WO2002029298A2

WO2002029298A2 - Convoluted tubing having a non-convoluted inner layer for handling hydrocarbon materials

Info

Publication number: WO2002029298A2
Application number: PCT/US2001/042440
Authority: WO
Inventors: James E. Ostrander
Original assignee: Itt Manufacturing Entreprises, Inc.
Priority date: 2000-10-02
Filing date: 2001-10-02
Publication date: 2002-04-11
Also published as: WO2002029298A3; AU2001296966A1

Abstract

An elongated multi-layer tubing (10) for connection to a motor vehicle system to handle fluids containing hydrocarbons comprises a substantially smooth, non-convoluted inner layer (14, 14') disposed radially innermost and having an inner surface capable of prolonged exposure to a fluid containing hydrocarbons; and an outer layer (12, 12'), sufficiently convoluted to provide a desired degree of flexibility, the outer layer being substantially non-reactive with an external environment to which it is exposed, and able to substantially withstand shocks, vibrational fatigue, changes in temperature, and exposure to corrosive or degradative compounds. The tubing may also comprise an intermediate bonding and/or barrier layer (16, 16') disposed between the inner layer and the outer layer.

Description

CONVOLUTED TUBING HAVING A NON-CONVOLUTED INNER LAYER FOR HANDLING HYDROCARBON MATERIALS

BACKGROUND OF THE INVENTION

[0001 ] The present invention relates to tubing for use in a motor vehicle.

More particularly, the present invention relates to a multi-layer tube which can be employed for transporting hydrocarbon fluids. For example, the multi-layer tube may be used as a fuel line and/or vapor recovery line of a motor vehicle.

[0002] Single layer fuel lines and vapor return lines of synthetic materials such as polyamides have been proposed and employed in the past. Fuel lines employing such materials generally have lengths of at least several meters. It is important that the line, once installed, not materially change during the length of operation, either by shrinkage or elongation or as a result of the stresses to which the line may be subject during use.

[0003] It is also becoming increasingly important that the lines employed be essentially impervious to hydrocarbon emissions due to permeation through the tubing. Governmental regulations fix the limit for permissible hydrocarbon emissions due to permeation through such lines. It is also imperative that the fuel line employed be impervious to interaction with corrosive materials present in the fuel such as oxidative agents and surfactants, as well as additives such as ethanol and methanol.

[0004] Various types of tubing have been proposed to address these concerns.

In general, the most successful of these have been co-extruded multi-layer tubing which employ a relatively thick outer layer composed of a material resistant to the exterior environment. The innermost layer is thinner and is composed of a material which is chosen for its ability to block diffusion of materials, such as aliphatic hydrocarbons, alcohols and other materials present in fuel blends, to the outer layer. The materials of choice for the inner layer of this tubing are polyamides such as nylon 6, nylon 6.6, nylon 11 and nylon 12.

[0005] In most automotive applications, the tubing employed must be capable of bending to a variety of angles throughout its length to conform to the layout and the space requirements in the specific vehicle design. However, various polymeric materials possess significant elastic memory which makes it difficult to successfully bend pieces of tubing into the permanent shape or contours necessary in the particular automotive application. Other polymeric materials are too rigid so that bends introduced into the material will cause crimping. This may undesirably restrict flow therethrough and may cause significant reductions in its useful life due to fatigue and stress at or near the bend region. Furthermore, bending previously known tubing may cause the differing layers to delaminate or fail due in part to the fact that the various layers each may have very different elasticity and fatigue characteristics.

[0006] In order to obviate this problem, it has been proposed that conventional mono- or multi-layer tubing be corrugated/convoluted throughout the length of the tubing. However, such convoluted tubing has heretofore only been suitable for use in vapor recovery applications. It has been found that the flow of liquid fuel through a convoluted tubing causes turbulence in the liquid fuel. This turbulence leads to the build up of static electricity, which is undesirable in fuel applications for a variety of reasons. Another drawback to the use of convoluted tubing is that it is not readily suitable for the insertion of quick connects or other fittings therein, as the inner convoluted wall would not provide a smooth wall for the fitting to seal against.

[0007] Thus, it is an object of the present invention to provide tubing which could advantageously be employed in motor vehicles, wherein the tubing is composed of at least an outer convoluted tubing layer and an inner, substantially smooth, non-convoluted tubing layer. It is a further object of the present invention to provide such tubing which advantageously substantially reduces turbulent flow therethrough and the concomitant generation of static electricity therefrom. Still further, it is an object of the present invention to provide such tubing which advantageously allows the facile insertion and sealing engagement of fittings therein.

SUMMARY OF THE INVENTION

[0008] The present invention addresses and solves the above-mentioned problems and meets the enumerated objects and advantages, as well as others not enumerated, by providing an elongated multi-layer tubing for connection to a motor vehicle system to handle fluids containing hydrocarbons. The multi-layer tube of the present invention is suitable for connection to a motor vehicle system to transport fluids containing hydrocarbons such as in a fuel line, a vapor return line or vapor recovery line. The elongated multi-layer tubing of the present invention comprises a substantially smooth, non-convoluted inner layer disposed radially innermost and having an inner surface capable of prolonged exposure to a fluid containing hydrocarbons. The inner layer may comprise one or more sub-layers; if so, the innermost sub-layer is substantially smooth and non-convoluted, while the other sublayers) may be either convoluted or non-convoluted. The tubing further comprises an outer layer, sufficiently convoluted to provide a desired degree of flexibility, the outer layer being substantially non-reactive with an external environment to which it is exposed, and able to substantially withstand shocks, vibrational fatigue, changes in temperature, and exposure to corrosive or degradative compounds. The tubing optionally comprises an intermediate bonding and/or barrier layer sufficiently adhered to both the inner layer and outer layer. The intermediate layer may be either convoluted or non-convoluted. Such tubing substantially reduces turbulent flow therethrough and the concomitant generation of static electricity therefrom, while providing the advantage of allowing the facile insertion and sealing engagement of fittings therein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other objects, features and advantages of the present invention will become apparent by reference to the following detailed description and drawings, in which:

[0010] Fig. 1 is a cross sectional view through a piece of tubing having four layers according to the present invention;

[0011] Fig. 2 is a cross sectional view taken on line 2-2 in Fig. 1;

[0012] Fig. 3 is a cross sectional view similar to Fig. 2, but showing a second embodiment of the invention;

