Method for curing polythionocarbamate-based substrates with salt catalyst

Abstract

The invention relates to a method for curing a transparent cast substrate based on polythiourethane, comprising providing a first component A comprising at least one polyisocyanate or polyisothiocyanate monomer A2, providing a second component B comprising a polythiourethane prepolymer B1 having thiol end groups, mixing the first component A and the second component B together and filling a mold cavity of a casting mold assembly with the resulting polymerizable mixture, curing the polymerizable mixture to obtain a transparent polythionocarbamate-based substrate, wherein the 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 relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B. Alternatively, the first component A comprises a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups and the second component B comprises at least one polythiol monomer B2.

Description

[0001] The present invention relates to a method for making polythiourethane-based substrates, and in particular optical substrates such as ophthalmic lenses, which typically have a medium or high refractive index of preferably at least 1.52, more preferably at least 1.54, more preferably at least 1.6, and even more preferably at least 1.67 in a short cure cycle.

[0002] Background and Summary of the Invention

[0003] Ophthalmic lenses made from polythiourethane-based substrates are typically prepared by a process that includes mixing appropriate monomers (such as a mixture of polyisocyanates and polythiols) in a tank, adding catalysts and additives, filling a mold cavity with the liquid mixture of monomers, polymerizing the monomer mixture, and thereafter recovering the polymerized polythiourethane-based substrate from the mold. The mixture is then subjected to a thermal cycle in an oven for a typical duration of 20 hours.

[0004] Application WO 00 / 26272 discloses a polymerizable composition for preparing a poly(thio)urethane resin, comprising at least one polyiso(thio)cyanate monomer, at least one polythiol monomer and a salt catalyst system (typically a mixture of KSCN and a crown ether).

[0005] The fast curing method is highly desirable compared to conventional methods, since shorter residence times in the curing oven allow for a significant increase in productivity, complex and demanding lens geometries can be obtained at higher yields due to lower shrinkage of the final polymerizable mixture than that obtained directly from the monomers, better compatibility with tape adhesives used for mold assembly, and reduced energy consumption during the polymerization cycle.

[0006] It is known to reduce the time required to cure a polymerizable composition injected into a mold assembly by at least partially replacing the monomers with prepolymers (or oligomers). The monomers are first pre-reacted to form oligomers (prepolymers), then blended with a catalyst (which provides high overall reactivity in a very small volume) or even blended by in-line mixing equipment, and then injected into the mold assembly which is subjected to a short polymerization cycle (typically a few hours).

[0007] In this regard, US2003 / 125410 discloses a method for rapidly curing a polythiourethane transparent casting substrate, the method comprising the following steps:

[0008] 1) providing a first component A comprising a polythiourethane prepolymer having isocyanate or isothiocyanate terminal groups,

[0009] 2) providing a second component B comprising a polythiourethane prepolymer having thiol end groups,

[0010] 3) mixing the first component A and the second component B together and filling the mold cavity of the casting mold assembly with the resulting mixture,

[0011] 4) Curing the mixture in the presence of 0.001% to 2.5% by weight of a highly reactive catalyst based on the total weight of polymerizable monomers to obtain a transparent solid substrate to significantly shorten the curing time of the polymerizable composition to within a typical 2 hours.

[0012] US 2007 / 098999 discloses a similar process involving two prepolymers.

[0013] If the viscosity is controlled, batch mixing of such mixtures is inherently safer than the customary method of mixing from monomers, since a portion of the available bonding energy has been released during oligomer formation (prepolymerization), which limits the formation of local hot spots in the final polymerizable mixture. The use of prepolymers allows a stable and steady reaction. Known catalysts for the synthesis of polythiourethanes are dibutyltin dichloride or a mixture of KSCN and 18-crown-6.

[0014] In applications WO 2021 / 182526, EP 3916470 and EP 3919967, different approaches are chosen for the rapid curing of polythiourethane optical materials, using a combination of monomers and prepolymers in the presence of a polymerization catalyst, typically a basic catalyst such as lutidine.

[0015] The choice of catalyst during the curing process of polythiourethane is very important, as it not only determines how quickly the material cures, but in certain cases it can also affect the final optical quality of the material. Often, a compromise must be made between reaction speed and material quality, as faster reaction rates can lead to uncontrolled polymerization and, therefore, higher streaking and more bubbles.

[0016] The object of the present invention is to provide a method for the rapid preparation of polythiourethane resins which remedies the disadvantages of the prior art methods, i.e. allows a better control of the reaction without increasing the curing time and avoids runaway reactions. Such a method should not impair the thermomechanical properties of the final material.

[0017] Another object of the present invention is to provide a method for curing polythiourethane-based cast substrates which are substantially free of optical defects, in particular free of bubbles and / or streaks resulting from the polymerization process, have high transmittance and clarity, as well as a low yellowness index and are resistant to aging.

[0018] The present inventors have discovered that replacing prior art catalysts with salt catalysts allows for the use of larger amounts of catalyst and better control of the polymerization of a polymerizable mixture comprising a polythiourethane prepolymer having isocyanate, isothiocyanate or thiol end groups and another monomer.

[0019] The present invention provides a method for rapidly curing a transparent polythiourethane-based cast substrate that can be used to manufacture optical articles such as ophthalmic lenses, the method comprising the following steps: 1), 2), 3), 4) and 5) or 1'), 2'), 3), 4) and 5):

[0020] 1) providing a first component A comprising at least one polyisocyanate or polyisothiocyanate monomer A2,

[0021] 2) providing a second component B comprising a polythiourethane prepolymer B1 having thiol end groups, said prepolymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer,

[0022] or:

[0023] 1') providing a first component A comprising a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups of the formula -NCX, wherein X is O or S, said prepolymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer,

[0024] 2') providing a second component B comprising at least one polythiol monomer B2,

[0025] 3) mixing the first component A and the second component B together and filling the mold cavity of the casting mold assembly with the resulting polymerizable mixture,

[0026] 4) curing the polymerizable mixture to obtain a polythiourethane-based transparent substrate, and

[0027] 5) recovering the polythiourethane-based transparent substrate from the mold assembly,

[0028] Wherein the curing step 4) is carried out in the presence of at least one salt catalyst, the amount of the salt catalyst relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B ranges from 0.015% to 0.15% by weight. DETAILED DESCRIPTION

[0029] The substrate of the present invention is an organic glass substrate made of a thermosetting resin. In some embodiments, the polymer matrix of the substrate is obtained from a material composition ("substrate composition") comprising at least one polymerizable prepolymer and at least two polymerizable prepolymers.

