Packaging News

Coding equipment: Make the best mark

Laser, thermal transfer, continuous inkjet and thermal inkjet – there are several different types of coder, which can make purchasing decisions tricky. Identifying which applications are best carried out by a thermal transfer coder is fairly straightforward – it is acknowledged as the technology of choice for high-speed coding on vertical baggers and flow wrappers.

"This technology is firmly established as the most effective solution to flexible film printing," says Chris Gent, director of Interactive Coding Equipment (ICE).

But with laser and continuous inkjet (CIJ) both capable of coding a range of substrates, including glass, plastic, cartonboard and metallic packs, decisions about which technology to use are far less clear-cut.

According to Will Edwards, Domino’s UK general manager, the preference is for laser where possible, as, despite being more expensive from a capital outlay perspective, laser coders don’t require consumables. "Generally people prefer laser if the substrate allows because it’s cleaner and the running costs are lower."

However, there are limitations to the use of laser. Take plastic containers. According to Gent, CIJ dominates as the method of choice here owing to its versatility and ability to create well-defined codes with good contrast. "Laser is more restricted, as it is only able to operate on a limited subset of plastic materials and sometimes the actual containers have to be modified to accept laser technology," he says.

Equipment manufacturers are working on solutions to such issues. For example, Domino’s blue laser tube technology is said to produce a clearer and more crystalline code contrast on PET bottles.

Glass is another substrate that can be coded using either CIJ or laser but at higher speeds laser tends to struggle due to the amount of energy needed to oblate codes on to glassware. "Speed becomes a challenge with glass because it is a very hard substrate so you have to code it for longer. On a high-speed line there might not be enough time to get a good laser code," says Edwards.

Clear advantage
Linx claims to have devised an answer to this problem in the form of its SL301 scribing laser coder. The coder incorporates the company’s proprietary Visicode technology, which was developed to deliver clear codes on glass without compromising on speed.

Laser’s inability to cope with high line speeds also limits its use on canning lines, according to Edwards. What’s more, only certain types of laser coder will work on metal surfaces. "To code on metal you need either a fibre or a YAG laser. If you try to code metal with a CO2 laser, you simply don’t get a mark," he says.

It’s not surprising, then, that CIJ is the preferred method for coding metal cans. Yet despite these limitations, there are companies who are using laser for canning applications.

"Traditionally, soft drink cans have been overprinted using CIJ technology, but laser should also be considered for printed metallic surfaces," says Markem-Imaje’s Mike Whiteoak. "Some major bottlers have achieved remarkable levels of speed and efficiency using our 7000 series laser coders."

Cartonboard is another substrate that can be coded using either laser or CIJ, as Gent explains: "The coding method of choice for cartonboard is either high-definition inkjet, or, if the cartons are modified with chemically sensitive ink, a large-area laser marking system may be adopted."

There is also an alternative inkjet technology – thermal inkjet (TIJ) – that is emerging as a serious rival to CIJ.

Although TIJ is not a new technology – it has been used on office desktop printers for years – the equipment has only recently become robust enough for industrial environments. The main benefits of TIJ stem from the use of ink cartridges – this prevents ink spillages during operation and changeovers.

TIJ printers look set to become a more regular sight on packaging lines, as do laser coders, as advances in new surface treatments forge ahead. But this doesn’t necessarily signal the decline of CIJ. It might be mature technology, but new inks are constantly being developed to extend its reach.