Sleeving as a primary decoration method has achieved significant penetration into a number of market sectors, notably beverages, household, foods, pharmaceuticals, toiletries and cosmetics markets (Figure 7.1), and currently is the fastest growing of all the labeling processes.
Figure 7.1 Typical shrink sleeve application
In the beverage sector it is used as a light-weighting vehicle for glass manufacture. On plastic bottles the advantages of film based sleeves that are compatible with the primary container have been recognized as an aid to re-cyclability.
In recent times innovative shrink films, new printing techniques and printing finishes and the development of efficient application machinery and shrink tunnels, have all contributed to the continued growth in sleeve decoration.
This article is designed to help the reader understand the different shrink sleeving processes and methods whilst maximizing the benefits derived from this exciting product decoration method (Figure 7.2).
Figure 7.2 Summary of the key decorative sleeving formats
There are 4 main sleeving formats used today:
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Pre-welded shrink sleeves
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Reel-fed wrapround sleeving
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Roll-on shrink-on sleeving (ROSO).
Each of these decoration methods will be dealt with in this article.
SHRINK SLEEVING – SUMMARY OF BENEFITS
The benefits of shrink sleeving include the following factors;
360 degree full length decoration
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Translucent colors, or transparent windows to view contents
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Total container coverage protecting against contamination
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Inventory reduction – containers can be labeled on-demand
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Matt or gloss finishes, or a combination of both
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Metalized, pearlized, photochromic and thermo-chromic finishes
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Ideal for labeling complex shaped containers
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Ability to incorporate promotional ideas
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An effective alternative to printed/coated container.
PRE-WELDED SHRINK SLEEVES
Simply put, a pre-welded sleeve is a pre-printed film web which is formed into a tube shape (with the printed image on the inside to give total scuff resistance) and with a small overlap that is then bonded together. The tube is seamed and welded to prepare it for the sleeve application machine (see the section on Seaming and Welding).
Sleeves are produced from specially formulated films, which are capable of shrinking biaxially. The main direction of shrink is in the transverse direction (TD) (Figure 7.3).
Figure 7.3 Direction of shrink machine direction (MD) v transverse direction (TD)
The application of heat causes them to tighten (shrink) around the container.
To label the product the tube is cut to the correct length and opened up for slipping over the pack, from where it is shrunk to a tight fit by the application of hot air, radiant heat or steam in a shrink tunnel placed over the conveyor line (Figure 7.4).
Figure 7.4 Principle of shrink sleeve labelingFigure 7.4 Principle of shrink sleeve labeling
Shrink sleeving is popular for 360 degree labeling on irregular shape packs but can perform a variety of useful roles as a tamper evident neck seal, or a banding device for special offer promotions (Figure 7.5).
Figure 7.5 Typical shrink sleeve applications
THE SHRINK SLEEVE MANUFACTURING PROCESS
An overview schematic of the shrink sleeve manufacturing/application process can be seen in Figure 7.6. The reels of shrink film are typically reverse printed on clear materials using a variety of printing processes. The material is slit to an overlap width ensuring that the edges of the material are uniform. The film is then seamed by applying an adhesive to the overlap area so as to form a tube, inspected and applied over the container before being shrunk in a heat tunnel.
Figure 7.6 Schematic of the shrink sleeve manufacturing and application process
Each of the stages from material to application will be explained in more detail below.
SHRINK SLEEVE MATERIALS
The type of films used for shrink sleeve production is called transverse (TD) or across-the-web oriented, which are capable of shrinking biaxially to form a tight fit under the application of heat.
Three main base resins are used for shrink films: polyvinyl chloride (PVC), polyester, glycol modified (PETG), and oriented polystyrene (OPS). Some polyester (PET) is also being used.
PVC, which is the predominant resin used in shrink sleeve materials has met with some disapproval amongst environmentalists, as there are some concerns that the burning of PVC films emits chlorine gas into the atmosphere.
The debate surrounding PVC has lead to the growth of alternative materials, such as PETG, styrene (OPS & SBS) and PET. PLA is an environmentally friendly material and is certified as compostable.
In addition to assuaging the environmental concerns of the public, these films can offer other benefits.
Blended polyolefin based films with a low specific gravity of less than one percent are often used ensuring that the sleeve separates from the bottle during recycling (water flotation). Figure 7.7 summarizes the major film types and structures used for sleeving applications.
