Polyolefin compositions and films obtained therefrom

Polyolefin compositions containing from 70 to 99 parts by weight of a composition (A) that includes (i) from 75 to 95% by weight of a copolymer of ethylene with an .alpha.-olefin CH.sub.2.dbd.CHR, where R is an alkyl radical having from 1 to 10 carbon atoms; and (ii) from 5 to 25% by weight of a copolymer of propylene with ethylene and/or an .alpha.-olefin CH.sub.2.dbd.CHR.sup.1, where R.sup.1 is an alkyl radical having from 2 to 10 carbon atoms, and from 1 to 30 parts by weight of a polyolefin component (B) that includes crystalline polybutene-1. The compositions can be used for making films.

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 .alpha.-olefin
 CH.sub.2.dbd.CHR.sup.1, wherein R.sup.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 .alpha.-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 .alpha.-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
 .alpha.-olefin CH.sub.2.dbd.CHR, wherein R is an alkyl radical having from
 1 to 10 carbon atoms, said copolymer containing up to 20% by mole of
 .alpha.-olefin and (ii) from 5 to 25% by weight of a copolymer of
 propylene with ethylene and/or an .alpha.-olefin CH.sub.2.dbd.CHR.sup.1,
 wherein R.sup.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.sub.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.sub.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
 .alpha.-olefin ranges between 4. and 15% by weight. When the copolymer
 (ii) is a terpolymer of the type ethylene/propylene/.alpha.-olefin, and
 this constitutes a preferred embodiment, the content of ethylene ranges
 from 2 to 8% by weight while the content of .alpha.-olefin
 CH.sub.2.dbd.CHR.sup.1 ranges between 2 and 7% by weight. However, the
 content of ethylene may also be higher than that of the .alpha.-olefin
 CH.sub.2.dbd.CHR.sup.1. The content of the various components is
 determined by IR and NMR analysis.
 The .alpha.-olefin CH.sub.2.dbd.CHR.sup.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.degree. C. and
 preferably between 120 and 140.degree. 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.sup.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 .alpha.-olefin CH.sub.2.dbd.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.sub.2.dbd.CHR may even be
 used as a mixture.
 The copolymer (i) is prepared by copolymerization of ethylene with an
 .alpha.-olefin CH.sub.2.dbd.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 comprising magnesium halide in active form. Examples of
 catalysts usable in the preparation of the copolymer (a) are described in
 U.S. Pat. No. 4,218,339 and U.S. Pat. No. 4,472,520. The catalysts may
 also be prepared according to the methods described in the U.S. patents
 U.S. Pat. No. 4,748,221 and 4,803,251.
 Particularly preferred are the catalysts comprising components having
 regular morphology, for example spherical or spheriforn. Examples of such
 catalysts are described in the patent applications EP-A-395083,
 EP-A-553805 and EP-A-553806.
 The polymeric compositions of the invention preferably comprise from about
 75 to about 95% by weight of copolymer (i) and from about 5 to about 25%
 by weight of copolymer (ii); preferably, the content of copolymer (i) is
 comprised between 75 and 90% by weight and the content of copolymer (ii)
 between 10% and 25% by weight.
 As explained above, the component (i) is preferably a copolymer of ethylene
 with 1-butene and/or hexene-1, and component (ii) is preferably a
 copolymer of propylene with ethylene and 1-butene.
 In the compositions of the invention the component (A) is preferably
 present in amounts of from 75 to 95 and more preferably from 80 to 95
 parts by weight.
 The component (A) of the invention may be prepared by mixing the components
 (i) and (ii) in the molten state, for example in a single or twin screw
 extruder. The components of the mixture may be fed directly into the
 extruder or may be premixed in the solid state. Preferably the said
 component (A) is directly prepared in polymerization operating in at least
 two reactors in series in which, whatever the order and using the same
 catalyst in the various reactors, in one of the reactors copolymer (a) is
 synthesized and in the other reactor copolymer (b) is synthesized. The
 polymerization is conveniently carried out in the gas phase using a
 fluidised bed reactor. In particular, the component (A) can be prepared
 directly by polymerization of the monomers in the gas phase, in the
 presence of a catalyst obtained from the reaction between:
 (i) a solid catalytic component comprising a titanium compound containing
 at least a titanium-halogen bond supported on a magnesium halide in active
 form and optionally an electron-donor compound;
 (ii) an Al-alkyl compound;
 (iii) optionally, an electron-donor compound; operating in two or more
 gas-phase reactors in series in which, in any order and using the same
 catalyst in the various reactors:
 (I) in one reactor a mixture of ethylene with an .alpha.-olefin
 CH.sub.2.dbd.CHR, where R is an alkyl radical having 1 to 10 carbon atoms,
 is polymerized to obtain a copolymer of ethylene with said olefin
 containing up to 20% by mole of .alpha.-olefin;
 (II) in another reactor a mixture of propylene, ethylene and/or an
