The present invention relates to an electrically conductive film comprising a plurality of electrically conductive nanoobjects which film preferably has adhesive properties. The invention further relates to products comprising and methods of making said electrically conductive film. The invention also relates to the use of a radiation-curable composition or a cured reaction product thereof for making an electrically conductive film.

Electrically conductive films comprising pluralities of electrically conductive nanoobjects, e.g. layers comprising nanowires of metals, in particular of silver (Ag) are suitable for a variety of purposes. For example, such films, preferably when transparent, are or can be used in the manufacture of transparent electrodes, flat panel displays, liquid crystal displays (LCD), touch screens, electrochromic windows, solar cells, transparent or thin film heaters, smart glasses/spectacles, smart watches (including activity trackers), electronic wristbands, electronic textiles in general, triboelectricity nanoenergy generators, supercapaci- tors and current collectors of batteries. In addition, if said films also have adhesive properties, products manufactured from said films or comprising said films have the additional advantage of being attachable to different kinds of surfaces, preferably smooth and/or hard and/or rigid surfaces. Specifically, electrically conductive, and preferably stretchable and/or adhesive and/or transparent, films can be useful as electronic displays and/or attachable electronic sticking or memo notes and/or attachable energy harvesters like solar cells. It has also been discussed in the prior art that stretchable electronics have potential applications in areas such as stretchable cyber skins for robotic devices or stretchable sensors. Stretchability of materials is known to be especially desired in electronic devices which need to be in contact with the human body or to be conformable with curved surfaces.

Further applications of said electrically conductive films can be conceived in the automotive and construction industries.

Electrically conductive films comprising pluralities of electrically conductive nanoobjects, e.g. layers comprising nanowires of metals, in particular of silver (Ag) have been reported to be suitable for a variety of purposes:

In document WO 2004/095536, for example, stretchable interconnects of an electrically conducting film or an elastomer material are described. The stretchable interconnect can be formed of a flat 2-dimensional conductive film covering an elastomeric or plastic substrate. When stretched in one or two dimensions, it can retain electrical conduction in both dimensions.

Document WO 2005/035460 A1 describes a radiation-curable coating agent containing aliphatic urethane (meth) acrylate.

In document WO 2007/022226 A2, a transparent conductor is described, including a conductive layer comprising a network of nanowires which may be embedded in a matrix.

Document US 2015/0310954 describes a stretchable conductive film based on silver na- noparticles. Films manufactured according to the methods disclosed in this document seem to exhibit an increase in conductivity under mechanical stress, i.e. stretching.

Document EP 2500170 A1 pertains to an electroconductive laminate and process for the production thereof. The conductive laminate described in this document is said to comprise a base resin layer and a conductive layer on at least one surface of a substrate, by stacking in the sequential order of the base resin layer and the conductive layer from the substrate side, and in which base resin layer comprises a resin including a urethane acrylate resin having a glycol skeleton, and a grafted resin having a hydrophilic group among side chains thereof. In an article by W. Hu et al. in Nanotechnology 23/34 (2012), intrinsically stretchable transparent electrodes based on silver-nanowire-crosslinked-polyacrylate composites are described. Stretchable transparent composites were synthesized consisting of a silver nan- owire (AgNW) network embedded in the surface layer of a crosslinked poly(acrylate) matrix. In an article by M.S. Miller et al., ACS Appl. Mater. Interfaces 5/20 (2013) 10165-10172, silver nanowire/optical adhesive coatings as transparent electrodes for flexible electronics are described. Flexible, transparent, and conductive coatings composed of an annealed silver nanowire network were embedded in a polyurethane optical adhesive.

It was a primary object of the present invention to provide an electrically conductive film which is preferably stretchable and/or preferably adhesive and/or self-adhesive and/or is preferably transparent and which can be useful for a variety of applications, e.g. where said film can be applied as a transparent, stretchable and/or adhesive electrode.

It was a further object of the invention to provide products comprising said electrically conductive film which is preferably stretchable and/or transparent and/or adhesive, e.g. trans- parent electronic devices like transparent displays, touch panels, solar cells, supercapaci- tors, reusable sticking notes and the like.

It was another object of the present invention to provide a method of making said electrically conductive film which is preferably stretchable and/or transparent and/or adhesive.

It was yet another object of the invention to provide a composition for making an electrically conductive film, preferably a stretchable and/or adhesive and/or transparent electrically conductive film, preferably a film according to the present invention.

The invention as well as preferred embodiments and preferred combinations of parameters, properties and elements thereof are defined in the appended claims.

The invention and its embodiments and preferred embodiments are also described and explained in more detail here below. If not indicated otherwise, preferred embodiments and/or preferred aspects of the invention can be combined with other embodiments and/or aspects of the invention as described herein, in particular with other preferred embodiments and/or preferred aspects. Combinations of preferred embodiments and/or preferred aspects with other preferred embodiments and/or preferred aspects of the invention will usu- ally also result in preferred embodiments and/or preferred aspects of the invention. Embodiments, aspects and/or characteristics which are described or set forth herein with respect to the electrically conductive film of the invention, or which are described or set forth in this respect as preferred, shall also be applicable mutatis mutandis with respect to the product or products of the invention, the method of making of the invention of said electrically conductive film and/or the uses according to the invention of a certain radiation- curable composition and/or an electrically conductive film, if not stated otherwise in a certain case.

Where an electrically conductive film, a product, a method of making or a use according to the invention are described herein which are "comprising" or "containing" certain (further defined) substances, embodiments, elements, features and/or parameters, this broader definition shall in each case also comprise the disclosure of the narrower definitions of the claimed subject matter which are "consisting of said substances, embodiments, elements, features and/or parameters, if not stated otherwise.

It has now been found that the primary object and other objects of the invention are accom- plished by providing an electrically conductive film; preferably a stretchable and/or, adhesive, electrically conductive film; comprising, i) a plurality of electrically conductive nanoobjects, dispersed in ii) a radiation-curable, preferably UV-curable, composition comprising

(a) as resin component, at least one aliphatic urethane (meth)acrylate, which has two ethylenically unsaturated double bonds per molecule and comprises, preferably in built-in form (i.e. as part of the aliphatic urethane (meth)acrylate molecule), at least one polytetrahydrofurandiol having a number average molecular weight M _n of at least 500 g/mol,

and

(b) as reactive diluent component, at least one monoethylenically unsaturated compound of formula I,

R

I

H ₂ C = C— O— (CH ₂ ) _k Y

(I)

comprising at least one aliphatic heterocycle as structural element, wherein R is hydrogen or methyl

k is an integer selected from 0, 1 , 2, 3 and 4, and

Y is a 5- or 6-membered, saturated heterocycle comprising one or two oxygen atoms, the heterocycle being unsubstituted or substituted , preferably mono-substituted, by Ci-C4-alkyl;

or a radiation-cured, preferably UV-cured, reaction product thereof. Thus, the electrically conductive film of the invention:

(A) comprises a dispersion of (i) a plurality of electrically conductive nanoobjects dispersed in (ii) a radiation-curable composition (as specified above), i.e. the film is present in an uncured state, or

(B) is a radiation-cured reaction product of such dispersion (A).

Correspondingly, specific preferred features and properties of an electrically conductive film of the present invention, which are described below in more detail, like stretchability, adhesion properties, flexibility etc. , directly apply to situation (B), where the film comprises the radiation-cured reaction product, whereas the corresponding dispersion (A) allows for generating these preferred features and properties, preferably by curing.

The skilled person understands that the radiation-cured reaction product is best defined by reference to the constituents of the corresponding radiation-curable composition.

The term "nanoobjects" as used herein is meant to denote objects with one, two or three of their external dimensions being in the nanoscale. Definitions as used herein to further describe and explain terms related to nanotechnologies are generally referring to standard technical specification ISO/TS 27687:2008 (first ed.). "Nanoscale" as used herein is therefore meant to comprise the size range of from about 1 to 100 nm. Nanoscale dimensions can be determined for the purposes of the present invention by means of transmission electron microscopy ("TEM"), known in the art. E.g . the thickness of nanoobjects or layers of nanoobjects which may be comprised by the electrically conductive film of the invention can be determined from TEM images of the cross-section of a sample from said film. Nanoscale dimensions can also be determined for the purposes of the present invention by scanning electron microscopy ("SEM"), e.g. by a field-emission scanning electron microscope, as known in the art. Samples for studying the cross-section(s) can be prepared by means of focused ion beam ("FIB") technology, as is known in the art. For practical purposes, TEM is preferred, if not indicated otherwise. Nanoobjects as used herein are elec- trically conductive and preferably comprise or consist of a material which has a high conductivity, preferably a material which has a conductivity of no less than 1 x 10 ⁵ S/m at 20 °C.

Electrically conductive nanoobjects for the purposes of the present invention are preferably selected from the group consisting of electrically conductive nanoparticles, nanoplates, nanoflakes, nanofibres, nanotubes, nanorods, nanospheres, nanoribbons and nanowires. Electrically conductive nanowires are preferred, in particular where the nanoobjects comprise or consist of metals or their alloys. Nanotubes are also preferred, in particular where the nanoobjects comprise or consist of carbon.

The term "nanoparticle" as used herein is meant to denote a nanoobject with all three ex- ternal dimensions being in the nanoscale, while typically the length of the longest axis and the length of the shortest axis of said nanoobject do not differ significantly.

The term "nanoplate" as used herein is meant to denote a nanoobject with one of its external dimensions being in the nanoscale while the two other external dimensions may be significantly larger (e.g. three times or more larger than the first, i.e. nanoscale external dimension) and not necessarily be in the nanoscale. The smallest external dimension is regarded as the thickness of the nanoplate. Another common term often used to denote nanoobjects which have only one dimension in the nanoscale is "nanoflakes".

The term "nanofiber" as used herein is meant to denote a nanoobject with two (preferably similar) external dimensions in the nanoscale and the third external dimension being sig- nificantly larger. Two external dimensions are considered to be similar if they differ in size by less than three times and the one significantly larger external dimension is considered to differ from the larger of the other two by three times or more and may not necessarily be in the nanoscale. Said largest external dimension corresponds to the length of the nanofiber. Nanofibers can be flexible or rigid. The term "nanotubes" as used herein is meant to denote a nanofiber which is hollow. The term "nanorod" as used herein is meant to denote a nanoobject with two similar external dimensions in the nanoscale and the third dimension being significantly larger and being rigid (i.e. not flexible). Nanorods can be regarded as solid (or rigid) nanofibers.

