Infusion resins options?

[magnus]

I am building a few sub 20 pound 11.5 foot solo canoes. Kayak paddle, sit on the bottom or kneel and freestyle with a canoe paddle. I am using a Resin Research epoxy infusion resin currently mainly because i am doing skin coats with no gelcoat to save weight and RR has UV protection built in to the product. I was using Jeffco which was taken over by Rhino, and liked it, thinner faster infusions, and better Tg but no UV protection. RR's background is surfboards so makes sense they would incorpoate UV additves.. The problem I am having is I switched from Kevlar to carbon and forgot the low Tg/HDT of RR resin. So on top of a car last summer at 90F full sun I got 160F black hulls that are rubbery. Now I have made some hulls with 1.5mm Soric LRC on the full hull and the inner skin must have been insulated enough by microballons that they felt OK. I moved to epoxy resin years ago to avoid print through from Vinylester resin with no gel coat. I would like to go back to a good iso or vinyl but the ones I have tried leave huge print through, I mean a little is acceptable. It amazes me how good the epoxy surfaces turn out, no shrinkage. If anyone knows of a vinyl or epoxy in the lower 48 that could help let me know. One more reason I would like to move from epoxy is post cure is a pain and I have limited shop space, seriously...Good day

 

[fallguy]

I can't recommend a resin, but Gurit seems to have the best.

And post curing seems wise for your worries. I realize the difficulties. Building an oven and maintaining the heat is not a simple task. I did it with 33.5' oal hulls!

 

[magnus]

fallguy
Gurit indeed does have several infusion resins. One system may even cure with UV. I do not think any are recommended for long term sunlight exposure. Their Tg/ HDT look to be around 67C or 152F with a post cure. Those temps are right where I am having problems with carbon canoes parked on rooftops with RR epoxy. It is a tough ask. Low viscosity, low shrinkage, UV resistance, and higher Tg. With epoxy I will always need to post cure. These were only cured at 125F overnight in the mold. Two weeks later these canoes were sitting in the sun for a day because I had no room in the shop. Several hours at about 70C and rubbery as I said. So I brought them out to cartops the next day hoping the sun treatment might have raised the Tg/HDT a bit but I was getting softening well below 70C. My fault, the resin system is not formulated for these temperatures. I would be curious if someone has experience good or bad with postcuring weeks after the initial cure. In my case an immediate low temp postcure at 53C/125F.

 

[fallguy]

fallguy
Gurit indeed does have several infusion resins. One system may even cure with UV. I do not think any are recommended for long term sunlight exposure. Their Tg/ HDT look to be around 67C or 152F with a post cure. Those temps are right where I am having problems with carbon canoes parked on rooftops with RR epoxy. It is a tough ask. Low viscosity, low shrinkage, UV resistance, and higher Tg. With epoxy I will always need to post cure. These were only cured at 125F overnight in the mold. Two weeks later these canoes were sitting in the sun for a day because I had no room in the shop. Several hours at about 70C and rubbery as I said. So I brought them out to cartops the next day hoping the sun treatment might have raised the Tg/HDT a bit but I was getting softening well below 70C. My fault, the resin system is not formulated for these temperatures. I would be curious if someone has experience good or bad with postcuring weeks after the initial cure. In my case an immediate low temp postcure at 53C/125F.

most post cure temps are higher than what the sun would offer

my hulls were post cured in a 40' ocean container, well after regular curing

the containers had a custom door fitted and a high volume propane heater heating the chamber; we had probes inside the container and inside the hull(s); ramp up took 4 hours to get the hull probe to 153F; then 2 hours at 153-158 and two hours ramp down...

You won't get away from rubbery without high temps. Be careful; nothing can be unholed as the pressures rise if so. And I had a hull section blow up once from being under a flat black tarp in the sun unvented.

 

[fallguy]

You can post cure in a solar oven. But the oven temps need to be maintained and you need to post cure to epoxy mfg spec. After paint would be trouble I'd say.

It sounds like you haven't actually gotten them hot enough. A sun surface temp of 125F is not very (warm) for the resin. My hulls did NOT get rubbery at 125F. The ramp up helps I suppose..but rubbery makes me wonder about the resin some.

 

[ondarvr]

Infusion epoxies are sometimes thinned with a solvent. While it allows for faster and easier Infusion, it can reduce the physical properties dramatically, this includes the HDT.

VE resins don't have good UV resistance either, VE blends can be a bit better, but still not very good.

Many epoxy/carbon parts use Duratec Sunshield as the in-mold UV protection coating. It can be used with VE also.

The advantage over gel coat is that it's epoxy compatible, plus can be sprayed much thinner than gel coat, so less than half as much can be used. This makes the finished parts much lighter.

 

[fallguy]

Infusion epoxies are sometimes thinned with a solvent. While it allows for faster and easier Infusion, it can reduce the physical properties dramatically, this includes the HDT.

VE resins don't have good UV resistance either, VE blends can be a bit better, but still not very good.

Many epoxy/carbon parts use Duratec Sunshield as the in-mold UV protection coating. It can be used with VE also.

The advantage over gel coat is that it's epoxy compatible, plus can be sprayed much thinner than gel coat, so less than half as much can be used. This makes the finished parts much lighter.

