Shrink sleeves: Challenges, learnings and the quest for perfection

The Pillsbury Doughboy in Figure 7.1 is a great example of a very effective combination of shape with graphics. 

The teddy bear in Figure 7.2 is equally impactful, and emphasizes the value of shape. The brand owner invested significantly in a custom glass container, incorporating all the physical features of the bear.

Shape does not always need to be exotic to be very effective, however. The high-gloss, extremely well-executed Sunsweet® prune container in Figure 7.3 is incredibly eye-catching. It oozes quality and is entirely practical, incorporating tamper evidence into its design.

Shape can also work against us, as we can observe in the next two examples. The herb grinder in Figure 7.4 is dressed in a self-adhesive label with a tamper evident sleeve. Because the container shape is devoid of a lip or a groove under or into which the tamper evident sleeve could be shrunk, the tamper evident sleeve can in fact be removed – and replaced – without any evidence of tampering!

As versatile as the shrink sleeve labeling technology is, it is not a given that it can or should be applied to every container shape. The Propel bottle in Figure 7.5 is effectively dressed in a shoulder shrink sleeve label – and the horizontal groove around the bottle has provided an effective means of anchoring the sleeve at the desired location. Conversely, the entirely smooth and gentle curves of the H2Oh! bottle provide no such anchoring – resulting in an inconsistent and unattractively decorated bottle on which the sleeve is crooked.

The material from which the container is made also has impact on the quality, look and feel of the final product on the retail shelf. Glass, for example, is a hard, rigid material (compared to plastic), and the sleeves on glass containers tend to get damaged as the containers bump against each other on conveyers or during transport. Damage such as that evident in Figure 7.6 is frequently observed with glass containers. 

While PET containers are among the most straightforward and flexible to sleeve, HDPE can be quite complex. HDPE expands in shrink tunnels and contracts upon cooling. So, sleeves that shrink to the expanded HDPE in the tunnel become loose-fitting once the container cools. This can result in a less-than-ideal presentation of the finished product, as is demonstrated in Figure 7.7. On round HDPE containers, it is quite common to add a heat-activated adhesive to the inside of the sleeve in order to prevent the sleeve from rotating on the container, due to its looseness.

THE IMPORTANCE OF FILM SELECTION

Figures 7.8 and 7.9 illustrate unfinished shrink in the high shrink areas of the container. While this may have been due to issues in the shrink tunnel, it bears all the hallmarks of an incorrect film selection. In other words, the film selected did not have enough shrink capability to form a perfect fit in the high shrink areas.

It is important to realize that shrink film is produced with a specific maximum shrink percentage, with a tolerance that varies by film supplier. Applying extra heat will not cause the film to shrink beyond that which it has been engineered to do. Furthermore, when selecting a shrink film for a particular container, it is important to incorporate a safety margin consistent with the shrink percentage tolerance offered by the film supplier – typically 2% to 5%. Allowance should also be made for the fact that printed film will not shrink to the same extent as raw film.

THE IMPORTANCE OF GRAPHICS

Graphic design is clearly a major element in the appeal and success of the shrink sleeve labeling format. Graphic appeal – and the successful marriage of graphics with shape – is simply foundational.

The most fundamental concept often missed in the design of shrink sleeve labels is the realization that the label is three-dimensional. It is not a flat label, like a self-adhesive or a roll-fed label.

Figures 7.10 and 7.11 are great examples of that which happens when a designer approaches shrink sleeve design with a two-dimensional mentality. They forget that their design will come together, or overlap, at the seam. With just a little forethought, the graphic of the chilies and garlic in Figure 7.10 might not have been cut off as they have been – and furthermore, the designer could have avoided drawing so much attention to the seam, which is otherwise fairly inconspicuous. 

The same is true of the soccer ball bottle in Figure 7.11. It would have cost nothing extra to have had a more complete and attractive finish at the seam. In contrast, the graphics in the seam area of Figures 7.12, 7.13 and 7.14 have been designed with a three-dimensional mindset. The seams are not accentuated, but rather camouflaged by the designer.

