Tough-Seal Cures

All the Tough-Seals cure to completion at ambient temperatures. Tough-Seal 21 and 31 are designed to have faster initial gelation times than Tough-Seal 22 and 32.

Subsequent operations can commence upon gel because the Tough-Seal doesn’t appreciably flow after gelation. If dimensional stability is required before the part is handled, then an overnight or 12 to 16 hour initial ambient cure is typically sufficient to attain a firm encapsulation that resembles a complete cure to all but the most discerning observer.
As a general guideline, 100% complete cure is attained within three to five days at room temperature.

Cure Schedules

To give you the information necessary optimize your production process, the curing schedule data for Tough-Seal is presented in this section. Ambient temperature curing, elevated temperature curing and yes even underwater curing is displayed for Tough-Seal. What could be more convincing that Tough-Seal is indeed not an isocyanate containing urethane than Tough-Seal’s ability to cure underwater?

Ambient Cure

The advancement of cured hardness from gelation through the first several weeks is shown in the first graph where the steep shoulders of the curves equate to early cure progression at room temperature. Again as a general guideline, complete cure is attained within three to five days at room temperature and cast parts are typically handle-able or demold-able overnight after the first 12 to 16 hours.

Are you used to dealing with the big exotherms from standard epoxies and urethanes as your pours get bigger? Relax, Tough-Seal is only mildly exothermic even in the largest pours. It is this low exotherm aspect that forms the low shrinkage and low embedment stress characteristics featured in Tough-Seal. Easy to control curing is an important first step in thermal cycling performance of potted assemblies.

Heat Cures & Post Cures

Want to get things moving? Tough-Seal is very responsive even to the mildest of heat cures. Heat curing as low as 66°C (150°F) or 80°C (175°F) greatly accelerates property accrual in Tough-Seal. Terminology wise in a heat cure, a freshly mixed and poured part is immediately heated. While under post curing, the potting compound is allowed to gel during an initial period at room temperature followed by some duration of elevated temperature curing.

In the table below, heat cure and post cure effects are shown for a 66°C heat cure, an 80°C heat cure and an 80°C post cure for Tough-Seal 21. Short durations of 15 and 30 minutes of heating are displayed alongside longer times of 1 and 2 hours. The accelerating effects of the heating is tracked by measuring the hardness development at room temperature for 1, 2, 5 and 10 days afterward. Shaded regions denote hardness accrual above 50 Shore A.

Tough-Seal 22 can be expected to behave similarly as shown. The softer Tough-Seal 31 and 32 products will trend much the same way but achieve lower ultimate hardness by design. These profiles are provided as guidance, individual results on your parts may vary based on heat transfer and heat sink effects and oven zone heating efficiencies.
66°C heat cure: Mix, then heat cure at 66°C, followed by RT cure
Mix & Heat Initial +1 Day RT +2 Days RT +5 Days RT +10 Days RT
15 min / 66°C 15A 40 A 43 A 53 A 65 A
30 min / 66°C 35 A 42 A 46 A 55 A 66 A
60 min / 66°C 38 A 47 A 50 A 56 A 66 A
120 min / 66°C 50 A 50 A 53 A 57 A 67 A
80°C heat cure: Mix, then heat cure at 80°C, followed by RT cure
Mix & Heat Initial +1 Day RT +2 Days RT +5 Days RT +10 Days RT
15 min / 80°C 32 A 42 A 44 A 55 A 63 A
30 min / 80°C 58 A 62 A 62 A 63 A 65 A
60 min / 80°C 62 A 63 A 64 A 65 A 68 A
120 min / 80°C 62 A 63 A 64 A 65 A 68 A
80°C post cure: Mix, then 1 hour at RT, then heat cure at 80°C, followed by RT cure
Mix & Heat Initial +1 Day RT +2 Days RT +5 Days RT +10 Days RT
15 min / 80°C 37 A 45 A 47 A 55 A 67 A
30 min / 80°C 52 A 55 A 58 A 60 A 67 A
60 min / 80°C 55 A 60 A 61 A 62 A 67 A
120 min / 80°C 58 A 62 A 62 A 63 A 68 A

Underwater Cures

Nothing says “I am not a urethane” like the ability to cure underwater. From a hardness development perspective, Tough-Seal is not phased by an underwater cure. Tough-Seal does not contain isocyanates so while urethanes can foam in your factory on a humid day, Tough-Seal cures void free even underwater. It’s the no-foam solution for your contract manufacturers in Southeast Asia or Central America where humidity effects plague perfect potting.

Tough-Seal 21 and 22 are heavier than water so they stayed put and didn’t float. In this study, Tough-Seal 21 was dispensed above water then immediately submersed to cure while Tough-Seal 22 was dispensed and applied completely underwater. Shown below is the hardness development versus time underwater immersion. The underwater cured castings appear similar to those potted in a controlled environment on a bench top.
While we are not suggesting that you should ever outsource your sensitive electronic potting operations to mermaids in Atlantis, one could imagine applications for rubbery elastomer castings in civil or marine applications or even electrical part and cable repair in the field under the worst of weather conditions. So don’t fret if Tough-Seal gets wet!