Shrink-wrapped containers and bundles are increasingly becoming primary packaging. Here’s how to help make them look good on shelf.

A lot more expectations have gotten bundled into shrink wrapping.

No longer is shrink wrap merely a way to unitize rigid containers for shipping. In club stores and other retail venues, shrink wrap is what consumers will encounter on the shelves. These convenient multipacks save shopping time and, in many cases, provide a price value for consumers. For brand owners, bundled packs usually mean selling more products per trip to the store.

“Shrink film has moved from just being a simple protective cover to get the product from Point A to Point B, and then ripped off the pack, to where now shrink film is used increasingly as the final retail pack,” says Ed Orick, director of beverage sales for Douglas Machine. “So it has to have consumer appeal.”

This means that the machinery that applies and shrinks the film has to operate more precisely than ever.

One of the biggest challenges is in handling printed film. It presents two major hurdles: applying the film so that the graphics appear in the right place, and shrinking it so that the graphics wind up looking as they should, with no distortion.

Applying the film is especially challenging because most printed film no longer comes with registration marks, the big bars that serve as guideposts for the application equipment. They’re efficient but unattractive, and most end users don’t want them. Instead, modern shrink wrap systems have cameras that can recognize specific portions of film graphics, and software that can translate the camera readings into guidance for the film applicators.

Film application is the first function of a shrink wrapping system, and important advances have taken place. Application has to be both fast and economical, to meet the needs of end users for ever-faster production and to counter the rising cost of film.

One improvement that helps speed up shrink wrapping is processing two or three lanes at a time. The most common way to do this was to split the film prior to application. This meant the system had to keep two or three film streams under control at the same time, plus positioning them correctly over each lane simultaneously. A new system from Douglas Machine uses a perf wheel, located between the two lanes, over which the film is drawn. This creates a perforation in the film, which is then applied over the packages in each lane. The packages enter the tunnel, and the force of the heat shrink separates them. This system is available on Douglas Contour Series machines.

Similarly, the Clear-Print shrink wrapper from Polypack, which can run dual lanes of clear or print registered film at up to 120 wrapped packages per minute, perforates film between wraps, which eliminates the complexity, size and costs associated with cutting, controlling and delivering separate lengths of film, according to company spokesperson Nadia Vizza.

Another widespread innovation, which helps with both speed and precision, involves how film is sealed around the package. Many modern shrink wrap systems, like the Standard-Knapp 296S Continuum, have bypassed the heated sealing bar often used in the wrapping stage. Instead, the Continuum overlaps the film around the package by 1.5 to 3 inches, which allows the shrink tunnel to effect the seal. This allows for a continuous motion and higher speeds.

Innovations in the shrink tunnel account for many of the modern advancements in shrink wrap systems. Kristofer Kolstad, vice president of sales of marketing for Standard-Knapp, calls tunnels “maybe the most high-tech component of the system.” That’s why wrappers and tunnels, even if they are separate modules, are almost always furnished by the same supplier.

“There’s a lot of know-how and a lot of science behind [the tunnel], and to have two companies, one supplying one and one the other, and things go wrong in the field, I would imagine that would be somewhere between a disaster and something that end users just would rather avoid,” Kolstad says.

The most profound improvements in shrink tunnels have to do with how the heat is applied. To get the film to shrink uniformly, ensuring a smooth appearance and graphics integrity, heat has to be applied as evenly as possible.

That is one reason why Lantech has instituted convection heating, as opposed to forced-air, in its shrink tunnels. The problem with forced-air heating is that temperatures near the intake ports tend to be lower than in the center, says Jean-Louis Limousin, Lantech's design engineer for shrink machinery. This makes the film liable to shrink unevenly, which can lead to “dog ears” (too-thick seam ends) and wrinkles.

Convection ovens, on the other hand, have no intake or discharge ports for air. Heating elements are inside the chamber, with low-speed fans behind the elements. The package and film receive both radiant heat from the elements and hot air; because the air is agitated much less than in a forced-air tunnel, the heat is applied more evenly.

Convection ovens have several advantages over forced-air systems besides even heating, Limousin says. Packages can be “re-shrunk” in another pass if necessary. The gentler airflow is less liable to damage the product—an important consideration for products with loose components, like pizza toppings. They can handle a wider variety of shapes than hot-air ovens. They generally run at lower temperatures, which saves on energy. And, in dual-lane and other applications that use perforated film, they are less liable to break the perforations prematurely.

Douglas Machine improved its tunnels a few years ago by “starting with a blank piece of paper,” Orick says. The company consulted with academic aerodynamics specialists and an electrical supplier and, as Orick jokes, “discovered that hot air rises.” They redesigned their tunnel to push heat up from below, allowing for better control and energy efficiency. They also made the tunnel shroud a moveable part that can be raised and lowered to accommodate different container heights.

One of the biggest challenges in modern shrink wrapping stems from downsizing of fiber-based material. To meet pressure to cut costs and reduce environmental impact, many end users are migrating from trays to pads—or, in some cases, nothing—underneath their rigid containers.

Douglas Contour Series systems deliver corrugated pads from underneath, just before the film is applied. They also have moving front-containment bars that prevent products from tipping over, which can happen when the system is suddenly stopped. Douglas systems can also accommodate a U-board, a pad with tabs on either end, which offers more support than a pad while using less material than a tray.

In many current applications, shrink wrappers have to do more with less. Judicious selection of machinery will make sure everything gets wrapped up tight.  

For more information
The following suppliers helped in the research of this article:

Polypack
727-578-5000; www.polypack.com