EP0973639A4

EP0973639A4 - Optical article with anti-reflecting coating, corresponding coating material and coating method

Info

Publication number: EP0973639A4
Application number: EP98913284A
Authority: EP
Inventors: Guillermo Guzman
Original assignee: Corning Inc
Current assignee: Corning SAS
Priority date: 1997-04-10
Filing date: 1998-03-30
Publication date: 2000-07-19
Also published as: JP2001526798A; CN1255889A; AR012580A1; WO1998045113A1; CA2285944A1; BR9808632A; EP0973639A1

Abstract

The invention relates to an optical article which comprises a mineral substrate and an anti-reflecting coating on at least one surface of said mineral substrate. In a characteristic way, said mineral substrate has a refractive index between 1.5 and 1.9 and said anti-reflecting coating is a single layer, nanoporous/nanograin structured coating, obtained by heat-treating a sol-gel film, constituted of strongly interconnected, inorganic polymers, also linked with inorganic particles, said polymers forming a tri-dimensional network which has the general formula M-OH/M-O-M, in which M represents a metal or a metalloid, advantageously selected from silicon, aluminium, zirconium, titanium and mixtures thereof. The invention also relates to a sol-gel material which is precursor of said anti-reflecting coating, and to a coating method for obtaining said optical article. Said device is advantageously an ophthalmic lens.

Description

OPTICAL ARTICLE WITH ANTI-REFLECTING COATING, CORRESPONDING COATING MATERIAL AND COATING METHOD

The present invention relates to an optical article comprising a transparent mineral substrate having a refractive index of 1.5 to 1.9 equipped with an anti- reflecting coating, a sol-gel material which is convenient for preparing said coating, and a method of preparation of said article. The anti-reflecting coating of the invention is particularly effective in terms of mechanical and chemical durability. In optical systems, a significant amount of light intensity is lost due to back reflection from the surface of the transmitting optical element. These losses may occur for example in ophthalmic lenses and vehicular and architectural windows. These losses are particularly serious in optical systems containing multiple optical elements since the losses become cumulative. Light reflectic i also creates problems by disturbing images on display screens such as television screens.

Numerous anti-reflection coating methods have been proposed to solve this problem. These methods involve modifying the refractive index of the surface of a light transmitting element relative to the refractive index of said element. The conventional approach to the problem has been to apply a transparent coating having a refractive index equal to the square root of the refractive index of the coated element. This is based on the following principle : the reflection of a light of a given wavelength is reduced to zero if the thickness of the coating crossed by said light is equal to a quarter of the value of this wavelength. A method commonly employed to produce an anti-reflecting film or coating is to vacuum deposit a film of material on the surface of a light-transmitting elementsuch as an instrument glass element or a spectacle lens. Another proposed technique involves leaching elements other than silica from a glass surface to produce a silica layer on the surface of an article. These methods require special materials and equipment, are difficult to carry out in a controlled manner, and are time-consuming. In order to broaden the effect across the visible spectrum, multiple coatings having different effective refractive indices have been applied. It has also been proposed to provide an index gradient in a coating for special purposes. This may be accomplished by varying application conditions in a controlled manner.

European Patent Application EP-A-514 773 refers to US Patent US-A-4,830,879 as disclosing a method wherein an alkoxide is allowed to react with water to form sol-gel solutions of different particle sizes. Successive layers of these solutions having increasing particle size are applied, for example, to a CRT face, and are dried. This enables obtaining increasing grain and pore size, and therefore decreasing density and refractive index from the substrate surface outwards. The European patent application cited above proposes a modification of the process described in said US patent, according to which the coating generated is a closed (non-porous) coating in which the degree of cross-linking of the gel increases outwardly. This results in the grain size of particles decreasing in size, in such a way that the refractive index also decreases. Various methods of varying the reaction conditions during gel formation are proposed. These include : (1) raising the temperature during gel formation, (2) progressively increasing the degree of acidity of the material applied, (3) progressively reducing the alkox^:de concentration in the material applied , and (4) using alkoxides having an increasing degree of hydrolysis.

Said methods, such as described in the Application EP-A-514 973 and US patent US-A-4,830,879 are of delicate implementation and have low reproducibility.

