28 августа, 2015 
Pokraskin A primer is a coating system that is additionally applied to a surface to be bonded prior to the application of the adhesive in order to protect the surface against uncontrolled, environmentally induced changes, or to improve the adhesion of an adhesive applied subsequently. In general, primers are highly diluted polymer solutions that wet the surfaces very well and sometimes may even remove minor impurities. Currently, due to problems posed by solvents, systems in the form ofaqueous solutions or even dry powders are also used, and may be applied by electrostatic means. Primers are generally applied at a dry-film thickness of a few micrometers.
From a chemical standpoint, primers may be similar to adhesives — that is, they may be cured separately when reactive components are used. In this case, their only purpose is to improve wetting and to protect the surfaces until the adhesive is applied. In particular, adherents coated with cured primers may be stored for up to three weeks (and even more) before application of the adhesive, and without any
impairment of adhesion quality. From experience, we know that it is less critical if contamination occurs on the primer rather than on freshly pretreated metal surfaces. Moreover, any contamination may be removed, if necessary, by using mild cleansers and without impairing the adhesion properties. As a consequence, primers may serve as useful auxiliary agents that can be used in order to provide for production steps, without any time constraints.
However, the composition of a primer may differ from that of an adhesive in order to obtain a specific effect on adhesion and corrosion resistance. As the primer coats are thin, the deformation properties of the primer do not play a predominant role within the overall joint. Therefore, it is preferable to incorporate any components which would adversely affect the adhesive into the primer; examples are inorganic pigments or brittle resin components, as well as adhesion promoters (see Section 5.10). The use of primers may also have an economical bearing since, owing to the small amounts of primer needed, adding these components to the primer may be cheaper than incorporating them into the adhesive. For example, if curing primers based on epoxy resins are used, then relatively cheap polyurethane adhesives with good plasticity may be applied later. But, without the use ofthe primer, their adhesion would have a weaker resistance to water, particularly on aluminum and steel alloys.
Although, the various possibilities of optimization that can be achieved with primers are often not well recognized, they may outweigh the disadvantage(s) of introducing an additional production step.
Опубликовано в рубрике 