Shrink sleeve labelling is a popular alternative to adhesive labels and is commonly used for high graphic labelling, promotional bundles and tamper-evident sleeves. While it can be done manually, large-scale producers and packagers use shrink tunnels best suited for their products and purposes.
Electric hot air shrink tunnels are automated for improved efficiency and productivity. Most use steam or circulated hot air to shrink full- or half-sleeves, while others use infrared heat for localised shrinking. When properly designed, shrink tunnels provide a conformed, wrinkle-free end product.
The main components of a shrink tunnel are a heat source, blower, and conveyor system. Secomak’s market-leading industrial solutions in washing, drying and industrial heating for the Food & beverage industry. Secomak offers a variety of solutions for food and beverage companies and other industries that use heat-shrinking materials for branding, packaging, and presentation.
Decoding the Shrink Sleeve Label
Shrink sleeve labels entered the world of packaging in the mid-1960s in Japan and have gained popularity since because of their adaptability and other advantages. They’re typically made from a heat-sensitive plastic or polymer film that clings to a product when heated and adheres to it without glue.
Many industries use shrink-sleeve labels on their packaging for safety reasons. However, these labels offer the added benefit of increased branding area on the product and space for adding more product or ingredient information. The graphics are typically printed on a reverse-printed film inside the label to protect them from wear and tear.
So, where are shrink-sleeve labels commonly used? The most obvious examples include the following:
- The beverage industry,
- The food industry,
- Cosmetics and personal care,
- Industrial and chemical products, and
- For promotional and limited-edition products.
From Reel to Real: Sleeving Bottles
Getting shrink sleeves from a reel onto a bottle or can involves a shrink sleeve application process. While the process can be done manually for small-scale operations, larger-scale productions use automated machinery.
The Manual Sleeve-Shrinking Process
The manual shrink-sleeving process is as follows:
- Prepare The Shrink Sleeves Reel
After printing, the shrink sleeve reels must be stored properly to avoid damage or distortion. The reel must be unrolled before the sleeves are individually cut (if necessary).
- Prepare The Bottles Or Containers
Before the sleeves can be applied to the bottles, the bottles must be cleaned and thoroughly dried. If necessary, the bottles can be preheated to facilitate sleeve shrinkage.
- Slide The Sleeve Onto The Bottle
The sleeve must be carefully slid over the bottle, ensuring correct placement.
- Heat Application
Once the sleeve is in position, a heat source (e.g., a heat gun) is used to evenly apply heat to shrink the sleeve. It is essential to move the heat source around the bottle to ensure uniform shrinking, not overheating and damaging the sleeve or bottle. As heat is applied, the shrink sleeve begins to shrink and conform snugly to the shape of the bottle.
The heated bottle must be allowed to cool completely before being handled to help set the shrink sleeve in place securely.
- Inspect And Check
Once cooled, the bottle is examined to ensure the shrink sleeve is adequately conformed and free from wrinkles, bubbles, or other defects.
The Technology Behind Automated Shrink Sleeve Machinery
Shrink sleeve labelling machines automate the manual process above, speeding up production and minimising human error. Some systems use steam to shrink the sleeves, while others use hot air shrink tunnels. Below is a summary of the technology and process behind automated shrink sleeve machinery:
- Machine Setup
The shrink sleeve labelling machine must be set up correctly and calibrated according to the specific bottle and label size.
- Load The Reel
The machine contains an “unwind mandrel” that feeds the sleeves onto the bottles. The reel of shrink sleeves must be loaded onto the mandrel.
- Adjust The Conveyor
Shrink sleeve machinery typically uses a conveyor system to feed the bottles through the machine for processing. The conveyor’s speed and bottle spacing must be set to match production requirements.
- Bottle Feeder
Bottles are then fed into the machine’s labelling station using a conveyor, although other automated mechanisms are also used.
- Label Application
As each bottle moves through the labelling station, the shrink sleeve is automatically cut from the reel, applied to the bottle, and secured.
- Hot Air Shrink Tunnel
After the label application, bottles usually pass through a hot air shrink tunnel. These tunnels provide controlled heat for the uniform shrinking of the sleeves, improving the total shrink rate.
