Print through

General Composites Discussions Composites Talk
#1

What can I do to prevent print through? I spray on duratec gel coat (about four full coats) then I lay up four layers of 5.7 oz 2x2 twill carbon fiber. I then infuse it with polyester infusion resin. I find that epoxy gets softer faster and easier allowing more print through. So I stay away from that. I also prefer polyester and vinyl ester because its easier to work with and I don’t have to do a post cure. I run a small shop and don’t have the option of a post cure or autoclave.

Anyways, After infusion I demold, trim, wet sand, clear coat, wet sand, clear coat, wet sand, buff, and polish. When I leave the parts in heat I still manage to get print through. Heat as indirect sunlight, under a heat lamp, leaving the buffer on it long enough to generate good friction.

I hate print through! I know inevitable, but still.

#2

Also, I was reading through some old threads and found some good information, but not much to help me with this situation…

I know post curing helps with print through since print through is caused by heat. But can polyester resin be post cured? The last time I tried heating up epoxy resin to 150 in the mold (which is polyester) the mold surface bubbled so it destroyed my mold. If I were to post cure each product (if polyester can be post cured) should I take it straight up to 150 degrees F or bump it up 10 degrees an hour or so? I’d speak to the manufacturer about it, but las time I asked them questions they didnt know… Also would it be better to leave it untrimmed to help it from distorting when post curing out of the mold? Lastly, when I cool it, do I drop the temperature slowly or just shut off the heat and let it cool its self?

I have 4 gallons left of this infusion resin I bought from fiberglasssupplies.com I think it is. I’d like to finish using it or get down to 1 gal before I start with epoxy. I’d also run some tests first…

Thanks!

#3

use some 2oz or 3oz fiberglass cloth between the gelcoat and carbon fiber.

let your cured parts sit for a couple weeks maybe before sanding and clear coating.

#4

I dont have that much time :(. The fiberglass cloth wont show through? Wouldnt I then get print through from that?

#5

The answers is 2 fold: A barrier between gelcoat and (relatively course) carbon always helps, you can use a fine glass fabric for that.

The problem you experience is when you heat the part over the “glass temperature”. This is the temperature at which the resin makes a transition from glass-like to rubbery, allowing for a bit of movement.

You can push up the glass temperature (Tg) by postcuring. You can postcure in the mould, but the mould should be able to take the heat as well.

You can also postcure free standing, but then the temperature should not be raised more than 10 degrees C (or 20 degrees F) per hour.

How high should your postcure temperature be?
Every single resin and hardener combo has its own “ultimate Tg”. You will never be able to push the Tg higher than that. For most polyesters this is in the 60 degrees C range, for epoxy this can be 40-50 degrees for cheaper systems, up to 200 degrees C if you have the money. 80-90 degrees C is a nice and affordable option. Check the datasheet of the epoxy for postcuring cycles. In general, ramp the temperature to some 10 degrees below ultimate Tg, then maintain that temperature for some 12-18 hours. (faster resins can develop a proper Tg faster, but slower resins might take longer)

#6

to my knowledge the fiberglass does not show through.

#7

you will still get a print, using a light weigh glass such as a 104 or 120 glass helps but because you have indifferent materials(fiber and matrix)you will have some level of texture unless it gets barried deep in gelcoats and barrier coats such as how all boats are made these days. But obviously that just adds unwanted weight. A good paint or clear job usually keeps print to a minimum. Proper post cure will also help a little.

#8

So lately I’ve been using the VE clear top coat by Duratec and its good stuff as far as not allowing print through, but my only problem is it makes all my parts TERRIBLY yellow. I have to post pictures later on.

My next question is…Could I ditch the VE top coat from duratec, go back to PE top coat from duratec, or even go back to Silmar surf board resin as a gel coat and infuse with VE resin?

Again, the parts HAVE to be good because I want to produce super high quality parts that are not only strong, but look great, and hold up well to the sun / engine bay temp. The engine bay parts just have to look good ,we arent making any vital engine components. Just engine covers, side panels, fascias, etc.

So I was thinking of using a clear PE resin as a top coat (coating the molds before laying up the parts) but I would like to lay it on at least 15 - 20 mills thick so that way it provides a decent layer between the clear coat and the carbon fiber and helps prevent print through. I’d imagine the thickness alone would help prevent print though. I still have to try a woven fine glass surface. I believe that will also provide a deeper 3D look. But if I have parts with multiple curves and can’t drape the fiberglass fabric in that means I have to make pleats and overlap. Won’t that show the fiberglass texture? Or will it still turn invisible? Back to the clear PE surf board resin as a gel coat / top coat in the mold for the CF parts. Would it hold up well to high heat temps? Say, between 150 - 250? It woudl be on top of VE resin that can take up to 250F. I’d hate to try this, then have the top coat crack and peal because of the heat.

T

#9

ok… please read the sherwin williams hpc-15 post in the products talk… for a production shop… i feel this stuff is awesome. and one gallon lasts a long time. as long as your net getting dry spots… print really isnt a problem anymore if you use this stuff.

no more spraying and waiting till morning before you sand all day and do it all over again…simply pull part, wipe it with chemical, spray, 7 minutes sand with da, spray, fine sand, spray and your done. all in the same day.

