Der oft unterschätzte Partner - Polyurethane Raw Materials for

42 TECHNIK // POLYURETHANE
Quelle: FarbeundLack.de
Der oft unterschätzte Partner
PU-VERNETZER // FÜR DIE LEISTUNGSFÄHIGKEIT EINER PU-BESCHICHTUNG UND DIE EFFIZIENZ DES
LACKIERPROZESSES WIRD MEISTENS DAS POLYOL VERANTWORTLICH GEMACHT.
DIE ROLLE DES HÄRTERS BESCHRÄNKT SICH NACH DIESER AUFFASSUNG DARAUF, MÖGLICHST GUT
ZUM POLYOL ZU PASSEN. EINE REIHE VON INNOVATIVEN HÄRTERN STELLT DIESE SICHTWEISE IN
FRAGE. DENN DIESE VERNETZER, DIE SICH ZUM BEISPIEL DURCH EXTREM NIEDRIGE VISKOSITÄT ODER
SEHR HOHE FUNKTIONALITÄT AUSZEICHNEN, KÖNNEN DIE EIGENSCHAFTEN DER RESULTIERENDEN
PU-BESCHICHTUNGEN WESENTLICH BEEINFLUSSEN.
FA RBE UN D L A C K / / 1 2 .2 0 1 5
TECHNIK // POLYURETHANE 43
Christoph Irle und Jan Weikard
P
U-Lacke haben sich bei Beschichtungsprozessen besonders dort als Industriestandard etabliert, wo es auf
Effizienz, Langlebigkeit und Höchstleistung ankommt
[1]. Schon Anfang der 1960er-Jahre rief Kuno Wagner
[2] die Technologie der aliphatischen Polyisocyanate
ins Leben, deren Evolution die treibende Kraft der weiteren Entwicklung wurde. Es entstand ein breites Spektrum von Rohstoffen (Polyole
und Vernetzer), um die Anforderungen der unterschiedlichen Industriebranchen weltweit zu erfüllen. Heute setzen PU-Lacke in vielen
Einsatzfeldern Maßstäbe. Beispiele sind die Erst- und Reparaturlackierung von Automobilen, der Korrosionsschutz und die industrielle
Beschichtung von Metall, Holz und Kunststoff.
PU-Rohmaterialien trugen von Anfang an dazu bei, den Energieverbrauch während des Beschichtungsprozesses zu senken, da sie sich
durch eine einzigartige Effizienz, auch in handwerklichen Anwendungen, auszeichnen. Während PU-Lackrohstoffe immer mehr Marktanteile eroberten, stieg zugleich stetig die Nachfrage nach möglichst
umweltverträglichen Beschichtungsprozessen. Daher entwickelten
Rohstoffhersteller und die Lackindustrie PU-Technologien mit deutlich
verringerten Lösemittel-Emissionen. Dazu zählen hauptsächlich wasserbasierte PU-Systeme und Lackrohstoffe mit hohem Festkörpergehalt. Diese Innovationen haben den Markt in den letzten Jahrzehnten
immer mehr durchdrungen, da sie helfen, Emissionen zu senken. Zugleich erfüllen sie höchste Ansprüche der Industrie an die Leistungsfähigkeit von Beschichtungen.
Abb. 1 // Zweidimensionale Erweiterung des Angebotes an StandardHärtern durch innovative, maßgeschneiderte Härter
Abb. 2 // Mit 500 mPas verfügt der neue Härter 2840 XP über eine
noch geringere Viskosität als das marktgängige Produkt N 3900
Der unterschätzter Härter
Wer PU-Lacke formuliert, beginnt meist mit der Auswahl des richtigen
Polyols. Man kann dabei auf eine riesige Auswahl an Alternativen zugreifen. Dies ist einer der Gründe für die unerreichte Wettbewerbsfähigkeit der PU-Technologie. Die Funktion des Härters wird meist sehr
einfach in einem Satz beschrieben: Er vernetzt das Polyol. Dabei sollte
er vor allem zur Polyol-Komponente passen. Weniger beachtet wird
üblicherweise der Einfluss des Härters darauf, wie effizient die Reaktion mit dem Polyol abläuft. Außerdem spielt bei Systemen, die nur
wenig flüchtige organische Komponenten (VOC) emittieren sollen, die
Viskosität des Härters eine wesentliche Rolle: Sie beeinflusst, wie viel
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Abb. 3 // Der neue Härter 2840 XP ermöglicht leicht mischbare
wässrige Formulierungen mit kleinen und homogenen Teilchen
Ergebnisse auf einen Blick
–
Innovative Härter für Polyurethan (PU)-Lacke zeichnen sich durch
besonders niedrige Viskosität oder hohe Funktionalität aus.
–
Der Einsatz solcher innovativen Härter führt zu effizienteren
Lackierprozessen und bringt einen erheblichen Mehrwert für die
resultierenden Beschichtungen.
