WO2019145391A1

WO2019145391A1 - Photochromic optically transparent electrically conductive film laminate

Info

Publication number: WO2019145391A1
Application number: PCT/EP2019/051697
Authority: WO
Inventors: Cornelis Johannes Gerardus Maria Van Peer
Original assignee: Nanogate Se
Current assignee: Nanogate Se
Priority date: 2018-01-25
Filing date: 2019-01-24
Publication date: 2019-08-01
Anticipated expiration: 2020-07-25

Abstract

The invention relates to an optically transparent electrically conductive film laminate comprising a self-supporting photochromic polymer film and an optically transparent electrically conductive layer, wherein the self-supporting photochromic polymer film comprises a thermoplastic polyurethane, optionally a ketone, and one or more organic T-type photochromic compounds. The invention also relates to a method for the manufacturing of such an optically transparent electrically conductive film laminate, and to articles comprising the optically transparent electrically conductive film laminate according to the invention.

Description

PHOTOCHROMIC OPTICALLY TRANSPARENT ELECTRICALLY CONDUCTIVE FILM LAMINATE

TECHNICAL FIELD

The invention relates to a photochromic optically transparent electrically conductive film laminate comprising a self-supporting photochromic polymer film and an optically transparent electrically conductive layer. The invention also relates to a method for the manufacturing of such a photochromic optically transparent electrically conductive film laminate and to a photochromic optically transparent electrically conductive film laminate obtainable by said method. Furthermore, the invention relates to articles comprising said photochromic optically transparent electrically conductive film laminate, such as visors, goggles, ophthalmic lenses, sunglasses, face-shields, architectural windows, automotive windows, and aeronautic windows.

BACKGROUND

Photochromism is a physical phenomenon which has been well-established since the first half of the 20^th century. It is the ability of a photochromic molecule to reversibly change from an inactivated rather colourless state, to an activated coloured state, through exposure to electromagnetic radiation, such as visible light or only UV light. In very simple terms, when exposed to visible light or UV light the photochromic molecules have a chemical bond broken causing them to rearrange into a species that absorbs light at longer wavelengths in the visible region.

Photochromic molecules are separated into two categories: inorganic and organic photochromic molecules. Inorganic photochromic molecules were the first to be discovered and applied in a commercial product.

The first true industrial application of a photochromic material was the introduction of photochromic ophthalmic lenses in the 1960s by a company named Corning. US3208860 is the first patent describing photochromic glass and an article made thereof. Coming’s Photogray® ophthalmic lenses were the result of this patent application. These photochromic ophthalmic lenses can turn grey upon stimulus by UV light, shading their wearers’ eyes from the sun. This first industrial application of photochromism used inorganic photochromic molecules known as silver halides.

There are several reasons why inorganic photochromic molecules are no longer widely used. Firstly, they are relatively slow to respond to light stimulus when compared to organic photochromic molecules. Secondly, they are relatively expensive to produce. Thirdly, even though they have a longer lifetime than plastic lenses containing organic photochromic molecules, the photochromic reaction of inorganic photochromic molecules, unlike organic photochromic molecules, gets stronger over time up to the point that materials containing inorganic photochromic molecules, such as silver halides, remain in their darkened state even without light stimulus therewith rendering them useless. Furthermore, silver halides cannot be used in plastic lenses, unlike organic photochromic molecules, and therefore have become less popular, since the use of glass lenses has decreased significantly, while the use of plastic lenses is now becoming standard. Nowadays, research mainly focuses on organic photochromic molecules. Generally speaking, there are two types of organic photochromic molecules. In this respect, reference is made to M.A. Chowdhury et al. , Journal of Engineered Fibers and Fabrics, 9(1 ) (2014), pp 107-123, which is incorporated by reference herein in its entirety. So-called P-type organic photochromic molecules change from an inactivated rather colourless state to an activated coloured state upon exposure to light of a certain wavelength and only revert back to the inactivated state upon exposure to light with a different wavelength. Examples of P-type organic photochromic molecules include diarylethenes.

T-type organic photochromic molecules, on the other hand, typically change from an inactivated rather colourless state to an activated coloured state upon exposure to light of a certain wavelength and revert back to the inactivated state upon removal of the illumination. This reversion to the inactivated state is driven thermally, meaning that the equilibrium shifts to the inactivated state at higher temperatures, leading to a perceived reduction in the coloration of the activated state. Likewise, the lower the temperature, the longer it will take to return to the inactivated state, but the more pronounced the colour will be in the activated state. As a direct consequence of this behaviour, the reversion to the rather colourless inactivated state can be accelerated by actively increasing the temperature.

Well-known examples of T-type organic photochromic molecules include spiropyrans, spirooxazines and naphthopyrans. These T-type organic photochromic molecules can be synthesised with varying substituents on the ring structure such they cover a range of colour spectra in the activated state, e.g. reds, blues, yellows, et cetera, and so could have industrial applications in many market segments. Applications include, but are not limited to, automotive and aircraft windows, helmet visors, ophthalmic lenses, self-shading sunglasses, and windowpanes for buildings.

However, current photochromic articles have a few drawbacks that limit their application in certain market segments. First of all, for applications in, for instance, helmet visors and automotive or aircraft windows, the photochromic back reaction from the activated coloured state to the rather colourless inactivated state is often too slow. Typically, photochromic films cut off 50% of light within the first minute and 80% within 15 minutes after exposure to light, but the back reaction is often much slower. After removal of the light causing activation, it typically takes about 5 minutes for the photochromic film to again reach a cut off of 60% of the light but it can take up to an hour for the photochromic film to clear completely. If a car or motorcyclist were to enter a tunnel, it would potentially be dangerous if the car windshield or the motorcyclist’s helmet visor needed up to an hour to become clear.

US2004/0034898A1 addressed this problem by applying, instead of an organic photochromic film, an electrically darkenable flexible liquid crystal film, which is described to have a response time of a few milliseconds. US2004/0034898A1 discloses helmet visors, glasses or lenses comprising an electrically darkenable flexible liquid crystal film. The helmet visors, glasses or lenses can be darkened by applying a voltage, supplied by a solar cell, to or over the electrically tintable layer. The helmet visors, glasses or lenses lose the tint in a de-energized state. It is describe that the electrically tintable layer can be incorporated between two transparent carrier body layers.

The state of the art further addressed this problem by applying a transparent electrically conductive layer on top of a photochromic film. The electrically conductive layer has a certain electrical resistance. When an electrical potential is applied over the electrically conductive layer, the electrically conductive layer is heated along with the photochromic film. In this way, the transition of the photochromic film from the activated coloured state to the inactivated rather colourless state is accelerated.

US2012/0235900A1 , for example, concerns see-through near-eye display glasses with a fast response photochromic film system for quick transition from dark to clear. US2012/0235900A1 discloses an optical assembly comprising a carrier layer, such as glass or plastic, with a photochromic layer and a heating layer applied on top of the photochromic layer. The heating layer comprises transparent indium tin oxide (ITO).

The use of an ITO film layers has several disadvantages. ITO is not resistant to high temperatures and therefore cannot be used in a lot of standard moulding and extrusion production methods. Moreover, ITO layers cannot be bent because bending will cause the ITO conductive tracks to break such that the layer loses its conductivity. Hence, ITO film layers can neither be used in flexible substrates nor in laminates that need to be transformed into three-dimensional structures.

There is a need for photochromic films for use in applications where quick transitions between light and dark states are necessary. Moreover, there is need for photochromic films that can be easily manufactured in various shapes.

It is therefore an objective of the invention to provide photochromic films that can transition between light and dark states within a few seconds and have sufficient flexibility to be used in flexible substrates such that they can be applied in three-dimensional structures. It is a further object of the invention to provide such photochromic films which are self-supporting, have high transparency, and have a good resistance to wear as regards loss of photochromic activity over time. Moreover, it is an object of the invention to provide a simple or simplified manufacturing process for such photochromic films.

SUMMARY

The inventors have established that one or more of the objectives can be achieved by treating a thermoplastic polyurethane film with a solvent selected from the group of ketones with one or more organic T-type photochromic compounds dissolved therein. This process surprisingly results in flexible self-supporting photochromic polymer films with a homogeneous distribution of the solvent selected from the group of ketones and the one or more organic T-type photochromic compounds across at least part of the thickness of the polyurethane film.

It was found that these self-supporting photochromic polymer films have an increased loss modulus under influence of the imbibed ketone in the thermoplastic polyurethane film, when compared to the loss modulus determined for the thermoplastic polyurethane film lacking the ketone. Thus, presence of the ketone in the photochromic self-supporting polymer film of the invention results in increased flexibility of the polymer molecules in the film, which increased flexibility is beneficial for the decay half time of the one or more one or more organic T-type photochromic compounds comprised by the self-supporting photochromic polymer film.

The inventors have further established that bonding an optically transparent electrically conductive layer to the self-supporting photochromic polymer film results in a optically transparent electrically conductive laminate that can, when putting an electrical potential over the optically transparent electrically conductive layer, transition between light and dark states within a few seconds and has sufficient flexibility to be used as or in a flexible laminate, such that it can be transformed into three-dimensional structures.

Accordingly, in a first aspect the invention provides a photochromic optically transparent electrically conductive film laminate, comprising a self-supporting photochromic polymer film which is bonded to an optically transparent electrically conductive layer,

wherein the self-supporting photochromic polymer film consists of a thermoplastic polyurethane film having a thickness and comprising between 0 and 12 wt%, based on the weight of the self- supporting photochromic polymer film, of a solvent selected from the group of ketones, and one or more organic T-type photochromic compounds,

wherein the solubility of the one or more organic T-type photochromic compounds in the solvent at a temperature of between 15°C and 30°C is at least 0, 1 wt%, based on the weight of the solution of the one or more organic T-type photochromic compounds in the solvent, and

wherein the one or more organic T-type photochromic compounds, and the solvent if present, are distributed across at least part of the thickness of the thermoplastic polyurethane film in the self- supporting photochromic polymer film.

