Optical article comprising a precursor coating of an anti-fog coating and a temporary layer made of metal fluorides or compounds including magnesium and oxygen

Abstract

Disclosed is an optical article, preferably an ophthalmic lens, including a substrate having at least one main surface and a precursor coating of an anti-fog coating, the precursor coating in direct contact with either the main surface of the substrate, or with a first coating, when the main surface of the substrate is coated with a first coating, the precursor coating being formed by a deposition of at least one hydrophilic compound A on the substrate or on the first coating, including an inner portion in which the compound A is grafted on the substrate or on the first coating, and an outer portion that can be removed by washing and/or wiping, resulting from the deposition of the compound A, and being coated with a temporary layer, in direct contact with the compound, including at least one compound selected from the metal fluorides and the compounds including magnesium and oxygen.

Claims

1. An optical article, comprising: a substrate having at least one main surface and a precursor coating for an antifogging coating, said precursor coating being in direct contact either with said main surface of the substrate, or with a first coating, when said main surface of the substrate is coated with a first coating, said precursor coating being formed by depositing at least one hydrophilic compound A on the substrate or, when it is present, on the first coating, wherein said precursor coating comprises an internal part in which said compound A is grafted to the substrate or, when it is present, to the first coating, and an external part that can be removed by washing and/or wiping, resulting from the deposition of the compound A, and wherein said precursor coating is coated with a temporary layer, in direct contact with it, comprising at least one compound selected from the group consisting of metal fluorides and compounds comprising magnesium and oxygen.

2. The optical article of claim 1, wherein the temporary layer comprises at least 70% by weight of at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen, with respect to the total weight of the temporary layer.

3. The optical article of claim 1, wherein the temporary layer comprises at least one compound selected from metal fluorides and magnesium oxides.

4. The optical article of claim 1, wherein the temporary layer comprises at least 70% by weight of MgF2, with respect to the total weight of the temporary layer.

5. The optical article of claim 1, wherein the temporary layer consists of a layer of MgF.sub.2.

6. The optical article of claim 1, wherein the temporary layer forms the external layer of the optical article.

7. The optical article of claim 1, wherein the temporary layer has a thickness ranging from 5 to 200 nm.

8. The optical article of claim 1, wherein the precursor coating for the antifogging coating has a thickness ranging from 3 to 100 nm.

9. The optical article of claim 1, wherein the compound A contains at least one polyoxyalkylene group.

10. The optical article of claim 1, wherein the compound A is an organosilane having at least one silicon atom bearing at least one hydrolyzable group.

11. The optical article of claim 10, wherein the organosilane compound is a compound of formula:
R.sup.1Y.sub.mSi(X).sub.3-m(I) wherein the Y groups, which are identical or different, are monovalent organic groups bonded to the silicon via a carbon atom, the X groups, which are identical or different, are hydrolyzable groups or hydroxyl groups, R1 is a group comprising a polyoxyalkylene functional group and m is an integer equal to 0, 1 or 2.

12. The optical article of claim 1, wherein the precursor coating for the antifogging coating has a surface energy of greater than or equal to 15 mJ/m.sup.2.

13. The optical article of claim 1, wherein at least one of the main surfaces of the substrate is coated with a first coating, said first coating being a single-layer or multilayer antireflective coating, or an abrasion-resistant and/or scratch-resistant coating.

14. The optical article of claim 1, wherein the optical article is an optical lens.

15. A process for preparing an optical article, comprising: a) providing a substrate having at least one main surface, b) depositing, on said main surface of the substrate or on a first coating, when said main surface of the substrate is coated with a first coating, at least one hydrophilic compound A, so as to obtain a precursor coating for an antifogging coating that comprises an internal part in which said compound A is grafted to the substrate or, when it is present, to the first coating, and an external part that can be removed by washing and/or wiping, c) depositing directly on the precursor coating for the antifogging coating at least one temporary layer comprising at least one compound selected from the group consisting of metal fluorides and compounds comprising magnesium and oxygen, d) removing said temporary layer and said external part of the precursor coating for an antifogging coating.

16. The process of claim 15, further comprising the following steps: e) attaching the optical article resulting from step d) to a holding device; f) mounting the holding device to which the optical article adheres in an edging device; g) edging the optical article by machining the periphery or the edge of the optical article; and h) recovering the edged optical article.

17. The process of claim 15, wherein the thickness of the precursor coating for the antifogging coating, after the removal of the temporary layer, is less than or equal to 5 nm.

18. The process of claim 15, wherein the temporary layer comprises at least 70% by weight of at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen, with respect to the total weight of the temporary layer.

19. The process of claim 15, wherein the temporary layer comprises at least one compound selected from metal fluorides and magnesium oxides.

20. The process of claim 15, wherein the temporary layer comprises at least 70% by weight of MgF.sub.2, with respect to the total weight of the temporary layer.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) According to one embodiment of the invention, the coating comprising silanol groups at its surface is a silica-based layer deposited on an abrasion-resistant coating, preferably deposited directly on this abrasion-resistant coating.

(2) According to another embodiment of the invention, which constitutes the preferred embodiment, the optical article according to the invention comprises an antireflective coating. When such a coating is present, it generally constitutes the first coating within the meaning of the invention. This antireflective coating can be any antireflective coating conventionally used in the optical field, in particular the field of ophthalmic optics.

