A blog by Aymeric Champion, PhD student at the University of Haute-Alsace in France and speaker at this year’s conference. Below his findings on the RTE Conference & Exhibition 2019 which was held on 15-16 October in Munich.

#radtech19 – Day 1

During two days, RadTech Europe 19 took place at the Westin Grand München hotel in Germany with a melting pot of industrials and academics mainly from Europe.

At 9 AM, after a brief introduction by Paul Kelly, the first speaker of the day, David Engberg (Perstorp), exposed the position of radiation curing in a world market overview. There are 3 main trends. The first one is population growing and it needs resource efficiency and it is solved by improving the reactivity of the system and the emerging use of 3D printing, which concerns now 3% of the market. The second one is the climate change and leads to lower energy consumption by using LED source and biobased product. The last trend is about health and radiation industry which needs to reduce the content of organic volatile compound and limit the migration in the final product. Wood coating still represents the main market with 39% of the 63kT of formulation produced each year.

Cost is always the first concern of industrial followed by physical properties, then productivity and finally environment respect. Indeed, despite of climate change in terms of ecology, economic climate is not at his top in our days. Even if environment is the fourth concern of UV industry more resin producer are selling biobased resin. Allnex produces a waterborne coating for wood industry with 22% of biorenewable content and Sartomer has a full range of oligomer and reactive diluent, Sarbio, with an interesting range of properties in term of glass transition temperature, viscosity and mechanical resistance.

The conference began at 10:30 AM with several sessions about the photocomposite field, a new photoinitating system for cationic polymerization which was developed by Liska’s team (TU Wien) with a reduced toxicity, compared to antimony based system and a higher reactivity. Surprisingly, at the end of the presentation, a demonstration was done by photopolymerized epoxide under water with just a little softening of the material at the interface. The Beer-lambert physical limitation of the light penetration in the matter was overtaken by 3 different ways in the University of Haute Alsace in Mulhouse, France. Indeed, Xavier Allonas presented a better understanding of TPO photobleaching and mechanical consequences for glass fiber photocomposite. Then, a method to produce high thickness composite using the oxygen inhibition to improve adhesion between sheet laminated material and dual cure combining photo and thermal polymerization was used to produce a 2mm carbon fiber composite. Higher volume of carbon fiber than 50% is always a technologic lock because of the dispersion of the heat needed to maintain the polymerization reaction. In the fields of reinforced photopolymer, thermic polymerization can’t be equalized in term of mechanical properties.

After lunch, functionalization of coating surface was conducted under a mercury lamp using affected oxygen layer in order to combine mechanical core and hydrophobic surface. Then, Perrine Theil from the silicone specialist Elkem, showed us how the importance of spacer in terms of thermal and abrasion resistance for aeronotic compliance.

Chris Orilall (Arkema) did a very interesting course about adhesives with a comparison of low and high molecular weight epoxide acrylate, polyester acrylate, polyurethane acrylate and other backbone. Using “Dahlquist criterion” it clearly demonstrated that adhesive properties are easy to measure and knowledge about chemical structure is essential. Moreover the presentation of UV cured binding that could be removed with heat allowed the creation of a new type of smart-adhesives.

Advantages of LED compared to arc or microwave lamp was done in terms of energy saving with David Ivarsson and Greta Thunberg (Efsen Egnineering).

At the end of the day, Petra Lenz (BYK Chemie) brought colors to our eyes with BYK additives for inkjet dye suspension stabilization.

#radtech19 – Day 2

Mostly every presentation used TPO or liquid alternative TPO-L in order to phopolymerized their product and most of them, surely were impacted by the Chinese raw material industry shutdown during the year. In order to comply industrial need, one of East-Europe agro-chemicals company started the production of European diphenyl (trimethylbenzoyle) phosphine oxide. Nevertheless, IGM Resins mentioned a quick reminder that TPO go from CMR 2 to CMR 1 class.

The potential of 3D market imply to have equivalent properties as injection molding and in the case of DLP, the two goals are ABS-like resin and no-shrinkage efficient formulation. Conferences about the 3D and biobased resins took place in the morning. Allnex, Mäder and Rahn presented interesting resin from biomass from 22 to 81% of biorenewable carbon content. The last one synthesized oligomers for material with high toughness and shape memory 3D printed with DLP material. Because of the source of the green synthons, it could be used for water soluble support.

At 1:30 PM, Liska (TU Wien) was up. Real time near infrared photorheology (RT-NIR) was used to measure chain transfer impact in the shrinkage of acrylate material with new reversible and irreversible agent. They allowed to reach higher conversion while delaying the gel point without shrinkage. To reach higher conversion at the gel point without shrinkage of methacrylate. They showed better mechanical resistance in term of toughness result compared to thiol with no odor or toxicity and a pot life of 9 months.

Then, an overview of photochemical reaction in order to create smart coating was done by Céline Croutxé-Barghorn from Mulhouse (Université de Haute Alsace). Indeed, the switch from Mercury lamp to LED leads to tacky surface and lack of mechanical properties due to low conversion of the system. Traditionally, radical polymerization is the most used way to create photopolymer and there is a limitation of this chain growth polymerization because of early-vitrification. Sol-gel, formation of glass at room-temperature with water, Photo-CuAAC and Aza-Michael, mixture of amine and acrylate, introduce the polyaddition leading to the delay of vitrification and have new properties as shape memory. This new technic allows to break glass transition limitation under LED irradiation with a material with 120°C reached.

Shrinkage, due to high crosslinking density of meth(acrylate) (3.40A bond vs 1.54 A bond), was reducing vinylcyclopropane transfer agent in order to produce methacrylate based dental composite with better quality and durability, Sebastian Schörpf from TU Wien in Austria presented. The classical camphorquinone/amine system was switched to a germanium based type I photoinitator system insensible to oxygen inhibition.

Another concern in 3D stereolithography, is the speed limitation. With continuous lithography, the effect of oxygen inhibition was used in order to create dead zone avoiding binding with substrate. During his conference at 3:30 PM, Taki (Kanazawa University) explained how the effect of oxygen and humidity could impact the polymerization of oxetane, epoxy and acrylic monomers. Moreover, he described the steps needed in order to simulate mechanical properties in SLA.

The writer of “Industrial Photonitator”, a reference book for photopolymerists since 2010, was here to talk about benzophenone’s derivatives. In a formulation with the CN 3715, acrylated amine, as hydrogen donor, Arthur Green explained how substitution of BP in the type II photoinitator impacts the kinetics of hydrogen transfer and improved the absorbance. For example, the 4-MeOBP allows to cure at 365nm.

The limitation in composites technologies, the economic climate, the growing market of 3D are the issues industrials and academics try to answer. For example with the ABS-like material solved by Sartomer and Shrinkage by the Austrian team are in good path to solve these limitations.

These two days were full with interesting talk shows, meetings and conferences. Interaction between industrials and academics always produce a variety of questions with economic, ground experiences and future technology to come.

Now, it is time to go back to the lab.

Aymeric CHAMPION from University of Haute-Alsace