Retortable solvent free lamination adhesives

A solvent-free, lamination adhesive kit comprising:

• a) a composition comprising:
• i) an isocyanate-functionalised, aliphatic polyurethane prepolymer comprising monomeric units derived from aliphatic isocyanate monomers, wherein an aliphatic polyurethane prepolymer is formed from aliphatic isocyanate monomers, wherein the identity of the isocyanate alone dictates the polyurethane as being aliphatic or aromatic, and wherein an aliphatic isocyanate monomer is one wherein the isocyanate group(s) is/are not directly attached to an aromatic ring;
• wherein the aliphatic isocyanate monomers are diisocyanates selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof;
• wherein the isocyanate-functionalised, aliphatic polyurethane prepolymer is derived from a polyester polyol and/or a polyether polyol;
• wherein the molar ratio of the NCO groups of the aliphatic isocyanate monomers to the HO groups of the polyol from which the isocyanate-functionalised, aliphatic polyurethane prepolymer is derived is from 5:1 to 2:1;
• and
• ii) a further aliphatic polyisocyanate selected from the group consisting of aliphatic polyisocyanate trimers, aliphatic polyisocyanate allophanates, aliphatic polyisocyanate biurets, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate uretdiones, and combinations thereof;
• and
• b) a polyol crosslinker, wherein the polyol crosslinker is a linear or branched polyether polyol and/or a linear or branched polyester polyol;
• wherein the amount of free isocyanate monomer present in the polyurethane prepolymer is less than or equal to 0.1% (w/w) of said prepolymer;
• wherein the amount of free isocyanate monomer is determined according to the method described in the description;
• and wherein the polyol crosslinker does not comprise a silane additive capable of reacting with isocyanates.