tailieunhanh - Coatings of Polymers and Plastics Part 8

Tham khảo tài liệu 'coatings of polymers and plastics part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 164 Yaneff Simple adhesion testing can be done by applying some sort of scribe into the painted part followed by applying a piece of tape rubbing it to ensure good adhesion and then rapidly lifting the tape in an upward motion. An example of this type of adhesion testing is ASTM D 3359. While many adhesion test variations exist cut patterns types of tape pull rates they all can quantify the amount of paint delamination numerically or relative to a standard. Low surfacetension agents in the coating can artificially reduce the adhesive strength of the tape to the coating and thus give false readings. Removing the surfactant from the surface through solvent wiping can ensure more meaningful and representative results. Multiple paints passing the tape adhesion test does not necessarily differentiate between adhesive strengths and more sophisticated testing can be useful. Peel strength testing can be performed on painted plastics using a tensile tester 7 . This destructive test procedure can give the energy necessary for paint removal and allows the comparison of one paint to another. More recently an in situ adhesion test described as compressive shear delamination CSD has been reported to quantify the adhesive cohesive strength of coatings to a variety of TPO substrates 8 that eliminates the artificial film between the paint and the adhesion promoter. Not only is adhesive testing carried out under dry conditions but also under wet conditions. Exposing the painted part to a humidity chamber typically 100 relative humidity at 38 C for 96 to 240 hours can increase the likelihood of paint delamination as moisture can penetrate through the coating layer into the substrate. Increasing the temperature to 140 or 160 C as in the Cleveland Humidity Chamber can further test the adhesive properties of the painted part. With the formulator performing testing under conditions that are much more severe than specified by the OEM it is likely to increase the chance of success at the .