[0013] Fig. 4 is a cross sectional view through a piece of tubing having four layers according to a third embodiment of the present invention;

[0014] Fig. 5 is a cross sectional view taken on line 5-5 in Fig. 4;

[0015] Fig. 6 is a cross sectional view similar to Fig. 5, but showing a fourth embodiment of the invention; [0016] Fig. 7 is an enlarged, cutaway, cross sectional view of an extruder head with the inventive smooth layer tip incorporated thereinto; and

[0017] Fig. 8 is a schematic diagram showing the process of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring now to Fig. 3, the present invention is a multi-layer fuel line/tube and/or vapor tube 10 which contains an inner, substantially smooth, non- convoluted layer 14, and an outer, convoluted layer 12. Outer layer 12 may be sufficiently convoluted to provide a desired degree of flexibility, and may or may not be convoluted throughout the length of tubing 10. If radially inner layers are also convoluted, such as for example, layers 16' and 20, such layers should preferably be convoluted complementarily to outer layer 12, as shown in Figs. 5 and 6. The tubing 10 of the present invention is, preferably, fabricated by co-extruding given thermoplastic materials in a conventional co-extrusion process. The tubing 10 may either be co-extruded to a suitable length or may be co-extruded in continuous length and cut to fit the given application subsequently. The tubing 10 of the present invention may have an outer diameter up to about 50 mm. However, in applications such as fuel lines and vapor recovery systems, outer diameters of up to about 63.5 mm (2.5 inches) may be preferred.

[0019] The tubing 10 may have any suitable wall thickness, as desired.

However, in automotive systems such as those described herein, wall thicknesses between about 0.5 mm and about 2.0 mm are generally employed, with wall thicknesses of approximately 0.8 mm to approximately 1.5 mm being preferred; and wall thicknesses between about 0.8 mm and about 1.25 mm being more preferred. While it is within the scope of this invention to prepare a tubing material having a plurality of overlying layers of various thermoplastic materials, the tubing 10 of the present invention generally has a maximum of five layers inclusive of bonding layers (if any). In the preferred embodiment, the tubing 10 has two to four layers. In a two layer tube, with the outer layer being convoluted and the inner layer being smooth, any suitable polymeric material could be used for each of the layers, as long as the two materials used were chemically similar for sufficient laminar adhesion. [0020] The tubing 10 of the present invention is suitable for use in motor vehicles, and may comprise an outer layer 12 which is non-reactive with the external environment and can withstand various shocks, vibrational fatigue, and changes in temperature, as well as exposure to various corrosive or degradative compounds to which it would be exposed through the normal course of operation of the motor vehicle. Suitable materials for use in the present invention may be composed of any melt-processible, extrudable thermoplastic material which is resistant to ultra violet degradation, extreme changes in heat, and exposure to gasoline and its additives. The material of choice may also exhibit resistance to environmental hazards such as exposure to zinc chloride, and resistance to degradation upon contact with materials such as engine oil and brake fluid.

[0021] It is anticipated that both the outer layer 12, and/or any interior layers, would be suitable for use at an outer service temperature range between about -40 °C and about 150°C, with a range of -20°C to 120°C being preferred. The various layers 12, 14, 16, 20 and 22 of the tubing 10 are sufficiently laminated to one another, and generally resistant to delamination throughout the lifetime of the tubing.

[0022] The tubing 10 thus formed will have a tensile strength of generally no less than about 25 N/mm² and an elongation value at break of generally at least about 150%. The tubing 10 will have a burst strength at -40 °C and 180°C of at least about 20 bar. The multi-layer tubing 10 of the present invention is sufficiently resistant to exposure to brake fluid, engine oil and peroxides such as those which may be found in gasoline. The multi-layer tube 10 has the capability of withstanding impacts of at least about 2 foot-pounds at temperatures below about -20 °C.

[0023] The thermoplastic material which may be employed in the inner layer

14 of the present invention is a melt-processible extrudable thermoplastic material resistant to extreme changes in heat and exposure to chemical components such as are found in engine oil and brake fluid. The thermoplastic material of choice may preferably be selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, zinc chloride resistant 6 carbon block polyamides, thermoplastic elastomers, and mixtures thereof. The zinc chloride resistant 6 carbon block polyamides preferably exhibit a level of zinc chloride resistance greater than or equal to that required by Performance Requirement 9.6 as outlined in SAE Standard J844, i.e. non-reactivity after 200 hours' immersion in a 50% by weight zinc chloride solution. A suitable 6-carbon block polyamide material is preferably a multi- component system comprised of a nylon-6 copolymer blended with other nylons and olefinic compounds. The zinc chloride resistant nylon-6 of choice will have a melt temperature between about 220 °C and 240 °C. Examples of nylon (PA) materials suitable for use in the tubing 10 of the present invention are materials which can be obtained commercially under the tradenames M-7551 fromNYCOA Corporation and ALLIED 1779 from Allied Chemical.

[0024] The thermoplastic elastomers which can successfully be employed in the tubing 10 of the present invention are commercially available under tradenames such as: SANTOPRENE®, a thermoplastic rubber commercially available from Advanced Elastomer Systems of St. Louis, MO; KRATON®, a thermoplastic rubber composed of a styrene-ethylene/butylene-styrene block copolymer commercially available from Shell Chemical Co. of Houston, TX; SARLINK, an oil resistant thermoplastic commercially available from Novacor Chemicals of Leominster, MA; NICHEM, a family of polyvinyl chloride compounds commercially available from Vichem Corporation of Allendale, Michigan; and UΝIPREΝE, which is a thermoplastic elastomer commercially available from Teknor Apex of Pawtucket, RI.

[0025] The thermoplastic material employed in the inner layer 14 of the tubing

10 may be a thermoplastic selected from those listed above to take advantage of specific properties of the various thermoplastics. In a preferred embodiment, the inner layer 14 is composed of a polyamide such as nylon 12.

[0026] The thermoplastic material employed in the inner layer 14 may be either modified or unmodified. If modified, it is anticipated that the material will contain various plasticizers as are readily known in the art. In the preferred embodiment, the polyamide will contain up to about 17% by composition weight plasticizer; with amounts between about 1% and about 13% being preferred.

