the frequency of the alternatingelectric field.

The process of film formation isa two step process involving thecoalescence of the powderparticles to form a continuouslayer, and the levelling of themelted coating to form a smoothfilm. The main parametersinfluencing the quality of the filmformation are the surface tensionof the powder and the meltviscosity, which changescontinuously during the filmformation process. The HaakeRheometer produces a rheologicalprofile during the cure cycle.Initially the viscosity falls to aminimum level during the meltperiod. As the curing reactionbegins the viscosity increasesuntil it reaches the gel pointwhere the system becomes moresolid than liquid and there isalmost no film mobility, signifyingthat film formation has ended.This is followed by the completionof the curing cycle when the filmacquires all of its properties.

This paper is explicit isdetailing the tests that are appliedto the laboratory samples and thewave-scan values, both long andshort wave, give an indication ofthe degree of levelling. Highervalues indicate worse levellingwith pronounced orange peeleffect, while lower values showgood levelling properties. Theresults correlate the influence ofminimum viscosity, gel times andfilm appearance. A low viscosityand a longer open time for themelting and flowing of the powderfilm improves the surfaceappearance. High ratios of Primidto polyester make the systemmore reactive with an adverseeffect on film flow and appearance.The correct amount of curingagent is a matter of compromisebetween the film appearance andthe optimum mechanicalproperties. In the examples shownthe ratio 95 polyester: 5 Primidoffers the best compromise. TheDEA kinetic studies are describedcomprehensively and are provedto be a useful tool to determinethe application changes during the

curing of any Cray Valley systemdesigned for use with Primidcuring agents.

This work is of more practicaluse to the formulator in creatinglow gloss powder systems basedon Primid. In formulating mattepowder coatings the most reliabletechnique has proved to be dryblending of two powder coatingswith differing rates of reactivity. Itis a peculiarity of Primid curedsystems that catalysts have noeffect on speeding the rate ofreaction, and the reactivitydifference has to be obtained byeither modifying the end groupsof the polyester resins orcombining two polyesters withwidely differing acid values.

A visual assessment of filmformation using an opticalmicroscope shows that themelting step proceeds up to130°C and above this temperaturethe film becomes completely flatand undisturbed until thecrosslinking reaction commences.At this point different degrees ofstructure are formed on the filmsurface dependent upon the gapbetween the reactivity of the twosystems. Surface roughnessbegins about one minute afterreaching the isothermal target of200°C and intensifies during thenext ten minutes. Thereafter, nofurther changes are observed.

The tests carried out on thepigmented powder systems canbe applied to selection of the dryblend matte systems, for DEAand rheological characterizationare especially useful tools forevaluating the curing kinetics.This allows an accurate selectionof the two powders involved inthe dry blend formulations andgood control of gloss and surfaceappearance can be achieved.

Paper entitled “Curing Behaviour and SurfaceProperties of ß-Hydroxyalkylamides BasedPowder Coatings” by researchers from CrayValley Iberica and a local University,presented at the recent InternationalWaterborne, High Solids and PowderCoatings Symposium, in New Orleans on 2-4Feb 2005. Bound copies of the symposiumpapers available from the organizers: TheUniversity of Southern Mississippi,Department of Polymer Science, Hattiesburg,Mississippi, MS 39406, USA

New dimensions in fluorocarbonpowder coatings

Fluoropolymers have been in usesince the mid sixties as highperformance liquid coatings thatcomply with Florida exposurerequirements. These systemswere based on PVDF(polyvinylidene difluoride) andhave shown outstanding durabilityafter more than 10 years Floridaexposure. They do, however,have significant draw backs sincethey are solvent based andcontain high levels of VOCs,require high temperature treatmentfor proper film formation, theiradhesion is rather poor and aprimer is needed, the surface issoft and easily marred, and theyare expensive not only in materialcost but the application mayrequire a four stage process.

As powder coatings becameaccepted as alternatives to thePVDF process, and the quality ofperformance steadily increased, itwas attempted to extend PVDFtechnology into the realm ofpowder coatings. Unfortunately,the Kynar based materials stillpossessed many of the faults ofthe liquid PVDF systems,requiring very high temperaturesfor processing (typically around450°F, or 220°C) and they alsorequire a primer to improve theadhesion. Since they arethermoplastic they are also softand there are limitations on thelevel of gloss that can beformulated, and only dull, lowgloss surfaces are possible. Thecost factor is also considerable interms of both material andprocess stages.

A paper by Maier of TigerDrylac describes a new polymerthat addresses theseshortcomings. It is fundamentallydifferent from existing PVDFmaterials and is based on FEVE(fluoroethylene vinylether), whichhas functional groups attached tothe polymer backbone making itcapable of thermosetting. Thismaterial, Lumiflon, gives a hardersurface than PVDF; theprocessing temperatures are lower

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than PVDF; adhesion is improvedto the point where a primer is nolonger necessary; and high glosssurfaces up to 80 at 60° can beformulated. The cost is lowersince only a one step process isneeded and the weatheringproperties are comparable toPVDF performance.

