Technological advancements in equipment and prepress are shortening the production cycle for this growing packaging niche.
Since the day store shelves were invented, brand owners have been trying to get their products to jump off of them, right into the customer’s face. And if ever a packaging technique was created to achieve that goal, the shrink label is it. For the past decade and more, this unusual form of labeling has overwhelmed the beverage industry and has worked its way into many others, such as health and beauty, household chemicals, pharmaceuticals, and foods such as dairy products, yogurts and desserts.
A shrink label is a printed piece of plastic, unsupported by liner or adhesive, that is placed around a container, seamed, and heated to a temperature that will cause the film to shrink to the exact contour of the container. Most shrink labels are plastic sheets that are formed into tubes, or sleeves, by the use of a seaming machine. The sleeve is then slipped onto the container and then shrunk in the heat tunnel. Another type of shrink label is called roll-on shrink-on. This process involves cutting the label directly from the printed roll of film, wrapping it around the container, seaming it at that point, and then heating it for the shrink process.
Worldwide, the shrink sleeve market is estimated to be about $3 billion. Growth has been erratic over the past few years, but market watchers are optimistic about the future.
“A couple of years ago, the shrink label market was ramping up at close to 8 percent a year, but when the economy went sour it dropped to 4 percent,” says Gary Gates, president of Gates Packaging Inc., Leander, TX, USA. “But a lot of new ideas are showing up worldwide in the sleeve market, and I think it will go back up to 6 percent in the not-too-distant future.” Gates, considered by many to be a top authority in the shrink field, has been a consultant in the industry for many years.
What is the big excitement over shrink sleeves among brand owners? The answer is space. The rectangular or circumferential labels traditionally applied to cylindrical containers contain a limited amount of area for the company to sell itself. The product name, the logo, descriptive copy, nutritional details, ingredients, bar code – all must show up in a limited space, which leaves little or no room for aesthetics, or any other treatment that gives the package the strength to jump off that shelf. The remaining space – on a beverage container, for example – is plastic or glass that may or may not reveal the drink in all its glory.
Increase the available space on the container to include all of its area, however, and now there is room for creativity, for design innovations, for appealing or appetizing graphics, for promotional content, for any number of useful treatments.
Gates says he was shopping recently and noticed new shrink labels showing up in the household chemical aisle, on detergents, bowl cleaners and softeners. “This takes a bit of share away from the in-mold label people,” he says. “One of the hardest things an in-mold labeler has to fight is that if the label isn’t going into the mold the right way during the molding process, the whole container has to be scrapped. By using a shrink label on the container instead of an in-mold label, if you make a mistake blowing a naked bottle you can grind it up and put it back into the extruder.”
|Inside shrink films
PVC as a sleeve material is easy to control during the shrink process and it is also cost-effective, has many good properties such as good scuff resistance, ease of printing, but is not environmentally friendly because of presence of chlorine atoms in the polymer macromolecule. PETG is also known as glycolized polyester. The “G” represents glycol modifiers, which are incorporated to minimize brittleness and premature aging that occur if unmodified amorphous polyethylene terephthalate. PETG films are amorphous, meaning the polymer molecules are not aligned or ordered within the material. Another material, polyethylene terephthalates (PET) offers a higher percentage of shrink, which is an advantage in some application.
Oriented polystyrene (OPS) represents very common alternative to PVC shrink films in Asia and Europe, but at this point it is not readily available in the USA. OPS is slightly higher priced than PVC film but more recyclable and has a greater shrink percentage.
The shrinkability of the film can be described using the degree of “total free shrink” of the film. Preferably, the film has a total free shrink at 185° F of about 25 percent, before the shrinking step is carried out. Very often the film before shrinking has a total free shrink from about 70 to 110 percent. The shrinkability of the films used in the packages provides tight fit around a container. The sleeve has to shrink by up to 62 percent to fit the bottles and/or tubes. A tight fit is achieved using a conventional hot air shrink system.
Excerpted from Shrink Sleeve Flexo Inks, by Veronika Pekarovicova, Alexandra Pekarovicova, and Paul D. Fleming III, Western Michigan University, 2006.
Rotogravure is still in wide use for the printing of shrink sleeves, but flexography has become popular, especially in the narrow web segment. Offset printing is preferred by others, including Gates.
“If you have an offset operator who knows the press, that person can do a wonderful job of reproduction of what you see in the fanciest offset printed magazines. It’s not so much the challenge of putting ink on film. As long as you know that the ink is the right ink – a flexible ink – and you know that you are getting good adhesion, a good press operator can turn out absolutely great things. They can do it with all the processes, flexo and gravure, but I think that offset is the wave of the future. Gravure was the darling at the beginning. Flexo does have its limitations and people understand that,” Gates says.
To produce high quality graphics on shrink film, the inks must be flexible. Every shrink label must undergo heat, and the ink not only has to endure that process and maintain its integrity, it also has to appear unaffected by the physical process of shrinking.
In the early days of shrink labels, the available inks would change in the shrinking process and show up with dark stripes on the finished product. This was the result of ink build-up in particular areas, which would appear as dark shadows in places where they were unwanted. All companies involved in the production of inks for this market have solved that challenge today.
The prepress challenge
From the earliest days of shrink label manufacturing until quite recently, the time to market has been long. Really long, the experts say. That’s because of the trials and errors required to create a perfect image on a piece of film that is distorted by heat. The image that the printer puts on the film looks nothing like the final version that appears on the container. The printer’s version is distorted, so that when the label is shrunk in the tunnel, via hot air or steam, onto a curved or angled (or both) container, it will look recognizable to the viewer.
