WATER BASED ANTI-ABRASION COATING

Abstract

The invention relates to a water based composition to be used for the preparation of anti-abrasion coatings on ophthalmic lenses. The composition comprises: the product of hydrolysis of an epoxyalkoxysilane SiXY.sub.3, wherein X represents a monovalent organic group linked to the silicon atom through a carbon atom and containing at least one epoxy function and Y represents an alkoxy group; cationic nanoparticles comprising silica, wherein a water sol of said cationic particles is stable at acidic pH; an inorganic non-hydrogen Lewis acid; a surfactant such that a water solution of 15 wt % of said surfactant exhibits a static surface tension below 25 mN/m at 20° C.; less than 0.5 wt % of a water miscible organic solvent less volatile than water. Moreover, the composition comprises no organic solvents other than said water miscible organic solvent less volatile than water and other than organic solvents that are a product of hydrolysis of the epoxyalkoxysilane.

Claims

1. A liquid hard coating composition comprising the following ingredients: (i) the product of hydrolysis of an epoxyalkoxysilane of formula (I): SiXY.sub.3, wherein the X group represents a monovalent organic group linked to the silicon atom through a carbon atom and containing at least one epoxy function and the Y groups are identical or different and represent alkoxy groups linked to the silicon atom in formula (I), preferably wherein the Y groups in formula (I) are methoxy or ethoxy groups or any mixture thereof and wherein the X group is of formula (II): ##STR00004## or of formula (III): ##STR00005## more preferably wherein the epoxyalkoxysilane of formula (I) is γ-glycidoxypropyltrimethoxysilane (glymo); (ii) cationic particles with an average diameter comprised between 5 nm and 100 nm, wherein a sol of said cationic particles dispersed in water is stable at acidic pH and wherein said cationic particles comprise silica, preferably said cationic particles are cationic alumina-coated silica particles; (iii) an inorganic non-hydrogen Lewis acid, preferably the inorganic non-hydrogen Lewis acid is an inorganic salt of a multivalent metal ion, more preferably wherein said multivalent metal ion is aluminum(III); (iv) a surfactant such that a water solution of 15 wt % of said surfactant relative to the total weight of said water solution exhibits a static surface tension below 25 mN/m at a temperature of 20° C., preferably said surfactant is a block or graft copolymer of dimethylsiloxane and alkylene oxide; (v) less than 0.5 wt % relative to the total weight of the composition of a water miscible organic solvent less volatile than water; wherein, the composition comprises no organic solvents other than said water miscible organic solvent less volatile than water and other than organic solvents that are a product of the hydrolysis of the epoxyalkoxysilane.

2. The composition according to claim 1, wherein the transmittance in the ultraviolet A region, corresponding to wavelengths between 315 nm and 380 nm, of a 1 cm thick sample of a dispersion of the cationic particles in water, wherein the weight of the particles represents 2% of the total weight of said dispersion, is below 40%.

3. The composition according to claim 2 further comprising between 0.02 wt % and 1 wt % of a UV absorbing material, relative to the total weight of the composition; preferably the UV absorbing material comprises inorganic nanoparticles, more preferably said inorganic nanoparticles are chosen from nanoparticles of titanium oxide, nanoparticles of zinc oxide, nanoparticles of cerium oxide and mixtures thereof.

4. The composition according to claim 1, comprising between 0.01 wt % and 0.5 wt % relative to the total weight of the composition of the water miscible organic solvent less volatile than water; preferably wherein the water miscible solvent less volatile than water is a propylene glycol ether is of formula (IV): ##STR00006## wherein: R is a methyl, an ethyl, a propyl or a butyl group and a is 2 or 3.

5. The composition according to claim 1, wherein: the sum W.sub.S={E.sub.eq+weight of the cationic particles+weight of the inorganic non-hydrogen Lewis acid} is comprised between 10% and 60% of the total weight of the composition, wherein E.sub.eq is the weight of the amount of epoxyalkoxysilane of formula (I) needed to obtain the amount of product of hydrolysis of the epoxyalkoxysilane of formula (I) present in the composition minus the weight of the Y groups in said amount of epoxyalkoxysilane; preferably wherein E.sub.eq is comprised between 45% and 65% of W.sub.S, the weight of the cationic particles is comprised between 30% and 50% of W.sub.S and the weight of the inorganic non-hydrogen Lewis acid is comprised between 0.1% and 2% of W.sub.S; more preferably wherein W.sub.S is comprised between 20% and 35% of the total weight of the composition, E.sub.eq is comprised between 52% and 62% of W.sub.S, the weight of the cationic particles is comprised between 37% and 47% of W.sub.S and the weight of the inorganic non-hydrogen Lewis acid is comprised between 0.2% and 1.5% of W.sub.S.

