Coating & Laminating
Meeting coating expectations
Tom Kerchiss, chairman at RK Print Coat Instruments, says OEMs, component manufacturers, supply chain providers and end users of all descriptions have high expectations – if it is a coated product, they expect it to be free from blemishes and of a uniform specified thickness
hey want a product that is functional and is optimised for the application. Looks may be important but generally customers want more than a glossy coat. Coating operatives and converters operating across many sectors must be prepared to explore new possibilities and look beyond the familiar because we live in a world that is rapidly changing. Like life, coating does not always go according to plan. Coating quality limiters may be due to any one of a number of processing disturbances. Problems may be tension control related or may be due to inconsistencies such as gauge band variation in a particular roll of material. Viscosity factors, the thickness or resistance to flow may affect quality and slow productivity. The C.O.F or co-efficient of friction – that is the skid resistance or slipperiness of material and coating may cause hold ups.
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Absorptive and non-absorptive stock may impact on drying, necessitating different process approaches. SS board is very absorptive whereas aluminium-foil and similar materials are not. Areas of application such as the coating of solar films, the production and processing of semi-conductors, latent imaging devices and coating of flat screen monitors as well as applying conductive coatings to smart phones, tablets and other devices places greater demands on coaters and on other web fed converting processes. Cost containment as well as performance requirements has meant that thinner coatings, often applied to thinner substrates and surfaces has raised the bar of quality.
Because of lower coat weights coating uniformity can be challenging with defects such as blemishes becoming more noticeable. If the wrong coating applicator is used uniformity and other performance related requirements may not be met. The most suitable coating technology for a given application may not always be obvious. Processing parameters such as substrate properties, dimensional stability, surface characteristics, thickness and uniformity, etc.,
that have briefly been outlined are of great importance, there are many other things that need to be thought about and discussed. It may be obvious but what is the intended end use of the product to be coated?
Is everyone connected with the coating commission aware of this and kept up to speed when requirements change? Does the job involve the application of for example, discrete amounts of an adhesive coating onto die-cut island wound care pads? Or, is the product to serve as a straight forward overprint varnish?
Different products require different pre- metered or post metered coating approaches. Coating for today and for tomorrow’s products is a fast-moving affair and more often than not it is situation specific. This can be difficult for product manufactures, research and development departments and for converters to be knowledgeable across all areas.
Product development, product monitoring and testing systems that enable users to experiment, to trial materials and consumables using different coating applicator technology; different drying, curing processes, which can be customised to the requirements of the customer, and which can also undertake small-scale production are of some merit. RK Print Coat Instruments VCML-Label pilot coater and customer bespoke VCM pilot/ production coater can be equipped for direct/ offset/reverse gravure, for knife-over-roll, reverse roll, flexo and many other print/coat heads and laminating technology. Slot-die is a precision pre- metered technology worthy of mention and is a VCM/VCML selectable option.
One of the advantages of slot die is that it is suited for many of today’s precision coating applications such as the production of transparent conductive films; flexible displays; medical imaging; wound care; medical devices and disposables; aerospace and scientific products. Unlike many other coat technologies, slot die is not open to the air. It offers a closed delivery path to provide for a more sterile atmosphere with minimal evaporation and minimal contamination. The amount of coating material in the RK closed loop pre-metered system is regulated by a pump. Because of the complexities of industrial and consumer coating, different types of monitoring and product development equipment and systems are needed. A customer bespoke VCM might be suitable for a packaging line but a more compact machine may be more suited for a laboratory or research centres engaged in specialised low volume coating of adhesives and other coated materials including inks. Precision defines most coating, proofing and adhesive related applications and with that in mind RK Print Coat Instruments have modified and brought out the K303S Mulicoater base unit with fully integrated servo drive and touch screen control. The unit is supplied with interchangeable gravure and flexographic print heads and offers meter bar capability.
Multiple coatings may be made simultaneously for comparison purposes and the maximum coating area measures 350 x 440mm with meter bar coating head. Bars are available for wet coatings from 4 to 500 microns. Vacuum beds are available. The K303S Multicoater can be used for quality control and colour comparison using various ink/ substrate combinations. The motor employed by the K303S is a servo-driven high-end unit capable of smooth operation at any speed. In operation a servo motor functions as a closed loop system and, citing the K303S Multicoater as an example are extremely accurate. Each proof or sample taken will be within the set point.
28
June 2023
www.convertermag.com
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