Using the right application and shrink tunnel technology

While converters will be most interested in how to produce a high value shrink sleeve label, it is also necessary to understand that the sleeve application process is as important as the steps in order to produce a finished product that the brand owner &#; and ultimately, the market &#; will value. Converters should always be tightly connected with the manufacturer of the application equipment in order to understand the specifications and tolerances required of the specific application equipment being used by each of their customers. In other words, there are no one-size-fits-all solutions in the successful application and shrinking of shrink sleeve labels. Prior to reviewing the shrink sleeve application machinery in some depth, let us review some of the key concepts that will bear importance in the application process.

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This article takes a closer look at the process of sleeve application and how the sleeve is shrunk onto the container (see Figure 6.1).

The layflat size and its tolerance &#; as well as the extent to which the layflat is over-sized relative to the container &#; is important because it determines the compatibility of both the container and the tooling on the application machinery with the shrink sleeve. The oversize is typically 2mm on a round container, but it may be as much as 7mm, depending on the container shape, size and the method of application.

The repeat length, or cut length, describes the length of the label being applied to the container. Each sleeve has a clear, non-printed area on the top and bottom. These clear areas are used for both manual and automatic application purposes. In manual application, the clear areas act as a guide for an automatic sensor to determine where to cut, or sheet, the individual sleeves. In automatic application, the clear areas also indicate where to cut the sleeve just prior to applying it onto the container. It is therefore always necessary to have these clear areas on any finished shrink sleeve.

Let&#;s now return to the concepts of smiling and frowning (Figure 6.2). Smiling and frowning comes about when the sleeve shrinks in both the machine direction (MD) and the transverse direction (TD), and an arching effect is created.

Fortunately, there are ways to overcome this issue. One method is to carefully select the type of film used and control for how the film shrinks into position on the container. Another method to control the issue of smiling and frowning labels is to incorporate machinery that lifts the container off the conveyor and allows the sleeve to shrink under the base of the container. Finally, a third method of mitigating smiling and frowning labels is through container design; specifically, either selecting or designing a container with a built-in notch to lock the sleeve label into place as it shrinks.

SHRINK SLEEVE LABEL TYPES

There are several types of shrink sleeves that brand owners seek for their products. Tamper evident or tamper bands (Figure 6.3) are used to produce a seal on a container that demonstrates tampering if the container is opened.

A part-body sleeve (Figure 6.4) is used when a container does not require a full-body decoration. A brand owner may require us to position a sleeve half way up a container or at the top of a container. 

One of the challenges with positioning a part body sleeve half way up a container is that it becomes necessary to somehow anchor the sleeve in the right position on the container. Some of the containers in Figure 6.4 incorporate a notch, which allows the clear area to shrink into the groove and provide a nice finish.

Full body sleeves, on the other hand, allow for 360-degree and top-to-toe container decoration. No other labeling technology allows for almost 100% of the container&#;s surface to be decorated and used to convey the brand&#;s message to the consumer.

It is also possible to have full body decoration but with the added functionality of a perforation (Figure 6.5), which aids the consumer in removing the label following consumption. This feature can be achieved in the label application process, as well as during the converting process (which precedes label application). It is particularly straightforward to achieve on the application equipment, as the tooling involved is easily installed and generally provides a lot of flexibility in the positioning and pattern of perforation. 

SHRINK SLEEVE LABELING PERFORMANCE CONSIDERATIONS

Achieving success in the final steps of applying and shrinking a shrink sleeve label hinges on decisions made at the very beginning of the process &#; decisions like what material the container will be made from and what film material was chosen for the sleeve. For example, glass containers present a very different scenario at the shrinking stage than do containers made from HDPE. Process conditions are important too &#; there are fundamental differences between shrinking onto a container that is full versus one that is empty.

Figure 6.6 captures some of the main variables that are in play as we set about applying and shrinking a finished shrink sleeve. Without the right combination of container type, film type and process conditions, a successful result will prove difficult to achieve. This, of course, assumes that all the other steps in the process have been completed with the appropriate focus on quality.

Container material considerations: Since glass is a heatsink, it can present challenges in the shrink tunnel by effectively stopping the film from shrinking evenly when the warm film comes in to contact with the colder surface of the glass. It is for this reason that glass containers are frequently pre-heated prior to applying the sleeve. PET containers, particularly if empty and lightweight, can be a challenge with regards to stability for sleeve application, and are susceptible to shrinking in the tunnel, along with the sleeve. On the other hand, HDPE containers expand in the tunnel &#; particularly when the containers are empty &#; and result in the sleeve shrinking around an expanded container, that then becomes loose-fitting after the HDPE contracts upon cooling. Metal containers behave similarly to glass in that they are a heatsink, while paperboards (as used for ice cream, for example) may require chilled conveyors and careful targeting of the heat in the tunnels to shrink the tamper band without melting the contents of the container!