(3) An antireflective coating is defined as a coating, deposited at the surface of an optical article, which improves the antireflective properties of the final optical article. It makes it possible to reduce the reflection of light at the article/air interface over a relatively broad portion of the visible spectrum.

(4) As is also well known, antireflective coatings conventionally comprise a single-layer or multilayer stack of dielectric materials. These are preferably multilayer coatings, comprising layers with a high refractive index (HI) and layers with a low refractive index (LI).

(5) In the present patent application, a layer of the antireflective coating is said to be a layer with a high refractive index when its refractive index is greater than 1.55, preferably greater than or equal to 1.6, better still greater than or equal to 1.8 and even better still greater than or equal to 2.0. A layer of an antireflective coating is said to be a layer with a low refractive index when its refractive index is less than or equal to 1.55, preferably less than or equal to 1.50 and better still less than or equal to 1.45. Unless otherwise indicated, the refractive indices to which reference is made in the present invention are expressed at 25 C. for a wavelength of 550 nm.

(6) The HI and LI layers are respectively conventional layers with a high refractive index and with a low refractive index well known in the art, the composition, the thickness and the method of deposition of which are described in particular in patent application WO 2010/109154.

(7) Preferably, the total thickness of the antireflective coating is less than 1 micrometer, better still less than or equal to 800 nm and even better still less than or equal to 500 nm. The total thickness of the antireflective coating is generally greater than 100 nm, preferably greater than 150 nm.

(8) Before the formation of the precursor for the antifogging coating on the first coating or on the bare substrate, it is normal to subject the surface of this first coating or of the substrate to a physical or chemical activation treatment intended to increase the adhesion of the precursor for the antifogging coating. These treatments can be chosen from those described above for the activation of the coating comprising silanol groups at its surface.

(9) According to the invention, the first coating, when it is present, is directly in contact with the precursor coating for the antifogging coating. According to another embodiment, the substrate is itself directly in contact with the precursor coating for the antifogging coating, which will now be described.

(10) The term precursor for an antifogging coating is understood to mean, in the present patent application, a coating which, by applying a liquid solution containing a surfactant to its surface so as to form a film, constitutes an antifogging coating within the meaning of the invention. The combination formed by the precursor coating and the film of solution based on surfactant constitutes the antifogging coating proper.

(11) The precursor coating for the antifogging coating is formed by depositing at least one hydrophilic compound A in a sufficient amount on the first coating or on the substrate.

(12) The term hydrophilic compound is understood to mean a compound of which a film formed at the surface of a substrate has a static contact angle with water of less than or equal to 60, preferably less than or equal to 55, better still less than or equal to 50. In the present patent application, the contact angles are measured in the manner described in patent application WO 2008/053020.

(13) The compound A is a film-forming compound. It preferably comprises at least one group selected from polyoxyalkylene, polyamine, polyol (polyhydroxylated group, for example a polysaccharide or polyglycerol group) and polyether (for example a polyol ether) groups, preferably a polyoxyalkylene group. The compound A generally comprises at least one group capable of establishing a covalent bond with a functional group present on the external surface of the substrate or of the first coating to which it will be grafted, said functional group preferably being a silanol group in the case where a first coating is present. This group, which is a reactive group, can be, without limitation, one of the following groups: an isocyanate, acrylate, methacrylate, haloalkyl, carboxylic acid, sulfonic acid, acyl chloride, chlorosulfonyl, chloroformate or ester group, a silicon atom bearing at least one hydrolyzable group or a group comprising an epoxy functional group, such as the glycidyl group, preferably a silicon atom bearing at least one hydrolyzable group.

(14) The compound A is preferably an organosilane compound, better still an organosilane compound having at least one silicon atom bearing at least one hydrolyzable group, even better still an organosilane compound having a polyoxyalkylene group and at least one silicon atom bearing at least one hydrolyzable group.

(15) Preferably, its polyoxyalkylene chain is functionalized at just one end or at both its ends, ideally at just one end, by at least one, preferably just one, group comprising at least one silicon atom bearing at least one hydrolyzable group. This organosilane compound preferably comprises a silicon atom bearing at least two hydrolyzable groups, preferably three hydrolyzable groups. Preferably, it does not comprise a urethane group. It is preferably a compound of formula:
R.sup.1Y.sub.mSi(X).sub.3-m(I)
wherein the Y groups, which are identical or different, are monovalent organic groups bonded to the silicon via a carbon atom, the X groups, which are identical or different, are hydrolyzable groups or hydroxyl groups, R.sup.1 is a group comprising a polyoxyalkylene functional group and m is an integer equal to 0, 1 or 2. Preferably, m=0.

(16) The X groups are preferably chosen from alkoxy groups OR.sup.3, in particular C.sub.1-C.sub.4 alkoxy groups, acyloxy groups OC(O)R.sup.4, where R.sup.4 is an alkyl radical, preferably a C.sub.1-C.sub.6 alkyl radical, preferably a methyl or ethyl radical, halogens, such as Cl and Br, or the trimethylsiloxy group (CH.sub.3).sub.3SiO, and the combinations of these groups. Preferably, the X groups are alkoxy groups, in particular methoxy or ethoxy groups and better still ethoxy groups.