Figure 7.7 Major film types and structures used for sleeving
PRINTING
Shrink sleeves are typically manufactured from clear, single film which is predominantly reverse printed.
If opacity is required for shrink sleeves the converter would reverse print the design and then add the overall opaque white background as part of the normal printing operation.
The benefits of reverse (under surface) printing are the protection of the printed image and the enhanced reflectiveness of metallic printed inks.
A variety of printing processes are used for the print of shrink sleeves, but the majority of long runs are gravure-printed (i.e. typically >500,000 sleeves).
However, whatever the sleeve printing process, and whether it is wide- or narrow-web, it is important to have an understanding of the inks used for sleeves. If the right pigment selection is not used, then the hot air blowing on the ink can change the ink color as it goes through the shrink tunnel.
It is also necessary to select resin materials that are going to provide good adhesion to the shrink films. Resins need to be very flexible and able to shrink in a similar way to the profile of the shrink films, whether PETGs, PVCs or other substrates. The ink chemistry needs to be compatible with the film selected and adhere to the film as it shrinks in the shrink tunnel.
With today’s advances in narrow and medium web printing technology, processes such as digital, flexo and offset are increasingly being used for shorter run lengths, as users demand shorter lead times and more frequent design changes.
A summary of the printing processes used in the manufacture of shrink sleeves along with their advantages and disadvantages is provided below.
GRAVURE
Gravure printing is an excellent method for printing smooth films and provides excellent color reproduction consistency, high speed and productivity.
It is a process that is ideal for reproducing demanding artwork and photographic elements. The major drawback of gravure printing is the fact that it is more expensive when compared with flexographic printing. The need to produce expensive cylinders makes gravure printing viable only for longer runs.
FLEXO
Flexographic printing in general is making steady inroads into the shrink sleeve market. The increased use of the technology is being driven by the need for quicker processing and reduced costs.
Major advances in terms of the quality of digital image transfer systems, inks and anilox rollers, combined with developments such as larger combination presses or laser-engraved plate technology, have increased its share of the shrink sleeve market.
Other innovations include the development of servo driven presses with individual drives which are more efficient and flexible in terms of substrate handling and the speed of changeovers.
UV FLEXO
UV flexo has a number of advantages over rival processes such as conventional water-based inks, particularly its ink key qualities, print resolution and productivity.
The uptake of UV flexo has risen due to the need to reduce solvent emissions, as required by European and national legislation.
DIGITAL PRINTING
Digital printing is used mainly for lower volumes, proofing and prototyping, but as in other markets it is gaining market share as the demand for shorter runs and rapid turnaround’s increases.
Digital printing is ideally suited for mass customization, variable data, multi-languages and product promotions (Figure 7.8).
Figure 7.8 Shrink sleeve labels printed using HP Indigo WS6000 digital press. Source- La Catrina Leverages Digital Print
PRESS CONFIGURATIONS
There are two primary printing press configurations that are particularly suited to shrink sleeve printing.
IN-LINE PRINTING
The in-line printing associated with gravure and narrow web presses can give more flexibility with the types of printing processes used, but it requires sophisticated electronic press registration systems and careful control of heat and web tension.
CI PRINTING
One of the main advantages of central impression (CI) press configurations is the maintaining of very close register on thin filmic substrates. The substrate is wrapped around a large central impression cylinder thus minimizing the movement and material stretch that can take place.
WIDE VERSUS NARROW WEB WIDTH PRESSES
The majority of sleeve printing is carried out using wide web printing formats (more than 1.5 meters).
Narrow web presses (less than 600mm) particularly those with presses adapted to filmic handling using servo drives, UV curing and chilled rollers are increasingly suited to filmic sleeve printing.
PRESS HANDLING CONSIDERATIONS
Shrink film is also more temperamental than other substrates used for labeling, especially when it comes to heat management.
There is a technique to printing film because (converting) equipment will generate heat. Even on press, care is required to avoid shrinking the film.
A one percent shrinkage in the film can prevent the label from sliding over the bottle in shrink sleeving applications.
A controlled temperature environment and heat management on press is very important.
PVC and PET, despite their higher percent shrink memory, are considered more 'converter friendly' than OPP. Heavier film gauges also assist conversion.
Shrinkable OPP, despite its lower percentage memory, requires more care when being converted. This can lead to slower press speeds. However, the leading converters involved in shrink sleeve manufacture are highly skilled and this normally presents no significant problems.
