EP0664863A1

EP0664863A1 - Corrugated multilayer tubing having at least two dissimilar polymeric materials

Info

Publication number: EP0664863A1
Application number: EP93924936A
Authority: EP
Inventors: David L. Noone; Frank L. Mitchell
Original assignee: Deutsche ITT Industries GmbH; ITT Industries Inc
Current assignee: ITT Manufacturing Enterprises LLC
Priority date: 1992-10-16
Filing date: 1993-10-14
Publication date: 1995-08-02
Also published as: BR9307258A; WO1994009302A1

Abstract

A multilayer tube suitable for use on motor vehicles composed of a cylindrical wall having an outer surface, and an inner surface essentially parallel to the outer surface. The cylindrical wall has a first region having an essentially uniform cross-sectional diameter and a second region which has a cross-sectional diameter differing from the essentially uniform cross-sectional diameter of the first region. The second region has at least one convolution contiguously adjacent to the cylindrical wall of the first region. The cylindrical wall is made up of a thick flexible outer layer having an inner and an outer face, composed of an extrudable melt processible thermoplastic; a thin intermediate bonding layer bonded to the inner face of the thick outer layer, composed of an extrudable melt processible thermoplastic capable of sufficiently permanent laminar adhesion to the outer layer; and an interior layer composed of an extrudable melt processible thermoplastic which is capable of sufficiently permanent laminar adhesion to the intermediate bonding layer, the thermoplastic material in the interior layer having an elongation value of at least 150 % and an ability to withstand impacts of at least 2 ft/lbs below about -20 °C, the inner layer having a thickness less than the thickness of the outer tubing.

Description

CORRUGATED MULTI-LAYER TUBING HAVING AT LEAST TWO DISSIMILAR POLYMERIC MATERIALS

I. Field of the Invention: The present invention relates to a corrugated tubing. More particularly, the present invention relates to multilayer tubing having at least one region of corrugation.

II. Background of the Invention: Single layer fuel lines and vapor return lines manufactured from 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.

It is also becoming increasingly important that the lines employed be essentially impervious to hydrocarbon emissions due to permeation through the tubing. It is anticipated that future Federal and state regulations will fix the limit for permissible hydrocarbon emissions due to permeation through such lines. Regulations which will be enacted in states such as California will fix the total passive hydrocarbon emission for a vehicle at 2 g/m² per 24 hour period as calculated by evaporative emission testing methods such as those outlined in Title 13 of the California Code of Regulations, section 1976, proposed amendment of

September 26, 1991. To achieve the desired total vehicle emission levels, a hydrocarbon permeation level for the lines equal to or below 0.5 g/m² per 24 hour period would be required. Finally, 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 ethanol.

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 are polyamides such as Nylon 6, Nylon 6.6, Nylon 11, and Nylon 12. Alcohol and aromatic compounds in the fluid conveyed through the tube diffuse at different rates through the tubing wall from the aliphatic components. The resulting change in the composition of the liquid in the tubing can change the solubility thresholds of the material so as, for example, to be able to crystalize monomers and oligomers of materials such as Nylon 11 and Nylon 12 into the liquid. The presence of copper ions, which can be picked up from the fuel pump, accelerates this crystallization. The crystallized precipitate can block filters and fuel injectors and collect to limit travel of the fuel-pump or carburetor float as well as build up on critical control surfaces of the fuel pump.

In U.S. Patent Number 5,076,329 to Brunnhofer, a five- layer fuel line is proposed which is composed of a thick corrosion-resistant outer layer formed of a material known to be durable and resistant to environmental degradation such as Nylon 11 or Nylon 12. The tubing disclosed in this reference also includes a thick intermediate layer composed of conventional Nylon 6. The outer and intermediate layers are bonded together by a thin intermediate bonding layer composed of a polyethylene or a polypropylene having active side chains of maleic acid anhydride. An thin inner layer of aftercondensed Nylon 6 with a low monomer content is employed as the innermost region of the tubing. The use of Nylon 6 as the material in the inner fluid contacting surface is designed to eliminate at least a portion of the monomer and oligomer dissolution which would occur with Nylon 11 or Nylon 12. The thin innermost layer is bonded to the thick intermediate layer by a solvent blocking layer formed of a copolymer of ethylene and vinyl alcohol with an ethylene content between about 30% and about 45% by weight. The use of a five layer system was mandated in order to obtain a tubing with the impact resistance of Nylon 12 with the low monomer/oligomer production of Nylon 6. It was felt that these characteristics could not be obtained in a tubing of less than five layers.

