Elsevier

European Polymer Journal

Volume 39, Issue 11, November 2003, Pages 2235-2241
European Polymer Journal

Characterization of UV-cured polyester acrylate films containing acrylate functional polydimethylsiloxane

https://doi.org/10.1016/S0014-3057(03)00133-2Get rights and content

Abstract

Acrylate functional polydimethylsiloxane (AF-PDMS) was tested as a reactive additive in UV-curable coating formulations. Pencil hardness, solvent resistance, and gloss of the UV-cured films were measured to study the influence of AF-PDMS content on coating properties. Depth-profile analysis by FTIR-ATR and Raman spectroscopy was also performed to investigate the effect of AF-PDMS on the behavior of film formation during UV curing. The kinetics of photopolymerization were monitored by photo differential scanning calorimetry (photo-DSC). Our results show that AF-PDMS containing coating formulations are very sensitive to oxygen inhibition, so that an inert environment such as nitrogen purging is required to avoid coating defects.

Introduction

The development of any coatings is generally a compromise between performance attributes (both in terms of the properties of the finished coating and the application of it) and cost. Neglecting the cost aspects for the moment, the first stages of the development of a coating concentrate on the polymeric binder. For a radiation-curable coating, this aspect is the same situation whether it is an epoxy, polyester, or urethane oligomer. Having chosen a suitable oligomer, the cure characteristics are considered. This is usually a compromise of photo-initiator level and type as well as functionality level. Lastly comes the additive package designed to cover the holes in the property portfolio or application method. While this may be a gross oversimplification of the development process of radiation-curable coatings, there can be little doubt that the additive package is usually the last resort of a frustrated formulator and its development is often afforded “art” status [1]. The most prevalent additive used is silicone. The use of silicone additives has progressed from the early days of polydimethylsiloxane (PDMS), as it is commonly known [2]. In addition to changing the surface tension of the coating, silicone additives also influence other properties such as slip, leveling, and mar and scratch resistance. PDMS contains no chemical groups that could take part in the cross-linking reactions of any binder. Therefore, it may be removed (at least partly) from the coating surface relatively easily, e.g., by cleaning the surface with solvents. This means that the improvement to wetting, slip properties, and scratch resistance by PDMS is only a temporary effect that gradually reduces as the concentration of silicone in the surface decreases. Thus the ability to incorporate and fix silicone functionality into a film has much appeal. Radiation-curable silicones offer this possibility, and radiation-curable silicone oligomers and monomers are now widely used in numerous applications. Any method of fixing silicone requires that reactive groups are attached to the PDMS structure. There are three approaches to preparing radiation-curable silicones: thiol/thiolene-type silicones, cationic epoxy silicones, and acrylate functional silicones. However, it is claimed that acrylate functional silicones offer the best comprise of overall properties, including better shelf life and producing fewer side effects [3], [4], [5]. Although many studies have investigated acrylate functional silicones [6], [7], [8], [9], [10], little attention has been given to depth-profile analysis of coating films containing AF-PDMS.

In the study reported in this paper, various methods were used to analyze the influence of the amount of AF-PDMS on the surface properties and the morphology of UV-cured films. In addition, the distribution of AF-PDMS in UV-cured films was observed at the film–air (FA) and film–substrate (FS) interfaces using FTIR-ATR and Raman spectroscopy.

Section snippets

Materials

Polyester acrylate (Ebecry 830: UCB chemicals) and trimethylol propane triacrylate (TMPTA: Miwon) were used as the oligomer and the triacrylate monomer, respectively. Tripropylene glycol diacrylate (TPGDA: Miwon) and 1,6-hexandial diacrylate (HDDA: BASF) were used as the diacrylate monomer. 2-Hydroxy-2-methyl-1-phenyl-propane-1-one (DC 1173: Ciba-Geigy) was added as the photoinitiator. The chemical structure of the silicone acrylate (α,ω-acryloxy organofunctional PDMS: Goldschmidt) used in the

Results and discussion

The effect of the inclusion of AF-PDMS on the surface properties of the UV-curable coating is summarized in Table 2. As the concentration of AF-PDMS in the formulation increases from 0% to 5%, pencil hardness increases to a maximum value for a concentration of 1% and then decreases at higher concentrations. It is apparent that solvent resistance and gloss show the same trend as pencil hardness. The first question is why there is a peak in the surface properties of coating film. It is expected

Conclusion

The effect of the amount of AF-PDMS included in UV-curable coatings on the properties of the cured film has been investigated. We have demonstrated that less than 1 wt.% of AF-PDMS should be added into a UV-curable polyester acrylate-based coating. If the AF-PDMS content is greater than this, surface and bulk properties decline dramatically. The depth-profile analysis shows that the degree of cure at the FA interface is higher than that at the film–substrate interface, which is due to oxygen

Acknowledgements

This study was supported by research funds from Chosun University, 2002.

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