Sticky, Tiny Plastic Balls Made from Acrylates
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.
Original patent title: “Acrylate copolymer microspheres”
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. Granted to Individual in 1972 with 18 claims and 382 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent details the creation of microscopic, solid balls, called microspheres, that are inherently sticky and can be dispersed in solvents but don't dissolve in them. They are made from a blend of acrylate esters (like iso-octyl acrylate) and a small amount of another chemical, either an ionic monomer or maleic anhydride. The process involves suspending these ingredients in water and using a specific amount of emulsifier, a substance that helps mix oil and water, to create the microspheres. The resulting tiny balls are described as infusible, meaning they can't be melted down, and elastomeric, meaning they can stretch and return to their original shape.
The gap
What does this patent NOT cover?
- Microspheres made from monomers other than alkyl acrylates and specific ionic monomers or maleic anhydride.
- Microspheres that are soluble in organic solvents.
- Microspheres created using polymerization processes that don't involve an aqueous suspension.
- Microspheres made with emulsifier amounts below the critical micelle concentration.
- Microspheres that are not inherently tacky or elastomeric.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The key innovation was creating microspheres that were simultaneously sticky yet removable, and stable in solvents, by precisely controlling the ratio of acrylate monomers to a small percentage of ionic or maleic anhydride monomers and using a specific aqueous suspension polymerization technique.
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
3M Post-it Notes
Repositionable adhesives
Specialty coatings
Why it matters
The bigger picture
These microspheres, particularly those with inherent tackiness, became foundational for the development of Post-it Notes by 3M. The unique combination of stickiness without permanent adhesion allowed for repositionable notes, a significant innovation in office supplies and organization.
Filed
March 9, 1970
Granted
September 12, 1972
Market context
Who's building on this
Companies in this space
3M, the original assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →'s spin-off, continues to be a major player in adhesive technologies. Many companies involved in specialty polymers and adhesives likely build upon the foundational principles of microsphere synthesis and adhesive formulation described in this patent.
Market impact
This patent enabled the creation of a completely new product category: repositionable notes. It fundamentally changed how people organize information in offices and homes, leading to a massive market for adhesive products that offer temporary, non-damaging adhesion.
Claim 1 — Plain English
What this patent covers
This patent details the creation of microscopic, solid balls, called microspheres, that are inherently sticky and can be dispersed in solvents but don't dissolve in them. They are made from a blend of acrylate esters (like iso-octyl acrylate) and a small amount of another chemical, either an ionic monomer or maleic anhydride. The process involves suspending these ingredients in water and using a specific amount of emulsifier, a substance that helps mix oil and water, to create the microspheres. The resulting tiny balls are described as infusible, meaning they can't be melted down, and elastomeric, meaning they can stretch and return to their original shape.
The clever bit
The key innovation was creating microspheres that were simultaneously sticky yet removable, and stable in solvents, by precisely controlling the ratio of acrylate monomers to a small percentage of ionic or maleic anhydride monomers and using a specific aqueous suspension polymerization technique.
What it does not cover
- Microspheres made from monomers other than alkyl acrylates and specific ionic monomers or maleic anhydride.
- Microspheres that are soluble in organic solvents.
- Microspheres created using polymerization processes that don't involve an aqueous suspension.
- Microspheres made with emulsifier amounts below the critical micelle concentration.
- Microspheres that are not inherently tacky or elastomeric.
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
12/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
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
$140K – $449K
Midpoint $281K · 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.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
18 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Silver, S. F. (1972). Sticky, Tiny Plastic Balls Made from Acrylates (U.S. Patent No. 3,691,140). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3691140/post-it-repositionable-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 Sticky, Tiny Plastic Balls Made from Acrylates cover?
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.
Who owns patent US 3691140?
Individual owns this patent, granted in 1972.
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 3691140 cited by?
This patent has been cited by 382 later patents that build on its ideas.
What problem does this patent solve?
These microspheres, particularly those with inherent tackiness, became foundational for the development of Post-it Notes by 3M. The unique combination of stickiness without permanent adhesion allowed for repositionable notes, a significant innovation in office supplies and organization.
What does this patent NOT cover?
Microspheres made from monomers other than alkyl acrylates and specific ionic monomers or maleic anhydride.
Same assignee
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