Silver nanowire ink

Abstract

The present invention relates to silver nanowire-based ink formulations. In particular, the present invention relates to silver nanowire-based ink formulations, said inks being stable, transparent and with improved conductivity.

Description

Title of the invention: Silver nanowire ink

[0001] The present invention relates to silver nanowire-based ink formulations. In particular, the present invention relates to silver nanowire-based ink formulations, said inks being stable, transparent and with improved conductivity. The present invention also relates to the use of the claimed silver nanowire-based ink for the manufacture of transparent conductive elements by additive manufacturing, in particular by screen printing; as well as the manufacture of transparent conductive electrodes from this claimed silver nanowire-based ink.

[0002] Transparent conductive films (which we will designate by the abbreviation recognized by those skilled in the art "TCF" in the remainder of the description) are present in many products such as liquid crystal displays ("LCD"), touch screens (telephones, tablets, Global Positioning System (designated by the abbreviation recognized by those skilled in the art "GPS"), etc.), organic light-emitting diodes or "OLED" (usually designated by its English acronym "OLED", for organic light-emitting diode) for lighting, photovoltaics (organic such as silicon) but also optics. These TCFs have a strong power of attraction given the enormous markets for the products in which they are incorporated.This TCF market is mainly occupied by indium tin oxide (usually referred to by its English acronym "ITO") because this ITO allows to achieve very good sheet resistances or also called square resistances (as low as 10 Q / D) as well as very good transparency, two important conditions for TCFs. However, TITO has two disadvantages: 1) ITO films are not very flexible and the sheet resistance increases sharply with the radius of curvature, which does not allow them to respond favorably to applications that require flexibility and 2) indium, which is one of the three constituents of ITO, is a substance for which there is no deposit as such, but which is extracted as a by-product of zinc mining (in very small quantities).Moreover, among the top 3 indium producing countries, there is no European country (China, Canada, Japan = about 75% of production). It has therefore been identified as one of the 14 key raw materials by the European Union.

[0003] In this context of an alternative to ITO, the applicant has developed conductive and transparent inks that can advantageously replace existing technologies while providing other advantages that will be listed in the present description. These inks can advantageously be used as transparent electrodes and / or heating circuits in markets such as 5G smartphones, "wearables" (an English acronym for which the French Academy has not yet found a synonym in French and which we will translate as "connected objects that can be worn"); among the claimed inks, some (in particular those comprising metal oxide nanoparticles) have also been designed and developed to improve the manufacturing costs of transparent conductive layers (for charge transport - for example "ETL" for "ElectronTransportLayer" and / or "HTL" for "HoleTransportLayer") for example for the organic photovoltaic markets (usually referred to by its English acronym "OPV", for "Organic Photovoltaics"), OLED, flat screens and optics.Furthermore, and this constitutes a particular embodiment according to the present invention, the claimed ink is particularly suitable for use in the field of screen printing, which makes it possible to directly print a transparent conductive design by additive manufacturing.

[0004] Ink

[0005] The present invention relates to an ink comprising as main compounds:

[0006] a. at least 0.1% by weight of silver nanowires, b. at least 0.75% by weight of monohydric alcohol having from 1 to 4 carbon atoms, preferably isopropyl alcohol, c. at least 2% by weight of hydroxypropyl methylcellulose, d. at least 20% by weight of water, e. at least 20% by weight of ethylene glycol, and f. at least 10% by weight of propylene glycol propyl ether,

[0007] the sum of the main compounds representing at least 60% by weight of the ink.

[0008] In a particular embodiment according to the present invention, the sum of the main compounds of the ink represents at least 65% by weight of the claimed ink, for example at least 75% by weight, preferably at least 90% by weight of the ink.

[0009] The development of this ink formulation encountered numerous technical problems, among which we will cite, by way of illustration, the formation of foam and drying. Indeed, it is neither the selection of solvents nor the selection of an antifoam agent which made it possible to arrive at an optimal formulation as claimed, but rather the combination of the selection of all the main compounds with their claimed contents. Thus, and this constitutes a particular embodiment according to the present invention, the ink formulation is also characterized in that the weight ratio between water and ethylene glycol ((water) / (ethylene glycol)) is between 0.5 and 2, for example between 0.8 and 1.2.

[0010] Ink viscosity

[0011] In a particular embodiment according to the present invention, the viscosity of the ink measured at a shear rate of 40 s 1 and at 20°C is between 500 and 50,000 mPa.s, preferably between 750 and 10,000 mPa.s, for example between 900 and 2000 mPa.s.

