The future starts now
Direct digital printing of PET containers
Dr Peter Stelter*Martin Schach**
At the time of writing PET beverage bottles are usually dressed in wrap-around labels made of plastic or paper which are applied by a roll-fed labeling machine. With its newly developed KHS-Innoprint printing machine KHS can now offer its clients direct digital printing, from which both marketing and production profit. The chief benefits of direct KHS-Innoprint printing lie in much greater flexibility and, accordingly, a very fast reaction time to new market demands, in minimized changeover times, and in even more sustainability. The resulting print has a high brilliance and excellent resolution. Bottle-to-bottle recycling is also possible.
Classic roll-fed labeling ...
In classic roll-fed labeling offset printing is utilized for the film and/or paper used in the labeling process. Rolls of labels are supplied to the beverage company, with labels being glued to the containers 'from the reel' and adhesive applied by a roller or nozzles. As a rule, it takes 12 to 14 weeks from label layouting to the sale of the filled bottle. Minimum quantities must be ordered to keep label costs economically viable.
... versus direct digital printing
Direct digital prints are applied to PET bottles using inkjet printing technology, for which only special inks are utilized. This not only means that shipping costs for materials are greatly reduced compared to the standard system but also that CO2 emissions are cut thanks to the smaller number of deliveries.
* Head of Technology Management, KHS GmbH, Germany. Phone: +49 231 569 1905.
* Head of Advance Development, Technology Management, KHS GmbH, Germany. Phone: +49 231 569 1707.
Time to market greatly reduced
The definitive argument for the beverage industry is, however, the extremely high level of flexibility direct digital printing gives them. Much shorter times to market are the result. There are no more time-consuming label printing processes or long shipping distances for label materials. The required print image is transfered straight from the computer to the labeler's control unit where it is broken down into the five colors white, cyan, magenta, yellow, and black. Other spot colors are also feasible if a specific logo needs to be printed in true color, for instance.
This procedure opens up an entire range of unprecedented opportunities for the industry. Take sports events, for example. One of the options direct printing presents is of providing participants with a filled PET bottle bearing the logo of the winning team shortly after the event. International companies also clearly profit from the new system, as all of their sites throughout the world which have an KHS-Innoprint can access centrally supplied data for new label designs. This enables products printed with the new labels to not only reach the markets faster but also at the same time. One good example here is the soccer World Cup. Should one of the sponsors suddenly wish to congratulate the winning team through its bottle labels on all continents simultaneously, direct printing is the answer.
Each bottle is individual
Another plus of the direct print system is that minimum order quantities for labeling materials are no longer an issue. Bottling plants can apply a specific motif to even the tiniest batch of bottles. The KHS-Innoprint control unit's very fast processing of the data it receives even allows each individual PET bottle to be printed with a different design if so desired. For example, on investing in the most powerful KHS-Innoprint machine a beverage concern with 36,000 employees could dress 36,000 PET bottles with individual photos of its personnel in just one hour of production time.
Seamless production of new image files
Another definite advantage of the KHS-Innoprint is that format changeovers are recipe controlled. As the bottles are handled by the neck and the print head is mobile, no elaborate manual changeover of format parts is necessary. If the bottle type isn't changed when a new image file is used, the transition in production is seamless and without interruption. If the bottle size is altered, the print head reacts within seconds to the new bottle diameter and/or height. The KHS-Innoprint is able to process a large number of different PET bottles, with containers holding from 0.33 to 1.5 liters all doable. Container diameters can vary between 40 and 120 mm.
Modular design
The KHS-Innoprint is designed to output 36,000 PET bottles per hour. Each color carousel in the machine has 12 printing segments. If this capacity is too high, smaller output rates are possible, with the number of segments in the carousels simply being reduced to this end. In order to produce a maximum of 12,000 bottles per hour, for example, only four print stations per color are needed. This well-thought-out concept allows companies to start out with a low machine output and boost this at a later stage if required.
