P O W D E R C O A T I N G SFOCUS ON

POWDER COATINGS POWDER COATINGS POWDER COATINGS POWDER COATINGS

AN INTERNATIONAL NEWSLETTER MONITORING TECHNICAL ANDCOMMERCIAL DEVELOPMENTS IN POWDER COATINGS ISSN 1364–5439

Although we are subjected todaily statistics implying that thelong awaited economic recoveryis under way there is littletangible evidence frommanufacturing industries tosupport these reports. It has beenclaimed that manufacturingindustry has been strengthenedby cost cutting and improvementsin process efficiency during theeconomic downturn – but what isthe reality? The increasing burdenof escalating raw material andhigher energy costs has notdiminished and the coatingsindustry has done little to developcost effective products andprocesses. Powder coatingproducers still offer theircustomers the same out-modedthermoset products in the beliefthat lower temperature curingcycles will resolve the problem ofenergy costs. They seemdetermined to avoid anycommitment to UV curablepowder coatings, despite theevidence that savings onconversion to this technologywould repay the cost of thecapital investment within one year.There will never be a better timeto press for a significanttechnology change!

If there is any encouragingnews to emerge from the annualreport figures of the majorcoatings producers it is containedin the profits resulting from theirAsian or Middle Easterninvestments. How long will these

markets continue to prosperbefore the Governments in theseregions of high expansion decideto give preference to their ownindustries? I have already seenthis trend in the Middle East, andChina is rapidly moving in thisdirection. The fallacy of cheaplabour benefits accruing from thevast transfer of manufacturingindustry will be exposed withinfive years. What will be ouralternative – capitulation orrenewed investment within ourown borders? New technology isthe key!

Sid Harris

TECHNICALNew photoluminuscent UV curedpowder coatings

UV curable powder coatings arean attractive choice due to thecombination of the properties ofpowder coatings and UV curing,which can be described as beingVOC-free technology, with lowenergy consumption, capable ofoverspray recycling andpossessing relatively fast curecompared to conventional powdercoatings.

A recent article by researchersat AIDO, Valencia, describes thedevelopment of a new formulationfor a photoluminescent powdercoating applied to metallic

THE WAY AHEAD?

A MONTHLY REPORT FROMSID HARRIS

APRIL 2010

In this issue

TECHNICAL 1-5New photoluminuscent UV

cured powder coatingsElectrostatic properties of

powder coatings

INDUSTRY NEWS 5-7PPG reports 4Q 2009 financial

resultsGrace announces sustainability

policyIndustrial Nanotech Inc

announces large order fromSaudi Arabia distributor forNansulate coatings

Loss of €60 M for AkzoNobel in 4Q 2009

NEW PRODUCTS 7-8New brilliance in coatings

design: Paliocrom BrilliantOrange from BASF

Arkema offers new Rilsan grades for outdoor furniture

MARKETS 8Updated profile of Russia

paint industry released

EVENTS 8

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F O C U S O N P O W D E R C O A T I N G S

substrates, and cured by UVirradiation. This technology canalso be applied to the coating ofheat sensitive substrates, used inemergency safety signs. The fastUV curing process was shown tobe efficient on thermo-sensitivepanels. The UV curing techniqueis an interesting polymerizationprocess: it is an environmentallyfriendly technique, which allowsthe polymerization reaction tooccur rapidly. Photoluminescentpigments have been used inliquid coatings, but in the case ofpowder coatings, the mainproblem with this process hasbeen to determine the extruderand mill parameters to preventthe loss of photoluminescentproperties and darkening of theproduct.

Coatings were formulated usingan unsatured polyester resin; aphotoluminescent pigment basedon strontium aluminate (SrAl2O4)and a photoinitiator, 1-4-[(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one.Benzoin, used as a degassingagent and flow agent (BYK 360P,acrylate additive), was added tothe mixtures. This flow agent is atypical standard anti-crater andleveling additive for pigmentedpowder coatings. It Improvesleveling of powder coatingsystems and prevents orangepeel. Additionally, it preventssurface defects specific to powdercoatings such as pinholes andfisheyes.

