The subject of water repellency often comes up in printing ink circles because there are a multitude of different needs and applications for those coatings that can impart varying degrees of water resistance to a substrate. Such uses include kraft paper bags, labels for beverages and other packaging containing detergent or other moisture sensitive food or chemicals. As we know, moisture can affect the shelf life of the contents of packaging, the freshness of the contents and the integrity of laminated packaging. In this article I'm going to focus on two main areas in the development of water based, water repellent varnishes: those coatings needed for water sensitive paper packaging for things like food and animal feed, and secondly those coatings needed for what are considered MVTR (or WVTR - Water vapor transmission rate) applications, which include items like detergent packaging.
MVTR is a measure of how fast water vapor will pass through a material under specified conditions. Specifically it is the measure of a specific volume of water vapor that will pass through a unit thickness of material per unit area per unit time per unit barometric pressure. Water repellency is the requirement of a coating to shed or repel any water that comes into contact with it.