Hi 

 Has anyone had any problems with pigments in PU resin loosing colour and becoming patchy over time? I am using Xencast toughened P6 with EC pigments, no fillers, mech mixed, de-gassed the parts are nice colourful and shiny when they come out the mould, after a few days the colour is dying back but the parts are still nice and glossy.

 Any help would be appreciated.

Thanks

Havent seen it in urethanes before, but it's a common issue with the transluscent dyes in epoxy. 

Have you got any photos showing what you mean? does it become even again when the surface is lightly abraded? 

I've not heard of pigment degradation like that.  What sort of percentage was used?


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Sorry for the delay Warren this is how it tends to go, It's not as prominent in the pic but it can be seen, as I say they start off all jet black, 8% is the ratio I am using.

Cheers

Any ideas Warren would be appreciated?

What sort of temperature where you curing at?  How accurately is your mix measured out?

We have seen slight issues like that where the resin  (for whatever reason) has not quite fully cured off at the time of demoulding.  What tends to happen, is that it will continue to cure slightly and as it does so there is movement as  PU leeches towards the surface which can cause patchy whitening like you are seeing.

Cool temperatures can cause it,  poor mixing or poor accuracy measurement also can cause it.

Is there any greasy feel on the resin surface?  If it is only a minor imbalance or a heat issue, a light sand or polish may restore some of the finish.  

This can happen in any resin system although PU's seem a bit more cure sensitive than others and P6 is quite a sensitive resin as it is in terms of moisture, mixing etc.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks Warren

 Accuracy is not the issue, it it metered out accurately, I'm also sure that mixing isn't as it is mechanically mixed and if used in an open mould there are no streaks on the back. So I'll have a look at the temperature this is the only thing really that could fluctuate in the process.

Thanks for your help!

On a side not are there any powders that give a strong black finish? I was thinking of trying charcoal.

Thanks

Graphite powder and milled carbon fibre will both be a nice charcoal black colour.  Milled carbon fibre will also add tensile strength to the plastic cast too due to the nature of it being very short strands of carbon.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hi Warren

 Thanks I have tried graphite I find it to be too grey in colour.

Thanks

Have you tried a small experiment in warmer curing conditions to see if it still happens? 


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant