Traditional stretch sleeves have been used for decades to decorate quart, gallon and other larger-size containers primarily for commodity products from bleach to milk and carbonated soft drinks.
Recent advancements in film, printing and applicating machinery have pushed the boundaries of stretch sleeves onto smaller containers to open up new opportunities for brand owners.
"This opens up stretch sleeving to ‘interesting' shape containers in the single-serve, 16-oz and 20-oz range," says Jim Mallon, vp sales and marketing of MRI Flexible Packaging, which supplies both shrink and stretch sleeves. The company has been working on higher-elasticity stretch sleeves for about three years.
"Stretch sleeving is a label decorating technique that hugs the product by conforming to the container shape," Mallon explains. "We've been developing films that can transform [this market]." MRI has worked closely with two film suppliers to provide stretch-application optimized linear-low density polyethylene (LLDPE) film in the same thickness as heat-shrink film: 2 mil.
"The film is in-house formulated with a balance between having the proper recovery or snapback properties and still enabling us to print it, dry the inks, register the film, seam it, roll it and those kinds of things," Mallon explains. MRI follows a careful process of incremental improvement to eliminate compromising any aspect of the processing and production requirements.
A standard stretch-sleeve label for larger containers and multipacks has a stretch rate of around 10 percent. MRI's C-FiT high-elasticity stretch-sleeve film is in the 35 to 40 percent range (see chart, right).
"We believe that range covers a fair amount of containers," offers Mallon, who says that he is surprised at the range of applicable container shapes. "These materials can stretch further, but not to 65 percent or above-films get too ‘stretchy' to the point the machinery won't be able to apply it."
Sleeve supplier CCL Label has been active, especially in Europe, with its Triple S (Super Stretch Sleeve) LDPE material that provides a whopping 55 percent stretchability for shaped plastic and glass bottles and jars and is suitable for hot fill. Applications include dairy products, juices, energy drinks and other carbonated and non-carbonated soft drinks. Available in water-resistant clear and white LDPE, Triple S can be flexo-printed in up to 10 colors. Decoration options include reverse printing, anti-scuffing properties, and high-gloss, metallic, UV and afterglow finishes.
Application examples include Lucozade for GlaxoSmithKline in the U.K. introduced in 2008, Don Simon for Jose Garcia Carrion (Spain) in 2012 and Gerolsteiner (Germany) introduced in 2013(shown at left). Both Don Simon and Gerolsteiner are applied using Krones-made equipment .
A typical Triple S structure is 2-mil LDPE, according to Wolfgang Plösch, business development director, CCL Label GmbH. CCL is capable of engineering film formulations and extrusion variables to influence the film according to customers' needs.
40 percent film savings vs shrink
Plösch sees high interest in stretch sleeves because of the attractive value preposition stretch offers related to full body decoration at lower cost (compared to shrink) and with a superior environmental profile: A stretch sleeve is approximately 40 percent smaller than a corresponding shrink sleeve. "The market is demanding cost reduction and improved sustainability," says Plösch.
While the European high-elasticity stretch-sleeve market is further developed than the U.S., CCL Label is starting a global rollout of its Triple S technology. Plösch says there are little differences in the films between customers across the Atlantic. "However, we receive a lot of questions regarding recycling from U.S. customers," he points out.
It's taken a combination of developments by converters, machinery suppliers and even ink makers to reach this point with further improvements ahead that include improved scuff resistance and clarity, according to Mallon, who identifies machinery as a key "enabler." He points to PDC Europe and, more recently, Krones, as having introduced high-speed stretch-sleeving machinery, which Mallon sees as an encouraging sign.
Krones' Sleevematic ES stretch-sleeving system relies on a newly designed, servo-motor-driven sleeve clamp to stretch out the film using 20 container platforms per carousel. CCL Label licenses its Triple S technology to Krones.
