WO2024133820A1

WO2024133820A1 - Method of curing a polythiourethane based substrate coupled to a microstructured wafer

Info

Publication number: WO2024133820A1
Application number: PCT/EP2023/087491
Authority: WO
Inventors: Pierre Fromentin; Laurie MASURE
Original assignee: Essilor International
Priority date: 2022-12-21
Filing date: 2023-12-21
Publication date: 2024-06-27

Abstract

The invention relates to a method of curing a polythiourethane-based casted substrate, comprising 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, providing a second component B comprising a polythiourethane pre-polymer B1 having thiol end groups or comprising at least one polythiol monomer B2, providing a microstructured wafer made of a thermoplastic material having an internal surface and an external surface, wherein the internal surface of the wafer bears a microstructure, mixing together first and second components A and B and filling a molding cavity with the resulting mixture, wherein said molding cavity is defined by the internal surface of the microstructured wafer and at least a portion of a mold part, curing said mixture and obtaining a polythiourethane-based substrate adhering to the microstructured wafer.

Description

METHOD OF CURING A POLYTHIOURETHANE BASED SUBSTRATE COUPLED TO A MICROSTRUCTURED WAFER

The present invention relates to a process for manufacturing polythiourethane-based substrates coupled to a wafer bearing a microstructure, and in particular optical substrates such as ophthalmic lenses, having generally a middle or high refractive index, preferably of at least 1.52, more preferably of at least 1.54, more preferably of at least 1.6 and even more preferably of at least 1 .67, within short curing cycles.

BACKGROUND AND SUMMARY OF THE INVENTION

Ophthalmic lenses made of polythiourethane based substrates are typically prepared by a process comprising mixing appropriate monomers in a tank, such as a mixture of a polyisocyanate and a polythiol, adding catalyst and additive, filling a molding cavity with this liquid mixture of monomers, polymerizing the monomer mixture and thereafter recovering the polymerized polythiourethane based substrate from the mold. The mixture is usually subjected to a thermal cycle in an oven, for a typical duration of 20 hours.

The application WO 00/26272 discloses a polymerizable compositions for making 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.

US 2007/098999 discloses a process for obtaining a polythiourethane polarized article, comprising positioning a polarized polyvinyl alcohol film in a molding cavity of a two-part mold assembly, pouring in the molding cavity a polymerizable composition comprising at least one poly(iso)thiocyanate monomer and at least one polythiol; or a mixture of at least one liquid NCO- or NCS-terminated poly(thio)urethane prepolymer and at least one liquid SH-terminated poly(thio)urethane prepolymer, curing the polymerizable composition and removing the polythiourethane polarized article from the molding cavity.

The application EP 3640714 discloses a method for encapsulating a microstructure such as microlenses, comprising forming a first optical member having an optical surface defining a plurality of concave recesses or a plurality of convex protrusions, placing said first optical member in a two-part mold assembly, introducing a moldable material into the molding cavity and forming a second optical member such that the second optical member is coupled to the first optical member and encapsulates the microstructure. Similar processes are described in EP 3640713 and EP 3910411 . However, these processes cannot be used to make a wafer an integral part of a polythiourethane lens starting from monomers, due to incompatibility issues.

Indeed, casting polythiourethane lenses with a functional wafer bearing a microstructure has been found to be challenging. When using standard polythiourethane monomers such as polyisocyanates mixed with polythiols, diffusion of the monomers from the surface of the wafer inside the wafer occurs and might lead to a swelling of the wafer (which is typically a polycarbonate wafer), leading to opaque final lenses, and/or an alteration of the microstructure geometry.

A technical solution bringing compatibility between the wafer and the mixture of polymerizable compounds forming the polythiourethane matrix and respecting the geometry of the microstructure is therefore needed.

US 2003/125410 discloses a method of curing polythiourethane transparent casted substrate, which comprises the steps of:

1) Providing a first component A comprising a polythiourethane pre-polymer having isocyanate or isothiocyanate end groups,

2) Providing a second component B comprising a polythiourethane pre-polymer having thiol end groups,

3) Mixing together first and second components A and B and filling a molding cavity of a casting mold assembly with the resulting mixture,

4) Curing said mixture to obtain a transparent solid substrate.

In applications EP 3916470 and EP 3919967, a different approach for curing a polythiourethane optical material has been chosen, combining the use of monomers and prepolymers in the presence of a polymerization catalyst, typically a basic catalyst. However, these methods have not been applied to prepare microstructured articles.

An objective of the present invention is to provide a method of obtaining a thermoset polythiourethane-based casted substrate coupled to a microstructured wafer which remedies to the drawbacks of the prior art methods observed at the interface between the wafer and the polymerized substrate. The method for casting a thermoset lens having a microstructure should preserve the design integrity of the microstructure.

Another object of the invention is to provide a method of curing polythiourethane based casted substrates substantially free from optical defects resulting from the polymerization process, having high transmittance and clarity, as well as low yellowness index.

The present inventors found that the use of polythiourethane pre-polymers having isocyanate or isothiocyanate end groups rather than isocyanate or isothiocyanate monomers allowed improved compatibility and prevented the swelling of the wafer that creates haziness at the polymers interface, and a modification of the microstructure geometry.

The present invention provides a method of curing a polythiourethane-based casted substrate, usable for making optical articles such as ophthalmic lenses, which comprises the following steps 1), 2), 3), 4), 5) and 6) or T), 2’), 3), 4), 5) and 6):

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 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:

T) 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) Providing a microstructured wafer made of a thermoplastic material having an internal surface and an external surface, wherein the internal surface of the wafer bears a microstructure,

4) Mixing together first and second components A and B and filling a molding cavity with the resulting mixture, wherein said molding cavity is defined by the internal surface of the microstructured wafer and at least a portion of a mold part,

5) Curing said mixture to obtain a polythiourethane-based substrate, and

6) Recovering said polythiourethane-based substrate adhering to said microstructured wafer.

The present process offers several advantages in addition to those mentioned above.

In the present process, some monomers are first pre-reacted to form oligomers, then poured into mold assemblies that are subjected to a short polymerization cycle, typically few hours. The time required to cure the polymerizable composition poured into mold assemblies is drastically reduced by at least partially replacing monomers with pre-polymers (or oligomers).

A fast cure process is highly desirable as the shorter residence time in curing oven enables a dramatic productivity gain, complex and demanding lens geometries can be obtained in better yield as the final polymerizable mixture shrinkage is lower than that of mixture obtained directly from monomers, compatibility with the adhesive of tape used for mold assembly is better, and energy consumption during polymerization cycles is reduced.