Powder coatings wereprepared containing 2%photoinitiator, 0.2% benzoin, 0.8%flow agent and photoluminescentpigment content (from 30 to 90%in weight ratio to resin). Sampleswere pre-mixed and the materialwas extruded in a twin screwextruder with a controlled screwspeed setting and heating zonesset at 95°C and 100°C. Thecooled extrudate was ground inan ultra-centrifugal mill andsieved at 10 microns.

The powder coating wasapplied to aluminium substrates.Test panels were degreased and

coated with white powder coating.After application, the panels wereplaced in an air-circulated ovenfor 2 min at 160°C to melt thepowder particles and then curedby UV irradiation. Photolumin-escent powder coating wascharacterized by luminance anddecay time, according to UNE23035-1:2003. This standarddescribes decay time parameteras the time for the luminanceemitted by the photoluminescentsample to reach 0.3 mcd/m2 afterthe excitation light over thesample is removed and, becausedecay time can be so long,describes a method to estimate itby extrapolation.

A salt spray test, according toISO 9227:2006 was carried outfor 96 h and the decay time wasmeasured again. If the differencebetween the values is not greaterthan 5%, the coatings aredeemed to pass the test.

Luminance and decay timemeasurements were carried outon samples using a LMT B510 Lphotometer, with heads forilluminance and luminancemeasurements. The light sourceused to excite the photolumin-escent sign was a non-diffusing,unfiltered, continuous short-arcxenon lamp of 180 W, providing amean illuminance value of 1000lx on the surface of each sample.Distance between the signal andthe diffuser must be enough togive a luminance value at thecentre of the illuminated area of1000 lx. This area must be 5 cmin diameter, which is similar tothat of the luminance headphotometer. In order to confirmthe luminance homogeneity overthis area, test patches formeasurements of luminance werepositioned in the centre of thearea of the test specimen and ateach of the four points 90° on theouter rim of the surface of thetest specimen. After checking thehomogeneous illumination overthe testing surface, the signalwas located at the centre of thisarea and was stimulated for 5min. Immediately after the lamp

was switched off, the luminancewas measured.

It was observed thatilluminance increases with thequantity of pigment used up to70%, and then decreases. Thevalues after accelerated salt fogspray test decrease by 5%. Both values, according to UNE23035-4:2000, establish that thecoatings will be classified as Bcategory, provided that the timetaken for the luminance todecrease to 0.3 mcd/m2 whentested under the excitationconditions was ≥840 min, and thedecrease on the initial values ofluminance was lower than 5%after 96 h of exposition. It canalso be seen that the decay timevaries significantly withphotoluminescent pigmentconcentration.

It is probable that, as aconsequence of these results,when photoluminescent pigmentincreases, the critical pigmentconcentration has been reached.Above this critical value, there isnot enough resin to cover thepigment surface and an importantamount of the polymer isabsorbed in the pigment. Thereare void structures in the film dueto insufficient polymer, but thepigment particles can still bethought of as being continuouslyconnected. A new phase, air, isnow present in the film and itsproperties drastically affect thoseof the film, especially with regardto density, mechanical, thermal,transport and optical properties.

The formulation conditions ofcoatings are decisive to theresults. In the experimentaldevelopment some difficultieswere experienced; possibly due tochemical structure, morphologyand particle size of pigment.Extruder conditions are important,the dwell time of pigment in thebarrel is critical, and it isnecessary to control screw speedto avoid discolouration of thecoating.

Ultra-centrifugal mill conditionsare important too. If the size ofsieve is not suitable, the

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photoluminescent pigment will notpass through the sieve, reducingthe percentage in the coatingand, therefore, the luminescencevalues.

Thickness also is a significantfactor. A chart shows decay timeof coatings formulated with 60%of photoluminescent pigmentconcentration at different thicknessvalues. Maximum decay time isobserved when coating thicknessis over 100 μm and this is loweredwhen the thickness is reduced.

The article provides fullexperimental details of theresearch programme. Opticalcharacteristics (such asilluminance and decay time) ofthese coatings prepared atdifferent photoluminescentpigment levels and applied withvariable thickness, were studied.

