Comment
RALF GUMBEL is a packaging consultant with over 30 years’ experience in various roles covering project and product management, business development, sales, and strategic planning at various companies. He currently provides his expertise in the printing supply and packaging industries, especially metal packaging, at Brandt & Partners.
Digital printing for metal packaging
Digital printing: Nothing sounds more modern and innovative in printing technology If you want to see the success of digital printing, go to the DIY store. In the case of floor coverings, digital printers were suddenly able to print patterns that weren’t identical from metre to metre, making the imitations recognisable even to a non-expert. The triumph of digital printing was overnight and changed the market totally.
In folding carton, flexible packaging, metal decorating and, to date, corrugated, digital printing has no relevant market share. But in glass printing about half the presses sold are digital. Why? The reference quality in glass printing is not offset but screen printing and the printing size is only the height of a beer glass and approx. max. 30cm. Due to that, the digital machines are less expensive, faster in make ready as silk screen and the customers avoid long, dirty and solvent loaded prepress work for screen printing. There are many advantages.
The next digital revolution will happen in corrugated printing, because in today’s corrugated printing process, flexo or offset printing creates light stripes in the areas of the liner that aren’t supported by the corrugation and therefore yield under pressure. In non- contact inkjet printing, theses stripes are only latently visible and like the pattern in floor coverings, creates a great quality advantage.
In general, digital printing in large formats, in high-quality, fast, variable and in some market’s food-safe, involves a lot of technical effort and cost. To compensate these costs, there must be some good additional advantages to be more competitive and successful than offset. The 1:1 replacement for offset printing machines isn’t enough; it even prevents digital printing from realising its full potential.
Not to forget, individualisation is almost impossible if the subsequent processes
involve coating, cutting, welding, necking, flanging and packaging. Every individual can or small print run has to start from scratch if the cans or blanks are damaged in the downstream processes.
Further, I must disappoint metal decorators who want to do short-runs in digital and long-runs in offset printing. There could be a problem called metamerism, because offset and inkjet inks for metal decorating are based on different pigments with different remission spectra.
On the printer’s desk, under standard D50 light conditions, the samples are identical, but on the customer’s desk, under fluorescent, incandescent or daylight light, the two prints will look completely different. The only way to solve this problem is to use the same pigments with the same reflectance curves. But this is difficult because of the long list of things the ink must resist like temperature of 240 °C, solvent resistance, food safety, to name a few.
This means either always use digital or offset printing, as identical logos or images on different jobs significantly increase the risk of complaints. Even if one run is printed by printer A and the other by printer B, the customer expects identical logos, even under different light sources. This is not necessarily the case with digital inks, especially with a limited range of pigments. The demands on a digital ink for metal printing are enormous, and in the end, only 1 or 2 types of pigments remain from the huge range of pigment manufacturers.
What does this mean for metal decorating? Digital printing for metal decorating only has a chance if it’s used at the right point in the workflow and/or if it’s underpinned by the right business principle. The closer digital printing is to the end of the production workflow the better, because there are also huge benefits for the customer, which, more than compensate for the higher printing
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costs of digital printing through savings in downstream processes and storage.
Let’s take an aerosol can of hairspray as an example. Fully filled and printed just before delivery, production could be reduced from weeks to days or even hours. For the customer, this would mean significantly reduced inventory, much faster time to market, improved cash flow due to reduced overall inventory, and fully customisable call- off and design. The hairspray manufacturer could sell its hairspray to the 400,000 or so hairdressing salons in Europe under the salon’s own label.
Such a digital press would, of course, have to print in the round, either as an in-house system at the bottler or manufacturer, or just before delivery to the bottler. In view of these possibilities, digital printing on large tin plates is rather inflexible.
For example, in glass printing and bottling line manufacturers are already trying to integrate digital presses into their lines. Integration into can welding is also conceivable. Here you have individual, flat blanks with a much smaller size. The blanks would already have to be conventionally precoated on the inside and white on the outside, or the white on the outside would have to be digitally printed and cured and then digitally multicoloured and overcoated.
Theoretically, this could be done using UV or LED curing, as the individual blanks would no longer be stacked but processed inline. As the blanks are round, there’s also no risk of set-off, i.e. the transfer of hazardous substances within from the front to the back of the tin plate stack. By eliminating the need for a new oven cycle, the need for inks resists is reduced.
I’m really convinced that a digital solution, placed on the right position in the workflow, will make our business more successful, reduce the production risks and convince more customers to use metal cans.
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