The present invention relates to a polyolefin masterbatch
which can be used to prepare polyolefin compositions suitable for injection molding
into relatively large articles. More particularly, the polyolefin compositions can
be injection molded into large objects which exhibit low values of thermal shrinkage
in combination with enhanced mechanical properties, like impact strength and elongation
An advantage of using a masterbatch composition is that
it can be added to many and different kinds of polyolefins to achieve a final polyolefin
composition ready for production, by injection molding, of large articles such as
automobile bumpers. Thus there is a constant need for masterbatch compositions able
to produce, by blending with various polyolefin materials, final compositions exhibiting
a good balance of properties. In particular, the reduction of thermal shrinkage
imparts a higher dimensional stability to the final articles.
polyolefin compositions with low values of coefficient of linear thermal
expansion and good mechanical properties are described, comprising (by weight) from
40 to 60% of a broad molecular weight distribution propylene polymer having a polydispersity
index from 5 to 15 and melt flow rate of from 80 to 200 g/10 min (according to ASTM-D
1238, condition L), and from 40 to 60% of a partially xylene-soluble olefin polymer
rubber containing at least 65% by weight of ethylene, the IVS/IVA
ratio between the intrinsic viscosity (IVS) of the portion soluble in
xylene of the polyolefin composition at room temperature and the intrinsic viscosity
(IVA) of the said propylene polymer ranging from 2 to 2.5.
These compositions typically have a flexural modulus of
from 650 to 1000 MPa.
European patent application No. 03018013
, corresponding to
US provisional application No. 60/496579
), polyolefin compositions having flexural modulus values of higher than
1000 MPa, in particular higher than 1100 MPa, still maintaining a good balance of
overall mechanical properties and low values of thermal shrinkage are described,
comprising (percentage by weight):
- A) from 60 to 85%, of a broad molecular weight distribution propylene polymer
(component A) having a polydispersity index from 5 to 15 and melt flow rate of from
20 to 78 g/10 min, and
- B) from 15 to 40 of a partially xylene-soluble olefin polymer rubber (component
B) containing at least 65% by weight of ethylene.
It has now been found that by properly selecting the ratio
between the melt flow rate values of the overall composition and the intrinsic viscosity
values of the xylene-soluble portion of the overall composition, in combination
with other features relating to the composition and the proportions of the components,
it is possible to obtain a masterbatch composition with a particularly valuable
set of physical and mechanical properties and particularly suited for preparing
final polyolefin compositions having excellent dimensional stability.
In particular, by using the masterbatch compositions of
the present invention, it is possible to obtain final compositions having flexural
modulus values of higher than 1000 MPa, with very low values of thermal shrinkage.
Thus the present invention relates to a masterbatch composition
comprising (percent by weight):
said masterbatch composition having (i) a value of the intrinsic viscosity [&eegr;]
of the fraction soluble in xylene at room temperature ([&eegr;]sol)
equal to or lower than 2.9 dl/g, preferably equal to or lower than 2.8 dl/g, in
particular from 0.9 to 2.7 dl/g, more preferably from 1.2 to 2.7 dl/g, and (ii)
a value of the ratio MFR / [&eegr;]sol of the melt flow rate (MFR) value
(of the total composition) to the [&eegr;] value of the fraction soluble in xylene
at room temperature, equal to or lower than 4, preferably equal to or lower than
- A) 15%-50%, preferably 20-40%, of a polypropylene component having a melt flow
rate of from 1 to 250 g/10 min., preferably from 5 to 200 g/10 min., in particular
from 10 to 180 g/10 min.; and
- B) 50%-85%, preferably 60-80%, of an olefin polymer partially soluble in xylene
at room temperature (about 25 °C), containing from 55% to 85%, preferably from
60% to 80% by weight of ethylene;
The melt flow rate values (MFR) are measured according
to ASTM-D 1238, condition L (230 °C, with 2.16 kg load).
