Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1987-12-15
1990-10-02
Lesmes, George F.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428367, 428379, 428383, 428361, B32B 516, B32B 1502, B32B 2704
Patent
active
049606425
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to pellets for making electromagnetic wave shielding material using conductive fibers as a filler and a method for manufacturing the same.
BACKGROUND ART
The following are conventional methods for manufacturing pellets for making electromagnetic wave shielding material with conductive fibers dispersed in a matrix resin:
(1) A method for manufacturing pellets through the kneading of a matrix resin and conductive fibers, cut about 5 mm long by, for example, an extruder and the dispersing of the conductive fibers in the matrix resin.
(2) A method for manufacturing pellets through the coating of a strand of conductive fibers directly with a matrix resin by an extruder and the cutting of the strand to a desired length.
(3) A method for manufacturing pellets by dipping a strand made up of conductive fibers into a hot-melt resin, to coat it with the resin and by cutting the coated strand into predetermined lengths.
(4) A method for manufacturing pellets by dipping conductive fibers into a solution of a matrix resin in a solvent to coat them with the matrix resin and by cutting them to a desired length.
In the method (1), during the kneading of the conductive fibers and resin by the kneader, the conductive fibers are cut shorter than their initially cut length due to the direct cutting of the conductive fibers by a screw and due to the shearing of the resin. Furthermore, where an electromagnetic wave shielding material is formed through the molding of the kneaded material, such as an extrusion molding or injection molding, the resultant conductive fibers become much shorter. Because of the dispersion of the thus-shortened conductive fibers (0.5 mm or below) in the resin it is not yet possible to obtain a practical shield effect due to an increase in multiple contacts among the conductive fibers and to the consequent increase of electrical resistance of the electromagnetic wave shielding material. In order to improve the shield effect, more conductive fibers need to be added to the resin, resulting in high costs. According to the method (2), it is possible to prevent the undesirable cutting of the conductive fibers. However, it is difficult to disperse the conductive fibers in the resin during the molding process. This is because the conductive fibers are not uniformly mixed in the resin due to a lessening of the wettability of the conductive fibers and matrix resin. It is not possible to obtain a shield effect because of the increased electrical resistance involved. Method (3) involves poor workability and is never economical. Method (4) cannot obtain the desired surface configuration and is high in costs because of the use of the solvent.
DISCLOSURE OF INVENTION
It is accordingly the object of this invention to provide electromagnetic wave shielding pellets and a method for manufacturing the same, which causes the impregnation of conductive fibers of a collective form with a resin (the surface treatment) and the coating of the impregnated unit with another resin to be sequentially performed through the use of respective extruders to allow the conductive fibers of a predetermined length to be better dispersed, whereby it is possible to obtain an excellent electromagnetic wave shield effect.
In one aspect of this invention, pellets for making shielding electromagnetic wave shielding material are manufactured by impregnating a desired number of conductive fibers of a desired length as a collective unit with thermoplastic resin oligomer and coating the outside of the integral unit with a thermoplastic resin.
In another aspect of this invention, a method for manufacturing the aforementioned pellets comprises the steps of:
transporting a desired number of conductive fibers as a collective unit;
impregnating under pressure the integral unit of fibers with a resin which is compatible with a thermoplastic resin;
coating the outside of the integral unit with the aforementioned thermoplastic resin through an extrusion process while the impregnating resin retains its fluidity; an
REFERENCES:
patent: 4169186 (1979-09-01), Tazaki
patent: 4332853 (1982-06-01), Hornbeck
patent: 4566990 (1986-01-01), Liu et al.
patent: 4596670 (1986-06-01), Liu
patent: 4664971 (1976-05-01), Soens
Kosuga Izumi
Matsumuto Kazuaki
Otani Kenichi
Gray J. M.
Lesmes George F.
The Furukawa Electric Co. Ltd.
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