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Pressure Sensitive Label Adhesives

The label adhesive is a tacky layer generally found on the reverse side of the label, that is capable of bonding to another surface when pressure is applied. There are several families of adhesives available; selecting the correct adhesive is largely dependant on the surface the label is to be applied to as well as the environmental conditions it will be exposed to.

Pressure Sensitive Adhesive Families

Rubber	Economical, short-term adhesive with good initial bond, suitable for indoor use. Rubber pressure sensitive adhesives have minimal chemical, heat and UV resistance and break down over an extended period of time.
Acrylic	Extremely stable bond that strengthens over time (see diagram below) and works well with most surfaces. Acrylic pressure sensitive adhesives have exceptional chemical, heat and UV resistance and are suitable for both indoor and outdoor use.
Silicone	Exceptional stability through a wide range of temperatures with excellent ozone and oxidation resistance. While less economical, silicone pressure sensitive adhesives are recommended for high temperature and cryogenic applications for exceptional reliability.

Acrylic Adhesion Cycle

Pressure Sensitive Label Adhesive Stress Properties

It is important to consider the stress level a label may be exposed to when choosing an adhesive.

Tensile Strength	equal stress is applied across the adhesive layer pulling the label straight and away
Shear	equal stress is applied across the adhesive layer in a parallel direction in a sliding motion
Cleavage	prying stress is applied to one edge of the label up and away from substrate
Peel	stress is applied along a thin line of the adhesive causing label to curl away from substrate (generally a curved or flexible surface)

Adhesive Stress Diagram

Pressure Sensitive Label Adhesion Strength

Adhesives are available in a range of adhesion strengths. In some cases a temporary or repositionable bond may be optimal for a particular application, while others may require an aggressive, long term solution.

Permanent	Typically not designed to be removed without tearing the stock or using solvents. The adhesion strength and speed can also be varied. For example, full adhesion can be nearly instant, or the label can be almost removable for a short period with full adhesion developing in minutes or hours. This is considered the most popular and cheapest option by many self adhesive paper manufacturers.
Semi-permanent (aka repositionable)	Adhesion strengthens fully after application (approx 48-72 hours), allowing the label to be removed easily if placed incorrectly and still be a permanent label.
Removable	Adhesion is fairly strong and will not fall off in normal circumstances, but the label can be removed relatively easily without tearing the base stock or leaving adhesive behind on the old surface. The adhesive is usually strong enough to be applied again elsewhere.
Ultra-removable	Adhesive allows a label to be removed from a surface without leaving any residue or causing any damage. The label can then be reapplied in another area and is not limited to the number of times it can be repositioned. Ultra-removable and repositionable adhesives do not gain permanency over time.
Freezer permanent	Special type of adhesive that remains fully permanent in extremely low temperatures. This is useful for labeling objects that are to be stored in a freezer for any length of time.
Tamper evident	Special types of label constructions that leave evidence when a label has been tampered with. Below are a few examples of tamper-evident constructions: Destructible Label - The material is weaker than the adhesive, causing the material to break into tiny pieces (Frangible) when lifted. Void Patterned Adhesive - A clear material with both a permanent and a removable adhesive applied in a text or image pattern leaving a visible pattern when lifted.

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