When selecting a label material for your new product label, there are hundreds of different options and combinations to choose from. But, perhaps the most complex part of choosing a stock is the adhesive. Chemistry and the environment that the label or sticker will be applied to are a major part in selecting the exact adhesive a label should have. We’ll take a deep dive into everything that needs to be taken into account when selecting the exact adhesive your product needs.
The immediate holding power of a label upon contact with a substrate is known as Initial Tack. Varying from high to low Initial Tack, a label will, either grab a material quickly, or show very low levels of attractiveness to the applied surface and may even come clean off.
Secondly is the Ultimate Adhesion which is the maximum holding power that a label can achieve after given time to “dwell” or set in. While not necessarily related to Initial Tack, Ultimate Adhesion is somewhat affected by the stiffness or shear of the adhesive, the roughness of the substrate surface and the temperature of the environment. Something else that comes into effect is the shape of the substrate, meaning that if the applied material is too sharply curved and the label is too stiff some lift-off and prevent Ultimate Adhesion from occurring.
The Shear Resistance is basically the internal cohesive strength of an adhesive. A High-Shear adhesive (firm) isn’t likely to split under stress because of its strong internal bonds and also won’t be very likely to flow freely which could lead to low Initial Tack. Low-Shear adhesives, on the other hand, are soft, with a high chance to split apart under stress, and more likely to flow freely leading to a higher Initial Tack.
Temperature Resistance is exactly what it sounds like; an adhesives ability to maintain its bond given outstanding temperatures. Cold resistance is the ability to stay attached to a substrate in lower than room temperature conditions, for example this is valuable for use on foods that stay in refrigerators or freezers for extended periods of time. Heat resistance is useful in environments that are well above room temperature, say, in the engine of a vehicle.
Typically there are three different categories of adhesive: Hot-Melt, Solvent, and Emulsion. From that first category each type can be broken up to either rubber-based or acrylic (but not always) and then from those subcategories divided into permanent and removable. In the end, the chemical composition for each are very different and thus, very complex without proper knowledge of what each adhesive chemical combination will excel at.
Hot-Melts are entirely rubber-based adhesives based on Styrenic block copolymers (SBCs) with oils, plasticizers and tackifiers occasionally mixed in to improve performance. Usually Hot-Melts, as their name suggests, are applied to a substrate in a liquid or molten state and then cool down quickly to bond the two materials together. Think of glue guns used in school arts and crafts projects. Some advantages to using Hot-Melt is it’s high initial tack, water resistance and relative cost-efficiency in comparison to the other categories of adhesive. However, some of the downsides to it are it’s low heat resistance and low plasticizer resistance, also can be affected by over-exposure to UV light.
A Solvent based adhesive made either of rubber or acrylic glue or adhesion product available in the form of a liquid, usually based in water, oil or low-boiling gasoline. The idea behind a solvent based adhesive is that by putting the adhesive in a more malleable/spreadable substance will make it significantly easier to apply to a substrate. Some of the perks of using a Solvent based adhesive is it’s strong initial tack, significant adhesion on curved, uneven and rough substrates, and its resistance to water and cold temperatures. On the other hand, Solvents are very expensive, not very ecological and do not resist plasticizers very well.
An Emulsion adhesive is a rubber or acrylic polymer adhesive suspended in water. Commonly used for packaging, labeling and tapes, but also used in things like household glue or carpenter’s wood glue. Emulsions are typically ecologically friendly, resistant to aging, heat, and are known to be fast acting. Some disadvantages of Emulsion adhesives is its weak adhesion on non-polar substrates and it’s low resistance to water and cold temperatures.
Not normally categorized in the most popular types of adhesives, UV adhesives have seen a rise in recent years. UV adhesives are acrylic based and also very unique because of the process in which they’re cured; by light. A dual stage process creates performance advantages which make nearly instantaneous bonds with incredible strength. There are few downsides to UV adhesives, but they include expensive process and low initial tack.
There are tons of different kinds of chemical compounds that allow you to adhere nearly any two materials together in just about every kind of scenario imaginable. The trouble is figuring out what works best in your situation. A great old knight once said, “You must choose. But choose wisely.”