Compositions – Electrically conductive or emissive compositions – Free metal containing
Patent
1992-04-28
1994-03-29
Lieberman, Paul
Compositions
Electrically conductive or emissive compositions
Free metal containing
252514, 252518, 106 118, 106 119, 156DIG101, H01B 100, H01B 120, H01B 122
Patent
active
052981940
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to polymer compositions and especially to electrically conductive compositions.
2. Introduction to the Invention
Electrically conductive adhesives are employed in a number of fields where good electrical continuity is required. For example, when a shielded electrical cable is terminated with an electrical connector, a screened enclosure, e.g.: in the form of a dimensionally recoverable article, may be located over the connector and cable to provide a continuous screening between the connector and the cable shield. Such articles are described in U.S. Pat. No. 4,467,002, the disclosure of which is incorporated herein by reference. It is important to maintain a good electrical connection between the screen and the enclosure and both the connector and the cable shield, and electrically conductive adhesives have been employed for this purpose.
Electrically conductive adhesives can be formed by blending a quantity of electrically conductive material, e.g. a metal, into a solutions of the adhesive in a suitable solvent and evaporating the solvent. Normally silver flake is employed for this purpose in view of the relatively low bulk resistivities that can be achieved. The bulk resistivity of the adhesive will fall sharply with the increase in volume loading of metal until a so-called "percolation threshold" is reached after which the resistivity is low and relatively constant with respect to the metal loading. The silver loading employed will depend on the type of adhesive, but loadings in the region of 12-15% by volume may be used, may be used.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an adhesive composition which comprises a solid fusible particulate polymer material and a quantity of metal particles that have been blended with the particles of polymer material to render the composition electrically conductive.
Preferably the metal particles have an aspect ratio (i.e. the ratio of their largest to smallest dimension) of at least 5 and especially at least 10, the particles preferably being in the form of flake.
We have observed that the metal flakes adhere to the surface of the polymer particles, which is at least partly due to tackiness of the polymer particles, so that when the adhesive is fused the metal flakes form a relatively nonuniform dispersion on a microscopic scale, in contrast with previously used adhesives in which a very uniform dispersion is obtained. On fusion of the adhesive particles, the metal flakes tend to remain in the same regions as before fusion, thereby forming a large number of metal-flake-rich conductive paths throughout the fused or resolidified composition. It has been found that the quantity of metal flake required in the composition to reach the percolation threshold can, at least in some cases, be significantly reduced. In addition it is possible to use the composition to form adhesive bonds whose electrical conductivity remains relatively constant over long periods of time at elevated temperatures.
BRIEF DESCRIPTION OF THE DRAWING
The invention is illustrated by the drawing in which, FIG. 1 is a section through an electrical cable of the invention;
FIGS. 2 to 4 are graphs of the bulk resistivity of compositions of the invention and comparative compositions as a function of the loading of silver particles in the composition;
FIG. 5 is a graph of the resistance of an adhesive composition of the invention as a function of storage time at different temperature; and
FIG. 6 is a graph of the resistance of an adhesive composition of the invention as a function of storage at elevated temperature.
The composition according to the present invention may be employed for a variety of purposes. For example, it may be employed as an adhesive where an electrically conductive adhesive joint is required. In such a case the polymer composition may for example be a hot-melt adhesive or a curable adhesive. In other cases the composition may be employed as a void filler or mastic.
REFERENCES:
patent: 4181775 (1980-01-01), Corke
patent: 4467002 (1984-08-01), Crofts
patent: 4569786 (1986-02-01), Deguchi
patent: 4581158 (1986-04-01), Lin
patent: 4596670 (1986-06-01), Liu
patent: 4603165 (1986-07-01), McDonald et al.
patent: 4707388 (1987-11-01), Park et al.
patent: 4937015 (1990-06-01), Krieg et al.
International Search Report, International Application No. PCT/GB90/01677, filed Nov. 1, 1990.
British Patent Office Search Report, British Patent Application No. 8924616.9 filed Nov. 1, 1989.
Carter Richard
Collett Derrick
Burkard Herbert G.
Gerstner Marguerite E.
Kopec M.
Lieberman Paul
Raychem Limited
LandOfFree
Electrically conductive polymer composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrically conductive polymer composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrically conductive polymer composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-789486