Epoxy thiol photolatent base clearcoats: curing and formulation

Abstract

Photolatent base crosslinked epoxy thiol coatings were characterized using transmission FTIR spectroscopy, Raman spectroscopy, UV spectroscopy, and Vickers micro-hardness testing. Curing rate constants were calculated for a series of formulations with varying concentrations of photolatent-DBN, ITX (2-isopropyl thioxanthone), and BP (benzophenone), as well as varying curing times. A design of experiments demonstrated that increased UV dose had the greatest impact on increasing the curing rate of the clearcoat system. BP wt% proved to have little impact on the clearcoat curing rate, while PL-DBN and ITX exhibited minimal improvement above 2.5 wt% and 1 wt%, respectively. Vickers micro-hardness results showed that irradiation dose had no impact on the final physical properties of the clearcoat. However, a 24-h ambient post-cure proved to increase the final hardness of the clearcoat under some conditions.

Analysis of the reaction mechanism of the thiol–epoxy addition initiated by nucleophilic tertiary amines

“…Thus, it is possible to use it not only in conventional reactive formulations but also in dual-curable systems with a controlled curing sequence such as thiol-ene/thiol-epoxy, [2][3][4][5] off-stoichiometric thiol-epoxy systems, 6 or even in combination with inorganic network precursors in hybrid systems. 7 Thiol-epoxy thermosets are highly transparent, which is favorable for their application as clearcoats 8 and generally highly flexible, 9 but this latter feature is also a drawback because their low T g can limit their use in more temperature-demanding applications. 10 In order to enhance the thermal-mechanical characteristics of thiol-epoxy, different strategies can be adopted, such as the use of more rigid and functional epoxy resins 10 and the development of novel highly-functional thiol crosslinkers 11 in stoichiometric thiol-epoxy systems, or the use of excess epoxy in off-stoichiometric thiol-epoxy systems.…”

Control of reactions and network structures of epoxy thermosets

“…Other typical hardeners of epoxy resins are polythiols [156][157][158][159] and polyisocyanates [160][161][162][163]. Like carboxylic acids, their nucleophilicity is usually much lower than amines or dihydrazides and base-catalyzed conditions must be used to observe adequate curing rates.…”

“…Again, the stability of the catalyzed formulation may be insured by using latent catalysts such as thermo-or photo-generated amines (see Section 3.2.) [157,161]. Typical thiol hardeners are polysulfides (Fig.…”

Fully bio-based aliphatic thermoset polyesters via self-catalyzed self-condensation of multifunctional epoxy monomers directly extracted from natural sources

“…7,8 Furthermore, the benefit of the epoxy group is that it can undergo reactions with numerous other functional groups such as acids, 7,9 anhydrides, 7,10 alcohols, 9,11 and thiols. 12,13 One group of bio-based epoxy functional structures that has obtained a significant amount of interest is epoxidized vegetable oils, e.g., epoxidized soybean oil. 3,14,15 These monomers have one or more secondary epoxy groups situated in the aliphatic chain on the site where the fatty acid initially had the unsaturation.…”