Elastomer-ethylene copolymer hot melt systems

DETAILED DESCRIPTION OF THE INVENTION The adhesive formulations of the invention broadly comprise an adhesive copolymer of ethylene and vinyl acetate and an olefin rubber as the elastomeric component.
The ethylene vinyl acetate copolymers having a 9 to 40 percent by weight content of vinyl acetate and a melt index of from 700 to 10,000 are known and the subject matter of copending U.
S.
patent application Ser.
No.
429,481 (of common assignee) wherein both the copolymer class and its method of preparation are disclosed and fully incorporated herein by reference thereto.
The olefin rubbers are produced from the polymerization of olefins and usefully have a Mooney viscosity (ML 4 at 250.
degree.
F.
) that vary over the range from about 20-70 with those providing the best results in adhesive blends having a viscosity varying over the range of about 20 to 45 and preferably 20 to 25.
Elastomeric polymers suitable for use in adhesive compositions of the present invention are those derived from olefin monomers, for example butyl rubbers.
Presently preferred for use are elastomeric polymers derived from monoolefinically unsaturated monomers in which the polymer has a saturated backbone.
Particularly preferred are the elastomeric copolymers of ethylene and propylene although other elastomers may be employed.
Useful ethylene-propylene copolymers ae those having from about 40-90% by weight combined ethylene, the balance propylene or propylene and a diene modifier, the latter to give the polymer a reactive group pendant to the polymer backbone.
Propylene will comprise at least about 10% by weight of the polymer and the diene comprises 0-10% by weight of the polymer.
If used the diene will preferably comprise 2-10% by weight of the polymer.
The diene modifiers are selected from non-conjugated dienes of which the following are a representative rather than exhaustive list: 1,4-hexadiene, 1,6-hexadiene, 1,4-pentadiene, bicyclopentadiene, and ethylidene norbornene.
Presently preferred polymers are those having a relatively low molecular weight and a relatively low ethylene content, the latter to cause the elastomer to have lower crystallinity, so as to minimize interfacial stress during adhesive bond formation