Flexible packaging adhesives are predominately based on urethane and acrylic chemistry. Backbone options create unique performance properties. Changes in composition determine whether it is solvent-based and solvent-free adhesive.
The general polyurethane adhesive contains some sort of polyol or mixtures, and some sort of an isocyanate or mixtures. Other extenders and alternate cross-linking chemistry may also be present.
The nature of the polyol defines the type of generic urethane created. The polyether backbone is generalized by the -C-O-C- linkage. When reacted or extended with isocyanate, the resulting adhesive could be called a polyether urethane adhesive.
Some properties derived from using an ether backbone in adhesives are:
- hydrolysis resistance - retain their properties longer in conditions of extreme moisture, such as those found in wet and humid environments, resistance to some oxidizing agents.
- Microbe resistance - resistance to biological decay and won’t degrade with soil or food contact.
- Low-temperature properties - retain their elasticity and flexibility at extremely low temperatures.
- Dynamic properties and resilience - exhibit excellent dynamic properties including high flexibility, elongation and tensile properties.
the polyester urethanes made from polyester polyols have higher polarity, and show generally better metal adhesion than adhesives derived from polyether polyols.
Some properties derived from using an ester backbone in adhesives are:
- Chemical resistance adhesive - resist absorption or attack by chemicals or solvents.
- Adhesion more polar, have a stronger specific adhesion to more materials.
- Low temperature properties - tend to be more brittle in low temperatures.
- Crystallinity - can have low to high backbone crystallinity, resulting in soft to hard segments that vary flexibility, adhesion and chemical resistance.
