A pressure-sensitive adhesive label peeling off a package.

Will Your Label Stick? A Guide to Choosing the Best Commercial Label Adhesive

One of the biggest advantages of pressure-sensitive label application is the choice of labels. By choosing different materials for each layer, you can create a custom solution that fits your product’s lifestyle, from application to recycling. This includes label adhesives, which are available in many forms, from easy peel to tamper-resistant. How do you choose the right label adhesive? Several factors are at play, including container shapes and environmental conditions such as temperature and exposure to light.

What is Pressure Sensitive Adhesive?

The adhesives used on pressure-sensitive labels are somewhere between liquid and solid. When a label is applied to a container, the adhesive flows onto the container’s surface. Once in place, the adhesive hardens, locking in its shape. Unlike structural adhesives, which need to change chemically to form a bond, pressure-sensitive label adhesives are already close to their maximum strength directly after application.

Types of Adhesive Labels

Adhesives used for label applications can be permanent, repositionable, or removable. Permanent adhesives cure quickly. Repositionable labels have a longer cure time, allowing them to be peeled off and reapplied shortly after application. Removable labels peel off easily, while reclosable adhesives are removable adhesives that maintain their ability to wet out after repeated applications.

How Does the Adhesive Coating Affect Label Application?

Four main factors control how well the label attaches to the container during installation.

1. Initial Tack

Initial tack is the initial attraction between the adhesive and the application surface. A high initial tack requires less pressure to get the adhesive to bond to the container.

2. Wetting

Wetting is the adhesive’s ability to spread out. As the adhesive wets out, it spreads across the surface, filling in surface imperfections to create a strong bond.

3. Adhesion

Adhesion is the strength of the bond between the adhesive and the application surface. High-quality adhesives used for permanent labels make it impossible to remove without destroying the label. Low-adhesive materials peel easily and don’t leave surface residue. Your choice needs to balance durability with the needs of the end user. For example, when labeling plastic containers, it’s important to choose an adhesive that releases during the recycling process.

4. Application Temperature

When label adhesives are used outside their temperature range, they don’t form a strong bond with the surface. High temperatures increase flow and prevent chemical bonds from forming, weakening the adhesive performance. Cold temperatures make the adhesive hard and brittle, keeping it from wetting out properly. Most adhesives can withstand the surface of hot-fill products, so manufacturers only quote minimum application temperatures.

What Are the Performance Factors for These Types of Labels?

Getting label materials onto your containers is just the start. Once they’re in place, they need to survive the entire life cycle of the product, whether it’s a shipping label that will see days of use or a chemical label that must survive years of weather exposure. These five factors are the biggest influence on the performance of label adhesives:

1. Ultimate Adhesion:

Ultimate adhesion measures the strength of the bond after the adhesive is fully cured. During curing, the adhesive crystallizes, locking in its shape to the container. This takes anywhere from a couple of hours to a full day, depending on the formula and storage conditions.

2. Shear:

Shear is the amount of force it takes to move the label parallel to its surface. This is important for labels on surfaces that come into contact with other objects, like drink bottles rubbing against a carton.

Shear strength is higher in adhesives that flow easily, increasing contact with the container surface. However, this increased wetting usually decreases the initial tack.

3. Mandrel hold:

Mandrel hold measures the adhesive’s flexibility. Adhesives with a high mandrel hold have no problem attaching to uneven surfaces. On round containers, this helps the label resist flagging. It also helps the label withstand surface changes on flexible containers.

4. Service temperature:

Service temperature is the temperature that the adhesive can handle while still maintaining the bond between the label and the container. Low temperatures can turn some adhesives brittle, breaking this bond. High temperatures can break down chemical bonds, letting the label slide or peel off the container.

5. UV resistance:

Ultraviolet light isn’t just a danger to label inks; it also breaks down some adhesives. UV-resistant adhesives are important for products that get sun exposure. It’s also important to consider if UV light is used in your label manufacturing process. The printing systems used by our print-and-apply labelers don’t use UV light, but your label supplier may use it to cure ink after printing.

Labeling Problems That Only Appear to be Adhesive Issues

If your labels aren’t sticking to your containers, the problem may not be the adhesive; several common issues cause problems applying and keeping labels on products.

Most “flat” containers aren’t actually flat. Plastic and glass containers have a slight taper to help them release from molds. Thin plastic containers bulge when filled, and small manufacturing defects are common on cheap glass bottles. Fortunately, our labeling machines can be calibrated to adjust for these issues, preventing flagging and skew.

Surface energy is a measure of how good a label material is at letting an adhesive wet out. Polystyrene, polyethylene, polypropylene, and TPO are low-energy materials, which makes it hard to get adhesives to stick to them. There aren’t adhesives that can overcome this problem, but surface energy can be increased by either heat treating the materials’ surface or by applying a primer. Make sure your container supplier knows you’re using pressure-sensitive labels so they can recommend compatible materials.

Moisture prevents most general-purpose adhesives from wetting out on the container’s surface. There are moisture-resistant adhesives, but it’s usually easier to fix the problem by removing moisture before application.

When you were in school, you might have seen a science demonstration where a balloon picks up small pieces of paper using static electricity. That same effect can cause the label and container to attract or repel each other. This reduces the pressure the applicator exerts on the label and can cause the label to slide, resulting in skewing and flagging. This often becomes a problem in winter, as the air doesn’t have enough moisture to discharge electricity before containers reach the applicator.

Food-safe plastics are semi-permeable, allowing them to off gas in storage. The gasses that leach through the plastic form bubbles underneath the label, peeling it away from the container. Switching to a permeable label addresses allows these gasses to pass through without interrupting the adhesive bond.

We Have the Right Equipment for Whatever You’re Labeling

Now that you know the ins and outs of label adhesives, you can choose the right label for your product. CTM Labeling Systems carries a wide range of labeling equipment to fit nearly any label needs. If you’re looking for a better way to label your products, give us a call so we can get you in touch with your local distributor. They’ll work with you to find the perfect labeling solution for your production system.