Know More about Hot Melt Pressure Sensitive Adhesive
Hot melt pressure sensitive adhesives require pressure to adhere to a substrate, unlike other adhesives, which often require a solvent, water or heat. How well a hot melt pressure sensitive adhesive will bond to a component is primarily determined by the amount of pressure applied and the adhesive’s composition, although other factors, such as surface energy, proper preparation and smoothness, also affect the strength of the bond.
Hot melt pressure sensitive adhesives are typically designed to function best at room temperature, extreme cold or heat can cause the adhesive to lose its tackiness or holding ability. However, pressure sensitive adhesive can be custom manufactured to withstand extreme temperatures and other conditions, depending on the chemical composition of the adhesive. Pressure sensitive label adhesives are commonly made from water based acrylic adhesives, with a smaller volume made using solvent based adhesives and hot melt adhesives
Pressure sensitive adhesives are comprised of a special adhesive tape, typically made of a fluid adhesive micro-web, and a composite structured backing. Typically, this type of adhesive can be applied using only the pressure exerted from a person’s fingers. The application process involved with pressure sensitive adhesives is much cleaner than with any other kind of adhesive, and the bonds they form are strong.
The basic chemical composition of pressure sensitive adhesives consists of an elastomer base material (depending on the specific adhesive), which can include any one of the following: natural rubber, nitriles, vinyl ethers, acrylics, butyl rubber, styrene block copolymers, and silicones. To increase the tackiness of the adhesive, the elastomer is combined with a tackifier, a low-weight molecular compound, which aids the elastomer during adhesion.
Tackifiers offer the added benefit of becoming stiff at higher strain rates and retaining higher stress compliance at low strain rates. Additionally, tackifiers have high viscoelasticity, which gives the adhesive similar properties to rubber, such as resistance to shear flow and strain when under stress. Common tackifiers include resins, such as terpenes, aromatic resins, hydrogenated hydrocarbon resins and terpene-phenol resins. Silicon rubber-based pressure sensitive adhesives are typically combined with special silicate resins.
The elastomer used in a pressure sensitive adhesive can offer varying advantages and limitations, depending both on the tackifier and the application it is used in. However, there are still several basic characteristics associated with commonly used elastomers.
Rubbers tend to offer good shear strength, flexibility and adherence, along with low-cost. They are suitable for use in both short- and long-term applications. However, rubber doesn’t age well and is prone to yellowing. It also does not fare well with high temperatures, and suffers from limited tack and adhesion in the absence of additives.
Acrylates are known for solid UV, solvent and hydrolosis resistance, as well as good shear strength. They can work in temperatures ranging from -45 to 121 degrees Celsius (C), and are easier to use than rubber. Acrylates are slightly more expensive when compared to rubber and silicone, and have low creep resistance, which may be limiting factors in certain applications.
Silicones possess a broader temperature range than acrylates and rubbers, and can be used in applications that range in temperature from -73 to 260 degrees C. They also feature high chemical and solvent resistance, as well as solid oxidation resistance. However, when compared with rubbers and acrylates, they tend to be more expensive.
There are several common variants of hot melt pressure sensitive adhesive based on the strength and type of adhesion. Based on application specifications, one type may be more appropriate than another.
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