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From bomb-proof bonding of bodywork parts to easily detachable sticky notes, adhesives not only need to bond, but also let go at the right time. This, in turn, raises the importance of adhesive raw materials whose chemical flexibility enables them to be adapted easily to a range of different substrates. With its ethylene-vinyl acetate copolymers (Levamelt), Leverkusen-based chemicals group LANXESS is driving forward the development of made-to-measure adhesive solutions. Last year, important testing standards in adhesives technology were established in the LANXESS rubber technical service center. Levamelt formulations have also helped LANXESS to solve the problem of aging-related increase in the pull-off and peel strengths of many adhesives.
“The market for adhesive raw materials is showing particular promise, and the prospects make for interesting reading,” says Michael Herrmann, adhesives expert in the LANXESS Technical Rubber Products business unit. “In 2004, some 9 million tons of polymers were used for adhesives around the world. This market is, therefore, larger than the technical rubber products market, where our business unit is enjoying success with high-performance rubbers - though it is much more diversified.
“However, this opens up considerable possibilities for a product such as Levamelt. We believe we have excellent prospects of winning market share on the specialty products market and of providing a better alternative to popular adhesive raw materials.”
Levamelt adhesive raw materials yield a range of benefits that make them ideal for use in special applications. For example, the polarity of the rubber can be adapted to the properties of the substrates being bonded by altering the ratio of vinyl acetate component in the polymer. In particular, the choice of suitable Levamelt grades ensures easy detachability free of residues. In this case, the user is not only reliant on the products supplied by LANXESS (with a vinyl acetate content of 40-80%), but all Levamelt grades can be mixed with one another with excellent results. Blends can also be produced with other polymers that significantly expand the opportunities of traditional adhesive “modular systems.”
“Levamelt adhesives are not only ideal for use in detachable stickers or films that protect new cars on their way to the dealer, they could also be used in the future in sheet-metal building cladding to prevent scratching prior to installation,” Herrmann says.
This innovation required a considerable amount of development input since prolonged storage at high temperatures causes an increase in the shear strength of many conventional adhesives, partly as a result of gradual polymer “flow” into ever-finer surface details. When this happens, the force required to remove the film increases.
“We can now counter this challenge with an effective solution - an additive called Mersolat, which ensures even bonding over a significant period of time and at temperatures of up to 120°C when added to the Levamelt formula in quantities as low as 0.5%,” says Herrmann. Notably, this additive has long been used successfully to reduce static charge in the plastics sector.
Further Levamelt applications include hot melts, which exhibit a broader service temperature interval, thanks to the EVM with its adjustable and higher glass-transition temperatures, or stickers that can not only be detached after use without leaving a residue, but can also be used several dozen times and may therefore develop into a real problem-solver in the advertising sector.
“We are convinced that many challenges in the adhesives sector can be met using Levamelt - and we are structuring and focusing our efforts on harnessing these new opportunities for our customers,” Herrmann says.
For more information, visit www.us.lanxess.com.