JPH0248588B2 - DODENSEIJUSHISOSEIBUTSUOYOBISONOSEIKEIHIN - 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 exhibits excellent conductivity and does not deteriorate in conductivity even in various environments, and molding thereof. Regarding products. (Prior Art) Conventionally, conductive resin compositions have been prepared by blending conductive fibers with thermoplastic resins, and the compositions have been used in conductive resin molded products. These materials have mainly been blended with carbon-based conductive fibers, but their main purpose 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 field shielding. However, when metal-based conductive fibers (hereinafter simply referred to as metal fibers) are blended, the specific gravity increases and the original properties of the resin are significantly impaired, so it is required to minimize the amount blended. There is. However, when the blending amount of these metal fibers is reduced, the conductivity decreases, and furthermore, the usage environment is also subject to significant restrictions. That is, due to the difference in thermal expansion between the resin used and the metal fiber, a problem arises in that the 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 are limited in their uses, and have problems such as unstable characteristics and low reliability. On the other hand, a method of blending a low melting point metal with a thermoplastic resin is also known, but the low melting point metal has poor adhesion with the resin, and it is difficult to dry the material when changing the color of the material.
There was a problem that the resin and the low melting point metal separated and only the metal was scattered, which was extremely dangerous in terms of the molding process. Furthermore, it is known to use metal fibers and low melting point metals, but when metal fibers are dried before forming, an oxide film is formed on the surface of the metal fibers, which deteriorates the wettability of the metal fibers. There was a problem that the conductivity deteriorated significantly. Additionally, when metal fibers and low-melting point metals are used together, there is a problem in that the mechanical strength of the resin is significantly reduced due to the oxidative deterioration rate accelerating due to the catalytic action of the metal, so a large amount of antioxidant is added. I will have to. However, this antioxidant has the function of inactivating the metal surface and also has the problem of inhibiting the wettability of metal fibers. (Problems to be Solved by the Invention) The present invention has been made to solve the above problems.The conductive fibers have good wettability and are strongly bonded to low melting point metals, and are conductive even at high temperatures. The object of the present invention is to provide a highly reliable conductive resin composition that does not deteriorate, has excellent stability over time, is safe in terms of molding process, and does not reduce mechanical strength, and molded products thereof. [Structure of the Invention] (Means for Solving the Problems) As a result of intensive research aimed at achieving the above object, the present invention has been developed to prevent the wettability of conductive fibers from being inhibited by oxidizing agents. First, a flux that improves the wettability of the conductive fibers is filled into a thermoplastic resin that coats the conductive fibers and a low-melting point metal.
In addition, by filling thermosetting resin pellets with an antioxidant that inhibits the wettability of conductive fibers and separating them from the conductive fibers, the wettability of the conductive fibers is improved and stabilized, and at the same time, the mechanical strength is reduced. The present invention was completed by discovering that this can be prevented. That is, the present invention consists of a conductive filler made of conductive fibers A and a low melting point metal B, coated with a thermoplastic resin D containing flux C, and cut into pellets, and master pellets E oxidized. A conductive resin composition characterized by being blended with F thermoplastic resin pellets containing an inhibitor, and this conductive resin composition is injection molded at a temperature higher than the melting point of a low melting point metal. This is a conductive resin molded product characterized by: The A conductive fibers 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. Alternatively, inorganic fibers may be used, and these may be used alone or in combination of two or more. Among these, copper fiber is most suitable because it can be used with a resin that exhibits wettability with the low-melting metal within the molding temperature range of the resin used and does not harm the mold or the like. The diameter of the conductive fibers is preferably about 5 to 100 μm, and the conductive fibers are aggregated with a low melting point metal (described later) to form a conductive filler, the surface of which is coated with a thermoplastic resin containing flux, and then the length is 5 μm. Cut into ~6 mm pellets to make master pellets. The amount of conductive fibers to be blended is preferably 0.5 to 30% by weight based on the total composition. If the amount is less than 0.5% by weight, the conductivity will be low.
Moreover, if it exceeds 30% by weight, the fluidity and other properties of the conductive resin composition will deteriorate, which is not preferable. The B low melting point metal used in the present invention is selected depending on the molding temperature of the thermoplastic resin used,
It is desirable that the resin has a slightly higher melting point than the thermoplastic resin. More desirably, a low melting point metal that melts at the lowest temperature part of the heating cylinder of the injection molding machine can be selected. As a low melting point metal,
Sn or Sn-Pb general solder, Sn-Pb-Ag
Examples include high-temperature solder based on Sn-Pb-Ei type and low-temperature solder based on Sn-Pb-Ei type, 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 amount of the low melting point metal is sufficient to bond and coat the conductive fibers, and the amount of the low melting point metal is 5 to 50% for the conductive fibers.