[0012] The viscosity may be measured using any appropriate method. For example, it may advantageously be measured using the following method:

[0013] • Device: AR-G2 Rheometer from TA Instrument • Conditioning time: Pre-shear at 100 s-1 for 3 minutes / equilibration for 1 minute • Test type: Shear bearings • Levels: 10 s1, 40 s1, 100 s1 and 1000 s1 • Duration of a level: 5 minutes • Mode: linear • Measurement: every 10 seconds • Temperature: 20°C • Curve reprocessing method: Newtonian • Reprocessed area: the entire curve.

[0014] Silver nanowires

[0015] The ink according to the present invention comprises at least 0.1% by weight of silver nanowires. Any type of silver nanowires may advantageously be used in the context of the present invention. The concentration of said silver nanowires in the ink is advantageously limited to 2% by weight of the ink; in a particular embodiment according to the present invention, the concentration of silver nanowires in the ink is between 0.15% and 1% by weight. Silver nanowires having an average nanowire length of between 5 and 50 μm, preferably between 10 and 30 μm and / or an average nanoparticle diameter of between 15 and 60 nm, preferably between 20 and 40 nm will be more particularly preferred.

[0016] This characterization of nanowire sizes can be carried out by any appropriate method. We will cite as an illustration the following method: photographs taken by microscope, in particular by means of a Field Emission Gun Scanning Electron Microscope (FE-SEM) type device - measurements carried out in ultra-high resolution mode (FoV=50pm), at an electron energy of 10 keV and different magnifications ranging from 7,000 times to 350,000 times. An average is carried out on a number of nanowires representative of the majority of the nanowires, for example 30 nanowires, which makes it possible to establish an average length and / or an average diameter of the nanowires.

[0017] The silver nanowires that can be preferred in the context of the present invention are generally available in the form of a dispersion in solvents such as isopropyl alcohol (which we will designate as “IPA” in the present description) and / or water; the concentration of these silver nanowires in their solvent(s) will be preferably greater than 0.5% by weight, for example greater than 0.8% by weight (weight of nanowires / (weight of solvent + weight of nanowires)).

[0018] Monohydric alcohol

[0019] The ink according to the present invention comprises at least 0.75% by weight of monohydric alcohol having from 1 to 4 carbon atoms. This alcohol will advantageously be selected from aliphatic monohydric alcohols, for example selected from the group consisting of methanol, ethanol, propanol and butanol, and / or a mixture of two or more of said aliphatic monohydric alcohols; isopropyl alcohol being the preferred alcohol.

[0020] The concentration of monohydric alcohol in the ink is advantageously limited to 5% by weight of the ink; in a particular embodiment according to the present invention, the concentration of monohydric alcohol in the ink is between 1% and 2% by weight.

[0021] HPMC

[0022] The ink according to the present invention comprises at least 2% by weight of hydroxypropyl methylcellulose ("HPMC"). The concentration of HPMC in the ink is advantageously limited to 4% by weight of the ink; in a particular embodiment according to the present invention, the concentration of HPMC in the ink is between 2.5% and 3.5% by weight.

[0023] Hydroxypropyl methylcellulose, also known as hypromellose, is an inert and viscoelastic cellulose ether. Its use is particularly well-known and widespread in the pharmaceutical, food (E464) and construction sectors.

[0024] The hydroxypropyl methylcellulose that can be preferred in the context of the present invention has the following characteristics:

[0025] - a methoxy group content of the HPMC of between 20 and 40% by weight, preferably between 27 and 30% by weight, and / or - a hydroxypropoxy group content of the HPMC of between 5 and 15% by weight, preferably between 7 and 12% by weight.

[0026] The hydroxypropyl methylcellulose that may be preferred in the context of the present invention is generally available in the form of a solution in water. A solution having a content of 5 to 20% by weight of hydroxypropyl methylcellulose in water - for example of the order of 12% by weight in water - will preferably be used; the viscosity measured at a shear rate of 40 s 1 and at 20°C of the solution of hydroxypropyl methylcellulose in water (at 12% by weight) will preferably be between 20 and 50 Pa.s at 20°C, for example between 25 and 35 Pa.s at 20°C.

[0027] Water

[0028] The ink according to the present invention comprises at least 20% by weight of water. The concentration of water in the ink is advantageously limited to 50% by weight of the ink; in a particular embodiment according to the present invention, the concentration of water in the ink is between 30% and 40% by weight.

