An adhesive is any substance which, when applied between two or more surfaces (i.e., substrates), holds, fastens, or bonds them together. The durability of this bond (i.e., the bond strength) largely depends on the type of bonding adhesives, i.e. it’s properties specifically the adhesion and cohesion.
Thermoplastic adhesive are plastic materials. The constituent of these adhesives are polymers that melt above a specific temperature and solidify upon cooling. Some examples would be different types of hotmelt adhesives, polyamides, polyvinyl acetate, polyacrylate, polyolefin and so on.
Thermosetting adhesives are also polymers, or plastics. They are supplied in an uncured state consisting of unlinked monomers. In other words, thermosets are generally a liquid material at room temperature which hardens irreversibly upon heating or chemical addition.
Rubber based adhesives also belong to the thermosetting adhesive family.
Thermoset resins, throughout the length of their polymer chain, have certain spots (the double bonds, or the unsaturation) that can be chemically activated and can create chemical bonding reactions with neighbouring polymer molecules. Since all thermosets carry these chemically reactive spots, often, they have the tendency to connect to one another. Such a process of forming chemical links across different thermosetting molecules is called crosslinking (or curing). Curing occurs after an exposure to heat and pressure or an exposure to moisture, radiation, or a catalyst. When thermosetting rubber adhesive is subjected to the correct curing temperature, it provides increased adhesion, solvent resistance & heat resistance. These crosslinks give the thermoset a permanent 3D structure (shown in the above picture) and makes them more resistant to melting. In thermoplastic these crosslinks are not formed.
Curing results in
After curing, the molecular weight of the thermosetting adhesive increases drastically thereby causing major changes in the material properties such as an increased melting point. The melting point can rise and reach a point that exceeds the decomposition point thus the thermoset polymer would decompose before it can melt, thereby illustrating why the process is irreversible.
|Molecular structure||Network polymers: high level of crosslinking with strong chemical molecular bonds|
|Melting point||Melting point higher than the degradation temperature|
|Mechanical properties||Strong and rigid. Strength comes from crosslinking.|
|Size||Size is expressed by crosslink density|
|Solubility||Does not dissolve in organic solvents|
By changing the tackifiers and hydrocarbon in the formulation of the thermosetting rubber adhesive, we obtain a higher quality product with a temperature resistance of 210oc.
Due to the chemical crosslinks formed in the thermosetting rubber, it makes the rubber more chemical and solvent resistant
Thermosetting pressure sensitive rubber adhesive tapes have great masking properties due to their chemical bonding process.
As per our aging study, shelf life of products with thermosetting rubber adhesive can withstand upto 3 years. [ASTM D1000]
The higher the dielectric constant, the better a material functions as an insulator. Rubber has an extremely high dielectric constant, so it is often used as a protective coating around high voltage wires.
Like rubber adhesives, thermosetting rubber allows very less heat to pass through the product. They also have no carbon atoms; thus, they are poor conductors of electricity and act as an insulator.
Thermosetting rubber adhesives are resistant to water and corrosion due to its strong double bonds.
Adhesive Specialities manufactures more than 200 types of pressure sensitive tapes which also include a wide range of thermosetting rubber adhesive tapes, some of which include:
The properties derived by thermosetting rubber adhesives have a great potential to open a wide variety of applications in the future. The R&D team at Adhesive Specialities takes immense pride in developing newer and better grades of thermosetting adhesive and have been able to reach a temperature resistance of up to 2100C.