Process conditions: The most fundamental starting point is with whether the container is filled or empty. Filled containers may be more stable on the line, but they may also have over-spill from the filling process that may require washing prior to sleeving. On the other hand, empty containers do not run the risk of over-fill contamination, but they do present greater instability on the line and have higher risks associated with their shrinkage or expansion in the tunnel. Filling temperatures can also present challenges. While ambient filling temperatures are generally straightforward, cold-filled products bring issues of condensation on the surface of containers, making it difficult to have sleeves slide down the container. Conversely, hot-filled products may cause the sleeve to pre-shrink on the container during application. 
All the foregoing comments also have bearing on the film selection &#; with the advantages and disadvantages of each film type. Each of the three components is important to understand, because if there are issues with any one of the three elements, an inferior shrink sleeve label may result.

APPLICATION TECHNOLOGIES

Having understood that there are multiple container types, process conditions and film material combinations called for in the marketplace &#; and that ultimate success depends on selecting a combination of these three elements that are compatible with each other, let&#;s now review various options for applying the shrink sleeve label to the container. Essentially, there are three heat shrink sleeve application technologies available to us:

1.  Rotational (carousel) systems
2.  Direct apply systems
3.  Mandrel systems (sometimes called bullet-style systems).

 

Carousel systems offer the advantage of facilitating a 'squaring' of the sleeves, which allows for better label placement, or rotational accuracy, on non-round containers. A carousel system will often be used to apply shrink sleeve labels to containers such as trigger bottles, like that pictured in Figure 6.7. The formation of square or rectangular sleeves prior to their application to non-round containers greatly increases the probability of the label panels being correctly positioned on the container after shrinking. 

You will notice from Figure 6.8 that carousel application systems are more tolerant of lower quality sleeve materials. This tolerance can be attributed to the fact that the carousel tooling comes into contact with the sleeve significantly less than is the case with a mandrel or 'bullet' type application system, thus the tolerance and fit are less of a concern with a carousel application system.

Figure 6.9 shows a carousel applicator machine in operation. The carousel system shapes the sleeve in such a fashion that it is well-positioned or centered on the non-round container as it is applied.

Direct apply systems are used primarily for tamper band applications. The process is simple: the sleeve passes through the tooling, where it is opened up into a round shape. As the container being sleeved moves along the conveyor, a guillotine cuts the sleeve, and it is dropped onto the container as it passes.

Direct apply systems (Figure 6.10) are very simple to use, they generally use low-tech change parts, and from an operator&#;s point of view, they offer simple and quick changeovers. 

Mandrel (or bullet-style) application systems are the most widely used style of application systems in the market. This system uses a mandrel, or cylinder-like tube, around which the sleeve is opened (see Figures 6.11 and 6.12). The mandrel is suspended within a system of drive rollers that move the opened sleeve down the mandrel before the sleeve is rotary-cut to fall (or be driven) directly onto the moving container. 

With this type of application, the mandrel comes into contact more extensively with the sleeve than does the tooling on a carousel application system. The layflat size tolerance &#; as well as the coefficient of friction (COF) characteristics of the inside of the sleeve &#; are much more critical on the mandrel style system than is the case with carousel or direct-apply systems.

With mandrel application systems, the speed at which the container is moving must be accurately timed with the mandrel as it fires the sleeve off and onto the container. It is for this reason that we use mandrel systems primarily for round or cylindrical containers as they present as better 'targets' for the sleeve as it is leaves the bottom of the mandrel, usually at high speed.

SHRINK TUNNELS

There are three main types of shrink sleeve tunnels:

1.  Hot air
2.  Radiant heat
3.  Steam

This section will summarize the technologies available and discuss the advantages and disadvantages of each.

Hot air tunnels (see Figure 6.13) are versatile, they are cost-effective to use, and they can connect to almost any power source. Hot air tunnels offer directional heat, so depending on the type of equipment used, the many different manifolds in these systems enable heat to be focused on those areas of the container that require the most shrinkage. This makes them good systems for focused heating on necks, recesses and grooves.

Hot air tunnels do have some disadvantages, however. Air is not a very efficient medium through which to transfer heat. Therefore, temperatures in hot air tunnels are generally higher to ensure enough heat is transferred to the film to start the shrink process.  Because of the higher temperatures, the leading edge of the container &#; or more specifically, the sleeve on the container &#; can be over-exposed to heat as it enters the tunnel, resulting in an uneven shrink finish. This can be particularly prevalent with certain container types and process conditions, such as with cold-filled plastic or glass containers. One way to mitigate this issue is to rotate the container as it passes through the tunnel using a spinning conveyor.