SHRINK SLEEVE SEAMING/WELDING PROCESS
Once the sleeving material has been printed, it needs to be slit and formed into a tube. Solvent is applied continuously and at high speed to the overlap edge on the welder.
The advice now is not to actually crease the film. It creates a memory which becomes difficult to iron out prior to application and creates a line on the decorated container. The aim is to have a U fold rather than a V fold (see Figure 7.11).
A big problem in the sleeve industry has arisen because the film material is not being properly slit. It is a heat sensitive material and If it is slit with the wrong slitting system or a dull blade, it tends to put burrs on the film edge and this will have an impact on the film and subsequent seaming and application process.
Figure 7.9 illustrates the seaming process featuring typical locations for solvent application. During this process the printed web is perforated at the required sleeve length and folded around a devise known as a 'shoe'.
Figure 7.9 The seaming process
As the edges of the tube are nipped together the solvent reacts with the surface of the material allowing the surfaces to 'meld' together forming a permanent and secure seal.
The weld areas are generally kept free of print to enhance the bond.
Figure 7.10 shows a picture of an automatic shrink sleeve seamer.
Figure 7.11 Highlights the key terminology used when discussing the seaming or welding processes and clearly shows the seam width, location and overlap requirements for this process.
Figure 7.10 Shrink sleeve seamer capable of running at 600 meters per minute. Source- Accraply
Figure 7.11 Sleeve welding key terminology and specification guidance
Seaming speeds and run times will vary according to the sophistication of the seaming equipment used, but turret rewind and unwinds will significantly reduce the running times.
It is always recommended that an inspection takes place after the seaming process has been completed.
SHRINK SLEEVING APPLICATION METHODS
Sleeve labels can be applied by hand or using automatic equipment.
During shrink label application the pack or container body is covered or partially covered by the sleeve, then shrunk to fit (Figure 7.4 earlier in the article).
Shrink applications can be categorized as follows;
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Tamper evident application – where a shrink band is applied to the neck of a container to produced a tamper evident seal
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Pre-forms – a partially shrunk/pre-shaped sleeve is used typically for tamper evident applications.
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Shoulder or part body sleeving – where a sleeve partially covers the shoulder or part of the container walls
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Full body decoration – total coverage of container walls
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Full body sleeve with in-built tamper-evidence – the body sleeve extends over the neck of the container to create a tamper evident sleeve
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Promotional decoration – where perhaps an additional gift or promotional item is shrunk to a product
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Multi-packs – where a number of items are collated and shrunk together to form a multi-pack
There are a variety of both manual and automatic sleeve application systems on offer that can cater for all of the above applications. Sleeving systems typically incorporate the sleeve applicator, shrink tunnel or shrink system (and product handling equipment). Each of the main application systems will be dealt with here.
Rotary-style applicators (Figure 7.12) offer specific advantages for multipacks and odd-shaped containers. Film is registered electronically and fed through a film guide that transforms the lay-flat into a square or rectangle for easier application. The film is then sent through a guillotine-style cutter creating a cut-piece.
The cut-piece is met with the rotary tooling and held by vacuum. As the tooling rotates, the cut-piece is introduced to the product running on the conveyor below.
Figure 7.12 Rotary style shrink sleeve applicator. Source- Accraply
These systems often have a lower capital cost compared to mandrel-style applicators. The rotary-style are designed to run at low-to-intermediate speeds and are most suitable for frequent change-over operations, due to the relatively lower cost of change parts. This style is also more tolerant of lower-quality sleeve material.
Direct-apply machines (Figure 7.13) offer a compact design and are generally low-tech and low-cost systems. They are limited to low-to-intermediate speeds and are often suited for large containers.
Figure 7.13 Direct apply shrink sleeve applicator. Source- Accraply
The film is fed through a guide similar to one found on a rotary-style applicator. It passes through a guillotine-style cutter where the cut-piece is then draped over the conveyor and introduced to the product passing underneath.
Direct-apply machines tend to have few electrical components, so cut-length is generally determined mechanically.
Mandrel-style applicators (Figure 7.14) also known as vertical or bullet applicators, are the most sophisticated of the three styles. They are most suitable for round or cylindrical containers and typically run at intermediate to high speeds. These are often chosen for continuous, 24/7 duties, and dedicated lines.
