1, low viscosity. Curing is based on CAD model, and resin is added layer by layer. After one layer is finished, it is difficult for liquid resin to automatically cover the surface of solidified solid resin because the surface tension of resin is greater than that of solid resin. The resin liquid level must be scraped once with the help of an automatic scraper, and the next layer can be processed only after the liquid level is leveled. This requires the resin to have low viscosity to ensure its good leveling and easy operation. At present, the viscosity of resin is generally required to be below 600 cp s (30℃).
2, the curing shrinkage is small. The distance between liquid resin molecules is the action distance of van der Waals force, which is about 0.3 ~ 0.5 nm. After curing, the molecules are crosslinked, and the intermolecular distance to form a network structure is converted into the valence bond distance of * *, which is about 0. 154nm. Obviously, the distance between molecules before and after curing has decreased. The distance of intermolecular addition polymerization will be reduced by 0. 1.25 ~ 0.325 nm. Although in the process of chemical change, C=C is transformed into C-C, and the bond length is slightly increased, its contribution to the change of intermolecular interaction distance is very small. So volume shrinkage after curing is inevitable. At the same time, it changes from disorder to order before and after curing, and volume shrinkage will also occur. Shrinkage is very unfavorable to the forming model, which will produce internal stress, easily lead to deformation, warping and cracking of the model parts, and seriously affect the accuracy of the parts. Therefore, the development of low shrinkage resin is the main problem facing SLA resin at present.
3, the curing speed is fast. Generally, the thickness of each layer is 0. 1 ~ 0.2 mm during molding, and it takes hundreds to thousands of layers to complete a part. Therefore, the curing rate is very important if the solid is to be manufactured in a short time. The exposure time of the laser beam to a point is only in the range of microseconds to milliseconds, which is almost equivalent to the excited state life of the photoinitiator used. The low curing rate not only affects the curing effect, but also directly affects the working efficiency of the molding machine, so it is difficult to be suitable for commercial production.
4. Small swelling. In the process of model forming, liquid resin always covers some solidified parts, and liquid resin can penetrate into the solidified parts, which makes the solidified resin expand and leads to the increase of parts size. Only when the swelling of the resin is small can the accuracy of the model be guaranteed.
5. High sensitivity. Because SLA uses monochromatic light, the wavelength of photosensitive resin and laser must be matched, that is, the wavelength of laser should be as close as possible to the maximum absorption wavelength of photosensitive resin. At the same time, the absorption wavelength range of photosensitive resin should be narrow, which can ensure curing only at the point of laser irradiation, thus improving the manufacturing accuracy of parts.
6. High curing degree. The shrinkage of the post-curing molding model can be reduced, thereby reducing the post-curing deformation.
7. High wet strength. High wet strength can ensure that the post-curing process will not produce deformation, expansion and delamination.