First Water Bottles With Ultrathin Glass Coating

German spring water and soft drink producer Vilsa Brunnen Otto Rodekohr GmbH has achieved what’s said to be a world first by demonstrating that even mineral water can benefit from a wafer-thin glass coating inside PET bottles. The company supplies premium mineral water containing various levels of carbonation, as well as fruit spritzers, soda pop and “near water” (flavored water) beverages. Vilsa is particularly proud of the pure, natural flavor of its spring water afforded by its pH and “gentle,” low-sodium mineral content. According to a Vilsa source, the extra barrier provided by the interior glass coating preserves carbonation and also prevents introduction of off-flavors — such as from acetaldehyde in the PET. In addition, Vilsa’s fruit spritzers benefit from oxygen protection provided by the glass coating.

In 2019, Vilsa switched all its nonreturnable bottles to rPET. Adding the coating technology furthers the company’s drive for sustainability, because the glass coating — unlike the use of additives to improve PET barrier — enables full bottle-to-bottle recycling as the interior coating is completely washed off during the reclaim process. Consequently, the company has adopted interior glass coatings for all its nonreturnable PET containers from 0.5 to 1.5 L. The first coated bottles were distributed to retailers this autumn.

At its mineral-water plant in Bruchhausen-Vilsen in Lower Saxony, Vilsa installed the latest-generation KHS innoPET Blomax stretch-blow molder. That unit was later combined with a KHS FreshSafe PET Plasmax barrier unit to form an InnoPET FreshSafe block. After stretch-blowing, cooling and transfer, the PET bottles are interior coated according to the Plasmax PICVD (plasma impulse chemical vapor deposition) process, which was first used in the pharmaceutical industry. The bottles are turned upside down and passed into the coating chamber, where a reaction gas mixture is introduced into the bottles in a vacuum and then is transformed into a plasma (ionized) state by microwaves. The result is a deposit of silicon dioxide (glass) inside the container — the coating is less than 0.1 microns (100 nm) thick and chemically bonded to the inside wall. The coating is completely transparent and flexible, so it will not flake off when the bottle is flexed, according to KHS. The coating separates from the PET only in the recycling process.

At Vilsa, bottles are blown and coated at rates as high as 24,500 bph. The most popular nonreturnable format is the 0.75 L bottle.

A number of well-known bottlers of juices and carbonated soft drinks have used Plasmax barrier technology for years, but Vilsa is the first to use it for mineral water. KHS specialists ran extensive simulations to achieve perfect distribution of the thin glass coating in Vilsa’s bottles. KHS Bottles and shapes technicians defined the exact recipe for each container size, product and CO₂ level.

According to KHS, full recyclability of FreshSafe coated PET bottles has been confirmed by the European PET Bottle Platform (EPBP) and North America’s Association of Plastic Recyclers (APR). The coating’s suitability for use with foods has been certified by the U.S. FDA.