[0030] The substrate is preferably an optical article substrate, more preferably an optical lens substrate. The optical article is preferably an ophthalmic lens, such as a plastic spectacle lens.

[0031] In this specification, unless otherwise specified, a substrate is understood to be transparent when no significant contrast loss is perceived when viewing an image through the substrate, i.e., when an image formed through the substrate is obtained without adversely affecting the quality of the image. Unless otherwise specified, this definition of the term "transparent" can be applied to all objects so defined in this specification.

[0032] The term "ophthalmic lens" is used to mean a lens that fits into a spectacle frame to protect the eyes and / or correct vision. The lens may be selected from afocal, monofocal, bifocal, trifocal, progressive and Fresnel lenses or any other type of lens with a discontinuous surface. Although ophthalmic optics is a preferred field of the present invention, it is understood that the present invention may be applied to other types of optical elements, such as lenses for optical instruments, filters (particularly filters for photography or astronomy), optical sight lenses, eye goggles, optics for lighting systems, screens, inlaid glass, etc.

[0033] If the optical article is an optical lens, it may be coated with one or more functional coatings on its front main surface, rear main side or both sides. As used herein, the back of the substrate is intended to mean the face closest to the wearer's eyes when the article is used. The back is usually a concave face. Conversely, the front of the substrate is the face farthest from the wearer's eyes when the article is used. The front is usually a convex face. The optical article may also be a flat light article.

[0034] In the sense of the present invention, a substrate is understood to mean an uncoated substrate and generally has two main faces. The substrate may in particular be an optically transparent material having the shape of an optical article, such as an ophthalmic lens destined to be mounted in spectacles. In this context, the term "substrate" is understood to mean the basic constituent material of an optical lens and more particularly an ophthalmic lens. This material may serve as a support for a stack of one or more coatings or layers.

[0035] The refractive index of the polythiourethane-based substrate is preferably 1.52 or more, more preferably 1.54 or more, more preferably 1.56 or more, more preferably 1.58 or more, more preferably 1.60 or more, and still more preferably 1.65 or more or 1.67 or more, and it is preferably 1.80 or less, more preferably 1.70 or less, and still more preferably 1.67 or less. Unless otherwise specified, the refractive index mentioned in the present application is expressed at 25° C., 550 nm wavelength.

[0036] The fast curing polymerizable compositions that produce polythiourethane-based materials are composed of two main components.

[0037] In a first embodiment of the invention, the first component A provided in step 1) consists of at least one polyisocyanate or polyisothiocyanate monomer A2. In step 2) of the first embodiment of the process of the invention, a second component B is provided which comprises a polythiourethane prepolymer B1 having thiol end groups and which has been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, the former being used in excess. The second component B thus comprises oligomers and unpolymerized initial monomers (when present).

[0038] In a second embodiment of the invention, a first component A comprising a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups is provided in step 1'), and the first component has been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, the latter being used in excess. The first component A thus comprises oligomers and unpolymerized initial monomers. The second component B provided in step 2') of the second embodiment of the method of the invention consists of at least one polythiol monomer B2.

[0039] Compared to the prior art methods which use only iso(thio)cyanate or thiol monomers, the present invention uses polythiourethane prepolymers.

[0040] Prepolymer means a polymer or oligomer comprising a prepolymer molecule. A prepolymer molecule means a macromolecule or oligomer molecule that is capable of entering into further polymerization through a reactive (polymerizable) group, thereby contributing more than one monomer unit to at least one chain of the final macromolecule. Prepolymer molecules are usually formed from two or more different monomers.

[0041] The polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer with at least one polythiol monomer, preferably in the absence of a catalyst, in a ratio such that the molar ratio of isocyanate or isothiocyanate groups to thiol groups NCX / SH is preferably in the range of 3:1 to 30:1, X being O or S.

[0042] The polythiourethane prepolymer B1 having thiol end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer with at least one polythiol monomer, preferably in the absence of a catalyst, in a ratio such that the molar ratio of thiol groups to isocyanate or isothiocyanate groups SH / NCX is preferably in the range of 3:1 to 30:1, X being O or S.

[0043] The polythiol and polyisocyanate or polyisothiocyanate compounds used to prepare the polythiourethane prepolymers A1 or B1 are considered monomers herein even when they are oligomers.

[0044] Polyisocyanate means any compound containing at least two isocyanate groups, in other words, diisocyanate, triisocyanate, etc. Polyisocyanate prepolymers can be used. The polyisocyanate can be any suitable polyisocyanate having two or more, preferably two or three isocyanate functional groups. The polyisocyanate can be used to prepare polythiourethane prepolymers A1 or B1, but can also be used directly in component A in step 1) of the method of the present invention.

[0045] The polyisocyanate may be selected from aliphatic, aromatic, cycloaliphatic or heterocyclic polyisocyanates and mixtures thereof.

[0046] Polyisothiocyanates are defined in the same manner as the above-mentioned polyisocyanates by replacing the "isocyanate" group with an "isothiocyanate" group.

[0047] In one embodiment of the present invention, the polyisocyanate or polyisothiocyanate monomer is a compound having formula (VI):

[0048] R 2 (NCX) n2 (VI)

[0049] wherein X represents O or S, n2 represents an integer ranging from 2 to 6, and R 2 represents an aliphatic, alicyclic, heterocyclic or aromatic group.

[0050] Preferred polyisocyanates or isothiocyanate monomers are those having the formula:

[0051]

[0052] Where R 1 independently H or C 1 -C 5 Alkyl, preferably CH 3 or C 2 H 5 ;

[0053] R 2 is H, halogen, preferably Cl or Br, or C 1 -C 5 Alkyl, preferably CH 3 or C 2 H 5 ;

[0054] Z is -N=C=X, wherein X is O or S, preferably O;

[0055] a is an integer ranging from 1 to 4, b is an integer ranging from 2 to 4, and a+b≤6; and

[0056] x is an integer of 1-10, preferably 1-6.