It is desirable to mix 30% by weight. If the blending amount is less than 5% by weight, binding and coating of the conductive fibers will be insufficient and the conductivity will be low, which is not preferable. Moreover, if it exceeds 30% by weight, low melting point metals will be liberated, which will deteriorate the physical properties of the resin, which is undesirable. Low melting point metals can be condensed into long conductive fibers,
Each conductive fiber may be coated with a molten low melting point metal, or the entire conductive fiber may be coated.
In short, it is important to integrate the conductive fiber and the low melting point metal. The material thus produced is used as a conductive filler. The C flux used in the present invention includes commonly used organic acids such as stearic acid, lactic acid,
Examples include oleic acid, glutamic acid, resin-based rosin, and activated rosin. Halogen-based fluxes are undesirable because they tend to corrode conductive 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 those having the following chemical formula. Since HCA (manufactured by Sanko Kagaku Co., Ltd., trade name) and the like exhibit good wettability, they can be used as the flux of the present invention. The blending ratio of flux is preferably in the range of 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 effective in improving the wettability of the conductive fibers, and if it exceeds 5% by weight, it will cause deterioration of the physical properties of the molded product and corrosion and staining of the mold, which is undesirable. The D thermoplastic resin used in the present invention includes polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile butadiene styrene resin, modified polyphenylene oxide resin,
Examples include polybutylene terephthalate resin, polycarbonate resin, etc., which may be used alone or in combination
Use as a mixture of more than one species. These thermoplastic resins are used to coat the surface of conductive fillers made of conductive fibers and low-melting metals, and then cut into master pellets. In this case, it is important to include flux in the thermoplastic resin. The E antioxidant used in the present invention may be any antioxidant suitable for the thermoplastic resin serving as the matrix. For example, phenol is suitable for polystyrene resin, acrylonitrile-butadiene-styrene copolymer resin, and modified polyphenylene oxide resin. Antioxidants, specifically MARK-AO-20, AO
-50, AO-80 (manufactured by Adeka Argus Chemical Co., Ltd., trade name), and phosphite antioxidants, specifically
It is best used in combination with MARK PEP-24G and PEP-36 (manufactured by Adeka Argus Chemical Co., Ltd., trade name). The blending ratio of antioxidant varies depending on the resin used, but it is based on 100 parts by weight of thermoplastic resin pellets.
It is desirable to range from 0.1 to 10 parts by weight. If the amount is less than 0.1 part by weight, the antioxidant effect will be poor, and if it exceeds 1.0 part by weight, the physical properties will deteriorate, such as a decrease in the heat distortion temperature of the thermoplastic resin, which is undesirable. It is preferable that the antioxidant be blended into the thermoplastic resin pellets. This is because, if blended with the thermoplastic resin of the master pellet, the antioxidant will inhibit the solder wettability of the conductive fibers, which is undesirable. The F thermoplastic resin pellets (also referred to as natural pellets) used in the present invention may be any pelletized thermoplastic resin, such as polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile-butadiene-styrene copolymer resin. , modified polyphenylene oxide resin, polybutylene terephthalate resin, polycarbonate resin, etc., and these may be used alone or as a mixture of two or more types. It may be the same kind or the same as the D thermoplastic resin described above, or it may be different. Further, 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 blended polymer. For example, modified as a thermoplastic resin in master pellets.