The term "nanospheres" as used herein is meant to denote approximately isometric nano- particles, i.e. nanoparticles where the aspect ratios of all three orthogonal external dimensions are close to 1 , e.g. smaller than 1 .1. The aspect ratio denotes the ratio of a longer to a shorter dimension of an object, e.g. the ratio of the longest to the shortest dimension of an object.

The term "nanoribbons" as used herein is meant to denote nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension (length) is significantly larger. Thus, nanoribbons have a nearly rectangular-shaped cross-section extending the third external dimension (length) perpendicularly.

The term "nanowire" as used herein is meant to denote an electrically conductive or semi- conductive nanofibre, preferably an electrically conductive nanofiber. The term "nanowire" is sometimes abbreviated as "NW" herein.

The term "electrically conductive" as used herein generally has the meaning that a material having this property is capable of allowing the flow of an electric current when an appropriate voltage is applied. The electrically conductive film of the invention comprises a plurality of electrically conductive nanoobjects. Said electrically conductive nanoobjects contribute to and more preferably essentially establish the electrically conductive properties of said electrically conductive film, "essentially" meaning that at least 90 % of the total conductivity is caused by said nanoobjects, preferably at least 95 %. The nature of the electrically conductive nanoobjects, their number and their arrangement in the electrically conductive film of the invention allows for, increases and/or determines the electrical conductivity of the electrically conductive film.

With respect to the electrically conductive nanoobjects as used in the present invention, "electrically conductive" preferably has the meaning that the respective nanoobjects have (respectively the material of which the electrically conductive nanoobjects are made has) a conductivity of no less than 1 x 10 ⁵ S/m at 20 °C, preferably in the range of from 1 x 10 ⁵ to 1 x 10 ⁹ S/m at 20 °C. The electrically conductive nanoobjects, in particular the nanowires, of the present invention can comprise or consist of one or more metals (also referred to as "metal nanoobjects" or "metal nanowires", as applicable) and/or of one or more non-metallic materials, including mixtures of one or more metallic (like e.g. Ag) and one or more non-metallic (like e.g. car- bon) materials.

A suitable non-metallic material for electrically conductive nanoobjects is carbon, in particular in the form of graphene and/or in the form of carbon nanotubes.

Preferably, the electrically conductive nanoobjects, in particular the nanowires, of the present invention can comprise or consist of one or more metals. Suitable metals are selected from the group consisting of cobalt (Co), copper (Cu), gold (Au), iron (Fe), molybdenum (Mo), nickel (Ni), palladium (Pd), silver (Ag), tin (Sn), tungsten (W) and - where possible - alloys made of two or more of said metals. Preferred metals are Ag, Au, Cu and Ni and any alloys made of two or more of said metals. Pure metals are preferred over alloys. Most preferred is Ag. With respect to all aspects of the present invention, metal nanoobjects, in particular metal nanowires, more in particular Ag nanowires (in the present text sometimes abbreviated as "AgNW"), are preferred electrically conductive nanoobjects. Thus in a preferred embodiment, the present invention relates to an electrically conductive film wherein the electrically conductive nanoobjects are metal nanoobjects, preferably metal nanowires, more prefera- bly silver nanowires.

With respect to all aspects of the present invention, particularly preferred metal nanowires have an average length (without any coating or adsorptive agent on their external surfaces) in the range of from 10 μιτι to 50 μιτι, preferably an average length in the range of from 15 μιη to 40 μιτι, more preferred an average length in the range of from 20 μιτι to 30 μιτι, e.g. a length of about 25 μιτι, and in each case an average diameter in the range of from 10 nm to 100 nm, preferably an average diameter in the range of from 15 nm to 80 nm, more preferred an average diameter in the range of from 20 nm to 50 nm, e.g. a diameter of about 30 nm.

Generally, electrically conductive nanoobjects as described herein and methods for pre- paring them are known in the art (see e.g. US 7,922,787 or US 8,049,333 and references cited therein in each case). Moreover, many of said electrically conductive nanoobjects are commercially available, in particular metal nanowires like Au or Ag nanowires. Insofar, typical commercial articles are e.g. alcoholic or aqueous dispersions of e.g. Ag or Au nanowires wherein suitable preservatives may be used which are coated or adsorbed to the surfaces of said nanowires, e.g. polyvinylpyrrolidone or polyethylene glycol. Non-metallic electrically conductive nanoobjects like carbon nanotubes and methods for their preparation and use are known in the art, see e.g. the publications in US 6,232,706; R. Chavan et al., International Journal of Pharmaceutical Sciences Review and Research, Vol. 13/1 (2012) 125-134 or K. Saeed et al., Carbon Letters Vol. 14/3 (2013) 131-144. Carbon nanotubes are also commercially available, e.g. from Sigma-Aldrich, see e.g. bro- chure by Sigma-Aldrich Co. "Material Matters" Vol. 4 No. 1 (2009).

In the electrically conductive film of the invention, the radiation-curable composition ii) is preferably curable by application of high energy radiation, more preferably by application of electron-beam radiation or UV radiation, as explained in more detail below.

The resin component (a) present in the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention comprises or consists of at least one aliphatic urethane (meth)acrylate which has two eth- ylenically unsaturated double bonds per molecule and comprises, preferably in built-in form (i.e. as part of the aliphatic urethane (meth)acrylate molecule), at least one polytetrahydro- furandiol having a number average molecular weight M _n of at least 500 g/mol. The term "(meth)acrylate" as used herein is meant to comprise the esters of acrylic acid and/or meth- acrylic acid.

Preferably, the resin component (a) is free of aromatic structural elements like phenylene, naphthalene or their derivatives. Resin component (a) may thus be regarded as comprising and/or representing aliphatic urethane (meth)acrylate monomers and/or oligomers, prefer- ably oligomers.

In a preferred embodiment of the present invention, the resin component (a) consists of at least one aliphatic urethane (meth)acrylate which has two ethylenically unsaturated double bonds per molecule and comprises, preferably in built-in form (i.e. as part of the aliphatic urethane (meth)acrylate molecule), at least one polytetrahydrofurandiol having a number average molecular weight Mn of at least 500 g/mol and/or the at least one aliphatic urethane (meth)acrylate of the resin component (a) comprises

(a-1 ) one or more aliphatic structural elements, preferably selected from the group consisting of Ci-C4-alkylen which is optionally mono-substituted or poly-substituted by Ci-C4-alkyl, preferably methyl, and/or which optionally contains one or more non- adjacent oxygen atoms; and C6-C2o-cycloalkylen which is optionally mono-substituted or poly-substituted by Ci-C4-alkyl, preferably methyl, and/or which optionally contains one or more nonadjacent oxygen atoms;

(a-2) urethane groups and

(a-3) two ethylenically unsaturated structural elements, preferably selected from the group consisting of vinyl groups which are optionally substituted, preferably mono- substituted, by Ci-C4-alkyl, preferably methyl; and allyl groups which are optionally substituted, preferably mono-substituted, by Ci-C4-alkyl, preferably methyl.

In the preferred component (a-1 ) of the resin component as defined here above, the aliphatic structural elements are preferably joined to one another via one or more joining groups selected from the group consisting of quaternary carbon atom, tertiary carbon atom, urea, biuret, uretdione, allophanate, cyanurate, urethane, ester, amide, ether oxygen atom and amine nitrogen atom. More preferably, the aliphatic structural elements are joined to one another via one or more joining groups selected from the group consisting of quaternary carbon atom, tertiary carbon atom, urea, biuret, uretdione, allophanate, cyanurate, ester, amide, ether oxygen atom and amine nitrogen atom. Yet more preferably, the aliphatic structural elements are joined to one another via one or more joining groups selected from the group consisting of biuret, cyanurate and urethane.

In the preferred component (a-3) of the resin component as defined here above, the two ethylenically unsaturated structural elements are preferably selected from the group consisting of acryloyl, more preferably acryloxy and acrylamido, and methacryloyl, more preferably methacryloxy and methacrylamido. More preferably, the two ethylenically unsaturated structural elements are both acryloxy. In a preferred embodiment of the present invention, the resin component (a) comprises as component (a-1 ) aliphatic structural elements which are joined to one another via one or more joining group selected from the group consisting of biuret, cyanurate and urethane, and further comprises as component (a-3) acryloxy groups as ethylenically unsaturated structural elements.

In the resin component (a) or in its preferred embodiments as stated above, the number average molecular weight M _n of the at least one urethane (meth)acrylate is preferably in the range of from 750 to 10000, more preferably in the range of from 1000 to 5000.

The aliphatic urethane (meth)acrylate resin component (a) according to the present inven- tion is generally known per se. Specific preferred aliphatic urethane (meth)acrylate resin components (a), preferably aliphatic urethane (meth)acrylate resin components (a) which are free of urethane groups, can preferably be produced according to the methods as disclosed in documents WO 2005/035460, US 2007/066704 and EP 1678094B1 , which documents and their disclosures are all incorporated herein by reference in their entireties. The reactive diluent component (b) present in the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention comprises or consists of at least one monoethylenically unsaturated compound of formula I as defined above, wherein Y is a 5- or 6-membered, saturated heterocycle comprising one or two oxygen atoms, the heterocycle being unsubstituted or substituted, preferably mono-substituted, by Ci-C4-alkyl, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl and/or tert.-butyl. Preferably, Y is selected from the group consisting of tetrahydrofuran, tetrahydropyran, 1 ,3-dioxolane, 1 ,3-dioxane and 1 ,4-dioxane, where all of the foregoing are unsubstituted or substituted, preferably mono-substituted, by C1-C4- alkyl. Preferred according to the invention are diluent components (b) which are selected from the group consisting of trimethylolpropaneformal monoacrylate (CAS RN 66492-51-1 ), glycerol monoformal acrylate, 4-tetrahydropyranyl acrylate, 2-tetrahydropyranyl methylacrylate, tetrahydrofurfuryl acrylate and mixtures thereof. Most preferred is a reactive diluent component (b) comprising or (preferably) consisting of trimethylolpropaneformal monoacrylate. In another preferred embodiment of the invention, the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention further comprises

(c) as modifier component, at least one bifunctional or polyfunctional ester of an α,β-ethylenically unsaturated carboxylic acid with a diol , preferably an aliphatic diol, or polyol, preferably an aliphatic polyol.