UV inks for demanding KHS specifications
The containers are printed with UV inks which meet KHS' extremely demanding specifications. So that they can be processed by an inkjet head they must have a low viscosity. The fast-drying ink matches the machine speed, has a good opacity, and allows individual colors to be overprinted. These inks also have a perfect adhesion on untreated PET bottles. The quality of the print is retained during further processing of the PET bottles on the line, shipping to the retail outlet, and handling by the consumer. Should the line stop for any reason, there is no risk of these inks thickening or forming sediment.
Brilliant imaging
One very important point to note is that the impressive printing quality produces a brilliant color image that is in no way inferior to the quality of classic roll-fed labeling – and in some cases even surpasses it. The optical resolution here is 1,080 x 1,080 pixels.
Low-migration inks used
The inks used are food grade. Investigations into their migration characteristics have revealed that the inks utilized by KHS are low-migration products which are well below the permissible limit values prevalent in the food-processing industry. The ink used by KHS is also practically odorless compared to conventional UV inks.
KHS-Innoprint can be monoblocked with a stretch blow molder
The KHS KHS-Innoprint only prints on empty containers which are usually fed to the machine by an air conveyor. The printer can also be monoblocked with a stretch blow molder, thus reducing the amount of space required.
Innovative bottle handling system
On the KHS-Innoprint the bottles are handled by their necks and the unfilled containers stabilized by sterile air or nitrogen being fed into the bottle interior. The mouth is sealed during direct printing to prevent germs and aerosols from entering the container. Clamping units (pucks) driven by a direct drive transport the PET bottles to the individual color carousels and lock each into place magnetically. At the end of the printing process the pucks are conveyed back through the color carousels towards the machine infeed where they pick up the next containers.
CYMK+W color model
The standard KHS-Innoprint has five color carousels, each of which applies one color. In order these are white, cyan, magenta, yellow, and black.
A very sophisticated printing process
Within each color carousel drops of ink in the stations are printed onto the untreated PET substrate by high-speed print heads where they gradually form the required pixel. In the print heads the ink flows continuously through piezoactive channels which can be activated by electrical pulses with a frequency of up to 50,000 Hz, and which through narrowing can create drops of varying fineness from 6 to 42 picoliters. This principle has proved itself to be especially robust and produces very sharp printing outlines. A pinning lamp briefly dries the applied ink in each printing station, ensuring that it cannot run during the next stages in the process and providing a high edge sharpness. After passing through all of the color carousels the PET bottles then travel through the UV curing unit where more intense UV light reliably hardens the ink and causes the ink to adhere perfectly to its PET base. As it saves energy, is sustainable, and has a long service life, modern LED UV technology is utilized on the KHS KHS-Innoprint.
Recess and emblem printing (embossing) also feasible
Recesses in or projections on the PET bottle can also be printed on as long as they keep to the minimum required distance of about 3 mm to the print head. If this feature is required, a camera unit is inserted upstream of the printing process and the bottles placed in their pucks according to the camera's specifications. This ensures the highest precision here, too.
Bottle-to-bottle recycling
One crucial aspect of this process is that PET bottles printed on the KHS-Innoprint are suitable for bottle-to-bottle recycling, as studies at various recycling plants have illustrated. Hardened inks can be completely removed from the flakes.
Consumption costs of €0.01–€0.02 per print
If we compare the cost of labeling using the KHS-Innoprint method with the labeling costs for classic labeling processes, we notice that direct digital printing is initially financially beneficial for small batches in particular. At present the printing process generates comparative cost advantages with small production runs of up to 100,000 PET bottles. Where the KHS-Innoprint setup is implemented, between 0.1 and 0.25 ml of ink is needed per bottle print, depending on the degree of coverage, resolution, and size of the printing area.
More flexibility for clear competitive advantages
To sum up, for many companies the chief advantage of direct printing lies in its great level of flexibility which is crucial if they are to stay highly competitive. A clear reduction in warehouse logistics, minimized changeover times and thus higher line availability, and a smaller carbon footprint thanks to less shipping of materials round off the wide range of KHS-Innoprint benefits.
