A type of pressure sensitive adhesive that is used to create repositionable labels; these adhesives are emulsion-based systems where the particles of the adhesive components are larger than those of the emulsion components (the liquid vehicle or carrier throughout which the adhesive components are dispersed). In a standard emulsion-based adhesive, the particles of the adhesive components and emulsion components are more equal in size, which gives the adhesive a continuous surface and creates stronger initial and ultimate adhesion (as there is a larger surface area over which the adhesive bond can form). Microsphere adhesives, however, have larger particles of adhesive components, which breaks up the continuity of the surface of the adhesive (only the adhesive components are in contact with the substrate) and creates lower initial and ultimate adhesion (as there is a smaller surface area over which the adhesive bond can form and only some of the adhesive particles are in contact with the substrate during an application – meaning other particles of adhesive may be in contact with the substrate when it is reapplied).
Repositionable labels require a careful balance between the amount of adhesive and emulsion components to ensure that the adhesion created by the adhesive will allow a label to be held firmly in place AND to remove cleanly from a substrate AND to be reapplied (over and over again). The size of the microspheres can also be adjusted (microspheres are usually between 1-1000 microns, those in adhesives are usually between 10-250 microns) to control the level of tack and repositionability so that microsphere adhesives can be purposefully made to suit a wider variety of substrates and surface types (including paper, wood, metal, ceramics, painted surfaces, and glass etc) or to suit specific label applications.
Microsphere adhesives have a number of other properties that make them useful for specific materials or applications; they offer excellent resistance to heat and UV light, are acid-free (so they won’t damage delicate substrates, such as photographs, over long periods of time), can be screen printed (allowing them to be used to create skins and wraps for phones, tablets, and laptops), and some meet FDA standards for indirect food contact (allowing them to be used to create resealable food packaging). They are commonly used to create repositionable post-it notes, shelf edge labels, skins for electronic devices, arts and crafts labels, and expanded or extended content labels (which can be lifted to reveal additional product information before being resealed for future use).