FEATURE BARCODING, LABELLING & PACKAGING
CONTACT OR CONTACT-FREE? T
What do the terms contact and contact-free mean in relation to industrial coding? Richard Pether of Rotech discusses the suitability of each method in often encountered scenarios
hermal inkjet (TIJ), continuous inkjet (CIJ) and laser coding are non-contact
coding techniques while thermal transfer is the contact coding method of choice. The distinction between contact and contact-less coding has to do with the way the ink is transferred onto the substrate. With CIJ and TIJ ink drops are forced out of nozzles through pressure so the ink is effectively ‘thrown’ at the substrate. With CIJ the high velocity of the ink droplets allows for a long throw distance of up to 10mm between printhead and substrate. TIJ has a shorter throw distance than CIJ; for optimum performance, substrates need to be less than 2mm away from the print head. Contact thermal transfer marking works
through heat being transmitted onto a ribbon (a tape coated with specially designed ink) which transfers the image to the label. To enable the printhead to touch the packaging substrate units must be installed directly onto a packaging machine or labelling system. How do you know whether to go for a contact or a contact-free coding method?
LATE STAGE CUSTOMISATION There is a growing trend toward late stage customisation; for example, buying in pre- branded packs and overprinting variable information such as product descriptions, ingredient lists, bar codes, date codes and batch codes on-line and on demand. Where that information is static, old school analogue hot stamp coding may offer sufficient functionality. However, the majority of today’s producers want the flexibility to print codes that are unique to every package, bringing digital methods to the fore. Where a large print area is needed, thermal transfer is the technology of choice as it is available with print widths of up to eight inches. In general, contact-less coding techniques are designed to apply small amounts of information, although there are also large format inkjet printers that will print onto the side of a box.
SMALL AMOUNTS OF DATA Usually, a contact-less technology will be more cost-effective for printing small amounts of information such as date and batch codes. TIJ printers come into their own in these applications as they are clean, compact and easy to use; the simple cartridge system combines a printhead
28 FEBRUARY 2017 | FACTORY EQUIPMENT
MACHINE READABLE CODES Bar codes and thermal transfer printers go hand in hand. When printing EAN13 bar codes for example, thermal transfer is widely accepted as producing high quality results. However, when it comes to datamatrix codes which usually measure 10 x 10mm thermal transfer is probably overkill. TIJs place their pixels more accurately and offer higher resolution printing (typically 300 dpi or above) than CIJ systems, making TIJ the obvious print technology of choice for 2D codes.
and ink supply system. With thermal transfer the larger print head size coupled with the cost of ribbons and inks makes it an unattractive option. However, the type of substrate comes into play and non- porous or glossy surfaces such as film may be best printed with a contact method.
SUBSTRATES OF VARYING THICKNESSES The challenge of printing on surfaces of varying thicknesses often arises in pharmaceutical carton applications. Typically, a pharmaceutical manufacturer
will want to print lot numbers and date codes on the end flap of a carton as well as some additional information along the body of the pack. Where the two end flaps overlap this creates a surface that is varying in thickness. Unless the coder can place all of the data on the area of the carton end that is double thickness a contact coder will not be suitable. TIJ and CIJ by contrast can print over seams, folds and different pack sections.
FILLED PACKS While thermal transfer printers come into their own for coding flexible packaging as it is being formed, when it comes to on- line coding of packs that have already been filled whether pre-made pouches or cartons; this will invariably be a job for a contact-less coder. Thermal transfer coders struggle to print on anything other than flat film.
TIJ has a shorter throw distance than CIJ; for optimum performance substrates need to be less than 2mm away from the print head
SHINY SURFACES Glossy surfaces are not a problem for thermal transfer coders because of the way heat is applied to melt ink to the material. The ink will bond onto the surface, giving a crisp and durable print. TIJ has been limited by the materials it can code onto; mainly porous and semi porous materials such as card and labels with smudging occurring on very shiny surfaces. However, developments in ethanol-based ink technology have expanded the range of substrates that can be printed with TIJ. Inks with exceptional adhesion qualities are now available for printing on previously problematic substrates such as polyethylene, POPP, cast PP and polyester/PET.
PRINTING IN COLOUR When printing on dark surfaces it may be necessary to print in white or silver to create a contrast between code and background. Thermal transfer allows you to change the ribbon for high contrast whereas with inkjet, printing in colour (especially white) is not as straightforward and can involve a lot of waste. These examples set out some general scenarios but in coding nothing is static and advancements in ink and packaging technologies are constantly eliminating barriers. For example, the development of ethanol-based inks and improvements in ink adhesion, blackness and durability are broadening the field of applications for TIJ. As developments unfold Rotech will draw
on its expertise in both contact and contact-less coding technologies to guide its customers towards to the optimum solution for their application.
Rotech Machines T 01707 393700
www.rotechmachines.com
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