My coating is seeing blocking issues; but what’s my option dealing with it?

Ole Martin Kristiansen | July 24, 2018

A familiar problem for producers of coatings and polyolefins is what literature calls blocking. When blocking occurs, it is the coatings ability to create adhesion to itself that causes the problems. There are many available technologies for avoiding this, in which some are synthetically derived, and others are derived directly from nature. Could a bio-based alternative give you the effect you are looking for? If you are looking for some ideas, this is the blog post to read.

What is blocking exactly and what is causing it?

There are several entrance points to the issue of blocking:

  • You are an industrial interior and furniture producer and would like to improve your warehouse performance (higher number of products in stock per m2 for instance). Your economy of scale means that you need to have an efficient warehouse
  • You are a consumer who has just purchased a coating for your 10-year-old windows and are about to re-paint. But you need to be fast and be able to close the windows fairly fast too.
  • You are a coating producer formulating new low-VOC or no-VOC waterborne coatings and you struggle with the blocking functionalities of your new paint.

In the two first cases, there are obvious end-user demands that requires a set of functionalities from the paint or coating. I have been painting doors and windows where weather conditions or other situations have forced me to close the items I have been working on or stacking them together. For large industrial producers, warehouse management is becoming an increasingly hot topic these days (read: automation and size efficiency). Many solvent-based coatings have been showing proper anti-blocking properties for ages. But the increased use of waterborne systems, which often creates a softer surface during drying (especially earlier stages), tend to create more problems with parts sticking to each other. It is also a more profound issue in high-gloss paints than low-gloss or flat paints. This is due to the rougher surface of the flat paints.

How can you solve blocking?

Sherwin-Williams, one of the largest producers of coatings and paints in the USA, are giving the general advice to either paint with an oil base or using a high quality semi-gloss or gloss latex with good blocking resistance. Primers can be used as well, but in industrial process this will take more time. Thus, there are alternatives on the additive side to cope with the problem, but it is very important that the additives do not affect the film formation negatively. Surface active additives have historically been used, which act as a release layer between two touching coating films.

Another option is to add an additive that can reinforce the surface. Colloidal silica is a good alternative, it makes the surface more hydrophilic which is allowing moisture to be entrained by surfaces during drying and this reduces tackiness. Silicone fluids are also used to increase the ability for two surfaces to slip past each other instead of sticking.

In addition, the newly developed cellulose fibril technology (where the fibril is nano in width and micro in length, and provides very small micro-networks) is starting to prove itself as an anti-blocking additive as well. The reason behind this technology working is in its small fibrils, and the way the film formation is taking place on the surface. So it may be an interesting alternative for new developments on anti-blocking or a new tool for trying to solve problems with the blocking effects.

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Written by:

Ole Martin Kristiansen

Ole Martin is the Marketing Manager of Exilva in Borregaard. He holds a bachelor's degree in Media Management and has been with the company since 2017.