Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1998-04-23
2000-03-28
Nutter, Nathan M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524121, 524123, 524127, 524186, 524195, 524214, 524216, 524413, 156155, C09J12308, C08K 338, C08K 500
Patent
active
060433043
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a flame-retarded hot-melt adhesive composition, which may be applicable to dimensionally heat-recoverable articles to flow and seal when the articles are heat-recovered in use.
Hot-melt adhesives based on non-flame-retarded ethylene/vinyl acetate (EVA) copolymer or polyamide (PAm) are well known in the heat-shrink field and other fields. Adhesives flame-retarded with halogenated organic additives for use on the inner surface of a heat-shrinkable tube are described in U.S. Pat. No. 5,346,539. The present invention improves on this by providing more environmentally-acceptable compositions flame-retarded with halogen-free additives, which can nevertheless pass stringent flammability test requirements at unexpectedly low additive levels, while surprisingly maintaining desirable heat softening and flow characteristics.
The invention accordingly provides a hot-melt adhesive composition based on ethylene/vinyl acetate copolymer (EVA) comprising not more than 35% (preferably not more than 30%, more preferably not more than 25%) by weight, based on the whole composition, of halogen-free char-forming (preferably phosphorus-containing) flame-retardant additive(s) in an amount at least sufficient to prevent flaming drips generated on burning of a strip of the adhesive from igniting the underlying absorbent cotton according to the 20 mm Vertical Burn Test of Underwriters Laboratories Test Method UL-94 (1993), V-1, preferably V-0.
It has been found according to the present invention that the EVA hot melts can be adequately flame retarded with halogen-free additives, preferably in the absence of further flame retardants or thixotropy-increasing fillers, which additives surprisingly do not achieve the same desirable effect at similar additive levels in polyamide-based hot melts. The polyamides moreover tend to be more expensive than the EVAs. It has also unexpectedly been found that a relatively high Melt Flow Index (MFI) assists the EVA adhesives in passing the above UL94 requirements.
The specified (preferably phosphorus-containing) additives are halogen-free, and it is preferred that the whole adhesive or mastic composition is substantially entirely halogen-free, except for possible negligible amounts of halogenated impurities. The compositions according to this invention are preferably substantially free of finely-divided silica, talc, or alumina fillers, and substantially free of all finely-divided thixotropy-increasing fillers.
In one preferred composition of the invention, the flame-retardant additive comprises ammonium phosphate, preferably ammonium polyphosphate; or an organic amine phosphate, preferably ethylene diamine phosphate. This composition preferably comprises at least 20%, preferably 25 to 35%, more preferably 25 to 30%, by weight of the ammonium phosphate or organic amine phosphate, preferably in the absence of other flame-retardant additives.
In another preferred embodiment of the invention, the composition comprises a synergist for the aforementioned ammonium polyphosphate, preferably poly{[6-(4-morpholinyl)-1,3,5-triazine-2,4-diyl]-1,4-piperazinediyl} (C.sub.11 H.sub.16 N.sub.6 O).sub.n. In this case, the composition preferably comprises at least 15%, preferably 15 to 30%, more preferably 15 to 20%, by weight of the combined ammonium phosphate and synergist, preferably in the absence of other flame-retardant additives.
In an especially-preferred embodiment of the invention, the flame-retardant additive comprises red phosphorus. Preferably, the composition comprises at least 1%, preferably at least 1.25%, more preferably at least 1.5%, by weight of the red phosphorus, preferably in the absence of other flame-retardant additives. It is also preferred that the composition comprises not more than 10%, preferably not more than 5%, more preferably not more than 3%, by weight of the red phosphorus. The red phosphorus will preferably be master-batched at about 50% by weight in a carrier polymer compatible with, preferably of the same or similar chemical type or more preferably the
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Novack Sheri M.
Nutter Nathan M.
Raychem Limited
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