Radiant heat tunnels (see Figure 6.14) were primarily designed for preheating glass containers &#; prior to sleeving &#; to mitigate the heatsink effect of the glass. However, they can also be very effectively used to shrink sleeves. Radiant systems deliver infrared heat and because the heat remains in the chamber, they create an oven-like shrinking environment.

Due to their high temperature of operation, radiant heat tunnels represent a very harsh shrinking environment with little opportunity to direct heat toward specific areas on a container. Additionally, it can be particularly difficult to get even, consistent shrink results. For instance, when the leading side of the sleeve entering the tunnel gets aggressively shrunk before the trailing edge, or when the sleeve on the two sides of the container are exposed to more intense heat than the leading and trailing sides, a 'pulled' or uneven finished shrink sleeve may result. A further complication of the high temperatures in radiant tunnels is the difficulty they can present with empty containers. For example, the task of shrinking a PET sleeve on a thin-walled empty PET container can be extremely challenging in a radiant tunnel.

Steam tunnels (see Figure 6.15) are the preferred medium for most shrink sleeve applications, and they offer some significant advantages in terms of the process window. Steam tunnels are the most versatile type of tunnel and work well with a variety of films. Steam distributes heat very evenly to the entire surface of the film as it envelopes the container passing through the tunnel. And, because it is steam &#; and water is over 20 times more efficient at transferring heat than is air &#; temperatures are lower and the environment in the tunnel is much less harsh. 

Despite steam tunnels being the most favored method of shrinking shrink sleeve labels due to their propensity to deliver the most even finished result, their initial installation is likely to be more involved and expensive due to the need for a steam generating boiler, as well as all the associated piping, extraction, valve gear and drainage required. The volume of steam &#; and hence the boiler requirements &#; will primarily be dictated by the volume of throughput required of the sleeving line.

It is common for containers to emerge wet from a steam tunnel. In situations where this presents a problem (e.g., with secondary packaging), air knives may be required to dry the containers.

In summary, this article has focused on the final steps in the shrink sleeve production process &#; applying the sleeve to a container, and shrinking it. As with all previous steps in the process, a focus on detail and a determination to make informed decisions and produce quality at each step throughout the process is essential to achieving perfection on the retail shelf. There are no one-size-fits-all solutions in the production of shrink sleeves as each container and each label produces its own set of challenges. Every decision that is made &#; right from the point of selecting the container shape and what material it will be made from &#; has influence on the best method of applying and shrinking that label at the end of the process. And, the earlier you involve your application and shrinking equipment manufacturer in the decision-making process, the greater your likelihood of success.

Table Of Content

When it comes to shrink film, manufacturers often prioritize cost and performance, unwittingly ignoring subtle quality issues that can significantly impact the final product. These issues not only compromise the integrity of the packaged goods but can also lead to added expenses in the long run.

The most common quality issues manufacturers face with shrink film include inconsistent shrinkage, film breakage, poor clarity, surface issues, and sealing problems. Knowing how to identify and address these issues can save you time, resources, and keep your production line running smoothly.

In the following article, we will delve deep into each of these five quality issues, providing practical solutions for manufacturers. It&#;s essential reading for anyone in the industry who wants to optimize their shrink film usage and sidestep potential pitfalls.

Understanding Shrink Film

Shrink film is a polymer-based material that contracts when exposed to heat, tightly enveloping the item it encases. This reaction results from the material&#;s unique molecular structure, which changes during the heating process. The film is commonly made of low-density polyethylene (LDPE) or polyvinyl chloride (PVC), among other materials. I&#;ve spent years in the packaging industry, and it&#;s remarkable to see how much this seemingly simple material can impact the entire production line.

Key Uses Of Shrink Film In Different Industries

Shrink film is incredibly versatile and widely used across various industries. Its primary function is to protect products from external elements like moisture and dirt, but it&#;s also vital for unitizing items and ensuring their safe transit.

1. Food and Beverage: Shrink film is indispensable in packaging perishable items like fruits, vegetables, and meats. It&#;s also commonly used for bundling cans or bottles together.
2. Pharmaceuticals: Safety is paramount in this sector, and shrink film offers a tamper-evident seal for medicines and other health-related products.
3. Retail: From toys to electronics, shrink film helps to improve the shelf appeal of products, besides providing a clear view of the item, which is essential for consumer trust.
4. Automotive: Parts like screws, nuts, and bolts are often bundled using shrink film to ensure they don&#;t get lost or mixed up during shipping.
5. Construction: Shrink film can be used for wrapping construction materials that need protection from moisture and other environmental factors.