In a second aspect, the invention provides a method for producing an optically transparent electrically conductive film laminate, comprising the steps of:

a) providing a thermoplastic polyurethane film having a thickness and having a first and a second surface;

b) providing one or more organic T-type photochromic compounds;

c) providing a solvent selected from the group of ketones;

d) preparing a solution by dissolving at least 0, 1 wt%, based on the weight of the solution, of the one or more organic T-type photochromic compounds of step (b) in the solvent of step (c);

e) treating at least part of at least the first surface of the thermoplastic polyurethane film of step (a) with at least 100 g/m² of the solution of step (d) for a period of at least 5 seconds at a temperature between 15 and 30°C, resulting in a self-supporting photochromic polymer film with swollen areas where the surface is treated with the solution, wherein the one or more organic T-type photochromic compounds and the solvent are distributed across at least part of the thickness of the thermoplastic polyurethane film;

f) optionally removing an excess of the solution applied in step (e) from the surface of the self- supporting photochromic polymer film obtained in step (e);

g) optionally drying the self-supporting photochromic polymer film obtained in step (e) or (f) to reduce the weight percentage of solvent in the self-supporting photochromic polymer film;

h) bonding at least part of an optically transparent electrically conductive layer to a surface of the self-supporting photochromic polymer film obtained in any one of steps (e) to (g);

i) optionally bonding at least part of the self-supporting photochromic polymer film obtained in step (h) to a first surface of an optically transparent first sheet made of a plastic or a glass; j) optionally bonding at least part of the optically transparent electrically conductive layer obtained in step (h) or (i) to a first surface of an optically transparent second sheet made of a plastic or a glass;

k) optionally bonding at least part of a second surface of the optically transparent first sheet obtained in step (i) or in steps (i) and (j) to, or coating at least part of a second surface of the optically transparent first sheet obtained in step (i) or in steps (i) and (j), with a third optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating; and

L) optionally bonding at least part of a second surface of the optically transparent second sheet obtained in step (j) or in steps (j) and (k) to, or coating at least part of a second surface of the optically transparent second sheet obtained in step (j) or in steps (j) and (k), with a fourth optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating.

In a third aspect, the invention provides an optically transparent electrically conductive film laminate obtained by or obtainable by the method as defined hereinbefore. It was found by the inventors that the method of the invention provides an optically transparent electrically conductive film laminate comprising a self-supporting photochromic film that has a homogeneous distribution of the one or more organic T-type photochromic compounds across at least part of the thickness of the film and further does not yellow upon exposure to e.g. ultraviolet light and xenon light. Thus, the optically transparent electrically conductive film laminate obtained by or obtainable by the method of the invention retains its transparency upon exposure to light, which is beneficial to the life time of the film when applied for its photochromic activity.

In a fourth aspect, the invention provides an optical article (i) comprising the optically transparent electrically conductive film laminate as defined hereinbefore or (ii) comprising the optically transparent electrically conductive film laminate obtained by or obtainable by the method as defined hereinbefore. The optical article is preferably selected from the group consisting of visors, goggles, ophthalmic lenses, sunglasses, face-shields, architectural windows, automotive windows, and aeronautic windows.

DEFINITIONS

The term‘film’ has its regular scientific meaning throughout the text, and here refers to a thin sheet of material that can be flexible and can be bonded to another material such as a sheet of material.

The term‘optical grade plastic’ has its regular scientific meaning throughout the text, and refers to a plastic that is suitable for the manufacturing of optical articles, such as the optical articles defined herein.

The term‘optical glass’ has its regular scientific meaning throughout the text, and here refers to a glass that is suitable for the manufacturing of optic articles, such as the optic articles defined herein.

The term‘float glass’ has its regular scientific meaning throughout the text, and refers to a sheet of glass made by floating molten glass on a bed of molten metal, giving the float glass sheet uniform thickness and two flat major surfaces.

The term‘busbars’ has its regular scientific meaning throughout the text, and here refers to metallic strips or bars that can carry electric current to distribute the electric power. The term ‘self-supporting’ has its regular scientific meaning throughout the text, and in the context of the thermoplastic polyurethane film of present invention refers to a coherent and consistent film while not being supported, by for example a carrier or a substrate.

The term ‘sheet resistance’, expressed in W/square, has its regular scientific meaning throughout the text, and here refers to the measure of electrical resistance of thin films that are uniform in thickness.

The term‘luminous transmittance’ , measured in accordance with ASTM D1003 - 2013, has its regular scientific meaning throughout the text, and here refers to the percentage of solar radiation that can pass through an optic article such as a laminate of polymer sheets or a sheet of glass.

The term‘haze’, measured in accordance with ASTM D1003 - 2013, has its regular scientific meaning throughout the text, and here refers to the amount of light that is subject to Wide Angle Scattering.

The term‘L a b values’ has its regular scientific meaning throughout the text, and here refers to the CIELAB measurement that measures colour differences, wherein‘L’ indicates lightness,‘a’ indicates the red/green coordinate and‘b’ indicates the yellow/blue coordinate.

The term‘decay half time’ as used herein refers to the time it takes for a photochromic material to reach the point where it is halfway to returning from its activated state to its original state before being activated.

ABBREVIATIONS USED

The abbreviation‘ UV-radiation’ has its regular scientific meaning throughout the text, and stands for‘ultraviolet radiation’, which is typically radiation having a wavelength of between 100 and 400 nm. In the context of the present invention, UV-radiation typically relates to that part of the radiation in the UV-spectrum that reaches see level in non-negligible amounts, such as radiation having a wavelength of between 280 and 400 nm.

The abbreviation‘CIELAB’ has it regular scientific meaning throughout the text, and stands for ‘Commission Internationale de I’Eclairage L*a*b color space’.

The abbreviation‘PEDOT:PSS’ has its regular scientific meaning throughout the text, and here stands for poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, which is a transparent conductive polymer mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1A shows a first embodiment (10) of the photochromic optically transparent electrically conductive film laminate according to the invention. The self-supporting photochromic polymer film (1 1 ) is bonded via interface (19) to the optically transparent electrically conductive layer (12). The self- supporting photochromic polymer film (1 1 ) has a non-bonded or free surface (13). Likewise, the optically transparent electrically conductive layer (12) has a non-bonded or free surface (14).

Figure 1 B shows a second embodiment (20) of the photochromic optically transparent electrically conductive film laminate according to the invention. The self-supporting photochromic polymer film (21 ) is bonded via interface (29) on one side to the optically transparent electrically conductive layer (22) and on the other side it is bonded via interface (29a) to a first surface of an optically transparent first sheet (25) made of a plastic or a glass. The optically transparent electrically conductive layer (22) is bonded via interface (29b) on its other side to a first surface of an optically transparent second sheet (26) made of a plastic or a glass. The optically transparent first sheet (25) has a non- bonded or free surface (23). Likewise, optically transparent second sheet (26) has a non-bonded or free surface (24).

Figure 1 C shows a third embodiment (30) of the photochromic optically transparent electrically conductive film laminate according to the invention. The self-supporting photochromic polymer film (31 ) is bonded via interface (39) on one side to the optically transparent electrically conductive layer (32) and on the other side it is bonded via interface (39a) to a first surface of an optically transparent first sheet (35) made of a plastic or a glass. The optically transparent electrically conductive layer (32) is bonded via interface (39b) on its other side to a first surface of an optically transparent second sheet (36) made of a plastic or a glass. The optically transparent first sheet (35) is coated on its second surface (39c) with an anti-scratch coating (37). The anti-scratch coating (37) has a non-bonded or free surface (33). The optically transparent second sheet (36) is coated on its second surface (39d) with an anti-fog coating (38). The anti-fog coating (38) has a non-bonded or free surface (34).

Figure 2A is a simplified representation of the photochromic optically transparent electrically conductive film laminate (30) of the third embodiment depicted in Figure 1 C, wherein the laminate has two non-bonded or free flat surfaces: an outer surface (33) and an inner surface (34).

Figure 2B is a simplified representation of the photochromic optically transparent electrically conductive film laminate (30) of the third embodiment depicted in Figure 1 C, wherein the laminate has two non-bonded or free curved surfaces: an outer convex surface (33) and an inner concave surface (34).

Figure 3A shows another embodiment of the photochromic optically transparent electrically conductive film laminate (30), comprising means (44a, 44b) for attaching the laminate (30) to a helmet visor (40) with a convex surface (43) and a concave surface (42). The convex surface (33) of the photochromic optically transparent electrically conductive film laminate (30) can be attached to the concave surface (42) of the helmet visor (40). The photochromic optically transparent electrically conductive film laminate (30) is secured to the helmet visor (40) using e.g. screws (44a, 44b). The helmet visor (40) comprising the photochromic optically transparent electrically conductive film laminate (30) can then be attached to a helmet using pre-made holes (41a, 41 b).

Figure 3B shows the completed product (50) of the process depicted in Figure 3A, wherein the photochromic optically transparent electrically conductive film laminate (30) has been attached to concave surface (42) of the helmet visor (40) and is secured with screws (44a, 44b). The completed visor with the laminate (50) can then be attached to a helmet using the pre-made holes (41a, 41 b) so that the convex surface (43) of the helmet visor (50) faces outwards. The completed visor with the laminate further contains electrical connections attached to the electrically conductive film laminate (30) (not shown). DETAILED DESCRIPTION

Photochromic optically transparent electrically conductive film laminate

In a first aspect the invention relates to a photochromic optically transparent electrically conductive film laminate, comprising a self-supporting photochromic polymer film which is bonded to an optically transparent electrically conductive layer,

In a preferred embodiment, the one or more organic T-type photochromic compounds, and the solvent if present, are homogeneously distributed across at least part of the thickness of the thermoplastic polyurethane film, preferably homogeneously distributed across the whole thickness of the thermoplastic polyurethane film in the self-supporting photochromic polymer film.

The self-supporting photochromic polymer film in the optically transparent electrically conductive film laminate as defined hereinbefore preferably comprises between 0 and 8 wt% of the solvent, more preferably between 0 and 5 wt%, even more preferably between 0 and 3 wt%, based on the weight of the self-supporting photochromic polymer film. Most preferably, the self-supporting photochromic polymer film in the optically transparent electrically conductive film laminate as defined hereinbefore comprises about 0 wt%, such as 0 wt%, of the solvent, based on the weight of the photochromic self- supporting polymer film. It is also preferred that the self-supporting photochromic polymer film in the optically transparent electrically conductive film laminate as defined hereinbefore comprises less than 0, 1 wt%, such as 0,05 wt% or 0,0 wt%, of the solvent, based on the weight of the photochromic self- supporting polymer film.

In another embodiment, the self-supporting photochromic polymer film in the optically transparent electrically conductive film laminate as defined hereinbefore preferably comprises between 0,1 and 12 wt% of the solvent, based on the weight of the self-supporting photochromic polymer film, more preferably between 0, 1 and 8 wt%, even more preferably between 0, 1 and 5 wt%, still more preferably between 0, 1 and 3 wt%.

The thermoplastic polyurethane film is preferably chosen from the group consisting of aliphatic thermoplastic polyurethanes films, more preferably from aliphatic polyester-based- and aliphatic polyether-based thermoplastic polyurethanes films.