[0029] Ethylene glycol

[0030] The ink according to the present invention comprises at least 20% by weight of ethylene glycol. The concentration of ethylene glycol in the ink is advantageously limited to 50% by weight of the ink; in a particular embodiment according to the present invention, the concentration of ethylene glycol in the ink is between 30% and 40% by weight.

[0031] Ethylene glycol, also known as glycol or ethane-1,2-diol, is mainly used as an antifreeze, refrigerant and reagent in (petro)chemistry.

[0032] Although the ink compositions according to the present invention may comprise other polyols, either as a replacement for ethylene glycol (which is not recommended), or as a complement to the latter (as an optional compound), the applicant has found that ethylene glycol should be preferred in order to optimally respond to the technical problems and objectives sought (for example drying, foam formation, conductivity, etc.).

[0033] Among these polyols, we will preferably cite those characterized by a boiling point lower than 260°C. Examples that will be mentioned are glycols, such as for example propylene glycol, diethylene glycol, trimethylene glycol, 1,3-Butylene glycol, 1,2-Butylene glycol, 2,3-Butylene glycol, Pentamethylene glycol, hexylene glycol, etc., and / or a mixture of two or more of the aforementioned compounds.

[0034] In a particular embodiment according to the present invention, if the ink compositions comprise, in addition to ethylene glycol, other polyols (optional compounds used), it will advantageously be ensured that the ratio of the total weight of said optional polyols entering into the ink composition divided by the weight of the ethylene glycol entering into the ink composition is less than 50%, for example less than 30%, or even less than 10%.

[0035] Propylene glycol propyl ether

[0036] The ink according to the present invention comprises at least 10% by weight of propylene glycol propyl ether. The concentration of propylene glycol propyl ether in the ink is advantageously limited to 40% by weight of the ink; in a particular embodiment according to the present invention, the concentration of propylene glycol propyl ether in the ink is between 20% and 35% by weight. Dowanol PNP (“Propylene glycol propyl ether”) was advantageously used in the examples.

[0037] Although the ink compositions according to the present invention may comprise other polyol ethers, either as a replacement for propylene glycol propyl ether (ce which is not recommended), or in addition to the latter (as an optional compound), the applicant noted that it was necessary to favor propylene glycol propyl ether to optimally respond to the technical problems and the objectives sought (for example drying, foam formation, conductivity, etc.).

[0038] Among these polyol ethers, we will preferably cite those characterized by a boiling point lower than 260°C.Examples include glycol ethers, for example glycol mono- or di-ethers, including ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether (butyl carbitol), propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, glymes, diethylene glycol diethyl ether, dibutylene glycol diethyl ether, diglymes, ethyl diglyme, butyl diglyme), and / or glycol ether acetates (for example, glycol acetates, ethyl diglyme, butyl diglyme, butyl diglyme, butyl ether ... 2-Butoxyethyl, di ethylene glycol monoethyl ether acetate, di ethylene glycol butyl ether acetate, propylene glycol methyl ether acetate), and / or a mixture of two or more of the above compounds.

[0039] In a particular embodiment according to the present invention, if the ink compositions comprise, in addition to propylene glycol propyl ether, other polyol ethers (optional compounds used), it will advantageously be ensured that the ratio of the total weight of said optional polyol ethers entering into the ink composition divided by the weight of the propylene glycol propyl ether entering into the ink composition is less than 50%, for example less than 30%, or even less than 10%.

[0040] Optional compounds

[0041] In a particular embodiment according to the present invention, the claimed ink may comprise up to 35% by weight of optional compounds as defined below. Among these optional compounds, we will cite by way of illustration:

[0042] • an alcohol different from that already used as the main compound above in the ink and chosen from monohydric alcohols having from 1 to 4 carbon atoms, • an antioxidant, • a membership promoter, • an anti-foam, • a leveling agent, • a compound consisting of metal oxide nanoparticles, and / or • a pigment and / or colorant.

[0043] In a particular embodiment according to the present invention, the sum of the main and optional compounds represents at least 95% by weight of the ink re-