In U.S. Patent Number 5,038,833 also to Brunnhofer, a three-layer fuel line without the resistance to monomer/oligomer dissolution is proposed in which a tube is formed having a co-extruded outer wall of Nylon 11 or Nylon 12, an intermediate alcohol barrier wall formed from an ethylene-vinyl alcohol copolymer, and an inner water-blocking wall formed from a polya ide such as Nylon 11 or Nylon 12. In DE 40 06 870, a fuel line is proposed in which an intermediate solvent barrier layer is formed of unmodified Nylon 6.6 either separately or in combination with blends of polyamide elastomers. The internal layer is also composed of polyamides, preferably modified or unmodified Nylon 6. The outer layer is composed of either Nylon 6 or Nylon 12.

Another tubing designed to be resistant to alcoholic media is disclosed in UK Application Number 2 204 376 A in which a tube is produced which has an thick outer layer composed of 11 or 12 block polyamides such as Nylon 11 or Nylon 12 which may be used alone or combined with 6 carbon block polyamides such as Nylon 6 or 6.6 Nylon. The outer layer may be co-extruded with an inner layer made from alcohol-resistant polyolefin co-polymer such as a co-polymer of propylene and maleic acid.

Heretofore it has been extremely difficult to obtain satisfactory lamination characteristics between dissimilar polymer layers. Thus all of the multi-layer tubing proposed previously has employed polyamide-based materials in most or all of the multiple layers. While many more effective solvent-resistant chemicals exist, their use in this area is limited due to limited elongation properties, strength and compatibility with Nylon 11 and 12.

In order to overcome these problems, multi¬ layer tubing material employing chemically different layers has been proposed in co-pending applications Serial Numbers PCT/US93/05531 and PCT/US93/03479, 07/897,302, 07/897,376 and 07/897,824 to Noone and Mitchell, inventors of the present invention. These tubing materials generally employ an outer polyamide layer bonded to an inner hydrocarbon resistant layer by means of a suitable intermediate bonding layer. While such materials do provide the desired characteristics of resistance to hydrocarbon permeation, the tubing produced is generally straight material which is difficult to successfully bend to conform to the contours in an automotive vehicle.

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. Various polymeric materials possess significant elastic memories 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; thereby restricting flow therethrough and can experience significant reductions in its useful life due to fatigue and stress at or near the bend region. Furthermore bending previously known tubing can cause the differing layers to delaminate or fail due, in part, to the fact that the various layers each have very different elasticity and fatigue characteristics.

In order to obviate this problem, it has been proposed that conventional mono-layer tubing be corrugated at the appropriate bend regions. The bend region may include a plurality of annularly oriented accordion-like pleats which permit the region in which the pleats are located to be bent without constricting the interior opening or posing undue stress on the tubing material. This is accomplished by compressing one side of the each of the annular pleats in on themselves while the opposing side of can be extended outwardly from one another to accommodate the necessary angular contour. Heretofore no corrugated multi-layer tubing has been produced which incorporates chemically different layer materials in a single uniformly laminated wall. Additionally no corrugated tubing has been produced or suggested which incorporates multiple layers of polymeric material having differing chemical properties. Without being bound to any theory, it is believed that conventional extrusion and tube forming processes are incapable of producing such material; particularly corrugated material having wall thicknesses below about 0.75 mm.

It would be desirable to provide a tubing material which could be employed in motor vehicles which would be durable and prevent or reduce permeation of organic materials therethrough. It would also be desirable to provide a tubing material which would be essentially nonreactive with components of the liquid being conveyed therein. It would also be desirable to provide a tubing material which exhibits these characteristics which has localized or overall areas of corrugation. SUMMARY OF THE INVENTION The present invention ia a multi-layer tube suitable for use on motor vehicles which is composed of a cylindrical wall which has an outer surface, and an inner surface essentially parallel to the outer surface which defines an essentially cylindrical interior opening extending longitudinally through the tube. The cylindrical wall is characterized by a first region in which the cylindrical wall is essentially parallel to a longitudinal axis running coaxially through the cylindrical interior.