[0027] The inner layer 14 may have a thickness sufficient to supply strength and chemical resistance properties to the multi-layer tubing 10. Specifically, the inner layer 14 is of sufficient thickness to impede permeation of aliphatic and aromatic hydrocarbon molecules and migration of those molecules through to the thick outer layer. In the present invention, the inner layer has a wall thickness less than that of the thick outer layer. In the preferred embodiment, the inner layer has a wall thickness between about 10% and 25% that of the outer layer; preferably less than between about 0.05 mm and about 0.4 mm; with a wall thickness between about 0.1 mm and about 0.3 mm being preferred.

[0028] In order to accomplish effective lamination of the two thermoplastic materials which compose the inner 14 and outer 12 layers, the tubing 10 of the present invention may also include at least one intermediate layer 16 interposed between the inner 14 and outer 12 layers which is capable of achieving a suitable homogeneous bond between itself and the two respective layers 14, 12.

[0029] In a preferred embodiment as shown in Figs. 1-3, the intermediate bonding layer 16 is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, polyvinyl acetate-urethane blends, and mixtures thereof. One preferred fluoroplastic material is a polyvinylidine derived from the thermal dehalogenation of chlorodifluoroethane. One preferred non- fluorocarbon material is a polyvinyl acetate/urethane blend. The material of choice exhibits an affinity to polymers employed in the inner layer 14 and/or outer layer 12 such as nylon 12 or nylon 6. Suitable fluoroplastic materials are commercially available under the tradename "ADEFLON A"; while suitable non-fluoroplastic materials are commercially available under the tradename "ADEFLON D" both from Atochem lnc. elf Aquitaine Group of Philadelphia, Pennsylvania.

[0030] In an alternate embodiment as shown in Figs. 4-6, the inner layer 14' may be a permeation resistant, chemical resistant, fuel resistant thermoplastic material which is melt processible in normal ranges of extrusion, i.e. between about 175°C to about 250 °C. As such, the inner layer 14' may alternately consist of a non- polyamide material which is capable of adhesion to a bonding layer 16' interposed between the thick outer layer 12 and the inner layer 14' in a manner which will be described subsequently. Thus, the thermoplastic material which comprises the alternate inner layer 14' may be formed from polybutylene terephthalate (PBT), polyethylene terephthalate (PETP), a fluoroplastic material selected from the group consisting of polyvinylidine fluoride (PVDF), polyvinyl fluoride (PNF), polytetrafluoroethyleneperfluoropropylene (PFEP), polychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers (ETFE), polytetrafluoro-ethylene (PTFE), a graft copolymer of the preceding materials together with a fluorine-containing polymer such as copolymers of vinylidine fluoride and chlorotrifluoroethane, and mixtures thereof.

[0031] The inner layer 14' in the alternate embodiment has a minimum wall thickness sufficient to achieve the permeation resistance desired. In general, the inner layer 14' is thinner than the outer layer 12, with the thickness of the outer layer 12 being between about 50% and about 60% of the total wall thickness of the multilayer tubing 10. Preferably, the inner wall thickness is between about 0.01 mm and about 0.2 mm with a thickness of about 0.05 mm and about 0.2 mm being preferred, and a thickness between about 0.05 mm and about 0.17 mm being more preferred. Most preferred would be a thickness ranging between about 0.1 mm and about 0.2 mm. The intermediate bonding layer 16 generally may have a thickness less than or equal to that of the inner layer 14.

[0032] The thermoplastic material employed in the inner layer 14' of the alternate embodiment is capable of serving as a hydrocarbon barrier to prevent significant permeation of the aromatic and aliphatic components of gasoline through to an alternate outer layer 12 composed of polyamide and thus, out to the surrounding environment.

[0033] Some suitable fluoroplastic materials useful for the invention herein include polyvinylidine fluoroplastic derived from the thermal dehalogenation of chlorodifluoroethane, commercially available under the tradenames "FLORAFLOΝ" and "KYΝAR" from Atochem Inc. elf Aquitaine Group of Philadelphia, Pennsylvania. A suitable ethylene tetrafluoroethylene copolymer employed herein is derived from the copolymerization of ethylene with tetrafluoroethylene. The preferred polymeric material has an ethylene-derived content between about 40% and about 70% and a tetrafluoroethylene content between about 30% and about 60% by total polymer weight with minor amounts of proprietary materials being optionally present. Suitable materials are commercially available under the tradenames "TEFZEL 210", "TEFZEL 200", and "TEFZEL 280" from E.I. duPont de Nemours, Co. of Wilmington, Delaware.

[0034] Electrostatic discharge can be defined as the release of electric charge built up or derived from the passage of charged particles through a medium or conduit composed of essentially non-conductive materials. The electrostatic charge is repeatedly replenished with the passage of additional volumes of fuel through the conduit. Discharge repeatedly occurs in the same localized area, gradually eroding the area and leading to eventual rupture of the tubing. Such a rupture of the tubing can lead to the danger of fire and explosion of the flammable contents of the tubing.

[0035] The inner layer 14, 14' of the present invention may, as illustrated in

Figs. 1, 2, 4 and 5 include an innermost electrostatic dissipation sub-layer 22 which is also capable of serving as a hydrocarbon barrier to assist in the prevention of permeation of aromatic and aliphatic compounds found in gasoline through to the outer layer 12 of the tubing 10 and, thus, out to the surrounding environment.

[0036] The electrostatic dissipation sub-layer 22 of the inner layer 14, 14' may be integrally bonded to the inner surface of an optional sub-layer 20 disposed between sub-layer 22 and the intermediate bonding layer 16. Preferably, the sublayers 20 and 22 are chemically similar materials in structure and composition. As used here, the term "chemically similar material" is defined as a thermoplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, a graft copolymer of the preceding materials together with a fluorine- containing polymer such as copolymers of vinylidine fluoride and chlorotrifluoroethane, a copolymer of a vinyl fluoride and chlorotrifluoroethylene, the vinyl fluoride material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, and mixtures thereof; ethylene tetrafluoroethylene copolymers (ETFE); a copolymer of vinyl fluoride material and ethylene tetrafluoroethylene; a non-fluorinated elastomer, and mixtures thereof.

[0037] The term "chemically similar material" is also defined herein as a thermoplastic material selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, zinc chloride resistant 6 carbon block polyamides, thermoplastic elastomers, and mixtures thereof. These materials are defined further herewithin.

