Polyurethane Prepolymer with Very Low Monomeric Isocyanate Content


 Number/Link: WO 2016/142513

Applicant/Assignee: Henkel

Publication date: 15-09-2016

Gist”: An NCO-ended prepolymer is reacted with a bis(alkoxysilylalkyl)amine

Why it is interesting: This invention is about laminating adhesives with a ‘primary aromatic amine migration limit’ of less than 10ppb, in accordance with the EU regulation for food packaging laminates. The low monomeric content is achieved by first making a NCO-ended prepolymer, which is then reacted with an monofunctional ‘H-acidic’ compound, preferably a bis(alkoxysilylalkyl)amine.  In an example a mixture of diols (OHv 108 to 236) was  reacted with 2.4-TDI down to an NCO value of 3.85%. Then 4,4′ MDI, trimethylolpropane and a triiso based on TDI were added to an NCO value of 2.2%.  Finally the prepolymer was reacted with bis(3-(triethoxysilyl)proplyl)amine at an NCO/NH ratio of 7:1.  Final NCO value was 2% with 0.05% (w/w) free 2,4-TDI and less than 0.01% free 4,4′-MDI. The prepolymer is said to be useful in 1K and 2K adhesive compositions and is said to have better adhesion properties and reactivity compared to NCO-free adhesives like sile silane-terminated PU adhesives.



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