Contiguous to the first region is a second region which is defined by at least one convolution in the cylindrical wall. Each convolution comprises a region of cylindrical wall which deviates from the flat planar surface defined in the first region. Thus, the first region is defined by flat cylindrical region having an essentially uniform cross-sectional diameter, while the second region which has a cross-sectional which varies depending on the given position on its length and has a diameter different from the essentially uniform cross-sectional diameter of the first region. The cylindrical wall of the tubing of the present invention comprises: a thick flexible outer layer having an inner and an outer face, the outer layer consisting essentially of an extrudable melt processible thermoplastic having an elongation value of at least 150% and an ability to withstand impacts of at least 2 ft/lbs at temperatures below about -20°C; a thin intermediate bonding layer bonded to the inner face of the thick outer tubing, the bonding layer consisting essentially of an extrudable melt processible thermoplastic resistant to permeation by short-chain hydrocarbons, the bonding layer consisting of a thermoplastic which is chemically dissimilar to the extrudable thermoplastic employed in the outer tubing and is capable of sufficiently permanent laminar adhesion to the inner face of the thick outer tubing; and an interior layer composed of an extrudable melt processible thermoplastic which is capable of sufficiently permanent laminar adhesion to the intermediate bonding layer, the thermoplastic material in the interior layer having an elongation value of at least 150% and an ability to withstand impacts of at least 2 ft/lbs below about -20°C, the inner layer having a thickness less than the thickness of the outer tubing.

DESCRIPTION OF THE DRAWING The objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the following drawing in which the Figure is a sectional view through a piece of tubing of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is a multi-layer fuel line and vapor tube which contains at least one bonding layer and at least an outer and an inner tubing layer. The tubing of the present invention is defined by at least one corrugated region located in its length to accommodate bending, flexing or twisting. The multilayer tubing with localized corrugated regions can be produced by a process in which linear tubing material having multiple laminated layers is formed by coextrusion is and molded to provide the corrugation and contour desired.

The tubing 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 of the present invention may have an outer diameter up to 50 mm. However, in applications such as fuel lines and vapor recovery systems, outer diameter of up to 2 inches are preferred. The material may have any suitable wall thickness desired. However, in automotive systems such as those described herein, wall thicknesses between 0.5 mm and 2.0 mm are generally employed with wall thicknesses of approximately 0.8 to 1.5 mm being preferred. While it is within the scope of this invention to prepare a tubing material having a plurality of overlaying layers of various thermoplastic materials, the tubing of the present invention generally has a maximum of five layers inclusive of the bonding layers. In the preferred embodiment, the tubing material has three or four.

The tubing 10 of the present invention is a material which is suitable for use in motor vehicles and comprises a relatively thick 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.

It is anticipated that both the outer tubing layer 12 as well as any interior layers bonded thereto 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 of tubing are integrally laminated to one another and resistant to delamination throughout the lifetime of the tubing. The tubing thus formed will have a tensile strength of no less than 25N/mm² and an elongation value of at least 150%. The tubing will have a burst strength at 23°C and 120°C of at least 20 bar. The multi-layer tubing 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 outer layer 12 may be composed of any melt- processible extrudable thermoplastic material which is resistant to ultra violet degradation, extreme changes in heat and exposure to environmental hazards such as zinc chloride, and degradation upon contact with engine oil and brake fluid. In general, the exterior layer is selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides as well as zinc chloride resistant 6 carbon block polyamides thermoplastic elastomers. These thermoplastic elastomers are proprietary compositions and commercially available under tradenames such as SANTOPRENE, KRATON, SARLINK and VICHEM. These materials which compose the outer layers can be present in their unmodified state or can be modified with various plasticizers, flame retardants and the like in manners which would be known to one reasonably skilled in the art.

In one preferred embodiment, a polyamide such as Nylon 12 can be effectively employed. It is anticipated that a thermoplastic such as Nylon 12 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 17% by composition weight plasticizer; with amounts between about 1% and about 13% being preferred. The Nylon outer layer 12 preferably has a wall thickness between about 0.5 mm and about 0.9 mm with a preferred range being between about 0.7 and about 0.8 mm. As indicated previously, the material is extruded by conventional co-extrusion methods to any continuous length desired.