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] sold, for example at least 99% by weight, preferably all of the ink. Alcohol optional It will be advantageous to ensure that the ratio of the weight of the optional alcohol compound entering into the ink composition divided by the weight of the main alcohol compound entering into the ink composition is less than 30%, for example less than 10%, or even less than 5%. The alcohol used as an optional compound is, for example, chosen from aliphatic monohydric alcohols having from 1 to 4 carbon atoms. Optional antioxidant agents In a particular embodiment according to the present invention, the claimed ink may comprise one or more antioxidant agents whose total concentration in the ink is advantageously between 0.1 and 5% by weight. Examples of antioxidant agents that may be used in the claimed inks include: • ascorbic acid or vitamin C (E300), sodium ascorbates (E301), calcium ascorbates (E302), diacetyl 5-6-1-ascorbic acid (E303), palmityl 6-1-ascorbic acid (E304); • citric acid (E330), sodium (E331), potassium (E332) and calcium (E333) citrates; • tartaric acid (E334), sodium tartrates (E335), potassium (E336) and sodium and potassium (E337); • butylated hydroxyanisole (E320) and butylated hydroxytoluol (E321); • octyl gallates (E311) or dodecyl gallates (E312); • sodium (E325), potassium (E326) or calcium (E327) lactates; • lecithins (E322); • natural tocopherols (E306), synthetic α-tocopherol (E307), synthetic γ-tocopherol (E308) and synthetic δ-tocopherol (E309), all of the tocopherols constituting vitamin E; • eugenol, thymol and / or cinnamaldehyde, • as well as a mixture of two or more of said antioxidants. Optional Membership Promoter In a particular embodiment according to the present invention, the claimed ink may comprise one or more adhesion promoters whose total concentration in the ink is advantageously between 0.1 and 5% by weight. Examples of adhesion promoters that may be used in the claimed inks are synthetic polymers, for example those selected from polyacrylics, polyvinyls, polyesters and / or polyurethanes, a silane, a siloxane, a polysiloxane, and / or a mixture of two or more of the aforementioned adhesion promoters.

[0053] Without wishing to be restricted to this explanation, these different adhesion promoters make it possible to selectively obtain good adhesion on different types of substrates such as, for example, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyamide, polyimide, polyetherimide, polyurethane, polyetheretherketone, polyphenylsulfone, fluoropolymers, chloropolymers, glass, silicon, epoxy resin-based composites, cellulose derivatives, electrophotoactive and charge transport layers of electronic devices, silicone, metallic and / or ITO-based coatings. As a preferred example, we will cite poly(vinylpyrrolidone-co-vinyl acetate) which makes it possible to have good adhesion on substrates of polymer types, cellulose derivatives, glass and metallic coatings among others.

[0054] Optional anti-foaming agents

[0055] In a particular embodiment according to the present invention, the claimed ink may comprise one or more anti-foaming agents (chemical additive), the total concentration of which in the ink is advantageously between 0.1 and 5% by weight. Without wishing to be restricted to this explanation, these different anti-foaming agents make it possible to prevent the formation of foam or to break up the foam already formed. Examples of antifoaming agents that may be used in the claimed inks include insoluble oils (ethylene bis stearamide (EBS), paraffins, waxes), polydimethylsiloxanes and other silicones (hydrophobic silica dispersed in a silicone oil), fatty alcohols having a long carbon chain (> C8), fatty esters (stearates for example), polyols (polyethylene glycol and polypropylene glycol copolymers), and / or a mixture of two or more of the aforementioned antifoaming agents.

[0056] Optional leveling agents

[0057] In a particular embodiment according to the present invention, the claimed ink may comprise one or more leveling agents, chemical additives, the total concentration of which in the ink is advantageously between 0.1 and 5% by weight. Without wishing to be restricted to this explanation, these different leveling agents make it possible to prevent the formation of craters and to obtain a smooth and flat deposit. These are molecules having surfactant properties whose mode of action is to reduce the surface tension of the deposited ink. Examples of leveling agents which may be used in the claimed inks are silicone polyacrylates (silicone acrylate copolymers) and fluorosurfactants (surfactants comprising a perfluoroalkyl group), and / or a mixture of said leveling agents.

[0058] Optional pigment and / or colorant

[0059] In a particular embodiment according to the present invention, the claimed ink may comprise one or more pigments and / or dyes whose total concentration in the ink is advantageously between 0.1 and 5% by weight.

[0060] Dyes are organic compounds, natural or synthetic, soluble in the medium they color. They are used in solution (often aqueous).

[0061] Pigments are compounds that are most often inorganic, natural or synthetic, insoluble in the medium in which they are dispersed. They confer a color that is not or only slightly affected by this medium.

[0062] For example, pigments are understood to mean white or colored particles, mineral or organic, intended to change the absorption wavelength, for example to change the coloring of the final film of the dry ink. By way of illustration, mention will be made of

[0063] • mineral pigments such as titanium, zirconium or cerium oxides as well as zinc, iron or chromium oxides, ferric blue, manganese violet, ultramarine blue and / or chromium hydrate, • inorganic pigments such as carbon blacks, lakes based on cochineal carmine, barium, strontium, calcium, • organic pigments, • and / or a mixture of two or more of the aforementioned pigments.

