JPH0212986B2 - - Google Patents

Description

[Detailed description of the invention]

[Objective of the invention] (Industrial application field) The present invention provides a highly reliable conductive resin composition that has excellent conductivity and exhibits little decrease in conductivity even in various environments, and its Regarding molded products. (Prior Art) In recent years, in order to protect electronic devices from electromagnetic waves generated in electronic circuits or to prevent leakage of electromagnetic waves to the outside, there has been a demand for the housings of electronic devices to be made of electromagnetic shielding materials. There is. and,
The molding material for this shield requires higher conductivity than conventional carbon fiber-filled materials, and at the same time requires excellent mechanical strength as a casing, so a metal-based conductive filler is used. It is being carried out to fill resin with 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 it is difficult to form a conductive resin composition when changing the color of the molding material. Air punching was extremely dangerous for the molding process, as the resin and low melting point metal separated and only the low melting point metal was scattered. 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 aimed at achieving the above object, the inventor of the present invention has developed a combination of conductive fibers and low-melting metal flux as a conductive filler. The present invention has been completed based on the discovery that a molded article that achieves the above object can be obtained by using a conductive resin composition using a thermoplastic resin containing a phosphorus antioxidant. be. That is, the present invention provides (A)
A pellet-like product in which the surface of a conductive filler consisting of conductive fibers, (B) a low-melting point metal, and (C) flux is coated with (D) a thermoplastic resin layer containing (D) a phosphorous antioxidant. This is a conductive resin composition characterized by blending master pellets of (F) and (F) thermoplastic resin pellets. 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 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 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 amount of conductive fiber blended in the master pellet is preferably 5 to 80% by weight. 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 containing Sn-Pb-Ag as a main component, and low-temperature solder alloys containing Sn-Pb-Bi as a main component. 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 within conductive fibers, by coating the surface of conductive fibers with low melting point metals, or by reducing the entire converged conductive fibers. Examples include coating with a melting point metal. In addition, there is a method of sprinkling and adhering granular low-melting point metal onto the surface of the conductive fibers, as long as the conductive fibers and the low-melting point metal are bundled together. The low melting point metal is desirably selected depending on the thermoplastic resin covering the conductive filler and the molding temperature of the natural pellet thermoplastic resin. 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 30% by weight.
This is because if it exceeds the weight percentage, 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. Halogens, amines, etc. corrode conductive fibers, molds, etc., so their use is not preferred.
The blending ratio of flux is based on the low melting point metal.
The content is preferably 0.1 to 5% by weight. The content is
If it is less than 0.1% by weight, it has no effect on the solder wettability of the conductive fibers, and if it exceeds 5% by weight, the physical properties of the resin deteriorate and the mold becomes corroded and stained, which is not preferable. It is preferable that the flux is normally filled in 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.
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 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 resin. The above components, that is, conductive fibers and low melting point metals containing flux, are assembled to form a conductive filler, and a thermoplastic resin containing a phosphorous antioxidant is coated and integrated on the surface of the conductive filler, Cut into master pellets. The thermoplastic resin pellets (F) used in the present invention (hereinafter referred to as natural pellets) may be the same or the same as the resin of the thermoplastic resin layer (E), or may be different. Further, the third synthetic resin formed at the interface by mixing with the thermoplastic resin (E) may have a reinforcing effect, that is, it may be a blended polymer. for example
(E) When using modified PPO resin, polycarbonate resin, etc. as the thermoplastic resin, good results can be obtained by using a styrene-based thermoplastic resin as the natural pellet. By doing so, the third synthetic resin formed at the interface has a reinforcing effect. By using these combinations, molded products with excellent properties can be obtained. The conductive resin composition of the present invention is usually produced as follows. This will be explained below using the drawings. FIGS. 1A to 1D are sketches of a conductive filler in which long-fiber conductive fibers and low-melting point 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, the collection of conductive fibers and low melting point metal can be carried out by conductive fibers 2 as shown in Figure 1b.
conductive fibers 2 coated with a low melting point metal 3 on the surface thereof, or conductive fibers 2 assembled as shown in Figure 1 c.
The entire body may be coated with a low melting point metal 3, or the
A conductive filler 1 is obtained by adhering and aggregating granular low-melting point metals 3 on the surface of conductive fibers 2 as shown in FIG. The master pellets 10 shown in FIGS. 1e to 1h are produced by coating the surface of the conductive filler 1 with a thermoplastic resin layer 4 containing a phosphorous antioxidant and cutting the same. The first cross-sectional view of the master pellet