In a second preferred embodiment,the exterior layer consists essentially of 6-carbon block polyamides, such as Nylon 6, which are resistant to degradation upon exposure to zinc chloride. The Nylon 6 which composes the outer layer can be employed can also be modified with various plasticizers, flame retardants and the like in manners which would be known to one reasonably skilled in the art.

In this second preferred embodiment, the outer layer is composed of a polyamide thermoplastic derived from the condensation polymerization of caprolactam. Such materials are commonly referred to as 6-carbon block polyamides or Nylon 6. In the preferred embodiment, the 6-carbon block polyamide contains sufficient quantities of modifying agents to impart a level of zinc chloride resistance greater than or equal to that required by test method SAE J844; non-reactivity after 200 hour immersion in a 50% by weight aqueous zinc chloride solution. In the preferred embodiment, the 6-carbon block polyamide material is a multi-component system comprised of a Nylon-6 copolymer blended with other Nylons and olefinic compound. The zinc-chloride resistant Nylon-6 of choice will have a melt temperature between about 220°C and 240°C. Examples of thermoplastic materials suitable for use in the tubing of the present invention are propriety materials which can be obtained commercially under the tradenames M-7551 from NYCOA Corporation and ALLIED 1779 from Allied Chemical.

As with the Nylon 12, the 6-carbon black polyamide may, optionally, include other modifying agents such as various plasticizing agents generally present in amounts between about 1.0% and about 13% by total weight of the thermoplastic composition, as are readily known in the art. The polyamide material employed, preferably, is an impact-modified material capable of withstanding impacts of at least 2 ft. lbs. at temperatures below about -20°C.

In the method of the present invention, the Nylon 6 or the Nylon 12 is continuously extruded from a suitable coextrusion head with a wall thickness sufficient to accommodate localized expansion and elongation in molded and contoured regions. The contoured regions may be evidence or experience a degree of localized stretching or thinning but will have sufficient initial thickness to withstand the expansion without compromising the integrity of the multilayer wall structure. In the preferred embodiment, the outer layer is extruded to an initial wall thickness between about 0.5 and about 2.5 mm with a preferred thickness between about 0.75 mm and about 1.25 mm.

The thermoplastic material 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 intervals such as are found in engine oil and brake fluid. The preferred material will have an elongation value of at least 150%. The thermoplastic material of choice is, preferably, chemically similar in structure and composition to the thermoplastic material employed in the thick outer layer. As used herein, the term "chemically similar material" is defined as a thermoplastic material selected from the group consisting of 12 carbon block polyamides, 11 carbon block polyamides as well as zinc chloride resistant 6 carbon block polyamides, thermoplastic elastomers and mixtures thereof. The thermoplastic elastomers which can successfully be employed in the tubing of the present invention are proprietary compositions commercially available under tradenames such as SANTOPRENE, KRATON, SARLINK and VICHEM.

The thermoplastic material employed in the inner layer of the tubing of the present invention either may be identical to the material employed in the thick outer layer or may be a different thermoplastic selected from those listed to take advantage of specific properties of the various thermoplastics. In the preferred embodiment, the inner layer 14 is composed of a material similar to or identical to the thick outer layer. Polyamides such as Nylon 12 can be effectively employed. Alternately, a polyamide derived from the condensation polymerization of caprolactam can be employed. Suitable materials are commonly referred to as 6-carbon block polyamides or Nylon 6. The 6-carbon block polyamides employed herein may contain sufficient quantities of modifying agents to impart a level of zinc chloride resistance greater than or equal to that required by test method SAE J844: i.e. non-reactivity after 200 hour immersion in a 50% by weight aqueous zinc chloride solution.

The thermoplastic 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 17% by composition weight plasticizer; with amounts between about 1% and about 13% being preferred.

Where a 6-carbon block polyamide material employed, it is generally part of a multi-component system comprised of a Nylon-6 copolymer blended with other Nylons and olefinic compounds. The 6-carbon block polyamide material of choice will is preferably resistant to zinc chloride and has a melt temperature between about 220°C and 240°C. Examples of thermoplastic materials suitable for use in the tubing of the present invention are propriety materials which can be obtained commercially under the tradena es M-7551 from NYCOA Corporation and ALLIED 1779 from Allied Chemical. In instances where the 6-carbon block polyamide material includes plasticizing agents, these materials are generally present in amounts between about 1.0% and about 13% by total weight of the thermoplastic composition.

