|  | The two major ingredients of adhesive formulations are the polymer and the tackifier.
The adhesive polymer provides the overall strength of the formulation, while the tackifier helps promote adhesion and tack. It also lowers the system viscosity into a useful working range.
The tackifier generally influences the adhesive color, odor and stability. The selection of a tackifier depends primarily on softening point, composition, molecular weight and molecular weight distribution. Other modifiers, such as oils and waxes, are also added primarily to further reduce viscosity. They may also influence other adhesive properties such as tack, open- and set-time, etc.
| Hot Melt Adhesives
Hot melt adhesives are thermoplastic materials, which are mixed and applied in the molten state at temperatures varying from 120 to 180°C.
Hot melt adhesives are composed of three main constituents:
- a high molecular weight polymer (e.g. EVA or synthetic rubber) acting as backbone and providing mainly the mechanical properties of the adhesive
- a tackifying resin to provide the wetting and adhesion properties
- a plasticizer, such as an oil or wax, to control mainly the viscosity of the blend and enabling the adhesive to be handled by simple machinery.
Pressure Sensitive Adhesives
A pressure sensitive adhesive -- PSA -- can be defined as a substance capable of holding materials together by instantaneous low pressure surface contact.
Most commonly, a PSA is based on selected elastomers modified to enhance tackifying and wetting properties.
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