Shrink labelers shape up out-of-shape bottles
When containers have funny shapes, putting shrink-sleeve labels on them can be not so amusing.
Shrink-sleeve labels have been gaining in popularity as a way to get good, full-coverage graphics without the expense of direct container decoration. But some end users are looking to combine shrink labels with unique container shapes. That can lead to problems if the container gets too unique.
When a rigid container is asymmetric, has unusual bulges or grooves, or otherwise departs from the norm of straight or gently tapered walls, getting a shrink label onto it reliably is often a challenge. Meeting that challenge can require adjustments in the label graphics or the equipment that deposits and fixes the labels.
These challenges are coming thick and fast, says George Albrecht, vice president of sales for Axon LLC, a division of Pro Mach. As with many packages, there is too often a disconnect between prototype and production.
“What we’re faced with all the time now is, marketing comes up with this very unique design, and the film suppliers all take it and mock up a sample and make it look perfect, because they’re holding it in their hand and using a heat gun. So they’re selling the project based on what they can do because they want to sell material,” Albrecht says. “But then you have a lot of unhappy customers, when they realize they’re not going to be able to do what they want to do because of the constraints of the container and so on.”
Label orientationThe biggest problem with unusual container shapes is orienting the label. The shrink film usually is formed into a tube or envelope that is deposited over the container, which then travels into a heat tunnel. The more eccentric the shape, the harder it is to orient the film. One of the biggest challenges is a container where the top or middle is larger in diameter than the bottom.
“You really can’t control it as that sleeve is coming down, to ensure that it’s going fall around the corners of that bottle where they want to orient it to,” Albrecht says.
One answer to such a challenge can be designing the graphics on the label in such a way that precise orientation is not required. This can be done by not locking the graphics in to precise corner points, so that it has to register exactly around the base of the container. In general, the graphics should not have any “hard” lines, either horizontal or vertical.
“With most labels you see out there in shrink-sleeve applications, there’s a lot of curviness to it, a lot of flow, waves, and so on,” Albrecht says. “The main reason for that is to take your eye away, distracting you from that primary copy, which may not be in the same spot every time.”
Another way to deal with unusual shapes is to affix the label to the container in a special way before it enters the heat tunnel. One popular way to do that is with a Leister gun, which tacks a portion of the label sleeve-usually the bottom-with a stream of hot air. This holds the label in place on its way to final shrinking.
One example of this use of a Leister gun is a polyethylene terephthalate (PET) bottle for SoBe 0-cal Lifewater from PepsiCo. The shrink-sleeve label features a stylized version of the trademark SoBe lizard. The lizard’s body and tail wrap completely around the bottle and align with a spiral indentation that also wraps around the bottle. To get the lizard to fit the groove, the bottler uses a system with a Leister gun to ensure that the label will not shift in the tunnel and throw the graphics out of register.
Generally speaking, Leisters are used for bottles that don’t have enough straight-walled space between the bottom of the bottle and the point where it starts to swell outward. If enough space exists, the label will start to attach to that straight-walled area in the heat tunnel, which is optimal for the shrink process. If there isn’t enough space, the heat won’t lock it in, and Leisters become an option.
Before a Leister gun can be used on containers, they have to be raised slightly off the conveyor belt. The usual way to do this is to have a segment of the belt with fixtures, like stumps, that have a diameter slightly smaller than the diameter of the conveyor’s base. The bottles would be shunted onto the fixtures, usually by a timing screw. This process would slow down the lineWhen shrink labels get tacked first to the bottom of a container, by a Leister gun or in the shrink tunnel, the label has a tendency to pull up in the machine direction (from the top to the bottom of the container). End users can counter this by specifying a film that is engineered not to shrink in the machine direction-some of them even gain slightly.
Another way to ensure proper shrink label alignment can be used when a container has a square or semi-square bottom. Many shrink labels come in the form of flattened tubes, folded down for easier transport and storage. This leaves creases on two sides. When the label is shrunk, it will have a tendency to pull back on those creases. The creases can be placed precisely over the bottle’s corners by a machine like Axon’s 400SL, which has a film-placement head that rotates. If the creases line up with the bottle’s corners, the rest of the label will fall into place in the shrink tunnel.
As with most packaging projects, especially the ones that incorporate unusual shapes, it’s best to bring suppliers into the planning process as soon as possible, Albrecht says.
“Ideally, what we’d like to do is work very closely with the customer at the conception of the design of the container,” he says. “There are certain minor things you can do that will help alleviate problems down the road. The important thing from our standpoint is, the earlier they can get the machine manufacturers involved in the design of the container, the less painful it’s going to be.” F&BP
For More Information