Alupa, Belgian manufacturer of vacuum metallized paper, produces over 18,000t of paper every year for use in a range of applications, mainly by manufacturers of labels, cigarette packaging and gift wrap.
Since 1996, Alupa has manufactured paper with widths of 2.2m and at a speed of 700m/min on a Polytype coating machine. This particular machine is set up to work with water based coatings. However, in order to achieve a better gloss finish on some specific products, the company decided to change the process and use solvent based lacquers.
On the first run, the paper is coated with a solvent based lacquer that closes the pores in the paper and gives it a smooth surface. The paper is then metallized with aluminium under vacuum conditions. Finally, the metallized paper goes through the coating machine again and is coated with a second solvent based lacquer, which serves as a primer for the subsequent printing process.
However, in practice, the first run on the high speed coating machine resulted in major unforeseen safety problems for Alupa. The treated paper was very dry and consequently became loaded with static charge, which resulted in ‘sparking’ in several areas, with the risk of fires or explosions.
The first attempt to resolve the problem relied on the installation of a large number of conventional AC static control bars. However, in order to provide effective control of the static, the bars had to be mounted very close to the web. This resulted in contamination of the bars due to splashing from the coating process and a rapid loss of ionization efficiency.
Alupa then turned to Meech International and its range of Ex products. It installed Meech’s explosion-proof 976Ex pulsed DC bars directly before and after the coating rollers. The ATEX certified bars are said to provide effective long range ionization without the need for air assistance. Alupa says the DC bars helped in avoiding contamination from the coating head. “The removable emitter pin assemblies also allowed quick and easy maintenance with minimum downtime,” it adds.
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