As a class of adhesives with excellent performance, polyurethane adhesives are widely used in industry and daily life. Polyurethane adhesives can be divided into various types according to their composition, solvent form, and application. The following are common ways to classify polyurethane adhesives.
1. Classification according to reaction components
According to the reactive components in the adhesive, polyurethane adhesives can be divided into the following categories:
(1) Polyisocyanate adhesives
This type of adhesive is mainly made of isocyanate monomers such as toluene diisocyanate, phenylmethane diisocyanate, etc. Due to its greater toxicity and rigidity, it is less widely used.
(2) Isocyanate-based polyurethane adhesives
It is prepared from the prepolymer of the isocyanate group, which is the product of the reaction of polyisocyanates and polyhydroxy compounds. Common types include one-component, two-component, solvent-based, and solvent-free. They have high bond strength and are suitable for a wide range of materials.
(3) Hydroxyl polyurethane adhesive
It is mainly synthesized by the reaction of diisocyanate and polyether diols, and is a two-component adhesive. Due to its linear structure, it is a thermoplastic polyurethane suitable for use with polyisocyanates.
2. Classification by use
According to the application field and characteristics of polyurethane adhesives, they can be divided into the following categories:
(1) General-purpose polyurethane adhesive
The two-component structure is widely used in the bonding of various materials. Component A is a prepolymer containing a hydroxyl group or terminal isocyanate, and component B is usually a low-molecular-weight polyol.
(2) Polyurethane adhesive for wood
Polyurethane adhesives are more environmentally friendly than traditional formaldehyde-based adhesives due to their low toxicity and less harm to the human body and the environment. It has excellent adhesion properties, especially in wet and dry environments.
(3) Polyurethane adhesive for shoes
Due to its strong bonding strength, it is widely used in footwear manufacturing. Through the prepolymerization process, the tensile strength and adhesive performance of shoe adhesive can be effectively improved.
(4) Polyurethane adhesive for composite film
Since the 1970s, it has been used in the preparation of composite films, and the technology has gradually matured. Nowadays, there are a wide range of applications at home and abroad, especially the application of waterborne polyurethane in the field of environmental protection is growing.
(5) Polyurethane adhesive for building materials
Due to its weather resistance and strong adhesion, it is suitable for the bonding of building materials such as flooring, wall panels and rubber materials. The new two-component formula solves the problem of insufficient peel strength in the past.
3. Classification according to solvent form
Depending on the form of the solvent used in the adhesive, polyurethane adhesives can be divided into the following categories:
(1) Solvent-based polyurethane adhesive
Organic solvent is used as the dispersion medium, which has good flexibility and low temperature resistance. Due to environmental regulations, the use of solvent-based polyurethanes is gradually decreasing.
(2) Water-based polyurethane adhesive
The use of water as the dispersion medium reduces the use of organic solvents and is more environmentally friendly. In recent years, the performance of waterborne polyurethane has gradually improved, and its market share has been increasing.
(3) Solvent-free polyurethane adhesive
No organic solvents are used, which has the advantages of environmental protection and safety, simple process and fast compounding speed. Despite challenges in terms of equipment demand and post-maturation, it is gaining momentum.
summary
The versatility and wide range of applications of polyurethane adhesives make them important materials for industrial and consumer applications. With the improvement of environmental awareness, water-based and solvent-free polyurethane adhesives are becoming the mainstream direction of future development.
