1. Why Does Tape Stick Without Waiting for Glue to Dry or Harden?
Some adhesives require specific steps to work, such as evaporation of solvents, exposure to ultraviolet light, chemical reactions, or cooling to harden. However, the adhesive on tape is characterized by its ability to bond with a surface simply by applying light pressure [1]. This property is often called pressure-sensitive adhesive, which literally means an adhesive that "feels" the pressure and sticks.
If tape sticks just by pressing it, the adhesive inside must have different properties from ordinary solid glue. In the next section, we will look inside the tape to understand its structure, and then consider how it sticks.
2. What Four Layers Fit Inside Tape That Is Only 0.05 mm Thick?
The thickness of Nichiban’s clear tape is about 0.05 mm, which is roughly 1/20th of a millimeter. It is said that four layers are stacked within this thin material: a release agent, cellophane, a primer, and the adhesive [3]. The release agent is the layer that makes it easy to pull the tape out of the roll. The primer is the layer that firmly bonds the cellophane to the adhesive [3]. This means that in addition to the adhesive that touches the surface you are sticking, there are layers prepared specifically for "pulling it out" and "connecting the tape body to the adhesive." However, this thickness is specific to Nichiban’s clear tape and varies by product and era.
According to the Tokyo Metropolitan Library’s Q&A, natural rubber-based adhesives are often used in cellophane tape [2]. Cellophane tape is said to have been developed by the 3M company in the United States in 1930 [4]. In Japan, the company Nichiban began manufacturing cellophane adhesive tape in 1947 and released it for sale in 1948. "Selo-tape" is a registered trademark of Nichiban, while the general name is cellophane tape [5].
3. Why Must Tape Adhesive Be Soft When Applied but Hard When Pulled?
For an adhesive to work, it must balance two opposing properties. It needs to be soft enough to flow when pressed and spread out (wet) into the tiny irregularities of the surface. At the same time, it needs to be hard enough that it does not stretch out completely when force is applied to peel it off [1]. If it only had one of these properties, it would either fall off after sticking or fail to stick in the first place.
Adhesives are described as behaving like viscous liquids when deformed over a long period, but like hard solids when deformed over a short time [6]. You can imagine this balance by thinking of the adhesive as soft when it slowly spreads out under pressure, but hard when it is pulled away suddenly.
4. How Do Weak Attractions Between Molecules Make Tape Stick?
The strength of adhesion is said to be largely related to attractive forces between molecules, such as van der Waals forces [1]. This is not a strong attraction like that of a magnet. It is a very weak attraction that works between molecules.
Although the force at any single point is extremely weak, if the adhesive wets and spreads across the surface, creating many points of contact, this contributes to the strength of the adhesion. The "softness" discussed in the previous section can be seen as a condition for maximizing this contact area. Adhesives are described as sticking through these intermolecular forces, rather than through chemical bonds [1].
5. Does Peeling Tape Slowly or Quickly Change the Force Needed?
Because adhesives behave like viscous liquids under slow deformation and like hard solids under rapid deformation, there is a tendency for the force required to peel the tape to increase as the peeling speed increases [6].
However, the force does not simply increase. In actual peeling, there are two types of separation: cohesive failure, where the adhesive tears within itself, and interfacial failure, where it separates at the boundary with the surface. Depending on which type occurs, the force does not simply increase [6]. Therefore, it is safer to interpret this as "generally becoming stronger with speed" rather than "always stronger with speed."
6. What Did Researchers Find When Peeling Tape in a Vacuum?
In 2008, researchers at UCLA (University of California, Los Angeles) peeled adhesive tape in a vacuum. They reported that short pulses of X-rays, lasting about one billionth of a second, were emitted [7]. One billionth of a second is the length of time equal to dividing one second into one billion parts.
These X-rays were reportedly strong enough to take an X-ray image of a finger [7]. This result was reported from an experiment conducted in a vacuum [8]. Since it has not been reported that the same thing happens in air, do not try the vacuum experiment at home.
The abstract of the Nature paper featuring this research states that peeling tape in a vacuum releases energy in the X-ray spectrum, and that the way this energy concentrates exceeds the predictions of current theories [8]. There are still parts of the familiar action of peeling tape that we cannot yet fully explain.
7. How Can You Compare Applying and Peeling Tape at Home?
You can compare different ways of applying and peeling using cellophane tape and paper you have at home. First, try comparing the feel when peeling a tape that was just lightly placed versus one that was firmly pressed with a finger. Second, try peeling a tape applied in the same way, once slowly and once quickly. Results may change depending on the type of paper and the length of the tape, so keep the conditions consistent and write down what you feel.
Natural rubber-based adhesives are said to oxidize and turn yellow over time, sometimes seeping into paper and becoming hard and brittle. For this reason, it is advised not to use cellophane tape for documents you want to preserve for a long time [2]. If you see tape on old documents or notices, observe its color.
If you want to know more, the abstract of the Nature paper on the X-ray phenomenon is publicly available [8]. You can refer to the original source from the citation list.