Degree of Cure Measured by Means of Extraction Techniques and FFIR Spectroscopy as a Function of Dose and Light Intensity

The reactive monomer diluents used in UV-curable formulations play a major
role. An ideal diluent should not only be an efficient viscosity reducer, it should
also have a low volatility, a high curing rate, a high degree of conversion and a
low toxicity. Since a complete polymerization is never achieved, there will
always remain a residual amount of uncured monomer in UV-cured systems
which might adversely affect their long-term properties. There are several ways
to improve the curing performance. One is to optimize the photoinitiator
concentration so that a sufficient light absorption is maintained throughout the
coating. An additional way is to optimize the radiation source so that its
emission spectra more efficiently overlaps the absorbance of the photoinitiator.
A third way is to increase the intensity of the incident radiation. This paper
deals with the last alternative. For most systems, a good compromise is to
optimize and combine all three alternatives.

It is clear that an increase in incident light intensity theoretically will increase
the rate of iniatiation and subsequently the rate of polymerization will be
affected.

The characterization of radiation curables involves many analytical techniques
such as Infrared spectroscopy, Differential Scanning Calorimetry, Gas
Chromatography, Thermogravimetric analysis, Ultraviolet spectroscopy etc. A
particularly interesting Real-time IR (RTIR) technique has been used by
Decker. In this study the effect of light intensity on the curing of acrylate
formulations with different functionalities and a difumarate/ divinylether
formulation is reported. The curing was assessed by FTIR spectroscopy and by
extraction and gas chromatography analysis of residual monomers.