Coating & Laminating Coating on trial By RK Print Coat Instruments Ltd’s Tom Kerchiss F


rom knife-over-roll and slot die, to the coating of hot melts and pressure sensitive adhesives; what tends to come to mind when you think of coating are those behemoth wide web width coating machines of a decade or so ago. You know, the ones that always looked so cool when they graced the pages of a print or converting publication. Although wide web width coating machines are around, narrow and medium web width coating systems have definitely gained ground. They are a good fit for niche or speciality runs, for the production of conductive materials for smart phone, tablets and for many other applications. Narrow or medium web width multi- process platform presses can be highly productive and are ideal for the production of chocolate and confectionery twist wrap and other flexible packaged items. These can include pet food pouches, sauces, catering and hospitality single-serve sachets and, of course, for those runs of targeted and regionalised pouched or sachet product samples so beloved of marketers. In today’s world, where the ability to set up and turn out products at short notice is a must, narrow web coaters, narrow web presses and pilot coating machines provide clear advantages with regards to speed of make-ready, flexibility and ability to throughput a wide range of products and often at far lower operating costs than their wider web width counterparts. Coating can be accomplished in some cases inline but there is the risk that if the press is forced for any reason to make an unscheduled stop that a processed roll of material may slip through with areas devoid of coatings. Stand-alone or off-line machines provide many advantages, not least of which is that they enable adhesives, inks and other coating materials to be trialled in conjunction with various materials or combination of materials to determine commercial and product viability. Systems, such as for example the VCML Lab/Pilot coater has a web width of up to 300mm and can be used to coat, print and laminate on all types of flexible substrates and on a reel-to-reel basis. Converters, packaging technologists and manufacturers across many product sectors


must be prepared to explore new possibilities and look beyond the familiar. While the ability to process a broader range of materials and output new and inventive products may revitalise a company’s operation and puts it in a more competitive and financially rewarding position it can be a challenge. Unfamiliar materials and processes present a learning curve to one and all.


Trialling new materials on a commercial line is frequently far from feasible, they lack flexibility and taking a production machine out of line for any length of time can be prohibitively expensive. The inevitable and unavoidable experimentation phase may be curtailed before all of the processing option have been explored due to pressure to bring the machine back into production. In many instances narrow web coaters are used in laboratories and research departments for R & D, quality control and if the chosen machine allows: as is the case with the VCML Lab/Pilot coater small scale production can be undertaken. The most suitable coating technology for a given application may not always be obvious. Practicalities and economics must be taken into account. Processing parameters such as substrate properties: the dimensional stability, surface characteristics, thickness and uniformity are important but there are many other processing considerations to take on board, such as what are we coating? What is the intended end use of the product, its form and function? For example, is the intended coating meant to serve as a straightforward overprint varnish or are we depositing discrete amounts of for example: an adhesive onto die cut shaped pads which will serve to dampen down noise and the vibration of engines for the automotive industry? Would a pre-metered or post metered be the most appropriate? Which of the many coating technologies available is the most appropriate and economical for a particular product? In some instances, technical parameters are known and the coating method is predetermined. However, circumstances may warrant investigation and experimentation. For cost and environmental reasons, and to enhance the functionality of many items, manufacturers and designers are


down gauging or making products that are increasingly thinner. When formulating thin coatings durability is a concern. Because of lower coating weights coating uniformity can be harder to achieve.


From the coating operative’s perspective, the masking of defects, minor blemishes and so forth may be possible when coating some products with a thicker coating, but this is definitely not the case when coating thin, and on a thin substrate and at high speeds. Some otherwise-perfectly-good coating techniques simply won’t work when coat weight is reduced. A conventional slot die cannot cope with ultra-thin requirements; equally knife coating can present problems. Roll coating methods might require some modification, i.e., adding an additional roller. Gravure coating on the other hand is well suited for many thin coating applications. Gravure roll coating, direct, reverse and offset are amongst a range of coating technologies that can be used with the VCML-Lab/Pilot coater. Gravure roll coating differs from other roll coating technologies in that one of the rolls is patterned with a surface engraving or gravure/anilox pattern. Gravure printing is also a selectable option. Gravure coating differs from gravure printing in that with regard to the latter, the design pattern is specific, in coating uniform coverage across the substrate is objective. With the reverse roll set up, a single roll system can be used that employs a kiss coating approach. A two-roll set up can be employed for when a web to be coated has a low tensile strength.


Gravure-offset is available as a printing technique. It is often used where a design benefits from the softening effect that a rubber offset roller provides. Areas of application include: simulating wood grain or the printing of some frozen food packaged products. As a coating method, gravure- offset is very much of interest for coating professionals involved in making products and materials with extremely low coat weights.


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