What is scotch tape made from, and how does it work?

Well, this is actually a tough one. The reason why it's so tough is the same reason no one can ask questions about how a particular brand comes up with a food product – it's a trade secret. You see, if 3M told everyone exactly how they made their tape, competitors would use the same formula and perhaps sell it cheaper so no one would buy 3M anymore. Or, 3M would have to lower its price. Which might be okay, but maybe the extra money they make goes into Research and Development (R&D). So, if less money was going into R&D then products might not get better over time. That's just one scenario. It's a complicated issue.

What I can tell you, however, is that tape is in a class of adhesive called a Pressure Sensitive Adhesive (PSA). Making tape with the ability to roll up and not stick together was definitely a materials science breakthrough. Adhesives come in all sorts of strengths -- the barely sticky Post-It note to the super strong duct tape. But, an adhesive can't be so strong that it remains stuck in a roll. Thomas Edison invented a gummed paper tape in 1879, used instead of twine for sealing packages. But the first super- practical tape was invented by a 3M chemist, Richard Drew, in the 1920s. He invented masking tape. By 1930, he had invented Scotch tape. What he did was adapt the adhesive attached to the paper that made masking tape to the see-through cellophane tape. (Way back in the 1920s, 3M only made sandpaper. Drew invented masking tape when he visited an automotive repair shop. The mechanics were having a hard time painting a car two-tone, very popular at the time. Whenever they peeled off a very heavy adhesive and butcher paper they pulled off the paint. Drew decided to tackle the problem and a new industry was created for 3M.)

One thing adhesives have in common is that they're made of polymers, which are chain molecules. Chain molecules get all tangled up, like the long strands of spaghetti some people eat every Wednesday night. (That would be me.) The Scotch tape Drew first invented had an adhesive formula that included oils, resins, and rubber. When the adhesive is applied to a backing it has to be in a liquid enough state (viscosity) to spread. Chemists then use a physical process (solvent evaporation, temperature cooling) or a chemical process (adding chemicals) to change the adhesive into a bonding agent. The method they use depends on how strong they want the adhesive to be. What 3M has said about Scotch tape is that it uses an acrylic polymer.

But even if we knew the industrial recipe for Scotch tape, scientists still have a hard time pinpointing exactly why adhesives stick. Two French physicists, however, came up with a pretty good idea: bubbles. Tape looks smooth, but it's not. If you look under a microscope, you would see that the adhesive side has mountains and valleys. Air bubbles get trapped in the valleys when the PSA is applied to an object. When you tug the object away, the lens-shaped bubbles swell in volume. The pressure inside the bubbles falls to a much lower level than outside the bubble and voila – the bubbles act like suction cups. Now, the mountains are attached to the object by bubbles as well because the object – as you can see when you look at it under a microscope – is not smooth either. What's interesting is that no one had to understand or have a bubble theory to make good adhesives. Ah, science.

Process design constraints Generate a wide roll of tape (wide) that can be slit to generate multiple individual rolls Polymer solubility – non-aqueous Remove heat of polymerization Deposit adhesive uniformly on the tape surface

Process solutions Calendaring