After years of popularity, people are no longer familiar with 3D printing technology . However, several recent demos of 3D printing on the Internet seem to be extraordinarily cool and special: in colorful liquids, models such as the Eiffel Tower and the hollow sphere in the shape of "fullerenes" are like magic. Pulled out on the liquid surface:
These magical images are from a recent research paper on 3D printing technology published in Science [1]. This new technology clearly conquered the editors of the journal, and the "inverted tower" printed on the liquid appeared on the cover of the journal. So, what is the beauty of this liquid 3D printing technology? How did the ball and tower "pull" out of the liquid?
3D printing on the cover of Science
How does the liquid become solid?
The idea of ​​turning a relatively easy-flowing liquid material into a solid is not new. Vulcanized rubber is a typical example of how this material is processed. So how does the curing process happen? Let's take a look at the picture below:
In the figure, small a, small b, small c, etc. are a group of active polymer molecules, because these chain molecules are easy to move with each other, so it looks like a sticky liquid (sometimes the viscosity may be Very large, such as natural rubber before vulcanization, which drops very slowly from the tree). One day, the devil mixed a simple kind of curing agent into the little brother. The little brother was still alive and there was no danger. Suddenly one day, the devil put the little brother of the beach together with a curing agent into a high temperature and high pressure (generally called vulcanizer/hot press), and then the seemingly harmless curing agent grows out of the claws. The little brothers, one after another, grasped the different brothers, and produced a lot of cross-linking structure, even if there is no high temperature and high pressure, it will not be released. Finally, the little brothers can no longer be free to move, and the liquid in the beach has become a hard piece - this is the dou (bi) interpretation of the curing process. Of course, some curing agents are cured by initiating the reaction of groups on the small molecule polymer, which is generally referred to as an initiator.
How is the ball pulled out?
Among the 3D printing technologies that "pull" solids out of liquids, the way to activate the curing agent changes from hot pressing to light, so this technique is called Stereo lithography Appearance (SLA). The liquid materials used herein are referred to as photosensitive resins, typically epoxy or unsaturated polyesters, which are doped with some photoinitiators that are sensitive to specific wavelengths. This type of technology is not new in itself, and its history dates back to 1984.
In simple terms, the process of stereoscopic light curing is to illuminate the surface of the photosensitive resin to cure it into a thin layer of solid. The cured portion is adhered to a substrate and gradually separated from the light-irradiated surface (usually Each time a dozen micrometers are moved, and then the next layer is irradiated and cured on the basis of the upper layer of the cured resin. After layering and solidification, a complete three-dimensional structure is finally formed. The following figure shows the basic structure of the SLA device. The curing reaction takes place at the interface between the printed resin and the transparent glass plate. Since the light-irradiated surface is below the liquid surface, the printing process looks like it is from the liquid. Pull out the same as the printed parts.
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