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
2000-11-15
2003-07-01
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
06586528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition based on propylene polymers exhibiting an improved compromise between rigidity and weldability. It relates more particularly to a composition suitable for use in making numerous articles such as expanded granules as well as to a process for preparation of such a composition.
2. Discussion of the Background
It is known that propylene polymers can be used for numerous applications such as the manufacture of preformed articles, films, sheets and cellular articles. In these applications, polypropylene is preferred to other plastic materials by virtue of its chemical resistance, its heat resistance and/or its impact resistance and rigidity.
For example, European Patent Application 0860457 describes the use of a propylene block copolymer containing 60 to 90 wt % of a propylene homopolymer and 40 to 10 wt % of a statistical propylene copolymer containing 1 to 10 wt % of ethylene for the manufacture of molded articles such as, in particular, bioriented bottles. The preferred compositions, which contain 20 wt % of a propylene homopolymer with high isotacticity, have insufficient weldability and excessively high rigidity for applications such as the manufacture of cellular articles.
In addition, European Patent Application 0893470 discloses the use, for the manufacture of expanded granules, of compositions containing 60 to 90 parts by weight of a propylene homopolymer having a melt flow index (MFI) ranging from 0.1 to 20 g/10 minutes and 40 to 10 parts by weight of a statistical propylene copolymer which contains 3 to 20 mol % of a comonomer such as ethylene and which has an MFI of 25 to 3000 g/10 minutes. However, the use of the preferred compositions, in which the ratio of the MFI of the copolymer to that of the homopolymer is greater than 20, leads to heterogeneities. In addition, the use of such resins is economically disadvantageous because of their high manufacturing cost.
Finally, German Patent Application 4420590 discloses polyolefin foam particles of uniform density obtained from a mixture compatible with at least two different propylene polymers, the majority of the said mixture being formed from propylene copolymers and terpolymers, at least one of which contains 1-butene. Again, the high cost of the compositions due to the butene copolymer or copolymers (low polymerization yield, cost of monomer recycling installations) prevents their widespread use.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a composition which does not suffer from the disadvantages of the conventional compositions.
Another object of the present invention is to provide a composition having improved processability.
Another object of the present invention is to provide a composition having a good balance of mechanical properties and sealing properties.
These and other objects have now been achieved by the present invention, the first embodiment of which provides a composition, which includes:
(a) from 55 to 74 parts by weight of a propylene polymer (A) which includes less than or equal to 1% by weight of ethylene and having a melt flow index (MFI) of 0.1 to 30 g/10 minutes, measured according to ASTM D 1238 (1986) under a load of 2.16 kg at 230° C.; and
(b) from 26 to 45 parts by weight of a polymer (b), which is a statistical copolymer of propylene including from 3.5 to 15 wt % of ethylene and having an MFI of 0.1 to 35 g/10 minutes.
Another embodiment of the invention provides an article, which includes the above-described composition.
Another embodiment of the invention provides a process for preparing the above-described composition, which includes two successive polymerization stages, wherein 55 to 74 parts by weight of polymer (A) and from 26 to 45 parts by weight of polymer (B) are respectively prepared.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.
Preferably, the composition according to the present invention includes:
from 55 to 74 parts by weight of a propylene polymer (A) not containing more than 1% by weight of ethylene and having a melt flow index (MFI) of 0.1 to 30 g/10 minutes, measured according to ASTM D 1238 (1986) under a load of 2.6 kg at 230° C., and
from 26 to 45 parts by weight of a polymer (B), which is a statistical copolymer of propylene containing from 3.5 to 15% of ethylene and having an MFI of 0.1 to 35 g/10 minutes.
Preferably, polymers (A) and (B) are semicrystalline within the meaning conveyed in “Plastics Engineering”, 2nd Edition, R. J. Crawford, Pergamon Press (1987), pages 3 and 4, the entire contents of which are hereby incorporated by reference. Preferably, they contain less than 1 wt % of monomeric units derived from 1-butene. Compositions whose polymers (A) and (B) do not contain any monomeric units derived from 1-butene are particularly preferred.
Preferably, polymer (A) has a modulus of elasticity in flexion (measured at 23° C. on an injection-molded specimen with a thickness of 4 mm in accordance with ASTM D 790 M-flexural modulus) of 1200 to 2000 MPa. More preferably the above-noted flexural modulus ranges from 1400 to 1800 MPa, and most preferably 1500 to 1600 MPa. These ranges include all values and subranges therebetween, including 1300, 1700 and 1900 MPa. Preferably polymer (B) has a flexural modulus of 300 to 800 MPa. More preferably, the flexural modulus of polymer (B) ranges from 400 to 700 MPa, and more particularly preferably from 500 to 600 MPa. These ranges include all values and subranges therebetween, including 350, 450, 550, and 750.
Preferably, polymer (A) contains at most 0.75 wt % of ethylene. More preferably polymer (A) contains at most 0.5% ethylene, more particularly preferably 0.25 wt %. Compositions in which polymer (A) is a propylene homopolymer yield particularly good results. These ranges include all values and subranges therebetween, including 0.7, 0.6, 0.4, 0.3 and 0.1 wt %.
Preferably, polymer (A) has an isotacticity index, appraised by the molar fraction of isotactic triads according to the method described in connection with the examples, of at most 98% and more preferably of at most 97%. More particularly preferably the index is at most 96%, and most preferably at most 95%. These ranges include all values and subranges therebetween, including 97.8, 97.7, 97.6, 97.5 and 97.3.
Preferably, polymer (B) contains at least 4 wt % of ethylene. More preferably, polymer (B) contains at least 5 wt % ethylene, more particularly preferably at least 6 wt %, and most preferably at least 8 wt %. Polymers (B) containing at most 10 wt % of ethylene are particularly preferred. These ranges include all values and subranges therebetween, including 4.5, 5.5, 6.5, 7, 8.5, 9 and 9.5 wt %.
The comonomer contents mentioned in the present specification are determined by Fourier transform IR spectrometry on the polymer worked into a pressed 200 &mgr;m film (thickness). The ethylene contents are estimated from the absorption bands at 732 and 720 cm
−1
.
Preferably, the MFI of polymers (A) and (B) (MFI
(A)
and MFI
(B)
) is at least 1 g/10 minutes, more preferably at least 2 g/10 minutes, more particularly preferably at least 3 g/10 minutes. These ranges include all values and subranges therebetween, including 1.1, 1.5, 1.75, 2.2, 2.5, 3.1, 4.4 and 5.5. Preferably, MFI
(A)
is at most 15 g/10 minutes, more preferably at most 10 g/10 minutes and more particularly preferably at most 5 g/10 minutes. These ranges include all values and subranges therebetween, including 14, 13, 12, 11, 9, 8, 7, 6, 4, and 2. Preferably, MFI
(B)
is at most 30 g/10 minutes, and more preferably at most 20 g/10 minutes, and most preferably at most 15 g/10minutes. These ranges include all values and subranges therebetween, including 28, 25, 23, 18, 16, 14, 12, 10, 8 and 7.
It is also pointed out that the MFI
(B)
Cuypers Herve
Delaite Emmanuel
Nutter Nathan M.
Oliver Wallace L.
Patel Nirav
Polypropylene Belgium (Naamlose Vennootshap)
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