According to the Pressure Sensitive Tape Council, three characteristics define a Pressure Sensitive Adhesive (PSA):
Unlike liquid adhesives, the chemistry in a tape is provided fully cured so there is no additional curing that takes place to form a bond. The bond is created by using mechanical interlocking and electrostatic interactions at the interface.
These characteristics give PSAs unique performance capabilities that can provide freedom when designing a product and increase production efficiency. Benefits may include:
Other benefits may include:
Pressure sensitive adhesives come in many formats and chemistries for various industrial bonding applications. Although specialty PSAs are available for specific applications, we will focus on providing a high-level overview of the three most common chemistries.
Development of acrylics for pressure sensitive adhesives began because of the tendency of natural rubber to yellow and degrade when exposed to UV. Acrylic chemistry also tends to have higher internal strength than rubber chemistry.
Acrylic tapes are the workhorse of industrial bonding. The ever-evolving capabilities of acrylic chemistry allow formulations to provide high or low temperature performance, adhesion to High, Medium, and Low Surface Energy (HSE, MSE, LSE) materials, or even unique properties such as flame retardancy. Acrylic tapes are provided in various thicknesses with and without carriers and functional foam cores. Functional foam cores of acrylic foam tapes offer specific performance benefits including strength and dynamic stress absorption. Acrylic tapes are found in nearly every industry.
Silicone-containing polymers can be used to create tape release liners due to their incredibly low surface energy but are also used to formulate the very adhesive itself.
Silicone tapes are best known for their ability to bond to silicone and to tolerate a very wide range of temperatures – from -40 °F (-40 °C) to over 500 °F (260 °C).
Rubber was the first material used to make pressure sensitive adhesives. Over the decades, rubber PSA technology has advanced to include both natural and synthetic rubber resins and a wide variety of tackifiers used to tune the adhesive for specific performance.
Rubber adhesives build the bond faster than other chemistries; they can bond to most surfaces including LSE and are relatively low cost. They are a versatile option for many applications, however their final bond strength is lower than acrylic PSAs and they are more vulnerable to the effects of aging (sunlight and oxidation).
Natural rubber (poly cis-isoprene) is mechanically worked to provide lower molecular weight polymers that can be readily dissolved or dispersed in a solvent. Synthetic polymers (such as styrene-isoprene block copolymers) may also be used. Tackifiers such as pinene (from pine sap, among other sources) are added to give the adhesive additional tackiness allowing it to be used as a PSA.
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