UV curing kinetic of high performance epoxy resin for Roll-to-Roll UV embossing

Abstract

In present work curing kinetics of UV-initiated cationic photo-polymerization of EPICLON series epoxy resin HP-820 and key cure process parameters, such as the extent of crosslinking and conversion, polymerization rate and the order of reactions have been studied by Photo-Differential Scanning Calorimetry (DPC). Different kinetics analysis results, including enthalpy of the reaction, induction time, peak maximum, percentage conversion were obtained for studied epoxy system at different isothermal temperatures (30-70 o C), allowing calculating activation energy. Two kinetic parameters -coefficient rate (k) and the order of the initiating reaction (m) were determined, using an autocatalytic kinetics model. IntroductionThe extensive development of the UV curing technology has opened the way to numerous end uses, more recently -in nonconventional micro-patterning technique -in a continuous Roll-to-Roll (R2R) UV embossing, which can provide a solution for high speed large area nano-and microscale patterning of different structures with greatly improved throughput [1-6]. One of the examples is microlens array (MLA) film, which among various application found in the field of optical sensors and communications, displays, lighting devices etc can be an effective solution in enhancing the light and increasing optical coupling efficiency [7].Among polymer-based lens materials having been extensively studied since 1990s, UV curable has been shown to be the most attractive not only from environmental point of view, introducing solvent free formulations and ambient temperature operations but also due to the high polymerization speed of resins, resulting in reduced cost of final product [2]. Tailor made properties -is another great advantage of materials, produced by UV induced polymerization [3].The market of photocurable resins is very large and diversified. Among two major classes of UV-curable resins available on the market and often used in various UV-assisted patterning processes and techniques -multifunctional acrylates, and multifunctional epoxides, the last ones present number of advantages. First of all, epoxies are cured via cationic, oxygen inhibition free curing mechanism, allowing avoiding special environmental conditions needed for acrylates, cured via radical mechanism [8]. More of that, its lower, compare, to acrylate resins shrinkage after curing allows more faithful pattern application. However, despite these advantages their market is still small, and one of the reason, beside the price is probably related to their lower than acrylate`s and methacrylate`s reactivity.

Impact of winding on nanoimprinted surfaces in roll‐to‐roll nanoimprint lithography

“…[20][21][22][23][24][25][26] Numerous studies have focused on the photopolymerization of the resist in the mold and its influence on the release forces and shape retention of the nanoimprints. [27][28][29][30][31][32] In this study, we focus on what occurs after the photopolymerization step, that is directly after UV light exposure. As the R2R UV-NIL process generally involves high speeds and short UV light exposure of high intensity, the conversion level of the resin coming out of the imprint rollers is relatively low.…”