Flexo and letterpress printers are intimately familiar with distortion factors in the production of printing plates, but this is not like that at all. The beverage container is not a simple cylinder. So how is the distortion created so that it looks right on the finished product?
A grid is created on a piece of film with squares one millimeter per side. The image is added to the grid and shrunk. The prepress people must locate the areas that will require the most shrinkage and the least, and apply the distortions there. Determining where all of this takes place is – here’s the secret – trial and error.
The images above show several steps in the creation of a shrink label for a pasta sauce using EskoArtwork’s Studio Toolkit for Shrink Sleeves. In the top image, the operator places the grid for the label around the virtual container. In the center image, the virtual heat tunnel has shrunk the label onto the container. The bottom image shows the printed label as well as how it will look when properly shrunk onto the container.
This year, however, software has been introduced that is changing the way the distortion process takes place. In the spring, EskoArtwork unveiled the Studio Toolkit for Shrink Sleeves. Studio is the name of a family of 3D design and production tools that have been compiled for use by packaging prepress people, and the shrink sleeve module takes aim directly at the trial-and-error method of image distortion in the shrink process via the computer.
“We had crude tools in proprietary prepress editors. Some designer upstream did a job in Adobe Illustrator. It was the prepress operator’s job to work with that. What occurred to us and a lot of others, is that if designers upstream could make a lot of decisions, if it became more clear what the designer’s intent was, that might be helpful,” says Susie Stitzel, solution manager, design lifecycle management for EskoArtwork.
“We have gone in that direction, giving the designer more tools. It is still the prepress operator’s responsibility to so some jobs, like warping, but if you have tools upstream to make decisions, subtle things like ‘Am I a premium brand at eye level on shelf? Or a small guy at the bottom?’ then you can make better decisions about where you put your logo, etc. This brings the design tools and prepress tools closer together.”
The virtual shrink tunnel
Here’s the fascinating part. Instead of running real-world shrink tests in the steam tunnel or the cauldron of hot water, “we have created a virtual shrink tunnel,” Stitzel says. “The operator can input the properties of the sleeve (horizontal versus vertical shrink, for instance), and out of that you get the distortion grid that you can then send to the designer, who can see the label in 3D and work with it.”
Stitzel reports positive feedback since the software was introduced. “Brand owners and designers are blown away by this,” she says. “It is a unique product; there’s nothing else like it. We plan to add a lot of things to it.”
Customarily, when EskoArtwork has delved into new projects it doesn’t hesitate to form partnerships with other companies who might specialize in one or more aspects of the project. “There wasn’t anything for shrink sleeves,” says Stitzel. “No 3D modeling. We decided to make one. It is a nice spinoff of other things we’re working on, such as flexible bags and pouches.”
Does the virtual design and prepress process take into account the vicissitudes of label materials? Stitzel says that EskoArtwork’s module has built in some default materials with which the company is familiar and which they have profiled for use in the module. “The software allows you to enter the subparameters yourself: a specialty shrink material, for example, that is specific to your product. You can enter the horizontal and vertical parameters. The users tend to know this stuff, such as the stiffness factor and stretch direction.”
Manipulation of a container and a shrink label in the virtual space has advantages for brand people who want their labels to shrink in specific ways to achieve a particular effect. “There might be subtle complexities: An irregularly shaped container could have a handle, or grip contours,” Stitzel observes. “In those particular cases there is a true front to the container, and the sleeve has to be in the precise orientation. There’s a mechanical part to this as well.”
She cites the SoBe Lifewater bottle and label as an example: “The bottle has an indentation, a spiral traveling around the container. The chameleon’s tail follows that same curve around the bottle. It has to be oriented correctly. The company really worked hard on that.”
Stitzel believes that the shrink market today is growing at about 7 percent a year. “On the one hand it will keep going, but one of the inhibitors of this particular packaging method has always been the long lead time. We hope that we can cut some of that out – moving it from being the bad child to the superstar. Lead times are definitely down using these tools.”
Several companies produce hardware for the creation of shrink sleeves and their application. Among these is Stanford Products, Salem, IL, USA, which manufactures seam machines and doctor machines for inspection and rewind.
The Stanford Seammachine operates at high speed with the goal of minimal waste and ease of operation. It can handle webs from 2" (50.8 mm) to 10" (254 mm) standard, 12" (304.8 mm) optional, 1" (25.4 mm) to 2" and less than 1" available as options. The unit’s speed can reach 1,650 fpm (m/min). It has a 30" (762 mm) unwind roll diameter and a 24" (609.6 mm) rewind roll diameter.
The seamer features an automatic solvent dispensing system, seam inspection options and lay-flat monitoring. It will form and seam PVC, PET, PETG, OPS and PLA films, and static elimination equipment is included.
Karlville Development Group makes adjustable forming plate seamers as well as a fixed forming plate model. All utilize the direct injection system with proportional solvent control. The direct injection system, the company says, is a precise and consistent method of applying solvent available on the market today. The K2 model is the company’s most popular seamer with more than 175 units manufactured. The stand alone machine operates at 300 mm/min (11.8") and forms the sleeves via an adjustable forming section. The machine is available in 300mm and 400mm (15.75") lay-flat models. The machine features fast changeover rewind and unwind air shafts, and can be upgraded with turret unwinds and rewinds.
Karlville, based in Miami, FL, USA, has teamed up with BST Pro Mark to offer one of BST’s inspection systems on a shrink sleeve seamer. The unit can measure the solvent in a seam, according to the company, and determine if the seam is complete.