Depending on the desired property profile of the electrically conductive film according to the invention, the radiation-curable composition ii) comprises component (b) and no modifier component (c), or component (b) and modifier component (c), preferably in amounts specified below. The modifier component (c) is preferably present in embodiments of the invention where a higher hardness of the electrically conductive film according to the invention is desired, and in these cases (if present) preferably in a weight ratio in a range of 1 :20 to 1 : 1 , more preferably in a ratio in a range of 1 :15 to 1 :1.5, relative to the weight of component (b) present in the radiation-curable composition ii).

The modifier component (c) is preferably selected from the group consisting of the esters of acrylic acid and the esters of methacrylic acid and mixtures thereof, more preferred from the group consisting of the diesters of acrylic acid with aliphatic diols and the triesters of acrylic acid with aliphatic triols and mixtures thereof. Preferably, the polyols and diols contain no further heteroatoms apart from the hydroxyl functions.

More preferably, the modifier component (c) is selected from the group consisting of bu- tanediol diacrylate, hexanediol diacrylate, 1 ,4-cyclohexanediol diacrylate, 1 ,4-bis(hy- droxymethyl)cyclohexane diacrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, dieth- ylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 1 ,4-cyclohexanediol di(meth)acry- late and 1 ,4-bis(hydroxymethyl) cyclohexane di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, in particular trimethylolpropane tri- acrylate (CAS RN 15625-89-5), and pentaerythritol tetra(meth)acrylate and mixtures thereof.

Particularly preferably, the modifier component (c) is selected from the group consisting of butanediol diacrylate, trimethylolpropane triacrylate, hexanediol diacrylate, 1 ,4-cyclohexanediol diacrylate, 1 ,4-bis(hydroxymethyl)cyclohexane diacrylate and mixtures thereof. In a preferred embodiment of the invention, the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention further comprises

(d) as UV-photoinitiator component, one or more compounds selected from the group consisting of ketones, ohydroxyketones, benzoin and/or benzyl derivatives, phenylglyoxylates; acyl phosphinoxides and mixtures thereof.

The UV-photoinitiator component (d) preferably initiates the polymerization of ethylenically unsaturated double bonds present in the resin component (a) upon irradiation with UV-light (UV radiation) of a suitable wavelength. The UV-photoinitiator component (d) is therefore preferably present in the preferred embodiment of the invention wherein the radiation-curable composition ii) is a UV-curable composition and/or wherein the electrically conductive film according to the invention comprises a UV-cured reaction product of the radiation-curable composition ii). In embodiments of the invention where the radiation-curable composition ii) is cured by application of high-energy radiation other than UV radiation, e.g. by electron-beam, the UV-photoinitiator component may be absent.

Generally, preferred UV-photoinitiator components (d) to be used in accordance with the present invention have one or more (at least one) absorption peaks (absorption maxima) in the ultraviolet to visible (UV VIS) part of the electromagnetic spectrum, preferably in a wavelength range of from 200 to 400 nm, more preferably in a range of from 200 to 350 nm, preferably as measured in methanol and in a suitable concentration in each case. Suitable concentrations of compounds for the purpose of measuring their UV VIS absorption spectra are familiar to those skilled in the art and are usually in the range of from 10 ^~2 to 10 ^{" 5} mol/L.

Further, and generally, preferred UV-photoinitiator components (d) to be used in accordance with the present invention are "non-yellowing", i.e. preferred UV-photoinitiator components (d) will only contribute to a low degree, preferably to a very low degree and most preferably will not at all contribute to any yellow colour in the UV-cured reaction product which is part of or constitutes the electrically conductive film of the present invention. The effects of yellowing or non-yellowing UV-photoinitiators and the selection of suitable non- yellowing UV photoinitiators are generally known to those skilled in the art. Preferably, the one or more compounds of the UV-photoinitiator component (d) comprised by an electrically conductive film according to the invention are selected from the group consisting of: ketones, preferably benzophenone; 4-phenyl-benzophenone; 4-chloro-benzo- phenone; Michler's ketone; 2,2-dimethoxy-2-phenylacetophenone; anthrone; an- thraquinone; b-methylanthraquinone; tert.-butyl anthraquinone and 2-methyl-1-[4- (methylthio)phenyl]-2-morpholinopropanone-1 ; ohydroxyketones, preferably 1-hydroxy-cyclohexyl-phenyl-ketone (also known as Irgacure® 184; CAS RN 7473-98-5); 2-hydroxy-4'-(2-hydroxyethoxy)-2- methylpropiophenone (CAS RN 106797-53-9); 2-hydroxy-2-methyl propiophenone (CAS RN 7473-98-5); 1 , 1 '-(methylenedi-4,1-phenylene)bis(2-hydroxy-2-methyl-1- propanone) (CAS RN 474510-57-1 ); 2-hydroxy-2,2-dimethylacetophenone and benzoin; benzoin derivatives, preferably benzoin methyl ether; benzoin ethyl ether; benzoin n-butyl ether and benzoin tert.-butyl ether, and benzil derivatives, preferably benzil dimethyl ketal; phenylglyoxylates, preferably methyl phenylglyoxylate (CAS RN 15206-55-0); oxy-phenyl-acetic acid-2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester (CAS RN 21 1510-16-6) and oxy-phenyl-acetic acid- 2-[2-hydroxy-ethoxy]-ethyl ester (CAS RN 442536-99-4); acyl phosphinoxides, preferably 2,4,6-trimethylbenzoyldiphenylphosphine oxide (also known as Lucirin® TPO; CAS RN 75980-60-8) and ethyl-2,4,6-trimethyl- benzoylphenylphosphinate (also known as Lucirin® TPO-L; CAS RN 84434-1 1-7); and mixtures thereof and/or more preferably the one or more compounds of the UV-photoinitiator component (d) are selected from the group consisting of 1-hydroxy-cyclohexyl-phenyl-ketone; 2-hydroxy-2- methyl propiophenone; 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone and mixtures of 1-hydroxy-cyclohexyl-phenyl-ketone with benzophenone, in particular a 50:50 (wt./wt.) mixture of 1-hydroxy-cyclohexyl-phenyl-ketone with benzophenone, also known as Irgacure® 500; and mixtures thereof; and/or most preferably the UV-photoinitiator component (d) according to the invention is 1-hy- droxy-cyclohexyl-phenyl-ketone.

In a preferred embodiment of the invention, the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present inven- tion further comprises

(e) as additional component, one or more further compounds, preferably selected from the group consisting of stabilizers, UV absorbers, catalysts and trace compounds.

Preferred stabilizers in additive component (e) are polymerization inhibitors (also some- times referred to as "free radical scavengers"), preferably selected from the group consisting of hydroquinones; hydroquinone monoalkyl ethers; 2,6-di-tert-butylphenols, in particular 2,6-di-tert-butylcresol; 4-methoxyphenol (CAS RN 150-76-5); nitrosamines; phenothia- zines; phosphorous esters and mixtures thereof. More preferred stabilizers in additive component (e) are 2,6-di-tert-butylcresol; 4-methoxyphenol and mixtures thereof Preferred UV absorbers in additional component (e) are common UV-absorbers and hindered amine light stabilizers (HALS). Common UV absorbers can either be used alone or in combination with suitable HALS. Preferred UV absorbers in additional component (e) are selected from the group consisting of common UV-absorbers, preferably oxanilides, tria- zines, benzotriazole and benzophenones and HALS, preferably 2,2,6,6-tetra-methylpiperi- dine, 2,6-di-tert-butylpiperidine and bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate. UV absorbers are e.g. additives improving weatherability of a UV-cured reaction product which is part of or constitutes the electrically conductive film of the present invention. In the production process, these additives are e.g. added in admixture with the UV-photoinitiator component (d). Additional component (e) can further comprise catalysts which are usually remainders from previous manufacturing processes, e.g. from previous processes for manufacturing the at least one aliphatic urethane (meth)acrylate component (a). Typical catalysts which may be present in additional component (e) are tin-containing catalysts, preferably dibutyltin di- laurate, tin (II) octoate or dibutyltin dimethoxide, or their degradation products in each case.

Additional component (e) can further comprise trace compounds. Trace compounds are preferably remainders from previous reactions like manufacturing reactions to produce any of the other components (a), (b), (c) and/or (d) of the radiation-curable composition ii) and/or can be fragments and/or degradation products of any of the other components (a), (b), (c) and/or (d) of the radiation-curable composition ii). For example, the additional component (e) may comprise 5-ethyl-1 ,3-dioxane-5-methanol as trace compound.

The radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention, comprises the polymerizable components (a) resin component and

(b) reactive diluent, and optionally

(c) modifier component.

The polymerizable components (a), (b) and (optionally) (c) of the radiation-curable composition ii), as defined above and in the claims are collectively also referred to as the "polymer- izable composition" in the following. The "polymerizable composition" is thus a part of the radiation-curable composition ii) as defined above and in the claims.

In a preferred embodiment of the present invention, the resin component (a) preferably consists of at least one aliphatic urethane (meth)acrylate as defined above or as defined above as preferred and is preferably present in the polymerizable composition (as defined above) in an amount in the range of from 40 to 80 wt.-%, more preferably in the range of from 50 to 80 wt.-% and still more preferably in an amount in the range of from 60 to 75 wt.-%, relative to the total weight of the polymerizable composition.

In a preferred embodiment of the present invention, the reactive diluent component (b) preferably consists of at least one monoethylenically unsaturated compound of formula I as defined above or as defined above as preferred and is preferably present in the polymerizable composition (as defined above) in an amount in the range of from 20 to 60 wt.-%, more preferably in the range of from 20 to 50 wt.-% and still more preferably in an amount in the range of from 25 to 40 wt.-%, relative to the total weight of the polymerizable com- position.

In a preferred embodiment of the present invention, the modifier component (c) preferably consists of at least one bifunctional or polyfunctional ester of an α,β-ethylenically unsaturated carboxylic acid with a diol or polyol as defined above or as defined above as preferred and is preferably present in the polymerizable composition (as defined above) in an amount in the range of from 0 to 20 wt.-%, more preferably in the range of from 0.5 to 10 wt.-% and still more preferably in an amount in the range of from 0.5 to 5 wt.-%, relative to the total weight of the polymerizable composition.

Preferably, the wt.-% values and preferred wt.-% values (i.e. the weight percentage values) as provided above for the resin component (a), the reactive diluent component (b) and the modifier component (c) relative to the polymerizable composition preferably add to 100 wt.- % in each case. Preferred wt.-% values for resin component (a), reactive diluent component (b) and modifier component (c) can be combined to result in preferred polymerizable compositions or radiation-curable compositions ii), respectively.

