Photopolymer Resins

Photopolymer refers to light-sensitive (photoactive) resins that solidify when exposed to ultraviolet (UV) light. In photopolymer based additive manufacturing processes, photoinitiators transform that energy into chemical energy when the liquid photopolymerizable resin meets a UV light source (typically a lamp, laser, or projector). Then, oligomers or “binders” and monomers combine, harden, and form bonds that create the polymer structure.

The functionalized oligomers (typically epoxides, urethanes, polyethers, or polyesters) present in the photocurable composite provide the properties of a photocured material, such as flexibility, adhesion and chemical resistance. An acrylate typically functionalizes each of these oligomers. The monomers used in UV-curable systems help control the speed of cure, crosslink density, final surface properties of the film and viscosity of the resin. Examples of monomers include styrene and acrylates.

According to data from VoxelMatters’ Polymer AM Market Report, photopolymer resins represent the largest portion of the additive manufacturing materials market and have various applications. There are two main photopolymerization-based 3D printing processes. Vat-based stereolithography was the first 3D printing technology to be patented and commercialized. Stereolithography has evolved into several vat photopolymerization (VPP) processes: SLA, DLP, continuous or layerless DLP, LCD and micro stereolithography. Another popular family of photopolymerization processes evolved from material jetting (or inkjetting), with PolyJet being the original technology to be patented. Material jetting processes can use several different materials (including materials that are not photopolymers); however, when they use photopolymers, these are “jetted” from a moving printhead onto a platform and subsequently cured by UV light.

Common monomers utilized for 3D printing include multifunctional acrylates and methacrylates, often combined with a non-polymeric component to reduce volume shrinkage or with higher quantities of thermoset materials to improve durability. A competing composite mixture of epoxide resins and cationic photoinitiators is becoming more common since its volume shrinkage upon ring-opening polymerization is significantly below those of acrylates and methacrylates.