I used Sunshield per ondarvr as an in mold coating for my helm console. It was tricky to get right on the mould. I had to get it pretty thick to stop it from beading if you go that route, but it came out fantastic. The pic may show some dirt, but the carbon/aramid layup had one flaw nearly invisible and it wasn't in the sunshield..it was like 1/16"x1/16" and might have been in the carbon/aramid glass or perhaps the roller caught the fabric. Anyhow, this thing came out almost flawless after two attempts. The first attempt I did not lay on the carbon because of the beading then had to get more sunshield.

ps. If you look close, I spilled some steering oil on my teak and it was too cold to mess with the bedding compound on the helm fixtures.

 

[ondarvr]

There is a newer version of Sunshield formulated for in-mold use. The older version was primarily designed for post applying, which is why it had a lower viscosity and was difficult to apply to a mold surface sometimes.

The new version was developed because the industry has moved more in the direction of in-mold epoxy and carbon fiber.

 

[magnus]

Thank you, I will look at Sunshield seriously. It opens a lot possibilities in resins. The question I still ask is do we trust supposedly UV stable resins. I may not have to make the next step to a spray in (which is tempting ) I have been considering Adtech 820 it is locally available for me. It is UV stabilized (whatever that means). With their 823 hardener it has a 350cps but only45 minutes at 77F ,post cure is only 150F and the HDT is good. I have a 22 inch infusion run from keel to gunnel. So it may make the infusion, no I think it will come up short , of course an aggressive flow media would help. I have been using a football shape which is not adequate with the Soric LRC. I think I need flow media within 3 inches of of the gunnel (perimeter) The other Sorics infuse faster. Ask me what I think about LRC. It is not all negative.

 

[magnus]

The Sunshield looks like UV stabilized clear gel coat. I am trying to stay away from the labor and the weight on these canoes. 15 mils of gel coat is a few pounds I need to avoid, I have been staying under 20 pounds with cherry trim and gunnels. I could shave a little weight with aluminum gunnels and trim or infusing them in (first canoe out of the mold) but that is tricky. It keeps me up at night. I do like Duratec products and have always bonded well with my epoxies.

Good thoughts on VE and UV tolerance or lack their of. It is one of those statements you hear for years but never know where it started. Wenonah canoes , about 200 miles south from me has always used VE for wet bagging as far as I know. They developed a resin through Corezyn (Interplastics) 8300 series at the time. If I travel 200 miles north to BWCA (boundary waters canoe area) I have seen hundreds of Mike's kevlar canoes sitting on outfitters racks. No one wants to portage a 60 pound canoe anymore. They are mustard/brownish colored and I think the outfitters would sell them to the public after maybe 3 years for half price. The Wenonahs have a good finish and you can get most models with gel coat and/or wood trim at more cost and weight. I talked to my area sales rep. for Corezyn because online I saw some promising infusion resins, although no mention of UV stabilization, He said I would have to buy a truckload and wait 5 months. I guess business is good?

 

[ondarvr]

Duratec is not like traditional gel coat, the chemistry is different. 6-7 mils is all that's needed.

If you want light and high performance, Google Pocock, they use sunshield for this exact reason.

I'm very familiar with Corezyn products. I started using them about 40 years ago, then sold them for a few more. You can enhance the UV resistance of polyester and VE resin by adding UV9, it helps a bit. Frequently these laminates are lightly coated with sunshield though.

 

[magnus]

I have been using Duratec Surface Primer for fast build up, maybe 30 mils at a time on plugs before sanding and polishing and forgot it was rated for 10 mils or maybe less.

Pocock the rowing shell guy, I will revisit him.

I looked up Guard Dog UV9 and got the impression small quantities may be difficult to find unless someone out their is repackaging. I found a university study which added UVA/HALS among many alternative additives to epoxy, UV tortured them all along with a straight epoxy control. It was disturbing but some other additives protected well . Of course UV9 was not listed for epoxy but was for polyesters as you said.

Ondarv, your in Wisconsin, any experience with Composite Enfusions? This winter I bought a gallon of their house brand VE infusion resin. I ran a small test infusion on glass to check surface finish. Excessive print through/shrinkage. I thought recently maybe I should have done it at 80F instead of my habitual 100F I infuse my epoxys at. At 80F I think it is thin enough to flow. Less shrinkage maybe?

If I was making carbon car hoods Sunshield sounds terrific. No post clear coat. These canoes should be sheltered most of the time...

Thank you for the input.

 

[KD8NPB]

Clear polyester gelcoat such as HK Research LHM1517 , spray at ~12 mils wet
Infuse with VE resin of your choice. AOC R015 is my current favorite.

Another option is Scott Bader Crestapol 1260, it's a 100% urethane acrylate. It'll give you almost all of the performance of epoxy without postcure requirements, and has been unaffected by base chemical shortages.

 

[magnus]

I ran a test using CORVE8101-50 VinylEster Infusion resin. Skin finish, looks very good, like epoxy and at room temperature. So I bought 5 gallons, I will let you know how it goes at scale. I will do a low temp post cure.

 

[magnus]

So it has been a while since I tested the Corve and the skin finish is not as good as epoxy, kept at room temp or above, but acceptable. The problem I personally have is the styrene odor. I have worked with only epoxy for 15 years so I have become spoiled. I may go back to epoxy.