(17) The Y group, present when m is not zero, is preferably a saturated or unsaturated hydrocarbon group, preferably a C.sub.1-C.sub.10 hydrocarbon group and better still a C.sub.1-C.sub.4 hydrocarbon group, for example an alkyl group, such as methyl or ethyl, a vinyl group or an aryl group, for example a phenyl group, which is optionally substituted, in particular by one or more C.sub.1-C.sub.4 alkyl groups. Preferably, Y represents the methyl group.

(18) According to a preferred embodiment, the compound of formula I comprises a trialkoxysilyl group, such as a triethoxysilyl or trimethoxysilyl group.

(19) The polyoxyalkylene group of the organosilane compound (R.sup.1 group) preferably comprises fewer than 80 carbon atoms, better still fewer than 60 carbon atoms and even better still fewer than 50 carbon atoms. The R.sup.1 group preferably meets these same conditions.

(20) The R.sup.1 group generally has the formula -L-R.sup.2, where L is a divalent group bonded to the silicon atom of the compounds of formula I or II via a carbon atom and R.sup.2 is a group comprising a polyoxyalkylene group bonded to the L group via an oxygen atom, this oxygen atom being included in the R.sup.2 group. Nonlimiting examples of L groups are linear or branched alkylene groups which are optionally substituted, cycloalkylene groups, arylene groups, the carbonyl group, the amido group or combinations of these groups, such as cycloalkylenealkylene, biscycloalkylene, biscycloalkylenealkylene, arylenealkylene, bisphenylene, bisphenylenealkylene or amidoalkylene groups, an example of which is the CONH(CH.sub.2).sub.3 group, or else the OCH.sub.2CH(OH)CH.sub.2 and NHC(O) groups. The preferred L groups are alkylene groups, preferably linear alkylene groups, preferably having 10 or fewer carbon atoms, better still 5 or fewer carbon atoms, for example the ethylene and propylene groups.

(21) The preferred R.sup.2 groups comprise a polyoxyethylene group (CH.sub.2CH.sub.2O).sub.n, a polyoxypropylene group or combinations of these groups.

(22) The preferred organosilanes of formula I are compounds of following formula II:
Y.sub.m(X).sub.3-mSi(CH.sub.2).sub.n-(L).sub.m(OR).sub.nO-(L).sub.mR(II)
where R is a hydrogen atom, an acyl group or an alkyl group which is linear or branched, which is optionally substituted by one or more functional groups and which can additionally comprise one or more double bonds, R is a linear or branched alkylene group, preferably a linear alkylene group, for example an ethylene or propylene group, L and L are divalent groups, X, Y and m are as defined above, n is an integer ranging from 1 to 10, preferably from 1 to 5, n is an integer ranging from 2 to 50, preferably from 5 to 30 and better still from 5 to 15, m is equal to 0 or 1, preferably 0, and m is equal to 0 or 1, preferably 0.

(23) The L and L groups, when they are present, can be chosen from the divalent groups L described above and preferably represent the OCH.sub.2CH(OH)CH.sub.2 group or the NHC(O) group. In this case, the OCH.sub.2CH(OH)CH.sub.2 or NHC(O) groups are connected to the adjacent groups (CH.sub.2).sub.n (in the case of an L group) and R (in the case of an L group) via their oxygen atom (for the OCH.sub.2CH(OH)CH.sub.2 group) or via their nitrogen atom (for the NHC(O) group).

(24) The O-(L).sub.mR group is preferably an alkoxy group (m=0, R=alkyl), ideally a methoxy group.

(25) Preferably, the compounds of formula (I) or (II) comprise just one silicon atom bearing at least one hydrolyzable group.

(26) According to one embodiment, m=0 and the hydrolyzable groups X denote methoxy or ethoxy groups. n is preferably equal to 3. According to another embodiment, R denotes an alkyl group having fewer than 5 carbon atoms, preferably the methyl group. R can also denote an aliphatic or aromatic acyl group, in particular the acetyl group.

(27) Finally, R can denote a trialkoxysilylalkylene or trihalosilylalkylene group, such as the (CH.sub.2).sub.nSi(R.sup.5).sub.3 group, where R.sup.5 is a hydrolyzable group, such as the X groups defined above, and n is an integer such as the n group defined above. An example of such an R group is the (CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3 group. In this embodiment, the organosilane compound comprises two silicon atoms bearing at least one hydrolyzable group.

(28) According to preferred embodiments, n is equal to 3 or else varies from 6 to 9, from 9 to 12, from 21 to 24 or from 25 to 30, preferably from 6 to 9.

