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What are hot-melt polyurethane reactive adhesives used for?
Martina said:Although hot-melt polyurethane reactive adhesives have been available more than 20 years, their novel properties and the development of diverse products have accelerated their recent growth. They are environmentally friendly materials because they are solventless.They are now found in many applications as products are developed to fit specific needs. In general, Hot-Melt PUR adhesives have these characteristics:
They possess hot melt's original high initial bonding strength to realize increases in productivity. They also possess reactivity (moisture curing, UV curing, moisture curing + UV curing) so they exhibit excellent bonding characteristics and durability.They are solid at room temperature, similar to other hot-melt adhesives that are thermoplastic polymers, such as ethylene vinylacetate (EVA), polyalphaolefin (PAO), polyester and polyamide.
The adhesive is melted using a specifically designed premelter and then applied to the article to be bonded. The temperature for application as a melt ranges from 85°C to 140°C (185°F to 284°F), which is less than that for typical thermoplastic hot melt products. The viscosity at the application temperature can be designed in a range from 2,000 to 60,000 cPs depending on the specific requirements.
Hot-Melt adhesives are being produced with open times varying from 10 seconds to 10 minutes to match application requirements.
The unique property that gives Hot-Melt PUR adhesives their performance advantage compared to thermoplastic hot melts is that they cure to a thermoset material that resists melting. This curing process is the reaction with moisture found in the air or in typical substrates to produce a strong, tough, temperature-resistant adhesive.
The advantages of Hot-Melt adhesives result from the properties that were described above. Some of these advantages are:
The polyurea structure effectively crosslinks the adhesive to prevent its remelting or dissolving as can occur with standard thermoplastic hot-melt adhesives.The cured adhesive has excellent temperature and environmental resistance. Many of the Hot-Melt PUR adhesives can withstand exposure to temperatures from -40°F to +200°F while maintaining strong bonds.
Minimal fixturing is needed due to the controlled set time and rapid development of green strength that can be designed into these products. They are typically applied by roll coating, slot-die coating, gravure printing, screen printing or spray coating (swirl or fiberized) and then briefly nipped or pressed to provide a bond with handling strength. Final cure and ultimate strength are achieved in a few hours to a few days depending on the adhesive, substrate and conditions in the plant.
Hot-Melt adhesives can be designed and developed with widely varying properties for specific applications. Hot-Melt adhesives are 100% solids and therefore have no volatile organic compounds (VOCs) and do not require drying ovens. This eliminates many of the environmental issues associated with solvent-based adhesives and the energy requirements for drying water-based and solvent-based products.
What are hot-melt polyurethane reactive adhesives used for?
Martina said:Although hot-melt polyurethane reactive adhesives have been available more than 20 years, their novel properties and the development of diverse products have accelerated their recent growth. They are environmentally friendly materials because they are solventless.They are now found in many applications as products are developed to fit specific needs. In general, Hot-Melt PUR adhesives have these characteristics:
They possess hot melt's original high initial bonding strength to realize increases in productivity. They also possess reactivity (moisture curing, UV curing, moisture curing + UV curing) so they exhibit excellent bonding characteristics and durability.They are solid at room temperature, similar to other hot-melt adhesives that are thermoplastic polymers, such as ethylene vinylacetate (EVA), polyalphaolefin (PAO), polyester and polyamide.
The adhesive is melted using a specifically designed premelter and then applied to the article to be bonded. The temperature for application as a melt ranges from 85°C to 140°C (185°F to 284°F), which is less than that for typical thermoplastic hot melt products. The viscosity at the application temperature can be designed in a range from 2,000 to 60,000 cPs depending on the specific requirements.
Hot-Melt adhesives are being produced with open times varying from 10 seconds to 10 minutes to match application requirements.
The unique property that gives Hot-Melt PUR adhesives their performance advantage compared to thermoplastic hot melts is that they cure to a thermoset material that resists melting. This curing process is the reaction with moisture found in the air or in typical substrates to produce a strong, tough, temperature-resistant adhesive.
The advantages of Hot-Melt adhesives result from the properties that were described above. Some of these advantages are:
The polyurea structure effectively crosslinks the adhesive to prevent its remelting or dissolving as can occur with standard thermoplastic hot-melt adhesives.The cured adhesive has excellent temperature and environmental resistance. Many of the Hot-Melt PUR adhesives can withstand exposure to temperatures from -40°F to +200°F while maintaining strong bonds.
Minimal fixturing is needed due to the controlled set time and rapid development of green strength that can be designed into these products. They are typically applied by roll coating, slot-die coating, gravure printing, screen printing or spray coating (swirl or fiberized) and then briefly nipped or pressed to provide a bond with handling strength. Final cure and ultimate strength are achieved in a few hours to a few days depending on the adhesive, substrate and conditions in the plant.
Hot-Melt adhesives can be designed and developed with widely varying properties for specific applications. Hot-Melt adhesives are 100% solids and therefore have no volatile organic compounds (VOCs) and do not require drying ovens. This eliminates many of the environmental issues associated with solvent-based adhesives and the energy requirements for drying water-based and solvent-based products.
