Polymer mixture with good workability

Details Polymer mixture with good workability Polymer mixture with good workability

2000-04-10

2002-02-26

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...

C525S199000, C525S240000

Reexamination Certificate

active

06350814

ABSTRACT:

The present invention relates to a polymer mixture comprising at least 40 but less than 85% by weight of an ethylene copolymer (A) which has a density of from 0.91 to 0.93 g/cm
3
, an HLMFR (190° C./21.6 kg) of from 5 to 60 g/10 min and a molar mass distribution M
w
/M
n
≦3, and more than 15 but at most 60% by weight of an ethylene copolymer (B) which is different from ethylene copolymer (A) and has a density of from 0.93 to 0.945 g/cm
3
, an HLMFR (190° C./21.6 kg) of from 8 to 20 g/10 min and a molar mass distribution M
w
/M
n
24 7, where the percentages by weight are in each case based on the total mass of the components (A) is and (B).
The invention further relates to the use of this polymer mixture for producing films, a process for producing films in which such a polymer mixture is used and also the films which have been produced from such a polymer mixture.
Ethylene copolymers having a narrow molar mass distribution, as can be obtained, for example, by means of metallocene catalysis, have particularly advantageous mechanical properties. However, their processability is in many cases unsatisfactory. Numerous attempts have therefore been made in the past to improve the processability without seriously impairing the mechanical properties.
LDPE as is obtained by free-radical high pressure polymerization displays a behavior which is in many ways complementary to that of these ethylene copolymers: LDPE can be very readily processed, but displays poorer mechanical properties. For this reason, experiments have been carried out on mixing ethylene copolymers prepared by means of metallocene catalysis with LDPE. Such polymer mixtures are described, for example, in WO 95/27005.
EP-B-0 662 989 likewise describes blends of metallocene copolymers with LDPE and also other ethylene copolymers. The metallocene-LLDPE component has a density of less than 0.92 g/cm
3
. As second component, mention is made not only of LDPE but also of LLDPE and VLDPE. This second component has to have a melting point which is at least 10° C. higher than that of the metallocene component and an orientation temperature which is at least 2° C. below its melting point. The molar mass distribution of the second component is not subject to any particular requirements.
WO 90/03414 describes mixtures of various ethylene copolymers where the components of the mixture have either the same molar mass and different comonomer contents or the same comonomer content and different molar masses or comonomer contents which increase with the molar mass. However, all constituents of the mixture have a narrow molar mass distribution M
w
/M
n
of≦3.
In terms of the combination of good mechanical properties and good processability, the known ethylene copolymer mixtures still leave something to be desired.
It is an object of the present invention to provide polymer mixtures based on ethylene copolymers which combine good is mechanical properties with good processability and are, in particular, suitable for the production of films.
We have found that this object is achieved by the polymer mixtures described at the outset, their use for producing films, a process for producing films in which such a polymer mixtures is used and also films which are produced from such a polymer mixture.
For the purposes of the present invention, the expression “HLMFR” means, as is customary, “high load melt flow rate” and is always determined at 190° C. under a load of 21.6 kg (190° C./21.6 kg).
The polymer mixtures of the present invention comprise as essential components the ethylene copolymers (A) and (B).
The ethylene copolymer (A) to be used according to the present invention has a density in the range from 0.91 to 0.93 g/cm
3
, preferably from 0.915 to 0.925 g/cm
3
, and a molar mass distribution M
w
/M
n
of≦3. Its HLMFR is in the range from 5 to 60 g/10 min, preferably from 10 to 40 g/10 min.