Figure 7.14 A mandrel style shrink sleeve applicator. Source- Accraply
Film is registered electronically and fed over the film guide fin and mandrel by the film drive rollers. These rollers send the film down to the rotary cutter creating a cut-piece. The cut-piece is forced onto the product passing on the conveyor by the film-drive rollers pulling film into the rotary cutter. They are more demanding of quality materials and have more expensive change parts.
Figures 7.15 and 7.16 show how the shrink sleeve film is guided, registered and fed over a mandrel into a rotary-style cutter.
Figure 7.15 Shrink sleeve is guided and registered onto the shrink sleeve applicator. Source- Accraply
Figure 7.16 Close up showing how shrink sleeve film is fed over a mandrel and into a rotary style cutter. Source- Accraply
There is a trend towards applicators capable of applying all label formats (self-adhesive, sleeves, ROSO, and wraparound) on a single machine.
SHRINK TUNNELS
Shrink sleeves are designed to shrink when exposed to heat and historically the choice of shrink system was dependent upon on a number of factors, such as:
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Whether the container was empty or pre-filled
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Container material - glass or plastic
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Type of product being handled e.g. are the products heat sensitive
New developments in shrink tunnel technology mean that these factors are less critical today.
Shrink tunnels, used in shrink sleeving tend to operate using hot-air, although infrared and steam are increasingly being used. Their successful performance is primarily a function of the speed and effectiveness with which they can transmit sufficient heat to the film to initiate the shrink action.
As exposure of the film in the tunnel is only a few seconds, the heat has no effect on the product; the hot-air only affects the film, causing it to shrink snugly around the product.
Different shrink films have different shrink characteristics, so shrink tunnels need to have a degree of adjustability. Most consist of a conveyor, a heat chamber and a hot-air recirculating system. There are many special types of tunnels available, with some having cooling chambers or pre-heating sections.
Figure 7.17 shows a hot air double tunnel for full body or tamper evident shrink sleeves.
Metallic inks used on some sleeving applications can affect heat transfer and lead to irregular film distortion. Different printed colors too can impact on film shrinkage, i.e. certain colors absorb more heat and therefore lead to an irregular shrink.
Figure 7.17 Hot air tunnel (open). Source- Accraply
Heat shadows caused by the container contours can cause uneven shrinking or distortion of the film and must be considered when designing the shrink system.
In most instances the use of steam shrinking can overcome many of these issues. There are however significant cost issues to consider when providing and managing steam sources. Figures 7.18 and 7.19 show two examples of steam shrink tunnels.
Figure 7.18 Steam shrink tunnel. Source- Accraply
Figure 7.19 Modular steam tunnel with multiple zones. Source- Accraply
It is worth noting that for some applications such as low speed, tamper evident sealing heat guns or shell reflectors may suffice as a simple shrink method.
PRE-PRESS ISSUES
There are certain key characteristic with shrink sleeves that need to be considered when designing a shrink sleeve.
The drawings in Figure 7.20 highlight the key dimensions, terminology and parameters to be considered when designing a sleeve label. It is important to note that overlap areas will need to be kept free of artwork.
Figure 7.20 Important shrink sleeve design parameters. Source- Esko
Printing on shrink film presents a number of challenges not encountered when printing on paper. For one, the way the label comes out on press is not the way it will look on the bottle. This is because the label will shrink to the contours of the container and distortion therefore will occur to the printed graphics. It is typical to avoid branding in high shrink areas of the sleeve or too close to the welded seam in order to avoid image distortion issues.
Consequently, calculating distortion correctly is paramount to a successful sleeve label. Traditionally the process was quite laborious. Converters would print a grid pattern on a film, sleeve it, put it on a container and put it through a shrink tunnel, or hit it with a high temperature heat gun to get it to shrink. Then they will cut that off and measure it.
From there the converter would go to a computer program and output the graphics, produce the sleeve, shrink it down, and make sure the graphics appear correctly after shrinking.
Today, there are many software solutions available that can simplify the shrink sleeve workflow process. In general, with these software programs, pre-press can be divided into three different steps or stages. The first step is to prepare the graphics. For that purpose, there are now software suites that conveniently plugs into Adobe Illustrator, so providing a low learning curve. This means that an operator can embrace the technology very quickly.
Once the shape has been created, the next step is to move to a studio designer program in which a virtual sleeve can be applied around the 3D object. This is where the typology, the 3D landscape, can be determined.