It is a purpose of the present invention to provide an optical article comprising a transparent mineral substrate having a single-layer anti-reflecting coating. It is also a purpose of the present invention to provide a relatively simple, inexpensive and rapid method, in particular a sol-gel type method, of producing such an anti- reflecting coating on said substrate which is chemically and mechanically durable and which is compatible with substrates having refractive indices ranging from 1.5 to 1.9, and to provide the sol-gel material which is convenient for preparing said coating.

Thus, the first object of the present invention is an optical article comprising a mineral substrate and an anti-reflecting coating on at least one surface of said mineral substrate. In a characteristic way, said mineral substrate has a refractive index between 1.5 and 1.9 and said anti-reflecting coating is a single layer, nanoporous/nanograin structured coating, obtained by heat-treating a sol-gel film, constituted of strongly interconnected, inorganic polymers, also linked with inorganic particles ; said polymers forming a tri-dimensional network which has the general formula M-OH/M-O-M, in which M represents a metal or a metalloid, advantageously selected from silicon, aluminum, zirconium, titanium and mixtures thereof. Said particles are oxides of M.

According to its second objet, the invention relates to the production of such an article and more specifically to a method which comprises :

- dissolving, in an organic solvent, at least one alkoxide, one acetylacetonate or one acetate of metal or metalloid M ;

- hydrolyzing and polymerizing said alkoxide, acetylacetonate or acetate in solution, by adding a large amount of inorganic acid catalyst, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers; said network being solvated by said organic solvent, having the general formula

M-OH/M-O-M and containing, connected to said polymers, inorganic particles ;

- applying a single layer of sol-gel of said hydrolyzed and polymerized alkoxide, acetylacetonate or acetate on at least one surface of a mineral substrate having a refractive index between 1.5 and 1.9, and

- heat-treating the substrate thus coated to form a nonoporous/nanograin structured anti-reflecting coating ; said heat-treatment being carried out in a device pre-heated to the treatment temperature.

Finally, the present invention also relates to a sol gel material which is notably appropriate for forming an anti-reflecting coating such as characterized above on a mineral substrate having a refractive index between 1.5 and 1.9. Said material consists of a solution, in an organic solvent, of at least one alkoxide, one acetylacetonate or one acetate of metal or metalloid M- said metal or metalloid M advantageously consisting of silicon, aluminum, zirconium or titanium - hydrolyzed and polymerized by an inorganic acid catalyst, advantageously consisting of hydrochloric acid, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers ; said network being solvated by said organic solvent, having the general formula M-OH/M-O-M and containing, connected to said polymers, inorganic particles (oxide(s) of M).

Each of said objects of the present invention shall now be described in detail. The optical article thus comprises an original anti-reflecting coating - single- layer coating of the film type such as described above - on a transparent mineral substrate. Said mineral substrate may be, amongst others, an optical element in inorganic or organic glass and more particularly it may consist of an ophthalmic lens. In order to describe the invention, this particular field of use may readily be referred to, but clearly the field of use of said invention is much wider : it includes any form of element which transmits light, and image display devices.

The coating of the invention is an anti-reflecting coating, compatible with substrates having refractive indices between 1.5 and 1.9. Further, it has good chemical and mechanical durability (resistance to abrasion and to the formation of scratches). The method of obtaining the coating is easy to carry out and is of short duration, typically in the order of one hour.

Said coating of the invention is advantageously based on a tri-dimensional network, of general formula Si-OH/Si-O-Si, which contains colloidal particles of silica. In other words, the first object of the present invention is very advantageously produced with M = Si (metalloid). According to other advantageous variants, and as mentioned above, M is also Al, Zr, Ti (metal). The intervention of a plurality of Ms within a network is in no way excluded.

The sol-gel film (which, heat-treated, consolidates the anti-reflecting coating and fixes it on the substrate), is advantageously obtained from a solution containing colloidal particles of silica, alumina, zircon and/or titanium oxide : the molar ratio of the metal and/or metalloid of said particles with respect to the total amount of intervening metal and/or metalloid being lower than 50 % , but at least 10 % .

Generally, the optical article of the invention has a coating of thickness lower than 150 nm. Said thickness is in fact generally between 70 and 150 nm. It is advantageously about 90 nm.

