Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Autogenously bonded nonwoven fabric
Reexamination Certificate
2000-07-31
2002-10-01
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Autogenously bonded nonwoven fabric
C428S198000, C428S297400, C428S298100, C428S299700, C264S322000, C264S494000
Reexamination Certificate
active
06458727
ABSTRACT:
This invention relates to processes for the production of polymer sheet materials from oriented olefin polymer fibers and to the products of such processes.
GB 2253420B describes a process whereby an assembly of fibers of an oriented polymer may be hot compacted to form a sheet having good mechanical properties. The process involves an initial processing step in which the fibers are brought to and held at the compaction temperature whilst subject to a pressure sufficient to maintain the fibers in contact, the contact pressure, and thereafter compacted at a higher pressure for a few seconds, the compaction pressure. In the process a proportion of the fibre surfaces—most preferably from 5 to 10% by weight—melts and subsequently recrystallises on cooling. This recrystallised phase binds the fibers together. Preferred materials for use in this process are homo- and co-polymers of polyethylene.
The process of GB 2253420B can be used to produce complicated and precisely shaped monolithic articles having high stiffness and strength, and good energy-absorbing properties. However, a drawback of this process is the criticality of the compaction temperature, especially for polyethylene. This is shown by Comparative Example A in GB 2253420B.
In accordance with the present invention there is provided a process for the production of a monolithic article in which process an assembly of fibers of an oriented polyolefin polymer is subjected to a compaction process wherein the assembly of fibers is maintained in intimate contact at an elevated temperature sufficient to melt a proportion of the polymer, and is compressed, characterised in that prior to the compaction process the fibers have been subjected to a crosslinking process.
In some embodiments (referred to herein as “2-step compactions”) the compaction process may comprise two distinct steps, namely a step of maintaining the assembly of fibers in intimate contact at an elevated temperature sufficient to melt a proportion of the fibre at a first, contact, pressure, and a subsequent compression step wherein the assembly is subjected to a second, compaction, pressure, higher than the contact pressure—as in GB 2253420B.
In some embodiments (referred to herein as “1-step compactions”) the compaction process may comprise a single step of maintaining the assembly of fibers in intimate contact at an elevated temperature sufficient to melt a proportion of the fibre, and at a given pressure. In such embodiments there is no subsequent step of applying a higher pressure.
Preferably the monolithic article is an article which is shape stable under its own weight, such as a plaque.
The crosslinking process may be a chemical crosslinking process, involving the use of a chemical reagent which forms reactive radicals under predetermined initiation conditions. Suitably the reagent may be a cumene compound, or a peroxide, for example DMTBH or DCP, or a silane, for example a vinyl silane, preferably vinylmethoxy silane.
The crosslinking process may be an irradiation crosslinking process involving an ionising step comprising irradiating the fibers with an ionising radiation, and then an annealing step comprising annealing the irradiated polymer at an elevated temperature.
For general information on known crosslinking processes, reference may be made to Sultan & Palmlöf, “Advances in Crosslinking Technology”, Plast. Rubb. and Comp. Process and Appl., 21, 2, pp. 65-73 (1994), and to the references therein.
Irradiation crosslinking is believed to be particularly suitable, for the process of the present application.
The pre-compaction process of crosslinking has been found to increase the “temperature window” available for the subsequent compaction stage, and thus to make the compaction stage much easier to control. Further, compacted products produced by the process of the present invention have exhibited superior hot strength properties, compared with compacted products made from fibers which have not been subject to prior crosslinking.
The term “fibers” is used herein in a broad sense to denote strands of polyolefin polymer, however formed. The fibers subjected to prior crosslinking may be non-woven fibers laid in a web, or may be comprised within yarns, or constituted by bands or fibrillated tapes, for example formed by slitting films. If comprised within yarns or constituted by bands or fibrillated tapes, those yarns, bands or fibrillated tapes may be laid together or they may be formed into a fabric, for example by weaving or knitting.
Suitably the fibers used in the process of the invention are formed from molten polymer, for example as melt spun filaments.
Preferably the fibers used in the present invention have a weight average molecular weight in the range 10,000 to 400,000, preferably 50,000 to 200,000.
The polyolefin polymer can be selected from polyethylene, polypropylene or polybutylene, or copolymers comprising at least one of those olefin polymers. The polyolefin polymer used in the process of the present invention may suitably be a polypropylene homopolymer or a copolymer containing a major proportion of polypropylene. Advantageously it may be a polyethylene homopolymer or a copolymer containing a major proportion of polyethylene.
A polyethylene copolymer comprising a major proportion of polyethylene as defined herein is one comprising more than 50% by weight of polyethylene. Preferably, it comprises more than 70% by weight of polyethylene, most preferably, more than 85% by weight of polyethylene.
A polyethylene polymer as defined herein may be unsubstituted, or substituted, for example by halogen atoms, preferably fluorine or chlorine atoms. Unsubstituted polyethylene polymers are however preferred.
A polyethylene copolymer comprising a major proportion of polyethylene may have one or more different copolymers, following copolymerisation of ethylene with, for example, one or more of propylene, butylene, butadiene, vinyl chloride, styrene or tetrafluoroethylene. Such a polyethylene copolymer may be a random copolymer, or a block or graft copolymer. A preferred polyethylene copolymer is a ethylene-propylene copolymer, having a major proportion of polyethylene and a minor proportion of polypropylene.
A polypropylene copolymer comprising a major proportion of polypropylene as defined herein is one comprising more than 50% by weight of polypropylene. Preferably, it comprises more than 70% by weight of polypropylene, most preferably, more than 85% by weight of polypropylene.
A polypropylene polymer as defined herein may be unsubstituted, or substituted, for example by halogen atoms, preferably fluorine or chlorine atoms. Unsubstituted polypropylene polymers are however preferred.
A polypropylene copolymer comprising a major proportion of polypropylene may have one or more different copolymers, following copolymerisation of propylene with, for example, one or more of ethylene, butylene, butadiene, vinyl chloride, styrene or tetrafluoroethylene. Such a polypropylene copolymer may be a random copolymer, or a block or graft copolymer. A preferred polypropylene copolymer is a propylene-ethylene copolymer, having a major proportion of polypropylene and a minor proportion of polyethylene.
It is essential in the practice of the present invention that the process employs fibers which have been subjected to a crosslinking process. However, the co-use of a polymer component (not necessarily a polyolefin) which has not been subjected to a crosslinking process, and/or of an inorganic filler material, is not excluded.
A polymer which has not been subjected to a crosslinking process may, when present, be present in an amount up to 50 vol % of the total polymer content of the article. Preferably, however, substantially the entire polymer content of the article derives from polyolefin polymer which has been subject to a crosslinking process.
An inorganic filler material may be present. An inorganic filler, when present, may be present in an amount up to 60 vol % of the article, preferably 20 to 50 vol %. An inorganic filler material may, for example, be selected from
Bonner Mark James
Hine Peter John
Jones Richard Albert
Ward Ian MacMillan
Morris Terrel
Nixon & Vanderhye
Ruddock Ula C.
University of Leeds Innovative Limited
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