In a preferred embodiment of the present invention, the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present invention is a UV-curable composition and comprises a UV-photoinitiator component (d) as defined above or as defined above as preferred. In this preferred embodiment, said UV- photoinitiator component (d) is preferably present in the radiation-curable composition ii) (or UV-curable composition) in an amount in the range of from 0.5 to 15 wt.-%, preferably in the range of from 1 to 10 wt.-%, more preferably in the range of from 2 to 7.5 wt.-%, and still more preferably in the range of from 3 to 7 wt.-%, relative to the total weight of the polymerizable composition.

In an embodiment of the present invention, the radiation-curable composition ii) as defined above and in the claims with respect to the electrically conductive film of the present inven- tion further comprises additional component (e) as defined above or as defined above as preferred. Preferably, additional component (e) consists of one or more further compounds, preferably selected from the group consisting of stabilizers, UV absorbers, catalysts and trace compounds, as defined above or as defined above as preferred. In this preferred embodiment, said additional component (e) is preferably present in the radiation-curable composition ii) in an amount in the range of from 0 to 15 wt.-%, preferably in the range of from 0 to 10 wt.-%, more preferably in the range of from 1 to 7.5 wt.-%, relative to the total weight of the polymerizable composition as defined above.

More in particular, in this preferred embodiment, stabilizers as defined above or as defined above as preferred, are present in the additional component (e) in an amount in the range of from 0 to 5 wt.-%, preferably in the range of from 0.1 to 3.5 wt.-%, more preferably in the range of from 0.1 to 1 wt.-%, relative to the total weight of the polymerizable composition as defined above.

Also more in particular, in this preferred embodiment, UV-absorbers as defined above or as defined above as preferred, are present in the additional component (e) in an amount in the range of from 0 to 5 wt.-%, preferably in the range of from 0 to 3.5 wt.-%, more preferably in the range of from 0.1 to 3.5 wt.-%, relative to the total weight of the radiation-curable composition ii). To the extent that one or more UV absorbers have an identical meaning as other components of the radiation-curable composition ii) (e.g. benzophenone may be an UV absorber and likewise may be a photoinitiator), the amounts (wt.-%) of said UV absorber and said other component of the radiation-curable composition ii) with identical meaning will be counted twice, i.e. will be counted separately under each component of the polymerizable composition as defined above.

Also more in particular, in this preferred embodiment, catalysts as defined above or as defined above as preferred, are present in the additional component (e) in an amount in the range of from 0 to 2 wt.-%, preferably in the range of from 0 to 1.5 wt.-%, more preferably in the range of from 0.01 to 1.5 wt.-%, relative to the total weight of the polymerizable composition as defined above.

Also more in particular, in this preferred embodiment, trace compounds as defined above or as defined above as preferred, are present in the additional component (e) in an amount in the range of from 0 to 5 wt.-%, preferably in the range of from 0.1 to 3.5 wt.-%, more preferably in the range of from 0.15 to 2.5 wt.-%, relative to the total weight of the polymerizable composition as defined above.

In one preferred specific embodiment of the present invention, the resin component (a) consists of at least one aliphatic urethane (meth)acrylate as defined above or as defined above as preferred and is present in the polymerizable composition (as defined above) in an amount in the range of from 50 to 80 wt.-%, more preferably in an amount in the range of from 60 to 75 wt.-%, relative to the total weight of the polymer- izable composition; the reactive diluent component (b) consists of at least one monoethylenically unsaturated compound of formula I as defined above or as defined above as preferred and is present in the polymerizable composition (as defined above) in an amount in the range of from 20 to 50 wt.-%, more preferably in an amount in the range of from 25 to 40 wt.-%, relative to the total weight of the polymerizable composition; the modifier component (c) as defined above or as defined above as preferred is present in the polymerizable composition (as defined above) in an amount in the range of from 0.5 to 10 wt.-%, preferably in an amount in the range of from 0.5 to 5 wt.-%, relative to the total weight of the polymerizable composition; the wt.-% values and preferred wt.-% values as provided above for the resin component (a), the reactive diluent component (b) and the modifier component (c) in this preferred embodiment in relation to the polymerizable composition adding to 100 wt.-% in each case; the UV-photoinitiator component (d) as defined above or as defined above as preferred is present in the radiation-curable composition ii) (or UV-curable composition) in an amount in the range of from 1 to 10 wt.-%, preferably in the range of from 2 to 7.5 wt.-% and more preferably in the range of from 3 to 7 wt.-%, relative to the total weight of the polymerizable composition and the additional component (e) consists of one or more further compounds, selected from the group consisting of stabilizers, UV absorbers, catalysts and trace compounds, as defined above or as defined above as preferred. In this preferred embodiment, said additional component (e) is preferably present in the radiation-curable composition ii) in an amount in the range of from 0 to 10 wt.-%, preferably in the range of from 1 to 7.5 wt.-%, relative to the total weight of the polymerizable composition.

In one particularly preferred specific embodiment of the present invention, the resin component (a) consists of at least one aliphatic urethane (meth)acrylate as defined above or as defined above as preferred and is present in the polymerizable composition (as defined above) in an amount in the range of from 60 to 75 wt.-%, relative to the total weight of the polymerizable composition; the reactive diluent component (b) is trimethylolpropaneformal monoacrylate and is present in the polymerizable composition (as defined above) in an amount in the range of from 25 to 40 wt.-%, relative to the total weight of the polymerizable composition; the modifier component (c) is trimethylolpropane triacrylate and is present in the polymerizable composition (as defined above) in an amount in the range of from 0.5 to 5 wt.-%, relative to the total weight of the polymerizable composition; the wt.-% values and preferred wt.-% values as provided above for the resin component (a), the reactive diluent component (b) and the modifier component (c) in this preferred embodiment in relation to the polymerizable composition adding to 100 wt.-% in each case; the UV-photoinitiator component (d) is 1-hydroxy-cyclohexyl-phenyl-ketone and is present in the radiation-curable composition ii) (or UV-curable composition) in an amount in the range of from 3 to 7 wt.-%, relative to the total weight of the polymerizable composition, and the additional component (e) consists of one or more further compounds, selected from the group consisting of stabilizers, UV absorbers, catalysts and trace compounds, as defined above or as defined above as preferred. In this preferred embodiment, said additional component (e) is preferably present in the radiation-curable composition ii) in an amount in the range of from 0 to 10 wt.-%, preferably in the range of from 1 to 7.5 wt.-%, relative to the total weight of the polymerizable composition.

Specific radiation-curable compositions ii) and cured products thereof as defined above and in the claims with respect to the electrically conductive film of the present invention are known per se and are e.g. disclosed in documents WO 2005/035460, US 2007/066704 and EP 1678094B1 (incorporated herein by reference, see above).

In the electrically conductive film of the invention, the plurality of electrically conductive nanoobjects is dispersed in a radiation-curable composition. The radiation-curable compo- sition comprising the dispersed plurality of electrically conductive nanoobjects can preferably be uncured, i.e. be a mere mixture of resin component (a), reactive diluent component (b) and optionally further components (modifier component (c), UV-photoinitiator component (d) and/or one or more further additives component (e)), or the UV-curable composi- tion can also be partially cured. Preferred is an electrically conductive film according to the invention, wherein the concentration of electrically conductive nanoobjects has a gradient in a direction perpendicular to an interface and/or surface of the film or - the concentration of electrically conductive nanoobjects is the same in all directions of the film.

The alternative where the concentration of electrically conductive nanoobjects in the electrically conductive film has a gradient in a direction perpendicular to an interface and/or surface of the film is more preferred and can preferably be obtained by first creating a layer of electrically conductive nanoobjects (also abbreviated to "nanoobject layer" hereinafter), subsequently applying and overlaying an excess amount of a matrix material onto the nanoobject layer so as to embed said nanoobject layer in the matrix material, preferably a matrix material constituted by the radiation-curable composition as defined above, and subsequently curing the radiation-curable composition. The nanoobject layer can be created by methods known in the art, e.g. by methods as set forth below in more detail.

Preferably, the above-defined plurality of electrically conductive nanoobjects, more preferably a plurality of metal nanoobjects (preferably metal nanowires), is arranged in an electrically conductive film of the invention and/or in a nanoobject layer as defined above, in the form of an electrically conductive network of adjacent and contacting nanoobjects (pref- erably metal nanowires). This network provides for sufficient interconnection (i.e. mutual contact) between individual electrically conductive nanoobjects (preferably electrically conductive metal nanoobjects, more preferably metal nanowires), so as to enable a flow of electrons along the interconnected electrically conductive nanoobjects or electrically conductive nanowires, preferably metal nanoobjects (more preferably metal nanowires), within the network. Where such network is built of electrically conductive nanowires, it will also be referred to as "nanowire network" ("metal nanowire network", respectively, whenever appropriate) herein. More preferably, the plurality of electrically conductive nanowires present in the electrically conductive film according to the invention is a plurality of AgNWs, most preferably a network of AgNWs.

Preferably, at least a portion of said electrically conductive nanoobjects (e.g. AgNWs) of said nanoobject layer is/are exposed on (or is/are exposed to) an interface and/or surface of the electrically conductive film, i.e. at least a portion of said electrically conductive nanoobjects reaches through the surface of the film and is available for direct contact, e.g. direct electrical contact. In a preferred embodiment, at least a portion of said electrically conductive nanoobjects is/are exposed on (or are exposed to) one surface of the electrically conductive film, while the electrically conductive nanoobjects are not or to a lower extent exposed on the opposite surface of the electrically conductive film. This preferred embodiment thus comprises an electrically conductive film which has two opposite surfaces (sides) with different electrical properties: one surface which shows electrical conductivity or which shows a higher electrical conductivity (and/or a lower sheet resistance) upon direct contact with the surface, e.g. direct contact with a suitable measuring instrument like a four-point probe ("surface A"; surface A has the higher concentration of electrically conductive nanoobjects), and one opposite surface which does not show or which shows a lower electrical conductivity (and/or a higher sheet resistance) upon direct contact with the surface, e.g. direct contact with a suitable measuring instrument like a four-point probe ("surface B"; surface B has the lower concentration of electrically conductive nanoobjects). Preferably such electrically conductive film of the invention has one (first) surface with better electrical (e.g. conductive) properties (in comparison with the opposite surface) and one (opposite) surface with better adhesive properties (in comparison with the first surface).