(29) Mention may be made, as examples of compounds of formula II, of the 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane compounds of formulae CH.sub.3O(CH.sub.2CH.sub.2O).sub.6-9(CH.sub.2).sub.3Si(OCH.sub.3).sub.3 (III) and CH.sub.3O(CH.sub.2CH.sub.2O).sub.9-12(CH.sub.2).sub.3Si(OCH.sub.3).sub.3 (IV), sold by Gelest Inc. or ABCR, the compound of formula CH.sub.3O(CH.sub.2CH.sub.2O).sub.3(CH.sub.2).sub.3Si(OCH.sub.3).sub.3 (VIII), the compounds of formula CH.sub.3O(CH.sub.2CH.sub.2O).sub.n(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3, where n=21-24, 2-[methoxy(polyethyleneoxy)propyl]trichlorosilanes, 2-[acetoxy(polyethyleneoxy)propyl]trimethoxysilane of formula CH.sub.3C(O)O(CH.sub.2CH.sub.2O).sub.6-9(CH.sub.2).sub.3Si(OCH.sub.3).sub.3, 2-[acetoxy(polyethyleneoxy)propyl]triethoxysilane of formula CH.sub.3C(O)O(CH.sub.2CH.sub.2O).sub.6-9(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3, 2[hydroxy(polyethyleneoxy)propyl]trimethoxysilane of formula HO(CH.sub.2CH.sub.2O).sub.6-9(CH.sub.2).sub.3Si(OCH.sub.3).sub.3, 2-[hydroxy(polyethyleneoxy)propyl]triethoxysilane of formula HO(CH.sub.2CH.sub.2O).sub.6-9(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3, the compounds of formulae HO(CH.sub.2CH.sub.2O).sub.8-12(CH.sub.2).sub.3Si(OCH.sub.3).sub.3 and HO(CH.sub.2CH.sub.2O).sub.8-12(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3, bis[(3-methyldimethoxysilyl)propyl]polypropylene oxide and compounds comprising two siloxane heads, such as bis[(3-triethoxysilylpropoxy)-2-hydroxypropoxy]polyethylene oxide of formula (V), bis[(N),N-(triethoxysilylpropyl)aminocarbonyl]polyethylene oxide of formula (VI) with n=10-15 and bis(triethoxysilylpropyl) polyethylene oxide of formula (VII):

(30) ##STR00001##

(31) The preferred compounds of formula II are the [alkoxy(polyalkyleneoxy)alkyl]trialkoxysilanes or their trihalo analogs (m=m=m=0, R=alkoxy).

(32) Preferably, the compound A according to the invention does not have a fluorine atom. Typically, the content by weight of fluorine in the precursor coating for the antifogging coating is less than 5% by weight, preferably less than 1% by weight and better still 0% by weight.

(33) Preferably, the molar mass of the compound A according to the invention ranges from 400 to 4000 g/mol, preferably from 400 to 1500 g/mol, better still from 400 to 1200 g/mol and even better still from 400 to 1000 g/mol.

(34) According to one embodiment of the invention, the precursor for the antifogging coating comprises more than 80% by weight, preferably more than 90% by weight, of compound A according to the invention, with respect to the total weight of the precursor for the antifogging coating. According to one embodiment, the precursor for an antifogging coating consists of a layer of said compound A.

(35) Preferably, the precursor for an antifogging coating of the invention comprises less than 5% by weight of metal oxide or metalloid oxide (for example silica or alumina), with respect to the total weight of the coating, and better still does not comprise it. When the organosilane compound used for the formation of the antifogging coating is deposited under vacuum, preferably no metal oxide is coevaporated with it, according to the technique for the coevaporation of at least one organic compound and of at least one inorganic compound described in the application EP 1 324 078.

(36) According to the invention, the deposition of the compound A forms a precursor coating for an antifogging coating comprising an internal part, in which said compound A is permanently (and not by simple adsorption) grafted to the first coating or to the substrate, and an external part which can be removed by washing and/or wiping.

(37) In order to arrive at such a structure, it is necessary to deposit an excess of compound A at the surface of the first coating or of the substrate, preferably comprising silanol groups. Adjusting the deposition parameters in order to arrive at such a configuration is within the scope of a person skilled in the art.

(38) The term excess is understood to mean an amount of compound A which is greater than the amount which would be necessary in order to form a layer of compound A grafted to the surface of the first coating or of the substrate.

(39) Thus, the precursor coating for the antifogging coating is a coating preferably having a thickness (before wiping) of greater than or equal to 3 nm, better 5 nm, better still 8 nm and ideally 10 nm. Its thickness is preferably less than 100 nm, better still 50 nm and even better still 20 nm. It typically ranges from 3 to 100 nm, preferably from 5 to 50 nm.

(40) The deposition of the compound A at the surface of the first coating or of the substrate according to the invention can be carried out according to usual techniques, preferably by gas-phase or liquid-phase deposition, ideally gas-phase deposition, by vacuum evaporation. The compound A can be dissolved beforehand in a solvent before being evaporated, in order to exert better control over the rate of evaporation and of deposition.

(41) According to one of the embodiments of the invention, the precursor coating is deposited by application of a composition comprising a hydrolyzate of the compound A, in the case where the latter is an organosilane. In this case, it is recommended to apply the composition fairly rapidly after hydrolysis, typically less than 2 hours, preferably less than 1 hour, better still less than 30 minutes, after having carried out the hydrolysis (by addition of an acidic aqueous solution, typically of HCl), in order to limit the formation of siloxane prepolymers before grafting. However, it is preferable to deposit said organosilane by the gaseous route.

(42) The external part of the precursor coating for the antifogging coating can be removed by washing and/or wiping, which means that it would be removed by subjecting it in particular to washing with soapy water (containing a surfactant), using a sponge, and then with deionized water, and/or to wiping for typically 20 seconds or less, using a CEMOI, Wypall or Selvith cloth which is dry or optionally impregnated with alcohol, typically isopropyl alcohol. This wiping operation can optionally be followed by a further rinsing with deionized water and by a final wiping with a rag.

