Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1994-11-14
1997-04-08
Hamilton, III, Thomas
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
524505, 524508, 524571, 524575, 524474, 524476, 525 89, C08L 2510, C08L 7112
Patent
active
056188820
DESCRIPTION:
BRIEF SUMMARY
This invention provides new and technically superior gel compositions comprising a styrene-(ethylene/propylene)-styrene (SEPS) block copolymer and at least 300 parts by weight (preferably at least 400 parts by weight, more preferably at least 500 parts by weight) of mender liquid per 100 parts by weight of the block copolymer, which liquid extends and softens the ethylene/propylene polymer blocks of the said copolymer. These proportions of extender can alternatively be expressed as percentages by weight of the copolymer, thus: 300=25%, 400=20%, 500=17%.
Known gels made from styrene-(ethylene/butylene)-styrene (SEBS) block copolymers, and test methods for defining and characterising gels, are described in WO-A-8800603 and WO-A-9005166, the disclosures of which are incorporated herein by reference.
Gels according to the present invention, however, made of SEPS copolymer having weight average molecular weight Mw of at least 180,000, preferably at least 200,000, more preferably at least 220,000, and polystyrene content of 25-45 weight percent, preferably 28-40 weight percent, more preferably 29 to 36 weight percent, and made with substantially non-aromatic extender liquid, tend to have improved high-temperature performance and improved ability to retain the extender liquid when subjected to pressure in various end uses. The SEPS gels of this invention also tend to have higher tack than the known SEBS gels, thus reducing the need for added tackifiers to achieve a desired level of adhesion to surfaces with which they are in contact in end use.
The SEPS gels are preferably soft, high-temperature-slump-resistant, springy gel compositions, by which is meant liquid-extended polymer compositions having an ultimate elongation (measured by ASTM D412 modified as described below) greater than 100%, with substantially elastic deformation (i.e. substantially no hysteresis) to an elongation of at least 100%; ultimate tensile strength (ASTM D412) less than 1 MegaPascal; dynamic storage modulus (as hereinafter described) less than 50000 Pascals; and substantially zero slump at temperatures up to 100.degree. C., preferably up to 120.degree. C., more preferably up to 135.degree. C., and especially up to 150.degree. C.
The invention for some end purposes is more particularly concerned with such gel compositions comprising from 4% to 20% by weight of the SEPS copolymer and at least 500 parts by weight of extender liquid per 100 parts by weight of the polymer, in which the SEPS copolymer comprises more than 50%, preferably more than 75%, more preferably more than 90%, and especially more than 95%, by weight, or substantially all, of the total gelling polymer present. Various additives may be present, for example the tackifiers described in WO-A-9005166 or the polyphenylene oxide described in WO-A-8800603, or styrene-alkylene di-block copolymers for reducing the loss of extender liquid as described in our co-pending British Application 9119261.7. However, the superior performance of the present SEPS gels may reduce or eliminate the need for such additives.
The SEPS gels, with which the present invention is concerned, are well suited, inter alia, for re-enterable sealing of electrical connection enclosures. In these and other uses, the gels are subjected to continuous pressure, in view of which their ability to retain the extender liquid is important.
The composition may be "substantially free of" polystyrene-compatible components which significantly raise or lower the softening temperature (Ts) of the composition, either in the sense that substantially no such components are present, or in the sense that the quantities of such components which are present are not sufficient to produce a significant effect on the softening temperature. The use of such components significantly to raise the softening temperature (Ts) is claimed in the aforementioned WO-A-8800603 and may be used in the present case. Lowering of Ts is generally undesirable for the present purposes, and the extender oil will therefore preferably be substantially non-arom
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Graulus Hendrik
Hammond Philip J.
Hudson John M.
Burkard Herbert G.
Chao Yuan
Hamilton, III Thomas
Raychem Limited
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