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.
Original patent title: “Tacky polymeric microspheres”
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. Granted to Minnesota Mining and Manufacturing Co in 1979 with 13 claims and 278 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
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.
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Post-it Notes
Scotch WallSafe Tape
Repositionable paper labels
Sticky flags and page markers
Why it matters
The bigger picture
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.
Filed
August 17, 1977
Granted
August 28, 1979
Market context
Who's building on this
Companies in this space
3M continues to dominate this technology space, but global adhesive manufacturers like Avery Dennison and Henkel have developed their own proprietary acrylic microsphere formulations for repositionable labels and protective films.
Market impact
This patent enabled the commercialization of the Post-it Note, creating a multi-billion dollar product category and establishing a new standard for pressure-sensitive, damage-free consumer adhesives.
Claim 1 — Plain English
What this patent covers
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.
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.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
9/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$90K – $288K
Midpoint $180K · expired or expiring · industry ×2.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
13 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Baker, W. A., & Ketola, W. D. (1979). The Sticky Microscopic Beads Behind Post-it Notes (U.S. Patent No. 4,166,152). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4166152/post-it-note-adhesive
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
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.
Same assignee
More from Minnesota Mining and Manufacturing Co
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