Provided that the viscosity is controlled, batch mixing of such mixtures is inherently safer than usual process using monomers, as part of the available bond forming energy has already been released during the oligomers formation (pre-polymerization), which limits formation of local heat points in the final polymerizable mixture. The use of pre-polymers allows stable and steady reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from a reading of the detailed description hereafter when considered in conjunction with the accompanying drawings, wherein figures 1 and 2 schematically represent the different stages of the present process, namely steps 4) and 6, figure 3 provides the haze values of three different optical articles prepared in the experimental part, and figure 4 provides the transmission (Tv) values of three different optical articles prepared in the experimental part. DETAILED DESCRIPTION OF THE INVENTION

The substrate of the invention is an organic glass substrate, made from a thermosetting resin. The polymer matrix of substrate is obtained from a material composition (“substrate composition”) comprising at least one polymerizable pre-polymer, and at least two polymerizable pre-polymer in some embodiments.

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 eyeglass lens.

In the present description, unless otherwise specified, a substrate is understood to be transparent when the observation of an image through said substrate is perceived with no significant loss of contrast, that is, when the formation of an image through said substrate is obtained without adversely affecting the quality of the image. This definition of the term “transparent” can be applied to all objects qualified as such in the description, unless otherwise specified.

The term “ophthalmic lens” is used to mean a lens adapted to a spectacle frame to protect the eye and/or correct the sight. Said lens can be chosen from afocal, unifocal, bifocal, trifocal, progressive lenses and Fresnel lenses or any other kind of lenses having a discontinuous surface. Although ophthalmic optics is a preferred field of the invention, it will be understood that this invention can be applied to optical elements of other types such as, for example, lenses for optical instruments, filters particularly for photography or astronomy, optical sighting lenses, ocular visors, optics of lighting systems, screens, glazings, etc.

If the optical article is an optical lens, it may be coated on its front main surface, rear main side, or both sides with one or more functional coatings. As used herein, the rear face of the substrate is intended to mean the face which, when using the article, is the nearest from the wearer's eye. It is generally a concave face. On the contrary, the front face of the substrate is the face which, when using the article, is the most distant from the wearer's eye. It is generally a convex face. The optical article can also be a piano article.

A substrate, in the sense of the present invention, should be 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, for example an ophthalmic lens destined to be mounted in glasses. In this context, the term “substrate” is understood to mean the base constituent material of the optical lens and more particularly of the ophthalmic lens. This material may act as support for a stack of one or more coatings or layers.

The refractive index of the polythiourethane based substrate is preferably 1.52 or greater, more preferably 1.54 or greater, more preferably 1 .56 or greater, more preferably 1.58 or greater, more preferably 1.60 or greater, and still more preferably 1.65 or greater, 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 indexes referred to in the present application are expressed at 25°C at a wavelength of 550 nm. The fast cure polymerizable composition leading to a polythiourethane based material is composed of two main components.

In a first embodiment of the invention, which is the preferred embodiment, the first component A is comprised of a polythiourethane pre-polymer A1 having isocyanate (NCO) or isothiocyanate (NCS) end groups; the second component B is comprised of a polythiourethane pre-polymer B1 having thiol (SH) end groups.

In step 1) of the first embodiment of present process (and step T of the second embodiment of the present process), a first component A comprising a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups is provided and 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 comprises therefore oligomers and the initial monomers that did not polymerize.

In step 2) of the first embodiment of present process, a second component B comprising a polythiourethane pre-polymer B1 having thiol end groups is provided and 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 comprises therefore oligomers and the initial monomers that did not polymerize.

In a second embodiment of the invention, the first component A is comprised of a polythiourethane pre-polymer A1 having isocyanate (NCO) or isothiocyanate (NCS) end groups; the second component B is comprised of at least one polythiol monomer B2.

Compared to prior art processes which use only iso(thio)cyanate or thiol monomers, the present invention uses at least one pre-polymer, in particular at least one polythiourethane prepolymer having isocyanate or isothiocyanate end groups.

By pre-polymer, it is meant a polymer or oligomer comprising pre-polymer molecules. By pre-polymer molecule, it is meant a macromolecule or oligomer molecule capable of entering, through reactive (polymerizable) groups, into further polymerization, thereby contributing more than one monomeric unit to at least one chain of the final macromolecule. It is generally formed from two or more different monomers.

The polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer and at least one polythiol monomer in a proportion such that the molar ratio of isocyanate or isothiocyanate groups to thiol groups NCX/SH preferably ranges from 3:1 to 30:1 , preferably in the absence of a catalyst, X being O or S.

The polythiourethane pre-polymer B1 having thiol end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer and at least one polythiol monomer in a proportion such that the molar ratio of the thiol groups to the isocyanate or isothiocyanate groups SH/NCX preferably ranges from 3:1 to 30:1 , preferably in the absence of a catalyst, X being O or S. Polythiol and polyisocyanate or polyisothiocyanate compounds used to prepare polythiourethane pre-polymer A1 or B1 are considered herein as monomers, even when they are oligomers.

By polyisocyanate, it is meant any compound comprising at least two isocyanate groups, in other words diisocyanates, triisocyanates, etc. Polyisocyanate pre-polymers may be used. The polyisocyanate may be any suitable polyisocyanate having two or more, preferably two or three isocyanate functions.

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

Polyisothiocyanate are defined in the same manner as polyisocyanates above, by replacing the “isocyanate” group by the “isothiocyanate” group.

The preferred polyisocyanate or isothiocyanate monomers are those having the formulae:

wherein R¹ is independently H or a C1-C5 alkyl group, preferably CH3 or C2H5;

R² is H, an halogen, preferably Cl or Br, or a C1-C5 alkyl group, preferably CH3 or C2H5; Z is -N=C=X, with X being O or S, preferably O; a is an integer ranging from 1 to 4, b is an integer ranging from 2 to 4 and a + b < 6; and x is an integer from 1 to 10, preferably 1 to 6.