(43) The precursor for an antifogging coating of the invention preferably has a static contact angle with water of strictly greater than 10 and of strictly less than 50, preferably less than or equal to 45, better still 40, even better still 30 and ideally 25. This contact angle preferably ranges from 15 to 40, better still from 20 to 30. Its surface energy is preferably at least 15 mJ/m.sup.2, better still at least 25 mJ/m.sup.2. These different values are confirmed by the precursor for an antifogging coating initially deposited (including an excess of compound A) and/or the precursor for an antifogging coating resulting from the removal of the temporary layer of the invention, preferably by both. The surface energies are calculated using the Owens-Wendt method described in the article: Estimation of the surface force energy of polymers OWENS D. K, WENDT R. G. (1969) J. APPL-POLYM-SCI, 13, 1741-1747.

(44) After the deposition of the compound A in accordance with the invention, the external part of the coating which can be removed by wiping is not removed, whether by washing or by wiping, or else can be removed but only partially. This precursor coating would thus exhibit problems of adhesion to the holding pad during edging.

(45) A temporary layer according to the invention comprises at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen and is formed directly on the precursor coating for the antifogging coating. Preferably, the temporary layer comprises at least 70% by weight of metal fluorides or of compounds comprising magnesium and oxygen (preferably magnesium oxides), with respect to the total weight of the temporary layer. It preferably comprises at least 70% by weight of metal fluorides or at least 70% by weight of compounds comprising magnesium and oxygen (preferably magnesium oxides), preferably at least 80%, 90% or 95% by weight.

(46) This temporary layer preferably constitutes the external layer of the optical article, that is to say, its layer which is in contact with the air. In a non-preferred manner, other temporary layers based on identical or different materials may be deposited on said temporary layer comprising at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen so as to form, for example, temporary bilayers.

(47) As examples of metal fluorides, mention may be made of magnesium fluoride MgF.sub.2, lanthanum fluoride LaF.sub.3, aluminum fluoride AlF.sub.3, cerium fluoride CeF.sub.3, ZrF.sub.4, CaF.sub.2, Na.sub.5Al.sub.3F.sub.14, Na.sub.3AlF.sub.6, BaF.sub.2, CdF.sub.2, HfF.sub.4, LiF, NaF, NdF.sub.3, PbF.sub.2, PrF.sub.3, SrF.sub.2 and ThF.sub.4. Preferably, use will be made of magnesium fluoride, CeF.sub.3, Na.sub.5Al.sub.3F.sub.14 or LaF.sub.3, ideally magnesium fluoride. Among the compounds comprising magnesium and oxygen, used may be made of magnesium hydroxide Mg(OH).sub.2 or MgO, the latter being preferred. The preferred magnesium oxide is MgO.

(48) This layer preferably comprises at least 80% by weight of at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen, with respect to the total weight of the temporary layer, better still at least 90% and even better still at least 95% by weight. According to one embodiment of the invention, the temporary layer consists of a layer of metal fluorides or of compounds comprising magnesium and oxygen (preferably a layer of magnesium oxides), preferably of MgF.sub.2 or MgO.

(49) When the temporary layer does not solely comprise metal fluorides or compounds comprising magnesium and oxygen, it comprises other materials which are preferably dielectric materials such as metal or metalloid oxides or hydroxides, preferably silica or alumina (Al.sub.2O.sub.3).

(50) The thickness of the temporary layer according to the invention is preferably 5 nm, better still 10 nm and preferably 200 nm, better still 100 nm and even better still 50 nm. It typically ranges from 5 to 200 nm, preferably from 5 to 100 nm, better still from 10 to 50 nm.

(51) The temporary layer preferably exhibits a static contact angle with water of less than 50, better still of less than 40 and even better still of less than 30. Its surface energy is preferably at least 15 mJ/m.sup.2, better still at least 25 mJ/m.sup.2.

(52) The temporary layer can be deposited by any suitable conventional process, in the vapor phase (vacuum deposition) or in the liquid phase, for example by spraying, centrifuging or dipping. The temporary layer is preferably deposited by the gaseous route, in particular by vacuum evaporation. This is because the deposition by vacuum treatment makes possible precise control of the thickness of the temporary layer and minimizes the dispersions, which is not necessarily the case with the other technical solutions available. In addition, this vacuum treatment exhibits the advantage of being able to be directly incorporated in the industrial process for the treatment of the optical articles, in particular when the latter are equipped with an antireflective coating.

(53) The temporary layer is preferably formed so that it completely covers the precursor coating for the antifogging coating.

(54) The material of the temporary layer according to the invention does not detrimentally affect the surface properties of the precursor coating for the antifogging coating, and is capable of being removed during a subsequent operation that precedes the edging step. The material of this temporary layer also has sufficient cohesive force so that the withdrawal of the temporary layer is carried out without leaving residues at the surface of the precursor coating for the antifogging coating.

(55) The temporary layer used in the present invention exhibits numerous advantages. It does not affect the transparency of the optical article, so that it remains possible to carry out, on the article coated with this temporary layer, conventional measurements of power by a lensmeter. It can be subjected to marking by means of various marking inks commonly used by a person skilled in the art for varifocal lenses.

(56) The temporary layer according to the invention exhibits the advantage of being able to be very easily removed. The stage of removing this layer is carried out before an optional edging step, which will be described in detail below. It may be carried out either in a liquid medium, or by wiping, in particular dry wiping, or also by a combined use of these two means. This step can be chosen from the abovementioned washing and wiping steps. Other methods for removal in a liquid medium are described in particular in the patent application WO 03/057641. Wiping by means of a cloth or rag is the preferred removal technique. It is preferably carried out manually.