In a very preferred embodiment, the thermoplastic polyurethane film is an aliphatic thermoplastic polyurethane film based on an aliphatic diisocyanate selected from 1 ,4-tetramethylene diisocyanate, 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate, 1 , 12-dodecamethylene diisocyanate, cyclohexane- 1 , 3-diisocyanate, cyclohexane-1 , 4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, isophorone diisocyanate, 5-isocyanato-1-(isocyanatomethyl)-1 ,3,3-trimethylcyclohexane, bis-(4- isocyanatocyclohexyl)-methane, 2,4’-dicyclohexylmethane diisocyanate, 1 ,3-bis(isocyanatometyl)- cyclohexane, 1 ,4-bis(isocyanatometyl)-cyclohexane, bis-(4-isocyanato-3-methylcyclohexyl)-methane, a,a,a’,a’-tetramethyl-1 ,3-xylylen diisocyanate, a,a,a’,a’-tetramethyl-1 ,4-xylylen diisocyanate, 1- isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6- hexahydrotoluylene diisocyanate, 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof, preferably selected from 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate, and mixtures thereof.

The thermoplastic polyurethane film preferably has a thickness of between 0,05 mm and 6,50 mm, more preferably between 0,08 mm and 2,60 mm, even more preferably between 0,09 mm and 0,68 mm, such as about 0,1 mm, about 0,38 mm or about 0,63 mm.

The self-supporting photochromic polymer film preferably has a thickness of between 0,05 mm and 6,50 mm, more preferably between 0,08 mm and 2,60 mm, even more preferably between 0,09 mm and 0,68 mm, such as about 0, 1 mm, about 0,38 mm or about 0,63 mm.

The inventors established that the whole thickness of the self-supporting photochromic polymer film can be homogeneously impregnated with the solvent selected from the group consisting of ketones and the one or more organic T-type photochromic compounds, when films having a thickness in the above mentioned range are applied.

The self-supporting photochromic polymer film can be presented as a transparent film after being subjected to heat and pressure according to methods commonly applied in the art. That is to say, when the self-supporting photochromic polymer film is for example subjected to a pressure of between 6 bar and 20 bar, such as about 8 bar, 12 bar or 15 bar, at a temperature of e.g. between 120°C and 165°C, for a time period of between for example 1 second and 1 hour, such as for about 1 second, 30 seconds, 4 minutes, 10 minutes or 20 minutes, a transparent film is obtainable.

The one or more organic T-type photochromic compounds are preferably selected from the group consisting of spiropyrans, spirooxazines, naphthopyrans and combinations thereof, more preferably from the group consisting of spirooxazines, naphthopyrans and combinations thereof. Examples of these organic T-type photochromic compounds are, for example, described in M.A. Chowdhury et al. , Journal of Engineered Fibers and Fabrics, 9(1 ) (2014), pp 107-123, which is incorporated by reference herein in its entirety.

More preferably, the one or more organic T-type photochromic compounds are selected from polydialkylsiloxane-substituted naphthopyrans, still more preferably from polydialkylsiloxane-substituted naphthopyrans capable of taking on a blue colour or a green colour when irradiated with ultraviolet radiation.

Polydialkylsiloxane-substituted naphthopyrans are for example described in US8,865,029B2, i.e. the photochromic molecules outlined in Example 3, column 46, line 42 to column 50, line 2, Example 4, column 50, line 4 to column 51 line 4, Example 6, column 62, line 50 to column 53, line 30, Example 7, column 53, line 32 to column 54, line 20, and Example 9, column 57, line 50 to column 63, line 20. Polydialkylsiloxane-substituted naphthopyrans, sufficiently soluble in e.g. cyclohexanone at room temperature, are for example Reversacol Pennine Green, Reversacol Sea Green and Reversacol Humber Blue (Vivimed Labs Ltd).

In a very preferred embodiment, the thermoplastic polyurethane film in the self-supporting photochromic polymer film comprises at least two organic T-type photochromic compounds.

Preferred organic T-type photochromic compounds are activated upon exposure to radiation having a wavelength of between 360 nm and 450 nm, preferably between 360 and 400 nm, between 370 nm and 390 nm, or between 360 and 380 nm.

The self-supporting photochromic polymer film can further comprise additives such as a light stabilizer and/or an anti-oxidant.

It is to be understood that the term‘solvent’ also encompasses mixtures of solvents selected from the group of ketones, as long as the different solvents are mutually soluble at a temperature of between 15°C and 30°C.

The solvent selected from the group of ketones is preferably selected from the group consisting of straight-chain ketones, branched ketones, unsubstituted cyclic ketones, cyclic ketones substituted with at least one alkyl group and mixtures thereof. More preferably, the solvent selected from the group of ketones is selected from the group consisting of straight-chain ketones, unsubstituted cyclic ketones and mixtures thereof.

In a particularly preferred embodiment, the solvent selected from the group of ketones is selected from the group consisting of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3-one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 4-methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2-cyclohexene-1-one, 5- methylhexan-2-one, 1-cyclohexylpropan-1-one, 1-cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one and mixtures thereof, even more preferably the solvent is selected from propan-2-one and cyclohexanone, most preferably the solvent is cyclohexanone.

The optically transparent electrically conductive layer preferably has a total luminous transmittance of at least 85% and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013).

The optically transparent electrically conductive layer preferably has a sheet resistance of between 10 and 120 W/square, more preferably between 40 and 100 W/square, even more preferably between 50 and 70 W/square, most preferably about 60 W/square.

The optically transparent electrically conductive layer preferably is a flexible layer.

Examples of particularly preferred optically transparent electrically conductive layers are selected from the group consisting of a carbon nanobud polycarbonate film, a layer of silver nanowires in a transparent mouldable glue, and a PEDOT-PSS layer on a carrier film.

The carrier film for the optically transparent electrically conductive layer can be made of polycarbonate or polyethylene terephthalate. Most preferably, the optically transparent electrically conductive layer is a carbon nanobud polycarbonate film. In this respect, reference is made to W02009/056686A1 , disclosing transparent carbon nanobud materials.

The optically transparent electrically conductive layer preferably has a thickness of between 0,1 mm and 0,5 mm, more preferably between 0, 15 mm and 0,3 mm, such as 0,175 mm or 0,250 mm. This thickness includes the thickness of the carrier layer. As will be appreciated by those skilled in the art, the carrier layer in the electrically conductive layer can be an optically transparent second sheet made of a plastic or a glass as defined hereinbefore or hereinafter such that further addition of such a layer, although still possible, can be dispensed with.

In a preferred embodiment, the photochromic optically transparent electrically conductive film laminate as defined hereinbefore can further comprise an optically transparent first sheet made of a plastic or a glass bonded to the self-supporting photochromic polymer film and/or an optically transparent second sheet made of a plastic or a glass bonded to the optically transparent electrically conductive layer. In this embodiment, the photochromic optically transparent electrically conductive film laminate comprises the following layers in the following order:

(1 ) optically transparent first sheet;

(2) self-supporting photochromic polymer film;

(3) optically transparent electrically conductive layer; and

(4) optically transparent second sheet.

In another preferred embodiment, the photochromic optically transparent electrically conductive film laminate as defined hereinbefore can further comprise, in addition to the optically transparent first sheet made of a plastic or a glass, a third optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating bonded to the optically transparent first sheet and/or, in addition to the optically transparent second sheet made of a plastic or a glass, a fourth optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating bonded to the optically transparent second sheet. In this embodiment, the photochromic optically transparent electrically conductive film laminate comprises the following layers in the following order:

(1a) third optically transparent layer;

(1 ) optically transparent first sheet;

(2) self-supporting photochromic polymer film;

(3) optically transparent electrically conductive layer;

(4) optically transparent second sheet; and

(4a) fourth optically transparent layer.

In a preferred embodiment, the optically transparent first sheet and/or the optically transparent second sheet are made of plastic, wherein the plastic is an optical grade plastic, more preferably an optical grade polycarbonate or an optical grade polymethylmethacrylate, even more preferably an optical grade polycarbonate based on the precursor monomer bisphenol A.

In another preferred embodiment, the optically transparent first sheet and/or the optically transparent second sheet are made of glass, wherein the glass is an optical glass, more preferably a float glass, even more preferably a soda-lime glass. Embodiments wherein the optically transparent first sheet and the optically transparent second sheet are different, such as for example a glass layer and a plastic layer, are encompassed by the invention.

The optically transparent first sheet and/or the optically transparent second sheet preferably have a total luminous transmittance of at least 85% and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013).

Embodiments wherein the third optically transparent layer and the fourth optically transparent layer are different are encompassed by the invention. In an embodiment, the third optically transparent layer is an anti-scratch coating whereas the fourth optically transparent layer is an anti-fog coating.

In a very preferred embodiment, all layers (1a) to (4a) are present.

The optically transparent electrically conductive film laminate as defined hereinbefore preferably has a total thickness of between 0,75 mm and 6,50 mm, more preferably between 0,75 mm and 2,60 mm, even more preferably between 0,75 mm and 1 ,00 mm, most preferably about 0,80 mm.

The optically transparent electrically conductive film laminate as defined hereinbefore preferably has a total luminous transmittance of at least 85% and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013) in an inactivated state.

In an embodiment, the optically transparent electrically conductive film laminate as defined hereinbefore is a flat laminate. In another embodiment, the optically transparent electrically conductive film laminate as defined hereinbefore is a curved laminate having a concave surface and a convex surface.

The optically transparent electrically conductive film laminate as defined hereinbefore preferably has two electrical connections, such as busbars, attached to the optically transparent electrically conductive film for connection to a power source. Preferably, the two electrical connections, such as busbars, are applied on opposite sides of the optically transparent electrically conductive film. As will be appreciated by those skilled in the art, the individual electrical connections, such as busbars, must not be in direct contact and are preferably applied along the perimeter of the optically transparent electrically conductive film such that homogeneous heating of the optically transparent electrically conductive film laminate in between the busbars is accomplished.

In an embodiment, the optically transparent electrically conductive film laminate as defined hereinbefore comprises means, e.g. screws or bolts, for attaching the laminate to an article.

In an embodiment, the optically transparent electrically conductive film laminate as defined hereinbefore comprises, mutatis mutandis, the self-supporting photochromic polymer film sandwiched between two optically transparent electrically conductive layers as defined hereinbefore.

In this embodiment, the photochromic optically transparent electrically conductive film laminate can comprise the following layers in the following order:

(1 ) optically transparent first sheet;

(3b) optically transparent electrically conductive layer;

(2) self-supporting photochromic polymer film;

(3a) optically transparent electrically conductive layer; and

(4) optically transparent second sheet. Alternatively, in this embodiment, the photochromic optically transparent electrically conductive film laminate can comprise the following layers in the following order:

(1a) third optically transparent layer;

(1 ) optically transparent first sheet;

(3b) optically transparent electrically conductive layer;

(2) self-supporting photochromic polymer film;

(3a) optically transparent electrically conductive layer;

(4) optically transparent second sheet; and

(4a) fourth optically transparent layer.