The polyisocyanates of the invention are preferably diisocyanates. Among the available diisocyanates may be cited toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, paraphenylene diisocyanate, xylylene diisocyanate, biphenyl-diisocyanate, 3,3'-dimethyl-4,4'-diphenylene diisocyanate, tetramethylene-1 ,4-diisocyanate, hexamethylene-1 ,6-diisocyanate, 2,2,4-trimethyl hexane-1 ,6-diisocyanate, lysine methyl ester diisocyanate, bis(isocyanatoethyl) fumarate, isophorone diisocyanate (IPDI), ethylene diisocyanate, dodecane-1 ,12-diisocyanate, cyclobutane-1 ,3-diisocyanate, cyclohexane-1 ,3-diisocyanate, cyclohexane-1 ,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene-2,4-diisocyanate, hexahydrotoluene-2,6- diisocyanate, hexahydrophenylene-1 ,3-diisocyanate, hexahydrophenylene-1 ,4-diisocyanate, perhydro diphenylmethane-2,4'-diisocyanate, perhydro phenylmethane-4,4'-diisocyanate (or bis- (4-isocyanatocyclohexyl)-methane, or 4,4'-dicyclohexyl methanedi isocyanate), bis(isocyanatomethyl) cyclohexane, dicyclohexylmethane diisocyanate, 2,5(or 2,6)- bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, and their mixtures.

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

The polythiols that may be used in the present invention are defined as compounds comprising at least two sulfhydryl (mercapto) groups, in other words dithiols, trithiols, tetrathiols etc. Polythiols pre-polymers may be used. The polythiol may be any suitable polythiol having two or more, preferably two or three thiol functions. The polythiol can be used for the preparation of polythiourethane pre-polymers A1 or B1 , but also directly in component B in step 2’) of the present process.

Among the preferred polythiol monomers and/or oligomers suitable in accordance with the present invention, there may be cited aliphatic polythiols such as trimethylolpropanetris(2- mercaptoacetate), trimethylolpropanetris(3-mercaptopropionate), trimethylolethanetris(2- mercaptoacetate), trimethylolethanetris(3-mercaptopropionate), pentaerythritol tetrakis(2- mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), bis(mercaptomethyl)sulfide, bis(mercaptomethyl)disulfide, bis(mercaptoethyl)sulfide, bis(mercaptoethyl)disulfide, bis(mercaptopropyl)sulfide, bis(mercaptopropyl)disulfide, 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’-mercapropylthio)-2,3-dimercaptopropane, 1 - (3’-mercapropylthio)-2,3-dimercaptopropane, 1 -(4’-mercabutylthio)-2,3-dimercaptopropane, 1 - (5’-mercapentylthio)-2,3-dimercaptopropane, 1 -(6’-mercahexylthio)-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 formulae below or can be found in WO 2014/133111 , EP 394495, US 4775733 or EP

1877839:

C₂H5C(CH2COOCH2CH₂SH)3

Preferred embodiments are combination of xylylene diisocyanate and pentaerythritol tetrakis(3-mercaptopropionate); combination of xylylene diisocyanate and 2,3-bis((2- mercaptoethyl)thio)-1 -propanethiol; 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; combination of xylylene diisocyanate and 4,8(or 4,7 or 5,7)- dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane; 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, shown below:

Preferably the polythiols have a viscosity at 25°C of 1 Pa.s or less, more preferably 5.10’ ¹ Pa.s or less, more preferably 2.5.1 O'¹ Pa.s or less, more preferably 2.1 O'¹ Pa.s or less, more preferably 10'¹ Pa.s or less and even more preferably of 0.5.1 O'¹ Pa.s or less.

Specific examples of polythiourethane resins suitable to the present invention are those marketed by the Mitsui Chemicals company as MR® series, in particular MR6®, MR7® (refractive index: 1.67), MR8® (refractive index: 1.6) resins, MR10® (refractive index: 1.67). These optical materials as well as the monomers used for their preparation are especially described in the patents US 4,689,387, US 4,775,733, US 5,059,673, US 5,087,758 and US 5,191 ,055.

Depending on the embodiment of the invention, components A and B are prepared by polymerizing mixtures of required amounts of at least one polyisocyanate and/or at least one polyisothiocyanate monomer and at least one polythiol monomer, and optionally polyols monomers or polyamines monomers. Typically, components A and B can be prepared through classical thermal polymerization including infrared heating. The amounts of polyisocyanate or polyisothiocyanate monomers and polythiol monomers in the reaction medium are preferably adapted in each case in such a way that the molar ratio of NCX/SH groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane pre-polymer A1 , preferably from 6:1 to 10:1 , and/or the molar ratio of SH/NCX groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane pre-polymer B1 , preferably from 6:1 to 10:1 , X being O or S.

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 results in pre-polymers of high stability in time. However, they can also be prepared using a catalyst as described below.

Generally, in the first embodiment of the invention, the pre-polymer A1 and the prepolymer B1 are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

Generally, in the second embodiment of the invention, the pre-polymer A1 and the at least one polythiol monomer of component B are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1 .2, preferably 1.

Preparation of pre-polymer B1 having thiol end groups has already been described in US 5908876. Similar process can be used to prepare component B of the present invention.

When component A of the present invention comprises polythiourethane pre-polymer A1 , it can be prepared in a similar manner but with the required ratio of polyisocyanate or polyisothiocyanate and polythiol monomers in order to obtain polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups.

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

The mixture polythiol/polyiso(thio)cyanate from which pre-polymer B1 is obtained may comprise 90% or less by weight of at least one polyol. Preferably, said mixture may comprise 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less by weight of at least one polyol. Also preferably, no polyol is used.

The mixture of components A and B according to the invention may also include additives which are conventionally employed in polymerizable compositions intended for molding optical articles, in particular ophthalmic lenses, in conventional proportions, namely inhibitors, dyes, photochromic agents, UV absorbers, perfumes, deodorants, antioxidants, resin modifiers, color balancing agents, chain extenders, crosslinking agents, free radical scavengers such as antioxidants or hindered amine light stabilizers (HALS), dyes, pigments, fillers, adhesion accelerators, anti-yellowing agents and mold release agents. In one embodiment, the additives are added to first component A prior to the mixing with second component B.

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

Said UV absorbers both protect the user’s eye from UV light and the substrate material itself, thus preventing it from weathering and becoming brittle and/or yellow. The UV absorber according to the invention can be, without limitation, a benzophenone-based compound, a benzotriazole-based compound or a dibenzoylmethane-based compound, preferably a benzotriazole compound. Suitable UV absorbers include without limitation 2-(2-hydroxyphenyl)- benzotriazoles such as 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole (Seesorb® 703 I Tinuvin® 326), or other allyl hydroxymethylphenyl chlorobenzotriazoles, 2-(5- chloro-2H-benzotriazol-2-yl)-6-(1 ,1-dimethylethyl)-4-methylphenol (Viosorb® 550), n-octyl-3-[3- tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl] propionate (Eversorb® 109), 2-(2- hydroxy-5-methoxyphenyl)benzotriazole, 2-(2-hydroxy-5-butoxyphenyl)benzotriazole and also Tinuvin® CarboProtect® from BASF. Preferred absorbers are of the benzotriazole family. Other examples of benzotriazole UV absorbers protecting from blue light can be found in WO 2017/137372.