Quality Issue #1: Inadequate Shrinkage

Inadequate shrinkage refers to the inability of the shrink film to tightly conform to the product it&#;s supposed to encase. This issue can result from various factors, such as improper heat settings during sealing or using a film type unsuitable for the item being packaged. I&#;ve encountered this issue multiple times in my years working in the packaging industry, and it can be a frustrating bottleneck in the production line if not addressed timely.

How It Affects The Manufacturing Process

Inadequate shrinkage can significantly undermine the effectiveness of your packaging. A loosely wrapped product can compromise its appearance and protective features, making it less appealing to consumers. It may also contribute to the risk of damage during transport or storage, thereby impacting the entire supply chain. These consequences can cost companies valuable time and resources, not to mention the potential damage to brand reputation.

Relevant Solutions

Based on my experience, the best approach to address inadequate shrinkage is a comprehensive one:

• Optimize Heat Settings: Regularly calibrating your heat tunnel ensures that the film receives the appropriate amount of heat for optimal shrinking.
• Material Selection: Choose a shrink film that&#;s tailored for your specific product. Some products may require high-barrier films for extended shelf life, while others might need more puncture-resistant options.
• Quality Checks: Implement a quality control system to catch problems early in the production line. If you find any issues, resolving them immediately is often quicker and less expensive than dealing with the fallout later.

Quality Issue #2: Poor Seal Strength

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Importance Of Seal Strength

Seal strength is arguably one of the most critical aspects of effective packaging. A strong seal ensures that the product within remains secure, protected from external factors like moisture, oxygen, and bacteria. It&#;s a topic I&#;ve frequently discussed with clients and colleagues alike, stressing that even the highest-quality shrink film would be ineffective if the sealing process is compromised.

How Poor Seal Strength Can Affect The Product

A poor seal can have immediate and long-term repercussions. In the short term, it can lead to package failure, causing the product to fall out during handling or shipping. This leads to an increase in damaged goods, customer complaints, and, ultimately, returns. Over time, poor seal strength can tarnish your brand&#;s reputation, impacting customer trust and sales.

Suggested Remedies

If you&#;re facing issues with poor seal strength, consider these steps to improve the situation:

• Machine Calibration: Periodically review the settings on your sealing machine. Timing, pressure, and temperature all need to be meticulously fine-tuned for optimum results.
• Material Compatibility: Ensure that your shrink film is compatible with the sealing technology you&#;re using. Not all films are created equal, and some may require specific sealing conditions for optimal performance.
• Regular Maintenance: A machine in top condition is less likely to produce poor seals. Normal upkeep can help prevent the majority of issues related to seal strength.
• Quality Audits: Incorporate frequent quality checks into your process. Use testing methods like peel tests to ascertain the quality of your seals.

Quality Issue #3: Uneven Film Thickness

Uneven film thickness is an issue where the shrink film does not have a consistent thickness across its surface. This usually occurs due to manufacturing defects or improper handling during the packaging process. Having dealt with this problem in various operational setups, I can say that it&#;s a subtle issue that can significantly impact the final product.

Its Implications In Manufacturing

The inconsistencies in film thickness can result in uneven shrinkage during the heat treatment, leading to a poorly wrapped product. Furthermore, thin areas are susceptible to tears and punctures, posing a product safety and integrity risk. These inconsistencies can be particularly problematic in industries like food and pharmaceuticals, where packaging plays a crucial role in product quality and safety.

Possible Solutions

Here are some steps to counteract the issue of uneven film thickness:

• Vendor Verification: Ensure you&#;re sourcing your shrink film from a reputable supplier. Regular audits of incoming materials can help catch inconsistencies before they become problematic.
• Machine Calibration: Your machinery must be in top form to ensure the film is stretched and sealed uniformly. Periodic calibrations can go a long way in maintaining consistency.
• Quality Control: Implement a robust quality control process to inspect the film before it hits the production line. High-resolution cameras and manual inspections can help identify inconsistent areas with no sickness.
• Employee Training: Make sure your staff knows how to handle the film properly to avoid introducing inconsistencies during the packaging process.

Quality Issue #4: Poor Clarity and Gloss

Why Clarity And Gloss Matter In Shrink Film

Clarity and gloss in shrink film are not merely aesthetic considerations; they play a vital role in the product&#;s marketability. Clear, glossy film allows optimal product visibility, enhancing consumer appeal and aiding branding efforts. I&#;ve seen how a simple switch to higher clarity, the outcome of a significantly more polished film, can dramatically affect the outcome. More polished cinema can make a significant difference in how customers receive a product.

