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Polymers have low-energy surfaces and are difficult to be adhered by waterborne inks due to their higher surface tension. An approach to prepare acrylic resin used as binder for waterborne printing inks on plastic films with excellent adhesion and water resistance is described in a study.

The epoxy resin is incorporated into the acrylic resin to enhance the molecular interactions between binder molecules in ink and surface molecules of plastic film.

Adhesion improvement with NHMA

The binder resin is obtained by esterifying epoxy resin with methyl acrylic acid and then co-polymerising the product with several acrylic monomers. The acrylic resin modified by bisphenol A epoxy resins (EP-MA-AR) shows significant enhancement over the acrylic resin without modification (AR) in adhesion between ink and PET film surface as well water resistance performance. N-hydroxymethyl acrylamide (NHMA) is introduced into the recipe to further enhance the interactions between the polymer chains in ink and the polar groups on the surface of non-polar PP film caused by the corona discharge treatment and improves the adhesion between ink and surface of PP film dramatically – whatever using AR or EP-MA-AR as binder.

EP-MA-AR as applicable binder

The adhesion between ink and PET film surface is also further improved by this method. The water resistance of AR and EP-MA-AR is also greatly improved under the appropriate content of NHMA. Two Tgs appear on the DSC curve of EP-MA-AR, suggesting the separated status of the epoxy modified acrylic chains and the acrylic chains without modification in EP-MA-AR. The experimental data of waterborne ink on PET and PP indicate the EP-MA-AR resin prepared in this way is an applicable binder of waterborne ink on plastic film.

The study is published in: Colloids and Surfaces A: Physicochemical and Engineering Aspects.