- Cooling Conveyor
Depending on the system, the bottles may pass through a cooling conveyor to ensure the shrink sleeves are cool and set properly.
- Quality Inspection
Once cooled, the bottles must be inspected for any labelling defects, wrinkles, or other issues as they exit the machine.
Ensuring a Smooth Finish: The Role of Heat
As with each process step, the heating process requires special consideration and planning. Automated setups like hot air shrink tunnels typically include a series of strategically placed nozzles that direct hot air evenly over the bottle simultaneously.
Even heating is essential for creating a smooth and professional-looking finish on the shrunken sleeve. For instance, the sleeve takes on the bottle shape, and the graphics appear as designed. In contrast, improper heating can result in distorted images, a deformed finish, bubbles, tears, or wrinkles. Such defects give a wrong impression and can make opening the bottle more challenging.
Electric Hot Air Tunnels vs. Steam Shrinking
A few variations of shrink tunnels are available, each with its benefits and limitations. The two more prevalent methods are electric hot air tunnels and steam tunnels. However, before we compare them, this is what they have in common:
- A heat source,
- A heat chamber, and
- A continuous conveyor that moves through the tunnel.
Electric Hot Air Tunnels
As the name suggests, these tunnels power the heaters and blowers with electricity. Three popular types of electric hot air tunnels include the following:
- Recirculating Shrink Tunnel
Recirculating shrink tunnels are arguably the most prevalent type of shrink tunnels. They work by circulating heat produced by heater coils, ensuring the heat is evenly distributed like a convection oven. The shrinking materials they use include Centrefold PVC and Polyolefin Shrink Wrap.
- Recirculating Bundle Shrink Tunnel
These shrink tunnels work on the same principle as recirculating shrink tunnels, except they are larger and can maintain higher temperatures without wearing the machine quickly. Bundle shrink tunnels are typically used for bundling beverages, and they contain additional fans outside the tunnel to speed up cooling and reduce heat-related injuries.
The thicker materials used for bundling are single-wound Polyethylene Bundling Film or Polypropylene.
- Infrared Shrink Tunnel
Infrared shrink tunnels differ from other tunnels as they do not use a blower to distribute the hot air. This is because these tunnels are used mainly for localised shrinking on bottles with heat-sensitive contents, e.g., where only the bottle cap and neck are heated.
As the bottle or rigid container moves through the tunnel, the heat from the strategically placed inner lamps warms the bottle cap or safety seal, causing it to shrink and conform to the bottle mouth. Usually, the materials used for this include PVC neck banding and shrink labels.
PETG-printed shrink sleeves are commonly used in steam tunnels. These tunnels create a sauna-type effect for bottles passing through on a conveyor. The steam heat allows for a total shrink rate, creating a uniform and neat finish. Then, the hot, wet bottles or cans pass through an industrial bottle dryer or can dryer to remove unwanted moisture on the packaging.
As effective as steam tunnels are, they are more expensive due to being made of stainless steel. Additionally, they have a larger footprint than other tunnels because they use more resources and have more waste.
Nailing the Process: Precision, Heat, and Outcome
Shrink tunnels must be designed to maximise efficiency and minimise waste while maintaining safety measures to prevent heat-related injuries. Part of the design’s efficiency includes the ideal placement of nozzles and blowers for even heat distribution, temperature regulation, and bottle-drying solutions.
When these are well designed and placed, the chances are better of achieving a wrinkle-free finish. However, suppose the nozzles and blowers aren’t optimally positioned, and heat regulation is problematic. In that case, there is an increased likelihood of irregularities like wrinkles and bubble formation, resulting in loss. Additionally, moisture on the packaging can cause damage or pose a safety risk.
Shrink-sleeving is an excellent means of showcasing and protecting a product, provided it’s done correctly. Secomak’s range of heaters, blowers, and air knives are ideally suited for shrink-sleeving and bottle-drying solutions as they can be tailored for many industrial applications requiring regulated hot air for bottle or can-drying solutions.
You can learn more about the products most commonly used in industrial bottle drying solutions by reading pertinent case studies where they’ve created solutions for their clients. Additionally, you can view their exceptional range of drying machines and other products and speak to one of their consultants for a solution.