[0057] The polyisocyanate of the present invention is preferably a diisocyanate. Among the diisocyanates available for use, there can be mentioned toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, biphenyl-diisocyanate, 3,3'-dimethyl-4,4'-diphenylene diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, 2,2,4-trimethylhexane-1,6-diisocyanate, lysine methyl ester diisocyanate, bis(isocyanatoethyl)fumarate, isophorone diisocyanate (IPDI), ethylene diisocyanate, dodecane-1,12-diisocyanate, cyclobutane-1,3-diisocyanate. cyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene-2,4-diisocyanate, tetramethylxylylene diisocyanate, hexahydrotoluene-2,6-diisocyanate, hexahydrophenylene-1,3-diisocyanate, hexahydrophenylene-1,4-diisocyanate, perhydrodiphenylmethane-2,4'-diisocyanate, perhydrophenylmethane-4,4'-diisocyanate (or bis-(4-isocyanatocyclohexyl)-methane or 4,4'-dicyclohexylmethane diisocyanate), bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, 2,5 (or 2,6)-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, and mixtures thereof.

[0058] Other non-limiting examples of polyisocyanates are isocyanurates from isophorone diisocyanate and 1,6-hexamethylene diisocyanate, both of which are commercially available. Further polyisocyanates suitable for use in the present invention are described in detail in WO 98 / 37115, WO 2014 / 133111 or EP 1877839.

[0059] The polythiol that can be used in the present invention is defined as a compound containing at least two sulfhydryl (mercapto) groups, in other words, dithiol, trithiol, tetrathiol, etc. Polythiol prepolymers can be used. The polythiol can be any suitable polythiol having two or more, preferably two or three thiol functional groups. The polythiol can be used to prepare the polythiourethane prepolymer A1 or B1, but can also be used directly in component B in step 2') of the method of the present invention.

[0060] In one embodiment of the present invention, the polythiol monomer is a compound having the following formula:

[0061] R 1 (SH) n1 (I)

[0062] wherein n1 represents an integer ranging from 2 to 6, and R 1 represents an aliphatic, alicyclic, heterocyclic or aromatic group.

[0063] Among the preferred polythiol monomers and / or oligomers suitable according to the invention, there may be mentioned aliphatic polythiols such as trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), trimethylolethane tris(2-mercaptoacetate), trimethylolethane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), bis(mercaptomethyl) sulfide, bis(mercaptomethyl) disulfide, bis(mercaptoethyl) sulfide, bis(mercaptoethyl) disulfide, bis(mercapto 1-(2-mercaptoethyl)thio)-1-propanethiol, 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol, 4,8 (or 4,7 or 5,7)-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 2,5-dimercaptomethyl-1,4-dithiane and 2,5-bis[(2-mercaptoethyl)thiomethyl]-1,4-dithiane, 1-(1'-mercaptoethylthio)-2,3-dimercaptopropane, 1-(2'-mercaptopropylthio)-2,3-dimercaptopropane, 1-(3'-mercaptopropylthio)-2,3-dimercaptopropane 1-(4'-mercaptobutylthio)-2,3-dimercaptopropane, 1-(5'-mercaptopentylthio)-2,3-dimercaptopropane, 1-(6'-mercaptohexylthio)-2,3-dimercaptopropane, 1,2-bis-(4'-mercaptobutylthio)-3-mercaptopropane, 1,2-bis-(5'-mercaptopentylthio)-3-mercaptopropane, 1,2-bis-(6'-mercaptohexylthio)-3-mercaptopropane, 1,2,3-tris(mercaptomethylthio)propane, 1,2, 3-tris-(3'-mercaptopropylthio)propane, 1,2,3-tris-(2'-mercaptoethylthio)propane, 1,2,3-tris-(4'-mercaptobutylthio)propane, 1,2,3-tris-(6'-mercaptohexylthio)propane, methanedithiol, 1,2-ethanedithiol, 1,1-propanedithiol, 1,2-propanedithiol, 1,3-propanedithiol, 2,2-propanedithiol, 1,6-hexanethiol-1,2,3-propanetrithiol, and 1,2-bis(2'-mercaptoethylthio)-3-mercaptopropane. Further examples of polythiols are shown in the following formula or can be found in WO 2014 / 133111, EP 394495, US 4775733 or EP 1877839:

[0064]

[0065]

[0066] In one embodiment of the present invention, the polythiol monomer is selected from the group consisting of pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (thioglycolate), tris (3-mercaptopropionate) trimethylolpropane, tris (thioglycolate) trimethylolpropane and compounds having formula (II) and (III):

[0067]

[0068] Preferred embodiments are a combination of xylylene diisocyanate and pentaerythritol tetrakis(3-mercaptopropionate); a combination of xylylene diisocyanate and 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol; a combination of 2,5(or 2,6)-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, pentaerythritol tetrakis(3-mercaptopropionate) and 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol; a combination of xylylene diisocyanate and 4 ,8 (or 4,7 or 5,7)-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane; a combination of dicyclohexylmethane diisocyanate and 4,8 (or 4,7 or 5,7)-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane; or a combination of bis(2,3-epithiopropyl) disulfide and 4,8 (or 4,7 or 5,7)-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane. The most preferred polythiol is 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol having formula (II).

[0069] Preferably, the polythiol has a value of 1 Pa.s or less, more preferably 5.10 -1 Pa.s or less, more preferably 2.5.10 -1 Pa.s or less, more preferably 2.10 -1 Pa.s or less, more preferably 10 -1 Pa.s or less, and even more preferably 0.5.10 -1 Viscosity at 25°C of Pa.s or less.

[0070] Specific examples of polythiourethane resins suitable for use in the present invention are those produced by Mitsui Chemicals Company under the trade name Those sold in series, especially (Refractive index: 1.67), (Refractive index: 1.6) resin, (Refractive index: 1.67). These optical materials and the monomers used for their preparation are described in particular in patents US Pat. Nos. 4,689,387, 4,775,733, 5,059,673, 5,087,758 and 5,191,055.

