LT Tank FEP Layer Bad?

I am using the LT Tank with the Dental Model resin and I know I have been a bad person by letting the resin sit in the tank for a good 2 -3 months between use.

Does/can the resin ruin the FEP layer when left in the tank for long periods of time… Started doing some prints (I did pour the resin back in to the container and shook them both well before pouring back into the tank) and the first compression layer actually stuck so bad that the Z axis would not go up.(About around 50-60% support coverage)

When first setting up the LT tank I had to back the z off .7mm to eliminate the “flash” but once I got it to print again got a bunch of flash again… Will be backing the z off another .2 or so but if the FEP/Silcone layer is shot from my mistake I will just order a new tank… Bummed as it has only been through 1.5 liters but that is my fault for leaving the resin in for so long if that is the issue.

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If the LT tank surface is indeed FEP, which it has all the reasons to be, Formlabs has not confirmed it AFAIK… then I see nothing that would be able to degrade the film that wouldn’t also make the resin incredibly dangerous to manipulate. I think the recommendation of not letting the resin set in the tank for long periods of time is due to the resin potentially altering the glue in between the window and the tank, with the risk of creating leaks.

I personally leave the resin in the tank at all times. I’ve had the same tank for Tough resin since December 2018… It’s being used regularly although it might have stayed in a cabinet for up to two weeks without use. Same thing for Rigid.
We check the seal on the tanks each time we get them out of the cabinet and into the machines, and so far have not had to replace a tank.

I would check what version of preform your running as I have had the same issue with having to raise my Z offset to .7 with all my LT tanks. Every time they release a update for preform they like to mess with compression and with this new release (2.20.0) they have added some controls for compression. (unfortunately they didn’t set the default to 0 for these new controls) If you were running an older version of preform and updated between your 2 or 3 month pause you may need to adjust these controls. ( I had to turn mine to zero as I was getting way to much compression when I print on the build plate.) The 2 controls added for compression are - Compression Correction for printing on the Build Platform & Base Merge Height.

I ran this version in beta and tried to work with it but found it troublesome so I leave the values at 0 or run under the previous version of preform. (2.19.3)

And as for the storage… We have 2 form 2’s and many trays with resin in them for over 6 months now and have no issues when printing other then with the flexible resin separating and leaving a film on the PDMS layer. I use a fine scraper to remove this layer and mix it back up.

Hope this helps

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