This article presents all the information you need to know about adhesive tape. Read further and learn more about:
Pressure-sensitive adhesive tapes consist of a backing material film coated with an adhesive intended for relatively low-stress applications. Light pressure, usually done by the fingertips, is applied to initiate the binding. In the sticking process, the fluid properties of the pressure-sensitive adhesive change rapidly to flow and set in the surface of the substrate.
Adhesive tapes first appeared in the mid-19th century for medical applications. In 1845, Dr. Horace Day created bandages from strips of fabric with rubber adhesive tapes. It was the inspiration behind Johnson and Johnson‘s Band-Aid. In 1923, the 3M Company formulated the first masking tapes. Adhesive tapes kept on evolving to materialize the present varieties of adhesive tapes (e.g., packing tape, painter‘s tape, and electrical tape) which serve their unique application. Nowadays, adhesive tapes are certainly found in most offices, households, shops, and industries which undoubtedly makes them one of the most useful tools ever invented.
Adhesive tapes are efficient and readily available to perform different functions such as joining, masking, sealing, splicing, bundling, and surface protection, which does not require machinery or any other special tools. Adhesive tapes are lightweight and efficient to store; it usually comes in rolls and is only unwound if there is a need for adhesive. Unlike the traditional mechanical fastening objects such as screws and bolts, it eliminates the need to pierce or punch the substrate which induces a stress area.
The principles behind the bonding of adhesives, which may be overlooked because of the simplicity of its process, will be discussed in this section.
The bonding layer made by an adhesive tape, shown macroscopically in the image below, presents a cross-section of a bond. The layer consists of an adhesion zone, cohesion zone, and a transition layer.
The adhesion zone is the interfacial layer between the adhesive and the substrate. The cohesion zone is the pure adhesive layer that holds the adhesive and the backing material, or another substrate if the adhesive is unsupported. The transition layer is intermediate between the adhesion and cohesion zones.
The mechanism of adhesive tape bonding occurs as follows. These steps can be accomplished instantly after the activation of the pressure-sensitive adhesive.
The three elements of a pressure-sensitive adhesive tape to achieve a successful bond are adhesion, cohesion, and tackiness.
Surface energy is one of the properties which determines the wettability of the substrate when it comes in contact with the adhesive. Wettability is important to penetrate the surface of the substrate, thus making a continuous bond.
Surface energy is defined as the sum of the intermolecular forces, and the attraction and repulsion energies which a liquid exerts on the surface of a solid. If the substrate has high surface energy, the adhesive will easily flow on its surface and more surface area will be covered. Some of the high-energy substrates include polycarbonate, polyvinyl chloride, and zinc. On the other hand, if the substrate has low surface energy, the adhesive will build up as "small beads" and only a small area will be covered. Low surface energy substrates include Teflon™, rubber, powder coatings, etc.
Surface contaminants prevent the fusion of the adhesive into the substrate. Therefore, it is important to keep the surface free from grease, dirt, and moisture before application of the adhesive tape.
Cohesive forces attract the neighboring molecules of a liquid by pulling it inward. Molecules at the surface of the liquid have greater attractive forces that bind them together. This phenomenon is responsible for the property of a liquid called surface tension. Surface tension is the ability of the adhesive to resist deformation on the surface of a solid, thus reducing its surface area. In the case of adhesive tapes, the molecules of the adhesive must be strong cohesive forces to hold and maintain the bond over time.
Silicone is an example of a liquid with high surface tension. If silicone is present as a coating on the surface of the substrate, it will be difficult to be wetted by the adhesive. If used as an adhesive, on the other hand, it will produce a durable bond.
Adhesion and cohesion must be considered when formulating or choosing the right adhesives. An ideal bond consists of a combination of a high surface energy substrate and a low surface tension adhesive. To achieve good wetting of the substrate, adhesive forces must be greater compared to cohesive forces and the contact angle must be less than 90°.
The phenomenon described is attributed to the viscoelasticity of the adhesive at room temperature. Viscoelastic objects are materials that possess both viscous and elastic characteristics. When gentle pressure is applied to the tape, it decreases its viscosity thus encouraging flow on the substrate at the microscopic level. Due to its elastic property, the original viscosity is regained with stronger intermolecular force with the substrate.
The Rolling Ball Test and Loop Tack Test are the most common quality control checks used to assess the tackiness of the adhesive tapes being produced.
Adhesive tapes consist of a carrier, adhesive, and release liner. Not all types of adhesive tapes are required to have all the components but are still dependent on the properties of the material and the intended storage of the tape itself. A more careful materials selection must be done on the carrier and adhesive especially when downstream processes, such as cutting, are involved. The adhesive tape may contain the following:
The carrier, or the backing material, is a thin flexible film that contains the adhesive. The carrier can have the following materials, depending on the end application of the adhesive tape:
This is the main component of every adhesive tape which primarily serves its purpose. Adhesives are the polymeric compounds that are applied to the surface of two items to connect them and resist their separation. The commonly used adhesives are enumerated below.
Rubber adhesives are commonly used in duct tapes, masking tapes, and carton sealing tapes. It may be derived from natural rubber or synthetic rubber.
Acrylic adhesives are available as water-based or solvent-based adhesives:
Silicone adhesives are found in tapes which are mainly used in the electronics industry, where significant amounts of heat are dissipated in electronic components. These adhesives are also found in splicing tapes and Teflon™ tapes.
A release liner is one of the components that must be present in double-coated tapes and adhesive transfer tapes. This layer is peeled-off before the bond is made to the substrate. It preserves the tackiness of the adhesive until it is ready to be used, and protects it from sticking from the carrier.
Adhesive tapes are categorized according to the arrangement of the carrier, adhesive, and release liner:
Double-coated tapes are used to bond substrates with different surface properties which require different bonding requirements. It is highly customizable and the thickness of the adhesive can be varied on the opposite sides. The thermal resistance of a double-coated tape depends on the properties of its carrier.
Benefits of pressure-sensitive adhesive tapes over glues, adhesives, and other fastening components are the following:
Pressure-sensitive adhesive tapes may not be suitable to use under some circumstances. They are not suitable for bonding some joint types and materials which are intended for high-stress applications due to their limited bonding strength. Pressure-sensitive adhesives have weaker adhesive forces produced compared to glues and sealants.
They also underperform at high and low temperatures. Tackiness is dependent on the temperature of the substrate. A poor bond is created when the temperature of the substrate is low. At high temperatures, the viscosity of the adhesives decreases causing the weakening of the bond. Glues and sealants are preferred when objects are exposed to thermal cycling. Pressure-sensitive adhesives are also sensitive to UV radiation and oxidative agents.
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