JPH0237120B2 - DODENSEIJUSHISOSEIBUTSUOYOBISONOSEIKEIHIN - 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 they have low conductivity and 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 such, conventional conductive resin compositions of metal fibers and molded products thereof have problems in that their applications are limited, their properties are unstable, and their reliability is low. 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 together 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 that the metal fibers were corroded, resulting in a significant deterioration of conductivity. (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 extensive research in an attempt to achieve the above object, the inventor of the present invention has discovered that by using conductive fibers and low melting point metals together, By using a thermoplastic resin containing an inhibitor, 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 during molding. The present invention was completed by discovering that a highly reliable conductive resin composition and molded products thereof, which are free from scattering and have improved moldability, can be obtained. That is, the present invention covers and integrally forms a (D) thermoplastic resin layer containing (C) a phosphorous antioxidant on the surface of a conductive filler made of (A) conductive fibers and (B) a low melting point alloy. This is a conductive resin composition characterized by blending pellet-like master pellets and (E) 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 include metal fibers such as long-fiber copper fibers, stainless steel fibers, brass fibers, aluminum fibers, and nickel fibers, and organic fibers having a metal layer of copper, aluminum, nickel, etc. on the surface. Examples include fibers and carbon fibers. The conductive fiber preferably has a diameter of about 5 to 100 μm. These conductive fibers are aggregated with a low-melting metal, which will be described later, to form a conductive filler, and a thermoplastic resin layer coated with a phosphorus-based antioxidant is integrated on the surface of the conductive fibers.Then, the fibers are cut into lengths of 5 to 8 mm and mastered. Make pellets.
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 is low;
If it exceeds % 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 containing Sn-Pb-Ag as a main component, and low-melting-point solder alloys containing Sn-Pb-Bi as a main component. These solders are fibrous,
The shape may be either granular or rod-like, and the shape is not particularly limited. These low melting point metals are desirably selected depending on the molding temperature of the thermoplastic resin to be mixed. The use of low melting point metals involves simply aggregating fibrous low melting point metals with conductive fibers, or
The surface of the conductive fibers may be coated with a low melting point metal, or the surface of the assembled conductive fibers may be coated with a low melting point metal. The low melting point metal is preferably blended in an amount sufficient to bond and coat the conductive fibers, and is desirably contained in a proportion of 5 to 30% by weight based on the conductive fibers. Content is 5
If the weight percentage is less than the last, binding and coating of the conductive fibers will be insufficient, and if it exceeds 30 weight%, only the low melting point metal will be liberated, reducing the physical properties of the resin.
This is because it is not desirable. Examples of the phosphorus antioxidant (C) 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 thermoplastic resin layer, which will be described later. The resin of the thermoplastic resin layer (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, Examples include polyetherimide resin. This thermoplastic resin is coated with a conductive filler consisting of conductive fibers and a low melting point metal to form a master pellet. The thermoplastic resin pellets (E) used in the present invention (hereinafter referred to as natural pellets) may be the same or the same type as the thermoplastic resin layer (D) described above.
Further, the third synthetic resin formed at the interface by mixing with the thermoplastic resin (D) may have a reinforcing effect, that is, it may be a blended polymer. For example, (D) modified as a thermoplastic resin.
When using PPO resin, polycarbonate resin, etc., good results can be obtained by using styrene-based thermoplastic resin as natural pellets. 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. Long conductive fibers and low melting point metals are aggregated to form a conductive filler, passed through an extruder die, and the surface of the conductive filler is coated with a thermoplastic resin layer containing a phosphorous antioxidant. form,
Next, the pellets are cut into appropriate sizes to form pellet-like master pellets. The master pellet usually has a circular cross section, but it does not have to be circular, but may have a flat or other shape, and the shape is not particularly controlled. 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. For the natural pellets to be blended, the thermoplastic resin and its amount are appropriately selected depending on the characteristics required for 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, excellent effects can be obtained by using conductive fibers and a low melting point metal together, and by blending a phosphorous antioxidant. In other words, when the conductive resin composition is kneaded with the thermoplastic resin and the conductive fibers in the heating cylinder of the injection molding machine, the oxide film of the conductive fibers formed during the manufacturing process and drying is removed by phosphorus-based oxidation. Removed by the reducing action of inhibitors. Next, the surface of the conductive fiber is firmly coated with a low melting point metal melted in the cylinder. In this case, if the conductive fibers have an oxide film and have poor solder wettability, the conductive fibers will corrode or the low melting point metal will be liberated, reducing the physical properties of the resin. Then, when the conductive resin composition is injected into a mold and cooled and solidified, the joining 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, and the conductivity will not deteriorate. 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 bonded. Therefore, it becomes possible to reduce the amount of conductive fibers filled.
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: 300 copper fibers with a diameter of 50 μm are bundled, and low melting point metal fibers with a diameter of 300 μm (Sn60%,
Toughflex 410 (ABS resin manufactured by Mitsubishi Monsanto Chemical Co., Ltd.) is aggregated to form a conductive filler.
HCA (phosphorous antioxidant manufactured by Sanko Kagaku Co., Ltd., trade name) was added to the material (trade name), and ABS resin was melted and coated on the surface of the conductive filler through a die of an extruder.
This was cooled and cut into lengths of 6 mm in the fiber direction using a pelletizer to obtain master pellets. The copper fiber filling rate of the master pellet was 60% by weight.
Toughflex 410 (mentioned above) is added to this master pellet.
A conductive resin composition was prepared by blending natural pellets. The filling rate of copper fibers in this case was 30% 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. In addition, the molded article was washed with methylene chloride to dissolve the resin, and the network state of the remaining conductive fibers was photographed using an electron microscope, which is shown in FIG. It can be seen that the conductive fibers 1 and 2 are tightly fused and bonded by the low melting point metal 3. The extremely significant effects of the present invention were confirmed. Comparative Example A master pellet, a conductive resin composition, and a molded article were prepared in the same manner as in the example except for the phosphorus antioxidant, and the molded articles were tested in the same manner. Therefore, 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 also contains phosphorus. By blending the antioxidant, the conductive fibers have good wettability and strong bonding between the conductive fibers, which makes it possible to reduce the amount of conductive fibers filled. There is no separation or scattering of the thermoplastic resin and low-melting point metal during processing, improving moldability. 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. Contains (C) a phosphorous antioxidant on the surface of a conductive filler made of (A) conductive fibers and (B) a low melting point metal (D)
1. A conductive resin composition comprising a pellet-like master pellet integrally coated with a thermoplastic resin and (E) a thermoplastic resin pellet. 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 fiber 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 contained in a proportion of 5 to 30% by weight based on the conductive fibers. 6 Phosphorous antioxidants are effective against thermoplastic resins.
The conductive resin composition according to any one of claims 1 to 5, wherein the conductive resin composition is contained in a proportion of 0.1 to 5% by weight. 7 Contains (C) a phosphorous antioxidant on the surface of a conductive filler made of (A) conductive fibers and (B) a low melting point metal (D)
A conductive resin composition is formed by integrally forming a coating with a thermoplastic resin layer and blending a pellet-like master pellet with (E) thermoplastic resin pellets, by injection molding at a temperature higher than the melting point of the low melting point metal. A conductive resin molded product characterized by: