Abstract
Lithography-based additive manufacturing was introduced in the 1980s, and is still the method of choice for printing accurate plastic parts with high surface quality. Recent progress in this field has made tough photopolymer resins and cheap LED light engines available. This study presents the influence of photoinitiator selection and post-processing on the thermomechanical properties of various tough photopolymers. The influence of three photoinitiators (Ivocerin, BAPO, and TPO-L) on the double-bond conversion and mechanical properties was investigated by mid infrared spectroscopy, dynamic mechanical analysis and tensile tests. It was found that 1.18 wt % TPO-L would provide the best overall results in terms of double-bond conversion and mechanical properties. A correlation between double-bond conversion, yield strength, and glass transition temperature was found. Elongation at break remained high after post-curing at about 80–100%, and was not influenced by higher photoinitiator concentration. Finally, functional parts with 41 MPa tensile strength, 82% elongation at break, and 112 °C glass transition temperature were printed on a 405 nm DLP (digital light processing) printer.
Highlights
Lithography-based additive manufacturing (L-AM) was introduced in the 1980s, along with the commercialization of stereolithography
L-AM is still unmatched in terms of the resolution and surface quality of the final printed parts
L-AM relies on photopolymers, which are selectively cured by light in a layer-based process
Summary
Lithography-based additive manufacturing (L-AM) was introduced in the 1980s, along with the commercialization of stereolithography. A few other processes were introduced for the additive manufacturing of polymeric parts. L-AM relies on photopolymers, which are selectively cured by light in a layer-based process. Using conventional photopolymers for L-AM leads to either very rigid—and brittle—parts; or soft parts, with a low glass transition temperature [1,2]. 4D-printing can make use of this low glass transition temperature in cross-linked photopolymers to enable shape-memory applications [3,4,5]. Recent research in this field has focused on increasing the toughness of such photopolymerizable resins. One important approach is the reduction of crosslink density within the cured photopolymer [6]
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