Method for producing an optically transparent electrically conductive film laminate

In a second aspect the invention relates to a method for producing an optically transparent electrically conductive film laminate, comprising the steps of:

b) providing one or more organic T-type photochromic compounds;

c) providing a solvent selected from the group of ketones;

i) optionally bonding at least part of the self-supporting photochromic polymer film obtained in step (h) to a first surface of an optically transparent first sheet made of a plastic or a glass;

j) optionally bonding at least part of the optically transparent electrically conductive layer obtained in step (h) or (i) to a first surface of an optically transparent second sheet made of a plastic or a glass;

k) optionally bonding at least part of a second surface of the optically transparent first sheet obtained in step (i) or in steps (i) and (j) to, or coating at least part of a second surface of the optically transparent first sheet obtained in step (i) or in steps (i) and (j), with a third optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating; and I) optionally bonding at least part of a second surface of the optically transparent second sheet obtained in step (j) or in steps (j) and (k) to, or coating at least part of a second surface of the optically transparent second sheet obtained in step (j) or in steps (j) and (k), with a fourth optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating.

The thermoplastic polyurethane film used in step (a) is preferably chosen from the group consisting of aliphatic thermoplastic polyurethane films, more preferably from aliphatic polyester-based and aliphatic polyether-based thermoplastic polyurethane films.

In a very preferred embodiment, the thermoplastic polyurethane film used in step (a) is an aliphatic thermoplastic polyurethane film based on an aliphatic diisocyanate selected from 1 ,4-tetramethylene diisocyanate, 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate, 1 , 12-dodecamethylene diisocyanate, cyclohexane-1 ,3-diisocyanate, cyclohexane-1 ,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, isophorone diisocyanate, 5-isocyanato-1-(isocyanatomethyl)-1 ,3,3- trimethylcyclohexane, bis-(4-isocyanatocyclohexyl)-methane, 2,4’-dicyclohexylmethane diisocyanate, 1 ,3-bis(isocyanatometyl)-cyclohexane, 1 ,4-bis(isocyanatometyl)-cyclohexane, bis-(4-isocyanato-3- methylcyclohexyl)-methane, a,a,a’,a’-tetramethyl-1 ,3-xylylen diisocyanate, a,a,a’,a’-tetramethyl-1 ,4- xylylen diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof, preferably selected from 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate, and mixtures thereof.

The thickness of the thermoplastic polyurethane film provided for in step (a) is preferably between 0,05 mm and 6,50 mm, more preferably between 0,08 mm and 2,60 mm, even more preferably between 0,09 mm and 0,68 mm, such as about 0, 1 mm, about 0,38 mm or about 0,63 mm.

The one or more organic T-type photochromic compounds provided for in step (b) are preferably selected from the group consisting of spiropyrans, spirooxazines, naphthopyrans and combinations thereof, more preferably from the group consisting of spirooxazines, naphthopyrans and combinations thereof. Examples of these organic T-type photochromic compounds are, for example, described in M.A. Chowdhury et al. , Journal of Engineered Fibers and Fabrics, 9(1 ) (2014), pp 107-123, which is incorporated by reference herein in its entirety.

More preferably, the one or more organic T-type photochromic compounds provided for in step (b) are selected from polydialkylsiloxane-substituted naphthopyrans, still more preferably from polydialkylsiloxane-substituted naphthopyrans capable of taking on a blue colour or a green colour when irradiated with ultraviolet radiation.

Polydialkylsiloxane-substituted naphthopyrans are for example described in US8,865,029B2, i.e. the photochromic molecules outlined in Example 3, column 46, line 42 to column 50, line 2, Example 4, column 50, line 4 to column 51 line 4, Example 6, column 62, line 50 to column 53, line 30, Example 7, column 53, line 32 to column 54, line 20, and Example 9, column 57, line 50 to column 63, line 20.

Polydialkylsiloxane-substituted naphthopyrans, sufficiently soluble in e.g. cyclohexanone at room temperature, are for example Reversacol Pennine Green, Reversacol Sea Green and Reversacol Humber Blue (Vivimed Labs Ltd).

In a very preferred embodiment, at least two organic T-type photochromic compounds are provided for in step (b).

Preferred organic T-type photochromic compounds are activated upon exposure to radiation having a wavelength of between 360 nm and 450 nm, preferably between 360 and 400 nm, such as about 380 nm or between 370 nm and 390 nm, or between 360 and 380 nm.

Step (c)

It is to be understood that the term‘solvent’ in step (c) also encompasses mixtures of solvents selected from the group of ketones, as long as the different solvents are mutually soluble at a temperature of between 15°C and 30°C.

The solvent selected from the group of ketones provided for in step (c) is preferably selected from the group consisting of straight-chain ketones, branched ketones, unsubstituted cyclic ketones, cyclic ketones substituted with at least one alkyl group and mixtures thereof. More preferably, the solvent selected from the group of ketones provided for in step (c) is selected from the group consisting of straight-chain ketones, unsubstituted cyclic ketones and mixtures thereof.

In a particularly preferred embodiment, the solvent selected from the group of ketones provided for in step (c) is selected from the group consisting of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3-one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4- methylpentan-2-one, 4-methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2- cyclohexene-1-one, 5-methylhexan-2-one, 1-cyclohexylpropan-1-one, 1-cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one and mixtures thereof, even more preferably the solvent is selected from propan-2-one and cyclohexanone, most preferably the solvent is cyclohexanone.

Step (d)

In step (d), a solution is prepared by dissolving at least 0, 1 wt%, based on the weight of the solution, of the one or more organic T-type photochromic compounds of step (b) in the solvent selected from the group of ketones of step (c). In a preferred embodiment, in step (d), a solution is prepared by dissolving at least 0, 1 wt%, based on the weight of the solution, of each of the one or more organic T- type photochromic compounds of step (b) in the solvent selected from the group of ketones of step (c). In another preferred embodiment, at least 0,5 wt% or about 0,5 wt%, based on the weight of the solution, of each of the one or more organic T-type photochromic compounds of step (b) is dissolved in the solvent selected from the group of ketones of step (c). As will be appreciated by those skilled in the art, solubility of the one or more organic T-type photochromic compounds depends on temperature. Hence, the concentration of the one or more organic T-type photochromic compounds in the solution of step (d) should preferably be lower than the solubility limits of the one or more organic T-type photochromic compounds at the temperature applied in step (e).

Step (e)

In step (e), at least part of at least the first surface of the thermoplastic polyurethane film of step (a) is treated with at least 100 g/m², preferably at least 200 g/m², more preferably at least 400 g/m², of the solution of step (d) for a period of at least 5 seconds at a temperature between 15 and 30°C, more preferably for a period of at least 40 seconds, even more preferably for a period of at least 60 seconds.

The unit‘m²’ relates to the surface area of the thermoplastic polyurethane film that is treated with the solution of step (d) and not to the complete surface area including any part that is not treated.

In a preferred embodiment, the whole first surface of the thermoplastic polyurethane film of step (a) is treated.

In another embodiment, both surfaces of the thermoplastic polyurethane film of step (a) are treated. This can for example be performed by completely immersing the polyurethane film of step (a) in the solution of step (d).

As explained in more detail in the experimental section, the treatment of the thermoplastic polyurethane film in step (e) with the solution prepared in step (d) results in swollen or plasticized areas where the surface of the thermoplastic polyurethane film is treated. This swelling is caused by the solvent selected from the group of ketones penetrating the thermoplastic polyurethane film along with the dissolved one or more organic T-type photochromic compounds. As a result, the one or more organic T-type photochromic compounds, and the solvent, are distributed across at least part of the thickness of the thermoplastic polyurethane film. As will be appreciated by those skilled in the art, if the thickness of the film is limited, and/or if both sides of the thermoplastic polyurethane film are treated and/or if the period of treatment is extended, the one or more organic T-type photochromic compounds and the solvent can be distributed across the whole thickness of the thermoplastic polyurethane film.

In a preferred embodiment, the one or more organic T-type photochromic compounds and the solvent, are homogeneously distributed across at least part of the thickness of the thermoplastic polyurethane film. In another preferred embodiment, the one or more organic T-type photochromic compounds and the solvent, are homogeneously distributed across the whole thickness of the thermoplastic polyurethane film.

The self-supporting photochromic polymer film obtained in any one of steps (e) to (g) preferably has a thickness of between 0,05 mm and 6,50 mm, more preferably between 0,08 mm and 2,60 mm, even more preferably between 0,09 mm and 0,68 mm, such as about 0,1 mm, about 0,38 mm or about 0,63 mm.

One of the benefits of the method of the invention is the omission of a curing step after applying the photochromic compound. Current methods for producing photochromic films require such a cumbersome /^'.e. , time- and material-consuming, additional curing step for the provision of photochromic film suitable for inclusion in laminate articles. Steps (f) and (g)

Before applying the bonding of at least part of an optically transparent electrically conductive layer to a surface of the self-supporting photochromic polymer film in step (h), the amount of the solvent selected from the group of ketones is preferably between 0 and 12 wt%, based on the weight of the self- supporting photochromic polymer film, more preferably between 0 and 8 wt%, even more preferably between 0 and 5 wt%, still more preferably between 0 and 3 wt%, most preferably about 0 wt%, such as 0 wt%.

Reduction of the amount of solvent selected from the group of ketones in the self-supporting photochromic polymer film to about 0 wt% prevents or reduces blistering in laminates prepared from the self-supporting photochromic polymer film.

In another embodiment, before applying the bonding of at least part of an optically transparent electrically conductive layer to a surface of the self-supporting photochromic polymer film in step (h), the amount of the solvent selected from the group of ketones is between 0, 1 and 12 wt%, based on the weight of the self-supporting photochromic polymer film, preferably between 0, 1 and 8 wt%, more preferably between 0, 1 and 5 wt%, still more preferably between 0, 1 and 3 wt%.

In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (f) as a mandatory step. Step (f) can for example be performed by wiping the excess of the solution applied in step (e) from the surface of the self-supporting photochromic polymer film obtained in step (e). Alternatively, the excess of the solution applied in step (e) can for example be removed by rubbing the surface with an absorbing cloth.

In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (g) as a mandatory step, more preferably steps (f) and (g). The drying of the self-supporting photochromic polymer film in step (f) is preferably performed in a hot air circulating oven, preferably at a temperature of between 45 and 75°C. In a very preferred embodiment step (g) is performed to reduce the weight percentage of solvent in the self-supporting photochromic polymer film to between 0 and 12 wt%, based on the weight of the self- supporting photochromic polymer film, more preferably between 0 and 8 wt%, even more preferably between 0 and 5 wt%, still more preferably between 0 and 3 wt%, most preferably about 0 wt%, such as 0 wt%.

In another embodiment step (g) is performed to reduce the weight percentage of solvent in the self-supporting photochromic polymer film to between 0,1 and 12 wt%, based on the weight of the self- supporting photochromic polymer film, preferably between 0, 1 and 8 wt%, more preferably between 0,1 and 5 wt%, even more preferably between 0,1 and 3 wt%.

