Double-layer preforms for milk bottles

At Drinktec 2017 (Munich, September 11-15), the Swiss injection moulding machine manufacturer Netstal produces double-layer Prelactia barrier preforms for milk bottles using a PET-Line 2400-4000/1000. In particular, milk products and drinks with a long shelf life can be packaged safely, economically and in a manner that is visually appealing when using Prelactia.

Netstal demonstrates the production of a Prelactia barrier preform for 0.5-liter milk bottles using a PET-LINE 2400-4000/1000. The additional 1000-series injection unit is positioned in a so-called L position toward the main injection unit. During the first step of the overmoulding process, a 1 mm-thin gray layer with integrated light barrier is injected into the 32+32 cavity mould. The blank is then coated with a 1.4 mm-thin pure white outer skin. The total cycle time of the application presented at the trade fair is 9 seconds.

The double-layer structure of the patented barrier preforms offers an enormous economic benefit compared to other processes. In order to produce pure white milk bottles, the white pigment titanium dioxide is added to the polymer for the production of the preform. The additive also provides an increased barrier effect against damaging UV light. For single-layer preforms, the proportion must be at least 15% of the preform's entire weight. When using Prelactia, however, the additive is only mixed into the outer layer, which allows the proportion of the additive to be reduced to five percent of the weight of the preform. Nearly 100% of the visible light is reliably blocked. This makes Prelactia particularly well-suited for milk products and milk drinks with a shelf life of up to six months. Since both layers are made from PET, empty Prelactia bottles can simply be put in a regular recycling bin.