Coating and Laminating Coating care
ByTom Kerchiss, chairman of RK Print Coat Instruments Ltd B
ringing a product to market is often a lengthy, complex and multi-step process. If the item is a wound dressing, a medical diagnostic or drug delivery device or is in any way care related, then there are various steps and protocols, such as product verification, validation, regulatory compliance and market placement considerations that must be met. Products must be manufactured to tight tolerance, which often involves depositing ultra thin coatings onto ultra thin materials with precision and at speed. Coating and coaters are important processes and product tools. Adhesive coated medical foams, PS-fixation constructs; diagnostic strips, grounding pads, breathable and drug/ blood delivery pouches and bags are reliant on converters proven to be able bring a concept to realisation, economically and to the satisfaction of regulatory agencies, health and safety executives and others.
The properties that make materials such as amorphous and/or impregnated hydrogels and coated polymer membrane dressings so indispensible: often make them problematic when coating and converting. They have the potential to be dimensionally unstable; they are prone to tear; are thin and require the careful deposition of coatings and require adhesives that are optimised to perform under the most difficult and challenging of conditions. Running thin webs, especially at high speeds
can be challenging. Material inconsistencies such as calliper variation or machine rollers that may have become misaligned can increase the risk of processing problems such as wrinkling and coating voids. Thinner webs tend to be less uniform than thicker grades and are affected to a great extent by heat and moisture, etc., thereby increasing the risk of problems during coating, drying and undertaking other converting processes.
The result of running a thin web with an ultra thin layer of coating (which may be an adhesive) without taking into account factors such as tension regulation or the characteristics of the substrate can be costly. If the web has a tendency to be brittle, then the risk of web breaks increases. Even a ductile material will break if a web goes momentarily slack due to fluctuations in tension.
Running new and unfamiliar materials can do more than test the patience of the operator; if a machine is at the edge of its performance envelope or the coating applicator technology is mismatched for the job there will be an
appreciable rise in waste, particularly at the winder due to bagginess, blocking, ridges and coating defects.
Some otherwise perfectly good coating technologies simply will not give of their best when coat weights are ultra thin. Knife coating can be difficult; roll coating may require modification, adding extra rollers, etc. Conversely gravure coating is suited to thin coating applications and is often favoured when coating applicator technology is considered.
Gravure coating and the associated variants: direct, offset-gravure, reverse, etc., differs from other roll coating methods in that one of the rolls is patterned with a surface or anilox engraving. The shape and size of the engraved pattern can be varied to accommodate the specific requirements of the application. Gravure can be ideal in situation such as the manufacture of electronic goods and OLEDs and flat screen items that require a thin and uniform coverage of large areas with precise edge definition.
The customer bespoke VCM have been designed, manufactured and supplied for health management applications and also for fuel cells, batteries, thin fi lms for solar control applications; printable electronics and other applications where precision is a must and where there is a need to meet stringent regulatory requirements The VCM can be confi gured for clean room conditions.
12 November 2025
Direct, reverse and off set-gravure are also an option with the VCM and VCML coaters. The diff erence between direct and reverse is that with reverse a speed diff erential is created between the applicator roll and the web being coated, with the roll rotating in the opposite direction to the web being coated. With off set-gravure, a rubber roller transfers the coating from the engraved roll to the web in a second nip.
One of the options available for the VCML and for the customer bespoke VCM pilot/production coater is reverse gravure. With its large wet coat range reverse gravure off ers key benefi ts such as uniformity and freedom from pinholes. Absence of pinholes is especially critical where an effective barrier against gasses, moisture, micro organisms and other spoilers need to be in place. Generally this is a requirement for medical disposables supplied in flexible pouches and bags and of course for foods that are supplied in flexible packaging. Sometimes it is advantageous not to exclude everything. For breathable fi lms in wound care that are designed to stick to the skin the aim is to provide a bacteria membrane to prevent infection getting in but at the same time allowing for moisture from the skin and wound to get out. The VCML and customer bespoke VCM are equipped with high specification web control and web tension systems and can be supplied with hot air, IR or UV curing. Selectable coating technologies include slot die, knife-over-roll, etc. Rotary screen print, flexo and gravure print are also available along with wet or dry laminating.
Perhaps one of the most important features of the VCML pilot coater is that it is able to undertake small-scale production.
www.convertermag.com
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