"ANTI-SCRATCH AND PHOTOCHROMIC COATING, RESPECTIVE METHOD

OF APPLICATION AND USE"

Technical domain

The present application describes an anti-scratch and photochromic coating, respective method of application and use .

Background

According to the state-of-the-art, some organic molecules change their colour when exposed to ultraviolet (UV) or solar radiation and return to their initial state when placed again in the dark. The basis of this process, called photochromism, is a chemical reaction, thermally and photochemically reversible, promoted in one direction by UV radiation. Thus when light is removed, the coloured substances spontaneously return to their original colourless forms [1] .

These organic molecules are not active in the solid state but may be dispersed in a polymer yielding a photochromic polymeric material, although the interaction between the polymer matrix and the photochromic molecules determines the final properties. The chemical nature of the polymer matrix significantly affects the colouration speed under sunlight exposure, the obtained colouration, the intensity of colouration and the discolouration speed in the dark and may even, in extreme cases, inhibit this phenomenon [2] .

The matrix, while still a liquid, can be applied on the surface of transparent plastic ophthalmic lenses, obtaining, after a heat treatment, a nanometric coating with photochromic properties. These ophthalmic lenses filter solar radiation depending on its intensity. They can acquire grey or brown tones when directly exposed to the sun, thus protecting the user from sunlight, and revert to the colourless state when entering in a low luminous intensity area [ 3 ] .

The most frequently used photochromic substances include several diarylnaphthopyrans that are able to develop yellow, red, blue or grey tones when in solution or dispersed in a polymer matrix and irradiated with sunlight [4] .

The sunlight exposure time required to obtain a high colour intensity and the discolouration time in the dark rely heavily on the available free volume within the polymer. The larger the available volume, the greater the colouration and discolouration speed of the material. This free volume depends on the flexibility of the polymer chains surrounding the photochromic molecule and therefore of the polymer glass transition temperature. Polyurethanes are examples of flexible polymers suitable for this purpose [5] .

The production of photochromic glass lenses containing inorganic compounds, such as silver halides, is well established, however these lenses have several disadvantages. In addition to being very heavy and uncomfortable, they present very low discolouration speed and very high residual colour in the dark [6] .

Plastic lenses are much lighter, comfortable and easy to work with [7]. The most commonly used materials include CR-39® (poly diethylene glycol bis (allyl carbonate) ) , Lexan® (polycarbonate) and MR-8 ( thiourethane ) which allow the incorporation of several organic photochromic compounds. Over time, several methods have been developed to make these materials photochromic . One of the methods, known as heat transfer, involves the application over the lens surface of a temporary coating varnish containing photochromic molecules, which is subsequently heated, promoting the transfer of photoactive molecules to the surface of the lens [5] .

Another method known as "cast-in-place" consists in the incorporation of photochromic compounds directly in a polymerizable mixture originating the lens material. In this case, the photochromic molecules are a part of the lens, being distributed throughout the material and not only on its surface. This technique has at least three disadvantages: 1) requires a larger amount of photochromic compound that is generally quite expensive; 2) the polymerization reaction initiators degrade the photochromic molecules reducing their performance and producing coloured products which confer a residual colour to the lens; 3) since the thickness of the lens is variable the colouration in the lens is not uniform [8] .

An alternative and widely used method consists in dissolving at least one photochromic molecule in a solution containing at least a monomer which is then dispersed in the lens surface. This is then subjected to a thermal or UV treatment to harden and form a thin coating that contains photochromic compounds. Typically, the solution contains the precursors of a polyurethane polymer whose organized final structure is obtained after heat treatment. In this case the nature of the lens base material is less important. Nevertheless, none of these methods results in a lens present exhibiting a rapid colouration and an equally fast discolouration.

The most recent photochromic lenses feature photochromic properties in addition to anti-scratch, antistatic, antireflective and hydrophobicity properties. To confer these properties to the lens it is necessary to put a second anti- scratch coating over the photochromic coating and make a final multilayer treatment that will confer antistatic, antireflective and hydrophobicity characteristics [9].

