New clarifying agent from Milliken saves energy too, tests with Arburg show

Plastics processors intending to produce high-clarity polypropylene mouldings now have two compelling reasons for using grades containing Milliken’s next-generation clarifying agent, Millad® NX8000. Not only does it yield unparalleled transparency in injection- and blow-mouldings, but it has also now been proven to allow significant savings in energy consumption through reduced processing temperatures and lower cycle times.

Trials recently carried out by Milliken in collaboration with leading injection moulding machine maker, Arburg, have shown that total energy savings of around 20% can be commonly achieved, with some evaluations showing savings as high as 35%.

Milliken carried out a series of trials using an all-electric Arburg machine Allrounder 520 A with a clamping force of 1500 kN to produce a utility drawer in two different grades of polypropylene, with melt flow rates of 25 and 60 g/10 min, both of them containing Millad NX8000. They showed that by reducing the processing temperature from 240°C to 200°C (while leaving the cooling and overall cycle times the same), the total energy consumption of the machine and its auxiliaries was reduced by 9%. And because cooling time could be reduced as a result, the cycle time could be improved by several seconds, yielding a total improvement in energy efficiency for the entire machine of 22%. Compared to running the machine at 280°C (not unusual for these types of resins), the energy saving amounted to 35%.

Energy savings achieved through temperature and cycle time reductions far outweighed any increases in consumption due to higher screw torque and injection pressures needed because of the higher viscosity of the resin under the new low temperature conditions.

The trials involved the production of a drawer weighing 42 g. In production runs using a 60-MFR resin, ‘standard’ production conditions at 240°C required a cycle time of 15.5 s; for a run consuming one tonne of material, the total energy cost was 81.9 euros (based on an average cost for industrial energy in the Eu of 0.1177 ?/kWh). Reducing the temperature to 200°C cut the energy cost to 74.6 ?/tonne, while reducing the temperature and then optimizing the cycle time at 11.5 s brought the figure down to 63.7 ?/tonne.

“We knew from previous evaluations that conventional clarifiers need a certain minimum level of energy input - which typically equated to temperatures over 220°C during processing - to ensure full solubility and hence performance in the final application,” says Adam Newberry, Technical Account Manager for Europe and the Middle East. “Millad NX8000 has much better solubility characteristics in PP, and these allow lower processing temperatures to be used.”

By using the lower processing temperatures, the converter has less heat to remove from the final part. This means they can reduce the cooling time and hence overall cycle time, leading to improved productivity. Millad NX8000’s broader processing capability leads not only to direct savings in energy costs but also to lower machine and labour requirements. Since labour and production costs are major contributors to the overall manufacturing costs, any improvement in productivity can lead to significant savings for the converter.

The Allrounder 520 A is ideal for these sorts of tests. Its Selogica “energy consumption measurement” function allows the machine operator to record and analyse both the average and the periodic power consumption of the running injection moulding process. If certain process modifications are made, this results in changes to the corresponding power consumption values. This data allows for real-time optimisation of the machine’s power consumption and a reduction of the energy consumption per part.

“All-electric machines are inherently low energy consumers and so the Allrounder 520 A provided the lowest baseline for our trials,” says Newberry. “Reducing temperatures on this machine has a more significant percentage effect on the total energy consumption than on a hydraulic machine because the heating requirements for all-electric machines comprise a greater percentage of the total energy consumption. But in terms of absolute values for energy reduction and productivity improvements, results across all machine types are likely to be very similar.