The inner layer 14 may have a thickness sufficient to supply strength and chemical resistance properties to the multi-layer tubing. Specifically, the inner layer 14 is of sufficient thickness to impede per eation 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 40% and 60% that of the outer layer; between about 0.05 mm and about 0.2 mm; with a wall thickness between about 0.05 mm and about 0.17 mm being preferred. The inner layer 14 may also, optionally, contain suitable material in sufficient quantities to impart electrostatic conductivity characteristics to the tubing of the present invention. When employed, the material is preferably capable of dissipation of electrostatic charges in the range of 10^"4 to 10~⁹ ohm/cm². The thermoplastic material employed in the present invention may include, in its composition, a conductive media in sufficient quantity to permit electrostatic dissipation in the range defined. 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 and 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. The amount of conductive material contained in the thermoplastic is generally limited by considerations of low temperature durability and resistance to the degradative effects of the gasoline or fuel passing through the tubing. The amount of conductive material employed may be that amount sufficient to impart electrostatic dissipation characteristics to the tubing. When employed, the maximum amount of conductive material in the thermoplastic material is less than 5% by volume.

The conductive material can either be interstitially integrated into the crystalline structure of the polymer or can be co-polymerized therewith.

Without being bound to any theory, it is believed that carbon-containing materials such as carbon black may be subject to carbon co-polymerization with the surrounding thermoplastic material. Materials such as stainless steel are more likely to be interstitially integrated into the crystalline structure of the polymer.

In order to accomplish effective lamination of the two thermoplastic materials which compose the inner and outer layers, the tubing of the present invention also includes at least one intermediate layer 16 interposed between the two previously described layers and co-extruded therewith which is capable of achieving a suitable homogeneous bond between itself and the two respective layers. The intermediate bonding layer 16 is generally composed of a more elastic material than that employed in the inner layer 14.

In the present invention, the interior bonding layer 16 is a chemically dissimilar, permeation resistant, chemical resistant, fuel resistant thermoplastic material which is melt processible in normal ranges of extrusion, i.e. about 175° to about 250°C. The material of choice has an elongation value greater than about 150% with an elongation value between about 150% and about 250% being preferred. By the term "chemically dissimilar", it is meant that the intermediate bonding layer 16 is a non-polyamide material which is capable of integral adhesion with and between the thick outer layer 12 and the inner layer 14 as a result of co-extrusion. The intermediate bonding layer 16 is composed of a thermoplastic material which permits the establishment of a homogeneous bond between the inner and outer layers and exhibits properties of resistance to permeation of aliphatic and aromatic materials such as those found in fuel. 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.

In the preferred embodiment, the thermoplastic material which comprises the interior bonding layer 16 is a thermoplastic polyester derived from ethylene glycol selected from the group consisting of polybutylene terepthalate, polyethylene terepthalate, polytere ethylene terepthalate, 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. The preferred material is selected from the group consisting of polybutylene terepthalate and copoly ers of ethylene and vinyl alcohol having an ethylene content between about 27% and about 35% by weight. Where ethylene vinyl alcohol copolymers are employed, polymers with an ethylene content between about 27% and about 32% are preferred. Suitable polybutylene terepthalate material is commercially available under the tradename 1607 ZE40 from Hϋls of Dusseldorf, Germany. Suitable EVA materials which can be employed in the tubing of the present invention include ethylene vinyl alcohol commercially available from EVA/LA.

The material employed in the intermediate bonding layer 14 can, optionally, exhibit conductive characteristics rendering it is capable of dissipation of electrostatic charges in the range of 10~⁴ to 10^"9 ohm/cm². The thermoplastic material employed in the present invention may include, in its composition, a conductive media in sufficient quantity to permit electrostatic dissipation in the range defined. 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 and 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.

The amount of conductive material contained in the thermoplastic is generally limited by considerations of low temperature durability and resistance to the degradative effects of the gasoline or fuel passing through the tubing. The amount of conductive material employed may be that amount sufficient to impart electrostatic dissipation characteristics to the tubing. When employed, the maximum amount of conductive material in the thermoplastic material is less than 5% by volume.

