Repositionable Microsphere Adhesive

In 1968 Spencer Silver at 3M, trying to make a very strong adhesive, made the opposite: an acrylate that formed tiny tacky spheres and held only lightly. For years it had no product. In 1974 his colleague Art Fry coated it on bookmarks for his church hymnal so they would stay put without tearing the pages; the sticky note reached shops in 1980. **US 3,691,140**, "Acrylate copolymer microspheres", Silver, filed 9. March 1970, granted 12. September 1972: "inherently tacky", elastomeric microspheres of an acrylate ester such as iso-octyl acrylate with a small share of an ionic monomer. **You measure what makes it different from tape**: the peel force over twenty re-sticks, side by side with masking tape, and the spheres themselves under a microscope.