The coating of the invention is generated on an appropriate substrate, as indicated above. The method described is easy to carry out, it does not require any considerable investment and is associated with a low cost. Said method basically comprises preparing a sol-gel type coating solution, depositing the coating as a single layer by dipping, spinning, or by any other known depositing method, and heat- treating said single layer in order to form said anti-reflecting coating. This heat- treatment allows transforming the sol-gel material, which has undergone a polymerization beforehand with a high degree of cross-linking, into a coating of pore/grain nanostructure; a coating which has the anti-reflecting character sought- after. Said material - sol-gel type solution - in fact constitutes the precursor of said expected coating.

Said material is prepared by dissolving at least one alkoxide, one acetylacetonate or one acetate of metal or metalloid M, in a compatible organic solvent such as an alcohol (e. g. ethanol). Said alkoxide advantageously has the general formula M(X)_n in which M is a metal or metalloid selected from aluminum, silicon, zirconium and titanium, X is an alkoxy group and n is an integer corresponding to the valency of M. When M = Si, an alkylalkoxysilane of formula R_nSiX4__n may more generally be brought to intervene in which R represents an alkyl group, X an alkoxy group and n an integer between 0 and 3, inclusive.

It will already have been understood that when n = 0, R_nSiX4__n = SiX The use of Si((Cι -C4)alkoxy)4 is most particularly recommended within the context of the present invention as alkoxide.

The terms alkyl and alkoxy used above generally stand for (Ci -Chal y 1 and (Cι -C5)alkoxy, advantageously (Cι -C3)alkyl, (Cι-C3)al oxy. In the same way, the acetylacetonates and/or acetates which may intervene advantageously have the respective formulae below :

M(CH3COCHCOCH₃)_n and M(CHj OO)_n in which M = Si, Al, Zr or Ti and n represents the valence of said M. The alkoxide, acetylacetonate or acetate of metal or metalloid (M) (which optionally consists of an alkylalkoxysilane) is hydrolyzed by adding an aqueous solution which contains a large amount of an inorganic acid catalyst. Preferably, the catalyst is a solution of a strong mineral acid such as HC1 or HNO3, which allows obtaining a pH lower than 2, and preferably lower than 1. The hydrolysis of all the functions, notably alkoxy, is accomplished in this strong acid medium to obtain a long chain inorganic polymer. In a characteristic way, said acid catalyst intervenes in a large amount. This notion is specified below in a manner which is by no means limiting. It constitutes in any case a trait of originality of the invention process. The molar ratio of the inorganic catalyst (such as HC1, HNO₃) to the alkoxide, the acetylacetonate, or the acetate which intervenes is advantageously greater than 0.5 and preferably stays lower than 1. A value of about 0.8 seems to be optimal. With reference to the hydrolyses of the prior art processes, it shall be noted that, within their context, these same molar ratios are much lower, generally much lower than 0.2. During the hydrolysis and the aging specified below, which allows polymerizing the solution of the alkoxide, acetylacetonate or acetate with a high degree of cross- linking, colloidal particles of oxide are formed in situ within the polymerized matrix having formula

M-OH/M-O-M. These inorganic colloidal particles are strongly connected to the tri-dimensional network of said matrix. The molar ratio of these particles (e. g. iθ2) with respect to the total amount of intervening alkoxide, acetylacetonate or acetate is at least 10 % but remains lower than 50 % . This has already been seen earlier in the present text. As for the process, in order to obtain such a result, it is recommended for example to initiate the hydrolysis by the addition of an acid catalyst to the solution of the alkoxide, acetylacetonate or acetate in such an amount that a pH of 3 to 4 is obtained (at this pH, particles of oxide(s) form), and then to lower the pH to a value lower than 1 in order to connect said colloidal particles of oxide(s) in situ to the polymerized matrix {vide infra).

It is furthermore highly recommended to submit the hydrolyzed solution to an aging in order to generate a high degree of polymerization within it. An aging of 15 to 90 days is recommended, advantageously an aging of about 1 month. During this aging, the solution is kept between 40 and 80°C, preferably about 60 °C. A tri- dimensional polymer network of strongly interconnected polymers is thus obtained (of the Si-OH/Si-O-Si type, containing colloidal particles of iθ2 for example) in the form of a sol-gel type material insofar as the solvent intervenes in excess. Within the hypothesis of the intervention of an insufficient amount of solvent, a rigid gel would be obtained.

