Coating & Laminating
of low adhesive coat weight. When an inadequate amount of adhesive is applied to a primary substrate, high and low spots will develop, allowing air bubbles and haziness to mar the appearance. By gradually increasing the adhesive coat weight, you should see the haziness disappear.
There are many systems now being marketed that provide the means whereby inks can be adjusted off press, colour matched and checked throughout the run. Devices, such as the FlexiProof 100 and variants FlexiProof UV and FlexiProof LED UV, can highlight developing problems associated with the use of inks and substrates, including substrate/ink miss-match and issues associated with UV curing off-press. This means problems can be highlighted quickly and resolved quickly. These benefits translate into higher production yields for the flexographic label or packaging press; less production machine waste and a better chance of the press speedily meeting production targets.
PROBLEM PINHOLES
I mentioned earlier that there are problems of blemishes and pinholes not appearing when a flexographic proof is taken to a conventional UV conveyor because of chemical changes that take place. RK Print Coat Instruments FlexiProof UV, and most recent variant, the FlexiProof LED UV, incorporate a miniaturised UV system, so the printing and curing and proofing can be carried out seamlessly, capturing defects such as pinholes and hickeys, before they dissipate and disappear. Let’s continue with pin holes and then briefly consider some other irritants that can slow down production. Pinholes or fish eyes generally pertain to areas where the ink has pulled back to reveal light or un-inked areas. The appearance of both is in the form of tiny voids that appear in the final printed image. Just to complicate matters, the causes can
be many. In water-based flexography, the problem may be due to ink surface tension that is too high or too excessive a use of a de-foamer. In solvent based operations, the problem may be that the film surface is contaminated, perhaps either by airborne contaminants or with the ink itself. When coating, the properties of the coating solution is critical for ongoing production of a high-quality product. The ability of the pre or post metered coating applicator to apply a fluid flow depends, to a large extent, on the most appropriate coating technology chosen, and on the rheological properties, stability and purity of the coating solution. The viscosity must be within prescribed and optimised levels. If not, ribbing, chatter, streaks and air entrapment will occur. Good housekeeping and partnering with a supplier pays dividends. A surprising number of industries have a need to match colour at some point in their processes. Although the most obvious needs centre around the manufacture and use of inks, plastic, paint, paper, brewing and baking industries also need to make colour communication checks. Variation in colour on a web of film that’s going to be used in packaging become markedly obvious, best to catch irregularities early before production line waste and downtime make themselves felt. The K303 Multicoater is available with interchangeable gravure, flexo and meter bar (or as they are sometimes referred to as Mayer rods) coating capability. As a standard gravure proofer, it is often used in laboratories or research departments for ink/substrate comparison but also for determining adhesion and printability. The addition of the meter bar coating head expands possibilities. The film applicator supplied can be used for all types of paper coatings, liquid printing inks, varnishes and even paint and other surface coatings. Bars are available for wet coatings,
The RK Print VCML Lab/Pilot Coater
from 4 to 500 microns. The samples are suitable for computer colour matching, visual colour matching, adhesion and gloss. Meter bar coating allows ease of coat weight adjustment; low set up times and costs. Meter bar coating is often first choice when converters or manufactures are investigating some relatively simple but accurate method for determining production.
The VCML Lab/Pilot coater has a working web width of up to 300mm and allows for the degree of experimentation that is needed to determine commercial and product viability. It can coat via slot die, extrusion coat; offers direct or offset gravure, knife over roll, flexo, reverse roll, 3-roll reverse and drying options that include hot air, infrared and UV curing. It can undertake wet or dry laminating and for many, most importantly it can undertake small scale production. Production or run time errors can be picked up early on which, because problems have been identified and solutions found, the production machine will be in a better position to meet desired product throughput levels.
The increasing complexities of coating and other processes has led to a niche gap in the machine manufacturing market for customer bespoke systems. No two machines are the same, the VCM is built under conditions of close commercial security and can incorporate best available coating applicator technology, drives, communication systems, and so on.
As with the VCML-Lab/Pilot coater the VCM can be made explosion proof using proven ATEX systems and can be configured for clean room conditions. The VCM is being used as a pilot and production machine.
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rkprint.com
convertermag.com
May 2021
23
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