The location and orientation of the barcode is another seemingly small detail that is frequently missed in the design of shrink sleeve labels. The first rule of thumb calls for barcodes to be placed in low shrink areas. The second rule of thumb suggests that they be vertically configured using ladder-style orientation. This orientation runs a lesser risk of distortion, as most shrink occurs in the transverse (i.e., horizontal) direction.

Figure 7.15 illustrates the horizontal placement of a barcode that is likely unreadable due to the extent of the transverse direction shrink.

Figure 7.16 illustrates the correct barcode placement and orientation. 

A final point on graphics – make use of the entire canvas! Figure 7.17 illustrates a shrink sleeve label being used to replace a front and back self-adhesive label – that looks exactly like a self-adhesive label! The full opportunity presented by the shrink sleeve format has been entirely missed in this case.

THE IMPORTANCE OF INK SELECTION

The challenges faced by ink in the shrink sleeve world frequently do not become apparent until after the shrinking process, which underscores the need for testing – in the actual production tunnel, whenever possible.

Figure 7.18 illustrates the concept of ‘ink pooling’, in which a color change has occurred due to a thickening, or pooling, of the ink. The removed label in Figure 7.19 confirms the diagnosis. The causes of this defect are most likely due to fundamental problems with the quality of the ink, or the degree to which the ink has been formulated for the harsh demands of shrink sleeves. The problem may be compounded by a lack of sufficient ‘slip characteristics’ that allow for the ink and the sleeve to move freely over the ribbed surface of the container during the shrink process. It may also be compounded by the tunnel causing the sleeve to be shrunk too quickly. A slower, more gradual shrink is usually more helpful.

Figure 7.20 illustrates the concept of ‘tree barking’ or ‘orange peeling’. The container on the right is exhibiting the defect in the high shrink shoulder area, whereas the container on the left appears just fine. The likely difference is that the container on the left has a lower volume of ink in this area, meaning that there is less ink to ‘bunch up’ as the film shrinks. Figure 7.21 confirms that the ink chemistry has not managed to stay with the film in this high shrink area; there is a clear lack of adhesion in the high shrink area.

Figures 7.22, 7.23 and 7.24 each present the most commonly misdiagnosed defect in shrink sleeve labeling. The question: is what we observe here is the ‘wet T-shirt’ effect or the ‘Sellotape’ effect? In summary, the ‘wet T-shirt’ effect happens when moisture gets trapped between the sleeve and the container while in a steam tunnel. It will disappear in time as the moisture evaporates. The ‘Sellotape’ effect is permanent, however. It derives from how light is refracted as two smooth surfaces – the surface of the container and the inner surface of the film – come in close contact with each other. The effect is most noticeable in transparent areas (see Figure 7.22), but as we can see in Figures 7.23, 7.24 and 7.25, it is not limited to just transparent areas. It is particularly evident from Figures 7.23 and 7.24 that the visual effect is most pronounced at those points where the film is under the most stress: on the corners of the containers. The effect is also more visible when the contents of the container are dark or black. This effect is often overcome by increasing the opacity of the ink when it is a printed sleeve, or by use of a clear varnish on clear sleeves or in transparent areas of printed sleeves. In any case, the most effective remedy is to introduce some separation between the two surfaces via a textured last down white or a varnish.

THE SECONDARY CONVERTING STEPS – SLITTING AND SEAMING

We will now draw attention to the three primary defects that emerge from the slitting and seaming steps in the process.

Figure 7.26 illustrates the raised edges on a slit roll that can result from the use of razor slitting or from an incorrect implementation of shear slitting. Figure 7.27 illustrates the scalloped edges that result. These scalloped edges make it difficult, at best, to overlap those edges, lay down a bead of solvent, and create a perfect and mostly invisible seam. In fact, given that the solvent has the viscosity of water, an operator runs the risk of solvent flowing where it is not intended, which can cause blocking in the roll. This reality often forces seamer operators to pull back from placing solvent to the very edge – where it is required for the perfect seam – resulting in an unsightly seam, as shown in Figure 7.28.

