JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011 - 43

a gelcoat which handles well and would be easy to apply by spray or brush. Five years later, this objective has been achieved with the successful development of Crystic Permabright marine-approved gelcoat, with its new D-Iso/NPG advanced resin chemistry.

What is a D-Iso/NPG resin?
This new D-Iso/NPG unsaturated polyester resin technology is unique to Scott Bader. It took over three years of research to develop this new resin chemistry, which derives its superior UV weathering properties from the chemical structure of the resin having a deconjugated polyester backbone. After many laboratory-scale formulation tests and trials, it was discovered that a deconjugated Iso/NPG polyester was much more resistant to degradation from sunlight and UV radiation. Further tests demonstrated that, when used as the base resin for a white pigmented gelcoat, the deconjugated polyester resin made a significant contribution to reducing yellowing and improving gloss retention.

Gelcoat formulation
Scott Bader’s Gelcoat technology team has long understood the importance of having not just the right base resin for a gelcoat matched to specific application needs, such as blistering and UV resistance for exterior marine applications, but also the need for other key ingredients in a gelcoat formulation to provide the best overall performance. Pigments and UV additives both play a critical part in the overall long-term weathering resistance of a gelcoat. As part of the development stage, significant R&D work was also carried out to evaluate all available pigments and UV additive combinations. They identified the best combinations in a gelcoat formulation which enhance weathering performance. The combination of the three critical factors of the base resin, the pigment and the UV additives is the key to having outstanding gelcoat weathering

For both sprayFig.1: Gelcoat UV weathering depends on three critical factors: base and brushresin chemistry, pigments and UV additives applied gelcoats, the new D-Iso/NPG polyester base resin has been combined with best-inMeasuring colour change class UV protection additives, only The accepted industry standard to using selected pigments in white, offmeasure a colour is to use the CIE white and cream colours which are able colour space L* a* b* values (Figure 2). to provide the highest level of longThe test results give delta E values, term colour stability. All the pigment which measure the total change in pastes used are proprietary, colour before and after exposure. Delta manufactured by the Company using b* is the specific measure of the colour their in-house milling and mixing change from blue to yellow. As facilities. reducing the yellowing of white and cream-coloured gelcoats was a critical The importance of having the right factor, this was a key colour change pigments and UV additives has been measure for this project. recognised by the team for a considerable time. This has been demonstrated by the proven long-term performance of existing Lloydsapproved marine-grade Crystic Iso and Iso/NPG gelcoat products, which have been successfully used for over 45 years in marine and other market applications. performance (Figure 1). Other additives were also evaluated in the overall formulation with respect to rheology, air release and handleability.

Colour stability testing and measuring

The prime objective was to develop a gelcoat with exceptional gloss retention and colour retention. This has been achieved with Crystic Permabright, which has undergone both QUVA and Xenon arc accelerated testing for colour change, as well as rigorous 12-month Florida natural weathering testing. Comparative colour change test results were obtained from plaques made and tested at the same time, measured accurately using an established methodology.

No67 August - September 2011 / jec composites magazine

Fig.2: CIE colour space L* a* b* values used to measure colour change in a gelcoat

Comparative colour change tests

The gelcoat was tested against a range of best-in-class white gelcoats which currently exist. The test plaques were made from gelcoats manufactured by both Scott Bader and competitor producers. A standard Iso gelcoat was tested alongside top-performing Iso and Iso/NPG marine-approved gelcoats.

Feature marine

JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011