Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1989-12-07
1993-06-08
Seccuro, Jr., Carman J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525240, 525197, C08L 2326, C08L 2318, C08L 2310, C08L 2304
Patent
active
052180468
DESCRIPTION:
BRIEF SUMMARY
Compositions consisting of ethylene polymers and polypropylene are already known.
Thus, document FR-A-2,529,563 describes compositions comprising from 10 to 40% by weight of isotactic polypropylene and from 60 to 90% by weight of at least one copolymer of ethylene and .alpha.-olefins containing at least 4 carbon atoms, with a relative density of between 0.905 and 0.940 and a melt index of between 0.2 and 3 dg/min, the content of .alpha.-olefin units in the copolymer being between 1 and 8 mol %. These compositions permit the manufacture of monooriented filaments exhibiting, in particular, a high tenacity.
Furthermore, document EP-A-0,052,557 describes compositions which have an improved impact strength and which contain from 40 to 98% by weight of isotactic polypropylene and from 2 to 60% by weight of a copolymer with a relative density not exceeding 0.935, obtained from 85 to 96% by weight of ethylene and from 4 to 15% by weight of at least one .alpha.-olefin.
Document FR-A-2,519,007 (U.S. Pat. No. 4,486,579) also discloses modified copolymers of ethylene and of at least one .alpha.-olefin containing from 3 to 12 carbon atoms, containing from 0.5 to 10 mol % of units derived from the said .alpha.-olefin, which are characterized in that their measured limiting viscosity is between 1.5 and 10 times their limiting viscosity calculated from the molecular mass distribution.
A way has now been found of obtaining thermoplastic compositions exhibiting improved mechanical properties, in particular low-temperature resilience, elongation at break and tensile strength, when compared with the known compositions, by using in combination with the polypropylene, instead of a copolymer of ethylene and .alpha.-olefins, a polyethylene or an ethylene/.alpha.-olefin co-polymer prepared by Ziegler catalysis and subjected to a modification such that the ratio of its measured and calculated limiting viscosities lies within a certain range.
The subject of the present invention is a thermoplastic composition containing: ethylene and, where appropriate, of at least one .alpha.-olefin containing from 3 to 12 carbon atoms, the said polymer containing at least 70 mol % of units derived from ethylene, and containing at least 85 mol % of units derived from at least one .alpha.-olefin containing from 3 to 12 carbon atoms and not more than 15 mol % of units derived from ethylene, which composition is characterized in that the polymer (A) is a modified polymer whose measured limiting viscosity is between 1.3 and 100 times its limiting viscosity calculated from the molecular mass distribution.
Polymer (A) is intended to mean a polymer obtained by homopolymerization of ethylene or by copolymerization of ethylene with at least one .alpha.-olefin containing from 3 to 12 carbon atoms in the presence of a Ziegler-type catalyst system comprising, for example, at least one catalyst based on a transition metal of groups IVB to VIB of the Periodic Classification and, where appropriate, at least one activator comprising a hydride and/or an organometallic derivative of a metal of groups IA to IIIA of the Periodic Classification, and modified, for example, by the action of a small quantity of at least one free radical initiator, so that its measured limiting viscosity lies between 1.3 and 100 times its limiting viscosity calculated from the molecular mass distribution. These concepts of modification and of limiting viscosities are described in detail in the document FR-A-2,519,007. The modification of the ethylene homopolymer or copolymer may also be carried out by dispersing the free radical initiator, before it acts upon the said homopolymer or copolymer, in a polymeric phase comprising at least one polymer containing at least 90 mol % of units derived from at least one .alpha.-olefin containing from 3 to 12 carbon atoms and not more than 10 mol % of units derived from ethylene, the said phase being present in such quantity that its proportion in the resulting composition is between 0.2 and 10% by weight.
The polymer (A) generally has a relative densi
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Audureau Joel
Crenna Vincent
Norsolor
Seccuro, Jr. Carman J.
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