Features

In the days when labour was cheap - or cheaper - it was cost-effective to employ somebody whose sole task it was to stand at the end of a conveyor, pick off the books or magazines and either put them in a box or bundle them up manually with a hand-strapper. These days, it's not cheap to take that route, and plenty of printers have made the choice to move towards more automated forms of handling at the end of the bindery's conveyors.

One technology that’s become popular in the past 10 years is shrink-wrapping – the process of putting film around a book or a stack of printed products, then heating it to make it closely conform to the shape of its contents. The contents could be anything from a single book or magazine to a full pallet-load; the capacity and format of the solutions available vary according to the application and the stage in the production process at which they operate. The most popular place for a shrink-wrapper is at the end of a bindery line, where it sits inline to the binder’s delivery conveyor, taking stacks of bound products and shunting them into a wrapper. The inline configuration cuts out a handling step, and therefore a salary.

However, for all its virtues, shrink-wrapping is not highly regarded among printers, and still less by trade finishers. “It adds no direct value to the product, and for that reason printers can be reluctant to invest,” admits Richard MacLean, sales specialist at UK agent for Sitma, Integra. “Often there has to be a clear return on investment directly resulting from a shrink-wrapper’s installation before a printer will make a buying decision.”

Steve Hampton, shrink-wrap specialist at Friedheim International, UK distributor for Beck, agrees: “We often see that while printers want to protect the product that they send off in their delivery vans, it can be a difficult decision. The investment comes straight off the bottom line, unless it can be offset by savings in labour. Or maybe the printer has a great commitment to quality, and has experienced damage in transit – that can also lead to an investment.”

While inline and full automation are two routes to save labour charges, there are plenty of shrink-wrapping machines on the market that require more labour input but much less capital investment. Smaller chamber-type machines, where the seal and shrink are integrated into a hand-loaded single machine, tend to be limited by the time taken to shrink – around four or five seconds, yielding a maximum throughput speed of 6-8 packs per minute (ppm). Friedheim sells chamber-type shrink-wrapping kit from Audion, including entirely manual integrated bagger/heat tunnel machines, and even separate wrapping modules with non-inline tunnels. Italian manufacturer Itadibipack, distributed in the UK by Graphic Arts Equipment, also produces a range of chamber-type equipment, including the BabyPack entry-level device for up to 6ppm, and the 6084 for 8ppm. Adpak’s British-designed L-sealers and shrink tunnels offer a mix-and-match choice between wrapping, sealing and shrinking, with models offering from 60 packs per hour up to 120; Kempner’s mix of chamber machines and automatic shrink-wrapping lines offer solutions from six to more than 100ppm.

Shrink-wrapping as a process has largely been ported to the print industry from its cousin, the packaging industry. In packaging, shrink-wrapping is the method of choice for protecting trays and stacks of products before they head into the distribution chain. However, the requirements of a packaging converter for shrink-wrapping can be very different from those of a printer, and it pays to check that the machine fulfils particular requirements for print-specific applications.

Broadly, a shrink-wrap bagging device – the section of the line that puts the film around the product – will use one of two working methods: a full-seal bag that seals 100% of the product inside with no holes or gaps, or a sleeve that is effectively a tube wrapping the top and bottom of the product but leaving a gap at each end.
This can be deliberate – for some heavy products a gap gives an in-built handle, for instance – but the unattractive puckered film at each end of the pack means that sleeve shrink-wrapping tends to be limited to intermediate transit applications.

Closing the gap
But some sleeve shrink-wrapping devices have inbuilt mechanisms for closing the gap. The two most popular methods are an air-blower (something like an industrial hairdryer) that rolls the ends of the heated film to press them together, and a set of heated paddles that press the edges inwards and seal them together.

Shrink-wrappers that bag their products ready for a 100% all-over seal use different methods of applying the film. This is the area where shrink-wrap crosses over with poly-wrapping: in effect, the postal poly-wrap mailing/bagging line is no different from the bagging section of this type of shrink-wrapper, although the materials used are different. Here, the bagger folds the film around the flat product and seals longitudinally down the centre of the product, plus tail and head.