Preferably, before bonding the optically transparent electrically conductive layer and the self- supporting photochromic polymer film in step (h), electrical connections, such as busbars, are attached to the surface of the optically transparent electrically conductive film. The electrical connections can for example be applied by means of screen printing or aerosol jet printing. Preferably, the two electrical connections, such as busbars, are applied on opposite sides of the optically transparent electrically conductive film. As will be appreciated by those skilled in the art, the individual electrical connections, such as busbars, must not be in direct contact and are preferably applied along the perimeter of the optically transparent electrically conductive film such that homogeneous heating of the optically transparent electrically conductive film laminate in between the busbars is accomplished.

Step (h)

The bonding in step (h) is preferably performed by laminating the optically transparent electrically conductive layer and the self-supporting photochromic polymer film obtained in any one of steps (e) to (g) in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes.

Before the bonding in step (h), the layers are preferably dried at a temperature of about 60°C, for about 8 hours.

In a very preferred embodiment, the self-supporting photochromic polymer film obtained in any one of steps (e) to (g) has the same surface area and the same two-dimensional form as the optically transparent electrically conductive layer and bonding in step (h) encompasses the whole contact area.

In a very preferred embodiment, the optically transparent electrically conductive layer is bonded to the side of the self-supporting photochromic polymer film that has been treated with the solution in step (e).

The optically transparent electrically conductive layer preferably has a sheet resistance of between 10 W/square and 120 W/square, more preferably between 40 W/square and 100 W/square, even more preferably between 50 W/square and 70 W/square, most preferably about 60 W/square.

Examples of particularly preferred optically transparent electrically conductive layers that can be applied in step (h) are selected from the group consisting of a carbon nanobud polycarbonate film, a layer of silver nanowires in a transparent mouldable glue, and a PEDOT-PSS layer on a carrier film.

Optically transparent electrically conductive layers can for example be produced by printing, such as ink jet printing or screen printing, conductive ink on a carrier layer.

The carrier film for the optically transparent electrically conductive layers can be made of polycarbonate or polyethylene terephthalate.

Most preferably, the electrically conductive layer applied in step (h) is a carbon nanobud polycarbonate film. In this respect, reference is made to W02009/056686A1 , disclosing transparent carbon nanobud materials.

The optically transparent electrically conductive layer preferably has a thickness of between 0, 1 mm and 0,5 mm, more preferably between 0, 15 mm and 0,3 mm, such as 0,175 mm or 0,250 mm. This thickness includes the thickness of the carrier layer. As will be appreciated by those skilled in the art, if the carrier layer in the electrically conductive layer is an optically transparent second sheet made of a plastic or a glass as defined hereinbefore or hereinafter, step (j) is not necessary, although it can still be performed as additional step. In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (i) as a mandatory step.

The bonding in step (i) is preferably performed by laminating the self-supporting photochromic polymer film obtained in step (h) and the optically transparent first sheet in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes.

Before the bonding in step (i), the layers are preferably dried at a temperature of about 60°C, for about 8 hours.

The self-supporting photochromic polymer film does not require any pre-preparation before being applicable for adhering to common transparent materials applied in for example construction, visors, glasses, lenses, car windows, et cetera. That is to say, the self-supporting photochromic polymer film adheres to sheets or foils or films of materials known in the art of photochromism.

In a very preferred embodiment, the self-supporting photochromic polymer film obtained in step (h) has the same surface area and the same two-dimensional form as the optically transparent first sheet and bonding in step (i) encompasses the whole contact area.

In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (j) as a mandatory step, more preferably steps (i) and (j).

The bonding in step (j) is preferably performed by laminating the optically transparent electrically conductive layer obtained in step (h) or (i) and the optically transparent second sheet in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes.

Before the bonding in step (j), the layers are preferably dried at a temperature of about 60°C, for about 8 hours.

In a very preferred embodiment, the optically transparent electrically conductive layer obtained in step (h) or (i) has the same surface area and the same two-dimensional form as the optically transparent second sheet and bonding in step (j) encompasses the whole contact area.

In a preferred embodiment, the optically transparent first sheet applied in step (i) and/or the optically transparent second sheet applied in step (j) are made of plastic, wherein the plastic is an optical grade plastic, more preferably an optical grade polycarbonate or an optical grade polymethylmethacrylate, even more preferably an optical grade polycarbonate based on the precursor monomer bisphenol A.

In another preferred embodiment, the optically transparent first sheet applied in step (i) and/or the optically transparent second sheet applied in step (j) are made of glass, wherein the glass is an optical glass, more preferably a float glass, even more preferably a soda-lime glass. Embodiments wherein the optically transparent first sheet applied in step (i) and the optically transparent second sheet applied in step (j) are different, such as for example a glass layer and a plastic layer, are encompassed by the invention.

The optically transparent first sheet applied in step (i) and/or the optically transparent second sheet applied in step (j) preferably have a total luminous transmittance of at least 85% and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013).

In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (i) and (k) as mandatory steps.

The bonding in step (k) is preferably performed by laminating the optically transparent first sheet obtained in step (i) and the third optically transparent layer in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes.

Before the bonding in step (k), the layers are preferably dried at a temperature of about 60°C, for about 8 hours.

In another preferred embodiment, the optically transparent first sheet in step (i) and the third optically transparent layer are bonded by coating the third optically transparent layer onto the optically transparent first sheet obtained in step (i).

In a very preferred embodiment, the optically transparent first sheet obtained in step (i) has the same surface area and the same two-dimensional form as the third optically transparent layer and bonding in step (k) encompasses the whole contact area.

In a preferred embodiment the method for producing an optically transparent electrically conductive film laminate as defined hereinbefore comprises step (j) and (I) as mandatory steps, more preferably steps (i), (j), (k) and (I).

The bonding in step (I) is preferably performed laminating the optically transparent second sheet obtained in step (j) and the fourth optically transparent layer in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes.

In another preferred embodiment, the optically transparent second sheet in step (j) and the fourth optically transparent layer are bonded by coating the fourth optically transparent layer onto the optically transparent second sheet obtained in step (j).

In a very preferred embodiment, the optically transparent second sheet obtained in step (j) has the same surface area and the same two-dimensional form as the fourth optically transparent layer and bonding in step (I) encompasses the whole contact area. Embodiments wherein the third optically transparent layer applied in step (k) and/or the fourth optically transparent layer applied in step (I) are different are encompassed by the invention. In an embodiment, the third optically transparent layer is an anti-scratch coating whereas the fourth optically transparent layer is an anti-fog coating.

In a very preferred embodiment, all steps (a) to (I) are mandatory.

The different bonding steps need not necessarily be separate steps. Steps (h) to (j) or (h) to (I) can also be performed in a single lamination step, for example in an autoclave at a temperature of between 90°C and 130°C, such as 120°C, and at a pressure of between 8 bar and 15 bar, such as 10 bar, for a period of time of at least 60 minutes, more preferably for a period of time of at least 90 minutes. Before the single lamination step is applied, the separate layers are preferably dried at a temperature of about 60°C, for about 8 hours.

Steps (i) and (k) can be taken together by using an optically transparent first sheet in step (i) that is already bonded to the third optically transparent layer. Likewise, steps (j) and (I) can be taken together by using an optically transparent second sheet in step (j) that is already bonded to the fourth optically transparent layer.

In an embodiment, the method as defined hereinbefore comprises, mutatis mutandis, in step (h) laminating the self-supporting photochromic polymer film obtained in any one of steps (e) to (g) between two optically transparent electrically conductive layers.

The optically transparent electrically conductive film laminate obtained by the method as defined hereinbefore preferably has a total thickness of between 0,75 mm and 6,50 mm, more preferably between 0,75 mm and 2,60 mm, even more preferably between 0,75 mm and 1 ,00 mm, most preferably about 0,80 mm.

The optically transparent electrically conductive film laminate obtained by the method as defined hereinbefore preferably has a total luminous transmittance of at least 85 % and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013).

In an embodiment, the optically transparent electrically conductive film laminate as obtained by the method as defined hereinbefore is a flat laminate. In an additional process step, the flat laminate can be transformed into a three-dimensional form, such as a curved laminate having a concave surface and a convex surface.

In a third aspect, the invention relates to an optically transparent electrically conductive film laminate obtained by or obtainable by the method as defined hereinbefore. It was found by the inventors that the method of the invention provides an optically transparent electrically conductive film laminate comprising a self-supporting photochromic film that has a homogeneous distribution of the one or more organic T-type photochromic compounds across at least part of the thickness of the film and further does not yellow upon exposure to e.g. ultraviolet light and xenon light. Thus, the optically transparent electrically conductive film laminate obtainable by the method of the invention retains its transparency upon exposure to light, which is beneficial to the life time of the film when applied for its photochromic activity.

In a fourth aspect, the invention relates to an optical article (i) comprising the optically transparent electrically conductive film laminate as defined hereinbefore or (ii) comprising the optically transparent electrically conductive film laminate obtained by or obtainable by the method as defined hereinbefore. The optical article is preferably selected from the group consisting of visors, goggles, ophthalmic lenses, sunglasses, face-shields, architectural windows, automotive windows, and aeronautic windows.

The optical article can further be combined with a power source connected to electrical connections attached to the surface of the optically transparent electrically conductive film. The optical article can further be combined with a light sensor and a processor for setting or adjusting the voltage over the optically transparent electrically conductive film to induce heating of the self-supporting photochromic film if the surrounding light of the optical article diminishes.

Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

All embodiments of the invention described hereinbefore can be combined, unless specified otherwise.

Furthermore, for a proper understanding of this document and its claims, it is to be understood that the verb‘to comprise’ and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

In addition, reference to an element by the indefinite article‘a’ or‘an’ does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article‘a’ or‘an’ thus usually means‘at least one’.

EXAMPLES

Example 1: preparation of self-supporting photochromic polymer films

A series of self-supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminate according to the invention were prepared as follows.

Aliphatic thermoplastic polyurethane films S123 and S158, obtained from PPG-Sierracin/Sylmar Corp. (Sylmar, USA), were provided. The aliphatic thermoplastic polyurethane sheets S123 and S158 have the following characteristics, respectively, as determined by the manufacturer. Specific gravity (g/cc; test method ASTM D-792-2013) of 1 ,08 and 1 ,08; shore hardness of 80 A and 64 A (test method ASTM D-2240-2015); tensile strength at 25°C of 6200 psi (42,75 MPa) and 3400 psi (23,44 MPa) (test method ASTM D-412C); modulus at 100% elongation at 25°C of 530 psi (3,54 MPa) and 370 psi (2,55 MPa) (test method ASTM D-412C); modulus at 300% elongation at 25°C of 1700 psi (1 1 ,72 MPa) and 740 psi (5, 10 MPa) (test method ASTM D-412C); ultimate elongation at 25°C of 620% and 860% (test method ASTM D-412C); tear strength at 25°C of 320 pli (kN/m) and 260 pli (test method ASTM D-624C), for S123 and for S158, respectively (all values are nominal values). Transmission of ultraviolet radiation is 10% and transmission of visible light is 85%. The films used had a size of about 1 m x 1 m and thicknesses of about 0,38 mm, 0,63 mm and 0,68 mm.

