| abstract |
The invention discloses a polyurethane firming agent with low free MDI monomers and a method for preparing the same. The invention solves the problems that the prior art has complex MDI polyurethane firming agent preparation process and high equipment investment. The technical proposal comprises the following steps that: the step one, a molecular weight modifying agent is added into a composition of MDI and polylol; prepolymerization reaction is carried out in a solvent, wherein, the equivalent proportion of NCO to OH is 3-5 to 1; and the adding amount of the molecular weight modifying agent is 1 to 1.5 percent of the MDI mass; step two, after the prepolymerization reaction is finished, a trimeric catalyzer is added into the solvent for trimerization reaction; the adding amount of the trimeric catalyzer is 0.1 to 0.3 percent of the residual MDI mass theoretically after the reaction in the step one; after the trimerization reaction is finished, a polymerization inhibitor is added into the solvent to terminate the reaction. The process method has low production cost and simple process equipment; the prepared firming agent has stable storage, low toxicity and performances which can meet various requirements of the firming agent of sizing agent for packing a composite membrane; when the solid content is 75 percent, the content of free MDI monomers is less than 2 percent of the firming agent mass. |