Although the result, after shrinking, will not be as bad as that shown in Figure 7.28, the seamed sleeve in Figure 7.29 will also fall short of perfection. Why? Again, the answer lies in the slitting. In addition to shear slitting producing rolls of film without those scalloped edges,  the correct implementation of shear slitting also produces a crisp and clean cut that facilitates the solvent flowing all the way to the edge. Without that crisp cut – or with the jagged cut that razor slitting delivers – the solvent does not make its way cleanly to the edge, and a less-than-perfect seam results. Figure 7.29 illustrates an example of where the solvent is not as ‘to the edge’ as perfection calls for. 

SLEEVE APPLICATION AND SHRINKING

As we approach the finish line and set about getting sleeves applied to containers and then shrunk, there are numerous challenges that can emerge. The challenges with root causes that trace back to earlier steps in the process are difficult to remedy at this point, but those challenges that are specifically associated with application and shrinking are certainly within our purview to correct.

With all shrink sleeve applications, there is a container handling component – that is, in the first instance, the containers should be delivered consistently to the applicator and the sleeves applied with consistent placement accuracy, relative to the shape of the container. Clearly, something went wrong in this regard with the products shown in Figure 7.34. The placement is different on each container, resulting in a very poor presentation on the retail shelf. Likely the shape of the container compounded the problem in this case, but this is an avoidable issue regardless. Moreover, the cut at the bottom and top of the sleeve is not in the right place, nor is it consistent. The same applies to Figure 7.35; using the heart-shaped icon on the lid as a center-line reference, we can observe just how inconsistently these labels were applied from one container to
the next.

Sticking with the theme of solvent, Figure 7.30 shows a burst seam. The burst has occurred in the area of greatest shrink where the seam is under most pressure. So, what may have caused the burst? Several explanations may exist, including: a solvent chemistry that is not a match for the film, resulting in a weak bond; contamination of ink or fountain solution in the seaming area, inhibiting a complete chemical bond; or a mechanical issue with the seamer that caused an insufficient delivery of solvent to this area.

One of the earliest learnings newcomers to shrink sleeves make is the impact that the sleeve color can have on shrink results in a tunnel. Figure 7.36 shows identical glass bottles that were passed through the same tunnel – one with a black sleeve, and the other with a white sleeve. The white sleeve shrunk perfectly, whereas the black sleeve did not. Simple physics is in play – white reflects heat and black absorbs heat; hence, the same tunnel and the same settings deliver different results. The impact of color is generally more pronounced in a radiant or hot air tunnel than it is in a steam tunnel. A tunnel adjustment should solve the problem with the black sleeve, unless there are also issues with the ink or the volume of ink laydown in the high shrink area. Oftentimes, to get the desired color density with black, the volume of ink is increased to a point where it is difficult to achieve a good shrink result.

Remaining on the topic of shrinking, Figure 7.37 presents the problem known as ‘fish eyes’. In other words, when the warm, and shrinking, film comes into contact with the colder surface of the glass bottle, the film’s shrinking is stunted. Invariably, the solution is to pre-heat the glass container prior to applying the shrink sleeve label. Fish eyes tend to be a greater problem with radiant and hot air tunnels. Steam will generally produce a better result on cold containers, so long as there is enough dwell time in the tunnel. The result in Figure 7.37 may be further impacted by the seam limiting the shrink in this high shrink area. 

SLEEVE APPLICATION AND SHRINKING

As we approach the finish line and set about getting sleeves applied to containers and then shrunk, there are numerous challenges that can emerge. The challenges with root causes that trace back to earlier steps in the process are difficult to remedy at this point, but those challenges that are specifically associated with application and shrinking are certainly within our purview to correct.

With all shrink sleeve applications, there is a container handling component – that is, in the first instance, the containers should be delivered consistently to the applicator and the sleeves applied with consistent placement accuracy, relative to the shape of the container. Clearly, something went wrong in this regard with the products shown in Figure 7.34. The placement is different on each container, resulting in a very poor presentation on the retail shelf. Likely the shape of the container compounded the problem in this case, but this is an avoidable issue regardless. Moreover, the cut at the bottom and top of the sleeve is not in the right place, nor is it consistent. The same applies to Figure 7.35; using the heart-shaped icon on the lid as a center-line reference, we can observe just how inconsistently these labels were applied from one container to
the next.