[0071] Depending on the embodiment of the invention, components A and B are prepared by polymerizing a mixture of the desired amounts of at least one polyisocyanate and / or at least one polyisothiocyanate monomer and at least one polythiol monomer and optionally a polyol monomer or a polyamine monomer. Typically, components A and B can be prepared by classical thermal polymerization including induction and infrared heating or UV irradiation.

[0072] The amounts of polyisocyanate or polyisothiocyanate monomers and polythiol monomers in the reaction medium are preferably adjusted in each case in such a way that the molar ratio of NCX / SH groups of the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers for the preparation of the polythiourethane prepolymer A1 is in the range from 3:1 to 30:1, preferably from 6:1 to 10:1, and / or the molar ratio of SH / NCX groups of the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers for the preparation of the polythiourethane prepolymer B1 is in the range from 3:1 to 30:1, preferably from 6:1 to 10:1, X being O or S.

[0073] In one embodiment, both components A and B are prepared without the use of a catalyst system, which allows better control of the polymerization reaction and produces prepolymers with high stability over time. However, they can also be prepared using a salt catalyst as described below or another catalyst as described below.

[0074] Typically, in a first embodiment of the invention, at least one polyisocyanate or polyisothiocyanate monomer A2 of component A and prepolymer B1 are contained in the mixture in such an amount that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0075] Typically, in the second embodiment of the invention, the prepolymer A1 and the at least one polythiol monomer B2 of component B are contained in the mixture in such an amount that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0076] The preparation of prepolymers B1 having thiol end groups has been described in US Pat. No. 5,908,876. A similar process can be used to prepare component B of the invention.

[0077] When component A of the invention comprises a polythiourethane prepolymer A1, it can be prepared in an analogous manner, but with the desired ratio of polyisocyanate or polyisothiocyanate to polythiol monomers in order to obtain a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups.

[0078] The mixture polythiol / polyiso(thio)cyanate from which the prepolymer A1 is obtained may contain 90% by weight or less of at least one polyol. Preferably, the mixture may contain 80% by weight or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less of at least one polyol. Also preferably, no polyol is used. Polyiso(thio)cyanate means polyisocyanate or polyisothiocyanate.

[0079] The mixture polythiol / polyiso(thio)cyanate from which the prepolymer B1 is obtained may contain 90% by weight or less of at least one polyol. Preferably, the mixture may contain 80% by weight or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less of at least one polyol. Also preferably, no polyol is used.

[0080] The mixture of components A and B according to the invention may also contain additives conventionally used in polymerizable compositions intended for molding optical articles, in particular ophthalmic lenses, in conventional proportions, namely inhibitors, dyes, photochromics, UV absorbers, fragrances, deodorants, antioxidants, resin modifiers, color balancers, chain extenders, crosslinkers, free radical scavengers such as antioxidants or hindered amine light stabilizers (HALS), dyes, pigments, fillers, adhesion promoters, anti-yellowing agents and release agents.

[0081] In one embodiment, the additive is added to the first component A prior to mixing with the second component B.

[0082] UV absorbers are often incorporated into optical articles in order to reduce or prevent UV light from reaching the retina (particularly in ophthalmic lens materials). UV absorbers that can be used in the present invention preferably have the ability to at least partially block light having a wavelength shorter than 400 nm, but may also have an absorption spectrum extending to the visible blue range of the electromagnetic spectrum (400-450 nm), particularly 420-450 nm.

[0083] The UV absorber protects the user's eyes from UV light and protects the substrate material itself, thereby preventing it from weathering and becoming brittle and / or yellowing. The UV absorber according to the present invention can be, but is not limited to, a benzophenone-based compound, a benzotriazole-based compound, or a dibenzoylmethane-based compound, preferably a benzotriazole compound. Suitable UV absorbers include, but are not limited to, 2-(2-hydroxyphenyl)-benzotriazole such as 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole ( 326), or other allyl hydroxymethylphenyl chlorobenzotriazole, 2-(5-chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)-4-methylphenol ( 550), n-octyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate ( 109), 2-(2-hydroxy-5-methoxyphenyl)benzotriazole, 2-(2-hydroxy-5-butoxyphenyl)benzotriazole and BASF Preferred absorbers are from the benzotriazole family. Further examples of benzotriazole UV absorbers that protect against blue light can be found in WO 2017 / 137372.

[0084] The amount of the UV absorber compound according to the present invention used herein is an amount sufficient to provide satisfactory protection from UV light, but not excessive to prevent precipitation. The UV absorber compound of the present invention is generally present in an amount ranging from 0.05% to 4% by weight, preferably from 0.1% to 3% by weight, more preferably from 0.1% to 2% by weight, relative to the total weight of the optical material (or per 100 parts by weight of the polymerizable compound present in the mixture of components A and B or relative to the weight of the optical material composition).

[0085] Among the release agents that can be used in the present invention, there can be mentioned mono- and dialkyl phosphates, alkyl phosphates, silicones, fluorinated hydrocarbons, fatty acids and ammonium salts. Preferred release agents are mono- and dialkyl phosphates, alkyl phosphates and mixtures thereof. Such release agents are disclosed in particular in US 4975 328 and EP 271 839. The release agent is preferably used in an amount less than or equal to 1% by weight, based on the total weight of the polymerizable compounds present in the mixture of components A and B.

[0086] The polymerizable mixture of the present invention may contain a solvent for promoting dissolution of the salt catalyst. In one embodiment, the curing step 4) is carried out in the presence of at least one solvent for the salt catalyst, preferably 2-mercaptoethanol.

[0087] Any polar organic solvent can be used, such as acetonitrile, tetrahydrofuran, dioxane, ethanol, 2-mercaptoethanol, acetone and 3-methyl-2-butene-1-ol. The amount of solvent is generally kept below 2% by weight, and preferably 0% to 0.5% by weight, based on the total weight of the polymerizable compounds present in the mixture of components A and B, to avoid turbidity and bubbling. In one embodiment, the catalyst is used in the form of a solution in a compound such as 2-mercaptoethanol.

[0088] In the present invention, at least one salt catalyst may be used in the process prior to the curing step 4). In one embodiment, the resulting mixture of step 3) comprises at least one salt catalyst.

