Appeal No. 1997-1750
Application No. 08/524,024
Ziegler-Natta catalyst system which, in addition to a
titanium-containing solid component based on a finely divided
carrier, selected from the group consisting of silica, alumina
and aluminosilicate, also contains, as cocatalyst, an aluminum
compound, which process comprises in a first polymerization
step, polymerizing propylene at from 60 to 90EC and at from 20
to 40 bar and at a mean residence time of the reaction mixture
of from 0.5 to 5 hours, then,
in a second polymerization step, polymerizing a mixture of
propylene and ethylene onto the polymer obtained from the
first polymerization step at from 40 to 110EC and from 5 to 30
bar, this pressure being at least 7 bar below the pressure in
the first polymerization step, and at a mean residence time of
the reaction mixture of from 0.2 to 4 hours, and then,
in a third polymerization step, polymerizing ethylene or a
mixture of ethylene and propylene onto the polymer obtained
from the second polymerization step at from 50 to 110EC and
from 5 to 30 bar and at a mean residence time of the reaction
mixture of from 0.1 to 5 hours, the weight ratio between the
monomers reacted in the first and second polymerization steps
being from 1:1 to 20:1 and the weight ratio between the
monomers reacted in the first two polymerization steps and
those reacted in the third polymerization step being from 1:2
to 20:1.
The examiner relies upon the following references as
evidence of obviousness:
Toyota et al. (Toyota) 4,547,552 Oct. 15, 1985
Kerth et al. (Kerth) 5,162,465 Nov. 10, 1992
Appellants' claimed invention is directed to a three-
stage process for preparing a propylene-ethylene copolymer
which employs a Ziegler-Natta catalyst system comprising a
-2-
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