The melt flow rate of the masterbatch composition can preferably
range from 0.1 to 15 g/10 min., more preferably from 0.1 to 10 g/10 min..
Component (A) is preferably a crystalline propylene homopolymer
or a crystalline copolymer of propylene with one or more comonomers selected from
ethylene and C4-C10 &agr;-olefins, or a mixture thereof.
Ethylene is the preferred comonomer. The comonomer content is preferably of from
0.5 to 3.5% by weight, more preferably from 0.5 to 2.5% by weight.
The content of fraction of component (A) which is soluble
in xylene at room temperature is typically equal to or lower than 10%, preferably
equal to or lower than 5% by weight. Such values of xylene-soluble content correspond
to isotactic index values equal to or higher than 90%, preferably equal to or higher
The component (B) used in the masterbatch composition of
the present invention can be a copolymer of ethylene with propylene and/or C4-C10
&agr;-olefins. It can optionally further contain a diene, the content of which
is preferably of from 1 to 10% by weight, more preferably from 1 to 5% by weight.
As previously said, component (B) is partially soluble
in xylene at room temperature. The content of fraction of component (B) which is
soluble in xylene at room temperature is preferably of about 50-80% by weight, more
preferably 50-75% by weight.
Illustrative C4-C10 &agr;-olefins
that can be present in (A) and (B) include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene
and 1-octene, with 1-butene being particularly preferred.
Other preferred features for the masterbatch composition
of the present invention are:
- ethylene content, with respect to the total weight of the composition, from
30% to 60% by weight, in particular from 40% to 60% by weight;
- amount of fraction soluble in xylene at room temperature of the overall composition
from 35% to 60% by weight.
The masterbatch composition of the present invention can
be prepared by a sequential polymerization, comprising at least two sequential steps,
wherein components (A) and (B) are prepared in separate subsequent steps, operating
in each step, except the first step, in the presence of the polymer formed and the
catalyst used in the preceding step. The catalyst is added only in the first step,
however its activity is such that it is still active for all the subsequent steps.
The polymerization, which can be continuous or batch, is
carried out following known techniques and operating in liquid phase, in the presence
or not of inert diluent, or in gas phase, or by mixed liquid-gas techniques. It
is preferable to carry out the polymerization in gas phase.
Reaction time, pressure and temperature relative to the
polymerization steps are not critical, however it is best if the temperature is
from 50 to 100 °C. The pressure can be atmospheric or higher.
The regulation of the molecular weight is carried out by
using known regulators, hydrogen in particular.
The masterbatch compositions of the present invention can
also be produced by a gas-phase polymerisation process carried out in at least two
interconnected polymerisation zones. The said type of process is illustrated in
European patent 782 587
In detail, the above-mentioned process comprises feeding
one or more monomer(s) to said polymerisation zones in the presence of catalyst
under reaction conditions and collecting the polymer product from the said polymerisation
zones. In the said process the growing polymer particles flow upward through one
(first) of the said polymerisation zones (riser) under fast fluidisation conditions,
leave the said riser and enter another (second) polymerisation zone (downcomer)
through which they flow downward in a densified form under the action of gravity,
leave the said downcomer and are reintroduced into the riser, thus establishing
a circulation of polymer between the riser and the downcomer.
In the downcomer high values of density of the solid are
reached, which approach the bulk density of the polymer. A positive gain in pressure
can thus be obtained along the direction of flow, so that it become to possible
to reintroduce the polymer into the riser without the help of special mechanical
means. In this way, a "loop" circulation is set up, which is defined by the balance
of pressures between the two polymerisation zones and by the head loss introduced
into the system.
Generally, the condition of fast fluidization in the riser
is established by feeding a gas mixture comprising the relevant monomers to the
said riser. It is preferable that the feeding of the gas mixture is effected below
the point of reintroduction of the polymer into the said riser by the use, where
appropriate, of gas distributor means. The velocity of transport gas into the riser
is higher than the transport velocity under the operating conditions, preferably
from 2 to 15 m/s.