How This Issue Can Affect Product Appearance And Sales

Poor clarity and gloss can obscure the product inside, making it difficult for consumers to gauge its quality. The outcome might appear dull or uninviting on the shelf, reducing sales and potentially harming your brand&#;s image. Poor film quality can be a deal-breaker in consumer-focused markets where first impressions count.

Effective Solutions

If you&#;re facing challenges with film clarity and gloss, here are some solutions to consider:

• Material Selection: Opt for high-quality films that offer superior clarity and gloss. They may be more expensive, but increased sales and consumer appeal usually justify the investment.
• Printing Techniques: If you&#;re printing on the film, use techniques and inks that don&#;t compromise the film&#;s natural clarity and gloss.
• Proper Storage: Incorrect storage can lead to film deterioration. Always store rolls in a cool, dry place, away from direct sunlight.
• Quality Control: As always, incorporate regular checks into your process to identify any issues with clarity and gloss before your product hits the shelves.

Quality Issue #5: Inadequate Durability

Importance Of Durability In Shrink Films

Durability in shrink films is a non-negotiable quality. The film needs to be flexible enough to shrink and fit your product and sturdy enough to protect it during handling, shipping, and shelf life. Having spent years observing various manufacturing settings, I can attest to the critical nature of film durability, especially in sectors like food, electronics, and pharmaceuticals, where even a minor compromise can lead to significant repercussions.

How Lack Of Durability Can Compromise Product Safety

A less durable film is susceptible to tears, punctures, or cracks, which could expose the product to external elements like moisture, dust, and contaminants. Consequently, you risk product spoilage, damage, or even legal issues related to compromised consumer safety. We&#;ve all heard the horror stories; don&#;t let your brand be the following cautionary tale.

Recommended Solutions

To address durability issues, consider these strategies:

• Material Selection: Opt for films made from high-quality resins. This will ensure the film has the necessary mechanical properties for optimal durability.
• Multi-layer Films: Consider using multi-layer films that combine the benefits of various materials to provide a robust and durable wrap.
• Handling Protocols: Ensure that your manufacturing and handling processes are designed to minimize stress on the film, which can otherwise lead to tears or ruptures.
• Quality Tests: Incorporate tests like puncture resistance and tensile strength into your quality control regimen.

3 Tips to Ensure Quality Shrink Film

1. Purchasing From Reliable Suppliers

One of the most straightforward ways to ensure you&#;re working with quality shrink film is to buy from reputable suppliers. Doing so dramatically decreases the likelihood of encountering any of the issues above. Based on years of interaction with various suppliers, I can vouch for the importance of checking certifications, reviews, and testing small batches before making a large-scale purchase. A reputable supplier is a cornerstone of quality control in any manufacturing setting.

2. Regular Quality Checks

Frequent quality checks at different stages of your manufacturing process are vital. It&#;s not just about checking the final product but also about verifying the quality of the shrink film before it even touches your product. I&#;ve seen operations turned around simply by implementing rigorous quality checks, which help in the early identification of problems and allow you to take corrective actions before they escalate.

3. Investing In High-Quality Materials And Machinery

Sometimes, the urge to cut costs can lead to poor decisions, like opting for cheaper materials or older machinery. However, I&#;ve noticed that investments in quality always yield long-term benefits. For example, high-quality shrink films and modern, well-maintained machines ensure consistency, durability, and fewer defects in the end product.

Manufacturers can mitigate the risks of poor-quality shrink film by focusing on these three areas. With the right supplier, regular quality checks, and an investment in top-notch materials and machinery, you&#;re well on your way to a smooth and efficient manufacturing process. Trust me, the initial investment will pay off manifold, not only in terms of product quality but also in brand reputation and consumer trust.

Conclusion

To sum it up, we&#;ve delved into the critical quality issues concerning shrink film, ranging from inadequate shrinkage and poor seal strength to uneven film thickness, lack of clarity, and insufficient durability. We also covered effective ways to circumvent these issues, such as sourcing from reliable suppliers, conducting regular quality checks, and investing in high-quality materials and machinery.

Addressing these quality issues isn&#;t just about avoiding production hiccups; it&#;s about building a brand that stands for quality and reliability. In my years of working closely with manufacturing processes, I&#;ve found that a commitment to quality isn&#;t just good practice&#;it. It&#;s essential for long-term success. A keen eye for detail and a proactive approach can save time and resources while helping to uphold your reputation in a competitive market.

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