The alternative where the concentration of electrically conductive nanoobjects in the electrically conductive film is the same in all directions of the layer can preferably be obtained by pre-mixing a suitable preparation of metal nanoobjects, e.g. a suitable preparation of metal nanowires like AgNWs, with at least one suitable component of the above-defined radiation-curable composition, preferably until a homogeneous distribution is reached in the pre-mixture, and using this (preferably homogeneous) pre-mixture for further processing, e.g. as further described below. To facilitate electrical conductivity in the resulting electrically conductive film, the concentration of electrically conductive nanoobjects in the pre-mixture can be adjusted to a suitable value in a manner known in the art.

The electrically conductive film of the invention preferably has a thickness of not more than 200 μιτι, preferably a thickness in the range of from 10 to 180 μιτι, more preferably in the range of from 20 to 150 μιτι. As will be understood by a skilled person, the thickness of the film can be adjusted or designed according to the main purpose or use for which said film is intended. If, for example, the intended use of the film requires or suggests higher flexibility, a thinner film may be beneficial, e.g. a film with a thickness in the range of from 10 to 50 μιτι. If, on the other hand, the intended use of the film requires higher durability or resistance to mechanical stress, a thicker film may be beneficial, e.g. a film with a thickness in the range of from 100 to 150 μιτι or in the range of from 100 to 180 μιτι.

It is surprising that the electrically conductive film of the invention could be produced in the minimal thickness as pointed out above and/or that the electrically conductive film of the invention of such minimal thickness as pointed out above nonetheless showed the beneficial mechanical properties (flexibility, stretchability, elasticity) and/or adhesive properties as described in this text.

Electrical conductivity is present in one or more directions and/or areas of the electrically conductive film of the present invention, and typically is at least present within said film in a direction and/or in one or more areas parallel to the surface of the film itself.

With respect to preferred electrically conductive film of the present invention, "electrical conductivity" can best be defined in terms of its "sheet resistance".

The sheet resistance (sometimes also referred to as "square resistance") is a measure of the resistance of a thin body (a sheet), namely uniform in thickness. The term "sheet resistance" implies that the current flow is along the plane of the sheet, not perpendicular to it. For a sheet having a thickness "t", a length "L" and a width "W", the resistance " " is given by the following equation (Eq. I):

R = p *— = ^ *— = R _sh *— Eq. l

Wt t W W wherein "R _S h" is the sheet resistance. Accordingly the sheet resistance R _S h is given by the following equation (Eq. II): In the equation (Eq. II) given above, the bulk resistance "R" is multiplied with a dimension- less quantity ("W/L") to obtain the sheet resistance R _S h, thus the unit of the sheet resistance is "Ohm". For the sake of avoiding confusion with the bulk resistance R, the value of the sheet resistance is commonly indicated as "Ohms per Square" (ohm/sq.) because in the specific case of a square sheet, the following relationships apply: W = L and R = R _S h.

The sheet resistance can be measured by non-contact sheet resistance measurement, also known as inductive measurement. Generally, this method measures the shielding ef- feet created by "eddy currents". Eddy currents (also called "Foucault currents") are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an alternating current electromag- net or transformer, for example, or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material. Thereby a high-frequency magnetic field is generated and the sample is placed in the magnetic field. The conductive material acts on the resonant circuit, such as a resistive load and thus leads to a change in the power consumption in the oscillator circuit. In one version of this technique a conductive sheet under test is placed between two coils. This non-contact sheet resistance measurement method also allows characterizing encapsulated thin-films or films with rough surfaces. Suitable measuring systems are known and are commercially available, e.g. from Suragus GmbH, Dres- den, Germany or from KITEC microelectronic technologie GmbH, Erding, Germany. Preferably, the measuring of sheet resistances by the non-contact sheet resistance measurement method is carried out for the purposes of the present invention according to standard procedure ASTM F1844 - 97 (2016).

Another method to measure sheet resistance is by applying a "four point-probe", as is known in the art. Devices for use in four point probes and instructions for carrying out associated methods can be obtained, for example, from Four Point Probes / Bridge Technology, Chandler Heights AZ, 85127, USA. Preferably, the measuring of sheet resistances by the four-point probe method can be carried out for the purposes of the present invention according to standard procedure ASTM F171 1 - 96 (2016). The two methods for measuring sheet resistances as provided herein (four point-probe and inductive measurement) are generally equivalent and sheet resistance values measured with any of the methods are usually essentially identical, within a reasonable measuring tolerance. The inductive measurement method is, however, sometimes preferred, in particular in cases where the electrically conductive medium (i.e. the plurality of electrically conductive nanoobjects) is not directly accessible or cannot directly be contacted, e.g. because it is covered by an insulating medium (e.g. by the matrix material in form of the radiation-curable composition or the corresponding cured material).

For all instructions or explanations of measuring methods and/or comparative measuring methods in the context of the present invention (e.g. measuring sheet resistance before and after stretching a stretchable, electrically conductive film of the invention) measuring is preferably conducted or to be conducted on the surface (side) of the film which is best suited for this purpose according to the common and usual scientific customs in the field, if not expressly stated otherwise. E.g. for comparative measuring, if a sheet resistance value has been measured on one surface of a film according to the invention (e.g. on surface A, as explained above), then the comparative measuring is to be done on this same surface of the film of the invention (surface A), in order to produce genuinely comparable results.

The electrically conductive, film according to the invention preferably has a sheet resistance in the range of from 5 to 150 ohm/sq, preferably in the range of from 10 to 100 ohm/sq, more preferably in the range of from 10 to 50 ohm/sq and yet more preferred in the range of from 10 to 40 ohm/sq, as measured on at least one (preferably both) of the film's surfaces -preferably in the unstretched state- by non-contact-type sheet resistance measurement (inductive measurement) according to standard procedure ASTM F1844 - 97(2016). The term "unstretched" shall mean for the purposes of the present invention that a film accord- ing to the invention with this property of being unstretched has - after its production - never been stretched before along any of its longer external dimensions to a significant extent, i.e. by more than 5 % in any of its length or width. Preferably, and in accordance with preferred films of the invention, the preferred sheet resistance is at least present on the respective surface of said electrically conductive film which has a higher concentration of electrically conductive nanoobjects and/or on which (or to which) at least a portion of said electrically conductive nanoobjects are exposed ("surface A" as explained above).

Preferably, the electrically conductive film of the invention is an electronically conductive film ("electronically conductive"being opposed to "ionically conductive"). Likewise, preferably the "electrically conductive nanoobjects" are electronically conductive nanoobjects. Preferably, the electrically conductive film comprising a plurality of electrically conductive nanoobjects is an electronically conductive film comprising a plurality of electronically conductive nanoobjects. Most preferably, in such an electronically conductive film comprising a plurality of electronically conductive nanoobjects, at least 90 % of the total electrical conductivity of the electronically conductive film is caused by the presence of said plurality of electronically conductive nanoobjects. As explained above, a preferred embodiment of the invention comprises an electrically conductive film which has two opposite surfaces (sides) with different electrical properties: one surface which shows electrical conductivity or which shows a higher electrical conductivity upon direct contact with the surface ("surface A") and one surface which does not show or which shows a lower electrical conductivity upon direct contact with the surface ("surface B"). In a preferred embodiment, the electrically conductive film of the invention therefore has different values of sheet resistance at its two opposite surfaces, preferably as measured in the unstretched state by non-contact-type sheet resistance measurement according to standard procedure ASTM F1844 - 97(2016). Preferably the ratio of sheet resistances of the two opposite surfaces (higher sheet resistance divided by lower sheet resistance) is above 1.1 , preferably above 2, more preferably above 10, preferably when measured in the unstretched state, as discussed above.

The electrically conductive film according to the invention preferably is also stretchable and/or tensile. The term "stretchable" in the context of the present invention preferably means that said film can be stretched along at least one of its longer external dimensions (length or width) by at least 20 %, preferably by at least 30 %, more preferably by at least 50 %, without tearing or breaking in each case. Insofar, the tensile properties of said film are undirectional. For example, a piece of a stretchable, electrically conductive film according to the invention which has, in the unstretched state, the dimensions 10 mm (width) X 30 mm (length) can be stretched in length to at least 36 mm, preferably to at least 39 mm, more preferably to at least 45 mm, without tearing or breaking. Upon removing the tensile strain, the stretched film preferably relaxes to approximately the dimensions it had before applying the tensile strength, thus exhibiting an elastomer-like behavior. Similar results were achieved with electrically conductive films according to the invention which had thick- nesses in the range of from 30 to 200 μιτι. Thus, a preferred electrically conductive film of the present invention is elastic.

More in particular, a stretchable, electrically conductive film according to the invention substantially retains its electrical properties when stretched and/or when tensile strain is applied to it. As a tendency, an approximately linear increase in sheet resistance is observed when the film according to the invention is stretched along at least one of its longer external dimensions, at least up to a stretch in length and/or width of 50 % and/or at least when the film is stretched for the first time. Surprisingly, according to own experiments a film according to the invention retained measurable electrical properties, in particular conductivity, up to and until the moment it tore or broke. Preferably, the sheet resistance of the electrically conductive film of the invention, as measured on at least one of the film's surfaces by non-contact-type sheet resistance measurement according to standard procedure ASTM F1844 - 97(2016), does not increase by more than 75 %, preferably by not more than 65 %, more preferably by not more than 60 %, when stretching it along at least one of its longer external dimensions (i.e. length or width) by 20 %. Preferably, the sheet resistance of the electrically conductive film of the invention, as measured on at least one of the film's surfaces by non-contact-type sheet resistance measurement according to standard procedure ASTM F1844 - 97(2016), does not increase by more than 125 %, preferably by not more than 1 10 %, more preferably by not more than 100 %, after stretching along at least one of its longer external dimensions (length or width) by 50 %. Preferably and where applicable, the sheet resistance is measured for these purposes on the surface (side) showing the lower sheet resistance (i.e., higher conductivity; "surface A" as explained above).

As explained above, a preferred stretchable, electrically conductive film of the invention, after stretching and removing the tensile strain, relaxes to approximately the dimensions it had before applying the tensile strain, thus exhibiting an elastomer-like behavior. Typically, an increased value of a film's sheet resistance is found, when measured (preferably on the surface (side) showing the lower conductivity, surface A), after stretching along at least one of its longer external dimensions (length or width) by 20 %, and subsequently removing the tensile strength, thus allowing the film to relax. The increase in sheet resistance of the stretched and subsequently relaxed film when measured under these conditions is preferably not higher than 50 %, preferably not higher than 40 % and more preferably not higher than 35 %, in comparison with the sheet resistance of the film of the present invention in its unstretched state. In a further preferred embodiment, the (preferably stretchable) electrically conductive film according to the invention is also flexible. The term "flexible" as used herein means that a material with this property can be folded, crumpled and/or bent in all directions without experiencing damage to its structure, while maintaining all or at least a substantial part of its electrical properties. E.g. simple bending should not cause a significant increase of the sheet resistance, e.g. an increase of more than 5 %. Those skilled in the art will understand the level of mechanical stress that can reasonably be applied when manipulating electronic components like the (preferably stretchable) electrically conductive film according to the invention.