The films of about 1 m x 1 m were immersed at room temperature in about 400-450 ml of varying solutions of different organic T-type photochromic compounds in different ketone solvents, i.e. both sides of the films were fully treated with the different solutions. The different ketone solvents used were cyclohexanone and acetone.

The organic T-type photochromic compounds applied were Pennine Green, Humber Blue and combinations thereof, and Sea Green. Pennine Green and Humber Blue and Sea Green are polydialkylsiloxane-substituted naphthopyrans, sold under the trademark Reversacol Photochromic dyes by Vivimed Labs Europe Ltd (Yorkshire, England). The Reversacol photochromic dyes were provided by the manufacturer as single-molecule neutral gray photochromic compounds in the form of a fine crystalline powder.

The concentration of the organic T-type photochromic compounds in the ketone solution was about 0,5 wt%, based on the weight of the solution, for each organic T-type photochromic compound present in the solution. Obviously, alternative organic T-type photochromic compounds known in the art, which are soluble to a similar extent as the currently applied organic T-type photochromic compounds, are equally applicable in the self-supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminate according to the invention.

All solutions of organic T-type photochromic compounds in the ketone solvents applied were clear, indicating complete dissolution.

The immersed films were subsequently dried to varying extents in a hot-air oven for about 90 minutes at a temperature of about 60°C to obtain varying residual weight percentages of ketone solvent in the self-supporting photochromic polymer films, based on the weight of the self-supporting photochromic polymer film. Obviously, alternative known methods for drying an immersed film are equally applicable. In Table 1 , an overview is provided of the series of self-supporting photochromic polymer films prepared.

In several comparative examples, photochromic polymer films not for application in the photochromic optically transparent electrically conductive film laminate according to the invention were produced using solvents other than ketones, namely isopropanol, toluene or tetrahydrofuran. In Table 2, an overview is provided of the photochromic polymer films of the comparative examples.

It was observed that the thermoplastic polyurethane films of the comparative examples CA, CB, CC, CD were not suitable as self-supportive photochromic polymer films. The organic T-type photochromic compounds did not dissolve properly in the solvent (e.g. comparative example CA and CB), and/or the resulting film did not remain sufficiently self-supporting, and/or the resulting film was stained to an unacceptable extent after immersion in solvent and subsequent drying thereafter, to name a few disadvantages of the use of isopropanol or tetrahydrofuran as solvents for dissolving the organic T-type photochromic compounds. Furthermore, with the solvents tetrahydrofuran and toluene, it was observed that the organic T-type photochromic compounds did dissolve to a sufficient extent, e.g. at least 0,5 wt% based on the weight of the solution, however, the tetrahydrofuran and toluene did not exert a plasticizing effect on the thermoplastic polyurethane film. Thus, immersion of the thermoplastic polyurethane film in tetrahydrofuran (comparative example CD) or in toluene (comparative example CC) did not beneficially result in a decreased value for the glass transition temperature T_g (Tan Delta), and/or did not beneficially result in a decreased value for the storage modulus, as is seen with the self- supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminate according to the invention. Therefore, the comparative polymer films were not subsequently tested in e.g. a set-up for determining the T_g.

After immersion of the thermoplastic polyurethane films detailed in Table 1 and the subsequent drying step, the flexibility of the obtained self-supporting photochromic films was improved compared to the untreated thermoplastic polyurethane films. The immersion in the ketone solvent improved the flexibility, when some ketone remained in the thermoplastic polyurethane film after drying, and the ketone acted as a plasticizer for the thermoplastic polyurethane films. It was further observed that immersion of the thermoplastic polyurethane films in the ketone solutions resulted in increased surface smoothness of the thermoplastic polyurethane films tested, as determined after drying of the films. The step of treating the thermoplastic polyurethane films with the ketone solution can also be conducted by subjecting a thermoplastic polyurethane film to a roll-to-roll process, known in the art. Also the subsequent step of drying the thus treated film, is applicable in such a roll-to-roll process.

Typically, the Young’s modulus of the self-supporting polymer films listed in Table 1 was below 10 MPa, typically 5 MPa or lower, such as 4 MPa or lower (ISO 527 [527-1 :2012; 527-2:2012; 527- 3: 1995; 527-4: 1997; 527-5:2009; ASTM D412, type C:2016).

The self-supporting photochromic polymer films listed in Table 1 for application in the photochromic optically transparent electrically conductive film laminates according to the invention were transparent or semi-transparent or opaque. All tested films turned transparent under influence of pressure and increased temperature, as observed after applying pressure and heat to the films in a heated film press. Transparent is here to be understood as a light transmission of at least 80% for light with a wavelength of between 400 nm and 750 nm. Several self-supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminates according to the invention, i.e. examples Z, AA and CC from Table 1 , were subjected to a pressure of 8 bar for 10 minutes at 140°C, resulting in transparent films.

Using a card press laminator (Oasys) known in the art, it was seen that self-supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminates according to the invention, i.e. examples Z, AA and CC from Table 1 , adhered to sheets of various materials commonly applied in the manufacturing of car windows, windows, glasses, devices and visors. For example, when applying a pressure of 8 bar for 10 minutes at 140°C on a self- supporting photochromic polymer film listed in Table 1 embedded in between two layers of such here aforementioned materials known in the art, good adherence of the films to said materials was obtained. For example, when applying a pressure of 15 bar for 1 second at 140°C on the self-supporting photochromic polymer film of example Z or example AA embedded in between two layers of such here aforementioned material known in the art, good adherence was obtained.

It was observed that self-supporting photochromic polymer films comprising a combination of Pennine Green and Humber Blue turned into a relatively dark brown colour upon exposure to ultraviolet radiation.

Self-supporting photochromic polymer films Z, AA and BB (see Table 1 ) were subjected to standardized Dynamic Mechanical Analysis (DMA) according to a set-up and procedures known in the art (ISO 6721 [6721-1 :201 1 ; 6721-2:2008; 6721-3:1994; 6721-4:2008; 6721-5: 1996; 6721-6: 1996; 6721-7: 1996; 6721-8: 1997; 6721-9: 1997; 6721-10:2015; 6721-1 1 :2012; 6721-12:2009]; Dynamic Mechanical Thermal Analysis, DMTA). For these three examples and for a S123 thermoplastic polyurethane film that was not treated with ketone solvent (control measurement for obtaining a reference value), the storage modulus between -80°C and 100°C was determined in MPa.

The loss modulus in the same temperature range was determined as well as the Tan Delta value for determining the glass-transition temperature, T_g (temperature was ramped at 3 Kelvin/minute, the set frequency was 1 Hz, the amplitude was 10 micrometer, the preload was 0,01 N). Samples of the self-supporting photochromic polymer films subjected to DMA were analyzed in tensile mode. These samples and the control reference film had a size of about 3 cm x about 4 cm at minimum. For the reference sample, the T_g was 12°C (Tan Delta). For Examples Z, AA and BB, the values for T_g were 16°C, 7°C and -1 °C, respectively. In similar analyses with thermoplastic polyurethane films obtained after immersion in cyclohexanone such that about 8% cyclohexanone was imbibed in the thermoplastic polyurethane film, based on the weight of the self-supporting photochromic polymer film, the T_g was comparable with the value obtained for example BB.

From these measurements and from further performed analyses with further examples of self- supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminates according to the invention, it is seen that the presence of ketone solvent in the self-supporting photochromic polymer films lowers the T_g, therewith inducing a softening of the thermoplastic polyurethane film applied in the method of the invention. The ketone solvent thus beneficially serves as a plasticizer. The plasticizing effect of the ketone solvent is further demonstrated by assessing the storage modulus for the examples Z, AA, BB and for the reference sample. With increasing weight percentage of imbibed ketone in the thermoplastic polyurethane film, the storage modulus expressed in MPa decreases between -80°C and 20°C and is 0 MPa for all samples tested at temperatures above about 20°C. For example, for example Z (0 wt% cyclohexanone in the film), the storage modulus is about 1400 MPa at -40°C, whereas the storage modulus at -40°C is about 800 MPa for example BB (10 wt% cyclohexanone in the film, all other things being equal).

In the DMA, a peak value for the loss modulus in MPa was measured for examples Z, AA and BB and the sample, at a temperature of about -43°C. It was observed that the loss modulus for example Z was similar to that of the reference sample, i.e. about 1800 MPa at about -43°C. However, the examples AA and BB, with 3 wt% and 10 wt% cyclohexanone in the thermoplastic polyurethane film, respectively after immersion and drying, showed an increased loss modulus up to about 2200 MPa and 2300 MPa at about -43°C. These data further show that immersion of the thermoplastic polyurethane film with a ketone induces an increase in the flexibility of the polymer material, thus the ketone acts as a plasticizer.

When cyclohexanone was replaced with acetone in the method of the invention, similar results were obtained.

Several self-supporting photochromic polymer films listed in Table 1 were laminated in between layers of various materials commonly applied in manufacturing of car windows, windows, glasses, devices, visors, et cetera. , by using an Oasys card press laminator, at for example 140°C, 8 bar for 10 minutes or at 135°C, 10 bar for 120 seconds, or by using an autoclave at 1 10°C, 8 bar for 4 hours.

For example, examples T, U, V, Z, AA, CC, DD, EE, FF and GG (see Table 1 ) were laminated in between two layers of various transparent materials commonly applied in car windows, construction, etc. For each separate experiment, the two sheets of material used for sandwiching the self-supporting photochromic polymer film were made of the same transparent material, or were made of two different materials (see Table 3).

The materials used for sandwiching the self-supporting photochromic polymer films were: i) soda-lime glass (AGC Nederland, Tiel Netherlands); ii) 0, 175 mm Lexan HP92W, polycarbonate foil with an UV-absorbing hard-coat (Sabic Innovative Plastics BV, Bergen op Zoom, Netherlands); and

iii) 0, 175 mm Lexan 8010MC, polycarbonate foil with UV-absorber in the foil (Sabic Innovative Plastics BV, Bergen op Zoom, Netherlands)

For the sandwiched self-supporting photochromic polymer films, the values for L, a and b were determined, according to standard procedures commonly applied in the art (CIELABS, 1976).

Initial colouring of the sandwiched self-supporting photochromic polymer films was measured using a spectrophotometer, when the sample had not yet been exposed to light. After the initial spectrophotometer measurement, the decay half time was measured when the sample had been exposed to light. This was done using the following method, according to the steps:

1. An initial measurement is done in a spectrophotometer before the sample is exposed to light to get initial Lab values.

2. After measurement of step 1., the spectrophotometer is set up to be ready to measure the colour of the sample again as soon as the sample has been exposed to light;

3. The sample is exposed to light for 1 minute using a Heraeus Suntest CPS (Heraeus Holding GmbH, Hanau, Germany), or comparable suntest equipment, using a 1500 W air-cooled xenon lamp irradiating the sample at a wavelength of between 400-750 nm;

4. After 1 minute has passed in step 3, the sample is removed from the suntester and immediately placed in the spectrophotometer (t=0 sec); this measurement gives the activated Lab values of the sample;

5. The colour of the sample is measured at an interval of every 5 seconds till t=120 sec is reached, these measurements will determine the decay half time; and

6. Once t=120 sec the final measurement at t=240 sec is performed.

Results of these measurements are shown below in Table 3. Commercially available photochromic laminates for use in ophthalmic lenses were used as control samples. Control 1 is a commercially available insert for motor visor and control 2 is a Transitions® ophthalmic lens (Transitions Optical Inc., Florida, USA).

The initial L value of all samples was relatively high, indicating that the sandwiched self- supporting photochromic polymer films and controls 1-2 all had a light colour, as defined by CIELAB.

The decay half time of all sandwiched self-supporting photochromic polymer films was shorter than the decay half time of the Transitions® control sample (control 2). The sample with the strongest photochromic reaction was the Transitions® control sample followed by experimental sample 2, experimental sample 1 , experimental sample 3 and finally the sample with the weakest photochromic reaction was the insert for motor visor control sample.

The activated L values after exposure of the sandwiched self-supporting photochromic polymer films to light were all lower than the initial L values, expressed as a decrease in the order of a few tens of the CIELAB L value. This indicates that in all samples tested a photochromic reaction occurred. Notably, for the tested samples, the change in colour from an essentially white (colourless) appearance to an essentially (dark) grey to black appearance, was mainly dependent on the change in L value, with a relatively small contribution of the a, b values (See the data in Table 3). For example, for the self- supporting photochromic polymer film‘CC’, the change in L value was about 35, whereas the change in a, b was about 0,5 and about 2, upon UV irradiation of the film CC.

In a next series of tests, several of the self-supporting photochromic polymer films for application in the photochromic optically transparent electrically conductive film laminate according to the invention listed in Table 1 were sandwiched in between layers of two separate materials. Similar to the previous series of tests, described here above, the initial L, a, b values were measured and recorded for all test samples, before and after exposure of the sandwiched self-supporting photochromic polymer films to Xenon light source (ISO 1 1341 :2004). Decay half time in seconds was determined as well as the loss of photochromic activity expressed as the percentage of the initial photochromic activity that was lost after exposure of the test samples for 100 hours to the xenon light source (ISO 1 1341 :2004). Thus, a value for the loss of photochromic activity of 0% depicts no loss of activity. According to ISO 1 1341 :2004, these activities are calculated based on measured values for L. Test results are displayed in Table 4. For comparison, the same two control samples as were applied in the previous tests, displayed in Table 3, were also tested.

From the test results in Table 4, it is seen that the decay half time for the various tested sandwiched self-supporting photochromic polymer films is relatively short, and is even below 5 seconds for, for example examples Z, AA and CC. In fact, the decay half time was shorter than 5 seconds and was estimated at about 1 second. More importantly, the reference sample‘control T turned useless when exposed to the xenon radiation for 100 hours according to ISO 1 1341 :2004, since the laminate material turned completely yellow indicating severe decay or break down of the photochromic film and/or the sandwiching material(s). In contrast, the tested sandwiched self-supporting photochromic polymer films resisted the exposure to Xenon light for 100 hours to a significant extent, i.e. even up to 91 % (Table 4). Reference control 2, “Transitions ophthalmic lens 2 mm”, had a relatively long decay half time compared to the sandwiched self-supporting photochromic polymer films tested, and in addition, Reference control 2 turned yellow upon exposure to the Xenon light source.

Example 2: preparation of a photochromic optically transparent electrically conductive film laminates according to the invention

A photochromic optically transparent electrically conductive film laminate according to the invention was prepared at follows.

In a first step, a self-supporting photochromic polymer film was prepared by immersing an untreated S123 thermoplastic polyurethane film, 0,38 mm thick, about 10 by about 25 cm, obtained from PPG-Sierracin/Sylmar Corp. (Sylmar, USA), in a bath containing about 400-450 ml of cyclohexanone containing 0,5 wt% Reversacol Pennine Green (P.G.) and 0,5 wt% Reversacol Humber Blue (H.B.), based on the weight of the solution. Reversacol Pennine Green and Reversacol Humber Blue were obtained from Vivimed Labs Europe Ltd (Yorkshire, England). After about 60 seconds, the films were removed from the bath and left to dry in a hot air circulating oven, set at a temperature of 60°C, for about 8 hours. Under these conditions, a self-supporting photochromic polymer film was obtained from which substantially all cyclohexanone had evaporated.

In a second step, a carbon nanobud (CNB) coated polycarbonate (PC) film (CNB™ Free Form Film), 0,25 mm thick, obtained from Canatu Oy (Helsinki, Finland) was provided. This film had a sheet resistance of about 60 W/square, a luminous transmittance of at least 85% and a haze of lower than 1 % measured in accordance with ASTM D1003 - 2013. Electrical connections (bus bar silver line system) were already screen printed onto the CNB™ Free Form Film. The resulting film was dried in a hot air circulating oven, set at a temperature of 60°C, for about 8 hours, to prepare it for the lamination process.

In a third step, a hard coat Lexan™ HP92S PC film, 0, 175 mm thick, obtained from Sabic Innovative Plastics BV (Bergen op Zoom, Netherlands) was dried in a hot air circulating oven, set at a temperature of 60°C, for about 8 hours, to prepare it for the lamination process.

In a fourth step, the self-supporting photochromic polymer film obtained in the first step, the carbon nanobud polycarbonate film obtained in the second step and the dried hard coat Lexan™ HP92S PC film were combined such that the order of layers was as follows:

(i) hard coat Lexan™ HP92S PC film with hard coat side facing outwards and polycarbonate side facing the self-supporting photochromic polymer film;

(ii) self-supporting photochromic polymer film;

(iii) carbon nanobud polycarbonate film with bus bar silver line system and carbon nanobud side facing the self-supporting photochromic polymer film and polycarbonate side facing outwards. In a fifth step, the combined layer structure obtained in the fourth step was put in a vacuum bag and all air was sucked out of the bag.

In a sixth step, the vacuum bag containing the combined layer structure was placed in an autoclave from AkarMak (Eski§ehir, Turkey), in which the lamination process was completed at a temperature of 120°C and a pressure of 10 bar, for a period of about 90 minutes, to result in a photochromic optically transparent electrically conductive film laminate according to the invention.

The total luminous transmittance of the photochromic optically transparent electrically conductive film laminate in the inactivated state was at least 85 % and the haze was lower than 1 % (both measured in accordance with ASTM D1003 - 2013).

Example 3: photochromic back reaction of a photochromic optically transparent electrically conductive film laminate according to the invention

The speed of the photochromic back reaction of the photochromic optically transparent electrically conductive film laminate of Example 2 was measured by the following steps.

The photochromic optically transparent electrically conductive film laminate of Example 2, before exposure to direct sunlight, had an initial transparency.

The photochromic optically transparent electrically conductive film laminate of Example 2 was exposed to sunlight on a sunny day, by placing it outside in the direct light of the sun. The laminate was left under direct sunlight until the photochromic reaction had finished and the laminate had achieved its darkest activated state. Once the darkest activated state was achieved, a small section of the photochromic transparent conductive film laminate was connected to a 16V battery via the bus bar silver line system. A voltage was applied over said section of the photochromic transparent conductive film laminate and the bleaching of the laminate, as well as the temperature change, was captured in a motion video.

It was observed that the area of the optically transparent electrically conductive film laminate to which the current was applied reaches the initial transparency, corresponding to the inactivated state before exposure to direct sunlight, within 5 seconds of applying the current and that the temperature of said area raised to 50°C.

Example 4: analysis of thermoplastic polyurethane film treated with cyclohexanone and organic T-type photochromic compounds dissolved therein

A first thermoplastic polyurethane film with a thickness of 0,38 mm (PPG Aerospace - Argotec) was sprayed with a solvent consisting of cyclohexanone with 0,5 wt% of Reversacol Humber Blue and 0,5 wt% Reversacol Pennine Green, based on the total weight of the solution, dissolved therein. Subsequently, the thermoplastic polyurethane film was dried:“TPU-SPRAY”.

A second thermoplastic polyurethane film with a thickness of 0,38 mm (PPG Aerospace - Argotec) was immersed at ambient temperature in a solvent consisting of cyclohexanone with 0,5 wt% of Reversacol Humber Blue and 0,5 wt% Reversacol Pennine Green, based on the total weight of the solution, dissolved therein. Subsequently, the TPU film was dried:“TPU-IMBIBED”. The TPU-SPRAY and TPU-IMBIBED samples were subjected to exposure to UV light. It was observed that only the major surface of TPU-SPRAY onto which the organic T-type photochromic compounds were sprayed, showed a colour change from colourless to dark purple. Further, it was observed that TPU-IMBIBED was presented as a homogenously dark purple coloured film after exposure to UV light, indicative for evenly distributed photochromic dyes throughout the whole film in three dimensions. Optical micrographs were obtained in reflection using a Motic STEREO SMZ-168T- LED microscope, equipped with a MOTICAM 580 camera and LED top light. Further, it was observed that both the colouring of the TPU-IMBIBED film upon exposure to light and the subsequent discolouring occurred evenly throughout the whole volume of the film, further showing that the organic T-type photochromic compounds were homogenously and evenly distributed in the thermoplastic polyurethane film upon immersion of the film in cyclohexanone with the organic T-type photochromic compounds dissolved therein.

Example 5: photochromic back reaction of two photochromic optically transparent electrically conductive film laminates

The speed of the photochromic back reaction of two photochromic optically transparent electrically conductive film laminates, prepared similarly to the manufacturing of the laminates detailed in Example 2 was measured by the following steps. The differences were the application of different photochromic dyes. In a first photochromic optically transparent electrically conductive film laminate, the photochromic dye impregnated in the self-supporting photochromic TPU film is a spirooxazine. In a second photochromic optically transparent electrically conductive film laminate, the photochromic dye impregnated in the self-supporting photochromic TPU film is a combination of two siloxane naphtopyrans, i.e. Reversacol Pennine Green and Reversacol Humber Blue (Vivimed Labs Europe Ltd).

These two photochromic optically transparent electrically conductive film laminates, before exposure to direct sunlight, had an initial transparency.