[0089] The salt catalyst is a system for accelerating the polymerization reaction. The salt catalyst should be used in the polymerizable composition in an amount sufficient to promote the polymerization of the mixture, i.e., in an amount ranging from 0.015% to 0.15% by weight, preferably from 0.0425% to 0.102% by weight, relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B.

[0090] Too low amounts of catalyst should be avoided to prevent the generation of bubbles, especially when prepolymer B1 is combined with polyisocyanate or polyisothiocyanate monomers A2, which may be due to heat convection generated during the polymerization process.

[0091] Too high amounts of catalyst should also be avoided in order to prevent premature gelling of the polymerizable mixture before it is introduced into the mold, especially when prepolymer A1 is combined with polythiol monomer B2.

[0092] In a first embodiment of the process of the invention, wherein the first component A is composed of at least one polyisocyanate or polyisothiocyanate monomer A2, and the second component B comprises a polythiourethane prepolymer B1 having thiol end groups, the at least one salt catalyst is preferably present in an amount ranging from 0.03% to 0.15% or from 0.034% to 0.102%, more preferably from 0.0595% to 0.102% by weight relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B. In one embodiment, the amount ranges from 0.0595% to 0.15% by weight relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B.

[0093] In a second embodiment of the process of the present invention, wherein the first component A is composed of a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups, and the second component B is composed of at least one polythiol monomer B2, the at least one salt catalyst is preferably present in an amount ranging from 0.015% to 0.0765%, more preferably from 0.017% to 0.068%, even more preferably from 0.0425% to 0.068% by weight relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B.

[0094] The use of salt catalysts of the present invention is advantageous because other catalysts such as amines (e.g., lutidine) or tin-based catalysts used in amounts similar to those in the process of the present invention result in runaway reactions, undesirable premature gelling of the polymerizable mixture, and / or materials with poor optical and thermomechanical properties. Salt catalysts according to the present invention allow for better control of the reaction without increasing the curing time because they can be used in higher amounts without causing runaway reactions with premature gelling.

[0095] The salt catalyst may be added at different stages of the process of the invention.

[0096] In one embodiment, the salt catalyst is added to the polythiol monomer B2, or to the polythiourethane prepolymer B1 having thiol terminal groups, as the case may be, during the preparation of component B. In other words, at least one salt catalyst is added to the second component B before step 4). In another embodiment, at least one salt catalyst is added to the first component A before step 4).

[0097] In one embodiment, the salt catalyst is added to the first component A obtained in step 1) or 1') before mixing with component B, or the salt catalyst is added to the second component B obtained in step 2) or 2') before mixing with component A. In this embodiment, the salt catalyst may be added to the prepolymers A1 and / or B1 after they are prepared, as the case may be.

[0098] In another preferred embodiment, a salt catalyst is added to the mixture of components A and B in step 3) of the process of the present invention.

[0099] In one embodiment, the salt catalyst is of formula salt compounds,

[0100] Among them, M p+ is a cation with a valence p selected from the group consisting of an alkali metal cation, an alkaline earth metal cation, a transition metal cation and a cation having the formula NR 4 + An ammonium group wherein R is an alkyl group preferably having 1 to 10 carbon atoms, Yq- is an anion, m, n, p and q are integers such that n×q=m×p; preferably q=1. Preferably, Y q- The corresponding acid YH (q-1)- It has a pKa satisfying the condition 0.5≤pKa≤14.

[0101] In the present application, pKa is preferably expressed at 25° C. pKa can be measured by potentiometric (pH) titration in water at standard pressure using a glass electrode and a pH meter.

[0102] The preferred metal cation of the salt is Li + 、Na + , K + , Cs + Mg 2+ , Ca 2+ , Mn 2+ 、Ag + , Ba 2+ and Al 3+ A particularly preferred metal cation is Li + 、Na + and K + , because they lack color and solubility in the composition. Transition metals are less preferred because their salts may result in colored compositions and thus produce colored polymeric resins. In one embodiment, the process according to the present invention does not use a tin-containing catalyst.

[0103] Preferred NR + 4 The group is one in which R is C 1 -C 8 Alkyl and more preferably those which are methyl, ethyl, propyl, butyl or hexyl.

[0104] Preferably, Y q- is an anion, making the corresponding acid YH (q-1)- The condition of 0.5≤pKa≤10, and more preferably 0.5≤pKa≤8 is satisfied.

[0105] Preferably, the anion Y q- Selected from the group consisting of thiocyanate, carboxylate anion, thiocarboxylate anion, acetylacetonate, diketone anion, acetoacetate anion, malonate anion, cyanoacetate anion, ketonitrile anion, malononitrile anion and anions having the formula RS - An anion of wherein R is a substituted or unsubstituted alkyl group preferably having 1 to 10 carbon atoms, or an aryl group preferably having 6 to 12 carbon atoms.

[0106] Preferred anions Y q- It is SCN- , acetylacetonate, acetate, thioacetate, formate and benzoate. The preferred salt catalyst is KSCN.

[0107] Among the additional catalysts that can be used in the process of the invention, amines such as tertiary amines (for example triethylamine or 3,5-lutidine), organometallic compounds such as alkyltins or alkyltin oxides (especially dibutyltin dilaurate, dibutyltin dichloride and dimethyltin dichloride) can also be mentioned. Several catalysts can be combined in the process of the invention.

[0108] In a preferred embodiment, the process according to the invention does not use any catalyst other than a salt catalyst.

[0109] Electron donor compounds can also be used in combination with salt catalysts, especially when the polymerizable composition contains poorly reactive thiols and / or iso(thio)cyanates. Typically, electron donor compounds stabilize the cations of the salt catalyst. They thus help dissociate anion / cation pairs and thus actually increase the anion reactivity in the polymerization medium and thus promote the polymerization reaction.

[0110] The electron donor compound is preferably selected from acetonitrile compounds such as malononitrile, amides, amines, imines, phosphines, sulfones, sulfoxides, trialkyl phosphites, triaryl phosphites, glycol ethers, crown ethers and cryptands. Preferred electron donor compounds are crown ethers, cryptands, trialkyl phosphites, triaryl phosphites, alkylene glycols and alkylene glycol ethers, and most preferred is 18-crown-6.

