With the huge capacity of film manufacture being added in South Asia currently, it is critical to innovate for the manufacture of laminates and films that are more attractive and with improved properties; both value addition and excellence are needed. The leading lights of Bobst’s R&D and manufacturing activity in this area based in Manchester took part in the Delhi event. The managing director Steve Carey to R&D director Nick Copeland and research scientist Carolin Struller and others addressed the highly technical and knowledge filled sessions during the day-long event.
The AlOx conversion process by which a high barrier transparent ceramic layer is bonded to packaging films using the K5 Expert vacuum metallizer is one of the key Bobst innovations being talked about since the open house in Manchester and the K exhibition in October 2016. This was addressed by Carolin Struller in the first technical session of the day.
Amongst the other sessions, one of the most interesting was the one that discussed process optimization for high barrier, low defect metallization by Nick Copeland. The DarkNight process Copeland described is a total system of metallizing using the new improved and modified K5 boat-based metallizer together with the Hawkeye quality monitoring system. As Copeland explained, apart from the high barrier properties provided by aluminum metallization, the light barrier that it provides is needed for preventing food products from becoming rancid.
Bobst’s Hawkeye monitoring system measures the thickness of the aluminum deposition on films and detects, counts and categorizes pinholes and other defects from 0.1 mm upwards for purposes of lightfastness. Copeland showed the six types of pinholes that can be used to establish quality benchmarks for metallized packaging films. He suggested that perhaps a limit of 2.5 to 6 defects per square meter was a desirable benchmark.
Improvement of metallization can also come from use of aluminum wire of higher purity but as Copeland suggested, using 99.99% or best quality aluminum wire can be 60% more expensive than just 99.9% pure wire. However, the use of 99.9% pure wire may well be justified since it costs only 10% more than the aluminum of 99.98 grade. In response to a question from the audience, Copeland explained that the grayness or lack of shiny reflective properties of the metallized coating is not as much a factor of aluminum wire purity as it is of the presence of oxygen or water in the process, or even the lack of smoothness in the film. Essentially, film turning gray or brown is because of oxidation and the best way to prevent oxidation is to have a good vacuum in the metallizer and a smooth based film.
Copeland’s technical presentation also addressed some of the other constraints of boat-based vacuum metallizers and how Bobst has been able to make several improvements in the new K5 by flattening the wire and feeding it from both sides to eliminate vibration. It can be said that DarkNight is a full process that includes Hawkeye for defect detection with the overall aim of producing the highest quality of metallized barrier films. It can also be used during the AlOx process to allow greater precision control and quality assurance.