Generally, the polymer and the gaseous mixture leaving
the riser are conveyed to a solid/gas separation zone. The solid/gas separation
can be effected by using conventional separation means. From the separation zone,
the polymer enters the downcomer. The gaseous mixture leaving the separation zone
is compressed, cooled and transferred, if appropriate with the addition of make-up
monomers and/or molecular weight regulators, to the riser. The transfer can be effected
by means of a recycle line for the gaseous mixture.
The control of the polymer circulating between the two
polymerisation zones can be effected by metering the amount of polymer leaving the
downcomer using means suitable for controlling the flow of solids, such as mechanical
The operating parameters, such as the temperature, are
those that are usual in gas-phase olefin polymerisation process, for example between
50 to 120 °C.
This process can be carried out under operating pressures
of between 0.5 and 10 MPa, preferably between 1.5 to 6 MPa.
Advantageously, one or more inert gases are maintained
in the polymerisation zones, in such quantities that the sum of the partial pressure
of the inert gases is preferably between 5 and 80% of the total pressure of the
gases. The inert gas can be nitrogen or propane, for example.
The various catalysts are fed up to the riser at any point
of the said riser. However, they can also be fed at any point of the downcomer.
The catalyst can be in any physical state, therefore catalysts in either solid or
liquid state can be used.
The said polymerizations are preferably carried out in
the presence of stereospecific Ziegler-Natta catalysts. An essential component of
said catalysts is a solid catalyst component comprising a titanium compound having
at least one titanium-halogen bond, and an electron-donor compound, both supported
on a magnesium halide in active form. Another essential component (co-catalyst)
is an organoaluminum compound, such as an aluminum alkyl compound.
An external donor is optionally added.
The catalysts generally used in the process of the invention
are capable of producing polypropylene with an isotactic index equal to or greater
than 93%, preferably equal to or greater than 95%. Catalysts having the above mentioned
characteristics are well known in the patent literature; particularly advantageous
are the catalysts described in
US patent 4,399,054
European patent 45977
The solid catalyst components used in said catalysts comprise,
as electron-donors (internal donors), compounds selected from the group consisting
of ethers, ketones, lactones, compounds containing N, P and/or S atoms, and esters
of mono- and dicarboxylic acids.
Particularly suitable electron-donor compounds are phthalic
acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.
Other electron-donors particularly suitable are 1,3-diethers
wherein RI and RII are the same or different and are C1-C18
alkyl, C3-C18 cycloalkyl or C7-C18 aryl
radicals; RIII and RIV are the same or different and are C1-C4
alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs
to a cyclic or polycyclic structure made up of 5, 6 or 7 carbon atoms and containing
two or three unsaturations.
Ethers of this type are described in published
European patent applications 361493
Representative examples of said dieters are 2-methyl-2-isopropyl-1,3-dimethoxypropane,
2-isopropyl-2-isoamyl-1,3-dimethoxypropane, 9,9-bis (methoxymethyl) fluorene.
The preparation of the above mentioned catalyst components
is carried out according to various methods.
For example, a MgCl2·nROH adduct (in particular
in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH
is ethanol, butanol or isobutanol, is reacted with an excess of TiCl4
containing the electron-donor compound. The reaction temperature is generally from
80 to 120° C. The solid is then isolated and reacted once more with TiCl4,
in the presence or absence of the electron-donor compound, after which it is separated
and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.
In the solid catalyst component the titanium compound,
expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The
quantity of electron-donor compound which remains fixed on the solid catalyst component
generally is 5 to 20% by moles with respect to the magnesium dihalide.
The titanium compounds which can be used for the preparation
of the solid catalyst component are the halides and the halogen alcoholates of titanium.
Titanium tetrachloride is the preferred compound.
The reactions described above result in the formation of
a magnesium halide in active form. Other reactions are known in the literature,
which cause the formation of magnesium halide in active form starting from magnesium
compounds other than halides, such as magnesium carboxylates.