The final step is to add the graphics to the 3D shape using, say, Adobe Illustrator. This enables the operator to visualize the decorated container, and even spin it around. It is also now possible to send that file to the customer.
There are free apps for iPhone where the customer open up the file on their iPhone, iPad or Android, or Windows mobile device and can view it. With their finger, they can even spin the design around, zoom in and zoom out.
REEL-FED WRAPAROUND LABELING
Other systems of labeling have emerged that can label containers without needing to use a pre-welded sleeve label.
The concept of reel-fed labeling was first introduced by B & H Manufacturing of Ceres, California in 1969 to cater for the high speed labeling of plastic containers.
These systems originally applied labels of paper or paper-PP laminates mainly to parallel sided containers.
The growth in usage of PET bottles in preference to glass, particularly for carbonated liquids, created a need for compatible label materials that would stretch with the pack and not wrinkle or tear.
This trend has driven the use in filmic materials, particularly for carbonated soft drinks and beers market (see Figure 7.21).
Figure 7.21 Typical roll-fed MD shrink sleeving application - Pepsi Co Gatorade Thirst Quencher and Gatorade
For wraparound labeling equipment is designed to use continuous rolls of materials, rather than pre-cut magazine fed labels or sleeves.
With reel-fed systems the cutting, gluing or welding operation takes place on the applicator.
ROLL FED SHRINK (RFS) AND ROSO TM (ROLL ON SHRINK ON) LABELING
In more recent times development in roll-fed shrink labeling has gathered pace.
The descriptions RFS (Roll Fed Shrink Labeling) and ROSO tm (Roll on Shrink On) are typically used to describe roll fed single ply mono-directional shrink materials used to create shrink sleeves. Labels are supplied in a flat roll format using materials that shrink in the machine direction rather than in the transverse direction (as is the case with pre-welded sleeves).
RFS labels use a metal mandrel on the labeling machine to form the seam, with the seam completed using laser or sonic welding or a heated bar. The completed tube is placed over the container before being shrunk into place.
ROSO mono directional (MD) shrink labels describe roll fed single ply materials that are formed into tubes using adhesives and the container as the mandrel during the application process.
Typically ROSO labels have low shrinkage rates of 12-20 percent compared with RFS labels that have higher shrinkage rates of up to 55 percent.
TYPICAL MANUFACTURING AND APPLICATION PROCESS
The process begins with a flat reel of material being printed using one of the major conventional and digital printing processes. On some materials polymer surface modification or coating may be required to improve printability.
The reel is slit to the correct width, inspected for quality and supplied to the end-user or filler for application.
With wraparound style applications the onus for seaming and the application onto the pack is passed onto the end-user.
Seaming and automatic application onto the pack takes place prior to the label being shrunk onto the container. Figure 7.22 highlights a typical manufacturing and application process for reel-fed shrink sleeving.
Figure 7.22 Schematic of the ROSO manufacturing/application process
For non-shrink applications labels are wrapped around the container and typically sealed with hot-melt adhesive.
Whilst acceptable for standard wrap round labeling applications, hot melt adhesives are unsuitable for ROSO applications. The hot air shrink process can re-melt the adhesive thus destroying the seam integrity.
The use of UV adhesive has however partially solved this problem although some improvements are required in order to resist the high shrink forces of steam methods. There are two versions of UV curable adhesive, one of which is water washable to aid removal/recyclability.
ROSO systems today also use other methods for seaming on the applicator such ultrasonic, laser, heat bars and solvent welding.
The label is cut to size prior to adhesive being applied to the leading and trailing edge of the label and then applied to the container (see schematic of the application process in Figure 7.23).
Figure 7.23 Schematic of the ROSO application process
Material is always square cut in order for a positive and secure overlap to be made at speed.
With lower shrink capabilities labeling is generally suitable for decorating parallel sides or areas of the pack with minimal contour deviations.
The containers then pass through a shrink tunnel, which shrinks the film to the contours of the container. Heat in the shrink tunnel need only be applied to the areas where shrinkage is required.
APPLICATION DEVELOPMENTS
Major labeling equipment companies, such as Krones, Sacmi and Trine, have developed roll-fed applicators that incorporate solvent seaming (rather than adhesive) in the trailing edge overlap seam.
Sidel has developed glueless labeling equipment that utilizes a heat bar to weld the label overlap. This process allows the use of higher shrinkage roll-fed shrink films, due to the greater strength of the welded seams.
