Session 23: UV-Technology
Chair: Dr. Katia Studer, Ciba, CHThe environmental and economic benefits of radiation curing underlie the growing popularity of this technology – the number of industrial applications keeps expanding as radiation-curing coatings rapidly evolve into high-performance products. The six papers of this session present novel methods, materials and opportunities around UV-Technology, including sol-gel chemistry, UV-inks as well as influences of adhesion of UV-coatings.
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Wednesday Afternoon 14.00 – 17.30 h
Room Kopenhagen
23.1 14.00 – 14.30 h Matting of nanocomposite acrylate coatings using 172 nm excimer irradiation Prof. Reiner Mehnert, Cetelon Nanotechnik, DE In radiaiton curing, where all formulation components are reactive, there is negligible loss of coating thickness during curing and, thereby the so-called 100% systems are known to be less effective in allowing deep matt coatings to be developed. Using a set-up consisting of a 172 nm excimer lamp and a medium pressure mercury lamp in line, wrinkles surface textures can be produced which allow to obtain gloss levels down to 0.5 (at 60°)depending on acrylate formulation, nanoparticle content, application and curing conditions. Moreover, the matt finished surfaces show enhanced surface hardness, and improved chemical and weathering resistance. The excimer matting technic has been scaled up to a web width of 2,3 m and web speeds up to 200 m/min. Examples are given which demonstrate the application range of excimer matting.  | ||
| 23.2 14.30 – 15.00 h UV cured organic-inorganic coatings combining sol-gel chemistry and cationic photopolymerization Prof. Celine Croutxé-Barghorn, University of Haute Alsace, FR Photopolymerizable organic-inorganic sol-gel coatings combine numerous advantages: good adhesion to substrates, abrasion and chemical resistance. Owing to the possibility of controlling the inorganic network density, sol-gel films can also form an effective barrier layer. Alcoxysilanes bearing an epoxy reactive function were photopolymerized in presence of a cationic photoinitiator. The corresponding generated Brönsted acids were found to be effective in catalyzing both epoxy ring-opening polymerization and alkoxysilane sol-gel polycondensation reactions. Therefore, this dual organic-inorganic UV-curing of ambifunctional precursors allows to achieve hybrid networks in a one-step process, opening up new opportunities for the UV cured coatings field. Competition between the formation of inorganic and organic phases was kinetically studied using real-time Fourier transform infrared spectroscopy (RT-FTIR). 29Si and 13C Solid state NMR measurements were also performed to investigate the structure of the UV-cured hybrid materials. | ||
15.30 – 16.00 h Networking: Refreshments & Coffee Break | ||
| 23.4 16.00 – 16.30 h Overcoming the oxygen inhibition in free radical photopolymerization: new methods for new opportunities Prof. Xavier Allonas, University of Haute Alsace, FR Oxygen inhibition is known as one of the major drawbacks in free radical photopolymerization, affecting the mechanical properties on the surface of the coatings. Generally, this effect is partly counterbalanced by use of high irradiation energy, high photoinitiator concentration or by addition of amine. In this paper, the different methods to overcome oxygen inhibition are briefly reviewed. Three new methods are presented that use new photoinitiating systems based on the silyl, thiyl or boryl radical chemistry. Photopolymerization rates and final conversions are monitored by real-time FTIR. Pendulum hardness and surface energy were measured for each sample. The results show that oxygen inhibition can be reduced. More interestingly, in the case of silane used as coinitiator, the photopolymerization can be more efficient in the presence of oxygen than under inert atmosphere. This shows clearly that oxygen can promote the free radical photopolymerization. Interestingly, the corresponding coatings exhibit excellent mechanical properties. | ||
| 23.5 16.30 – 17.00 h How to tackle pigment dispersion in UV curing inks Hélène DuCongpant, Sartomer Europe , FR The use of UV and EB is now well established in the printing technologies. The constant growth of penetration of UV/EB inks on the market clearly demonstrate the several advantages when compared to conventional technologies. Pigment dispersion in the formulation of an ink is still a challenge where space for improvement really exists. This paper will present an overview of the several parameters that influence the pigment dispersion, followed by an evaluation of different acrylated oligomers with different pigments. Finally, interpretation of the relationship between the pigment wetting and the oligomer physic properties will be discussed. As a conclusion the paper will demonstrate that selective choice of the oligomer will enable the formulator to optimise the properties of the dispersion. | ||
| 23.6 17.00 – 17.30 h Influencing the adhesion of UV-coatings on corona treated polyethylene Dr. Katharina Kugele, Research Institute for Pigments and Coatings (FPL), University of Stuttgart, DE The application of UV-curing coatings on plastics is of high economical and ecological interest. However, to achieve good adhesion of the cured coating on non-porous substrates, and on plastics such as polyethylene (PE) and polypropylene (PP) in particular, a special surface modification, e.g., oxidation by Corona discharge, is required before the application of the coating. The characterization of such modified surfaces of PE and PP foils by contact angle and XPS measurements gave important information about the influence of the physical and chemical properties of the polyolefin surface on the adhesion of the UV-cured coatings. In general, intense corona treatment significantly improves the wetting and adhesion. More specifically, it was found that for a satisfactory adhesion a polar contribution of surface tension of at least 20 mN m-1 is needed. Furthermore, as shown for the example of PE, structural characteristics of the components of the formulation have an essential effect on the adhesion of UV-cured coatings. E.g., binders with a flexible polymer backbone, or the addition of reactive thinners that retard the UV-curing, prevent the formation of internal stress in the polymer network, and positively effect the adhesion. | ||
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