Injection Molding: Two-Layer Light-Barrier Preforms For PET Milk Bottles

White PET preforms with black inner layer block out light while saving on expensive pigment.

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At the Drinktec beverage technology show this month in Munich, Germany, Netstal (U.S. office in Florence, Ky.) will present two-layer Prelactia light-barrier PET preforms for milk products and drinks with a long shelf-life (up to six months for milk). These preforms consist of a 1-mm inner layer of gray PET, which is overmolded with a 1.4-mm white outer skin. This approach is said to provide an improved light barrier—blocking nearly 100% of visible light—while cutting the use of expensive, UV-blocking titanium dioxide white pigment by two-thirds.

The molding system is a Netstal PET-Line 2400-4000/1000 240-metric-ton hybrid machine with two-stage screw/plunger injection and a second injector in an “L” position. The side injector first molds the gray inner layer, then the main injector overmolds the white outer skin. At the show, the 32 + 32 cavity mold for 17-g, 0.5L preforms will by supplied by Molmasa of Spain. The core plate shuttles up and down to transfer preforms between the two molding stations. A top-entry robot removes the preforms to a post-cooling station above the clamp. A second robot transfers the cooled preforms to a belt conveyor that carries them down to floor level. Overall cycle time is 9 sec.