Adhesive Applications The pressure is on in narrow web
Pressure sensitive adhesives were first developed in the mid nineteenth century, initially for wound care products such as plasters. It took many years before pressure sensitive adhesives were used for labels and for packaging purposes, and it was not until the late twentieth century that consumer and industrial product manufacturers started to use PS- tapes and conformable die cut shapes for fast moving production line purposes. Compared with most mechanical fasteners,
PSA-based products weigh less and are more efficient at distributing stress over a wide area to lessen component distortion. In other words, they provide many manufactured goods with a smoother, sleeker finished surface and a more attractive product finish. Early adhesives were derived from natural rubber and were applied by coating a solvent solution onto the base stock. Although this adhesive solution adhered to a wide range of material surfaces, ageing properties were not good, and the need to use large quantities of solvent in the coating process was a distinct disadvantage. The introduction of acrylic adhesives and silicones were advantageous; acrylics offered better ageing properties, while water-based emulsions were easier to coat and did not have the environmental drawbacks associated with solvent based adhesives. Hot melts, first unveiled in the 1960s, proved
to be a significant development. A productivity benefit of hot melts is that they can be coated at speed and at high coat weights. Another
significant benefit of hot melts is the elimination of an on-machine drying system. Both the application and performance requirements dictate the type of adhesive technology. Prior to any decision regarding product
selection it is necessary to consider whether or not the adhesive needs to meet any flammability requirements and whether an adhesive tape or die cut piece is going to be hand applied? If hand applied, the adhesive may need to allow for re-positioning. Other needs to consider is whether plasticiser resistance is necessary. This will be the case if the adhesive is to bond to PVC or rubber. Durability and weatherability are of importance as well. With regard to durability, PSA selection will depend upon whether the adhesive only needs to hold fast just temporarily during assembly placement, or whether the adhesive needs to remain firmly in place for the life of the product.
All those involved must have an
understanding of the substrate and the intended end use. With regard to the development of PS-labels the surface to which a label or a tape is to be fixed can present challenges. Surfaces can be deceptive, they may be friable or they may have traces of contaminants. Certain coatings, waxed surfaces, untreated polyolefin, silicon treated surfaces, and decayed pre-treatments, and some printing inks and polyamides may on occasion impact on adhesion.
Processors need to be aware that if an
inappropriate adhesive is used there is a risk of the substrate surface becoming damaged either during application or on removal. This often happens when using highly plasticised films such as acrylate films, thin films, some lacquered films and board, some over-varnishes on print, tarnishible metals, weak bonded surface finishes, some paper stocks, as well as natural fibers such as suede, leather and silks. Many products that are coated with an
adhesive in some way have to perform under harsh conditions. Coated adhesive package products that work well in deep freeze conditions may have lower adhesion properties when stored at room temperature. Some adhesive products have to perform outdoors so the formulator and coating specialist must take on board environmental factors such as extremes of temperature, moisture and UV light exposure. Cold and moist surfaces may reduce tack; abrupt changes in temperature and humidity over a period of time between applying a label and storage may also be problematic. Formulators, narrow web label and tape
converters are amongst those that are challenged to ensure products provide fail-free performance. Products need to be developed, trialed and run under real time/real world conditions. The Rotary Koater designed and developed
by RK Print Coat Instruments is a product development and quality control system that offers a wide choice of selectable coating, print head technologies for trialing different products, materials, formulations and consumables. With almost two-dozen coating and print head technologies to choose from including gravure, flexography, slot die coating, meter bar and reverse roll, the Rotary Koater has been purchased by adhesive manufacturers such as SCAPA and Evode.
www.rkprint.com
Labelexpo 2017 - Hall 6, Stand D21 RK Print Coat Instruments specialises in the design and manufacture of equipment used to produce repeatable samples of most surface coatings. Its portfolio includes reel to reel pilot coating machines. At entry level, the Rotary Koater is a versatile unit enabling users to refine and develop web coating and printing techniques in a lab environment. The more sophisticated standard coater, the VCML Lab/Pilot Coater, utilises integrated touch screen control for web widths up to 300mm suitable for both pilot and specialist production work, and the custom Versatile Coating Machine (VCM) is optimised to the specific requirements of the individual. The VCML pilot coater will be on display at RK Print’s Labelexpo stand this year.
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July/August 2017
www.convertermag.co.uk
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