One of the earliest learnings newcomers to shrink sleeves make is the impact that the sleeve color can have on shrink results in a tunnel. Figure 7.36 shows identical glass bottles that were passed through the same tunnel – one with a black sleeve, and the other with a white sleeve. The white sleeve shrunk perfectly, whereas the black sleeve did not. Simple physics is in play – white reflects heat and black absorbs heat; hence, the same tunnel and the same settings deliver different results. The impact of color is generally more pronounced in a radiant or hot air tunnel than it is in a steam tunnel. A tunnel adjustment should solve the problem with the black sleeve, unless there are also issues with the ink or the volume of ink laydown in the high shrink area. Oftentimes, to get the desired color density with black, the volume of ink is increased to a point where it is difficult to achieve a good shrink result.

Figure 7.42 presents an interesting opportunity to recap several learnings from throughout the book. The defect we are diagnosing is referred to as ‘curl back’, or ‘flowering’. It is occurring because the sleeve was cut through the print – in other words, there is no clear area at the top of the sleeve. Those clear areas are important because, without the presence of ink, they tend to shrink faster and farther, and they serve to aggressively pull the shrinking sleeve tight at the top of the container. In this example, without this clear area to control the process at the top of the sleeve, the ink enters the shrink equation and creates the likelihood of a shrink differential between the inside and the outside of the film. In other words, the film wants to shrink faster than the ink, and the resulting curl always happens from the inside out, as demonstrated in Figure 7.42. It will be especially pronounced in areas of high shrink, where the density of ink is greatest.

In conclusion, we set out promising an exciting journey through the shrink sleeve label production process, with a view to achieving nothing short of perfection at the end.

We have shown you the importance of selecting the right ‘ingredients’, partnering with your suppliers throughout, and focusing on the details in every step along the way. While we have illustrated the myriad challenges that exist throughout the process, we have also demonstrated the infinite opportunities presented by this exciting labeling technology.

Despite the potential for mistakes to happen in the process of learning the science of shrink sleeve labeling, provided that appropriate care and consideration is given to every step of the process, the successes that result will drive your level of knowledge beyond that which is contained in this book. Every project presents its own learning opportunity and contribution to knowledge – your knowledge and that of the industry. 

Figures 7.39, 7.40 and 7.41 all present identical issues around the neck of a bottle requiring a significant amount of shrink. In fact, this ‘neck collapse’ is a very common fault that is typically associated with attempts to shrink too quickly. As a general rule, you always want to shrink slowly, and from the bottom up. This progressive shrink may call for a zoned tunnel, or for multiple tunnels. In any case, the results shown in Figures 7.39, 7.40 and 7.41 are likely the result of tunnels that are too hot, causing the film to become soft and collapse on itself before the shrink to the bottle is complete.

Figure 7.42 presents an interesting opportunity to recap several learnings from throughout the book. The defect we are diagnosing is referred to as ‘curl back’, or ‘flowering’. It is occurring because the sleeve was cut through the print – in other words, there is no clear area at the top of the sleeve. Those clear areas are important because, without the presence of ink, they tend to shrink faster and farther, and they serve to aggressively pull the shrinking sleeve tight at the top of the container. In this example, without this clear area to control the process at the top of the sleeve, the ink enters the shrink equation and creates the likelihood of a shrink differential between the inside and the outside of the film. In other words, the film wants to shrink faster than the ink, and the resulting curl always happens from the inside out, as demonstrated in Figure 7.42. It will be especially pronounced in areas of high shrink, where the density of ink is greatest.

In conclusion, we set out promising an exciting journey through the shrink sleeve label production process, with a view to achieving nothing short of perfection at the end.

We have shown you the importance of selecting the right ‘ingredients’, partnering with your suppliers throughout, and focusing on the details in every step along the way. While we have illustrated the myriad challenges that exist throughout the process, we have also demonstrated the infinite opportunities presented by this exciting labeling technology.

Despite the potential for mistakes to happen in the process of learning the science of shrink sleeve labeling, provided that appropriate care and consideration is given to every step of the process, the successes that result will drive your level of knowledge beyond that which is contained in this book. Every project presents its own learning opportunity and contribution to knowledge – your knowledge and that of the industry.