| THURSDAY, October 18th 2007 |
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Session I: Film formation - a closer look
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Experimental studies of latex film formation
Dr. Joe Keddie, University of Surrey, UK |
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Latex film formation, which is the multi-stage process by which waterborne, colloidal polymer particles are transformed into a continuous film, has a profound influence on the final properties and performance of a coating. This lecture will summarise our recent work that aims to understand better this complex process using a variety of non-invasive techniques. Magnetic resonance profiling has been employed to understand how colloidal stability and the environmental conditions influence the distribution of water in a film during drying. Information on the packing of latex particles and on the correlation between particle nanostructure and deformation has been provided by atomic force microscopy. Confocal microscopy has provided insight into the phase distribution obtained from polymer/polymer nanocomposite particles and from blends of particles.
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Internal dynamics of drying latex films
Prof. Diethelm Johannsmann, Technical University of Clausthal, Germany |
The drying of polymer dispersions is typically described as a three-stage process, encompassing the evaporation of water until the particles touch (stage I), the coalescence of the particles (stage II), and polymer interdiffusion, leading to tough film (stage III). The contribution covers the stress distributions occurring in spatially heterogeneous drying, as well as studies of particle coalescence using fluorescent resonant energy transfer (FRET).
The results can be summarized as follows:
- When drying occurs from the edge to the center, there is a maximum of stress at the rim. For sufficiently thick films, the propagation of a stress front leads to cracking mechanism, by which cracks appear in the center (rather than the edge, which is more common case).
- The start and the end of the particle deformation stage (stage II) can be inferred from measurements of the fluorescence lifetime and the efficiency of energy transfer between donor- and acceptor particles, respectively. For soft particles, most of the deformation actually takes place before the particles touch.
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Monitoring of film formation and curing of waterborne 2K polyurethane coatings using inverse micro raman spectroscopy
Philippe Olier, Rhodia, France |
Over the last few years the trend has been to move from solvent-based technologies to waterborne ones. This is not only to meet new regulations but to satisfy customers' expectations for safer and more environmentally friendly products. In order to help paint manufacturers to offer 2K waterborne polyurethanes (PUR), Rhodia has developed patented water-dispersible polyisocyanate crosslinkers.
Previous works have shown that Inverse-Micro-Raman-Spectroscopy (IMRS) is a powerful technique to investigate concentration profiles and heterogeneities in transparent multi-component systems. With the non-invasive technique we can draw a map of the film without influencing the system. In this contribution, investigations of film drying and curing of two component waterborne PUR coatings are reported.
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Session II: Binder chemistry - innovations in the backbone
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A new class of Polycarbonate Macro diols for Polyurethane Dispersions with Excellent Performance
Henrik Bernquist, Jesper Fahlén, Rickard Martinsson and Birger Midelf
Perstorp Specialty Chemicals AB. Sweden |
Polycarbonate diols are becoming more and more interesting as a component in coating resins, due to its inherent attractive properties. However one limitation has been the limited number of polycarbonate diols available on the market. To broaden the available range of polycarbonate diols and increase the use of those in coating applications a new class of polycarbonate diols has been developed.
Waterborne coatings based on polycarbonate macrodiols are known to give coatings with superior weathering, chemical, hydrolysis, and abrasion resistance. The newly developed class of polycarbonate macrodiols (OxymerTM) based on homo- as well as co-polymers have been used to prepare waterborne polyurethane dispersions with excellent performance.
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Optimisation of flow in 2K waterborne clearcoats for stoving and room temperature cure
Ferry Thys, Nuplex Resins bv, Netherlands |
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Waterborne two component coatings are a route to solvent free clear coat applications.
Both for stoving and room temperature cure paint formulators are challenged with new problems.
New innovative concepts allow formulating clear coats with properties that are at par with their solvent borne counterparts.
This is illustrated in two cases: an oven dried clear coat based on a polyester emulsion for plastic parts, where the physicochemical behavior of the clear coat allows optimizing the leveling.
In a second case is illustrated how at room temperature cured acrylic emulsions can be tuned to optimal drying behavior.
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1K w/b clearcoats for stoving applications
Jean-Pierre Chevillotte, Cytec Surface Specialties, Belgium |
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w/b stoving clear-coats provide high film hardness combined with very high flexibility and excellent resistance against water and solvents. Their polymer structure is based on a condensation reaction of a hydroxyl-functional polyester and a carboxyl-functional polyacrylate. The final polymer becomes water-soluble after neutralization of the remaining carboxy-groups with an amine. The very good adhesion on various substrates like aluminium or galvanised steel enables to formulate coatings for e.g. bicycles, metal furniture, dipping and marine clear-coats.
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Waterborne clearcoats for industrial maintenance
Dr. Andrew Trapani, Rohm and Haas Company, France |
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The evaluation of clear waterborne acrylic coatings as topcoats in field-applied protective coating systems will be described. Clear coatings were evaluated over both waterborne and solventborne systems. The results of the effects of waterborne systems on properties such as corrosion resistance, gloss, and accelerated weathering will be discussed.
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Structure property relations in waterborne nanocomposite coatings
Professor Steven J. Picken, Technical University of Delft, Netherlands |
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Nanocomposite polyurethane dispersions for novel water based coating systems - fire retardant & easy to clean
Markus Dimmers, Alberdingk Boley GmbH, Germany |
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| FRIDAY, October 19th 2007 |
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Session II: Binder chemistry - innovations in the backbone (continued)
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Widening the application field of soft-touch coatings
Dr. Christoph Irle, Bayer MaterialScience AG, Germany |
Soft touch coatings have been established in the recent years as a popular way to provide a pleasant feel to molded plastic parts. The automotive industry for example has been a focus area where many soft touch coated parts are used today.