Another method is the L-sealer, also known as a form-shoulder machine although this applies more to the automated machines. Beck’s Multiplex pico is an L-sealer: it folds products inside a length of centre-folded film (at the converting stage, the film has been folded lengthways and wound onto a core) and then seals the bag on three sides before dispatching them into the heat tunnel.

Another shrink-wrapping methodology is a two-roll wrapper, producing a four-sided seal. The Beck Serienpacker is a four-sided sealer: one roll of film sits above, another below, the products to be wrapped and the sealing bars make a continuous side-seal along the length, with a cross-sealer handling the tail and head seal. The two-roll architecture is a good choice for printers who may need to use different types of film, for the very good reason that the film path is not, as with an L-sealer or form-shoulder machine, a complex one. With two rolls, the film is simply pulled in a straight path without folding or bending to cover the product – and this means the machine can usually handle relatively thick polyethylenes and even polypropylenes.

Problems and solutions
After the product has been bagged, it travels into the heat tunnel, usually a sealed box that circulates heated air around the pack. Here, there is a pitfall for users of polyolefin films: a wire mesh or bar-driven conveyor will leave ridges in the shrink-wrapped pack. Polyethylene films are one solution, as is a conveyor that uses rolling tunnel bars that rotate, leaving no indentations and exposing the whole pack to heat. Some manufacturers’ heating tunnels have rolling bars that can be switched on or off on a job-by-job basis.

Films used by shrink-wrappers tend to be, in the main, polyethylene, PVC or polyolefin. Each has its specific characteristics – polyethylenes, for instance, must be cooled after heating to gain additional shrink and to achieve higher throughput speeds – but one of the chief reasons is that each of these films possesses a certain quality of ‘glide’. This is a term that carries some scientific weight to shrink-wrap technologists, since the film must travel a sometimes-complicated path without resistance and crucially without generating an excess of static.

However, while glide is important during the wrapping process, it can cause its own problems when it comes to downstream handling: being quite slippery, it can be necessary to strap a pallet of shrink-wrapped trays or stacks at each course, to stop it slipping and falling.

While investment in new shrink-wrapping kit currently is very low, according to Integra’s MacLean, there is still a steady demand for replacement kit. “The only way we’d see spend on a new shrink-wrapping line right now is if a printer got a new contract,” he says. “But that’s balanced by the number of printers who are trying to streamline their operations for more efficiency. In this climate, suddenly machines that used to look time-efficient are wasteful and call for too much labour input. Sometimes the best way to keep costs low is to bring in new kit.”

SHRINK-WRAPPING AND THE ENVIRONMENT

With growing awareness of environmental issues among print buyers, many printers are trying to reduce their environmental footprint if not actively seeking environmental accreditations. Shrink-wrapping gets a big thumbs-down from environmentalists. Partly because the films themselves are manufactured from raw petrochemical materials, and are non-biodegradable or compostable, and partly because the heat used to shrink them is a non-recoverable resource.

There is no good reason, according to Integra’s MacLean, why shrink-wrapping films should not follow the lead of their poly-wrapping cousins and become recyclable, more readily biodegradable, or even compostable. “Except cost,” he says. “We found it would be three to five times more expensive.” And as shrink-wrapping is, in the main, a non-customer-facing form of protective packaging, that’s not likely to change, “unlike poly-wrapping, where the wrapper goes straight to the customer around the magazine and there’s a direct benefit to the publisher in being seen to be more responsible.”

The issue of heat generation and energy consumption by the average shrink-wrapping tunnel is not one that can be readily solved: heat tunnels must be heated, and the rapid entry and exit of stacks means it’s not possible to prevent some heat escape. However, it is more than possible to make a heat tunnel more energy-efficient, according to Friedheim’s Hampton. “Beck uses a circulation principle known as Vortex, which basically makes sure there are no cold spots in the tunnel,” he says. “Typically, with a conventional heat tunnel, you get these cold spots and have to turn up the heat of the whole tunnel just to bring the cold spots into temperature range – which is a massive waste of energy. The Vortex tunnels, you don’t have to do that, and you can use less electricity as well, because it’s distributed more efficiently.”