Pinneberg/Germany, March 17th, 2017
The material polypropylene shows different end results even when using the same primer. It depends on the previous processing of the PP and, for example, whether it is a syndiotactic or atactic PP.
To evaluate the suitable primer, it is usually applied on the plastic and is then coated by a varnish or another finish. This specimen generally undergoes the cross-cut-test.
In this test, the coating is scratched through to the substrate with a cutter knife. The optimum process should result in 10 squares 1 x 1 mm in size. The adhesion then is verified with an adhesive tape. This is a fast test but it only provides information about sufficient or insufficient adhesion. In general, the primers of the TRAPYLEN®/TRAPUR® product ranges pass this test. But a detailed distinction as to the particular adhesion strength is not available.
Further on the values determined vary considerably because of, for example, modified tension forces caused by tilting.
New testing procedure in use
TRAMACO GmbH has been using the LumiFrac appliance by the company LUM GmbH for the development of new products since 2016 which significantly facilitates the testing of adhesion pow- er and produces repeatable results. The principle is easy to ex- plain and easy to apply.A defined stamp is bonded with a plastic molded part or a foil which previously had been coated with a primer. This specimen is put into a measurement cell in a centrifuge. The centrifuge rotates as long as the stamp peels off from the surface due to the centrifugal forces caused by the rotations. This testing re- sults in an adhesion strength which is measured in Newton. Up to eight measurements can be carried out at the same time. Another advantage is the process time of a few minutes.
Actually TRAMACO offers its customers the possibility to measure substrates which had been coated with TRAPYLEN®/TRAPUR® to find the ideal primer for the customer’s application.