The two photochromic optically transparent electrically conductive film laminates were exposed to sunlight on a sunny day, by placing it outside in the direct light of the sun. The laminates were left under direct sunlight until the photochromic reaction had finished and the laminate had achieved its darkest activated state. Once the darkest activated state was achieved, a small section of the photochromic transparent conductive film laminate was connected to a battery via the bus bar silver line system. A voltage of 17,6 V was applied over said section of the photochromic transparent conductive film laminates and the bleaching of the laminate, as well as the temperature change, was determined.

It was observed that the area of the optically transparent electrically conductive film laminates to which the current was applied reaches the initial transparency, corresponding to the inactivated state before exposure to direct sunlight, within 5 seconds of applying the current and that the temperature of said area raised to about 67°C.

In addition, the extent of darkening of the here above outlined second photochromic optically transparent electrically conductive film laminate was compared to the extent of darkening of a Vision Ease laminate comprising spirooxazine dyes. For this purpose, extent of darkening upon exposure to direct sunlight was compared between the Vision Ease laminate in a current visor and the second photochromic optically transparent electrically conductive film laminate similarly attached in an injection- molded and coated visor, which visor absorbs all UV light which has a wavelength of 400 nm and shorter. It was observed that the second photochromic optically transparent electrically conductive film laminate, which comprises in the TPU film a combination of two siloxane naphtopyrans, i.e. Reversacol Pennine Green and Reversacol Humber Blue (Vivimed Labs Europe Ltd), turns significantly darker upon exposure to direct sunlight, compared to the Vision Ease laminate when subjected to the same test conditions.

Claims

1. A photochromic optically transparent electrically conductive film laminate, comprising a self- supporting photochromic polymer film which is bonded to an optically transparent electrically conductive layer,

wherein the solubility of the one or more organic T-type photochromic compounds in the solvent at a temperature of between 15°C and 30°C is at least 0,1 wt%, based on the weight of the solution of the one or more organic T-type photochromic compounds in the solvent, and wherein the one or more organic T-type photochromic compounds, and the solvent if present, are distributed across at least part of the thickness of the thermoplastic polyurethane film in the self- supporting photochromic polymer film.

2. Optically transparent electrically conductive film laminate according to claim 1 , wherein the one or more organic T-type photochromic compounds, and the solvent if present, are homogeneously distributed across at least part of the thickness of the thermoplastic polyurethane film, preferably homogeneously distributed across the whole thickness of the thermoplastic polyurethane film in the self-supporting photochromic polymer film.

3. Optically transparent electrically conductive film laminate according to claim 1 or 2, wherein the self-supporting photochromic polymer film comprises between 0 and 8 wt% of the solvent, preferably between 0 and 5 wt%, more preferably between 0 and 3 wt%, based on the weight of the photochromic self-supporting polymer film.

4. Optically transparent electrically conductive film laminate according to any one of claims 1 - 3, wherein the self-supporting photochromic polymer film comprises about 0 wt% of the solvent, based on the weight of the photochromic self-supporting polymer film.

5. Optically transparent electrically conductive film laminate according to any one of claims 1 - 3, wherein the self-supporting photochromic polymer film comprises at least 0,1 wt% of the solvent, based on the weight of the photochromic self-supporting polymer film.

6. Optically transparent electrically conductive film laminate according to any one of claims 1 - 5, wherein the thermoplastic polyurethane film is chosen from the group consisting of aliphatic thermoplastic polyurethanes films, preferably from aliphatic polyester-based and aliphatic polyether-based thermoplastic polyurethanes films.

7. Optically transparent electrically conductive film laminate according to claim 6, wherein the aliphatic thermoplastic polyurethane film is based on an aliphatic diisocyanate selected from 1 ,4- tetramethylene diisocyanate, 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate, 1 , 12- dodecamethylene diisocyanate, cyclohexane-1 , 3-diisocyanate, cyclohexane-1 , 4-diisocyanate, 1- isocyanato-2-isocyanatomethyl cyclopentane, isophorone diisocyanate, 5-isocyanato-1- (isocyanatomethyl)-l ,3,3-trimethylcyclohexane, bis-(4-isocyanatocyclohexyl)-methane, 2,4’- dicyclohexylmethane diisocyanate, 1 ,3-bis(isocyanatometyl)-cyclohexane, 1 ,4- bis(isocyanatometyl)-cyclohexane, bis-(4-isocyanato-3-methylcyclohexyl)-methane, a,a,a',a’- tetramethyl-1 ,3-xylylen diisocyanate, a,a,a’,a’-tetramethyl-1 ,4-xylylen diisocyanate, 1- isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate, 2,6-hexahydrotoluylene diisocyanate, 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate, or mixtures thereof, preferably selected from 4,4’-methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate, and mixtures thereof.

8. Optically transparent electrically conductive film laminate according to any one of claims 1 - 7, wherein the self-supporting photochromic polymer film has a thickness of between 0,05 mm and 6,50 mm, preferably between 0,08 mm and 2,60 mm, more preferably between 0,09 mm and 0,68 mm.

9. Optically transparent electrically conductive film laminate according to any one of claims 1 - 8, having a total luminous transmittance of at least 85% and a haze lower than 1 % (both measured in accordance with ASTM D1003 - 2013) in an inactivated state.

10. Optically transparent electrically conductive film laminate according to any one of claims 1 - 9, wherein the optically transparent electrically conductive layer has a sheet resistance of between 10 and 120 W/square, preferably between 40 and 100 W/square, more preferably between 50 and 70 W/square, most preferably about 60 W/square.

1 1. Optically transparent electrically conductive film laminate according to any one of claims 1 - 10, wherein the optically transparent electrically conductive layer is selected from the group consisting of a carbon nanobud polycarbonate film, a layer of silver nanowires in a transparent mouldable glue, and a PEDOT-PSS layer on a carrier film.

12. Optically transparent electrically conductive film laminate according to any one of claims 1 - 1 1 , wherein the optically transparent electrically conductive layer has a thickness of between 0,1 mm and 0,5 mm, preferably between 0, 15 mm and 0,3 mm.

13. Optically transparent electrically conductive film laminate according to any one of claims 1 - 12, having a total thickness of between 0,75 mm and 6,50 mm, preferably between 0,75 mm and 2,60 mm, more preferably between 0,75 mm and 1 ,00 mm, most preferably about 0,80 mm.

14. Optically transparent electrically conductive film laminate according to any one of claims 1 - 13, wherein the solvent selected from the group of ketones is selected from the group consisting of straight-chain ketones, branched ketones, unsubstituted cyclic ketones, cyclic ketones substituted with at least one alkyl group and mixtures thereof, preferably selected from straight- chain ketones, unsubstituted cyclic ketones and mixtures thereof.

15. Optically transparent electrically conductive film laminate according to any one of claims 1 - 14, wherein the solvent selected from the group of ketones is selected from the group consisting of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3-one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 4-methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2-cyclohexene-1-one, 5-methylhexan-2-one, 1- cyclohexyl propan- 1 -one, 1-cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one and mixtures thereof, preferably the solvent is selected from propan-2-one and cyclohexanone, most preferably the solvent is cyclohexanone.

16. Optically transparent electrically conductive film laminate according to any one of claims 1 - 15, wherein the thermoplastic polyurethane film in the self-supporting photochromic polymer film comprises one or more organic T-type photochromic compounds selected from the group consisting of spiropyrans, spirooxazines, naphthopyrans and combinations thereof.

17. Optically transparent electrically conductive film laminate according to claim 16, wherein the one or more organic photochromic compounds are selected from polydialkylsiloxane-substituted naphthopyrans, preferably from polydialkylsiloxane-substituted naphthopyrans capable of taking on a blue colour or a green colour when irradiated with ultraviolet radiation.

18. Optically transparent electrically conductive film laminate according to any one of claims 1 - 17, wherein the thermoplastic polyurethane film in the self-supporting photochromic polymer film comprises at least two organic T-type photochromic compounds.

19. Optically transparent electrically conductive film laminate according to any one of claims 1 - 18, wherein at least part of the self-supporting photochromic polymer film is bonded to a first surface of an optically transparent first sheet, wherein said optically transparent first sheet is made of a plastic or a glass.

20. Optically transparent electrically conductive film laminate according to any one of claims 1 - 19, wherein at least part of the optically transparent electrically conductive layer is bonded to a first surface of an optically transparent second sheet, wherein said optically transparent second sheet is made of a plastic or a glass.

21. Optically transparent electrically conductive film laminate according to claim 19 or 20, wherein, the first and/or second optically transparent sheet are made of an optical grade plastic, preferably an optical grade polycarbonate or an optical grade polymethylmethacrylate, more preferably an optical grade polycarbonate based on the precursor monomer bisphenol A.

22. Optically transparent electrically conductive film laminate according to any one of claims 19 - 21 , wherein, the first and/or second optically transparent sheet are made of an optical glass, preferably a float glass, more preferably a soda-lime glass.

23. Optically transparent electrically conductive film laminate according to any one of claims 19 - 22, wherein at least part of a second surface of the first optically transparent sheet is bonded to a third optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating.

24. Optically transparent electrically conductive film laminate according to any one of claims 20 - 23, wherein at least part of a second surface the second sheet is bonded to a fourth optically transparent layer selected from an anti-fog coating, a hard coat and an anti-scratch coating

25. Method for producing an optically transparent electrically conductive film laminate, comprising the steps of:

b) providing one or more organic T-type photochromic compounds;

c) providing a solvent selected from the group of ketones;

d) preparing a solution by dissolving at least 0, 1 wt%, based on the weight of the solution, of the one or more organic T-type photochromic compounds of step (b) in the solvent of step

(c);

e) treating at least part of the at least first surface of the thermoplastic polyurethane film of step (a) with at least 100 g/m² of the solution of step (d) for a period of at least 5 seconds at a temperature between 15 and 30°C, resulting in a self-supporting photochromic polymer film with swollen areas where the first surface is treated with the solution, wherein the one or more organic T-type photochromic compounds and the solvent are distributed across at least part of the thickness of the thermoplastic polyurethane film;

f) optionally removing an excess of the solution applied in step (e) from the surface self- supporting photochromic polymer film obtained in step (e);

g) optionally drying the self-supporting photochromic polymer film obtained in step (e) or (f) to reduce the weight percentage of solvent in the self-supporting photochromic polymer film; h) bonding at least part of an optically transparent electrically conductive layer to a surface of the self-supporting photochromic polymer film obtained in any one of steps (e) to (g); i) optionally bonding at least part of the self-supporting photochromic polymer film obtained in step (h) to a first surface of an optically transparent first sheet made of a plastic or a glass;

26. Optically transparent electrically conductive film laminate according to any one of claims 1 - 24 or obtained by or obtainable by the method of claim 25.

27. Optical article, comprising the optically transparent electrically conductive film laminate according to any one of claims 1 - 24 or obtained by or obtainable by the method of claim 25.

28. Optical article according to claim 27 selected from visors, goggles, ophthalmic lenses, sunglasses, face-shields, architectural windows, automotive windows and aeronautic windows.