Powder Coatings: New Advances and Remaining Challenges Dr Tom Straw AkzoNobel Powder Coatings

1. NEPIC INNOVATION DAY 15 November 2011 Powder Coatings: New Advances and Remaining ChallengesDr Tom StrawAkzoNobel Powder Coatings

2. 01 What is a Powder Coating?

3. What is a Powder Coating? Market Size Segmentation Producers Source: Akzo Nobel Powder Coatings Competitor Survey 2009

4. What is a Powder Coating? A solid thermosetting coating applied by electrostatic spray and baked to produce a cured coating. Tg ≥ 50°C to ensure a solid powder that is storage-stable and transportable in the glassy state to minimise pre-reaction over a 2 year shelf life. And hence substrates should be conducting and earthed. Curing reaction is typically a step-growth A+B type reaction with epoxy + carboxylic acid predominating, and β-hydroxy alklylamide + carboxylic acid being important (and problematic due to inability to catalyse and releasing H2O on cure). In-use performance of the cured coating is normally subject to international standards, specifying adhesion, impact resistance, behaviour on exposure to corrosive environments, UV resistance Baking is required to allow the applied particles to melt, coalesce, wet the substrate; all this while the curing reaction advances to conversions ≥ 80% in around 10-20 minutes for an economic process (normally in the range 160-200°C).

5. What is a Powder Coating? VIDEO

6. What is a Powder Coating? Intense electric field gradient polarises air molecules The solid particles adhere to the substrate by electrostatic attraction. Charging of the particles is (normally) via passing through a corona discharge. An alternate mechanism is tribostatic charging, where the particles are impinged against either PTFE or nylon liners inside the application gun, leading to the development of frictional charging. Particles feel the effects of: • Aerodynamic forces: relatively long-range and influence particles with higher surface area:mass ratio (i.e. fines). • Electrostatic forces: relatively short range and influence particels with higher surface area:volume ratio (a proxy for charge:mass). Particles become adhered when the electrostatic force captures it from the airstream. Air is ionised Powder coating particles moving through the ionised air pick up charge. 80-100 kV x -q +q Aerodynamic force charged powder particle substrate Electrostatic force “image” charge

7. 02 Technical Challenges

8. Refrigeration Cost for heating the oven Savings from lower baking Cost for air-conditioned storage Insulation Good storage Technical Challenges – Low Bake 100 % Volatility in fuel prices lead to pressure on curing oven costs. Carbon footprint considerations also will drive reduction in curing temperatures. The main driver for low bake, however, is access to new substrates… 80 % 60 % Energy consumption / % Linear relationship: hotter oven = greater energy requirement Variables: insulation, weight of metal being coated, oven air changes, gas price… 40 % Complex relationship: colder storage = greater energy requirement, but modified by stock size held, ambient climate/seasonality, distance from producer… 20 % Ambient cure 0 % 0 20 40 60 80 100 120 140 160 180 200 Temperature / °C

9. Technical Challenges – New Substrates Substrates not painted today by powder coatings are either damaged by the heat of the curing process, or electrical insulators, or both. These present substantial barriers to further market expansion by powder coatings. Traditional approaches to this problem tryto reduce the powder coating curing temperature to accommodate the demandsof the thermally sensitive substrate. The problems we have to contend with are rheology and reactivity. Review of various published heat distortion, softening, and glass transition temperatures for commonly-used polymers

10. Low Bake Powder Coatings I – Rheology Storage stability Conventional Formulations Normal polymer formulation allows reduction of melt viscosity at a given temperature (e.g. substitute aromatic diacids for aliphatic), BUT with a Tg penalty. Refridgeration of powder is not desirable and off-sets any benefits of low bake products. Dendritic Materials e.g. Boltorn H2O, ex. Perstorp Viscosity We’re no longer talking about powder coatings… Tg≥50°C Flow and levelling Temperature Semi-Crystalline Materials Our extrusion production process does not lend itself to incorporation of semi-crystalline materials. The quenching process does not give time for recrystallisation. The resulting product is difficult to grind.

11. Low Bake Powder Coatings II – Reactivity T=180°C T=140°C Conversion Conversion Catalysed system T=120°C Curing 160-200°C We now have appreciable conversion during the production process – probably even gelation! Extrusion 110-120°C Extrusion 110-120°C T=120°C Time Time Storage (upto 2 years) Minimise pre-reaction Develop properties on cure • How to retard (pre)reaction during production? • b-HAA + -CO2H reaction liberates H2O, and the pressure in the extruder can retard this reaction (but the reaction is too slow for low bake). • Addition of catalyst late in the extrusion process could delay pre-reaction (but adequate dispersion of the catalyst then becomes an issue). • “Latent” catalysts are typically mentioned at this point, but thermo-latent will not work when production and cure temperatures are matched. • Photolatent bases[1,2] could be triggered during the application process, but be inert during production. • Autocatalytic cure mechanisms (e.g. epoxy homopolymerisation) give a more “S-shaped” conversion-time profile, and may be more amenable to production. • Carroy, A., et. al., Prog. Org. Coat., 68(1-2), 2010, 37-41 • Meier, M, et. al., Paint & Coatings Industry, 2009.

12. 03 Alternate Approaches

13. Alternate Approaches I – Radiation Cure Viscosity softening, melt flow molecular weight build UV off UV on For powder coatings on wood, methacrylated unsaturated polyesters represent current state-of-the-art. Substrates are normally MDF, but plywood and some natural woods are possible (though the coating is normally then textured to hide defects). Time Separation of melt/flow and cure into two separate processes For powder coatings on metal, acrylated polyesters are included. This reduces the cross-link density and minimises adhesion issues. The main problem is obtaining through-cure to get adhesion while maintaining opacity in the visible region. Typical applications are pre-assembled parts (e.g. ball bearing assembly including lubricating grease).

14. In order to be able to offer differentiated solutions to these and other challenges, the World Wide RD&I Powder Coatings Teams have been supported by an on-going multi-million pound investment on Felling site: Buildings, Equipment & Personnel

15. New state-of-the-art Polymer Laboratory Fully automated 50L Resin Pilot Plant for Scale-Up trials Miniature resin plants for novel resin systems Powder paint application line for product testing and customer support

16. 04 Summary

17. Summary • Powder coatings represent a “green” finishing solution, with scope for further expansion. • New markets are likely to include “difficult” substrates, damaged by heat and possibly non-conducting. • Conventional step-growth cross-linking is limited by the constraints of being a powder coating: • Alternative technologies such as UV cure require further developments in polymer and application technology to overcome the current limitations. • Novel approaches are also being investigated with the aid of new investment in facilities and personnel. Storage stable powder Tg≥50°C, tstorage≤2 years Good flow at low bake h~50 Poise at T~140°C VS Manufactured by extrusion T~120-140°C, tresidence~60 s High degree of conversion at low bake T~120-140°C, t~10 mins, p≥80%

18. Thank You…