Transparent elastomeric thermoplastic polyolefin compositions

Details Transparent elastomeric thermoplastic polyolefin compositions Transparent elastomeric thermoplastic polyolefin compositions

2001-07-25

2004-01-06

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

06673869

ABSTRACT:

The present invention relates to an elastomeric thermoplastic polyolefin composition and a process for producing the composition and articles obtained therefrom.
The compositions of the present invention can be used in many applications, especially those where soft, transparent and impact resistant materials are required.
Compositions suitable for use in the same field as the present composition due to the similar mechanical, optical and tactile properties are already known. An example of said compositions is soft polyvinyl chloride. However, the polyvinyl chloride suffers from a number of disadvantages. The migration and extractability of plasticizers, discoloration and difficulty in treating its wastes are examples of said disadvantages. Hence, due to said shortcomings it is highly desirable to replace the polyvinyl chloride. In particular the migration and extractability of plasticizers in biologic liquids are unwelcome when the polyvinyl chloride is used in certain applications such as medical and food applications.
Hence, there is a need for substitutes for PVC in these applications.
Suitable known olefin-based compositions are made of polyethylene or thermoplastic elastomeric olefin polymers. Examples of the latter compositions are described in European patent application 666284. Said European patent application discloses a blend of an amorphous polypropylene with a crystalline propylene polymer or an olefin-based thermoplastic elastomer composition. These compositions are endowed with good transparency and high softness. However, they do not have good resistance to high temperatures such as the steam sterilization temperature.
A new polyolefin composition has now been found that does not have the above-mentioned shortcomings and has a good balance of softness, transparency, impact resistance at low temperatures and resistance to heat. Thanks to the high temperature resistance, the composition can be sterilized in an autoclave.
The good impact resistance at low temperatures (i.e., −20° C.) of the compositions according to the present invention is achieved without affecting the transparency and the heat resistance of the composition.
Moreover, a further advantage of the compositions of the present invention is the resistance to blooming. Blooming can be a severe problem in soft polymeric compositions because it causes surface stickiness.
Accordingly, the present invention provides an elastomeric thermoplastic polyolefin composition comprising:
(I) a crystalline propylene polymer (cPP) containing at least 80% by weight, preferably about 94% by weight, of a fraction insoluble in xylene at room temperature, the intrinsic viscosity being higher than 0.5 dl/g;
(II) an atactic or amorphous propylene polymer (aPP) having an intrinsic viscosity higher than 0.5 dl/g; and
(III) an elastomeric olefin polymer (eOP) consisting of copolymers of ethylene with a comonomer selected from C
3
-C
8
&agr;-olefins, the intrinsic viscosity ranging from 1 to 4 dl/g;
in said polyolefin composition the density of the elastomeric olefin polymer (d
eOP
) satisfies the following relationship:
d
eOP
±0.005=
{d
cPP
×[w
cPP
/(
w
cPP
+w
aPP
)]}+{
d
aPP
×[w
aPP
/(
w
cPP
+w
aPP
)]}  (1)
wherein w
cPP
and w
aPP
are the weight percentage content of components (I) and (II) respectively and d
cPP
and d
aPP
are the density at room temperature of components (I) and (II) respectively.
Room temperature means a temperature of about 23° C.
The polyolefin composition of the present invention can contain the above three components, i.e., cPP, aPP and eOP, in any amount, provided that the above relationship between the density is satisfied. However, particularly suitable compositions according to the present invention comprise 5-55 wt. %, preferably 5 less than 40 wt. %, such as 39 wt. %, of cPP, 1-55 wt. % of aPP and 1-55 wt. % of eOP, based on the total amount (100 wt. %) of components (I) to (III).
The crystalline propylene polymer (cPP) can be selected from both syndiotactic and isotactic polymers. They comprise both a propylene homopolymer and a random copolymer of propylene with recurring units derived from ethylene and/or 1-butene. The comonomer ranges preferably from 0.5 to 20% by mole.
Generally, the intrinsic viscosity of an isotactic propylene polymer ranges from 0.6 to 6 dl/g. Those polymers having an intrinsic viscosity higher than 1 dl/g, preferably higher than 1.5 dl/g, are the most suitable components for the composition of the present invention.
The melting temperature of an isotactic propylene polymer is generally between 110 and 160° C., and can even reach values above 160° C.
Particularly suitable for the composition of this invention are isotactic propylene polymers having a melting enthalpy greater than 80 J/g, preferably greater than 90 J/g.
The fraction of these polymers soluble in xylene at 23° C. is generally less than 10%.
The molecular weight distribution of these polymers M
w
/M
n
is generally broad, i.e., larger than 5.
Suitable isotactic propylene polymers are commercially available isotactic polypropylene, for example, which are produced by polymerizing the relevant monomer(s) according to known processes in the presence of conventional titanium- or vanadium-based heterogeneous Ziegler-Natta-type catalysts.
Metallocene-based isotactic propylene polymers having the above-described characteristics can also be used. Polymers made by means of metallocenes generally have narrow molecular weight distribution M
w
/M
n
, such as values of lower than 4. Suitable propylene polymers are described, for example, in European patent applications 576970 and 629632. Said polymers can be prepared according to known methods by using a catalytic system comprising the racemic form of dimethylsilanediyl-bis[1-(2-ethyl-4-phenylindenyl)]zirconium dichloride, for example, as the metallocene catalyst and an activating cocatalyst, such as alumoxane.
Generally, the intrinsic viscosity of syndiotactic propylene polymers ranges from 0.6 to 6 dl/g. Those polymers having an intrinsic viscosity higher than 1.0 dl/g, preferably higher than 1.3 dl/g, are the most preferred as components of the composition of the present invention.
The melting temperature of a syndiotactic propylene homopolymer is generally between 110 and 150° C. and the melting enthalpy is generally between 20 and 50 J/g. For the composition of the present invention those syndiotactic polymers having a melting enthalpy higher than 30 J/g, preferably higher than 40 J/g, are the most suitable.
Suitable syndiotactic polymers and catalytic systems are, respectively, described in EP-A-697436 and U.S. Pat. No. 4,892,851. Said polymers can be prepared according to known methods by using a catalytic system comprising isopropylidene(cyclopentadienyl)(9-fluorenyl) zirconium dichloride, for example, as the syndiospecific metallocene catalyst, and an activating cocatalyst.
The atactic or amorphous propylene polymer (aPP) is preferably a propylene homopolymer. However, it can also be a propylene copolymer with recurring units deriving from ethylene and/or 1-butene. The amount of comonomer ranges preferably from 0.5 to 13 mol %.
The aPP is substantially devoid of crystallinity. Its melting enthalpy is generally lower than about 20 J/g, preferably lower than 10 dl/g.
Preferably, the aPP suitable as a component for the composition of the present invention has an intrinsic viscosity equal to or higher than 1.0 dl/g, and it can reach values higher than 3 dl/g, for example. The molecular weight distribution M
w
/M
n
of aPP is lower than 5, preferably lower than 4, and more preferably lower than 3.
The structure of aPP determined by
13
C-NMR analysis appears substantially atactic, although the polymers have a varying content of isotactic and syndiotactic sequences.
Suitable aPP as well as the polymerization process thereof is described in the international patent application WO 00/1738. Said aPP generally has isotactic sequences, in particular pentads, more nu

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