Page 74 - Handbook of Adhesion Promoters

4.2 Surface treatment 67

Figure 4.14. Schematic diagram of corona discharge system. [Adapted, by permission, from Kim, K; Seomoon,
K, J. Ind. Eng. Chem., 47, 150-3, 2017.]

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corona discharge voltage and a decreasing film transfer speed. The interfacial adhesion
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was enhanced by treatment with a mild corona discharge. Figure 4.14 shows a schematic
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diagram of corona discharge system. Concentration of the alkyl methacrylate vapor was
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kept at 1 wt%. The corona discharge helps to incorporate oxygen in the form of O=C−O,
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C−O and C=O groups, changing the surface to more polar state. At a high discharge
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(voltage over 5 kV), corona-treated PVDF films exhibited poor adhesion to PVC.
Corona discharge and ultraviolet radiation treatments have been used as environmen-
tal friendly alternatives to the common surface treatment of halogenation for a styrene-
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butadiene-styrene rubber. Corona discharge and UV radiation treatments modified the
−
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rubber surface by creating C–O, C=O and COO moieties that improved wettability. The
corona treatment of styrene-butadiene-styrene rubber only slightly increased adhesion to
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polyurethane adhesive − explained by the lack of improvement of surface roughness.
The rapid ageing of corona discharge pretreated surfaces is a well-known problem. 35
Oxyfluorination process combined with the corona discharge treatment offers durable
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treatment.
Corona discharge is currently the most common method used for preparing poly-
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meric materials for printing, lacquering, metallizing, and adhesive lamination. The
corona discharge treatment increases surface energy, introduces surface crosslinking,
modifies surface morphology by increasing or reducing its roughness and crystallinity,
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and removes dirt and weak boundary layers. Figure 4.15. shows changes in surface mor-
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phology of poly(lactic acid) caused by corona surface treatment. Further details about
corona treatment of polyethylene, poly(ethylene terephthalate), polypropylene, polyvinyl-
chloride, ethylene vinyl acetate, polystyrene, and poly(lactic acid) can be found in a book
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chapter. The chapter also contains analysis of the durability of treatment of various poly-
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mers. Considering that it is easy to apply treatment as an in-line process, there is no need
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to delay its further processing.