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Latent-reactive adhesives for precoating of metal parts
Updated: 2006-03-08 00:00 Source: share:

Innovative raw materials developed by Bayer MaterialScience AG make possible the formulation of thermoactivated adhesives for an extended range of applications – and they also join metal and plastic better than ever before thanks to a waterborne dispersion layer. Using a new latent-reactive precoating for metals or other substrates, the Coatings, Adhesives, Sealants Business Unit (CAS) of Bayer MaterialScience has succeeded for the first time in creating a force transmitting adhesive bond to plastic melts. The company achieved the decisive breakthrough via the modified use of thermoactivated adhesives formulated with its own Dispercoll® U line of products. This method will allow such disparate materials as metal and plastic to be more effectively bonded in the future, and also offers numerous other advantages over conventional joining methods.

Hybrid components of coated or uncoated metal and thermoplastics, for example, previously could only be manufactured by means of a positive connection between the components brought about by an injection molding process. Thermoactivated adhesives now make possible a much more practical method. The trick: The waterborne, latent-reactive polyurethane dispersion layer – on average less than 100 micrometers thick – can be applied to the insert and dried quite some time prior to the actual bonding. This layer remains stable and block-free at room temperature. It is only later during injection molding or extrusion that the hot plastic melt of the hybrid partner initiates the bonding of both parts. Whereas good initial strength is achieved at contact temperatures from 70 to 80 degrees Celsius, a crosslinking reaction initiated in the same process step quickly enhances the initial strength to achieve a greater and largely irreversible final strength. The flat adhesive film on the insert surface not only bonds directly to the hardening melt, it also joins disparate substrates better than before with improved migration protection and exhibits significantly optimized heat stability
For the user this means that the application of the adhesive and the final production of the adhesive bond do not have to be
performed at the same time or even in the same place. A supplier can, for example, perform the first step and send the parts coated with the adhesive film on their way “ready for processing.” A classic win-win situation for all involved – the expanded range of services provided by the supplier allows its customers to streamline their logistics.

In addition to the use of innovative thermoactivated adhesives for hybrid metal/plastic components, Bayer MaterialScience can – as a supplier of raw materials – also imagine the use of textiles or films applied via back injection, for example in the automobile industry. The potential range of applications is very broad and after successful testing is not limited to metal inserts, where it has already proven effective. “The development of this novel bonding technique has positioned us as a source of ideas for the relevant industrial sectors,” said Dr. Horst Stepanski of the BU CAS Business Development department. “We are now very interested in seeing how much of this sticks with our contacts following this initial step.”

 

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