Laser marking of double coated board, 2012 Advanced Coating Fundamentals Symposium

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In the production of a multi-layer coated board, manufacturers have to balance many different properties and have access to a wide range of pigments, binders and additives to achieve this balance. As the major component of the coatings, the pigments play a significant part in controlling the properties. In many parts of the world, kaolin is more expensive than calcium carbonate and this leads to minimising the proportion of kaolin.

Previous work has shown the benefits of kaolin in precoating, in terms of coverage (both physical and optical) and smoothness. In addition, it has been shown that varnishability and topcoat binder demand can be affected. Some kaolin is also used in topcoating, primarily for gloss and printability.

In this work, we show how the distribution of calcium carbonate and kaolin can affect how effective laser marking is, both for unprinted and pre-printed coated board. A series of topcoats with increasing kaolin content was applied to two precoated boards (with and without kaolin). Two laser systems were used that had different wavelengths. A combination of optical microscopy, profilometry, infra-red spectroscopy and scanned images has been used to characterise the laser marked samples.