By using a concentration of silicon or other oxide which does not go above 40 g/1, it is possible to prepare solutions which remain stable for several months at ambient temperature. The preferred concentration is 30 g/1. It is possible to use a more concentrated solution in order to initiate the polymerization process, but when the viscosity increases rapidly, it is necessary to add solvent in order to prevent a gellation.

A single layer of coating is applied to at least one surface of the substrate in order to render it anti-reflecting. This application is preferably carried out by dip or spin coating. In dip coating, the substrate is dipped once into the solution. It must be removed at a constant speed with an even motion. This avoids any thickness variation in the deposited coating. Spin coating may be preferred where only one surface is to be coated. Within the context of display screens, a pulverization (spray) may advantageously be carried out. It has been seen previously that the final coating generally has a thickness between 70 and 150 nm. The size of the inorganic colloidal particles which form during the hydrolysis and aging must be compatible with such a thickness. From this, the thickness does not generally go over 150 nm and in general it is much lower than its 150 nm and it is preferably about 50 nm. As an example, a final coating of thickness of about 90 nm may have a grain size of 20 nm. Particle size refers to colloidal particles suspended in the coating solution .

Grain size refers to grain structure in the anti-reflecting film after heat treatment. In the present invention, particle size is directly related to grain size structure because, during the characteristic rapid heat treatment, the colloidal particles transforms directly into grains.

The mineral substrate coated with the sol-gel type material is initially dried in a uniform manner. Drying may be by infrared heating, or drying in an oven. The solvent is thus evaporated ; then, the dried article is placed in a preheated furnace for the final heat treatment that effects production of an anti-reflecting film with durable properties. The furnace temperature may range between 200 and 600 °C, preferably between 250 - 450°C. The time-temperature cycle varies inversely. For example, the time of this treatment at 250 °C may be 30 minutes to 2 hours, while at 450 °C it will be in the range of 5 to 30 minutes.

The coated article is then removed from the heat treating furnace and cooled to ambient temperature. The coating is densified to a metal oxide state by the heat treatment. Also, however, a small, residual nanoporosity is produced which confers the necessary low-refractive index to the coating. Said heat treatment also fixes said coating to said substrate. For example, pore size is in the order of 20 nm and coating thickness about 90 nm. The sol-gel type material such as described above with reference to the process of the invention constitutes the last object of the present invention.

The following may even be added in reference to said material and process. The sol-gel (solution) type material is particularly effective when it is used on substrates having a refractive index of 1.6 to 1.9. However, it can be slightly modified for use with substrates having a lower refractive index in the 1.5 - 1.6 range. This involves controlling the pH of the precursor solution to ensure that one part of colloidal particles is formed and chemically bonded with one part of polymeric network. The heat treatment of this coating corresponds to that described above for treatment of the higher index coated substrate. This treatment produces a nanoporous condition and nano particles from the colloidal part of the solution. This particular implementation makes up an integral part of the present invention. Although the method of preparing the sol-gel type material proceeds in a continuous manner, it may be carried out in two steps. The first step is the initiation of the hydrolysis-condensation of the alkoxide, acetylacetonate or acetate at a pH of 3 - 4. This forms a proto-colloidal solution. In the second step, the condensation is stopped and a hydrolysis-polymerization step is carried out by lowering the pH below

1. As a result, a solution composed of colloidal particles in a polymerized matrix is formed in situ.

In the sol-gel method, the polymerization and the condensation cannot be separated, and occur simultaneously. In accordance with the present invention, however, the equilibrium of the kinetics of the process is displaced and controlled by the pH modification.

It is possible within the context of the invention to obtain a polymeric silica - colloidal silica coating solution by hydrolyzing an adequate alkoxide, acetylacetonate or acetate with a large amount of acid catalyst. The molar ratio of acid catalyst to silicon « carrier » is higher than 0.8 and lower than 1.5. The hydrolysis is performed in the presence of an excess of water. The molar ratio of water with the silicon « carrier » is higher than 4 and lower than 36, preferentially between 5 and 8.

Generally, the color of the anti-reflecting coating of the invention is linked to its thickness. Furthermore, it is possible to easily obtain a gold or blue color by adjusting the speed of coating deposition (with slow deposition speeds a rather gold color is obtained ; with faster deposition speeds, the color evolves towards blue).