The effect of container profile on the decoration method.
The container profile and the required conformity of its decoration has the greatest effect on the choice of system and the labeling film that is utilized.
Complex container shapes requiring consistent substrate 'shrinkability' will currently only be successfully decorated using pre-welded shrink sleeves.
Many complex container shapes require film shrinkage factors of 40-70 percent (see illustrations in Figure 7.24).
Developments in applicator technology combined with new film developments will allow ROSO labeling to increasingly penetrate this sector.
ROSO is currently confined to those applications where less than 20 percent film shrink-ability is required i.e. simple container profiles (see illustrations in Figure 7.24).
Figure 7.24 Effect of container profile on the film selection
MATERIALS
Materials used for wraparound systems are supplied in flat web format and are significantly cheaper than those used for pre-welded sleeves.
It is believed that the differential between reel-fed and shrink sleeve films may be due to the increased volumes/yields for reel fed MD ROSO films and/or the method of building memory into MD ROSO films which may be less costly than the TD films used for sleeves.
Opaque and transparent materials used in typical wraparound systems (RFS/ROSO) include;
These materials are supplied in 40, 45 and 50 micron thicknesses, with little shrinkage in the transverse direction.
With clear films the labels can be reverse-side printed. White films provide an alternative to paper labels, offering improved gloss, excellent dispensing and better scuff and humidity resistance.
If a design or copy falls within the shrink areas then allowance needs to be made in the design and printing for distortion.
It is important to note that the type of labeler and seaming method being employed will determine the optimum polymer to use for each application.
SHRINK TUNNELS
The main methods of shrinking used for reel-fed wraparound labeling are detailed below.
STEAM SHRINK
Steam is increasingly being used on shrink sleeve applications for the consistency of shrink achieved.
Steam however is not suited to ROSO PP materials. PP needs a temperature of more than 100 degrees to start shrinking, thus it is impossible to use in steam application.
Advantages of steam shrinking includes;
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Energy saving versus hot air
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Uniformity of heating (like a 'sauna'), no need for rotation of the product.
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Easier to switch from one product to another (no redirection of hot air flow)
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Result is perfect at any shrink ratio.
HOT AIR SHRINK
When selecting hot air tunnels as the method of shrinking there are a number of key factors to consider.
HIGH ENERGY CONSUMPTION
Films above 18-20 percent shrinkage can be problematic due to the fans (inside the tunnel) a rotation is required (two conveyer belts at different speed) in order that the product gets heat uniformly.
In addition, the operator will also need to adjust the orientation of the fans inside the tunnel.
BOTTLE DRYING
In many applications containers that are to be decorated need to be completely dry before sleeving.
Sleeved containers that have been steam shrunk need to be dried prior to palletization and ROSO labels require an absolutely dry bottle to ensure blemish free application.
Investment in drying equipment is therefore an additional cost factor to be taken into account.
RECYCLING
A water flotation process is typically used to reclaim film label and container.
Plastic containers are flaked along with their filmic decoration (shrink sleeve or ROSO). The flakes are put through a flotation system which incorporates caustic soda, and which separates the film flakes from the container flakes. Essentially the PET flakes sink and the filmic label flakes float. The PET flakes are recycled, sometimes for use in producing the exterior of new PET containers, and in there are attempts now being made to even produce film from these flakes.
Label materials with a low specific gravity are suited to this method of separation.
PVC sleeved PET containers are problematic due to cross contamination issues.
One interesting environmental issue centers around the removal of the printing ink slurry which is produced during the melting and waste recycling process. The removal of ink slurry to ensure there is no contamination taking place can be problematic.
PROS AND CONS OF REEL-FED SYSTEMS
Some of the key advantages and disadvantages of roll-fed systems are highlighted here.
Advantages
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Reel-fed applications are generally lower cost versus pre-welded sleeves
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Supplied in a flat web allowing more labels per reel
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Process is relatively simple as it only entails printing and slitting
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No pre-seaming of sleeves required (including seam inspection)
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Possible to seam without adhesives and solvents therefore easier to recycle
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Non-adhesive based welding eliminates expensive UV lamps and difficulties associated with use of UV adhesives
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Higher labeling speeds possible
Disadvantages
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Shrinkage factors tend to be less than welded sleeve formats – limited shrinkage in transverse direction
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Less scope for full body coverage on difficult shaped container profiles
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High capital cost attached to reel-fed applicators, with expensive change parts and time consuming changeovers between bottle shapes and sizes
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The inclusion of tamper evident features is very difficult for ROSO applications.
