Polyurethane adhesives are a type of high-performance and widely applied high-molecular bonding materials. Their core features are mainly reflected in the following five aspects:
1. Excellent bonding performance and wide applicability
The most prominent advantage of polyurethane adhesives is their excellent bonding ability and wide applicability. Its molecular chain contains highly polar carbamate groups (-NH-COO-), which can form powerful van der Waals forces, hydrogen bonds, and even chemical bonds with the surfaces of various materials. Therefore, it can not only bond traditional high surface energy materials such as metal, glass and ceramics, but is also better at bonding low surface energy and non-polar materials such as plastic, rubber, wood, leather, fabric and paper, for example, difficult-to-bond polypropylene (PP), polyethylene (PE), etc. This "versatile" characteristic makes it an irreplaceable bonding solution in fields such as composite packaging, automotive manufacturing, shoemaking, and the wood industry.
2. Excellent low-temperature resistance and toughness
Unlike many adhesives that become brittle at low temperatures, such as epoxy resins, polyurethane adhesives can still maintain good bonding strength and excellent flexibility at extremely low temperatures. Its molecular chain segments are composed of soft segments and hard segments to form a microscopic phase separation structure. The soft segments can still maintain their mobility at low temperatures, endowing the adhesive layer with high elasticity and impact and vibration resistance. This feature makes it highly suitable for bonding equipment and vehicles in cold environments, as well as structures that need to withstand dynamic loads or thermal expansion and contraction, effectively avoiding cracking of the adhesive layer caused by stress concentration.
3. Adjustable curing method and performance
Another notable feature of polyurethane adhesives is that their performance is highly designable. By altering the types and proportions of polyols and isocyanates, the modulus, hardness, elongation and curing speed of adhesives can be precisely regulated. In terms of curing methods, it can be a single-component moisture-curing type, which undergoes cross-linking by absorbing moisture from the air and is convenient to use. It can also be a two-component type, achieving rapid curing through the precise mixing of the main agent and the curing agent, with controllable performance. This flexibility enables engineers to "tailor" the most suitable adhesive products for specific application scenarios.
4. Good wear resistance and fatigue resistance
Thanks to the excellent wear resistance of polyurethane materials themselves, their adhesive layers often also have good wear resistance after curing. Meanwhile, due to the fact that the internal molecular chains of the adhesive layer can effectively disperse and absorb energy through reversible physical cross-linking or hydrogen bonding, it has excellent fatigue resistance and can withstand repeated bending, twisting or vibration without being easily damaged. This characteristic is crucial in dynamic applications such as conveyor belt bonding, shoe sole bonding, and composite structures of elastomers and metals.
5. Comprehensive chemical resistance and weather resistance
Polyurethane adhesives have a certain resistance to oils, solvents, ozone and various chemical substances. Although its high-temperature resistance and hydrolysis resistance are relatively its shortcomings, they can be significantly improved through formulation techniques (such as using polyester polyols or adding hydrolysis stabilizers). In addition, high-quality polyurethane adhesives also have excellent weather resistance, which can resist the influence of ultraviolet radiation and atmospheric aging to a certain extent, ensuring long-term bonding stability when used outdoors.
