3m 77 spray adhesive in oven?

General Composites Discussions Composites Talk
#1

Hello,

I am making some large diameter tubes using prepreg carbon fiber. I’ve previously used wet layup to make these tubes and handling the large pieces of cloth required to make the tubes (22" diamter x 60" long) was a pain on multiple levels. I am considering using 3M 77 to tack the prepreg (on the dry side) in place while I lay up the part.

The cure cycle for my prepreg is ramp up, 250 F for 60 minutes, ramp down. I am concerned about outgassing from the 3M 77 causing problems.

Has anyone used 3M 77 in a prepreg process?

Are there spray adhesives specifically made to tack epoxy prepreg fabrics?

Thanks!

Dave

#2

Do you use ,semi-prepreg, (resin foil from one side)? With standard prepreg heating with heatgun should make it tacky enough.

#3

Yes, Pre-preg won’t need to be glued as it will stick to itself fairly well…

#4

I am using prepreg with the resin on one side. It is tacky at room temp but out in my workspace it is cool enough that the resin loses much of its stickiness.

Thanks for the suggestion regarding using a heat gun. I think that will do the trick.

Dave

#5

spray 77 is a contaminant, it will weaken your part. if its not structrual at all you do not need to worry too much, however if it is I highly recommend not using it. Use a heat gun to create tack or warm the tool. Even spray adhesives made for epoxy will lower the laminates properties.

#6

why not use the resin side on the tool? Is there a reason why you are starting on the dry side?

#7

I’m laying up the tube with a 3/4" honeycomb core so I want the epoxy side facing out to contact the honeycomb.

The outer layer will be epoxy side in to contact the honeycomb.

Dave

#8

I take it you are not concerned about print thru from the honeycomb?
Why not pre-cure the two skins and do a secondary bond for the h/c?

#9

ah. Hmm.
Welllll, you can try film adhesive. Cut one layer, place it one the tube, then you can use that tack to start bonding the fibers to the tube. Not sure which would have high tack, but I’m sure Cytec has something good. Then, if you need to, add that to the honeycomb after wrapping, and then add your outer skin.

#10

@dtandy: You may want to check with Cytec for the prices. Last time we contacted them, they were charging huge amount for an adhesive film required for us. You can also contact ACG and Hysol as they have some structural adhesive films.

#11

I’m not concerned about print through in my application.

I laid up a 16" diameter tube yesterday and it turned out well. The prepreg (at ambient temp of about 50 F) was just tacky enough to stay in place and with two pairs of hands we were able to lay up the prepreg without much hassle.

#12

sorry for this dumb question … prepreg comes with resin on one side only?? I thought it was completed impregnated with resin thruought the material?

#13

Me too as otherwise there isn’t enough resin to do a full wet out of the CF!

#14

they come either way depending on what you prefer.

#15

or the nature of the beast. It can also seep through the fabric over time. One PITA prepreg I have is VERY VERY VERY tacky one side, dry on the other. Normally, as the resin heats up, the viscosity decreases, so it flows into the fiber tows.