(57) The removal of the temporary layer (and of the excess of compound A deposited) can be monitored visually, since this layer has a colored reflection, if it is not too thin. It is consequently easy to differentiate the wiped surfaces from the non-wiped surfaces.

(58) After removal of the temporary layer, which also results in the removal of the surplus of the compound A deposited, that is to say of the external part of the precursor coating for the antifogging coating which can be removed by wiping, only the internal part of the precursor coating for the antifogging coating comprising the compound A actually grafted remains at the surface of the first coating according to the invention or of the substrate. The ungrafted molecules are thus removed.

(59) The thickness of the precursor coating for the antifogging coating remaining after this removal step is preferably less than or equal to 5 nm, better still less than or equal to 3 nm. The compound A deposited at the surface of the optical article thus preferably forms a monomolecular or virtually monomolecular layer.

(60) One of the main advantages of the use of the temporary layer based on metal fluorides or on compounds comprising magnesium and oxygen is that it makes it possible to facilitate the removal of the excess of compound A deposited by dividing the time needed to carry out this removal by a factor of between 5 and 10. Actually, the direct removal of the excess of compound A deposited at the surface of the first coating or of the substrate, which is generally carried out by manual wiping, is a long and tedious process for the production teams, which may prove painful in the long term. When this excess of compound A and the temporary layer of metal fluorides or of compounds comprising magnesium and oxygen are removed concomitantly, the process is easy, non-painful and rapid (removal time of the order of 5 seconds).

(61) The invention also relates to a process for preparing an optical article, preferably an ophthalmic lens, as defined above, comprising: a) providing a substrate having at least one main surface, b) depositing, preferably by vacuum evaporation, on said main surface of the substrate or on a first coating, when said main surface of the substrate is coated with a first coating, at least one hydrophilic compound A, so as to obtain a precursor coating for an antifogging coating that comprises an internal part in which said compound A is grafted to the substrate or, when it is present, to the first coating, and an external part that can be removed by washing and/or wiping, c) depositing directly on the precursor coating for the antifogging coating, preferably by vacuum evaporation, at least one temporary layer comprising at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen, d) removing said temporary layer and the external part of the precursor coating for an antifogging coating, preferably by washing and/or wiping.

(62) Preferably, the temporary layer comprises at least 70% by weight of at least one compound selected from metal fluorides and compounds comprising magnesium and oxygen, with respect to the total weight of the temporary layer.

(63) The process of the invention may furthermore comprise the following steps, carried out after the removal of the excess of compound A deposited, which make it a process for edging (or trimming) an optical article: e) attaching the optical article resulting from step d) to a holding device, preferably by means of an adhesive pad which adheres to the surface of the optical article (blocking); f) mounting the holding device to which the optical article adheres, preferably via the adhesive pad, in an edging device; g) edging the optical article by machining the periphery (or the edge) of the optical article; and h) recovering the edged optical article (deblocking).

(64) In the case where the optical article is an ophthalmic lens, the edging operation makes it possible to shape it to the dimensions and to the shape of the spectacle frame in which it is intended to be fitted.

(65) The edging is generally carried out on a grinder comprising diamond wheels which carry out the machining as defined above. The lens is held, during this operation, by axially acting clamping devices.

(66) For this, before the edging operation, a blocking operation is carried out on the optical article, that is to say that a holding means or block will be positioned on its surface (generally its convex surface). Typically, a holding pad (or fixing pad), such as a self-adhesive disk, for example a double-sided adhesive pad, is positioned between the block and the surface of the optical article. The block to which the optical article adheres via the adhesive pad is then mechanically fixed in the mounting axis of the grinder and an axial arm will lock the optical article by applying a central force to the face of the optical article opposite the block. During the machining, a tangential torque force is generated on the optical article.

(67) In the process of the invention, the optical article is firmly held during the edging operation, since its external surface, in contact with the holding pad, is at this stage a hydrophilic surface (namely the surface of the precursor for the antifogging coating), which enables a good adhesion, both normal and tangential, to the holding pad/(convex) surface of the optical article interface. Therefore, a reliable edging is carried out by avoiding the phenomena of slipping and offsetting, and also the phenomenon of untimely deblocking. This process provides optical articles which have undergone a maximum offsetting of 2 and optimally of less than or equal to 1.

(68) The blocking and deblocking steps and the holding systems which can be used during this process, which are conventional for a person skilled in the art, are described in more detail in the patent applications EP 1 392 613 and WO 2010/055261.

(69) It therefore appears that the role of the layer based on metal fluorides or on compounds comprising magnesium and oxygen of the invention is clearly different from that of the temporary layers of metal fluorides (typically MgF.sub.2) or of magnesium oxide used for example in patent applications EP 1 392 613, EP 1 633 684 and WO 03/057641. In these applications, the temporary layers based on metal fluorides or on magnesium oxide are formed at the surface of optical articles coated with hydrophobic (generally fluorinated) external layers in order to facilitate the edging thereof. According to the invention, the temporary layers based on metal fluorides or on compounds comprising magnesium and oxygen are deposited at the surface of optical articles coated with hydrophilic external layers and do not have the objective of facilitating the edging thereof. The term hydrophobic coating is understood to mean a coating that has a static contact angle with water of greater than 60, preferably of greater than or equal to 70, better still of less than or equal to 90.