Applying an anti-scratch coating to ophthalmic lenses is a well-known and extensively used process since the material of the as-prepared lens displays very low scratch resistance. These coatings are usually applied by immersing the lens in a mixture containing at least one monomer that is polymerized by thermal treatment or by irradiation with UV light [10] .

The anti-scratch polymers most commonly used come from monomers such as acrylates and aliphatic methacrylates , urethane (meth) acrylates or oligomers thereof, alkoxysilanes , colloidal silica and mixtures thereof. The resulting coating is transparent, very hard, and resistant to abrasion, resistant to chemicals and to degradation by sunlight. These polymers are capable of forming chemical bonds with the substrate of the lenses during polymerization resulting in coatings with excellent adhesion to the lens [9, 10] .

To confer antireflective, antistatic and hydrophobic characteristics to the surface of the lenses, it is common to apply a coating consisting of several layers of metal oxides, capable of adhering well to the scratch-resistant coating, alternating high refractive index layers with low refractive index layers, a layer of a conductive material, and finally a layer composed of a fluoropolymer [11] .

The general process of production of an ophthalmic lens with photochromic, anti-scratch, antireflective, anti-static and hydrophobic properties generally involves:

1 - Incorporation of the organic photochromic molecule in a polymerizable mixture.

2 - Deposition of this material over the side of the lens by spin-coating or dip-coating.

3 - Polymerization of the mixture by a thermal process, leading to the formation of a thin transparent coating.

4 - Preparation of an anti-scratch varnish.

5 - Spreading an anti-scratch coating over the photochromic layer by spin-coating or dip-coating.

6 - Curing the scratch-resistant coating by heat treatment or UV irradiation.

7 - A final multilayer treatment that will confer antistatic, antireflective and hydrophobic properties, usually applied by the physical vapour deposition technique.

The presence of several different coatings over the lens surface can lead to crack formation after a few months of use due to thermal expansion coefficient differences of each layer. On the other hand, the currently available lenses on the market present low discolouration speed which limits their performance [12] . In fact, these lenses, although blushing intensely in about 30 seconds after being under exposure to sunlight, take more than 8 minutes to fade completely in areas not exposed to sunlight, which constitutes a considerable limitation.

The present application discloses a technical solution developed to overcome the technical problems described above and allows obtaining photochromic lenses with less coatings and a better response to light stimulus.

Summary

The present application describes an anti-scratch and photochromic coating applied in the form of varnish with the following composition by weight:

- 33% to 75% of a mixture of alkoxysilanes;

- 5% to 50% of plasticizers;

- 0.5% to 2.5% of photochromic dyes;

- 5% to 15% of additives.

In one embodiment, the additives included in the anti-scratch and photochromic coating comprise colour stabilizers, UV blockers, antioxidants, and surfactants.

In another embodiment, the additives included in the anti- scratch and photochromic coating are 4,4'- isopropylidenediphenol and/or 4 , 4 ' -sulphonildiphenol and/or 1, 3, 5-trimethyl-2 , 4, 6-tris (3, 5-di-t-butyl-4-hydroxybenzyl ) benzene and/or 1-methylimidazole and/or 2- ( 2-hydroxy-5- methylphenyl ) benzotriazole and/or 2-hydroxy-4- methoxybenzophenone and/or 2-hydroxybenzophenone and/or 2- ( 2H-benzotriazol-2-yl ) -4 , 6-di-t-pentilphenol and/or 2,2'- dihydroxy-4-methoxybenzophenone and/or 1H, 1H, 2H, 2H- perfluorooctyl triethoxysilane and/or 1H, 1H, 2H, 2H- perfluorodecyl-triethoxysilane and/or 3-methyl-2-buten-l-ol and/or Pluronic 127®.

In yet another embodiment, the alkoxysilanes included in the anti-scratch and photochromic coating are methyltriethoxysilane and/or ( 3-glycidoxypropyl ) methyldiethoxysilane and/or tetraethoxysilane and/or vinyltriethoxysilane and/or ( 3-mercaptopropyl ) trimethoxysilane and/or ( 3-aminopropyl ) triethoxysilane and/or phenyltrietoxisilane and/or isocyanate-propyl- triethoxysilane .