Now…I have used the following to get some nice pieces but might not be right for you… but could.

cut all your fabric and bleeders and so on and build in the open mold. a little 77 spray works great to get it all together and stay together (when i say a little i mean a little). buid your vacuum bag and debulk. get this xxxxxx down as good as you would during infusion… hopefully (and after a few cracks at it it will) the 77 spray gets the whole stack up to come out it one piece. if you go as far as laying peel ply, ferf, and bleeder; tape and 77 spray is used to hold it together.

  • big envelopes that go completely around the mold work best. you can simply cut the bag open along one side and taky tape it again later.
  • taky tape on perimeters makes this a bit tricky but… when you debulk alot you do get good at it. 4 hands are better than two… especially if the two of you are both understanding whats going on when your opening up the debulk. otherwise… your making two bags… cussing at each other and so on.

so now you have a debulked laminate schedule laying on your table in one piece… because its still dry and still holding its shape… still with me? well… forget it cuz now your going to take a china brush and brush in a nice coat gel coat over that mold surace… be generous… when it starts to tack up “kick” (if your reading this this is where your first layer gets carefully layed neatly into the gel coat… its jelly at this point but getting very close to kicked.

now lay in the assembled stack on top of the first layer. re use bag. infuse…

this method was used when the shop transitioned from wet layup to vip of aircraft cosmetic parts… when we got the autoclave… we switched to using face coat in the tooling to fix print issues… but before that fancy autoclave… we made some SICK parts this way.

now… when it came down to it… 77 spray was a contaminate… so other adhesives were used. and often times gel coat was substituted to resin… so… im trying to relate your conditions to my experience…

this seems like alot more work… but… this does work on rather uncomplicated shapes… like say a fender hood… bike parts and so on. if you can dial in patterns you could effectively kit dry assemblies…

but no bother… if you use that sherwin williams… and do it the way youve been.

#10

hope this helps… and if you get lost… ill edit it a bit better.

#11

Good, low-shrink resins will reduce print through more than all the time consuming and heavy methods listed above.
It seems like some people are making parts with a thicker coating than the actual laminate! Geez, 4 coats of gelcoat AND several coats of clear?

#12

Here is my process…

Gel coat the mold, let tack up.
Layup mold (layer by layer with a little bit of super77. I’m switching to airtack 2 I think its called)
peel ply, flow media, hoses, bag, vacuum, let stand for a little bit.

I mix my resin (now I use Hydrex 100 for infusion) so far it works great!

demold
wet sand
clear coat (I do use Sherwin Williams HPC15)
wet sand
clear coat
wet sand, buff, polish.

Its working real well.

But I wan’t to stop using duratec vinyl ester top coat. Its very yellow, makes my parts look very amber, and the parts just look bad. I put 15mil thickness which is what I was told by several people to do.

Does anybody think if I use a clear gel coat with a HDT of 180, infuse with a VE resin with a HDT of 250, post cure at 200, and do two coats of clear coat with HPC15 I’ll have any problems with print through? My main worry being the clear gel coat (which actually would be Silmar 249 surfboard resin through a gun) damaging at heat higher than 180F. Especially if I’m post curing at 200 of maybe even higher.

#13

What’s the big issue with print through for these parts? Obviously they’re not being painted so the customer is well aware they’re composite parts. Texture under paint would be a different issue.

#14

this is soooo true… thats why they make carbon fiber vinyl graphics!!! lol

sadly using cheaper resins shrink and clear coat and gel seem to be the filler…

#15

about heating a fiberglass mold - Duratec makes a vinyl ester tooling gel coat, then use vinyl ester resin in the mold making.

both products should handle up to 230F degrees ( low temp oven use)

To make a higher temp fiberglass mold you would have to use tooling epoxy resin and surface coat. Most of those resins require post cure… post curing the mold.

Resin Services sells many tooling surface coats and resin - epoxy.

#16

So far here is the new process…

We use Hydrex 100 vinylester to make the molds. Then we use Hydrex 100LV to infuse the parts. We infuse with no gel coat. After we pull the part, we trim, sand, and then coat several coats of duratec vinyl ester top coat. Then sand, and clear coat with UV resistant 2K urethane clear. I’ve tested up to mid 200s and have seen minimal print through. Way better than before when we’d get print through by just buffing the parts…

BTW We post gel coat the parts as soon as we can after demolding so that way there is still some chemical window.

#17

When you get print due to buffing, either your resin is not cured enough, or has a too low Tg. Both I have discussed before in this thread.

Why no gelcoat? If you can source a MMA modified polyester gelcoat, you should be good to go. Keep the Tg in mind though. Ask datasheets before spending money.

#18

I make some very high quality parts where cosmetics is everything and good quality gel and resin do the trick. We post cure to 65C for 14 hours and then wet sand and polish the gelcoat. We used to clearcoat but now we get perfect results without and in way less time.
Quality of resin and gelcoat is everything. Look for a TG of around 80C

#19

I have done that a few times, but prefer clear coat due not being able to find a gel coat with UV resistance…

#20

I have a few ways to stop print through (which is very common in RTM light):

. use a material designed for that purpose. We use a coremat between the gelcoat and glass. This is pretty effective.

. measure your gelcoat thickness when it has been applied. If it iss too thin, print through is almost unavoidable. However, do not go overboard and apply too thick. I always work with 0.7mm. You can’t count the coats of gelcoat, it needs to be measured and applied to a controlled thickness.

. The biggest cause for me with print through is opening the mould or turning off vacuum too early. the longer you can leave the part in the mould, the better the surface finish will be.