Pipes and tubular conduits – Distinct layers – Bonded to each other
Reexamination Certificate
2000-05-23
2001-09-25
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Distinct layers
Bonded to each other
C138S137000, C138SDIG003, C138S140000, C428S035700, C428S036910
Reexamination Certificate
active
06293312
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to tubing and particularly to fuel transport tubing such as fuel filler and fuel filler neck tubing. More particularly, this invention relates to a thermoplastic tubing for transfer of hydrocarbon fuel comprising a fluoropolymer inner layer and a melt processible polyamide outer layer wherein at least one of the layers also includes an adhesion promoter which improves interlayer bonding.
Tubing assemblies for the transport of liquids and vapors are well known in the art. In fuel-line applications, tubing assemblies are exposed to a variety of deleterious and harmful conditions. The tubing is in nearly constant contact with fuel and other automotive fluids and additives. Also, there are external environmental factors such as stone impact and corrosive media (such as salt) to consider. Furthermore, temperatures often rise to extremely high levels, and in cold climates, there is exposure to extremely low temperatures as well.
This abundance of considerations has led to design of tubing having multiple layers. The materials of each layer have specific, and preferably complementary, properties. Inner tubing layers, for example, are typically designed to be resistant to permeation by liquids and gases, while outer layers possess mechanical strength and shock resistance.
The art contains numerous examples of multi-layer tubing assemblies. U.S. Pat. No. 3,561,493 to Maillard discloses tubing having two coextruded layers of different plastics, and a coextruded layer of adhesive therebetween. The layers are chosen from plastics having complementary properties. U.S. Pat. No. 4,643,927 to Luecke et al. discloses tubing having a central barrier layer of polyvinylidene chloride that is relatively gas impermeable. The barrier layer is surrounded by inner and outer adhesive layers which in turn are surrounded by inner and outer surface layers of polyethylene that protect the central barrier layer from degradation. U.S. Pat. No. 4,887,647 to Igarishi et al. shows multi-layer tubing having an inner fluororubber layer that prevents degradation due to amine-type additives and also exhibits improved adhesion to an outside rubber layer. U.S. Pat. No. 5,038,833 to Brunnhofer discloses tubing having a protective outer polyamide layer, a middle alcohol barrier layer of polyvinyl-alcohol, and an inner water barrier layer of polyamide. U.S. Pat. No. 5,076,329 to Brunnhofer shows a five-layer tubing assembly having outer, inner and middle layers of nylon, and intermediate bonding and solvent-blocking layers.
Another requirement for fuel lines is provision for discharge of internal static electricity. Accumulated, undissipated electric charge can eventually cause a breach in a fuel line. U.S. Pat. Nos. 3,166,688 to Rowand et al. and 3,473,087 to Slade disclose polytetrafluoroethylene (PTFE) tubing assemblies having electrically conductive inner layers to facilitate dissipation of static electrical energy.
More recent developments in multi-layer tubing design have been motivated by governmental regulations limiting permissible hydrocarbon emissions. It is known that fluoropolymers exhibit good permeation resistance to hydrocarbon fuels. Hence, recent multi-layer tubing assemblies have usually included at least one permeation-resistant fluoropolymer layer. Difficulties have been encountered, however, in finding a commercially viable design. Most fluoropolymers having strong mechanical properties, for example, do not bond well with other fluoropolymers. Conversely, fluoropolymers exhibiting good bondability(polyvinylidene fluoride (PVDF), in particular) tend to be mechanically weak.
U.S. Pat. No. 5,383,087 to Noone et al. discloses an outer impact-resistant polyamide layer, an intermediate bonding layer, an inner permeation-resistant fluoroplastic layer, and an innermost conductive fluoroplastic layer for dissipation of electrostatic charge. All layers are coextruded. The innermost conductive layer exhibits an exceptional electrostatic dissipation capacity in the range of 10
−4
to 10
−9
ohm/cm
2
. Materials possessing such extremely high conductivity, however, are typically metallic or brittle plastic. Consequently, they are difficult to extrude and also exhibit poor mechanical properties. Furthermore, most of the fluoropolymers disclosed in the '087 patent bond poorly with dissimilar polymers.
The fluoropolymer bonding problem is addressed in U.S. Pat. No. 5,419,374 to Nawrot et al. Nawrot et al. disclose multi-layer coextruded tubing having an outer layer of polyamide
12
, an inner PVDF layer, and a middle adhesion binder layer (a mixture of polyurethane and ethylene/vinyl acetate copolymer). Though, as discussed above, PVDF demonstrates better adhesion to the polyamide layer, PVDF multi-layer tubing suffers from poor cold impact-resistance. This is due to the fact that PVDF becomes brittle at low temperatures.
Other high performance fluoropolymers, such as ethylene tetrafluoroethylene (ETFE), exhibit better cold impact-resistance but again, have experienced bonding problems. One approach in the art has been to pretreat the ETFE surface using methods such as chemical etching, plasma discharge or corona discharge. European Patent Application publication no. 0 551 094, for example, discloses a multi-layer tubing assembly in which an inner ETFE layer is treated by corona discharge to enhance bonding to an outer polyamide layer. Similarly, PCT international application WO 95/23036 treats an inner ETFE layer with plasma discharge to achieve better bonding with an outer thermosetting elastomer layer. In the same vein, U.S. Pat. No. 5,170,011 etches a fluorocarbon inner layer to promote better bonding with a polyamide outer layer. These approaches, too, have their problems. Pretreatment processes such as corona and plasma discharge are expensive and can result in poor or variable degrees of adhesion. Furthermore, in many cases '(such as with corona treatment), only temporary bonding is achieved and delamination may occur with aging.
Accordingly, there is a need for an improved tubing for transfer of hydrocarbon fuels that provides the necessary durability and resistance to permeation through the utilization of a dual or multi-layer structure characterized by increased adhesive bond strength between the layers.
SUMMARY OF THE INVENTION
The present invention is a multi-layer thermoplastic tube for transfer of hydrocarbon fuel comprising an inner fluoroplastic layer and an outer polyamide layer bonded to the fluoroplastic layer wherein an adhesion promoter is included in at least one of the layers. The adhesion promoter is an unsubstituted or substituted phenol salt of 1,8-diazabicyclo-[5,4,0]undec-7-ene which functions to increase the adhesive bond strength between the two layers. The adhesion promoter provides a chemically bonded adhesion in addition to the mechanical adhesion associated with extrusion or lamination of the layers. The adhesion promoter increases the adhesion without adversely affecting the electrostatic dissipation properties of the tubing materials.
In a first embodiment of the invention, a thermoplastic multi-layer material comprising an inner layer of a thermoplastic form of a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) terpolymer and an outer layer of a melt processible polyamide bonded to said inner layer wherein at least one of the layers further comprises an adhesion promoter is provided. The adhesion promoter is an unsubstituted or substituted phenol salt of 1,8-diazabicyclo-[5,4,0]undec-7-ene (DBU). The multi-layer material is characterized by increased adhesive bonding between the layers as compared to a multi-layer material prepared without the adhesion promoter.
In a second embodiment of the invention, a tubing for transfer of hydrocarbon fuel having improved inter-layer bonding is provided. The tubing comprises an inner layer of a thermoplastic form of a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer and an outer layer of a mel
Brinson Patrick
Dayco Products Inc.
Tassone Joseph V.
LandOfFree
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