The beneficial mechanical properties of the electrically conductive film according to the invention, in particular its properties of being stretchable and/or flexible, make said film particularly suitable for use in products like electronic wristbands, electronic textiles, stretchable cyber skins for robotic devices and/or stretchable sensors.

In a particularly preferred embodiment, the (preferably stretchable) electrically conductive film according to the invention is also adhesive. The term "adhesive" and/or "self-adhesive" in the context of the present invention means that the film of the invention can be attached to surfaces of objects (i.e. substrates), preferably of rigid objects, more preferably to the surfaces of smooth, rigid objects, without any additional supporting substances or aids required in each case. Suitable objects to whose surfaces the film of the invention can be attached are preferably objects made of glass, plastics and/or wood. Suitable types of plas- tics are organic polymers, preferably organic polymers selected from the group consisting of polymethylmethacrylate (PMMA, commercially available e.g. as Plexiglas™), polycarbonate (PC), polyethylene (PE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), low density polypropylene (LDPP), polyethylene terephthalate (PET), glycol modified polyethylene terephthalate, polyethylene naphthalate (PEN), cellulose acetate butyrate, polylactide (PL), polystyrene (PS), polyvinyl chloride (PVC), polyiimides (PI), polypropyleneoxide (PPO), and mixtures of any of the foregoing organic polymers. PET and PEN are particularly preferred.

Preferably, the terms "adhesive" and/or "self-adhesive" in the context of the present invention have the meaning that a (preferably stretchable) electrically conductive film according to the invention with said adhesive and/or self-adhesive properties shows a peel strength of not less than 300 g/cm, preferably in a range of from 200 to 300 g/cm when measured according to standard test procedure ASTM D 903-98(2010) on a glass substrate in each case. See below for the difference of adhesive properties of opposite surfaces of preferred films according to the invention. Moreover, an adhesive (and preferably stretchable) electrically conductive film according to the invention is preferably also reusable in the sense that it can be removed from the object to which it had been attached and can be repositioned again to the same or a different object. The term "reusable" in the context of the present invention preferably has the meaning that said peel strength of not less than 300 g/cm, on a glass substrate, of an adhesive (preferably stretchable) electrically conductive film according to the invention film does not decrease by more than 20 % after two cycles of removing and repositioning the film on said glass substrate. As explained above, a preferred embodiment of the invention comprises a (preferably stretchable) electrically conductive film which has two opposite surfaces (sides) with different electrical properties: one surface which shows electrical conductivity or which shows a higher electrical conductivity upon direct contact with the surface ("surface A") and one surface which does not show or which shows a lower electrical conductivity upon direct contact with the surface ("surface B").

In a preferred embodiment, the (preferably stretchable) electrically conductive film of the invention also shows different values of peel strength at its two opposite surfaces, as measured according to standard test procedure ASTM D 903-98(2010), on a glass substrate. Preferably, the value of the sheet resistance is higher on the surface having the higher peel strength. Preferably, the value of the peel strength on the surface which shows the higher conductivity (lower sheet resistance; "surface A") is not less than 50 %, more preferably not less than 60 % and most preferably not less than 70 % of the value of the peel strength on the surface which shows the lower conductivity (higher sheet resistance; "surface B"). The beneficial and preferred adhesive properties of the (preferably stretchable) electrically conductive film according to the invention, in particular its preferred properties of being self- adhesive and/or reusable, make said film particularly suitable for use in products like thin film heaters, electronic wristbands, electronic textiles, triboelectricity nanoenergy generators, supercapacitors, current collectors of batteries, attachable electronic sticking/memo notes, stretchable cyber skins for robotic devices, stretchable sensors, articles in the automotive industry and/or articles in the construction industry.

Preferably, the (preferably stretchable) electrically conductive film according to the invention is transparent. Each of the terms "transparent", "transparency" or "optically transparent" in the context of the present invention means that an electrically conductive film according to the invention with these properties has a light transmission of 65 % or more, preferably of 70 % or more, more preferred of 75 % or more, yet more preferred of 80 % or more, even more preferred of 85 % or more and yet even more preferred of 90 % or more, in the visible region of the electromagnetic spectrum, i.e. in a range of from about 380 nm to 780 nm, more in particular in a range of from about 400 to 700 nm, when measured according to standard method ASTM D1003-13 (procedure A). As will be understood, the light transmission capacity of the film according to the invention is i.a. a function of its thickness and its material. Thus, a transparent film has a limited thickness.

The measurement of light transmission by means of a hazemeter is defined in ASTM D1003-13 as "Procedure A - Hazemeter". The values of light transmission (corresponding to the luminous transmittance as defined in ASTM D1003-13) given in the context of the present invention refer to this procedure.

The beneficial and preferred property of a stretchable, electrically conductive film according to the invention, in particular in its preferred embodiment as a stretchable, adhesive and/or self-adhesive and/or reusable, electrically conductive film, as being transparent, make said film particularly suitable in addition for use in products like transparent electrodes, flat panel displays, liquid crystal displays (LCD), touch screens, electrochromic windows, solar cells, transparent film heaters, smart glasses/spectacles, smart watches (including activity trackers), electronic displays, attachable electronic sticking/memo notes, attachable energy har- vesters (e.g. solar cells).

Particularly preferably, a stretchable, electrically conductive film of the invention therefore can have a combination of several beneficial properties, e.g. as being a stretchable, adhesive and/or self-adhesive and/or reusable, transparent, electrically conductive film.

Thus, a (preferably stretchable) electrically conductive film of the invention preferably has one or more, more preferably it has all, of the following properties:

A sheet resistance in the range of from 5 to 150 ohm/sq, preferably in the range of from 10 to 100 ohm/sq, more preferably in the range of from 10 to 50 ohm/sq and yet more preferred in the range of from 10 to 40 ohm/sq, as measured on at least one of the film's surfaces in the unstretched state by non-contact-type sheet re- sistance measurement (inductive measurement) according to standard procedure

ASTM F1844 - 97(2016). Preferably, if applicable, the sheet resistance is measured for this purpose on the respective surface of a stretchable, electrically conductive film which has a higher concentration of electrically conductive nanoobjects and/or on which (or to which) at least a portion of said electrically conductive nanoobjects are exposed ("surface A" as explained above).

A sheet resistance as measured on at least one of the film's surfaces by non-contact- type sheet resistance measurement according to standard procedure ASTM F1844 - 97(2016), which does not increase by more than 75 %, preferably by not more than 65 %, more preferably by not more than 60 %, after stretching along at least one of its longer external dimensions (length or width) by 20 % in each case. A peel strength of not less than 300 g/cm, preferably in a range of from 200 to 300 g/cm when measured according to standard test procedure ASTM D 903-98(2010) on a glass substrate and which peel strength preferably does not decrease by more than 20 % after two cycles of removing and repositioning the film under said condi- tions.

A light transmission of 65 % or more, preferably of 70 % or more, more preferred of 75 % or more, yet more preferred of 80 % or more, even more preferred of 85 % or more and yet even more preferred of 90 % or more, in the visible region of the electromagnetic spectrum, i.e. in a range of from about 380 nm to 780 nm, more in par- ticular in a range of from about 400 to 700 nm, when measured in each case according to standard method ASTM D1003-13 (procedure A).

The present invention also relates to a product, comprising a (preferably stretchable) electrically conductive film according to the invention. A suitable product can preferably be selected from the group comprising transparent electrodes, flat panel displays, liquid crystal displays (LCD), touch screens, electrochromic windows, solar cells, transparent film heaters, thin film heaters, smart glasses/spectacles, smart watches (including activity trackers), electronic wristbands, electronic textiles, triboelectricity nanoenergy generators, superca- pacitors, current collectors of batteries, electronic displays, attachable electronic sticking/memo notes, attachable energy harvesters (e.g. solar cells), stretchable cyber skins for robotic devices, stretchable sensors, articles in the automotive industry and articles in the construction industry.

The present invention also relates to a method of making a (preferably stretchable) electrically conductive film according to the invention, comprising the following steps: providing or preparing a radiation-curable composition, said radiation-curable com- position comprising

(a) as resin component, at least one aliphatic urethane (meth)acrylate, which has two ethylenically unsaturated double bonds per molecule and comprises at least one polytetrahydrofurandiol having a number average molecular weight Mn of at least 500 g/mol,

and

(b) as reactive diluent component, at least one monoethylenically unsaturated compound of formula I, R

I

H ₂ C = C— O— (CH ₂ ) _k Y

(I)

comprising at least one aliphatic heterocycle as structural element, wherein

R is hydrogen or methyl

k is an integer selected from 0, 1 , 2, 3 and 4, and

Y is a 5- or 6-membered, saturated heterocycle comprising one or two oxygen atoms, the heterocycle being unsubstituted or substituted, preferably mono-substituted, by Ci-C4-alkyl;

providing or preparing a mixture comprising a plurality of electrically conductive na- noobjects, applying said radiation-curable composition and said mixture comprising a plurality of electrically conductive nanoobjects to a surface of a substrate, in a single step after pre-mixing of said radiation-curable composition with said mixture comprising a plurality of electrically conductive nanoobjects or in separate steps without pre-mixing of said radiation-curable composition with said mixture comprising a plurality of electrically conductive nanoobjects and curing said radiation-curable composition by application of high-energy radiation. The preferred features and corresponding explanations set forth above with respect to the electrically conductive film of the invention apply also to the method of making of a (preferably stretchable) electrically conductive film according to the invention, mutatis mutandis.

In the method of making according to the invention, the radiation-curable composition can be prepared in a manner known in the art, e.g. by mixing resin component (a) with reactive diluent component (b) and photoinitiator component (c) in the weight ratios as prescribed above in either order.

In a preferred embodiment, resin component (a) can be mixed with reactive diluent component (b) in the weight ratios as defined above, e.g. reactive diluent component (b) can be added to and mixed with resin component (a) in an amount of 30 wt.-%, relative to the total weight of polymerizable components resin component (a) plus reactive diluent component (b). Photoinitiator component (d) may then be mixed in preferred quantities with the premixture of components (a) and (b) previously prepared and the resulting mixture of components (a), (b) and (d) may be used for additional preparation steps, as explained in more detail below.

