Impact resistant polyolefin compositions

Details Impact resistant polyolefin compositions Impact resistant polyolefin compositions

2001-05-14

2002-08-27

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

06441094

ABSTRACT:

The present invention concerns polyolefin compositions comprising two polymer fractions with different Melt Flow Rate values, selected from propylene homopolymers and propylene-ethylene and/or other &agr;-olefin random copolymers, and a copolymer of ethylene with C
4
-C
10
&agr;-olefins.
The compositions of the present invention present a unique balance of processability, mechanical properties and optical properties. In addition they present low/very low blush, reduced blooming and low content of fraction extractable in organic solvents. The said compositions can be easily processed by injection-molding and can be used for several applications, including housewares and toys, and in particular for food-contact applications.
Compositions comprising polypropylene and a rubbery phase formed by an elastomeric copolymer of ethylene with &agr;-olefins are already known in the art, and described in particular in European patents 170 255 and 373 660. Said compositions present impact resistance and, in the case of European patent 373 660, transparency values interesting for many applications, however the overall balance of properties is still not totally satisfactory in view of the high standards required by the market. Therefore there is a strong demand for compositions of this kind with improved properties. Such a goal has now been achieved by the polyolefin compositions of the present invention, comprising (percent by weight):
A) 60%-95%, preferably 70%-90%, more preferably 70%-88%, of a crystalline polypropylene component having a Melt Flow Rate (MFR
A
) value (measured at 230° C. with 2.16 Kg load) of from 2.5 to 50, preferably from 5 to 50, more preferably from 10 to 30 g/10 min., and containing from 20% to 80%, preferably from 40% to 60%, of a fraction A
I
) having a Melt Flow Rate (MFR
I
) value (measured at 230° C., with 2.16 Kg load) of from 0.5 to 8, preferably from 0.5 to 5, more preferably from 1 to 3 g/10 min., and from 20% to 80%, preferably from 40% to 60%, of a fraction A
II
);
B) 5%-40%, preferably 10%-30%, more preferably 12%-30%, of a copolymer of ethylene with one or more C
4
-C
10
&agr;-olefin(s) containing from 10 to 40%, preferably from 15 to 30%, more preferably from 15 to 25%, of said C
4
-C
10
&agr;-olefin(s);
said fractions A
I
) and A
II
) being independently selected from propylene homopolymers and random copolymers of propylene containing up to 15%, preferably up to 10%, of ethylene and/or C
4
-C
10
&agr;-olefin(s); the ratio MFR
A
/MFR
I
being from 2 to 25, preferably from 4 to 20; the percentages of A) and B) being referred to the sum of A) and B), and the percentages of A
I
) and A
II
) being referred to the sum of A
I
) and A
II
).
From the above definitions it is evident that the term “copolymer” includes polymers containing more than one kind of comonomers.
As previously said, the compositions of the present invention can be easily converted into various kinds of finished or semi-finished articles, in particular by using injection-molding techniques, as they possess relatively high values of MFR, associated with the said high balance of properties (in particular, of flexural modulus, impact resistance, ductile/brittle transition temperature, haze and gloss). The compositions of the present invention having values of MFR (230° C., 2.16 Kg) of the overall composition equal to or higher than 4 g/10 min., in particular equal to or higher than 5 g/10 min., are preferred.
The value of MFR of fraction A
II
) (MFR
II
) can be easily determined, on the basis of the above said ranges of MFR
I
and MFR
A
values, by means of the known correlation between the MFR of a polyolefin composition and the MFR of the separate components, which, in the present case, can be expressed as follows:
ln MFR
A
=(
W
A
I
/W
A
I
+W
A
II
)×
ln MFR
I
+(
W
A
II
/W
A
I
+W
A
II
)×
ln MFR
II
wherein W
A
I
and W
A
II
represent the weight of fractions A
I
) and A
II
) respectively.
Other preferred features for the compositions of the present invention are:
content of comonomer or comonomers in each of fractions A
I
) and A
II
) when at least one of them is selected from propylene copolymers: 0.5 to 15%, more preferably 0.5 to 10%, in particular 0.5 to 8% (0.5 to 5% when only ethylene is present, 1 to 10%, in particular 1 to 8%, when only C
4
-C
10
&agr;-olefin(s) are present);
content of polymer insoluble in xylene at room temperature (23° C.) (substantially equivalent to the Isotacticity Index) for fractions A
I
) and A
II
): not less than 80%, more preferably not less than 85%, in particular not less than 90%, for propylene copolymers; not less than 90%, more preferably not less than 95%, in particular not less than 97%, for propylene homopolymers, said percentages being by weight and referred to a single fraction;
Polydispersity Index (PI) for A): equal to or higher than 4, in particular from 4 to 12;
Intrinsic Viscosity [&eegr;] of the fraction (of the overall composition) soluble in xylene at room temperature: 0.8 to 2.5 dl/g, more preferably, when high transparency is desired, 0.8 to 2, most preferably 0.8 to 1.9, in particular 0.8 to 1.5 dl/g.
The compositions of the present invention present at least one melt peak, determined by way of DSC (Differential Scanning Calorimetry), at a temperature higher than 140-145° C. Component B) of the said compositions generally presents a melt peak, determined by way of DSC, at a temperature in the range from 120° C. to 135° C. Such melt peak, which is attributable to a polyethylenic-type crystallinity, is generally detectable in the DSC pattern of the overall composition, particularly when component A) is made of propylene homopolymers.
Moreover, the compositions of the present invention preferably have:
a Flexural Modulus of at least 700 MPa, in particular from 700 to 1300 MPa, when at least one of fractions A
I
) and A
II
) is selected from propylene copolymers, or of at least 1200 MPa, more preferably at least 1400 MPa, in particular from 1400 or 1500 to 2000 MPa, when component A) is made of propylene homopolymers (i.e., both A
I
) and A
II
) are propylene homopolymers);
Izod values at 23° C. of at least 50 J/m, more preferably of at least 60 J/m in particular from 50 or 60 to 500 J/m;
tensile strength at yield: 15-38 MPa;
elongation at break: higher than 40%;
substantially no whitening (blush) when bending a plaque 1 mm thick;
fraction extractable in hexane (FDA 177, 1520): less than 10%, more preferably less than 9%, in particular less than 5.5% by weight;
fraction soluble in xylene at room temperature: less than 20%, more preferably less than 15%.
The Ductile/Brittle transition temperature and the optical properties (Haze and Gloss) are strongly dependent upon the Intrinsic Viscosity (I.V.) of the fraction (of the overall composition) soluble in xylene at room temperature.
The ductile/brittle transition temperature is lower the greater the said I.V. and is generally equal to or lower than −2° C., preferably equal to or lower than −5° C., more preferably equal to or lower than −10° C., the lower limit being indicatively of about −60° C.
Haze is lower the lower the said I.V. and is preferably lower than 30%, more preferably equal to or lower than 25%, for compositions wherein component A) is made of propylene homopolymers, equal to or lower than 20%, more preferably equal to or lower than 15%, for compositions wherein at least one of fractions A
I
) and A
II
) is selected from propylene copolymers. Said Haze values are measured on 1 mm thick plaques, prepared from nucleated compositions (in particular with dibenzylidene sorbitols).
Gloss is higher the lower the said I.V. and is preferably in the range from 30 to 150‰, more preferably from 40 to 130‰, measured in the same conditions as for Haze. It is therefore clear that in addition to the previously said preferred ranges of I.V. of the fraction soluble in xylene at room temperature, applicable when excellent optical properties are desired, another preferred range of said I.V. exists, namely from mor

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