[0038] Preferably, the sub-layers 20 and 22 are composed of the same material, with the exception of the electrostatic dissipation sub-layer 22 including additional conductive material as described hereinafter. The sub-layers 20 and 22, intermediate bonding layer 16, 16', and outer layer 12 define a four layer tubing 10 as shown in Figs. 1, 2, 4 and 5.

[0039] The thermoplastic material which comprises the electrostatic dissipation sub-layer 22' of the inner layer 14' is selected from the group consisting of: a copolymer of a vinyl fluoride and chlorotrifluoro-ethylene, the vinyl fluoride material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, and mixtures thereof; a copolymer of vinyl fluoride material and ethylene tetrafluoroethylene; a non-fluorinated elastomer, ethylene tetrafluoroethylene copolymers (ETFE), and mixtures thereof.

[0040] The sub-layer 22' thermoplastic material employed in the present invention may preferably contain between about 10% and about 18% by weight of a vinylidine fluoride-chlorotrifluoroethylene copolymer, which itself has a vinylidine fluoride content between about 40% and 60% by copolymer weight. The material also preferably contains between about 50% and about 70% by weight of a vinylidine fluoride-tetraf-uoroethylene copolymer. The non-fluorinated elastomer is selected from the group consisting of polyurethanes and mixtures thereof. The sub-layer 22' thermoplastic material may contain between about 10% and about 25% by weight polyurethane.

[0041 ] The thermoplastic material which comprises the electrostatic dissipation sub-layer 22 of the inner layer 14 is selected from the group consisting of: 12 carbon block polyamides, 11 carbon block polyamides, zinc chloride resistant 6 carbon block polyamides, thermoplastic elastomers, and mixtures thereof.

[0042] The sub-layer 22, 22' thermoplastic material also preferably contains conductive media in quantities sufficient to permit electrostatic dissipation in a desired range. The electrostatic dissipation sub-layer 22, 22' of the inner layer 14, 14' exhibits electrostatic dissipative characteristics capable of dissipating electrostatic charges in the range of between about 10⁴ and 10⁹ Ohm/cm². Suitable material is commercially available under the tradename XPN-504KRC CEFRAL SOFT CONDUCTIVE. Sub-layer 22, 22' may also be selected from the group consisting of conductive nylon 6 (polyamide 6), conductive nylon 12 (polyamide 12), and mixtures thereof.

[0043] The electrostatic dissipation sub-layer 22, 22' of the inner layer 14, 14' is maintained at thicknesses suitable for achieving static dissipation and suitable laminar adhesion respectively; generally between about 10% and 20% of the outer layer 12. The thickness of the electrostatic dissipation sub-layer 22 of the inner layer 14 is preferably between about 0.1 mm and about 0.2 mm. The intermediate bonding layer 16, 16' preferably has a thickness approximately equal to the thickness of the electrostatic dissipation sub-layer 22, 22' preferably between about 0.05 mm and about 0.15 mm.

[0044] In any of the embodiments disclosed, at least one layer, preferably the inner layer 14, 14' and/or the intermediate bonding layer 16, 16' may exhibit conductive characteristics, rendering it capable of dissipation of electrostatic charge in the range of about 10⁴ to 10⁹ Ohm/cm². If a fluoroplastic material is employed in the conductive layer of the present invention, it may be inherently conductive in these ranges or, preferably, includes in its composition a conductive media in sufficient quantity to permit electrostatic dissipation in the range defined and/or in any suitable range as desired and/or necessary.

[0045] The conductive media may be any suitable material of a composition and shape capable of effecting this static dissipation. The conductive material may be selected from the group consisting of elemental carbon, stainless steel, highly conductive metals such as copper, silver, gold, nickel, silicon, and mixtures thereof. The term "elemental carbon" as used herein is employed to describe and include materials commonly referred to as "carbon black". The carbon black can be present in the form of carbon fibers, powders, spheres, and the like.

[0046] The amount of conductive material contained in the desired layer of tubing 10 is generally limited by considerations of low temperature durability and resistance to the degradative effects of the gasoline or fuel passing through the tubing 10. In the preferred embodiment, the fluoroplastic material contains conductive material in an amount sufficient to effect electrostatic dissipation. However, the maximum amount employed therein is preferably less than about 5% by volume with a concentration between about 2% and about 4% being preferred.

[0047] The conductive material can either be blended into the melt-processible desired layer of tubing 10 so as to be interstitially integrated into the crystalline structure of the polymer; or can be incorporated during polymerization of the monomers that make up the polymeric material. Without being bound to any theory, it is believed that carbon-containing materials such as carbon black may be incorporated during co-polymerization of the surrounding polymeric material. Materials such as stainless steel are more likely to be blended into the crystalline structure of the polymer.

[0048] In each of the embodiments, the intermediate bonding layer 16, 16' is composed of a thermoplastic material which also exhibits properties of resistance to permeation of aliphatic and aromatic materials such as those found in fuel. As such, layer 16, 16' serves as a barrier layer. The thermoplastic material employed herein is preferably a melt-processible co-extrudable thermoplastic which may or may not contain various plasticizers and other modifying agents.

[0049] The intermediate bonding layer 16, 16', in addition to permitting a homogeneous bond between the inner layer 14, 14' and outer layer 12, and exhibiting resistance to permeation of fuel components, also may exhibit conductive or static dissipative characteristics such as those described previously. Thus, the intermediate bonding layer 16, 16' may optionally include sufficient amounts of conductive media to effect electrostatic dissipation in the range of about 10⁴ to 10⁹ Ohm/cm². As with the inner layer 14', the intermediate bonding layer 16, 16' may be inherently electrostatically dissipative or may be rendered so by the inclusion of certain conductive material such as those selected from the group consisting of elemental carbon, stainless steel, copper, silver, gold, nickel, silicon and mixtures thereof.

[0050] It is preferred that the inner layer 14, 14' and the bonding layer 16, 16' be maintained at the minimum thickness necessary to prevent permeation of the fuel through the tubing material. It is preferred that the amount of hydrocarbon permeation through the tubing 10 be no greater than about 0.5 g/m² in a 24 hour interval. The thickness of the inner layer 14, 14' can be varied to accomplish this end.