The conductive material can either be interstitially integrated into the crystalline structure of the polymer or can be co-polymerized therewith. *.

The thermoplastic material employed in the interior layer 16 also exhibits characteristics which permit resistance to permeation by short chain aromatic and aliphatic compounds. These permeation resistant characteristics synergistically interact with the inner polyamide layer such that the total permeation resistance is unexpectedly increased when the thermoplastic interior layer is bonded to the inner polyamide layer. Thus, the resistance to permeation to short chain aromatic and aliphatic hydrocarbons exhibited by the multi-layer material exceeds the permeation resistance exhibited by individual layers of either polybutylene terepthalate or polyamide of a thickness equal to or greater than the multi-ply composite of the present invention.

The material employed in the inner layer generally has a degree of expansion greater than that of the outer layer. In general, the elongation value of the inner layer is between about 150% and about 250%. The material generally has an elastic memory which can result in the contraction of the material to about 200% of its elongated value upon stretching or other deformative activities.

In the preferred embodiment, the intermediate bonding layer 16 is preferably maintained at the minimum thickness necessary to achieve effective bonding between the inner and outer layers. Furthermore, the intermediate bonding layer can also function in concert with the inner layer to prevent permeation of the fuel through the tubing material. As indicated previously, it is preferred that the amount of hydrocarbon permeation not exceed 0.5 gm/m² in a 24 hour interval. Thus where the bonding layer contributes to permeation resistance, it is anticipated that the thickness of the inner and intermediate layers can be modified to accomplish this end. In addition to permitting the establishment of a homogeneous bond between the inner and outer layers, the intermediate bonding layer can also exhibit resistance to the permeation of aliphatic and aromatic compounds therethrough. Furthermore the intermediate bonding layer may exhibit conductive or static dissipative characteristics such as those described previously. Thus the intermediate bonding layer may optionally include sufficient amounts of conductive media to effect electrostatic dissipation in the range of 10^"4 to 10^"9 ohm/cm². As with the inner layer, the intermediate bonding layer may be inherently electrostatically dissipative or may be rendered so by the inclusion of certain conductive materials such as those selected from the group consisting of elemental carbon, stainless steel, copper, silver, gold, nickel, silicon, and mixtures thereof. The intermediate bonding layer is of sufficient thickness to permit an essentially homogeneous bond between the inner and outer layers. In general, the intermediate bonding layer can be thinner than the other two layers and can constitute between about 10% and about 50% of the total wall thickness or between about 20% and about 30% of the thickness of the outer layer. In the specified embodiment, the thickness of the intermediate bonding layer is between about 0.05 mm and about 0.2 mm with a thickness between about 0.05 mm and about 0.2 mm being preferred.

The multilayer tube 10 of the present invention is composed of an elongated cylindrical wall 18 which preferably has an essentially circular cross-section perpendicular to its longitudinal axis 20. The cylindrical wall 18 has an essentially uniform wall thickness throughout its length and circumference and is defined by an inner surface 22 and an opposed outer surface 24. The inner surface 22 defines an essentially cylindrical opening which extends longitudinally through the tubing 10 of the present invention essentially coaxial to the longitudinal axis 20.

The cylindrical wall 18 of the multi-layer tube 10 comprises at least two distinct regions. The cylindrical wall has a first region 26 in which the cylindrical wall 18 is essentially parallel to the longitudinal axis 20. Contiguous to the first region 26 is a second region 28 which is defined by at least one convolution 30 in the cylindrical wall 18. As used herein, the term convolution is defined as an area of cylindrical wall 18 which deviates from parallel to the longitudinal axis 20. Contiguous to the first region 26 is a second region 28 which is defined by at least one convolution 30 located in the cylindrical wall 18. As used herein, the term convolution is defined as an area of cylindrical wall 18 which deviates outward from a position parallel to the longitudinal axis 20. This deviation can produce an inner diameter which is between about 20% and 300% greater than the inner diameter of the first region 26 at its maximum. In the preferred embodiment, the inner diameter of the convolution 30 is between 20% and 100% greater than the inner diameter of the first region 26.