The new alternative to PVDF isclaimed to meet all of therequirements of AAMA 2605-02,which can also be met by speciallyformulated polyester powdercoatings, although the UVresistance is said to be significantlybetter. It is not intended that thiscoating is meant to compete withpolyester powder technology, butas an improvement to both liquidand solid Kynar technology.

The Lumiflon coatings arethermosetting and the crosslinkingagents are blocked isocyanatesgiving rise to volatile componentssuch as caprolactam. Work isprogressing to eliminate all VOCcomponents and futuredevelopments could allow theformulation of emission freepowder systems. There is aproblem with the choice ofpigments due to the extremedurability requirements and thedull earth colours of inorganicpigments are most suitable tomeet durability standards.

The flexibility of the Lumiflonpolymer is limited and postforming operations could causecracking that can lead tocorrosion problems. Nevertheless,this new product offers anattractive alternative to existingPVDF powder systems at lowercost whilst retaining equivalentUV resistance and durability.

Paper entitled “Producing Highly DurableSubstrates in New Dimensions with a New,Easy to Handle Fluorine Carbon Powder” byBurkhard Maier of Tiger Drylac Inc, USAoffered for presentation at the cancelledSymposium scheduled for 12-14 Apr inHannover, Germany. Copies of the paperscan be downloaded at http://www.coatings.de

Innovative maintenance service forpowder production machinery

Powder coatings manufacturers inEurope are currently under

pressure to meet the diverseneeds of a market that hasbecome fragmented by customerdemands for special colours, thetechnical demands of runningTGIC-free products to replace theolder established products, andthey also have to face additionalcompetitive pressures as moreproducers enter the market. It isbelieved that modern powdercoating production plants are onlyrunning at 50-60% efficiency,because of the maintenancedemands and the increased downtime between production batches.Modern equipment is now gearedto increased production rates withhigher work loads placed on theessential machinery andbreakdowns can occur morefrequently, particularly whenregular maintenance proceduresare sidelined to meet productiondemands. When breakdowns dooccur there is reluctance on thepart of the machinery suppliers toretrofit upgrades to an older line,preferring instead to supply costlynew equipment, which producersmay not be able to afford intoday’s economic climate. Theneed for rationalization ofproduction lines has, in manycases, reduced the in-house skillsto maintain and repair worn ordamaged machinery.

A new company has now beenset up to service the EuropeanPowder Coatings industry, andoffers to relieve this burden. Thecompany, Xtrutech, is based inthe UK, but is now in the processof setting up offices in Germanyand Italy to offer their expertise tothe whole European powdercoatings industry. It is theirintention to serve the industry byoffering more than just spareparts or servicing of machinery.Engineers can be sent to clientsto replace, upgrade and retro-fitparts and service machinery toallow powder producers toupgrade their equipment ifrequired. One unique facet ofXtrutech’s service is the ability totake parts from one machine anddesign an imitation that fits theinternal geometry of another

machine. They can take the bestdesign features of severalextruder manufacturers andincorporate them into onemachine.

Recently, Xtrutech installed anew design replacement clamshellbarrel for an 80mm twin screwextruder in the UK. This provideda cost saving and many technicaladvantages over the old stylebarrel, giving improvedperformance, better wear andchemical resistance.

The new service from Xtrutech is describedin an article entitled “Compounding theProblem” published in PPCJ Polymers, Paint,Colour Journal, Feb 2005, 195 (4485), 36-38

Improving antimicrobial coatings

Powder coatings with anti-microbial properties weredeveloped by BioCote in the midnineties and have since becomea profitable niche outlet for thespecialist powder coatingsproducer. In the early days, theanti-microbial agent was a blendof organic materials, or even asingle organic compound;incorporated as a solid material,at the hot melt blending stage ofmanufacture. It was later foundthat the silver ion was a moreeffective anti-microbial, particularlywhen the silver ions are carriedin the lattice of a zeolite material.Silver is attractive as an anti-microbial material because it hasa low or non-existent cytotoxicity,and it is widely approved for avariety of applications in themedical and food industries.Recently an article by MichaelWagener of Bio-gate describes analternative to the use of silverions carried in a zeolite. This newtechnique is based uponnanoparticles of pure metallicsilver. The anti-microbial activityof metallic silver depends stronglyon the surface area of the silverand, in this respect silvernanoparticles give a strong anti-microbial effect at lowconcentrations.

Using an inert gas evaporationand condensation process, highpurity silver (99.96%) is

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