[0051] The intermediate bonding layer 16' may also be composed of a thermoplastic material which may exhibit properties of resistance to the permeation of aliphatic and aromatic materials such as those found in fuel in addition to exhibiting suitable bonding characteristics. Such a suitable layer 16' material employed herein is preferably a melt-processible co-extrudable fluoroplastic blend which will exhibit an affinity to conventional polymers such as nylon 12, and may optionally contain various plasticizers and other modifying agents. The fluoroplastic blend which comprises the intermediate bonding layer 16' in the alternate embodiment shown in Figs. 4-6 comprises: a polyvinyl fluoride compound selected from the group consisting of: polyvinylidine fluoride polymers, polyvinyl fluoride polymers, a vinylidine fluoride-chlorotrifluoroethylene copolymer, ethylene tetrafluoroethylene copolymers (ETFE), and mixtures thereof; and a polyamide material selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, 6 carbon block polyamides, and mixtures thereof.

[0052] A fluoroplastic blend of choice comprises a blend of nylon 12 and

ETFE. One such suitable blend is commercially available from Daikin Industries, Ltd., located in Osaka, Japan under the tradename NEOFLON EA-LR Series Pellet. A preferred grade of the NEOFLON is EA-LR 43. Some representative chemical and physical properties are as follows. The EA-LR 43 material appears as a white pellet and has a melting point (1st peak) between about 168 °C and about 180°C. The specific gravity (H₂O = 1) at 23°C is between about 1.5 and about 1.7. It is insoluble in water.

[0053] The vinylidine fluoride-chlorotrifluoroethylene copolymer preferably, contains between about 60% and about 80% by weight polyvinylidine difluoride. The intermediate bonding layer 16' may consist essentially of between about 35% and about 45% by weight of a copolymer of vinylidine fluoride and chlorotrifluoroethylene; between 25% and about 35% by weight polyvinylidine fluoride; and between about 25% and about 35% by weight of a polyamide selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, and mixtures thereof. One such polymeric material suitable for use in the multi-layer tubing 10 of the present invention is commercially available from Central Glass of Ube City, Japan under the trade designation CEFRAL SOFT XUA- 2U. This material is a graft copolymer of a fluorine-containing elastomeric polymer with a fluorine-containing crystalline polymer. The elastomeric polymer is, preferably, a material copolymerized from an alkyl difluoride selected from the group consisting of vinyl difluoride, vinylidine difluoride, and mixtures thereof, and a chlorofluoroalkene selected from the group consisting of ethylene chlorotrifluoroethylene. The crystalline polymer is preferably a haloalkene such as ethylene chlorotrifluoroethylene.

[0054] The thermoplastic material which comprises the intermediate bonding layer 16 and/or 16' may alternately be a thermoplastic material selected from the group consisting of co-polymers of substituted or unsubstituted alkenes having less than four carbon atoms and vinyl alcohol, alkenes having less than four carbon atoms and vinyl acetate, and mixtures thereof. This thermoplastic material will be resistant to permeation by and interaction with short chain aromatic and aliphatic compounds such as those which would be found in gasoline. The preferred material is a copolymer of ethylene and vinyl alcohol which has an ethylene content between about 27% and about 35% by weight with an ethylene content between about 27% and about 32% being preferred. Examples of suitable materials which can be employed in the tubing of the present invention include: ethylene vinyl alcohol commercially available from EVA/LA.

[0055] In a preferred embodiment as shown in Figs. 1 and 2, sub-layer 22 comprises conductive nylon 12 (PA 12); sub-layer 20 comprises nylon 12 (PA 12); intermediate layer 16 comprises polyvinylidene fluoride (PVDF); and outer layer 12 comprises nylon 12 (PA 12).

[0056] In a second preferred embodiment as shown in Fig. 3, inner layer 14 comprises nylon 12 (PA 12); intermediate layer 16 comprises polyvinylidene fluoride (PVDF); and outer layer 12 comprises nylon 12 (PA 12). [0057] In a third preferred embodiment as shown in Figs. 4 and 5, sub-layer

22' comprises conductive ETFE; sub-layer 20 comprises ETFE; intermediate layer 16' comprises a blend of ETFE and nylon 12 (PA 12); and outer layer 12 comprises nylon 12 (PA 12).

[0058] In a fourth preferred embodiment as shown in Fig. 6, inner layer 14' comprises ETFE; intermediate layer 16' comprises a blend of ETFE and nylon 12 (PA 12); and outer layer 12 comprises nylon 12 (PA 12).

[0059] It is to be understood that the corrugated wall may be formed from various materials, and may be mono- or multi-layer. Similarly, the smooth inner wall may be formed from various materials, and may be mono- or multi-layer. For example, in Fig. 2, the smooth inner wall is a multi-layer configuration formed from layers 22, 20 and 16; and the corrugated layer is formed from layer 12. In Fig. 3, the smooth inner wall is a multi-layer configuration formed from layers 14 and 16; and the corrugated layer is formed from layer 12. In Fig. 5, the smooth inner wall is formed from layer 22'; and the corrugated layer is a multi-layer configuration formed from layers 20, 16' and 12. In Fig. 6, the smooth inner wall is formed from layer 14'; and the corrugated layer is a multi-layer configuration formed from layers 16' and 12.

[0060] It is to be understood that these four embodiments are illustrative of the layer combinations and which may exist, and thus are not to be considered exhaustive examples. It is also to be understood that any of the exemplary materials and/or equivalents thereof enumerated herein for the various layers of the specific embodiments may be used interchangeably to comprise many varied embodiments of tubing 10; eg. tubing 10 of the present invention may comprise inner layer 14, intermediate bonding layer 16', and outer layer 12. Similarly, tubing 10 of the present invention may comprise inner layer 14', intermediate bonding layer 16, and outer layer 12; and so on.