[0064] According to an alternative embodiment of the present invention, the ink may also contain nacres (for example iridescent particles, in particular produced by certain molluscs in their shell or synthesized) which we will call nacreous pigments. By way of illustration, we will cite white nacreous pigments such as mica coated with titanium, or bismuth oxychloride, colored nacreous pigments such as titanium mica with iron oxides, titanium mica with in particular ferric blue or chromium oxide, titanium mica with an organic pigment of the aforementioned type as well as nacreous pigments based on bismuth oxychloride, and / or a mixture of two or more of the aforementioned compounds.

[0065] According to an alternative embodiment of the present invention, the ink may also comprise colorless or white, mineral or synthetic, lamellar or non-lamellar particles. Illustrative examples include talc, zinc stearate, mica, kaolin, polyamide powders, polyethylene powders, tetrafluoroethylene polymer powders, starch, boron nitride, polymer microspheres such as those of polyvinylidene chloride / acrylonitrile, acrylic acid copolymers and silicone resin microbeads, elastomeric organopolysiloxanes, and / or a mixture of two or more of the aforementioned compounds.

[0066] According to an alternative embodiment of the present invention, the ink may also include water-soluble or fat-soluble dyes. Illustrative examples include fat-soluble dyes such as Sudan Red, DC Red 17, DC Green 6, [3-carotene, soybean oil, Sudan Brown, DC Yellow 11, DC Violet 2, DC Orange 5, quinoline yellow, water-soluble dyes such as beetroot juice, methylene blue, and / or a mixture of two or more of the above compounds.

[0067] Optional metal oxide nanoparticles

[0068] According to an alternative embodiment of the present invention, the claimed ink may comprise metal oxide nanoparticles whose total concentration in the ink is advantageously between 0.1 and 5% by weight. As an illustration of metal oxide nanoparticles, mention will be made of zinc oxide nanoparticles and / or tungsten oxide nanoparticles, and / or a mixture of the two. These are, for example, tungsten oxide (WO3) nanoparticles containing oxalic acid ligands (for example, from 5% to 15% by weight of oxalic acid ligands) and / or zinc oxide (ZnO) nanoparticles containing acetate ligands (for example, from 5% to 15% by weight of acetate ligands).

[0069] These nanoparticles can be of various and varied shapes; by way of illustration, mention will be made of beads (for example from 1 to 100 nm), rods (for example of length L < 200 to 300 nm), wires (for example of lengths having a few hundred nanometers or even a few microns), discs, stars, pyramids, tetrapods or crystals when they do not have a predefined shape.

[0070] According to an alternative embodiment of the present invention, the nanoparticles have dimensions between 1 and 50 nm, preferably between 2 and 20 nm.

[0071] According to an alternative embodiment of the present invention, the nanoparticles are spheroidal and / or spherical in shape. For the present invention and the claims that follow, the term "spheroidal in shape" means that the shape resembles that of a sphere but is not perfectly round ("quasi-spherical"), for example an ellipsoidal shape.

[0072] The size distribution of the nanoparticles may be measured using any appropriate method. For example, it may advantageously be measured using the following method: using a Malvern Nanosizer S type device with the following characteristics:

[0073] • DLS (Dynamic light scattering) measurement method: • Tank type: optical glass • Material: metal oxide, e.g. ZnO or WO3 • Refractive index of nanoparticles: 2.008 • Absorption: 0.001 • Dispersant: solvent for example methanol (for ZnO) or ethylene glycol (for WO3) • Temperature: 20°C • Viscosity: 0.5867 (for methanol) or 19.8316 (for ethylene glycol) • Dispersive refractive index: 1.326 (for methanol) or 1.423 (for ethylene glycol) • General Options: Mark-Houwink parameters • Analysis Model: General purpose • Balancing: 120 s • Number of measures: 4

[0074] D50 is the diameter for which 50% of the nanoparticles in number are smaller. This value is considered representative of the average grain size.

[0075] The shape and size of the nanoparticles can also advantageously be identified by means of photographs taken by microscope, in particular by means of a Transmission Electron Microscope (TEM) type device in accordance with the indications described below. The measurements are carried out by means of a Transmission Electron Microscope (TEM) type device from Thermofisher Scientific with the following characteristics:

[0076] • TEM-BF (Bright Field) images are taken at 300 kV,

[0077] • With 50 pm objective diaphragm for low magnifications and without objective diaphragm for high resolution, • Dimensional measurements are performed on TEM images using Digital Micrograph software, and an average is taken over a number of particles representative of the majority of particles, for example 20 particles, which makes it possible to establish an average area, an average perimeter, and / or an average diameter of the nanoparticles.

