Surface wetting

For all printing techniques, the surface energy of the wet ink should be lower than the surface energy of the substrate to achieve good surface wetting and a uniform ink distribution. If the surface energy of the ink is higher than the surface energy of the substrate, the contact angle of the liquid will be large and the liquid beads up and forms into globules, so that the wetting of the surface will be poor. If on the other hand, the surface energy of the substrate is equal to or higher than the surface energy of the liquid, the contact angle will be low and the ink can be spread evenly across the surface.

Special kits are available to test the surface energy of the substrate by applying liquids with known surface energy levels and watching the reaction. The test kits normally contain six to eight fluids, and are available in felt-tip pen form.

It is important that no additives used in the substrate , or added color masterbatches, can migrate to the surface. This may affect surface tension in a negative way and lead to an irregular thickness distribution.

Climatic conditions, like temperature and humidity, should be well-controlled for a good, reproducible printing result.

Foam molded parts cannot be printed immediately after molding. The gases produced by the foaming agents must first reach equilibrium with the ambient air. This outgassing may take 24 to 48 hours, depending on temperature and humidity. Premature printing may cause blistering.

Relation between surface contact angle and wetting of the surface by the ink

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•Surface wetting
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