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

Among the release agents that may be used in the invention, there may be cited mono and dialkyl phosphates, alkyl ester phosphates, silicones, fluorinated hydrocarbon, fatty acids and ammonium salts. The preferred release agents are mono and dialkyl phosphates, alkyl ester phosphates and mixtures thereof. Such release agents are disclosed inter alia in US 4975 328 and EP 271839. The release agent is preferably used in an amount lower 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.

The polymerizable mixture of the present invention can comprise a solvent for promoting the dissolution of the catalyst, especially if it is under the form of a salt.

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

In the present invention, at least one catalyst can be used in the process prior to curing step 5). In one embodiment, the resulting mixture of step 4) comprises at least one catalyst.

The catalyst is a system for accelerating the polymerization reaction. The catalyst can comprise one or more latent thermal catalysts.

The catalyst shall be used in the polymerizable composition in an effective amount, i.e. , an amount sufficient to promote the polymerization of the mixture. Generally, the at least one catalyst is used in a proportion of 0.01 to 5% by weight with respect to the total weight of polymerizable compounds present in the mixture of components A and B, more preferably from 0.02 to 2%.

The catalyst can be added at different stages of the present process.

In one embodiment, the catalyst is added to the polythiol monomers B2 during the preparation of component B, or to the polythiourethane pre-polymer B1 having thiol end groups, depending on the case.

In one embodiment, the catalyst is added to the first component A obtained in step 1) or 1 ’) prior to mixture with component B or to the second component B obtained in step 2) or 2’) prior to mixture with component A. In this embodiment, the catalyst can be added to pre-polymers A1 and/or B1 after their preparation, depending on the case.

In another preferred embodiment, the catalyst is added to the mixture of components A and B in step 4) of the present process.

In one embodiment, the catalyst is an anionic catalyst. The preferred catalysts are transition metal-based catalysts and ammonium salts of acids, these salts preferably fulfilling the condition 0.5 < pKa < 14. p_L. _

In one embodiment, the catalyst is a salt compound of formula M_m Y_n wherein M^p+ is a cation selected from the group consisting of alkaline metals, alkaline earth metals, transitions metals and ammonium groups of formula NR in which R is an alkyl group having preferably from 1 to 10 carbon atoms, Y’ is an anion such that the corresponding acid YH has a pKa fulfilling the condition 0.5 < pKa < 14, p is the valency of the cation, and n = m x p.

The preferred metallic cations of the salts are Li⁺, Na⁺, K⁺, R^b+, Mg²⁺, Ca²⁺, Ba²⁺ and Al³⁺. The particularly preferred metallic cations are Li⁺, Na⁺ and K⁺ due to their absence of color and solubility in the composition. Transition metals are less preferred because their salts can lead to colored compositions and therefore colored polymerized resins. In one embodiment, the method according to the invention does not use a catalyst containing tin.

The preferred NR groups are those in which R is a Ci-Cs alkyl group and more preferably, a methyl, ethyl, propyl, butyl or hexyl group.

Preferably, Y’ is an anion such that the corresponding acid YH which fulfills the condition 0.5 < pKa < 10 and more preferably 0.5 < pKa < 8. Preferably, the anion Y’ is selected from the group consisting of thiocyanate, carboxylate, thiocarboxylate, acetylacetonate, diketone anions, acetoacetic ester anions, malonic ester anions, cyanoacetic ester anions, ketonitrile anions and anions of formula RS' wherein R is a substituted or non-substituted alkyl group having preferably from 2 to 10 carbon atoms or phenyl group having preferably from 6 to 12 carbon atoms.

The preferred anions Y' are SON acetylacetonate, acetate, thioacetate, formate and benzoate. The preferred salt catalyst is KSCN.

Among catalysts that can be used in the method of the invention, there may also be cited amines, such as tertiary amines (e.g., triethylamine or 3,5-lutidine), organometallic compounds, such as alkyltins or alkyltin oxides, in particular dibutyltin dilaurate, dibutyltin dichloride and dimethyltin dichloride. Several catalysts according to the invention can be combined in the present process.

Electron-donor compounds may also be used in combination with the catalyst, preferably a salt catalyst, especially when the polymerizable composition comprises poorly reactive thiols and/or iso(thio)cyanates. Generally, electron-donor compounds stabilize the cation of the catalyst salt. They thus contribute to dissociate the anion/cation ion pair and thus do increase the anion reactivity in the polymerizing medium, and therefore promote the polymerization reaction.

Electron-donor compounds are preferably selected from acetonitrile compounds such as malononitriles, amides, amines, imines, phosphines, sulfones, sulfoxides, trialkyl phosphites, triaryl phosphites, ethylene glycol ethers, crown ethers and cryptands. Preferred electron -donor compounds are crown ethers, cryptands, trialkyl phosphites, triaryl phosphites and malononitriles.

Examples of acetonitrile compounds are:

^N=^C - ^CH2 - C=N and in which

R is an alkyl group, preferably a Ci-Ce alkyl group such as methyl, ethyl, propyl, butyl.

The amide compounds may be primary, secondary or tertiary amide compounds. The trialkylphosphites and triarylphosphites may be represented by formula:

OR

P\-OR' OR"' in which R, R’, R’” are either an alkyl group, preferably a 01 - 06 alkyl group or an aryl group having preferably 6 to 12 carbon atoms such as a phenyl group. Preferred are trialkylphosphites, for example (C2HsO)3P.

Electron-donor compounds may also be selected from crown ethers and cryptands. These cyclic molecules are usually chosen to exhibit a good compromise between the heteroatom or metal size and the “cage” size, i.e. , between the number of heteroatoms and the size and the “cage” size, i.e., between the number of heteroatoms and the size of the cycle.

The preferred crown ethers and cryptands may be represented by the following formulae:

wherein X¹ represents O, S or NH, xi is an integer from 3 to 6, preferably from 3 to 4, is 2 or 3,

X², X³ and X4 represent O, S, n2, ns, n4, y2, ya, y4 are 2 or 3 and X2, X3, X4, are 2 or 3.

Among the preferred crown ethers and cryptands there may be cited the following compounds:

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

The electron-donor compounds are preferably present in an amount ranging from 0 to 5% by weight, preferably 0 to 1% by weight, with respect to the total weight of polymerizable compounds present in the mixture of components A and B.