(70) The process of the invention may also comprise an additional stage of deposition of a film of a liquid solution comprising at least one surfactant at the surface of the precursor coating for the antifogging coating obtained after the removal of the temporary layer and of the external part of the precursor coating for the antifogging coating which can be removed by wiping, thus giving access to a temporary antifogging coating.

(71) An optical article having excellent antifogging properties is thus recovered, which means that the temporary layer according to the invention does not exert any negative effect on the antifogging properties of the article. Neither does it affect the durability of the properties of the antifogging coating.

(72) This solution provides the lenses with temporary protection against fogging by creating a uniform layer at their surface which helps in dispersing the water droplets over the surface of the lens so that they do not form visible fogging.

(73) The application of the surfactant solution can be carried out by any known technique, in particular by dipping, centrifuging or spraying.

(74) The surfactant solution is preferably applied by deposition of a drop of this solution at the surface of the precursor for the antifogging coating and by then spreading it so as to cover preferably all of said precursor coating. The surfactant solution applied is generally an aqueous solution, preferably comprising from 0.5% to 10% by weight, better still from 2% to 8% by weight, of surfactant.

(75) A great variety of surfactants can be employed. These can be ionic (cationic, anionic or amphoteric) or nonionic, preferably nonionic or anionic. However, a mixture of surfactants belonging to these different categories can be envisaged. Preferably, use is made of a surfactant comprising poly(oxyalkylene) groups. A commercially available surfactant solution for conferring an antifogging property is the Optifog Activator solution from Essilor.

(76) The antifogging coating of the invention preferably exhibits a static contact angle with water of less than or equal to 10, better still of less than or equal to 5.

(77) The following examples illustrate the invention in more detail but without implied limitation. Unless otherwise indicated, all the thicknesses appearing in the present patent application are physical thicknesses.

EXAMPLES

1. Materials and Optical Articles Used

(78) The organosilane compound A used in the examples to form the precursor for the antifogging coating is 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane having from 6 to 9 ethylene oxide units, of formula (III) and with a molar mass of 450-600 g/mol (CAS No.: 65994-07-2, Ref: SIM6492.7, supplied by Gelest Inc.).

(79) The vacuum evaporation device which makes it possible to deposit the different layers (antireflective, precursor coating for the antifogging coating, temporary layer) is a Satis 1200 DLF device (start-up pressure, at which the process will start: 3.510.sup.3 Pa).

(80) The lenses used in the examples according to the invention comprise a lens substrate made of poly(bisphenol A carbonate) (correction 8.00 diopters, +2.00 cylinder) comprising, on each of its faces, a polyurethane impact-resistant primer with a thickness of the order of 1 micron, itself coated with an abrasion-resistant coating with a thickness of the order of 3 microns by depositing and curing a composition as defined in example 3 of the patent EP 614 957, in its turn coated with an antireflective coating comprising five layers ZrO.sub.2/SiO.sub.2/ZrO.sub.2/ITO/SiO.sub.2 deposited on the abrasion-resistant coating by vacuum evaporation of the materials in the order in which they were mentioned (respective thicknesses of the layers: 29, 23, 68, 6.5 and 85 nm, respective deposition rates: 0.32, 0.7, 0.32, 0.13, 1.05 nm/s). The ZrO.sub.2 layers are deposited with introduction of passive O.sub.2 (610.sup.3 Pa) without ion assistance. The ITO layer is deposited under ion assistance of oxygen ions (2 A, 120 V), without contribution of passive O.sub.2. An ITO layer is an electrically conducting layer of indium oxide doped with tin (In.sub.2O.sub.3:Sn).

(81) Before the deposition of the antireflective coating, the lenses comprising the abrasion-resistant coating are subjected to a surface activation (IPC) treatment, which consists in carrying out an ion bombardment with argon ions, under vacuum, at a pressure typically of 3.510.sup.5 mbar (1 minute, 3 A, 150 V).

(82) In the examples, the antireflective coating is not subjected to any activation treatment before the deposition of the precursor for the antifogging coating.

2. Vapor-Phase Deposition of the Precursor for the Antifogging Coating

(83) The deposition is carried out on the antireflective coating of the lenses by vacuum evaporation using a Joule-effect heat source. 150 l of siloxane compound of formula (III) are poured into a copper dish and this dish is deposited on a heating support made of conducting tantalum. The evaporation pressure of the siloxane compound of formula (III) generally varies from 510.sup.4 to 810.sup.4 Pa (deposition rate: 0.3 nm/s). A layer with a thickness of 9 to 15 nm depending on the tests (thickness greater than that of a grafted layer, which therefore includes the surplus of siloxane compound), having a static contact angle with water of 13, is obtained.

3. Deposition of the Temporary Layer

(84) A temporary layer of MgF.sub.2 in accordance with the invention with a thickness of 20 nm was formed on the precursor coating for the antifogging coating described above by vacuum evaporation in a vacuum chamber (deposition rate: 0.7 nm/s, P=310.sup.3 Pa, without contribution of passive gas or ion assistance, total deposition time: around 1 minute). Ophthalmic lenses exhibiting a blueish appearance (which will disappear after wiping and/or washing) are obtained. Other colors are possible depending on the thickness and the refractive index of the temporary layer.

4. Removal of the Temporary Layer and of the Excess of Hydrophilic Compound by Wiping

(85) The temporary layer and the excess of compound A which are not grafted are wiped manually using a dry rag of Wypall type and easily removed (in 5 seconds, without pain for the operator), which makes it possible to obtain a lens comprising, as external layer, a precursor coating for the antifogging coating grafted to the surface of the lens, which exhibits no cosmetic defect (in particular, no greasy appearance).