In one embodiment, the plasticizers included in the anti- scratch and photochromic coating are amines and/or diamines and/or polyethylene glycols.

In another embodiment, the anti-scratch and photochromic coating comprises the presence of a catalyst.

In yet another embodiment, the catalyst used in the anti- scratch and photochromic coating is acetic acid and/or hydrochloric acid and/or nitric acid and/or sulfuric acid.

The present application also describes ophthalmic lens comprising the anti-scratch and photochromic coating described in any one of the preceding paragraphs of this subsection .

The present application further describes the method of applying the anti-scratch and photochromic coating comprising the following steps:

Preparation of a solution containing at least one photochromic molecule, a mixture of additives and a mixture of silanes and plasticizers;

- Deposition of this mixture on at least one of the sides of the lens;

- Perform a heat treatment of polymerization and hardening of the above mentioned coating;

- A multilayer treatment.

In one embodiment, preparing the solution for application in the anti-scratch and photochromic coating application method comprises the following steps:

- elaboration of a mixture of photochromic dye and additives using an organic solvent;

- elaboration of a mixture of alkoxysilanes and plasticizers with a solvent;

- addition of spacers to the mixture obtained in the previous step;

- addition of the mixture obtained in the first step to the mixture obtained in the previous step.

In another embodiment, the deposition of the mixture on the side of the lens, in the method of applying the anti-scratch and photochromic coating, is carried out by spin-coating.

In yet another embodiment, the deposition of the mixture on the side of the lens, in the method of applying the anti- scratch and photochromic coating, is carried out by dip- coating .

In one embodiment, the polymerization and hardening heat treatment used in the application method of the anti-scratch and photochromic coating implies placing the ophthalmic lens in an oven between 50-100°C, in a horizontal position for 12 to 48 hours.

In one embodiment, the polymerization and hardening heat treatment used in the application method of the anti-scratch and photochromic coating comprises subjecting the ophthalmic lens to an irradiation with UV or infrared (IR) light.

In yet another embodiment, the multilayer treatment used in the present invention comprises subjecting the lens to the electron beam vapour deposition technique, the oxide layers being applied between alternating low refractive index material and high refractive index material.

In one embodiment, in the electron beam vapour deposition method, a layer of In ₂ 0 ₃ -Sn02 (indium tin oxide, ITO) is applied between the different layers of oxides. General description

The present application describes an anti-scratch and photochromic coating, respective method of application and use .

Thus, preparation of a coating is described, for example, in the form of a varnish, which once applied on the surface of a lens and thermally treated will confer photochromic and anti- scratch properties simultaneously. The application process involves the use of a single coating for these two functions, which reduces the risk of crack formation and also allows reducing the response time of the lens to light stimulus, by making either colouration or discolouration faster.

Thus, a liquid varnish was developed, that when applied on the surface of ophthalmic plastic lenses and after polymerization would be able to confer anti-scratch and photochromic properties and thus generate transparent lens with high resistance to scratching susceptible of darkening upon exposure to the sun.

The varnish comprises a composition by weight that includes between 33% and 75% of a mixture of alkoxysilanes , between 5% and 50% plasticizers, 0.5% and 2.5% of photochromic dyes and between 5% and 15% of additives being deposited on the surface of the lens by spin-coating or dip-coating. The lens is then subjected to a heat treatment at atmospheric pressure between 40°C and 120°C.

The coating application method comprises the following steps:

Preparation of a solution containing at least one photochromic molecule, a mixture of additives including colour stabilizers, UV blockers, antioxidants, surfactants and a mixture of silanes and plasticizers;

Deposition of this mixture on at least one of the sides of the lens by spin-coating or dip-coating;

Perform a heat treatment for polymerization and hardening of the coating;

A multilayer treatment to confer antistatic, antireflective and hydrophobic properties.

The mixture of the elements in the solution preparation step comprises the following steps:

elaboration of a mixture of photochromic dye and additives using an organic solvent;

elaboration of a mixture of alkoxysilanes and plasticizers with a solvent;

addition of spacers to the mixture obtained in the previous step;

addition of the mixture obtained in the first step with the mixture obtained in the previous step.

