Hi!

When molding carbon parts with high Vf (>50%) the fibres touching the mold are leaving a residue on my mold surface. I don't know why this is happening. I just bought easy lease release agent, but it also happened with wax (Partall). In fact I thought the Partall wax had aged so I bought Easy Lease thanks to this forum. But unfortunately no difference. The parts are demolding easy though with easy lease.

I have been using different curing processes: 24h room temp, 48h room temp, 24h 30 degrees C, 48h 30 degrees C. All with the same outcome: a residue on the mold. The molds are machined of PU toolingboard (Renshape) and polished to a mirror surface. Epoxies used are L + GL2 / S / L and EPH161 from R&G. When making a hand layup of one ply of carbon without compaction there is no printthrough and also no residue on the mold surface after demolding just like when using a gelcoat prior to the lay up.  So it looks like the problem is related to the compaction of the fibre or it maybe an epoxy problem.

My initial thoughts are it might well be a problem with the surface of the board in combination with the additional compression under vacuum.  This is assuming your cure cycles are fine for the resin system you have (not being familiar with your resin I cant be 100% sure but the times look realistic for curing for most epoxies). Most modeling boards are to an extent porous dependent on density. The higher the density, the more solid they are. It could be you are on the borderline with that PU board such that you get away fine under hand lay but the vacuum pressure is just enough to cause issues. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks for your reply. It's renshape 5173 (1200 kg/m3). The supplier told me that this type doesn't have to be sealed, and I thought Easy Lease doesn't need a sealer anyway?

Unfortunately it's difficult for us to comment on what might be causing this issue because we don't know the behaviour of the resin or the board. As you've indicated, the Easy-Lease is releasing fine so the aspect that we know well does seem to be working correctly.

In the video that you've linked to, the surface of that mould is our Epoxy Tooling Gelcoat. The resin we're using is our IN2 Epoxy Infusion Resin and I can say for certain that this combination, with the Easy-Lease release agent did not and would not leave any residue on the mould surface. Mould is left perfectly clean and shiny and the part has a pristine finish.

To explain your problem, one possibility to consider is the fact that polyurethane boards, when used at elevated temperature, actually inhibit the cure of epoxy resin. This is a well-known phenomenon within composites circles dealing with prepregs where it's known that polyurethane board cannot be used as a tooling board for prepregs because the resin in contact with the board won't cure. In these situations, epoxy tooling board is required (which does not cause the same cure inhibition). It occurs to me that because you're using the board at elevated temperure and you're using epoxy reisn and you're not using a sealer (which might have helped to separate the board from the epoxy) you just might be experiencing this issue.

I hope this helps, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Thanks for pointing me in that direction and good to know you didn't have the problem in the video. I'll contact the supplier and post the outcome.

Adding a little heat isn't the problem i guess since the problem also occurs when curing at room temp for 2 days. I also want to point out that I'm not using resin infusion, but RTM (two A sides), so maybe the compression force from the fibre on the mold is a bit higher due to the higher vf.

I'm a bit hesitant to post because I don't know if this will help or hinder you, but I'll share my experience and you can decide if it helps you. 

Thanks! Appreciating every input and experience. Semi perms and RTM are new to me. After the last test I am also doubting if a lack of sealer is the problem. Maybe it's just about film thickness/strenght for this type of process. Although I thought one would have to apply multiple coats to ensure complete coverage. Or I don't understand how a semi perm works.

My gut feeling is that the issue will be chemical, like Matt was alluding to. I have had similar issues before when working with vinyl ester infusion resin, though because it was virtually a one off I never thought too much about the cause. 

Problems are gone! I guess my molds needed more coats of Easy Lease during break in time? Anyhow I found the masking tape test to be very useful. Thanks for all suggestions.