6. The composition according to claim 1, wherein the pH of the final composition at 25° C. is comprised between 2 and 6; preferably between 3 and 5.

7. A method for the preparation of a liquid hard coating composition comprising the following steps: (i) in a separate container, the mixing of a water solution of an inorganic Brønsted acid with a pKa in water at 25° C. inferior to 3 with an epoxyalkoxysilane of formula (I): SiXY.sub.3, wherein the X group represents a monovalent organic groups linked to the silicon atom through a carbon atom and containing at least one epoxy function and the Y groups are identical or different and represent alkoxy groups linked to the silicon atom in formula (I), preferably the epoxyalkoxysilane of formula (I) is γ-glycidoxypropyltrimethoxysilane; (ii) the mixing of the product of step (i) with a. an acidic sol comprising cationic particles with an average diameter comprised between 5 nm and 100 nm that are dispersed in water, wherein the cationic particles comprise of silica, preferably said cationic particles are cationic alumina-coated silica particles, b. an inorganic non-hydrogen Lewis acid, preferably said inorganic non-hydrogen Lewis acid is an inorganic salt of aluminum(III), c. a surfactant such that a water solution of 15 wt % of said surfactant relative to the total weight of said water solution exhibits a static surface tension below 25mN/m at a temperature of 20° C., preferably said surfactant is a block or graft copolymer of dimethylsiloxane and alkylene oxide and d. less than 0.5 wt % relative to the total weight of the final composition of a water miscible organic solvent less volatile than water, preferably wherein the water miscible solvent less volatile than water is a propylene glycol ether of formula (IV): ##STR00007## wherein R is a methyl, an ethyl, a propyl or a butyl group and a is 2 or 3; wherein no organic solvents other than said water miscible organic solvent less volatile than water and other than the organic solvents that may result from the hydrolysis of the epoxyalkoxysilane of formula (I) are introduced; preferably wherein the temperature of the reaction mixture during step (i) is maintained below 40° C., more preferably wherein, the molar amount of water added to the mixture in step (i) is at least equal to the molar amount of groups Y in the epoxyalkoxysilane of formula (I).

8. The method according to claim 7, wherein the transmittance in the ultraviolet A region, corresponding to wavelengths between 315 nm and 380 nm, of a 1 cm thick sample of a dispersion of the cationic particles in water, wherein the weight of the particles represents 2% of the total weight of said dispersion, is below 40%; more preferably wherein the method further comprises the addition after step (ii), of a UV absorbing material, even more preferably wherein the UV absorbing material comprises inorganic nanoparticles chosen from nanoparticles of titanium oxide, nanoparticles of zinc oxide, nanoparticles of cerium oxide and mixtures thereof.

9. The method according to claim 7, wherein: the sum W′={E′+weight of the cationic particles+weight of the inorganic non-hydrogen Lewis acid} is comprised between 20% and 35% of the weight of the final composition, wherein E′ is the weight of the amount of epoxyalkoxysilane of formula (I) introduced in step (i) minus the weight of the Y groups in said amount of epoxyalkoxysilane; preferably wherein E′ is comprised between 45% and 65% of W′, the weight of the cationic particles is comprised between 30% and 50% of W′ and the weight of the inorganic non-hydrogen Lewis acid is comprised between 0.1% and 2% of W′; more preferably wherein E′ is comprised between 52% and 62% of W′, the weight of the cationic particles is comprised between 37% and 47% of W′ and the weight of the inorganic non-hydrogen Lewis acid is comprised between 0.2% and 1.5% of W′.

10. The method according to claim 7, wherein the amount of inorganic Brønsted acid with a pKa in water at 25° C. inferior to 3 to be mixed with the epoxyalkoxysilane of formula (I) in step (i) is such that it introduces between 0.2 mmol and 1 mmol per 100 g of the final composition of protons with a pKa in water at 25° C. inferior to 3.

