The adhesion of our self adhesive labels depends on these four factors.
- The STRENGTH of the adhesive
- The length of TIME the label is stuck onto an item
- The TEMPERATURE the label is exposed to
- The type of SURFACE the label is stuck onto
Each of these four factors interact with each other, so each customer’s label application will be entirely unique. This is one of the main reasons that we offer a free sample service for all of our customers; getting a sample means that you can check that a particular label will work in the exact conditions you need it to.
There are many types of adhesive, which are manufactured with a specific range of desirable properties and characteristics in mind. One of the key characteristics of an adhesive is its permanency, i.e. whether it is designed to be a permanent or removable adhesive. Adhesives range from extremely strong permanent adhesives to very light removable adhesives, and each adhesive has its own unique level of initial tack and ultimate tack.
Tack refers to the “stickiness” of a material; the quality that allows immediate adhesion between two surfaces with a minimum of pressure and contact time, while the adhesive is in a fluid or semi-fluid state. Initial tack describes the strength of the bond that is created the moment a label is applied to a surface. After a label is applied the adhesive will harden and set; the strength of the bond between a label and a surface when an adhesive has fully set is known as the ultimate tack.
If you want a label that will create a strong, permanent bond with a surface, you will need an adhesive with excellent initial tack and excellent ultimate tack for long term adhesion. Alternatively, if you want a temporary label that is easy to remove when it is no longer needed, you will want an adhesive with low initial tack and low ultimate tack for short term adhesion.
All adhesives strengthen over time; when a label is first applied, the initial bond will strengthen until the adhesive sets into its ultimate adhesion. You should always allow labels time to set properly before testing the strength of the adhesive; many people will become tempted and try to peel up a corner of the label soon after it has been applied – some then believe that the adhesive is too weak for their purpose, when they simply haven’t allowed enough time for the adhesive to reach its ultimate tack.
This factor should also be considered when choosing removable labels or when considering purchasing labels that will be stored for future use. Removable adhesives are designed to have low initial and ultimate tack so that – when the label is no longer needed – the label will remove cleanly and easily from a surface. However, if a removable label is left for very extensive periods of time, the adhesive will eventually harden into a more permanent bond. Labels that are stored for extremely long periods of time may also begin to set before they can be used. To avoid this, labels should be stored in a cool, dry place out of direct sunlight and should be used within their recommended shelf life.
The temperatures an adhesive is exposed to can also have an impact.
- At the moment of application:
The reaction that takes place as an adhesive sets is influenced by temperature; a higher temperature will speed up the reaction, which means that labels applied at higher temperatures will usually have better adhesion than those applied at lower temperatures.
It should also be noted that extremely cold temperatures can also have an impact: the reaction may be slowed down, preventing a bond from forming properly, or the adhesive may solidify in extreme cold preventing any reaction – and therefore any adhesion – from taking place. This is why label products are supplied with a minimum application temperature – at lower temperatures, the adhesive simply won’t be able to function and the label won’t adhere to the item being labelled.
- During storage/use:
The temperatures that labels are exposed to during use and/or storage after they have been applied can also influence the adhesive bond; any extremes of heat or cold may interfere with an adhesive bond causing the bond to fail and leading to the label peeling up or falling off entirely.
Some surfaces are better suited to adhesives than others; the properties of the surface influence how well an adhesive is able to form a bond that is strong enough to hold a label in place on that surface. The most important factors are the texture of the surface, the shape of the surface, and the material the surface is made of.
- Texture: surfaces can have peaks and troughs of various depths, ranging from smooth, flat surfaces to rough, uneven ones. Adhesive bonds are most successful when there is a large surface area available for the adhesive to bond to. Labels on sheets tend to have adhesives that are in a semi-fluid state; this means that the adhesives have some ability to move into troughs in a surface, which means that the best bonds are created when a label is applied to a surface with some shallow troughs as this increases the surface area available between the label and the item being labelled.
If a surface has no troughs or if the troughs are too shallow, the adhesive has a smaller surface area available to adhere to. Similarly, if there are too many troughs or if the troughs are too deep, the adhesive will not be able to reach all of the available surface area before it sets.
- Shape: surfaces can be flat or shaped (e.g. curved). Adhesives will form stronger bonds on flat surfaces than on curved surfaces. This is because the adhesive has to fight against the “memory” of the material used to make the label; the memory of a material describes the quality that causes materials to try to return to their original shape when they are deformed (e.g. by bending or stretching the material). When a label is curved around a surface, the material will try to return to its original (flat) state; if the adhesive is not strong enough to overcome this force, then the label will simply peel away from the surface.
- Material: different materials have different properties which will influence how well an adhesive bonds with the surface of an object. Some of these properties have already been mentioned – such as the texture of the surface and the strength of the material’s memory. You should also remember to account for any treatments or coatings that a material has, which may interact with the adhesive or cause issues if the treatment or coating changes/disintegrates over time. This also explains why labels should always be applied to surfaces that are clean and dry; if, for example, a surface has droplets of water on it, the adhesive will not be able to reach the item itself and bond with it successfully because of the layer of water between them.
So, if you want to make sure that you pick the right adhesive for the job, the best thing to do is to Request A Sample and then test that sample in the EXACT CONDITIONS of the label application you have in mind.