Pre-Applied Wood Adhesives Open Production PossibilitiesIn industrial production, bonding plays an increasingly important role. Researchers have now succeeded in separating the processes of applying adhesive and the actual joining, opening up a new world of opportunities in woodworking and metalworking applications.

Adhesive bonding, especially in lightweight construction, is the preferred technique for joining wood, metal and other materials. However, since liquid adhesives need time to cure, they cannot be applied in every production step. Automotive supplier STANLEY Engineered Fastening – Tucker GmbH in Gießen turned to the researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Bremen, Germany, for a solution. They developed a process in which the adhesive is deposited on one of the parts and then dried to form a non-sticky layer. During a later step, the adhesive is hardened and the two parts are bonded together. Although two-step bonding techniques aren’t new, using them for industry is. And IFAM researchers have successfully developed a technique to allow a high-strength adhesive bond for industrial use.

“Once the adhesive is applied, it can’t be tacky and it has to withstand long storage times,” explains chemical engineer Andreas Lühring from Fraunhofer IFAM. But the adhesive has to do more than that. “The adhesive also has to be very reactive and harden quickly during joining.” The researchers’ concept combines resins and hardening agents that melt at different temperatures. “We use micro-dispersion to finely distribute hardening agents with considerably higher melting points throughout the resin base,” adds Professor Andreas Hartwig.

The resulting reactive, hot melt adhesive is used on fastening bolts, for instance. First the material is heated and then applied onto the fastener. After it cools, it solidifies again. The fastener can then be transported and stored without difficulty. To harden the actual adhesive, it must be heated to more than 150 degrees Celsius in a controlled way. “Only then is the actual hardening agent melted and the adhesive activated,” says Lühring.

IFAM experts also altered the composition of the adhesives so that they yield the best productivity and characteristics for a wide variety of wood and metal applications.

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