Coatings World - June 2014

Abstract

UV curing processes have been used extensively in many different industries such as packaging, printing inks and protective coatings for wood, plastics and metal. Advantages of UV curing are instant drying, low operating cost, improved quality and reduced space.

Waterborne UV curable coatings – green coatings – have been developed to replace conventional UV curable coatings with VOC emissions. It can be a challenge when light stabilizers are required to protect coatings to UV degradation.

The novel light stabilizer (NLS) is developed specifically for waterborne UV curable coats. This article is a comparison study of three different light stabilizers to disperse in water and waterborne UV curable coating. Test data showed that NLS in a waterborne clear UV curable coating would not have negative impacts to cure speed. The results confirmed that by increasing the concentration of NLS in the top coat can effectively protect from UV light degradation.

Introduction

UV curable coatings require direct UV light to initiate monomers and oligomers. It is converted from a liquid into a solid film. UV curing coatings feature speed in production and are faster in drying. However, most polymers are susceptible to degradation by UV and visible light. It requires light stabilizers to enhance the durability from sunlight degradation. To understand more on the light stabilizers, it can be divided into two groups: UV absorbers (UVA) and the Hinder Amine Light Stabilizers (HALS). UVA’s function is absorbing UV light and transforming it into heat and the HALS is best known to capture free radical to prevent material degradation.

It is important to know UV curable coatings especially in
dry faster system. Photo initiator absorbs UV energy to initiate
curing processes. UV absorber absorbs UV energy to prevent
coatings damages. As a result, UV absorber and photo initiator
are competing for UV energy to cause negative impacts about
cure speed. The NLS can meet this problem.
UV radiation is a well-accepted technology. However the UV
curable coatings have odor, emission monomers and not zero
VOC emission .
The UV curable waterborne coating has both the advantages
of waterborne coating and UV curable coating such as non tox-
ic, pollution-free, and safety in use. In recent years the research
and development has grown faster.

This subject of this article is to show the use of newly developed liquid NLS, designed for waterborne UV curable coatings, is effectively to protect from UV light degradation and would not have negative impacts to cure speed.

Experiment

The model formulation used in this study was classification of light stabilizers and compositions of waterborne UV curable coating. Their detail compositions are shown in Table 1 and Table 2. Design of Experiment (DOE) was used to design test runs as well as to analyze test data. DOE technique allows us to validate the data.