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Recently there has been announced a new 3d printing technology which uses UV light, from lasers or a projector, to harden slices of epoxy resin so that the printed object rises out of a pool of epoxy.

There is some information about an oxygen boundary and UV light, can someone explain the chemistry of the process?
https://www.youtube.com/watch?v=UpH1zhUQY0c

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  • $\begingroup$ I have seen the video, and wonder if the claim "can use all polymers, elastomers" is true, because you need a "handle" on the molecule to make it uv curable. In other words, if I would claim to use a certain polymer it would have been drastically modified,or not? $\endgroup$
    – user17951
    Commented Aug 6, 2015 at 7:56
  • $\begingroup$ Is a polymer drastically modified by putting a UV handle molecule on it? interesting question why don't you ask how that process works? there are uv cureable versions of polyester and rubbers, i don't know what they do. This printer if it becomes available for homes will have a mechanical transfer to a drying and cleaning area, otherwise it wil be unmarketable, to have dripping models coming out of a box at home! $\endgroup$
    – bandybabboon
    Commented Aug 6, 2015 at 9:09

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Actually, the technology isn't that new. It seems however, that the setups are becoming more affordable in the hobby market.

The technology is know as stereolithography and is a form of light-induced polymerization (UV curing).

The liquid monomers used have a substituent that can be activated using UV light. Out of practical considerations, UV is more convenient: polymerization of the resin will not occur under natural light.

In principle, the procedure is comparable to UV curing in dental repair. There, a lamp that irradiates the whole area is used: you want a fast hardening all over the tooth.

In 3D printing, this is obviously different! The light source is a laser with a narrow beam: you only want to irradiate a very small volume element at a time.

You don't want a rapid polymerization either: only the volume element irradiated should react!

The laser beam is focussed at the boundary of the resin and different volume elements are addressed by moving the focus in the $xy$ plane.

Rather than moving the (heavy) laser itself, the beam is "moved" using a mirror optic. This allows for a very fast adressing of reaction points within the plane.

UPDATE In the example linked, in the question and a comment, however, the setup is different from laser-based STL printers.

Irradiation from the bottom of of the resin tank through an oxygen-permeable membrane indicates indeed that the UV curing proceeds in the presence of oxygen. Anyway, if the light source would be just a lamp, one would nevertheless achieve homogenous curing of the whole layer. But the manufacturer doesn't use the term lamp or light source. Instead, they write about a projector and that's probably what they do:

They are not illuminating the whole layer, but are projecting masks for every slice of the object to be printed.

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    $\begingroup$ Ich habe mich auch maßlos über diese dreise "Neuheit" geärgert. $\endgroup$
    – Georg
    Commented Mar 19, 2015 at 19:01
  • $\begingroup$ AKA = i am also immeasurably annoyed by this Dreise "novelty" . Yes Georg it seems that the media is promoting this form of 3d printer as new. perhaps it's the first one that can print as fast and that has been filmed printing in one single movement? $\endgroup$
    – bandybabboon
    Commented Mar 19, 2015 at 20:17
  • $\begingroup$ I am curious about how they manage to focus the UV light into a point rather tan a line, and what the oxygen layer is inside the epoxy, if they inject oxygen through the base in some way. $\endgroup$
    – bandybabboon
    Commented Mar 19, 2015 at 20:19
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    $\begingroup$ @ufomorace there's a misunderstanding. there is no oxygen layer inside the resin, there's just air on the top of the basin. $\endgroup$
    – Klaus-Dieter Warzecha
    Commented Mar 19, 2015 at 20:22
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    $\begingroup$ What's new about the system isn't the hardware; stereolithography has been around for ages, but the chemistry is the interesting part (enough for an article in Science). Normal SLA is done iteratively, debonding the part from the window and applying new resin for each layer between exposures. By using this "dead zone", the part doesn't stick to the window and new resin is drawn under it as it is raised, allowing continuous exposure. And they do use a projector, with a DLP chip. $\endgroup$
    – Michael DM Dryden
    Commented Mar 20, 2015 at 21:37

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