Innovation plays a major role in this comparatively young coatings field and this paper reports about continuous improvements in properties, like better hydrolytic resistance, lower paint emissions and reduced thermal yellowing. These new polyurethane based dispersions extend the use of soft touch coatings. Very light colors or lower emissions in the automotive interior are some of those. As a view into the future this paper covers a new reverse coatings process that eliminates the need for spraying. Those film sheets are high pressure formed without losing the soft touch effect, providing even more interesting designs.
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Study of the rheology of aqueous radiation curable polyurethane dispersions modified with associative thickeners
Michel Tielemans , Cytec Surface Specialties, Belgium |
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The chemistry of radiation curable polyurethane dispersions is outlined with an emphasis on the microstructure of the aqueous polymer dispersion and the possible interactions with associative thickeners. The steady-shear flow was studied for two model dispersions prepared from the same unsaturated polyurethane but showing significantly different particle size distributions. An hydrophobic ethoxylated urethane (HEUR) associative thickener with a linear structure was incorporated at different amounts to the dispersions with varying particle volume fractions. The steady-state viscosity at 25°C and 10°C was always reached quickly after instant flow rate changes so that no significant thixotropic effects were reported within the experimental timescale. Without thickener, the flow curves of the two model dispersions exhibited a Newtonian behaviour except at the highest volume fractions where shear-thinning became apparent. The maximum packing values determined from the Krieger-Dougherty relationship were essentially the same for the two systems. In the presence of thickener, the flow curves were characterized by a Newtonian plateau followed by a marked shear thinning region even at low particle volume fractions. This behaviour typically suggests the formation of a physical network between polyurethane particles and thickener molecules partly adsorbed onto the polymer surface. The zero-shear viscosity of the two dispersions was compared with respect to (i) particle volume fraction and (ii) particle surface area at different HEUR concentrations. At a given volume fraction, the particle size affects the viscosity of thickened models. As a corollary, a relationship is found between the particles size and the level of thickener required to reach a target viscosity. This study offers practically relevant data in terms of application conditions and provides a better insight into the thickening protocol.
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Effect of hydroxy-isocyanate ratio on properties of waterborne 2-K coatings
Claudia Goemans, DSM NeoResins+, Netherlands |
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Non-functional PUDs for 1 and 2 pack polyurethane coatings
Dr. Rolf Gertzmann, BayerMaterialScience AG, Germany |
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Session III: Additives - tiny essentials
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Organic lightstabilizers for automotive waterborne coatings: a difficult task
Tom Landuydt, Ciba Specialty Chemicals. Switzerland |
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One of the most important current challenges for paint manufacturers is the reduction of volatile organic compounds (VOC) in their formulations. As a potential compliant technology for VOC reduction, water borne clear coats are predicted to develop strongly over the coming years. Needless to say that impairment of the light stabilising performance of these waterborne clear coats is unacceptable in the automotive industry. Due to the lack of techniques for the effective and homogeneous incorporation of light stabilizers, which are mostly hydrophobic substances, into waterborne clear coats, new product forms addressing this issue became mandatory. Progress has been made with the development of water compatible product forms of water insoluble hydrophobic additives by using micro-encapsulation techniques.
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Nanoparticles as functional additives: good dispersions are essential for high quality waterborne clearcoats
Dr. Detlef Burgard, Nanogate Advanced Materials GmbH / Air Products GmbH, Germany |
The growing availability of a reliable source of commercially produced nanoparticles has opened up significant technological advances in numerous applications, including transparent heat blocking coatings, exterior coatings with extended weatherability, and the addition of other novel properties, like long lasting UV protection, to coatings. However, the difficulty of dispersing nanoparticles and integrating them into systems has limited the commercialization of nanoparticle-enabled products as the potential of nano particles cannot be fully utilized.
We will discuss basic principles as well as specific examples that demonstrate the importance of good dispersion in the final material in order to impart novel performance properties to coating formulations using metal oxide nanoparticles.
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Novel matting agent technology for waterborne wood coatings
Dimitri Hussin, Degussa GmbH, Germany |
Matting Agents in waterborne clear coatings gain increased attention. Coating Formulators have choices between
different matting agents mainly all based on synthetic silicas like precipitated-, thermal silicas or silica gels.
Silica based Matting Agents can be untreated or treated . In case of treated Matting Agents state of the Art are
wax (mainly Polyethylen types) treated silicas. Those matting agents tends to influence very often negatively the
performance of the coatings in terms of reducing the viscosity(due to their strong adsorbtive characteristic).
This is mainly caused by an interaction of the synthetic silica and the network of associative thickener (mainly HEUR)
the binder and emulsifiers in the coating system.
This paper describes a new technology of treated silicas and their performance in water based wood coatings in terms
of viscosity stability and chemical resistance by discussing those improved properties in 2 different coating systems.
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Influence of new wax additives on aesthetic and protective properties in waterborne coatings
Petra Lenz, Byk Additives and Instruments, Germany |
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The addition of wax additives can improve a lot of properties. Not only a smoother "waxlike" surface is the target in high quality coating systems. The improvement of mechanical properties as well as influence on water repellency, slip - antislip and gloss will be explaned very detailed by using various products. Incorporation and distribution, settling or creaming of the waxes in coatings is changing due to raw materials and producing processes. A sufficient performance depends also on orientation of wax particles in the dried film. Melting point and particle size can help to foresee results, nevertheless the special modifications of products and especially the difference between blends and alloys are the main points which offers high performance.
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