An Extract:
"I really couldn’t write a book called Sticky without mentioning Post-It® Notes, especially because as I type, I am surrounded by them, each one covered in scrawled ideas for upcoming chapters. Originally patented by 3M and first released onto the market in 1980, these sheets of coloured paper backed with a small strip of adhesive are an office mainstay. Given that Post-Its are now so commonplace, it’s easy to forget how much engineering went into their development.
The story is the stuff of design legend, and it involves two scientists: Spencer Silver and rthur Fry. Back in the late 1960s, Silver had been working on ultra-strong adhesives for the aerospace industry, but a mistake in the lab led him to a discovery that he’d go on to patent – a sprayable, mildly sticky adhesive comprised of tiny acrylate spheres (each one between 5mm and 150mm, or 0.005mm to 0.15mm) suspended in a solvent. These spheres were pressure-sensitive but resilient, or as Silver wrote in the patent, ‘A force applied directly to one of the polymer spheres will deform it; however, the spherical shape is reassumed upon release of the stress.’ Going on to discuss how this material could be applied to different
surfaces, he described it as ‘a tacky adhesive layer which readily bonded paper, but permitted the paper to be removed, repositioned and rebonded’. It was several years before this barely sticky adhesive would find a commercial use. Fry, a colleague of Silver’s and a keen
member of his church choir, was frustrated that his carefully positioned bookmarks would frequently fall out of his hymn book. Looking for something that could stick to the page but be easily removed, he thought of Silver’s invention. The two began collaborating and
gradually assembled a team.
An issue they had to solve early on was that each time a proto-sticky note was removed from a surface, it would leave behind some of its polymer spheres, and be less sticky as a result. If they wanted the notes to be truly reusable, they’d need to find a way to keep the adhesive
on the note paper. Their solution was effectively a glue for their glue – a binder compound, applied to the notes before the adhesive spheres, which anchored them to the paper. In the patent for their ‘acrylate microsphere-surfaced sheet material’, the researchers stopped short of naming the specific binder they used, as well as the mechanism by which it works (there’s a mention of a ‘vacuum effect’, but that’s it). They described the spheres as being ‘partially embedded in and protruding from’ the binder. The result is a pebbled, pressure-sensitive adhesive film that stays firmly stuck onto the note, but which holds the note onto a surface with a very small amount of adhesive force.
From there, they had to design the machinery capable of mass-manufacturing sticky notes.
‘It’s not just a matter of smearing a little glue on the paper,’ Fry was quoted as saying in The Chemical Engineer. The early prototype of the kit, understood to have used rollers to apply the binder followed by the adhesive spheres, was built in Fry’s basement. Even after solving all the engineering challenges, the team still had to convince 3M management that the notes could be commercially viable – and that’s a story in itself. Once launched worldwide, under the trademark Post-It, Fry and Silver’s invention became immensely popular, and inspired other manufacturers to create their own versions. In 2019, the global market for sticky notes was estimated to be worth more than US$2 billion (almost £1.5 billion).
The other sticky superstar I want to highlight is superglue, which, it may surprise you to know, is not a trademark[1]. Most adhesive brands sell a product using this name, and all
of them are based on polymers called cyanoacrylates. They’re famed for their ability to stick to seemingly any surface, though that wasn’t initially seen as a positive by the man who would go on to patent their use as adhesives. During the Second World War, Eastman Kodak chemist Harry Coover was tasked with producing transparent gunsights for use by the military. While trialling different polymers, his team came across an exceptionally sticky formulation that stuck to – and permanently ruined – everything it touched.
Interesting, yes, but because it wasn’t what they needed, Coover set it aside. It wasn’t until six years later, while researching adhesives for use in jet aircraft, that he revisited
cyanoacrylates, and in 1956 he was granted the patent for them[2]. In the bottle or tube, cyanoacrylate adhesives are liquid, and they flow and behave as such. But as anyone who has ever accidentally stuck their fingers together will tell you, once they’re out of their container, they very quickly turn solid.
Contrary to popular belief, it’s not the oxygen in the air that kick-starts this curing reaction; it’s the water vapour. As soon as superglues are exposed to water, H2O molecules bond to the cyanoacrylates, joining together to form long, interconnected chains that set hard. Most surfaces on our gloriously damp planet are permanently clad in an ultra-thin layer of water, making cyanoacrylate a very useful, very versatile option for your adhesive needs. It does also mean that skin, which generates its own water layer through respiration, is especially vulnerable to its speedily forming bonds. This realisation later led to cyanoacrylate compounds being used to close wounds instead of traditional stitches, usually under trademarks like Dermabond, or SurgiSeal. As someone who had no sense of danger or self-preservation as a kid, I can attest to their effectiveness."
Sticky: The Secret Science of Surfaces by Laurie Winkless (Bloomsbury Sigma) is published in hardback, ebook and audiobook on the 11th November.
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[1] As far as I could find, Henkel were the most recent company to hold the trademark ‘Super Glue’, but it was abandoned in 2010. There is also a separate trademark for ‘The Original Super Glue’, which is held by Pacer Technology®/Super Glue Corporation.
[2] Patent US2768109, granted to Coover, H.W. 1956. Alcoholcatalyzed a-cyanoacrylate adhesive compositions. The product has gone by lots of names since Coover patented it. Originally called ‘Eastman #910’, it was quickly rebranded as ‘Superglue’. When Loctite later bought the technology from Kodak, they called it ‘Loctite Quick Set 404’, followed by ‘Super Bonder’.