Choosing the right pressure-sensitive adhesive for cold food packaging applications
The adhesive itself plays a huge role in the success of the finished product. However, not all adhesives are created equal.
As the cold food industry continues to experience increased growth and opportunity, cold food packaging is following suit. New cold food packaging trends are continually emerging—with the most recent and biggest being packaging that improves the quality, health and integrity of cold food products.
For cold food manufacturers, one of the key components in ensuring improved product packaging is producing packaging labels that are visually appealing, stick on easily and adhere as intended for the duration of the product’s life cycle.
While packaging labels consist of three core components—substrate, adhesive and liner—the adhesive itself, though not necessarily visible or exciting, plays a huge role in the success of the finished product. However, not all adhesives are created equal.
A brief overview
Pressure-sensitive adhesives (PSAs) are available in permanent, removable or repositionable form and can vary in composition. Some contain solvents while others may be produced using solvent-free processes such as UV curing or hot melting.
In general, there are two common types of PSA systems—rubber and acrylic. Each system has its own unique benefits. For example, rubber-based adhesives deliver excellent initial tack and good adhesion to low-energy substrates. Rubber-based adhesives also provide excellent water resistance and can be suitable for direct food contact applications. Acrylic adhesives offer a broad service temperature range, long shelf life and flexibility for wrapping small diameter cylinders or tubes.
When it comes to PSAs, there isn’t one standard that will deliver the same performance for every package labeling application every time. For optimal results in the cold food packaging market, food manufacturers and/or their contract packagers should select a PSA that is designed to meet the needs of the specific application.
Consider product life cycle and subjective conditions
To begin, cold food manufacturers need to think about the packaged product’s life cycle. Answer questions like: What packaging type will work best for the label? Where is the label being placed? What will happen to it once applied? How long does it need to stay there?
Once these questions are answered, the best way to predict future adhesive success is to consider three general categories of conditions that could further affect performance—surface, environment and application.
Surface conditions. With surface conditions, the focus is on the actual substrate. How rough or smooth is the substrate? Is it flat or curved? Is surface energy high or low? Are there any surface contaminate concerns? For example, in the cold food industry, water is often considered a surface contaminate as it can affect how well a pressure-sensitive label bonds to its application surface.
There are various ways to test or measure how surface conditions can affect adhesive performance.
· Initial tack is used to define how quickly a bond is formed between adhesive and surface. If initial tack is high, adhesion to the surface will be high.
· Peel strength determines the strength of adhesive bond to the surface by measuring the force needed to break the bond using standard parameters like peel angle or direction, application pressure and time of bond.
· Shear resistance shows the durability of adhesive bond. A high-shear adhesive is firmer and doesn’t flow into a surface as well, equating to lower initial tack, but making it less likely to split if stressed.
Additionally, determining adhesive mandrel hold helps depict how well the adhesive will hold up on a curved surface.
Environmental conditions. These conditions refer to potential label exposure, like UV light, humidity, the presence of solvents and chemicals in the environment or temperature extremes.
Take, for example, grocery store items, like meat or cheese, moving from one location to another, such as a consumer’s cold refrigerator to their warm car. These temperature changes can cause condensation, thus increasing the chances of labels falling off or lifting up on the label’s edge.
Application conditions. These conditions can affect how the label is applied. Is application by machine or hand? Is sufficient bonding pressure being used? Is pressure applied evenly over the entire label surface? How long is pressure being applied? What is the temperature and humidity during application?
For example, most PSAs take longer to bond in cold temperature conditions. By evaluating adhesive “cold flow,” one can look at the adhesive’s ability to bond to a container at below normal temperatures. This is another area where tack and peel are important.
Match adhesive to application
Before making a final decision, food manufacturers or co-packers should delve into the specifics of the end application to best pair adhesive with application. Does the application call for an all-temperature, cold temperature, freezer-grade, or direct food contact adhesive?
Cold temperature adhesives, for example, can work in temperatures as low as -20°F. However, when an adhesive isn’t designed for cold temperatures, it will stiffen and lose its strength as temperatures decrease.
Another factor to consider is if the application requires a no label look. This is becoming increasingly popular for sauces and condiment applications, calling for a clear adhesive and label that allows a consumer to see the actual product through the glass bottle or plastic container. Anything other than a clear, non-water, whitening adhesive could result in a cloudy or milky white label if the label is exposed to water or moisture.
And, what about manufacturers using high-pressure processing (HPP)? With HPP, the labeled product is submerged in water that is roughly 35°F in a pressure vessel. The pressure is raised to an extreme level, about 75,000 psi, for a few minutes and upon removal, the label is dripping wet. In this scenario, successful adhesion requires a film packaging label with a rubber-based, hot-melt adhesive.
With the vastness and continual evolution of cold food packaging applications, today’s food manufacturers and co-packers should work closely with their PSA suppliers for guidance and support when choosing the best adhesive for their application.