UV-Waterborne Nanocomposite Coatings :Curing Kinetics Study

Caroline Sow *, Bernard Riedl, Pierre Blanchet* Wood Sciences Ph. D. candidate,

Laval University, Québec

2009 International Conference on Nanotechnology for the Forest

Products Industry,June 25th, 2009

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Paint and coatings industriesUse important quantities of finishing products (solvent based)

Importance of environmental protection interestReview of regulations (VOCs emission)

Development of more eco-friendly productsUV-cured coatings

Wood products industryShift from solvent-based to waterborne coatings

UV-waterborne coatingsMeet requirements of the industry (mechanical properties)

Introduction

Investigation of nanocomposite approach

AdvantagesFastNo emission of VOCsExcellent mechanical properties (abrasion and scratch resistance)Good optical properties (gloss, yellowing)

DisadvantagesHigh water surface tension difficulties of wettingSensitive to oxygen polymerization inhibitionLower propertiesHigher price

UV-Waterborne Coatings

vs high solid content coatings

Some current nanoparticles and their properties

Nanoparticles

Nanoparticles Alumina Zinc oxide Silica Clays

Abrasion resistance

Hardness

UV Protection

Antimicrobial

Scratch resistance

Fire barrier

Mechanical properties

FormulationPUA resinPhotoinitiator

Nanoalumina and modified nanosilicaHigh specific surface area + Hydroxyl group

difficult dispersion in aqueous mediaSurface modification by trialkoxysilanes

dispersibility improvement in acrylate media

3 loading rates: 1, 3 and 5 wt%Suitable mechanical properties less quantities of nanoparticles

high efficiency

Material

Measure of the gloss retention at 60°Nanoparticle addition scratch resistanceCoatings based on nanosilica important of scratch resistanceGrafting trialkoxysilanes acrylate functions and acrylate double

bonds

Scratch resistance

Scra

tch

resi

stan

ce

Photo-DSC

Polymerization processUnderstanding is essentialFast and efficient polymerization

Optimize the curing process TemperatureResin type and concentration Photoinitiator type and concentrationUV-light intensity

Photo-DSCSimple and efficient wayEvaluate the curing kinetics

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ExperimentalNanoparticles dispersion

Ultrasound

Photo-DSC experimentsDifferential scanning calorimeterLight source = mercury-xenon lamp

ProcessPrevious dryingI = 47 mW/cm²T = 30°C, air flow

Exothermic curves Heat flow as a function of reaction time

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1 wt% nanoAl2O3 - 10 min (750 W à 50 %)

5 μm

2 μm

Atmospheric Conditions Effect

Exotherms under nitrogen conditions observed by 2 authorsDrying before UV-curing free-radical polymerization in solid stateHumidity in air atmosphere = plasticizer effect chain mobility in

dried films UV-curing efficiency

Nanoalumina Effect

Nanoalumina addition exothermsHigh specific surface area and –OH groups aggregates presenceEffect at 1, 3 et 5 wt% fairly equivalent aggregates effect more

important that loading effect

Nanosilica Effect

Nanosilica addition exothermsAggregates presenceEffect at 3 et 5 wt% fairly equivalent aggregates effect is predominant

Nanoparticle Type Effect

Exotherms FAnU1 < FSnU5 Surface modification of nanosilica aggregates size and amount

number of acrylates functions and reactive groups UV-curing efficiency

Conclusion

Mechanical propertiesExcellent scratch resistance

UV-curing processPresence of aggregates lower of efficiencyFastNo effect of air atmosphere

Surface modificationImprove mechanical and kinetics properties

Interesting Advantages for All Coatings Industries

Excellent properties with 1 wt% of nanosilica

ReferencesBauer, F.; Mehnert, R.; UV Curable Acrylate Nanocomposites : Properties and Applications, Journal of Polymer Research, 2005, 12, 483-491 Chen,C.-H.; Ou, M.-K.; Lin, S.-H.; Tsai, M.-S.; Mao, C.-F.; Yen, F.-S.; Preparation and application of an ultraviolet curable coating containing nanoscale α-aluminium oxide, J. Appl. Polymer. Sci., 2006, 102, 5747-5752Decker, C.; Lorinczova, I., UV-radiation curing of waterborne acrylate coatings, Jct Research, 2004, 1 (4), 247-256 Hajas J.; Lenz P.; Schulte K.; Enhancing mechanical properties of UV-curing wood varnishes by synergistic combinations of silicones and nano-alumina particles, RadTech Europe Conf, 2005Tauber, A.; Hartmann, E.; Glasel, H. J.; Bauer, E.; Mehnert, R., UV and electron beam crosslinkedpolyacrylate nanocomposites and their applications, Czechoslovak Journal of Physics, 2003, 53, A355-A367West R.D. et Malhorta V.M.; Rupture of nanoparticle agglomerates and formulation of Al2O3-epoxy nanocomposites using ultrasonic cavitations approach: Effects on the structural and mechanical properties, Polymer Engineering Sciences, 2006, 46 (4), 426-430 Decker, C.; Masson, F.; Schwalm, R.; How to Speed Up the UV Curing of Water-Based Acrylic Coatings, J . Coat. Technol. Res., 1 (2) (2004) 127-136Tauber, A.; Scherzer, T.; Mehnert, R.; UV curing of aqueous polyurethane acrylate dispersions. A comparative study by real-time FTIR spectroscopy and pilot scale curing, J. Coat. Technol., 72 (2000) 51-60

AcknowledgmentsFinancial support

Economic Development CanadaFond Québécois de Recherche sur la Nature et les Technologies FPInnovations-Division Forintek

Coating partner Canlak

Material SupportBykChemieCiba

UV-Waterborne Nanocomposite Coatings :Mechanical Properties and Curing Process Studies

Caroline Sow *, Bernard Riedl, Pierre Blanchet* Wood Sciences Ph. D. candidate,

Laval University, Québec

Thank you

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