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.

What it 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.

What it doesn't 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.

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.

Why it matters

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.

Real-world examples

• 1.3M Post-it Notes
• 2.Repositionable adhesives
• 3.Specialty coatings