What Is Urethane Adhesive?
Urethane adhesives are adhesives that use a urethane reaction, which is an addition reaction of polyisocyanate and polyol, and have high adhesive properties. Urethane adhesives are mainly composed of urethane resin and are available in one-component, two-component, and hot-melt types, with the two-component type used in a wide variety of structural adhesives. Two-component types are used in various applications, such as structural adhesives. In particular, they are used for resin applications because of their extremely high adhesion to resin. They are also more flexible than epoxy or acrylic adhesives and provide high-impact resistance and shock absorption.
Uses of Urethane Adhesive
Urethane adhesives are used in a variety of areas, including automotive parts, housing, and construction equipment. In particular, they are often used for resin adhesion applications due to their extremely high adhesion to resins. Recently, carbon fiber-reinforced plastics have been used more extensively to reduce the weight of automobiles, and demand for automotive parts applications is expanding. It also has excellent water and heat resistance and is used for products around water, such as unit baths and kitchens. Since it reacts with moisture in the air and hardens, care must be taken when storing it.
Principle of Urethane Adhesive
This section describes the curing principle of urethane adhesives and cautions for their use. There are three types of urethane adhesives: one-component type, two-component type, and hot-melt type. The curing principle of each adhesive is different.
1. One-Component Type
The one-component type adhesive is cured by reacting with moisture in the air. Since it is affected by the amount of moisture in the air, it should be noted that it takes longer to cure in winter when humidity is low. Conversely, in humid environments, one-component types are used mainly as sealants.
2. Two-Component Type
In the two-component type, mixing polyol (the main agent) and isocyanate (the hardener), an additional polymerization reaction proceeds, resulting in the curing. Since the mixing ratio of each is strictly regulated, incorrect measurements may result in failure to cure. In addition, polyols are highly water absorbent, so they must be sealed and stored in a place with low humidity.
3. Hot-Melt Type
This type cures by reacting with moisture in the air, but pretreatment is performed by heating. This has the advantage of providing high heat resistance, adhesiveness, and durability.