–
Mit den Vernetzern lassen sich Lacke formulieren, die sehr
schnell aushärten, einen äußerst geringen VOC-Gehalt haben und
mechanisch extrem belastbar sind.
–
Die Härter können außerdem dazu beitragen, dass Beschichtungen sehr elastisch sind oder die Fähigkeit zur Selbstheilung
sowie eine ausgezeichnete Haftung besitzen.
04/2015 AUGUST/SEPTEMBERPOLYURETHANES MAGAZINE INTERNATIONALEuropean fl exible foam industryInterview with L. Kjeldsen, EvonikInterview with T. Hankins, HuntsmanPolyester polyols with recycled contentwww.pu-magazine.comFurniture fi re solutionsSimplified formulations mean simplified processes andenhanced versatility to meet tomorrow’s challenges.Dow is making it happen with its broad portfolio ofproducts, including VORANOL™ 425XL Mannich polyol.Complementing a wide array of innovative solutions,VORANOL 425XL Mannich polyol offers formulatorsexceptional spray foam formulating flexibility.
Thisproduct features a built-in amine catalyst, providingsuperior green strength, dimensional stability andenhanced cold surface adhesion. It also offerssignificantly lower viscosity, enabling easier handling,SIMPLER FORMULATIONS.GREATER POSSIBILITIES.higher loading levels, lower B-side viscosity, better A/Bmixing and increased foam yield.VORANOL 425XL is just the beginning. As a globalleader in polyurethane chemistry, Dow has thededicated customer and technical services to help yousimplify your processes – and expand your business.www.dow.com/polyurethanes®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated
company of Dow312 PU MAGAZINE – VOL. 12, NO. 4 – AUGUST/SEPTEMBER 2015M. Wintermantel, F. Schade, T. Schüttler, K. H. WührerDr. Matthias [email protected] Schade,Thomas Schüttler,Karl H. WührerBusiness Unit Coatings, Adhesives, Specialties,Application Development Infrastructure-CoatingsCovestro (formerly Bayer MaterialScience AG),LeverkusenPaper, ETCC 2014 (European Technical CoatingsCongress), 3 – 5 September 2014, Cologne, GermanyPublished with kind permission of FATIPEC1 IntroductionA building’s external fl oor surfaces need towithstand a great deal. Roof gardens and
thevarious types of balconies are exposed tosunlight and weathering. What’s more, theyare often subject to signifi cant mechanicalstresses. Consequently, the supporting concretesubstrate needs to have a lightfast andresistant protective coating.This coating must retain its protective functioneven if cracks form in the concreteover time. This can happen, for example, asa result of the ground moving or the concretedrying out and shrinking. Without anappropriate protective coating, crackingallows moisture to penetrate into the concrete.When this freezes and subsequentlythaws again, the concrete spalls in someplaces. In the case of balconies, this maylead
to a reduced load-bearing capacity.The moisture may also penetrate into adjacentfl oor slabs.Like all systems for building applications,fl oor coatings also need to comply with theexisting VOC (volatile organic compound)directives. The Decopaint Directive(2004/42/EU), which regulates trade coating,is the principal directive throughout theEU. There are also national regulations suchas the evaluation system for VOC emissionsof the AgBB (Committee for Health-RelatedEvaluation of Building Products) in Germany.Coating systems are available on the marketthat meet these requirements in principle butleave something to be desired in terms of
theirapplication and, in particular, cost-effectiveness.Covestro has now developed a systemthat delivers signifi cant benefi ts in this respect.It is based on Pasquick polyaspartic technology,which has already demonstrated its effectivenessin other applications since the 1990s.Solvent-free polyaspartic coatings are basedon the reaction of an aliphatic polyisocyanatewith a polyaspartic ester. New, low-viscosityraw materials are now enabling this technologyto move into the fl oor coating market – in particularfor external building applications, butalso for comfort and sports fl ooring.Polyaspartic technology makes coating operations particularly cost-effi cient,
becausefewer coating layers are required in many cases. What’s more, the layers cure very quickly.However, two factors have previously restricted the use of polyaspartic systems for fl oorcoating applications. On the one hand, it was virtually impossible to formulate systems thatcould be applied manually. On the other, most polyaspartic coatings were not suffi cientlyfl exible to bridge any cracks forming in the concrete. As part of its Pasquick program,Covestro (formerly Bayer MaterialScience) has developed new, low-viscosity raw materialsthat overcome these limitations of polyaspartic technology.Effi cient path tofl exible fl oor coatingNew raw
