Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-03-08
2001-09-04
Woodward, Ana (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C428S035900, C428S036900, C428S474400, C428S474900, C428S475800, C428S475500, C428S476300
Reexamination Certificate
active
06284335
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to blends of fluoropolymer with polyamide.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,576,106 (Kerbow et al.) discloses a process for grafting an ethylenically unsaturated compound onto the surface of the particles of fluoropolymer powder. The ethylenically unsaturated compound provides polar functionality to the fluoropolymer, which is otherwise non-polar. The utility of the resultant grafted fluoropolymer powder is disclosed to be to act as an adhesive to adhere dissimilar materials together, such as tetrafluoroethylene/ethylene (ETFE) copolymer to polyamide. To demonstrate the interaction between the grafted powder and the polyamide, a blend of grafted powder and polyamide is made by simple mixing of these components in a weight ratio of 67:33 (55:45 by volume), and the resultant blend is compression molded to yield plaques which exhibit improved tensile elongation.
European Patent Application Publication EP 0 761 757 discloses a fluorine-containing polymer alloy of a grafted fluorine-containing polymer and a polymer containing no fluorine, the fluorine-containing polymer having hydrogen atoms bonded to carbon atoms of its main chain. The grafting is done by melt mixing a fluorine-containing polymer having hydrogen atoms bonded to mainchain carbon atoms, a grafting compound having a linking group and a functional group, and a radical-forming agent (peroxide), apparently either simultaneously with or prior to mixing with the polymer containing no fluorine to form the alloy. No amount of grafting compound actually grafted to the fluorine-containing polymer is disclosed, and the average particle size of the dispersed fluoropolymer is relatively large, i.e., 0.7 &mgr;m (700 nm) and larger. In attempts to evaluate this grafting technology, the maximum amount of maleic anhydride that could actually be grafted to ETFE fluoropolymer was no more than 0.2 wt %. The color of the product indicated residual decomposition products from the grafting chemistry, and no bond of such grafted fluorine-containing polymer to 6,6-polyarnide was obtained in coextrusion.
There remain needs for fuel hose of simple construction, for shaped articles for handling and containing fuel fluids, and for materials for use in fabricating such hose and articles.
SUMMARY OF THE INVENTION
It has now been discovered that polar-grafted fluoropolymer can be melt blended with polyamide to produce a dispersion of the fluoropolymer in a matrix of the polyamide, so as to provide enhanced utility such as in composite hose which is useful for conveying fuel in motorized vehicles, or in containers for handling fuel or fuel vapors. This invention, then, provides a melt-mixed blend, comprising polyamide as the matrix of the blend and fluoropolymer having polar functionality dispersed therein with average dispersed particle size of no more than 500 nm, said polar functionality being present as part of an ethylenically unsaturated compound grafted to said fluoropolymer. The blends of the present invention also exhibit surprisingly low permeability and improved chemical resistance relative to polyamide. Consequently, the melt-mixed blend has utility as a barrier to chemicals such as fuels having high vapor pressure, and thus in articles for transport and containment of such chemicals.
The melt-mixed blend is useful in structures made from the blend alone, and in composite structures with fluoropolymer and/or polyamide. In such composites, a separate adhesive layer is no longer necessary to adhere the components together.
DETAILED DESCRIPTION
Any polyamide can be used to constitute the polyamide component of the melt-mixed blend of the invention. Such polyamide should of course be melt extrudable, and preferably has a number average molecular weight of at least 5000. Examples of polyamides include those made by condensation of equimolar amounts of at least one saturated dicarboxylic acid containing 4 to 14 carbon atoms with at least one diamine containing 4 to 14 carbon atoms. Excess diamine, however can be used to provide an excess of amine end groups over carboxyl end groups in the polyamide. Specific examples include polyhexamethylene adipamide (66 nylon), polyhexamethylene azelaamide (69 nylon), polyhexamethylene sebacamide (610 nylon), polyhexamethylene dodecanoamide (612 nylon) and polycaprolactam (6 nylon). Aromatic polyamides that are melt extrudable (e.g., aliphatic-aromatic polyamides, as opposed to polyaramids) can also be used in the melt-mixed blends of the present invention. Examples of such semiaromatic polyamides include Amodel® A 1000 and copolymers of 2-methylpentamethylenediamineterephthalate and hexamethyleneterephthalamide such as Zytel® HTN 501 (DuPont). Elastomer-modified versions of such aliphatic and aromatic polyamides can also be used, e.g., Amodel® ET 1000 HSNT (Amoco). Polyamides are polar polymers that are well-known in the art. See, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., Vol. 19, p. 454 (1996).
The polyamide is present as the matrix of the melt-mixed blend of the present invention. That is, the polyamide component forms the continuous phase of the melt-mixed blend.
With respect to the fluoropolymer constituting the fluoropolymer component of the melt-mixed blend of the present invention, a wide variety of fluoropolymers can be used which are melt extrudable, such as indicated by a melt viscosity in the range of 0.5×10
3
to 60×10
3
Pa·s as normally measured for the particular fluoropolymer. The fluoropolymer is made from at least one fluorine-containing monomer, but may incorporate monomer which contains no fluorine or other halogen. Preferably at least one monomer contains hydrogen and in that regard the hydrogen/fluorine atomic ratio is preferably at least 0.1:1. The fluoropolymer, however, preferably contains at least 35 wt % fluorine. Fluorinated monomers include those which are fluoroolefins containing 2 to 8 carbon atoms and fluorinated vinyl ether (FVE) of the formula CY
2
═CYOR or CY
2
═CYOR′OR wherein Y is H or F and -R- and -R′- are independently completely fluorinated or partially fluorinated linear or branched alkyl and alkylene groups containing 1 to 8 carbon atoms. Preferred R groups contain 1 to 4 carbon atoms and are preferably perfluorinated. Preferred R′ groups contain 2 to 4 carbon atoms and are preferably perfluorinated. Hydrocarbon monomers that can be used include ethylene, propylene, n-butylene, and iso-butylene. Preferred fluoropolymers are the copolymers of ethylene with perhalogenated monomers such as tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), such copolymers being often referred to as ETFE and ECTFE, respectively. In the case of ETFE, minor amounts of additional monomer are commonly used to improve properties such as reduced high temperature brittleness. Perfluoro(propyl vinyl ether) (PPVE), perfluoro(ethyl vinyl ether) (PEVE), perfluorobutyl ethylene (PFBE), and hexafluoroisobutylene (HFIB) are preferred additional comonomers. ECTFE may also have additional modifying comonomer. Other fluoropolymers that can be used include vinylidene fluoride (VF
2
) polymers including homopolymers and copolymers with other perfluoroolefins, particularly hexafluoropropylene (HFP) and optionally TFE. TFE/HFP copolymer which contains a small amount of VF
2
, which copolymer is often referred to as THV, can also be used. Examples of perfluorinated copolymers include TFE with HFP and/or PPVE or perfluoro(ethyl vinyl ether). Such fluoropolymers are usually partially-crystalline as indicated by a non-zero heat of fusion associated with a melting endotherm as measured by DSC on first melting, and are considered to be fluoroplastics rather than fluoroelastomers.
The fluoropolymer is functionalized by having an ethylenically unsaturated compound grafted thereto which imparts polar functionality to the fluoropolymer, the polar functionality being present as part of the ethylenically unsaturated compound. More particularly, the polar-grafted fluoropolymer used
E. I. Du Pont de Nemours and Company
Woodward Ana
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