Figures e to h correspond to the conductive filler 1 shown in Figures 1a to d, in which conductive fibers and low melting point metals are aggregated, respectively. master pellet 1
0 usually has a circular cross section, but it may be flat or other shapes, and is not particularly limited in shape. As shown in Figure 2, the master pellet is
The conductive filler 11 assembled as shown in FIGS. 1 to d is passed through the die 13 of the extruder 12.
A thermoplastic resin is coated and integrated on the surface of the pellet, and then cutting 15 is performed to obtain a master pellet 16. Although it is economically advantageous to carry out the master pellet production process continuously, it is not necessarily necessary to carry out the process continuously, but it may also be carried out in batches. A conductive resin composition is prepared by blending natural pellets with the master pellets in a conventional manner. The type and amount of thermoplastic resin in the natural pellets to be blended are appropriately selected depending on the properties required of the conductive resin composition and its molded product. The conductive resin composition thus produced can be injection molded at a temperature higher than the melting point of the low melting point metal to form molded products such as housings and parts for electronic equipment, measuring equipment, communication equipment, 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 and fused with the conductive fibers. The conductive fibers are bonded together, and the conductive fibers form a network with the low melting point metal, and are cooled and solidified as they are.
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 and causing poor conductivity. Become. 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 2 rosin
% by weight and one long Sn-Pb solder (60% Sn, 40% Pb) with a diameter of 300 μm was collected and converged to form a conductive filler. on the surface of conductive filler
Toughflex 410 (ABS resin, trade name, manufactured by Mitsubishi Monsanto Chemical Co., Ltd.) containing 2% by weight of MARK PEP24 (manufactured by Adeka Argus Chemical Co., Ltd., trade name of phosphorus antioxidant) is coated and integrated with a die of an extruder, and after cooling, It was cut into master pellets. This master pellet had a diameter of 3 mm and a length of 6 mm.
A conductive resin composition was prepared by mechanically mixing 100 parts by weight of the master pellets with 500 parts by weight of natural pellets (Toughflex 410, supra). The filling rate of copper fibers in this case was 10% by weight. Using this conductive resin composition, injection molding was performed at a temperature equal to or higher than the melting point of the low melting point metal to obtain a molded article. The obtained molded product was tested for volume resistivity, shielding effect, bending strength, and isot impact strength, and the results are shown in Table 1. In addition, the molded product was washed with methylene chloride to dissolve the resin, and the network state of the remaining conductive fibers was photographed using an electron microscope, as shown in FIG. In the figure, conductive fiber 20
It can be seen that the conductive fibers 21 and 21 are firmly fused together by the low melting point metal 22. at 80℃
Even after heating for 3000 hours, the shielding effect did not decrease at all, and the mechanical strength was 83% of the initial value.
Thus, the extremely remarkable effects of the present invention were confirmed. Comparative Example Toughflex 410 (described above) was integrally coated on the surface of 300 long copper fibers with a diameter of approximately 50 μm using a die of an extruder, and after cooling, the fibers were cut to produce master pellets. This master pellet has a diameter of 3 mm.
It was 6mm long. Natural pellets (Toughflex 410) are added to 100 parts by weight of this master pellet.
A conductive resin composition was prepared by mechanically mixing 500 parts by weight. 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 master pellet in the present invention, and Figure 2 shows the manufacturing process of the master pellet in the present invention. FIG. 3, which is a conceptual diagram for explanation, is an electron micrograph showing the shape of conductive fibers fused and bonded in a network shape with a low-melting point metal in the molded article 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... Master 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 comprising a pellet-like master pellet formed by integrally forming a coating layer, and (F) a thermoplastic resin pellet. 2. Claim 1 in which the conductive fibers are long fibers such as copper fibers, brass fibers, stainless steel fibers, aluminum fibers, nickel fibers, or organic or inorganic fibers having a layer of copper, aluminum or nickel on the surface. The conductive resin composition described in . 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, or rosin or active rosin. 5 The conductive fibers are attached to the conductive resin composition.
The conductive resin composition according to any one of claims 1 to 4, containing 0.5 to 30% by weight. 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. The conductive resin composition according to any one of claims 1 to 7, wherein the phosphorus antioxidant is contained in a proportion of 0.1 to 5% by weight based on the thermoplastic resin of the master pellet. 9. The conductive resin composition according to any one of claims 1 to 8, wherein the thermoplastic resin of the master pellet and the resin of the thermoplastic resin pellet are the same. 10 Claims 1 to 9, wherein the thermoplastic resin of the master pellet and the resin of the thermoplastic resin pellet form a blend polymer.
2. The conductive resin composition according to any one of Items 1-1. 11 The surface of a conductive filler consisting of (A) conductive fibers, (B) a low melting point metal, and (C) flux is coated with (D) a thermoplastic resin layer containing a phosphorous antioxidant (E). A conductive resin characterized by being made by injection molding a conductive resin composition that is a blend of pellet-like master pellets and (F) thermoplastic resin pellets at a temperature higher than the melting point of a low-melting point metal. Molding.