Method of curing a polythiourethane based substrate with a salt catalyst

A method of curing a polythiourethane based transparent casted optical lens substrate, comprising the following steps 1), 2), 3), 4) and 5) or 1′), 2′), 3), 4) and 5):

• 1) providing a first component A comprising at least one polyisocyanate or polyisothiocyanate monomer A2;
• 2) providing a second component B comprising a polythiourethane pre-polymer B1 having thiol end groups, said pre-polymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer;
• or:
• 1′) providing a first component A comprising a polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups of formula —NCX where X is O or S, said pre-polymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer;
• 2′) providing a second component B comprising at least one polythiol monomer B2;
• 3) mixing together first and second components A and B and filling a molding cavity of a casting mold assembly with the resulting polymerizable mixture;
• 4) curing said polymerizable mixture to obtain a polythiourethane based transparent substrate;
• and
• 5) recovering the polythiourethane based transparent substrate from the casting mold assembly;
• wherein curing step 4) is carried out in the presence of at least one salt catalyst in an amount ranging from 0.015% to 0.15% by weight with respect to the total weight of polymerizable compounds present in the mixture of first and second components A and B.