materials open up further possibilities forPasquick polyaspartic technologyFormulation 1 2 3 4 5Standard PAE* / g 100.0 80.0 100.0 80.0 80.0Low-viscosity PAE / g – 20.0 – 20.0 20.0Standard PIC1** / g 70.6 – – – 29.3Standard PIC2 / g – 149.7 – – –New PIC / g – – 151 149.7 88Crosslinking / % 110 % 110 % 110 % 110 % 110 %Viscosity / mPas <1,500 <1,500 <1,500*PAE = polyaspartic ester; **PIC = polyisocyanateTab. 1: Overview of variouspolyaspartic formulationstested. Formulations 3, 4and 5 contain the newHDI polyester prepolymer(new PIC)Fig. 1: The working time ofvarious polyasparticformulations1 2 3Formulation4
5020406080100120Working time / minPU MAGAZINE – VOL. 12, NO. 4 – AUGUST/SEPTEMBER 2015 3132 Benefi t of polyasparticsPolyaspartic esters originally served as reactivediluents in solventborne, two-componentpolyurethane (PU) coatings. Nowadays, theyare mostly used as the main component forreaction with a polyisocyanate and enablethe formulation of coatings with very lowVOC contents. Polyaspartic coatings of thiskind offer a several benefi ts:• Easy to apply and require only standardequipment.• Quick curing at room temperature, whichenables the coated items to rapidly resumetheir function in machinery, buildingsor
installations, and molded parts to leaveproduction quickly. This results in far lowertotal coating costs.• Good film formation. Fewer layers areneeded than in other systems to producethe same total coating thickness.This, too, boosts productivity and costefficiency.• Resistance to weathering matches thehigh level achieved by two-componentpolyurethane coatings.These benefi ts are key factors in the successalready enjoyed by polyaspartic systemsin a number of applications. Amongother things, they are used to protect industrialplants, wind turbines, bridges and agriculturalor construction machinery againstcorrosion and as an automotive
refinishcoating. The systems are also already inuse for fl oor coatings, but the relevant formulationscannot be applied using a rolleror brush, and they are relatively hard andrigid.3 Low viscosity,new possibilitiesThe key to fl exible polyaspartic fl oor coatingsthat can be applied manually are bindersand crosslinking agents with a lowerviscosity than was previously available. Inthe polyaspartic ester context, Covestrointroduced a binder with a viscosity of just100 mPas and a comparatively low reactivityin 2013. It takes such formulations approximately1.5 hours to gel, which meansthe pot life is sufficiently long (formulation2; tab. 1 and fi g. 1). Previously,
theonly polyaspartic binders available werelow-viscosity ones that gelled with thecrosslinking agent after just a few minutesor had a viscosity of around 1,000 mPas(formulation 1). In conjunction with establishedbinders and crosslinking agents, thelow-viscosity binder made it possible to producesolvent-free, two-component floorcoatings that were easy to apply with a rolleror brush. Thanks to the rapid curing,several layers of such polyaspartic systemscan be applied in a single day and the surfacecan be walked on within just a fewhours. This minimizes downtimes on buildingsites and cuts costs, but the coatingsare hard and cannot bridge cracks (formulation2: fi g. 2).Consequently, Covestro developed a newcrosslinking agent, a hexamethylene diisocyanate(HDI) polyester prepolymer, with lessthan a quarter of the viscosity of the standardproduct (1,350 mPas vs. 6,000 mPas).A patent is pending for this crosslinkingagent, which now also enables the formulationof fl exible, solvent-free fl oor coatings(formulations 3 – 5: fi g. 2). The fl exibility ofthese coatings is also shown in fi gure 3,which gives a comparison of the elongationat break. Polyaspartic formulations based onthe new crosslinking agent and the low-viscositybinder thus meet all the demandsplaced on fl oor coatings for external
buildingapplications. The mechanical properties canbe tailored to the relevant application byvarying the mixing ratio of conventional andnew crosslinking agent, and of conventionaland low-viscosity binder.4 ConclusionA new HDI polyester prepolymer – a crosslinkingagent with very low viscosity – and alow-viscosity binder that has been availablesince 2013 are opening up completely newpotential applications for Pasquick polyaspartictechnology. The resulting coatings canbe applied using a roller, have crack-bridgingproperties, are lightfast and exhibit resistanceto chemicals and mechanical influences.They cure quickly, which helps reducedowntimes
and cut costs. What’s more, theycontain no monomers or reactive diluentsand comply with all VOC directives. The propertiesof polyaspartic fl oor coatings are thusunique and have the edge over other systems.Fig. 2: Hardness (Shore A and D) of various polyaspartic formulationsFig. 3: Relation of nominal elongation at break for the new crosslinking agent and low-viscosity binder2 3Formulation4 530405060708090Hardness / Shore A1 2 530405060708090FormulationHardness / Shore D3 d RT14 d RT3 d RT + 3 d 50 °C3 d RT + 7 d 50 °C3 d RT14 d RT3 d RT + 3 d 50 °C3 d RT + 7 d 50 °C2 3 4 50100200300400Relative elongationat break /
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Abb. 4 // Lacke auf Basis innovativer Härter machen die Oberfläche wetterfest und gleichzeitig mechanisch hoch belastbar (Quelle: Eisenmann SE)
FARBE UND LACK // 12.2015