In step 3) of the present process, a microstructured wafer made of a thermoplastic material having an internal (main) surface and an external (main) surface is provided. The internal surface of said wafer bears a microstructure. In another embodiment, the wafer has both main surfaces bearing identical or different microstructures, i.e. , its external surface also bears a microstructure.

The wafer or carrier is a thin supporting element made of a thermoplastic material. The wafer may comprise a variety of different constructions and materials. Such constructions include freestanding or non-laminated films, films with removable protective sheets, films with outer permanent protective coatings or supportive plastic layers and laminated films and wafers.

The wafer can be a preformed film, or a stack of several coatings supported by a film. Said coatings may be selected, without limitation, from an anti -reflection coating, an anti-fouling top coat, an anti-abrasion- and/or scratch-resistant coating, an impact-resistant coating, a polarized coating, a photochromic coating, a dyed coating, a printed layer, an antistatic coating. Such coatings and preparation of coated wafers are described in WO 2008/015223 and U.S. 6,562,466, which are hereby incorporated by reference. These coatings are applied onto the surface of the wafer in the reverse order with regard to the desired order of the coating stack on the substrate.

Examples of thermoplastic (co)polymers, which can be used for making the present wafer are polysulfones, aliphatic poly(meth)acrylates, such as poly(methyl methacrylate), polyethylene, polypropylene, polystyrene, SBM (styrene-butadiene-methyl methacrylate) block copolymers, polyphenylene sulfide, arylene polyoxides, polyimides, polyesters, polycarbonates such as bisphenol A polycarbonate, PVC, polyamides such as nylons, cellulose acetate butyrate, cellulose acetate, and cellulose triacetate, other copolymers thereof, and mixtures thereof. The microstructured wafer is preferably made of polycarbonate. Preferably, the wafer is made of a non-elastomer material.

If the curable composition that is employed is thermally cured, then the material of the wafer shall be selected to bear the curing temperature.

Generally, the wafer has a thickness of 0.25 to 5 mm, preferably 0.5 to 4 mm, more preferably 1 to 3 mm, even better 1 .5 to 2 mm.

By "internal surface of the wafer", it is meant the main surface of the wafer that will be in contact with a curable composition forming the polythiourethane-based substrate during the present process.

The internal surface of the wafer comprising the microstructure may be a concave or convex surface, depending on whether the wafer is overmolded on a concave surface or a convex surface of the polythiourethane-based substrate in the final optical article.

The working surface of the wafer (its internal surface) has a relief organized according to a pattern, in other words, a microstructured surface, which confers to the final optical article an optical surface having the properties imparted by the microstructure (for example prevent progression of myopia or hyperopia). Different techniques for obtaining microstructured mold parts are disclosed in WO 99/29494.

In one embodiment of the invention, the microstructure includes a plurality of lenslets. Lenslets may form bumps and/or recesses at the main surface they are arranged onto. The outline of the lenslets may be round or polygonal, for example hexagonal. In one embodiment, the internal surface of the wafer defines a plurality of concave recesses and/or a plurality of convex protrusions.

More particularly, lenslets may be microlenses, so that the microstructure comprises a plurality of microlenses. A microlens may be spherical, toric, or have an aspherical shape, rotationally symmetrical or not. A microlens may have a single focus point, or cylindrical power, or non-focusing point.

In preferred embodiments, lenslets or microlenses can be used to prevent progression of myopia or hyperopia. In that case, the resulting polythiourethane-based substrate adhering to the microstructured wafer provides an optical power for correcting myopia or hyperopia, and the microlenses or the lenslets may provide respectively an optical power greater than the optical power of the polythiourethane-based substrate if the wearer has myopia, or an optical power lower than the optical power of the polythiourethane-based substrate if the wearer has hyperopia.

In one embodiment, the internal surface of the wafer has at least one geometrically defined surface forming a Fresnel lens.

Lenslets or microlenses may also be Fresnel structures, diffractive structures defining each a Fresnel structure, permanent technical bumps or phase-shifting elements. It can also be a refractive optical element such as microprisms and a light-diffusing optical element such as small protuberances or cavities, or any type of element generating roughness on the substrate. It can also be TT-Fresnel lenslets as described in US 20211/09379, i.e., Fresnel lenslets which phase function has TT phase jumps at the nominal wavelength, as opposed to unifocal Fresnel lenses which phase jumps are multiple values of 2TT. Such lenslets include structures that have a discontinuous shape. In other words, the shape of such structures may be described by an altitude function, in terms of distance from the base level of the main surface of the optical article the lenslet belongs to, which exhibits a discontinuity, or which derivative exhibits a discontinuity.

Lenslets may have a contour shape being inscribable in a circle having a diameter greater than or equal to 0.5 micrometers (pm) and smaller than or equal to 1.5 millimeters (mm).

Lenslets may have a height, measured in a direction perpendicular to the main surface they are arranged onto, that is greater than or equal to 0.1 pm and less than or equal to 50 pm.

The internal surface of the wafer bearing the microstructure can be defined as a surface, that can be a piano, spherical, sphero-cylindrical or even complex surface, that includes the central point of every microstructure. This main surface can be a virtual surface, when microstructures are embedded in the lens or close or identical to the lens physical outer surfaces when microstructures are not embedded. The height of the microstructure can be then determined using local perpendicular axis to this main surface, and calculating for each point of the microstructure the difference between the maximum positive deviation minus the minimum negative deviation to the main surface, along the axis.

Lenslets may have periodical or pseudo periodical layout, but may also have randomized positions. Exemplary layouts for lenslets may be a grid with constant grid step, honeycomb layout, multiple concentric rings, contiguous, e.g., no space in between microstructures. These structures may provide optical wave front modification in intensity, curvature, or light deviation, where the intensity of wave front is configured such that structures may be absorptive and may locally absorb wave front intensity with a range from 0% to 100%, where the curvature is configured such that the structure may locally modify wave front curvature with a range of +/- 20 diopters, and light deviation is configured such that the structure may locally scatter light with angle ranging from +/- 1° to +/- 30°.

A distance between structures may range from 0 (contiguous) to 3 times the structure (separate microstructures).

Generally, the microstructure, especially for myopia control, comprises optical elements having at least a height of 0.1 pm or more, and preferably the following values (in micrometer) or more: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 , measured at the surface of the lens if the microstructure is situated at an interface microstructure/air or at an internal interface positioned inside the optical element.

The microstructure can comprise cylindrical annular refractive elements.

The wafer may be treated for improving its adhesion to the polythiourethane-based material. The treatment includes mechanical roughening, physical cleaning, chemical surface modification, plasma activation.

The preferred treatment is a chemical treatment comprising immersing wafer in a basic or acidic solution, such as but not limited to NaOH, KOH, HCI or HNO3 solution, rinsing and drying. These acids or bases can be used at normal concentrations of at least 0.001 N or greater. Treatment with a NaOH solution, typically a 5% NaOH solution, is preferred.

The mixing of first component A with second component B in step 4) can be performed by any known mixing technique such as those mentioned in US 5973098. Preferably, components A and B to be mixed are added in a small reactor chamber and then mixed with a screw mixer. In one embodiment, the viscosity at 25°C of the mixture of components A and B ranges from 0.01 Pa.s to 5 Pa.s, preferably from 0.05 Pa.s to 0.5 Pa.s, even more preferably from 0.1 Pa.s to 0.3 Pa.s.

During step 4), a molding cavity of a casting mold assembly is filled with the mixture of first and second components A and B. Said molding cavity is defined by the internal surface of the microstructured wafer and at least a portion of a mold part, typically made of mineral glass. Both can be held together using an annular closure.

The casting mold assembly generally comprises two mold parts defining two molding surfaces that cooperate to form a molding 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, e.g., to form a concave substrate surface, or concave, e.g., to form a convex substrate surface.

An annular closure member, such as a gasket or an adhesive tape, can be disposed around the periphery of the two mold pieces and attached to them. The conventional way to fill such a two-piece mold is by causing the (liquid) optical material composition to flow into the molding cavity against the wafer through a casting opening provided for this purpose in the closure member. In at least a partly automated process, the molding cavity to be filled is vertically aligned with a filling device that is adapted to deliver a particular quantity of molding material through a nozzle.

In a first embodiment, step 4) comprises positioning, in a molding cavity of a casting mold assembly, said microstructured wafer such that the external surface of the wafer is in contact with a surface of the casting mold assembly, i.e., a molding surface, wherein the casting mold assembly comprises said mold part. In this embodiment, the wafer is placed into the empty cavity of the casting mold assembly, which is generally a two-part casting mold assembly, the first part of which being said mold part and the second part of which being a second mold part.

In a second embodiment, as represented on figure 1 , step 4) is performed with a two-part casting mold assembly, the first part of which being said mold part 4 and the second part of which being said microstructured wafer 1. In other words, the microstructured wafer is used as a mold part in this embodiment. Figure 1 also represents tape 2 used to hold together the two mold parts and the mixture 3 of first and second components A and B poured in the molding cavity.

In a third embodiment, step 4) comprises positioning, in a molding cavity of a casting mold assembly, said microstructured wafer such that the external surface of the wafer is not in contact with a surface of the casting mold assembly, i.e., a molding surface, wherein the casting mold assembly comprises said mold part. In this embodiment, the wafer is placed into the empty cavity of the casting mold assembly, which is generally a two-part casting mold assembly, the first part of which being said mold part and the second part of which being a second mold part.

In this third embodiment of the invention, a first volume (first molding cavity) can be defined between the internal surface of the wafer bearing a microstructure and a first molding surface of a first mold part, and a second volume (second molding cavity) can be defined between the external surface of the wafer and a second molding surface of a second mold part. The two volumes can be filled with the same mixture or different mixtures of polymerizable compounds having identical or different indices of refraction. Generally, the second volume is filled with the same mixture of first and second components A and B as the first volume. Therefore, after curing, the wafer will be sandwiched between two substrates, a first substrate adhering to the microstructured (internal) side of the wafer and a second substrate adhering to the other (external) side of the wafer, which can optionally bear a microstructure identical or different from the microstructure of the internal side.

Depending on the desired characteristics of the resulting optical material, degassing can be performed under reduced pressure and/or filtration can be performed under increased pressure or reduced pressure before pouring the optical material composition in the mold assembly.

After pouring the composition, the casting mold assembly, preferably a lens casting mold assembly, can be heated in an oven or a heating device immersed in water according to a predetermined temperature program to cure the resin in the mold assembly. The resin molded product may be annealed if necessary. The curing step 5) of the mixture, which provides a polythiourethane-based substrate adhering to the microstructured wafer, can be performed in the presence of a catalyst, and can be implemented using any well known polymerization technique and in particular thermal polymerization including infrared heating, or radiation polymerization. The curing time of step 5) is preferably lower than 10 or 5 hours, more preferably lower than 4, 3 or 2 hours.

Thanks to the present proces, the diffusion of polymerizable compounds into the matrix of the wafer has been limited, thus preserving the integrity of the design of the microstructure. Preferably, no compound from the mixture prepared in step 4) has diffused into the microstructured wafer during steps 4) and 5).

As previously explained, casting a wafer to be an integral part of a final polythiourethane- based substrate using monomers, as in the prior art processes, presents incompatibility issues and causes swelling of the wafer, thus creating haziness at the polymers interface.

Without wishing to be bound by any theory, the inventors believe that polythiourethane pre-polymers having isocyanate or isothiocyanate end groups, which are larger molecules than the corresponding isocyanate or isothiocyanate monomers, are prevented from entering into the wafer network, thus giving a transparent final product. Pre-polymers (or oligomers) also decrease the shrinkage of the polythiourethane matrix compared to standard monomers, creating less stress for the wafer. Is is believed that monomers with low molecular weight and aromaticity such as isocyanates or isothiocyanates are stress-cracking agents to the wafer matrix.

In step 6) of the present process, as represented on figure 2, once the resin is molded onto the wafer, the cured polythiourethane-based substrate 5 adhering to the microstructured wafer 1 is recovered from the mold assembly. The overmolded substrate part typically has a thickness higher than 2 mm, preferably higher than 3 mm.

The present process can be used to manufacture a finished lens, having both sides at the required geometries, or a semi-finished lens, having one face that still needs to be surfaced at the required geometry.

The article resulting from the present process has satisfactory color properties, which can be quantified by the yellowness index Yi. The degree of whiteness of the inventive optical material may be quantified by means of colorimetric measurements, based on the CIE tristimulus values X, Y, Z such as described in the standard ASTM E313 with illuminant C observer 2°. 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 per ASTM method E313 through the relation Yi = (127.69 X - 105.92 Z)) I Y, where X, Y, and Z are the CIE tristimulus values.

The haze value of the polythiourethane-based substrate having the microstructured wafer adhered thereto as determined according to the standard ASTM D1003-00 is lower than or equal to 6 %, more preferably lower than or equal to 5 %, indicating a high level of clarity. Haze is preferably measured for a 2 mm thick sample.

