Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1994-03-04
1996-07-30
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
526340, C08L 5300
Patent
active
055412505
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a gel composition, preferably a soft, high temperature-slump-resistant, springy gel composition, by which is meant a liquid-extended polymer composition having a cone penetration value measured by a modified version of ASTM D217, as described in WO8800603 (RK308), the disclosure of which is incorporated hereto by reference, within the range from 100 to 400, (preferably 100 to 350), 10.sup.-1 millimetres; an ultimate elongation (measured by ASTM D412 as described in WO8800603) greater than 100%, with substantially elastic deformation (i.e. substantially no hysteresis) to an elongation of at least 100%; ultimate tensile strength (modified ASTM D412 as described in WO8800603) less than 1 MegaPascal; dynamic storage modulus (as described in WO8800603) less than 50000 Pascals; and substantially zero slump at temperatures up to 120.degree. C., preferably 150.degree. C., especially 180.degree. C. The composition may either contain a three-dimensional network of cross-linked molecular chains (gels) or may merely behave as if it contained such a network (gelloids), both being included in the term "gels" as used hereinafter.
The invention is more particularly concerned with such gel compositions comprising a styrene-elastomeric block-styrene triblock copolymer, preferably a styrene-alkylene-styrene block copolymer having relatively hard polystyrene end blocks and relatively elastomeric (preferably hydrogenated rubber) mid-block. Examples of such copolymers include polystrene-polybutadiene-polystyrene (SBS) and polystyrene-poly(ethylene/butylene) polystyrene (SEBS) triblock copolymers.
These soft, slump-resistant, springy, triblock copolymer gels with which the present invention is concerned, hereinafter referred to for brevity as "S-Gels", are well suited, inter alia, for re-enterable sealing of electrical connection enclosures. Examples of such S-Gels are described in WO90/05166 (RK403).
In use, it is often desirable to hold these gels under compression, the pressure encountered in practice being reasonably simulated in the laboratory by applying pressure of 50 kPa to 15 mm diameter round discs of the gel. At such pressures we have discovered that the S-gels containing more than 400 parts by weight, especially more than 500 parts by weight, of the extender liquid per 100 parts by weight of the gel-forming block copolymer (i.e. less than 20%, especially less than 16.79% copolymer) tend to suffer from exudation of the extender liquid. At higher pressures, gels containing as little as 300 parts by weight of the extender liquid per 100 parts by weight of the block copolymer may also suffer from such exudation. Gels of higher copolymer content are less affected by such exudation, but tend to be too firm for many of the purposes to which S-gels are put. The present invention reduces such exudation without unacceptably altering the other properties of the gel and also reduces the need for added tackifiers, for example hydrogenated styrenic tackifier resins, or liquid polybutene or liquid polyisoprene tackifiers.
The invention accordingly provides a gel composition comprising: block of which is compatible with extender E (specified below), the amount of D being sufficient to reduce by at least 10% the exudation of E from the composition when under compression in use; and by weight of extender liquid (E) per 100 parts by weight of T+D, which liquid extends and softens the elastomeric blocks of T and of D. whole composition and/or containing less than 20% by weight based on the whole composition of added hydrogenated styrenic tackifier resin, preferably of any added tackifier.
The composition will usually have, or may be adjusted by simple trial and error to have, a cone penetration value within the range from 100 to 400, (preferably 100 to 350), (10.sup.-1 millimetres); an ultimate elongation greater than 100%, with substantially elastic deformation to an elongation of at least 100%; ultimate tensile strength less than 1 MegaPascal; dynamic storage modulus less than 50000 Pascals; and substantially
REFERENCES:
patent: 4080348 (1978-03-01), Korpman
patent: 4136071 (1979-01-01), Korpman
patent: 4833193 (1989-05-01), Sieverding
Graulus Hendrik
Hudson John M.
Nixon Allen C.
Burkard Herbert G.
Cain Edward J.
Chao Yuan
Raychem Limited
Zavell A. Stephen
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