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PCNJ50a: thanks for that! Overnucleation would fit my observations perfectly: higher open-cell content, ridiculous densities and high moisture absorption. IRstuff: I did not know EPS came in such high densities; in that case we are talking about the same product as mine. I doubt whether TV...

IRstuff: I think you are talking about EPS foam, which generally has much lower density (30-60 kg/m³ i think, ours are about 200). As such, the profiles we make are a lot harder. Target hardness is that of MDF, though I doubt we'll get that far. Pat: Coextrusion has not yielded demonstrable...

Bubble coalescence/collapse on the surface means the surface will become rougher. This would be bad for market perception and volume of paint needed to apply.

Yes, we are experimenting with coextrusion as well. Forgot to mention that. We've tried extruding the coex layer together with the body of the profile but we haven't seen a significant increase in hardness from this. Possibly because of velocity discrepancies or because the blowing agent...

I'm currently searching for a way to make our profiles harder and (if possible) cheaper. Current density is about 250 kg/m³, durometer hardness 22-25 Sh.D. The obvious way is to use some kind of mineral filler. Preliminary tests have shown that both talcum and calcium carbonate can be dosed up...

Could a difference in velocity between both layers have a pronounced effect on the grafting? Also, from our calculations the coextruded layer seems to be stretched elongationally due to shear forces.

Point taken Pat. I'll definitely try using different resins. Generally the same resin mixture is used for both core and coex layer.

Thank you for your reply. Only additive used is a talcum-based nucleating agent which is distributed fairly evenly across the melt judging by the narrow cell size distribution we get. I've played around with the composition of the coex layer without significant results. Temperature might be...

I'm currently trying to extrude a thin profile consisting of a low-density foamed PS core material with a coextruded PS layer (foamed or compact) on top to improve compressive strength. Core is extruded at approx. 167°C, coextruded layer between 190 and 200°C. What we see is that the top...

Not sure about this but how about talcum? Cheap and definitely increases surface roughness/friction.

Yes, cooling down the mould helps by making the melt slightly tougher and so more resistant to deformation. Cooling down too far impedes proper foaming though, as the tensile strength of the outer layer then becomes too high. I guess we'll have to make do with a more dense product. Thank you...

Not both at once, no :) I always look for the pressure ceiling when testing so I know increasing melt pressure does not have a positive effect on the corrugation. Increasing the temperature is only possible when I decrease the amount of blowing agent, otherwise the pressure is insufficient to...

Yes, part density is on the low side, about 80-85 kg/m³. Upping the density to about 110-120 kg/m³ solves the problem but this makes our profit margin rather too low. We use pure CO2 as a blowing agent.

When trying to produce fairly large profiles in low-density XPS foam we are continually faced with corrugation. We thought memory effect interfered with the foaming when exiting the die but (greatly) increasing the land length of our die has had no effect at all. A tip, anyone?