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 such a combination, a molded article with even better properties can be obtained. 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 conductive fibers and a low-melting point metal, and extruded through a die of an extruder together with a thermoplastic resin containing flux to form a coating of thermoplastic resin on the surface of the conductive filler. Then, the pellets are cut into appropriate sizes to form master pellets. The master pellet usually has a circular cross section, but may have a flat or other shape, and is not particularly limited in shape. Although it is economically advantageous to carry out the process of producing master pellets continuously, it is not necessarily necessary to carry out the process continuously, and if necessary, the master pellets may be produced in batches. A conductive resin composition is produced by blending natural pellets made of a thermoplastic resin containing an antioxidant with the master pellets thus obtained. The shape of the natural pellets is not particularly limited as is the shape of the master pellets described above. For the natural pellets to be blended, the type and amount of thermoplastic resin are appropriately selected depending on the properties required of 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. (Function) According to the present invention, conductive fibers and a low melting point metal are coated with a thermoplastic resin containing flux and separated into master pellets, which are cut into pellets, and thermoplastic resin pellets containing an antioxidant. By doing so, excellent effects can be obtained. That is, when the conductive resin composition is kneaded in the heating cylinder of the injection molding machine, the conductive fibers contained in the master pellet are dispersed and kneaded, and the conductive fibers are mixed into the flux contained in the thermoplastic resin. Since the conductive fibers are in sufficient contact and wettability is imparted, the low melting point metal evenly covers the areas where the conductive fibers are in contact with each other. Since the conductive fibers come into contact with the flux before contacting with the antioxidant contained in the natural pellets, there is no inhibition of wettability by the antioxidant. In this way, the distribution
When the kneaded mixture is poured into a mold and cooled and solidified, the low melting point metal fuses the joints of the conductive fibers to form a network, which is cooled and solidified. In this way, the conductive fibers are firmly fused and bonded by the low-melting point metal without being separated from each other at the bonding points, so the conductivity does not deteriorate even if placed in a high-temperature environment. This can be clearly confirmed by dissolving the resin component of a conductive resin molded article with a solvent, and clearly confirming the state of a strongly fused network of conductive fibers. (Example) Next, the present invention will be specifically explained with reference to Examples. Example: 500 long copper fibers with a diameter of 50 μm were converged,
2 parts by weight of rosin and HCA (manufactured by Sanko Kagaku Co., Ltd., trade name) per 100 parts by weight of polystyrene resin are applied as a flux to the surface of a conductive filler that aggregates low-melting metals (60% Sn, 40% Pb) with a diameter of 500 μm. Dialex HT-91 (polystyrene resin manufactured by Mitsubishi Monsite Co., Ltd., trade name) containing 3 parts by weight was passed through a die of an extruder to form a coating. After cooling, the pellets were cut into lengths of 6 mm in the fiber direction using a pelletizer to obtain master pellets. Next, this master pellet contains 4 parts by weight each of MARK-AO-20 and MARK-PEP-36 (both are antioxidants manufactured by Adeka Argus Chemical Co., Ltd., trade names) based on 800 parts by weight of polystyrene resin. Dialex HT
-91 (mentioned above) natural pellets are blended,
A conductive resin composition was manufactured. The copper fiber filling rate in this case was 20% 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.
In particular, even after treatment at 80°C for 3000 hours, almost no deterioration of the shielding effect was observed, confirming the extremely remarkable effects of the present invention. Comparative example: 200 long copper fibers with a diameter of 50 μm are converged.
The conductive filler is a collection of low melting point metals (Sn60%, Pb40%) with a diameter of 300μm, and polystyrene resin is used as the conductive filler.
2.2 parts by weight of rosin per 1000 parts by weight HCA (as above)
3.3 parts by weight plus MARK-AO-20 and
Diaflex HT-91 (described above) containing 4.4 parts by weight of each MARK-PEP-36 was extruded through a die while being kneaded in an extruder to form a coating on the surface of the conductive filler, and cut into pellets. A conductive resin composition was obtained, and a molded article thereof was manufactured.
The same tests as in the examples were conducted on these and the results are shown in Table 1.

[Table] [Effects of the invention] As is clear from the above explanation and Table 1,
The conductive resin composition and molded article thereof of the present invention include:
Flux is blended into the thermoplastic resin side that covers the conductive filler, which is a collection of conductive fibers and low-melting metals, and an antioxidant is blended into the natural pellet side, which improves solder wetting of the conductive fibers. It has good conductivity without being inhibited by antioxidants, and is strongly fused with low-melting point metals, so there is no deterioration in conductivity even at high temperatures, and it has excellent stability over time. It is safe to mold and process, and has mechanical strength. A highly reliable molded product that does not deteriorate the quality can be obtained.

Claims (1)

[Scope of Claims] 1. Master pellets in which the surface of a conductive filler consisting of A conductive fibers and B low melting point metal is coated with D thermoplastic resin containing C flux and cut into pellets. 1. A conductive resin composition comprising: E and thermoplastic resin pellets F containing an antioxidant. 2. Claim 1, wherein the conductive fiber is a long fiber copper fiber, stainless steel fiber, brass fiber, aluminum fiber, nickel fiber, or an organic or inorganic fiber having a copper, aluminum or nickel layer on the surface. conductive 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 A conductive fiber and B a low melting point metal on the surface of a conductive filler D thermoplastic resin containing C flux is formed and integrated into a master pellet cut into pellets, and E contains an antioxidant. F. A conductive resin molded article, characterized in that it is made by injection molding a conductive resin composition blended with thermoplastic resin pellets at a temperature equal to or higher than the melting point of a low melting point metal.