[0111] In one embodiment, the curing step 4) is performed in the presence of at least one electron donor compound.

[0112] Examples of acetonitrile compounds are:

[0113]

[0114] R is an alkyl group, preferably C 1 -C 6 Alkyl groups, such as methyl, ethyl, propyl, and butyl.

[0115] The amide compound may be a primary, secondary or tertiary amide compound. Trialkyl phosphites and triaryl phosphites may be represented by the following formula:

[0116]

[0117] Wherein R, R', R"' is an alkyl group (preferably a C1-C6 alkyl group), or preferably an aryl group having 6 to 12 carbon atoms (such as a phenyl group). Preferred is a trialkyl phosphite, such as (C 2 H 5 O)3 P.

[0118] The electron donor compound may also be selected from crown ethers and cryptands. These cyclic molecules are generally chosen to exhibit a good compromise between heteroatom or metal size and "cage" size, i.e. between the number and size of heteroatoms and the size of the "cage", i.e. between the number of heteroatoms and the size of the ring.

[0119] Preferred crown ethers and cryptands can be represented by the following formula:

[0120]

[0121]

[0122] Where X 1 represents O, S or NH, x 1 is an integer of 3 to 6, preferably 3 to 4, n 1 is 2 or 3,

[0123] X 2 , X 3 and X4 represent O, S, n 2 、n 3 、n 4 ,y 2 ,y 3 ,y 4 is 2 or 3, and x 2 、x 3 、x 4 It is 2 or 3.

[0124] Among the preferred crown ethers and cryptands, the following compounds may be mentioned:

[0125]

[0126] Examples of preferred crown ethers are 18-crown-6, 18-crown-7, 15-crown-5 and 15-crown-6.

[0127] These electron donor compounds are preferably present in an amount ranging from 0% to 5% by weight, preferably from 0% to 1% by weight, more preferably from 0.06% to 0.6% by weight, even more preferably from 0.17% to 0.408% by weight, relative to the total weight of polymerizable compounds present in the mixture of components A and B.

[0128] The weight ratio of salt catalyst / electron donor compound (when the latter is present) preferably ranges from 1 / 3 to 1 / 5.

[0129] The mixing of the first component A and the second component B in step 3) can be carried out by any known mixing technique (such as those mentioned in US5973098). Preferably, the components A and B to be mixed are added to a small reactor chamber and then mixed with a screw mixer. In one embodiment, the viscosity of the mixture of components A and B at 25°C ranges from 0.01 Pa.s to 5 Pa.s, preferably from 0.05 Pa.s to 0.5 Pa.s, and even more preferably from 0.1 Pa.s to 0.3 Pa.s.

[0130] During step 3), the mold cavity of the casting mold assembly is filled with a mixture of the first component A and the second component B.

[0131] The casting mold assembly generally includes two mold parts defining two molding surfaces that cooperate to form a mold cavity when moved from an open position to a closed position. Each of the molding surfaces can be concave, convex, or planar, depending on the desired article shape. The molding surface can be convex, such as to form a concave substrate surface, or concave, such as to form a convex substrate surface.

[0132] More specifically, the optical material composition may be injected into the cavity of two mold parts that are held together using an annular closure (such as a gasket) or tape.

[0133] An annular closing member can be arranged around the periphery of the two mold pieces and attached to them. A conventional way of filling such a two-piece mold is by flowing the (liquid) optical material composition into the mold cavity through a casting opening provided for this purpose in the closing member. In an at least partially automated process, the mold cavity to be filled is vertically aligned with a filling device adapted to deliver a specific amount of molding material through a nozzle.

[0134] Depending on the desired characteristics of the resulting optical material, the optical material composition may be degassed under reduced pressure and / or may be filtered under increased or reduced pressure before being injected into the mold assembly. After pouring the composition, the mold assembly, preferably the lens mold assembly, may be heated in an oven or heating device immersed in water according to a predetermined temperature program to cure the resin in the mold assembly. If necessary, the resin molded product may be annealed.

[0135] The curing step 4) of the mixture providing the transparent substrate based on polythiourethane is carried out in the presence of at least one salt catalyst and can be carried out using any well-known polymerization technique, and in particular thermal polymerization (including induction and infrared heating) or radiation polymerization. The curing time of step 4) is preferably less than 10 or 5 hours, more preferably less than 4, 3 or 2 hours.

[0136] In step 5) of the method of the present invention, the polythiourethane-based transparent substrate is recovered from the mold.

[0137] The method of the present invention can be used to manufacture a finished lens with both sides having the required geometric shape, or a semi-finished lens (one side of which still needs to be surface-treated according to the required geometric shape).

[0138] The articles produced by the process of the invention have satisfactory color properties, which can be quantified by the yellowness index Yi. The whiteness of the optical material of the invention can be quantified by colorimetric measurement under illuminant C observer 2°, based on the CIE tristimulus values ​​X, Y, Z as described in standard ASTM E313. The optical article according to the invention preferably has a low yellowness index Yi, i.e. lower than 10, more preferably lower than 8, even better lower than 6, as measured according to the above standard. The yellowness index Yi is calculated according to ASTM method E313 by the relationship Yi=(127.69X-105.92Z)) / Y, where X, Y and Z are CIE tristimulus values.

[0139] The substrate according to the invention preferably has a relative humidity of less than or equal to 10, 5, 4, 2 or 1, and generally greater than or equal to 0 as measured in CIE (1976) L * a * b * Chroma coefficient b defined in the International Chroma Scale * (in transmission). Low chromaticity coefficient b * can be associated with a limited or non-yellow appearance (transmittance color). In fact, b * Positive values ​​on the axis indicate the amount of yellow, while negative values ​​indicate the amount of blue.

[0140] The following examples illustrate the invention in a more detailed but non-limiting manner. Unless otherwise stated, all thicknesses disclosed in this application relate to physical thicknesses.

[0141] Examples

[0142] Chemicals used

[0143] The optical material comprises a polymerizable monomer, a mold release agent The present invention discloses a method for preparing a polythiourethane transparent matrix having a refractive index of 1.67. ...

[0144] In Comparative Examples 3 to 10, dimethyltin dichloride was used as a comparative catalyst.

