General Vacuum in Lancashire, now part of the Bobst Group have been designing and building large industrial vacuum roll coaters for use in optical, electrical and general packaging applications since 1996.

Aluminium metallized polymer films can be used in packaging applications where there are a number of requirements including barrier protection (WVTR, OTR etc.). This type of packaging has proven essential to prevent product losses in storage, distribution and the preservation of food. The preservation of foodstuffs is achieved by the inherent design of the packaging structure, whose primary function is to provide optimised barrier performance to extend the shelf life of the product it’s protecting. Barriers to gases and light are essential depending on the packaging application. Historically these barrier properties were achieved with aluminium foil, aluminium foil/paper laminates and multi-laminated films. These barrier materials were not ideal due to the high energy content of the aluminium foil production and the mass of material employed.

Vacuum metallizing has become a viable substitution technology, depositing thin ‘nanometer’ metal coatings onto polymeric substrates. The physical vapour deposition technique works by vaporizing the metal in a vacuum chamber and allowing the metal to condense onto the passing substrate. The integrity of this extremely thin metal layer is found to provide an excellent barrier to light, water vapour, oxygen as well as other gases and aromas.

The advantages of using this technique are:

• A 0.00005 thickness offers the highest yield per m2 compared with other barrier materials
• The process requires a minimal amount of energy
• Substantial reduction of waste in packaging
• Recycling poses no problems

Thermal vacuum evaporation of aluminium onto polymer films has become a standard technique and such films are used widely for food packaging, where the gas permeation is the most important property. In order to maintain a high shelf life for a given content a high barrier against oxygen and/or water vapour permeation is necessary. Polyester, PET and OPP are the most widely used film types for such an application.

General Vacuum utilise the 8001 Oxygen Permeation Analyser and 7001 Water Vapour Permeation Analyser from Systech Illinois to test the barrier performance of their metallized coatings.

Nick Copeland of General Vacuum says, “The amount of metal deposited on the surface of a film will govern the oxygen, water vapour transmission and light barrier properties of that film. Systech Illinois’ permeation analysers are vital to accurately and reliably measure the rate of oxygen and water transmission through the film. This will help to determine the amount of metal that is required to meet a particular application.”