In the method of making according to the invention, said radiation-curable composition and said mixture comprising a plurality of electrically conductive nanoobjects are applied to a surface of a substrate. A preferred substrate for this purpose has a smooth surface, is inert under the conditions applied to reactions with any of the radiation-curable composition and/or the mixture comprising electrically conductive nanoobjects and allows detaching or peeling-off from its surface the final, cured, preferably fully cured and stretchable, electrically conductive film according to the invention, once this has been formed. Typically and preferably, said film can be detached or peeled-off from the surface of said suitable substrate without any damages to the film like tears, fissures, breaks or the like. A suitable substrate for this purpose preferably comprises or consists of one or more materials selected from the group consisting of glass, metals, sapphire, silicon (Si) and plastics. Preferred as plastics are organic polymers, more preferred the organic polymers as disclosed above as suitable objects (i.e. substrates) to which the electrically conductive film of the invention can be attached. In one preferred embodiment of said method of making, said radiation-curable composition and said mixture comprising a plurality of electrically conductive nanoobjects, without pre- mixing, are applied to a surface of a substrate in separate steps, wherein in a first application step said mixture comprising a plurality of electrically conductive nanoobjects is applied to the surface of the substrate and - subsequently, in a second application step, said radiation-curable composition is applied onto the mixture comprising a plurality of electrically conductive nanoobjects on the surface of the substrate or onto the plurality of electrically conductive nanoobjects on the surface of the substrate, so that an electrically conductive film comprising a plurality of electrically conductive nanoobjects is created on the substrate, wherein preferably the concentration of electrically conductive nanoobjects has a gradient in a direction perpendicular to an interface of the (preferably stretchable) electrically conductive film.

In this preferred embodiment of the method of making according to the invention, said first application step and said second application step can be carried out as many times as desired in order to create as many layers of mixtures comprising a plurality of electrically conductive nanoobjects and/or as many layers of radiation-curable composition as desired. Preferably, each of the first application step and second application step is only carried out once so that (by means of the single first application step) only one layer comprising a plurality of electrically conductive nanoobjects is created and by subsequently conducting the second application step only one composite layer comprising a radiation-curable com- position and said plurality of electrically conductive nanoobjects is created, this composite layer being an electrically conductive film of the invention.

The radiation-curable composition according to the method of making of the invention can e.g. be prepared and/or applied to a substrate (e.g. a plurality of electrically conductive nanoobjects as defined above or as defined above as preferred) and/or cured, in each case according to methods as disclosed in documents WO 2005/035460, US 2007/066704 and EP 1678094B1 , which documents and their disclosures are all incorporated herein by reference in their entireties, or in each case analogously to methods as disclosed therein.

In said method of making according to the invention, preferably the concentration of electrically conductive nanoobjects has a concentration gradient of said electrically conductive nanoobjects in a direction perpendicular to said surface of the substrate. Preferably, at least a portion of said electrically conductive nanoobjects is/are in this case exposed on the respective surface of the (preferably stretchable) electrically conductive film, contacting said surface of the substrate. In variations of this preferred embodiment of the method of making according to the invention, a plurality of electrically conductive nanoobjects, preferably of metal nanoobjects, can be deposited on a surface of a substrate in a manner so that junctions between adjacent and overlapping (contacting) electrically conductive nanoobjects are formed, preferably metal-metal junctions between adjacent and overlapping (contacting) metal nanoobjects. Typically, in this embodiment, a plurality of metal nanoobjects is applied to said surface of said substrate in the form of a suspension (sometimes referred to as an ink) comprising metal nanoobjects, dispersed in a carrier liquid. The carrier liquid usually has a boiling point below 120 °C. Commonly used carrier liquids are e.g. ethanol, isopropyl alcohol (propan- 2-ol), water or mixtures of any of the foregoing. Thus, disposing a plurality of metal nanoob- jects on a surface of a substrate in this alternative is usually carried out by: forming on a surface of said substrate a wet film by applying a suspension of metal nanoobjects dispersed in a carrier liquid to said surface of said substrate and partially or completely removing said carrier liquid from the wet film formed on said surface of said substrate. Preferably said ink is applied to said surface of said substrate by a technique selected from the group consisting of coating and printing techniques. Preferred techniques are selected from the group consisting of bar coating, (doctor) blade coating, slot-die coating, ink-jet printing, spin-coating and spray-coating (including air spraying and electrostatic spraying).

In further variations of this preferred method of making according to the invention, the plu- rality of electrically conductive nanoobjects may be arranged on a surface of said substrate in such manner that it extends over the complete surface of said substrate, or only within limited regions of said surface. In specific cases, the plurality of electrically conductive nanoobjects forms a pattern on said surface of said substrate. The pattern may be selected from any random and non-random structures, like grids, stripes, waves, dots and circles. Preferably, the coverage of the surface of said substrate by said plurality of metal nanoobjects is in the range of from 10 % to 65 %, preferably in the range of from 15 % to 35 %. For calculating the coverage, images of the surface having said plurality of metal nanoobjects disposed thereon are taken by optical microscopy or scanning electron microscopy, and the images are analyzed by means of an image analyzing software capable of differentiating within said images said metal nanoobjects from the bare surface of the substrate and calculating the fraction of the surface covered by the metal nanoobjects, as is known in the art. The thickness of a resulting layer comprising a plurality of electrically conductive nanoobjects, preferably metal nanoobjects, but not yet a radiation-curable composition as defined above, is usually in the range of from 10 to 150 nm, preferably in the range of from 20 to 100 nm. Said carrier liquid having a boiling point of less than 120 °C is usually removed from the wet film by evaporation (drying). Preferably, said carrier liquid having a boiling point of less than 120 °C is removed by exposing the wet film formed on said surface of said substrate for a suitable period of time, preferably in the range of from 5 min. to 20 min., more preferably in the range of from 5 min. to 15 min., to air having a temperature of less than 150 °C, preferably at a temperature in the range of from 20 °C to 120 °C, e.g. at about 80 °C. In some cases, the carrier liquid is removed at room temperature, i.e. at a temperature in the range of 20 to 23 °C.

After depositing said plurality of electrically conductive nanoobjects, preferably metal nanoobjects, on said surface of said substrate, said radiation-curable composition is prefera- bly applied onto the plurality of metal nanoobjects previously prepared. It is assumed that applying the radiation-curable composition onto the plurality of metal nanoobjects does not significantly alter the junctions between adjacent and overlapping (mutually contacting) metal nanoobjects of said plurality of metal nanoobjects disposed on said surface of said substrate. The radiation-curable composition according to the present invention , e.g. the uncured radiation-curable composition prepared in a manner as explained above, can be applied onto the plurality of electrically conductive nanoobjects, preferably on the metal nanoobjects and/or layer of nanoobjects, by a variety of coating methods, preferably by a coating method selected from the group comprising or consisting of (doctor) blade coating, slot-die coating, ink-jet printing, spin-coating and spray-coating (including air spraying and electrostatic spraying). The amount of radiation-curable composition of the invention used for coating can be adapted to the desired thickness of the resulting cured reaction product (preferably the electrically conductive film of the invention) by methods known in the art. For example, the radiation-curable composition may be applied in an amount in the range of from 0.05 to 5 g/m ² or in the range of from 0.1 to 2 g/m ² . In another embodiment of the method of making according to the invention where said radiation-curable composition and said mixture comprising a plurality of electrically conductive nanoobjects, after pre-mixing, are applied to a surface of a substrate, wherein said mixture comprising a plurality of electrically conductive nanoobjects is first pre-mixed with at least one component of said radiation-curable composition and - where required - is then mixed with one or more additional components of said radiation-curable composition to yield a final mixture, and subsequently said pre-mixture or said final mixture is applied to a surface of a substrate in a similar manner as pointed out above.

The radiation-curable composition applied to said plurality of electrically conductive na- noobjects as described above can subsequently be cured, preferably fully cured, by application of high-energy radiation. High-energy radiation is preferably selected from UV-light radiation and electron-beam radiation. Preferably, a radiation dose in the range of from 80 to 3000 mJ/cm ² is applied to the radiation-curable composition and/or is sufficient for fully curing it. Where the radiation-curable composition as defined above and in the claims with respect to the electrically conductive film of the present invention is cured by application of electron- beam radiation, the radiation-curable composition preferably comprises no UV- photoinitiatior component (d). Preferably, in this embodiment an electron-beam with an energy in a range of from 150 to 300 keV is applied to the radiation-curable composition. Where the radiation-curable composition as defined above and in the claims with respect to the electrically conductive film of the present invention is cured by application of UV-light radiation, the radiation-curable composition comprises UV-photoinitiatior component (d) as defined above or as defined above as preferred. In this embodiment, UV-light radiation is applied to the radiation-curable composition, preferably with a wavelength in the range of from 200 to 400 nm, more preferably in a range of from 200 to 350 nm, and for a suitable period of time, preferably for a period of time in the range of from 50 s to 600 s, more preferably in the range of from 75 s to 500 s and still more preferably in the range of from 100 s to 400 s. The UV-light radiation can be applied to the radiation-curable composition in a conventional UV irradiation device (also known as "UV chamber"), known per se. The embodiment where the radiation-curable composition is cured by application of UV- light is preferred according to the invention. In preferred embodiments of the method of making according to the invention, including its preferred embodiments and variations, said (preferably stretchable) electrically conductive film is subsequently detached from the surface of the substrate wherein detaching preferably comprises peeling-off the electrically conductive film from the surface of the substrate.

The preferred features and corresponding explanations set forth above with respect to the electrically conductive film of the invention apply also to the method of the invention of making an electrically conductive film, mutatis mutandis.

The present invention also relates to the use of a radiation-curable composition, said radiation-curable composition comprising

(b) as resin component, at least one aliphatic urethane (meth)acrylate, which has two ethylenically unsaturated double bonds per molecule and comprises at least one pol- ytetrahydrofurandiol having a number average molecular weight M _n of at least 500 g/mol,

and

(b) as reactive diluent component, at least one monoethylenically unsaturated compound of formula I,

R

I

H ₂ C = C— O— (CH ₂ ) _k Y

(I)

comprising at least one aliphatic heterocycle as structural element, wherein R is hydrogen or methyl

k is an integer selected from 0, 1 , 2, 3 and 4, and

Y is a 5- or 6-membered, saturated heterocycle comprising one or two oxygen atoms, the heterocycle being unsubstituted or substituted , preferably mono-substituted, by Ci-C4-alkyl;

or

of a cured reaction product thereof,

for making an (preferably stretchable) electrically conductive film, preferably a stretchable, adhesive, electrically conductive film. If the electrically conductive film is stretchable and a radiation-curable composition is used for making it, the radiation-curable composition needs to be sufficiently cured to give a product having the desired stretchability.

