In the past years we have heard and read about the idea of increasing the toughness of a resin by UV post-curing the parts very shortly. With our extended experience with resin 3D-printing and its properties, we do not advise to pursue this strategy for high demanding applications. Why? Read all about it in this article.
image by threebond group: schematic representation what happens during UV-post-curing.
What does post-curing to your 3D-printed part and toughness?
Liquid resins are build-up from acrylates or methacrylates. With a photoinitiator and additives added to this system, they can respond and polymerize to the right wavelength of light. The properties of a resin are coming from the backbone of the material, the chemical interaction of the molecules and the cross-link density. The last one has an huge effect on if a part feels brittle or not. What happens is that if you cure a resin longer, it will react more and will become more rigid i.e. creating more cross-links. By UV post-curing less you are actually creating less cross-links. This will (temporarily) give a tougher and more flexible polymer.
Why is this not a long-term solution?
We are always striving to get close to 100% polymerization in each polymer part by post-curing it long enough and often at elevated temperatures (during UV-curing in one step post-processing). This way your part does not change much anymore over time. Of course there is UV-aging or thermal aging when placing it in a more demanding environment. If you don’t cure your part 100%, trying to make it tougher with less post-curing. These parts will cure on its own on your desk, getting rigid and more brittle faster over-time. So it is advised to choose a more advanced resin which is actually tough when it is cured to almost 100%. Our tough polymers, Premium Tough, Tough-X and Clear Impact might be interesting for your application.
What about brittleness during thermal and UV-aging?
It is known that 3D-printing resins do age when exposed to thermal or UV sources for extended times. This process is different compared to the situation of low post-curing times explained below. If you have a 100% cured network, UV rays can damage the polymer chain and increase the cross-link density even higher even though the network is formed 100%. For 100% cured materials, the effect is much lower. Learn more in the links below to see which material fits your requirements.