Foamable polymeric composition

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

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Details

C525S197000, C525S232000, C525S233000, C525S238000, C525S240000, C525S241000

Reexamination Certificate

active

06221964

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a foamable polymeric composition, and particularly to a foamable thermoplastic elastomer composition comprising a polyolefin and a rubber (TPOE). The present invention also relates to a process for preparing a foamed polymeric article from the composition and to the resultant foamed polymeric article. It particularly relates to a flame retardant foamed polymeric article.
PRIOR ART
A foamable polymeric composition, as well as a foamed polymeric article, on the basis of a thermoplastic elastomer, which comprises a polyolefin and a rubber, is known from U.S. Pat. No. 4,898,760.
This foamable composition and articles prepared therefrom suffer from serious drawbacks. For instance, with foamed articles prepared from foamable compositions in which a polypropylene homo- or copolymer constitutes the thermoplastic phase, the foam cells are undesirably non-uniform. These and other properties need improvement, and particularly so in the case of low density foamed articles (density less than 600 kg/m
3
).
SUMMARY OF THE INVENTION
The foamable polymeric composition of the present invention provides a solution for the above problems. The invention resides in the use of a specific type of polypropylene homo- or copolymer, as a result of which improved polymeric foams are obtainable.
The invention deals with a foamable polymeric composition, comprising a thermoplastic elastomer on the basis of a polyolefin and a rubber, wherein the polyolefin is a polypropylene homo- or copolymer having:
a weight average molecular weight, M
w
, of at least 2*10
5
, and
an elongational viscosity (measured at 170° C., at a rate of elongation of 0.03 s
−1
and at a time of 10 s), EV(170/10), of at least 1.4*10
4
Pa.s.
The M
w
of the polypropylene is determined using gel permeation chromatografy (GPC), known in the art, at 145° C. The elongational viscosity (hereinafter abbreviated “EV”) is determined according to the procedures detailed in Meissner, Acta 8,78,1969 and Meisner, Acta 10,230,1971, the complete disclosures of which are incorporated herein by reference.
DETAILED DESCRIPTION OF THE INVENTION
The present invention recognizes the criticallity of the type of polypropylene to be used in the foamable polymeric composition. It has been found that the use of a polypropylene having the minimum M
w
and the minimum EV(170/10) results in a foamed article with improved physical properties; the cell-size is much more uniform, as a result of which a much lower density of the foam can be obtained.
The polypropylene in the composition of the present invention is either a homopolymer or a copolymer of propylene with other olefines. Other olefins that can be used are ethylene or an &agr;-olefin having 4-20 C-atoms; &agr;-olefin with more than 20 C-atoms can also be applied. Preferable the &agr;-olefin is selected from ethylene and &agr;-olefins having 4-10 C-atoms, like pentene-1, 4-methylpentene-1, hexene-1 and octene-1. Also mixtures of &agr;-olefins are applicable. In the case of copolymers the contents of propylene in such a copolymer is at least 75 wt %. The polypropylene polymer is (semi-)crystalline, behaves like a thermoplastic and has a DSC-crystallinity of at least 15% (DSC=differential scanning calorimetry, a known thermometric analytical device). The polypropylene has to have a M
w
of at least 2*10
5
, more preferably more than 4*10
5
; the elongational viscosity EV(170/10) of the polypropylene should be at least 1.4*10
4
Pa.s, more preferably more than 2.0*10
4
Pa.s.
The polypropylene in the composition of the present invention can also be characterized with an alternative elongational viscosity value: the polypropylene has to have an elongational viscosity (measured at a temperature of 190° C., at a rate of elongation of 0.03 s
−1
and at a time of 25 sec.), EV(190/25), of at least 1.5*10
4
Pa.s. More prefered the EV(190/25) has a value of at least 2.5*10
4
Pa.s.
The polypropylene in the composition of the present invention preferably has a storage modulus (measured at 1 rad/s and at a temperature of 170° C.), G′(170), of at least 6 kPa; more preferably G′(170) is at least 9 kPa.
The polypropylene preferably has a complex viscosity (measured at 1 rad/s and at a temperature of 170° C.), &eegr;*(170), of at least 10 kPa.s; more preferably &eegr;*(170:) is at least 15 kPa.s.
The polypropylene also has preferably an apparent shear viscosity (measured at 207 s
−1
and at a temperature of 250° C.) of at least 350 Pa.s; more preferably this apparent shear viscosity has a value of at least 500 Pa.s.
All the (above mentioned) dynamic mechanical properties of the polypropylene present in the composition of the present invention are determined with a Rheometrics Scientific RDA II® rheometer with dual force rebalance transducer.
The polypropylene in the composition of the present invention preferably has a number-average molecular weight, M
n
, of at least 8*10
4
; more preferably the polypropylene has a M
n
of at least 10
5
.
The improvements in polymeric foams obtained by the present invention can preferably be obtained, when not only the polypropylene is of a specific, above identified, nature, but also when the composition is of a specific nature: the foamable polymeric composition comprises a thermoplastic elastomer on the basis of a polypropylene and a rubber, wherein the polypropylene has a M
w
of at least 2*10
5
, preferably at least 4*10
5
, and the composition has an apparent shear viscosity (measured at 207 s
−1
and at a temperature of 200° C.) of at least 250 Pa.s; more preferably this apparent shear viscosity of the composition has a value of at least 300 Pa.s. The composition is found suitable for the preparation of foams according to the present invention, if the composition has a Goettfert Rheotens® elongational viscosity (measured at a temperature of 210° C., at a rate of elongation of 1 s
−1
), GREV, of at least 4.0*10
4
Pa.s; more preferably, the GREV has a value of at least 5.5*10
4
Pa.s. For the details of the measurement, reference is given to the Examples.
The effects of the invention become even more apparent, when the composition also contains at least one filler or filler-like material. The filler, which is preferably in its majority present in the polypropylene phase, has a dominant influence on the foamability of the composition, especially in those cases where the polypropylene is the phase which is substantially foamed (such as in the case where the rubber is at least partially vulcanized). The above is valid for all conventional fillers or additives (like pigments, UV-stabilizers, talc, glass fibers, carbon black, etc.). Preferably the filler is a flame retardant.
The rubber in the TPOE used according to the invention can be any rubber known in the art, provided that the rubber is stable under the foaming conditions. Preferred rubbers are butyl rubber (copolymer as well as terpolymer, and also in its halogenated form); ethylene/&agr;-olefin copolymer rubber (EAM) as well as ethylene/&agr;-olefin/diene terpolymer rubber (EADM); acrylonitrile/butadiene rubber (NBR); styrene/butadiene rubber (SBR); natural rubber (NR). In case of EAM or EADM rubber, the &agr;-olefin in such a rubber is preferably propylene; in such a case the rubber is referred to as EP(D)M. The amount of rubber in the TPOE is preferably in the range of 25-85 wt %, based on the weight of the polypropylene and the rubber
With more preference the TPOE is a thermoplastic polyolefin vulcanizate (TPOEV), in which the dispersed rubber is at least partially cured.
Here and hereinafter a TPOE is called a TPOEV when the rubber in the TPOE has a degree of vulcanization such that the amount of extractable rubber is less than 90%. The test to determine such an extractable amount is generally done with a solvent in which the polyolefin as well as the not-vulcanized rubber are soluble, but in which the vulcanized rubber is not soluble. A suitable solvent is boiling xylene.
By vulcanizing the rubber in a TPOE, the physica

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