Adhesive strength
Stability of the bond between a substrate and an attached coating or bonded joint. A value for the separating force (peel test, end load test) is to be directly applied as a criterion for the adhesive strength for bondings. In principle, however, a good adhesive strength is present if the adhesive force is higher than the cohesive force of at least one of the two bonding partners. This is the case when separation of adhesion occurs not by dissolution of the bond but by material breakage in one of the bond partners. Sufficiently good adhesion is present when the applied substance (coat, adhesive) wets the substrate completely. Wetting can be tested by:
Independent of the substrate and the coating, ist fast immer eine pretreatment is almost always required to achieve sufficient adhesive strength, because in almost all cases there are some factors impairing the adhesive strength. This pretreatment includes at least one or several of the following work steps:
- Cleaning:
In particular, removing the hydrocarbons (release agents, oils, greases). Plasma cleaning can remove these substances without any residues - Activation:
It is a prerequisite for adequate adhesion that the surface energy of the substrate is higher than the surface tension of the coating. By means of plasma activation , the surface energy can be increased to ensure sufficient adhesion in practically any material pair. - Surface enlargement: As a result of the larger effective interface, the adhesive strength on a (cleaned, activated) rough surface is higher than on a completely smooth surface.
Surface roughening (surface enlargement) is achieved by mechanical roughening: grinding, sandblasting - Etching: wet chemical etching, plasma etching, and micro-sandblasting
- Removing oxide layers:
Oxide layers can be removed by plasma treatment. entfernt werden.
