Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including strand or fiber material which is a monofilament...
Patent
1996-11-12
1998-03-10
Theisen, Mary Lynn
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including strand or fiber material which is a monofilament...
264104, 264126, 442401, B32B 2702
Patent
active
057261067
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to EMI shielding materials in form of plates, panels, and fabrics and methods for their preparation and for preparing the fibers therefor.
BACKGROUND ART
The harmful action of high intensity, high frequency electromagnetic radiation on sensitive micro electronics and especially on human body has been recognized for a long time. For shielding the source of radiation different absorbing or reflecting panels, blocks or plates are used. If the source cannot be completely shielded for protection of personnel different clothes made of fabrics with metallic or metallized fibers have been used. However, such materials are of reflecting type, i.e. are themselves secondary sources of radiation with uncontrollable power and directional pattern. The secondary radiation fields can irradiate unprotected parts of human body and penetrate areas that are closed to the direct action of primary fields.
Thus, for effective protection of personnel from electromagnetic radiation, elastic fabrics or textile materials of the absorbing type are required. Such fabrics can be produced from synthetic chemical fibers filled with particles of absorbing material.
The known method of production of fibers with magnetic particles comprise extrusion, which does not allow high concentration of absorbing component owing to the high viscosity of the resulting melt. According to another known method fibers are made by spinning from paste mixture of polymer and magnetic particles but the resulting fiber has a structure of shell-core type, with magnetic particles present either in the shell or the core, which reduces the effective filler concentration.
A known method for production of fabrics uses permanent magnet as a filler. However, said filler has very low absorption of electromagnetic waves, which makes fabrics made from fibers with this filler unsuitable for EMI shielding.
According to a known method for making EMI shielding panels, short thermoplastic fibers are mixed with conducting nonwoven material and the mixture is then pressure molded. However, this method does not provide uniform filler distribution in the material at high concentration which drastically reduces its effectiveness as EMI shielding material.
DISCLOSURE OF THE INVENTION
An object according to the present invention is to provide a method for production of highly filled ferromagnetic fibers.
Another object according to the present invention is to produce EMI shielding materials in form of panels and plates and fabrics manufactured by means of highly filled ferromagnetic fibers.
According to the present invention highly filled ferromagnetic fibers are made by wet spinning from dispersion containing a solution or gel of polymer and particles of ferromagnetic fillers. Components of said dispersion are treated in an ultrasonic dispenser or ball mill and the diameter of said fibers is 20-30 average diameter of the filler particles.
Effective absorber particles useful as fillers in the making of the highly loaded ferromagnetic fibers according to the present invention are e.g. carbonyl iron and magnetically soft ferrites. The filler particles are first treated either in an ultrasonic dispenser with a small amount of solvent added and in the presence of a small amount, e.g. 1 wt. % of binder polymer or in a ball mill. The particles of carbonyl iron are not changed by the treatment and remain in form of practically monodispersed particles of 2-5 .mu.m diameter. The ferrite particles are partially reduced in size during the treatment and a wide particle size distribution results with the fine fraction (d<0.1d.sub.av) being at least 10 wt. %.
Treatment of the filler in the presence of a small amount of binder polymer ensures high stability of dispersion through the mechanism of displacement stabilization even for high density fillers during the whole period of fiber spinning.
As a binder thermoplastic polymers are used, such as copolymers of tetrafluoroethylene, superhigh molecular weight polyethylene, etc.
The diameter of the fibers can be c
REFERENCES:
patent: 4699743 (1987-10-01), Nakamura et al.
patent: 4725490 (1988-02-01), Goldberg
Buts Aleksei Vladimirovich
Grinenko Elena Sergeevna
Klason Tore Carl Fredrik
Kubat Josef
Ponomarenko Anatoliy Tikhonovich
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