Hi there, as you may have noticed, formlabs has updated the Tough Resin to V3 (FLTOTL03). Now I have some questions, some of them right now only the formlabs staff may be able to answer (I already wrote a support request)
-The notched Izod (Impact resistance) has gone down noticeably from V2 (51.1 J/m) to V3 (32.6 J/m), according to the data sheets. Why the change, and why isn’t V2 available any more when an important material property of V3 is inferior to V2?
-The post cure overview table says to post cure 30min@45°C. In the data sheet, it says the test parts have been post cured 2 hours in a 30 W UVA curing chamber (V2) or 2.5 mW/cm² of 405 nm LED light
for 120 minutes at 60°C (V3). My experience with 4x9W 405nm UV LEDs in a Nail Spa is that 30min is totally insufficient, but even after 2 hours the parts are still somewhat soft (scratchable with finger nails) and sticky. (Yes, I did wash them properly in IPA and let them dry). Now how do I post-cure that resin properly? What is your experience about what works best? Will it be different with Tough V3?
According to Zachary Zguris’ white paper from 29.02.2016:
“The optimum radiant power that produces the maximum modulus and tensile strength is 1.25 mW/cm2. This is the flux generated by a single 10W LED array in the TCC. When radiant power decreases below this level, there is not enough light to post-cure well, and there is a decrease in mechanical properties. Using a higher flux also results in lesser mechanical properties. This is counterintuitive to the common assumption that more light will post-cure parts better.
Fundamentally, this can be explained by the competing radical reactions of initiation, propagation, and
termination. In addition, there is limited chain mobility of the crosslinked polymer network that plays a role1. A high flux will generate a large number of radicals. These are more likely to find each other and die rather than see an unreacted double bond in the network2. The results from investigating the temperature effects on post-curing imply that the mobility of unreacted double bonds is a limiting condition in overall conversion of double bonds. The propagating radical on the kinetic chain is limited spatially by the tethered backbone chain tying it into the crosslinked polymer network of the printed part2. This balance between initiation by radiant flux and kinetic chain mobility results in the maximum properties obtained that we see at approximately 1.25 mW/cm2.
For exposure levels above and below this optimum value, there is a decrease in the modulus of the cured part. When designing a cure chamber, this value of 1.25 mW/cm2 should be used to achieve the best possible post-cure properties.”
and
“Tough is completely post-cured in only 30 minutes at 44 ºC”
Thank you, I had already read that document. Didn’t help me very much though, as I wrote in my post (Parts still soft and scratchable on the surface after 30 min and a bit less so, but still not what I would call “fully cured” after 2 hours). As you see, the data sheet values for post curing don’t fit with the white paper at all, maybe someone from formlabs could explain this?