Pressure-sensitive adhesive (PSA) tapes are everyday marvels. The unique viscoelastic properties of PSA tapes provide a balance of strength and flexibility, enabling them to bond materials securely while remaining adaptable enough for repositioning or clean removal. These benefits can make it somewhat of a shock when tape fails.
As a distributor, your clients come to you for answers and recommendations. Knowing the root causes of tape failure (and, more importantly, how to fix them) can position you not just as a business partner but as a trusted advisor.
Tape failures can occur for many reasons. It can be difficult to identify a single cause of adhesion failure. However, knowing potential failure vectors can help you prevent and remediate them, as well as counsel your clients on how to avoid them. A basic understanding of adhesive vs cohesive failure causes will mitigate the potential for problems before they occur.
Types of adhesion failures
When PSA tape fails, it can be categorized by one of three different adhesion failures:
- Adhesive failure: Occurs when the tape separates from the substrate with the adhesive still intact, also known as delamination.
- Cohesive failure: Cohesion is how well the adhesive binds to itself. When cohesion fails, it is because the adhesive no longer adheres to itself rather than the substrate.
- Substrate failure: This occurs when the substrate breaks while the adhesive remains strong. In packaging, this is commonly known as a fiber tear, when the tape backing or a cardboard box substrate rips. Substrate failure is a type of cohesive failure in which the substrate ceases to bond to itself.
How can you tell these three failures apart? In an adhesive failure, the adhesive remains on one substrate but not both (most commonly on the tape backing rather than the bonded substrate). In a cohesive failure, adhesive residue will be present on both sides of the bond. Substrate failures are apparent when the tape or the bonding surface is damaged.
One way to visualize the relationship between cohesive vs adhesive failures is molasses. Molasses is sticky, which signals high adhesion. But when you pour it out of the jar onto toast, for example, it spreads, indicating relatively low cohesion. With candle wax, the opposite is true–high cohesion, low adhesion–because it sticks to itself and does not adhere well to other substances.
Environmental factors
Adhesion failures do not happen in a vacuum. Various environmental factors can affect the success of the bond:
- Surface characteristics: Rough surfaces require thicker adhesives and extended dwell times for flow, while contoured surfaces need softer, thicker tapes. High-surface-energy materials (e.g., glass) bond more easily than low-energy substrates like polypropylene.
- Environmental degradation: UV light, moisture, and chemical exposure can compromise tape integrity. Solvents can cause swelling or dissolution, while plasticizers in substrates may impair adhesion.
- Temperature extremes: Low temperatures increase brittleness and decrease wet-ability by reducing polymer flexibility. Conversely, high temperatures soften adhesives, potentially causing flow or creep.
- Stress and shock: Rapid stress application prevents polymer chains from reacting, leading to sudden failure (see the next section).
- Other common failure triggers: Potential adhesive failures are often driven by low application temperatures, low-surface-energy substrates, improper surface preparation, and harsh environmental conditions.
Other stressors
Load is a key stressor. When a load is static, it means force or weight is applied constantly in one direction. Imagine taping a five-pound dumbbell on a string to the corner of a kitchen table. The load is static; it does not change.
A dynamic load changes in intensity or direction. If we removed the dumbbell from our string taped to the kitchen table and instead pulled on it in different directions for different lengths of time, that would make the load dynamic.
Four other stress types are common in PSA applications:
- Tensile stress: Force distributed equally over the entire joint, perpendicular to the bond. Measured in pounds per inch of tape.
- Shear stress: Lateral force directed across the adhesive, forcing substrates to slide over one another; distributed across the entire bond area.
- Peel stress: Force concentrated at one edge of the bond where one substrate is flexible.
- Cleavage stress: Prying force at one end of the bond; similar to peel, but both substrates are rigid.
When choosing a tape for a particular application, you need to factor in tensile strength, as well as shear, peel, and cleavage resistance to help ensure a lasting bond.
The role of proper application
“User error” is a common scapegoat in the adhesive world. However, application mistakes are more common than most packaging teams would like to admit. Proper training is crucial to ensure the correct tape is applied the right way:
- Ensure the substrate is clean and, if necessary, treated with primer.
- Apply the proper tension and pressure when placing the tape on the substrate.
- Use tape guns or other applicators to help achieve a smooth seal with no air pockets.
- Allow enough time for the tape to bond fully and for the adhesive to “wet” out onto the substrate.
Also read: Pallet Strapping Tapes: Load Control in Industrial Packaging
Troubleshooting an adhesion failure: Adhesive vs cohesive vs substrate
First, determine the type of failure you are dealing with. Examine where the adhesive residue is found, either on the tape (adhesive failure), on both tape and substrate (cohesive failure), or if the adhesive is intact, where the substrate is damaged.
After this, determine what kind of forces are acting on the tape, static or dynamic, as well as tensile, shear, peel, or cleavage stresses. Next, identify environmental factors acting on the tape: UV, extreme temperatures, humidity, or chemical exposures. Lastly, drill down and review the application process to rule out user error.
Armed with this information, you should be able to pinpoint the problem. Sometimes the wrong tape is used with the wrong substrate, due to environmental factors, or with the wrong tension profile. At other times, a simple application error can lead to a costly mistake.
Expert guidance for your toughest bonding challenges
Understanding the difference between adhesive versus cohesive failure is only the first step; selecting the right solution for your specific application is where true performance happens. At Adherex, we take the guesswork out of tape selection.
Our in-house specialists evaluate your complete application—from material energy and environmental exposure to static vs. dynamic stress profiles—to recommend a product that delivers long-term reliability. Let us leverage our experience to secure your success. Get in touch to learn more about tape failure and help guide your clients in avoiding it.