The tubing 10 of the present invention can have as many convolutions with any length of cylindrical tubing optionally interposed therebetween as would be necessary to achieve the degree of flexibility required. The geometry of the convolutions can be of any cross- sectional profile desired. Thus the convolutions 30 may have angled , squared, or sinusoidal profiles as desired. In the preferred embodiment, it is anticipated that the tubing of the present invention will have sufficient convolutions positioned on the length of the tubing to accommodate bends of over 90° from vertical. It is to be understood that the tubing 10 of the present invention can be customized to suit the end user. Thus, in situations were such acute bends are not required, the tubing can has fewer or shallower convolutions.

In effecting a bend such as an angular bend in the tubing 10 of the present invention, a longitudinal area on one side of the second region 26 can be compressed so that the segments of the various convolutions 30 are brought into lateral contact with one another while the diametrically opposed longitudinal area is reciprocally elongated.

The tubing 10 may also include various molded flanges and the like such as hose barb 32 shown in the Figure. It is to be understood that in hose barb 38, as in all molded regions, the wall thickness remains essentially constant linearly throughout the outwardly expanded region as do the relative thicknesses of the various multiple layers.

Thus the present invention is a multi-layer tubing material which can accommodate the introduction of various bends and contours during installation. The material* thus produced is durable and resistant to delamination during installation and use.

Claims

What is claimed is:

1. A multi-layer tube suitable for use on motor vehicles comprising a cylindrical wall having an outer surface, and an inner surface essentially parallel to the outer surface, the inner surface defining an essentially cylindrical interior, said essentially cylindrical interior extending longitudinally through the coaxial to a longitudinal axis, the cylindrical wall itself comprising: a first region having an essentially uniform cross-sectional diameter in which the cylindrical wall has a flat in longitudinal cross-section, the cylindrical wall oriented essentially parallel to the coaxial longitudinal axis; and a second region in which the cylindrical wall has at least one convolution having a cross-sectional diameter which varies positionally depending on longitudinal location in the second region, the convolution having cross-sectional diameter different from the essentially uniform cross-sectional diameter of the first region, the tubing of the present invention comprising: a thick flexible outer layer having an inner and an outer face, the outer layer consisting essentially of an extrudable melt processible thermoplastic having an elongation value of at least 150% and an ability to withstand impacts of at least 2 ft/lbs at temperatures below about -20°C; a thin intermediate bonding layer bonded to the inner face of the thick outer tubing, the bonding layer consisting essentially of an extrudable melt processible thermoplastic resistant to permeation by short-chain hydrocarbons, the bonding layer consisting of a thermoplastic which is chemically dissimilar to the extrudable thermoplastic employed in the outer tubing and is capable of sufficiently permanent laminar adhesion to the inner face of the thick outer tubing; and an interior layer composed of an extrudable melt processible thermoplastic which is capable of sufficiently permanent laminar adhesion to the intermediate bonding layer, the thermoplastic material in the interior layer having an elongation value of at least 150% and an ability to withstand impacts of at least 2 ft/lbs below about -20°C, the inner layer having a thickness less than the thickness of the outer tubing.

2. The tubing as defined in claim 1 wherein the cylindrical diameter of the convolution is between about 20% and between about 300% greater than the inner diameter of the first region.

3. The tubing as defined in claim 2 wherein the cylindrical diameter of the convolution is between about 20 % and about 100% greater* than the ihner diameter of the first region.

4. The tubing of claim 2 wherein the convolution has an angled longitudinal cross-sectional profile.

.

5. The tubing of claim 2 wherein the convolution has a squared longitudinal cross-sectional profile.

6. The tubing of claim 2 wherein the convolution has a sinusoidal longitudinal cross-sectional profile.

7. The tubing of claim 2 wherein the inner diameter of the first region is less than about 2.0 inches.

8. The tubing of claim 1 wherein the inner hydrocarbon layer is capable of dissipating electrostatic energy, the electrostatic dissipation capacity being in a range between about 10~⁴ to 10^~9 ohm/cm².

9. The tubing of claim 1 wherein said outer layer is composed of a thermoplastic material selected from the group consisting of twelve-carbon block polyamides, eleven-carbon block polyamides, six-carbon block polyamides, thermoplastic elastomers, and mixtures thereof.

10. The tubing of claim 9 wherein the conductive material is selected from the group consisting of elemental carbon, copper, silver, gold, nickel, silicon, and mixtures thereof.

11. The tubing of claim 11 wherein the conductive material is present in an amount less than about 5% by volume of the polymeric material.