[0145] Evaluation of cured lenses

[0146] The following test procedure was used to evaluate optical articles prepared according to the present invention. Several samples were prepared for each system for measurement and the reported data are calculated as the average of the different samples.

[0147] The critical temperature of the article is measured 24 hours after its preparation in the manner indicated in application WO 2008 / 001011 for the measurement of the critical temperature, with the difference that the relative humidity is not 50% but >90%, typically 100%.

[0148] The mechanical properties of the lenses have been evaluated by DMA (Dynamic Mechanical Analysis).The modulus of elasticity E (or Young's modulus, or storage modulus, or tensile modulus of elasticity) makes it possible to evaluate the ability of a material to deform under the effect of an applied force.

[0149] Example 1-Example 13, Comparative Example 1-Comparative Example 10

[0150] Preparation of polythiourethane prepolymer A1 having isocyanate terminal groups

[0151] In a reactor equipped with a thermal probe and agitator, a determined amount of the polyisocyanate monomer meta-xylylene diisocyanate (XDI) was charged and heated to 120°C. Then, 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol was introduced and mixed with the polyisocyanate in such an amount that the molar ratio of isocyanate functional groups to thiol functional groups NCO / SH was 8:1 (89.7% polyisocyanate, 10.3% polythiol). The mixture was heated at 120°C for 3.5 hours. The resulting prepolymer A1 was then cooled to about 35°C and transferred to a suitable drum and stored in a cold room. Prepolymer A1 was prepared without the use of a catalyst.

[0152] Preparation of polythiourethane prepolymer B1 with thiol terminal groups

[0153] In a reactor equipped with a thermal probe and a stirrer, a determined amount of the polythiol monomer 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol was charged and heated to 95°C. Then, xylylene diisocyanate was introduced and mixed with the polythiol in such an amount that the final molar ratio of thiol functional groups to isocyanate functional groups SH / NCO was 8:1. The mixture was heated at 95°C for 3.5 hours. The resulting prepolymer B1 was then cooled to about 35°C and transferred to a suitable drum and stored in a cold room. Prepolymer B1 was prepared without using a catalyst.

[0154] Preparation of Transparent Polythiourethane Casting Substrate

[0155] The male and female molds were assembled by using adhesive tape. The center thickness was 2 mm. Prepolymers A1 and B1 were prepared as described above.

[0156] In Examples 1 to 7, a determined amount of cooled prepolymer A1 was mixed with a determined amount of Zelec Mix. The mixture was stirred and degassed at 15° C. for 1 hour, and degassed for 15 minutes without stirring to form component A. At the same time, a determined amount of polythiol monomer 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol B2 was mixed with 0.2%-0.8% by weight of the above catalyst solution (8.5% KSCN, 34.84% 18-crown ether-6, 56.66% 2-mercaptoethanol by weight). The mixture was stirred and degassed at 15° C. for 1 hour, and degassed for 15 minutes without stirring to form component B.

[0157] Components A and B were then mixed in a small reactor with a molar ratio of SH:NCO adjusted to 1:1 while stirring and degassing for 5 minutes at 15° C., and then further degassed for 2 minutes at 15° C. without stirring to prevent gelling. Once mixing was complete, the mold assembly was filled with the aid of a syringe and filter.

[0158] The assembled molds were kept at room temperature for 10 minutes, after which they were inserted into a convection oven preheated at 120°C. The mixture began to gel in the mold assembly at room temperature. The polymerization reaction was carried out by keeping the mold assemblies in the oven at 120°C for 3 hours. They were then cooled to 65°C.

[0159] In the context of the present invention, gel means the reaction product of components A and B, wherein the conversion of the reactive functional groups is very high. For example, the conversion ranges from 50% to 80%, and is preferably about 70%.

[0160] The mold assemblies were then disassembled to obtain lenses having a center thickness of 2 mm including a body of a polythiourethane transparent thermosetting substrate, and these mold assemblies were annealed at 120° C. for 1 h after disassembly. The refractive index of the lens was 1.67, and there were no optical defects such as striae.

[0161] Comparative Examples 3-6 were conducted similarly to Examples 1-7, except that the catalyst dimethyltin dichloride was used instead of KSCN.

[0162] In Examples 8 to 13, the protocols are the same except that a determined amount of the polyisocyanate monomer meta-xylylene diisocyanate A2 is mixed with a determined amount of Zelec Mix. The mixture was stirred and degassed at 15°C for 1 hour, and degassed for 15 minutes without stirring to form component A. At the same time, a determined amount of prepolymer B1 was mixed with 0.4% to 1.2% by weight of the above catalyst solution (8.5% KSCN, 34.84% 18-crown ether-6, 56.66% 2-mercaptoethanol by weight). The mixture was stirred and degassed at 15°C for 1 hour, and degassed for 15 minutes without stirring to form component B.

[0163] Comparative Examples 7-10 were conducted similarly to Examples 8-13, except that the catalyst dimethyltin dichloride was used instead of KSCN.

[0164] In Comparative Example 1-Comparative Example 2, the scheme is the same, except that a certain amount of polyisocyanate monomer meta-xylylene diisocyanate A2 is mixed with a certain amount of Zelec Mix. The mixture was stirred and degassed at 15° C. for 1 hour, and degassed for 15 minutes without stirring to form component A. At the same time, a determined amount of polythiol monomer 2,3-bis((2-mercaptoethyl)thio)-1-propanethiol B2 was mixed with 0.3%-0.4% by weight of the above catalyst solution (8.5% KSCN, 34.84% 18-crown ether-6, 56.66% 2-mercaptoethanol by weight). The mixture was stirred and degassed at 15° C. for 1 hour, and degassed for 15 minutes without stirring to form component B.

[0165] Composition and results

[0166] The amounts of catalyst used and the characterization results are shown in Table 1. The castings have been repeated and the data are the average of at least 3 tests.

[0167] Table 1

[0168]

[0169]

[0170]

[0171] After a fully controlled polymerization a lens is obtained which is free of any optical defects.

[0172] It can be observed that increasing catalyst concentration tends to increase the glass transition temperature of the resulting lens.

