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
2002-08-12
2004-09-21
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...
C525S211000, C525S217000, C525S221000, C525S222000, C525S231000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06794453
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymeric compositions and their uses, and more particularly to predominantly polypropylene-based, crosslinked compositions and articles suitable for use in a range of applications, including coating or insulating materials.
BACKGROUND OF THE INVENTION
Polypropylenes are ideally suited to the preparation of coatings and insulations designed for use at operating temperatures in excess of those that can be withstood by other polyolefins, for example, polyethylene, which exhibit lower softening and melting temperatures. Polyethylenes have a maximum melting point, as measured by differential scanning calorimetry (DSC), of about 135° C., whereas polypropylenes can have melting points as high as 175° C.
Other attractive features of polypropylenes are their high rigidity and toughness, low cost and relatively low density. Applications for these coatings and insulations would include polymeric insulation for electrical wires and cables, and heat-shrinkable protective sleeves for high-temperature transmission pipelines, or applications requiring greater toughness and rigidity than is afforded by polyethylene-based systems. For example, heat-shrinkable sleeves used for the corrosion protection of high temperature pipeline joints are required to maintain dimensional stability and integrity at the operating temperature of the pipeline. Hence it is necessary to use a material, such as polypropylene, with a softening temperature or melting point high enough to prevent creeping or sagging of the sleeve from the pipe at the continuous operating temperature of the pipeline.
In order to maximise heat-resistance and physical properties, it is necessary to impart some thermoset characteristic to the material. This is done by crosslinking the polymer to some required degree. Crosslinking is also necessary for the production of heat-shrinkable articles to impart controlled shrinkage characteristics.
Polymers in which the predominant chain units comprise an alpha olefin, such as polypropylenes, are known to preferentially depolymerise when exposed to free radicals required to effect crosslinking. Hence, unlike polyolefins such as polyethylenes and copolymers of polyethylene, it is not possible to crosslink polypropylene-based materials to satisfactory levels, as is required, for example, in the production of wire and cable insulations, and heat-shrinkable articles, such as tubing, sheet, and moulded shapes, by using standard free-radical methods of crosslinking, such as electron beam irradiation or peroxide initiated crosslinking.
Alternate methods for crosslinking polyolefins are known. One such method comprises grafting a vinyl silane onto an olefin homopolymer or copolymer, followed by catalyzed hydrolysis and condensation of the silane groups. This is described in U.S. Pat. No. 3,646,155 (Scott), issued on Feb. 29, 1972. Alternatively, the vinyl silane may be copolymerised directly with olefin monomers as described in U.S. Pat. No. 4,413,066 (Isaka et al.), issued on Nov. 1, 1983. Since these methods require a free-radical generator to initiate the silane grafting or copolymerisation reaction, polypropylene is also unsuited to these methods of crosslinking.
Although the prior art contains examples of polypropylene-containing compositions having some crosslinking, none of these compositions is a predominantly polypropylene-based, crosslinked composition having the desirable properties of polypropylene.
One example of a prior art composition is disclosed in International Publication No. WO98/23687 (Laughner et al.), published on Jun. 4, 1998. This publication relates to the production of thermoplastic elastomers (TPE's), which comprise a thermoplastic matrix substantially free of crosslinking and a discontinuous elastomer phase in the form of domains dispersed throughout the matrix. According to Laughner et al., the thermoplastic phase may comprise polypropylene and the elastomer domains comprising the discontinuous phase are grafted with silane and subsequently crosslinked to improve impact properties of the TPE. However, even after crosslinking, the continuous phase remains thermoplastic, thereby allowing the TPE to be re-melted for further processing. The materials taught by Laughner et al. do not have thermoset properties necessary for applications requiring high temperature resistance, and would be expected to creep, sag or melt upon exposure to temperatures experienced during operation of high temperature pipelines. Nor do the materials taught by Laughner et al. have thermoset properties required of heat-shrinkable articles, which must be heated above their melting point to effect shape recovery.
Another prior art composition is disclosed in U.S. Pat. No. 4,464,425 (Voigt et al.), issued on Aug. 7, 1994. This patent relates to foamed, rubber-like compositions produced from silane-grafted, crosslinked polymers. These compositions are disclosed as being useful in the manufacture of hoses, and would be expected to be flexible and rubber-like. These materials would not have the physical properties of a crosslinked, polypropylene-based composition.
U.S. Pat. No. 5,929,129 (Feichtinger), issued on Jul. 27, 1999, describes a process of blending a silane-grafted polyolefin with a non silane-grafted polypropylene. However, this patent is limited to the manufacture of foamed materials which do not have the physical properties of a crosslinked, polypropylene-based composition due to insufficient levels of crosslinking and blend mixture-compatibility.
SUMMARY OF THE INVENTION
The present invention overcomes the above-discussed problems of the prior art by providing predominantly polypropylene-based, moisture-crosslinked compositions and articles formed therefrom. The compositions according to the invention are comprised of a silane-modified ethylene-based polyolefin, at least 50 percent by weight of a non silane-modified polypropylene, and a silanol condensation catalyst.
Crosslinking provides the compositions of the invention with thermoset properties. The required degree of crosslinking is such that, when the composition is heated to a temperature above the crystalline melting point of the non silane-modified polypropylene, it is softened but does not become liquid.
The compositions according to the invention are suited for a wide range of applications, but are particularly well suited as coating or insulating materials, and are particularly well suited for use as sleeves for high temperature pipelines. The relatively high polypropylene content of the composition provides articles formed therefrom with a high softening or melting point, and the crosslinking provides sufficient thermoset properties to help stabilize the physical structure of the formed article at high temperatures, thereby preventing melting, sagging and creeping, and to permit the formed article to exhibit heat-shrinkability when heated above the crystalline melting point of the non silane-modified polypropylene. In other words, the compositions and articles according to the invention behave like crosslinked polypropylene compositions, which have not previously been produced due to the difficulties discussed above.
The composition according to the invention is preferably formed into a desired article by melt processing techniques such as extrusion and moulding, including multi-layer processing, for example co-extrusion of the blend with another material to form discrete but intimately bonded layers. The article thus formed is cross-linked in the presence of a silanol condensation catalyst under suitable conditions of heat and moisture, the catalyst being either blended with the composition during melt processing or added subsequently by coating the formed article, for example.
Accordingly, in one aspect, the present invention provides a crosslinked, predominantly polypropylene-based article comprising: a silane-modified ethylene-based polyolefin comprising either a silane-grafted polyolefin or a silane-olefin copolymer; at least 50 percent by weight of a non silane-modified
Heydrich Marcus P.
Jackson Peter
Steele Robert Edward
Tailor Dilip K.
Tathgur Amarjit
Nutter Nathan M.
ShawCor Ltd.
Shlesinger & Arkwright & Garvey LLP
LandOfFree
Crosslinked, predominantly polypropylene-based compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Crosslinked, predominantly polypropylene-based compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Crosslinked, predominantly polypropylene-based compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3211643