Take You into The World of Polyurethane Adhesives

Polyurethane adhesives usually refer to the components containing isocyanate groups (NCO) in two-component polyurethane products, which are mainly used in combination with components containing active hydrogen. Common components containing active hydrogen include polyether polyols, polyester polyols, epoxy resins, hydroxyl acrylic resins, etc. In these products, the addition of curing agents can not only improve the crosslinking degree and cohesive energy of the products, but also enhance the strength and weather resistance of the final products. Polyurethane curing agents are currently widely used in adhesives, coatings, inks and other fields.

Classification of polyurethane adhesives

Polyurethane adhesives can be classified into three categories: solvent-based, water-dispersible and blocked.

For most traditional products, solvent-based adhesives are more commonly used. This type of adhesives can give the product better strength, weather resistance, mechanical properties, etc.

As people's environmental awareness increases, waterborne polyurethane materials are gradually gaining attention. In two-component waterborne polyurethane products, the isocyanate component plays a vital role. Currently, the more common practice is to achieve dispersion in water by hydrophilic modification of isocyanate. The main modification methods include nonionic modification, anionic modification and anionic-nonionic modification.

The NCO group in the adhesive component is highly active and can react with water in the atmosphere at room temperature to deteriorate. In order to facilitate storage and reduce raw material loss, a blocking agent can be used to react with NCO to obtain a blocked adhesive that is stable at room temperature.

Blocked adhesives can be restored to their original isocyanate structure by heating and react with hydroxyl-containing components. The general idea of its formula design is to introduce a blocking agent on the basis of the above-mentioned common solvent-based and water-dispersible polyurethane curing agents, thereby blocking the excess NCO groups. Different blocking agents have different deblocking temperatures, and we can also choose different blocked adhesives according to specific usage scenarios.

Application of polyurethane adhesives

With the rapid development of polyurethane, its adhesives have also been produced and developed rapidly.

Polyurethane adhesives are used in adhesives, printing pastes and inks, etc., which can improve bonding performance and water washing fastness; as an external cross-linking agent, it is used in wood paint, coatings, leather finishing agents, etc., which can maintain high gloss, improve hardness, and improve water resistance and solvent resistance.

In some baking paint systems, such as paint for coil steel, closed polyurethane adhesives are mostly used. They are cured after being unsealed by heating. After film formation, the coating has better toughness, weather resistance and scratch resistance.

In some high-quality furniture industries, such as matte wood paint, the varnish coating with added matting agent has low transparency and poor media resistance. However, the adhesive can achieve the matte effect from the molecular structure. The same paint can be matched with matte curing agents of different structures to get the gloss we need.

In some food soft packaging fields, most of them use some solvent-based aromatic polyurethane adhesives, such as TDI-TMP adducts. In recent years, for food safety considerations, researchers are committed to developing low free NCO adhesives and alternative aliphatic polyurethane adhesives.