Price: 10.00
One of the biggest difficulties encountered when formulating UV curable matt coatings with
matting powders is rheology control. Because UV systems are normally 100% reactive, there is minimal loss of volume on application. With 100% UV curable systems, 10% matting powder in the liquid means 10% in the solid film. There is no effective increase in powder concentration by solvent or water loss, so it is often necessary to use relatively high levels of powder matting agents. The high speed of the UV curing mechanism can also restrict the mobility and orientation of particulate matting agents. Application temperature control can help, but is difficult at high
speeds. Techniques for formulating powder free matt UV systems, such as controlled use of incompatible materials, or use of controlled drying under inert gases are known and have their niches, but the majority of us still formulate matt systems with matting powders.
It is our experience that high concentration of large particle size powders in UV coatings can lead
to the following practical application problems:
• Tendency to thixotropy and I or gelled structure, which makes a lot of common application
techniques less efficient (eg "ribbing" or "roller marking" seen with roller application machines). To compound the problem, these effects often get worse with time.
• Variation in the consistency of the liquid, leads to poor film weight control and inconsistent
gloss results.
• The powder settles out with time so that, in the worst cases, it cannot be remixed.
• Poor wetting of the powder can lead to "chalking" and reduces the desired film properties.
For many formulators (myself included) the first reaction to these problems has been to reduce
the formulation with the "lowest available viscosity" diluent, resulting in a coating that can be up to 50% diluent and with compromised properties. We set out to find the most effective ways to incorporate the most widely used matting agents into 100% free radical curing UV systems with consistent, controllable rheology. We will not present the level of matt effect achievable by our variations, or the effect of variable cure on matting properties (these two properties are the subject of ongoing study).