[0173] The results from dynamic mechanical analysis and differential scanning calorimetry show that the storage modulus (E) and glass transition temperature (Tg) of the product are substantially unaffected by changing the method of combining the polyisocyanate or polyisothiocyanate monomer A2 with the polythiourethane prepolymer B1 having thiol terminal groups to a method of combining the polythiourethane prepolymer A1 having isocyanate or isothiocyanate terminal groups with the polythiol monomer B2.

[0174] Advantageously, no bubble problems were observed in the prepolymer systems according to the invention.

[0175] In Comparative Examples 3 to 10, where the catalyst dimethyltin dichloride was used instead of KSCN, undesirable premature gelation occurred and the mixture solidified at similar catalyst contents during mixing, before filling into the mold or at the time of filling. Therefore, it was not possible to measure the thermomechanical properties. In Examples 1-13, the mixture did not start to gel before being transferred into the mold, indicating that at the same catalyst concentration, the use of the salt catalyst of the present invention is superior to the use of other catalysts such as tin-based catalysts.

Claims

1. A method for curing a transparent cast optical lens substrate based on polythiourethane, the method 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 prepolymer B1 having thiol end groups, said prepolymer 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 prepolymer A1 having isocyanate or isothiocyanate end groups of the formula -NCX, wherein X is O or S, said prepolymer 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 the first component A and the second component B together and filling the mold cavity of the casting mold assembly with the resulting polymerizable mixture, 4) curing the polymerizable mixture to obtain a polythiourethane-based transparent substrate, and 5) recovering the polythiourethane-based transparent substrate from the mold assembly, Wherein the curing step 4) is carried out in the presence of at least one salt catalyst, the amount of the salt catalyst relative to the total weight of the polymerizable compounds present in the mixture of the first component A and the second component B ranges from 0.015% to 0.15% by weight.

2. The method according to claim 1, wherein: The salt catalyst is of formula salt compounds, Among them, M p+ is a cation having a valence p selected from the group consisting of an alkali metal cation, an alkaline earth metal cation, a transition metal cation and a cation having the formula NR4 + An ammonium group wherein R is an alkyl group preferably having 1 to 10 carbon atoms, Y q- is an anion, making the corresponding acid YH (q-1)- It preferably has a pKa satisfying the condition 0.5≤pKa≤14, and m, n, p and q are integers such that n×q=m×p.

3. The method according to claim 2, wherein: q＝1。 4. The method according to any one of claims 2 to 3, wherein: The cation M p+ Selected from the group consisting of: Li + 、Na + , K + , Cs + Mg 2+ , Ca 2+ , Mn 2+ 、Ag + , Ba 2+ and Al 3+ .

5. The method according to any one of claims 2 to 4, wherein: The anion Y q- Selected from the group consisting of thiocyanate, carboxylate anion, thiocarboxylate anion, acetylacetonate, diketone anion, acetoacetate anion, malonate anion, cyanoacetate anion, ketonitrile anion, malononitrile anion and anions having the formula RS - An anion of wherein R is a substituted or unsubstituted alkyl group preferably having 1 to 10 carbon atoms, or an aryl group preferably having 6 to 12 carbon atoms.

6. A method according to any one of the preceding claims, wherein: The salt catalyst was KSCN.

7. A method according to any one of the preceding claims, wherein: The at least one salt catalyst is present in an amount ranging from 0.0425% to 0.102% by weight relative to the total weight of polymerizable compounds present in the mixture of the first component A and the second component B.

8. A method according to any one of the preceding claims, wherein: The curing step 4) is carried out in the presence of at least one electron donor compound selected from the group consisting of trialkyl phosphites, triaryl phosphites, alkylene glycols, alkylene glycol ethers, crown ethers and cryptands, preferably 18-crown-6.

9. A method according to any one of the preceding claims, wherein: The curing step 4) is carried out in the presence of at least one solvent for the salt catalyst, preferably 2-mercaptoethanol.

10. A method according to any one of the preceding claims, wherein: The curing time of step 4) is less than 10 hours, preferably less than 5 hours.

11. A method according to any one of the preceding claims, wherein: The amounts of the polyisocyanate or polyisothiocyanate monomers and the polythiol monomers are adjusted so that the molar ratio of the NCX / SH groups of the mixture of the polyisocyanate or polyisothiocyanate monomers and the polythiol monomers used to prepare the polythiourethane prepolymer A1 is in the range of 3:1 to 30:1, and / or the molar ratio of the SH / NCX groups of the mixture of the polyisocyanate or polyisothiocyanate monomers and the polythiol monomers used to prepare the polythiourethane prepolymer B1 is in the range of 3:1 to 30:1, and X is O or S.

12. A method according to any one of the preceding claims, wherein: The polythiol monomer is a compound having the formula: R 1 (SH) n1 (I) wherein n1 represents an integer ranging from 2 to 6, and R 1 represents an aliphatic, alicyclic, heterocyclic or aromatic group.

13. A method according to any one of the preceding claims, wherein: The polythiol monomer is selected from the group consisting of pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(thioglycolate), tris(3-mercaptopropionate)trimethylolpropane, tris(thioglycolate)trimethylolpropane and compounds having formula (II) and (III):

14. A method according to any one of the preceding claims, wherein: The polyisocyanate or polyisothiocyanate monomer is a compound having formula (VI): R 2 (NCX) n2 (VI) wherein X represents O or S, n2 represents an integer ranging from 2 to 6, and R 2 represents an aliphatic, alicyclic, heterocyclic or aromatic group.

15. A method according to any one of the preceding claims, wherein: The polyisocyanate or polyisothiocyanate monomer is selected from the group consisting of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, biphenyl-diisocyanate, 3,3'-dimethyl-4,4'-diphenylene diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, 2,2,4-trimethylhexane-1,6-diisocyanate, lysine methyl ester diisocyanate, bis(isocyanatoethyl)fumarate, isophorone diisocyanate, ethylene diisocyanate, dodecane-1,12-diisocyanate esters, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene-2,4-diisocyanate, tetramethylxylylene diisocyanate, hexahydrotoluene-2,6-diisocyanate, hexahydrophenylene-1,3-diisocyanate, hexahydrophenylene-1,4-diisocyanate, perhydrodiphenylmethane-2,4'-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, 2,5-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane and 2,6-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane.

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