Acoustic monitoring of photopolymerization in UV curable coatings

  • Crosslinked materials formed by the polymerization of acrylate and methacrylate based coatings are used in many commercially applications like coatings, photonics or dental restorative materials. These systems are characterized by great flexibility in manufacturing. They can be polymerized under varying conditions, at different temperature and using thermal or UV radiation to start the polymerization reaction. Main advantage in using UV radiation to initiate the chain reaction lies in the very high polymerization rates that can be reached under intense illumination, so that the liquid to solid phase change takes place within a fraction of second. Another distinct feature of light-induced reactions is that the polymerization will occur only in the illuminated areas, thus allowing complex relief pattern to be produced after solvent development. Consequently, photoinitiated polymerization of multifunctional monomers, or UV-radiation curing, has found a large number of applications inCrosslinked materials formed by the polymerization of acrylate and methacrylate based coatings are used in many commercially applications like coatings, photonics or dental restorative materials. These systems are characterized by great flexibility in manufacturing. They can be polymerized under varying conditions, at different temperature and using thermal or UV radiation to start the polymerization reaction. Main advantage in using UV radiation to initiate the chain reaction lies in the very high polymerization rates that can be reached under intense illumination, so that the liquid to solid phase change takes place within a fraction of second. Another distinct feature of light-induced reactions is that the polymerization will occur only in the illuminated areas, thus allowing complex relief pattern to be produced after solvent development. Consequently, photoinitiated polymerization of multifunctional monomers, or UV-radiation curing, has found a large number of applications in various industrial sectors. This technology is now commonly utilised to perform the fast drying of protective coatings, varnishes, printing inks and adhesive, and to produce the high-definition images required in the manufacture of microcircuits and printing plates. Besides its great speed having spatial resolution, radiation curing presents a number of other advantages, in particular ambient temperature operations, solvent-free formulations, low energy consumption and the production of polymer materials having tailor-made properties. The printing industry represents, besides the chemical industry, the segment of major use for the UV curable coatings. The reason of using UV curable systems as alternative to the solvent-based coatings are their improved physical properties like brilliance, abrasion resistance, chemical resistance, adhesion to the substrate. Those systems are employed, because of their economical and environmental advantages by many products from packaging to newspapers and credit cards. The lack of solvent in the formulation of UV curable coatings avoids the emission of volatile organic compounds (VOC) and makes them environmentally friendly. Using UV curable systems it is possible to obtain very thin films with high density and in the meantime to realize a substantial cost reduction by saving material. Furthermore the UV cure is a very fast process which means reduction of manufacturing cycle time and increasing productivity. The polymer film build up through the curing process should be harmless for the consumer health. This request is very strict by the food packaging coatings. EU Regulation 1935/2004 requires that food packaging must not transfer any components onto the packed foodstuff in quantities that could endanger human health, alter its composition or bring about deterioration in the organoleptic properties of the foodstuff. As consequence, no substance is allowed to transfer from substrates or coating film to the packaged food in quantities that exceed the legal limits. The transfer of unalloyed substances is known as migration and occurs by the decomposition products of photoinitiators and non-reacted photoinitiators, residual monomers unreacted in the coating film or into the substrate or by an incomplete photopolymerization reaction due to an inappropriate cure. The practice learned that rest of photoinitiators and an inadequate cure represents the most commonly cause of migration. Part of the project and aim of this work was the development of a new, cost reduced, analytical method to investigate the photopolymerization process in UV curable coatings and clear coatings. The basic measurement principle is based on the idea that a variation in the viscoelastic properties of the material, due to crosslinking, causes changes in the vibration modes, specifically in the resonant frequency of the material exposed to a vibration motion. The remote material excitation was generated through a low frequency signal which was selected for its good propagation capabilities among various materials and for the simple equipment required to generate the signal itself. The arrangement was divided into two main parts, acoustic vibration excitation and acoustic vibration detection. The acoustic vibration excitation system consists in a loudspeaker connected to a function generator and a sample holder specifically designed for this purpose. The detection system consists of a laser beam and a photodiode as signal receiver unit. This arrangement was used to study two different modes: the damped, freely vibration mode and the forced vibration mode of the coatings. For each mode we employed a for this purpose developed software program to evaluate the collected data.show moreshow less
  • Ziel dieser Arbeit war die Entwicklung einer neuen, kostenreduzierten, analytischen Methode, um den Photopolymerisationsprozess in den UV härtbaren Lacken und Farben zu messen bzw. zu beobachten. Das Messprinzip basiert auf der Veränderung der viskoelastischen Eigenschaften des Materials, während der Polymerisation, die in direkter Verbindung mit der Änderungen der Resonanzfrequenz des Materials der einen freien bzw. erzwungenen Schwingung ausgesetzt wird. Eine Messmethode, in zwei Varianten verwendbar, ist entwickelt worden. Beide Varianten können durch zwei zweckgemäß entwickelte Software Programme betätigt werden.

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Metadaten
Author:Elena Magdalena De Ambroggi
URN:urn:nbn:de:bvb:384-opus-18140
Frontdoor URLhttps://opus.bibliothek.uni-augsburg.de/opus4/1605
Title Additional (German):Akustisches Monitoring der Photopolymerisation in UV härtbare Lacke und Farben
Advisor:Achim Wixforth
Type:Doctoral Thesis
Language:English
Publishing Institution:Universität Augsburg
Granting Institution:Universität Augsburg, Mathematisch-Naturwissenschaftlich-Technische Fakultät
Date of final exam:2011/07/21
Release Date:2012/01/26
Tag:UV Härtung
polymers; UV cure; UV coatings; vibrational modes
GND-Keyword:Polymere; Photopolymerisation; Ultraviolettlack; Viskoelastizität; Eigenschwingung
Institutes:Mathematisch-Naturwissenschaftlich-Technische Fakultät
Mathematisch-Naturwissenschaftlich-Technische Fakultät / Institut für Physik
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Licence (German):Deutsches Urheberrecht