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Metallized Paper
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Direct Metallizing vs. Transfer Metallizing.
The Medium is the Massage:
Lets say your company that has been given the task to design a label for a 17 year old Scottish Whisky, that illustrates its exclusive positioning, exquisite taste and strong Scottish heritage. Before you even choose the text, the font, the colour-pallette and any relevant images, the first thing you have to do select is the material on which all of the above are going to have to be presented. This label material has not only got to be visually appealing, it has also got to be technically superior in terms of offering good water resistance,good printability and will have to be durable.
A metallized label could be your answer.
What is metallizing?
Metallized materials are produced by melting and vaporizing a metal (usually aluminium) in a vacuum while passing a web or paper or film around a chilled roller and over the point of vaporization. The vaporized molecules then collect on the cool web, so providing the paper or film with a metallic finish. It can be carried out by direct metallizing onto the material surface, or by transfer metallizing where the vaporized metal particles are attracted in the vacuum chamber to a very smooth plastic carrier web and then transferred to the chosen substrate under pressure.
Direct Metallizing (DM):
FILMS:
Vacuum metallizing is a batch process. The film to be metallized is loaded onto the unwind zone of the vacuum chamber threaded around the cooling rollers and onto the rewind roll. The vacuum chamber is sealed and evacuated. Aluminium wire is then resistance heated in boron nitride boats to a temperature of ca. 1500°C and evaporates and condenses onto the film as it passes over the cooling roll.
The vacuum metallizing parameters are:
- The film length is commonly up to 24,000 m and even 36,000 m is possible (12 mic. PET)
- The vacuum is ca. 10 ì torr (99.9999% of the air removed)
- The evaporation temperature is ca. 1500°C.
- The deposited layer is ca 0.03-0.05 mic. Thick; ca. 1/250th the thickness of aluminium foil. At this thickness 1 kg of aluminium would cover two football fields.
- The traditional films which are vacuum metallized are:
o Polyester
o Polypropylene
o Polyethylene
o Polystyrene
o Cellulose
PAPER & BOARD:
When direct metallizing paper (and board) the paper is first primed to seal the paper surface and give an improved smoothness to the surface, vacuum metallized by the process, described above and then re-moisturised to replace the moisture lost in the vacuum processing and post-coated with a print receptive lacquer.
Transfer Metallizing (TM):
The process has four elements:
- Coating (of a carrier film with a release lacquer)
- Metallizing (onto the release lacquer on the carrier film)
- Laminating (the carrier film with paper/board/film)
- Splitting (the carrier film from the metallized paper/board/film) – with in-line Corona Discharge Treatment.
The lacquer which allowed the separation of the carrier film from the product remains totally on the transfer metallized product, protecting the metal and acting as a print receptive surface. The carrier film, after splitting, becomes available for re-use.
During the splitting process, the lacquer surface (The release lacquer) is Corona Discharge Treated to enhance print receptivity. This treated surface is stable for over 6 months when stored under appropriate conditions.
The process is very difficult to achieve in that one requires 100% adhesion of the lacquer to the carrier film during coating, metallizing and laminating and then 0% at splitting process. Thus the intimate relationship between the lacquer and the carrier film is of prime importance.
Essentially on each substrate is a conversion of about 3 g/m2 of lacquer and 3 g/m2 of adhesive, and the paper does not go into the metallizing chamber (as is the case with direct metallizing).
Transfer Metallizing (TM) - A better choice:
TM offers several benefits to the end user. These include:
- The process itself is almost self-monitoring as far as defects are concerned. If there is a coating defect during stage one such as a scratch mark etc., the metal will be deposited on the uncoated film at this spot and will not be separated from the carrier film, consequently the final product is defective, but of far more importance, the carrier film will be destroyed making it unusable for further processing. Likewise with the lamination stage, if again there is a defect - no adhesive spot - when the paper is separated from the complex it will not remove the lacquer and metal from this spot – again a defective product and an unusable carrier film is the result.
- TM products have the highest reflectivity in that the metallized layer reproduces the very smooth carrier film and not the relatively rough paper underneath, as is the case with DM, where the metal molecules are deposited directly on the rougher substrate.
- In TM, the lacquer which allowed the separation of the carrier film from the product remains totally on the TM product and protects the metal coating and acts as a print receptive surface.
- It is an extremely versatile process in that by only changing the substrate; completely different products can be produced – from 46 g/m2 to over 300 g/m2 and also transfer metallized non-paper substrates.
- Any finished product created using Transfer Metallizing, has 6 g/m2 of lacquer and adhesive, making the metallized paper considerably stronger than the original substrate and stronger than direct metallized products as they do not have the layer of adhesive and lacquer.
- Independent research carried out by TNO (NL) studying the recyclability of Transfer Metallized papers and Boards showed that “… 10% of Transfer Metallized Paper in domestic waste paper has no significant effect on the properties or appearance of the recycled paper products from it.” Likewise the PTS study concluded that “Transfer Metallized Papers and Boards used in applications such as gift-wrap, laminates and flexible packaging can be part of the normal household waste used paper stream and as such can be collected and recycled.”
What we can offer you:
At Smith & McLaurin we are working towards expanding our range of metallized products. Our Silver Transfer 74 face paper has been successfully trialled on our machines and is currently available to all our customers. It is a transfer metallised paper which provides a glossy, metallic finish for labels and is also available in gold. The paper is approved for direct food contact and meets the requirements of Article 11 of EC Packaging Directive 94/62/EC. Graphic print may be applied by a wide variety of techniques including Offset Litho, Letterpress, Flexographic and Gravure and is also suitable for light embossing. It offers the user all the benefits of a transfer metallized material including, smoother finish, proven recyclability and better durability.
Please contact Elaine Williamson on +44 (0) 1505 707706 for further information on our metallized range.
Posted on 09 February, 2009