From a practical point of view, the coating now disclosed may be used in any type of material to which is intended to confer anti-scratch and photochromic characteristics, such as ophthalmic lenses.

Brief Description of the Figures

For an easier understanding of the technique, see the attached figures, which represent preferred embodiments of the invention that are not intended, however, to limit the scope of this invention.

Figure 1 shows a photograph of a grey lens a) before and b) after exposure to UV radiation for 30 seconds. Figure 2 illustrates an absorption spectrum in the visible spectrum of a grey lens before and after exposure to UV radiation for 30 seconds.

Figure 3 illustrates a graph of the grey lens discolouration kinetics after exposure to UV radiation.

Figure 4 illustrates a photograph of the brown lens a) before and b) after exposure to UV radiation for 30 seconds.

Figure 5 illustrates a visible absorption spectrum of the brown lens described in example 2 before and after exposure to UV radiation for 30 seconds.

Figure 6 illustrates a brown lens discolouration kinetics after exposure to UV radiation.

Description of the embodiments

Next, some embodiments will now be described in more detail, which however are not intended to limit the scope of the present application.

The present application describes an anti-scratch and photochromic coating, respective application process and use.

Preparation of the coating

The coating is prepared by dissolving the photochromic dyes and several additives in an organic solvent to which, for the sake of clarity, will be referred to as solution A. This solution is then added to a solution B containing the necessary reagents for the formation of a siloxane-based organic/inorganic hybrid matrix, and stirred at room temperature to form a completely homogeneous solution.

Throughout this text, room temperature is considered. This is the most usual situation which allows a person to work comfortably, ranging approximately between 15 to 30°C, preferably between 20 to 25°C, more preferably between 21 to 23°C, without restricting however the temperatures below these limits and since it is an acceptable and recognized as room temperature, inside a building.

To obtain this coating at least one photochromic dye must be used. At least one of the photochromic dyes of Vivimed labs®, namely Volcanic Grey, Penine Green, Humble Blue, Graphite, Amber, Midnight Grey, Plum Red, Gold, Ruby, Corn Yellow, Cinnabar can be used.

The additives include several of the following compounds: 4,4'- isopropylidenediphenol and/or 4 , 4 ' -sulphonildiphenol and/or 1 , 3 , 5-trimethyl-2 , 4 , 6-tris ( 3 , 5-di-t-butyl-4- hydroxybenzyl ) benzene and/or 1-methylimidazole and/or 2- (2- hydroxy-5-methylphenyl ) benzotriazole and/or 2-hydroxy-4- methoxybenzophenone and/or 2-hydroxybenzophenone and/or 2- ( 2H-benzotriazol-2-yl ) -4 , 6-di-t-pentilphenol and/or 2,2'- dihydroxy-4-methoxybenzophenone and/or 1H, 1H, 2H, 2H- perfluorooctyl triethoxysilane and/or 1H, 1H, 2H, 2H- perfluorodecyl triethoxysilane and/or 3-methyl-2-buten-l-ol and/or Pluronic 127®. The Pluronic F-127® is a non-ionic, surfactant polyol with a molecular weight of approximately 12,500 daltons, which has the following chemical structure

H (OC ₂ H ₂ 0) 101 ( OCH2CH3CH ) 56 ( OCH2CH2 ) 101OH.

The suitable solvent for solution A may be tetrahydrofuran, dimethylsulfoxide or dimethylformamide . It is also important to note that all compounds are well dissolved so that the final lens does not contain any solid residue on its surface.

Solution B contains a mixture of several alkoxysilanes and several plasticizers . The alkoxysilanes include, for example, methyltriethoxysilane and/or ( 3-glycidoxypropyl ) methyldiethoxysilane and/or tetraethoxysilane and/or vinyltriethoxysilane and/or (3- mercaptopropyl ) trimethoxysilane and/or ( 3-aminopropyl ) triethoxysilane and/or phenyltrietoxisilane and/or isocyanate-propyl- triethoxysilane .

