Print-through is a phenomenonthat will always occur to some extent. You can do things to reduce it but itwill always be there, whether you’re using chunky fabrics and polyester ofvinylester resins or whether you’re using fine fabrics and epoxies. There aresome things of course that you can do to reduce the effect.
Things that makeprint-through worse:
- Using heavy weave fabrics like 12k or 24k fibres; they are physically more textured and so will ‘print through’ more onto the surface.
- Using resins systems with a high-shrinkage like polyesters or vinylesters. Epoxies have a much lower shrink and so will show print-through less.
- Releasing parts from the mould too early (i.e. before the resin has fully cured) - this can have a really dramatic effect.
- Post-curing parts ‘off the mould’ (i.e. after you have release them from the mould). This will increase print-through because without the mould to keep everything flat, as the resin softens slightly during the elevated temperature post-cure the fibre will ‘push’ on the surface and print-through.
Things that will makeprint-through better:
The obvious things areavoiding or reducing all of the above points such as using finer fabrics, usingepoxy resin, ensuring parts are fully cured before releasing and doing anypost-curing on the mould. The use of a compatible gelcoat will significantlyreduce or completely eliminate print-through.
In addition, you’re likely tofind that running higher resin ratios in your laminate will also reduce theeffect of print through since it’s the fibre that causes print-through; by ‘suspending’the fibre in more resin then it’s less inclined to push out its texture ontothe surface once the part is release from the flattening effect of the mould.
As with many post-curecycles for resins, the post-cure cycle for our IN2 Epoxy Infusion Resin is nottoo sensitive (which again explains a range of suggested cycles) and a range ofdifferent post-cure cycles will produce good results, specifically improvedmechanical performance and elevated HDT/operating temperature. Post-curingparts that will be used at or exposed to elevated operating temperatures (suchas vehicle bonnets/hoods in direct sunlight, engine-bay parts, car interiorparts etc.) is strongly recommended to prevent distortion of the parts whenthey are put into service and experience these higher temperatures.
Where possible,parts should be post-cured still inside the mould to reduce distortion andimprove surface finish (i.e. reduce 'print-through'). When post-curing parts inthe mould, it is important to post-cure them without demoulding at all (i.e.don’t demould and then put them back into the mould) otherwise you can get somestrange patterns on the surface where some areas are post cured in direct contactwith the mould surface and others are not.
A simple and veryeffective post-cure cycle with the IN2 Infusion Resin (or EL2 EpoxyLaminating Resin) is as follows:
CYCLE #1 SUITABLEFOR MOST SITUATIONS
- 24hrs at room temperature
- 6hrs at 60°C
If you’reencountering any surface finish issues (faint print-through) then you canexperiment with a slower 'ramp rate' which sometimes improves things:
CYCLE #2SUGGESTED FOR SUBTLE IMPROVEMENTS TO SURFACE FINISH
- 24hrs at room temperature
- 2hrs at 40°C
- 2hrs at 50°C
- 5hrs at 60°C
If you need topsuh the HDT of the finished part higher then you could increase post-cure upto a maximum of 80°C as follows:
CYCLE #3SUGGESTED FOR HIGHEST POSSIBLE HDT/OPERATING TEMPERATURE
- 24hrs at room temperature
- 2hrs at 40°C
- 2hrs at 50°C
- 2hrs at 60°C
- 2hrs at 70°C
- 4hrs at 80°C
These are all just suggestions. Most situations just call foroption #1; 6hrs at 60°C. Many customers also find that they can dispense withthe 24hrs cure at ambient and simply load newly infused parts into the oven tobegin the cure however this is something that you would need to experiment withyourself. A cure at ambient temeprature before post-cure is generally favouredwith most resin systems.
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant