Pre-Preg

[mbroberg]

I'm still working on getting an acceptable decal on carbon fiber cast. In my case it is actually fiberglass sleeve I am using, not carbon fiber. I've done a lot of reading on the possible causes of the failures. One of the threads I read was this one.

Marko50 talks about pre-pregging the carbon fiber with a thin epoxy prior to applying the decal. A Google of pre-pregging was not very helpful. I'm not sure if there is some sort of "thin" epoxy as there is a thin CA or the 2-part epoxy should be thinned with denatured alcohol, acetone or lacquer thinner. Most articles I read recommend against thinning 2 part epoxy but none suggest what should be done, or used instead.

Is pre-pregging just a fancy term for "smearing epoxy all over the outside of your blank", or is there a process and/or product I am unaware of.

Thanks

 

[CREID]

This is a great question. Although I don't or haven't done any casting (I would like to someday). I eagerly await the answer to this question.
Curt

 

[jttheclockman]

hello Mike

I am assuming you are still working on this pen.
http://www.penturners.org/forum/f178/decals-white-carbon-fiber-134912/

I have no idea what that word means but as i mentioned what I do is put my resin on the blank before I cast. Now I never cast a decal like this but i would think if you use epoxy, not quite sure what reaction to the resin you would get. I only use Silmar resin so can not answer about aluminite.

What problems are you still having???

 

[mbroberg]

John,

I've only tried 2 more since the last thread. The spotting has decreased but is not gone all the way. I feel as if what I'm looking for is right in front of me and I just can't quite reach it. My latest attempts were with PR resin (from Michaels). I did one where I built the blank up with CA, applied the decals and then cast, I did another where I cast the blank and turned it down, applied the decals and built back up with CA. Always just a couple of spots I'm not happy with. I don't know if the resin makes a difference but I have some Simlar ordered. It should arrive this week. Do you just brush, or wipe the resin on prior to casting? If so, do you add the catalyst prior to applying to the blank or just use the un-catalyzed resin to displace any air in the fiber then put it in the catalyzed resin to cast?

 

[jttheclockman]

Mike one of the two tries should have worked especially if you coated with CA. When you thinned a blank down and the added the decal. Did you notice any spots before you top coated with CA???

As I mentioned when I do my braiding blanks of any kind I alway use the same resin. I mix a small batch depending how many blanks I am preping. Usually an ounce is enough. I add my 4 drops of catalyst just like I would for casting. i brush with those small acid brushes because they are throw aways. I brush some on the tube. I slide the braiding over the tube. I pinch off the ends so to keep the braiding flat on the tube and then I slather some resin over the braiding. Just enough to seal it. I should mention I use a small plastic rod through the tube so that I can pinch off the tube to it. I use those tiny zip ties. I then set these rods on a rack I made. I rotate the tubes a couple times as the resin is curing so as to not get drops forming on the bottom.Usually within a half hour. Not that this matters much. Let sit for a day and then cast. This has worked well for me.

 

[mbroberg]

John,

I didn't notice any spots prior to applying the decals.

I am going to give your method a try tomorrow. Thanks for the information. I'll let you know how it turns out.

On, by the way, your blanks are fantastic!

 

[jttheclockman]

So what you are saying is that after you cast the blank and turned it back and applied the decals you did not see any spots???? It is after you top coated with CA to build the pen body back up that the spots appeared??? Just trying to get a clear picture. Forgive me.

 

[Charlie69]

Prepreg is carbon or fiberglass cloth that has been pre-impregnated with an epoxy matrix that uses a latent curative (hardener). Latent curatives prevent epoxy from curing until a chemical reaction is initiated by high temperature (oven or high temp cure epoxy). The curing process of prepreg almost always takes place under pressure in an autoclave or with heat shrink cellophane tape. One of the main advantages of using prepreg is your under no time pressure to lay up the epoxy soaked carbon fiber before the epoxy starts to harden. Fishing rods are made with prepreg.

I Believe Marko50 was saturating and coating the CF with epoxy resin and letting it harden. Nothing to do with prepreg as the term is commonly used in the composites world. Btw there are a ton of slow cure (thin) epoxies that would be suitable for what he was doing. Any of the commonly used rod building epoxies like flex coat lite, or pro-kote would work. Getting a level even finish with epoxy takes a bit of practice but if your going to cast over it I'm not sure that would be too important.

Hope this helps

 

[mbroberg]

So what you are saying is that after you cast the blank and turned it back and applied the decals you did not see any spots???? It is after you top coated with CA to build the pen body back up that the spots appeared??? Just trying to get a clear picture. Forgive me.

Forgive you? For what? I appreciate your input. That is correct. However, it very well could have been improper application of the decals. That one looked more like stretchmarks (for lack of a better description). I did not notice them before building the blank back up, and I was definitely looking. I think what I might have done was pull the decal too tight to try to compensate for the slight curvature at the end of the blank. As the blank spun while I applied CA, even though I kept the speed low, there might have been enough heat generated to cause the marks.

 

[NotURMailman]

As stated above, true prepreg is material that is impregnated with (usually) half of the two part epoxy as part of the manufacturing process and requires (normally) that the other part be added and heat applied to make it cure. Airplane wings and winglets are made from prepreg.

 

[healeydays]

Hi John,

Great explanation on what your process is. Have you ever thought of doing a step by step with pictures of your process making the blanks as a teaching tool here on the site?

Mike B

Mike one of the two tries should have worked especially if you coated with CA. When you thinned a blank down and the added the decal. Did you notice any spots before you top coated with CA???

As I mentioned when I do my braiding blanks of any kind I alway use the same resin. I mix a small batch depending how many blanks I am preping. Usually an ounce is enough. I add my 4 drops of catalyst just like I would for casting. i brush with those small acid brushes because they are throw aways. I brush some on the tube. I slide the braiding over the tube. I pinch off the ends so to keep the braiding flat on the tube and then I slather some resin over the braiding. Just enough to seal it. I should mention I use a small plastic rod through the tube so that I can pinch off the tube to it. I use those tiny zip ties. I then set these rods on a rack I made. I rotate the tubes a couple times as the resin is curing so as to not get drops forming on the bottom.Usually within a half hour. Not that this matters much. Let sit for a day and then cast. This has worked well for me.