The Tv factor, also called “luminous transmission" of the system, is such as defined in ISO standard 13666:1998 and is measured accordingly to standard ISO 8980-3. It is defined as the average in the 380-780 nm wavelength range that is weighted according to the sensitivity of the eye at each wavelength of the range and measured under D65 illumination conditions (daylight).

The relative light transmission factor in the visible spectrum Tv of the polythiourethane- based substrate having the microstructured wafer adhered thereto as determined according to the standard ISO 8980-3 is higher than or equal to 74 %, more preferably higher than or equal to 78 % or 80 %.

In some embodiments, the method does not comprise depositing a catalyst composition on the inside surface of a mold part and/or on at least one surface of a light filtering element thereafter positioned in the molding cavity.

In some embodiments, the method does not comprise depositing a catalyst composition on a surface of the microstructured wafer.

In some embodiments, the method does not comprise depositing a catalyst composition on the internal surface of the microstructured wafer.

In some embodiments, the method does not comprise depositing a catalyst composition on the external surface of the microstructured wafer.

In some embodiments, the method does not comprise depositing a catalyst composition in the molding cavity prior to the addition of the polymerizable composition in the molding cavity.

In some embodiments, the method does not comprise depositing a catalyst composition on the inside surface of at least one mold.

In some embodiments, the method does not comprise depositing a catalyst composition on at least one of the surfaces of a light filtering element.

In some embodiments, the method does not comprise depositing a catalyst composition on at least one of the surfaces of a light filtering element which is thereafter positioned in a mold assembly.

In one embodiment, the method according to the invention does not comprise a method of fast curing transparent casted substrate, usable for making optical articles such as ophthalmic lenses, which comprises the steps of:

- providing a fast room-temperature polymerizable composition;

- providing a catalyst composition;

- providing a casting mold assembly containing two unsealed molds each having an inside surface and an outside surface; and optionally providing a light filtering element placed or configured to be placed between the two molds

- depositing the catalyst composition:

- on the inside surfaces of at least one of the molds; and/or

- on at least one of the surfaces of the light filtering element which is thereafter positioned in the mold assembly ;

- closing the casting mold assembly so that the inside surfaces of the molds form together the molding cavity; - filling the fast room-temperature polymerizable composition in the molding cavity of the casting mold assembly already containing the catalyst composition deposited on the inside surface of at least one of the molds;

- curing the filled mold assembly to obtain a transparent solid substrate, said curing step comprising: a) a first step for polymerizing said composition at room temperature to obtain a gel; and b) a second step of post-curing the gel to obtain the transparent solid substrate; and

- recovering the transparent solid substrate from the casting mold assembly.

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

EXAMPLES

Chemicals used

Optical materials were prepared from a composition comprising polymerizable monomers, Zelec UN® (CAS 3896-11-5) as a mold release agent and a catalyst solution comprising 8.5 % KSCN (CAS 333-20-0), 34.84 % 18-crown-6 (CAS 17455-13-9) and 56.66 % mercaptoethanol (CAS 60-24-2), by weight. The monomers used in the present examples were xylylene diisocyanate (CAS 3634-83-1) and 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol (CAS 131538- 00-6), in order to produce a polythiourethane transparent matrix having a refractive index of 1 .67.

Evaluation of the lenses after curing

The following test procedures were used to evaluate the optical articles prepared according to the present invention. Several samples for each system were prepared for measurements and the reported data were calculated with the average of the different samples.

Colorimetric measurements of hue angle h, chroma C* and b* were carried out with a Zeiss spectrophotometer in the international colorimetric CIE (L*, a*, b*) space, taking into account the standard illuminant D65, and the standard observer 10°, in transmission mode, for an angle of incidence of 0°.

The light transmission factor in the visible spectrum Tv was measured in transmission mode (incidence angle: 0°) from a wearer’s view angle using a Cary 4000 spectrophotometer from Hunter, with the back (concave) side of the lens (2 mm thickness at the center) facing the detector and light incoming on the front side of the lens. Tv was measured under D65 illumination conditions (daylight).

Haze was measured as disclosed in WO 2012/173596, on a Hazeguard XL 211 Plus apparatus from BYK-Gardner in accordance with the standard ASTM D1003-00. As haze is a measurement of the percentage of transmitted light scattered more than 2.5° from the axis of the incident light, the smaller the haze value, the lower the degree of cloudiness.

The yellowness index Yi of the prepared lenses was calculated as described above, by measuring on a white background with the above spectrophotometer the CIE tristimulus values X, Y, Z such as described in the standard ASTM E 313-05, through reflection measures, with the front (convex) side of the lens facing the detector and light incoming on said front side. This way of measuring Yi, from an observer’s view angle, is the closest to the actual wearing situation.

Preparation of polythiourethane pre-polymer A1 having isocyanate end groups (Component A of examples 1 and 3)

In a reactor eguipped with a condenser, a thermal probe and an agitator, a determined amount of the polyisocyanate monomer m-xylylene diisocyanate (XDI) was charged and heated up to 120°C. Then, 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol was introduced and mixed with the polyisocyanate in an amount such that the molar ratio of the isocyanate functions to the thiol functions NCO/SH was 8:1 (89.7 % polyisocyanate, 10.3 % polythiol). The mixture was heated for 3.5 hours. The resulting pre-polymer A1 was then cooled to around 35°C and transferred into an appropriate drum, tapped with inert gas (nitrogen or argon) and stored in a cold room. The final pre-polymer with isocyanate end groups had a viscosity at 25°C of about 0.1 Pa.s. Prepolymer A1 was prepared without the use of catalyst.

Preparation of polythiourethane pre-polymer B1 having thiol end groups (Component B of examples 2 and 3)

In a reactor eguipped with a condenser, a thermal probe and an agitator, a determined amount of the polythiol monomer 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol was charged and heated up to 95°C. Then, xylylene diisocyanate was introduced and mixed with the polythiol in an amount such that the molar ratio of the thiol functions to the isocyanate functions SH/NCO was 8:1 . The mixture was heated for 3.5 hours. The end of the reaction was indicated by temperature reaching a peak and returning to 95°C (+/-2°C). The resulting pre-polymer B1 was then cooled to around 35°C and transferred into an appropriate drum, tapped with inert gas (nitrogen or argon) and stored in a cold room. Final pre-polymer with thiol end groups had a viscosity at 25°C of about 0.5 Pa.s. Pre-polymer B1 was prepared without the use of catalyst.

Mold assembly

Two-part casting mold assemblies were assembled by using a tape to have a center thickness of 2 mm.