11. A liquid hard coating composition able to be obtained by the method according to claim 7.

12. An optical article comprising a substrate bearing a hard coating obtainable by curing the composition according to claim 1, wherein the substrate comprises an optical plastic, preferably wherein the optical plastic is a diethylene glycol bis(allylcarbonate) polymer, a thermosetting polythiourethane resin having a refractive index of 1.60 or a thermosetting polythiourethane resin having a refractive index of 1.67.

13. The optical article according to claim 12, wherein the article comprises a primer coating on which the hard coating is directly deposited, said primer coating comprising polyurethane and an inorganic filler; preferably wherein said inorganic filler comprises silica nanoparticles.

14. The optical article according to claim 12, wherein the article further comprises at least one anti-reflective coating on the surface of the hard coating, preferably wherein the article further comprises at least one anti-fouling coating on the surface of said anti-reflective coating.

15. The optical article according to claim 12, wherein the optical article is an ophthalmic lens.

Description

EXAMPLES

[0194] Preparation of a Liquid Hard Coating Composition According to the Invention:

[0195] During the whole procedure, the reaction mixture is stirred by means of mechanical stirrer in a glass vessel.

[0196] 5.61 parts of a 0.1N solution of HCl are added dropwise to 24.53 parts of γ-glycidoxypropyltrimethoxysilane. The temperature of the reaction mixture is maintained below 40° C. during this addition. After the addition of the 0.1N solution of HCl is complete, the reaction mixture is left until it reaches room temperature. An acidic sol comprising cationic particles is then added to the mixture (amounts such that 10.9 parts of the solids content of the sol are introduced in the composition) and the mixture is left at room temperature for 30 minutes. Al(ClO.sub.4).sub.3 (0.2 parts), surfactant Borchi Gol LA50 (0.15 parts), optionally a UV absorber and deionized water to complete the final composition to 100 parts are then added to the mixture. The mixture is then left 60 min at room temperature and filtered on a 3 μ polypropylene filter (Sartorius) to give a ready to use liquid hard coating composition. For optimal conservation, the liquid hard coating composition is stored at 5° C.

[0197] Borchi Gol LA50 provided by OMG Borchers is a 50w % solution of a graft copolymer of dimethylsiloxane and alkylene oxide in dipropylene glycol n-butyl ether. A 15 wt % water solution of the graft copolymer contained in Borchi Gol LA50 exhibits a static surface tension of 23 mN/m at a temperature of 20° C.

[0198] Eleven samples were prepared (L1 to L11) with three different acidic sols and two different UV absorbers (see table 1).

TABLE-US-00002 TABLE 1 Particles UV absorber Sample Acidic sol diameter UV absorber content L1 ST-AK-ML 45 nm — — L2 ST-AK-ML 45 nm Nanobyk 3840 0.4 parts L3 ST-AK-ML 45 nm Nanobyk 3840 0.8 parts L4 ST-AK-ML 45 nm Nanobyk 3860 0.4 parts L5 ST-AK-ML 45 nm Nanobyk 3860 0.8 parts L6 CT16 PCL 17 nm — — L7 CT16 PCL 17 nm Nanobyk 3840 0.4 parts L8 CT16 PCL 17 nm Nanobyk 3840 0.8 parts L9 CT16 PCL 17 nm Nanobyk 3860 0.4 parts L10 CT16 PCL 17 nm Nanobyk 3860 0.8 parts L11 ST-AK 12.5 nm   — —

[0199] Acidic Sols

[0200] ST-AK-ML is an acidic (pH 3-5) dispersion of cationic alumina-coated silica particles in water with a solids content of 30% of the total weight of the dispersion provided by Nissan Chemical.

[0201] ST-AK is an acidic (pH 3-5) dispersion of cationic alumina-coated silica particles in water with a solids content of 20% of the total weight of the dispersion provided by Nissan Chemical.

[0202] ST-AK-ML and ST-AK both comprise more than 83 wt % silica and less than 17 wt % aluminum relative to the solids content of the dispersion.

[0203] Levasil CT16 PCL is an acidic (pH 3-4) dispersion of cationic alumina-coated silica particles in water with a solids content of 30% of the total weight of the dispersion provided by AkzoNobel.

[0204] The transmittance in the UVA region of a 1 cm thick sample of ST-AK-ML diluted with water to 2 wt % in solids content is 16% whereas the same measurement on diluted samples of ST-AK and CT16 PCL gives values of 45% and 49% respectively.

[0205] The average diameter of the particles in these three acidic sols is reported in table 1.