NEW DEVELOPMENTS
Adhesleeve – PE Labelers
This is a new development in pre-adhesive self-wound shrink labels from Italian applicator specialist PE Labelers.
PE Labelers has been in the labeling industry for 12 years and supply parts for Sidel and Ocme machinery.
Called 'Adhesleeve', the system uses a pre-applied clear adhesive strip on the back of the ROSO label. The adhesive is applied at the printing stage and cured in-line, so the reels are supplied to the application line with the graphics and adhesive completed.
The label is cut on-line, wrapped around the container and the trailing edge is then fixed to the adhesive strip creating a sleeve which is positioned on the container. The container then travels through the shrink tunnel and emerges ready for filling.
This new method of application allows the shrink label to be applied to a container without the need for a special hot-melt glue together with UV tunnels.
Eliminating the use of the hot-melt glue implies several advantages: from the absence of fumes produced by heating the hot melt, to the elimination of solvents to clean the application cylinder. Furthermore the label, as it is no longer contaminated by the hot melt, is 100 percent recyclable.
The development of the Adhesleeve project has lead to the realization of a new method of label cutting, no longer affected by the interaction of fixed and rotary cutting blades.
Thanks to this new cutting system the adjustments to the cutting unit in case of various film thickness, changes in the ambient temperature and worn out blades are no longer necessary and the replacement of the cutting devices, which do not require any servicing, is effected without tools.
All this allows a 100 percent elimination of production stops, thus improving the labeling efficiency.
(Note: it is speculated that the cutting method could be air knife or laser).
Sleeving summary
The popularity of shrink labeling shows no sign of abating, with double digit growth rates being achieved.
The penetration of ROSO labeling has suffered in the past through its inability to offer a solution to the decoration of containers with complex profiles/contours requiring high shrink MD films.
Developments in servo press technology and in UV flexo printing is encouraging narrow web converters to enter the shrink label market particularly for shorter runs.
The conversion costs attached to the seaming of shrink sleeves can significantly add to costs versus ROSO.
With ROSO technology the onus for seaming is passed to the end user. UV adhesives used for ROSO seaming are expensive and can be messy, however developments in welding technology are removing this barrier.
There are a number of new development films appearing both for ROSO and indeed sleeves (including PLA, COC, PET/OPS/PET).
The expansion of ROSO labeling for long run brands will be accelerated by the further development of high shrink blends.
A key driver for ROSO labeling remains the favourable raw material cost differential versus shrink sleeves and the higher yields it can achieve.
An interesting development is the Adhesleeve system from PE Labelers that eliminates seaming and glue problems using ROSO labels with a pre-applied adhesive strip.
Cut and stack film labels
Film labels when specially treated for static can be applied as cut singles by magazine fed applicators such as the Krones Canmatic.
Stretch sleeving
Stretch sleeves produced in low density polyethylene are designed to be smaller in circumference than the object bottle and are subsequently stretched during application.
The sleeve is securely held in place by the elastic properties of the film alone, therefore eliminating the need for heat or glue during application.
Stretch sleeves have had limited appeal and were seen primarily on large bottles of fruit juice and low quality, large container applications (motor oil) (Figure 7.25).
Figure 7.25 Examples of bottles decorated with high stretch sleeves (Triple S). Source- Labels & Labeling
Improvements in stretch sleeve materials and application processes are widening the appeal of this decoration method.
Key benefits
Heat shrink sleeving methods typically use an oversize shrinkable film tube, which will then be shrunk to a tight fit using a shrink tunnel. The latest stretch sleeve technology however takes an LDPE printed film tube and stretches it over the bottle or container and achieves a tight fit without any need for an energy-intensive shrink tunnel.
Stretch sleeving therefore uses less film and requires no shrink tunnel with significant potential cost saving and environmental benefits.
As the name implies stretch film will expand and contract with the bottle and is ideal for carbonated beverages and squeezable bottles that need to flex.
Not being heat sensitive, the stretch sleeving operation can be carried out on hot-filled containers.
LDPE stretch film used has a low density (0.91 gr/ccm) allowing easy and cleaner separation, thereby supporting PET and bottle-to-bottle recycling.
