I’m looking to see if there are any suppliers that sell a pre preg that can be cured at temperatures between 150 and 175F.
My idea is to layup a fairly flat mold with some pre preg, vacuum bag it, demold it, clear coat it, and hope the HDT is at least 150 - 175F as well. The molds would be pre gel coated with a PE marine clear gel coat so it should help with print through from the heat distortion.
Any thoughts?
Thanks!
Look up acg LTM/ VTM series. They cure from about 150F, but do better at 175F
Gurit in Europe do a hot melt epoxy pre-preg called se70 which cures at 70 degrees C which is close to the 170F you mention. Im not sure if this can be purchased in the US but I dont see why not. just try and cure it a bit above 70 degrees C!
I beleive TCR composities in utah sales some as well, and can make custom resin. try them out!
Thanks everybody! I’m looking to purchase a yard or two to play around with. I’ll post who sells what when I find it :).
Any luck on finding some?
-Tom
Sorry for never responding Tominator. I have not gotten a chance to purchase any yet, but I’ll be doing lots of research on everything regarding low temp cure pre pregs and hopefully be able to pick up a few yards within the next two weeks.
Does anybody know if I’ll be able to spray an in mold clear gel coat that can be baked with the pre preg? I’m not talking about baking the gel coat. I’m talking about a gel coat that can survive the 150F - 200F. The last thing I want is the gel coat cracking or yellowing up do to the heat.
My other question is with a pre preg properly cured with a HDT of 180 after full cure. Do I have to worry about a gel coat layer if I’m going to be clear coating the parts? The reason I’d gel coat is to add extra thickness to the surface to minimize print through while the part sits under the sun.
For the 5 + years I’ve been doing this, solving print through has been my white whale…
The only way to eliminate any chance of print through for a large part, is to use a resin with a Tg higher than 90°C. and cure it properly INTO the mould before demoulding.
Of course the mould must have the same CTE of the part.
If the part is little and thick enough can be postcured outside the mould, but you have to use a resin with a Tg higher than its cure temp.
Indeed. Print is all about Tg. Cure in the mould, high enough to withstand the heat during the life span, and use a resin which can reach that Tg.
Freestanding postcure is possible, but only if you can control your oven. (10C/h temp ramp, dwell at Tg minus 10C for 12-18 hours. (or longer if your resin is very unreactive). If you want to go scientific, make some tests, and send them to a lab for Tg testing. If you do not want a 3" thick report, but just the number, it is fairly cheap, and at least you know what you are doing.
You want to use a polyester gelcoat, and do epoxy prepreg behind it? I would be surprised if that would work.
Prepregs and gelcoat. Bit of inefficient regarding weight isn’t it.
When you are already in a curecycle, needing ovens, vacuum, etc. it is easier to just cure at a higher temperature. The curecycle will be faster too, so less time in the mould, and higher output.
Print will happen when the sun heats up the resin so much, that it will become somewhat rubbery, and allow for the fibres to expand and set again when it cools down, leaving print.
Black surfaces can heat up quick in the summer sun, so a high Tg is needed. Curing over the temperature that the part will reach in normal conditions, will not allow for the resin to become rubbery. So problem solved. Build some high temperature moulds (preferably out of the same fiber, or you could have issues demoulding) and cure at a higher temperature.
With prepregs I never had any print issues.
Except that one time. Freestanding postcure with a 2 degrees/minute ramp…
I’m trying do decide what would be faster. Creating all new high temp molds for pre preg or continuing on with vacuum infusion.
What do you guys think takes longer? laying up dry fabric with super 77 and infusing a part or pre preg and baking the part?
I worked out last night that if I take the labor into consideration, prepreg would actually come out a few dollars less per part on my cost. The saving was about 5% I believe per small part. I’m assuming the larger the parts, the more time saved when using prepreg.
Any thoughts?
Its also worth mentioning that I’d enjoy not getting Super77 resideu on the walls and floors if I were to switch to prepreg.
Half of these parts that I will be making will not require maximum structural stability. Most are carbon fiber parts for cosmetic purposes.
The larger the part, the more the balance goes towards infusion.
On Super77 on the floor and walls: what the $%^$#^are you tacking with it? Only use it if the fiber needs it. Which usually is only in small places. Or switch to something with less overspray. Tackstrip, or hotmelt.
Repreg without autoclave and pressure to get a cosmetic surface? A good infusion may take a bit longer than a prepreg, but the afterwork is less than with a prepreg. You will always have pinholes.
with ooa prepregs a good surface quality without pinholes can be achieved. Especially with the acg bodypanelsystem.
Does anyone try Deltapreg low temperature ooa prepregs? They say what its possible to achieve a class A finish.
Hmm… Now I’m leaning back towards infusion with VE or Epoxy resins.
I use the 3M allot because the parts I make have lots of shapes to them. The kinds of shapes where in order to get the straight perfect weave I want, I have to keep every inch tacked down so that way the fabric doesnt get disturbed with the subsequent layers and or the bagging.
Prepreg:
+No impregnation needed.
+No postcure needed.
+Selectable tackyness.
+No dry fibres in the air.
+precision placing, limited deformation of weaves.
+no pressure pot, no filled up lines
-limited out life.
-high temp moulds.
-Preferably computer controlled oven for optimum accuracy needed for good finish.
-debulking on thicker laminates
Infusion:
+No high temp moulds.
+more flexible in the use of materials.
+no debulking.
+no sticky pieces of frozen resin on the floor, which keep on sticking for weeks, and then are hard to get of. 
+Impregnate yourself, correct amount of resin, without separate glue films, etc.
-Seperate post cure to prevent print/deformation
-Impregnate yourself, extra work.
I must have forgotten a few, who fills in the gaps? 
With vinyl-ester a post cure isn’t always needed, less expensive, less sensitive for UV. I think with vinylester your better off infusing anyways.
I’m using it.
It’s true, but, like all the ooa prepregs you have to carefully debulk the first layer.
One side note: Deltapreg is the only supplier that is able to sell prepregs with combed and vibrated fabrics. This is a big advantage on cosmetic parts.