# The Sticky Microscopic Beads Behind Post-it Notes > 3M's 1977 patent on tiny, naturally sticky plastic beads that can stick to a surface, peel off easily without leaving residue, and be reused over and over again. - **Patent:** US 4166152 - **Original title:** Tacky polymeric microspheres - **Owner:** Minnesota Mining and Manufacturing Co - **Granted:** 1979 - **Status:** Public domain (expired) - **Times cited:** 278 - **Field:** materials ## What it does This patent describes microscopic, rubbery polymer spheres (microspheres) made from acrylate or methacrylate chemicals. These spheres are designed to be 'infusible' (they won't melt) and 'solvent-insoluble' (they won't dissolve), but they can be suspended in a liquid to be coated onto paper. Because they have a glass transition temperature below -20 degrees Celsius, they remain soft and sticky at room temperature. When coated onto a substrate like paper, these tiny spheres act as pressure-sensitive adhesive dots. Because they are spheres, they only touch a wall or desk at tiny contact points, creating a light bond that can be easily peeled off and restuck without leaving sticky residue behind. ## What it does NOT cover - Does not cover adhesives made of continuous, flat polymer films instead of discrete microspheres. - Does not cover microspheres made using non-ionic emulsifiers or ionic emulsifiers below their critical micelle concentration. - Does not cover microspheres with a glass transition temperature above -20 degrees Celsius, which would be rigid and non-tacky at room temperature. - Does not cover microspheres that dissolve completely in organic solvents. ## The clever bit Instead of making a flat sheet of glue, the inventors created microscopic, rubbery balls that only touch surfaces at their curved edges. This limited surface contact creates a weak physical bond that is strong enough to hold paper to a wall, but weak enough to peel away cleanly without tearing the paper. ## Real-world examples 1. Post-it Notes 2. Scotch WallSafe Tape 3. Repositionable paper labels 4. Sticky flags and page markers ## Why it matters This chemical process solved a major manufacturing hurdle for 3M, allowing them to reliably produce the low-tack, repositionable adhesive used on Post-it Notes. While Spencer Silver famously discovered the first sticky microspheres, this patent refined the suspension polymerization process to make the beads highly stable and commercially viable, securing 3M's dominance in the office supply market. ## Frequently asked questions ### What does The Sticky Microscopic Beads Behind Post-it Notes cover? 3M's 1977 patent on tiny, naturally sticky plastic beads that can stick to a surface, peel off easily without leaving residue, and be reused over and over again. ### Who owns patent US 4166152? Minnesota Mining and Manufacturing Co owns this patent, granted in 1979. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 4166152 cited by? This patent has been cited by 278 later patents that build on its ideas. ### What problem does this patent solve? This chemical process solved a major manufacturing hurdle for 3M, allowing them to reliably produce the low-tack, repositionable adhesive used on Post-it Notes. While Spencer Silver famously discovered the first sticky microspheres, this patent refined the suspension polymerization process to make the beads highly stable and commercially viable, securing 3M's dominance in the office supply market. ### What does this patent NOT cover? Does not cover adhesives made of continuous, flat polymer films instead of discrete microspheres. **Full plain-English explainer:** https://patentbrief.org/patent/us/4166152/post-it-note-adhesive **Original patent:** https://patents.google.com/patent/US4166152 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [Sticky, Tiny Plastic Balls Made from Acrylates](https://patentbrief.org/patent/us/3691140/post-it-repositionable-adhesive) — This 1972 patent describes how to make tiny, sticky, and durable plastic balls (microspheres) using a specific mix of acrylate chemicals and a special water-based process. - [How Richard Drew Invented Modern Transparent Adhesive Tape](https://patentbrief.org/patent/us/1760820/scotch-tape-adhesive-drew) — The 1930 patent for the first pressure-sensitive adhesive tape, which replaced messy glues and paper tapes with a convenient, clear, and sticky strip. - [How to Make Pill Coatings That Keep Medicine Stable Over Time](https://patentbrief.org/patent/us/5639476/nicoderm-nicotine-patch) — A method for coating pills with a specific plasticized acrylic polymer that ensures the medicine releases at a steady, predictable rate, even after sitting on a shelf for months. - [How to Make Durable Non-Slip Surfaces Using Electron Beam Curing](https://patentbrief.org/patent/us/5401560/polymer-backed-material-with-non-slip-surface-using-e-beam-cured-urethane-binder) — A method for creating flexible, non-slip materials by bonding mineral grit to plastic sheets using a special radiation-cured glue that stays strong even when stretched. - [Tiny Capsules for Electronic Paper Displays](https://patentbrief.org/patent/us/5961804/e-ink-electronic-paper-display) — MIT's 1999 patent on a special ink made of tiny capsules that can change color when an electric field is applied, forming the basis for early e-readers.