By way of specific embodiment, a glass substrate available from Corning under the Code D0035 and having a refractive index of 1.7, was coated in the manner according to the method of the invention (see Examples 1 and 2 as well as Figure 1 in annex). In another embodiment, another glass substrate, available from

Corning under the Code C0041TC and having a refractive index of 1.6 (see Example 3 as well as Figure 2 in annex) was coated.

Generally, the coated articles of the invention may be submitted to different tests. Viz : - in order to test their resistance to stain, they were smeared with lipstick, or with ink by means of a felt-tip pen for example, and they were then cleaned with ethanol or acetone ;

- in order to test their chemical resistance and resistance to adhesion, they were submitted to boiling water for 3 hours and/or to organic solvents (alcohol and acetone), and submitted to the action of adhesive tapes.

Generally, no deterioration of the coating was observed. In order to demonstrate the strong durability to scratches and abrasion, coated and non-coated samples were tested together in two different abrasion tests. In a tumbling test, samples were introduced into a tumbling barrel with an abrasive mixture and tumbled for a total time of two hours. Optical transmission measurements on both coated and non-coated samples were made every thirty minutes. In a second test, known as the Taber test, samples were placed on a turntable and subjected to rotating abrasive wheels. The percent haze of each abraded sample was checked optically after 10, 50 and 100 revolutions.

Generally, the results obtained are comparable to those obtained with commercial lenses which comprise an anti-reflecting coating deposited by the conventional evaporation methods. The articles of Examples 1 to 3 below were notably tested. The interest of the invention, which will not have escaped the attention of the person skilled in the art, is demonstrated in Figures 1 and 2 in annex.

Figure 1 is a graphical illustration in which wavelength in nanometers is plotted on the horizontal axis and percent transmission is plotted on the vertical axis.

Curve A is based on measurements made on the non-coated glass (D0035). Curve B is based on measurements made in the same manner on the glass after application of the coating of the invention (Example 1).

Figure 2 is a graphical illustration similar to that of Figure 1. It is based on measurements made on a film formed on a glass having a refractive index of 1.6

(C0041TC). Curve C in Figure 2 is based on measurements made on the non-coated glass. Curve D is based on measurements effected in the same manner on said glass after application of a coating of the invention (Example 3) . The present invention is illustrated in a more specific manner by the following non-limiting Examples.

Example 1 11.35 ml of an alkoxysilane Si(OCH3)4, is mixed with 33.3 ml of ethyl alcohol over a period of 10 minutes to obtain a homogeneous mixture. 5.4 1 of water, containing HCl to provide an HCl/Siθ2 molar ratio of 0.8, is added with magnetic stirring over a period of an hour. The resulting solution is placed in an oven at 60 °C for a period of 3 weeks to age. The material may now be stored or immediately used for coating purposes. A D0035 glass substrate from Corning having a refractive index of 1.7 and a thickness of 2 mm is cleaned and a film is deposited, by immersion, on the substrate, from the coating solution such as described above. Then the substrate is withdrawn from the solution at the speed of about 8 cm/min. Then, the coated substrate is dried at 60 °C by infrared heating. After drying, the coated substrate is placed in a pre- heated oven for 20 minutes at a temperature of about 4 )°C. Then, the coated substrate is removed from the oven and cooled to ambient temperature.

Optical transmission measurements were made to characterize the anti- reflective character of the coating and thus it was possible to compare the optical transmission of the coated substrate with that of the non-coated substrate, as shown in Fig. 1.

The thus coated substrate was then subjected to a series of standard tests for chemical and mechanical characterization. The following results are, in the tests of resistance: to boiling water and to adhesive tapes, for 3 hours : no surface modification (no lifting, no cracking or delamination) ; to organic solvents, alcohol and acetone : no surface modification ;

Tumbling test, 2 hours : the effect on the coated glass is superior only by 5 % over the effect on the non-coated glass ; to acid pH (pH = 4.5) and basic pH (pH = 8.8) : no surface modification ; to abrasion (Taber test) : the effect on the coated glass is superior by 4-6% only over the effect on the non-coated glass.

Example 2 The method of Example 1 was repeated using 127 ml of ethanol and 17 ml of an alkoxysilane Si(OC2H5)4. The same optical, chemical and mechanical tests were performed on the coated substrates with essentially the same results.

Example 3

The method of Example 1 was repeated with two variations : the substrate was glass C0041TC from Corning having a refractive index of 1.6 and a thickness of 2 mm, the coating solution was aged for 90 days.

