Engineering - Hardening and printing results
For testing purposes, a commercial resin called B9R-1-RED (B9Creations USA) was used. This resin is shipped with an integrated UV Photoinitiator and an integrated colourant.
For the self-produced resin, IRGACURE 819 (BASF Germany) was chosen as a photoinitiator as it provided sufficient extinction coefficients at concentrations about 0.1 % at wavelengths about 410 nm. As a colourant, Sudan I (Acros Organics USA) was used. A good mixing with the resin was achieved by either solving the photoinitiator in acetone, then adding the colourant Sudan I (Acros Organics USA). After these two substances were completely soluted in acetone, the mixture was put together with the resin and mixed again. Another mixing method which works without acetone requires mixing times of about 1 h.
Hardening tests were performed on both resins using a resin basin with a bottom made of Gorilla glass and a resin basin with a bottom made of Borosilicate glass. In the case of the uncoated Gorilla glass, the commercial resin formed a layer which adhered to the aluminum base plate after lighting for 15 s. It was cured after lighting for 17 s. Long lighting times > 60 s did not lead to a higher hardness. The lowest layer thickness produced were in the range of 120 μm. Layer thicknesses up to 300 μm were found to adhere on the aluminum base plate. Higher thicknesses did not adhere to the base plate but got stuck at the basin bottom. If the Gorilla glass was coated with Teflon, the results did not change.
Using uncoated Borosilicate, a high adhesion to the resin bottom was observed. However, this is not intended so the Borosilicate glass was coated with Teflon. Unfortunately this did not lower the adhesion force by a relevant amount. Another test was run by wrapping the resin basin into package tape. This significantly lowered the adhesion of the hardened resin to the basin but strongly lowered the lateral resolution of the printer so this is no sufficient solution. Concerning the layer thicknesses using Borosilicate yielded the same values as Gorilla glass. Therefore, it can be assumed that the transmission of Borosilicate glass is similar to the transmission of Gorilla glass at about 410 nm.
The self-manufactured resin could also be hardened but this took about 16 min and it was much softer than the commercial resin
In Figure 1 an image of a running hardening test using the commercial resin and a Petridish is shown. The resulting structure of the iGEM Logo can be seen in Figure 2.
The first real printing result of our printer is shown in Figure 3. Again, this print was done using the commercial resin.