PRINT IT - THEN APPLY IT

Changing patterns of food distribution have increased the demand for bar-coded and sequentially-numbered labels. National and pan-European supermarket groups now use computerised stock controls for instant data on turnover and sales, which has increased levels of specialisation at all levels. The trend towards smaller bar code formats demands high print resolution to ensure readability for first-time scans.

Labelling for food products also includes ‘print and apply’ price/weigh and bar coded labels produced with desktop direct thermal and thermal transfer technology. Rolls intended for direct (or chemi-) thermal printers are pre-printed in (usually) two to four colours by the converter and then re-reeled to send to the pre-packer or store for variable imaging with a price-weigh thermal print head, or for processing through weigh-price print apply systems.

Once a back-of-store issue, price-weigh labelling is now widely distributed throughout chilled and frozen food packaging factories, using automatic weighing, overprinting and application systems. Here, special deep-freeze grades are available that resist sudden changes in humidity without damage to the label, yet will accept variable-data overprinting.

Direct thermal materials comprise heat-sensitive dyes and other coatings on a base material. Directly applying a microprocessor-controlled heated printhead to the thermal layer creates the image. Smoother-surfaced grades have improved both image stability and densities, while base weights of 75-85 gsm allow easy conversion. Top-coated grades prevent vinyl and shrink-film plasticisers from penetrating the thermal layer, while back coatings prevent adhesive penetration. Coatings involving recycled bases and thermal synthetics, such as polyethylene and polypropylene, find usage among labellers of food product pallets, as well as recyclable plastics bottles and much else.

The direct thermal market has given food label printers reasonable levels of growth over the past decade, although it is not growing so fast as initially and in relation to such applications as industrial labelling and warehouse bar coding. The latter has benefited from the efforts of specialised coaters to improve the solvent resistance of their materials and the availability of affordable and portable printers.

Like direct thermal printers, thermal transfer printers also have fixed thermal printheads, but instead use an intermediate ink transfer ribbon for the actual data imaging. Although dedicated thermal transfer facestocks are not always necessary, the major coaters offer matt or gloss paper thermal label stocks and perhaps a matt coated polyethylene for both thermal transfer and cold-fusing laser printing. These are used where high definition and high-speed printability are essential.

While growth for direct thermal slows, thermal transfer labels are still enjoying above-average growth. This is of no help to food label printers since most thermal labels are electronically printed in-house. Others are produced by variable imaging bureaux, or form part of distribution, shipping, baggage handling and other operations. Indeed, most growth for thermal transfer now comes from non-food retail operations for product description, price, bar code and graphic information.

Recent years have seen several advances with print-receptive top coatings on self-adhesive substrates, with guaranteed splice-free reels for overprinting.