Can anyone say what a typical resin content is for OOA pre pregs?
We used OOA prepreg with 40% resin content.
37% for UD, 42% for woven is normal enough depends on the material such as weave, viscosity, etc.
See here for example
http://www.gurit.com/files/documents/se-84lvpdf.pdf
I had thought it may have been higher resin content than typical material.
Everything (200g twill carbon) I have used is usually 42 -45%.
I’ve always wondered whether a higher resin content would help, if an extra 10-20% was stuck on the surface side would that reduce pinholes?
Interestingly though, SPM from PREPREG (Mehmet) looks and feels very dry, bit actually comes out with a very good finish, so there is definitely something in the chemistry that makes a difference.
I don’t think it has anything to do with resin ratios, there is more than enough resin there to get a good surface.
I think the good OOA pre-pregs will have dry fibres; either with a resin film on one side only, a la Easypreg/VTF261 or with dry fibres interspersed through the resin. I believe the issue with pre-pregs and pinholes is more the difficulties with getting the air out from the surface and getting the resin to flow nicely, so more resin could actually hinder that process. Hence with dry fibres to help get the air out, and potentially also help with resin flow, those pre-preg fabrics with partial dry areas perform better.
Exactly my understanding Hanaldo, its all about air evacuation through a physical path/
Interesting. I have never had this issue with pre preg. The ones i’ve used generally give an excellent surface finish, so long as the mold is well prepared. The aluminium molds give an especially nice surface.
I generally debulk first ply, then every 3rd or 4th. With OOA prepregs the manufactures usually call for an edge breather. Some use perf, some use non perf release. Also giving an extended final debulk to ensure air is evacuated. The prepregs i used are in the 40% resin content, UD is less.
Some of the companies also make prepreg for beauty applications where the resin has UV inhibitor in it. I would think that a higher content resin would help with surface as well but, seems like normal ratio is good. And these are bath type pre pregs so both sides are fully resinated. I have use some that are dry on one side, just not on a surface.
When you say nice surface though, how critical are you? Are they actually 100% pinhole free, or are there tiny pin holes that just aren’t really noticeable?
If I can’t pull a part out of the mould, clean it up and give it a coat of paint without having to fix up tiny pinholes then it’s no good for me. Getting a good finish is easy, but getting a truly pinhole free surface is a bit trickier.
A good surface finish is found in prepregs without a resin film on one side, so the surface structure allows a vacuum to properly develop between prepreg and mould surface. Also, the rate of vacuum is important. More than 15 mbar abs is tricky. 10 mbar abs is nice. This also takes care of moisture related problems.
Make sure your vacuum can reach all areas, that can take longer than expected. So always give a good long time debulk before turning the heater on.
What materials do you use Hanaldo and Sammy? I’m currently balancing the cost of material against cost of surface repair, trying to figure out what to go for long term…
I use Cytec VTF261.
Thanks for the reply Hanaldo 
edit
Where do you buy it from? I’ve been trying to find my way around the Cytec website but can’t figure out which of the numerous contact options to use, and previously have had emails ignored.
Also what price do you pay if you don’t mind sharing? I’ve read that this is what easy composites sell as “easypreg” so I’d like to figure out of it’s a comparable price for easy’s low MOQ.
Cytec and Tencate.
Cytec is a pain to buy from… even when buying $50k of material. Maybe they just didn’t like us or something. And the orders took a very long time to receive from payment. I don’t think they like selling to small companies.
Price I would expect is like $100/yd but I don’t know what the current rate is.
Tencate has been easier to deal with. They should have vendors in europe, as they’re a european company. Though I think cytec prepreg gives a much better quality. The resin is very clear. They also have a UV inhibited prepreg available for beauty parts. Tencate resin has a milkyness to it.
You’re not the only one sharing that opinion 
Thanks for the replies chaps, from that rough price it sounds like easy composites are selling it with only a reasonable margin. I’ll go with them in the short term and not both trying to get a reply out of cytec.
I think I’ll also try and give SHD another try in the near future, see if they have anything with good clarity and a nice clean weave. I previously tried one of their materials but didn’t like the look of the weave… But it’s pinhole free, and for some reason it’s taken me 18 months to realise that of I’m ever going to make any parts I’m best off with pinhole free finish than a subjectively nicer weave!
Could you give a bit more detailed review of how this product has worked for you? Finish, workability, part thickness you have made with, cure schedule, rolling used? Thanks!
Which material did you try from SHD?