 .alpha.-olefin CH.sub.2.dbd.CHR.sup.1, where R.sup.1 is an alkyl radical
 having 2 to 10 carbon atoms, is polymerized to obtain the component (ii)
 in amounts of between 5 and 25% by weight with respect to the total
 polymer obtained in (I) and (II).
 The polyolefin compositions of the invention may be prepared by mixing the
 components (A) and (B) in the molten state, for example in a single or
 twin screw extruder. The components of the mixture may be fed directly
 into the extruder or may be premixed in the solid state. In alternative,
 said compositions can be prepared by sequential polymerization operating
 in at least three reactors in series in which., whatever the order, and
 using the same catalyst in the various reactors, in one of the reactors is
 synthesized the copolymer (i), in another reactor is synthesized copolymer
 (ii) thus obtaining component (A), and in another reactor is synthesized
 component (B). Also in this case the polymerization is conveniently
 carried out in the gas-phase using fluidized bed reactors. The films
 obtained from the compositions of the invention have impact resistance
 (Dart test) generally higher than that of the films obtained from the
 corresponding component (A) alone. In addition, also an improvement in the
 tear resistance, determined by the Elmendorf method, is observed. However,
 as it can be seen from the examples below the greater improvement is
 obtained in the processability of the composition. In fact, by using the
 compositions of the invention it is possible to save energy to an extent
 even higher than 30% with respect to the use of component (A) alone. It is
 worth noting that this improvement in processability is obtained without
 substantial worsening of the mechanical properties.
 Because of their high processability and mechanical strength
 characteristics, the compositions of the invention find applications in
 several sectors such as: blown films and cast films both monolayer and
 multilayer; coextruded films and laminates in which at least one layer
 consists of the composition of the invention, and at least one layer
 consists of a thermoplastic polymer, such as for example polypropylene
 homopolymer, copolymers of propylene with ethylene and/or .alpha.-olefin
 having 4-12 carbon atoms, polyethylene homopolymer (both LDPE and HDPE),
 copolymers of ethylene with .alpha.-olefin having 3-12 carbon atoms,
 ethylene-vinylacetate copolymers, polyvinylidene chloride; extrusion
 jackets for substrates and electric cables; injection molding; blow
 molding; thermoforning.
 The weight ranges described for the components of the present invention
 refer to the relative weight ratios of the components A [(i), and (ii)]
 and B. Obviously, in accordance with what is known by those skilled in the
 art or as may readily be determined by routine tests, further polymeric
 components, additives (such as, for example, adhesives, stabilizers,
 antioxidants, anti-corrosion agents, etc.) and fillers, of either organic
 or inorganic nature, that are capable of imparting specific properties to
 the films of the invention may be added.
 The following examples are given to illustrate and not to limit the
 invention.
 CHARACTERIZATION
 Determination of Isotactic Index (mmmm %). by .sup.13 C NMR
 The measurement is carried out by dissolving the sample in C.sub.2 Cl.sub.4
 D.sub.2 and recording the spectra at a temperature of 120.degree. C. with
 a DRX 500 MHz instrument operating at 125.7 MHz under proton Waltz 16
 decoupling in FT mode, with 10 Khz spectral width, 90.degree. pulse angle
 and 16 sec. puls repetition and 3600 scans.
 Determination of Melt Index
 ASTM D 1238 condition "E"
 Comonomer Content
 Percentage by weight of comonomer determined by NMR spectroscopy.
 Xylene Insolubility
 2.5 g of copolymer and 250 cm.sup.3 of .alpha.-xylene are placed in a glass
 flask fitted with a condenser and a magnetic stirrer. The temperature is
 increased to the boiling point of the solvent over 30 min. The clear
 solution thus formed is left at reflux with stirring for a further 30 min.
 The closed flask is then placed in a bath of ice-water for 30 min and then
 in a bath of water thermostatically adjusted to 25.degree. C. for 30 min.
 The solid formed is then filtered off on filter paper at a high filtration
 rate. 100 cm.sup.3 of the liquid obtained from the filtration are poured
 into a pre-weighed aluminum container, which is placed on a hot-plate to
 evaporate off the liquid under a stream of nitrogen. The container is then
 placed in an oven at 80.degree. C. and maintained under vacuum until a
 constant weight is obtained.
 Haze: ASTM D 1003;
 Dart test: ASTM D 1709;
 Elmendorf Tear Strength
 ASTM D 1922, determined both in machine direction (MD) and transversal
 direction (TD);

EXAMPLE 1
 Three polymeric compositions according to the invention were prepared by
 mechanical mixing the amounts of component (A) (obtained by sequential
 copolymeration carried out according to the procedure described in Ex. 3
 of WO 95/2009) and component (B) (random copolymer of butene-1 with
 ethylene commercialized by Shell under the name PB-8640) reported in Table
 1. The characteristics of the components used were the following: