Coating & Laminating
Tackling speed limiting factors when coating, laminating and printing
By RK Print Coat Instruments managing director Tom Kerchiss
M
achine speed is almost always touted as an important factor in production output, and it should be. After all, the faster the operator can run a web-based processing machine configured for roll-to-roll, roll-to-sheet, or any other combination thereof, the closer the converter will come to being able to ship the job out of the front door, so that another job can be bought in the back door. And, so the production and profit generating cycle begins again.
However, it’s always important not to forget that there are qualifiers and limitations in that a web-based processing machine, whether a flexographic press or a coater and laminator, in that a machine’s quoted production speed may not always pan out in reality, due to process limiting factors. In order to win out at the end of the day - that is to make money - the factors that limit production should be looked at, and where possible, tackled accordingly.
Day-end production totals are determined by a number of considerations; some conditioned by the machine itself, others due to the nature of the job and material. Since a converter may obtain short-, medium-, and long-run work, it is important to note that on long-run work, the issues that challenge
throughput are often job-specific, in that, machine set up and make ready times are going to be fewer or less than when engaged in short run work.
Job-intrinsic conditions that affect production yields and speed of delivery centre often are related to colour matching and ink and substrate compatibility issues; determining the most economic and compatible coating applicator when coating; contamination of the coated web as a result of airborne contamination and non-uniformity of a deposited coated flow. Problems associated with proofing a UV- cured printed sample as blemishes and pinholes fail to show when a sample is taken to a conventional conveyor. This is a tricky one and is due to chemical changes that take place rendering what should be visible and plain to see but is no longer the case. There is a solution to this but more later. Still, other defects that can arise are streaks and drips, which can be caused through fluid flow disturbances, such as ribbing. The latter is, in the main, caused by transverse variation of film thickness, giving rise to a regular striated pattern on the coated film.
Poor tension and web control limits throughput for a variety of reasons; one of which is that there is an increased risk of web
breaks and wrap around driven rolls. Poor tension control, it can be argued, has a bigger impact on the commercial effectiveness of a company and its ability to meet production targets when undertaking short-run work. The reason being, that the increased frequency of product changeover and make ready, coupled with process irregularities, can slow production speeds down further still, increasing the possibility that delivery times will be missed. When coating, accurate web management is necessary in order to maintain coating weight tolerance and to ensure freedom from cross bars, streaks, bubbles and many other coating defects. Tighter tolerances and a trend towards thinner coatings, often applied to thinner substrates, further underlines the need for precise tension control and watchfulness in other areas. For example, loss of colour-to- colour registration can occur when trying to run at high speed when printing. For these reasons, when check list procedures are followed to determine and resolve problems, tension related issues should be considered.
IDENTIFYING INCONSISTENCIES As with all converting processes undertaken at high speed, the possibility exists for blemishes or inconsistencies to become magnified, what may have been passable, if only just when running at low speed, immediately warrants attention at high speed. Laminating is a good example. A 2-ply bonded laminate comes off the laminator, and despite this seemingly being a straightforward job, the laminated material looks hazy. So, what is the cause? The operative should have a check list of commonly-encountered defects and then work through a process of elimination. In our example, it’s worth noting that this is a repeat job. Nothing has changed; or has it? It’s the same adhesive and substrate, so what can be causing the problem?
Possible candidates include drying temperature that has become elevated. Could it be a tension in-balance or is something to do with the adhesive coat weight? Maybe, in this instance, the substrate is absorbing a solvent or other additive. The tip-off is the hazy appearance; symptomatic
22
May 2021
convertermag.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
