Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in two or more physically distinct zones
Reexamination Certificate
1998-08-20
2001-05-01
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in two or more physically distinct zones
C526S075000, C526S095000, C526S114000, C526S351000
Reexamination Certificate
active
06225421
ABSTRACT:
The present invention relates to a process for the manufacture of a composition comprising ethylene polymers, comprising a homopolymer and a copolymer of ethylene, which makes use of several polymerization reactors connected in series. It also relates to the compositions comprising ethylene polymers capable of being obtained by this process and to their use in the manufacture of films and pipes.
Patent Application EP-A-0,603,935 (Solvay) discloses a process for the preparation of a composition comprising ethylene polymers comprising an ethylene polymer with a high melt flow index (MI
2
of 5 to 1000 g/10 min) and an ethylene polymer with a low melt flow index (MI
5
of 0.01 to 2 g/10 min) in at least two reactors arranged in series, the ratio by weight of these polymers being equal to (30 to 70):(70 to 30). This patent application more specifically discloses a composition, prepared in suspension in hexane, comprising an ethylene homopolymer having an M
2
of 168 g/10 min and a copolymer of ethylene and of butene having an MI
5
of 0.21 g/10 min.
Patent Application EP-A-0,580,930 discloses a process for the preparation of a composition comprising ethylene polymers in two loop reactors in the liquid phase in which, in a first reactor, ethylene and an alpha-olefin, such as hexene, are introduced, so as to prepare a copolymer of ethylene and of hexene having a melt flow index HLMI varying from 0.01 to 5 g/10 min, and then the mixture resulting from the first reactor is introduced into a second reactor fed with ethylene, so as to obtain a polymer of ethylene having an HLMI of greater than 5 g/10 min. As the mixture resulting from the first reactor still comprises unpolymerized hexene, the polymer formed in the second reactor is also a copolymer of ethylene and of hexene.
The compositions resulting from these processes generally exhibit processing and mechanical properties which render them suitable for being used in the manufacture of various shaped articles.
The aim of the present invention is to provide a process for the manufacture of compositions comprising ethylene polymers exhibiting a better compromise between the processing properties and the mechanical properties in comparison with the compositions obtained by the known processes of the state of the art.
The invention consequently relates to a process for the manufacture of a composition comprising ethylene polymers, in at least two polymerization reactors connected in series, according to which:
in a first reactor, ethylene is polymerized in suspension in a mixture comprising a diluent, hydrogen, a catalyst based on a transition metal and a cocatalyst, so as to form from 30 to 70% by weight with respect to the total weight of the composition of an ethylene homopolymer (A) having a melt flow index MI
2
of 5 to 1000 g/10 min,
the said mixture, additionally comprising the homopolymer (A), is withdrawn from the said reactor and is subjected to a reduction in pressure, so as to degas at least a portion of the hydrogen, then
the said at least partially degassed mixture comprising the homopolymer (A), as well as ethylene and 1-hexene and, optionally, at least one other &agr;-olefin, are introduced into a subsequent reactor and the suspension polymerization is carried out therein in order to form from 30 to 70% by weight, with respect to the total weight of the composition, of a copolymer of ethylene and of hexene (B) having a melt flow index MI
5
of 0.01 to 2 g/10 min.
For the purposes of the present invention, ethylene homopolymer (A) is understood to denote an ethylene polymer composed essentially of monomer units derived from ethylene and substantially devoid of monomer units derived from other olefins. Copolymer of ethylene and of hexene (B) is understood to denote a copolymer comprising monomer units derived from ethylene and monomer units derived from 1-hexene and, optionally, from at least one other &agr;-olefin. The other &agr;-olefin can be selected from olefinically unsaturated monomers comprising from 3 to 8 carbon atoms (with the exclusion of 1-hexene), such as, for example, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 3- and 4-methyl-1-pentenes and 1-octene. Preferred &agr;-olefins are propylene, 1-butene and 1-octene and more particularly still 1-butene. The copolymer (B) according to the invention generally comprises at least 90%, in particular at least 94%, by weight of monomer units derived from ethylene. It preferably comprises at least 96% by weight of monomer units derived from ethylene. The content of monomer units derived from 1-hexene in the copolymer (B), hereinafter referred to as hexene content, is generally at least 0.4% by weight, in particular at least 0.6% by weight, values of at least 1% by weight being favourable. The hexene content of the copolymer (B) is usually at most 10% by weight, preferably at most 6% by weight. A hexene content which does not exceed 4% by weight is particularly preferred. For the purposes of the present invention, the hexene content of the copolymer (B) is measured by
13
C NMR according to the method described in J. C. Randall, JMS-Rev. Macromol. Chem. Phys., C29(2&3), p. 201-317 (1989), that is to say that the content of units derived from hexene is calculated from the measurements of the integrals of the lines characteristic of hexene (23.4, 34.9 and 38.1 ppm), in comparison with the integral of the line characteristic of the units derived from ethylene (30 ppm). A copolymer (B) composed essentially of monomer units derived from ethylene and from 1-hexene is particularly preferred.
For the purposes of the present invention, melt flow index MI
2
, respectively MI
5
, is understood to denote the melt flow indices measured according to ASTM Standard D 1238 (1986) at a temperature of 190° C. under a load of 2.16 kg, respectively 5 kg. Furthermore, melt flow index HLMI is understood to denote the melt flow index measured according to ASTM Standard D 1238 (1986) at a temperature of 190° C. under a load of 21.6 kg.
The homopolymer (A) according to the invention preferably exhibits an MI
2
of at least 50, very particularly of at least 90, g/10 min. The MI
2
of the homopolymer (A) preferably does not exceed 700 g/10 min. The homopolymer (A) advantageously exhibits an HLMI of at least 100 g/10 min.
The homopolymer (A) advantageously exhibits an intrinsic viscosity &eegr;
A
(measured in tetrahydronaphthalene at 160° C.) of at least 0.50 dl/g, preferably of at least 0.58 dl/g. Its intrinsic viscosity generally does not exceed 1.50 dl/g, preferably it does not exceed 1.00 dl/g. A homopolymer for which &eegr;
A
does not exceed 0.86 dl/g is particularly preferred.
The melt flow index MI
5
of the copolymer (B) according to the invention is preferably at least 0.015 g/10 min. It preferably does not exceed 0.1 g/10 min. The copolymer (B) advantageously exhibits an HLMI of at least 0.1 g/10 min which, furthermore, does not exceed 20 g/10 min.
The copolymer (B) generally exhibits an intrinsic viscosity &eegr;
B
(measured in tetrahydronaphthalene at 160° C.) of at least 2.20 dl/g. Its intrinsic viscosity &eegr;
B
generally does not exceed 6.30 dl/g, preferably not 5.90 dl/g. A copolymer (B) for which the intrinsic viscosity does not exceed 4.00 dlg is particularly preferred.
Suspension polymerization is understood to denote the polymerization in a diluent which is in the liquid state under the polymerization conditions (temperature, pressure) used, these polymerization conditions or the diluent being such that at least 50% by weight (preferably at least 70%) of the polymer formed is insoluble in the said diluent.
The diluent used in the polymerization process according to the invention is usually a hydrocarbon-comprising diluent which is inert with respect to the catalyst, the cocatalyst and the polymer formed, such as, for example, a linear or branched alkane or a cycloalkane having from 3 to 8 carbon atoms. The diluent which has given the best results is isobutane. One advantage of the use of isobutane lies in particular in its ready recycling. This is because the use of i
Moens Bruno
Promel Michel
Lipman Bernard
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Solvay Polyolefins Europe--Belgium (Societe Anonyme)
Zalukaeva Tanya
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