Tests show big savings possible on APET thermoforming

Octal, a supplier of PET sheet founded in 2006 in Oman, and thermoforming machinery manufacturer GN Thermoforming Equipment say tests they've run using Octal's amorphous PET (polyethylene terephthalate) and GN's APET-specific thermoforming machinery prove that bottom-line savings can be significant for processors contrasted with standard APET sheet or RPET run on other makes of machine, especially ones that rely on radiant heating. The test results showed Octal's DPET brand of APET had a faster cycle time, was more efficient and could be run with lower clamping pressure than either standard APET or PET sheet extruded from post-consumer recyclate (RPET). The experiments were carried out in GN laboratories and in field trials at processors to confirm the basis of the cost models.

What exactly did the two companies do? Rolls of APET, RPET and DPET were tested in the GN laboratory. All sheet tested was 16 mil (400 microns) thick (nominal). The material was formed into trays with a 4:1 draw ratio on a 6-cavity mold. The criterion was to develop a DPET cycle time and then optimize the cycle for both relative clarity and formation of the part. A panel of three judged relative clarity and formation was judged by a GN technician.

DPET was first trialed using the standard APET cycle time. Preheats and cycle time were then adjusted to optimize the cycle time. The clarity and formation of parts were ranked at each change. Once an optimum cycle was obtained the recipe was noted. In this trial the formation of the part was always good, however the loss of clarity was noted if the temperature/time was pushed beyond optimum. The surface temperature was then measured using temperature strips. The temperature was noted to be approximately 100ºC. The cycle time for DPET was noted to be 4.08 seconds.

Once an optimum cycle was determined, a 10-minute trial of DPET was run, then the machine was left idle for over an hour and the DPET cycle was run again. The machine produced good parts on the second cycle and again had no trouble during the 10-minute run time. As a further test for reproducibility a second roll of DPET was mounted on the machine from a different cycle in the same production lot of DPET. Again the material produced good parts on the second cycle and performed well throughout the cycle test.

As a final trial, the original DPET roll was remounted on the machine; the trial was run to determine how fast DPET could be run. The cycle time was reduced to 3.32 seconds with good parts being formed.

RPET was then mounted on the machine. The first trial was run at the DPET settings. The resultant parts were well formed, but showed significant haze. The cycle time and temperatures were adjusted to obtain the clearest parts. The clearest parts were obtained when the preheat temperature was reduced and the dwell increased. The overall optimum cycle time for RPET was determined to be 4.43 seconds. The surface temperature was tested and found to be approximately 96ºC. The results of this test showed RPET cannot adsorb heat as fast as DPET and retain clarity.

A commercial grade of APET then was mounted on the machine and optimized per the same procedure as outlined. The results were a cycle time of 4.42 seconds for APET. Again the trial shows APET cannot adsorb heat as fast as DPET and retain clarity.

Other trials at GN had been run using 20-mil thick DPET sheet and the results were essentially the same, reports Octal, with DPET running faster than either RPET or APET. The average cycle time will vary with gauge and part configuration, but Octal claims that DPET consistently runs 10% faster than APET and RPET. Feedback from customers in the field has confirmed the results, say both companies.

Last year GN Thermoforming Equipment (Chester, NS) introduced its DX series of machines specifically for APET tray processing. These rely on conduction of heat into the plastic sheet from a heated platen (contact heating) as opposed to introducing heat into the sheet by electromagnetic waves or radiant heat. GN says its Tool Specific Heater platen allows quick tool changes (within 10 minutes), with the hot plate focusing heat and air more directly on each cavity for optimum clarity and material distribution.

Octal's APET sheet is produced using a newly patented process described in full here. In short, the DPET (Direct-to-PET) process brings melt from Octal's PET reactors straight into a sheet die. The melt never runs through an extruder screw, so there is no heat history added to the material,

Octal commissioned PIRA (Printing Industry Research Association) to conduct a comparison of the carbon footprint of DPET against APET and RPET. According to that Association, when compared to APET and RPET, DPET has a carbon footprint 27.6% lower than APET and only 0.2% higher than 50% RPET (50% RPET+50% APET) assuming that no energy is carried on from the post-consumer waste. But if one assumes a certain amount of energy is carried on from post-consumer waste, then DPET has 20% less carbon footprint than 50% RPET. In addition, says Octal, its DPET has a caliper control of  ±1% when compared to ±5% caliper control of some competing APET sheet suppliers, which means that the weight of one 252 by 110 mm APET tray weighs 9.355g, whereas the same tray in DPET weighs 8.607g. Thus the ±1% tight tolerance helps in reducing the weight of a formed part by about 9%.

Both companies have significantly more data available for interested processors, to include full-blown cost models. To obtain copies of cost models and other information, processors can contact Octal's Mohammed Razeem  or GN's Jerome Romkey. —Matt Defosse