[0078] Thus, according to this embodiment variant of the present invention, the nanoparticles are spheroidal and are preferably characterized by means of this TEM identification by an average nanoparticle area of ​​between 1 and 20 nm2, preferably between 5 and 15 nm2, and / or by an average nanoparticle perimeter of between 3 and 20 nm, preferably between 5 and 15 nm, and / or an average nanoparticle diameter of between 0.5 and 7 nm, preferably between 1 and 5 nm.

[0079] Deposit methods

[0080] Although any deposition method may be used for the claimed ink, for example by adapting the viscosity and / or the solid content of said ink, depositions by coating or by screen printing are particularly suitable for it, preferably deposition by screen printing.

[0081] As an illustration of screen printing deposition, we will cite the ATM A AT-45PA flatbed digital screen printing device which allows patterns to be printed by screen printing. Screen printing is a printing technique which uses stencils (masks) interposed between the ink and the support. The supports used can be varied (paper, cardboard, textile, metal, glass, wood, etc.). To define the pattern to be printed, the material constituting the screen is blocked in certain areas so that the ink does not pass through them. To do this, the screen is coated with a photosensitive emulsion and the areas where the ink must not pass through are exposed to UV, which has the effect of hardening the emulsion. The emulsion in the areas that have not been exposed to UV is removed with water. The ink will then be able to pass through the corresponding meshes of the screen. The ATMA machine is intended for printing high-quality flat supports such as flexible circuits, touch screens, rigid or flexible printed circuits, etc.To achieve screen printing deposition, a quantity of ink is deposited on the mask, the doctor blade and counter-doctor blade are impregnated with ink and then the ink is automatically transferred through the mask design onto the substrate.

[0082] In particular, the screen printing deposits carried out within the framework of the present invention were carried out with the following printing parameters:

[0083] Printing speed: 100 m / s

[0084] • Pressure: Indicator 9 • Scraper hardness: 75 shores • Squeegee angle: 22.5° • Screen printing mask properties: • Number of stitches: 230 stitches / inch • Mesh diameter: 48 pm • Mesh type: polyester • Emulsion thickness: 30 pm

[0085] Then the deposits are allowed to dry, for example in two stages - at room temperature for 90 seconds followed by heating at 90°C for 5 minutes. This method was used for the preparation of the samples whose transmittance and sheet resistance properties were measured.

[0086] Transparent conductive electrodes

[0087] The present invention also relates to the manufacture of transparent conductive elements based on the claimed ink by additive manufacturing, preferably by screen printing.

[0088] The present invention therefore also relates to the use of the claimed silver nanowire-based ink for the manufacture of transparent conductive elements by additive manufacturing, in particular by screen printing. The present invention also relates to said transparent conductive elements, for example transparent conductive electrodes, manufactured according to any one of the uses listed above, namely additive manufacturing, in particular screen printing.

[0089] Any type of suitable substrate may advantageously be used for the deposition of the claimed ink. We will cite as an illustration plastic materials such as polyesters, by PET (for example Folex® films, for example Folex X-130), PC, or even cellulose-based materials such as paper, nanocellulose.

[0090] The ink will advantageously be gently rehomogenized before use (for example manually) at room temperature for a period of time, for example for 30 minutes. Optionally, the ink is gravity filtered with a 60 μm porosity nylon filter.

[0091] As already indicated above, the preferred deposit is the screen printing one mentioned above.

[0092] The deposits are then allowed to dry, for example in two stages - at room temperature for 90 seconds followed by heating at 90°C for 5 minutes.

[0093] Transparency

[0094] The transparency of the ink is represented by measuring the transmittance of a sample prepared as detailed above in the description.

[0095] In a particular embodiment according to the present invention, the transparency of the claimed ink is characterized by a transmittance value of the sample of between 80 and 95% at a wavelength of 550 nm. The measurement of the transmittance is advantageously carried out using a Varian Cary 300 UV-Visible spectrophotometer (Agilent) using a halogen lamp and a deuterium (UV) lamp making it possible to carry out the measurement over a wavelength range from 200 to 800 nm (the visible range from 380 to 800 nm). The UV-Visible spectrophotometer makes it possible to measure the absorbance (unitless quantity) of a sample when it is crossed by a light beam. When light of intensity Io passes through a sample, a part of it is absorbed by this same sample. The intensity I of the transmitted light is therefore less than Io. The absorbance of the solution is defined with the following equation