[0061] The following is a brief description of the various exemplary, commercially available compounds suitable for use in the present invention. It is to be understood that these are examples of suitable compounds for illustrative purposes. Thus, it is to be further understood that other suitable compounds are contemplated and are within the scope of the present invention. [0062] SANTOPRENE®, commercially available from Advanced Elastomer

Systems, L.P. of St. Louis, Missouri is a thermoplastic rubber FR grade. Aside from the thermoplastic rubber, it also contains antimony trioxide flame retardant, and may contain carbon black, CAS No. 1333-86-4. SANTOPRENE® thermoplastic rubber may react with strong oxidizing chemicals, and also reacts with acetal resins at temperatures of 425 °F and above, producing decomposition of the acetal resins, and formaldehyde as a decomposition product. Decomposition of halogenated polymers and phenolic resins may also be accelerated when they are in contact with SANTOPRENE® thermoplastic rubber at processing temperatures. Physical characteristics of SANTOPRENE® include a slightly rubber-like odor, and the appearance of black or natural (colorable) pellets. It is thermally stable to 500°F. The flash ignition temperature is greater than 650°F by method ASTM-D 1929-77, and by the same method, self-ignition temperature is above 700 °F. The typical specific gravity is 0.90 to 1.28. The material has various hardnesses which are suitable in the present invention, however, in the preferred embodiment, the SANTOPRENE® thermoplastic rubber having an 80 Shore A hardness is utilized. The SANTOPRENE® thermoplastic rubber is designed to offer fluid and oil resistance equivalent to that of conventional thermoset rubbers such as neoprene. The resistance of the SANTOPRENE® rubber grades to oils can be classified by using the SAE J200/ASTM D2000 standard classification system for rubber.

[0063] UNIPRENE, commercially available from Teknor Apex of Pawtucket,

Rhode Island, is a thermoplastic vulcanizate which performs like cured EPDM rubber, but processes with the ease and speed of thermoplastic olefins. UNIPRENE thermoplastic vulcanizates have mechanical and recovery properties comparable to most vulcanized elastomers, and may be superior to many TPEs.

[0064] ADEFLON A is a polyvinylidene fluoride commercially available from

Atochem Inc. elf Aquitaine Group of Philadelphia, Pennsylvania. Its typical use is as a binding material for polyamides/polyvinylidene fluoride. The product is stable under normal use conditions, and above 230°C, there is a release of monomer traces. Physical properties include: at 20 °C the material is a granulated solid having a white/slightly yellow color and no odor. The crystal melting point is 175 °C, and beginning of decomposition is 230 ° C. In water at 20 ° C, the product is non-soluble. The density at 20 °C bulk is 1 to 1.1 g/cm³.

[0065] The Vichem Corporation vinyl compounds are polyvinyl chloride compounds composed of a vinyl resin and functioning additives. The ingredients include a stabilizer, a resin CAS No. 75-01-4, a plasticizer CAS No. 68515-49-1, an epoxy soya oil CAS No. 8013-07-8, a filler CAS No. 1317-65-3 and carbon black CAS No. 1333-85-4. The specific gravity is 1.35 and the compound has the appearance of pellets and has a characteristically bland odor.

[0066] KRATON®, commercially available from Shell Chemical Co. of

Houston, TX, is a thermoplastic rubber having a specific gravity of 0.90 to 1.90 and a hardness of 15A to 60D. The tensile strength is up to 2,500 psi. The elongation is up to 750% and the tear strength is up to 750 pli (130 kN/m). The flex modulus is 750 to 100,000 psi. The service temperature is -70°C to 150°C. The ozone resistance is excellent, UN resistance is excellent, fluid resistance is fair to excellent, and flame resistance is fair to excellent.

[0067] SARLIΝK is a thermoplastic elastomer commercially available from

Νovacor Chemicals Inc. of Leominster, Massachusetts. The specific gravity ranges from 1.13 to 1.22. The modulus at 100% ranges between 260 and 570 psi. The tensile strength ranges between 780 and 2,060 psi. The ultimate elongation ranges between about 345 and about 395%. The tear strength ranges between about 81 and about 196 pli. The tension set ranges between about 4 and 6%. It has excellent fluid resistance to acids and alkalis, aqueous solutions, organic solvents, petroleum oils and fuels, automotive fluids such as automatic transmission, power steering, etc. and industrial fluids. It has fair fluid resistance to automotive fluids such as hydraulic brake, lithium grease, antifreeze, etc. and poor resistance to organic solvents. The SARLIΝK product is a solid, black pellet material with a mildly pungent odor. It is insoluble in water at 20 °C.

[0068] KYΝAR, commercially available from Atochem Inc. elf Aquitaine

Group of Philadelphia, Pennsylvania, is a vinylidene fluoride-hexafluoropropylene copolymer. Its chemical name is 1-propene, 1, 1,2,3,3,3-hexafluoro-l, 1- difluoroethene polymer. Its melting point is 155 ° - 160 ° C. Its specific gravity is 1.77- 1.79 at 23 ° C. It appears translucent and has no odor.

[0069] A suitably conductive KYNAR material, known as KYNAR RC

10,098 is also commercially available from Atochem Inc. elf Aquitaine Group of Philadelphia, Pennsylvania. This compound is identified as a hexafluoropropylene- vinylidine fluoride copolymer, CAS No. 9011-17-0. The melting point is between about 155°C and about 160°C. It is not soluble in water. It appears as translucent pellets having no odor. It is stable under 300°C.

[0070] CEFRAL SOFT XUA-2U, commercially available from Central Glass

Company, Ltd., Chiyodaku, Tokyo, Japan is a copolymer containing 40% vinylidene fluoridechlorotri-fluoroethylene copolymer, 30% polyvinylidene fluoride and 30% nylon 12. The material has a specific gravity of 1.45 at 23 °C, a melting point of 173 °C and a mold temperature of 220°F. The material has an elongation at break of 478% and a tensile strength of 430 Kgf/cm².

[0071 ] XPV-504 KRC CEFRAL SOFT CONDUCTIVE is commercially available from Central Glass Company, Ltd., Chiyodaku, Tokyo, Japan and is a polymeric composition containing 14% vinylidene fluoride-chlorotrifluoro-ethylene copolymer; 63% vinylidene fluoride-tetrafluoroethylene copolymer; 20% polyurethane elastomer; and 3% carbon black. The material has a melt point of 165 ° C and a specific gravity of 1.80 at 23 ° C.

