Powder Coatings: New Advances and Remaining Challenges Powder Coatings: New Advances and Remaining Challenges Dr Tom Straw AkzoNobel Powder Coatings NEPIC.
<p>Powder Coatings: New Advances and Remaining Challenges Powder Coatings: New Advances and Remaining Challenges Dr Tom Straw AkzoNobel Powder Coatings NEPIC INNOVATION DAY 15 November 2011 Slide 2 What is a Powder Coating? 01 Slide 3 A solid  thermosetting coating  applied by electrostatic spray  and baked  to produce a cured coating . High performanceThermosetting coating cured above T g. Coating does not vitrify prematurely. Zero VOCMelt processed during manufacture. Electrostatically applied to the object being coated. Cured by heat. Materials efficientNo diluents/solvent/water to be transported with the coating. Over-sprayed powder can be automatically recycled. Waste from the process is minimal, and can be disposed of as non- hazardous waste. Toxicologically benignNo toxic pigments, minimal use of harmful materials. Any harmful materials are in the solid state, handled in an industrial environment and converted to non-hazardous forms in the cured films. 1T g 50C 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. 2Curing reaction is typically a step-growth A+B type reaction with epoxy + carboxylic acid predominating, and -hydroxy alklylamide + carboxylic acid being important (and problematic due to inability to catalyse and releasing H 2 O on cure). 3And hence substrates should be conducting and earthed. 4Baking 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 160-200C). 5In-use performance of the cured coating is normally subject to international standards, specifying adhesion, impact resistance, behaviour on exposure to corrosive environments, UV resistance Slide 4 Market Size Producers Segmentation Source: Akzo Nobel Powder Coatings Competitor Survey 2009 Slide 5 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 160-200C). 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 - hydroxy alklylamide + carboxylic acid being important (and problematic due to inability to catalyse and releasing H 2 O on cure). T g 50C 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. A solid thermosetting coating applied by electrostatic spray and baked to produce a cured coating. High performance Thermosetting coating cured above T g. Coating does not vitrify prematurely. Zero VOCMelt processed during manufacture. Electrostatically applied to the object being coated. Cured by heat. Materials efficient No diluents/solvent/water to be transported with the coating. Over-sprayed powder can be automatically recycled. Waste from the process is minimal, and can be disposed of as non-hazardous waste. Toxicologically benign No toxic pigments, minimal use of harmful materials. Any harmful materials are in the solid state, handled in an industrial environment and converted to non- hazardous forms in the cured films. Slide 6 VIDEO Slide 7 The solid particles adhere to the substrate by electrostatic attraction. Charging of the particles is (normally) via passing through a corona discharge.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. Electrostatic force Aerodynamic force +q image charge -q charged powder particlesubstrate x 80-100 kV Intense electric field gradient polarises air molecules Air is ionised Powder coating particles moving through the ionised air pick up charge. Slide 8 Technical Challenges 02 Slide 9 020406080100120140160200180 100 % 60 % 80 % 40 % 20 % 0 % Energy consumption / % Temperature / C Linear relationship: hotter oven = greater energy requirement Variables: insulation, weight of metal being coated, oven air changes, gas price Complex relationship: colder storage = greater energy requirement, but modified by stock size held, ambient climate/seasonality, distance from producer Cost for air- conditioned storage RefrigerationInsulation Good storage Cost for heating the oven Savings from lower baking 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 Ambient cure Slide 10 PolymerTemperature /C PET160 Nylon 6149 acetal copolymer141 Polypropylene135 TPO130 Polycarbonate125 PC-ABS110 PPE/Noryl110 Nylon99 acrylic90 HDPE88 ABS85 Polystyrene84 acetal80 PVC71 LDPE71 Polyamide70 Review of various published heat distortion, softening, and glass transition temperatures for commonly-used polymers Slide 11 Conventional Formulations Normal polymer formulation allows reduction of melt viscosity at a given temperature (e.g. substitute aromatic diacids for aliphatic), BUT with a T g penalty. Refridgeration of powder is not desirable and off-sets any benefits of low bake products. Dendritic Materials e.g. Boltorn H2O, ex. Perstorp Temperature Viscosity T g 50C Storage stability 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. Flow and levelling Were no longer talking about powder coatings Slide 12 Time Conversion Curing 160-200C Extrusion 110-120C Storage (upto 2 years) T=120C T=180C Minimise pre-reaction Develop properties on cure Time Conversion T=120C T=140C Extrusion 110-120C We now have appreciable conversion during the production process probably even gelation! Catalysed system How to retard (pre)reaction during production? -HAA + -CO 2 H reaction liberates H 2 O, 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. 1Carroy, A., et. al., Prog. Org. Coat., 68(1-2), 2010, 37-41 2Meier, M, et. al., Paint & Coatings Industry, 2009. Slide 13 -HAA + -CO 2 H Cure Mechanism Slide 14 Alternate Approaches 03 Slide 15 Separation of melt/flow and cure into two separate processes Degreasing for metal Sanding for wood/pre- coated metal Pre-heat if not fully conductive, or spraying of conductive solution. Substrate Preparation Corona charging guns 50-100 microns film thickness Over-spray can be recycled Powder Application Under IR or convection oven 90-130C 1-2 minutes Powder Melting V+H bulbs for pigmented systems H bulbs for clear-coats Powder Curing 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). 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). Time Viscosity softening, melt flow molecular weight build UV offUV on Slide 16 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 Slide 17 New state-of-the-art Polymer Laboratory Miniature resin plants for novel resin systems Fully automated 50L Resin Pilot Plant for Scale-Up trials Powder paint application line for product testing and customer support Slide 18 Summary04 Slide 19 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 T g 50C, t storage 2 years Manufactured by extrusion T~120-140C, t residence ~60 s Good flow at low bake ~50 Poise at T~140C High degree of conversion at low bake T~120-140C, t~10 mins, p80% VS Slide 20 </p>