Plasticizers include, but are not limited to, amines, such as for example octylamine and/or diethylenetriamine and/or triethylenetetramine and/or diamines, such as for example Jeffamine 230® and/or Jeffamine 400® and/or Jeffamine 600® and/or Jeffamine 900® and/or Jeffamine 2000® and polyethylene glycols, such as poly ( ethylene glycol) methyl ether 350 and/or poly ( ethylene glycol) dimethyl ether 500.

The presence of a catalyst is important to ensure the polycondensation time is appropriate or acceptable. One of the following compounds may be used: acetic acid and/or hydrochloric acid and/or nitric acid and/or sulfuric acid. The most suitable solvent for the solution B is an alcohol such as methanol, ethanol or isopropanol.

There are many types of precursors that may be used to form a polymer/siloxane hybrid matrix. The matrix proposed allows the formation of chemical cross-links among the several components resulting in a three-dimensional network, which imparts greater stiffness and higher thermal stability to the final material. On the other hand the presence of long chain spacers allow creating defects with a high free volume, suitable for incorporation of non-volatile molecules, such as photochromic dyes and additives, which will establish interactions via hydrogen bonding or van der Waals interactions with the chains.

Preferred compositions are those that give rise to/produce hybrids with high transparency and high resistance to scratching, but have no negative effect on the photoactivation of the photochromic molecules.

To start the formation of the hybrid matrix a small amount of water is added to the solution of the hybrid precursor and which is then placed at 50°C under stirring. Stirring time varies significantly depending on the composition, temperature and room humidity, and can thus be between 2 and 24 hours. The water will promote hydrolysis of the alkoxysilanes allowing the formation of chemical bonds between the different precursors present in the solution. During this very important step the viscosity of the solution progressively increases as the siloxane network is being formed. The photochromic molecules and the additives become trapped within the matrix while the solvent evaporates slowly. A high viscosity is fundamental to obtain a good coating .

Application process

The coating may be deposited on the convex side of the lens, or on both sides by a deposition technique, for example by spin-coating or dip-coating techniques. In the spin-coating technique the lens is placed under rotation on its central axis at a suitable speed, preferably between 50 and 500 rpm, and the solution is added in a few seconds, perpendicularly to the centre of the lens. During the rotation of the lens, most of the solution is expelled from its surface. The film thickness will depend on the rotation speed as well as on the mixture viscosity and on its surface tension. In order to obtain a homogeneous deposition it is fundamental that there exist no vibration or oscillation of the solution's addition axis over the lens and that the temperature and room humidity are controlled. It is recommended to maintain the room temperature between 20°C and 25°C and a level of humidity between 40% and 50%.

The lens is then carefully removed from the sample holder of the deposition machine and may preferentially be placed in an oven between 50-100°C, in a horizontal position for several hours, preferably between 12 and 48 hours, or subjected to irradiation with UV or IR light in order to evaporate all the solvent and to complete the formation of the siloxane network .

The multi-layer treatment used to confer antistatic, antireflective and hydrophobic properties may be electron beam vapour deposition technique. This coating consists of multiple layers, typically between 5 and 15, with thicknesses between 10 and 200 nanometers.

The coating now described may be applied to any type of ophthalmic lens such as prescription, non-prescription, monofocal or progressive lenses.

Application example 1

Solution A was prepared by dissolving two photochromic dyes, one antioxidant (4,4'- isopropylidenediphenol , 4,4'- sulphonildiphenol , 1 , 3 , 5-trimethyl-2 , 4 , 6-tris (3,5-di-t- butyl-4-hydroxybenzyl ) benzene, 0.1-0.5 g) ) , one colour stabilizer ( 1-methylimidazole, 2- ( 2-hydroxy-5-methylphenyl ) benzotriazole, 0.01-0.1 g) , one UV blocker ( 2-hydroxy-4- methoxybenzophenone, 2-hydroxybenzophenone, 2- (2H- benzotriazol-2-yl ) -4, 6-di-t-pentilphenol, 2,2' -dihydroxy-4- methoxybenzophenone, 0.01-0.1 g) , one surfactant

( 1H, 1H, 2H, 2H-perfluorooctyl triethoxysilane or 1H, 1H, 2H, 2H- perfluorodecyl triethoxysilane, or Pluronic F-127 or Pluronic F-123 0.05-0.5 g) , one anti-yellowing agent ( 3-methyl-2- buten-l-ol, 0.01-0.1 g) in tetrahydrofuran (1-5 ml) and placed under stirring for 20 min.