The two-part casting mold assembly is schematically represented on figure 1 . The first part of the mold assembly (back part) was a mineral glass mold part having a diameter of 71 mm, the second part of the mold assembly (front part I top mold) was a microstructured polycarbonate wafer (base 3.25, i.e., 76 mm, surfaced to a piano lens of 2 mm center thickness - 71 mm; the front radius was 167.81 mm) bearing microlenses pattern on its back side (concave side) for myopia control. It was previously cleaned with isopropyl alcohol to remove any dust or contamination.

The wafer was placed on top with its concave surface bearing the microstructure downwardly oriented. The glass mold part to be paired with the wafer was placed in the bottom with its concave surface downwardly oriented.

Preparation of polythiourethane transparent casted substrates

Example 3

Pre-polymers A1 and B1 were prepared as described above. A determined amount of cooled down pre-polymer A1 was mixed with a determined amount of Zelec UN®. This mixture was stirred at 15°C and degassed for 1 hour, degassed for 15 minutes without stirring, to form component A. A determined amount of pre-polymer B1 was mixed with a determined amount of the above-mentioned catalyst solution (KSCN, 18-crown-6, 2-mercaptoethanol). This mixture was stirred at 15°C and degassed for 1 hour, degassed for 15 minutes without stirring, to form component B. Components A and B were then mixed in a small reactor while stirring and degassing for 5 minutes at room temperature and then for 2 minutes at 15°C to prevent gelation. The resulting mixture had a viscosity at 25°C of about 0.1 to 0.3 Pa.s. Once the mixing was complete, the mold assemblies were filled with the help of a clean syringe. The assembled molds were held at room temperature for 10 minutes before inserting them in a convection oven preheated at 120°C. The mixture started gelation in the mold assemblies. The polymerization reaction was carried out by letting the mold assemblies in the oven for 3 hours at 120°C. Then, they were let to cool down to 65°C.

In the context of the present invention, a gel designates the reaction product of components A and B in which the conversion rate of the reactive functions is significantly high. For example, said conversion rate ranges from 50 to 80% and preferably is about 70%.

The mold assemblies were then disassembled to obtain lenses with 2 mm center thickness comprising an overmolded body of polythiourethane transparent thermoset substrate, which were annealed at 120°C for 1h. The lenses were cleaned by immersion and sonication in a surfactant solution, then rinsed and dried. They had a refractive index of 1.67 and no optical defects such as striations.

The polycarbonate wafer used as front mold was now an integral part of the final lens and could not be removed therefrom.

Example 1 The lens of example 1 was prepared similarly to example 3, except that component B comprised a determined amount of the polythiol monomer 2,3-bis((2-mercaptoethyl)thio)-1- propanethiol and a determined amount of the above-mentioned catalyst solution (KSCN, 18- crown-6, mercaptoethanol).

Comparative example 2

The lens of comparative example 2 was prepared similarly to example 3, except that component A comprised a determined amount of the polyisocyanate monomer m-xylylene diisocyanate and a determined amount of Zelec UN®.

Comparative example 3

Attempts were made to prepare a mixture of at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer to be injected in the casting mold assembly. However, the monomers reacted to form a gel at room temperature in less than 10 minutes, which was unable to be introduced in the molding cavity.

Compositions and results

The amounts (parts by weight) of the different compounds used and results of the characterizations are shown in table 1 :

Table 1

A comparison of example 1 and comparative example 2 shows an improvement of transmittance (see figure 4), yellowness index and clarity (see figure 3) when using pre-polymer A1 having isocyanate or isothiocyanate end groups instead of monomer A2 having isocyanate or isothiocyanate end groups. Lenses obtained by curing a composition comprising pre-polymer A1 having isocyanate or isothiocyanate end groups and either pre-polymer B1 having thiol end groups (example 3) or monomer B2 having thiol end groups (example 1) had both satisfactory yellowness index, transmittance and clarity. Using a mixture of two pre-polymers in example 3 allows to further improve the haze level, yellowness index and transmittance, as compared to example 1 or comparative example 2 which use only one pre-polymer.

Without wishing to be bound by any theory, the inventors believe that the casting of a prepolymer A1 having isocyanate or isothiocyanate end groups allowed to drastically lower the swelling of the wafer.

Claims

1. A method of curing a polythiourethane-based casted substrate, comprising the following steps 1), 2), 3), 4), 5) and 6) or T), 2’), 3), 4), 5) and 6):

5) Curing said mixture to obtain a polythiourethane-based substrate, and

2. The method of claim 1 , comprising the following steps 1) and 2):

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.

3. The method according to any one of the preceding claims, wherein the resulting mixture of step 4) comprises at least one catalyst.

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

5. The method according to any one of the preceding claims, wherein the amounts of polyisocyanate or polyisothiocyanate monomers and polythiol monomers are adapted so that the molar ratio of NCX/SH groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane prepolymer A1 and/or the molar ratio of SH/NCX groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane pre-polymer B1 , X being O or S.

6. The method according to any one of the preceding claims, wherein the substrate is an optical lens substrate.

7. The method according to any one of the preceding claims, wherein the microstructure comprises a plurality of microlenses.

8. The method according to any one of the preceding claims, wherein the internal surface of the wafer defines a plurality of concave recesses and/or a plurality of convex protrusions.

9. The method according to any one of the preceding claims, wherein the microstructured wafer is made of polycarbonate.

10. The method according to any one of the preceding claims, wherein the haze value of the polythiourethane-based substrate having the microstructured wafer adhered thereto as determined according to the standard ASTM D1003-00 is lower than or equal to 6 %.

11. The method according to any one of the preceding claims, wherein the relative light transmission factor in the visible spectrum Tv of the polythiourethane-based substrate having the microstructured wafer adhered thereto as determined according to the standard ISO 8980-3 is higher than or equal to 74 %.

12. The method according to any one of the preceding claims, wherein no compound from the mixture prepared in step 4) has diffused into the microstructured wafer during steps 4) and 5).

13. The method according to any one of the preceding claims, wherein step 4) comprises positioning, in a molding cavity of a casting mold assembly, said microstructured wafer such that the external surface of the wafer is in contact with a surface of the casting mold assembly, wherein the casting mold assembly comprises said mold part.

14. The method according to any one of claims 1 to 12, wherein step 4) is performed with a two-part casting mold assembly, the first part of which being said mold part and the second part of which being said microstructured wafer.

15. The method according to any one of the preceding claims, wherein the method does not comprise depositing a catalyst composition on the inside surface of a mold part and/or on at least one surface of a light filtering element thereafter positioned in the molding cavity.