Q & A
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.Read More
Parts of the Bond
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.
Mechanism of Action
The mechanism of adhesive tape bonding occurs as follows. These steps can be accomplished instantly after the activation of the pressure-sensitive adhesive.
- The pressure-sensitive adhesive on the tape is made to contact with the substrate by minimal pressure.
- Adhesive increases its surface area and penetrates through the surface of the substrate.
- Adhesive sets on the substrate, producing a strong bond.
The three elements of a pressure-sensitive adhesive tape to achieve a successful bond are adhesion, cohesion, and tackiness.
- Adhesion: Adhesion refers to the ability of an adhesive to stick on the surface of the substrate through adhesive forces. Adhesive forces refer to the attraction of two different materials. When the substrate and the adhesive molecules come in close proximity, adhesion forces occur at the microscopic level through intermolecular forces (e.g., van der Waals forces, dispersion forces) between them.
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.
- Cohesion: Cohesion is the inner strength of the adhesive. It refers to the bonding of the adhesive within itself. Cohesion holds the adhesive layer intact and prevents it from splitting.
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°.
- Tackiness: Tackiness refers to the characteristic of a pressure-sensitive tape by which the adhesive sticks to the surface of the substrate under minimal pressure. All pressure-sensitive adhesives are activated by an initial finger pressure applied to the tape, usually from 14.5 to 29 psi. The required pressure and contact time for the adhesive tape to stick varies according to the type of adhesive and substrate material. Less pressure and contact time are required to stick for adhesive tapes with higher tack.
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.
- Rolling Ball Test: The rolling ball test directly gauges the adhesive behavior of the adhesive tape. A steel ball with a standard weight and diameter is made to roll from the top of an inclined track which consists of the sticky side of the tape. The tackiness is measured by the distance traveled by the ball on the sticky tape track; the shorter the distance, the greater the tack.
- Loop Tack Test: The loop tack test is a quantitative and repeatable method to assess adhesive tape tackiness. A loop of adhesive tape is attached to the probe of a tensile tester machine. The loop is made to contact with a horizontal surface for a short time, then the tool pulls it away. Numerical values of the bond’s tensile strength are recorded and subjected to evaluation.
Reference: https://www.iqsdirectory.com/articles/tape-suppliers/adhesive-tape.html?msID=1f7798fc-4305-49eb-8ba4-85ca244c575d#different-types-of-adhesive-tapesRead More
Monomeric PVC vs. Polymeric PVC
Monomeric PVC uses plasticizers with low molecule size. These short-chained plasticizers exhibit more molecular migration. This means that the plasticizer has a greater possibility of migrating out of the film when exposed to tough conditions; this makes the PVC film brittle and inflexible, and it will eventually shrink. This type of film has a thickness ranging from 70 microns to 80 microns. It is best used for indoor, smooth, and flat applications such as promotional signage, stickers, and exhibitions. It can be used for short-term outdoor applications and typically lasts for two to five years.
Unlike monomeric PVC, polymeric PVC uses plasticizers with large molecule size. These long-chained molecules allow efficient binding of the plasticizer into the film; this reduces the chance of molecular migration. This kind of film is produced 60 microns to 80 microns thick. Generally, it is softer and more flexible than monomeric PVC, thus, it is less likely to shrink and can be used in applications with mild curves. Because of its durability, it is suitable both for indoor and outdoor use. Its lifespan could be five to seven years.
Over 12 Years of Calendered Vinyl Film Precision Coating | Surface Treatment & Adhesive Solutions Supply| Celadon Tech
Located in Taiwan, Celadon Technology Company Ltd., since 2007, is a film coating ( PVC, PET, paper, textile) manufacturer. Main product, including UV Tech Board, which is 100% looks like marble, 100% easier installation and maintenance, up to 300% cost saving. In addition to high-quality self adhesive vinyl product line, metallic film, glitter film, chrome film and so forth.
ISO 9001, 14001 and OHSAS18001 certified film supplies with thick coating technology that could coat up to 0.17mm and still maintain its stable, reliable quality. Partial Control Technology has allowed us to deliver coating solutions to RFID, solar panel, marine and car wrap sectors. As well as vinyl and decorative films for semiconductor industry's CMP pad, heavy duty and extreme condition outdoor sport adhesions.
Celadon Tech has been providing vinyl films, decorative films and industrial tapes to clients, both with advanced technology and 12 years of experience, Celadon Tech ensures each customer's demands are met.
- New PPF Developing
Cutting Age PPF is Under Development, TPU PPF's performance with reasonable price.Read More