Rapra examines rubber bonding.
Advances in analytical techniques are said to be providing greater insights into adhesive technology. Through low incidence x-ray diffraction analysis, Dr. William van Ooij from the University of Cincinnati has demonstrated that the sulfide film formed on the surface of brass-plated tire cord can become crystalline at high molding temperatures, causing a brittle interface and poor adhesion. The addition of cobalt and resin systems is said to improve aged adhesion as it delays the crystallinity of the sulfide film Current developments are examining the use of silanes to replace the brass and produce a more environmentally acceptable product.
Loughborough University presented a paper on the numerous surface treatments to improve the adhesion of rubber onto non-polar plastics. The use of surface analysis techniques such as XPS, SIMS and ATR has shown that the level of surface oxygen was not found to correlate with adhesion strength. Although some success was found with some treatments, the health and safety issues have not been fully resolved. This was also said to be a limiting factor with a paper by Phoenix Rubber Industrial on bonding rubber to PA11 and PVDF for hoses.
Premature failure of rubber-metal bonded pipelines has been experienced for a specific adhesive system. Leaching of elements (chloride and bromide) from the primer and adhesive can create aggressive corrosive acids. In addition, steel corrosion products can migrate into the rubber and accelerate rubber aging, particularly at elevated service temperatures. Chemical Innovations Limited discussed the advantages and disadvantages of one-component bonding systems; they have modified the adhesive chemistry to offer improved heat and corrosion resistant grades.
Regarding environmental issues, Rohm & Haas presented data on environmentally-friendly, robust rubber-to-metal bonding systems with resistance to boiling water, salt spray and glycol. An adhesive system suitable for swaging applications was presented. Lord has also been developing solvent-free systems.
The presentation by Henkel on the standard test method adopted by WDK (Wirtschaftsverband de Deutschen Kautschukindustrie) for the development of lead-free bonding agents for car engines and bushings sparked debate on adhesive testing methods. The flat metal stub method is said to give higher adhesion values and more rubber tear compared with the convex metal end stubs (ASTM D429 Method F).
Tack Service, based in Germany, presented a new machine that exposes polymers to UV light and ozone (Tack Treat AS3000). The treatment was claimed to be more effective than corona or plasma treatment and enables a wide range of rubber and plastics to be bonded. Initial take-up as been in the shoe industry, where it has permitted the use of water-based PU adhesives and reduces VOC emissions.
For the TPE market, ExxonMobil and PolyOne presented new polyolefin-based TPV grades with improved adherence to polar materials in over-molding applications. Improved bond strength was said to be achieved for the ExxonMobil grades without the need for thick sections or high process temperature. The proposed grades are not, however, a fix for all engineering thermoplastics. PolyOne also showed data for an improved TPE-S (Onflex S) with improved compression set and bonding to polar substrates. Both materials enable greater design flexibility, as softer, low cost, higher temperature performance elastomers can be used compared with a polar TPE such as TPU.
Heat-activated pressure-sensitive tapes are said to be gaining acceptance by the automotive industry for door and weather seals. Boss Polymer Technologies from Australia presented a novel technology specifically developed for use with TPE seals using generic double-sided PSA tape. The tapes are used in conjunction with a patented film interlayer, which is introduced directly into the extruder, thereby eliminating post manufacturing operations. Licensing agreements are being offered to promote new applications across a range of industries.
For increased product performance, NGF presented details of their modified surface treatments for glass cords used in weatherstrips and timing belts. The advantage for weatherstrips is said to be that it permits highly extended, low cost EPDM compounds to be used without significant loss of adhesion. For HNBR timing belts, improved product performance has enabled the belt to become a non-serviceable component.
This Rapra conference is biannual, and the next event is scheduled for February 2008. For further information, contact Dr. Sally Humphreys, tel.: +44 (0) 1939 250383; fax: +44 (0) 1939 251118.
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|Date:||Mar 1, 2006|
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