Polyurethane foam is a foam material that boasts the highest production output. Its relative density is generally between 0.03 and 0.06. When compared to cork or polystyrene foam, the thermal conductivity of hard foam is only about 40% of what is observed with these materials. This high-quality material is not only strong and durable but also resistant to oil while having the ability to bond. Its properties make it an excellent choice for sound insulation, heat insulation, and shockproofing. Due to its unique properties, polyurethane foam is widely used to insulate home appliances such as refrigerators, water heaters, freezers, beer barrels and incubators. It is also useful in the thermal insulation of various equipment such as heat supply and crude oil transport pipelines, refrigerated transport vehicles, passenger cars and tank bodies. With regards to building energy conservation, it can be used for external wall thermal insulation, cold storage, roofing thermal insulation, and anti-theft doors and garage doors. Its application extends to packaging as well as decoration, where it is used for making decorative boards, handicrafts, and even imitation wood furniture. Another variant of polyurethane foam is the flexible foam which is known for its excellent elasticity and is mostly used as an ideal cushion and mattress material.
According to its processing mode, polyurethane rubber can be categorized into three types: mixing type, thermoplastic type, and casting type. The mixing type involves the use of saturated or hydroxyl terminated polyurethane with a small amount of double bonds, which can be processed similar to ordinary rubber, but the output is comparatively low. Thermoplastic rubber can be further divided into full thermoplastic and semi thermoplastic. Full thermoplastic has a linear structure, while semi thermoplastic has a small amount of crosslinking. They can be formed using thermoplastic processing methods and equipment. On the other hand, cast rubber is commonly made by rapidly mixing liquid prepolymer and chain extender, and then casting or spraying it into shape. This type of rubber exhibits strong adaptability. Currently, about two-thirds of polyurethane rubber products are molded using the casting method. In recent years, there has been the emergence of reaction injection molding technology, which allows for direct injection of liquid monomer and rapid reaction molding. This technology offers advantages such as high production efficiency, minimal equipment investment, and excellent part performance.
The field of polyurethane coatings is commonly divided into two categories: single-component and two-component coatings. Two-component polyurethane coatings are typically based on polyether materials, whereby a solution of polyisocyanate and polyether are mixed together. In contrast, single-component polyurethane coatings are usually based on unsaturated polyester materials and encompass types such as oil-modified, wet-cured, and closed systems. Polyurethane coatings can be applied through a variety of methods including spray, electrodeposition, and impregnation. The coatings possess properties such as wear-resistance, resistance to gasoline, grease, water, and inorganic acid vapors, superior insulation and adhesion, as well as long-lasting bright colors.
Polyurethane adhesives are composed of polyisocyanates and hydroxyl containing polyester compounds. These two components are mixed together just before application, and the adhesive has a storage period of about 1-3 hours. To cure, the adhesive needs to be left for at least 24 hours at room temperature or heated to 100-150°C and pressurized at 0.03-0.05 MPa for 1-3 hours.
Polyurethane adhesives possess high adhesive force with a variety of materials, and they are highly resistant to water, mineral grease, fuel, aromatics, and atmospheric conditions. They have a wide temperature range of -200 to 120°C, but they are also expensive. These adhesives are mainly used in aviation, space technology, construction, machinery, and polymer film bonding applications. They also function as a bonding agent for soles and upper materials.