(86) The removal of the layer of metal fluorides may be monitored visually, since this layer is slightly colored.

(87) It has furthermore been verified by XPS (X-Ray Photoelectron Spectroscopy, on a Kratos Nova machine, source: monochromatized Al K, detection angle: normal (=0), depth analyzed: less than 10 nm, area analyzed: 300700 m.sup.2, 225 Watt) that after gentle wiping (a small amount of finger pressure on the region to be wiped in order to remove the layer of MgF.sub.2) with the dry rag, no trace of the elements F or Mg initially present at the surface of the lens remains (detection threshold: 0.1 atomic %, reproducibility <3%). This proves that gentle wiping is sufficient:

(88) TABLE-US-00001 atomic % Mg F Si O C F/Mg ratio Unwiped lens 20.1 43.2 2.0 11.8 22.9 2.1 Wiped lens 22.3 51.7 26.0

(89) The use of a temporary layer based on metal fluorides simplifies the removal of the excess of hydrophilic compound A deposited. The increase in productivity during the removal step is around 40 seconds per lens. Besides articles comprising the temporary layer of MgF.sub.2 described above, other articles were prepared, comprising temporary layers of CeF.sub.3, Na.sub.5Al.sub.3F.sub.14, LaF.sub.3 and MgO. Other articles comprising a second temporary layer, deposited by vacuum evaporation, of SiO.sub.2, L5 (mixture of SiO.sub.2 and Al.sub.2O.sub.3 sold by Umicore Materials AG), SnO.sub.2 or Al.sub.2O.sub.3 deposited on the temporary layer of MgF.sub.2 described above were also prepared. This temporary bilayer has a behavior similar to the temporary layer of MgF.sub.2 with regard to the removal thereof by wiping.

(90) In the absence of these temporary layers, the wiping is much longer (duration of the order of 50 seconds), since, in order to achieve a complete removal of the excess of compound A deposited, it requires wiping for several seconds with a dry rag of Wypall type, then using a Cmoi cloth and finally with isopropyl alcohol, which leaves traces on the lenses. Gentle wiping is not sufficient, it is necessary to powerfully wipe the lens, which causes pain to the operator (hands, fingers). Moreover, the lens obtained has a greasy surface.

(91) Furthermore, the wiping is sometimes random, since it is not possible, in the absence of a temporary layer, to visually detect which places have not been wiped, since the organosilane compound A forms a transparent layer.

(92) By way of comparison, a temporary layer consisting of alumina is difficult to remove with a dry or wet rag.

5. Formation of the Antifogging Coating and Evaluation of the Performance Thereof

(93) The Optifog Activator solution, sold by Essilor, containing surfactants (polyethylene glycols in solution in isopropanol), is applied just once to the surface of the lens obtained in 4.

(94) The lens is then placed for 24 hours in an environment that is temperature regulated (20-25 C.) and is at a humidity of 50%, then placed for 15 seconds above a heated receptacle containing water at 55 C. Immediately afterwards, a visual acuity chart located 5 m away is observed through the lens tested. An observer who has 10/10 vision and who has the lens placed in front of his eye obtains a visual acuity of 10/10.sup.th (in transmission, Snellen optotype chart placed 5 meters away, Armaignac Tridents, ref. T6 chart available from FAX INTERNATIONAL), and no fogging or visual distortion is observed. This test makes it possible to simulate the conditions of ordinary life where a wearer places his face above his tea, coffee or a saucepan of boiling water.

(95) It should be noted that materials such as alumina or tin oxide, when they are used pure, as temporary layer, are harmful to the antifogging performance of the lens, which might be explained by the precursor for an antifogging coating being contaminated or torn off during the removal of the temporary layer.

6. Edging of the Lens

(96) The lens obtained in 4 is edged on an Essilor Kappa grinder. During this operation, the adhesive holding pad employed (Leap II with a diameter of 24 mm, GAM200 from 3M) is directly in contact with the surface of the grafted precursor for the antifogging coating. The lens according to the invention does not undergo any offsetting (the protocol for measuring the offsetting undergone by the lenses during this operation is described in detail in patent application WO 2009/071818).

(97) It should be noted that, unlike the temporary layers of MgF.sub.2 or of silica described in patent applications PCT/FR2012/051044, EP 1 392 613, EP 1 633 684 and WO 03/057641, the presence of which at the surface of the optical article is imperative during the edging step, the temporary layer of MgF.sub.2 of the invention, deposited on an excess of ungrafted organosilane compound A, is removed before carrying out the edging operation, since the hold of the holding pad to the surface of this layer is poor, causing an untimely deblocking during the edging operation. Thus, the lens obtained in 3 fails during a deblocking test that consists in observing the hold of a block+holding pad assembly adhesively bonded to the convex face of the lens, this assembly being subjected to sprinkling with faucet water (water at 25 C.) for 45 seconds, so as to reproduce the exposure to the water commonly used during the edging operation.

(98) It should also be noted that the direct edging of the lens obtained in 2 (lens comprising, as external layer, a precursor for the antifogging coating deposited in excess with no temporary layer) cannot be carried out either, which does not enable good holding of the pad and leads to slipping of the article during the edging operation.