Even though the adhesive part of a pressure sensitive label is not seen, it can make or break your packaging presentation on the retail shelf. It doesn't matter how gorgeous your label design is, or how unique your container is – if your labels are wrinkling, peeling, or sliding off, your packaging is going to look bad.
Why Are There So Many Label Adhesive Choices?
Pressure sensitive adhesive is the unsung hero of the overall label package. You may not have given it much thought, but your label printer should be asking a lot of questions before producing your labels to determine which adhesive is right for your particular labels. That includes the type of containers to be used, the contents of those containers, and the environmental conditions your labels will be exposed to.
Pressure sensitive adhesives can be affected by warm or cool temperatures, moisture and humidity, the surface of the container they are applied to during normal use, and simply by rubbing against each other during shipping or storage.
With that in mind, we're going to break down the different types of adhesives and demystify some label adhesive terms.
What is a Pressure Sensitive Label?
A pressure sensitive label is one that is applied using only pressure. No heat, glue, or solvents are required. The most basic construction of a pressure sensitive label roll includes:
- The liner, or backing material. Most commonly a white or brown ("kraft") paper which is coated to allow your sticky labels to be easily removed from the roll.
- The adhesive. This is the sticky part we're talking about here. Some adhesives are stronger than others, and some even allow labels to be removed and reapplied repeatedly.
- The facestock (or substrate). This is the part of the label that is printed on and seen by your customers. The most common label material for facestock are paper, film, or foil.
For a more in-depth look at label construction, visit The Label Learning Hub on the Advanced Labels NW website.
Okay, Labels Need to Be Sticky, How Complicated Can That Be?
As we pointed out above, it's a big deal if the pressure sensitive adhesive on your labels fails. Label material suppliers have developed a wide variety of pressure sensitive label adhesives to meet the needs of brand owners for every industry and application.
There are different adhesives available for glass, plastic, and metal. Adhesives that work with flexible containers like squeezable tubes. Adhesives for labels that need to be easily removed, and adhesives for labels that you never want removed. Some adhesives work better than others on rough textured surfaces. There are also FDA guidelines for adhesives when used with certain food packaging.
It's also worth noting that not all adhesives are compatible with all substrates. If you have a label application that requires a certain adhesive, your label printer can recommend an appropriate facestock.
It is always best to test your label material and adhesive performance when creating a new product or changing containers or application types.
Common Label Adhesive Properties Explained
Ready to get technical? Here are some universal attributes of pressure sensitive label adhesives. Some of these will apply to your products, while others may not:
Minimum application temperature. Have you ever applied labels during cold winter months, or in a cold warehouse environment? Not all adhesives are created equal, and if you're not using one specifically designed for cold temperature application it can lose its pliability and become stiff (called crystallization), causing the adhesive to weaken the colder it is in your application space. The majority of adhesives are designed with a minimum application temperature between 40 to 50° Fahrenheit (4.4 to 10° Celsius). Special cold temp adhesives are available that will maintain their integrity during application in below freezing temps as low as -20° F (-28.9° C).
Service temperature. The range of temperatures your labels can withstand after being applied and the adhesive has been allowed to completely set (see "Ultimate adhesion" below). So for example, if you applied a common pressure sensitive label in the recommended temp range of 40 to 50° F and let them set up for 24 hours, your labels would keep their optimum adhesive strength in temps ranging all the way from -65 to 200° F (-54 to 93° C) with a paper facestock, and as high as 300° F (148.9° C) with a film facestock.
Cold flow. We're still talking about temperature... it must be important! Cold flow is an indication of how well an adhesive will adhere or bond to your containers when exposed to colder temperatures. The flow part of cold flow is a reference to the adhesive "flowing" over the surface of the container. If your application room is cold, if your containers are going to be cold during label application, or if they will remain in a cold environment during the time needed for the adhesive to fully set, you will likely need a cold temp or all temp label adhesive.
Initial tack. How hard the pressure sensitive adhesive immediately grabs the surface it is applied to. Low initial tack means you would be able to cleanly remove and reposition the label, because the adhesive is designed to get stronger over time. This makes a label with low initial tack repositionable but it does not mean it is removable like a coupon label – the adhesive will strengthen and reach ultimate adhesion typically between 24-48 hours. High initial tack means the adhesion will happen instantly and the label will bond with the container securely as soon as it is applied.
Ultimate adhesion. Under optimum conditions, this is the highest holding power a label can achieve when it bonds with a surface. Pressure sensitive labels will achieve ultimate adhesion if they are applied in the appropriate temperature range and allowed to set up or "rest" undisturbed for a designated time. How long? It depends on things like environmental conditions and texture of the surface being labeled, but typically between 24 to 48 hours. You may also hear this referred to as "dwell time".
Mandrel hold. Only relevant when applying pressure sensitive labels to curved containers like bottles, or any time a container requires your labels be applied to a tight radius surface. When a label is applied to curved containers it will try to "flag". Flagging is the term used to describe the multiple little bubbles or lifting along the edges of the label. With a good mandrel hold you should not have any flagging. The exception is when your label is too large for the bottle or container at the point of a curve or taper. No degree of mandrel hold will prevent flagging if your labels were not properly engineered for curves or tapers.
Shear resistance. This is important for containers that may flex or move beneath a label, like a squeezable tube. Think of label adhesives that have low shear as being "softer". They are more capable of flowing across the surface they are applied to. They will also have greater initial tack. Low shear labels are vulnerable to strain and stress and can break apart. On the other hand, high shear adhesives are more rigid, so they do not flow over the labeled surface as well. With high shear adhesives the initial tack is lower and they are less susceptible to cracking and tearing under stress.
Solvent resistance. When the label adhesive gets wet, will it lose adhesion? How well can the adhesive resist solvents like alcohol, plasticizers, petrochemicals, and the universal solvent: water? You may need a solvent resistant adhesive if your product can spill out or come into contact with your labels, or if water or any other solvents are going to get on your labels. While a top coating like varnish and laminate can protect the facestock, adhesive will still be vulnerable at the labels edge.
Adhesive properties are just one more reason we encourage careful planning of your label production. New or last minute rush projects are especially vulnerable to label failure, when communication between brand owners and label printers can break down. Testing blank label stock and adhesives will take much of the guesswork out of your packaging. Providing your label printer with a sample of your container is also a good idea. Remember to provide as much information as possible about your products, containers, and the conditions your labels need to stand up to.