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UV technology represents a good choice for the development of low VOC products. Nevertheless there are some problems. A 100% solid content system avoids emissions into the environment, but users have to deal with skin-irritant or sensitizing materials and, technically, formulators are faced with difficulties in matting. A less than 100% UV system opens up the possibility of getting good products for open pore wood applications, but solvents are introduced into the atmosphere. In recent years raw material suppliers have tried to develop alternative systems, promoting waterborne UV systems as one of the best for the future. This technology offers many advantages among which we can list the following:
- Friendly' products, both for humans and the environment
- Lacquers that don't need immediate irradiation, so are easier to handle
- Paints with good chemical resistance
- Easy to matt systems
- Both economical and technical advantages due to the low amount of photoinitiator required in
the formulations
- Good adhesion on wood substrates, due to the high molecular weight of the binders leading to
a decreased level of shrinkage during UV curing
- Products less sensitive to oxygen inhibition compared to the standard UV systems
Possible disadvantages could be:
- Lower speed of cure
- Inferior hardness of the paints
- Higher price
Together with the environmental benefit, ease of matting can be considered as one the best features of this young technology. Water evaporation avoids VOC emissions and provides the shrinkage necessary to achieve matt films. Because of this big difference compared with 100% UV systems, the silica grade can be chosen following the known "matting rules": the lower the treatment and the coarser the particle size distribution the higher the final matting effect. Various silica types perform well from this point of view, but often in selecting the matting agent other important features, above all those affecting rheological and surface parameters are not taken into consideration. This work evaluates the possible benefits achievable using silica gel based matting agents compared to other product types in UV curing waterborne lacquers, when focusing on selected critical features, such as viscosity behaviour, foaming and aeration, clarity and scratch resistance properties in addition to matting efficiency.
