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
2001-11-20
2003-09-16
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...
C525S216000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06620888
ABSTRACT:
The present invention relates to thermoplastic polymer compositions, particularly to thermoplastic compositions containing isotactic polypropylene and a flexible propylene polymer having reduced isotacticity and to a process for the preparation thereof. The invention relates also to manufactured articles obtainable from those compositions.
Isotactic polypropylene is usually obtained by using Ziegler-Natta catalysts, that produce highly isotactic polymers with a broad distribution of molecular weight. More recently metallocene-based catalysts have been used in the polymerization reaction of olefins. Operating in the presence of these catalysts, polymers characterised by a narrow molecular weight distribution and having structural characteristics of interest have been obtained. By polymerizing propylene in the presence of metallocene catalysts, amorphous or highly crystalline polypropylenes can be obtained depending on the metallocene used, such as for example as described in EP 604 908 and EP 485 820. Amorphous polypropylene shows a poor stiffness, while the highly stereoregular and crystalline polypropylene thus obtained is characterised by good stiffness, but is unsatisfactory when high flexibility is required.
Several attempts have been made to improve the elastic properties of isotactic polypropylene by blending it with a “softer” polymer. For example in U.S. Pat. No. 4,521,566 polypropylene compositions are prepared in a multistage process which comprises at least one stage of propylene homopolymerization and at least one stage of ethylene/propylene copolymerization in the presence, in both stages, of a catalyst comprising a compound of titanium supported on a magnesium halide in active form. U.S. Pat. No. 5,539,056 describes a blend of high molecular weight amorphous polypropylene with low molecular weight isotactic polypropylene.
In U.S. Pat. No. 5,589,549 and U.S. Pat. No. 5,648,422 there are described multistep processes wherein in a first step a porous isotactic polypropylene is prepared in the presence of a titanium-based catalyst. In a second step, in the presence of the said porous polymer and a metallocene-based catalyst one or more olefins are polymerized.
Compositions of propylene polymers have now been found which show an improved balance of flexible-mechanical properties. Thus, according to a first aspect of the present invention, it is provided a thermoplastic composition comprising:
(A) 10 to 99% by weight of a propylene polymer optionally containing from 0.1 to 5% by moles of units deriving from an olefin of formula CH
2
═CHR, R being hydrogen, a C
2
-C
20
-alkyl or a C
6
-C
12
-aryl group, having the following characteristics:
50<isotactic triads (mm)<85;
melting point (Tm) from 60° C. to 120° C.; and
(B) 1 to 90% by weight of a propylene polymer optionally containing from 0.1 to 5% by moles of units deriving from an olefin of formula CH
2
═CHR, R being hydrogen, a C
2
-C
20
-alkyl or a C
6
-C
12
-aryl group, having the following characteristic:
an essentially isotactic structure;
melting point (Tm) higher than 153° C.
The ratio of the quantities by weight of the components (A)/(B) of the composition according to the present invention is preferably comprised from 30:70 to 95:5, still more preferably from 40:60 to 90:10.
Preferably the polymer used as component (A) has a melting enthalpy<70 J/g.
Preferably, the melting point (Tm) of the propylene polymer used as component (B) is higher than 155° C., most preferably higher than 160° C.
It has been observed that the compositions according to the present invention have very good flexible-mechanical properties, even under high deformation, which are remarkably improved as compared to those of the single component. These elastic properties are reflected in improved impact strength. Thus, the compositions of the present invention are particularly useful for the manufacture of articles for which a high mechanical strength is required.
Propylene polymers that can be used as component (A) in the composition of the present invention as well as a process for the preparation thereof are described, for example, by U. Dietrich et al, in J. Am. Chem. Soc. 1999, 121, 4348-4355, the contents of which are to be incorporated by reference in the present description.
A particular useful method for obtaining the propylene polymer of component (A) of the composition of the present invention is described in the copending Application PCT/EP00/3191 in the name of the same Applicant.
The propylene polymers of component (A) have low crystallinity. Their melting enthalpy values (&Dgr;Hf) are preferably lower than <70 J/g. Their intrinsic viscosity values [&eegr;] are preferably higher than 0.5, more preferably higher than 0.8.
Preferably the propylene polymer of component (A) has a melting point (Tm) of from 80° C. to 120° C.
13
C-NMR analysis carried out on the above propylene polymer as used in component (A) of the composition of the present invention provides information on the tacticity of the polymer chains. It is observed that the percentage of isotactic triads (mm) is from 50 to 85. Preferably in the propylene polymer the isotactic triads (mm) satisfy the relation 60<isotactic triads (mm)<80.
The molecular weights of the above propylene polymers are distributed within fairly narrow ranges. Thus the molecular weight distribution M
w
/M
n
turns out to be generally lower than 5, preferably lower than 4, more preferably lower than 3.
Examples of isotactic polymers of propylene for use as component (B) are commercially available isotactic polypropylenes, which are produced by means of conventional titanium based heterogeneous Ziegler-Natta-type catalysts. Metallocene based isotactic polymers having the above-described characteristics can also be used. Suitable metallocenes of this type are described in WO 96/22995. Polymers made by means of metallocenes generally have narrow molecular weight distribution M
w
/M
n
, such as values of lower than 3.
Generally the essentially isotactic propylene polymer used as component (B) of the compositions of the present invention have the following characteristics:
melting enthalpy>70 J/g, and
% of isotactic triads mm (B)>% of isotactic triads mm (A).
The structure of the above propylene polymer used as component (B) in the thermoplastic composition according to the present invention is essentially isotactic. In fact the percentage of isotactic triads (mm) is preferably higher than 90, more preferably the percentage of isotactic triads (mm) is higher than 95.
The essentially isotactic propylene polymer used in component (13) of the composition of the present invention have intrinsic viscosity values [&eegr;] of preferably higher than 1 dl/g. The propylene polymer as used as components (A) and (B) in the composition of the present invention can contain co-monomer units, such as ethylene, 1-butene, styrene, 1,5-hexadiene, 4-methylpentene or allyltrimethylsilane.
In the thermoplastic composition according to the present invention, the melting enthalpy &Dgr;H in the melting range of from about 39° C. to about 130° C. is generally higher than 6 J/g, preferably higher than 20 J/g. The thermoplastic composition according to the present invention can contain additives which are conventionally employed in thermoplastic polymer compositions such as stabilisers, antioxidants, corrosion inhibitors and the like.
Moreover, the compositions of the present invention can contain inorganic, organic or polymeric fillers. The above additives and fillers can be used in conventional quantities, as is known to those skilled in the art. Generally said additives and fillers can be present in a quantity of 5% by weight of the overall composition. Another aspect of the present invention is a process for the preparation of a thermoplastic composition as defined above, comprising the steps:
(I) polymerizing propylene optionally with an olefin of the formula CH
2
═CHR, R being hydrogen, a C
1
-C
20
-alkyl or a C
6
-C
12
-aryl group, in one or more reactors, in the pre
Baruzzi Giovanni
Ferraro Angelo
Resconi Luigi
Basell Polyolefine GmbH
Nutter Nathan M.
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