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  Compacted olefin fibersUSPTO Application #: 20060178069Title: Compacted olefin fibers Abstract: A polyolefin plaque is made by hot compaction of an assembly of fibres of the oriented polymer. It has been found to be beneficial to subject the fibres to a prior crosslinking process. Hot compaction is then less temperature-sensitive and produces plaques with excellent hot strength properties. Preferably the fibres have been subjected to prior stages of irradiation and annealing, both in a non-oxidising environment, for example acetylene. (end of abstract) Agent: Nixon & Vanderhye, PC - Arlington, VA, US Inventors: Richard Albert Jones, Ian MacMillan Ward, Peter John Hine, Mark James Bonner USPTO Applicaton #: 20060178069 - Class: 442409000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Nonwoven Fabric (i.e., Nonwoven Strand Or Fiber Material), Autogenously Bonded Nonwoven Fabric The Patent Description & Claims data below is from USPTO Patent Application 20060178069. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of application Ser. No. 10/717,553, filed Nov. 21, 2003, which is a continuation of application Ser. No. 09/971,710, filed Oct. 9, 2001, which is a divisional of application Ser. No. 09/285,256, filed Apr. 2, 1999, which is a continuation of PCT/GB97/02675, filed Oct. 6, 1997, the entire content of which is hereby incorporated by reference in this application. [0002] This invention relates to processes for the production of polymer sheet materials from oriented olefin polymer fibres and to the products of such processes. BACKGROUND OF THE INVENTION [0003] GB 2253420B describes a process whereby an assembly of fibres 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 fibres are brought to and held at the compaction temperature whilst subject to a pressure sufficient to maintain the fibres 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 fibres together. Preferred materials for use in this process are homo- and co-polymers of polyethylene. [0004] 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. SUMMARY OF THE INVENTION [0005] In accordance with the present invention there is provided a process for the production of a monolithic article in which process an assembly of fibres of an oriented polyolefin polymer is subjected to a compaction process wherein the assembly of fibres 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 fibres have been subjected to a crosslinking process. [0006] 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 fibres 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. [0007] In some embodiments (referred to herein as "1-step compactions") the compaction process may comprise a single step of maintaining the assembly of fibres 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. [0008] Preferably the monolithic article is an article which is shape stable under its own weight, such as a plaque. [0009] 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. [0010] The crosslinking process may be an irradiation crosslinking process involving an ionising step comprising irradiating the fibres with an ionising radiation, and then an annealing step comprising annealing the irradiated polymer at an elevated temperature. [0011] For general information on known crosslinking processes, reference may be made to Sultan & Palmlof, "Advances in Crosslinking Technology", Plast. Rubb. and Comp. Process and Appl., 21, 2, pp. 65-73 (1994), and to the references therein. [0012] Irradiation crosslinking is believed to be particularly suitable, for the process of the present application. [0013] 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 fibres which have not been subject to prior crosslinking. [0014] The term "fibres" is used herein in a broad sense to denote strands of polyolefin polymer, however formed. The fibres subjected to prior crosslinking may be non-woven fibres 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. [0015] Suitably the fibres used in the process of the invention are formed from molten polymer, for example as melt spun filaments. [0016] Preferably the fibres 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. [0017] 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. [0018] 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. [0019] 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. [0020] 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. [0021] 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. [0022] 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. Continue reading... Full patent description for Compacted olefin fibers Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Compacted olefin fibers patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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