To achieve a high-quality and strong bond, the structure of the substrate has to met certain requirements, which include:
1.The substrate surface must have good wetting properties, i.e. the chosen adhesive should not form beads on the substrate surface but must rather distribute itself across the surface.
2.The substrate surface must have good bonding properties, i.e. there must be intermolecular and chemical interactions with the adhesive molecules.
3.The surface layer of the substrate must be securely attached to the substrate.
4.After the bonding process, the surface must not change in an uncontrolled way. E.g. ground steel rusts even under the adhesive film if the bond is in a moist environment. To create a bond having good long-term stability, solely grinding the steel surface is inadequate, and additionally, suitable measures must be taken to prevent rusting under the adhesive film when using this steel component in a moist environment.
In general, the above-mentioned means treating the materials such that: in a production environment, conditions for bonding are created that guarantee reproducible bond quality; wetting and adhesion are improved; the long-term stability of the bonded joints is improved.
A distinction is generally made between three broad types of “surface treatment”, namely surface preparation, surface pretreatment and surface post-treatment. Surface preparation covers cleaning/degreasing and preparation of the substrate surface, e.g. deburring. Surface pretreatment includes all mechanical processes like grinding and jet-cleaning, chemical processes and physical processes that alter the structure and/or chemical composition of the surface, relative to the starting base material. For example, the surface pretreatment of polyethylene is mentioned here. Without such pretreatment polyethylene is difficult to bond. The technique used for this pretreatment is the so-called corona method. In order to improve the adhesion properties for the manufacture of laminated films, electrical discharges in the presence of atmospheric oxygen at voltages of up to 60,000 volts are allowed to act on the materials. Surface post-treatment covers all techniques that serve to preserve the treated surface, e.g. application of a primer.
This article is reproduced from Adhesives.org/Sealants.org.