Preferred is a use of a radiation-curable composition according to the invention wherein said film comprises a plurality of electrically conductive nanoobjects.

Preferably, the use according to the invention of a radiation-curable composition for making an electrically conductive film is directed to making a preferred electrically conductive film according to the present invention as defined above. The preferred features and corresponding explanations set forth above with respect to the electrically conductive film of the invention and the method of making of the invention apply also to the use according to the invention of a radiation-curable composition, mutatis mutandis.

The present invention further relates to the use of an electrically conductive film according to the invention, preferably a stretchable, adhesive, electrically conductive film, for making reusable, stretchable, electrically conductive sticking notes and/or memo notes. The preferred features and corresponding explanations set forth above with respect to the electrically conductive film of the invention and the method of making of the invention apply also to the use according to the invention of an electrically conductive film according to the invention, mutatis mutandis.

Examples: The following examples are meant to further explain and illustrate the invention without limiting its scope.

If not otherwise stated, all experiments and/or measurements as provided herein were conducted under normal conditions (laboratory conditions: 20 °C, 1013 hPa).

For measuring light transmittance according to ASTM D1003-13 (procedure A), an UV VIS- spectrometer "Haze-Gard I" (BYK-Gardner Instruments) was used.

For measuring sheet resistances, a common non-contact sheet resistance measurement system was used. Sheet resistances were measured by the non-contact sheet resistance measurement method according to standard procedure ASTM F1844 - 97 (2016). Any cross-sectional specimens of layers, e.g. of electrically conductive films according to the invention, were prepared using a focused ion beam system (FIB, Helios Nanolab 450 F1 ).

For examining the surface and/or vertical morphology of any specimen, e.g. of electrically conductive films according to the invention, a field-emission scanning electron microscope (FE-SEM, Philips XL30 ESEM-FEG) was used.

Example 1 : Preparation of a stretchable, electrically conductive film according to the invention

Example 1a: Preparation of an AgNW network A plurality of Ag nanowires which had a length in a range of from about 15 to 30 μιτι (average length about 25 μιτι) and a diameter in a range of from about 20 to 40 nm (average diameter about 30 nm) was deposited on a surface of a substrate made of glass, by: forming on said surface of said substrate a wet film (layer) by means of doctor-blade- coating a suspension of the silver nanowires, dispersed in isopropyl alcohol as a carrier liquid, to said surface of said substrate and removing said carrier liquid from the wet film formed on said surface of said substrate by evaporation (drying with an air gun) for about 10 min. in air, at a temperature of about 80 °C, to produce an Ag nanowire network on the glass substrate.

The resulting AgNW network on the glass substrate had a thickness of about 40 to 200 nm and showed a sheet resistance (measured on the free surface, averted from the glass substrate) in a range of from 10 to 30 ohm/sq and a light transmission in the range of from 70 to 90 %.

Example 1 b: Preparation of a stretchable, electrically conductive film

A radiation-curable composition (comprising resin component (a) and reactive diluent com- position (b), both as defined above) was prepared analogously as described in Example 1 (section A)) of document WO 2005/035460, which had a dynamic viscosity in a range of from 15 to 25 Pa s at 23 °C. Dynamic viscosity of the radiation-curable composition can preferably be adjusted to a desired value by either varying the number average molecular weight (M _n ) of the polytetrahydrofurandiol used and/or preferably by varying the amount of reactive diluent component (trimethylolpropaneformal monoacrylate in the present case) used. To this prepared and filtered mixture, 1-hydroxy-cyclohexyl-phenyl-ketone (commercially available as "Irgacure® 184") was added as photoinitiator component (d) in an amount of 5 wt.-%, relative to the total mass of the previously prepared and filtered mixture. The resulting radiation (UV)-curable composition was then applied by doctor-blade-coating to the AgNW network on the glass substrate, as prepared according to Example 1a.

The glass substrate carrying the AgNW network coated with the UV-curable composition so prepared was brought into the reaction chamber of a common UV-light radiation device and irradiated at a wavelength in a range of from 200 to 350 nm for a period of 300 s to produce a cured, stretchable, electrically conductive film according to the invention, on a glass substrate.

After the UV-curing process was finished, the cured film was finally manually detached from the glass substrate to yield an unsupported (meaning "not attached to a support or sub- strate") stretchable, adhesive, transparent, electrically conductive film according to the invention. Said film had a thickness of about 70 μιτι (as determined by SEM) and showed a sheet resistance (measured on the surface with the higher concentration of AgNWs, i.e. the one which used to be on the glass substrate during manufacture of the film) in a range of from 15 to 35 ohm/sq, and a light transmission in a range of from 70 to 90 %.

Example 2: Peel strength on glass substrate

To the cleaned surface of a glass substrate (by consecutive cleaning steps with propan-2- ol, ethanol and water, in an ultrasonic bath for 30 s in each case/step) pieces (dimensions in each case W 10 mm X L 30 mm) of three different test articles were attached: Article 1 : Scotch tape "Magic®" (commercially available from 3M)

Article 2: Post-It® sticking note (commercially available from 3M; only the adhesive part was used)

Article 3: Stretchable, electrically conductive film according to the invention, as prepared according to the method described in Example 1 The attached three different articles were then repeatedly detached (removed) from the substrate by peeling off the respective article from the substrate's surface, and re-attached again, measuring the peeling force reguired for detaching (peeling off) the different articles from the glass substrate in each case. For this purpose, the one end of each article (tape, sticking note or film) was clamped by the grip of a tensile tester. By pulling up the grip, the adhesive force between the film and substrate was measured. The pulling speed was 3mm/s in each case. Attaching/detaching measuring cycles were carried out three times in total for each article. Article 3 (film according to the present invention) was in each case attached to the substrate with the surface (side) showing the higher adhesive strength ("surface B"). The forces ("peel strength") reguired for peeling off the different articles after each of the three adhesions (measuring cycles) are shown in table 1 below (mean values from five different samples per article).

Table 1 : Results of peel strength test on glass substrate

The results from Example 2 (see table 1 ) show that, upon repeated attaching and detaching to a glass substrate, the adhesive strength of a stretchable, electrically conductive film ac- cording to the invention decreased only insignificantly (by about 1 1 % after three measuring cycles) and about linearly, thus essentially preserving the adhesive strength after removing and repositioning the film several times. The results from Example 2 are therefore illustrative for the reusability characteristics of the film according to the invention. These reusability characteristics were more pronounced for the film according to the invention than for similar attachable systems from the prior art: Article 1 showed a sharp decrease (about 26 %) in adhesive strength after the 3 ^rd attaching/detaching measuring cycle. Article 2 showed a much lower adhesive strength from the beginning and lost most of it already after two measuring cycles.

Example 3: Peel strength on PET substrate To the cleaned surface of a PET substrate (by consecutive cleaning steps with propan-2- ol, ethanol and water, in an ultrasonic bath for 30 s in each case) pieces (dimensions in each case W 10 mm X L 30 mm) of three different test articles (Article 1 , Article 2 and Article 3, all as defined in Example 2) were attached.

The attached three different articles were then repeatedly detached (removed) from the substrate by peeling off the respective article from the substrate's surface, and re-attached again, measuring the peeling force required for detaching (peeling off) the different articles from the PET substrate in each case, as described in Example 2. Attaching/detaching measuring cycles were carried out three times in total for each article. Article 3 was in each case attached to the substrate with the surface (side) showing the higher adhesive strength ("surface B"). The forces ("peel strength") required for peeling off the different articles after each of the three adhesions (measuring cycles) are shown in table 2 below (mean values from five different samples per article). Table 2: Results of peel strength test on PET substrate

The results from Example 3 (see table 2) show that, upon repeated attaching and detaching to a PET substrate, the adhesive strength of a stretchable, electrically conductive film according to the invention decreased only slowly (by about 19 % after three measuring cycles) and about linearly, thus largely preserving the adhesive strength after removing and repositioning the film several times. The results from Example 3 are therefore also illustrative for the reusability characteristics of the film according to the invention. These reusability characteristics were more pronounced for the film according to the invention than for similar attachable systems from the prior art: Article 1 showed a significant decrease in adhesive strength after the 2 ^nd and 3 ^rd attaching/detaching measuring cycles (about 15 % per cycle). Article 2 again showed a much lower adhesive strength from the beginning and lost most of it already after two measuring cycles.

Example 4: Behaviour of sheet resistance under tensile strain (stretching)

A stretchable, electrically conductive film according to the invention was prepared accord- ing to the method as described in Example 1. A rectangular piece of said film (W 10 mm X L 30 mm; thickness 70 μιτι) was manually stretched along one of its longer external dimensions (here: along its length L) by two defined percentages of (additional) length (20 % and 50 %, see table 3, total length 30mm - 36 mm - 45 mm) and the respective resistance values were recorded and compared with the value of sheet resistance of the same film under unstretched conditions.

Then, on the same film, the tensile strain (stretch) was released again in two defined steps so that the film - due to its elastic properties - relaxed (to 20 %, 36mm and to 0 %, 30mm, respectively) and again the respective values of sheet resistance were recorded. Stretching and releasing was carried out on five different samples (i.e. rectangular pieces of film according to the invention, see above) for each test.

The resistance values were measured in each case by a two-point measuring method where two opposite ends of a sample were clamped in each case to the two electrodes of a common multimeter, and the resulting resistance was read out.

The results from the experiments of Example 4 are shown in table 3 (mean values from five different samples).

Table 3: Influence of tensile strain on film resistance

The results from Example 3 show that a stretchable, electrically conductive film according to the invention under significant mechanical stress (tensile strain, stretch by 20 % or 50 %, respectively), albeit impacted, remains electrically conductive. Furthermore, the results from Example 3 show that, once mechanical stress (tensile strain, stretch) is released, the value of the sheet resistance of the film according to the invention returns surprisingly closely to the value of the unstressed film. This effect was not expected as by stretching the film's delicate contacts between individual AgNWs are expected to be broken, and even a minor distance between wires would be expected to contribute to a significant increase of the electrical resistance. It appears that the preferable elastic properties of the electrically conductive film of the invention in combination with the use of the plurality of electrically conductive nanoobjects allows for this surprising effect.