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UV Coating - Overprintability and Adhesion PhenomenaPART II: Description of 4 Adhesion Phenomena Recommendations of Raw material Suppliers and Conclusion

SpecialChem / Nov 28, 2007

This is the second part of our article dedicated to UV-Coating and overprintability, in this part we present four other adhesion phenomena and recommendations of raw material suppliers for the design of overprintable varnishes. The conclusion gives a summary of the most important features leading to a set of criteria for the development of overprintable and glueable varnishes. Chemical adhesion occurs if a chemical bond is formed at the join. The strongest bonds are ionic and covalent bonding. A weaker bond is hydrogen bonding: formed if oxygen, nitrogen or fluorine atoms share an hydrogen nucleus. This theory states that if a proper adhesive bond is made, a lack of adhesion won't occur at the interface but will fail in either the adherent or the applied material. Bond fails due the presence of materials of low cohesive strength at the interface. Example of weak boundary layer are: - a polymer with low molecular weight additives at the surface, - an adherent with a greasy surface, - a polymer with low molecular weight polymer fractions at the surface.

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