12. The tubing of claim 12 wherein the conductive material is interstitially integrated into the thermoplastic material.

13. The tubing of claim 9 wherein the conductive material is elemental carbon and is copolymerized with the extrudable thermoplastic material.

14. The tubing of claim 1 wherein the extrudable thermoplastic of the thick outer tubing is a polyamide selected from the group consisting of Nylon 11, Nylon 12, zinc chloride resistant Nylon 6, Santoprene, Kraton, Vichem, Sarlink and mixtures thereof.

15. The tubing of claim 1 wherein the thermoplastic material employed in the intermediate bonding layer exhibits at least some resistance to interaction with short-chain hydrocarbon molecules present in material conveyed through the tubing.

16. The tubing of claim 11 wherein the thermoplastic material employed in the intermediate bonding layer includes as a major constituent an extrudable, melt processible thermoplastic polyester selected from the group consisting of polybutylene terepthalate, polyethylene terepthalate, polyteremethylene terepthalate, and mixtures thereof.

17. The tubing of claim 17 wherein the thermoplastic material employed in the intermediate bonding layer consists essentially of polybutylene terepthalate.

18. A multi-layer tube suitable for use on motor vehicles comprising a cylindrical wall having an outer surface, and an inner surface essentially parallel to the outer surface, the inner surface defining an essentially cylindrical interior, said essentially cylindrical interior extending longitudinally through the coaxial to a longitudinal axis, the cylindrical wall itself comprising: a first region having an essentially uniform cross-sectional diameter in which the cylindrical wall has a flat in longitudinal cross-section, the cylindrical wall oriented essentially parallel to the coaxial longitudinal axis; and a second region in which the cylindrical wall has at least one convolution having a cross- sectional diameter which varies positionally depending on longitudinal location in the second region, the convolution having cross-sectional diameter different from the essentially uniform cross-sectional diameter of the first region, the cross-sectional diameter of the convolution having a maximum value which exceeds the inner diameter of the first section by an amount between about 20% and About 300%, the tubing material comprising: an outer tubing having an inner and an outer face, the outer tubing consisting essentially of an extrudable polyamide having an elongation value of at least 150% and an ability to withstand impacts of at least 2 ft/lbs at temperatures below about -20°C; an intermediate bonding layer having a thickness between about 0.05 mm and about 0.2 mm bonded to the inner face of the thick outer layer, the bonding layer consisting essentially of an extrudable thermoplastic capable of sufficiently permanent laminar adhesion to the polyamide outer tubing and exhibiting at least some resistance to short-chain hydrocarbon molecules conveyed through the tubing; and an inner hydrocarbon barrier layer bonded to the intermediate bonding layer having a thickness between about 0.05 mm and about 0.2 mm and an elongation value greater than about 150%, the inner layer consisting essentially of an extrudable, melt process thermoplastic capable of sufficiently permanent laminar adhesion with the intermediate bonding layer selected from the group consisting of twelve-carbon block polyamides, eleven- carbon block polyamides, six-carbon block polyamides, thermoplastic elastomers, and mixtures thereof.

19. The tubing of claim 18 wherein the extrudable thermoplastic of the thick outer tubing is a polyamide selected from the group consisting of Nylon 11, Nylon 12, zinc chloride resistant Nylon 6, and mixtures thereof.

20. The tubing of claim 19 wherein the thermoplastic material of the inner hydrocarbon barrier layer is capable of dissipating electrostatic energy, the electrostatic dissipation capacity being in a range between about 10^"4 to 10^"9 ohm/cm².

21. The tubing of claim 19 wherein the thermoplastic material of the inner hydrocarbon barrier layer contains quantities of a conductive material sufficient to provide electrostatic dissipation capacity in a range between about 10^"4 to 10^-9 ohm/cm².

22. The tubing of claim 21 wherein the conductive material is selected from the group consisting of elemental carbon, copper, silver, gold, nickel, silicon, and mixtures thereof and is present in an amount less than about 5% by volume of the extrudable thermoplastic material.

23. The tubing of claim 22 wherein the conductive material is interstitially integrated into the melt processible thermoplastic material.

24. The tubing of claim 23 wherein the conductive material is elemental carbon and is copolymerized with the extrudable thermoplastic material.