The Al-alkyl compounds used as co-catalysts comprise the
Al-trialkyls, such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or
cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by
way of O or N atoms, or SO4 or SO3 groups.
The Al-alkyl compound is generally used in such a quantity
that the Al/Ti ratio be from 1 to 1000.
The electron-donor compounds that can be used as external
donors include aromatic acid esters such as alkyl benzoates, and in particular silicon
compounds containing at least one Si-OR bond, where R is a hydrocarbon radical.
Examples of silicon compounds are (tert-butyl)2Si(OCH3)2,
(cyclohexyl)(methyl)Si (OCH3)2, (phenyl)2Si(OCH3)2
and (cyclopentyl)2Si(OCH3)2. 1,3-diethers having
the formulae described above can also be used advantageously. If the internal donor
is one of these dieters, the external donors can be omitted.
Other catalysts that may be used in the process according
to the present invention are metallocene-type catalysts, as described in
EP-A-0 129 368
; particularly advantageous are bridged bis-indenyl metallocenes, for instance
as described in
EP-A-0 485 823
. Another class of suitable catalysts are the so-called constrained geometry
catalysts, as described in
EP-A-0 416 815 (Dow
EP-A-0 420 436 (Exxon
EP-A-0 671 404
EP-A-0 643 066
. These metallocene compounds may be used in particular to produce the
The catalysts can be pre-contacted with small amounts of
The masterbatch composition of the present invention can
also contain additives commonly employed in the art, such as antioxidants, light
stabilizers, heat stabilizers, colorants and fillers.
As previously said, the masterbatch composition of the
present invention can be advantageously compounded with additional polyolefins,
in particular propylene polymers such as propylene homopolymers, random copolymers,
and thermoplastic elastomeric polyolefin compositions. Accordingly, a second embodiment
of the invention relates to a thermoplastic polyolefin composition suitable for
injection molding, containing the above-defined masterbatch compositions. Preferably,
the said thermoplastic polyolefin composition comprises up to 60% by weight, typically
from 20% to 60% by weight, more preferably from 25% to 55% by weight of the masterbatch
composition according to the present invention.
Practical examples of the polyolefins to which the masterbatch
is added (i.e. the polyolefins other than those present in the masterbatch) are
the following polymers:
- 1) crystalline propylene homopolymers, in particular isotactic or mainly isotactic
- 2) crystalline propylene copolymers with ethylene and/or a C4-C10
&agr;-olefin, wherein the total comonomer content ranges from 0.05 to 20% by weight
with respect to the weight of the copolymer, and wherein preferred &agr;-olefins
are 1-butene; 1-hexene; 4-methyl-1-pentene and 1-octene;
- 3) crystalline ethylene homopolymers and copolymers with propylene and/or a
C4-C10 &agr;-olefin, such as HDPE;
- 4) elastomeric copolymers of ethylene with propylene and/or a C4-C10
&agr;-olefins, optionally containing minor quantities of a diene, such as butadiene,
1,4-hexadiene, 1,5-hexadiene and ethylidene-1-norbornene, wherein the diene content
is typically from 1 to 10% by weight;
- 5) a thermoplastic elastomeric composition comprising one or more of propylene
homopolymers and/or the copolymers of item 2) and an elastomeric moiety comprising
one or more of the copolymers of item 4), typically prepared according to known
methods by mixing the components in the molten state or by sequential polymerization,
and generally containing the said elastomeric moiety in quantities from 5 to 80%
The polyolefin composition may be manufactured by mixing
the masterbatch composition and the additional polyolefin(s) together, extruding
the mixture, and pelletizing the resulting composition using known techniques and
The polyolefin composition may also contain conventional
additives such as mineral fillers, colorants and stabilizers. Mineral fillers that
can be included in the composition include talc, CaCO3, silica, such
as wollastonite (CaSiO3), clays, diatomaceaous earth, titanium oxide
and zeolites. Typically the mineral filler is in particle form having an average
diameter ranging form 0.1 to 5 micrometers.
