Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2001-05-23
2003-04-29
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S035700, C428S036600, C428S036700, C428S036910, C428S411100, C428S476100, C264S171270, C264S173120, C264S209100, C264S209500, C264S508000, C264S510000, C264S512000, C264S513000, C264S514000, C264S515000, C138S118000, C138S121000, C138S124000, C138S125000, C138S140000, C138S141000, C138SDIG001, C138SDIG007
Reexamination Certificate
active
06555243
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to thermoplastic multilayer composites, particularly in the form of a multilayer hose, a multilayer pipe which more particularly can be a fuel line, or a multilayer container, containing at least one layer of a molding compound on the basis of ethylene/vinyl alcohol copolymers and layers of molding compounds on polyamide basis, as well as to methods of production thereof.
The invention refers in particular to hose lines or tubing for gaseous or liquid media consisting of plural polymer layers and exhibiting an improved barrier action specifically toward fuels. These fuels may also contain alcoholic components. Therefore, the multilayer motor vehicle tubing according to the invention also relates to the conduction of alcoholic media. These tubings are supposed to be alcohol-resistant, which means that the plastic pipe will not experience a disturbing elongation when conducting a fuel containing alcohol. Such a conduit is supposed to be suitable for conducting premium gasoline with an alcohol content of 5% and possibly more, without significant elongation. In ordinary linguistic usage, the term alcohol more particularly means methyl alcohol as well as ethyl alcohol and their mixtures with water, but also the higher-valent alcohols. In this connection, the term alcoholic medium designates, not only fuel with alcohol addition but also for instance liquids of a windscreen washer unit or pressurized media of a brake system.
BACKGROUND OF THE INVENTION
Already in the 1990s, known multilayer motor vehicle tubings have better satisfied enhanced safety requirements and tightened environmental regulations than polyamide monolayer pipes used earlier. This had also found a reflection in German standards DIN 73378 and DIN 74342.
Disturbing effects are triggered when alcohol is present in the medium to be conveyed in such tubing. The polyamide coming in direct contact with the alcohol somewhat swells, implying dimensional increases of 5-10%. However, the polyamide is also extracted by the alcohol, i.e., monomers, oligomers, plasticizers, stabilizers etc. are leached and transfer into the alcohol medium. The properties of the pipe thus change over time. Moreover, at lower temperatures the leached monomers and oligomers may precipitate and lead to clogging in the gasoline system (for instance in filters and nozzles). This phenomenon is apparent in particular with polyamide 11 and polyamide 12.
Previously known multilayer motor vehicle tubings had been satisfactory so long as the medium conveyed by them did not contain alcohol.
For this reason one could also perceive to use other plastic materials for the motor vehicle tubings, that is alcohol resistant ones, instead of the polyamide material. However, these do not satisfy the special requirements with respect to the systems used to convey media in motor vehicle construction, which range from lowest permeabilities for the media to superior mechanical stability with a low-temperature impact resistance of −40° C. to 100° C. and to high chemical resistance under the effect of highway salt.
The standard DIN 73378 mentioned above is the most important European standard for pipes of polyamides for motor vehicles. For custom-tailored polyamide types, it specifies the dimensions, the bursting strength as a function of temperature up to 130° C., the impact strengths at 23° C. and −40° C., stabilization, plasticizer content, flexibility (modulus in tension), and polyamide characteristics with defined short designations. It should be noted that already in this very old DIN 73378, only modified polyamide 12 and polyamide 11 materials are admitted for pipes laid underneath the body.
Even in the USA (SAE J 844d and J 1394), Great Britain (BS 5409), and Japan (JASO M 301), only modified polyamide 12 and polyamide 11 types are admitted, for instance, for brake lines and helical tubing.
The standard requirements to be met by current fuel lines (SAE J 2260) are manifold, as indicated above. In addition to typical mechanical and chemical polyamide properties, current fuel lines for reasons of environmental and health protection must possess highest barrier properties against volatile organic compounds. According to the current state of the art, a plastic fuel line for passenger vehicles consists of several layers of material. Here the properties of several polymers are deliberately combined. This occurs by coextrusion. It is necessary in such a case that the individual layers which are in direct mutual contact are compatible, so that good adhesion can be achieved over the full lifetime of the component. Therefore, adhesion promoter must be used between incompatible polymers.
Because of their good mechanical and chemical properties in these applications, polyamides, and in particular polyamide 11 (PA 11) or polyamide 12 (PA 12), are the preferred materials used in the outer tubing layers. While polyamides by themselves exhibit good mechanical properties, and in particular a good toughness, the barrier action with respect to alcoholic fuels is insufficient. Polar substances in particular readily migrate through polyamides. In fuel lines conducting alcohol-containing fuel, for instance, this is extremely disadvantageous. In view of considerations concerning environmental protection and safety arising in recent years, this is undesirable.
Development work has been performed, therefore, in order to produce multilayer pipes with improved barrier properties. Nowadays fluoropolymers such as PVDF and ETFE are commonly used as barrier layers. However, these materials are expensive. Even with very thin layers of this material, the material costs for the fill pipe are 40 to 60% higher than with a single-layer pipe of PA 11 or PA 12. Moreover, when fluoropolymers are used, additional safety precautions for man and environment are needed, both during processing and during elimination after product use.
Ethylene/vinyl alcohol copolymers, abbreviated EVAL or, in the English-speaking world, also designated as EVOH, are known barrier materials for nonpolar and polar solvents, and are proposed as barrier layers for multilayer motor vehicle lines (cf. DE 35 10 395 A1, DE 38 27 092 C1, and EP 0 428 834 A2). However, in practice the multilayer fuel lines with ethylene/vinyl alcohol copolymers as the barrier layers are hardly used, since a few years ago the availability of EVOH was still very limited. For EVOH to retain its excellent barrier properties, it must be protected against moisture. Therefore, it is preferably used as an intermediate layer not in direct contact with the fluid. It is further known that EVOH in a pure form can only be used in small layer thicknesses. In fact, ethylene/vinyl alcohol copolymers having the required barrier properties are known as extraordinarily brittle with low strain at break.
According to Kunststoff Taschenbuch of Saechtling, 26th edition, typical EVAL barrier types have a VAL (vinyl alcohol) content of 53 to 68% by weight. It follows that these materials have a considerable capacity for moisture uptake. It is described that these EVAL types lose their barrier effect at water contents of 3 to 8%. Saechtling recommends, therefore, to use EVAL as a multilayer film between PE (polyethylene), PP (polypropylene) and PA (polyamide) or PET (polyethylene terephthalate).
It would be desirable to find suitable polymers providing good, stable adhesion simultaneously to EVOH and to polyamides such as PA 11 and PA 12 of a multilayer composite. Here the EVOH interlayer, as already described in EP 0 428 833 B1, in addition to its major function as a barrier layer with respect to the medium (e.g., the fuel) has the second function that monomers, oligomers, and other substances from this layer and the layers disposed toward the outside will not dissolve in the transport medium (hence the additional designation of “dissolution inhibitor layer”).
EP 0 428 833 B1 (Technoflow), corresponding to DE 40 01 125 C1, describes five-layer motor vehicle tubings for alcohol-containing media consisting of an out
Flepp Albert
Hoffmann Michael
EMS-Chemie AG
Hampton-Hightower P.
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