1 to 5 for low melting point metals.
7. The conductive resin composition according to any one of claims 1 to 6, which contains the conductive resin composition in a proportion of % by weight. 8 Phosphorous antioxidants are effective against thermoplastic resins.
The conductive resin composition according to any one of claims 1 to 7, containing in a proportion of 0.1 to 5% by weight.