Although flexible packaging in Asia is dominated by gravure technology, central impression (CI) flexo technology – enhanced through the introduction of the chambered doctor blade – can offer a host of advantages, writes Debabrata Deb.
The flexible packaging industry faces several tough challenges. Surging consumption continues to drive strong growth but competition is fierce and buyers control pricing.
The industry must increase productivity, reduce wastage, become more energy efficient, respond faster – within hours rather than days – and handle short runs as well as long runs. One of the biggest obstacles to overcome is the set of difficulties encountered during printing.
In Asia, flexible packaging is mainly printed with gravure technology. This gives high print quality and skilled print supervisors, good inks and the latest generation cylinders are all available. But what are the drawbacks?
The challenge of wastage
The typical threadle through path in a gravure machine is 75–100m, depending on the number of colours. The minimum start wastage – threadle length plus 10m – therefore comes to 85–110m. If we add another 85–110m for register setting and 85–110m for shade match, the typical total start wastage comes to 255–330m for jobs with six to eight colours. For short run jobs, startup wastage could double to 510–660m, which would also be the case with critical jobs.
Thus, startup wastage for multicolour jobs ranges from 255 up to 660m, giving an average of about 400m. Process wastage would add another 100 to 200m, or an average of 150m. Printing wastage for a typical job therefore totals 550m.
The typical run length for a so-called long-run job is 20,000m and for a short-run job 2,000m. Taking an average run length of 11,000m, average printing wastage comes to 5% – a high figure that saps the flexible packaging industry’s profits.
While run lengths beyond 100,000m happen, with a printing wastage of about 0.5%, such jobs are few and far between, accessible only to a lucky few and priced very competitively.
Losses through solvent evaporation
The long web path and open ink pans also contribute to high solvent evaporation, particularly in summer. Gravure inks typically have an average solid percentage (including white) of 25%. Solvents constitute as much as 75% and need to be evaporated, exacting a heavy toll in energy.
Inks need to be brought down to machine viscosity. The viscosity parameter has to be maintained during the run by adding solvent, which further increases both the energy required in solvent drying as well as raw material costs.
Printing wastage involves two substrates, the base film and the ink (including the added solvent). Ink is the most expensive substrate. Base film costs less per kg but has a much higher gsm (gram per square metre) figure. For a base film of 15gsm costing $1.82/kg, the cost per square metre is 3 cents. For an ink deposition of 1.5 gsm and dry weight cost of $18.19/kg, the cost per square metre comes again to 3 cents. Thus, the total raw material cost per square metre of the printed substrate is 5 cents, which is substantial.