RK Print Coat
Flexible foils and metallized material possibilities

28.02.2020 Aluminium foil is one of those materials that garner a lot of attention, sometimes not for the best of reasons. From a raw material perspective, aluminium in its raw state bauxite is exceptional in that it is one of the most common materials on the planet. It is however subject to some controversy and scrutiny by environmental stewards.

Aluminium foil is a versatile material.
© Photo: @Madison Inouye – pexels.com
Aluminium foil is a versatile material.

Some say that because the manufacture of even a single tonne of aluminium may involve upwards of 1500W/h electrical energy to convert bauxite into aluminium through the process of melt-electrolysis that this is not only wasteful but environmentally damaging. Foil advocates counter by saying that this in more than offset by the fact that when processed the material itself is both lightweight and thin. Some might say that this is a ‘case of a little going a very long way,’ something that every packaging converter can attest too.  Any waste produced is combustible and as part of a household waste stream allows for the possibility to recover thermal energy from an incineration process rather than simply for any scrap to be directed to landfill.

Part of a laminate

When it comes to packaging, alufoil is often used as part of a laminate and may be produced in widths of 2 metres and is then rolled out to thicknesses of as little as 6 microns. Foil used in beverage packaging most commonly has a thickness of 6.65 microns, which produced in widths of 2 metres x 100 equates to 55m2 of packaging, or taking into account other components of the laminate - approximately 666 litre packs of fruit juice.

The barrier properties of foil are superior to many of the other materials associated with packaging production. Even the sheerest of foil when used in combination with filmic structures such as those associated with pouch production makes for a product that is impervious to liquids, gases and light.

Foil is not of course the only processing option. In situations where the marketer and brand owner seek to attract consumers with a reflective or shimmering look, and when barrier resistance is not quite so important, then metallized film may be considered appropriate. The process of metallization can be undertaken by air-to-air systems or via roll-to-roll systems. The process involves coating a plastic film with an extremely thin metal layer of around 10 to 18 microns under vacuum conditions onto a continuously moving web. The success of the process is dependent upon a number of factors such as good adhesion to the substrate, uniformity of appearance and precise tension control of the web.  Normally metallization is not the final process, subsequent converting processes to produce a saleable product may include cross cutting, varnishing, lamination and printing.

Conveying prestige and quality

The radiance of foil, metallized films, papers and speciality inks (ink – incorporating alu-platelets, etc) have long been appreciated for their ability to convey prestige and quality to many a packaging product.

Converters sometimes print reels of pre-metallized materials such as polypropylene (PP) in single ply on flexo or gravure presses. An alternative option is to laminate metallized oriented polypropylene (OPP) to another film prior to printing. If other films are involved processing options may vary. For instance, with a substrate such as polyester the tendency is to laminate to the backing film prior to printing. Sometimes metallized polyester is reverse printed prior to laminating.

No process is completely trouble-free, every process, material and consumables used are subject in one way or another and at different times to processing variables. Even foil when used as a layer within a lamination can be problematic, especially as foil tends to be ultra- thin. The foil is often prone to microscopic nicks as it travels at high speed through the laminator; metallized films can also be easily abraded or scratched during their travels through the laminator.

Stand up pouches allow for a visually different and a more practical approach for many food and beverage items with foils and metallics playing an important role in the structure of a pouch laminate. From a converter’s perspective a pouch could be configured in the following manner: PET/print/adhesive/metallized PET/adhesive/sealant or PET/print/adhesive/metallized OPP/sealant.

Printability and stiffness

PET provides printability and imparts stiffness to the structure and the metallized layer or ply serves as an oxygen and moisture barrier. The metallized filmic component also is aesthetically pleasing and enhances product appeal. If OPP is substituted then functionality is slightly altered though barrier against moisture and stiffness of structure is still obtained. Pouches can of course be co-extruded structures and a wide range of films/foil/papers may be used in a laminated pouch. A membrane of alu-foil will transform a simple pouch into a product, which behaves very much like an aseptic or sterilisable can. A pouch whether it is a stand up gusseted or a pillow pouch occupies a fraction of the space that a conventional can occupies and is of a lower weight.

In quality focussed markets top flight printers and converters must process to the highest of standards in order to minimise the risk of customer returns and to avoid when applicable penalty clauses. It is necessary to have quality control procedures in place and appropriate systems and technology to flag up potential problems; to trial unfamiliar materials/consumables; to determine processability and assess commercial and product/process viability and maintain colour fidelity, etc.                 

Packaging technologists and converters must weigh up the advantages and disadvantages of the various materials that they use and the various laminating components, the inks and adhesives and whether the technologies that they intend to print with, coat with and laminate with are the most suitable for the intended process.

Addressing the processing and commercial concerns

Systems such as the VCML-Lab/Pilot coater, available in working web widths of up to 300mm can be used to address the processing and commercial concerns of the customer: assisting in bringing new products, materials and formulae such as inks, adhesives and coatings onto the market more speedily. Suitable for conducting trials the VCML-Lab/Pilot coater is also able to undertake small-scale production runs.

It can print, coat and laminate on all types of flexible substrates including foils and metallized films/papers, etc and on a reel-to-reel basis.  Processes available include, but are not limited to: flexography, gravure, screen, knife over roll, slot die, direct/indirect gravure coating, reverse roll, hot melt, etc. Lamination both wet and dry can be undertaken and drying options include hot air, infrared and UV curing.  

Product appearance is critical in an age where so many similar products may be on the retail shelf vying for attention. With materials such as foils and metallized papers it is very noticeable when things go awry. The brilliance of the surface magnifies blemishes and colour inconsistencies. Colour communication devices such as the K Printing Proofer can prove valuable in ensuring that converting plants that use multi-print processes can consistently hit colour targets.

The K Printing Proofer enables users to obtain high quality proofs using gravure, gravure-offset or flexo inks.  Two or more inks can be printed simultaneously for comparison purposes and registration is included for overprinting. Adding to its versatility both wet and dry laminated samples can be produced using the gravure print head in conjunction with RKs own K-Lam laminating accessories.

Written by Tom Kerchiss, RK Print Coat Instruments Ltd