Solution B was prepared by dissolving 1-5 g of at least two silanes from among methyltriethoxysilane, tetraethoxysilane, ( 3-glycidoxypropyl ) methyldiethoxysilane, vinyltriethoxysilane ( 3-mercaptopropyl ) trimethoxysilane, (3- aminopropyl ) triethoxysilane, phenyltrietoxisilane or isocyanate-propyl-triethoxysilane in ethanol (1-5 mL) and placed under stirring for 5 min.

Several spacers, each constituting 5-50% of the final total solution, were added to solution B and this was stirred at room temperature for further 5 min.

Solution A was added to solution B and the resulting solution was stirred for 10 min. Water was added (1-5 mL) and the solution obtained was placed in a glycerin bath at 50°C under constant agitation of 150 rpm. The total volume is about 15 mL .

The viscosity of the solution was continuously measured and when a value between 600-1000 mPa was achieved, a volume of 5 mL was withdrawn by using a micropipette with a disposable tip. A lens was placed on a spin coater under rotation (100- 500 rpm) and the 5 ml of the above described solution were deposited in 3 seconds on the lens centre. After 2 min, the lens was removed and placed in an oven at 50°C for 2-18 h. To confer antireflective , antistatic and hydrophobic characteristics to the surface of the lenses, the electron beam vapour deposition technique was used. The as-prepared coating consists of several layers, typically between 5 and 15 with thicknesses between 10 and 200 nanometers.

The last layer is constituted by a commercial fluoropolymer : Satin (Satisloh) or Duralon AFP (COTEC) . The remaining layers are oxides, one with a high refractive index, between 2 and 2.5, and another with a low refractive index, between 1.3 and 1.79. These layers are applied by alternating a low refractive index material with layers of higher refractive index material.

The high refractive index material is one of the following: Ce0 ₂ (2.30-2.00), Zr0 ₂ (2.10-2.00), Ti0 ₂ (2.30-2.00), Ta ₂ 0 ₅

(2.30-2.00), ZnS (2.30-2.20) or Th0 ₂ (2.20-2.00). The low refractive index material is one of the following: MgF ₂

(1, 385), Si0 ₂ (1.46), ThF ₄ (1.5), LaF ₃ (1.56) or CeF ₃ (1.615) .

A conductive material, typically In ₂ 0 ₃ -Sn0 ₂ (ITO), is introduced between the layers of the coating to confer antistatic properties.

The final lens was exposed to the sun to determine the colouration and discolouration times. The colouration time was 30 s and the time necessary for its full discolouration was 2 min. The lens acquired a grey colour. The visible absorption spectrum was measured using a UV-Vis spectrophotometer (Cary 50) . In the activated state it exhibited a transmittance of 40% and in the non-activated state it presented a transmittance higher than 90%. Application example 2

Solution A was prepared by dissolving four photochromic dyes, one antioxidant (4,4'- isopropylidenediphenol , 4,4'- sulphonildiphenol , 1 , 3 , 5-trimethyl-2 , 4 , 6-tris (3,5-di-t- butyl-4-hydroxybenzyl ) benzene, 0.1-0.5 g) ) , one colour stabilizer ( 1-methylimidazole, 2- ( 2-hydroxy-5-methylphenyl ) benzotriazole, 0.01-0.1 g) , one UV blocker ( 2-hydroxy-4- methoxybenzophenone, 2-hydroxybenzophenone, 2- (2H- benzotriazol-2-yl ) -4, 6-di-t-pentilphenol, 2,2' -dihydroxy-4- methoxybenzophenone, 0.01-0.1 g) , one surfactant

( 1H, 1H, 2H, 2H-perfluorooctyl triethoxysilane or 1H, 1H, 2H, 2H- perfluorodecyl triethoxysilane, or Pluronic F-127® or Pluronic F-123®, 0.05-0.5 g) , one anti-yellowing agent (3- methyl-2-buten-l-ol, 0.01-0.1 g) in tetrahydrofuran (1-5 ml) and placed under stirring for 20 min.

Solution B was prepared by dissolving 1-5 g of two silanes (methyltriethoxysilane, tetraethoxysilane, (3- glycidoxypropyl ) methyldiethoxysilane, vinyltriethoxysilane (3-mercaptopropyl) trimethoxysilane, (3- aminopropyl ) triethoxysilane, phenyltrietoxisilane or isocyanate-propyl-triethoxysilane in ethanol (1-5 mL) and placed under stirring for 5 min. Several spacers, each constituting 5-50% of the total were added to Solution B and stirred at room temperature for further 5 min.

Solution A was added to solution B and the resulting solution was stirred for 10 min. Water was added (1-5 mL) and the solution obtained was placed in a glycerine bath at 50°C under constant agitation of 150 rpm. The total volume was about 15 mL .

The viscosity of the solution was measured continuously and when a value between 600-1000 mPa was reached, 5 ml were withdrawn using a micropipette with a disposable tip.

A lens was placed on a spin coater under rotation (100-500 rpm) and 5 ml of the above solution were deposited in 3 seconds under the lens centre. After 2 min, the lens was removed and placed in an oven at 50°C for 2-18 h.

To confer antireflective, antistatic and hydrophobic characteristics to the surface of the lenses, the electron beam vapour deposition technique was used. The as-prepared coating consists of several layers (between 5 and 15) with thickness between 10 and 200 nanometers.

The last layer is a commercial fluoropolymer : Satin (Satisloh) or Duralon AFP (COTEC) . The remaining layers are oxides, one with high refractive index (between 2 and 2.5) and another with low refractive index (between 1.3 and 1.7) . These layers are applied by alternating a low refractive index material with layers of higher refractive index material .

The high refractive index material is one of the following: Ce0 ₂ (2.30-2.00), Zr0 ₂ (2.10-2.00), Ti0 ₂ (2.30-2.00), Ta ₂ 0 ₅

(2.30-2.00), ZnS (2.30-2.20) or Th0 ₂ (2.20-2.00). The low refractive index material is one of the following: MgF ₂

(1, 385), Si0 ₂ (1.46), ThF ₄ (1.5), LaF ₃ (1.56) or CeF ₃ (1.615) .

A conductive material, typically ITO, is introduced between the layers of this coating to confer antistatic properties.

The lens was exposed to sun for determining the colouration and discolouration time. The colouration time was 30 s and the time necessary for its complete discolouration was 2 min. The lens acquires a brown colour. The visible absorption spectrum was measured using a UV-Vis spectrophotometer (Cary 50) . In the activated state it exhibits 40% transmittance and in the non-activated state presents transmittance higher than 90%.

Characterization of the properties of the lenses

The coatings obtained were characterized as to their photochromic, anti-scratch and adhesion to the lenses properties .

The adhesion degree of the coating to the substrate was evaluated by placing adhesive tape over a lens with 6 parallel cuts separated by a distance of 1 mm. When removing the adhesive tape it was found that the coating was not removed indicating good adhesion of the coating to the lens, in accordance with ISO 2409 standard of 2013.

To evaluate the scratch resistance of the produced lenses, these were placed on the bottom of a tray containing an abrasive agent (Alundum® ZF-12) by making the tray to oscillate with a frequency of 150 oscillations per minute, for 4 min. The lenses were removed and the degree of abrasion was evaluated by measuring the amount of scattered light using UV-Vis transmittance meter. The lenses present a low number of scratches indicative of high resistance to scratching, according to ATSM standard F735 of 2013.