PDC Europe provides rotary and linear sleeve applicators, the latter for moderate-rate lines. The company reports separate stretch-sleeve installations for the Model STA linear system in the U.S. in Q1 2013, one system at Producer's Dairy in California for single-serve milk bottles and the other at Verst Packaging, a contract decorator in Cincinnati that is said to be one of the largest suppliers of shrink-sleeved bottles stateside. The STA operates at rates to 60 bottles per minute and can accept shrink or stretch films.
"The STA has been specifically adapted to apply this material," says Alcyr Coelho, PDC Europe vp sales and marketing-Americas. The units feature a "star" opening where the film is stretched on four sides rather than two, a modification for the softer, more elastic films.
As Coelho points out, the elimination of heat tunnels and associated conveyors also greatly simplifies the production process and provides energy savings.
LCA for sleeve labels
A life-cycle assessment of Triple S stretch label validated by Columbia University's Lenfest Center for Sustainable Energy found that the Triple S material offered a carbon footprint four times smaller (4.6 g CO2 equivalent) than that of a standard shrink sleeve (17.9 g CO2 equivalent).
Because PE stretch films are less dense than water, they float, ostensibly a major benefit for PET recyclers. That's compared to PVC and PET and most other shrink films that have a specific density greater than 1.0 and thus sink and cannot be easily separated (if at all) from PET flake.
The Assn. of Plastic Recyclers (APR) and subsequently the National Assn. for PET Container Resources (NAPCOR) published white papers in 2012 that essentially declared that recyclers don't want bottles with those sinkable, problematic shrink-film labels.
By that definition, lighter-than-water PE stretch labels are good. Unfortunately, things are not so clear cut. As APR technical director John Standish informs Packaging Digest, recyclers are expecting polypropylene (mainly from closures) in those floatable materials and PE resins may contaminate the recovered material and reduce its value. And, Standish adds, printed inks that are found on film labels also sink and serve to further contaminate the PET flake.
To address this knotty problem, some solutions-by one count, there are six options-have been proposed. For example, in Japan, consumers are asked to separate bottles and labels. It's a task made easier if the bottles are stretch sleeved, but still culturally challenging to ask of U.S. consumers.
As in most consumer markets, graphics play an impactful role, and both CCL Label and MRI Flexible Packaging offer state-of-the-art printing capability into the High Definition level of resolution using central impression (CI) printing technology, the only method that can handle these high-stretch substrates.
In December 2012, MRI started up a Bobst F&K 20SIX CI press that is the first of its kind in North America. Capable of printing stretch or shrink films, the press also offers smart GPS mapping using radio-frequency identification (RFID) tags that help each station self-register. The press is paired with the company's new digital flexographic plate prepress system.
According to Mallon, this process imparts a flat, slightly concave ink dot rather than a typical conical profile. This extra bit of ink optimizes the print quality on stretch-sleeve labeled containers, he points out.
"That's important," he emphasizes. "For shrink films, the inks are compressed together to create a more ‘dense' color and with stretch the color is ‘thinned,' but this process accounts for that."
Even the inks need to be more elastic: MRI has worked with ink suppliers to improve the elasticity of the inks used to ensure the graphics don't crack when the printed film is stretched onto containers.
The substrates are reverse printed, but surface printing on white ink is optional as is the addition of a scuff-resistant overcoat, Mallon notes.
Final thoughts and cautions
Mallon acknowledges that stretch sleeves are not going to displace shrink, but are an alternative depending on what the customer is looking for in a specific application. One downside is that stretch sleeves cannot provide over-the-cap tamper-evidence as with shrink films, and thus may require a (small) secondary TE banding system if that feature is needed.
Mallon also points out that stretch application cannot reach the comparative high levels of stretch vs the 75 percent shrink that films like PET and PVC can, thus the technology is not applicable for large-diameter containers or those with dramatic circumference differences.
Still, it's not too much of a stretch to expect more of these applications in the months ahead.
Bobst North America Inc.,
973-226-8000
www.bobst.com
CCL Label, 508-872-4511
www.ccl-label.com/voelkermarkt
Krones, +49-9401-70-0
www.krones.com
MRI Flexible Packaging,
800-448-8183
www.mriflex.com
PDC Europe, 512-302-0194
www.pdceurope.com