The present invention also provides final articles, such
as bumpers and fascia, made of the said polyolefin composition.
The practice and advantages of the present invention are
disclosed below in the following examples. These Examples are illustrative only,
and are not intended to limit the scope of the invention in any manner whatsoever.
The following analytical methods are used to characterize
the polymer compositions.
Melt Flow Rate: ASTM-D 1238, condition L.
[&eegr;] intrinsic viscosity: determined in tetrahydronaphtalene at 135°C.
Ethylene content: I.R. Spectroscopy.
Flexural Modulus: ISO 178, measured 24 hours after moulding.
Tensile strength at yield: ISO 527, measured 24 hours after moulding.
Tensile strength at break: ISO 527, measured 24 hours after moulding.
Elongation at break and at yield: ISO 527, measured 24 hours after moulding.
Notched IZOD impact test: ISO 180/1A
The IZOD values are measured at 23 °C and -30 °C,
3 hours and 24 hours after moulding, and at -50 °C, 24 hours after moulding.
Xylene soluble and isoluble fractions
2.5 g of polymer and 250 cm3 of xylene are introduced
in a glass flask equipped with a refrigerator and a magnetical stirrer. The temperature
is raised in 30 minutes up to the boiling point of the solvent. The so obtained
clear solution is then kept under reflux and stirring for further 30 minutes. The
closed flask is then kept for 30 minutes in a bath of ice and water and in thermostatic
water bath at 25 °C for 30 minutes as well. The so formed solid is filtered
on quick filtering paper. 100 cm3 of the filtered liquid is poured in
a previously weighed aluminum container which is heated on a heating plate under
nitrogen flow, to remove the solvent by evaporation. The container is then kept
in an oven at 80 °C under vacuum until constant weight is obtained. The weight
percentage of polymer soluble in xylene at room temperature is then calculated.
The percent by weight of polymer insoluble in xylene at
room temperature is considered the isotacticity index of the polymer. This value
corresponds substantially to the isotacticity index determined by extraction with
boiling n-heptane, which by definition constitutes the isotacticity index of polypropylene.
Longitudinal and transversal thermal shrinkage
A plaque of 100 x 200 x 2.5 mm is moulded in an injection
moulding machine "SANDRETTO serie 7 190" (where 190 stands for 190 tons of clamping
The injection conditions are:
The plaque is measured 3 hours and 24 hours after moulding, through callipers, and
the shrinkage is given by:
- melt temperature = 250°C;
- mould temperature = 40°C;
- injection time = 8 seconds;
- holding time = 22 seconds;
- screw diameter = 55 mm.
wherein 200 is the length (in mm) of the plaque along the flow direction, measured
immediately after moulding;
100 is the length (in mm) of the plaque crosswise the flow direction, measured immediately
the read_value is the plaque length in the relevant direction.
Preparation of the masterbatch composition
The solid catalyst component used in polymerization is
a highly stereospecific Ziegler-Natta catalyst component supported on magnesium
chloride, containing about 2.5% by weight of titanium and diisobutylphthalate as
internal donor, prepared by analogy with the method described in the examples of
European published patent application 674991
CATALYST SYSTEM AND PREPOLYMERIZATION TREATMENT
Before introducing it into the polymerization reactors,
the solid catalyst component described above is contacted at -5 °C for 5 minutes
with aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS), in a TEAL/DCPMS
weight ratio equal to about 15 and in such quantity that the TEAL/Ti molar ratio
be equal to 65.
The catalyst system is then subjected to prepolymerization
by maintaining it in suspension in liquid propylene at 20 °C for about 20 minutes
before introducing it into the first polymerization reactor.
Into a first gas phase polymerization reactor a polypropylene
homopolymer (component (A)) is produced by feeding in a continuous and constant
flow the prepolymerized catalyst system, hydrogen (used as molecular weight regulator)
and propylene in the gas state.
Polymerization conditions are shown in Table I.
