Polyurethane curing agent with low free MDI monomer and method for preparing same

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.

Description

technical field [0001] The invention relates to a polyurethane curing agent used in adhesives for solvent-based packaging composite films, in particular to a polyurethane curing agent with low free MDI monomer. Background technique [0002] The food flexible packaging made of composite film material is suitable for people's daily needs due to its light weight, convenience, long shelf life, sanitation, easy storage, easy disassembly and good shelf effect, and is increasingly popular. The properties of these composites depend not only on the selected films but also on the properties of the adhesives used to bond the different film composites together. Usually this type of adhesive includes a main agent and a curing agent. Currently, the commonly used curing agent is a prepolymer of polyols such as toluene diisocyanate (TDI) and trimethylolpropane. Toluene diisocyanate monomer is a colorless transparent liquid with a strong irritating odor and a strong irritating effect on the...

AI Technical Summary

Problems solved by technology

[0008] In addition, free MDI monomers can cause health and safety hazards and reduce product performance. For example, too much free MDI monomers will undergo dimerization reactions, resulting in the precipitation of insoluble matter, making the product turbid and increasing the sensitivity of the product to humidity. property, the migration of small molecular monomers to the interface leads to a decrease in adhesion, etc.

Therefore, in the curing agent preparation process, the residual amount of MDI monomer should be reduced as much as possible. At present, foreign companies have complicated processes for removing free MDI monomer. The MDI monomer prepolymer with MDI monomer content requires the use of large-scale equipment such as scraper-type thin-film evaporators in the process. These equipment have high initial investment and complex process operations, which greatly increase the product cost.

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