The same chemical and mechanical tests were performed with essentially the same results as Example 1. The optical transmission spectra for the coated and non- coated glass are shown in Figure 2 of the drawings.

Claims

1. An optical article comprising a mineral substrate and an anti-reflecting coating on at least one surface of said mineral substrate, characterized in that said mineral substrate has a refractive index between 1.5 and 1.9 and in that said anti- reflecting coating is a single layer, nanoporous/nanograin structured coating, the coating being obtained by heat-treating a sol-gel film constituted of strongly interconnected, inorganic polymers, also linked with inorganic particles, said polymers foπning a tri-dimensional network which has the general formula M-OH/M-O-M, in which M represents a metal or a metalloid, advantageously selected from silicon, aluminum, zirconium, titanium and mixtures thereof.

2. Optical article according to claim 1, characterL ^d in that said mineral substrate is a glass optical element and advantageously consists of an ophthalmic lens.

3. Optical article according to one of claims 1 or 2, characterized in that said network has the general formula Si-OH/Si-O-Si.

4. Optical article according to any one of claims 1 to 3, characterized in that said sol-gel film is obtained from a solution containing colloidal particles of silica, alumina, zircon and/or titanium oxide; the molar ratio of the metal and/or metalloid of said particles with respect to the total amount of intervening metal and/ or metalloid being lower than 50 %, but at least 10 % .

5. Method of producing an optical article according n any one of preceding claims, characterized in that it comprises :

- dissolving at least one alkoxide, acetylacetonate or acetate of a metal or metalloid M , in an organic solvent,

- hydrolyzing and polymerizing said alkoxide, acetylacetonate or acetate in solution, by adding a large amount of inorganic acid catalyst, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers; said network being solvated by said organic solvent, having the general formula M-OH/M-O-M and containing, connected to said polymers inorganic particles ;

- heat-treating the substrate thus coated to form a nanoporous/nanograin structured anti-reflecting coating ; said heat-treatment being carried out in a device pre-heated to the treatment temperature.

6. Method according to claim 5, characterized in that it comprises dissolving, in an organic solvent, an alkylalkoxysilane of formula R_nSiX4__n, in which R represents an alkyl group, X an alkoxy group and n an integer between 0 and 3 (inclusive), or dissolving, in an organic solvent, a metal alkoxide of formula M(X)_n in which M is a metal selected from aluminum, zirconium and titanium, X an alkoxy group and n an integer corresponding to the valency of M.

7. Method according to one of claims 5 or 6, characterized in that it comprises hydrolyzing the alkoxide, acetylacetonate or acetate by adding an aqueous solution of an inorganic acid catalyst, such as hydrochloric acid, in such an amount that the molar ratio of the catalyst to the metal or metalloid alkoxide, acetylacetonate or acetate is greater than 0.5 but lower than 1.

8. Method according to any one of claims 5 to 7, characterized in that it comprises initiating hydrolysis by adding catalyst to the alkoxide, acetylacetonate or acetate solution in such an amount as to produce a pH of 3 to 4, and thereafter reducing the pH to less than 1 in order to connect the particles of colloidal oxide(s) to the polymerized matrix in situ.

9. Method according to any one of claims 5 to 8, characterized in that it further comprises aging said hydrolyzed and polymerized alkoxide, acetylacetonate or acetate, advantageously for a period of 15 to 90 days at a temperature of 40 to 80°C.

10. Method according to any one of claims 5 to 9, characterized in that the heat-treatment of the coated substrate is carried out at a temperature in the range of 200 and 600 °C, the time-temperature cycle is an inverse cycle varying advantageously from 30 min to 2 h at 250°C and from 5 to 30 min at 450°C.

11. Sol-gel material, notably convenient for forming an anti-reflecting coating on a mineral substrate having a refractive index of 1.5 to 1.9, characterized in that it consists of a solution of at least one alkoxide, one acetylacetonate or one acetate of a metal or metalloid M in an organic solvent, said metal or met dloid M advantageously consisting of silicon, aluminum, zirconium or titanium, hydrolyzed and polymerized by an inorganic acid catalyst, advantageously consisting of hydrochloric acid, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers ; said network being solvated by said organic solvent, having the general formula M-OH/M-O-M and containing, connected to said polymers, inorganic particles.

