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Adhesive tape is a material with an adhesive film applied to bond or join materials and protect surfaces. It has a backing or carrier material such as paper, plastic film, cloth, foam, or foil that has been coated with an adhesive and includes a release liner where necessary. Coated backings are wound into rolls slit into narrow bands for ease of use.
The application of adhesive tape can involve slight pressure, thermal activation, or moisture; pressure-sensitive (PSA) tapes are tacking, while heat-activated tapes require a heat source. Water-activated tapes, gummed paper, or gummed tapes are starch or animal glue-based with a kraft paper backing that becomes sticky when moistened. Non-adhesive tapes, films, or laminates are self-adhering.
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. Later, 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 have evolved into the present-day varieties that include packing tape, painter’s tape, and electrical tape, each designed to meet the needs of a specific application. The many types of adhesive tapes are found in offices, homes, shops, and industries, which has made them one of the most useful tools ever invented.
Efficient and readily available, adhesive tapes perform a wide array of functions such as joining, masking, sealing, splicing, bundling, and surface protection. Adhesive tapes gained popularity because their application does not require machinery or special tools. They are lightweight, easy to store, and come in rolls that can be unwound when needed. Unlike traditional mechanical fasteners, such as screws and bolts, adhesive tape eliminates the need to pierce or punch the substrate, creating stress on a surface.
Prior to the development of adhesive tape, glues and epoxies were used to secure or seal surfaces. They were messy and inconvenient, and they dried to a permanent hard finish that was difficult to remove. Glues and epoxies form a bond using a chemical reaction that is not applicable to small, everyday jobs.
Adhesive tapes use a tacky resin such as silicone, acrylics, or rubbers to create their stickiness and rely on physical action such as pressure to make their bonds. The solid adhesive in tape has a low energy surface where its molecules are in constant motion or energized, creating looser bonds, which allows the molecules to flow easily in solid form into the pores of the substrate. With a little pressure, the molecules flow into the substrate and form a solid physical bond.
The concept of adhesion is based on the idea that various substances can hold surfaces together by some form of attachment in which one set of molecules sticks to another type of molecule. In addition, the process uses the concept of cohesion, where molecules stick to themselves. Adhesive tape uses both adhesion and cohesion, where adhesive molecules adhere or stick to a substrate but also themselves. These two factors are necessary for adhesive tape to maintain its hold on a surface.
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.
Various mechanisms make it possible for two surfaces to adhere to each other. The process of adhesion involves four basic concepts that enable tape to bond to a substrate surface.
The foundation of the mechanism of adhesion is based on absorption theory, or the concept that substances stick together because of the contact between molecules. The four adhesion mechanisms substantiate and support the premise of absorption theory.
For adhesives to work, they must be spread over the surface of the substrate. In the sticking process, the adhesive surface of the tape sticks to the surface molecules of the substrate like millions of minuscule magnets. Stronger bonds are formed where the adhesive and the substrate merge to form a strong chemical bond. The combination of the adhesive and the substrate form a new chemical, a process referred to as chemisorption.
The concept of van der Waal forces is dependent on distance. When molecules are close, their forces are attractive. If the distance is 0.6 nanometers, the force is weak and cannot be seen. When the distance is less than 0.6 nanometers, attraction occurs, a foundational adhesion principle.
Surface energy determines the wettability of the substrate when it makes contact with the adhesive. The wettability of the adhesive allows it to penetrate the surface of the substrate to form a bond using one of the four adhesive mechanisms.
Surface energy is the sum of the intermolecular forces regarding their attraction and repulsion energies and how a liquid exerts force on the surface of a solid. Where the substrate has high surface energy, an adhesive easily flows over it and covers more area. Examples of high-energy substrates are polycarbonate, polyvinyl chloride, and zinc.
If the substrate has low surface energy, the adhesive builds up as “small beads” covering a minute area. Types of low surface energy substrates include polytetrafluoroethylene (PTFE), rubber, and powder coatings.
Surface contaminants reduce surface energy and prevent the fusion of an adhesive to the substrate. Types of surface contaminants include dust, fingerprints, oil, grease, moisture, and various forms of residue, such as coatings. For the adhesion process to be successful, pretreatment of the surface is necessary, which removes surface contaminants, enhances surface energy, and improves adhesive bonding.
Cohesive forces attract the molecules of a liquid by pulling them inward. Surface molecules of the liquid have attractive forces that bind them together, a phenomenon responsible for the property of a liquid referred to as surface tension.
In adhesion, surface tension is the ability of the adhesive to resist deformation on the surface of a solid, reducing its surface area. In the case of adhesive tapes, the molecules of the adhesive have to have strong, cohesive forces to hold and maintain the bond.
Silicone adhesive tape has good adhesion with low surface energy, but it is heat and weather-resistant with good electrical insulation properties and chemical resistance.
Adhesion and cohesion are the properties that engineers consider when designing tape. The two forces work together to form strong, consistent bonds for a high surface energy substrate for low surface tension adhesives. To have good wetting, adhesive forces must be greater than cohesive forces and contact at less than a 90° angle.
Viscoelastic materials are viscous and elastic. They behave like fluids and elastic solids and have particles that temporarily connect. Their flexibility allows them to slide along each other like fluids. When low pressure is applied to tape, its viscosity decreases, causing the adhesive to flow onto the substrate at a microscopic level. Its elastic properties help it regain its viscosity to form a strong intermolecular force with the substrate.
Rolling Ball and Loop Tack Tests are used as quality control checks to assess the tackiness of adhesive tapes.
Surfaces with LSE are difficult to bond because the surface resists the adhesive’s wetting out, creating low surface contact and adhesion. With HSE, the adhesive wets out easily, with increased surface contact forming a strong bond.
For adhesive tape to bond with an LSE substrate, the surface must be modified by changing its chemical composition to increase its surface energy. Techniques such as flames, plasma treatments, acid etching, and solvents may be used. In addition, there are specially formulated adhesives capable of bonding with LSE substrates that contain modified acrylics and synthetic adhesives. Rubber adhesives are often used since they are soft and flow well.
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. The materials of the carrier and adhesive must be selected carefully, 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. Adhesives are the polymeric compounds applied to the surface of two items to connect them and counteract 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 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 PTFE 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 that 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.
The benefits of pressure-sensitive adhesive tapes over glues, adhesives, and other fastening components are the following:
Pressure-sensitive adhesive tapes may not be suitable under some circumstances. They are not suitable for bonding some joint types and materials that 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 bond to weaken. 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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