Multi-layer polyamide system for conductive fuel lines
By Stephen Moore | October 9, 2013
There is an increasing demand for conductive automotive fuel lines due to safety reasons. The use of conductive plastic tubes for feed and return lines has become essential for US car manufacturers as well as for OEMs in Japan and Korea. Nowadays, even European OEMs are orienting towards this trend too. This is according to a key Japanese supplier of resins for this application; Ube Industries.
Explains Ube: “The flow of hydrocarbon and other non-polar liquids over plastics can cause static electricity build-up. Any spark due to sudden electrical discharge in the fuel lines can cause an explosive effect. Conductivity eliminates static electric charge build-up by dissipating the electric charge, avoiding risk of fuel ignition.” Consequently, OEM specifications and many global standards such as SAE J1645 require that supply and return lines for carrying liquid fuel shall have conductive properties to allow electrostatic discharge (ESD).
Tube structure of conductive Ecobesta 9T
• Inner layer of conductive PA9T
• Middle layer of non-conductive PA9T
• Outer layer of heat-stabilized PA12
Furthermore global warming and other environmental concerns have motivated the automotive industry to minimize the environmental impacts of cars. There is an increasing demand to meet the requirements of stringent emission regulations globally. In order to comply with these stringent regulations, the fuel system has to be equipped with barrier materials to minimize the permeation of the fuel.
To comply with the needs of high barrier performance, a wide range of MLT (Multi Layer Tube) systems based on polyamide (PA) 12 have been proposed, utilizing barrier materials such as polybutyleneterephthalate (PBT), polybutylenenaphthalate (PBN), polyvinylidenefluoride (PVDF), ethylene perfluoro ethylenepropene-copolymer (EFEP), ethylenetetrafluoroethylene-copolymer (ETFE), polyphenylene sulfide (PPS), and ethylene-vinylalcohol-copolymer (EVOH). In the proposed MLT systems, conductive versions of PA12, EFFE, and EFEP are being used for the innermost layer that comes into contact with the fuel.
Fuel injector technology is becoming more popular in automobiles but injector clogging caused by monomer and oligomer derived from PA 12 conductive material used in fuel lines can be a severe hindrance in terms of design and functionality according to Ube. “It is essential to offer alternative materials for the inner layer that are free of monomer /oligomer elution problems. On the other hand, EFFE and EFEP conductive materials have low monomer/oligomer content and essentially eliminate contamination of the fuel stream. However these fluorine-based materials are of high density, are also costly, meaning they are not an optimal choice for cost-competitive solutions.
At the last K Show in2010, Ube and fellow Japanese company Kuraray jointly introduced a new generation of multilayer tubing systems for fuel lines under the brand name Ecobesta-9T. The combination of Ube’s Ubesta PA 12 with Kuraray’s Genestar Polyamide 9T (PA 9T) fuel barrier material delivered a multilayer tube construction dedicated for use in low emission vehicles.
In response to increasing demand from the market for conductive and elution-free fuel lines at reasonable cost, Ube has expanded its portfolio of multi-layer fuel tube solutions with good ESD properties that also eliminate the clogging problem, even under long term exposure to severe fuel environments. A new generation of Ecobesta-9T conductive systems for fuel line has thus been developed.
These MLT systems based on heat stabilized Ubesta PA12 (outer layer), non-conductive PA 9T (middle layer) and newly developed conductive PA 9T (inner layer), reportedly provide lower permeation performance, excellent conductivity and negligible monomer/oligomer elution at a better cost/performance balance.
Ubesta PA 12 was chosen for its excellent cold impact resistance and chemical resistance, as well as its pressure resistance and long term stability at high temperatures. In addition, this material offers superior durability of adhesive strength against PA 9T over long term exposure to all standard fuels and with respect to heat aging.
The new conductive PA 9T developed by Kuraray delivers lower permeability to gasoline, especially to low alcohol-based types, together with excellent chemical resistance in contact with fuel and lower monomer/oligomer elution to prevent risks and problems from clogging in the fuel injector. Thanks to the lower loading of carbon black and its good dispersion, this conductive material reportedly provides outstanding process-ability and excellent mechanical properties.
Therefore the innovative Ecobesta-9T conductive system combines low permeation characteristics, long term electro-conductivity and excellent anti-clogging properties with increased long term durability under exposure to fuels for the mechanical properties, including impact strength at low temperatures and burst pressure.
A German OEM, one of the major global players in automotive market, is now evaluating this innovative conductive MLT system for all cars produced for the North America market because of safety issues and regulatory demands. The new conductive fuel line complies with stringent European OEM as well as Society of Automotive Engineers (SAE) standards.
The performance and test results obtained at Ube’s development laboratory have been confirmed by tube suppliers. Based on the positive feedback on evaluations from tube suppliers and OEMs, it has been proven that the new innovative system with conductive PA9T is a solution delivering increased safety, with environmental friendliness and cost efficiency to boot. In the near future, growing adoption of this new conductive tube system by various OEMs can be anticipated.
Ube plans to commercialize its jointly patented and advanced multilayer fuel line solutions, both conductive and nonconductive types under the brand names Ecobesta-9T (PA12/PA9T); Sunbesta (PA12/ETFE), and Sunbesta-ZV which combines the performance of Ecobesta 9T and Sunbesta in a combination of PA12 with PA9T and ETFE. The systems offer a wide range of high performance multilayer structures to meet specific applications and regional needs.
Ube will showcase its fuel line solutions at the K Show in Dusseldorf, October 16-23. The company is located at Hall 6 / Stand E08.