[0206] When the procedure above is reproduced using acidic sols comprising anionic particles, such as ST-OS, ST-O-40 or ST-OL provided by Nissan Chemical or Levasil CT16 PDL provided by AkzoNobel, instead of the acidic sol comprising cationic particles, the coatings resulting from the liquid compositions present cosmetic defects like a grainy aspect, spreading defects for the liquid composition and poor transparency of the coating).

[0207] UV Absorbers

[0208] NANOBYK®-3840 provided by BYK is a 40 wt % water dispersion of ZnO particles with a 40 nm average diameter.

[0209] NANOBYK®-3860 provided by BYK is a 50 wt % water dispersion of ZnO particles with a 40 nm average diameter.

[0210] The amounts listed in Table 1 correspond to amounts by weight of the dispersion comprising the ZnO particles and the water.

[0211] Preparation of a Reference Liquid Hard Coating Composition:

[0212] During the whole procedure, the reaction mixture is stirred by means of mechanical stirrer in a glass vessel.

[0213] 6.62 parts of a 0.1N solution of HCl are added dropwise to 18.6 parts of γ-glycidoxypropyltrimethoxysilane. The temperature of the reaction mixture is maintained below 40° C. during this addition. After the addition of the 0.1N solution of HCl is complete, 9.73 parts of dimethyldiethoxysilane are added dropwise. Care is taken during this addition to maintain the temperature of the reaction mixture below 50° C. The reaction mixture is left at room temperature for 20 hours to 24 hours. 60.1 parts of silica sol MA-ST (provided by Nissan Chemical) are then added to the mixture and the mixture is again left at room temperature for 30 minutes. Methylethylketone (3.65 parts), Al(acac).sub.3 (1.2 parts) and surfactant EFKA3034 (0.1 parts; provided by BASF) are then added to the mixture. The mixture is then left 60 min at room temperature and filtered on a 3 μ polypropylene filter (Sartorius) to give a ready to use liquid hard coating composition.

[0214] MA-ST is an acidic (pH 2-4) methanol dispersion of silica particles (average diameter 12.5 nm) with a solids content of 30% of the total weight of the dispersion. The transmittance in the UVA region of a 1 cm thick sample of MA-ST diluted with methanol to 2 wt % in solids content is 68%.

[0215] Preparation of the Coated Articles:

[0216] The optical articles used in the examples were round lenses (plano or −2.00 with a diameter of 68 mm) comprising an ORMA® substrate (obtained by polymerizing CR-39® diethylene glycol bis(allylcarbonate) monomer) or a polythiourethane substrate obtained by polymerizing MR7® from Mitsui Toatsu Chemicals (hereafter MR7 substrate).

[0217] The convex surface of the substrate was first corona treated and then optionally spin-coated with a primer composition yielding a primer coating of 1 p.m thickness after curing (precuring: 15 minutes at 75° C.; film forming: 3 hours at 100° C.). The convex surface of the optical article was then spin-coated with a liquid hard coating composition. The liquid hard coating composition provides, upon curing, a functional transparent hard coating of thickness 2.6 p.m having abrasion and/or scratch resistance (precuring: 15 minutes at 75° C.; film forming: 3 hours at 100° C.).

[0218] Procedures for the Anti-Reflective Coatings

[0219] Two different antireflective coatings were used. These coatings were deposited on the surface of the article after the deposition of a hard coating.

[0220] Antireflective coating I (Crizal Forte® disclosed in EP2524798) comprises alternating layers of ZrO.sub.2 and SiO.sub.2 is vacuum deposited on the convex surface.

[0221] Antireflective coating II (such as disclosed in EP2033021) comprises alternating layers of ZrO.sub.2 and SiO.sub.2+Al.sub.2O.sub.3.

[0222] Procedure for the Anti-Fouling Coatings

[0223] Two different anti-fouling coatings were used. These coatings were deposited on the surface of the article after the deposition of an antireflective coating.

[0224] Antifouling coating I is a hydrophobic and oleophobic top coat of thickness 2-5 nm. It is vacuum deposited by evaporation under vacuum of a modified perfluoropolyether (OPTOOL® DSX by Daikin, described in U.S. Pat. No. 6,183,872) on the convex surface of the optical article.

[0225] Antifouling coating II is as antifouling coating II except twice as thick.