12. Sol-gel material according to claim 11, characterized in that said metal alkoxide has the formula M(X)_n in which M is a metal selected from aluminum, zirconium and titanium, X an alkoxy group and n an integer corresponding to the valency of M, or consists of an alkylalkoxysilane of formula R_nSiX4__n, in which R represents an alkyl group, X an alkoxy group and n is an integer between 0 and 3 (inclusive).

13. Sol-gel material according to claim 12, characterized in that it contains colloidal particles of silica, alumina, zircon and/or titanium oxide ; said molar ratio of the metal and/or metalloid of said particles with respect to the total amount of intervening metal and/or metalloid being advantageously at least 10 % but remaining less than 50 % . AMENDED CLAIMS

[received by the International Bureau on 24 August 1998 (24.08.98); original claims 4,5 and 7-10 amended; remaining claims unchanged (3 pages)]

1. An optical article comprising a mineral substrate and an anti-reflecting coating on at least one surface of said mineral substrate, characterized in that said mineral substrate has a refractive index between 1.5 and 1.9 and in that said anti- reflecting coating is a single layer, nanoporous/nanograin structured coating, the coating being obtained by heat-treating a sol-gel film constituted of strongly interconnected, inorganic polymers, also linked with inorganic particles, said polymers forming a tri-dimensional network which has the general formula

M-OH/M-O-M, in which M represents a metal or a metalloid, advantageously selected from silicon, aluminum, zirconium, titanium and mixtures thereof.

2. Optical article according to claim 1, characterized in that said mineral substrate is a glass optical element and advantageously consists of an ophthalmic lens.

4. Optical article according to one of claims 1 or 2, characterized in that said sol-gel film is obtained from a solution containing colloidal particles of silica, alumina, zircon and/or titanium oxide; the molar ratio of the metal and/or metalloid of said particles with respect to the total amount of intervening metal and/or metalloid being lower than 50 %, but at least 10 %.

5. Method of producing an optical article according to claims 1 or 2, characterized in that the method comprises :

- hydrolyzing and polymerizing said alkoxide, acetylacetonate or acetate in solution, by adding a large amount of inorganic acid catalyst, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers; 10 said network being solvated by said organic solvent, having the general formula M- OH/M-O-M and containing, connected to said polymers inorganic particles ;

7. Method according to claim 5, characterized in that it comprises hydrolyzing the alkoxide, acetylacetonate or acetate by adding an aqueous solution of an inorganic acid catalyst, such as hydrochloric acid, in such an amount that the molar ratio of the catalyst to the metal or metalloid alkoxide, acetylacetonate or acetate is greater than 0.5 but lower than 1.

8. Method according to claim 5, characterized in that it comprises initiating hydrolysis by adding catalyst to the alkoxide, acetylacetonate or acetate solution in such an amount as to produce a pH of 3 to 4, and thereafter reducing the pH to less than 1 in order to connect the particles of colloidal oxide(s) to the polymerized matrix in situ.

9. Method according to claim 5, characterized in that it further comprises aging said hydrolyzed and polymerized alkoxide, acetylacetonate or acetate, advantageously for a period of 15 to 90 days at a temperature of 40 to 80°C.

10. Method according to claim 5, characterized in that the heat-treatment of the coated substrate is carried out at a temperature in the range of 200 and 600°C, the time-temperature cycle is an inverse cycle varying advantageously from 30 min to 2 h at 250°C and from 5 to 30 min at 450°C.

11. Sol-gel material, notably convenient for forming an anti-reflecting coating on a mineral substrate having a refractive index of 1.5 to 1.9, characterized in that it consists of a solution of at least one alkoxide, one acetylacetonate or one acetate of a metal or metalloid M in an organic solvent, said metal or metalloid M advantageously consisting of silicon, aluminum, zirconium or titanium, hydrolyzed and polymerized by an inorganic acid catalyst, advantageously consisting of hydrochloric acid, in order to form an inorganic tri-dimensional network of strongly interconnected inorganic polymers ; said network being solvated by said organic solvent, having the general formula M-OH M-O-M and containing, connected to said polymers, inorganic particles.

13. Sol-gel material according to claim 12, characterized in that it contains colloidal particles of silica, alumina, zircon and/or titanium oxide ; said molar ratio of the metal and/or metalloid of said particles with respect to the total amount of intervening metal and/or metalloid being advantageously at least 10 % but remaining less than 50 %.