[0072] TEFZEL is commercially available from DuPont Polymers, Specialty

Polymer Division, Wilmington, Delaware. The material designates a family of ethylene tetrafluoroethylene fluoropolymers having various commercial grades. The material has a melting point between 255 °C and 280 °C as determined by ASTM method DTAD3418. The specific gravity for the material is between 1.70 and 1.72 as determined by ASTM method D792. Impact strength for the material at -65 °F is between 2.0 ft-lbs/inch and 3.5 ft-lbs/inch as determined by ASTM method D256, commonly referred to as Notched Izod Impact Strength. The hardness durometer as determined by ASTM method D2240 for all grades of TEFZEL is D70. Tensile strength at 73 °F is between 5,500 psi and 7,000 psi. TEFZEL was first introduced in 1970 having outstanding mechanical strength, high temperature and corrosion resistance. The material is available in three production grades, TEFZEL 200, TEFZEL 210 and TEFZEL 280 which can be applied in the present invention. Ultimate elongation at break is between 150% and 300%, depending on the grade as determined by ASTM method D638.

[0073] In any of the embodiments disclosed herein, the tubing 10 of the present invention may include an outer jacket layer (not shown) which surrounds the inner tubing substrate 10. The jacket may be either co-extruded with the other layers during the extrusion process or may be disposed on the tubing substrate 10 in a subsequent process such as crosshead extrusion. The outer jacket may be made of any material chosen for its structural (such as abrasion resistance) or insulating characteristics, and may be of any suitable wall thickness. In the preferred embodiment, the outer jacket may be made of a thermoplastic material selected from the group consisting of zinc-chloride resistant nylon 6, nylon 11, nylon 12, polyether block amides, polypropylene, and thermoplastic elastomers such as: SANTOPRENE®, a thermoplastic rubber composition commercially available from Advanced Elastomer Systems of St. Louis, MO; KRATON®, a thermoplastic rubber composition composed of a styrene-ethylene/butylene-styrene block copolymer commercially available from Shell Chemical Co. of Houston, TX; VICHEM, a family of polyvinyl chloride compounds commercially available from Vichem Corporation of Allendale, Michigan; SARLINK, an oil resistant thermoplastic composition commercially available fromNovacor Chemicals of Leominster, MA; and UNIPRENE, a thermoplastic elastomer commercially available from Teknor Apex of Pawtucket, RI. One preferred grade of SANTOPRENE® is #101-73. If desired, these materials may be modified to include flame retardants, plasticizers and the like.

[0074] Referring now to Fig. 7, an extrusion head, designated generally as 30, includes two cylindrical cones, plates, modules and/or distributors 32. Each of cones 32 may be formed from any suitable material, however in the preferred embodiment, these cones 32 are formed from tool steel. Convoluter table 52 includes two convoluter blocks 34, which may be formed from any suitable material, but in the preferred embodiment are formed from tool steel. The polymeric material 36 of choice for the convoluted layer (a single layer, as shown in Figs. 2 and 3) or layers (multiple layers, as shown in Figs. 5 and 6) enters the head 30 at the area designated as 38. The resultant convoluted layer(s) exits the head 30 at the area designated as 40.

[0075] In order to render the substantially smooth, non-convoluted inner layer

(a single layer, as shown in Figs. 5 and 6) or layers (multiple layers, as shown in Figs. 2 and 3) of the present invention, an inventive tip 42 according to the present invention is operatively connected to head 30. Tip 42 includes both the entryway 38 for the outer, convoluted layer(s) and an end region 44 adapted to impart the smooth layer(s) on the interior surface of the convoluted layer(s). The polymeric material 48 of choice for the smooth inner layer(s) enters the head 30 at the area designated as 46. The resultant smooth layer(s) connected to the interior surface of the convoluted layer(s) exits the head 30 at the area designated as 40.

[0076] Fig. 8 shows a schematic diagram of the process of the present invention. As can be seen, with the present inventive tip 42 with smooth layer- rendering end region 44, the present inventive process may be incorporated into a standard multiple layer extrusion line. The process of the present invention comprises the step of introducing polymeric material(s) of choice into single or multiple extruders 50. The materials of choice flow into single or multilayer head 30. The process further comprises the step of convoluting the outer layer(s) of the tubing wherein the convoluter table 52 containing the convoluter blocks 34 therein slides back toward and then over the inventive tip 42. The tubing 10 then moves to the payoff box 54 at and/or after which time the tubing may be cut to predetermined length(s) as desired.

[0077] It is to be understood that any of the polymeric materials cited hereinabove for a particular layer may advantageously be used for any of the layers disclosed herein; for example, the polymeric materials recited as useful for the inner layer may also be suitable for use as the outer layer, and/or for use as the intermediate layer.

[0078] As disclosed herein, the tubing 10 of the present invention may advantageously be employed in motor vehicles as a conduit for liquid fuel and/or vapor recovery, wherein tubing 10 comprises at least an outer convoluted tubing layer and an inner, substantially smooth, non-convoluted tubing layer. The tubing 10 may also be used in a marine application or in an aerospace application. Such tubing 10 substantially reduces turbulent flow therethrough and the concomitant generation of static electricity therefrom. Tubing 10 also provides the advantage of allowing the facile insertion and sealing engagement of fittings (such as conventional quick connect fittings, spinweld fittings, blow-molded fittings, and/or hot plate welded fittings) therein. While preferred embodiments, forms and arrangements of parts of the invention have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

Claims

What is claimed is: 1. An elongated multi-layer tubing for connection to a motor vehicle system to handle fluids containing hydrocarbons, the tubing comprising: a substantially smooth, non-convoluted inner layer disposed radially innermost and having an inner surface capable of prolonged exposure to a fluid containing hydrocarbons; and an outer layer, sufficiently convoluted to provide a desired degree of flexibility, the outer layer being substantially non-reactive with an external environment to which it is exposed, and able to substantially withstand shocks, vibrational fatigue, changes in temperature, and exposure to corrosive or degradative compounds.

2. The multi-layer tubing as defined in claim 1 wherein the substantially smooth, non-convoluted inner layer is adapted to sealingly engage a fitting.

3. The multi-layer tubing as defined in claim 1, further comprising an intermediate bonding layer between the inner layer and the outer layer.

4. The multi-layer tubing as defined in claim 3 wherein the inner layer is formed from a melt-processible, extrudable thermoplastic material.

5. The multi-layer tubing as defined in claim 4 wherein the inner layer melt-processible thermoplastic material is selected from the group consisting of nylon 11, nylon 12, zinc chloride resistant nylon 6, thermoplastic elastomers, and mixtures thereof.

6. The multi-layer tubing as defined in claim 4 wherein the inner layer melt-processible thermoplastic material is permeation resistant, chemical resistant, and fuel resistant.

