Лако-красочные материалы — производство

When a designer is selecting an adhesive for a specific application, the engineering properties of the individual plastic will be considered carefully. All too often, however, the data supplied by the plastic manufacturer will include melting point, mould shrinkage, tensile modulus, hardness, dielectric properties, water absorption, density and thermal conductivity but almost never the surface energy of the plastic, which is one of the key properties required for the adhesive application engineer.

The use of surface-tension pens is a simple technique to measure surface energy. Each pen contains ink of a known surface tension and if the ink ‘globulates’ or breaks up, the surface energy of the tested surface is lower than the ink and if the pen is seen to write without the ink breaking into smaller particles, the surface energy of the tested surface is higher than the ink. The use of pens with different inks therefore provides a reasonably accurate measurement of the wetting properties of the tested surface. Most engineering adhesives have a surface tension of approximately 33 mN/m and the plastic needs only to be just above this for the adhesive to wet the surface and therefore bond. The degree of adhesion may well depend on other factors such as surface finish, the gaps between the mating parts and the type of plastic, but once the adhesive starts to wet the surface some degree of adhesion should be obtained. Unlike metals, plastics and elastomers do not have the large difference between the critical surface tension of the substrate and that of the adhesive and so when poor wetting occurs, there are methods to treat the surface for better bonding.