Photochromic properties, notably with regard to the colour developed under sun exposure, maximum colour intensity, discolouration speed and presence or absence of residual colour were determined using a UV lamp and a UV spectrophotometer . The absorbance spectrum of the lenses was measured, before and after exposure to UV light for 30 s, thus characterizing the obtained colouration. The results show a very significant increase in absorbance at any wavelength, as illustrated in Figures 2 and 5. After removing the light source, the absorbance at a given wavelength was recorded over time, allowing measurement of the lens discolouration kinetics, as illustrated in Figures 3 and 6.

It was found that after 30 s of solar exposition the lens acquire a grey or brown colouration with an intensity approximately 15% lower than that of conventional lenses. Nevertheless the discolouration speed of these lenses is much faster, as shown in the measurements of Table 1.

Table 1. Time required for the discolouration of the lenses, in the dark, after exposure to UV light for 30 s

While the colour of conventional lenses fades in about 8 min at room temperature, the colour of the here described lenses fade in about 2 min favouring their use. This means that when a user moves from an illuminated area to a non- illuminated area the proposed lens adapt very quickly to new conditions .

Beyond the clear benefit of these lenses in terms of speed of response to external luminosity, it is noted that the process is simpler, being possible to confer with a single coating, photochromic and anti-scratch properties simultaneously. Re erences

[1] The effect of a sulphur bridge on the photochromic properties of indeno-fused naphthopyrans . Coelho, PJ; Salvador, MA; Oliveira, MM; Carvalho, LM. Tetrahedron 2004, 60 (11) 2593-2599;

[2] a) Photochromic organic-inorganic hybrid materials. Pardo, R; Zayat, M; Levy, D. Chemical Society Reviews, 2011, 40 (2), 672-687; b) Applications of advanced hybrid organic-inorganic nanomaterials : from laboratory to market, C. Sanchez, P. Belleville, M. Popall and L. Nicole, Chemical Society Reviews, 2011, 40, 696-753; c) Mesoporous thin films: properties and applications, P. Innocenzi and L. Malfatti, Chemical Society Reviews, 2013, 42, 4198-4216.

[3] Intense colouring photochromic 2h-naphtho [ 1 , 2-b] pyrans and heterocyclic pyrans. David Allan Clarke, Stephen Nigel Corns, Christopher David Gabbutt, John David Hepworth, Bernard Mark Heron, Steven Michael Partington, WO1998042695 Al (1998);

[4] Fast and fully reversible photochromic performance of hybrid sol-gel films doped with a fused-naphthopyran . Paulo J. Coelho, Carlos J. R. Silva, Ceu Sousa and Sandra D. F. C. Moreira. Journal of Materials Chemistry C, 2013, 1, 5387;

[5] a) Abrasion and/or Scratch Resistant Article Comprising an Impact Resistant Photochromic Polyurethane Coating, and Process of Preparation Thereof. Christy Ford, Pamela McClimans. U.S. 6187444 (2008) ; b) Photochromic polyurethane laminate. Xuzhi Qin, Hideyo Sugimura, Michael Boulineau. US 20050233153 Al (2005); c) Lens with photochromic elastomer film and method of making it. Agustin Alberto deRo as, Pallapalayam Muthusamy

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[8] a) Process of integrating a photochromic substance into an ophthalmic lens and a photochromic lens of organic material. Lyliane Le Naour-Sene. US 4286957 A (1979); b) Photochromic plastic article and method for preparing same. Cletus N. Welch. US 4880667 A (1989)

[9] Photochromic article. Eric M. King, Kevin J. Stewart. US

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[10] Nanomechanical analysis of high performance materials. Atul Tiwari. Springer. 2013

[11] Antireflection coating design for plastic optics. Schulz, U. ; Schallenberg, U.B.; Kaiser, N. Applied optics 41 (2002), 16, S.3107-3110.

[12] Photochromic coating composition and photochromic synthetic resin ophthalmic lens. Takao Mogami, Hiroshi Kawashima. US 4556605 A (1985) .

The present technology is naturally not in any way restricted to the embodiments described herein and a person of ordinary skill in the art can provide many modification possibilities thereof without departing from the general idea, as defined in the claims.

All embodiments described above are obviously combinable with each other. The following claims further define preferred embodiments .