With the enormous influx of new SLA/DLP printers (a new printer is born about every week now), the choice of the materials is not always the right one for the purpose.
In search of the most cost-effective solutions, or just out of sheer ignorance, manufacturers do not always make the right choices for their materials. We see that with a lot of printers. The manufacturer chooses for instance for Polystyrene (PS) as a material to construct parts of their machines, instead of the slightly more expensive acrylic variant. Plastics like PS are hard and very clear and easy to shape. Besides that it is readily available in a broad range of colours.
The problem with ‘plastics’ like PS lies in the fact that they are prone to react with a high number of chemicals. Among them for instance is Isopropanol alcohol, which is commonly used as cleaning detergent for prints. Also, and this is more of an issue, it interacts with 90% of all resins. Several monomers commonly used in all formulas undergo a chemical reaction with PS. Some of them faster than others, but in all cases in the long term they have a deteriorating effect on PS.
Several ‘plastics’ are prone to this phenomenon. PVC, Vinyl, and Plastics with a high amount of plasticisers (softening agent) just to name a couple.
Producers often try to find a cheaper solution and change materials in later models, or even during the production of a certain model. Therefore, when working with a machine of a certain model it might be completely ok, while another machine from the same model might not. It might also not work with replacement parts (Like for instance a vat).
We do not test every product in the market, nor do we keep track of all changes in materials. We produce resins, it is the responsibility of the producers of the printers to use the right materials.
Therefore it is important to always check if your specific machine, or parts, are resistant to this phenomenon. Just rub a bit of resin on a place that is out of sight and where it won’t damage anything. When it is not the right material, the part will get a matt or milky appearance after some time.