[0096] [Math.l] >4 = 10^)

[0097] We also speak of transmittance defined by the relation

[0098] [Math.2] T = T

[0099] Thus,

[0100] [Math.3] a = -logr

[0101] Absorbance is a positive value, without unit. It is all the greater as the transmitted intensity is low. The Cary 300 spectrophotometer is a double beam instrument, the light is separated into two beams before reaching the sample. One of the beams is used as a reference and passes through a "blank" (the substrate in our case), the other passes through the sample (metal coating on PET substrate). The sample and the reference are positioned on a solid sample rack. The device alternately measures the transmitted beam of the reference sample and that of the analyzed sample. The analysis is carried out in double beam mode, with a measurement of the baseline beforehand and an automatic correction of this baseline during the measurement of the sample.The results are represented in the form of a graph representing the absorbance curve of the sample as a function of wavelengths and is reprocessed into a transmittance curve using the above equation. The transmittance values ​​of the examples described in the present invention come from measurements carried out specifically at 550 nm.

[0102] Conductivity

[0103] The conductivity of the ink is represented by measuring the sheet resistance of a sample prepared as detailed above in the description.

[0104] In a particular embodiment according to the present invention, the conductivity of the claimed ink is characterized by a sheet resistance value of the sample between 5 and 100 Ohm / .

[0105] The square resistance of conductive coatings can advantageously be measured using the 4-point method. For illustrative purposes, the equipment and software used for this method are the Microworld S302 resistivity bench coupled with an Agilent U8001A current source and an Agilent U3400 multimeter. The four-point method works by bringing four equally spaced, collinear probes into contact with the material to be characterized. A direct current is applied to the outer probes of the measuring head and the resulting voltage between the other two points of the head is high. Then, the square resistance is calculated by following this equation:

[0106] [Math.4] JF 4F / ¾ ™ ___ -x 4S3236— ta(2) / /

[0107] Rs is the square resistance (in Ohm / ), AV is the voltage variation measured between the inner probes (in Volt), and I is the current applied between the outer probes (in Ampere). The coefficient 4.53236 is provided by the user manual of the S302 resistivity bench and corresponds to ir / In (2) = 4.53236.

[0108] Examples

[0109] Table 1 below represents three representative ink compositions of the present invention.

[0110] [Tables 1] Table 1 Example 1 Example 2 Example 3 AgNWs 0.5 0.2 9.7 IPA 1.25 125 1.8 Water 32.5 32.5 35.8 EG •37 7 32.85 36 Dowanol PnP 30 30.15 .77 7 HPMC 3 3' 3 Edaphî LA4B 0.05 0.05

[0111] The percentages in the table are by weight.

[0112] “Ag NWs” refers to silver nanowires, with the following dimensions: diameter 25 + 3 nm and length 13 + 6 pm.

[0113] “IPA” is isopropyl alcohol, CAS number 67-63-0, from VWR, reference 84881 with a purity level of 99.9%.

[0114] “EG” is ethylene glycol, CAS number 107-21-1, from VWR, reference 24041.297 with a purity level of 100%.

[0115] “Dowanol™ PnP” is propylene glycol propyl ether, CAS number 1569-01-3, from DOW Inc with a purity level of 99%.

[0116] “HPMC” is hydroxy propyl methylcellulose used from a 12% by weight solution of HPMC, from Alfa Aesar, reference 44779, in reverse osmosis water from VWR, reference 102928H AnalaR NormaPur Grade 3 Max. 1 pS / cm.

[0117] “Edaplan® LA413” is a substituted polysiloxane additive from MUNZING, reference M9586, with a purity level of approximately 100%.

[0118] Table 2 below represents the characteristics of the inks and the corresponding deposits.

[0119] [T ables 2] 1 ablean 2 Inks Example 1 Example 2 Example 3 Viscosity @2 Oæ 1400 - ISO 1200 ± 60 1700 ±110 (cPs) 1100±12Û 1000 ± 60 1300 ±80 10 / 40 / 100 / 1000 s 1000± 80 900 ± 50 1100 ± 60 500 ±30 500 ±20 500 ±20 Support PET (polyethylene terephthalate) PET (polyethylene terephthalate) PET (polyethylene terephthalate) Conditions of TA, 90s r 90°C, 5 TA, 90s ± 90*C, 5 sehase min in in mia Deposition method Screen printing Screen printing Screen printing Square resistance (S2 / O) 8±2 50 ± 5 16 ±4 sa -i- 7 % 07 - ri % -X 5-.¾ À. xà lit @550sm (%)

[0120] PET is Folex X-130 PET (polyethylene terephthalate).

