Wylie Royce, officer & director of resin and additive supplier Royce Associates, East Rutherford, N.J., laid out how the impact of fillers and additives has grown in recent years with a “then and now” breakdown of how recipes, and processes, have changed:
Then: Loadings of 20%—mostly pigments—in commodity resins with melt-flow rates of 12-13 and 20-40 second cycles. The parts were heavy gauge with huge gates and processed with low shear under normal mixing. Let-down ratios up to 10%, with dry color used.
Now: Loadings of 80% for dyes and pigments in specialty resins, with cycle times of 4 seconds in tools utilizing hot runners making thin-gauge parts, under intensive mixing and high shear.
“The processing window keeps getting narrower and narrower, as demands get higher and higher,” Royce said, speaking at SPI’s recent Equipment and Moldmaker’s Leadership Summit.
Here, as in life, you can follow the money to the source of the problem: by displacing resin with fillers, the costs of the part can be lowered, and, often times, despite the impact on processing, additives can boost functionality in finished parts. In this new world where loadings can reach 80%, Royce offered some advice to processors dealing with dramatically altered recipes.
- Feeders: “Variations of 5% or more in a feeder can become very costly as prices escalate with heavy loads,” Royce said. “Adding only one or two pellets per 200-300 natural pellets requires much more accurate feeding since each pellet difference means greater color variation.”
- Wall Thickness: If the wall thickness of a part or the gauge of a sheet is reduced in half, the amount of colorant required to achieve the same color and opacity doubles.
- Part Weight: If part weight is reduced and the pigment is doubled, this could contribute to longer cycle times or warping.
- Sheet Extrusion: Noting that an extruder is a basically just a “pump,” Royce said processors need to be aware that they have mixing limitations and actually are more prone to visible color streaks than injection molding.
- Blow Molding: Blow molding, especially extrusion blow molding, has the same limitations as sheet extrusion.
- Loading Levels: Resins heavily loaded with pigments will have a lower flow even with the addition of melt enhancers.
- Carbon Black: Carbon black pigment reduces flow very quickly as the percent rises in the finished product.
- Dyes: Dyes act differently than pigments, melting, acting like oil, and taking melt flow “through the roof,” according to Royce.
“The real savings in using a higher loaded concentrate are not as straight forward as they would first appear,” Royce said. “Normal parameters, such as melt flow (MFR) can be dramatically affected by additives—don't just go by the resin manufacturer’s listed MFR. Always test a new tool or product with the concentrate that is going to be used. Don't test with natural resin; colors and additives can dramatically change processes.”