Preparation and Properties of Foamed Polyurethane Adhesives
Foamed one-component polyurethane adhesive (MPU) has no solvent, low viscosity, good foaming property, can be cured at room temperature, and has high bonding strength. It is used for bonding PVC plastic-coated steel plates and rock wool to meet the technical requirements of automatic production lines. It is a new type of material that can not be lost to shipbuilding and naval construction, especially shipbuilding.
1, the reaction principle
The synthesis of foamed one-component polyurethane adhesives is mainly the reaction of hydroxyl-containing compounds with isocyanate groups to generate NCO prepolymers:
OCN-R-NCO+HO~~OH→OCN-R-NHCOO~~OOC-NH-R-NCO
When solidified, water reacts with isocyano groups to form amines, and amine groups react with isocyano groups to form urea:
2. Preparation method
The main raw material is polyoxypropylene polyol (functionality 2 or 3), and the relative molecular weight is greater than 2000. Liquid polyisocyanate (PAPI) is a low molecular reinforcing agent.
The polyol component should be dehydrated beforehand. The reaction was carried out under a dry nitrogen atmosphere. The product is packed in a closed container and protected from light.
3, the impact of adhesive properties
I. Effect of NCO/OH (R Value) on Viscosity
As the NCO/OH molar ratio and NCO content increase, the viscosity of the adhesive decreases, as can be seen from the table
Normal > NCO/OH
Normal > 1.3/1
Normal > 2.3/1
Normal > 2.5/1
Normal > 2.7/1
Normal > NCO content /%
Normal > 1.6
Normal > 5.0
Normal > 5.4
Normal > 6.8
Normal > Viscosity (250C)/Pa.s
Normal > >100
Normal > 22.28
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