Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-12-17
2001-08-21
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000
Reexamination Certificate
active
06277918
ABSTRACT:
The present invention relates to polyolefin compositions endowed with improved processability. Furthermore, the present invention relates to the films obtained from said compositions which show very good mechanical and optical properties. The compositions according to the present invention comprise a first composition (A) comprising an ethylene copolymer (LLDPE type) and a copolymer of propylene with ethylene and/or an &agr;-olefin CH
2
═CHR
1
, wherein R
1
is an alkyl radical having from 2 to 10 carbon atoms, said copolymer of propylene having a relatively high insolubility in xylene, said first composition (A) being blended with (B) a crystalline polybutene-1.
Composition comprising an ethylene copolymer (LLDPE type) and a copolymer of propylene with ethylene and/or an &agr;-olefin are already known from WO93/03078 and WO 95/20009. Said compositions show improved processability over the conventional LLDPE polymers. As a consequence, some of the problems related to the use of LLDPE, such as the necessity of widening the slit or increasing the temperature of the extruder heads in order to keep the productivity unaltered, have been solved.
However, it would be desirable, in order to save energy when processing the polymer, to have available polyolefin composition, suitable for the preparation of films, having still improved processability. An improvement in processability for LLDPE polymers is generally achieved by blending them with low density polyethylene (LDPE) obtained by high pressure polymerization. By this way, however, the improvement in processability is obtained at damage of the mechanical properties of the films obtained from these compositions. Indeed, said mechanical properties decrease proportionally with the amount of LDPE used. It would therefore be desirable to have polyolefin compositions with improved processability and being capable, at the same time, to give films keeping very good mechanical and optical properties.
It has unexpectedly been found that the compositions obtained by blending crystalline polybutene-1 with the compositions comprising an ethylene copolymer (LLDPE type) and a copolymer of propylene with ethylene and/or an &agr;-olefin, are endowed with high processability and are capable to give films retaining very good mechanical properties.
It is therefore an object of the present invention to provide polyolefin compositions comprising from 70 to 99 parts by weight of a composition (A) comprising (i) from 75 to 95% by weight of a copolymer of ethylene with an &agr;-olefin CH
2
═CHR, wherein R is an alkyl radical having from 1 to 10 carbon atoms, said copolymer containing up to 20% by mole of &agr;-olefin and (ii) from 5 to 25% by weight of a copolymer of propylene with ethylene and/or an &agr;-olefin CH
2
═CHR
1
, wherein R
1
is an alkyl radical having from 2 to 10 carbon atoms, said copolymer containing from 80 to 98% by weight of propylene and being characterized by insolubility in xylene of higher than 70%; and from 1 to 30 parts by weight of a polyolefin component (B) comprising crystalline polybutene-1.
It is very surprisingly that, differently from what is observed when LDPE is used, the increase in processability, showed by the decreasing of the melt pressure in the extruder, is obtained without detriment of the mechanical properties of the films. Conversely, the presence of polybutene-1 provides an improvement of the mechanical properties over the film obtained from the composition A alone.
The crystalline polybutene-1 used as component (B) of the composition of the invention can be any of the polybutene-1, homo or copolymer with other olefins, having a predominantly isotactic structure. Such polymers are known in the art. The isotactic polybutene-1 (co)polymers can be prepared by polymerizing butene-1 in the presence of TiCl
3
based catalyst components together with alkylaluminum halides (such as diethylaluminum chloride—DEAC) as cocatalyst. Polybutene-1 (co)polymers can also be obtained by polymerizing the monomers in the presence of a stereospecific catalyst comprising (a) a solid component comprising a Ti compound and an electron-donor compound supported on MgCl
2
; (b) an alkylaluminum compound and, optionally, (c) an external electron-donor compound. A process of this type is disclosed for example in EP-A-017296. Preferably the polybutene-1 used has an isotacticity (expressed in terms of pentads mmmm %) higher than 80%, more preferably higher than 85%, and still more preferably higher than 90%.
The melt index (MIE) is generally comprised in the range of from 0.01 to 100 preferably of from 0.1 to 50 and more preferably from 0.1 to 20. When a butene copolymer with one or more other olefins is used, the olefin can be selected preferably from the group consisting of ethylene, propylene, pentene-1, hexene-1 and octene-1. Particularly preferred are the random copolymer with ethylene or propylene containing up to 20% by weight of units deriving from ethylene or propylene or both.
The component (B) in the composition of the invention is present in amounts comprised between 1 and 30 parts by weight, preferably from 5 to 25, and more preferably from 5 to 20 parts by weight.
In the component (A) of the present invention, the insolubility in xylene of component (ii) is preferably higher than 75%, more preferably higher than 85%. The insolubility is determined according to the method described below. Preferably in the said copolymer (ii), the content of propylene ranges between 85 and 96% by weight, and the content of ethylene and/or &agr;-olefin ranges between 4. and 15% by weight. When the copolymer (ii) is a terpolymer of the type ethylene/propylene/&agr;-olefin, and this constitutes a preferred embodiment, the content of ethylene ranges from 2 to 8% by weight while the content of &agr;-olefin CH
2
═CHR
1
ranges between 2 and 7% by weight. However, the content of ethylene may also be higher than that of the &agr;-olefin CH
2
═CHR
1
. The content of the various components is determined by IR and NMR analysis.
The &agr;-olefin CH
2
═CHR
1
may be selected, for example, among 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, and preferably is 1-butene or 1-hexene.
The fusion enthalpy of the copolymer (ii) is generally higher than 50 J/g, preferably higher than 60 J/g, more preferably higher than 70 J/g. The melting temperature of the copolymer (b) is less than 140° C. and preferably between 120 and 140° C.
The Melt Index (determined according to the method ASTM D-1238, condition L) of the copolymer (ii) has values generally ranging between 5 and 1000, preferably between 5 and 100, more preferably between 5 and 30.
The component (ii) of the polyolefin composition of the invention can be conveniently prepared using a highly stereospecific catalyst, of the type described in the patent application EP-A-395083.
The copolymer (i) used in the component (A) of the invention, has a density comprised between 0.88 and 0.945 g/cm
3
. Preferably, these values are comprised between 0.89 and 0.94, more preferably between 0.90 and 0.935.
The Melt Index (determined by the method ASTM D-1238, condition E) of the copolymer (i) has values generally comprised between 0.01 and 100 g/10 minutes, preferably comprised between 0.1 and 10 g/10 minutes, more preferably between 0.2 and 5 g/10 minutes.
The &agr;-olefin CH
2
═CHR may be, for example, selected among propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene; preferably 1-butene or 1-hexene is used. In the preparation of component (i) of the composition of the invention, the olefins CH
2
═CHR may even be used as a mixture.
The copolymer (i) is prepared by copolymerization of ethylene with an &agr;-olefin CH
2
═CHR, in the presence of a Ziegler-Natta type catalyst obtained by the reaction of an organometallic compound of a metal from groups II and III of the Periodic Table with a catalytic component comprising a transition metal belonging to groups IV, V or VI of the Periodic Table. Preferably the transition metal compound is supported on a solid carrier comp
Anibaldi Remo
Ciarafoni Marco
Collina Gianni
Montell Technology Company BV
Nutter Nathan M.
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