[0226] The reference primer composition is an aqueous dispersion (dry extract weight: 17%) comprising a polyurethane latex (U5200 from Alberdingk Boley, 76% of the dry extract weight of the composition) and colloidal silica (Bindzil CC401 from Eka chemicals, 23% of the dry extract weight of the composition) and a surfactant (L77 from De Sangosse, 1% of the dry extract weight composition).

[0227] The optical articles prepared with an ORMA® substrate are described in table 2.

TABLE-US-00003 TABLE 2 Sample S1 S2 S3 cS1 cS2 cS3 cS4 Primer — Ref. Ref. — Ref. Ref. Ref. Hard coating L1 L1 L1 Ref. Ref. Ref. Ref. Anti-reflective coating — — I — — I II Anti-fouling coating — — I — — I II

[0228] The optical articles prepared with an MR7 substrate are described in table 3.

TABLE-US-00004 TABLE 3 Sample mS1 mS2 mS3 mS4 mS5 mS6 mS7 mS8 mS9 mS10 mS11 cmS1 Primer — — — — — — — — — — — — Hard L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 Ref. coating

[0229] Results of the Tests

[0230] The results of the tests performed on the optical articles prepared with an ORMA® substrate are reported in table 4.

TABLE-US-00005 TABLE 4 Sample S1 S2 S3 cS1 cS2 cS3 cS4 Bayer sand 4.2 4.0 4.6 4.1 4.5 4.7 — HSW 3 3 — 3 3 — — T.sub.v 92.5 92.3 96.6 92.7 92.8 96.9 — Y.sub.i 1.0 1.5 1.9 0.9 1.2 2.0 — Q.sub.sun (80 hours) OK OK — OK OK — — T.sub.c 1 week (° C.) — — 50 — — 60 — T.sub.c 1 month (° C.) — — 50 — — 50 — FE.sub.mean (mJ) — — 3400 — — — 280 FE.sub.min (mJ) — — 1300 — — — 250

[0231] Bayer sand, T.sub.v and Y.sub.i values were measured on plano lenses, the other tests were performed on −2.00 lenses.

[0232] These results show that the performances of optical articles bearing hard coatings according to the invention are as satisfying as those of optical articles bearing reference hard coatings.

[0233] Moreover sample S3 shows an exceptional impact resistance much higher than the impact resistance of the reference sample cS4.

[0234] The tests performed on S1 and cS1 have also been performed on mS1 and cmS1 and are equally satisfactory except for the Q.sub.sun adhesion test.

[0235] The results of the Bayer sand test for mS6 and mS11 are slightly better than what is obtained with mS1 but the Q.sub.sun adhesion for mS6 and mS11 is degraded compared to mS1.

[0236] The results of the Q.sub.sun adhesion test performed on the optical articles prepared with an MR7 substrate are reported in table 5 and 6.

TABLE-US-00006 TABLE 5 Sample mS1 mS6 cmS1 UV exposure time t0 40 h 80 h t0 40 h 80 h t0 40 h 80 h Exp 1 OK fail fail OK fail fail OK fail fail Exp 2 OK OK fail OK fail fail OK fail fail Exp 3 OK fail fail OK fail fail OK fail fail Exp 4 OK OK fail OK fail fail OK fail fail

[0237] Table 5 shows the results of four repeat experiments (exp 1, exp 2, exp 3, exp 4) for three different samples at three different exposure times. Clearly mS1 shows improved Q.sub.sun adhesion compared to the reference sample cmS1 and compared to sample mS6 where the cationic particles are smaller and the transmittance of the sol in the UVA region is higher.

TABLE-US-00007 TABLE 6 Sample t0 40 h 80 h 120 h 160 h mS1 OK OK fail fail fail mS2 OK OK OK OK OK mS3 OK OK OK OK OK mS4 OK OK OK OK OK mS5 OK OK OK OK OK mS6 OK fail fail fail fail mS7 OK fail fail fail fail mS8 OK fail fail fail fail mS9 OK fail fail fail fail mS10 OK fail fail fail fail

[0238] Table 6 shows that adding either Nanobyk 3840 or Nanobyk 3860 to the composition enhances considerably the Q.sub.sun adhesion properties of the resulting optical articles when the composition comprises larger particles with lower transmittance in the UVA region (samples mS2 to mS5). On the other hand, the adjunction of Nanobyk 3840 or Nanobyk 3860 has no noticeable effect when the composition comprises smaller particles with higher transmittance in the UVA region (samples mS7 to mS10).