On Christmas Eve, one hundred years ago, right where you are now, a child just like you might have been wrapping a present. To do so, they would need some brown paper, scissors, and a burning candle. First, the paper was cut and folded around the present. Then, hot wax from the candle was dripped between the paper’s edges. The paper was held together with a finger until the wax cooled and became smooth and hard. The wax had turned from liquid to solid. The solid wax stuck to the paper, and kept the edges together. A bit of ribbon was added to make the package pretty.
People do not usually use wrap gifts with candle wax anymore. It is dangerous, and messy. In 1930, an American inventor named Richard Drew made wrapping gifts simpler and safer when he invented “sticky tape.” Part of his job for the company 3M was to play with sticky stuff and see what he could invent with it. Sticky tape was the result. Now, all over the world, whenever people want two pieces of paper to stay together, they use a piece of tape. No candle required.
Tape is a long strip of plastic with a layer of glue on one side. Only one side of tape – the side with the glue – is sticky. The other side has to be smooth so the glue does not stick to it, and we can unroll it. The smooth side is the side that we touch with our fingers. When Richard Drew was thinking about how to make tape, a clear, thin plastic called cellophane had just been invented. Cellophane, also known as plastic wrap, was first used to cover leftovers in the kitchen. It is cellophane that Richard Drew used to make his see-through, sticky tape.
Tape might be simple to use, but it is not simple to make. Richard Drew had to be very patient and he tried many recipes in his search for the perfect glue. More than thirty different ingredients are in sticky tape glue. Some of these ingredients are oils and some are plastics. All these ingredients were mixed together and tested until the glue was just right.
Glue that is too sticky would not come off the roll. Glue that is not sticky enough would not hold things together. Sticky tape glue works so well because it gets stickier when it is pushed down with your fingers. It is “pressure sensitive.” It comes easily off the roll, and then when you press it onto the paper, it stays there.
When fingers apply pressure to tape, it affects the molecules in the glue – it squishes them against the surface, causing them to spread out, just like squishing a jelly sandwich makes the jelly spread out. The glue – and the jelly – is flowing slowly, like a liquid. The harder the molecules are pressed against the surface, the more they flow, and the more they stick.
Tape sticks best to paper, glass, and metal. It does not stick as well to plastic like yogurt cups. Try it yourself; is it easier to get a piece of tape off glass, or a yogurt container? The next time you wrap a present, remember you are squishing molecules with your finger. You and your fingers are an important part of the tape’s stickiness.
The science of sticky tape is complicated. It has taken scientists a long time to understand how pressure sensitive glue works, and they still don’t have all the answers. There have been whole books written about the subject! This is one invention that works well, even though we do not fully understand how. It reminds us that even simple things can be full of surprises. Just like that Christmas present waiting for you under the tree.