Claims

Claims

1. An ink comprising as main components: a. at least 0.1% by weight of silver nanowires, b. at least 0.75% by weight of monohydric alcohol having from 1 to 4 carbon atoms, c. at least 2% by weight of hydroxypropyl methylcellulose, d. at least 20% by weight of water, e. at least 20% by weight of ethylene glycol, and f. at least 10% by weight of propylene glycol propyl ether, the sum of the main components representing at least 60% by weight of the ink.

2. Ink according to the preceding claim, characterized in that the weight ratio between water and ethylene glycol ((water) / (ethylene glycol)) is between 0.5 and 2, for example between 0.8 and 1.

2.

3. Ink according to any one of the preceding claims, characterized in that the concentration of silver nanowires in the ink is less than or equal to 2% by weight.

4. Ink according to any one of the preceding claims, characterized in that the concentration of silver nanowires in the ink is between 0.15% and 1% by weight.

5. Ink according to any one of the preceding claims characterized in that the concentration of monohydric alcohol in the ink is less than or equal to 5% by weight.

6. Ink according to any one of the preceding claims characterized in that the concentration of monohydric alcohol in the ink is between 1% and 2% by weight.

7. Ink according to any one of the preceding claims characterized in that the monohydric alcohol having from 1 to 4 carbon atoms is selected from aliphatic monohydric alcohols, for example selected from the group consisting of methanol, ethanol, propanol and butanol, and / or a mixture of two or more of said aliphatic monohydric alcohols.

8. Ink according to any one of the preceding claims, characterized in that the monohydric alcohol having from 1 to 4 carbon atoms is isopropyl alcohol.

9. Ink according to any one of the preceding claims characterized in that the concentration of hydroxypropyl methylcellulose in the ink is less than or equal to 4% by weight.

10. Ink according to any one of the preceding claims characterized in that the concentration of hydroxypropyl methylcellulose in the ink is between 2.5% and 3.5% by weight.

11. Ink according to any one of the preceding claims, characterized in that the water concentration in the ink is less than or equal to 50% by weight.

12. Ink according to any one of the preceding claims, characterized in that the water concentration in the ink is between 30% and 40% by weight.

13. Ink according to any one of the preceding claims characterized in that the concentration of ethylene glycol in the ink is less than or equal to 50% by weight.

14. Ink according to any one of the preceding claims characterized in that the concentration of ethylene glycol in the ink is between 30% and 40% by weight.

15. Ink according to any one of the preceding claims characterized in that the concentration of propylene glycol propyl ether in the ink is less than or equal to 40% by weight.

16. Ink according to any one of the preceding claims characterized in that the concentration of propylene glycol propyl ether in the ink is between 20% and 35% by weight.

17. Ink according to any one of the preceding claims, characterized in that the viscosity of the ink measured at a shear rate of 40 s 1 and at 20°C is between 750 and 10,000 mPa.s, for example between 900 and 2000 mPa.s.

18. Ink according to any one of the preceding claims, characterized in that the silver nanowires have an average nanowire length of between 5 and 50 pm, preferably between 10 and 30 pm and / or an average nanoparticle diameter of between 15 and 60 nm, preferably between 20 and 40 nm.

19. Ink according to any one of the preceding claims, characterized in that the hydroxypropyl methylcellulose has a methoxy group content of between 20 and 40% by weight, preferably between 27 and 30% by weight, and / or a hydroxypropoxy group content of between 5 and 15% by weight, preferably between 7 and 12% by weight.

20. Ink according to any one of the preceding claims characterized in that the sum of the main compounds represents at least 65% by weight of the ink, for example at least 75% by weight of the ink, preferably at least 90% by weight of the ink.

21. Ink according to any one of the preceding claims, characterized in that it comprises as optional compounds, a. an alcohol different from that already used as the main compound above in the ink and chosen from monohydric alcohols having from 1 to 4 carbon atoms, b. an antioxidant, c.d. an adhesion promoter, an antifoam, ef a leveling agent, a compound consisting of metal oxide nanoparticles, and / or g- a pigment and / or colorant,

22.

23. and in that the sum of the main and optional compounds represents at least 95% by weight of the ink, for example at least 99% by weight, preferably the entire ink. Manufacture of transparent conductive elements based on the ink according to any one of the preceding claims by additive manufacturing, preferably by screen printing. Transparent conductive element, for example transparent conductive electrode, manufactured according to the preceding claim.