Every time we pull some tape off a roll -- to wrap a present, hang macaroni art, temporarily fix a leaky pipe or seal a package for shipping -- we probably miss the genius of the roll itself. Most notably, why does the adhesive stick to the backing and to the substrate but not to itself?
Were tape not in roll form, it would likely be somewhat difficult to toss in a junk drawer. And "adhesive" that is not adhesive tape is usually glue -- drippy and permanent. It's the tape part that makes the product so neat, so compact and so easy.
The process of making tape is fairly uniform. All adhesive tape has four components.
- Backing -- The backing is what faces out after you apply the tape, and it doesn't stick to your fingers. Materials vary by application, but mixtures based on plastics, paper or cloth are typical.
- Primer -- An adhesive primer is applied to the backing to help the adhesive stick evenly and securely to the backing material once applied.
- Adhesive -- A thin layer of adhesive is sprayed onto the primed backing material.
- Release coating -- The adhesive is covered by a coat of anti-cohesion material (often polyvinyl carbamate) to keep it from sticking to itself when rolled up.
The layers are applied in large sheets, which are finally rolled up and cut into the 1-, 2- or 3-inch-wide rolls of tape you buy at the store.
The final coating -- the release -- emphasizes an interesting distinction in the world of stickiness: adhesion versus cohesion. In adhesion, one type of molecule is sticking to another type of molecule; in cohesion, one type of molecule is sticking to itself. Tape uses both. The molecules of the adhesive stick to the molecules of the substrate, or adhere, but they also stick to each other, or cohere. If this weren't the case, the adhesive substance wouldn't hold together. The release coating prevents cohesion at the surface of the tape so it can be unrolled easily.
And so, what began as masking tape and some very happy auto painters is now an industry unto itself. Adhesive tapes have wrapped the metal skeletons of blimps to prevent corrosion. They've insulated at least one lunar lander and helped Apollo 11 astronauts carry out some on-the-moon repairs to their lunar module's fender. They hold rearview mirrors onto cars and keep millions of scrapbookers from tearing their hair out when their placement is a millimeter off.