B6: UV-curable coatings

IA-based monomers and oligomers for UV curable coatings and inks

     UV and EB curing refers to a special way in which coatings, inks, adhesives, composites and other materials may be cured, rather than using traditional methods which are typically use more energy and create harmful emissions. In effect, the ultraviolet light spectrum in a UV lamp interact with specially formulated chemical compounds to cure materials-typically more quickly, using less energy and thereby at lower cost than by other methods. The advantages of UV are well-documented particularly when used with manufactured products that require fast processing and/or on substrates that are sensitive to heat. In addition, UV curing is considered environmentally sustainable since most of the solvents in traditional processes may be eliminated. UV curing typically describes the use of ultraviolet (UV) or visible light to polymerize a combination of monomers and oligomers onto a substrate. The UV material may be formulated into an ink, coating, adhesive or other product. The process is also known as radiation curing, because UV is radiant energy source. The energy sources for UV or visible light cure are typically medium pressure mercury lamps, pulsed xenon lamps, LEDs or lasers. The UV curing processing is solvent-free and require less than a second of exposure, the productivity gains can be tremendous compared to conventional coating techniques. Web line speeds can reach up to of 80 m/min and the product is immediately ready for testing and shipment. In addition, the process provides total control of the cure temperature making it ideal for application on heat sensitive substrates. Compositions are typically solvent-free so emissions and flammability are not a concern.

Monomers are the simplest building blocks from which synthetic organic materials are made. A simple monomer derived from petroleum feed are acrylated and methacrylate derivatives. These reactive chemical compounds are capable of reacting to form larger chemical materials called oligomers and polymers. Monomers are primarily used as diluents to lower the viscosity of the uncured material to facilitate application. They can be monofunctional, containing only one reactive (i.e. unsaturation) group or multifunctional. Multifunctional monomers, because they contain two or more reactive sites, form links between oligomer molecules and other monomers in the formulation. 

Oligomers are a special term used to designate those polymers which often can be further reacted to form a large combination of polymers. The reactive groups on oligomers and monomers alone will not undergo a reaction or crosslinking. The overall properties of any coating, ink, adhesive or binder crosslinked by radiant energy are determined primarily by the oligomers used in the UV curable mixture. Oligomers are moderately low molecular weight polymers, most of which are based bearing acrylated moieties to the chain ends of the oligomer.

Photoinitiators are mainly organic compounds which absorbs light and are responsible for the production of free radicals. Free radicals are very reactive species that promoting crosslinking between the unsaturation sites of monomers and oligomers. The most common additives used in UV curable mixtures are stabilizers, which prevent gelation in storage increasing the shelf life, pigments or dyes for ink productions and adhesion promoters, flatting agents having a wettability and leveling action on the surface substrate such as paper, polymer film, wood panel and aluminum foils.

Many other applications for the production of acrylated UV curable systems based on BioUPR or epoxydimethacrylates are not yet investigated. In Europe, the production of the itaconic acid by starch bio- transformation is very limited to the research scale. The main aims of the this technical action are on:

i) the photoreactivity of IA-based diester and trimester derivatives by using ethanol, propanol, butanol, trimethylyol propane (TMP) and pentaerythritol (PER) derived from renewable resources. The IA-based derivatives will be used as reacting diluents for thermo- and photo-initiated radical polymerization of bioUPR and commercially available epoxydimethacrylates.

ii) The photoreactivity of these UV curable mixtures will be studied in the lab scale for determining the photopolymerization rates and conversion degrees as a function of the photoinitiator contents by using photocalorimetry  and FTIR experimental techniques equipped with UV light sources. Some preliminary results have indicated that the conversion degrees and photopolymerization rates are comparable with those UV curable mixtures containing commercially available methacrylated and epoxydimethacrylates in presence of the same photoinitiators.

iii) the use of some chain transfer agents (e.g. for the thiol- ene reactions) during the photopolymerization can enhance the conversion degrees near to unity, while the photopolymerization rates are very similar to those obtained with other di-functional methacrylated monomers. The UV curing of IA based mixtures will be prepared for the starting production of paints, inks and adhesives.

The properties and experimental conditions of some UV curable mixtures based-itaconic monomers and oligomers will be prepared to develop the applications for production of biodegradable inks, adhesives and paints for biomedical and food packaging by using high irradiance UV equipment. The UV cured coatings and inks on PET films will be tested to determine surface hardness, scratch resistance, adhesion properties yellowing resistance. The preliminary results suggest that a possible application could for outdoor applications due to high yellowing resistance due to the aliphatic nature of the used monomers and resins.

Beneficiary responsible for implementation: APM

IA-based monomers and oligomers for UV curable coatings and inks

advanced polymer materials