7. The multi-layer tubing as defined in claim 6 wherein the inner layer melt-processible thermoplastic material is a non-polyamide material which is capable of adhesion to the intermediate bonding layer.

8. The multi-layer tubing as defined in claim 7 wherein the inner layer melt-processible thermoplastic material is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers (ETFE), a graft copolymer of the preceding materials together with a fluorine-containing polymer such as copolymers of vinylidine fluoride and chlorotrifluoroethane, and mixtures thereof.

9. The multi-layer tubing as defined in claim 1 wherein the outer layer is a melt-processible thermoplastic material selected from the group consisting of nylon 11, nylon 12, zinc chloride resistant nylon 6, thermoplastic elastomers, and mixtures thereof.

10. The multi-layer tubing as defined in claim 3 wherein the intermediate bonding layer is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, polyvinyl acetate-urethane blends, and mixtures thereof.

11. The multi-layer tubing as defined in claim 3 wherein the intermediate bonding layer is a fluoroplastic blend consisting essentially of: a polyvinyl fluoride compound selected from the group consisting of polyvinylidine fluoride polymers, polyvinyl fluoride polymers, a vinylidine fluoride- chlorotrifluoroethylene copolymer, ethylene tetrafluoroethylene copolymers (ETFE), and mixtures thereof; and a polyamide material selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, 6 carbon block polyamides, and mixtures thereof.

12. The multi-layer tubing as defined in claim 1 wherein at least one layer of the tubing is capable of dissipating electrostatic energy.

13. The multi-layer tubing as defined in claim 12 wherein the at least one layer contains quantities of a conductive material sufficient to provide electrostatic dissipation capability in a predetermined range.

14. The multi-layer tubing as defined in claim 13 wherein the conductive material is selected from the group consisting of elemental carbon, copper, silver, gold, nickel, silicon, and mixtures thereof.

15. The multi-layer tubing as defined in claim 3 wherein the inner layer is formed from nylon 12, the intermediate bonding layer is substantially smooth and non-convoluted and is formed from polyvinylidene fluoride, and the outer layer is formed from nylon 12.

16. The multi-layer tubing as defined in claim 3 wherein the inner layer is formed from ethylene tetrafluoroethylene (ETFE), the intermediate bonding layer is sufficiently convoluted to the same desired degree of flexibility as is the outer layer, and is formed from a blend of nylon 12 and ethylene tetrafluoroethylene (ETFE), and the outer layer is formed from nylon 12.

17. The multi-layer tubing as defined in claim 3 wherein the inner layer comprises a sub-layer and an electrostatic dissipation sub-layer integrally bonded to the inner surface of the sub-layer.

18. The multi-layer tubing as defined in claim 17 wherein the electrostatic dissipation sub-layer is formed from conductive nylon 12, the sub-layer is formed from nylon 12, the intermediate bonding layer is substantially smooth and non-convoluted and is formed from polyvinylidene fluoride, and the outer layer is formed from nylon 12.

19. The multi-layer tubing as defined in claim 17 wherein the electrostatic dissipation sub-layer is formed from conductive ethylene tetrafluoroethylene (ETFE); the sub-layer is sufficiently convoluted to the same desired degree of flexibility as is the outer layer, and is formed from ethylene tetrafluoroethylene (ETFE); the intermediate bonding layer is sufficiently convoluted to the same desired degree of flexibility as is the outer layer, and is formed from a blend of nylon 12 and ethylene tetrafluoroethylene (ETFE), and the outer layer is formed from nylon 12.

20. An elongated multi-layer tubing for connection to a motor vehicle system to handle fluids containing hydrocarbons, the tubing comprising: a substantially smooth, non-convoluted inner layer disposed radially innermost and having an inner surface capable of prolonged exposure to a fluid containing hydrocarbons; an outer layer, sufficiently convoluted to provide a desired degree of flexibility, the outer layer being substantially non-reactive with an external environment to which it is exposed, and able to substantially withstand shocks, vibrational fatigue, changes in temperature, and exposure to corrosive or degradative compounds; and an intermediate bonding layer between the inner layer and the outer layer; wherein the substantially smooth, non-convoluted inner layer is adapted to sealingly engage a fitting, and wherein at least one layer of the tubing is capable of dissipating electrostatic energy.

21. The multi-layer tubing as defined in claim 20 wherein the inner layer is formed from a melt-processible thermoplastic material selected from the group consisting of nylon 11, nylon 12, zinc chloride resistant nylon 6, thermoplastic elastomers, and mixtures thereof, wherein the outer layer is a melt-processible thermoplastic material selected from the group consisting of nylon 11, nylon 12, zinc chloride resistant nylon 6, thermoplastic elastomers, and mixtures thereof, and wherein the intermediate bonding layer is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, polyvinyl acetate- urethane blends, and mixtures thereof.

22. The multi-layer tubing as defined in claim 20 wherein the inner layer melt-processible thermoplastic material is a non-polyamide material which is capable of adhesion to the intermediate bonding layer, and wherein the inner layer melt-processible thermoplastic material is a fluoroplastic material selected from the group consisting of polyvinylidine fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers (ETFE), a graft copolymer of the preceding materials together with a fluorine-containing polymer such as copolymers of vinylidine fluoride and chlorotrifluoroethane, and mixtures thereof.

23. The multi-layer tubing as defined in claim 20 wherein the intermediate bonding layer is a fluoroplastic blend consisting essentially of: a polyvinyl fluoride compound selected from the group consisting of polyvinylidine fluoride polymers, polyvinyl fluoride polymers, a vinylidine fluoride- chlorotrifluoroethylene copolymer, ethylene tetrafluoroethylene copolymers (ETFE), and mixtures thereof; and a polyamide material selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides, 6 carbon block polyamides, and mixtures thereof.

24. The multi-layer tubing as defined in claim 20 wherein the inner layer is formed from nylon 12, the intermediate bonding layer is substantially smooth and non-convoluted and is formed from polyvinylidene fluoride, and the outer layer is formed from nylon 12.

25. The multi-layer tubing as defined in claim 20 wherein the inner layer is formed from ethylene tetrafluoroethylene (ETFE), the intermediate bonding layer is sufficiently convoluted to the same desired degree of flexibility as is the outer layer, and is formed from a blend of nylon 12 and ethylene tetrafluoroethylene (ETFE), and the outer layer is formed from nylon 12.