Powder coatings offer importantadvantages compared to liquidcoatings in relation to VOCreduction and maximizing materialutilization by recycling of theoverspray, and the application ofthicker coating layers in a singlecoat process. Compared toconventional coatings, UV powdercoatings offer high cure speedand economic advantagestogether with the capability tocoat thermo sensitive materialssuch as plastic or wood.

Article entitled “Development ofPhotoluminescent Powder Coatings by UVCuring Process” by researchers at AIDO,Valencia, Spain, published in Progress inOrganic Coatings, Feb 2010, 67 (2), 92-94

Electrostatic properties of powdercoatings

Powder handling operations leadmost often to electrostaticcharging of products due tocollisions with surfaces of adifferent material type(particle/particle or particle/wallcontacts). Although electrostaticphenomena play an important andever emerging role in manyindustrial applications (eg powdercoating, xerography, andpharmaceutical processing) theyare regarded by many as a

trouble and a hazard source. Infact, numerous processes such aspneumatic conveying, sieving,fluidization and mixing, result ontribo-charging of powders. Theelectrostatic charges acquired byparticles can thus affect thebehaviour of handled productsand their quality. Typical examplesare poor flowability, pipe foulingand electrostatic discharge thatcan ignite flammable dust cloudsor organic vapours. Factorsaffecting charging propertiesinclude particle size and shape,nature and work function of thecontacting surface and theparticulate material, area andfrequency of contacts, surfacepurity, and atmospheric conditions.However, electrostatics and theassociated charge generationmechanisms in such systems aremultifaceted and not fullyunderstood. In order to betterunderstand and control theelectrostatic consequences, it isimportant to develop laboratory-scale equipments allowing theproper measurement of tribo-electric charging of powders.

Among all manufacturingprocesses for automotiveproduction, the painting operationcontributes most to directenvironmental emissions. As aconsequence of recent restrictionsin European legislation concerningthe volatile organic compounds(VOC) emissions, the trend inalmost every finisher industrialfield is to replace the conventionalsolvent-borne paints by new low-emission paint systems, includingpowder coating systems. Powderpaints are very finely dividedsolvent-free polymer coatings,which present large advantagesover conventional paints fromecological and economical pointsof view.

PSA Peugeot-Citroën was thefirst car manufacturer to usemulti-colour powder primers andextend henceforth the use of thistechnology for new plants. In theelectrostatic powder coatingprocess, the powder paint isfluidized and transported through

a pipe to a special chargingcorona bell. In the corona bell,the powder is electrostaticallycharged and sprayed toward thegrounded work piece. Theadhered powder is then heated,melts and cross-links to form auniform layer over the work piece.In addition, unlike the liquid paintsystems in which non-depositedpaint is lost, the over sprayedpowder during the electrostaticapplication process can bereused.

Two powder primers were usedas the basis of this work, suppliedby two different manufacturers.The mean particle size of bothproducts measured by laserdiffraction analysis (Malvern,Mastersizer) was about 25 μmand their true density was 1350kg m-3 (Micromeritics, Accupyc1330). According to theseproperties the powders belong tothe cohesive group-C powders ofthe Geldart classification. Bothproducts were polyester/epoxythermosetting hybrid resins butcontained different types of flowconditioners. The powderdesignated A contained 0.2% offumed silica and the primer B thesame amount of another flowconditioner (fumed alumina). Notethat flow conditioners (also calledGlidants) are nano-sized powderyadditives used to improve theflowability of powders by coatingthe particles and decreasinginterparticle forces. The use offlow conditioners in powder paintsused in automotive industry isalmost unavoidable because ofsmall and narrow size distributionof particles that make them verycohesive. These particle sizecharacteristics are necessary forthe high-grade appearancerequested in car manufacturing.

Despite the similar physicalproperties and chemical nature,the application of the twopowders A and B revealed thatthey behave differently in theindustrial unit. In particular, thefilm thickness and the depositionefficiency (ie mass ratio ofdeposited and sprayed powder)