Life without tape to mend rips in our old photographs or seal a box shut before mailing it is difficult to imagine. Before tape entered the scene, people often used mechanical fasteners, liquid glue and string to hold things together. As early as 4,000 B.C., cracked earthenware pots were put back together again with an adhesive substance created from the sap of trees. Ancient Egyptian hieroglyphics from 1,500-1,000 B.C. point toward glues being made from animal-derived adhesives, while the Romans and Greeks developed adhesives from egg whites, blood, bones, hide, milk and vegetables.
These methods served their needed purposes at the time, but assembly was still a long, labor-intensive process. Then, in 1845, Dr. Horace Day developed the first pressure-sensitive adhesive. He applied a mixture of India rubber, pine gum, turpentine, litharge and the turpentine extract of cayenne pepper to strips of fabric to build a wound dressing that stuck on its own. It became the forerunner of the Band-Aid.
Over the years, engineers and scientists built on the uses for pressure-sensitive adhesives and ultimately found many benefits to assembling parts and materials with them. Today, pressure-sensitive tapes are used every day in applications such as taping off walls before painting them to highly specialized ones like the assembly of electronic devices. They are popular for use on electronic devices due to their instant fixture, flexibility, ability to bond well to difference surfaces and fairly simple application style.
The use of pressure-sensitive tapes for assembly applications provides both production efficiency and reduced labor costs. Other benefits include the ability to easily bond together various materials and the ability to make products thinner and lighter.
Today’s variety of assembly applications often requires pressure-sensitive adhesive tapes with specialized, high-performance properties. Adhesives have been developed to perform in applications requiring high or low temperature performance, chemical resistance, varying levels of insulation, clean removability, resistance to extreme weather, long-term performance, the ability to bond to rough or uneven surfaces, skin sensitive applications and the ability to bond to low-energy surfaces like polyethylene or silicone. When combined with other components or backings, performance properties can include cushioning, sound insulating, electrical dissipation, surface protection, gasketing, medical device suitability or reliable performance as an assembly aid in a continuous production process. The variety of applications for specialized tapes is truly astounding.
Now let’s jump into a deeper understanding of where and why these types of tapes are used in the real world.
One great example is the touch screen on your cell phone. There are layers of various pressure-sensitive coated films used in the assembly of the phone. One layer might hold the glass screen in place, but also provides an anti-shatter property if the glass screen were to break. In this application, the tape needs to have clarity and be strong enough to hold the glass together if it accidentally gets broken. The tape will also need to be able to withstand temperature fluctuations, perform for years, not react or fog the phone’s screen and not interfere with its electrical components. Another layer might be needed to protect the phone from electromagnetic interference, or EMI. By dissipating the EMI, the electrical components will continue to function properly.
Another application requiring a highly specialized double-sided tape is lens grinding and polishing. A lens is generally made of glass, although eyeglasses can be polycarbonate. In order to perform optimally, the glass needs to be ground and polished. This process involves an abrasive disc rotating in a liquid slurry. A slurry is a semi-liquid mixture, typically of fine particles suspended in water. The specialty double-coated tape must hold the abrasive disc to a steel platen while rotating. It also has to be able to perform for hours while submersed in the slurry. At the end of the polishing process, the tape is removed from the platen. It must remove cleanly without leaving any residue on the platen. Therefore, this application requires a special tape that provides all of these special properties.
Here’s an example that appears to be simpler at first glance: a label. More specifically, a label that is applied to a bullet-proof vest. The materials of each vest must be traceable for up to 50 years or longer. The label is critical should a recall or quality check of the specific product be needed. In this case, the label must have a strong bond to the outer vest material and it must not be able to be removed. It needs to have resistance to environmental conditions, abrasion and movement. It should also be flexible, ink receptive and non-smudging. On further reflection, it’s apparent even smaller items that stick to surfaces via adhesion have a complicated thought process behind them!
The pressure-sensitive tape industry has certainly come a long way since Dr. Day was creating liquid mixtures to help his bandages stick to patients. A deeper understanding of and appreciation for the many dynamic uses of adhesive tapes continues to grow. There is no doubt many more uses will be discovered in the future across countless industries.