David Atkinson, Pira International

By integrating print into the packing line, the economics of production change, offering various benefits to the supply chain including reduced cost, reduced timescales and opportunities to reduce or eliminate stock.

Print-on-demand (POD) production can be achieved in several different ways using both conventional and digital printing technologies. One such scenario is to print all packaging materials on (in-line) or near (off-line) the packing and filling lines, with two broad possibilities:

  • To print all graphics, bar codes and text on completely plain, generic packing materials
  • To print batch variable information on preprinted generic materials

Print options

Whether it is best to print in-line or near-line, whether to print on plain or preprinted generic materials, and which printing process will deliver the optimum result in the most cost-effective manner depends on a number of factors. These include total number of stock keeping units (SKUs), the number of plain or printed generic templates within these SKUs, print quality requirements, line speeds, product resistance properties and substrate type.

On-line and near-line POD solutions can potentially offer the greatest benefits to suppliers who pack and fill their own products and have a large number of printed designs. Within the total number of SKUs, there is often a much smaller number of plain or printed generic templates containing batch-variable information. When this is the case, the packer filler has the potential to greatly reduce the cost of packaging materials by purchasing generic materials and overprinting batch-variable information on the packing line.

Where there is no requirement for infinitely variable information, the use of digitally driven conventional technologies becomes an additional option to that of 100 per cent digital print engines.

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Printing options can be divided into three broad categories, within each of which there is a range of technologies:

  • 100 per cent digital presses (powder toner, liquid toner, inkjet)
  • Coding and marking print engines (inkjet, thermal transfer, laser scribing)
  • Digitally driven conventional print processes (DI litho, digital flexo, digital screen)

Print quality

With regard to quality, achieving acceptable typefaces can be as much of a challenge as matching high-quality graphics. Digital print engines require a high enough resolution to print typefaces that are comparable to conventionally printed typefaces and, in general, with 100 per cent digital printers, the higher the resolution the slower the speed, and visa versa. This is not the case with conventional technologies, where line speed remains relatively constant regardless of quality requirements.

Whichever approach is chosen, print quality has to be of a similar standard to that on the original packs and needs to meet the end-use requirements in a cost-effective manner.
If the pack graphics are mainly of a line and block nature, with bar codes and text, we can readily print all information in-line or near-line and have a wide range of print options to choose from. If the pack graphics are high-quality halftone process images and we wish to print all graphical information in-line or near-line, speed and unit print cost is likely to be more of an issue and the range of print options is more limited.

A better option when high-quality halftone graphics are present may be to order pre-printed generic blanks, where the main subject matter has been conventionally printed, and then to overprint the batch variable information in-line or near-line. The final choice will depend on various issues such as line speed, quality requirement, run lengths, investment and print cost.

For an in-line option, the printing speed has to match or better that of the packaging line, and print set-up time should ideally be less than the line clearance time. If we consider a packing line labelling 400 units a minute and using a label size of 125mm, to maintain the packaging line speed, a print speed of 50m/min is required with a single engine.

There is the possibility of more than one printer on each packing line, but this would add to cost, increase space requirements and further complicate the line, but may still prove to be a viable option.

For the near-line option to be viable, print output has to equal or better the requirements of more than one packing line. The more lines a single printing machine can satisfy, the lower the packaging unit cost of this option. With a near-line option, it is possible to increase output by investing in faster technology and/or by printing more than one across.

A near-line printing machine would need to run at 150m per minute, over the same shift pattern (with total down time equal to or less than that of the packing lines) to meet the requirements of three packaging lines. These requirements could also be met by printing three across at 50m per minute, but in this case it would also be necessary to die-cut and slit the web into single lanes of labels suitable for the label applicators.

Inks and substrates

For many packaging materials, such as cartons and labels, there are demanding end-use resistance requirements of the ink. Some ink systems such as UV-cured inks can meet these requirements, but with other ink technologies it may be necessary to apply a UV overvarnish or a laminate.

Substrates can also be a serious consideration as some digital printing technologies use heat and/or pressure to fuse the ink on to the substrate. This may make a process unsuitable for use with some polymers, which are used in the manufacture of ‘no look’ plastic labels and with precut pressure-sensitive labels. With some digital printing technologies, it may be necessary to condition materials during printing, adding to waste and down time. With other technologies, it may be necessary to buy specially coated substrates for good ink receptivity, adding to the cost of raw materials.

Potential benefits

There are many potential benefits that can be gained from printing generic packaging materials on or near to the packing and filling lines, not least a simplified purchasing process as there are fewer generic materials to order, and reduced cost of packaging materials through economy of scale, by being able to order larger volumes of generic materials.

With so many potential benefits, this is an area that packer fillers should investigate thoroughly.