Propylene polymer coupling and foams

Details Propylene polymer coupling and foams Propylene polymer coupling and foams

2002-05-21

2003-11-18

Foelak, Morton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S079000, C521S142000, C521S143000

Reexamination Certificate

active

06649666

ABSTRACT:

BACKGROUND OF THE INVENTION
Polypropylene can offer good impact properties because it is a semi-crystalline polymer which has a glass transition temperature substantially below room temperature. In addition, polypropylene can offer good temperature stability and high chemical resistance. However, until now, the production of polypropylene foams has been limited because of its low melt strength and melt elasticity and this makes it difficult to be foamed in comparison to the other plastics. If the melt strength and the melt elasticity are too weak, as in the case of polypropylene, the cell walls separating the bubbles will be too weak to bear the extensional force that is generated during the foaming process and the bubbles will rupture very easily. As a result, foamed polypropylene products are generally characterized by high open cell content, which makes them unsatisfactory in many applications.
Branched or lightly crosslinked polymers including polypropylene, such as may be obtained by chemical or irradiation branching or lightly crosslinking, are disclosed in U.S. Pat. Nos. 4,714,716 and 5,527,573. In co-pending U.S. patent application Ser. No. 09/133,576 filed Aug. 13, 1998 and WO-99/10424 in-situ rheology modification of polyolefins is disclosed as applied to, among others, polypropylenes resulting in polypropylenes having advantageous melt processing properties. Foams are mentioned among the possible end uses or applications of such rheology-modified propylene polymers.
There is a continuous demand for propylene polymer foams of a relatively high closed cell content, which do not suffer from the bubble stability problem generally experienced with polypropylene foams. The foams desirably are capable of being manufactured at high foam production rates on conventional foaming equipment while using a relatively low amount of blowing agent.
SUMMARY OF THE INVENTION
The present invention is a process to produce such improved propylene polymer foams. It has now been found that treatment of a propylene polymer, used as a feedstock for foam, with poly(sulfonyl azide) helps to retain or improve processability while subsequently building the molecular weight of the propylene polymer, enhancing its melt strength and improving its extensional properties. More preferably, by treating the propylene polymer starting materials by the process of the invention, one achieves at least one of greater throughput of polymer into foam (e.g., in pounds per hour) or lower density than with untreated starting material in the same foaming process while retaining equivalent or better crush strength or flexibility or both.
The invention includes a process for preparing a foam comprising the steps of: (i) introducing into a melt processing device (a) a propylene polymer and (b) a coupling amount of a poly(sulfonyl azide) and optionally an additional component such as (c) a nucleating agent, an additional thermoplastic polymer, a filler, a stabilizer, or mixtures thereof, forming a propylene polymer admixture wherein the additional component may be introduced before, during or after the coupling of the propylene polymer, (ii) exposing the propylene polymer admixture to a temperature sufficient to result in coupling of the propylene polymer forming a molten coupled propylene polymer composition, (iii) introducing a blowing agent before, during or after the coupling of the propylene polymer under a first pressure which maintains the blowing agent in the molten coupled propylene polymer composition, (iv) cooling the molten coupled propylene polymer composition comprising the blowing agent, (v) processing the molten coupled propylene polymer composition into a zone having a second pressure which allows for the blowing agent to escape from the molten coupled propylene polymer composition and (vi) forming a resulting foam. Preferably, the amount of poly(sulfonyl azide) is from about 10 parts per million to about 5 parts per hundred based on the weight of the propylene polymer; the melt process temperature is between about 200° C. and about 255° C.; the melt processing device is an extruder; or a combination thereof.
The poly(sulfonyl azide) preferably has a structure X-R-X wherein each X is SO
2
N
3
and R represents an unsubstituted or inertly substituted hydrocarbyl, hydrocarbyl ether or silicon-containing group; the poly(sulfonyl azide) has sufficient carbon, oxygen or silicon, atoms to separate the sulfonyl azide groups sufficiently to permit a facile reaction between the propylene polymer and the sulfonyl azide; R includes at least one aryl group between the sulfonyl groups; or a combination thereof.
Preferably, the resulting foam has a density of equal to or less than about 50 pounds per cubic foot and equal to or greater than about 0.6 pounds per cubic foot; a cell size of equal to or less than about 8 millimeters and equal to or greater than about 0.1 millimeters in diameter; or a combination thereof.
The invention also includes any composition comprising a foamed product formed by a process of the invention and any article formed from such a composition. Preferred articles are an automotive headliner, an automotive door liner, an automotive energy absorption counter measure, an automotive bumper, comfort cushioning foam, thermal insulation foam, sound insulation foam, building foam, construction foam, or packaging foam.
DETAILED DESCRIPTION OF THE INVENTION
The propylene polymer suitable for use in this invention is well known in the literature and can be prepared by known techniques. In general, the propylene polymer is in the isotactic form, although other forms can also be used (e.g., syndiotactic or atactic). The propylene polymer used for the present invention is preferably a homopolymer of polypropylene, a copolymer, for example, a random or block copolymer, of propylene and an alpha-olefin, preferably a ethylene, or C
4
to C
20
alpha-olefin or a random terpolymer of propylene and two or more monomers selected from ethylene and C
4
to C
20
alpha-olefins. The alpha olefins may be linear or branched, but are preferably linear. The alpha-olefin is present in the propylene polymer of the present invention in an amount less than or equal to about 7 percent by mole, preferably less than or equal to about 5 percent, even more preferably less than or equal to about 3 percent and most preferably less than or equal to about 1 percent by mole.
Examples of the C
4
to C
20
, alpha-olefins for constituting the propylene and alpha-olefin copolymer include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trimethyl-1-butene, 3-methyl-1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, 3,5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, dimethyloctene, ethyl-1-octene, methyl-1-nonene, vinylcyclopentene, vinylcyclohexene and vinylnorbornene, where alkyl branching position is not specified it is generally on position 3 or higher of the alkene.
The propylene polymer of the present invention can be prepared by various processes, for example, in a single stage or multiple stages, by such polymerization method as slurry polymerization, gas phase polymerization, bulk polymerization, solution polymerization or a combination thereof using a metallocene catalyst or a so-called Ziegler-Natta catalyst, which usually is one comprising a solid transition metal component comprising titanium. Particularly a catalyst consisting of, as a transition metal/solid component, a solid composition of titanium trichoride which contains as essential components titanium, magnesium and a halogen; as an organometalic component an organoaluminum compound; and if desired an electron donor. Preferred electron donors are organic compounds containing a nitrogen atom, a phosphorous atom, a sulfur atom, a silicon atom or a boron atom, and preferred are silicon compounds, est

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