Comonomers which may be present in copolymerized form in addition to ethylene in the copolymer (A), either individually or in admixture with one another, are all &agr;-olefins having from 3 to 8 carbon atoms, for example propene, butene, pentene, hexene, 4-methylpentene, heptene and octene. Copolymer (A) preferably comprises pentene, hexene, 4-methylpentene or octene in copolymerized form as comonomer unit. Particular preference is given to hexene. The comonomers are generally present in copolymerized form in the ethylene copolymer (A) in amounts of from 1 to 20% by weight, preferably from 2 to 15% by weight and in particular from 1 to 8% by weight, in each case based on the ethylene copolymer (A). The same applies for the comonomers which are present in copolymerized form in copolymer (B).
In the polymer mixture of the present invention, the ethylene copolymer (A) makes up at least 40% by weight but less than 85% by weight, preferably from 50 to 80% by weight, of the total mass of the ethylene copolymers (A) and (B).
The ethylene copolymers (A) can in principle be prepared using any catalyst or catalyst system which leads to products having the required narrow mass distribution. In general, these catalysts are single-site catalysts, for example metallocene catalysts, catalysts having azaallyl or &bgr;-diketiminate ligands or catalysts based on Pd or Ni and having substituted diazabutadiene ligands.
Preference is given to polymer mixtures in which the ethylene copolymer (A) present is an ethylene-&agr;-olefin copolymer prepared by means of metallocene catalysis.
The polymerization can here be carried out, for example, in the gas phase, in suspension, in solution or in the high pressure process, where the catalyst system used in a suspension or gas-phase process is preferably one which comprises
a) an inorganic or organic support,
b) a metallocene complex and
c) a compound capable of forming metallocenium ions.
Support materials a) used are preferably finely divided supports which preferably have a particle diameter in the range from 1 to 300 &mgr;m, in particular from 30 to 70 &mgr;m. Suitable inorganic supports are, for example, magnesium chloride or silica gels, preferably those of the formula SiO
2
.aAl
2
O
3
, where a is in the range from 0 to 2, preferably from 0 to 0.5; these are thus aluminosilicates or silicon dioxide. Such products are commercially available, eg. Silica Gel 332 from Grace. Suitable organic supports are, for example, finely divided polyolefins, eg. finely divided polypropylene.
The amount of support a) is preferably from 50 to 99.9% by weight, based on the total mass of support a) and metallocene complex (component b)).
Particularly suitable metallocene complexes b) are those of the formula I
where the substituents have the following meanings:
M is titanium, zirconium, hafnium, vanadium, niobium or tantalum, in particular zirconium,
X is fluorine, chlorine, bromine, iodine, hydrogen, C
1
-C
10
-alkyl, C
6
-C
15
-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl radical and from 6 to 20 carbon atoms in the aryl radical, —OR
7
or —NR
7
R
8
,
where
R
7
and R
8
can be identical or different and are, independently of one another, C
1
-C
10
-alkyl, C
16
-C
15
-aryl, alkylaryl, arylalkyl, fluoroalkyl or fluoroaryl each having from 1 to 10 carbon atoms in the alkyl radical and from 6 to 20 carbon atoms in the aryl radical,
R
2
to R
6
are identical or different and are hydrogen, C
1
-C
10
-alkyl, 5- to 7-membered cycloalkyl which may in turn bear a C
1
-C
10
-alkyl group as substituent, C
6
-C
15
-aryl or arylalkyl, where two adjacent radicals may also together form a saturated or unsaturated cyclic group having from 4 to 15 carbon atoms, or Si(R
9
)
3
where
R
9
is C
1
-C
10
-alkyl, C
3
-C
10
-cycloalkyl or C
6
-C
15
-aryl,
where the radicals
R
10
to R
14
are identical or different and are hydrogen, C
1
-C
10
-alkyl, 5- to 7-membered cycloalkyl which may in turn bear a C
1
-C
10
-alkyl as substituent, C
6
-C
15
-aryl or arylalkyl, where two adjacent radicals may also together form a saturated or unsaturated cyclic group having from 4 to 15 carbon atoms, or Si(R
15
)
3
where
R
15
is C
1
-C
10
-alkyl, C
6
-C

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