The polypropylene homopolymer coming from the first reactor
is discharged in a continuous flow and, after having been purged of unreacted monomers,
is introduced, in a continuous flow, into a second gas phase reactor, together with
quantitatively constant flows of hydrogen and ethylene in the gas state.
In the second reactor a propylene/ethylene copolymer (component
(B)) is produced. Polymerization conditions, molar ratio of the reactants and composition
of the copolymers obtained are shown in Table I.
The polymer particles exiting the second reactor, which
constitute the not stabilized masterbatch according to the present invention, are
subjected to a steam treatment to remove the reactive monomers and volatile substances,
and then dried.
Then the polymer particles are introduced in a rotating
drum, where they are mixed with 0.05% by weight of paraffin oil ROL/OB 30 (having
a density of 0.842 kg/l at 20 °C according to ASTM D 1298 and flowing point
of -10 °C according to ASTM D 97), 0.15% by weight of Irganox® B 215 (made
of about 34% Irganox® 1010 and 66% Irgafos® 168) and 0.04% by weight of
The said Irganox 1010 is 2,2-bis[3-[,5-bis(1,1-dimethylethyl)4-hydroxyphenyl)-1-oxopropoxy]methyl]-1,3-propanediyl-3,5-bis(1,1-dimethylethyl)-4-hydroxybenzene-propanoate,
while Irgafos 168 is tris(2,4-di-tert.-butylphenyl)phosphite.
Then, the polymer particles are extruded under nitrogen
in a screw extruder with a melt temperature of 200-250 °C.
The characteristics relating to this polymer composition,
reported in Table II, are obtained from measurements carried out on the so extruded
polymer, which constitute the stabilized masterbatch composition according to the
Preparation of blends of the stabilized masterbatch composition with propylene
1° REACTOR (component (A))
Temperature (° C)
Amount produced (wt%)
MFRA (g/10 min.)
Xylene soluble (wt%)
2° REACTOR (component (B))
Temperature (° C)
Amount produced (wt%)
C2 in (B) (wt%)
Xylene soluble in (B) (wt%)
Notes: C2 ≡ ethylene;
C3 ≡ propylene
NER (g/10 min)
Xylene soluble (wt%)
Ethylene content (wt%)
Flexural modulus (MPa)
Tensile strength at yield (MPa)
Elongation at yield (%a)
Tensile strength at break (MPa)
Elongation at break (%)
IZOD Impact Str. at -50° C (KJ/m2)
MFR / [&eegr;]sol
Note: N.B. = No Break
The stabilized masterbatch compositions prepared as described
above (hereinafter called SMC) are blended by extrusion under the previously described
conditions with a heterophasic polypropylene composition (hereinafter called HPP)
and the other additives hereinafter described, in the proportions reported below
and in Table III.. The properties of the so obtained final compositions are reported
in Table III.
In all the examples, the added amounts of components 2 to 5 are the following (percent
- 1 HPP: heterophasic polypropylene composition having MFR of 60 g/10 min., made
of 80% by weight of propylene homopolymer with isotactic index of 98%, and 20% by
weight of an ethylene/propylene copolymer containing 60% by weight of ethylene;
- 2 CB: carbon black masterbatch having MFR of about 40 g/10 min., made of 40%
by weight of carbon black and 20% of a copolymer of propylene with 7% by weight
- 3 ROL/OB 30: see above;
- 4 Irganox® B 225: made of about 50% Irganox® 1010 and 50% Irgafos®
- 5 HM05 talc: fine talc powder with average particle size of about 2 µm.
SMC of EXAMPLE
SMC amount (wt%)
HPP amount (wt%)
Flexural modulus (MPa)
Tensile strength at yield (MPa)
Elongation at yield (%a)
Tensile strength at break (MPa)
Elongation at break (%)
IZOD Impact Str. at -30° C (KJ/m2)
Longitudinal shrinkage (%)
Transversal shrinkage (%)
MFR (g/10 min)