Blow Molding: Mold Better PET Bottles 50% Faster

“Zero Cooling” is the name Nissei ASB Machine Co. applies to its new PET stretch-blow machine technology that promises an average of 50% higher productivity and up to 15% increased bottle topload strength, as well as improved container appearance. In one-step injection stretch-blow molding (ISBM), injection and cooling of the preforms in the first station of the machine always requires the longest time and therefore determines the overall cycle time, according to Nissei ASB.

In the company’s ASB series machines, the second station is used for preform conditioning—adjusting the temperature profile and/or shape of the preform before blowing in the third station. The new technology, which is being applied to all ASB Series models, moves preform cooling to the conditioning station, where it can be combined with the appropriate temperature-profile adjustment. The injection station is now available to start filling the cavity for the next injection cycle while cooling of the previous shot continues simultaneously in the conditioning station. This removal of cooling from the injection station accounts for the average productivity gain of 50% and for the name “Zero Cooling” for the process.

In standard PET blow molding, Nissei ASB says the only way to shorten the cooling time is to make the preform thinner, and therefore also larger for the same size container. This reduces the overall stretch ratio from preform to finished container, and thereby also reduces the mechanical properties of the container induced by strain hardening. Smaller, thicker preforms with Zero Cooling achieve higher stretch ratios and thus up to 15% higher container topload strength, the company claims. This improved strength reportedly also allows more opportunities for lightweighting.

Use of thicker preforms and higher stretch ratios also eliminates visual defects such as fisheyes, body ring, and orange peel, according to Nissei ASB. The company adds that faster molding of thicker containers is attractive for premium heavyweight cosmetics containers using standard PET grades while exhibiting no haziness.